Cross-linked polyester resin, adhesive composition and adhesive sheet

Abstract

The present invention aims to provide an adhesive sheet having high adhesion, high heat resistance, and high strength to a resin substrate such as polyimide film and a metal substrate such as copper foil, while exhibiting excellent insulation failure reliability and sheet life at room temperature; and a crosslinked polyester resin suitable for use therein. A crosslinked polyester resin (C) has a structure formed by reacting a polyester resin (A) with carboxyl groups on its side chains with an epoxy compound (B). When a vertical stress of 0.1 N is applied using a rheometer, the shear strain is set to 10%, and the time for the modulus of elasticity to reach 0.37 times the initial modulus of elasticity is 1 × 10¹ seconds to 1 × 10⁴ seconds, and the composition has at least one of the following (1) and (2): (1) Contains an ester exchange catalyst (D). (2) The aforementioned epoxy compound (B) is an epoxy amine compound (E) having tertiary amine groups.

Description

Technical Field

[0001] This invention relates to a crosslinked polyester resin. It also relates to adhesive compositions comprising the resin, adhesive sheets, and printed circuit boards and cover films comprising the resin as constituent elements. Prior Technology

[0002] In the past, epoxy adhesives were reviewed as bonding agents for circuit boards or flexible printed circuit boards (hereinafter referred to as FPCs). In addition to good adhesion to the substrate material, adhesives used for such applications also need to have high heat resistance to withstand high temperatures of over 200°C during component reflow.

[0003] Furthermore, in recent years, adhesive sheets made from adhesives in sheet form have been increasingly used for this application. However, the adhesive sheets used in this application utilize various materials with different coefficients of thermal expansion, thus necessitating measures to suppress the reduced connection reliability caused by thermal stress or to improve the embedding performance into the unevenness of the wiring substrate. As a means to solve this problem, one document proposes an adhesive sheet made by incorporating aliphatic or alicyclic epoxy resin into acrylic rubber (Patent Document 1). [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2011-159693 Summary of the Invention

[0005] [The problem the invention aims to solve]

[0006] However, the adhesive sheet in Patent Document 1 contains a hardener, causing the adhesive sheet to form a so-called B-stage (semi-cured state). Therefore, the curing reaction continues during storage, which raises concerns about the service life (sheet life) of the adhesive sheet. In addition, since it is a curing system, there is also the issue of curing shrinkage affecting the reliability of insulation failure.

[0007] The purpose of this invention is to provide an adhesive sheet that exhibits high adhesion, high heat resistance, and high strength to resin substrates such as polyimide films and metal substrates such as copper foil. It also demonstrates excellent insulation failure reliability and sheet life at room temperature, and is made from a suitable cross-linked polyester resin. [Solution to the Problem]

[0008] In order to solve the above-mentioned problems, the inventors conducted research and investigation, and found that the crosslinked polyester resin disclosed below can achieve the above-mentioned objectives, and thus completed the present invention. That is, the embodiments of the present invention are, for example, any one of [1] to

[11] below.

[0009] [1] A crosslinked polyester resin (C) having a structure formed by reacting a polyester resin (A) with carboxyl groups on its side chains with an epoxy compound (B), wherein when a vertical stress of 0.1 N is applied using a rheometer, the shear strain is set to 10%, and the time for the relaxed elastic modulus to reach 0.37 times the initial relaxed elastic modulus is 1 × 10¹ seconds to 1 × 10⁴ seconds, and the resin has at least one of the following (1) and (2): (1) containing an ester exchange catalyst (D), (2) the aforementioned epoxy compound (B) having a tertiary amine compound (E). [2] The crosslinked polyester resin (C) as described in [1], wherein the elastic modulus above the stress relaxation initiation temperature, measured using a dynamic viscoelasticity measuring device at a frequency of 1 Hz and a measuring temperature of -100 to 250°C, is 0.1 MPa to 1.2 MPa. [3] The crosslinked polyester resin (C) as described in [1] or [2] above, wherein the acid value of the polyester resin (A) having carboxyl groups on the side chain is 7 to 40 mg KOH / g. [4] The crosslinked polyester resin (C) as described in any one of [1] to [3] above, wherein the polyester resin (A) having carboxyl groups on the side chain comprises a high molecular weight polyol (a1) with a number average molecular weight of 7,000 or more, a high molecular weight polyol (a2) with a number average molecular weight of 1,000 or more but less than 7,000, and a tetracarboxylic acid dianhydride as structural units. [5] A method for manufacturing a crosslinked polyester resin (C) comprising: (i) heating a mixture containing a polyester resin (A) having carboxyl groups on the side chain, an epoxy compound (B), and a transesterification catalyst (D); or (ii) heating a mixture containing a polyester resin (A) having carboxyl groups on the side chain and an epoxy amine compound (E) having tertiary amine groups. [6] An adhesive composition comprising a crosslinked polyester resin (C) as described in any one of [1] to [4] above. [7] An adhesive sheet having an adhesive layer formed of a crosslinked polyester resin (C) as described in any one of [1] to [4] above. [8] An adhesive sheet as described in [7] above, wherein the 90° peel strength when bonding a polyimide film to a copper foil using the adhesive sheet is 0.5 N / mm or more. [9] A printed circuit board comprising an adhesive sheet as described in [7] or [8] above as a constituent element.

[10] A cover film comprising an adhesive sheet as described in [7] or [8] above as a constituent element.

[11] A method for manufacturing a printed circuit board as described in [9] above, comprising a step of heating to above the stress relaxation start temperature of the crosslinked polyester resin (C) and simultaneously bonding. [Effects of the Invention]

[0010] The cross-linked polyester resin of this invention forms a cross-linked structure at room temperature, thus exhibiting high strength and excellent adhesion, and even storage stability. Furthermore, it softens at high temperatures, thus demonstrating compliance with substrates and preventing cracking due to differences in thermal expansion between substrates, allowing for effective bonding. Therefore, it is suitable for use as an adhesive for printed circuit boards, and is particularly useful as an adhesive sheet with excellent sheet life or insulation failure reliability. Simple Explanation of the Diagram

[0011] Figure 1 is a graph showing the results of stress relaxation measurement of the cross-linked polyester resin obtained in Example 1. Figure 2 is a graph showing the results of insulation failure reliability measurement in Examples 5 and 7. Implementation

[0012] The cross-linked polyester resin associated with the embodiments of the present invention is a cross-linked polyester resin (C) that is a reaction product of a polyester resin (A) with carboxyl groups on its side chains and an epoxy compound (B).

[0013] <Polyester Resin with Carboxyl Groups in Side Chains (A)> Polyester resin with carboxyl groups in side chains (A) is a resin in which the side chains of a polyester resin have carboxyl groups. Here, the side chain can be a structure where a substituent (e.g., aliphatic hydrocarbon group, aromatic hydrocarbon group, alicyclic hydrocarbon group, etc.) branching from the main chain of the polyester resin has a carboxyl group, or it can be a structure where the polyester resin directly has a carboxyl group. It is preferable that the polyester resin directly has a carboxyl group. The acid value of the polyester resin (A) with carboxyl groups in side chains is preferably 7 mg KOH / g or higher. From the viewpoint of fully crosslinking with the epoxy compound (B) and improving heat resistance, it is more preferably 10 mg KOH / g or higher. Furthermore, the acid value is preferably 40 mg KOH / g or lower, and more preferably 30 mg KOH / g or lower. Additionally, the acid value generated by the carboxyl group in the side chain is preferably 5 mg KOH / g or higher, and more preferably 10 mg KOH / g or higher. If the acid value is above the aforementioned lower limit, the heat resistance is good due to the crosslinking of the epoxy compound (B). If the acid value is below the aforementioned upper limit, the molecular motion is not inhibited due to the appropriate crosslinking density, ester bond exchange is easy to occur, stress relaxation or softening is sufficient, and adhesion is good. Polyester resin (A) with carboxyl groups on the side chain is preferred, especially one in which multiple ester bonds and carboxyl groups are contained within the molecule.

[0014] The average molecular weight of the polyester resin (A) with carboxyl groups on its side chains is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 12,000 or more. Furthermore, it is preferably 50,000 or less, more preferably 25,000 or less, and even more preferably 20,000 or less. By setting it within the aforementioned range, the acid value of the polyester resin (A) with carboxyl groups on its side chains can be easily controlled.

[0015] The glass transition temperature of the polyester resin (A) with carboxyl groups on the side chain is preferably above 0°C, more preferably above 5°C, and even more preferably above 10°C. On the other hand, the glass transition temperature is preferably below 110°C, more preferably below 85°C, and even more preferably below 65°C.

[0016] Polyester resin (A) with carboxyl groups on its side chains must have side chains (hereinafter also referred to as branched structures) within its molecule. To give polyester resin (A) with carboxyl groups on its side chains a branched structure, the copolymerizing component used as its raw material preferably has a branched structure. Polyester resin (A) with carboxyl groups on its side chains is preferably a compound that has been given carboxyl groups by reacting a high-molecular-weight polyol (a) with a trivalent or higher-valence polycarboxylic acid component (copolymerization). However, it can also be a compound obtained by reacting a polycarboxylic acid component with a polyol component, or by adding a monomer with a carboxyl group to a polyester having a reaction site.

[0017] The acid value of the polymeric polyol (a) used in the polyester resin (A) having carboxyl groups on the side chain is preferably 0.1 mg KOH / g or higher, more preferably 0.2 mg KOH / g or higher, and even more preferably 0.3 mg KOH / g or higher. Furthermore, it is preferably 20 mg KOH / g or lower, more preferably 15 mg KOH / g or lower, and even more preferably 10 mg KOH / g or lower.

[0018] The glass transition temperature of the high molecular weight polyol (a) is preferably above -10°C, more preferably above 0°C, and even more preferably above 5°C. Furthermore, it is preferably below 100°C, more preferably below 80°C, and even more preferably below 60°C.

[0019] The number average molecular weight of the high molecular weight polyol (a) is preferably above 1000, more preferably above 2000, and even more preferably above 3000. In addition, it is preferably below 30000, more preferably below 25000, and even more preferably below 20000.

[0020] Polymer polyols (a) are preferably copolymers of polycarboxylic acid components and polyol components (polymer polyester polyols). From the viewpoint of improving the cohesive force and strength of the resin, aromatic dicarboxylic acid components are preferred for polymer polyester polyols. Aromatic dicarboxylic acid components are not particularly limited, and examples include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, biphenyl dicarboxylic acid, and biphenyl dicarboxylic acid. Additionally, aromatic dicarboxylic acids with sulfonic acid groups, such as sulfonic acid terephthalic acid, 5-sulfonic acid isophthalic acid, 4-sulfonic acid phthalic acid, 4-sulfonic acid naphthalene-2,7-dicarboxylic acid, and 5-(4-sulfonic acid phenoxy) isophthalic acid, as well as aromatic dicarboxylic acids with sulfonate groups, such as their metal salts and ammonium salts, can also be used. These can be used alone or in combination of two or more. Terephthalic acid, isophthalic acid, and mixtures thereof are particularly preferred.

[0021] Other polycarboxylic acid components include alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid and their anhydrides; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebaceous acid, dodecanoic acid, and dimer acids; and dicarboxylic acids containing unsaturated bonds such as fumaric acid and maleic acid and their anhydrides. Additionally, thiomalic acid, which has a thiol group in its molecular structure, and 2,5-furandicarboxylic acid (FDCA) derived from biomass can also be used.

[0022] For high-molecular-weight polyester polyols, diols are preferred. Among diols, aliphatic diols, alicyclic diols, diols containing aromatic groups, or diols containing ether bonds are preferred. Examples of aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 2-methyl-1,3-butanediol, 1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol (DMH), neopentyl hydroxypentanoate, dimethylolheptane, and 2,2,4-trimethyl-1,3-pentanediol. Examples of alicyclic diols include 1,4-cyclohexanediol, 1,4-cyclohexanediethanol, tricyclodecanediol, dihydroxymethyltricyclodecane, spirodiol, hydrogenated bisphenol A, ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, and dimer diols. Examples of diols containing ether bonds include diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, neopentyl glycol ethylene oxide adducts, and neopentyl glycol propylene oxide adducts. Examples of aromatic diols include p-xylene glycol, m-xylene glycol, o-xylene glycol, p-hydroxyphenylethanol, 1,4-benzene glycol, ethylene oxide adducts of 1,4-benzene glycol, bisphenol A, ethylene oxide adducts of bisphenol A, and propylene oxide adducts, which are diols obtained by adding 1 to several moles of ethylene oxide or propylene oxide to the two phenolic hydroxyl groups of bisphenols. Additionally, diol modifiers of aromatic dicarboxylic acids can also be used. Specific examples include bis-2-hydroxyethyl terephthalate (BHET), a ethylene glycol-modified terephthalic acid, a propylene glycol-modified terephthalic acid, an ethylene glycol-modified isophthalic acid, a propylene glycol-modified isophthalic acid, an ethylene glycol-modified phthalic acid, and a propylene glycol-modified phthalic acid. In addition, other examples of diol-modified aromatic dicarboxylic acids include diol-modified aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, biphenyl dicarboxylic acid, biphenyl dicarboxylic acid, 5-hydroxyisophthalic acid, sulfonic acid terephthalic acid, 5-sulfonic acid isophthalic acid, 4-sulfonic acid phthalic acid, 4-sulfonic acid naphthalene-2,7-dicarboxylic acid, 5-(4-sulfonic acid phenoxy)isophthalic acid, sulfonic acid terephthalic acid and / or their metal salts, ammonium salts, etc., having sulfonic acid groups or sulfonate groups. These can be used alone or in combination of two or more.

[0023] Polyester polyols can also contain polycarboxylic acid components with more than three functionalities or polyol components with more than three functionalities. Examples of polycarboxylic acid components with more than three functionalities used in polyester polyols include trimellitic acid, pyromellitic acid, ethylene glycol bis(dehydrated trimellitic acid ester), glyceryl succinate (dehydrated trimellitic acid ester), trimellitic anhydride, pyrocalcite anhydride (PMDA), oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic anhydride (BTDA), 3,3',4,4'-diphenyltetracarboxylic anhydride (BPDA), 3,3',4,4'-diphenyltetracarboxylic anhydride (DSDA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2'-bis[(dicarboxyphenoxy)phenyl]propane dianhydride (BSAA), etc. On the other hand, examples of polyols with more than three functions include glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, etc.

[0024] Other components used in high molecular weight polyester polyols may also be hydroxycarboxylic acid compounds with hydroxy and carboxyl groups in their molecular structure, such as 5-hydroxyisophthalic acid, p-hydroxybenzoic acid, p-hydroxyphenylpropionic acid, p-hydroxyphenylacetic acid, 6-hydroxy-2-naphthoic acid, and 4,4-bis(p-hydroxyphenyl)valeric acid.

[0025] The high molecular weight polyol (a) can be configured to contain two or more high molecular weight polyols, including a high molecular weight polyol (a1) with a number average molecular weight of 7,000 or more and a high molecular weight polyol (a2) with a number average molecular weight of 1,000 or more but less than 7,000. By configuring it as described above, heat resistance can be further improved. That is, the long-chain molecules of the long-chain high molecular weight polyol (a1) block contribute to heat resistance, while the introduction of short-chain high molecular weight polyol (a2) blocks allows for the introduction of a sufficient amount of carboxylic acid to impart heat resistance.

[0026] The copolymerization ratio of polymeric polyol (a1) and polymeric polyol (a2) in a polyester resin (A) with carboxyl groups on the side chain is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, relative to a total of 100 parts by mass of polymeric polyol (a1) and polymeric polyol (a2). Furthermore, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less. By setting the copolymerization ratio of polymeric polyol (a1) and polymeric polyol (a2) within the aforementioned range, better heat resistance can be achieved.

[0027] The copolymerization amount of the high molecular weight polyol (a1) in the polyester resin (A) with carboxyl groups on the side chain is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, it is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. Within the aforementioned range, due to the balance of copolymerization amount with the high molecular weight polyol (a2) or trivalent or higher polycarboxylic acid components, heat resistance or adhesion becomes good.

[0028] <Trivalent or higher polycarboxylic acid components> are not specifically limited to compounds that react (copolymerize) with high molecular weight polyols (a), as long as they have three or more carboxyl groups within the molecule. Carboxyl groups can also form anhydride groups within the molecule; in this case, one anhydride group can be counted as two carboxyl groups. Examples of polycarboxylic acid compounds with trivalent or higher valence include trimellitic acid, pyromellitic acid, ethylene glycol bis(dehydrated trimellitic acid ester), glyceryl succinate (dehydrated trimellitic acid ester), trimellitic anhydride, pyrocalcite anhydride (PMDA), oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic anhydride (BTDA), 3,3',4,4'-diphenyltetracarboxylic anhydride (BPDA), 3,3',4,4'-diphenyltetracarboxylic anhydride (DSDA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and 2,2'-bis[(dicarboxyphenoxy)phenyl]propane dianhydride (BSAA), among others.

[0029] The copolymerization ratio of the high molecular weight polyol (a) and the trivalent or higher polycarboxylic acid component in the polyester resin (A) with carboxyl groups on the side chain is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, relative to 100 parts by mass of the high molecular weight polyol (a). Furthermore, it is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less. By ensuring that the copolymerization ratio of the trivalent or higher polycarboxylic acid component is above the aforementioned lower limit, sufficient crosslinking is achieved, and heat resistance is improved. Conversely, if it is below the aforementioned upper limit, the crosslinking density will not become excessively high, ester bond exchange will easily occur, sufficient softening will be achieved, and the adhesion will be improved.

[0030] <Chain Extender> For polyester resins (A) containing carboxyl groups in the side chains, chain extenders can be used arbitrarily, in addition to using high molecular weight polyols (a1), high molecular weight polyols (a2), and trivalent or higher polycarboxylic acid components as copolymerizing agents, without compromising the aforementioned effects. By using chain extenders, acid values ​​can be efficiently imparted. When using chain extenders, the copolymerization amount is preferably 0.1 parts by mass or more relative to 100 parts by mass of high molecular weight polyol (a), more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more. Furthermore, it is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less. If the copolymerization amount is too high, it may result in difficulty in increasing the molecular weight, reactions between the chain extenders, and phenomena such as varnish cloudiness.

[0031] Chain extenders are preferably low molecular weight diols with a molecular weight below 1000, such as 2,2-dimethyl-1,3-propanediol or dimethylolbutyric acid. These can be used alone or in combination of two or more. From the viewpoint of solubility and miscibility, 2,2-dimethyl-1,3-propanediol is particularly preferred.

[0032] Polyester resins (A) with carboxyl groups on the side chains can also use quaternary ammonium salts or tertiary amines as reaction catalysts, to the extent that the above effects are not impaired. Examples include imidazole compounds such as 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, or 1-cyanoethyl-2-ethyl-4-methylimidazole; triethylamine, triethylenediamine, N'-methyl-N-(2-dimethylaminoethyl)piperazine, N,N-diisopropylethylamine, N,N-dimethylaminopyridine, 1,8-diazabicyclo(5,4,0)-undec-7-ene, 1,5-diazabicyclo(4 Tertiary amines such as (3,0)-non-5-ene or 6-dibutylamino-1,8-diazabicyclo(5,4,0)-undec-7-ene, and compounds in which these tertiary amines are converted into amine salts by phenol, octanoic acid, or tetraphenylborate, etc.; quaternary ammonium salts such as tetramethylammonium bromide, tetraethylammonium bromide, tetra-n-butylammonium bromide, tetramethylammonium chloride, trimethylbenzylammonium chloride, triethylbenzylammonium chloride, tetramethylammonium hydroxide, trimethylbenzylammonium hydroxide, and tetra-n-butylammonium hydroxide.

[0033] <Epoxy Compound (B)> Epoxy compound (B) is not particularly limited, but compounds with two or more epoxy groups within the molecule are preferred. Compounds with two or more epoxy groups within the molecule (epoxy crosslinking agents) are not particularly limited as long as they undergo a curing reaction with the carboxyl groups of a polyester resin (A) having carboxyl groups on their side chains. By using epoxy compound (B), the cured coating obtained from the crosslinked polyester resin (C) easily forms three-dimensional crosslinks, which improves heat resistance.

[0034] Epoxy compounds (B) can also be used in combination with other epoxy compounds. Examples include glycidyl ethers such as bisphenol A diglycidyl ether, bisphenol S diglycidyl ether, and brominated bisphenol A diglycidyl ether; glycidyl esters such as hexahydrophthalic acid glycidyl ester and dimer acid glycidyl ester; triglycidyl isocyanurate; 3,4-epoxycyclohexylmethylcarboxylate; epoxidized polybutadiene; and epoxidized soybean oil, which are alicyclic or aliphatic epoxy compounds. One or more of these compounds can be used alone or in combination.

[0035] From the perspective of crosslinking density, the number average molecular weight of epoxy compound (B) is preferably between 100 and 500, and between 200 and 400.

[0036] <Cross-linked polyester resin (C)> Cross-linked polyester resin (C) is the reaction product of the aforementioned polyester resin (A) with carboxyl groups on its side chains and the aforementioned epoxy compound (B). Furthermore, cross-linked polyester resin (C) has the following composition: (1) it contains an ester exchange catalyst (D), or (2) the aforementioned epoxy compound (B) is at least one of an epoxy amine compound (E) having tertiary amine groups. That is, cross-linked polyester resin (C) has the composition of (1) and / or (2). The reaction of the polyester resin (A) with carboxyl groups on its side chains and the epoxy compound (B) can be carried out in a solvent-free environment or in the presence of an organic solvent. Organic solvents are not particularly limited as long as they do not react with polyester resins (A), epoxy compounds (B), and cross-linked polyester resins (C) that have carboxyl groups on their side chains. Examples include aromatic organic solvents such as toluene and xylene, aliphatic organic solvents such as heptane and octane, ketone solvents such as methyl ethyl ketone, ether solvents such as tetrahydrofuran and diethyl ether, and amide solvents such as dimethylformamide and N-methylpyrrolidone. These can be used alone or in combination of two or more.

[0037] The reaction temperature of the aforementioned reaction is preferably above 80°C, more preferably above 100°C, and even more preferably above 120°C. Additionally, it is preferably below 200°C, more preferably below 180°C, and even more preferably below 160°C.

[0038] The reaction time of the aforementioned reaction is also affected by the reaction temperature, with 30 minutes or more being preferred, 1 hour or more being even more preferred, and 2 hours or more being even more preferred. In addition, 10 hours or less is preferred, 8 hours or less is even more preferred, and 5 hours or less is even more preferred.

[0039] The ratio of the amount of polyester resin (A) with carboxyl groups on its side chains to the amount of epoxy compound (B) in the crosslinked polyester resin (C) can be determined based on the molar ratio of the functional groups of the carboxyl groups on the side chains of the polyester resin (A) with carboxyl groups to the epoxy groups of the epoxy compound (B). From the viewpoint of crosslinking reaction efficiency or stress relaxation of the crosslinked polyester (C) after crosslinking, the ratio of the carboxyl groups in the aforementioned polyester resin (A) with carboxyl groups to the epoxy groups in the aforementioned epoxy compound (B) (carboxyl groups:epoxy groups) is preferably 100:50 to 100:150 (molars), and more preferably 100:80 to 100:120 (molars).

[0040] One example of a method for manufacturing crosslinked polyester resin (C) is to obtain it by heating a mixture of a polyester resin (A) with carboxyl groups on its side chains, an epoxy compound (B), and a transesterification catalyst (D) to carry out a crosslinking reaction via an epoxy ring-opening reaction. Alternatively, it can be obtained by heating a mixture of a polyester resin (A) with carboxyl groups on its side chains and an epoxy amine compound (E) with tertiary amine groups to carry out a crosslinking reaction via an epoxy ring-opening reaction.

[0041] The stress relaxation initiation temperature of crosslinked polyester resin (C) is preferably above 100°C, more preferably above 110°C, and even more preferably above 120°C. There is no particular upper limit; industrially, it is acceptable as long as it is below 300°C, and below 250°C is also acceptable.

[0042] For cross-linked polyester resin (C), when a vertical stress of 0.1 N is applied using a rheometer and the shear strain is set to 10%, the time required for the relaxed elastic modulus to reach 0.37 times the initial relaxed elastic modulus at 180°C must be between 1 × 10¹ seconds and 1 × 10⁴ seconds. If the time required for the relaxed elastic modulus to reach 0.37 times the initial relaxed elastic modulus at 180°C is less than 1 × 10⁴ seconds, the cross-linked polyester resin will exhibit appropriate stress relaxation and can suppress warping problems caused by hardening shrinkage, as well as cracking or circuit distortion caused by differences in thermal expansion between different layers when using adhesives to laminate insulating films onto metal substrates or mounting semiconductor devices on semiconductor substrates. Furthermore, a time of 1 × 10¹ seconds or more can suppress flow-out when used as an adhesive. The time required for the modulus of elasticity to reach 0.37 times the initial modulus of elasticity is preferably 2 × 10³ seconds or less, more preferably 1 × 10³ seconds or less, and even more preferably 5 × 10² seconds or less. Furthermore, 5 × 10¹ seconds or more is preferable, and 1 × 10² seconds or more is even better. Methods for adjusting to this range include, for example, adjusting the crosslinking density of the crosslinked polyester resin (C) and the transesterification reaction rate. Specifically, methods can be exemplified by adjusting the acid value of the polyester resin (A) with carboxyl groups on its side chains, or the type or reaction ratio of the epoxy compound (B) or the epoxide amine compound (E) with tertiary amine groups, and the content of the transesterification catalyst (D).

[0043] The elastic modulus of the crosslinked polyester resin (C) above the stress relaxation initiation temperature is preferably 0.1 MPa to 1.2 MPa. More preferably, it is 0.15 MPa or higher, and even more preferably 0.2 MPa or higher. Furthermore, 1.0 MPa or lower is preferred, and 0.8 MPa or lower is even more preferred. By ensuring the elastic modulus above the stress relaxation initiation temperature is within the aforementioned range, when used as an adhesive sheet, it adheres closely to the substrate, penetrates the unevenness of the substrate surface, improves adhesive strength, and also exhibits excellent insulation failure reliability. The method of adjusting the elastic modulus to the aforementioned range can be, for example, by adjusting the crosslinking density or transesterification reaction rate of the crosslinked polyester resin (C). Specifically, examples include adjusting the modulus by the acid value of the polyester resin (A) with carboxyl groups on the side chains, or the type or reaction ratio of the epoxy compound (B) or the tertiary amine compound (E), and the content of the transesterification catalyst (D). In addition, the elastic modulus here refers to the stored elastic modulus (E') value measured using a dynamic viscoelasticity measuring device at a frequency of 1 Hz and a measurement temperature of -100 to 250°C, at the temperature at which stress relaxation begins to occur.

[0044] <Ester Exchange Catalyst (D)> Ester exchange catalyst (D) is an ester exchange catalyst for polyester resin (A) with carboxyl groups on its side chains. Through ester exchange catalyst (D), the crosslinked polyester resin has "dynamic" covalent crosslinking that can be exchanged at high temperatures. Therefore, it has high strength at room temperature and can bond to substrates or films above the ester exchange activation temperature. In addition, it exhibits stress relaxation, which can suppress cracking or circuit distortion caused by the difference in thermal expansion between the insulating layer and the conductor layer.

[0045] Regarding transesterification catalysts (D), zinc acetate, triphenylphosphine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, and 1,8-diazabicyclo[5.4.0]undec-7-ene are examples, with zinc acetate being particularly preferred.

[0046] From the viewpoints of the mechanical strength of the polyester resin (A) with carboxyl groups on the side chain, the uniformity of the sample, or the stress relaxation of the cross-linked polyester (C), the content of the transesterification catalyst (D) in the cross-linked polyester resin (C) is preferably 10 to 40 mol parts relative to 100 mol parts of carboxyl groups in the polyester resin (A) with carboxyl groups on the side chain, and more preferably 10 to 30 mol parts.

[0047] <Epoxyamine Compounds with Tertiary Amine Groups (E)> The epoxy compound (B) in the cross-linked polyester resin (C) can be an epoxyamine compound (E) with intramolecular tertiary amine groups. The tertiary amine groups in the epoxyamine compound (E) have the same transesterification catalytic effect as the transesterification catalyst (D). By heating the cross-linked polyester resin (C), the hydroxyl groups contained in the cross-linked polyester resin (C), even without the incorporation of the transesterification catalyst (D), will attack the CO bonds of the ester groups present near the hydroxyl groups through the action of the tertiary amine groups. Bond exchange occurs due to the transesterification reaction, which can exhibit stress relaxation behavior.

[0048] Examples of epoxide amine compounds (E) with tertiary amino groups include N,N,N',N'-tetraglycidyl-m-phenylenediamine, 4,4'-methylenebis(N,N-diglycidylaniline), and triglycidyl-p-aminophenol. N,N,N',N'-tetraglycidyl-m-phenylenediamine is commercially available from Mitsubishi Gas Chemical Co., Ltd. as the multifunctional epoxy compound "TETRAD-X". Triglycidyl-p-aminophenol is commercially available from Mitsubishi Chemical Co., Ltd. as "jER630". 4,4'-methylenebis(N,N-diglycidylaniline) is available from Tokyo Chemical Industry Co., Ltd. (TCI). The epoxide amine compound (E) with tertiary amino groups is preferred, especially those with multiple tertiary amino groups per molecule. Specifically, N,N,N',N'-tetraglycidyl-m-phenylenediamine and 4,4'-methylenebis(N,N-diglycidyl-aniline) are preferred. Having multiple tertiary amino groups per molecule facilitates transesterification catalysis and enhances stress relaxation behavior. One or more epoxide amine compounds (E) with tertiary amino groups can be used. Furthermore, epoxide amine compounds (E) with tertiary amino groups can be used in combination with epoxide compounds without tertiary amino groups. Additionally, using epoxide amine compounds (E) with tertiary amino groups in conjunction with a transesterification catalyst (D) is also suitable.

[0049] The molecular weight of epoxide amine compounds (E) with tertiary amine groups is preferably below 800. By keeping the molecular weight below 800, the epoxide amine compound can enter between polyester chains, forming three-dimensional crosslinks, which easily improves heat resistance. The molecular weight of epoxide amine compounds (E) with tertiary amine groups is preferably below 700, and more preferably below 600. The lower limit of the molecular weight of epoxide amine compounds is, for example, above 250.

[0050] The ratio of the tertiary amine compound (E) in the crosslinked polyester resin (C) is preferably 3 to 40 mol parts per 100 mol parts of the tertiary amine compound (E) relative to the carboxyl groups of the polyester resin (A) with carboxyl groups in its side chains. More preferably, it is 5 mol parts or more, and even more preferably 10 mol parts or more. Furthermore, 35 mol parts or less is preferred, and even more preferably 30 mol parts or less. By setting the ratio of the tertiary amine compound (E) in the crosslinked polyester resin (C) within the aforementioned range, the crosslinking density becomes appropriate, and stress relaxation in the crosslinked polyester (C) can also be achieved.

[0051] <Adhesive Sheet> The aforementioned cross-linked polyester resin (C) is suitable for use as an adhesive sheet. The adhesive sheet associated with the embodiment only needs to have an adhesive layer composed of cross-linked polyester resin (C), and can be an adhesive sheet with two or more layers such as a substrate layer and a release layer, or it can be a single-layer adhesive sheet in which the cross-linked polyester resin (C) itself is processed into a sheet shape. The adhesive sheet associated with the embodiment may also have two or more adhesive layers formed of cross-linked polyester resin (C).

[0052] Regarding the manufacturing methods of the adhesive sheet related to the embodiments, examples include a hot melt coating method in which crosslinked polyester resin (C) is heated and stirred, and then extruded into a release film; a method in which a pre-crosslinked polyester resin mixture is dissolved in a solvent, coated onto a release film, and then the solvent is dried before crosslinking; and even a method in which a pre-crosslinked polyester resin mixture is stirred at high speed in water or a solvent to form an aqueous dispersion, coated onto a release film, and then the moisture is dried before crosslinking. Furthermore, by laminating a release substrate, it can function as a protective layer for the substrate. By using a release substrate to demold the adhesive sheet, the adhesive layer can be further transferred to other substrates.

[0053] Adhesive sheets can be obtained by coating various laminates with cross-linked polyester resin (C) using conventional methods and then drying them. Furthermore, after drying, if a release substrate is attached to the adhesive layer, backprinting on the substrate will not occur, allowing for easy winding and handling. The adhesive layer is also protected, resulting in excellent storage and ease of use. Additionally, by coating and drying the adhesive layer on a release substrate and then attaching it to other release substrates as needed, the adhesive layer itself can be transferred to other substrates.

[0054] The release substrate is not particularly limited. Examples include coatings of clay, polyethylene, polypropylene, etc., on both sides of molded paper, kraft paper, roll paper, cellophane, etc., followed by the application of polysiloxane, fluorine, or alkyd release agents on these coatings. Additionally, various olefin films such as polyethylene, polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer, both individually and on films such as polyethylene terephthalate and polyethylene naphthalate, can be coated with the aforementioned release agents. Considering the release force between the release substrate and the adhesive layer, and the adverse effects of polysiloxane on electrical properties, it is preferable to apply polypropylene filler to both sides of the molded paper and then use an alkyd release agent on it, or to use an alkyd release agent on polyethylene terephthalate.

[0055] Furthermore, the method for applying the adhesive composition to the substrate is not particularly limited; examples include comma-shaped doctor blade coaters and reverse roller coaters. Alternatively, the adhesive layer can be applied directly to the rolled copper foil or polyimide film of the printed circuit board constituent material, or by transfer, depending on the need. The thickness of the dried adhesive layer can be appropriately varied as needed, 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.

[0056] The term "printed circuit board" in the context of implementation refers to a laminate formed from metal foil that forms conductive circuits and a resin substrate. Printed circuit boards can be manufactured, for example, using a metal-laminated laminate and conventional methods such as subtraction. Depending on the need, flexible printed circuit boards (FPCs), flat cables, and tape-and-reel bonding (TAB) circuit boards are collectively referred to as such, where the conductive circuits formed from metal foil are partially or completely covered with a cover film or screen printing ink.

[0057] The printed circuit board can be configured with any layered structure that can be used in printed circuit boards. 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. Alternatively, 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.

[0058] In addition, a configuration in which two or more of the above-mentioned printed circuit boards are laminated may also be adopted as necessary.

[0059] The substrate is not particularly limited as long as it is coated with cross-linked polyester resin (C) and can form an adhesive layer after drying, or can be laminated after being bonded with an adhesive sheet made of cross-linked polyester resin (C). Examples of substrates include resin substrates such as thin film resins, metal substrates such as metal plates or foils, and paper.

[0060] 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 thin-film resin (hereinafter also referred to as a substrate thin film layer) is preferred.

[0061] The metal substrate can be any conventionally known conductive material applicable to circuit boards. Examples of materials include various metals and alloys such as SUS, copper, aluminum, iron, stainless steel, zinc, and nickel, platings, and metals treated with zinc or chromium compounds. Metal foil is preferred, and copper foil is more suitable. Copper foil can also be any product manufactured by rolling or electrolysis. To ensure adhesion to the cross-linked polyester resin composition layer, physical surface treatments such as roughening or chemical surface treatments such as pickling can be applied to the metal foil. 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. It is also preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. If the thickness is too thin, the circuit may not achieve sufficient electrical performance; conversely, if the thickness is too thick, the processing efficiency during circuit fabrication may decrease. Metal foil is usually provided in a roll form. The shape of the metal foil used in manufacturing printed circuit boards is not particularly limited. When using ribbon-shaped metal foil, its length is not particularly limited. Furthermore, its width is also not particularly limited, but approximately 250-500 cm is preferred. The surface roughness of the substrate is not particularly limited, but preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less. In practical applications, it is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 0.7 μm or more. Additionally, it is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1.5 μm or less.

[0062] Examples of paper types include molded paper, kraft paper, roll paper, and cellophane. Examples of composite materials include glass epoxy resin.

[0063] In terms of adhesion and durability to cross-linked polyester resin (C), 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.

[0064] The cover film associated with the embodiment is a film having an adhesive layer formed of cross-linked polyester resin (C) and an insulating film, for example, a film that serves to protect components such as the aforementioned printed circuit board or circuit. Regarding the aforementioned insulating film, any conventionally known insulating film can be used as the insulating film for the printed circuit board. For example, films made from various polymers such as polyimide, polyester, polyphenylene sulfide, polyethersulfone, polyetheretherketone, aramid, polycarbonate, polyarylate, polyamide-imide, liquid crystal polymers, syndiotactic polystyrene, and polyolefin resins can be used.

[0065] <Printed Circuit Board Manufacturing Method> One example of a printed circuit board manufacturing method related to the embodiment can be manufactured by a step of heating the cross-linked polyester resin (C) to above its stress relaxation initiation temperature and then bonding them together. That is, for example, the materials of the aforementioned layers are overlapped, heated to above the stress relaxation initiation temperature of the cross-linked polyester resin (C), and bonded together. Due to the properties of the cross-linked polyester resin (C), the components can be laminated even without a curing treatment, thus obtaining a printed circuit board.

[0066] In a suitable embodiment, an article formed by laminating a cross-linked polyester resin composition layer onto a cover film layer is manufactured (hereinafter referred to as a "cover film-side article"). On the other hand, an article formed by laminating a metal foil layer onto a substrate film layer to form a desired circuit pattern (hereinafter referred to as a "substrate film-side 2-layer article") or an article formed by laminating a cross-linked polyester resin composition layer onto a substrate film layer and then laminating a metal foil layer thereon to form a desired circuit pattern (hereinafter referred to as a "substrate film-side 3-layer article") (hereinafter, the substrate film-side 2-layer article and the substrate film-side 3-layer article are collectively referred to as "substrate film-side articles"). By bonding the cover film-side article and the substrate film-side article obtained in this manner, a 4-layer or 5-layer printed circuit board can be obtained.

[0067] Circuitry can be formed on a metal foil layer using methods already known. Additive or subtractive methods can be used. Subtractive methods are preferable.

[0068] For reinforcing material side products, such as those made of flexible, rollable reinforcing materials like polyimide films, it is suitable to manufacture them by coating the reinforcing material with an adhesive. Alternatively, for rigid, non-rollable reinforcing plates, such as those made of metal sheets like SUS or aluminum, or sheets made by curing glass fibers with epoxy resin, it is suitable to manufacture them by transferring an adhesive pre-coated to a release substrate. Furthermore, a cross-linking reaction can be performed in the applied adhesive as needed.

[0069] The resulting reinforcing material side product can be directly used for bonding to the back of a printed circuit board, or it can be used for bonding to a substrate film side product after bonding and storing the release film.

[0070] Substrate film-side product, cover film-side product, and reinforcing material-side product are all included in the laminate for printed circuit boards associated with the embodiment.

[0071] The wiring board associated with the embodiment of the <laminate> is an object in which cross-linked polyester resin (C) is laminated onto a substrate (a two-layer laminate of substrate / adhesive layer), or an object further bonded to a substrate (a three-layer laminate of substrate / adhesive layer / substrate). Here, the adhesive layer refers to an adhesive composition layer after the adhesive composition has been applied to the substrate and dried, or an adhesive composition layer after an adhesive sheet made of cross-linked polyester resin has been laminated to the substrate.

[0072] This invention claims priority based on Japanese Patent Application No. 2021-168544, filed on October 14, 2021. The entire contents of Japanese Patent Application No. 2021-168544, filed on October 14, 2021, are incorporated herein by reference. [Example]

[0073] To further illustrate the present invention in detail, examples and comparative examples are provided below; however, the present invention is not limited to these examples. Furthermore, the measured values ​​described in the examples and comparative examples were determined by the following methods. Unless otherwise specified, "parts" refers to "parts by mass," and "moles" refers to "mole parts."

[0074] (Example of Polymerization of Polyol (A1-1)) In a reaction vessel equipped with a stirrer, thermometer, and distillation condenser, 30 moles of terephthalic acid, 69 moles of isophthalic acid, 1 mole of trimellitic anhydride, 15 moles of 2-methyl-1,3-butanediol, 85 moles of 1,6-hexanediol, and 0.2 moles of tetrabutyl titanate were charged. The temperature was slowly raised to 250°C, and the distilled water was removed from the system while esterification was carried out. After esterification, the pressure was slowly reduced to 10 mmHg while initial polymerization was carried out, and the temperature was raised to 250°C. Further polymerization was then carried out at a pressure below 1 mmHg until the desired torque was achieved. Then, nitrogen was used to restore atmospheric pressure, and 1 mole of trimellitic anhydride was added. The reaction was carried out at 220°C for 30 minutes to obtain the polyol (A1-1). The composition and characteristic values ​​of the high molecular weight polyol (A1-1) obtained in this manner are shown in Table 1.

[0075] (Example of Polymerization of Polyol (A1-2)) A reaction vessel equipped with a stirrer, thermometer, and distillation condenser was charged with 50 moles of terephthalic acid, 50 moles of isophthalic acid, 55 moles of ethylene glycol, 45 moles of 2,2-dimethyl-1,3-propanediol, and 0.2 moles of tetrabutyl titanate. The temperature was slowly raised to 250°C, and the distilled water was removed from the system while an esterification reaction was carried out. After the esterification reaction, the pressure was slowly reduced to 10 mmHg while initial polymerization under reduced pressure was carried out, and the temperature was raised to 250°C. Further polymerization was then carried out at a pressure below 1 mmHg until a predetermined torque was achieved, yielding polyol (A1-2). The composition and properties of the polyol (A1-2) obtained in this manner are shown in Table 1.

[0076] Except for changing the types and amounts of raw materials as shown in Table 1, high molecular weight polyols (A1-3 to A1-4) were obtained using the same method as for high molecular weight polyol (A1-1). Their properties are shown in Table 1.

[0077] <Number Average Molecular Weight (Mn)> The sample (polyol (A) or polyester resin with carboxyl groups on the side chain (A)) was dissolved or diluted in tetrahydrofuran to a concentration of approximately 0.5% by mass, and filtered through a polytetrafluoroethylene membrane with a pore size of 0.5 μm to prepare the sample for determination. The number average molecular weight was determined by gel permeation chromatography using tetrahydrofuran as the mobile phase and a differential refractometer as the detector. The flow rate was set at 1 mL / min, and the column temperature was set at 30 °C. The molecular weight standard was monodisperse polystyrene. The calculation of the number average molecular weight omitted the portion equivalent to a molecular weight less than 1000.

[0078] <Acid Value> Dissolve 0.2 g of the sample (polyol (A1) and polyester resin with carboxyl groups on the side chain (A)) in 20 ml of chloroform. Titrate with 0.1 N potassium hydroxide (KOH) ethanol solution using phenolphthalein as an indicator. From the titration amount, convert the mg of KOH consumed for neutralization into the amount per 1 g of resin to calculate the acid value (mgKOH / g).

[0079] <Glass Transition Temperature> A differential scanning calorimeter (DSC220 model) manufactured by SEIKO Electronics Industries, Ltd. was used. 5 mg of the sample (polyol (A1) and polyester resin with carboxyl groups on the side chain (A)) was placed in an aluminum pan, sealed with a cap, and temporarily maintained at 250°C for 5 minutes. Then, it was rapidly cooled with liquid nitrogen, and subsequently heated from -100°C to 300°C at a rate of 20°C / min for measurement. The point of curvature of the obtained curve was defined as the glass transition temperature.

[0080] [Table 1] Element substance name A1-1 A1-2 A1-3 A1-4 composition (mol%) polycarboxylic acid components terephthalic acid 30 50 40 50 isophthalic acid 69 50 39 49 adipic acid 20 Triphenyltricarboxylic anhydride 1 1 1 polyol components Ethylene glycol 55 2,2-Dimethyl-1,3-propanediol 45 2-Methyl-1,3-butanediol 15 58 83 1,4-Butanediol 42 17 1,6-Hexanediol 85 Addition acid Triphenyltricarboxylic anhydride 1 1 1 physical properties Number average molecular weight (Mn) 15000 3000 12000 12000 Acid value (mgKOH / g) 5.1 0.3 6.5 5.6 Glass transfer temperature (°C) 7 55 10 40

[0081] (Example of synthesis of polyester resin with carboxyl groups in the side chain (A-1)) In a reaction vessel equipped with a stirrer, thermometer, and reflux duct, 80 parts of high molecular weight polyol (A1-1), 20 parts of high molecular weight polyol (A1-2), 2.6 parts of pyrocalcite anhydride, and 100 parts of toluene were charged. The mixture was slowly heated to 80°C while simultaneously dissolving in toluene. After dissolution, 0.05 parts of triethylamine were added as a reaction catalyst, and the temperature was then slowly increased to 105°C, allowing the reaction to proceed for 24 hours. After confirming the completion of the reaction by infrared spectroscopy (IR), the mixture was diluted with 54 parts of toluene to obtain a solution of polyester resin (A-1) with a solid content of 40% by mass. The composition and properties of the polyester resin (A-1) with carboxyl groups in the side chain obtained in this manner are shown in Table 2.

[0082] (Synthesis example of polyester resin with carboxyl group in side chain (A-2~A-3)) Polyester resin with carboxyl group in side chain (A-2~A-3) was obtained in the same manner as polyester resin with carboxyl group in side chain (A-1).

[0083] [Table 2] Polyester resins with carboxyl groups in the side chain (A) A-1 A-2 A-3 composition (parts by weight) Polyols (a1) A1-1 80 80 A1-3 90 Polyols (a2) A1-2 20 20 Tetracarboxylic acid dianhydride Pyrolithic anhydride 2.6 4.3 19.6 Chain extender 2,2-Dimethyl-1,3-propanediol 1 10 physical properties Number average molecular weight (Mn) 16000 15000 12000 Acid value (mgKOH / g) 17 26 91 Glass transfer temperature (°C) 15 15 10

[0084] <Example of Fabrication of Crosslinked Polyester Resin Film> As described below, a film-shaped crosslinked polyester resin (crosslinked polyester resin film) was fabricated. A single-film sample (film sample 1) and a polyimide film / crosslinked polyester resin laminate sample (film sample 2) were fabricated for use in the evaluations described later. (Method for fabricating the single-film sample (film sample 1)) A polyester resin (A) with carboxyl groups on its side chains and an epoxy compound (B) were dissolved in NMP (N-methyl-2-pyrrolidone), and the amount of carboxyl groups (mole equivalents) of the polyester resin (A) with carboxyl groups on its side chains and the amount of epoxy groups (mole equivalents) of the epoxy compound (B) were made in a specific ratio to obtain a resin solution with a solid content of 35% by mass. Next, a transesterification catalyst (zinc acetate; Zn(OAc)2) was dissolved in NMP (N-methyl-2-pyrrolidone) to obtain a catalyst solution with a solid content of 35% by mass. The two solutions were mixed in a Teflon (registered trademark) mold, and the amount (mole equivalent) of the carboxyl groups in the polyester resin (A) with carboxyl groups on the side chains and the amount (mole equivalent) of the transesterification catalyst were made into a specific ratio (hereinafter referred to as the pre-crosslinking polyester resin composition). The solvent was then evaporated at 80°C on a heater. This mixed sample was then heated sequentially at 130°C for 1 hour, at 140°C for 1 hour, and at 150°C for 3 hours to obtain a single-film sample (thickness 0.7 mm). This was used as film sample 1.

[0085] (Preparation Method of Polyimide Film / Cross-linked Polyester Resin Laminate Sample (Film Sample 2)) A resin solution and a catalyst solution were prepared using the same method as described for Film Sample 1. These two solutions were mixed to achieve a specific molar ratio between the amount of carboxyl groups (molar equivalents) of the polyester resin (A) with carboxyl groups on its side chains and the amount of transesterification catalyst (molar equivalents). The solution was coated onto a 12.5 μm thick polyimide film (manufactured by Kaneka Co., Ltd., APICAL (registered trademark)). The cross-linked polyester resin layer was dried to a thickness of 25 μm. After drying at 40°C for 30 minutes, it was further dried sequentially at 130°C for 1 hour, at 140°C for 1 hour, and at 150°C for 3 hours to obtain the polyimide film / cross-linked polyester resin laminate sample. This is used as Film Sample 2.

[0086] The following compounds are used for the epoxy compound (B) and transesterification catalyst (D): B-1: 1,4-Butanediol diglycidyl ether (epoxy group number 2) B-2: "jER630" manufactured by Mitsubishi Chemical Corporation (triglycidyl-p-aminophenol, epoxy group number 3, belongs to epoxide amine compound (E)) B-3: "TETRAD-X" manufactured by Mitsubishi Gas Chemical Corporation (N,N,N',N'-tetraglycidyl-m-phenylenediamine, epoxy group number 4, belongs to epoxide amine compound (E)) D-1: Zinc acetate (Zn(OAc)2)

[0087] <Example 1> A polyester resin with carboxyl groups on its side chains (A-1) was used, and an epoxy compound (B) of 1,4-butanediol diglycidyl ether was used. Based on 100 moles of carboxyl groups in the polyester resin (A), the materials were blended in the proportions shown in Table 3 to prepare single-film samples (film sample 1) and laminated samples (film sample 2) of crosslinked polyester resin films. The performance of the obtained crosslinked polyester resin films was evaluated, and the results are shown in Table 3.

[0088] <Examples 2-9, Comparative Examples 1-6> Similar to Example 1, using 100 moles of carboxyl groups in the polyester resin (A) with carboxyl groups in the side chain as a base, the types and proportions of the polyester resin (A), epoxy compound (B), and transesterification catalyst (D) with carboxyl groups in the side chain were varied as shown in Tables 3 and 4, and Examples 2-9 and Comparative Examples 1-6 were performed. The performance evaluation results are shown in Tables 3 and 4. In addition, in Comparative Examples 4-6, a high molecular weight polyol (a1) was used instead of the polyester resin (A) with carboxyl groups in the side chain.

[0089] <Tensile Testing> Tensile tests were conducted at room temperature using a Tensilon universal testing machine manufactured by A&D Corporation. Thin film specimens (sample 1) with a thickness of 0.7 mm, a width of 1 cm, and a length of 5 cm were used. The strength and Young's modulus were determined at a tensile speed of 20 mm / min.

[0090] <Stress Relaxation Test> A rheometer MCR302 (Anton Paar) was used to perform stress relaxation tests at 10°C intervals between 100°C and 250°C. A disc-shaped test piece with a diameter of 8 mm and a thickness of 0.7 mm, cut from the thin film sample 1, was used. The test was conducted in an N2 gas environment. To prevent slippage of the sample, a vertical stress of 0.1 N was applied. The shear strain was set at 10%. Stress relaxation is defined as the phenomenon where, during the stress relaxation test, the ratio of the initial stress σ₀ to the stress σ₀, σ / σ₀, becomes less than 0.7 within 1 × 10⁴ seconds. The temperature at which stress relaxation begins is defined as the stress relaxation initiation temperature. The stress relaxation time (180°C) is the time it takes for the elastic modulus to become 1 / e (=0.37) times the initial elastic modulus when measured at 180°C, and is recorded in the table. The results are shown in Tables 3 and 4. Figure 1 shows the results of the stress relaxation test in Example 1. The vertical axis represents the stress (σ) normalized to the initial stress (σ0), and the horizontal axis represents the elapsed time (seconds). As shown in Figure 1, no significant stress relaxation was observed at the measurement temperature of 100°C, while significant stress relaxation was observed at temperatures above 150°C. This is attributed to the transesterification reaction occurring at high temperatures, resulting in stress dispersion. Furthermore, if the measurement temperature is further increased from 150°C, the rate of stress relaxation increases with increasing temperature. This is attributed to the activation of the transesterification reaction by temperature.

[0091] <Dynamic Viscoelasticity Measurement> The dynamic viscoelasticity of thin film sample 1 was measured using a DVA-200 (manufactured by IT Measurement Control Co., Ltd.) in the range of -100℃ to 250℃. The measurements were performed under atmospheric conditions at a temperature change rate of 4℃ / min, with a measurement frequency of 1Hz. The stored elastic modulus (E') at the temperature at which stress relaxation begins during the stress relaxation measurement is shown in Tables 3 and 4.

[0092] <PI / Cu Foil Peel Strength (Adhesion)> The crosslinked polyester resin layer of the thin film specimen 2 was brought into contact with the shiny surface of the rolled copper foil of a copper-clad laminate with a thickness of 49 μm (manufactured by Nippon Steel Chemical & Material Co., Ltd., ESPANEX series, Cu / polyimide / Cu = 12 / 25 / 12 μm) and laminated. It was rolled for 280 seconds under pressure of 20.4 kgf / cm² at 170 °C to effect adhesion, and a laminated sample for peel strength evaluation was obtained. In the case where sufficient adhesion was not achieved under the lamination conditions at 170 °C with a stress relaxation start temperature of 150 °C or higher, samples were fabricated by raising the rolling temperature to 180 °C, 200 °C, and 220 °C (hereinafter referred to as the lamination temperature). The peel strength was measured at 25 °C by peeling the thin film at a tensile speed of 50 mm / min and performing a 90° peel test. This test represents the adhesion strength at room temperature. The results are shown in Tables 3 and 4. <Evaluation Criteria> ◎: 1.0 N / mm or more ○: 0.5 N / mm or more and less than 1.0 N / mm △: 0.35 N / mm or more and less than 0.5 N / mm ╳: Less than 0.35 N / mm

[0093] <Normal Welding Heat Resistance> Samples were fabricated in the same manner as the above PI / Cu foil peel strength measurement. A 2.0 cm × 2.0 cm sample piece was floated in a heated solder bath for 1 minute, and the upper limit temperature at which no swelling occurred was measured at intervals of 10 °C. Specifically, it was heated from 250 °C in 10 °C increments up to 280 °C. In this test, a higher measured value indicates better heat resistance. The results are shown in Tables 3 and 4. <Evaluation Criteria> ○: No swelling even at 270 °C or higher △: Swelling occurred at 260 °C or higher and less than 270 °C ╳: Swelling occurred below 260 °C

[0094] <Embedding Performance> Thin film sample 2 was bonded to a comb-shaped test pattern forming a circuit with a linewidth / space ratio of 50 μm / 50 μm. The test pattern was a comb-shaped wiring pattern formed on a 50 μm thick polyimide support substrate, with a linewidth / space ratio of 50 μm / 50 μm for the Cu wiring. An evaluation substrate with 10 lines on one side and a total of 20 lines on both sides was used in an alternating configuration. Bonding was performed by contacting the circuit surface with the cross-linked polyester resin layer of sample 2 and vacuum calendering at a pressure of 2 MPa for 280 seconds to produce an embedding performance evaluation sample. The temperature conditions during vacuum calendering were set to the same as the aforementioned lamination temperature. A Keyence digital microscope (VHX-2000) was used to observe whether an adhesive layer was embedded between the circuits in the calendered sample. The results are shown in Tables 3 and 4. <Evaluation Criteria> 〇: Adhesive layer embedded between circuits ╳: Insufficient embedding, gaps observed between circuits

[0095] <Insulation Breakdown Reliability> Insulation breakdown reliability assessment samples were prepared using the same method as the aforementioned embedding assessment samples. A voltage of 200V was applied to the obtained insulation breakdown reliability samples. After applying the voltage, the insulation resistance value was assessed at high temperature and high humidity (85°C, 85% RH) for 0–250 hours. The results are shown in Tables 3 and 4. Figure 2 shows the insulation breakdown reliability results for Examples 5 and 7. <Assessment Criteria> ◎: Resistance value exceeding 1 × 10¹⁰ Ω within 0–250 hours, with no change in appearance. ○: Resistance value between 1 × 10⁸ and 1 × 10¹⁰ Ω within 0–250 hours, with no change in appearance. ╳: Resistance value less than 1 × 10⁸ Ω within 0–250 hours, or abnormal appearance observed (ion migration).

[0096] <Long-term heat-resistant adhesion> Samples for long-term heat-resistant adhesion were prepared using the same method as the aforementioned PI / Cu foil peel strength test. Samples heated at 150°C and in atmospheric conditions for 1000 hours were subjected to 90° peeling at a tensile speed of 50 mm / min. The results are shown in Tables 3 and 4. <Evaluation Criteria> ◎: 90° peel strength after 1000 hours at 150°C exceeds 1.0 N / mm ○: 90° peel strength after 1000 hours at 150°C is 0.5~1.0 N / mm ╳: 90° peel strength after 1000 hours at 150°C is less than 0.5 N / mm

[0097] <Bending Resistance> Thin film sample 2 was bonded to the glossy surface of a 49 μm thick copper-coated laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., ESPANEX series, Cu / polyimide / Cu=12 / 25 / 12 μm). It was rolled for 280 seconds under a pressure of 20.4 kgf / cm² to bond it, obtaining the evaluation sample. The temperature conditions during rolling were the same as the aforementioned lamination temperature. This sample was cut into 10 cm × 1 cm strips, and the number of bends before cracking was recorded using a BE-202MIT bending resistance tester manufactured by TESTER Industrial Co., Ltd., under conditions of 300 g load, 0.25 mm clamp gap, and clamp tip R=0.38 mm. The results are shown in Tables 3 and 4. <Assessment Criteria> ◎: No cracking after more than 250 bends ○: No cracking after more than 200 bends ╳: Cracking occurred before 200 bends

[0098] <Stability at Room Temperature> (1) Gel Fraction: Weigh 0.125 g of film sample 1, immerse it in 25 mL of methyl ethyl ketone for 2 hours at room temperature, and then dry it at 80°C for 1 hour using a vacuum dryer. Measure the weight of the gel component only. Calculate the gel fraction according to the following formula: Gel Fraction (%) = Weight of gel component after immersion and drying ÷ Weight of sample before testing × 100 Room temperature stability (gel fraction) refers to the condition of storing cross-linked polyester resin film (film sample 1) at 25°C. The gel fraction is measured at the beginning of storage and after 6 months to assess the rate of change from the initial value. The rate of change is the absolute value of the difference between the gel fraction (%) before and after 6 months, as described in the following formula: Rate of Change = |Gel Fraction (%) after 6 months - Gel Fraction (%) at the beginning| <Evaluation Criteria> ○: Rate of change less than 10 △: Rate of change greater than 10 but less than 25 ╳: Rate of change greater than 25

[0099] (2) Presence or Absence of Softening Behavior: Room temperature storage stability (softening behavior) refers to assessing whether softening behavior occurs due to bond exchange reactions when film sample 1 is stored at 25°C for a long period (6 months) using stress relaxation testing. Film sample 1 was tested under the same conditions as the aforementioned stress relaxation test after 6 months of storage at 25°C to assess the presence or absence of softening behavior. The results showed that stress relaxation was observed in the sample after 6 months of storage at 25°C, maintaining the softening characteristics caused by bond exchange, and there was no change compared to the initial behavior during long-term storage at room temperature. The results are shown in Tables 3 and 4. <Evaluation Criteria> ○: Softening behavior present (stress relaxation occurs) ╳: No softening behavior (stress relaxation does not occur)

[0100] [Table 3] Examples and Comparative Examples Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 composition Types of polyester resins (A) with carboxyl groups in the side chain. A-1 A-1 A-1 A-1 A-1 A-1 A-1 A-2 A-2 Epoxy compounds (B) (100 moles of carboxyl group of (A)) B-1 50 50 90 - - - 25 50 - B-2 - - - 33 - - - - - B-3 - - - - 25 25 12.5 - 25 Ester exchange catalyst (D) (100 moles of carboxyl group of (A)) D-1 20 10 20 20 20 - 10 20 20 physical properties Stress relaxation start temperature ℃ 120 150 150 180 180 180 170 160 180 Stress relaxation time (180℃) sec 308 330 322 3732 3552 3590 1075 330 9000 The elastic modulus above the temperature at which stress relaxation occurs. MPa 0.264 0.529 0.101 0.975 0.287 0.667 0.169 0.275 0.531 Tensile test (strength) MPa 6.3 6.4 1.2 3.7 8.6 15.9 8.5 7.2 8.8 Tensile test (Young's modulus) GPa 0.003 0.004 0.001 0.004 0.04 0.008 0.003 0.006 0.05 Performance evaluation Lamination temperature ℃ 170 170 170 170 200 220 180 170 220 PI / Cu foil peel strength - ◎ ◎ ◎ ○ ○ ○ ◎ ○ ○ Normal welding heat resistance - ○ ○ ○ △ △ ○ ○ ○ ○ Embedded - ○ ○ ○ ○ ○ ○ ○ ○ ○ Insulation failure reliability - ○ ◎ ○ ○ ○ ◎ ◎ ○ ○ Long-term heat-resistant adhesion - ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ Bending resistance - ◎ ◎ ◎ ◎ ○ ○ ◎ ○ ○ Room temperature storage stability (gel fraction) - ○ ○ ○ ○ ○ ○ ○ ○ ○ Room temperature storage stability (softening behavior) - ○ ○ ○ ○ ○ ○ ○ ○ ○

[0101] [Table 4] Examples and Comparative Examples Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 composition Types of polyester resins (A) with carboxyl groups in the side chain. A-1 A-1 A-3 A1-1 A1-3 A1-4 Epoxy compounds (B) (100 moles of carboxyl group of (A)) B-1 50 - 50 50 50 50 B-2 - 33 - - - - B-3 - - - - - - Ester exchange catalyst (D) (100 moles of carboxyl group of (A)) D-1 - - 20 20 20 20 physical properties Stress relaxation start temperature ℃ none > 250 > 250 It cannot form a film, therefore it cannot be measured. Stress relaxation time (180℃) sec - >10000 >10000 The elastic modulus above the temperature at which stress relaxation occurs. MPa Measurement at 150℃ 1.249 Measured at 170℃ 1.711 - Tensile test (strength) MPa 6.3 3.7 15.5 Tensile test (Young's modulus) GPa 0.004 0.005 0.04 Performance evaluation Lamination temperature ℃ 220 220 220 It cannot form a film, therefore performance evaluation is not possible. PI / Cu foil peel strength - - - - Normal welding heat resistance - - - - Embedded - - - - Insulation failure reliability - - - - Long-term heat-resistant adhesion - - - - Bending resistance - - - - Room temperature storage stability (gel fraction) - ╳ ○ ○ Room temperature storage stability (softening behavior) - ╳ ○ ○

[0102] As shown in Tables 3 and 4, Examples 1-9 exhibit excellent room temperature storage stability. Due to their cross-linked structure, they possess high strength and, as adhesive sheets, demonstrate excellent adhesion to the substrate (polyimide, copper foil), weld heat resistance, and reliability against insulation failure. In contrast, Comparative Example 1 lacks an ester exchange catalyst (D) and does not exhibit stress relaxation. Therefore, its adhesion to the substrate at the lamination temperature is insufficient, making it impossible to produce film sample 2 of the laminate with the polyimide film, and thus its performance cannot be evaluated. Stress relaxation was observed in Comparative Examples 2-3; however, at 180°C, the modulus of elasticity did not reach 0.37 times the initial modulus of elasticity within 1 × 10⁴ seconds, failing to fully demonstrate the softening behavior resulting from bond exchange. Consequently, its adhesion to the substrate at the lamination temperature was insufficient, making it impossible to produce film sample 2 of the laminate with the polyimide film, and thus its performance cannot be evaluated. In Comparative Examples 4-6, the polyester resins lack carboxyl groups in their side chains, resulting in low crosslinking density with epoxy compounds, making it impossible to produce coatings and assess their industrial applicability.

[0103] The cross-linked polyester resin of this invention exhibits high adhesion to resin substrates such as polyimide and polyethylene terephthalate films, as well as metal substrates such as copper foil. It also provides high heat resistance, excellent room temperature stability, and superior insulation resistance (electrical properties). Furthermore, it softens at high temperatures, thus exhibiting compliance with the substrate and preventing cracking due to differences in thermal expansion between substrates, enabling effective bonding. Therefore, the cross-linked polyester resin of this invention can be used as an adhesive or adhesive sheet, and its properties are particularly useful in printed circuit board applications.

Claims

1. A crosslinked polyester resin (C) having a structure formed by reacting a polyester resin (A) with carboxyl groups on its side chains with an epoxy compound (B), wherein the time for the modulus of elasticity to reach 0.37 times the initial modulus of elasticity is 1×10¹ seconds to 1×10⁴ seconds when a vertical stress of 0.1 N is applied using a rheometer, the shear strain is set to 10%, and the test is conducted at 180 °C, and the resin has at least one of the following (1) and (2): the ratio of carboxyl groups in the polyester resin (A) with carboxyl groups on its side chains to epoxy groups in the epoxy compound (B), i.e., carboxyl groups: epoxy groups, is 100:50 to 100:150 moles; (1) it contains an ester exchange catalyst (D); and (2) the epoxy compound (B) is an epoxy amine compound (E) having tertiary amine groups.

2. The cross-linked polyester resin (C) as claimed in claim 1, wherein, Using a dynamic viscoelasticity measuring device, at a frequency of 1 Hz and a measurement temperature of -100 to 250°C, the elastic modulus above the stress relaxation initiation temperature is 0.1 MPa to 1.2 MPa.

3. The cross-linked polyester resin (C) as claimed in claim 1, wherein, The acid value of polyester resin (A) with carboxyl groups on the side chain is 7-40 mg KOH / g.

4. The cross-linked polyester resin (C) as claimed in claim 1, wherein, The polyester resin (A) with carboxyl groups on the side chain contains a number average molecular weight of 7,000 or more of a high molecular weight polyol (a1), a number average molecular weight of 1,000 or more but less than 7,000 of a high molecular weight polyol (a2), and a tetracarboxylic acid dianhydride as structural units.

5. A method for manufacturing a crosslinked polyester resin (C), comprising: (i) heating a mixture containing a polyester resin (A) having carboxyl groups on its side chains, an epoxy compound (B) and an ester exchange catalyst (D).

6. An adhesive composition comprising a crosslinked polyester resin (C) as claimed in any one of claims 1 to 4.

7. An adhesive sheet having an adhesive layer made of cross-linked polyester resin (C) as claimed in claim 1.

8. As in request item 7, the adhesive sheet, wherein, When using adhesive sheets to bond polyimide film to copper foil, the 90° peel strength is above 0.5 N / mm.

9. A printed circuit board comprising an adhesive sheet as a constituent element, as claimed in claim 7 or 8.

10. A cover film comprising an adhesive sheet as a constituent element, as claimed in claim 7 or 8.

11. A method of manufacturing a printed circuit board as claimed in claim 9, comprising the step of heating to above the stress relaxation initiation temperature of the crosslinked polyester resin (C) while simultaneously bonding.

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