A hydrophobic foldable polyimide film, and a preparation method and application thereof

Abstract

The application discloses a hydrophobic and foldable polyimide film and a preparation method and application thereof. The preparation method of the hydrophobic and foldable polyimide film comprises the following steps: 1) preparing a polyimide precursor solution; 2) preparing an anhydrous polyimide solution; 3) preparing a modified polyimide solution; 4) preparing a flexible polyimide solution; and 5) coating the flexible polyimide solution on a substrate to be cured into a film to obtain the hydrophobic and foldable polyimide film. The hydrophobic and foldable polyimide film has the advantages of excellent heat resistance, great toughness, excellent hydrophobicity and double-face heterogeneity, is suitable for being applied to the field of flexible display, and has the advantages of simple preparation method, stable process, low production cost, and is suitable for large-scale industrial production and application.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials technology, specifically to a hydrophobic, fold-resistant polyimide film, its preparation method, and its applications. Background Technology

[0002] BPDA-type polyimide refers to a class of polyimide (PI) materials polymerized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and various diamine monomers. Its molecular backbone has high rigidity and dense packing, resulting in excellent thermal stability and high mechanical strength. It is widely used in microelectronics, aerospace and flexible printed circuit board (FPC) fields.

[0003] However, the rigid structure of BPDA-type polyimide also leads to significant defects, mainly including the following aspects: 1) High brittleness and poor bending resistance: The high rigidity of BPDA-type polyimide results in low elongation at break after film formation, making it prone to brittle fracture when repeatedly folded or subjected to impact, limiting its application in flexible displays (e.g., foldable screens); 2) Difficult processing and poor solubility: Once BPDA-type polyimide undergoes high-temperature imidization and drying, its high crystallinity makes it extremely difficult to dissolve again in organic solvents. Therefore, it is not suitable for the traditional preparation route of "first synthesizing powder, then dissolving and modifying," forcing its preparation process to use high-boiling-point solvents or highly corrosive reagents; 3) Poor water resistance and difficult-to-control modification reaction: When BPDA-type polyimide is toughened and hydrophobically modified by introducing flexible hydrophobic side chains (e.g., silicone oil), the presence of multifunctional crosslinking agents makes the reaction system prone to irreversible gelation (bursting polymerization) under high-temperature conditions, ultimately leading to the inability to form a film. In summary, the existing BPDA-type polyimide for film formation of PI films still has obvious defects and cannot fully meet the growing practical application needs.

[0004] Therefore, developing a BPDA-type polyimide film with excellent heat resistance, high toughness, and excellent hydrophobicity is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrophobic, fold-resistant polyimide film, its preparation method, and its application.

[0006] The technical solution adopted in this invention is: A method for preparing a hydrophobic, fold-resistant polyimide film includes the following steps: 1) 3,3',4,4'-biphenyltetracarboxylic dianhydride and phenolic hydroxyl diamine were dissolved in a polar aprotic solvent and subjected to a polycondensation reaction to obtain a polyimide precursor solution; 2) Add the dehydrating agent to the polyimide precursor solution and reflux to separate the water, thereby obtaining an anhydrous polyimide solution; 3) Add the polymerization inhibitor and catalyst to the anhydrous polyimide solution, and then add glycidyl methacrylate to carry out a ring-opening esterification reaction to obtain a modified polyimide solution. 4) Hydrogen-containing polysiloxane and platinum catalyst were added to the modified polyimide solution to carry out a hydrosilylation reaction, resulting in a flexible polyimide solution; 5) Coat the flexible polyimide solution onto the substrate and cure it to form a film, thereby obtaining a hydrophobic and fold-resistant polyimide film.

[0007] Preferably, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride and phenolic hydroxyl diamine in step 1) is 1:0.95 to 1.05.

[0008] Preferably, the phenolic hydroxy diamine in step 1) is at least one of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BAFA), 3,3'-dihydroxy-4,4'-diaminobiphenyl (HAB), and 2,2-bis(3-amino-4-hydroxyphenyl)propane (BAPA).

[0009] Preferably, the polar aprotic solvent in step 1) is at least one of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO).

[0010] Preferably, the polycondensation reaction in step 1) is carried out at room temperature for 4 to 12 hours.

[0011] Preferably, the dehydrating agent in step 2) is at least one of toluene, xylene, chlorobenzene, and cyclohexane. The dehydrating agent can form an azeotrope with water, and the water generated during ring closure can be removed by azeotropic distillation until no water is generated.

[0012] Preferably, the reflux water separation in step 2) is carried out at a temperature of 160℃~180℃, and the reflux water separation time is 2h~6h.

[0013] Preferably, in step 3), the molar ratio of the side chain hydroxyl group of the polyimide to glycidyl methacrylate is 1:0.1 to 0.2.

[0014] Preferably, the mass ratio of polyimide, polymerization inhibitor, and catalyst in step 3) is 1:0.001~0.05:0.001~0.05.

[0015] Preferably, the polymerization inhibitor in step 3) is at least one of hydroquinone, p-hydroxyanisole (MEHQ), and 2,6-di-tert-butyl-p-cresol (BHT).

[0016] Preferably, the catalyst in step 3) is at least one of tetraethylammonium bromide (TEAB), tetrabutylammonium bromide, triethylamine, and triphenylphosphine.

[0017] Preferably, the ring-opening esterification reaction in step 3) is carried out at a temperature of 70℃ to 90℃ for a reaction time of 1h to 3h.

[0018] Preferably, the mass ratio of the modified polyimide and the hydrogen-containing polysiloxane in step 4) is 1:0.05 to 0.5.

[0019] Preferably, the mass ratio of the modified polyimide to the platinum catalyst in step 4) is 1:0.0001 to 0.01.

[0020] Preferably, the hydrosilylation reaction in step 4) is carried out at a temperature of 70°C to 90°C for a reaction time of 0.5 h to 3 h.

[0021] Preferably, the curing in step 5) includes the following operations: first, low-temperature curing at a temperature of 50℃~70℃, and then high-temperature curing at a temperature of 100℃~120℃.

[0022] A hydrophobic, fold-resistant polyimide film is prepared by the above-described method.

[0023] A flexible display device comprising the aforementioned hydrophobic, fold-resistant polyimide film.

[0024] Preferably, the flexible display device is one of a foldable screen mobile phone, a foldable screen computer, or a flexible wearable device.

[0025] The beneficial effects of the present invention are: the hydrophobic and fold-resistant polyimide film of the present invention has the advantages of excellent heat resistance, high toughness, excellent hydrophobicity, and bi-sided anisotropy, making it suitable for use in the field of flexible displays. Moreover, its preparation method is simple, the process is stable, and the production cost is low, making it suitable for large-scale industrial production and application.

[0026] Specifically: 1) Excellent toughness and folding resistance: The present invention introduces flexible polysiloxane side chains through chemical bonding, which induces the formation of a microphase separation structure (island structure) in the rigid PI matrix. This structure can effectively absorb stress and significantly improve the elongation at break and resistance to repeated folding of the PI film. 2) Unique surface properties: This invention introduces flexible polysiloxane side chains through chemical bonding. During the film formation process, the polysiloxane side chains spontaneously migrate to the air interface, giving the PI film a frosted texture and excellent hydrophobicity on one side (air side), while the bonding side remains glossy, exhibiting unique bi-sided anisotropy. 3) High process stability: The present invention adopts a "one-pot" process, which maintains the solution state throughout the process, avoiding the problem of poor solubility of BPDA-type polyimide. By precisely controlling the micro-grafting ratio and reaction temperature, the gelation problem in the modification process of multifunctional polysiloxanes is completely solved, making it suitable for large-scale industrial preparation. Attached Figure Description

[0027] Figure 1 This is a photograph of the hydrophobic, fold-resistant polyimide film of Example 1.

[0028] Figure 2 This is a photograph of the final product of Comparative Example 2.

[0029] Figure 3 The images show the FTIR spectra of the hydrophobic, fold-resistant polyimide film of Example 1 and the polyimide film of Comparative Example 1. Detailed Implementation

[0030] The present invention will be further explained and described below with reference to specific embodiments.

[0031] Example 1: A hydrophobic, fold-resistant polyimide film is prepared by the following method: 1) Add 10 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 10 mmol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to 35 mL of N-methyl-2-pyrrolidone and stir at room temperature for 6 h to obtain a polyimide precursor solution. 2) Add 15 mL of toluene to the polyimide precursor solution and stir and reflux at 165 °C for 3 h to obtain an anhydrous polyimide solution. 3) Add 0.01 g of hydroquinone and 0.02 g of tetraethylammonium bromide to anhydrous polyimide solution, then add 3 mmol of glycidyl methacrylate. The molar ratio of the side chain hydroxyl group of polyimide to glycidyl methacrylate is 1:0.15. Stir at 80℃ for 1.5 h to obtain modified polyimide solution. 4) Add 1g of hydrogen-containing polysiloxane and 0.01g of chloroplatinic acid to the modified polyimide solution and stir at 80°C for 1h to obtain a flexible polyimide solution (reddish-brown). 5) Coat the flexible polyimide solution onto the glass substrate, then cure at 60°C for 3 hours, and then cure at 120°C for 2 hours. Peel off the film to obtain a hydrophobic and fold-resistant polyimide film.

[0032] A physical image of the hydrophobic, fold-resistant polyimide film of this embodiment is shown below. Figure 1 As shown.

[0033] Depend on Figure 1It can be seen that the surface of the polyimide film is intact and crack-free when it is rolled up, and it has anisotropy on both sides (one side is bright and the other side is frosted).

[0034] Example 2: A hydrophobic, fold-resistant polyimide film is identical to Example 1 except that the amount of glycidyl methacrylate in step 3) is adjusted from "3 mmol" to "2 mmol" during preparation (the molar ratio of the side chain hydroxyl group of polyimide to glycidyl methacrylate is 1:0.1).

[0035] Example 3: A hydrophobic, fold-resistant polyimide film is identical to that in Example 1, except that the volumetric amount of "toluene" in step 2) is replaced with "xylene" during preparation.

[0036] Example 4: A hydrophobic, fold-resistant polyimide film is identical to that in Example 1, except that the molar amount of "2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane" in step 1) is replaced with "3,3'-dihydroxy-4,4'-diaminobiphenyl (HAB; fluorine-free)".

[0037] Example 5: A hydrophobic, fold-resistant polyimide film is identical to Example 1 except that the amount of glycidyl methacrylate in step 3) is adjusted from "3 mmol" to "4 mmol" during preparation (the molar ratio of the side chain hydroxyl groups of polyimide to glycidyl methacrylate is increased to the maximum limit of 1:0.2).

[0038] Comparative Example 1: A polyimide film, the preparation method of which is as follows: 1) Add 10 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 10 mmol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane to 35 mL of N-methyl-2-pyrrolidone and stir at room temperature for 6 h to obtain a polyimide precursor solution. 2) Add 15 mL of toluene to the polyimide precursor solution and stir and reflux at 165 °C for 3 h to obtain an anhydrous polyimide solution. 3) Coat anhydrous polyimide solution onto a glass substrate, then cure at 60°C for 3 hours, and then cure at 120°C for 2 hours. Peel off the film to obtain a polyimide film.

[0039] Comparative Example 2: A polyimide film (unsuccessfully prepared) is prepared by the following method: 0.01 g of hydroquinone and 0.02 g of tetraethylammonium bromide were added to anhydrous polyimide solution (same as in Example 1), followed by the addition of 18 mmol of glycidyl methacrylate. The molar ratio of the side-chain hydroxyl groups of polyimide to glycidyl methacrylate was 1:0.9. The mixture was stirred at 80°C for 2.5 h. The viscosity of the system increased sharply, and irreversible gelation (bursting polymerization) occurred. The final product was an insoluble and infusible jelly-like substance that could not be coated into a film. (This comparative example strongly demonstrates the necessity of controlling the molar ratio of the side-chain hydroxyl groups of polyimide to glycidyl methacrylate at 1:0.1 to 0.2 to prevent crosslinking, fully reflecting the inventiveness of the process parameters of this invention.)

[0040] The actual image of the final product in this comparative example is shown below. Figure 2 As shown.

[0041] Depend on Figure 2 It can be seen that irreversible gelation occurred in the system, and the final product is an insoluble and infusible jelly.

[0042] Performance testing: 1) The Fourier transform infrared (FTIR) spectra of the hydrophobic, fold-resistant polyimide film of Example 1 and the polyimide film of Comparative Example 1 are shown below. Figure 3 (The small image in the upper right corner of the image is a magnified view.)

[0043] Depend on Figure 3 It can be seen that: compared with the polyimide film of Comparative Example 1, the hydrophobic and fold-resistant polyimide film of Example 1 has a higher fold-resistantness at 1091 cm⁻¹. -1 The appearance of a new absorption peak indicates the successful grafting of polysiloxane segments.

[0044] 2) The appearance, surface contact angle, elongation at break, and folding endurance test results of the hydrophobic and fold-resistant polyimide films of Examples 1-5 and the polyimide film of Comparative Example 1 are shown in the table below: Table 1. Results of tests on appearance, surface contact angle, elongation at break, and flexural endurance.

[0045] Note: Elongation at break: Tested in accordance with "GB / T 1040.3-2006 Determination of tensile properties of plastics - Part 3: Test conditions for thin plastics and sheets".

[0046] Folding endurance: Tested in accordance with "GB / T 457-2008 Determination of folding endurance of paper and paperboard".

[0047] As shown in Table 1, the hydrophobic and fold-resistant polyimide films of Examples 1-5 have significantly increased elongation at break and significantly improved fold resistance compared to the polyimide film of Comparative Example 1. The polyimide films have achieved a transformation from brittle to tough, making them suitable for use in the field of flexible displays.

[0048] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a hydrophobic, fold-resistant polyimide film, characterized in that, Includes the following steps: 1) 3,3',4,4'-biphenyltetracarboxylic dianhydride and phenolic hydroxyl diamine were dissolved in a polar aprotic solvent and subjected to a polycondensation reaction to obtain a polyimide precursor solution; 2) Add the dehydrating agent to the polyimide precursor solution and reflux to separate the water, thereby obtaining an anhydrous polyimide solution; 3) Add the polymerization inhibitor and catalyst to the anhydrous polyimide solution, and then add glycidyl methacrylate to carry out a ring-opening esterification reaction to obtain a modified polyimide solution. 4) Hydrogen-containing polysiloxane and platinum catalyst are added to the modified polyimide solution to carry out a hydrosilylation reaction to obtain a flexible polyimide solution; 5) Coat the flexible polyimide solution onto the substrate and cure it to form a film, thereby obtaining a hydrophobic and fold-resistant polyimide film.

2. The preparation method according to claim 1, characterized in that: In step 1), the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to phenolic hydroxyl diamine is 1:0.95-1.05; the phenolic hydroxyl diamine in step 1) is at least one of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 3,3'-dihydroxy-4,4'-diaminobiphenyl, and 2,2-bis(3-amino-4-hydroxyphenyl)propane.

3. The preparation method according to claim 1, characterized in that: Step 2) The water-removing agent is at least one of toluene, xylene, chlorobenzene, and cyclohexane.

4. The preparation method according to claim 1, characterized in that: In step 3), the molar ratio of the side chain hydroxyl group of the polyimide to glycidyl methacrylate is 1:0.1 to 0.

2.

5. The preparation method according to claim 1, characterized in that: In step 4), the mass ratio of the modified polyimide to the hydrogen-containing polysiloxane is 1:0.05 to 0.

5.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The polar aprotic solvent in step 1) is at least one of N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the polymerization inhibitor in step 3) is at least one of hydroquinone, p-hydroxyanisole, and 2,6-di-tert-butyl-p-cresol; the catalyst in step 3) is at least one of tetraethylammonium bromide, tetrabutylammonium bromide, triethylamine, and triphenylphosphine.

7. The preparation method according to any one of claims 1 to 5, characterized in that: In step 3), the mass ratio of polyimide, polymerization inhibitor, and catalyst is 1:0.001-0.05:0.001-0.05; in step 4), the mass ratio of modified polyimide and platinum catalyst is 1:0.0001-0.

01.

8. The preparation method according to any one of claims 1 to 5, characterized in that: Step 1) The polycondensation reaction is carried out at room temperature for 4-12 hours; Step 2) The reflux water separation is carried out at 160-180°C for 2-6 hours; Step 3) The ring-opening esterification reaction is carried out at 70-90°C for 1-3 hours; Step 4) The hydrosilylation reaction is carried out at 70-90°C for 0.5-3 hours; Step 5) The curing includes the following operations: first, low-temperature curing at 50-70°C, and then high-temperature curing at 100-120°C.

9. A hydrophobic, fold-resistant polyimide film, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. A flexible display device, characterized in that, The hydrophobic, fold-resistant polyimide film as described in claim 9.

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