Adhesive composition, adhesive sheet, laminate, and printed wiring board

Abstract

The present application is an adhesive composition containing a polyester resin (A1), a polyester resin (A2), and an epoxy resin (B), which is used to obtain an adhesive composition that is excellent in adhesiveness and solder heat resistance, further exhibits excellent adhesiveness even after long exposure to a high-humidity environment, also satisfies softness and tackiness of a prepreg film, and a bonded sheet, a laminate, and a printed wiring board containing the same. The polyester resin (A1) has a number average molecular weight of less than 10,000, a glass transition temperature of less than 15°C, and has a component (a) having a total of 3 functional groups of a hydroxyl group and a carboxyl group per 1 molecule as a constituent unit, and has 3 mol% or more of the component (a) when the total polycarboxylic acid component constituting the polyester resin (A1) is taken as 100 mol%. The polyester resin (A2) has a number average molecular weight of 10,000 or more and a glass transition temperature of 15°C or more.

Description

Technical Field

[0001] This invention relates to an adhesive composition. More specifically, it relates to an adhesive composition for bonding resin substrates or to resin substrates or metal substrates. Particularly, it relates to an adhesive composition for flexible printed circuit boards (hereinafter referred to as FPCs), and adhesive sheets, laminates, and printed circuit boards comprising the same. Background Technology

[0002] Flexible printed circuit boards (FPCs) are substrates on which circuitry is formed by bonding a thin, flexible film, such as polyimide, with a conductive metal, such as copper foil using an adhesive. Unlike rigid substrates, FPCs are very thin and flexible, making them suitable for use in small spaces or curved, movable parts of electronic devices. Therefore, they are used in many everyday electronic devices such as personal computers and smartphones. Furthermore, in recent years, automobiles have also incorporated many FPCs, where high heat resistance and reliability of the adhesives are increasingly required.

[0003] Copolyesters are widely used as raw materials for resin compositions used in coating agents, inks, and adhesives, and are typically composed of polycarboxylic acids and polyols. Due to the ease of molecular design based on the selection and combination of polycarboxylic acids and polyols, and the ability to freely control the molecular weight, they are widely used in various applications, primarily as coating agents and adhesives.

[0004] Copolyesters exhibit excellent adhesion (peel strength) to metals including copper and can be blended with curing agents for use as adhesives for FPCs (e.g., Patent Document 1).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 6-104813 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, the solder using a copolyester adhesive described in Patent Document 1 has poor heat resistance and does not have the long-term heat resistance required for automotive applications.

[0010] This invention was made against the backdrop of the aforementioned prior art issues. Specifically, the object of this invention is to provide an adhesive composition that exhibits excellent adhesion and solder heat resistance, and thus maintains excellent adhesion even after prolonged exposure to high humidity environments, while also satisfying the requirements of flexibility and tackiness when forming a semi-cured coating, as well as adhesive sheets, laminates, and printed circuit boards comprising the composition.

[0011] Methods for solving problems

[0012] Through in-depth research, the inventors discovered that the aforementioned problems can be solved by the means shown below, thus completing this invention. Specifically, this invention has the following structure.

[0013] [1] An adhesive composition comprising polyester resin (A1), polyester resin (A2), and epoxy resin (B).

[0014] Polyester resin (A1): having a number average molecular weight of less than 10,000, a glass transition temperature of less than 15°C, and having a component (a) having a total of 3 functional groups of hydroxyl and carboxyl groups per molecule as a constituent unit, and having 3 or more of the said component (a) when all the polycarboxylic acid components constituting polyester resin (A1) are set to 100 mol%.

[0015] Polyester resin (A2): Number average molecular weight above 10,000, glass transition temperature above 15°C.

[0016] [2] The adhesive composition described in [1] is an adhesive for printed circuit boards.

[0017] [3] An adhesive sheet having an adhesive layer formed from the adhesive composition described in [1] or [2].

[0018] [4] A laminate having an adhesive layer formed from the adhesive composition described in [1] or [2].

[0019] [5] A printed circuit board comprising the laminate described in [4] as a constituent element.

[0020] The effects of the invention

[0021] The adhesive composition of the present invention exhibits excellent peel strength, solder heat resistance, and long-term heat resistance, while also satisfying the requirements for flexibility and tackiness in the semi-cured coating stage. Therefore, it is suitable for adhesives, adhesive sheets, laminates, and printed circuit boards used in automotive FPC applications. Detailed Implementation

[0022] Hereinafter, one embodiment of the present invention will be described in detail. However, the present invention is not limited thereto, and can be implemented in various ways with modifications added within the scope described.

[0023] <Polyester Resin (A1)>

[0024] The polyester resin (A1) used in this invention is a polyester resin with a number average molecular weight of less than 10,000, a glass transition temperature of less than 15°C, and a component (a) having a total of 3 functional groups of hydroxyl and carboxyl groups per molecule as a constituent unit. When all the polycarboxylic acid components constituting the polyester resin (A1) are set to 100 mol%, the component (a) has 3 mol% or more. By incorporating the polyester resin (A1) into the adhesive composition, both adhesion and long-term heat resistance are improved.

[0025] Polyester resin (A1) has a chemical structure obtained by the condensation polymerization of a polycarboxylic acid component and a polyol component, wherein the polycarboxylic acid component and the polyol component are each composed of one or more selected components. As the polycarboxylic acid component constituting polyester resin (A1), there are no limitations; the following polycarboxylic acids or their esters, as well as polycarboxylic anhydrides, can be used. Specifically, examples of polycarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, 2,5-furandicarboxylic acid, adipic acid, sebacic acid, dimer acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, fumaric acid, maleic acid, sodium dimethyl isophthalate-5-sulfonate, hydrogenated naphthalene dicarboxylic acid, and their esters. Examples of polycarboxylic anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, hexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride. In particular, aromatic polycarboxylic acid components are preferred, with naphthalene dicarboxylic acid and terephthalic acid being more preferred. The use of aromatic polycarboxylic acids can improve the heat resistance of the adhesive composition.

[0026] As a polyol component constituting polyester resin (A1), there are no particular limitations, and ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2-methyl-1,3-hexanediol, 2-methyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2- The adhesive composition may include polyalkylene ether glycols such as n-propyl-1,3-propanediol, 2,2-di-n-propyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 1,4-cyclohexanediol, tricyclodecanediol, polytetramethylene glycol, and polypropylene glycol; and polyols such as pentaerythritol, α-methylglucose, mannitol, sorbitol, and dimerized glycol. One or more of these polyols may be used. In particular, polyols having long-chain alkylene groups are preferred, and 1,6-hexanediol or dimerized glycol are more preferred. Using these polyols can improve the adhesive strength of the adhesive composition.

[0027] The polyester resin (A1) used in this invention comprises component (a) as a structural unit. Component (a) is a component with a total of three functional groups (hydroxyl and carboxyl groups per molecule). Additionally, the carboxyl group can be an anhydride, which is counted as two functional groups. All three functional groups can be carboxyl groups, all hydroxyl groups, or both. Examples of such component (a) include trimellitic acid, 4-hydroxyphthalic acid and their anhydrides, bisphenol A, dimethylolbutyric acid, dimethylolpropionic acid, pyromellitic acid, glycerol, trimethylolpropane, and trimethylolethane. Trimericic acid, 4-hydroxyphthalic acid, their anhydrides, and bisphenol A are preferred, as copolymerization of these can exhibit excellent solder heat resistance and long-term heat resistance. The rationale is not yet determined, but it is speculated that by introducing trifunctional components into the relatively low molecular weight polyester resin, a curable coating with high crosslinking density can be formed, thereby improving long-term heat resistance and solder heat resistance. When the total polycarboxylic acid content constituting the polyester resin (A1) is set to 100 mol%, component (a) must be 3 mol% or more, preferably 4 mol% or more. Furthermore, from the viewpoint of preventing gelation during polymerization, it is preferably 10 mol% or less, and more preferably 6 mol% or less.

[0028] The polyester resin (A1) used in this invention can also copolymerize polycarboxylic acid components with a valence of four or more and / or polyol components with a valence of four or more. Examples of polycarboxylic acid components with a valence of four or more include aromatic carboxylic acids such as pyromellitic acid, benzophenone tetracarboxylic acid, and pyromellitic anhydride (PMDA), and aliphatic carboxylic acids such as 1,2,3,4-butanetetracarboxylic acid; one or more of these can be used. Examples of polyol components with a valence of four or more include pentaerythritol, α-methylglucose, mannitol, and sorbitol; one or more of these can be used.

[0029] The polyester resin (A1) used in this invention can also be a copolylactone or co-lactam. For example, ε-caprolactone or ε-caprolactam can be used.

[0030] Methods for the polycondensation reaction of the polyester resin (A1) used in this invention include, for example: 1) heating a polycarboxylic acid and a polyol in the presence of a known catalyst, and carrying out a polyol-dehydration esterification process to perform a polyol-dehydration polycondensation reaction; 2) heating a polycarboxylic acid ester and a polyol in the presence of a known catalyst, and carrying out a polyol-dehydration polycondensation reaction via transesterification; 3) depolymerization methods; etc. In methods 1) and 2), some or all of the acid component may be replaced with an anhydride.

[0031] When manufacturing the polyester resin (A1) used in this invention, existing known polymerization catalysts can be used, such as titanium compounds like tetrabutyl titanate, tetraisopropyl titanate, and titanium acetylacetone oxide; antimony compounds like antimony trioxide and antimony tributoxy; and germanium compounds like germanium oxide and germanium tetrabutoxy. Other catalysts that can be used include acetates of magnesium, iron, zinc, manganese, cobalt, and aluminum can also be used. One or more of these catalysts can be used in combination.

[0032] The polyester resin (A1) used in this invention has a number average molecular weight of less than 10,000, more preferably 9,000 or less. Furthermore, it is preferably 1,000 or more, more preferably 3,000 or more, and even more preferably 4,000 or more. Within these ranges, adhesive compositions that are easy to handle in solvents and exhibit excellent adhesion can be prepared.

[0033] The polyester resin (Al) used in this invention has a glass transition temperature of less than 15°C, preferably less than 10°C. Furthermore, it is preferably -25°C or higher. Within this range, an adhesive composition that is easy to handle when forming a semi-cured coating and exhibits excellent adhesion can be prepared.

[0034] <Polyester Resin (A2)>

[0035] The polyester resin (A2) used in this invention is a polyester resin with a number average molecular weight of 10,000 or more and a glass transition temperature of 15°C or more. By incorporating polyester resin (A2) into the adhesive composition, good adhesion is achieved.

[0036] The polyester resin (A2) used in this invention has a number average molecular weight of 10,000 or more, preferably 11,000 or more, and more preferably 12,000 or more. Furthermore, it is preferably less than 100,000, more preferably less than 70,000, and even more preferably less than 50,000. Within these ranges, it is possible to achieve a solution viscosity suitable for easy handling, a flexible semi-cured coating, and a viscous semi-cured coating.

[0037] The polyester resin (A2) used in this invention has a glass transition temperature of 15°C or higher. Furthermore, it is preferably 100°C or lower, more preferably 50°C or lower. Within this range, an adhesive composition that is easy to handle when forming a semi-cured coating and exhibits excellent adhesion can be prepared.

[0038] Polyester resin (A2) has a chemical structure obtained by the condensation polymerization of polycarboxylic acid components and polyol components, wherein the polycarboxylic acid components and polyol components are each composed of one or more selected components. There are no particular limitations on the constituent components of polyester resin (A2), and the same constituent components as those of polyester resin (A1) can be used.

[0039] <Epoxy Resin (B)>

[0040] The adhesive composition of the present invention contains an epoxy resin (B). The epoxy resin (B) used in the present invention is not particularly limited as long as it has epoxy groups in its molecule, but preferably has two or more epoxy groups. Specifically, there are no particular limitations, but at least one selected from the group consisting of biphenyl-type epoxy resin, naphthalene-type epoxy resin, bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, phenolic varnish-type epoxy resin, alicyclic epoxy resin, dicyclopentadiene-type epoxy resin, tetraglycidyl diaminodiphenylmethane, triglycidyl p-aminophenol, tetraglycidyl diaminomethylcyclohexanone, N,N,N',N'-tetraglycidyl-m-xylenediamine, dimer acid-modified epoxy resin, and epoxy-modified polybutadiene can be used. Preferably, N,N,N',N'-tetraglycidyl-m-xylenediamine, biphenyl-type epoxy resin, phenolic varnish-type epoxy resin, dicyclopentadiene-type epoxy resin, or epoxy-modified polybutadiene are used. Using these epoxy resins can result in better adhesion.

[0041] In the adhesive composition of the present invention, the content of epoxy resin (B) is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, relative to a total of 100 parts by mass of polyester resin (A1) and polyester resin (A2). At or above the lower limit, sufficient curing effect can be obtained, exhibiting excellent adhesion and solder heat resistance. Furthermore, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. At or below the upper limit, long-term heat resistance becomes good. That is, within the above range, an adhesive composition with even better adhesion, solder heat resistance, and long-term heat resistance can be obtained.

[0042] <Adhesive Composition>

[0043] The adhesive composition of the present invention comprises polyester resin (A1), polyester (A2), and epoxy resin (B). By using two polyester resins with specific characteristics together, the bond strength after curing, the solder heat resistance, and the long-term heat resistance can be improved.

[0044] Regarding the mass ratio of polyester resin (A1) and polyester resin (A2) in the adhesive composition of the present invention, when the total mass of polyester resin (A1) and polyester resin (A2) is set to 100 parts by mass, the polyester resin (A1) is preferably 10 parts by mass or more and 90 parts by mass or less. More preferably, it is 20 parts by mass or more, and even more preferably, it is 25 parts by mass or more. Furthermore, it is more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less. By keeping the mass ratio of the two within the range described above, suitable adhesion of the semi-cured coating and excellent adhesion as well as solder heat resistance can be achieved simultaneously.

[0045] <Organic solvents>

[0046] The adhesive composition of the present invention may further contain organic solvents. The organic solvents used in the present invention are not particularly limited as long as they can dissolve the polyester resin and epoxy resin. Specifically, for example, aromatic hydrocarbons such as benzene, toluene, and xylene; 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; alcohol solvents such as methanol, ethanol, isopropanol, butanol, pentanol, hexanol, propylene glycol, and phenol; and acetone, methyl isobutyl ketone, methyl ethyl ketone, pentanol, hexanone, cyclohexanone, and isophorone. Ketone solvents such as acetophenone, cellosolvers such as methyl and ethyl cellosolvers, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and butyl formate, and glycol ether solvents such as ethylene glycol mono-n-butyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-isobutyl ether, triethylene glycol mono-n-butyl ether, and tetraethylene glycol mono-n-butyl ether can be used, either individually or in combination. Especially considering the working environment and drying properties, toluene and cyclohexanone are preferred.

[0047] The organic solvent is preferably in the range of 100 to 1000 parts by mass relative to the total 100 parts by mass of polyester resin (A1) and polyester resin (A2). Setting it above the lower limit improves the liquid state and shelf life. Furthermore, setting it below the upper limit is advantageous from the perspective of manufacturing and transportation costs.

[0048] Furthermore, the adhesive composition of the present invention may contain other components as needed. Specific examples of such components include flame retardants, tackifiers, fillers, and silane coupling agents.

[0049] Flame retardants

[0050] In the adhesive composition of the present invention, a flame retardant may be incorporated as needed. Examples of flame retardants include bromine-based, phosphorus-based, nitrogen-based, and metal hydroxide compounds. Phosphorus-based flame retardants are preferred, and phosphate esters, such as trimethyl phosphate, triphenyl phosphate, and tricresyl phosphate, can be used; phosphates, such as aluminum phosphinate, etc.; and phosphazenes and other known phosphorus-based flame retardants. These can be used alone or in combination of two or more. When containing a flame retardant, the amount of flame retardant is preferably in the range of 1 to 200 parts by weight relative to a total of 100 parts by weight of polyester resin (A1), polyester resin (A2), and epoxy resin (B), more preferably in the range of 5 to 150 parts by weight, and most preferably in the range of 10 to 100 parts by weight. By setting the amount within the range described above, flame retardancy can be exhibited while maintaining adhesion and solder heat resistance.

[0051] <Tackifier>

[0052] In the adhesive composition of the present invention, a tackifier may be added as needed. Examples of tackifiers include polyterpene resins, rosin-based resins, aliphatic petroleum resins, alicyclic petroleum resins, copolymer petroleum resins, styrene resins, and hydrogenated petroleum resins, which are used to improve adhesive strength. These can be used alone or in combination of two or more. When containing a tackifier, it is preferably contained in the range of 1 to 200 parts by weight relative to a total of 100 parts by weight of polyester resin (A1), polyester resin (A2), and epoxy resin (B), more preferably in the range of 5 to 150 parts by weight, and most preferably in the range of 10 to 100 parts by weight. By setting it within the range described above, the effect of the tackifier can be achieved while maintaining adhesion and solder heat resistance.

[0053] <packing>

[0054] In the adhesive composition of the present invention, fillers may be incorporated as needed. Examples of organic fillers include powders of heat-resistant resins such as polyimide, polyamide-imide, fluororesin, and liquid crystal polyester. Examples of inorganic fillers include, for instance, silica (SiO2), alumina (Al2O3), titanium dioxide (TiO2), tantalum oxide (Ta2O5), zirconium oxide (ZrO2), silicon nitride (Si3N4), boron nitride (BN), calcium carbonate (CaCO3), calcium sulfate (CaSO4), zinc oxide (ZnO), magnesium titanate (MgO·TiO2), barium sulfate (BaSO4), organobentonite, clay, mica, aluminum hydroxide, and magnesium hydroxide. Among these, silica is preferred from the perspective of ease of dispersion and improved heat resistance. As silica, hydrophobic silica and hydrophilic silica are generally known. Hydrophobic silica treated with dimethyldichlorosilane, hexamethyldisilazane, octylsilane, etc., is preferred for imparting moisture resistance. When incorporating silica, its amount is preferably 0.05 to 30 parts by mass relative to the total 100 parts by mass of polyester resin (A1), polyester resin (A2), and epoxy resin (B). Setting the amount above the lower limit allows for further heat resistance. Furthermore, setting the amount below the upper limit suppresses poor dispersion of silica or excessively high solution viscosity, resulting in better workability.

[0055] <Silane Coupling Agent>

[0056] In the adhesive composition of the present invention, a silane coupling agent may be incorporated as needed. The adhesion to metal and heat resistance are improved by incorporating a silane coupling agent, making it highly preferred. There are no particular limitations on the silane coupling agent; examples include silane coupling agents with unsaturated groups, silane coupling agents with epoxy groups, and silane coupling agents with amino groups. Among these, from the viewpoint of heat resistance, silane coupling agents with epoxy groups such as γ-epoxypropoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltriethoxysilane are further preferred. When incorporating a silane coupling agent, its amount is preferably 0.5 to 20 parts by mass relative to a total of 100 parts by mass of polyester resin (A1), polyester resin (A2), and epoxy resin (B). By setting it within this range, the heat resistance and adhesion of the solder can be improved.

[0057] <Layered Body>

[0058] The laminate of the present invention is a laminate formed by laminating an adhesive composition on a substrate (a two-layer laminate of substrate / adhesive layer), or a laminate formed by further bonding substrates (a three-layer laminate of substrate / adhesive layer / substrate). Here, the adhesive layer is a layer of the adhesive composition after the adhesive composition of the present invention has been applied to the substrate and dried. The laminate of the present invention can be obtained by applying the adhesive composition of the present invention to various substrates according to conventional methods and drying them, and by further laminating other substrates.

[0059] <Substrate>

[0060] In this invention, the substrate is any substrate that can be coated with the adhesive composition of this invention and dried to form an adhesive layer, and there is no particular limitation. Examples include resin substrates such as film resins, metal substrates such as metal plates or metal foils, and paper.

[0061] Examples of resin substrates include polyester resins, polyamide resins, polyimide resins, polyamide-imide resins, liquid crystal polymers, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resins, and fluorinated resins. A film-like resin (hereinafter also referred to as a substrate film) is preferred.

[0062] As the metal substrate, any existing known conductive material suitable for circuit boards can be used. Examples of materials include various metals such as SUS, copper, aluminum, iron, steel, zinc, and nickel, as well as their respective alloys, platings, and metals treated with zinc or chromium compounds. Metal foil is preferred, and copper foil is more preferred. The thickness of the metal foil is not particularly limited, but it is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 10 μm or more. Furthermore, it is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. When the thickness is too thin, it is sometimes difficult to obtain sufficient electrical performance of the circuit; on the other hand, when the thickness is too thick, the processing efficiency during circuit fabrication may decrease. The metal foil is usually provided in roll form. The form of the metal foil used in manufacturing the printed circuit board of the present invention is not particularly limited. When using a strip-shaped metal foil, its length is not particularly limited. Furthermore, its width is not particularly limited, but is preferably around 250 to 500 cm. The surface roughness of the substrate is not particularly limited, but is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less. Furthermore, practically, it is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 0.7 μm or more.

[0063] Examples of paper types include woodfree paper, kraft paper, roll paper, and cellophane. Examples of composite materials include glass epoxy resin.

[0064] From the perspective of adhesion and durability to the adhesive composition, the preferred substrates are polyester resin, polyamide resin, polyimide resin, polyamide-imide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, fluorinated resin, SUS steel plate, copper foil, aluminum foil, or glass epoxy resin.

[0065] <Adhesive sheet>

[0066] In this invention, the adhesive sheet is an adhesive sheet formed by laminating the laminate and the release substrate using an adhesive composition. Specific configurations include laminate / adhesive layer / release substrate, or release substrate / adhesive layer / laminate / adhesive layer / release substrate. By laminating the release substrate, it functions as a protective layer for the substrate. Furthermore, by using the release substrate, the release substrate can be demolded from the adhesive sheet, thereby transferring the adhesive layer onto other substrates.

[0067] The adhesive sheet of the present invention can be obtained by applying and drying the adhesive composition of the present invention onto various laminates using conventional methods. Furthermore, after drying, when a release substrate is adhered to the adhesive layer, it can be rolled up without backprinting onto the substrate, resulting in excellent operability. Simultaneously, since the adhesive layer is protected, it exhibits excellent storage properties and is easy to use. Moreover, after being applied to and dried on a release substrate, the adhesive layer itself can be transferred to other substrates if other release substrates are required.

[0068] <Molding Substrate>

[0069] There are no particular limitations on the release substrate. Examples include substrates made by applying a pore-filling agent coating layer such as clay, polyethylene, or polypropylene to both sides of paper such as wood pulp paper, kraft paper, roll paper, or cellophane, and then applying an organosilicon-based, fluorine-based, or alkyd-based release agent on top of each coating layer. Additionally, examples include various olefin films such as polyethylene, polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer, as well as substrates made by coating the aforementioned release agent onto films such as polyethylene terephthalate. Based on reasons such as the release force between the release substrate and the adhesive layer, and the adverse effects of organosilicon on electrical properties, substrates made by applying an alkyd-based release agent after polypropylene pore-filling treatment to both sides of wood pulp paper are preferred, as are substrates made by applying an alkyd-based release agent to polyethylene terephthalate.

[0070] Furthermore, the method for applying the adhesive composition to the substrate in this invention is not particularly limited, and examples include comma coating machines and reverse roller coating machines. Alternatively, the adhesive layer can be applied directly or by transfer onto rolled copper foil or polyimide film, which are components of the printed circuit board, as needed. The thickness of the dried adhesive layer can be appropriately varied as needed, but is preferably in the range of 5 to 200 μm. Sufficient adhesive strength can be obtained by setting the adhesive film thickness to 5 μm or more. In addition, by setting it to 200 μm or less, the amount of residual solvent in the drying process is easily controlled, and bubbling is less likely to occur during the pressing process of printed circuit board manufacturing. The drying conditions are not particularly limited, but the residual solvent rate after drying is preferably 1% by mass or less. By setting it to 1% by mass or less, foaming of residual solvent during the pressing of the printed circuit board can be suppressed, and bubbling is less likely to occur.

[0071] Printed Circuit Boards

[0072] The printed circuit board in this invention refers to an article containing a laminate formed of metal foil that forms conductive circuits and a resin substrate as a constituent element. Regarding printed circuit boards, for example, they are manufactured using metal-clad laminates and existing known methods such as subtractive processing. Depending on the need, so-called flexible printed circuit boards (FPCs), flat cables, and tape-on-board (TAB) circuit boards, which partially or completely cover the conductive circuits formed by metal foil using cover films or screen-printed inks, are collectively referred to as printed circuit boards.

[0073] The printed circuit board of the present invention can be configured with any layered structure that can be used as a printed circuit board. For example, it can be configured as a printed circuit board consisting of four layers: a substrate film layer, a metal foil layer, an adhesive layer, and a cover film layer. Furthermore, for example, it can be configured as a printed circuit board consisting of five layers: a substrate film layer, an adhesive layer, a metal foil layer, an adhesive layer, and a cover film layer.

[0074] Furthermore, it can be configured as a structure consisting of two or more of the aforementioned printed circuit boards stacked together, as needed.

[0075] The adhesive composition of the present invention is suitable for use in various adhesive layers of printed circuit boards. In particular, when used as an adhesive, the adhesive composition of the present invention exhibits high adhesion to existing resin substrates constituting printed circuit boards, such as polyimide, polyester film, copper foil, and aluminum foil, and provides resistance to solder reflow. Therefore, it is suitable as an adhesive composition for cover films, laminates, resin-coated copper foil, bonding sheets, and reinforcing materials.

[0076] In the printed circuit board of the present invention, any resin film conventionally used as a substrate for printed circuit boards can be used as the substrate film. Examples of resins used as the substrate film include polyester resin, polyamide resin, polyimide resin, polyamide-imide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, and fluorinated resin.

[0077] <Covering Film>

[0078] As a cover film, or as an insulating film for printed circuit boards, any known insulating film can be used. For example, films made from various polymers such as polyimide, polyester, polyphenylene sulfide, polyethersulfone, polyetheretherketone, aromatic polyamide, polycarbonate, polyarylate, polyamide-imide, liquid crystal polymer, syndiotactic polystyrene, and polyolefin resins can be used. Polyimide films are more preferred.

[0079] In addition to using the materials of the aforementioned layers, the printed circuit board of the present invention can also be manufactured using any of the known processes.

[0080] A preferred embodiment involves manufacturing a semi-finished product with an adhesive layer laminated on a cover film layer (hereinafter referred to as a "cover film-side semi-finished product"). Alternatively, a semi-finished product is manufactured in which a metal foil layer is laminated on a substrate film layer to form a desired circuit pattern (hereinafter referred to as a "substrate film-side 2-layer semi-finished product"), or a semi-finished product is manufactured in which an adhesive layer is laminated on a substrate film layer and a metal foil layer is laminated on top thereon to form a desired circuit pattern (hereinafter referred to as a "substrate film-side 3-layer semi-finished product"). (Hereinafter, the substrate film-side 2-layer semi-finished product and the substrate film-side 3-layer semi-finished product are collectively referred to as "substrate film-side semi-finished products"). By bonding the thus obtained cover film-side semi-finished product and the substrate film-side semi-finished product, a 4-layer or 5-layer printed circuit board can be obtained.

[0081] Regarding the substrate film-side semi-finished product, for example, it can be obtained by a manufacturing method including the following steps (A) and (B): (A) a step of coating the metal foil with a resin solution to form a substrate film and performing initial drying on the coating film; (B) a step of heat-treating / drying the laminate of the metal foil obtained in (A) and the initial dried coating film (hereinafter referred to as the "heat treatment / solvent removal step").

[0082] The circuitry in the metal foil layer can be formed using existing, known methods. Both additive and subtractive methods can be used. Subtractive methods are preferred.

[0083] The obtained substrate film-side semi-finished product can be directly used for bonding with the cover film-side semi-finished product, or it can be bonded and stored with the release film and then used for bonding with the cover film-side semi-finished product.

[0084] Regarding the cover film-side semi-finished product, for example, it can be manufactured by applying an adhesive to the cover film. If necessary, a cross-linking reaction can be carried out in the applied adhesive. In a preferred embodiment, the adhesive layer is semi-cured.

[0085] The obtained cover film side semi-finished product can be directly used for bonding with the substrate film side semi-finished product, or it can be bonded and stored with the release film and then used for bonding with the substrate film side semi-finished product.

[0086] The substrate film-side semi-finished product and the cover film-side semi-finished product can be stored separately in, for example, roll form, and then laminated to manufacture a printed circuit board. As a lamination method, any method can be used, such as using a press or rollers. Alternatively, the two can be laminated while being heated using a heated press or heated roller device.

[0087] Regarding the semi-finished product on the reinforcing material side, when the reinforcing material is a soft, rollable material such as a polyimide film, it is preferable to manufacture it by coating the reinforcing material with an adhesive. Furthermore, when the reinforcing material is a rigid, non-rollable sheet such as a metal sheet like SUS or aluminum, or a sheet made by curing glass fiber with epoxy resin, it is preferable to manufacture it by transferring an adhesive pre-coated to a release substrate. Additionally, a cross-linking reaction can be performed in the coated adhesive if necessary. In a preferred embodiment, the adhesive layer is semi-cured.

[0088] The obtained reinforcing material side semi-finished product can be directly used for bonding to the back of the printed circuit board, or it can be bonded and stored with a release film and then used for bonding to the substrate film side semi-finished product.

[0089] The substrate film-side semi-finished product, the cover film-side semi-finished product, and the reinforcing material-side semi-finished product are all laminates for printed circuit boards in this invention.

[0090] Example

[0091] The present invention will be specifically described below with examples. In addition, in this embodiment and comparative examples, the abbreviation "parts" refers to parts by mass.

[0092] (Methods for evaluating physical properties)

[0093] (Determination of the composition of polyester resin)

[0094] Using 400MHz 1 A nuclear magnetic resonance (NMR) spectrometer was used to quantify the molar ratios of the polycarboxylic acid and polyol components constituting the polyester resin. Deuterated chloroform was used as the solvent. Additionally, in Table 1, when the acid value of the polyester resin was increased by adding an acid, the total amount of polycarboxylic acid components other than the acid used in the added acid was set as 100 mol%, and the molar ratios of each component were recorded.

[0095] (Determination of glass transition temperature)

[0096] The determination was performed using a differential scanning calorimeter (SII, DSC-200). 5 mg of the sample (polyester resin) was placed in an aluminum capped container and sealed, then cooled to -50°C with liquid nitrogen. The temperature was then increased to 150°C at a rate of 20°C / min. In the endothermic curve obtained during the heating process, the temperature at the intersection of the extended baseline before the endothermic peak (below the glass transition temperature) and the tangent towards the endothermic peak (the tangent with the greatest slope between the rising portion of the peak and the apex) was taken as the glass transition temperature (unit: °C).

[0097] (Determination of number-average molecular weight)

[0098] The polyester resin sample was dissolved and / or diluted with tetrahydrofuran to a resin concentration of approximately 0.5% by weight, filtered through a 0.5 μm PTFE membrane filter, and used as the analytical sample. Molecular weight was determined by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase and a differential refractometer as the detector. The flow rate was 1 mL / min, and the column temperature was 30 °C. Showa Denko KF-802, 804L, and 806L columns were used. Monodisperse polystyrene was used as the molecular weight standard.

[0099] The following shows an example of the synthesis of the polyester resin used in this invention.

[0100] (Example of manufacturing polyester resin (a1))

[0101] In a reaction vessel equipped with a stirrer, condenser, and thermometer, 159 parts of terephthalic acid, 20 parts of trimellitic anhydride, 412 parts of isophthalic acid, 171 parts of 2-butyl-2-ethyl-1,3-propanediol, 503 parts of 1,6-hexanediol, and tetrabutyl titanate as a catalyst (at 0.03 mol% relative to the total polycarboxylic acid composition) were added. The mixture was heated from 160°C to 220°C over 4 hours, undergoing esterification simultaneously with a dehydration process. Next, in the polycondensation reaction, the system was depressurized to 5 mmHg for 20 minutes and further heated to 250°C. Then, the pressure was reduced to below 0.3 mmHg, and the polycondensation reaction was carried out for 60 minutes. After cooling to 220°C, 7 parts of trimellitic anhydride and 16 parts of pyromellitic anhydride were added, and the reaction was continued for 30 minutes before being removed. The obtained polyester resin (a1) was analyzed by NMR and found to be a copolyester of terephthalic acid / trimeric triphthalic anhydride / isophthalic acid / 2-butyl-2-ethyl-1,3-propanediol / 1,6-hexanediol / trimeric triphthalic anhydride / pyromellitic anhydride = 27 / 3 / 70 / 20 / 80 / 1 / 2 (molar ratio). Furthermore, it had a glass transition temperature of 7°C and a number-average molecular weight of 8300.

[0102] (Examples of manufacturing polyester resins (a2) to (a6))

[0103] Based on the manufacturing example of polyester resin (a1), by changing the types and proportions of raw materials, polyester resins (a2) to (a6) with the compositions shown in Table 1 were synthesized. The results are recorded in Table 1.

[0104] [Table 1]

[0105]

[0106] Hereinafter, examples of adhesive compositions that are embodiments of the present invention and examples of manufacturing adhesive compositions that are comparative examples are described.

[0107] In addition, the following substances are used as epoxy resin (B).

[0108] Epoxy Resin (b1): Cresol Phenolic Resin for Clear Varnish (YDCN-700-10 (manufactured by Nippon Steel Chemical & Material Co., Ltd.))

[0109] Epoxy resin (b2): Glycidylamine type epoxy resin (TETRAD-X (manufactured by Mitsubishi Gas Chemical Co., Ltd.))

[0110] <Example 1>

[0111] 30 parts by mass of polyester resin (a1) and 70 parts by mass of polyester resin (a2) obtained in the above synthesis example were dissolved in cyclohexanone to prepare a cyclohexanone varnish with a solid content concentration of 50% by mass. In this varnish, epoxy resin (b1) and epoxy resin (b2) were combined in such a way that 7 parts by mass and 1 part by mass were respectively relative to a total of 100 parts by mass of polyester resin (a1) and (a2) to obtain an adhesive composition (S1).

[0112] The obtained adhesive composition (S1) was evaluated for peel strength, solder heat resistance, semi-cured coating flexibility, semi-cured coating tackiness, and long-term heat resistance. The results are shown in Table 2.

[0113] <Examples 2-5, Comparative Examples 1-9>

[0114] The types and amounts of polyester resin and epoxy resin were changed as shown in Table 2. Otherwise, adhesive compositions (S2) to (S14) were prepared in the same manner as in Example 1, and each evaluation was performed. The results are recorded in Table 2.

[0115] <Evaluation of Adhesive Compositions>

[0116] (Peel strength (adhesion))

[0117] An adhesive composition was applied to a 12.5 μm thick polyimide film (manufactured by KANEKA Co., Ltd., Apical (registered trademark)) to achieve a dried thickness of 25 μm, and dried at 130°C for 3 minutes. The resulting adhesive film (B-grade product) was then laminated to an 18 μm thick rolled copper foil (manufactured by Nippon Steel Chemical & Material Co., Ltd., Espanex series). Lamination involved placing the glossy surface of the rolled copper foil against the adhesive layer and pressing it at 170°C under a pressure of 2 MPa for 280 seconds. The film was then heat-treated at 170°C for 3 hours to cure, yielding a sample for peel strength evaluation. Peel strength was measured under conditions of stretching the film at 25°C and peeling it at a tensile speed of 50 mm / min at a 90° angle. This test represents the adhesive strength at room temperature.

[0118] <Evaluation Criteria>

[0119] ◎: 1.0 N / mm or higher

[0120] ○: 0.5 N / mm or higher and less than 1.0 N / mm

[0121] ×: Less than 0.5 N / mm

[0122] (Solder heat resistance)

[0123] Evaluation samples were prepared using the same method as for peel strength testing. A 2.0 cm × 2.0 cm sample was immersed in a molten solder bath at 280°C to confirm any changes in appearance (existence of expansion).

[0124] <Rating Criteria>

[0125] ○: No expansion after 60 seconds

[0126] ×: Expansion occurs within 60 seconds.

[0127] (Semi-cured coating flexibility)

[0128] The adhesive composition was applied to a 100 μm thick Teflon (registered trademark) sheet to achieve a dried thickness of 25 μm, and dried at 130°C for 3 minutes. The condition of the coating was then checked when bent at 180°C or higher.

[0129] <Evaluation Criteria>

[0130] ○: No cracks

[0131] ×: Cracks present

[0132] (Semi-cured coating adhesion)

[0133] The adhesive composition was applied to a 100 μm thick Teflon (registered trademark) sheet to a dried thickness of 25 μm and dried at 130°C for 3 minutes. Next, a 12.5 μm thick polyimide film (manufactured by KANEKA Co., Ltd., Apical (registered trademark)) was overlapped onto the coated surface, and the adhesive strength was confirmed after applying a load of 2 MPa at 25°C for 10 seconds. The strength was measured under the same conditions as the peel strength test.

[0134] <Evaluation Criteria>

[0135] ○: Below 0.2 N / mm

[0136] ×: Greater than 0.2 N / mm

[0137] (Long-term heat resistance)

[0138] An adhesive composition was applied to a 12.5 μm thick polyimide film (manufactured by KANEKA Co., Ltd., Apical (registered trademark)) to achieve a dried thickness of 25 μm, and dried at 130°C for 3 minutes. The resulting adhesive film (B-grade product) was then laminated to an 18 μm thick rolled copper foil (manufactured by Nippon Steel Chemical & Material Co., Ltd., Espanex series). Lamination involved placing the glossy surface of the rolled copper foil against the adhesive layer and pressing it at 170°C under a pressure of 2 MPa for 280 seconds. The sample was then heat-treated at 170°C for 3 hours to cure, yielding a sample for peel strength evaluation. This sample was then placed in an oven at 150°C in air for 1000 hours, and the peel strength was measured after 1000 hours. Peel strength was measured under conditions of stretching the film at 25°C and peeling it at a tensile speed of 50 mm / min at a 90° angle. This test demonstrates the long-term reliability of the bond strength.

[0139] <Evaluation Criteria>

[0140] ○: 0.5 N / mm or higher

[0141] ×: Less than 0.5 N / mm

[0142] [Table 2]

[0143]

[0144] As shown in Table 2, Examples 1-5, containing all of polyester resin (A1), polyester resin (A2), and epoxy resin (B), exhibit excellent peel strength, solder heat resistance, semi-cured coating flexibility, semi-cured coating tackiness, and long-term heat resistance. On the other hand, the adhesive compositions of Comparative Examples 1-9, lacking any of polyester resin (A1), polyester resin (A2), and epoxy resin (B), cannot simultaneously satisfy all the characteristics of adhesion, solder heat resistance, semi-cured coating flexibility, semi-cured coating tackiness, and long-term heat resistance.

[0145] Industrial availability

[0146] The adhesive composition of the present invention is useful as an adhesive for FPCs used in automotive applications because it exhibits excellent adhesion and solder heat resistance, and thus excellent adhesion even after prolonged exposure to high-temperature environments.

Claims

1. An adhesive composition comprising polyester resin A1, polyester resin A2, and epoxy resin B, Polyester resin A1: The number average molecular weight is less than 10,000, the glass transition temperature is less than 15°C, and the component a, which has a total of 3 functional groups of hydroxyl and carboxyl groups per molecule, is used as a constituent unit. When all the polycarboxylic acid components constituting polyester resin A1 are set to 100 mol%, the component a has more than 3 mol%. Polyester resin A2: Number average molecular weight above 10,000, glass transition temperature above 15℃.

2. The adhesive composition according to claim 1, wherein it is an adhesive for printed circuit boards.

3. An adhesive sheet having an adhesive layer formed from the adhesive composition of claim 1 or 2.

4. A laminate having an adhesive layer formed from the adhesive composition of claim 1 or 2.

5. A printed circuit board comprising the laminate of claim 4 as a constituent element.

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