Sealant film, exterior material for secondary battery, secondary battery, all-solid-state battery, electronic device, electric vehicle, and electric aircraft

Abstract

To provide a sealant film excellent in heat seal strength and formability at high temperatures.SOLUTION: A sealant film whose main component is a polyolefin resin, has a crystallization temperature of 90°C or higher and 110°C or lower, and E1 is the storage modulus at 40°C and E2 is the storage modulus at 80°C, E1 and E2 satisfy the formula (1). 2.4≤(E1 / E2)≤3.5 (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sealant film that has excellent sealing strength and formability at high temperatures. [Background technology]

[0002] Lithium secondary batteries have a higher energy density than other secondary batteries and are used as batteries for electric vehicles and power storage.

[0003] Conventionally used lithium ion secondary batteries using non-aqueous electrolytes use a lithium hexafluorophosphate solution or the like as the electrolyte. This can cause the electrolyte to react with water to produce hydrofluoric acid, or the temperature inside the battery can rise due to overvoltage charging or overcurrent discharging, which can cause an increase in internal pressure.

[0004] Lithium secondary batteries using non-aqueous electrolytes use can-type exterior materials and laminate-type exterior materials, with the latter being preferred from the viewpoints of freedom in shape, thinness, and weight reduction. Patent Document 1 proposes a sealant film for laminate-type exterior materials that uses a resin with a high melting point or glass transition temperature (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-108263 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a resin with a high melting point or glass transition temperature as described in Patent Document 1 is used for the sealant film, the sealant film has high rigidity, and there is a concern that defects such as voids may occur when the packaging material is formed into a pouch.

[0007] An object of the present invention is to provide a sealant film that is excellent in heat seal strength and formability at high temperatures. [Means for solving the problem]

[0008] A preferred embodiment of the present invention is as follows. (1) A sealant film whose main component is a polyolefin resin, whose crystallization temperature is 90°C or higher and 110°C or lower, and in which, when E1 is the storage modulus at 40°C and E2 is the storage modulus at 80°C, E1 and E2 satisfy formula (1). 2.4≦(E1 / E2)≦3.5 ··· Formula (1) (2) A sealant film according to (1), which comprises at least one layer B, the layer B being primarily composed of a polypropylene resin and containing 1% by mass or more and 20% by mass or less of an elastomer consisting of a propylene-1-butene copolymer relative to the total mass of the layer B (100% by mass). (3) A sealant film according to (1) or (2), which comprises at least one layer B, wherein the layer B is primarily composed of a polypropylene resin and contains 50% by mass or less of block polypropylene relative to 100% by mass of the total mass of the layer B. (4) Storage modulus E2 at 80°C is 0.8 × 10 8 Pa or more 3.0×10 8 The sealant film according to any one of (1) to (3), which has a compressive strength of 0.1 Pa or less. (5) The sealant film according to any one of (1) to (4), which comprises at least three layers, Layer A, Layer B, and Layer C, laminated directly in this order. (6) The sealant film according to any one of (1) to (5), which has a tensile elongation at break of 250% or more. (7) The sealant film according to any one of (1) to (6), which is used as an exterior material for a secondary battery. (8) An outer casing material for a secondary battery, comprising the sealant film according to (7). (9) The packaging material for a secondary battery according to (8), wherein P2 / P1 is 0.8 or more, where P1 is the heat seal strength in a 60°C atmosphere and P2 is the heat seal strength in an 80°C atmosphere. (10) A secondary battery comprising the secondary battery packaging material according to (8). (11) An all-solid-state battery comprising the secondary battery packaging material according to (8). (12) An electronic device having the secondary battery according to (10) or the all-solid-state battery according to (11). (13) An electric vehicle having the secondary battery according to (10) or the all-solid-state battery according to (11). (14) An electric aircraft having the secondary battery according to (10) or the all-solid-state battery according to (11). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a sealant film that has excellent heat seal strength and formability at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described.

[0011] A preferred embodiment of the present invention is a sealant film containing a polyolefin resin as a main component, having a crystallization temperature of 90°C or higher and 110°C or lower, and in which, when the storage modulus at 40°C is E1 and the storage modulus at 80°C is E2, E1 and E2 satisfy formula (1). 2.4≦(E1 / E2)≦3.5 ··· Formula (1)

[0012] A preferred embodiment of the sealant film of the present invention is composed mainly of a polyolefin resin. In the sealant film of the present invention, "composed mainly of a polyolefin resin" means that the content of the polyolefin resin is 50% by mass or more when the entire sealant film is taken as 100% by mass.

[0013] The polyolefin resin used in the sealant film of the present invention may be any known polyolefin resin. For example, preferred examples include polyethylene resins such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and low-crystalline or amorphous ethylene-α-olefin copolymers; polypropylene resins such as homopolypropylene, random copolymers of propylene and ethylene and / or 1-butene (hereinafter referred to as random polypropylene), block polypropylene, propylene-α-olefin copolymer, propylene-ethylene-α-olefin copolymer, and acid-modified polypropylene; polybutene resins such as polybutene-1 (homopolymer) and 1-butene-α-olefin copolymer; and one or more selected from the group consisting of 4-methyl-1-pentene-α-olefin copolymer, ethylene-ethyl (meth)acrylate copolymer, ethylene-methyl (meth)acrylate copolymer, ethylene-n-butyl (meth)acrylate copolymer, and ethylene-vinyl acetate copolymer. Examples of the α-olefin include propylene, ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, and 1-heptene.

[0014] From the viewpoint of achieving both heat seal strength and formability of the sealant film of the present invention, the sealant film of the present invention preferably contains 50% by mass or more of a polypropylene resin among the above-mentioned polyolefin resins when the entire sealant film is taken as 100% by mass. The polypropylene resin preferably used in the sealant film of the present invention will be described later.

[0015] A preferred embodiment of the sealant film of the present invention has a crystallization temperature of 90°C or higher and 110°C or lower. The crystallization temperature of the sealant film is evaluated by the method described in the Examples. By setting the crystallization temperature of the sealant film of the present invention to 90°C or higher, when the sealant film is melted and solidified during the heat-sealing process, the stability of the crystalline and amorphous portions at the heat-sealed portion at high temperatures is improved, and appropriate rigidity is maintained even at high temperatures, thereby suppressing a decrease in heat-seal strength at high temperatures. From the same perspective, the crystallization temperature of the sealant film is more preferably 95°C or higher. Furthermore, by setting the crystallization temperature of the sealant film to 110°C or lower, when the sealant film of the present invention is formed by a melt extrusion method or the like, the rigidity is not too high and the film has appropriate flexibility, thereby achieving excellent formability. Furthermore, by setting the crystallization temperature to 110°C or lower, when the sealant film of the present invention is formed by a melt extrusion method or the like, the mechanical properties of the sealant film are less likely to change even when production conditions such as the melting temperature and solidification conditions are changed, and stable mechanical properties can be obtained. From these viewpoints, the crystallization temperature of the sealant film in the present invention is more preferably 105° C. or lower.

[0016] The heat seal strength at high temperatures referred to in the sealant film of the present invention refers to the heat seal strength in an atmosphere at a temperature above room temperature, and does not limit the use temperature. However, the sealant film of the present invention specifically has excellent heat seal strength in an atmosphere of 40°C or higher, and can exhibit particularly excellent heat seal strength even in an atmosphere of 80°C. Therefore, unless otherwise specified, the term "high temperature" will be used hereinafter to refer to the effect in an atmosphere of 80°C.

[0017] In a preferred embodiment of the sealant film of the present invention, when the storage modulus at 40° C. is E1 and the storage modulus at 80° C. is E2, E1 and E2 satisfy formula (1). 2.4≦(E1 / E2)≦3.5 ··· Formula (1)

[0018] The storage moduli E1 and E2 refer to values ​​measured by DMA (dynamic viscoelasticity measurement), and the measurement method is the method described in the Examples.

[0019] By controlling the crystallization temperature of the sealant film in the present invention within the above range and setting the ratio E1 / E2 (the storage modulus at 40°C, E1, and the storage modulus at 80°C, E2) to 2.4 or more, the balance and dispersion state of the amorphous and crystalline components of the resin constituting the sealant film are improved at high temperatures, thereby achieving excellent heat seal strength at high temperatures while also ensuring formability. From the same perspective, E1 / E2 is more preferably 2.8 or more. Furthermore, by controlling the crystallization temperature of the sealant film in the present invention within the above range and setting E1 / E2 to 3.5 or less, the decrease in cohesive strength of the sealant film at high temperatures can be suppressed, thereby suppressing a decrease in heat seal strength. From the same perspective, E1 / E2 is more preferably 3.2 or less.

[0020] The sealant film of the present invention has a storage modulus E2 of 0.8×10 at 80°C. 8 Pa or more 3.0×10 8 From the viewpoint of improving the heat seal strength at high temperatures, the E2 is preferably 1.2×10 8 Pa or more is more preferable, 2.5 × 10 8 Pa or less is more preferable.

[0021] From the viewpoint of achieving both heat seal strength and formability, the sealant film of the present invention preferably includes at least one layer B composed mainly of a polypropylene-based resin. Here, "composed mainly of a polypropylene-based resin" means that the content of the polypropylene-based resin in layer B is 50% by mass or more, when the entire layer B is taken as 100% by mass. The content of the polypropylene-based resin in layer B is more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0022] Examples of polypropylene resins used in Layer B of the sealant film of the present invention include homopolypropylene, random polypropylene, block polypropylene, propylene-α-olefin copolymer, propylene-ethylene-α-olefin copolymer, and acid-modified polypropylene. It is preferable to use one or more selected from these polypropylene resins. Examples of the α-olefins include propylene, ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, and 1-heptene.

[0023] From the viewpoint of achieving both heat seal strength and moldability at high temperatures, more preferred polypropylene-based resins for use in Layer B include homopolypropylene, random polypropylene, and block polypropylene. Of these, it is more preferred to contain at least block polypropylene, and it is most preferred to contain at least block polypropylene and random polypropylene.

[0024] From the viewpoint of achieving both heat seal strength and moldability of the sealant film, the content of the above-mentioned more preferred polypropylene-based resin in Layer B is preferably 50% by mass or more, and more preferably 70% by mass or more, when the entire Layer B is 100% by mass.

[0025] Furthermore, when block polypropylene is contained in Layer B, it is preferably 20% by mass or more from the viewpoint of improving moldability, and it is preferably 50% by mass or less from the viewpoint of controlling the E1 / E2 within a preferred range and achieving both moldability and heat seal strength at high temperatures.

[0026] When layer B contains block polypropylene, the average diameter of the domains dispersed in layer B is preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.5 μm or less, from the viewpoint of improving moldability and heat seal strength at high temperatures. The domains dispersed in layer B refer to the island phases when layer B forms a sea-island structure. The composition of the components constituting the island phases is not particularly limited, but examples include rubber components contained in the block polypropylene and other components incompatible with the sea phase.

[0027] The average diameter of the domains dispersed in Layer B can be determined by microtome-based ultrathin sections of the sealant film taken in the width direction (TD)-thickness direction, staining with RuO4, and then observing the cross sections using a transmission electron microscope. Ten randomly selected domains are examined to determine the maximum diameter in the thickness direction, and the arithmetic mean of the diameters is used to determine the average diameter of the domains dispersed in Layer B. The cross sections are observed at magnifications of 2,000x, 5,000x, 10,000x, and 20,000x. The average diameter determined from the image observed at 20,000x if the average domain diameter is less than 0.5 μm, 10,000x if the average domain diameter is 0.5 μm or more but less than 1 μm, 5,000x if the average domain diameter is 1 μm or more but less than 2 μm, and 2,000x if the average domain diameter is 2 μm or more is used as the average diameter of the domains dispersed in Layer B.

[0028] In addition, if the width direction (TD) of the sealant film is unknown, ultrathin sections with cross sections in each direction and the thickness direction are taken in a total of six directions at 30° intervals starting from any direction within the sealant film surface, stained with RuO4, and observed at any magnification using a transmission electron microscope.The direction in which the average length of the domains contained in any layer of the sealant film is longest is taken as the machine direction (MD) of the sealant film, and the direction 90° to this direction is taken as the width direction (TD).

[0029] In each evaluation of the sealant film of the present invention, evaluation of MD and / or TD is required, and if MD and TD are unknown, they can be determined by the method described above. If MD and TD are unknown and no domains are observed in the sealant film by the above observation, a tensile test is carried out five times in six directions at 30° intervals starting from any direction in the plane of the sealant film, and the arithmetic mean value of the tensile modulus is calculated. The direction with the highest tensile modulus among these is designated as MD, and the direction at 90° to that direction is designated as TD, and the evaluation described in the present invention can be performed.

[0030] The polypropylene resin preferably used for layer B has a melt flow rate (hereinafter referred to as MFR at 230°C) measured at 230°C under a load of 21.18 N, of preferably 1.0 g / 10 min or more, more preferably 2.0 g / 10 min or more, from the viewpoint of film-forming properties. The polypropylene resin preferably used for layer B has an MFR at 230°C of preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less, from the viewpoint of film-forming properties and moldability.

[0031] In order to maintain the E1 / E2 ratio at 2.4 or greater, Layer B of the sealant film of the present invention preferably contains, when taken as 100% by mass of Layer B, 1% to 20% by mass of a polyolefin elastomer in addition to the polypropylene resin preferably used in Layer B. Examples of polyolefin elastomers used in Layer B include elastomers made of ethylene-α-olefin copolymers, propylene-α-olefin copolymers, 1-butene-α-olefin copolymers, and 4-methyl-1-pentene-α-olefin copolymers. Examples of α-olefins include propylene, ethylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene, and 1-heptene. The polyolefin elastomer used in Layer B has improved compatibility with the polypropylene resin more preferably used in Layer B and controls the E1 / E2 to 2.4 to 3.5. Among the above-mentioned elastomers, elastomers made of propylene-α-olefin copolymers and 1-butene-α-olefin copolymers are more preferred, elastomers made of propylene-α-olefin copolymers are even more preferred, and elastomers made of propylene-1-butene copolymers are most preferred.

[0032] The content of the polyolefin elastomer in Layer B is more preferably 3% by mass or more, even more preferably 5% by mass or more, and particularly preferably 7% by mass or more, from the viewpoints of controlling E1 / E2 to 2.4 or more and improving heat seal strength at high temperatures and moldability.

[0033] The melting point of the polyolefin elastomer used in Layer B is preferably 50° C. or higher, more preferably 60° C. or higher, from the viewpoint of controlling the E1 / E2 ratio to 3.5 or lower and improving the heat seal strength at high temperatures. There are no particular upper limits to the melting point of the polyolefin elastomer used in Layer B, but it is substantially preferably 165° C. or lower.

[0034] The polyolefin elastomer used in Layer B preferably has an MFR of 1.0 g / 10 min or more, more preferably 2.0 g / 10 min or more, at 230°C, from the viewpoints of improving compatibility with the polypropylene resin used in Layer B and improving heat seal strength and moldability at high temperatures, and from the same viewpoints, preferably has an MFR of 15 g / 10 min or less, more preferably 10 g / 10 min or less.

[0035] In addition to the polyolefin resin and polyolefin elastomer described above, layer B of the sealant film of the present invention may contain other thermoplastic resins and additives within the scope of not impairing the object of the present invention.

[0036] The sealant film of the present invention may include a layer other than the above-mentioned Layer B, and more preferably has at least Layer A and Layer B laminated together, and even more preferably has at least three layers laminated together in this order: Layer A, Layer B, and Layer C. Layer A is located on the heat-sealed surface of the sealant film of the present invention, and Layer C is located on the surface opposite the heat-sealed surface. Layer A and Layer B may have the same composition and / or thickness, or may have different compositions and thicknesses.

[0037] In order to improve the heat seal strength, the layer A of the sealant film of the present invention preferably contains 50% by mass or more, and more preferably 70% by mass or more, of random polypropylene.

[0038] The MFR at 230° C. of the random polypropylene used in layer A is preferably 2 g / 10 min or more from the viewpoint of improving film-forming properties and heat-sealing properties, and is preferably 10 g / 10 min or less from the viewpoint of improving moldability.

[0039] The melting point of the random polypropylene used in layer A is preferably 130°C or higher in order to improve the heat seal strength at high temperatures, and is preferably 150°C or lower in order to improve the heat seal strength at room temperature.

[0040] Furthermore, from the viewpoint of improving formability, Layer A in the present invention preferably contains 100 ppm to 1000 ppm by mass of a fatty acid amide lubricant when the entire Layer A is taken as 100% by mass. If the content of the fatty acid amide lubricant is less than 100 ppm, the lubricating properties may deteriorate and formability may be impaired, while if it exceeds 1000 ppm, heat scattering increases during melt extrusion, contaminating the film-forming process and deteriorating film-forming properties, or contaminating the mold during molding, which may reduce molding yield and also reduce heat seal strength.

[0041] Preferred examples of the fatty acid amide lubricants include oleic acid amide, erucic acid amide, stearic acid amide, palmitic acid amide, and behenic acid amide, with erucic acid amide being particularly preferred from the standpoint of its dispersibility in the resin composition and its ability to exhibit lubricity.

[0042] Layer A preferably contains one or more inorganic particles and / or organic particles to the extent that the heat seal strength is not reduced. This improves slipperiness even when the content of fatty acid amide-based lubricant is reduced, and reduces defects such as wrinkles and poor air escape when the film is wound into a long length. The total amount of the particles contained in Layer A is preferably 300 ppm to 5000 ppm by mass. If the content of the particles in Layer A is 300 ppm or less, the slipperiness-imparting effect may not be achieved, and if it exceeds 5000 ppm, the heat seal strength may be reduced or particles may fall off.

[0043] Preferred examples of the inorganic particles include silica, zeolite, calcium carbonate, etc., and preferred examples of the organic particles include cross-linked polystyrene (PS), cross-linked polymethyl methacrylate (PMMA), etc. The average particle size of the particles is preferably in the range of 1 μm to 10 μm. If the average particle size is less than 1 μm, the effect of addition may not be observed, and if it exceeds 10 μm, the heat seal strength may decrease.

[0044] Layer A in the present invention may contain a resin other than random polypropylene. The other resin used in layer A is preferably at least one polyolefin resin selected from block polypropylene, low-density polyethylene, ethylene-α-olefin copolymer, and propylene-α-olefin elastomer, and block polypropylene is particularly preferred.

[0045] As described above, Layer C of the sealant film of the present invention is a layer that is placed on the opposite side to Layer A, and when the sealant film of the present invention is used in an exterior packaging material described below, it is the layer that is laminated with components that constitute the exterior packaging material other than the sealant film.

[0046] For the C layer in the present invention, a polypropylene-based resin selected from the group consisting of homopolypropylene, random polypropylene, and block polypropylene can be preferably used from the viewpoints of improving moldability, adhesion to other layers constituting the packaging material, and heat resistance. Furthermore, when the entire C layer is taken as 100% by mass, the C layer in the present invention preferably contains 50% by mass or more, and more preferably 70% by mass or more, of the polypropylene-based resin suitable for the C layer.

[0047] The MFR at 230° C. of the polypropylene resin preferably used for the layer C in the present invention is preferably 2 g / 10 min or more from the viewpoint of improving film formability, and preferably 10 g / 10 min or less from the viewpoint of improving moldability.

[0048] Layer C of the present invention may also contain a fatty acid amide-based lubricant. In this case, it is preferable that the lubricant be additive-free before film formation, as this increases the laminate strength with layers other than the sealant film that constitute the packaging material. When the sealant film of the present invention is composed of three or more layers including Layer A, Layer B, and Layer C, lubricants contained in other layers may migrate during co-extrusion film formation and aging of the film after film formation. However, the content of the fatty acid amide-based lubricant is preferably in the range of 10 to 500 ppm by mass, assuming that Layer C as a whole is 100% by mass. If the content of the fatty acid amide-based lubricant in Layer C is less than 10 ppm, the film's winding properties may deteriorate, and wrinkles or lumps due to trapped air may be more likely to occur. If the content exceeds 500 ppm, the laminate strength may decrease.

[0049] The layer C may also contain one or more inorganic particles and / or organic particles to the extent that the laminate strength is not reduced. The total amount of the particles in the layer C is preferably 300 ppm to 3,000 ppm by mass, assuming the entire layer C to be 100% by mass. This may improve slipperiness even when the content of the fatty acid amide-based lubricant is reduced, and may also reduce defects due to wrinkles and poor air escape when the film is wound into a long length. If the content of the particles in the layer C is less than 300 ppm, the slipperiness-imparting effect may not be achieved, while if it exceeds 3,000 ppm, the laminate strength may decrease or particles may fall off.

[0050] Preferred examples of the inorganic particles include silica, zeolite, calcium carbonate, etc., and preferred examples of the organic particles include cross-linked polystyrene (PS), cross-linked polymethyl methacrylate (PMMA), etc. The average particle size thereof is preferably in the range of 1 μm to 10 μm. If the average particle size is less than 1 μm, the effect of adding the particles may not be observed, and if it exceeds 10 μm, the laminate strength may decrease.

[0051] Furthermore, the ten-point average surface roughness Rz of the laminate layer is preferably in the range of 0.8 μm to 1.5 μm, as this improves the film's winding and laminating processability. If the ten-point average surface roughness Rz is less than 0.8 μm, wrinkles may easily occur during film winding and laminating, resulting in poor yield. If the Rz is more than 1.5 μm, the laminate strength may decrease. The ten-point average surface roughness Rz is determined in accordance with JIS B 0601-1994.

[0052] Each layer of the sealant film of the present invention may contain additives other than those described above, such as compatibilizers other than those described above for improving the dispersibility of the resins constituting each layer and interfacial strength, additives for improving the interlayer adhesion of each layer, antioxidants, plasticizers, ultraviolet absorbers, mildew inhibitors, colorants (pigments, dyes, etc.), antistatic agents, rust inhibitors, moisture absorbers, oxygen absorbers, etc.

[0053] The thickness of the sealant film of the present invention is not particularly limited, but the lower limit is preferably 10 μm, more preferably 30 μm, and the upper limit is preferably 500 μm, more preferably 300 μm or less, even more preferably 200 μm or less, and most preferably 120 μm or less. If the thickness of the sealant film is thinner than 10 μm, sufficient seal strength may not be obtained when an exterior material using the sealant film of the present invention is heat-sealed. If the thickness of the sealant film is thicker than 500 μm, the rigidity may be too high and it may not be possible to form a roll.

[0054] The tensile breaking elongation of the sealant film of the present invention is preferably 250% or more. The tensile breaking elongation is measured in an atmosphere of 23°C by the method described in the Examples. From the viewpoint of improving formability, the tensile breaking elongation is more preferably 400% or more, and even more preferably 600% or more. The upper limit of the tensile breaking elongation of the sealant film of the present invention is not particularly limited, but is substantially about 1,500%.

[0055] From the viewpoint of improving heat seal strength and formability at high temperatures, the sealant film of the present invention has an exothermic heat quantity measured by differential scanning calorimetry of preferably 40 J / g or more, more preferably 50 J / g or more, and even more preferably 55 J / g or more. From the same viewpoint, the exothermic heat quantity is preferably 80 J / g or less, more preferably 70 J / g or less, and even more preferably 65 J / g or less. The exothermic heat quantity can be determined from the exothermic peak when calculating the crystallization temperature described in the Examples.

[0056] In order to prevent opening of the heat-sealed portion when used at high temperatures, the sealant film of the present invention preferably has a P2 / P1 ratio of 0.8 or more, where P1 is the heat-seal strength in an atmosphere of 60°C and P2 is the heat-seal strength in an atmosphere of 80°C, and P2 is preferably 40 N / 15 mm or more. P2 and P1 are determined by the method described in the examples.

[0057] The sealant film of the present invention has excellent heat seal strength and formability at high temperatures, and therefore can be preferably used as an exterior packaging material for secondary batteries, and in particular can be more preferably used as an exterior packaging material for all-solid-state lithium batteries (all-solid-state batteries) that are used in higher temperature environments than conventional lithium ion batteries that use non-aqueous electrolytes. In addition to the sealant film, known components that constitute the exterior packaging material can be used, such as a heat-resistant substrate layer, a barrier layer, and an adhesive layer.

[0058] The presence of a heat-resistant substrate layer can ensure sufficient insulation and improve the physical strength and impact resistance of the packaging material. Known materials can be used to form the heat-resistant substrate layer, including polyamide films such as nylon films and polyester films, and oriented films thereof are preferred. Among these, biaxially oriented polyamide films such as biaxially oriented nylon films, biaxially oriented polybutylene terephthalate (PBT) films, biaxially oriented polyethylene terephthalate (PET) films, and biaxially oriented polyethylene naphthalate (PEN) films are particularly preferred. Examples of the nylon film include, but are not limited to, nylon 6 film, nylon 6,6 film, and MXD nylon film. The heat-resistant substrate layer may be formed as a single layer or as a multilayer structure consisting of, for example, a polyester film / polyamide film (e.g., a multilayer structure consisting of a PET film / nylon film).

[0059] The thickness of the heat-resistant base layer is preferably 2 μm to 200 μm. The upper limit of the thickness of the heat-resistant base layer is more preferably 100 μm or less, and even more preferably 50 μm or less. The lower limit of the thickness of the heat-resistant base layer is more preferably 5 μm or more. By setting the thickness at or above the preferred lower limit, it becomes easy to ensure sufficient strength as an exterior packaging material, and by setting the thickness at or below the preferred upper limit, it becomes easy to reduce stress during molding such as stretch molding and draw molding, thereby improving formability.

[0060] The barrier layer serves to impart barrier properties to the packaging material, preventing the intrusion of oxygen and moisture. Known barrier layers can be used, and are not particularly limited. Examples include aluminum foil, SUS foil (stainless steel foil), and copper foil. Of these, aluminum foil and SUS foil (stainless steel foil) are preferred. The thickness of the barrier layer is preferably 5 μm to 120 μm. Having a thickness of 5 μm or more facilitates the prevention of pinholes during rolling in the production of the barrier layer, while having a thickness of 120 μm or less reduces stress during forming, such as stretch forming and drawing, thereby facilitating improved formability. Among these, the thickness of the barrier layer is more preferably 10 μm to 80 μm.

[0061] The packaging material in the present invention may have an adhesive layer, if necessary, between the heat-resistant substrate layer and the barrier layer, for example, to enhance the adhesion between these layers. Similarly, an adhesive layer may also be provided between the barrier layer and the sealant film, if necessary. Furthermore, other functional layers may be provided within a range that does not impair the effects of the present invention. Known adhesive layers can be used.

[0062] The structure of an exterior packaging material using the sealant film of the present invention can be, for example, heat-resistant substrate layer / adhesive layer / barrier layer / adhesive layer / sealant film, in which case the sealant film of the present invention and the heat-resistant substrate layer / adhesive layer / barrier layer can be laminated via the adhesive layer (dry lamination method). Alternatively, the resin that constitutes the sealant film can be melt-extruded onto a laminate consisting of the heat-resistant substrate layer / adhesive layer / barrier layer, and then directly laminated onto the laminate (thermal lamination method).

[0063] The total thickness of the packaging material using the sealant film of the present invention is not particularly limited, but from the viewpoint of cost reduction, improvement of energy density, etc., it is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 500 μm or less, and from the viewpoint of maintaining the function of the packaging material to protect the battery element, it is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more.

[0064] The packaging material using the sealant film of the present invention is preferably used as a packaging material for secondary batteries such as lithium ion batteries using a non-aqueous electrolyte and all-solid-state lithium secondary batteries (all-solid-state batteries).Furthermore, the lithium ion batteries and all-solid-state batteries using a non-aqueous electrolyte using the sealant film of the present invention are preferably used as secondary batteries for electric devices such as electronic devices, electric automobiles, and electric aircraft. [Example]

[0065] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0066] (1) Melt flow rate (MFR) The MFR of the resins used in the examples and comparative examples was measured at 230° C. and a load of 21.18 N in accordance with JIS K7210-1997 using a melt indexer manufactured by Toyo Seiki Seisakusho.

[0067] (2) Thickness of each layer The thickness of each layer of the sealant film was measured by microtoming a 5 mm-wide cross-section of the sealant film in any direction in the plane and in the thickness direction, and the cross-section was platinum-coated to prepare an observation sample. Next, the cross-section of the sealant film was observed at any magnification using a Hitachi field emission scanning electron microscope (S-4800), and the thickness of each layer was measured at any 10 points on the observed image, and the average value was taken as the thickness of each layer.

[0068] (3) Crystallization temperature, melting point The resins and sealant films used in the Examples and Comparative Examples were measured using a differential scanning calorimeter (Rigaku Thermo plus EVO2 DSCvesta) in accordance with JIS K 7122 (2012) under a nitrogen atmosphere under the following conditions. The crystallization temperature and heat release of the sealant film were determined from the differential scanning calorimetry curve obtained in step (iii), and the melting point of the resin used in the Examples or Comparative Examples was determined from the differential scanning calorimetry curve obtained in step (v). When there were two or more crystallization temperatures, the higher peak temperature was taken as the crystallization temperature of the sealant film, and the heat release of the peak was taken as the heat release of the sealant film. When there were two or more melting points, the higher peak temperature was taken as the melting point of the resin. Sample amount: 5 mg Heating rate, cooling rate: 20℃ / min Temperature Program: Step (i) increasing the temperature from 30°C to 250°C; Step (ii) maintaining at 250°C for 5 minutes; Step (iii) lowering the temperature from 250°C to -30°C; Step (iv) keeping at -30°C for 5 minutes; Step (v) The temperature is increased from -30°C to 250°C.

[0069] (4) Storage modulus (E1, E2) and E1 / E2 The sealant film was cut into a 10 mm long rectangle, and measurements were carried out five times each in the machine direction (MD) and transverse direction (TD) (10 times in total) for each type of sealant film under the following conditions using a Seiko Instruments Inc. DMS6100 dynamic viscoelasticity measuring device based on the tensile vibration-non-resonance method of JIS K7244-4 (1999) [1]. The storage modulus E1 (Pa) at 40°C and the storage modulus E2 (Pa) at 80°C were then calculated from the arithmetic mean values ​​of 10 points, and E1 / E2 was then calculated. Measurement mode: Tensile Test piece width: 5mm Frequency: 10Hz Amplitude distortion: 0.05% Measurement temperature: 0℃ to 100℃ Heating rate: 3°C / min.

[0070] (5) Tensile elongation at break Using a tensile tester (Orientec's universal testing machine, Tensilon), tensile tests were performed five times in each of the machine direction (MD) and transverse direction (TD) of the sealant film at a temperature of 23°C and a speed of 300 mm / min in accordance with JIS K 7113 (1995), and the arithmetic mean value of the tensile elongation at break (arithmetic mean value of a total of 10 points) was taken as the tensile elongation at break of the sealant film. The test specimens used for the measurement were rectangular, 10 mm wide and 100 mm long, and the measurement was performed with a chuck distance of 30 mm.

[0071] (6) Fabrication of exterior materials A 12 μm-thick biaxially oriented PET film ("Lumirror" (registered trademark) S10, manufactured by Toray Industries) and a 15 μm-thick biaxially oriented nylon film ("Bonyl-® RX," manufactured by Kohjin Co., Ltd.) were bonded together via a 3 μm two-component curing urethane adhesive layer by dry lamination to prepare a substrate film. The nylon film side of the substrate film was then bonded to the non-glossy side of a 40 μm aluminum foil ("8079," manufactured by Toyo Aluminum Co., Ltd.) via a 3 μm two-component curing urethane adhesive layer by dry lamination to prepare a laminated film. The aluminum side of the laminated film was then bonded to the C layer side of a sealant film by dry lamination via a 3 μm two-component curing acrylic adhesive, and the resulting film was heated in a 40°C oven for 5 days before use as an exterior material. The C layer side of the sealant film had previously been corona-treated.

[0072] (7) Heat seal strength (P1, P2), P2 / P1, heat seal strength at high temperatures Two 100mm long x 15mm wide exterior packaging materials were heat-sealed with the sealant film layer A facing inward using a 15mm-wide flat heat sealer under conditions of 180°C upper and lower seal bar temperatures, 0.3MPa sealing pressure, and 2 seconds sealing time to prepare samples (size of heat-sealed area in sample: width 15mm, length 15mm). Two types of samples were prepared: one with the longitudinal direction in the machine direction (MD) of the exterior packaging material, and the other with the longitudinal direction in the transverse direction (TD) of the exterior packaging material. Then, using a tensile tester (Orientec's universal testing machine "Tensilon"®), the exterior packaging material was peeled five times in each of the machine direction (MD) and transverse direction (TD) under the following conditions: The arithmetic mean value of the peel load in a range of 5mm to 10mm from the peel start point was taken as the heat seal strength of the packaging material, and the arithmetic mean value of the seal strength measured five times in each of the machine direction (MD) and the cross direction (TD) (average value for a total of 10 times) was taken as the heat seal strength of the packaging material.The heat seal strength P1 in an atmosphere of 60°C and the heat seal strength P2 in an atmosphere of 80°C were determined, and P2 / P1 was calculated.The heat seal strength P2 in an atmosphere of 80°C was also evaluated as the heat seal strength at high temperatures according to the following criteria. Peeling temperature: 60°C or 80°C Peeling angle: 180° Peeling speed: 300 mm / min <Evaluation criteria> A: P2 is 50N / 15mm or more B: P2 is 40N / 15mm or more and less than 50N / 15mm C:P2 is less than 40N / 15mm.

[0073] (8) Formability Using a deep drawing molding machine manufactured by JMT Corporation, the exterior material was cut to 100 mm x 150 mm and deep drawn into a rectangular parallelepiped shape with a drawing depth of 8 mm and 10 mm under the following molding conditions so that the surface of the Layer A side of the exterior material was located inside the accommodation recess of the molded body, and the results were evaluated using the following criteria of A and B. Male mold: 89mm x 54mm, R=2mm Female mold: 118mm x 175mm, R=2mm Wrinkle suppression pressure: 0.5 MPa (air source pressure) Material: Stainless steel. Molding temperature: 23°C atmosphere <Evaluation criteria> A: No pinholes or whitening were observed in the exterior material after molding at both 8mm and 10mm drawing depths. B: Pinholes and / or whitening occurred in the exterior material after molding with a drawing depth of only 10 mm. C: Pinholes and / or whitening occurred in the exterior material after molding at both 8 mm and 10 mm drawing depths.

[0074] The raw materials constituting the sealant films of the Examples and Comparative Examples are shown below. Random polypropylene (EPC); melting point: 138°C, MFR 3g / 10min at 230°C, commercially available ethylene-propylene random copolymer Block polypropylene (BPP); melting point: 165°C, MFR 2g / 10min at 230°C, rubber content 28%. Homopolypropylene (HPP); Melting point: 158°C, MFR 3g / 10min at 230°C, commercially available homopolypropylene Polyolefin elastomer (POE1); melting point: 86°C, MFR at 230°C: 7g / 10min, propylene-1-butene copolymer elastomer (Mitsui Chemicals "XM-7080") Polyolefin elastomer (POE2); melting point: 102°C, MFR at 230°C: 8g / 10min, ethylene content: 4% by mass, density: 889kg / m 3 Elastomer consisting of propylene-ethylene copolymer (ExxonMobil "Vistamaxx3588FL") Polyolefin elastomer (POE3); melting point: 104°C, MFR at 230°C: 20g / 10min, ethylene content: 20% by mass, density: 863kg / m 3 Propylene-ethylene copolymer elastomer (ExxonMobil "Vistamaxx6202FL") EBSA: commercially available ethylene bisstearic acid amide Inorganic particles: Commercially available aluminosilicate particles with an average particle size of 4 μm

[0075] Example 1 The raw materials for Layers A, B, and C shown in Table 1 were melt-kneaded in advance in a twin-screw extruder at 250°C and used as the raw materials for Layers A, B, and C. A three-layer co-extrusion was performed using a T-die at 250°C, with Layers A, B, and C laminated in this order so that Layer A was 10 μm, Layer B was 60 μm, and Layer C was 10 μm, and the resulting film was cast on a cooling roll at 40°C to obtain an 80 μm-thick three-layer sealant film, which was then subjected to various evaluations.

[0076] (Examples 2 to 4, Comparative Examples 1 and 2) The same procedure as in Example 1 was carried out except that the raw materials for layers A, B, and C were as shown in Table 1.

[0077] [Table 1]

[0078] Examples 1 to 4 of the present invention were excellent in heat seal strength and moldability at high temperatures, while Comparative Examples 1 and 2 were poor in heat seal strength and / or moldability at high temperatures. [Industrial Applicability]

[0079] The sealant film of the present invention has excellent heat seal strength and moldability at high temperatures, and can therefore be preferably used as a sealant film for packaging materials for secondary batteries.

Claims

1. A sealant film containing a polyolefin resin as a main component, having a crystallization temperature of 90°C or higher and 110°C or lower, and wherein, when E1 is a storage modulus at 40°C and E2 is a storage modulus at 80°C, E1 and E2 satisfy formula (1). 2.4≦(E1 / E2)≦3.5... Formula (1)

2. 2. The sealant film according to claim 1, comprising at least one layer B, wherein the layer B is primarily composed of a polypropylene resin and contains 1% by mass or more and 20% by mass or less of an elastomer made of a propylene-1-butene copolymer, relative to 100% by mass of the total mass of the layer B.

3. 3. The sealant film according to claim 1 or 2, comprising at least one layer B, wherein the layer B is primarily composed of a polypropylene resin and contains 50% by mass or less of block polypropylene relative to 100% by mass of the total mass of the layer B.

4. Storage modulus E2 at 80°C is 0.8 x 10 ８ Pa or more 3.0×10 ８ The sealant film according to claim 1 or 2, wherein the viscosity is 100 Pa or less.

5. 3. The sealant film according to claim 1, wherein at least three layers are directly laminated in the order of layer A, layer B, and layer C.

6. The sealant film according to claim 1 or 2, which has a tensile elongation at break of 250% or more.

7. The sealant film according to claim 1, which is used as an exterior material for a secondary battery.

8. An outer casing for a secondary battery, comprising the sealant film according to claim 7.

9. 9. The exterior packaging material for a secondary battery according to claim 8, wherein P2 / P1 is 0.8 or more, where P1 is the heat seal strength in a 60°C atmosphere and P2 is the heat seal strength in an 80°C atmosphere.

10. A secondary battery comprising the packaging material for a secondary battery according to claim 8.

11. An all-solid-state battery comprising the secondary battery packaging material according to claim 8.

12. An electronic device comprising the secondary battery according to claim 10 or the all-solid-state battery according to claim 11.

13. An electric vehicle comprising the secondary battery according to claim 10 or the all-solid-state battery according to claim 11.

14. An electric aircraft comprising the secondary battery according to claim 10 or the all-solid-state battery according to claim 11.

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