Curing coating for PET pre-coated film, its preparation method, and a coating film

Abstract

This invention relates to a hardening coating for PET pre-coated films, its preparation method, and a coating film. It includes a primer coating and a topcoat coating; the primer coating is composed of epoxy-modified acrylate, polyurethane-modified acrylate, a photoinitiator, a cationic initiator, a leveling agent, and an organic solvent; the topcoat coating is composed of polyurethane-modified acrylate, a photoinitiator, an organofluorosilicone additive, a reactive diluent, fillers, and an organic solvent. The primer coating uses an epoxy-modified acrylate compounded with a polyurethane-modified acrylate, combined with a dual-initiation system of a free radical photoinitiator and a cationic initiator; the topcoat coating uses polyurethane-modified acrylate as the main component, combined with organofluorosilicone additives and functional fillers, achieving simultaneous improvement in coating hardness, hydrophobicity, and abrasion resistance.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a hardened coating for PET pre-coated film, its preparation method, and a coating film. Background Technology

[0002] Hardened coatings are the core material for surface protection of PET (polyethylene terephthalate) films, widely used in display panel protective films, 3C product protection, electronic decorative films, and high-end packaging. They have stringent requirements for surface hardness, abrasion resistance, hydrophobicity, and optical properties. Currently, most mass-produced PET hardened coatings use 188μm PET pre-coated films as the substrate, prepared using a double-sided coating process, resulting in a total coating thickness of 45-50μm. While this meets basic protection needs, it suffers from problems such as large substrate thickness, high cost, poor flexibility, and complex production processes, making it difficult to adapt to the trend of thinner, lower-cost high-end applications.

[0003] Chinese invention patent application CN116694222A discloses a high-hardness, wear-resistant UV-curable coating. While the coating's performance is optimized through resin compounding, its maximum hardness after modification only reaches 5H under a 500g load, indicating only average wear resistance. Furthermore, no investigation into its optical properties has been conducted, making it unsuitable for use as an optical-grade protective film. Other similar technologies, although optimizing the coating's optical properties, result in a significant decrease in hardness, reaching only H grade, failing to meet wear resistance standards. Thus, it is difficult to simultaneously achieve high hardness and high optical performance.

[0004] Furthermore, existing processes generally employ double-sided coating, which is difficult to roll up, cumbersome to operate, and results in low production efficiency. When switching to 125μm thin PET pre-coated films, the coating is prone to severe curling and warping, and the total coating thickness is difficult to reduce. The three core properties—hardness, hydrophobicity, and abrasion resistance—cannot be simultaneously achieved under thin coating and thin substrate conditions. Currently, the industry lacks a curing coating suitable for 125μm PET pre-coated films, employing a single-sided two-coat process, with a total film thickness of 35-40μm, and possessing 7H hardness, ≥108° water contact angle, and 2500 cycles of steel wool resistance. This hinders the development of PET curing films towards thinner, lower-cost, and higher-performance directions. Summary of the Invention

[0005] The first aspect of this invention provides a curing coating for PET pre-coated films, comprising a primer coating and a topcoat coating; the primer coating comprises the following components in parts by weight: 1-5 parts photoinitiator, 1-3 parts cationic initiator, 10-20 parts epoxy-modified acrylate, 25-45 parts polyurethane-modified acrylate, 30-50 parts organic solvent, and 0-1 parts leveling agent; the topcoat coating comprises the following components in parts by weight: 1-5 parts photoinitiator, 30-60 parts polyurethane-modified acrylate, 30-50 parts organic solvent, 5-10 parts reactive diluent, 0-3 parts organofluorosilicone additive, and 3-10 parts filler.

[0006] Existing curing coatings for PET pre-coated films mostly employ a single free radical curing system and a single-layer structure, which suffers from inherent defects such as large curing volume shrinkage and high internal stress. When coated on thin PET substrates of 125μm and below, severe curling and warping easily occur. Furthermore, they cannot simultaneously achieve high hardness, high hydrophobicity, and high abrasion resistance, often resulting in a technical bottleneck where increased hardness is accompanied by loss of flexibility, and abrasion resistance optimization leads to deterioration of optical performance. This invention creates a synergistic system through differentiated formulation design of the primer and topcoat. The primer employs a dual-initiation, dual-curing system, combining epoxy-modified acrylate and polyurethane-modified acrylate with a free radical photoinitiator and a cationic initiator. Under UV irradiation, the active free radicals generated by the cracking of the free radical photoinitiator can rapidly trigger the free radical polymerization reaction of carbon-carbon double bonds in polyurethane-modified acrylate, achieving rapid surface drying of the coating and the initial construction of a three-dimensional cross-linked network. The superacid generated by the cationic initiator under UV excitation can trigger the cationic ring-opening polymerization of epoxy groups in epoxy-modified acrylate. This polymerization process has no small molecule volatilization and the volume shrinkage rate is much lower than that of free radical polymerization, which can effectively offset the curing internal stress generated during free radical polymerization, fundamentally alleviating the curling and warping problem after coating of thin PET substrates. At the same time, the active hydroxyl groups generated by epoxy ring opening can form strong hydrogen bonds with the polar groups on the surface of PET substrate, greatly improving the interfacial adhesion between the coating and PET substrate. The rigid epoxy skeleton of epoxy-modified acrylate and the flexible polyurethane segments of polyurethane-modified acrylate form a micro-phase separation structure with soft and hard segments, which can ensure the basic hardness of the primer layer while taking into account the flexibility and impact resistance of the coating, providing a strong, low-stress, and smooth bearing substrate for the stable realization of the topcoat performance. The topcoat uses high-functionality polyurethane-modified acrylate as the main resin, which forms a dense three-dimensional network structure with high cross-linking density after UV curing, providing the core pencil hardness support for the coating. The organic fluorosilicone additives introduced into the system have extremely low surface energy and can spontaneously migrate and accumulate to the coating surface during the coating curing process. Without destroying the main cross-linking structure of the coating, it significantly reduces the surface tension of the coating and improves the water contact angle and stain resistance. The filler is uniformly dispersed in the resin cross-linking network. With its own high hardness and wear resistance, the filler forms a rigid and wear-resistant physical support skeleton inside the coating, which greatly improves the scratch resistance and steel wool friction resistance of the coating. At the same time, the small size effect of the filler can effectively avoid its negative impact on the optical smoothness and light transmittance of the coating. Ultimately, the primer solved the core problems of internal stress accumulation and insufficient interfacial adhesion in thin substrate coating through a dual-curing and resin compounding system, providing a stable structural foundation for the functional design of the topcoat. The topcoat, on the other hand, achieved precise improvement of the coating surface performance through the directional optimization of functional additives and fillers. The two formed a synergistic mechanism of "stable adhesion to the substrate and improved performance of the surface layer", which broke through the performance shortcomings of existing technologies and ultimately achieved a simultaneous and significant improvement in coating hardness, hydrophobicity, and wear resistance.

[0007] The photoinitiator includes a free radical photoinitiator, which may be any one or more grades selected from 184, 1173, TPO, 2959, KIP160, MBF, and 1212.

[0008] The cationic initiator includes cationic photoinitiators, comprising any one or more of diaryliodomonium salts, triarylthiomonium salts, triarylthiomonium phosphate salts, triarylthiomonium antimony salts, organometallic cationic initiators, and organosilane cationic initiators.

[0009] The epoxy-modified acrylates include bisphenol A type epoxy acrylates, bisphenol F type epoxy acrylates, alicyclic epoxy acrylates, phenolic type epoxy acrylates, and glycidyl ether type epoxy acrylates.

[0010] Optionally, the epoxy-modified acrylate includes any one or more grades of Yantai Donghua DR-323, DR-3260, Guangdong Haohui HE-3215, Dow ERL-4221, and Daicel CELLOXIDE2021P.

[0011] The functionality of the polyurethane-modified acrylate in both the primer and topcoat components is 6-15.

[0012] Optionally, the polyurethane-modified acrylate includes any one or more grades of Guangdong Haohui CR-90843, CR-92696, HP-6610, HP-6615, HP-6915, HP-90492, Kunshan Castel 7559C, Guangzhou Songda SD-1338B, Zhongshan DICZHU-2197, and Guangzhou Runao FSP-8638.

[0013] Optionally, the polyurethane-modified acrylate in both the primer and topcoat components has a functionality of 6-8 and a viscosity of 1000-4000 cps at 60°C.

[0014] Optionally, the weight ratio of epoxy-modified acrylate to polyurethane-modified acrylate in the primer coating component is 1:(2-5).

[0015] The organic solvent includes any one or more of ethyl acetate, butyl acetate, toluene, butanone, methyl isobutyl ketone, propylene glycol methyl ether acetate, diacetone alcohol, and ethylene glycol butyl ether.

[0016] The leveling agent includes any one or more grades of BYK-333, BYK-337, BYK-3700, TEGO432, TEGO2300, and Evcona 3034.

[0017] The reactive diluent includes at least one of IBOA, HEA, HPA, TPGDA, DPGDA, and HDDA.

[0018] The organofluorine-silicone additives include any one or more grades of Guangdong Aus Chemical APU-25, APU-25F, Guangdong Lancolo lencolo3007A, 2300, and Dongguan Xuyihua Chemical XHA61.

[0019] The particle size of the filler is 10-500 nm.

[0020] Optionally, the filler includes at least one of nano-alumina, nano-silica, nano-titanium dioxide, nano-zinc oxide, nano-calcium carbonate, nano-magnesium oxide, and nano-zirconia.

[0021] Optionally, the filler includes nano-alumina; optionally, the nano-alumina includes any one or more grades selected from Hangzhou Jiupeng New Materials AL-30P, Shanghai Xiaohuang Nano SL-300P, and Xuancheng Jingrui New Materials VK-L10WT.

[0022] Optionally, the particle size of the nano-alumina is 10-100 nm.

[0023] The second aspect of the present invention provides a method for preparing a coating, comprising the following steps: mixing an organic solvent, a photoinitiator, and a cationic initiator in a primer coating, adding the remaining components of the primer coating, mixing evenly to obtain a primer coating; mixing an organic solvent, a photoinitiator, and a cationic initiator in a topcoat coating, adding the remaining components of the topcoat coating, mixing evenly to obtain a topcoat coating.

[0024] A third aspect of the present invention provides a paint film comprising a substrate layer, a primer layer, and a topcoat layer stacked sequentially, wherein the primer layer comprises a base coating and the topcoat layer comprises a topcoat coating.

[0025] The thickness of the substrate layer is ≤180μm, the substrate layer includes a PET film, the thickness of the primer layer is 5-30μm, and the thickness of the topcoat layer is 5-20μm.

[0026] Optionally, the thickness of the substrate layer is ≤150μm, and the thickness of the primer layer is 10-25μm.

[0027] Optionally, the thickness of the substrate layer is ≤125μm.

[0028] The method for preparing the paint film includes the following steps: applying a primer coating to one surface of a substrate layer and drying it to obtain a composite layer; applying a topcoat coating to the surface of the primer coating of the composite layer and curing it to obtain a paint film.

[0029] Beneficial effects 1. The primer of this invention uses epoxy-modified acrylate combined with polyurethane-modified acrylate, combined with a dual initiation system of free radical photoinitiator and cationic initiator. The topcoat uses polyurethane-modified acrylate as the main body, combined with organofluorosilicone additives and functional fillers, to achieve simultaneous improvement of coating hardness, hydrophobicity and wear resistance.

[0030] 2. This invention limits the weight ratio of epoxy-modified acrylate and polyurethane-modified acrylate in the primer to 1:(2-5); while ensuring the adhesion of the coating, it significantly improves the basic hardness and anti-curling performance of the primer layer.

[0031] 3. The present invention limits the functionality of polyurethane modified acrylate in both the primer and topcoat to 6-15, preferably 6-8; it achieves a precise balance between coating hardness and flexibility, and can achieve a pencil hardness of up to 7H under a load of 750g, while ensuring that the coating does not warp severely on thin PET substrates, perfectly meeting the application requirements of lightweight PET hardened films.

[0032] 4. This invention introduces specific nanofillers into the topcoat system and utilizes the high hardness and high wear resistance of nano-inorganic materials to construct a rigid support skeleton in the cross-linked network of the resin formed by UV curing. This significantly improves the abrasion resistance of the coating. Without affecting the smoothness of the coating appearance, it achieves excellent wear resistance performance of 2500 times of friction with 0000# steel wool under a 1000g load without scratches. This solves the problems of mismatch between hardness improvement and wear resistance, and the inability to balance optical performance and wear resistance in the prior art.

[0033] 5. This invention defines the coating film as a sequentially stacked structure of a substrate layer, a primer layer, and a topcoat layer, specifying a substrate layer thickness of ≤180μm, a primer layer thickness of 5-30μm, and a topcoat layer thickness of 5-20μm. It also defines a step-by-step film-forming process of first applying and drying the primer, then applying and curing the topcoat. By adjusting the thickness ratio of the two coating layers, it flexibly adapts to different requirements for hardness, flexibility, and curl. Furthermore, under the condition that the substrate thickness is ≤125μm and the total coating thickness is ≤40μm, it can simultaneously meet the core performance indicators of 7H pencil hardness, ≥108° water contact angle, and 2500 cycles of scratch resistance against steel wool, perfectly adapting to high-end optical applications such as display panels and 3C product protection. Detailed Implementation

[0034] Examples 1-5 A curing coating for PET pre-coated film is composed of a primer coating and a topcoat coating, wherein the primer coating corresponds to Scheme 4 in Table 1, the topcoat coating corresponds to Scheme A in Table 1, and the blank spaces in Table 1 indicate that no coating was added.

[0035] A method for preparing a hardening coating for PET pre-coated film involves mixing the organic solvent, photoinitiator, and cationic initiator in a primer coating (500 rpm, stirring for 15 minutes), then sequentially adding epoxy-modified acrylate and polyurethane-modified acrylate from the primer coating components, followed by the remaining components of the primer coating, and mixing thoroughly (500 rpm, stirring for 20 minutes) to obtain the primer coating. The method also involves mixing the organic solvent and photoinitiator in a topcoat coating, then adding the polyurethane-modified acrylate from the topcoat coating components, followed by the remaining components of the topcoat coating, and mixing thoroughly to obtain the topcoat coating.

[0036] A coating film is composed of a substrate layer (125μm, PET), a primer layer and a topcoat layer stacked sequentially. The primer layer is composed of a base coating, and the topcoat layer is composed of a topcoat coating. The thicknesses are shown in Table 2.

[0037] The method for preparing the coating film includes the following steps: applying a primer coating onto one surface of a PET film using a wire rod, drying (baking temperature 80-100℃, baking time 2 min), and then allowing it to stand for 24 h to obtain a composite layer of a substrate layer and a PET film; applying a topcoat coating onto the surface of the substrate layer of the composite layer, and curing (light intensity 150 mW / cm²). 2 Curing energy 1200mJ / cm 2 The paint film is then obtained.

[0038] Table 1

[0039] Table 2

[0040] Examples 6-10 A curing coating for PET pre-coated film is composed of a primer coating and a topcoat coating, wherein the primer coating corresponds to Scheme 4 in Table 1 and the topcoat coating corresponds to Scheme B in Table 1.

[0041] A coating film is composed of a substrate layer (125μm, PET), a primer layer and a topcoat layer stacked sequentially. The primer layer is composed of a base coating, and the topcoat layer is composed of a topcoat coating. The thicknesses are shown in Table 3.

[0042] The preparation methods for the hardened coating and the paint film are the same as in Example 1.

[0043] Table 3

[0044] Examples 11-15 A curing coating for PET pre-coated film is composed of a primer coating and a topcoat coating, wherein the primer coating corresponds to Scheme 7 in Table 1 and the topcoat coating corresponds to Scheme C in Table 1.

[0045] A coating film is composed of a substrate layer (125μm, PET), a primer layer and a topcoat layer stacked sequentially. The primer layer is composed of a base coating, and the topcoat layer is composed of a topcoat coating. The thicknesses are shown in Table 4.

[0046] The preparation methods for the hardened coating and the paint film are the same as in Example 1.

[0047] Table 4

[0048] Comparative Examples 1-5 A curing coating for PET pre-coated film is composed of a primer coating and a topcoat coating, wherein the primer coating corresponds to Scheme 8 in Table 1 and the topcoat coating corresponds to Scheme C in Table 1.

[0049] A coating film is composed of a substrate layer (125μm, PET), a primer layer and a topcoat layer stacked sequentially. The primer layer is composed of a base coating, and the topcoat layer is composed of a topcoat coating. The thicknesses are shown in Table 5.

[0050] The preparation methods for the hardened coating and the paint film are the same as in Example 1.

[0051] Table 5

[0052] Comparative Examples 6-10 A curing coating for PET pre-coated film is composed of a primer coating and a topcoat coating, wherein the primer coating corresponds to Scheme 9 in Table 1 and the topcoat coating corresponds to Scheme C in Table 1.

[0053] A coating film is composed of a substrate layer (125μm, PET), a primer layer and a topcoat layer stacked sequentially. The primer layer is composed of a base coating, and the topcoat layer is composed of a topcoat coating. The thicknesses are shown in Table 6.

[0054] The preparation methods for the hardened coating and the paint film are the same as in Example 1.

[0055] Table 6

[0056] Performance testing methods 1. The primer prepared by schemes 1-5 was coated on the substrate (125μm, PET). The average thickness of the dry film was 13.5μm. After drying, the performance was tested, and the test data are listed in Table 7.

[0057] 2. The performance of the coatings prepared in Examples 1-5 was tested, and the test data are listed in Table 8.

[0058] 3. The properties of the paint films prepared in Examples 6-10 were tested, and the test data are listed in Table 9.

[0059] 4. The performance of the coatings prepared in Examples 11-15 was tested, and the test data are listed in Table 10.

[0060] 5. The properties of the paint films prepared in Comparative Examples 1-5 were tested, and the test data are listed in Table 11.

[0061] 6. The properties of the paint films prepared in Comparative Examples 6-10 were tested, and the test data are listed in Table 12.

[0062] The specific test items involved above are as follows: Appearance: Visual inspection shows no obvious defects such as graininess, orange peel texture, or rainbow patterns.

[0063] Adhesion: The QFH-A type cross-cut tester was used, and the test was conducted in accordance with GB / T9286-1998. The multi-blade cutter was used with a spacing of 1mm, and 3M 600 tape was used for the cross-cut test.

[0064] Pencil hardness test: Mitsubishi pencil, load requirement 750g, hardness requirement 7H / OK.

[0065] Steel Wool Resistance Test: The test is conducted using a multi-functional abrasion tester. The steel wool model is 0000#, the load is 1000g, the load area is 2cm×2cm, the friction speed is 60 times / min, and the number of friction cycles is 2500. After friction, the surface is observed with a magnifying glass to see if scratches appear. No scratches indicate OK, otherwise it is NG.

[0066] Water contact angle test: Use a contact angle measuring instrument to test. Cut the sample into 2cm×5cm pieces, clean the surface with anhydrous ethanol, and test after drying. The drop volume is 3mL. Measure 3-5 times and take the average value. The water contact angle should be ≥108°.

[0067] Performance test data Table 7

[0068] Table 8

[0069] Table 9

[0070] Table 10

[0071] Table 11

[0072] Table 12

[0073] This invention uses a 125μm thick PET film as the core substrate and focuses on three core variables: the composition of the primer formulation, the functional components of the topcoat, and the coating thickness ratio. It systematically verifies the key properties of the single-sided two-coat hardening coating system of this invention, such as appearance smoothness, substrate adhesion, anti-curling, pencil hardness, abrasion resistance, and hydrophobicity. It fully demonstrates the control law and technical advantages of the formulation design and process parameters on the comprehensive performance of the coating. The test results in Tables 7-12 show that, in the primer formulation verification stage, schemes 1-4, which use epoxy-modified acrylate and 6-9 functional polyurethane-modified acrylate combined with a cationic initiator dual-curing system, all achieved excellent appearance without defects and good adhesion to the PET substrate. Furthermore, the coating could naturally flatten without severe curling. Scheme 4, through the application of 6-functional polyurethane acrylate and a 1:4 epoxy-polyurethane resin ratio, achieved a hardness of 5H under a 500g load, perfectly balancing basic hardness and anti-curling performance. Scheme 5, which did not add a cationic initiator or epoxy-modified acrylate, achieved a hardness of 6H, but exhibited an inability to flatten. Scheme 6, with an excessively high proportion of epoxy-modified acrylate, had a slightly lower hardness, verifying the key regulatory role of the cationic-epoxy system in internal stress control and the further improvement of film performance by the epoxy and polyurethane acrylate combination.

[0074] In the overall performance verification of the dual-coat system, Examples 1-10, which did not add fillers, all achieved a water contact angle of ≥107° and a maximum pencil hardness of 7H. However, all of them failed the test of 2500 cycles of rubbing with 0000# steel wool under a 1kg load, directly confirming the decisive role of fillers in the wear resistance of the coating. Examples 11-15, which used the Scheme 7 primer with the required ratio and the C topcoat with added nano alumina filler, achieved the core performance indicators of 7H pencil hardness under a 750g load, 108-109° water contact angle, and 2500 cycles of scratch resistance with steel wool by precisely controlling the coating thickness. With the primer thickness of 15-20μm and the topcoat thickness of 12-18μm, the coating could naturally flatten without serious curling, achieving simultaneous compliance with the standards for hardness, hydrophobicity, wear resistance, and anti-curling properties under thin substrate and thin coating conditions. In the reverse verification of the comparative examples, comparative examples 1-5, where the epoxy to polyurethane ratio exceeded the 1:(2-5) range, all exhibited severe curling after coating, rendering them completely unusable. Comparative examples 6-10, which did not add cationic initiators and epoxy-modified acrylate, although the coating could be flattened and some groups achieved steel wool resistance, had a maximum pencil hardness of only 6H. The core hardness performance was significantly inferior to the optimal example, further confirming that the free radical-cationic dual initiation system and the precise blending of epoxy and polyurethane are the core prerequisites for achieving both high coating hardness and low curling.

[0075] The overall test results fully demonstrate that this invention, through differentiated design of the primer-topcoat dual system, precise control of resin functionality and ratio, synergistic effect of the dual curing system, directional optimization of functional fillers and fluorosilicone additives in the topcoat, and matching design of coating thickness, has successfully overcome the industry pain point of the existing thin PET pre-coated film coating process, which cannot simultaneously achieve high hardness, high wear resistance, high hydrophobicity, low curl, and excellent optical performance. It can achieve full compliance of core performance under the conditions of 125μm thin substrate and total coating thickness ≤40μm, verifying the advanced nature, stability, and industrial adaptability of this technical solution.

Claims

1. A curing coating for PET pre-coated film, characterized in that, Includes primer coatings and topcoat coatings; The primer coating comprises the following components by weight: 1-5 parts photoinitiator, 1-3 parts cationic initiator, 10-20 parts epoxy-modified acrylate, 25-45 parts polyurethane-modified acrylate, 30-50 parts organic solvent, and 0-1 part leveling agent. The topcoat comprises the following components by weight: 1-5 parts photoinitiator, 30-60 parts polyurethane-modified acrylate, 30-50 parts organic solvent, 5-10 parts reactive diluent, 0-3 parts organofluorosilicone additive, and 3-10 parts filler.

2. The coating according to claim 1, characterized in that, The epoxy-modified acrylate includes at least one of bisphenol A type epoxy acrylate, bisphenol F type epoxy acrylate, alicyclic epoxy acrylate, phenolic epoxy acrylate, and glycidyl ether type epoxy acrylate.

3. The coating according to claim 2, characterized in that, The functionality of the polyurethane-modified acrylate in both the primer and topcoat components is 6-15.

4. The coating according to claim 3, characterized in that, The functionality of the polyurethane-modified acrylate in both the primer and topcoat components is 6-8.

5. The coating according to claim 1, characterized in that, The weight ratio of epoxy-modified acrylate to polyurethane-modified acrylate in the primer coating component is 1:(2-5).

6. The coating according to claim 1, characterized in that, The filler includes at least one of nano-alumina, nano-silica, nano-titanium dioxide, nano-zinc oxide, nano-calcium carbonate, nano-magnesium oxide, and nano-zirconia.

7. A method for preparing the coating according to any one of claims 1-6, characterized in that, The process includes the following steps: mixing the organic solvent, photoinitiator, and cationic initiator in the primer coating, adding the remaining components of the primer coating, and mixing evenly to obtain the primer coating; mixing the organic solvent and photoinitiator in the topcoat coating, adding the remaining components of the topcoat coating, and mixing evenly to obtain the topcoat coating.

8. A paint film, characterized in that, It comprises a substrate layer, a primer layer and a topcoat layer stacked sequentially, wherein the primer layer comprises the base coating as described in any one of claims 1-6, and the topcoat layer comprises the topcoat as described in any one of claims 1-6.

9. The paint film according to claim 8, characterized in that, The thickness of the substrate layer is ≤180μm, the substrate layer includes a PET film, the thickness of the primer layer is 5-30μm, and the thickness of the topcoat layer is 5-20μm.

10. The paint film according to claim 9, characterized in that, The method for preparing the paint film includes the following steps: applying a primer coating to one surface of a substrate layer and drying it to obtain a composite layer; applying a topcoat coating to the surface of the primer coating of the composite layer and curing it to obtain a paint film.

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