A preparation method of an aluminum-plastic film for soft package battery coating

Abstract

This invention discloses a method for preparing an aluminum-plastic film for pouch battery coating, comprising the following steps: S1) providing aluminum foil and pre-treating the aluminum foil; S2) simultaneously casting a protective layer, an adhesive layer, and a heat-sealing layer on the upper and lower sides of the aluminum foil to obtain a four-layer composite film; S3) slitting the composite film; and S4) winding the slit composite film to obtain an aluminum-plastic film. The method for preparing an aluminum-plastic film for pouch battery coating provided by this invention employs a four-layer integrated casting method, which not only reduces the unevenness of the film surface caused by multiple composite winding processes, greatly improving production efficiency, but also ensures product consistency and electrolyte resistance by using a casting method for interlayer bonding, compared to traditional aluminum-plastic film adhesive layer bonding methods, and reduces the risk of interlayer separation.

Description

Technical Field

[0001] This invention relates to a method for preparing an aluminum-plastic film, and more particularly to a method for preparing an aluminum-plastic film for coating soft-pack batteries. Background Technology

[0002] In today's ever-evolving automotive industry, new energy vehicles have also made significant strides. Especially in the last two years, with the transformation and development of major automotive giants and the entry of other industries, new energy vehicles are rapidly gaining popularity. With the increasing prevalence of new energy vehicles, the soft-pack battery industry has also experienced rapid growth, driving continuous innovation in related industries. The aluminum-plastic film involved in this invention patent is one of the four major polymer materials for soft-pack batteries. According to incomplete statistics, over 90% of the aluminum-plastic film used in China currently comes from Japanese and South Korean companies. Its unit price is high, and due to its complex structure and production process, its output is low, resulting in a supply shortage. Furthermore, traditional Korean aluminum-plastic film typically consists of five layers; the protective film and heat-sealing layer need to be bonded to the aluminum foil with adhesives. This bonding method carries the risk of internal delamination due to the properties of the adhesive. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing an aluminum-plastic film for coating soft-pack batteries, which can ensure product consistency and electrolyte resistance, and reduce the risk of interlayer separation.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is to provide a method for preparing an aluminum-plastic film for coating soft-pack batteries, comprising the following steps: S1) providing aluminum foil and pre-treating the aluminum foil; S2) simultaneously casting a protective layer, an adhesive layer and a heat-sealing layer on the upper and lower sides of the aluminum foil to obtain a four-layer composite film; S3) slitting the composite film; S4) winding the slitting composite film to obtain an aluminum-plastic film.

[0005] Furthermore, step S1 includes performing a low-temperature treatment on the aluminum foil and pre-treating both sides of the aluminum layer with chromium-free passivation to generate a dense oxide protective layer.

[0006] Furthermore, in step S2, a casting device with three independently temperature-controlled die heads is used to simultaneously cast a protective layer, an adhesive layer, and a heat-sealing layer, with a casting speed of 5-10 m / min.

[0007] Furthermore, in step S2, the casting positions of the casting equipment are set as follows: the upper layer is a protective layer, the middle upper layer is an aluminum foil, the middle lower layer is an adhesive layer, and the lower layer is a heat-sealing layer. The thickness ratio of the protective layer to the adhesive layer is 1-3:1.

[0008] Furthermore, in step S2, the thickness of the protective layer is controlled to be 15-35 micrometers, and the tensile strength is greater than 35 MPa.

[0009] Furthermore, in step S2, the film thickness of the aluminum foil layer is controlled to be 30-40 micrometers, the cupping value is ≥7mm, and the tensile strength is greater than 90MPa.

[0010] Furthermore, in step S2, the adhesive layer is a modified polypropylene layer, the thickness of which is 5-8 micrometers and the melting point is 160-175℃; the modified polypropylene layer is maleic anhydride-grafted polypropylene, and the mass percentage content of maleic anhydride is 10-20%.

[0011] Furthermore, the heat-sealing layer in step S2 is a three-layer composite film composed of CPP, maleic anhydride-grafted PP, and CPP, with a thickness of 30-80 micrometers and a melting point of 140-170°C. The thickness ratio of each layer in the three-layer composite film is 2:1:2.

[0012] Furthermore, in step S2, the composite film is rapidly cooled within 10 seconds by a bidirectional water flow cooling roller; in step S3, the cooled composite film is pulled to the slitting shaft, and the number and position of the cutters on the slitting shaft are adjusted so that the slitting composite film has different widths.

[0013] Furthermore, during the winding process in step S4, the protective layer is on the outermost layer, and the heat-sealing layer is on the innermost layer.

[0014] Compared with existing technologies, this invention offers the following advantages: The method for preparing aluminum-plastic film for pouch battery coating provided by this invention employs a four-layer integrated casting process. Compared to traditional production processes, this process achieves integrated molding from raw material particles to the composite film, simplifying the traditional multi-step lamination and rewinding into a single step. This simplification of production steps not only reduces the problem of uneven film surface caused by multiple lamination and rewinding processes but also significantly improves production efficiency. Furthermore, the interlayer lamination through casting, compared to traditional aluminum-plastic film adhesive layer bonding methods, ensures product consistency and electrolyte resistance, and reduces the risk of interlayer separation. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the preparation process of the aluminum-plastic film used for coating soft-pack batteries according to the present invention. Detailed Implementation

[0016] The present invention will now be further described with reference to the accompanying drawings and embodiments.

[0017] Figure 1 This is a schematic diagram of the preparation process of the aluminum-plastic film used for coating soft-pack batteries according to the present invention.

[0018] Please see Figure 1 The method for preparing the aluminum-plastic film for coating soft-pack batteries provided by the present invention includes the following steps:

[0019] S1) Provide aluminum foil and pre-treat the aluminum foil; including low-temperature treatment of the aluminum foil and pre-treating both sides of the aluminum layer with chromium-free passivation to generate a dense oxide protective layer;

[0020] S2) A protective layer, an adhesive layer, and a heat-sealing layer are simultaneously cast onto the upper and lower sides of the aluminum foil to obtain a four-layer composite film. After the multi-layer film is cast and laminated, it is rapidly cooled by a bidirectional water flow cooling roller. The cooling process must be completed within 10 seconds.

[0021] S3) After the composite film cools, the film is pulled to the slitting shaft to slit the composite film; step S3 cuts the cast and cooled composite film into different widths and quantities by adjusting the number and position of the cutters on the slitting shaft.

[0022] S4) The slit composite film is wound up to obtain an aluminum-plastic film; when winding in step S4, it is preferable that the protective layer is on the outermost layer and the heat-sealing layer is on the innermost layer; if the positions are changed, it may cause wrinkles in the composite film.

[0023] The method for preparing aluminum-plastic film for soft-pack battery coating provided by this invention adopts a four-layer integrated casting method. Compared with the traditional production process, it not only reduces the problem of uneven film surface caused by multiple composite winding processes and greatly improves production efficiency, but also ensures product consistency and electrolyte resistance by using casting to achieve interlayer bonding, compared with the traditional aluminum-plastic film adhesive interlayer bonding method, and reduces the risk of interlayer separation.

[0024] Preferably, step S2 uses a casting device with three independently temperature-controlled die heads to simultaneously cast a protective layer, an adhesive layer, and a heat-sealing layer. The casting speed is 5-20 m / min, preferably 5-10 m / min. If the casting speed is too fast, the surface of the protective layer film may show spots or pits.

[0025] Preferably, the casting positions of the casting equipment in step S2 are set as follows: the upper layer is a protective layer, the upper middle layer is aluminum foil, the lower middle layer is an adhesive layer, and the lower layer is a heat-sealing layer. The thickness ratio of the protective layer to the adhesive layer is 1-3:1. A thicker protective layer results in better overall impact resistance of the aluminum-plastic film, but poorer bending resistance and adhesion. Experiments show that the best performance is achieved when the ratio of the protective layer to the adhesive layer is 2:1.

[0026] Protective layer: Adhesive layer ratio Impact resistance Bending resistance Peel strength 1:1 5mm 15 18N / 15mm 2：1 8mm 13 14N / 15mm 3：1 13mm 9 7N / 15mm

[0027] Preferably, in step S2, the thickness of the protective layer is controlled to be 15-35 micrometers, and the tensile strength is greater than 35 MPa; the protective layer is at least one of polyamide (PA), polyethylene terephthalate (PET), polypropylene (modified PP), rigid polyvinyl chloride (PVC), and polyurethane (PU).

[0028] Preferably, in step S2, the film thickness of the aluminum foil layer is controlled to be 30-40 micrometers, the cupping value is ≥7mm, and the tensile strength is greater than 90MPa.

[0029] Preferably, in step S2, the adhesive layer is a modified polypropylene layer with a thickness of 5-8 micrometers and a melting point of 160-175°C. The modified polypropylene layer is maleic anhydride-grafted polypropylene, wherein the amount of maleic anhydride added is above 10%; below 10%, the adhesive effect is poor. The preferred mass percentage of maleic anhydride is 10%-20%. When the mass percentage of maleic anhydride grafted onto the membrane is greater than 20%, the overall stiffness of the membrane increases, its flexibility decreases, and its adhesion performance is weak.

[0030]

[0031] Preferably, the heat-sealing layer in step S2 includes, but is not limited to, BOPP (Biaxially Oriented Polypropylene), CPP (Cast Polypropylene), PVC (Polyvinylchlorid), PE (Polyethylene), and their composite modified products, with a thickness of 30-80 micrometers and a melting point of 140-170℃. Verification has shown that among the four types of BOPP, CPP, PVC, and PE films mentioned above, pure CPP has the highest heat-sealing strength, but its high softening point and low bonding temperature affect the bonding effect. Adding maleic anhydride-grafted PP with a low softening point can lower the overall softening point of the film, resulting in more complete softening and better bonding at the same temperature, but the maleic anhydride film is harder. Considering tensile strength, breaking strength, and heat-sealing effect, a three-layer composite film of CPP, maleic anhydride-grafted PP, and CPP is preferred, and verification has shown that the thickness ratio of each layer in the three-layer composite film is 2:1:2, resulting in the best overall film performance.

[0032] Heat sealing layer solution BOPP CPP CPP composite film PVC PE Heat seal strength N / mm 74 80 105 65 38

[0033] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be defined by the claims.

Claims

1. A method for preparing an aluminum laminate film for a soft package battery, characterized by, Includes the following steps: S1) Provide aluminum foil and pre-treat the aluminum foil; S2) A protective layer, an adhesive layer and a heat-sealing layer are simultaneously cast onto the upper and lower sides of the aluminum foil to obtain a four-layer composite film. S3) Cut the composite membrane; S4) The slit composite film is wound up to obtain aluminum-plastic film; Step S2 uses a casting equipment with three independently temperature-controlled die heads to simultaneously cast a protective layer, an adhesive layer, and a heat-sealing layer, with a casting speed of 5-10 m / min. In step S2, the casting positions of the casting equipment are set as follows: the upper layer is a protective layer, the upper middle layer is an aluminum foil, the lower middle layer is an adhesive layer, and the lower layer is a heat-sealing layer. The heat-sealing layer in step S2 is a three-layer composite film composed of CPP, maleic anhydride-grafted PP and CPP, with a thickness of 30-80 micrometers and a melting point of 140-170℃. The thickness ratio of each layer in the three-layer composite film is 2:1:

2. The composite film in step S2 is then rapidly cooled within 10 seconds by a bidirectional water flow cooling roller.

2. The method for preparing an aluminum laminate film for a pouch battery according to claim 1, wherein Step S1 includes performing low-temperature treatment on the aluminum foil and pre-treating both sides of the aluminum layer with chromium-free passivation to generate a dense oxide protective layer.

3. The method for preparing an aluminum laminate film for a pouch battery according to claim 1, wherein In step S2, the thickness ratio of the protective layer to the adhesive layer is 1-3:

1.

4. The method for preparing an aluminum laminate film for a pouch battery according to claim 1, wherein In step S2, the thickness of the protective layer is controlled to be 15-35 micrometers, and the tensile strength is greater than 35 MPa.

5. The method for preparing the aluminum-plastic film for coating soft-pack batteries as described in claim 1, characterized in that, In step S2, the thickness of the aluminum foil layer is controlled to be 30-40 micrometers, the cupping value is ≥7mm, and the tensile strength is greater than 90 MPa.

6. The method for preparing the aluminum-plastic film for coating soft-pack batteries as described in claim 1, characterized in that, In step S2, the adhesive layer is a modified polypropylene layer with a thickness of 5-8 micrometers and a melting point of 160-175°C. The modified polypropylene layer is maleic anhydride-grafted polypropylene with a maleic anhydride content of 10-20% by mass.

7. The method for preparing the aluminum-plastic film for coating soft-pack batteries as described in claim 1, characterized in that, In step S3, the cooled composite film is pulled to the slitting shaft, and the number and position of the cutters on the slitting shaft are adjusted so that the slitting composite film has different widths.

8. The method for preparing the aluminum-plastic film for coating soft-pack batteries as described in claim 1, characterized in that, During the winding process in step S4, the protective layer is on the outermost layer, and the heat-sealing layer is on the innermost layer.

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