Propylene-based multilayer film for cell pouches with excellent adhesive performance and moldability.

Abstract

The present invention provides a polypropylene-based multilayer film comprising: a skin layer containing (a) a propylene-based binary copolymer, (f) a modified polyolefin, and (e) an antiblocking agent; a core layer containing (b1) an ethylene-propylene block copolymer and (c) an amorphous propylene rubber; and a seal layer containing (a) a propylene-based binary copolymer, (b2) an ethylene-propylene block copolymer, (d) a sleep agent, and (e) an antiblocking agent.

Description

Technical Field

[0001] The present invention relates to a polypropylene-based multilayer film, and more particularly, to a polypropylene-based multilayer film for a cell pouch.

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2020-0159121, filed on November 24, 2020, the entire disclosure of which is incorporated herein by reference.

Background Art

[0003] A secondary battery refers to a normal lithium secondary battery, which is a battery used in portable terminal devices such as notebook computers, smartphones, tablet PCs, video cameras, electric vehicles including hybrid vehicles, and energy storage smart grids. Research is being conducted to miniaturize, lighten, and thin the battery, as well as to overcome various environmental factors such as severe thermal environments and mechanical impacts.

[0004] Unlike conventional can-type packaging materials, rechargeable battery pouches are used as outer packaging materials for lithium batteries because they have the advantage of being able to freely change the shape of the battery. These pouches consist of a multilayer structure (for example, an internal resin layer, an aluminum layer, and an external resin layer). Typically used rechargeable battery pouch films are composed of a multilayer film structure consisting of an internal resin layer made of polyolefins such as polyethylene (PE), casted polypropylene (cPP), or polypropylene (PP), or copolymers thereof, which have heat-adhesive properties and act as a sealant; an aluminum layer, which is a metal foil that maintains mechanical strength and acts as a barrier layer against moisture and oxygen; and an external resin layer formed by a functional polymer film such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), nylon, or liquid crystal polymer (LCP) to protect the battery cells from external impacts.

[0005] Traditionally, packaging materials made from metal, particularly aluminum, pressed into cylindrical or parallelepiped shapes were primarily used. However, with such metal can packaging materials, the outer wall of the container is rigid, and the shape of the battery itself is determined by the shape of the metal can packaging material, which presents a limitation.

[0006] To overcome these constraints, technologies for packaging materials made of multilayer plastic films have been developed. For example, Patent Document 1 discloses a cell pouch consisting of a base layer, an adhesive layer, a barrier layer, a dry lamination layer, and a sealant layer, in which the sealant layer is composed of a low-flow polypropylene layer and a high-flow polypropylene layer. Patent Document 2 discloses a cell pouch laminated using biaxially oriented nylon, polyethylene terephthalate (PET), and polyolefin resin for the base film and surface protective layer, as well as a technology for coating the base film with a fluorine-based, silicone-based, or acrylic resin as a secondary processing step.

[0007] Pouch-type rechargeable batteries offer flexibility in form and have the advantage of realizing the same capacity in a smaller volume and mass. However, unlike can-type batteries, pouch-type batteries use a soft pouch as a container, which can be damaged for various reasons during various processes. For example, during the process of housing the electrode assembly inside the pouch, protruding parts such as electrode tabs and electrode leads can cause damage such as cracks in the PP or cPP layers inside the pouch. If the aluminum layer is exposed due to such damage, side reactions will occur due to its reaction with the electrolyte. The aluminum layer exposed to the electrolyte in this way will corrode as it chemically reacts with oxygen or moisture in the electrolyte that has penetrated or diffused into the battery, generating corrosive gases and causing a swelling phenomenon where the inside of the battery expands. Specifically, lithium hexafluorophosphate (LIPF6) reacts with water and oxygen to produce hydrofluoric acid (HF), a corrosive gas. Such hydrofluoric acid may react with aluminum to cause a rapid exothermic reaction. In a secondary reaction, it may be adsorbed onto the aluminum surface and penetrate into the tissue, increasing the brittleness of the tissue. This can lead to cracks in the pouch film even with minor impacts, and leakage of the electrolyte may cause lithium to react with the atmosphere, potentially leading to ignition.

[0008] Patent Document 3 describes a polymer film for cell packaging containing 1 to 30% by weight of low-density polyethylene (LDPE), 50 to 98% by weight of polypropylene (PP), and 1 to 20% by weight of a crosslinked resin. It states that LDPE is used to reduce the penetration rate of the electrolyte, PP is used to complement the heat resistance, and a crosslinked resin is used to improve the compatibility of LDPE and PP. However, it does not specifically mention changes in physical properties due to molecular weight, density, melting point, degree of crystallinity, comonomer content, etc.

[0009] Patent Document 4 discloses an aluminum pouch film for secondary batteries, which includes an outer resin layer made of polyethylene terephthalate, nylon, etc., a first adhesive layer, an aluminum layer, a second adhesive layer, and an inner resin layer made of polyolefin. However, it only describes the overall layer structure of the pouch and does not mention the specific composition of the polyolefin that constitutes the inner resin layer.

[0010] Patent Document 5 describes a polypropylene composite film comprising: Layer A, which mainly consists of a propylene-based random copolymer obtained by random copolymerizing propylene with ethylene or butene; Layer B, which consists of 60 to 90% by weight of a propylene polymer having a comonomer (ethylene or butene) content of 0 to 1.5% by weight, and 10 to 40% by weight of a propylene polymer having a comonomer (ethylene or butene) content of 10 to 40% by weight; and Layer C, which consists of a propylene-based ethylene or butene random copolymer. The invention is characterized in that Layer B contains 100 to 2000 ppm of a fatty acid amide lubricant and 0 to 20% by weight of metallocene catalyst-based low-density polyethylene. However, it does not provide detailed information on the remaining raw materials excluding those for Layer B. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Korean Published Patent No. 2003-0029141 [Patent Document 2] Korean Published Patent No. 2002-0030737 [Patent Document 3] Korean Registered Patent No. 1499740 [Patent Document 4] Korean Registered Patent No. 1485523 [Patent Document 5] Korean Published Patent No. 2019-0047104 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] This invention provides a multilayer film primarily used as a sealant layer for cell pouches, offering excellent adhesive performance and simultaneously satisfying moldability during post-processing. The present invention aims to provide a detailed description of its laminated composition.

[0013] Furthermore, we aim to provide a cell pouch that uses the aforementioned multilayer film as a sealant layer. [Means for solving the problem]

[0014] To solve the above problems, the present invention provides a skin layer comprising (a) a propylene binary copolymer, (f) a modified polyolefin, and (e) an antiblocking agent, a core layer comprising (b1) an ethylene propylene block copolymer and (c) amorphous propylene rubber, and (a) a propylene binary copolymer, (b2) an ethylene propylene block copolymer, and (d) Slip agent The present invention provides a polypropylene multilayer film comprising (e) a sealing layer containing an antiblocking agent, and (e) an antiblocking agent.

[0015] Furthermore, the (a) propylene-based binary copolymer contains ethylene in an amount of 2.0 to 6.5% by weight, the (b1) ethylene-propylene block copolymer contains ethylene in an amount of 2.0 to 6.0% by weight, the (b2) ethylene-propylene block copolymer contains ethylene in an amount of 6.0 to 10.0% by weight, the (c) amorphous propylene rubber contains ethylene or butene in an amount of 10 to 60% by weight, and the (d) Slip agent It is an amide type Slip agentThe present invention provides a polypropylene multilayer film characterized in that (e) the antiblocking agent is spherical silica, and (f) the modified polyolefin contains maleic anhydride in a content of 1 to 10% by weight and is grafted onto it.

[0016] Furthermore, the (a) propylene-based binary copolymer has a melting index (MI, 230°C, 2.16 kg load) of 2 to 12 g / 10 min, the (b1) ethylene propylene block copolymer has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, the (b2) ethylene propylene block copolymer has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, the (c) amorphous propylene rubber has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, and the (d) Slip agent These are amide systems with 14 to 22 carbon atoms. Slip agent A mixture of two or more of the above, wherein the antiblocking agent has an average particle size of 1.5 to 3.0 μm, a moisture content of less than 0.5% by weight, and a bulk density of 0.8 to 1.0 g / cm³. 3 The present invention provides a polypropylene-based multilayer film characterized by the following:

[0017] Furthermore, the skin layer contains (a) 80 to 99 parts by weight of a propylene-based binary copolymer, (f) 1 to 20 parts by weight of a modified polyolefin, and (e) 0.1 to 1 part by weight of an antiblocking agent; the core layer contains (b1) 50 to 90 parts by weight of an ethylene-propylene block copolymer and (c) 10 to 50 parts by weight of amorphous propylene rubber; the seal layer contains (a) 20 to 60 parts by weight of a propylene-based binary copolymer, (b2) 40 to 80 parts by weight of an ethylene-propylene block copolymer, and (d) Slip agent The present invention provides a polypropylene multilayer film characterized by containing (e) an antiblocking agent in an amount of 0.1 to 1.0 parts by weight of (a) and 0.1 to 1 part by weight of (b).

[0018] Also provided is a polypropylene-based multilayer film, wherein the multilayer film has a coefficient of friction (ASTM D1894, based on the surface of the seal layer, thickness 40 μm) of 0.5 or less, an aluminum peel strength of 8 N / 15 mm or more measured by the following method,and a thermal adhesion strength of60 N / 15 mm or more measured bythe following method.

[0019] [Method for Measuring Aluminum Peel Strength] Laminatethe multilayer film (thickness 40 μm), aluminum foil (thickness 50 μm, laminated on the skin layer of the multilayer film), and nylon (thickness 15 μm, laminated on the aluminum foil) at 130 °C, cure at 50 °C for 14 days, cut the laminated film into strips 15 mm wide, and measure the peel strength at a peel angle of 180° at a peel rate of 50 mm / min at 23 °C.

[0020] [Method for Measuring Thermal Adhesion Strength] Cut a sample produced by thermally adhering for 1 second under a pressure of 2 kgf / cm 2 so that the multilayer films in the laminated film face each other into strips 15 mm wide, and measure the peel strength at a peel angle of 180° at a peel rate of 100 mm / min at 23 °C using a tensile strength measuring instrument.

[0021] In order to solve the above-mentioned other problems, the present invention provides a cell pouch including a sealant layer made of the film, a barrier layer formed on the sealant layer, and an external resin layer formed on the barrier layer. [Advantages of the Invention]

[0022] According to the present invention, a specific laminated composition of a polypropylene-based multilayer film including a skin layer, a core layer, and a seal layer of a specific composition can be presented. The polypropylene-based multilayer film is used as a sealant layer of a cell pouch, has excellent adhesion performance, and simultaneously satisfies the formability in post-processing, while having excellent mechanical properties, surface characteristics, and transparency. [Embodiments for Carrying Out the Invention]

[0023] The present invention will now be described in detail through preferred embodiments. Before that, however, terms and words used in this specification and in the claims should not be interpreted only in their usual or dictionary sense, but should be interpreted in a sense and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Therefore, it should be understood that the configurations of the embodiments described herein are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that at the time of filing this application, there may be a variety of equivalents and variations that can substitute for them.

[0024] The inventors of the present invention faced the fact that there was no known specific composition for a film material used as a sealant layer in conventional cell pouches that simultaneously satisfies the required adhesive performance and moldability in post-processing. As a result of repeated research on numerous laminated compositions, they discovered that a specific composition of a skin layer, core layer, and seal layer centered on a propylene-based binary copolymer can provide excellent adhesive performance when used as a sealant layer in a cell pouch, while simultaneously satisfying moldability in post-processing, and possessing excellent mechanical properties, surface characteristics, and transparency, leading to the present invention.

[0025] Therefore, the present invention comprises a skin layer containing (a) a propylene-based binary copolymer, (f) a modified polyolefin, and (e) an antiblocking agent, a core layer containing (b1) an ethylene propylene block copolymer and (c) amorphous propylene rubber, and (a) a propylene-based binary copolymer, (b2) an ethylene propylene block copolymer, and (d) Slip agent The present invention discloses a polypropylene multilayer film comprising (e) a sealing layer containing an antiblocking agent, and (f) an antiblocking agent.

[0026] In the present invention, the (a) propylene-based binary copolymer is the main component of the skin layer and seal layer of a multilayer film, and is a copolymer of propylene and one α-olefin other than propylene, preferably a binary copolymer polymerized by simultaneously implanting propylene and ethylene. The polymerization method of the copolymer is a conventional method known in the art and is not particularly limited in the present invention.

[0027] The (a) propylene-based binary copolymer contributes to improving the aluminum peel strength because it contains propylene, the same as the olefin-based adhesive component, as a constituent component. However, the (a) propylene-based binary copolymer is a crystalline copolymer, not an amorphous propyleneethylene copolymer, and preferably contains ethylene in a content of 2 to 6.5% by weight, more preferably 2.5 to 3.5% by weight, and has a melting point (Tm) of 125 to 155°C, and more preferably 140 to 154°C. If the ethylene content of the (a) propylene-based binary copolymer is less than 2% by weight, it may not be flexible enough, which may cause whitening and edge collapse during forming, and may reduce wettability in the lamination process with the adhesive. Furthermore, if the ethylene content exceeds 6.5% by weight, it may not be heat resistant enough, which may cause appearance problems (deformation and distortion) due to heat generation during use.

[0028] On the other hand, the propylene-based binary copolymer (a) has a melting index (MI, 230°C, 2.16 kg load) of 2 to 12 g / 10 min, preferably 2 to 8 g / 10 min, and more preferably 5 to 8 g / 10 min. If the melting index is less than 2 g / 10 min, productivity decreases, and if it exceeds 12 g / 10 min, the effect of improving aluminum peel strength is minimal.

[0029] In the present invention, (b1) ethylene propylene block copolymer is the main component of the core layer of the multilayer film, and since its constituent materials are the same as those of (a) propylene-based binary copolymer (propylene and ethylene), delamination does not occur due to the affinity between the two phases. The polymerization method of (b1) ethylene propylene block copolymer is a conventional method known in the art and is not particularly limited in the present invention.

[0030] The (b1) ethylene-propylene block copolymer preferably contains ethylene in a content of 2 to 6% by weight, but more preferably contains ethylene in a content of 4 to 6% by weight. If the ethylene content of the (b1) ethylene-propylene block copolymer is less than 2% by weight, the effect of improving impact resistance is minimal, and if it exceeds 6% by weight, a large amount of fish eye phenomenon occurs due to undispersion.

[0031] On the other hand, the ethylene propylene block copolymer (b1) has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, preferably 2 to 5 g / 10 min. If the melting index is less than 1 g / 10 min, a large amount of fish eyes will be generated due to undispersion, and if it exceeds 5 g / 10 min, the improvement in impact resistance will be minimal.

[0032] In the present invention, (b2) ethylene propylene block copolymer is the main component of the sealing layer of the multilayer film, and since its constituent materials are the same as those of (a) propylene-based binary copolymer (propylene and ethylene), it exhibits excellent in-phase compatibility due to the affinity of the two phases, resulting in high uniformity of quality. The polymerization method for (b2) ethylene propylene block copolymer is a conventional method known in the art and is not particularly limited in the present invention.

[0033] The (b2) ethylene-propylene block copolymer preferably contains ethylene in a content of 6 to 10% by weight, but more preferably contains ethylene in a content of 6 to 8% by weight. If the ethylene content of the (b2) ethylene-propylene block copolymer is less than 6% by weight, sufficient thermal bonding strength cannot be achieved during thermal bonding, and if it exceeds 10% by weight, there is a disadvantage that the thermal bonding strength decreases due to thermal fusion between the thermal bonding layers during thermal bonding.

[0034] The (b2) ethylene propylene block copolymer has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, preferably 2 to 5 g / 10 min. If the melting index is less than 1 g / 10 min, a large amount of fish eyes will be generated due to undispersion, and if it exceeds 5 g / 10 min, the improvement in impact resistance will be minimal.

[0035] In the present invention, (c) amorphous propylene rubber is a secondary component of the core layer of a multilayer film, and is a copolymer of propylene and one α-olefin other than propylene. Preferably, propylene and ethylene or butene are injected simultaneously, but preferably the ethylene or butene is contained in a content of 10 to 60% by weight, more preferably ethylene in a content of 10 to 30% by weight, or butene in a content of 20 to 40% by weight. If the content of ethylene or butene is 10% by weight or less, the effect of improving impact resistance is minimal, and if it exceeds 60% by weight, a large amount of low molecular weight is included, causing the film to become sticky during molding, resulting in an uneven surface and low tensile strength. The polymerization method of the copolymer is a conventional method known in the art and is not particularly limited in the present invention.

[0036] In the present invention, the above (d) Slip agent (e) The antiblocking agent is a minor component of the sealing layer of the multilayer film, and (d) Slip agent In this case, as time passes in the sealing layer, the relevant organic compound migrates to the substrate surface. slip(e) In the case of antiblocking agents, by providing properties, they reduce the coefficient of friction in post-processing steps such as deep drawing, thereby improving moldability and workability.

[0037] (d) above Slip agent It is preferable that the compound is an amide-based organic compound synthesized from fatty acids, which has a high melting point and a neutral structure in which the hydroxyl group is replaced with an amino structure.

[0038] Such as (d) Slip agent These are amide systems with 14 to 22 carbon atoms. Slip agent A mixture of two or more of these, more specifically, a mixture of tetradecanamide, hexadecanamide, octadecanamide, and 13-cis-docosenamide, which are saturated and unsaturated amide organic compounds having 14 to 22 carbon atoms.

[0039] The (e) antiblocking agent is preferably a silica antiblocking agent having a spherical particle pattern and a uniform particle distribution, and the particles have a moisture content of less than 0.5% by weight when dried (under 105°C for 60 min conditions), an average particle size of 1.5 to 3.0 μm, preferably 2 to 3 μm, and a bulk density of 0.8 to 1.0 g / cm³. 3 It is preferable that this be the case.

[0040] The (f) modified polyolefin is a minor component of the skin layer of the multilayer film, and is a modified polypropylene grafted with maleic anhydride, which is a polar working group, in a content of 1 to 10% by weight, preferably 3 to 5% by weight. If the maleic anhydride content of the modified polypropylene is less than 1% by weight, the adhesion to the aluminum foil decreases, and if it exceeds 10% by weight, a large amount of polar working groups causes fish eyes and low molecular weights to be generated, resulting in a decrease in surface tension after corona surface treatment and a decrease in adhesion to the aluminum foil.

[0041] The above components (a) to (f) constitute the main or minor components of the skin layer, core layer, and seal layer, and are included in specific content ratios to achieve the desired adhesive performance and molded form in post-processing when used as a sealant layer for a cell pouch.

[0042] In other words, in the present invention, the skin layer contains (a) 80 to 99 parts by weight of a propylene-based binary copolymer, (f) 1 to 20 parts by weight of a modified polyolefin, and (e) 0.1 to 1 part by weight of an antiblocking agent; the core layer contains (b1) 50 to 90 parts by weight of an ethylene-propylene block copolymer and (c) 10 to 50 parts by weight of amorphous propylene rubber; the seal layer contains (a) 20 to 60 parts by weight of a propylene-based binary copolymer, (b2) 40 to 80 parts by weight of an ethylene-propylene block copolymer, and (d) Slip agent The material contains (a) a propylene-based binary copolymer in an amount of 0.1 to 1.0 parts by weight, and (e) an antiblocking agent in an amount of 0.1 to 1 part by weight, but preferably the skin layer contains (a) a propylene-based binary copolymer in an amount of 87 to 93 parts by weight, (f) a modified polyolefin in an amount of 7 to 13 parts by weight, and (e) an antiblocking agent in an amount of 0.1 to 0.9 parts by weight, the core layer contains (b1) an ethylene propylene block copolymer in an amount of 65 to 85 parts by weight, and (c) an amorphous propylene rubber in an amount of 15 to 35 parts by weight, the seal layer contains (a) a propylene-based binary copolymer in an amount of 25 to 55 parts by weight, (b2) an ethylene propylene block copolymer in an amount of 45 to 75 parts by weight, and (d) Slip agent (e) contains 0.1 to 0.4 parts by weight of (a) and 0.1 to 0.3 parts by weight of an antiblocking agent.

[0043] On the other hand, the resin composition of each layer constituting the polypropylene multilayer film according to the present invention may further contain one or more additives as needed, such as antioxidants, catalyst neutralizers, pigments, dispersants, weathering agents, antistatic agents, UV stabilizers, talc, etc., as long as the objective of the present invention is not impaired. The amount of such additives used is adjusted considering the total production volume and manufacturing process, within a range known to be usable without affecting the properties of the polypropylene multilayer film of the present invention.

[0044] In the present invention, the production of a multilayer film using the above components is carried out by a conventional method known in the industry. For example, the components constituting each layer are put into a Henschel mixer in the required amounts and mixed, then produced in pellet form at 180 to 240°C using an extruder, and finally melt-molded into a film using a multilayer film molding machine to produce a multilayer film.

[0045] The polypropylene multilayer film according to the present invention, when used as a sealant layer for cell pouches, exhibits excellent adhesive performance and moldability in post-processing, while simultaneously possessing excellent mechanical properties, surface characteristics, and transparency. More specifically, the polypropylene multilayer film according to the present invention has a tensile strength (ASTM D638) of 140 MPa or more, preferably 142 MPa or more; a surface treatment strength (ASTM D2578-09, based on the skin layer surface) of 40 dyne or more, preferably 42 dyne or more; a friction coefficient (ASTM D1894, based on a thickness of 40 μm and the seal layer surface) of 0.5 or less, preferably 0.3 or less; a haze (based on a thickness of 40 μm) of 20% or less, preferably 18% or less; an aluminum peel strength measured by the following method of 8 N / 15 mm or more, preferably 10 N / 15 mm or more; and a thermal adhesive strength measured by the following method of 60 N / 15 mm or more, preferably 73 N / 15 mm or more.

[0046] [Method for measuring aluminum peel strength] The aforementioned multilayer film (40 μm thick), aluminum foil (50 μm thick, laminated on the skin layer of the multilayer film), and nylon (15 μm thick, laminated on the aluminum foil) were laminated at 130°C and cured at 50°C for 14 days. The resulting laminated film was cut to a width of 15 mm, and the peel strength at a peel angle of 180° was measured at 23°C with a peeling speed of 50 mm / min.

[0047] [Method for measuring thermal bonding strength] Of the laminate film, the multilayer film faces each other at 2 kgf / cm².2 Samples prepared by heat bonding under pressure for 1 second are cut into strips 15 mm wide, and the peel strength at a peel angle of 180° is measured using a tensile strength measuring instrument at a peeling speed of 100 mm / min at 23°C.

[0048] The polypropylene multilayer film according to the present invention is mainly applied to the molding of cell pouches, but is not limited to this, and may of course be applied to the molding of packaging films, retort pouches, pouches for electronic materials, and the like. [Examples]

[0049] The present invention will be described in more detail below through specific manufacturing examples, embodiments, and comparative examples.

[0050] <Manufacturing example> (1)(a) Production of propylene binary copolymer Propylene and ethylene were injected into a reactor to carry out a bulk polymerization reaction, and a propylene-based binary copolymer was produced such that the ethylene content in the copolymer was 3% by weight. (2)(b1) Production of ethylene propylene block copolymer Propylene was injected into a reactor for polymerization, and then propylene and ethylene were injected into a gas-phase reactor to carry out a bulk polymerization reaction, producing a propylene-based block copolymer such that the ethylene content in the block copolymer was 5.5% by weight. (3)(b2) Production of ethylene propylene block copolymer Propylene was injected into a reactor for polymerization, and then propylene and ethylene were injected into a gas-phase reactor to carry out a bulk polymerization reaction, producing a propylene-based block copolymer such that the ethylene content in the block copolymer was 6% by weight.

[0051] <Examples 1 to 4, Comparative Examples 1 to 4> The following materials were used to produce propylene block copolymer mixed resin compositions for each layer by melting and mixing them at 220°C using a single-screw extruder in the composition ratios shown in Table 1 below (unit: parts by weight, with the addition of commonly added phenolic antioxidants, phosphate antioxidants, and hydrotalcite as a catalyst neutralizer) and forming pellets. Next, the produced layer-specific mixed resin compositions were melt-molded at 220°C using a multilayer film molding machine to form films, producing multilayer films with a thickness of 40 μm (ratio of skin layer:core layer:seal layer thickness 1:3:1).

[0052] <Example Test> Using the aforementioned manufactured pellets and films, test specimens were prepared, and their physical properties were measured or evaluated using the method described below. The results are shown in Table 1 below.

[0053] [Methods for measuring or evaluating physical properties] (1) Melt Index Measurements were taken under ASTM D1238 conditions at 230°C with a 2.16 kg load. (2) Melting point (Tm) Using a differential scanning calorimeter (trademark DSC, manufactured by Perkin-Elmer Co.), 10 mg of the specimen was pre-melted at 220°C for 5 minutes under nitrogen gas atmosphere, and then the temperature was reduced to 40°C at a rate of 5°C decelerating. Next, the temperature was increased at a heating rate of 5°C / min, and the peak temperature of the maximum peak in the obtained melting endothermic curve was defined as the melting point (Tm). The melting point of indium (In) measured using the aforementioned measuring device at a heating rate of 5°C / min was 156.6°C. (3) Ethylene content Using infrared absorption spectroscopy (FT-IR), at 720 and 730 cm. -1 The ethylene content was measured using the characteristic peaks. (4) Tensile strength Measurements were taken using the ASTM D638 method. (5) Surface treatment strength Measurements were taken according to the ASTM D2578-09 method. (6) Coefficient of friction The measurement was performed on a 40 μm thick film using the ASTM D1894 method. (7) Haze The measurement was performed on a 40 μm thick film using the ASTM D1003 method. (8) Peel strength of aluminum The aforementioned multilayer film (40 μm thick), aluminum foil (50 μm thick, laminated on the skin layer of the multilayer film), and nylon (15 μm thick, laminated on the aluminum foil) were laminated at 130°C and cured at 50°C for 14 days. The resulting laminated film was cut to a width of 15 mm, and the peel strength at a peel angle of 180° was measured at 23°C with a peeling speed of 50 mm / min. (9) Thermal adhesive strength Of the laminate film, the multilayer film faces each other at 2 kgf / cm². 2 Samples were prepared by heat bonding under pressure for 1 second, cut into strips 15 mm wide, and the peel strength at a peel angle of 180° was measured using a tensile strength meter at 23°C with a peel rate of 100 mm / min. (10) Electrolyte resistance The specimens used to measure the thermal adhesion strength were immersed in an electrolyte solution at 85°C for 75 hours, and then the peel strength was measured using the same method as the thermal adhesion strength measurement method. If the peel strength after immersion in the electrolyte solution was 90 parts or more compared to the peel strength before immersion in the electrolyte solution, it was indicated as "◎", if it was 70 parts or more but less than 90 parts, it was indicated as "△", and if it was less than 70 parts, it was indicated as "X". The electrolyte solution composition was [EC / DEC / DMC=1 / 1 / 1(v / v parts)+LiPF6(1mol / L)+H2O 300ppm], where EC is ethylene carbonate, DEC is diethyl carbonate, and DMC is dimethyl carbonate. (11) Forming performance The laminate film was placed on a picture frame-shaped metal mold (10cm x 10cm) with the nylon side touching the edge of the mold. The multi-layer film surface was then pressed down with a square pyramid to draw the film to a minimum depth of 9mm. The result was indicated as "◎" if there was no collapse at the corners of the laminate film, "△" if there was one to three collapses, and "X" if there were four collapses.

[0054] [Table 1]

[0055] Referring to Table 1, it was confirmed that the present invention provides a polypropylene multilayer film containing a skin layer, core layer, and seal layer in specific compositions, which exhibits excellent adhesive performance when used as a sealant layer for cell pouches (see aluminum peel strength and thermal adhesion strength), and simultaneously satisfies moldability in post-processing (see forming performance), while also achieving excellent mechanical properties, surface characteristics, and transparency. However, in terms of aluminum peel strength, when the skin layer is a mixture of (a) a propylene binary copolymer, (e) an antiblocking agent, and (f) a modified polyolefin, it was found that a composition in which (f) a relatively large amount of modified polyolefin is mixed (Examples 1, 3, and 4) is more preferable than a composition in which (f) a relatively small amount of modified polyolefin is mixed (Example 2), and is even more preferable than substituting (a) a propylene binary copolymer for (Comparative Example 1).

[0056] In contrast, when (a) propylene-based binary copolymer was used alone as the main component of the seal layer instead of mixing (a) propylene-based binary copolymer and (b2) ethylene-propylene block copolymer (Comparative Example 3), it was shown that the tensile strength of the film decreased, resulting in a slight decrease in thermal adhesion strength. Furthermore, when (c) amorphous propylene rubber, a minor component of the core layer, was replaced with (b1) ethylene-propylene block copolymer (Comparative Example 2), the rigidity of the film increased and the tensile strength improved, but the moldability in post-processing decreased significantly. Also, when (d) was used in the seal layer Slip agent (e) If an antiblocking agent is not included (Comparative Example 4), the moldability in post-processing may decrease, potentially leading to a decline in process efficiency during production.

[0057] From the above, it was found that there exists a specific laminated composition that satisfies excellent mechanical properties, surface characteristics, and transparency, along with adhesive performance and moldability in post-processing, for multilayer films used as sealant layers in cell pouches, and it was confirmed that the polypropylene-based multilayer film including the skin layer, core layer, and seal layer according to the present invention fully satisfies these requirements.

[0058] Preferred embodiments of the present invention have been described in detail. The description of the present invention is illustrative, and a person with ordinary skill in the art to which the present invention belongs should understand that it can be easily modified into other specific forms without changing the technical idea or essential features of the present invention.

[0059] Therefore, the scope of the present invention is indicated by the claims described below rather than by the detailed description above, and all modified or altered forms derived from the meaning, scope, and equivalent concepts of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. (a) a propylene-based binary copolymer, (f) a modified polyolefin, and (e) an antiblocking agent are included in the skin layer, (b1) a core layer comprising an ethylene propylene block copolymer and (c) amorphous propylene rubber, A sealing layer comprising (a) a propylene-based binary copolymer, (b2) an ethylene-propylene block copolymer, (d) a slip agent, and (e) an antiblocking agent, Includes, The (a) propylene-based binary copolymer contains ethylene in a content of 2.0 to 6.5% by weight, The (b1) ethylene propylene block copolymer contains ethylene in a content of 2.0 to 6.0% by weight, The (b2) ethylene propylene block copolymer contains ethylene in a content of 6.0 to 10.0% by weight, The (c) amorphous propylene rubber contains ethylene or butene in a content of 10.0 to 60.0% by weight. The slip agent (d) is an amide-based slip agent. The (e) antiblocking agent is spherical silica, The (f) modified polyolefin is characterized by being grafted with maleic anhydride in a content of 1 to 10.0% by weight, and is a polypropylene-based multilayer film for cell pouches.

2. The (a) propylene-based binary copolymer has a melting index (MI, 230°C, 2.16 kg load) of 2 to 12 g / 10 min. The (b1) ethylene propylene block copolymer has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min. The (b2) ethylene propylene block copolymer has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min. The (c) amorphous propylene rubber has a melting index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min. The slip agent (d) is a mixture of two or more amide-based slip agents having 14 to 22 carbon atoms. The (e) antiblocking agent is a particle having an average particle size of 1.5 to 3.0 μm, a moisture content of less than 0.5% by weight, and a bulk density of 0.8 to 1.0 g / cm³. ３ The polypropylene multilayer film for cell pouches according to claim 1, characterized in that it is the same as described in claim 1.

3. The skin layer contains (a) 80 to 99 parts by weight of a propylene-based binary copolymer, (f) 1 to 20 parts by weight of a modified polyolefin, and (e) 0.1 to 1 part by weight of an antiblocking agent. The core layer contains (b1) ethylene propylene block copolymer in an amount of 50 to 90 parts by weight, and (c) amorphous propylene rubber in an amount of 10 to 50 parts by weight. The polypropylene multilayer film for cell pouches according to claim 1, characterized in that the sealing layer contains (a) 20 to 60 parts by weight of a propylene binary copolymer, (b2) 40 to 80 parts by weight of an ethylene propylene block copolymer, (d) 0.1 to 1.0 part by weight of a slip agent, and (e) 0.1 to 1.0 part by weight of an antiblocking agent.

4. The polypropylene multilayer film for cell pouches according to claim 1 is characterized in that the multilayer film has a coefficient of friction (ASTM D1894, thickness 40 μm, based on the surface of the sealing layer) of 0.5 or less, an aluminum peel strength measured by the method described below of 8 N / 15 mm or more, and a thermal adhesive strength measured by the method described below of 60 N / 15 mm or more: [Method for measuring aluminum peel strength] The laminate film, consisting of a multilayer film (40 μm thick), aluminum foil (50 μm thick, laminated on the skin layer of the multilayer film), and nylon (15 μm thick, laminated on the aluminum foil), was laminated at 130°C and cured at 50°C for 14 days. The laminate film was then cut to a width of 15 mm, and the peel strength at a peel angle of 180° was measured at 23°C with a peel rate of 50 mm / min. [Method for measuring thermal bonding strength] The laminate film is treated with 2 kgf / cm² so that the multilayer films face each other. ２ A sample prepared by heat bonding under pressure for 1 second is cut into strips 15 mm wide, and the peel strength at a peel angle of 180° at a peel rate of 100 mm / min at 23°C is measured using a tensile strength measuring instrument.

5. A sealant layer comprising the film described in any one of claims 1 to 4, A barrier layer formed on the sealant layer, An outer resin layer formed on the barrier layer, Cell pouch containing [the product].

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