Preparation method of multi-layer scratch-resistant impact-resistant curved surface protective film

Abstract

The invention relates to the technical field of protective film preparation, and discloses a preparation method of a multi-layer scratch-resistant impact-resistant curved surface protective film, which comprises the following steps: S1, pretreating a base material; s2, carrying out surface hardening treatment, and forming a silicon nitride hardened layer on the upper surface of the base material layer through a physical vapor deposition technology; s3, compounding a functional layer, and coating the lower surface of the base material layer with an acrylate-organosilicon copolymer adhesive layer; s4, curved surface hot press molding is carried out, and the composite film layer is placed in a mold; and S5, a rolling process is carried out, and a dynamic tension control system is adopted for rolling. The orientation of molecular chains of the TPU base material is regulated and controlled through a two-way stretching process, the elongation at break of the TPU base material is increased to be larger than or equal to 500%, the gradient functional layer design and the transition layer chemical bonding technology are matched, multi-stage dissipation of stress waves is achieved, the structure effectively avoids edge warping during curved surface attachment, the interlayer peeling strength is improved, and the service life of the TPU base material is prolonged. The problem of stress concentration caused by modulus abrupt change of a traditional multi-layer composite film is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of protective films, and specifically to a method for preparing a multi-layer scratch-resistant and impact-resistant curved protective film. Background Art

[0002] Curved display elements have added values such as conforming to the curvature of the human retina, enhancing the user's visual experience, and providing privacy for the user's screen information, and are becoming increasingly popular among users. The conventional protective film structure on the surface of components on the market is mainly a laminated structure. The substrate layer selects plastic films such as PET, PMMA, and PC, and a silicone layer, a TPU layer, or an acrylic coating is laminated on the top and bottom. The surface of the film layer is then subjected to hardening, anti-fouling, and anti-glare treatments.

[0003] After retrieval, the patent with the Chinese patent number CN108690516A discloses a protective film for a curved element, which is, from top to bottom, a first polymer resin mixed layer, a second polymer resin mixed layer, an adhesive layer, and a release film. By weight, the composition of the first polymer resin mixed layer is: 20-30 parts of TPU, 6-10 parts of filler, 5-10 parts of wear-resistant agent, 2-4 parts of dispersant, 4-8 parts of antistatic agent, and 0.2-0.5 parts of leveling agent; the composition of the second polymer resin mixed layer is: 15-25 parts of TPU, 2-5 parts of filler, 1-2 parts of dispersant, 5-8 parts of adhesion promoter, and 0.1-0.4 parts of wetting agent. The protective film of this invention can be used on flat and curved display elements. The film is soft and has a high elongation rate. The protective film has good conformability to the curve, and it is not easy to stretch, break, or deform when spreading and stretching the film; the protective film has good scratch resistance, oil resistance, water resistance, and dust resistance.

[0004] After retrieval, the patent with the Chinese patent number CN107033799B discloses a curved protective film with a multi-functional layer and its preparation method, which has anti-fouling and anti-fingerprint effects and high cleanliness. In this invention, a UV curing layer is introduced on the upper surface of the first substrate, a protective film layer is provided on the UV curing layer, a silicone layer is introduced on the lower surface of the second substrate, a fluorine release film is provided under the silicone layer, a high-viscosity adhesive layer is introduced on the upper surface of the second substrate, and the high-viscosity adhesive layer is bonded to the other side of the first substrate away from the UV curing layer. This invention has an anti-blue light effect and can protect the eyes; the double-layer PET increases the thickness of the use layer, thereby increasing the buffering capacity.

[0005] However, in the above-mentioned multi-layer laminating structure, such as the PET / TPU / silicone composite system, stress concentration is likely to occur in the high-curvature area of the curved surface, resulting in delamination between film layers or edge warping. Although the above uses a TPU substrate to improve ductility, there is still a risk of glue separation due to the difference in thermal expansion coefficient when the temperature of its adhesive layer changes, and the edge glue separation rate will further increase in a high-temperature environment in summer. At the same time, most existing protective films rely on material stacking to improve the protective performance. The above patent increases the buffering capacity through double-layer PET, but the bending modulus of the hard substrate is insufficient and it is difficult to withstand high-energy impacts. Although flexible materials such as TPU can fit the curved surface, their scratch resistance is weak and it is difficult to cope with daily wear. Based on this, the present invention designs a preparation method for a multi-layer scratch-resistant and impact-resistant curved surface protective film to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method for a multi-layer scratch-resistant and impact-resistant curved surface protective film, which solves the problems of glue separation and buffering in the background technology.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A preparation method for a multi-layer scratch-resistant and impact-resistant curved surface protective film includes the following steps:

[0009] Step S1, substrate pretreatment: Use a thermoplastic polyurethane film with a thickness of 100-150 μm as the substrate layer, and adjust the molecular chain orientation through a biaxial stretching process.

[0010] Step S2, surface hardening treatment: Form a silicon nitride hardening layer on the upper surface of the substrate layer through physical vapor deposition technology, and make its light transmittance ≥ 90%. An anti-fingerprint coating is also provided on the surface of the silicon nitride hardening layer. The anti-fingerprint coating is composed of perfluoropolyether acrylate and nano-titanium dioxide compounded in a mass ratio of 3:1, and the coating thickness is 0.5-2 μm.

[0011] Step S3, functional layer lamination: Coat an acrylate-silicone copolymer adhesive layer on the lower surface of the substrate layer, and form an intermediate functional layer after curing. The functional layer includes an impact-resistant layer and a buffer layer. The impact-resistant layer and the buffer layer form a gradient structure through hot pressing lamination. The impact-resistant layer is made of a blend of polycarbonate and nano-silica and has a thickness of 50-80 μm, and the buffer layer is made of foamed TPU material and has a thickness of 100-120 μm.

[0012] Step S4, curved surface hot pressing forming: Place the composite film layer in a mold, and perform hot pressing forming under the conditions of a temperature of 80-100 °C and a pressure of 0.5-1.2 MPa to fit a 3D curved surface with a curvature radius ≤ 5 mm.

[0013] Step S5, winding process, using a dynamic tension control system for winding. The winding speed matches the production speed of the protective film to avoid film layer damage caused by loose winding or excessive tension.

[0014] Preferably, in step S1, before the biaxial stretching process, the thermoplastic polyurethane film is pretreated, including surface cleaning, drying, and preheating. The preheating temperature is 50 - 70°C, and the preheating time is 5 - 10 minutes to ensure that the molecular chains of the film can be uniformly oriented during the stretching process.

[0015] Preferably, in step S2, before the physical vapor deposition technology, the upper surface of the substrate layer is pretreated with plasma to improve the adhesion between the silicon nitride hardening layer and the substrate layer. Radio frequency plasma pretreatment is used, with a power of 100 - 300W and a treatment time of 1 - 5 minutes.

[0016] Preferably, in step S3, during the coating process of the acrylate - silicone copolymer adhesive layer, high - precision doctor blade coating is used, and pre - curing treatment is carried out after coating. The pre - curing temperature is 60 - 80°C, and the pre - curing time is 2 - 5 minutes to ensure that the adhesive layer is preliminarily cured before complete curing.

[0017] Preferably, in step S4, before the curved surface hot pressing forming, the composite film layer is preheated. The preheating temperature is 60 - 80°C, and the preheating time is 5 - 10 minutes to reduce the internal stress of the film layer during the hot pressing process and improve the forming quality.

[0018] Preferably, in step S5, when using a dynamic tension control system for winding, the flatness and quality of the wound protective film are simultaneously detected. Ensure that the wound protective film has no wrinkles, no loose winding, no excessive tension, and no damage between the film layers; the quality detection includes optical transmittance scanning, infrared spectrum analysis, and thickness uniformity detection, where the transmittance deviation ≤ ±1.5%, and the thickness fluctuation is controlled within the range of ±3μm.

[0019] Preferably, in step 2, the anti - fingerprint coating is prepared by the solution coating method. A mixed solution of perfluoropolyether acrylate and nano - titanium dioxide is coated on the surface of the silicon nitride hardening layer, with a coating thickness of 0.5 - 2μm. After coating, it is cured at 80 - 120°C for 10 - 20 minutes to form an anti - fingerprint coating; in step S3, a transition layer is also provided. The transition layer is located between the anti - impact layer and the buffer layer. The transition layer is made of polyurethane - acrylate copolymer, with a thickness of 10 - 20μm, to improve the adhesion performance between the anti - impact layer and the buffer layer.

[0020] Preferably, in step S4, the surface of the mold is polished with high precision, and the surface roughness Ra ≤ 0.1 μm to ensure the surface finish of the formed protective film; in step S5, the wound protective film rolls are packaged with anti-static packaging materials and stored in a constant temperature and humidity environment.

[0021] Preferably, the acrylate-silicone copolymer adhesive layer further contains 0.5%-1.5% by mass of a silane coupling agent. The silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the mixing mass ratio is 1:2. The curing of the acrylate-silicone copolymer adhesive layer adopts a combination of ultraviolet curing and thermal curing to ensure complete curing of the adhesive layer.

[0022] Preferably, it further includes step S6 aging test. The wound protective film is subjected to 100 thermal cycle tests in an environment of -40°C to 120°C, and the temperature change rate ≥ 10°C / min.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0024] 1. In the present invention, the molecular chain orientation of the TPU substrate is regulated by the biaxial stretching process, so that its elongation at break is increased to ≥ 500%. Combined with the gradient functional layer design and the transition layer chemical bonding technology, the multi-stage dissipation of stress waves is realized. This structure effectively avoids edge warping during curved surface fitting, and the interlayer peel strength is improved, solving the stress concentration problem caused by modulus mutation in traditional multi-layer composite films.

[0025] 2. In the present invention, by designing a silicon nitride hardening layer and an anti-fingerprint coating on the substrate layer, the hardness and wear resistance of the protective film are significantly improved, effectively resisting daily wear and scratches. At the same time, the gradient structure design of the impact-resistant layer and the buffer layer is introduced. The blended material of polycarbonate and nano-silica is used to disperse the impact energy, and the closed-cell structure of the foamed TPU material is used to absorb stress waves, realizing efficient impact resistance performance and effectively protecting the attached object from external impact damage.

[0026] 3. In the present invention, through radio frequency plasma pretreatment and the introduction of the transition layer, the adhesion performance between layers is significantly enhanced, avoiding the risk of interlayer peeling; at the same time, a dynamic tension control system is used for winding, ensuring the precise matching of the winding speed and the production speed of the protective film, avoiding film layer damage caused by improper tension. The flatness detection and quality detection of the wound protective film, including optical transmittance scanning, infrared spectrum analysis and thickness uniformity detection, also ensure the quality stability and consistency of the finished product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the protective film of the present invention;

[0028] Figure 2 is the process flow chart for the preparation of the present invention;

[0029] Figure 3 is the winding schematic diagram of the dynamic tension control system of the present invention;

[0030] Figure 4 is the schematic diagram of the aging test of the present invention. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Embodiment 1;

[0033] Please refer to Figures 1 - 4 , in the embodiment of the present invention, a preparation method of a multi-layer scratch-resistant and impact-resistant curved surface protective film includes the following steps:

[0034] Step S1, substrate pretreatment: Use a thermoplastic polyurethane film with a thickness of 100-150 μm as the substrate layer, and adjust the molecular chain orientation through a biaxial stretching process;

[0035] Step S2, surface hardening treatment: Form a silicon nitride hardening layer on the upper surface of the substrate layer through physical vapor deposition technology, and make its light transmittance ≥ 90%. An anti-fingerprint coating is also provided on the surface of the silicon nitride hardening layer. The anti-fingerprint coating is composed of perfluoropolyether acrylate and nano-titanium dioxide compounded in a mass ratio of 3:1, and the coating thickness is 0.5-2 μm;

[0036] Step S3, functional layer lamination: Coat an acrylate-silicone copolymer adhesive layer on the lower surface of the substrate layer, and form an intermediate functional layer after curing. The functional layer includes an impact-resistant layer and a buffer layer. The impact-resistant layer and the buffer layer form a gradient structure through hot pressing lamination. The impact-resistant layer is made of a blend of polycarbonate and nano-silica and has a thickness of 50-80 μm, and the buffer layer is made of a foamed TPU material and has a thickness of 100-120 μm;

[0037] Step S4, curved surface hot pressing forming: Place the composite film layer in a mold, and perform hot pressing forming under the conditions of a temperature of 80-100 °C and a pressure of 0.5-1.2 MPa to adapt to a 3D curved surface with a curvature radius ≤ 5 mm;

[0038] Step S5, winding process, using a dynamic tension control system for winding, with the winding speed matching the production speed of the protective film, to avoid film layer damage caused by loose winding or excessive tightness.

[0039] In step S1, before the biaxial stretching process, the thermoplastic polyurethane film is pretreated, including surface cleaning, drying, and preheating. The preheating temperature is 50 - 70°C, and the preheating time is 5 - 10 minutes, to ensure that the molecular chains of the film can be uniformly oriented during the stretching process.

[0040] In step S2, before the physical vapor deposition technology, the upper surface of the substrate layer is pretreated with plasma to improve the adhesion between the silicon nitride hardening layer and the substrate layer. Radio frequency plasma pretreatment is used, with a power of 100 - 300W and a treatment time of 1 - 5 minutes.

[0041] In step S3, during the coating process of the acrylate - silicone copolymer adhesive layer, high - precision blade coating is used, and pre - curing treatment is carried out after coating. The pre - curing temperature is 60 - 80°C, and the pre - curing time is 2 - 5 minutes, to ensure that the adhesive layer is preliminarily cured before complete curing.

[0042] In step S4, before the curved surface hot pressing forming, the composite film layer is preheated. The preheating temperature is 60 - 80°C, and the preheating time is 5 - 10 minutes, to reduce the internal stress of the film layer during the hot pressing process and improve the forming quality.

[0043] In step S5, when using a dynamic tension control system for winding, the flatness and quality of the wound protective film are detected simultaneously, ensuring that the wound protective film has no wrinkles, no loose winding, no excessive tightness, and no damage between the film layers; the quality detection includes optical transmittance scanning, infrared spectrum analysis, and thickness uniformity detection, where the transmittance deviation ≤ ±1.5%, and the thickness fluctuation is controlled within the range of ±3μm.

[0044] The working principle of the embodiment of the present invention is as follows: In the substrate pretreatment stage, a thermoplastic polyurethane film with a thickness of 100 - 150μm is selected as the substrate layer. This material has good flexibility and mechanical properties and can adapt to the shape of the curved surface. Through the biaxial stretching process, the molecular chains in the film are uniformly oriented in the transverse and longitudinal directions, thereby enhancing the tensile strength and dimensional stability of the substrate layer. Before biaxial stretching, the film is subjected to surface cleaning, drying, and preheating treatment. The preheating temperature is controlled at 50 - 70°C, and the preheating time is maintained at 5 - 10 minutes. This step ensures that the molecular chains of the film can be uniformly oriented during the stretching process, avoiding unstable film performance caused by non - uniform molecular chain orientation.

[0045] In the surface hardening treatment stage, physical vapor deposition technology is used to form a silicon nitride hardening layer on the upper surface of the substrate layer. This technology ionizes the silicon nitride target material in a vacuum environment and deposits it on the surface of the substrate to form a dense and uniform hardening layer, which significantly improves the surface hardness and wear resistance of the protective film, enabling it to effectively resist scratches and wear. At the same time, in order to ensure good adhesion between the silicon nitride hardening layer and the substrate layer, before physical vapor deposition, the upper surface of the substrate layer is pre-treated with radio frequency plasma, the power is set at 100-300W, and the treatment time is controlled at 1-5 minutes. Through the bombardment of plasma, a micro-rough structure is formed on the surface of the substrate, thereby enhancing the bonding between the two. In addition, the surface of the silicon nitride hardening layer is also provided with an anti-fingerprint coating, which is composed of perfluoropolyether acrylate and nano-titanium dioxide in a mass ratio of 3:1. The coating thickness is 0.5-2μm, which can effectively reduce the adhesion of fingerprints and keep the surface of the protective film clean and beautiful.

[0046] The cured adhesive layer is used as the basis of the intermediate functional layer, and the impact-resistant layer and the buffer layer are compounded on it in turn to form an intermediate functional layer with a gradient structure. The impact-resistant layer is made of a blend of polycarbonate and nano-silicon dioxide, with a thickness of 50-80μm. Polycarbonate itself has excellent impact resistance, and the addition of nano-silicon dioxide further improves the rigidity and wear resistance of the material, enabling it to effectively resist external impact and protect the attached object from damage; the buffer layer is made of foamed TPU material with a thickness of 100-120μm. Foamed TPU has good elasticity and toughness, and can absorb and disperse part of the impact energy when impacted, reducing the direct effect of the impact force on the object, and also helps to alleviate the slight deformation of the object during use, further enhancing the protection effect.

[0047] The impact-resistant layer and the buffer layer are composited by hot pressing to form a gradient structure. This structural design enables the protective film to have different mechanical properties in different areas, which not only ensures the overall impact resistance, but also takes into account flexibility and fit, so that it can better adapt to the shape and stress conditions of the curved surface.

[0048] The composite film layer is preheated before hot pressing at a temperature of 60-80°C for 5-10 minutes, so that the film layer has better flexibility and plasticity during the hot pressing process, reduces internal stress, ensures that the protective film can fit the curved surface tightly, avoids bubbles and falling off caused by loose fitting, improves molding quality, and protects curved objects.

[0049] The rewinding process adopts a dynamic tension control system, which can monitor and adjust the tension in real time during the rewinding process to match the production speed of the protective film. By precisely controlling the tension, problems such as excessive stretching and deformation or even breakage of the film layer caused by excessive tension, and loose winding and wrinkles caused by too small tension are avoided.

[0050] Example 2;

[0051] Please refer to Figures 1 - 4 , in the embodiment of the present invention, in step 2, the anti-fingerprint coating is prepared by solution coating method. A mixed solution of perfluoropolyether acrylate and nano-titanium dioxide is coated on the surface of the silicon nitride hardening layer, and the coating thickness is 0.5 - 2 μm. After coating, it is cured at 80 - 120 °C for 10 - 20 minutes to form an anti-fingerprint coating; in step S3, a transition layer is also provided. The transition layer is located between the anti-impact layer and the buffer layer and is made of polyurethane-acrylate copolymer with a thickness of 10 - 20 μm, which is used to improve the adhesion performance between the anti-impact layer and the buffer layer.

[0052] In step S4, the surface of the mold is polished with high precision, and the surface roughness Ra ≤ 0.1 μm to ensure the surface smoothness of the formed protective film; in step S5, the wound protective film rolls are packaged with anti-static packaging materials and stored in a constant temperature and humidity environment.

[0053] The acrylate-silicone copolymer adhesive layer also contains 0.5% - 1.5% by mass of silane coupling agent. The silane coupling agent is a mixture of γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane, and the mixing mass ratio is 1:2. The curing of the acrylate-silicone copolymer adhesive layer adopts a combination of ultraviolet curing and thermal curing to ensure complete curing of the adhesive layer.

[0054] It also includes step S6 aging test. The wound protective film is subjected to 100 thermal cycle tests in an environment of -40 °C to 120 °C, and the temperature change rate ≥ 10 °C / min.

[0055] The working principle of the embodiment of the present invention is: The anti-fingerprint coating is prepared by solution coating method. Perfluoropolyether acrylate and nano-titanium dioxide are mixed in a mass ratio of 3:1 to form a uniform solution. Through a high-precision coating device, this mixed solution is coated on the surface of the silicon nitride hardening layer, and the coating thickness is precisely controlled within the range of 0.5 - 2 μm. After coating, the coating is placed in a hot air circulation oven at 80 - 120 °C and cured for 10 - 20 minutes to form a dense and uniform anti-fingerprint coating. The low surface energy property of perfluoropolyether acrylate makes fingerprints difficult to adhere, while nano-titanium dioxide has photocatalytic performance and can decompose the attached fingerprint grease to keep the screen clear and beautiful.

[0056] The transition layer is made of polyurethane-acrylate copolymer and has a thickness of 10-20 μm. The transition layer forms a firm interfacial bond with the impact-resistant layer and the buffer layer through chemical bonding, effectively transmitting stress and avoiding delamination between layers. When an external impact force acts, the transition layer can coordinate the rigidity of the impact-resistant layer and the elasticity of the buffer layer, enabling the impact energy to be efficiently transmitted and dissipated among the three layers, further enhancing the impact resistance of the protective film.

[0057] During the curved surface thermoforming process, the surface of the mold is treated with high-precision polishing, and the surface roughness Ra ≤ 0.1 μm. Such an ultrasmooth mold surface ensures that the protective film has a mirror-like finish after thermoforming, reducing surface defects and stress concentration points, and enhancing the optical properties and mechanical strength of the protective film. At the same time, the high-precision mold, combined with precise temperature and pressure control, enables the protective film to perfectly fit a 3D curved surface with a curvature radius ≤ 5 mm, achieving precise protection for complex curved surfaces.

[0058] The silane coupling agent forms a chemical bridge between the adhesive layer, the substrate layer, and the functional layer, enhancing the interfacial bonding force and preventing delamination between layers. The curing of the adhesive layer adopts a combination of ultraviolet curing and thermal curing. First, the adhesive layer is rapidly preliminarily cured by ultraviolet irradiation to form a certain network structure, and then thermal curing is carried out at 60-80 °C to completely cure the adhesive layer, ensuring that the adhesive layer has excellent adhesion performance and mechanical strength, and achieving a firm bond between the layers of the protective film.

[0059] In the winding process, the wound protective film roll is packaged with an anti-static packaging material, which can effectively prevent the generation and accumulation of static electricity, avoiding electrostatic adsorption pollution and discharge damage to the surface of the protective film; at the same time, the protective film is stored in a constant temperature and humidity environment, with the temperature controlled at 20-25 °C and the humidity maintained at 40%-60%. Such environmental conditions can prevent problems such as dimensional changes, warping, and blistering of the protective film caused by temperature and humidity changes during storage, ensuring the performance stability of the protective film.

[0060] In addition, the present invention further includes step S6 aging test, which can comprehensively evaluate the performance stability of the protective film under extreme temperature conditions, ensuring that it can withstand various temperature changes during actual use and meet the high reliability requirements of precision electronic devices for the protective film.

[0061] Example 3;

[0062] Please refer to Figures 1 - 4 , in the embodiment of the present invention, a specific embodiment is provided, including the following steps:

[0063] Step S1: Substrate pretreatment

[0064] Select a thermoplastic polyurethane film with a thickness of 120 μm, and regulate the molecular chain orientation through a biaxial stretching process. The longitudinal stretching ratio is 2.0 times, the transverse stretching ratio is 1.8 times, and the preheating temperature is 60 °C.

[0065] Step S2: Surface hardening treatment

[0066] The surface of the substrate is pretreated by radio frequency plasma (power 100 - 300 W, time 3 minutes), and then a silicon nitride hardening layer is formed by physical vapor deposition with a thickness of 1.2 μm and a light transmittance of ≥90%. The anti-fingerprint coating is formed by mixing perfluoropolyether acrylate and nano-titanium dioxide at a mass ratio of 3:1 and coating it with a thickness of 0.5 - 2 μm. After curing, the surface hardness reaches 8H.

[0067] Step S3: Functional layer lamination

[0068] An acrylate-silicone copolymer adhesive layer is coated on the lower surface of the substrate, and the pre-curing temperature is 60 - 80 °C to form an intermediate adhesive layer with a thickness of 50 - 80 μm. The anti-impact layer is a blend of polycarbonate and nano-silica with a thickness of 50 - 80 μm; the buffer layer selects a foamed TPU material with a thickness of 100 - 120 μm.

[0069] Step S4: Curved hot pressing

[0070] The composite film layer is placed in a mold with a curvature radius ≤5 mm, the preheating temperature is 60 - 80 °C, and it is hot pressed at a pressure of 0.5 - 1.2 MPa. The residual stress ≤1.2 MPa.

[0071] Step S5: Rewinding and inspection

[0072] It is rewound by a dynamic tension control system, the light transmittance deviation ≤±1.5%, the thickness fluctuation is ±3 μm, and it is stored in a constant temperature and humidity environment after anti-static packaging.

[0073] The working principle of the embodiment of the present invention is: through plasma interface activation, gradient modulus design and supercritical foaming technology, the energy absorption rate of the protective film reaches 82% under an impact energy of 5 J, the light transmittance is 90.5%, the haze ≤1.5%, and the curved surface fitting accuracy is ±0.03 mm, meeting the 3D fitting requirements with a screen curvature radius ≤5 mm.

[0074] Working principle: The substrate layer uses a 100 - 150 μm thermoplastic polyurethane (TPU) film, and the molecular chain orthogonal network is reconstructed through a biaxial stretching process. The preheating temperature of 60 °C makes the TPU in a highly elastic state, reducing the molecular chain slip resistance and providing a uniform substrate for subsequent coating.

[0075] The surface hardening layer uses physical vapor deposition (PVD) silicon nitride coating, combined with radio frequency plasma pretreatment (power 100 - 300 W), to form a 1.2 μm thick Si3N4 layer on the substrate surface, with a surface hardness of 8H. The micron-scale pits (depth 50 - 100 nm) formed by plasma etching increase the interfacial bonding strength to 5 MPa. Combining with a perfluoropolyether acrylate / nano-TiO2 (3:1) anti-fingerprint coating achieves the synergy of a friction coefficient ≤ 0.15 and a light transmittance ≥ 90%. The photocatalytic effect of nano-TiO2 can decompose organic stains and maintain the surface cleanliness.

[0076] The intermediate functional layer adopts an impact-resistant layer - buffer layer gradient structure: the impact-resistant layer (polycarbonate / nano-silica) disperses the impact energy through rigid materials, and the buffer layer (foamed TPU) uses a closed-cell structure to absorb and dissipate stress waves. The introduction of the transition layer enhances the interfacial bonding force through chemical bonding, coordinates the rigid-elastic transition, avoids interfacial delamination, and achieves hierarchical energy dissipation.

[0077] The internal stress of the film layer is reduced through the preheating - hot pressing interlock process. Combining with a high-precision mold (surface roughness Ra ≤ 0.1 μm) achieves 3D curved surface fitting with a curvature radius ≤ 5 mm. The dynamic tension control system optimizes the tension matching during the winding process to avoid film layer damage; anti-static packaging and constant temperature and humidity storage ensure the stability of the finished product, and the aging test verifies the reliability at extreme temperatures, meeting the protection requirements of precision devices. This technical system realizes a light transmittance ≥ 90%, a curved surface fitting accuracy of ±0.03 mm, and high-efficiency impact resistance through material modification and process synergy, and is applicable to the protection requirements of curved screens such as smartphones and folding screens.

[0078] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a multi-layer anti-scratch and impact-resistant curved surface protective film, characterized in that: The following steps are involved: Step S1, substrate pretreatment, using a thermoplastic polyurethane film with a thickness of 100-150 μm as the substrate layer, and adjusting the molecular chain orientation through a biaxial stretching process; Step S2, surface hardening treatment, forming a silicon nitride hardened layer on the upper surface of the substrate layer by physical vapor deposition technology, and making its transmittance ≥ 90%, and an anti-fingerprint coating is also provided on the surface of the silicon nitride hardened layer, and the anti-fingerprint coating is composited by perfluoropolyether acrylate and nano titanium dioxide in a mass ratio of 3:1, and the coating thickness is 0.5-2 μm; Step S3, functional layer compounding, coating an acrylate-organic silicon copolymer adhesive layer on the lower surface of the substrate layer, and forming an intermediate functional layer after curing, wherein the functional layer includes an impact-resistant layer and a buffer layer, wherein the impact-resistant layer and the buffer layer are compounded by hot pressing to form a gradient structure, wherein the impact-resistant layer is made of a blend of polycarbonate and nano-silicon dioxide and has a thickness of 50-80 μm, and the buffer layer is made of a foamed TPU material and has a thickness of 100-120 μm; Step S4, curved surface hot pressing molding, placing the composite film layer in a mold, and hot pressing molding at a temperature of 80-100° C. and a pressure of 0.5-1.2 MPa to adapt to a 3D curved surface with a curvature radius of ≤5 mm; Step S5, a winding process, adopts a dynamic tension control system for winding, and the winding speed matches the production speed of the protective film to avoid film damage caused by loose winding or excessive tension.

2. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: In the step S1, before the biaxial stretching process, the thermoplastic polyurethane film is pretreated, including surface cleaning, drying and preheating. The preheating temperature is 50-70° C. and the preheating time is 5-10 minutes to ensure that the molecular chains of the film can be uniformly oriented during the stretching process.

3. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: In the step S2, before performing the physical vapor deposition technology, the upper surface of the substrate layer is subjected to plasma pretreatment to improve the adhesion between the silicon nitride hardening layer and the substrate layer. The radio frequency plasma pretreatment is used with a power of 100-300W and a treatment time of 1-5 minutes.

4. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: In step S3, during the coating process of the acrylate-silicone copolymer adhesive layer, high-precision scraping is used, and a pre-curing treatment is performed after coating. The pre-curing temperature is 60-80° C. and the pre-curing time is 2-5 minutes to ensure that the adhesive layer is initially cured before being fully cured.

5. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: In the step S4, before the curved surface hot pressing molding, the composite film layer is preheated at a temperature of 60-80° C. for 5-10 minutes to reduce the internal stress of the film layer during the hot pressing process and to improve the molding quality.

6. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: In the step S5, when the dynamic tension control system is used for winding, the flatness inspection and quality inspection of the protective film after winding are performed at the same time to ensure that the protective film after winding has no wrinkles, no loose winding and no excessive tension, and no damage between film layers; the quality inspection includes optical transmittance scanning, infrared spectrum analysis and thickness uniformity inspection, wherein the transmittance deviation is ≤±1.5%, and the thickness fluctuation is controlled within the range of ±3μm.

7. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: In the step 2, the anti-fingerprint coating is prepared by a solution coating method, and a mixed solution of perfluoropolyether acrylate and nano-titanium dioxide is coated on the surface of the silicon nitride hardening layer with a coating thickness of 0.5-2 μm. After coating, the coating is cured at 80-120° C. for 10-20 minutes to form an anti-fingerprint coating; in the step S3, a transition layer is also provided, and the transition layer is located between the impact-resistant layer and the buffer layer. The transition layer is made of a polyurethane-acrylate copolymer and has a thickness of 10-20 μm, which is used to improve the adhesion performance between the impact-resistant layer and the buffer layer.

8. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 3, characterized in that: In the step S4, the mold surface is polished with high precision, and the surface roughness Ra≤0.1μm to ensure the surface smoothness of the protective film after molding; in the step S5, the rolled protective film coil is packaged with antistatic packaging materials and stored in a constant temperature and humidity environment.

9. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: The acrylate-silicone copolymer adhesive layer also contains 0.5%-1.5% by weight of a silane coupling agent, which is a mixture of γ-aminopropyltriethoxysilane and γ-glycidyloxypropyltrimethoxysilane in a mixing ratio of 1:

2. The acrylate-silicone copolymer adhesive layer is cured by combining ultraviolet curing with thermal curing to ensure that the adhesive layer is completely cured.

10. The method for preparing a multi-layer anti-scratch and anti-impact curved surface protective film according to claim 1, characterized in that: The method also includes an aging test in step S6, in which the rolled protective film is subjected to a thermal cycle test for 100 times in an environment of -40°C to 120°C, with a temperature change rate of ≥10°C / min.

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