Film, film surface modification process and application

Abstract

The invention discloses a film, a film surface modification process and application. The film comprises a film main body, the polymer layers are arranged on the surfaces of the two sides of the thin film main body and are cured into films on the surfaces of the thin film main body; and the surface of the polymer layer is provided with a function. The process comprises the following steps: biaxially stretching a film main body, and pretreating the film main body; spraying a polymer material on the surface of the pretreated film main body to make the polymer layer fill the surface defects of the film main body; curing a polymer on the surface of the film main body to form a polymer layer with a preset thickness; and evaporating a functional layer on the surface of the polymer layer. The defects on the surface of the film can be effectively filled through the polymer, and the dielectric strength, dielectric constant, film temperature resistance, film surface binding force and barrier property of the film can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin films, and in particular relates to a thin film, a thin film surface modification process and an application thereof. Background Art

[0002] Biaxially oriented films such as Bopp and PET can be used in metallized capacitors, composite current collectors for lithium batteries, high-barrier films for photovoltaics, and high-barrier films for packaging. While the biaxial stretching process improves the film's mechanical strength and dimensional stability through molecular chain orientation and crystallization, it can also introduce structural defects, leading to some performance degradation.

[0003] For example, during biaxial stretching, highly oriented molecular chains may form local stress concentration areas, causing microcracks or interface defects (such as micropores at grain boundaries). On the one hand, microdefects can easily become breakdown starting points under an electric field, reducing the dielectric strength. On the other hand, stretching regularizes the molecular chains, restricts the movement of polar groups (such as C-H bonds in PP), and weakens the polarization response ability, resulting in a decrease in the dielectric constant. At the same time, excessive stretching reduces the slip energy barrier of the molecular chains, making thermal relaxation more likely to occur at high temperatures, affecting the temperature resistance of the film. In addition, stretching highly orients the surface molecular chains, forming a dense and smooth surface layer, which reduces the chemical bonding ability with the metal plating / coating and leads to a weakening of the membrane surface bonding force. Finally, non-uniform stretching may destroy the continuous phase structure, forming penetrating microchannels that allow gas to pass easily, reducing the barrier properties of the film. Summary of the Invention

[0004] The purpose of the present invention is to provide a film, a film surface modification process and its application to solve the problems in the prior art, specifically including: Designing a film, comprising: a film body; A polymer layer, the polymer layer being disposed on at least one side of the film body and solidified into a film on the surface of the film body, the polymer layer filling defects in the film body to improve the dielectric strength, dielectric constant, temperature resistance, film surface adhesion, and barrier properties of the film body; A functional layer is provided on the surface of the polymer layer, and the functional layer is used to expand the functionality of the film.

[0005] As a further description of the above technical solution, the polymer layer includes a polymer layer 1, and the polymer layer 1 is arranged on the surface of the film body.

[0006] As a further description of the above technical solution, the polymer layer includes polymer layer 1 and polymer layer 2, the polymer layer 1 is arranged on one side surface of the film body, and the polymer layer 2 is arranged on the other side surface of the film body.

[0007] As a further description of the above technical solution, the polymer layer is a resin material, and the liquid resin is applied to the surface of the film body by thermal evaporation or coating, and the resin material is cured on the surface of the film body by electron beam or UV light.

[0008] As a further description of the above technical solution, the thickness of the polymer layer is 0.1-2 μm; The functional layer includes a metal layer. The material of the metal layer is any one of aluminum, zinc, copper or magnesium. The thickness of the metal layer is 100 nm-1 μm.

[0009] As a further description of the above technical solution, the film body is made of BOPP or PET material, and the thickness of the film body is 1.8-12 μm.

[0010] A film surface modification process is also designed, including: S100, biaxially stretching the film body described in any one of the above items, and pre-treating the film body; S200, thermally evaporating or coating a polymer material on the surface of the film body pretreated in step S100, so that the polymer layer fills the surface defects of the film body; S300, curing the polymer on the surface of the film body to form a polymer layer of a preset thickness; S400: Vapor-depositing a functional layer on the surface of the polymer layer.

[0011] As a further description of the above technical solution, the step of pre-treating the film body in step S100 includes: performing corona treatment on the surface of the film body to increase the surface energy of the film body to 5-15 dyn / cm.

[0012] As a further description of the above technical solution, the method further includes step S500 of curing the polymer on the surface of the metal layer to form a polymer layer of a preset thickness; S600: vapor-depositing a functional layer on the surface of the polymer layer again.

[0013] Disclosed is an application of a film, wherein the film is applied to the fields of metallized capacitors, composite current collectors for lithium batteries, photovoltaic high-barrier diaphragms, and packaging high-barrier diaphragms.

[0014] Beneficial effects: 1. This invention provides a film and surface modification process. Surface defects (fisheyes or crystals) in BOPP films can be effectively filled with polymer, effectively improving the film's dielectric strength, dielectric constant, temperature resistance, surface adhesion, and barrier properties. A functional layer (metal layer) is then deposited on the polymer film surface. While maintaining the conductive properties of the metallized film capacitor, the filling of the BOPP film's defects effectively improves the film's breakdown field strength and withstand voltage.

[0015] 2. The present invention provides a film and a process for modifying the film surface. The polymer can be an acrylic acid-like film. Compared with directly vapor-depositing the functional layer on the surface of the BOPP film, the acrylic acid-like film (polymer film) has a higher surface energy and can form chemical bonds or physical adsorption with metal atoms. It can obtain better adhesion without complex pretreatment, and can more effectively improve the adhesion effect of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] Figure 1 Schematic diagram of a thin film body with surface defects provided by the present invention.

[0018] Figure 2 Schematic diagram of the film body and polymer layer provided by the present invention cooperating to fill surface defects.

[0019] Figure 3 This is a schematic diagram of the cooperation between the film body, polymer layer and metal layer provided by the present invention.

[0020] Figure 4 This is a schematic diagram of another embodiment of the cooperation between the film body, the polymer layer and the metal layer provided by the present invention.

[0021] Figure 5 The present invention provides a flow chart of the film surface modification process. DETAILED DESCRIPTION

[0022] The present invention can be more readily understood with reference to the following detailed description of preferred embodiments of the present invention and the included Examples. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those generally understood by those of ordinary skill in the art to which the present invention belongs. In the event of a conflict, the definitions in this specification shall prevail.

[0023] The present invention provides a film and a film surface modification process, which solves the problem in the prior art that defects (usually referred to as fisheyes or crystal points) occasionally form in the BOPP film during the biaxial stretching production process. The diameter of the defects is generally tens to hundreds of microns. The presence of defects has a negative impact on the dielectric and mechanical properties of the BOPP film and limits its application. When the film area is expanded or the thickness is further reduced, the defects on the surface of the BOPP film are the main factor that limits and reduces its breakdown field strength. At the same time, it can solve the problem in the prior art that the defects caused in the biaxial stretching production process lead to a decrease in the film's electrical strength, dielectric constant, film temperature resistance, film surface adhesion and barrier properties. Existing technologies are limited by inherent material defects and insufficient stretching process precision, limiting the ability to improve the withstand voltage performance of BOPP or PET films. Metallized film capacitors typically consist of a BOPP film and an electrode (metal layer) on its surface. To ensure the film's conductivity, an insulating polymer layer is applied to the electrode surface to improve its barrier and oxidation resistance. While electrodes on the BOPP film can, to a certain extent, fill surface defects, the inherent defects of the film remain due to the material differences between the metal dielectric and the BOPP film. This limits and reduces the film's breakdown field strength, further limiting its withstand voltage performance.

[0024] The technical concept of this application is to spray a layer of polymer onto the surface of a BOPP film, effectively filling surface defects (fisheyes or crystal points) in the film. Then, a layer of electrode (metal layer) is vapor-deposited onto the polymer film. This ensures the conductive properties of the metallized film capacitor while effectively improving the breakdown field strength and withstand voltage of the entire BOPP film due to the filling of the film's defects. Furthermore, the polymer in this application can be an acrylic acid-based polymer, similar to the film itself. After bonding with the film, it serves as a base material for vapor-depositing metal to form a metal film.

[0025] like Figure 1-3 As shown, the present invention provides an embodiment of a film, comprising: The main film 1 is a BOPP film or a PET film. BOPP film is made from polypropylene (PP) resin and is subjected to a longitudinal and transverse biaxial stretching process (usually performed at 130-165°C) to orient the molecular chains and form a highly crystalline film structure. The thickness of the main film 1 is 1.8-12μm. Due to the trend of miniaturization, lightweighting, and high capacitance of electronic products, the thinner the film, the better. However, the thinner the film, the more defects (such as Figure 1In the present invention, the thickness of the film body 1 is controlled to be 1.8-12 μm, which can minimize defects while keeping the film body 1 thin.

[0026] The polymer layer is provided on one side or both sides of the film body 1 (e.g. Figure 1 As shown), and solidified to form a film on the surface of the film body 1. In this embodiment, the polymer layer is polymer layer 1-2. Specifically, the solidified polymer is sprayed onto the surface of the film body 1, and the solidified polymer fills the defects on the surface of the film body 1 and covers the surface of the BOPP film. After electron beam curing, a polymer film (as shown) is formed on the surface of the film body 1. Figure 2 (as shown). The polymer film has a thickness of 0.08-0.12 μm. Preferably, the polymer film has a thickness of 0.1 μm. Simply put, the polymer layer fills the defects in the film body 1 to ensure consistent thickness across the surface of the film body 1 and improve its pressure resistance.

[0027] A functional layer is provided on the surface of the polymer layer. In some embodiments, the functional layer can be a metal layer, which serves as an electrode. The metal layer effectively improves the film's electrical conductivity and enables its function as a capacitor. In this embodiment, the thickness of the metal layer is 100nm-1μm. In this embodiment, an acrylic-like material can be used for the polymer layer. Acrylic polymers (such as PMMA and PAA) have high surface polarity, with surface energies of 40-50mN / m, and exhibit a stronger affinity for metals (such as Al and Ag). Polar groups such as hydroxyl (-OH) and carboxyl (-COOH) groups on their surfaces can form chemical bonds or physical adsorption with metal atoms, achieving good adhesion without the need for complex pretreatment. Compared with the existing technology in which the metal layer is directly connected to the BOPP film, by setting a polymer layer between the two, not only can the voltage resistance of the BOPP film be improved, but also the pretreatment process of the BOPP film can be effectively reduced (the surface energy of conventional BOPP film is low and needs to be improved through corona treatment, plasma treatment or primer coating), and the connection strength of the metal layer (electrode) can be further improved, thereby improving the performance of the entire metallized film capacitor.

[0028] Furthermore, the material of the metal layer is any one of aluminum, aluminum, zinc, copper, magnesium or other conductive metal materials, which can be selected according to actual needs.

[0029] refer to Figure 3Another embodiment provided herein differs from the aforementioned embodiment in that the polymer layer comprises polymer layer 1 2 and polymer layer 2 4 . Polymer layer 1 2 is disposed on the surface of film body 1 , while polymer layer 2 4 is disposed on the surface of the metal layer. Specifically, polymer layer 2 4 is sprayed onto the surface of the metal layer. Polymer layer 1 2 and polymer layer 2 4 can be made of the same acrylic acid-based material. By spraying polymer layer 2 4 onto the surface of the metal layer and curing it into a film, polymer layer 2 4 acts as an insulating layer, protecting the metal layer surface and effectively preventing oxidation of the metal layer, thereby ensuring the performance of the metallized film capacitor.

[0030] refer to Figure 4 Another embodiment provided herein differs from the above-mentioned embodiment in that the metal layer comprises metal layer 1 3 and metal layer 2 5, and the polymer layer comprises polymer layer 1 2 and polymer layer 2 4. The overall layer structure is: metal layer 2 5, polymer layer 2 4, film body 1, polymer layer 1 2, and metal layer 1 3. Metal layer 1 3 serves as a conventional electrode, while metal layer 2 5 is disposed on the other side of film body 1, resulting in a double-sided metallized film. Both sides of the double-sided metallized film are plated with a metal layer (such as aluminum or zinc), effectively increasing the surface area of the electrodes. For the same volume, a larger electrode area (A) directly increases capacitance. This allows capacitors to achieve higher capacitance within a smaller volume, making it suitable for high-density circuit designs with limited space. Furthermore, the double-sided metallization structure provides more conductive paths, reducing current transmission resistance. The double-sided distribution of the metal layer shortens charge movement distances and optimizes current distribution. This reduces energy loss and heat generation, improving efficiency in high-frequency applications, particularly in switching power supplies and inverters. Furthermore, when a local breakdown occurs in the dielectric, the metal layer surrounding the breakdown point instantly evaporates, forming an isolation defect in the insulating zone. Double-sided metallization makes this process more efficient, as both metal layers can simultaneously participate in the isolation process. This improves the reliability and lifespan of the capacitor, reduces the risk of fault propagation, and is suitable for high-voltage or high-voltage fluctuation environments. Finally, double-sided metallized films can be stacked more tightly in wound capacitors, reducing interlayer gaps and allowing the use of thinner dielectric layers without sacrificing strength. This optimizes volumetric efficiency and reduces overall weight, making it suitable for applications requiring lightweighting, such as electric vehicles and new energy devices.

[0031] refer to Figure 5 , the present application provides a thin film surface modification process, the specific steps include: S100, biaxially stretching the film body 1 and pre-treating the film body 1, wherein the step of pre-treating the film body 1 includes: performing corona treatment on the surface of the film body 1 to increase the surface energy of the film body 1 to 5-15 dyn / cm. In some other embodiments, since the metal layer is not directly provided on the surface of the film body 1, the film body 1 may not be subjected to corona treatment.

[0032] S200, spraying a polymer material onto the surface of the film body 1 in step S100, so that the polymer layer fills the surface defects of the film body 1, wherein the polymer material can be acrylic acid-based. Specifically, the spraying can be performed by a vacuum evaporation spraying process: in a high vacuum environment (air pressure <10-3Pa), the evaporation chamber is precisely heated to 200-300°C, so that the liquid acrylic polymer material is vaporized and then directionally deposited on the metal surface through a precision nozzle. Subsequently, electron beam / UV curing is performed using 20-150kV (or higher depending on process requirements). This process forms a nano-scale dense interface through vapor deposition, which has high bonding strength. Alternatively, the liquid polymer precursor is evenly coated on the metal surface by slot coating or micro-gravure roller coating, and then cured by 20-150kV (or higher depending on the process requirements) electron beam / UV.

[0033] S300, curing the polymer on the surface of the film body 1 by electron beam to form a polymer layer of a preset thickness; S400: A functional layer, such as a metal layer, is deposited on the surface of the polymer layer. For example, during the metal deposition process, a thin film web passes over an evaporator module at a constant speed. The evaporated material is heated within a vacuum chamber (at approximately 4E-4 mbar) until it evaporates. Radiation heating or resistance heating can be used to heat the material, allowing the evaporated material to move freely under vacuum. When the evaporated material contacts the substrate surface, it cools and forms a coating. Cooling by cold rollers maintains the temperature between -10°C and -25°C.

[0034] In some other embodiments, the process steps further include: S500, solidifying the polymer on the other side surface of the film body 1 to form a polymer layer of a preset thickness, namely the second polymer layer 4. The second polymer layer 4 can effectively fill the surface defects on the other side of the film body 1, further improving the performance of the entire film.

[0035] S600, a metal layer is again evaporated on the surface of the polymer layer on the other side, namely Metal Layer 25. The double-sided metal layer effectively increases the surface area of the electrode. At the same time, the double-sided metallized structure provides more conductive paths, reducing the resistance of current transmission. This improves the reliability and life of the capacitor, reduces the risk of fault propagation, and is suitable for high-voltage or high-fluctuation environments. Finally, the double-sided metallized film can be stacked more tightly in the wound capacitor, reducing the gap between layers and allowing the use of thinner dielectric layers without sacrificing strength. Optimizing volumetric efficiency and reducing overall weight, it is suitable for fields with high lightweight requirements such as electric vehicles and new energy equipment.

[0036] The present application also provides an application of a thin film, which is used in the fields of metallized capacitors, lithium battery composite current collectors, photovoltaic high-barrier diaphragms, and packaging high-barrier diaphragms.

[0037] For example: The application of thin films in composite current collectors for lithium batteries involves replacing copper and aluminum foil with copper or aluminum plating on both sides of BOPP / PET film, significantly reducing battery weight and improving flexibility. PET's high modulus makes it suitable for high-speed winding processes; BOPP's elasticity cushions volume changes, inhibiting lithium dendrite penetration, providing a new path for high-energy-density batteries. However, as a non-polar material, BOPP has low surface energy and lacks reactive groups, resulting in weak chemical bonding with the metal layer. Furthermore, its surface is too smooth, resulting in insufficient mechanical adhesion. Furthermore, the significant difference in thermal expansion coefficient between BOPP and metal can cause interfacial stress and affect adhesion. Furthermore, biaxial stretching highly orients the surface molecular chains, forming a dense and smooth surface layer (increasing the contact angle by 5°-10°), which reduces chemical bonding with metal plating / coatings. Excessive stretching reduces the slip barrier of the molecular chains, making thermal relaxation more likely at high temperatures.

[0038] By solidifying the liquid acrylic polymer on the surface of the film in this application, on the one hand, the defects and holes caused by stretching of the film can be filled, and the temperature and pressure resistance of the film can be improved; on the other hand, the solidified substance can enhance the polarity of the film surface, increase the adhesion of the film, and improve the mechanical properties of the film.

[0039] Another example: Thin films are used in photovoltaic and packaging high-barrier films. BOPP film, through co-extrusion with EVOH or coating with aluminum oxide, improves its water vapor barrier performance by a hundredfold, supporting perovskite module encapsulation. PET film coated with silicon oxide offers even better barrier properties and UV resistance, making it suitable for long-term outdoor service. Through multi-layer composite technology, these two materials form a key barrier against environmental corrosion in photovoltaic modules. BOPP coated with PVDC provides a low-cost oxygen barrier and is widely used in food packaging. PET, through coating technologies such as nano-silicon oxide, achieves ultra-low oxygen permeability and withstands high-temperature sterilization, making it suitable for high-end medical and pre-prepared food applications. Their differentiated performance covers packaging applications from daily consumer to industrial use. However, as a non-polar material, BOPP has low surface energy and lacks reactive groups, resulting in weak chemical bonding with metal layers. Furthermore, its surface is too smooth, resulting in insufficient mechanical adhesion. Furthermore, the significant difference in thermal expansion coefficient between BOPP and metal can cause interfacial stress and affect adhesion. Furthermore, biaxial stretching highly orients the surface molecular chains, forming a dense and smooth surface layer (increasing the contact angle by 5°-10°), which reduces the chemical bonding ability with metal plating / coatings. Excessive stretching reduces the molecular chain slip barrier, making thermal relaxation more likely to occur at high temperatures.

[0040] This application solidifies liquid acrylic polymer on the surface of the film to fill the penetrating microchannels caused by the stretching of the film, thereby improving the barrier properties of the film itself. On this basis, continuing to plate aluminum oxide can further improve the barrier properties, and the cured film has better adhesion.

[0041] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A film, characterized in that include: Film body; A polymer layer, the polymer layer being disposed on at least one side of the film body and solidified into a film on the surface of the film body, the polymer layer filling defects in the film body to improve the dielectric strength, dielectric constant, temperature resistance, film surface adhesion, and barrier properties of the film body; A functional layer is provided on the surface of the polymer layer, and the functional layer is used to expand the functionality of the film.

2. The film according to claim 1, characterized in that The polymer layer includes a first polymer layer, and the first polymer layer is arranged on the surface of the film body.

3. The film according to claim 1, characterized in that The polymer layer includes a first polymer layer and a second polymer layer. The first polymer layer is disposed on one side surface of the film body, and the second polymer layer is disposed on the other side surface of the film body.

4. The film according to claim 1, characterized in that The polymer layer is a resin material, and the liquid resin material is applied to the surface of the film body by thermal evaporation or coating, and the resin material is solidified on the surface of the film body by electron beam or UV light.

5. The film according to claim 1, characterized in that The thickness of the polymer layer is 0.1-2 μm; The functional layer includes a metal layer. The material of the metal layer is any one of aluminum, zinc, copper or magnesium. The thickness of the metal layer is 100 nm-1 μm.

6. The film according to claim 1, characterized in that The film body is made of BOPP or PET material, and the thickness of the film body is 1.8-12 μm.

7. A thin film surface modification process, characterized in that: include: S100, biaxially stretching the film body according to any one of claims 1 to 7, and pre-treating the film body; S200, thermally evaporating or coating a polymer material on the surface of the film body pretreated in step S100, so that the polymer layer fills the surface defects of the film body; S300, curing the polymer on the surface of the film body to form a polymer layer of a preset thickness; S400: Vapor-depositing a functional layer on the surface of the polymer layer.

8. The thin film surface modification process according to claim 8, characterized in that: The step of pre-treating the film body in step S100 includes: performing corona or plasma treatment on the surface of the film body.

9. The thin film surface modification process according to claim 8, characterized in that: The method further includes step S500 of curing the polymer on the other side surface of the film body to form a polymer layer of a preset thickness; S600: vapor-depositing a functional layer on the surface of the polymer layer again.

10. Use of the film according to claim 1, wherein the film is used in the fields of metallized capacitors, lithium battery composite current collectors, photovoltaic high-barrier films, and packaging high-barrier films.

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