CN118165262A

CN118165262A - Polyimide film with high elongation at break and low thermal expansion coefficient, and preparation method and application thereof

Info

Publication number: CN118165262A
Application number: CN202410299802.0A
Authority: CN
Inventors: 李月蓉; 娜菲莎·穆什塔奇; 谭丽芸; 宁开凤; 方省众; 陈国飞
Original assignee: Ningbo Institute of Material Technology and Engineering of CAS
Current assignee: Ningbo Institute of Material Technology and Engineering of CAS
Priority date: 2024-03-15
Filing date: 2024-03-15
Publication date: 2024-06-11

Abstract

The invention relates to the technical field of high polymer material modification, and discloses a polyimide film with high elongation at break and low thermal expansion coefficient, a preparation method and application thereof, wherein the polyimide film is prepared by reacting raw materials comprising dianhydride and diamine to obtain polyamic acid, adding imidazole organic base to mix to obtain polyamic acid composition, and imidizing to obtain the polyimide film; the dianhydride is one or more than two of 1,2,4, 5-pyromellitic dianhydride, 3', 4' -benzophenone tetracarboxylic dianhydride and 3,3', 4' -biphenyl tetracarboxylic dianhydride; the diamine is one or more than two of 4,4' -diaminodiphenyl ether and 2- (4-aminophenyl) -5-aminobenzoxazole; the imidazole organic base is one or more of imidazole, 1, 2-dimethyl imidazole and benzimidazole. The invention adopts the combined action of the rigid structure and the imidazole organic alkali, can effectively give consideration to the low thermal expansion coefficient and the high elongation at break, and has excellent comprehensive performance.

Description

Polyimide film with high elongation at break and low thermal expansion coefficient, and preparation method and application thereof

Technical Field

The invention relates to the technical field of high polymer material modification, in particular to a polyimide film with high elongation at break and low thermal expansion coefficient, and a preparation method and application thereof.

Background

Polyimide (PI) is an aromatic heterocyclic polymer compound with an imide structure in a main chain repeating unit, has good mechanical properties, high temperature resistance, dimensional stability, solvent resistance, excellent electrical properties and the like, and is widely applied to the industries of aerospace, automobile manufacturing, electronic and electric appliances, mechanical and chemical engineering and the like. In recent years, with the rapid development of the fields of smart phones, tablet computers, LCD displays, LED backlight modules and the like, the demand for PI films is rapidly growing. Polyimide is widely used as a Flexible Copper Clad Laminate (FCCL) base film due to excellent mechanical properties and dimensional stability, but with the development of technology towards short, small, light and thin directions, higher requirements are put on the performance and the process of a circuit board, in particular to the aspects of reducing the Coefficient of Thermal Expansion (CTE), improving the elongation at break and the like.

Polyimide with excellent insulating properties is often selected as a benchmark, which requires polyimide films with excellent tensile properties, i.e. higher elongation at break. In addition, the flexible copper-clad plate and the wrapping electromagnetic wire also require the polyimide film to have good elongation at break. Therefore, polyimide films with high elongation at break are gaining increasing attention. A method for producing a flexible printed circuit board comprising a polyimide thin layer and a metal foil, which has excellent properties in terms of heat resistance, electrical properties and mechanical properties and is free from curling, wrinkling, warping and the like.

In the report (high molecular theory report, 2021,52 (10): 1308-1315), 2- (4-aminophenyl) -5-aminopyridine (PD) was copolymerized with diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA), and the ratio of the rigid and flexible structural units in the molecular chain was controlled to prepare a series of polyimide copolymers. The results show that: when the content of the rigid diamine PD containing pyridine structure in the polyimide is 50-80% of the diamine content, the thermal expansion coefficient is reduced from 7.3ppm/K to-1.7 ppm/K, but the elongation at break of the film is also reduced from 44.8% to 26%. However, the synthesis of rigid diamine (PD) containing pyridine structure has more steps, the yield is only 60 percent, and the rigid diamine is not commercialized, thus being not beneficial to industrial use.

In the report (Song supernatural. Preparation and performance of polyimide film with low thermal expansion coefficient [ D ]. Nanjing university of chemical industry, 2019.), the main chain structure is controlled by adjusting monomer content of pyromellitic dianhydride (PMDA), 2, 3',4' -biphenyl tetracarboxylic dianhydride (BPDA) and p-Phenylenediamine (PDA), so as to realize the regulation of thermal expansion coefficient. However, as the pyromellitic dianhydride (PMDA) content increased, the CTE decreased from 12.63 to 5.42ppm/K and the elongation at break decreased from 9.54% to 7% when the PMDA content was half the total dianhydride molar amount. Although this method can reduce the thermal expansion coefficient of the polyimide film, it cannot simultaneously meet the requirement of increasing the elongation at break of the polyimide film.

In report (Chinese Journal of Polymer Science,2019,37 (3): 268-278), a method was adopted to prepare high performance polyimide films by using chemical imidization, i.e. in pyromellitic dianhydride (PMDA): 2, 2-bis [4- (4-aminophenoxy) phenyl ] propane (BAPP): the polyimide acid solution with the molar ratio of p-Phenylenediamine (PDA) of 2:1:1 is added with a certain amount of dehydrating agent and catalyst, and then imidization film forming measurement data, especially when the molar ratio of PMDA to acetic anhydride to isoquinoline is 1:4:1, the thermal expansion coefficient of chemical imidization is 44.9ppm/K, the thermal imidization data is 9.8ppm/K, 78% is reduced, and the elongation at break is improved by 300% from 4% of thermal imidization to 16% of chemical imidization. This method can reduce the thermal expansion coefficient of the polyimide film and improve the elongation at break of the film. However, the film is prepared by chemical imidization, and the film has complex operation, easy gelation and large smell.

Therefore, there is an urgent need for a polyimide resin and a method for preparing the same that is simple to operate, reduces the thermal expansion coefficient of the polyimide film, and improves the elongation at break of the film.

Disclosure of Invention

Aiming at the problem that the low thermal expansion coefficient and the high elongation at break of the polyimide film can not be achieved, the polyimide film with the high elongation at break and the low thermal expansion coefficient is provided, and the polyimide film with the high elongation at break and the low thermal expansion coefficient can be effectively achieved by adopting the combined action of a rigid structure and imidazole organic base, so that the polyimide film has excellent comprehensive performance.

In order to achieve the above purpose, the invention adopts the following technical scheme:

a polyimide film with high elongation at break and low thermal expansion coefficient, which is prepared by reacting raw materials containing dianhydride and diamine to obtain polyamic acid, adding imidazole organic alkali to mix to obtain polyamic acid composition, and imidizing to obtain the polyimide film;

the dianhydride is one or more than two of 1,2,4, 5-pyromellitic dianhydride, 3', 4' -benzophenone tetracarboxylic dianhydride and 3,3', 4' -biphenyl tetracarboxylic dianhydride; the structure is as follows:

The diamine is one or more than two of 4,4' -diaminodiphenyl ether and 2- (4-aminophenyl) -5-aminobenzoxazole; the structure is as follows:

The imidazole organic base is one or more of imidazole, 1, 2-dimethyl imidazole and benzimidazole.

According to the invention, the polyamide acid is prepared by using dianhydride containing a rigid structure and diamine containing a certain flexible chain segment, then imidazole organic alkali is utilized to attack carbon atoms on carboxyl in polyamide acid PAA as an affinity reagent, and hydrogen atoms are transferred to carboxyl, so that hydrogen is trapped on an amide bond, acid group cyclodehydration ring imidization is promoted, the CTE of a film is reduced by adjusting the type, the proportion and the molecular ordering of dianhydride diamine monomer, the lower the system CTE with better linearity is, the lower the film CTE with a rigid rod-shaped structure on the main chain can be, and finally, the polyimide film resin with high thermal dimensional stability and good mechanical property is obtained, the CTE is reduced, and the elongation at break is improved.

Preferably, the raw material for preparing the polyamic acid by polymerization further comprises a third monomer;

The third monomer is p-phenylenediamine and/or 4,4' -diaminoanilide, and the structure is specifically as follows:

Because of the action of imidazole organic alkali, the elongation at break of the polyimide film is improved, but the CTE is slightly improved, in some embodiments, a third monomer with higher rigidity can be added to improve the modulus of the material, the chain segment is shorter, the rigidity is higher, and the thermal expansion coefficient of the material can be reduced to a certain extent. The addition of p-Phenylenediamine (PDA) or 4,4' -Diaminoanilide (DABA) can reduce the CTE of the film and improve the mechanical property of the film. This is because the PDA structure is short and rigid, making the PI segments more closely aligned and the intermolecular forces greater; the amide bond of DABA is a non-planar structure, -H is positioned on one side of the benzene ring plane, so that the steric hindrance influence can be reduced, and a tight hydrogen bond is formed between the amide bond and N of the imide ring, so that PI molecular chains are stacked more tightly, the intermolecular interaction is enhanced, the linear expansion coefficient is reduced, and the mechanical property is improved.

The molar amount of the third monomer is 40% or less of the molar amount of the diamine. The addition in this range can effectively reduce the thermal expansion coefficient with less influence on the elongation at break. Preferably, the molar amount of the third monomer is 5 to 40% of the molar amount of the diamine.

The molar ratio of the dianhydride to the diamine is 0.98-1.05:1. Preferably, the molar ratio of dianhydride to diamine is 1.02:1, because dianhydride is easily hydrolyzed by moisture in air or solvent, and is deactivated, thereby affecting the relative molecular mass of the polyamic acid, and thus the addition of dianhydride monomer is required to be slightly excessive in order to prepare a high molecular weight polyamic acid solution.

The molar ratio of the imidazole organic base to the diamine is 0.5-5:1. Preferably, the molar ratio of imidazole organic base to diamine is 1-1.8:1. The upper limit of the amount of the organic base is preferably 2.0 times. Even if the organic base is added at a ratio of 2.0 times or more, the imidization effect is not significantly different from that of the addition of the organic base at a ratio of 2.0 times. In contrast, when the amount of the organic base exceeds 2.0 times, part of the organic base remains in the film, and there is a possibility that the production line is contaminated as an impurity in the steps of preparing a printed circuit substrate or the like.

The thermal expansion coefficient of the polyimide film is less than or equal to 22ppm/K, and the elongation at break is more than or equal to 20%.

The invention also provides a preparation method of the polyimide film with high elongation at break and low thermal expansion coefficient, which comprises the following steps:

step 1, mixing dianhydride and diamine in a polar organic solvent for reaction to obtain polyamic acid solution; adding imidazole organic base into the mixture to form salt, so as to obtain a polyamic acid composition;

and 2, coating the polyamic acid composition on a support, and heating and imidizing to obtain the polyimide film.

The preparation method disclosed by the invention is simple in process, and the solid content of the polyamic acid solution is 8-20%.

Preferably, the polyamic acid solution has a solids content of 8 to 15%. Too low a solids content results in a low viscosity of the polyamic acid solution; too high a solids content can lead to a rapid increase in the viscosity of the system and possibly to the appearance of gels, which are not easy to process.

Preferably, the raw material for preparing the polyamic acid solution in step 1 further includes a third monomer, and the molar amount of the third monomer is 40% or less of the diamine.

Further preferably, in step 1, the dianhydride and diamine are mixed and then the third monomer is added for mixing. After the diamine monomer is introduced, the amide bond is more prone to form hydrogen bond action with N in the main chain, so that the interval between PI molecular chains is reduced, the arrangement is more compact, the rotation of chain segments is effectively inhibited, the linear expansion coefficient is reduced, and the mechanical property is improved.

The polar organic solvent comprises one or more of N, N '-dimethylformamide, N' -dimethylacetamide, N-methylpyrrolidone, m-cresol and dimethyl sulfoxide.

In the step 1, the mixed reaction temperature is between minus 10 and 50 ℃ and the reaction time is between 6 and 24 hours; further preferably, the reaction temperature is about 0-10 ℃ and the reaction time is 8-18h. The reaction for forming the polyamic acid is exothermic, and the low temperature is favorable for the reaction, so that the prepared polyamic acid has higher viscosity, namely high molecular weight.

The time for mixing the salt in the step 1 is 1-10h. Preferably, the salification time is 2-4 hours. The longer the mixing temperature of the salt is at room temperature, the higher the viscosity is, and the film formation is not easy.

The polyamic acid solution is directly cast into a film and heated to prepare a polyimide film; the residual solvent in the polyamic acid film can be removed by further heating at 80-350 deg.c for 1-24 hr in step 2.

Preferably, the heating process is: the temperature is kept at 80-90 deg.C, 95-105 deg.C, 140-160 deg.C, 190-220 deg.C, 240-260 deg.C and 280-310 deg.C for 0.5-1.5h, and then at 340-360 deg.C for 0.5-1h.

The support body can be a glass plate, a plastic plate, a metal plate or the like as long as the surface is clean and smooth and has certain rigidity. Preferably, the support is a clean dry glass plate.

The invention also provides application of the polyimide film with high elongation at break and low thermal expansion coefficient in FCCL or flexible display.

Compared with the prior art, the invention has the following beneficial effects:

(1) The polyimide film is prepared by using dianhydride with a certain rigid structure and diamine with a certain flexible structure, and the imidization speed can be increased by adding imidazole organic base, so that the orientation degree of the film surface is improved, the linear expansion coefficient of the film surface can be effectively reduced, and the polyimide film with both low thermal expansion coefficient and high elongation at break is obtained.

(2) The polyimide film disclosed by the invention is simple in preparation method, the CTE of a product is less than or equal to 22ppm/K, the breaking elongation of the product can be improved to more than 20%, the raw materials are cheap, the experimental operation is simple and convenient, and further technological popularization is easy to realize.

Drawings

FIG. 1 is an ATR spectrum of a polyimide resin prepared in example 1 of the present invention;

FIG. 2 shows the general reaction scheme in examples 1-7 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. Modifications and equivalents will occur to those skilled in the art upon understanding the present teachings without departing from the spirit and scope of the present teachings.

The raw materials used in the following embodiments are all commercially available.

Example 1

The embodiment provides a preparation method of polyimide film resin, which comprises the following steps:

Step (1) 2.0024g (0.01 mol) of 4,4' -diaminodiphenyl ether (ODA) was added to a 100mL three-necked flask equipped with a nitrogen inlet and mechanical stirring, and dissolved in 16.9g of organic solvent N, N-dimethylacetamide (DMAc) with stirring. When the diamine was completely dissolved 2.2248g (0.0102 mol) of pyromellitic dianhydride (PMDA) were added in 2 portions with stirring. The solution was stirred at room temperature for 12 hours, and diluted with 32g of DMAc to finally obtain a viscous polyamic acid solution having a solid content of 8%. The inherent viscosity was 1.98dL/g.

And (2) adding 0.9613g (0.010 mol) of 1, 2-dimethyl imidazole (DMI) into the polyimide acid reaction solution in the step (1), and mechanically stirring for 2 hours at room temperature to obtain a uniformly mixed polyamic acid salt solution.

Step (3), immediately taking 12.5g of the polyamic acid solution in the step (2), uniformly pouring onto a clean and dried glass plate (25 cm. Times.15 cm), and putting into a common oven. The temperature program is as follows: the temperature is kept at 80 ℃, 100 ℃, 150 ℃, 200 ℃, 250 ℃ and 300 ℃ for 1h and at 350 ℃ for 0.5h. Soaking the obtained glass plate with the polyimide film in hot water, stripping the glass plate to obtain an independent polyimide film, and drying the moisture in a drying oven at 100 ℃ to obtain a final polyimide film, wherein the structure is as follows:

FTIR characterization of the structure of the prepared film resulted in a graph showing the characteristic absorption peaks of imide ring c=o at 1775cm ^-1 (c=o asymmetric stretching vibration) and 1709cm ^-1 (symmetric stretching vibration) and the peak of imide ring C-N stretching vibration at 1365cm ^-1, as evident from the graph. Meanwhile, no characteristic absorption peak of amic acid (absorption peak of C=O in 1660cm ^-1 -COOH) appears, which indicates that PAA is subjected to thermal imidization treatment, imidization reaction is complete, and polyimide film with very high imidization degree is obtained, and meanwhile, the intrinsic viscosity of the polyamide acid precursor of the system is 1.98dL/g, which indicates that the polymer with high molecular weight is prepared.

Example 2

Step (1), a polyamic acid solution was produced in the same manner as in step (1) in example 1.

Step (2), 1.4420g (0.015 mol) of 1, 2-Dimethylimidazole (DMI) was added to step (1)

Adding the mixture into the reaction solution, and mechanically stirring the mixture at room temperature for 2 hours. The polyamic acid solution which is evenly mixed is obtained.

Step (3), preparing a PI film according to the method of the step (3) in the example 1, wherein the PI film has the following structure:

Example 3

Step (1) 1.4017g (0.007 mol) of 4,4' -diaminodiphenyl ether (ODA) and 0.3244g (0.003 mol) of p-phenylenediamine (p-PDA) were added to a 100mL three-necked flask equipped with a nitrogen inlet and mechanical stirring, and dissolved in 15.8g of organic solvent N, N-dimethylacetamide (DMAc) with stirring. When the diamine was completely dissolved 2.2248g (0.0102 mol) of pyromellitic dianhydride (PMDA) was added with stirring. The solution was stirred at room temperature for 12 hours, and 30g of DMAc was added to reduce the viscosity, to finally obtain a polyamic acid viscous solution having a solid content of 8%. The intrinsic viscosity was 1.5dL/g.

And (2) adding 1.4420g (0.015 mol) of 1, 2-Dimethylimidazole (DMI) into the polyimide acid reaction solution in the step (1), and mechanically stirring at room temperature for 2 hours to obtain a uniformly mixed polyamic acid salt solution.

Example 4

Step (1) 1.4017g (0.007 mol) of 4,4' -diaminodiphenyl ether (ODA) was added to a 100mL three-necked flask equipped with a nitrogen inlet and mechanical stirring, and dissolved in N, N-dimethylacetamide (DMAc) as an organic solvent under stirring. When the ODA was completely dissolved, 2.2248g (0.0102 mol) of pyromellitic dianhydride (PMDA) was added with stirring, and 0.3244g (0.003 mol) of p-phenylenediamine (p-PDA) was added immediately after stirring. The solution was stirred at room temperature for 12 hours, and 30g of DMAc was added to reduce the viscosity, to finally obtain a polyamic acid viscous solution having a solid content of 8%. The intrinsic viscosity was 1.3dL/g.

Example 5

Step (1) A polyamic acid solution was produced in the same manner as in step (1) in example 3, except that the amount of p-PDA added was changed to 0.003mol and 0.002 mol.

And (2) adding 1.5381g (0.016 mol) of 1, 2-dimethyl imidazole (DMI) into the polyimide acid reaction solution in the step (1), and mechanically stirring at room temperature for 2 hours to obtain a uniformly mixed polyamic acid salt solution.

Step (3), preparing a PI film according to the method of the step (3) in the example 3, wherein the PI film has the following structure:

Example 6

Step (1) 1.4017g (0.007 mol) of 4,4 '-diaminodiphenyl ether (ODA) and 0.68178g (0.003 mol) of 4,4' -Diaminobenzidine (DABA) were added to a 100mL three-necked flask equipped with a nitrogen inlet and mechanical stirring, and dissolved in 17g of organic solvent N, N-dimethylacetamide (DMAc) with stirring. When the diamine was completely dissolved 2.2248g (0.0102 mol) of pyromellitic dianhydride (PMDA) was added with stirring. The solution was stirred at room temperature for 12 hours, and a proper amount of DMAc was added to reduce the viscosity, to finally obtain a polyamic acid viscous solution having a solid content of 8%. The intrinsic viscosity was 1.31dL/g.

Example 7

Step (1), a polyamic acid solution was produced in the same manner as in step (1) in example 6, except that the amount of DABA added was changed to 0.0038 mol.

And (2) adding 0.96133g (0.010 mol) of 1, 2-dimethyl imidazole (DMI) into the polyimide acid reaction solution in the step (1), and mechanically stirring at room temperature for 2 hours to obtain a uniformly mixed polyamic acid salt solution.

Step (3), preparing a PI film according to the method of the step (3) in the example 6, wherein the PI film has the following structure:

The general formulas of the reaction processes in examples 1-7 are shown, wherein Ar in examples 1 and 2 is ODA, ar in examples 3, 4 and 5 is ODA and PDA, and Ar in examples 6 and 7 is ODA and DABA.

Comparative example 1 contains no organic base

Step (2), preparing a PI film according to the method of step (3) in example 1, wherein the PI film has the following structure:

Comparative example 2

And (2) adding 11g of DMAC into the step (1), and stirring at room temperature to reduce the solid content of the polyamic acid solution to 8% for later use. 1.9374g (0.015 mol) of Isoquinoline (IQL) was added to the above reaction mixture and stirred at room temperature for 2h. The polyamic acid salt solution which is evenly mixed is obtained.

Comparative example 3

Step (2), 1.9226g (0.020 mol) of 1, 2-Dimethylimidazole (DMI) was added to step (1)

Adding the mixture into the reaction solution, and stirring the mixture at room temperature for 2 hours. The polyamic acid salt solution which is evenly mixed is obtained.

Comparative example 4

Step (1) in a 100mL three-necked flask equipped with a nitrogen inlet and mechanical stirring, 2.0024g (0.01 mol) of 4,4' -diaminodiphenyl ether (ODA) was added to N, N-dimethylacetamide (DMAc) as an organic solvent and dissolved by stirring. When the diamine was completely dissolved 3.1642g (0.0102 mol) of 4,4' -oxydiphthalic anhydride (ODPA) were added in 2 portions with stirring. The solution was stirred at room temperature for 12 hours, and diluted with an appropriate amount of DMAc to finally obtain a polyamic acid viscous solution having a solid content of 10%. The intrinsic viscosity was 1.05dL/g.

Step (2), 1.4420g (0.015 mol) of 1, 2-Dimethylimidazole (DMI) was added to the reaction solution in step (1), and the mixture was stirred at room temperature for 2 hours. The polyamic acid salt solution which is evenly mixed is obtained.

Comparative example 5

Step (2), 1.5179g (0.015 mol) of triethylamine was added to the reaction mixture in step (1), and the mixture was stirred at room temperature for 2 hours. The polyamic acid salt solution which is evenly mixed is obtained.

Film Performance test

The films of examples 1-7 and comparative examples 1-5 were tested for elastic modulus (GPa), tensile strength (MPa), elongation at break (%), model Instron Model 5567, using a universal material tester according to test standard ASTM D882, with a tensile mode for measurement and a speed control of 5mm/min at room temperature. The test sample film is 120mm long, 10mm wide and 20-30 μm thick, and the average value of 3-5 times of parallel tests is taken.

The CTE of the film was measured using a static thermo-mechanical analyzer, model TMA Q400V 22.5 Build31. The protective gas is nitrogen, the load is 20 mu N, the temperature interval is 25-210 ℃, the temperature rising rate is 3 ℃/min, the film sample is 18mm long, 8mm wide and the thickness is about 20-30 mu m.

Performance data of the polyimide films of examples and comparative examples as shown in table 1, it was found that by comparing the data of examples 1-2 and comparative example 1, it was possible to increase the elongation at break while lowering the CTE, compared with the case where DMI was not used, by subjecting the polyamic acid solution containing DMI in a certain addition amount range to thermal imidization. However, in comparative example 3, when the DMI addition amount was 2 times, the elongation at break was also decreased. From these results, it is found that the addition of a small amount of DMI to the polyamic acid solution is useful for producing a polyimide film having low CTE and excellent mechanical properties.

As can be seen from examples 3 and 4, if dianhydride and diamine are mixed uniformly, then the third monomer is added, the mechanical properties of the material can be improved to a certain extent compared with the method that the dianhydride and diamine are added together, ODA-PMDA chain segments are formed in example 4, and compared with the method of blending in example 3, the method of sequencing of the chain segments in example 4 is regular, so that the mechanical properties of the material can be improved again to a certain extent.

Comparative examples 3, 5, 7 show that the amount of the third monomer used increases the mechanical properties of the material, decreases the coefficient of thermal expansion, and when added to 38% of the diamine molar amount, the elongation at break of the material decreases slightly, as further increases may make it difficult to achieve a better combination of properties. When the content of the third monomer is within a certain range, the rigidity of the molecular chain can be improved, and the chain segment is not easy to break, so that the mechanical property is improved.

Example 6 shows that after DABA monomer is introduced first, amide bond is more prone to form hydrogen bond with N in the main chain, so that the interval between PI molecular chains is reduced, the arrangement is more compact, the rotation of chain segments is effectively inhibited, and therefore, the linear expansion coefficient is reduced and the mechanical property is improved.

As can be seen from comparative examples 2 and 5, the mechanical properties of the polyimide film can be improved and the thermal expansion coefficient can be reduced when the imidization degree of the polyamic acid precursor is improved to a certain degree only by singly improving the mechanical properties of the film or reducing the CTE using isoquinoline or triethylamine. The isoquinoline plays a plasticizing role in the thermal imidization stage of the polyimide film, and when the film is heated to a certain temperature, the isoquinoline volatilizes, but the plasticizing effect is reserved, so that the elongation at break of the film is improved. In addition, due to the organic base such as triethylamine, the alkalinity is strong, and the molecular chain of polyimide can be attacked and weakened, so that the elongation at break of the polyimide is reduced.

Comparative example 4 shows that the structural selection of dianhydride or diamine is not suitable, and even if imidazole organic base is used, it is difficult to ensure both elongation at break and CTE.

Table 1 PI film performance tables for examples and comparative examples

Claims

1. A polyimide film with high elongation at break and low thermal expansion coefficient is characterized in that raw materials comprising dianhydride and diamine are reacted to obtain polyamic acid, imidazole organic alkali is added to the polyamic acid to be mixed to obtain a polyamic acid composition, and imidization is carried out to obtain the polyimide film;

The dianhydride is one or more than two of 1,2,4, 5-pyromellitic dianhydride, 3', 4' -benzophenone tetracarboxylic dianhydride and 3,3', 4' -biphenyl tetracarboxylic dianhydride;

The diamine is one or more than two of 4,4' -diaminodiphenyl ether and 2- (4-aminophenyl) -5-aminobenzoxazole;

2. The polyimide film with high elongation at break and low coefficient of thermal expansion according to claim 1, wherein the raw material for preparing polyamic acid by polymerization further comprises a third monomer;

the third monomer is p-phenylenediamine and/or 4,4' -diaminoanilide, and the molar quantity of the third monomer is less than 40% of the molar quantity of diamine.

3. The polyimide film having a high elongation at break and a low coefficient of thermal expansion according to claim 1, wherein the molar ratio of dianhydride to diamine is 0.98 to 1.05:1.

4. The polyimide film of claim 1, wherein the molar ratio of imidazole organic base to diamine is 0.5 to 5:1.

5. The polyimide film with high elongation at break and low thermal expansion coefficient according to claim 1, wherein the thermal expansion coefficient of the polyimide film is not more than 22ppm/K, and the elongation at break is not less than 20%.

6. The method for producing a polyimide film having a high elongation at break and a low thermal expansion coefficient according to any one of claims 1 to 5, comprising the steps of:

7. The method for producing a polyimide film having a high elongation at break and a low thermal expansion coefficient according to claim 6, wherein the polar organic solvent comprises one or more of N, N '-dimethylformamide, N' -dimethylacetamide, N-methylpyrrolidone, m-cresol and dimethylsulfoxide.

8. The method for producing a polyimide film having a high elongation at break and a low coefficient of thermal expansion according to claim 6, wherein the mixing reaction temperature in step 1 is-10 to 50 ℃ and the reaction time is 6 to 24 hours;

the time for mixing the salt in the step 1 is 1-10h.

9. The method for producing a polyimide film having a high elongation at break and a low coefficient of thermal expansion according to claim 6, wherein the heating imidization temperature in step 2 is 80 to 350℃and the reaction time is 1 to 24 hours.

10. Use of a polyimide film of high elongation at break and low coefficient of thermal expansion according to claim 1 in FCCL or flexible displays.