Polyimide compositions, resin films, laminates, coverlay films, resin-coated copper foils, metal-clad laminates, and circuit boards

Abstract

To provide a polyimide composition capable of forming a resin film having a low dielectric loss tangent and excellent adhesion using a thermoplastic polyimide.SOLUTION: There is provided a polyimide composition comprising (A) a thermoplastic polyimide and (B) a polystyrene elastomer having a weight average molecular weight of 100000 or less, wherein the content of the component (B) is 50 pts.wt. or more and 120 pts.wt. of less based on the 100 pts.wt. of the component (A). The thermoplastic resin layer obtained by forming the polyimide composition into a film preferably has a dielectric loss tangent (Tanδ) at 20 GHz of 0.0011 or less as measured by a split-post dielectric resonator (SPDR) after humidity conditioning for 24 hours under constant temperature and humidity conditions of 23°C and RH of RH 50% RH.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polyimide compositions, resin films, laminates, coverlay films, resin-coated copper foils, metal-clad laminates, and circuit boards that are useful as adhesives in circuit boards such as printed wiring boards. [Background technology]

[0002] In recent years, with the miniaturization, weight reduction, and space-saving of electronic devices, the demand for flexible printed circuit boards (FPCs) has been increasing. These FPCs are thin, lightweight, flexible, and possess excellent durability even after repeated bending. Because FPCs enable three-dimensional and high-density mounting even in limited spaces, their applications are expanding to include wiring in the moving parts of electronic devices such as HDDs, DVDs, and mobile phones, as well as components such as cables and connectors.

[0003] In addition to the aforementioned increase in density, the advancement of equipment performance has necessitated the ability to handle higher frequencies of transmitted signals. In information processing and information communication, efforts are being made to increase transmission frequencies in order to transmit and process large amounts of information, and printed circuit board materials are required to reduce transmission loss by thinning the insulating layer and improving the dielectric properties of the insulating layer. In the future, the insulating layer (including the adhesive layer) that makes up FPCs will increasingly require reduced transmission loss and the ability to handle higher frequencies. For example, in order to transmit signals with frequencies of around 20-60 GHz using a direct conversion method, the FPCs used will also need to have even greater reductions in transmission loss than before.

[0004] Regarding the improvement of the dielectric properties of printed circuit board materials, a resin composition has been proposed that includes a polyimide, which is a reaction product of an aromatic tetracarboxylic anhydride and a diamine containing an aliphatic diamine having 4 to 40 carbon atoms, and a resin powder made of a resin material mainly composed of fluororesin (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-104843 [Overview of the project] [Problems that the invention aims to solve]

[0006] Thermoplastic polyimides made from aliphatic diamines are useful resin materials as adhesives because they are soluble in solvents, have excellent adhesive properties, and are easy to handle. However, in order to cope with the future advancement of high-frequency technology, in addition to satisfying the above-mentioned properties, there is a need for even lower dielectric loss tangent.

[0007] Therefore, an object of the present invention is to provide a polyimide composition that can form a resin film with low dielectric loss tangent and excellent adhesion using thermoplastic polyimide. [Means for solving the problem]

[0008] The polyimide composition of the present invention comprises the following components (A) and (B); (A) Thermoplastic polyimide, and (B) Polystyrene elastomers with a weight-average molecular weight of 100,000 or less. It contains the above, and the content of component (B) relative to 100 parts by weight of component (A) is within the range of 50 parts by weight or more and 120 parts by weight or less.

[0009] The polyimide composition of the present invention may have an acid value of component (B) of 10 mg KOH / g or less.

[0010] The polyimide composition of the present invention may have a content ratio of styrene units of polystyrene elastomer in component (B) within the range of 10% by weight or more and 65% by weight or less.

[0011] In the polyimide composition of the present invention, the thermoplastic polyimide may be obtained by reacting a tetracarboxylic anhydride component with a diamine component, and may contain 40 mol% or more of an aliphatic diamine relative to the diamine component.

[0012] The polyimide composition of the present invention may also be a dimer amine composition in which the aliphatic diamine is mainly composed of a dimer amine obtained by substituting the two terminal carboxylic acid groups of a dimer acid with primary aminomethyl groups or amino groups.

[0013] The polyimide composition of the present invention may further contain an amino compound having at least two primary amino groups as functional groups.

[0014] The resin film of the present invention is a resin film comprising a thermoplastic resin layer, The thermoplastic resin layer comprises the following components (A) and (B); (A) Thermoplastic polyimide, and (B) Polystyrene elastomers with a weight-average molecular weight of 100,000 or less. It contains the above, and is characterized in that the content of component (B) relative to 100 parts by weight of component (A) is within the range of 50 parts by weight or more and 120 parts by weight or less.

[0015] The resin film of the present invention may have an acid value of component (B) of 10 mg KOH / g or less.

[0016] In the resin film of the present invention, the thermoplastic resin layer may have a dielectric loss tangent (Tanδ) at 20 GHz measured by a split post dielectric resonator (SPDR) of 0.0011 or less after being conditioned for 24 hours under constant temperature and humidity conditions of 23°C and 50% RH.

[0017] The laminate of the present invention is a laminate comprising a base material and an adhesive layer laminated on at least one surface of the base material, wherein the adhesive layer is made of the resin film described above.

[0018] The coverlay film of the present invention is a coverlay film having a film material layer for coverlay and an adhesive layer laminated on the film material layer for coverlay, wherein the adhesive layer is made of the above resin film.

[0019] The copper foil with resin of the present invention is a copper foil with resin in which an adhesive layer and a copper foil are laminated, and the adhesive layer is made of the above resin film.

[0020] The metal-clad laminate of the present invention is a metal-clad laminate having an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, and at least one layer of the insulating resin layer is made of the above resin film.

[0021] The circuit board of the present invention is formed by wiring the metal layer of the above metal-clad laminate. [Effect of the Invention]

[0022] Since the polyimide composition of the present invention contains a thermoplastic polyimide and a polystyrene elastomer having a weight average molecular weight of 100,000 or less, it is possible to form a resin film having a practically sufficient adhesiveness while maintaining an extremely low dielectric tangent. Therefore, the polyimide composition and the resin film of the present invention can be particularly preferably used as a circuit board material such as an FPC in an electronic device that requires high-speed signal transmission. Further, since the resin film of the present invention has very excellent dielectric properties, it can also be applied to, for example, a receiver of a direct conversion system. Furthermore, because it has a practically sufficient adhesiveness, it can be applied as a highly reliable low-dielectric adhesive to electronic devices of any structure. [Embodiments for Carrying Out the Invention]

[0023] Hereinafter, embodiments of the present invention will be described.

[0024] [Polyimide Composition] A polyimide composition according to one embodiment of the present invention comprises the following components (A) and (B); (A) Thermoplastic polyimide, and (B) Polystyrene elastomers with a weight-average molecular weight of 100,000 or less. It contains.

[0025] <(A) Component: Thermoplastic polyimide> The thermoplastic polyimide of component (A) is a solvent-soluble thermoplastic polyimide, obtained by reacting a tetracarboxylic anhydride component with a diamine component to form a precursor polyamic acid, which is then imidized. Generally, "thermoplastic polyimide" refers to a polyimide that softens upon heating, solidifies upon cooling, and can repeat this process, and whose glass transition temperature (Tg) can be clearly determined. In this invention, however, it refers to a polyimide whose glass transition temperature can be clearly determined in a temperature range of less than 150°C. Furthermore, from the viewpoint of thermocompression bonding at low temperatures, a polyimide whose glass transition temperature can be clearly determined in a temperature range of less than 100°C is preferred, and whose storage modulus at 30°C, as measured using a dynamic viscoelasticity analyzer (DMA), is 1.0 × 10⁻⁶. 8 The storage modulus is 3.0 × 10⁻¹⁰ at a glass transition temperature of +30°C, and the storage modulus at +30°C is 3.0 × 10⁻¹⁰. 7 Polyimides with a storage modulus of less than Pa are more preferred. Furthermore, "non-thermoplastic polyimides" generally refer to polyimides that do not soften or become adhesive when heated, but in this invention, the storage modulus at 30°C measured using a dynamic viscoelasticity analyzer (DMA) is 1.0 × 10⁻⁶. 9 The Pa is greater than or equal to the storage modulus of elasticity at 300°C, and the storage modulus of elasticity at 300°C is 3.0 × 10⁻⁶. 8 This refers to polyimides with a Pa rating of 1.5 or higher.

[0026] (Tetracarboxylic acid anhydride component) The thermoplastic polyimide of component (A) may contain tetracarboxylic acid residues derived from tetracarboxylic anhydrides commonly used in thermoplastic polyimides without particular limitations, but it is preferable that it contains a total of 90 mol% or more of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) relative to the total tetracarboxylic acid residues. It is preferable to include a total of 90 mol% or more of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) relative to the total tetracarboxylic acid residues, as this makes it easier to achieve both flexibility and heat resistance in the polyimide. If the total amount of tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) is less than 90 mol%, the solvent solubility of the polyimide tends to decrease.

[0027] [ka]

[0028] In general formula (1), X represents a single bond or a divalent group selected from the following formulas.

[0029] [ka]

[0030] In the above formula, Z represents -C6H4-, -(CH2)n-, or -CH2-CH(-OC(=O)-CH3)-CH2-, where n is an integer from 1 to 20.

[0031] Examples of tetracarboxylic anhydrides represented by the above general formula (1) include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), p-phenylenebis(trimellitic acid monoester anhydride) (TAHQ), and ethylene glycol bisanhydrotrimellitate (TMEG). In particular, when using 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), the adhesion of the polyimide can be improved, and the ketone group present in the molecular skeleton may react with the amino group of the amino compound used for crosslinking (described later) to form a C=N bond, which easily exhibits an effect of improving heat resistance. From this viewpoint, it is preferable to contain 50 mol% or more, more preferably 60 mol% or more, of tetravalent tetracarboxylic residues derived from BTDA (BTDA residues) relative to the total tetracarboxylic residues.

[0032] The thermoplastic polyimide of component (A) may contain tetracarboxylic acid residues derived from acid anhydrides other than the tetracarboxylic acid anhydride represented by the general formula (1) above, to the extent that it does not impair the effects of the invention.There are no particular restrictions on such tetracarboxylic acid residues, but examples include pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic acid dianhydride, 2,2',3,3'- or 2,3,3',4'-benzophenonetetracarboxylic acid dianhydride, 2,3',3,4'-diphenyl ether tetracarboxylic acid dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3- or 3,4-Dicarboxyphenyl)-propane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or 3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3- or 3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-, 1,2,6,7- or 1,2,9,10-phenanthrene-tetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 2,3,5,6- Cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic acid dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic acid dianhydride Examples include tetracarboxylic acid residues derived from aromatic tetracarboxylic acid dianhydrides such as aqueous products, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene-tetracarboxylic acid dianhydrides, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydrides, pyrazine-2,3,5,6-tetracarboxylic acid dianhydrides, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydrides, thiophene-2,3,4,5-tetracarboxylic acid dianhydrides, and 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydrides.

[0033] (Diamine component) The thermoplastic polyimide of component (A) preferably uses a diamine component as a raw material that contains at least 40 mol%, more preferably 60 mol%, of aliphatic diamines relative to the total diamine components. In other words, the thermoplastic polyimide of component (A) preferably contains at least 40 mol%, more preferably 60 mol%, of diamine residues derived from aliphatic diamines relative to the total diamine residues. By including diamine residues derived from aliphatic diamines in the above amounts, the dielectric properties of the polyimide can be improved, as can the thermocompression bonding properties by lowering the glass transition temperature (low Tg) of the polyimide, and internal stress can be relieved by lowering the elastic modulus. If the amount of diamine residues derived from aliphatic diamines relative to the total diamine residues is less than 40 mol%, the improvement effect on dielectric loss tangent and thermocompression bonding properties may not be sufficiently obtained. Here, as the aliphatic diamine, an aliphatic diamine having 4 to 60 carbon atoms is preferred. For example, a dimer amine composition mainly consisting of a dimer amine in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups, hexamethylenediamine, dodecanediamine, cyclohexanediamine, polyoxyalkyleneamine, 4,4-diaminodicyclohexylmethane, etc. can be used, and among these, the dimer amine composition is particularly preferred.

[0034] (Dimer amine composition) The dimer amine composition contains component (a) as the main component, while the amounts of components (b) and (c) are controlled.

[0035] (a) dimer amine; (a) The dimeramine in component (a) refers to a diamine in which the two terminal carboxylic acid groups (-COOH) of a dimer acid are replaced with primary aminomethyl groups (-CH2-NH2) or amino groups (-NH2). Dimer acids are known dibasic acids obtained by the intermolecular polymerization reaction of unsaturated fatty acids, and their industrial production process is almost standardized in the industry. They are obtained by dimerizing unsaturated fatty acids with 11 to 22 carbon atoms using a clay catalyst or the like. Industrially obtained dimer acids mainly consist of dibasic acids with 36 carbon atoms obtained by dimerizing unsaturated fatty acids with 18 carbon atoms, such as oleic acid, linoleic acid, and linolenic acid. However, depending on the degree of purification, they also contain arbitrary amounts of monomeric acids (18 carbon atoms), trimer acids (54 carbon atoms), and other polymeric fatty acids with 20 to 54 carbon atoms. Furthermore, although double bonds remain after the dimerization reaction, in this invention, dimer acids are also included in those obtained by further hydrogenation to reduce the degree of unsaturation. (a) The dimer amine of component (a) can be defined as a diamine compound obtained by substituting the terminal carboxylic acid group of a dibasic acid compound having 18 to 54 carbon atoms, preferably 22 to 44 carbon atoms, with a primary aminomethyl group or an amino group.

[0036] One characteristic of dimer amines is that they can impart properties derived from the dimer acid skeleton. Specifically, since dimer amines are macromolecules with a molecular weight of approximately 560-620 and are aliphatic, they can increase the molar volume of the molecule and relatively reduce the polar groups of polyimide. These characteristics of dimer acid-type diamines are thought to contribute to improving dielectric properties by reducing the relative permittivity and dielectric loss tangent while suppressing the decrease in the heat resistance of polyimide. Furthermore, because they have two freely moving hydrophobic chains with 7-9 carbon atoms and two chain-like aliphatic amino groups with lengths close to 18 carbon atoms, they not only give polyimide flexibility but can also create asymmetric and non-planar chemical structures, thus enabling the reduction of the dielectric constant and dielectric loss tangent of polyimide.

[0037] The dimer amine composition should preferably be purified by methods such as molecular distillation to increase the dimer amine content of component (a) to 96% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more. By increasing the dimer amine content of component (a) to 96% by weight or more, the broadening of the molecular weight distribution of the polyimide can be suppressed. Ideally, if technically possible, the entire dimer amine composition (100% by weight) should consist of dimer amine of component (a).

[0038] (b) Monoamine compounds obtained by substituting the terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group; Monobasic acid compounds with 10 to 40 carbon atoms are a mixture of monobasic unsaturated fatty acids with 10 to 20 carbon atoms derived from the raw materials of dimer acid, and monobasic acid compounds with 21 to 40 carbon atoms that are by-products during the production of dimer acid. Monoamine compounds are obtained by substituting the terminal carboxylic acid group of these monobasic acid compounds with a primary aminomethyl group or an amino group.

[0039] (b) The monoamine compound is a component that suppresses the increase in molecular weight of polyimide. During polymerization of polyamic acid or polyimide, the monofunctional amino group of the monoamine compound reacts with the terminal acid anhydride group of the polyamic acid or polyimide, thereby encapsulating the terminal acid anhydride group and suppressing the increase in molecular weight of the polyamic acid or polyimide.

[0040] (c) Amine compounds obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group in the range of 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the dimer amines mentioned above); Polybasic acid compounds having hydrocarbon groups within the range of 41 to 80 carbon atoms are polybasic acid compounds mainly composed of tribasic acid compounds within the range of 41 to 80 carbon atoms, which are by-products of the production of dimer acid. They may also contain polymerized fatty acids other than dimer acid with 41 to 80 carbon atoms. Amine compounds are obtained by substituting the terminal carboxylic acid groups of these polybasic acid compounds with primary aminomethyl groups or amino groups.

[0041] (c) The amine compounds in component (c) are components that promote an increase in the molecular weight of polyimide. Trifunctional or higher amino groups, mainly triamine compounds derived from trimer acids, react with the terminal acid anhydride groups of polyamic acid or polyimide, causing a rapid increase in the molecular weight of polyimide. In addition, amine compounds derived from polymerized fatty acids other than dimer acids with 41 to 80 carbon atoms also increase the molecular weight of polyimide and cause gelation of polyamic acid or polyimide.

[0042] When quantifying each component of the above dimer amine composition using gel permeation chromatography (GPC), a sample of the dimer amine composition treated with acetic anhydride and pyridine is used to facilitate the identification of the peak start, peak top, and peak end of each component, and cyclohexanone is used as an internal standard. Using the sample prepared in this way, each component is quantified by the area percentage of the GPC chromatogram. The peak start and peak end of each component are defined as the minimum values ​​of each peak curve, and the area percentage of the chromatogram can be calculated based on these values.

[0043] Furthermore, the dimeramine composition used in this invention preferably has a total area percentage of components (b) and (c) of 4% or less, more preferably less than 4%, in the chromatogram obtained by GPC measurement. By keeping the total of components (b) and (c) at 4% or less, the broadening of the molecular weight distribution of polyimide can be suppressed.

[0044] Furthermore, the area percentage of the chromatogram of component (b) is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. By keeping it within this range, the decrease in the molecular weight of the polyimide can be suppressed, and the range of molar ratios of the tetracarboxylic anhydride component and the diamine component can be broadened. Note that component (b) does not have to be included in the dimer amine composition.

[0045] Furthermore, the area percentage of the chromatogram of component (c) is 2% or less, preferably 1.8% or less, and more preferably 1.5% or less. By keeping it within this range, a rapid increase in the molecular weight of the polyimide can be suppressed, and furthermore, the increase in the dielectric loss tangent of the resin film over a wide frequency range can be suppressed. Note that component (c) does not necessarily have to be included in the dimer amine composition.

[0046] Furthermore, when the ratio of the area percentages of the chromatograms of components (b) and (c) (b / c) is 1 or greater, the molar ratio of the tetracarboxylic anhydride component and the diamine component (tetracarboxylic anhydride component / diamine component) is preferably 0.97 or greater and less than 1.0. By using such a molar ratio, it becomes easier to control the molecular weight of the polyimide.

[0047] Furthermore, if the ratio (b / c) of the area percentages of the chromatograms of components (b) and (c) is less than 1, the molar ratio of the tetracarboxylic anhydride component and the diamine component (tetracarboxylic anhydride component / diamine component) is preferably 0.97 or more and 1.1 or less. By using such a molar ratio, it becomes easier to control the molecular weight of the polyimide.

[0048] The weight-average molecular weight of thermoplastic polyimide is preferably in the range of 10,000 to 200,000. Furthermore, when applied as an adhesive for FPC, for example, the weight-average molecular weight of polyimide is more preferably in the range of 20,000 to 150,000, and even more preferably in the range of 40,000 to 150,000. If the weight-average molecular weight of polyimide is less than 20,000, flow resistance tends to deteriorate. On the other hand, if the weight-average molecular weight of polyimide exceeds 150,000, the viscosity increases excessively, making it insoluble in solvents, and defects such as uneven thickness and streaks in the adhesive layer tend to occur during coating work.

[0049] The dimer amine composition is preferably purified to reduce components other than the dimer amine in component (a). The purification method is not particularly limited, but known methods such as distillation and precipitation purification are preferred. The dimer amine composition before purification is commercially available, for example, PRIAMINE 1073 (trade name), PRIAMINE 1074 (trade name), and PRIAMINE 1075 (trade name) manufactured by Croda Japan.

[0050] Aromatic diamine compounds can be used in thermoplastic polyimides other than aliphatic diamines. Specific examples include 1,4-diaminobenzene (p-PDA; paraphenylenediamine), 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 2,2'-n-propyl-4,4'-diaminobiphenyl (m-NPB), 4-aminophenyl-4'-aminobenzoate (APAB), 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)biphenyl, and bis[1-(3-aminophenoxy 4,4'-Diaminobiphenyl, 4,4'-Methylenedi-O -Toluidine, 4,4'-Methylenedi-2,6-Xylidine, 4,4'-Methylene-2,6-Diethylaniline, 3,3'-Diaminodiphenylethane, 3,3'-Diaminobiphenyl, 3,3'-Dimethoxybenzidine, 3,3''-Diamino-p-Terphenyl, 4,4'-[1,4-Phenylenebis(1-Methylethylidene)]bisaniline, 4,4'-[1,3-Phenylenebis(1-Methylethylidene)]bisaniline, Bis(p-Aminocyclohexyl)methane, Bis(p-β-Amino-t-Butylphenyl) Ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,Examples of diamine compounds include 5-diamino-1,3,4-oxadiazole, piperazine, 2'-methoxy-4,4'-diaminobenzanilide, 4,4'-diaminobenzanilide, 1,3-bis[2-(4-aminophenyl)-2-propyl]benzene, 6-amino-2-(4-aminophenoxy)benzoxazole, and 1,3-bis(3-aminophenoxy)benzene.

[0051] Thermoplastic polyimides can be produced by reacting the above-mentioned tetracarboxylic anhydride component and diamine component in a solvent to produce polyamic acid, which is then cyclized by heating. For example, polyamic acid, a precursor of polyimide, can be obtained by dissolving the tetracarboxylic anhydride component and diamine component in approximately equimolar amounts in an organic solvent and allowing a polymerization reaction to occur by stirring at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours. In the reaction, the reactants are dissolved in the organic solvent in a range of 5 to 50% by weight, preferably 10 to 40% by weight, to produce the precursor. Examples of organic solvents used in polymerization reactions include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, methylcyclohexane, dioxane, tetrahydrofuran, diglyme, triglime, methanol, ethanol, benzyl alcohol, and cresol. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination. There are no particular restrictions on the amount of such organic solvents used, but it is preferable to adjust the amount used so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 50% by weight.

[0052] The synthesized polyamic acid is usually advantageous to use as a reaction solvent solution, but it can be concentrated, diluted, or replaced with other organic solvents as needed. Furthermore, polyamic acid is advantageous to use because it generally has excellent solvent solubility. The viscosity of the polyamic acid solution is preferably in the range of 500 cps to 100,000 cps. Outside this range, defects such as uneven thickness and streaks are more likely to occur in the film during coating operations using a coater or the like.

[0053] The method for imidizing polyamic acid to form polyimide is not particularly limited, and a heat treatment such as heating in the aforementioned solvent at a temperature in the range of 80 to 400°C for 1 to 24 hours is preferably employed. Furthermore, the heating may be performed at a constant temperature, or the temperature may be changed during the process.

[0054] In the thermoplastic polyimide of component (A), the dielectric properties, coefficient of thermal expansion, tensile modulus, glass transition temperature, etc., can be controlled by selecting the types of tetracarboxylic anhydride and diamine components, and the molar ratios of each component when two or more tetracarboxylic anhydride or diamine components are applied. Furthermore, in the thermoplastic polyimide of component (A), if there are multiple polyimide structural units, they may exist as blocks or randomly, but random arrangement is preferable.

[0055] The imide group concentration of component (A), the thermoplastic polyimide, is preferably 22% by weight or less, more preferably 20% by weight or less. Here, "imide group concentration" means the value obtained by dividing the molecular weight of the imide group (-(CO)2-N-) in the polyimide by the molecular weight of the entire polyimide structure. If the imide group concentration exceeds 22% by weight, the molecular weight of the resin itself decreases, and the low hygroscopicity deteriorates due to the increase in polar groups, while the Tg and tensile modulus increase.

[0056] The thermoplastic polyimide of component (A) is most preferably in a completely imidized structure. However, a portion of the polyimide may be in the form of an amide acid. The imidization rate can be determined by measuring the infrared absorption spectrum of the polyimide thin film using a Fourier transform infrared spectrophotometer (commercially available: JASCO Corporation, product name: FT / IR620) by the single-reflection ATR method, where the imidization rate is 10¹⁵ cm⁻¹. -1 Using a nearby benzene ring absorber as a reference, 1780 cm -1 It can be calculated from the absorbance of the C=O stretching originating from the imide group.

[0057] (B) Component: Polystyrene elastomer The polystyrene elastomer of component (B) is a copolymer of styrene or a derivative thereof and a conjugated diene compound, and includes its hydrogenated form. Here, the styrene or its derivative is not particularly limited, but examples include styrene, methylstyrene, butylstyrene, divinylbenzene, vinyltoluene, etc. The conjugated diene compound is not particularly limited, but examples include butadiene, isoprene, 1,3-pentadiene, etc. Furthermore, it is preferable that the polystyrene elastomer is hydrogenated. Hydrogenation further improves its thermal stability, making it less susceptible to degradation such as decomposition and polymerization, and also enhances its aliphatic properties, thereby increasing its compatibility with the thermoplastic polyimide of component (A).

[0058] The copolymer structure of component (B) polystyrene elastomer may be a block structure or a random structure. Preferred specific examples of polystyrene elastomers include, but are not limited to, styrene-butadiene-styrene block copolymer (SBS), styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene·propylene-styrene block copolymer (SEEPS).

[0059] The weight-average molecular weight of the polystyrene elastomer in component (B) is 100,000 or less, preferably in the range of 50,000 to 100,000, and more preferably in the range of 70,000 to 100,000. By having a weight-average molecular weight of 100,000 or less for the polystyrene elastomer, it becomes possible to blend a relatively large amount of component (B) with component (A), which significantly improves the dielectric properties of the resin film. Specifically, for example, even if component (B) is blended in the range of 50 to 120 parts by weight per 100 parts by weight of component (A), the increase in viscosity of the polyimide composition is suppressed, and the dielectric loss tangent reduction effect due to the blending of polystyrene elastomer can be maximized. On the other hand, if the weight-average molecular weight of the polystyrene elastomer exceeds 100,000, the viscosity of the polyimide composition increases, which can make it difficult to produce resin films.

[0060] The acid value of the polystyrene elastomer in component (B) is preferably 10 mg KOH / g or less, more preferably 1 mg KOH / g or less, and even more preferably 0 mg KOH / g. By incorporating a polystyrene elastomer with an acid value of 10 mg KOH / g or less into the polyimide composition, the dielectric loss tangent when a resin film is formed can be reduced while maintaining good peel strength. On the other hand, if the acid value exceeds 10 mg KOH / g, the dielectric properties deteriorate due to the increase in polar groups, and the compatibility with component (A) worsens, resulting in reduced adhesion when a resin film is formed. Therefore, the lower the acid value, the better, and an acid-unmodified polystyrene elastomer (i.e., one with an acid value of 0 mg KOH / g) is most suitable as component (B) of the present invention. In the present invention, excellent adhesion can be achieved when the thermoplastic polyimide of component (A) contains residues derived from aliphatic diamines, so even when an acid-unmodified (i.e., strongly aliphatic) polystyrene elastomer is used, a decrease in adhesive strength can be avoided.

[0061] The polystyrene elastomer of component (B) preferably has a styrene unit [-CH2CH(C6H5)-] content of 10% to 65% by weight, more preferably 20% to 65% by weight, and most preferably 30% to 60% by weight. If the styrene unit content in the polystyrene elastomer is less than 10% by weight, the elastic modulus of the resin decreases, worsening the handling properties as a film. If it exceeds 65% by weight, the resin becomes rigid, making it difficult to use as an adhesive, and the amount of rubber component in the polystyrene elastomer decreases, leading to a deterioration of dielectric properties. Furthermore, because the styrene unit content is within the above range, the proportion of aromatic rings in the resin film is increased. This makes it possible to enhance the absorption of ultraviolet light when forming via holes (through holes) and blind via holes by laser processing during the manufacturing of circuit boards using the resin film, thereby improving laser processability.

[0062] (B) As the polystyrene elastomer, commercially available products can be appropriately selected and used. As such commercially available polystyrene elastomers, for example, MD1653MO (trade name) and G1726VS (trade name) manufactured by KRATON can be preferably used.

[0063] [Amount] Even a small amount of component (B) relative to 100 parts by weight of component (A) in a polyimide composition can yield a dielectric loss reduction effect in proportion to its amount. For example, if the content of component (B) relative to 100 parts by weight of component (A) exceeds 20 parts by weight, the dielectric loss tangent (Tanδ) of the resin film at 20 GHz can be reduced to 0.0015 or less. However, if the aim is to achieve an even more significant reduction in dielectric loss tangent, it is preferable to set the content of component (B) relative to 100 parts by weight of component (A) to 50 parts by weight or more. More specifically, it is preferable to set the content of component (B) relative to 100 parts by weight of component (A) to within the range of 50 parts by weight or more and 120 parts by weight or less, more preferably within the range of 50 parts by weight or more and 100 parts by weight or less, and even more preferably within the range of 60 parts by weight or more and 100 parts by weight or less. In addition to having a weight-average molecular weight of 100,000 or less, the polystyrene elastomer of component (B) has a structural unit in which the styrene portion is a hard segment (crystalline phase) and the butadiene portion is a soft segment (amorphous phase). Since this combination of structural units is similar to the combination of structural units of the thermoplastic polyimide of component (A), it is thought to exhibit excellent compatibility with component (A). As a result, it is easy to increase the blending ratio of component (B) to component (A) to 50 parts by weight or more, and the dielectric loss tangent of the resin film can be made extremely low. If the content of component (B) is less than 50 parts by weight per 100 parts by weight of component (A), the effect of significantly reducing the dielectric loss tangent may not be sufficiently realized. On the other hand, if the weight ratio of component (B) exceeds 120 parts by weight, the adhesion when a resin film is formed decreases, and the solid content concentration in the polyimide composition becomes too high, increasing viscosity and potentially reducing handling properties.

[0064] [Optional ingredients] (A) When the thermoplastic polyimide of component (A) has a ketone group, a crosslinked structure can be formed by reacting the ketone group with the amino group of an amino compound having at least two primary amino groups as functional groups (sometimes referred to as "crosslinking amino compound" in this specification) to form a C=N bond. The formation of the crosslinked structure can improve the heat resistance of the thermoplastic polyimide that forms the adhesive layer. Therefore, the polyimide composition of this embodiment may contain a crosslinking amino compound as an optional component.

[0065] For forming a polyimide having a ketone group, a preferred tetracarboxylic anhydride is, for example, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and for the diamine compound, an aromatic diamine such as 4,4'-bis(3-aminophenoxy)benzophenone (BABP) or 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB) can be cited. For the purpose of forming a crosslinked structure, the polyimide composition of this embodiment preferably contains the thermoplastic polyimide of component (A) and the crosslinking amino compound, which preferably contain 50 mol% or more, more preferably 60 mol% or more of BTDA residues derived from BTDA, relative to the total tetracarboxylic acid residues.

[0066] Examples of amino compounds for crosslinking include (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds tend to form crosslinked structures even at room temperature, raising concerns about the storage stability of the varnish, while aromatic diamines require high temperatures to form crosslinked structures. Thus, using dihydrazide compounds allows for both storage stability of the varnish and a reduction in curing time. Examples of dihydrazide compounds include dihydrazide oxalate, dihydrazide malonic acid, dihydrazide succinate, dihydrazide glutarate, dihydrazide adipic acid, dihydrazide pimelic acid, dihydrazide suberic acid, dihydrazide azelaic acid, dihydrazide sebacate, dihydrazide dodecanediic acid, dihydrazide maleate, dihydrazide fumarate, and diglyceride. Dihydrazide compounds such as cholic acid dihydrazide, tartrate dihydrazide, malate dihydrazide, phthalate dihydrazide, isophthalate dihydrazide, terephthalate dihydrazide, 2,6-naphthoenioate dihydrazide, 4,4-bisbenzene dihydrazide, 1,4-naphthoate dihydrazide, 2,6-pyridinedioate dihydrazide, and itaconic acid dihydrazide are preferred. These dihydrazide compounds may be used individually or in combination of two or more.

[0067] Furthermore, amino compounds such as (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines can be used in combination of two or more types, even across categories, for example, a combination of (I) and (II), a combination of (I) and (III), or a combination of (I), (II), and (III).

[0068] Furthermore, from the viewpoint of making the network structure formed by crosslinking with the crosslinking amino compound denser, the crosslinking amino compound used in the present invention preferably has a molecular weight (weight-average molecular weight if the crosslinking amino compound is an oligomer) of 5,000 or less, more preferably 90 to 2,000, and even more preferably 100 to 1,500. Among these, a crosslinking amino compound having a molecular weight of 100 to 1,000 is particularly preferred. When the molecular weight of the crosslinking amino compound is less than 90, only one amino group of the crosslinking amino compound forms a C=N bond with the ketone group of the polyimide resin, and the area around the remaining amino group becomes sterically bulky, making it difficult for the remaining amino group to form a C=N bond.

[0069] When crosslinking the ketone groups in the thermoplastic polyimide of component (A) with the crosslinking amino compound, the above-mentioned crosslinking amino compound is added to the resin solution containing component (A) to cause a condensation reaction between the ketone groups in the thermoplastic polyimide and the primary amino groups of the crosslinking amino compound. This condensation reaction causes the resin solution to harden into a cured product. In this case, the amount of crosslinking amino compound added can be 0.004 moles to 1.5 moles, preferably 0.005 moles to 1.2 moles, more preferably 0.03 moles to 0.9 moles, and most preferably 0.04 moles to 0.6 moles of primary amino groups per mole of ketone groups. When the amount of crosslinking amino compound added is such that the total amount of primary amino groups is less than 0.004 moles per mole of ketone groups, the crosslinking by the crosslinking amino compound is insufficient, and the heat resistance after curing tends to be poor. When the amount of crosslinking amino compound added exceeds 1.5 moles, the unreacted crosslinking amino compound acts as a thermoplastic, which tends to reduce the heat resistance of the adhesive layer.

[0070] The conditions for the condensation reaction for crosslinking are not particularly limited, as long as the ketone groups in the thermoplastic polyimide of component (A) react with the primary amino groups of the crosslinking amino compound to form imine bonds (C=N bonds). The temperature for the heating condensation is preferably in the range of 120 to 220°C, and more preferably in the range of 140 to 200°C, for reasons such as releasing the water produced by the condensation from the system or simplifying the condensation step when the heating condensation reaction is carried out immediately after the synthesis of the thermoplastic polyimide of component (A). The reaction time is preferably about 30 minutes to 24 hours. The endpoint of the reaction is 1670 cm⁻¹, for example, by measuring the infrared absorption spectrum using a Fourier transform infrared spectrophotometer (commercially available: FT / IR620, JASCO Corporation). -1 A decrease or disappearance of absorption peaks originating from ketone groups in the nearby polyimide resin, and at 1635 cm⁻¹. -1 This can be confirmed by the appearance of absorption peaks originating from nearby imine groups.

[0071] The heating condensation between the ketone group of the thermoplastic polyimide of component (A) and the primary amino group of the above crosslinking amino compound is, for example, (1) A method in which an amino compound for crosslinking is added and heated following the synthesis (imidization) of the thermoplastic polyimide of component (A), (2) A method in which an excess amount of amino compound is pre-charged as the diamine component, and following the synthesis (imidization) of the thermoplastic polyimide of component (A), the remaining amino compound that does not participate in imidization or amidization is used as a crosslinking amino compound and heated together with the thermoplastic polyimide, or (3) A method of heating a polyimide composition to which a crosslinking amino compound has been added, after it has been processed into a predetermined shape (for example, after being applied to an arbitrary substrate or after being formed into a film), This can be done by means of, for example.

[0072] In order to impart heat resistance to the thermoplastic polyimide of component (A), the formation of imine bonds by the formation of a crosslinked structure was explained, but the method is not limited to this, and as a curing method for the thermoplastic polyimide of component (A), it is also possible to cure it by incorporating, for example, epoxy resin, epoxy resin curing agent, maleimide, activated ester resin, or a compound having unsaturated bonds such as a resin having a styrene skeleton.

[0073] The polyimide composition of this embodiment may further contain, as optional components, inorganic fillers, organic fillers, plasticizers, curing accelerators, coupling agents, pigments, flame retardants, etc., to the extent that they do not impair the effects of the invention. Examples of inorganic fillers include silicon dioxide, aluminum oxide, beryllium oxide, niobium oxide, titanium oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, magnesium fluoride, potassium silicofluoride, and metal phosphinate salts. These can be used individually or in combination of two or more. In addition, other resin components such as epoxy resins, fluororesins, and olefin resins may be added as optional components.

[0074] Furthermore, the polyimide composition of this embodiment may contain a solvent such as an organic solvent. Since the thermoplastic polyimide of component (A) is solvent-soluble, and the polystyrene elastomer of component (B) also shows good solubility in aromatic hydrocarbon solvents such as xylene and toluene, the polyimide composition of this embodiment can be prepared as a polyimide solution (varnish) containing a solvent. As the organic solvent, a single solvent may be used, but it is preferable to use a polar organic solvent and a non-polar organic solvent in combination. By using a mixed solvent that uses a polar organic solvent and a non-polar organic solvent in combination, the SP value can be adjusted, and an optimal solubility state can be created for both component (A) and component (B). In addition, by using solvents with different boiling points, it is possible to control the drying state in the drying process after casting the polyimide composition, and a defect-free film can be obtained by having the high-boiling point solvent remain until the final stage of drying.

[0075] Examples of preferred polar organic solvents include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglime, cresol, and methyl ethyl ketone (MEK). Among these, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), and cyclohexanone are preferred. Two or more polar organic solvents can be used in combination.

[0076] Preferred nonpolar organic solvents include, for example, xylene, toluene, ethylbenzene, styrene, cumene, mesitylene, cymene, diethylbenzene, naphthalene, hexane, cyclohexane, and methylcyclohexane. Among these, xylene and toluene are preferred. Two or more nonpolar organic solvents can be used in combination.

[0077] Furthermore, it is preferable that the content ratio of polar organic solvents relative to the total amount of polar and nonpolar organic solvents be within the range of 25% by mass or more and less than 60% by mass, and more preferably within the range of 30% by mass or more and 55% by mass or less. By keeping the content ratio of polar organic solvents within the above range, the effects of using polar and nonpolar organic solvents together as described above are maximized.

[0078] While there are no particular restrictions on the solvent content, it is preferable to use an amount such that the total solid content of components (A) and (B) in the polyimide composition, plus any optional component, is preferably in the range of 15 to 35% by weight, more preferably in the range of 18 to 32% by weight.

[0079] [viscosity] The viscosity of the polyimide composition is preferably in the range of 3,000 cps to 100,000 cps, and more preferably in the range of 5,000 cps to 50,000 cps, in order to improve handling when coating the polyimide composition and to facilitate the formation of a coating film of uniform thickness. If the viscosity is outside the above range, defects such as uneven thickness and streaks are likely to occur in the film during coating work with a coater or the like.

[0080] [Preparation of polyimide compositions] A polyimide composition can be prepared, for example, by compounding and mixing a polystyrene elastomer with a resin solution of thermoplastic polyimide prepared using any solvent. In this case, in order to uniformly mix the thermoplastic polyimide and the polystyrene elastomer, the polystyrene elastomer may be mixed in a dissolved state in the solvent, or a solvent that exhibits high solubility for polystyrene elastomer may be added.

[0081] The polyimide composition of this embodiment exhibits excellent flexibility and thermoplasticity when used to form an adhesive layer. Therefore, it has desirable properties for applications such as adhesive layer materials in FPCs and rigid-flex circuit boards, and adhesives for coverlay films that protect wiring.

[0082] [Resin film] The resin film of this embodiment is a resin film consisting of one or more layers including a thermoplastic resin layer, wherein the thermoplastic resin layer is formed by forming a film with the solid content (the remainder after removing the solvent) of the polyimide composition as the main component. In other words, the thermoplastic resin layer consists of component (A) and component (B); (A) Thermoplastic polyimide, and (B) Polystyrene elastomer with an acid value of 10 mg KOH / g or less The resin film contains the above-mentioned components, and the content of component (B) relative to 100 parts by weight of component (A) is within the range of 50 parts by weight or more and 120 parts by weight or less. The resin film of this embodiment has excellent high-frequency characteristics and excellent adhesion (especially peel strength). The resin film of this embodiment preferably consists only of the above-mentioned thermoplastic resin layer.

[0083] The resin film in this embodiment is not particularly limited as long as it is an insulating resin film containing the thermoplastic resin layer described above. It may be a film (sheet) made only of insulating resin, or an insulating resin film laminated on a substrate such as copper foil, glass plate, polyimide film, polyamide film, polyester film, or other resin sheet.

[0084] In the resin film of this embodiment, the thermoplastic resin layer may contain optional components (excluding solvents) similar to those in the polyimide composition. In this case, from the viewpoint of fully exhibiting the effects of the invention, the total amount of component (A) and component (B) relative to the entire thermoplastic resin layer is preferably in the range of 60 to 100% by weight, more preferably in the range of 64 to 95% by weight.

[0085] (Relative permittivity) In the resin film of this embodiment, the thermoplastic resin layer has a relative permittivity (ε) at 20 GHz after 24 hours of conditioning under constant temperature and humidity conditions of 23°C and 50%RH, preferably 3.3 or less, and more preferably 3.1 or less, in order to ensure impedance matching when used in circuit boards such as FPCs, and to reduce electrical signal loss. If this relative permittivity exceeds 3.3, problems such as electrical signal loss are likely to occur in the transmission path of high-frequency signals when used in circuit boards such as FPCs.

[0086] (Dielectric loss tangent) Furthermore, in the resin film of this embodiment, the dielectric loss tangent (Tanδ) at 20 GHz after 24 hours of conditioning under constant temperature and humidity conditions of 23°C and 50%RH is preferably less than 0.0015, more preferably 0.0011 or less, and more preferably 0.0010 or less, in order to reduce electrical signal loss when used in circuit boards such as FPCs. Such an extremely low dielectric loss tangent effectively reduces transmission loss when the resin film of this embodiment is applied as an adhesive layer for circuit boards such as FPCs. In particular, when the dielectric loss tangent (Tanδ) at 20 GHz after 24 hours of conditioning under constant temperature and humidity conditions of 23°C and 50%RH is 0.0011 or less, transmission loss can be sufficiently reduced even in applications where signals with frequencies of 20 to 60 GHz are transmitted using a direct conversion method. On the other hand, if the dielectric loss tangent exceeds 0.0011, problems such as electrical signal loss are more likely to occur in the transmission path when the resin film of this embodiment is applied to FPCs used in the above applications.

[0087] (Glass transition temperature) In the resin film of this embodiment, the thermoplastic resin layer preferably has a glass transition temperature (Tg) of 250°C or less, and more preferably within the range of 40°C to 200°C. A Tg of 250°C or less in the resin film allows for thermocompression bonding at low temperatures, thereby mitigating internal stresses generated during lamination and suppressing dimensional changes after circuit processing. If the Tg of the resin film exceeds 250°C, the bonding temperature becomes high, potentially impairing dimensional stability after circuit processing.

[0088] (Thickness) The resin film of this embodiment preferably has a thickness in the range of 5 μm to 125 μm, and more preferably in the range of 8 μm to 100 μm. If the thickness of the resin film is less than 5 μm, problems such as wrinkles may occur during transportation in the manufacturing of the resin film, while if the thickness of the resin film exceeds 125 μm, there is a risk of a decrease in the productivity of the resin film.

[0089] (Tensile modulus of elasticity) In this embodiment, the resin film preferably has a tensile modulus in the range of 0.1 GPa to 3.0 GPa, and more preferably in the range of 0.2 GPa to 2.0 GPa, from the viewpoint of reducing wrinkle formation, preventing air bubbles from getting trapped during lamination, and handling properties.

[0090] (Maximum elongation) In this embodiment, the resin film preferably has a maximum elongation in the range of 30% to 200%, and more preferably in the range of 60% to 160%, from the viewpoint of flexibility and crack prevention when applied as an insulating resin layer of an FPC.

[0091] The resin film of this embodiment has a low dielectric loss tangent and excellent adhesion, making it useful as an adhesive layer in coverlay films, an adhesive layer in circuit boards, multilayer circuit boards, resin-coated copper foil, bond ply, bonding sheet, and the like.

[0092] [Laminated structure] A laminate according to one embodiment of the present invention comprises a substrate and an adhesive layer laminated on at least one surface of the substrate, wherein the adhesive layer is made of the resin film described above. The laminate may also include any other layers. Examples of substrates in the laminate include inorganic materials such as copper foil and glass plates, and resin materials such as polyimide films, polyamide films, and polyester films. Preferred embodiments of the laminate include coverlay films and resin-coated copper foils.

[0093] [Coverlay film] A coverlay film, which is one embodiment of a laminate, comprises a coverlay film material layer as a base material and an adhesive layer laminated on one side of the coverlay film material layer, wherein the adhesive layer is made of the resin film. The coverlay film may also include any other layers.

[0094] The material of the coverlay film layer is not particularly limited, but for example, polyimide films such as polyimide resin, polyetherimide resin, and polyamideimide resin, as well as polyamide films and polyester films can be used. Among these, it is preferable to use a polyimide film that has excellent heat resistance. Furthermore, the coverlay film material may contain black pigments to effectively exhibit light-shielding, opacity, and design properties, and may also contain optional components such as matte pigments that suppress surface gloss, as long as they do not impair the effect of improving dielectric properties.

[0095] The thickness of the coverlay film layer is not particularly limited, but is preferably in the range of 5 μm to 100 μm. Furthermore, while the thickness of the adhesive layer is not particularly limited, it is preferably in the range of 10 μm to 75 μm.

[0096] The coverlay film of this embodiment can be manufactured by the method illustrated below. First, as a first method, a coverlay film having a coverlay film layer and an adhesive layer can be formed by applying a varnish-like polyimide composition containing a solvent to one side of a coverlay film material layer, and then drying it at a temperature of, for example, 80 to 180°C to form an adhesive layer.

[0097] As a second method, a varnish-like polyimide composition containing a solvent can be applied to any substrate, dried at a temperature of, for example, 80 to 180°C, and then peeled off to form a resin film for the adhesive layer. This resin film can then be heat-pressed onto a film material layer for the coverlay at a temperature of, for example, 60 to 220°C to form a coverlay film.

[0098] [Copper foil coated with resin] Another form of the laminate, the resin-coated copper foil, is formed by laminating an adhesive layer on at least one side of a copper foil base material, wherein the adhesive layer is made of the resin film described above. The resin-coated copper foil of this embodiment may also include any other layers.

[0099] The thickness of the adhesive layer in resin-coated copper foil is preferably in the range of 2 to 125 μm, and more preferably in the range of 2 to 100 μm. If the thickness of the adhesive layer is less than the lower limit, problems such as insufficient adhesion may occur. On the other hand, if the thickness of the adhesive layer exceeds the upper limit, problems such as reduced dimensional stability may occur. Furthermore, from the viewpoint of lowering the dielectric constant and lowering the dielectric loss tangent, it is preferable to have an adhesive layer thickness of 3 μm or more.

[0100] In resin-coated copper foil, the copper foil material is preferably composed mainly of copper or a copper alloy. The thickness of the copper foil is preferably 35 μm or less, and more preferably in the range of 5 to 25 μm. From the viewpoint of production stability and handling, the lower limit of the copper foil thickness is preferably 5 μm. The copper foil may be rolled copper foil or electrolytic copper foil. In addition, commercially available copper foil can be used as the copper foil.

[0101] The resin-coated copper foil may be prepared, for example, by sputtering a metal onto a resin film to form a seed layer, and then forming a copper layer by copper plating, for example, or by laminating the resin film and copper foil by a method such as thermocompression bonding. Furthermore, to form an adhesive layer on the copper foil, the resin-coated copper foil may be prepared by casting a coating solution of a polyimide composition, drying it to form a coating film, and then performing the necessary heat treatment.

[0102] [Metal-clad laminate] (First aspect) A metal-clad laminate according to one embodiment of the present invention comprises an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, wherein at least one layer of the insulating resin layer is made of the resin film described above. The metal-clad laminate of this embodiment may also include any other layers.

[0103] (Second aspect) Another embodiment of the present invention is a so-called three-layer metal-clad laminate comprising, for example, an insulating resin layer, an adhesive layer laminated on at least one side of the insulating resin layer, and a metal layer laminated on the insulating resin layer via the adhesive layer, wherein the adhesive layer is made of the resin film described above. The three-layer metal-clad laminate may also include any other layers. In the three-layer metal-clad laminate, the adhesive layer may be provided on one or both sides of the insulating resin layer, and the metal layer may be provided on one or both sides of the insulating resin layer via the adhesive layer. In other words, the three-layer metal-clad laminate may be a single-sided metal-clad laminate or a double-sided metal-clad laminate. A single-sided or double-sided FPC can be manufactured by processing the metal layer of the three-layer metal-clad laminate into a wiring circuit, such as by etching.

[0104] The insulating resin layer in the three-layer metal-clad laminate is not particularly limited as long as it is made of an electrically insulating resin, and examples include polyimide, epoxy resin, phenolic resin, polyethylene, polypropylene, polytetrafluoroethylene, silicone, and ETFE, but it is preferably made of polyimide. The polyimide layer constituting the insulating resin layer may be a single layer or multiple layers, but it is preferable to include a non-thermoplastic polyimide layer.

[0105] In a three-layer metal-clad laminate, the thickness of the insulating resin layer is preferably in the range of 1 to 125 μm, and more preferably in the range of 5 to 100 μm. If the thickness of the insulating resin layer is less than the lower limit, problems such as insufficient electrical insulation may occur. On the other hand, if the thickness of the insulating resin layer exceeds the upper limit, problems such as warping of the metal-clad laminate may occur.

[0106] In a three-layer metal-clad laminate, the thickness of the adhesive layer is preferably in the range of 0.1 to 125 μm, and more preferably in the range of 0.3 to 100 μm. In the three-layer metal-clad laminate of this embodiment, if the thickness of the adhesive layer is less than the lower limit, problems such as insufficient adhesion may occur. On the other hand, if the thickness of the adhesive layer exceeds the upper limit, problems such as reduced dimensional stability may occur. Furthermore, from the viewpoint of lowering the dielectric constant and reducing the dielectric loss tangent of the entire insulating layer, which is a laminate of the insulating resin layer and the adhesive layer, the thickness of the adhesive layer is preferably 3 μm or more. Furthermore, the ratio of the thickness of the insulating resin layer to the thickness of the adhesive layer (thickness of the insulating resin layer / thickness of the adhesive layer) is preferably in the range of 0.1 to 3.0, and more preferably in the range of 0.15 to 2.0. By using such a ratio, warping of the three-layer metal-clad laminate can be suppressed. In addition, the insulating resin layer may contain fillers as needed. Examples of fillers include silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, and metal salts of organic phosphinic acid. These can be used individually or in mixtures of two or more.

[0107] [Circuit board] A circuit board according to an embodiment of the present invention is formed by wiring a metal layer of a metal-clad laminate according to any of the above embodiments. A circuit board such as an FPC can be manufactured by processing one or more metal layers of a metal-clad laminate into a pattern by a conventional method to form a wiring layer (conductor circuit layer). The circuit board may also include a coverlay film that covers the wiring layer. [Examples]

[0108] The features of the present invention will be explained in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In the following examples, unless otherwise specified, various measurements and evaluations are performed as described below.

[0109] [Measurement of Weight-Average Molecular Weight (Mw)] The weight-average molecular weight was measured by gel permeation chromatography (manufactured by Tosoh Corporation, trade name; HLC-8220GPC). Polystyrene was used as the standard substance, and tetrahydrofuran (THF) was used as the eluent solvent.

[0110] [Glass Transition Temperature (Tg)] The glass transition temperature (Tg) was measured using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, trade name; RSA-G2) on a resin sheet with a size of 5 mm × 20 mm. The temperature was raised from 30 °C to 200 °C at a rate of 4 °C / min and measured at a frequency of 11 Hz. The temperature at which the change in elastic modulus (tanδ) was maximum was defined as the glass transition temperature.

[0111] [Measurement of Viscosity] The viscosity at 25 °C was measured using an E-type viscometer (manufactured by Brookfield, trade name; DV-II+Pro). The rotation speed was set so that the torque was 10% - 90%, and after 2 minutes from the start of measurement, the value when the viscosity became stable was read.

[0112] [Method for Measuring Amine Value] Weigh approximately 2 g of the dimer diamine composition into a 200 - 250 mL Erlenmeyer flask, use phenolphthalein as an indicator, and titrate with 0.1 mol / L ethanolic potassium hydroxide solution until the solution shows a faint pink color, then dissolve it in about 100 mL of neutralized butanol. Add 3 - 7 drops of phenolphthalein solution thereto, and titrate with 0.1 mol / L ethanolic potassium hydroxide solution while stirring until the sample solution turns faint pink. Add 5 drops of bromophenol blue solution thereto, and titrate with 0.2 mol / L hydrochloric acid / isopropanol solution while stirring until the sample solution turns yellow. The amine value is calculated by the following formula (1). Amine value = {(V2 × C2) - (V1 × C1)} × M KOH / m ···(1) Here, the amine value is the value expressed in mg-KOH / g, and M KOHThe molecular weight of potassium hydroxide is 56.1. V and C represent the volume and concentration of the solution used in the titration, respectively, and the subscripts 1 and 2 represent a 0.1 mol / L ethanolic potassium hydroxide solution and a 0.2 mol / L hydrochloric acid / isopropanol solution, respectively. Furthermore, m is the sample weight in grams.

[0113] [Calculation of area percentage for GPC and chromatogram] For GPC analysis, a 100 mg solution of 20 mg of dimer amine composition, pretreated with 200 μL of acetic anhydride, 200 μL of pyridine, and 2 mL of tetrahydrofuran (THF), was prepared and diluted with 10 mL of THF (containing 1000 ppm cyclohexanone). The prepared sample was measured using a Tosoh Corporation HLC-8220GPC under the following conditions: column: TSK-gel G2000HXL, G1000HXL, flow rate: 1 mL / min, column (oven) temperature: 40°C, injection volume: 50 μL. Cyclohexanone was used as a standard substance to correct for efflux time.

[0114] At this time, the peak top of the cyclohexanone main peak is adjusted so that the retention time is between 27 and 31 minutes, and the time from the peak start to the peak end of the cyclohexanone main peak is between 2 minutes, and the peak top of the main peaks excluding the cyclohexanone peak is between 18 and 19 minutes, and the time from the peak start to the peak end of the main peaks excluding the cyclohexanone peak is between 2 minutes and 4 minutes 30 seconds, under the conditions that each component (a) to (c) is analyzed; (a) The component represented by the main peak; (b) Components represented by GPC peaks detected at times later than the minimum retention time at the main peak; (c) Components represented by GPC peaks detected earlier than the minimum retention time at the main peak; Detected.

[0115] [Evaluation of dielectric properties] Using a vector network analyzer (Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator, the relative permittivity (ε) and dielectric loss tangent (Tanδ) of a polyimide film (cured polyimide film) were measured at a frequency of 20 GHz after being left for 24 hours under conditions of temperature: 23°C and humidity: 50%RH.

[0116] [Measurement of Peel Strength] Multiple samples were prepared by cutting a double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: Espanex MB12-25-12UEG) to a width of 50 mm and a length of 100 mm, and then etching off the copper foil on one side, resulting in a laminate of copper foil and a resin layer. An adhesive sheet was placed on the copper foil side of one sample, and the copper foil side of another sample was placed on top of it, sandwiching the adhesive sheet from the outside. The samples were then pressed under vacuum conditions at a temperature of 160°C, a pressure of 3.5 MPa, and a time of 60 minutes to prepare a first laminate with a layer structure of resin layer / copper foil / adhesive sheet / copper foil / resin layer. Furthermore, an adhesive sheet was placed on the resin layer side of another sample, and the resin layer side of yet another sample was placed on top of it, sandwiching the adhesive sheet from the outside. The mixture was then pressed under vacuum conditions at a temperature of 160°C, a pressure of 3.5 MPa, and a time of 60 minutes to prepare a second laminate with a layer structure of copper foil / resin layer / adhesive sheet / resin layer / copper foil. Each of the first and second laminates was cut into 5 mm wide test pieces. Using a tensile testing machine (manufactured by Toyo Seiki Seisakusho, product name: Strograph VE), three layers (copper foil, resin layer, and adhesive layer) were gripped from one side, and the remaining two layers (copper foil and resin layer) were pulled at a speed of 50 mm / min in a 180° direction from the test piece. The peel strength between the adhesive layer (adhesive sheet) on the gripped side and the copper foil on the pulled side in the first laminate, or between the adhesive layer (adhesive sheet) on the gripped side and the resin layer on the pulled side in the second laminate, was measured and defined as the peel strength.

[0117] [Method for evaluating film defects] Polyimide varnish was applied to one side of a release-treated PET film, dried at 100°C for 5 minutes, then dried at 120°C for 10 minutes, and the condition of the peeled film was observed. At this time, films without streaks (dragging marks) caused by aggregates or poor solubility of the elastomer resin were classified as "good," and those with streaks were classified as "unacceptable."

[0118] [Acid value] The acid value is the number of milligrams of potassium hydroxide (KOH) required to neutralize 1 g of the sample. This can be measured, for example, by the following method: First, the sample is accurately weighed and placed in a 250 mL flask. 50 mL of ethanol or an equal volume mixture of ethanol and ether is added, and the sample is heated to dissolve. The sample is then titrated with 0.1 N potassium hydroxide solution, stirring as needed (indicator: phenolphthalein). The titration endpoint is the point where the solution remains pale pink for 30 seconds. Next, a blank test is performed in the same manner to correct the result, and the acid value is calculated using the following formula. Acid value = [Amount of 0.1N potassium hydroxide solution consumed (mL) × 5.611] / [Amount of sample (g)]

[0119] The abbreviations used in this example indicate the following compounds. BTDA:3,3',4,4'-benzophenonetetracarboxylic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane DDA: Distilled and purified from PRIAMINE1075, manufactured by Croda Japan Co., Ltd. (component a: 99.2%, component b: 0%, component c: 0.8%, amine value: 210 mg KOH / g) N-12: Dodecane dioxide dihydrazide NMP:N-methyl-2-pyrrolidone Elastomer resin 1: Manufactured by Kraton, product name: MD1653MO (hydrogenated polystyrene elastomer, styrene unit content: 30% by weight, Mw: 80,499, no acid value) Elastomer resin 2: Manufactured by Asahi Kasei Corporation, product name: ToughTec M1911 (hydrogenated polystyrene elastomer, styrene unit content: 30% by weight, Mw: 131,236, acid value: 2 mgKOH / g) In the above DDA, the "%" for components a, b, and c represents the area percentage of the chromatogram measured by GPC. The molecular weight of DDA was calculated using the following formula (1). Molecular weight = 56.1 × 2 × 1000 / Amine value ... (1)

[0120] (Synthesis Example 1) A polyamic acid solution was prepared by adding 21.34 g of BTDA (0.06622 mol), 12.99 g of BPDA (0.04414 mol), 46.7042 g of DDA (0.08741 mol), 8.97104 g of BAPP (0.02185 mol), 126 g of NMP, and 84 g of xylene to a 500 ml separable flask and mixing well at 40°C for 1 hour. This polyamic acid solution was heated to 190°C, stirred for 5 hours, and 65 g of xylene was added to complete the imidation process to prepare polyimide solution 1 (solids content: 31% by weight, weight-average molecular weight: 35,886, Tg: 63°C, viscosity: 2.580 mP·s, thermoplastic polyimide).

[0121] [Example 1] Polyimide varnish 1a was prepared by adding 0.6 g of N-12 and 8.6 g of elastomer resin 1 to 56 g of polyimide solution 1 prepared in Synthesis Example 1, diluting with xylene to a solid content of 26.5% by weight, and stirring.

[0122] [Example 2] Polyimide varnish 2a was prepared by adding 0.5 g of N-12 and 13.0 g of elastomer resin 1 to 42 g of polyimide solution 1 prepared in Synthesis Example 1, diluting with xylene to a solid content of 26.5% by weight, and stirring.

[0123] Comparative Example 1 Polyimide varnish 3a was prepared by adding 0.9 g of N-12 and 5.0 g of elastomer resin 2 to 81 g of polyimide solution 1 prepared in Synthesis Example 1, diluting with xylene and NMP to a solid content of 31.0% by weight, and stirring.

[0124] Comparative Example 2 Polyimide varnish 4a was prepared by adding 1.1 g of N-12 to 97 g of polyimide solution 1 prepared in Synthesis Example 1, diluting with xylene to a solid content of 31.0% by weight, and stirring.

[0125] Table 1 shows the formulations of Examples 1 and 2 and Comparative Examples 1 and 2.

[0126] [Table 1]

[0127] [Example 3] Polyimide varnish 1a prepared in Example 1 was applied to one side of a release-treated PET film, dried at 100°C for 5 minutes, then dried at 120°C for 10 minutes, and peeled off to prepare adhesive sheet 1b (thickness: 25 μm). The evaluation results for adhesive sheet 1b are as follows: Relative permittivity: 2.5, Dielectric loss tangent: 0.0011, Peel strength (copper foil side): 1.6 kN / m, Peel strength (resin side): 2.1 kN / m, Film defects: Good

[0128] [Example 4] Using polyimide varnish 2a, adhesive sheet 2b was prepared in the same manner as in Example 3. The evaluation results for adhesive sheet 2b are as follows: Relative permittivity: 2.2, Dielectric loss tangent: 0.0008, Peel strength (copper foil side): 1.5 kN / m, Peel strength (resin side): 1.6 kN / m, Film defects: Good

[0129] Comparative Example 1 Using polyimide varnish 3a, an adhesive sheet 3b was prepared in the same manner as in Example 3. The evaluation results for adhesive sheet 3b are as follows: Relative permittivity: 2.7, Dielectric loss tangent: 0.0015, Peel strength (copper foil side): 1.6 kN / m, Peel strength (resin side): 2.0 kN / m, Film defects: Good

[0130] Comparative Example 2 Using polyimide varnish 4a, adhesive sheet 4b was prepared in the same manner as in Example 3. The evaluation results for adhesive sheet 4b are as follows: Relative permittivity: 2.6, Dielectric loss tangent: 0.0016, Peel strength (copper foil side): 0.8 kN / m, Peel strength (resin side): 0.7 kN / m, Film defects: Good

[0131] The results above are summarized in Table 2.

[0132] [Table 2]

[0133] Table 2 shows that, compared to adhesive sheet 3b of Comparative Example 3, adhesive sheets 1b and 2b of Examples 3 and 4, which were formulated with elastomer resin 1 in 50 parts by weight and 100 parts by weight respectively per 100 parts by weight of component (A), had a dielectric loss tangent of 0.0011 or less and were free of film defects. These results confirm that the adhesive sheet as a resin film according to this embodiment can be expected to reduce transmission loss in high-frequency bands of 20 GHz or higher, for example, and that a good sheet without film defects can be obtained.

[0134] On the other hand, in Comparative Example 3, which used elastomer resin 2 with a high weight-average molecular weight, a good film was obtained by using a smaller amount than adhesive sheets 1b and 2b in Examples 3 and 4, but the dielectric loss tangent was not sufficiently low. Furthermore, no improvement in dielectric properties was observed in Comparative Example 4, which did not contain polystyrene elastomer.

[0135] Based on the results described above, it has been confirmed that the resin film according to this embodiment is suitable for use as a circuit board material, such as for millimeter-wave compatible FPCs.

[0136] Although embodiments of the present invention have been described in detail above for illustrative purposes, the present invention is not limited to the above embodiments and various modifications are possible.

Claims

1. The following components (A) and (B); (A) A thermoplastic polyimide having a storage modulus of 1.0 × 10⁸ Pa or higher at 30°C and a storage modulus of less than 3.0 × 10⁷ Pa at the glass transition temperature + 30°C, as measured using a dynamic viscoelasticity measuring device (DMA), and (B) Polystyrene elastomer having a weight-average molecular weight of 100,000 or less. It contains the above, and the content of component (B) relative to 100 parts by weight of component (A) is within the range of 50 parts by weight or more and 120 parts by weight or less. A polyimide composition in which the content ratio of styrene units of polystyrene elastomer in component (B) is in the range of 10% by weight or more and 65% by weight or less.

2. The polyimide composition according to claim 1, wherein the acid value of component (B) is 10 mg KOH / g or less.

3. The thermoplastic polyimide is obtained by reacting a tetracarboxylic anhydride component with a diamine component, and the polyimide composition according to claim 1 or 2 contains 40 mol% or more of an aliphatic diamine relative to the diamine component.

4. The polyimide composition according to claim 3, wherein the aliphatic diamine is a dimer amine composition mainly comprising a dimer amine in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups.

5. Furthermore, the polyimide composition according to any one of claims 1 to 4, further comprising an amino compound having at least two primary amino groups as functional groups.

6. A resin film comprising a thermoplastic resin layer, The thermoplastic resin layer comprises the following components (A) and (B): (A) A thermoplastic polyimide having a storage modulus of 1.0 × 10⁸ Pa or higher at 30°C and a storage modulus of less than 3.0 × 10⁷ Pa at the glass transition temperature + 30°C, as measured using a dynamic viscoelasticity measuring device (DMA), and (B) Polystyrene elastomer having a weight-average molecular weight of 100,000 or less. It contains the above, and the content of component (B) relative to 100 parts by weight of component (A) is within the range of 50 parts by weight or more and 120 parts by weight or less. A resin film characterized in that the content ratio of styrene units of polystyrene elastomer in component (B) is within the range of 10% by weight or more and 65% by weight or less.

7. The resin film according to claim 6, wherein the acid value of component (B) is 10 mg KOH / g or less.

8. The resin film according to claim 6 or 7, wherein the thermoplastic resin layer has a dielectric loss tangent (Tanδ) at 20 GHz measured by a split post dielectric resonator (SPDR) after being conditioned for 24 hours under constant temperature and humidity conditions of 23°C and 50% RH, and the result is 0.0011 or less.

9. A laminate comprising a base material and an adhesive layer laminated on at least one surface of the base material, A laminate characterized in that the adhesive layer is made of the resin film described in any one of claims 6 to 8.

10. A coverlay film having a coverlay film material layer and an adhesive layer laminated on the coverlay film material layer, wherein the adhesive layer is made of the resin film described in any one of claims 6 to 8.

11. A resin-coated copper foil in which an adhesive layer and copper foil are laminated, The resin-coated copper foil is characterized in that the adhesive layer is made of the resin film described in any one of claims 6 to 8.

12. A metal-clad laminate having an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer, wherein at least one layer of the insulating resin layer is made of the resin film described in any one of claims 6 to 8.

13. A circuit board obtained by wiring the metal layer of the metal-clad laminate according to claim 12.

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