High-dielectric conductive composite film and preparation method thereof

Abstract

The invention discloses a high-dielectric conductive composite film and a preparation method thereof. The composite film comprises a surface layer, a filler layer, a matrix layer and an interface layer which are sequentially connected from top to bottom, the surface layer comprises a cured dynamic cross-linking agent and a methyl methacrylate and divinyl benzene adhesive; the filler layer comprises a primary mixture arranged in an oriented manner; the matrix layer comprises a cured methyl methacrylate and divinyl benzene adhesive; the interface layer comprises the preliminary mixture, and a compound of methyl methacrylate and a divinyl benzene adhesive through a dynamic cross-linking agent and a hydrogen bond. Through cooperation of the surface layer, the filler layer, the matrix layer and the interface layer, the dielectric property and the conductivity of the composite film are synchronously improved, and the dielectric property and the conductivity of the composite film are improved through the primary mixture in oriented arrangement in the filler layer; meanwhile, the conductive network can be further improved under the action of the dynamic cross-linking agent in the surface layer and the interface layer, so that the dielectricity and the conductivity of the composite film are ensured.

Description

Technical Field

[0001] The present invention relates to the field of composite film preparation, and particularly to a highly dielectric and conductive composite film and a preparation method thereof. Background Art

[0002] Composite films play a crucial role in flexible electronics and pulsed power devices, mainly reflected in their dielectric properties, conductive regulation, and mechanical flexibility. Such composite films are usually composed of high-dielectric polymers and inorganic fillers, possessing both flexibility and excellent electrical properties. In addition, in flexible electronics and pulsed power devices, in order to meet the requirements of high performance, lightweight, and deformability, it is also necessary for the composite film to have the function of high dielectric conductivity.

[0003] Currently, for the composite films prepared by traditional methods, due to the significant anisotropy of dielectric properties caused by the disordered dispersion of nano-fillers, breakdown occurs due to local electric field distortion under high voltage. At the same time, the poor interfacial compatibility between nano-fillers and polymers leads to the fracture of the conductive network in the obtained composite film, and the conductivity is usually lower than 10 S / m. In addition, the high filler content in the composite film exacerbates agglomeration, forming insulating regions, making it difficult to simultaneously improve the dielectric and conductive properties of the composite film.

[0004] Therefore, a highly dielectric and conductive composite film and a preparation method thereof are proposed to solve the problem that it is difficult to simultaneously improve the dielectric and conductive properties of the above composite film. Summary of the Invention

[0005] The purpose of the present invention is to provide a highly dielectric and conductive composite film and a preparation method thereof to solve the problem that it is difficult to simultaneously improve the dielectric and conductive properties of the composite film.

[0006] To achieve this purpose, the present invention adopts the following technical solutions: A highly dielectric and conductive composite film, which comprises a surface layer, a filler layer, a matrix layer, and an interface layer connected in sequence from top to bottom; The surface layer comprises a cured dynamic crosslinking agent and a methyl methacrylate and divinylbenzene adhesive; the filler layer comprises an initially aligned mixture; the matrix layer comprises a cured methyl methacrylate and divinylbenzene adhesive; the interface layer comprises a combination of an initially aligned mixture, a methyl methacrylate and divinylbenzene adhesive through a dynamic crosslinking agent and hydrogen bonds.

[0007] A preparation method of a highly dielectric and conductive composite film, which is applied to the highly dielectric and conductive composite film as described above, and the preparation method comprises the following steps: Step S1, treating the surfaces of CNT and MXene to increase the carboxyl and amino contents on their surfaces and obtaining an initially aligned mixture; Step S2: Mix methyl methacrylate with divinylbenzene adhesive to obtain a first mixture, then add the preliminary mixture to the first mixture and perform ultrasonic treatment to obtain a second mixture, and then add a photoinitiator and a dynamic crosslinking agent to the second mixture and mix to obtain a third mixture; Step S3: Let the third mixture pass through a spiral channel and perform ultrasonic treatment to obtain a fourth mixture; Step S4: After placing a mold between the two electrodes of the electric field device, inject the fourth mixture into the mold, and then apply an electric field by the electric field device to obtain a fifth mixture; Step S5: Cure the fifth mixture in the mold, and then perform a repair treatment on the fifth mixture to obtain a composite film.

[0008] The specific steps of Step S1 include: Step S11: Mix equal masses of CNT and MXene by a planetary ball mill to obtain a pre-mixture; Step S12: Place the pre-mixture in a radio frequency plasma reactor for treatment and introduce an Ar / O2 mixed gas; Step S13: Uniformly purge the pre-mixture after Step S12 with nitrogen.

[0009] In Step S11, the rotational speed of the planetary ball mill is 100 - 300 rpm and the mixing time is 1 - 4 h; In Step S12, the power of the radio frequency plasma reactor is 100 - 200 W, the radio frequency is 13.56 MHz, the treatment time is 20 - 40 min, and the volume ratio of Ar to O2 in the Ar / O2 mixed gas is (3.8 - 4.2):(1.2 - 0.8); before introducing the Ar / O2 mixed gas into the radio frequency plasma reactor, evacuate the radio frequency plasma reactor to 5×10 -3 Pa, and then introduce the Ar / O2 mixed gas to 30 - 70; In Step S13, the nitrogen purging time is 5 - 15 min.

[0010] The specific steps of Step S2 include: Step S21: Mix methyl methacrylate with divinylbenzene adhesive and stir for 20 - 40 min to obtain a first mixture; Step S22: Add the preliminary mixture to the first mixture and perform an ice bath first ultrasonic pulse treatment for 0.5 - 2 h; Step S23: Mix the second mixture, the photoinitiator and the dynamic crosslinking agent and stir for 20 - 40 min.

[0011] In the step S21, the stirring speed is 300 - 700 rpm, the mass percentage of methyl methacrylate in the first mixture is 90 - 98%, and the rest is divinylbenzene adhesive; In the step S22, the first ultrasonic pulse is an ultrasonic cycle of pausing for 1 s every 2 s of operation, and the frequency of the first ultrasonic pulse is 20 - 60 kHz and the power is 300 - 700 W; In the step S23, the stirring speed is 400 - 500 rpm, and the dynamic crosslinking agent includes a furan - maleimide type Diels - Alder prepolymer.

[0012] The step S3 specifically includes: Step S31: Place the spiral channel in a constant temperature water bath, and then let the third mixture pass through the spiral channel; Step S32: Perform a second ultrasonic pulse treatment on the third mixture flowing in the spiral channel for 35 - 45 min.

[0013] In the step S31, the temperature of the constant temperature water bath is 50 - 70 °C, the flow rate of the third mixture is 0.3 - 1 mL / min, the Reynolds number Re = 50 - 150 (laminar flow), the inner diameter of the spiral channel is 0.5 - 2 mm, the length is 3 - 8 m, and the pitch is 1 - 4 cm; In the step S32, the intensity of the second ultrasonic pulse is 30 - 70 W / cm², and the second ultrasonic pulse is an ultrasonic cycle of pausing for 1 s every 1 s of operation.

[0014] The step S4 specifically includes: Step S41: Place a mold between two electrode plates of an electric field device; Step S42: Inject the fourth mixture into the mold, and let the electric field device apply a gradient electric field to the fourth mixture; When the electric field device applies a gradient electric field to the fourth mixture, the gradient electric field is increased to 1 - 5 kV at 50 - 200 V / s, and a gradient electric field of 1 - 5 kV / cm is maintained for 10 - 30 min, and then the gradient electric field is turned off at 30 - 70 V / s.

[0015] The step S5 specifically includes: Step S51: Perform ultraviolet curing on the fifth mixture in the mold for 3 - 10 min, and obtain a preliminary film after curing; Step S52: Place the preliminary film in a hot press for hot press repair to obtain a composite film; In the step S51, the intensity of the ultraviolet light is 5 - 15 mW / cm².

[0016] In the step S52, the hot pressing temperature of the hot press is 100-140°C, the hot pressing pressure is 3-7 MPa, and the hot pressing time is 10-20 min.

[0017] Compared with the prior art, the present invention has the following beneficial effects: A high-dielectric conductive composite film and a preparation method thereof according to the present invention realize the synchronous improvement of the dielectric property and conductivity of the composite film through the cooperation of a surface layer, a filler layer, a matrix layer, and an interface layer. The preliminary mixture arranged in an oriented manner in the filler layer improves the dielectric property and conductivity of the composite film. The preliminary mixture is arranged under the action of a gradient electric field to form a highly conductive and low-loss conductive network. At the same time, under the action of a dynamic cross-linking agent in the surface layer and the interface layer, the conductive network can be further improved, and the continuity of the conductive network is maintained to ensure the dielectric property and conductivity of the composite film. In addition, the surface layer can also form a protective layer on the matrix layer, thereby cooperating with the matrix layer to protect the filler layer and improving the mechanical properties of the composite film. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limited conditions for the implementation of the present invention. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size should still fall within the scope that can be covered by the technical content disclosed in the present invention without affecting the effects that the present invention can produce and the purposes that can be achieved.

[0020] Figure 1 It is a flow block diagram of the preparation method in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] In order to make the object, features, and advantages of the present invention more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the following described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0022] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component present at the same time.

[0023] Example 1: A high-dielectric conductive composite film in this embodiment, the composite film includes a surface layer, a filler layer, a matrix layer and an interface layer connected in sequence from top to bottom.

[0024] Specifically, the surface layer includes a cured dynamic crosslinking agent and a part of methyl methacrylate and divinylbenzene adhesive, which can provide self-healing ability; the filler layer includes an orientationally arranged preliminary mixture layer, which can provide a high-conductivity and low-loss network to simultaneously improve the dielectric property and conductivity of the composite film; the matrix layer includes a cured methyl methacrylate and divinylbenzene adhesive, and the matrix layer is the mechanical support of the composite film; the interface layer includes a combination of a preliminary mixture, methyl methacrylate and divinylbenzene adhesive through a dynamic crosslinking agent and hydrogen bonds to enhance the interfacial bonding strength.

[0025] It should be noted that the preliminary mixture is composed of CNT (carbon nanotube) and MXene, and MXene is specifically Ti3C2T x (titanium-based carbide); MXene is a new type of two-dimensional transition metal carbide or carbonitride, which is generally prepared by selectively removing the A atomic layer in the MAX phase through methods such as chemical etching; the dynamic crosslinking agent contains a furan-maleimide type Diels-Alder prepolymer; the photoinitiator is specifically a TPO photoinitiator, which is an efficient free radical type and has absorption in a long wavelength range.

[0026] Example 2: Please refer to Figure 1 , a preparation method of a high-dielectric conductive composite film in this embodiment, the preparation method is applied to the high-dielectric conductive composite film as in Example 1, and the preparation method includes the following steps: Step S1, treat the surfaces of CNT and MXene to increase the carboxyl and amino contents on their surfaces and obtain a preliminary mixture.

[0027] Specifically, after the carboxyl and amino group contents on the surfaces of CNT and MXene are increased, high-density grafting of carboxyl and amino groups on the surfaces of CNT and MXene is achieved, the dispersibility is improved, the interfacial bonding strength is enhanced, and the electric field response ability is optimized.

[0028] Step S1 specifically includes: Step S11: Mix equal masses of CNT and MXene through a planetary ball mill to obtain a premix; In step S11, the rotational speed of the planetary ball mill is 100 - 300 rpm and the mixing time is 1 - 4 h; Step S12: Place the premix in a radio frequency plasma reactor for treatment and introduce an Ar / O2 mixed gas; In step S12, the power of the radio frequency plasma reactor is 100 - 200 W, the radio frequency is 13.56 MHz, the treatment time is 20 - 40 min, and the volume ratio of Ar to O2 in the Ar / O2 mixed gas is (3.8 - 4.2):(1.2 - 0.8); before introducing the Ar / O2 mixed gas into the radio frequency plasma reactor, evacuate the radio frequency plasma reactor to 5×10 -3 Pa, and then introduce the Ar / O2 mixed gas to 30 - 70; Step S13: Uniformly purge the premix that has undergone step S12 with nitrogen.

[0029] In step S13, the nitrogen purging time is 5 - 15 min.

[0030] Preferably, step S1 specifically includes: Step S11: Mix equal masses of CNT and MXene through a planetary ball mill to obtain a premix; In step S11, the rotational speed of the planetary ball mill is 200 rpm and the mixing time is 2 h; It should be noted that by mixing CNT and MXene, CNT is embedded in MXene to form a three-dimensional interpenetrating network, which increases the specific surface area of the premix.

[0031] Step S12: Place the premix in a radio frequency plasma reactor for treatment and introduce an Ar / O2 mixed gas; In step S12, the power of the radio frequency plasma reactor is 150 W, the radio frequency is 13.56 MHz, the treatment time is 30 min, and the volume ratio of Ar to O2 in the Ar / O2 mixed gas is 4:1; before introducing the Ar / O2 mixed gas into the radio frequency plasma reactor, evacuate the radio frequency plasma reactor to 5×10 -3 Pa, and then introduce the Ar / O2 mixed gas to 50 Pa; It should be noted that after introducing an Ar / O2 mixed gas into the radio frequency plasma reactor, the radio frequency electric field excites the ionization of Ar / O2 to generate a high-density plasma. The Ar ions bombard the surface of the pre-mixture, etching amorphous carbon impurities and activating surface sites. O2 dissociates into reactive oxygen species under the action of high-energy electrons and reacts with carbon / titanium atoms on the surface of the pre-mixture to form carboxyl and amino groups.

[0032] Step S13: Uniformly purge the pre-mixture that has undergone step S12 with nitrogen.

[0033] In step S13, the nitrogen purging time is 10 min; It should be noted that after the pre-mixture has undergone the treatment in step S12, nitrogen is introduced into the radio frequency plasma reactor to purge the pre-mixture with nitrogen, which can prevent the obtained preliminary mixture from being over-oxidized, thereby improving the quality of the obtained preliminary mixture and avoiding the influence of the reduced quality of the preliminary mixture on the quality of the finally formed composite film.

[0034] It should also be noted that after the surfaces of CNT and MXene are treated, the carboxyl and amino group contents on their surfaces are 10 ± 2%, forming a preliminary mixture. The preliminary mixture is covalently connected through amide bonds, enhancing the interfacial bonding strength; the Zeta potential of the preliminary mixture is increased, and agglomeration is inhibited through electrostatic repulsion, enhancing the electrostatic stable dispersion. After the dispersion of the preliminary mixture is improved, the ultrasonic treatment time required in the subsequent step S2 can be reduced, improving the working efficiency. At the same time, the increase in the Zeta potential of the preliminary mixture increases its surface charge density and optimizes the electric field response ability.

[0035] Step S2: Mix methyl methacrylate and divinylbenzene adhesive to obtain a first mixture, then add the preliminary mixture to the first mixture for ultrasonic treatment to obtain a second mixture, and then add a photoinitiator and a dynamic crosslinking agent to the second mixture and mix to obtain a third mixture.

[0036] Specifically, by ultrasonically treating the mixed preliminary mixture and the first mixture, the preliminary mixture can be uniformly dispersed in the first mixture to obtain a second mixture with a stable suspension system. After the second mixture, the photoinitiator, and the dynamic crosslinking agent are mixed, the interfacial compatibility of the third mixture can be improved, thereby providing reliable materials for the subsequent formation of the composite film.

[0037] It can be known that when the preliminary mixture is mixed with the first mixture, the carboxyl and amino groups on the surface of the preliminary mixture form hydrogen bonds with the ester groups of methyl methacrylate in the first mixture, improving the wettability, and the amino groups have a coordination effect with the photoinitiator, promoting the uniform distribution of the photoinitiator.

[0038] Step S2 specifically includes: Step S21: Mix methyl methacrylate and divinylbenzene adhesive and stir for 20 - 40 min to obtain a first mixture; In step S21, the stirring speed is 300 - 700 rpm, and the mass percentage of methyl methacrylate in the first mixture is 90 - 98%, with the rest being divinylbenzene adhesive; Step S22: Add the preliminary mixture to the first mixture and perform the first ultrasonic pulse treatment in an ice bath for 0.5 - 2 h; In step S22, the first ultrasonic pulse is an ultrasonic cycle of working for 2 s and pausing for 1 s, and the frequency of the first ultrasonic pulse is 20 - 60 kHz and the power is 300 - 700 W; Step S23: Mix the second mixture, photoinitiator and dynamic crosslinking agent and stir for 20 - 40 min.

[0039] In step S23, the stirring speed is 400 - 500 rpm.

[0040] Preferably, step S2 specifically includes: Step S21: Mix methyl methacrylate and divinylbenzene adhesive and stir for 30 min to obtain a first mixture; In step S21, the stirring speed is 500 rpm, and the mass percentage of methyl methacrylate in the first mixture is 95%, with the rest being divinylbenzene adhesive; It should be noted that the first mixture formed by mixing methyl methacrylate and divinylbenzene adhesive provides a low - resistance environment for the dispersion of the preliminary mixture, making the dispersion of the preliminary mixture more efficient.

[0041] Step S22: Add the preliminary mixture to the first mixture and perform the first ultrasonic pulse treatment in an ice bath for 1 h; In step S22, the first ultrasonic pulse is an ultrasonic cycle of working for 2 s and pausing for 1 s, and the frequency of the first ultrasonic pulse is 40 kHz and the power is 500 W; It should be noted that through the first ultrasonic pulse, ultrasonic waves can generate periodic compression and expansion in the first mixture, form micron - sized bubbles and instantaneously collapse, releasing shock waves to break up the aggregates of the preliminary mixture. At the same time, under the high - frequency vibration of the ultrasonic waves, the preliminary mixture can be evenly distributed in the first mixture. Moreover, under the action of the intermittent first ultrasonic pulse and the ice - bath environment, it can also avoid the pre - polymerization situation caused by the ultrasonic waves increasing the temperature of the first mixture, thus improving the dispersion efficiency.

[0042] In addition, by performing the first ultrasonic pulse treatment, the viscosity of the first mixture can also be reduced to improve the arrangement effect of the preliminary mixture in the subsequent process.

[0043] Step S23: Mix the second mixture, photoinitiator, and dynamic crosslinking agent and stir for 30 min.

[0044] In step S23, the stirring speed is 300 rpm, and the dynamic crosslinking agent includes a furan-maleimide type Diels-Alder prepolymer.

[0045] It should be noted that the furan group in the dynamic crosslinking agent is pre-bound to the amino group on the MXene surface through hydrogen bonds, improving the interfacial compatibility, thus ensuring the continuity of the subsequent conductive network and mechanical properties. In addition, the photoinitiator can also shorten the subsequent curing time and improve the curing efficiency.

[0046] Step S3: Let the third mixture pass through a spiral channel and perform ultrasonic treatment to obtain a fourth mixture.

[0047] Specifically, through the synergistic effect of microfluidic shear and ultrasonic cavitation in the spiral channel, the polymerization kinetics of the third mixture and the dispersion state of the preliminary mixture are synchronously regulated, and the phase separation and agglomeration of the preliminary mixture are inhibited.

[0048] It can be known that when the third mixture is ultrasonically treated, the surface charge density of the preliminary mixture increases to inhibit secondary agglomeration during ultrasonic treatment. At the same time, the amino group of CNT in the preliminary mixture and the carboxyl group of MXene form electrostatic attraction, maintaining the three-dimensional interpenetrating network of CNT and MXene.

[0049] Step S3 specifically includes: Step S31: Place the spiral channel in a constant temperature water bath, and then let the third mixture pass through the spiral channel; In step S31, the temperature of the constant temperature water bath is 50 - 70 °C, the flow rate of the third mixture is 0.3 - 1 mL / min, the Reynolds number Re = 50 - 150 (laminar flow), the inner diameter of the spiral channel is 0.5 - 2 mm, the length is 3 - 8 m, and the pitch is 1 - 4 cm; Preferably, in step S31, the temperature of the constant temperature water bath is 60 °C, the flow rate of the third mixture is 0.5 mL / min, the Reynolds number Re = 80 (laminar flow), the inner diameter of the spiral channel is 1 mm, the length is 5 m, and the pitch is 2 cm; It should be noted that the spiral channel is a stainless steel pipe with an inner diameter of 1 mm, a length of 5 m, and a pitch of 2 cm; when the third mixture flows through the spiral pipe, the spiral structure of the spiral channel can induce Dean vortices, enhance radial mixing, avoid axial segregation of the preliminary mixture, and the laminar flow of the spiral channel ensures uniform distribution of shear force, breaking the remaining agglomerates of the preliminary mixture. At the same time, the heat provided by the constant temperature water bath maintains the polymerization reaction temperature of the third mixture.

[0050] Step S32: Perform a second ultrasonic pulse treatment on the third mixture flowing in the spiral channel for 35 - 45 minutes.

[0051] In step S32, the intensity of the second ultrasonic pulse is 30 - 70 W / cm², and the second ultrasonic pulse is an ultrasonic cycle with 1 second of operation followed by 1 second of pause.

[0052] Preferably, in step S32, perform a second ultrasonic pulse treatment on the third mixture flowing in the spiral channel for 40 minutes.

[0053] In step S32, the intensity of the second ultrasonic pulse is 50 W / cm², and the second ultrasonic pulse is an ultrasonic cycle with 1 second of operation followed by 1 second of pause.

[0054] It should be noted that the ultrasonic waves generated by the second ultrasonic pulse act on the third mixture, can produce a cavitation effect, and trigger microscale turbulence through high-frequency vibration, promoting the synchronization of monomer diffusion and free radical chain growth in the third mixture, and the intermittent second ultrasonic pulse can also prevent the secondary aggregation of the preliminary mixture.

[0055] It should also be noted that through the spiral channel and the second ultrasonic pulse treatment in step S3, the preliminary mixture in the third mixture can be dispersed, facilitating the subsequent treatment of step S and reducing the resistance of the electric field orientation in the subsequent step S.

[0056] Step S4: After placing a mold between the two electrodes of the electric field device, inject the fourth mixture into the mold, and then apply an electric field by the electric field device to obtain a fifth mixture.

[0057] Specifically, by applying a gradient electric field to the fourth mixture, the gradient electric field can be used to drive the preliminary mixture to be oriented, construct a through-conductive network and reduce the dielectric anisotropy.

[0058] It can be known that the content of carboxyl and amino groups on the surface of the preliminary mixture increases, enhancing the dielectrophoretic response ability of the filler, improving the electric field sensitivity. After the interfacial bonding strength of the preliminary mixture is enhanced, it can also promote the arrangement of the preliminary mixture.

[0059] Step S4 specifically includes: Step S41: Place a mold between the two electrode plates of the electric field device; It should be noted that the gradient electric field control module in the electric field device forms a linear voltage gradient decreasing along the thickness direction of the mold through a voltage dividing resistor network to form a gradient electric field; the generation of a gradient electric field by the operation of the electric field device is well-known to those skilled in the art, and will not be described in this embodiment.

[0060] Step S42: Inject the fourth mixture into the mold and make the electric field device apply a gradient electric field to the fourth mixture; It should be noted that by applying a gradient electric field, chain-like agglomeration of the preliminary mixture is avoided. When the gradient electric field is applied, the carboxyl groups and amino groups on the preliminary mixture undergo dielectrophoresis in the gradient electric field. The CNTs in the preliminary mixture are connected end to end along the electric field direction to form a continuous conductive network. MXene is stacked perpendicular to the electric field direction, and in-plane stacking is inhibited by electrostatic repulsion, reducing dielectric loss. At the same time, methyl methacrylate and divinylbenzene adhesive in the fourth mixture are partially polymerized under the action of the gradient electric field, providing moderate rigidity and locking the preliminary mixture after orientation arrangement to form an oriented structure.

[0061] When the electric field device applies a gradient electric field to the fourth mixture, the gradient electric field is increased to 3 kV at a rate of 100 V / s and the gradient electric field of 3 kV / cm is maintained for 20 min, and then the gradient electric field is turned off at a rate of 50 V / s.

[0062] Preferably, when the electric field device applies a gradient electric field to the fourth mixture, the gradient electric field is increased to 1 - 5 kV at a rate of 50 - 200 V / s, the gradient electric field of 1 - 5 kV / cm is maintained for 10 - 30 min, and then the gradient electric field is turned off at a rate of 30 - 70 V / s.

[0063] It should also be noted that when applying a gradient electric field to the fourth mixture, the fourth mixture needs to be maintained at 60 ± 1 °C, and after the application of the gradient electric field is completed, the fourth mixture is slowly cooled. By controlling the temperature of the fourth mixture, the viscosity of the fourth mixture can be reduced to reduce the resistance during the orientation of the preliminary mixture, improving the orientation efficiency. It can also effectively prevent premature polymerization and curing of MMA monomers in the preliminary mixture, which may affect the orientation arrangement of the preliminary mixture. It can be known that through the fourth mixture obtained in step S3, the size of the preliminary mixture inside is reduced, which facilitates the orientation arrangement of the preliminary mixture. Its viscosity is also adjusted to meet the requirements of gradient electric field orientation arrangement. In addition, an oriented structure is formed in the fifth mixture, which can provide support for subsequent processing.

[0064] Step S5: Cure the fifth mixture in the mold and then perform a repair treatment on the fifth mixture to obtain a composite film.

[0065] Specifically, repairing after curing the fifth mixture can eliminate microdefects caused by curing shrinkage, improve the interfacial bonding strength, and thus improve the high density, high mechanical strength, and high breakdown field strength of the obtained composite film.

[0066] Step S5 specifically includes: Step S51: Perform ultraviolet curing on the fifth mixture in the mold for 3 - 10 min to obtain a preliminary film after curing. Step S52: Place the preliminary film in a hot press for hot press repair to obtain a composite film. In step S51, the ultraviolet light intensity is 5 - 15 mW / cm².

[0067] In step S52, the hot pressing temperature of the hot press is 100 - 140 °C, the hot pressing pressure is 3 - 7 MPa, and the hot pressing time is 10 - 20 min.

[0068] Preferably, step S5 specifically includes: Step S51: Perform ultraviolet curing on the fifth mixture in the mold for 5 min. After the curing is completed, a preliminary film is obtained. In step S51, the ultraviolet light intensity is 10 mW / cm². It should be noted that during the curing of the fifth mixture, the photoinitiator in the fifth mixture absorbs ultraviolet light and generates active free radicals, triggering the copolymerization of methyl methacrylate and divinylbenzene adhesive to form a crosslinked network. Part of the unpolymerized methyl methacrylate and divinylbenzene adhesive are completely cured, and the orientation structure of the preliminary mixture is locked.

[0069] In addition, the fifth mixture can form a rigid solid film after curing, with strong tensile resistance. At the same time, under the action of covalent bond binding, the interfacial shear strength is also improved.

[0070] It should also be noted that the fifth mixture obtained by the gradient electric field is partially cured. When transferring the fifth mixture to the curing location, it needs to be transferred together with the mold.

[0071] Step S52: Place the preliminary film in a hot press for hot pressing to obtain a composite film. In step S52, the hot pressing temperature of the hot press is 120 °C, the hot pressing pressure is 5 MPa, and the hot pressing time is 15 min.

[0072] It should be noted that by hot pressing the cured fifth mixture, the furan - maleimide Diels - Alder bond of the dynamic crosslinking agent in the fifth mixture can reversibly break at 120 °C, releasing internal stress and recombining during cooling to fill the micro - defects caused by curing shrinkage, thereby improving the quality of the finally obtained composite film.

[0073] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-dielectric conductive composite film, characterized in that, The composite film includes a surface layer, a filler layer, a matrix layer, and an interface layer that are sequentially connected from top to bottom; The surface layer includes a cured dynamic crosslinking agent and a methyl methacrylate and divinylbenzene adhesive; the filler layer includes a preliminarily aligned mixture; the matrix layer includes a cured methyl methacrylate and divinylbenzene adhesive; the interface layer includes a combination of a preliminarily aligned mixture, a methyl methacrylate and divinylbenzene adhesive through a dynamic crosslinking agent and hydrogen bonds.

2. A method for preparing a high dielectric conductive composite film, characterized in that, The preparation method is applied to the high-dielectric-conductivity composite film as described in claim 1, and the preparation method includes the following steps: Step S1: Treat the surfaces of CNT and MXene to increase the carboxyl and amino contents on their surfaces and obtain a preliminarily aligned mixture; Step S2: Mix the methyl methacrylate and divinylbenzene adhesive to obtain a first mixture, then add the preliminarily aligned mixture to the first mixture and perform ultrasonic treatment to obtain a second mixture, and then add a photoinitiator and a dynamic crosslinking agent to the second mixture and mix to obtain a third mixture; Step S3: Let the third mixture pass through a spiral channel and perform ultrasonic treatment to obtain a fourth mixture; Step S4: After placing a mold between two electrodes of an electric field device, inject the fourth mixture into the mold, and then apply an electric field by the electric field device to obtain a fifth mixture; Step S5: Cure the fifth mixture in the mold, and then perform a repair treatment on the fifth mixture to obtain a composite film.

3. The preparation method of the high-dielectric-conductivity composite film according to claim 2, wherein The specific content of step S1 includes: Step S11: Mix equal masses of CNT and MXene by a planetary ball mill to obtain a pre-mixture; Step S12: Place the pre-mixture in a radio frequency plasma reactor for treatment and introduce an Ar / O2 mixed gas; Step S13: Uniformly purge the pre-mixture passing through step S12 with nitrogen.

4. The preparation method of the high-dielectric-conductivity composite film according to claim 3, wherein In step S11, the rotation speed of the planetary ball mill is 100 - 300 rpm and the mixing time is 1 - 4 h; In the step S12, the power of the radio frequency plasma reactor is 100 - 200 W, the radio frequency is 13.56 MHz, the treatment time is 20 - 40 min, and the volume ratio of Ar to O2 in the Ar / O2 mixed gas is (3.8 - 4.2):(1.2 - 0.8); before introducing the Ar / O2 mixed gas into the radio frequency plasma reactor, the radio frequency plasma reactor is evacuated to 5×10 -3 Pa, and then the Ar / O2 mixed gas is introduced until the pressure reaches 30 - 70; In step S13, the nitrogen purging time is 5 - 15 min.

5. The preparation method of the high-dielectric-conductivity composite film according to claim 2, wherein The specific content of step S2 includes: Step S21: Mix the methyl methacrylate and divinylbenzene adhesive and stir for 20 - 40 min to obtain a first mixture; Step S22: Add the preliminarily aligned mixture to the first mixture and perform an ice bath first ultrasonic pulse treatment for 0.5 - 2 h; Step S23: Mix and stir the second mixture, the photoinitiator, and the dynamic crosslinking agent for 20 - 40 min.

6. The preparation method of the high-dielectric-conductivity composite film according to claim 5, wherein In step S21, the stirring speed is 300 - 700 rpm, and the mass percentage of methyl methacrylate in the first mixture is 90 - 98%, and the rest is divinylbenzene adhesive; In the step S22, the first ultrasonic pulse is an ultrasonic cycle with a pause of 1 s for every 2 s of operation. The frequency of the first ultrasonic pulse is 20 - 60 kHz, and the power is 300 - 700 W. In the step S23, the stirring speed is 400 - 500 rpm, and the dynamic crosslinking agent includes a furan - maleimide type Diels - Alder prepolymer.

7. The method for preparing a highly dielectrically conductive composite film according to claim 2, wherein The step S3 specifically includes: Step S31: Place the spiral channel in a constant temperature water bath, and then allow the third mixture to pass through the spiral channel. Step S32: Perform a second ultrasonic pulse treatment on the third mixture flowing in the spiral channel for 35 - 45 min.

8. The method for preparing a highly dielectrically conductive composite film according to claim 7, wherein In the step S31, the temperature of the constant temperature water bath is 50 - 70 °C, the flow rate of the third mixture is 0.3 - 1 mL / min, the Reynolds number Re = 50 - 150 (laminar flow), the inner diameter of the spiral channel is 0.5 - 2 mm, the length is 3 - 8 m, and the pitch is 1 - 4 cm. In the step S32, the intensity of the second ultrasonic pulse is 30 - 70 W / cm², and the second ultrasonic pulse is an ultrasonic cycle with a pause of 1 s for every 1 s of operation.

9. The method for preparing a highly dielectrically conductive composite film according to claim 2, wherein The step S4 specifically includes: Step S41: Place a mold between two electrode plates of an electric field device. Step S42: Inject the fourth mixture into the mold, and allow the electric field device to apply a gradient electric field to the fourth mixture. When the electric field device applies a gradient electric field to the fourth mixture, the gradient electric field is increased from 0 to 1 - 5 kV at a rate of 50 - 200 V / s, and a gradient electric field of 1 - 5 kV / cm is maintained for 10 - 30 min, and then the gradient electric field is turned off at a rate of 30 - 70 V / s.

10. The method for preparing a highly dielectrically conductive composite film according to claim 2, wherein The step S5 specifically includes: Step S51: Perform ultraviolet curing on the fifth mixture in the mold for 3 - 10 min. After curing is completed, a preliminary film is obtained. Step S52: Place the preliminary film in a hot press for hot press repair to obtain a composite film. In the step S51, the intensity of the ultraviolet light is 5 - 15 mW / cm². In the step S52, the hot press temperature is 100 - 140 °C, the hot press pressure is 3 - 7 MPa, and the hot press time is 10 - 20 min.

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