Battery pack and use of adhesive sheet

Abstract

This battery pack includes a battery cell, a cooling plate, and a battery case for storing the battery cell and the cooling plate. The battery pack includes an adhesive sheet for bonding the battery cell and the cooling plate. The adhesive sheet has a thermal diffusivity reduction rate of 4.5% or more before and after heating represented by formula (1) when heated at 285°C for 5 minutes. (1) ((Thermal diffusivity before heating – Thermal diffusivity after heating) / Thermal diffusivity before heating) × 100. According to the present invention, it is possible to provide a battery pack provided with an adhesive sheet that combines contradictory properties of good thermal conductivity in normal times and excellent insulation when there is thermal runaway.

Description

Using the battery pack and adhesive sheet

[0001] The present invention relates to a battery pack and the use of an adhesive sheet for use in a battery pack.

[0002] Battery packs used in electric vehicles, hybrid vehicles, and the like have a structure in which a number of battery modules, each including a plurality of battery cells, are connected to obtain high output, and each battery cell includes a positive electrode and a negative electrode current collector, a separator, an active material, an electrolyte, etc., and can be repeatedly charged and discharged through electrochemical reactions between the components. Meanwhile, in recent years, with the increasing need for large-capacity structures, including for use as an energy storage source, there has been a demand for battery packs with a multi-module structure in which a number of battery modules, each including a number of secondary batteries connected in series or parallel, are assembled.

[0003] Because multi-module battery packs are manufactured with multiple rechargeable batteries packed into a small space, it is important to easily dissipate the heat generated by each rechargeable battery. Heat is generated by electrochemical reactions during the charging and discharging processes of rechargeable batteries. If the heat generated in the battery module during the charging and discharging processes is not effectively removed, heat accumulation occurs, which can accelerate deterioration of the battery module and, in some cases, lead to fire or explosion. Therefore, high-power, large-capacity battery modules and battery packs equipped with them require a cooling device to cool the battery cells contained therein.

[0004] Because the power that can be produced by a single secondary battery cell is not large, a required number of battery cells are typically stacked and packaged within a module case. To cool the heat generated during the electricity production process in each battery cell and maintain an appropriate temperature for the secondary battery, a number of cooling fins corresponding to the area of ​​the battery cells are inserted between the battery cells as heat dissipation members. The cooling fins absorb heat from each battery cell and transfer the heat to the cooling plate, which is connected to a cooling plate. The cooling plate transfers the heat transferred from the cooling fins to a heat sink, which is cooled by coolant or coolant air.

[0005] Generally, when a battery cell and a cooling fin are joined, a heat transfer material that can minimize thermal resistance between the contact interfaces is applied to the interface to bond the battery cell and the cooling fin. However, because it is difficult to uniformly apply the heat transfer material to the battery cell and the cooling fin, the contact surface may become uneven after drying, resulting in reduced cooling performance. Furthermore, if the battery cell swells, the contact surface may separate, reducing cooling performance. Furthermore, if the battery cell is used for a long period of time, the contact interface may separate. In response to the above issues, Patent Literature 1 proposes a battery module including a plurality of battery cells arranged in at least one direction facing each other, a cooling plate positioned below the plurality of battery cells, and a heat transfer tape that transfers heat from the battery cells to the cooling plate and is attached to the battery cells.

[0006] Special table 2018-530896 publication

[0007] The battery module disclosed in Patent Document 1 is preferable because it effectively transfers heat from the battery cells to the cooling plate under normal conditions, but if one battery cell experiences thermal runaway, the heat from the thermally runaway battery cell will be transferred to other surrounding battery cells via the cooling plate, causing a chain reaction of thermal runaway. For this reason, it is preferable for the battery module to have thermal insulation that thermally isolates the battery cell from the cooling plate during thermal runaway.

[0008] Under the circumstances described above, the present invention aims to provide a battery pack equipped with an adhesive sheet that combines the contradictory properties of good thermal conductivity under normal conditions and excellent insulation properties in the event of thermal runaway.

[0009] As a result of intensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by using a specific adhesive sheet as the adhesive sheet for bonding the battery cell and the cooling plate, and thus completed the present invention.

[0010] That is, the present invention provides the following: [1] A battery pack having a battery cell, a cooling plate, and a battery case that stores the battery cell and the cooling plate, comprising an adhesive sheet that bonds the battery cell and the cooling plate together, wherein the adhesive sheet has a thermal diffusivity decrease rate of 4.5% or more before and after heating at 285°C for 5 minutes, as expressed by the following formula (1): ((thermal diffusivity before heating - thermal diffusivity after heating) / thermal diffusivity before heating) x 100 ... (1) [2] A battery pack having a battery cell, a cooling plate, and a battery case that stores the battery cell and the cooling plate, comprising an adhesive sheet that bonds the battery cell and the cooling plate together, wherein the adhesive sheet has an adhesive strength decrease rate of 15% or more before and after heating at 285°C for 5 minutes, as expressed by the following formula (2): ((Adhesive strength before heating−Adhesive strength after heating) / Adhesive strength before heating)×100 (2) [3] The battery pack according to the above [1] or [2], wherein the adhesive sheet contains an adhesive material. [4] The battery pack according to the above [3], wherein the adhesive material contains a modified polyolefin resin. [5] The battery pack according to the above [3] or [4], wherein the adhesive material contains a thermally expandable flame retardant and / or a thermally expandable foaming agent. [6] The battery pack according to the above [4] or [5], wherein the modified polyolefin resin is graft-modified with an unsaturated carboxylic acid and / or a derivative thereof. [7] The battery pack according to the above [5] or [6], wherein the thermally expandable flame retardant contains a phosphorus-based flame retardant. [8] The battery pack according to any one of the above [5] to [7], wherein the thermally expandable flame retardant contains an intumescent flame retardant. [9] The battery pack according to any one of [5] to [8] above, wherein the thermally expandable foaming agent includes a chemical foaming agent and / or a physical foaming agent, and a thermoplastic resin capsule that encapsulates them.

[10] The battery pack according to any one of [5] to [9] above, wherein the adhesive material further includes a dispersant.

[11] The battery pack according to

[10] above, wherein the dispersant includes a copolymer of an α-olefin and an unsaturated carboxylic acid.

[12] The battery pack according to any one of [4] to

[11] above, wherein the adhesive material further contains a polyethylene-based resin and / or a polypropylene-based resin.

[13] The battery pack according to any one of [1] to

[12] above, wherein the adhesive sheet is further provided between battery cells to bond the battery cells to each other.

[14] The battery pack according to any one of [1] to

[13] above, wherein the battery case is a resin housing.

[0011]

[15] Use of the adhesive sheet in a battery pack having battery cells, a cooling plate, and a battery case that stores the battery cells and the cooling plate, the adhesive sheet bonding the battery cells and the cooling plate, wherein the adhesive sheet exhibits a rate of decrease in thermal diffusivity before and after heating of 4.5% or more when heated at 285°C for 5 minutes, as shown in the following formula (1): ((thermal diffusivity before heating - thermal diffusivity after heating) / thermal diffusivity before heating) x 100 ... (1)

[16] Use of the adhesive sheet in a battery pack having battery cells, a cooling plate, and a battery case that stores the battery cells and the cooling plate, the adhesive sheet bonding the battery cells and the cooling plate, wherein the adhesive sheet exhibits a rate of decrease in adhesive strength before and after heating of 15% or more when heated at 285°C for 5 minutes, as shown in the following formula (2): ((Adhesive strength before heating - Adhesive strength after heating) / Adhesive strength before heating) x 100 (2)

[17] Use of the adhesive sheet according to

[15] or

[16] above, wherein the adhesive sheet comprises an adhesive material.

[18] Use of the adhesive sheet according to

[17] above, wherein the adhesive material comprises a modified polyolefin resin.

[19] Use of the adhesive sheet according to

[17] or

[18] above, wherein the adhesive material comprises a thermally expandable flame retardant and / or a thermally expandable blowing agent.

[20] Use of the adhesive sheet according to

[18] or

[19] above, wherein the modified polyolefin resin is graft-modified with an unsaturated carboxylic acid and / or a derivative thereof.

[21] Use of the adhesive sheet according to

[19] or

[20] above, wherein the thermally expandable flame retardant comprises a phosphorus-based flame retardant.

[22] Use of the adhesive sheet according to any one of

[19] to

[21] above, wherein the thermally expandable flame retardant comprises an intumescent flame retardant.

[23] Use of the adhesive sheet according to any one of

[19] to

[22] above, wherein the thermally expandable foaming agent comprises a chemical foaming agent and / or a physical foaming agent, and a thermoplastic resin capsule encapsulating these.

[24] Use of the adhesive sheet according to any one of

[19] to

[23] above, wherein the adhesive material further comprises a dispersant.

[25] Use of the adhesive sheet according to

[24] above, wherein the dispersant comprises a copolymer of an α-olefin and an unsaturated carboxylic acid.

[26] Use of the adhesive sheet according to any one of

[18] to

[25] above, wherein the adhesive material further comprises a polyethylene-based resin and / or a polypropylene-based resin.

[27] Use of the adhesive sheet according to any one of

[15] to

[26] above, wherein the adhesive sheet is further provided between battery cells to bond the battery cells to each other.

[28] Use of the adhesive sheet according to any one of

[15] to

[27] above, wherein the battery case is a resin housing.

[0012] According to the present invention, it is possible to provide a battery pack equipped with an adhesive sheet that combines contradictory properties of good thermal conductivity under normal conditions and excellent heat insulation in the event of thermal runaway.

[0013] FIG. 1 is a conceptual diagram showing a battery pack of the present invention.

[0014] Hereinafter, embodiments of the present invention will be described in detail, but the following description is merely an example of an embodiment of the present invention, and the present invention is not limited to the contents thereof.

[0015] [Battery Pack] The battery pack of the present invention will be described with reference to Fig. 1. The battery pack 1 of the present invention includes a battery cell 11, a cooling plate 14, and a battery case 15 that houses the battery cell 11 and the cooling plate 14. The battery pack 1 is characterized by including an adhesive sheet 13 that bonds the battery cell 11 to the cooling plate 14. The adhesive sheet 13 transfers heat between the cooling plate 14 and the battery cell 11 and is used as the adhesive sheet 13 that is bonded to the battery cell 11, and while it provides good thermal conductivity normally, it can also contribute to blocking heat during thermal runaway.

[0016] <Thermal Diffusivity> When the adhesive sheet 13 is heated at 285°C for 5 minutes, the thermal diffusivity decrease rate before and after heating, as expressed by the following formula (1), is 4.5% or more. Hereinafter, this may be referred to as the first embodiment. ((Thermal diffusivity before heating - Thermal diffusivity after heating) / Thermal diffusivity before heating) × 100 (1) If the thermal diffusivity decrease rate is 4.5% or more, if a battery cell 11 becomes abnormally hot for some reason, heat is less likely to be conducted from the abnormally hot battery cell 11 to the cooling plate 14, thereby preventing adverse effects on other battery cells through the cooling plate 14. From the above perspectives, the thermal diffusivity decrease rate is more preferably 5% or more, even more preferably 7% or more, even more preferably 10% or more, particularly preferably 13% or more, and especially preferably 20% or more. Meanwhile, the upper limit of the thermal diffusivity decrease rate is not particularly limited, and may be 100% or less, 90% or less, 70% or less, or 50% or less.

[0017] While thermal conductivity is a quantity that indicates the rate at which thermal energy is transferred when a steady temperature gradient exists, thermal diffusivity is a quantity that indicates the rate at which the temperature distribution relaxes and reaches a thermal equilibrium state. The relationship between thermal conductivity and thermal diffusivity is as follows: Thermal conductivity (λ) = Density (ρ) × Specific heat (C) × Thermal diffusivity (α). Note that if the battery pack has bus bars that can conduct large amounts of current between battery cells, it is preferable to design the bus bars so that they will not function if at least one of the battery cells experiences an abnormally high temperature.

[0018] <Adhesive Strength> When the adhesive sheet 13 is heated at 285°C for 5 minutes, the adhesive strength reduction rate before and after heating, as expressed by the following formula (2), is 15% or more. Hereinafter, this may be referred to as the second embodiment. ((Adhesive Strength Before Heating - Adhesive Strength After Heating) / Adhesive Strength Before Heating) × 100 (2) If the adhesive strength reduction rate is 15% or more, if the battery cell becomes abnormally hot for some reason, the adhesive strength of the adhesive sheet 13 will decrease, and the adhesion between the battery cell 11 and the cooling plate 14 will decrease. This makes it difficult for heat to be conducted from the abnormally hot battery cell 11 to the cooling plate 14, preventing adverse effects on other battery cells through the cooling plate 14. From the above perspectives, the adhesive strength reduction rate is more preferably 20% or more, even more preferably 25% or more, even more preferably 30% or more, particularly preferably 35% or more, particularly preferably 50% or more, and most preferably 60% or more. On the other hand, the upper limit of the adhesive strength reduction rate is not particularly limited, and may be 100% or less, or may be 99% or less, 95% or less, 93% or less, or 90% or less.

[0019] The mechanism of action of the first aspect is to suppress heat conduction from the abnormally high-temperature battery cell 11 to the cooling plate 14 when the battery cell becomes abnormally hot for some reason, thereby avoiding adverse effects on other battery cells through the cooling plate 14. On the other hand, the mechanism of action of the second aspect is to reduce the adhesion between the abnormally high-temperature battery cell 11 and the cooling plate 14 when the battery cell becomes abnormally hot for some reason, thereby suppressing heat conduction from the battery cell 11 to the cooling plate 14. Therefore, similar to the first aspect, adverse effects on other battery cells through the cooling plate 14 can be avoided. As described above, although the first aspect and the second aspect have different mechanisms of action, both suppress heat conduction from an abnormally high-temperature battery cell. Therefore, although the effects of the present invention can be achieved with only the first aspect or only the second aspect, it is more preferable in terms of effects that both the first aspect and the second aspect function.

[0020] Furthermore, in the battery pack of the present invention, the adhesive sheet for bonding the battery cells and the cooling plate as described above is an essential component. In addition, the adhesive sheet can also be used as an adhesive sheet for bonding each battery cell to another. By using the adhesive sheet of the present invention, heat generated in each battery cell is electrically heated between the battery cells via the adhesive sheet, maintaining a good condition. On the other hand, if a battery cell becomes abnormally hot for some reason, the adhesive strength of the adhesive sheet decreases, reducing the adhesion between the battery cells. This makes it difficult for heat to be conducted from the abnormally hot battery cell to adjacent battery cells, preventing adverse effects on other battery cells. Note that the battery pack shown in FIG. 1 includes spacers 12 between the battery cells 11. In this case, the adhesive sheet of the present invention is used to bond the battery cells 11 and the spacers 12, and the spacers 12 and the adhesive sheet can provide thermal insulation between the battery cells 11 in the event of an abnormality.

[0021] <Adhesive Sheet> An important component of the battery pack of the present invention is the adhesive sheet 13. The effects of the present invention are achieved by the adhesive sheet 13 changing its thermal diffusivity and / or adhesive strength when heated as described above. That is, when used as a battery, the battery cells 11 and the cooling plate 14 are firmly bonded, and the cooling plate 14 functions effectively, thereby sufficiently cooling the battery cells 11. On the other hand, if the battery cells 11 become abnormally hot, the heat reduces the thermal diffusivity and / or adhesive strength of the adhesive sheet 13, thereby reducing the thermal conductivity between the battery cells 11 and the cooling plate 14 and suppressing heat transfer through the cooling plate 14. Furthermore, as described above, when an adhesive sheet is disposed between the battery cells 11 (not shown), the reduction in the thermal diffusivity and / or adhesive strength of the adhesive sheet similarly suppresses heat transfer between the battery cells 11.

[0022] The thickness of the adhesive sheet according to the present invention is preferably in the range of 0.05 mm to 2 mm. When the thickness of the adhesive sheet is 0.05 mm or more, the adhesive strength between the battery cell and the cooling plate is sufficient, and when the thickness is 2 mm or less, an effective heat transfer suppression effect is obtained when the battery cell becomes abnormally hot. From the above viewpoints, the thickness of the adhesive sheet is more preferably in the range of 0.1 mm to 1 mm.

[0023] The adhesive sheet according to the present invention is prepared by molding a material containing the adhesive material described below into a sheet.

[0024] (Adhesive Material) The adhesive sheet according to the present invention preferably contains a specific adhesive material. There are various adhesive materials available, but they are not particularly limited as long as they achieve the effects of the present invention. In the present invention, the adhesive sheet containing the adhesive material may have sufficient adhesiveness when used as a battery, and may have the property of reducing adhesive strength in response to an external stimulus applied at any time. In the present invention, the external stimulus is preferably heat. Using heat as the external stimulus makes it possible to suppress chain reaction in battery cells that have gone into thermal runaway. Examples of adhesive materials include reactive polymers such as degradable polymers, and materials that reduce adhesive strength by reducing interfacial interactions between the adherends or by changing the elastic modulus. In the present invention, a thermoplastic resin that has been given adhesive properties through modification is preferably used, and a modified polyolefin-based resin is particularly preferred. That is, the adhesive material preferably contains a modified polyolefin-based resin.

[0025] (Thermoplastic resin imparted with adhesiveness by modification) As described above, the adhesive material constituting the adhesive sheet preferably contains a thermoplastic resin imparted with adhesiveness by modification (hereinafter, sometimes referred to as "adhesive thermoplastic resin"). The unmodified thermoplastic resin is not particularly limited as long as it achieves the effects of the present invention, and examples thereof include polyolefin resin, polycarbonate resin, polyester resin, polyamide resin, etc., and among these, from the viewpoint of recyclability, polyolefin resin is preferred as the unmodified thermoplastic resin. In other words, the thermoplastic resin imparted with adhesiveness by modification preferably contains a modified polyolefin-based resin, and more preferably is a modified polyolefin-based resin.

[0026] (Modified Polyolefin Resin) A modified polyolefin resin is a resin in which at least one of the main chain terminal and the side chain of an unmodified polyolefin resin is modified. The modification position is not particularly limited.

[0027] Specific examples of unmodified polyolefin resins include ethylene homopolymers such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), ethylene-α-olefin copolymers such as ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-hexene copolymers, ethylene-octene copolymers, ethylene-propylene-butene copolymers, ethylene-propylene-hexene copolymers, ethylene-propylene-octene copolymers, ethylene-butene-hexene copolymers, ethylene-butene-octene copolymers, and ethylene-hexene-octene copolymers, ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid copolymers, and ethylene-methyl (meth)acrylate copolymers. Examples of the copolymers include ethylene-based copolymers such as copolymers, ethylene-ethyl (meth)acrylate copolymers, and ethylene-(meth)acrylic acid-methyl (meth)acrylate copolymers; propylene homopolymers (propylene homopolymers), propylene-ethylene random copolymers, propylene-butene random copolymers, propylene-ethylene-hexene random copolymers, propylene-ethylene-octene random copolymers, propylene-butene-hexene random copolymers, propylene-butene-octene random copolymers, propylene-hexene-octene random copolymers, and propylene-ethylene block copolymers; butene homopolymers and butene-based copolymers. Hereinafter, polymers and copolymers may be collectively referred to as "(co)polymers." "(Meth)acrylic acid" means acrylic acid and / or methacrylic acid. The same applies hereinafter.

[0028] The above-mentioned ethylene copolymer, propylene copolymer, and butene copolymer refer to copolymers containing ethylene, propylene, or butene in a proportion of 50 mol % or more of the total monomer units constituting the copolymer, respectively. These raw polyolefin resins may be used alone or in any combination and ratio of two or more.

[0029] Among these, from the viewpoint of recyclability, propylene-based copolymers such as propylene homopolymer, propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-hexene random copolymer, propylene-ethylene-octene random copolymer, propylene-butene-hexene random copolymer, propylene-butene-octene random copolymer, propylene-hexene-octene random copolymer, and propylene-ethylene block copolymer are preferred.

[0030] The density of the raw material polyolefin resin (JIS K7112-1) is not particularly limited, but is preferably 0.85 g / cm ３ More preferably, 0.87 g / cm ３ or more, while 0.98 g / cm ３ Preferably, it is 0.97 g / cm or less, more preferably 0.97 g / cm ３ The melt flow rate (MFR) of the raw material polyolefin resin is not particularly limited, but from the viewpoint of moldability, it is preferably 0.01 g / 10 min or more and 50 g / 10 min or less, and more preferably 0.1 g / 10 min or more and 30 g / 10 min or less. Here, the MFR of the polyolefin resin means the value at 190°C and a load of 2.16 kg when the polyolefin resin is an ethylene (co)polymer or a butene (co)polymer, and means the value at 230°C and a load of 2.16 kg when the polyolefin resin is a propylene (co)polymer.

[0031] The modified polyolefin resin contained in the adhesive material of the present invention is obtained by introducing a modifying group into the unmodified polyolefin resin. The modifying group is not particularly limited, but is preferably at least one functional group selected from the group consisting of acid anhydride groups, carboxyl groups, amino groups, imino groups, alkoxysilyl groups, silanol groups, silyl ether groups, hydroxyl groups, and epoxy groups. Among these, polyolefin resins modified with at least one selected from the group consisting of unsaturated carboxylic acids and their derivatives, and unsaturated silanes are preferred, and polyolefin resins graft-modified with unsaturated carboxylic acids and / or their derivatives are more preferred. "Graft-modification" refers to bonding an unsaturated carboxylic acid and / or its derivative to a polyolefin resin. As mentioned above, the modification position of the unmodified polyolefin resin is not particularly limited, as long as at least one of the main chain terminal and side chain of the polyolefin resin is modified.

[0032] Examples of unsaturated carboxylic acids used for graft-modifying unmodified polyolefin resins include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, which may be used alone or in combination. Examples of derivatives of unsaturated carboxylic acids include acid anhydrides, esters, amides, imides, and metal salts, which may be used alone or in combination.

[0033] Specific examples of the derivative of unsaturated carboxylic acid include maleic anhydride, himic anhydride, itaconic anhydride, citraconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, glycidyl acrylate, maleic acid monoethyl ester, maleic acid diethyl ester, itaconic acid monomethyl ester, itaconic acid diethyl ester, acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide, maleic acid-N,N-diethylamide, maleic acid-N,N-monobutylamide, maleic acid-N,N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monobutylamide, fumaric acid-N,N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, and potassium methacrylate.

[0034] The unsaturated carboxylic acid and / or its derivative may be used singly or in any combination and ratio of two or more. Among these, maleic acid or its anhydride is particularly preferred because of its low electron density and high reactivity.

[0035] The density of the modified polyolefin resin is not particularly limited, but the density measured according to JIS K7112-1 is preferably 0.85 g / cm ３ More preferably, 0.87 g / cm ３ or more, and preferably 0.98 g / cm ３ or less, more preferably 0.97 g / cm ３ The following is the result.

[0036] The melt flow rate (MFR) of the modified polyolefin resin is not particularly limited, but is preferably 0.01 g / 10 min to 1000 g / 10 min, more preferably 0.1 g / 10 min to 500 g / 10 min. When the raw polyolefin resin is an ethylene-based (co)polymer or a butene-based (co)polymer, the MFR of the modified polyolefin resin means the value at 190°C and a load of 2.16 kg. When the raw polyolefin resin is a propylene-based (co)polymer, the value at 230°C, a load of 2.16 kg, and a 2 mm orifice may be used. However, when the molecular weight of the modified polyolefin resin is low and measurement is difficult, the value may be measured under conditions of 180°C, a load of 2.16 kg, and a 1 mm orifice.

[0037] The melting point of the modified polyolefin resin is preferably 170°C or lower, more preferably 165°C or lower, and even more preferably 160°C or lower. When the melting point of the modified polyolefin resin is 170°C or lower, the thermally expandable flame retardant and thermally expandable blowing agent described below expand when the resin is molten, and the blowing agent (excluding thermally expandable blowing agents) described below foams, thereby achieving better thermal insulation. The melting point of the modified polyolefin resin can be measured using a differential scanning calorimeter in accordance with JIS K 7121.

[0038] Hereinafter, a method for producing a graft-modified polyolefin resin among modified polyolefin resins will be described. Graft modification of a raw polyolefin resin (unmodified polyolefin resin) can be carried out by various conventionally known methods. Modification methods include, but are not limited to, a melt modification method in which an unsaturated carboxylic acid and / or a derivative thereof is added to a molten raw polyolefin resin to perform graft copolymerization, and a solution modification method in which an unsaturated carboxylic acid and / or a derivative thereof is added to a raw polyolefin resin dissolved in a solvent to perform graft copolymerization. Of these, from the viewpoint of hygiene, the melt modification method, which does not require the use of a solvent, is preferred, and graft modification using an extruder is more preferred. For efficient graft modification, modification in the presence of a radical initiator is preferred.

[0039] The radical initiator is not particularly limited, but is preferably an organic peroxide or an azo compound, and particularly preferably an organic peroxide. Specifically, dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 1,4-bis(t-butylperoxyisopropyl)benzene, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, 2,2-bis(4,4-t-butylperoxycyclohexyl)propane, 2,2-bis(t-butylperoxy)butane, and 1,1-bis(t-butylperoxy)cyclododecane; t-butylperoxyacetate, t-butylperoxy-2-ethylhexanoate, t-butylperoxypivalate, t-butylperoxylaurate, t-butylperoxybenzoate, t-butylperoxyisopropyl peroxyesters such as dibenzoyl peroxide, t-butyl peroxymaleic acid, di-t-butylperoxyisophthalate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexyne-3, and 2,5-dimethyl-2,5-di(toluylperoxy)hexane; diacyl peroxides such as di-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, and dibenzoyl peroxide; hydroperoxides such as t-butyl hydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, p-menthane hydroperoxide, and 2,5-dimethyl-2,5-di(hydroperoxy)hexane; and ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, but are not particularly limited to these.

[0040] Among these, radical initiators having a decomposition temperature of 100°C or higher, at which the half-life is 1 minute, are preferred from the viewpoint of graft modification efficiency. Specifically, dialkyl peroxides such as di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, and peroxyesters such as t-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexyne-3 are preferred.

[0041] The radical initiator may be used alone or in any combination and ratio of two or more. The amount of radical initiator used is not particularly limited, but is preferably 0.001 to 5 parts by mass per 100 parts by mass of the raw material polyolefin resin.

[0042] The content of unsaturated carboxylic acid and / or its derivative in the modified polyolefin resin (hereinafter sometimes referred to as graft rate) varies depending on the type of raw material polyolefin resin and the unsaturated carboxylic acid and / or its derivative used for modification, and is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and is preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 5 mass% or less, relative to the total amount of the modified polyolefin resin. If the graft rate is equal to or greater than the lower limit of the above-mentioned preferred value, the adhesive properties of the adhesive material will be good, while if it is equal to or less than the upper limit of the above-mentioned preferred value, partial crosslinking of the raw material polyolefin resin itself during grafting, which would result in reduced moldability, or deterioration of the product appearance due to the generation of fisheyes or foreign matter, etc., can be prevented.

[0043] The graft ratio can be measured by press-molding the modified polyolefin resin into a sheet having a thickness of 100 μm to prepare a test sample, and using infrared absorption spectroscopy, the graft ratio can be determined from the absorption characteristic of the carboxylic acid and / or its derivative in the resin. －１In the graft modification of a raw polyolefin resin, unsaturated carboxylic acid and / or derivatives thereof that have not reacted with the raw polyolefin resin may remain, but the graft ratio in this specification means the value measured by the above-mentioned method for the modified polyolefin resin, as described above.

[0044] Commercially available modified polyolefin resins suitable for use in the present invention may also be used. For example, a product having the above properties may be appropriately selected from the "Modic (registered trademark)" series manufactured by Mitsubishi Chemical Corporation.

[0045] The proportion of the adhesive thermoplastic resin relative to the total mass of the adhesive material is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, and is preferably 95% by mass or less, more preferably 93% by mass or less, and even more preferably 90% by mass or less. When the proportion of the adhesive thermoplastic resin is equal to or greater than the lower limit, the adhesiveness and thermal conductivity are excellent. When the proportion is equal to or less than the upper limit, the content of the thermally expandable flame retardant and thermally expandable foaming agent described below in the adhesive material can be ensured. The proportion of the adhesive thermoplastic resin relative to the total mass of the adhesive material may be, for example, 1% by mass or more and 95% by mass or less, 2% by mass or more and 93% by mass or less, or 3% by mass or more and 90% by mass or less.

[0046] (Thermal Expandable Material) The adhesive material constituting the adhesive sheet according to the present invention preferably contains a thermal expandable material. Examples of the thermal expandable material include a thermal expandable flame retardant and a thermal expandable foaming agent, which will be described later, and the thermal expandable material preferably contains a thermal expandable flame retardant and / or a thermal expandable foaming agent. That is, the adhesive material preferably contains a thermal expandable flame retardant and / or a thermal expandable foaming agent.

[0047] (Thermal Expandable Flame Retardant) The adhesive material constituting the adhesive sheet according to the present invention preferably contains a thermal expandable flame retardant. By including a thermal expandable flame retardant, flame retardancy and flame protection can be exhibited, preventing the spread of fire, even in the event of a runaway reaction and combustion of a battery cell. The thermal expandable flame retardant is not particularly limited as long as it has the property of expanding upon heating. For example, there is a thermal expandable flame retardant that imparts flame retardancy by forming a carbonized coating upon combustion, and the coating expands to form an expansion layer. Furthermore, from the viewpoint of improving flame protection, it is preferable that the thermal expandable flame retardant contains a phosphorus-based flame retardant. Furthermore, in terms of classification focusing on the mechanism of action of flame retardants, it is preferable that the thermal expandable flame retardant contains an intumescent flame retardant from the viewpoint of improving flame protection. Furthermore, from the viewpoint of environmental friendliness, it is preferable that the thermal expandable flame retardant be a non-halogen flame retardant.

[0048] The adhesive material contains a thermally expandable flame retardant, which causes the adhesive sheet to heat and expand when the battery cell reaches an abnormally high temperature, forming an insulating layer (expansion layer). This insulating layer blocks heat from the hot battery cell, suppressing heat transfer to other battery cells, and also improves heat insulation by reducing the adhesion between the battery cell and the cooling plate.

[0049] Phosphorus-based flame retardants are phosphorus compounds, i.e., compounds containing phosphorus atoms in the molecule. Phosphorus-based flame retardants exert their flame retardant effect by forming char (carbonized film) when an adhesive sheet containing an adhesive material is burned. Phosphorus-based flame retardants may be known compounds, such as (poly)phosphates and (poly)phosphate esters. Here, "(poly)phosphates" refers to phosphates or polyphosphates, and "(poly)phosphate esters" refers to phosphate esters or polyphosphate esters. It is preferable that the phosphorus-based flame retardant is solid at 80°C.

[0050] As the phosphorus-based flame retardant, (poly)phosphates are preferred in terms of flame retardancy. Examples of (poly)phosphates include ammonium polyphosphate, melamine polyphosphate, piperazine polyphosphate, piperazine orthophosphate, melamine pyrophosphate, piperazine pyrophosphate, melamine orthophosphate, calcium phosphate, magnesium phosphate, etc. In addition, in the above examples, compounds in which melamine or piperazine is replaced with other nitrogen compounds can also be used. Examples of other nitrogen compounds include N,N,N',N'-tetramethyldiaminomethane, ethylenediamine, N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, 1,2-propanediamine, 1,3-propanediamine, ... Tramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, trans-2,5-dimethylpiperazine, 1,4-bis(2-aminoethyl)piperazine, 1,4-bis(3-aminopropyl)piperazine, acetoguanamine, benzoguanamine, acrylguanamine, 2,4-diamino-6-nonyl-1,3 ,5-triazine, 2,4-diamino-6-hydroxy-1,3,5-triazine, 2-amino-4,6-dihydroxy-1,3,5-triazine, 2,4-diamino-6-methoxy-1,3,5-triazine, 2,4-diamino-6-ethoxy-1,3,5-triazine, 2,4-diamino-6-propoxy-1,3,5-triazine, 2,4-diamino-6-isopropoxy-1,3,5-triazine, 2,4-diamino-6- Examples of the methyl methyl mercapto-1,3,5-triazine include mercapto-1,3,5-triazine, 2-amino-4,6-dimercapto-1,3,5-triazine, ammeline, benzguanamine, acetoguanamine, phthalodiguanamine, melamine cyanurate, butylenediguanamine, norbornenediguanamine, methylenediguanamine, ethylenedimelamine, trimethylenedimelamine, tetramethylenedimelamine, hexamethylenedimelamine, and 1,3-hexylenedimelamine.These (poly)phosphates may be used alone or in combination of two or more.

[0051] Among the above-mentioned thermally expandable flame retardants, salts of (poly)phosphoric acid and nitrogen compounds are preferred, and these are flame retardants known as intumescent flame retardants. Intumescent flame retardants suppress the combustion of materials by forming a surface expansion layer (intemescent) that prevents the diffusion of radiant heat from the combustion source and combustion gases and smoke from the burning material to the outside. The formation of the surface expansion layer suppresses the diffusion and heat transfer of decomposition products, thereby exhibiting excellent flame retardancy. Examples of nitrogen compounds in intumescent flame retardants include ammonia, melamine, piperazine, and the other nitrogen compounds described above. Specific examples include ammonium salts and amine salts of (poly)phosphoric acid, such as ammonium polyphosphate, melamine polyphosphate, piperazine polyphosphate, ammonium pyrophosphate, melamine pyrophosphate, and piperazine pyrophosphate. Furthermore, zinc oxide may be added as a flame retardant aid. This is preferred because it further improves flame retardancy.

[0052] The thermally expandable flame retardant preferably contains a compound having a melamine structure or a piperazine structure, and may be, for example, a mixture containing a compound having a melamine structure and a compound having a piperazine structure.

[0053] Commercially available thermally expandable flame retardants include Adekastab FP-2100J, FP-2200, and FP-2500S (manufactured by ADEKA Corporation).

[0054] The above thermally expandable flame retardants may be used alone or in combination of two or more.

[0055] In the adhesive material, the proportion of the thermally expandable flame retardant is preferably 10 parts by mass or more and 100 parts by mass or less relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be optionally contained in the adhesive material. By having the proportion of the thermally expandable flame retardant relative to the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be optionally contained in the adhesive material within this range, when used in combination with a dispersant as described below, a significant decrease in the mechanical properties of the adhesive sheet can be prevented and high flame retardancy can be achieved. However, the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be optionally contained in the adhesive material refers to the content of the adhesive thermoplastic resin if the adhesive material does not contain polyethylene-based resin or polypropylene-based resin; if the adhesive material contains either polyethylene-based resin or polypropylene-based resin, it refers to the total mass of the adhesive thermoplastic resin plus the polyethylene-based resin or polypropylene-based resin contained; and if the adhesive material contains polyethylene-based resin and polypropylene-based resin, it refers to the total mass of the adhesive thermoplastic resin + polyethylene-based resin + polypropylene-based resin (hereinafter the same). It should be noted that the polyethylene resin and polypropylene resin referred to here are unmodified resins, i.e., unmodified polyethylene resin and unmodified polypropylene resin, and do not fall under the category of adhesive thermoplastic resin.

[0056] In particular, the proportion of the thermally expandable flame retardant relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, still more preferably 55 parts by mass or more, and is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 75 parts by mass or less, and still more preferably 70 parts by mass or less. The proportion of the thermally expandable flame retardant relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed may be, for example, 20 parts by mass or more and 90 parts by mass or less, 40 parts by mass or more and 80 parts by mass or less, 45 parts by mass or more and 75 parts by mass or less, or 55 parts by mass or more and 70 parts by mass or less.

[0057] The proportion of the thermally expandable flame retardant relative to the total mass of the adhesive material is preferably 15% by mass or more, more preferably 25% by mass or more, and even more preferably 35% by mass or more, and is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. When the proportion of the thermally expandable flame retardant is above the lower limit, the flame retardancy is superior and the heat insulating properties can be improved. When the proportion is below the upper limit, the inherent physical properties of the adhesive thermoplastic resin contained in the adhesive material and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed are more likely to be exhibited. The proportion of the thermally expandable flame retardant relative to the total mass of the adhesive material may be, for example, 15% by mass or more and 70% by mass or less, 25% by mass or more and 60% by mass or less, or 35% by mass or more and 50% by mass or less.

[0058] (Thermal Expandable Foaming Agent) The adhesive material constituting the adhesive sheet according to the present invention preferably contains a thermal expandable foaming agent. The thermal expandable foaming agent is not particularly limited as long as it has the property of expanding when heated. For example, a foaming agent containing a chemical foaming agent and / or a physical foaming agent and a thermoplastic resin capsule encapsulating these may be suitably used. A thermal expandable foaming agent containing a chemical foaming agent and / or a physical foaming agent and a thermoplastic resin capsule encapsulating these encapsulates the foaming agent inside the thermoplastic resin. Therefore, when heated, the shell resin softens and the pressure of the foaming agent present inside increases, resulting in a rapid volume expansion.

[0059] The adhesive material contains a thermally expandable foaming agent, which causes the adhesive sheet to heat and expand when the battery cell reaches an abnormally high temperature, forming an insulating layer (expansion layer). This insulating layer blocks heat from the hot battery cell, suppressing heat transfer to other battery cells, and also improves heat insulation by reducing the adhesion between the battery cell and the cooling plate.

[0060] Examples of chemical blowing agents include azodicarbonamide (ADCA), N,N'-dinitropentamethylenetetramine (DPT), and 4,4'-oxybisbenzenesulfonylhydrazide (OBSH). Examples of physical blowing agents include hydrocarbon compounds with relatively low boiling points. Among these, the thermally expandable blowing agent is preferably one that contains a physical blowing agent and a thermoplastic resin capsule that encapsulates the physical blowing agent, and more preferably one that contains a physical blowing agent containing a hydrocarbon compound and a thermoplastic resin capsule that encapsulates the physical blowing agent.

[0061] As the thermally expandable foaming agent, commercially available products can be used, such as "Matsumoto Microsphere" (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), "EXPANCEL" (manufactured by Nippon Phillite Co., Ltd.), "Advancell EM Series" (manufactured by Sekisui Chemical Co., Ltd.), and "Microsphere" (manufactured by Kureha Corporation).

[0062] In the adhesive material, the proportion of the thermally expandable foaming agent is preferably 1 part by mass or more and 20 parts by mass or less relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed in the adhesive material. When the proportion of the thermally expandable foaming agent relative to the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed is within this range, the inherent physical properties of the adhesive thermoplastic resin contained in the adhesive material and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed are likely to be expressed while maintaining thermal insulation.

[0063] In particular, the proportion of the thermally expandable foaming agent relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed is preferably 1 part by mass or more, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. The proportion of the thermally expandable foaming agent relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed may be, for example, 1 part by mass or more and 20 parts by mass or less, 3 parts by mass or more and 15 parts by mass or less, or 5 parts by mass or more and 10 parts by mass or less.

[0064] The proportion of the thermally expandable foaming agent relative to the total mass of the adhesive material is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 7% by mass or less. When the proportion of the thermally expandable foaming agent is equal to or greater than the lower limit, the heat insulating properties can be improved. When the proportion is equal to or less than the upper limit, the inherent physical properties of the adhesive thermoplastic resin contained in the adhesive material and the polyethylene-based resin and / or polypropylene-based resin that may be optionally contained therein can be easily exhibited. The proportion of the thermally expandable foaming agent relative to the total mass of the adhesive material may be, for example, 1% by mass or more and 20% by mass or less, 3% by mass or more and 15% by mass or less, 3% by mass or more and 10% by mass or less, or 4% by mass or more and 7% by mass or less.

[0065] (Dispersant) The adhesive material constituting the adhesive sheet according to the present invention preferably further contains a dispersant. The dispersant is not particularly limited as long as it can disperse the thermally expandable flame retardant and the thermally expandable foaming agent in the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed. However, polymeric dispersants are preferred in terms of compatibility with the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed. Polymeric dispersants having functional groups are preferred. From the viewpoint of dispersion stability, polymeric dispersants having functional groups such as carboxyl groups, phosphate groups, sulfonic acid groups, primary, secondary, or tertiary amino groups, quaternary ammonium bases, and groups derived from nitrogen-containing heterocycles such as pyridine, pyrimidine, and pyrazine are preferred. In this embodiment, polymeric dispersants having carboxyl groups are preferred, and copolymers of α-olefins and unsaturated carboxylic acids are more preferred. The use of such dispersants can improve the dispersibility of the thermally expandable flame retardant and the thermally expandable foaming agent, thereby reducing the content of the thermally expandable flame retardant and the thermally expandable foaming agent. The polymer dispersant having a functional group excludes modified polyolefin resins used as adhesive materials.

[0066] In this embodiment, in the above-mentioned "copolymer of α-olefin and unsaturated carboxylic acid" (hereinafter sometimes simply referred to as "copolymer"), the proportion of α-olefin units in a total of 100 mol% of α-olefin units and unsaturated carboxylic acid units is preferably 20 mol% or more and 80 mol% or less. In the copolymer, the proportion of α-olefin units relative to the total amount of α-olefin units and unsaturated carboxylic acid units is more preferably 30 mol% or more, and more preferably 70 mol% or less. When the proportion of α-olefin is equal to or greater than the lower limit, the compatibility with adhesive thermoplastic resins and polyethylene-based resins and / or polypropylene-based resins that may be contained as needed is improved, and when the proportion is equal to or less than the upper limit, the compatibility with thermally expandable flame retardants and thermally expandable blowing agents is improved.

[0067] In the copolymer, the α-olefin is more preferably an α-olefin having from 10 to 80 carbon atoms. If the α-olefin has 10 or more carbon atoms, compatibility with the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed tends to be better, and if the α-olefin has 80 or less carbon atoms, it is advantageous in terms of raw material costs. From the above viewpoints, the number of carbon atoms in the α-olefin is more preferably from 12 to 70, even more preferably from 15 to 65, and particularly preferably from 18 to 60.

[0068] In the copolymer, examples of unsaturated carboxylic acids include (meth)acrylic acid, maleic acid, methylmaleic acid, fumaric acid, methylfumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid, glutaconic acid, norbornane-5-ene-2,3-dicarboxylic acid, and esters, anhydrides, and imides of these unsaturated carboxylic acids. Note that "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. Specific examples of unsaturated carboxylic acid esters, anhydrides, and imides include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and glycidyl (meth)acrylate; dicarboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic anhydride; and maleimide compounds such as maleimide, N-ethylmaleimide, and N-phenylmaleimide. These may be used alone or in combination of two or more. Among these, esters and dicarboxylic acid anhydrides are preferred from the viewpoint of copolymerization reactivity. Among them, dicarboxylic acid anhydrides are preferred, and maleic anhydride is particularly preferred from the viewpoint of compatibility with thermally expandable flame retardants and thermally expandable blowing agents.

[0069] The weight-average molecular weight of the copolymer is preferably 2,000 or more, more preferably 3,000 or more, and even more preferably 5,000 or more, while it is preferably 50,000 or less, more preferably 30,000 or less, and even more preferably 10,000 or less. If the weight-average molecular weight of the copolymer is within the above range, the dispersibility of the thermally expandable flame retardant and the thermally expandable blowing agent will be better. The weight-average molecular weight of the copolymer is a value calculated in terms of standard polystyrene, measured by dissolving the copolymer in tetrahydrofuran (THF) and performing gel permeation chromatography.

[0070] Commercially available copolymers include Ricorb CE2 (manufactured by Clariant Japan Co., Ltd.) and Diacarna 30M (manufactured by Mitsubishi Chemical Corporation).

[0071] When the adhesive material contains a thermally expandable flame retardant, the ratio of dispersant to the thermally expandable flame retardant (100% by mass) in the adhesive material is preferably 10% by mass or less. In particular, the ratio of dispersant to the thermally expandable flame retardant (100% by mass) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and particularly preferably 3% by mass or more, while more preferably 8% by mass or less, even more preferably 7% by mass or less, even more preferably 6% by mass or less, and particularly preferably 5% by mass or less. By having the ratio of dispersant to the thermally expandable flame retardant (100% by mass) within the above range, an adhesive sheet can be obtained that has high flame retardancy and heat insulation while maintaining high mechanical strength.

[0072] In the adhesive material of the present invention, the ratio of the dispersant to the thermally expandable flame retardant (100% by mass) may be, for example, 0.01% by mass or more and 10% by mass or less, 0.05% by mass or more and 8% by mass or less, 0.1% by mass or more and 7% by mass or less, 0.1% by mass or more and 6% by mass or less, 0.5% by mass or more and 6% by mass or less, 1% by mass or more and 6% by mass or less, or 3% by mass or more and 5% by mass or less.

[0073] When the adhesive material contains a thermally expandable flame retardant, the proportion of the dispersant relative to the total mass of the adhesive material is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more, and is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. When the proportion of the dispersant is equal to or greater than the lower limit, the thermally expandable flame retardant is well dispersed, improving the flame retardancy of the adhesive material, as well as the heat insulating properties and the appearance of the resulting adhesive sheet. When the proportion of the dispersant is equal to or less than the upper limit, the effect of the dispersant on the flame retardancy of the adhesive material can be suppressed. The proportion of the dispersant relative to the total mass of the adhesive material of the present invention may be, for example, 0.01% by mass or more and 10% by mass or less, 0.1% by mass or more and 5% by mass or less, or 1% by mass or more and 3% by mass or less.

[0074] When the adhesive material contains a thermally expandable flame retardant, the proportion of dispersant relative to the total mass of the adhesive thermoplastic resin, the polyethylene resin and / or polypropylene resin that may be optionally contained, and the thermally expandable flame retardant in the adhesive material is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, while preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. If the proportion of dispersant is above the lower limit, the thermally expandable flame retardant is more dispersed, improving the flame retardancy of the adhesive material, the heat insulating properties, and the appearance of the resulting adhesive sheet. If the proportion of dispersant is below the upper limit, the effect of the dispersant on the flame retardancy of the adhesive material can be further suppressed.

[0075] The ratio of the dispersant to the total mass of the adhesive thermoplastic resin, the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed, and the thermally expandable flame retardant may be, for example, 0.01 mass% or more and 5 mass% or less, 0.1 mass% or more and 4 mass% or less, 1 mass% or more and 3 mass% or less, or 1.5 mass% or more and 3 mass% or less.

[0076] When the adhesive material contains a thermally expandable foaming agent, the ratio of the dispersant to the thermally expandable foaming agent (100% by mass) in the adhesive material is preferably 30% by mass or less. In particular, the ratio of the dispersant to the thermally expandable foaming agent (100% by mass) is preferably 0.03% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1% by mass or more, even more preferably 2% by mass or more, and particularly preferably 3% by mass or more, while more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less. By having the ratio of the dispersant to the thermally expandable foaming agent (100% by mass) within the above range, an adhesive sheet with heat insulating properties can be obtained while maintaining high mechanical strength.

[0077] In the adhesive material of the present invention, the ratio of the dispersant to the thermally expandable foaming agent (100% by mass) may be, for example, 0.03% by mass or more and 30% by mass or less, 0.3% by mass or more and 30% by mass or less, 0.5% by mass or more and 30% by mass or less, 1% by mass or more and 20% by mass or less, 2% by mass or more and 15% by mass or less, or 3% by mass or more and 10% by mass or less.

[0078] When the adhesive material contains a thermally expandable foaming agent, the proportion of the dispersant relative to the total mass of the adhesive material is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. When the proportion of the dispersant is equal to or greater than the lower limit, the thermally expandable foaming agent is well dispersed, resulting in good heat insulation and the appearance of the resulting adhesive sheet. When the proportion of the dispersant is equal to or less than the upper limit, the effect of the dispersant on the adhesive performance of the adhesive material can be further suppressed. The proportion of the dispersant relative to the total mass of the adhesive material of the present invention may be, for example, 0.1% by mass or more and 3% by mass or less, 0.2% by mass or more and 2% by mass or less, or 0.3% by mass or more and 1% by mass or less.

[0079] When the adhesive material contains a thermally expandable foaming agent, the proportion of dispersant relative to the total mass of the adhesive thermoplastic resin, the polyethylene resin and / or polypropylene resin that may be optionally contained, and the thermally expandable foaming agent in the adhesive material is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. If the proportion of dispersant is above the lower limit, the thermally expandable foaming agent is more dispersed, improving the heat insulation and the appearance of the resulting adhesive sheet. If the proportion of dispersant is below the upper limit, the effect of the dispersant on the adhesive performance of the adhesive material can be further suppressed.

[0080] The ratio of the dispersant to the total mass of the adhesive thermoplastic resin, the polyethylene-based resin and / or polypropylene-based resin that may be contained as necessary, and the thermally expandable foaming agent may be, for example, 0.05 mass% or more and 5 mass% or less, 0.1 mass% or more and 3 mass% or less, 0.2 mass% or more and 2 mass% or less, or 0.3 mass% or more and 1 mass% or less.

[0081] The ratio of the total mass of the adhesive thermoplastic resin, thermally expandable material, and dispersant to the total mass of the adhesive material is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, particularly preferably 45% by mass or more, and may be 100% by mass. For example, when the total mass of the adhesive thermoplastic resin, thermally expandable material, and dispersant is 100% by mass, the adhesive thermoplastic resin, thermally expandable material (thermally expandable flame retardant and thermally expandable foaming agent), and dispersant can be appropriately selected from the above-mentioned ranges so that the total of the three components is 100% by mass.

[0082] (Polyethylene-based resin) The adhesive material constituting the adhesive sheet according to the present invention may further contain a polyethylene-based resin. By including a polyethylene-based resin, adhesion to the adherend can be achieved at lower temperatures, and formability can be improved when the adhesive material according to the present invention is processed into a film or sheet. Note that the polyethylene-based resin referred to here is an unmodified resin, i.e., an unmodified polyethylene-based resin, and does not fall under the adhesive thermoplastic resins such as modified polyolefin-based resins. Also excluded are those using polyolefin-based resins, such as the dispersants mentioned above.

[0083] The polyethylene resin is not particularly limited, but examples thereof include ethylene homopolymers and copolymers of ethylene with other monomers, and examples of such other monomers include α-olefins having 3 to 20 carbon atoms, such as propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, and 1-octadecene, as well as vinyl acetate, vinyl alcohol, (meth)acrylic acid, and (meth)acrylic acid esters. Here, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid (the same applies hereinafter).

[0084] Specific examples of polyethylene-based resins are the same as those listed as specific examples of the unmodified polyolefin-based resins. Specific examples include ethylene homopolymers such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), ethylene-propylene copolymers, ethylene-butene copolymers, ethylene-hexene copolymers, ethylene-octene copolymers, ethylene-propylene-butene copolymers, ethylene-propylene-hexene copolymers, ethylene-propylene-octene copolymers, ethylene-butene-hexene copolymers, ethylene-butene-octene copolymers, and ethylene-hexene-octene copolymers, as well as ethylene-based (co)polymers such as ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid copolymers, ethylene-methyl(meth)acrylate copolymers, ethylene-ethyl(meth)acrylate copolymers, and ethylene-(meth)acrylic acid-methyl(meth)acrylate copolymers. Here, "(co)polymer" is a general term for polymers and copolymers (the same applies hereinafter). Here, the ethylene copolymer means a copolymer containing ethylene in the largest amount among all the monomer units constituting the copolymer, and preferably a copolymer containing ethylene in a proportion of more than 50 mol %. These polyethylene resins can be used alone or in any combination and ratio of two or more kinds.

[0085] Among these, as the polyethylene-based resin, ethylene homopolymer, ethylene-α-olefin copolymer, and ethylene-vinyl acetate copolymer, which are ethylene-based (co)polymers, are preferred because they are inexpensive, easily available, and are economically advantageous, and from the viewpoint of improving processability, low-density polyethylene and ethylene-α-olefin copolymer are more preferred.

[0086] When the adhesive material contains a polyethylene-based resin, the proportion of the polyethylene-based resin relative to the total mass of the adhesive material is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, and is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. When the proportion of the polyethylene-based resin is equal to or greater than the lower limit, film formability can be improved. In particular, neck-in is reduced. When the proportion of the polyethylene-based resin is equal to or less than the upper limit, heat resistance is maintained. The proportion of the polyethylene-based resin relative to the total mass of the adhesive material of the present invention may be, for example, 0.5% by mass or more and 20% by mass or less, 1.0% by mass or more and 10% by mass or less, or 1.5% by mass or more and 5% by mass or less.

[0087] When the adhesive material contains a polyethylene-based resin, the ratio of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin to the total mass of the adhesive material is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and even more preferably 5% by mass or more, and is preferably 98% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less, and even more preferably 95% by mass or less. If the total mass ratio of the adhesive thermoplastic resin and the polyethylene-based resin is above the lower limit, both the adhesive strength before heating and film formability can be achieved. If the total mass ratio of the adhesive thermoplastic resin and the polyethylene-based resin is below the upper limit, excellent adhesion is achieved.

[0088] The total mass ratio of the adhesive thermoplastic resin and the polyethylene-based resin may be, for example, 2% by mass or more and 98% by mass or less, 3% by mass or more and 97% by mass or less, 4% by mass or more and 96% by mass or less, or 5% by mass or more and 95% by mass or less.

[0089] (Polypropylene-based resin) The adhesive material constituting the adhesive sheet according to the present invention may further contain a polypropylene-based resin. The inclusion of a polypropylene-based resin provides excellent adhesive properties. It also contributes to improved heat resistance and mechanical strength. Note that the polypropylene-based resin referred to here is an unmodified resin, an unmodified polypropylene-based resin, and does not fall under the adhesive thermoplastic resins such as modified polyolefin-based resins. It also excludes those using polyolefin-based resins such as the dispersants mentioned above.

[0090] The polypropylene-based resin is not particularly limited, but examples thereof include a homopolymer of propylene and a copolymer of propylene with another monomer. Examples of the other monomer include α-olefins having from 3 to 20 carbon atoms, such as ethylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, and 1-octadecene.

[0091] Specific examples of polypropylene-based resins are the same as those listed as specific examples of unmodified polyolefin-based resins. Specific examples include propylene homopolymers (propylene homopolymers), propylene-ethylene random copolymers, propylene-butene random copolymers, propylene-ethylene-hexene random copolymers, propylene-ethylene-octene random copolymers, propylene-butene-hexene random copolymers, propylene-butene-octene random copolymers, propylene-hexene-octene random copolymers, and propylene-ethylene block copolymers. Here, "(co)polymer" is a general term for polymers and copolymers (the same applies hereinafter). Here, a propylene-based copolymer refers to a copolymer that contains the largest amount of propylene among all the monomer units constituting the copolymer, and is preferably a copolymer containing propylene at a ratio of more than 50 mol%. These polypropylene-based resins can be used alone, or two or more types can be used in any combination and ratio.

[0092] Among these, as the polypropylene-based resin, propylene-based (co)polymers such as propylene homopolymer, propylene-ethylene random copolymer, and propylene-ethylene-butene copolymer are preferred because they are inexpensive, easily available, and have excellent economical properties, and from the viewpoints of adhesiveness and mechanical properties, propylene homopolymer and propylene-ethylene random copolymer are more preferred.

[0093] When the adhesive material contains a polypropylene-based resin, the proportion of the polypropylene-based resin relative to the total mass of the adhesive material is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. When the proportion of the polypropylene-based resin is equal to or greater than the lower limit, the adhesive material has excellent heat resistance, moldability, and adhesiveness. When the proportion of the polypropylene-based resin is equal to or less than the upper limit, the adhesive material has excellent releasability and adhesion to metal plates. The proportion of the polypropylene-based resin relative to the total mass of the adhesive material of the present invention may be, for example, 10% by mass or more and 95% by mass or less, 20% by mass or more and 90% by mass or less, or 30% by mass or more and 85% by mass or less.

[0094] When the adhesive material contains a polypropylene-based resin, the ratio of the total mass of the adhesive thermoplastic resin and the polypropylene-based resin to the total mass of the adhesive material is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more, and is preferably 98% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less, and even more preferably 95% by mass or less. If the total mass ratio of the adhesive thermoplastic resin and the polypropylene-based resin is above the lower limit, the adhesiveness to the metal plate is excellent. If the total mass ratio of the adhesive thermoplastic resin and the polypropylene-based resin is below the upper limit, sufficient releasability is ensured.

[0095] The total mass ratio of the adhesive thermoplastic resin and the polypropylene-based resin may be, for example, 10% by mass or more and 98% by mass or less, 20% by mass or more and 97% by mass or less, 30% by mass or more and 96% by mass or less, or 40% by mass or more and 95% by mass or less.

[0096] When the adhesive material contains a polyethylene-based resin and a polypropylene-based resin, the ratio of the total mass of the adhesive thermoplastic resin, polyethylene-based resin, and polypropylene-based resin to the total mass of the adhesive material is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 45% by mass or more, and is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 97% by mass or less, even more preferably 96% by mass or less, and particularly preferably 95% by mass or less. When the total mass ratio of the adhesive thermoplastic resin, polyethylene-based resin, and polypropylene-based resin is above the lower limit, both adhesion and film formability can be achieved. When the total mass ratio of the adhesive thermoplastic resin, polyethylene-based resin, and polypropylene-based resin is below the upper limit, sufficient releasability is ensured.

[0097] The total mass ratio of the adhesive thermoplastic resin, polyethylene-based resin, and polypropylene-based resin may be, for example, 30% by mass or more and 99% by mass or less, 35% by mass or more and 98% by mass or less, 40% by mass or more and 97% by mass or less, 45% by mass or more and 96% by mass or less, or 45% by mass or more and 95% by mass or less.

[0098] The proportion of the total mass of the adhesive thermoplastic resin, the thermally expandable material, the dispersant, and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed relative to the total mass of the adhesive material is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may even be 100% by mass. For example, when the total mass of the adhesive thermoplastic resin, the thermally expandable material, the dispersant, the polyethylene-based resin and / or the polypropylene-based resin is 100% by mass, the adhesive thermoplastic resin, the thermally expandable material (thermally expandable flame retardant and thermally expandable foaming agent), the dispersant, the polyethylene-based resin and / or the polypropylene-based resin can be appropriately selected from the above-mentioned ranges so that the total of the four or five components is 100% by mass.

[0099] (Preferred Aspect) The adhesive material constituting the adhesive sheet according to the present invention preferably contains an adhesive thermoplastic resin and a thermally expandable material. In such a case, the adhesive thermoplastic resin preferably contains a modified polyolefin resin, and the thermally expandable material preferably contains a thermally expandable flame retardant and / or a thermally expandable foaming agent. That is, the adhesive material of the present invention preferably contains a modified polyolefin resin and a thermally expandable flame retardant and / or a thermally expandable foaming agent. The adhesive material constituting the adhesive sheet according to the present invention preferably contains a dispersant in addition to the adhesive thermoplastic resin and the thermally expandable material. In such a case, the dispersant preferably contains a copolymer of an α-olefin and an unsaturated carboxylic acid.

[0100] (Foaming Agent) The adhesive material may contain a foaming agent (excluding thermally expandable foaming agents). By containing a foaming agent, a foamed layer can be formed by the foaming agent. When the adhesive material contains the above-mentioned thermally expandable flame retardant or thermally expandable foaming agent and a foaming agent, in addition to the expansion layer formed by the thermally expandable flame retardant or thermally expandable foaming agent during combustion, a foamed layer can also be formed by the foaming agent. For example, when the foaming temperature of the foaming agent is lower than the expansion temperature of the thermally expandable flame retardant or thermally expandable foaming agent, a foamed layer can be formed by the foaming agent first, followed by the expansion layer formed by the thermally expandable flame retardant or thermally expandable foaming agent, thereby more effectively exhibiting heat-shielding properties during thermal runaway.

[0101] The blowing agent is one that foams upon heating, and specific examples of the blowing agent include water; low-boiling hydrocarbons such as propane, butane, pentane, hexane, heptane, cyclopropane, cyclobutane, cyclopentane, cyclohexane, and cycloheptane; chlorinated aliphatic hydrocarbon compounds such as dichloroethane, propyl chloride, isopropyl chloride, butyl chloride, isobutyl chloride, pentyl chloride, and isopentyl chloride; trichloromonofluoromethane, trichloroisopropyl fluoride, and trichloroisopropyl fluoride; Fluorine compounds such as chlorotrifluoroethane; hydrofluorocarbons such as CHF3, CH2F2, and CH3F; dichloromonofluoroethane (for example, HCFC141b (1,1-dichloro-1-fluoroethane)), HCFC22 (chlorodifluoromethane), HCFC142b (1-chloro-1,1-difluoroethane), HFC-245fa (1,1,1,3,3-pentafluoropropane), and HFC-365mfc (1,1,1,3,3-pentafluorobutane) hydrofluoroolefin compounds such as HFO-1233zd (trans-1-chloro-3,3,3-trifluoropropene), HFO-1234yf (2,3,3,3-tetrafluoro-1-propene), and HFO-1234ze (trans-1,3,3,3-tetrafluoropropene); organic physical blowing agents such as ether compounds such as diisopropyl ether, or mixtures of these compounds; and inorganic physical blowing agents such as nitrogen gas, oxygen gas, argon gas, carbon dioxide gas, or subcritical fluids and / or supercritical fluids thereof (the above gases and their subcritical fluids / supercritical fluids may be mixed gases). Among these, water and organic physical blowing agents are preferred, and water and hydrofluoroolefin compounds are more preferred.

[0102] The content of the foaming agent is preferably in the range of 0.1 to 40 parts by mass, more preferably 0.1 to 35 parts by mass, relative to 100 parts by mass of the total mass of the adhesive thermoplastic resin and the polyethylene-based resin and / or polypropylene-based resin that may be contained as needed. When the content of the foaming agent is 0.1 part by mass or more, foaming is promoted, and when it is 40 parts by mass or less, a foam is formed.

[0103] (Other Flame Retardants or Flame Retardant Coagents) Examples of other flame retardants or flame retardant coagents include conventionally known phosphorus-based flame retardants, bromine-based flame retardants, antimony-based flame retardants, and halogen-free organic or inorganic flame retardants or flame retardant coagents other than the above-mentioned thermally expandable flame retardants. Examples of such flame retardants or flame retardant coagents include at least one selected from the group consisting of triazine ring-containing compounds, silicone-based flame retardants, metal hydroxides, metal oxides, boric acid compounds, and expandable graphite.

[0104] Examples of triazine ring-containing compounds include melamine, ammeline, benzguanamine, acetoguanamine, phthalodiguanamine, melamine cyanurate, butylenediguanamine, norbornenediguanamine, methylenediguanamine, ethylenedimelamine, trimethylenedimelamine, tetramethylenedimelamine, hexamethylenedimelamine, and 1,3-hexylenedimelamine. Examples of silicone flame retardants include silicone oil, silicone rubber, and silicone resin. Examples of metal hydroxides include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, barium hydroxide, zinc hydroxide, and Kismer 5A (a trademark of magnesium hydroxide manufactured by Kyowa Chemical Industry Co., Ltd.). Examples of metal oxides include inorganic compounds such as zinc oxide, titanium oxide, aluminum oxide, magnesium oxide, titanium dioxide, and hydrotalcite, as well as surface-treated products thereof. Specific examples of metal oxides include TIPAQUE R-680 (a trademark of titanium oxide manufactured by Ishihara Sangyo Kaisha, Ltd.), Kyowamag 150 (a trademark of magnesium oxide manufactured by Kyowa Chemical Industry Co., Ltd.), DHT-4A (hydrotalcite manufactured by Kyowa Chemical Industry Co., Ltd.), and Alkamiser 4 (a trademark of zinc-modified hydrotalcite manufactured by Kyowa Chemical Industry Co., Ltd.). Examples of boric acid compounds include zinc borate. These flame retardants or flame retardant assistants may be used alone or in combination of two or more.

[0105] (Other Components) The adhesive material may contain other components as long as they do not impair the effects of the present invention. The other components may include at least one selected from the group consisting of inorganic fiber fillers, interfacial strength improvers, antioxidants, UV absorbers, light stabilizers, and antioxidants. For example, the inorganic fiber filler may include at least one inorganic fiber filler selected from the group consisting of glass fibers and carbon fibers. One type of inorganic fiber filler may be used alone, or two or more types may be used in combination. As the interfacial strength improver, a polymer having an olefin skeleton (excluding modified polyolefin resins and copolymers) is preferred, particularly in terms of compatibility with modified polyolefin resins, which are suitable as adhesive thermoplastic resins. The compatibility of the olefin skeleton with the modified polyolefin resin further improves interfacial strength. Commercially available interfacial strength improvers include, for example, UMEX 1001 and 1010 (manufactured by Sanyo Chemical Industries, Ltd.) and KAYABRID 002PP and 003PP (manufactured by Nouryon Chemical Co., Ltd.).

[0106] Examples of antioxidants include phenol-based antioxidants, phosphorus-based antioxidants, and thioether-based antioxidants. Examples of ultraviolet absorbers include 2-hydroxybenzophenones, 2-(2'-hydroxyphenyl)benzotriazoles, benzoates, substituted oxanilides, cyanoacrylates, and triaryltriazines. Examples of light stabilizers that can be used include hindered amine-based compounds.

[0107] In addition to the above, the adhesive material may contain plasticizers, fluorine-containing anti-dripping agents, and commonly used additives such as crosslinking agents, antistatic agents, metal soaps, fillers, anti-fogging agents, anti-plate-out agents, surface treatment agents, fluorescent agents, anti-fungal agents, bactericides, foaming agents, metal deactivators, release agents, pigments, processing aids, and the like, within ranges that do not impair the effects of the present invention.

[0108] (Method for Producing Adhesive Material) Any method can be used to produce the adhesive material. For example, an adhesive thermoplastic resin, a heat-expandable flame retardant, a heat-expandable foaming agent, a dispersant, and optionally a polyethylene resin, a polypropylene resin, other flame retardants, flame retardant auxiliaries, and other components can be thoroughly mixed using a premixing means such as a V-type blender, a Henschel mixer, a mechanochemical device, or an extrusion mixer, and optionally granulated using an extrusion granulator or a briquetting machine, and then melt-kneaded and extruded in a melt kneader. The process for obtaining the adhesive material may be a one-step process in which all raw materials are fed into an extruder at once and melt-kneaded, or a two-step process in which only some of the raw materials, for example, the resin components, more specifically, the adhesive thermoplastic resin, the polyethylene resin, and the polypropylene resin, are pre-kneaded to prepare a mixture, and the mixture is then melt-kneaded with the heat-expandable flame retardant, the heat-expandable foaming agent, and the dispersant.

[0109] Examples of the melt kneader include twin-screw extruders such as vented twin-screw extruders, Banbury mixers, kneading rolls, single-screw extruders, and multi-screw extruders having three or more screws. The temperature during melt kneading is, for example, 170° C. or higher and 260° C. or lower. The adhesive material extruded as described above is directly cut and pelletized by a device such as a pelletizer, or is cooled to form strands, and then the strands are cut and pelletized by a device such as a pelletizer.

[0110] <Battery Case> The battery case in the battery pack of the present invention is not particularly limited, but the resin battery casing (hereinafter sometimes referred to as "resin casing") is not particularly limited, and at least one of a thermosetting resin and a thermoplastic resin can be used. Of these, a thermoplastic resin is particularly preferred. That is, the resin casing is preferably made of a molded article containing a thermoplastic resin. Examples of thermoplastic resins include polyolefin resin, polycarbonate resin, polyester resin, acrylonitrile-styrene resin, ABS resin, polyamide resin, and modified polyphenylene oxide. In particular, at least one selected from polypropylene, polyethylene terephthalate, and nylon is preferred, and polypropylene is more preferred.

[0111] The thickness of the resin casing is not particularly limited, but is, for example, 5 μm or more and 200 μm or less. Furthermore, the resin casing is sealed (sealed) within the casing by joining the peripheral portions of two exterior bodies into a ring shape by heat fusion, adhesive, or the like. Alternatively, one resin casing may be folded and the peripheral portions joined by heat fusion, adhesive, or the like to seal (seal) the liquid and insulating material. The resin casing is preferably flexible (elastic), but may not be flexible. It is preferable that the internal air pressure of the resin casing be lower than the external air pressure in order to sufficiently increase the opening temperature. Therefore, it is particularly preferable to vacuum seal the resin casing.

[0112] <Cooling Plate> The cooling plate in the battery pack of the present invention is not particularly limited and may be made of either resin or metal, but a metal plate is preferably used from the viewpoint of heat transfer efficiency. The metal plate is not particularly limited as long as it is a metal generally used as a cooling plate for a battery, and metals with high thermal conductivity, such as SUS, aluminum, and copper, are preferably used. The thickness of the metal plate is preferably in the range of 0.5 mm to 5 mm, and more preferably in the range of 1 mm to 3 mm. When the thickness is equal to or greater than the lower limit, sufficient heat conduction is achieved, resulting in a sufficient cooling effect for the battery cells. On the other hand, when the thickness is equal to or less than the upper limit, it is preferable from the viewpoint of reducing the weight of the battery.

[0113] <Battery Cell> The battery cell in the battery pack of the present invention is not particularly limited, but is usually configured by housing a positive electrode, a negative electrode, a separator, and an electrolyte solution in the battery cell. Examples of the material for the battery cell include metals such as iron, aluminum, and aluminum alloys; laminate films, etc. From the viewpoints of weight reduction and cost, metals and laminate films are preferred as the material for the battery cell, and iron is more preferred from the viewpoint of pressure resistance.

[0114] The positive electrode contains a positive electrode active material on at least a portion of the surface of a current collector. The positive electrode active material is not particularly limited as long as it is capable of electrochemically absorbing and releasing metal ions.

[0115] Examples of positive electrode active materials include lithium transition metal compounds, sodium transition metal compounds, and potassium transition metal compounds. One type of positive electrode active material may be used alone, or two or more types may be used in any ratio and combination. From the viewpoint of increasing the energy density of the battery, the positive electrode active material is preferably a lithium transition metal compound, a sodium transition metal compound, or a potassium transition metal compound, more preferably a lithium transition metal compound, and even more preferably a lithium transition metal composite oxide. Examples of the structure of the lithium transition metal composite oxide include a spinel structure, an olivine structure, and a layered structure. From the viewpoint of battery capacity and durability, the structure of the lithium transition metal composite oxide is preferably a spinel structure, an olivine structure, or a layered structure, and from the viewpoint of increasing battery capacity, a layered structure is more preferred.

[0116] Examples of materials for the positive electrode current collector include metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, etc. From the viewpoint of increasing the energy density of the battery, aluminum is preferred as the material for the positive electrode current collector.

[0117] The negative electrode includes a negative electrode active material on at least a portion of the surface of a current collector. The negative electrode active material is not particularly limited as long as it is capable of electrochemically absorbing and releasing metal ions.

[0118] Examples of negative electrode active materials include carbon-based materials and metal materials. The negative electrode active material may be used alone, or two or more types may be used in any ratio and combination. From the viewpoints of cycle characteristics and continuous charging characteristics, the negative electrode active material is preferably a carbon-based material, a metal material, or a mixture of a carbon-based material and a metal material. Examples of carbon-based materials that can be used as the negative electrode active material include natural graphite such as uncoated natural graphite, amorphous carbon-coated natural graphite, graphite-coated natural graphite, and resin-coated natural graphite; artificial graphite; and amorphous carbon. One type of carbon-based material may be used alone, or two or more types may be used in any ratio and combination. Natural graphite is preferred from the viewpoint of increasing battery capacity. Examples of natural graphite include scaly natural graphite, scaly natural graphite, and natural graphite obtained by subjecting such graphite to spheroidization or densification. One type of natural graphite may be used alone, or two or more types may be used in any ratio and combination. The natural graphite is preferably spherical natural graphite from the viewpoints of packing property and charge / discharge rate characteristics. The metal material serving as the negative electrode active material is a material containing a metal element and / or a metalloid element that can be alloyed with an alkali metal, and from the viewpoint of increasing capacity, silicon, silicon oxide, and oxide of silicon carbide are preferred.

[0119] Examples of the material for the negative electrode current collector include metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, etc. Copper is preferred as the material for the negative electrode current collector because it does not alloy with alkali metals and is inexpensive.

[0120] The separator is preferably made of polyethylene, polypropylene, cellulose, or polyvinylidene fluoride, more preferably polyethylene or polypropylene. The separator is preferably in the form of a porous film or nonwoven fabric, more preferably a porous film.

[0121] The electrolytic solution usually contains an electrolyte and a non-aqueous solvent. From the viewpoint of increasing solubility, the electrolyte is preferably an alkali metal salt, more preferably a lithium salt, a sodium salt, or a potassium salt, and from the viewpoint of improving cycle characteristics, a lithium salt is even more preferable. Examples of the lithium salt include lithium fluoroborate salt, lithium fluorophosphate salt, lithium tungstate salt, lithium carboxylate salt, lithium sulfonate salt, lithium imide salt, lithium methide salt, lithium oxalate salt, and fluorine-containing organic lithium salt. One type of lithium salt may be used alone, or two or more types may be used in any ratio and combination. From the viewpoint of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, and cycle characteristics, the lithium salt is preferably LiBF ４ , LiPF ６ , Li ２ P.O. ３ F, LiPO ２ F ２ , LiFSO ３ , C.H. ３ SO ３ Li, CF ３ SO ３ Li, C.H. ３ SO ４ Li, CF ３ SO ４ Li, C ２ H ５ SO ４ Li, C ２ F ５ SO ４ Li, C ３ H ５ SO ４ Li, C ３ H ３ SO ４ Li, LiN (FSO ２ ) ２ , LiN(FSO ２ ) (CF ３ SO ２ ), LiN(CF ３ SO ２ ) ２ , LiN(C ２ F ５ SO ２ ) ２, lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC(FSO ２ ) ３ , LiC(CF ３ SO ２ ) ３ , LiC(C ２ F ５ SO ２ ) ３ , lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate are preferred, and from the viewpoint of further improving low-temperature output characteristics, high-rate charge-discharge characteristics, impedance characteristics, high-temperature storage characteristics, and cycle characteristics, LiBF ４ , LiPF ６ , LiPO ２ F ２ , LiN(FSO ２ ) ２ , lithium bis(oxalato)borate, LiFSO ３ is more preferable, and from the viewpoint of further improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, and cycle characteristics, LiPF ６ is more preferable.

[0122] The non-aqueous solvent is preferably an organic solvent from the viewpoint of suppressing oxidation-reduction decomposition in the battery. Examples of the organic solvent include saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, cyclic carboxylic acid esters, ether-based compounds, and sulfone-based compounds. One organic solvent may be used alone, or two or more organic solvents may be used in any ratio and combination. From the viewpoint of suppressing oxidation-reduction decomposition in the battery, saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, cyclic carboxylic acid esters, ether-based compounds, and sulfone-based compounds are preferred as the organic solvent, with saturated cyclic carbonates, chain carbonates, and chain carboxylic acid esters being more preferred.

[0123] The electrolytic solution may contain other compounds in addition to the electrolyte and the non-aqueous solvent. Examples of the other compounds include unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, isocyanate group-containing organic compounds, isocyanuric acid skeleton-containing organic compounds, sulfur-containing organic compounds, phosphorus-containing organic compounds, silicon-containing compounds, aromatic compounds, cyano group-containing organic compounds, acid anhydride compounds, and triple bond-containing compounds. One type of the other compounds may be used alone, or two or more types may be used in any ratio and combination. From the viewpoint of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, and cycle characteristics, the other compounds are preferably unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, isocyanate group-containing organic compounds, isocyanuric acid skeleton-containing organic compounds, sulfur-containing organic compounds, phosphorus-containing organic compounds, silicon-containing compounds, aromatic compounds, cyano group-containing organic compounds, acid anhydride compounds, and triple bond-containing compounds, more preferably unsaturated cyclic carbonates, fluorine-containing cyclic carbonates, isocyanate group-containing organic compounds, and isocyanuric acid skeleton-containing organic compounds, and even more preferably unsaturated cyclic carbonates and fluorine-containing cyclic carbonates.

[0124] [Use of Adhesive Sheet] A first aspect of the use of the adhesive sheet of the present invention is use of the adhesive sheet in a battery pack having battery cells, a cooling plate, and a battery case that stores the battery cells and the cooling plate, the battery pack including an adhesive sheet that adheres the battery cells and the cooling plate, wherein the adhesive sheet is characterized in that when heated at 285°C for 5 minutes, the decrease in thermal diffusivity before and after heating, as expressed by the following formula (1), is 4.5% or more: ((thermal diffusivity before heating - thermal diffusivity after heating) / thermal diffusivity before heating) x 100 ... (1) By having the decrease in thermal diffusivity before and after heating be 4.5% or more, preferably 5% or more, more preferably 7% or more, even more preferably 10% or more, particularly preferably 13% or more, and especially preferably 20% or more, when a battery cell becomes abnormally hot, heat is less likely to be conducted from the abnormally hot battery cell to the cooling plate, and adverse effects will not be exerted on other battery cells via the cooling plate. In other words, the diffusion of heat from an abnormally high temperature battery cell to other battery cells is suppressed, preventing a chain reaction of battery cells becoming hotter, and so-called thermal runaway can be suppressed.

[0125] A second aspect of the use of the adhesive sheet of the present invention is its use as the adhesive sheet in a battery pack similar to the first aspect described above, characterized in that the adhesive sheet exhibits a decrease in adhesive strength of 15% or more before and after heating at 285°C for 5 minutes, as expressed by the following formula (2): ((Adhesive strength before heating - Adhesive strength after heating) / Adhesive strength before heating) x 100 (2) When the decrease in adhesive strength before and after heating is 15% or more, preferably 20% or more, more preferably 25% or more, even more preferably 30% or more, particularly preferably 35% or more, particularly preferably 50% or more, and most preferably 60% or more, when a battery cell becomes abnormally hot, the adhesion between the abnormally hot battery cell and the cooling plate decreases, and no adverse effects are exerted on other battery cells through the cooling plate. In other words, the diffusion of heat from an abnormally hot battery cell to other battery cells is suppressed, preventing a chain reaction of battery cell temperatures and so-called thermal runaway. In addition, when the battery cells are bonded together with an adhesive sheet, the reduction in adhesive strength suppresses the diffusion of heat between the battery cells, thereby preventing thermal runaway.

[0126] As described above, the first and second aspects have different mechanisms of action, but both suppress heat conduction from battery cells that have reached abnormally high temperatures. Therefore, although the effects of the present invention can be achieved with only the first or second aspect, it is more preferable from the standpoint of effectiveness that both the first and second aspects function.

[0127] As described above, the adhesive sheet according to the present invention is used as an adhesive sheet for bonding battery cells and a cooling plate, thereby providing excellent thermal conductivity under normal conditions and heat insulation that thermally insulates the battery cells from the cooling plate in the event of thermal runaway, thus combining contradictory properties. Another preferred embodiment of the adhesive sheet according to the present invention is when the adhesive sheet is provided between battery cells to bond the battery cells together. If a battery cell becomes abnormally hot for some reason, the adhesive strength of the adhesive sheet decreases, reducing the adhesion between the battery cells. This makes it difficult for heat to be conducted from the abnormally hot battery cell to adjacent battery cells, thereby preventing adverse effects on the other battery cells. The adhesive sheet, including its preferred ranges, is similar to the adhesive sheet described above.

[0128] The present invention will be described in detail below using examples, but the present invention is not limited to these examples. In particular, the process for obtaining the adhesive material of the present invention may be a one-step process in which all raw materials are fed into an extruder at once and melt-kneaded, or a two-step process in which only some of the raw materials, for example, resin components (adhesive thermoplastic resin, polyethylene-based resin, polypropylene-based resin), are pre-kneaded to prepare a mixture, and this mixture is then melt-kneaded with a thermally expandable material and a dispersant as raw materials.

[0129] (Evaluation Method) 1. Thermal Diffusivity Reduction Rate The thermal diffusivity was measured before and after heating by the following method, and the reduction rate of the thermal diffusivity before and after heating was calculated. (Thermal Diffusivity) For the thermal diffusivity test piece described below, the thermal diffusivity was measured in the thickness direction of the thermal diffusivity test piece at a measurement temperature of 25°C by the laser flash method using a Xe flash analyzer LFA447 Nanoflash manufactured by Netsch Japan Co., Ltd., and the result was used as the thermal diffusivity before heating. The thermal diffusivity (mm ２Since there are no JIS standards for the thermal diffusivity and thermal conductivity of resin-based materials, JIS R1611:2010 (Method for measuring thermal diffusivity, specific heat capacity, and thermal conductivity of fine ceramics by the flash method) was used as reference. Since the standard stipulates that "the sample thickness shall be 0.5 mm or more and 5 mm or less," the thickness of the test piece was set to 1.0 mm, as described below. Next, the thermal diffusivity test piece was heated at 285°C for 5 minutes and held at room temperature (25°C) overnight, after which the thermal diffusivity was measured in the same manner as above, and this was taken as the thermal diffusivity after heating. (Reduction in thermal diffusivity) The reduction in thermal diffusivity was calculated based on the following formula (1): Reduction in thermal diffusivity (%) = ((thermal diffusivity before heating - thermal diffusivity after heating) / thermal diffusivity before heating) x 100 (1)

[0130] 2. Adhesion Strength Reduction Rate The adhesion strength before and after heating was measured using the following method, and the reduction rate of the adhesion strength before and after heating was calculated. (Adhesion Strength) An adhesion test piece described below was sandwiched between an aluminum plate (Standard Test Plate A5052P, Nippon Test Panel Co., Ltd.) measuring 100 mm in length, 25 mm in width, and 1.6 mm in thickness, and press-bonded at 160°C. The peel strength between the adhesion test piece and the aluminum plate was measured using an Inteslon 200X universal testing machine in accordance with JIS K6850-1999 <Test Method for Tensile Shear Adhesion Strength of Adhesives - Rigid Adherends>. Measurements were performed three times for each sample, and the average value was used as the adhesion strength before heating. Next, the adhesion test piece sandwiched between the aluminum plates was heated at 285°C for 5 minutes, held at room temperature (25°C) overnight, and then the peel strength was measured in the same manner as above. Measurements after heating were also performed three times for each sample, and the average value was used as the adhesion strength after heating. (Decrease in Adhesive Strength) The decrease in adhesive strength was calculated based on the following formula (2): Decrease in adhesive strength (%) = ((Adhesive strength before heating - Adhesive strength after heating) / Adhesive strength before heating) × 100 (2)

[0131] 3. Expansion Evaluation A test piece for thermal diffusivity measurement, which will be described later, was heated at 285°C for 5 minutes and then held at room temperature (25°C) overnight. The length, width, and thickness of the test piece for thermal diffusivity measurement were then measured to calculate the volume. Note that test pieces containing a thermally expandable material formed a fine expansion layer / foam layer upon heating at 285°C for 5 minutes. It is believed that the higher the expansibility of the test piece, the greater the proportion of the expansion layer / foam layer, and therefore the greater the heat conduction suppression effect. A (excellent): The sample volume after heating was 2.0 times or more the sample volume before heating. B (good): The sample volume after heating was more than 1.5 times but less than 2.0 times the sample volume before heating. C (poor): The sample volume after heating was 1.5 times or less the sample volume before heating.

[0132] (Raw Materials for Adhesive Sheet) (A-1) Modified Polyolefin Resin A modified polyolefin resin consisting of a binary copolymer obtained by graft polymerizing maleic acid onto a polyolefin resin ("Modic X2036H" manufactured by Mitsubishi Chemical Corporation, MFR (180°C, load 2.16 kg, 1 mm diameter orifice): 0.5 g / 10 min, melting point: 125°C). (A-2) Modified Polyolefin Resin A modified propylene polymer obtained by graft-modifying a commercially available propylene homopolymer [MFR (230°C, load 2.16 kg, 2 mm diameter orifice): 10.0 g / 10 min, melting point: 162°C] with maleic anhydride [modification rate (graft rate): 2.5 mass%, MFR (180°C, load 2.16 kg, 1 mm diameter orifice): 300 g / 10 min, melting point: 158°C]. (A-3) Modified Polyolefin Resin A modified propylene polymer obtained by graft-modifying 56% by mass of a commercially available propylene-ethylene random copolymer [MFR (230°C, load 2.16 kg, 2 mm diameter orifice): 7 g / 10 min, melting point: 135°C] and 44% by mass of a commercially available propylene-ethylene random copolymer [MFR (230°C, load 2.16 kg, 2 mm diameter orifice): 8 g / 10 min, melting point: 59°C] with maleic anhydride [modification rate (graft rate): 0.9% by mass, MFR (180°C, load 2.16 kg, 1 mm diameter orifice): 8 g / 10 min, melting point: 132°C] (A-4) Modified Polyolefin Resin A modified propylene polymer [modification ratio (graft ratio): 0.9 mass%, MFR (180°C, load 2.16 kg, 1 mm diameter orifice): 11 g / 10 min, melting point: 136°C] obtained by graft-modifying 60 mass% of a commercially available propylene-ethylene random copolymer [MFR (230°C, load 2.16 kg, 2 mm diameter orifice): 30 g / 10 min, melting point: 143°C], 20 mass% of a commercially available propylene-ethylene random copolymer [MFR (230°C, load 2.16 kg, 2 mm diameter orifice): 7 g / 10 min, melting point: 135°C], and 20 mass% of a commercially available propylene-ethylene random copolymer [MFR (230°C, load 2.16 kg, 2 mm diameter orifice): 3 g / 10 min, melting point: 95°C] with maleic anhydride.

[0133] (B-a) Thermally Expandable Flame Retardant: Phosphorus-based flame retardant (ADEKA CORPORATION, Adeka STAB FP-2500S, an intumescent flame retardant containing 50 to 60% by mass of piperazine pyrophosphate, 35 to 45% by mass of melamine pyrophosphate, and 3 to 6% by mass of zinc oxide, relative to the total mass of the phosphorus-based flame retardant composition). (B-b) Thermally Expandable Foaming Agent: Thermally expandable microcapsules containing a foaming component (hydrocarbon) inside an acrylic resin (in the examples, Kureha Microsphere MB-S6LC, manufactured by Kureha Corporation, was used. However, MB-S6LC is a masterbatch of the thermally expandable foaming agent and low-density polyethylene (LDPE: (D-2) polyethylene resin), and MB-S6LC contains 50% by mass of the thermally expandable foaming agent relative to its total mass).

[0134] (C) Dispersant: α-olefin / maleic anhydride copolymer (manufactured by Mitsubishi Chemical Corporation, Diacarna 30M, weight average molecular weight 7,800)

[0135] (D-1) Polyethylene resin: Low density polyethylene [MFR (190°C, load 2.16 kg, 2 mm diameter orifice): 4 g / 10 min, melting point: 107°C] (D-2) Polyethylene resin: Low density polyethylene (LDPE)

[0136] (E-1) Polypropylene-based resin Propylene homopolymer [MFR (230 ° C, load 21.2 N, orifice 2 mm diameter): 11.0 g / 10 min, melting point: 170 ° C] (E-2) Polypropylene-based resin Propylene-ethylene random copolymer [MFR (230 ° C, load 21.2 N, orifice 2 mm diameter): 20 g / 10 min, melting point: 145 ° C] (E-3): Polypropylene-based resin Propylene-ethylene random copolymer [MFR (230 ° C, load 21.2 N, orifice 2 mm diameter): 2 g / 10 min, melting point: 125 ° C] (E-4): Polypropylene-based resin Propylene-ethylene random copolymer [MFR (230 ° C, load 21.2 N, orifice 2 mm diameter): 3 g / 10 min, melting point: 95 ° C]

[0137] Example 1 The above-mentioned (A-1) modified polyolefin resin, (B-a) thermally expandable flame retardant, and (C) dispersant were mixed by hand blending so that the ratio of each raw material was as shown in Table 1 below. Thereafter, the mixture was melt-kneaded using a φ30 mm co-rotating twin-screw extruder (model name "BT-30", manufactured by Plastics Engineering Research Institute Co., Ltd., L / D = 30) at a screw rotation speed of 250 rpm and a cylinder temperature of 200°C to obtain a pellet-shaped adhesive material (hereinafter sometimes referred to as the present pellets). Note that "L / D" indicates the ratio of the screw length (L) to the screw diameter (D). Next, the following molded articles (adhesive sheets) were produced using the present pellets, and various evaluations were performed. The evaluation results are shown in Table 1.

[0138] The obtained pellets were press-molded using a 40-ton high-performance, high-temperature vacuum press (model "VH1-1747", manufactured by Kitagawa Seiki Co., Ltd.) at a molding temperature of 200°C and a molding pressure of 3.0 MPa to obtain an adhesive sheet (length 200 mm x width 150 mm x thickness 1.0 mm). A 10 mm length x 10 mm width specimen was cut from this adhesive sheet and used as a thermal diffusivity test piece. The obtained pellets were press-molded using a 40-ton high-performance, high-temperature vacuum press (model "VH1-1747", manufactured by Kitagawa Seiki Co., Ltd.) at a molding temperature of 200°C and a molding pressure of 3.0 MPa to obtain an adhesive sheet (length 200 mm x width 150 mm x thickness 1.6 mm). A 12.5 mm length x 25 mm width strip was cut from this adhesive sheet and used as an adhesive strength test piece.

[0139] Example 2: 8% by mass of (A-2) modified polyolefin resin, 5% by mass of (D-1) polyethylene resin, 5% by mass of (E-1) polypropylene resin, and 82% by mass of (E-2) polypropylene resin were mixed in advance by dry blending, and melt-kneaded using a twin-screw extruder TEX25 (manufactured by JSW Corporation) at a temperature of 200°C, a screw rotation speed of 300 rpm, and an extrusion rate of 20 kg / h. The mixture was extruded into a strand, cooled, and then cut to obtain a pellet-shaped mixture. Subsequently, a molded article (adhesive sheet) was produced in the same manner as in Example 1, except that this mixture was used instead of (A-1), and various evaluations were performed. The final adhesive material composition and the evaluation results are shown in Table 1.

[0140] Example 3 A molded article (adhesive sheet) was produced and evaluated in the same manner as in Example 1, except that 89.5% by mass of (A-1) modified polyolefin resin, 10% by mass of MB-S6LC (i.e., 5% by mass of (B-b) thermally expandable foaming agent and 5% by mass of (D-2) polyethylene resin LDPE), and 0.5% by mass of (C) dispersant were used. The final composition of the adhesive material and the evaluation results are shown in Table 1.

[0141] Example 4: 8% by mass of (A-2) modified polyolefin resin, 5% by mass of (D-1) polyethylene resin, 5% by mass of (E-1) polypropylene resin, and 82% by mass of (E-2) polypropylene resin were mixed in advance by dry blending, and melt-kneaded using a twin-screw extruder TEX25 (manufactured by JSW Corporation) at a temperature of 200 ° C., a screw rotation speed of 300 rpm, and an extrusion rate of 20 kg / h. The mixture was extruded into a strand, cooled, and then cut to obtain a pellet-shaped mixture. Subsequently, a molded product (adhesive sheet) was produced in the same manner as in Example 3, except that this mixture was used instead of (A-1), and various evaluations were performed. The final composition of the easily dismantlable adhesive material and its evaluation results are shown in Table 1.

[0142] Example 5: (A-2) 3% by mass of modified polyolefin resin, (A-3) 15% by mass of modified polyolefin resin, (D-1) 10% by mass of polyethylene resin, (E-3) 20% by mass of polypropylene resin, and (E-4) 52% by mass of polypropylene resin were mixed in advance by dry blending, and melt-kneaded using a twin-screw extruder TEX25 (manufactured by JSW Corporation) at a temperature of 200 ° C., a screw rotation speed of 300 rpm, and an extrusion rate of 20 kg / h. The mixture was extruded into a strand, cooled, and then cut to obtain a pellet-shaped mixture. Subsequently, a molded product (adhesive sheet) was produced in the same manner as in Example 3, except that this mixture was used instead of (A-1), and various evaluations were performed. The final composition of the easily dismantlable adhesive material and its evaluation results are shown in Table 1.

[0143] Example 6: 30% by mass of (A-4) modified polyolefin resin, 10% by mass of (D-1) polyethylene resin, 15% by mass of (E-3) polypropylene resin, and 45% by mass of (E-4) polypropylene resin were mixed in advance by dry blending, and melt-kneaded using a twin-screw extruder TEX25 (manufactured by JSW Corporation) at a temperature of 200 ° C., a screw rotation speed of 300 rpm, and an extrusion rate of 20 kg / h. The mixture was extruded into a strand, cooled, and then cut to obtain a pellet-shaped mixture. Subsequently, a molded product (adhesive sheet) was produced in the same manner as in Example 3, except that the mixture was used instead of (A-1), and various evaluations were performed. The final composition of the easily dismantlable adhesive material and the evaluation results are shown in Table 1.

[0144] Comparative Example 1 A molded article (adhesive sheet) was produced using 100% by mass of the (A-1) modified polyolefin resin, and various evaluations were carried out. The final composition of the easily dismantlable adhesive material and the evaluation results are shown in Table 1.

[0145] Comparative Example 2 (A-2) modified polyolefin resin 8% by mass, (D-1) polyethylene resin 5% by mass, (E-1) polypropylene resin 5% by mass, and (E-2) polypropylene resin 82% by mass were mixed in advance by dry blending, and melt-kneaded using a twin-screw extruder TEX25 (manufactured by JSW Corporation) at a temperature of 200 ° C., a screw rotation speed of 300 rpm, and an extrusion rate of 20 kg / h. The mixture was extruded into a strand, cooled, and then cut to obtain a pellet-shaped mixture. Subsequently, a molded body (adhesive sheet) was produced using 100% by mass of the mixture, and various evaluations were performed. The final composition of the easily dismantlable adhesive material and the evaluation results are shown in Table 1.

[0146]

[0147] The battery pack of the present invention has contradictory properties of good thermal conductivity under normal conditions and excellent insulation properties in the event of thermal runaway. When used as a battery material, it is excellent in terms of battery efficiency and safety, and is of great industrial value.

[0148] REFERENCE SIGNS LIST 1 battery pack 11 battery cell 12 spacer 13 adhesive sheet 14 cooling plate (metal plate) 15 battery case

Claims

1. A battery pack having a battery cell, a cooling plate, and a battery case storing the battery cell and the cooling plate, comprising an adhesive sheet for adhering the battery cell and the cooling plate, the adhesive sheet having a thermal diffusivity decrease rate of 4.5% or more before and after heating at 285°C for 5 minutes, as shown in the following formula (1): ((thermal diffusivity before heating - thermal diffusivity after heating) / thermal diffusivity before heating) x 100 ... (1) 2. A battery pack having a battery cell, a cooling plate, and a battery case storing the battery cell and the cooling plate, comprising an adhesive sheet for adhering the battery cell and the cooling plate, the adhesive sheet having a rate of decrease in adhesive strength before and after heating, as shown in the following formula (2), of 15% or more when heated at 285°C for 5 minutes: ((adhesive strength before heating - adhesive strength after heating) / adhesive strength before heating) x 100 ... (2) 3. The battery pack according to claim 1 or 2, wherein the adhesive sheet comprises an adhesive material.

4. The battery pack according to claim 3, wherein the adhesive material includes a modified polyolefin resin.

5. The battery pack according to claim 3, wherein the adhesive material includes a thermally expandable flame retardant and / or a thermally expandable foaming agent.

6. The battery pack according to claim 4, wherein the modified polyolefin resin is graft-modified with an unsaturated carboxylic acid and / or a derivative thereof.

7. The battery pack according to claim 5, wherein the thermally expandable flame retardant comprises a phosphorus-based flame retardant.

8. The battery pack according to claim 5, wherein the thermally expandable flame retardant includes an intumescent flame retardant.

9. The battery pack according to claim 5, wherein the thermally expandable foaming agent includes a chemical foaming agent and / or a physical foaming agent, and a thermoplastic resin capsule that encapsulates the chemical foaming agent and / or the physical foaming agent.

10. The battery pack of claim 5, wherein the adhesive material further comprises a dispersant.

11. The battery pack of claim 10, wherein the dispersant comprises a copolymer of an α-olefin and an unsaturated carboxylic acid.

12. The battery pack according to claim 4, wherein the adhesive material further includes a polyethylene-based resin and / or a polypropylene-based resin.

13. The battery pack according to claim 1 or 2, wherein the adhesive sheet is further provided between the battery cells to adhere the battery cells to each other.

14. The battery pack according to claim 1 or 2, wherein the battery case is a plastic housing.

15. Use of an adhesive sheet in a battery pack having a battery cell, a cooling plate, and a battery case storing the battery cell and the cooling plate, the battery pack including an adhesive sheet for adhering the battery cell and the cooling plate, the adhesive sheet having a thermal diffusivity decrease rate of 4.5% or more before and after heating, as shown in the following formula (1), when heated at 285°C for 5 minutes: ((thermal diffusivity before heating - thermal diffusivity after heating) / thermal diffusivity before heating) x 100 ... (1) 16. Use of an adhesive sheet in a battery pack having a battery cell, a cooling plate, and a battery case storing the battery cell and the cooling plate, the battery pack including an adhesive sheet for adhering the battery cell and the cooling plate, the adhesive sheet having a rate of decrease in adhesive strength before and after heating, as shown in the following formula (2), of 15% or more when heated at 285°C for 5 minutes: ((adhesive strength before heating - adhesive strength after heating) / adhesive strength before heating) x 100 ... (2) 17. Use of the adhesive sheet according to claim 15 or 16, wherein the adhesive sheet comprises an adhesive material.

18. Use of the adhesive sheet according to claim 17, wherein the adhesive material comprises a modified polyolefin resin.

19. Use of the adhesive sheet according to claim 17, wherein the adhesive material comprises a thermally expandable flame retardant and / or a thermally expandable foaming agent.

20. Use of the adhesive sheet according to claim 18, wherein the modified polyolefin resin is graft-modified with an unsaturated carboxylic acid and / or a derivative thereof.

21. Use of the adhesive sheet according to claim 19, wherein the thermally expandable flame retardant comprises a phosphorus-based flame retardant.

22. Use of the adhesive sheet according to claim 19, wherein the thermally expandable flame retardant comprises an intumescent flame retardant.

23. Use of the adhesive sheet according to claim 19, wherein the thermally expandable foaming agent comprises a chemical foaming agent and / or a physical foaming agent, and a thermoplastic resin capsule that encapsulates these.

24. Use of the adhesive sheet according to claim 19, wherein the adhesive material further comprises a dispersing agent.

25. Use of the adhesive sheet according to claim 24, wherein the dispersing agent comprises a copolymer of an α-olefin and an unsaturated carboxylic acid.

26. Use of the adhesive sheet according to claim 18, wherein the adhesive material further comprises a polyethylene-based resin and / or a polypropylene-based resin.

27. Use of the adhesive sheet according to claim 15 or 16, wherein the adhesive sheet is further provided between battery cells to adhere the battery cells to each other.

28. Use of the adhesive sheet according to claim 15 or 16, wherein the battery case is a plastic housing.

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