Heat-resistant conductive polyimide composite film and preparation method thereof

Abstract

The present invention belongs to the field of polymer material technology, and in particular to a kind of heat-resistant conductive polyimide composite film and preparation method thereof.First, equimolar diamine monomer 4,4-diaminobiphenyl-2,2-dicarboxylic acid and dianhydride monomer 4,4'-oxydiphthalic anhydride are reacted in N, N-dimethylacetamide having been purified by dehydration to form a polyamic acid solution, which is cast on a glass plate and placed in a muffle furnace for thermal imidization to obtain a polyimide film with high heat resistance, and then the prepared AgNWs mixed solution is uniformly sprayed on the PI surface layer by a spray gun, and finally a layer of PAI is applied to form a three-layer composite film. The heat-resistant conductive polyimide film structure provided by the present invention is novel, and the composite film heat resistance, optical performance, electrical conductivity, mechanical performance of the obtained composite film are excellent, and there is good electromagnetic shielding effectiveness, and there is very good prospect in the field of optical electromagnetic materials.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a heat-resistant conductive polyimide composite film and a preparation method thereof. Background Art

[0002] With the widespread use of electronic devices, electromagnetic interference (EMI) has become an extremely acute problem in modern society. Severe EMI can cause sensitive electronic devices to fail, and even worse, cause significant harm to human health. Therefore, there is an urgent market demand for electromagnetic shielding materials that can eliminate EMI.

[0003] Traditional EMI shielding materials, such as metals like Cu and Ag, have drawbacks such as heavy weight, low corrosion resistance, poor heat resistance, and complex processing, which limit their application at high temperatures. In recent years, conductive polymer composites, which offer high electromagnetic interference protection, have attracted widespread attention due to their lightweight and corrosion-resistant properties.

[0004] Due to its unique chemical structure - the presence of imide ring, polyimide has extremely high heat resistance. In addition, the various properties of PI are in line with the needs of the optoelectronic materials market, so it has good commercial prospects. Summary of the Invention

[0005] The present invention provides a polyimide resin having the following repeating units:

[0006]

[0007] 1000 <n<5000;

[0008] The preparation method of polyimide resin comprises the following steps:

[0009]

[0010] The specific preparation steps are as follows:

[0011] (1) Preparation of polyimide film

[0012] Add the dehydrated N-N-dimethylacetamide (DMAc) solvent to a three-necked flask equipped with a mechanical stirrer. Add the diamine monomer all at once. After the diamine monomer is completely dissolved in the solvent (approximately 30 minutes), add the dianhydride monomer all at once. Replace the atmosphere with nitrogen 3-5 times to isolate the apparatus from air and prevent premature hydrolysis of the dianhydride monomer. After 2 hours of reaction, move the reaction from the air environment to an ice-water bath and allow the reaction to continue overnight.

[0013] The diamine monomer is 4,4-diaminobiphenyl-2,2-dicarboxylic acid (TFDB), and the dianhydride monomer is 4,4'-oxydiphthalic anhydride (ODPA);

[0014] The molar ratio of dianhydride to diamine is 1:1;

[0015] (2) The PAA acid solution obtained in step (1) is cast on a glass substrate, and the glass substrate is placed in a muffle furnace and subjected to gradient heating to perform gradient thermal imidization to obtain a polyimide film.

[0016] The temperature gradient of thermal imidization is: 80°C-2h, 110°C-1h, 140°C-1h, 180°C-1h, 220°C-1h, 260°C-1h.

[0017] A second objective of the present invention is to provide a heat-resistant, shielding polyimide composite film with high light transmittance and excellent electromagnetic shielding effectiveness, meeting the market requirements for commercial electromagnetic shielding materials (dB). Furthermore, the strength and toughness of the single-sided conductive composite film provided by the present invention are adjustable, meeting the needs of various applications.

[0018] The heat-resistant conductive polyimide composite film of the present invention is a three-layer composite film, which uses a polyimide film as a substrate. An AgNWs nanowire mixed solution is evenly sprayed on the polyimide film substrate by a spray gun to form a conductive layer. Finally, a layer of PAI solution is coated and dried to form a composite film.

[0019] Among them, the thickness of the PI substrate film is about 100-150 μm, the AgNWs mixed solution exists on the substrate as a conductive electromagnetic shielding layer with a thickness of about 5-30 μm, and the thickness of the PAI layer is about 10 μm.

[0020] The structural formula of PAI is shown below:

[0021]

[0022] The preparation method of AgNWs is as follows: weigh polyvinyl pyrrolidone and dissolve it completely in ethylene glycol under magnetic stirring at 60°C; then add AgNO3 and 0.6mmol / L FeCl3 solution in sequence; stir magnetically for 5 minutes, and heat the mixture to 130°C, transfer it to a three-necked flask, ensure that the temperature of the mixture is at 130°C, and let it stand for 5 hours without stirring to grow nanowires; collect the obtained product, centrifuge it at 4000rpm for 10 minutes, and then flocculate it three times with acetone, wash it with ethanol and water, filter it, and dry it to obtain silvery-white silver nanowires.

[0023] A third aspect of the present invention provides a method for preparing a heat-resistant, conductive, and electromagnetic shielding polyimide composite film, comprising the following steps:

[0024] (1) The polyimide film was placed in a 120°C oven for preheating for 5 min, and the AgNWs mixed solution was evenly sprayed on the surface of the polyimide film substrate layer by a spray gun and dried for 3 to 10 min to obtain a double-layer high heat-resistant single-sided conductive composite film;

[0025] (2) The PAI mixed solution was drop-coated on the film obtained in step (1), and the composite film was dried in an oven at 120° C. for 10 to 20 minutes, and then the composite film was peeled off the glass substrate to obtain a three-layer high heat-resistant conductive composite film.

[0026] The present invention has the following characteristics:

[0027] The highly heat-resistant conductive composite film prepared by the present invention exhibits ultra-high conductivity (surface resistance of 0.28Ω and virtually no change in resistance upon heating within 300°C) and mechanical properties. It also exhibits excellent electromagnetic shielding effectiveness (exceeding 40dB in the 320MHz to 3.2GHz range). Compared to other commercially available electromagnetic shielding materials, this composite film has superior light transmittance and outstanding heat resistance, promising broad applications in the electromagnetic shielding field. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 IR spectra of the polyamic acid solution (PAA) and polyimide film (ODPA-TFDB) synthesized in Example 1.

[0029] Figure 2 This is the thermogravimetric diagram of the polyimide film (ODPA-TFDB) prepared in Example 1.

[0030] Figure 3 This is the stress-strain curve of the polyimide film composite film prepared in Example 1.

[0031] Figure 4 The transmittance curves of the polyimide film (ODPA-TFDB) and its composite film prepared in Example 1 are shown.

[0032] Figure 5 The surface resistance of the composite film prepared in Example 1 changes at different temperatures.

[0033] Figure 6 This is a graph showing the electromagnetic shielding effectiveness of the composite film prepared in Example 1. DETAILED DESCRIPTION

[0034] In order to illustrate the present invention more clearly, the present invention is further described below in conjunction with embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0035] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. The experimental materials, reagents, etc. used in the following experimental examples can be obtained through commercial channels or known experimental methods.

[0036] Example 1

[0037] The structural formula of polyimide resin (PI) is shown below:

[0038]

[0039] 1000 of them <n<5000。

[0040] The preparation method of polyimide resin ODPA-TFDB is as follows:

[0041] (1) Water removal and purification of N-dimethylacetamide (DMAc):

[0042] Place 60 ml of DMAc into a 100 ml single-necked flask, add a rotor and 0.4 g of CaH2, seal the flask with a balloon, and stir magnetically at room temperature for 24 hours to allow for complete reaction. After stirring, set the flask to a vacuum distillation apparatus. Since DMAc has a boiling point of 163°C, set the vacuum distillation temperature to 155°C. Separate the first and last fractions, and collect and seal the remaining fractions. Yield: 80%.

[0043] (2) Preparation of polyimide:

[0044] The dianhydride monomer, 4,4'-oxydiphthalic anhydride (ODPA), was pretreated in an oven at 170°C for 12 hours. In a three-necked flask equipped with a mechanical stirrer, 45 ml of dehydrated DMAc was added, along with 4,4-diaminobiphenyl-2,2-dicarboxylic acid TFDB (2.7226 g, 10 mmol). The atmosphere was then purged with nitrogen three times to ensure air removal. The mixture was stirred for 30 minutes until completely dissolved.

[0045] The dianhydride monomer, 4,4'-oxydiphthalic anhydride (ODPA) (3.10215 g, 10 mmol), was added all at once. The viscosity was observed and the reaction was continued for 4 h. Then, 3 ml of solvent (DMAc) was added until the final solid content reached 12 wt %. The mixture was stirred in an ice-water bath for 18 h, and the resulting PAA acid solution was collected.

[0046] The glass sheet was preheated in a muffle furnace in advance, and then the PAA acid solution obtained above was drop-coated on the glass sheet for thermal imidization (80°C-2h, 110°C-1.5h, 140°C-1.5h, 180°C-1h, 210°C-1h, 240°C-1h) to obtain a PI film with a thickness of 150 μm.

[0047] (3) Preparation of AgNWs mixed solution

[0048] Weigh 0.2g of polyvinylpyrrolidone (PVP) and completely dissolve it in 25ml of ethylene glycol (EG) under magnetic stirring at 60°C (the magnetic speed is set to 150, which takes about 4 hours). Add 0.25g of AgNO3 and 3.5g of 0.6mmol / L FeCl3 solution to the resulting reaction solution. Stir magnetically for 5 minutes and heat the mixture to 130°C. Prepare a three-necked flask, thermometer, etc. After the mixture temperature reaches 130°C, transfer it to a three-necked flask and insert a thermometer to easily monitor the temperature of the mixture. Ensure that the temperature of the mixture remains at 130°C during the reaction. Let it stand for 5 hours without stirring to grow nanowires.

[0049] The resulting product was collected and centrifuged at 4000 rpm for 10 minutes. It was then flocculated three times with acetone, washed five times with ethanol and five times with water, and then filtered and dried to obtain silvery-white silver nanowires.

[0050] Finally, AgNWs (0.1 g) were added to isopropanol (10 mL) to obtain an AgNWs mixed solution.

[0051] (4) Preparation of conductive composite films

[0052] The PI film from step (2) was preheated in a 120°C forced air oven for 5 minutes. The prepared AgNWs mixed solution was then evenly sprayed onto the surface of the PI film using a spray gun, forming a 10 μm conductive network. After 5 minutes in the oven, a layer of PAI solution (30 ml of a 0.5 g / 12 ml solution in NMP) was applied to the top layer (10 μm thick) and dried in the oven for 10 minutes. The film was peeled off the glass plate to obtain a conductive composite film with PI as the substrate layer and AgNWs as the conductive layer.

[0053] The infrared data of the polyimide film provided by the present invention are as follows: Figure 1 As shown:

[0054] FTIR(KBr,ν,cm -1 ):3446,1739,1610,1368,1261,1104,823,724.

[0055] Example 2

[0056] The difference between this embodiment and embodiment 1 is that the thickness of the PI matrix layer in the prepared composite film is 100 μm, and other processing methods are the same as those in embodiment 1. The electromagnetic shielding performance of the polyimide-based composite film at 3.2 GHz is 49.32 dB.

[0057] Example 3

[0058] The difference between this embodiment and embodiment 1 is that the thickness of the conductive layer in the prepared composite film is 5 μm, and other processing methods are consistent with those in embodiment 1.

[0059] Example 4

[0060] The difference between this embodiment and embodiment 1 is that the thickness of the conductive layer in the prepared composite film is 30 μm, and other processing methods are consistent with those in embodiment 1.

[0061] Example 5

[0062] The difference between this embodiment and embodiment 1 is that the drying time of the AgNWs mixed solution in step (4) is 10 minutes, and the other processing methods are the same as those in embodiment 1.

[0063] Comparative Example 1

[0064] The difference between this embodiment and embodiment 1 is that the drying time of the AgNWs mixed solution in step (4) is 1 hour, and the other processing methods are the same as those in embodiment 1.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 1 is that the material used for the intermediate conductive layer is a multi-walled carbon nanotube (CNT) layer, and other processing methods are consistent with those in Example 1.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 1 is that the composite film prepared in step (4) is a double-layer structure of PI / AgNWs, and the other processing methods are consistent with Example 1.

[0069] Due to the lack of the PAI protective layer, the surface resistance and electromagnetic shielding performance stability of the composite film are somewhat lower than those of Example 1. Under ultrasonic and acid-base conditions, the conductive layer is easily detached, resulting in a significant reduction in electromagnetic shielding performance.

[0070] The following performance tests were performed on the prepared polyimide film, and the test results are shown in Table 1:

[0071] Optical transmittance: The optical transmittance of ODPA-TFDB was tested using an UltraScan PRO automatic colorimeter with a wavelength of 375-1000 nm and a film thickness of 150 μm.

[0072] Mechanical properties: The mechanical properties of ODPA-TFDB were tested according to the national standard GB / T 1040.3-2006 using a WDT-10 electronic universal testing machine.

[0073] Thermal stability testing of ODPA-TFDB was conducted on a PerkinElmer TGA 4000 thermogravimetric analyzer. Specific parameters included: sample mass: 40.2 mg; test temperature: 30-800°C; heating rate: 10°C / min; and test environment: nitrogen atmosphere.

[0074] Table 1

[0075] sample Optical transmittance% Tensile strength MPa Young's modulus GPa Elongation at break % Initial decomposition temperature oC ODPA-TFDB 84 121 2.36 19 397 Example 1 73 104 1.62 38 / Example 2 74 78 1.64 39 / Example 3 79 102 1.62 38 / Example 4 66 100 1.6 36 / Example 5 74 102 1.63 37 / Comparative Example 1 76 104 1.63 38 / Comparative Example 2 32 99 1.54 33 / Comparative Example 3 75 93 1.72 35 /

[0076] The following tests were performed on the prepared composite film. The test results are shown in Table 2. The changes in the surface resistance of the composite film at different temperatures are shown in Chart 3:

[0077] Optical transmittance: The optical transmittance of the composite film was tested by UltraScan PRO automatic colorimeter, with a wavelength of 375-1000 nm and a film thickness of 160 μm.

[0078] Surface resistance: The surface resistance of the composite film was measured by using an ST2253 digital four-probe surface resistance tester to select the sheet resistance.

[0079] Electromagnetic shielding performance: The electromagnetic shielding performance of the composite film was tested using the ZN31300 flange coaxial shielding effectiveness tester and the DSA800E series spectrum analyzer. The film was a circular film with a diameter of 10 cm.

[0080] Table 2

[0081] sample Optical transmittance% Surface resistance Ω Electromagnetic shielding effect dB Example 1 73 0.28 52.01 Example 2 74 0.29 49.32 Example 3 79 3.2 46.27 Example 4 66 0.21 54.98 Example 5 74 9.4 45.79 Comparative Example 1 76 25 38.2 Comparative Example 2 32 528 26.64 Comparative Example 3 75 0.31 50.29

[0082] Table 3

[0083] sample 10℃ / Ω 50℃ / Ω 100℃ / Ω 150℃ / Ω 200℃ / Ω 250℃ / Ω Example 1 0.28 0.33 0.37 0.42 0.44 0.39 Comparative Example 3 0.25 0.32 0.54 0.89 1.33 2.5

[0084] Table 4 shows the electromagnetic shielding performance of the composite film at different pH values ​​and the percentage of electromagnetic shielding performance at room temperature.

[0085] Table 4

[0086] sample PH2 / % PH5 / % PH7 / % PH9 / % PH12 / % Example 1 94.3 95.05 97.49 93.28 89.99 Comparative Example 3 69.5 84.29 92.33 79.58 61.1

[0087] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this patent can make slight changes or modifications to equivalent embodiments using the above-mentioned technical contents without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A heat-resistant conductive polyimide composite film, characterized in that: The heat-resistant conductive polyimide composite film is a three-layer composite film, with a polyimide film as the base, and an AgNWs nanowire mixed solution is evenly sprayed on the polyimide film base by a spray gun, and dried for 10 minutes to form a conductive layer; finally, a layer of polyamide-imide solution is applied and dried to form a composite film; The steps of preparing the polyimide substrate film are as follows: (1) In a purified NN dimethylacetamide solvent, the diamine monomer 4,4-diaminobiphenyl-2,2-dicarboxylic acid and the dianhydride monomer 4,4'-oxydiphthalic anhydride are fully reacted to obtain a polyimide precursor polyamic acid solution; (2) subjecting the polyimide precursor obtained in step (1) to gradient thermal imidization to obtain a polyimide base film having the following repeating units: ， Where n is the repeating structural unit, which is 1000 <n<5000; The structural formula of the polyamide-imide (PAI) is shown below: ； The thickness of the polyimide base film is 100-150 μm, the thickness of the conductive layer is 10-30 μm, and the thickness of the PAI layer is 10 μm.

2. The heat-resistant conductive polyimide composite film according to claim 1, characterized in that: The preparation method of AgNWs nanowires is as follows: weigh polyvinyl pyrrolidone and dissolve it completely in ethylene glycol under magnetic stirring at 60°C; then add AgNO3 and 0.6 mmol / L FeCl3 solution in sequence; stir magnetically for 5 minutes, and heat the mixture to 130°C, transfer it to a three-necked flask, ensure that the temperature of the mixture is at 130°C, and let it stand for 5 hours without stirring to grow nanowires; collect the obtained product, centrifuge it at 4000 rpm for 10 minutes, and then flocculate it with acetone three times, wash it with ethanol and water, filter it, and dry it to obtain silvery-white silver nanowires.

3. The heat-resistant conductive polyimide composite film according to claim 1, characterized in that: In step (1), the structural formulas of the dianhydride monomer and the diamine monomer are as follows: 。 4. The heat-resistant conductive polyimide composite film according to claim 1, characterized in that: The temperature gradient of thermal imidization in step (2) is: 80°C-2 h, 110°C-1 h, 140°C-1 h, 180°C-1 h, 220°C-1 h, 260°C-1 h.

5. The heat-resistant conductive polyimide composite film according to claim 1, characterized in that: The steps of the preparation method of the heat-resistant conductive polyimide composite film are as follows: (1) The polyimide substrate film was placed in a 120°C oven for preheating for 5 min, and the AgNWs mixed solution was evenly sprayed on the surface of the polyimide film substrate layer through a spray gun and dried for 10 min to obtain a double-layer high heat-resistant single-sided conductive composite film; (2) A layer of PAI solution was drop-coated on the film obtained in step (1), and the composite film was dried in an oven at 120°C for 10 to 20 minutes, and then the composite film was peeled off the glass substrate to obtain a three-layer highly heat-resistant conductive composite film.

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