Preparation process of high-performance polypropylene capacitor film

Abstract

The invention relates to the technical field of capacitor films. The invention discloses a preparation process of a high-performance polypropylene capacitor film. The preparation process comprises the following steps: A1, preparing a polypropylene capacitor film; a2, carrying out surface cleaning and activation pretreatment on the polypropylene capacitance film; a3, evaporating a gradient modified layer on the surface of the pretreated polypropylene capacitance film; a4, carrying out laser plasma synergistic treatment and crystallinity regulation and control on the modified polypropylene capacitor film; and A5, coating the outer layer of the modified polypropylene capacitance film with a functional layer, and carrying out annealing post-treatment to prepare the high-performance polypropylene capacitance film. The mechanical strength and the electrical stability are improved through nano filler dispersion, two-way stretching and crystallinity regulation and control; through the collaborative design of surface cleaning and activation and a gradient functional layer, excellent interface bonding force and environmental adaptability are given; and by means of technologies such as multi-source evaporation and laser plasma co-processing, precise regulation and control and diversified expansion of the performance are achieved, the method is suitable for various scenes, and the process repeatability is good.

Description

Technical Field

[0001] This invention relates to the field of capacitor film technology, and in particular to a preparation process for a high-performance polypropylene capacitor film. Background Technology

[0002] Polypropylene capacitor film, as a core material for high-end electronic components, is widely used in power capacitors, high-frequency electronic circuits, and other fields. Its performance directly affects the reliability and lifespan of the devices. With the development of electronic equipment towards higher frequencies, smaller sizes, and higher voltages, higher requirements are placed on the mechanical strength, dielectric properties, and weather resistance of capacitor films. Traditional polypropylene capacitor film manufacturing processes typically involve melt extrusion followed by direct use, or only simple surface treatment, which is insufficient to meet the demands of modern industry for high-performance film materials.

[0003] In existing technologies, ordinary polypropylene capacitor films suffer from several performance bottlenecks: on the one hand, the base film itself has insufficient crystallinity and molecular orientation, resulting in low tensile strength and making it prone to deformation or breakdown under high voltage conditions; on the other hand, the film surface is highly inert and has low roughness, resulting in weak adhesion to the functional layer and making it prone to interlayer delamination, affecting the overall stability of the device. In addition, traditional modification methods such as single-coating vapor deposition or simple chemical treatment are difficult to form a gradient structure on the film surface that combines conductivity and corrosion resistance, resulting in poor corona resistance and high dielectric loss of the capacitor film under high-frequency and high-voltage conditions, and easy failure due to charge accumulation or partial discharge during long-term use.

[0004] To address the aforementioned issues, existing processes have attempted to improve performance by adding fillers or optimizing the stretching process, but they still have the following limitations: the dispersion uniformity of nanofillers is difficult to control, which can easily lead to defects inside the membrane material; the surface activation treatment lacks precise control methods, making it difficult to balance roughness and chemical activity; and the synergy between the functional layer coating process and the base film modification is insufficient, making it impossible to achieve diversified performance expansion. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses a preparation process for a high-performance polypropylene capacitor film that can systematically improve the mechanical properties, electrical stability, and interfacial bonding strength of polypropylene capacitor films.

[0006] This invention discloses a process for preparing a high-performance polypropylene capacitor film, comprising:

[0007] A1: Preparation of polypropylene capacitor film;

[0008] A2: Surface cleaning and activation pretreatment of polypropylene capacitor film;

[0009] A3: A gradient modification layer is vapor-deposited on the surface of the pretreated polypropylene capacitor film to form a modified polypropylene capacitor film;

[0010] A4: Laser plasma synergistic treatment and crystallinity control of modified polypropylene capacitor film;

[0011] A5: A high-performance polypropylene capacitor film is prepared by coating a functional layer on the outer layer of a modified polypropylene capacitor film and then performing an annealing post-treatment.

[0012] Furthermore, the method for preparing the polypropylene capacitor film in A1 includes:

[0013] S1: Dissolve polypropylene particles in one or more organic solvents, such as xylene, tetrahydrofuran, or 1,2-dichloroethane, and control the concentration of the polypropylene solution to be 15-30 wt%. Heat and stir until completely dissolved to obtain a polypropylene solution.

[0014] S2: Add one or more of nano-sized Al2O3, TiO2 or SiO2 as inorganic fillers to the polypropylene solution. The amount of inorganic filler added is 1-5% of the mass of polypropylene. Disperse the mixture evenly by ultrasonication to obtain a mixed spinning solution.

[0015] S3: The mixed spinning solution is cast into a film by casting at a temperature of 180-250℃ and a casting speed of 0.5-2m / min. Then, it is subjected to biaxial stretching and orientation treatment in a stretching machine at a stretching temperature of 120-160℃, wherein the longitudinal stretching ratio is 3-6 and the transverse stretching ratio is 3-5, to obtain the initial film.

[0016] S4: Heat-treat the initial film at a temperature of 140-180℃ for 5-30 minutes to obtain the polypropylene capacitor film.

[0017] Furthermore, the surface cleaning and activation pretreatment in A2 includes:

[0018] Using a surface activation device and a plasma treatment unit, the polypropylene film was sequentially subjected to corona treatment and plasma etching to improve the surface roughness to 1-5 μm.

[0019] A dual-optical-path interferometry system is used to monitor changes in the surface contact angle, ensuring that the contact angle drops below 50°.

[0020] Furthermore, the vapor-deposited gradient modification layer in A3 includes:

[0021] A gradient modified layer is deposited by evaporating using a multi-source evaporation boat, a gradient temperature control device, and a dynamic mask system.

[0022] The dynamic mask system includes a programmable microelectromechanical system array that can adjust the mask pattern accuracy to 50 μm in real time;

[0023] The gradient modification layer includes:

[0024] The base source is a copper phthalocyanine / polypyrrole composite system with a melting point of 90-95℃;

[0025] The inorganic nanolayer source is an indium tin oxide-graphene quantum dot mixed slurry with a melting point of 100-110℃;

[0026] The modification source is silane coupling agent vapor with a boiling point of 80-85℃.

[0027] Furthermore, the laser-plasma synergistic processing and crystallinity control in A4 include:

[0028] Using a picosecond laser emitter, an radio frequency plasma source, and a real-time spectrometer, the roughening, impurity removal, and surface functional group modification of the modified polypropylene capacitor film are completed simultaneously.

[0029] A three-section temperature-controlled roller and an ultrasonic atomization cooling device are used to control the crystallinity of the interface functional layer to 30%-45%.

[0030] Furthermore, the coating of the functional layer in A5 and the subsequent annealing process include:

[0031] The modified polypropylene capacitor film includes a base film layer and a functional layer disposed on at least one side of the base film layer, wherein the functional layer is coated with a functional coating liquid;

[0032] The functional coating liquid is composed of the following raw materials in parts by weight: 20-30 parts polypropylene wax, 8-12 parts vinyl silane coupling agent, 5-8 parts nano alumina, 3-5 parts titanate coupling agent, 2-4 parts plasticizer, and 10-15 parts xylene.

[0033] The particle size of the nano-alumina is 50-100nm, and the plasticizer is either dioctyl phthalate or tributyl citrate.

[0034] Furthermore, A2 specifically includes the following steps:

[0035] Pretreatment-activation coupling: First, treat the polypropylene capacitor film with 8-12kV corona for 1-3s, then etch it with Ar plasma for 25-35s to reduce the surface contact angle to below 50°.

[0036] Furthermore, A3 specifically includes the following steps:

[0037] Composite vapor deposition - gradient control, at 10 -3 -10 -2 Simultaneous evaporation under a vacuum of Pa:

[0038] Base source: Copper phthalocyanine / polypyrrole composite system deposited at a rate of 0.4-0.6 nm / s for 45-55 nm;

[0039] Inorganic nanolayer source: Indium tin oxide-graphene quantum dots were deposited at a rate of 0.2-0.4 nm / s to a depth of 25-35 nm;

[0040] Modification source: Silane coupling agent is deposited at a rate of 0.15-0.25 nm / s for 8-12 nm;

[0041] During the vapor deposition process, the polypropylene capacitor film passes through the composite vapor deposition zone at a speed of 1.5-2.5 m / min. The temperature fluctuation of each evaporation boat is controlled within ±2℃, and the vacuum fluctuation is ≤10%.

[0042] Furthermore, A4 specifically includes the following steps:

[0043] Ultrasonic gradient cooling: After vapor deposition, the polypropylene capacitor film first passes through a cooling roller at -8℃ to -10℃ for 0.8-1.2s, and then is ultrasonically atomized and cooled to 23-27℃.

[0044] Laser-plasma synergistic processing, in a vacuum of less than 10 -4 Under Pa conditions, a 335-375 nm picosecond laser was used to scan the coating, while Ar / O2 plasma was simultaneously introduced, and the 1720 cm⁻¹ infrared spectrum was monitored in real time. -1 The peak intensity changes until the absorption intensity stabilizes at 0.78-0.82 Abs, at which point the treatment is stopped.

[0045] The laser scanning speed is 100-500 mm / s, and the scanning line spacing is 10-50 μm.

[0046] Furthermore, the preparation process of the functional coating liquid is as follows:

[0047] Vinyl silane coupling agent, nano alumina, and titanate coupling agent are placed in a mixing device according to the weight ratio and mixed at 300-400 r / min for 15-25 min. Then, polypropylene wax, plasticizer, and xylene are added and dispersed at 1000-1200 r / min for 30-40 min to obtain the functional coating liquid.

[0048] A5 specifically includes the following steps:

[0049] Step 1: The polypropylene raw material is melt-extruded into a film, and then subjected to biaxial stretching treatment to obtain a polypropylene film layer;

[0050] Step 2: Apply the functional coating solution evenly to the surface of the base film layer and bake at 80-100℃ for 20-30 minutes to form the functional layer;

[0051] Step 3: Anneal the coated film at 120-150℃ and cool it to obtain a polypropylene capacitor film.

[0052] The temperature for biaxial stretching is 120-150℃, the longitudinal stretching ratio is 3-5 times, and the transverse stretching ratio is 4-6 times; the annealing time is 40-60 min, and the pressure is -0.05 to -0.08 MPa.

[0053] The beneficial effects of this invention are:

[0054] This invention achieves a dual breakthrough in the mechanical strength and electrical stability of polypropylene capacitor films through nanofiller dispersion, biaxial stretching, and crystallinity control processes. In the base film preparation stage, the introduction of nano-Al2O3 and TiO2 fillers combined with ultrasonic dispersion technology avoids filler agglomeration while forming a rigid support structure between molecular chains. After biaxial stretching, the tensile strength is increased by 40%-110% compared to traditional unmodified films, reaching 140-180 MPa. Combined with heat treatment at 140-180℃ to eliminate internal stress, the thermal shrinkage rate at 120℃ is reduced to 0.5%-1.2%, a reduction of 70%-87.5% compared to ordinary films. In terms of electrical performance, the evaporation of the gradient modified layer forms a conductive network, increasing the breakdown field strength from 25 kV / μm to 30-38 kV / μm and reducing the dielectric loss to 0.0015-0.0020, effectively reducing energy loss under high-frequency operating conditions.

[0055] The synergistic design of surface cleaning and activation with gradient functional layers endows the membrane material with excellent interfacial adhesion and environmental adaptability. Corona treatment and Ar plasma etching introduce polar groups and form a nano-rough structure on the membrane surface, increasing the interfacial peel strength between the vapor-deposited modified layer and the base film by more than 60%, reaching 4.5-5.5 N / cm. The -SiOH groups released by the silane coupling agent modified layer further reduce the surface contact angle to 42°-48°, providing an ideal substrate for functional layer coating. Corona resistance lifetime tests show that the membrane material prepared by this process has a service life of 180-250 hours under 50kV conditions, which is 2.6-5 times better than the control sample without the modified layer. The indium tin oxide-graphene quantum dot layer effectively blocks corona corrosion. Combined with the interpenetrating interface layer formed by annealing post-treatment, the moisture absorption rate is reduced from 0.01% to below 0.003%, meeting the long-term reliability requirements under high-voltage environments.

[0056] The introduction of technologies such as multi-source evaporation and laser-plasma synergistic processing has enabled precise control and diversified expansion of membrane material properties. Dynamic masking systems and gradient temperature control result in a modified layer exhibiting a compositional gradient structure; simultaneous processing with picosecond lasers and Ar / O2 plasma precisely controls the interface crystallinity between 30% and 45%, balancing the membrane material's flexibility and strength. The combination of functional coating solutions and vacuum annealing processes can impart antistatic and scratch-resistant properties to the membrane material as needed, making it suitable for applications such as high-voltage DC capacitors and high-frequency electronic components. Process repeatability errors are ≤3%, providing a stable quality control method for large-scale production. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of one embodiment of the present application. Detailed Implementation

[0058] To enable those skilled in the art to better understand the present invention, the technical solutions in the specific embodiments of the present invention will be clearly and completely described below.

[0059] This invention discloses a process for preparing a high-performance polypropylene capacitor film, comprising:

[0060] A1: Preparation of polypropylene capacitor film;

[0061] A2: Surface cleaning and activation pretreatment of polypropylene capacitor film;

[0062] A3: A gradient modification layer is vapor-deposited on the surface of the pretreated polypropylene capacitor film to form a modified polypropylene capacitor film;

[0063] A4: Laser plasma synergistic treatment and crystallinity control of modified polypropylene capacitor film;

[0064] A5: A high-performance polypropylene capacitor film is prepared by coating a functional layer on the outer layer of a modified polypropylene capacitor film and then performing an annealing post-treatment.

[0065] A1. Polypropylene capacitor films are prepared using conventional film-forming processes. By controlling the raw material ratios and film-forming parameters, polypropylene capacitor films with basic mechanical and electrical properties are obtained. A2. The surface of the polypropylene capacitor film is cleaned using physical or chemical methods to remove impurities and activate the surface, giving it suitable roughness and active sites to provide conditions for subsequent modification layer bonding. This stage ensures the cleanliness and enhanced activity of the polypropylene capacitor film surface, preventing impurities from affecting subsequent processes, while also enhancing the bonding ability between the surface and the modified layer, ensuring overall structural stability. A3. On the pretreated polypropylene capacitor film surface, a modified layer with a gradient in composition or structure is formed through a vapor deposition process, enabling good bonding between the modified layer and the polypropylene capacitor film and subsequent functional layers. A4. The modified film undergoes synergistic laser and plasma treatment. By adjusting the treatment parameters, the film surface structure is optimized, and the crystallinity of the film is directionally controlled, improving the film's physical and electrical properties. The introduction of the gradient modified layer enhances the interlayer bonding force, and the synergistic treatment further optimizes the surface characteristics and internal crystalline structure of the film, improving its overall performance. A5 involves coating a functional layer material onto the outer layer of the modified membrane using a suitable coating process to ensure uniform adhesion. Subsequent annealing treatment ensures full bonding between the functional layer and the modified membrane, stabilizing the structure. The functional layer imparts specific functions to the membrane, while annealing promotes the orderly arrangement of molecular chains, improving the membrane's dimensional stability and long-term performance. This step achieves effective adhesion of the functional layer and optimization of the membrane structure, enabling the capacitor membrane to possess the target function and meet the stability requirements of practical applications.

[0066] As one specific implementation method, the method for preparing the polypropylene capacitor film in A1 includes:

[0067] S1: Dissolve polypropylene particles in one or more organic solvents, such as xylene, tetrahydrofuran, or 1,2-dichloroethane, and control the concentration of the polypropylene solution to be 15-30 wt%. Heat and stir until completely dissolved to obtain a polypropylene solution.

[0068] S2: Add one or more of nano-sized Al2O3, TiO2 or SiO2 as inorganic fillers to the polypropylene solution. The amount of inorganic filler added is 1-5% of the mass of polypropylene. Disperse the mixture evenly by ultrasonication to obtain a mixed spinning solution.

[0069] S3: The mixed spinning solution is cast into a film by casting at a temperature of 180-250℃ and a casting speed of 0.5-2m / min. Then, it is subjected to biaxial stretching and orientation treatment in a stretching machine at a stretching temperature of 120-160℃, wherein the longitudinal stretching ratio is 3-6 and the transverse stretching ratio is 3-5, to obtain the initial film.

[0070] S4: Heat-treat the initial film at a temperature of 140-180℃ for 5-30 minutes to obtain the polypropylene capacitor film.

[0071] S1. Polypropylene particles are dissolved in organic solvents such as xylene, tetrahydrofuran, or 1,2-dichloroethane, with the solution concentration controlled at 15-30 wt%. The solution is heated and stirred until completely dissolved, forming a homogeneous and transparent polypropylene solution. S2. 1-5% of nano-sized Al2O3, TiO2, or SiO2 fillers are added to the solution. Ultrasonic dispersion technology is used to ensure uniform dispersion of the fillers and prevent agglomeration. This process ensures complete dissolution of polypropylene through solvent selection and concentration control. The nano-sized dispersion of the fillers effectively improves the mechanical strength and dielectric properties of the polypropylene capacitor film, providing a uniform and stable spinning solution for subsequent film formation, thus ensuring the consistency of the film material from the raw material end. S3. The mixed spinning solution is cast into a film at 180-250℃ using a casting method, with the casting speed controlled at 0.5-2 m / min. After forming the initial film, it is biaxially stretched in a stretching machine at 120-160℃, with a longitudinal stretch ratio of 3-6 and a transverse stretch ratio of 3-5. Precise control of casting temperature and speed ensures uniform film thickness, while biaxial stretching orients the polypropylene molecular chains, significantly improving crystallinity and orientation. The tensile strength of the pre-stretched film is increased by 40%-60% compared to the unstretched state, and the breakdown field strength increases from 25kV / μm to over 30kV / μm, laying the structural foundation for high-performance polypropylene capacitor films. S4 heat-treats the pre-stretched film at 140-180℃ for 5-30 minutes, using high temperature to further rearrange the molecular chains, forming a more complete crystalline structure. Optimization of heat treatment temperature and time eliminates residual internal stress from the stretching process, improving the film's dimensional stability by over 30% and reducing the long-term thermal shrinkage rate from 4% to below 1.2%. This step, through controllable thermally induced crystallization, significantly enhances the film's temperature resistance and structural stability without reducing its flexibility, meeting the requirements of high-end capacitors for long-term reliable operation of the film material.

[0072] Example

[0073] Raw material preparation: Dissolve 100g of polypropylene granules in 400g of xylene, heat to 150℃ and stir for 2 hours until completely dissolved to obtain a 20wt% polypropylene solution; add 3g of nano Al2O3 filler to the solution and ultrasonically disperse for 30 minutes until there is no obvious particle agglomeration.

[0074] Film formation process: The mixture is cast at 220℃ at a casting speed of 1m / min. The resulting initial film is subjected to biaxial stretching at 140℃ with a longitudinal stretching ratio of 4 and a transverse stretching ratio of 4. Subsequently, it is heat-treated at 160℃ for 15 minutes to obtain a polypropylene capacitor film with a thickness of 50μm.

[0075] Performance parameters: The membrane has a tensile strength of 150MPa, a breakdown field strength of 32kV / μm, a heat shrinkage rate of 0.8% at 120℃, and a surface roughness Ra≤0.2μm. All indicators meet the requirements for membranes used in high voltage DC capacitors.

[0076] As a specific implementation, the surface cleaning and activation pretreatment in A2 includes using a surface activation device and a plasma treatment unit to sequentially perform corona treatment and plasma etching on the polypropylene film, improving the surface roughness to 1-5 μm. A dual-path interference system is used to monitor changes in the surface contact angle, ensuring that the contact angle is reduced to below 50°.

[0077] A high-frequency, high-voltage electric field is generated using a surface activation device, and an 8-12kV voltage is applied to the surface of a polypropylene film for corona treatment, with the treatment time controlled within 1-3 seconds. The plasma generated by the corona discharge effectively bombards the film surface, removing contaminants such as oil and dust, while simultaneously breaking the surface molecular chains and introducing polar groups such as hydroxyl and carbonyl groups. This step increases the surface tension of the film from 32mN / m to over 45mN / m, creating a clean and activated substrate for subsequent plasma etching and significantly enhancing the chemical bonding between the surface and the modified layer. Using a plasma treatment unit, working gases such as argon, oxygen, or air are introduced, and the corona-treated film is etched under conditions of 10-100Pa pressure and 50-200W power. The high-energy ions in the plasma directionally bombard the film surface, and through the synergistic effect of physical sputtering and chemical reaction, the surface roughness is increased from below 0.2μm to 1-5μm, forming a nanoscale uneven structure. This roughening treatment increases the film surface area by 30%-50%, providing more anchoring sites for the vapor-deposited gradient modified layer, effectively improving the interlayer mechanical bonding strength and preventing the modified layer from detaching. A dual-path interferometry system is used to monitor the change in the film surface contact angle in real time during the treatment process, using deionized water as the test solution to ensure that the contact angle gradually decreases from an initial above 80° to below 50°. When the contact angle meets the standard, the system automatically terminates the treatment to avoid excessive etching that could damage the film surface. This closed-loop monitoring mechanism can precisely control the degree of activation, ensuring that the surface hydrophilicity meets the requirements of subsequent coating processes while preventing adhesion defects caused by insufficient treatment. This improves the interfacial adhesion between the modified layer and the polypropylene capacitor film by more than 40%, providing quantitative assurance for the overall stability of the capacitor film's performance.

[0078] As one specific implementation, the vapor-deposited gradient modification layer in A3 includes:

[0079] A gradient modified layer is deposited by evaporating using a multi-source evaporation boat, a gradient temperature control device, and a dynamic mask system.

[0080] The dynamic mask system includes a programmable microelectromechanical system array that can adjust the mask pattern accuracy to 50 μm in real time;

[0081] The gradient modification layer includes:

[0082] The base source is a copper phthalocyanine / polypyrrole composite system with a melting point of 90-95℃;

[0083] The inorganic nanolayer source is an indium tin oxide-graphene quantum dot mixed slurry with a melting point of 100-110℃;

[0084] The modification source is silane coupling agent vapor with a boiling point of 80-85℃.

[0085] A multi-source evaporation boat was used to load a copper phthalocyanine / polypyrrole composite system, an indium tin oxide-graphene quantum dot mixed slurry, and a silane coupling agent, respectively. A gradient temperature control device was used to set the evaporation boat temperature to 90-95℃, 100-110℃, and 80-85℃, allowing the base layer source, inorganic nanolayer source, and modification source to evaporate in sequence according to their melting or boiling points. A programmable microelectromechanical system (MEMS) array of a dynamic masking system adjusted the mask pattern in real time with an accuracy of 50μm, ensuring that the three layers formed a compositional and structural gradient from the polypropylene capacitor film to the outer layer during evaporation: first, a 50-80nm copper phthalocyanine / polypyrrole base layer was deposited on the polypropylene capacitor film surface, then a 30-60nm indium tin oxide-graphene quantum dot inorganic nanolayer was deposited, and finally a 10-20nm silane coupling agent modification layer was formed on the surface. The three layers achieved interpenetrating fusion of the interfacial molecular chains through temperature gradient control. The conjugated molecular structure of copper phthalocyanine / polypyrrole substrate can significantly improve the surface conductivity of the film, reducing the surface resistivity from 10... 13 Ω・cm decreased to 10 11 Below Ω·cm, it provides a pathway for uniform charge distribution; the intermediate indium tin oxide-graphene quantum dot inorganic nanolayer, with its high specific surface area and conductive network, endows the film with excellent corona corrosion resistance, extending corona aging life and effectively resisting partial discharge damage under high voltage conditions; the outermost silane coupling agent modified layer, by releasing polar groups such as -SiOH, reduces the film surface contact angle from above 70°, significantly enhancing surface hydrophilicity and providing an ideal substrate for the uniform coating of subsequent functional layers, avoiding pinholes or peeling of the coating. The dynamic masking system achieves regional gradient distribution of the modified layer on the film surface through pattern control with a precision of 50μm. For example, increasing the deposition of inorganic nanolayers and silane coupling agents in the edge region of the capacitor film increases the breakdown field strength at the edge by 15%, effectively solving the breakdown problem caused by electric field concentration at the edge of traditional film materials. The three-layer gradient structure, through the layer-by-layer optimization of material functions and the synergistic effect of interface molecules, increases the interlayer peel strength between the modified layer and the polypropylene capacitor film to over 5 N / cm, which is stronger than the single coating structure. At the same time, it takes into account conductivity, weather resistance and surface activity, providing structural protection for the long-term stable operation of the capacitor film under high-frequency and high-voltage environments.

[0086] As a specific implementation method, the laser-plasma synergistic processing and crystallinity control in A4 involves using a picosecond laser emitter, a radio frequency plasma source, and a real-time spectrometer to simultaneously roughen, remove impurities, and modify the surface functional groups of the modified polypropylene capacitor film. A three-stage temperature-controlled roller and an ultrasonic atomization cooling device are used to control the crystallinity of the interfacial functional layer between 30% and 45%.

[0087] The laser-plasma synergistic treatment employs a picosecond laser emitter with a wavelength of 532 nm and a pulse width of 50 ps, ​​scanning the modified film surface at an energy density of 0.8-1.5 J / cm². Through laser micro-melting, a 1-5 μm nanoscale uneven structure is formed on the film surface, simultaneously removing residual contaminants. A matching 13.56 MHz radio frequency plasma source, purged with a mixture of argon and oxygen gas at a pressure of 20-50 Pa, generates plasma to bombard the laser-treated surface for 30-60 seconds, introducing functional groups such as hydroxyl and carboxyl groups through physical sputtering and chemical reactions. A real-time spectrometer acquires the surface infrared spectrum in real time, automatically terminating the treatment when the characteristic peak intensity of the functional groups reaches the target, ensuring that surface roughening, cleaning, and functional group modification are completed simultaneously.

[0088] The crystallinity control process utilizes a three-stage temperature-controlled roller to control the temperature gradient of the treated membrane material. The first stage, the preheating roller, is set at 100-120℃ to initially soften the membrane material. The second stage, the main control roller, is heated to 140-160℃ to activate the polypropylene molecular chain segments. Simultaneously, an ultrasonic atomizing cooling device evenly sprays deionized water mist onto the roller surface at a cooling rate controlled at 5-10℃ / s, inducing directional crystallization of the molecular chains. The third stage, the setting roller, maintains a temperature of 80-90℃ to stabilize the crystalline structure. By adjusting the speed and temperature difference of the three rollers, the crystallinity of the interfacial functional layer is precisely controlled between 30% and 45%, avoiding excessive crystallization that could increase the membrane material's brittleness.

[0089] Laser-plasma synergistic treatment improved the membrane surface roughness from 0.3 μm to 1.2-3.5 μm, increased the specific surface area by 40%, and reduced the surface contact angle from 65° to below 45°, significantly enhancing surface hydrophilicity and the anchoring ability of subsequent functional layers. The introduced polar functional groups increased the density of active sites on the membrane surface by 50%, promoting chemical bonding with functional layers. Crystallinity regulation, through the ordered arrangement of molecular chains, increased the tensile strength of the membrane from 120 MPa to 150-180 MPa and the breakdown field strength from 32 kV / μm to 35-38 kV / μm, while maintaining an elongation at break of over 8%, effectively balancing mechanical and electrical properties. Real-time spectral monitoring and three-stage temperature control technology ensured process repeatability errors ≤3%, providing a stable quality control method for large-scale production.

[0090] In one specific embodiment, the coating of the functional layer and subsequent annealing treatment in A5 includes: The modified polypropylene capacitor film includes a base film layer and a functional layer disposed on at least one side of the base film layer, the functional layer being coated with a functional coating liquid. The functional coating liquid consists of the following raw materials in parts by weight: 20-30 parts polypropylene wax, 8-12 parts vinyl silane coupling agent, 5-8 parts nano-alumina, 3-5 parts titanate coupling agent, 2-4 parts plasticizer, and 10-15 parts xylene. The nano-alumina has a particle size of 50-100 nm, and the plasticizer is either dioctyl phthalate or tributyl citrate.

[0091] The functional coating solution is prepared and coated using the following methods: Weigh 20-30 parts by weight of polypropylene wax, 8-12 parts by weight of vinyl silane coupling agent, 5-8 parts by weight of 50-100nm nano-alumina, 3-5 parts by weight of titanate coupling agent, and 2-4 parts by weight of dioctyl phthalate or tributyl citrate plasticizer. Add these to 10-15 parts by weight of xylene and mechanically stir at 60-80℃ for 30-60 minutes until completely dispersed to form a uniform and stable functional coating solution. Using slot coating or gravure printing, uniformly coat the modified polypropylene capacitor film surface with the coating solution at a coating speed of 5-10 m / min, controlling the coating thickness to 1-5 μm to ensure the functional layer is free of bubbles, missed areas, and uneven thickness.

[0092] The post-annealing process involves placing the coated membrane material into a tunnel annealing furnace. Under a nitrogen protective atmosphere, the temperature is increased to 120-150℃ at a rate of 5-10℃ / min, held for 30-60 minutes, and then allowed to cool naturally to room temperature. During annealing, the polypropylene wax and the polypropylene molecular chains of the base film diffuse and intertwine through thermal motion. The vinyl silane coupling agent undergoes a condensation reaction with the polar groups on the surface of the polypropylene capacitor film to form Si-OC chemical bonds. At high temperatures, nano-alumina particles embed into the nanopores on the surface of the polypropylene capacitor film, forming a mechanically anchored structure. A three-stage temperature control system ensures uniform heating of the membrane material, with the temperature difference controlled within ±2℃.

[0093] The polypropylene wax in the functional layer imparts a low coefficient of friction and scratch resistance to the membrane surface. Vinyl silane coupling agent enhances the adhesion between the functional layer and the polypropylene capacitor film to over 8 N / cm. Nano-alumina particles increase the surface hardness of the membrane from 2H to 3H, effectively resisting external mechanical damage. The addition of plasticizers maintains the elongation at break of the functional layer above 30%, preventing coating brittleness. Annealing promotes the formation of a 1-3 μm interpenetrating interface layer between the functional layer and the polypropylene capacitor film, reducing the overall dielectric loss of the membrane from 0.0025 to 0.0018, while simultaneously reducing the thermal shrinkage rate from 3.5% to below 1.0%. This process, through the synergy of component design and heat treatment, achieves enhanced surface functionality and stable internal structure of the capacitor film, meeting the weather resistance and reliability requirements for long-term service under high voltage and high frequency environments.

[0094] As a specific implementation method, A2 specifically includes the following steps: pretreatment-activation coupling, first treating the polypropylene capacitor film with 8-12kV corona for 1-3s, and then etching it with Ar plasma for 25-35s to reduce the surface contact angle to below 50°.

[0095] A high-voltage (8-12kV) discharge field is applied to the surface of the polypropylene capacitor film using a corona treatment device, creating a high-frequency discharge field to corona treat the film for 1-3 seconds. The high-energy electrons generated by the discharge collide with oxygen and nitrogen molecules in the air, producing active particles such as ozone and nitrogen oxides. These particles effectively bombard the film surface, removing contaminants such as oil and dust, while simultaneously breaking the polypropylene molecular chains and introducing polar groups such as hydroxyl and carbonyl groups. This step increases the film surface tension from 30-35mN / m to 45-50mN / m, providing a clean and pre-activated substrate for subsequent plasma etching and significantly enhancing surface chemical activity.

[0096] After corona treatment, the polypropylene capacitor film enters a plasma etching chamber, where argon gas with a purity ≥99.9% is introduced. Etching is performed for 25-35 seconds at a pressure of 10-50 Pa and a power of 50-150 W. Argon ions, accelerated by an electric field, directionally bombard the film surface, removing the weak boundary layer through physical sputtering. Simultaneously, a nanoscale uneven structure is formed on the film surface, increasing the roughness from 0.1-0.3 μm to 0.5-1.5 μm. The etching process does not introduce new chemical groups; it only increases the surface area by 30%-40% through physical action, providing more mechanical anchoring sites for subsequent vapor deposition of modified layers.

[0097] The step-by-step implementation of corona treatment and Ar plasma etching gradually reduces the contact angle of the polypropylene capacitor film surface from the initial 70°-80° to below 50°, achieving a triple effect of cleaning, activation, and roughening. The chemical activation of corona treatment and the physical roughening of plasma etching complement each other: polar groups enhance the surface chemical bonding force, and the roughened structure strengthens the interlayer mechanical interlocking. The synergy of these two processes increases the interfacial adhesion between the modified layer and the polypropylene capacitor film by more than 60% compared to a single treatment method, effectively avoiding coating peeling or uniformity defects during the vapor deposition process, and laying a stable foundation for subsequent functional layer coating.

[0098] As a specific implementation method, A3 includes the following steps:

[0099] Composite vapor deposition - gradient control, at 10 -3 -10 -2 Simultaneous evaporation under a vacuum of Pa:

[0100] Base source: Copper phthalocyanine / polypyrrole composite system deposited at a rate of 0.4-0.6 nm / s for 45-55 nm;

[0101] Inorganic nanolayer source: Indium tin oxide-graphene quantum dots were deposited at a rate of 0.2-0.4 nm / s to a depth of 25-35 nm;

[0102] Modification source: Silane coupling agent is deposited at a rate of 0.15-0.25 nm / s for 8-12 nm;

[0103] During the vapor deposition process, the polypropylene capacitor film passes through the composite vapor deposition zone at a speed of 1.5-2.5 m / min. The temperature fluctuation of each evaporation boat is controlled within ±2℃, and the vacuum fluctuation is ≤10%.

[0104] At a vacuum degree of 10 -3 -10 -2 Under Pa conditions, A2-treated polypropylene capacitor film is conveyed through a composite evaporation zone at a speed of 1.5-2.5 m / min. Three independently temperature-controlled evaporation boats are loaded with a copper phthalocyanine / polypyrrole composite system, an indium tin oxide-graphene quantum dot mixed slurry, and a silane coupling agent, respectively. The temperatures of the evaporation boats are stabilized at 90-95℃, 100-110℃, and 80-85℃ respectively using a precision temperature control system, with temperature fluctuations controlled within ±2℃. Copper phthalocyanine / polypyrrole is deposited at a rate of 0.4-0.6 nm / s to form a 45-55 nm base layer, indium tin oxide-graphene quantum dots are deposited at a rate of 0.2-0.4 nm / s to form a 25-35 nm inorganic nanolayer, and the silane coupling agent is deposited at a rate of 0.15-0.25 nm / s to form an 8-12 nm modified layer. During the simultaneous evaporation of the three layers, a gradient interface structure from organic to inorganic is formed on the film surface.

[0105] By precisely controlling the deposition rate and time of each evaporation source, the modified layer exhibits a gradient change in composition and properties. The conjugated structure of copper phthalocyanine / polypyrrole in the base layer has good compatibility with the polypropylene capacitor film, enhancing the interfacial bonding force. The indium tin oxide in the middle inorganic nanolayer provides conductivity, while graphene quantum dots enhance mechanical properties. The synergy of these two elements reduces the surface resistivity of the film to 10. 11 Ω・cm; The outer silane coupling agent forms -SiOH groups through hydrolysis, reducing the surface contact angle to 40°-50° and enhancing the wettability of subsequent functional layer coatings. Temperature fluctuations in each evaporation boat are ≤±2℃ to ensure stable material evaporation rates, and vacuum fluctuations are ≤10% to avoid the introduction of impurity gases, ensuring the uniformity and repeatability of the gradient structure.

[0106] The gradient structure formed by simultaneous vapor deposition achieves an interfacial shear strength of 4.5-5.5 N / cm between the modified layer and the polypropylene capacitor film, an improvement of over 80% compared to single-layer coating. Surface roughness Ra is controlled at 0.1-0.3 μm, ensuring coating uniformity while avoiding the risk of tip discharge. The gradient conductivity distribution results in more uniform charge distribution, extending partial discharge tolerance to over 200 hours and increasing breakdown field strength to 38-42 kV / μm. The outer layer of silane coupling agent effectively blocks moisture penetration, reducing the film's moisture absorption rate from 0.01% to below 0.003%. This process, through multi-material synergy and gradient structure design, achieves a comprehensive improvement in the dielectric properties, mechanical properties, and weather resistance of the capacitor film, meeting the stringent requirements of high-voltage, high-frequency capacitors.

[0107] As a specific implementation method, A4 includes the following steps: ultrasonic-gradient cooling: after vapor deposition, the polypropylene capacitor film is first passed through a cooling roller at -8℃ to -10℃ for 0.8-1.2s, and then ultrasonically atomized and cooled to 23-27℃. Laser-plasma synergistic treatment: under a vacuum of less than 10⁻⁴ Pa, a 335-375nm picosecond laser is used to scan the coating, while Ar / O₂ plasma is simultaneously introduced. The intensity change of the 1720cm⁻¹ peak in the infrared spectrum is monitored in real time until the absorption intensity stabilizes at 0.78-0.82 Abs, at which point the treatment stops. The laser scanning speed is 100-500mm / s, and the scanning line spacing is 10-50μm.

[0108] The vapor-deposited polypropylene capacitor film is first passed through a cooling roller with a temperature controlled at -8℃ to -10℃ for 0.8-1.2 seconds. This rapid cooling of the roller surface quickly solidifies the coating, inhibiting excessive crystallization of the modified layer. Subsequently, an ultrasonic atomizing device atomizes deionized water into droplets with a diameter of 5-10μm, creating a uniform cooling field on the film surface and gradually reducing the film temperature to 23-27℃. This gradient cooling process combines rapid and slow cooling to prevent internal stress caused by excessive temperature differences in the coating. Simultaneously, it controls the interfacial crystallinity between the polypropylene capacitor film and the modified layer, increasing the crystallinity of the interfacial functional layer from 25% to 30%-40%, thus enhancing the tightness of the interlayer molecular chain entanglement.

[0109] When the vacuum degree is less than 10 -4 Within a sealed chamber, a picosecond laser with a wavelength of 335-375 nm is used to scan the coating surface at a speed of 100-500 mm / s, with the scanning line spacing controlled at 10-50 μm. This laser micro-melting effect creates nanoscale pits on the film surface. Simultaneously, a 9:1 volume ratio Ar / O2 mixed gas is introduced to generate plasma, which bombards and modifies the laser-treated area. A real-time spectrometer continuously monitors the infrared spectrum at 1720 cm⁻¹. -1 The carbonyl characteristic peak intensity is measured, and the processing automatically stops when the absorption intensity stabilizes at 0.78-0.82 Abs, ensuring that the degree of surface functional group modification is uniform and controllable.

[0110] Ultrasonic gradient cooling increases the interfacial peel strength between the modified layer and the polypropylene capacitor film by 30%, reaching 6-7 N / cm, effectively preventing interlayer delamination. Laser treatment creates a nanoscale rough structure, increasing the surface area by 20%-30%. The introduction of polar groups such as carbonyl and hydroxyl groups by plasma reduces the surface contact angle to below 45°, significantly enhancing the adhesion of subsequent functional layers. Real-time infrared spectroscopy monitoring ensures consistent functional group density on the surface of each batch of film material, with a repeatability error of ≤2%. This process, through synergistic cooling control and surface modification, increases the breakdown field strength of the capacitor film from 35kV / μm to over 40kV / μm, while simultaneously improving corona aging resistance, meeting the requirements for long-term stable operation under high-voltage environments.

[0111] As a specific implementation method, the preparation process of the functional coating liquid is as follows: Vinyl silane coupling agent, nano alumina, and titanate coupling agent are placed in a mixing device according to the weight ratio and mixed at 300-400 r / min for 15-25 min. Then, polypropylene wax, plasticizer, and xylene are added and dispersed at 1000-1200 r / min for 30-40 min to obtain the functional coating liquid.

[0112] A5 specifically includes the following steps:

[0113] Step 1: The polypropylene raw material is melt-extruded into a film, and then subjected to biaxial stretching treatment to obtain a polypropylene film layer;

[0114] Step 2: Apply the functional coating liquid evenly to the surface of the polypropylene capacitor film and bake at 80-100℃ for 20-30 minutes to form a functional layer.

[0115] Step 3: Anneal the coated film at 120-150℃ and cool it to obtain a polypropylene capacitor film.

[0116] The temperature for biaxial stretching is 120-150℃, the longitudinal stretching ratio is 3-5 times, and the transverse stretching ratio is 4-6 times; the annealing time is 40-60 min, and the pressure is -0.05 to -0.08 MPa.

[0117] Vinyl silane coupling agent, 50-100nm nano-alumina, and titanate coupling agent are added to a mixing device according to the weight ratio and mixed at a low speed of 300-400 rpm for 15-25 minutes to ensure sufficient contact and coating of the inorganic filler with the coupling agent. Then, polypropylene wax, dioctyl phthalate or tributyl citrate plasticizer, and xylene solvent are added and dispersed at a high speed of 1000-1200 rpm for 30-40 minutes. Shear force breaks down filler agglomerates, forming a uniform coating liquid with a solid content of 25%-35%. Low-speed mixing ensures effective reaction between the polar groups on the filler surface and the coupling agent, while high-speed dispersion promotes molecular fusion of the polypropylene wax and solvent, stabilizing the viscosity of the coating liquid at 50-80 mPa·s to meet the flowability requirements of subsequent coating processes.

[0118] Step 1 involves melt-extruding the polypropylene raw material into a film at 180-220℃, followed by biaxial stretching at 120-150℃ (3-5 times longitudinally and 4-6 times transversely) to orient the molecular chains, increasing crystallinity from 30% to 45%-50% and tensile strength to 130-160 MPa. Step 2 uses slot coating or roller coating to uniformly coat the functional coating liquid onto the polypropylene capacitor film surface at a wet film thickness of 5-10 μm. The film is then baked in an oven at 80-100℃ for 20-30 minutes. During this process, the xylene solvent evaporates, and the vinyl silane coupling agent undergoes initial hydrolysis to form silanol groups, which initially bond with polar sites on the polypropylene capacitor film surface, forming a semi-cured functional layer with a thickness of 1-3 μm. Biaxial stretching provides the polypropylene capacitor film with an excellent mechanical framework, and the coating and baking process ensures the initial anchoring of the functional layer to the polypropylene capacitor film, laying the structural foundation for subsequent annealing.

[0119] Step 3 involves placing the coated film in an annealing furnace with a vacuum of -0.05 to -0.08 MPa, heating it to 120-150°C at a rate of 5-10°C / min, holding it at that temperature for 40-60 minutes, and then cooling it in the furnace. The vacuum environment prevents oxygen from entering and causing material oxidation. The medium-temperature holding promotes the interdiffusion of polypropylene wax molecules and polypropylene segments in the polypropylene capacitor film, forming a 1-2 μm interpenetrating molecular interface layer. The silane coupling agent is completely hydrolyzed and condenses with the hydroxyl groups on the surface of the polypropylene capacitor film to form Si-OC covalent bonds, increasing the adhesion between the functional layer and the polypropylene capacitor film from 4 N / cm to 8-10 N / cm. Annealing also eliminates residual stress within the film, reducing the thermal shrinkage rate from 2.5% to below 0.8% and the dielectric loss tangent from 0.003 to 0.0015, significantly improving the stability and reliability of the capacitor film under high-frequency conditions.

[0120] Example 1: Nano-Al2O3 filler and gradient modified layer

[0121] A1: Preparation of polypropylene capacitor film

[0122] S1 solution preparation: 100g of polypropylene particles were dissolved in 400g of xylene, heated in an oil bath at 150℃ and stirred at 300r / min for 2 hours to obtain a 20wt% polypropylene solution.

[0123] S2 filler dispersion: 3g of nano Al2O3 with a particle size of 50nm and accounting for 3% of the mass of polypropylene was added to the solution and ultrasonically dispersed for 30 minutes until no agglomeration occurred.

[0124] S3 casting and stretching: The mixture is cast into a film at 220℃ with a casting speed of 1m / min. The resulting initial film is then subjected to bidirectional stretching with a longitudinal stretching ratio of 4 and a transverse stretching ratio of 4 in a stretching machine at 140℃.

[0125] S4 heat treatment involves heat-treating the initial film in an oven at 160℃ for 15 minutes to obtain a 50μm thick polypropylene capacitor film.

[0126] A2: Surface pretreatment

[0127] Using a high-frequency electric field device, the surface tension of the polypropylene capacitor film was increased to 45 mN / m by treating the surface of the film for 2 seconds at 8 kV.

[0128] By introducing 99.9% high-purity Ar gas and etching for 30 seconds at 30Pa pressure and 100W power, the surface roughness reached 0.8μm and the contact angle was reduced to 45°.

[0129] A3: Evaporation gradient modified layer

[0130] Place the polypropylene capacitor film in the vacuum chamber and evacuate to 10°C. -3 Pa;

[0131] Multi-source evaporation:

[0132] Substrate: Copper phthalocyanine / polypyrrole composite system, mass ratio 1:1, evaporation boat temperature 95℃, deposition of 50nm at a rate of 0.5nm / s;

[0133] Inorganic layer: 50nm indium tin oxide and 10nm graphene quantum dots mixed slurry, volume ratio 3:1, evaporated at 105℃, deposited at a rate of 0.3nm / s for 30nm;

[0134] Modified layer: γ-methacryloyloxypropyltrimethoxysilane, evaporated at 85℃, deposited at a rate of 0.2nm / s for 10nm;

[0135] Membrane material transport: The polypropylene capacitor membrane passes through the evaporation zone at a speed of 2m / min, and the temperature fluctuation of each evaporation boat is ≤±2℃.

[0136] A4: Laser-plasma synergistic processing;

[0137] First, it is contacted by a -9℃ cooling roller for 1 second, then ultrasonically atomized to a water mist particle size of 5μm, and cooled to 25℃;

[0138] Using a 355nm picosecond laser with a pulse width of 50ps, scanning at a speed of 300mm / s, a line spacing of 30μm, and an energy density of 1.0J / cm²;

[0139] Simultaneous introduction of Ar / O2 at a volume ratio of 9:1, treatment at 20 Pa pressure for 40 seconds, and real-time monitoring of the 1720 cm⁻¹ infrared spectrum. -1 The peak intensity was stopped at 0.80 Abs, and the interfacial crystallinity was adjusted to 38%.

[0140] A5: Coating and Annealing

[0141] Weigh out 25 parts by weight of polypropylene wax, 10 parts by weight of vinyl silane coupling agent, 6 parts by weight of nano Al2O3 with a particle size of 50 nm, 4 parts by weight of titanate coupling agent, 3 parts by weight of dioctyl phthalate, add 12 parts by weight of xylene, and disperse at 1000 r / min for 30 minutes at 60℃.

[0142] A slit coating process was used to coat the film at a speed of 5 m / min, followed by baking at 80°C for 20 minutes to form a 2 μm wet film.

[0143] High-performance polypropylene capacitor film was prepared by heating to 130°C at a vacuum of -0.06 MPa at a rate of 5°C / min, holding at that temperature for 50 minutes, and then cooling.

[0144] Example 2: Optimization of nano-TiO2 filler and laser treatment

[0145] A1: Preparation of polypropylene capacitor film;

[0146] S1: 25wt% polypropylene tetrahydrofuran solution, 100g polypropylene and 300g solvent, stirred and dissolved at 160℃;

[0147] S2: Add 5g of nano TiO2 with a particle size of 100nm, 5% addition amount, and ultrasonically disperse for 40 minutes;

[0148] S3: Casting at 200℃, 1.5m / min, longitudinal stretch ratio 3 and transverse stretch ratio 5 at 120℃;

[0149] S4: Heat treatment at 140℃ for 30 minutes to prepare polypropylene capacitor film.

[0150] A2: Preprocessing;

[0151] 10kV corona treatment for 1 second, Ar plasma etching for 25 seconds, contact angle 42°.

[0152] A3: Vapor deposition;

[0153] Vacuum 10 -2 Pa, base layer 0.6nm / s×45nm, inorganic layer 0.2nm / s×35nm, modified layer 0.15nm / s×12nm, film speed 2.5m / min.

[0154] A4: Collaborative Processing

[0155] -8℃ cooling roller contact for 1.2 seconds, 335nm laser, 500mm / s, line spacing 10μm, and Ar plasma treatment, crystallinity 40%.

[0156] A5: Coating Annealing

[0157] The functional liquid contains tributyl citrate plasticizer, and is annealed at 120℃ for 60 minutes under vacuum of -0.05MPa to prepare a high-performance polypropylene capacitor film.

[0158] Example 3: High draw ratio and gradient temperature vapor deposition

[0159] A1: Preparation of Polypropylene Capacitor Film

[0160] S1: 15wt% polypropylene 1,2-dichloroethane solution, 100g and 567g solvent, dissolved at 180℃;

[0161] S2: Add 1g of nano-SiO2 and ultrasonically disperse for 20 minutes;

[0162] S3: Casting at 250℃, 0.5m / min, longitudinal stretch ratio 6 and transverse stretch ratio 3 at 150℃;

[0163] S4: Heat treatment at 180℃ for 5 minutes.

[0164] A2: Pretreatment, 12kV corona for 3 seconds, Ar etching for 35 seconds, contact angle 48°.

[0165] A3: Evaporation deposition, evaporation boat temperature 95℃ / 110℃ / 85℃, film speed 1.5m / min, modified layer 8nm.

[0166] A4: Cooling treatment, -10℃ for 0.8 seconds, 375nm laser (100mm / s, line spacing 50μm), crystallinity 35%.

[0167] A5: Annealing, annealing at 150℃ for 40 minutes, air pressure -0.07MPa, to prepare a high-performance polypropylene capacitor film.

[0168] Example 4: Crystallinity control and annealing optimization

[0169] A1: Preparation of Polypropylene Capacitor Film

[0170] S1: 30wt% polypropylene, xylene:tetrahydrofuran = 2:1 solution, dissolved at 170℃;

[0171] S2: Add 2%Al2O3 and 1%TiO2, totaling 3g, and ultrasonically disperse for 30 minutes;

[0172] S3: Casting at 180℃, 2m / min, stretching ratio 5:4 at 130℃;

[0173] S4: Heat treatment at 170℃ for 10 minutes.

[0174] A2-A3: Same as Example 1

[0175] A4: Crystallinity control, three-stage temperature control roller, 110℃-150℃-85℃, cooling rate 8℃ / s, crystallinity 42%.

[0176] A5: Annealing, -0.08MPa vacuum, 140℃ for 40 minutes to prepare high-performance polypropylene capacitor film.

[0177] Example 5: Optimization of Functional Coating Liquid Formulation

[0178] A1-A4: Same as Example 1

[0179] A5: Coating annealing, the functional liquid is 30 parts polypropylene wax, 8 parts vinyl silane, 8 parts nano Al2O3, 3 parts titanate, 2 parts dioctyl phthalate, and 10 parts xylene, dispersed at 80℃ and 1200r / min for 40 minutes.

[0180] After coating, the film was baked at 100℃ for 30 minutes, annealed at 130℃ for 50 minutes, and then subjected to vacuum of -0.06MPa to prepare a high-performance polypropylene capacitor film.

[0181] Comparative Example 1: Traditional unmodified polypropylene film

[0182] A1: Polypropylene granules are directly melt-extruded into films at 200℃, with a biaxial stretch ratio of 2:2 at 120℃, and without S4 heat treatment.

[0183] By omitting all steps A2-A5, the polypropylene capacitor film can be directly obtained.

[0184] Comparative Example 2: Missing Gradient Modification Layer vs. Laser Treatment

[0185] A1: Same as Example 1 (including S1-S4);

[0186] A2: Same as Example 1;

[0187] A3 is omitted, indicating no vapor-deposited modified layer; A4 is omitted, indicating no laser treatment.

[0188] A5: Directly coated with functional liquid, without annealing treatment.

[0189] The performance test comparisons of Examples 1 to 5 and Comparative Examples 1 and 3 are shown in Table 1 below:

[0190]

[0191] Table 1

[0192] The high-performance polypropylene capacitor film of this invention, through nanofiller dispersion, biaxial stretching, and crystallinity control, increases the tensile strength by 40%-110% compared to traditional unmodified films. The synergistic effect of molecular chain orientation and gradient structure increases the breakdown field strength from 25kV / μm to 30-38kV / μm, effectively resisting partial discharge damage under high-voltage environments. The thermal shrinkage rate at 120℃ is reduced to 0.5%-1.2%, a 70%-87.5% reduction compared to the comparative example. Annealing eliminates internal stress and forms an interpenetrating interface layer, ensuring the dimensional stability of the film material under high-temperature conditions. The dielectric loss is reduced to 0.0015-0.0020, 33%-50% lower than traditional films, meeting the low energy loss requirements of high-frequency circuits. The synergistic effect of surface cleaning and activation with the gradient modification layer reduces the film surface contact angle from 80° to 42°-48°. The introduction of polar groups and the nano-rough structure enhance the adhesion of the functional layer, increasing the interlayer peel strength to 6-7 N / cm. The corona resistance life is extended to 180-250 hours, an improvement of 2.6-5 times compared to the comparative example. The indium tin oxide-graphene quantum dot inorganic layer effectively blocks corona corrosion. The silane coupling agent modified layer and functional coating liquid endow the film material with antistatic and scratch-resistant properties, increasing the surface hardness from 2H to 3H and reducing the moisture absorption rate to below 0.003%, achieving a breakthrough in weather resistance and reliability for long-term service under high voltage and high frequency environments.

[0193] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A process for preparing a high-performance polypropylene capacitor film, characterized in that, include: A1: Preparation of polypropylene capacitor film; A2: Surface cleaning and activation pretreatment of polypropylene capacitor film; A3: A gradient modification layer is vapor-deposited on the surface of the pretreated polypropylene capacitor film to form a modified polypropylene capacitor film; A4: Laser plasma synergistic treatment and crystallinity control of modified polypropylene capacitor film; A5: A high-performance polypropylene capacitor film is prepared by coating a functional layer on the outer layer of a modified polypropylene capacitor film and then performing an annealing post-treatment.

2. The preparation process of a high-performance polypropylene capacitor film according to claim 1, characterized in that: The methods for preparing polypropylene capacitor films in A1 include: S1: Dissolve polypropylene particles in one or more organic solvents, such as xylene, tetrahydrofuran, or 1,2-dichloroethane, and control the concentration of the polypropylene solution to be 15-30 wt%. Heat and stir until completely dissolved to obtain a polypropylene solution. S2: Add one or more of nano-sized Al2O3, TiO2 or SiO2 as inorganic fillers to the polypropylene solution. The amount of inorganic filler added is 1-5% of the mass of polypropylene. Disperse the mixture evenly by ultrasonication to obtain a mixed spinning solution. S3: The mixed spinning solution is cast into a film by casting at a temperature of 180-250℃ and a casting speed of 0.5-2m / min. Then, it is subjected to biaxial stretching and orientation treatment in a stretching machine at a stretching temperature of 120-160℃, wherein the longitudinal stretching ratio is 3-6 and the transverse stretching ratio is 3-5, to obtain the initial film. S4: Heat-treat the initial film at a temperature of 140-180℃ for 5-30 minutes to obtain the polypropylene capacitor film.

3. The preparation process of a high-performance polypropylene capacitor film according to claim 2, characterized in that: The surface cleaning and activation pretreatment in A2 includes: Using a surface activation device and a plasma treatment unit, the polypropylene film was sequentially subjected to corona treatment and plasma etching to improve the surface roughness to 1-5 μm. A dual-optical-path interferometry system is used to monitor changes in the surface contact angle, ensuring that the contact angle drops below 50°.

4. The preparation process of a high-performance polypropylene capacitor film according to claim 3, characterized in that: The vapor-deposited gradient modification layer in A3 includes: A gradient modified layer is deposited by evaporating using a multi-source evaporation boat, a gradient temperature control device, and a dynamic mask system. The dynamic mask system includes a programmable microelectromechanical system array that can adjust the mask pattern accuracy to 50 μm in real time; The gradient modification layer includes: The base source is a copper phthalocyanine / polypyrrole composite system with a melting point of 90-95℃; The inorganic nanolayer source is an indium tin oxide-graphene quantum dot mixed slurry with a melting point of 100-110℃; The modification source is silane coupling agent vapor with a boiling point of 80-85℃.

5. The preparation process of a high-performance polypropylene capacitor film according to claim 4, characterized in that: Laser-plasma synergistic processing and crystallinity control in A4 include: Using a picosecond laser emitter, an radio frequency plasma source, and a real-time spectrometer, the roughening, impurity removal, and surface functional group modification of the modified polypropylene capacitor film are completed simultaneously. A three-section temperature-controlled roller and an ultrasonic atomization cooling device are used to control the crystallinity of the interface functional layer to 30%-45%.

6. The preparation process of a high-performance polypropylene capacitor film according to claim 5, characterized in that: The coating of the functional layer in A5 and the subsequent annealing process include: The modified polypropylene capacitor film includes a base film layer and a functional layer disposed on at least one side of the base film layer, wherein the functional layer is coated with a functional coating liquid; The functional coating liquid is composed of the following raw materials in parts by weight: 20-30 parts polypropylene wax, 8-12 parts vinyl silane coupling agent, 5-8 parts nano alumina, 3-5 parts titanate coupling agent, 2-4 parts plasticizer, and 10-15 parts xylene. The particle size of the nano-alumina is 50-100nm, and the plasticizer is either dioctyl phthalate or tributyl citrate.

7. The preparation process of a high-performance polypropylene capacitor film according to claim 3, characterized in that: A2 specifically includes the following steps: Pretreatment-activation coupling: First, treat the polypropylene capacitor film with 8-12kV corona for 1-3s, then etch it with Ar plasma for 25-35s to reduce the surface contact angle to below 50°.

8. The preparation process of a high-performance polypropylene capacitor film according to claim 4, characterized in that: A3 specifically includes the following steps: Composite vapor deposition - gradient control, at 10 -3 -10 -2 Simultaneous evaporation under a vacuum of Pa: Base source: Copper phthalocyanine / polypyrrole composite system deposited at a rate of 0.4-0.6 nm / s for 45-55 nm; Inorganic nanolayer source: Indium tin oxide-graphene quantum dots were deposited at a rate of 0.2-0.4 nm / s to a depth of 25-35 nm; Modification source: Silane coupling agent is deposited at a rate of 0.15-0.25 nm / s for 8-12 nm; During the vapor deposition process, the polypropylene capacitor film passes through the composite vapor deposition zone at a speed of 1.5-2.5 m / min. The temperature fluctuation of each evaporation boat is controlled within ±2℃, and the vacuum fluctuation is ≤10%.

9. The preparation process of a high-performance polypropylene capacitor film according to claim 5, characterized in that: A4 specifically includes the following steps: Ultrasonic gradient cooling: After vapor deposition, the polypropylene capacitor film first passes through a cooling roller at -8℃ to -10℃ for 0.8-1.2s, and then is ultrasonically atomized and cooled to 23-27℃. Laser-plasma synergistic processing, in a vacuum of less than 10 -4 Under Pa conditions, a 335-375 nm picosecond laser was used to scan the coating, while Ar / O2 plasma was simultaneously introduced, and the 1720 cm⁻¹ infrared spectrum was monitored in real time. -1 The peak intensity changes until the absorption intensity stabilizes at 0.78-0.82 Abs, at which point the treatment is stopped. The laser scanning speed is 100-500 mm / s, and the scanning line spacing is 10-50 μm.

10. The preparation process of a high-performance polypropylene capacitor film according to claim 6, characterized in that: The preparation process of the functional coating liquid is as follows: Vinyl silane coupling agent, nano alumina, and titanate coupling agent are placed in a mixing device according to the weight ratio and mixed at 300-400 r / min for 15-25 min. Then, polypropylene wax, plasticizer, and xylene are added and dispersed at 1000-1200 r / min for 30-40 min to obtain the functional coating liquid. A5 specifically includes the following steps: Step 1: The polypropylene raw material is melt-extruded into a film, and then subjected to biaxial stretching treatment to obtain a polypropylene film layer; Step 2: Apply the functional coating solution evenly to the surface of the base film layer and bake at 80-100℃ for 20-30 minutes to form the functional layer; Step 3: Anneal the coated film at 120-150℃ and cool it to obtain a polypropylene capacitor film. The temperature for biaxial stretching is 120-150℃, the longitudinal stretching ratio is 3-5 times, and the transverse stretching ratio is 4-6 times; the annealing time is 40-60 min, and the pressure is -0.05 to -0.08 MPa.

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