Adhesive composition, and adhesive sheet, metal-clad laminate and printed circuit board containing same

Abstract

Provided are an adhesive composition and an adhesive sheet which have excellent dielectric characteristics, a low coefficient of linear expansion, and excellent adhesiveness. Also provided are: a metal-clad laminate which uses this improved adhesive sheet and which is useful for manufacturing electronic circuit boards for high-speed communication; and a printed circuit board manufactured using the metal-clad laminate.　Provided are the adhesive composition comprising: a resin (Y) having a carboxyl group or anhydride thereof; and an inorganic nanofiber (X), Also provided are the adhesive sheet, the metal-clad laminate, and the printed circuit board containing the same.

Description

Adhesive composition, and adhesive sheet, metal-clad laminate, and printed wiring board containing the same

[0001] The present invention relates to an adhesive composition having excellent dielectric properties and achieving both adhesion and a low coefficient of linear expansion, an adhesive sheet produced using the adhesive composition, a metal-clad laminate produced using the adhesive sheet, and a printed wiring board produced using the metal-clad laminate, which are particularly suitable for electronic circuit boards for high-speed communication.

[0002] In recent years, there has been active development of materials for high-speed communications such as 5G, and to improve signal transmission speeds, there is a demand for resin materials with low dielectric constants and dielectric loss tangents in the high-frequency band of 10 GHz or higher. Similar needs exist for materials that make up electronic circuit boards, and this is particularly important for resin materials that are used in close proximity to conductive metal layers.

[0003] As resin materials for forming circuit boards compatible with high frequencies, fluororesins (Patent Document 1), cyclic olefins (Patent Document 2), liquid crystal polymers (Patent Document 3), syndiotactic polystyrene (Patent Document 4), etc. have been reported. However, although these resin materials have low dielectric constants and dielectric dissipation factors, they have poor adhesion to metals, and there is a problem in that adhesion to metal layers cannot be ensured unless special surface treatments such as discharge treatment or chemical treatment are performed.

[0004] Furthermore, resin materials generally have a higher thermal expansion coefficient than metal layers, posing various problems during the circuit formation process. In the process of manufacturing wiring boards by forming circuits from metal-clad laminates with resin material as the substrate layer, the laminates are exposed to environments with large temperature changes. In environments with large temperature changes, differences in the thermal expansion coefficients between the substrate layer and the metal layer can lead to problems such as delamination of the metal layer or cracks in the substrate layer. Furthermore, differences in the thermal expansion coefficients between the materials constituting the circuit board can also cause similar problems in the through-hole plating layers formed to conduct electricity between the front and back wiring. Furthermore, in mounting boards with electronic components such as IC chips mounted on wiring boards, differences in the thermal expansion coefficients between the electronic components and the resin substrate can lead to cracks at the joints and on the surface of the board, reducing the reliability of electrical connections. Therefore, reducing the difference in the thermal expansion coefficients between the materials constituting the laminate can be an effective measure to prevent delamination, misalignment, cracks, and other problems caused by temperature changes and ensure electrical connection reliability. Furthermore, since the linear expansion coefficient of resin materials is often several times higher than that of metal materials, reducing the linear expansion coefficient of the resin material in laminates with metal layers can also be an effective measure.

[0005] As a measure to reduce the linear expansion coefficient, it is known to incorporate an inorganic filler into the composition of the resin material that constitutes the substrate, which is said to bring the linear expansion coefficient of the substrate closer to that of metal or IC chips and prevent the occurrence of cracks. For example, in Patent Documents 5 to 7, spherical silica is incorporated at a high concentration into the resin material that constitutes the substrate, thereby reducing the linear expansion coefficient while maintaining low relative permittivity and dielectric loss tangent in the high frequency range.

[0006] However, while the incorporation of inorganic fillers such as silica has the effect of reducing the linear expansion coefficient, a drawback is that the resin material becomes brittle at high incorporation amounts. In the process of forming circuits from metal-clad laminates into wiring boards, brittle resin materials are prone to cracking during external processing such as cutting and drilling, which is undesirable. Furthermore, a lower resin content in the resin material also reduces adhesion. Therefore, it is difficult to simultaneously ensure adhesion and suppress embrittlement while reducing the linear expansion coefficient by adding inorganic fillers such as silica. While there are many known fillers other than silica, the fillers that can be used are limited due to the requirement that they have low conductivity when added to insulating layers and do not impair dielectric properties because they are used in high-frequency materials.

[0007] WO2019 / 008876 JP 2022-003669 JP 2006-135179 JP 2015-002334 JP 2021-070592 JP 2011-132310 JP 2021-070727

[0008] As described above, the resin substrate of Patent Document 1 has poor adhesion to metal layers and a high thermal expansion coefficient, so when used as a circuit board, it faces various problems, such as peeling, misalignment, and cracking of wiring during the circuit formation process and electronic component mounting process. Similar problems also exist in processed circuit boards and mounted boards. Furthermore, Patent Documents 2, 3, and 4 have problems with adhesion despite an improved thermal expansion coefficient. Furthermore, Patent Documents 5, 6, and 7 have problems with difficult contour processing and reduced adhesion despite an improved linear expansion coefficient.

[0009] As a result of extensive research aimed at solving the above problems, the present inventors have discovered that by incorporating inorganic nanofibers into an adhesive composition, it is possible to achieve excellent dielectric properties, a low linear expansion coefficient, and adhesion, and have completed this invention. Specifically, the present invention provides an adhesive composition that has excellent dielectric properties, a low linear expansion coefficient, and excellent adhesion. The present invention also provides an adhesive sheet containing the adhesive composition. Furthermore, the present invention provides a metal-clad laminate that uses this improved adhesive sheet and is useful for producing electronic circuit boards for high-speed communication, and a printed wiring board manufactured using the metal-clad laminate.

[0010] The present invention is as follows. [1] An adhesive composition comprising a resin (Y) having a carboxyl group or an anhydride group thereof and inorganic nanofibers (X). [2] The adhesive composition according to [1], wherein the resin (Y) having a carboxyl group or an anhydride thereof comprises an acid-modified styrene-based elastomer (a) and an acid-modified polyolefin (b). [3] The adhesive composition according to [1] or [2], wherein the resin (Y) comprises an epoxy resin (c) and a carbodiimide (d). [4] The adhesive composition according to any one of [1] to [3], wherein the inorganic nanofibers (X) have an average primary fiber diameter of 200 nm or less. [5] The adhesive composition according to any one of [1] to [4], wherein the inorganic nanofibers (X) have an aspect ratio of 100 or more. [6] The adhesive composition according to any one of [1] to [5], wherein the inorganic nanofibers (X) are made of alumina. [7] The adhesive composition according to any one of [1] to [6], wherein the dielectric loss tangent at 10 GHz is 0.004 or less. [8] An adhesive sheet containing the adhesive composition according to any one of [1] to [7]. [9] A metal-clad laminate having a metal layer (iii) laminated on at least one surface of an insulating resin layer (i) via the adhesive sheet according to [8].

[10] The metal-clad laminate according to [9], wherein the insulating resin layer (i) contains any one of a fluorine-based resin, a cyclic olefin, a liquid crystal polymer, and a syndiotactic polystyrene.

[11] A printed wiring board containing the metal-clad laminate according to [9] or

[10] as a component.

[12] The printed wiring board according to

[11] , wherein a part or all of the metal layer (iii) forms a conductor circuit.

[13] The adhesive composition according to any one of [1] to [7], wherein the acid-modified styrene-based elastomer (a) is a copolymer mainly composed of a block and random structure of a conjugated diene compound and an aromatic vinyl compound, or a hydrogenated copolymer of a conjugated diene compound and an aromatic vinyl compound modified with an unsaturated carboxylic acid.

[14] The adhesive composition according to any one of [1] to [7], wherein the acid-modified polyolefin (b) is a polyolefin resin grafted with at least one of an α,β-unsaturated carboxylic acid and an acid anhydride thereof.

[15] The adhesive composition according to any one of [1] to [7], wherein the epoxy resin (c) comprises at least one selected from the group consisting of biphenyl-type epoxy resins, naphthalene-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, novolac-type epoxy resins, alicyclic epoxy resins, dicyclopentadiene-type epoxy resins, tetraglycidyldiaminodiphenylmethane, triglycidyl para-aminophenol, tetraglycidyl bisaminomethylcyclohexanone, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and epoxy-modified polybutadiene.

[0011] The adhesive composition of the present invention and the adhesive sheet containing the adhesive composition have excellent adhesive properties (peel strength) and have reduced dielectric constants, dielectric loss tangents, and linear expansion coefficients. As a result, metal-clad laminates produced using the adhesive composition and printed wiring boards produced using the metal-clad laminates can have reduced transmission loss and be prevented from warping, peeling, misalignment, and cracking due to stress caused by temperature changes.

[0012] [Adhesive Composition] The adhesive composition contains a resin (Y) containing a carboxyl group or its anhydride group and inorganic nanofibers (X). The adhesive composition is preferably prepared by blending inorganic nanofibers (X) into an adhesive comprising an acid-modified styrene-based elastomer (a), an acid-modified polyolefin (b), an epoxy resin (c), and a carbodiimide (d). The inclusion of components (a) to (d) enables excellent adhesion to low-polarity resin substrates such as liquid crystal polymers (LCPs) and syndiotactic polystyrene (SPS) and metal substrates. Electronic circuit boards manufactured using these components also exhibit excellent transmission characteristics and adhesive properties. Furthermore, the inclusion of inorganic nanofibers (X) can suppress peeling, slippage, cracking, and other problems caused by differences in the linear expansion coefficient during laminate formation.

[0013] <Resin (Y) Having a Carboxyl Group or an Anhydride Group Thereof> The resin (Y) having a carboxyl group or an anhydride group thereof is not particularly limited as long as it is a resin having a carboxyl group or an anhydride group thereof, but it preferably contains an acid-modified styrene-based elastomer (a) and / or an acid-modified polyolefin (b), and it is particularly preferable that it contains both the acid-modified styrene-based elastomer (a) and the acid-modified polyolefin (b).

[0014] <Acid-Modified Styrenic Elastomer (a)> The acid-modified styrene-based elastomer (a) (hereinafter also referred to as component (a)) is one of the main components of the adhesive composition. In addition to improving adhesiveness and flexibility of the cured product, it also reduces the dielectric constant and dielectric dissipation factor, thereby reducing transmission loss when used in an electronic circuit board (hereinafter, this effect is referred to as electrical properties). From the viewpoints of electrical properties, curability, and heat resistance, this acid-modified styrene-based elastomer (a) is preferably a copolymer mainly composed of a block or random structure of a conjugated diene compound and an aromatic vinyl compound, or a hydrogenated product of such a copolymer modified with an unsaturated carboxylic acid. Examples of aromatic vinyl compounds include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylstyrene, N,N-diethyl-p-aminoethylstyrene, vinyltoluene, and p-tert-butylstyrene. Examples of the conjugated diene compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene.

[0015] The acid-modified styrene-based elastomer (a) can be produced, for example, by copolymerizing an unsaturated carboxylic acid during polymerization of a styrene-based elastomer. Alternatively, the acid-modified styrene-based elastomer (a) can be produced by heating and kneading a styrene-based elastomer and an unsaturated carboxylic acid in the presence of an organic peroxide. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, maleic anhydride, itaconic anhydride, and fumaric anhydride. The amount of modification with the unsaturated carboxylic acid in the acid-modified styrene-based elastomer (a) is preferably 0.1 to 10% by mass.

[0016] The acid value of the acid-modified styrene-based elastomer (a) is preferably 0.1 to 25 mgKOH / g, more preferably 0.5 to 23 mgKOH / g. From the viewpoint of sufficiently promoting the curing reaction of the adhesive composition, the acid value of the acid-modified styrene-based elastomer (a) is preferably 0.1 mgKOH / g or more, which tends to result in excellent adhesion and heat resistance and enable control of the amount of runoff. On the other hand, from the viewpoint of maintaining electrical properties, the acid value is preferably 25 mgKOH / g or less, which results in an adhesive sheet with excellent low dielectric properties. Furthermore, the adhesive sheet is easily peeled from the release substrate, is less likely to shrink after peeling, and is easy to handle during operation, resulting in good handleability.

[0017] The weight-average molecular weight of the acid-modified styrene-based elastomer (a) is preferably 10,000 to 500,000, more preferably 30,000 to 300,000, and even more preferably 50,000 to 200,000. When the weight-average molecular weight of the acid-modified styrene-based elastomer (a) is within the above range, it tends to exhibit excellent adhesive properties and electrical properties. In this specification, the weight-average molecular weight is the value obtained by converting the molecular weight measured by gel permeation chromatography (hereinafter also referred to as "GPC") into polystyrene equivalent.

[0018] Specific examples of the acid-modified styrene-based elastomer (a) include styrene-butadiene block copolymers, styrene-ethylene-propylene block copolymers, styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-ethylene-butylene-styrene block copolymers, and styrene-ethylene-propylene-styrene block copolymers modified with unsaturated carboxylic acids. These acid-modified styrene-based elastomers (a) may be used alone or in combination of two or more. Among these copolymers, styrene-ethylene-butylene-styrene block copolymers and styrene-ethylene-propylene-styrene block copolymers are preferred from the viewpoints of adhesiveness and electrical properties. Furthermore, the mass ratio of styrene / ethylene-butylene in the styrene-ethylene-butylene-styrene block copolymer and the mass ratio of styrene / ethylene-propylene in the styrene-ethylene-propylene-styrene block copolymer are preferably 10 / 90 to 50 / 50, and more preferably 20 / 80 to 40 / 60. When the mass ratios are within these ranges, an adhesive composition with excellent adhesive properties can be obtained.

[0019] The content of the acid-modified styrene-based elastomer (a) is preferably 20 to 70 parts by mass relative to 100 parts by mass of the total resin solids content of the adhesive composition. The content of the acid-modified styrene-based elastomer (a) is more preferably 30 to 70 parts by mass, and even more preferably 50 to 70 parts by mass. When the content of the (a) component is equal to or greater than the lower limit, sufficient adhesiveness tends to be obtained, while when the content of the (a) component is equal to or less than the upper limit, handleability tends to be good. By keeping the content of the (a) component within the above range, excellent dielectric properties, adhesiveness, and handleability can be achieved simultaneously.

[0020] <Acid-Modified Polyolefin (b)> The acid-modified polyolefin (b) (hereinafter also referred to simply as component (b)) is not limited, but is preferably one obtained by grafting at least one of an α,β-unsaturated carboxylic acid and its acid anhydride onto a polyolefin resin. Polyolefin resin refers to polymers primarily composed of a hydrocarbon skeleton, such as polymers of monomers exemplified by ethylene, propylene, butene, butadiene, isoprene, etc., copolymers with other monomers, and hydrogenated or halides of these polymers and copolymers. In other words, the acid-modified polyolefin (b) is preferably one obtained by grafting at least one of an α,β-unsaturated carboxylic acid and its acid anhydride onto at least one of polyethylene, polypropylene, and propylene-α-olefin copolymer.

[0021] Propylene-α-olefin copolymers are copolymers of propylene as the main component with an α-olefin. As the α-olefin, for example, one or more of ethylene, 1-butene, 1-heptene, 1-octene, 4-methyl-1-pentene, vinyl acetate, etc. can be used. Among these α-olefins, ethylene and 1-butene are preferred. The ratio of the propylene component to the α-olefin component in the propylene-α-olefin copolymer is not limited, but the propylene component is preferably 50 mol% or more, and more preferably 70 mol% or more.

[0022] Examples of the α,β-unsaturated carboxylic acid and at least one of its acid anhydrides include maleic acid, itaconic acid, citraconic acid, and their acid anhydrides. Among these, acid anhydrides are preferred, and maleic anhydride is more preferred. That is, specific examples of the acid-modified polyolefin (b) include maleic anhydride-modified polypropylene, maleic anhydride-modified propylene-ethylene copolymer, maleic anhydride-modified propylene-butene copolymer, maleic anhydride-modified propylene-ethylene-butene copolymer, etc., and these maleic anhydride-modified polyolefins can be used alone or in combination of two or more. It is more preferable to use a maleic anhydride-modified propylene-butene copolymer as the acid-modified polyolefin (b).

[0023] From the viewpoint of solder heat resistance and adhesion to resin substrates and metal substrates, the acid value of the acid-modified polyolefin (b) is preferably 5 mgKOH / g or more, more preferably 6 mgKOH / g or more, even more preferably 7 mgKOH / g or more, and particularly preferably 10 mgKOH / g or more. At or above the lower limit, the reactivity with the carbodiimide (d) tends to be improved, the adhesive strength tends to be excellent, and the crosslinking density tends to be high, resulting in excellent solder heat resistance. The upper limit of the acid value of the acid-modified polyolefin (b) is preferably 30 mgKOH / g or less, more preferably 28 mgKOH / g or less, and even more preferably 25 mgKOH / g or less. At or below the upper limit, the adhesive properties tend to be excellent. Furthermore, the viscosity and stability of the solution tend to be excellent, and the pot life tends to be long. Therefore, production efficiency can be further improved, which is preferable. That is, the acid value of the acid-modified polyolefin (b) is preferably 5 to 30 mgKOH / g, more preferably 6 to 28 mgKOH / g, still more preferably 7 to 25 mgKOH / g, and particularly preferably 10 to 25 mgKOH / g.

[0024] The number average molecular weight (Mn) of the acid-modified polyolefin (b) is preferably in the range of 10,000 to 50,000. The number average molecular weight (Mn) of the acid-modified polyolefin (b) is more preferably in the range of 15,000 to 45,000, even more preferably in the range of 20,000 to 40,000, and particularly preferably in the range of 22,000 to 38,000. If the Mn is equal to or greater than the lower limit, the cohesive strength tends to be strong and the adhesiveness tends to be excellent. On the other hand, if the Mn is equal to or less than the upper limit, the fluidity tends to be high and the operability during adhesion tends to be good.

[0025] The acid-modified polyolefin (b) is preferably crystalline, which means that it shows a clear melting peak during the temperature rise from −100° C. to 250° C. at a rate of 20° C. / min using a differential scanning calorimeter (DSC).

[0026] The melting point (Tm) of the acid-modified polyolefin (b) is preferably in the range of 50°C to 120°C. The melting point (Tm) of the acid-modified polyolefin (b) is more preferably in the range of 60°C to 100°C, and most preferably in the range of 70°C to 90°C. At or above the lower limit, the cohesive force derived from crystals becomes strong, and adhesive properties and solder heat resistance tend to be excellent. On the other hand, at or below the upper limit, solution stability and fluidity tend to be high, and operability during bonding tends to be excellent.

[0027] The heat of fusion (ΔH) of the acid-modified polyolefin (b) is preferably in the range of 5 J / g to 60 J / g. The heat of fusion (ΔH) of the acid-modified polyolefin (b) is more preferably in the range of 10 J / g to 50 J / g, and most preferably in the range of 20 J / g to 40 J / g. At or above the lower limit, the cohesive force derived from the crystals becomes stronger, and the adhesiveness and solder heat resistance tend to be excellent. On the other hand, at or below the upper limit, the solution stability and fluidity tend to be high, and the operability during adhesion tends to be excellent.

[0028] The method for producing the acid-modified polyolefin (b) is not particularly limited, and examples thereof include a radical graft reaction (i.e., a reaction in which radical species are generated on a polymer that becomes a main chain, and an unsaturated carboxylic acid and an acid anhydride are graft-polymerized using the radical species as a polymerization initiation point).

[0029] The radical generator is not particularly limited, but is preferably an organic peroxide. Examples of the organic peroxide include, but are not particularly limited to, peroxides such as di-tert-butyl peroxyphthalate, tert-butyl hydroperoxide, dicumyl peroxide, benzoyl peroxide, tert-butyl peroxybenzoate, tert-butylperoxy-2-ethylhexanoate, tert-butyl peroxypivalate, methyl ethyl ketone peroxide, di-tert-butyl peroxide, and lauroyl peroxide; and azonitriles such as azobisisobutyronitrile and azobisisopropionitrile.

[0030] The content of the acid-modified polyolefin (b) is not particularly limited, but is preferably 10 to 70 parts by mass relative to 100 parts by mass of the total resin solids content of the adhesive. The content of the acid-modified polyolefin (b) is more preferably 10 to 50 parts by mass, and even more preferably 10 to 30 parts by mass. Within this range, the adhesive sheet tends to have excellent handleability.

[0031] <Epoxy Resin (c)> The epoxy resin (c) (hereinafter also referred to simply as component (c)) is not particularly limited as long as it has a glycidyl group in the molecule, but preferably has two or more glycidyl groups in the molecule. Specific examples of the epoxy resin (c) include, but are not limited to, at least one selected from the group consisting of biphenyl-type epoxy resins, naphthalene-type epoxy resins, bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, novolac-type epoxy resins, alicyclic epoxy resins, dicyclopentadiene-type epoxy resins, tetraglycidyldiaminodiphenylmethane, triglycidyl para-aminophenol, tetraglycidyl bisaminomethylcyclohexanone, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and epoxy-modified polybutadiene. Among these, biphenyl-type epoxy resins, novolac-type epoxy resins, dicyclopentadiene-type epoxy resins, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and epoxy-modified polybutadiene are preferred. Among these, novolac epoxy resins, dicyclopentadiene epoxy resins, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and epoxy-modified polybutadiene are more preferred, and novolac epoxy resins and N,N,N',N'-tetraglycidyl-m-xylylenediamine are particularly preferred.

[0032] <Carbodiimide (d)> The carbodiimide (d) is not particularly limited as long as it has a carbodiimide group in the molecule. The carbodiimide (d) is preferably a polycarbodiimide having two or more carbodiimide groups in the molecule. By using a polycarbodiimide, the carboxyl group of the acid-modified polyolefin (b) reacts with the carbodiimide group, thereby enhancing the interaction between the adhesive composition and the substrate, and improving the adhesiveness and solder heat resistance. The polycarbodiimide may be any of an aromatic carbodiimide compound, an alicyclic carbodiimide compound, or an aliphatic carbodiimide compound, which may be used alone or in combination of two or more. Examples of aromatic carbodiimide compounds include poly-m-phenylenecarbodiimide, poly-p-phenylenecarbodiimide, polytolylenecarbodiimide, poly(diisopropylphenylenecarbodiimide), poly(methyldiisopropylphenylenecarbodiimide), poly(4,4'-diphenylmethanecarbodiimide), etc. Examples of alicyclic carbodiimide compounds include poly-m-cyclohexylcarbodiimide, poly-p-cyclohexylcarbodiimide, poly(4,4'-dicyclohexylmethanecarbodiimide), poly(3,3'-dicyclohexylmethanecarbodiimide), etc. Examples of aliphatic carbodiimide compounds include either linear or branched aliphatic carbodiimide compounds. Linear aliphatic carbodiimide compounds are preferred, specifically polymethylenecarbodiimide. , polyethylene carbodiimide, polypropylene carbodiimide, polybutylene carbodiimide, polypentamethylene carbodiimide, polyhexamethylene carbodiimide, etc. Among these, aromatic carbodiimide compounds or alicyclic carbodiimide compounds are preferred. Examples of commercially available polycarbodiimides include Carbodilite (registered trademark) V-02B, Elastostab H01, V-03, V-09, and V-09GB, both of which are manufactured by Nisshinbo Chemical Inc.

[0033] The total content of the epoxy resin (c) and the carbodiimide (d) is preferably 1 to 12 parts by mass relative to 100 parts by mass of the total resin solids content of the adhesive composition. The total content of the epoxy resin (c) and the carbodiimide (d) is more preferably 2 to 8 parts by mass. At or above the lower limit, the curing reaction tends to proceed sufficiently, and the adhesive composition tends to have excellent adhesion. At or below the upper limit, the dielectric constant and dielectric loss tangent tend to be low, and the dielectric properties tend to be excellent.

[0034] The ratio of the epoxy resin (c) to the carbodiimide (d) is, on a mass basis, (c) / (d) = 5 / 1 to 1 / 1, preferably (c) / (d) = 4 / 1 to 2 / 1. When the ratio of the amount of the (c) component to the amount of the (d) component is within the above range, the reactivity tends to be excellent and uncured portions tend not to occur, and the dielectric constant and dielectric loss tangent tend to be low, resulting in excellent dielectric properties.

[0035] <Inorganic nanofibers (X)> Examples of components constituting the inorganic nanofibers (X) include montmorillonite (MMT), mica, wollastonite, carbon, silicon nitride, silicon carbide, alumina, nickel, and glass. From the viewpoints of electrical properties, thermal expansion coefficient, and heat resistance, as well as easy availability, wollastonite, alumina, and glass are preferred, and alumina is more preferred. Note that the inorganic nanofibers (X) may or may not be surface-modified.

[0036] The average primary fiber diameter of the inorganic nanofibers (X) is preferably 200 nm or less, more preferably 50 nm or less, even more preferably 10 nm or less, and particularly preferably 5 nm or less, but is not limited thereto. The average primary fiber diameter of the inorganic nanofibers (X) is preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 3 nm or more, but is not limited thereto. That is, the average primary fiber diameter of the inorganic nanofibers (X) is preferably 1 to 200 nm, more preferably 2 to 50 nm, even more preferably 3 to 10 nm, and particularly preferably 3 to 5 nm.

[0037] The average primary fiber length of the inorganic nanofibers (X) is preferably 30,000 nm or less, more preferably 15,000 nm or less, even more preferably 8,000 nm or less, and particularly preferably 4,000 nm or less, but is not limited thereto. The average primary fiber length of the inorganic nanofibers (X) is preferably 100 nm or more, more preferably 300 nm or more, even more preferably 1,000 nm or more, and particularly preferably 2,500 nm or more, but is not limited thereto. That is, the average primary fiber length of the inorganic nanofibers (X) is preferably 100 to 30,000 nm, more preferably 300 to 15,000 nm, even more preferably 1,000 to 8,000 nm, and particularly preferably 2,500 to 4,000 nm.

[0038] The inorganic nanofibers (X) preferably have a high aspect ratio, and the value (average primary fiber length / average primary fiber diameter) is preferably 100 or more, more preferably 200 or more, even more preferably 300 or more, and particularly preferably 500 or more, but is not limited thereto. When the aspect ratio of the inorganic nanofibers (X) is 100 or more, the effect of reducing the linear expansion coefficient is sufficiently exhibited. To achieve the objects of the present invention, the higher the aspect ratio of the inorganic nanofibers (X), the better, but the upper limit is generally about 1000 due to industrial availability and other factors. That is, the aspect ratio of the inorganic nanofibers (X) is preferably 100 to 1000, more preferably 200 to 1000 nm, even more preferably 300 to 1000 nm, and particularly preferably 500 to 1000 nm.

[0039] The inorganic nanofibers (X) are preferably dispersed in an organic solvent from the viewpoints of the dispersibility and stability of the inorganic nanofibers (X) themselves, or the processability and workability during adhesive production. Examples of the organic solvent that can be used include conventionally known organic solvents such as methyl isobutyl ketone (MIBK), methyl ethyl ketone, dimethylformamide, dimethyl sulfoxide, diethylene glycol dimethyl ether, and tetrahydrofuran.

[0040] The content of inorganic nanofibers (X) is preferably 1 to 7 parts by mass relative to 100 parts by mass of the total resin solids content of the adhesive. The content of inorganic nanofibers (X) is more preferably 2 to 6 parts by mass, and even more preferably 3 to 5 parts by mass. When the content is equal to or greater than the lower limit of the above range, the effect of reducing the linear expansion coefficient tends to be excellent. Furthermore, when the content is equal to or less than the upper limit of the above range, the electrical properties tend to be excellent.

[0041] The adhesive composition may further contain other components as needed, provided that the effects of the present invention are not impaired. Specific examples of such components include conventionally known components such as flame retardants, tackifiers, fillers, silane coupling agents, and other resin components. The addition of other resin components can particularly improve heat resistance. Examples of other resin components include maleimide-based, benzoxazine-based, polyphenylene ether-based, and oligophenylene ether-based resins. These may be used alone or in any combination of two or more.

[0042] The adhesive composition may further contain an organic solvent. The organic solvent is not particularly limited as long as it dissolves the acid-modified styrene-based elastomer (a), the acid-modified polyolefin (b), the epoxy resin (c), and the carbodiimide (d). Specific examples of the organic solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane, heptane, octane, and decane; alicyclic hydrocarbons such as cyclohexane, cyclohexene, methylcyclohexane, and ethylcyclohexane; halogenated hydrocarbons such as trichloroethylene, dichloroethylene, chlorobenzene, and chloroform; alcohol-based solvents such as methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, and propanediol; phenol-based solvents such as phenol; acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclohexanone, isophorone, and the like. Ketone solvents such as acetophenone, cellosolves such as methyl cellosolve and ethyl cellosolve, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and butyl formate, glycol ether solvents such as ethylene glycol mono-n-butyl ether, ethylene glycol mono-iso-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-iso-butyl ether, triethylene glycol mono-n-butyl ether, and tetraethylene glycol mono-n-butyl ether can be used, and one or more of these can be used in combination. Among these, it is preferable to use at least one solvent selected from the group consisting of aromatic hydrocarbons, alicyclic hydrocarbons, and ketone solvents, particularly from the viewpoint of working environment and drying properties. Methylcyclohexane is preferred as the alicyclic hydrocarbon, toluene is preferred as the aromatic hydrocarbon, and methyl ethyl ketone is preferred as the ketone solvent.

[0043] The amount of organic solvent used is preferably in the range of 100 to 700 parts by mass, more preferably in the range of 200 to 600 parts by mass, and most preferably in the range of 300 to 500 parts by mass, per 100 parts by mass of the total of the resin component and the inorganic nanofibers (X). Below the upper limit, the viscosity of the varnish tends to be too high, making it less likely to gel and providing excellent coatability. Above the lower limit, the viscosity of the varnish tends to be too low, making it more likely to provide excellent coatability to release substrates.

[0044] The adhesive composition preferably has a dielectric loss tangent (Df) at 10 GHz of 0.0050 or less, more preferably 0.0045 or less, even more preferably 0.004 or less, and particularly preferably 0.0030 or less. The dielectric loss tangent of the adhesive composition may be measured by a cavity resonator perturbation method at a temperature of 23°C and a frequency of 10 GHz.

[0045] [Adhesive Sheet] Embodiments of the present invention also include adhesive sheets containing the adhesive composition described above. The adhesive sheet is produced by applying the adhesive composition to a release substrate and drying it. After drying, the adhesive sheet is transferred to an adherend such as an insulating sheet or metal foil for use. The curing stage (degree of crosslinking) after application and drying is usually a semi-cured state, but the object of the present invention can be achieved even in an uncured or fully cured state by appropriately setting the subsequent processing conditions. The adhesive sheet refers to an adhesive composition processed into a sheet, and as described above, the curing stage includes any of an uncured state, a semi-cured state, and a fully cured state. Hereinafter, the adhesive sheet obtained by processing the adhesive composition into a sheet may be referred to as adhesive layer (ii).

[0046] The method for applying and drying the adhesive composition on a release substrate is not particularly limited, but includes conventionally known methods such as a comma coater or a reverse roll coater. The thickness of the adhesive layer (ii) after drying can be adjusted as needed, but is preferably in the range of 5 to 200 μm. If the thickness of the adhesive layer (ii) is less than 5 μm, the adhesive strength may be insufficient. If the thickness of the adhesive layer (ii) is 200 μm or more, drying may be insufficient, resulting in a large amount of residual solvent in the adhesive, which can cause problems such as blisters during printing, such as pressing, during the production of printed wiring boards. The residual solvent content after drying is usually preferably 1% by mass or less. The drying conditions are not particularly limited, but are appropriately set so that the residual solvent content after drying is 1% by mass or less. Drying conditions are, for example, 100°C to 130°C and 3 to 10 minutes.

[0047] A typical method for producing an adhesive sheet will be described. The most common method for production is preferably a method in which an adhesive composition is applied to a release substrate, dried, and temporarily cured. If necessary, a release substrate can be further laminated thereon. Specific configurations include, for example, a laminated structure of a release substrate and an adhesive layer (ii), and a laminated structure of a release substrate, an adhesive layer (ii), and another release substrate. Laminating a release substrate functions as a protective layer for the adhesive layer (ii). Furthermore, the release substrate can be released from the adhesive layer (ii) (adhesive sheet), and the adhesive layer (ii) can be transferred to another substrate.

[0048] <Release Substrate> The release substrate is not particularly limited, but examples include those in which a coating layer of a filler such as clay, polyethylene, or polypropylene is provided on both sides of paper such as fine paper, kraft paper, roll paper, or glassine paper, and a silicone-based, fluorine-based, or alkyd-based release agent is further applied to each of these coating layers. Other examples include various olefin films such as polyethylene, polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer alone, and films such as polyethylene terephthalate to which the release agent is applied. Due to factors such as the release force between the release substrate and the adhesive layer (ii) and the adverse effect of silicone on electrical properties, it is preferable to use a polypropylene-sealed film on both sides of fine paper and then apply an alkyd-based release agent thereon, or an alkyd-based release agent on polyethylene terephthalate.

[0049] In the present invention, if necessary, the adhesive layer (ii) can be provided directly or by a transfer method on a rolled copper foil, which is a printed wiring board constituent material, or a film-like or sheet-like resin substrate (substrate) containing a component such as a polyester resin, a polyamide resin, a polyimide resin, a polyamideimide resin, a liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, or a polyolefin resin.

[0050] [Metal-clad laminate] An embodiment of the present invention also includes a metal-clad laminate in which a metal layer (iii) is laminated on at least one surface of an insulating resin layer (i) via the above-mentioned adhesive sheet [i.e., adhesive layer (ii)].

[0051] <Metal layer (iii)> As the material for constituting the metal layer (iii), any conventionally known conductive material that can be used for circuit boards can be used. Examples of the material for the metal layer (iii) include various metals such as SUS, copper, aluminum, iron, steel, zinc, nickel, and their alloys, plated products, and metals treated with other metals such as zinc or chromium compounds. The metal layer (iii) is preferably a metal foil, more preferably a copper foil. Types of copper foil include electrolytic foil and rolled foil, and both copper foils can be used in the metal-clad laminate of the present invention.

[0052] Metal foil is usually provided in a roll form. The form of metal foil used when manufacturing a printed wiring board is not particularly limited. When a ribbon-shaped metal foil is used, its length is not particularly limited. Its width is also not particularly limited, but is preferably about 250 to 500 cm.

[0053] The surface roughness (Rz) of the metal layer (iii) surface in contact with the adhesive layer (ii) is preferably in the range of 0.1 μm or more and 7.0 μm or less, more preferably in the range of 0.3 μm or more and 5.0 μm or less, even more preferably 0.5 μm or more and 3.0 μm or less, and most preferably 0.8 μm or more and 1.5 μm or less. If the surface roughness (Rz) is less than 0.1 μm, adhesion may be insufficient, and if the surface roughness (Rz) is more than 7.0 μm, the transmission loss may be large when the metal-clad laminate is used as an electronic circuit board. By keeping the surface roughness (Rz) of the metal layer (iii) surface in contact with the adhesive layer (ii) within the above range, excellent adhesion and low transmission loss can be achieved, and the metal-clad laminate can be suitably used as an electronic circuit board.

[0054] The thickness of the metal layer (iii) is preferably 1 μm or more, preferably 3 μm or more, and more preferably 10 μm or more. The thickness of the metal layer (iii) is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less. That is, the thickness of the metal layer (iii) is preferably 1 to 50 μm, more preferably 3 to 30 μm, and even more preferably 10 to 25 μm. If the thickness of the metal layer (iii) is less than 1 μm, sufficient electrical performance of the electronic circuit may not be obtained. On the other hand, if the thickness of the metal layer (iii) exceeds 50 μm, the processing efficiency during the production of the electronic circuit may decrease.

[0055] <Insulating resin layer (i)> Examples of materials constituting the insulating resin layer (i) include polyester resins, polyamide resins, polyimide resins, polyamideimide resins, liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resins, cyclic olefins, and fluorine-based resins. Among these, the insulating resin layer (i) preferably contains any of fluorine-based resins, cyclic olefins, liquid crystal polymers, and syndiotactic polystyrene, and more preferably syndiotactic polystyrene. The resin form of the insulating resin layer (i) is preferably a film-like resin or a sheet-like resin. Furthermore, these films and sheets may be surface-treated.

[0056] In the present invention, the metal-clad laminate refers to a laminate in which the metal layer (iii) is laminated on at least one surface of the insulating resin layer (i) via the adhesive sheet [i.e., adhesive layer (ii)]. The metal-clad laminate can be produced by a known method. For example, after peeling the release substrate from the adhesive sheet, it is laminated on the insulating resin layer (i), and the other release substrate is peeled off and then laminated to the metal layer (iii). The resulting laminate consisting of the insulating resin layer (i) / adhesive layer (ii) / metal layer (iii) can be bonded and cured by pressing under vacuum, for example, at 180°C and 2 MPa for about 60 minutes. Alternatively, the laminate can be produced by directly applying a varnish of the adhesive composition to the insulating resin layer (i), temporarily curing the coating, and then laminating it to the metal layer (iii). Alternatively, the insulating resin layer (i) may be laminated on the metal layer (iii) after applying a varnish of the adhesive composition to the metal layer (iii) and temporarily curing the coating.

[0057] [Printed Wiring Board] Embodiments of the present invention also include printed wiring boards that include the above-mentioned metal-clad laminate as a component. A "printed wiring board" includes, as a component, a laminate formed from a metal layer (iii) that forms a conductor circuit and a resin substrate. A printed wiring board is manufactured, for example, by a conventionally known method such as a subtractive method using the metal-clad laminate. This generic term refers to so-called flexible circuit boards (FPCs), flat cables, circuit boards for tape automated bonding (TAB), etc., in which a conductor circuit formed by a metal layer (iii) is partially or entirely covered with a cover film, screen printing ink, etc., as necessary.

[0058] The printed wiring board can have any laminated structure that can be used as a printed wiring board. For example, it can be a printed wiring board consisting of four layers: a base film layer, a metal layer (iii), an adhesive layer (ii), and a cover film layer. Alternatively, it can be a printed wiring board consisting of five layers: a base film layer, an adhesive layer, a metal layer (iii), an adhesive layer (ii), and a cover film layer. Furthermore, if necessary, it can be a structure in which two or more of the above printed wiring boards are laminated. The adhesive composition used in the present invention can be suitably used for each adhesive layer of a printed wiring board.

[0059] This application claims the benefit of priority based on Japanese Patent Application No. 2023-170465, filed on September 29, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-170465 are incorporated herein by reference.

[0060] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. The coating direction during adhesive sheet preparation is defined as the MD direction, and the direction perpendicular to the MD direction is defined as the TD direction. A metal-clad laminate was produced in which a metal layer (iii) was laminated on one side of an insulating resin layer (i) via an adhesive sheet containing the adhesive composition described below.

[0061] [Method of producing adhesive sheet] The adhesive composition of each Example and Comparative Example was applied to a 100 μm thick Teflon (registered trademark) sheet so that the thickness after drying and curing would be 25 μm, and then dried at 130° C. for 5 minutes to produce a provisionally cured product. Hereinafter, this provisionally cured product may be referred to as an adhesive sheet (provisionally cured product) or just an adhesive sheet.

[0062] [Method for producing metal-clad laminate] The adhesive sheet (provisionally cured product) produced by the method described above was overlapped on the laminate side of a 12 μm thick non-roughened electrolytic copper foil (CF-T9D-SV-12, manufactured by Fukuda Metal Foil & Powder Co., Ltd.), and a syndiotactic polystyrene resin sheet was laminated on the other side of the adhesive sheet so that the sheet was in contact with the syndiotactic polystyrene resin sheet. The resulting mixture was pressed under vacuum at 180° C. for 1 hour to obtain a metal-clad laminate.

[0063] [Evaluation Method] <Method of Preparing Sample for Evaluating the Physical Properties of the Cured Adhesive Composition Layer> The adhesive sheet (preliminarily cured product) was cured by heat treatment at 180°C for 1 hour, and then peeled from the Teflon (registered trademark) sheet. The cured adhesive composition layer peeled from the Teflon (registered trademark) sheet was used as a sample for evaluating the physical properties of the cured adhesive composition layer. Hereinafter, the cured adhesive composition layer may be referred to as adhesive layer (ii).

[0064] <Elastic modulus (tensile test)> The adhesive layer (ii) was cut to prepare a strip-shaped test piece of 10 mm x 50 mm. The longitudinal direction of the strip-shaped test piece was set to the MD direction. Using a tension-compression tester (TG-2kN, manufactured by MinebeaMitsumi Inc.), the initial sample length was set to 35 mm, and a tensile test was performed under conditions of a temperature of 25°C, a relative humidity of 50% RH, and a tension speed of 50 mm / min. The elastic modulus was calculated from the obtained S-S curve using the following formula: ε Ｌ = (ΔL ０ / L ０ ) × 100 E = σ / ε Ｌ ε Ｌ : Tensile strain (%) ΔL ０ : Increase in gauge length (mm) L ０ : Gauge distance (mm) E: Tensile modulus of elasticity (MPa) σ: Tensile stress (MPa)

[0065] <Tensile storage modulus E'> The adhesive layer (ii) was cut into strips of 4 mm x 30 mm and used as measurement samples. The longitudinal direction of the strip-shaped test pieces was set to the MD direction. Using a dynamic viscoelasticity measuring device DVA-200 (IT Measurement Control Co., Ltd.), measurements were performed under conditions of a frequency of 10 Hz, a temperature rise rate of 4°C / min, and a temperature rise from -100°C to 300°C. From the obtained measurement data, the tensile storage moduli E' at 20°C, 80°C, and 120°C were extracted and listed in Table 1.

[0066] <Coefficient of linear expansion (CTE)> The adhesive layer (ii) was cut to prepare a strip-shaped test piece of 3 mm x 30 mm. The longitudinal direction of the strip-shaped test piece was set to the MD direction. Using a thermomechanical analyzer (TA7100, manufactured by Hitachi High-Tech Science), the load was set to 20 mN in tension mode, and the temperature was raised from room temperature to 200 ° C. at a rate of 1 ° C. / min to measure the elongation of the strip-shaped test piece. The reading range of the measurement results was 25 ° C. to 200 ° C. ｇｌ The temperature difference ΔT was calculated from the following formula: ｇｌ -25 [℃] Sample elongation ΔL = L ｇｌ -L ２５ [mm] Linear expansion coefficient CTE=ΔL / (ΔT・L ２５ ) [ppm / °C] T ｇｌ In the TMA curve measured from room temperature to 200°C, there is generally a point where the slope changes suddenly, and the temperature at this point of change is called T ｇｌ When the change in elongation of the rectangular specimen is gradual and it is difficult to determine the change point, the intersection of the slope in the early measurement period and the slope in the later measurement period is used as T. ｇｌ And so. ２５ L: Length of strip test piece at 25 ° C ｇｌ : T ｇｌ Length of the strip test piece

[0067] <Peel Strength> The metal layer side of the metal-clad laminate was reinforced with Kapton tape (Kapton (registered trademark) roll, thickness 0.075 mm, manufactured by DuPont-Toray Co., Ltd.), and a 5 mm wide cut was made in the sample to prepare a measurement sample. Using a tension-compression tester (TG-2kN, manufactured by MinebeaMitsumi Inc.), the sample was peeled at 90° at a tensile speed of 50 mm / min, and the peel strength of the interface between the insulating resin layer (i) and the adhesive layer (ii) was measured. This test indicates the adhesive strength at room temperature.

[0068] <Relative permittivity (Dk) and dielectric loss tangent (Df)> The adhesive layer (ii) was cut into strips of 80 mm x 3 mm to prepare test samples. The longitudinal direction of the strip-shaped test pieces was set to the MD direction. The relative permittivity (εc) and dielectric loss tangent (tanδ) were measured using a network analyzer (manufactured by Anritsu Corporation) by a cavity resonator perturbation method at a temperature of 23°C and a frequency of 10 GHz.

[0069] [Method for preparing adhesive composition] (Example 1) A varnish was prepared by blending 65 parts by mass of C5025, 11 parts by mass of CO-3, 1.3 parts by mass of polycarbodiimide V-09GB, a total of 3.9 parts by mass of jER152 and TETRAD-X as epoxy resin (c), 19 parts by mass of OPE-2St2200 (oligophenylene ether styrene modified product, manufactured by Mitsubishi Gas Chemical Company, Inc.), and 319 parts by mass (solids concentration 23.9 parts by mass) of an organic solvent (methylcyclohexane / toluene / methyl ethyl ketone=13 / 86 / 1). ２ O ３ % MIBK dispersion) was added, and the mixture was stirred and degassed to obtain an adhesive composition. The blending amounts, elastic modulus, tensile storage modulus, linear expansion coefficient, peel strength, and electrical properties are shown in Table 1.

[0070] Examples 2 to 6 Examples 2 to 6 were carried out in the same manner as Example 1, except that the types and ratios of resins used and the inorganic nanofiber (X) were changed as shown in Table 1. The elastic modulus, tensile storage modulus, linear expansion coefficient, peel strength, and electrical properties are shown in Table 1.

[0071] Comparative Examples 1 and 2 were carried out in the same manner as in Example 1, except that inorganic nanofibers (X) were not used and the types and ratios of the resins used were changed as shown in Table 1. The elastic modulus, tensile storage modulus, linear expansion coefficient, peel strength, and electrical properties are shown in Table 1.

[0072] The acid-modified styrene-based elastomer (a), acid-modified polyolefin (b), epoxy resin (c), carbodiimide (d), and inorganic nanofiber (X) shown in Table 1 are as follows.

[0073] <Acid-modified styrene-based elastomers (a)> M1943 (Tuftec M1943 (registered trademark) manufactured by Asahi Kasei Corporation): styrene ratio = 20 mass%, MFR = 8.0 g / 10 min, measurement temperature: 230°C, load: 2.16 kg, acid value = 10 mgKOH / g C5025 (Tuftec C5025 (registered trademark) manufactured by Asahi Kasei Corporation): styrene ratio = 12 mass%, MFR = 10.0 g / 10 min, measurement temperature: 230°C, load: 2.16 kg, acid value = 4 mgKOH / g

[0074] <Acid-modified polyolefin (b)> 100 parts by mass of propylene-butene copolymer (Mitsui Chemicals, Inc. "TAFMER (registered trademark) XM7080"), 150 parts by mass of toluene, 11 parts by mass of maleic anhydride, and 6 parts by mass of di-tert-butyl peroxide were added to a 1 L autoclave, and the mixture was heated to 140 ° C. and stirred for an additional 3 hours. Thereafter, the resulting reaction liquid was cooled and poured into a container containing a large amount of methyl ethyl ketone to precipitate a resin. Thereafter, the liquid containing the resin was centrifuged to separate and purify maleic anhydride and the graft-polymerized acid-modified propylene-butene copolymer from (poly)maleic anhydride and low molecular weight components. Thereafter, the mixture was dried under reduced pressure at 70 ° C. for 5 hours to obtain a maleic anhydride-modified propylene-butene copolymer (CO-3, acid value = 11 mg KOH / g, number average molecular weight = 33,000, Tm = 80 ° C., ΔH = 25 J / g).

[0075] <Epoxy Resin (c)> jER152: cresol novolac epoxy resin, epoxy equivalent 278 g / eq, manufactured by Mitsubishi Chemical Corporation TETRAD-X: N,N,N',N'-tetraglycidyl-m-xylenediamine, epoxy equivalent 95 to 110 g / eq, manufactured by Mitsubishi Gas Chemical Company, Inc.

[0076] <Carbodiimide (d)> V-09GB: polycarbodiimide, carbodiimide equivalent 216 g / eq, manufactured by Nisshinbo Chemical Inc.

[0077] <Inorganic nanofiber (X)> ANF1: organoalumina sol, fibrous, average primary fiber diameter: 4 nm, average primary fiber length: 3000 nm, aspect ratio: 750, dispersion medium: MIBK (methyl isobutyl ketone), solid content: 5 mass%, manufactured by Kawaken Fine Chemicals Co., Ltd.

[0078]

[0079] As is clear from the above description, according to the present invention, the adhesive composition and sheet thereof described in the examples have excellent dielectric properties, linear expansion coefficients, and peel strength, and are therefore expected to be used in applications such as high-frequency circuit board materials. Specifically, the product of the present invention is expected to be used in electronic components and antenna components for communication devices that require high-speed communication such as 5G.

Claims

1. An adhesive composition comprising a resin (Y) having a carboxyl group or an anhydride group thereof and an inorganic nanofiber (X).

2. The adhesive composition according to claim 1, wherein the resin (Y) having a carboxyl group or an anhydride thereof comprises an acid-modified styrene-based elastomer (a) and an acid-modified polyolefin (b).

3. The adhesive composition according to claim 1, comprising an epoxy resin (c) and a carbodiimide (d).

4. The adhesive composition according to claim 1, wherein the inorganic nanofibers (X) have an average primary fiber diameter of 200 nm or less.

5. The adhesive composition according to claim 1, wherein the inorganic nanofiber (X) has an aspect ratio of 100 or more.

6. The adhesive composition according to claim 1, wherein the inorganic nanofibers (X) are made of alumina.

7. The adhesive composition according to claim 1, having a dielectric loss tangent at 10 GHz of 0.004 or less.

8. An adhesive sheet comprising the adhesive composition according to any one of claims 1 to 7.

9. A metal-clad laminate comprising an insulating resin layer (i) and a metal layer (iii) laminated on at least one surface thereof via the adhesive sheet according to claim 8.

10. The metal-clad laminate according to claim 9, wherein the insulating resin layer (i) contains any one of a fluorine-based resin, a cyclic olefin, a liquid crystal polymer and a syndiotactic polystyrene.

11. A printed wiring board comprising the metal-clad laminate according to claim 9 as a component.

12. The printed wiring board according to claim 11, wherein a part or the whole of the metal layer (iii) forms a conductor circuit.

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