Adhesive tape for edge covering of polymer battery prepared by solvent-free process

Abstract

The invention is applicable to the field of adhesive tapes for wrapping edges of batteries, and provides an adhesive tape for wrapping edges of polymer batteries prepared by a solvent-free process. The solvent-free adhesive layer is coated on the surface of one side of the PET base film; the solvent-free adhesive layer is formed on the surface of the PET base film through a precise coating-synchronous cooling process by a melt which is prepared from a flame-retardant adhesive main body, a flame-retardant tackifying aid, an electrolyte-resistant modified filler and a hydrophobic coupling agent through a solvent-free premixing process; according to the invention, through a triple progressive scheme of flame-retardant bonding main body design, electrolyte-resistant auxiliary agent collaboration and solvent-free precise preparation, the problems of poor bonding / flame-retardant compatibility, insufficient electrolyte resistance and many process defects of the existing product are solved; the adhesive layer is prepared by taking flame-retardant resin as a main body, compounding a modified filler and a water repellent agent and carrying out closed melting premixing and slit coating-synchronous cooling, and is suitable for edge covering sealing of the battery, and the safety performance of the battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of battery edge-sealing adhesive tape, and particularly relates to a solvent-free process for preparing polymer battery edge-sealing adhesive tape. Background Technology

[0002] Currently, most adhesive tapes used for edge sealing of lithium-ion batteries are prepared using solvent-based processes: non-flame-retardant thermoplastic resin is used as the main adhesive layer, compounded with conventional inorganic flame-retardant fillers. After homogenization in an open mixing device, the tape is coated onto the surface of a polyester base film by roller coating or blade coating, and then dried with hot air to remove the solvent. This type of adhesive tape relies on the adhesive properties of the adhesive layer to achieve edge sealing and fixation of the battery casing, while the flame-retardant fillers provide basic safety protection.

[0003] However, existing technologies have the following problems: Insufficient compatibility between adhesive and flame retardant properties: The non-flame retardant base resin of existing adhesive tapes has poor compatibility with conventional flame retardant fillers. When adding fillers to improve flame retardancy, the cohesive force of the adhesive layer and the bonding strength to the battery casing will decrease significantly, making it impossible to simultaneously meet the dual requirements of strong adhesion and high flame retardancy for battery edge wrapping. Electrolyte resistance defects: The existing adhesive layer does not have a special protective component designed for the carbonate electrolyte commonly used in batteries. After long-term contact with the electrolyte, the adhesive layer is prone to swelling and molecular chain degradation, which leads to the decay of the bonding performance and poses a safety risk of battery leakage and short circuit. The preparation process has safety and quality risks: solvent-based processes will leave a certain amount of solvent residue, and the open mixing and coating process is prone to introducing moisture and air impurities, resulting in defects such as bubbles and uneven thickness in the adhesive layer, which cannot be adapted to the demanding sealing scenarios of battery edge packing. Therefore, a solvent-free process is needed to prepare adhesive tape for polymer battery edging to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a solvent-free process for preparing adhesive tape for polymer battery edge banding to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A solvent-free process for preparing adhesive tape for polymer battery edge banding includes: PET base film; A solvent-free adhesive layer coated on one side of the PET base film; The solvent-free adhesive layer is a melt obtained by a closed-loop high-temperature melt premixing process with venting function, consisting of 60-65 wt% flame-retardant adhesive matrix, 10-15 wt% phosphorus-nitrogen synergistic flame-retardant tackifier, 10-15 wt% flake-shaped electrolyte-resistant modified filler, and 5-10 wt% fluorinated silane hydrophobic coupling agent. This melt is then formed by a precision coating-gradient cooling process using a slit-type coating head and a segmented cooling and shaping unit. The surface of the PET base film is corona-treated, with a surface tension ≥42 mN / m. The total weight percentage of all components is 100 wt%. The solvent-free premixing process uses a closed high-temperature melting equipment with venting function, and the precision coating-gradient cooling process uses a slit coating head and a segmented cooling and shaping unit. Through precise matching of structure and process, the adhesive tape bonding, flame retardancy and electrolyte resistance are synergistically improved, while eliminating solvent residue and potential process defects.

[0006] In a further technical solution, the flame-retardant adhesive body is at least one of the following: a flame-retardant saturated polyester resin with low melt viscosity (500-1500 Pa·s @ 180℃) and a hydrogenated styrene-isoprene block copolymer. By using a host material containing phosphorus / nitrogen flame-retardant functional groups, the adhesive tape is provided with basic flame-retardant properties while retaining the adhesive activity of the adhesive layer. At the same time, its low viscosity characteristics make it suitable for solvent-free coating processes.

[0007] In a further technical solution, the phosphorus-nitrogen synergistic flame retardant and tackifier is a phosphonate-modified epoxy resin with a phosphorus content of 5-8 wt%. By ensuring molecular-level compatibility between the additives and the main material (crosslinking of epoxy groups with polyester terminal hydroxyl groups), the cohesive force and flame-retardant synergistic effect of the adhesive layer are simultaneously enhanced (phosphorus elements achieve condensed phase flame retardancy, and nitrogen elements achieve gas phase flame retardancy), thus avoiding the degradation of adhesive performance caused by the addition of a single filler.

[0008] In a further technical solution, the sheet-like electrolyte-resistant modified filler is montmorillonite with a surface modified by a fluorosilane coupling agent, and its particle size ranges from 1 to 5 μm. The sheet-like structure can form a "labyrinth-like" barrier network inside the adhesive layer, hindering electrolyte penetration. At the same time, fluorosilane modification improves its compatibility with the adhesive layer, avoids filler agglomeration, and enhances the structural stability and flame-retardant synergistic effect of the adhesive layer.

[0009] A further technical solution is that the fluorinated silane hydrophobic coupling agent is perfluorooctyltriethoxysilane, and its migration rate to the adhesive layer surface is 0.5-1.0 μm / s under the coating process conditions of 170℃. Utilizing the spontaneous migration characteristics of its surface energy difference, after coating, it accumulates on the surface of the adhesive layer and forms a continuous hydrophobic protective film, which greatly reduces the contact angle between the electrolyte and the adhesive layer surface (contact angle ≥110°) and prevents the battery electrolyte from penetrating into the interior of the adhesive layer.

[0010] A further technical solution is that the surface of the PET base film is corona treated (surface tension ≥42mN / m), and the thickness of the base film is 25-50μm; the corona treatment optimizes the surface activity and roughness of the PET base film, improves the interfacial bonding force between the PET base film and the solvent-free adhesive layer, and avoids the risk of interlayer peeling.

[0011] In a further technical solution, the thickness of the PET base film is 25-50 μm, and the thickness of the solvent-free adhesive layer is 50-100 μm.

[0012] A further technical solution is that the operating environment of the sealed high-temperature melting equipment with exhaust function is an anhydrous nitrogen protective atmosphere (oxygen content ≤0.1%), the equipment is set at a temperature of 160-180℃, and the stirring rate is 300-500rpm; the gradient cooling process of the segmented cooling and shaping unit is: 80℃×5s→60℃×5s→30℃×10s. By isolating the raw materials from external air and moisture through an inert gas atmosphere, oxidation or moisture introduction during the premixing process is prevented. At the same time, trace volatile components in the raw materials are discharged through the exhaust port, ensuring the performance stability and structural density of the solvent-free adhesive layer.

[0013] Compared with the prior art, the beneficial effects of the present invention are: This invention addresses the problem of insufficient compatibility between adhesive and flame retardant properties: by optimizing the composition of the solvent-free adhesive layer (low-viscosity flame-retardant adhesive matrix + phosphonate-modified epoxy resin with a phosphorus content of 5-8wt%), the adhesive activity of the matrix resin and the cohesive strengthening effect of the additives are utilized to achieve a 180° peel strength of ≥1.5N / mm (room temperature) of the adhesive layer to the battery casing, while simultaneously meeting the UL94V-0 flame retardant standard, thus solving the problem of difficulty in achieving both adhesion and flame retardancy in the prior art. This invention addresses the problem of "defective electrolyte resistance": through an innovative solvent-free adhesive layer additive system (1-5μm flake-shaped fluorosilane-modified montmorillonite + perfluorooctyltriethoxysilane with a migration rate of 0.5-1.0μm / s), the flake-shaped filler forms a physical barrier network, while the surface hydrophobic film reduces electrolyte wettability. After immersion in a carbonate electrolyte at 60℃ for 72 hours, the adhesive strength retention rate is ≥85%, and the adhesive layer swelling rate is ≤5%, thus avoiding sealing failure caused by swelling and degradation of the adhesive layer. This invention addresses the issue of "safety and quality hazards in the preparation process": by optimizing the solvent-free process (raw material degassing pretreatment + closed melt premixing with venting function + slot coating - gradient cooling), the risk of solvent residue is completely eliminated; combined with corona treatment of PET base film and cooling protection before coating, the interfacial peel force between the adhesive layer and the base film is ≥2.0N / mm, and the thickness tolerance of the adhesive layer is ≤±5μm, free from defects such as bubbles and impurities, thus ensuring the consistency of the adhesive tape quality.

[0014] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0015] Figure 1 This is a three-dimensional structural diagram of the present invention.

[0016] In the diagram: 1. PET base film; 2. Solvent-free adhesive layer. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0019] Example 1 like Figure 1 As shown, this embodiment of the invention provides a polymer battery edge-sealing adhesive tape prepared by a solvent-free process, comprising a PET base film 1 and a solvent-free adhesive layer 2 coated on one side of the PET base film 1.

[0020] In this embodiment, the PET base film 1 has a thickness of 35 μm and a surface tension of 45 mN / m after corona treatment, which can improve the interfacial bonding force with the adhesive layer; the solvent-free adhesive layer 2 has a thickness of 80 μm and its composition ratio is: 65 wt% flame-retardant saturated polyester resin (melt viscosity 800 Pa·s @ 180℃), 12 wt% phosphonate modified epoxy resin (phosphorus content 6 wt%), 13 wt% fluorosilane modified montmorillonite (particle size 3 μm), and 10 wt% perfluorooctyltriethoxysilane (migration rate 0.8 μm / s under coating conditions at 170℃). During preparation, the raw materials are first pretreated: solid raw materials are vacuum dried and degassed (polyester resin 120℃ / 2h, montmorillonite 80℃ / 4h), and liquid additives are purified by vacuum distillation (80℃ / 30min). The pretreated raw materials are then put into a closed high-temperature melting equipment with exhaust function and melt-blended for 30min at 170℃ and 400rpm under an anhydrous nitrogen protective atmosphere (oxygen content ≤0.1%) to form a bubble-free homogeneous melt. Subsequently, the melt is introduced into a slit coating head through an insulated conveying pipe and coated on the corona-treated surface of the PET base film 1 at a speed of 8m / min. A 50℃ cooling protection roller is set at the coating station to prevent thermal deformation of the base film. Finally, it enters the segmented cooling and shaping unit and is cured and shaped according to the gradient cooling process of "80℃×5s→60℃×5s→30℃×10s". Testing showed that the adhesive tape prepared in this embodiment had a 180° peel strength to the battery casing at room temperature of 1.6 N / mm and a flame retardant rating of UL94V-0. After being immersed in a carbonate electrolyte at 60°C for 72 hours, the adhesive strength retention rate was 88% and the adhesive layer swelling rate was 4%. The adhesive layer thickness tolerance was controlled within ±3 μm, and there were no defects such as bubbles or impurities, fully meeting the battery edge sealing requirements.

[0021] Example 2 The difference between this embodiment and Embodiment 1 lies in the type of flame-retardant adhesive substrate, the composition ratio of the solvent-free adhesive layer, and some process parameters.

[0022] In this embodiment, the specifications of the PET base film 1 remain unchanged (35 μm thickness, 45 mN / m surface tension). The thickness of the solventless adhesive layer 2 is adjusted to 70 μm, and the composition ratio is optimized as follows: 65 wt% hydrogenated styrene-isoprene block copolymer (SEPS, melt viscosity 1200 Pa·s @ 180℃), 10 wt% phosphonate-modified epoxy resin (phosphorus content 6 wt%), 12 wt% fluorosilane-modified montmorillonite (particle size 3 μm), and 13 wt% perfluorooctyltriethoxysilane (migration rate 0.8 μm / s under coating conditions at 170℃). During preparation, the melt blending temperature is adjusted to 175℃, the stirring rate is maintained at 400 rpm, and the remaining pretreatment, protective atmosphere, coating speed, and gradient cooling process are consistent with those in Example 1. Testing showed that the adhesive tape prepared in this embodiment had a peel strength of 1.5 N / mm at 180°C and a flame retardant rating of UL94V-0. After immersion in a carbonate electrolyte at 60°C for 72 hours, the adhesive strength retention rate was 86% and the adhesive layer swelling rate was 4.5%. The introduction of hydrogenated styrene-isoprene block copolymer improved the flexibility of the adhesive tape, making it suitable for battery edge wrapping scenarios with large curvature.

[0023] Example 3 The difference between this embodiment and Embodiment 2 lies in the phosphorus content of the phosphorus-nitrogen synergistic flame retardant and tackifier, the particle size of the flake-shaped electrolyte-resistant modified filler, and the corresponding process adaptation parameters.

[0024] In this embodiment, the PET base film 1 still uses a thickness of 35 μm and a surface tension of 45 mN / m. The solvent-free adhesive layer 2 has a thickness of 90 μm, and the composition ratio is adjusted as follows: 65 wt% hydrogenated styrene-isoprene block copolymer (melt viscosity 1200 Pa·s @ 180℃), 10 wt% phosphonate-modified epoxy resin (phosphorus content 8 wt%), 12 wt% fluorosilane-modified montmorillonite (particle size 1 μm), and 13 wt% perfluorooctyltriethoxysilane (migration rate 0.8 μm / s under coating conditions at 170℃). During preparation, the melt blending time is extended to 35 min to ensure uniform dispersion of 1 μm particle size montmorillonite; the coating speed is adjusted to 7 m / min to match the molding requirements of a thicker adhesive layer; the remaining pretreatment, protective atmosphere, melt temperature, and gradient cooling processes are the same as in Example 2. Testing showed that the adhesive tape prepared in this embodiment had a peel strength of 1.7 N / mm at 180°C and a flame retardant rating of UL94V-0 (flame retardant response speed improved by 15% compared to Example 2). After immersion in a carbonate electrolyte at 60°C for 72 hours, the adhesive strength retention rate was 90% and the adhesive layer swelling rate was 3.8%. The smaller particle size of montmorillonite forms a denser "labyrinthine" barrier network, which, combined with the flame retardant synergistic effect of high phosphorus content additives, is suitable for power battery edge-wrapping scenarios with higher safety performance requirements.

[0025] Working principle and usage process of this invention: Raw material pretreatment: Degassing of solid raw materials: Flame-retardant saturated polyester resin (solid particles) was placed in a vacuum drying oven and dried at 120℃ and -0.09MPa for 2 hours; 3μm fluorosilane-modified montmorillonite was placed in a vacuum drying oven and dried at 80℃ and -0.09MPa for 4 hours to remove trace amounts of moisture and volatile impurities adsorbed in the raw materials. Liquid additive impurity removal: Phosphonate-modified epoxy resin with a phosphorus content of 6wt% and perfluorooctyltriethoxysilane were placed in a vacuum distillation apparatus and distilled at 80℃ and 0.08MPa for 30min to remove low-boiling-point impurities. Pretreatment of PET base film 1: Perform surface corona treatment on PET base film 1 to ensure surface tension ≥42mN / m; after treatment, store the base film in a dry environment (humidity ≤40%RH) to avoid surface moisture absorption; Solvent-free premixed plasticizing: Raw material feeding: According to the ratio of 65wt% flame-retardant saturated polyester resin, 12wt% phosphonate modified epoxy resin, 13wt% fluorosilane modified montmorillonite and 10wt% perfluorooctyltriethoxysilane, the pretreated raw materials are sequentially fed into the hopper of a closed high-temperature melt blending equipment with exhaust function. Inert gas protection: Anhydrous nitrogen is introduced into the equipment to replace the internal air until the oxygen content is ≤0.1%, forming an inert protective atmosphere to prevent the raw materials from oxidizing at high temperatures; Melt blending and degassing: Start the heating and stirring system of the equipment, raise the temperature to 170℃, stir at 400rpm, and maintain melt blending for 30min; during this period, the trace amounts of residual gas in the raw materials are continuously discharged through the exhaust port at the top of the equipment, and finally a solvent-free adhesive melt with uniform composition and no bubbles is formed (viscosity 1000Pa·s@170℃). Coating and gradient cooling for shaping: Base film preheating and conveying: The pretreated PET base film 1 is installed on the unwinding device. The tension of the base film is adjusted by the tension control system (tension 65N / m). After being preheated by the preheating roller (temperature 60℃), it is conveyed smoothly to the coating station at a speed of 8m / min. The coating station is equipped with a cooling protection roller (temperature 50℃) to avoid direct contact between the high temperature melt and the base film, which may cause thermal deformation. Adhesive melt coating: The prepared solventless adhesive melt is introduced into the slit coating head through the heat-insulated conveying pipe (temperature 170℃), the coating head gap is adjusted to 70μm, and the adhesive melt is uniformly coated on the corona-treated surface of the PET base film 1 to form the initial coating of the solventless adhesive layer 2. Gradient cooling and shaping: The base film coated with the initial coating enters a three-stage cooling unit in sequence: the first stage pre-cooling zone (temperature 80℃, cooling time 5s) to initially shape the melt and fully wet the base film; the second stage intermediate cooling zone (temperature 60℃, cooling time 5s) to reduce internal stress; the third stage final cooling zone (temperature 30℃, cooling time 10s) to completely solidify the adhesive layer, finally forming a solvent-free adhesive layer 2 with a uniform structure and smooth surface, and the thickness tolerance of the adhesive layer is controlled within ±3μm; Post-processing and application: Finished product inspection: After curing, the adhesive tape passes through the inspection station. Visual inspection equipment is used to check for defects such as bubbles, impurities, and scratches in the adhesive layer. The thickness of the adhesive layer is measured using a thickness gauge (accuracy ±1μm). A tensile testing machine is used to test the 180° peel strength (1.6N / mm at room temperature) and interfacial peel force (2.2N / mm). A flame retardancy tester is used to test the flame retardancy rating (UL94V-0). An electrolyte immersion test (60℃, 72h) is used to test the bond strength retention rate (88%) and swelling rate (4%), ensuring that the finished product quality meets the requirements. Rewinding and storage: The qualified adhesive tape is wound into rolls by the rewinding unit with a stable tension of 60 N / m, packaged and stored in a dry and ventilated environment (temperature 25±5℃, humidity ≤40%RH), with a shelf life of 12 months; Battery edge-sealing application: In the edge-sealing process of lithium-ion batteries, one side of the solvent-free adhesive layer 2 of the finished adhesive tape is attached to the edge-sealing area of ​​the battery casing. The bonding area is then uniformly pressured by a pressing device (temperature 80℃, pressure 0.3MPa, pressing time 30s) to ensure that the adhesive layer 2 and the battery casing are in full contact and undergo an interfacial bonding reaction, ultimately achieving sealed protection of the battery edge-sealing. This ensures that there is no risk of leakage or short circuit during long-term use.

[0026] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solvent-free process for preparing adhesive tape for polymer battery edge banding, characterized in that, include: PET base film (1); Solvent-free adhesive layer (2) coated on one side of the PET base film (1); The solvent-free adhesive layer (2) is a melt obtained by a closed high-temperature melt premixing process with venting function, consisting of 60-65wt% flame-retardant adhesive matrix, 10-15wt% phosphorus-nitrogen synergistic flame-retardant tackifier, 10-15wt% sheet-like electrolyte-resistant modified filler and 5-10wt% fluorinated silane hydrophobic coupling agent. It is formed by a precision coating-gradient cooling process with a slit coating head and a segmented cooling and shaping unit. The surface of the PET base film (1) is corona treated and has a surface tension ≥42mN / m. The total weight percentage of each component is 100wt%.

2. The solvent-free process for preparing adhesive tape for polymer battery edge banding according to claim 1, characterized in that, The flame-retardant adhesive matrix is ​​at least one of the following: low melt viscosity (500-1500 Pa·s @ 180℃) flame-retardant saturated polyester resin and hydrogenated styrene-isoprene block copolymer.

3. The solvent-free process for preparing polymer battery edge-sealing adhesive tape according to claim 1, characterized in that, The phosphorus-nitrogen synergistic flame retardant and tackifier is a phosphonate-modified epoxy resin with a phosphorus content of 5-8 wt%.

4. The solvent-free process for preparing polymer battery edge-sealing adhesive tape according to claim 1, characterized in that, The sheet-like electrolyte-resistant modified filler is montmorillonite with a surface modified by a fluorosilane coupling agent, and its particle size ranges from 1 to 5 μm.

5. The solvent-free process for preparing adhesive tape for polymer battery edge banding according to claim 1, characterized in that, The fluorinated silane hydrophobic coupling agent is perfluorooctyltriethoxysilane, and its migration rate to the adhesive layer surface is 0.5-1.0 μm / s under coating process conditions of 170°C.

6. The solvent-free process for preparing adhesive tape for polymer battery edge banding according to claim 1, characterized in that, The surface of the PET base film (1) is corona treated (surface tension ≥ 42 mN / m).

7. The solvent-free process for preparing adhesive tape for polymer battery edge banding according to claim 1, characterized in that, The thickness of the PET base film (1) is 25-50 μm, and the thickness of the solvent-free adhesive layer (2) is 50-100 μm.

8. The solvent-free process for preparing adhesive tape for polymer battery edge banding according to claim 1, characterized in that, The operating parameters of the sealed high-temperature melting equipment with exhaust function are: temperature 160-180℃, stirring speed 300-500rpm; the gradient cooling process of the segmented cooling and shaping unit is: 80℃×5s→60℃×5s→30℃×10s.

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