阅读说明：本技术 一种无色透明、高模量聚酰亚胺薄膜及其制备方法 (Colorless transparent high-modulus polyimide film and preparation method thereof ) 是由 江艳艳 任茜 王振中 肖立国 于 2019-09-29 设计创作，主要内容包括：本发明提供一种聚酰亚胺前体溶液及一种由所述聚酰亚胺前体溶液制造的透明聚酰亚胺薄膜。所述聚酰亚胺前体溶液包括二胺、含有联苯结构的第一二酐、刚性脂环族结构的第二二酐、非脂环结构的第三二酐及有机溶剂。所述聚酰亚胺薄膜骨架结构中,至少包含一种联苯和刚性脂环族结构。该透明聚酰亚胺薄膜的模量可达4.5GPa以上,玻璃化转变温度(Tg)为370℃以上,黄度指数不超过3.0,可作为基材应用于薄膜晶体管(TFT)、触摸屏(TSP)和有机发光二极管(OLED)、柔性液晶显示器(LCD)等柔性显示领域或者其他领域盖板膜。(The invention provides a polyimide precursor solution and a transparent polyimide film manufactured from the polyimide precursor solution. The polyimide precursor solution comprises diamine, first dianhydride containing a biphenyl structure, second dianhydride containing a rigid alicyclic structure, third dianhydride containing a non-alicyclic structure and an organic solvent. The polyimide film skeleton structure at least comprises one biphenyl and a rigid alicyclic structure. The transparent polyimide film has the modulus of more than 4.5GPa, the glass transition temperature (Tg) of more than 370 ℃ and the yellowness index of not more than 3.0, and can be used as a substrate to be applied to flexible display fields such as Thin Film Transistors (TFT), Touch Screens (TSP), Organic Light Emitting Diodes (OLED), flexible Liquid Crystal Displays (LCD) and the like or cover plate films in other fields.)

1. A polyimide precursor solution obtained by polymerizing a diamine and a dianhydride in an organic solvent, wherein the dianhydride comprises a first dianhydride comprising a biphenyl structure, a second dianhydride comprising a rigid alicyclic structure and a third dianhydride comprising a non-alicyclic structure, and wherein the dianhydride is present in an amount of 100 mol% based on the total dianhydride,

the content of the first dianhydride containing a biphenyl structure is in the range of 10 to 80 mol%,

the second dianhydride comprising a rigid cycloaliphatic structure is present in an amount ranging from 10 to 80 mole%,

the content of the non-alicyclic structure third dianhydride is in the range of 10 to 80 mol%.

2. The polyimide precursor solution according to claim 1, wherein the diamine is one or more selected from the group consisting of 2,3,5, 6-tetrafluoro-1, 4-phenylenediamine, 2, 5-diaminobenzotrifluoride, 4 '-diaminooctafluorobiphenyl, and 2,2' -bis (trifluoromethyl) diaminobiphenyl.

3. The polyimide precursor solution according to claim 1, wherein the first dianhydride comprising a biphenyl structure is represented by the following formula (I):

in the above formula (I), R₁And R₂Each independently selected from hydrogen, halogen atom, nitro group, C_1-4Haloalkoxy, C_1-10Alkyl radical, C_1-10Haloalkyl and C_6-20An aryl group;

the rigid cycloaliphatic structural dianhydride is represented by the following formula (II):

ac in the chemical formula (II) is selected from any one of the following groups:

The non-alicyclic structure third dianhydride is selected from one or more of 4,4 '-hexafluoroisopropyl phthalic anhydride, 9-bis (phthalic anhydride) fluorene, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 4,4' - (4,4 '-isopropyl diphenoxy) bis (phthalic anhydride), 4,4' -oxydiphthalic anhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride and 3,3',4,4' -diphenyl sulfone tetracarboxylic dianhydride.

4. The polyimide precursor solution according to claim 1, wherein the organic solvent is one or more selected from the group consisting of N-methyl-2-pyrrolidone, dimethylacetamide, dimethylsulfoxide, dimethylformamide, m-cresol, diethylacetate, acetone, and γ -butyrolactone.

5. A colorless transparent polyimide film prepared from the polyimide precursor solution of claim 1.

6. The polyimide film according to claim 5, wherein the polyimide film has the following characteristics:

the yellowness index is not more than 3;

young modulus is above 4.5Gpa, tensile strength is not lower than 110 Mpa;

a glass transition temperature Tg of 370 ℃ or higher, and

the light transmittance at 550nm is not lower than 89%, and the haze is not more than 1%.

7. A method for preparing the polyimide film according to claim 5, wherein the method is selected from one or more of a thermal imidization method, a chemical imidization method, and a combination thereof.

8. The method according to claim 7, wherein the chemical imidization comprises the steps of:

(1) adding a catalyst and a dehydrating agent into the polyimide precursor solution of claim 1, and continuously stirring for 1-12 hours to obtain a mixed solution;

(2) pouring the mixed solution on a glass substrate, and drying to remove the solvent to obtain a precoating film;

(3) a transparent polyimide film was prepared with the precoat film.

9. The method according to claim 8, wherein the solvent removal in step (2) is performed by heating at 50-180 ℃ for 8-60 minutes.

10. The manufacturing method according to claim 8, wherein the step (3) of manufacturing the transparent polyimide film means directly reheating the pre-coated film at a high temperature.

11. The method according to claim 8, wherein the step (3) of preparing the transparent polyimide film comprises peeling the precoat film from the glass substrate, fixing the precoat film on a stainless steel frame, and heating the frame at a temperature ranging from 250 to 500 ℃ for 10 to 120 minutes.

12. The preparation method according to claim 8, wherein the catalyst of step (1) is selected from the group consisting of pyridine, isoquinoline compounds, quinolone compounds, imidazole compounds, benzimidazole compounds, and combinations thereof; the dehydrating agent is selected from acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, and combinations thereof.

13. Use of the colorless transparent polyimide film of claim 5 in the preparation of flexible display substrates and cover films.

Technical Field

The present invention provides a polyimide precursor solution and a colorless transparent, high glass transition temperature (Tg) and high tensile strength polyimide film having an enhanced modulus.

Background

In recent years, flexible displays have attracted attention in the field of portable electronics, such as smart phones, smart watches, and wearable flexible displays, due to their excellent overall performance. In display technology, a substrate is often used as a support for functional parts such as a Thin Film Transistor (TFT), a Touch Sensor Panel (TSP), and a cover plate for protecting a viewing screen and a display device. They have a crucial role in the overall performance and lifetime of the display device. The substrate and cover plate materials conventionally used for the manufacture of display devices such as OLED and LCD are mainly glass, but with the lightness, thinness, miniaturization, foldability and curling of displays, glass is gradually replaced by transparent plastic substrates. And the colorless transparent polyimide film has excellent thermomechanical performance and may be used as the most preferable material for the application field.

At present, the materials of the flexible substrate and the cover plate not only need to have the characteristics of good heat resistance, high transmittance and the like of common transparent polyimide, but also need to have high strength and higher modulus.

Yellow polyimide films having high modulus, high strength and high heat resistance have been reported more. These researchers have used aromatic diamines and dianhydrides having a rigid structure to produce polyimide films having a high modulus, and have also used a method of introducing an imidazole or oxazole type structure into a polyimide skeleton. However, due to the existence of the intramolecular aromatic compound structure, the electron transition is easy to occur between molecules or within molecules so as to form an electron transfer complex, so that the color of the film is amber yellow or dark brown. In addition, the film has low flexibility and poor bending resistance due to high rigidity of imidazole or oxazole ring, and is difficult to apply to the field of durable flexible display.

In general, transparent polyimide films having high modulus and excellent optical properties have been reported less frequently, and particularly have both high tensile strength and high heat resistance. In addition, it is not common to investigate the preparation of these colorless, transparent polyimide films or to further improve the mechanical, thermal and optical properties of the films.

U.S. published patent 2016/0237214A 1 reports a method of preparing a transparent polyimide film with improved modulus. By incorporating 10 mol% of 5-amino-2- (4-aminophenyl) benzoxazole (6ABO) in the polyimide backbone, the modulus of the polyimide film increased from 5.6GPa to 6.5GPa, but the Yellowness Index (YI) increased from 2.2 to 3.8, and the patent does not report the thermal properties of the film, making it difficult to assess whether the heat resistance requirements for flexible device fabrication are met.

Patent CN 108424540A, university of homo, discloses a transparent polyimide film, which can be prepared from 2,2' -bis (trifluoromethyl) biphenyldiamine (TFMB), 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) and other dianhydrides, and has better light transmittance. However, only thermal imidization is used, and imidization is accomplished by heating the polyamic acid solution under a low temperature process condition with a maximum temperature of not more than 270 ℃. In addition, when the imidization temperature exceeds 300 ℃, the film transmittance decreases.

U.S. published patent 2017/0342215A 1 provides a method by which transparent polyimide films having moduli in excess of 4.0GPa can be prepared. The polyimide film reported in this patent mainly comprises a structure of 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA) and 2,2 '-dimethyl-4, 4' -diaminobiphenyl (m-TD), and the film is imidized by using a base catalyst in an equivalent ratio of not more than 4 mol.

Chinese patent 108431086 a discloses a transparent polyimide film prepared by reacting a mixture of 2,2 '-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and CBDA with TFMB or a mixture of TFMB/4,4' -diamino sulfone (DDS). The polyimide film is prepared by heating at a maximum temperature of not more than 300 ℃ by a thermal imidization method, and has good low-birefringence optical properties, but the modulus of the film is not reported.

Chinese patent 105131286B discloses a transparent polyimide film with high Tg and low CTE prepared by thermal imidization. The polyimide is prepared by reacting p-phenylenediamine (p-PDA) with not more than 20 mole percent of 1, 3-dimethyl-1, 2,3, 4-cyclobutanetetracarboxylic dianhydride (MCBDA) and at least 80 mole percent of 3,3',4,4' -biphenyltetracarboxylic dianhydride (s-BPDA), but the maximum transmittance of these films is not more than 84% due to internal charge transfer interactions resulting from the high stack density of the aromatic diamine and dianhydride molecules, and it is highly likely to have a higher yellowness index.

Chinese patent 109651630a reports a method for preparing a transparent polyimide film by a full chemical imidization method. Calculated as polyimide repeat units, 1mol equivalent of catalyst and more than 3mol equivalents of dehydrating agent are mixed with the polymer. Wherein, acetic anhydride is used as a dehydrating agent, and picoline or isoquinoline is used as a catalyst. A colorless transparent polyimide film containing 12% of a fluorine atom structure (e.g., 4' - (4,4' -isopropyldiphenoxy) bis (phthalic anhydride) (BPADA)/TFMB, 2,2' -bis [4- (4-aminophenoxy) phenoxy ] Hexafluoropropane (HFBAPP)/TFMB) was prepared by a full chemical imidization method, and then the film had high flexibility but poor heat resistance compared to a polyimide having a rigid structure due to the flexible-O-bond contained in these monomers.

With the rapid development of flexible display technology, development of a transparent polyimide film having excellent thermal, mechanical and optical properties as a substrate material is urgently required. Many documents are reported about polyimide films having high modulus, high tensile strength, high heat resistance, excellent optical properties and preparation process, but all the strict requirements and related properties required for manufacturing and use in flexible display applications cannot be simultaneously achieved. The high modulus transparent polyimide film can improve the lifespan of a flexible display, and is particularly suitable for manufacturing a flexible assembly requiring high temperature processing, in which high heat resistance (350 ℃ or more) and dimensional stability of the film are required. Therefore, it is of great significance to develop transparent polyimide with good mechanical properties and heat resistance.

Disclosure of Invention

The polyimide precursor solution is prepared by polymerizing diamine and dianhydride in an organic solvent, wherein the dianhydride comprises first dianhydride containing a biphenyl structure, second dianhydride containing a rigid alicyclic structure and third dianhydride containing a non-alicyclic structure.

Wherein the first dianhydride containing a biphenyl structure is contained in an amount ranging from 10 to 80 mol% based on 100 mol% of the total dianhydrides;

the content of the second dianhydride comprising a rigid alicyclic structure ranges from 10 to 80 mol%;

the content of the non-alicyclic structure third dianhydride is in the range of 10 to 80 mol%.

Wherein the diamine may be selected from one or more of 2,3,5, 6-tetrafluoro-1, 4-phenylenediamine, 2, 5-diaminobenzotrifluoride, 4 '-diaminooctafluorobiphenyl, and 2,2' -bis (trifluoromethyl) diaminobiphenyl;

wherein the first dianhydride comprising a biphenyl structure is represented by the formula:

in the above chemical formula, R in the above chemical formula₁And R₂Each independently selected from hydrogen (-H), halogen atoms, such as-F, -Cl, -Br, -I nitro (-NO)₂)、C_1-4Haloalkoxy, C_1-10Alkyl radical, C_1-10Haloalkyl and C_6-20An aryl group;

a second dianhydride comprising a rigid cycloaliphatic structure is represented by the formula:

in the chemical formula, Ac can be selected from any one of the following groups:

and is

The non-alicyclic structure third dianhydride is selected from one or more of 4,4 '-hexafluoroisopropyl phthalic anhydride, 9-bis (phthalic anhydride) fluorene, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 4,4' - (4,4 '-isopropyl diphenoxy) bis (phthalic anhydride), 4,4' -oxydiphthalic anhydride, 3',4,4' -benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride and 3,3',4,4' -diphenyl sulfone tetracarboxylic dianhydride.

The organic solvent for the polymerization of diamine and dianhydride of the present invention may be one or more selected from cyclic ester solvents such as gamma-valerolactone, gamma-butyrolactone and α -methyl-gamma-butyrolactone, amide solvents such as N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide and dimethylsulfoxide, phenol solvents such as p-cresol and m-cresol, and other solvents such as sulfolane and acetophenone.

According to one embodiment, the organic solvent used in the present invention may be selected from one or more of N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), Dimethylformamide (DMF), m-cresol, diethyl acetate, acetone, or γ -butyrolactone.

According to one embodiment, the molar ratio of the total amount of diamine to the total amount of dianhydride is 1:0.95 to 1:1.2, preferably 1:0.98 to 1:1.05, and the polyimide precursor solution is prepared by reacting for 4 to 48 hours in a nitrogen or argon atmosphere at a reaction temperature of-20 ℃ to 60 ℃.

The polyimide precursor solution has a solid content of 10 to 35 wt%, preferably 15 to 30 wt%, relative to the total amount of the polyimide polymer and the solvent.

Another object of the present invention is to provide a polyimide film obtained from the polyimide precursor solution. The polyimide film provided by the invention has a yellowness index of less than 3.0, a haze of not more than 1.0%, an average light transmittance at 550nm of not less than 89%, and a glass transition temperature (Tg) of not less than 370 ℃. Further, it has a modulus of not less than 4.5GPa and a tensile strength of not less than 110 MPa.

Still another object of the present invention is to provide a method for preparing a polyimide film, which mainly comprises the steps of:

the polyimide precursor solution is subjected to thermal imidization, chemical imidization or other combined methods to prepare the polyimide film.

In the film preparation method of the present invention, the "thermal imidization method" means that a polyimide precursor solution is cast on a glass plate, and then imidization is completed in a high-temperature oven.

The chemical imidization method is that polyimide precursor solution is mixed with catalyst and dehydrating agent, and then poured on a glass plate, and then imidization is completed in a high-temperature oven.

The catalyst for chemical imidization of the invention can be one or more selected from pyridine, quinoline, isoquinoline compounds, quinolone compounds, imidazole compounds, benzimidazole compounds and the like. The dehydrating agent can be one or more selected from acetic anhydride, propionic anhydride, butyric anhydride and benzoic anhydride.

In addition, the polyimide precursor solution poured on glass or other base materials or the mixed solution of the polyimide precursor solution, a catalyst and a dehydrating agent is placed on an oven or a heating plate at the temperature of 50-180 ℃ for drying for 8-60 min to remove most of the solvent, then the mixture is continuously heated at the temperature of 250-500 ℃ for 10-120 min to finish imidization, or the mixture is peeled off from the glass plate after most of the solvent is removed and fixed on a stainless steel frame to be continuously heated to finish imidization, so that the polyimide film is prepared.

In general, a polyimide film is easily oxidized to yellow in a high-temperature imidization process, and heat treatment is generally performed in an inert gas atmosphere, such as a nitrogen or helium atmosphere, preferably a nitrogen atmosphere, in order to prevent oxidation.

The thickness of the polyimide film of the present invention is not particularly limited, but is preferably 5 to 250 μm, and more preferably 10 to 125 μm.

In the preparation method, the invention realizes the display of excellent optical, mechanical and thermal properties required by the application on the film by adopting a full-chemical imidization method. The colorless transparent polyimide film has the performances of high modulus, excellent optical performance, high tensile strength, high heat resistance and the like, the modulus can reach more than 4.5GPa, the glass transition temperature (Tg) is more than 370 ℃, the yellowness index does not exceed 3.0, and the colorless transparent polyimide film can be used as a TFT (thin film transistor), a TSP (TSP) substrate and a cover plate film in the fields of flexible display, cover plate application and the like.

Detailed Description

The present invention will be described in detail below with reference to examples and comparative examples, but the scope of the present invention is not limited to the following examples and comparative examples.