Adhesive composition or two-component curing adhesive

Abstract

The present invention provides an adhesive composition that exhibits high adhesion to metal bodies such as battery casings, high heat dissipation, excellent vibration damping properties, high stability even at high temperatures, and excellent lightweight properties. [Solution] An adhesive composition comprising a polymerizable (meth)acrylic monomer (A) containing a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), an elastomer component (B), an organic peroxide (C), a reducing agent (D), and aluminum hydroxide particles (E) having an average particle size of 30 μm or more and less than 100 μm.

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition or a two-component curable adhesive. [Background Art]

[0002] In recent years, electric vehicles using batteries such as lithium-ion secondary batteries have become widespread. Since a battery used in an electric vehicle has a configuration in which a plurality of cells are connected, it is important to control heat generation accompanying charging and discharging. For example, when a lithium-ion secondary battery is exposed to abnormal environments such as overcharging, short circuiting, reverse connection, and heat exposure, the internal pressure and temperature of the battery rapidly increase, creating a risk of explosion and fire. Therefore, for electric vehicle batteries using lithium-ion secondary batteries, heat dissipation measures to cool the battery are implemented, such as fixing battery cells to a cooling plate using an adhesive, and thermal management of the battery is performed.

[0003] As an adhesive for fixing a battery to a cooling plate, high adhesiveness to metals such as battery outer casings and cooling plates is required, and when the battery is a lithium-ion secondary battery, flame retardancy is also required. In view of this, Patent Document 1 discloses a flame-retardant adhesive composition containing a polymerizable vinyl monomer, a polymerization initiator, a reducing agent, a phosphate, and a metal hydroxide as a flame-retardant resin composition suitable for bonding metals.

[0004] Furthermore, as an adhesive for fixing a battery to a cooling plate, an adhesive having high thermal conductivity and excellent heat dissipation is required in order to promote efficient heat dissipation to the cooling plate. In view of this, Patent Document 2 discloses a curable resin composition having high thermal conductivity, which contains a (meth)acrylic acid ester monomer, an organic peroxide, a decomposition accelerator for the organic peroxide, and an inorganic filler. [Prior Art Literature] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-271037 [Patent Document 2] International Publication No. 2005 / 061615 [Overview of the project] [Problems that the invention aims to solve]

[0006] Thus, adhesives used to secure electric vehicle batteries require high adhesion to metals such as the battery casing and cooling plates, and high thermal conductivity to efficiently dissipate heat from the battery to the cooling plates. Furthermore, since electric vehicle batteries are used for long periods in environments with a lot of vibration, they need to have vibration resistance (flexibility) to dampen vibrations, and a high glass transition temperature and high heat resistance at high temperatures so that the strength of the adhesive does not decrease even when the battery generates heat and the adhesive becomes hot. Furthermore, since electric vehicles and similar vehicles require a large number of battery cells because the total energy capacity of the battery affects the driving range, a large amount of adhesive is used to fix these battery cells to the cooling plate. The weight increase due to the adhesive leads to a decrease in the energy efficiency of electric vehicles, so there is a demand for adhesives with a low specific gravity and excellent lightweight properties. However, adhesives with the compositions described in the aforementioned Patent Documents 1-2 could not fully satisfy the above performance requirements, and there was a need for an adhesive composition that could satisfy the above performance requirements and be suitably used for fixing electric vehicle batteries.

[0007] The present invention aims to provide an adhesive composition and a two-component curing adhesive that exhibit high adhesion to metal bodies such as battery casings, high heat dissipation, excellent vibration damping properties, high heat resistance at high temperatures, and excellent lightweight properties. [Means for solving the problem]

[0008] The present invention is essentially an adhesive composition described in any of the following (1) to (9). (1) An adhesive composition comprising: (1) a polymerizable (meth)acrylic monomer (A) containing a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3); an elastomer (B); an organic peroxide (C); a reducing agent (D); and aluminum hydroxide particles (E) having an average particle size of 30 μm or more and less than 100 μm. (2) The adhesive composition according to (1) above, wherein the aluminum hydroxide particles (E) are contained in an amount of 40% by weight or more and 65% by weight or less of the total adhesive composition. (3) The adhesive composition according to (1) above, wherein the polymerizable (meth)acrylic monomer (A) comprises the polyfunctional (meth)acrylate (a1) in an amount of 5% by weight or more and 40% by weight or less, the hydroxyalkyl (meth)acrylate (a2) in an amount of 30% by weight or more and 85% by weight or less, and the alkyl (meth)acrylate (a3) ​​in an amount of 10% by weight or more and 50% by weight or less. (4) The adhesive composition according to (1) above, wherein the polyfunctional (meth)acrylate (a1) is a compound having multiple uncondensed aromatic rings. (5) The adhesive composition according to (1) above, wherein the hydroxyalkyl (meth)acrylate (a2) is a compound in which the hydroxyalkyl group has 3 or fewer carbon atoms. (6) The adhesive composition according to (1) above, wherein the alkyl (meth)acrylate (a3) ​​is a compound in which the alkyl group has 8 or more carbon atoms. (7) The adhesive composition according to (1) above, wherein the elastomer (B) is one or more selected from butadiene polymer, (meth)acrylonitrile-butadiene-(meth)acrylic acid copolymer, (meth)acrylonitrile-butadiene-methyl(meth)acrylate copolymer, methyl(meth)acrylate-butadiene-(meth)acrylonitrile-styrene copolymer, butadiene-styrene-methyl(meth)acrylate copolymer, and (meth)acrylonitrile-butadiene rubber, linear polyurethane, and styrene-butadiene. (8) The adhesive composition according to (1) above, wherein the aluminum hydroxide particles (E) contain two types of aluminum hydroxide particles with different average particle diameters, the average single particle diameter being within the range of 30 μm or more and less than 100 μm. (9) The adhesive composition according to (1) above, wherein the thermal conductivity after curing is 0.5 W / mk or more and the solid specific gravity after curing is less than 1.60. Furthermore, the present invention is essentially a two-component curing adhesive as described in (10) below. (10) The adhesive composition according to any one of (1) to (9) above, comprising a main component comprising the polymerizable (meth)acrylic monomer (A), the organic peroxide (C), and the aluminum hydroxide particles, and a curing agent comprising the polymerizable (meth)acrylic monomer (A), the reducing agent (D), and the aluminum hydroxide particles (E). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an adhesive composition and a two-component curing adhesive that have high adhesion to metal bodies such as battery casings, high heat dissipation, excellent vibration damping properties, high heat resistance at high temperatures, and excellent lightweight properties. It should be noted that no adhesive composition or two-component curing adhesive that satisfies all of the above characteristics at a high level has been known to date. [Modes for carrying out the invention]

[0010] The following describes embodiments of the adhesive composition and two-component curing adhesive according to the present invention.

[0011] In this specification, "(meth)acrylic" or "(meth)acrylate" refers to acrylic and methacrylic as a general term, or acrylate and methacrylate as a general term, or to one or both of these.

[0012] Furthermore, in this specification, "~" means a range that includes the numbers at both ends (greater than or equal to or less than or equal to).

[0013] Furthermore, in this specification, "after curing" refers to a state in which the reaction rate measured by Fourier transform infrared spectroscopy (FT-IR) is 50% or higher. Specifically, for example, this can be measured using a Nicolet is5 Fourier transform infrared spectrometer (manufactured by Thermo Fisher Scientific Co., Ltd.). The measurement method can also be, for example, the following method. (1) 810 cm in the adhesive composition before reaction -1 The peak intensity la is measured using FT-IR. (2) 810 cm in the adhesive composition after reaction -1 The peak intensity lb is measured using FT-IR. (3) The reaction rate of the adhesive composition after the reaction is calculated using the following formula, and if it is 50% or more, it is determined to be in the "cured" state. (Formula) Reaction rate of the adhesive composition after reaction (%) = {1 - (lb / la)} × 100

[0014] The adhesive composition according to this embodiment is characterized by containing a polymerizable (meth)acrylic monomer (A) comprising a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), an elastomer (B), an organic peroxide (C), a reducing agent (D), and aluminum hydroxide particles (E) having an average particle size of 30 μm or more and less than 100 μm.

[0015] [Polymerizable (meth)acrylic monomer (A)] The polymerizable (meth)acrylic monomer (A) mainly comprises a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3). In this specification, "main component" means that it accounts for 50% by weight or more of the polymerizable (meth)acrylic monomer (A), preferably 60% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0016] [Polyfunctional (meth)acrylate (a1)] A polyfunctional (meth)acrylate is a compound having two or more (meth)acryloyl groups in one molecule. As the polymerizable functional group in the polyfunctional (meth)acrylate, it may have only an acryloyl group, may have only a methacryloyl group, or may have both an acryloyl group and a methacryloyl group. The number of (meth)acryloyl groups contained in the polyfunctional (meth)acrylate is not particularly limited, but is preferably 2 to 18, more preferably 2 to 6, and still more preferably 2 to 3.

[0017] As bifunctional and polyfunctional (meth)acrylates, for example, alkanediol di(meth)acrylates such as 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate; polyethylene glycol di(meth)acrylates such as bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol F ethylene oxide modified di(meth)acrylate; polypropylene glycol di(meth)acrylate, urethane di(meth)acrylate, epoxy di(meth)acrylate, hydrogenated bisphenol A di(meth)acrylate, hydrogenated bisphenol A alkylene oxide modified di(meth)acrylate, hydrogenated bisphenol A caprolactone modified di(meth)acrylate, hydrogenated bisphenol A glycy Hydrogenated bisphenol-modified di(meth)acrylates such as diyl ether-modified di(meth)acrylate, hydrogenated bisphenol F di(meth)acrylate, hydrogenated bisphenol F caprolactone-modified di(meth)acrylate, hydrogenated bisphenol F alkylene oxide-modified di(meth)acrylate, hydrogenated bisphenol F glycidyl ether-modified di(meth)acrylate; bisphenol-modified di(meth)acrylates such as bisphenol A di(meth)acrylate, bisphenol A alkylene oxide-modified di(meth)acrylate, bisphenol A caprolactone-modified di(meth)acrylate, bisphenol A glycidyl ether-modified di(meth)acrylate, bisphenol F di(meth)acrylate, bisphenol F caprolactone-modified di(meth)acrylate, bisphenol F alkylene oxide-modified di(meth)acrylate, bisphenol F glycidyl ether-modified di(meth)acrylate;Examples include fluorene (meth)acrylate, fluorene alkylene oxide-modified di(meth)acrylate, isobornyl di(meth)acrylate, tricyclodecanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, adamantyl di(meth)acrylate, dioxane glycol di(meth)acrylate, isosorbide di(meth)acrylate, and isosorbide alkylene oxide-modified di(meth)acrylate.;

[0018] Further, examples of 3- to 6-functional polyfunctional (meth)acrylates include ethylene oxide-modified (meth)acrylates such as dipentaerythritol hexa(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethylene oxide-modified dipentaerythritol hexa(meth)acrylate, and ethylene oxide-modified pentaerythritol tetra(meth)acrylate; isocyanuric acid-modified tri(meth)acrylates such as isocyanuric acid ethylene oxide-modified tri(meth)acrylate and ε-caprolactone-modified tris(acryloxyethyl) isocyanurate; and pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, and pentaerythritol triacrylate toluene diisocyanate urethane prepolymer.

[0019] Further, examples of 7 or more functional polyfunctional (meth)acrylates include urethane acrylates such as dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, and dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, and acrylic acrylates in which (meth)acrylate is introduced to the side chains or terminals of an acrylic resin.

[0020] The polyfunctional (meth)acrylate can be configured to use only one type of polyfunctional (meth)acrylate, or it can be configured to use two or more types of polyfunctional (meth)acrylates.

[0021] Furthermore, in this embodiment, the polyfunctional (meth)acrylate is preferably a cyclic compound, more preferably a compound having an aromatic ring, even more preferably a compound having multiple aromatic rings, and particularly preferably a compound having multiple uncondensed aromatic rings. By incorporating a polyfunctional (meth)acrylate having multiple uncondensed aromatic rings, a cross-linked structure can be formed during curing, improving adhesion (tensile shear strength) and heat resistance, as well as providing appropriate flexibility, which contributes to improved vibration resistance. In particular, as the polyfunctional (meth)acrylate having multiple uncondensed aromatic rings, a polyfunctional (meth)acrylate containing bisphenols is preferred.

[0022] The polyfunctional (meth)acrylate content in the polymerizable (meth)acrylic monomer (A) is not particularly limited, but from the viewpoint of improving adhesion and heat resistance, it is preferably 5% by weight or more, more preferably 7.5% by weight or more, and even more preferably 10% by weight or more. Furthermore, there is no particular upper limit, but from the viewpoint of flexibility, it is preferably 40% by weight or less, more preferably 30% by weight or less, and even more preferably 20% by weight or less.

[0023] [Hydroxyalkyl (meth)acrylate (a2)] Hydroxyalkyl (meth)acrylates are ester compounds of (meth)acrylates, and are compounds having an alcohol-derived hydroxyalkyl group at the ester terminal of (meth)acrylate.

[0024] Examples of hydroxyalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, diethylene glycol mono (meth)acrylate, and polypropylene glycol (meth)acrylate. Hydroxyalkyl (meth)acrylates may be used individually or in combination of two or more types.

[0025] Hydroxyalkyl (meth)acrylates have the property of enhancing adhesion to substrates such as metals through hydrogen bonding between the hydroxyalkyl group and the metal, and also tend to increase the glass transition temperature (Tg), thus improving heat resistance at high temperatures. In this embodiment, it is preferable that the hydroxyalkyl (meth)acrylate has three or fewer carbon atoms in the hydroxyalkyl group. Hydroxyalkyl (meth)acrylates with three or fewer carbon atoms have excellent heat resistance properties as well as excellent flexibility.

[0026] The content of hydroxyalkyl (meth)acrylate in the polymerizable (meth)acrylic monomer (A) is not particularly limited, but from the viewpoint of improving the adhesion and heat resistance of the adhesive composition, it is preferable that it be in a larger proportion than the other components (a1) and (a3). Specifically, the content of hydroxyalkyl (meth)acrylate is preferably 30% by weight or more, more preferably 40% by weight or more, even more preferably 50% by weight or more, and particularly preferably 55% by weight or more. Furthermore, the upper limit is preferably 85% by weight or less, more preferably 75% by weight or less, and even more preferably 70% by weight or less.

[0027] [Alkyl (meth)acrylate (a3)] Alkyl (meth)acrylates are ester compounds of (meth)acrylates, and are compounds having a linear or branched alkyl group at the ester terminal of the (meth)acrylate. Examples of alkyl groups with 1 to 24 carbon atoms include compounds with 1 to 24 carbon atoms. Alkyl (meth)acrylates can be used individually or in combination of two or more types.

[0028] Alkyl (meth)acrylate (a3) ​​includes methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, and undecyl (meth)acrylate. Examples of (meth)acrylates having linear or branched alkyl groups include syl(meth)acrylate, lauryl(meth)acrylate, tridecyl(meth)acrylate, tetradecyl(meth)acrylate, pentadecyl(meth)acrylate, hexadecyl(meth)acrylate, heptadecyl(meth)acrylate, octadecyl(meth)acrylate, stearyl(meth)acrylate, isostearyl(meth)acrylate, nonadecyl(meth)acrylate, eicosyl(meth)acrylate, behenyl(meth)acrylate, 2-decyl-1-tetradecanyl(meth)acrylate, and 2-tetradecyl-1-octadecanyl(meth)acrylate.

[0029] Alkyl (meth)acrylates have the property of imparting flexibility to adhesive compositions, and to enhance vibration resistance, a structure having an alkyl group with 8 or more carbon atoms is preferred, and a structure having 12 or more alkyl groups is more preferred.

[0030] The alkyl (meth)acrylate content in polymerizable (meth)acrylic monomers is not particularly limited, but if the content is too high, the tensile shear strength and glass transition temperature tend to decrease. Therefore, it is preferably 50% by weight or less, more preferably 40% by weight or less, and even more preferably 30% by weight or less. Furthermore, the lower limit of the alkyl (meth)acrylate content is not particularly limited, but from the viewpoint of flexibility, it is preferably 10% by weight or more, more preferably 15% by weight or more, and even more preferably 20% by weight or more.

[0031] [(a4) (meth)acrylate monomers other than those listed in (a1) to (a3) ​​above] As polymerizable (meth)acrylic monomers, other (meth)acrylate monomers (a4) besides (a1) to (a3) ​​above may be included, and are not particularly limited. Examples include (meth)acrylic acid; monofunctional (meth)acrylates having a phenyl group such as phenoxyethyl (meth)acrylate; monofunctional (meth)acrylates having a cyclic ether skeleton such as furfuryl (meth)acrylate; monofunctional methacrylates having an alicyclic structure such as isobornyl (meth)acrylate; epoxy (meth)acrylate obtained by addition reaction of (meth)acrylic acid to epoxy resin; and urethane (meth)acrylate.

[0032] In addition, as (a4) other than (a1) to (a3) ​​above, acidic phosphate esters having a (meth)acryloyloxy group can be mentioned. Examples of such esters include mono(meth)acryloyloxyethyl phosphates such as mono(2-hydroxyethyl methacrylate) phosphate, di(meth)acryloyloxyethyl phosphate, mono(meth)acryloyloxypropyl phosphate, di(meth)acryloyloxypropyl phosphate, mono(meth)acryloyloxy-β-chloropropyl phosphate and di(meth)acryloyloxy-β-chloropropyl phosphate.

[0033] [Elastomer (B)] In this embodiment, the elastomer refers to a polymeric substance that has rubber-like elasticity at room temperature, and is preferably one that can be dissolved or dispersed in polymerizable monomers. It is a component that provides appropriate elasticity to the cured body, enhances toughness, improves adhesion such as tensile shear strength, and improves vibration resistance. There are no particular limitations on the elastomer, but examples include butadiene polymers, (meth)acrylonitrile-butadiene-(meth)acrylic acid copolymers, (meth)acrylonitrile-butadiene-methyl(meth)acrylate copolymers, methyl(meth)acrylate-butadiene-(meth)acrylonitrile-styrene copolymers, butadiene-styrene-methyl(meth)acrylate copolymers, as well as various synthetic rubbers such as (meth)acrylonitrile-butadiene rubber, linear polyurethane, and styrene-butadiene, natural rubber, and various thermoplastic elastomers. If there are no compatibility issues, one or more of these elastomer components may be used.

[0034] The elastomer may or may not have polymerizable unsaturated double bonds at its terminals. When the elastomer has polymerizable unsaturated double bonds at its terminals, compounds having polymerizable unsaturated double bonds at both ends of the elastomer are preferred. As for the polymerizable unsaturated double bond, a (meth)acryloyl group and / or a vinyl group are preferred, and a (meth)acryloyl group is more preferred, due to their good reactivity.

[0035] The elastomer content in the adhesive composition is not particularly limited, but to improve adhesion and vibration resistance, it is preferably 20 parts by weight or more, more preferably 30 parts by weight or more, and even more preferably 40 parts by weight or more, per 100 parts by weight of polymerizable (meth)acrylic monomer. Furthermore, the upper limit of the elastomer is not particularly limited, but it is preferably 100 parts by weight or less, more preferably 90 parts by weight or less, and even more preferably 80 parts by weight or less.

[0036] [Organic peroxide (C)] Organic peroxides are compounds that function as radical polymerization initiators for polymerizable (meth)acrylic monomers. Examples include ketone peroxides, dialkyl peroxides, diacyl peroxides, peroxyesters, and hydroperoxides. These organic peroxides can be used individually or in combination of two or more. Among these, hydroperoxides and peroxyesters are preferred from the viewpoint of curability and storage stability. Examples of hydroperoxides include t-butyl hydroperoxide, p-menthane hydroperoxide, cumene hydroperoxide, and diisopropylbenzene hydroperoxide, while examples of peroxyesters include t-butyl peroxylaurate, t-butyl peroxybenzoate, and t-butyl peroxide dodecanoate.

[0037] The content of organic peroxides in the adhesive composition is not particularly limited, but from the viewpoint of curing speed, it is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight or more, even more preferably 1 part by weight or more, and particularly preferably 3 parts by weight or more, per 100 parts by weight of polymerizable (meth)acrylic monomer. Furthermore, the upper limit of organic peroxides is not particularly limited, but from the viewpoint of storage stability, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less, and particularly preferably 6 parts by weight or less.

[0038] [Reducing agent (D)] The reducing agent can be any known reducing agent that reacts with an organic peroxide to generate a radical. Examples include tertiary amines, thiourea derivatives, and transition metal salts that form a redox catalytic system with the organic peroxide. These can be used individually or in combination of two or more. Examples of tertiary amines include triethylamine, tripropylamine, tributylamine, and N,N-dimethylparatoluidine. Examples of thiourea derivatives include ethylenethiourea, diethylthiourea, tetramethylthiourea, monoacetylthiourea, monobenzoylthiourea, diphenylthiourea, and dicyclohexylthiourea. Examples of transition metal salts include vanadium compounds such as vanadium acetylacetonate, vanadyl acetylacetonate, vanadyl stearate, vanadium naphthenate, vanadium benzoylacetonate, and vanadium pentoxide, as well as copper compounds such as copper acetylacetonate, copper chloride, copper acetate, and copper naphthenate.

[0039] The content of the reducing agent in the adhesive composition is not particularly limited, but from the viewpoint of curing speed, it is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, even more preferably 0.1 parts by weight or more, and particularly preferably 0.5 parts by weight or more, per 100 parts by weight of polymerizable (meth)acrylic monomer. Furthermore, the upper limit of the reducing agent is not particularly limited, but from the viewpoint of storage stability, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 3 parts by weight or less.

[0040] [Aluminum hydroxide particles (E)] In the adhesive composition according to this embodiment, aluminum hydroxide particles are included as heat-dissipating fine particles to enhance heat dissipation. In addition to aluminum hydroxide, other heat-dissipating fine particles include alumina, aluminum nitride, boron nitride, titanium dioxide, graphene, CMF (Coated Carbon Foam), and carbon nanofibers. However, aluminum hydroxide is used in the adhesive composition according to this embodiment because it has high thermal conductivity and a relatively low specific gravity, and also because of its dispersibility with polymerizable (meth)acrylic monomers, storage stability due to compatibility with the adhesive composition, and its influence on the strength of adhesion.

[0041] In this embodiment, the average particle size of the aluminum hydroxide particles is 30 μm or more, preferably 40 μm or more, and more preferably 50 μm or more. Aluminum hydroxide particles with an average particle size smaller than 30 μm reduce the adhesion of the adhesive composition, increase the hardness after curing, and result in insufficient impact resistance. Furthermore, when the same amount of aluminum hydroxide particles with different average particle sizes are blended into the adhesive composition, aluminum hydroxide particles with an average particle size smaller than 30 μm have inferior thermal conductivity compared to aluminum hydroxide particles with an average particle size of 30 μm or more. This necessitates a larger blending amount to achieve comparable thermal conductivity, resulting in a higher specific gravity. The reason for this is unclear, but it is presumed that a larger average particle size of aluminum hydroxide particles reduces the number of contact points between particles, allowing for efficient heat conduction, while a smaller average particle size increases the number of contact points between particles, hindering heat conduction. The average particle size of the aluminum hydroxide particles is less than 100 μm, preferably 90 μm or less, and more preferably 80 μm or less. If the average particle size of aluminum hydroxide particles exceeds 100 μm, the aluminum hydroxide particles will precipitate, making it impossible to disperse them in the adhesive composition. The average particle size of aluminum hydroxide particles can be measured, for example, using a laser diffraction scattering particle size distribution analyzer (product name: LS-13 320) manufactured by Beckman Coulter. The average particle size can be the average particle size of aggregated particles, measured without homogenization before the measurement process. If a manufacturer's catalog value is provided, that value can be used.

[0042] Furthermore, in this embodiment, as long as the average particle diameter of the aluminum hydroxide particles is in the range of 30 μm or more and less than 100 μm, two or more types of aluminum hydroxide particles with different average particle diameters can be mixed and used. For example, the adhesive composition can contain aluminum hydroxide particles with an average particle diameter of 50 μm and aluminum hydroxide particles with an average particle diameter of 80 μm. In this case, the mixing ratio of the two types of aluminum hydroxide particles is not particularly limited, and they can be mixed in a weight ratio of 1:9 to 9:1, preferably 1:4 to 4:1.

[0043] Furthermore, commercially available aluminum hydroxide particles can be used as two or more types of aluminum hydroxide particles with different average particle diameters. The above-mentioned "two or more types of aluminum hydroxide particles with different average particle diameters" can refer to two or more types of aluminum hydroxide particles with different average particle diameters as indicated on the product packaging. Alternatively, the particle diameter of aluminum hydroxide particles can be measured using a known method, and a group of aluminum hydroxide particles with two or more peaks in the average primary particle diameter within the range of 30 μm or more and less than 100 μm can be used as "two or more types of aluminum hydroxide particles with different average primary particle diameters within the range of 30 μm or more and less than 100 μm."

[0044] The content of aluminum hydroxide particles is not particularly limited, but it is preferably 30% by weight or more of the total adhesive composition, more preferably 40% by weight or more, and can be 50% by weight or more. This is because if the aluminum hydroxide content is less than 30% by weight of the total adhesive composition, sufficient heat dissipation cannot be obtained. Furthermore, the content of aluminum hydroxide particles is preferably 80% by weight or less of the total adhesive composition, more preferably 70% by weight or less, and can be 65% by weight or less. If the aluminum hydroxide content is higher than 80% by weight of the total adhesive composition, the adhesiveness tends to decrease, and the specific gravity of the adhesive composition after curing becomes too high.

[0045] The adhesive composition according to this embodiment may further contain other components not mentioned above, to the extent that the effects of the present invention are obtained. Other components include stabilizers and fillers. Stabilizers are components that enhance the storage stability of the adhesive composition at room temperature. Examples of stabilizers include radical polymerization inhibitors and chelating agents, such as 2,6-di-t-butyl-4-methylphenol, 2,2-methylenebis(4-methyl-6-t-butylphenol), benzoquinone, quinhydron, hydroquinone, sodium ethylenediaminetetraacetate, oxalic acid, malic acid, N-methyl-N-nitroaniline, and N-nitrosodiphenylamine. The content of stabilizers in the adhesive composition is not particularly limited, but is preferably 0.01 to 5 by weight per 100 parts by weight of polymerizable (meth)acrylic monomer. Examples of fillers include silica, glass, talc, mica, calcium carbonate, kaolin clay, clay minerals, alumina, aluminum nitride, and carbon, and can be appropriately blended to the extent that they do not hinder the objectives of the present invention.

[0046] [Adhesive composition] As described above, the adhesive composition according to this embodiment contains a polymerizable (meth)acrylic monomer (A) containing a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), an elastomer (B), an organic peroxide (C), a reducing agent (D), and aluminum hydroxide particles (E) having an average particle size of 30 μm or more and less than 100 μm. As a result, the adhesive composition according to this embodiment can satisfy the adhesive properties, heat dissipation properties, vibration resistance, adhesive stability at high temperatures, and lightweight properties suitable for applications such as fixing batteries of electric vehicles to cooling plates.

[0047] The adhesive composition according to this embodiment can achieve a tensile shear strength of 14 MPa or more at 23°C by appropriately blending each component within the above-described range of composition. A value of 14 MPa or more allows for stable fixing of battery casings of electric vehicles and the like to cooling plates, and also enables use in harsh environments exposed to vibrations, etc. Furthermore, a tensile shear strength of 15 MPa or more at 23°C is more preferable, 16 MPa or more is even more preferable, and 18 MPa or more is particularly preferable. The method for measuring tensile shear strength will be described later.

[0048] The adhesive composition according to this embodiment preferably has a tensile shear strength of 10 MPa or more, more preferably 11 MPa or more, even more preferably 12 MPa or more, and particularly preferably 13 MPa or more, not only in an environment of 23°C, but also in low-temperature environments of -25°C and high-temperature environments of 55°C. Having a tensile shear strength of 10 MPa or more in both -25°C and 55°C environments allows it to withstand use in high-temperature environments in summer and low-temperature environments in winter.

[0049] The adhesive composition according to this embodiment can achieve a cured thermal conductivity of 0.5 W / mk or higher by appropriately blending each component within the above-described range of composition. A value of this or higher enables efficient heat exchange from the battery to the cooling plate through the adhesive, which is advantageous for battery thermal management. Furthermore, a thermal conductivity of 0.65 W / mk or higher, 0.70 W / mk or higher, 0.80 W / mk or higher, 0.90 W / mk or higher, or 1.00 W / mk or higher is more preferable. The method for measuring thermal conductivity will be described later.

[0050] The adhesive composition according to this embodiment can have a specific gravity of 1.60 or less after curing by appropriately blending each component within the above-described range of composition. If the specific gravity is below this value, the weight increase due to the adhesive used to fix the battery cell to the cooling plate, etc., can be suppressed, which is advantageous for improving the energy efficiency of electric vehicles, etc. A specific gravity of 1.55 or less, 1.50 or less, 1.45 or less, or 1.40 or less is more preferable. The method for measuring the specific gravity can be any conventionally known method and is not particularly limited, but examples include the liquid weighing method, gas displacement method, Le Chatelier specific gravity bottle method, liquid immersion method, etc.

[0051] Furthermore, the adhesive composition according to this embodiment can be a two-component curing adhesive. For example, the main component and the curing agent each contain in equal amounts a polymerizable (meth)acrylic monomer (A) containing a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), an elastomer (B), and aluminum hydroxide particles (E) having an average particle size of 30 μm or more and less than 100 μm. In addition, the main component contains an organic peroxide (C) and the curing agent contains a reducing agent (D). By mixing the main component and the curing agent, radical polymerization can be initiated to polymerize the acrylic monomer.

[0052] The two-component curable resin according to this embodiment consists of a main component containing an organic peroxide as a polymerization initiator and a curing agent containing a reducing agent that forms a redox catalyst system with the organic peroxide. As a result, the adhesive composition can be cured at room temperature (30°C or below) simply by mixing the main component and the curing agent. This allows, for example, the battery of an electric vehicle, such as a lithium-ion battery made of heat-sensitive materials, to be fixed with the adhesive composition without heating or UV irradiation, thereby improving workability. [Examples]

[0053] Next, we will describe a test example of the adhesive composition (two-component curing adhesive) according to the present invention. In this example, we aimed to obtain an adhesive composition that is suitable for bonding electric vehicle batteries to each other or to a battery and a cooling plate, which not only has high adhesion to metal bodies such as battery casings, but also high heat dissipation to facilitate heat exchange in the battery, vibration resistance (flexibility) to dampen vibrations in electric vehicles, excellent workability as it can be cured without heating for heat-sensitive batteries, high adhesive stability that allows it to be fixed without softening even at high temperatures, and excellent lightweight properties, as shown in Table 1 below. First, we verified the composition of the polymerizable (meth)acrylic monomer that forms the base of the adhesive composition according to the present invention.

[0054] [Table 1]

[0055] In this embodiment, adhesiveness was measured using the tensile shear strength at 23°C as an indicator for nickel-plated steel sheets, which are commonly used in the exterior of lithium-ion batteries for electric vehicles, with the goal of achieving a tensile shear strength of 14 MPa or higher. For heat dissipation, thermal conductivity was used as an indicator, with the goal of achieving a thermal conductivity of 0.5 W / m·K or higher. Furthermore, for vibration resistance, the hardness after curing (Shore D) one day after the start of curing was used as an indicator, with the goal of achieving a hardness (Shore D) within the range of 50 to 70. This is because a hardness (Shore D) of less than 50 is too soft to properly fix the battery, and a hardness (Shore D) exceeding 70 is too hard and susceptible to vibration. In addition, for workability, the goal was to provide a two-component, room-temperature curing adhesive composition that can be cured without heating. Finally, for stability, the glass transition temperature was used as an indicator, with the goal of achieving a glass transition temperature of 60°C or higher. Furthermore, for lightweight construction, specific gravity was used as an indicator, with the goal of achieving a specific gravity of 1.6 or less. Details of the measurement methods for each indicator will be described later.

[0056] In this example, in order to obtain an adhesive composition having the performance shown in Table 1 above, we first investigated suitable polymerizable (meth)acrylic monomer compositions for the adhesive composition. In particular, among the performance shown in Table 1 above, the polymerizable (meth)acrylic monomer composition that forms the base of the adhesive composition contributes significantly to adhesion, vibration resistance, and stability. Therefore, we first measured the tensile shear strength, glass transition temperature (Tg), hardness after curing (Shore D), and thermal conductivity at 23°C for the compositions of Reference Examples 1-3, which have the compositions shown in Table 2 below, against nickel-plated steel sheets.

[0057] [Table 2]

[0058] In Table 1 above, components corresponding to polyfunctional (meth)acrylates are indicated by (a1), components corresponding to hydroxyalkyl (meth)acrylates are indicated by (a2), and components corresponding to alkyl (meth)acrylates are indicated by (a3). Specifically, in Table 2 above, BPE is bisphenol A ethylene oxide-modified dimethacrylate and corresponds to polyfunctional (meth)acrylate (a1). HPMA is hydroxypropyl methacrylate and HEMA is hydroxyethyl methacrylate, both of which correspond to hydroxyalkyl (meth)acrylate (a2). Furthermore, LMA is lauryl methacrylate and corresponds to alkyl (meth)acrylate (a3). In Table 2 above, MAA is methacrylic acid and IBX is isobornyl methacrylate, both of which correspond to (meth)acrylate monomers other than (a1) to (a3) ​​(a4). MBS is a methyl methacrylate-butadiene-styrene copolymer, and VTBNX is a butadiene-acrylonitrile rubber containing terminal vinyl groups, both corresponding to elastomer (B). In Table 2 above, the content of each component is expressed in parts by weight, and the total amount of polymerizable (meth)acrylic monomers is adjusted to 100 parts by weight.

[0059] [Tensile shear strength] In this example, first, the compositions according to Reference Examples 1-3 were divided equally. To one part, 4 parts by weight of cumene hydroperoxide, an organic peroxide, was added per 100 parts by weight of polymerizable (meth)acrylic monomer to serve as the main component. To the other part, 0.5 parts by weight of vanadyl acetylacetonate was added as a reducing agent per 100 parts by weight of polymerizable (meth)acrylic monomer (A) to serve as the curing agent, thereby preparing a two-component curing adhesive composition. In addition, a pair of cold-rolled nickel-plated steel sheets measuring 100 mm in length, 25 mm in width, and 1.6 mm in thickness were prepared. Equal amounts of the main component and curing agent were applied to one of the nickel-plated steel sheets in an atmosphere of 23°C and 50% RH. Then, the other nickel-plated steel sheet was bonded and fixed in place and allowed to cure. After 24 hours, the tensile shear strength was measured in an atmosphere of 23°C and 50% RH in accordance with ASTM D 1002-64.

[0060] In addition, when measuring tensile shear strength, the fracture shape of the adhesive composition after shearing was visually confirmed and evaluated. Specifically, when the adhesive composition was peeled off from the nickel-plated steel sheet, if the peeling occurred at the interface between the adhesive composition and the nickel-plated steel sheet, it was evaluated as "interfacial peeling," and if the adhesive composition fractured internally and peeled off, it was evaluated as "cohesive failure."

[0061] [Glass transition temperature] As described above, the compositions related to Reference Examples 1-3 were divided equally to prepare two-component, room-temperature adhesive compositions consisting of a main component and a curing agent. Next, the prepared adhesive compositions were mixed and cured in an atmosphere of 23°C and 50% RH for more than 24 hours to produce a cured adhesive composition with a film thickness of 1 mm. After that, it was cut into a 40 mm x 10 mm rectangle to obtain a measurement sample. Then, using a dynamic viscoelasticity analyzer (Hitachi High-Tech Science Corporation, model number: DMA7100), the chuck distance was set to 20 mm in tensile mode, and the temperature was increased at a constant frequency (1 Hz) at 2°C / min to measure the storage modulus (E') and loss modulus (E'') in the temperature range of -50 to 250°C. The loss tangent was calculated from the obtained values, and a curve plot of the loss tangent and temperature was performed. The temperature at which the loss tangent showed a maximum value was defined as the glass transition temperature Tg.

[0062] [Hardness after curing] Five of the above-mentioned measurement samples were stacked to a total thickness of 5 mm, and the hardness of the resulting cured material was measured using a Type D durometer as the degree of curing hardness (Shore D) of the compositions related to Reference Examples 1-3.

[0063] [Thermal conductivity] As described above, the compositions according to Reference Examples 1-3 were divided equally to prepare two-component, room-temperature adhesive compositions consisting of a main component and a curing agent. Next, the prepared adhesive compositions were mixed and cured in an atmosphere of 23°C and 50% RH for more than 24 hours to produce a cured adhesive composition with a film thickness of 1 mm. After that, it was cut into a 10 mm x 10 mm rectangle to obtain a measurement sample. Next, gold deposition was performed on one surface of the obtained measurement sample using an ion sputtering apparatus (JEOL Ltd., model number: JFC-1100E) at 10 mV and 600 s. Then, the thermal conductivity of the measurement sample was measured in a 25°C atmosphere using a xenon flash analyzer (NETZSCH, model number: LFA 467 HyperFlash).

[0064] As shown in Table 2 above, the measurement results showed that the tensile shear strength at 23°C for nickel-plated steel sheets significantly exceeded the target of 14 MPa for the compositions in Reference Example 1 and Reference Example 2, but fell below the target of 14 MPa for the composition in Reference Example 3. Furthermore, regarding the hardness after curing (Shore D), the composition in Reference Example 1 had a hardness of 70, which was within the target range (D50~70), but the compositions in Reference Examples 2 and 3 had a hardness after curing (Shore D) of 80, which was higher (harder) than the target range.

[0065] From the above, it was found that among the compositions related to Reference Examples 1-3, the composition related to Reference Example 1 is the closest to an adhesive composition with the target performance. However, since the thermal conductivity of the composition related to Reference Example 1 is low at 0.21 W / m·K, which is an indicator of heat dissipation, it is desirable to increase the thermal conductivity by adding heat-dissipating fine particles. However, if heat-dissipating fine particles are added to the composition related to Reference Example 1, the hardness after curing (Shore D) is expected to increase and exceed the target of 70. Therefore, next, we attempted to prepare a composition of polymerizable (meth)acrylic monomer that has an even lower (softer) hardness after curing (Shore D) than the composition related to Reference Example 1.

[0066] Specifically, based on the polymerizable (meth)acrylic monomer composition of Reference Example 1 in Table 2 above, compositions according to Reference Examples 4-11 were prepared as shown in Table 3 below. In Table 3 below, the content of each component is expressed in parts by weight, and the total amount of polymerizable (meth)acrylic monomers was adjusted to 100 parts by weight. Compared with the composition according to Reference Example 1, the composition according to Reference Example 4-5 does not contain lauryl methacrylate (LMA) as alkyl (meth)acrylate (a3), but instead contains 2-ethylhexyl methacrylate (EHMA). Furthermore, the composition according to Reference Example 6-7 contains both lauryl methacrylate (LMA) and 2-ethylhexyl methacrylate (EHMA) as alkyl (meth)acrylate (a3). In addition, the composition according to Reference Example 8 has the same components as the composition according to Reference Example 1, but with a different blending ratio. Furthermore, the composition according to Reference Example 9 contains hydroxypropyl methacrylate (HPMA) and hydroxyethyl methacrylate (HEMA) as hydroxyalkyl (meth)acrylate (a2). In addition, the compositions according to Reference Examples 10 and 11 contain hydroxyethyl methacrylate (HEMA) instead of hydroxypropyl methacrylate (HPMA) as hydroxyalkyl (meth)acrylate (a2) compared to the composition according to Reference Example 1.

[0067] [Table 3]

[0068] Then, the hardness (Shore D), tensile shear strength, and glass transition temperature of the composition related to Reference Example 4-11 shown in Table 3 above were measured. In Table 3 above, the hardness (Shore D), tensile shear strength, and glass transition temperature of the composition related to Reference Example 4-11 were measured in the same manner as the measurement method for the compositions related to Reference Examples 1-3 shown in Table 2 above. For the sake of explanation, the measurement results for the composition related to Reference Example 1 are also shown in Table 3 above.

[0069] As shown in Table 3 above, in the compositions of Reference Examples 4-5, 2-ethylhexyl methacrylate (EHMA) was added instead of lauryl methacrylate (LMA) as alkyl (meth)acrylate (a3), but the hardness after curing (Shore D) did not decrease from 70. On the other hand, in the compositions of Reference Examples 6-8, increasing the amount of lauryl methacrylate (LMA), which is alkyl (meth)acrylate (a3), reduced the hardness after curing (Shore D), but in Reference Example 8, the tensile shear strength decreased to 13 MPa, falling below the target of 14 MPa.

[0070] Furthermore, in Reference Example 9, where a portion of the hydroxypropyl methacrylate (HPMA) as hydroxyalkyl (meth)acrylate (a2) was replaced with hydroxyethyl methacrylate (HEMA), the hardness after curing (Shore D) decreased to 60, and the glass transition temperature also increased to 70°C. In Reference Examples 10 and 11, the hydroxyalkyl (meth)acrylate (a2) did not contain hydroxypropyl methacrylate (HPMA) but contained hydroxyethyl methacrylate (HEMA), resulting in a lower hardness after curing (Shore D) of 65 or less, a higher tensile shear strength of 15 MPa or more, and a higher glass transition temperature of 104°C or more. In particular, in Reference Example 11, the tensile shear strength increased to 19 MPa.

[0071] Thus, the composition according to Reference Example 11 exhibited lower post-curing hardness (Shore D), higher tensile shear strength (19 MPa), and a higher glass transition temperature compared to Reference Example 1. Therefore, in the following section, we investigated whether an adhesive composition with the initially targeted performance could be obtained by adding heat-dissipating fine particles to the composition according to Reference Example 11 as a base.

[0072] Specifically, as shown in Tables 4 and 5 below, adhesive compositions for Comparative Examples 1-13 and Examples 1-3 were prepared, containing the composition related to Reference Example 11 and also containing heat-dissipating fine particles. The tensile shear strength, hardness after curing (Shore D), specific gravity, and thermal conductivity of the adhesive compositions for Comparative Examples 1-13 and Examples 1-3 were then measured. In Tables 4 and 5 below, the values ​​listed under aluminum hydroxide, alumina, alumina nitride, and boron nitride indicate the proportion of aluminum hydroxide particles, etc., in the entire adhesive composition. For example, 50% by weight of aluminum hydroxide particles means that the adhesive composition is 50% by weight, totaling 100% by weight. Furthermore, in Tables 4 and 5 below, areas where the tensile shear strength, hardness after curing (Shore D), specific gravity, and thermal conductivity at 23°C for nickel-plated steel sheets did not reach the target values ​​shown in Table 1 are highlighted in gray.

[0073] [Table 4] [Table 5]

[0074] More specifically, based on the composition of Reference Example 11, the adhesive composition of Comparative Example 1 had 50% by weight of aluminum hydroxide particles with an average particle size of 16 μm added to the total adhesive composition, the adhesive composition of Comparative Example 2 had 50% by weight of aluminum hydroxide particles with an average particle size of 23 μm added to the total adhesive composition, and the adhesive composition of Comparative Example 3 had 67% by weight of aluminum hydroxide particles with an average particle size of 23 μm added. Furthermore, based on the resin composition of Reference Example 11, the adhesive composition of Example 1 had 50% by weight of aluminum hydroxide particles with an average particle size of 55 μm added to the total adhesive composition, the adhesive composition of Example 2 had 62.5% by weight of aluminum hydroxide particles with an average particle size of 55 μm added to the total adhesive composition, and the adhesive composition of Example 3 had 50% by weight of aluminum hydroxide particles with an average particle size of 80 μm added to the total adhesive composition. Furthermore, based on the composition of Reference Example 11, the adhesive composition of Comparative Example 4 was modified by adding 50% by weight of aluminum hydroxide particles with an average particle size of 100 μm to the entire adhesive composition; the adhesive composition of Comparative Example 5 was modified by adding 33% by weight of alumina particles with an average particle size of 20 μm to the entire adhesive composition; the adhesive composition of Comparative Example 6 was modified by adding 50% by weight of alumina particles with an average particle size of 20 μm to the entire adhesive composition; the adhesive composition of Comparative Example 7 was modified by adding 67% by weight of alumina particles with an average particle size of 20 μm to the entire adhesive composition; and the adhesive composition of Comparative Example 8 was modified by adding 50% by weight of alumina particles with an average particle size of 50 μm to the entire adhesive composition. In addition, based on the composition of Reference Example 11, the adhesive composition of Comparative Example 9 was modified by adding 33% by weight of alumina nitride particles with an average particle size of 20 μm to the entire adhesive composition; the adhesive composition of Comparative Example 10 was modified by adding 50% by weight of alumina nitride particles with an average particle size of 20 μm to the entire adhesive composition; the adhesive composition of Comparative Example 11 was modified by adding 60% by weight of alumina nitride particles with an average particle size of 20 μm to the entire adhesive composition; the adhesive composition of Comparative Example 12 was modified by adding 67% by weight of alumina nitride particles with an average particle size of 20 μm to the entire adhesive composition; and the adhesive composition of Comparative Example 13 was modified by adding 33% by weight of boron nitride particles with an average particle size of 30 μm to the entire adhesive composition.

[0075] As shown in Table 4 above, the adhesive compositions of Comparative Examples 1-3 contained aluminum hydroxide particles with an average particle diameter of 23 μm or less. In this case, the tensile shear strength, hardness after curing (Shore D), and thermal conductivity could not meet the target performance. In particular, it was found that when the particle diameter of the heat-dissipating fine particles was 23 μm or less, the thermal conductivity tended to be low, while the hardness after curing tended to be high. Furthermore, it was found that increasing the amount of fine particles to increase thermal conductivity significantly reduced the adhesiveness (tensile peel strength).

[0076] Furthermore, as shown in Table 4 above, the adhesive composition according to Comparative Example 4 contained aluminum hydroxide particles with an average particle size of 100 μm, but in this case, the aluminum hydroxide particles precipitated and could not be dispersed.

[0077] Furthermore, as shown in Table 5 above, the adhesive composition according to Comparative Example 5 contained 33% by weight of alumina particles with an average particle size of 20 μm relative to the total adhesive composition, but its thermal conductivity was 0.32 W / m·K, which is below the target of 0.5 W / m·K. In addition, the adhesive compositions according to Comparative Examples 6-7 contained 50-67% by weight of alumina particles with an average particle size of 20 μm relative to the total adhesive composition, but in this case, the specific gravity was 1.67 or higher, which is greater than the target of 1.6. Moreover, the adhesive composition according to Comparative Example 8 contained alumina particles with an average particle size of 50 μm, but in this case, the alumina particles precipitated and could not be dispersed. This result of the alumina particles with an average particle size of 50 μm precipitation indicates poor compatibility with polymerizable (meth)acrylic monomers and poor dispersibility.

[0078] In addition, the adhesive composition of Comparative Example 9 contained 33% by weight of alumina nitride particles with an average particle size of 20 μm relative to the total adhesive composition, but its thermal conductivity was 0.39 W / m·K, which is below the target of 0.5 W / m·K. Similarly, the adhesive composition of Comparative Example 10 contained 50% by weight of alumina nitride particles with an average particle size of 20 μm relative to the total adhesive composition, but its hardness after curing (Shore D) was 71, exceeding the target of 70. Furthermore, the adhesive compositions of Comparative Examples 11-12 contained 60% or more by weight of alumina nitride particles with an average particle size of 20 μm relative to the total adhesive composition, but in addition to a hardness after curing exceeding 70, their specific gravity was 1.79 or higher, which is greater than the target of 1.6. Finally, the adhesive composition of Comparative Example 13 contained 33% by weight of boron nitride particles with an average particle size of 30 μm relative to the total adhesive composition, but its tensile shear strength at 23°C was 11.3 MPa, which is below the target of 14 MPa. In the adhesive compositions of Comparative Examples 9-13, alumina nitride particles or boron nitride were contained as heat-dissipating fine particles. However, the storage stability of the main component, which contains polymerizable (meth)acrylic monomers, organic peroxides, and fine particles, was poor, and the main component turned red after 3-7 days. Even when the discolored main component was mixed with the curing agent, curing failure occurred, suggesting that some reaction occurred between the alumina nitride particles or boron nitride and the organic peroxides, causing curing inhibition.

[0079] On the other hand, as shown in Table 4 above, the adhesive compositions according to Examples 1-3 contained aluminum hydroxide particles with an average particle size of 50 μm to 80 μm, and in this case, the tensile shear strength, hardness after curing (Shore D), specific gravity, and thermal conductivity all met the target performance. From this, it was found that in an adhesive composition containing a polymerizable (meth)acrylic monomer (A) having a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), and an elastomer (B), by including aluminum hydroxide particles with an average particle size of 50 μm or 80 μm as heat-dissipating fine particles, an adhesive composition with high adhesion, high heat dissipation, excellent vibration resistance, and excellent lightweight properties can be obtained. Furthermore, while precipitation occurred in alumina particles at an average particle size of 50 μm, no precipitation occurred in aluminum hydroxide particles up to an average particle size of 100 μm. This indicates that aluminum hydroxide particles have good compatibility with polymerizable (meth)acrylic monomers and excellent dispersibility. This is presumed to be because the hydroxyalkyl (meth)acrylate contained in both aluminum hydroxide particles and polymerizable (meth)acrylic monomers has hydroxyl groups, resulting in good compatibility and excellent dispersibility.

[0080] Next, the tensile shear strength, cured hardness (Shore D), specific gravity, and thermal conductivity were measured for adhesive compositions containing a mixture of two types of aluminum hydroxide particles with different average particle sizes. Table 6 below shows the measurement results. For the sake of explanation, Table 6 also shows the measurement results for the adhesive composition of Example 1. In Table 6, as well as in Table 1, areas that did not reach the target values ​​shown in Table 1 are indicated with gray fill.

[0081] [Table 6]

[0082] As shown in Table 6 above, the adhesive compositions of Examples 4-6 contained a mixture of aluminum hydroxide particles with an average particle size of 50 μm and an average particle size of 80 μm. In all of Examples 4-6, the tensile shear strength, hardness after curing (Shore D), specific gravity, and thermal conductivity all met the target performance. Furthermore, the adhesive compositions of Examples 4-6 showed a tendency for improved tensile shear strength when mixed with aluminum hydroxide particles with an average particle size of 80 μm. On the other hand, the adhesive compositions of Comparative Examples 14 and 15 contained a mixture of 55 μm aluminum hydroxide particles and 23 μm aluminum hydroxide particles. In this case, the hardness after curing (Shore D) was found to be 72 or higher, exceeding the target of 70. From this, it was found that in an adhesive composition having a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), even when the heat-dissipating fine particles are a mixture of two or more types of aluminum hydroxide particles with different average particle sizes, within the range of an average particle size larger than 23 μm and less than 100 μm, an adhesive composition with high adhesion, high heat dissipation, and excellent vibration resistance can be obtained.

[0083] As described above, the adhesive composition according to this embodiment contains a composition comprising a polymerizable (meth)acrylic monomer (A) having a polyfunctional (meth)acrylate (a1), a hydroxyalkyl (meth)acrylate (a2), and an alkyl (meth)acrylate (a3), and an elastomer (B), and aluminum hydroxide particles (E) having an average particle size of 30 μm or more and less than 100 μm. In the adhesive composition according to this embodiment, by including a polyfunctional (meth)acrylate (a1) having a plurality of (meth)acryloyl groups, it is possible to form a crosslinked structure, which not only improves the adhesion and vibration resistance of the cured adhesive composition, but also increases the glass transition temperature and improves adhesive stability at high temperatures. Furthermore, in the adhesive composition according to this embodiment, by having a plurality of uncondensed aromatic rings as the polyfunctional (meth)acrylate (a1), it is considered possible to provide appropriate flexibility and further improve vibration resistance. Furthermore, by including hydroxyalkyl (meth)acrylate (a2) in the adhesive composition according to this embodiment, adhesion to metal bodies such as battery casings can be improved, and the glass transition temperature Tg can be raised to improve heat resistance at high temperatures. In particular, by using a compound with 3 or fewer carbon atoms in the hydroxyalkyl group as hydroxyalkyl (meth)acrylate (a2), excellent heat resistance can be achieved, as well as flexibility and excellent impact resistance. In addition, by including alkyl (meth)acrylate (a3) ​​in the adhesive composition according to this embodiment, flexibility can be imparted to the cured adhesive composition and vibration resistance can be improved. In particular, by using a compound with 12 or fewer carbon atoms in the alkyl group as alkyl (meth)acrylate (a3), high vibration resistance can be imparted to the cured adhesive.

[0084] Furthermore, the adhesive composition according to this embodiment contains aluminum hydroxide particles (E) with an average particle diameter of 30 μm or more and less than 100 μm in order to enhance heat dissipation. By setting the average particle diameter of the aluminum hydroxide particles to 30 μm or more, adhesion to batteries and the like can be increased, and by setting it to less than 100 μm, fine particles can be properly dispersed without settling. In addition, the adhesive composition according to this embodiment can also be configured to contain a mixture of two types of aluminum hydroxide particles with different particle diameters, within the range of an average single particle diameter of 30 μm or more and less than 100 μm. In this case, as shown in Examples 4-6 of Table 6, the hardness after curing (Shore D) can be set to the target of 70 or less, while the tensile shear strength can be increased to around 20 MPa, which is well above the target of 14 MPa.

[0085] Furthermore, in the adhesive composition according to this embodiment, by setting the content of alkyl (meth)acrylate (a3) ​​in the polymerizable (meth)acrylic monomer (A) to 10% by weight or more and 50% by weight or less, an adhesive composition can be provided that is excellent in vibration resistance as well as adhesiveness and heat resistance. In addition, in the adhesive composition according to this embodiment, by setting the content of polyfunctional (meth)acrylate (a1) in the polymerizable (meth)acrylic monomer (A) to 5% by weight or more and 30% by weight or less, adhesiveness and heat resistance can be improved. Furthermore, in the adhesive composition according to this embodiment, by setting the content of hydroxyalkyl (meth)acrylate (a2) in the polymerizable (meth)acrylic monomer (A) to 30% by weight or more and 85% by weight or less, adhesiveness and heat resistance can be enhanced. Furthermore, in the adhesive composition according to this embodiment, by setting the content of aluminum hydroxide particles to 40% or more and 65% or less by weight of the total adhesive composition, it is possible to ensure tensile shear strength, enhance heat dissipation, and achieve a post-curing hardness in a suitable range of Shore D50 to 70, while also achieving excellent lightness. Thus, the content (blending ratio) of each of the polymerizable (meth)acrylic monomer (A) containing polyfunctional (meth)acrylate (a1), hydroxyalkyl (meth)acrylate (a2), and alkyl (meth)acrylate (a3), the elastomer (B), and aluminum hydroxide particles (E) with an average particle diameter of 30 μm or more and less than 100 μm, is in a trade-off relationship where some of the performance required for the adhesive composition according to this embodiment is improved while other performance is reduced. However, as described above, by adjusting the blending amounts, an adhesive composition that more favorably satisfies the performance required for the adhesive composition according to this embodiment can be obtained.

[0086] In addition, in this embodiment, by using a two-component curing adhesive composed of a main component containing the adhesive composition and an organic peroxide (B), and a curing agent containing the adhesive composition and a reducing agent (D), the adhesive composition can be cured simply by mixing the main component and the curing agent, even in narrow spaces such as between battery cells or between the battery and the cooling plate, or in spaces where UV irradiation is difficult, thereby improving the workability of the bonding process. Furthermore, with the two-component curing adhesive according to this embodiment, the adhesive composition can be cured simply by mixing the main component and the curing agent, even at room temperature (for example, 30°C or below). Therefore, even if the battery is a lithium-ion battery using heat-sensitive materials, bonding can be performed without heating.

[0087] Although preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the embodiments described above. Various modifications and improvements can be made to the above embodiments, and such modified or improved forms are also included in the technical scope of the present invention.

[0088] For example, in the embodiments described above, a two-component curing adhesive composition was exemplified as the adhesive composition, but a primer-type adhesive composition or an adhesive composition that hardens by mixing three or more components can also be used.

Claims

1. Polyfunctional (meth)acrylate (a1) and Hydroxyalkyl (meth)acrylate (a2) and, A polymerizable (meth)acrylic monomer (A) containing an alkyl (meth)acrylate (a3), Elastomer (B) and, Organic peroxides (C) and Reducing agent (D), An adhesive composition comprising aluminum hydroxide particles (E) having an average particle diameter of 30 μm or more and less than 100 μm.

2. The adhesive composition according to claim 1, wherein the aluminum hydroxide particles (E) are contained in an amount of 40% by weight or more and 65% by weight or less of the total adhesive composition.

3. The polymerizable (meth)acrylic monomer (A) is The polyfunctional (meth)acrylate (a1) is present in an amount of 5% by weight or more and 40% by weight or less. The hydroxyalkyl (meth)acrylate (a2) is present in an amount of 30% by weight or more and 85% by weight or less, The adhesive composition according to claim 1, comprising the alkyl (meth)acrylate (a3) ​​in an amount of 10% by weight or more and 50% by weight or less.

4. The adhesive composition according to claim 1, wherein the polyfunctional (meth)acrylate (a1) is a compound having a plurality of uncondensed aromatic rings.

5. The adhesive composition according to claim 1, wherein the hydroxyalkyl (meth)acrylate (a2) is a compound in which the hydroxyalkyl group has 3 or fewer carbon atoms.

6. The adhesive composition according to claim 1, wherein the alkyl (meth)acrylate (a3) ​​is a compound in which the alkyl group has 8 or more carbon atoms.

7. The adhesive composition according to claim 1, wherein the elastomer (B) is one or more selected from butadiene polymer, (meth)acrylonitrile-butadiene-(meth)acrylic acid copolymer, (meth)acrylonitrile-butadiene-methyl(meth)acrylate copolymer, methyl(meth)acrylate-butadiene-(meth)acrylonitrile-styrene copolymer, butadiene-styrene-methyl(meth)acrylate copolymer, and (meth)acrylonitrile-butadiene rubber, linear polyurethane, and styrene-butadiene.

8. The adhesive composition according to claim 1, wherein the aluminum hydroxide particles (E) contain two types of aluminum hydroxide particles having different average particle diameters, within the range of 30 μm or more and less than 100 μm.

9. The adhesive composition according to claim 1, wherein the adhesive composition has a thermal conductivity of 0.5 W / mk or more after curing and a solid specific gravity of 1.60 or less after curing.

10. The adhesive composition according to any one of claims 1 to 9, comprising a main component comprising the polymerizable (meth)acrylic monomer (A), the organic peroxide (C), and the aluminum hydroxide particles, and a curing agent comprising the polymerizable (meth)acrylic monomer (A), the reducing agent (D), and the aluminum hydroxide particles (E).

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