A polyimide, a film containing the same, and a preparation method and application thereof

Abstract

The present invention belongs to the technical field of optical materials, and provides a polyimide, a film containing the same, and a preparation method and application thereof. The polyimide is prepared by reacting a dianhydride and a diamine; the dianhydride is an alicyclic dianhydride and / or an aromatic dianhydride; the polyimide obtained by copolymerizing the dianhydride and the diamine with special structures selected in the present invention and the film containing the same have a low coefficient of thermal expansion CTE, a low birefringence Δn, and a high glass transition temperature Tg, and have the characteristics of high temperature resistance, good light transmittance, high strength, etc.; and have wide applications in the preparation of flexible optical materials such as flexible solar substrates, flexible display materials or flexible wearable electronic materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical materials, and relates to a polyimide, a film containing the same, and a preparation method and application thereof. Background Art

[0002] Polyimide is a kind of polymer material that takes into account thermal properties, mechanical properties and insulating properties. With the rapid development of technologies such as flexible display, flexible electronic skin, flexible solar cell, wearable device, and optical fiber communication in the new energy, new display, and new technology fields, the optical properties of polyimide, including light transmittance, color, refractive index, birefringence, optical retardation, etc., have attracted attention and become key indicators for realizing the functions of optical devices.

[0003] Among the optical property indicators, birefringence is a property indicator reflecting the anisotropy of a material, which is the difference between the refractive indices in-plane and out-of-plane, and the optical retardation of a material is obtained by multiplying the birefringence by the thickness, reflecting the optical retardation degree of the material at a certain thickness. For the pancake-folded optical path design of VR devices, the birefringence effect of the material lens causes ghost images; in optical fibers, the birefringence phenomenon is the direct cause of image skew; for IPS panels, yellow light leakage often occurs when inappropriate birefringent materials are applied; and for the development of flexible solar cells, there is an urgent need for polymer materials that can replace glass to achieve flexibility, light weight, easy processing, etc. Compared with currently widely commercial rigid amorphous silicon solar cells, there are still obvious deficiencies in the improvement of the conversion efficiency of flexible solar cells. Different from isotropic glass substrates, plastic substrates basically exhibit large anisotropy and high birefringence due to the influence of structure, processing, etc.; in addition, due to the requirements of the structure design and processing technology of flexible solar cells, there are also high requirements for the thermal properties and processability of the substrate; ordinary PET and PEN materials cannot meet the performance requirements of flexible solar substrates, and polyimide materials have received wide attention due to their excellent comprehensive properties.

[0004] By designing the chemical structure of polyimide and reducing the charge transfer effect, the optical property requirements of transparency and colorlessness can be achieved. However, the benzene rings and imidization and other rigid structures contained in polyimide tend to be oriented in the plane. Especially, polyimide films are generally preformed or fully processed on the surface of the substrate, making them exhibit large anisotropy and birefringence, and processes such as stretching and imidization will all affect the magnitude of birefringence to a certain extent. Therefore, the design and preparation of low-birefringence polyimide films are key technical problems that need to be solved urgently.

[0005] Chinese invention patent application CN112759775A discloses the use of diamines such as 4,4'-bis(3-aminophenoxy)diphenyl sulfone (mBAPS), bicyclo[2.2.1]heptane dimethylamine (NBDA) and hexafluorodianhydride (6FDA) or bisphenol A diether dianhydride (BPADA) to react to obtain a polyimide precursor, adding an appropriate amount of acetic anhydride and 3-methylpyridine, and controlling the stretching process and baking temperature to exceed the Tg temperature by 20°C to achieve continuous production of a transparent polyimide film with a triaxial (xyz) refractive index standard deviation of less than 0.00120. However, according to reports, the Tg of the film is about 200-268°C.

[0006] Chinese invention patent application CN103987763A discloses a thermally stable low birefringence copolymer polyimide prepared from alicyclic dianhydride, aromatic cyclic diamine and aromatic diamine containing free carboxyl groups, the birefringence of the film is less than 0.001, and a multifunctional epoxide is added to the polymer to prepare a film resistant to NMP solvent, but the CTE of the film is about 48-61 ppm / K.

[0007] Chinese invention patent application CN113429785A discloses a polyimide containing alicyclic dianhydride, aromatic dianhydride and condensation of aromatic diacid chloride and aromatic diamine, with a birefringence of 0.008-0.021, but according to reports, the glass transition temperature Tg of the film is about 363-382°C.

[0008] Although the above technologies have achieved the low birefringence characteristics of polyimide, they also have defects such as high CTE, low glass transition temperature, poor solubility, and difficulty in processing and molding. Therefore, the process for improving the birefringence characteristics of polyimide still needs to be further developed. Summary of the invention

[0009] The present invention aims at solving the undesirable problems of birefringence, CTE, glass transition and the like of polyimide in the prior art, and provides a polyimide, a film containing the same, and a preparation method and application thereof, while achieving the characteristics of low coefficient of thermal expansion CTE, low birefringence, and high glass transition temperature Tg of the polyimide and its film, so that it has a wide range of applications in the field of flexible optical materials.

[0010] One of the technical solutions of the present invention is:

[0011] A polyimide is prepared from dianhydride and diamine, and the polyimide is prepared by the reaction of dianhydride and diamine.

[0012] The dianhydride is an alicyclic dianhydride and / or an aromatic dianhydride.

[0013] The alicyclic dianhydride is selected from structure A or structure B; the aromatic dianhydride is selected from the compounds in the general structural formula C, specifically as follows:

[0014]

[0015] Among them, in the general structural formula C, R1-R4 are independently selected from any one of -H, -F, and C1-C3 alkyl substituents.

[0016] Furthermore, the degree of polymerization of the polyimide ≤ 1000.

[0017] Preferably, the dianhydride is an aliphatic dianhydride and an aromatic dianhydride.

[0018] More preferably, the dianhydride is 5-95 wt.% of an alicyclic dianhydride and 5-95 wt.% of an aromatic dianhydride.

[0019] In some embodiments of the present invention, the dianhydride is any one of structural formula A, structural formula B, and structural formula C.

[0020] In some embodiments of the present invention, the dianhydride is structural formula A and structural formula C; preferably 5-95 wt.% of structural formula A and 5-95 wt.% of structural formula C.

[0021] In some embodiments of the present invention, the dianhydride is structural formula B and structural formula C; preferably 5-95 wt.% of structural formula B and 5-95 wt.% of structural formula C.

[0022] The diamine is selected from one or more of structural formula D, E, F, and G;

[0023]

[0024] Among them, R1-R6 are independently selected from any one of -H, -F, and C1-C3 alkyl substituents;

[0025] Preferably, it is one or more of 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(3-fluoro-4-aminophenyl)fluorene, 9,9-bis[4-(4-aminobenzamide)phenyl]fluorene, 9,9-bis[4-(4-aminophenyl ester)phenyl]fluorene, 2,2'-bis(trifluoromethyl)-4,4'-bis[4-(4-aminobenzamide)]biphenyl, and 2,2'-bis(trifluoromethyl)-4,4'-bis[4-(4-amino-5-methyl-benzamide)]biphenyl.

[0026] The structure is as follows:

[0027]

[0028] The second technical solution of the present invention lies in:

[0029] The preparation method of the above polyimide is provided, and the polyimide is obtained by dehydration and imidization after a prepolymerization reaction of a dianhydride and a diamine.

[0030] Further, the molar percentage of the dianhydride and the diamine is 0.9 - 1.1:1.

[0031] Further, the solvent for the prepolymerization reaction is selected from one or more of γ-butyrolactone, N-methylpyrrolidone (NMP), and γ-caprolactone; the boiling point of the solvent > 200 °C.

[0032] Further, the solvent for the imidization reaction is selected from toluene and / or xylene.

[0033] Further, the catalyst in the imidization process is selected from one or more of pyridine, isoquinoline, methylpyridine, quinoline, imidazole, methylimidazole, and triethylamine.

[0034] Further, the dosage of the catalyst is 0.1 - 20% of the total mass of the dianhydride and the diamine.

[0035] The third technical solution of the present invention lies in:

[0036] A polyimide film is provided, which is prepared from the above polyimide or the polyimide prepared by the above preparation method.

[0037] Further, the preparation method of the polyimide film is: dissolving the polyimide in a solvent, casting it on a substrate, and curing to obtain it.

[0038] Furthermore, the solvent for dissolution is a polar solvent, any one of N,N-dimethylacetamide, N,N-dimethylformamide, γ-butyrolactone, N-methylpyrrolidone, and γ-caprolactone.

[0039] Still further, the substrate is any one of stainless steel, glass, and silicon wafer.

[0040] The fourth technical solution of the present invention lies in:

[0041] An application of the above polyimide, the polyimide prepared by the above preparation method, or the above polyimide film in the preparation of flexible optical materials is provided.

[0042] The flexible material is a flexible solar substrate, a flexible display material, or a flexible wearable electronic material.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The polyimide of the present invention is prepared from aliphatic and / or aromatic dianhydrides, especially dianhydrides containing cycloalkane or fluorene structural units, and diamines containing fluorene and biphenyl structures, and has more excellent optical properties, low birefringence, low coefficient of thermal expansion (CTE), and high glass transition temperature (Tg). Its birefringence Δn is 0.0000 - 0.0097, the glass transition temperature Tg is 401 - 458 °C, and the coefficient of thermal expansion CTE is 21.05 - 55.56 ppm / K.

[0045] 2. The present invention further optimizes the selection of dianhydrides and diamines. The polyimide prepared by using mixed dianhydrides and / or mixed diamines further improves the coefficient of thermal expansion CTE and the glass transition temperature Tg, and reduces the birefringence Δn; or further reduces the birefringence Δn while maintaining comparable coefficient of thermal expansion CTE and glass transition temperature Tg.

[0046] 3. The polyimide film prepared by the present invention also has excellent mechanical properties, such as high tensile strength and large elongation at break.

[0047] 4. At the same time, the polyimide of the present invention has a light transmittance of 86.8 - 90.21% after being processed at 400 °C. It has the characteristics of high temperature resistance and high transparency, and has a wide range of applications in the preparation of flexible optical materials, such as flexible solar substrates, flexible display materials, or flexible wearable electronic materials. Detailed Embodiments

[0048] The following non - restrictive examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary illustration of the scope claimed by the present invention. Those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope claimed by the present invention.

[0049] The structures of the dianhydrides and diamines used in the examples and comparative examples of the present invention are as follows:

[0050]

[0051] Example 1

[0052] (1) Preparation of polyimide resin:

[0053] In a 1L flask equipped with a stirring device, nitrogen was introduced for protection. Then, 75 g of N,N-dimethylacetamide (DMAc), 285 g of γ-butyrolactone, and 104.532 g (0.3 mol) of FDA were charged. After stirring until FDA was dissolved, 64.47 g (0.301 mol) of ccHPMDA was added and stirred until the viscosity was stable to obtain a polyamic acid resin. Then, 2 g of triethylamine and 120 g of toluene were added, and the temperature was raised to 180 °C. Toluene was rapidly distilled off and all the water was carried out. Subsequently, toluene was distilled off, and the solution was poured into an ethanol / water solution (volume percentage 50%) to precipitate a polyimide resin product. Then, it was dried to remove the residual solvent to obtain a completely dry polyimide resin product.

[0054] (2) Preparation of polyimide film:

[0055] Weigh 10 g of the obtained completely dry polyimide resin product in a beaker, add it to 30 g of DMAc solvent, stir well until the resin is completely dissolved, and perform vacuum degassing. Use a spatula to evenly scrape and coat the resin on a PET film to a certain thickness, and pre-bake it at 80 °C for 1 hour to remove most of the solvent to obtain a pre-baked film. After peeling off the pre-baked film, fix it on a metal frame and gradually raise the temperature to complete curing to prepare a film with a thickness of about 25 μm. The highest curing temperature is 400 °C and the time is 1 hour.

[0056] Examples 2-19, Comparative Examples 1-5

[0057] The monomers and compositions used in the polyimide preparation process are shown in Table 1;

[0058] The polyimide preparation process is the same as that in Example 1.

[0059] Table 1 Monomers and Compositions for Synthesizing Polyimide in Each Example and Comparative Example

[0060] Group Monomer and Composition Example 1 cc-HPMDA:FDA = 100:100 Example 2 ct-HPMDA:FDA = 100:100 Example 3 cc-HPMDA:FFDA = 100:100 Example 4 ct-HPMDA:FFDA = 100:100 Example 5 cc-HPMDA:FDAADA = 100:100 Example 6 ct-HPMDA:FDAADA = 100:100 Example 7 cc-HPMDA:FDAADE = 100:100 Example 8 ct-HPMDA:FDAADE = 100:100 Example 9 cc-HPMDA:FDA:FDAADA = 100:95:5 Example 10 ct-HPMDA:FDA:FDAADE = 100:90:10 Example 11 FDAn:FDAADA = 100:100 Example 12 FDAn:ABTFMB = 100:100 Example 13 FDAn-MABTFMB = 100:100 Example 14 cc-HPMDA:FDAn:FDA = 90:10:100 Example 15 ct-HPMDA:FDAn:FFDA = 80:20:100 Example 16 cc-HPMDA:FDAn:FDAADA = 5:95:100 Example 17 ct-HPMDA:FDAn:FDAADE = 15:85:100 Example 18 cc-HPMDA:FDAn:ABTFMB = 30:70:100 Example 19 ct-HPMDA:FDAn:MABTFMB = 40:60:100 Comparative Example 1 cc-HPMDA:ct-HPMDA:AOFL = 50:50:100 Comparative Example 2 FDAn:HMDA = 100:100 Comparative Example 3 BPDA:FDAADA = 100:100 Comparative Example 4 CBDA:ABTFMB = 100:100 Comparative Example 5 PMDA:MABTFMB = 100:100

[0061] After using the method described in Example 1 to prepare the polyamic acid resin in Comparative Examples 3-5, it was impossible to complete imidization cyclization by the reflux dehydration method because the resin solubility was insufficient and the reaction process directly gel-precipitated. Therefore, the polyimide film preparation process was directly completed using the polyamic acid resin, but there was a film rupture phenomenon during the film preparation process, and the processing performance and various properties were inferior to those of Examples 1-19;

[0062] The performance detection methods for the polyimide and its film of the present invention are as follows:

[0063] (1) The light transmittance of the film was measured using a Hitachi U-3210 spectrophotometer, and the measurement range was 380 - 780 nm;

[0064] (2) The chromaticity b* and haze are obtained by testing with an X-rite Ci7800 color difference meter, with a D65 light source;

[0065] (3) The refractive index n is tested with a Metricon 2010 / M prism coupler, with a 632.8 nm light source. The birefringence (Δn) = |n TE - n TM |, and the optical retardation R in the thickness direction th = n * d, where d = 10 μm;

[0066] (4) The mechanical properties (tensile strength Ts, elongation at break Eb, and modulus of elasticity TM) are tested with a Shimadzu AG-X plus universal tensile electronic testing machine, with a sample size of 10 mm wide and a test speed of 100 mm / min;

[0067] (5) The glass transition temperature Tg is tested with a TA Instruments DMA800 dynamic thermomechanical analyzer, with a heating rate of 3 K / min;

[0068] (6) The coefficient of thermal expansion CTE is tested with a TA Instruments Q400 thermo-mechanical analyzer. The temperature range for the first heating is 50 - 250 °C, and the heating rate is 10 K / min;

[0069] (7) The solubility test method is to dissolve 1 g of polyimide resin in 9 g of different solvents at room temperature and stir for 24 h.

[0070] The optical property results of the polyimide films prepared in the examples and comparative examples of the present invention are shown in Table 2; the mechanical and thermal property results are shown in Table 3; the solubility is shown in Table 4;

[0071] Table 2 Optical Property Test Results

[0072]

[0073]

[0074] Table 3 Mechanical and Thermal Property Test Results

[0075]

[0076]

[0077] Table 4 Solubility of Polyimide

[0078]

[0079]

[0080] Note: "++" indicates complete dissolution, "+" indicates partial dissolution, and "-" indicates no dissolution.

[0081] As can be seen from Table 2-4, for the polyimide films prepared in Examples 1-19, △n is 0.0000 - 0.0097, Rth is 0 - 97 nm, Tg is 401 - 458 °C, and CTE is 21.05 - 55.56 ppm / K; while for the polyimide prepared in the comparative example, △n is 0.042 - 0.0877, Rth is 420 - 877 nm, Tg is below 390 °C, and CTE is 56 - 68 ppm / K; thus, it can be known that the polyimide film prepared by the present invention has the characteristics of low birefringence n, high glass transition temperature Tg, low coefficient of thermal expansion CTE, high temperature resistance, and high transparency.

[0082] In addition, the light transmittance of the polyimide films prepared in Examples 1-19 of the present invention after being processed at 400 °C is 86.8 - 90.21%, and they have good solubility in solvents such as NMP, DMAc, γ-butyrolactone, and THF, which is very beneficial for processing and forming, and can stably prepare a transparent film with high Tg, low CTE, high temperature resistance, and high transparency; the polyimide film prepared by the present invention also has excellent mechanical properties such as high tensile strength and large elongation at break.

[0083] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art does not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A polyimide, characterized in that, The polyimide is prepared by reacting a dianhydride and a diamine. The dianhydride is of structure A or structure B; the diamine is a combination of structure D and structure F, or a combination of structure D and structure G; wherein, R1-R6 are independently selected from any one of -H, -F, and C1-C3 alkyl substituents.

2. The polyimide according to claim 1, characterized in that, The diamine is 9,9-bis(4-aminophenyl)fluorene and 9,9-bis[4-(4-aminobenzamide)phenyl]fluorene, or 9,9-bis(4-aminophenyl)fluorene and 9,9-bis[4-(4-aminophenyl ester)phenyl]fluorene.

3. The method for preparing polyimide according to claim 1 or 2, characterized in that, The polyimide is obtained by generating a polyamic acid through a prepolymerization reaction of a dianhydride and a diamine, and then undergoing dehydration and imidization; the molar percentage of the dianhydride and the dianhydride is 0.9-1.1:

1.

4. The preparation method according to claim 3, characterized in that, The solvent for the prepolymerization reaction is selected from one or more of γ-butyrolactone, N-methylpyrrolidone (NMP), and γ-caprolactone; The solvent for the imidization reaction is selected from toluene and / or xylene.

5. The preparation method according to claim 3, wherein The catalyst used in the imidization process is selected from one or more of pyridine, isoquinoline, methylpyridine, quinoline, imidazole, methylimidazole, and triethylamine; the dosage of the catalyst is 0.1-20% of the total mass of the dianhydride and the diamine.

6. A polyimide film, characterized in that, It is prepared from the polyimide prepared by the polyimide described in claim 1 or 2 or the preparation method described in any one of claims 3-5.

7. The polyimide film according to claim 6, wherein The preparation method of the polyimide film is: dissolving the polyimide in a solvent, flowing it onto a substrate, and curing to obtain it.

8. The polyimide film according to claim 7, characterized in that, The solvent is a polar solvent and is selected from any one of N,N-dimethylacetamide, N,N-dimethylformamide, γ-butyrolactone, N-methylpyrrolidone, and γ-caprolactone.

9. Use of the polyimide according to claim 1 or 2, or the polyimide prepared by the preparation method according to any one of claims 3-5, or the polyimide film according to any one of claims 6-8 in the preparation of flexible optical materials, characterized in that, The flexible material is a flexible solar substrate, a flexible display material, or a flexible wearable electronic material.

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