CN117207623A - Preparation method of PTFE (polytetrafluoroethylene) -based composite film with high dielectric property - Google Patents
Preparation method of PTFE (polytetrafluoroethylene) -based composite film with high dielectric property Download PDFInfo
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- 239000004810 polytetrafluoroethylene Substances 0.000 title claims abstract description 124
- 229920001343 polytetrafluoroethylene Polymers 0.000 title claims abstract description 124
- 239000002131 composite material Substances 0.000 title claims abstract description 46
- 238000002360 preparation method Methods 0.000 title claims abstract description 25
- -1 polytetrafluoroethylene Polymers 0.000 title claims description 6
- 239000000835 fiber Substances 0.000 claims abstract description 51
- 238000010438 heat treatment Methods 0.000 claims abstract description 43
- 238000009987 spinning Methods 0.000 claims abstract description 39
- 238000007731 hot pressing Methods 0.000 claims abstract description 35
- 238000000034 method Methods 0.000 claims abstract description 32
- 238000010041 electrostatic spinning Methods 0.000 claims abstract description 18
- 238000001816 cooling Methods 0.000 claims abstract description 14
- 239000002002 slurry Substances 0.000 claims abstract description 13
- 239000000243 solution Substances 0.000 claims description 32
- 239000000839 emulsion Substances 0.000 claims description 21
- 239000002562 thickening agent Substances 0.000 claims description 13
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 claims description 11
- 239000002904 solvent Substances 0.000 claims description 11
- 239000000758 substrate Substances 0.000 claims description 10
- 238000005266 casting Methods 0.000 claims description 9
- 238000001035 drying Methods 0.000 claims description 8
- 238000007790 scraping Methods 0.000 claims description 8
- 239000005457 ice water Substances 0.000 claims description 5
- 230000008569 process Effects 0.000 claims description 5
- 238000002347 injection Methods 0.000 claims description 4
- 239000007924 injection Substances 0.000 claims description 4
- 238000003756 stirring Methods 0.000 claims description 4
- 229920000259 polyoxyethylene lauryl ether Polymers 0.000 claims description 3
- 239000007787 solid Substances 0.000 claims description 3
- 238000010345 tape casting Methods 0.000 abstract description 6
- 239000011159 matrix material Substances 0.000 abstract description 5
- 238000005516 engineering process Methods 0.000 abstract description 2
- 239000010408 film Substances 0.000 description 103
- 239000004697 Polyetherimide Substances 0.000 description 79
- 229920001601 polyetherimide Polymers 0.000 description 79
- 239000010410 layer Substances 0.000 description 32
- 239000002245 particle Substances 0.000 description 10
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 9
- 238000004146 energy storage Methods 0.000 description 7
- 230000007547 defect Effects 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 239000000919 ceramic Substances 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 229920000642 polymer Polymers 0.000 description 3
- 229920006254 polymer film Polymers 0.000 description 3
- WPMWEFXCIYCJSA-UHFFFAOYSA-N Tetraethylene glycol monododecyl ether Chemical compound CCCCCCCCCCCCOCCOCCOCCOCCO WPMWEFXCIYCJSA-UHFFFAOYSA-N 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 239000011229 interlayer Substances 0.000 description 2
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- 239000002861 polymer material Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
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- 239000010409 thin film Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- UBOXGVDOUJQMTN-UHFFFAOYSA-N 1,1,2-trichloroethane Chemical compound ClCC(Cl)Cl UBOXGVDOUJQMTN-UHFFFAOYSA-N 0.000 description 1
- 241001391944 Commicarpus scandens Species 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- 239000004721 Polyphenylene oxide Substances 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
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- 239000003989 dielectric material Substances 0.000 description 1
- 238000001523 electrospinning Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 229920000295 expanded polytetrafluoroethylene Polymers 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 125000001072 heteroaryl group Chemical group 0.000 description 1
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- 229920000570 polyether Polymers 0.000 description 1
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Abstract
The invention discloses a preparation method of a PTFE-based composite film with high dielectric property, which comprises the following steps: preparing PTFE slurry; preparing a PTFE wet film by a tape casting method; heat treatment, cooling and stripping to obtain a PTFE base film; preparing PEI spinning solution; preparing PEI fiber layers on the surfaces of two sides of the PTFE base film by using PEI spinning solution through an electrostatic spinning method; and carrying out hot pressing on the PTFE base film provided with the PEI fiber layer to obtain the PTFE base composite film. According to the invention, the PTFE film with compact internal morphology prepared by the tape casting method is used as a matrix material, PEI fibers are attached to two sides of the PTFE film by an electrostatic spinning technology, and finally the PEI fiber is prepared into the composite film by hot pressing, so that the dielectric constant of the PTFE film can be effectively improved while the low dielectric loss of the PTFE film is kept, and the prepared composite film has the advantages of light weight, good flexibility, high output and the like, and can be applied to emerging fields such as flexible electronics and intelligent wearing.
Description
Technical Field
The invention relates to the technical field of dielectric energy storage polymer materials, in particular to a preparation method of a PTFE-based composite film with high dielectric property.
Background
With the rapid development of electronic power systems, thin film dielectric materials having excellent processability and small size and light weight are attracting attention. Polytetrafluoroethylene (PTFE) is expected to be applied to high-temperature and high-pressure thin film capacitors because of its excellent high-temperature stability and low dielectric loss. The ideal dielectric energy storage material has higher breakdown field strength and dielectric constant, however, the PTFE film prepared by the tape casting method has compact internal morphology and excellent breakdown field strength and energy storage performance, but has lower dielectric constant, thus limiting the application.
In the prior art, the dielectric constant of a polymer material is generally improved by adding ceramic filler, for example, a nano modified dielectric energy storage polymer film and a preparation method thereof disclosed in the patent with publication number CN115304822A are disclosed, and a nano ferroelectric material is used for modifying a polyvinylidene fluoride film, so that the dielectric energy storage polymer film has the characteristics of high breakdown strength, high charge and discharge efficiency, high energy density and strong corrosion resistance.
Although the ceramic filler has higher dielectric constant, when the dielectric property of the polymer film is improved, the compatibility between the nano ceramic particles and the polymer matrix is poor, and the ceramic particles are easy to agglomerate, so that the dielectric loss of the composite material is greatly increased while the dielectric constant is improved. Therefore, it is a great difficulty in the art how to increase the dielectric constant of PTFE films while maintaining low dielectric loss.
Disclosure of Invention
The invention aims to overcome the problems of the PTFE dielectric energy storage film in the prior art, and provides a preparation method of a PTFE-based composite film with high dielectric properties, wherein a PTFE film with compact internal morphology prepared by a tape casting method is used as a matrix material, PEI fibers are attached to two sides of the PTFE film by an electrostatic spinning technology, and finally the PTFE film is prepared into the composite film by hot pressing, so that the dielectric constant of the PTFE film can be effectively improved while the low dielectric loss of the PTFE film is maintained, and the prepared composite film has the advantages of light weight, good flexibility, high output and the like, and can be applied to the emerging fields of flexible electronics, intelligent wearing and the like.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a preparation method of a PTFE-based composite film with high dielectric property comprises the following steps:
(1) Preparation of PTFE slurry: adding a thickening agent into the PTFE emulsion, stirring uniformly, and then performing vacuum deaeration to obtain PTFE slurry; (2) method for preparing PTFE wet film by casting method: scraping the PTFE slurry on a substrate to obtain a PTFE wet film;
(3) Heat treatment and cooling stripping: drying the PTFE wet film, performing heat treatment, and then cooling to separate the PTFE wet film from the substrate to obtain a PTFE base film;
(4) Preparing PEI spinning solution: dissolving PEI in a solvent to obtain PEI spinning solution;
(5) And (3) electrostatic spinning: preparing PEI fiber layers on the surfaces of two sides of the PTFE base film by using PEI spinning solution through an electrostatic spinning method;
(6) Hot pressing: and (3) carrying out hot pressing on the PTFE base film provided with the PEI fiber layer to obtain the PTFE base composite film with high dielectric property.
Polyetherimide (PEI) is a heteroaromatic polymer which has a higher dielectric constant than PTFE and a lower dielectric loss, and the use of this polyether to modify PTFE films increases the dielectric constant of the PTFE film while maintaining a low dielectric loss. However, since PTFE emulsion is an aqueous dispersion and PEI is an oil-soluble substance, it is difficult to blend PTFE emulsion and PEI solution, and a composite film cannot be produced by a single solution casting method. The composite film is formed into a film alone and then is subjected to lamination, and has the problem of poor interlayer bonding property, which leads to an increase in dielectric loss of the composite film.
The invention firstly prepares a PTFE film with compact internal morphology by a tape casting method, then uses the PTFE film as a matrix material, attaches PEI fibers on two sides of the film by an electrostatic spinning method, and finally prepares the composite film by hot pressing. The PEI fiber layer prepared by the electrostatic spinning method is firmly attached to the surface of the PTFE base film, and can be compacted after hot pressing, so that the pore content of the PEI fiber layer is reduced, the compactness of the PEI fiber layer is improved, and the PEI fiber layer is tightly combined with the PTFE base film, so that the composite film can keep lower dielectric loss. Therefore, the composite film prepared by the method has good interlayer bonding property between the PEI layer and the PTFE base film, and effectively avoids the improvement of dielectric loss of the composite film. The dielectric constant of the composite film prepared by the invention can be improved from 2-2.1 to 3-3.1 of the pure PTFE film, and the dielectric loss can still be kept in the low loss range of 0.0001-0.00015. The composite film has the advantages of light weight, good flexibility, high output and the like, and can be applied to the emerging fields of flexible electronics, intelligent wearing and the like.
Preferably, the solid content of the PTFE emulsion in the step (1) is 55 to 65wt%; the thickening agent is polyoxyethylene lauryl ether, and the addition amount of the thickening agent is 5-6% of the volume of the PTFE emulsion. Because PTFE emulsion has high fluidity and is extremely easy to break emulsion in the casting process, the performance of the prepared PTFE base film is affected. According to the invention, the thickening agent is added into the PTFE emulsion, so that the dispersion stability of the PTFE emulsion can be improved, the prepared slurry meets the requirements of casting processing, demulsification is avoided in the casting process, and the prepared PTFE base film has good dielectric property.
Preferably, in step (1), the thickener is slowly added dropwise to the PTFE emulsion for a period of 7 to 9 minutes.
Preferably, the substrate in the step (2) is a PI substrate, the temperature during scraping is less than 35 ℃, the humidity is more than 40%, and the scraper speed is 4-6 mm/s.
Preferably, the drying temperature in the step (3) is 40-50 ℃ and the drying time is 60-90 min; the heat treatment method comprises the following steps: heating to 230-250 ℃ at a heating rate of 90-110 ℃/h, and preserving heat for 15-25 min; then heating to 340-360 ℃ at a heating rate of 55-65 ℃/h; finally, heating to 375-385 ℃ at a heating rate of 90-110 ℃/h, and preserving heat for 35-45 min; the cooling method is ice water bath cooling. The invention strictly controls the temperature rising rate and the temperature during heat treatment, ensures that small molecular substances such as a thickener and the like can be fully volatilized and removed, and simultaneously ensures that PTFE can be fully melted, can avoid micro defects generated in the heat treatment process as far as possible, and is beneficial to improving the high-temperature energy storage performance of the PTFE base film. In addition, the film is cooled in an ice-water bath mode after heat treatment, so that the prepared PTFE base film has good compactness and high stability, and further has excellent dielectric property.
Preferably, the PTFE base film obtained in the step (3) has a thickness of 8 to 9. Mu.m.
Preferably, the solvent in the step (4) is N-methylpyrrolidone. When N-methyl pyrrolidone is used as a solvent, the solvent cannot volatilize under the action of an external electric field in the electrostatic spinning process, the spinnability of the spinning solution is good, and the spinneret cannot be blocked.
Preferably, the mass concentration of the PEI spinning solution prepared in the step (4) is 20-40%. When the concentration of the spinning solution is too low, the residual solvent can cause the existence of beading in the fiber, the uniformity of the fiber is poor, and more defects are caused in the PEI fiber layer after hot pressing, so that the dielectric constant of the composite film is reduced; when the concentration of the spinning solution is too high, the fiber diameter is increased, partial fibers are adhered, the fibers are also uneven, more defects exist in the PEI fiber layer after hot pressing, and the dielectric constant of the composite film is not improved.
Preferably, in the step (5), the environment temperature is 25-35 ℃, the humidity is 25-35%, the push injection speed is set to be 0.1-0.2 mm/min, the positive pressure is 4-6 kV, the negative pressure is-6-4 kV, the receiving distance is 10-15 cm, and the front and back spinning time is 25-35 min.
Preferably, the hot pressing temperature in the step (6) is 230-260 ℃, the hot pressing pressure is 8-12 MPa, and the hot pressing time is 25-35 min. In the hot pressing temperature, the PEI fiber layer can be melted in the hot pressing process, so that the PEI fiber layer is compacted under the action of pressure, the pore content of the PEI fiber layer is reduced, the compactness of the PEI fiber layer is improved, and the PEI fiber layer can be tightly combined with the PTFE base film to obtain the composite film with higher dielectric property.
Therefore, the invention has the following beneficial effects:
(1) The PEI fiber layer is used for modifying the PTFE base film, so that the dielectric constant of the PTFE film can be improved, and meanwhile, the low dielectric loss of the PTFE film can be kept;
(2) Firstly preparing a PTFE base film by a tape casting method, then attaching PEI fibers on two sides of the PTFE base film by an electrostatic spinning method, and finally forming a composite film by hot pressing; the internal morphology of the PTFE base film and the PEI fiber layer after hot pressing is compact, and the PEI fiber layer is tightly combined with the PTFE base film, so that the improvement of the dielectric loss of the composite film is avoided;
(3) The composite film has the advantages of light weight, good flexibility, high output and the like, and can be applied to the emerging fields of flexible electronics, intelligent wearing and the like;
(4) The thickening agent is added into the PTFE emulsion, so that the dispersion stability of the PTFE emulsion is improved, and the prepared slurry cannot be demulsified in the casting process; and optimizing the heat treatment and cooling modes of the PTFE film, so that the prepared PTFE base film has compact internal morphology and the dielectric property of the PTFE base film is improved;
(5) The composition and the concentration of the PEI spinning solution are optimized, the spinnability of the PEI spinning solution is improved, the fibers in the prepared PEI spinning layer are uniform, a compact PEI layer is formed after hot pressing, and the dielectric constant of the composite film is improved.
Drawings
FIG. 1 is a morphology diagram of PEI fibers obtained by electrostatic spinning in examples 1-5 of the present invention under an optical microscope;
in the figure, (a) example 2; (b) example 3; (c) example 1; (d) example 4; (e) example 5;
FIG. 2 shows dielectric spectra of the composite films prepared in examples 1 to 5 of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and detailed description.
In the present invention, all the equipment and raw materials are commercially available or commonly used in the industry, and the methods in the following examples are conventional in the art unless otherwise specified.
General examples:
a preparation method of a PTFE-based composite film with high dielectric property comprises the following steps:
(1) Placing PTFE emulsion in a three-neck flask, and starting stirring; slowly dripping polyoxyethylene lauryl ether (Brij 30) serving as a thickening agent into the PTFE emulsion, wherein the addition amount of the thickening agent is 5-6% of the volume of the PTFE emulsion, and the dripping time is 7-9 min; after the dripping is finished, the three-mouth flask is closed, a connected circulating water vacuum pump is opened, and the vacuum defoaming treatment is carried out on the three-mouth flask for 15-25 min to obtain PTFE slurry;
(2) Casting method for preparing PTFE wet film: scraping the PTFE slurry on a PI film substrate to obtain a PTFE wet film; the temperature is less than 35 ℃ and the humidity is more than 40% when scraping, and the scraper speed is 4-6 mm/s;
(3) Heat treatment and cooling stripping: drying the PTFE wet film at 40-50 ℃ for 60-90 min, and carrying out heat treatment after the surface is dried, wherein the heat treatment method comprises the following steps: heating to 230-250 ℃ at a heating rate of 90-110 ℃/h, and preserving heat for 15-25 min; then heating to 340-360 ℃ at a heating rate of 55-65 ℃/h; finally, heating to 375-385 ℃ at a heating rate of 90-110 ℃/h, and preserving heat for 35-45 min; demoulding by adopting an ice water bath cooling mode after the heat treatment is finished to obtain a PTFE base film with the thickness of 8-9 mu m;
(4) Preparing PEI spinning solution: dissolving PEI in a solvent N-methylpyrrolidone (NMP) to obtain a PEI spinning solution with the concentration of 20-40 wt%;
(5) And (3) electrostatic spinning: preparing PEI fiber layers on the surfaces of two sides of the PTFE base film by using PEI spinning solution through an electrostatic spinning method; the spinning environment temperature is 25-35 ℃, the humidity is 25-35%, the push injection speed is 0.1-0.2 mm/min, the positive pressure is 4-6 kV, the negative pressure is-6 to-4 kV, the receiving distance is 10-15 cm, and the front and back spinning time is 25-35 min;
(6) Hot pressing: carrying out hot pressing on the PTFE base film provided with the PEI fiber layer to obtain a PTFE base composite film with high dielectric property, wherein the thickness of the PTFE base film is 10-11 mu m; the hot pressing temperature is 230-260 ℃, the hot pressing pressure is 8-12 MPa, and the hot pressing time is 25-35 min.
Example 1:
a preparation method of a PTFE-based composite film with high dielectric property comprises the following steps:
(1) 200mL of PTFE emulsion (Japanese Dajin D210C, solid content of 60%, average particle diameter of 200 nm) was placed in a three-necked flask, and stirring (rotation speed 200 r/min) was started; slowly dripping 10.75mL Brij 30 into PTFE emulsion for 8min; after the dripping is finished, the three-mouth flask is closed, a connected circulating water vacuum pump is opened, and vacuum defoaming is carried out on the three-mouth flask for 20min to obtain PTFE slurry;
(2) Casting method for preparing PTFE wet film: scraping the PTFE slurry on a PI film substrate to obtain a PTFE wet film; controlling the thickness of the scraper to be 30 mu m, the temperature to be 25 ℃ and the humidity to be 50%, and controlling the scraper speed to be 5mm/s and the film scraping solution to be 5mL;
(3) Heat treatment and cooling stripping: drying the PTFE wet film at 45 ℃ for 1h, and carrying out heat treatment after the surface is dried, wherein the heat treatment method comprises the following steps: heating to 240 ℃ from room temperature at a heating rate of 100 ℃/h, preserving heat for 20min, heating to 350 ℃ at a heating rate of 60 ℃/h, heating to 380 ℃ at a heating rate of 100 ℃/h, and preserving heat for 40min; demoulding by adopting an ice water bath cooling mode after the heat treatment is finished to obtain a PTFE base film with the thickness of 8 mu m;
(4) Preparing PEI spinning solution: 3g PEI particles (SABIC-1000, average molecular weight 54000) were dissolved in 10mL NMP to give a PEI dope with a concentration of 30 wt%;
(5) And (3) electrostatic spinning: preparing PEI fiber layers on the surfaces of two sides of the PTFE base film by using PEI spinning solution through an electrostatic spinning method; the spinning environment temperature is 30 ℃, the humidity is 30%, the push injection speed is set to be 0.1mm/min, the positive pressure is 5kV, the negative pressure is-5 kV, the receiving distance is 13cm, the PTFE base film is taken as a spinning matrix, and the front side and the back side of the spinning time are both 30min;
(6) Hot pressing: carrying out hot pressing on the PTFE base film provided with the PEI fiber layer to obtain a PTFE base composite film with high dielectric property and thickness of 10 mu m; the hot pressing temperature is 240 ℃, the hot pressing pressure is 10MPa, and the hot pressing time is 30min.
Example 2:
example 2 differs from example 1 in that in the preparation of the PEI dope in step (4), 2.4g PEI particles were dissolved in 10mL NMP to give a PEI dope with a concentration of 24 wt%; the remainder was the same as in example 1.
Example 3:
example 3 differs from example 1 in that in the preparation of the PEI dope in step (4), 2.6g PEI particles were dissolved in 10mL NMP to give a PEI dope with a concentration of 26 wt%; the remainder was the same as in example 1.
Example 4:
example 4 differs from example 1 in that in the preparation of the PEI dope in step (4), 3.2g PEI particles were dissolved in 10mL NMP to give a PEI dope with a concentration of 32 wt%; the remainder was the same as in example 1.
Example 5:
example 5 differs from example 1 in that in the preparation of the PEI dope in step (4), 3.6g PEI particles were dissolved in 10mL NMP to give a PEI dope with a concentration of 36 wt%; the remainder was the same as in example 1.
Comparative example 1:
comparative example 1 differs from example 1 in that in the preparation of the PEI dope in step (4), 3g PEI particles were dissolved in 10mL methylene chloride (DCM) to give a PEI dope with a concentration of 30 wt%; the remainder was the same as in example 1.
Comparative example 2:
comparative example 2 differs from example 1 in that in the preparation of the PEI dope in step (4), 3g PEI particles were dissolved in 10mL 1, 2-Trichloroethane (TCE) to give a PEI dope with a concentration of 30 wt%; the remainder was the same as in example 1.
In examples 1 to 5, PEI spinning solution was prepared by using NMP as a solvent, and the process was very continuous without blocking of the spinneret during the whole spinning process, so that a uniform PEI fiber layer could be obtained on the surface of the PTFE base film. In contrast, in comparative examples 1 and 2, when DCM and TCE are used as spinning solvents, most of the solvents are volatilized under the action of an external electric field, and polymer gel is formed at the nozzle to block the nozzle, so that when DCM and TCE are used as solvents, the PEI spinning solution does not have spinnability, and a uniform PEI fiber layer cannot be obtained on the surface of the PTFE base film, and a composite film cannot be prepared.
The morphology of the PEI fibers after electrospinning in examples 1 to 5 was observed with an optical microscope, and the results are shown in FIG. 1. Evaporating copper electrodes on the surfaces of the composite films and PTFE base films prepared in examples 1-5 respectively, wherein the diameter of the electrodes is 2mm, and the thickness of the electrodes is 0.5 mu m; the dielectric properties of each composite film were then measured and the results are shown in fig. 2 and table 1.
Table 1: and (5) testing the dielectric property of the composite film.
As can be seen from fig. 1 to 2 and table 1, the dielectric constants of the composite films prepared in examples 1 to 5 after the PET fiber layer was provided on the surface of the PTFE base film were significantly improved as compared with the PTFE base film without the PEI fiber layer, while the dielectric loss of the composite films could be kept low.
When the concentration of the PEI spinning solution is less than or equal to 30wt%, the dielectric constant of the composite film is increased along with the increase of the concentration of the PEI spinning solution, and when the concentration of the spinning solution is 30wt%, the dielectric constant of the composite film is maximum. When the concentration of PEI spinning solution is lower than 30wt%, the residual solvent can cause beads to exist in the fiber (fig. 1 (a) and (b)), the uniformity of the fiber is poor, and more defects exist in the PEI fiber layer after hot pressing, so that the dielectric constant of the composite film is reduced; when the concentration of the spinning solution is 30wt%, the PEI fiber obtained by electrostatic spinning has good and uniform morphology (FIG. 1 (c)), and the PEI fiber layer after hot pressing has fewer defects, so the PEI fiber layer has a high dielectric constant.
When the PEI spinning solution is more than 30wt%, the dielectric constant is reduced along with the increase of the concentration of the solution; this is mainly due to the fact that as the concentration of the spinning solution continues to increase, the fiber diameter increases, and at the same time, part of the fibers are adhered (fig. 1 (d) and (e)), which also causes non-uniformity of fibers in the PEI fiber layer, more defects in the layer after hot pressing, and affects the dielectric constant of the composite film.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by the person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (10)
1. The preparation method of the PTFE-based composite film with high dielectric property is characterized by comprising the following steps:
(1) Preparation of PTFE slurry: adding a thickening agent into the PTFE emulsion, stirring uniformly, and then performing vacuum deaeration to obtain PTFE slurry;
(2) Casting method for preparing PTFE wet film: scraping the PTFE slurry on a substrate to obtain a PTFE wet film;
(3) Heat treatment and cooling stripping: drying the PTFE wet film, performing heat treatment, and then cooling to separate the PTFE wet film from the substrate to obtain a PTFE base film;
(4) Preparing PEI spinning solution: dissolving PEI in a solvent to obtain PEI spinning solution;
(5) And (3) electrostatic spinning: preparing PEI fiber layers on the surfaces of two sides of the PTFE base film by using PEI spinning solution through an electrostatic spinning method;
(6) Hot pressing: and (3) carrying out hot pressing on the PTFE base film provided with the PEI fiber layer to obtain the PTFE base composite film with high dielectric property.
2. The preparation method of claim 1, wherein the solid content of the PTFE emulsion in the step (1) is 55-65 wt%; the thickening agent is polyoxyethylene lauryl ether, and the addition amount of the thickening agent is 5-6% of the volume of the PTFE emulsion.
3. The preparation method according to claim 1 or 2, wherein in the step (1), the thickener is slowly added dropwise to the PTFE emulsion for 7 to 9 minutes.
4. The preparation method of claim 1, wherein the substrate in the step (2) is a PI substrate, the temperature during scraping is less than 35 ℃, the humidity is more than 40%, and the scraper speed is 4-6 mm/s.
5. The preparation method according to claim 1, wherein the drying temperature in the step (3) is 40-50 ℃ and the drying time is 60-90 min; the heat treatment method comprises the following steps: heating to 230-250 ℃ by adopting a heating rate of 90-110 ℃/h, and preserving heat for 15-25 min; then heating to 340-360 ℃ at a heating rate of 55-65 ℃/h; finally, heating to 375-385 ℃ at a heating rate of 90-110 ℃/h, and preserving heat for 35-45 min; the cooling method is ice water bath cooling.
6. The method according to claim 1, wherein the PTFE-based film obtained in the step (3) has a thickness of 8 to 9 μm.
7. The process according to claim 1, wherein the solvent in step (4) is N-methylpyrrolidone.
8. The preparation method of claim 1 or 7, wherein the mass concentration of the PEI spinning solution prepared in the step (4) is 20-40%.
9. The preparation method of the electrostatic spinning machine according to claim 1, wherein in the step (5), the environment temperature is 25-35 ℃, the humidity is 25-35%, the injection speed is set to be 0.1-0.2 mm/min, the positive pressure is 4-6 kV, the negative pressure is-6 to-4 kV, the receiving distance is 10-15 cm, and the front and back spinning time is 25-35 min.
10. The preparation method of claim 1, wherein the hot pressing temperature in the step (6) is 230-260 ℃, the hot pressing pressure is 8-12 MPa, and the hot pressing time is 25-35 min.
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