Transparent polyimide film
Patent Information
- Authority / Receiving Office
- TW · TW
- Patent Type
- Applications
- Current Assignee / Owner
- TAIMIDE TECH INC
- Filing Date
- 2025-01-23
- Publication Date
- 2026-08-01
AI Technical Summary
Existing polyimide films used in flexible displays suffer from coloration issues due to charge transfer complexes and contain fluorine, which raises environmental concerns, and they lack the mechanical properties required for display applications.
A fluorine-free transparent polyimide film is developed through chemical cyclization of specific diamine and dianhydride monomers, achieving a Young's modulus greater than 4 GPa and a yellow index less than 5, using diamines like 4,4'-diamino-2,2'-dimethylbiphenyl and dianhydrides like 1,2,3,4-cyclobutanetetracarboxylic dianhydride, with optional additives for improved optical properties.
The film exhibits high mechanical strength and minimal coloration, making it suitable for display covers without the environmental hazards associated with fluorinated materials.
Abstract
Description
Technical Field
[0001] The present invention relates to a transparent polyimide film, specifically a transparent polyimide film that does not contain fluorine atoms, having a Young's modulus greater than 4 GPa and a yellow index (YI) less than 5. Prior Technology
[0002] Display devices are currently widely used in mobile phones and tablets. In the past, glass was used as a cover for displays. However, with the development of flexible displays, glass covers cannot meet the requirements of flexibility. Therefore, polyimide optical film has been proposed as one of the alternative materials to glass.
[0003] Polyimide films possess superior mechanical properties, heat resistance, dimensional stability, and electrical properties compared to other polymer films, and are currently widely used in flexible printed circuit boards, aerospace, automotive, and other electronic materials. However, for display applications, excellent optical properties are required. Since the charge transfer complex (CTC) in polyimide resin forms a dark brown color, introducing fluorine-containing groups can effectively solve the coloring problem of the film, and this is a commonly used technique.
[0004] In recent years, with the rise of environmental awareness, perfluorinated and polyfluoroalkyl substances (PFAS) have become a hot topic in the global environmental and health fields. These man-made chemicals are widely used in daily life due to their excellent water, oil, and stain repellency. However, it is precisely this ubiquity, coupled with their environmental persistence, that makes PFAS a thorny global problem. Transparent polyimides, which use fluorinated monomers, may release PFAS or form PFAS during degradation. Some studies are exploring fluorine-free alternatives or improved synthesis methods, and industry is actively seeking PFAS substitutes.
[0005] This invention proposes a transparent polyimide film, specifically a transparent polyimide film that does not contain fluorine atoms, having a Young's modulus greater than 4 GPa and a yellow index (YI) less than 5. Summary of the Invention
[0006] This invention relates to a transparent polyimide film, which is obtained by chemical cyclization of polyamide formed by polymerizing diamine and dianhydride. The diamine comprises one or a combination of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB), 3,3'-diaminodiphenyl phosphate (33DDS), 4,4'-diaminodiphenyl phosphate (44DDS), bis[4-(3-aminophenoxy)phenyl]phosphate (m-BAPS), or bis[4-(4-aminophenoxy)phenyl]phosphate (p-BAPS). Methylbiphenyl (m-TB) accounts for 40-60 mol% of the total diamine molar; the dianhydride includes one or a combination of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) or 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride (BPADA), and the 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) accounts for 65-85 mol% of the total dianhydride molar; making the Young's modulus of the transparent polyimide film greater than 4 GPa and the yellow index (YI) less than 5.
[0007] The polyamide further contains copolymer segments composed of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA).
[0008] The molar ratio of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) to 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) in the copolymer segment can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95.
[0009] The molar ratio of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) to 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) in the copolymer segment is more preferably 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95.
[0010] The transparent polyimide film has a Young's modulus of 4.5 GPa or higher, preferably 5 GPa or higher.
[0011] The transparent polyimide film may contain at least one colorant, which accounts for 5 to 40 ppm of the film, so that the yellow index (YI) of the film is less than 4.
[0012] The transparent polyimide film may contain at least one ultraviolet absorber.
[0013] The ultraviolet absorber may be a benzophenone, a benzotriazole, a triazine, or an oxanilide.
[0014] The ultraviolet absorber accounts for 1 to 15 wt% of the film.
[0015] This transparent polyimide film has a transmittance of more than 87%. Implementation
[0016] This invention relates to a transparent polyimide film, which is obtained by chemical cyclization after polymerization of diamine and dianhydride to form polyamide. The diamine comprises one or a combination of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB), 3,3'-diaminodiphenyl phosphate (33DDS), 4,4'-diaminodiphenyl phosphate (44DDS), bis[4-(3-aminophenoxy)phenyl]phosphate (m-BAPS), or bis[4-(4-aminophenoxy)phenyl]phosphate (p-BAPS). The m-TB component accounts for 40-60 mol% of the total diamine molar number; the dianhydride includes one or a combination of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), or 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride (BPADA), wherein the 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) accounts for 65-85 mol% of the total dianhydride molar number; and the transparent polyimide film has a Young's modulus greater than 4 GPa and a yellow index (YI) less than 5.
[0017] Polyamide production
[0018] Transparent polyimide films are obtained by chemical cyclization of polyamide formed by polymerizing diamine and dianhydride in an organic solvent.
[0019] The diamine includes one or a combination of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB), 3,3'-diaminodiphenyl sulfonium (33DDS), 4,4'-diaminodiphenyl sulfonium (44DDS), bis[4-(3-aminophenoxy)phenyl]sulfonium (m-BAPS), and bis[4-(4-aminophenoxy)phenyl]sulfonium (p-BAPS).
[0020] Dicarboxylic anhydrides include one or a combination of 1,2,3,4-cyclobutanetetracarboxylic anhydride (CBDA), 3,3',4,4'-biphenyltetracarboxylic anhydride (BPDA) or 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride (BPADA).
[0021] Solvents: Dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), γ-butyrolactone (GBL), and N,N-dimethylformamide (DMF) can be used in the preparation of polyacrylic acid. In this invention, dimethylacetamide is used as a solvent.
[0022] Production of transparent polyimide film
[0023] Polyamide, catalyst, and dehydrating agent are stirred evenly and then chemically cyclized. The dehydrating agent can be acetic anhydride or benzoic anhydride. In this invention, acetic anhydride is selected as the dehydrating agent. The catalyst can be pyridine, 3-methylpyridine, 2-methylpyridine, 4-methylpyridine, isoquinoline, quinoline, or triethylamine. Pyridine, 3-methylpyridine, 2-methylpyridine, and 4-methylpyridine are preferred. In this invention, 3-methylpyridine is selected as the catalyst.
[0024] The catalysts and dehydrating agents mentioned above can be used alone or diluted with solvents and then added to the mixture.
[0025] The polyimide mixture containing dehydrating agent and catalyst was uniformly stirred and then degassed using a centrifugal degassing machine. The degassed solution was poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 40 minutes, then heated to 170°C for 10 minutes, and finally heated to 260°C for 10 minutes as the final treatment. After baking, the glass was placed in water, and the film was removed to obtain a transparent polyimide film.
[0026] [<Detection Method>]
[0027] The mechanical and optical properties of the transparent polyimide films obtained in the following examples were measured using the following methods.
[0028] Yellow index (YI): Measured using a Nippon Denshoku NE-4000 instrument in accordance with ASTM E313 specifications.
[0029] Young's modulus: Measured using a Hounsfield H10K-S tensile testing machine in accordance with ASTM D882 specifications.
[0030] [Example 1]
[0031] Manufacturing of polyacrylic acid solution
[0032] 20.117 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 35.292 g of 4,4'-diaminodiphenyl ether (44DDS) was added. After complete dissolution, 30.197 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring for a certain period of time, 24.394 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. The final product was a polyacrylic acid solution with a solid content of 20%.
[0033] Production of transparent polyimide film
[0034] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1. 3-methylpyridine (AP) and DMAc were then diluted at a weight ratio of 1:1. 4.16 mL of AA diluent and 1.66 mL of AP diluent were added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, followed by a final heating at 6.0°C / min to 260°C and baked for 10 minutes.
[0035] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0036] [Example 2]
[0037] Manufacturing of polyacrylic acid solution
[0038] 20.117 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 14.866 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring continuously for 3 hours, a copolymer segment of m-TB and CBDA was formed. Then, 35.292 g of 4,4'-diaminodiphenyl ether (44DDS) was added to the solution. After complete dissolution, 15.331 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring for a certain period of time, 24.394 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. Finally, a polyacrylic acid solution with a solid content of 20% was obtained.
[0039] Production of transparent polyimide film
[0040] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1. 3-methylpyridine (AP) and DMAc were then diluted at a weight ratio of 1:1. 4.16 mL of AA diluent and 1.66 mL of AP diluent were added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, followed by a final heating at 6.0°C / min to 260°C and baked for 10 minutes.
[0041] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0042] [Example 3]
[0043] Manufacturing of polyacrylic acid solution
[0044] 20.117 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 16.724 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring continuously for 3 hours, a copolymer segment of m-TB and CBDA was formed. Then, 35.292 g of 4,4'-diaminodiphenyl ether (44DDS) was added to the solution. After complete dissolution, 13.472 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring for a certain period of time, 24.394 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. Finally, a polyacrylic acid solution with a solid content of 20% was obtained.
[0045] Production of transparent polyimide film
[0046] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1. 3-methylpyridine (AP) and DMAc were then diluted at a weight ratio of 1:1. 4.16 mL of AA diluent and 1.66 mL of AP diluent were added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, followed by a final heating at 6.0°C / min to 260°C and baked for 10 minutes.
[0047] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0048] [Example 4]
[0049] Manufacturing of polyacrylic acid solution
[0050] 20.117 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 13.008 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring continuously for 3 hours, a copolymer segment of m-TB and CBDA was formed. Then, 35.292 g of 3,3'-diaminodiphenyl ether (33DDS) was added to the solution. After complete dissolution, 17.189 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring for a certain period of time, 24.394 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. Finally, a polyacrylic acid solution with a solid content of 20% was obtained.
[0051] Production of transparent polyimide film
[0052] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1. 3-methylpyridine (AP) and DMAc were then diluted at a weight ratio of 1:1. 4.16 mL of AA diluent and 1.66 mL of AP diluent were added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, followed by a final heating at 6.0°C / min to 260°C and baked for 10 minutes.
[0053] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0054] [Example 5]
[0055] Manufacturing of polyacrylic acid solution
[0056] 16.249 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 10.507 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring continuously for 3 hours, a copolymer segment of m-TB and CBDA was formed. Then, 49.654 g of bis[4-(3-aminophenoxy)phenyl]monophosphate (m-BAPS) was added to the solution. After complete dissolution, 13.884 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring for a certain period of time, 19.705 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. Finally, a polyacrylic acid solution with a solid content of 20% was obtained.
[0057] Production of transparent polyimide film
[0058] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1, and 3-methylpyridine (AP) and DMAc were diluted at a weight ratio of 1:1. 3.36 mL of AA diluent and 1.34 mL of AP diluent were then added to each solution. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven and baked for 20 minutes, then the temperature was increased to 170°C at a rate of 6°C / min and baked for 10 minutes, and finally increased to 260°C at a rate of 6.0°C / min and baked for 10 minutes as the final treatment.
[0059] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0060] [Example 6]
[0061] Manufacturing of polyacrylic acid solution
[0062] 21.121 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 15.608 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring continuously for 3 hours, a copolymer segment of m-TB and CBDA was formed. Then, 43.027 g of 4,4-bis(3-aminophenoxy)phenylene oxide (p-BAPS) was added to the solution. After complete dissolution, 9.755 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring for a certain period of time, 20.489 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. Finally, a polyacrylic acid solution with a solid content of 20% was obtained.
[0063] Production of transparent polyimide film
[0064] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1, and 3-methylpyridine (AP) and DMAc were diluted at a weight ratio of 1:1. 3.5 mL of AA diluent and 1.39 mL of AP diluent were then added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, and finally heated to 260°C at a rate of 6.0°C / min and baked for 10 minutes as the final treatment.
[0065] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0066] [Example 7]
[0067] Manufacturing of polyacrylic acid solution
[0068] 21.004 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 36.849 g of 4,4'-diaminodiphenyl ether (44DDS) was added. After complete dissolution, 41.230 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring for a certain period of time, 10.916 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. The final product was a polyacrylic acid solution with a solid content of 20%.
[0069] Production of transparent polyimide film
[0070] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1. 3-methylpyridine (AP) and DMAc were then diluted at a weight ratio of 1:1. 4.35 mL of AA diluent and 1.73 mL of AP diluent were added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, followed by a final heating at 6.0°C / min to 260°C and baked for 10 minutes.
[0071] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0072] [Example 8]
[0073] Manufacturing of polyacrylic acid solution
[0074] 27.806 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 21.681 g of 4,4'-diaminodiphenyl ether (44DDS) was added. After complete dissolution, 32.107 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring for a certain period of time, 28.405 g of 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride (BPADA) was finally added, and the temperature of the solution was maintained at 25°C. The final product was a polyacrylic acid solution with a solid content of 20%.
[0075] Production of transparent polyimide film
[0076] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1, and 3-methylpyridine (AP) and DMAc were diluted at a weight ratio of 1:1. 3.83 mL of AA diluent and 1.53 mL of AP diluent were then added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was baked in an 80°C oven for 20 minutes, then the temperature was increased to 170°C at a rate of 6°C / min and baked for 10 minutes, and finally increased to 260°C at a rate of 6.0°C / min and baked for 10 minutes as the final treatment.
[0077] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0078] [Example 9]
[0079] Manufacturing of polyacrylic acid solution
[0080] 20.117 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 11.150 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring continuously for 3 hours, a copolymer segment of m-TB and CBDA was formed. Then, 35.292 g of 4,4'-diaminodiphenyl ether (44DDS) was added to the solution. After complete dissolution, 19.047 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring for a certain period of time, 24.394 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. Finally, a polyacrylic acid solution with a solid content of 20% was obtained.
[0081] Production of transparent polyimide film
[0082] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1. 3-methylpyridine (AP) and DMAc were then diluted at a weight ratio of 1:1. 4.16 mL of AA diluent and 1.66 mL of AP diluent were added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven for 20 minutes, then heated to 170°C at a rate of 6°C / min and baked for 10 minutes, followed by a final heating at 6.0°C / min to 260°C and baked for 10 minutes.
[0083] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0084] [Comparative Example 1]
[0085] Preparation of polyacrylic acid solution
[0086] 15.585 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 47.622 g of bis[4-(3-aminophenoxy)phenyl] benzo[m-BAPS] was added. After complete dissolution, 14.396 g of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was added. After stirring for a certain period of time, 32.397 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. The final product was a polyacrylic acid solution with a solid content of 20%.
[0087] Production of transparent polyimide film
[0088] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1, and 3-methylpyridine (AP) and DMAc were diluted at a weight ratio of 1:1. 3.41 mL of AA diluent and 1.22 mL of AP diluent were then added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was baked in an 80°C oven for 20 minutes, then the temperature was increased to 170°C at a rate of 6°C / min and baked for 10 minutes, and finally increased to 260°C at a rate of 6.0°C / min and baked for 10 minutes as the final treatment.
[0089] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0090] <Comparative Example 2>
[0091] Preparation of polyacrylic acid solution
[0092] 7.547 g of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) was added to 440 g of N,N-dimethylacetamide (DMAc). After complete dissolution, 61.495 g of bis[4-(3-aminophenoxy)phenyl] benzo[m-BAPS] was added. After complete dissolution, 22.656 g of 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) was added. After stirring for a certain period of time, 18.303 g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) was finally added, and the temperature of the solution was maintained at 25°C. The final product was a polyacrylic acid solution with a solid content of 20%.
[0093] Production of transparent polyimide film
[0094] 49 g of polyacrylic acid solution and 21 g of N,N-dimethylacetamide (DMAc) were uniformly mixed. After thorough mixing, acetic anhydride (AA) and DMAc were diluted at a weight ratio of 5:1, and 3-methylpyridine (AP) and DMAc were diluted at a weight ratio of 1:1. 3.3 mL of AA diluent and 1.18 mL of AP diluent were then added to each diluent. After uniform mixing, the solution was degassed using a centrifuge. The degassed solution was then poured onto a glass substrate and coated using a doctor blade with a 900 μm gap. The coated sample was placed in an 80°C oven and baked for 20 minutes, then the temperature was increased to 170°C at a rate of 6°C / min and baked for 10 minutes, and finally increased to 260°C at a rate of 6.0°C / min and baked for 10 minutes as the final treatment.
[0095] A glass substrate is immersed in water, and a transparent polyimide film with a thickness of 50 μm is peeled off from the glass substrate.
[0096] The following is a comparison table of the test results for the examples and comparative examples:
[0097] Example 1 shows that the Young's film weight of the transparent polyimide film is greater than 4 GPa, and the yellow index (YI) is less than 5.
[0098] Examples 2 to 6 show that when the molar ratio of mTB to CBDA copolymer segments is 0.6 or higher, the Young's film weight of the transparent polyimide film is greater than 5 GPa.
[0099] Example 9 shows that when the molar ratio of mTB to CBDA copolymer segments is less than 0.6, the Young's membrane of the transparent polyimide film is less than 5 GPa.
[0100] Comparative Example 1 shows that when CBDA accounts for less than 65 mol% of the total dianhydride molar number, the Young's modulus of the transparent polyimide film is less than 4 GPa, and the yellow index (YI) of the film is greater than 5, resulting in a darker color and a softer material, which is not conducive to the application of display cover plates.
[0101] Comparative Example 2 shows that when mTB accounts for less than 40 mol% of the total dianhydride molar number, the Young's modulus of the transparent polyimide film is less than 4 GPa, and the yellow index (YI) of the film is greater than 5, resulting in a darker color and a softer material, which is not conducive to the application of display cover plates.
[0102] The specific embodiments described above are for the purpose of illustrating the present invention in detail. However, these embodiments are for illustrative purposes only and are not intended to limit the present invention. Those skilled in the art will understand that various changes or modifications made to the present invention without departing from the scope defined in the appended claims fall within a part of the present invention.
Claims
1. A transparent polyimide film, which is obtained by chemical cyclization after polymerization of diamine and dianhydride to form polyamide, wherein, The diamine includes one or a combination of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB), 3,3'-diaminodiphenyl phosphate (33DDS), 4,4'-diaminodiphenyl phosphate (44DDS), bis[4-(3-aminophenoxy)phenyl]phosphate (m-BAPS), and bis[4-(4-aminophenoxy)phenyl]phosphate (p-BAPS), wherein the 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) accounts for 40-60% of the total diamine molar number. The dianhydride comprises 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), and one or a combination of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) or 4,4'-(4,4'-isopropyldiphenoxy)phthalic anhydride (BPADA), wherein the 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) accounts for 65-85 mol% of the total dianhydride molar number; and the transparent polyimide film has a Young's modulus greater than 4 GPa and a yellow index (YI) value less than 5.
2. The transparent polyimide film as described in claim 1, wherein the polyimide comprises a copolymer segment composed of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) and 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA).
3. The polyamide as described in claim 2, wherein the molar ratio of 4,4'-diamino-2,2'-dimethylbiphenyl (m-TB) to 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride (CBDA) in the copolymer segment must be greater than 0.
6.
4. The transparent polyimide film of claim 1 contains at least one colorant.
5. The transparent polyimide film of claim 1 contains at least one ultraviolet absorber.
6. The transparent polyimide film as described in claim 1, wherein the film thickness is less than 75 μm.