WO2024116571A1

WO2024116571A1 - Adhesive composition

Info

Publication number: WO2024116571A1
Application number: PCT/JP2023/034529
Authority: WO
Inventors: 武久家根; 哲生川楠; 隆幸米澤; 正也柿本; 真山本
Original assignee: 東洋紡エムシー株式会社; 住友電気工業株式会社; 住友電工プリントサーキット株式会社
Priority date: 2022-11-28
Filing date: 2023-09-22
Publication date: 2024-06-06
Also published as: TW202436579A; CN119317682A

Abstract

Provided is an adhesive composition that sufficiently and simultaneously satisfies the adhesiveness, insulation reliability, and soldering heat resistance suitable for flexible printed wiring board applications. The adhesive composition contains an imide group-containing resin (A) and an epoxy resin (B) and is characterized in that the imide group-containing resin (A) has, as constituent units, an acid dianhydride compound (C) having an ester group or an ether group, and a dimer acid (D). The adhesive composition according to the present invention can further contain a phosphorus-based flame retardant (E). The adhesive composition according to the present invention can be suitably used in flexible printed wiring board applications such as, in particular, a copper-clad laminate, a coverlay film, and an adhesive sheet.

Description

Adhesive Composition

The present invention relates to an adhesive composition that combines a polyimide resin and a curing agent, and more specifically, to an adhesive composition that has excellent adhesion, insulation reliability, and solder heat resistance, and is suitable for flexible printed wiring board applications such as copper-clad laminates, coverlay films, and adhesive sheets.

Flexible printed circuit boards are circuit boards that are widely used in electronic devices that require flexibility and space-saving features, such as smartphones, tablets, and digital cameras. As devices become smaller and more sophisticated, the number of components mounted on them increases, and flexible printed circuit boards are required to form wiring at a finer pitch than before.

Polyimide resins are one of the materials used in flexible printed wiring boards. Polyimide resins are mainly synthesized from aromatic monomers, and because they exhibit high heat resistance, insulating reliability, and mechanical strength, they are used as base films for copper-clad laminates and coverlay films.

On the other hand, adhesives are required for copper-clad laminates made by bonding a base film to copper foil for wiring, coverlay films to protect circuits, and adhesive sheets for bonding boards together, and the production process requires the use of heat-curing adhesives. However, polyimide resins made from aromatic monomers have a high glass transition temperature, making it difficult to bond them together using a normal heat press, and therefore difficult to use as adhesives.

Therefore, in order to use polyimide resins as adhesives while maintaining their characteristics such as heat resistance, insulating reliability, and mechanical strength, methods are being investigated that involve copolymerizing long-chain monomers and oligomers such as aliphatic ones to impart fluidity and flexibility when bonding, and then combining them with a curing agent.

Patent Document 1 proposes using modified polyamideimide, a polyimide resin in which siloxane containing an amine, a reactive functional group, has been introduced to the molecular chain end, as the main component of the adhesive.

In addition, Patent Document 2 proposes using modified polyamideimide, a polyimide resin in which acrylonitrile-butadiene rubber containing a carboxylic acid, a reactive functional group, has been introduced to the molecular chain end, as the main component of the adhesive.

JP2005-179513 Patent No. 3931387

The polyimide resin with the siloxane structure described in Patent Document 1 requires the use of a starting material with a very expensive siloxane bond to impart a level of flexibility that allows its use as an adhesive, and is therefore less economical. There was also concern that the adhesiveness of the resin would decrease as the amount of siloxane structure introduced increased. In addition, in order to achieve sufficient adhesiveness with the modified polyamideimide described in Patent Document 2, it is necessary to introduce a large amount of acrylonitrile-butadiene rubber, and as a result, insulation reliability decreases due to the influence of moisture absorption by the nitrile in the acrylonitrile-butadiene rubber, making it difficult to use for wiring with a narrow pitch. Therefore, in applications for flexible printed wiring boards, a polyimide resin that can be used as an adhesive is desired, but conventional technology has not been able to obtain a resin that satisfies both adhesiveness and insulation reliability at the same time.

The present invention was made to solve the problems of the conventional technology described above, and its purpose is to provide an adhesive composition that is suitable for use in flexible printed wiring boards and that simultaneously satisfies the adhesive properties, insulation reliability, and solder heat resistance.

The inventors conducted extensive research to achieve the above-mentioned objective, and discovered that introducing a dimer acid as a long-chain monomer constituting a polyimide resin and further introducing an acid dianhydride compound having an ester group or ether group can provide fluidity and flexibility during lamination without using a highly hygroscopic raw material such as acrylonitrile-butadiene rubber, and thus the present invention was completed.

That is, the present invention comprises the following configurations [1] to [9].
[1] An adhesive composition comprising an imide group-containing resin (A) and an epoxy resin (B), wherein the imide group-containing resin (A) has an acid dianhydride compound (C) having an ester group or an ether group, and a dimer acid (D) as structural units.
[2] The adhesive composition according to [1], wherein the acid dianhydride compound (C) is an alkylene glycol bisanhydrotrimellitate.
[3] The adhesive composition according to [1], characterized in that the acid dianhydride compound (C) is 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic dianhydride or oxydiphthalic dianhydride.
[4] The adhesive composition according to any one of [1] to [3], characterized in that, when the total amount of polycarboxylic acid components constituting the imide group-containing resin (A) is taken as 100 mol %, the copolymerization amounts of the acid dianhydride compound (C) and the dimer acid (D) are each in the range of 1 to 80 mol %.
[5] The adhesive composition according to any one of [1] to [3], further comprising a phosphorus-based flame retardant (E).
[6] A copper-clad laminate comprising an insulating plastic film and a copper foil laminated on at least one surface of the insulating plastic film via the adhesive composition according to any one of [1] to [3].
[7] A coverlay film comprising an adhesive layer made of the adhesive composition according to any one of [1] to [3] and an insulating plastic film laminated thereon.
[8] An adhesive sheet comprising an adhesive layer made of the adhesive composition according to any one of [1] to [3] and a peelable protective film laminated thereon.
[9] A flexible printed wiring board comprising a layer made of the adhesive composition according to any one of [1] to [3].

The adhesive composition of the present invention can simultaneously exhibit excellent adhesion, high insulation reliability, and solder heat resistance. Therefore, the adhesive composition of the present invention can be suitably used as an adhesive for flexible printed wiring boards. In particular, since the adhesive composition of the present invention has high insulation reliability after curing and high fluidity before curing, it can be suitably used as a coverlay film and lamination adhesive film for flexible printed wiring boards for fine pitches with narrow wiring spacing between circuits and flexible printed wiring boards for coils that generate strong magnetic forces.

The following describes in detail an embodiment of the present invention, but the present invention is not limited to this.

The adhesive composition of the present invention contains an imide group-containing resin (A), an epoxy resin (B), and, if necessary, a flame retardant, and is characterized in that the imide group-containing resin (A) has, as structural units, an acid dianhydride compound (C) having an ester group or an ether group (hereinafter also referred to as the acid dianhydride compound (C) or simply as the (C) component), and a dimer acid (D).

<Imido Group-Containing Resin (A)>
The imide group-containing resin (A) is a resin having imide groups as a repeating unit, and refers to a so-called polyimide resin. In addition to imide groups, the resin may also have other bonds, such as amide groups, urethane groups, ester groups, and ether groups, as repeating units.

<Acid dianhydride compound (C)>
The acid dianhydride compound (C) having an ester group or an ether group has the effect of enhancing the interaction between the adhesive and the surface of the adherend due to the polarity of the ester group or ether group when the resulting imide group-containing resin (A) is used as an adhesive composition, thereby enabling the adhesive to exhibit stronger adhesive strength. As a result, it also has the effect of making peeling and swelling less likely to occur in solder heat resistance evaluation.

Examples of the acid dianhydride compound (C) having an ester group include alkylene glycol bisanhydrotrimellitates such as ethylene glycol bisanhydrotrimellitate, propylene glycol bisanhydrotrimellitate, 1,4-butanediol bisanhydrotrimellitate, hexamethylene glycol bisanhydrotrimellitate, polyethylene glycol bisanhydrotrimellitate, and polypropylene glycol bisanhydrotrimellitate. Examples of the acid dianhydride compound (C) having an ether group include 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic dianhydride and oxydiphthalic dianhydride. Hydrogenated versions of any of these compounds can also be used. These can be used alone or in combination. The copolymerization amount of the (C) component is preferably 1 to 80 mol%, more preferably 10 to 60 mol%, and even more preferably 15 to 50 mol%, when the total amount of polycarboxylic acid components constituting the imide group-containing resin (A) is taken as 100 mol%. If the amount of copolymerization of component (C) is less than the lower limit, the adhesiveness may be poor, and if it is more than the upper limit, the raw material cost may become high, which may be industrially disadvantageous.

<Dimer acid (D)>
Dimer acid (D) is a dicarboxylic acid having 36 carbon atoms produced by dimerization of an unsaturated fatty acid having 18 carbon atoms. As dimer acid (D), one in which the unsaturated bond has been hydrogenated can also be used.

Aromatic polyimide resins have poor fluidity and flexibility during the adhesive bonding process, making it difficult to obtain sufficient adhesive strength. The imide group-containing resin (A) used in the present invention is copolymerized with dimer acid (D) as a structural unit, and the aliphatic chain imparts fluidity and flexibility to the resin, allowing it to fill in unevenness on the adherend surface during thermocompression bonding, thereby improving adhesion. The copolymerization amount of dimer acid (D) is preferably 1 to 80 mol%, more preferably 10 to 70 mol%, and even more preferably 30 to 60 mol%, when the total amount of polycarboxylic acid components constituting the imide group-containing resin (A) is taken as 100 mol%. If the copolymerization amount of dimer acid (D) is less than the lower limit, adhesion may be poor, and if it is more than the upper limit, the imide group-containing resin may not have good heat resistance.

The imide group-containing resin (A) may have a polycarboxylic acid component other than the above-mentioned (C) component and dimer acid (D). As such a polycarboxylic acid component, it is preferable to use a polycarboxylic acid component having an aromatic ring from the viewpoint of improving the heat resistance of the obtained imide group-containing resin (A) and adhesive composition. Examples of polycarboxylic acid components having an aromatic ring include trimellitic anhydride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, naphthalene tetracarboxylic dianhydride, diphenyl sulfone tetracarboxylic dianhydride, perylene tetracarboxylic dianhydride, (hexafluoroisopropylidene) diphthalic anhydride, terephthalic acid, isophthalic acid, orthophthalic acid, and naphthalenedicarboxylic acid. These may be used alone or in combination. In order to balance heat resistance, flexibility, and adhesive strength, the copolymerization amount of the polycarboxylic acid component having an aromatic ring is preferably 20 to 90 mol%, more preferably 30 to 80 mol%, and even more preferably 40 to 70 mol%, when the total amount of polycarboxylic acid components constituting the imide group-containing resin (A) is taken as 100 mol%. Note that if the acid dianhydride compound (C) has an aromatic ring, it is included in this calculation.

In addition to the polycarboxylic acid components having an aromatic ring already described, aliphatic or alicyclic polycarboxylic acids or monoanhydrides or dianhydrides of polycarboxylic acids can be used as the polycarboxylic acid component to the extent that the effects of the present invention are not impaired. For example, any of the above-mentioned polycarboxylic acid components having an aromatic ring may be hydrogenated, meso-butane-1,2,3,4-tetracarboxylic acid dianhydride, pentane-1,2,4,5-tetracarboxylic acid dianhydride, cyclobutane tetracarboxylic acid dianhydride, cyclopentane tetracarboxylic acid dianhydride, cyclohex-1-ene-2,3,5,6-tetracarboxylic acid dianhydride, cyclohexane dicarboxylic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octanedioic acid, azelaic acid, sebacic acid, undecadioic acid, dodecanedioic acid, 2-methylsuccinic acid, etc. may be used alone or in combination.

The imide group-containing resin (A) can be obtained by polymerizing a polycarboxylic acid component and an amine component or an isocyanate component as the main raw materials. Here, the amine component can be a compound with an amino group having two or more functionalities, and the isocyanate component can be a compound with an isocyanate group having two or more functionalities.

As the isocyanate component constituting the imide group-containing resin (A), one having an aromatic ring is preferable from the viewpoint of improving the heat resistance of the adhesive composition, and examples thereof include diphenylmethane-4,4'-diisocyanate and its structural isomers, as well as dimethyldiphenylmethane diisocyanate, diethyldiphenylmethane diisocyanate, dimethoxydiphenylmethane diisocyanate, diphenylether diisocyanate, benzophenone diisocyanate, diphenylsulfone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, 4,4'-[2,2-bis(4-phenoxyphenyl)propane]diisocyanate, dimethylbiphenyl diisocyanate, diethylbiphenyl diisocyanate, dimethoxybiphenyl diisocyanate, diethoxybiphenyl diisocyanate, and structural isomers thereof. In addition, examples of the amine component include those in which the isocyanate group of the isocyanate component is replaced with an amino group. These may be used alone or in combination with one another.

In addition to the isocyanate component or amine component having an aromatic ring already described, an aliphatic or alicyclic isocyanate component or amine component can be used as the isocyanate component or amine component to the extent that the effect of the present invention is not impaired. For example, any of the isocyanate components or amine components having an aromatic ring described above that have been hydrogenated, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, ethylene diisocyanate, propylene diisocyanate, hexamethylene diisocyanate, etc. can be mentioned, and the amine component can be any of these isocyanate components in which the isocyanate group has been replaced with an amino group. These may be used alone or in combination. From the viewpoint of the heat resistance and flame retardancy of the resulting adhesive composition using the imide group-containing resin (A), the copolymerization amount of these components is preferably 50 mol% or less, and more preferably 20 mol% or less, when the total amount of isocyanate components and amine components is taken as 100 mol%.

In order to increase the number of reaction sites with the curing agent and improve the heat resistance of the resulting adhesive composition, it is possible to copolymerize a compound having three or more functional groups with the imide group-containing resin (A). Examples include polyfunctional carboxylic acids such as trimesic acid, dicarboxylic acids having a hydroxyl group such as 5-hydroxyisophthalic acid, dicarboxylic acids having an amino group such as 5-aminoisophthalic acid, compounds having three or more hydroxyl groups such as glycerin and polyglycerin, and compounds having three or more amino groups such as tris(2-aminoethyl)amine. The amount of copolymerization is preferably 20 mol% or less when the total amount of all polycarboxylic acid components, or the total amount of all isocyanate components and all amine components is taken as 100 mol%. If it exceeds 20 mol%, there is a risk of gelation or the generation of insoluble matter during resin polymerization.

The imide group-containing resin (A) can be copolymerized with polyesters, polyethers, polycarbonates, polysiloxanes, etc., as components that impart flexibility to the resulting resin, to an extent that does not impair the effects of the present invention. In this case, if the copolymerization amount of these components in the imide group-containing resin (A) is large, there is a risk that the heat resistance, insulation reliability, and economic efficiency will be impaired, so it is preferable that the copolymerization amount of these components is 10 mol % or less when the total amount of all polycarboxylic acid components, or the total amount of all isocyanate components, and the total amount of all amine components is taken as 100 mol %.

The content of the imide group-containing resin (A) in the adhesive composition of the present invention is preferably 1 to 80 mass %, and more preferably 10 to 70 mass %, assuming that the entire non-volatile content of the adhesive composition is 100 mass %. If the content of the imide group-containing resin is too low, the adhesive composition will contain less high molecular weight components, which may make it brittle and difficult to handle. On the other hand, if the content of the imide group-containing resin is too high, the proportion of the epoxy resin, which is a thermosetting component, will decrease, which may result in insufficient curing and reduced heat resistance.

<Method for producing imide group-containing resin (A)>
The imide group-containing resin (A) can be produced by known methods such as a method of reacting a polycarboxylic acid component with an isocyanate component (isocyanate method), a method of reacting a polycarboxylic acid component with an amine component to form an amic acid and then ring-closing the amic acid (direct method), or a method of reacting a compound having a carboxylic acid anhydride and a carboxylic acid chloride with an amine component (acid chloride method). From an industrial perspective, the isocyanate method is advantageous in that the by-product carbon dioxide is removed from the system as a gas.

The following describes the method of producing imide group-containing resins, typically using the isocyanate method, but imide group-containing resins can also be produced using the direct method and acid chloride method by using compounds that contain the corresponding amine components or carboxylic acid chlorides.

The polymerization reaction of the imide group-containing resin (A) can be carried out by stirring the polycarboxylic acid component and the isocyanate component in a solvent while heating them to 60°C to 200°C. At this time, the molar ratio of the polycarboxylic acid component/isocyanate component is preferably in the range of 90/100 to 100/90. Generally, the content (copolymerization amount) of the polycarboxylic acid component and the isocyanate component in the imide group-containing resin is the same as the ratio of each component during polymerization. In addition, in order to promote the reaction, catalysts such as alkali metals such as sodium fluoride, potassium fluoride, and sodium methoxide, amines such as triethylenediamine, triethylamine, 1,8-diazabicyclo[5,4,0]-7-undecene, and 1,5-diazabicyclo[4,3,0]-5-nonene, and dibutyltin dilaurate can be used. If the amount of these catalysts is too small, the desired catalytic effect will not be fully achieved, and if the amount is too large, side reactions may occur, so it is preferable to use 0.01 to 5 mol%, and more preferably 0.1 to 3 mol%, of the polycarboxylic acid component or the isocyanate component, whichever is larger, taken as 100 mol%.

Solvents that can be used in the polymerization reaction of the imide group-containing resin (A) include, for example, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, γ-butyrolactone, dimethylimidazolidinone, dimethylsulfoxide, dimethylformamide, dimethylacetamide, cyclohexanone, and cyclopentanone. Among these, N-methyl-2-pyrrolidone or dimethylacetamide is preferred because of the solubility of the resulting imide group-containing resin and the efficiency of the polymerization reaction. After the polymerization reaction, the non-volatile content and solution viscosity can be adjusted by diluting with the solvent used in the polymerization reaction or another low-boiling point solvent. These may be used alone or in combination.

Low boiling point solvents for dilution include aromatic solvents such as toluene and xylene, aliphatic solvents such as hexane, heptane, and octane, alcohol solvents such as methanol, ethanol, propanol, butanol, and isopropanol, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone, ether solvents such as diethyl ether and tetrahydrofuran, and ester solvents such as ethyl acetate, butyl acetate, and isobutyl acetate.

<Epoxy resin (B)>
The adhesive composition of the present invention contains an epoxy resin (B). By using a combination of the imide group-containing resin (A) and the epoxy resin (B), the state in which the imide group-containing resin (A), which has excellent heat resistance, is sufficiently adhered to a substrate can be strengthened by reaction with the epoxy resin (B), and excellent solder heat resistance is imparted, making the adhesive composition suitable as an adhesive for flexible printed wiring board applications.

The epoxy resin (B) may be modified with silicone, urethane, polyimide, polyamide, etc., and may contain sulfur atoms, nitrogen atoms, etc. in the molecular skeleton. Examples of the epoxy resin (B) include bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin, novolac type epoxy resins such as phenol novolac type epoxy resin and cresol novolac type epoxy resin, alicyclic epoxy resins such as hexahydrophthalic acid glycidyl ester, hydrogenated products of the bisphenol type epoxy resins, and hydrogenated products of the novolac type epoxy resins, linear aliphatic epoxy resins such as dimer acid glycidyl ester, epoxidized polybutadiene, and epoxidized soybean oil. These may be used alone or in combination. From the viewpoint of the heat resistance of the obtained cured product, the epoxy equivalent of the epoxy resin (B) is preferably 100 to 300 g/eq, and more preferably 150 to 200 g/eq. In addition, the type of epoxy resin (B) is preferably one having an aromatic ring, and bisphenol-type epoxy resins and novolac-type epoxy resins are more preferred.

Commercially available epoxy resins (B) include, for example, bisphenol A type epoxy resins such as jER828 and 1001 manufactured by Mitsubishi Chemical Corporation, hydrogenated bisphenol A type epoxy resins such as ST-2004 and 2007 manufactured by Nippon Steel Chemical & Material Co., Ltd., bisphenol F type epoxy resins such as EXA-9726 manufactured by DIC Corporation and YDF-170 and 2004 manufactured by Nippon Steel Chemical & Material Co., Ltd., phenolic resins such as jER152 and 154 manufactured by Mitsubishi Chemical Corporation and DEN-438 manufactured by The Dow Chemical Company. Volac type epoxy resins, dicyclopentadiene type epoxy resins such as HP7200 and HP7200H manufactured by DIC Corporation, YDCN-700 series manufactured by Nippon Steel Chemical & Material Co., Ltd., cresol novolac type epoxy resins such as EOCN-125S, 103S, and 104S manufactured by Nippon Kayaku Co., Ltd., flexible epoxy resins such as YD-171 manufactured by Nippon Steel Chemical & Material Co., Ltd., Epon 1031S manufactured by Mitsubishi Chemical Corporation, Araldite 0163 manufactured by BASF Japan Ltd., Nagase Chemtec Co., Ltd. Examples of the epoxy resins include polyfunctional epoxy resins such as DENACOL EX-611, EX-614, EX-622, EX-512, EX-521, EX-421, EX-411, and EX-321 manufactured by Nippon Steel Corporation; heterocycle-containing epoxy resins such as EPICOAT 604 manufactured by Mitsubishi Chemical Corporation, YH-434 manufactured by Nippon Steel Chemical & Material Co., Ltd., and Araldite PT810 manufactured by BASF Japan Ltd.; alicyclic epoxy resins such as CELLOXIDE 2021 and EHPE3150 manufactured by Daicel Chemical Industries, Ltd., and ERL4234 manufactured by UCC Corporation; Examples of such epoxy resins include bisphenol S type epoxy resins such as Epiclon EXA-1514 (trade name) manufactured by Nissan Chemical Industries, Ltd., triglycidyl isocyanurates such as TEPIC (trade name) manufactured by Nissan Chemical Industries, Ltd., bixylenol type epoxy resins such as YX-4000 (trade name) manufactured by Mitsubishi Chemical Corporation, bisphenol type epoxy resins such as YL-6056 (trade name) manufactured by Mitsubishi Chemical Corporation, TETRAD-X and TETRAD-C (trade names) manufactured by Mitsubishi Gas Chemical Company, Inc., GAN (trade name) manufactured by Nippon Kayaku Co., Ltd., and ELM-120 (trade name) manufactured by Sumitomo Chemical Co., Ltd., and other glycidyl amine type epoxy resins.

The content of the epoxy resin (B) in the adhesive composition of the present invention is preferably 1 to 50 mass %, and more preferably 10 to 40 mass %, assuming that the entire non-volatile content of the adhesive composition is 100 mass %. If the epoxy resin content is too low, sufficient thermosetting properties cannot be obtained, and as a result, the heat resistance of the adhesive composition may be poor. If the epoxy resin content is too high, the flexibility of the adhesive composition may be impaired, reducing the adhesive strength, or the insulation reliability may be reduced due to impurities contained in the epoxy resin.

<Flame retardants>
A flame retardant can be added to the adhesive composition of the present invention for the purpose of imparting flame retardancy. The flame retardant used in the present invention is not limited, but is preferably non-halogen-based from an environmental perspective. Although non-halogen flame retardants include nitrogen-based and metal hydroxide flame retardants, phosphorus-based flame retardants (E) are preferred because of their excellent flame retardant effect. The phosphorus-based flame retardant (E) is not particularly limited as long as it contains a phosphorus atom in its structure, but phosphinic acid derivatives and phosphazene-based flame retardants are preferred from the standpoints of hydrolysis resistance, heat resistance, and low bleed-out properties. These may be used alone or in combination of two or more types. The content of the flame retardant in the adhesive composition of the present invention is preferably 1 to 50 mass% of the non-volatile content of the adhesive composition, and more preferably 10 to 40 mass%. If the content of the flame retardant is low, sufficient flame retardancy may not be obtained, and if the content of the flame retardant is high, the heat resistance, adhesion, and insulation reliability of the adhesive composition may be reduced.

Phosphinic acid derivatives that are preferred are phenanthrene-type phosphinic acid derivatives, such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (manufactured by Sanko Co., Ltd., product name: HCA), 10-benzyl-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (manufactured by Sanko Co., Ltd., product name: BCA), 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (manufactured by Sanko Co., Ltd., product name: HCA-HQ), and XZ-92741 manufactured by Olin.

The phosphazene flame retardant is represented by the following general formula (1) or (2) (wherein X may be the same or different and is hydrogen, a hydroxyl group, an amino group, an alkyl group, an aryl group, a phenoxy group, an allyl group, a cyanophenoxy group, a hydroxyphenoxy group, or the like, and n is an integer of 3 to 25).

Commercially available phosphazene flame retardants include, for example, cyclic phenoxyphosphazene (manufactured by Otsuka Chemical Co., Ltd., product names: SPB-100, SPE-100), cyclic cyanophenoxyphosphazene (manufactured by Fushimi Pharmaceutical Co., Ltd., product name: FP-300), and cyclic hydroxyphenoxyphosphazene (manufactured by Otsuka Chemical Co., Ltd., product name: SPH-100).

As the phosphorus-based flame retardant (E), it is preferable to use in combination (i) a phosphorus-based flame retardant that does not have a functional group that reacts with an epoxy group, and (ii) a phosphorus-based flame retardant that has a functional group that reacts with an epoxy group, especially a phosphorus-based flame retardant that has two or more functional groups that react with an epoxy group. The ratio of the phosphorus-based flame retardants (i) and (ii) is preferably 1:9 to 9:1, more preferably 2:8 to 8:2, by mass. If there is too much phosphorus-based flame retardant (i), the insulation reliability may decrease, and if there is too much phosphorus-based flame retardant (ii), the adhesion may decrease.

(i) Phosphorus-based flame retardants that do not have a functional group that reacts with epoxy groups are not incorporated into the crosslinked structure during heat curing, and therefore play a role in imparting flexibility to the adhesive after heat curing. Examples of such flame retardants include the aforementioned cyclic phenoxyphosphazene (manufactured by Otsuka Chemical Co., Ltd., product names: SPB-100, SPE-100), cyclic cyanophenoxyphosphazene (manufactured by Fushimi Pharmaceutical Co., Ltd., product name: FP-300), 10-benzyl-10-hydro-9-oxa-10-phosphaphenanthrene-10-oxide (manufactured by Sanko Co., Ltd., product name: BCA), and phosphate ester-based flame retardants (manufactured by Daihachi Chemical Co., Ltd., product name: PX-200). (ii) Phosphorus-based flame retardants that have a functional group that reacts with epoxy groups are incorporated into the crosslinked structure during heat curing, and thus play a role in suppressing bleed-out and preventing a decrease in heat resistance. For example, the aforementioned cyclic hydroxyphenoxyphosphazene (manufactured by Otsuka Chemical Co., Ltd., product name: SPH-100), 10-(2,5-dihydroxyphenyl)-10-H-9-oxa-10-phosphaphenanthrene-10-oxide (manufactured by Sanko Co., Ltd., product name HCA-HQ), and Olin's XZ-92741 fall into this category. Here, if there is only one functional group that reacts with epoxy, it becomes the end of the crosslinked structure and cuts the network, so there is a possibility that the effect of not reducing heat resistance (ii) will be insufficient.

In addition to the above phosphorus-based flame retardants, other phosphorus-based flame retardants may be used alone or in combination of two or more types as necessary, as long as the flame retardancy, solder heat resistance, and low bleed-out properties are not impaired.

<Other ingredients>
The adhesive composition of the present invention may contain an additional curing agent for curing the epoxy resin (B) or a curing catalyst for promoting the reaction between the epoxy resin (B) and the imide group-containing resin, as long as the properties are not impaired. Such a curing agent is not particularly limited as long as it is a compound that reacts with the epoxy resin (B), and examples thereof include amine-based curing agents, compounds having a phenolic hydroxyl group, compounds having a carboxylic acid, and compounds having an acid anhydride. These curing agents are used to adjust the functional group equivalent between the epoxy resin (B) and the imide group-containing resin. The curing catalyst is not particularly limited as long as it promotes the reaction between the epoxy resin (B) and the imide group-containing resin and the curing agent. For example, imidazole derivatives such as 2MZ, 2E4MZ, C11Z, C17Z, 2PZ, 1B2MZ, 2MZ-CN, 2E4MZ-CN, C11Z-CN, 2PZ-CN, 2PHZ-CN, 2MZ-CNS, 2E4MZ-CNS, 2PZ-CNS, 2MZ-AZINE, 2E4MZ-AZINE, C11Z-AZINE, 2MA-OK, 2P4MHZ, 2PHZ, and 2P4BHZ manufactured by Shikoku Chemical Industry Co., Ltd.; guanamines such as acetoguanamine and benzoguanamine; diaminodiphenylmethane, m-phenylenediamine, m- Xylylenediamine, diaminodiphenylsulfone, dicyandiamide, urea, urea derivatives, melamine, polyamines such as polybasic hydrazides, organic acid salts and/or epoxy adducts thereof, amine complexes of boron trifluoride, triazine derivatives such as ethyldiamino-S-triazine, 2,4-diamino-S-triazine, and 2,4-diamino-6-xylyl-S-triazine, trimethylamine, triethanolamine, N,N-dimethyloctylamine, N-benzyldimethylamine, pyridine, N-methylmorpholine, hexa(N-methyl)melamine, 2,4,6-tris(dimethylaminophenol), tetramethylguanidine, DBU(1,8- tertiary amines such as diazabicyclo[5,4,0]-7-undecene (DBN) and DBN-5-nonene (DBN), organic acid salts thereof and/or tetraphenylborate, polyvinylphenol, polyvinylphenol bromide, organic phosphines such as tributylphosphine, triphenylphosphine and tris-2-cyanoethylphosphine, quaternary phosphonium salts such as tri-n-butyl(2,5-dihydroxyphenyl)phosphonium bromide, hexadecyltributylphosphonium chloride and tetraphenylphosphonium tetraphenylborate, benzyltrimethylammonium chloride, phenyltributary phosphate, etc. Examples of the curing agent and curing catalyst include quaternary ammonium salts such as tetraphenylammonium chloride, the polycarboxylic acid anhydrides, diphenyliodonium tetrafluoroborate, triphenylsulfonium hexafluoroantimonate, 2,4,6-triphenylthiopyrylium hexafluorophosphate, photocationic polymerization catalysts such as Irgacure 261 (manufactured by Ciba Specialty Chemicals Co., Ltd.) and Optomer SP-170 (manufactured by ADEKA Corporation), styrene-maleic anhydride resins, equimolar reactants of phenylisocyanate and dimethylamine, and equimolar reactants of organic polyisocyanates such as tolylene diisocyanate and isophorone diisocyanate and dimethylamine. These curing agents and curing catalysts can be used alone or in combination of two or more.

A silane coupling agent can be added to the adhesive composition of the present invention to improve adhesion. Specific examples include aminosilane, mercaptosilane, vinylsilane, epoxysilane, methacrylsilane, isocyanatesilane, ketiminesilane, or mixtures or reactants thereof, or compounds obtained by reacting these with polyisocyanates. Examples of such silane coupling agents include aminosilanes such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldiethoxysilane, bistrimethoxysilylpropylamine, bistriethoxysilylpropylamine, bismethoxydimethoxysilylpropylamine, bisethoxydiethoxysilylpropylamine, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, and N-2-(aminoethyl)-3-aminopropylethyldiethoxysilane; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane, and γ-mercaptopropylethyldiethoxysilane; vinyl silanes such as tris-(2-methoxyethoxy)vinyl silane, γ-glycidoxypropyl trimethoxy silane, γ-glycidoxypropyl dimethyl ethoxy silane, γ-glycidoxypropyl methyl diethoxy silane, β-(3,4-epoxycyclohexyl) ethyl methyl dimethoxy silane, γ-glycidoxypropyl trimethoxy silane, β-(3,4-epoxycyclohexyl) ethyl trimethoxy silane, etc. Examples of the silane coupling agent include methacrylsilanes such as epoxy silane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane; isocyanate silanes such as isocyanatepropyltriethoxysilane and isocyanatepropyltrimethoxysilane; and ketimine silanes such as ketimine propyltrimethoxysilane and ketimine propyltriethoxysilane. These may be used alone or in combination of two or more. Among these silane coupling agents, epoxy silane has a reactive epoxy group and can react with an imide group-containing resin, so it is preferable in terms of improving heat resistance and moist heat resistance. The amount of the silane coupling agent is preferably 0 to 3 mass%, and more preferably 0 to 2 mass%, when the entire non-volatile content of the resin composition is 100 mass%. If the amount exceeds the above range, the heat resistance tends to decrease.

The adhesive composition of the present invention may contain an organic or inorganic filler for the purpose of improving the solder heat resistance, as long as the effect of the present invention is not impaired. Examples of the organic filler include powders of heat-resistant resins such as polyimide and polyamideimide. Examples of inorganic fillers include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), titania (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), zirconia (ZrO ₂ ), silicon nitride (Si ₃ N ₄ ), barium titanate (BaO.TiO ₂ ), barium carbonate (BaCO ₃ ), lead titanate (PbO.TiO ₂ ), lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), gallium oxide (Ga ₂ O ₃ ), spinel (MgO.Al ₂ O ₃ ), mullite (3Al ₂ _O 3.2SiO ₂ ), cordierite (2MgO.2Al ₂ O _3.5SiO ₂ ), talc (3MgO.4SiO _2.H ₂ O), aluminum titanate (TiO ₂ -Al ₂ O ₃ ), yttria-containing zirconia (Y ₂ O ₃ -ZrO ₂ ), barium silicate (BaO.8SiO ₂ ), boron nitride (BN), calcium carbonate (CaCO ₃ ), calcium sulfate (CaSO ₄ ), zinc oxide (ZnO), magnesium titanate (MgO.TiO ₂ ), barium sulfate (BaSO ₄ ), organic bentonite, clay, mica, aluminum hydroxide, magnesium hydroxide, metal phosphinate, etc. are included. Among these, silica is preferred because of its ease of dispersion and heat resistance improvement effect. These may be used alone or in combination of two or more. The amount of these organic fillers and inorganic fillers added is preferably 1 to 30 mass % and more preferably 3 to 15 mass % based on the non-volatile components of the adhesive composition. If the amount of organic filler or inorganic filler added is too large, the adhesive coating film may become embrittled, and if the amount added is too small, the effect of improving heat resistance may not be sufficient.

<Flexible printed wiring board>
The adhesive composition of the present invention is suitable for use in flexible printed wiring boards. As components constituting flexible printed wiring boards, the adhesive composition of the present invention can be used for copper-clad laminates, coverlay films, and adhesive sheets.

The copper-clad laminate of the present invention has a structure in which copper foil is bonded to at least one side of an insulating plastic film using the adhesive composition of the present invention. The copper foil is not particularly limited, but rolled copper foil or electrolytic copper foil that is conventionally used in flexible printed wiring boards can be used.

The coverlay film of the present invention has a structure in which an adhesive layer made of the adhesive composition of the present invention and an insulating plastic film are laminated, and in particular has a structure of insulating plastic film/adhesive layer or insulating plastic film/adhesive layer/protective film. The insulating plastic film is a film made of plastic such as polyimide, polyamideimide, polyethylene terephthalate, polyethylene naphthalate, liquid crystal polymer (LCP), fluororesin, polyphenylene sulfide, polyethersulfone, polyetheretherketone, aramid, polycarbonate, polyarylate, etc., having a thickness of 1 to 200 μm, and a plurality of films selected from these may be laminated. There are no particular restrictions on the protective film as long as it can be peeled off without impairing the properties of the adhesive, and examples of the protective film include plastic films such as polyethylene, polypropylene, polyolefin, polyester, polymethylpentene, polyvinyl chloride, polyvinylidene fluoride, polyphenylene sulfide, etc., films coated with silicone, fluoride, or other release agents, paper laminated with these, and paper impregnated or coated with peelable resin.

The adhesive sheet of the present invention has a structure in which an adhesive layer made of the adhesive composition of the present invention and a peelable protective film are laminated together, and in particular has a structure of protective film/adhesive layer or protective film/adhesive/protective film. An insulating plastic film layer may be provided within the adhesive layer. The adhesive sheet can also be used for multilayer printed circuit boards.

In any of the above applications, a solution of the adhesive composition of the present invention is applied onto the insulating plastic film or copper foil substrate, the solvent is dried, and the adhesive is thermocompressed to the adherend and then thermoset before use. In order to adjust the fluidity of the adhesive during thermocompression, a heat treatment may be performed after the solvent is dried to cause a partial reaction between the imide group-containing resin and the curing agent. The state before thermocompression is called the B stage.

In any of the above applications, heat resistance, adhesion, flexibility, and insulation are required after heat curing, and flame retardancy is preferable. In addition, in the case of coverlay films and adhesive sheets, it is common to wind, store, cut, punch, and perform other processing in the B-stage state, so flexibility in the B-stage state is also necessary. On the other hand, in the case of copper-clad laminates, it is common to perform thermocompression bonding and thermocuring immediately after forming the B-stage state, so flexibility in the B-stage state is not required as much as in the case of coverlay films and adhesive sheets. The coverlay films and adhesive sheets using the adhesive of the present invention have high fluidity in the B-stage state and high insulation after heat curing, and flexible printed wiring boards using them can accommodate fine pitch patterns with circuit widths and circuit spacings of several μm to 20 μm, and can also accommodate flexible printed wiring boards for coils with a large ratio of circuit height to circuit width (aspect ratio) and narrow circuit spacing.

The effects of the present invention will be demonstrated below with examples, but the present invention is not limited to these. The characteristics in the examples were evaluated using the following methods.

(Method of Evaluating Adhesion)
The solution of the adhesive composition was applied to a polyimide film (Apical 12.5NPI, manufactured by Kaneka) so that the thickness after drying was 20 μm, and dried in a hot air dryer at 140 ° C for 3 minutes to obtain a sample in a B-stage state. The adhesive-coated surface of this B-stage sample was overlapped with the glossy surface of a copper foil (BHY, manufactured by JX Nippon Oil & Gas Exploration Co., Ltd., thickness 18 μm), set in a press, heated from room temperature, and thermocompressed at 60 minutes x 30 kg / cm ² after reaching 180 ° C. For the sample after thermocompression, the polyimide film was peeled off in a 180 ° direction at a speed of 50 mm / min in an atmosphere of 25 ° C. using a tensile tester (Autograph AG-X plus, manufactured by Shimadzu), the adhesive strength was measured, and the adhesiveness was evaluated according to the following evaluation criteria.
(Evaluation criteria)
◎: Adhesive strength is 0.7 N/mm or more. ○: Adhesive strength is 0.5 N/mm or more and less than 0.7 N/mm. ×: Adhesive strength is less than 0.5 N/mm.

(Method of evaluating flame retardancy)
A B-stage sample was prepared in the same manner as in the adhesiveness evaluation method, and the adhesive-coated surface and a polyimide film (Apical 12.5NPI, manufactured by Kaneka) were thermocompression-bonded at 180° C. for 60 minutes. The flame retardancy of the thermocompression-bonded sample was evaluated according to the following evaluation criteria in accordance with the UL-94VTM standard.
(Evaluation criteria)
○: VTM-0 is satisfied. ×: VTM-0 is not satisfied.

(Evaluation method for insulation reliability-1)
Similar to the adhesiveness evaluation method, a B-stage sample was prepared and thermocompression-bonded to a polyimide printed circuit board formed with copper foil in a comb-shaped circuit pattern with a circuit width L and a circuit spacing S of L/S=50 μm/50 μm at 180° C. for 60 minutes. After that, a voltage of 50 V was applied for 1000 hours in an environment of a temperature of 85° C. and a humidity of 85%, and the insulation reliability was evaluated according to the following evaluation criteria.
(Evaluation criteria)
◯: Resistance after 1000 hours is 5×10 ⁸ Ω or more, and no dendrites have been generated. ×: Resistance after 1000 hours is less than 5×10 ⁸ Ω, or dendrites have been generated (evaluation method for insulation reliability-2).
Insulation reliability-2 is an evaluation method in which the L/S of the comb-type circuit pattern is narrower than that in insulation reliability-1, making the conditions stricter.
A B-stage sample was prepared in the same manner as in the evaluation of insulation reliability-1, and was thermocompression bonded to a comb-shaped circuit pattern with L/S=10 μm/10 μm formed by a semi-additive method at 180° C. for 60 minutes. Thereafter, a voltage of 50 V was applied for 500 hours in an environment of a temperature of 85° C. and a humidity of 85%, and the insulation reliability was evaluated according to the following evaluation criteria.
(Evaluation criteria)
⊚: Resistance after 500 hours is 1×10 ⁸ Ω or more, and no dendrites are generated. ◯: Resistance after 500 hours is 1×10 ⁸ Ω or more, but slight dendrites are generated. ×: Dielectric breakdown occurs within 500 hours.

(Method of evaluating solder heat resistance)
Similar to the method for evaluating adhesion, samples were prepared after thermocompression bonding, cut into 20 mm squares, and floated in a solder bath at 280°C or 300°C for 1 minute with the polyimide film side facing up, and the solder heat resistance was evaluated according to the following evaluation criteria.
(Evaluation criteria)
⊚: No blistering or peeling occurred at either 280°C or 300°C. ◯: No blistering or peeling occurred at 280°C, but blistering or peeling occurred at 300°C. ×: Blistering or peeling occurred at 280°C.

(Production Example of Imido Group-Containing Resin (A1))
In a four-necked separable flask equipped with a stirrer, a cooling tube, a nitrogen inlet tube and a thermometer, 30 molar parts of trimellitic anhydride, 20 molar parts of BPADA, 50 molar parts of dimer acid, 100 molar parts of diphenylmethane diisocyanate and N-methyl-2-pyrrolidone as a polymerization solvent were added so that the concentration of the resin after decarbonation was 40% by mass, and the mixture was heated to 100° C. under nitrogen and reacted for 2 hours, and further heated to 150° C. and reacted for 5 hours. Thereafter, the mixture was diluted with cyclohexanone as a dilution solvent so that the concentration of the resin was 30% by mass, to obtain a solution of imide group-containing resin (A1).

(Production Examples of Imido Group-Containing Resins (A2) to (A12))
Solutions of imide group-containing resins (A2) to (A12) were prepared in the same manner as for imide group-containing resin 1, except that the types and amounts of raw materials and solvents were changed so as to obtain the resin compositions shown in Table 1.

Details of the raw materials used in Table 1 are as follows.
Dimer acid: PRIPOL1013 manufactured by Croda
Hydrogenated dimer acid: PRIPOL1009 manufactured by Croda
BPADA: Fujifilm Wako Pure Chemical Industries, Ltd. 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride ODPA: Tokyo Chemical Industry Co., Ltd. Oxydiphthalic dianhydride TMEG: New Japan Chemical Co., Ltd. Ethylene glycol bisanhydrotrimellitate TMPG: Trylead Chemical Co., Ltd. Propylene glycol bisanhydrotrimellitate TMA: Fujifilm Wako Pure Chemical Industries, Ltd. Trimellitic anhydride NBR: HUNTSMAN CTBN1300x13NA, acrylonitrile-butadiene rubber having carboxy groups at both ends MDI: Fujifilm Wako Pure Chemical Industries, Ltd. Diphenylmethane diisocyanate TDI: Tokyo Chemical Industry Co., Ltd. Tolylene diisocyanate ToDI: Nippon Soda Co., Ltd. o-Tolidine diisocyanate NMP: Fujifilm Wako Pure Chemical Industries, Ltd. N-Methyl-2-pyrrolidone DMAc: N,N-dimethylacetamide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

Example 1
An adhesive composition was prepared by mixing 55 parts by mass of a solution of the imide group-containing resin (A1) as a solid content, 25 parts by mass of jER828 (epoxy resin (B)) as a solid content, 10 parts by mass of BCA (phosphorus-based flame retardant (E)) as a solid content, and 6 parts by mass of ZX-92741 (phosphorus-based flame retardant (E)) as a solid content. Note that for jER828, BCA, and ZX-92741, a dimethylacetamide solution with a solid content of 30% by mass was prepared in advance and used. The adhesive composition obtained was evaluated for adhesion, flame retardancy, insulation reliability, and solder heat resistance. The results are shown in Table 2.

<Examples 2 to 13 and Comparative Examples 1 to 3>
Adhesive compositions were prepared in the same manner as in Example 1, except that the types and amounts of the imide group-containing resin (A), the epoxy resin (B), and the phosphorus-based flame retardant (E) were changed to obtain the adhesive composition formulation shown in Table 2. Note that for the epoxy resin (B) and the phosphorus-based flame retardant (E), a dimethylacetamide solution with a solid content of 30 mass% was prepared in advance and used. The adhesive compositions obtained were evaluated for adhesion, flame retardancy, insulation reliability, and solder heat resistance. The results are shown in Table 2.

Details of the epoxy resin (B) and phosphorus-based flame retardant (E) used in Table 2 are as follows.
jER828: Mitsubishi Chemical epoxy resin (bisphenol type epoxy resin, epoxy equivalent: 189 g/eq)
jER152: Epoxy resin manufactured by Mitsubishi Chemical (phenol novolac type epoxy resin, epoxy equivalent: 177 g/eq)
jER1001: Mitsubishi Chemical epoxy resin (bisphenol type epoxy resin, epoxy equivalent: 475 g/eq)
BCA: 10-benzyl-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide HCA: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide ZX-92741: Olin, phosphorus phenol compound having two phenolic hydroxyl groups

As can be seen from Table 2, the adhesive compositions of Examples 1 to 13, which satisfy the requirements of the present invention, were able to simultaneously exhibit excellent adhesion, high insulation reliability, and solder heat resistance. In contrast, in Comparative Example 1, the imide group-containing resin did not have dimer acid as a constituent unit, so the flexibility as an adhesive was insufficient and the adhesive properties could not be satisfied. In Comparative Example 2, the imide group-containing resin did not have an acid dianhydride compound having an ester group or ether group as a constituent unit, so the solder heat resistance was poor. In Comparative Example 3, the imide group-containing resin did not have dimer acid as a constituent unit, and instead acrylonitrile-butadiene rubber (NBR) was used as a raw material, so the insulation reliability was poor due to the influence of moisture absorption by the nitrile in the NBR.

The adhesive composition of the present invention has excellent adhesion, insulation reliability, and solder heat resistance, making it suitable for use in coverlay films, adhesive sheets, copper-clad laminates, and the like. Therefore, the present invention is extremely useful in this industry.

Claims

An adhesive composition containing an imide group-containing resin (A) and an epoxy resin (B), characterized in that the imide group-containing resin (A) has an acid dianhydride compound (C) having an ester group or an ether group, and a dimer acid (D) as structural units.
The adhesive composition according to claim 1, characterized in that the acid dianhydride compound (C) is an alkylene glycol bisanhydrotrimellitate.
The adhesive composition according to claim 1, characterized in that the acid dianhydride compound (C) is 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic dianhydride or oxydiphthalic dianhydride.
The adhesive composition according to any one of claims 1 to 3, characterized in that the copolymerization amounts of the acid dianhydride compound (C) and the dimer acid (D) are each in the range of 1 to 80 mol % when the total amount of polycarboxylic acid components constituting the imide group-containing resin (A) is taken as 100 mol %.
The adhesive composition according to any one of claims 1 to 3, further comprising a phosphorus-based flame retardant (E).
A copper-clad laminate comprising an insulating plastic film and a copper foil laminated on at least one side thereof via the adhesive composition according to any one of claims 1 to 3.
A coverlay film characterized by being formed by laminating an adhesive layer made of the adhesive composition according to any one of claims 1 to 3 and an insulating plastic film.
An adhesive sheet comprising an adhesive layer made of the adhesive composition according to any one of claims 1 to 3 and a peelable protective film laminated thereon.
A flexible printed wiring board having a layer made of the adhesive composition according to any one of claims 1 to 3.