Solid state polycondensation polyester film and preparation method thereof, composite current collector

Abstract

The application discloses a solid-phase polycondensation polyester film and a preparation method thereof, a composite current collector, a pole piece and a battery, and belongs to the technical field of composite current collector production, and comprises a heat treatment-solid-phase polycondensation enhancement process, wherein the heat treatment-solid-phase polycondensation enhancement process refers to sending a polyester film into a heat treatment system for solid-phase polycondensation reaction, specifically, the polyester film is heat treated at a temperature of 180-230 DEG C for 5-60 min, in the polyester film treated by the heat treatment-solid-phase polycondensation enhancement process, chemical reactions occur between the terminal carboxyl groups and the terminal hydroxyl groups of polyester macromolecules and between the terminal hydroxyl groups, therefore, the heat resistance and tensile strength of the polyester film can be improved, and the heat resistance is better when the solid-phase polycondensation polyester film after enhancement is used to prepare a composite current collector. The composite current collector can be used to prepare a pole piece, and then can be used to prepare a battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite current collector production, and particularly relates to a solid-phase polycondensation polyester film and a preparation method thereof, and a composite current collector. BACKGROUND

[0002] The metalized polyester film is widely used in the fields of electronics, packaging, printing and the like due to its excellent conductivity, barrier, flexibility and light weight. The common metalized polymer film products on the market include: composite current collector, thin film electrode, packaging aluminized film, printing film and the like. In the traditional technology, the metalized polyester film is usually prepared by directly depositing metal on the surface of polyester high polymer film through physical vapor deposition technology.

[0003] In the preparation process of the metalized polyester film, the polyester base film is prone to breakage due to its low tensile strength, thereby resulting in a low yield of the product. Meanwhile, in the process of the end application, the coating and product composite forming processes involved also have a relatively high requirement on the tensile strength of the base film. In addition, the metalized polyester film has a poor heat resistance problem, i.e., the polymer film substrate shrinks too much at a high temperature, resulting in separation of the base material from the metal layer. Therefore, in order to prepare a metalized polyester film with high performance and yield, it is necessary to improve the tensile strength and heat resistance of the polyester base film. SUMMARY

[0004] The present application aims to provide a solid-phase polycondensation polyester film and a preparation method thereof, and a composite current collector, so as to solve the technical problems mentioned in the background.

[0005] In order to achieve the above-mentioned purpose, the present application discloses a preparation method of a solid-phase polycondensation polyester film, comprising a heat treatment-solid-phase polycondensation enhancement process, wherein the heat treatment-solid-phase polycondensation enhancement process refers to sending the polyester film into a heat treatment system for solid-phase polycondensation reaction.

[0006] Further, the heat treatment-solid-phase polycondensation enhancement process comprises preheating and heat treatment.

[0007] Further, in the preheating process, the polyester film is preheated by dry hot air.

[0008] Further, in the heat treatment process, the preheated polyester film is first heated for solid-phase polycondensation reaction, and then pre-cooling and cooling are performed.

[0009] Further, in the heat treatment process, the heating temperature is 180-230℃, and the heat treatment time is 5-60min. Preferably, the heat treatment time is 10-50min, and more preferably 30-50min.

[0010] Further, the polyester film is prepared by a melt extrusion-stretching film forming process before the heat treatment-solid phase polycondensation enhancement process.

[0011] The melt extrusion-stretching film forming process comprises: compounding, melt extrusion and stretching.

[0012] The three raw materials are A material, B material and C material, and the A material, the B material and the C material each comprise a main material and an additive; the main material is selected from one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polyarylate (PAR), or a derivative or copolymer thereof; and the additive is selected from one or more of a slip agent, an antioxidant, an antistatic agent or a nucleating agent.

[0013] The content of the main material in the A material is 90-97%, and the content of the additive is 3-10%; the content of the main material in the B material is 95-99%, and the content of the additive is 1-5%; and the content of the main material in the C material is 90-97%, and the content of the additive is 3-10%.

[0014] The A material, the B material and the C material are added into a screw extruder, heated and melted, and then three-layer co-extruded through a die to obtain an A / B / C three-layer co-extruded film, wherein the mass ratio of the extrusion amounts of the A layer, the B layer and the C layer is (5-30%):(40%-90%):(5-30%).

[0015] The stretching comprises longitudinal stretching and transverse stretching.

[0016] The application also claims a solid phase polycondensation polyester film prepared by the above preparation method.

[0017] The application also claims a composite current collector, which is a metallized polymer film using the above solid phase polycondensation polyester film, and the composite current collector comprises a composite positive current collector and a composite negative current collector, the composite positive current collector is formed by arranging an aluminum layer on the solid phase polycondensation polyester film, and the composite negative current collector is formed by arranging a copper layer on the solid phase polycondensation polyester film.

[0018] The above composite current collector can be used to prepare a pole piece. The pole piece comprises a positive pole piece and a negative pole piece, wherein the positive pole piece is formed by loading a positive active material on the composite positive current collector, and the negative pole piece is formed by loading a negative active material on the composite negative current collector.

[0019] The above pole piece can be used to prepare a battery, and the above positive pole piece and negative pole piece are used in the battery.

[0020] The polyester film after the heat treatment-solid phase polycondensation enhancement process, in the heat treatment stage, the esterification reaction between the terminal carboxyl group and the terminal hydroxyl group of the polyester macromolecule, and the ester exchange reaction between the terminal hydroxyl groups, realize the crosslinking of the polyester macromolecule, can improve the heat resistance and tensile strength of the polyester film.

[0021] The application proposes a polyester film preparation method based on the idea of improving the mechanical properties of polymers by increasing the molecular weight through solid phase polycondensation reaction in polyester synthesis chemistry, and adds a post-treatment (i.e. heat treatment-solid phase polycondensation enhancement) process on the basis of the biaxial stretching process. A solid phase polycondensation polyester film is prepared by the method, and the tensile strength and heat resistance of the prepared polyester film are obviously improved. The metalized film prepared by taking the solid phase polycondensation polyester film as the base film can effectively solve the problems of low yield rate caused by the low tensile strength of the base film and the poor heat resistance of the metalized polyester film during the preparation and application of the metalized film.

[0022] Compared with the prior art, the solid phase polycondensation polyester film, the preparation method thereof and the composite current collector have the following advantages:

[0023] (1) The preparation method of the solid phase polycondensation polyester film of the application involves simple and easy-to-implement processing technology, which is easy to scale up for mass production.

[0024] (2) The solid phase polycondensation polyester film obtained by the preparation method of the application has obviously improved tensile strength and heat resistance. The solid phase polycondensation polyester film prepared as the base material for the composite current collector can effectively solve the problem of low yield rate caused by the low tensile strength of the base film during the preparation and application of the composite current collector, and improve the heat resistance of the prepared composite current collector.

[0025] (3) The composite current collector prepared by using the solid phase polycondensation polyester film of the application can be further used to prepare an electrode sheet, and the electrode sheet can be further used to prepare a battery. Due to the high tensile strength and good heat resistance of the solid phase polycondensation polyester film, the electrode sheet and the battery also have excellent performance. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 : The structural diagram of the solid phase polycondensation polyester film obtained by the application.

[0027] Among them, 1, A layer; 2, B layer; 3, C layer. DETAILED DESCRIPTION

[0028] A preparation method of a solid phase polycondensation polyester film, comprising the following steps:

[0029] I. melt extrusion-stretching film process, and II. heat treatment-solid phase polycondensation enhancement process.

[0030] Wherein, one, melt extrusion-stretching film forming process, specifically includes:

[0031] (1) batching; (2) crystallization drying; (3) melt extrusion; (4) casting; (5) longitudinal stretching; (6) transverse stretching; (7) winding.

[0032] Wherein, in step (1) batching, three raw materials need to be prepared, which are A material, B material and C material. A material, B material and C material all include a main body material and an additive.

[0033] Wherein, the main body material is selected from one or more of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polyarylate (PAR), or their derivatives or copolymers;

[0034] The additive is selected from one or more of a slip agent, an antioxidant, an antistatic agent or a nucleating agent. The slip agent is selected from one or more of titanium dioxide, silicon dioxide, calcium carbonate, talc, kaolin, diatomite, siloxane or acrylate. The antioxidant is selected from one or more of phosphonate (such as antioxidant 1222, antioxidant 300) or bisphenol A phosphite. The antistatic agent is selected from one or more of magnesium oxide, copper oxide, aluminum oxide, carbon black, graphite, glycerol, polyglycerol, polyethylene glycol, polyether ester or conductive fiber. The nucleating agent is selected from one or more of magnesium oxide, zinc oxide, aluminum oxide, barium sulfate, talc, calcium carbonate, sodium carbonate, triphenyl phosphate, benzophenone, polyethylene glycol, polycaprolactone, magnesium stearate or sodium benzoate.

[0035] In terms of weight percentage, the content of the main body material in A material is 90-97%, and the content of the additive is 3-10%; the content of the main body material in B material is 95-99%, and the content of the additive is 1-5%; the content of the main body material in C material is 90-97%, and the content of the additive is 3-10%.

[0036] Wherein, in step (2) crystallization drying, the prepared A, B and C three raw materials are respectively added to the crystallizer for crystallization, and the process conditions are as follows: crystallization temperature 140-180℃, crystallization treatment time 20-120min; the crystallized crystals are added to the drying tower for drying, and the process conditions are as follows: drying temperature 140-170℃, crystallization treatment time 120-300min.

[0037] Wherein, in step (3) melt extrusion, the A, B and C three raw materials after crystallization drying are added to the screw extruder, heated and melted, and then three-layer co-extrusion is carried out through the die to obtain A / B / C three-layer co-extruded film, wherein the mass ratio of the extrusion amount of A, B and C three layers is (5-30%):(40%-90%):(5-30%).

[0038] In step (4), the molten polyester stream extruded from the die is cast onto a casting roll and formed by the casting roll and water cooling.

[0039] In step (5), the longitudinal stretching specifically includes the following steps:

[0040] ① Preheating: the cast film formed before stretching needs to be preheated, and the preheating conditions are as follows: the preheating temperature is 70-100℃;

[0041] ② Stretching: after the cast film is preheated, it is stretched longitudinally, and the stretching process conditions are as follows: the stretching ratio is (3-4.5):1, and the stretching temperature is 80-120℃;

[0042] ③ Heat setting: after the film is stretched, it is heat set, and the heat setting temperature is 165-180℃;

[0043] ④ Cooling: after the film is heat set, it is cooled, and the cooling temperature is 30-50℃.

[0044] In step (6), the transverse stretching specifically includes the following steps:

[0045] ① Preheating: the film needs to be preheated before transverse stretching, and the preheating conditions are as follows: the preheating temperature is 80-120℃;

[0046] ② Stretching: after the cast film is preheated, it is stretched longitudinally, and the stretching process conditions are as follows: the stretching ratio is (3-4.5):1, and the stretching temperature is 90-140℃;

[0047] ③ Heat setting: after the film is stretched, it is heat set, and the heat setting temperature is 150-250℃;

[0048] ④ Cooling: after the film is heat set, it is cooled, and the cooling temperature in the middle cooling zone is 80-150℃, and the cooling temperature in the cooling zone is 25-45℃.

[0049] In step (7), the film after transverse stretching is drawn into the winding system by the traction system for film winding.

[0050] In step (7), the film after transverse stretching is drawn into the winding system by the traction system for film winding.

[0051] (a) unwinding; (b) preheating; (c) heat treatment-solid phase polycondensation; (d) winding.

[0052] In step (a), the film obtained by the melt extrusion-film stretching process is placed in the unwinding system for unwinding;

[0053] In step (b) of preheating, the film after unwinding is sent into a preheating treatment system (specifically a hot air oven), and the heating gas source in the system is dry hot air, the air volume is 2000-3000 m 3 / h, the preheating temperature is 110-160℃, and the treatment time is 5-30 min. The role is to reduce the moisture content of the film and improve the crystallinity.

[0054] In step (c) of heat treatment-solid phase polycondensation, the following process is included:

[0055] First, the reaction is carried out: after the film is preheated, it is sent into a heat treatment system (specifically a hot air oven), and the heating gas source in the system is nitrogen, the air volume is 1000-2000 m 3 / h, the heating temperature is 180-230℃, and the treatment time is 5-60 min. In this stage, esterification reaction occurs between the terminal carboxyl groups and the terminal hydroxyl groups of the polyester macromolecule, and ester exchange reaction occurs between the terminal hydroxyl groups, realizing the crosslinking of the polyester macromolecule. Nitrogen is selected as the heating gas source because as an inert gas, nitrogen will not cause oxidative degradation and hydrolysis of the polyester macromolecule during heating, and can carry away the ethylene glycol and water produced by the polyester crosslinking reaction, improving the reaction rate. The nitrogen used is treated by a purification system and can be recycled;

[0056] Then, precooling is carried out: the film after the reaction zone is first sent into a precooling zone for preliminary cooling, and the cooling temperature is 140-170℃;

[0057] Finally, cooling is carried out: the film after the precooling zone is sent into a cooling zone for further cooling, and the cooling temperature is 30-50℃;

[0058] In step (d) of winding, the film after the above treatment is sent into a winding system through a traction system for winding, i.e. a solid phase polycondensation polyester film is prepared.

[0059] As shown in Figure 1 , it is a structural schematic diagram of the solid phase polycondensation polyester film obtained by the present application, and the solid phase polycondensation polyester film includes A / B / C three-layer structure.

[0060] The technical scheme of the present application will be described in detail through specific examples and comparative examples.

[0061] Example 1

[0062] 1. Preparation of solid phase polycondensation polyester film:

[0063] Material selection: the selected high molecular polyester is commercialized polyethylene terephthalate (PET) with intrinsic viscosity of 0.675 dL / g; the additives are antioxidant 300, silicon dioxide and aluminum oxide, and the size of the additives is 50-100 nm.

[0064] Preparation process:

[0065] I. Melt extrusion-stretching film process:

[0066] (1) Blending: In A material, including PET, antioxidant 300, silicon dioxide and aluminum oxide with mass content of 94%, 1%, 2% and 3% respectively; In B material, including PET, antioxidant 300, silicon dioxide and aluminum oxide with mass content of 97%, 1%, 1% and 1% respectively; C material is the same as A material.

[0067] (2) Crystallization and drying: The above three raw materials are transported into the crystallizer and treated at 150℃ for 30min. Then, the three raw materials after crystallization treatment are transported into the drying tower and dried at 160℃ for 150min.

[0068] (3) Melt extrusion: The above A, B, C three raw materials are added into the corresponding double screw extruder, heated and melted (temperature is 280℃), and extruded through the die by the metering pump, and the extrusion amount proportion of A, B, C three layers is controlled at 20%:60%:20%.

[0069] (4) Casting: The melt PET material extruded from the die is cast onto the casting roller, and is cooled and shaped by the casting roller and water cooling, and is cast into a thick sheet with a thickness of 96μm.

[0070] (5) Longitudinal stretching: First, the casting sheet is preheated at 90℃ before longitudinal stretching, and then is stretched longitudinally at 110℃, and the stretching ratio is 4:1. After stretching, the film is heat set treated at 170℃. Finally, it is cooled and shaped at 40℃.

[0071] (6) Transverse stretching: First, the casting sheet is preheated at 90℃ before transverse stretching, and then is stretched transversely at 120℃, and the stretching ratio is 4:1. After stretching, the film is heat set treated at 170℃. Finally, it is cooled and shaped at 90℃ in the cold zone and at 35℃ in the cooling zone.

[0072] (7) Winding: The film after transverse stretching enters the winding system through the traction system for film winding, and a 6μm thick film is prepared.

[0073] II. Heat treatment-solid phase polycondensation enhancement process:

[0074] (a) Unwinding: The film prepared in the melt extrusion-stretching film process is placed in the unwinding system of the process for unwinding.

[0075] (b) Preheating: The unwound film enters the preheating treatment system (hot air oven) and is dried in the dry hot air with air volume of 2000m 3 / h and temperature of 120℃ for 15min.

[0076] (c) Heat treatment - solid state polycondensation: After preheating, the film enters the heat treatment system (hot air oven) for solid state polycondensation for 10 min in nitrogen with a flow rate of 1000 m 3 / h and a temperature of 210°C. The nitrogen used is treated by a purification system and recycled. Then, the film coming out of the reaction zone enters the pre-cooling zone for preliminary cooling at 150°C. Finally, the film enters the cooling zone for further cooling at 40°C.

[0077] (d) Winding: The treated film enters the winding system through the traction system for film winding, i.e. the solid state polycondensation PET film is prepared.

[0078] The solid state polycondensation PET film obtained is denoted as S1.

[0079] 2. Preparation of composite current collector: The solid state polycondensation polyester film prepared by the above method is used to prepare a composite negative electrode current collector and a composite positive electrode current collector:

[0080] 2.1. Preparation of composite negative electrode current collector:

[0081] First, preparation of metal conductive layer: the solid state polycondensation PET film prepared above is placed in the vacuum evaporation cabin, and the high-purity copper wire (purity greater than 99.99%) in the metal evaporation chamber is melted and evaporated at a high temperature of 1400-2000°C. The metal atoms after evaporation pass through the cooling system in the vacuum coating chamber and deposit on the two surfaces of the polymer-based film to form a copper metal conductive layer with a thickness of 1 μm. Second, preparation of protective layer: 1 g of graphene is uniformly dispersed in 999 g of N-methyl pyrrolidone (NMP) solution by ultrasonic dispersion method to prepare a coating liquid with a solid content of 0.1 wt%, then the coating liquid is uniformly coated on the surface of the metal conductive layer by die coating process, and the coating amount is controlled at 80 μm, and finally dried at 100°C.

[0082] The composite negative electrode current collector obtained is denoted as F1.

[0083] 2.2. Preparation of composite positive electrode current collector:

[0084] First, the preparation of the conductive metal layer: The solid-phase polycondensation PET film prepared above is placed in a vacuum evaporation chamber. High-purity aluminum wire (purity greater than 99.99%) in the metal evaporation chamber is melted and evaporated at a high temperature of 1300-2000℃. The evaporated metal atoms are cooled by the cooling system in the vacuum coating chamber and deposited on both surfaces of the polymer base film to form an aluminum conductive metal layer with a thickness of 1μm. Second, the preparation of the protective layer: 1g of carbon nanotubes are uniformly dispersed in 999g of N-methylpyrrolidone (NMP) solution by ultrasonic dispersion to prepare a coating solution with a solid content of 0.1wt%. Then, the coating solution is uniformly coated onto the surface of the conductive metal layer by a die coating process, with the coating thickness controlled at 90μm. Finally, it is dried at 100℃.

[0085] The resulting composite positive current collector is denoted as Z1.

[0086] Example 2

[0087] The process is basically the same as Example 1, except that: in the second heat treatment-solid phase polycondensation reinforcement process, the heat treatment time is 30 minutes.

[0088] The obtained solid-phase polycondensation polyester film is denoted as S2, the obtained composite negative electrode current collector is denoted as F2, and the obtained composite positive electrode current collector is denoted as Z2.

[0089] Example 3

[0090] The process is basically the same as in Example 1, except that: in the second part, the heat treatment time in the solid-state polycondensation reinforcement process is 50 minutes.

[0091] The obtained solid-phase polycondensation polyester film is denoted as S3, the obtained composite negative electrode current collector is denoted as F3, and the obtained composite positive electrode current collector is denoted as Z3.

[0092] Example 4

[0093] The process is basically the same as in Example 1, except that in the second heat treatment-solid phase polycondensation reinforcement process, the heating temperature is 200°C.

[0094] The obtained solid-phase polycondensation polyester film is denoted as S4, the obtained composite negative electrode current collector is denoted as F4, and the obtained composite positive electrode current collector is denoted as Z4.

[0095] Example 5

[0096] The process is basically the same as in Example 1, except that: in the second heat treatment-solid phase polycondensation reinforcement process, the heating temperature is 220°C.

[0097] The obtained solid-phase polycondensation polyester film is denoted as S5, the obtained composite negative electrode current collector is denoted as F5, and the obtained composite positive electrode current collector is denoted as Z5.

[0098] Example 6

[0099] Preparation of solid state polycondensation polyester film:

[0100] Material selection: The selected high molecular polyester is commercialized polyethylene terephthalate (PET) with intrinsic viscosity of 0.675 dL / g; the additives are bisphenol A phosphite, silicon dioxide, magnesium oxide and talc powder, and the size of the additives is 50-100 nm.

[0101] Preparation process:

[0102] I. Melt extrusion-stretching film process:

[0103] (1) Blending: In A material, the mass content of PET, bisphenol A phosphite, silicon dioxide, magnesium oxide and talc powder is 92%, 2%, 1%, 2% and 3% respectively; in B material, the mass content of PET, bisphenol A phosphite, silicon dioxide, magnesium oxide and talc powder is 95%, 1%, 2%, 1% and 1% respectively; C material is the same as A material.

[0104] (2) Crystallization and drying: The above three raw materials are transported into the crystallizer and treated at 140°C for 100 min. Then, the three raw materials after crystallization treatment are transported into the drying tower and dried at 170°C for 220 min.

[0105] (3) Melt extrusion: The above A, B and C three raw materials are added into the corresponding twin-screw extruder, heated and melted (temperature is 280°C), and then extruded through the die by means of the metering pump, and the extrusion amount proportion of A, B and C three layers is controlled at 15%:70%:15%.

[0106] (4) Casting: The melt PET extruded from the die is cast onto the casting roller, and then cooled and shaped by the casting roller and water cooling, and finally cast into a thick sheet with a thickness of 96 μm.

[0107] (5) Longitudinal stretching: First, the casting sheet is preheated at 80°C before longitudinal stretching, and then stretched longitudinally at 120°C with a stretching ratio of 3:1. After stretching, the film is heat set at 175°C. Finally, it is cooled and shaped at 50°C.

[0108] (6) Transverse stretching: First, the casting sheet is preheated at 85°C before transverse stretching, and then stretched transversely at 140°C with a stretching ratio of 3.8:1. After stretching, the film is heat set at 200°C. Finally, it is cooled and shaped at 100°C in the cold zone and at 30°C in the cooling zone.

[0109] (7) Winding: The film after transverse stretching is introduced into the winding system through the traction system for film winding, and a 6 μm thick film is prepared.

[0110] II. Heat treatment - solid-state polycondensation reinforcement process:

[0111] (a) Unwinding: The film roll prepared in the melt extrusion-stretch film forming process is placed in the unwinding system of the process for unwinding.

[0112] (b) Preheating: The unwound film enters the preheating system (hot air oven) at an airflow rate of 2530 m³ / h. 3 Dry in hot, dry air at 140°C for 25 minutes per hour.

[0113] (c) Heat Treatment - Solid-State Polycondensation: After preheating, the membrane enters the heat treatment system (hot air oven) at an airflow rate of 1500 m³ / h. 3 Solid-phase polycondensation is performed in nitrogen gas at 230°C for 5 minutes per hour. The nitrogen gas used is purified and recycled. Then, the membrane exiting the reaction zone enters the pre-cooling zone for initial cooling at 140°C. Finally, the membrane enters the cooling zone for further cooling at 30°C.

[0114] (d) Winding: The treated film is wound into the winding system via the traction system to produce a solid-phase polycondensation PET film.

[0115] The resulting solid-phase polycondensation polyester film is designated as S6.

[0116] Composite negative current collector and composite positive current collector were prepared using the method in Example 1. The resulting composite negative current collector was denoted as F6, and the resulting composite positive current collector was denoted as Z6.

[0117] Example 7

[0118] It is basically the same as Example 3, except that the selected polymer polyester is commercially available polybutylene terephthalate (PBT).

[0119] Meanwhile, in the second heat treatment-solid phase polycondensation reinforcement process, the heating temperature is 180℃ and the heat treatment time is 60min.

[0120] The obtained solid-phase polycondensation polyester film is denoted as S7, the obtained composite negative electrode current collector is denoted as F7, and the obtained composite positive electrode current collector is denoted as Z7.

[0121] Comparative Example 1

[0122] Compared with Example 1, Comparative Example 1 only uses a melt extrusion-stretching film forming process to prepare a PET film, denoted as B1. The composite negative current collector prepared using this PET film is denoted as BF1, and the composite positive current collector is denoted as BZ1.

[0123] Comparative Example 2

[0124] In the heat treatment-solid phase polycondensation enhancement process in the comparative example 2, the heating temperature is 150℃, and the heat treatment time is 80min. A PBT film is prepared, which is recorded as B2. A composite negative current collector prepared by using the PBT film is recorded as BF2, and a composite positive current collector is recorded as BZ2.

[0125] Test evaluation:

[0126] The purpose of preparing the solid phase polycondensation polyester film as described above is to improve the heat resistance and tensile strength of the polyester film. The tensile strength and thermal shrinkage of the polyester films obtained in the examples and comparative examples are evaluated, and the test method refers to the national standards GB / T 1040.3-2006 and GB / T 10003-2008, and the test results are shown in Table 1, wherein MD represents the longitudinal direction of the film, and TD represents the transverse direction of the film; the thermal shrinkage is the data after heating at 150℃ for 30min.

[0127] Table 1 Performance test results of polyester film

[0128]

[0129] The composite negative current collector and the composite positive current collector prepared as described above are also subjected to performance tests, and the film breaking rate, the tensile strength and the thermal shrinkage are tested, and the test results are shown in Table 2 and Table 3, respectively, wherein the thermal shrinkage is the data after heating at 150℃ for 15min.

[0130] Table 2 Performance test results of composite negative current collector

[0131]

[0132] Table 3 Performance test results of composite positive current collector

[0133]

[0134]

[0135] It can be seen that, compared with the polyester film prepared without using the heat treatment-solid phase polycondensation enhancement process, the tensile strength of the polyester film prepared by using the method of the present application is significantly increased, and the thermal shrinkage is also significantly decreased, which indicates that the solid phase polycondensation polyester film is prepared by using the method of the present application, and the mechanical properties and heat resistance of the composite current collector prepared by using the polyester film as the base film are also obviously improved.

[0136] The above only describes the preferred embodiments of the present application, and is not used to limit the application. Any modification, equivalent replacement, improvement, etc. within the design concept of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing a solid-state polycondensation polyester film, characterized by: The heat treatment-solid phase polycondensation enhancement process refers to sending the polyester film into a heat treatment system for solid phase polycondensation reaction; The heat treatment-solid phase polycondensation enhancement process comprises preheating and heat treatment; In the heat treatment process, the heating temperature is 180-230℃, and the heat treatment time is 5-60min; In the preheating process, the polyester film is preheated by dry hot air; In the heat treatment process, the preheated polyester film is first heated for solid phase polycondensation reaction, and then pre-cooling and cooling are performed; Before the heat treatment-solid phase polycondensation enhancement process, a melt extrusion-stretching film forming process is adopted to prepare the polyester film; The melt extrusion-stretching film forming process comprises: batching, melt extrusion and stretching; In the batching, three raw materials, i.e. A material, B material and C material, are prepared, and the A material, the B material and the C material each comprise a main body material and an additive; the main body material is selected from one or more of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate or polyarylate, or a derivative or copolymer thereof; the additive is selected from one or more of a slip agent, an antioxidant, an antistatic agent or a nucleating agent; In the A material, the content of the main body material is 90-97%, and the content of the additive is 3-10%; in the B material, the content of the main body material is 95-99%, and the content of the additive is 1-5%; in the C material, the content of the main body material is 90-97%, and the content of the additive is 3-10%; In the melt extrusion, the A material, the B material and the C material are added into a screw extruder, heated and melted, and then three-layer co-extruded through a die to obtain a three-layer co-extruded film of A layer, B layer and C layer, wherein the mass ratio of the extrusion amount of the A layer, the B layer and the C layer is (5-30%):(40%-90%):(5-30%); The stretching comprises longitudinal stretching and transverse stretching.

2. A solid phase polycondensation polyester film obtained by the preparation method of claim 1.

3. A composite current collector using the solid state polycondensation polyester film according to claim 2, characterized in that: The composite current collector comprises a composite positive current collector and a composite negative current collector, the composite positive current collector is formed after an aluminum layer is arranged on the solid phase polycondensation polyester film, and the composite negative current collector is formed after a copper layer is arranged on the solid phase polycondensation polyester film.

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