Casting polypropylene film and aluminum plastic film

Abstract

The invention relates to the technical field of materials, in particular to a casting polypropylene film and an aluminum plastic film, and the casting polypropylene film comprises a composite layer, a core layer and a heat sealing layer which are sequentially stacked; wherein the core layer is prepared from the following materials in parts by weight: 30 to 50 parts of block polypropylene, 20 to 40 parts of first atactic polypropylene, 10 to 30 parts of first elastomer, 0.1 to 2 parts of first antioxidant and 0 to 5 parts of first aid. The casting polypropylene film has better interlayer stability, so that the casting polypropylene film does not generate self-layering when being stripped from a base material, and the reliability of a corresponding aluminum-plastic film is improved.

Description

Technical Field

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

[0002] In recent years, the demand for the domestic aluminum-plastic film industry has increased significantly. Aluminum-plastic film companies have seized the development opportunities and embarked on a new journey of vigorously developing aluminum-plastic film and related technology industries. Common dry aluminum-plastic films are generally composed of three layers of main materials, namely nylon (PA) / aluminum foil / cast polypropylene (CPP) film. The PA material and the aluminum foil are compounded with corresponding adhesives, and the CPP and the aluminum foil can be compounded with adhesives (dry method), or they can be compounded by hot pressing, hot showering and other processes (hot method). As the innermost material of the aluminum-plastic film, the CPP film has attracted more and more attention because it can better solve the problem of gas expansion of soft-pack lithium-ion secondary batteries. At the same time, the good electrolyte resistance, heat sealing performance, and stamping formability of the aluminum-plastic film need to be achieved by optimizing the relevant properties of the innermost CPP film. The heat sealing performance is related to the safety of soft-pack lithium batteries. Once there are safety hazards such as electrolyte leakage, gas expansion and bulging, the soft-pack lithium battery will generally bulge first, or crack from the weak point of the seal. PA and aluminum foil have high strength. In addition to adhesives, CPP film is likely to be the weak point of the soft-pack lithium battery packaging seal. In particular, CPP film with poor interlayer stability may be delaminated during use. The electrolyte may penetrate through the interlayer gap of the CPP film, causing electrolyte leakage and fire and other safety issues. Therefore, the interlayer stability and heat sealing performance of CPP film for aluminum-plastic film are important properties of CPP film products.

[0003] The study found that after the CPP film with good cohesion was compounded to form an aluminum-plastic film, it could still maintain itself without delamination even if it had a high interlayer peeling force with the aluminum foil; while the CPP film with poor cohesion separated from the aluminum foil at the composite layer and the core layer. In particular, after the core layer material was made of block polypropylene with a high rubber phase content for the purpose of toughening, its cohesion decreased significantly, and the delamination of the corresponding aluminum-plastic film increased, mainly between the composite layer and the core layer, and there were also cases of delamination of the core layer due to poor cohesion, and delamination of the core layer and the heat-sealing layer.

[0004] At present, the existing technologies mostly improve the packaging performance from the perspectives of improving the packaging peel strength, composite strength, and reducing the packaging temperature. For example, in the existing technology, a laminated CPP is configured with metallocene polypropylene and block polypropylene in different proportions in the core inner layer and the heat-sealed inner layer. The co-extruded core inner layer and the heat-sealed inner layer are tightly fused between the layers, and the peel strength with the aluminum foil composite structure is good. This solution focuses on the internal stratification problem of the CPP film, but cannot solve the problem of stratification of the layers when the aluminum-plastic film is peeled off at high temperature after packaging. As mentioned above, the research results show that the block polypropylene in the core layer affects the adhesion strength with the composite layer at high temperature, thereby affecting the safety performance of the aluminum-plastic film and introducing safety hazards during the use of lithium-ion batteries. However, no corresponding solution has been provided. Summary of the invention

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

[0006] To this end, the first aspect of the present invention provides a cast polypropylene film, the cast polypropylene film comprising a composite layer, a core layer and a heat-sealing layer stacked in sequence;

[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 auxiliary agent.

[0008] Aiming at the problem of delamination of the composite layer and the core layer of the cast polypropylene film during high-temperature peeling of the aluminum-plastic film package, the present invention provides a cast polypropylene film, wherein random polypropylene is added 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 guaranteed even when the core layer contains toughened block polypropylene, so that the aluminum-plastic film does not produce self-delamination during high-temperature heat-sealing peeling, and the hand-torn peeling appearance of uniform whitening on both sides is achieved, thereby improving the use safety of the cast polypropylene film corresponding to the aluminum-plastic film. Among them, the hand-torn peeling appearance of uniform whitening on both sides indicates that the heat-sealing layers are evenly separated, no aluminum foil is leaked, the interface is between the two heat-sealing layers, there is no drawing and delamination in the film, and the peeling force is stable.

[0009] According to an embodiment of the present invention, the first random polypropylene includes binary random polypropylene and ternary random polypropylene, and the melting point of the first random polypropylene is 125° C.-145° C.

[0010] According to an embodiment of the present invention, the block polypropylene comprises an ethylene-propylene block copolymer, and the ethylene content is 15 wt%-50 wt%.

[0011] According to an embodiment of the present invention, the first elastomer includes a propylene-α-olefin copolymer elastomer.

[0012] According to an embodiment of the present invention, the first auxiliary agent includes at least one of a polymer processing aid, an antistatic agent or a slip and opening agent.

[0013] According to an embodiment of the present invention, the material forming the composite layer includes 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 auxiliary agent.

[0014] According to an embodiment of the present invention, the polypropylene blend includes homopolypropylene and optionally homopolypropylene grafts, and the grafting rate of the homopolypropylene grafts is 0%-1%.

[0015] According to an embodiment of the present invention, 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.

[0016] According to an embodiment of the present invention, the second elastomer includes a propylene-α-olefin copolymer elastomer.

[0017] According to an embodiment of the present invention, the second auxiliary agent includes at least one of a polymer processing aid, an antistatic agent or a slip and opening agent.

[0018] According to an embodiment of the present invention, the material forming the heat-sealing layer includes block copolymer polypropylene, ethylene-propylene, and an antioxidant.

[0019] According to an embodiment of the present invention, the thickness ratio of the composite layer, the core layer and the heat-sealing layer is (1-4):8:(1-4).

[0020] The second aspect of the present invention provides an aluminum-plastic film, wherein the aluminum-plastic film comprises the cast polypropylene film described in the first aspect. Thus, the aluminum-plastic film has good interlayer stability and reliability, and the delamination phenomenon of the high-temperature peeling test after heat sealing is significantly improved. When the aluminum-plastic film is used as a lithium battery packaging material, during the formation and use process, the internal or ambient temperature of the battery rises, and the aluminum-plastic film can also maintain overall stability under the action of external stress, without the risk of delamination and rupture, and generating potential safety hazards, and at the same time, it will not affect other properties of the cast polypropylene film such as electrolyte resistance.

[0021] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0023] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Further, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more.

[0024] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0025] In order to make the present invention more easily understood, certain technical and scientific terms are specifically defined below. Unless otherwise clearly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by those skilled in the art to which the present invention belongs.

[0026] In this document, the terms “include” or “comprising” are open expressions, that is, including the contents specified in the present invention but not excluding other contents.

[0027] As used herein, the terms "optionally", "optional" or "optionally" generally mean that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0028] According to an embodiment of the present invention, a first aspect of the present invention provides a cast polypropylene film, the cast polypropylene film comprising a composite layer, a core layer and a heat-sealing layer stacked in sequence;

[0029] 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 auxiliary agent.

[0030] The toughness of cast polypropylene film determines the punching performance of the corresponding aluminum-plastic film during molding. In order to achieve the toughening of cast polypropylene film, block polypropylene with a high rubber phase content is added to the core layer. Under high temperature conditions, the rubber phase and the polypropylene chain break interval are easily separated, resulting in the core layer itself and the composite layer and heat-sealing layer being delaminated during high-temperature packaging and peeling. In view of the problem that the cast polypropylene film itself has poor cohesion and delamination occurs during hot peeling after packaging, a certain amount of random polypropylene is added to the core layer to strengthen the interlayer entanglement of the cast polypropylene film, which greatly improves the interlayer stability of the cast polypropylene film and solves the problem of delamination between the composite layer and the core layer during hot peeling of packaging, while not affecting the packaging strength. This is because the macromolecular chain break regularity of random polypropylene is poor and the branch content is high. When the cast polypropylene film is co-extruded, it is easy to form entanglements with the materials in the two side layers, thereby strengthening the cohesion between the layers; on the other hand, the melting point of random polypropylene is low, which makes the melting point of the core layer material closer to the materials of the other two layers, and has better compatibility. The addition of random polypropylene enhances the mechanical properties and stability of the material, so that the cast polypropylene film will not produce self-delamination under strong external forces, which greatly improves the safety of the cast polypropylene film corresponding to the aluminum-plastic film. In addition, random polypropylene has stable performance, good chemical resistance, acid resistance, and water vapor barrier properties, and adding it to the cast polypropylene film material will not affect other properties.

[0031] According to a specific embodiment of the present invention, the first random polypropylene includes binary random polypropylene and ternary random polypropylene, and the melting point of the first random polypropylene is 125°C-145°C. When the content of random polypropylene in the cast polypropylene film is high, it is easy to cause poor cohesion of the core layer, and when the content is low, it is easy to cause the compatibility with the composite layer to be unable to be improved, and there is a risk of delamination. Among them, the binary random polypropylene should be understood as ethylene-propylene copolymer polypropylene, and the ternary random polypropylene should be understood as ethylene-propylene-butyl copolymer polypropylene.

[0032] According to a specific embodiment of the present invention, the block polypropylene includes an ethylene-propylene block copolymer, and the ethylene content is 15wt%-50wt%. The purpose of adding the resin is to toughen the cast polypropylene film. If the ethylene content is low, the rubber phase and the polypropylene chain will not be significantly separated, and the risk of stratification of the cast polypropylene film is reduced, but at the same time, the toughness of the core layer is reduced, and the impact resistance of the aluminum-plastic film is deteriorated, thereby bringing risks. Only when the ethylene content is within the above range can a better toughening effect be obtained, but the risk of stratification increases at high temperatures, and the addition of random copolymers can solve this problem.

[0033] According to a specific embodiment of the present invention, 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-α-olefin copolymer elastomer. Vinyl elastomer is avoided here because it easily leads to a coarse dispersed particle size of the rubber phase.

[0034] According to a specific embodiment of the present invention, the first auxiliary agent includes but is not limited to a polymer processing aid, an antistatic agent, and a slip-opening agent. The first auxiliary agent can be added according to the situation during the formation of the core layer.

[0035] According to a specific embodiment of the present invention, the material forming the composite layer includes 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 auxiliary agent.

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

[0037] According to a specific embodiment of the present invention, 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 random polypropylene content is high, the cohesion of the composite layer decreases, and when the polypropylene blend contains acid-modified polypropylene, the cast polypropylene film can be used as a thermal film. A high random polypropylene content will result in a lower thermal bonding strength with aluminum foil. Among them, the binary random polypropylene should be understood as ethylene-propylene copolymer polypropylene, and the ternary random polypropylene should be understood as ethylene-propylene-butyl copolymer polypropylene.

[0038] According to a specific embodiment of the present invention, the types of the second elastomer and the second auxiliary agent are not particularly limited, and the second elastomer includes but is not limited to propylene-α-olefin copolymer elastomer. The second auxiliary agent includes but is not limited to polymer processing aid, antistatic agent or slippery opening agent. In the process of forming the composite layer, the second elastomer and the second auxiliary agent can be added according to the situation.

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

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

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

[0042] According to a specific embodiment of the present invention, the method for preparing the cast polypropylene film is not particularly limited. The raw materials of each layer are mixed separately, and then formed into a film through a casting process, and the composite surface is corona treated to obtain the final product.

[0043] According to an embodiment of the present invention, a second aspect of the present invention provides an aluminum-plastic film, which includes the cast polypropylene film described in the first aspect.

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

[0045] The scheme of the present invention will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. Where specific techniques or conditions are not indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used are not indicated by the manufacturer and are all conventional products that can be obtained commercially.

[0046] The compositions of the composite layer, the core layer and the heat-sealing 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] Among them, " / " means not added.

[0052] Test Case

[0053] In Example 1-3 and Comparative Example 1-3, the raw materials for forming the composite layer, the core layer and the heat-sealing layer are mixed respectively according to the above-mentioned weight ratio, and put into the corresponding hopper of the three-layer co-extrusion casting machine, and the thickness ratio of the three layers is set to 1:4:1. A 50μm cast polypropylene film is made by a co-extrusion casting process, and the composite surface is corona treated.

[0054] The cast polypropylene films of Examples 1-3 and Comparative Examples 1-3 were compounded on the aluminum foil surface of PA / Al. After the glue was matured, the aluminum-plastic film was heat-sealed at 185°C, 0.3Mpa, and 3s. The packaging peeling force was tested at 25°C and 85°C (tested at a speed of 300mm / min), and its hand-tear peeling appearance was observed. 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 after heat sealing in high-temperature peeling test is significantly improved, and the interlayer bonding force is stronger.

[0056] Table 2

[0057]

[0058]

[0059] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0060] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

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 auxiliary agent.

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° C.-145° C.

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

4. The cast polypropylene film according to claim 1, characterized in that The first elastomer includes a propylene-alpha olefin copolymer elastomer.

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

6. The cast polypropylene film according to claim 1, characterized in that 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 auxiliary agent.

7. The cast polypropylene film according to claim 6, characterized in that The polypropylene blend comprises homopolypropylene and optional homopolypropylene grafts, and the grafting rate of the homopolypropylene grafts 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° C.-145° C.; Optionally, the second elastomer comprises a propylene-alpha olefin copolymer elastomer; Optionally, the second auxiliary agent includes at least one of a polymer processing aid, an antistatic agent or a slip and opening agent.

8. The cast polypropylene film according to claim 1, characterized in that The material forming the heat sealing layer includes block copolymer polypropylene, ethylene-propylene elastomer and antioxidant.

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

10. An aluminum-plastic film, characterized in that: The invention comprises the cast polypropylene film according to any one of claims 1 to 9.

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