Packaging material for battery cell, battery cell, and battery cell module

Abstract

To provide a packaging material for a battery cell which can detect with a detector whether a battery cell is covered with the packaging material, can distinguish even when a foreign object or air bubble is mixed between the packaging material and the battery cell, exhibits stable adhesive strength regardless of the type of adherend, and has excellent repulsion resistance.SOLUTION: In a packaging material for a battery cell having a substrate and an adhesive layer provided on one or both sides of the substrate, the adhesive layer has a glass transition temperature (Tg) of -30°C or higher and 15°C or lower, and the packaging material for a battery cell has a total light transmittance of 35% to 85%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a packaging material for a battery cell, a battery cell, and a battery cell module. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries and nonaqueous electrolyte secondary batteries are used in portable devices, hybrid and electric vehicles, home storage batteries, etc. In particular, hybrid and electric vehicles and home storage batteries are required to have high output, so they are often used in a form in which multiple battery cells are connected together. Such secondary batteries normally have a circuit board for controlling voltage and the like, and this circuit board and the secondary battery body are covered with an outer frame made of metal, synthetic resin or the like.

[0003] Therefore, from the standpoint of safety and maintaining performance, these secondary batteries are often used with the battery cells covered with a packaging material such as a film or tube for insulation, waterproofing, and protection against external impact. The packaging material may be required to be colored in order to use a detector to detect whether the battery cell is covered by the packaging material. In this case, depending on the degree of color of the packaging material, foreign matter or air bubbles may not be visible even if they are mixed in between the battery cell and the packaging material, so it is also required to make it easy to detect foreign matter, etc.

[0004] As colored packaging materials used for battery cells of conventional secondary batteries, there has been disclosed an exterior material for an electricity storage device that has an identification mark printed on its surface that is highly identifiable in a yellow room or under an orange to yellow lamp light source (for example, Patent Document 1). In addition, there has been disclosed a battery packaging material that allows foreign matter to be easily detected and is also excellent in insulation and water vapor barrier properties (for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 138059 [Patent Document 2] JP 2017-103221 A Summary of the Invention [Problem to be solved by the invention]

[0006] When packaging material is applied to battery cells, battery cells that have air gaps or foreign objects mixed in must be removed during the manufacturing process. This is because, in the case of high-output secondary batteries that generate a large amount of heat during charging and discharging, if an air gap with low thermal conductivity is created due to foreign objects, heat can accumulate and damage the inside of the secondary battery, shortening the life of the secondary battery. In addition, if the foreign object is conductive, there is also the problem of insufficient insulation resistance of the packaging material that covers the battery cells.

[0007] However, when battery cells are packaged in a packaging material such as that described in Patent Document 1, the total light transmittance of the packaging material is low, so it is presumed that it would be difficult to detect any foreign matter or air bubbles that may have become mixed in between the packaging material and the battery cell.

[0008] On the other hand, in the battery packaging material disclosed in Patent Document 2, when a metal can such as aluminum is used as the casing of a battery cell, when the heat-sealable resin layer of the packaging material is heat-sealed to the surface of the battery cell, the metal can absorbs heat and inhibits plasticization of the heat-sealable resin layer, requiring a long heating time, reducing production efficiency, or insufficient plasticization may result in poor adhesion. Furthermore, if the plasticization of the heat-sealable resin layer of the packaging material is insufficient, the adhesion between the packaging material and the battery cell will decrease, resulting in poor rebound resistance, and floating will occur between the packaging material and the battery cell, leading to the creation of an air gap or the inclusion of foreign matter.

[0009] Therefore, an object of the present invention is to provide a packaging material for battery cells that can detect with a detector whether a battery cell is covered by a packaging material, can distinguish if foreign matter or air bubbles have been mixed in between the packaging material and the battery cell, and exhibits stable adhesive strength and excellent resilience regardless of the type of substrate. [Means for solving the problem]

[0010] The present invention has the following aspects. [1] A packaging material for battery cells having a substrate and a pressure-sensitive adhesive layer provided on one or both sides of the substrate, The pressure-sensitive adhesive layer has a glass transition temperature (Tg) of -30°C or more and 15°C or less, The packaging material for battery cells has a total light transmittance of 35% to 85%. [2] The packaging material for battery cells according to [1], wherein the pressure-sensitive adhesive layer has a gel fraction of 20% or more and 90% or less. [3] The packaging material for battery cells according to [1] or [2], wherein the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive. [4] The battery cell packaging material according to any one of [1] to [3], wherein the pressure-sensitive adhesive layer contains a curing agent. [5] The packaging material for battery cells according to any one of [1] to [4], wherein at least one of the pressure-sensitive adhesive layer and the substrate contains a colorant, or the substrate has a colored layer on a surface thereof. [6] A packaging material for battery cells according to any one of [1] to [5], in which the floating distance related to the rebound resistance measured under a temperature condition of 60°C is less than 3 mm. [7] The pressure-sensitive adhesive layer has a storage viscoelastic modulus of 1×10 at 60° C. 4 Pa or more 1×10 6 The packaging material for battery cells according to any one of [1] to [6], wherein the resistance is 0.001 Pa or less. [8] The packaging material for battery cells according to any one of [1] to [7], having a 180° peel adhesive strength of 5 N / 25 mm or more. [9] The tensile modulus of the substrate is 1×10 8 Pa or more 1×10 10 The packaging material for battery cells according to any one of [1] to [8], wherein the resistance is 0.001 Pa or less.

[10] The packaging material for battery cells according to any one of [1] to [9], wherein the thickness of the substrate is 20 μm or more and 125 μm or less.

[11] The packaging material for battery cells according to any one of [1] to

[10] , having a dielectric breakdown voltage of 2 kV or more.

[12] The packaging material for battery cells according to any one of [1] to

[11] , having a thickness of 25 μm or more and 175 μm or less.

[13] A battery cell having at least a portion of its outer surface covered with the battery cell packaging material according to any one of [1] to

[12] .

[14]

[13] A battery cell module constructed using a plurality of the battery cells according to the present invention. Effect of the Invention

[0011] According to the battery cell packaging material of the present invention, it is possible to detect by a detector whether the battery cell is covered with the packaging material, and it is also possible to determine whether foreign matter or air bubbles have entered between the packaging material and the battery cell. Furthermore, according to the battery cell packaging material of the present invention, stable adhesive strength is exhibited regardless of the type of adherend, and it can be used for battery cells in various types of housings. Furthermore, since it has excellent repulsion resistance, it is possible to suppress the generation of an air layer between the packaging material and the battery cell and the entry of foreign matter. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram for explaining an outline of a repulsion resistance test in a 60° C. environment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The packaging material for battery cells of the present invention (hereinafter also referred to as "the packaging material") has a substrate and a pressure-sensitive adhesive layer provided on one or both sides of the substrate, the pressure-sensitive adhesive layer has a glass transition temperature (Tg) of -30°C or more and 15°C or less, and the packaging material for battery cells has a total light transmittance of 35% to 85%. The packaging material for battery cells of the present invention will be described in detail below.

[0014] In order to enable a detector to detect whether the battery cell is covered by the packaging material, the packaging material has a total light transmittance of 35% to 85%. As long as the total light transmittance of the packaging material is within the above range, the method for adjusting the total light transmittance of the packaging material is not particularly limited and can be appropriately selected. For example, the total light transmittance can be adjusted by the substrate of the packaging material containing a colorant, by coating the surface of the substrate with a paint containing a colorant to provide a colored layer, by the adhesive layer of the packaging material containing a colorant, or by a combination of these. The color of the packaging material is not particularly limited as long as it can exhibit predetermined optical properties, and may be, for example, an achromatic color such as white, black, gray, etc., or a chromatic color such as red, blue, yellow, etc. The same can be said for the color of the base material when the base material contains a colorant, the color of the adhesive layer when the adhesive layer contains a colorant, and the color of the colored layer when a colored layer is provided on the surface of the base material, which will be described later.

[0015] When the substrate of the present packaging material contains a colorant, a colored resin film having a colorant added to a resin film can be used as the substrate. The colorant is not particularly limited, and can be a pigment, a dye, a mixture thereof, etc. In addition, the colorant can be selected appropriately from one or more colorants of each color, such as white, black, red, yellow, blue, etc., depending on the color and purpose required for the substrate and packaging material. Examples of the white colorant include inorganic white pigments such as titanium dioxide, barium sulfate, calcium carbonate, zinc oxide, silica, talc, and clay. Examples of black colorants include inorganic black pigments such as carbon black, graphite, copper oxide, manganese dioxide, aniline black, perylene black, titanium black, cyanine black, activated carbon, ferrite, magnetite, chromium oxide, iron oxide, molybdenum disulfide, chromium complexes, and composite oxide-based black pigments, organic black pigments such as aniline black, azo pigments, and anthraquinone-based organic black pigments, and nigrosine-based black dyes, etc. Among these, carbon black, which has excellent color development and dispersibility, is preferred as the black colorant. Examples of red and yellow colorants include oxide-based inorganic pigments such as iron trioxide, condensed polycyclic organic pigments such as azo and quinacridone pigments, anthraquinone dyes, and verinone dyes. Examples of blue colorants include phthalocyanine organic pigments and anthraquinone dyes.

[0016] Examples of methods for incorporating a colorant into a substrate include a method of adding a pellet-shaped master batch containing the colorant at a high concentration in the same type of resin as the substrate, or a powdered dry color in which the colorant is dispersed with a metal soap or the like, to the resin that forms the substrate.

[0017] When the resin film contains a colorant, the content of the colorant, assuming the resin film to be 100% by mass, is preferably 0.01% by mass or more from the viewpoint of ensuring detectability of the packaging material covering the battery cell, and is preferably 1.0% by mass or less from the viewpoint of detectability of foreign matter or air bubbles between the packaging material and the battery cell.

[0018] Similarly, when a paint containing a colorant is applied to the surface of a substrate to provide a colored layer, examples of the colorant contained in the paint include the colorants listed above. The paint contains a binder resin for forming a film in addition to the colorant, and the binder resin is not particularly limited, but polyester resin, acrylic resin, urethane resin, etc. can be used. Among them, from the viewpoint of adhesion between the resin film and the colored layer, a binder resin made of the same material as the resin film described below is preferred, and for example, when polyethylene terephthalate is used as the resin film, it is preferred to use a polyester resin as the binder resin.

[0019] When a colored layer is provided on the surface of a substrate, the thickness of the colored layer is preferably 1 μm or more from the viewpoint of ensuring uniformity in the thickness of the colored layer, and is preferably 10 μm or less from the viewpoint of preventing blocking of the paint and suppressing warping of the resin film due to hardening of the binder resin that forms the coating.

[0020] Any method can be used as a method for coating the substrate surface of the present packaging material with a paint containing a colorant, and examples of such methods include a method in which the paint dissolved in a solvent is applied to a certain thickness using a gravure coater or the like, and the solvent in the paint is dried to laminate a colored layer on the substrate surface. The colored layer may be provided on one side or both sides of the substrate.

[0021] The colorant content of the paint is preferably 0.1% by mass or more, assuming the solid content in the paint to be 100% by mass, from the viewpoint of ensuring detectability of the packaging material covering the battery cell, and is preferably 10% by mass or less, from the viewpoints of detectability of foreign matter or air bubbles between the packaging material and the battery cell and of adhesion to the resin film.

[0022] The base material of this packaging material is insulating, and from the viewpoint of the insulating properties of the packaging material, the volume resistivity of the base material is 1×10 13 The volume resistivity of the substrate is preferably 1×10 14 Ω cm or more, and more preferably 1×10 15The volume resistivity of the substrate was measured in accordance with JIS-K6911 using a resistivity meter (Advantest digital ultra-high resistance / microammeter R8340, TR42 box) by applying a voltage of 500 V in the thickness direction.

[0023] The substrate is not particularly limited as long as it has at least insulating properties, foldability for packaging, and heat resistance for withstanding heat from the battery cell, and is usually a resin film. In addition to the resin film, insulating paper laminated with a thermoplastic resin such as polyethylene naphthalate (PEN) or polyimide (PI) on a paper substrate, porous sheets such as nonwoven fabric, etc. can also be used.

[0024] The resin film is not particularly limited, but examples thereof include olefin resins such as polyethylene or polypropylene, ester resins such as polybutylene terephthalate, polyethylene terephthalate or polyethylene naphthalate, acetate resins, ABS resins, polystyrene, vinyl chloride resins, polyimides, polyamides, polyurethanes, fluorine-based resins, polycarbonates, acrylic resins, polyether ether ketones, etc., and resin films made of mixtures of these resins. From the viewpoints of insulation and heat resistance, olefin resin films or ester resin films are preferred, and polypropylene films or polyethylene terephthalate films are more preferred.

[0025] The resin film used may be a uniaxially or biaxially stretched film or an unstretched film. The substrate may be a single layer or a multilayer of these films. In the case of a multilayer structure, the resin films in each layer may be the same or different.

[0026] The thickness of the substrate is preferably 20 μm or more and 125 μm or less, more preferably 20 μm or more and 75 μm or less, and even more preferably 23 μm or more and 50 μm or less, from the viewpoints of preventing wrinkles from occurring when packaging a battery cell with this packaging material and suppressing the repulsive force of this packaging material so that it is less likely to float up from the battery cell.

[0027] The tensile modulus of the base material of the present packaging material is 1×10 in both the machine direction and the width direction, independently, from the viewpoint of the strength of the present packaging material described later. 8 Pa or more 1×10 10 From the viewpoint of the balance between the attachability to the battery cell and the repulsion resistance when packaging the battery cell with the packaging material, the tensile modulus of the base material is preferably 1×10 9 More than 6×10 9 Pa or less is more preferable, and 2×10 9 5×10 or more 9 Pa or less is most preferable. The tensile modulus of elasticity of the substrate can be measured by the method described in the Examples below.

[0028] From the viewpoint of suppressing the occurrence of wrinkles due to heat generated when packaging a battery cell with the packaging material and / or when using the battery after packaging, a base material that does not have shrinkability, in particular does not have heat shrinkability, is preferred. The heat shrinkage of the substrate is preferably 5% or less, more preferably 2% or less, when left at 80° C. for 1 hour, as measured by a method conforming to JIS K7133:1999.

[0029] In addition, when packaging a battery cell using this packaging material, it is preferable that the difference in the stretch ratio between the MD and TD of the substrate is small so that the substrate does not have a difference in hardness or elongation depending on the packaging direction, which may cause a misalignment in the application position. The ratio of the stretch ratio in the TD to the stretch ratio in the MD of the substrate is preferably 0.9 to 1.2, more preferably 0.9 to 1.1. The stretching ratio in the MD direction of the substrate is calculated by the ratio of the length of the stretched resin film to the length of the resin film before stretching, and the stretching ratio in the TD direction of the substrate is calculated by the ratio of the width of the stretched resin film to the width of the resin film before stretching.

[0030] As such a substrate, a non-stretched film, a uniaxially stretched film or a biaxially stretched film in which heat shrinkage is suppressed by annealing after uniaxial or biaxial stretching is preferable. Among them, a biaxially stretched film is more preferable because the tensile strength of the substrate is excellent and the difference in hardness and elongation of the substrate in the MD and TD directions is unlikely to occur.

[0031] The adhesive layer of the packaging material is a layer containing an adhesive. The adhesive used is preferably an adhesive containing a polymer as a main component from the viewpoint of ease of handling. The main component is the component contained in the largest amount in the adhesive, and is, for example, a component contained in 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more of 100% by mass of the adhesive. Examples of the polymer include rubber-based polymers, acrylic-based polymers, silicone-based polymers, urethane-based polymers, vinyl ether-based polymers, etc. Examples of the form of the adhesive when forming the adhesive layer include water-based adhesives such as solvent-based adhesives, emulsion-type adhesives, and water-soluble adhesives, and solventless adhesives such as hot-melt-type adhesives, UV-curable adhesives, and EB-curable adhesives.

[0032] The adhesive may be a polymer-containing adhesive composition containing a tackifier resin as required. The adhesive is preferably an acrylic adhesive containing an acrylic copolymer as a polymer from the viewpoints of high cohesive strength at high temperatures (e.g., under an atmosphere of 60°C), adhesive strength, and ease of handling, and is preferably an acrylic adhesive composition containing an acrylic copolymer having a structural unit derived from a (meth)alkyl acrylate having an alkyl group having 1 to 14 carbon atoms and a structural unit derived from a polar group-containing vinyl monomer, and a tackifier resin as required.

[0033] Examples of (meth)alkyl acrylates having an alkyl group having 1 to 14 carbon atoms include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, octyl acrylate, lauryl acrylate, and isobornyl acrylate, and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate. These (meth)alkyl acrylates having 1 to 14 carbon atoms may be used alone in copolymerization, or two or more of them may be used in combination in copolymerization.

[0034] Among (meth)acrylates having an alkyl group with 1 to 14 carbon atoms, it is preferable to use an alkyl (meth)acrylate having an alkyl group with 4 to 9 carbon atoms, and it is more preferable to use an alkyl acrylate having an alkyl group with 4 to 9 carbon atoms. As the alkyl acrylate having an alkyl group having 4 to 9 carbon atoms, n-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate are more preferable from the viewpoint of easily ensuring suitable adhesive strength.

[0035] From the viewpoint of the balance between the adhesive strength and the cohesive strength of the obtained adhesive composition, n-butyl acrylate or 2-ethylhexyl acrylate is more preferable among (meth)alkyl acrylates having an alkyl group with 1 to 14 carbon atoms, and n-butyl acrylate is most preferable in terms of adjusting the glass transition temperature (Tg) of the adhesive layer to a desired range. In addition, the content of the structural unit derived from the (meth)alkyl acrylate having an alkyl group with 1 to 14 carbon atoms in the acrylic copolymer is preferably 50% by mass or more, more preferably 70% by mass or more. When the (meth)alkyl acrylate having an alkyl group with 1 to 14 carbon atoms is n-butyl acrylate or 2-ethylhexyl acrylate, the content of the structural unit derived from each of them in the acrylic copolymer is preferably 50% by mass or more, more preferably 70% by mass or more.

[0036] Examples of the polar group-containing vinyl monomer include vinyl monomers having a polar group such as a hydroxyl group, a carboxyl group, or an amide group.

[0037] Examples of the vinyl monomer having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, hydroxypropyl (meth)acrylate, caprolactone-modified (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, etc. Among these, 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate are preferred.

[0038] Examples of the vinyl monomer having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, a dimer of acrylic acid or methacrylic acid, ethylene oxide modified succinic acid acrylate, etc. Among these, acrylic acid is preferred in terms of obtaining high cohesive strength required for repulsion resistance and reworkability at high temperatures.

[0039] Examples of the vinyl monomer having an amide group include N-vinyl-2-pyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, isopropylacrylamide, 2-(perhydrophthalimide-N-yl)ethyl acrylate, etc. Among these, N-vinyl-2-pyrrolidone, N,N-dimethylacrylamide, and isopropylacrylamide are preferred in terms of obtaining high cohesive strength required for repulsion resistance and reworkability at high temperatures.

[0040] Examples of vinyl monomers having a polar group other than those mentioned above include vinyl acetate, acrylonitrile, glycidyl (meth)acrylate, maleic anhydride, and itaconic anhydride.

[0041] The content of the structural unit derived from the vinyl monomer having a hydroxyl group in the acrylic copolymer is preferably 0.1% by mass or more, more preferably 1% by mass or more, based on the acrylic copolymer being 100% by mass, from the viewpoint of the processing characteristics and adhesive strength of the adhesive. The content of the structural unit derived from the vinyl monomer having a hydroxyl group is usually 20% by mass or less. From the viewpoint of the cohesive strength, holding strength, and adhesiveness of the adhesive, the content of the structural unit derived from the vinyl monomer having a hydroxyl group in the acrylic copolymer is more preferably 1% by mass to 15% by mass, more preferably 2% by mass to 12% by mass.

[0042] The content of the structural unit derived from the vinyl monomer having a carboxyl group in the acrylic copolymer is preferably 0.1% by mass or more, more preferably 1% by mass or more, based on the acrylic copolymer being 100% by mass, from the viewpoint of the processing characteristics and adhesive strength of the adhesive. The content of the structural unit derived from the vinyl monomer having a carboxyl group is usually 20% by mass or less. From the viewpoint of the cohesive strength, holding strength, and adhesiveness of the adhesive, the content of the structural unit derived from the vinyl monomer having a carboxyl group in the acrylic copolymer is more preferably 1% by mass to 15% by mass, more preferably 2% by mass to 12% by mass.

[0043] The content of the structural unit derived from the vinyl monomer having an amide group in the acrylic copolymer is preferably 0.1% by mass or more, more preferably 1% by mass or more, based on the acrylic copolymer being 100% by mass, from the viewpoint of the processing characteristics and adhesive strength of the adhesive. The content of the structural unit derived from the vinyl monomer having an amide group is usually 20% by mass or less. From the viewpoint of the cohesive strength, holding power, and adhesiveness of the adhesive, the content of the structural unit derived from the vinyl monomer having an amide group in the acrylic copolymer is more preferably 1% by mass to 15% by mass, more preferably 2% by mass to 12% by mass.

[0044] The acrylic copolymer can be produced by polymerizing the monomers by a polymerization method such as solution polymerization or bulk polymerization. The weight average molecular weight of the acrylic copolymer is preferably 400,000 to 1,200,000, more preferably 500,000 to 900,000. If the weight average molecular weight is within the above range, the adhesive strength of the adhesive can be easily adjusted, and the adhesiveness to the battery cell can be easily ensured.

[0045] The weight average molecular weight can be measured by gel permeation chromatography (GPC). For example, the weight average molecular weight can be determined in terms of polystyrene by measuring under the following GPC measurement conditions using a GPC measuring device "SC8020" manufactured by Tosoh Corporation. (GPC measurement conditions) Sample concentration: 0.5% by mass in tetrahydrofuran solution Sample injection volume: 100μL Eluent: Tetrahydrofuran (THF) ·Flow rate: 1.0mL / min Column temperature (measurement temperature): 40℃ Column: Tosoh Corporation's "TSKgel GMHHR-H" Detector: Differential Refraction

[0046] The pressure-sensitive adhesive may further contain a tackifier resin to enhance adhesion and peel resistance. In particular, the pressure-sensitive adhesive preferably contains the above-mentioned polymer and tackifier resin. Examples of the tackifier resin include petroleum resins such as aliphatic petroleum resins, aromatic petroleum resins, and alicyclic petroleum resins, rosin resins, rosin ester resins, disproportionated rosin resins, polymerized rosin resins, polymerized rosin ester resins, and rosin phenol resins, terpene resins such as diterpene polymers and α-pinene-phenol copolymers, terpene phenol resins, styrene resins, phenolic resins, and xylene resins. These tackifier resins may be used alone or in combination of two or more.

[0047] Among the tackifier resins, rosin-based resins are preferred, and polymerized rosin pentaerythritol esters are more preferred.

[0048] The tackifier resin is usually used in the range of 10 to 60 parts by mass relative to 100 parts by mass of the polymer, and when importance is attached to adhesiveness, it is preferably used in the range of 15 to 40 parts by mass.

[0049] When an acrylic adhesive containing the acrylic copolymer and a tackifier resin is used as an adhesive, the content of the tackifier resin in the acrylic adhesive is preferably 3% by mass or more, more preferably 5% by mass or more, based on 100% by mass of the acrylic adhesive, from the viewpoint of peel resistance. The content of the tackifier resin in the acrylic adhesive is preferably 40% by mass or less, from the viewpoint of obtaining good low-temperature adhesion.

[0050] The adhesive layer may contain a colorant for the purpose of adjusting the total light transmittance of the packaging material, similar to the substrate. The colorant used is the same as the material exemplified as the colorant used in the substrate. The method of adding a colorant to the adhesive layer is the same as the method of adding a colorant to the substrate, for example, a pellet-shaped colorant called a master batch or a powder-shaped colorant called a dry color is added to the adhesive.

[0051] When the adhesive layer contains a colorant, the content of the colorant is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.10 parts by mass or more, based on 100 parts by mass of the adhesive, from the viewpoint of detectability of the packaging material being attached to the battery cell surface by a detector, and is preferably 1.0 part by mass or less, more preferably 0.8 part by mass or less, and even more preferably 0.6 part by mass or less, from the viewpoint of maintaining the properties of the packaging material.

[0052] The pressure-sensitive adhesive layer may contain a curing agent for the purpose of improving the cohesive strength of the pressure-sensitive adhesive layer. The curing agent is not particularly limited and can be appropriately selected depending on the purpose. For example, the curing agent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the curing agent include isocyanate-based curing agents, epoxy-based curing agents, aziridine-based curing agents, polyvalent metal salt-based curing agents, metal chelate-based curing agents, ketohydrazide-based curing agents, oxazoline-based curing agents, carbodiimide-based curing agents, silane-based curing agents, and glycidyl(alkoxy)epoxysilane-based curing agents. Among the above curing agents, isocyanate-based curing agents and epoxy-based curing agents are preferred from the viewpoints of excellent reactivity and stability and easy securing of suitable cohesive force.

[0053] The adhesive may contain additives in addition to the polymer and the tackifier resin that can be optionally contained. For example, a silane coupling agent may be contained as the additive for the purpose of improving adhesion depending on the material of the battery cell housing. When the silane coupling agent is contained, it is preferable to use the silane coupling agent in a range of 0.001 to 0.005 parts by mass relative to 100 parts by mass of the adhesive. In addition, as other additives, a thermally conductive filler, a plasticizer, a filler, a flame retardant, etc. may be used as necessary.

[0054] The adhesive layer of the packaging material (hereinafter referred to as "the adhesive layer") contains the adhesive and is formed on one or both sides of the substrate. The adhesive layer can be formed, for example, by applying an adhesive solution obtained by dissolving the adhesive in a solvent or the like to the substrate using a roll coater, a die coater, or the like, or by forming an adhesive layer on a release liner in the same manner as described above and then transferring the layer to the substrate. As the release liner, for example, a release layer formed of a silicone compound, a melamine compound, etc. on paper such as polyethylene laminated paper, glassine paper, clay-coated paper, etc., or on a film such as a polyester film or a polypropylene film, etc., can be suitably used. Among these, the use of a film release liner is preferred from the viewpoint of suppressing the inclusion of air bubbles during application. The adhesive solution is usually adjusted to a solid content concentration of 20% by mass to 60% by mass.

[0055] In addition, when the packaging material has an adhesive layer on only one side of the substrate, the release layer may be formed on the surface of the substrate on which the adhesive layer is not provided, and the packaging material consisting of the substrate and the adhesive layer may be wound into a roll without laminating a release liner or protective liner on the surface of the adhesive layer.

[0056] The gel fraction of the present pressure-sensitive adhesive layer is preferably 20% or more, more preferably 40% or more, and even more preferably 60% or more, from the viewpoint of reworkability. The gel fraction of the pressure-sensitive adhesive layer is preferably 90% or less, and more preferably 80% or less, from the viewpoint of preventing peeling due to exposure to high temperatures upon receiving heat from the battery cell when the packaging material is used to package a battery cell.

[0057] The gel fraction is a value expressed as a percentage of the mass ratio of the pressure-sensitive adhesive layer that is insoluble in an organic solvent, such as toluene, and can be calculated by the following formula. Mass of adhesive layer remaining after immersion in toluene / Mass of adhesive layer before immersion x 100 If the gel fraction is below the specified range, the cohesive strength to withstand the repulsive force of the substrate is insufficient, and in a packaging form in which a battery cell is packaged with this packaging material, peeling is likely to occur at the contact points with the battery cell, at the bent points, etc., due to exposure to high temperatures due to heat from the battery cell. In addition, the reduced cohesive strength also reduces reworkability, making it more likely that glue will remain when peeled from the battery cell. On the other hand, if the gel fraction exceeds the specified range, the adhesive strength required for adhesion to the battery cell is reduced, and peeling is likely to occur at the adhesion points with the battery cell and at the bent points in the packaging form.

[0058] The glass transition temperature (Tg) of the pressure-sensitive adhesive layer is −30° C. or higher, preferably −20° C. or higher, and more preferably −15° C. or higher, from the viewpoints of cohesive strength and repulsion resistance required for reworkability at high temperatures. The glass transition temperature (Tg) of the pressure-sensitive adhesive layer is 15° C. or lower, preferably 0° C. or lower, from the viewpoints of exhibiting stable adhesive strength regardless of the type of adherend and maintaining cohesive strength and repulsion resistance required for reworkability at high temperatures. The glass transition temperature (Tg) of the pressure-sensitive adhesive layer is determined by measuring the storage modulus and tan δ of the pressure-sensitive adhesive layer from -40°C to 100°C using a viscoelasticity tester described in the Examples below, and the glass transition temperature (Tg) of the pressure-sensitive adhesive layer is the peak temperature of tan δ obtained by measuring the storage modulus and tan δ of the pressure-sensitive adhesive layer from -40°C to 100°C using a viscoelasticity tester described in the Examples below.

[0059] The storage modulus at 23°C (hereinafter referred to as "storage modulus at 23°C") of the pressure-sensitive adhesive layer is 2×10 to 400 mm from the viewpoint of maintaining the thickness of the pressure-sensitive adhesive layer and suppressing extrusion of the pressure-sensitive adhesive layer from the base material due to pressure. 4 Pa or more is preferable, 5×10 4 Pa or more is preferable, 8×10 4 Pa or more is more preferable. The storage modulus of this adhesive layer at 23°C is 2×10 6 Pa or less is preferable, 8×10 5 Pa or less is more preferable, and 6×10 5 Pa or less is most preferable.

[0060] The storage modulus at 60°C (hereinafter referred to as "storage modulus at 60°C") of the pressure-sensitive adhesive layer measured by a dynamic viscoelastic spectrum measured at a frequency of 1 Hz is set to 1×10 4 Pa or more is preferable, 3×10 4 Pa or more is preferable, 5×10 4 Pa or more is more preferable. The storage modulus of the adhesive layer at 60°C is set to 1×10 6 Pa or less is preferable, and 7×10 5 Pa or less is more preferable, and 5×10 5 Pa or less is most preferable.

[0061] The ratio (tan δ) of the loss modulus to the storage modulus at 60°C measured in a dynamic viscoelasticity spectrum measured at a frequency of 1 Hz of this adhesive layer (hereinafter referred to as "tan δ60") is preferably 0.10 or more, more preferably 0.15 or more, and even more preferably 0.20 or more, in order to obtain suitable resilience at high temperatures of this packaging material. From the viewpoint of the repulsion resistance and reworkability of the packaging material at high temperatures, the tan δ60 of the pressure-sensitive adhesive layer is preferably 0.60 or less, and more preferably 0.4 or less.

[0062] The storage modulus and tan δ60 refer to the storage modulus measured at 23°C, 60°C and a frequency of 1 Hz using a viscoelasticity tester described in the Examples below, in which a test piece cut into a circle with a diameter of 8 mm and layered to a thickness of 2 mm is sandwiched between parallel disks, which are the measuring part of the tester, and the storage modulus and tan δ60 refer to the value calculated based on the storage modulus and loss modulus.

[0063] When at least one of the storage modulus and tan δ60 exceeds the predetermined range, the pressure-sensitive adhesive layer is easily plastically deformed, and peeling is easily caused by the repulsive force of the substrate. When tan δ60 is below the predetermined range, the pressure-sensitive adhesive layer is less likely to follow the deformation caused by the repulsive force of the substrate, and peeling is easily caused at the adhesive interface between the adherend and the pressure-sensitive adhesive layer.

[0064] The thickness of the adhesive layer after drying is preferably 5 μm to 50 μm, more preferably 10 μm to 30 μm. By setting the thickness of the adhesive layer within the above range, the packaging material can have good adhesive strength, and the surface of the packaging material is less likely to become dirty and blocking is less likely to occur when the packaging material is wound into a roll.

[0065] The total light transmittance of the packaging material is 35% to 85%. From the viewpoint of the detectability of the packaging material being attached to the surface of the battery cell by a detector, the total light transmittance is preferably 80% or less, and more preferably 75% or less. Furthermore, from the viewpoint of the confirmability of the presence or absence of foreign matter or air bubbles, the total light transmittance is preferably 40% or more, and more preferably 45% or more. When the total light transmittance of the packaging material is within the above-mentioned predetermined range, it is possible to detect with a detector whether the battery cell is covered by the packaging material, and it is also possible to determine even if foreign matter or air bubbles are present between the packaging material and the battery cell. The total light transmittance of the packaging material can be measured by the method described in the Examples below.

[0066] The detector for detecting whether the battery cell is covered with the present packaging material can be appropriately selected without particular limitations as long as it observes the surface of the battery cell housing from the outside using a camera, etc. For example, there is a device that inspects the product by taking an image of the surface of the battery cell housing as it moves on the production line with a camera in the same way as visual inspection, and processing and analyzing the image data.

[0067] The present packaging material preferably has a floating distance related to repulsion resistance of 3 mm or less when measured at a temperature condition of 60° C., and from the viewpoint of further reducing the air gap between the present packaging material and the battery cell, sufficiently suppressing the decrease in thermal conductivity, and maintaining the cooling performance of the battery cell, the floating distance is preferably 2 mm or less, and more preferably 1.5 mm or less. By setting the floating distance related to repulsion resistance measured at a temperature condition of 60° C. within the above range, when a battery cell is packaged with the present packaging material, even if the present packaging material is exposed to high temperatures due to heat from the battery cell, an air gap is unlikely to be generated between the battery cell and the present packaging material. The minimum floating distance related to repulsion resistance measured under a temperature condition of 60°C is 0 mm, but as long as the effects of the present invention can be achieved, the minimum floating distance may be more than 0 mm, or may be 0.1 mm. The floating distance related to the repulsion resistance measured at a temperature condition of 60° C. is a value measured by the method described in the examples below.

[0068] The repulsion resistance of the present packaging material measured at a temperature condition of 60°C can be adjusted at least by the gel fraction and glass transition temperature of the present pressure-sensitive adhesive layer, and can further be adjusted by the elastic modulus and thickness of the substrate. Therefore, by setting these factors within appropriate ranges, the repulsion resistance of the present packaging material measured at a temperature condition of 60°C can be set within a desired range. The appropriate ranges of the factors are selected, for example, from the above-mentioned preferred ranges depending on the application and usage environment of the present packaging material.

[0069] The thickness of the present packaging material is preferably 25 μm or more and 175 μm or less, more preferably 35 μm or more and 125 μm or less, and even more preferably 43 μm or more and 100 μm or less, from the viewpoint of preventing wrinkles during packaging and preventing high repulsive force. The thickness of the packaging material is the sum of the thickness of the base material and the thickness of the adhesive layer after drying.

[0070] The 180° peel adhesive strength of the present packaging material is preferably 20 N / 25 mm or less, more preferably 18 N / 25 mm or less, and even more preferably 15 N / 25 mm or less. By setting the 180° peel adhesive strength of the present packaging material within the above-mentioned range, it is possible to provide excellent reworkability that allows the packaging shape to be maintained while suppressing the occurrence of adhesive residue and damage to the adhered surface when the packaging material is peeled off, and allows the material to be easily peeled off and repackaged, while also providing adhesive strength that allows the packaging shape to be maintained while suppressing the occurrence of adhesive residue and damage to the adhered surface when the packaging material is peeled off, and provides excellent reworkability that allows the material to be easily peeled off and repackaged. In order to maintain the peel resistance after the packaging material is attached to the battery cell, the 180° peel adhesive strength of the packaging material is preferably 5 N / 25 mm or more, more preferably 7 N / 25 mm or more, and even more preferably 9 N / 25 mm or more. The 180° peel adhesive strength is measured by the method for measuring 180° peel adhesive strength which will be described in the Examples below. The 180° peel adhesive strength of the present packaging material can be adjusted, for example, by the thickness, gel fraction, storage modulus at 23°C, glass transition temperature, modulus of elasticity and thickness of the substrate, etc. Therefore, by setting these factors within appropriate ranges, the 180° peel adhesive strength of the present packaging material can be set within a desired range. The appropriate ranges of the factors are selected, for example, from the preferred ranges, depending on the area to which the present packaging material is applied, the material of the adherend, rework conditions, etc.

[0071] This packaging material is insulating because it packages battery cells, but high insulation properties may be required depending on the application of the battery cells packaged in this packaging material. Therefore, the dielectric breakdown voltage of the present packaging material is preferably 2 kV or more, more preferably 4 kV or more, and even more preferably 6 kV or more. The dielectric breakdown voltage can be measured in accordance with JIS C 2110-1:2016. The breakdown voltage of the packaging material can be adjusted to a desired level by, for example, selecting the resin and thickness used for the substrate. The breakdown voltage can be adjusted by, for example, the thickness and material of the substrate, the elastic modulus of the substrate, the thickness of the packaging material, etc. Therefore, by setting these factors to appropriate ranges, the breakdown voltage of the packaging material can be adjusted to a desired level. The appropriate ranges of the factors are selected, for example, from the preferred ranges, depending on the application, the required level of repulsion resistance, the usage environment, etc.

[0072] In addition, the volume resistivity of this packaging material is 1×10 13 Ω cm or more is preferable, and 1×10 14 Ω cm or more is preferable, and 1×10 15 The volume resistivity can be measured in accordance with JIS-K6911 using a resistivity meter (Advantest digital ultra-high resistance / microammeter R8340, TR42 box) by applying a voltage of 500 V in the thickness direction.

[0073] The packaging material may be in the form of a long piece or a roll, and may have a release film or a protective film on the surface of the pressure-sensitive adhesive layer opposite to the substrate.

[0074] The packaging material can be manufactured by forming the pressure-sensitive adhesive layer on the substrate. The method of forming the pressure-sensitive adhesive layer is as described above. The pressure-sensitive adhesive layer is formed on the substrate by the above method while unrolling the roll-shaped substrate, and then rolled again to form a roll, or the pressure-sensitive adhesive layer is formed on a release liner in the same manner as described above, and then transferred to the substrate, and then rolled again to form a roll. Roll to Roll is preferable from the viewpoint of productivity. Before winding up the packaging material, it is preferable to provide a release film or a protective film on the surface of the pressure-sensitive adhesive layer opposite the substrate, but a release layer may be formed on the surface of the substrate on which the pressure-sensitive adhesive layer is not laminated, and the substrate may be wound up in a roll without laminating a release liner or a protective film.

[0075] A battery cell having at least a portion of its outer surface covered with the packaging material is suitable for use as a battery cell module. Examples of the battery cell include battery cells used in non-aqueous electrolyte secondary batteries or solid electrolyte secondary batteries. Examples of the battery include paper-type batteries, button-type batteries, coin-type batteries, laminated-type batteries, cylindrical batteries, and square-type batteries. The resulting battery cell modules can be used in portable devices, hybrid and electric vehicles, home storage batteries, and more.

[0076] As described above, the present packaging material does not impair the cooling effect of the battery cells, and the shortening of the life span of the battery cells is suppressed. While the present packaging material and the battery cell module in which at least a portion of the outer surface of the battery cell is covered with the present packaging material have been described above, the present invention is not limited to the configurations of the above-described embodiments. This packaging material and the battery cell module in which at least a portion of the outer surface of the battery cell is covered with this packaging material may have any other configuration added to the configuration of the above embodiment, or may be replaced with any configuration that performs a similar function. EXAMPLES

[0077] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the examples and comparative examples, the various physical properties were measured by the following methods.

[0078] [Measurement method] Gel fraction The packaging materials produced in the Examples and Comparative Examples were cut into test pieces of 40 mm x 50 mm, and the masses of the test pieces were measured using a balance. The test pieces were then immersed in toluene and allowed to stand at room temperature for 24 hours. The test piece after being left to stand was dried in a dryer at 105° C. for 1 hour, and then cooled to room temperature, and its mass was measured.

[0079] The substrate constituting the test piece was cut to a size of 40 mm x 50 mm and prepared separately, and the mass was measured. Next, the mass of the substrate was subtracted from the mass of the test piece before immersion in toluene to determine the mass of only the pressure-sensitive adhesive layer, and the mass of the substrate was subtracted from the mass of the test piece after immersion in toluene to determine the mass of only the pressure-sensitive adhesive layer that did not dissolve in toluene and remained. From the masses of the pressure-sensitive adhesive layer before and after the immersion, the proportion of the mass of the toluene-insoluble portion of the pressure-sensitive adhesive layer was calculated as a percentage using the following formula, and this was taken as the gel fraction. Gel fraction (%) = [mass of adhesive layer remaining after immersion / mass of adhesive layer before immersion] x 100

[0080] Storage modulus and tan δ The storage modulus of the adhesive layer at 23°C and 60°C and the tan δ of the adhesive layer at 60°C were measured using a viscoelasticity tester (manufactured by TA Instruments Japan, product name: ARES-G2) by sandwiching a test piece between parallel disks, which are the measuring part of the tester, at a temperature rise rate of 5°C / min from -40°C to 100°C. The tan δ at 60°C was calculated based on the storage modulus at 23°C and 60°C measured at a frequency of 1 Hz, and the ratio of the storage modulus to the loss modulus at 60°C, loss modulus (Pa) / storage modulus (Pa). The test pieces used were made by stacking the pressure-sensitive adhesive layers prepared in the Examples and Comparative Examples to a thickness of 2 mm, and cutting them into a circle with a diameter of 8 mm. The pressure-sensitive adhesive layer having a thickness of 2 mm was formed by stacking a plurality of pressure-sensitive adhesive layers to be measured. The same applies to the test pieces used for measuring the glass transition temperature (Tg) described later.

[0081] Glass transition temperature (Tg) In the measurements of the storage modulus and tan δ, the peak temperature at which tan δ was determined when measurements were made from −40° C. to 100° C. using the viscoelasticity tester was taken as the glass transition temperature (Tg) of the pressure-sensitive adhesive layer.

[0082] Volume resistivity The packaging materials of the Examples and Comparative Examples were measured in accordance with JIS-K6911 using a resistivity meter (Advantest digital ultra-high resistance / microammeter R8340, TR42 box) by applying a voltage of 500 V in the thickness direction.

[0083] Tensile Modulus The substrates used in the packaging materials of the Examples and Comparative Examples were cut into type 2 test pieces in the machine direction and width direction in accordance with JIS K7127:1999, and the tensile modulus was measured from the slope of the strain between 0.05% and 0.25% when pulled at a pulling speed of 200 mm / min at 23°C and 50% RH. The tensile tester was A&D Co., Ltd.'s RTH-1310, and the measurement was performed using a non-contact extensometer.

[0084] Breakdown Voltage Measurements were performed in accordance with JIS C 2110-1: 2016. Test pieces measuring 100 mm x 100 mm were cut from the packaging materials obtained in the examples and comparative examples, and conditioned for 24 hours or more in an atmosphere of 23°C and 50% RH. The surrounding medium was Type 1 No. 2 oil specified in JIS C 2320, and the temperature was 23±2°C. The electrode shape was a cylinder of φ25 mm at the top and a cylinder of φ25 mm at the bottom, with the same diameter electrode, and the voltage rise rate was set to approximately 1,000 V / s and the frequency was set to 60 Hz, and the breakdown voltage was determined by a short-term test.

[0085] 180° peel adhesion The 180° peel adhesive strength was measured by cutting the packaging materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 to a width of 25 mm, and attaching them to a 0.5 mm thick aluminum plate (A1050 aluminum plate compliant with JIS H-4000:2014, manufactured by Fujiwara Seisakusho Co., Ltd.) in an environment of 23°C and 50% RH by applying pressure once back and forth with a 2 kg roller, and leaving them in the same environment for 24 hours.After that, the peel resistance was measured when the packaging material was pulled in the 180° direction from the aluminum plate at a speed of 300 mm / min using a tensile tester (RTH-1310 manufactured by A&D Co., Ltd.). For Comparative Example 3, the packaging material obtained in Comparative Example 3 was cut to a width of 25 mm and attached to a 0.5 mm thick aluminum plate (A1050 aluminum plate compliant with JIS H-4000:2014, manufactured by Fujiwara Seisakusho Co., Ltd.) in an environment of 23°C and 50% RH by applying pressure with a 2 kg roller in one round trip. The material was then heated and pressed for 10 seconds using a heat press device (heat press machine TP-750 air press manufactured by Tester Sangyo Co., Ltd.) at a pressure of 1 MPa and a temperature of 120°C. The material was then left in an environment of 23°C and 50% RH for 24 hours, after which the peel resistance was measured when the packaging material was pulled in a tensile tester in a 180° direction from the aluminum plate at a speed of 300 mm / min.

[0086] Total light transmittance The packaging materials produced in the examples and comparative examples were measured for haze, transmittance, and reflectance using a HR-100 haze / transmittance / reflectance meter (manufactured by Murakami Color Research Laboratory Co., Ltd.) under conditions in accordance with JIS K7361-1:1997.

[0087] Packaging material attachment detection evaluation Based on the measured values ​​of the total light transmittance of the packaging material obtained in the examples and comparative examples, the detectability when detecting that this packaging material was attached to the surface of a battery cell using an image detector (an appearance inspection device using a CCD camera) was judged according to the following criteria. ◯: The total light transmittance was less than 85%, which is detectable by the detector without any problems. ×: The total light transmittance was 85% or more, which was undetectable by the detector.

[0088] Air bubble contamination check evaluation The packaging materials obtained in the examples and comparative examples were cut into 25 mm squares and attached to the same 0.5 mm thick aluminum plate used in the measurement of the 180° peel adhesive strength. At this time, the packaging material was attached to the aluminum plate from the periphery so that air bubbles were mixed in the center, and an air bubble with a diameter of 1 cm was created between the packaging material and the aluminum plate. Under indoor fluorescent lights of 500 to 750 lux, the presence of air bubbles was visually confirmed from the packaging material side at a distance of 30 cm from the surface of the packaging material, and evaluated according to the following criteria. ○: Air bubbles were visible ×: No air bubbles were visible

[0089] Reworkability evaluation The packaging materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were cut to a width of 25 mm and attached to the same aluminum plate of thickness 0.5 mm used in the measurement of the 180° peel adhesive strength in an environment of 23°C and 50% RH by applying pressure with a 2 kg roller back and forth once. After leaving the material in the same environment for 24 hours, the material was peeled off by hand in the 120° direction at a speed of about 10 m / min, and the ease of peeling and the presence or absence of adhesive residue were evaluated according to the following criteria. For Comparative Example 3, the packaging material obtained in Comparative Example 3 was cut to a width of 25 mm and attached to the same aluminum plate of thickness 0.5 mm as that used in the measurement of the 180° peel adhesive strength in an environment of 23°C and 50% RH by applying pressure with a 2 kg roller in one reciprocating motion. Then, using a heat press device (heat press machine TP-750 air press manufactured by Tester Sangyo Co., Ltd.), the material was heated and pressed for 10 seconds at a pressure of 1 MPa and a temperature of 120°C. The material was then left in an environment of 23°C and 50% RH for 24 hours, after which it was peeled off by hand in the 120° direction at a speed of about 10 m / min, and the ease of peeling and the presence or absence of adhesive residue were evaluated according to the following criteria. ◎: Easy to peel off, no adhesive residue left ○: Easy to peel off, but adhesive residue was 1mm or less over a width of 25mm △: It was difficult to peel off, but the adhesive residue was more than 1mm and less than 3mm in a width of 25mm. ×: Peeling was difficult and the adhesive residue exceeded 3 mm.

[0090] Rebound resistance at 60℃ The packaging materials obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were cut into pieces 25 mm wide and 50 mm long to prepare test pieces, and the test pieces were attached to two surfaces of an L-shaped aluminum plate (Alinco Corporation, aluminum plate FA115N) having a thickness of 2.0 mm, two sides of 30 mm long, and a width of 200 mm in an atmosphere of 23°C and 50% RH, so as to cover the corners of the L shape so that each surface was 25 mm long. Each surface of the test piece was pressed back and forth once at a speed of 300 mm / min with a roller weighing 2 kg. For Comparative Example 3, the packaging material obtained in Comparative Example 3 was cut to a width of 25 mm and a length of 50 mm to prepare a test piece, and the test piece was attached to two sides of an L-shaped aluminum plate (manufactured by Alinco Corporation, aluminum plate FA115N) having a thickness of 2.0 mm, two sides of 30 mm, and a width of 200 mm in an atmosphere of 23°C and 50% RH, so as to cover the corners of the L-shape so that each side had a length of 25 mm. After pressing each side of the test piece once with a roller weighing 2 kg at a speed of 300 mm / min, a heat press device (heat press machine TP-750 air press manufactured by Tester Sangyo Co., Ltd.) was used to apply a pressure of 1 MPa and a temperature of 120°C to each side for 10 seconds to heat and press the test piece. For all test specimens, a silicone adhesive tape (626001-NB, manufactured by Hitachi Maxell, Ltd.) cut to a length of 30 mm and a width of 50 mm was attached entirely to one of the surfaces of the test specimen with the tip of the adhesive tape at the folding position, and the test specimen was fixed to an L-shaped aluminum plate so that only the floating length of the remaining surface of the test specimen was measured. The L-shaped aluminum plate with the prepared test piece attached was left in an atmosphere of 60°C and 90% RH for 96 hours with the side of the test piece not fixed with the adhesive tape facing up, and then returned to 23°C and 50% RH, and the length of the test piece that had floated at the 90° point of the L-shape (floating distance) was measured. Fig. 1 is a schematic diagram for explaining the outline of the repulsion resistance test in a 60°C environment, illustrating an L-shaped aluminum plate with a test specimen attached. In Fig. 1, reference numeral 1 indicates the test specimen (packaging material), reference numeral 2 indicates the L-shaped aluminum plate, reference numeral 3 indicates the silicone adhesive tape, reference numeral S indicates the floating part of the test specimen (part where an air layer exists), and reference numeral L indicates the length of the test specimen that is floating at the 90° point (floating distance). The repulsion resistance in a 60°C environment was evaluated according to the following criteria, based on the largest peeling (floating distance) among the peeling on any side. ◎: Less than 1.5mm ○: 1.5 to less than 2 mm △: 2mm or more and less than 3mm ×: 3mm or more

[0091] <Preparation of acrylic copolymer (a-1)> In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel and nitrogen gas inlet, 89.5 parts by mass of n-butyl acrylate, 10.0 parts by mass of acrylic acid, 0.5 parts by mass of 2-hydroxyethyl acrylate, 0.5 parts by mass of 2,2'-azobisisobutylnitrile as a polymerization initiator, and a mixed solvent of 140 parts by mass of ethyl acetate and 24 parts by mass of toluene were dissolved, and after nitrogen replacement, polymerization was carried out at 80°C for 8 hours to obtain a solution of acrylic copolymer (a-1) with a solid content of 30% by mass and a weight average molecular weight of 860,000.

[0092] <Preparation of Acrylic Copolymer Composition (a-2)> In a reaction vessel equipped with a stirrer, reflux condenser, thermometer, dropping funnel, and nitrogen gas inlet, 79.94 parts by mass of n-butyl acrylate, 10.0 parts by mass of cyclohexyl acrylate, 6.0 parts by mass of 2-ethylhexyl acrylate, 4.0 parts by mass of acrylic acid, 0.06 parts by mass of 4-hydroxybutyl acrylate, and 0.5 parts by mass of 2,2'-azobisisobutylnitrile as a polymerization initiator were dissolved in 164 parts by mass of ethyl acetate, and after nitrogen replacement, the mixture was polymerized at 80°C for 8 hours to obtain an acrylic copolymer solution (b-2) with a solid content of 30% by mass and a weight average molecular weight of 800,000. Furthermore, a solution prepared by dissolving 15 parts by mass of HARIESTER PCJ (Harima Chemicals Co., Ltd., polymerized rosin pentaerythritol ester) and 5 parts by mass of FTR-6125 (Mitsui Chemicals, Inc., aromatic hydrocarbon resin) in 40 parts by mass of ethyl acetate as a tackifier resin was mixed in an amount of 30 parts by mass with 100 parts by mass of the acrylic copolymer solution (b-2) to prepare an acrylic copolymer composition (a-2) with a solid content of 31% by mass.

[0093] <Preparation of styrene-based block copolymer composition (a-3)> Styrene-isoprene block copolymer (Zeon Corporation "Quintac 3433N", styrene amount 16% by mass) 100 parts by mass, C5 petroleum resin (Zeon Corporation "Quinton R100", softening point 96 ° C.) 40 parts by mass, polymerized rosin ester resin (Arakawa Chemical Industries Co., Ltd. "Pensel D-125", softening point 125 ° C.) 40 parts by mass, low molecular weight polybutene (ENEOS Corporation "HV-100") as a softener, and tetrakis-[methylene-3-(3'5'-di-t-butyl-4-hydroxyphenyl)propionate]methane 2 parts by mass as an antioxidant were blended, and dissolved in 240 parts by mass of methylcyclohexane, 40 parts by mass of ethyl acetate, and 23 parts by mass of isopropyl alcohol as a solvent to prepare a styrene-based block copolymer composition (a-3) with a solid content of 40% by mass.

[0094] <Preparation of heat-fusible adhesive composition (a-4)> A heat-fusible adhesive composition (a-4) with a solid content of 31.2% by mass was prepared by mixing 60 parts by mass of Vylon BX10SS (solid content 30% by mass, number average molecular weight 21,000, glass transition temperature -18°C, manufactured by Toyobo Co., Ltd.) as a polyester resin and 40 parts by mass of Vylon UR1350 (solid content 33% by mass, number average molecular weight 36,000, glass transition temperature 46°C, manufactured by Toyobo Co., Ltd.) as a polyester urethane resin.

[0095] <Example 1> To 100 parts by mass of the acrylic copolymer (a-1) with a solid content of 30% by mass, 0.20 parts by mass of MHI Black #220 (manufactured by Mikuni Color Co., Ltd., pigment content 33% by mass, solid content 40.3% by mass) was added as a black colorant so that the colorant content in the adhesive layer was 0.22% by mass, and then stirred with a disperser for 15 minutes. 2.0 parts by mass of E-05X (manufactured by Soken Chemical Industries, Ltd., epoxy-based curing agent, solid content 0.5% by mass) was added as a curing agent, and then stirred with a disperser for 10 minutes. The mixture was applied onto the silicone-based release agent of a release liner (PET film with a silicone-based release agent applied to one side, manufactured by Fujimori Kogyo Co., Ltd., 38E-0010BD) so that the thickness after drying was 27 μm, and the solvent was dried to prepare an adhesive layer a. Next, the mixture was laminated with a transparent PET film (manufactured by Toray Industries, Inc., S10) with a thickness of 23 μm to prepare a packaging material A.

[0096] <Example 2> To 100 parts by mass of the acrylic copolymer (a-1) with a solid content of 30% by mass, 0.06 parts by mass of MHI Black #220 (manufactured by Mikuni Color Co., Ltd., pigment content 33% by mass, solid content 40.3% by mass) was added as a black colorant so that the colorant content in the adhesive layer was 0.07% by mass, and then stirred with a disperser for 15 minutes. 2.0 parts by mass of E-05X (manufactured by Soken Chemical Industries, Ltd., epoxy-based curing agent, solid content 0.5% by mass) was added as a curing agent, and then stirred with a disperser for 10 minutes. The mixture was applied onto the silicone-based release agent of a release liner (a PET film with a silicone-based release agent applied to one side, manufactured by Fujimori Kogyo Co., Ltd., 38E-0010BD) so that the thickness after drying was 27 μm, and the solvent was dried to prepare an adhesive layer b. Next, the mixture was laminated with a transparent PET film (manufactured by Toray Industries, Inc., S10) with a thickness of 23 μm to prepare a packaging material B.

[0097] <Example 3> To 100 parts by mass of the acrylic copolymer (a-1) with a solid content of 30% by mass, 0.60 parts by mass of MHI Black #220 (manufactured by Mikuni Color Co., Ltd., pigment content 33% by mass, solid content 40.3% by mass) was added as a black colorant so that the colorant content in the adhesive layer was 0.65% by mass, and then stirred with a disperser for 15 minutes. 2.0 parts by mass of E-05X (manufactured by Soken Chemical Industries, Ltd., epoxy-based curing agent, solid content 0.5% by mass) was added as a curing agent, and then stirred with a disperser for 10 minutes. The mixture was applied onto the silicone-based release agent of a release liner (a PET film with a silicone-based release agent applied to one side, manufactured by Fujimori Kogyo Co., Ltd., 38E-0010BD) so that the thickness after drying was 27 μm, and the solvent was dried to prepare an adhesive layer c. Next, the mixture was laminated with a transparent PET film (manufactured by Toray Industries, Inc., S10) with a thickness of 23 μm to prepare a packaging material C.

[0098] <Example 4> To 100 parts by mass of the acrylic copolymer composition (a-2) with a solid content of 31% by mass, 0.83 parts by mass of MHI Magenta #889 (manufactured by Mikuni Color Co., Ltd., pigment content 15% by mass, solid content 18.9% by mass) was added as a red colorant so that the colorant content in the adhesive layer was 0.38% by mass, and then stirred with a disperser for 15 minutes, and 3.4 parts by mass of Burnock KW-40 (manufactured by DIC Corporation, isocyanate-based curing agent, solid content 40% by mass) was added as a curing agent, and then stirred with a disperser for 10 minutes, and the thickness after drying was 25 μm in the same manner as in Example 1 to prepare an adhesive layer d. Next, the adhesive layer d was prepared by laminating it to a 50 μm transparent PET film (manufactured by Toray Industries, Inc., S10) to prepare a packaging material D.

[0099] <Example 5> To 100 parts by mass of the styrene-based block copolymer composition (a-3) having a solid content of 40% by mass, 1.0 part by mass of DICTON BLACK B-5261 (manufactured by DIC Corporation, pigment content 15% by mass, solid content 60% by mass) as a black colorant was added so that the colorant content in the adhesive layer was 0.37% by mass, and the mixture was stirred with a disperser for 15 minutes, and then the adhesive layer e was prepared so that the thickness after drying was 20 μm in the same manner as in Example 1. Next, the adhesive layer e was prepared by laminating it to a 23 μm transparent PET film (manufactured by Toray Industries, Inc., S10) to prepare a packaging material E.

[0100] <Comparative Example 1> Packaging material F was prepared in the same manner as in Example 1, except that MHI Black #220 was not added as a black colorant to the acrylic copolymer (a-1) having a solid content of 30% by mass, and the colorant content was 0% by mass.

[0101] <Comparative Example 2> Packaging material G was prepared in the same manner as in Example 1, except that the amount of MHI Black #220 added as a black colorant to the acrylic copolymer (a-1) having a solid content of 30 mass% was increased from 0.20 mass parts to 1.00 mass parts, and the colorant content in the adhesive layer was 1.1 mass%.

[0102] <Comparative Example 3> To 100 parts by mass of the heat-fusible adhesive composition (a-4) with a solid content of 31.2% by mass, 0.20 parts by mass of MHI Black #220 (manufactured by Mikuni Shikiso Co., Ltd., pigment content 33% by mass, solid content 40.3% by mass) was added as a black colorant so that the colorant content in the adhesive layer was 0.21% by mass, and the mixture was stirred with a disperser for 15 minutes, after which 1.20 parts by mass of Burnock DN980 (manufactured by DIC Corporation, hexamethylene diisocyanate type, solid content 75% by mass) was added as an isocyanate-based curing agent and stirred for 10 minutes, and then the mixture was applied to a transparent PET film (manufactured by Toray Industries, Inc., S10) with a thickness of 23 μm so that the thickness after drying was 27 μm, and the solvent was dried to prepare an adhesive layer h. Next, the mixture was laminated with a release liner (PET film with a non-silicone release agent applied to one side, manufactured by Fujimori Kogyo Co., Ltd., 38E-0010NSD) to prepare a packaging material H.

[0103] [Table 1]

[0104] [Table 2]

[0105] As is clear from the above results, the adhesive tape described in the examples can detect whether the battery cell is covered with a packaging material by a detector, and can also distinguish whether foreign matter or air bubbles are mixed between the packaging material and the battery cell. Therefore, when used as a packaging material for battery cells, it is considered that the cooling effect of the battery cell is not impaired and the shortening of the life of the battery cell is suppressed. In addition, the packaging material of the examples was shown to be excellent in reworkability, with the occurrence of glue residue being suppressed in the reworkability evaluation. In addition, Comparative Example 3 having a heat-sealable adhesive layer has poor adhesion to the aluminum plate used as the housing material of the battery cell, and is inferior in adhesion and repulsion resistance, whereas the adhesive tape described in the examples has excellent adhesion to the aluminum plate and repulsion resistance, suppresses lifting and peeling, does not impair the cooling effect of the battery cell, and is considered to suppress the shortening of the life of the battery cell. [Explanation of symbols]

[0106] 1. Test piece (packaging material) 2. L-shaped aluminum plate 3. Silicone adhesive tape S: Floating part of the test piece (part where air space exists) L: The length of the test piece that is lifted at the 90° point (lift distance)

Claims

1. A packaging material for battery cells having a substrate and a pressure-sensitive adhesive layer provided on one or both sides of the substrate, The pressure-sensitive adhesive layer has a glass transition temperature (Tg) of −30° C. or higher and 15° C. or lower; The packaging material for battery cells has a total light transmittance of 35% to 85%.

2. The packaging material for battery cells according to claim 1 , wherein the pressure-sensitive adhesive layer has a gel fraction of 20% or more and 90% or less.

3. The packaging material for battery cells according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive.

4. The packaging material for battery cells according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains a curing agent.

5. The packaging material for battery cells according to claim 1 or 2, wherein at least one of the pressure-sensitive adhesive layer and the substrate contains a colorant, or the substrate has a colored layer on a surface thereof.

6. 3. The packaging material for battery cells according to claim 1, wherein the floating distance related to the repulsion resistance measured under a temperature condition of 60°C is less than 3 mm.

7. The pressure-sensitive adhesive layer has a storage viscoelastic modulus of 1×10 at 60° C. ４ Pa or more 1×10 ６ The packaging material for battery cells according to claim 1 or 2, wherein the viscosity of the packaging material is 0.01 Pa or less.

8. 3. The packaging material for battery cells according to claim 1 or 2, having a 180° peel adhesive strength of 5 N / 25 mm or more.

9. The tensile modulus of the substrate is 1×10 ８ Pa or more 1×10 １０ The packaging material for battery cells according to claim 1 or 2, wherein the viscosity of the packaging material is 0.01 Pa or less.

10. The packaging material for battery cells according to claim 1 or 2, wherein the substrate has a thickness of 20 μm or more and 125 μm or less.

11. 3. The packaging material for battery cells according to claim 1 or 2, having a dielectric breakdown voltage of 2 kV or more.

12. 3. The packaging material for battery cells according to claim 1 or 2, having a thickness of 25 μm or more and 175 μm or less.

13. A battery cell, at least a part of the outer surface of which is covered with the packaging material for battery cells according to claim 1 or 2.

14. A battery cell module constructed using a plurality of the battery cells according to claim 13.

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