Graphene grafted modified polytrifluorochloroethylene electret composite film

Abstract

The present application relates to a kind of graphene grafting modified polytrifluorochloroethylene electret composite film, the electret composite film includes upper layer, middle layer and lower layer, the middle layer is graphene grafting modified polytrifluorochloroethylene film, the upper layer and lower layer are polytrifluorochloroethylene film.The present application is modified by grafting graphene to polytrifluorochloroethylene molecular chain, improves the charge storage stability of composite film under high temperature and high humidity environment, and compared with blending addition method, graphene and polytrifluorochloroethylene have better compatibility.

Description

Technical Field

[0001] This invention relates to the field of polymers, and more specifically to graphene-grafted modified polychlorotrifluoroethylene electret composite films. Background Technology

[0002] An electret is a functional dielectric material capable of storing electrical charge over a long period of time. Commonly used electret materials are divided into polymer electret materials and inorganic electret materials.

[0003] Highly insulating fluoropolymers are among the most important polymer electret materials, commonly including polytetrafluoroethylene (PTFE), fusible PTFE, polychlorotrifluoroethylene (PTFE), and perfluoroethylene-propylene copolymers. Due to the inclusion of fluorine and chlorine atoms in their molecular structure, as well as their molecular composition and spatial configuration, these polymers possess excellent dielectric properties, outstanding chemical inertness, superior high and low temperature characteristics, and water vapor barrier properties, resulting in their remarkable space charge storage capacity.

[0004] Xia Zhongfu (Characteristics of Electrets of Polychlorotrifluoroethylene, Journal of Tongji University, September 1990, Vol. 18, No. 3) disclosed the electret characteristics of polychlorotrifluoroethylene. Polychlorotrifluoroethylene exhibits similar charge storage capacity and decay lifetime after positive and negative corona electreting, making it indispensable in electret devices requiring symmetry. However, due to the presence of chlorine atoms in the polychlorotrifluoroethylene molecule, its charge storage stability is poor at high temperatures, limiting its use as an electret in high-temperature environments.

[0005] Patent document CN107663276A discloses a method for preparing a gold nanoparticle-polytetrafluoroethylene (PTFE) composite electret film. The method involves preparing a uniformly dispersed gold nanoparticle-PTFE (Au-PTFE) composite dispersion by mixing gold nanoparticles and PTFE dispersion in a specific weight ratio. This dispersion is then directly spin-coated onto a surface-treated aluminum sheet. After drying, heat treatment, and corona charging, the Au-PTFE composite electret film is obtained. The electret performance of this composite electret film can be maintained at over 80% after immersion in water, rinsing, and drying. However, this film preparation method requires a solvent due to the dispersion-based film-forming process, making the process complex. Furthermore, it does not address the issue of poor charge storage stability of the electret film in high-temperature environments. Summary of the Invention

[0006] The present invention aims to provide a graphene-grafted modified polychlorotrifluoroethylene electret composite film, which has good charge storage stability and excellent water vapor barrier properties under high temperature and high humidity conditions, and thus can play a normal electret role in high temperature and high humidity working environment.

[0007] The technical solution of the present invention is as follows:

[0008] A graphene-grafted modified polychlorotrifluoroethylene electret composite film comprises an upper layer, an intermediate layer, and a lower layer, wherein the intermediate layer is a graphene-grafted modified polychlorotrifluoroethylene resin, and the upper and lower layers are conventional polychlorotrifluoroethylene films.

[0009] The preparation method of graphene-grafted modified polychlorotrifluoroethylene resin of the present invention includes the following steps: (1) a mixture of graphene, silane coupling agent and alcohol solvent is refluxed, filtered and dried to obtain modified graphene; (2) polychlorotrifluoroethylene resin, modified graphene and initiator are reacted at high temperature to obtain graphene-grafted modified polychlorotrifluoroethylene resin; preferably, the preparation method of graphene-grafted modified polychlorotrifluoroethylene resin includes the following steps: (1) a mixture of graphene, silane coupling agent and alcohol solvent is refluxed at 60-90°C for 3-5 hours, filtered and dried at 100-130°C for 1-3 hours to obtain modified graphene; (2) conventional polychlorotrifluoroethylene resin, modified graphene and initiator are mixed at 230-260°C for 5-10 minutes to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0010] The solid content in the mixture described in step (1) is 20-30%.

[0011] The mass ratio of silane coupling agent to graphene in step (1) is 0.1 to 5:100; preferably, the mass ratio of silane coupling agent to graphene is 0.5 to 2:100.

[0012] The graphene mentioned in step (1) is selected from one or more of graphene oxide, reduced graphene oxide, hydrogenated graphene or fluorinated graphene.

[0013] The size of the graphene described in step (1) can meet the requirements of this invention; preferably, the size of the graphene is 5 to 50 μm; more preferably, the size of the graphene is 5 to 20 μm.

[0014] The silane coupling agent mentioned in step (1) is selected from one or more of 3-(2,3-epoxypropoxy)propyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, methacryloyloxypropyltrimethoxysilane, aminopropyltriethoxysilane, aminoethylaminopropyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltritert-butoxysilane, vinyltritert-butylperoxysilane, or vinyltriacetoxysilane; preferably, the silane coupling agent is selected from one or more of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltritert-butoxysilane, vinyltritert-butylperoxysilane, or vinyltriacetoxysilane.

[0015] The alcohol solvent mentioned in step (1) is a solvent applicable in the art; preferably, the alcohol solvent is selected from one or both of methanol and ethanol.

[0016] In step (2), the mass ratio of polychlorotrifluoroethylene resin, modified graphene and initiator is 100:1~4:0.01~0.1; preferably, the mass ratio of polychlorotrifluoroethylene resin, modified graphene and initiator is 100:2~3:0.01~0.1.

[0017] The initiator mentioned in step (2) is an initiator applicable in the art; preferably, the initiator is selected from one or more of benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide or tert-butyl hydrogen peroxide.

[0018] The reaction vessel in step (2) is a reaction vessel applicable in the art; preferably, the reaction vessel is a torque rheometer, in which the screw speed is 90 to 150 r / min.

[0019] The intermediate layer of the present invention comprises graphene-grafted modified polychlorotrifluoroethylene resin.

[0020] The intermediate layer of the present invention comprises polychlorotrifluoroethylene resin and graphene-grafted modified polychlorotrifluoroethylene resin, wherein the mass ratio of polychlorotrifluoroethylene resin to graphene-grafted modified polychlorotrifluoroethylene resin is 100:5-20; preferably, the mass ratio of polychlorotrifluoroethylene resin to graphene-grafted modified polychlorotrifluoroethylene resin is 100:5-10.

[0021] The melt flow index of the polychlorotrifluoroethylene resin described in this invention is 5–50 g / 10 min; preferably, the melt flow index of the polychlorotrifluoroethylene resin is 10–30 g / 10 min. The melt flow index is tested according to ASTM D1238-2010, with a test temperature of 265°C and a load weight of 21.6 kg.

[0022] The thickness of the intermediate layer described in this invention is a thickness commonly used for thin films in the art. Preferably, the thickness of the intermediate layer is 10–50 μm; more preferably, the thickness of the intermediate layer is 10–25 μm.

[0023] The thickness of the upper or lower layer described in this invention is a thickness commonly used for thin films in the art. Preferably, the thickness of the upper or lower layer is 10 to 50 μm; more preferably, the thickness of the upper or lower layer is 10 to 25 μm.

[0024] The graphene-grafted modified polychlorotrifluoroethylene electret composite film of the present invention is composited by any method applicable in the art. Preferably, the upper layer, middle layer and lower layer are composited by molding to obtain the composite film. The molding includes hot pressing and cold pressing steps. The hot pressing temperature is 230-260°C, the pressure is 5-10 MPa and the time is 3-5 min. The cold pressing temperature is 20-30°C, the pressure is 5-10 MPa and the time is 2-5 min.

[0025] The graphene-grafted modified polychlorotrifluoroethylene electret composite film of the present invention is electretted by any method applicable in the art. Preferably, the composite film is electretted by bombardment with a low-energy electron beam with an energy of 15.0-25.0 keV.

[0026] The technical solution of the present invention has the following technical advantages compared with the prior art:

[0027] (1) Grafting graphene onto the polychlorotrifluoroethylene molecular chain not only improves the charge storage stability of the film under high temperature environment, but also has better compatibility with polychlorotrifluoroethylene compared with the blending method.

[0028] (2) The upper and lower layers are made of conventional polychlorotrifluoroethylene film, which makes the composite film have excellent water vapor barrier properties and can still maintain the electret effect in high humidity environment. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0030] The conventional polychlorotrifluoroethylene resin referred to in this invention is unmodified polychlorotrifluoroethylene resin.

[0031] Example 1

[0032] (1) Preparation of modified graphene:

[0033] 100g of fluorinated graphene with a size of 15μm, 1g of vinyltrimethoxysilane coupling agent, and 400g of methanol were thoroughly mixed. The mixture was refluxed at 70℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified fluorinated graphene.

[0034] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0035] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min, 3.75g of modified fluorinated graphene, and 0.05g of benzoyl peroxide were premixed and added to a torque rheometer. The mixture was stirred for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0036] (3) Preparation of the intermediate layer of the composite film:

[0037] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min and 80g of graphene-grafted modified polychlorotrifluoroethylene resin were co-extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 23μm.

[0038] (4) Preparation of composite films:

[0039] The 23 μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 23 μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 245°C and a pressure of 10 MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25°C and a pressure of 10 MPa. The composite film is then demolded.

[0040] (5) Preparation of electret composite thin films:

[0041] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0042] Under an ambient humidity of 85%, when the temperature of the electret composite film was raised from room temperature to 140°C, its surface potential decreased to 53% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, its surface potential decreased to 31% of its initial value.

[0043] Example 2

[0044] (1) Preparation of modified graphene:

[0045] 100g of fluorinated graphene with a size of 15μm, 1g of vinyltriethoxysilane coupling agent, and 400g of ethanol were thoroughly mixed. The mixture was refluxed at 80℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified fluorinated graphene.

[0046] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0047] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 25g / 10min, 3.75g of modified fluorinated graphene, and 0.05g of dicumyl peroxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0048] (3) Preparation of the intermediate layer of the composite film:

[0049] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 25g / 10min and 80g of graphene-grafted modified polychlorotrifluoroethylene resin were co-extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 23μm.

[0050] (4) Preparation of composite films:

[0051] The 23 μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 23 μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 245°C and a pressure of 10 MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25°C and a pressure of 10 MPa. The composite film is then demolded.

[0052] (5) Preparation of electret composite thin films:

[0053] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0054] Under an ambient humidity of 85%, when the temperature of the electret composite film was raised from room temperature to 140°C, its surface potential decreased to 57% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, its surface potential decreased to 34% of its initial value.

[0055] Example 3

[0056] (1) Preparation of modified graphene:

[0057] 100g of 15μm hydrogenated graphene, 2g of vinyltri-tert-butylperoxysilane coupling agent, and 400g of ethanol were thoroughly mixed. The mixture was refluxed at 80℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified hydrogenated graphene.

[0058] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0059] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 30g / 10min, 3g of modified hydrogenated graphene, and 0.1g of tert-butyl hydrogen peroxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0060] (3) Preparation of the intermediate layer of the composite film:

[0061] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 30g / 10min and 75g of graphene-grafted modified polychlorotrifluoroethylene resin were blended and extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 15μm.

[0062] (4) Preparation of composite films:

[0063] The 15μm thick film obtained in step (3) is used as the middle layer, and the top and bottom layers are conventional polychlorotrifluoroethylene films with a thickness of 23μm. The three films are placed between two metal molds and hot-pressed for 4 minutes at a temperature of 240℃ and a pressure of 8MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25℃ and a pressure of 8MPa. The composite film is then demolded.

[0064] (5) Preparation of electret composite thin films:

[0065] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0066] Under an ambient humidity of 85%, when the temperature of the electret composite film was raised from room temperature to 140°C, its surface potential decreased to 49% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, its surface potential decreased to 28% of its initial value.

[0067] Example 4

[0068] (1) Preparation of modified graphene:

[0069] 150g of fluorinated graphene with a size of 10μm, 2.25g of vinyltriethoxysilane coupling agent, and 400g of ethanol were thoroughly mixed. The mixture was refluxed at 80℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified fluorinated graphene.

[0070] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0071] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 25g / 10min, 4.5g of modified fluorinated graphene and 0.1g of dicumyl peroxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0072] (3) Preparation of the intermediate layer of the composite film:

[0073] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 25g / 10min and 100g of graphene-grafted modified polychlorotrifluoroethylene resin were blended and extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 23μm.

[0074] (4) Preparation of composite films:

[0075] The 23 μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 23 μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 245°C and a pressure of 10 MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25°C and a pressure of 10 MPa. The composite film is then demolded.

[0076] (5) Preparation of electret composite thin films:

[0077] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0078] Under an ambient humidity of 85%, when the temperature of the electret composite film was raised from room temperature to 140°C, its surface potential decreased to 62% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, its surface potential decreased to 38% of its initial value.

[0079] Example 5

[0080] (1) Preparation of modified graphene:

[0081] 150g of graphene oxide with a size of 10μm, 0.75g of vinyltrimethoxysilane coupling agent, and 400g of methanol were thoroughly mixed. The mixture was refluxed at 70℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified graphene oxide.

[0082] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0083] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min, 3.75g of modified graphene oxide, and 0.05g of dicumyl peroxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0084] (3) Preparation of the intermediate layer of the composite film:

[0085] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min and 80g of graphene-grafted modified polychlorotrifluoroethylene resin were co-extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 15μm.

[0086] (4) Preparation of composite films:

[0087] The 15μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 23μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 240℃ and a pressure of 8MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25℃ and a pressure of 8MPa. The composite film is then demolded.

[0088] (5) Preparation of electret composite thin films:

[0089] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0090] Under an ambient humidity of 85%, when the temperature of the electret composite film was raised from room temperature to 140°C, its surface potential decreased to 51% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, its surface potential decreased to 29% of its initial value.

[0091] Example 6

[0092] (1) Preparation of modified graphene:

[0093] 150g of graphene oxide with a size of 10μm, 0.75g of vinyltriethoxysilane coupling agent, and 400g of ethanol were thoroughly mixed. The mixture was refluxed at 80℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified graphene oxide.

[0094] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0095] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 25g / 10min, 4.5g of modified graphene oxide and 0.05g of benzoyl peroxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0096] (3) Preparation of the intermediate layer of the composite film:

[0097] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 25g / 10min and 100g of graphene-grafted modified polychlorotrifluoroethylene resin were blended and extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 23μm.

[0098] (4) Preparation of composite films:

[0099] The 23 μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 23 μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 245°C and a pressure of 10 MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25°C and a pressure of 10 MPa. The composite film is then demolded.

[0100] (5) Preparation of electret composite thin films:

[0101] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0102] Under an ambient humidity of 85%, when the temperature of the composite film was raised from room temperature to 140°C, the surface potential of the film decreased to 58% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, the surface potential of the film decreased to 37% of its initial value using a surface potentiometer.

[0103] Example 7

[0104] (1) Preparation of modified graphene:

[0105] 150g of fluorinated graphene with a size of 15μm, 2.25g of vinyltritert-butylperoxysilane coupling agent, and 400g of ethanol were thoroughly mixed. The mixture was refluxed at 80℃ for 4h. The refluxed mixture was filtered, and the product was dried at 120℃ for 2h to obtain modified fluorinated graphene.

[0106] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0107] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min, 4.5g of modified graphene oxide and 0.1g of tert-butyl hydroperoxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0108] (3) Preparation of the intermediate layer of the composite film:

[0109] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min and 100g of graphene-grafted modified polychlorotrifluoroethylene resin were blended and extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 23μm.

[0110] (4) Preparation of composite films:

[0111] The 23 μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 23 μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 245°C and a pressure of 10 MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25°C and a pressure of 10 MPa. The composite film is then demolded.

[0112] (5) Preparation of electret composite thin films:

[0113] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0114] Under an ambient humidity of 85%, when the temperature of the composite film is raised from room temperature to 140°C, its surface potential decreases to 60% of its initial value using a surface potentiometer; when the temperature is raised to 150°C, its surface potential decreases to 37% of its initial value.

[0115] Example 8

[0116] (1) Preparation of modified graphene:

[0117] 100g of fluorinated graphene with a size of 10μm, 1g of vinyltriethoxysilane coupling agent, and 400g of ethanol were thoroughly mixed. The mixture was refluxed at 80℃ for 4h. After reflux, the mixture was filtered and the product was dried at 120℃ for 2h to obtain modified fluorinated graphene.

[0118] (2) Preparation of graphene-grafted modified polychlorotrifluoroethylene resin:

[0119] 150g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min, 3.75g of modified fluorinated graphene, and 0.05g of dicumyl peroxide were premixed and added to a torque rheometer. The torque rheometer was used to mix the resin for 8 minutes at 250℃ and 120r / min to obtain graphene-grafted modified polychlorotrifluoroethylene resin.

[0120] (3) Preparation of the intermediate layer of the composite film:

[0121] 1000g of conventional polychlorotrifluoroethylene resin with a melt index of 20g / 10min and 80g of graphene-grafted modified polychlorotrifluoroethylene resin were co-extruded using a screw extruder to prepare a composite film intermediate layer with a thickness of 15μm.

[0122] (4) Preparation of composite films:

[0123] The 15μm thick film obtained in step (3) is used as the middle layer, and the upper and lower layers are conventional polychlorotrifluoroethylene films with a thickness of 15μm. The three films are placed between two metal molds and hot-pressed for 5 minutes at a temperature of 240℃ and a pressure of 8MPa using a flat vulcanizing machine. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25℃ and a pressure of 8MPa. The composite film is then demolded.

[0124] (5) Preparation of electret composite thin films:

[0125] Electret composite thin film material was prepared by bombarding the composite thin film with a low-energy electron beam of 20.0 keV.

[0126] Under an ambient humidity of 85%, when the temperature of the composite film was raised from room temperature to 140°C, the surface potential of the film decreased to 46% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, the surface potential of the film decreased to 25% of its initial value using a surface potentiometer.

[0127] Comparative Example 1

[0128] Electret composite film made of three layers of conventional polychlorotrifluoroethylene film

[0129] (1) Preparation of composite thin films:

[0130] Three conventional polychlorotrifluoroethylene films with a melt index of 25 g / 10 min and a thickness of 23 μm were taken as the top, middle and bottom layers of the composite film. The three layers of film were placed between two metal molds and hot-pressed for 5 min at a temperature of 245℃ and a pressure of 10 MPa using a flat vulcanizing machine. Then the molds and films were transferred to a cold press and cold-pressed for 3 min at a temperature of 25℃ and a pressure of 10 MPa. The composite film was then demolded.

[0131] (2) Preparation of electret composite thin film materials:

[0132] Electret composite thin film material was prepared by bombarding the composite thin film with a low-energy electron beam of 20.0 keV.

[0133] Under an ambient humidity of 85%, when the temperature of the composite film is raised from room temperature to 140°C, its surface potential decreases to 30% of its initial value using a surface potentiometer; when the temperature is raised to 150°C, its surface potential decreases to 0% of its initial value.

[0134] Comparative Example 2

[0135] The raw materials and proportions of Example 8 are used, except that graphene is added by blending.

[0136] (1) Preparation of modified polychlorotrifluoroethylene film:

[0137] A composite film intermediate layer with a thickness of 23 μm was prepared by co-extrusion of 3 g of fluorinated graphene with a size of 15 μm and 1000 g of conventional polychlorotrifluoroethylene resin with a melt index of 20 g / 10 min using a screw extruder.

[0138] (2) Preparation of composite films:

[0139] Using the 23μm thick film obtained in step (1) as the middle layer, and the upper and lower layers as conventional polychlorotrifluoroethylene films with a thickness of 23μm, the three films are placed between two metal molds. Using a flat vulcanizing machine, the film is melt-pressed for 5 minutes at a temperature of 245℃ and a pressure of 10MPa. Then the mold and film are moved to a cold press and cold-pressed for 3 minutes at a temperature of 25℃ and a pressure of 10MPa. The composite film is then demolded.

[0140] (3) Preparation of electret composite thin films:

[0141] An electret composite film was prepared by bombarding the composite film with a low-energy electron beam of 20.0 keV.

[0142] Under an ambient humidity of 85%, when the temperature of the composite film was raised from room temperature to 140°C, its surface potential decreased to 42% of its initial value using a surface potentiometer; when the temperature was raised to 150°C, its surface potential decreased to 21% of its initial value.

[0143] Table 1. Electret performance of electret composite films prepared in the examples and comparative examples under high temperature and high humidity conditions.

[0144]

[0145] Note: The initial potential of the electret composite films prepared in Examples 1-8 and Comparative Examples 1-2 is 100%.

Claims

1. A graphene-grafted modified polychlorotrifluoroethylene electret composite film, comprising an upper layer, an intermediate layer, and a lower layer, characterized in that: The intermediate layer comprises graphene-grafted modified polychlorotrifluoroethylene resin, and the upper and lower layers are polychlorotrifluoroethylene films. The preparation method of the intermediate layer includes a step of co-extruding polychlorotrifluoroethylene resin and graphene-grafted modified polychlorotrifluoroethylene resin at a mass ratio of 100:5-20, wherein the mass percentage of graphene in the intermediate layer is 1-3‰. The melt index of the polychlorotrifluoroethylene resin is 5-50 g / 10 min; The preparation method of the graphene-grafted modified polychlorotrifluoroethylene resin includes the following steps: (1) Modified graphene was prepared by reflux, filtration and drying of a mixture of graphene, silane coupling agent and alcohol solvent. (2) Polychlorotrifluoroethylene resin, modified graphene, and an initiator are reacted at high temperature to prepare graphene-grafted modified polychlorotrifluoroethylene resin. In step (2), the mass ratio of polychlorotrifluoroethylene resin, modified graphene and initiator is 100:1~4:0.01~0.

1.

2. The graphene-grafted modified polychlorotrifluoroethylene electret composite film according to claim 1, characterized in that: In step (1), the solid content in the mixture is 20-30%.

3. The graphene-grafted modified polychlorotrifluoroethylene electret composite film according to claim 1, characterized in that: In step (1), the mass ratio of silane coupling agent to graphene is 0.1 to 5:

100.

4. The graphene-grafted modified polychlorotrifluoroethylene electret composite film according to claim 1, characterized in that: The thickness of the intermediate layer is 10–50 μm, and the thickness of the upper or lower layer is 10–50 μm.

5. The graphene-grafted modified polychlorotrifluoroethylene electret composite film according to claim 1, characterized in that: The upper, middle, and lower layers are combined through hot-pressing and cold-pressing steps to obtain a composite film. The hot-pressing temperature is 230–260°C, the pressure is 5–10 MPa, and the time is 3–5 min. The cold-pressing temperature is 20–30°C, the pressure is 5–10 MPa, and the time is 2–5 min.

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