阅读说明：本技术 一种高尺寸稳定和力学强度的无色透明聚酰亚胺膜及其制备方法 (Colorless transparent polyimide film with high dimensional stability and mechanical strength and preparation method thereof ) 是由 金亚东 王雄伟 宋明雄 朱正平 于 2020-12-23 设计创作，主要内容包括：本发明属于聚酰亚胺薄膜技术领域,具体涉及一种具有高尺寸稳定和力学强度的无色透明聚酰膜的制备方法。该方法包括如下步骤：1)将合成的无色透明聚酰亚胺均匀浆料定量输送至狭缝式涂头上,通过狭缝涂布头将聚酰亚胺浆料涂布于支撑膜上；2)然后以3-8m/min的机速依次通过低温段烘箱各区T-1-T-3,除去85%以上的溶剂,其中T-1温度为40-80℃、T-2温度为90-110℃、T-3温度为120-150℃；3)然后从支撑膜上剥离进入高温段烘箱区进行热处理,热处理温度T-4为270-310℃；4)最后冷却、收卷。该方法通过低温和高温两个烘烤制程的搭配来提高无色透明聚酰亚胺膜的尺寸稳定性和力学性能。(The invention belongs to the technical field of polyimide films, and particularly relates to a preparation method of a colorless transparent polyimide film with high dimensional stability and mechanical strength. The method comprises the following steps: 1) quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head, and coating the polyimide slurry on a support membrane through the slit coating head; 2) then sequentially passes through all zones T of the low-temperature section drying oven at the machine speed of 3-8m/min 1 ‑T 3 Removing more than 85% of the solvent, wherein T 1 The temperature is 40-80 ℃ and T 2 The temperature is 90-110 ℃ and T 3 The temperature is 120-150 ℃; 3) then peeling off the support film and entering a high-temperature section oven area for heat treatment at a heat treatment temperature T 4 310 ℃ at the temperature of 270 ℃; 4) and finally, cooling and rolling. The method improves the dimensional stability of the colorless transparent polyimide film by matching the two baking processes of low temperature and high temperatureMechanical properties.)

1. A method for preparing a colorless transparent polyimide film, which is characterized by comprising the following steps:

1) quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head, and coating the polyimide slurry on a support membrane through the slit coating head;

2) sequentially passes through all the zones T of the low-temperature section drying oven at the machine speed of 3-8m/min₁-T₃Wherein T is₁The temperature is 40-80 ℃ and T₂The temperature is 90-110 ℃ and T₃The temperature is 120-150 ℃, and the total drying time of the low-temperature drying box section is 6-12 min;

3) stripping from the support film and entering a high-temperature section oven area for heat treatment at a heat treatment temperature T₄At the temperature of 270-;

4) and (6) cooling and rolling.

2. The production method according to claim 1, wherein the thickness of the colorless transparent polyimide film is 10 to 50 μm.

3. The method according to claim 1, wherein the temperature rise interval comprises two temperature rise intervals, i.e., a low temperature interval and a high temperature interval, and T of the low temperature interval₁At 60-80 deg.C, T₂At a temperature of 90-100 ℃ and T₃130 ℃ and 140 ℃, and the heat treatment temperature T of the high-temperature section₄Is 280-300 ℃.

4. The method of claim 1, wherein T is₁Drying at a temperature of 1-3min, T₂Drying at a temperature of 2-4min, T₃Drying at temperature for 3-5 min.

5. The production method according to claim 1, wherein the support film is a PET film, a PET release film, a PI release film, or a PTFE film.

6. The production method according to claim 5, wherein the thickness of the support membrane is 30 to 180 μm.

7. The method according to claim 1, wherein the colorless transparent polyimide paste has a solid content of 5 to 18 wt%.

8. The method according to claim 1, wherein the solvent of the colorless transparent polyimide paste is one or more selected from the group consisting of N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide and propylene glycol methyl ether acetate.

9. The method according to claim 1, wherein the solvent of the colorless transparent polyimide paste is N, N-dimethylacetamide or propylene glycol methyl ether acetate.

10. The colorless transparent polyimide film prepared by the method according to any one of claims 1 to 9, wherein the colorless transparent polyimide film has a transmittance at full wavelength of 90 to 92%, a yellow index of 1.4 to 1.8, a tensile strength of 130 and 160MPa, and a coefficient of thermal expansion of 20 to 30ppm/° C.

Technical Field

The application belongs to the technical field of polyimide films, and particularly relates to a preparation method of a colorless transparent polyimide film with high dimensional stability and mechanical strength.

Background

In recent years, flexible displays represented by foldable handsets have exhibited a rapidly growing situation and great market potential. The flexible display technology core is a flexible OLED display panel which is manufactured based on a polymer flexible substrate and consists of a substrate, a TFT layer, a light emitting layer, a blocking layer, a circular polarizer, a touch layer and a cover plate. The flexible and bendable characteristic requires that the display unit needs to be flexible, other functional layers including the TFT substrate, the touch unit and the cover plate also need to be flexible, and the colorless transparent polyimide film is a key supporting material for realizing the flexible and bendable screen. The main application scenes of the flexible and bendable AMOLED panel are a touch conductive base film and a cover plate base film. In addition, the colorless transparent polyimide film has a great application potential in flexible solar cells and wearable electronic equipment in the future.

Compared with yellow polyimide films, colorless transparent polyimide films have extremely high added value due to the characteristics of high light transmittance and low chroma. The steel belt casting method is the main method for producing colorless and transparent polyimide film at present, and comprises the procedures of casting, drying, double-drawing, imidization, rolling and the like, but the equipment is expensive, the monomer investment is 4-5 hundred million, and the process requirement is very high to achieve the optical grade effect. Considering that the colorless transparent polyimide film has relatively lower requirements on mechanical strength compared with an electronic grade yellow polyimide film, and is mainly prepared by a chemical imidization method, the requirements on high-temperature processing and biaxial stretching are relatively lower. Therefore, by reasonably improving the traditional coating equipment and matching with a proper slurry formula and a support film, the production of the optical-grade transparent polyimide film by a precise coating technology is expected to be realized. More importantly, the precision coating equipment has the advantages of low investment and easier control compared with steel strip casting equipment. The patent publication CN201810207427.7 reports that a non-silicon PET release film with the thickness of 25-50 μm is used for producing an ultrathin polyimide film by an auxiliary coating method, but the process is mainly used for producing black polyimide with the thickness of 6-8 μm, and according to experience, the PET release film with the thickness of 25-50 μm is easy to warp and deform at a high-temperature process with the temperature of more than 120 ℃, and the appearance of the obtained PI film is seriously influenced. In addition, the patent publication CN201811140409.8 reports a method for preparing a transparent polyimide film by using a 188 μm PET release film assisted coating method, but only a low-temperature baking process of drying at 80-160 ℃ for 5-15min easily results in more residual stress inside the film and poorer dimensional thermal stability, and meanwhile, the residual amount of solvent in the film is relatively higher, thereby losing the mechanical properties of the film. Therefore, the research on a novel coating process to realize the colorless transparent polyimide film with excellent comprehensive properties such as high transparency, high dimensional stability, high mechanical strength and the like has a general significance.

Disclosure of Invention

Aiming at the defects of the prior art, the application provides a preparation method of a colorless transparent polyimide film, and the method can volatilize a solvent at a relatively stable speed through gradient temperature rise in a low-temperature section, gradually solidify to form a film, and keep the appearance of the film smooth, good light transmittance and low haze; the heat treatment of the high-temperature section can play a role in deep imidization and further removing residual solvent, and meanwhile, when the heat treatment temperature reaches the vicinity of the glass transition temperature of the film, the movement rearrangement of the chain segments can release the stress in the film, thereby playing a role in heat setting. Finally, the prepared colorless transparent polyimide film has high light transmittance, high dimensional thermal stability and high mechanical property due to the reasonable matching of the gradient temperature rise in the low-temperature section and the heat treatment in the high-temperature section.

In order to achieve the above object, the present application adopts the following technical solutions:

a method for preparing a colorless transparent polyimide film, comprising the steps of:

1) quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head, and coating the polyimide slurry on a support membrane through the slit coating head;

2) sequentially passes through all the zones T of the low-temperature section drying oven at the machine speed of 3-8m/min₁-T₃Wherein T is₁The temperature is 40-80 ℃ and T₂The temperature is 90-110 ℃ and T₃The temperature is 120-150 ℃, and the total drying time of the low-temperature drying box section is 6-12 min;

3) stripping from the support film and entering a high-temperature section oven area for heat treatment at a heat treatment temperature T₄At the temperature of 270-;

4) and (6) cooling and rolling.

Preferably, the colorless transparent polyimide film can be produced by a thermal imidization method or a chemical imidization method, and a chemical imidization method is more preferred. Preferably, the thickness of the colorless transparent polyimide film is 10-50 μm.

Preferably, the temperature rise device comprises a low-temperature section and a high-temperature section, wherein T of the low-temperature section is₁At 60-80 deg.C, T₂At a temperature of 90-100 ℃ and T₃130 ℃ and 140 ℃, and the heat treatment temperature T of the high-temperature section₄Is 280-300 ℃.

Preferably, the total drying time of the low-temperature oven section is 6-12min, the heat treatment time of the high-temperature oven section is 5-10min, and the preferable time is 5-8min

Preferably, T is₁Drying at a temperature of 1-3min, preferably 1-2min, T₂Drying at a temperature of 2-4min, preferably 2-3min, T₃Drying at temperature for 3-5 min.

Preferably, the support film is a PET film, a PET release film, a PI release film or a PTFE film.

Preferably, the thickness of the support film is 30 to 180 μm. The width can be adjusted according to actual production requirements, and the final result of the application is not influenced.

Preferably, the colorless transparent polyimide paste has a solid content of 5 to 18 wt%. And more preferably 10-18%, too low solid content makes the thickness uniformity of the film difficult to control, while too high solid content can block the coating head, resulting in uneven coating.

Preferably, the solvent of the colorless transparent polyimide paste is one of N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, or propylene glycol methyl ether acetate, and N, N-dimethylacetamide and propylene glycol methyl ether acetate are preferred.

Further, the application also discloses the colorless transparent polyimide film prepared by the method, wherein the transmittance of the colorless transparent polyimide film at full wavelength is 90-92%, the yellow index is 1.4-1.8, the tensile strength is 130-160MPa, and the thermal expansion coefficient is 20-30 ppm/DEG C.

The technical scheme that this application provided has following beneficial effect: the colorless transparent polyimide film is prepared by adopting a precise coating method, so that the equipment cost can be obviously reduced; and further, the colorless transparent polyimide film prepared by reasonably matching the gradient temperature rise of the low-temperature section and the high-temperature heat treatment has high light transmittance, dimensional stability and mechanical strength, and meanwhile, the preparation method is simple in production process, low in overall production cost and wide in application prospect.

Drawings

FIG. 1 is a schematic view of an apparatus for a method of preparing a colorless transparent polyimide film according to the present application.

The specific implementation mode is as follows:

the following detailed description of the preferred embodiments of the present application is provided to enable those skilled in the art to more readily understand the advantages and features of the present application and to thereby more clearly define the scope of the present application.

Example 1

Quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 2

The difference from example 1 lies in the high temperature section T₄The heat treatment temperature is different as follows:

the synthesized colorless transparent polyimide uniform slurry is quantified by a gear quantitative pumpConveying the polyimide slurry to a slit coating head, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 280 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 3

The difference from example 1 lies in the high temperature section T₄The heat treatment time is different, specifically as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 5min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 4

The difference from example 1 lies in the high temperature section T₄The heat treatment time is different, specifically as follows:

the synthesized colorless transparent polyimide is evenly mixed with slurryQuantitatively conveying the polyimide slurry to a slit type coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 10min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 5

The difference from example 1 lies in the low temperature section T₃The different heat preservation time is as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 3min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 6

The difference from example 1 is the difference in the thickness of the PET support film used, in particular as follows:

the synthesized colorless transparent polyimide isThe uniform slurry is quantitatively conveyed to a slit type coating head through a gear quantitative pump, the polyimide slurry is coated on a 150-micron PET support film through the slit coating head, the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 7

The difference from the example 1 is that the support film is a PET release film, which is specifically as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125 mu mPE release film with the release force of 100gf through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, staying for 5min, peeling off the cured film from the release film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 8

The difference from example 1 is that the colorless transparent polyimide paste used is different in solvent, specifically as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is propylene glycol monomethyl ether acetate. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 9

The difference from example 1 is the solid content of the colorless transparent polyimide paste, which is as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 10 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 13 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 10

The difference from example 8 is that the colorless transparent polyimide paste used is different in solvent, specifically as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 10 wt%, and the used organic solvent is propylene glycol monomethyl ether acetate. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 13 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 11

The difference from the example 8 is that the support film used is a PET release film, which is specifically as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125 mu mPE release film with the release force of 100gf through the slit coating head, wherein the solid content of the slurry is 10 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 13 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 12

The difference from example 8 lies in the low temperature section T₃The different heat preservation time is as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 10 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 3min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 ℃ for 8min, and finally cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 13 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 13

The difference from example 1 is the solid content of the colorless transparent polyimide paste, which is as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 20 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 deg.C for 8min, cooling, and rolling to obtain colorless transparent polyimide film with thickness of 50 μm. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 14

The difference from example 12 is that the colorless transparent polyimide paste used was different in solvent as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 20 wt%, and the used organic solvent is propylene glycol monomethyl ether acetate. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 deg.C for 8min, cooling, and rolling to obtain colorless transparent polyimide film with thickness of 50 μm. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 15

The difference from the example 12 is that the support film used is a PET release film, which is specifically as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125 mu mPE release film with the release force of 100gf through the slit coating head, wherein the solid content of the slurry is 20 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 deg.C for 8min, cooling, and rolling to obtain colorless transparent polyimide film with thickness of 50 μm. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Example 16

The difference from example 12 lies in the low temperature section T₃The different heat preservation time is as follows:

quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 20 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 3min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 deg.C for 8min, cooling, and rolling to obtain colorless transparent polyimide film with thickness of 50 μm. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Comparative example 1

Quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit coating head through a gear quantitative pump, and coating the polyimide slurry on a 125-micron PET support film through the slit coating head, wherein the solid content of the slurry is 15 wt%, and the used organic solvent is N, N-dimethylacetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃And keeping the temperature of the zone at 130 ℃ for 5min, then stripping the cured film from the supporting film by using a stripping roller, cooling and rolling to obtain a finished colorless transparent polyimide film with the thickness of 25 mu m. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

Comparative example 2

Quantitatively conveying the synthesized colorless transparent polyimide uniform slurry to a slit type coating head through a gear quantitative pump, coating the polyimide slurry on a 125-micron PET support film through the slit coating head, and sizingThe solid content of the material is 15 wt%, and the organic solvent is N, N-dimethyl acetamide. The supporting film loaded with uniform slurry sequentially passes through the T of the low-temperature section drying oven under the action of the traction roller₁-T₃Zone, wherein T₁The zone temperature is 80 deg.C, the residence time is 1min, T₂The zone temperature is 100 ℃, the residence time is 3min, T₃The zone temperature is 130 deg.C, standing for 5min, peeling off the cured film from the support film with a peeling roller, and continuously entering into a high-temperature section oven zone for heat treatment at a heat treatment temperature T₄Standing at 300 deg.C for 12min, cooling, and rolling to obtain 25 μm thick colorless transparent polyimide film. The appearance and properties of the obtained colorless transparent polyimide film are shown in Table 1.

TABLE 1 appearance and Properties of colorless transparent polyimide films in the technical solutions described in examples 1 to 16 and comparative examples 1 to 2

As can be seen from Table 1, the reasonable combination of the gradient temperature rise in the low temperature section and the heat treatment in the high temperature section, and the selection of the proper baking temperature, baking time, solvent and peeling force, compared with the gradient temperature rise process only in the low temperature section, the thermal dimensional stability and mechanical strength of the colorless transparent polyimide film can be significantly improved, so that the full-wavelength transmittance of the prepared colorless transparent polyimide film is 90-92%, the yellow index is 1.4-1.8, the tensile strength is 130-160MPa, and the thermal expansion coefficient is 20-30 ppm/DEG C.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.