High-temperature-resistant film based on electrostatic adsorption and vacuum adsorption and preparation method thereof

Abstract

The application discloses a high-temperature-resistant forming film based on electrostatic adsorption and vacuum adsorption and a preparation method thereof. The PTFE film is difficult to be bonded and compounded with other materials due to the extremely low surface energy. The forming film comprises a first PTFE film layer, a second PTFE film layer and an intermediate substrate layer between the two; the surfaces of the first PTFE film layer and the second PTFE film layer are provided with negative charges; the intermediate substrate layer contains positively charged polymer colloidal particles; the first PTFE film layer and the second PTFE film layer are respectively attached to the two side surfaces of the intermediate substrate layer through electrostatic adsorption, and the air is discharged under the adhesion pressure to form vacuum adsorption by means of the micro-groove structure on the surface of the intermediate substrate layer. The application realizes the glue-free adhesion of the PTFE film and the intermediate substrate layer, the combination is firm, the forming is good, the organic silicon is not transferred, the process is environmentally friendly and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and auxiliary materials for printed circuit board manufacturing. Specifically, it relates to a high-temperature resistant molding film based on electrostatic adsorption and vacuum adsorption, and a method for preparing the high-temperature resistant molding film based on electrostatic adsorption and vacuum adsorption. Background Technology

[0002] The molding film is an important auxiliary molding material used in the production of printed circuit boards (PCBs). Its main function is to change the shape of the molding film according to the complex pattern on the surface of the circuit board during the hot pressing and bonding of precision circuit board materials, so as to apply uniform pressure to various parts of the circuit board and make the precision components tightly bonded.

[0003] With the rapid development of 5G, AI, and other fields, the market demand for high-temperature resistant molding films is becoming increasingly urgent. Traditional PET-based molding films cannot meet the requirements of high-temperature (above 200℃) lamination due to the inherent temperature resistance limitations of the material itself. Polytetrafluoroethylene (PTFE) films have excellent chemical stability, ductility, and extremely low surface energy. They can undergo significant deformation along with the molding layer material without breaking, and they also have a self-release effect and no silicone transfer. Therefore, they have attracted widespread attention in the field of high-temperature lamination.

[0004] However, PTFE has extremely low surface energy, making it difficult to bond and composite with other materials, which severely limits its application in multifunctional composite materials. To increase the bonding strength of PTFE with other materials, existing technologies typically employ plasma treatment or sodium naphthalene solution treatment (sodium washing). Plasma treatment is less effective, offering only limited improvement in bonding strength; sodium washing suffers from high cost, significant pollution, blackening of the PTFE surface, and even affecting its high-temperature shaping properties. Furthermore, attempts have been made to use adhesives to composite PTFE with other substrates, but adhesives are prone to silicone transfer, decomposition, or carbonization during high-temperature pressing, failing to meet the high-temperature requirements above 200°C and increasing costs and environmental burden.

[0005] Therefore, there is an urgent need for a PTFE-containing molded membrane that requires no adhesives, does not damage the properties of PTFE, and has a strong bond. Summary of the Invention

[0006] To address the problem in existing technologies where PTFE films are difficult to bond and composite with other materials due to their extremely low surface energy, this invention provides a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, and its preparation method. By utilizing the synergistic effect of electrostatic adsorption and vacuum adsorption, adhesive-free bonding between the PTFE film and the intermediate substrate layer is achieved. The bonding is strong, it can withstand high temperatures, has good shaping properties, and there is no organosilicon transfer. At the same time, the process is environmentally friendly and low-cost.

[0007] In a first aspect, the present invention provides a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, the shaped film comprising: A first PTFE film layer, a second PTFE film layer, and an intermediate substrate layer located between the two; Both the first PTFE film and the second PTFE film have negative charges on their surfaces; The intermediate substrate layer contains positively charged polymer colloidal particles; The first PTFE film layer and the second PTFE film layer are respectively bonded to the two sides of the intermediate substrate layer by electrostatic adsorption. At the bonding interface, air is expelled under bonding pressure to form a vacuum adsorption by means of the micro-groove structure on the surface of the intermediate substrate layer.

[0008] Furthermore, the intermediate substrate layer is a single-layer PE layer, and the positively charged polymer colloidal particles are dispersed in the PE layer; or, the intermediate substrate layer is a three-layer composite film, consisting of a first EVA layer, an intermediate PE layer, and a second EVA layer, in sequence, and the positively charged polymer colloidal particles are dispersed in the first EVA layer and the second EVA layer.

[0009] Furthermore, the positively charged polymer colloidal particles are polystyrene colloidal particles, hematite colloidal particles, goethite colloidal particles, or polymer particles adsorbed with metal ions, all of which have a positively charged surface. The polystyrene colloidal particles have a particle size of 150~200nm and a surface charge density of 1~3μC / cm².

[0010] Furthermore, the surface roughness Ra on both sides of the intermediate substrate layer is 0.2~0.4μm.

[0011] Furthermore, the 180° peel force between the first PTFE film layer and the intermediate substrate layer, as well as between the second PTFE film layer and the intermediate substrate layer, is greater than 8g / 25mm.

[0012] In a second aspect, the present invention provides a method for preparing a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, for preparing a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption as described in any of the preceding claims, the method comprising: The first and second PTFE membranes are brushed to give their surfaces a negative charge. Positively charged polymer colloidal particles are prepared, and the colloidal particles are mixed with polymer base material and granulated. An intermediate substrate layer is obtained by molding, and the intermediate substrate layer contains positively charged polymer colloidal particles. The treated first PTFE film and second PTFE film are respectively bonded to the two sides of the intermediate substrate layer and hot-pressed together. At the same time, the micro-groove structure on the surface of the intermediate substrate layer is used to expel air under the bonding pressure to form a vacuum adsorption, thus obtaining a high-temperature resistant PTFE film with double sides.

[0013] Furthermore, the intermediate substrate layer is a single-layer PE film or a three-layer composite film, wherein the three-layer composite film consists of a first EVA layer, an intermediate PE layer, and a second EVA layer in sequence; when the intermediate substrate layer is a single-layer PE film, the colloidal particles are dispersed in the PE layer; when the intermediate substrate layer is a three-layer composite film, the colloidal particles are dispersed in the first and second EVA layers.

[0014] Furthermore, the brush treatment uses a brush roller, the PTFE film feed speed is 5~10m / min, and the ambient humidity is <60%; the hot pressing is performed using a double-roller hot pressing machine, the pressing temperature is 80~120℃, the pressure is 0.2~0.5MPa, and the pressing speed is 5~10m / min; no adhesive is used in the preparation method.

[0015] Furthermore, the positively charged polymer colloidal particles are polystyrene colloidal particles with positive surface charges; The preparation of positively charged polymer colloidal particles includes: ODMAEMA was obtained by reacting N,N-dimethylaminoethyl methacrylate with 1-bromooctane in a molar ratio of 1:1 to 1.2 in a ketone solvent at 30 to 50 °C for 20 to 28 h. A two-step soap-free emulsion polymerization method was adopted. Styrene and ODMAEMA were used as monomers and AIBA was used as initiator under nitrogen protection at 70~80℃. The reaction was carried out for 20~28h. After centrifugation and purification, a colloidal particle emulsion with a particle size of 150~200nm and a surface charge density of 1~3μC / cm² was obtained.

[0016] Furthermore, when the intermediate substrate layer is a three-layer composite film, the step of mixing and granulating the colloidal particles with the polymer base material, and then molding to obtain the intermediate substrate layer, includes: The prepared colloidal particles were added to EVA raw materials and silane crosslinking agent for mixing and granulation, and a three-layer composite film was prepared by three-layer co-extrusion. The mixing ratio of the granulation is as follows by weight: 100 parts EVA, 1-5 parts of colloidal particles (dry weight), and 0.2-1 parts of silane crosslinking agent. The VA content of the EVA is 20%-35%, and the silane crosslinking agent is vinyltrimethoxysilane.

[0017] This invention provides a high-temperature resistant shaped membrane based on electrostatic adsorption and vacuum adsorption, and its preparation method. By imbuing the PTFE membrane surface with a negative charge and the intermediate substrate layer with a positive charge, initial bonding is achieved through electrostatic attraction. Simultaneously, the microgroove structure on the surface of the intermediate substrate layer facilitates vacuum adsorption by expelling interfacial air under bonding pressure, further enhancing the tightness of the bond between the two layers. This method eliminates the need for any adhesives, avoiding the risks of adhesive decomposition, carbonization, or organosilicon transfer during high-temperature pressing. It also eliminates the need for destructive plasma treatment or highly polluting sodium washing of the PTFE, making it economical and environmentally friendly. Tests show that the 180° peel force between the PTFE membrane and the intermediate substrate layer reaches 18g / 25mm, meeting the structural integrity requirements during cutting, punching, transportation, and storage. This shaped membrane can be used neutrally in high-temperature hot-pressing environments of 200~320℃, effectively transmitting pressure, conforming to shape, and easily peeling off after pressing without residue or pollution. Therefore, this invention effectively solves the technical problem of PTFE lamination, and realizes a glue-free, high-temperature resistant, excellent shaping, environmentally friendly and low-cost shaping film product. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the hot-pressing and vacuum adsorption process of the intermediate substrate and PTFE film layer in an embodiment of the present invention. Figure 2 A schematic flowchart illustrating a method for preparing a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, as provided in an embodiment of the present invention; Figure 3 This is a physical image of a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption provided in Embodiment 1 of the present invention; Figure 4 This is a structural diagram of the shaped film product provided in Embodiment 1 of the present invention after the edge is torn open; Figure 5 This is a diagram showing the test results of the perforation and cutting bonding force of the shaped film product provided in Embodiment 1 of the present invention; Figure 6 The image shows the hot pressing molding test results of the molding film product provided in Embodiment 1 of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0022] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0023] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0024] This invention aims to provide a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, and its preparation method, to solve the technical problems of existing PTFE films, such as difficulty in firmly bonding with other materials due to their extremely low surface energy, poor or polluting effects of traditional surface treatments (plasma treatment, sodium washing), and the easy failure or organosilicon transfer of adhesives at high temperatures. Through the synergistic effect of electrostatic adsorption and vacuum adsorption, adhesive-free bonding between the PTFE film and the intermediate substrate layer is achieved. This allows the product to have sufficient peel strength at room temperature to meet processing and storage requirements. Simultaneously, it exhibits good shaping and clean release when used in a high-temperature pressing environment of 200~320℃, and the process is environmentally friendly and cost-effective.

[0025] To better understand the above technical solutions, the present disclosure will be further described below with reference to specific embodiments, but the scope of protection of the present disclosure is not limited thereto.

[0026] This invention provides a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, the shaped film comprising: A first PTFE film layer, a second PTFE film layer, and an intermediate substrate layer located between the two; Both the first PTFE film and the second PTFE film have negative charges on their surfaces; The intermediate substrate layer contains positively charged polymer colloidal particles; The first PTFE film layer and the second PTFE film layer are respectively bonded to the two sides of the intermediate substrate layer by electrostatic adsorption. At the bonding interface, air is expelled under bonding pressure to form a vacuum adsorption by means of the micro-groove structure on the surface of the intermediate substrate layer.

[0027] This invention provides a high-temperature resistant shaped membrane based on electrostatic adsorption and vacuum adsorption. The shaped membrane adopts a symmetrical bilayer polytetrafluoroethylene (PTFE) structure, specifically comprising: a first PTFE film layer, a second PTFE film layer, and an intermediate substrate layer located between the two. The surfaces of both the first and second PTFE film layers carry a negative charge; the intermediate substrate layer contains positively charged polymer colloidal particles. The two PTFE film layers are respectively bonded to the two sides of the intermediate substrate layer. The bonding force at the bonding interface originates from the synergy of two physical actions: firstly, electrostatic adsorption occurs between the negative charge on the PTFE film surface and the positive charge on the intermediate substrate layer surface; secondly, as... Figure 1 As shown, a microgroove structure is pre-formed on the surface of the intermediate substrate layer. Under the pressure of the bonding roller, interfacial air is expelled along the microgrooves, creating a local vacuum and generating adsorption force. The combined effect of these two factors allows the PTFE film and the intermediate substrate layer to be firmly bonded together without the use of any adhesives.

[0028] As a preferred embodiment, the intermediate substrate layer can have two different structural forms to adapt to different application requirements and process conditions.

[0029] The first structural form: The intermediate substrate layer is a single-layer PE (polyethylene) layer, with positively charged polymer colloidal particles uniformly dispersed throughout the PE layer. This structural form is simple and suitable for applications requiring thinner thickness and simpler processing steps. The PE can be low-density polyethylene (LDPE), which has good melt flowability and is easy to mix uniformly with the colloidal particles.

[0030] The second structural form: the intermediate substrate layer is a three-layer composite film, consisting of a first EVA layer (ethylene-vinyl acetate copolymer layer), an intermediate PE layer, and a second EVA layer. Positively charged polymer colloidal particles are dispersed only in the upper and lower EVA layers, while the intermediate PE layer is pure PE and contains no colloidal particles. This structure utilizes the lower melting point and higher flexibility of EVA compared to PE, making it easier to form uniform microgrooves during hot-pressing, thereby enhancing the vacuum adsorption effect. Simultaneously, the intermediate PE layer provides sufficient mechanical support and thermal stability. The VA content of EVA is preferably 20%~35%, more preferably 28%, as EVA within this range exhibits both good flexibility and dimensional stability after hot pressing.

[0031] To form the desired microgroove structure on the surface of the intermediate substrate layer, the pressure rollers require special treatment during the fabrication process. Specifically, chrome-plated steel rollers with sandblasted surfaces are used. By adjusting the pressure roller pressure (e.g., 0.3~0.5MPa) and the composite film travel speed (e.g., 5~10m / min), the surface roughness Ra of both sides of the final intermediate substrate layer is controlled within 0.2~0.4μm. This roughness range provides sufficient microchannels for degassing and vacuum adsorption without reducing the effective contact area for electrostatic adsorption due to excessive roughness, thus achieving an optimal balance between the two adsorption mechanisms.

[0032] The positively charged polymer colloidal particles used in this invention can be positively charged polystyrene colloidal particles, hematite colloidal particles, goethite colloidal particles, or polymer particles adsorbed with metal ions. In a preferred embodiment, positively charged polystyrene colloidal particles with a particle size of 150-200 nm and a surface charge density of 1-3 μC / cm² are used. This particle size range ensures good dispersibility of the colloidal particles in the polymer matrix, while the moderate charge density provides sufficient electrostatic attraction and avoids particle aggregation due to excessive charge.

[0033] The preparation method of the above-mentioned polystyrene colloidal particles includes two steps: quaternization reaction and soap-free emulsion polymerization. First, N,N-dimethylaminoethyl methacrylate and 1-bromooctane are reacted with each other in a ketone solvent (e.g., acetone) at a molar ratio of 1:1 to 1.2 at 30 to 50 °C for 20 to 28 h to obtain methacryloyloxyethyl-N-octyldimethylammonium bromide (ODMAEMA). Then, a two-step soap-free emulsion polymerization method is used to prepare monodisperse polymer colloidal particles with positively charged surfaces. A certain amount of ultrapure water is added to a four-necked flask equipped with a mechanical stirrer, a nitrogen purging device, and a temperature control device. Nitrogen gas is introduced and the temperature is raised to 70 to 80 °C. The stirring speed is controlled at 300 r / min. A certain amount of styrene and methacryloyloxyethyl-N-octyldimethylammonium bromide (ODMAEMA) are added to the flask. After being dispersed evenly, the initiator 2,2'-azo(2-methylpropylamidine) dihydrochloride (AIBA) is added. After reacting for 1-3 hours, a second feeding is performed, adding a certain amount of styrene, methacryloyloxyethyl-N-octyldimethylammonium bromide (ODMAEMA), and 2,2'-azo(2-methylpropylamidine) dihydrochloride (AIBA) sequentially. The rotation speed and temperature are maintained, and the reaction continues for 20-24 hours. After the reaction is complete, a small amount of agglomerate in the system is filtered off, and after centrifugation and purification, a styrene colloidal particle emulsion with a positive surface charge is obtained. The particles prepared by this method have good monodispersity, and the surface positive charge density is controllable.

[0034] Surface charge density was determined by conductivity titration. An emulsion with a solid content of 0.5% was prepared and titrated with a standard HCl solution (0.01 mol / L). The surface charge density of the colloidal particles could then be calculated using the following formula:

[0035] In the formula: F is the Faraday constant 96485 C / mol, a is the radius of the colloidal particle (nm), is the volume fraction of the 0.5% emulsion used in the conductivity titration, and c is the concentration of the emulsion used in the conductivity titration (mol / L). The prepared styrene colloidal particles with positive surface charge are 150-200 nm in size and have a surface charge density of 1-3 μC / cm³. 2 .

[0036] Colloidal particles carry a large amount of positive charge on their surface. The particles repel each other under the influence of the charge, which helps to disperse the colloidal particles.

[0037] The preparation process of the intermediate substrate layer varies depending on the selected structural form.

[0038] For single-layer PE structures: The prepared colloidal particle emulsion (dry weight) is mixed with PE granules and a silane crosslinking agent (e.g., vinyltrimethoxysilane) in a specific ratio and then granulated. By weight, for 100 parts of PE, 1-5 parts of colloidal particles (dry weight) and 0.2-1 parts of silane crosslinking agent are added. Mixing and granulation can be performed using a twin-screw extruder, with the granulation temperature controlled at 140-165℃. After granulation, the film is formed into a PE film through single-layer extrusion or calendering, while the surface roughness Ra is adjusted to 0.2-0.4 μm using the aforementioned sandblasting rollers. The film thickness can be controlled as needed from 50-250 μm, with a typical value of 200 μm.

[0039] For a three-layer composite membrane structure: Colloidal particle emulsion (dry weight) and silane coupling agent are added to EVA granules for mixing and granulation, used for the upper and lower EVA layers; the middle PE layer uses pure PE granules (without colloidal particles and crosslinking agents). By weight, for 100 parts of EVA, 1-5 parts of colloidal particles (dry weight) and 0.2-1 parts of silane coupling agent are added. The mixing and granulation conditions are similar to those for a single layer. After granulation, the composite membrane is formed through a three-layer co-extrusion process: the mixture of upper and lower EVA layers and the pure PE granules for the middle layer are added to three extruders respectively, controlling the extrusion temperature at 140-165℃ and the die temperature at 165℃. After converging through the co-extrusion die, the membrane flows out and is cooled and shaped on a 15℃ water-cooled roller, while the surface roughness is adjusted by a sandblasting roller. The total thickness of the resulting composite membrane can be 80-250 μm, typically 200 μm, with the middle PE layer approximately 160 μm thick and the upper and lower EVA layers each approximately 20 μm thick.

[0040] The PTFE membrane is then brushed to impart a negative charge to its surface. Specifically, a nylon brush roller (brush length approximately 15mm, density approximately 20 bristles / cm², hardness A60) is used, or a layer of felt is wrapped around a guide roller. The PTFE membrane feed speed is 5-10 m / min, and the relative humidity is controlled below 60%. The brush and PTFE membrane contact solely through gravity, without additional pressure. After passing through the brush roller, the PTFE membrane surface acquires a stable negative charge, the surface charge density of which can be adjusted by friction time, speed, and ambient humidity. The thickness of the treated PTFE membrane is typically 25-100 μm, preferably 25 μm.

[0041] Finally, hot pressing is performed. The first and second PTFE films, after being brushed, are guided to both sides of the intermediate substrate layer and laminated using a two-roller hot press. The lamination temperature is controlled at 80~120℃, the lamination pressure is 0.2~0.5MPa (preferably 0.3~0.5MPa), and the lamination speed is 5~10m / min. During this process, the micro-grooves on the surface of the intermediate substrate layer act as exhaust channels. The pressure of the rollers forces the air between the two PTFE films and the intermediate substrate layer along the grooves, forming a local negative pressure, thereby generating vacuum adsorption force. At the same time, the negative charge on the surface of the PTFE film and the positive charge on the surface of the intermediate substrate layer generate electrostatic attraction. The synergistic effect of these two factors allows the PTFE film and the intermediate substrate layer to be firmly bonded without the use of any adhesives or without plasma treatment or sodium washing of the PTFE.

[0042] The high-temperature resistant molded film prepared according to the above method has the following beneficial effects: (i) Good bonding strength at room temperature: Using a 180° peel force test (referencing GB / T2790-1995, peel speed 100mm / min, test environment 23℃ / 50%RH), the peel forces between the first PTFE film layer and the intermediate substrate layer, as well as between the second PTFE film layer and the intermediate substrate layer, are both greater than 8g / 25mm. In the preferred embodiment, the initial peel force can reach about 18g / 25mm, and after being placed in an 85℃ oven for 24 hours or stored under natural conditions for 3 months, the peel force still remains above 17g / 25mm, without significant decrease. This bonding strength is sufficient to meet the requirements for anti-delamination and anti-edge lifting during cutting, punching, transportation, and storage.

[0043] (II) Excellent high-temperature shaping and release properties: This shaping film can be used in one go within the hot pressing temperature range of 200~320℃. In a simulated hot pressing test at 260℃, 2.5MPa, and 1h, the shaping film can deform with the complex pattern on the circuit board surface. The intermediate substrate layer (especially the EVA layer) melts and flows to fill the uneven areas of the pattern, transmitting uniform pressure. The PTFE film, as the release cover layer, remains intact and can be easily peeled off from the circuit board surface after pressing, with no silicone transfer or residue, demonstrating excellent shaping and filling effects.

[0044] (III) Environmental protection and economy: The entire preparation process does not use organic solvent-based adhesives, avoiding the high pollution and high cost of sodium naphthalene solution treatment or ineffective plasma treatment of PTFE membrane. There are no harmful waste emissions during the production process, the raw material cost is controllable, and it is in line with the concept of green manufacturing.

[0045] (iv) Flexible structure: By providing two structural forms, a single-layer PE intermediate layer or a three-layer EVA / PE / EVA composite intermediate layer, users can flexibly choose according to the specific pressing process (such as the required hot pressing temperature, pressure, and pattern complexity), thus expanding the product's applicability.

[0046] In summary, the high-temperature resistant molding film based on electrostatic adsorption and vacuum adsorption provided by this invention, through the synergistic effect of electrostatic adsorption and vacuum adsorption and reasonable material and structural design, successfully solves the technical problem of PTFE's difficulty in being compounded with other materials, and realizes a glue-free, high-temperature resistant, and highly reliable molding film product, which has significant technological progress and industrial application value.

[0047] This invention also provides a method for preparing a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, used to prepare the high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption as described in any of the preceding embodiments, such as... Figure 2 As shown, the method includes: Step S100: The first PTFE membrane and the second PTFE membrane are brushed to make their surfaces negatively charged; Step S200: Prepare positively charged polymer colloidal particles, mix the colloidal particles with polymer base material and granulate, and then form an intermediate substrate layer, wherein the intermediate substrate layer contains positively charged polymer colloidal particles. Step S300: The processed first PTFE film and second PTFE film are respectively bonded to the two sides of the intermediate substrate layer and hot-pressed. At the same time, the micro-groove structure on the surface of the intermediate substrate layer is used to expel air under the bonding pressure to form a vacuum adsorption, thereby obtaining a high-temperature resistant PTFE double-sided PTFE film.

[0048] The method for preparing the high-temperature resistant molded film of the present invention achieves a firm bond between the PTFE film and the intermediate substrate layer through the synergistic effect of electrostatic adsorption and vacuum adsorption, without using adhesives or subjecting the PTFE to plasma treatment or sodium washing, ultimately obtaining a high-temperature resistant molded film of double-sided PTFE. The method is described in detail below.

[0049] The preparation method includes three main steps: Brush treatment: The first PTFE membrane and the second PTFE membrane are brushed to give their surfaces a negative charge.

[0050] Preparation of intermediate substrate layer: Prepare positively charged polymer colloidal particles, mix the colloidal particles with polymer base material and granulate, and then form an intermediate substrate layer containing positively charged polymer colloidal particles.

[0051] Hot-press lamination: The treated first PTFE film and second PTFE film are respectively laminated to the two sides of the intermediate substrate layer and hot-pressed. At the same time, the micro-groove structure on the surface of the intermediate substrate layer is used to expel air under lamination pressure to form a vacuum adsorption, thereby obtaining a high-temperature resistant PTFE film with double sides.

[0052] The above method does not use any adhesives throughout the entire process, and does not involve plasma treatment or sodium washing of the PTFE membrane, making it environmentally friendly and cost-controllable.

[0053] Specifically, the brush treatment employs a brush roller, with nylon bristles (approximately 15mm in length, 20 bristles / cm² density, and A60 hardness) as the preferred material. Alternatively, a loop of felt can be wrapped around the guide roller of the equipment before hot pressing, allowing friction against the PTFE membrane. The PTFE membrane feed speed is controlled at 5-10 m / min, and the relative humidity is kept below 60%. There is no additional pressure between the brush and the PTFE membrane; contact is solely based on the brush's own weight. After passing through the brush roller, the PTFE membrane surface acquires sufficient negative charge, the surface charge density of which can be fine-tuned by adjusting the feed speed and ambient humidity. The resulting PTFE membrane thickness is typically 25-100 μm, preferably 25 μm.

[0054] The preparation of positively charged polymer colloidal particles: The positively charged polymer colloidal particles used in this invention are preferably polystyrene colloidal particles with a positively charged surface. The preparation method includes two steps: quaternization reaction and soap-free emulsion polymerization.

[0055] (1) Preparation of ODMAEMA by quaternization reaction

[0056] N,N-dimethylaminoethyl methacrylate (DMAEMA) and 1-bromooctane were added to a ketone solvent (e.g., acetone) at a molar ratio of 1:1 to 1.2 and reacted at 30–50 °C for 20–28 h. After the reaction was complete, the solvent was removed by rotary evaporation, the product was washed with n-hexane, and dried under vacuum to obtain methacryloyloxyethyl-N-octyldimethylammonium bromide (ODMAEMA). This product is a white, waxy solid, and the yield is usually greater than 85%.

[0057] (2) Two-step feeding soap-free emulsion polymerization

[0058] Ultrapure water was added to a four-necked flask equipped with a mechanical stirrer, nitrogen purging device, and temperature control device. Nitrogen gas was introduced and the temperature was raised to 70-80°C, with the stirring speed controlled at 300 rpm. First, styrene and ODMAEMA (mass ratio approximately 9:1) were added and dispersed evenly. Then, the initiator AIBA (2,2'-azo(2-methylpropylamidine) dihydrochloride) was added. After reacting for the first period of 20-28 hours (e.g., 120 minutes), a second addition of the same proportions of styrene, ODMAEMA, and AIBA was made. The temperature and stirring were maintained, and the reaction continued for the total time of 20-28 hours. After the reaction, a small amount of agglomerates was filtered off, and the emulsion was purified by centrifugation (e.g., centrifugation at 15000 rpm for 30 minutes, repeated 3 times) to obtain a monodisperse polystyrene colloidal particle emulsion with a particle size of 150-200 nm and a surface charge density of 1-3 μC / cm². The resulting emulsion can be adjusted to a solid content of approximately 10% for later use.

[0059] The colloidal particles have a large number of positive charges on their surface. Like charges repel each other, which is beneficial for uniform dispersion in polymer base materials.

[0060] The intermediate substrate layer can be prepared using two different structures depending on the actual needs: a single-layer PE film or a three-layer composite film (sequentially consisting of a first EVA layer, an intermediate PE layer, and a second EVA layer). The preparation processes for the two structures are described below.

[0061] (a) Single-layer PE film structure

[0062] When the intermediate substrate layer is a single-layer PE film, positively charged polymer colloidal particles are dispersed within the PE layer. The specific preparation process is as follows: The prepared colloidal particle emulsion (dry weight) is mixed with PE granules (preferably LDPE) and a silane crosslinking agent (vinyltrimethoxysilane, VTMS) in a specific ratio and then granulated. By weight, for 100 parts of PE, 1-5 parts of colloidal particles (dry weight) and 0.2-1 parts of silane crosslinking agent are added. Mixing can be performed using a twin-screw extruder, with the granulation temperature controlled at 140-165℃. After granulation, the material is dried (80℃ hot air drying for 4 hours) and then formed into a PE film through single-layer extrusion or calendering. During the forming process, a chrome-plated pressure roller (pressure 0.3-0.5 MPa) with a sandblasted surface is used to adjust the surface roughness of the film, ensuring that the surface roughness Ra on both sides reaches 0.2-0.4 μm. The film thickness can be controlled as needed from 50-250 μm (e.g., 200 μm). This microgroove structure will play a role in venting and creating a vacuum during subsequent hot-pressing lamination.

[0063] (ii) Three-layer composite membrane structure (EVA / PE / EVA)

[0064] When the intermediate substrate layer is a three-layer composite film (sequentially consisting of a first EVA layer, an intermediate PE layer, and a second EVA layer), the positively charged polymer colloidal particles are only dispersed in the upper and lower EVA layers, while the intermediate PE layer is pure PE and contains no colloidal particles. The specific preparation process is as follows: (1) Mixed granulation The prepared colloidal particle emulsion (dry weight) was mixed with EVA granules and silane crosslinking agent VTMS in the following weight ratio: EVA 100 parts, colloidal particles 1-5 parts (dry weight), and silane coupling agent 0.2-1 parts. The VA content of the EVA was preferably 20%-35% (e.g., 28%). Granulation was performed using a twin-screw extruder at a granulation temperature of 140-165℃ and a screw speed of 250 rpm. After granulation, the mixture was dried with hot air at 80℃ for 4 hours to obtain a mixture of upper and lower EVA layers. The middle PE layer used pure LDPE granules without the addition of colloidal particles or crosslinking agents.

[0065] (2) Three-layer co-extrusion molding

[0066] The mixture of upper and lower EVA layers and the pure PE granules for the middle layer are fed into three extruders and combined through a three-layer co-extrusion die to form a three-layer composite film in a single extrusion. The temperature of each section of the extruder is controlled at 140~165℃, and the die temperature is 165℃. After the melt flows out, it is cooled and shaped by a 15℃ water-cooled roller, and the surface roughness is adjusted by a sandblasted and chrome-plated pressure roller (pressure 0.3~0.5MPa). The total thickness of the resulting composite film can be 80~250μm (typical value 200μm), of which the thickness of the middle PE layer is about 160μm, and the thickness of each of the upper and lower EVA layers is about 20μm. The surface roughness Ra of both sides is measured to be 0.2~0.4μm using a roughness tester.

[0067] Hot-press lamination specifically involves guiding the first and second PTFE films, treated with brushes, to the two sides of the intermediate substrate layer, respectively, and then laminating them using a two-roller hot press laminator. The lamination temperature is controlled at 80~120℃, the lamination pressure is 0.2~0.5MPa (preferably 0.3~0.5MPa), and the lamination speed is 5~10m / min. During this process, the micro-grooves on the surface of the intermediate substrate layer act as exhaust channels. The pressure of the rollers forces the air between the two PTFE films and the intermediate substrate layer along the grooves, forming a local negative pressure, thereby generating a vacuum adsorption force. Simultaneously, the negative charge on the surface of the PTFE film and the positive charge on the surface of the intermediate substrate layer generate electrostatic attraction. The synergistic effect of these two factors ensures a firm bond between the PTFE film and the intermediate substrate layer, and no adhesive is used throughout the entire process.

[0068] The present invention provides a method for preparing a high-temperature resistant molded film based on electrostatic adsorption and vacuum adsorption. Through the synergistic effect of electrostatic adsorption and vacuum adsorption and the design of reasonable process parameters, it successfully solves the technical problem that PTFE is difficult to combine with other materials, and realizes the industrial preparation of glue-free, high-temperature resistant, and highly reliable molded films. It has significant technological progress and industrial application value.

[0069] Example 1

[0070] 1. Preparation of positively charged polystyrene colloidal particles

[0071] (1) Quaternization reaction: 15.7 g (0.1 mol) of N,N-dimethylaminoethyl methacrylate (DMAEMA), 21.2 g (0.11 mol) of 1-bromooctane and 100 mL of acetone were added to a reaction flask equipped with a stirrer, and the mixture was stirred in a water bath at 40 °C for 24 h. After the reaction was completed, the acetone was removed by rotary evaporation, the residue was washed three times with n-hexane, and dried under vacuum at 40 °C to constant weight to obtain a white waxy solid ODMAEMA with a yield of 86.2% and a purity of 97.6%.

[0072] (2) Two-step soap-free emulsion polymerization: 400g of ultrapure water was added to a four-necked flask equipped with a mechanical stirrer, a nitrogen purging device, and a temperature control device. Nitrogen gas was introduced and the temperature was raised to 75℃, with a stirring speed of 300r / min. 18g of styrene and 2g of ODMAEMA were added, and after uniform dispersion, 0.1g of initiator AIBA was added, and the reaction was carried out for 120min. Then, 18g of styrene, 2g of ODMAEMA, and 0.1g of AIBA were added, and the temperature and stirring speed were maintained to continue the reaction for 24h. After the reaction was completed, a small amount of clumps were filtered off, and the emulsion was centrifuged at 15000rpm for 30min. The supernatant was discarded, and the precipitate was ultrasonically dispersed with ultrapure water and centrifuged again. This process was repeated 3 times. Finally, the precipitate was dispersed in ultrapure water, and the solid content was adjusted to 10% to obtain a polystyrene colloidal particle emulsion with a positively charged surface. Dynamic light scattering analysis showed that the particle size was 210nm, and the PDI was 0.05. The surface charge density was measured to be 2.8μC / cm² by conductivity titration.

[0073] 2. Preparation of three-layer composite membrane

[0074] The above-mentioned colloidal particle emulsion (dry weight) was mixed with EVA granules (VA content 28%) and silane crosslinking agent (vinyltrimethoxysilane, VTMS) at a weight ratio of EVA:colloidal particles (dry weight):VTMS = 100:3:0.5. Granulation was performed using a twin-screw extruder (feed section 140℃, melting section 160℃, mixing section 165℃, discharge section 155℃, screw speed 250 rpm). After granulation, the mixture was dried with hot air at 80℃ for 4 hours to obtain a mixture of upper and lower EVA layers. The middle PE layer used pure LDPE granules (Qatar Petrochemical FD0274).

[0075] A three-layer co-extrusion system was used: three extruders respectively supplied the upper and lower EVA layer mixture and the middle PE layer granules. The temperature of each section of the extruder was 140~165℃, and the die temperature was 165℃. The total extrusion rate was controlled at 60kg / h, with the main extruder (middle layer) rotating at 80rpm and the auxiliary extruders (upper and lower layers) rotating at 45rpm. The melt flowed out after converging through the three-layer co-extrusion dies, and was cooled and shaped on a 15℃ water-cooled roller. At the same time, the surface roughness was adjusted by sandblasting and chrome-plated pressure rollers (pressure 0.3MPa). The total thickness of the resulting composite film was 200μm, with the middle PE layer being 160μm thick and the upper and lower EVA layers each being 20μm thick. The surface roughness Ra of the two sides was measured using a roughness meter (Mitutoyo SJ-210, ISO4287 standard) to be 0.28μm and 0.36μm, respectively (both within the range of 0.2~0.4μm).

[0076] 3. Brush treatment of PTFE membrane

[0077] A PTFE membrane with a thickness of 25μm was taken and passed through a nylon brush roller (brush length 15mm, density 20 bristles / cm², hardness A60, contact only by gravity) at a film speed of 8m / min and an ambient humidity of 55%. The surface of the PTFE membrane was then charged with a negative charge.

[0078] 4. Hot pressing and bonding

[0079] The first and second PTFE films, after being brushed, are guided to both sides of the three-layer composite film and then laminated using a two-roller hot press. The lamination temperature is 100℃, the lamination pressure is 0.4MPa, and the lamination speed is 8m / min. During the lamination process, the microgrooves on the surface of the composite film expel interfacial air, forming a vacuum adsorption. This, combined with electrostatic adsorption, results in a high-temperature resistant PTFE film on both sides.

[0080] The product after bonding in this embodiment is as follows: Figure 3 As shown, the product material is uniform after lamination, and there is no delamination during bending tests. The peel force between PTFE and the interlayer is 15-20g / 25mm. Hot-pressing tests show good material shaping ability. It can be used within the hot-pressing temperature range of 200-320℃ (depending on the interlayer material and processing technology), exhibiting good peel, shaping, and filling effects, with no silicone transfer. The diagram shows the structure of the laminated product after the edge is torn open. Figure 4 As shown.

[0081] 5. Performance Testing

[0082] (1) Peel strength test: According to GB / T2790-1995, the peel strength was 180°, the peel speed was 100 mm / min, the test environment was 23℃±2℃, 50%±5%RH, and the sample width was 25 mm. The initial peel strength was measured to be 18.2 g / 25 mm. After the sample was placed in an 85℃ oven for 24 h, the peel strength was 17.8 g / 25 mm; after being stored under natural conditions (23℃±5℃, 50%±10%RH) for 3 months, the peel strength was 17.6 g / 25 mm. All test values ​​were greater than 8 g / 25 mm.

[0083] (2) Bending test: Fold the sample 180° and flatten it, repeat 5 times, and observe whether there is any delamination or edge lifting at the edge.

[0084] (3) Drilling and Cutting Bonding Strength Test: The results of the drilling and cutting bonding strength test are as follows: Figure 5 As shown, the three layers of material are tightly bonded, and there will be no curling or delamination during the manufacturing process, such as bending, punching, and cutting, as well as during storage and transportation.

[0085] (4) Hot-press molding test: The molding film was placed on a circuit board simulation substrate with concave and convex patterns and hot-pressed at 260℃ and 2.5MPa for 1 hour. After pressing, it was allowed to cool naturally, and the molding film was observed; the hot-press molding test results are as follows. Figure 6 As shown, the PTFE layer is unbroken, and the composite layer uniformly fills the recessed areas of the pattern, demonstrating good shaping. When the PTFE film is peeled off from the composite layer, there is no silicone residue on the circuit board surface, indicating excellent release effect.

[0086] Example 2 (Single-layer PE structure)

[0087] 1. Preparation of positively charged polystyrene colloidal particles

[0088] Same as Part 1 of Example 1.

[0089] 2. Preparation of single-layer PE film

[0090] The colloidal particle emulsion (dry weight), LDPE granules, and silane crosslinking agent VTMS were mixed at a weight ratio of LDPE:colloidal particles (dry weight):VTMS = 100:3:0.5. The mixture was granulated using a twin-screw extruder (process as in Example 1) and then dried. A single-layer extrusion casting process was employed: the extruder temperature was 150~170℃ in each section, the die temperature was 165℃, and the film was cooled and shaped using a 15℃ water-cooled roller. Simultaneously, the surface roughness was adjusted using a sandblasted chrome-plated pressure roller (pressure 0.3MPa). The resulting PE film had a thickness of 200μm, and the surface roughness Ra on both sides was 0.36μm (0.2~0.4μm).

[0091] 3. PTFE membrane brushing and hot-pressing lamination

[0092] Same as Parts 3 and 4 of Example 1.

[0093] 4. Performance Testing

[0094] Test results: Initial peel strength 15.6 g / 25 mm (>8 g / 25 mm), 14.2 g / 25 mm after aging at 85℃ for 24 h, and 14.6 g / 25 mm after 3 months of storage. No delamination was observed during bending tests. Good hot-pressing performance at 260℃ with no silicone transfer was observed. Compared to Example 1, the peel strength is slightly lower by approximately 15%, but still meets the usage requirements.

[0095] Comparative Example 1 (No electrostatic adsorption: The composite membrane does not contain positively charged colloidal particles)

[0096] Preparation process: Same as in Example 1, but no colloidal particles are added to the upper and lower EVA layers (i.e., pure EVA layers) when preparing the three-layer composite film. The rest of the process is exactly the same.

[0097] Test results: The PTFE membrane and the composite membrane showed almost no adhesion after lamination, and separated with slight shaking, making peel force testing impossible. This indicates that without electrostatic adsorption (the interaction of positive and negative charges), vacuum adsorption (microgrooving for air removal) alone cannot firmly bond the PTFE membrane and the EVA layer.

[0098] Comparative Example 2 (No Vacuum Adsorption: No Microgrooves on the Surface of the Composite Membrane)

[0099] Preparation process: Same as in Example 1, but in the composite film preparation process, a mirror-finish roller (surface roughness Ra<0.05μm) is used instead of a sandblasting roller to make the surface of the composite film smooth and free of micro-grooves. The rest of the process is exactly the same.

[0100] Test results: After bonding, the sample showed localized air bubbles and uneven peel force, ranging from a low of 0.2g / 25mm to a high of 6.8g / 25mm. Furthermore, the edges were prone to delamination after cutting. During hot-pressing, residual air at the interface caused blistering and poor shaping. This indicates that vacuum adsorption (microgroove venting) is crucial for eliminating interfacial air bubbles and ensuring uniform bonding.

[0101] Comparative Example 3 (PTFE membrane without brush treatment)

[0102] Preparation process: Same as in Example 1, but the PTFE membrane is not treated with a brush roller (the surface is basically free of negative charge). The rest of the process is exactly the same.

[0103] Test results: The initial peel force was only 7.8g / 25mm (less than 8g / 25mm), and slight delamination appeared at the edges after the bending test. This indicates that brush treatment to make PTFE negatively charged is a necessary condition for obtaining sufficient electrostatic adsorption force.

[0104] Comparative Example 4 (PTFE treated with sodium naphthalene solution and coated with adhesive)

[0105] Preparation process: The PTFE membrane was immersed in sodium naphthalene treatment solution for 30 seconds, then removed, washed and dried, and the PTFE surface turned dark brown. Then, high-temperature epoxy adhesive was coated on the treated PTFE membrane, and then it was hot-pressed with the three-layer composite membrane (without colloidal particles) in Example 1 at 100°C and 0.4 MPa.

[0106] Test results: The initial peel strength reached 362g / 25mm (very high), but the PTFE film was black in color and failed the appearance test. In the 260℃ hot pressing test, the epoxy adhesive layer carbonized, bubbles appeared between the PTFE film and the composite layer, and the PTFE film was difficult to peel off from the circuit board after shaping (adhesion occurred). This indicates that the sodium washing and adhesive method is not only highly polluting and costly, but also that the epoxy adhesive layer and other bonding processes have a significant impact on the shaping effect, which will greatly reduce the shaping effect.

[0107] Comparative Example 5 (PTFE treated with plasma, then bonded with adhesive)

[0108] Preparation process: The PTFE membrane was subjected to atmospheric pressure plasma treatment (power 1KW, treatment speed 3m / min). Since the membrane could not be bonded without adhesive after plasma treatment, a high-temperature epoxy adhesive was applied. Then, it was hot-pressed with the three-layer composite membrane (containing colloidal particles) from Example 1 at 100℃ and 0.4MPa. Test results: The initial peel force was 327g / 25mm; the same problem as with sodium naphthalene solution treatment and adhesive application occurred, significantly affecting the shaping effect.

[0109] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

[0110] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, preferred embodiments are described in order to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art can make other changes and modifications to these embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of this invention.

[0111] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the spirit and scope of this invention; if these modifications and variations of this invention fall within the scope of the claims of this invention and their equivalents, then this invention also intends to include these modifications and variations.

Claims

1. A high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, characterized in that, The shaping film includes: A first PTFE film layer, a second PTFE film layer, and an intermediate substrate layer located between the two; Both the first PTFE film and the second PTFE film have negative charges on their surfaces; The intermediate substrate layer contains positively charged polymer colloidal particles; The first PTFE film layer and the second PTFE film layer are respectively bonded to the two sides of the intermediate substrate layer by electrostatic adsorption. At the bonding interface, air is expelled under bonding pressure to form a vacuum adsorption by means of the micro-groove structure on the surface of the intermediate substrate layer.

2. The shaping film according to claim 1, characterized in that, The intermediate substrate layer is a single-layer PE layer, and the positively charged polymer colloidal particles are dispersed in the PE layer; or, the intermediate substrate layer is a three-layer composite film, consisting of a first EVA layer, an intermediate PE layer, and a second EVA layer, and the positively charged polymer colloidal particles are dispersed in the first EVA layer and the second EVA layer.

3. The shaping film according to claim 1, characterized in that, The positively charged polymer colloidal particles are polystyrene colloidal particles, hematite colloidal particles, goethite colloidal particles, or polymer particles adsorbed with metal ions, which have positively charged surfaces. The polystyrene colloidal particles have a particle size of 150~200nm and a surface charge density of 1~3μC / cm².

4. The shaping film according to claim 1, characterized in that, The surface roughness Ra of both sides of the intermediate substrate layer is 0.2~0.4μm.

5. The high-temperature resistant molding film according to claim 1, characterized in that, The 180° peel force between the first PTFE film layer and the intermediate substrate layer, and between the second PTFE film layer and the intermediate substrate layer, is greater than 8g / 25mm.

6. A method for preparing a high-temperature resistant shaped film based on electrostatic adsorption and vacuum adsorption, characterized in that, The method for preparing a high-temperature resistant shaped membrane based on electrostatic adsorption and vacuum adsorption as described in any one of claims 1-5 comprises: The first and second PTFE membranes are brushed to give their surfaces a negative charge. Positively charged polymer colloidal particles are prepared, and the colloidal particles are mixed with polymer base material and granulated. An intermediate substrate layer is obtained by molding, and the intermediate substrate layer contains positively charged polymer colloidal particles. The treated first PTFE film and second PTFE film are respectively bonded to the two sides of the intermediate substrate layer and hot-pressed together. At the same time, the micro-groove structure on the surface of the intermediate substrate layer is used to expel air under the bonding pressure to form a vacuum adsorption, thus obtaining a high-temperature resistant PTFE film with double sides.

7. The preparation method according to claim 6, characterized in that, The intermediate substrate layer is a single-layer PE film or a three-layer composite film, wherein the three-layer composite film consists of a first EVA layer, an intermediate PE layer, and a second EVA layer in sequence; when the intermediate substrate layer is a single-layer PE film, the colloidal particles are dispersed in the PE layer; when the intermediate substrate layer is a three-layer composite film, the colloidal particles are dispersed in the first and second EVA layers.

8. The preparation method according to claim 6, characterized in that, The brush treatment uses a brush roller, the PTFE film feed speed is 5~10m / min, and the ambient humidity is <60%; the hot pressing is performed using a double roller hot pressing machine, the pressing temperature is 80~120℃, the pressure is 0.2~0.5MPa, and the pressing speed is 5~10m / min; no adhesive is used in the preparation method.

9. The preparation method according to claim 6, characterized in that, The positively charged polymer colloidal particles are polystyrene colloidal particles with positive surface charges. The preparation of positively charged polymer colloidal particles includes: ODMAEMA was obtained by reacting N,N-dimethylaminoethyl methacrylate with 1-bromooctane in a molar ratio of 1:1 to 1.2 in a ketone solvent at 30 to 50 °C for 20 to 28 h. A two-step soap-free emulsion polymerization method was adopted. Styrene and ODMAEMA were used as monomers and AIBA was used as initiator under nitrogen protection at 70~80℃. The reaction was carried out for 20~28h. After centrifugation and purification, a colloidal particle emulsion with a particle size of 150~200nm and a surface charge density of 1~3μC / cm² was obtained.

10. The preparation method according to claim 7, characterized in that, When the intermediate substrate layer is a three-layer composite film, the step of mixing and granulating the colloidal particles with the polymer base material, and then molding to obtain the intermediate substrate layer includes: The prepared colloidal particles were added to EVA raw materials and silane crosslinking agent for mixing and granulation, and a three-layer composite film was prepared by three-layer co-extrusion. The mixing ratio of the granulation is as follows by weight: 100 parts EVA, 1-5 parts of colloidal particles (dry weight), and 0.2-1 parts of silane crosslinking agent. The VA content of the EVA is 20%-35%, and the silane crosslinking agent is vinyltrimethoxysilane.

Images