Polyester film for composite current collector and its preparation method

Abstract

The present invention discloses a polyester film for a composite current collector and a preparation method thereof. The polyester film constitutes the base material layer of the composite current collector. The polyester film is a single-layer polyester film containing 5-20 wt% of a polyester functional masterbatch, or a three-layer polyester film comprising layer A, layer B, and layer C, where layer A and layer C contain 5-20 wt% of the polyester functional masterbatch. Among them, the polyester functional masterbatch is prepared from raw materials including the following parts by weight: 30-50 parts by weight of poly(m-phthaloyldiaminodiphenylmethane), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silicon dioxide, and 50-100 parts by weight of PET. The polyester film constituting the current collector base material of this application is added with a polyester functional masterbatch. The resulting polyester film has characteristics such as low porosity, low water absorption rate, and low oxygen transmission rate. There is no obvious crack propagation in the conductive layer formed on the outside, and the structural consistency on both sides is better.

Description

Technical Field

[0001] The present application relates to a composite current collector in the field of energy storage technology, and particularly to a polyester film for a composite current collector and a preparation method thereof. Background Art

[0002] CN 110165223 A discloses a current collector, a pole piece, a battery and a method for manufacturing the current collector. The prior art points out that after a conductive layer is formed on an insulating layer of a composite current collector, during subsequent cold pressing, due to different cold pressing elongation rates of the insulating layer and the conductive layer, the conductive layer and the insulating layer are prone to separation, reducing the use stability of the current collector. In addition, the conductive layers on both sides of the insulating layer are usually separated, resulting in a large resistance of the current collector. The composite current collector of the prior art has a plurality of through holes formed in the insulating layer; the conductive layer includes a first conductive layer, a second conductive layer and a connecting layer connecting the first conductive layer and the second conductive layer. The first conductive layer and the second conductive layer are arranged on opposite sides of the insulating layer, and the connecting layer is arranged on the inner wall surface of the through hole. Such a design enables the conductive layer to wrap around the insulating layer, which can alleviate the situation where the conductive layer completely detaches from the insulating layer. In addition, since the connecting layer is part of the conductive layer and the connecting layer is also conductive, by connecting the first conductive layer and the second conductive layer on opposite sides of the insulating layer through the connecting layer, the resistance of the current collector can be reduced.

[0003] The solution proposed in the above prior art only alleviates the situation where the conductive layer completely detaches from the insulating layer. The fundamental reason is that the surface structure of the insulating layer is uneven, resulting in insufficient adhesion of the conductive layer to the insulating layer. Taking the formation of the conductive layer by vacuum sputtering process as an example, since the thickness of the insulating layer made of polymer material is very thin and it is difficult to withstand long-term high-temperature sputtering, it is necessary to sputter while winding and moving. Therefore, the thickness of the conductive layer that can be formed on the surface of the insulating layer in each sputtering chamber is very limited. To reach the required thickness of the conductive layer, it needs to be formed by layer-by-layer stacking of target bombardment in different chambers, and it may even be necessary to repeatedly sputter the insulating layer coil in the equipment. At this time, once the surface performance of the insulating layer is poor, the surface differences of the conductive layers formed by sputtering in each chamber will be gradually amplified, and it is very easy to delaminate after multiple stackings, and the stacked layers will fall off and powder in the subsequent processing. Summary of the Invention

[0004] The technical problem to be solved by the present application is to provide a polyester film for a composite current collector and a preparation method thereof to reduce or avoid the problems mentioned above.

[0005] To solve the above technical problems, the present application provides a polyester film for a composite current collector. The polyester film forms the base material layer of the composite current collector, and the conductive layers of the composite current collector are attached to both sides of the base material layer. It is characterized in that the polyester film is a single-layer polyester film containing 5-20 wt% of a polyester functional masterbatch, or a three-layer polyester film comprising layer A, layer B, and layer C, where layer A and layer C contain 5-20 wt% of the polyester functional masterbatch. The polyester functional masterbatch is prepared from raw materials in the following parts by weight: 30-50 parts by weight of poly(m-phthaloyldiamine), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silicon dioxide, and 50-100 parts by weight of PET.

[0006] In addition, the present application also provides a method for preparing a polyester film for a composite current collector. The polyester film forms the base material layer of the composite current collector, and the conductive layers of the composite current collector are attached to both sides of the base material layer. The polyester film is a single-layer polyester film containing 5-20 wt% of a polyester functional masterbatch. The preparation method includes the following steps: Components in the following weight ratios, namely 80-95 wt% of PET resin and 5-20 wt% of the polyester functional masterbatch, are respectively weighed by an electronic scale and enter a mixing bin to be mixed into a mixture; then the mixture enters an exhaust-type twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 270°C - 280°C; after the materials are melted in the extruder, they are filtered and extruded into thick sheets; the thickness and profile of the thick sheets can be adjusted by the extrusion amount of the extruder, the rotation speed of the casting roll, and the die opening; the above thick sheets are preheated at a temperature of 50°C - 90°C, enter an infrared heating zone of 300°C - 500°C, and are longitudinally stretched at a linear speed of 40 - 150 m / min, with a longitudinal stretching ratio of 4.0, to obtain stretched sheets; the stretched sheets are preheated at a temperature of 90°C - 120°C and transversely stretched at a temperature of 100°C - 160°C, with a transverse stretching ratio of 3.8; then they are shaped at a temperature of 160°C - 240°C and cooled from 160°C to 50°C to obtain the polyester film for a composite current collector.

[0007] The present application also provides another method for preparing a polyester film for a composite current collector. The polyester film constitutes the base material layer of the composite current collector, and the conductive layers of the composite current collector are attached to both sides of the base material layer. The polyester film is a three-layer polyester film including an A layer, a B layer, and a C layer, where the A layer and the C layer contain 5-20 wt% of a polyester functional masterbatch. The preparation method includes the following steps: Components with the following weight ratios: 80-95 wt% of PET resin and 5-20 wt% of the polyester functional masterbatch are respectively metered by an electronic scale and enter a mixing bin for mixing to form a mixture; then the mixture enters an exhaust-type twin-screw extruder E; 100% of the PET resin is put into a pre-crystallizer and pre-crystallized at a temperature of 160°C for 15 minutes, and then the PET material enters a drying tower and is dried at a temperature of 160°C for 6 hours, and then enters a single-screw extruder F; the temperatures of the twin-screw extruder E and the single-screw extruder F are adjusted to 270°C - 280°C; after the materials are melted in the two extruders, they are filtered. The materials extruded from the twin-screw extruder E are used as the A layer and the C layer on the surface, and the materials extruded from the single-screw extruder F are used as the middle B layer, and a three-layer composite thick sheet is formed through a multi-layer co-extrusion process; the thickness and profile of the thick sheet can be adjusted by the extrusion amount of the extruder, the rotation speed of the casting roll, and the die opening; the above thick sheet is preheated at a temperature of 50°C - 90°C, enters an infrared heating zone of 300°C - 500°C, and is longitudinally stretched at a linear speed of 40 - 150 m / min, and the longitudinal stretching ratio is 4.0 to obtain a stretched sheet; the stretched sheet is preheated at a temperature of 90°C - 120°C and transversely stretched at a temperature of 100°C - 160°C, and the transverse stretching ratio is 3.8; then it is shaped at a temperature of 160°C - 240°C and cooled from 100°C to 50°C to obtain the three-layer polyester film.

[0008] In addition, the preparation method further includes the preparation step of the polyester functional masterbatch: At room temperature, 50-100 parts by weight of powdered PET, 20-30 parts by weight of nano-silica, 30-50 parts by weight of powdered poly-m-phenylene isophthalamide, 1-3 parts by weight of powdered cobalt neodecanoate, 3-5 parts by weight of powdered dibutylhydroxytoluene, and 5-10 parts by weight of powdered 1,4-diiodobenzene are added to a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1500-2000 rpm for 30-60 minutes to form a mixture; then it is melt-extruded through a twin-screw extruder, and then water-cooled granulated or sliced to obtain the polyester functional masterbatch.

[0009] The polyester film constituting the current collector base material of the present application is added with a polyester functional masterbatch. The resulting polyester film has characteristics such as low porosity, low water absorption rate, and low oxygen permeability. No obvious crack propagation is seen in the conductive layer formed on the outside, and the structural consistency on both sides is better. Description of the Drawings

[0010] The following drawings are only intended to illustrate and explain the present application, and do not limit the scope of the present application.

[0011] Among them, Figure 1 It shows a schematic structural diagram of a composite current collector according to a specific embodiment of the present application.

[0012] Figure 2 It shows a schematic structural diagram of a composite current collector according to another specific embodiment of the present application.

[0013] Figure 3 It shows a schematic structural diagram of a substrate layer according to a specific embodiment of the present application.

[0014] Figure 4 It shows a schematic structural diagram of a conductive layer according to a specific embodiment of the present application. Detailed Description of the Invention

[0015] In order to have a clearer understanding of the technical features, objectives, and effects of the present application, the specific implementation manners of the present application will now be described with reference to the drawings. Among them, the same components are denoted by the same reference numerals.

[0016] As Figure 1-2 shown, the composite current collector of the present invention is composed of a substrate layer 1 and conductive layers 2 attached to both sides of the substrate layer 1. Among them, the substrate layer 1 is made of a polyester film added with a polyester functional masterbatch, and the substrate layer 1 may be a single-layer polyester film added with a polyester functional masterbatch ( Figure 1 ), or a three-layer polyester film including layer A, layer B, and layer C with the polyester functional masterbatch added to the surface layer ( Figure 2 ).

[0017] The polyester referred to in the present invention means a polyester formed by one or more selected from polycarboxylic acids containing dibasic acids and their ester-forming derivatives, and one or more selected from polyols containing diols; or a polyester formed by hydroxycarboxylic acids and their ester-forming derivatives; or a polyester formed by cyclic esters. The polyester can be manufactured according to existing well-known methods. For example, taking the preparation of PET as an example, it can be obtained by the following methods: a method of polycondensation after esterification of terephthalic acid and ethylene glycol; or a method of polycondensation after transesterification of an alkyl ester of terephthalic acid such as dimethyl terephthalate and ethylene glycol. The polyester of the present invention is preferably PET.

[0018] In order to improve the performance of the conductive layer 2, a barrier layer 11 of a metal (such as chromium oxide) or a non-metallic material (such as silicon dioxide) can also be sputtered or evaporated on the outer side of the substrate layer 1 between the conductive layer 2 and the substrate layer 1, as Figure 3As shown, it is a schematic structural diagram of a substrate layer according to a specific embodiment of the present application. The dotted line represents the conductive layer outside the substrate layer, and a decomposed view is shown.

[0019] The conductive layer 2 can be an aluminum conductive layer, a copper conductive layer, or a conductive layer of other metals formed by vacuum sputtering or evaporation. In order to reduce the resistivity, the conductive layer 2 can also be a multi-layer conductive structure formed by different processes. For example, the bottom layer of the conductive layer 2 can be a bottom coating layer 21 with a thickness of 5-15 nm formed by vacuum sputtering process, and the surface layer of the conductive layer 2 can be a surface coating layer 22 with a thickness of 100-500 nm grown on the bottom coating layer by hydroelectroplating process. The surface of the conductive layer 2 can also be passivated by electroplating or chemical etching process to form a dense protective layer 23, as Figure 4 As shown, it is a schematic structural diagram of the conductive layer according to a specific embodiment of the present application. The dotted line represents the substrate layer inside the conductive layer, and a decomposed view is shown.

[0020] As described above, in order to reduce the influence of the surface performance of the composite current collector on the production and performance of the battery, the present invention provides a polyester film for a composite current collector. The polyester film constitutes the substrate layer of the composite current collector, and the conductive layers of the composite current collector are attached to both sides of the substrate layer. Among them, the polyester film is a single-layer polyester film containing 5-20 wt% of polyester functional masterbatch, or a three-layer polyester film including layer A, layer B, and layer C, where layer A and layer C contain 5-20 wt% of polyester functional masterbatch. The polyester functional masterbatch is prepared from raw materials including the following parts by weight: 30-50 parts by weight of poly(m-xylylene adipamide), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silicon dioxide, and 50-100 parts by weight of PET.

[0021] The polyester functional masterbatch of the present invention can be prepared in the form of granules or slices and added to ordinary polyester during the production of polyester film to obtain the substrate layer 1 of the present invention. For example, 80-95 wt% of polyester without other components can be melt-blended with 5-20 wt% of the polyester functional masterbatch of the present invention, and then a single-layer substrate layer 1 can be produced through processes such as stretching, or the surface structure of the substrate layer 1 of the present invention can be obtained through a multi-layer co-extrusion process.

[0022] Each raw material component of the polyester functional masterbatch of the present invention can be uniformly mixed in the form of pellet materials and then extruded and granulated using equipment such as an extruder to obtain the polyester functional masterbatch of the present invention.

[0023] In a specific embodiment, at room temperature, 50 - 100 parts by weight of powdered PET, 20 - 30 parts by weight of nano - silica, 30 - 50 parts by weight of powdered poly - metaphenylene isophthalamide, 1 - 3 parts by weight of powdered cobalt neodecanoate, 3 - 5 parts by weight of powdered dibutylhydroxytoluene, and 5 - 10 parts by weight of powdered 1,4 - diiodobenzene are added to a high - speed mixer for pre - dispersion mixing at a rotation speed of 1500 - 2000 rpm for 30 - 60 minutes to form a mixed material. Then, melt extrusion is carried out through a twin - screw extruder, and then water cooling granulation or slicing is performed to obtain the polyester functional masterbatch.

[0024] In another specific embodiment, for example, after obtaining the slices of the polyester functional masterbatch, 5 - 20 wt% of the polyester functional masterbatch is taken and added to 80 - 95 wt% of PET particles for uniform mixing, and the two are melt - blended. Finally, a single - layer substrate layer 1 is produced through processes such as stretching, or the surface structure of the three - layer substrate layer 1 is obtained through a multi - layer co - extrusion process, etc.

[0025] Taking a single - layer polyester film as an example, the preparation method of the polyester film for a composite current collector of the present invention is further described below. The preparation method of the polyester film for a composite current collector of the present invention includes the following steps:

[0026] Components with the following weight ratios: 80 - 95 wt% of PET resin and 5 - 20 wt% of the polyester functional masterbatch are respectively metered by an electronic scale and enter a mixing bin for mixing to form a mixed material.

[0027] Then, the mixed material enters an exhaust - type twin - screw extruder, and the temperature of the twin - screw extruder is adjusted to 270°C - 280°C.

[0028] After the material is melted in the extruder, it is filtered and extruded into a thick sheet. The thickness and profile of the thick sheet can be adjusted by the extrusion amount of the extruder, the rotation speed of the casting roll, and the die opening.

[0029] The above - mentioned thick sheet is pre - heated at a temperature of 50°C - 90°C, enters an infrared heating zone at 300°C - 500°C, and is longitudinally stretched at a linear speed of 40 - 150 m / min with a longitudinal stretching ratio of 4.0 to obtain a stretched sheet.

[0030] The stretched sheet is pre - heated at a temperature of 90°C - 120°C, transversely stretched at a temperature of 100°C - 160°C with a transverse stretching ratio of 3.8. Then, it is shaped at a temperature of 160°C - 240°C and cooled from 160°C to 50°C to obtain the polyester film for a composite current collector.

[0031] Taking a three-layer polyester film as an example, the preparation method of the polyester film for composite current collectors of the present invention will be further described. The preparation method of the polyester film for composite current collectors of the present invention includes the following steps:

[0032] Components with the following weight ratios: 80-95 wt% of PET resin and 5-20 wt% of polyester functional masterbatch are respectively metered by an electronic scale and enter a mixing bin for mixing to form a mixture.

[0033] After that, the mixture enters an exhaust-type twin-screw extruder E.

[0034] 100% of the PET resin is put into a pre-crystallizer and pre-crystallized at a temperature of 160 °C for 15 minutes. After that, the PET material enters a drying tower and is dried at a temperature of 160 °C for 6 hours, and then enters a single-screw extruder F.

[0035] Adjust the temperatures of the twin-screw extruder E and F to 270 °C - 280 °C.

[0036] After the materials are melted in the two extruders, they are filtered. The materials extruded from the twin-screw extruder E are used as the A layer and the C layer on the surface, and the materials extruded from the single-screw extruder F are used as the B layer in the middle, and a three-layer composite thick sheet is formed through a multi-layer co-extrusion process. The thickness and profile of the thick sheet can be adjusted by the extrusion amount of the extruder, the rotation speed of the casting roll, and the opening of the die head.

[0037] The above-mentioned thick sheet is preheated at a temperature of 50 °C - 90 °C, enters an infrared heating zone of 300 °C - 500 °C, and is longitudinally stretched at a linear speed of 40 - 150 m / min. The longitudinal stretching ratio is 4.0 to obtain a stretched sheet.

[0038] The stretched sheet is preheated at a temperature of 90 °C - 120 °C and transversely stretched at a temperature of 100 °C - 160 °C. The transverse stretching ratio is 3.8. After that, it is shaped at a temperature of 160 °C - 240 °C and then cooled from 160 °C to 50 °C to obtain the polyester film with the three-layer structure.

[0039] Examples 1 - 5

[0040] According to the raw material weight part ratios in the following table, polyester functional masterbatch slices are respectively prepared and obtained, and then put into ordinary PET resin to prepare a single-layer structure polyester film for composite current collectors.

[0041] Example 1 Example 2 Example 3 Example 4 Example 5 Poly(m-xylylene adipamide) 30 35 40 45 50 Cobalt neodecanoate 1 1.5 2 2.5 3 Butylated hydroxytoluene 3 3.5 4 4.5 5 1,4-Diiodobenzene 5 7 7.5 8 10 Silica 20 22 25 27 30 PET 50 65 75 85 100 Slicing amount for preparing single-layer substrate layer 5wt% 10wt% 13wt% 15wt% 20wt% Substrate layer thickness μm 6 7 8 9 10

[0042] Comparative Examples 6 - 10

[0043] According to the same method as in the above examples, polyester films for comparison are prepared according to the raw material weight part ratios in the following table.

[0044] Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Poly(m-xylylene adipamide) 0 35 40 45 50 Cobalt neodecanoate 1 0 2 2.5 3 Butylated hydroxytoluene 3 3.5 0 4.5 5 1,4-Diiodobenzene 5 7 7.5 0 10 Silica 20 22 25 27 0 PET 80 66.5 79 93 130 Slicing amount for preparing single-layer substrate layer 5wt% 10wt% 13wt% 15wt% 20wt% Substrate layer thickness μm 6 7 8 9 10

[0045] The performance parameters of each polyester film were tested separately during preparation. Meanwhile, a 8-μm-thick film made of pure PET without adding any functional masterbatch was used for comparison. The performance parameters are shown in the following table.

[0046]

[0047]

[0048] Pure copper metal layers were formed on both side surfaces of the polyester films described in the above table through a vacuum sputtering process. The thickness of the pure copper metal layers on both sides controlled by vacuum sputtering was 5 nm, and the surface crack parameters of the prepared films were tested.

[0049]

[0050] From the performance parameters of the above film layers and the crack conditions of the metal coatings, it can be seen that for the polyester films prepared by adding the polyester functional masterbatch of the present application, their properties such as porosity, water absorption rate, and oxygen transmission rate have been greatly improved, and no obvious crack propagation is observed after forming the metal conductive layer.

[0051] Furthermore, the resistivity differences between the pure copper metal layers on both sides of the polyester films shown in the above table were tested, as shown in the following table.

[0052]

[0053] For the polyester films prepared by adding the polyester functional masterbatch of the present application, the resistivity differences of the metal conductive layers formed thereon are significantly smaller than those of the films without adding the functional masterbatch, indicating that the structures on both sides thereof have better consistency.

[0054] In summary, the polyester film constituting the current collector substrate of the present application is added with a polyester functional masterbatch. The thus formed polyester film has characteristics such as low porosity, low water absorption rate, and low oxygen transmission rate. No obvious crack propagation is observed in the conductive layer formed on the outside, and the structural consistency on both sides is better.

[0055] Those skilled in the art should understand that although the present application is described in the manner of multiple embodiments, not every embodiment contains only one independent technical solution. Such a description in the specification is only for clarity. Those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as ways that can be combined with each other to form different embodiments to understand the protection scope of the present application.

[0056] The above are only illustrative specific embodiments of the present application and are not intended to limit the scope of the present application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of the present application shall fall within the scope of protection of the present application.

Claims

1. A polyester film for a composite current collector, the polyester film constituting the base material layer of the composite current collector, and conductive layers of the composite current collector being attached to both sides of the base material layer, characterized in that, The polyester film is a single-layer polyester film containing 5-20 wt% of a polyester functional masterbatch, or a three-layer polyester film comprising layers A, B, and C, where layers A and C contain 5-20 wt% of the polyester functional masterbatch. The polyester functional masterbatch is prepared from the following raw materials in parts by weight: 30-50 parts by weight of poly(m-xylylene adipamide), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silica, and 50-100 parts by weight of PET.

2. A method for preparing a polyester film for a composite current collector, the polyester film constituting the base material layer of the composite current collector, and the conductive layers of the composite current collector being attached to both sides of the base material layer. The polyester film is a single-layer polyester film containing 5-20 wt% of a polyester functional masterbatch. The preparation method includes the following steps: The components with the following weight ratios: 80-95 wt% of PET resin and 5-20 wt% of polyester functional masterbatch are respectively metered by an electronic scale and enter a mixing bin for mixing to form a mixture; among them, The polyester functional masterbatch is prepared from the following raw materials in parts by weight: 30-50 parts by weight of poly(m-xylylene adipamide), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silica, and 50-100 parts by weight of PET; Thereafter, the mixture enters an exhaust-type twin-screw extruder, and the temperature of the twin-screw extruder is adjusted to 270°C to 280°C; After the material is melted in the extruder, it is filtered and extruded into a thick sheet. The thickness and profile of the thick sheet are adjusted by the extrusion amount of the extruder, the rotation speed of the casting roll, and the die opening; The above thick sheet is preheated at a temperature of 50°C to 90°C, enters an infrared heating zone at 300°C to 500°C, and is longitudinally stretched at a linear speed of 40-150 m / min. The longitudinal stretching ratio is 4.0 to obtain a stretched sheet; The stretched sheet is preheated at a temperature of 90°C to 120°C, transversely stretched at a temperature of 100°C to 160°C, and the transverse stretching ratio is 3.8; thereafter, it is shaped at a temperature of 160°C to 240°C and then cooled from 160°C to 50°C to obtain a polyester film for a composite current collector.

3. A method for preparing a polyester film for a composite current collector, the polyester film constituting the base material layer of the composite current collector, and the conductive layers of the composite current collector being attached to both sides of the base material layer. The polyester film is a three-layer polyester film comprising layers A, B, and C, where layers A and C contain 5-20 wt% of the polyester functional masterbatch. The preparation method includes the following steps: The components with the following weight ratios: 80 to 95 wt% of PET resin and 5 to 20 wt% of polyester functional masterbatch are respectively metered by an electronic scale and enter a mixing bin to be mixed into a mixed material; among them, The polyester functional masterbatch is prepared from the following raw materials in parts by weight: 30-50 parts by weight of poly(m-xylylene adipamide), 1-3 parts by weight of cobalt neodecanoate, 3-5 parts by weight of dibutylhydroxytoluene, 5-10 parts by weight of 1,4-diiodobenzene, 20-30 parts by weight of silica, and 50-100 parts by weight of PET; Thereafter, the mixture enters an exhaust-type twin-screw extruder E; Put 100% PET resin into the pre-crystallizer and pre-crystallize it at 160°C for 15 minutes. Then the PET material enters the drying tower and is dried at 160°C for 6 hours. After that, it enters the single-screw extruder F. Adjust the temperatures of the twin-screw extruder E and F to 270°C - 280°C. After the material is melted in the two extruders, it is filtered. The material extruded from the twin-screw extruder E is used as the A layer and C layer on the surface, and the material extruded from the single-screw extruder F is used as the B layer in the middle. A three-layer composite sheet is made through the multi-layer co-extrusion process. The thickness and profile of the sheet are adjusted by the extrusion volume of the extruder, the rotation speed of the casting roll, and the opening of the die head. Preheat the above-mentioned sheet at 50°C - 90°C, enter the infrared heating zone at 300°C - 500°C, and conduct longitudinal stretching at a linear speed of 40 - 150 m / min. The longitudinal stretching ratio is 4.0 to obtain a stretched sheet. Preheat the stretched sheet at 90°C - 120°C, conduct transverse stretching at 100°C - 160°C, and the transverse stretching ratio is 3.

8. Then it is shaped at 160°C - 240°C and cooled at 160°C - 50°C to obtain the polyester film with the three-layer structure.

4. The preparation method according to claim 2 or 3 further includes the preparation step of the polyester functional masterbatch: At room temperature, add 50 - 100 parts by weight of powdered PET, 20 - 30 parts by weight of nano-silica, 30 - 50 parts by weight of powdered poly(m-phenylene isophthalamide), 1 - 3 parts by weight of powdered cobalt neodecanoate, 3 - 5 parts by weight of powdered dibutylhydroxytoluene, and 5 - 10 parts by weight of powdered 1,4-diiodobenzene into a high-speed mixer for pre-dispersion and mixing at a rotation speed of 1500 - 2000 rpm for 30 - 60 minutes to form a mixed material. Then melt and extrude it through a twin-screw extruder, and then water-cool and pelletize or slice to obtain the polyester functional masterbatch.

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