High-transmittance, high-strength, radiation-resistant, foldable cover sheet and preparation method thereof

Abstract

The application belongs to the technical field of aerospace material preparation, and discloses a high-transparency, high-strength, radiation-resistant and foldable cover sheet and a preparation method thereof. The cover sheet is a polyimide sheet prepared by one-pot polymerization with 2,2'-bis(trifluoromethyl)diaminobiphenyl and 4,4'-(hexafluoroisopropyl)dititanium acid anhydride as synthetic monomers, N,N-dimethylacetic acid as a solvent, and acetyl citric acid tributyl ester as a modifier. The average transmittance of the cover sheet to visible light-near infrared light (400-1800 nm) is 91.16%, the tensile strength is 244.0 MPa, the elongation at break is 12.2%, and the cover sheet is foldable. After 500 hours of ultraviolet radiation, the average transmittance and the tensile strength attenuation rate of the cover sheet are only 0.066% and 1.967%, respectively. The cover sheet is particularly suitable for solar cells in the field of aerospace.

Description

Technical Field

[0001] This invention belongs to the field of aerospace material preparation technology, specifically relating to a high-transmittance, high-strength, radiation-resistant, foldable cover sheet and its preparation method. Background Technology

[0002] For aerospace and wearable electronic devices, "lightweight and flexible" have become important development directions for solar cells. Solar cells generally require high-transmittance, high-strength, and UV-resistant glass (transparent) covers for protection. Space solar cells, in addition to UV radiation, must also withstand cosmic ray radiation and atomic oxygen erosion, requiring even higher protective capabilities from the covers. Flexible cells naturally require flexible covers for protection. The emerging foldable batteries further demand foldable flexible covers. For rigid cells or arrays, the application of flexible covers can not only reduce weight and lower spacecraft launch costs but also avoid the fragility of rigid glass. Therefore, developing a high-transmittance, high-strength, radiation-resistant, and foldable cover is of paramount importance. Some organic polymers possess high transmittance, light weight, and good bending properties, but their mechanical properties and radiation resistance are insufficient to meet the requirements of solar cells in the aerospace field.

[0003] Polyimide (PI) possesses excellent dielectric, mechanical, and flame-retardant properties, a low coefficient of thermal expansion, and resistance to both low temperatures (-269℃) and high temperatures (500℃), making it suitable for fabricating films, sheets, coatings, and fibers. However, traditional PI tends to form low-transmittance electron-transfer complexes (CTCs), resulting in a pale yellow or brownish-yellow background color in PI films, significantly limiting its application in optoelectronics. Improving the transmittance of PI films typically requires introducing large-volume structural units into the PI backbone to suppress CTC formation, but molecular design complicates the synthesis process. Lowering the thermal imidization temperature can also improve transmittance. Currently, the two-step PI synthesis method requires inert gas protection and a thermal imidization temperature exceeding 300℃. While the one-step PI synthesis method can lower the imidization temperature, it often requires the addition of catalysts and dehydrating agents, the amounts of which are difficult to control accurately, leading to significant waste and negatively impacting PI performance. While some PI samples exhibit flexibility, their large bending radii make them difficult to fold. Furthermore, their optical properties, flexibility, and mechanical strength significantly decrease under ultraviolet light irradiation. Pure PI cannot simultaneously possess high light transmittance, high mechanical strength, radiation resistance, and foldability to meet the requirements of aerospace and wearable devices.

[0004] Patent CN 113387817 A discloses a fluorinated aromatic diamine compound, its preparation method, and a colorless and transparent PI film with high light transmittance, but its tensile strength is only 121-133 MPa, and its UV resistance is not mentioned. Patent 109280166 discloses a high-performance colorless and transparent polyimide film and its preparation method. The film is prepared using 2,7-bis(3-aminophenoxy)thienyl(APOT) diamine with a meta-substituted structure and aromatic dianhydride, achieving a light transmittance of ≥86% at 450 nm, but its flexibility is poor. Patent CN 114891212 A discloses a method for preparing a high-temperature resistant PI film. The prepared PI film exhibits both high heat resistance and high light transmittance (84%), but its high-temperature imidization process requires the addition of a specific imidization catalyst (e.g., a quinoline compound), and the imidization temperature is 400-500℃. The catalyst and high temperature result in significant raw material waste and a complex preparation process, thus limiting its widespread application. Patent CN 110467728 B discloses a transparent PI film and its preparation method and application. Although the film has high light transmittance, it requires the addition of equimolar amounts of acetic anhydride and isoquinoline with carboxylic acid groups as dehydrating agents and catalysts to a polyamic acid solution. This makes its industrialization less technically and economically viable, which is not conducive to its application and development.

[0005] Qian et al. prepared a composite PI transparent film, but its transmittance at 500 nm decreased by up to 37.54% after exposure to atomic oxygen, making it unsuitable for devices requiring high radiation resistance. (Qian M.: Adv. Mater. Technol., 2021, 6: 12; DOI: 10.1002 / admt.202100603). Li et al. treated mica with a coupling agent and then composited it with PI. The composite film achieved a tensile strength of 131.5 MPa, but its transmittance, flexibility, and radiation resistance were poor. (Li DX: Polym. Bull., 2021, 78: 863-883; DOI: 10.1007 / s00289-020-03143-1). Wang et al. prepared a PI / mesoporous SiO2 composite film with excellent mechanical properties and thermal stability, but its low light transmittance made it unsuitable for devices requiring high transmittance. (Wang C.: RSC Adv., 2017, 7: 26420-26427; DOI: 10.1039 / C7RA01568B).

[0006] In summary, there are few reports on products and their preparation methods that can be used as cover sheets for solar cells and possess high light transmittance, high strength, radiation resistance, and foldability.

[0007] This invention provides a high-transmittance, high-strength, radiation-resistant, foldable cover sheet and its preparation method. Compared with existing technologies or products, the product of this invention has stable physicochemical properties, and simultaneously possesses high light transmittance, high radiation resistance, high mechanical properties, and foldability. Furthermore, the preparation process is simple and highly technical and economical. Summary of the Invention

[0008] The purpose of this invention is to provide a high-transmittance, high-strength, radiation-resistant, foldable cover plate and its preparation method, overcoming the defects and shortcomings of the prior art or products. The cover plate prepared by the method of this invention simultaneously possesses high light transmittance, high radiation resistance, high mechanical properties, and foldability, and the preparation method is simple and easy to industrialize. The specific technical solution is as follows:

[0009] A high-transmittance, high-strength, radiation-resistant, foldable cover sheet and its preparation method are disclosed. The cover sheet is characterized by being a polyimide (PI) sheet polymerized in a one-pot process from 2,2′-di(trifluoromethyl)diaminobiphenyl, 4,4′-(hexafluoroisopropyl)diatitanic anhydride, N,N-dimethylacetamide (DMAc), and tributyl acetyl citrate (ATBC). The diamine 2,2′-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4′-(hexafluoroisopropyl)diatitanic anhydride are monomers in an equimolar ratio for the polymerization reaction. DMAc is used as a solvent, and the amount of ATBC added is 15-85% of the total molar amount of the diamine and the dianhydride. This invention uses ATBC as a modifier to prepare the PI cover sheet, adjusting the cover sheet's transmittance, mechanical strength, foldability, and UV radiation resistance by adjusting the amount of ATBC added. The cover plate exhibits excellent light transmittance in both the visible and near-infrared bands (400-1800nm), with an average transmittance of 91.16%. It also possesses superior mechanical properties, with a tensile strength of 244.0MPa and an elongation at break of 12.2%, and is foldable. Furthermore, it exhibits high resistance to ultraviolet radiation; after 500 hours of ultraviolet radiation, the average transmittance and tensile strength attenuation rates are only 0.066% and 1.967%, respectively, making it suitable for solar cells in the aerospace field.

[0010] A high-transmittance, high-strength, radiation-resistant, foldable cover plate and its preparation method, comprising the following steps:

[0011] (1) Raw material preparation: Accurately weigh the raw materials and modifiers respectively. The cover sheet raw material is composed of 2,2′-di(trifluoromethyl)diaminobiphenyl, 4,4′-(hexafluoroisopropyl)diatitanic anhydride, DMAc and ATBC. The diamine 2,2′-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4′-(hexafluoroisopropyl)diatitanic anhydride are in an equimolar ratio. DMAc is used as a solvent. The amount of ATBC added is 15-85% of the total molar amount of diamine and dianhydride.

[0012] (2) One-pot polymerization: The raw materials are accurately weighed according to the stoichiometric ratio of the target product, poured into a clean beaker, placed on a magnetic stirrer, and stirred at 100-600 r / min for 1-48 hours at 20-35℃ to ensure that the raw materials are completely mixed and homogeneous, and then carried out one-pot polymerization.

[0013] (3) Thermal imidization: The above sol is rolled onto a glass plate at 20-35℃. Alternatively, a wet film blank can be obtained by spin coating, spraying, or pulling. The film blank is then kept in a muffle furnace at 50-300℃ for 1-48 hours for thermal imidization, and then naturally cooled to room temperature to obtain a PI cover sheet with high light transmittance, high strength, radiation resistance, and foldability.

[0014] This invention improves the light transmittance, mechanical properties, foldability, and UV resistance of PI cover sheets by adding the modifier ATBC to regulate the PI molecular chain. This facilitates the detangling of PI molecular chains, making their movement easier and increasing the light transmittance, foldability, mechanical strength, and UV resistance of PI. A one-pot polymerization method is used for preparation, which is simple, fast, and efficient. This is a safe and effective method for preparing PI cover sheets, ensuring sufficient quantity while reducing production costs.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects:

[0016] This invention uses 2,2′-bis(trifluoromethyl)diaminobiphenyl and 4,4′-(hexafluoroisopropyl)titanium anhydride as monomers, DMAc as solvent, and ATBC as modifier to prepare PI cover sheets via a one-pot polymerization method. The PI cover sheets exhibit stable physicochemical properties, a simple preparation process, low cost, and are easily industrialized. The amount of ATBC added as a modifier adjusts the transmittance, mechanical strength, foldability, and UV resistance of the PI cover sheets. The cover sheets show good transmittance in both the visible and near-infrared bands (400-1800 nm), with an average transmittance of 91.16%. The cover sheets possess excellent mechanical properties, with a tensile strength of 244.0 MPa and an elongation at break of 12.2%, and are foldable. The cover sheets also exhibit excellent UV resistance; after 500 hours of UV irradiation, the average transmittance and tensile strength decrease by only 0.066% and 1.967%, respectively, making them suitable for use in solar cells in the aerospace field. Detailed Implementation

[0017] A high-transmittance, high-strength, radiation-resistant, foldable cover sheet and its preparation method are disclosed. The cover sheet is prepared by one-pot polymerization of 2,2′-di(trifluoromethyl)diaminobiphenyl, 4,4′-(hexafluoroisopropyl)diatitanic anhydride, DMAc, and ATBC. The diamine 2,2′-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4′-(hexafluoroisopropyl)diatitanic anhydride are in an equimolar ratio, DMAc is used as a solvent, and the amount of ATBC added is 15-85% of the total molar amount of the diamine and dianhydride. The preparation method includes the following steps: raw material preparation, one-pot polymerization, and thermal imidization.

[0018] The present invention will be further described in detail below with reference to embodiments:

[0019] Example 1

[0020] A high-transmittance, high-strength, radiation-resistant, foldable cover sheet and its preparation method, comprising the following steps:

[0021] (1) Raw material preparation: Weigh the PI raw material and modifier separately. The cover sheet raw material is composed of 2,2′-di(trifluoromethyl)diaminobiphenyl, 4,4′-(hexafluoroisopropyl)diatitanic anhydride, DMAc and ATBC. The diamine 2,2′-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4′-(hexafluoroisopropyl)diatitanic anhydride are in an equimolar ratio. DMAc is used as a solvent. The amount of ATBC added is 15% of the total molar amount of diamine and dianhydride.

[0022] (2) One-pot polymerization: The raw materials are accurately weighed according to the stoichiometric ratio of the target product, poured into a clean beaker, placed on a magnetic stirrer, and stirred at 100-600 r / min for 1-48 hours at 20-35℃ to ensure that the raw materials are completely mixed and the reaction is complete and thorough, so as to achieve one-pot polymerization to obtain a sol with a certain viscosity and fluidity.

[0023] (3) The above sol is applied to a glass plate at 20-35℃ and kept at 50-300℃ for 1-48 hours for thermal imidization. Then it is naturally cooled to room temperature to obtain a PI cover sheet with high light transmittance, high strength, radiation resistance and foldability.

[0024] Example 2

[0025] A high-transmittance, high-strength, radiation-resistant, foldable cover sheet and its preparation method, comprising the following steps:

[0026] (1) Raw material preparation: Weigh the PI raw material and modifier separately. The cover sheet raw material is composed of 2,2′-di(trifluoromethyl)diaminobiphenyl, 4,4′-(hexafluoroisopropyl)diatitanic anhydride, DMAc and ATBC. The diamine 2,2′-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4′-(hexafluoroisopropyl)diatitanic anhydride are in an equimolar ratio. DMAc is used as a solvent. The amount of ATBC added is 50% of the total molar amount of diamine and dianhydride.

[0027] (2) One-pot polymerization: The raw materials are accurately weighed according to the stoichiometric ratio of the target product, poured into a clean beaker, placed on a magnetic stirrer, and stirred at 100-600 r / min for 1-48 hours at 20-35℃ to ensure that the raw materials are completely mixed and homogeneous, and then the one-pot polymerization is carried out.

[0028] (3) The above sol is applied to a glass plate at 20-35℃ and kept at 50-300℃ for 1-48 hours for thermal imidization. Then it is naturally cooled to room temperature to obtain a PI cover sheet with high light transmittance, high strength, radiation resistance and foldability.

[0029] Example 3

[0030] (1) Raw material preparation: Weigh the PI raw material and modifier separately. The cover sheet raw material is composed of 2,2′-di(trifluoromethyl)diaminobiphenyl, 4,4′-(hexafluoroisopropyl)diatitanic anhydride, DMAc and ATBC. The diamine 2,2′-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4′-(hexafluoroisopropyl)diatitanic anhydride are in an equimolar ratio. DMAc is used as a solvent. The amount of ATBC added is 85% of the total molar amount of diamine and dianhydride.

[0031] (2) One-pot polymerization: The raw materials are accurately weighed according to the stoichiometric ratio of the target product, poured into a clean beaker, placed on a magnetic stirrer, and stirred at 100-600 r / min for 1-48 hours at 20-35℃ to ensure that the raw materials are completely mixed and homogeneous, and then the one-pot polymerization is carried out.

[0032] (3) The above sol is applied to a glass plate at 20-35℃ and kept at 50-300℃ for 1-48 hours for thermal imidization. Then it is naturally cooled to room temperature to obtain a PI cover sheet with high light transmittance, high strength, radiation resistance and foldability.

[0033] The PI coverslips obtained in the above examples, containing 15%, 50%, and 85% of the total molar amount of diamine and dianhydride ATBC, respectively, are denoted as T1 / PI, T2 / PI, and T3 / PI. Attached Figure Description

[0034] Figure 1The transmittance spectra of PI coverslips with different amounts of ATBC added in the visible-near-infrared band (400-1800nm) provided in the embodiments of the present invention are the transmittance spectra of PI coverslips with different amounts of ATBC added in the visible-near-infrared band (400-1800nm).

[0035] Figure 2 (ac) are scanning electron microscope images, macroscopic morphology images, and foldability images of PI coverslips (T2 / PI) with ATBC added at 50% of the total molar amount of diamine and dianhydride provided in the embodiments of the present invention.

[0036] Figure 3 These are the transmittance and mechanical properties of PI coverslips with different amounts of ATBC added, provided in the embodiments of the present invention, before ultraviolet irradiation, wherein the amount of PI-3 added is 0.

[0037] Figure 4 The present invention provides PI cover sheets with different amounts of ATBC added after ultraviolet irradiation, exhibiting transmittance, mechanical properties, and attenuation rates, wherein the amount of PI-3 added is 0.

[0038] Figure 1 The transmittance spectrum of PI with different amounts of ATBC in the visible-near infrared band (400-1800nm).

[0039] Figure 2 (ac) is a scanning electron microscope image, macroscopic morphology image, and foldability diagram of a PI cover plate containing ATBC at a total molar amount of 50% of the total molar amount of diamine and dianhydride.

[0040] Figure 3 The transmittance and mechanical properties of PI coverslips with different amounts of ATBC added before ultraviolet irradiation are shown, where the amount of PI-3 added is 0.

[0041] Figure 4 The transmittance, mechanical properties and attenuation rate of PI coverslips with different amounts of ATBC added after ultraviolet irradiation are shown, where the amount of PI-3 added is 0.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-transmittance, high-strength, radiation-resistant, foldable PI cover sheet, characterized in that: The cover sheet is a polyimide (PI) sheet polymerized in a one-pot process from 2,2'-di(trifluoromethyl)diaminobiphenyl, 4,4'-(hexafluoroisopropyl)phthalic anhydride, N,N-dimethylacetamide (DMAc), and tributyl acetyl citrate (ATBC). The diamine 2,2'-di(trifluoromethyl)diaminobiphenyl and the dianhydride 4,4'-(hexafluoroisopropyl)phthalic anhydride are monomers in an equimolar ratio for the polymerization reaction. DMAc is used as a solvent, and the amount of ATBC added is 15-85% of the total molar amount of the diamine and the dianhydride.

2. The high-transmittance, high-strength, radiation-resistant, foldable PI cover sheet according to claim 1, characterized in that, Adding ATBC modifies PI synthesized from 2,2'-bis(trifluoromethyl)diaminobiphenyl and 4,4'-(hexafluoroisopropyl)phthalic anhydride. The amount added can control the light transmittance, mechanical strength, flexibility and UV radiation resistance of PI coverslips.

3. A high-transmittance, high-strength, radiation-resistant, foldable PI cover sheet according to claim 1 or claim 2, characterized in that, The cover plate exhibits excellent light transmittance in both the visible and near-infrared bands (400-1800nm), with an average transmittance of 91.16%. It also possesses superior mechanical properties, with a tensile strength of 244.0MPa and an elongation at break of 12.2%, and is foldable. Furthermore, it exhibits high resistance to ultraviolet radiation, with an average transmittance and tensile strength degradation rate of only 0.066% and 1.967%, respectively, after 500 hours of ultraviolet irradiation, making it suitable for solar cells in the aerospace field.

4. A method for preparing a high-transmittance, high-strength, radiation-resistant, foldable PI cover sheet according to claim 1 or claim 2, characterized in that, The PI film or sheet is prepared by one-pot polymerization. The 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-(hexafluoroisopropyl)phthalic anhydride, DMAc, and ATBC are poured into a clean beaker and placed on a magnetic stirrer. The mixture is stirred at 10-600 r / min for 1-48 hours at 20-35°C to ensure complete reaction of the raw materials, thus obtaining a sol for preparing the film or sheet. The sol is then poured onto a glass plate at 20-35°C and rolled to form a film preform, or prepared by spin coating, spraying, or dip coating. The preform is then kept in a muffle furnace at 50-300°C for 1-48 hours to ensure complete thermal imidization, followed by natural cooling to room temperature to obtain the PI cover sheet.

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