JP7716415B2 - 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 one type of electronic component, are required to process large amounts of data at high speed, and progress is being made in supporting high frequencies.
With the practical application of 5G, improvements in communication speeds and frequencies are predicted, requiring the realization of excellent low transmission loss and the stability of large-capacity communication. Accordingly, progress is currently being made in the development of low-dielectric materials for FPCs and adhesives that make up the adhesive layer.

In order to achieve high adhesive properties while maintaining good electrical properties, a laminate has been proposed that uses an adhesive composition containing a carboxyl group-containing styrene-based elastomer (A) and an epoxy resin (B), and that is composed of an adhesive layer made of the adhesive composition and a substrate film (see, for example, Patent Document 1).

International Publication No. 2016/017473

The manufacturing process for printed wiring boards involves a thermocompression bonding process, but if the adhesive has poor mechanical properties, it may not be possible to bond the board to the specified thickness or size.
For example, problems may arise such as resin flow occurring during thermocompression bonding due to the adhesive being soft, or deformation occurring during thermocompression bonding due to a large coefficient of thermal expansion (CTE).
When an inorganic filler is added to prevent the resin from flowing, problems arise such as deterioration of the electrical properties of the adhesive layer or a decrease in the adhesive strength of the adhesive layer.
Therefore, it is desirable to provide a laminate with an adhesive layer that can prevent resin flow during thermocompression bonding by controlling the mechanical properties, exhibits good electrical properties, and has good adhesion between the adhesive layer and the base film.

The present invention aims to provide an adhesive composition that can prevent resin flow during thermocompression bonding by controlling its mechanical properties, exhibits good electrical properties, and can form an adhesive layer with good adhesion.

As a result of extensive research to solve the above problems, the inventors discovered that the above problems could be solved by adding a specific inorganic filler to a styrene-based elastomer, and thus completed the present invention.

The present invention includes the following aspects.
(1) An adhesive composition containing a resin composition containing at least a styrene-based elastomer and an inorganic filler,
the content of the inorganic filler is 1 to 180 parts by mass relative to 100 parts by mass of the resin composition,
the inorganic filler has a plate-like or scaly shape,
An adhesive composition, wherein the adhesive layer obtained by curing the adhesive composition has a relative dielectric constant of 3.5 or less at a frequency of 28 GHz, and a dielectric loss tangent of the adhesive layer at a frequency of 28 GHz of 0.005 or less.
(2) The adhesive composition according to (1), wherein the inorganic filler has an aspect ratio of 5 to 500.
(3) The adhesive composition according to (1) or (2), wherein the inorganic filler has an average particle size of 3.0 μm or less.
(4) The adhesive composition according to any one of (1) to (3), wherein the inorganic filler comprises at least one of a silicon-based inorganic filler and boron nitride.
(5) The adhesive composition according to any one of (1) to (4), wherein the silicon-based inorganic filler contains at least one of mica and talc.
(6) The adhesive composition according to any one of (1) to (5), wherein the styrene-based elastomer is a carboxyl group-containing styrene-based elastomer.
(7) The adhesive composition according to any one of (1) to (5), wherein the styrene-based elastomer is an amino group-containing styrene-based elastomer.
(8) The adhesive composition according to any one of (1) to (7), wherein the resin composition contains an epoxy resin.
(9) The adhesive composition according to (8), wherein the content of the epoxy resin is 1 to 25 parts by mass per 100 parts by mass of the resin composition.
(10) The adhesive composition according to any one of (1) to (9), wherein the adhesive layer of the adhesive composition before curing has a storage modulus of 1.0E+5 Pa or more at 150°C.
(11) The adhesive composition according to any one of (1) to (10), wherein the adhesive layer obtained by curing the adhesive composition has a coefficient of thermal expansion (CTE) of 500 ppm/K or less.
(12) a base film;
and an adhesive layer made of the adhesive composition according to any one of (1) to (10).
(13) The laminate according to (12), wherein the substrate film contains polyether ether ketone (PEEK) resin.
(14) A coverlay film with an adhesive layer, comprising the laminate according to (12) or (13).
(15) A copper-clad laminate comprising the laminate according to (12) or (13).
(16) A printed wiring board comprising the laminate according to (12) or (13).
(17) A shielding film comprising the laminate according to (12) or (13).
(18) A printed wiring board with a shielding film, comprising the laminate according to (12) or (13).

According to the present invention, by controlling the mechanical properties, it is possible to provide an adhesive composition that can prevent resin flow during thermocompression bonding, exhibits good electrical properties, and can form an adhesive layer with good adhesion.

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 resin composition containing at least a styrene-based elastomer and an inorganic filler.
The inorganic filler contained in the adhesive composition of the present invention has a plate-like or scale-like shape.
The content of the inorganic filler contained in the adhesive composition of the present invention is 1 to 180 parts by mass per 100 parts by mass of the resin composition.
The adhesive layer obtained by curing the adhesive composition of the present invention has a relative dielectric constant of 3.5 or less at a frequency of 28 GHz, and a dielectric loss tangent of the adhesive layer at a frequency of 28 GHz of 0.005 or less.
The adhesive composition may contain other components in addition to the resin composition and inorganic filler, as required.

<Resin composition>
The resin composition according to the present invention contains at least a styrene-based elastomer, and among the styrene-based elastomers, it is preferable to contain a styrene-based elastomer containing a carboxy group or a styrene-based elastomer containing an amino group.
The resin composition may contain an epoxy resin.
The resin composition may contain other resin components in addition to the styrene-based elastomer and the epoxy resin, as needed.

<<Styrene-based elastomer>>
Styrene elastomers have excellent electrical properties because they do not contain highly polar bonding groups, and because they have cohesive strength due to the interaction between styrene structures and their molecular weights are easily adjustable, they are resins whose flexibility and adhesive strength can be adjusted. Furthermore, modification can improve the dispersibility and adhesive strength of inorganic fillers.
The styrene elastomer refers to a copolymer mainly composed of a block or random structure of a conjugated diene compound 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, vinyltoluene, etc. Examples of conjugated diene compounds include butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, etc.
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-based elastomers may be used alone or in combination of two or more. Of the above copolymers, styrene-ethylenebutylene-styrene block copolymers and styrene-ethylenepropylene-styrene block copolymers are preferred from the standpoints of adhesiveness and electrical properties. Furthermore, the mass ratio of styrene/ethylenebutylene in the styrene-ethylenebutylene-styrene block copolymer and the mass ratio of styrene/ethylenepropylene in the styrene-ethylenepropylene-styrene block copolymer are preferably 10/90 to 50/50, and more preferably 20/80 to 40/60. When the mass ratios are within these ranges, an adhesive composition with excellent adhesive properties can be obtained.

The content of the styrene-based elastomer is preferably 10.0 to 99.0 parts by mass per 100 parts by mass of the solid content of the resin composition.

<<<Carboxy group-containing styrene elastomer>>>
Carboxy group-containing styrene elastomers have high adhesiveness, can impart flexibility to the cured product, and are effective as a component that imparts good electrical properties.
The adhesive composition contains a carboxyl group-containing styrene elastomer, which allows the flexible adhesive composition to conform sufficiently to the surface of the adherend, even if the adherend has good electrical properties and low polarity, such as a substrate film or metal foil, and the highly polar carboxyl group can exhibit adhesion, thereby improving the adhesion of the adhesive layer. Furthermore, because the carboxyl group-containing styrene elastomer is reactive, epoxy curing also improves the heat resistance and chemical resistance of the adhesive layer.
Furthermore, the inclusion of a carboxy group improves the dispersibility of the inorganic filler in the dispersion liquid.
The carboxyl group-containing styrene elastomer is a copolymer mainly consisting of block and random structures of a conjugated diene compound and an aromatic vinyl compound, or a hydrogenated product thereof modified with an unsaturated carboxylic acid.
The types of aromatic vinyl compounds and conjugated diene compounds 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 30 mgKOH/g, more preferably 0.5 to 25 mgKOH/g, and even more preferably 0.5 to 5 mgKOH/g. When this acid value is 0.1 mgKOH/g or higher, the dispersibility of the inorganic filler is improved. When the acid value is 0.5 mgKOH/g or higher, the adhesive composition cures sufficiently, resulting in good adhesion and heat resistance. On the other hand, when the acid value is 30 mgKOH/g or lower, the cohesive strength of the adhesive composition is suppressed, resulting in excellent adhesiveness and electrical properties. When the acid value is 5 mgKOH/g or lower, the adhesive strength with the PEEK substrate is improved.

The weight-average molecular weight of the carboxyl group-containing styrene elastomer is preferably 10,000 to 500,000, more preferably 30,000 to 300,000, and even more preferably 50,000 to 200,000. If the weight-average molecular weight is equal to or greater than the lower limit, excellent adhesive properties can be exhibited, and the coatability when dissolved in a solvent and applied is also improved. If the weight-average molecular weight is equal to or less than the upper limit, compatibility with epoxy resins is improved.
If the weight average molecular weight is within the above range, the mechanical properties can be controlled within an appropriate range, and both prevention of resin flow and dispersibility of the inorganic filler in the dispersion can be achieved.
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.

The content of the carboxyl group-containing styrene elastomer is preferably 10.0 to 99.0 parts by mass per 100 parts by mass of the solid content of the resin composition. If the content is within this range, an adhesive composition with excellent adhesive properties can be obtained.
It is more preferable that the content is 20 to 49 parts by mass per 100 parts by mass of the solid content of the resin composition. If the content is within the above range, the mechanical properties can be controlled within an appropriate range, and both prevention of resin flow and dispersibility of the inorganic filler in the dispersion can be achieved.

<<<Styrene-based elastomer containing amino groups>>>
The inclusion of an amino group-containing styrene elastomer in the adhesive composition increases reactivity and improves the adhesiveness of the adhesive layer. Furthermore, because the amino group-containing styrene elastomer is reactive, the adhesive layer also improves heat resistance and chemical resistance upon epoxy curing.
The amino group improves adhesion to metals.
Furthermore, since it contains amino groups, it is highly reactive with epoxy resins, and can be cured before the resin flows out, effectively preventing the resin from flowing out.
The amino group-containing styrene elastomer is an amine-modified copolymer of a conjugated diene compound and an aromatic vinyl compound, which is mainly composed of block and random structures, or a hydrogenated product thereof.
The types of aromatic vinyl compounds and conjugated diene compounds and specific examples of styrene-based elastomers are as described above in the section <<Styrene-based elastomers>>.

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.

The weight-average molecular weight of the amino group-containing styrene elastomer is preferably 10,000 to 500,000, more preferably 30,000 to 300,000, and even more preferably 50,000 to 200,000. If the weight-average molecular weight is equal to or greater than the lower limit, excellent adhesive properties can be exhibited, and the coatability when dissolved in a solvent and applied is also improved. If the weight-average molecular weight is equal to or less than the upper limit, compatibility with epoxy resins is improved.
If the weight average molecular weight is within the above range, the mechanical properties can be controlled within an appropriate range, and both prevention of resin flow and dispersibility of the inorganic filler in the dispersion can be achieved.

The content of the amino group-containing styrene-based elastomer is preferably 10.0 to 99.0 parts by mass per 100 parts by mass of the solid content of the resin composition. It is even more preferably 20 to 49 parts by mass per 100 parts by mass of the solid content of the resin composition. A content of 10.0 to 99.0 parts by mass can result in an adhesive composition with excellent adhesive properties. A content of 20 to 49 parts by mass can control the mechanical properties within an appropriate range, preventing resin flow and achieving both dispersibility of the inorganic filler in the dispersion.

By mixing unmodified styrene-based elastomers with modified styrene-based elastomers, it is possible to adjust hardness and control MFR while maintaining adhesive properties.

<<Epoxy resin>>
The epoxy resin is a component that reacts with the carboxy group in the carboxy group-containing styrene-based elastomer or the amino group in the amino group-containing styrene-based elastomer, thereby imparting high adhesion to the adherend and heat resistance to the cured adhesive.

Examples of epoxy resins include bisphenol A epoxy resins, bisphenol F epoxy resins, and hydrogenated versions of these; glycidyl ester-based epoxy resins such as phthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, p-hydroxybenzoic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, succinic acid diglycidyl ester, adipic acid diglycidyl ester, sebacic acid diglycidyl ester, and trimellitic acid triglycidyl ester; ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, and glycidyl esters of 1,4-butanediol diglycidyl ester. Examples of epoxy resins that can be used include, but are not limited to, glycidyl ether-based epoxy resins such as glycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, tetraphenylglycidyl ether ethane, triphenylglycidyl ether ethane, polyglycidyl ether of sorbitol, and polyglycerol polyglycidyl ether; glycidyl amine-based epoxy resins such as triglycidyl isocyanurate and tetraglycidyldiaminodiphenylmethane; and linear aliphatic epoxy resins such as epoxidized polybutadiene and epoxidized soybean oil. Additionally, novolac-type epoxy resins such as xylene structure-containing novolac epoxy resins, naphthol novolac-type epoxy resins, phenol novolac epoxy resins, o-cresol novolac epoxy resins, and bisphenol A novolac epoxy resins can also be used.

Further, examples of epoxy resins that can be used include brominated bisphenol A type epoxy resins, phosphorus-containing epoxy resins, fluorine-containing epoxy resins, dicyclopentadiene skeleton-containing epoxy resins, naphthalene skeleton-containing epoxy resins, anthracene type epoxy resins, tertiary butylcatechol type epoxy resins, triphenylmethane type epoxy resins, tetraphenylethane type epoxy resins, biphenyl type epoxy resins, bisphenol S type epoxy resins, etc. These epoxy resins may be used alone or in combination of two or more.
Among the above epoxy resins, epoxy resins without hydroxyl groups are preferred because they yield adhesive compositions with excellent electrical properties and have good compatibility with styrene-based elastomers. In particular, novolac epoxy resins and epoxy resins such as those shown in the following structure are more preferred because they have a moderately flexible backbone, making the cured product less susceptible to brittle fracture, improving the performance stability of the cured adhesive composition over long-term use, and also improving heat resistance due to their high number of functional groups. Epoxy compounds of styrene-butadiene block copolymers are more preferred. Epoxy compounds of styrene-butadiene block copolymers can accelerate the reaction rate and increase crosslink density by involving unsaturated bonds in addition to aromatic rings such as olefin backbones and vinyl groups in the reaction of the epoxy structure, resulting in improved heat resistance and chemical resistance even at low loadings. Furthermore, epoxy compounds of styrene-butadiene block copolymers have a high molecular weight and contain epoxy groups, which act as dispersants and further improve the dispersibility of inorganic fillers. As the epoxy compound for the styrene-butadiene block copolymer, commercially available epoxy compounds can also be used, and examples thereof include CELLOXIDE 2021P, CELLOXIDE 2081, CELLOXIDE 2000 (manufactured by Daicel Corporation), EPOLEAD GT401, EPOLEAD PB3600, EPOLEAD PB4700 (manufactured by Daicel Corporation), EPOFRIEND AT501, and EPOFRIEND CT310 (manufactured by Daicel Corporation).

(R is a structure containing methylene-aryl-methylene or a structure containing an aliphatic hydrocarbon structure having 6 or more carbon atoms, and examples of the aryl include benzene, xylene, naphthalene, and biphenyl, and examples of the aliphatic hydrocarbon include hexane, dimethylcyclohexane, and dicyclopentadiene.)
Specific examples of novolac-type epoxy resins include "YX7700" (xylene structure-containing novolac-type epoxy resin) manufactured by Mitsubishi Chemical Corporation, "NC7000L" (naphthol novolac-type epoxy resin) manufactured by Nippon Kayaku Co., Ltd., "ESN485" (naphthol novolac-type epoxy resin) manufactured by Nippon Steel Chemical & Material Co., Ltd., "N-690" (cresol novolac-type epoxy resin) manufactured by DIC Corporation, and "N-695" (cresol novolac-type epoxy resin) manufactured by DIC Corporation.

Furthermore, epoxy resins containing amino groups can improve workability by shortening the curing time and lowering the curing temperature due to the catalytic action of the amino groups. In addition, the amino groups improve adhesion to metal layers.
In particular, it is more preferable that the epoxy resin is a glycidylamine-type epoxy resin. Glycidylamine-type epoxy resins are multifunctional, so they can be cured with a small amount, and because they contain amines in their molecular skeleton, they have good compatibility with amino-group-containing styrene-based elastomers and also have a reaction-accelerating effect. In addition, because they contain amino groups, they can improve adhesion to metal layers.
Specific examples of glycidylamine-type epoxy resins include tetraglycidyldiaminodiphenylmethane, such as "jER604" manufactured by Mitsubishi Chemical Corporation, "Sumiepoxy ELM434" manufactured by Sumitomo Chemical Co., Ltd., "Araldite MY720,""AralditeMY721,""AralditeMY9512,""AralditeMY9612,""AralditeMY9634," and "Araldite MY9663" manufactured by Huntsman Advanced Materials, Inc., and "TETRAD-X" and "TETRAD-C" manufactured by Mitsubishi Gas Chemical Company, Inc.

The epoxy resin used in this invention preferably has two or more epoxy groups per molecule. This is because a crosslinked structure is formed upon reaction with the carboxyl group-containing styrene-based elastomer, allowing for high heat resistance. Furthermore, when an epoxy resin with two or more epoxy groups is used, the degree of crosslinking with the carboxyl group-containing styrene-based elastomer is sufficient, resulting in sufficient heat resistance.

The content of the epoxy resin is preferably 1 to 25 parts by mass per 100 parts by mass of the resin composition. If the content of the epoxy resin is equal to or greater than the lower limit, the adhesive composition will cure sufficiently and good heat resistance and chemical resistance can be ensured. On the other hand, if the content of the epoxy resin is too high, adhesion will decrease, so if the content is equal to or less than the upper limit, good adhesion can be ensured.

The softening point or melting point of the above epoxy resin is preferably 90°C or lower. If the softening point or melting point of the epoxy resin is 90°C or lower, the glass transition point of the adhesive composition can be lowered, the elastic modulus of the adhesive composition at high temperatures before curing can be lowered, and the elastic modulus of the adhesive composition at room temperature after curing can be increased. In addition, it is preferable for the epoxy resin to be molten at the reaction temperature, as this will speed up the reaction.

<<Other resin components>>
In addition to the above-mentioned styrene-based elastomer and the epoxy resin that is appropriately contained, the resin composition may contain other thermoplastic resins other than the styrene-based elastomer to an extent that does not affect the function of the adhesive composition.

Examples of the other thermoplastic resins include phenoxy resin, polyamide resin, polyester resin, polycarbonate resin, polyphenylene oxide resin, polyurethane resin, polyacetal resin, polyethylene resin, polypropylene resin, and polyvinyl resin. These thermoplastic resins may be used alone or in combination of two or more.

<Inorganic filler>
The inorganic filler has a plate-like or scale-like shape.
The content of the inorganic filler contained in the adhesive composition of the present invention is 1 to 180 parts by mass per 100 parts by mass of the resin composition.
The content of the inorganic filler is more preferably 30 to 175 parts by mass relative to 100 parts by mass of the resin composition.
If the content of the inorganic filler is within the above range, the mechanical properties can be controlled within an appropriate range, and both prevention of resin flow and good adhesion can be achieved.

The inorganic filler according to the present invention is not particularly limited in type as long as it has a plate-like or scaly shape and can be appropriately selected depending on the purpose, but for example, silicon-based inorganic fillers and boron nitride are preferred from the viewpoint of heat resistance and dielectric properties. Furthermore, among silicon-based inorganic fillers, natural mica, synthetic mica, and natural talc are more preferred from the viewpoint of aspect ratio, and among these, synthetic mica is even more preferred from the viewpoint of water absorption.
These may be used alone or in combination of two or more.
In the present invention, an adhesive composition is prepared by incorporating a specific amount of inorganic filler having a specific shape into the adhesive composition, and the adhesive layer is formed from the adhesive composition. The resulting adhesive layer is capable of preventing resin flow during thermocompression bonding, exhibits good electrical properties, and exhibits good adhesion.

The inorganic filler used in the present invention preferably has an average particle size of 3.0 μm or less. The average particle size of the inorganic filler can be calculated, for example, using a laser scattering method. Furthermore, from the viewpoints of coefficient of thermal expansion (CTE) and film strength, the aspect ratio of the inorganic filler is preferably 5 or more and 500 or less.

[Aspect ratio measurement]
The aspect ratio of the inorganic filler can be determined, for example, by observing the film using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and averaging the measured values. For example, the aspect ratio of the inorganic filler present in a film (layer) can be determined by embedding the film in an epoxy resin, then ion milling the cross section of the film using an ion milling device to prepare a sample for cross-section observation, observing the cross section of the obtained sample using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and averaging the measured values of the length and thickness in the planar direction of the inorganic filler.

The content of the inorganic filler in the film is preferably 1 to 50% by volume, and more preferably 2 to 30% by volume.
When the content of the inorganic filler is equal to or greater than the lower limit, resin flow in the adhesive layer can be prevented. When the content of the inorganic filler is 50% by volume or less, the dispersibility and heat resistance of the inorganic filler can be improved. When the content of the inorganic filler is 30% by volume or less, good adhesion can be ensured.

<Other ingredients>
In addition to the above-described styrene-based elastomer and inorganic filler, the adhesive composition may contain other components such as a tackifier, a flame retardant, a curing agent, a curing accelerator, a coupling agent, a heat aging inhibitor, a leveling agent, an antifoaming agent, a pigment, and a solvent, to an extent that the functionality of the adhesive composition is not affected.

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.

Examples of the curing agent include, but are not limited to, amine-based curing agents and acid anhydride-based curing agents. Examples of the amine-based curing agent include melamine resins such as methylated melamine resin, butylated melamine resin, and benzoguanamine resin, dicyandiamide, and 4,4'-diphenyldiaminosulfone. Examples of the acid anhydride include aromatic acid anhydrides and aliphatic acid anhydrides. These curing agents may be used alone or in combination of two or more.
The content of the curing agent is preferably 0.5 to 100 parts by mass, and more preferably 5 to 70 parts by mass, per 100 parts by mass of the adhesive composition.

The curing accelerator is used for the purpose of accelerating the reaction between the carboxyl group-containing styrene-based elastomer and the epoxy resin, and examples of the curing accelerator that can be used include tertiary amine-based curing accelerators, tertiary amine salt-based curing accelerators, and imidazole-based curing accelerators.
By adding the curing accelerator, the reaction proceeds quickly, allowing the resin to cure before it flows out, and effectively preventing the resin from flowing out.

Tertiary amine curing accelerators include benzyldimethylamine, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, tetramethylguanidine, triethanolamine, N,N'-dimethylpiperazine, triethylenediamine, 1,8-diazabicyclo[5.4.0]undecene, etc.

Tertiary amine salt curing accelerators include the formate, octylate, p-toluenesulfonate, o-phthalate, phenolate, or phenol novolac resin salt of 1,8-diazabicyclo[5.4.0]undecene, and the formate, octylate, p-toluenesulfonate, o-phthalate, phenolate, or phenol novolac resin salt of 1,5-diazabicyclo[4.3.0]nonene.

Imidazole curing accelerators include 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-methyl-4-ethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(1')]ethyl-s-triazine, 2,4-diamino-6-[2' 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, etc. These curing accelerators may be used alone or in combination of two or more.

When the adhesive composition contains a curing accelerator, the content of the curing accelerator is preferably 0.05 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the adhesive composition. When the content of the curing accelerator is within the above range, the reaction between the styrene-based elastomer and the epoxy resin, and the reaction between epoxy resins themselves, can proceed easily, making it easier to ensure adhesion and heat resistance.

Further examples of the coupling agent include silane-based coupling agents such as vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-ureidopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane, and imidazole silane; titanate-based coupling agents; aluminate-based coupling agents; and zirconium-based coupling agents. These may be used alone or in combination of two or more.

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.

<Characteristics of adhesive layer made of adhesive composition>
The adhesive layer made of the adhesive composition of the present invention is formed by forming the adhesive composition into a film and curing it.
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 to 100 μm from the viewpoint of thinning, more preferably 5 to 70 μm to ensure adhesion, and even more preferably 10 to 50 μm to enable more accurate control of resin flow.

The adhesive layer obtained by curing the adhesive composition of the present invention has a relative dielectric constant (εr) of 3.5 or less at a frequency of 28 GHz, and a dielectric dissipation factor (tanδ) of 0.005 or less at a frequency of 28 GHz. It is further desirable that the relative dielectric constant is 3.2 or less and the dielectric dissipation factor is 0.002 or less.
If the dielectric constant is 3.5 or less and the dielectric dissipation factor is 0.005 or less, the material can be suitably used in FPC-related products that require strict electrical properties. If the dielectric constant is 3.2 or less and the dielectric dissipation factor is 0.002 or less, attenuation can be further reduced even in high-frequency transmission.

[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.

From the viewpoint of adhesive strength when laminated, the storage modulus at 25°C of the adhesive layer after curing of the adhesive composition of the present invention is preferably 1.0E+8 Pa or more. Furthermore, the storage modulus at 25°C of the adhesive layer after curing of the adhesive composition is preferably 1.0E+9 Pa or less. When the storage modulus is within the above range, it is possible to maintain adhesive strength when laminated.
From the viewpoint of adhesion, the storage modulus of the adhesive layer of the adhesive composition of the present invention before curing is preferably 1.0E+5 Pa or more and 1.0E+8 Pa or less at 150°C. From the viewpoint of conformability to the surface of the adherend, it is more preferably 1.0E+5 Pa or more and 1.0E+7 Pa or less, and from the viewpoint of resin flow, it is even more preferably 1.0E+6 Pa or more and 1.0E+7 Pa or less.
It is preferable that the storage modulus is within the above range, since it is possible to control the mechanical properties during thermocompression bonding and to achieve both resin flow and adhesive strength.

[Storage modulus (Pa)]
The storage modulus of the adhesive layer is determined, for example, by preparing a 100 μm thick adhesive film for a sample made of the adhesive layer and measuring it using a viscoelasticity measuring device (RSA-G2 manufactured by TA Instruments) under conditions of a measurement frequency of 1 Hz and a temperature rise rate of 5° C./min in accordance with JIS K7244.

The adhesive layer obtained by curing the adhesive composition of the present invention preferably has a coefficient of thermal expansion (CTE) of 500 ppm/K or less. A coefficient of thermal expansion of this value or less is preferred because deformation during thermocompression bonding is small.
The thermal expansion coefficient can be measured, for example, by using a thermomechanical analyzer (Hitachi High-Tech Science Corporation, product name: SII//SS7100) in a tensile mode under a load of 50 mN, raising the temperature from 25°C to 250°C at a rate of 5°C/min, measuring the change in dimension with temperature, and determining the linear expansion coefficient from the slope in the range from 25°C to 125°C.

<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 a resin composition containing at least a styrene-based elastomer, an inorganic filler, and, if necessary, other resin components and other components. The mixing method is not particularly limited as long as the adhesive composition is homogeneous. Since the adhesive composition is preferably used in the form of a solution or dispersion, a solvent is usually also used.
Examples of the solvent 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, and mesitylene; esters such as methyl acetate, ethyl 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.
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.

(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, and liquid crystal polymer 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.

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 150°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 150°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 of 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.

(Carboxy group-containing styrene elastomer)
The product used was "Tuftec M1913" (maleic acid-modified styrene-ethylene butylene-styrene block copolymer) manufactured by Asahi Kasei Corporation. The copolymer had an acid value of 10 mg KOH/g, a styrene/ethylene butylene ratio of 30/70, and a weight-average molecular weight of 67,000.
(Carboxy group-containing styrene elastomer)
The product used was "Tuftec M1911" (maleic acid-modified styrene-ethylene butylene-styrene block copolymer) manufactured by Asahi Kasei Corporation. The copolymer had an acid value of 2 mg KOH/g, a styrene/ethylene butylene ratio of 30/70, and a weight-average molecular weight of 69,000.
(Carboxy-free styrene-based elastomer)
The copolymer used was "Tuftec P1500" (hydrogenated styrene-based elastomer) manufactured by Asahi Kasei Corporation. The copolymer had an acid value of 0 mgKOH/g, a styrene/ethylene butylene ratio of 30/70, and a weight average molecular weight of 67,000.
(Amino group-containing styrene elastomer)
The product used was "Tuftec MP10" (amine-modified hydrogenated styrene-butadiene copolymer (amine-modified styrene-ethylenebutylene-styrene copolymer) manufactured by Asahi Kasei Corporation. The styrene ratio of this copolymer was 30, and the weight average molecular weight was 78,000.
(epoxy resin)
The product used was "HP-7200" (epoxy resin, softening point 56-66°C) manufactured by DIC Corporation.
(epoxy 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 methyl ethyl ketone (mass ratio = 90:10) was used.
(Base film)
As the substrate film, "Shin-Etsu Sepla Film PEEK" (polyether ether ketone, thickness 50 μm) manufactured by Shin-Etsu Polymer Co., Ltd. was used.
(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.
(filler)
As the filler, the fillers described below were used.
MK-100DS Micro Mica (manufactured by Katakura Coop Appli Co., Ltd.)
Aspect ratio 27.5
UHP-S2 hexagonal boron nitride (Showa Denko K.K.)
Aspect Ratio 6
MX-300 Acrylic Particles (Soken Chemical Co., Ltd.)
SQ-C8 Silica (manufactured by Admatechs Co., Ltd.)
MC6000 Melamine Isocyanurate (Nissan Chemical Co., Ltd.)

Example 1
Resin compositions were prepared by mixing the components constituting the resin compositions shown in Table 1 in the proportions shown in Table 1.
Next, the components constituting the adhesive layer shown in Table 2 were dissolved in a solvent in the proportions shown in Table 2 to prepare a resin varnish with a solids concentration of 20 mass %.
The shapes and average particle sizes of the fillers used are shown in Table 2.
The surface of the substrate film was subjected to a corona treatment.
The resin varnish was applied to the surface of a substrate film, dried in an oven at 110°C for 4 minutes, and the toluene was volatilized to form an adhesive layer, yielding a substrate film with an adhesive. The adhesive layer of the adhesive laminate was placed in contact with the shiny side of the electrolytic copper foil, and thermal lamination was performed at 120°C to obtain a pre-cured adhesive laminate. The pre-cured adhesive laminate was pressed at 180°C and 3 MPa for 3 minutes, and then after-cured at 180°C for 30 minutes to cure the adhesive layer, yielding a cured adhesive laminate.
After curing, the adhesive strength (N/cm) between the electrolytic copper foil and the substrate film of the adhesive laminate of Example 1 was measured.

[Adhesion strength (N/cm)]
The adhesive strength was measured by cutting the cured adhesive laminate into a 25 mm wide test piece, and measuring the peel strength when peeling the electrolytic copper foil from the adhesive-attached substrate 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).

In addition, the storage modulus (Pa) was measured at 25°C after curing and at 150°C before curing.

[Storage modulus (Pa)]
The storage modulus of the adhesive layer was measured using a viscoelasticity measuring device (RSA-G2 manufactured by TA Instruments) in accordance with JIS K7244 under conditions of a measurement frequency of 1 Hz and a temperature rise rate of 5°C/min. 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 thermally laminated at 120°C so that the adhesive surfaces were in contact with each other to form a pre-cure adhesive film (thickness 100 μm), and a pre-cure adhesive film (100 mm x 100 mm) was produced. The release film was peeled off from the adhesive film, and the storage modulus (Pa) of the pre-cure adhesive layer was measured.
Furthermore, a 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 × 100 mm). The release film was peeled off from the adhesive film, and the storage modulus (Pa) of the cured adhesive layer was measured.

The relative dielectric constant and dielectric loss tangent at a frequency of 28 GHz were also measured for the adhesive layer in the cured adhesive laminate 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 120 ° 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.

The coefficient of thermal expansion (CTE) of the adhesive layer in the cured adhesive laminate of Example 1 was also measured at 30 to 50°C.

[Coefficient of thermal expansion (CTE)]
The thermal expansion coefficient was measured in a tensile mode using a thermomechanical analyzer (Hitachi High-Tech Science Corporation, product name: SII//SS7100) with a load of 50 mN, by increasing the temperature from 25°C to 125°C at a rate of 5°C/min, measuring the change in dimension with temperature, and determining the linear expansion coefficient from the slope in the range from 30°C to 50°C.

A solder heat resistance test was performed on the cured adhesive laminate of Example 1.

[Solder heat resistance test]
For the solder heat resistance test, the cured adhesive laminate was placed with the substrate film side facing up in a solder bath at 288°C for 10 seconds three times, and the adhesive layer was checked for any external abnormalities such as swelling _or peeling.
The heat resistance of the laminate was evaluated according to the following evaluation criteria.
◎ No abnormalities (no dissolution).
○ No abnormalities are found in the final product, but the adhesive layer softens during the test.
△: No peeling, but the adhesive layer has softened and a "stain pattern" has formed.
× Peeling off.

A resin flow test was conducted on the adhesive layer of the laminate of Example 1 during the production of the laminate.

[Resin flow test]
For the resin flow test, the adhesive-backed substrate film was cut to a size of 30 mm x 90 mm, and three 5 mm diameter holes were punched using a belt punch. The adhesive-backed substrate film was placed so that the adhesive layer was in contact with the shiny side of the electrolytic copper foil, and the films were thermally laminated at 150°C and pressed at 180°C, 3 MPa, and 3 minutes. The length of the resin that protruded onto the copper foil was measured at 12 points (4 points x 3 points) using a microscope [manufactured by KEYENCE Corporation, product name: DIGITAL MICROSCOPE VHX-500, lens magnification: 300x], and the average value was recorded.

The measurement results are shown in Table 3.

(Examples 2 to 11)
Laminates of Examples 2 to 11 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 Tables 1 and 2.
The laminate thus produced was evaluated in the same manner as in Example 1.
The results are shown in Table 3.

(Comparative Examples 1 to 8)
Laminates of Comparative Examples 1 to 8 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 Tables 1 and 2.
The laminate thus produced was evaluated in the same manner as in Example 1.
The results are shown in Table 3.

As shown in the examples, the adhesive layer made of the adhesive composition of the present invention can prevent resin flow during thermocompression bonding by controlling the mechanical properties, and also exhibits good electrical properties and excellent adhesion.

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 (10)

An adhesive composition containing a resin composition including at least an amino group -containing styrene-based elastomer and an inorganic filler,
the content of the inorganic filler is 1 to 180 parts by mass relative to 100 parts by mass of the resin composition,
the inorganic filler has a plate-like or scaly shape,
An adhesive composition, wherein the adhesive layer obtained by curing the adhesive composition has a relative dielectric constant of 3.5 or less at a frequency of 28 GHz, and a dielectric loss tangent of the adhesive layer at a frequency of 28 GHz of 0.005 or less. The adhesive composition according to claim 1, wherein the inorganic filler has an aspect ratio of 5 to 500. The adhesive composition according to claim 1 or 2, wherein the inorganic filler has an average particle size of 3.0 μm or less. The adhesive composition according to any one of claims 1 to 3, wherein the inorganic filler includes at least one of a silicon-based inorganic filler and boron nitride. The adhesive composition according to claim 4, wherein the silicon-based inorganic filler includes at least one of mica and talc. The adhesive composition according to any one of claims 1 to 5 , wherein the resin composition contains an epoxy resin. The adhesive composition according to claim 6 , wherein the content of the epoxy resin is 1 to 25 parts by mass per 100 parts by mass of the resin composition. The adhesive composition according to any one of claims 1 to 7 , wherein the adhesive layer of the adhesive composition before curing has a storage modulus of 1.0E+5 Pa or more at 150°C. A base film;
An adhesive layer made of an adhesive composition,
The adhesive composition comprises:
An adhesive composition containing a resin composition containing at least a styrene-based elastomer and an inorganic filler,
the content of the inorganic filler is 1 to 180 parts by mass relative to 100 parts by mass of the resin composition,
the inorganic filler has a plate-like or scaly shape,
an adhesive layer formed by curing the adhesive composition has a relative dielectric constant of 3.5 or less at a frequency of 28 GHz, and a dielectric loss tangent of the adhesive layer at a frequency of 28 GHz of 0.005 or less;
The laminate , wherein the substrate film contains a polyether ether ketone (PEEK) resin . A printed wiring board comprising the laminate of claim 9 .