Adhesive sheets, cured products using the same, laminates, and automotive exterior materials

Abstract

To provide an epoxy resin-based adhesive sheet which can keep thickness of an adhesive layer even after heating and curing, can suppress occurrence of warpage after adhesion to an adherend having different coefficients of linear expansion, and has good adhesive strength to an adherend such as a steel sheet and aluminum.SOLUTION: An adhesive sheet includes a resin layer (A) composed of an epoxy resin composition (a), and a resin layer (B) composed of an epoxy resin composition (b), wherein a gel fraction is 30 mass% or more and 95 mass% or less, and the resin layer (B) is uncured.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an adhesive sheet using an epoxy resin, a cured product using the same, a laminate, and an automotive exterior material. Background Art

[0002] In recent years, from the viewpoints of suppressing global warming and protecting the environment, studies on weight reduction of structures have been progressing for the purpose of improving fuel efficiency in transportation vehicles such as automobiles and aircraft. As a method for achieving this weight reduction, extensive studies have been conducted on thinning by using ultra-high-strength steel sheets with increased strength instead of conventionally used steel sheets, and on utilizing lightweight alternative materials to steel sheets such as aluminum and CFRP (Carbon Fiber Reinforced Plastics).

[0003] However, while these materials contribute to weight reduction, they have problems such as being inferior to steel sheets in terms of cost, strength, fatigue resistance, electrical properties and other characteristics. Therefore, these materials are rarely used alone, and replacement of steel sheets is being studied mainly for portions where these materials can be used as alternatives for various characteristics. As a result, a plurality of members are joined for use, and situations have arisen where joining is difficult with conventional welding techniques.

[0004] Furthermore, when such a plurality of members are joined by welding, metal fastening or the like, metal corrosion (electrolytic corrosion) occurs due to the difference in potential between the joined members, so joining using an insulating material is required. Furthermore, in production lines including the step of joining members in factories, improvement in the efficiency of operations that have conventionally been performed by joining via welding is expected. As described above, the introduction of joining techniques that replace welding has become important in recent years.

[0005] One alternative joining technology to welding is the use of liquid or film-type structural adhesives. Film-type adhesives, in particular, are highly reliable after bonding because they eliminate the need for adhesive application, allow for a uniform adhesive layer thickness, and minimize uneven application. They are especially useful in production lines that include processes for joining components in factories. Examples of such structural adhesives include epoxy adhesives, second-generation acrylic adhesives (hereinafter referred to as SGA), urethane resin adhesives, and silicone resin adhesives. Among these, epoxy adhesives are widely used due to their high adhesion to various materials such as metals and CFRP, as well as their high heat resistance.

[0006] For example, Patent Document 1 proposes an adhesive structure in which adherends having a difference in thermal expansion are bonded to each other via an adhesive layer, wherein the adhesive layer has a two-layer structure, and at least one of the layers is formed of a flexible epoxy composition mainly composed of an epoxy resin having two or more epoxy groups and being flexible in the cured state, in which adherends having a difference in thermal expansion are bonded to each other. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2004-323639 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in Patent Document 1, a flexible epoxy composition is first applied to a first adherend and cured at a temperature higher than the heat resistance temperature of the adherend, and then the cured flexible epoxy composition and the second adherend are bonded and cured together with another adhesive to bond adherends that have a difference in thermal expansion, which may result in uneven application of the adhesive. Furthermore, since the bonding process requires a temperature higher than the heat resistance temperature of the adherend, bonding to adherends such as steel plates, aluminum, glass, and super engineering plastics, where the adherend's temperature exceeds the thermal decomposition temperature of the adhesive, becomes difficult. Furthermore, when epoxy adhesives are used as structural adhesives, curing by heating is usually required. When multiple materials are laminated using epoxy adhesive and the adhesive is heated to cure, the viscosity of the adhesive decreases as it heats up, causing it to flow. This prevents the final thickness of the adhesive layer from being maintained, and significant warping occurs in the laminate due to the differences in the coefficients of thermal expansion of each material, so further improvements are needed.

[0009] The present invention aims to provide an epoxy resin-based adhesive sheet that maintains the thickness of the adhesive layer even after heat curing, suppresses the occurrence of warping after bonding with adherends having different coefficients of thermal expansion, and exhibits good adhesive strength to adherends such as steel plates and aluminum. [Means for solving the problem]

[0010] However, in view of these circumstances, the present inventors have succeeded in completing an adhesive sheet that can suppress the occurrence of warping after bonding with adherends having different coefficients of thermal expansion, and that has good adhesive strength. An adhesive sheet according to one aspect of the present invention comprises a resin layer (A) made of epoxy resin composition (a) and a resin layer (B) made of epoxy resin composition (b), wherein the gel fraction is 30% by mass or more and 95% by mass or less.

[0011] That is, the present invention has the following aspects. <1> An adhesive sheet comprising a resin layer (A) made of epoxy resin composition (a) and a resin layer (B) made of epoxy resin composition (b), wherein the gel fraction is 30% by mass or more and 95% by mass or less, and the resin layer (B) is uncured. <2> The thickness retention rate after applying pressure of 50 kPa at 150°C is 50% or more. <1> The adhesive sheet described above. <3> The tensile elongation is 5% or more. <1> or <2> The adhesive sheet described above. <4> After heat treatment at 180°C for 20 minutes, the tanδ peak, as determined by dynamic viscoelasticity measurement, is present above 80°C. <1> ~ <3> Adhesive sheet as described in any of the following. <5> The adhesive sheet according to claim 4, wherein, after heat treatment at 180°C for 20 minutes, the tanδ peak determined by dynamic viscoelasticity measurement is present even below 80°C. <6> In an adhesive sheet heat-treated at 180°C for 20 minutes, the resin layer (A) has a tanδ peak below 80°C, and the resin layer (B) has a tanδ peak at 80°C or higher. <5> The adhesive sheet described above. <7> In an adhesive sheet heat-treated at 180°C for 20 minutes, the difference between the tanδ peak temperature of resin layer (A) and the tanδ peak temperature of resin layer (B) is 40°C or more. <1> ~ <6> Adhesive sheet as described in any of the following. <8> In an adhesive sheet heat-treated at 180°C for 20 minutes, the ratio of the storage moduli of the resin layer (A) and the resin layer (B) at 25°C, (B) / (A), is 10 or more. <1> ~ <7> Adhesive sheet as described in any of the following. <9> The epoxy resin composition (a) contains a bifunctional epoxy compound having an aliphatic skeleton and an aromatic skeleton. <1> ~ <8> Adhesive sheet as described in any of the following. <10> The epoxy resin composition (b) contains a difunctional aromatic epoxy compound. <1> ~ <9> Adhesive sheet as described in any of the following. <11> The entire structure consists of multiple layers having at least a surface layer, an intermediate layer, and a back layer, wherein the resin layer (B) is the surface layer and the back layer, and the resin layer (A) is the intermediate layer. <1> ~ <10> Adhesive sheet as described in any of the following. <12> The thickness is 100 μm or more. <1> ~ <11> Adhesive sheet as described in any of the following. <13> The adhesive sheet according to any one of <1> to <12>, wherein a thickness ratio (A) / (B) of the resin layer (A) to the resin layer (B) is 0.25 or more. <14> The adhesive sheet according to any one of <1> to <13>, wherein a thickness of the resin layer (A) is 50 µm or more. <15> A cured product obtained by curing the adhesive sheet according to any one of <1> to <14>. <16> A laminate comprising a first material on one surface of the adhesive sheet according to any one of <1> to <14> and a second material on the other surface of the adhesive sheet, wherein the first material and the second material have different coefficients of linear expansion from each other. <17> The laminate according to <16>, wherein the first material contains aluminum. <18> The laminate according to <16> or <17>, wherein the second material contains iron. <19> An automotive exterior material using the laminate according to any one of <16> to <18>. Effects of the Invention

[0012] The adhesive sheet of the present invention can maintain the thickness of the adhesive layer even after heat curing, can suppress the occurrence of warpage after adhesion to adherends having different coefficients of linear expansion, and also has good adhesive strength to adherends such as steel sheets and aluminum. Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail based on example embodiments of the present invention, but the present invention is not limited to these embodiments.

[0014] <<Adhesive Sheet>> The adhesive sheet according to an embodiment of the present invention (hereinafter referred to as "the present adhesive sheet") comprises a resin layer (A) composed of an epoxy resin composition (a) and a resin layer (B) composed of an epoxy resin composition (b).

[0015] The adhesive sheet only needs to have at least one resin layer (A) and one resin layer (B), but from the viewpoint of adhesion to the material, it is preferable that the entire sheet consists of multiple layers having at least a surface layer, an intermediate layer and a back layer, with resin layer (B) being the surface layer and back layer, and resin layer (A) being the intermediate layer.

[0016] This adhesive sheet has a gel fraction of 30% to 95% by mass, and the resin layer (B) is uncured. From the viewpoint of suppressing the flow of the resin when heated, it is preferable that the resin layer (A) is fully cured. By inserting this adhesive sheet between the members to be joined and curing the resin layer (B) by heating and cooling, the members can be joined with good adhesive strength without causing resin flow or other issues. Because this adhesive sheet has a gel fraction of 30% to 95% by mass, resin flow during heating is suppressed and the thickness of the adhesive layer can be maintained. Therefore, even when joining members with different coefficients of thermal expansion, distortion due to the difference in coefficients of thermal expansion can be mitigated and warping can be suppressed. In this invention, "uncured" refers to a state in which the epoxy resin composition (b) has not been completely cured, and further curing of the epoxy resin composition (b) will proceed if heat or energy rays are applied. Whether the resin layer (B) is uncured can be determined, for example, after heat treatment at 180°C for 40 minutes, or by applying an integrated light intensity of 5000 mJ / cm². 2 This can be confirmed by whether the gel fraction increases by 5% by mass or more after UV irradiation. If the change in gel fraction after heat treatment is less than 5% by mass, the epoxy resin composition (b) is either not curable or has already fully cured.

[0017] (Gel fraction) From the viewpoint of suppressing the flow of resin between the layers of the members to be joined, the gel fraction of this adhesive sheet is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. From the viewpoint of improving wettability with the interface of the members to be joined and interaction with the members through reaction, the gel fraction is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less. The gel fraction of the adhesive sheet can be specifically measured by the method described in the examples. The gel fraction of this adhesive sheet can be adjusted by the types of components in resin layers (A) and (B), such as the main resin and curing agent, as well as the thickness ratio of resin layers (A) and (B).

[0018] (Thickness) The thickness of this adhesive sheet is preferably 100 μm or more, and more preferably 150 μm or more, from the viewpoint of absorbing the shear stress generated by the difference in the coefficient of thermal expansion between the joined members. Furthermore, since the tensile shear adhesive strength of the adhesive layer improves as the thickness of the adhesive layer decreases, the thickness of this adhesive sheet is preferably 2 mm or less, and more preferably 1.5 mm or less.

[0019] (Thickness of resin layer (A)) The thickness of the resin layer (A) can be adjusted as appropriate depending on the type of joining member. For example, when joining members with different coefficients of thermal expansion, high shear stress is generated in the adhesive sheet due to the difference in expansion rates during heating. From the viewpoint of reducing this shear stress, the thickness of the resin layer (A) in the adhesive sheet is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. Furthermore, from the viewpoint of the shear adhesion of the members after bonding, it is preferably 1000 μm or less, more preferably 900 μm or less, and even more preferably 800 μm or less. The thickness of the resin layer (A) can be calculated from cross-sectional observation of the adhesive sheet or from the thickness of the remaining sheet after gel fraction measurement, as described later.

[0020] (Thickness of resin layer (B)) The thickness of the resin layer (B) can be adjusted as appropriate depending on the type of bonding member. From the viewpoint of interfacial adhesion with the adherend, the thickness of the resin layer (B) is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, from the viewpoint of reducing contamination of the adherend and surrounding members due to resin flow during heat curing, it is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and even more preferably 60 μm or less. If there are multiple resin layers (B) in this adhesive sheet, it is preferable that the thickness of each layer is within the above range. The thickness of the resin layer (B) can be calculated by observing the cross-section of the adhesive sheet, or by subtracting the thickness of the remaining sheet after the gel fraction measurement described later from the thickness of the adhesive sheet.

[0021] (Thickness ratio) The thickness ratio (A) / (B) of resin layer (A) and resin layer (B) is preferably 0.25 or more, more preferably 0.5 or more, even more preferably 0.75 or more, and even more preferably 1 or more. Furthermore, it is preferably 1.2 or more, more preferably 1.4 or more, even more preferably 1.50 or more, even more preferably 1.6 or more, and particularly preferably 1.8 or more. If there are multiple resin layers (A) and resin layers (B) in this adhesive sheet, it is preferable that the ratio of the total thickness of resin layer (A) to the total thickness of resin layer (B) is within the above range. When (A) / (B) is greater than or equal to the lower limit above, the flow of the resin during heating is suppressed, which helps maintain the thickness of the adhesive layer and tends to suppress the occurrence of warping after bonding with adherends having different coefficients of thermal expansion.

[0022] (Thickness retention rate) From the viewpoint of suppressing resin flow, the thickness retention rate of this adhesive sheet is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. Furthermore, since it is preferable to allow some flow to improve adhesion with the joining members, the thickness retention rate is preferably less than 100%, more preferably 99.5% or less, and even more preferably 99.0% or less. The thickness retention rate of this adhesive sheet can be calculated by measuring the thickness (Ta) of the adhesive sheet, inserting it into two SPCC steel plates, heating it to 150°C under pressure of 50kPa, holding it for 20 minutes to cure, measuring the thickness (Tb) of the adhesive sheet after curing, and then calculating Tb / Ta × 100 (%).

[0023] (Tensile elongation) The tensile elongation (%) of this adhesive sheet after heat curing is preferably 5% or more, more preferably 7% or more, and even more preferably 10% or more, from the viewpoint of mitigating the shear stress caused by the difference in expansion rates during heating when joining members with different coefficients of linear expansion. Furthermore, there is no particular upper limit, but it is preferable that it is within a range that does not suppress the reduction in adhesive strength due to a reduction in rigidity or the displacement of members due to deformation. From these viewpoints, it is preferably 500% or less, more preferably 300% or less, and even more preferably 100% or less. The tensile elongation can be measured specifically by the method described in the examples.

[0024] (tanδ peak) After heat-treating the adhesive sheet at 180°C for 20 minutes, the tanδ peak determined by dynamic viscoelasticity measurement contributes to improving the high-temperature heat resistance and shear adhesive strength at room temperature of the adhesive sheet. From the above viewpoint, the tanδ peak of this adhesive sheet is preferably located at 80°C or higher, more preferably at 90°C or higher, and even more preferably at 100°C or higher. Regarding the above tanδ peak, it is preferable that there be one or more tanδ peaks within the above range, and two or more may also be present. Furthermore, there is no particular upper limit, but since the tanδ peak temperature is usually also the glass transition temperature (Tg), as it increases, it becomes easier to set a higher curing temperature for complete curing. From the viewpoint of productivity, it is preferable to lower the heating process temperature of the adhesive, so the tanδ peak temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower. The tanδ peak at 80°C or higher is preferably present in the epoxy resin composition (b) and preferably in the resin layer (B).

[0025] Preferably, this adhesive sheet has one or more tanδ peaks below 80°C. Having tanδ peaks below 80°C helps to alleviate shear stress due to differences in thermal expansion when different materials are used as joining members. The tanδ peaks below 80°C are preferably at 70°C or below, more preferably at 60°C or below, even more preferably at 50°C or below, and even more preferably at 40°C or below. The lower limit is not particularly limited, but from the viewpoint of adhesive strength due to crosslinking density and epoxy resin structure, it may be -80°C or above, preferably -40°C or above, more preferably 0°C or above, and even more preferably 20°C or above. From the viewpoint of performing stress relaxation without impairing adhesion, the tanδ peak below 80°C is preferably present in the epoxy resin composition (a) and preferably in the resin layer (A).

[0026] To adjust the tanδ peak temperature of this adhesive sheet to the above range, for example, one may adjust the type and amount of each epoxy resin and curing agent constituting epoxy resin compositions (a) and (b), introduce low Tg components such as olefin structures or high Tg components such as benzene skeletons into each epoxy resin and curing agent constituting epoxy resin compositions (a) and (b) by polymerization or reaction, blend in other compatible materials such as plasticizers, reactive silane oligomers, or urethane oligomers, or add surface treatments, finely milled rubber components, or inorganic fillers to epoxy resin compositions (a) and (b). However, the method is not limited to these methods.

[0027] In this adhesive sheet, the difference in tanδ peak temperature between resin layer (A) and resin layer (B) is preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, and particularly preferably 70°C or higher. On the other hand, there is no particular limit to the upper limit, but it is usually preferably 300°C or lower, more preferably 250°C or lower, even more preferably 200°C or lower, and particularly preferably 150°C or lower. If it is above the lower limit, it is easier to mitigate the strain caused by the difference in linear expansion coefficients when joining members with different linear expansion coefficients.

[0028] Furthermore, in terms of the storage modulus at 25°C determined by dynamic viscoelasticity measurement, the storage modulus ratio (B) / (A) between the resin layer (A) and the resin layer (B) is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more. On the other hand, there is no particular upper limit, but it is usually preferably 100 or less, more preferably 80 or less, and even more preferably 60 or less. If it is above the lower limit, it is easier to mitigate the strain caused by the difference in linear expansion coefficients when joining members with different linear expansion coefficients.

[0029] <Epoxy resin compositions (a) and (b)> Both epoxy resin compositions (a) and (b) contain epoxy resin. It is preferable that epoxy resin is the main component of epoxy resin compositions (a) and (b). Herein, "main component" as used herein means the component that has the highest content (mass%) among the components constituting epoxy resin compositions (a) and (b). The content of the main component in epoxy resin compositions (a) and (b) is preferably 50% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, and more preferably 90% by mass or more (it may also be 100% by mass). The epoxy resin compositions (a) and (b) may be the same or different, but it is preferable that they be different in terms of ease of enjoying the effects of the present invention.

[0030] (Epoxy resin) Next, epoxy resins that can be used in epoxy resin compositions (a) and (b) will be described. It is preferable to select and use a type of epoxy resin from among these that will provide the above-mentioned physical properties required for this adhesive sheet.

[0031] As the epoxy resins of epoxy resin compositions (a) and (b), for example, difunctional aromatic epoxy compounds such as bisphenols such as bisphenol A, bisphenol F, bisphenol B, bisphenol C, bisphenol AD, and bisphenolacetophenone; bifunctional phenol-type epoxy compounds having a skeleton such as biphenol, catechol, resorcinol, hydroquinone, and dihydroxynaphthalene; difunctional aliphatic epoxy compounds such as difunctional glycidyl ether-type epoxy compounds, difunctional glycidyl ester-type epoxy compounds, difunctional glycidylamine-type epoxy compounds, and difunctional linear aliphatic epoxy compounds; difunctional alicyclic epoxy compounds; difunctional heterocyclic epoxy compounds; and hydrogenated epoxy compounds such as hydrogenated bisphenol A-type epoxy compounds can be used. Only one of the above epoxy resins may be used, or two or more may be used in any combination and ratio.

[0032] In particular, as the epoxy resin in this embodiment, it is preferable to use an epoxy resin having at least one skeleton from among the phenyl skeleton (phenol skeleton), naphthalene skeleton, fluorene skeleton, biphenyl skeleton, anthracene skeleton, pyrene skeleton, xanthene skeleton, adamantane skeleton, and dicyclopentadiene skeleton. From the viewpoint of heat resistance, it is more preferable to use an epoxy resin having at least one of the phenyl skeleton, fluorene skeleton, and biphenyl skeleton. From the viewpoint of ease of manufacture and heat resistance, it is even more preferable to use an epoxy resin having at least one skeleton from among the bisphenol A skeleton, bisphenol F skeleton, and biphenyl skeleton. The type and structure of epoxy resins can be confirmed by NMR (nuclear magnetic resonance spectroscopy), IR (infrared spectroscopy), SEM (scanning electron microscopy) analysis, IPC (inductively coupled plasma) emission spectroscopy, TGA (thermogravimetric analysis), DSC (differential scanning calorimetry), and various chromatography methods.

[0033] In this embodiment, it is even more preferable that the epoxy resin contains one obtained from the epoxy resin precursor and curing agent described below, among the epoxy resins mentioned above.

[0034] (Epoxy resin precursor) In this embodiment, the epoxy resin precursor refers to a compound containing one or more epoxy compounds that can be cured to produce an epoxy resin. The epoxy compound is a compound having an epoxy group in its molecule, and is a compound that can be subjected to an addition reaction or self-polymerization reaction by at least one of the curing agent and curing catalyst described later, thereby constituting a thermosetting resin.

[0035] Examples of the epoxy compounds that can be used include bisphenols such as bisphenol A, bisphenol F, bisphenol B, bisphenol C, bisphenol AD, and bisphenolacetophenone; bifunctional aromatic epoxy compounds such as biphenol, catechol, resorcinol, hydroquinone, and dihydroxynaphthalene-type bifunctional phenol-type epoxy compounds; bifunctional aliphatic epoxy compounds such as bifunctional glycidyl ether-type epoxy compounds, bifunctional glycidyl ester-type epoxy compounds, bifunctional glycidylamine-type epoxy compounds, and bifunctional linear aliphatic epoxy compounds; bifunctional alicyclic epoxy compounds; bifunctional heterocyclic epoxy compounds; and hydrogenated epoxy compounds such as hydrogenated bisphenol A-type epoxy compounds. In this embodiment, the epoxy resin precursor may be one of the epoxy compounds exemplified above, or two or more may be used in any combination and ratio.

[0036] In this embodiment, it is preferable that the epoxy resin precursor contains one or more compounds, including the epoxy compounds exemplified above.

[0037] From the viewpoint of the flexibility of the adhesive sheet, the epoxy resin composition (a) more preferably contains at least one difunctional aliphatic epoxy compound as an epoxy resin precursor, and even more preferably contains a difunctional aliphatic epoxy compound and an aromatic compound.

[0038] As the above-mentioned bifunctional aliphatic epoxy compound, an aliphatic epoxy compound derived from diglycidyl ether with a purity of 90% by mass or higher can be used, obtained by reacting a diol having 2 to 12 carbon atoms with an epihalohydrin and then purifying it by distillation. Examples of the above-mentioned difunctional aliphatic epoxy compounds include glycidyl ether of ethylene glycol, glycidyl ether of propylene glycol, glycidyl ether of 1,4-butanediol, glycidyl ether of 1,6-hexanediol, glycidyl ether of 1,8-octanediol, glycidyl ether of 1,10-decanediol, glycidyl ether of 2,2-dimethyl-1,3-propanediol, glycidyl ether of diethylene glycol, glycidyl ether of triethylene glycol, glycidyl ether of tetraethylene glycol, glycidyl ether of hexaethylene glycol, and glycidyl ether of 1,4-cyclohexanedimethanol. One of the above-mentioned difunctional aliphatic epoxy compounds may be used alone, or two or more may be used in any combination and ratio. Among these, it is preferable to use glycidyl ether of 1,4-butanediol, glycidyl ether of 1,6-hexanediol, glycidyl ether of 1,4-cyclohexanedimethanol, or glycidyl ether of 2,2-dimethyl-1,3-propanediol, as these have a significant effect in reducing the viscosity of the epoxy resin precursor and minimize the decrease in the heat resistance of the cured product.

[0039] Examples of the above aromatic compounds include bisphenols such as bisphenol A, bisphenol F, bisphenol B, bisphenol C, bisphenol AD, and bisphenolacetophenone, as well as compounds having a skeleton such as biphenol, catechol, resorcinol, hydroquinone, and dihydroxynaphthalene. One of the aromatic compounds exemplified above may be used alone, or two or more may be used in any combination and ratio. Among these, it is preferable to use at least one of bisphenol A and bisphenol F from the viewpoint of the rigidity and heat resistance of the resulting epoxy resin.

[0040] In other words, the epoxy resin precursor of epoxy resin composition (a) in this embodiment is more preferably a difunctional aliphatic epoxy compound and at least one compound of bisphenol A and bisphenol F.

[0041] In this embodiment, if the epoxy resin precursor contains two or more compounds including an epoxy compound, it is preferable to use a mixture and / or reaction of the two or more compounds as the epoxy resin precursor, and it is more preferable to use a mixture of the two or more compounds and a polymerization initiator, followed by a polymerization reaction. As the polymerization initiator mentioned above, the same curing agent used for curing the epoxy resin precursor can be used. Among these, thermal polymerization initiators such as phosphonium salts, sulfonium salts, benzothiazonium salts, and ammonium salts are preferred, with phosphonium salts being more preferred.

[0042] In other words, as the epoxy resin precursor in this embodiment, it is preferable to use one obtained by mixing the difunctional aliphatic epoxy compound exemplified above with an aromatic compound and a polymerization initiator and performing a polymerization reaction, and it is more preferable to use one obtained by mixing the difunctional aliphatic epoxy compound with at least one compound of bisphenol A and bisphenol F and a polymerization initiator and performing a polymerization reaction.

[0043] Therefore, it is particularly preferable that the epoxy resin precursor of epoxy resin composition (a) in this embodiment contains a bifunctional epoxy compound having both an aliphatic skeleton and an aromatic skeleton.

[0044] Furthermore, from the viewpoint of the rigidity of the adhesive sheet and adhesion to the member, the epoxy resin composition (b) more preferably contains at least one difunctional aromatic epoxy compound, and even more preferably contains at least one difunctional phenolic epoxy compound. In particular, it is even more preferable to contain bisphenol A and / or bisphenol F.

[0045] (average molecular weight) There are no particular restrictions on the molecular weight of the epoxy resin precursor in epoxy resin compositions (a) and (b). The molecular weight of the epoxy resin precursor is typically 100 or more, preferably 200 or more, and more preferably 300 or more, based on the mass-average molecular weight (Mw) in polystyrene terms, as measured by gel permeation chromatography (GPC). On the other hand, the molecular weight of the epoxy resin precursor is typically 200,000 or less, preferably 100,000 or less, and more preferably 50,000 or less. Furthermore, the number-average molecular weight (Mn) of the epoxy resin precursor is usually 100 or more, preferably 200 or more, and more preferably 300 or more. On the other hand, the number-average molecular weight of the epoxy resin precursor is usually 100,000 or less, preferably 80,000 or less, and more preferably 50,000 or less. Having the molecular weight of the epoxy resin precursor within the above range is preferable because it improves the solubility of the curing agent and each component in the epoxy resin precursor, resulting in an adhesive with properties such as viscosity that are easy to handle with conventional manufacturing equipment, and thus improving adhesion.

[0046] (Epoxy group equivalent) The epoxy group equivalent (or epoxy equivalent) of the epoxy resin precursor in epoxy resin compositions (a) and (b) can be measured by the method specified in JIS K 7236. The epoxy group equivalent of the epoxy resin precursor is usually 50 or more, preferably 80 or more, more preferably 100 or more, even more preferably 120 or more, and particularly preferably 150 or more. On the other hand, the epoxy group equivalent of the epoxy resin precursor is usually 100,000 or less, preferably 10,000 or less, more preferably 3,000 or less, even more preferably 1,500 or less, and particularly preferably 1,000 or less. If the epoxy equivalent of the epoxy resin precursor is below the above upper limit, the amount of epoxy groups and hydroxyl groups produced after the reaction increases, which increases the interaction with the first and second materials that become the adherends, and tends to result in excellent adhesion after curing. On the other hand, if the epoxy equivalent of the epoxy resin precursor is above the above lower limit, the crosslinking density decreases, and flexibility and elasticity improve, which tends to result in a superior effect in reducing warping in the laminate. Methods for adjusting the epoxy group equivalent of an epoxy resin precursor include reducing the degree of polymerization in the epoxy resin skeleton or introducing a skeleton with a small molecular weight.

[0047] (Hardening agent) Examples of curing agents in this embodiment include thermosetting agents that start reacting with heat, and photocuring agents that start reacting with light. The curing agent can be appropriately selected from known curing agents depending on the curing method of the adhesive in the laminate of this embodiment. For example, a photocuring agent (photopolymerization initiator) can be selected when using a photocuring method, and a thermocuring agent (thermal polymerization initiator) can be selected when using a thermocuring method. The photocuring method is a curing method that uses at least one of the active energy ray curing methods, namely ultraviolet light, visible light, and infrared light. In this embodiment, if it is desired to cure the epoxy resin precursor in an environment where light irradiation is difficult, it is preferable to cure it by a thermocuring method. In this embodiment, it is preferable to use a thermocuring agent or to use a combination of a thermocuring agent and a photocuring agent.

[0048] =Thermosetting agent= Examples of thermosetting agents in this embodiment include phenolic curing agents; amine curing agents such as aliphatic amines, polyetheramines, alicyclic amines, and aromatic amines; acid anhydride curing agents; amide curing agents; urea curing agents; tertiary amines; imidazoles and their derivatives; organophosphines; phosphonium salts; tetraphenylboron salts; organic acid dihydrazides; boron halogenated amine complexes; polymercaptan curing agents; isocyanate curing agents; and blocked isocyanate curing agents.

[0049] Of the above, phenolic curing agents, amine curing agents, acid anhydride curing agents, etc., are incorporated into the epoxy resin framework by reacting with the epoxy resin precursor. Therefore, the most preferable amount of curing agent to be blended into the epoxy resin in this embodiment is an amount such that the epoxy group and the active part (active hydrogen part, acid anhydride part) are in chemical equivalent (1.0). However, the amount of curing agent may be adjusted to control viscosity, reaction rate, and physical properties after curing. In this case, the amount of curing agent blended relative to the epoxy group is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, based on chemical equivalent. Furthermore, a chemical equivalent of 5.0 or less is preferred, more preferably 4.0 or less, and even more preferably 3.0 or less. It is preferable that the blending amount is within the above range, as this prevents the elution of unreacted components and insufficient crosslinking density during use, resulting in good heat resistance and moisture resistance of the epoxy resin.

[0050] Furthermore, curing agents other than phenolic, amine, and acid anhydride-based curing agents typically act primarily as curing catalysts or co-catalysts in the self-polymerization of epoxy resin precursors. The amount of curing agent to be added is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of epoxy resin precursor. On the other hand, the amount of curing agent to be added 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, per 100 parts by mass of epoxy resin precursor. If the amount of the compound is above the lower limit, the curing reaction of the epoxy resin precursor tends to be accelerated. Conversely, if the amount of the compound is below the upper limit, the resin composite material tends to be less prone to a decrease in physical properties such as heat resistance and moisture resistance due to residual curing agent, and less prone to catalyst bleed-out during use.

[0051] -Phenol-based curing agent- Examples of the above-mentioned phenolic curing agents include bisphenol A, bisphenol F, 4,4'-dihydroxydiphenylmethane, 4,4'-dihydroxydiphenyl ether, 1,4-bis(4-hydroxyphenoxy)benzene, 1,3-bis(4-hydroxyphenoxy)benzene, 4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl ketone, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxybiphenyl, 2,2'-dihydroxybiphenyl, 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, phenol novolac, bisphenol A novolac, o-cresol novolac, m-cresol novolac, p-cresol novolac, xylenol novolac, poly-p-hydroxystyrene, hydroquinone, resorcinol, catechol, and t-butylcatechol. t-butylhydroquinone, fluoroglycinol, pyrogallol, t-butylpyrogallol, allylated pyrogallol, polyallylated pyrogallol, 1,2,4-benzenetriol, 2,3,4-trihydroxybenzophenone, 1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene Examples include 1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,4-dihydroxynaphthalene, 2,5-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, 2,8-dihydroxynaphthalene, allylated and polyallylated dihydroxynaphthalenes, allylated bisphenol A, allylated bisphenol F, allylated phenol novolac, allylated pyrogallol, and the like.

[0052] - Amine-based curing agents - Aliphatic amines, polyetheramines, alicyclic amines, aromatic amines, and the like can be used as the amine-based curing agent. Examples of aliphatic amines include ethylenediamine, 1,3-diaminopropane, 1,4-diaminopropane, hexamethylenediamine, 2,5-dimethylhexamethylenediamine, trimethylhexamethylenediamine, diethylenetriamine, iminobispropylamine, bis(hexamethylene)triamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N-hydroxyethylethylenediamine, and tetra(hydroxyethyl)ethylenediamine. Examples of polyetheramines include triethylene glycol diamine, tetraethylene glycol diamine, diethylene glycol bis(propylamine), polyoxypropylenediamine, and polyoxypropylene triamines. Examples of alicyclic amines include isophoronediamine, metacenediamine, N-aminoethylpiperazine, bis(4-amino-3-methyldicyclohexyl)methane, bis(aminomethyl)cyclohexane, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro(5,5)undecane, and norbornenediamine. Aromatic amines include tetrachloro-p-xylenediamine, m-xylenediamine, p-xylenediamine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2,4-diaminoanisole, 2,4-toluenediamine, 2,4-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diamino-1,2-diphenylethane, 2,4-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, m-aminophenol, m-aminobenzylamine, benzyldimethylamine, 2-(dimethylaminomethyl)phenol, triethanolamine, methylbenzylamine, α-(m-aminophenyl)ethylamine, α-(p-aminophenyl)ethylamine, diaminodiethyldimethyldiphenylmethane, and α,α'-bis(4-aminophenyl)-p-diisopropylbenzene.

[0053] -Acid anhydride curing agent- Examples of the above acid anhydride-based curing agents include dodecenyl succinic anhydride, polyadipic anhydride, polyazelaic anhydride, polysebacic anhydride, poly(ethyl octadecanediic acid) anhydride, poly(phenylhexadecanedioic acid) anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, methylhymic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexenedicarboxylic acid anhydride, methylcyclohexenetetracarboxylic acid anhydride, phthalic anhydride Examples include acids, trimellitic anhydride, pyromellitic anhydride, benzophenonetetracarboxylic anhydride, ethylene glycol bistrimellitate dianhydride, hetic anhydride, nadic anhydride, methylnadic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexane-1,2-dicarboxylic anhydride, 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid dianhydride, and 1-methyl-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid dianhydride.

[0054] - Amide-based curing agent - Examples of the above-mentioned amide-based curing agents include dicyandiamide and polyamide resins.

[0055] -Urea-based hardening agent- Examples of the above-mentioned urea-based curing agents include urea compounds such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-phenyl-1,1-dimethylurea, toluenebis(dimethylurea), isophoronebisurea, and 4,4'-methylenebis(phenyldimethylurea).

[0056] -Tertiary amine- Examples of the above-mentioned tertiary amines include 1,8-diazabicyclo(5,4,0)undecene-7, triethylenediamine, benzyldimethylamine, triethanolamine, dimethylaminoethanol, and tris(dimethylaminomethyl)phenol.

[0057] - Imidazole and its derivatives - Examples of the above imidazoles and their derivatives include 1-cyanoethyl-2-phenylimidazole, 2-phenylimidazole, 2-ethyl-4(5)-methylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyano-2-phenylimidazole, 1-cyanoethyl-2-undecylimidazole trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[ Examples include 2'-methylimidazolyl-(1')-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and compounds obtained by adding these imidazoles to epoxy compounds.

[0058] -Organophosphines- Examples of the above-mentioned organic phosphines include tributylphosphine, methyldiphenylphosphine, triphenylphosphine, diphenylphosphine, and phenylphosphine.

[0059] -Phosphonium salt- Examples of the phosphonium salts mentioned above include tetraphenylphosphonium-tetraphenylborate, tetraphenylphosphonium-ethyltriphenylborate, and tetrabutylphosphonium-tetrabutylborate.

[0060] -Tetraphenylborone salt- Examples of the tetraphenylborone salts mentioned above include 2-ethyl-4-methylimidazole tetraphenylborate and N-methylmorpholine tetraphenylborate.

[0061] =Photocuring agent= Examples of photocuring agents in this embodiment include acetophenones, benzophenones, benzoin ethers, hydroxyketones, acylphosphine oxides, diazonium cationonium salts, iodonium cationonium salts, sulfonium cationonium salts, and the like.

[0062] Specific examples of photocuring agents include 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 1-hydroxy-cyclohexylphenyl ketone, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoylphenylethoxyphosphine oxide, and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,2-hydroxy C-2-methyl-1-phenylpropan-1-one, 2-[methyl-1-(4-methylthio)phenyl]-2-morpholinopropan-1-one, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2-hydroxy-2-methyl-[4-(1-methylvinyl)phenyl]propanol oligomer, isopropylthioxanthone, o-benzoylbenzoic acid Methyl, [4-(methylphenylthio)phenyl]phenylmethane, 2,4-diethylthioxanthone, 2-chlorothioxanthone, benzophenone, ethylanthraquinone, benzophenone ammonium salt, thioxanthone ammonium salt, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, 4,4'-bisdiethylaminobenzophenone, 1,4-dibenzoylbenzene, 10 -Butyl-2-chloroacridone, 2,2'-bis(o-chlorophenyl)-4,5,4',5'-tetrakis(3,4,5-trimethoxyphenyl)-1,2'-biimidazole, 2,2'-bis(o-chlorophenyl)-4,5,4',5'-tetraphenyl-1,2'-biimidazole, 2-benzoylnaphthalene, 4-benzoylbiphenyl, 4-benzoyldiphenyl ether, acrylic benzophenone, dibenzoyl, bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-Difluoro-3-(1H-pyrrole-1-yl)-phenyl)titanium, o-methylbenzoyl benzoate, p-dimethylaminobenzoate ethyl ester, p-dimethylaminobenzoate isoamyl ethyl ester, activated tert-amine, carbazole-phenone photopolymerization initiator, acridine photopolymerization initiator, triazine photopolymerization initiator, benzoyl, triallylsulfonium, hexafluorophosphate salt, phosphorus hexafluoride-based aromatic sulfonium salt, antimony hexafluoride-based aromatic sulfonium salt, antimony hexafluoride-based aromatic sulfonium Salt, antimony hexafluoride-based aromatic sulfonium salt, triallylsulfonium, hexafluoroantimony, 4-methylphenyl-[4-(2-methylpropyl)phenyl]-iodonium hexafluorophosphate, 1,2-octanedione, 1-[4-(phenylthio)-2-(o-benzoyl oxime)], 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-1-(o-acetyloxime), ethyl-4-dimethylaminobenzoate, ethyl-4-dimethylaminobenzoate, 2-ethylhexyl-4 -Dimethylaminobenzoate, (9-oxo9H-xanthene-2-yl)phenyliodonium hexafluorophosphate, bis[4-n-alkyl(C10~13)phenyl]iodonium hexafluorophosphate, bis[4-n-alkyl(C10~13)phenyl]iodonium hexafluoroantimony, triphenylsulfonium trifluorosulfonate, triphenylsulfonium bicyclo[2.2.1]heptan-1-methanesulfonate, (9-oxo-9H-xanthene-2-yl)phenylsulfonium hexafluoro Lophosphate, p-azidobenzaldehyde, p-azidoacetophenone, p-azidobenzoic acid, p-azidobenzaldehyde-2-sulfonate sodium salt, p-azidobenzalacetophenone, 4,4'-diazidochalcone, 4,4'-diazidodiphenyl sulfide, 3,3'-diazidodiphenyl sulfide, 2,6-bis-(4'-azidobenzal)-4-methylcyclohexane, 1,3-bis-(4'-azidobenzal)-propanone, 4,4'-diazidochalcone-2-sulfonate sodium salt, 4,4'-diazidostilbene-2,2'-Sodium disulfonate, 1,3'-Bis-(4'-azidobenzal)-2'-Sodium disulfonate-2-propanone, 2,6-Bis-(4'-azidobenzal)-2'-Sulfonic acid (sodium salt) cyclohexanone, 2,6-Bis-(4'-azidobenzal)-2'-Sulfonic acid (sodium salt) 4-methylcyclohexanone, α-Cyano-4,4'-Dibenzostilbene, 2,5-Bis-(4'-azidobenzalsulfonic acid Sodium salt) cyclopentanone, 3-sulfonyl azidobenzoic acid, 4-sulfonyl azidobenzoic acid, cinnamic acid, α-cyanocinnamyrideneacetone acid, p-azido-α-cyanocinnamic acid, p-phenylenediacrylic acid, p-phenylenediacrylate diethyl ester, polyvinyl cinnamate, polyphenoxy-isopropyl cinnamyridene acetate, polyphenoxy-isopropyl-α-cyanocinnamyridene acetate, naphthoxy Non(1,2)diazide(2)-4-sulfonate sodium salt, naphthoquinone(1,2)diazide(2)-5-sulfonate sodium salt, naphthoquinone(1,2)diazide(2)-5-sulfonate ester (I), naphthoquinone(1,2)diazide(2)-5-sulfonate ester (II), naphthoquinone(1,2)diazide(2)-4-sulfonate salt, 2,3,4,4'-tetrahydroxybenzophenone tri(naphthoquinone diazide sulfonate Examples include esters, naphthoquinone-1,2,5-(trihydroxybenzophenone) triester, 1,4-iminoquinone-diazide(4)-2-sulfoamide(I), 1-diazo-2,5-diethoxy-4-p-trimercaptobenzene salt, 5-nitroacenaphthene, N-acetylamino-4-nitronaphthalene, organoboron compounds, and other photoacid generators that generate cations upon exposure to light, and photobase generators that generate anions upon exposure to light.

[0063] In this embodiment, the curing agent may be one of the curing agents exemplified above used alone, or two or more may be used in any combination and ratio. Furthermore, the curing agent may form a complex with a solvent or the like. It may also form a polymer. The curing agent may be completely decomposed, partially decomposed, or not decomposed at all after the manufacture of the laminate using this adhesive sheet.

[0064] As the curing agent in epoxy resin composition (a), an amine-based curing agent that exhibits excellent curing properties at low temperatures is preferred, and an alicyclic amine curing agent is more preferred. Furthermore, as the curing agent in epoxy resin composition (b), at least one selected from amide-based curing agents, urea-based curing agents, and imidazole and its derivatives, which have excellent storage stability and rapid curing at high temperatures, is preferred, and a combination of amide-based and urea-based curing agents is more preferred. In addition, a latent curing agent is preferred as the curing agent in epoxy resin composition (b). A latent curing agent is a curing agent that, when blended with epoxy resin, can be stored stably at room temperature (23°C) and has the ability to rapidly cure due to heat, light, pressure, etc.

[0065] (solvent) The epoxy resin compositions (a) and (b) may optionally contain a solvent. Examples of solvents include alcohols such as methanol, ethanol, and isopropyl alcohol; aromatic hydrocarbons such as toluene and xylene; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and dimethylformamide. These solvents can also be used as mixed solvents of two or more types as appropriate.

[0066] (Other ingredients) The epoxy resin compositions (a) and (b) may optionally contain other components, such as sensitizers, crosslinking agents, UV absorbers, polymerization inhibitors, silane coupling agents, fillers, antioxidants, leveling agents, slip agents, fine particles, dispersants, organic peroxides, reducing agents, radical polymerizable compounds; antioxidants, plasticizers, defoamers, polymerization initiators, inorganic fine particles, elastomers, and other various additives. For example, by incorporating elastomers, the viscosity of the adhesive sheet and the flexibility and impact resistance of its cured product can be adjusted. Furthermore, by incorporating polymerization initiators such as peroxides, azo compounds, and photopolymerization initiators, the strength of the cured product obtained from this adhesive sheet can be adjusted.

[0067] <Method for manufacturing this adhesive sheet> This adhesive sheet can be manufactured, for example, by forming an epoxy resin composition (a) into a film and then heating and curing it to create a resin layer (A), and then subsequently creating an uncured resin layer (B) from an epoxy resin composition (b), and then bonding the films together by applying pressure to adhere them. More specifically, one method involves applying the epoxy resin composition (b) to the above-mentioned release film, drying it to create an uncured resin layer (B), and then transferring it to the resin layer (A).

[0068] Alternatively, for example, an epoxy resin composition (a) can be formed into a film and then heated to create a resin layer (A). The epoxy resin composition (b) can then be applied to at least one surface of this resin layer (A) and dried.

[0069] Furthermore, the epoxy resin compositions (a) and (b) can also be produced by extruding them onto a release film or the like in a laminated state of two types in two layers or two types in three layers using a die such as a T-die, then molding them with a cast roll or the like, and heating to cure only the resin layer (A). However, the manufacturing method of this adhesive sheet is not limited to this method.

[0070] (Release film) This adhesive sheet may have a release film on its outermost surface to improve handling. Preferably, the release film is peeled off when the adhesive sheet is attached to the substrate. The thickness of the release film is preferably 1 to 500 μm, more preferably 5 to 300 μm, even more preferably 10 to 200 μm, and even more preferably 20 to 150 μm. If there are multiple release films on the adhesive sheet, it is preferable that the thickness of each layer is within the above range. The thickness (average thickness) of the release film is measured using a micrometer and determined by the arithmetic mean of these measurements.

[0071] Examples of substrates for release films include thin sheets made from materials such as paper, resin, and metal. In particular, sheets made of paper or resin are preferred because they are inexpensive, easy to process, and easy to dispose of or recycle, with resin being even more preferred in terms of transparency.

[0072] As for the paper, for example, high-quality paper, kraft paper, glassine paper, parchment paper, supercalendered kraft paper, etc., that have been treated with a silicone coating on their surface can be used.

[0073] As the resin film, for example, films mainly composed of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyimide, or polycarbonate can be used. The peel strength may be adjusted by applying a silicone resin release agent, a melamine-based resin release agent, a fluorine-based release agent, etc., to the surface of these films. Furthermore, from the standpoint of appearance, ease of processing, durability, heat resistance, and cost, the release film preferably includes a resin film mainly composed of polyester. As long as it does not exceed the scope of the present invention, the resin film may be a single layer or a multilayer structure of two or more layers. Furthermore, "main component resin" refers to the resin that makes up the largest proportion of the resins constituting the base material, specifically resins that account for 50% or more by mass, more specifically 70% or more by mass, more specifically 80% or more by mass, and more specifically 90% or more by mass (including 100% by mass).

[0074] The polyester described above is preferably obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. The polyester may be a polyester composed of one aromatic dicarboxylic acid and one aliphatic glycol, or it may be a copolymerized polyester obtained by further copolymerizing one or more other components. Examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid, while examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. On the other hand, dicarboxylic acids that can be used as other components of copolymerized polyesters include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, and sebacic acid, while glycol components include ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol. Oxycarboxylic acids such as p-oxybenzoic acid can also be used. Typical polyesters include polyethylene terephthalate, obtained by polycondensation of terephthalic acid and ethylene glycol, and polyethylene naphthalate, obtained by polycondensation of 2,6-naphthalenedicarboxylic acid and ethylene glycol.

[0075] The polyester film may be either an unoriented or oriented film, but an oriented film is preferred from the viewpoint of mechanical strength, and a biaxially oriented film is more preferred. Furthermore, the polyester film may be pre-treated with surface treatments such as corona treatment or plasma treatment.

[0076] The release film is preferably a mat-like film with minute irregularities formed on its surface, from the viewpoint of facilitating the transfer of the resin layer (B) to the resin layer (A) and improving the wettability of the resin layer (B) to the release film during film formation. The method for making the film mat-like is not particularly limited and includes methods such as providing a release layer containing a filler on the surface and sandblasting (sand mat treatment).

[0077] <Cured product> This adhesive sheet can be cured by heating and cooling, which also hardens the resin layer (B).

[0078] The heating temperature during the curing process is preferably 60°C or higher. However, if the heating temperature is too high, the adhesive properties and reliability may decrease due to decomposition or oxidative degradation of the epoxy resin composition. Therefore, the heating temperature is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. On the other hand, it is preferably 250°C or lower, and more preferably 200°C or lower. The heating time is not particularly limited as long as it is sufficient time for the curing reaction of the composition constituting the adhesive sheet to proceed. Typically, it is between 5 minutes and 200 hours, and preferably between 10 minutes and 150 hours.

[0079] Furthermore, from the viewpoint of productivity and other factors, the cooling rate during the curing process is preferably 0.1°C / min or higher, more preferably 0.5°C / min or higher, and even more preferably 1°C / min or higher. On the other hand, to reduce the decrease in adhesiveness, uneven adhesion, uneven appearance, and warping that occur due to cooling distortion within the components and adhesive, the cooling time is preferably 40°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less.

[0080] <Laminate> By laminating this adhesive sheet between a first material and a second material having different coefficients of thermal expansion, the occurrence of warping after heat curing can be suppressed. In other words, the laminate according to one embodiment of the present invention is a laminate comprising a first material on one side of the adhesive sheet and a second material on the other side, wherein the first material and the second material have different coefficients of thermal expansion.

[0081] The first and second materials in this embodiment are not particularly limited as long as their coefficients of thermal expansion are different from each other. For example, metal, resin, glass, etc., can be used as the first and second materials. Only one of these materials may be used, or two or more may be used in any combination and ratio. Examples of the above-mentioned metals include aluminum, iron, copper, titanium, magnesium, and alloys containing one or more of these metals. Furthermore, as the above-mentioned resins, for example, curable resins such as epoxy resin, phenolic resin, vinyl ester resin, urethane resin, melamine resin, urea resin, silicone resin, acrylic resin, and unsaturated polyester resin can be used; polyester resins such as polyethylene resin, polypropylene resin, polyamide resin, polystyrene resin, ABS (acrylonitrile-butadiene-styrene copolymer) resin, acrylic resin, polyvinyl chloride resin, polyethylene terephthalate, and PBT (polybutylene terephthalate); polyoxymethylene resin, polyamide resin, fluororesin, polyimide resin, polyaminoamide resin, PES (polyethersulfone) resin, PPS (polyphenylene sulfide) resin, PEI (polyetherimide) resin, PPE (polyphenylene ether) resin, poly-p-phenylene benzoxazole resin, PEEK (polyetheretherketone resin), polyacetal resin, polycarbonate resin, and polyamideimide resin can be used. Furthermore, a fiber-reinforced resin can be used, which is obtained by adding reinforcing fibers to the above-mentioned resin. Examples of such reinforcing fibers include inorganic fibers such as carbon fibers, silicon carbide fibers, alumina fibers, boron fibers, and glass fibers; organic fibers such as polyester fibers, polyethylene terephthalate fibers, poly(p-phenylenebenzobisoxazole) fibers, aramid fibers, polyacetal fibers, polyethylene fibers, and polyacrylonitrile fibers; and natural fibers such as cellulose fibers.

[0082] The present invention can be suitably used in combinations of the first and second materials described above, particularly when the first and second materials are metals, when the first or second material contains aluminum or iron, and even more specifically when the first material contains aluminum and the second material contains iron.

[0083] Furthermore, if the first and second materials are both metals, the difference in the coefficient of thermal expansion between the first and second materials is 2 × 10⁻⁶. -6 If the coefficient of thermal expansion is [1 / K] or greater, in particular, if the difference in coefficient of thermal expansion is 5 × 10 -6 The present invention can be suitably used when the temperature is [1 / K] or higher. There is no particular upper limit to the difference in the coefficient of thermal expansion between the first material and the second material, but 1 × 10 -4 If it is less than or equal to [1 / K], in particular, 9 × 10 -5 If it is less than or equal to [1 / K], more specifically, 7 × 10 -5 The present invention can be suitably used when the temperature is [1 / K] or less.

[0084] In this embodiment, the thickness of the first and second materials is preferably 0.1 to 10 mm, and more preferably 0.3 to 5 mm, respectively. By keeping the thickness within this range, it is possible to achieve both lightness and rigidity, making them suitable for use in automotive applications, and particularly as exterior materials for automobiles.

[0085] <Method for manufacturing laminates> The laminate according to one embodiment of the present invention can be manufactured by laminating and bonding the adhesive sheet between layers of the first material and the second material, and then curing the adhesive layer by heating and cooling.

[0086] The lamination method may be any known method. For example, one method is to place the adhesive sheet on the first material and adhere it, and then place the second material on the other side of the adhesive sheet and adhere it.

[0087] The heating temperature during the curing process of this adhesive sheet is preferably 60°C or higher. However, if the heating temperature is too high, the adhesive properties and reliability may decrease due to decomposition or oxidative degradation of the epoxy resin composition. Therefore, the heating temperature is preferably 60°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. On the other hand, it is preferably 250°C or lower, and more preferably 200°C or lower. The heating time is not particularly limited as long as it is sufficient time for the curing reaction of the composition constituting the adhesive sheet to proceed. Typically, it is between 5 minutes and 200 hours, and preferably between 10 minutes and 150 hours.

[0088] Furthermore, from the viewpoint of productivity and other factors, the cooling rate during the curing process is preferably 0.1°C / min or higher, more preferably 0.5°C / min or higher, and even more preferably 1°C / min or higher. On the other hand, from the viewpoint of reducing the decrease in adhesiveness, uneven adhesion, uneven appearance, and warping caused by the occurrence of cooling distortion inside the components and adhesive, the cooling time is preferably 40°C / min or less, more preferably 30°C / min or less, and even more preferably 20°C / min or less.

[0089] The laminate of this embodiment is a laminate with minimal warping, formed by laminating multiple materials with different coefficients of thermal expansion. Therefore, it can be suitably used as an exterior material for automobiles, aircraft, and other vehicles where improved strength and weight reduction are required, and where relatively large material areas are necessary. [Examples]

[0090] The present invention will be specifically described below with reference to examples. However, the present invention is not limited in any way by the following examples.

[0091] <Materials for resin layer (A)> As the material for the resin layer (A), an epoxy resin composition (a-1) obtained by the following method was used.

[0092] [Production of epoxy resin precursor (α)] A copolymer of bisphenol F and 1,6-hexanediol diglycidyl ether, prepared by the following method, was used as the epoxy resin precursor (α1). Specifically, 141.8 parts by mass of 1,6-hexanediol and 0.51 parts by mass of ethyl boron trifluoride, preheated to 45°C, were charged into a 1 L glass flask equipped with a stirrer, dropping funnel, and thermometer, and heated to 80°C. 244.3 parts by mass of epichlorohydrin were added dropwise over time, ensuring the temperature did not exceed 85°C. The mixture was aged for 1 hour while maintaining a temperature of 80-85°C, and then cooled to 45°C. 528.0 parts by mass of a 22% by mass sodium hydroxide aqueous solution were added, and the mixture was vigorously stirred at 45°C for 4 hours. The mixture was cooled to 23°C to separate and remove the aqueous phase, and then heated under reduced pressure to remove unreacted epichlorohydrin and water, yielding 283.6 parts by mass of crude 1,6-hexanediol diglycidyl ether. This crude 1,6-hexanediol diglycidyl ether was purified by distillation in an Oldashaw distillation column (15 stages), and the fraction obtained at a pressure of 1300 Pa and a temperature of 170-190°C was selected as the main fraction, yielding 127.6 parts by mass of 1,6-hexanediol diglycidyl ether with a diglycidyl purity of 97% by mass, a total chlorine content of 0.15% by mass, and an epoxy equivalent of 116 g / eq as determined by gas chromatography. 100 parts by mass of the obtained bifunctional epoxy compound (1,6-hexanediol diglycidyl ether), 69.3 parts by mass of bisphenol F (phenolic hydroxyl group equivalent: 100 g / eq), and 0.13 parts by mass of ethyltriphenylphosphonium iodide (30% by mass methyl cellosolve solution) were placed in a pressure-resistant reaction vessel, and a polymerization reaction was carried out at 165-170°C for 5 hours under a nitrogen gas atmosphere to obtain an epoxy resin precursor (α1), which is a copolymer of bisphenol F and 1,6-hexanediol diglycidyl ether with an epoxy equivalent of 1000 g / eq and a number average molecular weight of 3000.

[0093] [Production of epoxy resin composition (a-1)] 100 g of epoxy resin precursor (α1) and 9.5 g of "ST-14" (manufactured by Mitsubishi Chemical Corporation, active hydrogen equivalent: 85) as a curing agent were mixed in a poly container and stirred for 5 minutes using a rotary-orbital stirrer to obtain epoxy resin composition (a-1).

[0094] <Materials for resin layer (B)> As the material for the resin layer (B), epoxy resin compositions (b-1) to (b-4) obtained by the following method were used.

[0095] [Epoxy resin composition (b-1)] Epoxy resin composition (b-1) was obtained by mixing 15 g of bisphenol A type epoxy resin "jER828" (manufactured by Mitsubishi Chemical Corporation), 100 g of bisphenol A type epoxy resin "jER1256B40" (manufactured by Mitsubishi Chemical Corporation, 60% solids by mass) dissolved in methyl ethyl ketone (MEK), 6 g of dicyandiamide "DICY7" as a latent curing agent, 1.5 g of 3-(3,4-dichlorophenyl)-1,1-dimethylurea "DCMU" as a curing accelerator, and 10 g of MEK, and stirring for 5 minutes using a rotation-and-revolution type stirrer.

[0096] [Epoxy resin composition (b-2)] 45 g of bisphenol A type epoxy resin "jER828" (manufactured by Mitsubishi Chemical Corporation) was mixed with 50 g of bisphenol A type epoxy resin "jER1256B40" (manufactured by Mitsubishi Chemical Corporation, 60% solids by mass) dissolved in MEK, 6 g of dicyandiamide "DICY7" as a latent curing agent, 1.5 g of 3-(3,4-dichlorophenyl)-1,1-dimethylurea "DCMU" as a curing accelerator, and 30 g of MEK. The mixture was stirred for 5 minutes using a rotary-orbiting stirrer to obtain epoxy resin composition (b-2).

[0097] [Epoxy resin composition (b-3)] 15 g of bisphenol F type epoxy resin "jER807" (manufactured by Mitsubishi Chemical Corporation) was mixed with 100 g of bisphenol A type epoxy resin "jER1256B40" (manufactured by Mitsubishi Chemical Corporation, 60% solids by mass) dissolved in MEK, 6 g of dicyandiamide "DICY7" as a latent curing agent, 1.5 g of 3-(3,4-dichlorophenyl)-1,1-dimethylurea "DCMU" as a curing accelerator, and 10 g of MEK. The mixture was stirred for 5 minutes using a rotary-orbiting stirrer to obtain epoxy resin composition (b-3).

[0098] [Epoxy resin composition (b-4)] 45 g of bisphenol F type epoxy resin "jER807" (manufactured by Mitsubishi Chemical Corporation) was mixed with 50 g of bisphenol A type epoxy resin "jER1256B40" (manufactured by Mitsubishi Chemical Corporation, 60% solids by mass) dissolved in MEK, 6 g of dicyandiamide "DICY7" as a latent curing agent, 1.5 g of 3-(3,4-dichlorophenyl)-1,1-dimethylurea "DCMU" as a curing accelerator, and 30 g of MEK. The mixture was stirred for 5 minutes using a rotary-orbiting stirrer to obtain epoxy resin composition (b-4).

[0099] <Example 1> An epoxy resin composition (a-1) was sandwiched between two release PET films "SPPET100-O1BU" (manufactured by Mitsui Chemicals Tohcello, 100 μm) and introduced into a heated twin-screw roll heated to 60°C to form a film. The molded resin film was heat-treated at 40°C for 12 hours, followed by heat-treatment at 80°C for 4 hours to produce a 103 μm thick film (A) with curing between the release PET film layers. In addition, the prepared epoxy resin composition (b-1) was applied onto a mat-type release PET film "LSM-100X" (manufactured by Lintec, 100 μm), and heat-treated at 25°C for 12 hours, followed by heat-treatment at 80°C for 1 hour to evaporate the solvent, forming a film on the release PET film to produce two 34 μm thick films (B). The release PET film on one side of film (A) was peeled off, and film (B) was bonded to the peeled side using a hand roller. Subsequently, the release PET film on the other side of film (A) was peeled off, and another film (B) was similarly attached using a hand roller to create an adhesive sheet.

[0100] <Example 2> An adhesive sheet was prepared in the same manner as in Example 1, except that the material of film (B) was an epoxy resin composition (b-2) and the thickness of film (B) was 28 μm.

[0101] <Example 3> An adhesive sheet was prepared in the same manner as in Example 1, except that the material of film (B) was an epoxy resin composition (b-3) and the thickness of film (B) was 26 μm.

[0102] <Example 4> An adhesive sheet was prepared in the same manner as in Example 1, except that the material of film (B) was an epoxy resin composition (b-4) and the thickness of film (B) was 35 μm.

[0103] <Comparative Example 1> The adhesive sheet was prepared using the same method as in Example 1, except that the thickness of film (A) was 25 μm and the thickness of film (B) was 176 μm.

[0104] <Comparative Example 2> An adhesive sheet was prepared in the same manner as in Example 1, except that the thickness of film (A) was 30 μm, the material of film (B) was epoxy resin composition (b-2), and the thickness of film (B) was 77 μm.

[0105] <Comparative Example 3> An adhesive sheet was prepared using only the film (A) prepared in Example 1.

[0106] <Comparative Example 4> An epoxy resin composition (b-1) was applied onto a mat-type release PET film "LSM-100X" (Lintec Corporation, 100 μm), and the solvent was evaporated by heat treatment at 25°C for 12 hours followed by 80°C for 1 hour to form a film on the release PET film, thereby producing an adhesive sheet with a thickness of 34 μm.

[0107] <Comparative Example 5> An epoxy resin composition (b-2) was applied onto a mat-type release PET film "LSM-100X" (Lintec Corporation, 100 μm), and the solvent was evaporated by heat treatment at 25°C for 12 hours followed by 80°C for 1 hour to form a film on the release PET film, thereby producing an adhesive sheet with a thickness of 28 μm.

[0108] <Comparative Example 6> An epoxy resin composition (b-3) was applied onto a mat-type release PET film "LSM-100X" (Lintec Corporation, 100 μm), and the solvent was evaporated by heat treatment at 25°C for 12 hours followed by 80°C for 1 hour to form a film on the release PET film, thereby producing an adhesive sheet with a thickness of 26 μm.

[0109] <Comparative Example 7> An epoxy resin composition (b-4) was sandwiched between two release PET films, "SPPET100-O1BU" (manufactured by Mitsui Chemicals Tohcello Co., Ltd., 100 μm thick), and introduced into a heated twin-screw roll heated to 60°C to form a film. The molded resin film was heat-treated at 40°C for 12 hours to produce an adhesive sheet with a thickness of 35 μm.

[0110] <Comparative Example 8> The adhesive sheet prepared in Example 1 was subjected to heat treatment at 180°C for 40 minutes to produce a cured adhesive sheet.

[0111] <Evaluation Method> The physical properties and other characteristics of the samples prepared in the examples and comparative examples were measured and evaluated using the methods described below.

[0112] (Measurement of glass transition temperature and storage modulus) The glass transition temperature and storage modulus of film (A) and film (B) were measured as follows. Single-layer film samples prepared in Comparative Examples 3 to 7 were heat-treated at 180°C for 20 minutes. After that, the release PET film was peeled off each sample, and the glass transition temperature (Tg) and storage modulus (E') at 25°C were read from the tanδ peak using a dynamic viscoelasticity analyzer (IT Measurement Control Co., Ltd. "DVA-200") with a tensile jig at a measurement temperature of -100 to 250°C, a frequency of 10 Hz, and a heating rate of 3°C / min.

[0113] (Gel fraction) The release PET film was peeled off from the samples prepared in the examples and comparative examples, and the remaining adhesive sheet was cut out in the range of 0.3 to 0.5 g to be used as the measurement sample. The measurement sample was placed on a wire mesh, and the wire mesh was immersed in acetone and left to stand at 23°C for 48 hours. After that, the wire mesh was removed from the acetone and vacuum dried. The ratio of the mass after immersion to the mass before immersion of the sample was defined as the gel fraction.

[0114] (Tensile shear bond strength) The tensile shear adhesive strength of cold-rolled steel sheets (SPCC) was evaluated in accordance with JIS-K6850. Samples prepared in the examples and comparative examples were cut to a width of 25 mm and a length of 12.5 mm and used as measurement samples. After degreasing and cleaning two 25 mm wide x 100 mm long x 1.6 mm thick cold-rolled steel sheets (SPCC) with ethanol, the measurement sample was inserted between two SPCC sheets and pressed together using clamps. The sheet was then placed in a constant temperature bath and heated at 160°C for 60 minutes. The adhesive sheet was then cured by cooling to 50°C in a circulating oven at a cooling rate of 1 to 20°C / min to prepare peel test specimens. Tensile shear tests were performed on the prepared peel test specimens using an INTEXCO 2050X tensile testing machine (manufactured by INTEXCO) at a speed of 5 mm / min for a total of n=5 tests.

[0115] (Tensile elongation) For the tensile elongation of the adhesive sheets, tensile test specimens were prepared by heat-treating the samples prepared in the examples and comparative examples at 180°C for 20 minutes, and then cutting them into strips measuring 10 mm wide x 150 mm long. The prepared peel test specimens were subjected to tensile testing using an INTEXCO 205X ​​tensile testing machine (manufactured by INTEXCO) at a speed of 100 mm / min for a number of tests n=5, and the elongation was measured when the gauge length was set to 100 mm.

[0116] (Thickness retention rate) The thickness (Ta) of the adhesive sheets prepared in the examples and comparative examples was measured using a micrometer. Next, an adhesive sheet was inserted between two SPCC sheets measuring 25 mm wide x 100 mm long x 1.6 mm thick. The sheet was then heated to 150°C under pressure of 50 kPa and held for 20 minutes to cure. The remaining thickness of the adhesive sheet (Tb) was measured by subtracting the thickness of the two SPCC steel sheets from the thickness of the cured laminate. The thickness retention rate was calculated using the formula Tb / Ta × 100 (%) based on the thickness of the adhesive sheet (Ta) and the remaining thickness of the adhesive sheet (Tb).

[0117] (Fe / Al warping) For the warp evaluation, an aluminum plate (A5052P, with a coefficient of linear expansion of 23.7 × 10) measuring 25 mm wide × 100 mm long × 1.6 mm thick was used as the adherend. -6 [1 / K]), and SPCC (cold-rolled steel sheet, coefficient of linear expansion 12 x 10) with a width of 25 mm x length of 150 mm x thickness of 1.6 mm. -6 [1 / K]) was used as the standard test specimen. After placing the samples prepared in the examples and comparative examples onto the entire surface of the aluminum plate, the aluminum plate was positioned so as to be in the center of the steel plate, and clamped in place. The samples were then heat-treated in a hot air drying oven at 180°C for 20 minutes, after which they were allowed to cool naturally and the clamps were removed to prepare the test specimens. These test specimens were placed on top of the SUS (stainless steel) with the aluminum plate facing downwards. The total thickness of the test specimen and the SUS was measured at four corners and one center point using an ABS Digimatic Indicator (Mitutoyo "ID-SX"), and the amount of warpage was calculated based on the following formula (1). Curvature = (Thickness at the center point) - (Average thickness at the four corner points) ... (1)

[0118] [Table 1]

[0119] The adhesive sheets of Examples 1-4 had a gel fraction of 30% to 95% by mass, which reduced resin flow after pressure bonding and maintained the thickness of the adhesive layer even after heat curing. They also exhibited excellent tensile shear bonding strength and good overall adhesive strength. These adhesive sheets also suppressed warping after bonding aluminum plates and SPCC with different coefficients of thermal expansion. On the other hand, in Comparative Examples 1 and 2, the gel fraction of the adhesive sheets was less than 30% by mass, which resulted in resin flow after pressure bonding and a reduced thickness retention rate of the adhesive layer. The adhesive sheet in Comparative Example 3 had a gel fraction of 99% by mass, resulting in lower adhesive strength. The adhesive sheets of Comparative Examples 4-7 had a gel fraction of 0% by mass, resulting in low adhesive strength and no reduction in warping after bonding aluminum plates with different coefficients of thermal expansion to SPCC. The adhesive sheet of Comparative Example 8 could not be bonded because the adhesive layer (B) had hardened.

[0120] As described above, laminates formed by bonding multiple materials with different coefficients of thermal expansion using the adhesive sheets of Examples 1 to 4 are suitable for use as automotive exterior materials because they exhibit minimal warping. [Industrial applicability]

[0121] This adhesive sheet can be suitably used in various types of laminates because, when used to bond multiple materials with different coefficients of thermal expansion, the resulting laminate exhibits minimal warping. In particular, it is useful for exterior material applications such as those for automobiles, aircraft, and other vehicles.

Claims

1. An adhesive sheet comprising a resin layer (A) made of epoxy resin composition (a) and a resin layer (B) made of epoxy resin composition (b), wherein the gel fraction is 30% by mass or more and 95% by mass or less, and the resin layer (B) is uncured, The epoxy resin composition (a) contains a bifunctional epoxy compound having an aliphatic skeleton and an aromatic skeleton, The epoxy resin composition (b) contains a difunctional aromatic epoxy compound, The resin layer (B) is the surface layer and the back layer, and the resin layer (A) is the intermediate layer. In an adhesive sheet heat-treated at 180°C for 20 minutes, the tanδ peak temperature of resin layer (A), determined by dynamic viscoelasticity measurement at a frequency of 10 Hz, is less than 80°C, and the tanδ peak temperature of resin layer (B) is 80°C or higher. An adhesive sheet in which the difference between the tanδ peak temperature of the resin layer (A) and the tanδ peak temperature of the resin layer (B) is 40°C or more.

2. The adhesive sheet according to claim 1, wherein the thickness retention rate after applying pressure of 50 kPa at 150°C for 20 minutes is 50% or more.

3. The adhesive sheet according to claim 1 or 2, wherein the tensile elongation after heat treatment at 180°C for 20 minutes is 5% or more.

4. The adhesive sheet according to any one of claims 1 to 3, wherein, after heat treatment at 180°C for 20 minutes, the ratio of the storage moduli of the resin layer (A) and the resin layer (B) at 25°C, (B) / (A), determined by dynamic viscoelasticity measurement at a frequency of 10 Hz, is 10 or more.

5. An adhesive sheet according to any one of claims 1 to 4, wherein the thickness is 100 μm or more.

6. The adhesive sheet according to any one of claims 1 to 5, wherein the thickness ratio (A) / (B) of the resin layer (A) to the resin layer (B) is 0.25 or more.

7. The adhesive sheet according to any one of claims 1 to 6, wherein the thickness of the resin layer (A) is 50 μm or more.

8. A cured product obtained by curing the adhesive sheet according to any one of claims 1 to 7.

9. A laminate comprising an adhesive sheet according to any one of claims 1 to 7, wherein one side of the adhesive sheet is provided with a first material and the other side is provided with a second material, the first material and the second material having different coefficients of thermal expansion.

10. The laminate according to claim 9, wherein the first material includes aluminum.

11. The laminate according to claim 9 or 10, wherein the second material contains iron.

12. Automotive exterior material using the laminate described in any one of claims 9 to 11.

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