Highly transparent flame-retardant double-sided adhesive tape with substrate activation treatment and method for preparing the same

Abstract

The present application relates to the technical field of flame-retardant double-sided adhesive tape, and particularly relates to a high-transparency flame-retardant double-sided adhesive tape with substrate activation treatment and a preparation method thereof, which comprises a first release film layer, a first flame-retardant acrylate pressure-sensitive adhesive layer, a surface-activated modified PET substrate layer, a second flame-retardant acrylate pressure-sensitive adhesive layer and a second release film layer arranged in sequence. The PET substrate is modified by plasma activation, and the pressure-sensitive adhesive layer adopts a halogen-free flame-retardant system matched with the refractive index of the adhesive matrix. The product has high light transmittance, excellent flame retardancy and stable bonding performance. The present application solves the pain point that the transparency and flame retardancy of traditional flame-retardant double-sided adhesive tape cannot be compatible, improves the interfacial bonding force and bonding stability, simplifies the production process, and adapts to the harsh use requirements in multiple fields.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant double-sided adhesive technology, specifically to a highly transparent flame-retardant double-sided adhesive with substrate activation treatment and its preparation method. Background Technology

[0002] With the increasing precision of consumer electronics, the safety upgrade of the new energy industry, and the growing demands for both optical and fire-resistant performance in building decoration and LED lighting, PET double-sided tape has become a core adhesive material in these fields due to its excellent dimensional stability, mechanical properties, and weather resistance. At the same time, the industry has put forward stringent requirements for it to have high light transmittance, high flame retardancy, and high bonding reliability in synergy, and existing technologies have always struggled to overcome the performance contradictions among these three aspects.

[0003] Currently, the technical approaches to achieving flame retardant functionality in PET double-sided adhesive tape mainly fall into two categories. One approach involves adding flame retardants to the PET substrate to achieve overall flame retardancy. However, this method is prone to agglomeration due to uneven dispersion of the flame retardant in the substrate resin. This not only damages the optical uniformity of the substrate, causing defects such as decreased light transmittance, increased haze, and whitening, but also degrades the mechanical properties of the substrate. Furthermore, it requires additional processes such as high-shear dispersion and multi-stage filtration, significantly increasing production difficulty and manufacturing costs, making it difficult to consistently guarantee product yield. Secondly, flame retardant components are introduced into the pressure-sensitive adhesive layer. In this approach, traditional flame retardants have poor compatibility with the acrylic pressure-sensitive adhesive matrix. During storage and use, flame retardant precipitation and adhesive layer delamination are likely to occur. This not only continuously damages the transparency of the product but also leads to a decrease in adhesive layer peel strength and tack, resulting in insufficient initial tack. The wettability and adhesion compatibility with difficult-to-bond substrates such as PC, mica, and foam are significantly reduced. Furthermore, increasing the amount of flame retardant added to meet flame retardant requirements will further exacerbate the deterioration of optical and adhesive properties, creating a vicious cycle of performance degradation.

[0004] In addition, existing technologies generally overlook the core issue of the low surface energy of the PET substrate itself, resulting in insufficient interfacial bonding between the substrate and the pressure-sensitive adhesive layer. Under complex working conditions such as humid heat aging and high and low temperature cycling, interfacial debonding is very likely to occur, and the bonding stability is difficult to meet the requirements for long-term use. At present, there is no mature solution to simultaneously solve the industry pain point of synergistic optimization of interfacial bonding, optical transparency and flame retardant performance through substrate surface activation modification. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a highly transparent flame-retardant double-sided adhesive with substrate activation treatment and its preparation method.

[0006] (II) Technical Solution A highly transparent flame-retardant double-sided adhesive with substrate activation treatment includes a first release film layer, a first flame-retardant acrylate pressure-sensitive adhesive layer, a surface-activated modified PET substrate layer, a second flame-retardant acrylate pressure-sensitive adhesive layer, and a second release film layer stacked sequentially. The surface-activated modified PET substrate layer is a PET substrate treated with plasma activation, with a water contact angle of 35°~45° and a surface roughness Ra of 2nm~8nm. The first and second flame-retardant acrylate pressure-sensitive adhesive layers are the same halogen-free flame-retardant pressure-sensitive adhesive layers, comprising the following components by mass: 80~95 parts of acrylate prepolymer, 3~15 parts of halogen-free flame retardant, 0.1~2 parts of crosslinking agent, 0.05~1 part of initiator, and 0.1~1 part of leveling agent. The halogen-free flame retardant is a phosphorus-nitrogen transparent flame retardant with a refractive index difference of ≤0.02 from that of the acrylate prepolymer and a particle size of 50nm~200nm.

[0007] Preferably, the thickness of the surface-activated modified PET substrate layer is 12μm~100μm, and the plasma activation treatment is atmospheric pressure air plasma treatment with a processing power of 800W~2000W and a processing speed of 5m / min~20m / min.

[0008] Preferably, the halogen-free flame retardant is one or more of phosphate ester flame retardants, phosphonate flame retardants, and melamine cyanurate flame retardants, and the dispersion of the flame retardant in the acrylate prepolymer is ≥98%.

[0009] Preferably, the acrylate prepolymer is prepared by free radical prepolymerization of soft monomers, hard monomers and functional monomers, wherein the soft monomers are one or two of butyl acrylate and isooctyl acrylate, accounting for 70% to 85% of the total mass of the prepolymer; the hard monomers are one or two of methyl methacrylate and styrene, accounting for 10% to 25% of the total mass of the prepolymer; and the functional monomers are one or more of acrylic acid, hydroxyethyl acrylate and glycidyl methacrylate, accounting for 2% to 8% of the total mass of the prepolymer.

[0010] Preferably, the dry adhesive thickness of both the first flame-retardant acrylate pressure-sensitive adhesive layer and the second flame-retardant acrylate pressure-sensitive adhesive layer is 5μm~50μm, and the thickness deviation between the two adhesive layers is ≤±0.5μm.

[0011] Preferably, both the first release film layer and the second release film layer are single-sided PET release films with a release force of 3g / in to 15g / in, a visible light transmittance of ≥92%, and a thickness of 25μm to 75μm.

[0012] Preferably, the preparation method of the highly transparent flame-retardant double-sided adhesive with substrate activation treatment includes the following steps: S1 Substrate Activation Treatment: Take a PET substrate and perform plasma activation treatment on its upper and lower surfaces to obtain a surface-activated modified PET substrate layer; Preparation of S2 flame retardant pressure-sensitive adhesive: Weigh the acrylate prepolymer, halogen-free flame retardant, crosslinking agent, initiator and leveling agent according to the formula, mix them and stir at high speed for 30 min to 60 min at room temperature. The stirring speed is 1500 rpm to 3000 rpm. After vacuum degassing, the flame retardant pressure-sensitive adhesive is obtained. S3 Coating and Curing: The flame-retardant pressure-sensitive adhesive liquid prepared in S2 is uniformly coated on the release surfaces of the first release film layer and the second release film layer, respectively. After being cured in sections in an oven, the first flame-retardant acrylic pressure-sensitive adhesive layer and the second flame-retardant acrylic pressure-sensitive adhesive layer with release film are obtained respectively. S4 Composite Winding: The first flame-retardant acrylic pressure-sensitive adhesive layer and the second flame-retardant acrylic pressure-sensitive adhesive layer obtained in S3 are respectively laminated to the upper and lower surfaces of the surface-activated modified PET substrate layer obtained in S1. After curing and slitting, the high-transparency flame-retardant double-sided adhesive with substrate activation treatment is obtained.

[0013] Preferably, the specific parameters of the plasma activation treatment in S1 are: treatment power of 800W~2000W, treatment atmosphere of normal pressure air, distance between electrode and substrate surface of 2mm~5mm, number of single-sided treatments of 1~3 times, and water contact angle of substrate surface stabilized at 35°~45° after treatment.

[0014] Preferably, the temperature of the oven segmented curing in S3 is divided into four segments: 60℃~80℃, 90℃~110℃, 110℃~120℃, and 90℃~100℃, with a total curing time of 1min~3min.

[0015] Preferably, the curing temperature in S4 is 40℃~60℃, the curing time is 24h~72h, the compounding pressure in the compounding process is 0.2MPa~0.5MPa, and the compounding speed is 10m / min~30m / min.

[0016] (iii) Beneficial technical effects Compared with existing technologies, the beneficial effects of this invention are: By performing surface activation modification on the PET substrate, the surface energy of the substrate is effectively improved, and the interfacial wettability and adhesion between the substrate and the flame-retardant pressure-sensitive adhesive layers on both sides are significantly improved. This fundamentally avoids the problem of interface debonding during product use and significantly improves the bonding stability and aging resistance of the product under complex working conditions. At the same time, this modification treatment does not damage the optical uniformity of the PET substrate itself and does not introduce additional optical defects, providing a solid foundation for the high transparency of the product.

[0017] By optimizing the flame-retardant pressure-sensitive adhesive system and selecting a halogen-free flame retardant that matches the refractive index of the pressure-sensitive adhesive matrix, the industry pain point of poor compatibility between traditional flame retardants and acrylic pressure-sensitive adhesives has been solved. This effectively avoids problems such as flame retardant aggregation, precipitation, and adhesive layer delamination. Excellent flame-retardant protection effect is achieved without compromising the transparency of the adhesive layer. At the same time, the adhesive performance of the adhesive layer is not sacrificed due to the introduction of flame-retardant components, thus achieving a synergistic balance between flame-retardant performance and optical and adhesive performance.

[0018] This invention eliminates the need to add flame-retardant components to the PET substrate, avoiding a series of defects caused by uneven dispersion of flame retardants in the substrate. It greatly simplifies the production process, eliminates the need for additional complex dispersion and filtration processes, reduces production difficulty and manufacturing costs, and provides excellent uniformity of adhesive coating, good batch stability of products, and excellent adhesion compatibility to a variety of difficult-to-bond substrates. It achieves an excellent balance between initial tack and holding power. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method for preparing highly transparent flame-retardant double-sided adhesive with substrate activation treatment disclosed in this invention; Figure 2 This is a bar and line graph comparing the core performance of the embodiments and comparative examples; Figure 3 This is a line graph comparing the weathering stability performance of the examples and the comparative examples; Figure 4 This is a radar chart showing the combined performance of the embodiments and comparative examples. Detailed Implementation

[0020] according to Figures 1 to 4 The specific embodiments of the present invention are as follows: The high-transparency flame-retardant double-sided adhesive of the present invention has a five-layer symmetrical layered structure, consisting of a first release film layer, a first flame-retardant acrylic pressure-sensitive adhesive layer, a surface-activated modified PET substrate layer, a second flame-retardant acrylic pressure-sensitive adhesive layer, and a second release film layer from top to bottom. The first flame-retardant acrylic pressure-sensitive adhesive layer and the second flame-retardant acrylic pressure-sensitive adhesive layer use the exact same formula and preparation process, ensuring that the double-sided adhesive performance is completely consistent and avoiding the problem of uneven double-sided performance, thus adapting to the symmetrical bonding requirements of different scenarios.

[0021] The following is a complete and detailed explanation of the technical details of each layer of the product: First, the surface-activated modified PET substrate layer serves as the supporting core layer for the double-sided adhesive. Optical-grade PET substrate is selected, with a visible light transmittance ≥93% and haze ≤0.5%. The thickness can be adjusted within the range of 12μm~100μm depending on the application scenario; commonly available thicknesses are 12μm, 25μm, 50μm, 75μm, and 100μm. In this invention, both the upper and lower surfaces of the PET substrate undergo atmospheric pressure air plasma activation treatment. The treatment process uses a continuous roller-to-roll plasma treatment device, suitable for large-scale industrial production. The processing power is controlled at 800W~2000W, the processing speed at 5m / min~20m / min, the distance between the electrode and the substrate surface is controlled at 2mm~5mm, and the number of treatments per side is 1~3. Through the above parameter adjustment, the water contact angle of the treated PET substrate surface is stabilized at 35°~45°, and the surface roughness Ra is controlled at 2nm~8nm. This activation process involves bombarding the substrate surface with plasma to introduce polar active groups such as hydroxyl and carboxyl groups into the PET molecular chain, significantly increasing the surface energy of the substrate. At the same time, it does not etch or damage the optical flatness of the substrate. This solves the problems of low surface energy and weak interfacial bonding between traditional PET substrates and pressure-sensitive adhesives, and completely avoids negative impacts on the optical performance of the substrate, ensuring the high light transmittance of the product from the core layer.

[0022] Second, the flame-retardant acrylic pressure-sensitive adhesive layer, namely the first and second flame-retardant acrylic pressure-sensitive adhesive layers, has a dry adhesive thickness of 5μm to 50μm. This thickness can be adjusted synchronously according to bonding requirements, and the coating thickness deviation between the two layers is strictly controlled within ±0.5μm to ensure consistent double-sided adhesion performance. This pressure-sensitive adhesive layer is a halogen-free flame-retardant acrylic pressure-sensitive adhesive. By weight, the core formulation components are: 80-95 parts acrylic prepolymer, 3-15 parts halogen-free flame retardant, 0.1-2 parts crosslinking agent, 0.05-1 part initiator, and 0.1-1 part leveling agent. The selection and function of each component are explained in detail below: The acrylate prepolymer is prepared by free radical prepolymerization of soft monomers, hard monomers, and functional monomers, with a solid content controlled at 30%–50% and a rotational viscosity of 3000–8000 mPa·s at 25°C, suitable for coating process requirements. The soft monomers are one or a combination of butyl acrylate and isooctyl acrylate, accounting for 70%–85% of the total prepolymer mass, and are used to impart excellent flexibility and initial tack to the adhesive layer. The hard monomers are one or a combination of methyl methacrylate and styrene, accounting for 10%–25% of the total prepolymer mass, and are used to improve the cohesive strength and holding power of the adhesive layer. The functional monomers are one or a combination of acrylic acid, hydroxyethyl acrylate, and glycidyl methacrylate, accounting for 2%–8% of the total prepolymer mass, and are used to provide crosslinking reaction sites, while simultaneously improving the wettability and adhesion of the adhesive layer to the substrate. The refractive index of the prepolymer at 589 nm visible light is 1.47–1.49, providing a basis for subsequent refractive index matching with flame retardants.

[0023] The halogen-free flame retardant uses a phosphorus-nitrogen-based environmentally friendly transparent flame retardant, specifically one or more of phosphate ester flame retardants, phosphonate flame retardants, and melamine cyanurate flame retardants in combination. This type of flame retardant achieves high-efficiency flame retardancy through the synergistic effect of gas-phase and condensed-phase flame retardancy, resulting in halogen-free and low-smoke performance that meets environmental protection requirements. The flame retardant used in this invention has a refractive index difference of ≤0.02 between the flame retardant and the acrylate prepolymer under 589nm visible light, fundamentally avoiding light scattering problems caused by refractive index differences and ensuring high transparency of the adhesive layer. Simultaneously, the particle size of the flame retardant is strictly controlled within 50nm~200nm, a nanoscale dispersed particle size, enabling uniform dispersion in the acrylate prepolymer with a dispersion degree ≥98%. It does not form agglomerated particles, avoiding optical defects and performance degradation caused by agglomeration of traditional flame retardants. It also solves the problems of poor compatibility and easy precipitation and delamination between the flame retardant and the pressure-sensitive adhesive.

[0024] The crosslinking agent is selected from either isocyanate or epoxy crosslinking agents, used to react with the functional monomers in the prepolymer to construct a three-dimensional network structure, regulate the cohesive force of the adhesive layer, and balance the initial tack and holding power; the initiator is selected from either azo or peroxide initiators, used to initiate the prepolymerization reaction and the curing crosslinking reaction after coating; the leveling agent is selected from either silicone or acrylate leveling agents, used to reduce the surface tension of the adhesive, improve the leveling properties of the adhesive on the release film and substrate surfaces, and ensure uniform adhesive layer thickness without defects such as pinholes and shrinkage cavities.

[0025] Third, both the first and second release film layers are made of single-sided optical-grade PET release film, with an organosilicon release agent coated on the release side. The release force is controlled at 3g / in to 15g / in, which is a light release force design, making it easy to peel off quickly during use without leaving any residue or peeling. The release film itself has a visible light transmittance of ≥92%, a haze of ≤0.8%, and a thickness of 25μm to 75μm. 25μm, 50μm, and 75μm are commonly available. It effectively protects the flame-retardant pressure-sensitive adhesive layer during production and storage, preventing the adhesive layer from being contaminated or damaged.

[0026] The complete preparation method of the double-sided adhesive of the present invention is described in detail below. This method is a continuous industrial-scale roller-to-roll preparation process, which specifically includes the following steps: S1 Substrate Activation Treatment: Select optical-grade PET substrate, unwind it, and pass it through a continuous atmospheric pressure air plasma treatment device to perform plasma activation treatment on the upper and lower surfaces of the substrate. During the treatment, strictly control the equipment parameters: treatment power 800W~2000W, treatment atmosphere is atmospheric pressure air, the distance between the electrode and the substrate surface is 2mm~5mm, the number of single-sided treatments is 1~3 times, and the treatment speed is 5m / min~20m / min. After the treatment, the water contact angle of the substrate surface is detected online to ensure that the contact angle is stable at 35°~45° and the surface roughness Ra is 2nm~8nm, to obtain the surface-activated modified PET substrate layer, which is then wound up for later use. The winding tension is controlled at 3N~8N to avoid stretching deformation of the substrate.

[0027] Preparation of S2 Flame-Retardant Pressure-Sensitive Adhesive Solution: According to the preset formula mass parts, weigh out the acrylate prepolymer, halogen-free flame retardant, crosslinking agent, initiator, and leveling agent in sequence. First, add the acrylate prepolymer to a sealed stirred tank, then add the halogen-free flame retardant. Pre-disperse at room temperature at a speed of 800 rpm to 1000 rpm for 10 min to 15 min, then increase the speed to 1500 rpm to 3000 rpm and stir at high speed for 30 min to 60 min to ensure that the flame retardant is completely and uniformly dispersed in the prepolymer. Then add the crosslinking agent, initiator, and leveling agent in sequence, and continue stirring at a speed of 1500 rpm for 15 min to 20 min to ensure that all components are mixed evenly. After mixing, transfer the solution to a vacuum degassing tank and degas at a vacuum degree of -0.08 MPa to -0.1 MPa for 15 min to 30 min to remove air bubbles from the solution, obtaining the flame-retardant pressure-sensitive adhesive solution. Let it stand for later use. The solid content and viscosity of the solution should be tested in advance to ensure that they meet the coating process requirements.

[0028] S3 Coating and Curing: The flame-retardant pressure-sensitive adhesive liquid prepared in S2 is added to the material tanks of two micro-gravure coating machines, corresponding to the coating processes of the first and second release film layers, respectively. The optical-grade PET release film is unwound so that the release surface faces the coating roller. The adhesive liquid is evenly coated onto the release surface of the release film by micro-gravure coating. The coating thickness is precisely controlled by the rotation speed and line count of the coating roller to ensure that the dry adhesive thickness meets the preset requirements. The coated release film is then passed into a segmented hot air oven for curing. The oven temperature is set in four gradients, starting at 6 degrees Celsius. The curing temperatures range from 0℃ to 80℃, 90℃ to 110℃, 110℃ to 120℃, and 90℃ to 100℃, with a total curing time of 1 min to 3 min. By gradually increasing the temperature, the solvent in the adhesive solution is allowed to evaporate slowly and evenly before the cross-linking curing reaction is initiated. This avoids defects such as pinholes, bubbles, and edge shrinkage in the adhesive layer caused by rapid solvent evaporation. After curing, a first flame-retardant acrylic pressure-sensitive adhesive layer and a second flame-retardant acrylic pressure-sensitive adhesive layer with a release film are obtained. The thickness of the adhesive layers is monitored online to ensure that the thickness deviation between the two adhesive layers is ≤ ±0.5 μm.

[0029] S4 Composite Winding: The surface-activated modified PET substrate layer prepared in S1 is unwound, and the first flame-retardant acrylate pressure-sensitive adhesive layer and the second flame-retardant acrylate pressure-sensitive adhesive layer prepared in S3 are simultaneously unwound. Using a dual-station composite roller, the release liner side of the first flame-retardant acrylate pressure-sensitive adhesive layer is laminated to the upper activated surface of the PET substrate layer, and the release liner side of the second flame-retardant acrylate pressure-sensitive adhesive layer is laminated to the lower activated surface of the PET substrate layer. During the lamination process, the lamination pressure is controlled at 0.2MPa~0.5MPa, and the lamination speed is 10m / min~30m / min to ensure that the lamination interface is free of bubbles and wrinkles. After lamination, the product is wound up and transferred to a constant-temperature curing chamber for curing treatment. The curing temperature is controlled at 40℃~60℃, and the curing time is 24h~72h to ensure complete cross-linking reaction of the adhesive layer and stabilize the adhesive properties and cohesive properties of the adhesive layer. After curing, the product is cut and packaged according to usage requirements to obtain the high-transparency flame-retardant double-sided adhesive product with activated substrate.

[0030] The following are specific embodiments and comparative examples. All embodiments adopt the complete preparation process described above, only adjusting the specific process parameters and formula ratios. All parameters fall within the protection scope of the claims. The comparative examples are existing technical solutions or solutions that exceed the protection scope of this invention, used to form a comparison with the embodiments, clearly demonstrating the feasibility and technical advantages of the technical solution of this invention. Example 1

[0031] The high-transparency flame-retardant double-sided adhesive with substrate activation treatment in this embodiment has a five-layer symmetrical structure. The parameters and formulations of each layer are as follows: The surface-activated modified PET substrate layer uses a 25μm thick optical-grade PET substrate, which undergoes double-sided atmospheric pressure air plasma activation treatment with a treatment power of 1200W, a treatment speed of 10m / min, an electrode spacing of 3mm, and two treatments on one side. After treatment, the water contact angle of the substrate surface is 40°, and the surface roughness Ra is 5nm. The dry adhesive thickness of the first and second flame-retardant acrylic pressure-sensitive adhesive layers is 20μm, and the formulation by mass parts is: 90% acrylic prepolymer. The composition includes 8 parts of halogen-free flame retardant, 0.8 parts of isocyanate crosslinking agent, 0.3 parts of azobisisobutyronitrile initiator, and 0.9 parts of acrylate leveling agent; wherein the acrylate prepolymer is prepared by prepolymerization of 80% isooctyl acrylate, 15% methyl methacrylate, and 5% hydroxyethyl acrylate, with a refractive index of 1.478; the halogen-free flame retardant is bisphenol A bis(diphenyl phosphate), with a refractive index of 1.479, a refractive index difference of 0.001 from the prepolymer, and a particle size of 100nm; the first and second release films are 50μm thick optical-grade PET release films with a release force of 8g / in and a light transmittance of 93%.

[0032] The preparation method is performed according to the aforementioned steps S1-S4, wherein the substrate activation treatment parameters in S1 are the same as those in the above substrate parameters; in S2, the pre-dispersion speed of the adhesive solution is 1000 rpm for 10 min, the high-speed stirring speed is 2000 rpm for 45 min, and the vacuum degassing is performed at a vacuum degree of -0.09 MPa for 20 min; in S3, the oven temperatures for coating and curing are 70℃, 100℃, 115℃, and 95℃ respectively, with a total curing time of 2 min; in S4, the composite winding pressure is 0.3 MPa, the composite speed is 20 m / min, the curing temperature is 50℃, and the curing time is 48 h. Example 2

[0033] The high-transparency flame-retardant double-sided adhesive with substrate activation treatment in this embodiment has the following parameters and formulations for each layer: The surface-activated modified PET substrate layer uses a 12μm thick optical-grade PET substrate, undergoes double-sided atmospheric pressure air plasma activation treatment, with a treatment power of 800W, a treatment speed of 20m / min, an electrode spacing of 5mm, and one treatment per side. After treatment, the substrate surface has a water contact angle of 45° and a surface roughness of Ra2nm; the dry adhesive thickness of the first and second flame-retardant acrylate pressure-sensitive adhesive layers is 5μm, and the formulation by mass parts is: 95 parts acrylate prepolymer, halogen-free... The composition includes 3 parts of flame retardant, 0.1 parts of isocyanate crosslinking agent, 0.05 parts of benzoyl peroxide initiator, and 0.85 parts of silicone leveling agent. The acrylate prepolymer is prepared by prepolymerization of 85% butyl acrylate, 10% methyl methacrylate, and 5% acrylic acid, with a refractive index of 1.472. The halogen-free flame retardant is resorcinol bis(diphenyl phosphate), with a refractive index of 1.474, a difference of 0.002 from the refractive index of the prepolymer, and a particle size of 50 nm. The first and second release films are 25 μm thick optical-grade PET release films with a release force of 3 g / in and a light transmittance of 92.5%.

[0034] The preparation method is performed according to the aforementioned steps S1-S4, wherein the substrate activation treatment parameters in S1 are the same as those in the above substrate parameters; in S2, the pre-dispersion speed of the adhesive solution is 800 rpm for 15 min, the high-speed stirring speed is 1500 rpm for 60 min, and the vacuum degassing is performed at a vacuum degree of -0.08 MPa for 30 min; in S3, the oven temperatures for coating and curing are 60℃, 90℃, 110℃, and 90℃ respectively, with a total curing time of 3 min; in S4, the composite winding pressure is 0.2 MPa, the composite speed is 30 m / min, the curing temperature is 40℃, and the curing time is 72 h. Example 3

[0035] The high-transparency flame-retardant double-sided adhesive with substrate activation treatment in this embodiment has the following parameters and formulations for each layer: The surface-activated modified PET substrate layer uses a 100μm thick optical-grade PET substrate, undergoes double-sided atmospheric pressure air plasma activation treatment, with a treatment power of 2000W, a treatment speed of 5m / min, an electrode spacing of 2mm, and three treatments on one side. After treatment, the substrate surface has a water contact angle of 35° and a surface roughness Ra of 8nm. The dry adhesive thickness of the first and second flame-retardant acrylate pressure-sensitive adhesive layers is 50μm, and the formulation by mass parts is: 80 parts acrylate prepolymer, 1 part halogen-free flame retardant... 5 parts, epoxy crosslinking agent 2 parts, azobisisobutyronitrile initiator 1 part, organosilicon leveling agent 2 parts; wherein the acrylate prepolymer is prepared by prepolymerization of 70% isooctyl acrylate, 25% styrene and 5% glycidyl methacrylate, with a refractive index of 1.488; the halogen-free flame retardant is a compound of aluminum diethylphosphines and melamine cyanurate in a 7:3 ratio, with a refractive index of 1.490 after compounding, the difference in refractive index between the compound and the prepolymer is 0.002, and the particle size is 200nm; the first and second release films are 75μm thick optical grade PET release films, with a release force of 15g / in and a light transmittance of 92%.

[0036] The preparation method is performed according to the aforementioned steps S1-S4, wherein the substrate activation treatment parameters in S1 are the same as those in the above substrate parameters; in S2, the pre-dispersion speed of the adhesive solution is 1000 rpm for 15 min, the high-speed stirring speed is 3000 rpm for 30 min, and the vacuum degassing is performed at a vacuum degree of -0.1 MPa for 15 min; in S3, the oven temperatures for coating and curing are 80℃, 110℃, 120℃, and 100℃ respectively, with a total curing time of 1 min; in S4, the composite winding pressure is 0.5 MPa, the composite speed is 10 m / min, the curing temperature is 60℃, and the curing time is 24 h. Example 4

[0037] The high-transparency flame-retardant double-sided adhesive with substrate activation treatment in this embodiment has the following parameters and formulations for each layer: The surface-activated modified PET substrate layer uses a 50μm thick optical-grade PET substrate, undergoes double-sided atmospheric pressure air plasma activation treatment, with a treatment power of 1500W, a treatment speed of 12m / min, an electrode spacing of 4mm, and two treatments per side. After treatment, the substrate surface has a water contact angle of 38° and a surface roughness Ra of 6nm. The dry adhesive thickness of the first and second flame-retardant acrylic pressure-sensitive adhesive layers is 25μm, and the formulation by mass parts is: 88 parts acrylic prepolymer, 10 parts halogen-free flame retardant, and isocyanate... The composition includes 1.2 parts ester crosslinking agent, 0.4 parts azobisisobutyronitrile initiator, and 0.4 parts acrylate leveling agent; the acrylate prepolymer is prepared by prepolymerization of 75% butyl acrylate, 20% methyl methacrylate, and 5% hydroxyethyl acrylate, with a refractive index of 1.475; the halogen-free flame retardant is a compound of bisphenol A bis(diphenyl phosphate) and melamine cyanurate in an 8:2 ratio, with a refractive index of 1.476 after compounding, a difference of 0.001 from the refractive index of the prepolymer, and a particle size of 150 nm; the first and second release films are 50 μm thick optical-grade PET release films with a release force of 10 g / in and a light transmittance of 93%.

[0038] The preparation method is performed according to the aforementioned steps S1-S4, wherein the substrate activation treatment parameters in S1 are the same as those in the above substrate parameters; the pre-dispersion speed of the adhesive preparation in S2 is 900 rpm for 12 min, the high-speed stirring speed is 2500 rpm for 40 min, and the vacuum degassing is performed at a vacuum degree of -0.095 MPa for 25 min; the oven temperatures for coating and curing in S3 are 75℃, 105℃, 118℃ and 98℃ respectively, with a total curing time of 1.5 min; the composite winding in S4 has a composite pressure of 0.35 MPa, a composite speed of 18 m / min, a curing temperature of 55℃ and a curing time of 36 h.

[0039] Comparative Example 1 The only difference between this comparative example and Example 1 is that the PET substrate was not subjected to any plasma activation treatment; the rest of the formulation, structural parameters, and preparation process are completely consistent with Example 1.

[0040] Comparative Example 2 The only difference between this comparative example and Example 1 is that the halogen-free flame retardant used is a traditional micron-sized magnesium hydroxide flame retardant with a particle size of 5 μm and a refractive index difference of 0.18 with that of the acrylate prepolymer. All other formulations, structural parameters, and preparation processes are completely consistent with Example 1.

[0041] Comparative Example 3 This comparative example represents a prior art method for adding flame retardants to the substrate. Specifically, 10% of a brominated flame retardant is added during the preparation of the PET substrate to produce a flame-retardant PET substrate with a thickness of 25 μm. No plasma activation treatment is performed. The pressure-sensitive adhesive layer is a common acrylic pressure-sensitive adhesive without added flame retardants. All other structural parameters and preparation processes are consistent with those in Example 1.

[0042] Comparative Example 4 The only difference between this comparative example and Example 1 is that the amount of halogen-free flame retardant added is 20 parts; the rest of the formulation, structural parameters, and preparation process are completely consistent with Example 1.

[0043] The optical and flame-retardant properties of the examples and comparative examples are compared in the table below: Table 1 The following table compares the bonding performance and stability of the examples and comparative examples: Table 2 As can be seen from the above two sets of performance test results, the high-transparency flame-retardant double-sided adhesive prepared by the substrate activation treatment in each embodiment of the present invention achieves a synergistic balance of optical performance, flame-retardant performance, adhesive performance and weather resistance stability, and its comprehensive performance is superior to the existing technical solutions and comparative examples whose parameters deviate from the protection scope of the present invention.

[0044] In terms of optical and flame retardant performance, all embodiments met the highest flame retardant standard of UL94 V-0, while the visible light transmittance remained stable above 90%, the haze was controlled within 1.5%, and the appearance was colorless and highly transparent, without defects such as agglomerated particles, whitening, or crystal points. This completely solved the core pain point of traditional flame-retardant double-sided tape, which is that "flame retardancy and high transparency are incompatible." However, Comparative Example 2 suffered from a significant decrease in transmittance to 62.5% and complete devitrification due to the mismatch between the refractive index of the flame retardant and the pressure-sensitive adhesive matrix and the excessively large particle size. Comparative Example 3 adopted the existing technical solution of adding flame retardant to the substrate, which not only achieved a flame retardant rating of only V-1, but also showed problems such as decreased transmittance and whitening. Comparative Example 4 also showed defects such as increased haze and deteriorated optical performance due to the excessive amount of flame retardant added.

[0045] Regarding adhesion and stability, the products of this invention exhibit a 180° peel force ≥17N / 25mm, a ball initial tack ≥13#, and a holding power exceeding 48h under a 1kg load. After 72h of humid heat aging at 85℃ / 85%RH, the peel force retention rate is above 93%. No abnormalities such as debonding, blistering, or delamination are observed after high and low temperature cycling. The substrate activation modification significantly improves the interfacial bonding force between the substrate and the adhesive layer, ensuring the long-term stability of the product under complex working conditions. In contrast, Comparative Example 1, which did not undergo substrate activation treatment, showed a significant decrease in peel force, initial tack, and holding power. After aging, localized debonding and edge lifting occurred at the interface. Comparative Example 2 showed a significant deterioration in adhesion and aging resistance due to the agglomeration and precipitation of flame retardant. Comparative Example 4 also experienced a decrease in adhesive layer cohesion and a deterioration in weather resistance due to excessive addition of flame retardant.

[0046] Overall, this invention overcomes the technical bottleneck of the inability to achieve high transparency, high flame retardancy, and high adhesion performance in the prior art through substrate activation modification and halogen-free flame retardant system optimization with refractive index matching. The product has excellent comprehensive performance and can fully meet the stringent requirements for double-sided tape in fields such as precision electronics, new energy, and building decoration.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-transparency flame-retardant double-sided adhesive with a substrate activated by treatment, characterized in that, The material comprises, in sequence, a first release film layer, a first flame-retardant acrylate pressure-sensitive adhesive layer, a surface-activated modified PET substrate layer, a second flame-retardant acrylate pressure-sensitive adhesive layer, and a second release film layer; the surface-activated modified PET substrate layer is a PET substrate treated with plasma activation, with a water contact angle of 35°~45° and a surface roughness Ra of 2nm~8nm; the first and second flame-retardant acrylate pressure-sensitive adhesive layers are identical halogen-free flame-retardant pressure-sensitive adhesive layers, comprising, by mass parts: 80~95 parts of acrylate prepolymer, 3~15 parts of halogen-free flame retardant, 0.1~2 parts of crosslinking agent, 0.05~1 part of initiator, and 0.1~1 part of leveling agent; the halogen-free flame retardant is a phosphorus-nitrogen transparent flame retardant with a refractive index difference ≤0.02 from that of the acrylate prepolymer and a particle size of 50nm~200nm.

2. The high-transparency flame-retardant double-sided adhesive with substrate activation treatment according to claim 1, characterized in that, The thickness of the surface-activated modified PET substrate layer is 12μm~100μm, and the plasma activation treatment is atmospheric pressure air plasma treatment with a processing power of 800W~2000W and a processing speed of 5m / min~20m / min.

3. The high-transparency flame-retardant double-sided adhesive with substrate activation treatment according to claim 1, characterized in that, The halogen-free flame retardant is one or more of the following: phosphate ester flame retardant, phosphonate flame retardant, and melamine cyanurate flame retardant, and the dispersion of the flame retardant in the acrylate prepolymer is ≥98%.

4. The high-transparency flame-retardant double-sided adhesive with substrate activation treatment according to claim 1, characterized in that, The acrylate prepolymer is prepared by free radical prepolymerization of soft monomers, hard monomers and functional monomers, wherein the soft monomers are one or two of butyl acrylate and isooctyl acrylate, accounting for 70% to 85% of the total mass of the prepolymer; the hard monomers are one or two of methyl methacrylate and styrene, accounting for 10% to 25% of the total mass of the prepolymer; and the functional monomers are one or more of acrylic acid, hydroxyethyl acrylate and glycidyl methacrylate, accounting for 2% to 8% of the total mass of the prepolymer.

5. The high-transparency flame-retardant double-sided adhesive with substrate activation treatment according to claim 1, characterized in that, The dry adhesive thickness of both the first flame-retardant acrylic pressure-sensitive adhesive layer and the second flame-retardant acrylic pressure-sensitive adhesive layer is 5μm~50μm, and the thickness deviation between the two adhesive layers is ≤±0.5μm.

6. The high-transparency flame-retardant double-sided adhesive with substrate activation treatment according to claim 1, characterized in that, Both the first and second release film layers are single-sided PET release films with release force of 3g / in to 15g / in, visible light transmittance ≥92%, and thickness of 25μm to 75μm.

7. A method for preparing a highly transparent flame-retardant double-sided adhesive with a substrate activated as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1 Substrate Activation Treatment: Take a PET substrate and perform plasma activation treatment on its upper and lower surfaces to obtain a surface-activated modified PET substrate layer; Preparation of S2 flame retardant pressure-sensitive adhesive: Weigh the acrylate prepolymer, halogen-free flame retardant, crosslinking agent, initiator and leveling agent according to the formula, mix them and stir at high speed for 30 min to 60 min at room temperature. The stirring speed is 1500 rpm to 3000 rpm. After vacuum degassing, the flame retardant pressure-sensitive adhesive is obtained. S3 Coating and Curing: The flame-retardant pressure-sensitive adhesive liquid prepared in S2 is uniformly coated on the release surfaces of the first release film layer and the second release film layer, respectively. After being cured in sections in an oven, the first flame-retardant acrylic pressure-sensitive adhesive layer and the second flame-retardant acrylic pressure-sensitive adhesive layer with release film are obtained respectively. S4 Composite Winding: The first flame-retardant acrylic pressure-sensitive adhesive layer and the second flame-retardant acrylic pressure-sensitive adhesive layer obtained in S3 are respectively laminated to the upper and lower surfaces of the surface-activated modified PET substrate layer obtained in S1. After curing and slitting, the high-transparency flame-retardant double-sided adhesive with substrate activation treatment is obtained.

8. The method for preparing the highly transparent flame-retardant double-sided adhesive with substrate activation treatment according to claim 7, characterized in that, The specific parameters of the plasma activation treatment described in S1 are as follows: treatment power of 800W~2000W, treatment atmosphere of normal pressure air, distance between electrode and substrate surface of 2mm~5mm, number of single-sided treatments of 1~3 times, and water contact angle of substrate surface stabilized at 35°~45° after treatment.

9. The method for preparing the highly transparent flame-retardant double-sided adhesive with substrate activation treatment according to claim 7, characterized in that, The oven curing temperature described in S3 is divided into four segments: 60℃~80℃, 90℃~110℃, 110℃~120℃, and 90℃~100℃, with a total curing time of 1min~3min.

10. The method for preparing the highly transparent flame-retardant double-sided adhesive with substrate activation treatment according to claim 7, characterized in that, The curing temperature in S4 is 40℃~60℃, and the curing time is 24h~72h; the compounding pressure in the compounding process is 0.2MPa~0.5MPa, and the compounding speed is 10m / min~30m / min.

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