High-temperature-resistant PI / PET composite release film with gradient structure and preparation method of high-temperature-resistant PI / PET composite release film

Abstract

The invention provides a high-temperature-resistant PI / PET composite release film with a gradient structure and a preparation method thereof.The composite release film is composed of a PET base material and a PI composite reinforcing layer, the PI composite reinforcing layer is prepared through electrostatic spinning, and the porosity and the aperture of an electrostatic spinning layer in the PI composite reinforcing layer are gradually increased in the thickness direction of the release film. The PI composite enhancement layer in the release film has an efficient heat-conducting gradient structure, so that the temperature resistance of the PET release film is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of release films, and particularly to a high-temperature resistant PI / PET composite release film with a gradient structure and a preparation method thereof. Background Art

[0002] With the rapid development of high-tech fields such as the electronics industry, aerospace, and new energy, the demand for high-performance materials is increasing day by day. Among them, high-temperature resistant release films, as a key functional material, play an important role in processes such as flexible circuit board lamination, electronic packaging demolding, and high-temperature lamination. Polyethylene terephthalate (PET) has become one of the main base materials for release films due to its excellent mechanical properties, transparency, recyclability, and relatively high temperature resistance. However, the performance of traditional PET release films still has many limitations in high-temperature environments and is difficult to meet the increasingly stringent industrial requirements. Currently, the PET release films on the market usually use silicone oil as a release agent, and its temperature resistance is limited. Generally, it can only withstand high temperatures of 180 - 200°C for a short time. When exposed to high-temperature environments for a long time, it is prone to embrittlement, edge retraction and curling, or even atomization, seriously affecting its service life and application range. In addition, silicone oil release agents are prone to migration at high temperatures, which may lead to short circuits or poor processing of electronic components. This problem is particularly prominent in high-end electronic manufacturing fields that are sensitive to silicon elements. To improve the high-temperature resistance of PET release films, researchers have tried to optimize their performance through various modification methods. For example, by adding inorganic fillers (such as nano-silica, diatomite, etc.) or introducing high-temperature resistant additives (such as organic high-temperature resistant additive SL-11), the thermal stability and high-temperature resistance limit of PET release films can be significantly improved, enabling them to withstand high temperatures of 200°C for 2 hours or 180°C for 8 - 10 hours. In addition, the company uses polyimide (PI) or silica (SiO2) to composite-modify PET in patent CN 119287676A, which can further improve its high-temperature resistance and enable it to maintain stable physical and chemical properties in extreme environments. However, the process flow is complex and it is difficult to prepare SiO2 microspheres. Therefore, developing a PET release film with high temperature resistance, environmental protection, easy processability, and economy has become an important research direction in the field of materials science. Summary of the Invention

[0003] Technical Problem to be Solved: The purpose of the present invention is to develop a PET release film with high temperature resistance, environmental protection, easy processability, and economy. The PI composite reinforcement layer in this release film has a gradient structure with high heat conduction, which improves the high-temperature resistance of the PET release film.

[0004] Technical solution: A high-temperature resistant PI / PET composite release film with a gradient structure, the composite release film is composed of a PET substrate and a PI composite reinforcing layer, the PI composite reinforcing layer is prepared by electrospinning, and the porosity and pore size of the electrospinning layer in the PI composite reinforcing layer gradually increase along the thickness direction of the release film. Preferably, the PI composite reinforcing layer further includes a micro-nano particle layer loaded on the surface of the electrospinning layer. Preferably, the preparation method of the PI composite reinforcing layer includes the following steps: S11. Dissolve ODA in DMAc solvent, after stirring and dissolving, add PMDA in portions, and stir to make the ODA and PMDA monomers fully react to obtain a PAA precursor solution; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters to obtain a PAA nanofiber membrane with a gradient change; S13. Perform thermal imidization treatment on the PAA nanofiber membrane to obtain a PI composite reinforcing layer. Preferably, the concentration of the PAA precursor solution in step S11 is 14-18 wt%; and / or, The spinning parameters in step S12 are: the initial spinning voltage is 18-20 kV, the feeding speed is 1.5-2.0 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h; The middle spinning voltage is 14-16 kV, the feeding speed is 1.2-1.6 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h; The final spinning voltage is 10-12 kV, the feeding speed is 1.0-1.5 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h; and / or, The parameters of the thermal imidization treatment in step S13 are: gradient heating at a heating rate of 2-4 °C / min, and perform thermal imidization treatment according to the program of 150-160 °C / 1 h + 180-210 °C / 1 h + 280-300 °C / 1 h. Preferably, the preparation method of the PI composite reinforcing layer further includes the following steps: S21. Heat and dissolve PET in DMF to obtain a dilute PET solution; S22. Add porous ceramic powder to the dilute PET solution to obtain an electrospray solution; S23. Use the PI composite reinforcing layer as the receiving surface and perform electrospray to obtain a PI composite reinforcing layer with a micro-nano particle layer loaded on the surface. Preferably, the concentration of the PET dilute solution is 1-3 wt%; and / or, The porous ceramic powder is any one of SiO2, Al2O3 or TiO2, and the mass ratio of the porous ceramic powder to the PET dilute solution is 3-6:100; and / or, the voltage of the electrospray is 15-20 kV, the receiving distance is 15 cm, the feeding speed is 0.6-1 mL / h, the rotational speed of the receiving roller is 300-400 r / min, and the spinning time is 0.5-1 h. The preparation method of the above-mentioned high-temperature resistant PI / PET composite release film with a gradient structure comprises the following steps: S1. Heat and dissolve PET in DMF to obtain a PET solution; S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure. Preferably, the concentration of the PET solution is 10-15 wt%. Beneficial effects: The composite release film of the present invention has the following advantages: 1. Compared with CN 119287676 A, the technical solution of the present invention is simpler and easier to obtain. Only by controlling the parameters of electrospinning, a PI composite reinforcing layer with a gradient distribution can be prepared, and by controlling the pore size and porosity in the PI composite reinforcing layer, the effect of improving the high-temperature resistance of the PET release film can be achieved; 2. In the release film of the present invention, the PI composite reinforcing layer forms a functional gradient pore structure from the functional surface to the non-functional surface, and the porosity gradient is: functional layer dense (low porosity) → intermediate transition layer → non-functional layer loose (high porosity), and the pore size gradient is: functional layer small pore size → non-functional layer large pore size (micrometer level). By matching the gradient change with the temperature change requirement, local stress concentration is reduced, and the overall performance is improved; at the same time, stress is generated due to thermal expansion of PET, and the gradient pores absorb / disperse the stress step by step, reducing the overall shrinkage deformation; 3. The surface of the functional layer of the release film of the present invention can also be loaded with porous micro-nano thermal conductive ceramic powder. The porous ceramic powder has a high specific surface area and porosity, and can provide stress buffering and heat diffusion channels. Specific embodiments The present invention will be further described below in conjunction with embodiments. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments: Example 1 The preparation method of the high-temperature resistant PI / PET composite release film with a gradient structure comprises the following steps: S1. Heat and dissolve PET in DMF to obtain a PET solution with a concentration of 10 wt%; S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcing layer includes the following steps: S11. Dissolve ODA in the DMAc solvent, stir to dissolve, add PMDA in portions, and after stirring to make the ODA and PMDA monomers fully react, obtain a PAA precursor solution with a concentration of 14 wt%; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters. The spinning parameters are: the initial spinning voltage is 18 kV, the feeding speed is 1.5 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 1 h; the intermediate spinning voltage is 14 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 0.5 h; the final spinning voltage is 10 kV, the feeding speed is 1.0 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 0.5 h; obtain a PAA nanofiber membrane with a gradient change; S13. Perform thermal imidization treatment on the PAA nanofiber membrane, gradually heat up at a heating rate of 2 °C / min, and perform thermal imidization treatment according to the program of 160 °C / 1 h + 210 °C / 1 h + 300 °C / 1 h to obtain the PI composite reinforcing layer. Example 2 A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a PET solution with a concentration of 15 wt%; S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcing layer includes the following steps: S11. Dissolve ODA in the DMAc solvent, stir to dissolve, add PMDA in portions, and after stirring to make the ODA and PMDA monomers fully react, obtain a PAA precursor solution with a concentration of 18 wt%; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters. The spinning parameters are as follows: the initial spinning voltage is 20 kV, the feeding speed is 2.0 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 0.5 h; the intermediate spinning voltage is 16 kV, the feeding speed is 1.2 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 1 h; the final spinning voltage is 12 kV, the feeding speed is 1.5 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 1 h; to obtain a PAA nanofiber membrane with gradient changes; S13. Perform thermal imidization treatment on the PAA nanofiber membrane, with a heating rate of 4 °C / min for gradient heating, and perform thermal imidization treatment according to the program of 150 °C / 1 h + 180 °C / 1 h + 280 °C / 1 h to obtain a PI composite reinforcement layer. Example 3 A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure, comprising the following steps: S1. Heat and dissolve PET in DMF to obtain a 12 wt% PET solution; S2. Immerse the PI composite reinforcement layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcement layer includes the following steps: S11. Dissolve ODA in DMAc solvent, after stirring and dissolving, add PMDA in portions, and stir to make the ODA and PMDA monomers fully react to obtain a 16 wt% PAA precursor solution; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters. The spinning parameters are as follows: the initial spinning voltage is 18 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; the intermediate spinning voltage is 15 kV, the feeding speed is 1.4 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; the final spinning voltage is 10 kV, the feeding speed is 1.2 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; to obtain a PAA nanofiber membrane with gradient changes; S13. Thermally imidize the PAA nanofiber membrane, with a temperature increase rate of 3 °C / min for gradient temperature increase, and conduct thermal imidization treatment according to the program of 155 °C / 1 h + 190 °C / 1 h + 290 °C / 1 h to obtain a PI composite reinforcement layer. Use a differential scanning calorimeter (DSC) of a comprehensive thermal analyzer to test the glass transition temperature T g (°C) and the initial decomposition temperature T s (°C) of the double-sided high-temperature release film; Test according to the method of the release film for optical functional films in GB / T 25256-2010, with a peeling rate of 300 mm / min. Table 1 shows the performance indicators of the release films in Examples 1-3 Example 1 Example 2 Example 3 <![CDATA[T g / ℃]]> 98.2 97.6 97.5 <![CDATA[T s / ℃]]> 433.6 431.9 432.2 <![CDATA[Peeling force at room temperature / cN·(25mm) -1 > 2.5 2.6 2.4 <![CDATA[Peeling force / cN·(25 mm) after 12 h at 100℃ -1 > 3.2 3.3 3.2 Residual adhesion force / % after 12 h at 100 °C 85.5 86.3 88.1 Example 4 A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a 10 wt% PET solution; S2. Immerse the PI composite reinforcement layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcement layer includes the following steps: S11. Dissolve ODA in a DMAc solvent, and after stirring and dissolving, add PMDA in portions. After stirring to make the ODA and PMDA monomers fully react, obtain a 14 wt% PAA precursor solution; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and conduct electrospinning with different spinning parameters. The spinning parameters are: the initial spinning voltage is 18 kV, the feeding speed is 1.5 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 0.5 h; the intermediate spinning voltage is 14 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 0.5 h; the final spinning voltage is 10 kV, the feeding speed is 1.0 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 0.5 h; obtain a PAA nanofiber membrane with gradient changes; S13. Thermally imidize the PAA nanofiber membrane, with a temperature increase rate of 2 °C / min for gradient temperature increase, and conduct thermal imidization treatment according to the program of 160 °C / 1 h + 210 °C / 1 h + 300 °C / 1 h to obtain a PI composite reinforcement layer; S14. Heat and dissolve PET in DMF to obtain a 1 wt% PET dilute solution; S15. Add micro-nano porous SiO2 to the dilute PET solution. The mass ratio of micro-nano porous SiO2 to the dilute PET solution is 3:100. Stir evenly to obtain an electrospray solution. S16. Using the side with the smallest pore size and porosity of the PI composite reinforcement layer as the receiving surface, perform electrospraying. The electrospraying voltage is 20 kV, the receiving distance is 15 cm, the feeding speed is 0.6 mL / h, the receiving roller rotation speed is 400 r / min, and the spinning time is 1 h to obtain a PI composite reinforcement layer with a surface-loaded micro-nano particle layer. Example 5 A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a 15 wt% PET solution. S2. Immerse the PI composite reinforcement layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure. Among them, the preparation method of the PI composite reinforcement layer includes the following steps: S11. Dissolve ODA in the DMAc solvent, stir to dissolve, and add PMDA in portions. After stirring to make the ODA and PMDA monomers fully react, obtain a 18 wt% PAA precursor solution. S12. Use the PAA precursor solution prepared in step S1 as the spinning solution and perform electrospinning with different spinning parameters. The spinning parameters are: the initial spinning voltage is 20 kV, the feeding speed is 2.0 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 0.5 h; the middle spinning voltage is 16 kV, the feeding speed is 1.2 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 1 h; the final spinning voltage is 12 kV, the feeding speed is 1.5 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 1 h; to obtain a PAA nanofiber membrane with a gradient change. S13. Perform thermal imidization treatment on the PAA nanofiber membrane, with a temperature increase rate of 4 °C / min for gradient temperature increase, and perform thermal imidization treatment according to the program of 150 °C / 1 h + 180 °C / 1 h + 280 °C / 1 h to obtain a PI composite reinforcement layer. S14. Heat and dissolve PET in DMF to obtain a 3 wt% dilute PET solution. S15. Add micro-nano porous SiO2 to the dilute PET solution. The mass ratio of micro-nano porous SiO2 to the dilute PET solution is 6:100. Stir evenly to obtain an electrospray solution. S16. Using the side with the smallest pore size and porosity of the PI composite reinforcing layer as the receiving surface, electrospray is carried out. The voltage of electrospray is 15 kV, the receiving distance is 15 cm, the feeding speed is 1 mL / h, the rotational speed of the receiving roller is 300 r / min, and the spinning time is 1 h, to obtain a PI composite reinforcing layer with a surface-loaded micro-nano particle layer. Example 6 A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure, comprising the following steps: S1. Heating and dissolving PET in DMF to obtain a PET solution with a concentration of 12 wt%; S2. Immersing the PI composite reinforcing layer into the PET solution, scraping off the excess solution on the surface, and after drying, obtaining a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcing layer comprises the following steps: S11. Dissolving ODA in DMAc solvent, after stirring and dissolving, adding PMDA in portions, and stirring to make the ODA and PMDA monomers fully react, to obtain a PAA precursor solution with a concentration of 16 wt%; S12. Using the PAA precursor solution prepared in step S1 as the spinning solution, electrospinning is carried out with different spinning parameters. The spinning parameters are: the initial spinning voltage is 18 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 15 cm, the rotational speed of the receiving roller is 350 r / min, and the spinning time is 0.6 h; the middle spinning voltage is 15 kV, the feeding speed is 1.4 mL / h, the spinning receiving distance is 18 cm, the rotational speed of the receiving roller is 350 r / min, and the spinning time is 0.6 h; the final spinning voltage is 10 kV, the feeding speed is 1.2 mL / h, the spinning receiving distance is 20 cm, the rotational speed of the receiving roller is 350 r / min, and the spinning time is 0.6 h; to obtain a PAA nanofiber membrane with a gradient change; S13. Performing thermal imidization treatment on the PAA nanofiber membrane, gradually heating up at a heating rate of 3 °C / min, and performing thermal imidization treatment according to the program of 155 °C / 1 h + 190 °C / 1 h + 290 °C / 1 h, to obtain a PI composite reinforcing layer; S14. Heating and dissolving PET in DMF to obtain a dilute PET solution with a concentration of 2 wt%; S15. Adding micro-nano porous SiO2 to the dilute PET solution, and the mass ratio of micro-nano porous SiO2 to the dilute PET solution is 5:100, and stirring evenly to obtain an electrospray solution; S16. Using the side with the smallest pore size and porosity of the PI composite reinforcing layer as the receiving surface, electrospray is carried out with an electrospray voltage of 18 kV, a receiving distance of 15 cm, a feeding speed of 0.8 mL / h, a receiving roller rotation speed of 350 r / min, and a spinning time of 0.6 h to obtain a PI composite reinforcing layer with a surface-loaded micro-nano particle layer. Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that the PI composite reinforcing layer does not adopt a PI composite reinforcing layer with a gradient change; A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a 12 wt% PET solution; S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcing layer includes the following steps: S11. Dissolve ODA in DMAc solvent, and after stirring and dissolving, add PMDA in portions. After stirring to make the ODA and PMDA monomers fully react, obtain a 16 wt% PAA precursor solution; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and carry out electrospinning. The spinning parameters are: spinning voltage is 15 kV, feeding speed is 1.4 mL / h, spinning receiving distance is 18 cm, receiving roller rotation speed is 350 r / min, and spinning time is 2 h to obtain a PAA nanofiber membrane; S13. Carry out thermal imidization treatment on the PAA nanofiber membrane, with a temperature increase rate of 3 °C / min for gradient temperature increase, and carry out thermal imidization treatment according to the program of 155 °C / 1 h + 190 °C / 1 h + 290 °C / 1 h to obtain a PI composite reinforcing layer. Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that the PI composite reinforcing layer adopts a PI composite reinforcing layer with a gradient change, and the functional surface of the release film is the side with the largest porosity and the largest pore size in the PI composite reinforcing layer. Comparative Example 3 The difference between Comparative Example 3 and Example 3 is the difference in the spinning process parameters of the PAA nanofiber membrane in step S12; A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a 12 wt% PET solution; S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcing layer includes the following steps: S11. Dissolve ODA in the DMAc solvent, stir to dissolve it, and then add PMDA in portions. After stirring to make the ODA and PMDA monomers fully react, obtain a PAA precursor solution with a concentration of 16 wt%; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters. The spinning parameters are: the initial spinning voltage is 18 kV, the feeding speed is 2.5 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 200 r / min, and the spinning time is 0.6 h; the intermediate spinning voltage is 15 kV, the feeding speed is 1.8 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 200 r / min, and the spinning time is 0.6 h; the final spinning voltage is 10 kV, the feeding speed is 1.8 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 200 r / min, and the spinning time is 0.6 h; obtain a PAA nanofiber membrane; S13. Perform thermal imidization treatment on the PAA nanofiber membrane, increase the temperature gradient at a rate of 3 °C / min, and perform thermal imidization treatment according to the program of 155 °C / 1 h + 190 °C / 1 h + 290 °C / 1 h to obtain the PI composite reinforcing layer. Comparative Example 4 The difference between Comparative Example 4 and Example 3 lies in: the difference in the spinning process parameters of the PAA nanofiber membrane in step S12; A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a PET solution with a concentration of 12 wt%; S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcing layer includes the following steps: S11. Dissolve ODA in the DMAc solvent, stir to dissolve it, and then add PMDA in portions. After stirring to make the ODA and PMDA monomers fully react, obtain a PAA precursor solution with a concentration of 16 wt%; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters. The spinning parameters are as follows: the initial spinning voltage is 18 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; the intermediate spinning voltage is 15 kV, the feeding speed is 1.4 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 0.6 h; the final spinning voltage is 10 kV, the feeding speed is 1.2 mL / h, the spinning receiving distance is 15 m, the receiving roller rotation speed is 250 r / min, and the spinning time is 0.6 h; to obtain a PAA nanofiber membrane with a gradient change; S13. Perform thermal imidization treatment on the PAA nanofiber membrane, with a heating rate of 3 °C / min for gradient heating, and perform thermal imidization treatment according to the program of 155 °C / 1 h + 190 °C / 1 h + 290 °C / 1 h to obtain a PI composite reinforcement layer. Table 2 shows the porosity % of the PAA nanofiber membranes in Example 3 and Comparative Examples 1, 3 - 4 Table 3 shows the pore sizes of the PAA nanofiber membranes in Example 3 and Comparative Examples 1, 3 - 4 Comparative Example 5 The difference between Comparative Example 5 and Example 6 is that the SiO2 added in step S15 is solid particles; A method for preparing a high-temperature resistant PI / PET composite release film with a gradient structure, comprising the following steps: S1. Heat and dissolve PET in DMF to obtain a 10 wt% PET solution; S2. Immerse the PI composite reinforcement layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure; Among them, the preparation method of the PI composite reinforcement layer includes the following steps: S11. Dissolve ODA in DMAc solvent, after stirring and dissolving, add PMDA in portions, and stir to make the ODA and PMDA monomers fully react to obtain a 14 wt% PAA precursor solution; S12. Use the PAA precursor solution prepared in step S1 as the spinning solution and perform electrospinning with different spinning parameters. The spinning parameters are as follows: the initial spinning voltage is 18 kV, the feeding speed is 1.5 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 1 h; the intermediate spinning voltage is 14 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 400 r / min, and the spinning time is 0.5 h; the final spinning voltage is 10 kV, the feeding speed is 1.0 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 300 r / min, and the spinning time is 0.5 h; to obtain a PAA nanofiber membrane with gradient changes. S13. Perform thermal imidization treatment on the PAA nanofiber membrane, with a heating rate of 2 °C / min for gradient heating, and perform thermal imidization treatment according to the program of 160 °C / 1 h + 210 °C / 1 h + 300 °C / 1 h to obtain a PI composite reinforcement layer. S14. Heat and dissolve PET in DMF to obtain a 1 wt% PET dilute solution. S15. Add micro-nano solid SiO2 to the PET dilute solution, and the mass ratio of micro-nano porous SiO2 to the PET dilute solution is 3:100, and stir evenly to obtain an electrospray solution. S16. Using the side with the smallest pore size and porosity of the PI composite reinforcement layer as the receiving surface, perform electrospraying. The voltage of the electrospraying is 20 kV, the receiving distance is 15 cm, the feeding speed is 0.6 mL / h, the receiving roller rotation speed is 400 r / min, and the spinning time is 1 h to obtain a PI composite reinforcement layer with a micro-nano particle layer loaded on the surface. Comparative Example 6 The difference between Comparative Example 6 and Example 6 is that in step S16, the side with the largest pore size and porosity of the PI composite reinforcement layer is used as the receiving surface. A preparation method of a high-temperature resistant PI / PET composite release film with a gradient structure includes the following steps: S1. Heat and dissolve PET in DMF to obtain a 12 wt% PET solution. S2. Immerse the PI composite reinforcement layer in the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure. Among them, the preparation method of the PI composite reinforcement layer includes the following steps: S11. Dissolve ODA in the DMAc solvent, and after stirring and dissolving, add PMDA in portions, and stir to make the ODA and PMDA monomers fully react to obtain a 16 wt% PAA precursor solution. S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters. The spinning parameters are as follows: the initial spinning voltage is 18 kV, the feeding speed is 1.6 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; the intermediate spinning voltage is 15 kV, the feeding speed is 1.4 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; the final spinning voltage is 10 kV, the feeding speed is 1.2 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h; to obtain a PAA nanofiber membrane with gradient changes; S13. Perform thermal imidization treatment on the PAA nanofiber membrane, with a heating rate of 3 °C / min for gradient heating, and perform thermal imidization treatment according to the program of 155 °C / 1 h + 190 °C / 1 h + 290 °C / 1 h to obtain a PI composite reinforcing layer; S14. Heat and dissolve PET in DMF to obtain a 2 wt% PET dilute solution; S15. Add micro-nano porous SiO2 to the PET dilute solution, and the mass ratio of micro-nano porous SiO2 to the PET dilute solution is 5:100, and stir evenly to obtain an electrospray solution; S16. Using the side with the largest pore size and porosity of the PI composite reinforcing layer as the receiving surface, perform electrospraying. The electrospraying voltage is 18 kV, the receiving distance is 15 cm, the feeding speed is 0.8 mL / h, the receiving roller rotation speed is 350 r / min, and the spinning time is 0.6 h to obtain a PI composite reinforcing layer with a micro-nano particle layer loaded on the surface. Table 4 shows the performance indicators of the release films in Examples 4-6 and Comparative Examples 1-6 Tested by the method for release films of optical functional films in GB / T 25256-2010, the peeling rate is 300 mm / min. The above has introduced the method provided by the present invention in detail. Specific examples are used in this article to elaborate on the structure and working principle of the present invention. The description of the above embodiments is only used to help understand the method and core idea of the present invention. The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Moreover, the above embodiments are only examples given for clear illustration and are not limitations on the implementation manners. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-temperature resistant PI / PET composite release film with a gradient structure, characterized in that: The composite release film is composed of a PET substrate and a PI composite reinforcement layer. The PI composite reinforcement layer is prepared by electrospinning, and the porosity and pore size of the electrospun layer in the PI composite reinforcement layer gradually increase along the thickness direction of the release film.

2. The high-temperature resistant PI / PET composite release film with a gradient structure according to claim 1, wherein: The PI composite reinforcement layer further includes a micro-nano particle layer loaded on the surface of the electrospun layer.

3. The high-temperature resistant PI / PET composite release film with a gradient structure according to claim 2, characterized in that: The preparation method of the PI composite reinforcement layer includes the following steps: S11. Dissolve ODA in DMAc solvent. After stirring and dissolving, add PMDA in portions. After stirring to make the ODA and PMDA monomers fully react, a PAA precursor solution is obtained. S12. Use the PAA precursor solution prepared in step S1 as the spinning solution, and perform electrospinning with different spinning parameters to obtain a PAA nanofiber membrane with a gradient change. S13. Perform thermal imidization treatment on the PAA nanofiber membrane to obtain a PI composite reinforcement layer.

4. The high-temperature resistant PI / PET composite release film with a gradient structure according to claim 3, wherein: In step S11, the concentration of the PAA precursor solution is 14-18 wt%; and / or, In step S12, the spinning parameters are: the initial spinning voltage is 18-20 kV, the feeding speed is 1.5-2.0 mL / h, the spinning receiving distance is 15 cm, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h; The intermediate spinning voltage is 14-16 kV, the feeding speed is 1.2-1.6 mL / h, the spinning receiving distance is 18 cm, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h; The final spinning voltage is 10-12 kV, the feeding speed is 1.0-1.5 mL / h, the spinning receiving distance is 20 cm, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h; and / or, In step S13, the parameters of the thermal imidization treatment are: gradient heating at a heating rate of 2-4 °C / min, and performing thermal imidization treatment according to the program of 150-160 °C / 1 h + 180-210 °C / 1 h + 280-300 °C / 1 h.

5. The high-temperature resistant PI / PET composite release film with a gradient structure according to claim 3, wherein: The preparation method of the PI composite reinforcement layer further includes the following steps: S21. Heat and dissolve PET in DMF to obtain a dilute PET solution. S22. Add porous ceramic powder to the dilute PET solution to obtain an electrospray solution. S23. Use the PI composite reinforcement layer as the receiving surface and perform electrospray to obtain a PI composite reinforcement layer with a micro-nano particle layer loaded on the surface.

6. The high-temperature resistant PI / PET composite release film with a gradient structure according to claim 5, wherein: The concentration of the dilute PET solution is 1-3 wt%; and / or, The porous ceramic powder is any one of SiO2, Al2O3 or TiO2, and the mass ratio of the porous ceramic powder to the dilute PET solution is 3-6:100; and / or, The voltage of the electrospray is 15-20 kV, the receiving distance is 15 cm, the feeding speed is 0.6-1 mL / h, the receiving roller rotation speed is 300-400 r / min, and the spinning time is 0.5-1 h.

7. The preparation method of the high-temperature resistant PI / PET composite release film with a gradient structure according to claim 1, characterized in that Include the following steps: S1. Heat and dissolve PET in DMF to obtain a PET solution. S2. Immerse the PI composite reinforcing layer into the PET solution, scrape off the excess solution on the surface, and after drying, obtain a high-temperature resistant PI / PET composite release film with a gradient structure.

8. The preparation method of the high-temperature resistant PI / PET composite release film with a gradient structure according to claim 1, characterized in that: The concentration of the PET solution is 10-15 wt%.

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