Thermosetting adhesive sheet, laminate, and method for producing laminate

Abstract

The present invention relates to: a thermosetting adhesive sheet having an adhesive layer that contains (A) a binder resin, (B) a thermosetting component, and (C) a filler, the arithmetic average surface roughness (Ra) of the surface of the adhesive layer being 200 nm or less; a cured product layer obtained by heat-treating the adhesive layer at 170 DEG C for 2 hours has a dielectric loss tangent of 0.005 or less at 23 DEG C and a frequency of 10-40 GHz, and a gel fraction of 40 mass% or more of the cured product layer obtained by heat-treating the adhesive layer at 170 DEG C for 2 hours; the present invention also relates to a laminate which is provided with a conductive layer and an insulating layer formed on the conductive layer, and which is a layer obtained by curing the adhesive layer of the thermosetting adhesive sheet, and a method for producing the same. According to the present invention, it is possible to provide: an adhesive sheet having excellent low dielectric properties in a high-frequency band and excellent bending resistance; a laminate having a conductive layer and an adhesive layer formed from the adhesive sheet; and a method for producing the laminate.

Description

Technical Field

[0001] The present invention relates to a thermosetting adhesive sheet having excellent low dielectric properties and bending resistance in a high frequency band, a laminate comprising a conductive layer and an adhesive layer of the thermosetting adhesive sheet, and a method for producing the laminate. Background Art

[0002] In recent years, electronic devices have been miniaturized, lightweighted, and improved in performance. Flexible printed circuits (FPCs) used as wiring components are also required to have higher density mounting, lighter weight, and higher reliability. In addition, with the recent increase in the speed of transmission signals in wiring components such as FPCs, the frequency of transmission signals has also been increasing. Therefore, the materials used in wiring components are being sought to reduce the loss of electrical signals in high-frequency bands. Furthermore, adhesive sheets used for interlayer adhesive layers of wiring components and adhesive sheets used as surface protective films (i.e., coverlay films) of wiring components are also being sought to have excellent low dielectric properties in high-frequency bands.

[0003] Therefore, to date, in order to transmit high-frequency electrical signals at high speed and with reduced transmission loss, attempts have been made to improve the low-dielectric properties (low dielectric constant and low dielectric loss tangent) of the insulators (base materials or adhesives, etc.) that constitute wiring components (Patent Documents 1 to 5, etc.). In addition, in recent years, electronic devices have become thinner and smaller, and there has been a search for adhesive sheets that have excellent electrical properties (low dielectric constant, low dielectric loss tangent) in high-frequency bands and excellent bending resistance.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: WO2016 / 147984

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2016-089137

[0008] Patent Document 3: WO2019 / 230531

[0009] Patent Document 4: WO2019 / 026927

[0010] Patent Document 5: Japanese Patent Application Publication No. 2019-172803 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] However, although the above-mentioned Patent Documents 1 to 5 describe resin compositions having low dielectric properties, they do not describe excellent bending resistance and are not satisfactory in terms of bending resistance.

[0013] The present invention has been completed in view of these actual conditions, and its object is to provide a thermosetting adhesive sheet having excellent low dielectric properties in a high frequency band and excellent bending resistance, a laminate having a conductive layer and an adhesive layer formed by the thermosetting adhesive sheet, and a method for manufacturing the laminate.

[0014] Means for solving problems

[0015] The present inventors have conducted intensive studies on a thermosetting adhesive sheet having an adhesive layer in order to solve the above-mentioned problems, and have consequently completed the present invention.

[0016] Therefore, according to the present invention, there are provided the thermosetting adhesive sheets described in the following [1] to [8], the laminated body described in [9], and the methods for producing the laminated bodies described in

[10] and

[11] .

[0017] [1] A thermosetting adhesive sheet having an adhesive layer, wherein the adhesive layer is a layer containing the following components (A), (B), and (C).

[0018] (A) Component: Binder resin

[0019] (B) Component: Thermosetting component

[0020] (C) Ingredient: Filler

[0021] The arithmetic average surface roughness (Ra) of the adhesive layer surface is less than 200 nm,

[0022] The dielectric loss tangent of the cured layer obtained by heating the adhesive layer at 170°C for 2 hours at 23°C and a frequency of 10 to 40 GHz is 0.005 or less, and

[0023] The gel fraction of the cured product layer obtained by heat-treating the adhesive layer at 170° C. for 2 hours is 40% or more.

[0024] [2] The thermosetting adhesive sheet described in [1], wherein, when the gel fraction of the adhesive layer before curing is set to α (%) and the gel fraction of the cured layer obtained by curing the adhesive layer is set to β (%), the increase rate (%) of the gel fraction expressed by the formula: [(β-α) / α]×100 is 60% or more.

[0025] [3] The thermosetting adhesive sheet according to [1] or [2], wherein the tensile modulus of a cured layer obtained by heat-treating the adhesive layer at 170°C for 2 hours is 0.5 GPa or more at 25°C.

[0026] [4] The thermosetting adhesive sheet described in [1] or [2], wherein when the thickness of the adhesive layer is set to X (μm) and the average particle size of the (C) component is set to Y (μm), the formula: Y / X<1 is satisfied.

[0027] [5] The thermosetting adhesive sheet according to [1] or [2], wherein the component (C) is an inorganic filler that has not been surface-treated.

[0028] [6] The thermosetting adhesive sheet according to [1] or [2], wherein the component (C) is a spherical filler.

[0029] [7] The thermosetting adhesive sheet according to [1] or [2], wherein the adhesive layer further contains a thermal polymerization initiator as component (D).

[0030] [8] The thermosetting adhesive sheet described in [1] or [2], which is used to form an insulating layer of a device.

[0031] [9] A laminate comprising a conductive layer and an insulating layer formed on the conductive layer, wherein the insulating layer is a layer formed by curing the adhesive layer of the thermosetting adhesive sheet according to [1] or [2].

[0032]

[10] A method for producing a laminate according to [9], comprising:

[0033] Step (I), obtaining a laminate by laminating the thermosetting adhesive sheet described in [1] or [2] on the conductive layer, and

[0034] In step (II), the laminate is heated to a predetermined temperature to cure the adhesive layer of the thermosetting adhesive sheet.

[0035]

[11] The method for producing a laminate described in

[10] , wherein after the step (I) and before the step (II), there is a step (I-1) of forming a protective layer on the thermosetting adhesive sheet described in [1] or [2].

[0036] Effects of the Invention

[0037] According to the present invention, there is provided a thermosetting adhesive sheet having an adhesive layer imparting a cured product having excellent low dielectric properties in a high frequency band and excellent bending resistance. The laminate of the present invention has a layer (hereinafter sometimes described as a "cured product layer") formed by curing the adhesive layer of the thermosetting adhesive sheet of the present invention, and therefore has excellent low dielectric properties in a high frequency band and excellent bending resistance. In addition, according to the manufacturing method of the present invention, the laminate of the present invention can be manufactured efficiently. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a flow chart illustrating a method for producing the laminate of the present invention. DETAILED DESCRIPTION

[0039] Hereinafter, the present invention will be divided into 1) a thermosetting adhesive sheet, 2) a laminate, and 3) a method for producing the laminate, and will be described in detail.

[0040] In this specification, "high frequency band" refers to the frequency region of 10 to 40 GHz. In this specification, "excellent low dielectric properties" means that the cured layer obtained by heat-treating the adhesive layer at 170°C for 2 hours has a low dielectric loss tangent (the dielectric loss tangent at 23°C and a frequency of 10 to 40 GHz is preferably 0.005 or less), and the transmission loss in the high frequency band is small. In this specification, "excellent bending resistance" means that, for a thermosetting adhesive sheet, when the adhesive sheet is deformed, the adhesive layer will not be damaged and has the ability to follow the deformation. Whether the thermosetting adhesive sheet has excellent bending resistance can be confirmed by, for example, the bending test described in the examples. In this specification, "relative humidity α%" is sometimes expressed as "α%RH" (RH: Relative humidity).

[0041] 1) Thermosetting adhesive sheet

[0042] The present invention first provides a thermosetting adhesive sheet having an adhesive layer, characterized in that: (α) the adhesive layer comprises the components (A), (B), and (C); (β) the adhesive layer has an arithmetic mean surface roughness (Ra) of 200 nm or less; (γ) a cured layer obtained by heat-treating the adhesive layer at 170°C for 2 hours has a dielectric loss tangent of 0.005 or less at 23°C and a frequency of 10 to 40 GHz; and (δ) a cured layer obtained by heat-treating the adhesive layer at 170°C for 2 hours has a gel fraction of 40% or greater. It should be noted that in this specification, "thermosetting adhesive sheet" may sometimes be simply referred to as "adhesive sheet."

[0043] [Component (A): Binder resin]

[0044] The adhesive layer of the present invention preferably contains a binder resin as component (A). The binder resin is a polymer component that imparts film-forming properties to the adhesive layer and imparts suitable flexibility to the resulting adhesive layer. The adhesive layer of the present invention contains a binder resin, which helps it maintain its shape as an adhesive layer.

[0045] As binder resin, as long as can bring into play above-mentioned film-forming property and give the polymer component of gained adhesive layer flexibility, be not particularly limited.For example, olefin resin, acrylic polymer, polyester resin, polyvinyl alcohol resin, polyvinyl butyral, polyvinyl chloride, phenoxy resin, polyamide resin, cellulose material, polyvinyl ether, polyimide resin, styrene elastomer etc. can be enumerated.Among these, from the cured product that easily obtains low dielectric properties excellence, preferred olefin resin, styrene elastomer.Binder resin can use 1 kind alone, or combine 2 or more uses.

[0046] An olefin resin refers to a polymer containing repeating units derived from an olefin monomer. The olefin resin may be a polymer composed solely of repeating units derived from an olefin monomer, or a polymer composed of repeating units derived from an olefin monomer and repeating units derived from a monomer copolymerizable with the olefin monomer. However, from the perspective of easily obtaining a cured product having excellent low dielectric properties, a polymer composed solely of repeating units derived from an olefin monomer is preferred.

[0047] As the olefin monomer, an α-olefin having 2 to 8 carbon atoms is preferred, ethylene, propylene, 1-butene, isobutylene or 1-hexene is more preferred, and ethylene or propylene is further preferred. One of these olefin monomers may be used alone, or two or more thereof may be used in combination. Examples of monomers copolymerizable with the olefin monomer include vinyl acetate, (meth)acrylate, and styrene. Here, in this specification, "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. One of these monomers copolymerizable with the olefin monomer may be used alone, or two or more thereof may be used in combination.

[0048] As olefin resins, preferably mentioned are ultra-low density polyethylene (VLDPE), low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene, polypropylene (PP), ethylene-propylene copolymer, olefin elastomer (TPO), ethylene-vinyl acetate copolymer (EVA), ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate copolymer, etc.

[0049] Examples of the styrene-based elastomer include block copolymers having a hard segment composed of a block obtained by polymerization of styrene and a soft segment composed of a block obtained by polymerization of an aliphatic olefin such as ethylene, butadiene, or isoprene, or hydrogenated products thereof.

[0050] Specific examples of styrene-based elastomers include preferably styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-butadiene-styrene copolymers (SBS), styrene-isoprene-styrene copolymers (SIS), styrene-isoprene-butadiene-styrene copolymers (SIBS), styrene-ethylene copolymers, styrene-ethylene-propylene-styrene copolymers (SEPS), and styrene-ethylene-butylene-styrene copolymers (SEBS).

[0051] As the binder resin, a resin having a reactive functional group is preferably used. By using a resin having a reactive functional group as the binder resin, a cross-linked structure can be constructed in the adhesive layer (and the cured product layer) that facilitates the effects of the present invention. In particular, a cured product layer with a high gel fraction and excellent bending resistance can be easily formed. In addition, a cured product layer can be formed that is easily and fully bonded even to difficult-to-bond substrates.

[0052] Examples of the reactive functional group include a carboxyl group, a carboxylic anhydride group, a carboxylate group, a hydroxyl group, an epoxy group, an amide group, an ammonium group, a nitrile group, an amino group, an imide group, an isocyanate group, an acetyl group, a thiol group, an ether group, a thioether group, a sulfone group, a phosphine group, a nitro group, a carbamate group, an alkoxysilyl group, a silanol group, and a halogen atom.

[0053] Examples of resins having reactive functional groups include the modified polyolefin resins described below, or the phenoxy resins and cellulose materials mentioned above as binder resins. Other examples include modified versions of the aforementioned binder resins, excluding olefin resins. Modified polyolefin resins or modified styrene elastomers are preferred as binder resins because they facilitate the production of a cured layer with a high gel fraction, low dielectric properties, and excellent flexural resistance.

[0054] The modified polyolefin resin is an olefin resin into which a reactive functional group is introduced, which is obtained by modifying an olefin resin as a precursor using a modifier (a compound having a functional group in the molecule).

[0055] From the viewpoint of forming a cured layer with superior adhesive strength, an acid-modified polyolefin resin is preferably used as the modified polyolefin resin. By curing the adhesive composition containing the acid-modified polyolefin resin, a cured layer with superior adhesive strength can be formed.

[0056] Acid-modified polyolefin resins are those obtained by graft-modifying olefin resins with acids or acid anhydrides. Examples include those obtained by reacting unsaturated carboxylic acids or unsaturated carboxylic acid anhydrides (hereinafter sometimes referred to as "unsaturated carboxylic acids, etc.") with olefin resins to introduce carboxyl groups or carboxylic acid anhydride groups (graft-modified).

[0057] Examples of unsaturated carboxylic acids that react with olefin resins include maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic acid, tetrahydrophthalic acid, and aconitic acid; and unsaturated carboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride, aconitic anhydride, norbornene dicarboxylic anhydride, and tetrahydrophthalic anhydride. These can be used alone or in combination of two or more. Among these, unsaturated carboxylic acid anhydrides are preferred, with maleic anhydride being particularly preferred, from the perspective of easily obtaining a cured product with superior bonding strength.

[0058] The amount of the unsaturated carboxylic acid or the like to react with the olefin resin is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, and even more preferably 0.2 to 1 part by mass, relative to 100 parts by mass of the olefin resin.

[0059] The method for introducing an unsaturated carboxylic acid or the like into an olefin resin is not particularly limited. For example, the following methods may be mentioned: a method in which an olefin resin and an unsaturated carboxylic acid or the like are heated and melted at a temperature above the melting point of the olefin resin in the presence of a free radical generator such as an organic peroxide or azonitrile to cause a reaction; a method in which an olefin resin and an unsaturated carboxylic acid or the like are dissolved in an organic solvent and then heated and stirred in the presence of a free radical generator to cause a reaction; and a method in which an unsaturated carboxylic acid or the like is graft-copolymerized onto an olefin resin.

[0060] As the acid-modified polyolefin resin, commercially available products may also be used. Examples of commercially available products include Admer (registered trademark, manufactured by Mitsui Chemicals, Inc.), Unistole (registered trademark, manufactured by Mitsui Chemicals, Inc.), BondyRam (registered trademark, manufactured by Polyram), Orevac (registered trademark, manufactured by ARKEMA), and Modic (registered trademark, manufactured by Mitsubishi Chemical Corporation).

[0061] Examples of the modified styrene-based elastomer include styrene-based elastomers modified with unsaturated carboxylic acids, etc. Examples of methods for modifying styrene-based elastomers include methods of grafting the above-mentioned styrene-based elastomers with unsaturated carboxylic acids, etc.

[0062] As the unsaturated carboxylic acid and the like, the same unsaturated carboxylic acids as those exemplified above as the unsaturated carboxylic acid to be reacted with the olefin-based resin can be used.

[0063] Examples of commercially available modified styrene-based elastomers include Tuftec M series manufactured by Asahi Kasei Corporation and Kraton FG series manufactured by Kraton Polymer Japan.

[0064] The number average molecular weight (Mn) of the binder resin is not particularly limited, but is preferably 10,000 to 150,000, and more preferably 30,000 to 100,000. This imparts desired film-forming properties and easily imparts flexibility to the resulting adhesive layer, thereby easily producing a product with excellent bending resistance. The number average molecular weight (Mn) of the binder resin can be determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0065] In the adhesive layer involved in the present invention, the content of the binder resin is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, particularly preferably 12 to 30% by mass, and further preferably 14 to 20% by mass. Thus, the film-forming property for forming the adhesive layer can be imparted, and the resulting adhesive layer can be imparted with suitable flexibility. It is easy to make materials such as thermosetting components or cross-linking agents described later blend in a desired ratio. In addition, it is easy to meet the physical properties described later, and then it is easy to obtain an adhesive layer in which excellent low dielectric properties and bending resistance coexist.

[0066] [Component (B): Thermosetting component]

[0067] The adhesive layer of the present invention preferably contains a thermosetting component (hereinafter sometimes referred to as "thermosetting component (B)") as component (B). Thermosetting component (B) is a compound that undergoes a curing reaction upon heating. If component (A) is a resin having reactive functional groups, it can react with the reactive functional groups to form a crosslinked structure, thereby providing a cured product having a desired crosslink density.

[0068] The thermosetting component (B) is not particularly limited as long as it is a compound that initiates a curing reaction upon heating. From the perspective of easily forming an adhesive layer having more excellent low dielectric properties and excellent bending resistance, preferred examples include the following components (B1) and (B2). It should be noted that component (B2) is not included in component (B1).

[0069] (B1) Component: A thermosetting compound that is liquid at 25°C

[0070] (B2) ingredient: polyphenylene ether resin

[0071] The thermosetting component (B) may be used alone or in combination of two or more. However, in the present invention, from the viewpoint of easily forming an adhesive layer having both excellent low dielectric properties and bending resistance, it is preferred to use one or more components (B1) and one or more components (B2) in combination.

[0072] The component (B1) is preferably a thermosetting compound that is liquid at 25°C (hereinafter sometimes referred to as "thermosetting compound (B1)"), and is particularly preferably a non-aromatic thermosetting compound that is liquid at 25°C. Here, "liquid at 25°C" means having fluidity at 25°C. For example, a compound that is liquid at 25°C means a compound having a viscosity of 2 to 10,000 mPa·s as measured at 25°C and 1.0 rpm using an E-type viscometer.

[0073] The thermosetting compound (B1) may be any of aromatic, anti-aromatic, and non-aromatic compounds, but non-aromatic compounds are preferred because the resulting adhesive layer easily satisfies the physical properties described below and can easily achieve both low dielectric properties and flex resistance. A non-aromatic compound refers to a compound that does not have an aromatic ring.

[0074] Thermosetting compound (B1) preferably has a heterocyclic skeleton. Thus, it is easy to form an adhesive layer that gives a cured product with excellent bonding strength and low dielectric properties. As heterocyclic skeletons, isocyanurate skeletons or glycoluril skeletons can be listed. The heterocyclic skeleton preferably has an n-fold rotation axis as a symmetric element. The adhesive layer containing a thermosetting compound (B1) with such a heterocyclic skeleton has a tendency to have excellent low dielectric properties.

[0075] The molecular weight of the thermosetting compound (B1) is preferably 100 to 1,000, more preferably 150 to 800, even more preferably 200 to 600, and particularly preferably 250 to 500. This tends to satisfy the aforementioned requirement of being liquid at 25°C, contributing to excellent miscibility with other materials, resulting in good film-forming properties. Furthermore, even when heat-treated during formation or use of the adhesive layer, the compound is less likely to volatilize, making it easier to obtain a cured product having the physical properties described below. In particular, the resulting cured layer tends to exhibit good flex resistance.

[0076] Preferred thermosetting compounds (B1) include, for example, compounds having two or more hydrocarbon groups with terminal double bonds (hereinafter sometimes referred to as "thermosetting compound (B1')"). The use of thermosetting compounds (B1') facilitates the formation of an adhesive layer having a cured product exhibiting superior low dielectric properties.

[0077] The carbon number of the hydrocarbon group with a double bond at the end is preferably 1 to 10, more preferably 2 to 5, and particularly preferably 3 to 4. Examples of the hydrocarbon group with a double bond at the end include vinyl, allyl, 3-butenyl, 4-pentenyl, 5-hexenyl, isopropenyl, 1-methyl-2-propenyl, vinylbenzyl, and vinylnaphthyl. Among these, vinyl and allyl are preferred, and allyl is particularly preferred. In addition, the number of hydrocarbon groups with a double bond at the end is preferably 1 or more, and particularly preferably 2 or more. This makes it easy to satisfy the physical properties described later and to easily form an adhesive layer that imparts a cured product with better bonding strength or heat resistance. In particular, the resulting cured product layer easily exhibits good bending resistance. In addition, the upper limit of the number of hydrocarbon groups is not particularly limited. From the perspective of suppressing the occurrence of cracks by making the cross-linked structure formed in the cured product moderately sparse, it is preferably 10 or less, more preferably 6 or less, further preferably 4 or less, and particularly preferably 3 or less.

[0078] Examples of the thermosetting compound (B1′) include thermosetting compounds having an isocyanurate skeleton and thermosetting compounds having a glycoluril skeleton. Examples of the thermosetting compound having an isocyanurate skeleton include compounds represented by the following formula (1) or (2).

[0079] [Chemical Formula 1]

[0080]

[0081] In formula (1), R 1 、R 2 Each independently represents a hydrocarbon group having a double bond at the end, R 3 It represents a saturated hydrocarbon group having 1 to 15 carbon atoms, or an alkyl group having 2 to 15 carbon atoms substituted with an alkoxy group.

[0082] [Chemical Formula 2]

[0083]

[0084] In formula (2), R 4 、R 5 、R 6 Each independently represents a hydrocarbon group having a double bond at the terminal.

[0085] R 1 、R 2 、R 4 、R 5 、R 6 The hydrocarbon group having a double bond at the terminal represented is as described above.

[0086] R 3 The number of carbon atoms in the saturated hydrocarbon group represented by is preferably 1 to 15, more preferably 5 to 15, and more preferably 8 to 15.3 The saturated hydrocarbon group represented by the group may preferably be methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, isobutyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl or the like.

[0087] R 3 The carbon number of the alkyl group substituted by the alkoxy group represented is 1 to 15, preferably 2 to 12, and more preferably 3 to 10. 3 Preferred examples of the alkoxy-substituted alkyl group include methoxymethyl, ethoxymethyl, 2-methoxyethoxymethyl, and benzyloxymethyl.

[0088] Examples of the thermosetting compound having a glycoluril skeleton include compounds represented by the following formula (3).

[0089] [Chemical Formula 3]

[0090]

[0091] In formula (3), R 7 、R 8 、R 9 、R 10 Each independently represents a hydrocarbon group having 1 to 15 carbon atoms, and at least two of them are hydrocarbon groups having a double bond at the terminal. 11 、R 12 It is a hydrogen atom or a saturated hydrocarbon group having 1 to 15 carbon atoms.

[0092] Among these, the thermosetting compound (B1′) is preferably a compound having an isocyanurate skeleton, more preferably a compound represented by formula (1), and even more preferably a compound represented by the following formula, from the viewpoint of easily obtaining a cured product that easily satisfies the physical properties described later, has a moderate crosslinking density, is excellent in low dielectric properties, and is also excellent in bending resistance.

[0093] [Chemical Formula 4]

[0094]

[0095] In the formula, R represents a saturated hydrocarbon group having 5 to 15 carbon atoms, and preferably a saturated hydrocarbon group having 8 to 15 carbon atoms.

[0096] When the adhesive layer contains a thermosetting compound (B1), its content in the adhesive layer is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, further preferably 15 to 30% by mass, and particularly preferably 18 to 25% by mass. This makes it easy to satisfy the physical properties described below and easily form an adhesive layer that provides a cured product with excellent bonding strength and low dielectric properties. In particular, the resulting cured product layer easily exhibits good bending resistance.

[0097] Component (B2) is a polyphenylene ether resin (hereinafter sometimes referred to as "polyphenylene ether resin (B2)"). A polyphenylene ether resin is a resin having a polyphenylene ether backbone in its main chain. The polyphenylene ether backbone is a backbone having repeating units represented by the following formula, or repeating units in which hydrogen atoms in the above formula are substituted.

[0098] [Chemical Formula 5]

[0099]

[0100] Since the polyphenylene ether resin (B2) has a polyphenylene ether skeleton, the adhesive layer containing the polyphenylene ether resin (B2) has excellent low dielectric properties. In addition, the polyphenylene ether resin (B2) preferably has a reactive functional group. Thus, the cured product of the adhesive layer easily satisfies the physical properties described below and has excellent heat resistance and bending resistance.

[0101] Examples of the polyphenylene ether skeleton include those represented by the following formula (4).

[0102] [Chemical Formula 6]

[0103]

[0104] In formula (4), X is a divalent group represented by the following formula (5) or formula (6), and Y is each independently a divalent group represented by the following formula (7). a and b are integers from 0 to 100, and at least one of a and b is 1 or greater. * represents a bond (the same applies hereinafter).

[0105] [Chemical Formula 7]

[0106]

[0107] In formula (5), R 13 、R 14 、R 15 、R 16 、R 17 、R 18 、R 19 、R 20 Each independently represents a hydrogen atom, a halogen atom, an alkyl group having 6 or less carbon atoms, or a phenyl group, and is preferably a hydrogen atom or a methyl group.

[0108] [Chemical Formula 8]

[0109]

[0110] In formula (6), R 21 、R 22 、R 23 、R 24 、R 25 、R26 、R 27 、R 28 Each is independently a hydrogen atom, a halogen atom, an alkyl group having 6 or less carbon atoms, or a phenyl group, preferably a hydrogen atom or a methyl group. A is a linear, branched, or cyclic divalent hydrocarbon group having 20 or less carbon atoms.

[0111] [Chemical Formula 9]

[0112]

[0113] In formula (7), R 29 、R 30 、R 31 、R 32 Each independently represents a hydrogen atom, a halogen atom, an alkyl group having 6 or less carbon atoms, or a phenyl group, and is preferably a hydrogen atom or a methyl group.

[0114] Specific examples of the polyphenylene ether skeleton include, but are not limited to, those represented by the following formulae (8a) and (8b).

[0115] [Chemical Formula 10]

[0116]

[0117] [Chemical Formula 11]

[0118]

[0119] In formulas (8a) and (8b), a and b are integers of 0 to 100, and at least one of a and b is 1 or greater.

[0120] Examples of the reactive functional groups in the polyphenylene ether resin (B2) include groups having ethylenically unsaturated bonds, such as vinyl, allyl, acryloyl, methacryloyl, cyclopentenyl, vinylbenzyl, and vinylnaphthyl; epoxy groups; and hydroxyl groups. Of these, groups having ethylenically unsaturated bonds are preferred from the perspective of easily satisfying the physical properties described below and easily obtaining a cured product having excellent low dielectric properties. From the perspective of easily obtaining a cured product that exhibits good flex resistance, methacryloyl and vinylbenzyl are more preferred, and vinylbenzyl is even more preferred.

[0121] As the polyphenylene ether resin (B2) having a reactive functional group, preferably one having a reactive functional group at any position of the polyphenylene ether skeleton, preferably one having a reactive functional group at both ends of the polyphenylene ether skeleton. Thus, it is easy to satisfy the physical properties described below and to easily obtain a cured product having excellent low dielectric properties and excellent bending resistance.

[0122] The number average molecular weight (Mn) of the polyphenylene ether resin (B2) is not particularly limited, but is preferably 500 to 5,000, more preferably 500 to 3,000. As a result, it is easy to satisfy the physical properties described below, and it is easy to obtain a cured product having excellent low dielectric properties and excellent bending resistance. In addition, the adhesion to the adherend is easy to be excellent. It should be noted that the number average molecular weight (Mn) can be obtained as a standard polystyrene conversion value by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent.

[0123] When the adhesive layer contains a polyphenylene ether resin (B2), its content in the adhesive layer is preferably 10 to 70% by mass, more preferably 20 to 60% by mass, further preferably 25 to 55% by mass, particularly preferably 30 to 50% by mass, and preferably 35 to 45% by mass. This facilitates good adhesion to the adherend, easily satisfies the physical properties described below, and easily forms an adhesive layer that imparts a cured product with excellent bonding strength and low dielectric properties. In particular, the resulting cured product layer easily exhibits good bending resistance.

[0124] [(C) ingredient: filler]

[0125] The adhesive layer of the present invention preferably contains a filler (hereinafter sometimes referred to as "filler (C)") as component (C). The presence of a suitable amount of filler (C) in the crosslinked structure formed by the binder resin (A) or the thermosetting component (B) facilitates obtaining a cured product having increased film strength and resistance to external forces such as bending. In particular, it facilitates satisfying the physical properties described below and easily yields an adhesive layer with excellent bending resistance.

[0126] The shape of the filler (C) can be fixed or amorphous. From the perspective of film-forming properties, a fixed-shaped filler is preferred. As fixed-shaped fillers, spherical, powdery, fibrous, needle-shaped, and flaky shapes can be listed. Among them, spherical is preferred, and a true spherical is more preferred. Thus, the filler is easily evenly dispersed in the adhesive layer, has excellent film-forming properties and film strength, easily satisfies the physical properties described below, and easily obtains an adhesive layer with excellent bending resistance. In addition, since the filler is difficult to protrude from the surface of the adhesive layer, it is easier to obtain an adhesive layer with an arithmetic mean surface roughness (Ra) of less than 200 nm on the surface, which has excellent adhesion to the adherend.

[0127] Specific examples of fillers (C) include preferably inorganic fillers composed of silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, titanium dioxide, zirconium dioxide, etc.; organic fillers composed of acrylic resins, acrylic-styrene copolymers, melamine resins, polycarbonate resins, polyethylene resins, polystyrene resins, benzoguanamine resins, epoxy resins, etc.; organic-inorganic fillers composed of silicon-containing compounds having an intermediate structure between inorganic and organic, etc. Among them, from the perspective of film forming properties and bending resistance, inorganic fillers or organic-inorganic fillers are preferred, inorganic fillers are particularly preferred, and from the perspective of easily satisfying the physical properties described below, silica fillers are further preferred. Filler (C) can be used alone or in combination of two or more.

[0128] The filler (C) may be surface-treated or unsurface-treated. From the perspective of film-forming properties and the ease of satisfying the physical properties described below, unsurface-treated fillers are preferred. This facilitates obtaining an adhesive layer having excellent adhesion to adherends, low dielectric properties, and excellent flexural resistance.

[0129] From the perspective of film-forming properties and obtaining an adhesive layer with a good coating surface, the average particle size of the filler (C) is preferably smaller than the thickness of the adhesive layer involved in the present invention, preferably 0.01 to 10 μm, more preferably 0.05 to 7 μm, further preferably 0.1 to 4 μm, further preferably 0.2 to 3 μm, preferably 0.3 to 2.5 μm, and most preferably 0.4 to 2 μm. Thus, it is easy to meet the physical properties described later, and it helps to form an adhesive layer with excellent adhesion to the adherend, low dielectric properties, and excellent bending resistance. The average particle size of the filler can be measured by centrifugal sedimentation light transmission method.

[0130] The content of filler (C) is preferably 1 to 80 parts by mass, more preferably 5 to 65 parts by mass, further preferably 10 to 55 parts by mass, particularly preferably 15 to 45 parts by mass, relative to 100 parts by mass of the total amount of component (A), component (B), and component (C). From the perspective of improving the tensile modulus, it is preferably 20 to 40 parts by mass, particularly preferably 25 to 35 parts by mass. This makes it easy to satisfy the physical properties described below and easily obtain an adhesive layer with an excellent balance between low dielectric properties and bending resistance.

[0131] In the adhesive layer, the content of filler (C) is preferably 1 to 70% by mass, more preferably 4 to 60% by mass, further preferably 8 to 50% by mass, particularly preferably 12 to 40% by mass, and from the viewpoint of improving the tensile modulus, preferably 16 to 34% by mass, with 20 to 28% by mass being preferred. Thus, it is easy to show good adhesion to the adherend, and it is easy to satisfy the physical properties described below, and it is easy to obtain a cured layer with excellent bonding strength and low dielectric properties. In particular, the resulting cured layer easily exhibits good bending resistance.

[0132] [Component (D): Thermal polymerization initiator]

[0133] The curing reaction of the adhesive layer of the present invention is preferably accompanied by a thermal polymerization reaction. Therefore, the adhesive layer of the present invention preferably contains a thermal polymerization initiator (hereinafter sometimes referred to as "thermal polymerization initiator (D)"). Thus, the curing reaction of the adhesive layer can be carried out efficiently.

[0134] A thermal polymerization initiator (D) is a compound that generates active species such as free radicals or cations that initiate polymerization upon heating. When a thermal polymerization initiator (D) is used, the polymerization reaction can be uniformly initiated in the adhesive layer under an environment where heat is easily and evenly transferred throughout the adhesive layer, such as by heating the adhesive layer in a heated space maintained at a constant temperature.

[0135] When the adhesive layer-forming composition described later contains an organic solvent, the temperature at which the half-life of the thermal polymerization initiator (D) reaches 1 minute is preferably higher than the boiling point of the organic solvent. This makes it difficult for the reaction to proceed during the adhesive layer production process (particularly the solvent drying step), and facilitates the desired curing reaction during the annealing step for obtaining the cured product layer.

[0136] Examples of the thermal polymerization initiator (D) include thermal cationic polymerization initiators and radical polymerization initiators. The thermal polymerization initiator (D) can be used alone or in combination of two or more.

[0137] A radical polymerization initiator is a compound that generates radicals that initiate polymerization upon heating, and a thermal cationic polymerization initiator is a compound that generates cationic species that initiate polymerization upon heating.

[0138] Examples of the thermal cationic polymerization initiator include sulfonium salts, quaternary ammonium salts, Salt, diazonium salt, iodine Salt, etc.

[0139] Examples of the sulfonium salt include triphenylsulfonium tetrafluoroborate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluoroarsenate, tris(4-methoxyphenyl)sulfonium hexafluoroarsenate, and diphenyl(4-phenylthiophenyl)sulfonium hexafluoroarsenate.

[0140] Examples of the quaternary ammonium salt include tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium hydrogensulfate, tetraethylammonium tetrafluoroborate, tetraethylammonium p-toluenesulfonate, N,N-dimethyl-N-benzylanilinium hexafluoroantimonate, N,N-dimethyl-N-benzylanilinium tetrafluoroborate, N,N-dimethyl-N-benzylpyridinium hexafluoroantimonate, N,N-diethyl-N-benzyl trifluoromethanesulfonate, N,N-dimethyl-N-(4-methoxybenzyl)pyridinium hexafluoroantimonate, and N,N-diethyl-N-(4-methoxybenzyl)toluinium hexafluoroantimonate.

[0141] As Salts such as ethyltriphenylphosphine Hexafluoroantimonate, tetrabutyl Hexafluoroantimonate, etc.

[0142] As iodine Salts such as diphenyl iodide Hexafluoroarsenate, bis(4-chlorophenyl)iodide Hexafluoroarsenate, bis(4-bromophenyl)iodide Hexafluoroarsenate, phenyl (4-methoxyphenyl) iodide Hexafluoroarsenate, etc.

[0143] Examples of the radical polymerization initiator include dialkyl peroxides such as benzoyl peroxide, acetyl peroxide, decanoyl peroxide, lauroyl peroxide, cumyl peroxide, and di-tert-butyl peroxide; hydroperoxides such as tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, cumene hydroperoxide, and tert-butyl hydroperoxide; tert-hexyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-butyl peroxyneoheptanoate, and amyl peroxide. tert-Hexyl peroxide, tert-Butyl peroxyvalerate, dilauroyl peroxide, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, disuccinic acid peroxide, tert-Hexyl peroxy-2-ethylhexanoate, tert-Butyl peroxy-2-ethylhexanoate, 1,1-bis(tert-Hexylperoxy)cyclohexane, 1,1-bis(tert-Butylperoxy)cyclohexane, tert-Hexyl peroxyisopropyl monocarbonate, tert-Butyl peroxymaleate, 3,5-dimethylperoxy , tert-butyl 5-trimethylhexanoate, tert-butyl peroxyisopropyl monocarbonate, tert-butyl peroxy2-ethylhexyl monocarbonate, tert-butyl peroxylaurate, tert-hexyl peroxybenzoate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, n-butyl 4,4-bis(tert-butylperoxy)valerate, dicumyl peroxide, di-tert-hexyl peroxide, di-tert-butyl peroxide, p-menthane hydroperoxide, etc. (Organic) peroxides such as thermal Polymerization initiators; azo-based thermal polymerization initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-cyanovaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(methyl isobutyl ester), and 1,1'-azobis(1-cyclohexanecarbonitrile).

[0144] The thermal polymerization initiator (D) is preferably a thermal cationic polymerization initiator, particularly preferably a sulfonium salt-based thermal cationic polymerization initiator. This allows the adhesive layer of the present invention to form a desired crosslinked structure, facilitates the development of the physical properties described below, and readily yields a cured layer with excellent adhesive strength and low dielectric properties. In particular, the resulting cured layer exhibits excellent flexural resistance.

[0145] The content of the thermal polymerization initiator (D) is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 15 parts by mass, further preferably 1 to 10 parts by mass, and particularly preferably 2 to 5 parts by mass, relative to 100 parts by mass of the total amount of component (A), component (B), and component (C). This makes it easier to satisfy the physical properties described below and to obtain an adhesive layer having an excellent balance between low dielectric properties and bending resistance.

[0146] When the adhesive layer contains a thermal polymerization initiator (D), its content in the adhesive layer is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, particularly preferably 1 to 6% by mass, and even more preferably 2 to 4% by mass. This forms the desired cross-linked structure, facilitates the development of the physical properties described below, and more efficiently forms a cured layer with excellent adhesive strength and low dielectric properties. In particular, the resulting cured layer exhibits good flexural resistance.

[0147] [Component (E): silane coupling agent]

[0148] The adhesive layer of the present invention preferably contains a silane coupling agent as component (E) (hereinafter sometimes referred to as "silane coupling agent (E)"), which improves adhesion to an adherend and facilitates formation of an adhesive layer with higher adhesive strength.

[0149] As the silane coupling agent (E), known silane coupling agents can be used, but among them, organic silicon compounds having at least one alkoxysilyl group in the molecule are preferred.

[0150] Examples of the silane coupling agent (E) include silane coupling agents having a (meth)acryloyl group, silane coupling agents having a vinyl group, silane coupling agents having an epoxy group, silane coupling agents having a styryl group, silane coupling agents having an amino group, silane coupling agents having an isocyanurate skeleton, silane coupling agents having a urea group, silane coupling agents having a halogen atom, silane coupling agents having a mercapto group, silane coupling agents having an isocyanate group, silane coupling agents having an allyl group, silane coupling agents having a hydroxyl group, and silane coupling agents having an acid anhydride structure. Among these, from the viewpoint of easily obtaining an adhesive layer that provides a cured product layer with higher bonding strength by thermal curing, preferred are silane coupling agents having an epoxy group, silane coupling agents having an isocyanate group, silane coupling agents having an allyl group, silane coupling agents having a hydroxyl group, silane coupling agents having an isocyanurate skeleton, silane coupling agents having a mercapto group, and silane coupling agents having an acid anhydride structure. Silane coupling agents having an epoxy group, silane coupling agents having a hydroxyl group, and silane coupling agents having an acid anhydride structure are particularly preferred, and silane coupling agents having an acid anhydride structure are preferred. Silane coupling agents (E) may be used alone or in combination of two or more.

[0151] When the adhesive layer of the present invention contains a silane coupling agent (E), its content in the adhesive layer is preferably 0.01 to 5% by mass, more preferably 0.04 to 3% by mass, further preferably 0.08 to 1% by mass, particularly preferably 0.10 to 0.70% by mass, and particularly preferably 0.12 to 0.40% by mass. This facilitates the development of the physical properties described below, and easily forms a cured layer with excellent adhesive strength and low dielectric properties. In particular, the resulting cured layer exhibits good flexural resistance.

[0152] [Component (F): crosslinking agent]

[0153] The adhesive layer of the adhesive sheet of the present invention preferably contains a crosslinking agent (hereinafter sometimes referred to as "crosslinking agent (F)") as component (F) that is reactive with components (A) and (B). This facilitates obtaining an adhesive layer that readily satisfies the physical properties described below, and also facilitates forming a cured layer having a desired crosslinking density by heat treatment.

[0154] The crosslinking agent (F) is preferably a substance that undergoes a thermal curing reaction upon heating, and is particularly preferably a compound that reacts well with the component (A). Specifically, the crosslinking agent (F) preferably has a reactive group or reactive site that is reactive with the reactive functional group in the binder resin (A).

[0155] Examples of the crosslinking agent (F) include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, ammonium salt crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, Oxazoline crosslinking agents, metal alkoxide crosslinking agents, aziridine crosslinking agents, etc. Among these, isocyanate crosslinking agents, epoxy crosslinking agents, and metal chelate crosslinking agents are preferred from the viewpoint of storage stability. Metal chelate crosslinking agents are particularly preferred from the viewpoint of easily satisfying the physical properties described below. It should be noted that the crosslinking agent (F) can be used alone or in combination of two or more.

[0156] An isocyanate crosslinking agent is a compound having two or more isocyanate groups in the molecule. Examples of isocyanate crosslinking agents include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated xylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, diphenylmethane-4,4-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, adducts of these polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret forms or isocyanurate forms of these polyisocyanate compounds.

[0157] Epoxy crosslinking agents are compounds with two or more epoxy groups in their molecules. Examples of epoxy crosslinking agents include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, and diglycidylamine.

[0158] Metal chelate crosslinking agents are chelate compounds having metal ions that function as crosslinking points. Examples of metal chelate crosslinking agents include metal chelate compounds in which the metal ions are aluminum ions, zirconium ions, titanium ions, zinc ions, iron ions, tin ions, and the like. Among these, aluminum chelate compounds are preferred.

[0159] Examples of the aluminum chelate compound include tris(acetylacetate)aluminum, bis(ethylacetylacetate)acetylacetate aluminum, diisopropoxymonooleylacetylacetate aluminum, and monoisopropoxybisoleylacetylacetate aluminum.

[0160] When the adhesive layer contains a crosslinking agent (F), its content in the adhesive layer is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, further preferably 0.1 to 2% by mass, particularly preferably 0.15 to 1% by mass, particularly preferably 0.2 to 0.7% by mass, and most preferably 0.22 to 0.4% by mass. This makes it easier to satisfy the physical properties described below, forming a cured layer with excellent adhesive strength and low dielectric properties, exhibiting desired dielectric properties, and exhibiting good flex resistance.

[0161] [Other ingredients]

[0162] Adhesive layer involved in the present invention may also contain the composition (other components) beyond the above-mentioned scope without hindering the effect of the present invention. As other components, additives such as ultraviolet light absorber, antistatic agent, light stabilizer, antioxidant, oxygen absorber, infrared absorber, colorant, rust preventer, tackifier, resin stabilizer, filler, extender, dispersant, softener can be enumerated. These can be used alone or in combination of more than two kinds. When the raw material composition contained these additives, its content can be suitably determined according to purpose.

[0163] [Dispersant]

[0164] The adhesive layer of the present invention preferably contains a dispersant, which facilitates uniform dispersion of the filler (C) in the adhesive layer-forming composition described below, and consequently facilitates formation of a high-quality adhesive layer in which the filler (C) is uniformly dispersed.

[0165] Examples of the dispersant include monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, pearly acid, and stearic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, and dodecanedicarboxylic acid. azelaic acid, etc.; dibasic acids having 12 to 28 carbon atoms, such as dimer acid; alicyclic dicarboxylic acids, such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic anhydride, 3-methylhexahydrophthalic anhydride, 2-methylhexahydrophthalic anhydride, dicarboxy hydrogenated bisphenol A, dicarboxy hydrogenated bisphenol S, dimer acid, hydrogenated dimer acid, hydrogenated naphthalene dicarboxylic acid, and tricyclodecane dicarboxylic acid; hydroxycarboxylic acids, such as hydroxybenzoic acid and lactic acid; trivalent or higher carboxylic acids, such as trimellitic anhydride and pyromellitic anhydride; unsaturated dicarboxylic acids, such as fumaric acid and maleic acid; carboxylic acid diols, such as dimethylolbutanoic acid and dimethylolpropionic acid; Disperbyk-2155 (trade name: manufactured by BYK), etc.

[0166] The amount of dispersant used is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 15 parts by mass, further preferably 1.0 to 10 parts by mass, and particularly preferably 1.4 to 5 parts by mass, relative to 100 parts by mass of filler (C). This facilitates uniform dispersion of the filler in the adhesive, resulting in an adhesive layer that readily exhibits the physical properties described below. Furthermore, the adhesive layer exhibits excellent dielectric properties and excellent flex resistance.

[0167] (Preparation of Adhesive Layer-Forming Composition)

[0168] The adhesive layer-forming composition can be prepared by mixing a binder resin (A), a thermosetting component (B), a filler (C), a thermal polymerization initiator (D), a silane coupling agent (E), a crosslinking agent (F), and a dispersing material as other components. Taking into account operability or coating properties, an organic solvent may also be contained. As the solvent used, aromatic hydrocarbon solvents such as benzene and toluene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as n-pentane, n-hexane, and n-heptane; alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane, and methylcyclohexane. These solvents can be used alone or in combination of two or more. The content of the solvent can be appropriately determined in consideration of coating properties, etc.

[0169] [Formation of Adhesive Layer]

[0170] The adhesive layer can be formed using an adhesive layer-forming composition. The adhesive layer can be formed by applying a predetermined amount of the adhesive layer-forming composition on a processing sheet (or a release sheet described later) and drying the resulting coating.

[0171] As the processing sheet, materials known in the past can be used. As the base material of the processing sheet, resin film and paper can be listed. As the resin of the resin film, polyethylene terephthalate, polyethylene, polypropylene, polybutene, polybutadiene, polymethylpentene, polyvinyl chloride, vinyl chloride copolymer, polybutylene terephthalate, polyurethane, ethylene-vinyl acetate copolymer, ionomer resin, ethylene-(methyl) acrylic acid copolymer, polystyrene, polycarbonate, fluororesin, low-density polyethylene, linear low-density polyethylene and triacetyl cellulose can be listed. As paper, high-quality paper, coated paper, glassine paper and laminated paper can be listed. It should be noted that, from the viewpoint of SDGs, as the material constituting the processing sheet, materials with high biomass content can be used, materials that can be recycled or reused can also be used, and materials after recycling or reuse can also be used. These can be used alone or in combination of two or more.

[0172] The thickness of the processed sheet is not particularly limited, but is usually about 20 to 150 μm.

[0173] Examples of a method for applying the adhesive layer-forming composition include spin coating, spray coating, bar coating, knife coating, roll coating, doctor blade coating, die coating, and gravure coating.

[0174] Examples of methods for drying the coating include conventional drying methods such as hot air drying, hot roll drying, and infrared irradiation. The coating can be dried, for example, at a drying temperature of 80 to 150° C. for a drying time of 30 seconds to 5 minutes.

[0175] The thickness of the adhesive layer of the present invention is generally 1 to 100 μm, preferably 4 to 80 μm, more preferably 8 to 60 μm, even more preferably 12 to 50 μm, particularly preferably 15 to 40 μm, and particularly preferably 18 to 30 μm. This facilitates achieving appropriate bonding strength and the physical properties described below, and easily produces a product with an excellent balance between low dielectric properties and flexural resistance.

[0176] With respect to the adhesive layer involved in the present invention, when the thickness of the adhesive layer is set to X (μm) and the average particle size of the filler (C) is set to Y (μm), it is preferred to satisfy the formula: Y / X<1, more preferably satisfy the formula: Y / X<0.5, further preferably satisfy the formula: Y / X<0.2, particularly preferably satisfy the formula: Y / X<0.1, more preferably satisfy the formula: Y / X<0.08, further preferably satisfy the formula: Y / X<0.07. The lower limit of the above-mentioned Y / X is not particularly limited, usually exceeds 0, is preferably 0.001 or more, more preferably 0.004 or more, further preferably 0.008 or more, and particularly preferably 0.01 or more. Thus, it is easy to satisfy the appropriate bonding strength and the physical properties described later, and it is easy to become a product with excellent balance between low dielectric properties and bending resistance.

[0177] By performing the above operation, an adhesive sheet having a layer structure of a processing sheet (or release sheet) / adhesive layer can be obtained. In the case of storing or transporting the adhesive sheet, a release sheet can also be arranged on the surface of the adhesive layer for the purpose of protecting the surface of the adhesive layer. As the release sheet, the same material as the above-mentioned processing sheet can be used. The processing sheet and the release sheet are peeled off and removed during use. It should be noted that, when the adhesive layer has processing sheets or release sheets on both sides, from the perspective of operability, when comparing the release force when peeling off one processing sheet (or release sheet) with the release force when peeling off another processing sheet (or release sheet), it is preferred that there is a difference in the release force.

[0178] As used herein, the release surface of a processing sheet or release sheet refers to the surface of the release sheet that exhibits releasability, including both surfaces that have been subjected to a release treatment and surfaces that exhibit releasability without a release treatment. It should be noted that the release surface of the release sheet (particularly the surface in contact with the adhesive layer) is preferably subjected to a release treatment. Examples of release agents used for release treatment include alkyd, silicone, fluorine, rubber, long-chain alkyl, unsaturated polyester, polyolefin, and wax release agents, with non-silicone release agents being preferred.

[0179] (Curing of Adhesive Layer)

[0180] The adhesive layer of the adhesive sheet of the present invention is cured by heating to form a cured product layer. The curing conditions for the adhesive layer can be appropriately determined based on the curable component contained in the adhesive layer. The heating temperature is generally 140°C or higher, preferably 150-180°C. The heating time is generally 0.5-3 hours, preferably 1-2 hours.

[0181] The adhesive sheet of the present invention has the following characteristics.

[0182] (1) Arithmetic mean surface roughness (Ra)

[0183] The arithmetic mean surface roughness (Ra) of the surface of the adhesive layer possessed by the adhesive sheet of the present invention is less than 200nm, preferably 0 to 150nm, more preferably 0.1 to 100nm, further preferably 1 to 75nm, particularly preferably 2 to 50nm, wherein preferably 48nm. Thus, the adhesive layer is a good coating surface with little transmission loss. It is easy to exert the desired bonding strength, especially easy to exert excellent bending resistance. The arithmetic mean surface roughness (Ra) of the adhesive layer surface is the average of the absolute value of the height of the roughness curve in the reference length specified in ISO25178, and can be measured according to the method described in the embodiment.

[0184] (2) Dielectric constant

[0185] The adhesive layer of the adhesive sheet of the present invention has excellent low dielectric properties. The dielectric constant of the cured layer of the adhesive layer of the adhesive sheet of the present invention obtained by heat treating the adhesive layer at 170°C for 2 hours at 23°C and a frequency of 10 to 40 GHz is preferably 3.0 (F / m) or less, more preferably 2.8 (F / m) or less, and further preferably 2.7 (F / m) or less. The lower limit of the dielectric constant is not specific, but is usually 2.00 (F / m) or more. The dielectric constant of the cured layer at 23°C and a frequency of 10 to 40 GHz can be measured according to the method described in the examples.

[0186] (3) Dielectric loss tangent

[0187] The dielectric loss tangent of the cured product layer of the adhesive sheet of the present invention at 23°C and a frequency of 10 to 40 GHz obtained by heat treating the adhesive layer at 170°C for 2 hours is 0.005 or less, preferably 0.0045 or less, and more preferably 0.004 or less. Thus, when the adhesive sheet of the present invention is used as a forming material for the insulating layer of an electronic device, the transmission loss of the insulating layer is small. The dielectric loss tangent of the cured product layer at 23°C and a frequency of 10 to 40 GHz can be measured according to the method described in the Examples.

[0188] (4) Gel fraction

[0189] The adhesive layer of the adhesive sheet of the present invention preferably has a gel fraction of 10 to 70%, more preferably 13 to 60%, even more preferably 16 to 50%, and particularly preferably 20 to 40%. This improves workability and facilitates the formation of an adhesive layer with excellent curability and adhesion to an adherend.

[0190] The gel fraction of the cured product layer obtained by heat-treating the adhesive layer of the adhesive sheet of the present invention at 170°C for 2 hours is preferably 40-90%, more preferably 45-85%, even more preferably 50-80%, particularly preferably 50-80%, and particularly preferably 50-80%. This allows the cross-linked structure of the cured product layer to be fully formed, making it easier to exhibit particularly strong adhesive strength. Consequently, the adhesive layer imparting this cured product layer has excellent flexural resistance. The gel fractions of the adhesive layer and the cured product layer can be measured according to the methods described in the Examples.

[0191] (5) Increase rate of gel fraction

[0192] When the gel fraction before curing of the adhesive layer possessed by the adhesive sheet of the present invention is set to α (%), and the gel fraction of the cured product layer obtained by curing the adhesive layer is set to β (%), the rate of increase (%) of the gel fraction represented by the formula: [(β-α) / α] × 100 is preferably 60% or more, more preferably 80% or more, further preferably 100% or more, particularly preferably 110% or more, wherein preferably 120% or more, and most preferably 130% or more. The upper limit of the rate of increase is not particularly limited, but is preferably 800% or less, more preferably 600% or less, further preferably 400% or less, particularly preferably 350% or less, and from the viewpoint of having a tendency to increase the tensile modulus, is preferably 300% or less, wherein preferably 250% or less. Thus, it is easy to become a product with an excellent balance between low dielectric properties and bending resistance. Generally, a large amount of cross-linked structures are formed in the cured product layer formed by curing the adhesive layer compared to the adhesive layer. Therefore, the gel fraction of the cured product layer is usually a value larger than the gel fraction of the adhesive layer. When the cured product of the adhesive layer functions as an adhesive member, a protective member, an insulating member, or the like, the cured product is preferably one in which the curing reaction has fully progressed.

[0193] (6) Tensile elastic modulus (E')

[0194] The tensile modulus of elasticity at 25°C of the cured product layer obtained by heat treating the adhesive layer of the adhesive sheet of the present invention at 170°C for 2 hours is not particularly limited, but is preferably 0.5 to 10 GPa, more preferably 1.0 to 7.0 GPa, further preferably 1.5 to 5.0 GPa, particularly preferably 1.6 to 3.0 GPa, and preferably 1.7 to 2.0 GPa. As a result, it is easy to become a product with excellent dielectric properties and bending resistance in the high frequency band. The tensile modulus of elasticity at 25°C of the cured product layer obtained by heat treating the adhesive layer at 170°C for 2 hours can be measured according to the method described in the examples.

[0195] The thermosetting adhesive sheet of the present invention is suitable for use as an adhesive sheet for electronic devices. For example, the adhesive layer constituting the thermosetting adhesive sheet of the present invention can be used to bond various components in electronic devices or to form an insulating layer for conductive layers (e.g., circuits) in electronic devices. Examples of electronic devices include communication devices such as smartphones and tablet computers.

[0196] The thermosetting adhesive sheet of the present invention is suitable for use as an adhesive sheet for cover films. Cover films are laminated films used, for example, to protect the surface of flexible printed wiring boards and typically comprise an insulating resin layer and an adhesive layer. For example, a cover film can be produced by (thermo)compression bonding the adhesive layer of the thermosetting adhesive sheet of the present invention to an insulating resin film.

[0197] 2) Laminated body

[0198] The present invention secondly provides a laminate comprising a conductive layer and an insulating layer formed on the conductive layer, wherein the insulating layer is a cured layer formed by curing the adhesive layer of the thermosetting adhesive sheet of the present invention.

[0199] Examples of the conductive layer include conductive layers (circuits, etc.) in electronic devices, for example, layers constituting wiring serving as electrical signal conductors in printed wiring boards made of metal-clad laminates.

[0200] Examples of the metal used as a raw material for the conductive layer include copper, aluminum, silver, gold, zinc, nickel, tin, iron, and alloys thereof. Among these, copper or alloys containing copper are particularly preferred from the perspective of electrical conductivity.

[0201] The thickness of the conductive layer according to the present invention is preferably 1 to 1000 μm, more preferably 10 to 800 μm, further preferably 40 to 600 μm, particularly preferably 80 to 500 μm, and particularly preferably 120 to 400 μm.

[0202] The laminate of the present invention uses the adhesive sheet of the present invention and has both excellent low dielectric properties and bending resistance.

[0203] 3) Method for manufacturing laminate

[0204] The third aspect of the present invention is a method for producing a laminate of the present invention, comprising: step (I) of laminating the adhesive layer of the thermosetting adhesive sheet of the present invention onto a conductive layer to obtain a laminate; and step (II) of heating the laminate to a predetermined temperature to cure the adhesive layer of the thermosetting adhesive sheet. Figure 1 The manufacturing method of the present invention will be described at the same time.

[0205] First, if Figure 1 As shown in (a), a thermosetting adhesive sheet 10 having release sheets 2a and 2b on both sides of an adhesive layer 1 according to the present invention is prepared. The release sheets 2a and 2b are peeled off and removed during use (during production of a laminate).

[0206] Then, if Figure 1 As shown in (b), after peeling off the release sheet 2a, the conductive layer 3 is bonded to the exposed surface of the adhesive layer 1. Then, the release sheet 2b is peeled off, and the insulating resin layer 4 is formed on the exposed surface of the adhesive layer 1, thereby obtaining a laminate 20 (step I-1). The insulating resin layer 4 can be formed by applying a composition for forming an insulating resin layer to the exposed surface of the adhesive layer 1 and drying the resulting coating, or by bonding an insulating resin film to the exposed surface of the adhesive layer 1.

[0207] Examples of materials for the insulating resin layer 4 include polyimides obtained by reacting tetracarboxylic dianhydride with diamines; phenolic resin-modified polyimides; novolac resin-modified polyimides; polyvinylphenol-modified polyimides; polyurethane-modified polyimides containing phenolic hydroxyl groups; and polyurea-modified polyimides containing phenolic hydroxyl groups, which are modified polyimides obtained by modifying polyimides with other resins. From the perspective of sustainable development goals (SDGs), the insulating resin layer can be made of materials with a high biomass content, recyclable or reusable materials, or recycled or reused materials. These materials can be used alone or in combination of two or more.

[0208] The thickness of the insulating resin layer 4 of the present invention is preferably 1 to 100 μm, more preferably 4 to 80 μm, further preferably 8 to 60 μm, particularly preferably 16 to 40 μm, and particularly preferably 20 to 30 μm.

[0209] Afterwards, if Figure 1 As shown in (c), by heating and pressing the laminate 20, the adhesive layer 1 is cured, and the laminate 30 of the present invention can be obtained as a cured product layer 5. Any method can be used to heat and cure the adhesive layer 1. For example, hot pressing or methods using a heated roller device can be used. According to the production method of the present invention, the laminate of the present invention can be produced efficiently.

[0210] The embodiments described above are described to facilitate understanding of the present invention and are not intended to limit the present invention. Therefore, the elements disclosed in the embodiments described above are intended to include all design changes and equivalents that fall within the technical scope of the present invention.

[0211] In this specification, when "α to β" is described (α and β are arbitrary numerical values), unless otherwise specified, it also includes the meaning of "α or more and β or less", as well as "preferably greater than α" or "preferably less than β". In addition, when "α or more" (α is an arbitrary number) is described, it also includes the meaning of "preferably greater than α" unless otherwise specified, and when "β or less" (β is an arbitrary number) is described, it also includes the meaning of "preferably less than β" unless otherwise specified.

[0212] Example

[0213] The present invention will be described in more detail below with reference to the following examples, but the present invention is not limited to the following examples.

[0214] [Compounds used in Examples or Comparative Examples]

[0215] (1-1) Binder resin (A1)

[0216] Acid-modified α-olefin polymer (manufactured by Mitsui Chemicals, trade name: Unistole H-200)

[0217] (1-2) Binder resin (A2)

[0218] Acid-modified styrene elastomer (manufactured by Kraton Polymer Co., Ltd., trade name: FG-1901)

[0219] (2-1) Thermosetting component (B1a): a diallyl compound having an isocyanurate skeleton (manufactured by Shikoku Chemical Industry Co., Ltd., trade name: L-DAIC)

[0220] (2-2) Thermosetting component (B2a): Vinylbenzyl-modified polyphenylene ether [manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name: OPE-2St 2200]

[0221] (3-1) Filler (C1): High-purity spherical silica fine particles (average particle size: 1.5 μm, manufactured by Nippon Shokubai Co., Ltd., trade name: SEAHOSTAR KE-S150)

[0222] (3-2) Filler (C2): High-purity spherical silica fine particles (average particle size: 0.5 μm, manufactured by Nippon Shokubai Co., Ltd., trade name: SEAHOSTAR KE-S50)

[0223] (3-3) Amorphous silica (C3) (average particle size: 2.7 μm, manufactured by Fuji Silysia Chemical Co., Ltd., trade name: Sylysia 530)

[0224] (3-4) Filler (C4): Spherical silica fine particles with functional groups (average particle size: 1.5 μm, manufactured by Nippon Shokubai Co., Ltd., trade name: SEAHOSTAR KE-E150)

[0225] (4) Thermal polymerization initiator (D1): Sulfonium salt-based thermal cationic polymerization initiator (manufactured by Sanshin Chemical Co., Ltd., trade name: San-Aid SI-B3)

[0226] (5) Silane coupling agent (E1): 3-trimethoxysilylpropylsuccinic anhydride (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: X-12-967C)

[0227] (6) Crosslinking agent (F1): tris(2,4-pentanedionato)aluminum(III) (manufactured by Soken Chemical Co., Ltd., trade name: M-5A)

[0228] (7) Dispersant: (manufactured by BYK, trade name: DISPAERBYK 2155)

[0229] (Examples 1 to 4, Comparative Examples 1 to 4)

[0230] 100 parts by mass of a binder resin (A1) (solid content conversion value; the same applies hereinafter), 130 parts by mass of a thermosetting component (B1a), 250 parts by mass of a thermosetting component (B2a), 100 parts by mass of a filler (C1), 15 parts by mass of a thermal polymerization initiator (D1), 1.0 parts by mass of a silane coupling agent (E1), 1.5 parts by mass of a crosslinking agent (F1), and 1.7 parts by mass of a dispersant were uniformly mixed with a solvent and stirred thoroughly to prepare a composition for forming an adhesive layer.

[0231] Next, a composition for forming an adhesive layer was applied to a heavy-peelable release sheet R1, on which one side of a polyethylene terephthalate film was subjected to a peeling treatment with a rubber-based release agent (non-silicone-based release agent), using a coating machine. The resulting coating was then dried at a drying temperature of 100°C for 2 minutes to form a coating layer with a thickness of 25 μm. Next, the coating layer on the release sheet R1 obtained above and a light-peelable release sheet R2, on which one side of a polyethylene terephthalate film was subjected to a peeling treatment with a rubber-based release agent (non-silicone-based release agent), were laminated so that the peeling-treated surface of the release sheet R2 contacted the coating layer, and the adhesive was aged for 7 days at 23°C and 50% RH. Thus, an adhesive sheet having an adhesive layer with a thickness of 25 μm was manufactured, i.e., a thermosetting adhesive sheet consisting of a structure of release sheet R1 / adhesive layer (thickness: 25 μm) / release sheet R2.

[0232] The thickness of the adhesive layer is measured in accordance with JIS K7130 using a constant-pressure thickness gauge (manufactured by Teclock, product name "PG-02"). Furthermore, the release forces of the release sheets R1 and R2 in the resulting thermosetting adhesive sheet were confirmed to be greater for release sheet R1 than for release sheet R2.

[0233] (Examples 2 to 4, Comparative Examples 1 to 4)

[0234] Adhesive layers were formed in the same manner as in Example 1 except that the composition of the adhesive layer-forming composition was changed to the ratio shown in Table 1 below. Adhesive sheets of Examples 2 to 4 and Comparative Examples 1 to 4 were produced.

[0235] [Table 1]

[0236] Table 1

[0237]

[0238] (Production of Laminated Body)

[0239] The release sheet R2 was peeled off from the adhesive sheet obtained in the embodiment or comparative example to expose the adhesive layer. Then, the obtained adhesive sheet was overlapped on a copper foil (manufactured by Kansai Electronics Industry Co., Ltd., trade name: C1100P, glossy, thickness 300 μm). Next, the release sheet R1 was peeled off from the adhesive layer, and a modified polyimide (MPI) film (manufactured by PIAdvanced Materials Co., Ltd., Korea, product number: PI FG100, thickness: 25 μm) was attached to the exposed adhesive layer to obtain a laminate (layer structure of MPI film / adhesive layer / copper foil). The laminate was subjected to a pre-annealing treatment (1 MPa, 160°C, 5 minutes) using a vacuum laminator (manufacturer name: Nikko-Materials Co., Ltd., model: V130), and then an annealing treatment (170°C, 2 hours) was applied under pressureless conditions. Thus, laminates having a layer structure of MPI film / cured material layer / copper foil were obtained, each having a cured material layer after curing the adhesive layer of the adhesive sheet of Examples 1 to 4 and Comparative Examples 1 to 4.

[0240] [Physical property evaluation]

[0241] The obtained adhesive sheet samples were evaluated for various physical properties according to the following (test and evaluation methods).

[0242] (1) Evaluation of film-forming properties

[0243] The adhesive layer-forming compositions of the Examples and Comparative Examples were applied to release sheet R1 using a coater. The resulting coatings were dried at 100°C for 2 minutes to form coating layers with a thickness of 25 μm. The coating layers were evaluated as having good appearance if no signs of wrinkling, streaks, or spot defects were observed on the surface. Wrinkles, streaks, or spot defects were observed on the surface of the coating layers, indicating poor appearance. The evaluation was given as ×. The results are shown in Table 2.

[0244] (2) Arithmetic mean surface roughness (Ra)

[0245] The surface roughness [arithmetic mean surface roughness (Ra; nm)] of the adhesive layer was measured using a surface roughness measuring device in accordance with ISO 25178. The results are shown in Table 2.

[0246] (3) Gel fraction of adhesive layer

[0247] After cutting the adhesive sheet obtained in the embodiment or comparative example into a size of 80 mm long and 80 mm wide, both release sheets were peeled off to obtain an adhesive layer. Next, the obtained adhesive layer was wrapped in a polyester mesh (mesh size 200) whose mass had been measured in advance to prepare a test sample. After the test sample was allowed to stand in an environment with a temperature of 23°C and 50% RH for 24 hours, the mass of the test sample was weighed with a precision balance. Based on the obtained measurement value, the mass of the adhesive layer before immersion (M1) was calculated. Then, the test sample was immersed in 0.2 L of toluene at room temperature (23°C) for 72 hours. After immersion, the test sample was taken out, dried in an oven at 100°C for 2 hours, and then allowed to stand in an environment with a temperature of 23°C and 50% RH for 24 hours. The mass of the dried test sample was weighed with a precision balance. Based on the obtained measurement value, the mass of the adhesive layer after immersion and drying (M2) was calculated. From the values ​​of M1 and M2, the gel fraction of the adhesive layer was calculated according to the following formula. The results are shown in Table 2.

[0248] [Mathematical formula 1]

[0249] Gel fraction (mass %) = (M2 / M1) × 100

[0250] (4) Gel fraction of cured layer

[0251] The adhesive sheets obtained in the Examples or Comparative Examples were cut into 80 mm long x 80 mm wide pieces and heated in an oven at 170°C for 2 hours. The release sheet was peeled off, and the resulting cured product layer was used in the same manner as above to calculate the gel fraction of the cured product. The results are shown in Table 2.

[0252] (5) Gel fraction increase rate

[0253] The gel fraction increase rate (%) was calculated using the gel fraction α (%) calculated in (3) and the gel fraction β (%) of the same sample after curing calculated in (4) from the following formula.

[0254] [Mathematical formula 2]

[0255] Gel fraction increase rate (%) = [(β-α) / α] × 100

[0256] (6) Dielectric constant (Dk), dielectric loss tangent (Df)

[0257] The adhesive sheets obtained in the Examples or Comparative Examples were cut into 80 mm long x 80 mm wide sheets and annealed at 170°C for 2 hours to obtain the adhesive layer as the cured product layer. Subsequently, both release sheets were peeled off to obtain a cured product layer sample. The dielectric constant and dielectric loss tangent of these samples were measured using a cavity resonator dielectric constant analyzer (TE mode, frequencies: 10 GHz, 28 GHz, and 40 GHz) in accordance with JIS R1641 IPC-TM6502.5.5.13.

[0258] .Analyzer: Anritsu, model MS46122B

[0259] .Resonator: Made by AET, 10, 28, 40 GHz

[0260] (7) Tensile elastic modulus (E')

[0261] The adhesive layer of the adhesive sheet obtained in the embodiment or comparative example was laminated to a thickness of 200 μm, and the obtained adhesive layer (thickness: 200 μm) was cut into a size of 20 mm long × 5 mm wide. Using a vacuum laminator (made by Nikko Materials, model: V130), a pre-annealing treatment (1 MPa, 160°C, 5 minutes) was applied, and then an annealing treatment (170°C, 2 hours) was applied under pressureless conditions to obtain a measurement sample. The obtained measurement sample was measured using a dynamic viscoelasticity measuring device (made by Netzsch, model: DMA 242E Artemis, mode: tensile, frequency: 1 Hz, distance between chucks of the measurement sample: 10 mm, width of the measurement sample: 5 mm) to measure the tensile elastic modulus (E' (GPa)) of the cured layer at 25°C.

[0262] (8) Bendability test

[0263] The laminate having the MPI film / cured material layer / copper foil structure was repeatedly bent under the following conditions using a planar unloaded U-shaped stretch tester (manufactured by Yuasa System Equipment Co., Ltd., product name "CL09-typeD01-FSC90"). The bent portion was then visually inspected, and the bendability was evaluated according to the following evaluation criteria.

[0264] Test structure: MPI film / cured material layer / copper foil

[0265] Minimum bending diameter: 3mmφ

[0266] Bending times: 100,000 times

[0267] Sample size: 50mm×200mm

[0268] Test temperature: 23°C

[0269] <Evaluation Criteria>

[0270] ○: No line originating from a bending mark exists at the bent portion.

[0271] △: Lines originating from the bending traces are present at the bent portion, and the lines are visible even when viewed from the front (true surface) and at an angle of 60°.

[0272] ×: The cured product layer (adhesive layer) was broken.

[0273] (9) Bonding strength

[0274] The adhesive layer exposed by peeling off release sheet R2 from the adhesive sheet obtained in the Examples or Comparative Examples was transferred to the glossy side of a copper foil (manufactured by Kansai Electronics Industry Co., Ltd., trade name: C1100P, glossy, 300 μm thick) using a rubber roller heated to 100°C at a pressure of 0.2 MPa. The resulting test piece was cut into a 1.0 cm wide x 10 cm long test piece. Next, the adhesive layer exposed by peeling off release sheet R1 from the test piece was bonded to the MPI film surface of a laminate of the above-mentioned MPI films bonded to an aluminum plate via an adhesive layer using a rubber roller heated to 100°C at a pressure of 0.2 MPa. This was used as a test sample (MPI film / adhesive layer / copper foil laminate). This test sample was pre-annealed (1 MPa, 160°C, 1 minute) using a vacuum laminator (Nikko Materials, Model: V130) and then annealed (170°C, 2 hours) under pressureless conditions to obtain a measurement sample (a laminate of MPI film / cured layer / copper foil). This measurement sample was allowed to stand for 24 hours in an environment of 23°C and 50% RH, and then the adhesive strength was measured using a tensile tester under conditions of a 90° peel angle and a peel rate of 50 mm / min.

[0275] The above measurement results and evaluation results are summarized in Table 2 below.

[0276] [Table 2]

[0277]

[0278] The following can be seen from the above table.

[0279] The thermosetting adhesive sheets of Examples 1 to 4, which contain components (A), (B), and (C), have an arithmetic mean surface roughness (Ra) of the adhesive layer of 200 nm or less, a dielectric loss tangent of the cured layer at 23°C at 10 to 40 GHz of 0.005 or less, and a gel fraction of the cured layer of 40% or more, and exhibit excellent bending resistance and high adhesive strength.

[0280] On the other hand, the thermosetting adhesive sheet of Comparative Example 1 exhibited poor film-forming properties, making it impossible to measure various physical properties of the cured layer, such as the dielectric constant, dielectric loss tangent, and tensile modulus. The adhesive layer of the thermosetting adhesive sheet of Comparative Example 2 was insufficiently cured, exhibiting a low rate of increase in the gel fraction of the adhesive layer before and after curing, resulting in poor bending resistance. The cured layer of the thermosetting adhesive sheet of Comparative Example 3 exhibited a low tensile modulus, resulting in fracture during the bend test, resulting in poor bending resistance. Furthermore, the thermosetting adhesive sheet of Comparative Example 4 exhibited poor dielectric properties at 10 to 40 GHz.

[0281] Explanation of symbols

[0282] 1 Adhesive layer

[0283] 2a, 2b peeling sheet

[0284] 3 Conductive layer

[0285] 4 Insulating resin layer

[0286] 5 Cured material layer

[0287] 10 Thermosetting adhesive sheet

[0288] 20 Layers

[0289] 30 laminates

Claims

1. A thermosetting adhesive sheet having an adhesive layer, characterized in that: The adhesive layer is a layer containing the following components (A), (B), and (C). (A) Component: Binder resin (B) Component: Thermosetting component (C) Ingredient: Filler The arithmetic average surface roughness (Ra) of the adhesive layer surface is less than 200 nm, The dielectric loss tangent of the cured layer obtained by heating the adhesive layer at 170°C for 2 hours at 23°C and a frequency of 10 to 40 GHz is 0.005 or less, and The gel fraction of the cured product layer obtained by heat-treating the adhesive layer at 170° C. for 2 hours is 40% or more.

2. The thermosetting adhesive sheet according to claim 1, wherein When the gel fraction of the adhesive layer before curing is set to α (%) and the gel fraction of the cured layer obtained by curing the adhesive layer is set to β (%), the increase rate (%) of the gel fraction expressed by the formula: [(β-α) / α]×100 is greater than 60%.

3. The thermosetting adhesive sheet according to claim 1 or 2, wherein: The tensile elastic modulus of a cured layer obtained by heat-treating the adhesive layer at 170° C. for 2 hours at 25° C. is 0.5 GPa or more.

4. The thermosetting adhesive sheet according to claim 1 or 2, wherein When the thickness of the adhesive layer is X (μm) and the average particle size of the component (C) is Y (μm), the following equation is satisfied: Y / X<1.

5. The thermosetting adhesive sheet according to claim 1 or 2, wherein The component (C) is an inorganic filler that has not been surface treated.

6. The thermosetting adhesive sheet according to claim 1 or 2, wherein: The component (C) is a spherical filler.

7. The thermosetting adhesive sheet according to claim 1 or 2, wherein: The adhesive layer further contains a thermal polymerization initiator as the component (D).

8. The thermosetting adhesive sheet according to claim 1 or 2, which is used to form an insulating layer of a device.

9. A laminate comprising a conductive layer and an insulating layer formed on the conductive layer, wherein: The insulating layer is a layer formed by curing the adhesive layer of the thermosetting adhesive sheet according to claim 1 or 2.

10. A method for producing the laminate according to claim 9, comprising: Step (I), obtaining a laminate by laminating the thermosetting adhesive sheet according to claim 1 or 2 on a conductive layer, and In step (II), the laminate is heated to a predetermined temperature to cure the adhesive layer of the thermosetting adhesive sheet.

11. The method for producing a laminate according to claim 10, wherein: After the step (I) and before the step (II), there is a step (I-1) of forming an insulating resin layer on the thermosetting adhesive sheet according to claim 1 or 2.

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