CN108424540B

CN108424540B - Colorless transparent polyimide film and preparation method thereof

Info

Publication number: CN108424540B
Application number: CN201810397632.4A
Authority: CN
Inventors: 路庆华; 徐文华; 苏远海
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2018-04-28
Filing date: 2018-04-28
Publication date: 2020-08-04
Anticipated expiration: 2038-04-28
Also published as: CN108424540A

Abstract

① adding fluorine-containing diamine into polar aprotic solvent protected by nitrogen or inert gas, stirring at 10-50 ℃ to completely dissolve the fluorine-containing diamine, adding co-polyanhydride and aliphatic anhydride with a certain mole fraction, controlling the mole ratio of diamine to anhydride to be 1: 1-1.02, reacting for 6-24 hours to obtain transparent polyamic acid solution, ② uniformly coating the polyamic acid solution obtained in the step ① on a clean substrate with a predetermined thickness, then placing the substrate in a vacuum oven for programmed heating to a certain temperature to remove the solvent and carrying out thermal imidization, cooling the temperature of the vacuum oven to ambient temperature, taking out a glass plate, demoulding and drying to obtain the transparent polyimide film.

Description

Colorless transparent polyimide film and preparation method thereof

Technical Field

The invention relates to the field of polymer films, and particularly discloses a transparent polyimide film and a preparation method thereof.

Background

Polyimide (PI) has excellent thermal, mechanical and electrical properties and excellent comprehensive properties, and is widely applied to the industries of aviation, aerospace, automobiles, machinery and the like. However, their application in the field of microelectronics and optoelectronics is severely limited by their darker color and poor light transmittance. The traditional polyimide film is brownish yellow, has lower light transmittance to visible light (wavelength of 400-700nm), and has light transmittance of less than 40% to visible light of 500 nm; visible light with a wavelength of 400nm is 100% absorbed, which severely limits its application in the field of optoelectronics. The color of polyimides is mainly due to the formation of intermolecular and intramolecular charge transfer complexes of aromatic polyimides, of which dianhydrides are electron acceptors and diamines are electron donors.

The application potential of the transparent polyimide in the flexible optoelectronic device greatly promotes the commercialization process of the transparent polyimide; the optical film is applied to flexible light-emitting diodes, flexible solar cells or photovoltaic cells, flexible thin film transistors, flexible printed circuit boards and other aspects, and higher requirements are put forward on the performance of polyimide; especially the excellent comprehensive performance, which is not possessed by a plurality of current commercial materials. To meet these requirements, many different types of polyimides have been developed and commercialized in the fields of organic polymerization chemistry and chemical engineering to further improve their properties.

At present, the common methods for preparing transparent polyimide are as follows: 1) introducing a fluorine-containing group, 2) introducing a substituent group with larger volume, 3) introducing an aliphatic, especially alicyclic structure unit, 4) adopting a monomer capable of bending a main chain, 5) introducing an asymmetric structure, 6) reducing a conjugated double bond structure and the like. Wherein, fluorine atoms are introduced into a polyimide main chain or a branched chain, so that the polyimide has high electronegativity and large free volume; meanwhile, the lower polarizability of the C-F bond can improve the optical transparency of the polyimide, improve the solubility of the polyimide and reduce the dielectric constant. Aliphatic polyimides have excellent transparency, mainly due to the introduction of aliphatic monomers, which effectively inhibit charge transfer interactions based on their low molecular density and low polarity. The invention provides a transparent polyimide film and a preparation method thereof by combining the comprehensive advantages of fluorine-containing polyimide and aliphatic polyimide.

Disclosure of Invention

The invention aims to obtain a transparent polyimide film with excellent comprehensive performance, and provides the transparent polyimide film and a preparation method thereof.

The technical scheme for realizing the purpose of the invention is as follows:

① adding fluorine-containing diamine into a polar aprotic solvent protected by nitrogen or inert gas, stirring at 10-50 ℃ to completely dissolve the fluorine-containing diamine, adding a co-polyacid anhydride and a certain mole fraction of aliphatic anhydride, controlling the mole ratio of the diamine to the anhydride to be 1: 1-1.02, and reacting for 6-24 hours to obtain a transparent polyamic acid solution;

② coating the polyamic acid solution obtained from step ① onto clean substrate with preset thickness, heating to certain temperature in vacuum oven to remove solvent and imidize, cooling to ambient temperature, taking out substrate, demolding and drying to obtain transparent polyimide film.

In one embodiment of the first aspect, the fluorinated diamine in step ① is one or more selected from 2,2 '-bis (trifluoromethyl) -4,4' -diaminophenyl ether and 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl.

In one embodiment of the first aspect, the polyanhydride used in step ① is one or more of 1,2,4, 5-pyromellitic dianhydride, 3,3 ', 4,4' -benzophenonetetracarboxylic dianhydride, 4,4' -diphenyl ether dianhydride, 3,3,4, 4-diphenyl dianhydride, and 4, 4-hexafluoroisopropyl phthalic anhydride.

In one embodiment of the first aspect, the certain mole fraction described in step ① is between 0% and 100%.

In one embodiment of the first aspect, the aliphatic anhydride described in step ① is one of the following structures:

in one embodiment of the first aspect, the certain temperature set forth in step ② is 270 ℃.

In one embodiment of the first aspect, the substrate comprises a glass plate.

In a second aspect, the present application provides a transparent polyimide film prepared by the method of the first aspect.

Compared with the prior art, the thickness range of the transparent polyimide film obtained by the invention is about 50 μm, the ultraviolet transmittance of the transparent polyimide film is up to 90% at 500nm, the ultraviolet transmittance of 400nm is up to more than 75%, the ultraviolet cut-off wavelength is up to 312nm, the temperature of 5% weight loss is more than 430 ℃, and the mechanical property is excellent.

Drawings

FIG. 1 is a photograph of an optical photograph of transparent polyamic acid solutions and corresponding transparent polyimide films prepared according to the examples, wherein the transparent polyimide films prepared using PMDA are yellow;

FIG. 2 is an infrared spectrum of a transparent polyimide film prepared by the example and having different mole fractions of aliphatic anhydride;

FIG. 3 is a UV-Vis spectrum of a transparent polyimide film from which different co-polyanhydrides were prepared according to the examples;

FIG. 4 is a chart of UV-Vis spectra of transparent polyimide films with different mole fractions of aliphatic anhydrides prepared in examples;

FIG. 5 is a graph of the thermal weight loss of transparent polyimide films prepared according to the examples and having different mole fractions of aliphatic anhydrides.

The numbering in the drawings corresponds to the embodiment as follows: PI-6FDA-50 indicates 6FDA of the co-polymeric anhydride and 50% of the aliphatic anhydride, for example 1; PI-PMDA-50 indicates that the co-polymeric anhydride was PMDA and the aliphatic anhydride was 50%, for example 3; PI-BTDA-50 indicates that the co-polymeric anhydride was BTDA and the aliphatic anhydride was 50%, for example 4; PI-BPDA-50 indicates that the co-polymeric anhydride is BPDA, the aliphatic anhydride mass fraction is 50%, and the embodiment 5 is shown; PI-ODPA-50 shows that the weight fraction of the aliphatic anhydride is 50 percent, and the weight fraction of the aliphatic anhydride is ODPA, which is the weight fraction of the aliphatic anhydride in example 6; PI-6FDA-70 means that the weight fraction of the aliphatic anhydride is 70%, and the weight fraction of the co-polymeric anhydride is 6FDA, which is example 7; PI-6FDA-90 means that the mass fraction of the aliphatic anhydride is 90%, and the mass fraction of the co-polymeric anhydride is 6FDA, which is example 8; PI-6FDA-100 indicates that the mass fraction of the aliphatic anhydride is 100 percent, and the mass fraction of the aliphatic anhydride is 6FDA, which is the weight fraction of the aliphatic anhydride in example 9; PI-6FDA-30 indicates that the weight fraction of the aliphatic anhydride is 30 percent, and the weight fraction of the aliphatic anhydride is 6FDA, and the aliphatic anhydride is the embodiment 10; PI-6FDA-10 indicates that the weight fraction of the aliphatic anhydride is 10 percent, and the weight fraction of the aliphatic anhydride is 6FDA, which is the weight fraction of the aliphatic anhydride, and is the weight fraction of the aliphatic anhydride, which is the weight fraction of the aliphatic anhydride, in example 11; PI-6FDA-0 indicates 6FDA as the comonomer anhydride, and 0% by weight as the aliphatic anhydride, as example 12.

Detailed Description

Example 1

This example enables the preparation of a transparent polyimide film by:

firstly, 21.62g of fluorine-containing diamine 2,2 '-bis (trifluoromethyl) -4,4' -diaminophenyl ether was added to 238.83g of a polar aprotic solvent (N, N-dimethylacetamide) under nitrogen or inert gas shielding, and after completely dissolving the mixture by stirring at 10 to 30 ℃, the molar ratio of diamine to acid anhydride was controlled to 1: 1-1.02, adding 4, 4-hexafluoroisopropyl phthalic anhydride of the copolymerized acid and cyclobutane tetracarboxylic dianhydride with the mole fraction of aliphatic anhydride of 50 percent, and reacting for 24 hours to obtain transparent polyamic acid solution. As used herein, the mole fraction of aliphatic anhydride refers to the ratio of moles of aliphatic to the sum of moles of co-polymeric anhydride and moles of aliphatic anhydride.

And secondly, uniformly coating the polyamic acid solution obtained in the step one on a clean glass plate, then placing the glass plate in a vacuum oven for programmed heating to 270 ℃ to remove the solvent and carrying out thermal imidization, taking out the glass plate after the temperature of the vacuum oven is reduced to the ambient temperature, demolding and drying to obtain the transparent polyimide film.

Example 2

In the first step, the fluorine-containing diamine is 2,2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl. Otherwise, as in example 1, the following functions were performed: the flexibility of the transparent polyimide film is reduced, and the mechanical property is better.

Example 3

The co-poly acid anhydride in the step one is 1,2,4, 5-pyromellitic dianhydride. Otherwise, as in example 1, the following functions were performed: the transparency of the transparent polyimide film is different from that of the transparent polyimide film due to the difference of the polyanhydrides.

Example 4

The said copolyester anhydride in step one is 3,3 ', 4,4' -benzophenonetetracarboxylic dianhydride. Otherwise, as in example 1, the following functions were performed: the transparency of the transparent polyimide film is different from that of the transparent polyimide film due to the difference of the polyanhydrides.

Example 5

The co-poly acid anhydride in the step one is 3,3,4, 4-biphenyl dianhydride. Otherwise, as in example 1, the following functions were performed: the transparency of the transparent polyimide film is different from that of the transparent polyimide film due to the difference of the polyanhydrides.

Example 6

The copolyester anhydride in the step one is 4,4' -diphenyl ether dianhydride. Otherwise, as in example 1, the following functions were performed: the transparency of the transparent polyimide film is different from that of the transparent polyimide film due to the difference of the polyanhydrides.

Example 7

The mole fraction of the aliphatic anhydride in the first step is 70%. Otherwise, as in example 1, the following functions were performed: the mole fraction of the aliphatic anhydride is increased, and the transparency of the transparent polyimide film is improved.

Example 8

The mole fraction of the aliphatic anhydride in the first step is 90%. Otherwise, as in example 1, the following functions were performed: the mole fraction of the aliphatic anhydride is increased, and the transparency of the transparent polyimide film is improved.

Example 9

The mole fraction of the aliphatic anhydride in the first step is 100%. Otherwise, as in example 1, the following functions were performed: the mole fraction of the aliphatic anhydride is increased, and the transparency of the transparent polyimide film is improved.

Example 10

The mole fraction of the aliphatic anhydride in the first step is 30%. Otherwise, as in the embodiment, the functions are as follows: the mole fraction of the aliphatic acid anhydride is reduced and the transparency of the transparent polyimide film is lowered.

Example 11

The mole fraction of the aliphatic anhydride in the first step is 10%. Otherwise, as in example 1, the following functions were performed: the mole fraction of the aliphatic acid anhydride is reduced and the transparency of the transparent polyimide film is lowered.

Example 12

The mole fraction of the aliphatic anhydride in the first step is 0%. Otherwise, as in example 1, the following functions were performed: the mole fraction of the aliphatic acid anhydride is reduced and the transparency of the transparent polyimide film is lowered.

Example 13

The aliphatic acid anhydride in the first step is:

otherwise, as in example 1, the following functions were performed: the aliphatic acid anhydride is dimethyl substituted cyclobutane tetracarboxylic dianhydride, and the transparency of the transparent polyimide film is reduced.

Comparative example 14

And (4) raising the temperature to 300 ℃ by the program in the first step. Otherwise, as in example 1, the following functions were performed: the imidization temperature increases and the transparency of the transparent polyimide film decreases.

The transparent polyamic acid solution and the transparent polyimide film with different kinds of anhydride prepared in the experiment are used as optical photos. Almost, when the different co-polyanhydrides of the transparent polyimide film have 3,3,4, 4-biphenyldianhydride and 4, 4-hexafluoroisopropylphthalic anhydride as the co-polyanhydrides, the optical photograph of the film shows that it is almost transparent, and the polyimide film of the other co-polyanhydrides has a pale yellow color.

The transparent polyimide films with different mole fractions of aliphatic anhydride prepared by the experiment are subjected to infrared spectrum test. As shown in FIG. 2, 1781, 1713cm^-1Is imine ring C ═ O stretching vibration peak, 1373cm^-1Is an imine ring C-N stretching vibration peak of 1248cm^-1Is the C-O stretching vibration peak, which indicates that the polyimide has been successfully prepared.

The transparent polyimide films with different co-polymeric anhydrides prepared in the experiment are tested by ultraviolet-visible spectrogram. As shown in fig. 3, the transparency of the transparent polyimide film is different according to the anhydride copolymer; when the content of the aliphatic anhydride is 50%, the ultraviolet transmittance at 400nm is sequentially PI-PMDA-50< PI-BTDA-50< PI-BPDA-50< PI-ODPA-50< PI-6 FDA-50.

The transparent polyimide films with different mole fractions of aliphatic acid anhydride prepared by the experiment are tested by ultraviolet-visible spectrum. As shown in FIG. 4, the transparency of the transparent polyimide film is improved with the increasing mole fraction, the ultraviolet cut-off wavelength is as high as 310nm, the ultraviolet transmittance at 400nm is more than 75%, the ultraviolet transmittance at 500nm is as high as 90%, and the transparency is excellent.

The transparent polyimide film of this example was subjected to a thermogravimetric analysis test. As shown in FIG. 5, in the nitrogen atmosphere, the 5% weight loss temperature is 433-522 ℃, the 10% weight loss temperature is 460-547 ℃, the carbon residue rate at 800 ℃ is as high as 45-50%, and the thermal performance is excellent.

The embodiments described above are intended to facilitate the understanding and appreciation of the application by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present application is not limited to the embodiments herein, and those skilled in the art who have the benefit of this disclosure will appreciate that many modifications and variations are possible within the scope of the present application without departing from the scope and spirit of the present application.

Claims

1. A preparation method of a transparent polyimide film is characterized by comprising the following steps:

① adding fluorine-containing diamine into polar aprotic solvent protected by nitrogen or other inert gases, stirring at 10-50 deg.C to completely dissolve, adding co-polyacid anhydride and aliphatic anhydride, controlling the molar ratio of fluorine-containing diamine and anhydride at 1: 1-1.02, reacting for 6-24 hr to obtain transparent polyamic acid solution;

② coating the polyamic acid solution obtained in step ① onto a clean substrate with a predetermined thickness, heating in a vacuum oven to a certain temperature to remove the solvent and perform thermal imidization, cooling the vacuum oven to ambient temperature, taking out the substrate, demolding, and drying to obtain a transparent polyimide film;

wherein the fluorine-containing diamine is 2,2 '-bis (trifluoromethyl) -4,4' -diaminophenyl ether;

wherein the co-poly acid anhydride is 4, 4-hexafluoroisopropyl phthalic anhydride;

wherein the aliphatic anhydride is one of the following structures:

wherein the mole fraction of the aliphatic acid anhydride is 10-70%, and the mole fraction of the aliphatic acid anhydride refers to the proportion of the mole number of the aliphatic acid anhydride in the sum of the mole number of the co-polycarboxylic acid anhydride and the mole number of the aliphatic acid anhydride.

2. The method for preparing a transparent polyimide film according to claim 1, wherein the temperature in step ② is 270 ℃.

3. The method of preparing a transparent polyimide film according to claim 1, wherein the substrate comprises a glass plate.

4. A transparent polyimide film produced by the method for producing a transparent polyimide film according to any one of claims 1 to 3.