A bend-resistant polyimide-based graphite film and a method of making the same

Abstract

The application discloses a bending-resistant polyimide-based graphite film and a preparation method thereof, and belongs to the technical field of polyimide-based graphite film preparation. The preparation method of the bending-resistant polyimide-based graphite film comprises the following steps: using polyamide acid solution I containing an inorganic foaming aid as an intermediate layer, using polyamide acid solution II containing a cross-linking network as upper and lower layers, and preparing a polyimide film with a three-layer structure through an extrusion method; and sequentially performing carbonization, graphitization and calendering on the polyimide film with the three-layer structure to obtain the bending-resistant polyimide-based graphite film. The prepared graphite film has regular and compact upper and lower surface layers and an intermediate layer containing a micro-crease structure, so that the graphite film can be bent and stretched when being bent, stress concentration is avoided, and thus the graphite film is endowed with excellent bending-resistant performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyimide-based graphite film preparation, and particularly relates to a bending-resistant polyimide-based graphite film and a preparation method thereof. BACKGROUND

[0002] A polyimide (PI) film is carbonized and graphitized at high temperature to prepare a polyimide-based graphite film, which has performance advantages such as high thermal conductivity and high specific heat capacity and is widely used in terminal fields such as smart phones, tablet computers and notebook computers and is one of the mainstream heat dissipation materials in the current consumer electronics field.

[0003] With the continuous improvement of the market penetration rate of folding screen intelligent terminal products, the market demand for flexible AMOLED is increasing, and the demand for polyimide-based graphite film as a heat dissipation material for intelligent terminal screens is also increasing. Since the flexible AMOLED has a foldable feature, the polyimide-based graphite film is also required to have high bending resistance.

[0004] The polyimide-based graphite film is prepared by preparing a polyamide acid resin, casting, drying, stretching and imidization to prepare a polyimide film, and then heating the film to above 1000 DEG C for vacuum carbonization, removal of non-carbon atoms (N, H and O), microcrystalline aggregation at 2000-2500 DEG C to form graphite crystals, and gradual perfection of the crystal lattice above 2500 DEG C to gradually form a regular and dense graphite hexagonal net layer structure. However, the breaking and reformation of chemical bonds at high temperatures and the removal of non-carbon atoms will cause crystal defects in the microstructure, resulting in a decrease in the flexibility of the graphite film and poor bending resistance. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide a bending-resistant polyimide-based graphite film and a preparation method thereof, which solves the problems in the prior art.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] A preparation method of a bending-resistant polyimide-based graphite film, comprising the following steps:

[0008] An inorganic foaming aid-containing polyamide acid solution I is used as an intermediate layer, and a crosslinked network-containing polyamide acid solution II is used as an upper and lower layer, respectively, to prepare a polyimide film with a three-layer structure by an extrusion method;

[0009] The polyimide film with the three-layer structure is sequentially subjected to carbonization, graphitization and calendering to obtain a bending-resistant polyimide-based graphite film.

[0010] Further, the preparation process of the polyamide acid solution I is as follows: adding inorganic foaming aid into aprotic polar solvent and uniformly ultrasonic dispersing, then adding diamine monomer to dissolve, and then adding dianhydride in batches to prepare by polycondensation reaction.

[0011] Further, in the polyamide acid solution I, the inorganic foaming aid is at least one of barium carbonate, calcium hydrogen phosphate and strontium sulfate, and the average particle size of the inorganic foaming aid is 0.5 um-5 um.

[0012] Further, in the polyamide acid solution I, the aprotic polar solvent is DMAc, the diamine monomer is p-phenylenediamine and 4,4'-diamino diphenyl ether, and the dianhydride monomer is 1,2,4,5-benzene tetracarboxylic dianhydride.

[0013] Further, in the polyamide acid solution I, the mass ratio of the inorganic foaming aid is 0.05-0.2%.

[0014] Further, the preparation process of the polyamide acid solution II is as follows: dissolving diamine monomer and triamine monomer in aprotic polar solvent, and then adding dianhydride monomer in batches to prepare by crosslinking reaction.

[0015] Further, in the polyamide acid solution II, the triamine monomer is 2,4,6-pyridine triamine, the diamine monomer is p-phenylenediamine and 4,4'-diamino diphenyl ether, the dianhydride monomer is 1,2,4,5-benzene tetracarboxylic dianhydride, and the aprotic polar solvent is DMAc.

[0016] Further, the process for preparing the polyimide film with three-layer structure by extrusion method is as follows: connecting the polyamide acid solution I and the polyamide acid solution II to the three-layer co-extrusion slit die at the same time, and then preparing by casting, drying, stretching and pressure amine.

[0017] Further, the carbonization process includes: under vacuum, first increasing the temperature to 600-800℃ at a rate of 3-5℃ / min, keeping for 60-90min, then increasing the temperature to 800-1000℃ at a rate of 3-5℃ / min, keeping for 60-90min, and then increasing the temperature to 1000-1200℃ at a rate of 3-5℃ / min, keeping for 60-90min.

[0018] Further, the specific process of graphitization includes: under inert gas protection, first increasing the temperature to 1800-2400℃ at a rate of 10-30℃ / min, keeping for 90-120min, then increasing the temperature to 2400-2800℃ at a rate of 10-30℃ / min, keeping for 90-120min, and finally increasing the temperature to 2800-3000℃ at a rate of 10-30℃ / min, keeping for 120-180min.

[0019] Further, the calendering adopts a double-roller calender, and the calendering speed is 1-3 m / min.

[0020] A bending-resistant polyimide-based graphite film is prepared by the above preparation method.

[0021] The present application has the following beneficial effects:

[0022] In the preparation of the polyimide-based graphite film, the upper and lower polyimide films containing cross-linked networks limit the movement of macromolecular segments, so that the macromolecular segments are arranged regularly. After carbonization and graphitization, a regular and dense hexagonal network structure of graphite is formed. The intermediate polyimide film contains inorganic foaming aids, which form microvoids in the graphite film after high-temperature decomposition. After rolling to remove the air in the microvoids, microfolds are formed. The regular and dense upper and lower surface layers of the graphite film and the intermediate layer containing microfolds make the graphite film "flexible and stretchable" when bending, avoiding damage caused by stress concentration, thereby imparting excellent bending resistance to the graphite film. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0024] The preparation method of a bending-resistant polyimide-based graphite film will be specifically described below through the following embodiments.

[0025] Embodiment 1

[0026] S1, preparation of polyamide acid solution I containing inorganic foaming aids:

[0027] 0.118 g of barium carbonate with an average particle size of 1 um was added to 190 g of DMAc and ultrasonically dispersed uniformly. Then, 3.93 g of p-phenylenediamine and 17.00 g of 4,4'-diaminodiphenyl ether were added and dissolved completely, and then 25.9 g of 1,2,4,5-benzenetetracarboxylic dianhydride was added in batches for reaction, to obtain the polyamide acid solution I containing inorganic foaming aids.

[0028] S2, preparation of polyamide acid solution II containing cross-linked networks:

[0029] 3.93 g of p-phenylenediamine, 12.14 g of 4,4'-diaminodiphenyl ether, and 3.01 g of 2,4,6-pyridine triamine were dissolved in 190 g of DMAc. After complete dissolution, 25.9 g of 1,2,4,5-benzenetetracarboxylic dianhydride was added in batches for reaction, to obtain the polyamide acid solution II containing cross-linked networks.

[0030] S3, simultaneously connecting polyamide acid solution I and polyamide acid solution II to a three-layer co-extrusion slit die (polyamide acid solution I as the middle layer, and polyamide acid solution II as the upper and lower layers), and preparing a three-layer structure polyimide film with a total thickness of 75 um through casting, drying, stretching, and imidization.

[0031] S4, preparing a polyimide-based graphite film:

[0032] The 75 um three-layer structure polyimide film is placed in a vacuum environment, first heated to 700℃ at a heating rate of 5℃ / min, kept for 60 min, then heated to 900℃ at a heating rate of 5℃ / min, kept for 60 min, and then heated to 1100℃ at a heating rate of 5℃ / min, kept for 90 min for carbonization;

[0033] Under argon protection, heated to 2000℃ at a heating rate of 20℃ / min, kept for 90 min, then heated to 2500℃ at a heating rate of 20℃ / min, kept for 90 min, and then heated to 3000℃ at a heating rate of 20℃ / min, kept for 120 min for graphitization; after cooling, the film is taken out and calendered using a double roll calender at a calendering rate of 1 m / min, to prepare a polyimide-based graphite film.

[0034] Example 2

[0035] S1, preparing an inorganic foaming aid-containing polyamide acid solution I:

[0036] 0.237 g of dicalcium phosphate with an average particle size of 0.5 um is added to 190 g of DMAc and ultrasonically dispersed uniformly, then 3.93 g of p-phenylenediamine and 17.00 g of 4,4'-diaminodiphenyl ether are added and dissolved completely, and then 25.9 g of 1,2,4,5-benzene-tetracarboxylic dianhydride is added in batches for reaction, to obtain the inorganic foaming aid-containing polyamide acid solution I.

[0037] S2, preparing a cross-linked network-containing polyamide acid solution II:

[0038] 3.93 g of p-phenylenediamine, 12.14 g of 4,4'-diaminodiphenyl ether, and 3.01 g of 2,4,6-triaminopyridine are dissolved in 190 g of DMAc, and after complete dissolution, 25.9 g of 1,2,4,5-benzene-tetracarboxylic dianhydride is added in batches for reaction, to obtain the cross-linked network-containing polyamide acid solution II.

[0039] S3, simultaneously connect the polyamide acid solution I and the polyamide acid solution II to the three-layer co-extrusion slit die (the polyamide acid solution I as the middle layer, and the polyamide acid solution II as the upper and lower layers), prepare a three-layer structure polyimide film with a total thickness of 75 um through casting, drying, stretching, and press amine.

[0040] S4, prepare a polyimide-based graphite film:

[0041] The 75 um three-layer structure polyimide film is placed in a vacuum environment, first heated to 600℃ at a heating rate of 3℃ / min, kept for 60 min, then heated to 800℃ at a heating rate of 3℃ / min, kept for 60 min, and then heated to 1000℃ at a heating rate of 3℃ / min, kept for 60 min for carbonization;

[0042] Under argon protection, heat to 1800℃ at a heating rate of 10℃ / min, keep for 90 min, then heat to 2400℃ at a heating rate of 10℃ / min, keep for 90 min, and then heat to 2800℃ at a heating rate of 10℃ / min, keep for 120 min, take out the film after cooling, and prepare a polyimide-based graphite film using a double roller calender with a calendering rate of 1 m / min.

[0043] Example 3

[0044] S1, prepare a polyamide acid solution I containing inorganic foaming aid:

[0045] 0.475 g of strontium sulfate with an average particle size of 5 um is added to 190 g of DMAc, ultrasonically dispersed uniformly, then 3.93 g of p-phenylenediamine and 17.00 g of 4,4'-diaminodiphenyl ether are added and dissolved completely, and then 25.9 g of 1,2,4,5-benzene-tetracarboxylic dianhydride is added in batches for reaction to obtain the polyamide acid solution I containing inorganic foaming aid.

[0046] S2, prepare a polyamide acid solution II containing cross-linked network:

[0047] 3.93 g of p-phenylenediamine, 12.14 g of 4,4'-diaminodiphenyl ether, and 3.01 g of 2,4,6-triamine pyridine are dissolved in 190 g of DMAc, and after complete dissolution, 25.9 g of 1,2,4,5-benzene-tetracarboxylic dianhydride is added in batches for reaction to obtain the polyamide acid solution II containing cross-linked network.

[0048] S3, simultaneously connect the polyamide acid solution I and the polyamide acid solution II to the three-layer co-extrusion slit die (the polyamide acid solution I as the middle layer, and the polyamide acid solution II as the upper and lower layers), prepare a three-layer structure polyimide film with a total thickness of 75 um through casting, drying, stretching, and press amine.

[0049] S4, preparing polyimide-based graphite film:

[0050] The 75-μm three-layer structure polyimide film was placed in a vacuum environment, first heated to 800°C at a heating rate of 5°C / min, kept for 90 min, then heated to 1000°C at a heating rate of 5°C / min, kept for 90 min, and then heated to 1200°C at a heating rate of 5°C / min, kept for 90 min for carbonization;

[0051] Heated to 2400°C at a heating rate of 30°C / min under argon protection, kept for 120 min, then heated to 2800°C at a heating rate of 30°C / min, kept for 120 min, and then heated to 3000°C at a heating rate of 30°C / min, kept for 180 min, and the film was taken out after cooling, and was calendered using a double-roller calender at a calendering rate of 3 m / min to prepare a polyimide-based graphite film.

[0052] Comparative Example 1

[0053] S1, preparing polyamide acid solution I containing inorganic foaming aid:

[0054] 0.118 g of barium carbonate with an average particle size of 1 μm was added to 190 g of DMAc and ultrasonically dispersed uniformly, 3.93 g of p-phenylenediamine and 17.00 g of 4,4'-oxydianiline were then added and dissolved completely, and 25.9 g of 1,2,4,5-benzenetetracarboxylic acid dianhydride was added in batches for reaction to obtain polyamide acid solution I containing inorganic foaming aid.

[0055] S2, the polyamide acid solution I was connected to a single-layer extrusion slit die, and a single-layer structure polyimide film with a total thickness of 75 μm was prepared through casting, drying, stretching, and pressure amination.

[0056] S3, preparing polyimide-based graphite film:

[0057] The 75-μm single-layer structure polyimide film was placed in a vacuum environment, first heated to 700°C at a heating rate of 5°C / min, kept for 60 min, then heated to 900°C at a heating rate of 5°C / min, kept for 60 min, and then heated to 1100°C at a heating rate of 5°C / min, kept for 90 min for carbonization; heated to 2000°C at a heating rate of 20°C / min under argon protection, kept for 90 min, then heated to 2500°C at a heating rate of 20°C / min, kept for 90 min, and then heated to 3000°C at a heating rate of 20°C / min, kept for 120 min, and the film was taken out after cooling, and was calendered using a double-roller calender at a calendering rate of 1 m / min to prepare a polyimide-based graphite film.

[0058] Comparative Example 2

[0059] S1, preparation of a polyamic acid solution without inorganic foaming aid:

[0060] 3.93 g of p-phenylenediamine and 17.00 g of 4,4'-oxydianiline were dissolved in 190 g of DMAc solvent, after complete dissolution, 25.9 g of 1,2,4,5-benzene-tetracarboxylic dianhydride was added in batches for reaction, to obtain a polyamic acid solution without inorganic foaming aid.

[0061] S2, the polyamic acid solution was connected to a single-layer extruded slit die, and a single-layer structure polyimide film with a total thickness of 75 um was prepared by casting, drying, stretching and pressure amination.

[0062] S3, preparation of a polyimide-based graphite film:

[0063] The 75 um single-layer structure polyimide film was placed in a vacuum environment, first heated to 700℃ at a heating rate of 5℃ / min, kept for 60 min, then heated to 900℃ at a heating rate of 5℃ / min, kept for 60 min, then heated to 1100℃ at a heating rate of 5℃ / min, kept for 90 min for carbonization; under argon protection, heated to 2000℃ at a heating rate of 20℃ / min, kept for 90 min, then heated to 2500℃ at a heating rate of 20℃ / min, kept for 90 min, then heated to 3000℃ at a heating rate of 20℃ / min, kept for 120 min, after cooling, the film was taken out, and a double-roller calender was used for calendering, the calendering rate was 1 m / min, to obtain a polyimide-based graphite film.

[0064] Experimental test

[0065] The polyimide-based graphite films prepared in Examples 1-3 and Comparative Examples 1-2 of the present application were evaluated, and the specific evaluation properties and indexes are as follows:

[0066] The bending resistance of the graphite film was evaluated using a MIT folding strength tester (bending angle 135±2°, R2). The test results are shown in Table 1;

[0067] Table 1: Bending performance test results

[0068] Sample Number of folds Film surface condition Example 1 100000 No change Example 2 100000 No change Example 3 100000 No change Comparative Example 1 20000 Obvious creases Comparative Example 2 1000 Cracked

[0069] From Table 1, it can be seen that:

[0070] The polyimide-based graphite film prepared by carbonizing, graphitizing and calendering the polyimide film of Comparative Example 1 containing the inorganic foaming aid has a micro-fold structure, but the micro-fold structure also exists in the surface layer of the graphite film, resulting in a large surface gap of the graphite film and easy damage when bending, thus the bending resistance of the graphite film is insufficient. The polyimide-based graphite film prepared by carbonizing, graphitizing and calendering the polyimide film of Comparative Example 2 not containing the inorganic foaming aid does not contain the micro-fold structure, and cannot avoid stress concentration and damage when bending. The graphite films of Examples 1-3 contain the micro-fold structure in the middle layer, and the upper and lower surface layers are regular and dense, thus the graphite films have excellent bending resistance.

[0071] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0072] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A method for preparing a bend-resistant polyimide-based graphite film, characterized in that, The method comprises the following steps: A three-layer polyimide film is prepared by an extrusion method using a polyamide acid solution I containing an inorganic foaming aid as an intermediate layer and a polyamide acid solution II containing a crosslinked network as upper and lower layers; The three-layer polyimide film is sequentially subjected to carbonization, graphitization and calendering to obtain a bend-resistant polyimide-based graphite film.

2. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The polyamide acid solution I is prepared by adding an inorganic foaming aid into aprotic polar solvent and ultrasonic dispersion, then adding diamine monomers to dissolve and adding dianhydride monomers in batches for polycondensation reaction.

3. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, In the polyamide acid solution I, the inorganic foaming aid is at least one of barium carbonate, calcium hydrogen phosphate and strontium sulfate, and the average particle size of the inorganic foaming aid is 0.5-5 μm.

4. The method for preparing a bend-resistant polyimide-based graphite film according to claim 2, characterized in that, In the polyamide acid solution I, the aprotic polar solvent is DMAc, the diamine monomers are p-phenylenediamine and 4,4'-diamino diphenyl ether, and the dianhydride monomers are 1,2,4,5-benzene tetra-carboxylic dianhydride.

5. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The mass fraction of the inorganic foaming aid in the polyamide acid solution I is 0.05-0.2%.

6. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The polyamide acid solution II is prepared by dissolving diamine monomers and triamine monomers in aprotic polar solvent and then adding dianhydride monomers in batches for crosslinking reaction.

7. The method for preparing a bend-resistant polyimide-based graphite film according to claim 6, characterized in that, In the polyamide acid solution II, the triamine monomers are 2,4,6-pyridine triamine, the diamine monomers are p-phenylenediamine and 4,4'-diamino diphenyl ether, the dianhydride monomers are 1,2,4,5-benzene tetra-carboxylic dianhydride, and the aprotic polar solvent is DMAc.

8. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The three-layer polyimide film is prepared by an extrusion method by connecting the polyamide acid solution I and the polyamide acid solution II to a three-layer co-extrusion slit die, and then performing casting, drying, stretching and ammoniumization to obtain the three-layer polyimide film.

9. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The carbonization step comprises the following steps: first, increasing the temperature to 600-800℃ at a rate of 3-5℃ / min under vacuum, then increasing the temperature to 800-1000℃ at a rate of 3-5℃ / min, and then increasing the temperature to 1000-1200℃ at a rate of 3-5℃ / min.

10. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The graphitization step comprises the following steps: first, increasing the temperature to 1800-2400℃ at a rate of 10-30℃ / min under inert gas protection, then increasing the temperature to 2400-2800℃ at a rate of 10-30℃ / min, and finally increasing the temperature to 2800-3000℃ at a rate of 10-30℃ / min.

11. The method for preparing a bend-resistant polyimide-based graphite film according to claim 1, characterized in that, The calendering is performed by a double-roller calendering machine at a calendering rate of 1-3 m / min.

12. A bend-resistant polyimide-based graphite film, characterized by, The method is prepared by any one of claims 1-11.