PET release film applied to polaroid field and preparation method thereof

Abstract

The invention discloses a PET release film applied to the field of polarizers and a preparation method of the PET release film in the technical field of optical functional film materials, the release film takes a two-way stretching PET film as a base material, and the surface of the release film is coated with a protective coating containing a specific modified compound. The modified compound comprises a hyperbranched polymer containing a phosphazene thiazoline structure and a graphene polyhedral oligomeric silsesquioxane hybrid material, and forms a stable cross-linked network with a sulfur-containing cross-linking agent under the action of an acid catalyst through accurate proportioning. The preparation process comprises the steps of corona treatment of the base membrane, preparation of a coating solution, micro gravure coating, stepped heating curing and the like. The problems that a traditional release film is poor in heat resistance, insufficient in flame retardance, weak in mechanical property and the like are effectively solved, the obtained product has excellent high-temperature resistance, flame retardance and mechanical strength, meanwhile, the good optical property is kept, and the release film is particularly suitable for the field of high-end polaroid manufacturing.

Description

Technical Field

[0001] This invention relates to the field of optical functional thin film materials technology, specifically to a PET release film for use in polarizers and its preparation method. Background Technology

[0002] As a core component of liquid crystal displays (LCDs), polarizers require various functional thin-film materials in their manufacturing process, among which polyester release films play a crucial role. An ideal release film not only needs to provide stable protection during polarizer processing but also should be able to be cleanly peeled off without leaving residue during final assembly. As display technology continues to evolve towards higher resolution and flexibility, the performance requirements for release films are also increasing. Traditional polyester release films mainly use ordinary silicone coatings. These materials have gradually revealed many limitations in long-term use, particularly their insufficient stability at high temperatures, making it difficult to meet the demands of modern display device manufacturing processes. Currently, the industry urgently needs a new type of release film material that can withstand high-temperature processes and possesses excellent overall performance.

[0003] Several significant drawbacks exist in existing polyester release films. Firstly, they exhibit poor heat resistance; when ambient temperatures exceed a certain limit, the film material is prone to deformation or degradation, leading to unstable release force and impacting polarizer production yield. Secondly, their flame retardant properties are insufficient; ordinary silicone materials have low limiting oxygen indices, posing safety hazards and failing to meet the stringent safety requirements of high-end display devices. Furthermore, traditional release films have limited mechanical strength, making them more susceptible to cracking in the trend towards thinner designs. These technological bottlenecks severely restrict the further development of display technology. Although recent research has attempted to improve performance by adding inorganic nanoparticles or performing surface modification, it is often difficult to simultaneously achieve multiple performance indicators, particularly the unresolved issues of nanomaterial dispersion and interfacial compatibility within the polymer matrix.

[0004] To address the aforementioned technical challenges, existing improvement solutions still have significant shortcomings. Some studies use ordinary nano-zinc oxide or silica as reinforcing fillers, which improves heat resistance to some extent but leads to a decline in optical performance. Other methods improve surface properties by introducing fluorine-containing compounds, but neglect overall compatibility with the base film. Still others have attempted to use multilayer composite structures, which, while solving some performance problems, complicates the manufacturing process and significantly increases costs. None of these solutions fundamentally resolve the inherent contradictions within the release film material system. Therefore, developing a functional material with a novel molecular structure to achieve synergistic improvement in various properties of release films has become a crucial issue urgently needing breakthrough in this technical field. This invention, against this technical background, proposes a novel solution through molecular structure innovation and material system optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a PET release film for use in the field of polarizers and its preparation method, which solves the technical problems of insufficient heat resistance, poor flame retardancy, low mechanical strength and unsatisfactory surface compatibility of existing PET release films.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] A method for preparing a PET release film, comprising the following steps:

[0008] S1. The biaxially oriented PET film is subjected to corona treatment; the corona treatment conditions are: power of 4-6kW, processing speed of 20-22m / min, and electrode spacing of 2-3mm.

[0009] S2. Dissolve the hyperbranched polymer containing the phosphazene-thiazoline structure in a mixed solvent of butanone and toluene and stir mechanically; then add the graphene-cage-type silsesquioxane hybrid material and disperse it ultrasonically; subsequently add 2,2'-dithiodibenzoic acid and p-toluenesulfonic acid and continue stirring at room temperature to form a coating solution.

[0010] S3. Using a micro-gravure coating method, the coating solution is applied to the corona-treated PET base film. The coated film is then dried in an eight-section oven with stepped temperature increases: section 1: 60℃, section 2: 80℃, section 3: 100℃, section 4: 120℃, section 5: 140℃, section 6: 160℃, section 7: 180℃, and section 8: 200℃. Finally, the dried film is wound up at 34-36℃ and cured in an environment of 44-46℃.

[0011] In this invention, the film-forming mechanism of the PET release film is a complex physicochemical process involving interactions and phase transitions among multiple components. During the coating solution preparation stage, the hyperbranched polymer containing a phosphazene-thiazoline structure serves as the film-forming host. It first dissolves and unfolds in the mixed solvent, with the molecular chains gradually extending from a coiled state to a random coil conformation. Subsequently, the added graphene-cage-type silsesquioxane hybrid material is uniformly distributed in the polymer solution through ultrasonic dispersion, and its surface active groups initially interact with the hyperbranched polymer molecular chains. The addition of crosslinking agent molecules triggers a chemical reaction in the system. Under the action of an acidic catalyst, the thiazoline ring in the hyperbranched polymer undergoes a specific reaction with the carboxyl groups of the crosslinking agent molecules. After the thiazoline ring opens, it forms an amide bond with the carboxyl group, and the released thiol groups can further participate in the secondary crosslinking reaction. This crosslinking process begins in the solution state, but the main reaction occurs in the subsequent curing stage. After coating and film formation, the system undergoes a series of complex changes during the stepped temperature drying process: the low-temperature stage mainly completes solvent evaporation and initial film formation; the medium-temperature stage accelerates the crosslinking reaction, forming a three-dimensional network structure between molecules; and the high-temperature stage achieves complete crosslinking and final film structure shaping. Throughout the curing process, the two functional compounds work synergistically, with the hyperbranched polymer constructing a continuous phase matrix, while the hybrid material acts as a nano-reinforcing unit dispersed within it, strengthening the film structure through interfacial chemical bonding. The resulting release film possesses a precise microstructure and exhibits suitable release properties on its surface, while the internal crosslinking network ensures the material's thermal stability and mechanical strength, meeting the stringent application requirements in the manufacturing of high-end polarizers.

[0012] According to a preferred embodiment of the present invention, in step S2, the stirring time at room temperature is 2-4 hours; the mass ratio of the hyperbranched polymer containing the phosphazene-thiazoline structure to the graphene-cage-silsesquioxane hybrid material is (5-10):1; the mass ratio of the hyperbranched polymer containing the phosphazene-thiazoline structure to 2,2'-dithiobenzoic acid is (3-4):1; and the mass of the p-toluenesulfonic acid is 1-3% of the mass of 2,2'-dithiobenzoic acid.

[0013] According to a preferred embodiment of the present invention, in step S3, the curing time in an environment of 44-46°C is 48-50 hours.

[0014] According to a preferred embodiment of the present invention, the preparation method of the hyperbranched polymer containing the phosphazene-thiazoline structure includes: A1, under nitrogen protection, adding hexachlorocyclotriphosphazene and tetrahydrofuran to a three-necked flask, stirring and dissolving, then adding a mixed solution of 4-hydroxybenzaldehyde and triethylamine dropwise at 50-55°C, and after the addition is complete, raising the temperature to 64-66°C for reaction; after the reaction is completed, filtering and rotary evaporating to obtain the aldehyde-modified phosphazene intermediate; A2, subsequently, redissolving the aldehyde-modified phosphazene intermediate in N,N-dimethylformamide, adding 2-amino-2-thiazoline and p-toluenesulfonic acid, and reacting at 90-95°C under a nitrogen atmosphere; after the reaction is completed, pouring the reaction mixture into cold diethyl ether to precipitate, filtering, recrystallizing with a methanol / water mixed solvent, and drying in a vacuum drying oven at 58-62°C.

[0015] In this invention, the preparation mechanism of hyperbranched polymers containing phosphazene-thiazoline structures involves a multi-step, precisely controlled molecular construction process. The synthesis uses hexachlorocyclotriphosphazene as the core starting material, whose six active chlorine atoms provide ample reaction sites for subsequent functionalization modifications. In the first stage reaction, after hexachlorocyclotriphosphazene forms a homogeneous system with tetrahydrofuran solvent, it undergoes a nucleophilic substitution reaction with an aldehyde-containing benzaldehyde derivative in the presence of an alkaline catalyst. The key to this step lies in the gradual substitution of chlorine atoms on the phosphazene ring; the two chlorine atoms attached to each phosphorus atom are replaced by organic groups, forming a stable phosphorus-nitrogen skeleton structure. Strict temperature and feeding rate control are required during the reaction to ensure the substitution reaction proceeds gradually and avoids crosslinking side reactions. The intermediate molecule obtained after substitution retains the thermal stability and flame-retardant properties of the phosphazene ring while introducing active aldehyde functional groups, laying the foundation for the subsequent expansion of hyperbranched structures. In the second stage of the reaction, the aldehyde intermediate undergoes a condensation reaction with an amine compound containing a thiazoline ring. The aldehyde group and the amino group first form an imine bond, and then, under acidic conditions, the thiazoline ring undergoes ring-opening recombination, forming a new heterocyclic structure with specific groups in the molecular chain. This process is accompanied by the extension of the molecular chain and the formation of branching sites. By precisely controlling the molar ratio of the reactants and the reaction conditions, a hyperbranched polymer with a three-dimensional structure is finally constructed. This polymer molecule simultaneously contains the rigid structural unit of the phosphazene ring and the active reactive site of the thiazoline ring, endowing the material with unique thermal stability and chemical reactivity.

[0016] According to a preferred embodiment of the present invention, in step A1, the reaction time is 12-14 hours after the temperature is raised to 64-66°C.

[0017] According to a preferred embodiment of the present invention, in step A2, the reaction time at 90-95°C is 18-20 h; the drying time in the vacuum drying oven is 24-30 h.

[0018] According to a preferred embodiment of the present invention, the preparation method of the graphene-cage-type silsesquioxane hybrid material includes: dispersing graphene oxide in N-methylpyrrolidone and ultrasonically treating it to obtain a graphene oxide dispersion; dissolving octaaminophenyl POSS in N-methylpyrrolidone and adding it to the graphene oxide dispersion, and mechanically stirring and mixing; subsequently, adding triethylamine and reacting at 94-96°C under nitrogen protection; after the reaction is completed, centrifuging the mixture, collecting the solid product, and washing it alternately with N-methylpyrrolidone and ethanol; finally, drying it in a vacuum drying oven at 68-72°C.

[0019] According to a preferred embodiment of the present invention, the reaction time at 94-96°C is 36-40 hours.

[0020] In this invention, the preparation process of graphene-cage-silsesquioxane hybrid materials embodies the principle of molecular self-assembly at the nanoscale. Graphene oxide, as a two-dimensional nanomaterial substrate, provides active sites for subsequent chemical reactions due to its abundant oxygen-containing functional groups on its surface. During ultrasonic dispersion, graphene oxide sheets are effectively exfoliated, forming monolayer or few-layer dispersions, greatly increasing the specific surface area and reactivity. Cage-silsesquioxanes are a class of nanomaterials with a regular three-dimensional structure. Their molecular skeleton consists of a cage-like framework formed by silicon-oxygen bonds, with reactive amino groups attached to the periphery. During synthesis, the epoxy groups on the graphene oxide surface undergo a nucleophilic ring-opening reaction with the amino groups surrounding the cage-silsesquioxanes. This reaction requires the promotion of an alkaline catalyst. In the initial stage of the reaction, the amino groups attack the carbon atoms on the epoxy ring, leading to ring opening and the formation of secondary hydroxyl groups and new carbon-nitrogen bonds. As the reaction proceeds, multiple cage-silsesquioxane molecules are covalently grafted onto the surface of the graphene oxide sheets, forming a uniformly distributed core-shell structure. This grafting process not only effectively prevents the recombination of graphene sheets but also introduces the unique nanoporous structure and surface properties of cage-like silsesquioxanes. The two components in the hybrid material achieve molecular-level compositeness through chemical bonding, retaining the excellent thermal conductivity and mechanical strength of graphene while combining the high thermal stability and surface modifiability of cage-like silsesquioxanes. The resulting three-dimensional network structure achieves functional synergy at the nanoscale, laying the structural foundation for the subsequent preparation of high-performance composite materials.

[0021] The present invention also provides a PET release film, which is prepared according to the method for preparing the PET release film.

[0022] The present invention also provides an application of the PET release film described above in the field of polarizers.

[0023] The beneficial effects of this invention are as follows:

[0024] Firstly, significant advancements have been achieved in heat resistance and flame retardancy. By introducing a hyperbranched polymer containing phosphazene rings and thiazoline structures, this release film constructs a stable thermal protection system at the molecular level. The phosphorus and nitrogen elements in the phosphazene rings produce a synergistic flame-retardant effect, forming a dense charred protective layer under high-temperature conditions, effectively blocking the transfer of heat and oxygen. Simultaneously, the hybrid material of graphene and cage-like silsesquioxane forms a uniformly dispersed nano-insulating network in the matrix, significantly improving the material's thermal stability. Experiments have demonstrated that this composite design substantially improves the release film's temperature tolerance compared to traditional products, enabling it to adapt to higher-temperature processing environments. Regarding flame retardancy, this material system promotes char formation and inhibits the generation of combustible gases when heated, giving the product excellent fire safety and fully meeting the stringent requirements for flame retardancy ratings in high-end display devices.

[0025] Secondly, it exhibits significant advantages in mechanical properties and durability. The three-dimensional network structure of the hyperbranched polymer, combined with the nano-reinforcing effect of the hybrid materials, forms a stable dual-composite cross-linked system. This structure not only improves the tensile strength and tear resistance of the material but also endows the coating with good flexibility and adhesion. Particularly noteworthy is the dynamic disulfide bonds introduced into the molecular structure, which endow the material with a certain degree of self-healing ability, allowing it to partially recover its properties when subjected to minor damage, thereby extending the product's service life. In practical applications, this release film demonstrates excellent fatigue resistance, maintaining stable release force even after multiple windings and uses, effectively preventing coating peeling or transfer, and ensuring the reliability and consistency of the polarizer production process.

[0026] Finally, an ideal balance was achieved between optical and practical performance. Thanks to the precise control of nanomaterials and the optimization of processing technology, this release film maintains excellent mechanical properties while acquiring outstanding optical characteristics. The uniform dispersion of graphene hybrid materials in the matrix effectively reduces light scattering, giving the film high transmittance and low haze, without adversely affecting the brightness and color reproduction of the display. Furthermore, by precisely controlling the coating process and curing conditions, a uniform and smooth coating is formed on the product surface, ensuring the stability and consistency of the release force. This fabrication process has good repeatability and scalability, making it suitable for large-scale industrial production and providing a reliable material solution for the manufacturing of high-end display devices. Detailed Implementation

[0027] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0028] The following is information on domestic suppliers of key related equipment and materials:

[0029] The 2,2'-dithiodibenzoic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0030] The p-toluenesulfonic acid was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0031] The eight-section drying oven was purchased from Shanghai Jinghong Experimental Equipment Co., Ltd.

[0032] The hexachlorocyclotriphosphazene was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0033] The 4-hydroxybenzaldehyde was purchased from Tianjin Xiens Biochemical Technology Co., Ltd.

[0034] The triethylamine was purchased from Chengdu Xiya Chemical Co., Ltd.

[0035] The 2-amino-2-thiazoline was purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.

[0036] The graphene oxide was purchased from Suzhou CarbonFeng Technology Co., Ltd.

[0037] The octaaminophenyl POSS was purchased from Beijing Huawirui Chemical Technology Co., Ltd.

[0038] Example 1

[0039] First, a hyperbranched polymer containing a phosphazene-thiazoline structure was prepared. Under nitrogen protection, 50.00 g of hexachlorocyclotriphosphazene and 300.0 mL of tetrahydrofuran were added to a 2000 mL three-necked flask. A mechanical stirrer, thermometer, and reflux condenser were installed. The mixture was stirred at 350 rpm until dissolved, then heated to 52.0 °C in an oil bath and maintained at this temperature. A mixed solution of 45.00 g of 4-hydroxybenzaldehyde and 20.00 g of triethylamine was slowly added dropwise at a rate of 2 drops per second using a constant-pressure dropping funnel. The dropping rate was controlled to ensure that the reaction temperature fluctuation did not exceed ±0.5 °C. The dropping process lasted for 120 minutes. After the addition was complete, the reaction system was heated to 65.0 °C and maintained at this temperature for 780 minutes. During the reaction, samples were taken every 60 minutes for thin-layer chromatography analysis to monitor the reaction progress. The reaction mixture was prepared using a petroleum ether to ethyl acetate volume ratio of 3:1. Using solvent 1, the spot changes were observed under UV light. After the reaction, the triethylamine hydrochloride was removed by vacuum filtration using a Buchner funnel. The filter cake was washed three times with 50 mL of tetrahydrofuran. The combined filtrates were concentrated to 100 mL using a rotary evaporator at a water bath temperature of 60.0℃ and a vacuum degree of -0.09 MPa to obtain the aldehyde-modified phosphazene intermediate. Subsequently, the intermediate was completely dissolved in 150.0 mL of N,N-dimethylformamide and transferred to a 500 mL three-necked flask. 30.00 g of 2-amino-2-thiazoline and 1.500 g of p-toluenesulfonic acid were added. The air in the reaction system was purged three times with high-purity nitrogen. The reaction temperature was raised to 92.0℃ and maintained under reflux for 1140 minutes under a nitrogen atmosphere. During the reaction, samples were taken every 240 minutes for Fourier transform infrared spectroscopy analysis at 1650 cm⁻¹. -1The intensity of the characteristic peak of thiazoline was observed. After the reaction was completed, the reaction mixture was poured into 1000 mL of diethyl ether pre-cooled to 0.0 °C while still hot to precipitate. After standing and aging for 180 minutes, the solid product was collected by filtration using a sintered glass funnel. The product was purified by recrystallization three times with a methanol-water solution at a volume ratio of 1:1, using 150 mL of solvent each time. Finally, the product was dried continuously in a vacuum drying oven at 60.0 °C for 24 hours to obtain a pale yellow solid product. The yield was calculated to be 86.5% by weight. Next, a graphene-cage-type silsesquioxane hybrid material was prepared. 15.00 g of graphene oxide was dispersed in 600.0 mL of N-methylpyrrolidone and subjected to ultrasonic treatment at 800 W power and 40 kHz frequency for 180 minutes in an ultrasonic cell disruptor to fully exfoliate the graphene oxide. Separately, 40.00 g of octaaminophenyl POSS was dissolved in 200.0 mL of N-methylpyrrolidone to form a clear solution. Under mechanical stirring, the POSS solution was slowly added to the graphene oxide dispersion at 500 rpm, maintaining this stirring speed for mixing. The mixture was pre-dispersed for 60 minutes, and then 10.00 g of triethylamine was added as a catalyst. The reaction apparatus was then placed under a nitrogen protective atmosphere and reacted at an oil bath temperature of 95.0℃ for 2160 minutes. After the reaction, the mixture was transferred to a high-speed centrifuge and centrifuged at 12000 rpm for 20 minutes to collect the solid product. The product was washed three times alternately with N-methylpyrrolidone and ethanol, using 100 mL of solvent each time. Finally, the product was dried in a vacuum drying oven at 70.0℃ for 2880 minutes to obtain a gray-black powdery hybrid material. The yield was calculated to be 90.2%.Finally, a PET release film was prepared. A biaxially oriented PET film with a thickness of 38.0 μm was subjected to corona treatment. The treatment parameters were set as follows: power 5.00 kW, treatment speed 21.0 m / min, and electrode spacing 2.50 mm. The surface tension of the film was tested with a corona pen to ensure it reached more than 50 dyne / cm. 18.00 g of the hyperbranched polymer containing the phosphazene-thiazoline structure prepared above was weighed and dissolved in a mixed solvent composed of 11.00 g of butanone and 4.000 g of toluene. The mixture was stirred at 400 rpm for 40 minutes to ensure complete dissolution. Then, 3.000 g of graphene-cage-type silsesquioxane hybrid material was added, and the mixture was transferred to an ultrasonic cleaner and ultrasonically dispersed at 40 kHz frequency and 600 W power for 60 minutes. Subsequently, 2,2'-dithiodibenzoyl peroxide was added. 6.000g of acid and 0.1200g of p-toluenesulfonic acid were stirred for 180 minutes at room temperature (25.0℃) to form a uniform coating solution. The coating solution was then applied to the corona-treated PET base film using a micro-gravure coating machine, with a wet coating thickness of 15.0μm and a coating speed of 15.0m / min. The coated film was then dried in an eight-section oven with stepped temperature increases. The temperatures of each section were set to 60.0℃, 80.0℃, 100.0℃, 120.0℃, 140.0℃, 160.0℃, 180.0℃, and 200.0℃, respectively. The dwell time in each section was 15.0 seconds, and the total drying time was 120 seconds. Finally, the dried film was wound up at 35.0℃ and cured at a constant temperature of 45.0℃ for 2940 minutes to obtain the final product.

[0040] Example 2

[0041] The specific implementation method is the same as in Example 1, except that: firstly, a hyperbranched polymer containing a phosphazene thiazoline structure is prepared. Under nitrogen protection, 48g of hexachlorocyclotriphosphazene and 280mL of tetrahydrofuran are added to a 2000mL three-necked flask. A mechanical stirrer and a reflux condenser are installed, and the mixture is stirred at 300rpm to dissolve. The temperature is then raised to 51°C in an oil bath and maintained at a constant temperature. A mixed solution of 43g of 4-hydroxybenzaldehyde and 19g of triethylamine is slowly added dropwise using a constant pressure dropping funnel. The dropping rate is controlled so that the reaction temperature fluctuation does not exceed ±1°C. The dropping process lasts for 2 hours. After the dropping is completed, the reaction system is heated to 64°C and maintained at this temperature for 12 hours. The reaction progress is monitored by thin-layer chromatography during the reaction. After the reaction is completed, the triethylamine hydrochloride generated is removed by vacuum filtration using a Buchner funnel. The filtrate is then evaporated in a rotary evaporator at a water bath temperature of 60°C. The aldehyde-modified phosphazene intermediate was obtained by concentrating the solution to one-third of its original volume at a certain temperature. This intermediate was then completely dissolved in 150 mL of N,N-dimethylformamide and transferred to a 500 mL three-necked flask. 28 g of 2-amino-2-thiazoline and 1.3 g of p-toluenesulfonic acid were added. Nitrogen gas was introduced to purge the air from the reaction system three times. The reaction temperature was raised to 91 °C and maintained under reflux for 18 hours under a nitrogen atmosphere. Samples were taken every 4 hours during the reaction for Fourier transform infrared spectroscopy analysis to monitor changes in the characteristic peaks of the thiazoline. After the reaction was completed, the reaction mixture was poured hot into 800 mL of diethyl ether pre-cooled to 0 °C to precipitate the product. After standing for 2 hours, the solid product was collected by filtration and purified by recrystallization three times with a 1:1 volume ratio of methanol-water solution. Finally, the product was continuously dried in a vacuum drying oven at 60 °C for 24 hours to obtain a pale yellow solid product. Next, a graphene cage-like silsesquioxane hybrid material was prepared. 14g of graphene oxide was dispersed in 600mL of N-methylpyrrolidone and subjected to ultrasonic treatment at 800W for 3 hours in an ultrasonic cell disruptor to fully exfoliate the graphene oxide. Separately, 38g of octaaminophenyl POSS was dissolved in 200mL of N-methylpyrrolidone to form a clear solution. The POSS solution was slowly added to the graphene oxide dispersion under mechanical stirring and mixed at 500rpm for 1 hour to ensure full pre-dispersion. Then, 9g of triethylamine was added as a catalyst, and the reaction apparatus was transferred to a nitrogen protective atmosphere and reacted at 94℃ in an oil bath for 37 hours. After the reaction, the mixture was transferred to a high-speed centrifuge and centrifuged at 12000rpm for 20 minutes to collect the solid product. The product was washed three times alternately with N-methylpyrrolidone and ethanol to remove unreacted substances. Finally, the product was dried in a vacuum drying oven at 70℃ for 48 hours to obtain a gray-black powdery hybrid material.Finally, a PET release film was prepared. A 38 μm thick biaxially oriented PET film was subjected to corona treatment with parameters set as follows: power 5 kW, processing speed 21 m / min, and electrode spacing 2.5 mm, to achieve a film surface tension of over 50 dyne / cm. 16 g of the hyperbranched polymer containing a phosphazene thiazoline structure was dissolved in a mixed solvent of 10 g methyl ethyl ketone and 3 g toluene. The solution was stirred at 400 rpm for 40 minutes to ensure complete dissolution. Then, 2 g of graphene cage-type silsesquioxane hybrid material was added, and the mixture was ultrasonically dispersed at 40 kHz for 1 hour. Subsequently, 2 g of... 5g of 2'-dithiodibenzoic acid and 0.1g of p-toluenesulfonic acid were stirred for 3 hours at room temperature (25℃) to form a uniform coating solution. The coating solution was then applied to the corona-treated PET base film using a micro-gravure coating machine, with the wet coating thickness controlled at 15μm. The coated film was then dried in an eight-section oven with stepped temperature increases. The temperatures of each section were set to 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, and 200℃, with a dwell time of 15 seconds per section and a total drying time of 2 minutes. Finally, the dried film was rolled up at 35℃ and cured at a constant temperature of 44℃ for 48 hours to obtain the final product.

[0042] Example 3

[0043] The specific implementation method is the same as in Example 1, except that: firstly, a hyperbranched polymer containing a phosphazene thiazoline structure is prepared; under nitrogen protection, 52g of hexachlorocyclotriphosphazene and 320mL of tetrahydrofuran are added to a 2000mL three-necked flask, a mechanical stirrer and a reflux condenser are installed, and the mixture is stirred at 350rpm to dissolve. The temperature is then raised to 54°C in an oil bath and maintained at a constant temperature. A mixed solution of 47g of 4-hydroxybenzaldehyde and 21g of triethylamine is slowly added dropwise using a constant pressure dropping funnel, controlling the dropping rate to ensure that the reaction temperature fluctuation does not exceed ±1°C. The dropping process lasts for 2.5 hours. After the dropping is completed, the reaction system is heated to 66°C and maintained at this temperature for 14 hours. The reaction progress is monitored by thin-layer chromatography during the reaction. After the reaction, the generated triethylamine hydrochloride is removed by vacuum filtration using a Buchner funnel. The filtrate is then evaporated in a rotary evaporator at a water bath temperature of 65°C. The aldehyde-modified phosphazene intermediate was obtained by concentrating the solution to one-quarter of its original volume at a certain temperature. This intermediate was then completely dissolved in 180 mL of N,N-dimethylformamide and transferred to a 500 mL three-necked flask. 32 g of 2-amino-2-thiazoline and 1.7 g of p-toluenesulfonic acid were added. Nitrogen gas was purged through the reaction system three times to replace the air. The reaction temperature was raised to 94 °C and maintained under reflux for 20 hours under a nitrogen atmosphere. Samples were taken every 5 hours during the reaction for Fourier transform infrared spectroscopy analysis to monitor changes in the characteristic peaks of the thiazoline. After the reaction was completed, the reaction mixture was poured hot into 1000 mL of diethyl ether pre-cooled to 0 °C to precipitate the product. After standing and aging for 3 hours, the solid product was collected by filtration and purified by recrystallization three times with a 1:1 volume ratio of methanol-water solution. Finally, the product was continuously dried in a vacuum drying oven at 60 °C for 24 hours to obtain a pale yellow solid product. Next, a graphene cage-like silsesquioxane hybrid material was prepared. 16g of graphene oxide was dispersed in 600mL of N-methylpyrrolidone and ultrasonically treated with 850W power for 3 hours in an ultrasonic cell disruptor to fully exfoliate the graphene oxide. Separately, 42g of octaaminophenyl POSS was dissolved in 200mL of N-methylpyrrolidone to form a clear solution. The POSS solution was slowly added to the graphene oxide dispersion under mechanical stirring and mixed at 550rpm for 1 hour to ensure full pre-dispersion. Then, 11g of triethylamine was added as a catalyst, and the reaction apparatus was transferred to a nitrogen protective atmosphere and reacted at 96℃ in an oil bath for 38 hours. After the reaction, the mixture was transferred to a high-speed centrifuge and centrifuged at 12000rpm for 20 minutes to collect the solid product. The solid product was washed three times alternately with N-methylpyrrolidone and ethanol to remove unreacted substances. Finally, the mixture was dried in a vacuum drying oven at 70℃ for 48 hours to obtain a gray-black powdery hybrid material.Finally, a PET release film was prepared. A 38 μm thick biaxially oriented PET film was subjected to corona treatment with the following parameters: power 5 kW, processing speed 21 m / min, and electrode spacing 2.5 mm, to achieve a film surface tension of over 50 dyne / cm. 20 g of the hyperbranched polymer containing a phosphazene thiazoline structure was dissolved in a mixed solvent of 12 g of butanone and 5 g of toluene. The solution was stirred at 450 rpm for 40 minutes to ensure complete dissolution. Then, 4 g of graphene cage-type silsesquioxane hybrid material was added, and the mixture was ultrasonically dispersed at 40 kHz for 1 hour. Subsequently, 2,2 7g of '-dithiodibenzoic acid and 0.15g of p-toluenesulfonic acid were stirred for 3 hours at room temperature (25℃) to form a uniform coating solution. The coating solution was then applied to the corona-treated PET base film using a micro-gravure coating machine, with the wet coating thickness controlled at 15μm. The coated film was then dried in an eight-section oven with stepped temperature increases. The temperatures of each section were set to 60℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, and 200℃, with a dwell time of 15 seconds per section and a total drying time of 2 minutes. Finally, the dried film was rolled up at 35℃ and cured at a constant temperature of 46℃ for 50 hours to obtain the final product.

[0044] Comparative Example 1

[0045] The specific implementation method is the same as in Example 1, except that no hyperbranched polymer containing phosphazene thiazoline structure and graphene cage-type silsesquioxane hybrid material are added in the preparation of the PET release film.

[0046] Comparative Example 2

[0047] The specific implementation method is the same as in Example 1, except that only hyperbranched polymers containing phosphazene thiazoline structures are added in the preparation of PET release film, and no graphene cage-type silsesquioxane hybrid materials are added.

[0048] Comparative Example 3

[0049] The specific implementation method is the same as in Example 1, except that only graphene cage-type silsesquioxane hybrid material is added in the preparation of PET release film, and no hyperbranched polymer containing phosphazene thiazoline structure is added.

[0050] Performance testing

[0051] Release force test: Performed according to GB / T42921-2023 "Method for Determining the Adhesion of Protective Films of Polyethylene Terephthalate (PET) for Optical Functional Films". After bonding the release film to a standard pressure-sensitive tape (or a pressure-sensitive adhesive layer for a specific polarizing film) under a specific pressure, a 180° peel test is conducted using an electronic tensile testing machine at a peel speed of (300±5) mm / min. The effective peel distance is 150 mm, and the results are reported as N / 25 mm or gf / in. Heat resistance temperature test: Referencing the principle of GB / T1735-2023 "Method for Determining the Heat Resistance of Coating Films". The sample is placed in a precision thermal aging test chamber and heated at a rate of 3°C per minute. Continuous monitoring is conducted through an observation window or internal camera system, recording the temperature points at which obvious discoloration, blistering, wrinkling, or significant attenuation of release force (e.g., attenuation exceeding 10%) occurs on the sample surface. Limiting Oxygen Index Test: According to GB / T2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". The cut sample is vertically fixed in a combustion chamber, and a precisely controlled oxygen-nitrogen mixture is introduced. The minimum oxygen concentration percentage required for the sample to maintain flaming combustion in a vertical state is measured. Tensile Strength Test: According to GB / T1040.3-2022 "Determination of Tensile Properties of Plastics - Part 3: Test Conditions for Films and Sheets". A dumbbell-shaped (usually type 5B) sample with a gauge length of 25 mm or 50 mm is used. Tension is applied at a speed of (50±5) mm / min on a universal testing machine until fracture. The maximum load is recorded, and the tensile strength is calculated. Light Transmittance and Haze Test: According to GB / T2410-2023 "Determination of Light Transmittance and Haze of Transparent Plastics". Using an integrating sphere haze meter equipped with a C or D65 light source, measure the total transmittance (Tt) and scattered light transmittance (Td) of the sample in the visible light band (typically 380-780nm). The haze value (H) is calculated using the formula H=(Td / Tt)×100%. Heat shrinkage rate test: Refer to GB / T13519-2023 "Polyethylene Heat Shrinkable Film for Packaging". After marking a baseline of a certain length on the sample, place it flat in a forced-air drying oven at (150±2)℃ for (30±1) minutes. After cooling to room temperature, measure the change in the baseline length and calculate the heat shrinkage rate. Coating adhesion (optional): Refer to GB / T33049-2016 "Determination of Adhesion of Optical Film Coatings for Polarizing Films" for a cross-cut test to evaluate the bonding strength between the coating and the PET base film. Scratch resistance (optional): Refer to GB / T34261-2017 "Test method for scratch resistance of optical films for polarizers" and use a pencil of specific hardness or a scratch tester to evaluate the mechanical scratch resistance of the film surface.

[0052] Performance test results:

[0053] Table 1: Performance test results of each embodiment and comparative example

[0054] Test item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Release force (gf / in) 9.8 10.5 9.2 15.3 11.2 13.8 Heat resistance temperature (°C) 185 178 192 98 165 142 Limiting oxygen index (%) 32.5 30.2 34.8 19.5 28.3 25.6 Tensile strength (MPa) 238 225 245 135 195 168 Transmittance (%) 93.5 94.1 92.8 86.2 90.5 88.7 Haze (%) 1.8 1.5 2.2 6.8 3.2 4.5 Heat shrinkage (150°C, 30 min, %) 1.0 1.3 0.8 3.5 2.1 2.8

[0055] As can be seen from Table 1, Examples 1 to 3, compared to Comparative Examples 1 to 3, fully demonstrate that the present invention successfully solves the key technical problems existing in the current PET release film by introducing a hyperbranched polymer containing a phosphazene-thiazoline structure and a graphene-cage-type silsesquioxane hybrid material. Specifically, Comparative Example 1 uses a traditional material system, with a heat resistance temperature of only 98°C, a limiting oxygen index of 19.5%, a tensile strength of 135 MPa, and a release force as high as 15.3 gf / in. It also has low light transmittance and high haze, clearly demonstrating the comprehensive deficiencies of traditional products in terms of heat resistance, flame retardancy, mechanical strength, and optical performance. Examples 1 to 3, through the synergistic effect of two innovative compounds, significantly increased the heat resistance temperature to the range of 178°C to 192°C. This is mainly attributed to the thermally stable network jointly constructed by the rigid framework of the phosphazene ring and the POSS cage structure. The limiting oxygen index reached 30.2% to 34.8%, significantly better than the 19.5% of Comparative Example 1, demonstrating the highly efficient flame-retardant synergistic effect of phosphorus-nitrogen elements and silicon elements. The tensile strength increased to 225 MPa to 245 MPa, far exceeding the 135 MPa of Comparative Example 1, proving that the three-dimensional network of the hyperbranched polymer and the nano-reinforcement effect of the hybrid material effectively enhanced the mechanical properties of the material. In addition, the release force of the examples remained stable in the ideal range of 9.2 gf / in to 10.5 gf / in, and the light transmittance exceeded 92% and the haze was less than 2.2%, indicating that the novel compounds improved the interfacial compatibility between the coating and the base film, achieving uniform film formation. Comparative Examples 2 and 3 each used only one modified compound. While their performance was superior to Comparative Example 1, it was significantly lower than either example. For instance, the heat resistance temperature of Comparative Example 2, lacking the hybrid material, was only 165°C, and the limiting oxygen index of Comparative Example 3, lacking the hyperbranched polymer, was only 25.6%. This definitively proves the indispensability of both compounds and their core value of synergistic effect. In summary, this invention, through molecular structure innovation and composite system design, fundamentally breaks through the technical bottleneck of traditional PET release films.

[0056] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a PET release film, characterized in that the steps include... include: S1. The biaxially oriented PET film is subjected to corona treatment; the corona treatment conditions are: power of 4-6kW, processing speed of 20-22m / min, and electrode spacing of 2-3mm. S2. Dissolve the hyperbranched polymer containing the phosphazene-thiazoline structure in a mixed solvent of butanone and toluene and stir mechanically; then add the graphene-cage-type silsesquioxane hybrid material and disperse it ultrasonically; subsequently add 2,2'-dithiodibenzoic acid and p-toluenesulfonic acid and continue stirring at room temperature to form a coating solution. S3. Using a micro-gravure coating method, the coating solution is applied to the corona-treated PET base film. The coated film is then dried in an eight-section oven with stepped temperature increases: section 1: 60℃, section 2: 80℃, section 3: 100℃, section 4: 120℃, section 5: 140℃, section 6: 160℃, section 7: 180℃, and section 8: 200℃. Finally, the dried film is wound up at 34-36℃ and cured in an environment of 44-46℃.

2. The method for preparing the PET release film according to claim 1, characterized in that, In step S2, the stirring time at room temperature is 2-4 hours; the mass ratio of the hyperbranched polymer containing the phosphazene-thiazoline structure to the graphene-cage-silsesquioxane hybrid material is (5-10):1; the mass ratio of the hyperbranched polymer containing the phosphazene-thiazoline structure to 2,2'-dithiobenzoic acid is (3-4):1; and the mass of p-toluenesulfonic acid is 1-3% of the mass of 2,2'-dithiobenzoic acid.

3. The method for preparing the PET release film according to claim 1, characterized in that, In step S3, the curing time is 48-50 hours in an environment of 44-46℃.

4. The method for preparing the PET release film according to claim 1, characterized in that, The preparation method of the hyperbranched polymer containing the phosphazene-thiazoline structure includes: A1. Under nitrogen protection, hexachlorocyclotriphosphazene and tetrahydrofuran are added to a three-necked flask, stirred and dissolved, and a mixed solution of 4-hydroxybenzaldehyde and triethylamine is added dropwise at 50-55℃. After the addition is complete, the temperature is raised to 64-66℃ for reaction. After the reaction is completed, the mixture is filtered and rotary evaporated to obtain the aldehyde-modified phosphazene intermediate; A2. Subsequently, the aldehyde-modified phosphazene intermediate is redissolved in N,N-dimethylformamide, and 2-amino-2-thiazoline and p-toluenesulfonic acid are added. The mixture is reacted at 90-95℃ under a nitrogen atmosphere. After the reaction is completed, the reaction mixture is poured into cold diethyl ether to precipitate, filtered, recrystallized with a methanol / water mixed solvent, and dried in a vacuum drying oven at 58-62℃.

5. The method for preparing the PET release film according to claim 4, characterized in that, In step A1, the temperature is raised to 64-66℃ and the reaction time is 12-14 hours.

6. The method for preparing the PET release film according to claim 4, characterized in that, In step A2, the reaction time at 90-95℃ is 18-20 hours; the drying time in the vacuum drying oven is 24-30 hours.

7. The method for preparing the PET release film according to claim 1, characterized in that, The preparation method of the graphene-cage-type silsesquioxane hybrid material includes: dispersing graphene oxide in N-methylpyrrolidone and ultrasonically treating it to obtain a graphene oxide dispersion; dissolving octaaminophenyl POSS in N-methylpyrrolidone and adding it to the graphene oxide dispersion, and mechanically stirring and mixing; subsequently, adding triethylamine and reacting at 94-96℃ under nitrogen protection; after the reaction is completed, centrifuging the mixture, collecting the solid product, and washing it alternately with N-methylpyrrolidone and ethanol; finally, drying it in a vacuum drying oven at 68-72℃.

8. The method for preparing the PET release film according to claim 7, characterized in that, The reaction time is 36-40 hours at 94-96℃.

9. A PET release film, characterized in that, The PET release film is prepared by the method of any one of claims 1-8.

10. An application of the PET release film according to claim 9 in the field of polarizers.