CN108864426B - Ultralow-expansion fluorine-containing polyimide film and preparation method and application thereof - Google Patents

Ultralow-expansion fluorine-containing polyimide film and preparation method and application thereof Download PDF

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CN108864426B
CN108864426B CN201810600971.8A CN201810600971A CN108864426B CN 108864426 B CN108864426 B CN 108864426B CN 201810600971 A CN201810600971 A CN 201810600971A CN 108864426 B CN108864426 B CN 108864426B
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范琳
白兰
翟磊
何民辉
莫松
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Abstract

The invention relates to an ultralow-expansion fluorine-containing polyimide film, a preparation method and application thereof, belongs to the technical field of polyimide, and solves the problems that the linear thermal expansion coefficient of the polyimide film in a wide temperature range is not low enough, and other properties of the polyimide film are difficult to obtain while the linear thermal expansion coefficient is reduced in the prior art. The molecular main chain structure of the ultralow-expansion fluorine-containing polyimide film contains a linear rigid unit, a polar amide group and a fluorine-containing group; the preparation raw materials comprise aromatic dianhydride and diamine with amide groups and fluorine-containing groups. The preparation method comprises the steps of dissolving aromatic diamine with amide groups and fluorine-containing groups, and adding aromatic dianhydride to obtain polyamide acid homogeneous phase solution; coating, curing, stripping and drying; and (3) paving the polyimide film on a substrate, fixing and annealing to obtain the polyimide film. The ultralow-expansion fluorine-containing polyimide film and the preparation method and application thereof realize wide application in the fields of electronics and flexible display.

Description

Ultralow-expansion fluorine-containing polyimide film and preparation method and application thereof
Technical Field
The invention relates to the technical field of polyimide, in particular to an ultralow-expansion fluorine-containing polyimide film and a preparation method and application thereof.
Background
In the fields of photoelectric display, optical communication and the like, devices will gradually show development trends of flexibility, curling, light weight, thinning and wearability, for example, flexible liquid crystal displays (L CD), flexible organic electroluminescent devices (O L ED), flexible solar cells and the like, and related electronic and optical devices face new requirements of weight reduction, light weight, thinning, flexibility and the like.
However, the thermal dimensional stability of the traditional polyimide film is not ideal, and the coefficient of linear thermal expansion (CTE) is about 40-80 ppm/DEG C, so that the strict requirement of high-precision devices on the single-digit CTE of substrate materials cannot be met. The linear thermal expansion coefficient of the polyimide film can be reduced to a certain extent by introducing rigid groups into the molecular structure and doping inorganic particles such as metal/ceramic/montmorillonite, but the mechanical property of the film is lost. In addition, the applicable temperature range of the existing low-expansion polyimide film is narrow, and the temperature range for thermal expansion is usually below 250 ℃, such as 50-200 ℃ or 100-250 ℃, which is not in line with the practical application requirements of the material.
As described above, the conventional polyimide film has a problem that the linear thermal expansion coefficient is not sufficiently low in a wide temperature range (30 to 300 ℃), and the mechanical properties, water absorption rate and other properties of the polyimide film are hardly compatible with each other while the linear thermal expansion coefficient is reduced.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide an ultralow expansion fluorine-containing polyimide film, and a preparation method and an application thereof, so as to solve the problems that the linear thermal expansion coefficient of the existing polyimide film is not low enough in a wide temperature range (30-300 ℃), and the mechanical properties, the water absorption rate, and other properties of the polyimide film are difficult to be obtained at the same time of reducing the linear thermal expansion coefficient.
The ultralow-expansion fluorine-containing polyimide film provided by the invention is mainly realized by the following technical scheme:
a ultralow-expansion fluorine-containing polyimide film comprises a molecular main chain structure of polyimide, wherein the molecular main chain structure of the polyimide contains a linear rigid unit, a polar amide group and a fluorine-containing group; the raw materials for preparing the polyimide film comprise aromatic dianhydride and diamine with amide groups and fluorine-containing groups.
The ultralow-expansion fluorine-containing polyimide film has the following beneficial effects:
according to the invention, through the molecular structure design, on one hand, a rigid unit is introduced into a polyimide molecular main chain, so that the molecular main chain of the polyimide is linear rigid, the stacking density of a molecular chain can be effectively improved, and the chain segments are favorably highly oriented in the imidization process, thereby improving the heat resistance of the polyimide film, and the heat resistance temperature is above 400 ℃. On the other hand, the polar amide group is introduced into the main chain of the polyimide molecule, so that the main chain of the polyimide molecule has an amide structure, and the molecular chains have stronger hydrogen bond interaction, thereby being beneficial to the accumulation and oriented arrangement of the molecular chains, effectively inhibiting the free volume of the molecule and the thermal expansion behavior brought by the molecular motion, and achieving the purpose of reducing the thermal expansion coefficient of the polyimide film. More importantly, the electronegative fluorine atoms and fluorine-containing groups are introduced into the main chain of the polyimide molecule, so that other good performances of the polyimide, such as high mechanical strength, low water absorption and other excellent performances, can be effectively endowed, and the other performances are improved on the basis of ensuring the heat resistance and the thermal dimension stability of the polyimide film. The ultralow-expansion polyimide film provided by the invention not only has an ultralow linear thermal expansion coefficient in a wide temperature range of 30-300 ℃, but also has other excellent properties such as high mechanical strength, low water absorption and the like, and has important application value in the fields of flexible photoelectricity and the like.
On the basis of the scheme, the invention is further improved as follows:
further, the diamine having an amide group and a fluorine-containing group is an aromatic diamine, and the aromatic diamine is N, N '-bis (2-fluoro-4-aminophenyl) -terephthalamide, N' -bis (3-fluoro-4-aminophenyl) -terephthalamide, N '-bis (2, 5-difluoro-4-aminophenyl) -terephthalamide, N' -bis (2-trifluoromethyl-4-aminophenyl) -terephthalamide, N '-bis (3-trifluoromethyl-4-aminophenyl) -terephthalamide, N' -bis (2, 5-bistrifluoromethyl-4-aminophenyl) -terephthalamide, or a salt thereof, N, N ' -3,3 ' -difluoro- (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -2,2 ' -difluoro- (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -2, 6-difluoro- (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -3,3 ' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -2,2 ' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 ' -diaminobenzamide and N, N ' -2, 6-bis (trifluoromethyl) - (1, 1-biphenyl) -4, 4' -diaminobenzamide.
Since the aromatic diamine has a high polarity, the diamine having an amide structure in the present invention is selected as the aromatic diamine. Among a plurality of aromatic diamines, the aromatic diamine has stronger polarity, so that intermolecular hydrogen bond formed in a polyimide main chain has stronger action, the molecular chain arrangement is more regular, the movement of the molecular chain can be more effectively inhibited in the temperature rising process, and the thermal expansion coefficient of the polyimide film is further reduced. Therefore, the present invention selects one or more of the above aromatic diamines to introduce into the main chain of the polyimide molecule. More importantly, the above aromatic diamine has not only the polar amide group to be introduced in the present invention but also the fluorine-containing group to be introduced in the present invention. The introduction of fluorine atoms or fluorine-containing groups can effectively reduce the water absorption and give consideration to other properties on the basis of ensuring the heat resistance and the thermal dimension stability of the polyimide film.
Further, the aromatic dianhydride is one or more of 1,2,4, 5-pyromellitic dianhydride (PMDA), 3 ', 4, 4' -biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,6, 7-naphthalenetetracarboxylic dianhydride (BNDA), 3 ', 4, 4' -benzophenonetetracarboxylic dianhydride (s-BTDA), 3 ', 4, 4' -dibenzoic acid terephthalamide tetracarboxylic dianhydride, and 3,3 ', 4, 4' -diphenylsulfonetetracarboxylic dianhydride (DSDA).
In order to realize the molecular main chain structure of the linear rigid unit, the polyimide of the present invention is prepared from an aromatic dianhydride and an aromatic diamine having an amide group and a fluorine-containing group.
A large number of experiments show that among a plurality of aromatic dianhydrides, the aromatic dianhydride can effectively improve the stacking density of molecular chains and is more beneficial to high orientation of polyimide chain segments in the imidization process, so that the heat resistance of the polyimide film is further improved. Therefore, the present invention selects one or more of the above aromatic dianhydrides to be incorporated into the main chain of the polyimide molecule.
Further, the polyimide has the general formula I shown below:
Figure BDA0001693205970000041
in the general formula I, n is the number of polymer structural units, Ar is any one of the following aromatic structures:
Figure BDA0001693205970000042
r is one of a general formula II or a general formula III shown as follows:
Figure BDA0001693205970000043
Figure BDA0001693205970000051
in the general formula II, X is H, F or CF3Y is H, F or CF3And at least one of X, Y is F or CF3；
In the general formula III, the structure of M is selected from any one of the following structures:
Figure BDA0001693205970000052
the invention also provides a preparation method of the ultralow-expansion fluorine-containing polyimide film, which is mainly realized by the following technical scheme:
a preparation method of an ultralow-expansion fluorine-containing polyimide film comprises the following steps:
step 1: under the protection of inert gas, dissolving aromatic diamine with amide groups and fluorine-containing groups in an organic solvent, and adding aromatic dianhydride to obtain polyamide acid homogeneous phase solution;
step 2: coating the polyamide acid homogeneous phase solution on a substrate, curing, stripping and drying to obtain a polyimide film to be treated;
and step 3: the polyimide film to be treated is laid on a substrate, fixed and annealed to obtain the final polyimide film;
the curing comprises the following steps: curing at 60-100 ℃ for 1-2 hours, curing at 160-250 ℃ for 1-2 hours, and curing at 300-350 ℃ for 1-2 hours.
A part of the beneficial effects of the preparation method of the ultralow expansion fluorine-containing polyimide film of the present invention are the same as the beneficial effects of the ultralow expansion fluorine-containing polyimide film, and are not repeated herein. The other part of the beneficial effects of the preparation method are as follows: by means of curing and annealing treatment, the thermal history can be further eliminated, the aggregation state structure of the polyimide is further regulated and controlled, the ordered structure content is increased, and the heat resistance and the thermal dimension stability of the polyimide film are improved. The preparation method has simple process, can realize continuous production and has good industrial application value.
In step 1 of the above preparation method, the addition of the aromatic dianhydride is performed at a low temperature because the reaction between the aromatic diamine and the aromatic dianhydride is a polycondensation reaction, a large amount of heat is released during the reaction, and in order to proceed the reaction in the direction of the formation of the polyamic acid, it is necessary to offset the large amount of heat released during the reaction, and therefore, the addition of the aromatic dianhydride in the preparation method of the present invention is performed at a low temperature.
A large number of experiments show that the reaction is most favorably carried out in the direction of generating polyamic acid at the temperature of-5-25 ℃, so that the aromatic dianhydride is added under the low-temperature condition of-5-25 ℃ in the preparation method.
In step 3, the polyimide film to be treated is laid on the substrate and then fixed, so that a certain tensile stress is applied to the film, the thermal stress in the film is eliminated, the aggregation state structure of the polyimide is further regulated, the content of the ordered structure is increased, and the heat resistance and the thermal dimension stability of the polyimide film are improved.
In order to enable the polyamic acid to be completely cured, obtain a polyimide film having not only a low coefficient of thermal expansion, but also good heat resistance, particularly good high heat resistance over a wide temperature range (30-300 ℃) and an ultra-low coefficient of expansion (<3ppm/° c), the above preparation method is finally selected to be cured comprising the following steps, through repeated experiments at different curing temperatures and different curing times: curing at 60-100 ℃ for 1-2 hours, curing at 160-250 ℃ for 1-2 hours, and curing at 300-350 ℃ for 1-2 hours.
In the above preparation method, the substrate for coating in step 2 may be any one of a glass plate, a stainless steel plate, a silicon plate, or a polymer resin plate.
Further, the annealing treatment comprises the following steps: at the temperature of 250 ℃ and 300 ℃ for 0.5-1 hour, and at the temperature of 350 ℃ and 400 ℃ for 15-40 minutes.
In the preparation method, the prepared polyimide film is annealed at different temperatures and times, and a large number of experiments show that the polyimide film obtained after the treatment at the temperature of 250-300 ℃ for 0.5-1 hour and the treatment at the temperature of 350-400 ℃ for 15-40 minutes has good comprehensive performance and can not cause serious quality problems of warping, deformation, cracking and the like of a photoelectric device. Therefore, the present invention selects the above annealing process step to prepare the polyimide film.
Further, the solid content of the polyamic acid homogeneous solution is from 10 wt.% to 30 wt.%; the molar ratio of the aromatic diamine to the aromatic dianhydride is (0.95-1.02): 1.
In experiments, when the solid content of the polyamic acid homogeneous solution is too low, the film forming effect is poor or even no film is formed when the polyamic acid homogeneous solution is coated on a substrate; and when the solid content of the polyamic acid homogeneous solution is too high, the solution is too viscous, and the finally prepared polyimide film has poor comprehensive performance. Therefore, in the above production method, the solid content of the polyamic acid homogeneous solution is controlled to 10 wt.% to 30 wt.%.
Further, in step 3, the means for laying and fixing the polyimide film to be treated on the substrate is a means capable of applying a tensile stress to the film. The means used to lay down and fix the polyimide film to be treated on the substrate are illustratively metal frames, glass blocks or any special means that can apply a certain tensile stress to the film.
Further, the organic solvent is one or more of N-methylpyrrolidone (NMP), N '-dimethylacetamide (DMAc), N' -Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), cyclopentanone, and γ -butyrolactone.
The aromatic diamine and the aromatic dianhydride selected by the invention have high solubility in the organic solvent, and molecular chains can be fully stretched, so that the polyamide acid homogeneous phase solution obtained after mixing is uniform and stable, the subsequent preparation steps are convenient to carry out, and the prepared polyimide film has excellent comprehensive performance. Therefore, in the above preparation method, the organic solvent is selected from one or more of N-methylpyrrolidone (NMP), γ -butyrolactone, N '-dimethylacetamide (DMAc), N' -Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and cyclopentanone.
The ultralow-expansion fluorine-containing polyimide film is used as a substrate material and is applied to the fields of electronics and flexible display.
The ultralow-expansion polyimide film provided by the invention not only has ultralow linear thermal expansion coefficient in a wide temperature range of 30-300 ℃, but also has other excellent properties such as high mechanical strength, low water absorption and the like, so that the ultralow-expansion polyimide film provided by the invention can be widely applied to the fields of electronics, flexible display and the like.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is an infrared spectrum of a polyimide film prepared in example 1.
FIG. 2 is a DMA curve of the polyimide film prepared in example 1.
FIG. 3 is a TMA curve of the polyimide film prepared in example 1.
Detailed Description
The present invention will be further illustrated with reference to the following specific examples, but the present invention is not limited to the following examples. The following examples select representative fluorine-containing groups and diamine and aromatic dianhydride monomers containing amide groups to prepare ultralow-expansion fluorine-containing polyimide films with different main chain structures, the diamine and/or dianhydride monomers in the examples are replaced by other diamine and/or dianhydride monomers described in the disclosure of the invention, and the prepared homopolymerization type or copolymerization type polyimide films have the same and similar effects as the embodiments by adopting the preparation method and conditions described in the disclosure of the invention.
In the present invention, the percentage content and the percentage concentration are both the mass percentage content and the mass percentage concentration unless otherwise specified. The starting materials are commercially available from published sources unless otherwise specified. In the embodiment, the thickness of the polyimide film can be regulated and controlled by regulating the type of the coating roller and the solid content of the polyamic acid homogeneous solution.
Example 1
(1) 19.12 g (0.05 mol) of N, N '-bis (2-fluoro-4-aminophenyl) terephthalamide and 270 g of N-methylpyrrolidone (NMP) are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer under the protection of inert gas at room temperature and stirred until the N, N' -bis (2-fluoro-4-aminophenyl) terephthalamide and the NMP are completely dissolved; the system is cooled to the low temperature of-5 ℃, 11.12 g (0.051 mol) of 1,2,4, 5-pyromellitic dianhydride is added, and the polyamic acid homogeneous solution with the solid content of 10 wt.% is obtained after complete dissolution and low-temperature stirring for 18 hours.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating and curing the glass plate in a nitrogen atmosphere, wherein the heating and curing are 60 ℃/2 hours, 180 ℃/1.5 hours and 350 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a metal support frame, placing the film in a high-temperature oven, and gradually heating the film to 250 ℃/0.5 hour and 350 ℃/20 minutes to finish annealing treatment of the film; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 2
(1) 22.92 g (0.0475 mol) of N, N ' -bis (2-trifluoromethyl-4-aminophenyl) terephthalamide and 110 g of N, N ' -dimethylacetamide (DMAc) are added into a three-neck flask with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer under the protection of inert gas, and stirred at room temperature until the N, N ' -bis (2-trifluoromethyl-4-aminophenyl) terephthalamide and the DMAc are completely dissolved; the system is cooled to 0 ℃ at low temperature, 13.41 g (0.05 mol) of 2,3,6, 7-naphthalene tetracarboxylic dianhydride (BNDA) is added, and the mixture is stirred at low temperature for 24 hours after being completely dissolved, so that the polyamic acid homogeneous solution with the solid content of 25 wt.% is obtained.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry glass plate with a smooth and flat surface, placing the glass plate in an oven, and heating and curing the glass plate in a nitrogen atmosphere, wherein the heating and curing are specifically 80 ℃/1 hour, 200 ℃/1 hour and 350 ℃/2 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a metal support frame, placing the film in a high-temperature oven, and gradually heating to 250 ℃/40 minutes and 350 ℃/30 minutes to finish film annealing treatment; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 3
(1) Under the protection of inert gas, 20.92 g (0.05 mol) of N, N ' -bis (2, 5-difluoro-4-aminophenyl) terephthalamide and 200 g of N, N ' -Dimethylformamide (DMF) are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the N, N ' -bis (2, 5-difluoro-4-aminophenyl) terephthalamide and the DMF are completely dissolved; the system is cooled to 5 ℃ and 14.71 g (0.05 mol) of 3,3,4, 4-biphenyltetracarboxylic dianhydride (s-BPDA) is added, and after complete dissolution, the mixture is stirred at low temperature for 20 hours to obtain a polyamic acid homogeneous solution with a solid content of 15 wt.%.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry stainless steel plate with a smooth and flat surface, placing the stainless steel plate in an oven, and heating and curing the polyamide acid homogeneous solution in a nitrogen atmosphere, wherein the heating and curing are performed at 100 ℃/1 hour, 250 ℃/2 hour and 350 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a glass block, placing the film in a high-temperature oven, and gradually heating to 280 ℃/1 hour and 400 ℃/35 minutes to finish film annealing treatment; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 4
(1) Under the protection of inert gas, 23.38 g (0.051 mol) of N, N '-3, 3' -difluoro- (1, 1-biphenyl) -4,4 '-diaminobenzamide and 158 g of N, N' -dimethylacetamide (DMAc) are added into a three-neck flask which is provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the N, N '-diaminobenzamide and the N, N' -dimethylacetamide (DMAc) are completely dissolved; the system is cooled to 10 ℃ and 16.11 g (0.05 mol) of 3,3,4, 4-benzophenone tetracarboxylic dianhydride is added, and the mixture is stirred at low temperature for 12 hours after being completely dissolved, so that the polyamic acid homogeneous phase solution with the solid content of 20 wt.% is obtained.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry stainless steel plate with a smooth and flat surface, placing the dry stainless steel plate in an oven, and heating and curing the solution in a nitrogen atmosphere, wherein the heating and curing are performed at 60 ℃/2 hours, 160 ℃/2 hours and 320 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a metal support frame, placing the film in a high-temperature oven, and gradually heating to 280 ℃/0.5 hour and 400 ℃/40 minutes to finish film annealing treatment; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 5
(1) Under the protection of inert gas, 27.93 g (0.05 mol) of N, N '-2, 2' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 '-diaminobenzamide and 240 g of a mixed solvent of N-methylpyrrolidone (NMP) and cyclopentanone (volume ratio of 2:1) are added into a three-neck flask provided with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the N, N' -2,2 '-bis (trifluoromethyl) - (1, 1-biphenyl) -4, 4' -diaminobenzamide and the N-methylpyrrolidone (NMP) are completely dissolved; the system is cooled to 20 ℃ and 14.71 g (0.05 mol) of 3,3 ', 4, 4' -biphenyltetracarboxylic dianhydride is added, and the mixture is stirred at low temperature for 24 hours after being completely dissolved, so that the polyamic acid homogeneous phase solution with the solid content of 15 wt.% is obtained.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry polymer resin plate with a smooth and flat surface, placing the polyamic acid homogeneous solution in an oven, and heating and curing the polyamic acid homogeneous solution in a nitrogen atmosphere at 100 ℃/1 hour, 250 ℃/1.5 hour and 350 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a metal support frame, placing the film in a high-temperature oven, and gradually heating the film to 300 ℃/0.5 hour and 400 ℃/15 minutes to finish annealing treatment of the film; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 6
(1) Under the protection of inert gas, 27.93 g (0.05 mol) of N, N ' -2, 6-bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 ' -diaminobenzamide and 108 g of a mixed solvent (volume ratio is 1:1) of N, N ' -dimethylacetamide (DMAc) and gamma-butyrolactone are added into a three-neck flask provided with a mechanical stirring port, a nitrogen inlet and a nitrogen outlet and a thermometer, and the mixture is stirred at room temperature until the mixture is completely dissolved; the system was cooled to 0 ℃ and 17.92 g (0.05 mol) of 3,3 ', 4, 4' -diphenylsulfone tetracarboxylic dianhydride was added and stirred at low temperature for 30 hours after complete dissolution to give a polyamic acid homogeneous solution with a solid content of 30 wt.%.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry polymer resin plate with a smooth and flat surface, placing the polyamic acid homogeneous solution in an oven, and heating and curing the polyamic acid homogeneous solution in a nitrogen atmosphere, wherein the heating and curing are 60 ℃/1.5 hours, 200 ℃/1.5 hours and 300 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a glass block, placing the film in a high-temperature oven, and gradually heating to 300 ℃/1 hour and 400 ℃/25 minutes to finish film annealing treatment; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 7
(1) Under the protection of inert gas, 19.12 g (0.05 mol) of N, N ' -bis (3-fluoro-4-aminophenyl) terephthalamide and 135 g of N, N ' -dimethylacetamide (DMAc) are added into a three-neck flask with a mechanical stirring device, a nitrogen inlet and a nitrogen outlet and a thermometer, and stirred at room temperature until the N, N ' -bis (3-fluoro-4-aminophenyl) terephthalamide and the DMAc are completely dissolved; the system temperature was controlled at 25 ℃, 7.64 g (0.035 mol) of 1,2,4, 5-pyromellitic dianhydride and 6.85 g (0.015 mol) of 3,3,4, 4-dibenzoic acid terephthalamide tetracarboxylic dianhydride were added, and after complete dissolution, stirring was carried out at low temperature for 20 hours to obtain a polyamic acid homogeneous solution having a solid content of 20 wt.%.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry stainless steel plate with a smooth and flat surface, placing the dry stainless steel plate in an oven, and heating and curing the solution in a nitrogen atmosphere, wherein the heating and curing are performed at 60 ℃/2 hours, 200 ℃/1 hour and 350 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a metal frame, placing the film in a high-temperature oven, and gradually heating to 300 ℃/40 minutes and 380 ℃/30 minutes to finish film annealing treatment; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Example 8
(1) In a three-necked flask equipped with a mechanical stirrer, a nitrogen inlet and outlet, and a thermometer under inert gas, 9.56 g (0.025 mol) of N, N '-bis (2-fluoro-4-aminophenyl) terephthalamide and 13.96 g (0.025 mol) of N, N' -2,2 '-bis (trifluoromethyl) - (1, 1-biphenyl) -4, 4' -diaminobenzamide, and 155 g of N-methylpyrrolidone (NMP) were charged and stirred at room temperature until completely dissolved; the system was cooled to 10 ℃ and 10.91 g (0.05 mol) of 1,2,4, 5-pyromellitic dianhydride was completely dissolved and stirred at low temperature for 32 hours to obtain a polyamic acid homogeneous solution having a solid content of 18 wt.%.
(2) And (2) filtering and vacuum defoaming the polyamic acid homogeneous solution obtained in the step (1), coating the polyamic acid homogeneous solution on a dry stainless steel plate with a smooth and flat surface, placing the dry stainless steel plate in an oven, and heating and curing the solution in a nitrogen atmosphere, wherein the heating and curing are specifically 90 ℃/1 hour, 200 ℃/2 hour and 350 ℃/1 hour. And then cooling to room temperature, soaking the substrate in deionized water, automatically stripping the film, and drying in an oven.
(3) Flatly paving the dried film obtained in the step (2) on a substrate, fixing the film by adopting a glass block, placing the film in a high-temperature oven, and gradually heating to 260 ℃/1 hour and 400 ℃/15 minutes to finish film annealing treatment; then cooling to room temperature to prepare the final polyimide film.
The main properties of the polyimide film prepared in this example are shown in table 1.
Table 1 shows the main properties of the homo-and copolyimide films prepared in examples 1 to 8.
TABLE 1 Main Properties of polyimide films prepared in examples 1 to 8
Figure BDA0001693205970000141
Figure BDA0001693205970000151
Note: a negative coefficient of thermal expansion indicates shrinkage of the polyimide film during the test.
The heat resistance of the film was measured by a dynamic analyzer (DMA) in a nitrogen atmosphere.
b, measuring the thermal dimensional stability of the film by using a static mechanical analyzer (TMA) in a nitrogen atmosphere at the test temperature of 30-300 ℃.
And c, testing the tensile property of the film according to the national standard GB/T1040.3-2006, measuring on a universal testing machine, and averaging at least five groups of test samples.
d, the water absorption of the film is measured by soaking a polyimide film sample (5cm × 5cm × 0.005.005 cm) in deionized water for 24 hours at room temperature, taking out the film sample, wiping off the surface moisture, weighing, and calculating according to the weight difference before and after soaking to obtain the water absorption of the sample.
As can be seen from Table 1, the polyimide films prepared in examples 1 to 8 have excellent heat resistance, and the absolute value of the coefficient of thermal expansion is less than 3, indicating that the polyimide film of the present invention has an ultra-low coefficient of thermal expansion, with a coefficient of thermal expansion of-1.7 to 2.1 ppm/DEG C over a wide temperature range of 30 to 300 ℃. In addition, the films have high mechanical tensile strength and low water absorption. The good comprehensive performance is directly related to the amide group and the fluorine-containing group contained in the polyimide structure. Therefore, the polyimide film prepared from the aromatic dianhydride and the aromatic diamine containing fluorine and an amide structure, which is provided by the invention, has good heat-resistant dimensional stability in a wide temperature range of 30-300 ℃, high tensile strength and low water absorption rate, and can be applied to the fields of flexible photoelectricity and the like.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (9)

1. The ultralow-expansion fluorine-containing polyimide film is characterized in that a molecular main chain structure of the polyimide contains a linear rigid unit, a polar amide group and a fluorine-containing group; the preparation raw materials of the polyimide film comprise aromatic dianhydride and diamine with amide groups and fluorine-containing groups;
the polyimide has the general formula I shown below:
Figure FDA0002486505150000011
in the general formula I, n is the number of polymer structural units, Ar is any one of the following aromatic structures:
Figure FDA0002486505150000012
r is one of the following general formulas II:
Figure FDA0002486505150000013
in the general formula II, X is H, F or CF3Y is H, F or CF3And at least one of X, Y is F or CF3；
Or, R is one of the following general formula III:
Figure FDA0002486505150000014
Figure FDA0002486505150000021
in the general formula III, the structure of M is selected from any one of the following structures:
Figure FDA0002486505150000022
the preparation process of the ultralow-expansion fluorine-containing polyimide film with the general formula II and the general formula III is subjected to annealing treatment, and the annealing treatment comprises the following steps: at the temperature of 250 ℃ and 300 ℃ for 0.5-1 hour, and at the temperature of 350 ℃ and 400 ℃ for 15-40 minutes.
2. The ultra-low expansion fluorine-containing polyimide film according to claim 1, wherein the diamine having an amide group and a fluorine-containing group is an aromatic diamine, and the aromatic diamine is N, N '-bis (2-fluoro-4-aminophenyl) -terephthalamide, N' -bis (3-fluoro-4-aminophenyl) -terephthalamide, N '-bis (2, 5-difluoro-4-aminophenyl) -terephthalamide, N' -bis (2-trifluoromethyl-4-aminophenyl) -terephthalamide, N '-bis (3-trifluoromethyl-4-aminophenyl) -terephthalamide, N' -bis (2, 5-bistrifluoromethyl-4-aminophenyl) -terephthalamide, N ' -3,3 ' -difluoro- (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -2,2 ' -difluoro- (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -2, 6-difluoro- (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -3,3 ' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 ' -diaminobenzamide, N ' -2,2 ' -bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 ' -diaminobenzamide and one or more of N, N ' -2, 6-bis (trifluoromethyl) - (1, 1-biphenyl) -4,4 ' -diaminobenzamide.
3. The ultra-low expansion fluorine-containing polyimide film according to claim 1, wherein the aromatic dianhydride is one or more of 1,2,4, 5-pyromellitic dianhydride, 3 ', 4, 4' -biphenyltetracarboxylic dianhydride, 2,3,6, 7-naphthalenetetracarboxylic dianhydride, 3 ', 4, 4' -benzophenonetetracarboxylic dianhydride, 3 ', 4, 4' -dibenzoic acid terephthalamide tetracarboxylic dianhydride and 3,3 ', 4, 4' -diphenylsulfonetetracarboxylic dianhydride.
4. A method for preparing an ultralow expansion fluorine-containing polyimide film according to any one of claims 1 to 3, comprising the steps of:
step 1: under the protection of inert gas, dissolving aromatic diamine with amide groups and fluorine-containing groups in an organic solvent, and adding aromatic dianhydride to obtain polyamide acid homogeneous phase solution;
step 2: coating the polyamide acid homogeneous phase solution on a substrate, curing, stripping and drying to obtain a polyimide film to be treated;
and step 3: the polyimide film to be treated is laid on a substrate, fixed and annealed to obtain the polyimide film;
the curing comprises the following steps: curing at 60-100 ℃ for 1-2 hours, curing at 160-250 ℃ for 1-2 hours, and curing at 300-350 ℃ for 1-2 hours.
5. The method for preparing the ultralow-expansion fluorine-containing polyimide film according to claim 4, wherein the annealing treatment comprises the following steps: at the temperature of 250 ℃ and 300 ℃ for 0.5-1 hour, and at the temperature of 350 ℃ and 400 ℃ for 15-40 minutes.
6. The method for preparing the ultralow expansion fluorine-containing polyimide film according to claim 4, wherein the solid content of the polyamic acid homogeneous solution is 10-30 wt.%; the molar ratio of the aromatic diamine to the aromatic dianhydride is (0.95-1.02): 1.
7. The method according to claim 4, wherein the means for fixing the polyimide film to be treated on the substrate in step 3 is a means capable of applying a tensile stress to the film.
8. The method for preparing an ultralow expansion fluorine-containing polyimide film according to any one of claims 4 to 7, wherein said organic solvent is one or more of N-methylpyrrolidone, γ -butyrolactone, N '-dimethylacetamide, N' -dimethylformamide, dimethyl sulfoxide and cyclopentanone.
9. The ultralow expansion fluorine-containing polyimide film according to any one of claims 1 to 3, which is used as a substrate material in the fields of electronics and flexible display.
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