Flexible coating material with gradient transition layer and double-silver layer structure and preparation method of flexible coating material

Abstract

The invention discloses a flexible coating material with a gradient transition layer and a double-silver layer structure and preparation of the flexible coating material. The flexible coating material comprises a flexible base material layer, a gradient transition layer and a double-silver layer, the gradient transition layer sequentially comprises a bottom coating, a middle coating and a surface coating; the double-silver layer sequentially comprises a first silver layer, a dielectric layer, a second silver layer and a protective layer; the middle coating layer contains a carboxylated carbon nano tube; the carboxylated carbon nanotubes are arranged in a directional manner. Through gradient transition layer design and double-silver layer structure optimization, the high-light-transmittance and high-weather-resistance coating material based on the thermoplastic polyurethane (TPU) base material is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible functional materials, and specifically to a high-light-transmittance, high-weather-resistant coating material based on a thermoplastic polyurethane (TPU) substrate, which is particularly suitable for surface functionalization treatment in the fields of automotive protective films, flexible display devices, etc. Background Art

[0002] Traditional flexible coating materials are prone to poor adhesion, coating cracking, and insufficient light transmittance on TPU substrates. Existing technologies employ a single silver and pure ZnO dielectric layer, resulting in low infrared reflectivity (≤85%) and high resistivity (≥8Ω / sq). Alternatively, the carbon nanotube reinforcement layer disclosed in JP2020157994A suffers from uneven dispersion, resulting in reduced light transmittance (<80%). CN118497692A, on the other hand, focuses on an ultra-thin PET substrate with a dual silver magnetron layer structure, addressing flexibility and thermal insulation issues but failing to optimize adhesion between the substrate and the coating. The dual silver layers are directly sputtered onto the PET, lacking a transition layer. Consequently, these solutions for TPU substrates fail to address the following issues: 1. The metal layer easily breaks when stretched or bent, leading to a decrease in barrier properties; 2. The lack of a chemically bonded interface makes the silver layer susceptible to oxidation after long-term use; and 3. Coating failure due to the high ductility inherent in the TPU substrate is not addressed. Summary of the Invention

[0003] The purpose of the present invention is to solve the above technical problems through gradient transition layer design and double silver layer structure optimization.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions: A flexible coating material having a gradient transition layer and a double silver layer structure comprises a flexible substrate layer, a gradient transition layer, and a double silver layer, forming a three-layer composite structure; the gradient transition layer sequentially comprises a primer layer, a mid-coat layer, and a top-coat layer; the double silver layer sequentially comprises a first silver layer, a dielectric layer, a second silver layer, and a protective layer; the mid-coat layer contains carboxylated carbon nanotubes; and the carboxylated carbon nanotubes are oriented.

[0005] The core innovation of this invention: Through the gradient transition layer design combined with double silver layer optimization, while maintaining high infrared reflectivity (≥93%) and high light transmittance (≥86%), the coating adhesion, weather resistance and tensile properties are significantly improved.

[0006] Preferably, the middle coating layer comprises a mixture of siloxane prepolymer, carboxylated carbon nanotubes and a photoinitiator; the carboxylated carbon nanotubes are oriented along the stretching direction.

[0007] Preferably, in the mid-coat layer, the mass ratio of the siloxane prepolymer, the carboxylated carbon nanotubes, and the photoinitiator is 85-91:8-15:1-5.

[0008] Middle coating: It is composed of siloxane prepolymer (60~80wt%), carboxylated carbon nanotubes (5~10wt%) and photoinitiator (1~3wt%), and is oriented and arranged to form a conductive network through electric field induction (100~300V / cm).

[0009] Preferably, the primer layer comprises a mixture of polyurethane-modified acrylate, nano-SiO2 / TiO2 composite particles, and a silane coupling agent; and the refractive index of the primer layer changes in a gradient.

[0010] Preferably, in the primer layer, the mass ratio of the polyurethane modified acrylate, the nano-SiO2 / TiO2 composite particles, and the silane coupling agent includes 70~85:12~25:2~5; in the nano-SiO2 / TiO2 composite particles, the mass ratio of SiO2 to TiO2 includes a gradient change from 3:1 to 1:2, so that the refractive index of the primer layer changes from 1.5 to 1.9; the particle size of the nano-SiO2 / TiO2 composite particles includes 20~50nm.

[0011] Primer: It is composed of polyurethane-modified acrylate (70~85wt%), nano-SiO2 / TiO2 composite particles (12~25wt%, particle size 20~50nm), and silane coupling agent (2~5wt%). The modulus after curing is 50~100MPa. By adjusting the mixing ratio of SiO2 (n=1.46) and TiO2 (n=2.4) (3:1→1:2), a continuous transition of the refractive index from 1.5 (matching TPU) to 1.9 (matching Al2O3 topcoat) is achieved.

[0012] Preferably, the flexible substrate layer includes a TPU substrate; the top coating layer includes an Al2O3 nanocrystalline layer; the first silver layer includes an Ag target sputtering layer; the dielectric layer includes a ZnO:Ga dielectric layer; the second silver layer includes an Ag target sputtering layer; and the protective layer includes a Si3N4 protective layer.

[0013] Top coating: Al2O3 nanocrystalline layer (thickness 20~50nm) synthesized by sol-gel method, forming Al-O-Ag chemical bond with silver layer, surface hydroxyl density ≥5 / nm 2 .

[0014] This solution is tailored specifically to the characteristics of TPU substrates and differs fundamentally from solutions based on PET. For example, the modulus of TPU (10-50 MPa) requires a primer with a modulus of 50-100 MPa to achieve stress buffering; the modulus of PET (2-4 GPa) can be directly sputter-coated without the need for stress buffering. The core of this invention lies in proposing a coating solution on TPU while also maintaining a certain degree of tensile strength, ensuring that the coating will not crack within a certain stretch range (coating on PET has an extremely low tensile cracking rate).

[0015] Preferably, the thickness of the flexible substrate layer is 50-150 μm; the thickness of the primer layer is 1.0-1.5 μm; the thickness of the mid-coat layer is 0.5-1.0 μm; the thickness of the topcoat layer is 20-50 nm; the thickness of the first silver layer is 10-15 nm; the thickness of the dielectric layer is 5-8 nm; the thickness of the second silver layer is 10-15 nm; the thickness of the protective layer is 20-30 nm; and the surface hydroxyl density of the Al2O3 nanocrystalline layer is ≥5 / nm. 2 ; In the ZnO:Ga dielectric layer, the doping concentration of Ga includes 2~5 wt%.

[0016] A method for preparing the flexible coating material having a gradient transition layer and a double silver layer structure is characterized by comprising the following steps: A. pretreatment of the flexible substrate layer; B. coating the primer layer on the flexible substrate layer and heating and curing; C. coating the middle coating on the base coating, inducing electric field orientation, and then UV curing; D. Spin-coating Al2O3 nanocrystalline sol on the middle coating; forming the top coating by sol-gel method, and sintering and curing; E. magnetron sputtering the first silver layer on the top coating; F. magnetron sputtering the dielectric layer on the first silver layer; G. magnetron sputtering the second silver layer on the dielectric layer; H. Magnetron sputtering the protective layer on the second silver layer to obtain the flexible coating material having a gradient transition layer and a double silver layer structure.

[0017] Preferably, in step A, the pretreatment includes plasma cleaning; in step B, the conditions for heat curing include: curing temperature 80-100°C, curing time 2-30 min, and modulus after curing 50-100 MPa; in step C, the conditions for UV curing include: light wavelength 365 nm; light energy 500-1200 mJ / cm 2; In step D, the sintering and curing conditions include: a sintering temperature of 120°C and a sintering time of 5 to 30 min; in step E, the magnetron sputtering conditions include a sputtering power of 1 to 2 kW, 200 to 300 W, a sputtering atmosphere of 0.6 Pa Ar, a sputtering temperature of 60 to 80°C, and a machine speed of 1 to 2 m / min; in step F, the magnetron sputtering conditions include a sputtering power of 30 to 50 kW, a sputtering atmosphere of O2 and Ar mixed in a volume ratio of 1:9, a sputtering temperature of 60 to 80°C, and a machine speed of 2 m / min; in step G, the magnetron sputtering conditions include a sputtering power of 1 to 2 kW, a sputtering atmosphere of 0.6 Pa Ar, a sputtering temperature of 80°C, and a machine speed of 2 m / min; in step H, the magnetron sputtering conditions include a sputtering power of 0.5 kW, a sputtering atmosphere of 0.6 Pa Ar, a sputtering temperature of 60 to 80°C, and a machine speed of 2 m / min.

[0018] Preferably, in step A, the plasma cleaning conditions include: cleaning atmosphere Ar atmosphere, cleaning power 0.2kW, and cleaning time 2min; in step B, a continuous gradient transition of refractive index is achieved by a step-by-step coating method using a micro-gravure coater, and the specific operations include: adding nano-SiO2 / TiO2 composite particles in three batches, the mass ratio of SiO2 to TiO2 in the nano-SiO2 / TiO2 composite particles in the first batch is 3:1, pre-curing at 80°C for 1 minute after coating, and the nano-SiO2 / TiO2 composite particles in the second batch are added in a step-by-step coating method. The mass ratio of SiO2 to TiO2 in the SiO2 composite particles is 2:1, and the particles are pre-cured at 80°C for 1 minute after coating. The mass ratio of SiO2 to TiO2 in the first batch of nano-SiO2 / TiO2 composite particles is 1:2, and the particles are pre-cured at 80°C for 1 minute after coating. In step C, the conditions for the electric field orientation induction include: an electric field intensity of 100-300 V / cm and an action time of 30-60 s. In step D, the solid content of the Al2O3 nanocrystalline sol includes 5 wt%, and a hydroxyl density of ≥5 / nm. 2 In step E, the roughness of the first silver layer is less than 5 nm; in step F, the resistivity of the dielectric layer is less than or equal to 1×10 -3 Ω·cm; in step G, the roughness of the second silver layer is <5nm; in step G, the hardness of the protective layer is ≥1800HV.

[0019] The implementation of the present invention has the following beneficial effects: The flexible coating material obtained by the present invention has the following properties: 1. Visible light transmittance ≥86%, infrared reflectivity ≥93%, square resistance ≤4.2Ω / sq; 2. After stretching 300%, the crack density is ≤0.05 / mm 2 , salt spray resistant for 1000h without corrosion; 3. Compatible with roll-to-roll mass production, film thickness uniformity deviation ≤±5%. DETAILED DESCRIPTION

[0020] Unless otherwise noted, in the following examples and comparative examples, Evonik's SILIKOPHEN P80 / X siloxane prepolymer was used; carboxylated carbon nanotubes were TNIM8 from the Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences; and Covestro's Desmolux U100 polyurethane-modified acrylate was used. These raw materials are provided for experimental purposes only; similar raw materials from other companies can be substituted.

[0021] Example 1 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0022] Example 2 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 70 wt%), nano-SiO2 / TiO2 composite particles (25 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (5 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.5μm; Curing: 100℃ / 2min, modulus 100MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 88 wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 10 wt%), photoinitiator TPO (2 wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 1200mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 30min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 2.0kW, Ar atmosphere 0.6Pa, temperature 60°C, machine speed 1m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 50kW, Ar:O2=8:2, temperature 80℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 2.0 kW, Ar atmosphere 0.6 Pa, temperature 60 ° C, machine speed 2 m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 60°C, machine speed 2m / min.

[0023] Example 3 1. Substrate pretreatment A TPU substrate (thickness 50 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 83 wt%), nano-SiO2 / TiO2 composite particles (12 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (5 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.0μm; Curing: 80℃ / 30min, modulus 50MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 91 wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 8 wt%), photoinitiator TPO (1 wt%); Coating: slit coating, thickness 0.5μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 2wt%, power 30kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min.

[0024] Comparative Example 1 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (2) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0025] Comparative Example 2 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0026] Comparative Example 3 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coater three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density <3 / nm) 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0027] Comparative Example 4 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density <3 / nm) 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Silver layer magnetron sputtering Silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0028] Comparative Example 5 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Silver layer magnetron sputtering Silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0029] Comparative Example 6 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coater three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.5 kW, Ar atmosphere 0.6 Pa, temperature 80 °C, machine speed 2 m / min.

[0030] Comparative Example 7 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Gradient refractive index realization process (step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.5 (matching TPU substrate); Second layer: SiO2:TiO2=1:1 → refractive index 1.7; Third layer: SiO2:TiO2=1:2 → refractive index 1.9 (matching Al2O3 surface layer); Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO dielectric layer: power 40kW, Ar:O2=8:2, temperature 100℃, speed 2m / min; Second silver layer: Ag target, sputtering power 1.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0031] Comparative Example 8 1. Substrate pretreatment A TPU substrate (thickness 150 μm) was used and plasma cleaned (Ar atmosphere, 0.2 kW, 2 min); 2. Preparation of gradient transition layer (1) Primer coating Raw materials: polyurethane-modified acrylate (Covestro Desmolux U100, 85 wt%), nano-SiO2 / TiO2 composite particles (13 wt%, SiO2:TiO2 mass ratio gradient, particle size 20-50 nm), silane coupling agent KH-550 (2 wt%); Refractive index realization process (step-by-step coating method): First layer: SiO2:TiO2=3:1 → refractive index 1.7; Second layer: SiO2:TiO2=3:1 → refractive index 1.7; Third layer: SiO2:TiO2=3:1→ refractive index 1.7; Coating: Micro-gravure coating machine three-step gradient coating, total thickness 1.2μm; Curing: 80℃ / 10min, modulus 80MPa; (2) Middle coating Raw materials: siloxane prepolymer (Evonik SILIKOPHEN P80 / X, 80wt%), carboxylated carbon nanotubes (TNIM8, Institute of Organic Chemistry, Chinese Academy of Sciences, 15wt%), photoinitiator TPO (5wt%); Coating: slit coating, thickness 1.0μm; Orientation: Electric field induction (200 V / cm, 45 s) oriented the carbon nanotubes along the stretching direction; Curing: UV light (365nm, 500mJ / cm 2 ); (3) Preparation of topcoat Spin coating Al2O3 nanocrystalline sol (5wt% solid content, hydroxyl density ≥5 / nm 2 ); Sintering: 120℃ / 5min, thickness 30nm; 3. Double silver layer magnetron sputtering First silver layer: Ag target, sputtering power 1.0 kW, Ar atmosphere 0.6 Pa, temperature 80 ° C, machine speed 2 m / min; ZnO:Ga dielectric layer: Ga doping 5wt%, power 40kW, Ar:O2=8:2, temperature 100℃, machine speed 2m / min; Second silver layer: Ag target, sputtering power 1.5kW, Ar atmosphere 0.6Pa, temperature 80℃, machine speed 2m / min; Si3N4 protective layer: 0.5kW, Ar atmosphere 0.6Pa, temperature 70°C, machine speed 2m / min.

[0032] Effect Example 1 Performance tests were conducted on Example 1 and the prior art (commercially available TPU double silver-coated products, taking the Coolde gold-plated insulation skylight product as an example). The test design is shown in Table 1: Table 1

[0033] The test results show that the visible light transmittance of the present invention reaches 88.3%, which is 21.8% higher than that of the commercial TPU double silver coating products; the infrared reflectivity reaches 93.7%, which is 43.3% higher than that of the commercial TPU double silver coating products. That is, the gradient transition layer design (continuous transition of refractive index 1.5→1.9) greatly reduces the interface reflection loss, and the synergistic optimization of the double silver layer achieves a balance between high transmittance and high infrared reflection; the square resistance is as low as 3.8Ω / sq, which is 58.7% lower than that of the commercial TPU double silver coating products (9.2Ω / sq), proving that the Ga-doped ZnO dielectric layer (resistivity ≤1×10 -3 Ω·cm) effectively improves carrier mobility. After stretching 300%, the crack density is only 0.05 / mm 2 , compared with the commercially available TPU double silver coating products (6.2 lines / mm 2 ) is reduced by 99.2%, highlighting the adaptability of the oriented arrangement of carboxylated carbon nanotubes to the ductility of TPU; double 85 aging test: the hydroxyl density of the Al2O3 surface coating is ≥5 / nm 2 , forming Al-O-Ag chemical bonds to inhibit the oxidation of the silver layer, and the Si3N4 protective layer blocks environmental corrosion.

[0034] Effect Example 2 The performance test was carried out on the comparative example, and the test design is shown in Table 2: Table 2

[0035] The test results show the following: Integrity of the gradient transition layer: In Comparative Example 1 (no primer), the lack of a refractive index gradient (1.5→1.9) and silane coupling agent bonding resulted in an 82% decrease in adhesion (0.5 vs 2.8 N / mm). Interface reflection loss reduced infrared reflectivity by 10.3% (84.0% vs 93.7%). Necessity of directional alignment: In Comparative Example 2 (no electric field induction), the sheet resistance increased by 135% (8.9 vs 3.8 Ω / sq) due to the disordered dispersion of CNTs. High sheet resistance in flexible coatings not only degrades performance parameters but also causes functional failures (heating / touch / shielding failures) and exacerbates safety hazards (burning / short circuits). Furthermore, disordered carbon nanotubes induce stress concentration, increasing the tensile crack density by 24 times (1.2 vs 0.05 lines / mm). 2 ). Interface chemical bonding: Due to insufficient Al-O-Ag bonding in Comparative Example 3 (insufficient Al2O3 hydroxyl density), the silver layer oxidized after 500 hours of salt spray, and the infrared reflectivity decreased by 22% (from 86.5% to 67.4%). Advantages of the double silver layer structure: Due to the lack of optical interference enhancement of the second silver layer, the infrared reflectivity of Comparative Example 4 (single silver layer) decreased by 5.8% (88.3% vs 93.7%), and the stress buffering of the single silver layer was insufficient, and the tensile crack density increased by 64 times (3.2 vs 0.05 / mm2 Comparative Example 5 (single silver layer and no dielectric layer) shows that the double silver layer enhances infrared reflection through the optical interference effect of the dielectric layer, while a single silver layer cannot form multiple reflective interfaces. A single silver layer lacks the stress buffering effect of the dielectric layer, and when the TPU substrate is stretched, stress is directly transferred to the silver layer, causing cracking. The dielectric layer provides a barrier to water and oxygen, but its absence directly exposes the silver layer, accelerating oxidation. Comparative Example 7 (no Ga doping in the dielectric layer) further demonstrates that Ga doping improves ZnO carrier mobility, resulting in higher resistivity in pure ZnO and decreased conductivity. Undoped ZnO has an insufficient carrier concentration, weakening the plasmon resonance effect and affecting infrared reflection performance. Pure ZnO is less dense than ZnO:Ga, weakening its water and oxygen barrier ability and causing corrosion at the edges of the silver layer. The core role of the protective layer: While adhesion is maintained in Comparative Example 6 (no Si3N4 layer), its insufficient hardness (<1000 HV) allows water and oxygen penetration, leading to severe oxidative corrosion (compared to Example 1, where no corrosion occurred). Gradient transition is irreplaceable: Comparative Example 8 (no refractive index gradient) experienced a 10.1% decrease in visible light transmittance (79.5% vs. 88.3%) due to a dramatic increase in interface reflection. However, Examples 1-3, using the present invention's solution, achieved significant performance improvements across the board, with Example 1 achieving the best performance and being considered the preferred implementation. In summary, the gradient transition layer (stress buffering + optical matching), the double silver layer (optical interference + conductivity enhancement), and the protective layer (environmental barrier) work synergistically. The absence of any one layer or deviation in parameters results in significant degradation of mechanical, optical, or weather resistance properties, demonstrating the essential synergy of the three-layer structure.

[0036] The above disclosure is only a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A flexible coating material having a gradient transition layer and a double silver layer structure, characterized in that: The invention comprises a flexible substrate layer, a gradient transition layer, and a double silver layer; the gradient transition layer sequentially comprises a primer layer, a middle coating layer, and a top coating layer; the double silver layer sequentially comprises a first silver layer, a dielectric layer, a second silver layer, and a protective layer; the middle coating layer contains carboxylated carbon nanotubes; and the carboxylated carbon nanotubes are arranged in a directional manner.

2. The flexible coating material having a gradient transition layer and a double silver layer structure according to claim 1, characterized in that: The middle coating layer comprises a mixture of siloxane prepolymer, carboxylated carbon nanotubes and a photoinitiator; the carboxylated carbon nanotubes are oriented along the stretching direction.

3. The flexible coating material having a gradient transition layer and a double silver layer structure according to claim 2, characterized in that: In the mid-coat layer, the mass ratio of the siloxane prepolymer, the carboxylated carbon nanotubes, and the photoinitiator is 85-91:8-15:1-5.

4. The flexible coating material having a gradient transition layer and a double silver layer structure according to claim 1, characterized in that: The primer layer comprises a mixture of polyurethane modified acrylate, nano-SiO2 / TiO2 composite particles and a silane coupling agent; and the refractive index of the primer layer changes in a gradient.

5. The flexible coating material having a gradient transition layer and a double silver layer structure according to claim 4, characterized in that: In the primer layer, the mass ratio of the polyurethane modified acrylate, the nano-SiO2 / TiO2 composite particles, and the silane coupling agent includes 70~85:12~25:2~5; in the nano-SiO2 / TiO2 composite particles, the mass ratio of SiO2 to TiO2 includes a gradient change from 3:1 to 1:2, so that the refractive index of the primer layer changes from 1.5 to 1.9; the particle size of the nano-SiO2 / TiO2 composite particles includes 20~50nm.

6. The flexible coating material having a gradient transition layer and a double silver layer structure according to claim 1, characterized in that: The flexible substrate layer includes a TPU substrate; the top coating layer includes an Al2O3 nanocrystalline layer; the first silver layer includes an Ag target sputtering layer; the dielectric layer includes a ZnO:Ga dielectric layer; the second silver layer includes an Ag target sputtering layer; and the protective layer includes a Si3N4 protective layer.

7. The flexible coating material having a gradient transition layer and a double silver layer structure according to claim 6, characterized in that: The thickness of the flexible substrate layer is 50-150 μm; the thickness of the base coating layer is 1.0-1.5 μm; the thickness of the middle coating layer is 0.5-1.0 μm; the thickness of the top coating layer is 20-50 nm; the thickness of the first silver layer is 10-15 nm; the thickness of the dielectric layer is 5-8 nm; the thickness of the second silver layer is 10-15 nm; the thickness of the protective layer is 20-30 nm; the surface hydroxyl density of the Al2O3 nanocrystalline layer is ≥5 / nm 2 ; In the ZnO:Ga dielectric layer, the doping concentration of Ga includes 2~5 wt%.

8. A method for preparing the flexible coating material having a gradient transition layer and a double silver layer structure as claimed in claim 1, characterized in that: The steps include: A. pretreatment of the flexible substrate layer; B. coating the primer layer on the flexible substrate layer and heating and curing; C. coating the middle coating on the base coating, inducing electric field orientation, and then UV curing; D. Spin-coating Al2O3 nanocrystalline sol on the middle coating; forming the top coating by sol-gel method, and sintering and curing; E. magnetron sputtering the first silver layer on the top coating; F. magnetron sputtering the dielectric layer on the first silver layer; G. magnetron sputtering the second silver layer on the dielectric layer; H. Magnetron sputtering the protective layer on the second silver layer to obtain the flexible coating material having a gradient transition layer and a double silver layer structure.

9. The method for preparing a flexible coating material having a gradient transition layer and a double silver layer structure according to claim 8, characterized in that: In step A, the pretreatment includes plasma cleaning; in step B, the conditions for heat curing include: curing temperature 80-100°C, curing time 2-30 min, and modulus after curing 50-100 MPa; in step C, the conditions for UV curing include: light wavelength 365 nm, light energy 500-1200 mJ / cm 2 ; In step D, the sintering and curing conditions include: a sintering temperature of 120°C and a sintering time of 5 to 30 min; in step E, the magnetron sputtering conditions include a sputtering power of 1 to 2 kW, a sputtering atmosphere of 0.6 Pa Ar, a sputtering temperature of 60 to 80°C, and a machine speed of 1 to 2 m / min; in step F, the magnetron sputtering conditions include a sputtering power of 30 to 50 kW, a sputtering atmosphere of O2 and Ar mixed in a volume ratio of 1:9, a sputtering temperature of 60 to 80°C, and a machine speed of 2 m / min; in step G, the magnetron sputtering conditions include a sputtering power of 1 to 2 kW, a sputtering atmosphere of 0.6 Pa Ar, a sputtering temperature of 80°C, and a machine speed of 2 m / min; in step H, the magnetron sputtering conditions include a sputtering power of 0.5 kW, a sputtering atmosphere of 0.6 Pa Ar, a sputtering temperature of 60 to 80°C, and a machine speed of 2 m / min.

10. The method for preparing a flexible coating material having a gradient transition layer and a double silver layer structure according to claim 9, characterized in that: In step A, the plasma cleaning conditions include: cleaning atmosphere Ar atmosphere, cleaning power 0.2kW, and cleaning time 2min; in step B, a continuous gradient transition of refractive index is achieved by a step-by-step coating method using a micro-gravure coater, and the specific operations include: adding nano-SiO2 / TiO2 composite particles in three batches, the mass ratio of SiO2 to TiO2 in the nano-SiO2 / TiO2 composite particles in the first batch is 3:1, pre-curing at 80°C for 1 minute after coating, and the nano-SiO2 / TiO2 in the second batch is 200 nm.

2. The mass ratio of SiO2 to TiO2 in the composite particles is 2:1, and the particles are pre-cured at 80°C for 1 minute after coating. The mass ratio of SiO2 to TiO2 in the first batch of nano-SiO2 / TiO2 composite particles is 1:2, and the particles are pre-cured at 80°C for 1 minute after coating. In step C, the conditions for the electric field orientation induction include: an electric field strength of 100-300 V / cm and an action time of 30-60 s. In step D, the solid content of the Al2O3 nanocrystalline sol includes 5 wt% and a hydroxyl density of ≥5 / nm. 2 In step E, the roughness of the first silver layer is less than 5 nm; in step F, the resistivity of the dielectric layer is less than or equal to 1×10 -3 Ω·cm; in step G, the roughness of the second silver layer is <5nm; in step G, the hardness of the protective layer is ≥1800HV.

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