An acrylate UV curing pressure sensitive adhesive for battery cell film and a preparation method thereof

Abstract

The application belongs to the technical field of adhesives, and specifically relates to an acrylate UV curing pressure-sensitive adhesive for battery core film pasting and a preparation method thereof, wherein the pressure-sensitive adhesive comprises, by weight, 15-30 parts of an acrylate prepolymer modified by a C9-C12 long-chain aliphatic dibasic acid, 60-100 parts of a composite dilution system containing monofunctional, bifunctional and trifunctional acrylate monomers, 1-5 parts of a photoinitiator and 0-10 parts of an additive. The introduction of the long-chain aliphatic chain enhances the flexibility of the prepolymer, effectively relieving internal stress under curing and high temperature; by regulating the ratio of different functionality monomers in the composite monomer, a three-dimensional network with high crosslinking density and moderate chain segment activity is synergistically constructed. The pressure-sensitive adhesive has the characteristics of zero VOC and fast curing speed, and the adhesive layer after curing has excellent initial adhesion, and is particularly suitable for insulating protection film pasting on the surface of an aluminum shell of a lithium ion battery of a new energy vehicle, significantly improving the long-term use safety and reliability of the battery.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, square lithium-ion batteries have been widely used due to their high energy density and structural reliability. During battery manufacturing, an insulating protective film (commonly known as "blue film") needs to be applied to the surface of the aluminum or steel casing to provide electrical insulation, mechanical protection, and corrosion resistance. Currently, this process mainly uses solvent-based acrylic pressure-sensitive adhesives. This process suffers from problems such as volatile organic compound emissions, high energy consumption, and low production efficiency. More importantly, the shear strength of traditional solvent-based adhesives decreases significantly at the cell's operating temperature (typically 60°C or higher), easily leading to film peeling and detachment, posing safety hazards.

[0003] Solvent-free UV curing technology is considered an ideal alternative due to its environmental friendliness and high efficiency. Existing technologies have attempted to use UV-curable materials for battery protection. For example, Chinese patent application CN120209632A discloses a UV inkjet adhesive that focuses on solving the problems of inkjet process compatibility, curing speed, and electrolyte resistance through a combination of monomers containing allyl hydrogen and specific oligomers. However, its application involves direct spraying and curing to form a hard coating, without addressing the balance between initial tack, peelability, and high cohesive strength required for pressure-sensitive adhesives. Chinese patent application CN117229744A discloses a fast-curing UV adhesive for battery outer layer protection, pursuing high reliability through a ternary prepolymer system. However, it also focuses on forming a hard protective coating and is not designed for the high-temperature shear strength retention rate required for pressure-sensitive adhesive tapes.

[0004] The technical challenge of pressure-sensitive adhesive tapes for battery cell bonding lies in the need for a sufficiently high crosslinking density after UV curing to ensure cohesive strength (especially resistance to shear creep at high temperatures), while simultaneously retaining an appropriate amount of linear segments or low-crosslinking regions to provide necessary initial tack and wetting ability for rough surfaces. In existing technologies, increasing the crosslinking density often leads to a harder adhesive layer and a decrease in initial tack; conversely, ensuring initial tack often sacrifices cohesive strength, resulting in insufficient holding power, especially leading to failure at high temperatures.

[0005] Therefore, there is an urgent need to develop a UV-curable pressure-sensitive adhesive specifically for battery cell bonding, which can fundamentally solve the contradiction between high-temperature shear strength and initial tack, and meet the stringent requirements for environmental aging resistance. Summary of the Invention

[0006] This invention proposes an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding and its preparation method, aiming to solve the technical problem in the prior art of achieving a balance between high crosslinking density (ensuring high-temperature shear strength) and high initial tack in UV-curable materials.

[0007] In a first aspect, the present invention provides an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding films, comprising the following components by weight: 15-30 parts of acrylate prepolymer, 60-100 parts of composite diluted monomer; 1-5 parts of photoinitiator; 0-10 parts of additives; The acrylate prepolymer is prepared by a two-step esterification reaction of a polyol, a long-chain aliphatic diacid, and acrylic acid, wherein the long-chain aliphatic diacid has 9 to 12 carbon atoms.

[0008] The technical advantage of the acrylic UV-curable pressure-sensitive adhesive for battery cell bonding disclosed in this invention is that it utilizes long-chain aliphatic dicarboxylic acids (such as azelaic acid and sebacic acid) with carbon chain lengths of C9-C12 in the prepolymer synthesis. According to polymer chain conformation theory, long methylene segments possess extremely low rotational barriers, endowing the molecular chains with excellent flexibility. When these flexible segments are introduced into the crosslinking network, they can act as "micro-elastic units," effectively absorbing and dissipating internal stress generated by polymerization shrinkage or thermal expansion. This avoids interfacial adhesion failure or cohesive fracture of the rigid network due to stress concentration at high temperatures, thereby fundamentally improving the shear strength retention rate of the adhesive layer at high temperatures.

[0009] Furthermore, the long-chain aliphatic dicarboxylic acid is selected from at least one of azelaic acid, sebacic acid, undecanoic acid, and dodecanoic acid.

[0010] Furthermore, the composite diluent monomer is composed of monofunctional acrylate monomers, difunctional acrylate monomers and trifunctional acrylate monomers, wherein the monofunctional acrylate monomer accounts for 80% to 95% of the total mass of the composite diluent monomer, the difunctional acrylate monomer accounts for 2% to 10%, and the trifunctional acrylate monomer accounts for 0% to 3%.

[0011] Furthermore, the monofunctional acrylate monomer is isooctyl acrylate or butyl acrylate; the difunctional acrylate monomer is 1,6-hexanediol diacrylate; and the trifunctional acrylate monomer is trimethylolpropane triacrylate.

[0012] Furthermore, the photoinitiator comprises 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone, with a mass ratio of 1:0.5 to 1:2.

[0013] Furthermore, the additives include colorants and adhesion promoters; the colorant content is 0.5% to 5% by total weight of the composition, and the adhesion promoter is a phosphate ester compound with a content of 0.1% to 2%.

[0014] Secondly, the present invention provides a method for preparing an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding films, the method comprising the following steps: S1, a polyol is reacted with a long-chain aliphatic dicarboxylic acid at 150°C to 180°C in a first esterification reaction until the acid value drops below 50 mgKOH / g; then the temperature is lowered to 90°C to 110°C, acrylic acid or methacrylic acid, a catalyst and a polymerization inhibitor are added, and a second esterification reaction is carried out until the acid value drops below 10 mgKOH / g; the acrylate prepolymer is obtained after post-treatment. S2, the acrylate prepolymer, composite diluent monomer, photoinitiator and additives are mixed evenly under light-protected conditions.

[0015] The technical advantage of the method for preparing acrylate UV-curable pressure-sensitive adhesive for battery cell film disclosed in this invention is that the method can efficiently and controllably synthesize a prepolymer with a flexible long-chain structure through a specific two-step esterification process, and uniformly mix it with components such as composite diluted monomers, thereby stably and reliably preparing the pressure-sensitive adhesive composition with consistent and excellent performance.

[0016] Thirdly, the present invention also provides a pressure-sensitive adhesive tape for battery cell bonding, comprising a substrate and an adhesive layer coated on at least one side of the substrate, wherein the adhesive layer is formed by curing the pressure-sensitive adhesive by ultraviolet light irradiation.

[0017] Furthermore, the substrate is a polyethylene terephthalate film or a polyimide film with a thickness of 20 μm to 100 μm; the adhesive layer has a thickness of 15 μm to 40 μm.

[0018] Furthermore, the pressure-sensitive tape is used to adhere an insulating protective film to the surface of the metal casing of a lithium-ion battery cell.

[0019] The technical advantages of the pressure-sensitive adhesive tape for battery cell bonding disclosed in this invention are as follows: By coating and curing the pressure-sensitive adhesive composition described in this invention onto a substrate, this tape product directly achieves core properties such as high initial tack, excellent high-temperature shear strength, and superior weather resistance, providing a reliable and high-performance insulation and protection solution for battery cell bonding. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating the pressure-sensitive adhesive technology solution and its performance advantages proposed in the embodiments of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding. This technical solution cleverly resolves the contradiction between high cohesive strength and high initial tack in pressure-sensitive adhesives by addressing both the prepolymer structure design and the synergistic effect of the diluted monomer system, particularly maintaining excellent shear performance even at high temperatures. The following specific examples will compare and analyze the pressure-sensitive adhesive of this invention with existing technologies.

[0023] This invention provides an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding, comprising the following components by weight: The composition includes 15-30 parts of acrylate prepolymer, 60-100 parts of composite diluent monomer, 1-5 parts of photoinitiator, and 0-10 parts of additives. The acrylate prepolymer is prepared by a two-step esterification reaction of polyol, long-chain aliphatic diacid and acrylic acid, wherein the long-chain aliphatic diacid has 9 to 12 carbon atoms.

[0024] The experimental materials and general testing methods are as follows: Main raw materials: 1,4-Butanediol, azelaic acid, adipic acid, acrylic acid, isooctyl acrylate (2-EHA), 1,6-hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), and 1-hydroxycyclohexylphenyl ketone (184), all of which are industrial grade. Blue UV pigment and phosphate ester adhesion promoter (P-2M) are commercially available products.

[0025] Prepolymer synthesis: Prepolymer A (this invention, long-chain type, P-C9): In a four-necked flask equipped with a stirrer, thermometer, water separator, and nitrogen inlet tube, add 1,4-butanediol (108.12 g, 1.2 mol, excess) and azelaic acid (188.2 g, 1.0 mol). Heat in an oil bath to 170°C under a nitrogen atmosphere and react for about 4 hours until the acid value drops to 48 mg KOH / g. Cool to 105°C and add acrylic acid (34.44 g, 0.48 mol, appropriate amount), p-toluenesulfonic acid (3.0 g), and hydroquinone (0.3 g). Continue reacting at 105°C for 6 hours until the acid value ≤ 9 mg KOH / g. Subsequently, remove residual monomers and water by vacuum distillation, and filter to obtain a light yellow viscous acrylate prepolymer A.

[0026] Prepolymer B (comparison, short-chain type): The synthesis steps are the same as those for prepolymer A, the only difference being that azelaic acid is replaced with an equimolar amount of adipic acid (146.1 g).

[0027] Pressure-sensitive adhesive formulation and tape molding: According to the formulations shown in Tables 1 to 4, the components were mixed uniformly under light-protected conditions to obtain a UV-curable pressure-sensitive adhesive solution. The adhesive solution was uniformly coated onto a 25 μm thick PET film using a bar coater, with the wet film thickness controlled at 35 μm. A 25 μm thick PET release film was then applied. Under nitrogen protection, the tape was cured by irradiation with a UV-LED surface light source (main peak wavelength 365 nm, irradiance 500 mW / cm²) at a cumulative energy of 800 to 1200 mJ / cm² to obtain the test tape.

[0028] The performance testing standards are as follows: 180° peel strength: Refer to GB / T2792, test the force of the tape peeling off from the stainless steel plate at a rate of 300 mm / min.

[0029] Shear strength: In accordance with GB / T7124, aluminum-aluminum single lap shear test specimens with an overlap area of ​​12.5mm×25mm were prepared and tested in constant temperature chambers at 25℃ and 60℃ respectively, with a tensile rate of 5mm / min.

[0030] Holding power: Refer to GB / T4851, test the time it takes for the tape to slip off a standard steel plate at 40℃ and 500g load.

[0031] To verify the rationality of the component range and proportion in the claims of this invention and the technical effect, the following embodiments and comparative examples were designed.

[0032] 1. Verification of the range of prepolymer dosage.

[0033] The purpose of this experiment was to verify the necessity of the acrylate prepolymer dosage range (15-30 parts by weight) of the present invention. The composite diluent monomer (2-EHA / HDDA / TMPTA mass ratio 90 / 8.5 / 1.5) was fixed at 75 parts, the photoinitiator (TPO / 184=1 / 1) at 3 parts, and the additives (color paste at 2 parts, P-2M at 1 part) at 3 parts, while the dosage of prepolymer A was varied.

[0034] Table 1: Effect of Prepolymer Dosage on Performance As shown in Comparative Example 1, when the amount of prepolymer is less than 15 parts, the cohesive strength of the adhesive layer is severely insufficient, and the high-temperature shear performance deteriorates sharply. Within the range of 15-30 parts (Examples 1-3), all performance indicators reach excellent levels, with Example 2 (25 parts) exhibiting the best overall performance. When the amount increases to 35 parts (Comparative Example 2), the initial viscosity of the system becomes too high, affecting the coating processability, and the initial tack begins to decrease significantly. Therefore, 15-30 parts is an effective range that balances excellent performance and good processability, with 25 parts being the preferred value.

[0035] 2. Verification of the Functionality Ratio of Composite Diluted Monomers. This group of experiments aimed to determine the functionality ratio range of composite diluted monomers. With prepolymer A fixed at 25 parts and photoinitiator and auxiliaries totaling 9 parts, the mass percentages of monofunctional (2-EHA), difunctional (HDDA), and trifunctional (TMPTA) monomers in the composite diluted monomers were varied.

[0036] Table 2: Effect of the functional ratio of composite diluted monomers on performance As shown in Comparative Example 3, when the proportion of monofunctional monomers is too high (85%), the crosslinking density of the system is insufficient, leading to severe deterioration of high-temperature shear strength and holding power. When the proportion of difunctional monomers is increased to 25% (Example 2), and synergistically combined with 5% trifunctional monomers, the highest 60°C shear strength (4.1 MPa) and holding power can be obtained while maintaining excellent initial tack (17.2 N / 25 mm). Further increasing the proportion of difunctional or trifunctional monomers (Example 5, Comparative Example 4) results in a continuous decrease in initial tack. Therefore, monofunctional:difunctional:trifunctional mass ratios within the range of (70-80):(15-25):(5-10) exhibit excellent performance, with 70:25:5 being the optimal balance point. That is, Example 2 (70 / 25 / 5) exhibits the highest shear strength at both 25°C and 60°C, demonstrating the optimal balance of crosslinking density. Comparative Example 3 (85 / 10 / 5) showed a significant decrease in high-temperature shear strength due to its low crosslinking density; Comparative Example 4 (50 / 40 / 10) showed a decrease in initial tack and a slight decline in shear strength at 25℃ due to its high crosslinking density. The peel strength and shear strength exhibited a downward-opening parabolic curve with respect to HDDA and TMPTA, consistent with a parabolic trend. The comprehensive performance comparison is shown in Table 3 below. Table 3: Overall Performance Comparison Compared to Comparative Example 5: Simply changing the prepolymer from long-chain (C9) to short-chain (C6) resulted in a significant drop in shear strength at 60℃ from 4.1 MPa to 2.6 MPa, demonstrating that using C9-C12 long-chain aliphatic dicarboxylic acids to synthesize the prepolymer is key to obtaining high-temperature shear resistance. Compared to Comparative Example 6: While the initial tack was slightly higher after lacking the trifunctional monomer TMPTA, the cohesive strength was severely insufficient, leading to a significant decrease in shear strength and holding power. This demonstrates the necessity of a specific monomer ratio (including trifunctional monomers) for constructing a high-cohesive network. Compared to Comparative Example 7, the existing blue film technology exhibits only 2.0 MPa shear strength at 25℃ and less than 0.5 MPa shear strength at 60℃, fully showcasing the high-temperature, high-shear advantages of UV blue films.

[0037] Compared with Comparative Example 7: After adopting the formulation approach of the prior art (CN120209632A) which focuses on electrolyte resistance and spraying process, the overall performance of the pressure-sensitive adhesive (especially cohesive strength and holding power) of the obtained product is much lower than that of the present invention. This proves that the technical solution of the present invention is a non-obvious design that addresses the specific contradictions of pressure-sensitive adhesive for battery cell film, and has achieved unexpected technical effects.

[0038] Based on the same inventive concept, this invention also provides a pressure-sensitive adhesive tape for battery cell bonding, comprising a substrate and an adhesive layer coated on at least one side of the substrate, wherein the adhesive layer is formed by curing the pressure-sensitive adhesive under ultraviolet light. The pressure-sensitive adhesive is applied using the adhesive formulation of the example (optimal composition). See Table 4 for details.

[0039] Table 4: Effects of substrate type and thickness on tape performance As shown in Comparative Example 8, when using non-polar or low surface energy substrates such as polypropylene (PP), the adhesion of the adhesive layer decreases significantly, leading to deterioration of various properties and poor electrolyte resistance. PET and PI substrates (Examples 6 and 7) exhibit excellent performance when bonded to the adhesive layer of this invention due to their good surface polarity, mechanical strength, and chemical stability. Therefore, limiting the substrate to PET or PI is necessary and preferred.

[0040] Table 5: Effect of adhesive layer thickness on tape performance The thickness of the adhesive layer directly affects the coating process, cost, and final mechanical properties. When the thickness is less than 15 μm (Comparative Example 9), the amount of adhesive is insufficient, easily leading to low bond strength and exposed substrate defects. Within the thickness range of 15-40 μm (Examples 8-10), the performance is reliable, with 25-35 μm (Example 9) being the optimal range, balancing excellent performance with optimal adhesive usage and economy. When the thickness exceeds 40 μm (Comparative Example 10), curing may be incomplete, and the coating process window narrows, making defects more likely.

[0041] This group of experiments aims to verify the reliability of the pressure-sensitive tape of the present invention in a specific application scenario of bonding an insulating protective film to the metal casing of a lithium-ion battery cell. Harsh environmental tests were conducted simulating actual working conditions. The test methods are as follows: Sample preparation: The preferred adhesive tape (PET 25μm, adhesive layer 25μm) obtained in Example 9 was adhered to the surface of an aluminum plate (simulating the aluminum shell of a battery cell). High temperature and high humidity storage: Stored in an environment of 85°C and 85% relative humidity for 1000 hours (double 85 test). High and low temperature cycling: Performed 300 cycles between -40°C and 85°C, with each cycle lasting 12 hours.

[0042] Table 6: Reliability Testing of Adhesive Tape in Simulated Battery Cell Application Environment Comparative experiment: The same test was conducted on Comparative Example 5 (short-chain prepolymer tape) and commercially available solvent-based blue film tape for battery cells.

[0043] Table 7: Application Performance Comparison The data in Tables 6 and 7 fully demonstrate that the pressure-sensitive tape provided by the present invention exhibits excellent and stable bonding reliability in the harsh application environment simulating battery cells, especially in terms of high temperature and humidity and resistance to electrolyte corrosion, its performance far exceeds that of comparative examples and existing technology products.

[0044] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in conjunction with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in conjunction with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention as set forth in the appended claims.

Claims

1. An acrylic UV-curable pressure-sensitive adhesive for battery cell bonding film, characterized in that, By weight, it includes the following components: 15-30 parts of acrylate prepolymer, 60-100 parts of composite diluted monomer; 1-5 parts of photoinitiator; 0-10 parts of additives; The acrylate prepolymer is prepared by a two-step esterification reaction of a polyol, a long-chain aliphatic diacid, and acrylic acid, wherein the long-chain aliphatic diacid has 9 to 12 carbon atoms.

2. The pressure-sensitive adhesive according to claim 1, characterized in that, The long-chain aliphatic dicarboxylic acid is selected from at least one of azelaic acid, sebacic acid, undecanoic acid, and dodecanoic acid.

3. The pressure-sensitive adhesive according to claim 1, characterized in that, The composite diluent monomer is composed of monofunctional acrylate monomers, difunctional acrylate monomers and trifunctional acrylate monomers, wherein the monofunctional acrylate monomer accounts for 80% to 95% of the total mass of the composite diluent monomer, the difunctional acrylate monomer accounts for 2% to 10% and the trifunctional acrylate monomer accounts for 0% to 3%.

4. The pressure-sensitive adhesive according to claim 3, characterized in that, The monofunctional acrylate monomer is isooctyl acrylate or butyl acrylate; the difunctional acrylate monomer is 1,6-hexanediol diacrylate; and the trifunctional acrylate monomer is trimethylolpropane triacrylate.

5. The pressure-sensitive adhesive according to claim 1, characterized in that, The photoinitiator comprises 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 1:0.5 to 1:

2.

6. The pressure-sensitive adhesive according to claim 1, characterized in that, The additives include colorants and adhesion promoters; the colorant content is 0.5% to 5% by total weight of the composition, and the adhesion promoter is a phosphate ester compound with a content of 0.1% to 2%.

7. A method for preparing an acrylic UV-curable pressure-sensitive adhesive for battery cell bonding, the method being used to prepare the pressure-sensitive adhesive according to any one of claims 1 to 6, characterized in that, The method includes the following steps: S1, a polyol is reacted with a long-chain aliphatic dicarboxylic acid at 150°C to 180°C in a first esterification reaction until the acid value drops below 50 mgKOH / g; then the temperature is lowered to 90°C to 110°C, acrylic acid or methacrylic acid, a catalyst and a polymerization inhibitor are added, and a second esterification reaction is carried out until the acid value drops below 10 mgKOH / g; the acrylate prepolymer is obtained after post-treatment. S2, the acrylate prepolymer, composite diluent monomer, photoinitiator and additives are mixed evenly under light-protected conditions.

8. A pressure-sensitive adhesive tape for attaching film to battery cells, characterized in that, It includes a substrate and an adhesive layer coated on at least one side of the substrate, the adhesive layer being formed by curing the pressure-sensitive adhesive according to any one of claims 1 to 6 under ultraviolet light.

9. The pressure-sensitive tape according to claim 8, characterized in that, The substrate is a polyethylene terephthalate film or a polyimide film with a thickness of 20 μm to 100 μm; the adhesive layer has a thickness of 15 μm to 40 μm.

10. The pressure-sensitive tape according to claim 8, characterized in that, The pressure-sensitive tape is used to adhere an insulating protective film to the surface of the metal casing of a lithium-ion battery cell.

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