A low-swell high-viscosity retention rate acrylate terminated adhesive and a preparation method thereof

Abstract

This invention relates to the field of adhesive preparation, specifically to an acrylate terminating adhesive with low swelling and high viscosity retention, and its preparation method. The terminating adhesive comprises, by mass percentage: 20-30% prepolymer, 70-85% composite acrylate diluent monomer, 0.5-2% electrolyte-resistant reinforcing filler, 1-5% additives, and 1-5% composite photoinitiator. The composite diluent monomer is a blend of soft, hard, crosslinked, and low surface energy monomers in a ratio of 75-82:10-18:3-7:1-3. The reinforcing filler is 20-50nm hydroxyethyl acrylate grafted modified boehmite nanoparticles. The photoinitiator is a blend of halogen-free pyrolysis type and hydrogen-abstracting type in a ratio of 1:1-3:2. This invention effectively reduces the surface energy of the adhesive layer, improves electrolyte barrier performance, improves the compatibility between filler and resin matrix, optimizes the uniformity of adhesive layer curing and crosslinking, reduces the swelling rate after electrolyte immersion, improves viscosity retention, eliminates adhesive overflow issues, and meets the long-term service requirements for termination protection of power lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and more particularly to an acrylic terminating adhesive with low swelling and high viscosity retention and its preparation method. Background Technology

[0002] In recent years, the installed capacity of new energy power and energy storage lithium batteries has continued to climb. With the advantages of high energy density and excellent safety performance, the application ratio of soft-pack lithium batteries in the power and energy storage fields has been increasing year by year, which puts forward higher requirements for the halogen-free environmental protection, electrolyte corrosion resistance, and long-term service adhesion stability of the matching termination adhesive.

[0003] The first mainstream existing technology is a solvent-based acrylic pressure-sensitive adhesive used to prepare the terminating adhesive. It uses linear acrylic copolymers as the main component, combined with multifunctional isocyanate crosslinking agents, and is thermosetting into an adhesive. The production process is mature, and the initial bond strength is high, making it widely used in consumer electronics lithium batteries. However, the crosslinking density of this type of adhesive is generally low, and it lacks electrolyte resistance modification. After immersion in 85℃ carbonate electrolyte for 24 hours, the volume swelling rate generally exceeds 3%, and the aluminum foil peel strength retention rate is less than 70%. During service, it is prone to delamination and adhesive overflow, making it unsuitable for the long-term high-temperature service requirements of power lithium batteries. Furthermore, some products add halogenated flame retardants to meet flame retardant requirements, which does not comply with the halogen-free requirements of global environmental regulations such as EU RoHS.

[0004] The second mainstream existing technology is a UV-curable acrylate terminator, which uses acrylate prepolymers combined with reactive diluent monomers and cured by UV curing. This method has high production efficiency and no organic solvent emissions. Some modified formulations add unmodified nano-boehmite to improve the rigidity and electrolyte resistance of the adhesive layer. However, this type of formulation does not perform functional compounding of the diluent monomers, resulting in a high surface energy of the adhesive layer. This allows electrolyte to easily penetrate into the adhesive layer, causing swelling. The unmodified boehmite has poor interfacial compatibility with the acrylate matrix, which can easily lead to filler agglomeration and insufficient adhesive layer density. In addition, it often uses a single-component photoinitiator, resulting in insufficient UV curing and uneven cross-linking distribution of the adhesive layer. This further aggravates the swelling and viscosity decay problems after electrolyte immersion. The long-term viscosity retention rate under halogen-free systems is still difficult to meet the standards for use in power lithium batteries.

[0005] Existing terminator adhesives cannot simultaneously meet the multiple requirements of halogen-free environmental protection, low swelling, and high viscosity retention. There is a significant technical gap in dedicated terminator adhesive products suitable for the service scenarios of power lithium batteries, and there is an urgent need to develop corresponding technical solutions to fill the application gap. Summary of the Invention

[0006] To address the shortcomings of existing acrylate stop adhesives, such as poor electrolyte resistance, high swelling rate, low viscosity retention, and inability to meet halogen-free environmental protection requirements, this invention provides an acrylate stop adhesive with low swelling and high viscosity retention, as well as its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A halogen-free acrylate terminating adhesive with low swelling and high viscosity retention comprises the following raw material components by weight percentage: Prepolymer 20-30%, composite acrylate diluted monomer 70-85%, electrolyte-resistant reinforcing filler 0.5-2%, additives 1-5%, composite photoinitiator 1-5%; The composite acrylate diluent monomer is obtained by compounding soft monomers, hard monomers, crosslinking monomers and low surface energy functional monomers in a mass ratio of 75-82:10-18:3-7:1-3. The soft monomer is selected from at least one of isooctyl acrylate and butyl acrylate, and has a glass transition temperature of -70°C to -50°C. The hard monomer is selected from at least one of methyl methacrylate and isobornyl methacrylate, and has a glass transition temperature of 80°C to 150°C; the crosslinking monomer is selected from at least one of trimethylolpropane triacrylate and pentaerythritol tetraacrylate. The low surface energy functional monomer is selected from at least one of isobornyl oxyethyl acrylate and isodecyl methacrylate, and has a glass transition temperature of -60°C to -30°C. The electrolyte-resistant reinforcing filler is nano-boehmite with a surface grafted with hydroxyethyl acrylate and a particle size of 20-50 nm. The composite photoinitiator is obtained by compounding a halogen-free pyrolysis photoinitiator and a halogen-free hydrogen abstraction photoinitiator in a mass ratio of 1:1 to 3:2. The maximum absorption wavelength of the pyrolysis photoinitiator is 250-360 nm, and the maximum absorption wavelength of the hydrogen abstraction photoinitiator is 350-420 nm.

[0008] Preferably, the prepolymer is selected from one or a mixture of two of acrylate prepolymers and epoxy acrylate prepolymers. The acrylate prepolymer has a weight-average molecular weight of 10,000-30,000, a molecular weight distribution coefficient of 1.2-1.8, a double bond functionality of 2-3, and a rotational viscosity of 5,000-15,000 mPa·s at 60°C. The epoxy acrylate prepolymer is a bisphenol A type epoxy acrylate or a phenolic type epoxy acrylate, with a functionality of 2-3, an acid value ≤5 mgKOH / g, and a rotational viscosity of 8,000-20,000 mPa·s at 60°C.

[0009] Preferably, the surface grafting modification of the nanoboehmite is achieved in the following manner: nanoboehmite is dispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 10-15%, γ-methacryloyloxypropyltrimethoxysilane is added at a mass of 2-5% of the total mass of the suspension, the pH value is adjusted to 4-5, and the mixture is stirred and reacted at 60-70°C for 3-4 hours. Then, hydroxyethyl acrylate at a mass of 3-6% of the total mass of the suspension is added, and the reaction is continued for 2-3 hours. After centrifugation and washing, the nanoboehmite is obtained by vacuum drying.

[0010] Preferably, the additives comprise, by mass percentage, 1-3% pigment, 0.1-0.5% chain transfer agent, 0.5-1.5% adhesion promoter, and 0.05-0.2% polymerization inhibitor; the pigment is selected from at least one of green azo pigment and blue phthalocyanine pigment, with an average particle size ≤100nm; the chain transfer agent is dodecyl mercaptan or isooctyl mercaptoacetate; the adhesion promoter is γ-methacryloyloxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane; and the polymerization inhibitor is hydroquinone monomethyl ether or 2,6-di-tert-butyl-p-cresol.

[0011] Preferably, the pyrolytic photoinitiator is selected from at least one of 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and the hydrogen-abstracting photoinitiator is selected from at least one of isopropylthioxanthone and benzophenone; when the prepolymer is an acrylate prepolymer, the mass ratio of the pyrolytic photoinitiator to the hydrogen-abstracting photoinitiator is 1:1 to 3:2, and when the prepolymer is an epoxy acrylate prepolymer, the mass ratio of the pyrolytic photoinitiator to the hydrogen-abstracting photoinitiator is 3:2.

[0012] Preferably, the adhesive comprises a substrate layer, an adhesive layer, and a release film layer sequentially bonded together. The adhesive layer is prepared by UV curing the halogen-free acrylate terminating adhesive according to any one of claims 1-5. The adhesive layer has a thickness of 5-30 μm and a crosslinking density of 2.5 × 10⁻⁶ after curing. -3 -4.0×10 -3 mol / cm 3 The gelation rate is ≥95%, the contact angle is ≥105°, the volume swelling rate after soaking in 85℃ carbonate electrolyte for 24h is ≤0.5%, and the aluminum foil peel strength retention rate is ≥92%.

[0013] Preferably, the substrate layer is selected from any one of PET, BOPP, and PI, and the thickness of the substrate layer is 5-25μm; the corona-treated surface of the substrate layer is treated with plasma at a power of 800-1200W and a speed of 10-20m / min. When the substrate layer is PET or PI, the dyn value after treatment is ≥48dyn; when the substrate layer is BOPP, the dyn value after treatment is >38dyn; the non-corona-treated surface of the substrate layer is coated with a non-silicone release agent, the dry film thickness is 0.1-0.5μm, the surface dyn value is <30dyn, and the release force is 5-20gf / 25mm.

[0014] Preferably, the release film layer is a PET silicone release film with a thickness of 19-150μm. The release layer is prepared using addition-type siloxane, and after curing, the degree of crosslinking is ≥90%, the release force is 3-300gf / 25mm, the residual adhesion is ≥90%, and the release force change rate after aging at 70℃ for 72h after bonding with the adhesive layer is ≤10%.

[0015] Preferably, it includes the following steps: S1. Premixing the adhesive: Weigh the prepolymer and the diluted monomer of the composite acrylate according to the ratio, heat to 40-50℃ under light-protected conditions, stir at 300-500 rpm for 10-20 min until the prepolymer is completely dissolved, then add the electrolyte-resistant reinforcing filler, disperse at 800-1200 rpm for 20-30 min, and then mill at 1500-2000 rpm for 1-2 h until the filler particle size is ≤100nm to obtain the premix. Place the obtained premix under a negative pressure environment with a vacuum degree of -0.09MPa to -0.1MPa and slowly stir at 200-400 rpm for 20-40 min to degas, to obtain the degassed premix, for later use; S2. Additive compounding: Add the additives and composite photoinitiator to the degassing premix in sequence. Stir at 300-500 rpm for 30-60 minutes under light-protected conditions and at 25-30℃. After mixing evenly, filter through a 5-10μm precision filter to obtain a uniform coating adhesive. S3. Substrate pretreatment: The corona-treated surface of the substrate layer is subjected to online plasma treatment, with the treatment power controlled at 800-1200W and the treatment speed at 10-20m / min. After the dyne value meets the requirements, it is ready for use. The non-corona-treated surface is pre-coated and cured with a non-silicone release agent. S4. Coating and Lamination: The adhesive is applied to the corona surface of the substrate layer using a micro-gravure coating process. The wet film thickness is controlled by adjusting the micro-gravure roller line count and speed to achieve a dry film thickness of 5-30μm. The release surface of the release film layer is then laminated under a pressure of 0.2-0.3MPa. S5. UV Curing: The bonded materials are cured in stages using a medium-pressure mercury lamp UV light source or an LED UV light source. The curing energy for the first stage is 150-250 mJ / cm².2 The curing time is 10-20 seconds, allowing the adhesive layer to initially gel and set. The second stage of curing energy is 100-200 mJ / cm². 2 The curing time is 20-30 seconds, which allows the adhesive layer to fully cross-link. S6. Post-treatment: After curing, the material is left to stand for 24-48 hours at 23±2℃ and 50±5%RH to eliminate substrate stress. Then, the release film layer is peeled off by controlling the peeling angle to 180° and the peeling speed to 5-10m / min. The halogen-free acrylate termination tape is then rolled up to obtain the finished product.

[0016] Preferably, when using an LED UV light source, a dual-wavelength combination of 365nm and 395nm is adopted, with a power ratio of 2:1 between the two wavelengths and an illumination distance of 10-15cm; when using a medium-pressure mercury lamp UV light source, the main emission wavelength is 365nm, the power density is 80-120W / cm, and the illumination distance is 15-20cm; during the curing process, the surface temperature of the adhesive layer is controlled at 40-60℃; the winding tension is 8-15N / m, the winding unevenness is ≤±0.5mm, and after the finished tape is aged in an environment of 85℃ and 85%RH for 72h, there is no overflow or migration of adhesive layer.

[0017] The present invention has the following beneficial effects: This invention prepares a composite acrylate diluent monomer by compounding soft monomers, hard monomers, crosslinking monomers, and low surface energy functional monomers in a specific ratio. By matching the appropriate glass transition temperature range of each component, the flexibility, crosslinking density, and surface hydrophobic and oleophobic properties of the adhesive layer are synergistically controlled. This effectively solves the problems of high surface energy of the adhesive layer, easy penetration of electrolyte into the interior causing excessive swelling, and rapid viscosity decay during service in the prior art. The halogen-free design of all components complies with the requirements of various mainstream environmental protection regulations.

[0018] This invention uses nano-boehmite with a surface grafted with hydroxyethyl acrylate as an electrolyte-resistant reinforcing filler. The grafted active groups can form chemical bonds with the acrylate matrix, improving the interfacial compatibility between the filler and the resin matrix, preventing filler agglomeration, and further enhancing the density and electrolyte barrier properties of the adhesive layer. This effectively solves the problems of poor compatibility between unmodified nanofillers and the matrix, easy agglomeration leading to insufficient adhesive layer density, and poor resistance to electrolyte erosion in the prior art.

[0019] This invention uses a composite photoinitiator obtained by combining halogen-free pyrolysis type and hydrogen abstraction type photoinitiators with different absorption wavelengths. Combined with a segmented UV curing process, it achieves full and uniform cross-linking of the adhesive layer from the surface to the inside, improves the overall cross-linking density and gel rate of the adhesive layer, and effectively solves the problem of poor long-term service stability of the adhesive layer caused by insufficient curing and uneven cross-linking distribution of a single photoinitiator in the prior art.

[0020] The terminating adhesive and corresponding terminating tape prepared by this invention are compatible with a variety of commonly used substrates and can be widely used in scenarios such as tab fixing and edge sealing of different types of soft-pack lithium batteries. They are suitable for the long-term service requirements of lithium batteries in multiple fields such as power, energy storage, and consumer electronics. They are halogen-free, environmentally friendly, and have excellent electrolyte resistance, and have high industry promotion value. Attached Figure Description

[0021] Figure 1 This invention presents a schematic flowchart of a method for preparing an acrylic terminating tape with low swelling and high viscosity retention. Figure 2 This is a bar chart comparing the core performance indicators of the present invention. Figure 3 Radar chart showing the overall service performance of this invention; Figure 4 This is a line graph showing the change in the swelling rate of the electrolyte after immersion in the present invention. Detailed Implementation

[0022] The following will refer to the appendices in the embodiments of the present invention. Figures 1-4 The technical solutions in the embodiments of the present invention are clearly and completely described herein. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] I. Pre-preparation of electrolyte-resistant reinforced fillers Modified nanoboehmite sample 1: Nanoboehmite with an average particle size of 20 nm was dispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 10%. γ-methacryloyloxypropyltrimethoxysilane was added at a mass fraction of 2% of the total suspension. The pH was adjusted to 4 with glacial acetic acid and stirred at 60 °C for 3 h. Then, hydroxyethyl acrylate at a mass fraction of 3% of the total suspension was added and the reaction was continued for 2 h. After the reaction was completed, the sample was washed three times by centrifugation with anhydrous ethanol and dried under vacuum at 60 °C for 12 h to obtain grafted modified nanoboehmite sample 1.

[0024] Modified nanoboehmite sample 2: Nanoboehmite with an average particle size of 50 nm was dispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 15%. 5% of γ-methacryloyloxypropyltrimethoxysilane was added to the suspension. The pH was adjusted to 5 with glacial acetic acid. The mixture was stirred at 70 °C for 4 h. Subsequently, 6% of hydroxyethyl acrylate was added to the suspension, and the reaction was continued for 3 h. After the reaction was completed, the mixture was washed three times by centrifugation with anhydrous ethanol and dried under vacuum at 60 °C for 12 h to obtain grafted modified nanoboehmite sample 2.

[0025] II. Implementation Examples Example 1 The halogen-free acrylate terminator with low swelling and high viscosity retention in this embodiment comprises the following raw material components by mass percentage: 20% prepolymer, 75.5% composite acrylate diluent monomer, 0.5% electrolyte-resistant reinforcing filler, 3% additives, and 1% composite photoinitiator. The prepolymer is an acrylate prepolymer with a weight-average molecular weight of 10,000, a molecular weight distribution coefficient of 1.2, a double bond functionality of 2, and a rotational viscosity of 5,000 mPa·s at 60°C. The composite acrylate diluent monomer is obtained by compounding soft monomers, hard monomers, crosslinking monomers, and low surface energy functional monomers in a mass ratio of 75:18:5:2. The soft monomer is isooctyl acrylate with a glass transition temperature of -70°C, the hard monomer is methyl methacrylate with a glass transition temperature of 80°C, the crosslinking monomer is trimethylolpropane triacrylate, and the low surface energy functional monomer is isobornyl oxyethyl acrylate with a glass transition temperature of -60°C. The electrolyte-resistant reinforcing filler is modified nano-boehmite sample 1. The additives, by mass percentage, include 1.5% green azo pigment, 0.1% dodecyl mercaptan, 1.3% γ-methacryloyloxypropyltrimethoxysilane, and 0.1% hydroquinone monomethyl ether. The average particle size of the green azo pigment is 80 nm. The composite photoinitiator is obtained by compounding a halogen-free pyrolysis photoinitiator and a halogen-free hydrogen abstraction photoinitiator in a mass ratio of 1:1. The pyrolysis photoinitiator is 1-hydroxycyclohexylphenyl ketone with a maximum absorption wavelength of 323 nm, and the hydrogen abstraction photoinitiator is benzophenone with a maximum absorption wavelength of 350 nm.

[0026] The halogen-free acrylate termination tape of this embodiment includes a substrate layer, an adhesive layer, and a release film layer sequentially bonded together. The substrate layer is a 12μm thick PET, and the corona-treated surface of the substrate layer is plasma-treated with a treatment power of 800W and a treatment speed of 20m / min, resulting in a dyn value of 48dyn after treatment. The non-corona-treated surface of the substrate layer is coated with a non-silicone release agent, with a dry film thickness of 0.1μm, a surface dyn value of 28dyn, and a release force of 5gf / 25mm. The release film layer is a 19μm thick PET silicone release film, prepared using addition-type siloxane, with a crosslinking degree of 90% after curing, a release force of 3gf / 25mm, and a residual adhesion of 90%. The adhesive layer is prepared by UV curing of the above termination adhesive, with a dry film thickness of 5μm.

[0027] The method for preparing the termination tape in this embodiment includes the following steps: S1. Premixing of adhesive: Weigh the prepolymer and composite acrylate diluent monomers according to the proportion, heat to 40°C under light-protected conditions, stir at 300 rpm for 20 min until the prepolymer is completely dissolved, then add the electrolyte-resistant reinforcing filler, disperse at 800 rpm for 30 min, and then mill at 1500 rpm for 2 h until the filler particle size is ≤100 nm to obtain the premix. Place the obtained premix under a vacuum of -0.09 MPa and slowly stir at 200 rpm for 40 min to degas, to obtain the degassed premix for later use. S2, Additive compounding: Additives and composite photoinitiator are added to the degassing premix in sequence. Stir at 300 rpm for 60 min under light-protected conditions and 25°C. After mixing evenly, filter through a 5μm precision filter to obtain a uniform coating adhesive. S3. Substrate pretreatment: The corona-treated surface of the substrate layer is subjected to online plasma treatment, with the treatment power controlled at 800W and the treatment speed at 20m / min. After the dyne value meets the requirements, it is ready for use. The non-corona-treated surface is pre-coated and cured with a non-silicone release agent. S4. Coating and Lamination: The adhesive is applied to the corona surface of the substrate layer using a micro-grooving coating process. The wet film thickness is controlled by adjusting the micro-grooving roller line count and speed to achieve a dry film thickness of 5μm. The release surface of the release film layer is then laminated under a pressure of 0.2MPa. S5. UV Curing: A medium-pressure mercury lamp UV light source is used to cure the bonded materials in stages. The main emission wavelength of the medium-pressure mercury lamp is 365nm, the power density is 80W / cm², the illumination distance is 20cm, and the surface temperature of the adhesive layer is controlled at 40℃ during the curing process; the curing energy for the first stage is 150mJ / cm². 2 The curing time is 20 seconds, allowing the adhesive layer to initially gel and set. The second stage of curing energy is 100 mJ / cm². 2 The curing time is 30 seconds, which allows the adhesive layer to fully cross-link. S6. Post-treatment: After curing, the material is left to stand for 24 hours at 23±2℃ and 50±5%RH to eliminate substrate stress. Then, the release film layer is peeled off by controlling the peel angle to 180° and the peel speed to 5m / min. The halogen-free acrylate termination tape is then rolled up to obtain the finished product. The winding tension is 8N / m and the winding unevenness is ±0.5mm.

[0028] Example 2 The halogen-free acrylate terminator with low swelling and high viscosity retention in this embodiment comprises the following raw material components by mass percentage: 25% prepolymer, 70% composite acrylate diluent monomer, 2% electrolyte-resistant reinforcing filler, 1.5% additives, and 1.5% composite photoinitiator. The prepolymer is an acrylate prepolymer with a weight-average molecular weight of 30,000, a molecular weight distribution coefficient of 1.8, a double bond functionality of 3, and a rotational viscosity of 15,000 mPa·s at 60°C. The composite acrylate diluent monomer is obtained by compounding soft monomers, hard monomers, crosslinking monomers, and low surface energy functional monomers in a mass ratio of 82:10:6:2. The soft monomer is butyl acrylate with a glass transition temperature of -50°C, the hard monomer is isobornyl methacrylate with a glass transition temperature of 110°C, the crosslinking monomer is pentaerythritol tetraacrylate, and the low surface energy functional monomer is isodecyl methacrylate with a glass transition temperature of -30°C. The electrolyte-resistant reinforcing filler is modified nano-boehmite sample 2. The additives, by mass percentage, include 0.8% blue phthalocyanine pigment, 0.1% isooctyl mercaptoacetate, 0.55% γ-aminopropyltriethoxysilane, and 0.05% 2,6-di-tert-butyl-p-cresol. The average particle size of the blue phthalocyanine pigment is 90 nm. The composite photoinitiator is obtained by compounding a halogen-free pyrolysis photoinitiator and a halogen-free hydrogen abstraction photoinitiator at a mass ratio of 3:2. The pyrolysis photoinitiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide with a maximum absorption wavelength of 360 nm, and the hydrogen abstraction photoinitiator is isopropylthioxanthone with a maximum absorption wavelength of 420 nm.

[0029] The halogen-free acrylate termination tape of this embodiment includes a substrate layer, an adhesive layer, and a release film layer sequentially bonded together. The substrate layer is a 25μm thick PI material. The corona-treated surface of the substrate layer is plasma-treated with a power of 1200W and a speed of 10m / min, resulting in a dyn value of 52dyn. The non-corona-treated surface of the substrate layer is coated with a non-silicone release agent, resulting in a dry film thickness of 0.5μm, a surface dyn value of 27dyn, and a release force of 20gf / 25mm. The release film layer is a 150μm thick PET silicone release film, prepared using addition-type siloxane. After curing, the crosslinking degree is 95%, the release force is 300gf / 25mm, and the residual adhesion is 95%. The adhesive layer is prepared by UV curing of the aforementioned termination adhesive, resulting in a dry film thickness of 30μm.

[0030] The method for preparing the termination tape in this embodiment includes the following steps: S1. Premixing of adhesive: Weigh the prepolymer and composite acrylate diluent monomers according to the proportion, heat to 50°C under light-protected conditions, stir at 500 rpm for 10 min until the prepolymer is completely dissolved, then add electrolyte-resistant reinforcing filler, disperse at 1200 rpm for 20 min, and then mill at 2000 rpm for 1 h until the filler particle size is ≤100 nm to obtain the premix. Place the obtained premix under a vacuum of -0.1 MPa and slowly stir at 400 rpm for 20 min to degas, to obtain the degassed premix for later use. S2, Additive compounding: Additives and composite photoinitiator are added to the degassing premix in sequence. Stir at 500 rpm for 30 minutes under light-protected conditions and 30°C. After mixing evenly, filter through a 10μm precision filter to obtain a uniform coating adhesive. S3. Substrate pretreatment: The corona-treated surface of the substrate layer is subjected to online plasma treatment, with the treatment power controlled at 1200W and the treatment speed at 10m / min. After the dyne value meets the requirements, it is ready for use. The non-corona-treated surface is pre-coated and cured with a non-silicone release agent. S4. Coating and Lamination: The adhesive is applied to the corona surface of the substrate layer using a micro-grooving coating process. The thickness of the wet film is controlled by adjusting the micro-grooving roller line count and speed to achieve a dry film thickness of 30μm. The release surface of the release film layer is then laminated under a pressure of 0.3MPa. S5. UV Curing: LED UV light source is used to cure the bonded materials in stages, employing a dual-wavelength combination of 365nm and 395nm with a power ratio of 2:1. The illumination distance is 10cm, and the surface temperature of the adhesive layer is controlled at 60℃ during curing. The curing energy for the first stage is 250mJ / cm². 2 The curing time is 10 seconds, allowing the adhesive layer to initially gel and solidify. The second stage of curing energy is 200 mJ / cm². 2 The curing time is 20 seconds, which allows the adhesive layer to fully cross-link. S6. Post-treatment: After curing, the material is left to stand for 48 hours at 23±2℃ and 50±5%RH to eliminate substrate stress. Then, the release film layer is peeled off by controlling the peel angle to 180° and the peel speed to 10m / min. The halogen-free acrylate termination tape is then rolled up to obtain the finished product. The winding tension is 15N / m and the winding unevenness is ±0.3mm.

[0031] Example 3 The halogen-free acrylate terminator with low swelling and high viscosity retention in this embodiment has the following raw material components by mass percentage: 30% prepolymer, 63% composite acrylate diluent monomer, 1.5% electrolyte-resistant reinforcing filler, 2% additives, and 3.5% composite photoinitiator. The prepolymer is a bisphenol A type epoxy acrylate with a functionality of 2, an acid value of 4 mgKOH / g, and a rotational viscosity of 8000 mPa·s at 60℃. The composite acrylate diluent monomer is obtained by compounding soft monomers, hard monomers, crosslinking monomers, and low surface energy functional monomers in a mass ratio of 78:15:4:3. The soft monomer is a mixture of isooctyl acrylate and butyl acrylate in a mass ratio of 1:1 with a glass transition temperature of -60℃. The hard monomer is a mixture of methyl methacrylate and isobornyl methacrylate in a mass ratio of 1:1 with a glass transition temperature of 110℃. The crosslinking monomer is a mixture of trimethylolpropane triacrylate and pentaerythritol tetraacrylate in a mass ratio of 1:1. The low surface energy functional monomer is a mixture of isobornyl oxyethyl acrylate and isodecyl methacrylate in a mass ratio of 1:1 with a glass transition temperature of -45℃. The electrolyte-resistant reinforcing filler is a mixture of modified nano-boehmite sample 1 and sample 2 in a mass ratio of 1:1. The additives, by mass percentage, include 1.2% of a mixture of green azo pigment and blue phthalocyanine pigment in a 1:1 mass ratio, 0.2% of dodecyl mercaptan, 0.5% of γ-methacryloyloxypropyltrimethoxysilane, and 0.1% of hydroquinone monomethyl ether. The average particle size of the pigment is 85 nm. The composite photoinitiator is obtained by compounding a halogen-free pyrolysis photoinitiator and a halogen-free hydrogen abstraction photoinitiator in a 3:2 mass ratio. The pyrolysis photoinitiator is a mixture of 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide in a 1:1 mass ratio, and the hydrogen abstraction photoinitiator is a mixture of benzophenone and isopropylthioxanthraphenone in a 1:1 mass ratio.

[0032] The halogen-free acrylate termination tape of this embodiment includes a substrate layer, an adhesive layer, and a release film layer sequentially bonded together. The substrate layer is a 25μm thick BOPP, and the corona-treated surface of the substrate layer is plasma-treated with a treatment power of 1000W and a treatment speed of 15m / min, resulting in a dyn value of 40dyn after treatment. The non-corona-treated surface of the substrate layer is coated with a non-silicone release agent, with a dry film thickness of 0.3μm, a surface dyn value of 28dyn, and a release force of 12gf / 25mm. The release film layer is a 50μm thick PET silicone release film, prepared using addition-type siloxane, with a crosslinking degree of 92% after curing, a release force of 50gf / 25mm, and a residual adhesion of 92%. The adhesive layer is prepared by UV curing of the above termination adhesive, with a dry film thickness of 15μm.

[0033] The method for preparing the termination tape in this embodiment includes the following steps: S1. Premixing of adhesive: Weigh the prepolymer and composite acrylate diluent monomers according to the proportion, heat to 45°C under light-protected conditions, stir at 400 rpm for 15 min until the prepolymer is completely dissolved, then add the electrolyte-resistant reinforcing filler, disperse at 1000 rpm for 25 min, and then mill at 1800 rpm for 1.5 h until the filler particle size is ≤100 nm to obtain the premix. Place the obtained premix under a negative pressure environment with a vacuum degree of -0.095 MPa and slowly stir at 300 rpm for 30 min to degas, to obtain the degassed premix for later use. S2, Additive compounding: Additives and composite photoinitiator are added to the degassing premix in sequence. Stir at 400 rpm for 45 min under light-protected conditions and 28℃. After mixing evenly, filter through an 8μm precision filter to obtain a uniform coating adhesive. S3. Substrate pretreatment: The corona-treated surface of the substrate layer is subjected to online plasma treatment, with the treatment power controlled at 1000W and the treatment speed at 15m / min. After the dyne value meets the requirements, it is ready for use. The non-corona-treated surface is pre-coated and cured with a non-silicone release agent. S4. Coating and Lamination: The adhesive is applied to the corona surface of the substrate layer using a micro-grooving coating process. The thickness of the wet film is controlled by adjusting the micro-grooving roller line count and speed to achieve a dry film thickness of 15μm. The release surface of the release film layer is then laminated under a pressure of 0.25MPa. S5. UV Curing: A medium-pressure mercury lamp UV light source is used to cure the bonded materials in stages. The main emission wavelength of the medium-pressure mercury lamp is 365nm, the power density is 100W / cm², the illumination distance is 18cm, and the surface temperature of the adhesive layer is controlled at 50℃ during the curing process; the curing energy for the first stage is 200mJ / cm². 2 The curing time is 15 seconds, allowing the adhesive layer to initially gel and solidify. The second stage of curing energy is 150 mJ / cm². 2 The curing time is 25 seconds, which allows the adhesive layer to fully cross-link. S6. Post-treatment: After curing, the material is left to stand for 36 hours at 23±2℃ and 50±5%RH to eliminate substrate stress. Then, the release film layer is peeled off by controlling the peel angle to 180° and the peel speed to 8m / min. The halogen-free acrylate termination tape is then rolled up to obtain the finished product. The winding tension is 12N / m and the winding unevenness is ±0.4mm.

[0034] III. Comparative Example This comparative example uses a conventional UV-curable acrylate stop adhesive: the stop adhesive, by weight percentage, consists of 25% ordinary acrylate prepolymer, 72% conventionally diluted monomers (a mixture of isooctyl acrylate and methyl methacrylate in an 8:2 weight ratio), 1% unmodified nano-boehmite (average particle size 30nm), 1% additives, and 1% single-type pyrolytic photoinitiator 1-hydroxycyclohexylphenyl ketone. No low surface energy functional monomers were added, the filler was not grafted, and a single type of photoinitiator was used. The stop adhesive tape in this comparative example was prepared using a conventional single-pass UV curing process with a single-pass curing energy of 300mJ / cm². 2 The curing time was 30 seconds, and the other substrates and coating parameters remained the same as in Example 3.

[0035] IV. Performance Test Data Table Table 1 Comparison of Core Components and Formulation Parameters of Terminating Adhesive This table clearly presents the differences in core formulation parameters between the three sets of examples and the comparative examples. The comparative examples did not add low surface energy functional monomers, used unmodified boehmite fillers, and adopted a single type of photoinitiator, which can intuitively reflect the improvement points of the technical solution of the present invention and provide an accurate basis at the formulation level for attributing the subsequent performance differences.

[0036] Table 2 Comparison of Core Performance Test Results of Termination Tape Note: All tests were performed according to the corresponding standard methods, and the test environment was 23℃ and 50%RH.

[0037] This table presents the core performance test results of each group of samples. All performance indicators of the three sets of examples meet the requirements of the claims. Compared with the comparative examples, the swelling rate of the adhesive layer is reduced, the peel strength retention rate is significantly improved, and there is no problem of adhesive overflow. This fully verifies that the present invention effectively solves the three core defects of the prior art through the technical means of low surface energy monomer compounding, filler grafting modification, and compound photoinitiator segmented curing. The technical effect is stable.

[0038] V. Performance Testing Methods The crosslinking density test method adopts the equilibrium swelling method: the cured adhesive layer is peeled off from the substrate, about 0.2g of sample is weighed and immersed in toluene, swelled and equilibrated at 25℃ for 48h, and then weighed. The crosslinking density is calculated according to the Flory-Rehner equation.

[0039] The gelation rate test method involves accurately weighing the cured gel layer and recording it as M0, refluxing it with acetone as solvent using a Soxhlet extractor for 24 hours, and then drying it under vacuum at 80°C to constant weight and recording it as M1. The gelation rate is calculated as M1 / M0 × 100%.

[0040] The contact angle test method uses the seated drop method, with deionized water as the test liquid and a drop volume of 3 μL. The average value is taken at 5 different positions on the adhesive surface.

[0041] The swelling rate test method involves cutting the adhesive layer into 20mm×20mm samples, weighing the initial mass m0, immersing them in a mixed electrolyte of dimethyl carbonate / ethylene carbonate / ethyl methyl carbonate (volume ratio 1:1:1) at 85℃, sealing and placing them for 24 hours, then removing them, quickly absorbing the residual electrolyte on the surface, and immediately weighing m1. The swelling rate is calculated as (m1-m0) / m0×100%, and the average value is taken for each group of 3 tests.

[0042] The method for testing the peel strength retention rate of aluminum foil is as follows: the tape is adhered to the surface of a 100μm thick aluminum foil, and rolled three times with a 2kg roller. After being placed at 25℃ and 50%RH for 24 hours, the initial 180° peel strength F0 is tested. The adhered sample is then immersed in the above electrolyte, sealed at 85℃ for 24 hours, removed, cooled to room temperature, and the 180° peel strength F1 is tested. The retention rate is calculated as F1 / F0×100%, and the average value is taken for each group of 5 tests.

[0043] The release force test method is in accordance with GB / T2792 standard. The tape is attached to the standard test plate and peeled off at 180° with a peeling speed of 300mm / min.

[0044] The residual adhesion test method is performed according to the FINAT FTM-9 standard.

[0045] The dyne value test method is in accordance with GB / T14216 standard, and a series of dyne pens are used for testing.

[0046] The method for testing adhesive overflow involves aging the finished tape in an environment of 85℃ and 85%RH for 72 hours, and then measuring the maximum distance the adhesive layer extends outward from the edge under a microscope.

[0047] refer to Figure 2 This figure visually presents the differences in four core aspects of electrolyte resistance and adhesion performance among the four groups of samples. The water contact angles of the three examples are significantly higher than those of the comparative examples, directly verifying that the low surface energy functional monomer compound can effectively reduce the surface energy of the adhesive layer and solve the defect of easy electrolyte penetration in existing technologies. The swelling rate of the examples is only 6%-15% of that of the comparative examples, and the peel force retention rate is 24-29 percentage points higher than that of the comparative examples. There is no glue overflow problem. The corresponding improvements in adhesive layer density due to grafted modified boehmite and crosslinking uniformity due to compounded photoinitiator clearly distinguish the performance gap between the technical solution of this invention and existing conventional solutions, providing intuitive support for the visual verification of technical effects. All data are from standard tests and have strong repeatability. Reference Figure 3This figure normalizes and presents the comprehensive service performance of the four groups of samples. The polygon coverage area of ​​the three examples is much larger than that of the comparative example, indicating no obvious performance shortcomings, thus verifying the synergistic effect of the three improvement technologies of this invention. The comparative example has the lowest scores in all dimensions, corresponding to the insufficient comprehensive performance caused by the three defects of existing technologies: poor filler compatibility, insufficient curing, and high surface energy. Example 2 has the highest scores in all dimensions, corresponding to its higher degree of filler modification and more optimized photoinitiator compounding ratio. This intuitively demonstrates that the technical solution of this invention has stable comprehensive performance superior to existing technologies in different parameter ranges, providing a reference for parameter adaptation in application scenarios.

[0048] refer to Figure 4 This figure presents the swelling rate trends of four groups of samples after different immersion times in an electrolyte at 85℃. The swelling rate growth rate of the three examples slows rapidly over time, stabilizing after 24 hours. This verifies the high density of the adhesive layer and the difficulty of continuous electrolyte penetration, addressing the shortcomings of existing technologies where swelling continuously intensifies and viscosity rapidly decreases during long-term service. The comparative example shows an approximately linear increase in swelling rate with immersion time, maintaining a high growth rate even after 24 hours, corresponding to insufficient adhesive layer density and low cross-linking degree. This figure visually demonstrates the long-term electrolyte stability of the present invention, providing intuitive support for verifying the adaptability of energy storage devices in long-cycle service scenarios.

[0049] 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 halogen-free acrylate terminating adhesive with low swelling and high viscosity retention, characterized in that, The raw material components are included by weight percentage as follows: Prepolymer 20-30%, composite acrylate diluted monomer 70-85%, electrolyte-resistant reinforcing filler 0.5-2%, additives 1-5%, composite photoinitiator 1-5%; The composite acrylate diluent monomer is obtained by compounding soft monomers, hard monomers, crosslinking monomers and low surface energy functional monomers in a mass ratio of 75-82:10-18:3-7:1-3. The soft monomer is selected from at least one of isooctyl acrylate and butyl acrylate, and has a glass transition temperature of -70°C to -50°C. The hard monomer is selected from at least one of methyl methacrylate and isobornyl methacrylate, and has a glass transition temperature of 80°C to 150°C; the crosslinking monomer is selected from at least one of trimethylolpropane triacrylate and pentaerythritol tetraacrylate. The low surface energy functional monomer is selected from at least one of isobornyl oxyethyl acrylate and isodecyl methacrylate, and has a glass transition temperature of -60°C to -30°C. The electrolyte-resistant reinforcing filler is nano-boehmite with a surface grafted with hydroxyethyl acrylate and a particle size of 20-50 nm. The composite photoinitiator is obtained by compounding a halogen-free pyrolysis photoinitiator and a halogen-free hydrogen abstraction photoinitiator in a mass ratio of 1:1 to 3:

2. The maximum absorption wavelength of the pyrolysis photoinitiator is 250-360 nm, and the maximum absorption wavelength of the hydrogen abstraction photoinitiator is 350-420 nm.

2. The halogen-free acrylate terminating adhesive with low swelling and high viscosity retention according to claim 1, characterized in that, The prepolymer is selected from one or a mixture of two of acrylate prepolymers and epoxy acrylate prepolymers. The acrylate prepolymer has a weight-average molecular weight of 10,000-30,000, a molecular weight distribution coefficient of 1.2-1.8, a double bond functionality of 2-3, and a rotational viscosity of 5,000-15,000 mPa·s at 60°C. The epoxy acrylate prepolymer is a bisphenol A type epoxy acrylate or a phenolic type epoxy acrylate, with a functionality of 2-3, an acid value ≤5 mgKOH / g, and a rotational viscosity of 8,000-20,000 mPa·s at 60°C.

3. The halogen-free acrylate terminating adhesive with low swelling and high viscosity retention according to claim 1, characterized in that, The surface grafting modification of the nano-boehmite is specifically achieved as follows: nano-boehmite is dispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 10-15%, γ-methacryloyloxypropyltrimethoxysilane is added at a mass of 2-5% of the total suspension, the pH value is adjusted to 4-5, and the reaction is stirred at 60-70℃ for 3-4 hours. Then, hydroxyethyl acrylate at a mass of 3-6% of the total suspension is added, and the reaction is continued for 2-3 hours. After centrifugation and washing, the nano-boehmite is obtained by vacuum drying.

4. The halogen-free acrylate terminating adhesive with low swelling and high viscosity retention according to claim 1, characterized in that, The additives, by mass percentage, comprise 1-3% pigment, 0.1-0.5% chain transfer agent, 0.5-1.5% adhesion promoter, and 0.05-0.2% polymerization inhibitor; the pigment is selected from at least one of green azo pigment and blue phthalocyanine pigment, with an average particle size ≤100nm; the chain transfer agent is dodecyl mercaptan or isooctyl mercaptoacetate; the adhesion promoter is γ-methacryloyloxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane; and the polymerization inhibitor is hydroquinone monomethyl ether or 2,6-di-tert-butyl-p-cresol.

5. The halogen-free acrylate terminating adhesive with low swelling and high viscosity retention according to claim 1, characterized in that, The pyrolytic photoinitiator is selected from at least one of 1-hydroxycyclohexylphenyl ketone and 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and the hydrogen-abstracting photoinitiator is selected from at least one of isopropylthioxanthone and benzophenone. When the prepolymer is an acrylate prepolymer, the mass ratio of the pyrolytic photoinitiator to the hydrogen-abstracting photoinitiator is 1:1 to 3:2, and when the prepolymer is an epoxy acrylate prepolymer, the mass ratio of the pyrolytic photoinitiator to the hydrogen-abstracting photoinitiator is 3:

2.

6. A halogen-free acrylic termination tape with low swelling and high viscosity retention, characterized in that, The product comprises a substrate layer, an adhesive layer, and a release film layer bonded together in sequence. The adhesive layer is prepared by UV curing of the halogen-free acrylate terminating adhesive according to any one of claims 1-5. The adhesive layer has a thickness of 5-30 μm and a crosslinking density of 2.5 × 10⁻⁶ after curing. -3 -4.0×10 -3 mol / cm 3 The gelation rate is ≥95%, the contact angle is ≥105°, the volume swelling rate after soaking in 85℃ carbonate electrolyte for 24h is ≤0.5%, and the aluminum foil peel strength retention rate is ≥92%.

7. The halogen-free acrylate termination tape with low swelling and high viscosity retention according to claim 6, characterized in that, The substrate layer is selected from any one of PET, BOPP, and PI, and the thickness of the substrate layer is 5-25μm. The corona-treated surface of the substrate layer is treated with plasma at a power of 800-1200W and a speed of 10-20m / min. When the substrate layer is PET or PI, the dyn value after treatment is ≥48dyn; when the substrate layer is BOPP, the dyn value after treatment is >38dyn. The non-corona-treated surface of the substrate layer is coated with a non-silicone release agent, the dry film thickness is 0.1-0.5μm, the surface dyn value is <30dyn, and the release force is 5-20gf / 25mm.

8. The halogen-free acrylate termination tape with low swelling and high viscosity retention according to claim 6, characterized in that, The release film layer is a PET silicone release film with a thickness of 19-150μm. The release layer is prepared using addition-type siloxane, and after curing, the degree of crosslinking is ≥90%, the release force is 3-300gf / 25mm, the residual adhesion is ≥90%, and the release force change rate after bonding with the adhesive layer and aging at 70℃ for 72h is ≤10%.

9. A method for preparing a halogen-free acrylate termination tape with low swelling and high viscosity retention, used to prepare the halogen-free acrylate termination tape of claim 6, characterized in that, Includes the following steps: S1. Premixing the adhesive: Weigh the prepolymer and the diluted monomer of the composite acrylate according to the ratio, heat to 40-50℃ under light-protected conditions, stir at 300-500 rpm for 10-20 min until the prepolymer is completely dissolved, then add the electrolyte-resistant reinforcing filler, disperse at 800-1200 rpm for 20-30 min, and then mill at 1500-2000 rpm for 1-2 h until the filler particle size is ≤100nm to obtain the premix. Place the obtained premix under a negative pressure environment with a vacuum degree of -0.09MPa to -0.1MPa, stir slowly at 200-400 rpm for 20-40 min to degas, and obtain the degassed premix for later use. S2. Additive compounding: Add the additives and composite photoinitiator to the degassing premix in sequence. Stir at 300-500 rpm for 30-60 minutes under light-protected conditions and at 25-30℃. After mixing evenly, filter through a 5-10μm precision filter to obtain a uniform coating adhesive. S3. Substrate pretreatment: The corona-treated surface of the substrate layer is subjected to online plasma treatment, with the treatment power controlled at 800-1200W and the treatment speed at 10-20m / min. After the dyne value meets the requirements, it is ready for use. The non-corona-treated surface is pre-coated and cured with a non-silicone release agent. S4. Coating and Lamination: The adhesive is applied to the corona surface of the substrate layer using a micro-gravure coating process. The wet film thickness is controlled by adjusting the micro-gravure roller line count and speed to achieve a dry film thickness of 5-30μm. The release surface of the release film layer is then laminated under a pressure of 0.2-0.3MPa. S5. UV Curing: The bonded materials are cured in stages using a medium-pressure mercury lamp UV light source or an LED UV light source. The curing energy for the first stage is 150-250 mJ / cm². 2 The curing time is 10-20 seconds, and the curing energy for the second stage is 100-200 mJ / cm². 2 The curing time is 20-30 seconds; S6. Post-treatment: After curing, the material is left to stand for 24-48 hours at 23±2℃ and 50±5%RH. Then, the release film layer is peeled off by controlling the peeling angle to 180° and the peeling speed to 5-10m / min. The halogen-free acrylate termination tape is then rolled up to obtain the finished product.

10. The method for preparing the halogen-free acrylate termination tape with low swelling and high viscosity retention according to claim 9, characterized in that, When using an LED UV light source, a dual-wavelength combination of 365nm and 395nm is employed, with a power ratio of 2:1 between the two wavelengths and an illumination distance of 10-15cm. When using a medium-pressure mercury lamp UV light source, the main emission wavelength is 365nm, the power density is 80-120W / cm, and the illumination distance is 15-20cm. During the curing process, the surface temperature of the adhesive layer is controlled at 40-60℃. The winding tension is 8-15N / m, and the winding unevenness is ≤±0.5mm. After the finished tape is aged in an environment of 85℃ and 85%RH for 72 hours, there is no overflow or migration of adhesive in the adhesive layer.

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