A cast polypropylene film, an aluminum-plastic film

Abstract

The application relates to the technical field of materials, in particular to a cast polypropylene film and an aluminum-plastic film, the cast polypropylene film comprising a composite layer, a core layer and a heat-sealing layer which are sequentially stacked; wherein the material forming the core layer comprises 30-50 parts by weight of block polypropylene, 20-40 parts by weight of first random polypropylene, 10-30 parts by weight of first elastomer, 0.1-2 parts by weight of first antioxidant and 0-5 parts by weight of first auxiliary agent. The cast polypropylene film has good interlayer stability, does not produce self-layering when being peeled from a base material, and improves the reliability of the corresponding aluminum-plastic film.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of materials, in particular to a cast polypropylene film and an aluminum-plastic film. BACKGROUND

[0002] In recent years, the demand for aluminum-plastic film in China has grown significantly. Aluminum-plastic film enterprises have seized the opportunity for development and embarked on a new journey of developing aluminum-plastic film and related technology industries. Common dry aluminum-plastic film is generally composed of three main materials, namely nylon (PA) / aluminum foil / cast polypropylene (CPP) film. PA material and aluminum foil are combined with the corresponding adhesive. CPP and aluminum foil can be combined with adhesive (dry method) or through processes such as hot pressing and hot printing (hot method). CPP film, as the innermost layer of aluminum-plastic film, has received increasing attention because it can better solve the problem of soft-pack lithium-ion secondary battery gas expansion. At the same time, the good electrolyte resistance, heat sealing performance, and punch forming performance of aluminum-plastic film need to be achieved by optimizing the related properties of the innermost CPP film. The heat sealing performance is related to the safety of soft-pack lithium batteries. Once there is a safety hazard such as electrolyte leakage and gas swelling, soft-pack lithium batteries will generally first swell or crack at weak sealing points. In addition to the adhesive, CPP film is likely to be the weak point of the soft-pack lithium battery package seal due to its high strength. Especially the CPP film with poor interlayer stability may delaminate during use, and the electrolyte may penetrate through the interlayer gap of the delaminated CPP film, causing electrolyte leakage and fire safety problems. Therefore, the interlayer stability and heat sealing performance of CPP film for aluminum-plastic film are important properties of CPP film products.

[0003] Research has found that CPP films with good cohesion can maintain their integrity even after being combined with aluminum foil to form aluminum-plastic film, even if they have high interlayer peeling force. However, CPP films with poor cohesion may separate at the composite layer and core layer when peeled off from the aluminum foil. In particular, after using block polypropylene with a high content of rubber phase in the core layer for toughening purposes, the cohesion of the core layer material decreases significantly, and the delamination of the corresponding aluminum-plastic film increases, mainly in the composite layer and core layer, as well as the core layer itself and the core layer and heat sealing layer.

[0004] The prior art currently improves the packaging performance from the aspects of improving the packaging peeling strength, composite strength, reducing the packaging temperature, etc. For example, a kind of showering CPP in the prior art is prepared by co-extrusion of the different proportions of metallocene polypropylene and block polypropylene two kinds of resins in the core inner layer and heat sealing inner layer, and the interlayer fusion of the core inner layer and heat sealing inner layer is close, and the peeling strength of the composite structure with aluminum foil is good. The scheme focuses on the layering problem in the CPP film, but cannot solve the problem of delamination of each layer of the aluminum plastic film at high temperature after packaging. As described above, the research results show that the block polypropylene in the core layer affects the adhesion fastness at high temperature with the composite layer, thereby affecting the safety performance of the aluminum plastic film, introducing safety hazards during the use of lithium ion battery, but no corresponding solution is provided at present. SUMMARY

[0005] The present application aims to solve at least one of the technical problems in the related art. To this end, the present application provides a cast polypropylene film, a composite packaging film, which has good interlayer stability, so that it does not produce self delamination when peeled off from the substrate, and improves the reliability of the corresponding composite film.

[0006] To this end, the present application provides a cast polypropylene film, a composite packaging film, which has good interlayer stability, so that it does not produce self delamination when peeled off from the substrate, and improves the reliability of the corresponding composite film.

[0007] The material forming the core layer includes 30-50 parts by weight of block polypropylene, 20-40 parts by weight of first random polypropylene, 10-30 parts by weight of first elastomer, 0.1-2 parts by weight of first antioxidant, and 0-5 parts by weight of first additive.

[0008] In view of the problem of delamination of the composite layer and the core layer of the cast polypropylene film when the aluminum plastic film is packaged and peeled off at high temperature, the present application provides a cast polypropylene film, which adds random polypropylene to the core layer to promote the interlayer molecular entanglement of the co-extruded cast polypropylene film, so that the interlayer stability of the cast polypropylene film can be ensured even if the core layer contains toughened block polypropylene, so that the aluminum plastic film does not produce self delamination when peeled off at high temperature, realizes the appearance of uniform whitening on both sides when peeled off by hand, and improves the safety of the cast polypropylene film corresponding to the aluminum plastic film. The hand tearing and peeling appearance of uniform whitening on both sides indicates that the heat sealing layer is uniformly separated, there is no aluminum foil leakage, the interface is between the two heat sealing layers, there is no wire drawing and layering in the film, and the peeling force is stable.

[0009] According to the embodiments of the present application, the first random polypropylene includes binary random polypropylene and ternary random polypropylene, and the melting point of the first random polypropylene is 125-145℃.

[0010] According to the embodiments of the present application, the block polypropylene includes ethylene-propylene block copolymer, and the ethylene content is 15wt%-50wt%.

[0011] According to embodiments of the present application, the first elastomer comprises a propylene-alpha olefin copolymer elastomer.

[0012] According to embodiments of the present application, the first aid agent comprises at least one of a polymer processing aid, an antistatic agent or a slip opening agent.

[0013] According to embodiments of the present application, the material forming the composite layer comprises 50-80 parts by weight of the polypropylene blend, 10-20 parts by weight of the second random polypropylene, 0-15 parts by weight of the second elastomer, 0.1-2 parts by weight of the second antioxidant, 0-5 parts by weight of the second aid agent.

[0014] According to embodiments of the present application, the polypropylene blend comprises a homopolymer polypropylene and optionally a homopolymer polypropylene graft, the grafting rate of the homopolymer polypropylene graft being 0%-1%.

[0015] According to embodiments of the present application, the second random polypropylene comprises at least one of a binary random polypropylene, a ternary random polypropylene, the melting point of the second random polypropylene being 125-145℃.

[0016] According to embodiments of the present application, the second elastomer comprises a propylene-alpha olefin copolymer elastomer.

[0017] According to embodiments of the present application, the second aid agent comprises at least one of a polymer processing aid, an antistatic agent or a slip opening agent.

[0018] According to embodiments of the present application, the material forming the heat-seal layer comprises a block copolymer polypropylene, an ethylene-propylene, an antioxidant.

[0019] According to embodiments of the present application, the thickness ratio of the composite layer, the core layer and the heat-seal layer is (1-4):8:(1-4).

[0020] The second aspect of the present application provides an aluminum-plastic film, the aluminum-plastic film comprising the cast polypropylene film of the first aspect. Thus the aluminum-plastic film has good interlayer stability and reliability, and the delamination phenomenon is obviously improved after heat-sealing. When the aluminum-plastic film is used as a lithium battery packaging material, during formation and use, the internal or ambient temperature of the battery rises, and the aluminum-plastic film can also maintain overall stability under external stress, without the risk of delamination and rupture, and without affecting the electrolyte resistance and other properties of the cast polypropylene film.

[0021] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION

[0022] Embodiments of the present application are described in detail below. The embodiments described below are exemplary only and are not intended to limit the present application, as the present application can be embodied in various ways.

[0023] It should be noted that the terms "first", "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or a specific order of limiting the technical features indicated. Thus, features limited by "first", "second" can explicitly or implicitly include one or more of the features. Further, in the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0024] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be roughly about the ranges or values. For ranges, the endpoints are included as well as intervening points within the ranges. For values, the values include the stated value as well as approximately the stated value.

[0025] In order that the present application can be more readily understood, certain technical and scientific terms are specifically defined below. Unless specifically defined herein, all other technical and scientific terms used in this document concur in meaning with the general use of those terms by those skilled in the art to which the present application pertains.

[0026] In this document, the terms "comprising" or "including" are open-ended, that is, the inclusion of unspecified features or steps is not precluded.

[0027] In this document, the terms "optionally", "optional" or "optional" generally mean that the subsequently described event or circumstance can or can not occur, and the description includes instances where the event or circumstance occurs and instances where it does not.

[0028] According to embodiments of the present application, a first aspect of the present application provides a cast polypropylene film, comprising a composite layer, a core layer and a heat-seal layer which are sequentially stacked;

[0029] The material forming the core layer comprises 30-50 parts by weight of block polypropylene, 20-40 parts by weight of first random polypropylene, 10-30 parts by weight of first elastomer, 0.1-2 parts by weight of first antioxidant, and 0-5 parts by weight of first auxiliary.

[0030] The toughness of the cast polypropylene film determines the punching performance of the corresponding aluminum-plastic film during molding. In order to realize the toughening of the cast polypropylene film, a block polypropylene with a relatively high rubber phase content is added in the core layer. In a high temperature state, the rubber phase and the polypropylene chain break interval are prone to phase separation, resulting in the delamination of the core layer itself and the composite layer and the heat sealing layer during high temperature packaging and peeling. In view of the poor cohesion of the cast polypropylene film itself and the delamination problem during high temperature packaging and peeling, a certain amount of random polypropylene is added in the core layer to strengthen the interlayer winding of the cast polypropylene film, which greatly improves the interlayer stability of the cast polypropylene film and solves the delamination problem of the composite layer and the core layer during packaging and peeling, and does not affect the packaging strength. This is because the random polypropylene has poor macromolecular chain break regularity and a relatively high content of branched chains. During the co-extrusion of the cast polypropylene film, the random polypropylene is prone to entanglement with the materials in the two side layers, thereby strengthening the interlayer cohesion. On the other hand, the random polypropylene has a relatively low melting point, so that the melting point of the core layer material is closer to that of the other two layers, and the compatibility is better. The addition of the random polypropylene enhances the mechanical properties and stability of the material, so that the cast polypropylene film will not delaminate under the action of a relatively strong external force, greatly improving the use safety of the corresponding aluminum-plastic film. In addition, the random polypropylene has stable performance, good chemical resistance, acid resistance and water vapor barrier property, and will not affect other properties when added to the cast polypropylene film material.

[0031] According to a specific embodiment of the present application, the first random polypropylene includes binary random polypropylene and ternary random polypropylene, and the melting point of the first random polypropylene is 125-145°C. When the content of the random polypropylene in the cast polypropylene film is relatively high, the cohesion of the core layer is poor, and when the content is relatively low, the compatibility with the composite layer cannot be improved, and there is a risk of delamination. The binary random polypropylene is understood as ethylene-propylene copolymer polypropylene, and the ternary random polypropylene is understood as ethylene-propylene-butylene copolymer polypropylene.

[0032] According to a specific embodiment of the present application, the block polypropylene includes ethylene-propylene block copolymer, and the ethylene content is 15wt%-50wt%. The purpose of adding this resin is to toughen the cast polypropylene film. If the ethylene content is relatively low, the rubber phase and the polypropylene chain break will not significantly phase separate, the risk of delamination of the cast polypropylene film is reduced, but at the same time, the toughness of the core layer is reduced, and the aluminum-plastic film has poor punching performance, thereby causing risks. Only when the ethylene content is in the above range, can a good toughening effect be obtained, but the delamination risk at high temperature increases, and the addition of random copolymer can solve this problem.

[0033] According to a specific embodiment of the present application, the types of the first elastomer and the first auxiliary agent are not particularly limited, and the first elastomer includes but is not limited to propylene-alpha olefin copolymer elastomer. Ethylene-based elastomers are avoided here, which are prone to cause relatively coarse rubber phase dispersion particle size.

[0034] According to a specific embodiment of the present application, the first additive includes, but is not limited to, polymer processing aid, antistatic agent, slip agent. The first additive can be added during the formation of the core layer.

[0035] According to a specific embodiment of the present application, the material forming the composite layer includes 50-80 parts by weight of polypropylene blend, 10-20 parts by weight of second random polypropylene, 0-15 parts by weight of second elastomer, 0.1-2 parts by weight of second antioxidant, 0-5 parts by weight of second additive.

[0036] According to a specific embodiment of the present application, the polypropylene blend includes homopolymer polypropylene and optional homopolymer polypropylene graft, the grafting rate of the homopolymer polypropylene graft is 0%-1%. The homopolymer polypropylene graft can be acid-modified homopolymer polypropylene, which is modified by grafting unsaturated carboxylic acid, unsaturated anhydride or carboxyl-containing acrylic monomer onto homopolymer polypropylene.

[0037] According to a specific embodiment of the present application, the second random polypropylene includes at least one of binary random polypropylene and ternary random polypropylene, and the melting point of the second random polypropylene is 125°C-145°C. When the content of random polypropylene is high, the cohesion of the composite layer decreases, and when the acid-modified polypropylene is contained in the polypropylene blend, the cast polypropylene film can be used as a hot film. A higher content of random polypropylene will result in a smaller hot bonding strength with aluminum foil. The binary random polypropylene is understood to be ethylene-propylene copolymer polypropylene, and the ternary random polypropylene is understood to be ethylene-propylene-butylene copolymer polypropylene.

[0038] According to a specific embodiment of the present application, the types of the second elastomer and the second additive are not particularly limited, and the second elastomer includes, but is not limited to, propylene-alpha olefin copolymer elastomer. The second additive includes, but is not limited to, polymer processing aid, antistatic agent or slip agent. The second elastomer and the second additive can be added during the formation of the composite layer.

[0039] According to a specific embodiment of the present application, the material forming the heat-seal layer includes block copolymer polypropylene, ethylene-propylene elastomer, antioxidant.

[0040] According to a specific embodiment of the present application, the content of ethylene in the block copolymer polypropylene is 15wt%-50wt%.

[0041] According to a specific embodiment of the present application, the thickness ratio of the composite layer, the core layer and the heat-seal layer is (1-4):8:(1-4).

[0042] According to a specific embodiment of the present application, the method for preparing the cast polypropylene film is not particularly limited, and can be prepared by mixing the raw materials of each layer respectively, then forming a film through a casting process, and performing corona treatment on the composite surface to obtain the final product.

[0043] According to an embodiment of the present application, the second aspect of the present application provides an aluminum-plastic film comprising the cast polypropylene film of the first aspect.

[0044] Specifically, the aluminum-plastic film can further comprise a PA / Al composite film, and the composite layer of the cast polypropylene film is combined with the Al surface of the composite film.

[0045] The solutions of the present application will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. If the specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in the art or according to the product instructions are used. If the reagents or instruments are not specified by the manufacturer, they are all conventional products that can be obtained by purchase.

[0046] The compositions of the composite layer, the core layer and the heat-seal layer in each embodiment and comparative example are shown in Table 1. In addition, Comparative Example 4 uses a commercially available cast polypropylene film product CPP-M.

[0047] Table 1

[0048]

[0049]

[0050]

[0051] wherein " / " means no addition.

[0052] Test Examples

[0053] Examples 1-3 and Comparative Examples 1-3 were prepared by mixing the raw materials for forming the composite layer, the core layer and the heat-seal layer according to the above weight ratio, respectively, and then putting them into the corresponding hoppers of a three-layer co-extrusion casting machine, setting the thickness ratio of the three layers to be 1:4:1, and then forming a 50 μm cast polypropylene film through a co-extrusion casting process, and then performing corona treatment on the composite surface.

[0054] The cast polypropylene films of Examples 1-3 and Comparative Examples 1-3 were combined with the aluminum foil surface of PA / Al, and after the glue maturation was completed, the aluminum-plastic film was heat-sealed at 185°C, 0.3Mpa, 3s, and the packaging peel force was tested at 25°C and 85°C (tested at a speed of 300mm / min), and the hand-tearing peel appearance was observed, and the results are shown in Table 2.

[0055] The results show that compared with Comparative Examples 1-4, the delamination phenomenon of the aluminum-plastic film prepared in Examples 1-3 is obviously improved after heat sealing, and the interlayer adhesion is stronger.

[0056] Table 2

[0057]

[0058]

[0059] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms are not necessarily directed to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples, without contradiction.

[0060] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A cast polypropylene film, characterized in that, It includes a composite layer, a core layer, and a heat-sealing layer stacked in sequence; The material forming the core layer includes 30-50 parts by weight of block polypropylene, 20-40 parts by weight of first random polypropylene, 10-30 parts by weight of first elastomer, 0.1-2 parts by weight of first antioxidant, and 0-5 parts by weight of first additive. The materials forming the composite layer include 50-80 parts by weight of a polypropylene blend, 10-20 parts by weight of a second random polypropylene, 0-15 parts by weight of a second elastomer, 0.1-2 parts by weight of a second antioxidant, and 0-5 parts by weight of a second additive. The first elastomer includes a propylene-α-olefin copolymer elastomer; The second elastomer includes a propylene-α-olefin copolymer elastomer.

2. The cast polypropylene film according to claim 1, characterized in that, The first random polypropylene includes binary random polypropylene and ternary random polypropylene, and the melting point of the first random polypropylene is 125℃-145℃.

3. The cast polypropylene film according to claim 1, characterized in that, The block polypropylene includes an ethylene-propylene block copolymer with an ethylene content of 15wt%-50wt%.

4. The cast polypropylene film according to claim 1, characterized in that, The first additive includes at least one of a polymer processing aid, an antistatic agent, or a slippery opening agent.

5. The cast polypropylene film according to claim 1, characterized in that, The polypropylene blend comprises homopolymer polypropylene and optional homopolymer polypropylene graft, wherein the grafting rate of the homopolymer polypropylene graft is 0%-1%; Optionally, the second random polypropylene includes at least one of binary random polypropylene and ternary random polypropylene, and the melting point of the second random polypropylene is 125℃-145℃. Optionally, the second additive includes at least one of a polymer processing aid, an antistatic agent, or a slip-forming agent.

6. The cast polypropylene film according to claim 1, characterized in that, The materials forming the heat-sealing layer include block copolymer polypropylene, ethylene-propylene elastomer, and antioxidants.

7. The cast polypropylene film according to claim 1, characterized in that, The thickness ratio of the composite layer, core layer and heat-sealing layer is (1-4):8:(1-4).

8. An aluminum-plastic film, characterized in that, Includes the cast polypropylene film according to any one of claims 1-7.

Images