Surface protection film and use thereof

Abstract

The application relates to a surface protection film and a preparation method thereof, and belongs to the technical field of protective films. The surface protection film comprises a surface layer, a core layer and a bonding layer arranged in sequence; the surface layer comprises a first polypropylene base resin, an organic ultraviolet absorber and an inorganic ultraviolet shielding agent; the core layer comprises a second polypropylene base resin, polyaryletherketone nanofibers and flaky mica powder coated with cerium oxide; and the bonding layer comprises a thermoplastic SEBS elastomer, a hydrogenated bonding resin, an organic zinc compound, an ultraviolet light stabilizer and an epoxy group-containing plasticizer. The surface protection film has excellent ultraviolet aging resistance and high temperature resistance, the adhesion can be kept within a certain range under ultraviolet irradiation and high temperature conditions, the surface protection film can be easily unwound under high temperature conditions, and no residual glue is precipitated.

Description

Technical Field

[0001] This invention relates to the field of protective film technology, specifically to a surface protective film that is UV-resistant, high-temperature resistant, maintains a certain adhesion, is easy to unwind at high temperatures, and leaves no residual adhesive. It can be applied to the surface protection of materials that require UV resistance and high-temperature resistance. Background Technology

[0002] With the rapid development of precision manufacturing, electronic displays, and high-end building materials, the demand for temporary surface protection during processing, transportation, and storage is increasing. As a key protective material, protective films effectively prevent product surfaces from being damaged by scratches, contamination, abrasion, or chemical corrosion through physical isolation mechanisms. Surface protective films typically consist of a surface layer, a core layer, and an adhesive layer. They possess moderate initial adhesion to ensure a firm bond while also allowing for easy unwinding. They maintain adhesion stability even after long-term use, preventing edge lifting, bubble formation, and adhesive residue. For surface protection of materials requiring UV and high-temperature resistance, such as automotive displays, photovoltaic modules (e.g., solar panels), high-end home appliances, and non-imaging optical components (e.g., decorative parts, light diffusers, signs), surface protective films also need to possess antistatic properties and excellent weather resistance, such as resistance to UV aging and high-temperature resistance. Currently, traditional surface protective films often suffer from poor weather resistance. For example, under long-term outdoor ultraviolet radiation, molecular chains will break, causing the film to yellow, become brittle, and powder, losing its protective function. Or, under summer sun exposure, heat processing (such as metal spray painting baking), or high temperature environments, the adhesive layer of the protective film will soften, causing cohesive damage, resulting in residual adhesive or permanent adhesion to the surface of the protected object, making it impossible to peel off.

[0003] In the prior art, such as Chinese invention patent publication number CN118813155A, a self-adhesive protective film is disclosed. The film includes a heat-resistant self-adhesive layer, a high-temperature resistant core layer, and a functional back layer stacked sequentially from bottom to top. The high-temperature resistant core layer is made of the following components in parts by weight: 100 parts polypropylene, 10-20 parts polyolefin elastomer (POE), and 3-10 parts modified silica. The heat-resistant self-adhesive layer is made of the following components: 40-60 parts low-density polyethylene, 20-30 parts metallocene polyethylene, 5-40 parts SEBS, and 1-3 parts anti-aging agent. The functional back layer is made of the following components: 100 parts polypropylene, 2-20 parts polyethylene, and 1-10 parts fluorinated release agent. Although the above solutions mention improvements in high temperature resistance and UV aging resistance, the POE component in the core layer has poor heat resistance and lacks UV aging resistance protection in the functional back layer. Relying solely on the modified silica in the core layer may affect the overall high temperature resistance and UV aging resistance of the protective film. Summary of the Invention

[0004] The purpose of this invention is to provide a surface protective film and its application, and further improve the composition of the protective film and the formulation of each layer in order to solve the above-mentioned technical problems.

[0005] The specific technical solution is explained below:

[0006] A surface protective film includes a surface layer, a core layer, and an adhesive layer arranged sequentially.

[0007] The surface layer comprises a first polypropylene matrix resin, an organic ultraviolet absorber, and an inorganic ultraviolet shielding agent. The organic ultraviolet absorber is composed of a first organic ultraviolet absorber with an absorption band of 290-350 nm and a second organic ultraviolet absorber with an absorption band of 300-400 nm, in a mass ratio of (4.5-6.75):(2.5-3.75). The organic ultraviolet absorber accounts for 7-10.5% of the mass of the surface layer, and the mass ratio of the organic ultraviolet absorber to the inorganic ultraviolet shielding agent is 1.55-3.5.

[0008] The core layer comprises a second polypropylene matrix resin, polyaryletherketone nanofibers, and flaky mica powder coated with cerium oxide; the nanofibers account for 5-12% of the mass percentage of the core layer, and the flaky mica powder accounts for 5-10% of the mass percentage of the core layer.

[0009] The adhesive layer comprises thermoplastic SEBS elastomer, hydrogenated adhesive resin, organozinc composite, UV stabilizer, and epoxy-containing plasticizer, wherein the UV stabilizer accounts for 5-10% of the adhesive layer by mass; SEBS is a linear triblock copolymer with polystyrene as the end block and ethylene-butene copolymer obtained by hydrogenation of polybutadiene as the middle elastic block, and its full English name is Styrene Ethylene Butylene Styrene.

[0010] In the above technical solution, the surface layer is compounded with organic ultraviolet absorbers that complement each other in their wavelength range, achieving balanced absorption of ultraviolet light across the entire wavelength range. This avoids the saturation effect caused by excessive single absorber, meaning the mass ratio of the two is controlled within the aforementioned range, forming an "intermolecular energy transfer" mechanism. That is, after one molecule absorbs ultraviolet light, it can transfer energy more efficiently to another molecule and dissipate it as heat, thus delaying the premature failure of a single absorber due to "fatigue". At the same time, the inorganic ultraviolet shielding agent contained in the surface layer and the flaky mica powder with cerium oxide coating on the core layer can respectively reflect and scatter ultraviolet light. The ultraviolet light stabilizer contained in the adhesive layer can inhibit the photo-oxidative degradation of polymers. The synergistic effect of these components results in a high performance retention rate of the surface protective film after 500 hours of ultraviolet aging test chamber (QUV), achieving excellent ultraviolet aging resistance of the protective film.

[0011] The polyaryletherketone nanofibers contained in the core layer form a three-dimensional mechanical support network in the core layer in the form of nanofibers, which restricts the slippage of the second polypropylene matrix resin molecular chains. Meanwhile, the flaky mica powder coated with cerium oxide is arranged in parallel in the core layer to form a barrier layer, which inhibits the thermal motion of the second polypropylene matrix resin molecular chains at high temperature, so that the thermal shrinkage rate of the surface protective film at 120℃ is ≤1%, which improves the high temperature dimensional stability of the protective film.

[0012] The zinc ions in the organic zinc complex contained in the adhesive layer can capture acidic small molecules such as hydrogen chloride generated during processing and use, preventing them from catalyzing the degradation reaction of the polymer. They can also coordinate with unsaturated sites on the SEBS molecular chain and interact with epoxy groups in the plasticizer to form a dynamic cross-linking network in the system, inhibiting the slippage of the molecular chain and ensuring that the adhesive layer does not soften, migrate, or precipitate residual adhesive at high temperatures.

[0013] In addition, for mica powder coated with cerium oxide, the anti-ultraviolet effect is achieved through the scattering and reflection of the cerium oxide layer. Using flaky mica as a carrier can prevent cerium oxide agglomeration, thereby improving the light transmittance of the protective film.

[0014] The surface protective film of this application achieves excellent UV aging resistance and high temperature resistance through the synergistic effect of three specially designed layers: surface layer, core layer, and adhesive layer.

[0015] Preferably, the first organic ultraviolet absorber is one of 4-octylbenzophenone and 2-hydroxy-4-n-octyloxybenzophenone.

[0016] Preferably, the second organic ultraviolet absorber is one of benzotriazole and 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole.

[0017] Preferably, the ultraviolet stabilizer is one of di(2,2,6,6-tetramethyl-4-piperidine) sebacate or bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidine) sebacate.

[0018] In a preferred embodiment, the first polypropylene matrix resin is selected from random block polypropylene, and the second polypropylene matrix resin is selected from isotactic homopolymer polypropylene.

[0019] In the above technical solution, the first polypropylene matrix resin is random block polypropylene, which has moderate crystallinity and excellent transparency, which is conducive to the uniform dispersion of ultraviolet absorbers and the maintenance of optical properties. The second polypropylene matrix resin is high isotactic homopolymer polypropylene, which imparts high rigidity and heat resistance to the core layer, further improving the high temperature resistance of the surface protective film.

[0020] In a further embodiment, the surface layer further includes open-cell silica masterbatch.

[0021] In the above technical solution, the addition of silica open masterbatch can form micron-level protrusions on the film surface, effectively reducing the contact area between film layers, preventing adhesion during winding, and ensuring that the protective film is easy to unwind.

[0022] In a preferred embodiment, the inorganic ultraviolet shielding agent is silane coupling agent modified nano zinc oxide.

[0023] In the above technical solution, the silane coupling agent significantly improves the dispersibility of nano-zinc oxide in the core layer, prevents particle agglomeration, and enhances interfacial bonding. Its organic long chain interacts with the first polypropylene matrix resin and organic UV absorber through entanglement, significantly reducing light scattering caused by inorganic / organic interface incompatibility. When the amount of modified nano-zinc oxide added is increased, the haze of the surface protective film can still be ≤3.5%, reducing the impact of the addition of inorganic UV shielding agent on the transparency and haze of the surface protective film.

[0024] In a further embodiment, the core layer further includes maleic anhydride-grafted polypropylene.

[0025] In the above technical solution, maleic anhydride-grafted polypropylene is used as a compatibilizer. Its anhydride groups can interact with the functional groups on the surface of polyaryletherketone nanofibers, improve interfacial compatibility, promote uniform dispersion of nanofibers, and further improve the high temperature resistance of the protective film. It can also form a tough and flexible interface layer between the nanofibers and the second polypropylene matrix resin, so that when the protective film is subjected to impact, the stress can be effectively transferred from the matrix resin to the fiber, thereby improving the impact resistance of the surface protective film.

[0026] In a further embodiment, the organozinc complex is selected from one of the complexes of zinc stearate and β-diketone compounds, and the complex of hydrotalcite and zinc salts.

[0027] In a preferred embodiment, the epoxy-containing plasticizer is selected from one of epoxidized soybean oil, epoxidized linseed oil, epoxidized castor oil, epoxidized palm oil, and di(2-ethylhexyl) 4,5-epoxytetrahydrophthalic acid.

[0028] In a preferred embodiment, the hydrogenated adhesive resin is a mixture of hydrogenated petroleum resin and highly hydrogenated terpene resin.

[0029] In a preferred embodiment, the thickness of the surface layer is 7-9 μm, the thickness of the core layer is 17-26 μm, and the thickness of the adhesive layer is 3-4 μm.

[0030] In the above technical solution, the thickness of the surface layer ensures sufficient UV protection component content without excessively affecting the flexibility and cost of the film; the thickness of the core layer provides the main structural support and mechanical properties, ensuring the flatness and dimensional stability of the film; the thickness of the adhesive layer ensures sufficient adhesion while avoiding flow problems and increased costs caused by excessive thickness.

[0031] In a preferred embodiment, the performance parameters of the surface protective film are:

[0032] After 500 hours of QUV aging: tensile strength retention rate >80%, yellowing index <3, peel force change rate <12%, high performance retention rate, and the protective film has excellent UV aging resistance.

[0033] The heat shrinkage rate at 120℃ for 30 minutes is less than 1.0%, indicating that the protective film has excellent high-temperature resistance.

[0034] The surface protective film was adhered to a glass plate and placed in an oven at 120°C for 1 hour before being peeled off without any residue.

[0035] After the surface protective film was placed in a constant temperature and humidity chamber at 60℃ and 85%RH for 30 days, there was no change in appearance, the unwinding force was ≤1.0N / 25mm, and the long-term stability was excellent.

[0036] The surface protective film described in any of the above technical solutions is used for surface protection of materials that require UV resistance and high temperature resistance.

[0037] Examples of the materials mentioned are as follows:

[0038] (1) High-end display modules: OLED / LCD screens for smartphones and tablets, especially automotive displays for surface protection of materials that require UV resistance and high temperature resistance;

[0039] (2) Photovoltaic modules: The protective film can be used for temporary protection of the surface of solar panels to meet outdoor weather resistance requirements;

[0040] (3) Non-imaging optical components: such as decorative parts, light diffusers, signs, etc.

[0041] The method for preparing the surface protective film according to any of the above technical solutions includes the following steps:

[0042] The raw materials for the surface layer, core layer, and adhesive layer are blended and granulated separately.

[0043] Then, the individual particles are co-extruded into a surface protective film using a three-layer co-extrusion casting unit in the order of surface layer, core layer, and adhesive layer.

[0044] The surface layer extrusion temperature is 200~210℃, the core layer extrusion temperature is 210~220℃, and the adhesive layer extrusion temperature is 180~195℃.

[0045] In the above preparation method, the surface layer, core layer and adhesive layer are first blended and granulated, and then three layers are co-extruded and cast. This method can improve the dispersibility of each component, especially the high-temperature resistant reinforcing agent of polyarylether ketone nanofibers, and avoid the decomposition of sensitive additives (such as organic UV absorbers and UV stabilizers) by high temperature, thus ensuring the consistency and stability of the protective film performance.

[0046] In a further embodiment, the raw material for the surface layer includes open-face silica masterbatch;

[0047] When the raw materials for the surface layer are blended and granulated, the first polypropylene matrix resin and silica open masterbatch are blended and granulated first, and then organic UV absorbers and inorganic UV shielding agents are added.

[0048] In the above preparation method, the first polypropylene matrix resin and silica open-face masterbatch are blended and granulated before the organic UV absorber and inorganic UV shielding agent are added. This is to avoid the high-temperature decomposition of the organic UV absorber.

[0049] In summary, the technical solution described in this invention has the following main beneficial effects:

[0050] Compared with existing technologies, the technical solution of this invention achieves excellent UV aging resistance and high temperature resistance by constructing a surface layer composite UV protection system, a core layer nanofiber reinforcement system and an adhesive layer thermal stability system. The adhesion can still be maintained within a certain range under UV irradiation and high temperature conditions, and it can also be easily unwound under high temperature conditions without residual adhesive precipitation.

[0051] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Detailed Implementation

[0052] The present invention will be further explained in conjunction with the embodiments:

[0053] The core technical problem faced by the technical solution of this application embodiment stems from the inventor's accurate understanding of the prior art. Therefore, how to improve the UV aging resistance and high temperature resistance of the protective film, and ensure that it has a certain adhesion, is easy to unwind, and has no residual adhesive exudation is a technical problem that the inventor urgently needs to solve.

[0054] It should be noted that the embodiments do not constitute a limitation on the scope of protection of the claims of this invention. All technical solutions that can be reasonably expected by those skilled in the art based on the technical concepts provided / proved by the embodiments should be covered within the scope of protection of the claims of this invention.

[0055] The specific implementation examples are detailed below:

[0056] Example 1:

[0057] A surface protective film includes a surface layer, a core layer, and an adhesive layer arranged sequentially, with the following formulations for each layer:

[0058] Surface layer formulation (parts by weight):

[0059] Random block copolymer polypropylene (Ryander Basel Moplen RP340R): 78 parts;

[0060] 10 parts of silica open-face masterbatch (silica content 40%, particle size 3~5μm, carrier is LDPE);

[0061] 4-Octylated benzophenone (BASF Uvinul 3008): 5.4 parts;

[0062] 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole (BASF Tinuvin 329): 3.0 parts;

[0063] Silane coupling agent KH-570 modified nano zinc oxide (particle size 30~50nm): 3.6 parts.

[0064] Core layer formulation (parts by weight):

[0065] High isotactic homopolymer polypropylene (ExxonMobil Achieve™ 3930): 82 parts;

[0066] Polyaryletherketone (PAEK) nanofibers (diameter 80~150nm, aspect ratio >30): 8 parts;

[0067] Flake mica powder with cerium oxide coating (flake diameter 10~15μm): 6 parts;

[0068] Maleic anhydride-grafted polypropylene (grafting rate 0.8%, Dow Polybond 3150): 4 parts.

[0069] Adhesive layer formulation (parts by weight):

[0070] SEBS elastomer (30% styrene content, Kronen G1643): 45 parts;

[0071] Hydrogenated C9 petroleum resin (softening point 105℃, ExxonMobil Escorez 5600): 22 parts;

[0072] Highly hydrogenated terpene resin (softening point 115℃, Arakawa Tamanol 901, Japan): 16 parts;

[0073] Di(2,2,6,6-tetramethyl-4-piperidine) sebacate (BASF Tinuvin 770): 6 parts;

[0074] Complexes of zinc stearate and β-diketone compounds (Struktol TR 451, Rhein Chemical): 4 parts;

[0075] Epoxidized soybean oil (Emery Industries Drapex 39, Germany): 7 parts.

[0076] When the following examples and comparative examples involve the same raw materials, they all have the same product model as in Example 1.

[0077] Example 2:

[0078] A surface protective film comprises, in sequence, a surface layer, a core layer, and an adhesive layer, with the following formulation for each layer:

[0079] This embodiment demonstrates that, without changing the core system, excellent performance can still be obtained by fine-tuning the proportions and replacing similar additives, proving the rationality of the protection scope of the solution.

[0080] Surface layer formulation (parts by weight):

[0081] Random block copolymer polypropylene: 75 parts;

[0082] Silica open-face masterbatch: 12 parts;

[0083] 4-Octylated benzophenone: 6.0 parts;

[0084] 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole: 3.4 parts;

[0085] 3.6 parts of nano zinc oxide modified with silane coupling agent KH-570.

[0086] Core layer formulation (parts by weight):

[0087] High isotactic homopolymer polypropylene: 80 parts;

[0088] Polyaryletherketone (PAEK) nanofibers: 10 parts;

[0089] Flake mica powder with cerium oxide coating: 7 parts;

[0090] Maleic anhydride-grafted polypropylene: 3 parts.

[0091] Adhesive layer formulation (parts by weight):

[0092] SEBS elastomer: 48 parts;

[0093] Hydrogenated C9 petroleum resin: 22 parts;

[0094] Highly hydrogenated terpene resin: 16 parts;

[0095] Bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidine) sebacate (BASF Tinuvin 123): 5 parts;

[0096] Complexes of zinc stearate and β-diketone compounds: 3 parts;

[0097] Epoxidized soybean oil: 6 parts.

[0098] Example 3:

[0099] A surface protective film comprises a surface layer, a core layer, and an adhesive layer, wherein the formulation of each layer has been adjusted compared to the aforementioned embodiment, as follows:

[0100] Surface layer formulation (parts by weight):

[0101] Random block copolymer polypropylene: 77.5 parts;

[0102] Silica open-face masterbatch: 11 parts;

[0103] 4-Octylated benzophenone: 4.5 parts;

[0104] 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole: 2.5 parts;

[0105] 4.5 parts of nano zinc oxide modified with silane coupling agent KH-570.

[0106] Core layer formulation (parts by weight):

[0107] High isotactic homopolymer polypropylene: 82 parts;

[0108] Polyaryletherketone (PAEK) nanofibers: 5 parts;

[0109] 10 parts of flaky mica powder coated with cerium oxide;

[0110] Maleic anhydride-grafted polypropylene: 3 parts.

[0111] Adhesive layer formulation (parts by weight):

[0112] SEBS elastomer: 41 parts;

[0113] Hydrogenated C9 petroleum resin: 20 parts;

[0114] Highly hydrogenated terpene resin: 18 parts;

[0115] Di(2,2,6,6-tetramethyl-4-piperidine) sebacate: 10 parts;

[0116] Complexes of zinc stearate and β-diketone compounds: 4 parts;

[0117] Epoxidized soybean oil: 7 parts.

[0118] Example 4:

[0119] A surface protective film comprises a surface layer, a core layer, and an adhesive layer, wherein the formulation of each layer has been adjusted compared to the aforementioned embodiment, as follows:

[0120] Surface layer formulation (parts by weight):

[0121] Random block copolymer polypropylene: 78 parts;

[0122] Silica open-face masterbatch: 9 parts;

[0123] 4-Octylated benzophenone: 6.5 parts;

[0124] 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole: 3.5 parts;

[0125] 3.0 parts of nano zinc oxide modified with silane coupling agent KH-570.

[0126] Core layer formulation (parts by weight):

[0127] High isotactic homopolymer polypropylene: 79 parts;

[0128] Polyaryletherketone (PAEK) nanofibers: 12 parts;

[0129] Flake mica powder with cerium oxide coating: 5 parts;

[0130] Maleic anhydride-grafted polypropylene: 4 parts.

[0131] Adhesive layer formulation (parts by weight):

[0132] SEBS elastomer: 41 parts;

[0133] Hydrogenated C9 petroleum resin: 20 parts;

[0134] Highly hydrogenated terpene resin: 18 parts;

[0135] Di(2,2,6,6-tetramethyl-4-piperidine) sebacate: 10 parts;

[0136] Complexes of zinc stearate and β-diketone compounds: 4 parts;

[0137] Epoxidized soybean oil: 7 parts.

[0138] Example 5:

[0139] Replace the epoxidized soybean oil in Example 1 with epoxidized flaxseed oil.

[0140] Example 6:

[0141] The epoxidized soybean oil in Example 1 was replaced with di(2-ethylhexyl) 4,5-epoxytetrahydrophthalic acid.

[0142] Example 7:

[0143] The complex of zinc stearate and β-diketone in Example 1 was replaced with a complex of hydrotalcite and zinc salt.

[0144] Comparative Example 1:

[0145] The protective film is a conventional cast polypropylene film (CPP film) without any added UV-resistant or high-temperature-resistant protective agents.

[0146] Surface layer formulation (parts by weight):

[0147] Homopolymer polypropylene: 100 parts;

[0148] Silica open-face masterbatch: 5 parts;

[0149] Core layer formulation (parts by weight):

[0150] Homopolymer polypropylene: 100 parts;

[0151] Adhesive layer formulation (parts by weight):

[0152] SEBS elastomer: 50 parts;

[0153] C5 petroleum resin: 45 parts;

[0154] Naphthenic oil: 5 parts.

[0155] Comparative Example 2:

[0156] This protective film has no surface UV protection components.

[0157] This comparative example only lacks the surface UV protection system, removing both types of UV absorbers and modified nano zinc oxide, to demonstrate that this system is the primary and most critical component for UV protection.

[0158] Surface layer formulation (parts by weight):

[0159] Random block copolymer polypropylene: 78 parts;

[0160] 10 parts of silica open-face masterbatch.

[0161] Core layer formulation (parts by weight):

[0162] It is exactly the same as Example 1.

[0163] Adhesive layer formulation (parts by weight):

[0164] It is exactly the same as Example 1.

[0165] Comparative Example 3:

[0166] The core layer of the protective film is reinforced with polyaryletherketone (PAEK) nanofibers and supplemented with an equal amount of polypropylene (PP) to demonstrate that it provides a core heat-resistant skeleton for the protective film and contributes to the main high-temperature dimensional stability.

[0167] Surface layer formulation (parts by weight):

[0168] It is exactly the same as Example 1.

[0169] Core layer formulation (parts by weight):

[0170] High isotactic homopolymer polypropylene: 90 parts;

[0171] Flake mica powder with cerium oxide coating: 6 parts;

[0172] Maleic anhydride-grafted polypropylene: 4 parts.

[0173] Adhesive layer formulation (parts by weight):

[0174] It is exactly the same as Example 1.

[0175] Comparative Example 4:

[0176] This protective film has no adhesive layer stabilization system, while the comparative example has only an adhesive layer stabilization system, demonstrating that the hydrogenated resin and organozinc composite are crucial for preventing high-temperature adhesive residue and maintaining long-term adhesive stability.

[0177] Surface layer formulation (parts by weight):

[0178] It is exactly the same as Example 1.

[0179] Core layer formulation (parts by weight):

[0180] It is exactly the same as Example 1.

[0181] Adhesive layer formulation (parts by weight):

[0182] SEBS elastomer: 50 parts;

[0183] Non-hydrogenated C5 petroleum resin: 45 parts;

[0184] Naphthenic oil: 5 parts.

[0185] Note: Conventional, non-aging-resistant petroleum resins and naphthenic oils were used instead of hydrogenated resins, organozinc complexes, UV stabilizers, and epoxy-containing plasticizers.

[0186] Comparative Example 5:

[0187] The surface layer of this protective film uses unmodified nanoparticles. This comparative example simply replaces the modified nano zinc oxide on the surface with unmodified nanoparticles to directly demonstrate that surface modification technology is the key to solving nanoparticle aggregation and achieving high functionality and high transparency compatibility.

[0188] Surface layer formulation (parts by weight):

[0189] Random block copolymer polypropylene: 78 parts;

[0190] Silica open-face masterbatch: 10 parts;

[0191] 4-Octylated benzophenone: 5.4 parts;

[0192] 2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole: 3.0 parts;

[0193] Unmodified nano zinc oxide: 3.6 parts.

[0194] Core layer formulation (parts by weight):

[0195] It is exactly the same as Example 1.

[0196] Adhesive layer formulation (parts by weight):

[0197] It is exactly the same as Example 1.

[0198] The method for preparing the surface protective film in this embodiment is as follows:

[0199] Preparation of surface layer masterbatch:

[0200] First, random block copolymer polypropylene and silica open-face masterbatch are premixed in a high-speed mixer at 800 rpm for 5 minutes. Then, they are melt-blended and granulated in a co-rotating twin-screw extruder at a temperature range of 190-200℃ with a screw speed of 250 rpm. After the base masterbatch cools to below 80℃, 4-octylbenzophenone, benzotriazole UV absorber, and modified nano zinc oxide are added, and the mixture is mixed at low speed at 60℃ for 8 minutes.

[0201] Core layer masterbatch preparation:

[0202] High isotactic homopolymer polypropylene, polyaryletherketone nanofibers, cerium oxide-coated mica powder, and maleic anhydride-grafted polypropylene were mixed in a high-speed mixer at 1000 rpm for 15 minutes. Then, the mixture was melt-extruded and granulated at 210-220°C using a co-rotating twin-screw extruder with a screw length-to-diameter ratio of 44:1.

[0203] Preparation of binder masterbatch:

[0204] SEBS elastomer, hydrogenated petroleum resin, hydrogenated terpene resin, UV stabilizer and organozinc complex were pre-plasticized in a mixer at 175°C for 6 minutes. Finally, an epoxy-containing plasticizer was added, and the mixture was continued to be mixed for 3 minutes before being discharged and granulated.

[0205] Three-layer co-extrusion molding:

[0206] The masterbatch was added to an ABC-type three-layer co-extrusion casting machine, with the surface temperature set at 200~210℃, the core temperature at 210~220℃, and the binder temperature at 180~190℃. After the melt was extruded through a T-die (die lip gap 0.8mm), it was rapidly cooled and shaped on a 28℃ cooling roller at a traction speed of 25m / min, and then corona treated (processing power 4kW, surface tension 42dyn / cm) before being wound up to obtain a protective film with a total thickness of 30±2μm, of which the surface layer is 8±0.5μm, the core layer is 19±1μm, and the binder layer is 3±0.3μm.

[0207] The performance testing method and process of the surface protective film prepared by the embodiment are as follows:

[0208] The performance of all embodiments and comparative examples was characterized by the following test methods. All tests were conducted in a standard environment with a temperature of 23±2℃ and a relative humidity of 50±5%.

[0209] ① Optical performance testing:

[0210] Test standard: ASTM D1003;

[0211] Testing procedure: Using a haze meter, the protective film sample was flattened and fixed in the test window, and the transmittance and haze value were measured at a wavelength of 550nm. Each sample was measured 5 times at different positions, and the average value was taken.

[0212] ② Peel force test:

[0213] Test standard: ASTM D3330;

[0214] Test procedure: The protective film was cut into 25mm wide samples and peeled off from a 304 stainless steel test plate at a 180° angle and a speed of 300mm / min. The average force value during the peeling process was recorded as the peeling force. The formula for calculating the rate of change of peeling force before and after aging is: [(peeling force after aging - initial peeling force) / initial peeling force] × 100%.

[0215] ③ UV aging resistance test:

[0216] Test standard: ASTM G154 (Cycle 1), UVB-313 lamp, irradiance 0.67W / m²;

[0217] Test procedure: The samples were placed in a QUV aging test chamber and irradiated with ultraviolet light at 60°C for 8 hours, followed by condensation at 50°C for 4 hours, and the cycle was repeated for 500 hours. Tensile strength was tested before and after the test according to ASTM D638 standard, and the retention rate was calculated; yellowing index (ΔYI) was tested according to ASTM E313 standard.

[0218] ④ High temperature resistance test

[0219] Heat shrinkage rate test: According to GB / T 13519 standard, place a 100mm×100mm sample in a 120℃ forced-air drying oven for 30 minutes, and measure the dimensional change after cooling to calculate the heat shrinkage rate.

[0220] Residual Adhesive Test: The protective film is adhered to a glass plate and placed in a 120℃ oven for 1 hour. After cooling, it is peeled off at a 180° angle and a speed of 300mm / min. The residual adhesive is visually inspected and rated on a 5-level scale. Level 1: Complete failure, residual adhesive area > 50%, large-area adhesive transfer, the protective film cannot be completely peeled off, or it leaves a muddy or clump-like residue after peeling. Level 2: Poor, severe residual adhesive, residual adhesive area 25% ~ 50%, large areas of continuous sheet-like residue. Level 3: Moderate, noticeable residual adhesive, residual adhesive area 5% ~ 25%, visible dots, streaks, or discontinuous sheet-like residue. Level 4: Good, very slight residual adhesive, residual adhesive area < 5%, only fine, sparse, hazy residue visible under specific lighting conditions. Level 5: Excellent, no visible residue, the protected surface is clean, and there are no sticky substances remaining.

[0221] ⑤ Long-term stability test

[0222] Damp heat aging test: Place the sample in a constant temperature and humidity chamber at 60℃ and 85%RH for 30 days and observe the changes in appearance.

[0223] Unwinding force test: The unwinding force of the film roll after storage is measured according to ASTM D3330 standard to evaluate the opening performance.

[0224] The performance test results of the implementation method are shown in Tables 1 and 2 below:

[0225] Table 1 Performance test results of the surface protective films prepared in Examples 1-7

[0226]

[0227] Table 2 Performance test results of the surface protective films prepared in Comparative Examples 1-5

[0228]

[0229] As can be seen from Tables 1 and 2, compared with the prior art, Embodiments 1-7 of the present invention have the following significant beneficial effects:

[0230] Synergistic UV resistance: The surface layer innovatively combines two organic UV absorbers (4-octylbenzophenone and benzotriazole) with complementary wavelengths and an inorganic UV shielding agent (modified nano zinc oxide), forming a synergistic protection system of "physical shielding + chemical absorption", which achieves broad-spectrum and efficient protection against UVA and UVB bands and greatly delays the photo-oxidative aging of the material.

[0231] Therefore, compared with Comparative Example 2, which did not add UV protection components to the surface layer in Example 1, the surface protective film prepared therein showed a significant decrease in tensile strength, yellowing index and peel force change rate after QUV aging for 500h, and a slight decrease in long-term stability.

[0232] Compared to Comparative Example 5, which added unmodified nano-zinc oxide to the surface layer of Example 1, the initial transmittance of the prepared surface protective film decreased, while the initial haze increased significantly. The addition of inorganic UV shielding agent had almost no effect on the transparency and haze of the surface protective film.

[0233] Excellent high temperature resistance: The core layer incorporates polyaryletherketone (PAEK) nanofibers as a high temperature resistance reinforcing agent, which significantly improves the overall heat distortion temperature and dimensional stability of the protective film; the adhesive layer uses hydrogenated petroleum resin and terpene resin, combined with an organic zinc composite heat stabilizer, to ensure that the adhesive layer does not soften or migrate at high temperatures, thereby avoiding adhesive residue.

[0234] Therefore, compared to Comparative Example 3, which did not add polyaryletherketone nanofibers to the core layer in Example 1, the surface protective film prepared there exhibits a significantly increased thermal shrinkage rate at 120°C.

[0235] Compared to Example 1, which did not add hydrogenated resin, organic zinc complex, UV stabilizer and epoxy-containing plasticizer to the adhesive layer, the surface protective film prepared there showed a slight decrease in tensile strength retention rate after QUV aging for 500h, while the yellowing index and peel strength change rate increased significantly. At the same time, the residual adhesive rating at 120℃ / 1h was only level 2, and the long-term stability also decreased significantly.

[0236] Excellent performance balance: Through the precise design of the functions of each layer, the protective film of this invention maintains good initial tack and peelability (no residue) while also having high light transmittance (>89%) and low haze (<3.5%) optical performance, meeting the protection needs of high-end optical devices;

[0237] As a comparative example 1 of conventional cast polypropylene film, the surface protective film prepared therein has performance inferior to that of Example 1 in all aspects except for the initial light transmittance.

[0238] Process innovation: The preparation process combines stepwise masterbatch pretreatment with three-layer co-extrusion casting, which effectively solves the dispersion problem of various additives (especially nanofillers) and avoids the decomposition of sensitive additives at high temperatures, thus ensuring the stability and consistency of product performance.

[0239] In summary, the self-adhesive protective film provided in this application achieves a perfect combination of UV aging resistance and high temperature resistance by constructing a three-layer synergistic structure of "surface composite UV protection system - core nanofiber reinforcement system - adhesive layer thermal stability system". It not only maintains excellent anti-yellowing performance and mechanical strength under long-term UV irradiation, but also maintains stable dimensional properties and adhesion in high-temperature environments, ensuring no adhesive residue upon peeling. At the same time, it has optical properties of high light transmittance and low haze, providing a comprehensive and reliable surface protection solution for demanding applications such as automotive displays, photovoltaic modules, and high-end home appliances.

[0240] In the description of this specification, the references to terms such as "embodiment," "basic embodiment," "preferred embodiment," "other embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0241] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0242] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A surface protective film, comprising a surface layer, a core layer, and an adhesive layer disposed sequentially; Its features are: The surface layer comprises a first polypropylene matrix resin, an organic ultraviolet absorber, and an inorganic ultraviolet shielding agent. The organic ultraviolet absorber is composed of a first organic ultraviolet absorber with an absorption band of 290-350 nm and a second organic ultraviolet absorber with an absorption band of 300-400 nm, in a mass ratio of (4.5-6.75):(2.5-3.75). The organic ultraviolet absorber accounts for 7-10.5% of the mass of the surface layer, and the mass ratio of the organic ultraviolet absorber to the inorganic ultraviolet shielding agent is 1.55-3.

5. The core layer comprises a second polypropylene matrix resin, polyaryletherketone nanofibers, and flaky mica powder coated with cerium oxide; the nanofibers account for 5-12% of the mass percentage of the core layer, and the flaky mica powder accounts for 5-10% of the mass percentage of the core layer. The adhesive layer comprises thermoplastic SEBS elastomer, hydrogenated adhesive resin, organozinc compound, UV stabilizer, and epoxy-containing plasticizer, wherein the UV stabilizer accounts for 5-10% of the adhesive layer by mass. The inorganic ultraviolet shielding agent is silane coupling agent modified nano zinc oxide; The organozinc complex is selected from one of the following: a complex of zinc stearate and β-diketone compounds, or a complex of hydrotalcite and zinc salts.

2. The surface protective film according to claim 1, characterized in that: The first polypropylene matrix resin is random block polypropylene, and the second polypropylene matrix resin is isotactic homopolymer polypropylene.

3. The surface protective film according to claim 1 or 2, characterized in that: The surface layer also includes open silica masterbatch.

4. The surface protective film according to claim 1 or 2, characterized in that: The core layer also includes maleic anhydride-grafted polypropylene.

5. The surface protective film according to claim 1, characterized in that: The plasticizer is selected from one of epoxidized soybean oil, epoxidized linseed oil, epoxidized castor oil, epoxidized palm oil, and di(2-ethylhexyl) 4,5-epoxytetrahydrophthalic acid.

6. The surface protective film according to claim 1, characterized in that: The ultraviolet light stabilizer is one of di(2,2,6,6-tetramethyl-4-piperidine) sebacate or bis(1-octoxy-2,2,6,6-tetramethyl-4-piperidine) sebacate.

7. The surface protective film according to claim 1, characterized in that: After QUV aging for 500 hours: tensile strength retention rate > 80%, yellowing index < 3, peel force change rate < 12%; The heat shrinkage rate at 120℃ for 30 minutes is <1.0%; The surface protective film was adhered to the glass plate and placed in an oven at 120°C for 1 hour before being peeled off without any residue. After the surface protective film was placed in a constant temperature and humidity chamber at 60℃ and 85%RH for 30 days, there was no change in appearance, and the unwinding force was ≤1.0N / 25mm.

8. The application of the surface protective film according to any one of claims 1 to 7, characterized in that: For surface protection of materials that require UV resistance and high temperature resistance.

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