Adhesive composition, laminate and adhesive sheet

Abstract

To provide an adhesive composition which has good adhesion to a base material such as LCP, and is also excellent in low dielectric characteristics.SOLUTION: An adhesive composition contains (A) a bismaleimide resin represented by the following general formula (1), (B) an epoxy resin, (C) an active ester-based curing agent, and (D) a curing accelerator, wherein the component (D) contains at least one selected from the group consisting of an imidazole-based compound, an amine-based compound and a peroxide-based compound, and a content of the component (B) is 2.0 to 15.0 pts.mass based on 100 pts.mass of the total amount of the component (A), the component (B) and the component (C) [wherein R1 represents a divalent hydrocarbon group derived from a dimer acid, Q represents a C1-C100 substituted or unsubstituted aliphatic group, a substituted or unsubstituted aromatic group or a substituted or unsubstituted heteroaromatic group, and n represents an integer of 0 to 100.]SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition, a laminate, and an adhesive sheet. More specifically, the present invention relates to an adhesive composition used for bonding a resin substrate to another resin substrate or a metal substrate, and particularly to an adhesive composition used for bonding to a substrate having low dielectric properties such as a liquid crystal polymer (hereinafter abbreviated as "LCP"). [Background technology]

[0002] In recent years, the speed of transmitted signals on printed wiring boards has increased, leading to an increase in the frequency of the signals. Accordingly, there is an increasing demand for flexible printed wiring boards (hereinafter referred to as "FPCs") to have low dielectric properties (low dielectric constant, low dielectric dissipation factor) in the high-frequency range. In response to this demand, substrate films with low dielectric properties, such as LCP, syndiotactic polystyrene (SPS), and polyphenylene sulfide (PPS), have been proposed as alternatives to conventional polyimide (PI) and polyethylene terephthalate films for use in FPCs.

[0003] However, because base films with low dielectric properties have low polarity, when conventional epoxy or acrylic adhesives are used, the adhesive strength is weak, making it difficult to produce FPC components such as coverlay films and laminates. Furthermore, epoxy and acrylic adhesives do not have excellent low dielectric properties, which can impair the dielectric properties of FPCs.

[0004] On the other hand, polyolefin resins are known to have low dielectric properties. Therefore, adhesive compositions for FPCs using polyolefin resins have been proposed. For example, Patent Document 1 proposes a modified polyamide adhesive composition incorporating an olefin skeleton to improve the electrical properties of FPCs. Patent Document 2 also proposes an adhesive and a coverlay for flexible printed wiring boards using an aromatic olefin oligomer-type modifier and an epoxy resin. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-284515 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-63306 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the adhesive compositions described in Patent Documents 1 and 2 have the problem that, although they can provide adhesion to polyimide films, they have difficulty in providing adhesion to substrate films with low dielectric properties such as LCP, etc. Furthermore, the adhesive compositions described in Patent Documents 1 and 2 have the problem of poor dielectric properties.

[0007] When using an LCP substrate, a two-layer substrate can be produced by melting the LCP without using adhesive and laminating it with copper foil. However, this method has problems such as the need for a high-temperature laminating device or machine, and the substrate is prone to wrinkling during processing, resulting in low yields.

[0008] The present invention has been made in view of the problems associated with the prior art described above, and has an object to provide an adhesive composition that has good adhesion to substrates such as LCP and also has excellent low dielectric properties, as well as a laminate and an adhesive sheet that use the same. [Means for solving the problem]

[0009] As a result of extensive research aimed at solving the above problems, the present inventors have discovered that an adhesive composition containing a specific bismaleimide resin having a structure derived from a dimer acid, an epoxy resin, an active ester curing agent, and a curing accelerator having a specific structure exhibits excellent low dielectric properties and has high adhesion to resin substrates having low dielectric properties, such as LCP, and have thus completed the present invention.

[0010] That is, the present invention provides the following inventions. [1] An adhesive composition comprising (A) a bismaleimide resin represented by the following general formula (1), (B) an epoxy resin, (C) an active ester curing agent, and (D) a curing accelerator, wherein the component (D) comprises at least one compound selected from the group consisting of imidazole compounds, amine compounds, and peroxide compounds: [ka] [In formula (1), R 1 represents a divalent hydrocarbon group derived from a dimer acid, Q represents a substituted or unsubstituted aliphatic group having 1 to 100 carbon atoms, a substituted or unsubstituted aromatic group, or a substituted or unsubstituted heteroaromatic group, and n represents an integer of 0 to 100. [2] The adhesive composition according to [1] above, wherein the content of the component (B) is 2.0 to 30.0 parts by mass, relative to 100 parts by mass of the total amount of the components (A), (B), and (C). [3] The adhesive composition according to [1] or [2] above, wherein the content of the component (C) is 2.0 to 35.0 parts by mass, relative to 100 parts by mass of the total amount of the components (A), (B), and (C). [4] The adhesive composition according to any one of [1] to [3] above, wherein the content of the component (D) is 0.1 to 5.0 parts by mass per 100 parts by mass of the total amount of the components (A), (B), and (C). [5] The adhesive composition according to any one of the above [1] to [4], which is used for bonding a resin substrate to another resin substrate or a metal substrate. [6] A laminate comprising a substrate and an adhesive layer formed on the substrate using the adhesive composition according to any one of [1] to [5] above. [7] A laminate comprising a resin substrate and a resin or metal substrate bonded together with the adhesive composition according to any one of [1] to [5] above. [8] An adhesive sheet comprising the laminate according to [6] or [7] above. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an adhesive composition that has good adhesion to substrates such as LCP and also has excellent low dielectric properties, as well as a laminate and an adhesive sheet that use the same. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below based on preferred embodiments thereof.

[0013] [Adhesive composition] The adhesive composition of this embodiment contains (A) a bismaleimide resin represented by general formula (1) (hereinafter also referred to as "component (A)"), (B) an epoxy resin (hereinafter also referred to as "component (B)"), (C) an active ester-based curing agent (hereinafter also referred to as "component (C)"), and (D) a curing accelerator (hereinafter also referred to as "component (D)"). In the adhesive composition of this embodiment, component (D) contains at least one curing accelerator selected from the group consisting of imidazole-based compounds, amine-based compounds, and peroxide-based compounds. Furthermore, the adhesive composition of this embodiment may contain (E) an organic solvent (hereinafter also referred to as "component (E)").

[0014] <Component (A): Bismaleimide resin> (A) Bismaleimide resin is a compound represented by the following general formula (1), and can be obtained by reacting dimer diamine, which is a diamine derived from dimer acid, with tetracarboxylic dianhydride and maleic anhydride.

[0015] [ka] In formula (1), R 1represents a divalent hydrocarbon group derived from a dimer acid, Q represents a substituted or unsubstituted aliphatic group having 1 to 100 carbon atoms, a substituted or unsubstituted aromatic group, or a substituted or unsubstituted heteroaromatic group, and n represents an integer of 0 to 100. From the viewpoints of obtaining better adhesion to resin substrates having low dielectric properties such as LCP and better low dielectric properties, Q in formula (1) is preferably an unsubstituted aromatic group. Furthermore, from the viewpoints of obtaining better adhesion to resin substrates having low dielectric properties such as LCP and better low dielectric properties, n in formula (1) is preferably an integer of 5 to 30.

[0016] Dimer diamines are compounds derived from dimer acids, which are dimers of unsaturated fatty acids such as oleic acid, as described in, for example, JP-A-9-12712. In this embodiment, any known dimer diamine can be used without particular limitation, but those represented by the following general formula (3) and / or general formula (4) are preferred.

[0017] [ka] [ka]

[0018] In formulas (3) and (4), p, q, r, and s each represent an integer of 1 or greater selected so that p+q=6 to 17 and r+s=8 to 19, and may be an integer of 1 to 12. In addition, in formulas (3) and (4), the bond shown by a dashed line represents a carbon-carbon single bond or a carbon-carbon double bond. However, when the bond shown by a dashed line is a carbon-carbon double bond, formulas (3) and (4) have a structure in which the number of hydrogen atoms bonded to each carbon atom constituting the carbon-carbon double bond is subtracted by one from the number shown in formulas (3) and (4).

[0019] As the dimer diamine, from the viewpoints of the organic solvent solubility of the resulting bismaleimide resin, and the heat resistance, heat-resistant adhesion, low viscosity, and the like of the adhesive composition when the bismaleimide resin is used as a material for the adhesive composition, the dimer diamine represented by the above general formula (4) is preferred, and the compound represented by the following formula (4-1) is particularly preferred. [ka]

[0020] Commercially available dimer diamine products include, for example, PRIAMINE 1075 and PRIAMINE 1074 (both manufactured by Croda Japan Co., Ltd.).

[0021] Examples of tetracarboxylic dianhydrides include pyromellitic anhydride; 1,2,3,4-cyclobutanetetracarboxylic dianhydride; 1,4,5,8-naphthalenetetracarboxylic dianhydride; 3,4,9,10-perylenetetracarboxylic dianhydride; bicyclo(2.2.2)oct-7-ene-2,3,5,6-tetracarboxylic dianhydride; diethylenetriaminepentaacetic dianhydride; ethylenediaminetetraacetic dianhydride; 3,3',4,4'-benzophenonetetracarboxylic dianhydride; 3,3',4,4'-biphenyltetracarboxylic dianhydride; 4,4'-oxydiphthalic anhydride; 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride; 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride; and 4,4'-bisphenol A. Examples of suitable phthalic anhydrides include diphthalic anhydride, 5-(2,5-dioxytetrahydro)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, ethylene glycol bis(trimellitic anhydride), hydroquinone diphthalic anhydride, allyl nadic anhydride, 2-octen-1-ylsuccinic anhydride, 1,2,3,6-tetrahydrophthalic anhydride, and 3,4,5,6-tetrahydrophthalic anhydride. Among these, pyromellitic anhydride is preferred from the viewpoint of heat resistance. These may be used alone or in combination of two or more.

[0022] The weight average molecular weight of the (A) bismaleimide resin is preferably 3,000 to 70,000, more preferably 5,000 to 50,000, and even more preferably 7,000 to 30,000, from the viewpoint of obtaining better adhesion to resin substrates having low dielectric properties such as LCP, and better low dielectric properties.

[0023] As the (A) bismaleimide resin, commercially available compounds can be used. Specifically, for example, BMI-3000 (synthesized from dimer diamine, pyromellitic dianhydride, and maleic anhydride), BMI-1500, BMI-1700, BMI-5000, and the like manufactured by DESIGNER MOLECURES Inc. can be suitably used.

[0024] <Component (B): Epoxy resin> The (B) epoxy resin is not particularly limited, but from the viewpoint of adhesion to substrates such as LCP, epoxy resins having a bisphenol A skeleton, epoxy resins having a bisphenol F skeleton, polyfunctional epoxy resins having a novolac skeleton, biphenyl-type epoxy resins, and the like are preferred.

[0025] Examples of epoxy resins having a bisphenol A skeleton and epoxy resins having a bisphenol F skeleton include compounds represented by the following general formula (2): From the viewpoint of obtaining better adhesion to substrates such as LCP, the epoxy resins having a bisphenol A skeleton and epoxy resins having a bisphenol F skeleton are preferably epoxy resins represented by the following general formula (2-1):

[0026] [ka] [ka] In formula (2) and formula (2-1), R 2 represents a hydrogen atom or a methyl group, and R 3represents a divalent organic group, and m represents an integer of 0 to 30. In formula (2) and formula (2-1), m is preferably an integer of 0 to 10, from the viewpoint of obtaining better adhesion to resin substrates having low dielectric properties, such as LCP, and better low dielectric properties. 3 Examples of R include a substituted or unsubstituted alkylene group, a substituted or unsubstituted alkylene oxide group, and a substituted or unsubstituted aromatic group. 3 When is a substituted or unsubstituted alkylene group or a substituted or unsubstituted alkylene oxide group, it can impart low elasticity to the epoxy resin.

[0027] Examples of polyfunctional epoxy resins having a novolac skeleton include compounds having a structural unit represented by the following general formula (5) or (6), such as novolac epoxy resins, naphthalene skeleton-modified novolac epoxy resins, biphenyl novolac epoxy resins, and cresol novolac epoxy resins. The number of epoxy groups in the polyfunctional epoxy resins having a novolac skeleton is preferably 3 or more, and more preferably 5 or more. From the viewpoint of low dielectric properties, A in the following general formula (5) is preferably an unsubstituted aromatic group such as a naphthalene skeleton or a biphenyl skeleton.

[0028] [ka] [ka] In formula (5) and formula (6), R 4 represents a hydrogen atom or a methyl group, A represents a divalent organic group having a substituted or unsubstituted aliphatic group having 1 to 30 carbon atoms, a substituted or unsubstituted aromatic group, or a substituted or unsubstituted heteroaromatic group, and x and y each independently represent an integer of 1 or more. When x is 2 or more, multiple R 4 may be the same or different. When y is 2 or more, multiple A's may be the same or different.

[0029] The biphenyl type epoxy resin is not particularly limited as long as it is an epoxy resin having a biphenyl skeleton, but for example, an epoxy resin represented by the following general formula (7) is preferred. [ka]

[0030] In formula (7), R 8 represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, or an aromatic group having 4 to 18 carbon atoms, and may all be the same or different, and t is an average value and represents a number from 0 to 10. From the viewpoint of compatibility with component (A), the value of t is preferably 3 or less, and more preferably 1 or less.

[0031] The content of the epoxy resin (B) is preferably 2.0 to 30.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, and particularly preferably 5.0 to 10.0 parts by mass, based on 100 parts by mass of the total amount of components (A), (B), and (C). When the content of component (B) is 2.0 parts by mass or more, better adhesive strength with the LCP substrate tends to be easily obtained, and when it is 30.0 parts by mass or less, better low dielectric properties tend to be easily obtained.

[0032] <Component (C): Active ester curing agent> (C) The active ester curing agent is a compound that itself participates in the curing reaction, and by using this, it is possible to obtain the effect of reducing the dielectric characteristics.

[0033] The active ester curing agent is not particularly limited, but from the viewpoint of more fully achieving the effect of reducing dielectric properties, compounds having one or more highly reactive ester groups per molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, are preferably used. More specific examples of active ester curing agents include "EPICLON HPC8000-65T," "EPICLON HPC8000-L-65MT," and "EPICLON HPC8150-60T" (all trade names manufactured by DIC Corporation). These can be used alone or in combination of two or more.

[0034] It is believed that the active ester curing agent reacts with the epoxy resin (B) during the curing reaction as shown in the following formula (I): In the reaction between the active ester curing agent (C) and the epoxy resin (B), no hydroxyl groups are produced, and even if a side reaction occurs, hydroxyl groups are unlikely to be produced, which is believed to result in low dielectric properties.

[0035] [ka] In the formula, R 11 , R 12 and R 13 Each independently represents a monovalent organic group, but may be a monovalent organic group having an aromatic ring, as this allows the effects of the present invention to be more fully achieved.

[0036] The content of the (C) active ester curing agent is preferably 2.0 to 35.0 parts by mass, more preferably 3.0 to 20.0 parts by mass, and particularly preferably 5.0 to 15.0 parts by mass, based on 100 parts by mass of the total amount of components (A), (B), and (C). When the content of component (C) is 2.0 parts by mass or more, better low dielectric properties tend to be easily obtained, and when it is 35.0 parts by mass or less, better adhesive strength with the LCP substrate tends to be easily obtained.

[0037] <Component (D): Curing accelerator> The (D) curing accelerator contains at least one selected from the group consisting of imidazole compounds, amine compounds, and peroxide compounds. The (D) curing accelerator may consist solely of the specific curing accelerator, or may further contain other curing accelerators in addition to the specific curing accelerator.

[0038] Examples of imidazole compounds include 1-(2-cyanoethyl)-2-phenylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-methylimidazole, 2-ethylimidazole, 2,4-dimethylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 2-phenyl Examples of suitable imidazole compounds include 1-(2-cyanoethyl)-2-phenylimidazole, 1,2-dimethylimidazole, 2-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-vinyl-2-methylimidazole, 1-propyl-2-methylimidazole, 2-isopropylimidazole, 1-cyanomethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, and 1-cyanoethyl-2-phenylimidazole. Among these, preferred imidazole compounds are 1-(2-cyanoethyl)-2-phenylimidazole, 1,2-dimethylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, and 2-ethyl-4-methylimidazole. The use of these compounds further accelerates the reaction of the (A) bismaleimide resin, resulting in improved heat resistance of the resulting cured product. Furthermore, as the imidazole compound, 1-(2-cyanoethyl)-2-phenylimidazole and 1,2-dimethylimidazole are preferred, and 1-(2-cyanoethyl)-2-phenylimidazole is more preferred, since they tend to provide higher adhesion to resin substrates with low dielectric properties, such as LCP. These compounds may be used alone or in combination of two or more.

[0039] Examples of amine compounds include triethylamine, dimethylbenzylamine, triethylenediamine, tripropylamine, tributylamine, dimethylethanolamine, triethanolamine, 4-aminopyridine, 2-aminopyridine, N,N-dimethyl-4-aminopyridine, 4-diethylaminopyridine, 2-hydroxypyridine, 2-methoxypyridine, and 4-methoxypyridine.

[0040] Examples of peroxide compounds include dicumyl peroxide, diisopropylbenzene hydroperoxide, t-butylcumyl peroxide, benzoyl peroxide, dilauryl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1-bis(t-butylperoxy)-3,5,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)-cyclohexane, cyclohexanone peroxide, t-butylperoxybenzoate, t-butylperoxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxy-2-ethylhexanoate, and cumyl peroxyoctoate.

[0041] Examples of curing accelerators other than the specific curing accelerators include phosphorus-based curing accelerators, such as primary phosphines (e.g., alkylphosphines, phenylphosphine, etc.), secondary phosphines (e.g., dialkylphosphines, diphenylphosphine, etc.), tertiary phosphines (e.g., trialkylphosphines, triphenylphosphine, etc.), and phosphine compounds, as well as phosphonium salt compounds.

[0042] The adhesive composition of this embodiment may contain the phosphorus-based curing accelerator, but a low content is preferable, and the composition may not contain a phosphorus-based curing accelerator. The inventors have found that when a phosphorus-based curing accelerator and an active ester-based curing agent (C) are used in combination, adhesion to substrates such as LCP may decrease. The inventors speculate that the reason for this is as follows. Specifically, to improve adhesion, the (B) epoxy resin and (C) active ester-based curing agent, which contribute to adhesion, must react with the (A) bismaleimide resin, which is the base resin, and be incorporated into the main chain. Furthermore, the reactivity of each component varies depending on the type of curing accelerator. When a phosphorus-based curing accelerator is used, it is thought that the (B) epoxy resin and (C) active ester-based curing agent are less likely to be incorporated into the main chain of the (A) bismaleimide resin, making it difficult to improve adhesion. In contrast, when at least one curing accelerator selected from the group consisting of imidazole-based compounds, amine-based compounds, and peroxide-based compounds is used, it is thought that the (B) epoxy resin and the (C) active ester-based curing agent are more likely to be incorporated into the main chain of the (A) bismaleimide resin, and the adhesiveness is more likely to be improved.

[0043] In order to more easily improve adhesion to substrates such as LCP, the content of at least one curing accelerator selected from the group consisting of imidazole compounds, amine compounds, and peroxide compounds in the curing accelerator (D) is preferably 80 to 100 mass%, more preferably 90 to 100 mass%, and even more preferably 95 to 100 mass%, based on the total amount of the curing accelerator (D).

[0044] Furthermore, since adhesion to substrates such as LCP is more likely to be improved, the content of the phosphorus-based curing accelerator in the (D) curing accelerator is preferably 0 to 20 mass%, more preferably 0 to 10 mass%, and even more preferably 0 to 5 mass%, based on the total amount of the (D) curing accelerator.

[0045] The content of (D) curing accelerator is not particularly limited, but from the viewpoint of further improving adhesion to substrates such as LCP and the heat resistance of the resulting cured product, it is preferably 0.1 to 5.0 parts by mass, and more preferably 1.0 to 3.0 parts by mass, per 100 parts by mass of the total amount of the bismaleimide resin (A), the epoxy resin (B), and the active ester curing agent (C).

[0046] <Component (E): Organic solvent> The adhesive composition of this embodiment may further contain (E) an organic solvent. The organic solvent used in this embodiment is not particularly limited as long as it dissolves (A) the bismaleimide resin, (B) the epoxy resin, (C) the active ester-based curing agent, and (D) the curing accelerator. Specific examples of (E) the organic solvent include aromatic hydrocarbons such as benzene, toluene, xylene, and mesitylene; aliphatic hydrocarbons such as hexane, heptane, octane, and decane; alicyclic hydrocarbons such as cyclohexane, cyclohexene, methylcyclohexane, and ethylcyclohexane; halogenated hydrocarbons such as trichloroethylene, dichloroethylene, chlorobenzene, and chloroform; alcoholic solvents such as methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, propanediol, and phenol; acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclohexane, and phenol. Ketone-based solvents such as xanone, isophorone, and acetophenone; cellosolves such as methyl cellosolve and ethyl cellosolve; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and butyl formate; and glycol ether-based solvents such as ethylene glycol mono-n-butyl ether, ethylene glycol mono-iso-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-iso-butyl ether, triethylene glycol mono-n-butyl ether, and tetraethylene glycol mono-n-butyl ether. These can be used alone or in combination of two or more. A preferred embodiment is an aromatic hydrocarbon, and in particular, toluene or xylene is preferably used.

[0047] The adhesive composition of the present embodiment is prepared according to a commonly employed method. Examples of the preparation method include melt mixing, powder mixing, solution mixing, etc. In addition to the essential components of the present embodiment, other additives such as inorganic fillers, release agents, flame retardants, ion trapping agents, antioxidants, adhesion promoters, stress reducing agents, colorants, and coupling agents may be added within a range that does not impair the effects of the present invention.

[0048] <Inorganic filler> The inorganic filler is added to reduce the thermal expansion coefficient of the adhesive composition and improve the moisture resistance reliability. Examples of the inorganic filler include silicas such as fused silica, crystalline silica, and cristobalite, alumina, silicon nitride, aluminum nitride, boron nitride, titanium oxide, glass fiber, and magnesium oxide. The average particle size and shape of these inorganic fillers can be selected depending on the application. Among these, spherical alumina, spherical fused silica, and glass fiber are preferred.

[0049] <Release agent> The mold release agent is added to improve releasability from the mold, and any of the known mold release agents can be used, such as carnauba wax, rice wax, candelilla wax, polyethylene, polyethylene oxide, polypropylene, montanic acid, montan wax which is an ester compound of montanic acid with saturated alcohol, 2-(2-hydroxyethylamino)ethanol, ethylene glycol, glycerin, etc., stearic acid, stearic acid ester, stearic acid amide, etc.

[0050] <Flame retardant> The flame retardant is added to impart flame retardancy. Any known flame retardant can be used, and there is no particular limitation. Examples of the flame retardant include phosphazene compounds, silicone compounds, zinc molybdate-supported talc, zinc molybdate-supported zinc oxide, aluminum hydroxide, magnesium hydroxide, and molybdenum oxide.

[0051] <Ion trapping agent> The ion trapping agent is added to the liquid adhesive composition to capture ionic impurities and prevent thermal and moisture-absorbing deterioration. Any known ion trapping agent can be used, and there are no particular limitations. Examples of the ion trapping agent include hydrotalcites, bismuth hydroxide compounds, and rare earth oxides.

[0052] [Laminate] The laminate of this embodiment is a laminate in which an adhesive composition is laminated onto a substrate (a two-layer laminate of substrate / adhesive layer), or a three-layer laminate of substrate / adhesive layer / substrate). Here, the adhesive layer refers to the layer of adhesive composition remaining after the adhesive composition of this embodiment is applied to a substrate and dried. The laminate of this embodiment can be obtained by applying the adhesive composition of this embodiment to various substrates and drying them according to a conventional method, and then laminating another substrate on top.

[0053] <Base material> In this embodiment, the substrate is not particularly limited as long as it is possible to apply the adhesive composition of this embodiment to the substrate and dry it to form an adhesive layer. Examples of the substrate include resin substrates such as film-like resins, metal substrates such as metal plates and metal foils, and paper.

[0054] Examples of materials for the resin substrate include polyester resin, polyamide resin, polyimide resin, polyamideimide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, fluorine-based resin, etc. The resin substrate is preferably a film-like resin (hereinafter also referred to as "substrate film layer").

[0055] The metal substrate can be any conventionally known conductive material that can be used for circuit boards. Examples of materials include various metals such as SUS, copper, aluminum, iron, steel, zinc, and nickel, as well as their alloys, plated products, and metals treated with other metals such as zinc or chromium compounds. The metal substrate is preferably a metal foil, more preferably a copper foil. The thickness of the metal foil is not particularly limited, but is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 10 μm or more. The thickness of the metal foil is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the thickness is too thin, it may be difficult to obtain sufficient electrical performance of the circuit. On the other hand, if the thickness is too thick, processing efficiency during circuit fabrication may decrease. Metal foils are usually provided in a roll form, but the form of metal foil used in the production of printed wiring boards, as described below, is not particularly limited. When ribbon-shaped metal foil is used, its length is not particularly limited. Its width is also not particularly limited, but is preferably about 250 to 500 cm.

[0056] Examples of the paper include fine paper, kraft paper, roll paper, glassine paper, etc. Examples of the composite material include glass epoxy, etc.

[0057] From the viewpoints of adhesive strength with the adhesive composition and durability, the material of the substrate is preferably polyester resin, polyamide resin, polyimide resin, polyamideimide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, fluorine-based resin, SUS steel plate, copper foil, aluminum foil, or glass epoxy.

[0058] <Adhesive sheet> The adhesive sheet of this embodiment includes the above-described laminate, for example, laminated with a release substrate via an adhesive composition. Specific configurations include laminate (substrate / adhesive layer) / release substrate, laminate (substrate / adhesive layer / substrate) / adhesive layer / release substrate, or release substrate / adhesive layer / laminate (substrate / adhesive layer / substrate) / adhesive layer / release substrate. The release substrate functions as a protective layer for the adhesive layer that constitutes the adhesive sheet. Furthermore, by using a release substrate, the release substrate can be released from the adhesive sheet and the adhesive layer can be transferred to another substrate.

[0059] The adhesive sheet of this embodiment can be obtained by applying the adhesive composition of this embodiment to various laminates and drying them according to a conventional method. After drying, by attaching a release substrate to the adhesive layer, the laminate can be wound up without causing transfer to the substrates that make up the laminate, resulting in excellent operability and excellent storage stability due to the protection of the adhesive layer, and easy use. Furthermore, if the adhesive composition is applied to a release substrate, dried, and then another release substrate is attached as needed, it becomes possible to transfer the adhesive layer itself to another substrate.

[0060] <Release base material> The release substrate is not particularly limited, but examples include high-quality paper, kraft paper, roll paper, glassine paper, etc., with coating layers of clay, polyethylene, polypropylene, or other filler on both sides, and then a silicone-based, fluorine-based, or alkyd-based release agent coated on each of these coating layers. Other examples include various olefin films such as polyethylene, polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer alone, and films such as polyethylene terephthalate coated with the above-mentioned release agent. Due to factors such as the release force between the release substrate and the adhesive layer and the adverse effect of silicone on electrical properties, it is preferable to use high-quality paper with polypropylene sealing on both sides and an alkyd-based release agent on the polypropylene sealing, or polyethylene terephthalate coated with an alkyd-based release agent.

[0061] In this embodiment, the method for coating the adhesive composition onto a substrate is not particularly limited, but examples include a comma coater and a reverse roll coater. Alternatively, if necessary, an adhesive layer can be formed directly or by transfer onto rolled copper foil or polyimide film, which are constituent materials of the printed wiring board. The thickness of the adhesive layer after drying can be appropriately adjusted as needed, but is preferably in the range of 5 to 200 μm. If the thickness of the adhesive layer is less than 5 μm, the adhesive strength may be insufficient. If the thickness is 200 μm or more, drying may be insufficient, resulting in a large amount of residual solvent, which may cause blisters during pressing in the production of printed wiring boards. The drying conditions are not particularly limited, but the residual solvent content after drying is preferably 1% by mass or less. If it exceeds 1% by mass, the residual solvent may foam during pressing in the production of printed wiring boards, which may cause blisters.

[0062] <Printed wiring board> The printed wiring board in this embodiment includes, as a component, a laminate formed from a metal foil that forms a conductor circuit and a resin substrate. The printed wiring board can be manufactured by a conventionally known method such as a subtractive method using a metal-clad laminate. The printed wiring board in this embodiment is a general term for so-called flexible circuit boards (FPCs), flat cables, circuit boards for tape automated bonding (TAB), etc., in which a conductor circuit formed from metal foil is partially or completely covered with a cover film, screen printing ink, etc., as necessary.

[0063] The printed wiring board of this embodiment can have any laminated structure that can be used as a printed wiring board. For example, it can be a printed wiring board consisting of four layers: a base film layer, a metal foil layer, an adhesive layer, and a cover film layer. Alternatively, it can be a printed wiring board consisting of five layers: a base film layer, an adhesive layer, a metal foil layer, an adhesive layer, and a cover film layer.

[0064] Furthermore, if necessary, two or more of the above printed wiring boards may be stacked.

[0065] The adhesive composition of this embodiment can be suitably used in each adhesive layer of a printed wiring board. In particular, when the adhesive composition of this embodiment is used as an adhesive, it has high adhesion not only to conventional polyimide, polyester film, and copper foil that constitute printed wiring boards, but also to low-polarity resin substrates such as LCP, and can achieve solder reflow resistance, and the adhesive layer itself has excellent low dielectric properties. Therefore, it is suitable as an adhesive composition for use in coverlay films, laminates, resin-coated copper foils, and bonding sheets.

[0066] In the printed wiring board of this embodiment, any resin film conventionally used as a substrate for printed wiring boards can be used as the substrate film. Examples of resins for the substrate film include polyester resins, polyamide resins, polyimide resins, polyamideimide resins, liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, polyolefin-based resins, and fluorine-based resins. The adhesive composition of this embodiment has excellent adhesion, particularly to low-polarity substrates such as liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, and polyolefin-based resins.

[0067] <Cover film> The cover film can be any insulating film conventionally known as an insulating film for printed wiring boards. For example, films made from various polymers such as polyimide, polyester, polyphenylene sulfide, polyether sulfone, polyether ether ketone, aramid, polycarbonate, polyarylate, polyimide, polyamide-imide, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, and polyolefin resins can be used. Polyimide film or liquid crystal polymer film is more preferred. [Example]

[0068] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0069] [Physical property evaluation method] <Weight average molecular weight (Mw)> The weight-average molecular weight (Mw) was measured by gel permeation chromatography (GPC). A sample prepared by dissolving maleimide resin in tetrahydrofuran (THF) to a concentration of 3% by mass was injected in an amount of 50 μL into a column (one GL-R420 (Hitachi High-Tech Fielding Corporation), one GL-R430 (Hitachi High-Tech Fielding Corporation), and one GL-R440 (Hitachi High-Tech Fielding Corporation)) heated to 30°C. Measurements were performed using THF as the developing solvent at a flow rate of 1.6 mL / min. The detector used was an L-3350 RI detector (Hitachi, Ltd.), and the weight-average molecular weight (Mw) was calculated from the elution time using a molecular weight / elution time curve prepared using standard polystyrene (Tosoh Corporation).

[0070] <Preparation of resin film> The adhesive compositions obtained in the examples and comparative examples described below were applied using an applicator onto Purex (registered trademark) A31 (polyester film, product name, manufactured by Teijin DuPont Co., Ltd.) so that the thickness after drying would be 65 μm, and the coating was dried in an oven at 130°C for 10 minutes to produce a resin film.

[0071] <Adhesive strength> The resin film from which Purex A31 had been peeled was laminated with a 0.7 mm thick glass plate and a 75 μm thick LCP film (manufactured by Kuraray Co., Ltd., product name "Vecstar") with the resin film in the center. The laminate was then thermocompressed at 200°C, 2 MPa, and 1 hour using a heat press to obtain a laminate consisting of a glass plate, a cured resin film, and an LCP film laminated in that order. The adhesive strength of the resulting laminate was measured by peeling the LCP film. The peel strength was measured at room temperature and a pulling rate of 5 mm / s using a 90° peel tester (manufactured by Yamaden Co., Ltd., product name "RHEONER II CREEP METER RE2-3305B"). The peel position (peel mode) during peeling was also observed.

[0072] <Dielectric constant and dielectric loss tangent> The resin film from which Purex A31 had been peeled was laminated with two sheets of copper foil (product name "F2WS-18" manufactured by Furukawa Electric Co., Ltd.) with the roughened side of the copper foil facing the resin film. The laminate was then thermocompressed at 200°C, 2 MPa, and 1 hour to obtain a copper foil laminate consisting of copper foil, cured resin film, and copper foil in that order. The copper foil on both sides of the resulting copper foil laminate was removed by etching, and the laminate was dried at 130°C for 30 minutes. 5 cm x 5 cm test specimens were then prepared. The dielectric constant and dielectric loss tangent were measured at a frequency of 2 MHz using an Agilent Technologies E4980A Precision LCR Meter and at a frequency of 10 GHz using an Agilent Technologies 8364B Vector Network Analyzer. In the present examples and comparative examples, the dielectric constant tends to be slightly lower when measured at a frequency of 2 MHz, and the dielectric loss tangent tends to be slightly lower when measured at a frequency of 10 GHz, but no significant fluctuations were observed in the measured values. Therefore, except for some examples, the dielectric constant and dielectric loss tangent were measured at either a frequency of 2 MHz or a frequency of 10 GHz.

[0073] [Synthesis of bismaleimide resin] <Synthesis Example 1> A 1 L flask equipped with a condenser, a nitrogen inlet tube, a thermocouple, and a stirrer was charged with 60.8 parts by mass of pyromellitic dianhydride (manufactured by Daicel Corporation), 400.4 parts by mass of mesitylene (manufactured by Toyo Gosei Co., Ltd.), and 90.7 parts by mass of ethanol (manufactured by Wako Pure Chemical Industries, Ltd.). After charging, the temperature was raised to 80°C and maintained at that temperature for 0.5 hours, and 201.3 parts by mass of dimer diamine (trade name "PRIAMINE 1075", manufactured by Croda Japan Co., Ltd.) was added dropwise. After the dropwise addition, 4.3 parts by mass of methanesulfonic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was added. The temperature was then raised to 165°C, and a dehydration ring-closing reaction was carried out at 165°C for 1 hour. Water and ethanol were removed from the reaction solution, and an intermediate polyimide resin was obtained. Subsequently, the obtained polyimide resin was cooled to 80°C, 27.3 parts by mass of maleic anhydride (manufactured by Fuso Chemical Co., Ltd.) was added, the temperature was raised to 160°C, and a dehydration ring-closing reaction was carried out at 160°C for 2 hours, and water in the reaction solution was removed to obtain a bismaleimide resin.

[0074] The resulting bismaleimide resin was placed in a separatory funnel, and 1,000 parts by mass of pure water was added. The separatory funnel was shaken and allowed to stand. After standing, the aqueous and organic layers separated, and only the organic layer was recovered. The recovered organic layer was placed in a 1 L glass vessel equipped with a condenser, nitrogen inlet tube, thermocouple, stirrer, and vacuum pump, heated to 88-93°C, and the water was removed. The vessel was then heated to 150°C and the solvent was removed for 1 hour under a reduced pressure of 0.1 MPa from atmospheric pressure, yielding bismaleimide resin (A-1) (weight average molecular weight 16,000) of component (A).

[0075] [Example 1] A 500 ml four-neck flask equipped with a stirrer was charged with 80 parts by mass of the maleimide resin (A-1) obtained in Synthesis Example 1, 9 parts by mass of an epoxy resin (trade name "YX-4000" manufactured by Mitsubishi Chemical Corporation), and 100 parts by mass of toluene, and the mixture was stirred at 60°C for 1 hour. To the resulting solution, 11 parts by mass of an active ester curing agent (trade name "HPC-8000-65T" manufactured by DIC Corporation) was added, and the mixture was stirred at 60°C for 0.5 hours. Furthermore, 2 parts by mass of a curing accelerator (trade name "2PZCN" manufactured by Shikoku Kasei Co., Ltd.) was added to the resulting solution, and the mixture was stirred at 60°C for 3 hours to obtain an adhesive composition. The amounts of each component and the results of physical property evaluation are shown in Table 1. In Table 1, the amounts of components (A) to (E) are shown in parts by mass.

[0076] [Examples 2 to 12, Comparative Examples 1 and 2] Adhesive compositions of Examples 2 to 12 and Comparative Examples 1 and 2 were obtained in the same manner as Example 1, except that the type and amount of one or more of the bismaleimide resin, epoxy resin, active ester curing agent, and curing accelerator were changed as shown in Table 1 or Table 2. The amount of each component and the results of physical property evaluation are shown in Tables 1 and 2. In Tables 1 and 2, the amounts of components (A) to (E) are shown in parts by mass. Details of components (A) to (E) are as follows:

[0077] Component (A): Bismaleimide resin (A-1) Bismaleimide resin of Synthesis Example 1 (weight average molecular weight 16,000)

[0078] (B) Component: Epoxy resin (B-1) Biphenyl-type epoxy resin: YX-4000 (manufactured by Mitsubishi Chemical Corporation) (B-2) Bisphenol F type epoxy resin: YDF-8170C (manufactured by Nippon Steel Sumikin Chemical Co., Ltd.)

[0079] Component (C): Active ester curing agent (C-1) HPC-8000-65T (DIC Corporation) (C-2) HPC-8000L-65MT (DIC Corporation)

[0080] Component (D): Curing accelerator (D-1) 1-(2-cyanoethyl)-2-phenylimidazole: 2PZCN (manufactured by Shikoku Chemicals Co., Ltd.) (D-2) 2-Ethyl-4-methyl-imidazole: 2E4MZ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (D-3) 1,2-Dimethylimidazole: 1,2-DMZ (manufactured by Shikoku Chemicals Co., Ltd.) (D-4) Dimethylbenzylamine: DMBA (Fujifilm Wako Pure Chemical Industries, Ltd.) (D-5) Triethylamine: TEA (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (D-6) Dicumyl peroxide: DCP (NOF Corporation) (D-7) Tetrabutylphosphonium-1,2-cyclohexyldicarboxylic acid (cation species:anion species=1:1): TBP-3S (manufactured by Hokko Chemical Co., Ltd.)

[0081] [Table 1]

[0082] [Table 2]

[0083] As is clear from the results shown in Tables 1 and 2, it was confirmed that adhesive compositions (Examples) containing a specific bismaleimide resin of the present invention, an epoxy resin, an active ester-based curing agent, and a curing accelerator exhibit high adhesive strength with LCP. In particular, it was confirmed that adhesive strength could be dramatically improved compared to when an imidazole-based compound, an amine-based compound, and a peroxide-based compound were contained in component (D) (Examples) and when a phosphorus-based compound was contained in component (D) (Comparative Example 1). Furthermore, it was confirmed that the adhesive compositions (Examples) of the present invention also had low dielectric constants and dielectric dissipation factors, and had excellent low dielectric properties. [Industrial Applicability]

[0084] The present invention provides an adhesive composition that exhibits high adhesion to low-polarity resin substrates such as LCPs, which have lower dielectric properties than conventional polyimides, and also exhibits excellent low dielectric properties, as well as laminates and adhesive sheets bonded using the same. Due to these properties, the adhesive composition of the present invention is useful for flexible printed wiring board applications, particularly FPC applications, which require low dielectric properties (low dielectric constant, low dielectric dissipation factor) in the high-frequency range.

Claims

1. (A) a bismaleimide resin represented by the following general formula (1), (B) an epoxy resin, (C) an active ester curing agent, and (D) a curing accelerator, the component (D) contains at least one compound selected from the group consisting of an imidazole compound, an amine compound, and a peroxide compound, the content of the at least one curing accelerator selected from the group consisting of the imidazole-based compounds, the amine-based compounds, and the peroxide-based compounds in the component (D) is 80 to 100 mass% based on the total amount of the component (D), an adhesive composition in which the content of the component (B) is 2.0 to 15.0 parts by mass, relative to 100 parts by mass of the total amount of the component (A), the component (B), and the component (C). 【Chemical 1】 [In formula (1), R １ represents a divalent hydrocarbon group derived from a dimer acid, Q represents a substituted or unsubstituted aliphatic group having 1 to 100 carbon atoms, a substituted or unsubstituted aromatic group, or a substituted or unsubstituted heteroaromatic group, and n represents an integer of 0 to 100.

2. 2. The adhesive composition according to claim 1, wherein the content of the component (C) is 2.0 to 35.0 parts by mass, relative to 100 parts by mass of the total amount of the component (A), the component (B), and the component (C).

3. 3. The adhesive composition according to claim 1, wherein the content of the component (D) is 0.1 to 5.0 parts by mass per 100 parts by mass of the total amount of the component (A), the component (B), and the component (C).

4. The adhesive composition according to any one of claims 1 to 3, which is used for bonding a resin substrate to another resin substrate or a metal substrate.

5. A laminate comprising a substrate and an adhesive layer formed on the substrate using the adhesive composition according to any one of claims 1 to 4.

6. A laminate comprising a resin substrate and a resin substrate or a metal substrate bonded with the adhesive composition according to any one of claims 1 to 4.

7. An adhesive sheet comprising the laminate according to claim 5 or 6.

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