A polyimide film, a method for preparing the same, and an application thereof

Abstract

The present application relates to a kind of polyimide film and its preparation method and application, mainly solve the optical transparency of polyimide film in prior art and the dimensional stability difficult to be compatible with the problem of difficulty.This colorless transparent polyimide film provided by the present application has excellent comprehensive performance, simple preparation method, wide raw material source, and has excellent application prospect in the field of flexible display, advanced microelectronics and the like.

Description

Technical Field

[0001] This invention belongs to the field of polymer films, and specifically relates to a polyimide film, its preparation method, and its application. Background Technology

[0002] In recent years, the rapid development of flexible display technology has spurred innovation in flexible substrate materials. As the supporting and protective component of flexible display devices, flexible substrates place high demands on material performance. Currently, the manufacturing process for large-size flexible display devices mainly relies on oxide-thin-film transistor (OTFT) bottom-emission technology. This process requires the substrate material to have a transmittance exceeding 80% in the visible light range and a glass transition temperature above 300℃. Simultaneously, the substrate material must possess excellent dimensional stability to prevent issues such as interlayer delamination and warping from threatening the device's operational stability. Transparent polymer films, due to their transparency, flexibility, and lightweight properties, have become the preferred material for flexible substrates. Among them, polyimide (PI) is one of the polymer materials with the best heat resistance and, thanks to its excellent comprehensive performance and the diversity and designability of its structure, has become one of the most promising flexible substrate materials. However, due to the traditional intra-chain / inter-chain charge transfer complex (CTC) effect, traditional polyimide exhibits a characteristic yellow color. Whether polyimide can be applied in bottom-emission flexible display devices hinges on whether it can simultaneously meet the requirements of high optical transparency and low coefficient of thermal expansion.

[0003] For polyimide films, optical transparency can be improved by introducing flexible ether bonds, aliphatic units, ester groups, bulky side groups, or blended nanoparticles into the molecular chain. However, the introduction of these structural units often fails to guarantee the dimensional stability of the film. For example, patent application CN 202011355207.2 discloses a method for preparing a colorless transparent polyimide film by introducing ester units and blending with glass powder. Its transparency in the visible light region can reach over 85%, but its coefficient of thermal expansion is higher than that of copper (~15ppm / ℃), failing to meet usage requirements. Patent application CN201210119407.7 discloses a method for preparing a colorless transparent polyimide film containing trifluoromethyl, biphenyl, and alicyclic units. Although the light transmittance (transmittance > 82%) is improved through the isolating effect of trifluoromethyl and the blocking effect of the alicyclic units, the film's heat resistance is poor (glass transition temperature T). g <300℃), poor dimensional stability (CTE=17-19ppm / ℃). Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a dimensionally stable colorless and transparent polyimide film, its preparation method and application, so as to overcome the problem that the transparency and dimensional stability of polyimide films are difficult to reconcile in the prior art.

[0005] A polyimide film according to the present invention is characterized in that the polyimide has the following general structural formula:

[0006]

[0007] Ar1 is one of the following structures:

[0008]

[0009] Ar2 is one of the following structures:

[0010]

[0011] The present invention discloses a polyimide film, wherein the polyimide is obtained by reaction using raw materials containing diamine monomer, dibenzoic acid monomer, and catalyst, and the synthesis reaction route is shown in the figure below:

[0012]

[0013] Ar1 is one of the following structures:

[0014]

[0015] Ar2 is one of the following structures:

[0016]

[0017] The diamine monomer used in the synthesis is:

[0018] At least one of them;

[0019] The dibenzoic acid monomer mentioned in the synthesis is

[0020] At least one of them.

[0021] A method for preparing a polyimide film according to the present invention includes:

[0022] (1) Mix diamine monomer, dibenzoic acid monomer, and aprotic polar solvent, and add catalyst, antioxidant and desiccant, react, purify, dry, and then dissolve in aprotic polar solvent. After degassing and filtration, a polyimide solution is obtained.

[0023] (2) The polyimide solution is cast into a film and biaxially stretched to obtain a polyimide film.

[0024] In step (1), the diamine monomer is

[0025] At least one of them;

[0026] The dibenzoic acid monomer is

[0027] At least one of them.

[0028] Preferably, in step (1), the molar ratio of diamine to dibenzoic acid is 1:(1-1.05), the mass fraction of reactants (diamine monomer and dibenzoic acid monomer) is 15-22 wt%, and the mass ratio of catalyst, antioxidant and desiccant is (5-8):(5-8):(3-1).

[0029] Preferably, in step (1), the catalyst is at least one of pyridine, isoquinoline, and triethylamine; the antioxidant is at least one of tris(2,4-di-tert-butylphenyl phosphite), triphenyl phosphite, and tris(2,4-di-tert-butylphenyl phosphite); the desiccant is anhydrous calcium chloride; and the aprotic polar solvent is at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP).

[0030] Preferably, the reaction in step (1) is carried out under nitrogen protection by heating to 120-150°C and refluxing for 10-12 hours; the purification is specifically carried out by cooling the reaction solution to room temperature and pouring it into water to precipitate polyimide, followed by filtration and repeated washing with deionized water; the drying is carried out under vacuum for 12-18 hours.

[0031] Preferably, the casting process in step (2) specifically involves: preparing a polyimide nascent film by casting and baking a polyimide solution;

[0032] Preferably, the bidirectional stretching in step (2) specifically involves the nascent membrane undergoing simultaneous longitudinal and transverse thermal stretching treatment.

[0033] Preferably, the residual solvent content in the polyimide nascent film is 5-9 wt%.

[0034] More preferably, the baking temperature is 60-80℃ and the baking time is 1-3 hours.

[0035] More preferably, the bidirectional thermal stretching temperature is 300-380℃, and the longitudinal and transverse stretching ratios are preferably 1.2 to 1.6.

[0036] The present invention relates to the application of the polyimide film in flexible displays or advanced microelectronics.

[0037] The polyimide of this invention contains biphenyl, amide, and choger base (or helical indole, tripterene) units in its main chain, while its side chains contain bulky trifluoromethyl groups. The aliphatic ring choger base (or helical indole, tripterene) units in the main chain effectively block the transfer of charge-transfer complexes (CTCs) within the chain, while the trifluoromethyl groups and rigidly twisted aliphatic ring units in the side chains help suppress close packing of the molecular chains and hinder the inter-chain CTC effect, thus forming a unique structure of "intra-chain blocking and inter-chain isolation" CTC effect, giving the film its colorless and transparent characteristics. Simultaneously, the rigid chain units such as biphenyl and amide in the main chain help reduce the coefficient of thermal expansion of the polyimide film, ensuring excellent dimensional stability.

[0038] The polyimide of this invention is mainly synthesized directly at high temperature by diamine and dibenzoic acid under the catalysis of a catalyst.

[0039] This invention involves molecular structure design and synthesis, as well as process control during thin film forming.

[0040] This invention achieves highly oriented molecular chains and synergistic improvement in the optical transparency and dimensional stability of polyimide films while suppressing the macromolecular CTC effect.

[0041] Beneficial effects

[0042] (1) The present invention contains biphenyl, amide, and choger base (or helical indole, tripterene) units on the main chain of the polyimide molecule, while the side chain contains a large trifluoromethyl group. The aliphatic ring choger base (or helical indole, tripterene) unit in the main chain is beneficial to blocking the transfer of charge transfer complexes (CTC) within the chain, while the trifluoromethyl group and rigidly twisted aliphatic ring unit in the side chain are beneficial to suppressing the close packing of molecular chains and hindering the CTC effect between molecular chains, thereby forming a unique structure of "intra-chain blocking and inter-chain isolation" CTC effect, giving the film the characteristics of being colorless and transparent.

[0043] (2) In this invention, the biphenyl unit is a rigid straight chain structure. At the same time, the amide unit and the imide ring carbonyl group are easy to form inter-chain hydrogen bonds, which are beneficial to reducing the thermal expansion coefficient of the film and improving the dimensional stability.

[0044] (3) In this invention, by controlling the content of residual solvent in the polyimide nascent film, it can play the role of plasticizer, which is beneficial to the biaxial stretching of the polyimide film and regulates the high orientation of the molecular chain.

[0045] (4) The colorless and transparent polyimide film provided by the present invention has excellent comprehensive performance, simple preparation method and wide source of raw materials, and has excellent application prospects in flexible display, advanced microelectronics and other fields. Attached Figure Description

[0046] Figure 1 The infrared spectra of the polyimides synthesized in Examples 1 and 2 are shown, with the peak value at 1780 cm⁻¹. -1 1720cm -1 The characteristic peak of the imide ring appears at 3100 cm⁻¹. -1 The presence of characteristic peaks for imide indicates that the product is consistent with the designed structure;

[0047] Figure 2 Photographs and UV transmittance curves of the colorless transparent polyimide films of Examples 1 and 3 are shown.

[0048] Figure 3 The CTE test curve of the colorless transparent polyimide film prepared in Example 1. Detailed Implementation

[0049] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0050] The thin film performance test conditions in the embodiments and comparative examples of this invention are as follows:

[0051] Glass transition temperature: Tested using a Q800 dynamic mechanical thermal analyzer from TA Instruments, USA, in the range of 50-450℃, with a heating rate of 5℃ / min and a scanning frequency of 1Hz.

[0052] UV-Vis testing: The test was performed using a Lambda 950 UV-Vis spectrophotometer from Perkin Elmer, USA, with a film thickness of 30 μm and a wavelength range of 250-800 nm.

[0053] CTE testing: Thermomechanical analyzer (Q400) from TA Instruments, USA, was used for testing. Rectangular strips of polyimide film, 4-5 mm wide, were fixed to a fixture. The test temperature was set to 50-400℃, and the preload force was set to 0.05 N. Nitrogen protection was used, with a nitrogen flow rate of 50 mL / min and a heating rate of 5℃ / min.

[0054] Example 1

[0055] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in NMP solvent at a molar ratio of 1:1 (choger base diamine: meta-trifluoromethyl diacid). Triethylamine, triphenyl phosphite, and calcium chloride were then added to the flask in a mass ratio of 8:8:1, with the reactant mass fraction controlled at 15 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the precipitate was poured into deionized water. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, degassed, and filtered to obtain a polyimide solution. Polyimide films were prepared using a casting method, baked at 60°C for 3 hours, and the residual NMP solvent content in the nascent film was controlled at 8 wt%. Finally, the nascent film was subjected to biaxial stretching at 350°C, with both longitudinal and transverse stretching ratios of 1.5 times, to ultimately prepare a colorless and transparent polyimide film.

[0056] Example 2

[0057] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in NMP solvent at a molar ratio of helical indole diamine: ortho-trifluoromethyl diacid = 1:1. Pyridine, triphenyl phosphite, and calcium chloride were then added to the flask, with a mass ratio of triethylamine, triphenyl phosphite, and calcium chloride of 5:8:1, controlling the reactant mass fraction to be 15 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction was continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the mixture was poured into deionized water to precipitate the reactants. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, and after degassing and filtration, a polyimide solution was obtained. Polyimide films were prepared using a casting method, baked at 60°C for 3 hours, and the residual NMP solvent content inside the nascent film was controlled to be 8 wt%. Finally, the nascent film was subjected to biaxial stretching at 350°C, with both longitudinal and transverse stretching ratios of 1.5 times, to ultimately prepare a colorless and transparent polyimide film.

[0058] Example 3

[0059] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in NMP solvent at a molar ratio of 1:1 (choger base diamine: meta-trifluoromethyl diacid). Triethylamine, triphenyl phosphite, and calcium chloride were then added to the flask in a mass ratio of 8:8:1, with the reactant mass fraction controlled at 15 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction was continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the mixture was poured into deionized water to precipitate the reactants. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, degassed, and filtered to obtain a polyimide solution. Polyimide films were prepared using a casting method and baked at 60°C for 3 hours, with the residual NMP solvent content in the nascent film controlled at 9 wt%. Finally, the nascent film was subjected to biaxial stretching at 380°C, with both longitudinal and transverse stretching ratios of 1.6 times, to ultimately prepare a colorless and transparent polyimide film.

[0060] Example 4

[0061] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in NMP solvent at a molar ratio of triphenylamine: meta-trifluoromethyl diacid = 1:1. Triethylamine, triphenyl phosphite, and calcium chloride were then added to the flask in a mass ratio of 8:8:3, with the reactant mass fraction controlled at 20 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction was continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the mixture was poured into deionized water to precipitate the reactants. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, and after degassing and filtration, a polyimide solution was obtained. Polyimide films were prepared using a casting method and baked at 60°C for 3 hours, with the residual NMP solvent content in the nascent film controlled at 9 wt%. Finally, the nascent film was subjected to biaxial stretching at 380°C, with both longitudinal and transverse stretching ratios of 1.6 times, to ultimately prepare a colorless and transparent polyimide film.

[0062] Example 5

[0063] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in DMAc solvent at a molar ratio of Choger base diamine: meta-trifluoromethyl diacid = 1:1. Isoquinoline, tris(2,4-di-tert-butylphenyl) phosphite, and calcium chloride were then added to the flask, with a mass ratio of triethylamine, tris(2,4-di-tert-butylphenyl) phosphite, and calcium chloride of 8:8:3, controlling the reactant mass fraction to 22 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction was continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the precipitate was poured into deionized water, causing precipitation. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, and after degassing and filtration, a polyimide solution was obtained. Polyimide films were prepared by casting and baked at 60°C for 3 hours, with the residual NMP solvent content inside the nascent film controlled at 9 wt%. Finally, the nascent film was subjected to biaxial stretching at 370°C, with both longitudinal and transverse stretching ratios of 1.6 times, to finally prepare a colorless and transparent polyimide film.

[0064] Comparative Example 1

[0065] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in NMP solvent at a molar ratio of m-phenylenediamine: m-imide diacid (molecular formula below) = 1:1. Then, triethylamine, triphenyl phosphite, and calcium chloride were added to the flask, with a mass ratio of 8:8:1, controlling the reactant mass fraction to be 15 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the mixture was poured into deionized water to precipitate the reactants. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, and after degassing and filtration, a polyimide solution was obtained. Polyimide films were prepared using a casting method, baked at 60°C for 3 hours, and the residual NMP solvent content inside the nascent film was controlled to be 8 wt%. Finally, the nascent film was subjected to biaxial stretching at 350°C, with both longitudinal and transverse stretching ratios of 1.5 times, to ultimately prepare a polyimide film.

[0066]

[0067] Comparative Example 2

[0068] Under nitrogen protection, in a three-necked flask, the diamine and diacid monomers were pre-dissolved in NMP solvent at a molar ratio of Choger base diamine: meta-trifluoromethyl diacid = 1:1. Triethylamine, triphenyl phosphite, and calcium chloride were then added to the flask in a mass ratio of 8:8:1, with the reactant mass fraction controlled at 15 wt%. The mixture was mechanically stirred under nitrogen protection until completely dissolved, and the reaction was continued for 3 hours. The reaction system temperature was raised to 120°C under nitrogen protection, and the reaction was carried out at this temperature for 10 hours. After cooling to room temperature, the precipitate was poured into deionized water. The precipitate was then filtered and repeatedly washed with deionized water, and finally dried in a vacuum drying oven for 12 hours. It was then redissolved in an aprotic polar solvent, and after degassing and filtration, a polyimide solution was obtained. Polyimide films were prepared using a casting method, and the films were baked at 60°C for 10 hours to completely remove residual NMP solvent.

[0069] Table 1 compares the performance of the colorless transparent polyimide film of the present invention with that of the prior art colorless transparent polyimide film, wherein the prior art PI fiber is the polyimide film obtained by Chinese patents with application numbers 202011355207.2 and 201210119407.7.

[0070] Table 1

[0071]

[0072]

[0073] Compared with Comparative Example 1, since the diacid monomers used in Examples 1-5 contain -CF3, their large-volume side groups are beneficial to weakening the CTC effect between molecular chains. Therefore, they have higher transparency in the visible light region and better optical transparency, while maintaining good heat resistance and dimensional stability.

[0074] Compared to Comparative Example 2, the membrane prepared in Example 1 exhibits a higher TL because the control of solvent residue in the nascent membrane in Example 1 allows for better biaxial stretching, under the same processing temperature conditions. g With lower CTE, the effect is significant.

Claims

1. A polyimide film characterized by comprising: The polyimide structure general formula is as follows: ； Ar1 is one of the following structures: ； Ar2 is one of the following structures: ； The polyimide is a raw material of a diamine monomer, a diphenic acid monomer and a catalyst, and is obtained by reaction; wherein the diamine monomer is one of the following: The diphenic acid monomer is one of the above.

2. A preparation method of the polyimide film of claim 1, comprising: (1) mixing the diamine monomer, the diphenic acid monomer and the aprotic polar solvent, adding the catalyst, the antioxidant and the water absorption agent, reacting, purifying, drying, then dissolving in the aprotic polar solvent, and deaerating and filtering to obtain a polyimide solution; (2) casting and forming a film of the polyimide solution, and bidirectional stretching to obtain the polyimide film.

3. The preparation method according to claim 2, characterized in that, The diamine monomer in step (1) is one of the following compounds; The diphenic acid monomer is one of the group consisting of 4. The preparation method according to claim 2, characterized in that, In step (1), the molar ratio of the diamine to the diphenic acid is 1: (1-1.05), and the mass fraction of the reactants is 15-22 wt%; the mass ratio of the catalyst, the antioxidant and the water absorption agent is (5-8):(5-8):(3-1).

5. The preparation method according to claim 2, characterized in that, In step (1), the catalyst is at least one of pyridine, isoquinoline and triethylamine; the antioxidant is at least one of tris (2, 4-di-tert-butylphenyl) phosphite, triphenyl phosphite and tris (2, 4-di-tert-butylphenyl) phosphite; the water absorption agent is anhydrous calcium chloride; and the aprotic polar solvent is at least one of N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone.

6. The preparation method according to claim 2, characterized in that, In step (1), the reaction is carried out under nitrogen protection, and the temperature is raised to 120-150℃ and refluxed for 10-12 h; the purification is specifically as follows: the reaction liquid is cooled to room temperature, and then poured into water to precipitate the polyimide, followed by filtration and repeated washing with deionized water; and the drying is vacuum drying for 12-18 h.

7. The preparation method according to claim 2, characterized in that, In step (2), the film casting is specifically as follows: the polyimide solution is cast and baked to prepare a polyimide nascent film; In step (2), the bidirectional stretching is specifically as follows: the nascent film is subjected to synchronous longitudinal and transverse hot stretching.

8. The preparation method according to claim 7, characterized in that, The residual solvent content in the polyimide nascent film is 5-9 wt%; the baking is at 60-80℃ for 1-3 h; The bidirectional stretching temperature is 300-380℃, and the longitudinal and transverse stretching multiples are 1.2-1.

6.

9. The polyimide film of claim 1 in the field of flexible display or microelectronics.

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