TRANSPARENT POLYIMIDE FILMS AND METHOD OF PREPARATION

Abstract

A transparent polyimide film with low birefringence, high glass transition temperature (T.sub.g) consists of polyimide essentially comprising non-linear structure. This polyimide is prepared by a mixture of dianhydrides and diamines, comprising at least 10 mol % of asymmetric dianhydride and 50 mol % or less of meta-substituted diamine. This transparent polyimide film has a transmittance of 85% or more at 550 nm, a birefringence value of 0.005 or less and a T.sub.g of 300 C. or more. The present invention relates to the low birefringence required electro-optic field, including the substrate and cover window for flexible OLED and LCD displays.

Claims

1. A polyimide film, comprising: a condensation polymerization reaction of at least two dianhydrides and at least two diamines; wherein the molar ratio of the at least two diamines to the at least two dianhydrides is in the range of from 0.95 to 1.1; wherein the at least two dianhydrides comprise an asymmetric dianhydride and at least one other dianhydride, with the asymmetric dianhydride present at between 20 and 80 mol % of the at least two dianhydrides; wherein the at least two diamines comprise at least one meta-substituted diamine and at least one other diamine, with the meta-substituted diamine present at no more than 50 mol % of the at least two diamines; wherein the asymmetric dianhydride is selected from the group consisting of: 2,3,3,4-biphenyl dianhydride (a-BPDA), 3,4-(hexafluorobenzophenone) diphthalic anhydride (a-6FDA), 2,3,3,4-benzophenone dianhydride (a-BTDA), 2,2,3,4-diphenylsulfonetetracarboxylic dianhydride (a-DSDA) and 2,3,3,4-diphenyl ether tetracarboxylic acid dianhydride (a-ODPA); wherein each of the at the least one other dianhydrides is selected from the group consisting of: 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA), 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA), 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3,4,4-diphenylsulfonetetracarboxylic dianhydride (DSDA), bicyclo[2,2,2]otc-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA), bis-(3-phthalyl anhydride) ether (ODPA), 4,4-(4,4-isopropylidenediphenoxy)bis(phthalic anhydride) (HBDA), 4-(2,5-Dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), cyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA); wherein each of the meta-substituted diamines is selected from the group consisting of: 1,3-benzenediamine (m-PDA), 3,3-diaminodiphenylsulfone (3,3-DDS), 1,3-cyclohexanediamine (1,3-CHDA), 1,3-cyclohexanebis(methylamine) (CBMA), 3,4-oxydianiline (3,4-ODA), 3-(3-aminophenoxy)aniline (3,3-ODA), 3-aminobenzylamine, 3,3-diaminodiphenylmethane, 2,7-diaminofluorene, 1,3-bis(aminomethyl)benzene (MXDA), 1,3-bis (3-aminophenoxy)benzene (1,3,3-APB), 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane (DBOH), 2,2-bis(3-aminophenyl)hexafluoropropane (3,3-6F), 1,4-bis (3-aminophenoxy)benzene (1,4,3-APB), 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane, bis[4-(3-aminophenoxy)-phenyl] sulfone, 3,3-diaminobenzophenone, 3,4-diaminodiphenyl ether, 3,3-trifluoromethylbenzidine (3,3-TFMB), 5-trifluoromethyl-1,3-benzenediamine, 1,2-bis(3-aminophenoxy) benzene (1,2,3-BAPB); and wherein each of the at least one other diamines is selected from the group consisting of: 2,2-trifluoromethylbenzidine (TFMB), 4,4-[1,4-phenylenebis(oxy)]bis[3-(trifluoromethyl]benzenamine (6FAPB), 2,2-bis-trifluoromethoxy-biphenyl-4,4-diamine (BTMBD), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (HFBAPP), 2,2-bis(4-aminophenyl)hexafluoropropane, 9,9-bis(4-amino-3-fluorophenyl)fluorene (FFDA), 1,4-cyclohexylenediamine (1,4-CHDA), 1,4-cyclohexanedimethanamine (1,4-CHDMA), 1,1-bis(4-aminophenyl)-cyclohexane, 4,4-diaminooctafluorobiphenyl.

2. The polyimide film of claim 1, wherein: the asymmetric dianhydride is 2,3,3,4-biphenyl dianhydride (a-BPDA); and the at least one other dianhydride is 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and, optionally, 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA); wherein 40-80 mol % of the total dianhydride is 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA).

3. The polyimide film of claim 2, wherein: the at least two diamines comprise 1,3-benzenediamine (m-PDA) and 2,2-trifluoromethylbenzidine (TFMB); wherein 20 to 50 mol % of the total diamine is 1,3-benzenediamine (m-PDA).

4. The polyimide film of claim 1, wherein: the at least two diamines comprise 1,3-benzenediamine (m-PDA) and 2,2-trifluoromethylbenzidine (TFMB); wherein 20 to 50 mol % of the total diamine is 1,3-benzenediamine (m-PDA).

5. The polyimide film of claim 2, wherein the diamine comprises 2,2-trifluoromethylbenzidine (TFMB).

6. The polyimide film of claim 1, wherein the diamine comprises 2,2-trifluoromethylbenzidine (TFMB).

7. The polyimide film of claim 1, wherein the molar ratio of dianhydride and diamine is from 0.981.05.

8. The polyimide film of claim 1, wherein: the film is characterized by all three of the following features: a transmittance at 550 nm of at least 85%; a birefringence of 0.005 or less; and a glass transition temperature of at least 300 C.

9. A method for producing the polyimide film of claim 1, comprising the following steps: preparing a polyamic acid solution by a condensation polymerization reaction of at least two dianhydrides and at least two diamines in at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), dimethylsulfoxide (DMSO), m-cresol, chloroform, terahydrofuran (THF), -butyrolactone, 3-methoxy-N,N-dimethylpropanamide; completing the imidization of the polyamic acid to obtain a polyamide film, using at least one of a thermal imidization and a chemical imidization method; removing the solvent from the polyimide film and fixing the polyimide film to a frame using steel pins; and curing the polyimide film at 80 C. to 400 C. for 30 to 120 minutes in a high temperature oven.

10. The method of claim 9, wherein: a catalyst, selected from the group consisting of: pyridine, methyl pyridines, quinoline, isoquinoline, 1-methyl imidazole, 1, 2-dimethyl imidazole and 2-methyl imidazole, is added to the polyamic acid solution; a dehydrating agent, selected from the group consisting of: acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, is added to the polyamic acid solution; the polyamic acid solution is cast on a glass plate; the imidization is completed in a high temperature oven.

11. The method of claim 9, wherein the polyimide film is heated at 200 to 400 C. for 2 to 60 mins after the curing process.

12. A substrate or cover window of a flexible organic light emitting diode (OLED) display or a flexible liquid crystal display (LCD), comprising a polyimide film of claim 1.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] Examples of the inventive concept are presented as described below. Nevertheless, the examples are only for elaborating the inventive concept and are not intended to limit the present invention thereto.

Example 1

[0042] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stir was added 245.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 23.52 g (0.08 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 5.88 g (0.02 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1200 poise.

[0043] The polyamic acid solution obtained above was cast on a glass plate and imidized by thermal method to provide a 50 m cured film. The glass plate with the wet polyamic acid film was heated at 100 C. for 15 mins to remove part of the solvent, and the semi-dried film was removed from the plate and restrained onto a steel pin frame. The film was then thermally imidized in the forced nitrogen oven at the following temperature, 150 C. for 30 mins, 250 C. for 30 mins, 300 C. for 30 mins, 350 C. for 20 mins. The film was removed from the steel frame and analyzed.

[0044] 100.00 g of polyamic acid solution obtained above was stirred with 1.28 g pyridine and 1.65 g acetic anhydride. Then the solution mixture was cast on a glass plate and imidized in an oven to remove part of the solvent. The semi-dried film was peeled off from the plate and constrained in a pin frame and heated in the forced nitrogen oven at following temperatures, 150 C. for 30 mins, 250 C. for 30 mins, 300 C. for 20 mins. The film was removed from the steel frame and analyzed.

[0045] The refractive indices along the principal directions, n(TE) and n(TM) were measured by Metricon Prism Coupler 2010 at 637.3 nm by detecting the appropriate polarization of the incident laser beam and by rotating the sample direction. The difference between the refractive index in TE and TM mode was regarded as in-plane/out-of-plane birefringence (n), which is calculated as n=n(TE)n(TM).

[0046] Transmittance, b*, yellow index and haze values were measured by x-rite UV-Vis Ci7800 spectrophotometric detector.

[0047] The glass transition temperature was measured by a TA Q20 instrument from 50 C.-400 C., at a ramp rate of 3 K/min. To remove the heat history, the second scan was done up to the T.sub.g of polyimide film.

Example 2

[0048] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stir was added to 245.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 17.64 g (0.06 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 11.76 g (0.04 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 800 poise.

[0049] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.27 g pyridine and 1.63 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 3

[0050] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 245.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 11.76 g (0.04 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 17.64 g (0.06 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 300 poise.

[0051] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.25 g pyridine and 1.62 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 4

[0052] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 245.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 5.88 g (0.02 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 23.52 g (0.08 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 100 poise.

[0053] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.24 g pyridine and 1.61 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 5

[0054] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 293.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 35.52 g (0.08 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 5.88 g (0.02 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1700 poise.

[0055] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.07 g pyridine and 1.38 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 6

[0056] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 281.60 g of solvent N,N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 26.64 g (0.06 mol) 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 11.76 g (0.04 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 900 poise.

[0057] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.11 g pyridine and 1.43 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 7

[0058] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 269.60 g of solvent N,N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 17.76 g (0.04 mol) 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 17.64 g (0.06 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 400 poise.

[0059] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.15 g pyridine and 1.37 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 8

[0060] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 257.60 g of solvent N,N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 8.88 g (0.02 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 23.52 g (0.08 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 100 poise.

[0061] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.19 g pyridine and 1.53 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 9

[0062] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 228.64 g of solvent N,N-dimethylacetamide followed by 25.60 g (0.08 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 2.16 g (0.02 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 23.52 g (0.08 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 5.88 g (0.02 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1700 poise.

[0063] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.37 g pyridine and 1.77 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 10

[0064] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 211.68 g of solvent N, N-dimethylacetamide followed by 19.20 g (0.06 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 4.32 g (0.04 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 17.64 g (0.06 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 11.76 g (0.04 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1600 poise.

[0065] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.46 g pyridine and 1.89 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 11

[0066] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stir was added to 203.20 g of solvent N, N-dimethylacetamide followed by 16.00 g (0.05 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 5.40 g (0.05 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 17.64 g (0.06 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 11.76 g (0.04 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 700 poise.

[0067] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.51 g pyridine and 1.95 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 12

[0068] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stir was added to 203.20 g of solvent N, N-dimethylacetamide followed by 16.00 g (0.05 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 5.40 g (0.05 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 5.88 g (0.02 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 23.52 g (0.08 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 300 poise.

[0069] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.49 g pyridine and 1.93 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 13

[0070] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 276.64 g of solvent N, N-dimethylacetamide followed by 25.60 g (0.08 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 2.16 g (0.02 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 35.52 g (0.08 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 5.88 g (0.02 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1900 poise.

[0071] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.13 g pyridine and 1.49 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 14

[0072] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 247.68 g of solvent N, N-dimethylacetamide followed by 19.20 g (0.06 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 4.32 g (0.04 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 26.64 g (0.06 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 11.76 g (0.04 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1300 poise.

[0073] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.25 g pyridine and 1.62 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 15

[0074] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 227.20 g of solvent N, N-dimethylacetamide followed by 16.00 g (0.05 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 5.40 g (0.05 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 17.76 g (0.04 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 17.64 g (0.06 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 600 poise.

[0075] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.25 g pyridine and 1.62 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Example 16

[0076] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 215.20 g of solvent N, N-dimethylacetamide followed by 16.00 g (0.05 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 5.40 g (0.05 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 8.88 g (0.02 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 23.52 g (0.08 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 200 poise.

[0077] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.41 g pyridine and 1.83 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Comparative Example 1

[0078] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 245.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 29.40 g (0.1 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) was added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1540 poise.

[0079] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.29 g pyridine and 1.66 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Comparative Example 2

[0080] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 305.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 44.40 g (0.1 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1200 poise.

[0081] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.03 g pyridine and 1.34 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Comparative Example 3

[0082] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 245.60 g of solvent N,N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 26.46 g (0.09 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) and 2.94 g (0.01 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1420 poise.

[0083] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.28 g pyridine and 1.65 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Comparative Example 4

[0084] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 299.60 g of solvent N, N-dimethylacetamide followed by 32.00 g (0.1 mol) of 2,2-trifluoromethylbenzidine (TFMB). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 39.96 g (0.09 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2.94 g (0.01 mol) 2,3,3,4-biphenyl tetracarboxylic dianhydride (a-BPDA) were added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1100 poise.

[0085] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.05 g pyridine and 1.36 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Comparative Example 5

[0086] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 211.68 g of solvent N, N-dimethylacetamide followed by 19.20 g (0.06 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 4.32 g (0.04 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 29.40 g (0.10 mol) 3,3,4,4-biphenyl tetracarboxylic dianhydride (BPDA) was added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 2130 poise.

[0087] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 1.49 g pyridine and 1.93 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Comparative Example 6

[0088] A 500 ml three neck round bottom flask fitted with a nitrogen inlet and mechanical stirrer was added to 318.72 g of solvent N, N-dimethylacetamide followed by 19.20 g (0.06 mol) of 2,2-trifluoromethylbenzidine (TFMB) and 4.32 g (0.04 mol) of 1,3-benzenediamine (m-PDA). The mixture was stirred at 50 C. to dissolve the diamines to get a clear solution. Then, 44.40 g (0.10 mol) 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was added slowly to react with diamine. The mixture was then stirred at an ice water bath for 15 hours, to get a polyamic acid solution with a viscosity of 1600 poise.

[0089] The polyamic acid solution obtained above was cast and imidized by thermal method and chemical method to make 50 um polyimide film. 0.98 g pyridine and 1.26 g acetic anhydride was added into the polyamic acid solution as a chemical conversion agent, the film casting and imidization procedure is the same as Example 1 describes. The obtained polyimide film was used to do a related test.

Test Results

[0090] The properties test results of examples are listed in Table.12, of comparative examples are listed in Table.3.

[0091] In the data below, the examples 1 to 8 suggest that the polyimide film comprising asymmetric dianhydride, and examples 9-16 suggest that polyimide film containing asymmetric dianhydride and meta-substituted diamine together all have low birefringence and high T.sub.g. However, the polyimide films obtained in comparative example 1 to 6, which don't comprise non-linear structure, like asymmetric dianhydride and meta-substituted diamine have a larger birefringence than films obtained in example 1 to 16. Consequently, the polyimide obtained in example 1 to 6 with a low birefringence and high T.sub.g can be applied in an electro-optic field such as flexible OLED and LCD displays.

TABLE-US-00001 TABLE 1 The properties of polyimide film in example 1~8 Number Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Chemical Dianhydride s-BPDA 8 6 4 2 structure 6FDA 8 6 4 2 a-BPDA 2 4 6 8 2 4 6 8 Diamine TFMB 10 10 10 10 10 10 10 10 m-PDA Thermal Thickness (m) 50 2 50 2 50 2 50 2 50 2 50 2 50 2 50 2 imidization Transmit- 400-700 nm 81.25 81.42 83.54 84.75 88.62 87.88 87.03 86.49 method tance (%) 550 nm 88.09 88.23 88.84 88.92 89.87 89.50 88.78 88.07 n 0.0043 0.0032 0.0016 0.0007 00042 0.0027 0.0018 0.0006 Rth (nm, @50 m) 215 160 80 35 210 135 90 30 Tg ( C.) 312 309 304 301 317 315 311 310 b* 4.05 3.82 3.70 2.60 2.42 2.66 3.31 3.58 Yellowness index 6.72 6.37 6.15 4.51 4.02 4.45 5.49 5.76 Haze (%) 0.02 0.00 0.04 0.03 0.02 0.00 0.06 0.05 Chemical Thickness (m) 50 2 50 2 50 2 50 2 50 2 50 2 50 2 50 2 imidization Transmit- 400-700 nm 81.72 82.35 82.67 85.69 88.76 88.56 87.59 86.74 method tance (%) 550 nm 88.23 88.78 89.01 89.27 90.03 89.87 89.16 88.35 n 0.0048 0.0039 0.0017 0.0009 0.0049 0.0034 0.0019 0.0008 Rth (nm, @50 m) 245 195 85 45 245 175 95 40 Tg ( C.) 316 312 306 304 321 319 313 312 b* 3.82 3.41 3.49 2.51 2.13 2.31 3.07 3.36 Yellowness index 6.26 5.64 5.83 4.22 3.50 3.87 5.08 5.57 Haze (%) 0.45 0.32 0.16 0.17 0.43 0.23 0.25 0.27

TABLE-US-00002 TABLE 2 The properties of polyimide film in example 9~16 Number Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Ex. 16 Chemical Dianhydride s-BPDA 8 6 4 2 structure 6FDA 8 6 4 2 a-BPDA 2 4 6 8 2 4 6 8 Diamine TFMB 8 6 5 5 8 6 5 5 m-PDA 2 4 5 5 2 4 5 5 Thermal Thickness (m) 50 2 50 2 50 2 50 2 50 2 50 2 50 2 50 2 imidzation Transmit- 400-700 nm 80.76 80.62 79.43 80.01 87.11 85.26 83.12 83.43 method tance (%) 550 nm 87.42 86.03 85.70 86.12 88.35 87.95 86.23 86.75 n 0.0041 0.0015 0.0006 0.0004 0.0033 0.0010 0.0004 0.0004 Rth (nm, @50 m) 205 75 30 20 165 50 20 20 Tg ( C.) 315 319 317 315 313 320 319 317 b* 8.6 9.56 10.32 10.11 3.62 6.00 9.26 9.43 Yellowness index 13.98 15.83 17.11 16.84 5.97 9.94 15.28 15.72 Haze (%) 0.18 0.05 0.14 0.09 0.00 0.03 0.02 0.04 Chemical Thickness (m) 50 2 50 2 50 2 50 2 50 2 50 2 50 2 50 2 imidization Transmit- 400-700 nm 81.69 80.87 80.24 80.32 87.32 85.41 83.50 83.84 method tance (%) 550 nm 87.47 86.35 87.12 86.57 88.92 88.04 86.92 86.98 n 0.0048 0.0031 0.0017 0.0008 0.0049 0.0025 0.0016 0.0008 Rth (nm, @50 m) 245 155 75 40 245 125 80 40 Tg ( C.) 317 330 323 319 313 322 320 318 b* 6.35 6.04 8.63 9.94 3.24 5.77 8.69 9.10 Yellowness index 10.37 9.89 14.21 16.20 5.41 9.58 14.34 15.01 Haze (%) 0.13 0.01 0.07 0.08 0.02 0.13 0.15 0.03

TABLE-US-00003 TABLE 3 The properties of polyimide film in comparative examples 1~6 Number Comp. 1 Comp. 2 Comp. 3 Comp. 4 Comp. 5 Comp. 6 Chemical Dianhydride s-BPDA 10 9 10 structure 6FDA 10 9 10 a-BPDA 1 1 Diamine TFMB 10 10 10 10 6 6 m-PDA p-PDA 4 4 Thermal Thickness (m) 50 2 50 2 50 2 50 2 50 2 50 2 imidzation Transmittance 400-700 nm 82.22 88.26 82.43 88.31 65.02 72.04 method (%) 550 nm 86.99 89.44 86.97 89.66 76.62 83.13 n 0.0440 0.0320 0.0230 0.0181 0.1014 0.1121 Rth (nm, @50 m) 2200 1600 1150 905 5205 5605 Tg ( C.) 332 337 327 341 358 353 b* 8.49 2.02 8.03 2.01 30.58 25.41 Yellowness index 14.57 3.30 13.87 3.27 47.56 40.39 Haze (%) 5.31 0.16 4.22 0.14 10.09 7.23 Chemical Thickness (m) 50 2 50 2 50 2 50 2 50 2 50 2 imidization Transmittance 400-700 nm 83.36 89.01 83.67 89.03 65.31 76.32 method (%) 550 nm 87.85 89.93 88.12 89.91 76.84 84.16 n 0.0461 0.0410 0.0270 0.0290 0.1087 0.1141 Rth (nm, @50 m) 2305 2050 1350 1450 5435 5705 Tg ( C.) 347 345 342 344 363 354 b* 4.30 1.71 4.13 1.80 27.64 21.79 Yellowness index 7.12 2.70 6.42 2.92 42.12 34.50 Haze (%) 0.71 0.26 0.57 0.09 8.34 6.12