Propylene-based multilayer film for cell pouches with excellent adhesive properties and formability

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 to and the benefit of Korean Patent Application No. 10-2020-0159121, filed on November 24, 2020, the entire text of which is incorporated herein by reference. [Background technology]

[0003] Secondary batteries generally refer to lithium secondary batteries, which are used in portable terminal devices such as laptops, smartphones, tablet PCs, and video cameras, electric vehicles including hybrid vehicles, and smart grids for energy storage. Research is underway to make them smaller, lighter, and thinner, while also overcoming various environmental factors such as harsh thermal environments and mechanical shocks.

[0004] Unlike conventional can-type packaging, rechargeable battery pouches are used as packaging materials for these lithium batteries, as they have the advantage of being able to freely change the shape of the battery. Typical rechargeable battery pouch films have a multilayer structure: an inner resin layer made of an adhesive layer of polyolefins such as polyethylene (PE), cast polypropylene (cPP), or polypropylene (PP) or copolymers thereof, which has thermal adhesive properties and acts as a sealant; an aluminum layer, which is a metal foil that acts as a base material to maintain mechanical strength and a barrier layer against moisture and oxygen; and an outer resin layer made of a functional polymer film such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), nylon, or liquid crystal polymer (LCP), which protects the battery cell from external impacts.

[0005] Conventionally, metal packaging, especially aluminum, has been used as a cylindrical or parallelepiped shape by pressing it. However, this metal can packaging has limitations in that the outer wall of the container is hard and the shape of the battery itself is determined by the shape of the metal can packaging.

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

[0007] Pouch-type secondary batteries have the advantage of being flexible in shape and capable of producing a rechargeable battery with the same capacity but with a smaller volume and weight. However, unlike can-type batteries, pouch-type batteries use a flexible pouch as a container, which can be damaged for various reasons during various processes. For example, during the process of inserting the electrode assembly into the pouch, protruding parts such as electrode tabs and electrode leads can cause cracks in the PP or cPP layer inside the pouch. If such damage exposes the aluminum layer, it can react with the electrolyte and cause side reactions due to its reactivity with the electrolyte. The aluminum layer exposed to the electrolyte can corrode due to a chemical reaction with the electrolyte that has permeated or diffused into the battery, oxygen, or moisture. This generates corrosive gases, resulting in swelling, which causes the battery to expand. Specifically, lithium hexafluorophosphate (LIPF6) reacts with water and oxygen to produce the corrosive gas hydrofluoric acid (HF). This hydrofluoric acid can react with aluminum and cause a sudden exothermic reaction. If it is adsorbed onto the aluminum surface in a secondary reaction and penetrates into the tissue, it can increase the tissue's brittleness. Even a small impact can cause the pouch film to crack, and electrolyte leakage can cause the lithium to react with the air, potentially resulting in fire.

[0008] Patent Document 3 describes a polymer film for cell packaging that contains 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 cross-linked resin, and describes that LDPE is used to reduce the permeation rate of the electrolyte, PP is used to enhance heat resistance, and the cross-linked resin is used to increase the compatibility between LDPE and PP, but does not specifically mention changes in physical properties due to molecular weight, density, melting point, 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, or the like, a first adhesive layer, an aluminum layer, a second adhesive layer, and an inner resin layer made of polyolefin. However, the document only describes the overall layer structure of the pouch and does not mention the specific composition of the polyolefin that makes up the inner resin layer.

[0010] Patent Document 5 describes a polypropylene composite film comprising Layer A, whose main component is a propylene-based random copolymer obtained by randomly copolymerizing propylene with ethylene or butene; Layer B, which is composed of 60 to 90 wt% of a propylene polymer having a comonomer (ethylene or butene) content of 0 to 1.5 wt% and 10 to 40 wt% of a propylene polymer having a comonomer (ethylene or butene) content of 10 to 40 wt%; and Layer C, which is composed of a propylene-based ethylene or butene random copolymer, characterized in that Layer B contains 100 to 2000 ppm of a fatty acid amide-based lubricant and 0 to 20 wt% of a metallocene catalyst-based low-density polyethylene. However, it does not mention in detail the remaining raw materials excluding the raw materials of Layer B. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 2003-0029141 [Patent Document 2] Korean Patent Publication No. 2002-0030737 [Patent Document 3] Korean Patent No. 1499740 [Patent Document 4] Korean Patent No. 1485523 [Patent Document 5] Korean Patent Publication No. 2019-0047104 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention is directed to a multilayer film that is mainly used as a sealant layer for cell pouches, has excellent adhesive properties, and simultaneously satisfies formability in post-processing, and presents its lamination composition in detail.

[0013] The present invention also provides a cell pouch that uses the multilayer film as a sealant layer. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a rubber composition 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 rubber composition comprising (a) a propylene-based binary copolymer, (b2) an ethylene-propylene block copolymer, and (d) an antiblocking agent. slip agent and (e) a sealing layer comprising an antiblocking agent.

[0015] In addition, the (a) propylene-based binary copolymer contains 2.0 to 6.5 wt % of ethylene, the (b1) ethylene-propylene block copolymer contains 2.0 to 6.0 wt % of ethylene, the (b2) ethylene-propylene block copolymer contains 6.0 to 10.0 wt % of ethylene, the (c) amorphous propylene rubber contains 10 to 60 wt % of ethylene or butene, and the (d) slip agent is an amide slip agentThe (e) antiblocking agent is spherical silica, and the (f) modified polyolefin contains 1 to 10 wt % maleic anhydride and is grafted thereto.

[0016] In addition, the (a) propylene-based binary copolymer has a melt index (MI, 230°C, 2.16 kg load) of 2 to 12 g / 10 min, the (b1) ethylene-propylene block copolymer has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, the (b2) ethylene-propylene block copolymer has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, the (c) amorphous propylene rubber has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, and the (d) slip agent is an amide having 14 to 22 carbon atoms slip agent and (e) the 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 / cm. 3 The present invention provides a polypropylene-based multilayer film characterized by:

[0017] 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 an amorphous propylene rubber, and 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, (d) slip agent and (e) an antiblocking agent in an amount of 0.1 to 1 part by weight.

[0018] The multilayer film is also characterized by having a coefficient of friction (ASTM D1894, thickness 40 μm, seal layer surface standard) of 0.5 or less, an aluminum peel strength measured by the following method of 8 N / 15 mm or more, and a thermal adhesive strength measured by the following method of 60 N / 15 mm or more.

[0019] [Method for measuring aluminum peel strength] The 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 was measured at a peel angle of 180° at a peel rate of 50 mm / min at 23°C.

[0020] [Method for measuring thermal adhesive strength] The laminate film is heated to 2 kgf / cm so that the multilayer film faces each other. 2 The sample is cut to a width of 15 mm, and the peel strength at a peel angle of 180° is measured at 23°C, a peel speed of 100 mm / min, and a tensile strength tester.

[0021] In order to solve the other problem, 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 outer resin layer formed on the barrier layer. [Effects of the Invention]

[0022] According to the present invention, a specific laminate composition of a polypropylene-based multilayer film including a skin layer, a core layer, and a seal layer of specific compositions can be presented, which is used as a sealant layer of a cell pouch and has excellent adhesive performance, satisfies formability in post-processing, and has excellent mechanical properties, surface characteristics, and transparency. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in detail below through preferred embodiments. Prior to this, the terms and phrases used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts consistent with the technical concept of the present invention, based on the principle that the inventor can appropriately define the concepts of terms to best describe his or her invention. Therefore, it should be understood that the configuration of the embodiment described in this specification is merely the most preferred embodiment of the present invention and does not fully represent the technical concept of the present invention, and therefore, at the time of filing this application, various equivalents and modifications that can replace them may exist.

[0024] The present inventors have faced the fact that no specific composition of a film material that can be used as a sealant layer for conventional cell pouches and that simultaneously satisfies the required adhesive performance and formability in post-processing has been known, and as a result of repeated research into numerous lamination compositions, they have discovered that a specific composition of skin layer, core layer, and seal layer that mainly comprises a propylene-based binary copolymer can provide excellent adhesive performance when used as a sealant layer for a cell pouch, while also satisfying formability in post-processing and having excellent mechanical properties, surface characteristics, and transparency, thereby arriving at the present invention.

[0025] Therefore, the present invention provides a rubber composition 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 composite layer containing (a) a propylene-based binary copolymer, (b2) an ethylene-propylene block copolymer, and (d) an antiblocking agent. slip agent and (e) a sealing layer comprising an antiblocking agent.

[0026] In the present invention, the (a) propylene-based binary copolymer is a main component of the skin layer and seal layer of the multilayer film, and is a copolymer of propylene and one α-olefin other than propylene, preferably a binary copolymer obtained by simultaneous injection and polymerization of propylene and ethylene. The polymerization method for 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 improved aluminum peel strength because it contains the same propylene as the olefin-based adhesive component. However, the (a) propylene-based binary copolymer is a crystalline copolymer, not an amorphous propylene-ethylene copolymer, and preferably contains 2 to 6.5 wt% ethylene, more preferably 2.5 to 3.5 wt% ethylene, with a melting point (Tm) of 125 to 155°C, and even more preferably 140 to 154°C. If the ethylene content of the (a) propylene-based binary copolymer is less than 2 wt%, the flexibility may be insufficient, which may result in whitening and edge crumbling during forming and reduced wetting during the adhesive lamination process. Furthermore, if the ethylene content exceeds 6.5 wt%, the heat resistance may be insufficient, which may result in appearance problems (deformation and distortion) due to heat generation during use.

[0028] Meanwhile, the (a) propylene-based binary copolymer has a melt 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 melt index is less than 2 g / 10 min, productivity decreases, and if it exceeds 12 g / 10 min, the improvement in aluminum peel strength is negligible.

[0029] In the present invention, (b1) ethylene-propylene block copolymer is the main component of the core layer of the multilayer film, and since the constituent materials of (a) propylene-based binary copolymer are the same (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 2 to 6 wt% ethylene, more preferably 4 to 6 wt% ethylene. If the (b1) ethylene propylene block copolymer contains less than 2 wt%, the impact resistance improvement effect is negligible, and if it exceeds 6 wt%, a large amount of fish eyes occur due to non-dispersion.

[0031] Meanwhile, the melt index (MI, 230°C, 2.16 kg load) of the (b1) ethylene propylene block copolymer is 1 to 5 g / 10 min, preferably 2 to 5 g / 10 min. If the melt index is less than 1 g / 10 min, a large number of fish eyes occur due to non-dispersion, and if it exceeds 5 g / 10 min, the improvement in impact resistance is negligible.

[0032] In the present invention, (b2) ethylene-propylene block copolymer is the main component of the seal layer of the multilayer film, and since the constituent materials of (a) propylene-based binary copolymer are the same as those of (a), propylene and ethylene, the affinity between the two phases results in excellent interphase compatibility and high quality uniformity. The polymerization method of (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 6 to 10 wt % ethylene, more preferably 6 to 8 wt % ethylene. If the (b2) ethylene propylene block copolymer has an ethylene content of less than 6 wt %, sufficient thermal adhesive strength cannot be achieved during thermal bonding. If the ethylene content exceeds 10 wt %, thermal adhesive strength is reduced due to thermal fusion between the thermal adhesive layers during thermal bonding.

[0034] The (b2) ethylene propylene block copolymer has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min, preferably 2 to 5 g / 10 min. If the melt index is less than 1 g / 10 min, a large number of fish eyes occur due to non-dispersion, and if it exceeds 5 g / 10 min, the improvement in impact resistance is negligible.

[0035] In the present invention, the amorphous propylene rubber (c) is a minor component of the core layer of the multilayer film and is a copolymer of propylene and an α-olefin other than propylene. Preferably, propylene and ethylene or butene are co-injected, with the ethylene or butene content being 10-60 wt%, and more preferably 10-30 wt% ethylene or 20-40 wt% butene. If the ethylene or butene content is less than 10 wt%, the impact resistance improvement effect is minimal. If it exceeds 60 wt%, the content of low molecular weight compounds is high, resulting in a sticky film during film formation, an uneven surface, and reduced tensile strength. The polymerization method for 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 (d) slip agent and (e) an antiblocking agent is a minor component of the sealing layer of the multilayer film; and (d) slip agent In this case, the organic compounds in question migrate to the substrate surface over time in the sealing layer. slipBy providing this property, it reduces the coefficient of friction in post-processing such as deep drawing, thereby improving formability and workability. In the case of (e) anti-blocking agents, it forms irregularities on the film surface, thereby alleviating the sticky (blocking) phenomenon in post-processing such as deep drawing, thereby improving formability and workability.

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

[0038] Such (d) slip agent is an amide having 14 to 22 carbon atoms slip agent More specifically, it is a mixture of tetradecaneamide, hexadecanamide, octadecanamide, and 13-cis-docoseneamide, which are saturated and unsaturated amide-based organic compounds having 14 to 22 carbon atoms.

[0039] The antiblocking agent (e) is preferably a silica antiblocking agent having a spherical particle shape and a uniform particle distribution, and the particles have a moisture content of less than 0.5% by weight when dried (105°C, 60 min), 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 / cm. 3 It is preferable that:

[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, a polar functional group, at a content of 1 to 10 wt%, preferably 3 to 5 wt%. If the maleic anhydride content of the modified polypropylene is less than 1 wt%, the adhesive strength with aluminum foil decreases. If it exceeds 10 wt%, the large amount of polar functional groups causes fisheyes and small molecules to form, which reduces the surface tension after corona surface treatment and reduces the adhesive strength with aluminum foil.

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

[0042] That is, 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 an amorphous propylene rubber, and 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 and (e) an antiblocking agent in an amount of 0.1 to 1.0 parts by weight, but preferably, the skin layer contains (a) 87 to 93 parts by weight of a propylene-based binary copolymer, (f) 7 to 13 parts by weight of a modified polyolefin, and (e) 0.1 to 0.9 parts by weight of an antiblocking agent, the core layer contains (b1) 65 to 85 parts by weight of an ethylene-propylene block copolymer, and (c) 15 to 35 parts by weight of an amorphous propylene rubber, and the seal layer contains (a) 25 to 55 parts by weight of a propylene-based binary copolymer, (b2) 45 to 75 parts by weight of an ethylene-propylene block copolymer, and (d) slip agent and (e) an antiblocking agent in an amount of 0.1 to 0.3 parts by weight.

[0043] Meanwhile, the resin composition of each layer constituting the polypropylene-based multilayer film according to the present invention may further contain one or more additives, such as antioxidants, catalyst neutralizers, pigments, dispersants, weathering agents, antistatic agents, UV stabilizers, talc, etc., as needed, as long as the object of the present invention is not impaired. The amount of each additive used is adjusted taking into account the total production amount and production process, within a range known to be usable for the polypropylene-based multilayer film of the present invention without affecting its properties.

[0044] In the present invention, the multilayer film using the above components is manufactured by a conventional method known in the art, for example, by mixing the required amounts of the components constituting each layer in a Henschel mixer, forming the mixture into pellets at 180 to 240°C using an extruder, and melt-molding the pellets into a film using a multilayer film molding machine to manufacture the multilayer film.

[0045] The polypropylene-based multilayer film according to the present invention has excellent adhesive properties when used as a sealant layer of a cell pouch, and can be made to have excellent mechanical properties, surface characteristics, and transparency while simultaneously satisfying formability in post-processing. Specifically, the polypropylene-based 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 coefficient of friction (ASTM D1894, 40 μm thickness, based on the seal layer surface) of 0.5 or less, preferably 0.3 or less, a haze (based on a 40 μm thickness) of 20% or less, preferably 18% or less, an aluminum peel strength measured by the method described below of 8 N / 15 mm or more, preferably 10 N / 15 mm or more, and a thermal adhesive strength measured by the method described below of 60 N / 15 mm or more, preferably 73 N / 15 mm or more.

[0046] [Method for measuring aluminum peel strength] The 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 was measured at a peel angle of 180° at a peel rate of 50 mm / min at 23°C.

[0047] [Method for measuring thermal adhesive strength] The laminate film is heated to 2 kgf / cm so that the multilayer film faces each other.2 The sample is cut to a width of 15 mm, and the peel strength at a peel angle of 180° is measured at 23°C, a peel speed of 100 mm / min, and a tensile strength tester.

[0048] The polypropylene-based multilayer film according to the present invention as described above is primarily applied to the formation of cell pouches, but is not limited thereto and may, of course, also be applied to the formation of packaging films, retort pouches, pouches for electronic materials, and the like. [Example]

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

[0050] <Production example> (1)(a) Production of Propylene-Based Binary Copolymers Propylene and ethylene were injected into the reactor to carry out bulk polymerization reaction, and a propylene-based binary copolymer was produced so that the ethylene content in the copolymer was 3 wt %. (2)(b1) Production of ethylene propylene block copolymer Propylene was injected into the reactor for polymerization, and then propylene and ethylene were injected into the gas phase reactor for bulk polymerization reaction to produce a propylene-based block copolymer with an ethylene content of 5.5 wt% in the block copolymer. (3)(b2) Production of ethylene propylene block copolymer Propylene was injected into the reactor for polymerization, and then propylene and ethylene were injected into the gas phase reactor for bulk polymerization reaction to produce a propylene-based block copolymer with an ethylene content of 6 wt% in the block copolymer.

[0051] <Examples 1 to 4, Comparative Examples 1 to 4> The propylene block copolymer mixed resin compositions for each layer were prepared by melt-mixing and pelletizing them in a single-screw extruder at 220°C according to the composition ratios (unit: parts by weight, including commonly added phenolic antioxidant, phosphate antioxidant, and hydrotalcite as a catalyst neutralizer) shown in Table 1. The prepared mixed resin compositions for each layer were then melt-molded at 220°C in a multilayer film molding machine to form films, producing multilayer films with a thickness of 40 μm (skin layer:core layer:seal layer thickness ratio: 1:3:1).

[0052] <Test example> The pellets and films were used to prepare test specimens, and their properties were measured and evaluated according to the following methods. The results are shown in Table 1 below.

[0053] [Methods for measuring and evaluating physical properties] (1) Melt Index Measured under ASTM D1238 conditions at 230°C and a load of 2.16 kg. (2) Melting point (Tm) Using a differential scanning calorimeter (DSC, manufactured by Perkin-Elmer Co.), 10 mg of specimen was pre-melted at 220°C for 5 minutes under a nitrogen gas atmosphere, and then the temperature was decreased to 40°C at a rate of 5°C. The temperature was then increased at a rate of 5°C / min, and the peak temperature of the maximum peak of the melting endothermic curve obtained was defined as the melting point (Tm). The melting point of indium (In) measured using this measuring device at a heating rate of 5°C / min was 156.6°C. (3) Ethylene content Using infrared absorption spectroscopy (FT-IR), 720 and 730 cm -1 The ethylene content was measured using the characteristic peak of (4) Tensile strength Measured according to ASTM D638 method. (5) Surface treatment strength Measured according to ASTM D2578-09 method. (6) Friction coefficient Measured by the method of ASTM D1894 on a 40 μm thick film. (7) Haze Measured by the method of ASTM D1003 on a 40 μm thick film. (8) Aluminum peel strength The 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 was measured at a peel angle of 180° at a peel rate of 50 mm / min at 23°C. (9) Thermal adhesive strength The laminate film is heated to 2 kgf / cm so that the multilayer film faces each other. 2 The prepared sample was heat-bonded for 1 second under a pressure of 1000 psi and cut to a width of 15 mm. The peel strength was measured at 23°C, a peel rate of 100 mm / min, and a peel angle of 180° using a tensile strength tester. (10) Electrolyte resistance The specimens used to measure the thermal adhesive strength were immersed in an electrolyte at 85°C for 75 hours, and then the peel strength was measured using the same method as for measuring the thermal adhesive strength. If the peel strength after immersion in the electrolyte was 90 parts or more compared to the peel strength before immersion in the electrolyte, it was marked with "◎", if it was 70 parts or more but less than 90 parts, it was marked with "△", and if it was less than 70 parts, it was marked with "X". The composition of the electrolyte was [EC / DEC / DMC = 1 / 1 / 1 (v / v parts) + LiPF6 (1 mol / L) + HO 300 ppm], where EC is ethylene carbonate, DEC is diethyl carbonate, and DMC is dimethyl carbonate. (11) Forming performance The laminate film was placed on a frame-shaped metal mold (10 cm x 10 cm) with the nylon surface touching the edge of the mold, and a square pyramid was pressed onto the multilayer film surface to draw to a minimum depth of 9 mm. If there was no collapse at the corners of the laminate film, it was marked with "◎", if there was one to three collapses, it was marked with "△", and if there was four collapses, it was marked with "X".

[0054] [Table 1]

[0055] Referring to Table 1, it was confirmed that the polypropylene-based multilayer film having specific compositions for the skin layer, core layer, and seal layer according to the present invention exhibits excellent adhesive performance when used as a sealant layer for a cell pouch (see aluminum peel strength and thermal adhesion strength), while simultaneously satisfying formability in post-processing (see forming performance), and exhibits excellent mechanical properties, surface characteristics, and transparency. However, in terms of aluminum peel strength, when the skin layer is made by mixing (a) a propylene-based binary copolymer, (e) an antiblocking agent, and (f) a modified polyolefin, it is more preferable to mix a relatively large amount of (f) modified polyolefin (Examples 1, 3, and 4) than to mix a relatively small amount of (f) modified polyolefin (Example 2), and it is even more preferable than replacing the (f) modified polyolefin with (a) a propylene-based binary copolymer (Comparative Example 1).

[0056] In contrast, when (a) propylene-based binary copolymer and (b2) ethylene-propylene block copolymer were mixed as the main component of the seal layer, but when (a) propylene-based binary copolymer was used alone (Comparative Example 3), the tensile strength of the film was reduced, resulting in a slight decrease in thermal adhesive strength. Furthermore, when (c) amorphous propylene rubber, a secondary component of the core layer, was replaced with (b1) ethylene-propylene block copolymer (Comparative Example 2), the rigidity of the film increased, resulting in an increase in tensile strength, but the formability in post-processing was significantly reduced. Furthermore, when (d) slip agent And (e) when no antiblocking agent is contained (Comparative Example 4), moldability in post-processing may be reduced, which may reduce processability during production.

[0057] From the above, it has been found that there is a specific lamination composition in a multilayer film used as a sealant layer of a cell pouch that satisfies all of the following requirements: adhesive performance, formability in post-processing, excellent mechanical properties, surface characteristics, and transparency. It has been confirmed that the polypropylene-based multilayer film according to the present invention, comprising a skin layer, a core layer, and a seal layer, satisfies these requirements sufficiently.

[0058] Although the preferred embodiments of the present invention have been described in detail above, the description of the present invention is for illustrative purposes only, and it should be understood by those skilled in the art that the present invention may be easily modified into other specific forms without changing the technical concept or essential features of the present invention.

[0059] Therefore, the scope of the present invention is indicated by the claims below rather than the above detailed description, and all modifications and variations 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 skin layer comprising (a) a propylene-based binary copolymer, (f) a modified polyolefin, and (e) an antiblocking agent; (b1) a core layer comprising an ethylene propylene block copolymer and (c) an 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; Including, (a) the propylene-based copolymer contains 2.0 to 6.5 wt % of ethylene; The (b1) ethylene propylene block copolymer contains 2.0 to 6.0 wt % of ethylene; The (b2) ethylene propylene block copolymer contains 6.0 to 10.0 wt % of ethylene; (c) the amorphous propylene rubber contains 10.0 to 60.0 wt. % of ethylene or butene; the (d) slip agent is an amide-based slip agent; the antiblocking agent (e) is spherical silica, The polypropylene-based multilayer film for cell pouches is characterized in that the modified polyolefin (f) contains 1 to 10.0 wt % of maleic anhydride and is grafted thereon.

2. The (a) propylene-based copolymer has a melt index (MI, 230°C, 2.16 kg load) of 2 to 12 g / 10 min; The (b1) ethylene propylene block copolymer has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min; The (b2) ethylene propylene block copolymer has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min; The (c) amorphous propylene rubber has a melt index (MI, 230°C, 2.16 kg load) of 1 to 5 g / 10 min; the (d) slip agent 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 wt %, and a bulk density of 0.8 to 1.0 g / cm ３ 2. The polypropylene-based multilayer film for cell pouches according to claim 1, wherein

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 comprises (b1) 50 to 90 parts by weight of an ethylene propylene block copolymer and (c) 10 to 50 parts by weight of an amorphous propylene rubber; 2. The polypropylene-based multilayer film for a cell pouch according to claim 1, wherein the sealing layer comprises (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, (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 anti-blocking agent.

4. 2. The polypropylene-based multilayer film for cell pouches according to claim 1, wherein the multilayer film has a coefficient of friction (ASTM D1894, thickness 40 μm, seal layer surface standard) of 0.5 or less, an aluminum peel strength measured by the following method of 8 N / 15 mm or more, and a thermal adhesive strength measured by the following method of 60 N / 15 mm or more: [Method for measuring aluminum peel strength] The 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 laminate film was cut to a width of 15 mm, and the peel strength was measured at 23°C, a peel rate of 50 mm / min, and a peel angle of 180°. [Method for measuring thermal adhesive strength] The laminate film is subjected to a pressure of 2 kgf / cm so that the multilayer films face each other. ２ The prepared sample is cut to a width of 15 mm, and the peel strength at a peel angle of 180° is measured at 23° C., a peel rate of 100 mm / min, and a tensile strength tester.

5. A sealant layer comprising the film according to any one of claims 1 to 4; a barrier layer formed on the sealant layer; an outer resin layer formed on the barrier layer; A cell pouch containing:

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