High temperature resistant aclar composite sheet and method of making

Abstract

This invention discloses a high-temperature resistant Aclar composite sheet and its preparation method, belonging to the field of pharmaceutical packaging materials. The composite sheet is composed of a PCTFE barrier layer, a chemical interface layer, a reactive adhesive resin layer, and a PVC substrate layer stacked sequentially. The chemical interface layer includes a polydopamine coating and a covalently grafted polyethyleneimine layer; the polydopamine coating is deposited on the PCTFE surface through dopamine oxidative self-polymerization, and the polyethyleneimine is covalently grafted onto the polydopamine coating. The reactive adhesive resin layer is a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer, which reacts with polyethyleneimine during hot lamination to generate covalent amide bonds, thereby constructing a complete covalent bond bridge between the PCTFE barrier layer and the adhesive resin layer. The composite sheet of this invention exhibits high peel strength retention at high temperatures, while its water vapor barrier properties and optical transparency are essentially unaffected.

Description

Technical Field

[0001] This invention belongs to the field of pharmaceutical packaging materials technology, specifically relating to a high-temperature resistant Aclar composite sheet and its preparation method. Background Technology

[0002] In the pharmaceutical packaging field, the chemical stability of drugs is highly dependent on the comprehensive barrier properties of packaging materials against external factors such as moisture, oxygen, and light. Aclar composite sheets, with polychlorotrifluoroethylene (PCTFE) as the core barrier layer, have been used in high-end pharmaceutical packaging for over forty years due to their extremely low water vapor transmission rate, excellent optical transparency, and outstanding chemical inertness. They are widely recognized as the industry benchmark material for high-barrier pharmaceutical blister packaging.

[0003] Currently, mainstream Aclar composite sheets are mainly divided into three categories based on the number of layers: the first category is a "duplex" structure, typically composed of PVC / PCTFE; the second category is a "triplex / sandwich" structure, typically composed of PVC / PCTFE / PVC or PVC / PE / PCTFE; and the third category is a multi-layer co-extrusion structure, such as PVC / EVOH-PE / Aclar / PVC. In these structures, the layers are usually bonded together through dry lamination (using solvent-based polyurethane adhesives) or hot-press lamination (using polyethylene-based hot-melt adhesive resins).

[0004] Although Aclar composite sheets have been widely used, delamination occurs between the PCTFE barrier layer and adjacent polymer layers when subjected to high-temperature use or processing environments (such as steam sterilization above 121°C, hot air drying at 150°C, and high-temperature heat sealing). Within the temperature range of 80–150°C, the peel strength decreases sharply, leading to blistering, peeling, or even complete separation between the PCTFE layer and adjacent PVC or adhesive layers. Water vapor can then directly penetrate along the interfacial channels, causing the entire batch of medicine to deteriorate due to moisture and become unusable. The main reasons for this problem are: firstly, PCTFE has extremely low surface energy, meaning traditional adhesives can only achieve physical adsorption through van der Waals forces; secondly, the coefficient of thermal expansion of PCTFE differs significantly from that of polyethylene-based adhesive layers, making it prone to large strain differences upon heating, which can cause the initiation and propagation of interfacial microcracks.

[0005] The main solutions currently available are as follows: (1) Surface physical pretreatment: Corona discharge, oxygen plasma or flame treatment is used to break the CF bond and introduce oxygen-containing polar groups. The effect of this method decays rapidly (the surface energy gradually drops back within hours to days), and the introduced groups and the adhesive resin still have secondary valence bonds such as hydrogen bonds, resulting in insufficient high-temperature stability. (2) Co-extrusion composite: PCTFE and the functional layer are co-extruded in the molten state, and an interpenetrating network is formed by molecular chain diffusion. However, the melting point difference between PCTFE and the high-temperature layer material is too large, PCTFE is prone to thermal degradation, and the interfacial bonding is essentially still a physical entanglement, which also faces the risk of disentanglement at high temperatures. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature resistant Aclar composite sheet and its preparation method. By forming a covalent chemical bond bridge between the PCTFE barrier layer and the adhesive resin layer, the interlayer bonding mechanism is changed from physical adsorption to dominant covalent bonding. This endows the composite sheet with excellent interlayer bonding stability under steam sterilization at temperatures above 121°C and short-term heat treatment at 150°C, while maintaining the inherent ultra-low water vapor barrier properties and optical transparency of PCTFE.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-temperature resistant Aclar composite sheet, which is composed of the following layered structure stacked from top to bottom: a PCTFE barrier layer (1) with a thickness of 15 to 100 μm; The chemical interface layer (2) comprises, from the inside out, a polydopamine coating (2a) and a polyethyleneimine graft layer (2b) covalently grafted onto the polydopamine coating (2a), and the total thickness of the chemical interface layer is 10 to 500 nm. A reactive adhesive resin layer (3) has a thickness of 15–50 μm, wherein the reactive adhesive resin is a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer (MAH-g-EVA), wherein the maleic anhydride grafting rate is 0.3–1.5 wt%. PVC substrate layer (4), with a thickness of 200-300μm; The polydopamine coating (2a) is anchored to the lower surface of the PCTFE barrier layer (1) through multiple non-covalent interactions of its catechol groups and indole structure; the polyethyleneimine graft layer (2b) is covalently connected to the polydopamine coating (2a) through Michael addition reaction and Schiff base condensation reaction; the reactive adhesive resin layer (3) generates covalent amide bonds by in-situ ring-opening crosslinking reaction between its maleic anhydride functional groups and the primary and secondary amines of the polyethyleneimine graft layer (2b) under thermal lamination conditions, thereby forming a complete covalent bond bridge between the PCTFE barrier layer (1) and the reactive adhesive resin layer (3) that runs through the polydopamine coating and the polyethyleneimine graft layer.

[0008] Furthermore, the polyethyleneimine has a branched structure, a number-average molecular weight Mn of 600–10,000, preferably 600–2,000, and a molar ratio of primary amine: secondary amine: tertiary amine of approximately 1:2:1.

[0009] In this invention, the use of PEI with a lower molecular weight is beneficial for its efficient penetration and diffusion into the micro-nano pores of the polydopamine coating in aqueous solution, while the higher amine group density provides abundant active sites for the subsequent in-situ ring-opening crosslinking reaction with maleic anhydride functional groups in the adhesive resin.

[0010] Furthermore, the composite sheet retains no less than 80% of its T-peel strength after being sterilized with saturated steam at 121°C for 30 minutes, and no less than 70% of its T-peel strength after being treated with hot air at 150°C for 30 minutes. Moreover, the water vapor transmission rate (under 38°C / 90%RH conditions) does not change by more than 5% compared with the same structure composite sheet without surface modification.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned high-temperature resistant Aclar composite sheet, comprising the following steps: Step S1: Preparation of biomimetic coating on PCTFE thin film surface Cut the PCTFE film to the required size, and then ultrasonically clean it in anhydrous ethanol and deionized water for 5-15 minutes each to remove surface oil and processing aid residues. After cleaning, dry it with nitrogen.

[0012] To prepare a Tris-HCl buffer solution with a concentration of 9–11 mmol / L (pH 8.3–8.7, preferably pH 8.5 ± 0.1): Weigh 1.10–1.35 g of tris(hydroxymethyl)aminomethane (Tris), dissolve it in 800–900 mL of deionized water, adjust the pH with 0.5–2 mol / L hydrochloric acid solution under magnetic stirring, and then transfer it to a volumetric flask and bring the volume to 1000 mL.

[0013] Preparation of dopamine hydrochloride buffer solution: Weigh 1.0 to 3.0 g of dopamine hydrochloride (purity ≥98%), dissolve it in the above Tris-HCl buffer solution, and stir magnetically until completely dissolved to obtain a buffer solution with a dopamine hydrochloride concentration of 1.0 to 3.0 g / L (5.2 to 15.7 mmol / L).

[0014] The clean PCTFE film was completely immersed in the above-mentioned hydrochloric acid dopamine buffer solution and allowed to stand for 6 to 24 hours under constant temperature conditions of 25 to 35°C.

[0015] Dopamine hydrochloride, as a stable salt form of dopamine, contains catechol groups and protonated amino groups. Under weakly alkaline conditions, it can effectively initiate an oxidative self-polymerization reaction, gradually forming cross-linked polydopamine oligomers and nanoparticles. These polydopamine nanoaggregates irreversibly adsorb and deposit on the PCTFE surface through hydrogen bonds (between the catechol hydroxyl groups and the fluorine / chlorine atoms of PCTFE), π-π stacking (between the indole aromatic ring and the carbon skeleton of PCTFE), and cation-π interactions (between the protonated amino groups and the PCTFE surface), forming a continuous and dense nanoscale polydopamine coating.

[0016] After the reaction is complete, remove the PCTFE film and rinse the surface thoroughly with plenty of deionized water 3 to 5 times (immersing and shaking for 5 to 10 minutes each time) to remove unadhered polydopamine loose aggregates and residual reactants. Then dry it with nitrogen gas and dry it in an oven at 50 to 70°C for 1 to 2 hours to obtain PCTFE-PDA film.

[0017] Step S2: Construction of high-density amine-grafted layer Preparation of polyethyleneimine (PEI) aqueous solution: Weigh 1.0 to 10.0 g of polyethyleneimine (branched structure, Mn = 600 to 10,000, preferably Mn = 600 to 2,000), dissolve it in 90 to 99 mL of deionized water, stir magnetically until completely dissolved, and adjust the pH to 8.0 to 9.0 (preferably pH 8.5 ± 0.5) with 0.5 to 2 mol / L hydrochloric acid solution or sodium hydroxide solution to obtain an aqueous solution with a PEI concentration of 1 to 10 wt% (preferably 3 to 7 wt%).

[0018] The PCTFE-PDA film prepared in step S1 is completely immersed in the above PEI aqueous solution and allowed to stand for 3 to 12 hours under constant temperature conditions of 35 to 45°C.

[0019] PEI molecules are covalently grafted onto the surface of polydopamine coatings via Michael addition and Schiff base condensation reactions.

[0020] After the reaction is complete, the film is removed and rinsed with plenty of deionized water more than 3 times (shaking for 5 to 10 minutes each time) to fully remove the physically adsorbed free PEI molecules. Then, it is dried with nitrogen and dried in an oven at 40 to 60°C for 0.5 to 1.5 hours to obtain PCTFE-PDA-PEI film.

[0021] Step S3: Reactive hot-pressing composite and in-situ chemical cross-linking of the interface Preparation of reactive adhesive resin layer: Select maleic anhydride grafted modified ethylene-vinyl acetate copolymer (MAH-g-EVA) granules with a maleic anhydride grafting rate of 0.3-1.5 wt%, and melt extrude them at 150-170℃ using a single screw extruder to cast them into an adhesive film with a thickness of 15-50 μm.

[0022] The layers are stacked in the following order: PVC substrate layer / MAH-g-EVA adhesive film / PCTFE-PDA-PEI film. The stacked structure is placed in a hot press, and the hot pressing temperature is set to 135-160℃ (preferably 140-150℃), the hot pressing pressure is set to 0.3-1.5MPa (preferably 0.5-1.0MPa), and the temperature and pressure are maintained for 3-10 minutes (preferably 4-6 minutes).

[0023] Under the above hot-pressing conditions, the maleic anhydride functional groups in the MAH-g-EVA adhesive resin undergo an in-situ ring-opening crosslinking reaction with the primary and secondary amine groups in the PEI graft layer on the surface of the PCTFE-PDA-PEI film.

[0024] After hot pressing, maintain pressure and allow to cool naturally to below 50°C before releasing the pressure and removing the sheet. Place the composite sheet at room temperature (23±5°C) for 24–48 hours for stress relaxation and sufficient cooling stabilization treatment, then cut it to the specified size to obtain the high-temperature resistant Aclar composite sheet product described in this invention.

[0025] Compared with the prior art, this application has the following beneficial effects: This invention creatively combines the PDA-PEI amine-functionalized surface with the in-situ ring-opening crosslinking reaction of MAH-g-EVA adhesive resin, forming a complete covalent bond bridge of "PDA anchoring—PEI amine amplification—in-situ ring-opening amide crosslinking". It achieves, for the first time, a fully covalent interfacial connection between the fluorinated barrier layer and the adhesive resin. Compared with the interfacial adhesion mechanisms in existing technologies that rely solely on physical adsorption or a single PDA coating, the amide covalent bond energy at the interface of this invention is 1-2 orders of magnitude higher, thus fundamentally solving the problem of interlayer delamination under high-temperature conditions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the layer structure of the high-temperature resistant Aclar composite sheet of the present invention.

[0027] Figure 2 This is a flowchart illustrating the preparation process of the high-temperature resistant Aclar composite sheet of the present invention.

[0028] Figure 3 This is a bar chart comparing the T-shaped peel strength of Example 1 of the present invention with that of control groups 1-3. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are only for explaining the invention and not for limiting it. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0031] Example 1: Preparation of high-temperature Aclar composite sheets (e.g.) Figure 2 ) Step S1: Preparation of polydopamine coating The PCTFE film (51 μm thick) was cut into 150 mm × 150 mm samples. The samples were then ultrasonically cleaned for 10 minutes each in anhydrous ethanol and deionized water, and dried with nitrogen gas.

[0032] Accurately weigh 1.211 g of Tris, dissolve it in 800 mL of deionized water, and adjust the pH to 8.50 ± 0.02 by adding 1 mol / L HCl dropwise with magnetic stirring. Transfer the solution to a 1000 mL volumetric flask and make up to volume to obtain a 10 mmol / L Tris-HCl buffer solution (pH 8.5).

[0033] Accurately weigh 2.00 g of dopamine hydrochloride and dissolve it in 1000 mL of the above Tris-HCl buffer solution. Stir magnetically until completely dissolved to obtain a 2.0 g / L dopamine hydrochloride buffer solution.

[0034] The cleaned PCTFE membrane was completely immersed in the above solution and allowed to react in a constant temperature water bath at 30±1℃ for 12 hours.

[0035] After the reaction was complete, the membrane was removed and thoroughly rinsed three times with deionized water (shaking and soaking for 5 minutes each time), dried with nitrogen, and then dried in an oven at 60°C for 2 hours. The resulting membrane was labeled PCTFE-PDA.

[0036] Step S2: Polyethyleneimine (PEI) grafting Accurately weigh 5.00 g of PEI (Mn≈600, branched structure) and dissolve it in 95 mL of deionized water. Stir magnetically until completely dissolved. Adjust the pH to 8.5 ± 0.1 with 1 mol / L HCl.

[0037] The PCTFE-PDA film prepared in step S1 was completely immersed in the above PEI aqueous solution and allowed to react in a constant temperature water bath at 40±1℃ for 8 hours.

[0038] After the reaction was complete, the membrane was removed, rinsed three times with deionized water (shaking for 10 minutes each time), dried with nitrogen, and then dried in an oven at 50°C for 1 hour. The resulting membrane was labeled PCTFE-PDA-PEI.

[0039] Step S3: Reactive hot pressing composite Reactive adhesive resin (MAH-g-EVA) granules are melt-extruded in a single-screw extruder (feeding section 140℃ / compression section 155℃ / metering section 160℃ / die 160℃) at a screw speed of 25 rpm to cast an adhesive film with a thickness of 30 μm.

[0040] Stack the PVC rigid sheet (250μm) / MAH-g-EVA adhesive film (30μm) / PCTFE-PDA-PEI film (51μm) in that order.

[0041] The laminated structure was placed in a flatbed hot press, with the temperature set at 145±3℃ and the pressure at 0.8MPa, and held at that temperature and pressure for 5 minutes. The pressure was maintained until it cooled naturally to below 48℃ before being depressurized and removed. It was then left at room temperature (23±2℃) for 24 hours to relax the stress, and cut into test strips (see schematic diagram of the layered structure). Figure 1 ).

[0042] Performance testing T-type peel strength test method: According to GB / T8808-2023 standard, the sample width is 25mm and the peeling speed is 50mm / min.

[0043] Test conditions: Condition A: Room temperature 23±2℃ (initial peel strength); Condition B: 121℃ saturated steam sterilization for 30 minutes → remove and cool to room temperature → test; Condition C: 150℃ hot air circulation treatment for 30 minutes → remove and cool to room temperature → test.

[0044] Water vapor transmission rate test: according to GB / T1037-2021 standard, conditions 38℃ / 90%RH.

[0045] Optical transparency test: UV-Vis spectrophotometer is used to test the transmittance in the 400-800nm ​​visible light band.

[0046] Performance test results: Initial peel strength at room temperature (23℃): 11.2±0.6N / 25mm.

[0047] After sterilization with saturated steam at 121℃ for 30 minutes, the peel strength was 9.8±0.5N / 25mm, with a retention rate of 87.5%.

[0048] After hot air treatment at 150℃ for 30 minutes, the peel strength was 8.6±0.5N / 25mm, and the retention rate was 76.8%.

[0049] Water vapor transmission rate (38℃ / 90%RH): 0.018±0.001g / (m 2 •24h).

[0050] Visible light transmittance: 89.2%.

[0051] Example 2: The dopamine polymerization time in step S1 of Example 1 was shortened to 6 hours, the PEI grafting time in step S2 was shortened to 4 hours, and the other conditions remained unchanged.

[0052] Performance test results: Initial peel strength at room temperature: 9.5±0.5N / 25mm.

[0053] After sterilization at 121℃ for 30 minutes, the peel strength was 7.8±0.4N / 25mm, and the retention rate was 82.1%.

[0054] After treatment at 150℃, the peel strength was 6.7±0.4N / 25mm, and the retention rate was 70.5%.

[0055] Even with a shortened process window, the high-temperature adhesive retention rates can still exceed 80% and 70% respectively, making it suitable for high-efficiency continuous production.

[0056] Example 3: While keeping other conditions unchanged in Example 1, branched PEI with molecular weights of Mn=600, Mn=1800, and Mn=10000 were used for grafting (step S2) to compare and examine the effect of PEI molecular weight on the properties of the final composite sheet. See Table 1: Table 1. Effect of PEI molecular weight on the properties of the final composite sheet It can be seen that PEI with Mn=600 has the best overall performance. Its lower molecular weight is conducive to penetration and diffusion into the micro-nano pores of the PDA coating, thus improving the grafting efficiency. PEI with Mn=10000 has a lower grafting efficiency due to its high solution viscosity and large molecular chain size, but it is still significantly better than the control group D2.

[0057] Example 4: While keeping other conditions unchanged in Example 1, the coating in step S1 was prepared using three concentrations of dopamine hydrochloride: 1.0 g / L, 2.0 g / L, and 3.0 g / L, respectively. The effect of PDA coating thickness on the final performance was compared. See Table 2: Table 2. Effect of PDA coating thickness on final performance It can be seen that the 2.0 g / L concentration achieves the best balance between peel strength, high-temperature retention, and light transmittance. The 1.0 g / L coating is too thin, resulting in limited anchoring and grafting efficiency, while the 3.0 g / L coating is too thick, which may slightly degrade high-temperature performance due to insufficient cohesive strength of the PDA layer itself and decreased light transmittance.

[0058] Control group 1: The raw PCTFE film without any surface treatment was directly hot-pressed with MAH-g-EVA adhesive film and PVC rigid sheet under the same hot-pressing conditions as in Example 1 (145°C, 0.8 MPa, 5 minutes).

[0059] Performance test results: Initial peel strength at room temperature: 2.8±0.3N / 25mm.

[0060] After sterilization at 121℃ for 30 minutes, the peel strength was 0.7±0.2N / 25mm, and the retention rate was 25.0%.

[0061] After treatment at 150℃, the peel strength was 0.4±0.2N / 25mm, and the retention rate was 14.3%.

[0062] Water vapor transmission rate (38℃ / 90%RH): 0.017±0.001g / (m 2 •24h).

[0063] Visible light transmittance is 90.5%.

[0064] Control group 2: The PCTFE film was coated with PDA (the operation was exactly the same as step S1 in Example 1, with a dopamine concentration of 2.0 g / L, pH 8.5, 30°C, and 12 hours), without PEI grafting, and then laminated with MAH-g-EVA adhesive film and PVC rigid sheet using the same hot pressing process.

[0065] Performance test results: Initial peel strength at room temperature: 4.5±0.4N / 25mm.

[0066] After sterilization at 121℃ for 30 minutes, the peel strength was 2.3±0.3N / 25mm, and the retention rate was 51.1%.

[0067] After treatment at 150℃, the peel strength was 1.5±0.3N / 25mm, and the retention rate was 33.3%.

[0068] Water vapor transmission rate (38℃ / 90%RH): 0.018±0.001g / (m 2 •24h).

[0069] Visible light transmittance is 90.0%.

[0070] Control group 3: The PCTFE film was subjected to oxygen plasma surface activation treatment (RF power 200W, oxygen flow rate 50sccm, working pressure 20Pa, treatment time 60 seconds), and then laminated with MAH-g-EVA adhesive film and PVC rigid sheet using the same hot pressing process.

[0071] Performance test results: Initial peel strength at room temperature: 5.8±0.5N / 25mm.

[0072] After sterilization at 121℃ for 30 minutes, the peel strength was 2.8±0.4N / 25mm, and the retention rate was 48.3%.

[0073] After treatment at 150℃, the peel strength was 1.6±0.4N / 25mm, and the retention rate was 27.6%.

[0074] Water vapor transmission rate (38℃ / 90%RH): 0.017±0.001g / (m 2 •24h).

[0075] Visible light transmittance: 89.5%.

[0076] The bar chart comparing the T-shaped peel strength of Example 1 with control groups 1-3 is shown below. Figure 3 As shown, the initial peel strength of control group 1 was low and almost completely lost after high-temperature treatment. Although the initial peel strength of control group 2 was increased to 4.5 N / 25 mm due to the multiple non-covalent anchoring of PDA, the high-temperature retention rates were only 51.1% and 33.3%, respectively, far lower than those of the present invention. Although the plasma physical treatment of control group 3 improved the effect, it still did not meet the actual requirements of sterilization above 121°C and heat processing at 150°C. The peel strength of Example 1 under both room temperature and two high-temperature conditions was significantly better than that of all control groups, demonstrating thermodynamic stability under high-temperature conditions.

[0077] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A high-temperature resistant Aclar composite sheet, comprising the following layers stacked sequentially from top to bottom: The product comprises a PCTFE barrier layer, a chemical interface layer, a reactive adhesive resin layer, and a PVC substrate layer, characterized in that the chemical interface layer, from the inside out, sequentially includes a polydopamine coating and a polyethyleneimine graft layer covalently grafted onto the polydopamine coating, and the reactive adhesive resin layer is a maleic anhydride graft-modified ethylene-vinyl acetate copolymer.

2. The high-temperature resistant Aclar composite sheet according to claim 1, characterized in that, The polyethyleneimine has a branched structure, a number-average molecular weight Mn of 600–2,000, and a molar ratio of primary amine: secondary amine: tertiary amine of 1:2:

1.

3. The high-temperature resistant Aclar composite sheet according to claim 1, characterized in that, The maleic anhydride grafting rate in the maleic anhydride-grafted modified ethylene-vinyl acetate copolymer is 0.3–1.5 wt%.

4. The high-temperature resistant Aclar composite sheet according to claim 1, characterized in that, The thickness of the PCTFE barrier layer is 15–100 μm; the total thickness of the chemical interface layer is 10–500 nm; the thickness of the reactive adhesive resin layer is 15–50 μm; and the thickness of a single PVC substrate layer is 200–300 μm.

5. The high-temperature resistant Aclar composite sheet according to claim 1, characterized in that, The polydopamine coating is anchored to the lower surface of the PCTFE barrier layer through multiple non-covalent interactions of catechol groups and indole structures; the polyethyleneimine graft layer is covalently connected to the polydopamine coating through Michael addition reaction and Schiff base condensation reaction; the reactive adhesive resin layer generates covalent amide bonds by in-situ ring-opening crosslinking reaction between its maleic anhydride functional groups and the primary and secondary amines of the polyethyleneimine graft layer under thermal lamination conditions.

6. A method for preparing a high-temperature resistant Aclar composite sheet according to any one of claims 1-5, characterized in that, Includes the following steps: Step S1: Immerse the cleaned PCTFE film in Tris-HCl buffer solution with a dopamine concentration of 1.0-3.0 g / L, and let it stand for 6-24 hours under constant temperature of 25-35℃. The polydopamine coating is deposited on the surface of the PCTFE film by the oxidative self-polymerization reaction of dopamine. After removal, wash with deionized water and dry to obtain PCTFE-PDA film. Step S2: Immerse the PCTFE-PDA film in an aqueous solution of polyethyleneimine with a concentration of 1-10 wt% and a pH of 8.0-9.0, and allow it to stand for 3-12 hours at a constant temperature of 35-45°C. Polyethyleneimine is covalently grafted onto the surface of the polydopamine coating through Michael addition reaction and Schiff base condensation reaction. After removal, thoroughly wash with deionized water to remove free PEI molecules and dry to obtain PCTFE-PDA-PEI film. Step S3: The PVC substrate layer, the maleic anhydride-grafted modified ethylene-vinyl acetate copolymer adhesive resin layer, and the PCTFE-PDA-PEI film are stacked sequentially, ensuring that the PEI grafted surface faces the adhesive resin layer. Hot-pressing is performed at a temperature of 135-160℃ and a pressure of 0.3-1.5MPa for 3-10 minutes to allow the maleic anhydride functional groups in the MAH-g-EVA adhesive resin layer to undergo an in-situ ring-opening crosslinking reaction with the primary and secondary amines in the polyethyleneimine grafted layer of the PCTFE-PDA-PEI film to generate covalent amide bonds. After cooling, the pressure is released, and the material is left at room temperature for 24-48 hours to relax the stress, thus obtaining the high-temperature resistant Aclar composite sheet.

7. The method for preparing the high-temperature resistant Aclar composite sheet according to claim 6, characterized in that, In step S1, the concentration of dopamine hydrochloride is 1.5–2.5 g / L, the pH of the Tris-HCl buffer is 8.5 ± 0.1, the reaction temperature is 28–32 °C, and the reaction time is 8–16 hours.

8. The method for preparing the high-temperature resistant Aclar composite sheet according to claim 6, characterized in that, The concentration of the polyethyleneimine aqueous solution in step S2 is 3-7 wt%, the pH is 8.3-8.7, the reaction temperature is 38-42℃, and the reaction time is 4-8 hours.

9. The method for preparing the high-temperature resistant Aclar composite sheet according to claim 6, characterized in that, In step S3, the temperature for hot pressing is 140–150°C, the pressure is 0.5–1.0 MPa, and the holding time is 4–6 minutes.

10. The method for preparing the high-temperature resistant Aclar composite sheet according to claim 6, characterized in that, In step S3, the cooling method is to maintain the pressure and allow it to cool naturally until it drops below 50°C before releasing the pressure.

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