A pet for electrochromic light modulation film and a preparation method thereof

Abstract

The application belongs to the technical field of electrochromic materials and polymer composite films, and particularly relates to PET for electrochromic light modulation film and a preparation method thereof; the adhesion between a PET substrate and a conductive layer is insufficient, which can easily lead to peeling problems in recycling; the PET substrate is chemically activated and nano-physical roughened through ultraviolet-ozone synergistic treatment, and then a triblock copolymer interface layer is coated; after the interface layer is annealed in a toluene vapor atmosphere, a gradient interface layer with vertical phase separation structure can be formed, wherein the PGMA block is enriched on the surface; through reaction with a material containing an amino functional group and heat curing, a firm covalent bond connection and interpenetrating network structure are formed at the interface.

Description

Technical Field

[0001] This invention belongs to the field of electrochromic materials and polymer composite films, specifically relating to a PET for electrochromic color-changing films and its preparation method. Background Technology

[0002] Electrochromic color-changing film is a smart material that can reversibly change its optical transmittance under the action of an electric field. It is widely used in fields such as dimmable windows and smart automotive glass (CN120704027A). PET film is often used as a substrate for electrochromic color-changing film due to its excellent properties such as transparency, flexibility, and weather resistance.

[0003] However, the PET substrate surface is chemically inert and hydrophobic, resulting in weak interfacial adhesion between it and the conductive layer coated on it. In existing technologies, methods such as plasma treatment, ultraviolet and ozone treatment, chemical etching, or coating with adhesion promoters are commonly used to modify the PET surface to improve interfacial adhesion. For example, plasma, ultraviolet, and ozone treatments can introduce oxidative functional groups to increase surface energy, but improper treatment may lead to excessive surface embrittlement or decreased optical performance, and the resulting modified layer has limited stability during long-term cyclic use. Chemical etching can roughen the surface but may weaken the mechanical properties of the film. While ordinary primer adhesive coatings improve adhesion to some extent, these coatings themselves may affect the photoelectric properties of the electrochromic layer and may delaminate under environmental aging conditions. During repeated electrochromic cycles or mechanical bending, the interface between the PET substrate and the conductive layer often peels off, leading to deterioration of dimming performance, shortened device lifespan, and severely limiting the reliability and application range of electrochromic dimming films.

[0004] In conclusion, there is an urgent need for a new technical approach to fundamentally enhance the bonding strength between the PET substrate and the conductive layer, improve interface stability without sacrificing optical performance, and solve the peeling problem during recycling. Summary of the Invention

[0005] This invention provides a PET for electrochromic color-changing films and its preparation method. Through special surface activation and roughening treatment and functionalized block copolymer interface layer design, the adhesion between the PET substrate and the conductive layer is significantly improved, thereby solving the technical problem of easy peeling of the interface during recycling.

[0006] The specific technical solution is as follows:

[0007] A PET for use in electrochromic color-changing films and its preparation method are as follows:

[0008] S1: PET substrate treatment.

[0009] S11: The PET film is ultrasonically cleaned in acetone and ethanol in sequence, then rinsed in deionized water for 30-60 seconds and dried to obtain the pretreated PET substrate.

[0010] S12: The pretreated PET substrate prepared in S11 is subjected to ultraviolet-ozone synergistic treatment to obtain activated and roughened PET substrate.

[0011] S2: Preparation of triblock copolymer.

[0012] S21: Methyl methacrylate, 2-dodecyl trithiocarbonate, and azobisisobutyronitrile are mixed in dehydrated toluene, and then subjected to three deoxygenation cycles. The mixture is stirred at 70°C for 8 hours, cooled in an ice-water bath, and then ethanol is added while stirring. The mixture is filtered, washed, and dried to obtain PMMA macromolecular chain transfer agent (PMMA-CTA).

[0013] S22: The PMMA-CTA prepared in S21 was mixed with butyl acrylate and azobisisobutyronitrile in dehydrated toluene, and then subjected to three deoxygenation cycles. The mixture was stirred at 70°C for 12 hours, cooled in an ice-water bath, and then added dropwise to a mixture of methanol and deionized water in a volume ratio of 9:1. The mixture was filtered, washed, and dried to obtain the PMMA-PBA diblock copolymer.

[0014] S23: The PMMA-PBA diblock copolymer prepared in S22 was mixed with glycidyl methacrylate and azobisisobutyronitrile in dehydrated tetrahydrofuran, and then subjected to three deoxygenation cycles. The mixture was stirred at 70°C for 10 h, cooled in an ice-water bath, and then added dropwise to n-hexane to precipitate. After filtration, thermal removal, and drying, the PMMA-PBA-PGMA triblock copolymer was obtained.

[0015] S3: Coating and self-assembly.

[0016] S31: The PMMA-PBA-PGMA triblock copolymer prepared in S23 is added to the mixed solvent and stirred in the dark to prepare a polymer solution with a mass concentration of 3%.

[0017] S32: The polymer solution prepared in S31 is spin-coated onto the activated and roughened PET substrate prepared in S12, annealed in stages, and cooled to room temperature under vacuum to obtain a PET substrate with a gradient interface layer on the surface.

[0018] The drying process described in S11 has the following parameters: temperature 50-60℃, duration 10-15min.

[0019] The ultraviolet-ozone synergistic treatment described in S12 has the following parameter settings: temperature 25℃, ultraviolet light intensity 10~50mW / cm². 2The ultraviolet wavelengths are 185nm and 254nm, the oxygen flow rate is 50-150sccm, and the duration is 5-30min.

[0020] Furthermore, the molar ratio of methyl methacrylate, 2-dodecyl trithiocarbonate, and azobisisobutyronitrile described in S21 is 100:1:0.1.

[0021] The deoxygenation cycle described in S21 has the following parameter settings: Step 1: -78℃ dry ice-acetone bath for 3 minutes; Step 2: Vacuuming to 5 Pa; Step 3: Filling with nitrogen to atmospheric pressure; Step 4: Natural thawing.

[0022] The drying process described in S21 has the following parameters: temperature 40°C, duration 24 hours.

[0023] The molar ratio of the PMMA macromolecular chain transfer agent described in S22 to butyl acrylate and azobisisobutyronitrile is 1:217:0.1.

[0024] The molar ratio of the PMMA-PBA diblock copolymer described in S23 to glycidyl methacrylate and azobisisobutyronitrile is 1:100:0.2.

[0025] The drying process described in S23 has the following parameters: temperature 35°C, duration 48 hours.

[0026] Furthermore, the mixed solvent described in S31 is toluene and tetrahydrofuran, with a volume ratio of 3:1 to 4:1.

[0027] The spin coating described in S32 has the following parameter settings: rotation speed 1000-1300 rpm, duration 30-60 s.

[0028] The segmented annealing described in S32 has the following parameter settings: the first stage uses toluene for room temperature steam annealing for 3 to 6 hours; the second stage is vacuum annealing at a temperature of 90 to 120°C, a vacuum degree of -0.095 MPa, and a duration of 24 to 48 hours.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. This invention achieves chemical activation and nanoscale physical roughening of the PET surface through ultraviolet-ozone synergistic treatment, laying a solid foundation for the firm adhesion of the subsequent interface layer.

[0031] 2. This invention uses PMMA-PBA-PGMA triblock copolymer as the interface material. Its unique block structure can spontaneously form a vertical layered structure with a gradient of chemical composition through annealing self-assembly, which meets the adhesion requirements of PET in flexible devices. Attached Figure Description

[0032] Figure 1 This is a process flow diagram for the preparation of PET for electrochromic color-changing films.

[0033] Figure 2 This is a flowchart of the preparation process of triblock copolymers.

[0034] Figure 3 These are FTIR comparison images of PET before and after coating with the conductive layer.

[0035] Figure 4 This is an XRD pattern of a PET with a gradient interface layer on its surface prepared in Example 1. Detailed Implementation

[0036] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0037] This invention proposes a PET substrate for electrochromic color-changing films and its preparation method. By constructing a gradient interface layer with chemical bonding and interpenetrating network structure between the PET substrate and the conductive layer, the problem of insufficient adhesion between the two is solved. (See attached diagram) Figure 1 The image shows a PET used for electrochromic color-changing films and its preparation method. The detailed technical solution is as follows:

[0038] 1. PET substrate treatment.

[0039] The PET film was ultrasonically cleaned in acetone and ethanol in sequence, then rinsed in deionized water for 30-60 seconds and dried to obtain a pretreated PET substrate. Then, it was subjected to ultraviolet-ozone synergistic treatment to obtain an activated and roughened PET substrate.

[0040] Most organic dirt is dissolved using moderately polar acetone, followed by a transition and displacement solvent using highly polar ethanol, and finally a final rinse with highly polar deionized water. This is combined with ultrasound, which uses cavitation to generate countless tiny bubbles in the liquid that burst instantly, releasing localized impact force to physically remove contaminants from irregular surfaces and microscopic depressions.

[0041] 254nm ultraviolet light is absorbed by PET surface molecules, directly breaking the CH bonds and weaker C / C bonds in the main chain or side chains, generating a large number of active sites such as alkyl radicals and benzene ring radicals. Simultaneously, reactive oxygen atoms and ozone generated from the cleavage of oxygen by 185nm ultraviolet light diffuse to the PET surface. Surface PET radicals rapidly react with reactive oxygen atoms or ozone, chemically grafting strongly polar oxygen-containing functional groups such as -C=O, -COOH, -COH, and -COO- onto the PET molecular chains, increasing the polarity and surface energy of the PET surface. The amorphous regions of PET have loosely packed molecular chains, making them more susceptible to ultraviolet light oxidation. The rate of molecular chain breakage and the escape rate of small oxidized molecules (CO2, H2O) are faster. In contrast, the crystalline regions have a dense structure and are more resistant to oxidative etching. This difference in etching rate between the amorphous and crystalline regions results in a nanoscale textured surface on the treated PET, with the crystalline regions forming "protrusions" and the amorphous regions forming "recesses." Chemical activation and physical roughening occur simultaneously and promote each other. The introduction of polar groups improves wettability, allowing subsequent coating solutions to spread and penetrate better into the nanotexture. Meanwhile, the nanotexture provides a larger reaction contact area, consolidating the effect of chemical bonding. Together, they constitute a robust, multi-scale, and multi-mechanism bonding foundation.

[0042] 2. Preparation of triblock copolymers

[0043] Methyl methacrylate (MMA), 2-dodecyl trithiocarbonate (DDMAT), and azobisisobutyronitrile (AIBN) were mixed in dehydrated toluene and subjected to three deoxygenation cycles. The mixture was stirred, cooled, and ethanol was added while stirring. The mixture was filtered, washed, and dried to obtain a PMMA macromolecular chain transfer agent (PMMA-CTA). This was then mixed with butyl acrylate (BA) and azobisisobutyronitrile in dehydrated toluene, and subjected to three deoxygenation cycles. The mixture was stirred, cooled, and then added dropwise to a mixture of methanol and deionized water. The mixture was filtered, washed, and dried to obtain a PMMA-PBA diblock copolymer. The PMMA-PBA diblock copolymer was then mixed with glycidyl methacrylate (GMA) and azobisisobutyronitrile in dehydrated tetrahydrofuran and subjected to three deoxygenation cycles. The mixture was stirred, cooled, and then added dropwise to n-hexane to precipitate the product. The precipitate was filtered, thermally removed, and dried to obtain a PMMA-PBA-PGMA triblock copolymer.

[0044] Polymethyl methacrylate (PMMA) exhibits polarity similar to that of surface-treated PET, resulting in good compatibility. As the first synthesized block, it possesses a RAFT chain transfer agent (2-dodecyl trithiocarbonate) group at one end and an active growth end at the other, providing a foundation for subsequent chain extension. Polybutyl acrylate (PB) has a very low glass transition temperature (-54°C), and its segments possess extremely high mobility at annealing temperatures. During subsequent vacuum annealing, it promotes chain movement and rearrangement of the entire triblock molecule, driving microphase separation and acting as an intermediate flexible buffer layer. The glycidyl methacrylate (GMMA) side chains contain highly reactive epoxy groups. This block is located on the surface of the interfacial layer, and its epoxy groups can undergo ring-opening addition reactions with the amino groups in the precursor to form strong covalent bonds. Figure 2 The flowchart shows the preparation process of the triblock copolymer. With the help of AIBN, MMA is reacted with RAFT reagent to generate PMMA-CTA, then BA is added to generate PMMA-b-PBA-CTA, then GMA is added to generate PMMA-b-PBA-b-PGMA-CTA, and finally PMMA-PBA-PGMA-CTA is formed by thermal removal.

[0045] 3. Coating and Self-Assembly

[0046] The PMMA-PBA-PGMA triblock copolymer was added to a mixed solvent and stirred in the dark to prepare a polymer solution with a mass concentration of 3%. The solution was then spin-coated onto an activated and roughened PET substrate, annealed (first stage toluene vapor annealing, second stage vacuum annealing), and cooled to room temperature to obtain a PET substrate with a gradient interface layer on the surface.

[0047] The driving force for self-assembly stems from two aspects: firstly, PMMA, PBA, and PGMA possess different surface energies and polarities, tending towards phase separation; secondly, the PET surface is rich in polar oxygen-containing groups, resulting in lower interfacial energy with the more polar PMMA blocks. Therefore, air is a low-energy surface on the PET surface, and the lower-energy PGMA blocks (whose side-chain epoxy rings have a certain degree of hydrophobicity) tend to migrate towards the air interface to reduce the total energy of the system. The extremely low glass transition temperature of PBA blocks provides the entire molecular chain with high mobility at the annealing temperature, enabling the molecular chain to overcome energy barriers and complete long-range ordered rearrangement. Toluene vapor causes the polymer film to swell, lowering the glass transition temperature of the polymer chains. This allows the chain segments to acquire mobility at a glass transition temperature far below their bulk, thus initiating the phase separation process under mild conditions and contributing to the formation of more regular phase regions with fewer defects. Furthermore, prolonged vacuum annealing on top of solvent vapor annealing can further drive phase separation to thermodynamic equilibrium, resulting in clearer phase boundaries and a more stable gradient structure.

[0048] 4. Adhesive Applications

[0049] An amino-containing oligomer (or other amino-containing aniline oligomers, pyrrole or thiophene derivatives), an oxidant (ammonium persulfate), a doped acid (camphor sulfonic acid, p-toluene sulfonic acid or hydrochloric acid), and a solvent (N-methylpyrrolidone, dimethyl sulfoxide or N,N-dimethylformamide) are mixed and ultrasonically dissolved to obtain a precursor solution. This precursor solution is then spin-coated onto a PET substrate with a gradient interface layer and subjected to thermosetting to obtain a PET substrate containing a conductive layer.

[0050] The prepared PET substrate with a gradient interface layer has PGMA blocks enriched with highly reactive epoxy groups on its surface. These blocks form chemical covalent bonds with the reactive solution (containing functional groups that can react with epoxy groups, such as -NH2, -COOH, -SH) processing layer. The amino functional groups carried by the conductive layer material undergo ring-opening reactions with the epoxy groups. FTIR tests were performed on the PET before and after coating the conductive layer: the sample surface to be tested was attached to an ATR crystal for scanning (resolution 4 cm⁻¹). -1 (64 scans). Figure 3 As shown, after curing, 910cm -1 The characteristic absorption peaks of the nearby epoxy ring should be significantly reduced or disappear, while the absorption peaks in the 3300–3500 cm⁻¹ range should also be reduced. -1 A broad peak of hydroxyl (ring-opening product) appeared at the position, indicating that PGMA underwent a ring-opening crosslinking reaction with the amino group, confirming the environment in which the surface and amino group can be covalently bonded.

[0051] Example 1

[0052] A PET for use in electrochromic color-changing films and its preparation method are as follows:

[0053] Table 1 Main Raw Materials

[0054]

[0055] S1: PET substrate treatment.

[0056] S11: The PET film is ultrasonically cleaned sequentially in acetone and ethanol, then rinsed in deionized water for 30-60 seconds and dried to obtain the pretreated PET substrate. The ultrasonic cleaning parameters are set as follows: ultrasonic frequency 40kHz, power 250W, duration 15min; the drying parameters are set as follows: temperature 55℃, duration 12.5min.

[0057] S12: The pretreated PET substrate prepared in S11 was subjected to UV-ozone synergistic treatment to obtain an activated and roughened PET substrate. The UV-ozone synergistic treatment parameters were set as follows: temperature 25℃, UV light intensity 30mW / cm². 2The ultraviolet wavelengths were 185nm and 254nm, the oxygen flow rate was 100sccm, and the duration was 18min.

[0058] S2: Preparation of triblock copolymer.

[0059] S21: Methyl methacrylate, 2-dodecyl trithiocarbonate, and azobisisobutyronitrile were mixed in dehydrated toluene and then subjected to three deoxygenation cycles (step 1: -78℃ dry ice-acetone bath for 3 min; step 2: vacuum to 5 Pa; step 3: nitrogen purging to atmospheric pressure; step 4: natural thawing). The mixture was stirred at 70℃ for 8 h, cooled in an ice-water bath, and then ethanol was added while stirring. The mixture was filtered, washed, and dried at 40℃ for 24 h to obtain PMMA macromolecular chain transfer agent (PMMA-CTA). The molar ratio of methyl methacrylate, 2-dodecyl trithiocarbonate, and azobisisobutyronitrile was 100:1:0.1.

[0060] S22: The PMMA macromolecular chain transfer agent prepared in S21 was mixed with butyl acrylate and azobisisobutyronitrile in dehydrated toluene, and then subjected to three deoxygenation cycles (first step: -78℃ dry ice-acetone bath for 3 min; second step: vacuum to 5 Pa; third step: nitrogen gas to atmospheric pressure; fourth step: natural thawing). The mixture was stirred at 70℃ for 12 h, cooled in an ice-water bath, and then added dropwise to a mixture of methanol and deionized water (volume ratio 9:1). The mixture was filtered, washed, and dried to obtain the PMMA-PBA diblock copolymer. The molar ratio of the PMMA macromolecular chain transfer agent to butyl acrylate and azobisisobutyronitrile was 1:217:0.1.

[0061] S23: The PMMA-PBA diblock copolymer prepared in S22 was mixed with glycidyl methacrylate and azobisisobutyronitrile in dehydrated tetrahydrofuran, and then subjected to three deoxygenation cycles (first step: -78℃ dry ice-acetone bath for 3 min; second step: vacuum to 5 Pa; third step: nitrogen gas to atmospheric pressure; fourth step: natural thawing). The mixture was stirred at 70℃ for 10 h, cooled in an ice-water bath, and then added dropwise to n-hexane to precipitate. After filtration and thermal removal, the precipitate was dried at 35℃ for 48 h to obtain the PMMA-PBA-PGMA triblock copolymer. The molar ratio of the PMMA-PBA diblock copolymer to glycidyl methacrylate and azobisisobutyronitrile was 1:100:0.2.

[0062] S3: Coating and self-assembly.

[0063] S31: The PMMA-PBA-PGMA triblock copolymer prepared in S23 is added to a mixed solvent (a mixed solution of toluene and tetrahydrofuran with a volume ratio of 3.5:1), and stirred in the dark to prepare a polymer solution with a mass concentration of 3%.

[0064] S32: The polymer solution prepared in S31 is spin-coated onto the activated and roughened PET substrate prepared in S12, followed by segmented annealing and cooling to room temperature under vacuum to obtain a PET substrate with a gradient interface layer on the surface. The spin-coating parameters are set as follows: spin speed 1150 rpm, spin time 45 s.

[0065] Example 2

[0066] The composition and preparation process are the same as in Example 1, except that:

[0067] In step S11 of the preparation process, the ultrasonic cleaning parameters are set as follows: ultrasonic frequency 40kHz, power 200W, duration 10min. The drying parameters are set as follows: temperature 50℃, duration 10min. Other steps are the same.

[0068] The parameters for the UV-ozone synergistic treatment in the S12 preparation process are set as follows: temperature 25℃, UV light intensity 10mW / cm². 2 The ultraviolet wavelengths were 185nm and 254nm, the oxygen flow rate was 50sccm, the duration was 5min, and the other steps were the same.

[0069] In step S31 of the preparation process, toluene and tetrahydrofuran are in a volume ratio of 3:1, and the other components are the same.

[0070] In the S32 preparation process, the spin coating parameters are set as follows: spin speed 1000 rpm, duration 30 s. The segmented annealing parameters are set as follows: the first stage uses toluene for room temperature steam annealing for 3 h, and the second stage is vacuum annealing at 90℃, vacuum degree -0.095 MPa, duration 24 h. Other steps are the same.

[0071] Example 3

[0072] The composition and preparation process are the same as in Example 1, except that:

[0073] In step S11 of the preparation process, the ultrasonic cleaning parameters are set as follows: ultrasonic frequency 40kHz, power 300W, duration 20min. The drying parameters are set as follows: temperature 60℃, duration 15min. Other steps are the same.

[0074] The parameters for the UV-ozone synergistic treatment in the S12 preparation process are set as follows: temperature 25℃, UV light intensity 50mW / cm². 2 The ultraviolet wavelengths were 185nm and 254nm, the oxygen flow rate was 150sccm, the duration was 30min, and the other steps were the same.

[0075] In process S31, toluene and tetrahydrofuran are in a volume ratio of 4:1, and other components are the same.

[0076] In the S32 preparation process, the spin coating parameters are set as follows: spin speed 1300 rpm, duration 60 s. The segmented annealing parameters are set as follows: the first stage uses toluene for room temperature steam annealing for 6 h, and the second stage is vacuum annealing at 120℃, vacuum degree -0.095 MPa, duration 48 h. Other steps are the same.

[0077] Example 4

[0078] The composition and preparation process are the same as in Example 1, except that:

[0079] In step S11 of the preparation process, the ultrasonic cleaning parameters are set as follows: ultrasonic frequency 40kHz, power 280W, duration 102min. The drying parameters are set as follows: temperature 58℃, duration 14min. Other steps are the same.

[0080] The parameters for the UV-ozone synergistic treatment in the S12 preparation process are set as follows: temperature 25℃, UV light intensity 40mW / cm². 2 The ultraviolet wavelengths were 185nm and 254nm, the oxygen flow rate was 120sccm, the duration was 22min, and the other steps were the same.

[0081] In process S31, the volume ratio of toluene to tetrahydrofuran is 3.3:1, and the other components are the same.

[0082] In the S32 preparation process, the spin coating parameters are set as follows: spin speed 1250 rpm, duration 40 s. The segmented annealing parameters are set as follows: the first stage uses toluene for room temperature steam annealing for 4.2 h, and the second stage is vacuum annealing at 110℃ and a vacuum of -0.095 MPa for 40 h. Other steps are the same.

[0083] Comparative Example 1

[0084] The composition and preparation process are the same as in Example 1, except that:

[0085] The PET substrate is treated with the same UV-ozone process as in S1, without coating the triblock copolymer interface layer. The silane coupling agent 3-aminopropyltriethoxysilane is spin-coated using a traditional method, and then the precursor solution is directly spin-coated onto the activated PET.

[0086] Comparative Example 2

[0087] The composition and preparation process are the same as in Example 1, except that:

[0088] Step S23 in the preparation process is omitted, and only the PMMA-PBA diblock copolymer is synthesized; the other steps remain the same.

[0089] Samples of the PET substrate with a gradient interface layer on the surface prepared in Example 1 were taken and subjected to XRD tests: the samples were cut into 1cm×1cm pieces, the surface was purged with nitrogen to remove dust, and then fixed to the sample stage with conductive tape. The vacuum was then drawn to 1×10⁻⁶. -6 Pa, with an Al X-ray source, initial measurements were performed (energy 125 eV, step size 1 eV, beam size 350 μm), followed by high-resolution measurements (energy 25 eV, step size 0.1 eV, beam size as before), with measurements taken at angles ranging from 15° to 90°. Figure 4 As shown, as the detection angle becomes shallower, the concentration of elemental signals representing PGMA characteristics should increase significantly, while the signal representing PMMA should decrease relatively, proving that a gradient structure has been formed.

[0090] Based on Examples 1-4 and Comparative Examples 1-2, samples of the final PET substrates used for electrochromic color-changing films were taken for initial adhesion strength testing: PET substrates with a gradient interface layer on the surface were cut into uniformly sized cubes (25mm × 25mm). Simultaneously, a sufficiently rigid and flat aluminum plate was prepared. The surface of the aluminum plate was cleaned with anhydrous ethanol. An adhesive was applied to the cleaned aluminum plate. An amino-containing aniline precursor solution was applied to the PET substrate with the gradient interface layer and thermosetting. The substrate was then aligned and bonded to the substrate coated with adhesive (3M DP190). Uniform pressure was applied, and the substrate was cured. After the epoxy adhesive was fully cured, a metal pull-out head was bonded to the exposed surface of the PET substrate using the same high-strength epoxy adhesive. Using a universal testing machine, the metal pull-out head of the sample was clamped in the upper fixture, and the bonded rigid substrate was clamped in the lower fixture. Tension was applied at 3mm / min at 23°C and 50% relative humidity for five tests, and the average adhesion strength was calculated.

[0091] Based on Examples 1-4 and Comparative Examples 1-2, the PET samples prepared for the electrochromic color-changing film were sampled and tested for adhesion strength retention. An amino-containing aniline precursor solution was coated onto the PET substrate with a gradient interface layer and thermosetting. Conductive silver paste or clamps were used to lead wires out from the edge of the conductive layer as the working electrode and counter electrode. Using an electrochemical workstation (coloring voltage +0.8V, fading voltage -0.2V, coloring time 30s, fading time 30s, cycle count 500 times), the test area of ​​the device was immersed in an electrolyte solution (1mol / L LiClO4) at room temperature for cyclic testing. After the cycle, the sample was removed, gently rinsed with acetonitrile and thoroughly dried. It was then conditioned at 23°C and 50% relative humidity for 4 hours. Subsequent steps were the same as the initial adhesion strength test steps.

[0092] Based on Examples 1-4 and Comparative Examples 1-2, samples of the PET substrates used for electrochromic color-changing films were taken and subjected to interface state testing after 1000 bending tests. The PET substrates with gradient interface layers on the surface were cut into strips of uniform size (20 mm wide and 150 mm long). The bending axis was lightly marked in the middle of the sample with a fine marker. The initial performance of the sample was measured and recorded as a reference. The sample was mounted straight on a bending tester (bending radius 5 mm, bending angle 180°, bending frequency 0.5 Hz) and subjected to 1000 reciprocating bending cycles. Then, macroscopic visual observation and microscopic morphology inspection were performed.

[0093] The specific test results are shown in Table 2. Figure 2 , Figure 3 , Figure 4 As shown:

[0094] Table 2 Comparison of core performance of Examples 1-4 and Comparative Examples 1-3

[0095]

[0096] The comparison results above show that Example 1 exhibits the best overall performance. The moderate ultrasonic power effectively removed impurities without excessively damaging the PET surface. The UV-ozone treatment introduced suitable active sites such as carboxyl and hydroxyl groups into the PET surface, providing a solid foundation for subsequent interface layer anchoring. The PMMA-PBA-PGMA gradient interface layer design demonstrates good affinity between the PMMA segment and the activated PET surface, while the middle PBA soft segment provides flexibility and stress buffering. The terminal PGMA segment contains highly reactive epoxy groups. This indicates that Example 1 successfully solved the peeling problem caused by insufficient adhesion, meeting the application requirements of PET in flexible devices. Examples 2 to 4 show slightly lower overall performance. The adhesion level was lower than in Example 1 but still remained high, indicating that excellent adhesion was achieved despite a wide range of parameter variations. Comparative Example 1 eliminated the triblock copolymer interface layer and used a traditional silane coupling agent. The silane coupling agent had poor film-forming properties and stability on PET, and its bonding with the PET surface was mainly physical adsorption and a small amount of hydrogen bonding, which could not form a strong and tough interface with a gradient transition. Comparative Example 2 used a diblock copolymer containing only PMMA-PBA. This polymer lacked segments with reactive functional groups at the ends and could not form a strong in-situ covalent bond with the upper electrochromic layer. The interface bonding relied on physical entanglement and van der Waals forces, and relative slippage and peeling were prone to occur under long-term stress.

[0097] In summary, it can be clearly seen from the above embodiments and comparative examples that the PET for electrochromic color-changing films provided by the present invention solves the peeling problem caused by insufficient adhesion.

Claims

1. A PET for use in electrochromic color-changing films, comprising a PET substrate and an interface layer, characterized in that: The PET substrate undergoes a UV-ozone synergistic treatment to introduce polar groups and form a nanoscale rough structure on its surface. This UV-ozone synergistic treatment is performed by introducing oxygen under UV irradiation at wavelengths of 185 nm and 254 nm, creating a nanoscale textured surface with polar groups. The interface layer is a vertically phase-separated gradient structure composed of an anchoring phase, a dissipative phase, and a reactive phase. This vertically phase-separated gradient structure is formed by the phase separation and enrichment of a PMMA-PBA-PGMA triblock copolymer driven by toluene-tetrahydrofuran mixed solvent vapor annealing. PMMA is enriched in the anchoring phase and adsorbed onto the PET substrate surface based on the nanoscale rough structure. PBA is enriched in the dissipative phase, and PGMA is enriched in the reactive phase, forming surface reaction regions that readily covalently bond with amino groups. The method for preparing the PET used in the electrochromic color-changing film. Includes the following steps: S1: PET substrate treatment; S11: The PET film is ultrasonically cleaned in acetone and ethanol in sequence, then rinsed in deionized water for 30-60 seconds and dried to obtain the pretreated PET substrate. S12: The pretreated PET substrate prepared in S11 is subjected to UV-ozone synergistic treatment to obtain an activated and roughened PET substrate; S2: Preparation of triblock copolymer; S21: Methyl methacrylate, 2-dodecyl trithiocarbonate, and azobisisobutyronitrile are mixed in dehydrated toluene, and then subjected to three deoxygenation cycles. The mixture is stirred at 70°C for 8 hours, cooled in an ice-water bath, and then ethanol is added while stirring. The mixture is filtered, washed, and dried to obtain PMMA macromolecular chain transfer agent PMMA-CTA. S22: The PMMA-CTA prepared in S21 was mixed with butyl acrylate and azobisisobutyronitrile in dehydrated toluene, and then subjected to three deoxygenation cycles. The mixture was stirred at 70°C for 12 hours, cooled in an ice-water bath, and then added dropwise to a mixture of methanol and deionized water in a volume ratio of 9:

1. The mixture was filtered, washed, and dried to obtain the PMMA-PBA diblock copolymer. S23: The PMMA-PBA diblock copolymer prepared in S22 was mixed with glycidyl methacrylate and azobisisobutyronitrile in dehydrated tetrahydrofuran, and then subjected to three deoxygenation cycles. The mixture was stirred at 70°C for 10 h, cooled in an ice-water bath, and then added dropwise to n-hexane to precipitate. The precipitate was filtered, removed by heat, and dried to obtain the PMMA-PBA-PGMA triblock copolymer. S3: Coating and self-assembly; S31: The PMMA-PBA-PGMA triblock copolymer prepared in S23 is added to the mixed solvent and stirred in the dark to prepare a polymer solution with a mass concentration of 3%. S32: The polymer solution prepared in S31 is spin-coated onto the activated and roughened PET substrate prepared in S12, annealed in stages, and cooled to room temperature under vacuum to obtain a PET substrate with a gradient interface layer on the surface; the deoxygenation cycle has the following operation steps: Step 1 -78℃ dry ice-acetone bath for 3 min, Step 2 evacuate to 5 Pa, Step 3 fill with nitrogen to atmospheric pressure, Step 4 thaw naturally.

2. The PET for electrochromic color-changing film according to claim 1, characterized in that: The ultrasonic cleaning described in S11 has the following parameter settings: ultrasonic frequency 40kHz, power 200-300W, and duration 10-20min. The drying process described in S11 has the following parameters: temperature 50-60℃, duration 10-15min.

3. The PET for electrochromic color-changing film according to claim 1, characterized in that: The ultraviolet-ozone synergistic treatment described in S12 has the following parameter settings: temperature 25℃, ultraviolet light intensity 10~50mW / cm². 2 Oxygen flow rate 50-150 sccm, duration 5-30 min.

4. The PET for electrochromic color-changing film according to claim 1, characterized in that: The molar ratio of methyl methacrylate, 2-dodecyl trithiocarbonate, and azobisisobutyronitrile described in S21 is 100:1:0.

1. The drying process described in S21 has the following parameters: temperature 40°C, duration 24 hours.

5. The PET for electrochromic color-changing film according to claim 1, characterized in that: The molar ratio of the PMMA macromolecular chain transfer agent described in S22 to butyl acrylate and azobisisobutyronitrile is 1:217:0.

1.

6. The PET for electrochromic color-changing film according to claim 1, characterized in that: The molar ratio of the PMMA-PBA diblock copolymer described in S23 to glycidyl methacrylate and azobisisobutyronitrile is 1:100:0.

2. The drying process described in S23 has the following parameters: temperature 35°C, duration 48 hours.

7. The PET for electrochromic color-changing film according to claim 1, characterized in that: The mixed solvent described in S31 is toluene and tetrahydrofuran, with a volume ratio of 3:1 to 4:

1.

8. The PET for electrochromic color-changing film according to claim 1, characterized in that: The spin coating described in S32 has the following parameter settings: rotation speed 1000-1300 rpm, duration 30-60 s; The segmented annealing described in S32 has the following parameter settings: the first stage uses toluene for room temperature steam annealing for 3 to 6 hours; the second stage is vacuum annealing at a temperature of 90 to 120°C, a vacuum degree of -0.095 MPa, and a duration of 24 to 48 hours.

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