Colorless transparent polyimide film as well as preparation method and application thereof

Abstract

The preparation method comprises the following steps: firstly, synthesizing polyamide acid by adopting a monomer polymerization strategy, pouring the polyamide acid onto a glass plate, casting to form a film, demolding with deionized water, washing and drying to successfully prepare the colorless transparent polyimide film. Secondly, colorless transparent polyimide films with different proportions are prepared by regulating and controlling the monomer proportion, and the physical and chemical properties are analyzed. A novel molecular main chain is constructed by utilizing different groups of different monomers, the colorless transparent polyimide film is prepared, and the colorless transparent polyimide film has excellent optical performance, thermal performance, mechanical performance and the like, can be used on a flexible organic light-emitting diode substrate, is crucial to the development of a flexible display technology, and has wide application prospects. And meanwhile, the method has far-reaching significance on development of portable electronic products such as wearable equipment and smart phones in the future.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymer film material preparation, and more particularly, relates to a colorless transparent polyimide film and a preparation method and application thereof. BACKGROUND

[0002] At present, display technologies can be mainly divided into four types of LCD, OLED, Mini LED and Micro LED, among which LCD is the most mature technology with the lowest price, but has the disadvantages of slow response speed, high power consumption, etc. OLED is the most advanced display technology in the mainstream market, has the characteristics of long service life, wide color gamut, high brightness, pure color, etc., and can be made into high-end products suitable for flexible display screens due to its bending characteristics, and can be widely applied in electronic, industrial, medical and other fields. In recent years, especially in emerging application fields such as intelligent devices and automotive electronics, the demand for higher quality and larger area flexible display electronic products has grown significantly.

[0003] At present, CPI film has accounted for more than 90% of the consumption of colorless transparent polymer film. As the world's largest electronic consumer product production and consumption market, China maintains strong demand for CPI film. However, due to the lack of core technology patents of domestic CPI production enterprises, high-quality CPI film products are in short supply, which is difficult to support the huge market demand in China, and the situation of relying on imports is serious. This situation needs to be improved. Due to the small number of monomers used in the production of CPI film in China, and the suboptimal production process, it is often difficult to achieve the application requirements of a single indicator, and all indicators cannot be improved simultaneously. In addition, technical bottlenecks, process defects and unclear mechanisms have led to extremely low domestic production of CPI film, which has seriously hindered the development of the flexible display industry. The most difficult problem to overcome in CPI film is how to achieve high optical transparency and high temperature resistance without sacrificing mechanical properties and dielectric properties. SUMMARY

[0004] An object of the present application is to solve at least the above problems and / or defects, and to provide at least the advantages to be described later.

[0005] To achieve these objects and other advantages in accordance with the present application, a colorless transparent polyimide film is provided, which has the following structural formula: wherein m is in the range of 0-8, and n is in the range of 2-10.

[0006] Preferably, the thickness of the colorless transparent polyimide film is in the range of 20-30 microns.

[0007] A preparation method of a colorless transparent polyimide film includes the following steps: Step one, double [4- (3-aminophenoxy) phenyl] sulfone is added to the reaction vessel, and N, N-dimethylacetamide is added, stirring at room temperature; then 4, 4'- (hexafluoroisopropylidene) diphthalic anhydride and 2, 3, 3', 4'-biphenyl tetracarboxylic dianhydride are added, and the reaction is continued at room temperature; Step two, after the reaction in the above step is completed, a polyamic acid solution is obtained, the polyamic acid solution is poured onto a dry and clean glass plate to flow into a film, and then gradient heating is carried out in an oven to imidize to obtain a colorless transparent polyimide film; Step three, after the film is cooled to room temperature, it is soaked in deionized water for demolding, then washed with deionized water, dried, and a colorless transparent polyimide film is obtained.

[0008] Preferably, in the step one, the mass ratio of double [4- (3-aminophenoxy) phenyl] sulfone, 4, 4'- (hexafluoroisopropylidene) diphthalic anhydride, 2, 3, 3', 4'-biphenyl tetracarboxylic dianhydride and N, N-dimethylacetamide is 0.43g: 0.09 ~ 0.44g: 0 ~ 0.23g: 4.5ml.

[0009] Preferably, in the step two, the stirring time at room temperature is 0 ~ 1h, and the reaction time at room temperature is 24h.

[0010] Preferably, in the step two, a magnetic stirrer is added during stirring, and the rotating speed of the magnetic stirrer is 200 ~ 300 rmin -1 .

[0011] Preferably, in the step two, the gradient heating is respectively heating to 75 ~ 85℃, holding for 9 ~ 12h; heating to 105 ~ 115℃, holding for 1 ~ 2h; heating to 135 ~ 145℃, holding for 1 ~ 2h; heating to 165 ~ 175℃, holding for 1 ~ 2h; finally heating to 200 ~ 210℃, holding for 2 ~ 4h.

[0012] Preferably, in the step three, the soaking time in deionized water is 1 ~ 3h, the drying temperature in the oven is 70 ~ 90℃, and the drying time is 24h.

[0013] A colorless transparent polyimide film is applied as a substrate for a flexible organic light emitting diode.

[0014] The present application at least comprises the following beneficial effects: the present application adopts molecular structure design, monomer proportion regulation strategy, utilizes a dianhydride 2,3,3',4'-biphenyl tetracarboxylic dianhydride (a-BPDA) with a non-fair surface structure, a dianhydride 4,4'- (hexafluoroisopropylidene) diphthalic anhydride (6FDA) with a trifluoromethyl group, and a diamine bis[4- (3-aminophenoxy) phenyl] sulfone (m-BAPS) with a sulfone group and an ether bond, construct a new type of molecular structure, which is beneficial to the synthesis of colorless and transparent polyimide, can inhibit the CTC effect, thereby improving the transmittance of the film, and maintaining excellent thermal performance and mechanical performance, and can be efficiently applied to flexible organic light emitting diode substrate, thereby having better performance.

[0015] Other advantages, objects, and features of the present application will be apparent from the following specification, and will be understood by persons skilled in the art. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The synthesis route of the colorless and transparent polyimide film of the present application is shown in the figure; Figure 2 The infrared spectrum of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 is shown in the figure; Figure 3 The colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 is shown in the figure; 1 H-NMR spectrum; Figure 4 The mechanical strength and elongation at break of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 are shown in the figure; Figure 5 The transmittance of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 is shown in the figure; Figure 6 The thermal gravimetric (Td) of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 is shown in the figure; Figure 7 The glass transition temperature (Tg) of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 is shown in the figure; Figure 8 The coefficient of thermal expansion (CTE) of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 is shown in the figure; Figure 9 The actual photos of the colorless and transparent polyimide film of the present application examples 1~4, comparative example 1 are shown in the figure. DETAILED DESCRIPTION

[0017] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0018] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof. Example 1 like Figure 1 As shown, this embodiment provides a method for preparing colorless and transparent polyimide, including the following steps: Step 1: Add 0.43 g of bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) (1 mmol) to a 50 ml flask, and add 4.5 ml of N,N-dimethylacetamide (DMAc). Stir at room temperature. Then add 0.09 g of 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) (0.2 mmol) and 0.23 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (m-BPDA) (0.8 mmol). Continue the reaction at room temperature for 24 h. Step 2: After the reaction in the previous step is completed, a polyamic acid solution is obtained. The polyamic acid solution is then poured onto a dry and clean glass plate to be cast into a film. Subsequently, it is kept in an oven at 80°C for 10 hours, at 100°C for 1 hour, at 110°C for 1 hour, at 140°C for 1 hour, at 170°C for 1 hour, and at 200°C for 2 hours to imidize it, thereby obtaining a colorless and transparent polyimide film. Step 3: After the membrane cools to room temperature, immerse it in deionized water to demold it, then wash it with deionized water and place it in an oven to dry at 80°C for 24 hours.

[0019] The colorless and transparent polyimide film prepared in this embodiment is designated as CPI-2.

[0020] Example 2 This embodiment provides a method for preparing colorless and transparent polyimide, including the following steps: Step 1: Add 0.43 g of bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) (1 mmol) to a 50 ml flask, and add 4.5 ml of N,N-dimethylacetamide (DMAc). Stir at room temperature. Then add 0.17 g of 4,4′-(hexafluoroisopropene)phthalic anhydride (6FDA) (0.4 mmol) and 0.17 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (m-BPDA) (0.6 mmol). Continue the reaction at room temperature for 24 h. Step two: after the reaction in the above step is completed, a polyamic acid solution is obtained, and the polyamic acid solution is poured onto a dry and clean glass plate to flow into a film, and then the film is kept in an oven at 80°C for 10 h, at 100°C for 1 h, at 110°C for 1 h, at 140°C for 1 h, at 170°C for 1 h, and at 200°C for 2 h to imidize the film to obtain a colorless and transparent polyimide film; Step three: after the film is cooled to room temperature, the film is soaked in deionized water for demolding, and then washed with deionized water and placed in an oven for drying at 80°C for 24 h.

[0021] The colorless and transparent polyimide film prepared in this experiment is denoted as CPI-4.

[0022] Example 3 The present example provides a method for preparing a colorless and transparent polyimide, comprising the following steps: Step one: 0.43 g of bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) (1 mmol) is added to a 50 ml flask, and 4.5 ml of N,N-dimethylacetamide (DMAc) is added, and stirred at room temperature; then 0.26 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) (0.6 mmol) and 0.11 g of 2,3,3',4'-biphenyl tetracarboxylic dianhydride (m-BPDA) (0.4 mmol) are added, and the reaction is continued at room temperature for 24 h; Step two: after the reaction in the above step is completed, a polyamic acid solution is obtained, and the polyamic acid solution is poured onto a dry and clean glass plate to flow into a film, and then the film is kept in an oven at 80°C for 10 h, at 100°C for 1 h, at 110°C for 1 h, at 140°C for 1 h, at 170°C for 1 h, and at 200°C for 2 h to imidize the film to obtain a colorless and transparent polyimide film; Step three: after the film is cooled to room temperature, the film is soaked in deionized water for demolding, and then washed with deionized water and placed in an oven for drying at 80°C for 24 h.

[0023] The colorless and transparent polyimide film prepared in this experiment is denoted as CPI-6.

[0024] Example 4 The present example provides a method for preparing a colorless and transparent polyimide, comprising the following steps: Step one: 0.43 g of bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) (1 mmol) was added into a 50 ml flask, and 4.5 ml of N,N-dimethylacetamide (DMAc) was added, and stirred at room temperature; then 0.35 g of 4,4'- (hexafluoroisopropylidene) diphthalic anhydride (6FDA) (0.8 mmol) and 0.05 g of 2,3,3',4'-biphenyltetracarboxylic dianhydride (m-BPDA) (0.2 mmol) were added, and the reaction was continued at room temperature for 24 h; Step two: after the reaction in the above step was completed, a polyamic acid solution was obtained, and the polyamic acid solution was then cast into a film on a dry and clean glass plate, and then the film was kept in an oven at 80°C for 10 h, at 100°C for 1 h, at 110°C for 1 h, at 140°C for 1 h, at 170°C for 1 h, and at 200°C for 2 h to imidize the film to obtain a colorless and transparent polyimide film; Step three: after the film was cooled to room temperature, the film was soaked in deionized water for demolding, and then washed with deionized water, and then placed in an oven and dried at 80°C for 24 h.

[0025] The colorless and transparent polyimide film prepared in this experiment was denoted as CPI-8.

[0026] Comparative Example 1 This comparative example provides a method for preparing a colorless and transparent polyimide, comprising the following steps: Step one: 0.43 g of bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) (1 mmol) was added into a 50 ml flask, and 4.5 ml of N,N-dimethylacetamide (DMAc) was added, and stirred at room temperature; then 0.44 g of 4,4'- (hexafluoroisopropylidene) diphthalic anhydride (6FDA) (1 mmol) was added, and the reaction was continued at room temperature for 24 h Step two: after the reaction in the above step was completed, a polyamic acid solution was obtained, and the polyamic acid solution was then cast into a film on a dry and clean glass plate, and then the film was kept in an oven at 80°C for 10 h, at 100°C for 1 h, at 110°C for 1 h, at 140°C for 1 h, at 170°C for 1 h, and at 200°C for 2 h to imidize the film to obtain a colorless and transparent polyimide film; Step three: after the film was cooled to room temperature, the film was soaked in deionized water for demolding, and then washed with deionized water, and then placed in an oven and dried at 80°C for 24 h.

[0027] The colorless and transparent polyimide film prepared in this experiment was denoted as CPI-8.

[0028] Comparative Example 2 This comparative example comprises the following steps: Step 1: 0.43 g of bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) (1 mmol) was added into a 50 ml flask, and 4.5 ml of N,N-dimethylacetamide (DMAc) was added, and stirred at room temperature; then 0.29 g of 2,3,3',4'-biphenyl tetracarboxylic dianhydride (m-BPDA) (1 mmol) was added, and the reaction was continued at room temperature for 24 h; Step 2: The results show that the polymerization of bis[4-(3-aminophenoxy)phenyl]sulfone and 2,3,3',4'-biphenyl tetracarboxylic dianhydride cannot be achieved after the reaction, and a polyamic acid solution cannot be obtained, so a colorless and transparent polyimide film cannot be obtained.

[0029] The actual photos of the colorless and transparent polyimide films of Examples 1-4 and Comparative Example 1 are shown in Figure 9 .

[0030] The chemical structures of Examples 1-4 and Comparative Example 1 were characterized by Fourier transform attenuated total reflection infrared (ATR-FTIR) spectroscopy and nuclear magnetic resonance, Figure 2 The ATR-FTIR spectrum of the colorless and transparent polyimide film prepared for Examples 1-4 and Comparative Example 1 shows that the peaks at 1790 cm −1 and 1680 cm −1 can be attributed to the symmetric and asymmetric stretching vibrations of C=O in the imide ring. The characteristic absorption peak of C−F is at 1237 cm −1 and the characteristic absorption peak of S=O double bond is at 1149 cm −1 . The stretching vibration peaks of C-N in the imide ring are at 1368 cm −1 and 717 cm −1 , indicating the formation of polyimide and the successful preparation of CPI-X film. Figure 3 The 1 H-NMR spectrum of the colorless and transparent polyimide film shows that the peaks at 8.21 ppm (H1), 8.15 ppm (H3), and 8.05 ppm (H2) correspond to the protons in the aromatic ring of a-BPDA. The peaks at 7.91 ppm (H11, H12) and 7.70 ppm (H10) correspond to the protons in the aromatic ring of 6FDA, and the peaks at 7.55 ppm (H6), 7.32 ppm (H7, H8), 7.25 ppm (H4), and 7.19 ppm (H5, H9) correspond to the protons on the aromatic ring of m-BAPS, indicating that the polymer has been successfully synthesized and a transparent colorless polyimide film has been successfully prepared.

[0031] The physical and chemical properties of the transparent colorless polyimide films prepared in each example were tested by the following methods: (1) Mechanical properties The mechanical properties of the diaphragm can be tested using an electronic universal testing machine at room temperature, with a tensile rate of 10 mm / min. -1 The membrane was tested at least three times in the experiment, and the average value was taken. The formulas for calculating the maximum tensile strength (S) and elongation at break (E) of the membrane are as follows: in, S The maximum tensile strength of the membrane (MPa). F The maximum stress (N) at which the membrane breaks. d and L These represent the thickness (μm) and length (mm) at the center of the membrane, respectively. E This indicates the elongation at break of the membrane (%). L 'Indicates the absolute elongation (mm) at which the membrane breaks. The mechanical strength and elongation at break of the colorless transparent polyimide films prepared in Examples 1-4 and Comparative Example 1 are tested as follows: Figure 4 As shown, from Figure 4 It can be seen that CPI-X (X represents 2, 4, 6, 8, 10) have excellent mechanical properties and can meet the requirements of flexible display applications. The tensile strength and elongation at break of CPI-X are in the range of 57~95mPa and 5.8~7.3%, respectively. Among them, CPI-6 is better than the other four examples and far better than Comparative Example 1. This is attributed to the synergistic effect of a-BPDA and 6FDA. The large volume side groups of 6FDA provide appropriate non-coplanarity and toughening channels, while the rigid biphenyl of a-BPDA maintains the strength of the skeleton. The two work together to improve mechanical properties.

[0032] (2) Optical performance The optical properties of the film were tested using a UV spectrophotometer at wavelengths ranging from 190 to 800 nm, with the film thickness controlled at approximately 25 μm. The transmittance of the transparent colorless polyimide films from Examples 1-4 and Comparative Example 1 was obtained as follows: Figure 5 As shown, CPI-X exhibits excellent optical performance within the transmittance range of 68% to 86% at 450 nm, which can be attributed to the following three reasons: i) trifluoromethyl and sulfone groups have strong electron-withdrawing capabilities, resulting in reduced charge transfer; ii) the non-coplanar structure of α-BPDA and the large-volume side groups of 6FDA loosen the molecular structure and increase the free volume; iii) the optical performance of CPI-6 film is superior to other ratios because of the synergistic effect of α-BPDA and 6FDA. The appropriate amount of trifluoromethyl groups in 6FDA and α-BPDA work together to improve transmittance.

[0033] (3) Thermal properties The thermal stability of the film mainly includes thermal decomposition temperature, glass transition temperature and coefficient of thermal expansion. The test conditions of the thermogravimetric analyzer are as follows: nitrogen atmosphere, heating rate of 20℃ / min, and temperature range of room temperature-800℃. −1 The test conditions of the static thermal analyzer are as follows: nitrogen atmosphere, preloading force of 0.05 N, test temperature range of 50-350℃, and heating rate of 5℃ / min. −1 The test conditions of the dynamic thermal mechanical analyzer are as follows: double cantilever mode, test frequency of 1 Hz, heating rate of 10℃ / min, test temperature range of 30-450℃, and amplitude of 20μm. −1 The thermal gravimetric (Td), glass transition temperature (Tg) and coefficient of thermal expansion (CTE) of Examples 1-4 and Comparative Example 1 obtained by the test are shown in Figure 6 、 Figure 7 、 Figure 8 The Tg, Td5% (temperature at 5% weight loss) and CTE of CPI-X are 244.6-258.5℃, 460.8-494.1℃ and 68-88ppm / k, respectively, all of which have good thermal stability, due to the dense aromatic rings in the molecular structure, the biphenyl units form a π-π stacking network between the molecular chains, which can inhibit chain slipping and delay main chain rupture when the molecular chains vibrate violently at high temperature. CPI-6 has the best thermal performance, because the steric hindrance caused by the trifluoromethyl group provided by 6FDA can prevent the aromatic rings from being too tightly packed, avoiding stress concentration, and the thermal stability is improved by the cooperation of 6FDA and a-BPDA.

[0034] The number of devices and the scale of processing described herein are intended to be illustrative of the application. Applications, modifications and variations of the application will be apparent to those skilled in the art.

[0035] Although embodiments of the present application have been disclosed as above, it is not limited to the applications and embodiments listed in the specification and examples, and can be applied to various fields suitable for the present application, and additional modifications can be easily made by those skilled in the art, and therefore the present application is not limited to specific details and the figures shown and described herein, and the general concept defined by the claims and their equivalents.

Claims

1. A colorless and transparent polyimide film, characterized in that, The structural formula of the colorless and transparent polyimide film is: Where m ranges from 0 to 8, and n ranges from 2 to 10.

2. The colorless and transparent polyimide film as described in claim 1, characterized in that, The thickness of the colorless and transparent polyimide film is 20~30μm.

3. A method for preparing a colorless and transparent polyimide film as described in claim 1, characterized in that, Includes the following steps: Step 1: Add bis[4-(3-aminophenoxy)phenyl]sulfone to the reaction vessel, and add N,N-dimethylacetamide. Stir at room temperature. Then add 4,4′-(hexafluoroisopropene) phthalic anhydride and 2,3,3',4'-biphenyltetracarboxylic dianhydride. Continue the reaction at room temperature. Step 2: After the reaction in the previous step is completed, a polyamic acid solution is obtained. The polyamic acid solution is poured onto a dry and clean glass plate and cast into a film. Then, the film is subjected to gradient heating in an oven to imidize it and obtain a colorless and transparent polyimide film. Step 3: After the film cools to room temperature, immerse it in deionized water to demold it, then wash it with deionized water and dry it to obtain a colorless and transparent polyimide film.

4. The method for preparing the colorless and transparent polyimide film as described in claim 3, characterized in that, In step one, the mass ratio of bis[4-(3-aminophenoxy)phenyl]sulfone, 4,4′-(hexafluoroisopropene)phthalic anhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride and N,N-dimethylacetamide is 0.43g : 0.09~0.44g : 0~0.23g : 4.5ml.

5. The method for preparing the colorless and transparent polyimide film as described in claim 3, characterized in that, In step two, the stirring time at room temperature is 0-1 hour, and the reaction time at room temperature is 24 hours.

6. The method for preparing the colorless and transparent polyimide film as described in claim 3, characterized in that, In step two, a magnetic stir bar is added during the stirring process, and the magnetic stir bar rotates at a speed of 200-300 rpm. -1 .

7. The method for preparing the colorless and transparent polyimide film as described in claim 3, characterized in that, In step two, the gradient heating is as follows: heating to 75~85℃ and holding for 9~12h; heating to 100~115℃ and holding for 1~2h; heating to 135~145℃ and holding for 1~2h; heating to 165~175℃ and holding for 1~2h; and finally heating to 200~210℃ and holding for 2~4h.

8. The method for preparing the colorless and transparent polyimide film as described in claim 3, characterized in that, In step three, the soaking time in deionized water is 1-3 hours, the drying temperature in the oven is 70-90℃, and the drying time is 24 hours.

9. An application of the colorless and transparent polyimide film as described in claim 1, characterized in that, The colorless and transparent polyimide film is used as a substrate for flexible organic light-emitting diodes.

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