PET (Polyethylene Terephthalate) base film for composite current collector and preparation method of PET base film

Abstract

The invention relates to a PET (Polyethylene Terephthalate) base film for a composite current collector and a preparation method of the PET base film. The PET base film comprises PET slices, modified PET, modified silicon dioxide, a lubricant and an antioxidant, wherein the modified PET is obtained by esterification and polycondensation of terephthalic acid, ethylene glycol and an imidazole-containing diol monomer; the imidazole-containing diol monomer is composed of a compound A shown in the formula and a compound B shown in the formula, the modified silicon dioxide is obtained by treating nano silicon dioxide particles by using a silane coupling agent KH560 and then carrying out ring-opening grafting reaction on the treated nano silicon dioxide particles and a compound A. According to the invention, a bi-component diol monomer containing an imidazolyl group is introduced into a PET main chain, and a compound A is grafted on the surface of nano silicon dioxide, so that dual enrichment of the imidazolyl group on a base film body and the surface is realized, the mechanical modulus and the heat resistance of the base film are enhanced, the base film is not easy to deform in a high-temperature coating environment, and the service life of the base film is prolonged. And meanwhile, the problem that the metal layer is easy to fall off is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of composite current collector base film technology, specifically to a PET base film for composite current collectors and its preparation method. Background Technology

[0002] Composite current collectors are a new type of material developed to replace traditional electrolytic copper foil for negative electrodes or rolled aluminum foil for positive electrodes. They consist of a sandwich structure formed by depositing a metal layer on the surface of an ultra-thin organic polymer film, creating a metal layer + organic film layer + metal layer. This effectively reduces the amount of metal material used, lightens the weight, and improves battery stability. The organic film layer in the composite current collector plays a crucial role in its performance and is typically made of polyethylene terephthalate (PET), polypropylene (PP), or polyimide (PI).

[0003] PET is a colorless, transparent, and glossy film with high hardness and toughness, excellent puncture and abrasion resistance, and good optical properties. Therefore, it is used in many fields such as composite current collector films, electrical insulation films, release films, capacitor films, polarizer protective films, and packaging films. However, different chemical or physical modifications are required for different applications to meet varying performance requirements. For composite current collector base films, since the composite current collector is formed by depositing metal atoms onto an organic base film layer through coating processes such as vacuum evaporation, magnetron sputtering, and PVD vacuum sputtering, high demands are placed on the heat resistance and mechanical strength of the substrate. If PET film is used directly as the substrate, it often faces insufficient strength, and the coating is prone to peeling off. This is mainly because the glass transition temperature of PET base film is relatively low, making it prone to deformation under high-temperature coating environments. Furthermore, the adhesion between its surface and the metal layer is weak, and thermal stress easily causes the metal layer to peel off from the substrate surface. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention introduces diol compounds containing imidazole groups, part of which is polymerized in situ within PET, and part of which is grafted onto nano-silica. The mixture is then mixed with the PET substrate to form a film, effectively enhancing its adhesion to the metal layer.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A PET base film for composite current collectors comprises, by weight: 70-90 parts PET chips, 10-30 parts modified PET, 4-8 parts modified silica, 0.5-1 part lubricant, and 0.2-0.8 parts antioxidant; The modified PET is obtained by esterification and polycondensation of terephthalic acid, ethylene glycol and imidazole diol-containing monomers; the imidazole diol-containing monomers are composed of compound A shown in formula 1) and compound B shown in formula 2). ; Equation 1) Equation 2) The modified silica is obtained by treating nano-silica particles with silane coupling agent KH560 and then reacting them with compound A via ring-opening grafting.

[0006] Furthermore, in the preparation of the modified PET, the molar ratio of terephthalic acid, ethylene glycol, and imidazole-containing monomer is 1:1.0~1.2:0.05~0.3; the molar ratio of compound A to compound B in the imidazole-containing monomer is 0.3~0.5:0.5~0.7.

[0007] Furthermore, the preparation process of the modified PET is as follows: Terephthalic acid, ethylene glycol, and imidazole glycol monomer were added to a reaction vessel, along with a catalytic amount of antimony glycolate. The esterification reaction was carried out under nitrogen protection at a temperature of 250-260°C and a pressure of 0.3-0.4 MPa. After the esterification reaction is completed, the stabilizer triphenyl phosphite and the polycondensation catalyst antimony trioxide are added to the reactor, and a vacuum is simultaneously drawn. The temperature is raised to 250~270℃ and the reaction is carried out for 2~3 hours. After the reaction is completed, the material is cooled and cut to obtain the final product.

[0008] Furthermore, the preparation process of the modified silica is as follows: Nano-sized silica particles were ultrasonically dispersed in anhydrous ethanol, and silane coupling agent KH560 was added. The temperature was increased and the mixture was refluxed for 8 hours. After the reaction was completed, the particles were centrifuged, rinsed with anhydrous ethanol, and dried for later use. The dried solid was redispersed in anhydrous ethanol, compound A was added, and the mixture was stirred at 70-90°C for 8-12 hours. After the reaction was completed, the particles were centrifuged, washed with ethanol 3-5 times, and dried under vacuum at 60-80°C to constant weight to obtain imidazole-functionalized modified silica.

[0009] Furthermore, the lubricant is at least one of ethylene bis-stearamide, pentaerythritol stearate, and butyl stearate.

[0010] Furthermore, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0011] A second objective of this invention is to provide a method for preparing a PET-based film for composite current collectors as described above, comprising the following steps: 1) Weigh out the measured amounts of PET chips, modified PET, modified silica, lubricant, and antioxidant, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder and melt-blend it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95~105℃ and a stretching ratio of 2.5~3.5 times; then transverse stretching is performed at a temperature of 100~120℃ and a stretching ratio of 3.0~4.0 times. 3) The biaxially stretched film is heat-set at 200~230℃, then cooled, stretched, and wound up.

[0012] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention introduces a two-component diol monomer containing imidazole groups into the PET backbone (compound A introduces imidazole groups into the PET backbone, and compound B introduces imidazole groups into the PET side chain), and simultaneously grafts compound A onto the surface of nano-silica, thereby achieving dual enrichment of imidazole groups in the substrate and on the surface. This forms strong coordination bonds during the subsequent deposition of the metal layer, effectively solving the problem of easy metal layer detachment.

[0013] 2. The phenyl and imidazolium ring structures in compound A increase the rigidity of the PET molecular chain and effectively improve its heat resistance. The side chains of compound B regulate the steric hindrance effect. Together, these two components effectively enhance the mechanical strength of the modified PET. Furthermore, the nano-silica modified from the homologous compound A can be uniformly dispersed in the PET matrix, further enhancing the mechanical modulus and heat resistance of the base film, making it less prone to deformation under high-temperature coating conditions. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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.

[0015] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0016] Example: A PET base film for composite current collectors comprises, by weight: 70-90 parts PET chips, 10-30 parts modified PET, 4-8 parts modified silica, 0.5-1 part lubricant, and 0.2-0.8 parts antioxidant; The modified PET is obtained by esterification and polycondensation of terephthalic acid, ethylene glycol, and imidazole diol-containing monomers in a molar ratio of 1:1.0~1.2:0.05~0.3; the imidazole diol-containing monomers are composed of compound A (formula 1) and compound B (formula 2) in a molar ratio of 0.5:0.5; the specific process is as follows: Terephthalic acid, ethylene glycol, and imidazole glycol monomers are added to a reactor, along with a catalytic amount of antimony glycolate. An esterification reaction is carried out under nitrogen protection at a temperature of 250–260°C and a pressure of 0.3–0.4 MPa. After the esterification reaction, the stabilizer triphenyl phosphite and the polycondensation catalyst antimony trioxide are added to the reactor, and a vacuum is simultaneously applied. The temperature is raised to 250–270°C and reacted for 2–3 hours. After the reaction is complete, the mixture is cooled and cut to obtain the final product.

[0017] By changing the molar ratio of terephthalic acid, ethylene glycol, and imidazole-containing monomers in the above reaction process, the following modified PET was obtained.

[0018] The modified silica is obtained by treating nano-silica particles with silane coupling agent KH560 and then reacting them with compound A via a ring-opening grafting reaction, as follows: Nano-sized silica particles were ultrasonically dispersed in anhydrous ethanol, and an equal amount of silane coupling agent KH560 was added. The temperature was raised and the mixture was refluxed for 8 hours. After the reaction was completed, the particles were centrifuged, rinsed with anhydrous ethanol, and dried for later use. The dried solid was redispersed in anhydrous ethanol, and 20% (by weight) of compound A was added. The mixture was stirred at 70°C for 12 hours. After the reaction was completed, the particles were centrifuged, washed with ethanol 3-5 times, and dried under vacuum at 60-80°C to constant weight to obtain imidazole-functionalized modified silica.

[0019] In the embodiments of this application, most of the raw materials used are conventional materials in the art, which can be purchased on the market and have little impact on the reaction. The sources and preparation methods of some raw materials are as follows: PET chips: purchased from Yizheng Chemical Fiber, model FG610, intrinsic viscosity 0.65±0.02 dL / g.

[0020] Nano silica particles: Purchased from Lingwei Technology, model CTT300.

[0021] Compound A: Structural formula: The preparation process is as follows: An aldehyde solution was prepared by dissolving 5 mmol of phenylglyoxal hydrate (CAS: 78146-52-8) and 5 mmol of formaldehyde in 20 ml of dilute hydrobromic acid aqueous solution in an ice-water bath. Then, 10 mmol of ethanolamine and 20 ml of dilute hydrobromic acid aqueous solution were added to the reaction flask in an ice-water bath and stirred until homogeneous. After purging with nitrogen for 30 min, the mixed aldehyde solution was slowly added dropwise to the reaction flask. Under nitrogen protection, the temperature was raised to 60 °C and stirred continuously for 5 h. After cooling to room temperature, the solvent was removed by vacuum distillation. The obtained product was washed several times with diethyl ether. The reaction yield was 91.1 wt%.

[0022] Compound B: Structural formula Chemical name: 3-(1H-imidazol-1-yl)propane-1,2-diol (CAS No.: 34793-28-7) Example 1: A PET-based film for composite current collectors 1) Weigh 70 parts of PET chips, 30 parts of modified PET sample 1, 8 parts of modified silica, 0.8 parts of lubricant ethylene bis-stearamide, and 0.8 parts of antioxidant 1010, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder and melt-blend and extrude it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 100℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 120℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0023] Example 2: A PET-based film for composite current collectors 1) Weigh 80 parts of PET chips, 20 parts of modified PET sample 1, 6 parts of modified silica, 0.6 parts of lubricant ethylene bis-stearamide, and 0.8 parts of antioxidant 1010, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder and melt-blend it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 115℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0024] Example 3: A PET-based film for composite current collectors 1) Weigh 90 parts of PET chips, 10 parts of modified PET sample 1, 4 parts of modified silica, 0.5 parts of lubricant ethylene bis-stearamide, and 0.8 parts of antioxidant 1010, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder and melt-blend and extrude it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 100℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 120℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0025] Example 4: A PET-based film for composite current collectors 1) Weigh 80 parts of PET chips, 20 parts of modified PET sample 2, 6 parts of modified silica, 0.6 parts of lubricant ethylene bis-stearamide, and 0.8 parts of antioxidant 1010, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder, melt-blend and extrude it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 115℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0026] Example 5: A PET-based film for composite current collectors 1) Weigh 80 parts of PET chips, 20 parts of modified PET sample 3, 6 parts of modified silica, 0.6 parts of lubricant ethylene bis-stearamide, and 0.8 parts of antioxidant 1010, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder and melt-blend it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 115℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0027] Comparative Example 1: A PET-based film for composite current collectors 1) Weigh 100 parts of PET chips, 6 parts of modified silica, 0.6 parts of lubricant ethylene bis-stearamide and 0.8 parts of antioxidant 1010, put them into a high-speed mixer and mix them evenly to obtain a mixture; then feed it into a twin-screw extruder and melt-blend extrusion at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 115℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0028] Comparative Example 2: A PET-based film for composite current collectors 1) Weigh 80 parts of PET chips, 20 parts of modified PET sample 3, 0.6 parts of lubricant ethylene bis-stearamide and 0.8 parts of antioxidant 1010, put them into a high-speed mixer and mix them evenly to obtain a mixture; then feed it into a twin-screw extruder and melt-blend and extrude it at 260~280℃, and cast it onto the cooling roller through the die head to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95℃ and a stretching ratio of 3; then transverse stretching is performed at a temperature of 115℃ and a stretching ratio of 3.5. 3) The biaxially stretched film is heat-set at 220°C, then cooled, stretched, and wound up.

[0029] The base films prepared in the above embodiments and comparative examples were subjected to performance tests. All tests followed national or international standards, and the test items included: Tensile strength and elongation at break: Refer to GT / T1040.3-2006; Heat shrinkage rate (150℃, 30min): Refer to GB / T12027-2004; Peel strength: The composite current collector is obtained by electroplating a copper layer onto the surface of the base film. The composite current collector is subjected to a 180° peel test (T-type peel) with a sample width of 15 mm.

[0030] Table 1 Analyzing the data in Table 1, in Examples 1-3, as the proportions of modified PET and modified silica in the formulation decreased, the tensile strength decreased, the heat shrinkage rate increased, and the peel strength gradually decreased. Observing Examples 2, 5, and 6, with fixed amounts of modified PET and modified silica, different modified PET samples were selected; as the amount of imidazole monomer introduced decreased, the peel strength significantly decreased. Observing Comparative Examples 1 and 2, the modified PET containing imidazole units had the greatest impact on peel strength; therefore, the composite current collector composed of the base film prepared in Comparative Example 1 (without modified PET) had the lowest peel strength. Of course, the imidazole-modified silica also improved the peel strength to some extent. Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A PET-based film for composite current collectors, characterized in that, By weight, it includes: 70-90 parts PET chips, 10-30 parts modified PET, 4-8 parts modified silica, 0.5-1 part lubricant, and 0.2-0.8 parts antioxidant; The modified PET is obtained by esterification and polycondensation of terephthalic acid, ethylene glycol and imidazole diol-containing monomers; the imidazole diol-containing monomers are composed of compound A shown in formula 1) and compound B shown in formula 2). Equation 1) Equation 2) The modified silica is obtained by treating nano-silica particles with silane coupling agent KH560 and then reacting them with compound A via a ring-opening grafting reaction.

2. The PET-based film for composite current collectors according to claim 1, characterized in that, In the preparation of the modified PET, the molar ratio of terephthalic acid, ethylene glycol, and imidazole-containing monomers is 1:1.0~1.2:0.05~0.3; the molar ratio of compound A to compound B in the imidazole-containing monomers is 0.3~0.5:0.5~0.

7.

3. The PET-based film for composite current collectors according to claim 1, characterized in that, The preparation process of the modified PET is as follows: Terephthalic acid, ethylene glycol, and imidazole glycol monomer were added to a reaction vessel, along with a catalytic amount of antimony glycolate. The esterification reaction was carried out under nitrogen protection at a temperature of 250-260°C and a pressure of 0.3-0.4 MPa. After the esterification reaction is completed, the stabilizer triphenyl phosphite and the polycondensation catalyst antimony trioxide are added to the reactor, and a vacuum is simultaneously drawn. The temperature is raised to 250~270℃ and the reaction is carried out for 2~3 hours. After the reaction is completed, the material is cooled and cut to obtain the final product.

4. The PET-based film for composite current collectors according to claim 1, characterized in that, The preparation process of the modified silica is as follows: Nano-sized silica particles were ultrasonically dispersed in anhydrous ethanol, and silane coupling agent KH560 was added. The temperature was increased and the mixture was refluxed for 8 hours. After the reaction was completed, the particles were centrifuged, rinsed with anhydrous ethanol, and dried for later use. The dried solid was redispersed in anhydrous ethanol, compound A was added, and the mixture was stirred at 70-90°C for 8-12 hours. After the reaction was completed, the particles were centrifuged, washed with ethanol 3-5 times, and dried under vacuum at 60-80°C to constant weight to obtain imidazole-functionalized modified silica.

5. The PET-based film for composite current collectors according to claim 1, characterized in that, The lubricant is at least one of ethylene bis-stearamide, pentaerythritol stearate, and butyl stearate.

6. The PET-based film for composite current collectors according to claim 1, characterized in that, The antioxidant is at least one of antioxidant 1010, antioxidant 1076, and antioxidant 168.

7. The method for preparing a PET-based film for composite current collectors as described in any one of claims 1-6, characterized in that, Includes the following steps: 1) Weigh out the measured amounts of PET chips, modified PET, modified silica, lubricant, and antioxidant, and mix them evenly in a high-speed mixer to obtain a mixture; then feed it into a twin-screw extruder and melt-blend it at 260~280℃, and cast it onto a cooling roller through a die to obtain a cast sheet; 2) The casting sheet is subjected to biaxial stretching, with longitudinal stretching at a temperature of 95~105℃ and a stretching ratio of 2.5~3.5 times; then transverse stretching is performed at a temperature of 100~120℃ and a stretching ratio of 3.0~4.0 times. 3) The biaxially stretched film is heat-set at 200~230℃, then cooled, stretched, and wound up.

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