JP7812373B2 - adhesive composition - Google Patents

Description

The present invention relates to an adhesive composition. More specifically, it relates to an adhesive composition that can be used for bonding electronic components, etc.

BACKGROUND ART As electronic devices become smaller and lighter, the adhesive applications for electronic components and the like are becoming more diverse, and the demand for laminates with adhesive layers is increasing.
Furthermore, flexible printed circuit boards (hereinafter also referred to as FPCs), which are electronic components, are required to process large amounts of data at high speed, and are becoming increasingly compatible with high frequencies. The increased frequency of FPCs requires lower dielectric constants for their components, and low-dielectric substrate films and low-dielectric adhesives are being developed. In particular, to efficiently transmit signals with frequencies in the 6 GHz and 28 GHz bands used in fifth-generation mobile communication systems (hereinafter also referred to as 5G), substrate films and adhesives with low loss even in the 28 GHz millimeter-wave band are becoming increasingly important.

However, low-dielectric adhesives have low polarity in the main molecule, making it difficult for them to adhere to base films and other components related to electronic parts. Similarly, low-dielectric base films can also have poor adhesion to adhesives, so there is a demand for improved adhesion.
Therefore, in order to meet the requirement for high adhesion while maintaining good electrical properties (low dielectric constant and low dielectric loss tangent), a laminate has been proposed which uses an adhesive composition containing a carboxyl group-containing styrene-based elastomer (A) and an epoxy resin (B), and which comprises an adhesive layer made of the adhesive composition and a substrate film (see, for example, Patent Document 1).

International Publication No. 2016/017473

However, low-dielectric adhesives have problems with chemical resistance and heat resistance because the main molecule has low polarity and the crosslink density is low.
From the viewpoint of providing a low dielectric adhesive layer that adheres well even to low dielectric substrate films with poor adhesion and that also has chemical resistance and heat resistance, the adhesive described in Patent Document 1 above was not satisfactory and there was room for improvement.

The present invention therefore aims to provide an adhesive composition for forming a low-dielectric adhesive layer that has good electrical properties (dielectric properties) compatible with 5G, exhibits good adhesion even to low-dielectric substrate films with poor adhesion, and combines heat resistance and chemical resistance (solvent resistance).

As a result of extensive research into solving the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by adding an amino group-containing styrene-based elastomer, a bismaleimide resin, and a benzoxazine resin to the adhesive composition, and thus completed the present invention.

The present invention includes the following aspects.
[1] An adhesive composition containing a styrene-based elastomer, a bismaleimide resin, and a benzoxazine resin,
The adhesive composition, wherein the styrene-based elastomer contains an amino group-containing styrene-based elastomer.
[2] The adhesive composition according to [1], containing 30 to 80 parts by mass of the amino group-containing styrene-based elastomer per 100 parts by mass of the adhesive composition.
[3] The adhesive composition according to [1] or [2], containing 5 to 50 parts by mass of the bismaleimide resin per 100 parts by mass of the adhesive composition.
[4] The adhesive composition according to any one of [1] to [3], containing 1 to 25 parts by mass of the benzoxazine resin per 100 parts by mass of the adhesive composition.
[5] The adhesive composition according to any one of [1] to [4], wherein the melting point or softening point of the bismaleimide resin is lower than 120°C.
[6] The adhesive composition according to any one of [1] to [5], wherein the adhesive composition contains at least two or more types of styrene-based elastomers.
[7] The adhesive composition according to any one of [1] to [6], wherein the styrene-based elastomer contains a styrene-based elastomer having a weight average molecular weight of 30,000 to 300,000.
[8] The adhesive composition according to any one of [1] to [7], wherein the styrene-based elastomer contains a styrene-based elastomer having a styrene ratio of 20 to 60.
[9] The adhesive composition according to any one of [1] to [8], wherein the melting point or softening point of the benzoxazine resin is lower than 120°C.
[10] The adhesive composition according to any one of [1] to [9], wherein when the adhesive composition contains an epoxy resin, the content of the epoxy resin per 100 parts by mass of the adhesive composition is less than 10 parts by mass.
[11] The adhesive composition according to any one of [1] to [9], wherein the adhesive composition does not contain an epoxy resin.
[12] An adhesive layer obtained by curing the adhesive composition according to any one of [1] to [11].
[13] The adhesive layer according to [12], wherein the adhesive layer has a relative dielectric constant of 3.5 or less and a dielectric loss tangent of 0.005 or less, measured at a frequency of 28 GHz.
[14] A base film;
[12] or [13], and the adhesive layer according to [14].
[15] The laminate according to [14], wherein the substrate film contains a polyether ether ketone (PEEK) resin.
[16] A coverlay film with an adhesive layer, comprising the laminate according to [14] or [15].
[17] A copper-clad laminate comprising the laminate according to [14] or [15].
[18] A printed wiring board comprising the laminate according to [14] or [15].
[19] A shielding film comprising the laminate according to [14] or [15].
[20] A printed wiring board with a shielding film, comprising the laminate according to [14] or [15].

According to the present invention, an adhesive composition can be provided for forming a low-dielectric adhesive layer that has good electrical properties (dielectric properties) compatible with 5G, exhibits good adhesion even to low-dielectric substrate films with poor adhesion, and combines heat resistance and chemical resistance (solvent resistance).

The adhesive composition of the present invention, a laminate including an adhesive layer made of the adhesive composition, and electronic component-related components including the laminate are described in detail below. However, the description of the constituent elements described below is an example of one embodiment of the present invention and is not intended to be limiting.

(Adhesive composition)
The adhesive composition of the present invention contains a styrene-based elastomer, a bismaleimide resin, and a benzoxazine resin.
The styrene elastomer used in the present invention includes an amino group-containing styrene elastomer.

<Styrene-based elastomer>
The styrene elastomer contained in the adhesive composition contains a modified styrene elastomer. The modified styrene elastomer contains at least an amino group-containing styrene elastomer.
The styrene elastomer used in the present invention may contain a modified styrene elastomer other than the amino group-containing styrene elastomer, or may contain an unmodified styrene elastomer other than the modified styrene elastomer.
The adhesive composition of the present invention preferably contains at least two types of styrene elastomers from the viewpoint of satisfying the various properties required of an adhesive composition.
The styrene elastomer is a copolymer mainly composed of block and random structures of an unsaturated hydrocarbon and an aromatic vinyl compound, and a hydrogenated product 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.

The styrene-based elastomer used in the present invention preferably has a weight-average molecular weight of 30,000 or more, more preferably 70,000 or more. A weight-average molecular weight of 30,000 or more can exhibit excellent adhesive properties. A weight-average molecular weight of 70,000 or more improves film-forming properties when dissolved in a solvent and applied, reducing the occurrence of thickness unevenness due to pinholes and dripping, thereby minimizing performance variations on the coated surface and reducing the likelihood of insufficient adhesion and chemical resistance. This also facilitates thickness control, which is important when fabricating printed wiring boards. Furthermore, it is preferable to contain a styrene-based elastomer with a weight-average molecular weight of 100,000 or more. When a styrene-based elastomer with a weight-average molecular weight of 100,000 or more is contained, excessive resin flow of the adhesive composition that would deviate from the design size can be suppressed even when stress is applied during thermocompression bonding during printed wiring board fabrication. The weight-average molecular weight of the styrene-based elastomer is preferably 300,000 or less, and more preferably 200,000 or less. A weight-average molecular weight of 300,000 or less improves compatibility between the bismaleimide resin and the benzoxazine resin, resulting in excellent chemical resistance. A weight-average molecular weight of 200,000 or less can suppress an increase in viscosity when dissolved in a solvent and applied, improving leveling properties and allowing for film formation with a smooth surface. As a result, there is little variation in performance on the coated surface, and insufficient adhesion or chemical resistance is unlikely to occur, making it easier to control thickness, which is important when fabricating printed wiring boards.
The weight average molecular weight is a value obtained by measuring the molecular weight by gel permeation chromatography (hereinafter also referred to as "GPC") and converting it into polystyrene equivalent.
Furthermore, the styrene-based elastomer used in the present invention preferably has a styrene ratio of 20 or more, more preferably 30 or more. A styrene ratio of 20 or more allows excellent adhesive properties to be exhibited. A styrene ratio of 30 or more allows the adhesive composition to exhibit heat resistance. Furthermore, it is preferable to contain a styrene-based elastomer having a styrene ratio of 40 or more. When a styrene-based elastomer having a styrene ratio of 40 or more is contained, the compatibility between the bismaleimide resin and the benzoxazine resin is improved, allowing excellent adhesive properties and chemical resistance to be exhibited. The styrene ratio of the styrene-based elastomer is preferably 80 or less, more preferably 60 or less. A styrene ratio of 80 or less increases fluidity during heating, allowing the elastomer to sufficiently conform to the surface of the substrate film and exhibit excellent adhesive strength. A styrene ratio of 60 or less makes it easy to procure the styrene-based elastomer.
When two or more types of styrene elastomers are contained, it is preferable that the styrene ratio of at least one of the styrene elastomers is 40 or more.

Examples of styrene-based elastomers include styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-ethylene copolymers, their random copolymers, block copolymers, and hydrogenated products thereof. As the styrene-based elastomer, a hydrogenated product of a styrene-butadiene block copolymer is preferred. The hydrogenated product of a styrene-butadiene block copolymer has a block structure mainly composed of styrene that can improve compatibility with bismaleimide resins and benzoxazine resins, and the block structure mainly derived from butadiene imparts high flexibility, thereby enabling the development of excellent adhesive properties.
Specific examples of the styrene-based elastomer include a styrene-butadiene block copolymer, a styrene-ethylene propylene block copolymer, a styrene-butadiene-styrene block copolymer, a styrene-isoprene-styrene block copolymer, a styrene-ethylenebutylene-styrene block copolymer, and a styrene-ethylene propylene-styrene block copolymer.
These styrene elastomers may be used alone or in combination of two or more.
Among the above copolymers, styrene-ethylene butylene-styrene block copolymers and styrene-ethylene propylene-styrene block copolymers are preferred for the above reasons, as well as from the viewpoints that they can impart electrical properties (dielectric properties) to the adhesive composition, and that the molecular structure can be relatively easily controlled, making it easy to adjust the properties of the adhesive composition.
The styrene elastomer of the present invention includes modified styrene elastomers in which a substituent has been introduced into the above structure, and unmodified styrene elastomers in which no substituent has been introduced.

<<Modified styrene-based elastomer>>
The adhesive composition of the present invention contains a modified styrene-based elastomer, which reacts with the bismaleimide resin, benzoxazine resin, crosslinking agent, etc., described below, and cures to exhibit excellent adhesion and chemical resistance. Furthermore, because the introduced substituents have a strong interaction with metals, the inclusion of the modified styrene-based elastomer improves the adhesive strength between the adhesive composition and metal substrates.
Modified styrene elastomers are copolymers primarily consisting of block and random structures of unsaturated hydrocarbons and aromatic vinyl compounds, and hydrogenated products thereof, to which substituents such as carboxyl groups, amino groups, epoxy groups, isocyanate groups, acryloyl groups, hydroxyl groups, mercapto groups, imide groups, and alkoxysilyl groups have been introduced.
The adhesive composition of the present invention contains, as the modified styrene-based elastomer, a styrene-based elastomer containing at least an amino group.
The adhesive composition of the present invention may contain modified styrene elastomers other than the amino group-containing styrene elastomer, as long as the effects of the present invention are not impaired.

<<<Styrene-based elastomer containing amino groups>>>
The adhesive composition contains a styrene-based elastomer containing an amino group, which exhibits strong interaction with the low-dielectric substrate film, and the amino group enhances the reactivity of the adhesive composition, thereby improving the adhesiveness of the adhesive composition. Furthermore, because the styrene-based elastomer containing an amino group is reactive, it reacts with the bismaleimide resin and the benzoxazine resin, and hardens to form a three-dimensional crosslinked structure, improving the heat resistance and chemical resistance of the adhesive composition.
The amino group improves adhesion to metals.
The amino group-containing styrene elastomer is a copolymer mainly consisting of block and random structures of unsaturated hydrocarbons and aromatic vinyl compounds, and a hydrogenated product thereof, which is modified with an amine.

There are no particular limitations on the method for amine-modifying a styrene-based elastomer, and known methods can be used. Examples include a method of amine-modifying a (hydrogenated) block copolymer by polymerizing it using a polymerization initiator having an amino group, a method of amine-modifying a (hydrogenated) copolymer by using an unsaturated monomer having an amino group as a copolymerization raw material, and a method of amine-modifying a styrene-based elastomer containing a carboxyl group by reacting it with an amine modifier having two or more amino groups to form an amide structure or an imide structure.

Specific examples of styrene-based elastomers containing amino groups include those in which amino groups have been introduced into the aforementioned styrene-based elastomers.

From the viewpoint of ensuring good electrical properties (low dielectric constant, low dielectric loss) and adhesion (adhesion) of the adhesive composition, the total nitrogen content in the amino group-containing styrene-based elastomer is preferably 50 to 5000 ppm, and more preferably 200 to 3000 ppm. When the total nitrogen content is equal to or greater than the above lower limit, excellent adhesion can be achieved. When the total nitrogen content is equal to or less than the above upper limit, excellent electrical properties can be achieved.
The total nitrogen content in the amino group-containing styrene elastomer can be determined in accordance with JIS-K2609 using a trace nitrogen analyzer ND-100 (manufactured by Mitsubishi Chemical Corporation).

From the perspective of achieving both chemical resistance and heat resistance, the content of the amino group-containing styrene-based elastomer in the adhesive composition is preferably 30 to 80 parts by mass per 100 parts by mass of the adhesive composition of the present invention. From the perspective of further improving chemical resistance, the content is more preferably 40 to 70 parts by mass.

<<<Carboxy group-containing styrene elastomer>>>
Carboxy group-containing styrene elastomers are effective as a component that imparts electrical properties in addition to adhesive properties and flexibility to the cured product.
Carboxy group-containing styrene elastomers are copolymers mainly consisting of block and random structures of unsaturated hydrocarbons and aromatic vinyl compounds, and hydrogenated products thereof, which are modified with unsaturated carboxylic acids.
The types of aromatic vinyl compounds and unsaturated hydrocarbons and specific examples of styrene-based elastomers are as described above in the section <Styrene-based elastomers>.

The modification of a carboxyl group-containing styrene elastomer can be carried out, for example, by copolymerizing an unsaturated carboxylic acid during polymerization of the styrene elastomer, or by heating and kneading the styrene elastomer and the unsaturated carboxylic acid in the presence of an organic peroxide.
Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid, maleic anhydride, and itaconic anhydride.
The amount of modification with the unsaturated carboxylic acid is preferably 0.1 to 10% by mass.
The acid value of the carboxyl group-containing styrene-based elastomer is preferably 0.1 to 25 mgKOH/g, and more preferably 0.5 to 23 mgKOH/g. When this acid value is 0.1 mgKOH/g or more, the adhesive composition cures sufficiently, and good adhesion and heat resistance are obtained. On the other hand, when the acid value is 30 mgKOH/g or less, the cohesive strength of the adhesive composition is suppressed, resulting in excellent adhesion and excellent electrical properties.

<<Unmodified styrene-based elastomer>>
The adhesive composition of the present invention may contain an unmodified styrene elastomer in addition to the modified styrene elastomer.
The unmodified styrene elastomer may be used alone or in combination of two or more.

The unmodified styrene elastomer is a copolymer mainly composed of block and random structures of an unsaturated hydrocarbon and an aromatic vinyl compound, and a hydrogenated product thereof.
The low number of highly polar bonding groups in the molecule gives the composition good electrical properties (dielectric properties). Another advantage is that, compared to other types of elastomers, the molecular weight can be easily controlled, allowing for stable production of adhesive compositions with consistent properties.
The types of aromatic vinyl compounds and unsaturated hydrocarbons and specific examples of styrene-based elastomers are as described above in the section <Styrene-based elastomers>.

The content of unmodified styrene-based elastomer per 100 parts by mass of amino group-containing styrene-based elastomer is preferably 35 to 100 parts by mass. If the content of unmodified styrene-based elastomer per 100 parts by mass of amino group-containing styrene-based elastomer is within the above range, the incorporation of the unmodified styrene-based elastomer is likely to produce the effect of adjusting the elastic modulus and flowability of the adhesive composition.

The weight-average molecular weight (Mw) of the unmodified styrene-based elastomer is preferably 100,000 or more, and more preferably 100,000 to 200,000. Within this range, it is possible to achieve both control of fluidity and adhesion.

The unmodified styrene-based elastomer used in the present invention preferably has a styrene ratio of 40 to 80. When a styrene-based elastomer with a styrene ratio of 40 or more is contained, the compatibility between the bismaleimide resin and the benzoxazine resin is improved, resulting in excellent adhesion and chemical resistance.

<Bismaleimide resin>
Bismaleimide resins have good metal adhesion, contain unsaturated bonds, and are capable of crosslinking. The adhesive composition of the present invention containing a bismaleimide resin has a high crosslink density and is excellent in heat resistance, solvent resistance, and the like.
Because the bismaleimide resin contains an imide skeleton, it imparts high metal adhesion to the adhesive composition and makes it difficult for acids or bases to penetrate between the cured product of the adhesive composition and the metal, thereby improving chemical resistance.
The bismaleimide resin reacts with the amino group-containing styrene-based elastomer or benzoxazine resin to form a crosslinked structure, which increases the crosslink density of the adhesive composition, thereby enabling the adhesive composition to exhibit high adhesion to adherends and heat resistance in a cured adhesive material.

Examples of bismaleimide resins include 1-methyl-2,4-bismaleimidebenzene, N,N'-m-phenylene bismaleimide, N,N'-p-phenylene bismaleimide, N,N'-m-toluylene bismaleimide, N,N'-4,4-biphenylene bismaleimide, N,N'-4,4-(3,3'-dimethyl-biphenylene) bismaleimide, and N,N'-4,4-(3,3'-dimethyldiphenylmethane) bismaleimide. , N,N'-4,4-(3,3'-diethyldiphenylmethane)bismaleimide, N,N'-4,4-diphenylmethane bismaleimide, N,N'-4,4-diphenylpropane bismaleimide, N,N'-4,4-diphenylether bismaleimide, N,N'-3,3-diphenylsulfone bismaleimide, and the like, as well as polymers obtained by polymerizing amine-modified products such as dimer acid and trimer acid with maleic anhydride, pyromellitic acid, or the like.

The melting point or softening point of the bismaleimide resin is preferably less than 120°C from the viewpoints of imparting fluidity to the adhesive composition at the temperature of thermal lamination or thermal pressing, allowing the adhesive composition to conform sufficiently to the surface of the substrate film or metal substrate, and exhibiting excellent adhesion and chemical resistance during curing.
From the viewpoint of achieving both chemical resistance and heat resistance, the content of the bismaleimide resin in the adhesive composition is preferably 5 to 50 parts by mass per 100 parts by mass of the adhesive composition. The content of the bismaleimide resin in the adhesive composition is more preferably 12 parts by mass or more per 100 parts by mass of the adhesive composition. When the content of the bismaleimide resin is 12 parts by mass or more, the adhesive composition can be imparted with appropriate fluidity even when mixed with a styrene-based elastomer having a high styrene ratio, and it is possible to achieve both suppression of resin flow and the expression of high chemical resistance due to conformity to the substrate surface.
The bismaleimide resin used in the present invention preferably has a weight-average molecular weight of 3,000 or more, more preferably 5,000 or more. A weight-average molecular weight of 3,000 or more can impart appropriate flexibility to the cured product of the adhesive composition. A weight-average molecular weight of 5,000 or more can exhibit excellent adhesive properties. The bismaleimide resin preferably has a weight-average molecular weight of 20,000 or less, more preferably 15,000 or less. A weight-average molecular weight of 20,000 or less can contain an imide skeleton that can exhibit sufficient metal adhesion. A weight-average molecular weight of 15,000 or less improves the compatibility between the styrene-based elastomer and the benzoxazine resin, thereby improving chemical resistance.

<Benzoxazine resin>
The benzoxazine resin reacts with the styrene-based elastomer or bismaleimide resin to increase the crosslink density of the adhesive composition, thereby enabling the adhesive composition to exhibit high adhesion to the adherend and heat resistance of the cured adhesive. The benzoxazine resin reacts with the styrene-based elastomer or bismaleimide resin to form a crosslinked structure.
The benzoxazine preferably has a structure containing two or more oxazine skeletons in the molecule, from the viewpoint of increasing the content of the styrene-based elastomer or bismaleimide resin, which has high adhesiveness, while improving the crosslink density.

Examples of benzoxazine resins include 6,6-(1-methylethylidene)bis(3,4-dihydro-3-phenyl-2H-1,3-benzoxazine) and 6,6-(1-methylethylidene)bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazine), and two or more may be combined. The nitrogen atom in the oxazine ring may be bonded to a phenyl group, methyl group, cyclohexyl group, or the like. Specific examples of benzoxazine resins include "Benzoxazine F-a," "Benzoxazine P-d," and "Benzoxazine ALP-d," all manufactured by Shikoku Chemicals Corporation.

The melting point or softening point of the benzoxazine resin is preferably less than 120°C from the viewpoints of imparting fluidity to the adhesive composition at the temperature of thermal lamination or thermal pressing, allowing the adhesive composition to conform sufficiently to the surface of the substrate film or metal substrate, and exhibiting excellent adhesion and chemical resistance during curing.
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 and improving the adhesive strength.
Furthermore, from the viewpoint of exhibiting chemical resistance and heat resistance, the content of the benzoxazine resin in the adhesive composition is preferably 1 part by mass or more per 100 parts by mass of the adhesive composition. Furthermore, the content of the benzoxazine resin is preferably 25 parts by mass or less, and more preferably 15 parts by mass or less. When the content of the benzoxazine resin is 25 parts by mass or less, excellent chemical resistance to the substrate film can be exhibited. When the content of the benzoxazine resin is 15 parts by mass or less, excellent dielectric properties can be exhibited. When the content of the benzoxazine resin is 10 parts by mass or less, the dielectric properties can be further improved.

The adhesive composition of the present invention may contain, in addition to the styrene-based elastomer, resin components other than the styrene-based elastomer or other components.

<Other resin components>
The adhesive composition of the present invention may contain other resin components in addition to the styrene-based elastomer, bismaleimide resin, and benzoxazine resin.
The adhesive composition according to the present invention may contain, for example, a thermoplastic resin other than the styrene-based elastomer to an extent that the function of the adhesive composition is not affected.
Examples of the other thermoplastic resins include phenoxy resins, polyamide resins, polyester resins, polycarbonate resins, polyphenylene oxide resins, polyurethane resins, polyacetal resins, polyethylene-based resins, polypropylene-based resins, polybutadiene-based resins, polyvinyl-based resins, etc. These thermoplastic resins may be used alone or in combination of two or more.

<Other ingredients>
The resin composition used in the present invention may contain other components in addition to the resin components such as the styrene-based elastomer, bismaleimide resin, benzoxazine resin and the other resin components described above.
Examples of other components include a crosslinking agent that reacts with the styrene elastomer, bismaleimide resin, or benzoxazine resin to form a crosslinked structure. If necessary, a reaction accelerator may be included to accelerate the reaction between the styrene elastomer, bismaleimide resin, or benzoxazine resin and the crosslinking agent.
In addition to the above, other components include, for example, fillers, tackifiers, flame retardants, heat aging inhibitors, leveling agents, antifoaming agents, inorganic fillers, and pigments. These may be contained to an extent that they do not affect the functionality of the adhesive composition.

<<Crosslinking agent>>
Examples of the crosslinking agent include epoxy resins, isocyanate resins, phenolic resins, cyanate resins, polyamides, polyurethanes, organic peroxides, silane coupling agents, etc. Only one type of crosslinking agent may be used, or two or more types may be contained.
[0033] The adhesive composition of the present invention contains a bismaleimide resin or benzoxazine resin that can react with the styrene-based elastomer to form a good crosslinked structure. Therefore, in order to effectively utilize the bismaleimide in curing the oxazine, it is preferable that the adhesive composition contains almost no or no crosslinking agent for the epoxy resin. The content of the epoxy resin in the adhesive composition is preferably less than 10 parts by mass, more preferably less than 5 parts by mass, and even more preferably less than 1 part by mass, per 100 parts by mass of the adhesive composition. It is desirable that the adhesive composition contains substantially no epoxy resin or no epoxy resin at all. If the epoxy resin content is less than the above value, it is possible to reduce the dielectric properties.

<<Filler>>
The adhesive composition of the present invention preferably contains a filler.
As the filler according to the present invention, inorganic fillers are preferred from the viewpoint of heat resistance and control of the mechanical properties of the adhesive composition, and as inorganic fillers, silicon-based inorganic fillers and boron nitride are preferred from the viewpoint of electrical properties. Furthermore, as silicon-based inorganic fillers, for example, mica and talc are preferred, which enable control of the mechanical properties of the adhesive composition even with a small amount and also have excellent electrical properties.
Furthermore, as the filler according to the present invention, an organic filler is preferred from the viewpoint of, for example, dispersibility and brittleness, and as the organic filler, a styrene-based spherical filler is preferred from the viewpoint of electrical properties, and a styrene-based hollow filler is more preferred.
These may be used alone or in combination of two or more.
The content of the filler contained in the adhesive composition of the present invention is preferably 0.5 to 25 parts by volume, and more preferably 1 to 15 parts by volume, per 100 parts by volume 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 a spherical inorganic filler or a non-spherical inorganic filler, but from the viewpoint of the coefficient of thermal expansion (CTE) and film strength, a non-spherical inorganic filler is preferred. The shape of the non-spherical inorganic filler may be any three-dimensional shape other than a spherical shape (approximately perfect sphere), and examples thereof include plate-like, scale-like, columnar, chain-like, and fibrous shapes. Among these, from the viewpoint of the coefficient of thermal expansion (CTE) and film strength, plate-like and scale-like inorganic fillers are preferred, and plate-like inorganic fillers are more preferred.

Examples of the tackifier include coumarone-indene resin, terpene resin, terpene-phenol resin, rosin resin, p-t-butylphenol-acetylene resin, phenol-formaldehyde resin, xylene-formaldehyde resin, petroleum-based hydrocarbon resin, hydrogenated hydrocarbon resin, and turpentine-based resin. These tackifiers may be used alone or in combination of two or more.

The above 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 amido phosphate, ammonium amido polyphosphate, carbamate phosphate, carbamate polyphosphate, aluminum trisdiethylphosphinate, aluminum trismethylethylphosphinate, aluminum trisdiphenylphosphinate, zinc bisdiethylphosphinate, zinc bismethylethylphosphinate, zinc bisdiphenylphosphinate, titanyl bisdiethylphosphinate, titanium tetrakisdiethylphosphinate, titanyl bismethylethylphosphinate, titanium tetrakismethylethylphosphinate, titanyl bisdiphenylphosphinate, and titanium tetrakisdiphenylphosphinate; nitrogen-based flame retardants such as triazine-based compounds such as melamine, melam, and melamine cyanurate, cyanuric acid compounds, isocyanuric acid compounds, triazole-based 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; zinc carbonate, magnesium carbonate, barium carbonate, zinc borate, and hydrated glass. Two or more of these flame retardants can be used in combination.

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, triethylene glycol-bis[3 phenol-based antioxidants such as 3-(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 alone or in combination of two or more.

Examples of the inorganic filler include powders made of titanium oxide, aluminum oxide, zinc oxide, carbon black, silica, copper, silver, etc. These may be used alone or in combination of two or more.

(adhesive layer)
The adhesive layer according to the present invention is formed using the adhesive composition according to the present invention.
The adhesive composition that forms the adhesive layer is allowed to cure.
The curing method is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include thermal curing.
The thickness of the adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. 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 exerted, and if it is 5 μm or more, it can follow the steps of the pattern of the printed wiring board. If the thickness of the adhesive layer is 50 μm or less, the laminate can be made thinner, and if it is 30 μm or less, the resin flow can be accurately controlled.

<Method of manufacturing adhesive layer>
An adhesive layer can be produced by forming the adhesive composition into a film.
The adhesive composition can be produced by mixing the above-mentioned styrene-based elastomer, bismaleimide resin, and benzoxazine resin. The mixing method is not particularly limited as long as the adhesive composition becomes homogeneous. Since the adhesive composition is preferably used in the form of a solution or dispersion, 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 alone or in combination of two or more. Adding a small amount of cyclohexanone to toluene, which is particularly capable of dissolving low-polarity resins, improves compatibility with curing agents and the like, allowing for a uniform adhesive layer.
When the adhesive composition is a solution or dispersion containing a solvent (resin varnish), coating onto a substrate film and formation of an 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 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 is 80% by mass or less, the viscosity of the solution is appropriate, and uniform application is facilitated.
In a more specific embodiment of the method for producing an adhesive layer, a resin varnish containing the adhesive composition and a solvent is applied to the surface of a substrate film to form a resin varnish layer, and then the solvent is removed from the resin varnish layer to form a B-stage adhesive layer. Here, the B-stage adhesive layer refers to an adhesive composition in an uncured state or a semi-cured state in which a portion of the adhesive composition has begun to cure, and refers to a state in which curing of the adhesive composition progresses further by heating or the like.
Here, the method for applying the resin varnish onto the substrate film is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include spraying, spin coating, dipping, roll coating, blade coating, doctor roll method, doctor blade method, curtain coating, slit coating, screen printing, inkjet method, and dispensing method.
The adhesive layer in the B-stage state can be further heated or the like to form a cured adhesive layer.

<Characteristics of the adhesive layer>
The adhesive layer obtained by curing the adhesive composition of the present invention preferably has a relative dielectric constant (εr) of 3.5 or less, more preferably 2.7 or less at a frequency of 28 GHz, and preferably has a dielectric loss tangent (tanδ) of 0.005 or less, more preferably 0.0025 or less, and even more preferably 0.0015 or less at a frequency of 28 GHz.
If the dielectric constant is 3.5 or less and the dielectric dissipation factor is 0.005 or less, the material can be used in high-frequency FPC-related products that require strict electrical properties. Furthermore, if the dielectric constant is 2.7 or less and the dielectric dissipation factor is 0.0025 or less, the material can satisfy the electrical properties expected of components of 5G-compatible high-frequency FPC-related products, exhibiting electrical properties equivalent to those of LCP, making it suitable for use in 5G high-frequency FPC-related products that require strict electrical properties. Furthermore, if the dielectric dissipation factor is 0.0015 or less, the material can be suitable for use in high-frequency FPC-related products that utilize millimeter waves.

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

(Laminate)
The laminate of the present invention comprises a substrate film and the above-described adhesive layer on at least one surface of the substrate film.

<Base film>
The substrate 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 a copper-clad laminate (CCL), examples of the substrate film include polyimide films, polyether ether ketone films, polyphenylene sulfide films, aramid films, polyethylene naphthalate films, liquid crystal polymer films, polyphenylene ether films, and syndiotactic polystyrene films. Among these, polyimide films, polyether ether ketone (PEEK) films, polyethylene naphthalate films, and liquid crystal polymer films are preferred from the viewpoints of adhesiveness and electrical properties.
The storage modulus of the base film at 200°C is preferably 1 x ¹⁰ or more. Resin flow is accompanied by deformation of the edges of the base film, and the greater the deformation, the greater the resin flow. Therefore, the higher the storage modulus at the compression bonding temperature, the more the resin flow of the adhesive composition can be suppressed.

Furthermore, when the laminate of the present invention is used as a bonding sheet, the base film must be a release film, such as polyethylene terephthalate film, polyethylene film, polypropylene film, silicone release-treated paper, polyolefin resin-coated paper, TPX (polymethylpentene) film, and fluorine-based resin film.

When the laminate of the present invention is used as a shielding film, the base film must be a film with electromagnetic wave shielding ability, such as a laminate of a protective insulating layer and a metal foil.

(Coverlay film)
A preferred embodiment of the laminate according to the present invention is a coverlay film.
When manufacturing an FPC, a laminate with an adhesive layer called a "coverlay film" is usually used to protect the wiring portion. This coverlay film has an insulating resin layer and an adhesive layer formed on the surface of the insulating resin layer.
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 peeling of the base film and the adhesive layer is generally difficult.
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 equal to or less than the upper limit, the coverlay film can be made thinner. If the thickness of the base film is equal to or greater than the lower limit, the printed wiring board can be easily designed and handled.
As a method for producing a coverlay film, for example, a resin varnish containing the adhesive composition and a solvent is applied to the surface of the base film to form a resin varnish layer, and then the solvent is removed from the resin varnish layer, thereby producing a coverlay film having a B-stage adhesive layer formed thereon.
The drying temperature when removing the solvent is preferably 40 to 250°C, more preferably 70 to 170°C.
Drying is carried out by passing the laminate coated with the adhesive composition through a furnace in which hot air drying, far infrared heating, high frequency induction heating, or the like is performed.
If necessary, a release film may be laminated on the surface of the adhesive layer for storage, etc. As the release film, known films such as polyethylene terephthalate film, polyethylene film, polypropylene film, silicone release-treated paper, polyolefin resin-coated paper, TPX film, and fluorine-based resin film can be used.
The coverlay film according to the present invention uses the low-dielectric adhesive composition of the present invention, which enables high-speed transmission in electronic devices and also provides excellent adhesion stability to electronic devices.

(Bonding sheet)
A preferred embodiment of the laminate according to the present invention is a bonding sheet.
The bonding sheet is a sheet in which the adhesive layer is formed on the surface of a release film (substrate film). The bonding sheet may also be in a form in which the adhesive layer is provided between two release films. When using the bonding sheet, the release film is peeled off. The release film may be the same as that described in the above (coverlay film) section.
The thickness of the substrate 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 substrate film is within the above range, the bonding sheet is easy to manufacture and easy to handle.
A bonding sheet can be produced, for example, by applying a resin varnish containing the adhesive composition and a solvent to the surface of a release film and drying it in the same manner as in the case of the coverlay film.
The bonding sheet according to the present invention uses the low-dielectric adhesive composition of the present invention, which enables high-speed transmission in electronic devices and also provides excellent adhesive stability to electronic devices.

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

One method for producing a copper-clad laminate is to bring the adhesive layer of the laminate into face-to-face contact with copper foil, thermally laminate the laminate at 80°C to 200°C, and then cure the adhesive layer by after-curing. After-curing conditions can be, for example, 100°C to 200°C in an inert gas atmosphere for 30 minutes to 4 hours. The copper foil is not particularly limited, and electrolytic copper foil, rolled copper foil, etc. can be used.

(Printed wiring board)
A preferred embodiment of the laminate of the present invention is a printed wiring board obtained by laminating copper wiring to the adhesive layer in the laminate of the present invention.
A printed wiring board can be obtained by forming an electronic circuit on the copper-clad laminate.
The printed wiring board is formed by bonding a base film and copper wiring using the 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 wiring board is manufactured by using a heat press or the like to attach a coverlay film via an adhesive layer to a surface having wiring portions.
The printed wiring board according to the present invention uses the low-dielectric adhesive composition of the present invention, and therefore enables high-speed transmission in electronic devices and has excellent adhesive stability.
A method for producing the printed wiring board according to the present invention includes, for example, contacting the adhesive layer of the laminate with copper wiring, 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 and 30 minutes to 4 hours. The shape of the copper wiring is not particularly limited, and an appropriate shape can be selected as desired.

(Shielding film)
A preferred embodiment of the laminate according to the present invention is a shielding film.
Shielding film is a film used to shield various electronic devices, such as computers, mobile phones, and analytical equipment, in order to cut out electromagnetic noise that can affect these devices and cause them to malfunction. It is also called electromagnetic wave shielding film.
The electromagnetic wave shielding film is formed by laminating, for example, an insulating resin layer, a metal layer, and the adhesive layer according to the present invention in this order.
The shielding film of the present invention uses the low-dielectric adhesive composition of the present invention, which enables high-speed transmission in electronic devices and also provides excellent adhesion stability to electronic devices.

(Printed wiring board with shielding film)
A preferred embodiment of the laminate according to the present invention is a printed wiring board with a shielding film.
A printed wiring board with a shielding film is a printed wiring board having a printed circuit provided on at least one surface of the substrate, and the electromagnetic wave shielding film is attached to the printed wiring board.
A printed wiring board with a shielding film includes, for example, a printed wiring board, an insulating film adjacent to the surface of the printed wiring board on which the printed circuit is provided, and the electromagnetic wave shielding film.
The printed wiring board with a shielding film according to the present invention uses the low-dielectric adhesive composition of the present invention, and therefore enables high-speed transmission in electronic devices and has excellent adhesive stability.

The present invention will be described in further detail below with reference to examples, but the scope of the present invention is not limited to these examples. In the following, parts and percentages are by weight unless otherwise specified.

(Amino group-containing styrene elastomer)
The product used was "Tuftec MP10" (amine-modified hydrogenated styrene-butadiene copolymer (amine-modified styrene-ethylene butylene-styrene copolymer) manufactured by Asahi Kasei Corporation. The styrene ratio of this copolymer was 30, and the weight-average molecular weight was 78,000. The total nitrogen content of this copolymer was 430 ppm (μg/g).
(Unmodified styrene elastomer)
Kraton A1535 (hydrogenated styrene-butadiene copolymer) was used. The acid value of this copolymer was 0 mgKOH/g, and the weight average molecular weight was 135,700. The styrene ratio of this copolymer was 58.
(Unmodified styrene elastomer)
The copolymer used was "Tuftec P1500" (hydrogenated styrene-based elastomer) manufactured by Asahi Kasei Corp. The copolymer had an acid value of 0 mgKOH/g, a styrene ratio of 30, and a weight average molecular weight of 67,000.
(Carboxy group-containing styrene elastomer)
Kraton FG1901 (maleic acid-modified hydrogenated styrene-butadiene copolymer (maleic acid-modified styrene-ethylene butylene-styrene copolymer)) manufactured by Kraton Corporation was used. The copolymer had an acid value of 19 mg KOH/g, a styrene ratio of 30, and a weight-average molecular weight of 81,000.
(bismaleimide resin)
The product used was "SLK-3000-T50" manufactured by Shin-Etsu Chemical Co., Ltd. It had a softening point of 40°C and a weight average molecular weight of 12,545.
(bismaleimide resin)
The product used was "SLK-2600-A50" manufactured by Shin-Etsu Chemical Co., Ltd. It had a softening point of 120°C and a weight average molecular weight of 10,603.
(benzoxazine resin)
A product name "ALP-d" (liquid) manufactured by Shikoku Chemicals Corporation was used.
(benzoxazine resin)
The product used was "Pd" manufactured by Shikoku Chemicals Corporation, Ltd. Its softening point was 80°C.
(Epoxy modified resin)
The product used was "Epofriend CT310" (epoxidized styrene-butadiene block copolymer) manufactured by Daicel Corporation. The styrene/ethylene-butylene ratio of this copolymer was 40/60, the weight-average molecular weight was 93,000, and the epoxy equivalent was 2125 g/eq.
(solvent)
A mixed solvent of toluene and cyclohexanone (mass ratio = 97:3) was used.
(Base film)
The substrate film used was "Shin-Etsu Sepla Film PEEK" (polyether ether ketone, thickness 50 μm) manufactured by Shin-Etsu Polymer Co., Ltd. The storage modulus of the substrate film at 200° C. was 5×10 ⁸ .
(electrolytic copper foil)
The electrolytic copper foil used was "TQ-M7-VSP" manufactured by Mitsui Mining & Smelting Co., Ltd. (electrolytic copper foil, thickness 12 μm, shiny side Rz 1.27 μm, shiny side Ra 0.197 μm, shiny side Rsm 12.95 μm). The surface roughness of the shiny side was determined from a roughness curve measured using a laser microscope in accordance with JIS B 0601:2013 (ISO 4287:1997 Amd.1:2009).
(Release film)
As the release film, NP75SA (silicone release PET film, 75 μm) manufactured by Panac Corporation was used.

Example 1
Each component constituting the adhesive layer shown in Table 1-1 was contained in the proportion shown in Table 1-1, and these components were dissolved in a solvent to prepare a resin varnish, which was an adhesive composition with a solid content concentration of 15 mass %.
The components constituting the resin composition in the adhesive composition are as shown in Table 1-1.

The relative dielectric constant and dielectric loss tangent at a frequency of 28 GHz were measured for the adhesive layer obtained by curing using the resin varnish of Example 1.

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

Using the resin varnish of Example 1, a cured adhesive laminate was prepared using the following method.

<Laminate with adhesive after curing>
The surface of the substrate film was subjected to a corona treatment.
The resin varnish prepared above was applied to the surface of a substrate film, dried in an oven at 130°C for 4 minutes, and the solvent was evaporated to form an adhesive layer (15 μm), yielding an adhesive-attached substrate film (adhesive-attached laminate). The adhesive layer of the adhesive-attached laminate was placed in contact with the shiny side 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 200°C for 1 hour to cure the adhesive layer, yielding a cured adhesive-attached laminate.

For the cured adhesive-attached laminate of Example 1, the adhesion strength (N/cm) between the electrolytic copper foil and the base film was measured.
The cured adhesive laminate of Example 1 was subjected to a chemical resistance test.

[Adhesion strength (N/cm)]
The adhesion strength was measured by cutting the cured adhesive-attached laminate into a 25 mm wide test specimen, and measuring the peel strength when peeling the electrolytic copper foil from the adhesive-attached base film fixed to a support at a peel speed of 0.3 m/min and a peel angle of 180° in accordance with JIS Z0237:2009 (Test methods for adhesive tapes and adhesive sheets).

[Chemical resistance test]
For the chemical resistance test, the cured adhesive laminate was cut into 30 mm × 30 mm test pieces, which were immersed in a 10% HCl solution for 1 hour, then in a 10% NaOH solution for 1 hour, and then in _a 10% _H2SO4 solution for 1 hour, and the chemical resistance was evaluated according to the following criteria.
No peeling occurs.
There is some peeling at the corners.
Peeling is also observed on the edges.
× Completely peeled off.

[Resin flow (resin outflow) (mm)]
The adhesive laminate was cut into a 30 mm x 90 mm test piece, and three 5 mm diameter holes were punched in it using a belt punch.
The adhesive layer was cured by placing the adhesive layer on the shiny side of the electrolytic copper foil so as to contact the shiny side, pressing the adhesive layer using a vacuum press at 180°C under a pressure (3 MPa) of 10 hPa for 3 minutes, and then after-curing at 200°C for 1 hour. The length of the resin protruding onto the copper foil was measured at 12 points (4 points x 3 locations) using a microscope, and the average value was recorded.
Microscope (KEYENCE Digital Microscope VHX-500): Lens magnification 300x

The measurement results are shown in Table 1-2.

(Examples 2 to 10)
Laminates of Examples 2 to 10 were prepared in the same manner as in Example 1, except that the types and amounts of components constituting the adhesive layer in Example 1 were changed as shown in Table 1-1.
The laminate thus produced was evaluated in the same manner as in Example 1.
The results are shown in Table 1-2.

(Comparative Examples 1 to 3)
Laminates of Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the types and blending amounts of the components constituting the adhesive layer in Example 1 were changed as shown in Table 1-1.
The laminate thus produced was evaluated in the same manner as in Example 1.
The results are shown in Table 1-2.

As shown in the examples, the adhesive layer made from the adhesive composition of the present invention exhibits good electrical properties (dielectric properties) that are compatible with 5G, and also has excellent adhesion, heat resistance, and chemical resistance (solvent resistance).

Laminates having an adhesive layer made from 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, laptops, and medical devices.

Claims (11)

an adhesive layer made of an adhesive composition containing a styrene-based elastomer, a bismaleimide resin, and a benzoxazine resin;
The styrene-based elastomer contains an amino group - containing styrene-based elastomer ,
the content of the amino group-containing styrene-based elastomer per 100 parts by mass of the adhesive composition is 30 to 80 parts by mass;
the content of the bismaleimide resin is 5 to 50 parts by mass per 100 parts by mass of the adhesive composition;
the content of the benzoxazine resin relative to 100 parts by mass of the adhesive composition is 1 to 25 parts by mass,
The styrene-based elastomer contains a styrene-based elastomer having a weight average molecular weight of 30,000 to 300,000,
The styrene-based elastomer contains a styrene-based elastomer having a styrene ratio of 20 to 60,
The type of the styrene-based elastomer is selected from styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-ethylene copolymers, random copolymers thereof, block copolymers thereof, and hydrogenated products thereof;
The melting point or softening point of the bismaleimide resin is less than 120°C,
The melting point or softening point of the benzoxazine resin is less than 120°C,
The benzoxazine resin has a structure containing two or more oxazine skeletons in the molecule,
The adhesive layer, when cured, has a relative dielectric constant of 3.5 or less and a dielectric loss tangent of 0.005 or less, measured at a frequency of 28 GHz. The adhesive layer according to claim 1 , wherein the adhesive composition contains at least two or more types of styrene-based elastomers. The adhesive layer according to claim 1 , wherein when the adhesive composition contains an epoxy resin, the content of the epoxy resin is less than 10 parts by mass per 100 parts by mass of the adhesive composition. The adhesive layer of claim 1 , wherein the adhesive composition does not contain an epoxy resin. A base film;
A laminate comprising the adhesive layer according to claim 1 . The laminate according to claim 5 , wherein the substrate film contains a polyether ether ketone (PEEK) resin. A coverlay film with an adhesive layer comprising the laminate according to claim 5 . A copper clad laminate comprising the laminate of claim 5 . A printed wiring board comprising the laminate of claim 5 . A shielding film comprising the laminate according to claim 5 . A printed wiring board with a shielding film comprising the laminate according to claim 5 .