Maleic anhydride grafted polypropylene composite film and lithium battery coating material made therefrom

Abstract

The application discloses a maleic anhydride grafted polypropylene composite film which is formed by co-extrusion of three layers of A, B and C; the A layer is a contact layer with an aluminum foil and comprises the following components in percentage by mass: mPP particles 40-60%, maleic anhydride grafted particles MAH 54-38%, and initiator BPO 6.0-2.0%; the B layer is a core layer and comprises the following components in percentage by mass: PP-C particles 95-99% and slip agent masterbatch 5-1%; and the C layer is a heat sealing layer and comprises the following components in percentage by mass: copolymerized PP particles 97-99% and opening anti-blocking agent 3-1%. The above composite film is hot-pressed with the aluminum foil to form an aluminum-plastic composite film for lithium battery packaging, does not need to be hot-pressed at a high temperature of 160 DEG C, avoids negative effects on the toughness and formability of the aluminum-plastic film, and does not use traditional adhesive any more, so that the electrolyte resistance can be greatly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, and in particular to a maleic anhydride-grafted polypropylene composite film and a lithium battery coating material made therefrom. Background Technology

[0002] The structure of aluminum-plastic film includes: an outer layer of BOPA or BOPET (1), a middle layer of Al (3), an inner layer of CPP (5), and adhesives (2) and (4) between each layer, such as Figure 1 As shown.

[0003] Currently, the inner layer of most aluminum-plastic composite films is a chlorinated polypropylene (PP-C) layer. In typical dry-process production, the aluminum foil and cast polypropylene film are bonded together using traditional adhesives. After prolonged immersion in electrolyte, the adhesives are prone to failure, causing delamination and corrosion of the aluminum-plastic film. In the thermal process, the aluminum foil and cast polypropylene film are bonded together with hot-melt adhesive resin, and then thermally synthesized under slow pressure. This process uses mPP, which has high thermal bonding performance, so no adhesive is needed between the aluminum foil layer and the CPP film, resulting in better electrolyte resistance and water resistance. However, due to the high-temperature melting at around 160℃, the toughness and formability of the aluminum-plastic film are inferior to those of the dry process. It also has poorer deep-drawing performance, short-circuit protection, appearance, and cutting performance. Furthermore, the thermal process requires relatively high-end equipment.

[0004] Therefore, there is an urgent need to develop a maleic anhydride-grafted polypropylene composite membrane and a lithium battery coating material made from it. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a maleic anhydride-grafted polypropylene composite film and a lithium battery coating material made therefrom. This invention involves blending and melt-grafting maleic anhydride-grafted particles, chlorinated polypropylene (PP-C) particles, and metallocene mPP particles from a thermal process with maleic anhydride-grafted particles and an initiator under specific conditions, followed by extrusion molding to obtain a maleic anhydride-grafted polypropylene composite film. The mPP in the aluminum foil contact layer of this composite film is modified, eliminating the need for high-temperature hot pressing at 160°C, thus avoiding negative impacts on the toughness and formability of the aluminum-plastic film. Furthermore, since traditional adhesives are no longer used, electrolyte resistance is significantly improved.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A maleic anhydride-grafted polypropylene composite film, characterized in that the composite film is co-extruded from three layers A, B, and C;

[0008] The A layer is the contact layer with the aluminum foil and includes the following components by mass percentage: 40-60% mPP particles, 54-38% maleic anhydride grafted particles MAH, and 6.0-2.0% initiator BPO.

[0009] The B layer is the core layer, comprising the following components by mass percentage: 95-99% PP-C particles and 5-1% slip agent masterbatch;

[0010] The C layer is a heat-sealing layer, comprising the following components by mass percentage: 97-99% copolymer PP granules and 3-1% anti-blocking agent.

[0011] Preferably, the total thickness of the composite film is 20-120 μm; wherein the thickness of layer A is 3-8 μm, the thickness of layer C is 3-8 μm, and the remainder is layer B.

[0012] Preferably, the slip agent is one or a combination of erucamide, oleamide, and stearamide.

[0013] Preferably, the opening anti-blocking agent is one or a combination of silica, calcium carbonate, talc, and diatomaceous earth.

[0014] Preferably, the composite membrane is prepared as follows: the raw materials of each layer are mixed evenly according to the formula and then metered and fed in a clean environment. The mixture is then co-extruded through its respective extruder, metering pump, disc filter, melt pipeline, distributor, and T-die to obtain a continuous sheet melt. The continuous sheet melt is then rapidly cooled and formed by a chilling roller with a surface temperature of 18-25°C. The melt is then subjected to online non-contact thickness measurement, and the uniformity of the melt thickness is automatically adjusted. Finally, the edges are automatically trimmed and the melt is wound into a roll.

[0015] Preferably, the temperatures of the extruder, metering pump, disc filter, melt pipe, distributor, and T-die are set at 200-270°C.

[0016] Preferably, the winding speed of the composite film is 50-200 m / min.

[0017] Another objective of this invention is to disclose an aluminum-plastic composite film for lithium battery packs, which is made by hot pressing the above-mentioned composite film and aluminum foil at 80-120°C for 1-3 seconds and the hot pressing pressure is 0.2-0.5 MPa.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention discloses a maleic anhydride-grafted polypropylene composite film, which is produced by blending and melt-grafting maleic anhydride grafted particles, chlorinated polypropylene (PP-C) particles, and metallocene mPP particles from a thermal process with maleic anhydride grafted particles and an initiator under certain conditions, followed by extrusion molding. This invention also discloses an aluminum-plastic composite film for lithium battery coating, which uses a maleic anhydride-grafted polypropylene composite film instead of the traditional inner CPP layer and adhesive. Because the maleic anhydride-grafted polypropylene composite film and the aluminum foil contact layer mPP are modified, high-temperature hot pressing at 160°C is not required, avoiding negative impacts on the toughness and formability of the aluminum-plastic film. Furthermore, the elimination of traditional adhesives significantly improves electrolyte resistance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of existing aluminum-plastic film. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0022] A maleic anhydride-grafted polypropylene composite film, characterized in that the composite film is co-extruded from three layers A, B, and C;

[0023] The A layer is the contact layer with the aluminum foil and includes the following components by mass percentage: 40-60% mPP particles, 54-38% maleic anhydride grafted particles MAH, and 6.0-2.0% initiator BPO.

[0024] The B layer is the core layer, comprising the following components by mass percentage: 95-99% PP-C particles and 5-1% slip agent masterbatch;

[0025] The C layer is a heat-sealing layer, comprising the following components by mass percentage: 97-99% copolymer PP granules and 3-1% anti-blocking agent.

[0026] The total thickness of the composite membrane is 20-120 μm. Among them, the thickness of layer A is 3-8 μm, the thickness of layer C is 3-8 μm, and the rest is layer B.

[0027] The slip agent is one or a combination of erucamide, oleamide, and stearamide. The anti-blocking agent for openings is one or a combination of silica, calcium carbonate, talc, and diatomaceous earth.

[0028] The composite membrane is prepared as follows: the raw materials of each layer are mixed evenly according to the formula and then metered and fed into a clean environment. The mixture is then co-extruded through its respective extruder, metering pump, disc filter, melt pipeline, distributor, and T-die to obtain a continuous sheet melt. The continuous sheet melt is then rapidly cooled and formed by a chilling roller with a surface temperature of 18-25℃. The melt is then measured online without contact, and the uniformity of the melt thickness is automatically adjusted. Finally, the edges are automatically trimmed and the membrane is wound into a roll.

[0029] The temperatures of the extruder, metering pump, disc filter, melt pipe, distributor, and T-die are set at 200-270℃. The winding speed of the composite film is 50-200 m / min.

[0030] To better illustrate the technical effects of the present invention, comparisons are now made between Examples 1-12 and existing conventional dry-process aluminum-plastic films and conventional thermal-process aluminum-plastic films:

[0031] Table 1 shows the formulations and thicknesses of each layer of the maleic anhydride-grafted polypropylene composite membranes in Examples 1-12.

[0032] Table 1 Formulation of Maleic Anhydride-Grafted Polypropylene Composite Membrane

[0033]

[0034]

[0035] An aluminum-plastic composite film for lithium battery coating is prepared by hot-pressing the composite film obtained in Examples 1-12 with aluminum foil at 80-120°C for 1-3 seconds and the hot-pressing pressure is 0.2-0.5 MPa. Specifically, Table 2 shows the hot-pressing conditions for preparing the aluminum-plastic composite film from the composite films of Examples 1-12.

[0036] Table 2 Hot-pressing conditions for preparing aluminum-plastic composite films in Examples 1-12 (Table 2)

[0037] Hot pressing temperature ℃ Hot pressing time s Hot pressing pressure (MPa) Example 1 80 1.5 0.3 Example 2 80 1.5 0.3 Example 3 80 1.5 0.3 Example 4 80 1.5 0.3 Example 5 95 1.5 0.3 Example 6 95 1.5 0.3 Example 7 95 1.5 0.3 Example 8 95 1.5 0.3 Example 9 110 1.5 0.3 Example 10 110 1.5 0.3 Example 11 110 1.5 0.3 Example 12 110 1.5 0.3

[0038] Table 3 compares the test results of Examples 1-12 with those of conventional dry-process aluminum-plastic film and conventional thermal-process aluminum-plastic film.

[0039] Table 3 Comparison of Detection Results

[0040]

[0041]

[0042] As can be seen from Table 3, conventional dry-process aluminum-plastic film has significantly inferior electrolyte resistance, and conventional hot-process aluminum-plastic film has significantly inferior drawing performance. However, the aluminum-plastic composite film for lithium battery packs obtained by hot pressing maleic anhydride-grafted polypropylene composite film and aluminum foil in Examples 1-12 has both good electrolyte resistance and good drawing performance.

[0043] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A maleic anhydride-grafted polypropylene composite membrane, characterized in that, The composite film is co-extruded from three layers: A, B, and C. Layer A is the contact layer with the aluminum foil and comprises the following components by mass percentage: 40-60% metallocene mPP particles, 38-54% maleic anhydride grafted particles MAH, and 2.0-6.0% initiator BPO; Layer B is the core layer, comprising the following components by mass percentage: 95-99% chlorinated polypropylene (PP-C) particles and 1-5% slip agent masterbatch; The C layer is a heat-sealing layer, comprising the following components by mass percentage: 97-99% copolymer PP particles, and 1-3% anti-blocking agent for openings; The slip agent is one or a combination of erucamide, oleamide, and stearamide; the opening anti-blocking agent is one or a combination of silica, calcium carbonate, talc, and diatomaceous earth. The composite membrane is prepared as follows: the raw materials of each layer are mixed evenly according to the formula, then cleaned, metered, and fed. They are then co-extruded through their respective extruders, metering pumps, disc filters, melt pipes, distributors, and T-die heads. Copolymerized PP particles, chlorinated polypropylene PP-C particles, metallocene mPP particles, maleic anhydride grafted particles MAH, and initiator are blended, melt-grafted, and extruded at 200-270℃ to obtain a continuous sheet melt. The continuous sheet melt is rapidly cooled and formed by a chilling roller with a surface temperature of 18-25℃. Then, online non-contact thickness measurement is performed, and the uniformity of the melt thickness is automatically adjusted. Finally, the edges are automatically trimmed and the melt is wound into rolls.

2. The maleic anhydride-grafted polypropylene composite membrane according to claim 1, characterized in that, The total thickness of the composite film is 20-120 μm; wherein, the thickness of layer A is 3-8 μm, the thickness of layer C is 3-8 μm, and the remainder is layer B.

3. The maleic anhydride-grafted polypropylene composite membrane according to claim 1, characterized in that, The winding speed of the composite film is 50-200m / min.

4. An aluminum-plastic composite film for lithium battery packing, characterized in that, It is made by hot pressing the composite film according to any one of claims 1-3 with aluminum foil at 80-120°C for 1-3 seconds, with a hot pressing pressure of 0.2-0.5 MPa.

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