Preparation method of UV-cured halogen-free flame-retardant conductive shielding adhesive tape

Abstract

The invention relates to a preparation method of a UV-cured halogen-free flame-retardant conductive shielding adhesive tape. The preparation method comprises the following steps: 1) flame-retardant dispersion: heating modified polyurethane acrylate UV glue, stirring, defoaming, controlling the viscosity to be m1, adding a flame retardant in batches, grinding, dispersing and defoaming to obtain a material A; 2) conductive flame-retardant dispersion: adding a conductive filler into the material A in batches, heating to h2, stirring for 25-30 minutes at the speed of a4, and performing vacuum stirring to obtain glue B; 3) coating and curing: cooling and defoaming the glue B, coating a substrate with the glue B, and performing UV curing to obtain the flame-retardant shielding film. 4) press-fit forming: attaching the flame-retardant shielding film to the flame-retardant conductive base material to obtain the flame-retardant conductive shielding adhesive tape; the flame retardant is formed by mixing a plurality of materials selected from nano-scale aluminum hydroxide, micron-scale magnesium hydroxide and graphene sheets. The adhesive tape obtained by the production process has better shielding effectiveness, flame retardant property, adhesion stability and weather resistance.

Description

Technical Field

[0001] The present application relates to the field of functional adhesive tapes, and in particular to a method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape. Background Art

[0002] The field of functional adhesive tape technology has experienced rapid growth in recent years, particularly in consumer electronics. Conductive tape, as a key component, has a direct impact on the stability and safety of these devices. As electronic products evolve toward thinner, lighter, and higher-performance designs, the demands placed on conductive tape are increasing. Not only must it exhibit excellent electrical conductivity, but it must also meet multiple requirements, such as flame retardancy and environmental friendliness. This poses significant challenges to tape manufacturing technology. This is especially true in complex operating environments, such as those characterized by high temperature and humidity, where the tape must maintain stable adhesion, further increasing the technical complexity.

[0003] In existing technology, the following methods are commonly used to achieve both flame retardancy and electrical conductivity in conductive tapes: First, conventional conductive tapes containing halogen flame retardants are used to achieve flame retardancy by adding halogen-based substances; second, conductive tapes with a single particle size of halogen-free flame retardant are used to achieve flame retardancy by utilizing a flame retardant of a specific size; third, solvent-based conductive tapes are used to dissolve and evenly disperse the flame retardant and conductive filler in an organic solvent; and fourth, shielding flame-retardant tapes are formed by hot-pressing a halogen-free flame-retardant plain weave conductive fabric with a conductive film. While these methods address some of the functional requirements of conductive tapes to a certain extent, they still have limitations.

[0004] However, existing technologies still have significant drawbacks. For one thing, compounding halogen-free flame retardants with conductive fillers is difficult, making it difficult to achieve both excellent flame retardancy and electrical conductivity. Furthermore, in UV-curable adhesive systems, the addition of flame retardants and conductive fillers can affect UV curing efficiency and adhesive layer adhesion, limiting the overall performance of the tape. More importantly, in high-temperature and high-humidity environments, existing tapes exhibit poor adhesion stability and are prone to detachment, severely impacting their practical application. These issues urgently need to be addressed through innovative technological solutions. Summary of the Invention

[0005] The purpose of this application is to overcome the above technical problems and provide a method for preparing a UV curable halogen-free flame retardant conductive shielding tape. A method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape is prepared by the following method: 1) Flame retardant dispersion: Heat the modified polyurethane acrylate UV glue to h1, stir at a rate a1 until it is fully fluid, remove bubbles, control the viscosity at m1, then add the flame retardant in batches, each time with an interval of b1, stir at a rate a2 for 25-35 minutes, then grind and disperse, deaerate, and obtain material A; 2) Conductive flame retardant dispersion: Add the conductive filler to Material A in batches, with an interval of b2 each time and a stirring rate of a3. After all the filler is added, heat up to h2 and stir at a rate of a4 for 25 - 30 min, then perform vacuum stirring to obtain Glue B; 3) Coating and curing: Cool Glue B to h3, control the viscosity at m2, remove bubbles, coat it on the substrate under a pressure of P1, and then perform UV curing to obtain a flame retardant shielding film; 4) Pressing and forming: Bond the flame retardant shielding film with the flame retardant conductive substrate, and then press it under a pressure of P2 at a pressing temperature of h4. Conduct quality inspection to obtain a flame retardant conductive shielding tape; The m1 is 3500 ± 200 mPa·s, and the ratio of m1 to m2 is greater than 2; h3 > h1 > h2 > h4, and the difference between adjacent values is ≤ 20°C; a1 < a3 ≤ a2 < a4, and the difference between adjacent values is ≤ 700 rpm, and a1 ≥ 300 rpm; b1 ≤ b2, and b1 ≥ 3 min; the conductive filler is silver-coated copper powder; the flame retardant is a mixture of multiple components including nano-scale aluminum hydroxide, micro-scale magnesium hydroxide, and graphene sheets.

[0006] By adopting the above technical solutions, the following effects can be achieved: By controlling parameters such as the viscosity, temperature, and stirring rate of the modified polyurethane acrylate UV glue during the flame retardant dispersion process, ensure that the flame retardant is evenly dispersed in the system, avoid agglomeration, and thus improve the flame retardant performance.

[0007] In the conductive flame retardant dispersion step, by optimizing the addition method of the conductive filler and the stirring conditions, the conductive filler and the flame retardant are fully mixed to form a stable conductive network, significantly improving the conductive performance without affecting the flame retardant effect.

[0008] During the coating and curing process, by precisely controlling the viscosity of the glue and the coating pressure, ensure the uniformity of the coating thickness, improve the coating quality, and at the same time, combined with the staged UV curing process, enhance the adhesion and weather resistance of the glue layer.

[0009] In the pressing and forming step, by regulating the pressing temperature and pressure, ensure the tight combination of the flame retardant shielding film and the conductive substrate, further improving the overall performance of the product.

[0010] The collaborative optimization design between various process parameters, such as the ratio of m1 to m2, the gradient setting of each temperature, and the reasonable combination of stirring rates, effectively improves the mixing uniformity of the raw material system, and the finally prepared halogen-free flame retardant conductive shielding tape has excellent flame retardant, conductive, and environmental protection properties.

[0011] Furthermore, in steps 1) to 4), by strictly controlling the initial viscosity m1 at 3500±200mPa·s and ensuring that the ratio of m1 to the final viscosity m2 is greater than 2, combined with adjusting the temperatures h3, h1, h2, and h4 in a strictly descending order with a difference of no more than 20°C, and gradually optimizing the stirring rates a1, a3, a2, and a4, and rationally setting the time intervals b1 and b2, the uniform dispersion and stable bonding of the raw material system are effectively ensured. The precise control of these parameters not only improves the uniformity of the distribution of the flame retardant and conductive filler in the glue system, but also enhances the peel strength of the tape, thereby achieving a comprehensive improvement in flame retardancy, conductivity, and adhesion, and giving the final flame-retardant conductive shielding tape even better overall performance.

[0012] At the same time, modified polyurethane acrylate UV glue has better adhesion, weather resistance and dispersibility; the conductive filler is silver-coated copper powder; the flame retardant is a mixture of multiple nano-scale aluminum hydroxide, micron-scale magnesium hydroxide, and graphene sheets, as well as the production process of this application, so that the obtained tape can obtain better flame retardant effect and shielding effectiveness, while having better peel strength and higher tolerance to high temperature and high humidity.

[0013] Preferably, the UV curing process is divided into three stages: In the pre-curing stage, use a UV light source with 30% power and an irradiation time of 3-5 seconds; During the main curing stage, use a UV light source at 80% power for 8-12 seconds; In the post-curing stage, a UV light source with 50% power is used and the irradiation time is 3-5 seconds.

[0014] By adopting the above technical solutions, precise control of the UV curing process is achieved, with the following specific effects: In the pre-curing stage, a 30% power UV light source is used for 3-5 seconds, which can quickly form an initial cure on the surface of the adhesive layer and effectively prevent contamination and deformation of the adhesive layer surface during subsequent processing.

[0015] During the main curing stage, a UV light source with 80% power is used for 8-12 seconds to ensure that the adhesive layer is fully cross-linked, thereby improving the overall strength and adhesion of the adhesive layer, while ensuring the stability of the flame retardant and conductive filler in the adhesive layer.

[0016] In the post-curing stage, a UV light source with 50% power is used for 3-5 seconds to further improve the curing degree of the adhesive layer surface, optimize the surface properties of the adhesive layer, and enhance weather resistance.

[0017] Preferably, the grinding and dispersing process is carried out using a three-roller mill, and the roller gaps are 40 microns, 30 microns, and 20 microns, respectively.

[0018] By adopting the above technical solution, it is possible to achieve fine dispersion of flame retardants and conductive fillers in UV-curable adhesive systems. Specifically, grinding and dispersion are carried out using a three-roll mill, and the roller gaps are set to 40 microns, 30 microns, and 20 microns, respectively. This can effectively reduce particle agglomeration and achieve nano- or micron-level dispersion of flame retardants and conductive fillers. This process not only improves the uniformity of flame retardant distribution and enhances flame retardant properties, but also optimizes the network structure of the conductive filler and reduces the volume resistivity, thereby significantly improving the conductivity and EMI shielding effectiveness of the tape. At the same time, fine dispersion also helps maintain UV curing efficiency and ensures the stability of adhesive layer adhesion and mechanical properties.

[0019] Preferably, the modified polyurethane acrylate UV glue is prepared by the following method: Premixed UV resin: Weigh 70-80 parts by weight of aliphatic polyurethane acrylate, heat to b1, add 20-30 parts by weight of epoxy acrylate, stir evenly, then add 0.5-1 part by weight of antioxidant, stir at 45-55°C for 30 minutes to obtain premixed UV resin; Functional additive: Weigh 3-4 parts of hydroxyketone photoinitiator and 1-2 parts of amine photoinitiator by weight, pre-mix them at temperature b2, then add 1-2 parts of silane coupling agent and 0.5-1 part of polyether-modified polysiloxane dispersant, stir well, and obtain a functional additive; Modified polyurethane acrylate UV glue: cool the premixed UV resin to b3, stir and add functional additives at a rate of 2-3 ml / min, heat to b4, stir and homogenize, evacuate, and control the viscosity to m3 to obtain modified polyurethane acrylate UV glue.

[0020] By adopting the above technical solution, the synergistic effect of the pre-mixed UV resin and functional additives significantly improves the comprehensive performance of the modified polyurethane acrylate UV glue. Specifically, the base resin system formed by the compounding of aliphatic polyurethane acrylate and epoxy acrylate has good mechanical properties and adhesion, and the addition of antioxidants effectively prevents material aging. The combination of hydroxyketone photoinitiators and amine photoinitiators in the functional additives significantly improves the UV curing efficiency and ensures rapid cross-linking of the glue during the UV curing process. The introduction of silane coupling agents and polyether-modified polysiloxane dispersants further enhances the dispersibility and stability of the system and avoids filler agglomeration. The final modified polyurethane acrylate UV glue has moderate viscosity and is suitable for precision coating processes, providing a guarantee for the uniform dispersion of subsequent flame retardants and conductive fillers. It also has better moisture resistance and heat resistance, reducing the possibility of the tape detaching during long-term use in high-humidity and high-temperature environments.

[0021] Preferably, the aliphatic polyurethane acrylate has an average molecular weight of 2000-3000 and a functionality of 3-4; the epoxy value of the epoxy acrylate is 180-220 and a viscosity of 8000-12000 mPa·s.

[0022] By employing this technical solution, the fundamental properties of modified polyurethane acrylate UV adhesives can be precisely controlled. Specifically, by limiting the average molecular weight and functionality of the aliphatic polyurethane acrylate, the crosslinking density and mechanical properties of the modified polyurethane acrylate UV adhesive are effectively improved. Simultaneously, by specifying the epoxy value and viscosity range of the epoxy acrylate, good compatibility and reactivity with the aliphatic polyurethane acrylate are ensured, thereby optimizing the adhesive's overall performance stability. This precise formulation not only improves UV curing efficiency but also enhances the adhesion and weather resistance of the resulting halogen-free, flame-retardant, conductive shielding tape.

[0023] Preferably, the flame retardant is a mixture of one or more of nano-sized aluminum hydroxide, micron-sized magnesium hydroxide, and graphene sheets.

[0024] By adopting the above technical solution, the flame retardant is mixed with one or more of nano-scale aluminum hydroxide, micron-scale magnesium hydroxide, and graphene sheets to form a multi-scale synergistic flame retardant system. Nano-scale aluminum hydroxide provides efficient surface coverage and refines combustion products, micron-scale magnesium hydroxide enhances physical barriers and thermal stability, and graphene sheets further enhance flame retardancy through their excellent thermal stability and shielding effect. This compounding method not only improves the flame retardant efficiency, but also optimizes the comprehensive performance of the material, enabling the flame retardant conductive shielding tape to meet the UL94 V-0 flame retardant standard while maintaining good conductivity and environmental protection properties. Specifically, the synergistic effect of multi-scale flame retardants significantly increases the oxygen index to 32-35%, eliminates the burning dripping phenomenon, and significantly improves the heat resistance and moisture resistance of the tape.

[0025] Preferably, the surface modified flame retardant is prepared by the following method: The coupling agent is weighed and dissolved in an ethanol solution, the pH is adjusted to 4-5, the solution is hydrolyzed, a flame retardant is added, the mixture is mixed evenly, filtered, and dried to obtain a surface-modified flame retardant.

[0026] By adopting the above technical solution, the surface modified flame retardant can significantly improve the dispersibility and compatibility of the flame retardant in the modified polyurethane acrylate UV glue system. The specific effects are as follows: The introduction of the coupling agent forms a stable chemical bond layer, reduces the agglomeration of flame retardant particles, and makes the flame retardant evenly dispersed in the glue system.

[0027] The interfacial bonding between the modified flame retardant and the UV resin matrix is ​​enhanced, which improves the stability of the overall material and avoids delamination or sedimentation problems.

[0028] Surface modification optimizes the distribution of flame retardants, reducing the negative impact on conductive properties while ensuring flame retardancy, thus achieving a balance between flame retardancy and conductivity.

[0029] Preferably, the coupling agent is a bifunctional silane coupling agent.

[0030] By employing this technical solution, a bifunctional silane coupling agent can significantly improve the compatibility between flame retardants and UV-curable resin systems. Specific benefits include: 1) One end of the coupling agent chemically bonds with the flame retardant surface, while the other end bonds to the UV resin molecules, effectively reducing flame retardant aggregation in the system; 2) improving the dispersion uniformity of the flame retardant in the modified polyurethane acrylate UV adhesive, ensuring stable flame retardant performance; and 3) improving the interfacial interaction between the flame retardant and the conductive filler, achieving an optimal balance between flame retardancy and conductivity.

[0031] Preferably, the conductive filler consists of flaky silver-coated copper powder and spherical silver-coated copper powder.

[0032] By adopting the above technical solution, the uniform dispersion of conductive fillers in the adhesive system and the construction of an effective conductive network are achieved. The synergistic effect of flaky silver-coated copper powder and spherical silver-coated copper powder makes the prepared flame-retardant conductive shielding tape have excellent electrical conductivity and mechanical properties. Specifically, the flaky silver-coated copper powder provides good in-plane conductivity, while the spherical silver-coated copper powder enhances the Z-direction conductivity, thereby significantly reducing the volume resistivity and improving the EMI shielding effectiveness. At the same time, the combination of the two forms of conductive fillers improves the adhesion and stability of the adhesive layer, ensuring the reliable performance of the tape in a variety of environments.

[0033] Preferably, the conductive filler is a pretreated conductive filler, which is prepared by the following method: mixing a polyacrylate dispersant with the conductive filler, and grinding the mixture step by step to obtain the pretreated conductive filler.

[0034] By adopting the above technical solution, the conductive filler can significantly improve its dispersibility and stability in the modified polyurethane acrylate UV adhesive system after surface dispersion treatment. Specifically, the mixing of the polyacrylate dispersant and the conductive filler and the step-by-step grinding process form a protective layer on the surface of the conductive filler, effectively preventing the agglomeration of the filler particles. This treatment method not only improves the uniformity of the conductive network, but also enhances the conductivity and mechanical properties of the adhesive layer, resulting in a tape with lower volume resistivity and higher EMI shielding effectiveness. In addition, the introduction of pre-treated conductive fillers helps maintain the stability of the adhesive layer during the UV curing process, ensuring that the tape exhibits excellent conductivity and reliability in practical applications.

[0035] In summary, this application includes at least one of the following beneficial technical effects: In steps 1) to 4), by strictly controlling the initial viscosity m1 at 3500±200mPa·s and ensuring the ratio of m1 to the final viscosity m2 is greater than 2, combined with adjusting the temperatures h3, h1, h2, and h4 in a strictly descending order with a difference of no more than 20°C, and gradually optimizing the stirring rates a1, a3, a2, and a4, and rationally setting the time intervals b1 and b2, the uniform dispersion and stable bonding of the raw material system are effectively ensured. Precise control of these parameters not only improves the uniformity of the distribution of the flame retardant and conductive filler in the adhesive system but also enhances the peel strength of the tape, thereby achieving a comprehensive improvement in flame retardancy, conductivity, and adhesion, giving the final flame-retardant conductive shielding tape even better overall performance.

[0036] At the same time, modified polyurethane acrylate UV glue has better adhesion, weather resistance and dispersibility; the conductive filler is silver-coated copper powder; the flame retardant is a mixture of multiple nano-scale aluminum hydroxide, micron-scale magnesium hydroxide, and graphene sheets, as well as the production process of this application, so that the obtained tape can obtain better flame retardant effect and shielding effectiveness, while having better peel strength and higher tolerance to high temperature and high humidity. DETAILED DESCRIPTION

[0037] The present application is further described in detail below with reference to the embodiments.

[0038] Nano-aluminum hydroxide: particle size is 1-5 microns, specific surface area is 80-120m 2 / g; Micron magnesium hydroxide: particle size is 10-20 microns, specific surface area is 15-25m 2 / g; Flake silver-coated copper powder: flake diameter 15-20 microns, thickness 1-3 microns; Spherical silver-coated copper powder: particle size 18-22 microns, purity ≥99.9%; Graphene sheet: sheet diameter 15-20 microns, thickness 1-3 microns; The aliphatic polyurethane acrylate has an average molecular weight of 2000-3000 and a functionality of 3-4, and is mainly prepared from pentaerythritol triacrylate, hexamethylene diisocyanate, and polytetramethylene glycol. The epoxy acrylate has an epoxy value of 180-220 and a viscosity of 8000-12000 mPa·s. The molecular weight of hydroxyketone photoinitiators is 250-350; The molecular weight of amine photoinitiators is 350-450; Preparation Example of Surface Modified Flame Retardant Preparation Example 1 The surface modified flame retardant is prepared by the following method: Nano-aluminum hydroxide and magnesium hydroxide were weighed in a weight ratio of 1:1, mixed evenly, and placed in an oven at 80° C. for drying for 4 hours to obtain a flame retardant.

[0039] A coupling agent (γ-glycidyloxypropyltrimethoxysilane) was dissolved in a 90% by mass ethanol solution, acetic acid was added to adjust the pH to 4, and the mixture was hydrolyzed for 30 minutes. Then, a flame retardant was added, the mixture was heated to 60°C, stirred for 2 hours, and filtered. The filter residue was placed in an oven at 70°C for drying for 6 hours to obtain a surface-modified flame retardant, wherein the amount of the coupling agent was 1.5 wt% of the amount of the flame retardant.

[0040] Preparation Example 2 Preparation Example 2 differs from Preparation Example 1 in that the flame retardant is composed of nano-sized aluminum hydroxide, micron-sized magnesium hydroxide, and graphene sheets in a weight ratio of 5:3:1.

[0041] Preparation Example 3 Preparation Example 3 is different from Preparation Example 1 in that the coupling agent consists of γ-glycidyloxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

[0042] Preparation example of pretreated conductive filler Preparation Example 4 A pretreated conductive filler is prepared by the following method: The flaky silver-coated copper powder and the spherical silver-coated copper powder were placed in an oven at 80° C. and dried for 4 hours to obtain the dried flaky silver-coated copper powder and the spherical silver-coated copper powder.

[0043] A thiol surface treatment agent (3-mercaptopropyltrimethoxysilane) was dissolved in isopropyl alcohol, and silver-coated copper powder (flaky silver-coated copper powder or spherical silver-coated copper powder) was added, with the thiol surface treatment agent being 0.5 wt % based on the mass of the silver-coated copper powder. The mixture was heated to 45° C. and stirred for 1 hour. The mixture was filtered, and the filter residue was dried in a vacuum drying oven at 50° C. for 2 hours to obtain surface-treated flaky silver-coated copper powder and spherical silver-coated copper powder, respectively.

[0044] Screening: The surface-treated flaky and spherical silver-coated copper powders are graded using an airflow classifier to ensure an aspect ratio of 15-20 microns and a thickness of 1-3 microns. The spherical silver-coated copper powders are then screened to select particles with a sphericity ≥ 0.95 and a particle size distribution concentrated within 20 ± 2 microns. The morphological characteristics of the screened conductive fillers are then observed using a scanning electron microscope. Finally, the screened flaky and spherical silver-coated copper powders are dried under vacuum at 60°C for 2 hours for subsequent use.

[0045] The screened flaky and spherical silver-coated copper powders were weighed and mixed in a weight ratio of 2:3. One part by weight of a polyacrylate dispersant (SNF FLOSPERSE 3000) was then added, along with two parts by weight of the flaky silver-coated copper powder. The mixture was pre-dispersed in a high-speed disperser at 1500 rpm for 10 minutes. The pre-dispersed mixture was then transferred to a three-roll mill and ground three times with roller gaps of 30, 25, and 20 microns. The ground conductive filler was then collected. The flaky and spherical silver-coated copper powders formed an interlocking network structure, laying the foundation for low resistivity and high shielding effectiveness.

[0046] Preparation example of modified polyurethane acrylate UV glue Preparation Example 5 A modified polyurethane acrylate UV glue is prepared by the following method: Premixed UV resin: In a closed reactor, add 80 parts by weight of aliphatic polyurethane acrylate, raise the temperature to c1 (50°C), then add 20 parts by weight of epoxy acrylate, continue heating and stirring evenly, add 0.5-1 parts by weight of antioxidant (2,6-di-tert-butyl-p-cresol) and mix evenly, then adjust the temperature to c2 (55°C) and stir at a speed of 600 rpm for 30 minutes to obtain a premixed UV resin.

[0047] Functional additives: 3 parts by weight of hydroxyketone photoinitiator (photoinitiator 8700) and 2 parts by weight of amine photoinitiator (photoinitiator EDB) are placed in a stirring device and pre-mixed evenly at c3 (40°C). 1 part by weight of silane coupling agent (γ-glycidyloxypropyltrimethoxysilane) and 1 part by weight of polyether-modified polysiloxane dispersant (brand Huaxiang Kejie, model SP-983) are added in sequence and mixed evenly. Stir under vacuum conditions for 15 minutes to obtain a functional additive.

[0048] Modified polyurethane acrylate UV glue: Cool the pre-mixed UV resin to c4 (40°C), continue stirring, and slowly add the functional additive at a rate of 2 ml / min. After the addition is complete, heat to c5 (45°C), homogenize at a stirring speed of 700 rpm for 30 minutes, and then vacuum degas for 15 minutes at a temperature of 5000 mPa·s to obtain modified polyurethane acrylate UV glue. c3 = c4 <c5<c1<c2,c3=40℃。

[0049] Preparation Example 6 Preparation Example 6 differs from Preparation Example 5 in that the amounts of the raw materials used are different, as follows: Pre-mixed UV resin: 70 parts by weight of aliphatic polyurethane acrylate; 30 parts by weight of epoxy acrylate; Functional additives include: 4 parts of hydroxyketone photoinitiator; 1 part of amine photoinitiator; a drop rate of 3 ml / min; 2 parts of silane coupling agent (γ-glycidyloxypropyltrimethoxysilane) and 0.5 parts of polyether-modified polysiloxane dispersant. Example

[0050] Example 1 A UV curable halogen-free flame retardant conductive shielding tape is prepared by the following method: 1) Flame Retardant Dispersion: The entire modified polyurethane acrylate UV adhesive obtained in Preparation Example 5 was placed in a stirring device, heated to h1 (45°C), and the stirring speed was adjusted to a1 (300 rpm) to ensure sufficient fluidity of the adhesive system. Vacuum was then applied for 15 minutes to eliminate any remaining bubbles in the modified polyurethane acrylate UV adhesive. The viscosity and pH of the adhesive were tested to ensure that the viscosity was within m1 (3500 mPa·s) and the pH was within 7. This yielded activated modified polyurethane acrylate UV adhesive.

[0051] Maintaining a stirring rate of 300 rpm, 2 parts by weight of a flame retardant (obtained by mixing nano-aluminum hydroxide and micron-sized magnesium hydroxide) was added to the activated modified polyurethane acrylate UV glue in 5 batches, with an interval of 3 minutes between each batch. After all were added, the stirring speed was gradually increased to a2 (800 rpm) and stirred for 30 minutes. The obtained material was then transferred to a three-roll mill for grinding and dispersion, and the roller gaps were 40 microns, 30 microns, and 20 microns, respectively. The material was ground three times step by step, and the material obtained after grinding was degassed in a vacuum degassing machine at 60 ° C for 20 minutes to obtain material A.

[0052] 2) Conductive Flame-retardant Dispersion: Weigh flaky silver-coated copper powder and spherical silver-coated copper powder in a weight ratio of 2:3 and mix them evenly to obtain a conductive filler. Six parts by weight of the conductive filler were then added to Material A in three batches, with a 5-minute interval between each batch, while maintaining stirring at a3 (800 rpm). After all the fillers were added, the temperature was raised to h2 (65°C), the stirring speed was increased to a4 (1200 rpm), and high-speed stirring was continued for 30 minutes. The mixture was then transferred to a vacuum stirring apparatus and stirred at a vacuum of -0.08 MPa for 2 hours to uniformly distribute the conductive filler throughout the system, thereby obtaining Glue B. By controlling the stirring speed and vacuum level, the flaky silver powder and spherical silver powder formed a three-dimensional conductive network within the flame-retardant, reinforced modified polyurethane acrylate UV adhesive system, while preventing agglomeration of the conductive filler.

[0053] 3) Coating and curing: Glue B is transferred to the feeding system of the coating equipment and cooled to h3 (30°C). The viscosity of the glue is then tested to ensure that it is within m2 (10,000 mPa·s). The glue B in the feeding tank is degassed using a vacuum degassing system to ensure that there are no bubbles in the glue. The glue is then coated on the surface of the PET release film at a coating pressure of p1 (0.20 MPa). The coating line speed is maintained at 10 m / min during the coating process. The coating temperature is maintained at 28°C and the ambient humidity is maintained at 50% RH. The coating thickness is 30 μm.

[0054] The coated adhesive layer is transported to the UV curing area under nitrogen protection. The oxygen content in the nitrogen environment is controlled below 200ppm. Secondly, a dual-band UV-LED light source system is used for curing, including a wavelength of 365nm (energy density 700mJ / cm 2 ) and wavelength 395nm (energy density 500mJ / cm 2 ) of the UV light source. Then, the UV curing process is divided into three stages: 1. Pre-curing stage: Use a UV light source with 30% power and irradiation time of 3 seconds to achieve initial curing of the adhesive layer surface; 2. Main curing stage: Use 80% power UV light source, irradiation time 12 seconds to ensure sufficient cross-linking inside the adhesive layer; 3. Post-curing stage: Use a UV light source with 50% power and irradiation time of 3 seconds to improve the curing degree of the adhesive layer surface.

[0055] After UV curing, it is rolled up with a 6-inch tube core to obtain the corresponding flame retardant shielding film.

[0056] 4) Compression molding: The flame retardant shielding film and the selected flame retardant conductive cloth substrate (thickness of 50 microns) are passed through a precision hot pressing laminating device, with the upper material being the flame retardant shielding film and the lower material being the flame retardant conductive cloth substrate. After peeling off the light release film of the flame retardant conductive adhesive film, they are simultaneously hot pressed and laminated to the flame retardant conductive cloth substrate (the laminating pressure is controlled at p2 (0.4 MPa), the hot pressing temperature is controlled at h (80°C), and the hot pressing time is 1s), the laminating line speed is 10 m / min, and the flame retardant conductive shielding tape is wound up.

[0057] The ratio of m1 to m2 is greater than 2; h3>h1>h2>h4, a1 <a3≦a2<a4,a1=300rpm;b<b2,b1=3min。

[0058] Example 2 The difference between Example 3 and Example 2 is that the conductive filler is replaced by the pretreated conductive filler obtained in Preparation Example 4.

[0059] Example 3 The difference between Example 3 and Example 2 is that the flame retardant is a surface-modified flame retardant, and the surface-modified flame retardant is obtained by using the surface-modified flame retardant obtained in Preparation Example 1.

[0060] Example 4 The difference between Example 4 and Example 2 is that the surface-modified flame retardant is obtained by using Preparation Example 2.

[0061] Example 5 The difference between Example 5 and Example 2 is that the surface-modified flame retardant is obtained by using Preparation Example 3.

[0062] Example 6 The difference between Example 6 and Example 2 is that the modified polyurethane acrylate UV glue is replaced by the modified polyurethane acrylate UV glue obtained in Preparation Example 6.

[0063] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the materials are added and mixed at one time; the details are as follows: 1) Flame Retardant Dispersion: The entire modified polyurethane acrylate UV adhesive obtained in Preparation Example 5 was placed in a stirring device, heated to h1 (45°C), and the stirring speed was adjusted to a1 (300 rpm) to ensure sufficient fluidity of the adhesive system. Vacuum was then applied for 15 minutes to eliminate any remaining bubbles in the modified polyurethane acrylate UV adhesive. The viscosity and pH of the adhesive were tested to ensure that the viscosity was within m1 (3500 mPa·s) and the pH was within 7. This yielded activated modified polyurethane acrylate UV adhesive.

[0064] Then, 2 parts by weight of flame retardant and 6 parts by weight of conductive filler were added to the activated modified polyurethane acrylate UV adhesive. Stirring was maintained at a3 (800 rpm) for 2 hours. The temperature was then raised to h2 (65°C), and the stirring speed was increased to a4 (1200 rpm). High-speed stirring was continued for 30 minutes. The mixture was then transferred to a vacuum stirring apparatus and stirred at -0.08 MPa for 2 hours to uniformly distribute the conductive filler throughout the system, yielding Glue B. By controlling the stirring speed and vacuum level, the flaky and spherical silver powders formed a three-dimensional conductive network within the flame-retardant, reinforced modified polyurethane acrylate UV adhesive system, while preventing agglomeration of the conductive filler. The remaining steps remained unchanged.

[0065] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the temperatures of h1, h2 and h3 are all equal to 30°C.

[0066] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the rotation speeds of a1, a3, a2, and a4 are all equal to 300 rpm.

[0067] Performance testing Testing method / test method Flame retardant grade: The flame retardant shielding films obtained in Examples 1-6 and Comparative Examples 1-3 were tested, and the reference standard was ASTM D3801; EMI shielding effectiveness (100 MHz-1 GHz): The flame retardant shielding films obtained in Examples 1-6 and Comparative Examples 1-3 were tested with reference to GB / T 30142-2013.

[0068] Peel strength (180°): The adhesive tapes obtained in Examples 1-6 and Comparative Examples 1-3 were tested with reference to GB / T 2792-2014.

[0069] Heat resistance (85℃ / 168h): Place the sample tested for peel strength at 85℃ for 168h. After drying, test the peel strength again and calculate the peel strength retention rate (dividing the peel strength after the test by the peel strength before the test and multiplying by 100%). Moisture resistance (60°C, 90% RH / 168h): Place the samples tested for peel strength at 60°C, 90% RH for 168h. After drying, retest the peel strength and calculate the peel strength retention (post-test value divided by pre-test value multiplied by 100%).

[0070] Table 1 Experimental data of Examples 1-6 and Comparative Examples 1-3 Combining Example 1 and Comparative Example 1 and Table 1, it can be seen that the flame retardant level, shielding effectiveness, peel strength, and peel strength retention rate of Comparative Examples 1-3 are all lower than those of Example 1, indicating that the preparation method of the present application can fully mix the raw materials and combine them to form a tightly bonded structure, thereby achieving better flame retardancy and shielding effectiveness while improving adhesion stability and reducing the possibility of falling off in high temperature and high humidity environments.

[0071] By comparing Example 1 and Example 2 and combining with Table 1, it can be seen that the flame retardant grade, shielding effectiveness, peel strength, and peel strength retention rate of Comparative Examples 1-3 are all lower than those of Example 1, indicating that the pretreated conductive filler obtained by the preparation method of the present application can be used in the production process of the present application to obtain better comprehensive performance.

[0072] By comparing Example 2 and Example 3 and combining them with Table 1, it can be seen that the flame retardant grade, shielding effectiveness, peel strength, and peel strength retention rate of Comparative Examples 1-3 are all lower than those of Example 1, indicating that the pretreated conductive filler obtained by the preparation method of the present application can be used in the production process of the present application to obtain better comprehensive performance.

[0073] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape, characterized in that: Prepared by the following method: 1) Flame retardant dispersion: Heat the modified polyurethane acrylate UV glue to h1, stir at a rate of a1 until fully flowing, defoam, control the viscosity at m1, then add the flame retardant in batches, with an interval of b1 each time, stir at a rate of a2 for 25 - 35 min, then carry out grinding dispersion and defoaming to obtain Material A; 2) Conductive flame retardant dispersion: Add the conductive filler to Material A in batches, with an interval of b2 each time, and the stirring rate is a3. After all are added, heat to h2, stir at a rate of a4 for 25 - 30 min, then carry out vacuum stirring to obtain Glue B; 3) Coating and curing: Cool Glue B to h3, control the viscosity at m2, defoam, coat on the substrate under a pressure of P1, and then carry out UV curing to obtain the flame retardant shielding film; 4) Pressing and forming: Bond the flame retardant shielding film with the flame retardant conductive substrate, and then press under a pressure of P2, with a pressing temperature of h4, and conduct quality inspection to obtain the flame retardant conductive shielding tape; The m1 is 3500 ± 200 mPa·s, and the ratio of m1 to m2 is greater than 2; h3 > h1 > h2 > h4, and the adjacent difference is ≤ 20 °C; a1 < a3 ≤ a2 < a4, and the adjacent numerical difference is ≤ 700 rpm, and a1 ≥ 300 rpm; b1 ≤ b2, and b1 ≥ 3 min; the conductive filler is silver-coated copper powder; the flame retardant is a mixture of multiple components including nanoscale aluminum hydroxide, micron-scale magnesium hydroxide, and graphene sheets.

2. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 1, characterized in that: The UV curing process is divided into three stages: Pre-curing stage: Use a UV light source with 30% power and irradiate for 3 - 5 seconds; Main curing stage: Use a UV light source with 80% power and irradiate for 8 - 12 seconds; Post-curing stage: Use a UV light source with 50% power and irradiate for 3 - 5 seconds.

3. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 1, characterized in that: The grinding dispersion process is carried out using a three-roll mill, and the roll gaps are 40 microns, 30 microns, and 20 microns in sequence.

4. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 1, wherein: The modified polyurethane acrylate UV glue is prepared by the following method: Pre-mix UV resin: Weigh 70 - 80 parts by weight of aliphatic polyurethane acrylate, heat to c1, add 20 - 30 parts by weight of epoxy acrylate, stir evenly, then add 0.5 - 1 part by weight of antioxidant, and stir at a temperature of c2 for 30 min to obtain the pre-mixed UV resin; Functional additives: Weigh 3 - 4 parts of hydroxy ketone photoinitiator and 1 - 2 parts of amine photoinitiator by weight, pre-mix at a temperature of c3, then add 1 - 2 parts of silane coupling agent and 0.5 - 1 part of polyether-modified polysiloxane dispersant in sequence, and stir evenly to obtain the functional additives; Modified polyurethane acrylate UV glue: Cool the pre-mixed UV resin to c4, stir and drop the functional additives while controlling the dropping rate at 2 - 3 ml / min, heat to c5, stir and homogenize, evacuate, and control the viscosity at m3 to obtain the modified polyurethane acrylate UV glue; c3 = c4 < c5 < c1 < c2, and c3 ≥ 40 °C.

5. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 1, wherein: The aliphatic polyurethane acrylate has an average molecular weight of 2000-3000 and a functionality of 3-4; the epoxy value of the epoxy acrylate is 180-220 and the viscosity is 8000-12000 mPa·s.

6. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 1, characterized in that: The flame retardant consists of nano-scale aluminum hydroxide, micron-scale magnesium hydroxide and graphene sheets.

7. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 6, characterized in that: The surface modified flame retardant is prepared by the following method: The coupling agent is weighed and dissolved in an ethanol solution, the pH is adjusted to 4-5, the solution is hydrolyzed, a flame retardant is added, the mixture is mixed evenly, filtered, and dried to obtain a surface-modified flame retardant.

8. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 7, characterized in that: The coupling agent is a bifunctional silane coupling agent.

9. The method for preparing a UV-curable halogen-free flame-retardant conductive shielding tape according to claim 1, characterized in that: The conductive filler consists of flaky silver-coated copper powder and spherical silver-coated copper powder.

10. The method for preparing a UV curable halogen-free flame retardant conductive shielding tape according to claim 1, characterized in that: The conductive filler is a pretreated conductive filler, which is prepared by the following method: The silver-coated copper powder is first treated with a mercaptan surface treatment agent, dried, and screened to obtain flaky silver-coated copper powder and spherical silver-coated copper powder, which are then mixed uniformly to obtain filler C; The polyacrylate dispersant is mixed with the filler C and ground step by step to obtain a pretreated conductive filler.

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