A colorless and transparent polyimide film and preparation method thereof

Abstract

The present invention relates to a colorless transparent polyimide film and a preparation method thereof. The preparation method of the colorless transparent polyimide film is as follows: dissolving and dispersing a diamine monomer in an organic solvent, then adding a dibasic anhydride monomer, and obtaining polyamic acid through a polycondensation reaction; performing an imidization reaction on the polyamic acid, a catalyst, and a dehydrating agent to obtain a polyimide; dissolving the polyimide in an organic solvent to prepare a solution, then casting it onto a support to form a film, and peeling it off from the support after pre-baking to obtain a polyimide wet film; drying and stretching the polyimide wet film to obtain the colorless transparent polyimide film. The colorless transparent polyimide film prepared by using the diamine and dibasic anhydride monomers of the present invention has excellent properties of good heat resistance, high strength, and high light transmittance, and can be used as a flexible substrate in optoelectronic devices.

Description

Technical Field

[0001] The invention belongs to the technical field of materials, and in particular relates to a colorless and transparent polyimide film and a preparation method thereof. Background Art

[0002] At present, flexible display technology is an important development direction in the field of flat panel displays. However, traditional display substrate inorganic transparent glass materials have been eliminated due to their heavy weight, fragility, and inability to bend. Transparent flexible polymer transparent engineering plastic materials such as polyethylene terephthalate (PET) cannot meet the high-temperature processing requirements of flexible substrates above 300°C due to their low heat resistance. Colorless transparent polyimide (CPI) film has excellent heat resistance, is easy to bend, and has good transparency, making it a must-have material in the field of optical displays.

[0003] Generally, in order to achieve high transparency of polyimide films, fluorine-containing monomers, alicyclic monomers, etc. are usually used to make polyimide. However, these transparent polyimide films usually have low modulus and strength, are not resistant to bending, and have a high thermal expansion coefficient. Although the polyimide films made using aromatic compounds have high modulus and strength, they have low transparency and high yellowness. Chinese patent CN118271659A discloses a colorless transparent polyimide film, a preparation method and an application thereof, wherein a diamine monomer is dissolved and dispersed in an organic solution; then a dianhydride monomer is added to react to obtain a uniform and viscous polyamic acid resin solution; the polyamic acid resin solution is defoamed, and then a film is cast onto a mirror steel belt through a die head to form a self-supporting film; the self-supporting film is passed through an imidization furnace, and longitudinally and transversely imidized, and then rolled up and slit to obtain a colorless transparent polyimide film; wherein the dianhydride monomer is at least one of 3,3',4,4'-biphenyltetracarboxylic dianhydride, bisphenol A diether dianhydride, pyromellitic dianhydride, hexafluoroisopropylphthalic anhydride and 3,3',4,4'-benzophenonetetracarboxylic dianhydride; and the structural formula of the diamine monomer is as follows. The polyimide film prepared by the method has a thickness of 50-55 μm, a tensile strength of 163-181 MPa, an elongation at break of 10%-15%, an elastic modulus of 4.7-5.1 GPa, a light transmittance of 87%-89%, a yellowness of 2-5, a Tg of 320-336°C, and a thermal expansion coefficient of 20-29 ppm / K. The tensile strength, elongation at break, thermal expansion coefficient and other properties of the polyimide film need to be further improved.

[0004]

[0005] Therefore, the current transparent polyimide is not satisfactory in the application field of flexible display. Summary of the invention

[0006] The purpose of the present invention is to provide a polyimide film with better light transmittance, higher strength and high yellowness, and to provide a preparation method for the film.

[0007] The polyimide film provided by the present invention is prepared by the following method:

[0008] Step 1: dissolving a diamine monomer in an organic solvent, then adding a dibasic anhydride monomer, and obtaining polyamic acid through a polycondensation reaction;

[0009] The structural formula of the diamine monomer is:

[0010] The structure of the dibasic anhydride monomer is:

[0011] Step 2: subjecting polyamic acid to imidization reaction with a catalyst and a dehydrating agent to obtain polyimide; the catalyst is selected from any one of pyridine, p-pyrroline, dimethylpyridine, collidine, and quinoline; the dehydrating agent is selected from any one of acetic anhydride, trifluoroacetic anhydride, and propionic anhydride;

[0012] Step 3: dissolving polyimide in an organic solvent to prepare a polyimide solution, casting the polyimide solution onto a support to form a film, and peeling the film from the support after pre-baking to obtain a polyimide wet film;

[0013] Step 4: Dry and stretch the polyimide wet film to obtain a colorless and transparent polyimide film.

[0014] In the above step 1, the molar ratio of the diamine monomer to the dibasic anhydride monomer is preferably 1:0.8-1.2.

[0015] In the above step 1, the polycondensation reaction is preferably carried out by stirring at room temperature for 3 to 8 hours.

[0016] In the above step 2, preferably, the molar ratio of the catalyst to the diamine monomer in step 1 is 1.3-1.7:1, and the molar ratio of the dehydrating agent to the diamine monomer in step 1 is 1.8-2.2:1.

[0017] In the above step 2, the imidization reaction is preferably carried out at 80 to 90° C. for 0.5 to 1 hour.

[0018] In the above step 3, the solid content of the polyimide solution is preferably 8 wt % to 15 wt %.

[0019] In the above steps 1 and 3, the organic solvent is selected from any one of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

[0020] In the above step 3, it is preferred to use a dryer to spray hot air at 90 to 110° C. for pre-drying.

[0021] In the above step 4, it is preferred to use a dryer to blow hot air at 110-150° C. to the surface of the polyimide wet film for drying for 15-30 minutes, then blow hot air at 180-220° C. to dry for 15-30 minutes, continue to blow hot air at 280-320° C. to dry for 15-30 minutes, and then use a tentering machine to stretch the wet film 1-1.5 times in the longitudinal and transverse directions at 140-160° C. to obtain a colorless and transparent polyimide film.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The present invention introduces diamine monomers and dibasic anhydride monomers with large volume steric hindrance containing electron-withdrawing groups into the polymer molecular chain; on the one hand, the selected monomers have large spatial volume steric hindrance, thereby reducing the conjugated unit, weakening the CTC effect within and between polymer chain molecules, and ensuring the transparency of the polyimide film; on the other hand, the selected monomers contain a trifluoromethyl (-CF3) structure, which is an electron-withdrawing group, which can reduce the CTC effect, thereby further improving the transparency of the polyimide film. At the same time, the selected diamine monomers and dibasic anhydride monomers also take into account the high modulus and high strength brought by aromatic compounds.

[0024] 2. The colorless and transparent polyimide film prepared from the diamine monomer and the dianhydride monomer used in the present invention has a simple preparation process and low cost, and also has excellent optical properties, mechanical properties and thermal stability, good heat resistance, high strength and high light transmittance, and can be used as a flexible substrate in optoelectronic devices. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0026] Example 1

[0027] Step 1: Under N2 protection environment, add 5.32g (10mmol) of diamine monomer (CAS: 2102351-80-2) and 85mL of dehydrated N,N-dimethylacetamide to the reactor, stir and dissolve completely, then add 6.28g (10mmol) of dibasic anhydride monomer (CAS: 61778-79-8), stir and react at room temperature for 12h after the addition is completed to obtain a polyamic acid solution.

[0028] Step 2: Under stirring conditions, add 1.19 g of pyridine (15 mmol) as an imidizing agent to the obtained polyamic acid solution, evenly disperse it for 24 hours, then add 2.04 g of acetic anhydride (20 mmol) as a dehydrating agent, stir again for 0.5 hours, heat to 85 ° C and stir for 0.5 hours, cool to room temperature, slowly add the reaction solution into 500 mL of methanol for precipitation, wash the precipitate three times with 75 ° C hot water, and then dry it at 100 ° C for 6 hours. After crushing, 9.32 g of solid powder is obtained, which is polyimide.

[0029] Step 3: dissolving the polyimide in step 2 into 100 mL of N,N-dimethylacetamide to obtain a polyimide solution with a solid content of 10 wt%; delivering the obtained polyimide solution to a casting die, casting it on a smooth steel belt to form a film, using a dryer to spray hot air at 100° C. for pre-baking, removing most of the N,N-dimethylacetamide, and then peeling off the polyimide wet film from the steel belt.

[0030] Step 4: Use a dryer to blow hot air at 130°C to the surface of the above-mentioned polyimide wet film for 20 minutes, then blow hot air at 200°C to dry it for 20 minutes, continue to blow hot air at 300°C to dry it for 30 minutes, and then use a tentering machine at 150°C to stretch the wet film 1.2 times longitudinally and transversely to obtain a colorless and transparent polyimide film with a thickness of 25 μm.

[0031] Example 2

[0032] Step 1: Under N2 protection environment, add 5.32g (10mmol) of diamine monomer (CAS: 2102351-80-2) and 95mL of dehydrated N,N-dimethylacetamide to the reactor, stir and dissolve completely, then add 7.54g (12mmol) of dianhydride monomer (CAS: 61778-79-8), stir and react at room temperature for 12h after the addition is completed to obtain a polyamic acid solution.

[0033] Step 2: This step is the same as step 2 of Example 1 to obtain polyimide.

[0034] Step 3: This step is the same as step 3 of Example 1 to obtain a polyimide wet film.

[0035] Step 4: This step is the same as step 4 of Example 1, and a colorless and transparent polyimide film with a thickness of 29 μm is obtained.

[0036] Example 3

[0037] Step 1: Under N2 protection environment, add 5.32g (10mmol) of diamine monomer (CAS: 2102351-80-2) and 75mL of dehydrated N,N-dimethylacetamide to the reactor, stir and dissolve completely, then add 5.03g (8mmol) of dianhydride monomer (CAS: 61778-79-8), stir and react at room temperature for 12h after the addition is completed to obtain a polyamic acid solution.

[0038] Step 2: In this step, pyridine in Example 1 is replaced by an equal molar amount of p-pyrroline, and the other steps are the same as Step 2 of Example 1 to obtain polyimide.

[0039] Step 3: This step is the same as step 3 of Example 1 to obtain a polyimide wet film.

[0040] Step 4: This step is the same as Step 4 of Example 1, and a colorless and transparent polyimide film with a thickness of 27 μm is obtained.

[0041] Example 4

[0042] Step 1: Under N2 protection environment, add 5.32g (10mmol) of diamine monomer (CAS: 2102351-80-2) and 75mL of dehydrated N,N-dimethylformamide to the reactor, stir and dissolve completely, then add 5.03g (8mmol) of dianhydride monomer (CAS: 61778-79-8), stir and react at room temperature for 12h after the addition is completed to obtain a polyamic acid solution.

[0043] Step 2: In this step, acetic anhydride in Example 1 is replaced by an equal molar amount of trifluoroacetic anhydride, and the other steps are the same as Step 2 of Example 1 to obtain polyimide.

[0044] Step 3: This step is the same as step 3 of Example 1 to obtain a polyimide wet film.

[0045] Step 4: This step is the same as step 4 of Example 1, and a colorless and transparent polyimide film with a thickness of 34 μm is obtained.

[0046] Example 5

[0047] Step 1: Under N2 protection environment, add 5.32g (10mmol) of diamine monomer (CAS: 2102351-80-2) and 75mL of dehydrated N-methylpyrrolidone into the reactor, stir and dissolve completely, then add 5.03g (8mmol) of dianhydride monomer (CAS: 61778-79-8), stir and react at room temperature for 12h after the addition is completed to obtain a polyamic acid solution.

[0048] Step 2: In this step, quinoline is used to replace the pyridine in Example 1 in equal moles, and the other steps are the same as Step 2 of Example 1 to obtain polyimide.

[0049] Step 3: This step is the same as step 3 of Example 1 to obtain a polyimide wet film.

[0050] Step 4: This step is the same as step 4 of Example 1, and a colorless and transparent polyimide film with a thickness of 34 μm is obtained.

[0051] Comparative Example 1

[0052] Step 1: Under N2 protection, add 1.08 g (10 mmol) of p-phenylenediamine monomer and 30 mL of dehydrated N,N-dimethylacetamide to the reactor, stir and dissolve completely, then add 2.94 g (10 mmol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride monomer, stir and react at room temperature for 12 hours after the addition is completed to obtain a polyamic acid solution.

[0053] Step 2: This step is the same as step 2 of Example 1 to obtain polyimide.

[0054] Step 3: This step is the same as step 3 of Example 1 to obtain a polyimide wet film.

[0055] Step 4: This step is the same as Step 4 of Example 1, and a colorless and transparent polyimide film with a thickness of 29 μm is obtained.

[0056] The colorless and transparent polyimide films prepared in Examples 1 to 5 and Comparative Example 1 were tested for performance, and the testing method was as follows:

[0057] (1) Thickness: Tested using a film thickness gauge.

[0058] (2) Tensile strength, elongation at break, and elastic modulus: The samples were made into tensile specimens using a microcomputer injection molding machine. With reference to the national standard GB / T1040-2006, a microcomputer-controlled electronic universal testing machine WDT-10 (Shenzhen Kaiqiang Experimental Instrument Co., Ltd.) was used. The tensile rate was 20 mm / min, and the tensile strength, elongation at break, and elastic modulus of the specimens were recorded.

[0059] (3) Transparency: Use an ultraviolet spectrophotometer to test the transmittance at 500 nm light.

[0060] (4) Yellowness: The yellowness index was measured using an ultraviolet spectrophotometer according to ASTM E313.

[0061] (5) Haze: The haze was measured using a haze meter according to ASTM D1003.

[0062] (6) Glass transition temperature (Tg): The glass transition temperature was measured using a dilatometer.

[0063] (7) Thermal expansion coefficient: The thermal expansion coefficient of the film is measured by laser method

[0064] The test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, the colorless and transparent polyimide film prepared by using the diamine monomer (CAS: 2102351-80-2) and the dibasic anhydride monomer (CAS: 61778-79-8) of the present invention has excellent properties of good heat resistance, high strength and high light transmittance, and can be used as a flexible substrate in optoelectronic devices.

Claims

1. A method for preparing a colorless and transparent polyimide film, characterized in that: The method comprises the following steps: Step 1: dissolving a diamine monomer in an organic solvent, then adding a dibasic anhydride monomer, and obtaining polyamic acid through a polycondensation reaction; Step 2: subjecting polyamic acid to imidization reaction with a catalyst and a dehydrating agent to obtain polyimide; the catalyst is selected from any one of pyridine, p-pyrroline, dimethylpyridine, collidine, and quinoline; the dehydrating agent is selected from any one of acetic anhydride, trifluoroacetic anhydride, and propionic anhydride; Step 3: dissolving polyimide in an organic solvent to prepare a polyimide solution, casting the polyimide solution onto a support to form a film, and peeling the film from the support after pre-baking to obtain a polyimide wet film; Step 4: drying and stretching the polyimide wet film to obtain a colorless and transparent polyimide film; The structural formula of the diamine monomer is: The structure of the dibasic anhydride monomer is:

2. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 1, the molar ratio of the diamine monomer to the dibasic anhydride monomer is 1:0.8-1.

2.

3. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 1, the polycondensation reaction is stirred at room temperature for 3 to 8 hours.

4. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 2, the molar ratio of the catalyst to the diamine monomer in step 1 is 1.3-1.7:1, and the molar ratio of the dehydrating agent to the diamine monomer in step 1 is 1.8-2.2:

1.

5. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 2, the imidization reaction is carried out at 80-90° C. for 0.5-1 hour.

6. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 3, the solid content of the polyimide solution is 8wt% to 15wt%.

7. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 1 and step 3, the organic solvent is selected from any one of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone.

8. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 3, pre-drying is performed by spraying hot air at 90 to 110° C. using a dryer.

9. The method for preparing a colorless and transparent polyimide film according to claim 1, characterized in that: In step 4, a dryer is used to blow hot air at 110-150° C. to the surface of the polyimide wet film for drying for 15-30 minutes, and then hot air at 180-220° C. is blown for drying for 15-30 minutes, and hot air at 280-320° C. is continued to be blown for drying for 15-30 minutes, and then the wet film is stretched 1-1.5 times in the longitudinal and transverse directions at 140-160° C. using a tentering machine to obtain a colorless and transparent polyimide film.

10. The colorless and transparent polyimide film obtained by the preparation method according to any one of claims 1 to 9.

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