Adhesive composition

Abstract

The present invention provides: a resin composition for forming a low-dielectric adhesive layer that has excellent 5G-compatible electrical properties (low-dielectric properties), ensures high adhesiveness, suppresses the occurrence of air bubbles, and exhibits a small linear coefficient of thermal expansion (CTE); and an adhesive composition containing said resin composition.　This adhesive composition contains a resin composition containing: a maleimide resin having a molecular weight of 1,000 or more; and a benzoxazine resin. The benzoxazine resin has a site represented by formula (1). (In formula (1), R represents a hydrocarbon group having 4 or more carbon atoms. The hydrocarbon group may have an unsaturated bond site.)

Description

[Technical Field]

[0001] This invention relates to an adhesive composition. More specifically, it relates to an adhesive composition that can be used for bonding electronic components and the like. [Background technology]

[0002] With the miniaturization and weight reduction of electronic devices, the applications for bonding electronic components and other materials have diversified, and the demand for laminates with adhesive layers is increasing. Furthermore, flexible printed circuit boards (FPCs), a type of electronic component, require high-speed processing of large amounts of data, and progress is being made in supporting high frequencies. Increasing the frequency of FPCs requires reducing the dielectric strength of the constituent elements, and development of low-dielectric substrate films and low-dielectric adhesives is underway. In particular, in order to efficiently transmit signals with frequencies in the 6GHz and 28GHz bands used in fifth-generation mobile communication systems (5G), substrate films and adhesives with low loss even in the 28GHz millimeter-wave band are becoming increasingly important.

[0003] However, low-dielectric adhesives have low polarity in their main component molecules, making it difficult for them to adhere well to substrate films and other components related to electronic parts. Similarly, low-dielectric substrate films can also have poor adhesion to adhesives, and there is a need to improve adhesion. Incidentally, thermosetting resin compositions containing a bismaleimide compound (a compound having a maleimide group), a benzoxazine compound, and a triazine compound have been proposed with the aim of obtaining good heat resistance and adhesion (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-227542 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the resin composition described in Patent Document 1 above, although a cured product with low dielectric strength and excellent heat resistance is produced by curing a low molecular weight maleimide compound with a benzoxazine compound, it is not sufficient from the viewpoint of ensuring high adhesion, and there was room for improvement. In order to improve adhesion, the inventors prepared a resin composition using a high molecular weight maleimide resin. They found that while the adhesion improved when using a high molecular weight maleimide resin, a problem arose where air bubbles formed in the adhesive layer using the resin composition. Furthermore, a high coefficient of linear thermal expansion (CTE) can cause warping of the laminate, leading to poor processability and reduced dimensional stability and adhesion of the film. Therefore, a resin composition capable of forming an adhesive layer with a low CTE value is desirable.

[0006] Therefore, the present invention aims to provide a resin composition for forming a low-dielectric adhesive layer that has good electrical properties (low dielectric properties) that are compatible with 5G, ensures high adhesion, suppresses the occurrence of abnormalities such as bubbles, and has a low coefficient of linear thermal expansion (CTE), and an adhesive composition containing the resin composition. [Means for solving the problem]

[0007] As a result of diligent research to solve the above problems, the present inventors have found that a resin composition containing a high molecular weight maleimide resin and a specific benzoxazine resin can solve the above problems, and have completed the present invention.

[0008] The present invention encompasses the following embodiments. [1] An adhesive composition comprising a resin composition containing a maleimide resin with a molecular weight of 1000 or more and a benzoxazine resin, An adhesive composition wherein the benzoxazine resin has a moiety represented by the following formula (1). [ka] (In formula (1), R represents a hydrocarbon group having 4 or more carbon atoms. The hydrocarbon group may have an unsaturated bond site.) [2] The adhesive composition according to [1], wherein the number of carbon atoms in R in formula (1) is 20 or less. [3] The adhesive composition according to [1] or [2], wherein R in formula (1) has a linear structure. [4] The adhesive composition according to any one of [1] to [3], wherein the hydrocarbon group R in formula (1) has at least one unsaturated bond site. [5] The adhesive composition according to [1], wherein R in formula (1) comprises any of the groups represented by the following formulas (i) to (iv). [ka] (In equations (i) to (iv) above, * represents a bond.) [6] The adhesive composition according to any one of [1] to [5], wherein the content of the benzoxazine resin is more than 0 parts by mass and 20 parts by mass or less per 100 parts by mass of the resin composition. [7] The adhesive composition according to any one of [1] to [6], wherein the softening point of the maleimide resin is 30°C or higher. [8] The adhesive composition according to any one of [1] to [7], wherein the softening point of the maleimide resin is 130°C or lower. [9] The adhesive composition according to any one of [1] to [8], wherein the resin composition further contains an epoxy resin, and the content of the epoxy resin is 25 parts by mass or less per 100 parts by mass of the resin composition.

[10] The resin composition is an adhesive composition according to any one of [1] to [8], wherein the resin composition does not contain an epoxy resin.

[11] An adhesive composition according to any one of [1] to

[10] , which contains a filler in addition to the resin composition.

[12] An adhesive layer obtained by curing the adhesive composition described in

[11] .

[13] The adhesive layer according to

[12] , wherein the relative permittivity of the adhesive layer measured at a frequency of 28 GHz is 3.5 or less and the dielectric loss tangent is 0.005 or less.

[14] A base film, and an adhesive layer as described in

[12] or

[13] , and has a laminate.

[15] The laminate according to

[14] , wherein the base film contains a polyetheretherketone (PEEK) resin.

[16] A coverlay film with an adhesive layer containing the laminate according to

[14] or

[15] .

[17] A copper-clad laminate containing the laminate according to

[14] or

[15] .

[18] A printed wiring board containing the laminate according to

[14] or

[15] .

[19] A shield film containing the laminate according to

[14] or

[15] .

[20] A printed wiring board with a shield film containing the laminate according to

[14] or

[15] . [Effect of the Invention]

[0009] According to the present invention, there can be provided a resin composition for forming a low dielectric adhesive layer having good electrical characteristics (low dielectric characteristics) compatible with 5G, ensuring high adhesion, suppressing the generation of bubbles, and having a small coefficient of linear thermal expansion (CTE), and an adhesive composition containing the resin composition. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, the adhesive composition of the present invention, a laminate including an adhesive layer made of the adhesive composition, and a component related to an electronic component including the laminate will be described in detail. However, the description of the constituent elements described below is an example as one embodiment of the present invention, and is not limited to these contents.

[0011] (Adhesive Composition) The adhesive composition of the present invention contains a resin composition. The resin composition contains a maleimide resin having a molecular weight of 1000 or more and a benzoxazine resin having a moiety represented by the following formula (1).

[0012] [Chemical formula]

[0013] In formula (1) above, R represents a hydrocarbon group having 4 or more carbon atoms. The hydrocarbon group may have an unsaturated bond site.

[0014] The resin composition may contain, as necessary, other resin components in addition to a maleimide resin component with a molecular weight of 1000 or more and a benzoxazine resin having the moiety represented by formula (1) above. In addition to the resin composition contained as a resin component, the adhesive composition of the present invention may also contain other components such as fillers, curing accelerators, and various additives. In this specification, "resin composition" consists of resin components and does not include other components such as fillers (especially inorganic fillers), curing accelerators, or various additives. By incorporating a high molecular weight maleimide resin and a benzoxazine resin having specific moieties into the adhesive composition, a low-dielectric adhesive layer exhibiting good electrical properties (low dielectric properties), high adhesion, bubble suppression, and low CTE can be formed.

[0015] <Maleimide resin> The resin composition according to the present invention contains a maleimide resin having a molecular weight of 1000 or more. Maleimide resin is a resin having maleimide groups, and in the present invention, it is more preferable that the maleimide resin is a bismaleimide resin having two maleimide groups. Maleimide resin has good metal adhesion, possesses unsaturated bonds, and is crosslinkable. The adhesive composition of the present invention containing maleimide resin has a high crosslink density and excellent heat resistance, solvent resistance, and other properties. Because maleimide resin contains an imide skeleton, it imparts high metal adhesion to adhesive compositions, making it difficult for acids and bases to penetrate between the cured adhesive composition and the metal, thereby improving chemical resistance. Maleimide resin reacts with benzoxazine resin to form a crosslinked structure. By reacting with benzoxazine resin and increasing the crosslinking density of the adhesive composition, high adhesion to the adherend, as well as heat resistance and a low coefficient of thermal expansion (CTE) of the cured adhesive, can be achieved.

[0016] Examples include modified maleimides obtained by modifying maleimide resin with a compound containing a primary amine, and polymers obtained by extending the chain with amine-modified products such as dimer acid and trimer acid, and maleic anhydride or pyromellitic acid. Maleimide resin can also be a commercially available compound; specifically, for example, products such as "SLK-3000-T50" and "SLK-2600-A50" manufactured by Shin-Etsu Chemical Co., Ltd. can be suitably used.

[0017] In the present invention, maleimide resin is preferably used as the main component of the resin composition. Therefore, the maleimide resin content is preferably more than 50 parts by mass per 100 parts by mass of the resin composition, from the viewpoint of reducing dielectric constant and improving adhesion. More specifically, the lower limit of the maleimide resin content in the resin composition is more preferably 80 parts by mass or more from the viewpoint of enabling further reduction of dielectric constant, and even more preferably 90 parts by mass or more from the viewpoint of further improving adhesion. On the other hand, the upper limit of the maleimide resin content in the resin composition is more preferably 99.8 parts by mass or less, and even more preferably 99 parts by mass or less. Maleimide resin may be used by mixing multiple types of different maleimide resins. When using a mixture of multiple types of maleimide resins, the above content shall be the total amount of each type of maleimide resin added together.

[0018] The melting point or softening point of the maleimide resin is preferably 30°C or higher and preferably 130°C or lower, from the viewpoint of providing fluidity to the adhesive composition at the temperature of heat lamination or heat pressing, allowing it to sufficiently conform to the surface of the base film or metal substrate, and exhibiting excellent adhesion and chemical resistance during curing.

[0019] The maleimide resin used in this invention has a weight-average molecular weight of 1,000 or more, preferably 3,000 or more, and more preferably 5,000 or more. If the weight-average molecular weight is 3,000 or more, the cured product of the adhesive composition can be imparted with appropriate flexibility. If the weight-average molecular weight is 5,000 or more, excellent adhesive properties can be achieved. The maleimide resin has a weight-average molecular weight of 40,000 or less, more preferably 20,000 or less, and even more preferably 15,000 or less. If the weight-average molecular weight is 40,000 or less, it can contain an imide skeleton that can exhibit sufficient metal adhesion. If the weight-average molecular weight is 15,000 or less, compatibility with benzoxazine resin is improved.

[0020] <Benzoxazine resin> The benzoxazine resin reacts with the maleimide resin to increase the crosslinking density of the adhesive composition, thereby enabling high adhesion to the adherend. The benzoxazine resin reacts with the maleimide resin to form a crosslinked structure, resulting in a low coefficient of thermal expansion (CTE).

[0021] The benzoxazine resin according to the present invention has a part represented by the following formula (1).

[0022] [ka]

[0023] In formula (1) above, R represents a hydrocarbon group having 4 or more carbon atoms. In the reaction between benzoxazine resin and maleimide resin, overreaction generates low molecular weight decomposition products, which cause bubbles. However, because R in the benzoxazine resin is a hydrocarbon group having 4 or more carbon atoms, the volatility of the decomposition products during the curing reaction can be reduced, suppressing the generation of bubbles. In addition, compatibility with high molecular weight maleimide resin is improved, and the curing temperature can be lowered. The hydrocarbon group may have an unsaturated bonding site. Although the detailed reaction mechanism is unknown, the presence of an unsaturated bonding site in the hydrocarbon group lowers the reaction temperature with the maleimide resin, allowing for a low coefficient of thermal expansion even at low temperatures. Furthermore, an increase in crosslinking density can also reduce the coefficient of thermal expansion. The adhesive composition of the present invention contains a resin composition comprising a high molecular weight maleimide resin and a specific benzoxazine resin having a moiety represented by formula (1) above. As a result, the adhesive composition of the present invention exhibits good low dielectric properties, forms a good film (adhesive layer) upon low-temperature curing, and the formed adhesive layer exhibits excellent adhesion, bubble suppression, and low CTE. In formula (1) above, the number of carbon atoms in R is more preferably 12 or more from the viewpoint of further improving compatibility, more preferably 14 or more from the viewpoint of reducing steric hindrance during the reaction of the unsaturated bond site, and particularly preferably 15 or more. Furthermore, the number of carbon atoms in R is preferably 20 or less from the viewpoint of facilitating the procurement of benzoxazine resin.

[0024] In formula (1), R is preferably a linear structure. This ensures excellent flexibility of the adhesive layer.

[0025] In formula (1), R is preferably one of the groups represented by the following formulas (i) to (iv).

[0026] [ka] (In equations (i) to (iv) above, * represents a combination.)

[0027] Furthermore, the benzoxazine resin according to the present invention is not limited to a benzoxazine resin in which R is represented by only one type, but may also be a benzoxazine resin in which multiple types of benzoxazine resins with different types of R in formula (1) are mixed, that is, at least two or more types. For example, if the product contains a benzoxazine resin having the R portion represented by formulas (i) to (iv) above, R is not limited to a benzoxazine resin represented by any one of the formulas (i) to (iv) above, but may be a benzoxazine resin in which multiple different types of benzoxazine resins selected from the formulas (i) to (iv) above are mixed. More specifically, for example, A benzooxazine resin having a moiety represented by formula (1) in which R in formula (1) is the group represented by formula (i), A benzooxazine resin having a moiety represented by formula (1) in which R in formula (1) is a group represented by formula (ii), A benzoxazine resin having a moiety represented by formula (1) in which R in formula (1) is a group represented by formula (iii), and A benzoxazine resin having a moiety represented by formula (1) in which R in formula (1) is a group represented by formula (iv), It may also contain at least two benzoxazine resins selected from the group.

[0028] The benzoxazine resin preferably has a structure containing two or more oxazine skeletons in its molecule. This allows for an increase in the content of the highly adhesive maleimide resin while improving the crosslinking density.

[0029] Examples of benzoxazine resins include those represented by the following formula (2).

[0030] [ka] In equation (2) above, R 1 and R 2 The definitions of R in each of these are the same as those of R in formula (1) above. X represents a divalent organic group. For example, it represents an alkylene group with 1 to 5 carbon atoms, or a group represented by formula (3) below.

[0031] [ka] In formula (3) above, X1 represents an alkylene group having 1 to 5 carbon atoms. * represents a bond.

[0032] In equation (2) above, R 1 and R 2 Preferably, each represents one of the alkyl groups represented by the above formulas (i) to (iv).

[0033] The benzoxazine resin content is preferably 1 part by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of the resin composition, from the viewpoint of increasing reactivity. Furthermore, the benzoxazine resin content is preferably 20 parts by mass or less from the viewpoint of enabling low dielectric properties, and more preferably 10 parts by mass or less from the viewpoint of increasing the relative amount of maleimide resin and improving adhesion. If the benzoxazine resin content is within the above range, the low dielectric properties and adhesion of the adhesive layer formed using the adhesive composition containing the resin composition can be well ensured. Benzooxazine resin may be used by mixing multiple types of different benzooxazine resins. When using a mixture of multiple types of benzooxazine resins, the above content shall be the total amount of each type of benzooxazine resin added together.

[0034] The melting point or softening point of the benzoxazine resin is preferably below 120°C, from the viewpoint of providing fluidity to the adhesive composition at the temperature of heat lamination or heat pressing, suppressing whitening, allowing it to sufficiently conform to the surface of the substrate film or metal substrate, and exhibiting excellent adhesion. The melting point or softening point of the benzoxazine resin is preferably 40°C or higher, from the viewpoint of increasing the elastic modulus of the adhesive composition at room temperature, improving adhesion, and suppressing whitening.

[0035] As for the mixing ratio of maleimide resin and benzoxazine resin, for example, from the viewpoint of reducing dielectric constant and improving adhesion, a mass ratio of maleimide resin:benzoxazine resin = 50:50 to 99:1 is preferred, from the viewpoint of enabling reduced dielectric constant, 80:20 to 99:1 is more preferred, and from the viewpoint of further improving adhesion, 90:10 to 95:5 is even more preferred.

[0036] The resin composition according to the present invention may contain, in addition to maleimide resin and benzoxazine resin, other resin components as long as they do not impair the effects of the present invention.

[0037] <Other resin components> The resin composition according to the present invention may contain thermosetting resins other than the maleimide resin and the benzoxazine resin mentioned above. Alternatively, the resin composition according to the present invention may contain styrene elastomers or other thermoplastic resins.

[0038] Other thermosetting resins include epoxy resins, phenolic resins, unsaturated imide resins (excluding the maleimide resin mentioned above), cyanate resins, isocyanate resins, oxetane resins, amino resins, unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, triazine resins, and melamine resins. Among these, epoxy resins are superior in terms of moldability and electrical insulation, but adhesion can be achieved by blending maleimide resins and oxazine resins, and from the viewpoint of dielectric properties, it is preferable to contain almost no epoxy resin. Therefore, when a resin composition contains epoxy resin, the epoxy resin content is preferably less than 25 parts by mass per 100 parts by mass of the resin composition from the viewpoint of low dielectric, and it is even more preferable to omit it from the viewpoint of suppressing whitening and low dielectric.

[0039] Styrene elastomers are copolymers mainly composed of unsaturated hydrocarbons and aromatic vinyl compounds with block and random structures, as well as hydrogenated versions thereof. Examples of aromatic vinyl compounds include styrene, t-butylstyrene, α-methylstyrene, divinylbenzene, 1,1-diphenylethylene, N,N-diethyl-p-aminoethylstyrene, and vinyltoluene. Examples of unsaturated hydrocarbons include ethylene, propylene, butadiene, isoprene, isobutene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene.

[0040] Other thermoplastic resins include, for example, phenoxy resins, polyamide resins, polyester resins, polycarbonate resins, polyphenylene oxide resins, polyurethane resins, polyacetal resins, polyethylene resins, polypropylene resins, polybutadiene resins, and polyvinyl resins. These thermoplastic resins may be used individually or in combination of two or more types.

[0041] <Other ingredients> In addition to a resin composition containing maleimide resin, benzoxazine resin, and the above-mentioned other resin components, the adhesive composition of the present invention may also contain other components such as fillers, curing accelerators, and various additives. Other components include, for example, fillers, curing accelerators, flame retardants, heat aging inhibitors, leveling agents, defoamers, and pigments. These can be included in amounts that do not affect the function of the adhesive composition.

[0042] <<Filler>> The adhesive composition of the present invention preferably contains a filler. As the filler according to the present invention, inorganic fillers are preferred, for example, from the viewpoint of heat resistance and control of the mechanical properties of the adhesive composition. Examples of inorganic fillers include silica, alumina, titanium oxide, mica, beryllia, barium titanate, potassium titanate, strontium titanate, calcium titanate, aluminum carbonate, magnesium hydroxide, aluminum silicate, calcium carbonate, calcium silicate, magnesium silicate, silicon nitride, boron nitride, clay, talc, aluminum borate, silicon carbide, quartz powder, glass short fibers, glass fine powder, and hollow glass. Among these, silica, mica, talc, quartz powder, glass short fibers, glass fine powder, and hollow glass are preferred from the viewpoint of dielectric properties, heat resistance, and low thermal expansion, and silica is more preferred from the viewpoint of being able to be made into a thin film. Examples of silica include precipitated silica with a high water content produced by the wet process, and dry-process silica that contains almost no bound water, etc., produced by the dry process. Inorganic fillers may be surface-treated with a coupling agent. Furthermore, the filler according to the present invention may contain, for example, an organic filler, from the viewpoint of dispersibility and brittleness. As for organic fillers, styrene-based spherical fillers are preferred from the viewpoint of electrical properties, and styrene-based hollow fillers are more preferred. These can be used individually or in combination of two or more types. The filler content in the adhesive composition of the present invention is preferably 50 to 1000 parts by mass per 100 parts by mass of the resin composition, from the viewpoint of achieving a low coefficient of linear expansion, and more preferably 80 to 500 parts by mass per 100 parts by mass of the resin composition, from the viewpoint of achieving low dielectric properties and adhesion. Furthermore, from the viewpoint of improving adhesion, it is even more preferably 150 to 350 parts by mass per 100 parts by mass of the resin composition. The shape of the filler is not particularly limited and can be appropriately selected depending on the purpose. For example, the inorganic filler may be spherical or non-spherical, but from the viewpoint of thermal expansion coefficient (CTE) and film strength, non-spherical inorganic fillers are preferred. The shape of the non-spherical inorganic filler can be any three-dimensional shape other than spherical (approximately perfectly spherical), such as plate-like, flake-like, columnar, chain-like, or fibrous. Among these, plate-like and flake-like inorganic fillers are preferred from the viewpoint of thermal expansion coefficient (CTE) and film strength, and plate-like inorganic fillers are more preferred.

[0043] The above-mentioned flame retardant may be either an organic flame retardant or an inorganic flame retardant. Examples of organic flame retardants include phosphorus-based flame retardants such as melamine phosphate, melamine polyphosphate, guanidine phosphate, guanidine polyphosphate, ammonium phosphate, ammonium polyphosphate, ammonium phosphate, ammonium polyphosphate, carbamate phosphate, carbamate polyphosphate, aluminum tris-diethylphosphinate, aluminum tris-methylethylphosphinate, aluminum tris-diphenylphosphinate, zinc bis-diethylphosphinate, zinc bis-methylethylphosphinate, zinc bis-diphenylphosphinate, titanyl bis-diethylphosphinate, titanium tetrakis-diethylphosphinate, titanyl bis-methylethylphosphinate, titanium tetrakis-methylethylphosphinate, titanyl bis-diphenylphosphinate, and titanium tetrakis-diphenylphosphinate; nitrogen-based flame retardants such as triazine compounds like melamine, melam, and melamine cyanurate, as well as cyanuric acid compounds, isocyanuric acid compounds, triazole compounds, tetrazole compounds, diazo compounds, and urea; and silicon-based flame retardants such as silicone compounds and silane compounds. Examples of inorganic flame retardants include metal hydroxides such as aluminum hydroxide, magnesium hydroxide, zirconium hydroxide, barium hydroxide, and calcium hydroxide; metal oxides such as tin oxide, aluminum oxide, magnesium oxide, zirconium oxide, zinc oxide, molybdenum oxide, and nickel oxide; and zinc carbonate, magnesium carbonate, barium carbonate, zinc borate, and hydrated glass. Two or more of these flame retardants can be used in combination.

[0044] The above-mentioned heat aging inhibitors include 2,6-di-tert-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenol), and triethylene glycol-bis[3 Examples include phenol-based antioxidants such as -(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate; sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate and dimyristyl-3,3'-dithiopropionate; and phosphorus-based antioxidants such as trisnonylphenyl phosphite and tris(2,4-di-tert-butylphenyl) phosphite. These may be used individually or in combination of two or more.

[0045] (adhesive layer) The adhesive layer according to the present invention is formed using the adhesive composition of the present invention described above. The adhesive composition forms an adhesive layer and can be cured. There are no particular limitations on the curing method; it can be appropriately selected depending on the purpose, for example, thermal curing. The thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose, but for example, it is preferably 3 μm or more, more preferably 5 μm or more. It is also preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less. If the thickness of the adhesive layer is 3 μm or more, sufficient adhesion can be achieved, and if it is 5 μm or more, it can follow steps such as patterns on printed circuit boards. If the thickness of the adhesive layer is 50 μm or less, thinning of the laminate is possible, and if it is 30 μm or less, the resin flow can be accurately controlled.

[0046] <Method for manufacturing adhesive layer> An adhesive layer can be manufactured by forming the above adhesive composition into a film. The above adhesive composition can be produced by mixing the maleimide resin and benzoxazine resin described above. The mixing method is not particularly limited, as long as the adhesive composition is homogeneous. Since the adhesive composition is preferably used in solution or dispersion form, a solvent is usually also used. Examples of solvents include alcohols such as methanol, ethanol, isopropyl alcohol, n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, benzyl alcohol, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, and diacetone alcohol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, and isophorone; aromatic hydrocarbons such as toluene, xylene, ethylbenzene, mesitylene, and anisole; esters such as methyl acetate, ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate, and 3-methoxybutyl acetate; and aliphatic hydrocarbons such as hexane, heptane, cyclohexane, and methylcyclohexane. These solvents may be used individually or in combination of two or more. In particular, adding a small amount of cyclohexanone to toluene, which can dissolve resins with low polarity, improves compatibility with curing agents and other components, allowing for a more uniform adhesive layer. If the adhesive composition is a solvent-containing solution or dispersion (resin varnish), coating onto the substrate film and forming the adhesive layer can be carried out smoothly, and an adhesive layer of the desired thickness can be easily obtained. When the adhesive composition contains a solvent, the solid content concentration is preferably in the range of 3 to 80% by mass, more preferably 10 to 50% by mass, from the viewpoint of workability, including the formation of the adhesive layer. When the solid content concentration is 80% by mass or less, the viscosity of the solution is appropriate, and it is easy to apply uniformly. A more specific embodiment of the method for manufacturing the adhesive layer is to apply a resin varnish containing the above-mentioned adhesive composition and solvent to the surface of a substrate film to form a resin varnish layer, and then remove the solvent from the resin varnish layer to form a B-stage adhesive layer. Here, a B-stage adhesive layer refers to a state in which the adhesive composition is uncured or partially cured, and in which the curing of the adhesive composition progresses further due to heating or the like. There are no particular restrictions on the method of applying the resin varnish to the substrate film, and it can be appropriately selected depending on the purpose. Examples include the spray method, spin coating method, dip method, roll coating method, blade coating method, doctor roll method, doctor blade method, curtain coating method, slit coating method, screen printing method, inkjet method, and dispensing method. The above-mentioned B-stage adhesive layer can be further heated or otherwise treated to form a hardened adhesive layer.

[0047] <Characteristics of the adhesive layer> The relative permittivity (εr) of the adhesive layer obtained by curing the adhesive composition of the present invention at a frequency of 28 GHz is preferably 3.5 or less, and more preferably 2.7 or less. The dielectric loss tangent (tanδ) of the adhesive layer at a frequency of 28 GHz is preferably 0.005 or less, more preferably 0.0025 or less, and even more preferably 0.0015 or less. If the relative permittivity is 3.5 or less and the dielectric loss tangent is 0.005 or less, it can be used in high-frequency FPC-related products with stringent electrical characteristics. Furthermore, if the relative permittivity is 2.7 or less and the dielectric loss tangent is 0.0025 or less, it can satisfy the electrical characteristics expected of components in 5G-compatible high-frequency FPC-related products, achieving electrical characteristics equivalent to LCP, and can be suitably used in 5G high-frequency FPC-related products with stringent electrical characteristics. Moreover, if the dielectric loss tangent is 0.0015 or less, it can be suitably used in high-frequency FPC-related products utilizing millimeter waves.

[0048] [Relative permittivity and dielectric loss tangent] The relative permittivity and dielectric loss tangent of the adhesive layer can be measured using the open-type resonator method with a network analyzer MS46122B (Anritsu) and an open-type resonator Fabry-Perot DPS-03 (KEYCOM) at a temperature of 23°C and a frequency of 28 GHz.

[0049] The upper limit of the linear thermal expansion coefficient (CTE) (CTE at 20°C to 140°C) of the adhesive layer obtained by curing the adhesive composition of the present invention is preferably less than 500 ppm / K from the viewpoint of suppressing warping of the laminate, and more preferably less than 20 ppm / K from the viewpoint of ensuring dimensional stability and adhesion of the film. It is even more preferably less than 100 ppm / K from the viewpoint of being suitably usable with commonly used low-dielectric base films such as LCP and MPI. The lower limit of the linear thermal expansion coefficient (CTE) (CTE at 20°C to 140°C) of the adhesive layer is preferably 10 ppm / K or more, and more preferably 20 ppm / K or more.

[0050] The linear thermal expansion coefficient (CTE) can be determined by thermomechanical analysis (TMA) in accordance with JIS K 7197:1991. For example, it can be performed by using a thermomechanical analyzer (product name: SII / / SS7100, manufactured by Hitachi High-Tech Science Co., Ltd.) in tensile mode, measuring in the range from 10°C to 200°C under conditions of a load of 50mN and a heating rate of 5°C / min, and then determining the linear thermal expansion coefficient (ppm / K) from the slope in the range from 20°C to 140°C.

[0051] (Laminated structure) The laminate of the present invention comprises a base film and the adhesive layer on at least one surface of the base film.

[0052] <Base film> The base film used in the present invention can be selected depending on the application of the laminate. For example, when the laminate is used as a coverlay film or copper-clad laminate (CCL), examples include polyimide film, polyetheretherketone film, polyphenylene sulfide film, aramid film, polyethylene naphthalate film, and liquid crystal polymer film, polyphenylene ether film, syndiotactic polystyrene film, etc. Among these, polyimide film, polyetheretherketone (PEEK) film, polyethylene naphthalate film, and liquid crystal polymer film are preferred from the viewpoint of adhesion and electrical properties. The base film may contain fillers. There are no particular restrictions on the type of filler, and it can be selected as appropriate depending on the purpose, but for example, the fillers mentioned above can be used.

[0053] Furthermore, when the laminate of the present invention is used as a bonding sheet, the base film must be a release film, and examples include polyethylene terephthalate film, polyethylene film, polypropylene film, silicone release treated paper, polyolefin resin coated paper, TPX (polymethylpentene) film, and fluororesin film.

[0054] When the laminate of the present invention is used as a shielding film, the base film must be a film that has electromagnetic wave shielding ability, and examples include a laminate of a protective insulating layer and a metal foil.

[0055] (Coverlay film) A coverlay film is a preferred embodiment of the laminate according to the present invention. When manufacturing FPCs (Flexible Printed Circuits), a laminate with an adhesive layer called a "coverlay film" is typically used to protect the wiring. This coverlay film comprises an insulating resin layer and an adhesive layer formed on its surface. For example, a coverlay film is a laminate in which the adhesive layer is formed on at least one surface of the base film, and the base film and the adhesive layer are generally difficult to separate. The thickness of the base film included in the coverlay film is preferably 5 to 100 μm, more preferably 5 to 50 μm, and even more preferably 5 to 30 μm. If the thickness of the base film is below the above upper limit, the coverlay film can be made into a thin film. If the thickness of the base film is above the above lower limit, the design of the printed circuit board can be easily performed and handling is also good. As a method for producing a coverlay film, for example, a resin varnish containing the above-mentioned adhesive composition and solvent can be applied to the surface of the base film to form a resin varnish layer, and then the solvent can be removed from the resin varnish layer to produce a coverlay film in which a B-stage adhesive layer has been formed. The drying temperature when removing the solvent is preferably 40 to 250°C, and more preferably 70 to 170°C. Drying is performed by passing the laminate coated with the adhesive composition through a furnace that is subjected to hot air drying, far-infrared heating, and high-frequency induction heating, etc. If necessary, a release film may be laminated onto the surface of the adhesive layer for storage purposes. Known release films such as polyethylene terephthalate film, polyethylene film, polypropylene film, silicone release treated paper, polyolefin resin coated paper, TPX film, and fluororesin film can be used. Because the coverlay film according to the present invention uses the low dielectric adhesive composition of the present invention, it enables high-speed transmission in electronic devices and also exhibits excellent adhesive stability with electronic devices.

[0056] (Bonding sheet) A preferred embodiment of the laminate according to the present invention is a bonding sheet. A bonding sheet has the adhesive layer described above formed on the surface of a release film (base film). Alternatively, the bonding sheet may have an adhesive layer between two release films. When using the bonding sheet, the release film is peeled off. The release film can be the same as that described in the (coverlay film) section above. The thickness of the base film included in the bonding sheet is preferably 5 to 100 μm, more preferably 25 to 75 μm, and even more preferably 38 to 50 μm. If the thickness of the base film is within the above range, the bonding sheet is easy to manufacture and easy to handle. One method for manufacturing a bonding sheet is to apply a resin varnish containing the above-mentioned adhesive composition and solvent to the surface of a release film and dry it in the same manner as in the case of the coverlay film. Because the bonding sheet according to the present invention uses the low dielectric adhesive composition of the present invention, it enables high-speed transmission of electronic devices and also exhibits excellent adhesive stability with electronic devices.

[0057] (Copper-clad laminate (CCL)) A preferred embodiment of the laminate according to the present invention is a copper-clad laminate obtained by bonding copper foil to an adhesive layer in the laminate of the present invention. The copper-clad laminate is formed by laminating copper foil onto the above-mentioned laminate, and is composed, for example, in the order of base film, adhesive layer, and copper foil. The adhesive layer and copper foil may be formed on both sides of the base film. The adhesive composition used in this invention also exhibits excellent adhesion to articles containing copper. The copper-clad laminate according to the present invention uses the low-dielectric adhesive composition of the present invention, enabling high-speed transmission in electronic devices and providing excellent adhesive stability.

[0058] One method for manufacturing copper-clad laminates involves bringing the adhesive layer of the laminate into surface contact with the copper foil, performing thermal lamination at 80°C to 200°C, and then curing the adhesive layer by after-curing. The after-curing conditions can be, for example, 100°C to 200°C for 30 minutes to 4 hours under an inert gas atmosphere. The copper foil is not particularly limited, and electrolytic copper foil, rolled copper foil, etc., can be used.

[0059] (Printed circuit board) A preferred embodiment of the laminate according to the present invention is a printed circuit board in which copper wiring is bonded to an adhesive layer in the laminate of the present invention. A printed circuit board is obtained by forming electronic circuits on the copper-clad laminate mentioned above. The printed circuit board is constructed by laminating a base film and copper wiring using the above-mentioned laminate, and is composed of the base film, adhesive layer, and copper wiring in that order. The adhesive layer and copper wiring may be formed on both sides of the base film. For example, a printed circuit board is manufactured by using a heat press or the like to attach a coverlay film to the surface having the wiring portion via an adhesive layer. Because the printed circuit board according to the present invention uses the low dielectric adhesive composition of the present invention, it enables high-speed transmission in electronic devices and has excellent adhesive stability. One method for manufacturing a printed circuit board according to the present invention is to bring the adhesive layer of the laminate into contact with the copper wiring, perform heat lamination at 80°C to 200°C, and then cure the adhesive layer by after-curing. The after-curing conditions can be, for example, 100°C to 200°C for 30 minutes to 4 hours. The shape of the copper wiring is not particularly limited, and an appropriate shape may be selected as desired.

[0060] (Shielding film) A preferred embodiment of the laminate according to the present invention is a shield film. Shielding film is a film used to shield various electronic devices, such as computers, mobile phones, and analytical instruments, by cutting out electromagnetic noise that can affect them and cause malfunctions. It is also called electromagnetic shielding film. The electromagnetic wave shielding film is formed by laminating, for example, an insulating resin layer, a metal layer, and an adhesive layer according to the present invention in this order. Because the shielding film according to the present invention uses the low dielectric adhesive composition of the present invention, it enables high-speed transmission of data in electronic devices and also exhibits excellent adhesive stability with electronic devices.

[0061] (Printed circuit board with shielding film) A preferred embodiment of the laminate according to the present invention is a printed circuit board with a shielding film. A printed circuit board with a shielding film is a printed circuit board on which printed circuits are provided on at least one side of the board, with the electromagnetic shielding film attached to it. A printed circuit board with a shielding film comprises, for example, a printed circuit board, an insulating film adjacent to the side of the printed circuit board on which the printed circuit is provided, and the electromagnetic wave shielding film. The printed circuit board with a shielding film according to the present invention uses the low-dielectric adhesive composition of the present invention, thereby enabling high-speed transmission of electronic devices and providing excellent adhesive stability. [Examples]

[0062] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. In the following, parts and % are by mass unless otherwise specified.

[0063] (Bismalimide resin) The product used was "SLK-3000-T50," manufactured by Shin-Etsu Chemical Co., Ltd. Its softening point is 40°C, and its weight-average molecular weight is 12,545. (Bismalimide resin) The product used was "SLK-6895-M90," manufactured by Shin-Etsu Chemical Co., Ltd. Its softening point is 60°C, and its weight-average molecular weight is 980. (Benzoxazine resin) The product used was "CR-276," manufactured by Tohoku Chemical Co., Ltd. "CR-276" has the structure shown in formula (1-1) below, and R 1 and R 2 The benzoxazine resin is represented by any of the following formulas (i) to (iv), where each of the elements may be different.

[0064] [ka]

[0065] [ka] (In equations (i) to (iv) above, * represents a combination.) The benzoxazine resin in "CR-276" is liquid at room temperature. (Benzoxazine resin) The product used was "BZ-LB-MDA," manufactured by Tohoku Chemical Co., Ltd. "BZ-LB-MDA" has the structure shown in formula (1-2) below, and R 1 and R 2 The benzoxazine resin is represented by any of the following formulas (i) to (iv), where each of the elements may be different.

[0066] [ka]

[0067] [ka] (In equations (i) to (iv) above, * represents a combination.) (Benzoxazine resin) We used "ALP-d" (liquid), a product manufactured by Shikoku Chemicals, Inc. (Inorganic filler (silica)) The product name "SO-C2" manufactured by Admatechs was used. The particle size was 0.4 to 0.6 μm, and the specific surface area was 4 to 7 m 2 / g. (Solvent) A mixed solvent consisting of toluene and cyclohexanone (mass ratio = 97:3) was used. (Base film) As the base film, "Shin-Etsu Sepla Film PEEK" (polyether ether ketone, thickness 50 μm) manufactured by Shin-Etsu Polymer Co., Ltd. was used. The storage modulus of the base film at 200 °C was 5×10 8 Pa. (Electrolytic copper foil) As the electrolytic copper foil, "TQ-M7-VSP" (electrolytic copper foil, thickness 12 μm, gloss surface Rz 1.27 μm, gloss surface Ra 0.197 μm, gloss surface Rsm 12.95 μm) manufactured by Mitsui Mining & Smelting Co., Ltd. was used. (Release film) As the release film, NP75SA (silicone release PET film, 75 μm) manufactured by Panac Co., Ltd. was used.

[0068] (Example 1) Each component constituting the adhesive layer shown in Table 1 was contained in the ratio shown in Table 1, and these components were dissolved in a solvent to prepare a resin varnish which is an adhesive composition with a solid content concentration of 50% by mass. Each component constituting the resin composition in the adhesive composition is as shown in Table 1.

[0069] For the adhesive layer obtained by curing using the resin varnish of Example 1, the relative permittivity and the dielectric tangent at a frequency of 28 GHz were measured.

[0070] [Relative permittivity and dielectric tangent] The dielectric constant and dielectric loss tangent of the adhesive layer were measured using the open-type resonator method with a network analyzer MS46122B (Anritsu) and an open-type resonator Fabry-Perot DPS-03 (KEYCOM) at a temperature of 23°C and a frequency of 28 GHz. For the measurement sample, a resin varnish was roll-coated onto a release film, and then this coated film was placed in an oven and dried at 110°C for 4 minutes to form a B-stage adhesive layer (thickness 50 μm). Next, this adhesive layer was heat-laminated at 150°C with the adhesive surfaces in contact to form a pre-cured adhesive film (thickness 100 μm). This pre-cured adhesive film (thickness 100 μm) was placed in an oven and heat-cured at 180°C for 60 minutes to produce a cured adhesive film (100 mm × 100 mm). After curing, the release film was peeled off the adhesive film, and the relative permittivity and dielectric loss tangent of the adhesive layer were measured.

[0071] [Evaluation Criteria for Relative Permittance] ○ Less than 3.0 △ 3.0 or higher and less than 3.5 × 3.5 or more

[0072] [Evaluation Criteria for Dielectric Loss Tangent] Less than 0.003 △ 0.003 or higher and less than 0.005 × 0.005 or higher

[0073] The linear thermal expansion coefficient (CTE) (CTE from 20°C to 140°C) of the adhesive layer obtained by curing the resin varnish of Example 1 at 150°C or 200°C for 60 minutes was determined and evaluated according to the following criteria.

[0074] [Coefficient of linear thermal expansion (CTE) (ppm / K)] The linear thermal expansion coefficient (CTE) was measured in tensile mode using a thermomechanical analyzer (product name: SII / / SS7100, manufactured by Hitachi High-Tech Science Co., Ltd.) under conditions of a load of 50 mN and a heating rate of 5°C / min, in the range from 10°C to 200°C. The linear thermal expansion coefficient (ppm / K) was determined from the slope in the range from 20°C to 140°C. The measurement was taken in the width direction (TD) of the resin film.

[0075] [Criteria for evaluating CTE (ppm / K)] ○ CTE is less than 200 △ CTE is between 200 and 500 × CTE is 500 or more

[0076] The adhesive layer obtained by curing using the resin varnish of Example 1 was checked to see if a white mark remained (whitening) when bent at 180°. The evaluation criteria for whitening are as follows.

[0077] [Whitening] 〇 Does not turn white even when bent. × Whitening occurs

[0078] Using the resin varnish from Example 1, a laminate with adhesive after curing was prepared by the following method.

[0079] <Laminate with adhesive after curing> The surface of the base film was subjected to corona treatment. The resin varnish prepared above was applied to the surface of the base film and dried in a 130°C oven for 4 minutes to evaporate the solvent, forming an adhesive layer (25 μm) and obtaining an adhesive-backed base film (adhesive-backed laminate). The adhesive-backed laminate was placed so that the adhesive layer was in contact with the glossy surface of the electrolytic copper foil, and pressed using a vacuum press at 180°C, under pressure (3 MPa) and 10 hPa for 3 minutes, followed by after-curing at 180°C for 1 hour to cure the adhesive layer and obtain a cured adhesive-backed laminate.

[0080] For the adhesive-coated laminate of Example 1 after curing, the peel force (adhesion force) (N / cm) between the electrolytic copper foil and the substrate film was measured.

[0081] [Peeling force (N / cm)] The peel strength was measured by cutting a 25mm wide test specimen from the cured adhesive laminate and, in accordance with JIS Z0237:2009 (Test Methods for Adhesive Tapes and Adhesive Sheets), by measuring the peel strength when peeling the electrolytic copper foil from the adhesive substrate film fixed to the support at a peeling speed of 0.3m / min and a peeling angle of 180°. The peel strength was then evaluated according to the following criteria.

[0082] [Evaluation Criteria for Peeling Force] ◎ 8N / cm or more ○ 7 N / cm or more and less than 8 N / cm △ 6N / cm or more and less than 7N / cm × Less than 6 N / cm

[0083] The adhesive-coated laminate from Example 1 was visually inspected to determine whether or not air bubbles had formed in the adhesive layer after curing. The evaluation criteria for air bubbles are as follows:

[0084] [bubbles] ○ No bubbles have formed. × Bubbles are forming.

[0085] Table 2 shows the evaluation results for the adhesive layer and the laminate with the adhesive layer in Example 1.

[0086] (Examples 2 to 6) Except for changing the types and amounts of components constituting the adhesive layer in Example 1 as shown in Table 1, the adhesive layers and laminates with adhesive layers of Examples 2 to 6 were prepared in the same manner as in Example 1. The fabricated adhesive layer and the laminate with the adhesive layer were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0087] (Comparative Example 1 to Comparative Example 5) Except for changing the types and amounts of components constituting the adhesive layer in Example 1 as shown in Table 1, the adhesive layers and laminates with adhesive layers of Comparative Examples 1 to 5 were prepared in the same manner as in Example 1. The fabricated adhesive layer and the laminate with the adhesive layer were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0088] [Table 1]

[0089] [Table 2]

[0090] As shown in the examples, the adhesive composition of the present invention exhibits good electrical properties (low dielectric properties) suitable for 5G applications, forms a good film (adhesive layer) upon low-temperature curing, and the formed adhesive layer exhibits excellent adhesion, bubble suppression, and low CTE. [Industrial applicability]

[0091] Laminates having an adhesive layer made of the adhesive composition of the present invention can be suitably used in the manufacture of FPC-related products for electronic devices such as smartphones, mobile phones, optical modules, digital cameras, game consoles, laptop computers, and medical devices.

Claims

1. An adhesive composition comprising a resin composition containing a maleimide resin with a molecular weight of 3000 or more and a benzoxazine resin, The benzoxazine resin has a portion represented by the following formula (1): An adhesive composition in which the mixing ratio (mass ratio) of the maleimide resin and the benzoxazine resin is maleimide resin:benzoxazine resin = 50:50 to 99:

1. 【Chemistry 1】 (In formula (1), R represents a hydrocarbon group having four or more carbon atoms. The hydrocarbon group may have an unsaturated bond site.)

2. The adhesive composition according to claim 1, wherein the number of carbon atoms in R in formula (1) is 20 or less.

3. The adhesive composition according to claim 1, wherein R in formula (1) is a linear structure.

4. The adhesive composition according to claim 1, wherein the hydrocarbon group R in formula (1) has at least one unsaturated bond site.

5. The adhesive composition according to claim 1, wherein R in formula (1) contains any of the groups represented by the following formulas (i) to (iv). 【Chemistry 2】 (In equations (i) to (iv) above, * represents a coupling.)

6. The adhesive composition according to claim 1, wherein the content of the benzoxazine resin is more than 0 parts by mass and 20 parts by mass or less, per 100 parts by mass of the resin composition.

7. The adhesive composition according to claim 1, wherein the softening point of the maleimide resin is 30°C or higher.

8. The adhesive composition according to claim 1, wherein the softening point of the maleimide resin is 130°C or lower.

9. The adhesive composition according to claim 1, wherein if the resin composition further contains an epoxy resin, the amount of the epoxy resin is 25 parts by mass or less per 100 parts by mass of the resin composition.

10. The adhesive composition according to claim 1, wherein the resin composition does not contain an epoxy resin.

11. The adhesive composition according to claim 1, further comprising a filler in addition to the resin composition.

12. An adhesive layer obtained by curing the adhesive composition according to claims 1 to 11.

13. The adhesive layer according to claim 12, wherein the relative permittivity of the adhesive layer measured at a frequency of 28 GHz is 3.5 or less, and the dielectric loss tangent is 0.005 or less.

14. A base film and A laminate having the adhesive layer described in claim 12.

15. A coverlay film with an adhesive layer, comprising the laminate described in claim 14.

16. A copper-clad laminate comprising the laminate described in claim 14.

17. A printed circuit board comprising the laminate described in claim 14.

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