Heat sealing layer and application thereof in preparation of CPP film and aluminum plastic film

Abstract

The invention discloses a heat sealing layer and application thereof in preparation of a CPP film and an aluminum plastic film, first raw materials for forming the heat sealing layer comprise 58-82% of polypropylene random copolymer and 10-30% of homo-polypropylene, the polypropylene random copolymer is a propylene, ethylene and butylene ternary random copolymer, the density of the polypropylene random copolymer is 0.88-0.93 g / cm < 3 >, the melt index is 4-12 g / 10 min, and the melting point is 120-140 DEG C; the density of the homo-polypropylene is 0.88-0.93 g / cm < 3 >, the melt index is 6-14 g / 10 min, and the melting point is 160-170 DEG C. The heat-sealing layer is used for preparing the CPP film, and the CPP film has good low-temperature heat-sealing performance, high heat-sealing strength, good electrolyte resistance, stable friction before and after high-temperature curing, high peel strength and uniform whitening effect after one-sealing and two-sealing.

Description

Technical Field

[0001] The invention belongs to the field of lithium ion battery packaging materials, and in particular relates to a heat sealing layer and application thereof in preparing a CPP film and an aluminum-plastic film. Background Art

[0002] According to the different packaging forms, lithium-ion batteries are generally divided into three categories: cylindrical lithium batteries, square lithium batteries and soft-pack lithium batteries packaged with aluminum-plastic composite films. Cylindrical or square lithium batteries are generally packaged with stainless steel or aluminum alloy materials, so they are also called hard-shell lithium batteries. Soft-pack lithium batteries generally use aluminum-plastic composite films as packaging materials. They are small in size, light in weight, flexible in shape and size, and can be designed in a variety of ways. They can meet various complex battery shapes and higher energy density requirements, and adapt to the development trend of "thinner" and "smaller" batteries. At the same time, soft-pack batteries have quite good ductility. When the internal core of the soft pack has air bulging, the excellent ductility of the aluminum-plastic film can provide sufficient buffer space for the gas. Before reaching the battery explosion threshold, the aluminum-plastic film will be torn, avoiding the possibility of battery explosion, and ensuring safety performance. Therefore, the use of aluminum-plastic composite film packaging materials as shells will be the future development direction of various lithium-ion batteries.

[0003] Dry-process lithium battery aluminum-plastic film packaging materials mainly include PET, nylon, aluminum foil, CPP, and glue layer. From outside to inside, the structure is generally PET / PA / AL / CPP. The thickness of PET is generally 12um, and its main function is to prevent the electrolyte from dripping and corroding the nylon layer on the surface during processing, and to protect the nylon; the thickness of nylon is generally 25um, and its main function is to ensure the mechanical strength of the battery packaging, scratch resistance, puncture resistance, impact resistance, and prevent external force from damaging the battery; the thickness of aluminum foil is generally 40~50um, and its main function is to block, shading and ensure molding ductility. The thickness of CPP is generally 40~80um, and its main function is to prevent the electrolyte from corroding the aluminum foil and the key heat sealing function; each layer of material is connected together by 2~4um glue. As a heat-sealing layer material, CPP film has extremely high requirements for sealing temperature, heat-sealing strength, bonding strength with aluminum foil, and electrolyte resistance, and is one of the main technical problems in the aluminum-plastic film packaging industry. Among them, the heat sealing layer is an important factor affecting the low-temperature heat sealing performance, heat sealing strength and electrolyte resistance of CPP film. However, the existing heat sealing layer makes it difficult for CPP film to have good low-temperature heat sealing performance, heat sealing strength, electrolyte resistance and uniform whitening effect of one seal and two seals. Summary of the invention

[0004] In view of the shortcomings of the prior art, the heat sealing layer provided by the present invention is used to prepare a CPP film, and the CPP film has good low-temperature heat sealing performance, high heat sealing strength, good electrolyte resistance, stable friction before and after high-temperature aging, high peel strength and uniform whitening effect of one seal and two seals.

[0005] The object of the present invention is to provide a heat-sealing layer, wherein the first raw material forming the heat-sealing layer comprises, by weight percentage, 58-82% of random copolymerized polypropylene and 10-30% of a first homopolymerized polypropylene, wherein the random copolymerized polypropylene is a ternary random copolymer of propylene, ethylene and butene, and the density of the random copolymerized polypropylene is 0.88-0.93 g / cm 3 , the melt index is 4-12 g / 10 min, the melting point is 120-140 ° C; the density of the first homopolymer polypropylene is 0.88-0.93 g / cm 3 , the melt index is 6~14g / 10min, and the melting point is 160~170℃.

[0006] In some embodiments of the present invention, the first raw material further includes 0.5-6% of a silica opening agent and 0.5-6% of an erucic acid amide type lubricant.

[0007] Another object of the present invention is to provide a CPP film, wherein the CPP film comprises a heat-sealing layer, a core layer and a composite layer which are sequentially stacked.

[0008] In some embodiments of the present invention, the second raw material for forming the core layer includes 51-88% block copolymer polypropylene and 2-15% high-density polyethylene, in terms of mass percentage, wherein the block copolymer polypropylene is an alternating block copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.88-0.92 g / cm 3 , the melt index is 1~6g / 10min, the melting point is 150~163℃; the density of the high-density polyethylene is 0.955~0.97g / cm 3 , melt index is 6~14g / 10min, melting point is 128~140℃.

[0009] In some embodiments of the present invention, the second raw material further comprises 10-30% of a polyolefin elastomer, wherein the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.85-0.90 g / cm 3 , the melting point is 60~100℃ and the melting index is 1~6g / 10min.

[0010] In some embodiments of the present invention, the second raw material further includes 0.2-4% of erucamide type lubricant.

[0011] In some embodiments of the present invention, the third raw material forming the composite layer includes 95-100% of the second homopolypropylene and 0-5% of the silica opening agent, and the density of the second homopolypropylene is 0.88-0.93 g / cm 3 , the melt index is 6~14g / 10min, and the melting point is 160~170℃.

[0012] In some embodiments of the present invention, in the CPP film, the thickness percentage of the heat-sealing layer, the core layer and the composite layer is 5-25%: 50-90%: 5-25%. Specifically, the thickness percentage of the heat-sealing layer, the core layer and the composite layer includes but is not limited to 5%: 90%: 5%, 10%: 80%: 10%, 15%: 70%: 15%, 20%: 60%: 20%, 25%: 50%: 25%.

[0013] In some embodiments of the present invention, the thickness of the CPP film is 30-100 um.

[0014] Another object of the present invention is to provide a method for preparing the CPP film, which adopts a multi-layer co-extrusion casting method to form a heat-sealing layer, a core layer and a composite layer which are stacked in sequence.

[0015] Another object of the present invention is to provide an aluminum-plastic film, comprising the CPP film.

[0016] In some embodiments of the present invention, the aluminum-plastic film further comprises a PET layer, a nylon layer and an aluminum foil layer, and the nylon layer, the aluminum foil layer and the CPP film are sequentially stacked on the PET layer.

[0017] In some embodiments of the present invention, the thickness of the PET layer is 10-14 um.

[0018] In some embodiments of the present invention, the thickness of the nylon layer is 20-30 um.

[0019] In some embodiments of the present invention, the thickness of the aluminum foil layer is 40-50 um.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The heat-sealing layer CPP film of the present invention has a low sealing temperature, high heat-sealing strength, and can be quickly heat-sealed, thereby improving product packaging efficiency and being suitable for applications such as 3C electronic products or small batteries.

[0022] (2) The CPP film of the present invention has a low heat-sealing temperature and high heat-sealing strength; the friction is stable before and after high-temperature aging; the first and second sealing sols of the CPP film are uniformly whitened after high-temperature lamination; the peeling strength with the aluminum foil is maintained high before and after immersion in the electrolyte; the product has good electrolyte resistance and excellent crystal point level after being placed for a long time after being filled with electrolyte. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the whitening effect of a sealed CPP film in Example 1.

[0024] Figure 2 This is the double seal whitening effect of the CPP film of Example 1.

[0025] Figure 3 This is the whitening effect of one seal of the CPP film of Comparative Example 1.

[0026] Figure 4 This is the whitening effect of the second seal of the CPP film of Comparative Example 1. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0028] The raw materials used in the present invention are all conventionally commercially available.

[0029] Example 1

[0030] This embodiment provides a CPP film, and the specific process is as follows:

[0031] The raw materials for forming the heat sealing layer are, by weight percentage, 82% random copolymer polypropylene, 10% homopolymer polypropylene, 4% silica anti-blocking agent and 4% erucic acid amide type slip agent, wherein the random copolymer polypropylene is a ternary random copolymer of propylene, ethylene and butene, and the density of the random copolymer polypropylene is 0.88~0.93g / cm 3 , the melt index is 4~12g / 10min, the melting point is 120~140℃; the density of homopolymer polypropylene is 0.88~0.93g / cm 3 , the melting point is 160~170℃;

[0032] The raw materials for forming the core layer are: block copolymer polypropylene 63%, high-density polyethylene 10%, polyolefin elastomer 25% and erucic acid amide type lubricant 2%, wherein the block copolymer polypropylene is an alternating block copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.88~0.92g / cm 3 , the melt index is 1~6g / 10min, the melting point is 150~163℃; the density of the high-density polyethylene is 0.955~0.97g / cm 3 , the melt index is 6~14g / 10min, the melting point is 128~140℃; the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.85~0.90g / cm 3 , melt index is 1~6g / 10min, melting point is 60~100℃;

[0033] The raw materials for forming the composite layer are: 95% homopolymer polypropylene and 5% silica opening agent, wherein the density of homopolymer polypropylene is 0.88~0.93g / cm 3 , the melting point is 160~170℃;

[0034] According to the percentage by mass, the raw materials of the heat sealing layer, the core layer and the composite layer are melted at high temperature in the screw according to the above required proportions, and put into the three extruders corresponding to the three-layer co-extrusion casting machine, and the thickness percentage of the three layers is set to 15%:70%:15%, and the extrusion temperature of the die head is 180~270℃. Among them, the temperature of the extruder for forming the heat sealing layer is 180~270℃, the extrusion rate is 90~200kg / h, and the temperature of the extruder for forming the core layer is 180~2 70℃, extrusion rate is 400~700kg / h, the extruder temperature for forming the composite layer is 180~260℃, the extrusion rate is 90~200kg / h, the film is cooled and shaped on the smooth roller, the temperature of the smooth roller is 20~60℃, and it is stretched by guide rollers, tempered, corona treated, thickness detected, online defect monitoring, flash, and winding. The production line speed is 50~150m / min, and the winding tension is 5~20kg to obtain a 40μm CPP film.

[0035] Example 2

[0036] This embodiment provides a CPP film, and the specific process is as follows:

[0037] The difference from Example 1 is that the mass percentage of the raw materials for forming the heat-sealing layer and the thickness percentage of the three layers are different, and the others are the same as Example 1; in terms of mass percentage, the raw materials for forming the heat-sealing layer in this embodiment are: 58% random copolymer polypropylene, 30% homopolymer polypropylene, 6% silica opening agent and 6% erucic acid amide type slip agent, wherein the random copolymer polypropylene is a ternary random copolymer of propylene, ethylene and butene, and the density of the random copolymer polypropylene is 0.88-0.93 g / cm 3 , the melt index is 4~12g / 10min, the melting point is 120~140℃; the density of homopolymer polypropylene is 0.88~0.93g / cm 3 , the melt index is 6~14g / 10min, the melting point is 160~170℃; the thickness percentage of the three layers is set to 5%:90%:5%; and a 50μm CPP film is obtained.

[0038] Example 3

[0039] This embodiment provides a CPP film, and the specific process is as follows:

[0040] The difference from Example 1 is that the mass percentage of the raw materials for forming the heat-sealing layer and the thickness percentage of the three layers are different, and the others are the same as Example 1; in terms of mass percentage, the raw materials for forming the heat-sealing layer in this embodiment are: 74% random copolymer polypropylene, 25% homopolymer polypropylene, 0.5% silica opening agent and 0.5% erucic acid amide type slip agent, wherein the random copolymer polypropylene is a ternary random copolymer of propylene, ethylene and butene, and the density of the random copolymer polypropylene is 0.88-0.93 g / cm 3 , melt index is 4~12g / 10min, melting point is 120~140℃; density of homopolymer polypropylene is 0.88~0.93g / cm 3 , the melt index is 6~14g / 10min, the melting point is 160~170℃; the thickness percentage of the three layers is set to 25%:50%:25%; and a 45μm CPP film is obtained.

[0041] Example 4

[0042] This embodiment provides a CPP film, and the specific process is as follows:

[0043] The difference from Example 1 is that the raw materials for forming the heat sealing layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the heat sealing layer in this embodiment are: 72% random copolymer polypropylene and 28% homopolymer polypropylene, wherein the random copolymer polypropylene is a ternary random copolymer of propylene, ethylene and butene, and the density of the random copolymer polypropylene is 0.88-0.93 g / cm 3 , melt index is 4~12g / 10min, melting point is 120~140℃; density of homopolymer polypropylene is 0.88~0.93g / cm 3 , the melt index is 6~14g / 10min, and the melting point is 160~170℃.

[0044] Example 5

[0045] This embodiment provides a CPP film, and the specific process is as follows:

[0046] The difference from Example 1 is that the raw materials for forming the core layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the core layer in this embodiment are: 51% block copolymer polypropylene, 15% high-density polyethylene, 30% polyolefin elastomer and 4% erucic acid amide type lubricant, wherein the block copolymer polypropylene is a copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.9-0.92 g / cm 3 , the melt index is 3-9 g / 10 min, the melting point is 145-160 ° C; the density of the high-density polyethylene is 0.955-0.97 g / cm 3, the melt index is 6~14g / 10min, the melting point is 128~140℃; the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.85~0.90g / cm 3 , the melting point is 60~100℃ and the melting index is 1~6g / 10min.

[0047] Example 6

[0048] This embodiment provides a CPP film, and the specific process is as follows:

[0049] The difference from Example 1 is that the raw materials for forming the core layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the core layer in this embodiment are: block copolymer polypropylene 87.8%, high-density polyethylene 2%, polyolefin elastomer 10% and erucic acid amide type lubricant 0.2%, wherein the block copolymer polypropylene is an alternating block copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.88~0.92g / cm 3 , the melt index is 1~6g / 10min, the melting point is 150~163℃; the density of the high-density polyethylene is 0.957~0.97g / cm 3 , the melt index is 2~9g / 10min, the melting point is 130~140℃; the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.85~0.90g / cm 3 , the melting point is 60~100℃ and the melting index is 1~6g / 10min.

[0050] Example 7

[0051] This embodiment provides a CPP film, and the specific process is as follows:

[0052] The difference from Example 1 is that the raw materials for forming the core layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the core layer in this embodiment are: 63% block copolymer polypropylene, 10% high-density polyethylene, 25% polyolefin elastomer and 2% erucic acid amide type lubricant, wherein the block copolymer polypropylene is an alternating block copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.88-0.92 g / cm 3 , the melt index is 1~6g / 10min, the melting point is 150~163℃; the density of the high-density polyethylene is 0.955~0.97g / cm 3 , the melt index is 6~14g / 10min, the melting point is 128~140℃; the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.86~0.9g / cm 3 , the melting point is 55~95℃.

[0053] Example 8

[0054] This embodiment provides a CPP film, and the specific process is as follows:

[0055] The difference from Example 1 is that the raw materials for forming the core layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the core layer in this embodiment are: 65% block copolymer polypropylene, 10% high-density polyethylene, and 25% polyolefin elastomer, wherein the block copolymer polypropylene is an alternating block copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.88~0.92g / cm 3 , the melt index is 1~6g / 10min, the melting point is 150~163℃; the density of the high-density polyethylene is 0.955~0.97g / cm 3 , the melt index is 6~14g / 10min, the melting point is 128~140℃; the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.85~0.90g / cm 3 , the melting point is 60~100℃ and the melting index is 1~6g / 10min.

[0056] Example 9

[0057] This embodiment provides a CPP film, and the specific process is as follows:

[0058] The difference from Example 1 is that the raw materials for forming the composite layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the composite layer in this embodiment are: 95% homopolypropylene and 5% silica opening agent, wherein the density of homopolypropylene is 0.89-0.92 g / cm 3 , the melting point is 158~166℃.

[0059] Example 10

[0060] This embodiment provides a CPP film, and the specific process is as follows:

[0061] The difference from Example 1 is that the raw materials for forming the composite layer are different, and the rest are the same as Example 1; in terms of mass percentage, the raw materials for forming the composite layer in this embodiment are: 100% homopolypropylene, wherein the density of the homopolypropylene is 0.88-0.93 g / cm 3 , the melt index is 6~14g / 10min, and the melting point is 160~170℃.

[0062] Comparative Example 1

[0063] This comparative example provides a CPP film, and the specific process is as follows:

[0064] The difference from Example 1 is that the raw material random copolymer polypropylene for forming the heat seal layer is different. The other aspects are the same as Example 1. The raw material random copolymer polypropylene for forming the heat seal layer in this comparative example is a copolymer of ethylene and propylene, and the density of the random copolymer polypropylene is 0.86~0.9g / cm 3 , melt index is 5~13g / 10min, melting point is 125~145℃.

[0065] Comparative Example 2

[0066] This comparative example provides a CPP film, and the specific process is as follows:

[0067] The difference from Example 1 is that the raw material homopolypropylene for forming the heat seal layer is different. The other aspects are the same as Example 1. The density of the raw material homopolypropylene for forming the heat seal layer in this comparative example is 0.89-0.92 g / cm 3 , the melting point is 155~168℃.

[0068] Performance Testing:

[0069] The CPP film before compounding in Table 1 and Table 2 is represented, and the aluminum-plastic film after compounding is represented, that is, the aluminum-plastic film obtained by sequentially laminating the PET layer, the nylon layer, the aluminum foil layer and the CPP film of Examples 1 to 10 or Comparative Examples 1 to 2, wherein the thickness of the PET layer is 12 um, the thickness of the nylon layer is 25 um, and the thickness of the aluminum foil layer is 45 um.

[0070] Heat seal strength at various heat sealing temperatures: QB / T 2358; First seal refers to direct sealing at the sealing point after lamination, without the need to apply electrolyte, while second seal refers to applying electrolyte at the sealing point before heat sealing.

[0071] Electrolyte resistance: Cut the composite aluminum-plastic film into strips with a width of 15 mm and a length of 100 mm, soak them in a container filled with electrolyte and 1000-1500 ppm water, and place them at 85°C. The peel strength between the CPP film and the aluminum foil was tested at different time periods (initial value, 8h, 1 day, 2 days, 5 days, 7 days, 14 days, 30 days, and 60 days).

[0072] Friction coefficient: refer to GB / T 10006; friction coefficient before compounding, friction coefficient after compounding and aging at 60℃ for 5 days.

[0073] Table 1. Performance test results of CPP film or aluminum-plastic film.

[0074]

[0075] As can be seen from Table 1, the raw materials of the core layer and the composite layer of the present invention have little effect on the low-temperature heat-sealing performance and heat-sealing strength of the CPP film or the aluminum-plastic film, and the silica opening agent and erucic acid amide type slip agent of the heat-sealing layer have little effect on the low-temperature heat-sealing performance and heat-sealing strength of the CPP film or the aluminum-plastic film.

[0076] Table 2. CPP film or aluminum-plastic film performance test results.

[0077]

[0078] It can be seen from Table 1 and Table 2 that the random copolymer polypropylene and homopolypropylene used in the heat sealing layer of the present invention can effectively improve the low-temperature heat sealing performance, heat sealing strength, electrolyte resistance and one-seal and two-seal uniform whitening effect of the CPP film or aluminum-plastic film; while the electrolyte resistance and one-seal and two-seal heat sealing strength of the random copolymer polypropylene used in the heat sealing layer of Comparative Example 1 are both reduced; the heat sealing strength of the homopolypropylene used in the heat sealing layer of Comparative Example 2 before heat sealing and one-seal and two-seal heat sealing strength after heat sealing are both reduced.

[0079] Depend on Figure 1 and Figure 2 It can be seen that after the two surfaces of the CPP film obtained in Example 1 are peeled off, there is still a thin film on the surface protecting the aluminum foil, and there is no aluminum leakage. It can be judged that the electrolyte does not pass through the CPP film into the aluminum foil layer, and then corrode the aluminum foil. Whether it is one seal or two seals, they are uniformly whitened. The CPP films obtained in Examples 2 to 10 have similar effects to those in Example 1; while after the two surfaces of the CPP film obtained in Comparative Example 1 are peeled off, the film at the sealing portion is broken, and the sealing whitening effect is poor.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading the specification of this application, the technicians can still modify or replace the specific implementation mode of the present invention with equivalents, but these modifications or changes do not deviate from the scope of protection of the pending claims of the present application.

Claims

1. A heat seal layer, characterized in that: In terms of mass percentage, the first raw material forming the heat seal layer includes: 58-82% of random copolymer polypropylene and 10-30% of first homopolymer polypropylene, wherein the random copolymer polypropylene is a ternary random copolymer of propylene, ethylene and butene, and the density of the random copolymer polypropylene is 0.88-0.93 g / cm 3 , the melt index is 4-12 g / 10 min, the melting point is 120-140 ° C; the density of the first homopolymer polypropylene is 0.88-0.93 g / cm 3 , the melt index is 6~14g / 10min, and the melting point is 160~170℃.

2. The heat seal layer according to claim 1, characterized in that The first raw material also includes 0.5-6% of a silicon dioxide opening agent and 0.5-6% of an erucic acid amide type lubricant.

3. A CPP film, comprising a heat-sealing layer, a core layer and a composite layer stacked in sequence, characterized in that: The heat sealing layer is the heat sealing layer according to any one of claims 1 to 2.

4. The CPP film according to claim 3, wherein the second raw material of the core layer comprises 51-88% block copolymer polypropylene and 2-15% high-density polyethylene, in terms of mass percentage, wherein the block copolymer polypropylene is an alternating block copolymer of ethylene and propylene, and the density of the block copolymer polypropylene is 0.88-0.92 g / cm 3 , the melt index is 1~6g / 10min, the melting point is 150~163℃; the density of the high-density polyethylene is 0.955~0.97g / cm 3 , melt index is 6~14g / 10min, melting point is 128~140℃.

5. The CPP film according to claim 4, characterized in that: The second raw material also includes 10-30% of polyolefin elastomer, the polyolefin elastomer is a copolymer of ethylene and propylene, and the density of the polyolefin elastomer is 0.85-0.90 g / cm 3 , the melting point is 60~100℃ and the melting index is 1~6g / 10min.

6. The CPP film according to claim 4, characterized in that The second raw material also includes 0.2-4% of erucamide type lubricant.

7. The CPP film according to claim 3, characterized in that In terms of mass percentage, the third raw material of the composite layer includes 95-100% of the second homopolypropylene and 0-5% of the silica opening agent, and the density of the second homopolypropylene is 0.88-0.93 g / cm 3 , the melt index is 6~14g / 10min, and the melting point is 160~170℃.

8. The CPP film according to any one of claims 3 to 7, characterized in that In the CPP film, the thickness percentages of the heat-sealing layer, the core layer and the composite layer are 5-25%: 50-90%: 5-25%.

9. A method for preparing a CPP film according to claims 3 to 7, characterized in that: A multi-layer co-extrusion casting method is adopted to form a heat-sealing layer, a core layer and a composite layer which are stacked in sequence.

10. An aluminum-plastic film, comprising a CPP film, characterized in that: The CPP film is the CPP film according to any one of claims 3 to 8.

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