Adhesive compositions, adhesive sheets, laminates, and printed circuit boards

Abstract

An adhesive composition having excellent adhesion and solder heat resistance, further exhibiting excellent adhesion even after exposure to a high-temperature environment for a long time, and satisfying flexibility and tackability in a semi-cured film, and an adhesive composition containing a polyester resin (A1), a polyester resin (A2), and an epoxy resin (B) for an adhesive sheet, a laminate, and a printed circuit board containing the same. Polyester resin (A1): A polyester resin 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) as a constituent unit having three functional groups as a sum of hydroxyl and carboxyl groups per molecule, wherein the component (a) is 3 mol% or more when the total polycarboxylic acid component constituting the polyester resin (A1) is 100 mol%. Polyester resin (A2): A polyester resin having a number average molecular weight of 10,000 or more and a glass transition temperature of 15°C or more.

Description

Technology Field

[0001] The present invention relates to an adhesive composition. More specifically, it relates to an adhesive composition used for bonding a resin substrate to a resin substrate or a metal substrate. In particular, it relates to an adhesive composition for a flexible printed circuit board (hereinafter abbreviated as FPC), and to an adhesive sheet, a laminate, and a printed circuit board containing the same. Background Technology

[0002] Flexible Printed Circuit Boards (FPCs) refer to substrates in which electrical circuits are formed on a substrate in which a thin, soft film with insulating properties, such as polyimide, and a conductive metal, such as copper foil, are bonded together with an adhesive. Unlike rigid substrates, they are very thin and flexible, allowing them to be used in tight gaps or bending moving parts of electronic devices; therefore, they are used in many electronic devices such as personal computers and smartphones. Furthermore, as many FPCs are recently being installed in automobiles, high heat resistance and reliability are often required for the adhesives.

[0003] Copolymerized polyesters are widely used as raw materials for resin compositions utilized in coatings, inks, and adhesives, and are generally composed of polycarboxylic acids and polyhydric alcohols. Because molecular design is easy through the selection and combination of polycarboxylic acids and polyhydric alcohols, and molecular weights can be freely controlled, they are widely used in various applications, including coatings and adhesives.

[0004] Copolymer polyester has excellent adhesion (peel strength) to metals including copper, and has been used in adhesives for FPCs by incorporating a curing agent (e.g., Patent Document 1). Prior art literature

[0005] Patent Document 1: Japanese Patent Publication No. Hei 6-104813 The problem to be solved

[0006] However, the adhesive using copolymer polyester described in Patent Document 1 has poor solder heat resistance and does not have the long-term heat resistance required for automotive applications.

[0007] The present invention was made against the background of the problems of the prior art. That is, the objective of the present invention is to provide an adhesive composition that has excellent adhesion and solder heat resistance, further exhibits excellent adhesion even after being exposed to a high-temperature environment for a long time, and satisfies flexibility and tackiness when formed into a semi-cured film, and an adhesive sheet, laminate, and printed circuit board containing the same. means of solving the problem

[0008] As a result of careful examination, the inventors discovered that the above problem can be solved by means described below, and thus arrived at the present invention. That is, the present invention includes the following configuration.

[0009] [1] An adhesive composition containing polyester resin (A1), polyester resin (A2) and epoxy resin (B).

[0010] Polyester resin (A1): a polyester resin 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) as a constituent unit having three functional groups as a sum of hydroxyl groups and carboxyl groups per molecule, wherein the total polycarboxylic acid component constituting the polyester resin (A1) is 100 mol%, and the component (a) is 3 mol% or more.

[0011] Polyester resin (A2): Polyester resin having a number average molecular weight of 10,000 or more and a glass transition temperature of 15°C or more.

[0012] [2] The adhesive composition described in [1] above, which is an adhesive for printed circuit boards.

[0013] [3] An adhesive sheet having an adhesive layer comprising the adhesive composition described in [1] or [2] above.

[0014] [4] A laminate having an adhesive layer comprising the adhesive composition described in [1] or [2] above.

[0015] [5] A printed circuit board comprising the laminate described in [4] above as a component. Effects of the invention

[0016] The adhesive composition of the present invention has excellent peel strength, solder heat resistance, and long-term heat resistance, and also satisfies flexibility and tackiness in semi-cured films. For this reason, it is suitable for adhesives for FPCs for automotive applications, adhesive sheets, laminates, and printed circuit boards. Specific details for implementing the invention

[0017] Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited thereto and may be implemented in various modified forms within the scope described.

[0018] Polyester resin (A1)

[0019] The polyester resin (A1) used in the present invention 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) as a constituent unit having three functional groups in total, including hydroxyl groups and carboxyl groups per molecule, and is a polyester resin having 3 mol% or more of the component (a) when the total polycarboxylic acid component constituting the polyester resin (A1) is 100 mol%. By having the polyester resin (A1), the adhesive composition has good adhesion and long-term heat resistance.

[0020] The polyester resin (A1) has a chemical structure obtained by a polycondensation of a polycarboxylic acid component and a polyalcohol component, wherein the polycarboxylic acid component and the polyalcohol component each comprise one or more selected components. The polycarboxylic acid component constituting the polyester resin (A1) may use polycarboxylic acids or esters thereof and polycarboxylic acid anhydrides as described below, although not limited thereto. Specifically, polycarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic 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, 5-sodium sulfodimethylisophthalic acid, hydrogenated naphthalenedicarboxylic acid, and esters thereof. Polycarboxylic acid anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, etc. In particular, aromatic polycarboxylic acid components are preferred, and among them, naphthalenedicarboxylic acid or terephthalic acid is more preferred. The heat resistance of the adhesive composition can be improved by using an aromatic polycarboxylic acid.

[0021] The polyhydric alcohol component constituting the polyester resin (A1) is not particularly limited, but includes 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-n-propyl-1,3-propanediol, 2,2-din-propyl-1,3-propanediol, Polyalcohol components such as 2-n-butyl-2-ethyl-1,3-propanediol, 2,2-din-butyl-1,3-propanediol, 2,4-diethyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, polyalkylene ether glycols such as polytetramethylene glycol and polypropylene glycol, pentaerythritol, α-methylglucose, mannitol, sorbitol, and dimer diol may be used, and one or more of these may be used. In particular, polyalcohol components having long-chain alkylene groups are preferred, and among them, 1,6-hexanediol or dimer diol is more preferred. By using these polyalcohol components, the adhesive strength of the adhesive composition can be improved.

[0022] The polyester resin (A1) used in the present invention comprises component (a) as a constituent unit. Component (a) is a component in which the sum of hydroxyl groups and carboxyl groups per molecule is three functional groups. Additionally, the carboxyl group may be an acid anhydride group, and the acid anhydride group is counted as two functional groups. The three functional groups may be entirely carboxyl groups or entirely hydroxyl groups, or may have both carboxyl groups and hydroxyl groups. Examples of such component (a) include trimellitic acid, 4-hydroxyphthalic acid and their acid anhydrides, diphenolic acid, dimethylolbutanoic acid, dimethylolpropionic acid, trimesic acid, glycerin, trimethylolpropane, and trimethylolethane. Preferably, trimellitic acid, 4-hydroxyphthalic acid and their anhydrides, and diphenolic acid are copolymerized, thereby exhibiting excellent solder heat resistance and long-term heat resistance. Although the reason for this is unclear, it is inferred that by introducing branches as three functional components into a relatively low-molecular-weight polyester resin, a cured film capable of building a high crosslinking density is formed, thereby improving long-term heat resistance and solder heat resistance. Component (a) needs to be 3 mol% or more when the total polycarboxylic acid component constituting the polyester resin (A1) is 100 mol%, and preferably 4 mol% or more. In addition, from the viewpoint of preventing gelation during polymerization, it is preferable that it be 10 mol% or less, and more preferable that it be 6 mol% or less.

[0023] The polyester resin (A1) used in the present invention may copolymerize a polycarboxylic acid component with four or more valent carboxylic acids and / or a polyalcohol component with four or more valent carboxylic acids. Examples of polycarboxylic acid components with four or more valent carboxylic acids include aromatic carboxylic acids such as pyromellitic acid, benzophenone tetracarboxylic acid, and pyrromellitic anhydride (PMDA), and aliphatic carboxylic acids such as 1,2,3,4-butane tetracarboxylic acid, and one or more of these may be used. Examples of polyalcohol components with four or more valent carboxylic acids include pentaerythritol, α-methylglucose, mannitol, and sorbitol, and one or more of these may be used.

[0024] The polyester resin (A1) used in the present invention may copolymerize a lactone or a lactam. For example, ε-caprolactone or ε-caprolactam may be used.

[0025] As a method of polymerization condensation reaction for producing the polyester resin (A1) used in the present invention, for example, 1) a method of heating a polycarboxylic acid and a polyalcohol in the presence of a known catalyst and undergoing a dehydration esterification process to perform a depolyalcohol-polycondensation reaction, 2) a method of heating an alcohol ester of a polycarboxylic acid and a polyalcohol in the presence of a known catalyst and undergoing an ester exchange reaction to perform a depolyalcohol-polycondensation reaction, and 3) a method of performing depolymerization. In the above methods 1) and 2), some or all of the acid components may be replaced with acid anhydrides.

[0026] When manufacturing the polyester resin (A1) used in the present invention, conventionally known polymerization catalysts may be used, such as titanium compounds including tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetylacetonate; antimony compounds including antimony trioxide and tributoxycyantimony; germanium compounds including germanium oxide and tetra-n-butoxygermanium; and other acetates such as magnesium, iron, zinc, manganese, cobalt, and aluminum. One or more of these catalysts may be used in combination.

[0027] The number average molecular weight of the polyester resin (A1) used in the present invention is less than 10,000, and more preferably 9,000 or less. In addition, it is preferable that it be 1,000 or more, more preferable that it be 3,000 or more, and even more preferably 4,000 or more. Within the above range, it is possible to make an adhesive composition that is easy to handle when dissolved in a solvent and has excellent adhesion.

[0028] The glass transition temperature of the polyester resin (A1) used in the present invention is less than 15°C and preferably 10°C or lower. In addition, it is preferably -25°C or higher. Within the above range, it is possible to make an adhesive composition that is easy to handle and has excellent adhesion when formed into a semi-cured film.

[0029] Polyester resin (A2)

[0030] The polyester resin (A2) used in the present invention is a polyester resin having a number average molecular weight of 10,000 or more and a glass transition temperature of 15°C or more. By having the polyester resin (A2), the adhesive composition has good adhesion.

[0031] The number average molecular weight of the polyester resin (A2) used in the present invention is 10,000 or more, preferably 11,000 or more, more preferably 12,000 or more. In addition, it is preferable that it be less than 100,000, more preferably less than 70,000, and even more preferably less than 50,000. Within the above range, easy-to-handle solution viscosity, flexibility of the semi-cured film, and tackiness of the semi-cured film can be satisfied.

[0032] The glass transition temperature of the polyester resin (A2) used in the present invention is 15°C or higher. In addition, it is preferable that it be 100°C or lower, and more preferable that it be 50°C or lower. Within the above range, it is possible to make an adhesive composition that is easy to handle and has excellent adhesion when formed into a semi-cured film.

[0033] The polyester resin (A2) has a chemical structure obtained by a polycondensation of a polycarboxylic acid component and a polyalcohol component, wherein the polycarboxylic acid component and the polyalcohol component each comprise one or more selected components. The constituent components of the polyester resin (A2) are not particularly limited and may be the same as those of the polyester resin (A1).

[0034] <Epoxy Resin (B)>

[0035] 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 an epoxy group in its molecule, but preferably has two or more epoxy groups in its molecule. Specifically, although not particularly limited, 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, novolak-type epoxy resin, alicyclic epoxy resin, dicyclopentadiene-type epoxy resin, tetraglycidyl diaminodiphenylmethane, triglycidyl para-aminophenol, tetraglycidyl bisaminomethylcyclohexanone, N,N,N',N'-tetraglycidyl-m-xylylenediamine, dimer acid-modified epoxy, and epoxy-modified polybutadiene may be used. Preferably, N,N,N',N'-tetraglycidyl-m-xylylenediamine, biphenyl-type epoxy resin, novolak-type epoxy resin, dicyclopentadiene-type epoxy resin, or epoxy-modified polybutadiene are used, and using these can exhibit superior adhesion.

[0036] In the adhesive composition of the present invention, the content of the epoxy resin (B) is preferably 0.1 parts by mass or more and more preferably 1 part by mass or more per 100 parts by mass of the total of the polyester resin (A1) and the polyester resin (A2). If the content is above the lower limit, a sufficient curing effect is obtained, and excellent adhesion and solder heat resistance can be exhibited. In addition, it is preferably 20 parts by mass or less and more preferably 10 parts by mass or less. If the content is below the upper limit, good long-term heat resistance is achieved. That is, by keeping the content within the above range, an adhesive composition having better adhesion, solder heat resistance, and long-term heat resistance can be obtained.

[0037] <Adhesive Composition>

[0038] The adhesive composition of the present invention comprises a polyester resin (A1) and a polyester (A2) and an epoxy resin (B). By using two types of polyester resins having specific characteristics, the adhesive strength after curing, solder heat resistance, and long-term heat resistance can be improved.

[0039] In the adhesive composition of the present invention, the mass ratio of the polyester resin (A1) and the polyester resin (A2) is preferably such that when the total of the polyester resin (A1) and the polyester resin (A2) is 100 parts by mass, the polyester resin (A1) is 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 25 parts by mass or more. Furthermore, it is more preferable that it is 80 parts by mass or less, and even more preferably 75 parts by mass or less. By keeping the mass ratio of both within the above range, appropriate tackability of the semi-cured film, excellent adhesion, and solder heat resistance can be achieved simultaneously.

[0040] Organic solvents

[0041] The adhesive composition of the present invention may further contain an organic solvent. The organic solvent used in the present invention is not particularly limited as long as it dissolves the polyester resin and the 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, chlorbenzene, and chloroform; alcohol-based solvents such as methanol, ethanol, isopropyl alcohol, butanol, pentanol, hexanol, propanediol, and phenol; ketone-based solvents such as acetone, methylisobutyl ketone, methyl ethyl ketone, pentanone, hexanone, cyclohexanone, isophorone, and acetophenone; cellosolves such as methyl cellosolve and ethyl cellosolve; and ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, methyl propionate, and butyl formate. 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 may be used, and one or more of these may be used in combination. In particular, toluene or cyclohexanone is preferred in terms of working environment and drying properties.

[0042] It is preferable that the organic solvent be in the range of 100 to 1,000 parts by mass per 100 parts by mass of the total of the polyester resin (A1) and the polyester resin (A2). By making it above the lower limit value, the liquid phase and pot life properties are improved. In addition, by making it below the upper limit value, it becomes advantageous in terms of manufacturing costs and transportation costs.

[0043] In addition, the adhesive composition of the present invention may further contain other components as needed. Specific examples of such components include flame retardants, tackifiers, fillers, and silane coupling agents.

[0044] Flame retardant

[0045] Flame retardants may be incorporated into the adhesive composition of the present invention as needed. Examples of flame retardants include bromine-based, phosphorus-based, nitrogen-based, and metal hydroxide compounds. Among these, phosphorus-based flame retardants are preferred, and known phosphorus-based flame retardants such as phosphate esters (e.g., trimethylphosphate, triphenylphosphate, tricrezylphosphate), phosphates (e.g., aluminum phosphine), and phosphazene may be used. These may be used individually or two or more may be used in combination. When a flame retardant is included, it is preferable to include the flame retardant in a range of 1 to 200 parts by mass per 100 parts by mass of the total of the polyester resin (A1), polyester resin (A2), and epoxy resin (B), a range of 5 to 150 parts by mass is more preferable, and a range of 10 to 100 parts by mass is most preferable. By keeping the range within the above, flame retardancy can be exhibited while maintaining adhesiveness and solder heat resistance.

[0046] <Tackifier>

[0047] A tackifier may be incorporated into the adhesive composition of the present invention as needed. Examples of tackifiers include polyterpene resin, rosin-based resin, aliphatic petroleum resin, alicyclic petroleum resin, copolymer petroleum resin, styrene resin, and hydrogenated petroleum resin, and are used for the purpose of improving adhesive strength. These may be used individually or two or more may be used in a combination of at any time. When a tackifier is included, it is preferable to include it in a range of 1 to 200 parts by mass per 100 parts by mass of the total of polyester resin (A1), polyester resin (A2), and epoxy resin (B), a range of 5 to 150 parts by mass is more preferable, and a range of 10 to 100 parts by mass is most preferable. By keeping it within the above range, the effect of the tackifier can be exhibited while maintaining adhesiveness and solder heat resistance.

[0048] Filler

[0049] Fillers may be incorporated into the adhesive composition of the present invention as needed. Examples of organic fillers include powders of heat-resistant resins such as polyimide, polyamideimide, fluoropolymer, and liquid crystal polyester. In addition, examples of inorganic fillers include silica (SiO2), alumina (Al2O3), titania (TiO2), tantalum oxide (Ta2O5), zirconia (ZrO2), silicon nitride (Si3N4), boron nitride (BN), calcium carbonate (CaCO3), calcium sulfate (CaSO4), zinc oxide (ZnO), magnesium titanate (MgO·TiO2), barium sulfate (BaSO4), organic bentonite, clay, mica, aluminum hydroxide, magnesium hydroxide, etc. Among these, silica is preferred due to its ease of dispersion and the effect of improving heat resistance. Generally, hydrophobic silica and hydrophilic silica are known as silica, but here, hydrophobic silica treated with dimethyldichlorosilane, hexamethyldisilazane, octylsilane, etc. is preferred for imparting moisture resistance. When silica is incorporated, the amount of silica is preferably 0.05 to 30 parts by mass per 100 parts by mass of the total of polyester resin (A1), polyester resin (A2), and epoxy resin (B). By making it above the lower limit value, further heat resistance can be exhibited. In addition, by making it below the upper limit value, poor dispersion of silica or excessively high solution viscosity is suppressed, and workability is improved.

[0050] Silane coupling agents

[0051] A silane coupling agent may be incorporated into the adhesive composition of the present invention as needed. Incorporating a silane coupling agent is highly desirable because it improves adhesion to metal and heat resistance properties. As for the silane coupling agent, examples include those having unsaturated groups, epoxy groups, or amino groups. Among these, silane coupling agents having epoxy groups, such as γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, are more preferred from the perspective of heat resistance. When incorporating a silane coupling agent, the amount of the agent is preferably 0.5 to 20 parts by mass per 100 parts by mass of the total of the polyester resin (A1), polyester resin (A2), and epoxy resin (B). By keeping the amount within the above range, the heat resistance and adhesion of the solder can be improved.

[0052] Laminated structure

[0053] The laminate of the present invention is a two-layer laminate of a substrate and an adhesive composition laminated thereon (a two-layer laminate of a substrate and an adhesive layer) or a three-layer laminate of a substrate, an adhesive layer, and a substrate. Here, the adhesive layer refers to a layer of the adhesive composition after the adhesive composition of the present invention has been applied to a substrate and dried. The laminate of the present invention can be obtained by applying the adhesive composition of the present invention to various substrates and drying it according to a conventional method, and then laminating another substrate.

[0054] <Information>

[0055] In the present invention, the term "substrate" is not particularly limited as long as it is capable of forming an adhesive layer by applying and drying the adhesive composition of the present invention, but may include resin substrates such as film-type resins, metal substrates such as metal plates or metal foils, paper, etc.

[0056] Examples of resin substrates include polyester resin, polyamide resin, polyimide resin, polyamideimide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin-based resin, and fluorine-based resin. Preferably, it is a film-type resin (hereinafter also referred to as a substrate film layer).

[0057] Any conventionally known conductive material suitable for use in circuit boards may be used as the metal substrate. Examples of materials include various metals such as SUS, copper, aluminum, iron, steel, zinc, and nickel, as well as their respective alloys, plated products, and metals treated with other metals such as zinc or chromium compounds. Preferably, it is a metal foil, and more preferably, a copper foil. There are no particular limitations regarding the thickness of the metal foil, but it is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 10 μm or more. Additionally, it is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the thickness is excessively thin, it may be difficult to obtain sufficient electrical performance of the circuit, while if the thickness is excessively thick, processing efficiency during circuit fabrication may decrease. The metal foil is typically provided in a roll form. The shape of the metal foil used when manufacturing the printed circuit board of the present invention is not particularly limited. When using a ribbon-shaped metal foil, its length is not particularly limited. In addition, the width is not particularly limited, but it is preferably about 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. In addition, for practical purposes, it is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 0.7 μm or more.

[0058] Examples of paper products include high-quality paper, kraft paper, roll paper, glassine paper, etc. In addition, examples of composite materials include glass epoxy, etc.

[0059] When considering adhesion strength and durability with respect to the adhesive composition, polyester resin, polyamide resin, polyimide resin, polyamideimide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin resin, fluorine resin, SUS steel sheet, copper foil, aluminum foil, or glass epoxy is preferred as the substrate.

[0060] <Adhesive Sheet>

[0061] In the present invention, the adhesive sheet is formed by laminating the above-mentioned laminate and a release substrate through an adhesive composition. Specific configurations include a laminate / adhesive layer / release substrate or a release substrate / adhesive layer / laminated 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 released from the adhesive sheet, and the adhesive layer can also be transferred to another substrate.

[0062] An adhesive sheet of the present invention can be obtained by applying and drying the adhesive composition of the present invention onto various laminates according to a conventional method. Furthermore, if a release substrate is attached to the adhesive layer after drying, it can be wound without bleeding to the back side of the substrate, resulting in excellent workability. Additionally, since the adhesive layer is protected, it offers excellent preservation and is easy to use. Moreover, if another release substrate is attached as needed after applying and drying the adhesive layer onto the release substrate, it becomes possible to transfer the adhesive layer itself to another substrate.

[0063] <Illegible Text>

[0064] As for the release substrate, although not specifically limited, examples include forming a coating layer of a filler such as clay, polyethylene, or polypropylene on both sides of paper such as high-quality paper, kraft paper, roll paper, or glassine paper, and applying a silicone-based, fluorine-based, or alkyd-based release agent on each coating layer. Additionally, examples include applying the above release agent to various olefin films such as polyethylene, polypropylene, ethylene-α-olefin copolymer, or propylene-α-olefin copolymer alone, or to films such as polyethylene terephthalate. Due to reasons such as the release force of the release substrate and the adhesive layer, and the adverse effect of silicone on electrical properties, it is preferable to apply a polypropylene filler treatment to both sides of high-quality paper and use an alkyd-based release agent thereon, or to use an alkyd-based release agent on polyethylene terephthalate.

[0065] In addition, the method for coating the adhesive composition onto a substrate in the present invention is not particularly limited, but may include a comma coater, a reverse roll coater, etc. Alternatively, if necessary, an adhesive layer may be formed directly or by a transfer method on a rolled copper foil or a polyimide film, which is a constituent material of a printed circuit board. The thickness of the adhesive layer after drying is appropriately changed as needed, but is preferably in the range of 5 to 200 μm. Sufficient adhesive strength is obtained by making the adhesive film thickness 5 μm or more. In addition, by making it 200 μm or less, it becomes easier to control the amount of residual solvent in the drying process, making it difficult for expansion to occur during the pressing process for manufacturing a printed circuit board. The drying conditions are not particularly limited, but the residual solvent ratio after drying is preferably 1 mass% or less. By making it 1 mass% or less, the foaming of the residual solvent during the pressing process of the printed circuit board is suppressed, making it difficult for expansion to occur.

[0066] Printed Wiring Board

[0067] The printed circuit board in the present invention comprises, as a component, a laminate formed of a metal foil forming a conductive circuit and a resin substrate. The printed circuit board is manufactured, for example, by a conventionally known method such as the subtractive method using a metal-clad laminate. Depending on the needs, the term collectively refers to so-called flexible circuit boards (FPC), flat cables, and circuit boards for tape automation bonding (TAB), in which the conductive circuit formed by the metal foil is partially or completely covered using a cover film or screen printing ink.

[0068] The printed circuit board of the present invention may be any laminated configuration that can be employed as a printed circuit board. For example, it may be a printed circuit board composed of four layers, such as a substrate film layer, a metal foil layer, an adhesive layer, and a cover film layer. In addition, it may be a printed circuit board composed of five layers, such as a substrate film layer, an adhesive layer, a metal foil layer, an adhesive layer, and a cover film layer.

[0069] In addition, if necessary, the above-mentioned printed circuit boards may be configured by stacking two or three or more of them.

[0070] The adhesive composition of the present invention can be suitably used in each adhesive layer of a printed circuit board. In particular, when the adhesive composition of the present invention is used as an adhesive, it has high adhesion to resin substrates such as conventional polyimide, polyester film, copper foil, and aluminum foil constituting the printed circuit board, and solder reflow resistance can be obtained. Therefore, it is suitable as an adhesive composition used in coverlay films, laminates, resin-coated copper foil, bonding sheets, and reinforcing materials.

[0071] In the printed circuit board of the present invention, any resin film conventionally used as a substrate for printed circuit boards may be used as the substrate film. Examples of resins for the substrate film include polyester resin, polyamide resin, polyimide resin, polyamideimide resin, liquid crystal polymer, polyphenylene sulfide, syndiotactic polystyrene, polyolefin-based resin, and fluorine-based resin.

[0072] Cover Film

[0073] For the cover film, any conventionally known insulating film for printed circuit boards may be used. For example, films made of various polymers such as polyimide, polyester, polyphenylene sulfide, polyethersulfone, polyetheretherketone, aramid, polycarbonate, polyarylate, polyamideimide, liquid crystal polymer, syndiotactic polystyrene, and polyolefin resin may be used. More preferably, it is a polyimide film.

[0074] The printed circuit board of the present invention can be manufactured using any conventionally known process, except for using the materials of each layer described above.

[0075] In a preferred embodiment, a semi-finished product (hereinafter referred to as the "semi-finished product on the cover film side") is manufactured by laminating an adhesive layer onto a cover film layer. On the other hand, a semi-finished product (hereinafter referred to as the "two-layer semi-finished product on the base film side") is manufactured by laminating a metal foil layer onto a base film layer to form a desired circuit pattern (hereinafter referred to as the "three-layer semi-finished product on the base film side") or a semi-finished product (hereinafter referred to as the "three-layer semi-finished product on the base film side") is manufactured by laminating an adhesive layer onto a base film layer and laminating a metal foil layer thereon to form a desired circuit pattern (hereinafter referred to as the "three-layer semi-finished product on the base film side"). By joining the semi-finished product on the cover film side and the semi-finished product on the base film side obtained in this way, a four-layer or five-layer printed circuit board can be obtained.

[0076] The semi-finished product on the substrate film side is obtained by a manufacturing method including, for example, (A) a process of applying a resin solution that becomes the substrate film to the metal foil and initially drying the coating film, and (B) a process of heat-treating and drying the laminate of the metal foil obtained in (A) and the initially dried coating film (hereinafter referred to as the "heat treatment and desoldering process").

[0077] The formation of circuits in the metal foil layer may utilize conventionally known methods. An additive method or a subtractive method may be used. Preferably, the subtractive method is used.

[0078] The obtained semi-finished product on the base film side may be used as is for bonding with the semi-finished product on the cover film side, or it may be used for bonding with the semi-finished product on the cover film side after attaching a release film and storing it.

[0079] The semi-finished product on the cover film side is manufactured, for example, by applying an adhesive to the cover film. If necessary, a cross-linking reaction can be performed on the applied adhesive. In a preferred embodiment, the adhesive layer is semi-cured.

[0080] The obtained semi-finished product on the cover film side may be used as is for bonding with the semi-finished product on the base film side, or it may be used for bonding with the semi-finished product on the base film side after attaching a release film and storing it.

[0081] The semi-finished product on the base film side and the semi-finished product on the cover film side are each stored, for example, in the form of rolls, and then joined together to manufacture a printed circuit board. Any method may be used for joining, and for example, they may be joined using a press or a roll. Additionally, the two may be joined while heating by using a heating press or a heating roll device.

[0082] For the semi-finished product on the reinforcing side, in the case of a soft and windable reinforcing material, such as a polyimide film, it is suitable to manufacture it by applying an adhesive to the reinforcing material. In addition, in the case of a rigid and non-windable reinforcing plate, such as a metal plate like SUS or aluminum, or a plate made of glass fiber cured with epoxy resin, it is suitable to manufacture it by transfer-applying an adhesive that has been previously applied to a release substrate. Furthermore, if necessary, a cross-linking reaction can be performed on the applied adhesive. In a preferred embodiment, the adhesive layer is semi-cured.

[0083] The semi-finished product on the reinforcing side obtained may be used as is for bonding with the back side of the printed circuit board, or it may be used for bonding with the semi-finished product on the base film side after attaching a release film and storing it.

[0084] The semi-finished product on the base film side, the semi-finished product on the cover film side, and the semi-finished product on the reinforcing material side are all laminates for a printed circuit board according to the present invention.

[0085] Examples

[0086] The present invention will be specifically explained below with reference to examples. Meanwhile, in the examples and comparative examples, "part" simply denotes a part by mass.

[0087] (Method for evaluating physical properties)

[0088] (Measurement of polyester resin composition)

[0089] 400 MHz 1 Using an H-nuclear magnetic resonance spectrum device (hereinafter abbreviated as NMR), the molar ratios of polycarboxylic acid components and polyalcohol components constituting the polyester resin were quantified. Dichloroform was used as the solvent. In addition, in Table 1, when the acid value of the polyester resin was increased by post-acid addition, the total of polycarboxylic acid components other than the acid component used for post-acid addition was set to 100 mol%, and the molar ratios of each component were indicated.

[0090] (Measurement of glass transition temperature)

[0091] Measurements were taken using a differential scanning calorimeter (DSC-200, SII). 5 mg of the sample (polyester resin) was placed in an aluminum press-type container, sealed, and cooled to -50°C using liquid nitrogen. Then, the temperature was increased to 150°C at a heating rate of 20°C / min, and the glass transition temperature (unit: °C) was defined as the temperature at the intersection of the extension of the baseline before the endothermic peak (below the glass transition temperature) and the tangent line toward the endothermic peak (the tangent line representing the maximum slope between the vertical rise portion of the peak and the apex of the peak) of the endothermic curve obtained during the heating process.

[0092] (Measurement of number-average molecular weight)

[0093] A sample of polyester resin was dissolved and / or diluted with tetrahydrofuran to a resin concentration of approximately 0.5 wt%, and filtered through a polytetrafluoroethylene membrane filter with a pore diameter of 0.5 μm to be used as the measurement sample. The molecular weight was measured by gel permeation chromatography (GPC) using tetrahydrofuran as the mobile phase and a differential refractometer as the detector. The flow rate was set to 1 mL / min and the column temperature to 30°C. Showa Denko's KF-802, 804L, and 806L columns were used. Monodisperse polystyrene was used as the molecular weight standard.

[0094] The following describes a synthesis example of a polyester resin used in the present invention.

[0095] (Example of preparation of polyester resin (a1))

[0096] In a reaction vessel equipped with a stirrer, a condenser, and a 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 0.03 mol% of tetrabutyl orthotitanate as a catalyst relative to the total polycarboxylic acid components were injected, and an esterification reaction was carried out by increasing the temperature from 160°C to 220°C over 4 hours and undergoing a dehydration process. Subsequently, for the polycondensation reaction process, the pressure inside the system was reduced to 5 mmHg over 20 minutes, and the temperature was increased to 250°C. Next, the pressure was reduced to 0.3 mmHg or less, and a polycondensation reaction was carried out for 60 minutes. Afterward, the mixture was cooled to 220°C, 7 parts of trimellitic anhydride and 16 parts of pyromellitic anhydride were added, and the mixture was reacted for 30 minutes and then removed. The obtained polyester resin (a1) was a copolymer polyester with a molar ratio of terephthalic acid / trimellitic anhydride / isophthalic acid / 2-butyl-2-ethyl-1,3-propanediol / 1,6-hexanediol / trimellitic anhydride / pyromellitic anhydride = 27 / 3 / 70 / 20 / 80 / 1 / 2, as determined by compositional analysis by NMR. Additionally, the glass transition temperature was 7°C and the number average molecular weight was 8300.

[0097] (Examples of preparation of polyester resins (a2) to (a6))

[0098] Polyester resins (a2) to (a6) having compositions as shown in Table 1 were synthesized by changing the type of raw materials and the mixing ratio according to the example of manufacturing polyester resin (a1). The results are listed in Table 1.

[0099]

[0100] Hereinafter, examples of the preparation of an adhesive composition that is an embodiment of the present invention and an adhesive composition that is a comparative example are described.

[0101] In addition, the following was used as the epoxy resin (B).

[0102] Epoxy resin (b1): Cresol novolak type epoxy (YDCN-700-10 (manufactured by Nittetsu Chemical & Material Co., Ltd.))

[0103] Epoxy resin (b2): Glycidylamine type epoxy (Tetrad X (manufactured by Mitsubishi Gas Chemical Co., Ltd.))

[0104] <Example 1>

[0105] 30 parts by mass of polyester resin (a1) and 70 parts by mass of polyester resin (a2) obtained in the above-described synthesis example were dissolved in cyclohexanone to prepare a cyclohexanone varnish with a solid content concentration of 50 mass%. An adhesive composition (S1) was obtained by mixing epoxy resin (b1) and epoxy resin (b2) into this varnish in such a ratio of 7 parts by mass and 1 part by mass, respectively, with respect to a total of 100 parts by mass of polyester resin (a1) and (a2).

[0106] Regarding the obtained adhesive composition (S1), each evaluation of peel strength, solder heat resistance, semi-cured film flexibility, semi-cured film tackiness, and long-term heat resistance was performed. The results are listed in Table 2.

[0107] <Examples 2–5, Comparative Examples 1–9>

[0108] Adhesive compositions (S2) to (S14) were prepared in the same manner as in Example 1, except that the types and amounts of polyester resin and epoxy resin were changed as shown in Table 2, and each was evaluated. The results are listed in Table 2.

[0109] <Evaluation of Adhesive Composition>

[0110] (Peel strength (adhesion))

[0111] The adhesive composition was applied to a polyimide film with a thickness of 12.5 μm (manufactured by Kaneka Co., Ltd., Apical (registered trademark)) to a thickness of 25 μm after drying, and dried at 130°C for 3 minutes. The adhesive film obtained in this way (B-stage sample) was bonded to a rolled copper foil with a thickness of 18 μm (manufactured by Nittetsu Chemical & Material Co., Ltd., Espanex series). For bonding, the glossy surface of the rolled copper foil was placed in contact with the adhesive layer, and the film was pressed at 170°C under a pressure of 2 MPa for 280 seconds to bond. Subsequently, the film was heat-treated at 170°C for 3 hours to cure, thereby obtaining a sample for peel strength evaluation. Peel strength was measured under conditions of 25°C, film pulling, a tensile speed of 50 mm / min, and 90° peeling. This test represents the adhesive strength at room temperature.

[0112] <Evaluation Criteria>

[0113] ◎: 1.0 N / mm or higher

[0114] ○: 0.5 N / mm or more and less than 1.0 N / mm

[0115] ×: Less than 0.5 N / mm

[0116] (Solder heat resistance)

[0117] Evaluation samples were prepared using the same method as for measuring peel strength. A 2.0 cm × 2.0 cm sample piece was immersed in a solder bath melted at 288°C to check for changes in appearance (presence or absence of expansion).

[0118] <Evaluation Criteria>

[0119] ○: No expansion for more than 60 seconds

[0120] ×: Expansion in less than 60 seconds

[0121] (Semi-cured film flexibility)

[0122] The adhesive composition was applied to a Teflon (registered trademark) sheet with a thickness of 100 μm so that the thickness after drying was 25 μm, and dried at 130°C for 3 minutes. Subsequently, the condition of the coating film was checked when it was bent at an angle of 180 degrees or more.

[0123] <Evaluation Criteria>

[0124] ○: No cracks

[0125] ×: Cracks present

[0126] (Semi-cured film tackiness)

[0127] The adhesive composition was applied to a Teflon (registered trademark) sheet with a thickness of 100 μm so that the thickness after drying was 25 μm, and dried at 130°C for 3 minutes. Subsequently, a polyimide film with a thickness of 12.5 μm (manufactured by Kaneka Co., Ltd., Apical (registered trademark)) was placed on the coated surface, and the adhesive strength was checked after applying a load of 2 MPa at 25°C for 10 seconds. The measurement of strength was carried out under the same conditions as the measurement of peel strength.

[0128] <Evaluation Criteria>

[0129] ○: 0.2 N / mm or less

[0130] ×: Exceeds 0.2 N / mm

[0131] (Long-term heat resistance)

[0132] An adhesive composition was applied to a polyimide film with a thickness of 12.5 μm (manufactured by Kaneka Co., Ltd., Apical (registered trademark)) to a thickness of 25 μm after drying, and dried at 130°C for 3 minutes. The adhesive film obtained in this way (B-stage sample) was bonded to a rolled copper foil with a thickness of 18 μm (manufactured by Nittetsu Chemical & Material Co., Ltd., Espanex series). Bonding was performed by placing the glossy surface of the rolled copper foil in contact with the adhesive layer and pressing at 170°C under a pressure of 2 MPa for 280 seconds. Subsequently, the film was heat-treated at 170°C for 3 hours to cure it, thereby obtaining a sample for peel strength evaluation. This sample was placed in an oven at 150°C in an air atmosphere for 1000 hours, and the peel strength after 1000 hours was measured. Peel strength was measured under conditions of 25°C, film pulling, tensile speed of 50 mm / min, and 90° peel. This test demonstrates the long-term reliability of adhesive strength.

[0133] <Evaluation Criteria>

[0134] ○: 0.5 N / mm or higher

[0135] ×: Less than 0.5 N / mm

[0136]

[0137] As is evident from Table 2, since Examples 1 to 5 contain all of the polyester resin (A1), polyester resin (A2), and epoxy resin (B), they exhibited excellent peel strength, solder heat resistance, semi-cured film flexibility, semi-cured film tackability, and long-term heat resistance. On the other hand, since the adhesive compositions of Comparative Examples 1 to 9 do not contain any of the polyester resin (A1), polyester resin (A2), and epoxy resin (B), they could not simultaneously satisfy all characteristics of adhesion, solder heat resistance, semi-cured film flexibility, semi-cured film tackability, and long-term heat resistance. Industrial applicability

[0138] The adhesive composition of the present invention has excellent adhesion and solder heat resistance, and furthermore, exhibits excellent adhesion even after being exposed to a high-temperature environment for a long time, so it is useful as an adhesive for FPCs for automotive applications.

Claims

Claim 1 An adhesive composition comprising a polyester resin (A1), a polyester resin (A2), and an epoxy resin (B). Polyester resin (A1): A polyester resin 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) as a constituent unit having three functional groups as a sum of hydroxyl groups and carboxyl groups per molecule, wherein the component (a) is 3°C or more when the total polycarboxylic acid component constituting the polyester resin (A1) is 100°C. Polyester resin (A2): A polyester resin having a number average molecular weight of 10,000 or more and a glass transition temperature of 15°C or more. Claim 2 In claim 1, an adhesive composition that is an adhesive for printed circuit boards. Claim 3 An adhesive sheet having an adhesive layer comprising the adhesive composition described in claim 1 or 2. Claim 4 A laminate having an adhesive layer comprising the adhesive composition described in claim 1 or 2. Claim 5 A printed circuit board comprising the laminate described in paragraph 4 as a component.

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