JP7706828B2 - Polyimide composition, resin film, laminate, coverlay film, resin-coated copper foil, metal-clad laminate, and circuit board - Google Patents

Description

The present invention relates to a polyimide composition, a resin film, a laminate, a coverlay film, a resin-coated copper foil, a metal-clad laminate, and a circuit board that are useful as an adhesive in circuit boards such as printed wiring boards.

In recent years, with the progress of miniaturization, weight saving, and space saving of electronic devices, there is an increasing demand for flexible printed circuits (FPCs) that are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow three-dimensional and high-density mounting even in a limited space, their applications are expanding to include wiring for moving parts of electronic devices such as HDDs, DVDs, and mobile phones, as well as components such as cables and connectors.

In addition to the above-mentioned high density, the performance of equipment has improved, and it is also necessary to respond to the high frequency of transmission signals. In information processing and information communication, efforts are being made to increase the transmission frequency 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 constitutes the FPC will be increasingly required to reduce transmission loss and respond to high frequencies. Regarding the improvement of the dielectric properties of printed circuit board materials, an adhesive composition containing an acid-modified polystyrene elastomer resin, a carbodiimide resin, and an epoxy resin has been proposed (for example, Patent Document 1). However, Patent Document 1 states that if the acid value of the acid-modified polystyrene elastomer resin is low, the compatibility with other components is reduced and the adhesive strength is not expressed. In addition, although it is related to an adhesive for fixing a semiconductor wafer to a support when polishing it, an adhesive composition containing an acid-modified polystyrene elastomer resin has been proposed (for example, Patent Document 2).

It has been proposed to apply a crosslinked polyimide resin obtained by reacting a thermoplastic polyimide made from a diamine compound derived from an aliphatic diamine such as dimer acid (dimer fatty acid) with an amino compound having at least two primary amino groups as functional groups to the adhesive layer of a coverlay film (for example, Patent Document 3). In the examples of Patent Document 3, it is also disclosed that flaky talc is blended with a thermoplastic polyimide composition made from an aliphatic diamine. Here, the dimer acid is a dimerized fatty acid obtained by Diels-Alder reaction using natural fatty acids such as soybean oil fatty acid, tall oil fatty acid, rapeseed oil fatty acid, and the like, and oleic acid, linoleic acid, linolenic acid, erucic acid, and the like, which are refined from these, as raw materials, and it is known that a polybasic acid compound derived from a dimer acid is obtained as a composition of the raw fatty acid and a trimer or higher fatty acid (for example, Patent Document 4).

Patent No. 6705456 International Publication No. WO2013/153904 Patent No. 5777944 JP 2017-137375 A

Thermoplastic polyimides made from aliphatic diamines are soluble in solvents, have excellent adhesive properties, and are easy to handle, making them a useful resin material for use as an adhesive. However, to keep up with the increasing demand for higher frequencies in the future, in addition to satisfying the above characteristics, there is a demand for even lower dielectric tangents.

Therefore, the object of the present invention is to provide a polyimide composition using a thermoplastic polyimide that can form a resin film having both a low dielectric tangent and excellent adhesion.

The polyimide composition of the present invention comprises the following components (A) and (B):
(A) a thermoplastic polyimide, and (B) a polystyrene elastomer resin having an acid value of 10 mgKOH/g or less;
and the content of the (B) component is within the range of 10 parts by weight or more and 100 parts by weight or less per 100 parts by weight of the (A) component.

The polyimide composition of the present invention may have a styrene unit content in the (B) component in the range of 10% by weight or more and 65% by weight or less.

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.

The polyimide composition of the present invention may be a dimer diamine composition in which the aliphatic diamine is a dimer diamine in which the two terminal carboxylic acid groups of a dimer acid are substituted with primary aminomethyl groups or amino groups.

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

The resin film of the present invention is a resin film including a thermoplastic resin layer,
The thermoplastic resin layer comprises the following components (A) and (B):
(A) a thermoplastic polyimide,
and (B) a polystyrene elastomer resin having an acid value of 10 mgKOH/g or less;
and the content of the (B) component relative to 100 parts by weight of the (A) component is within the range of 10 parts by weight or more and 100 parts by weight or less.

In the resin film of the present invention, the thermoplastic resin layer may have a dielectric loss tangent (Tan δ) of 0.0020 or less at 10 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.

The laminate of the present invention is a laminate having a substrate and an adhesive layer laminated on at least one surface of the substrate, and is characterized in that the adhesive layer is made of the above-mentioned resin film.

The coverlay film of the present invention is a coverlay film having a coverlay film material layer and an adhesive layer laminated on the coverlay film material layer, characterized in that the adhesive layer is made of the above-mentioned resin film.

The resin-coated copper foil of the present invention is a resin-coated copper foil formed by laminating an adhesive layer and a copper foil, and is characterized in that the adhesive layer is made of the above-mentioned resin film.

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 is characterized in that at least one layer of the insulating resin layer is made of the above-mentioned resin film.

The circuit board of the present invention is formed by wiring the metal layer of the metal-clad laminate.

The polyimide composition of the present invention contains a thermoplastic polyimide and a polystyrene elastomer resin having a specific acid value, and therefore can form a resin film with excellent adhesiveness and sufficient peel strength for practical use while maintaining a low dielectric tangent. Therefore, the polyimide composition and resin film of the present invention can be particularly suitably used as a circuit board material such as an FPC in electronic devices that require high-speed signal transmission. In addition, by improving the dielectric properties of the resin film, it can be applied to direct conversion type receivers. Furthermore, since the peel strength of the resin film can be improved, it can be applied to electronic devices of any structure as a highly reliable low dielectric adhesive.

The following describes an embodiment of the present invention.

[Polyimide composition]
The polyimide composition according to one embodiment of the present invention comprises the following components (A) and (B):
(A) a thermoplastic polyimide, and (B) a polystyrene elastomer resin having an acid value of 10 mgKOH/g or less;
Contains:

<Component (A): Thermoplastic polyimide>
The thermoplastic polyimide of the component (A) is a solvent-soluble thermoplastic polyimide, which is obtained by imidizing a precursor polyamic acid obtained by reacting a tetracarboxylic anhydride component with a diamine component. The term "thermoplastic polyimide" generally refers to a polyimide that can be softened by heating and solidified by cooling, and this can be repeated, and has a clearly confirmed glass transition temperature (Tg). In the present invention, however, it means a polyimide whose glass transition temperature can be clearly confirmed in a temperature range of less than 150°C. In addition, from the viewpoint of thermocompression bonding at low temperatures, a polyimide whose glass transition temperature can be clearly confirmed in a temperature range of less than 100°C is preferable, and a polyimide whose storage modulus at 30°C measured using a dynamic mechanical analyzer (DMA) is 1.0 x 10 ⁸ Pa or more and whose storage modulus at glass transition temperature + 30°C is less than 3.0 x 10 ⁷ Pa is more preferable. In addition, the term "non-thermoplastic polyimide" generally refers to a polyimide that does not soften or exhibit adhesiveness even when heated, but in the present invention, it refers to a polyimide having a storage modulus of 1.0 x 10 ⁹ Pa or more at 30°C and a storage modulus of 3.0 x 10 ⁸ Pa or more at 300°C, as measured using a dynamic mechanical analyzer (DMA).

(Tetracarboxylic acid anhydride component)
The thermoplastic polyimide of component (A) may contain tetracarboxylic acid residues derived from tetracarboxylic anhydrides generally used in thermoplastic polyimides without any particular restrictions, but preferably contains tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) in a total amount of 90 mol % or more relative to all tetracarboxylic acid residues. By containing tetracarboxylic acid residues derived from tetracarboxylic anhydrides represented by the following general formula (1) in a total amount of 90 mol % or more relative to all tetracarboxylic acid residues, it is easy to achieve both flexibility and heat resistance of the polyimide, which is preferable. 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.

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

In the above formula, Z represents —C ₆ H ₄ —, —(CH ₂ )n— or —CH ₂ —CH(—O—C(═O)—CH ₃ )—CH ₂ —, where n represents an integer of 1 to 20.

Examples of tetracarboxylic acid 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). Among these, when 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) is used, the adhesion of the polyimide can be improved, and the ketone group present in the molecular skeleton may react with the amino group of an amino compound for crosslinking (described later) to form a C=N bond, which is likely to produce an effect of improving heat resistance. From this perspective, it is preferable that the content of tetravalent tetracarboxylic acid residues derived from BTDA (BTDA residues) is preferably 50 mol% or more, more preferably 60 mol% or more, of all tetracarboxylic acid residues.

The thermoplastic polyimide of component (A) may contain tetracarboxylic acid residues derived from acid anhydrides other than the tetracarboxylic acid anhydride represented by the above general formula (1) within the scope of the invention. There are no particular limitations on such tetracarboxylic acid residues, and examples thereof include pyromellitic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'- or 2,3,3',4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-diphenylethertetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, 3,3'',4,4''-, 2,3,3'',4''- or 2,2'',3,3''-p-terphenyltetracarboxylic 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-anthracene tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)tetrafluoropropane dianhydride, 2,3,5,6- Cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride, 2,6- or 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-(or 1,4,5,8-)tetrachloronaphthalene-1,4,5,8-(or 2,3,6,7-)tetracarboxylic dianhydride Examples of the tetracarboxylic acid residues include those derived from aromatic tetracarboxylic dianhydrides such as hydrate, 2,3,8,9-, 3,4,9,10-, 4,5,10,11- or 5,6,11,12-perylene tetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, and 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride.

(Diamine component)
The thermoplastic polyimide of component (A) is preferably made of a diamine component containing 40 mol% or more, more preferably 60 mol% or more of aliphatic diamines relative to the total diamine components. In other words, the thermoplastic polyimide of component (A) is preferably made of 40 mol% or more, more preferably 60 mol% or more of diamine residues derived from aliphatic diamines relative to the total diamine residues. By containing the diamine residues derived from aliphatic diamines in the above amount, the dielectric properties of the polyimide are improved, and the thermocompression bonding properties are improved by lowering the glass transition temperature (lowering Tg) of the polyimide, and the internal stress due to the lowering of the elastic modulus can be alleviated. If the diamine residues derived from aliphatic diamines are less than 40 mol% relative to the total diamine residues, the effect of improving the dielectric tangent and thermocompression bonding properties may not be sufficiently obtained. Examples of the aliphatic diamine that can be used herein include dimer diamine compositions mainly composed of dimer diamine 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, and 4,4-diaminodicyclohexylmethane, and the like. In particular, dimer diamine compositions are preferred.

(Dimer diamine composition)
The dimer diamine composition contains the following component (a) as a main component, with the amounts of components (b) and (c) being controlled.

(a) dimer diamine;
The dimer diamine of the component (a) means a diamine in which two terminal carboxylic acid groups (-COOH) of a dimer acid are replaced by primary aminomethyl groups (-CH ₂ -NH ₂ ) or amino groups (-NH ₂ ). Dimer acid is a known dibasic acid obtained by intermolecular polymerization of unsaturated fatty acids, and its industrial production process is almost standardized in the industry, and is obtained by dimerizing unsaturated fatty acids having 11 to 22 carbon atoms using a clay catalyst or the like. Industrially obtained dimer acid is mainly composed of a dibasic acid having 36 carbon atoms obtained by dimerizing unsaturated fatty acids having 18 carbon atoms, such as oleic acid, linoleic acid, and linolenic acid, but contains any amount of monomer acid (having 18 carbon atoms), trimer acid (having 54 carbon atoms), and other polymerized fatty acids having 20 to 54 carbon atoms depending on the degree of purification. In addition, although double bonds remain after the dimerization reaction, in the present invention, those which have been further subjected to a hydrogenation reaction to reduce the degree of unsaturation are also included in the dimer acid. The dimer diamine of the component (a) can be defined as a diamine compound obtained by substituting the terminal carboxylic acid group of a dibasic acid compound having a carbon number of 18 to 54, preferably 22 to 44, with a primary aminomethyl group or an amino group.

Dimer diamine has the characteristic of being able to impart properties derived from the dimer acid skeleton. In other words, since dimer diamine is a macromolecular aliphatic molecule with a molecular weight of about 560 to 620, it is possible to increase the molecular molar volume and relatively reduce the polar groups of the polyimide. It is believed that such characteristics of dimer acid type diamine contribute to improving the dielectric properties by reducing the relative dielectric constant and dielectric loss tangent while suppressing the deterioration of the heat resistance of the polyimide. In addition, since it has two freely moving hydrophobic chains with 7 to 9 carbon atoms and two chain-like aliphatic amino groups with a length close to 18 carbon atoms, it not only gives flexibility to the polyimide, but also allows the polyimide to have an asymmetrical chemical structure or a non-planar chemical structure, which is believed to enable the polyimide to have a low dielectric constant and low dielectric loss tangent.

It is advisable to use a dimer diamine composition in which the dimer diamine content of component (a) has been increased to 96% by weight or more, preferably 97% by weight or more, and more preferably 98% by weight or more, by a purification method such as molecular distillation. By increasing the dimer diamine content of component (a) to 96% by weight or more, it is possible to suppress the broadening of the molecular weight distribution of the polyimide. If technically possible, it is best that all of the dimer diamine composition (100% by weight) is composed of component (a) dimer diamine.

(b) a monoamine compound obtained by substituting a terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group;
The monobasic acid compound having 10 to 40 carbon atoms is a mixture of a monobasic unsaturated fatty acid having 10 to 20 carbon atoms derived from the raw material of dimer acid, and a monobasic acid compound having 21 to 40 carbon atoms which is a by-product during the production of dimer acid. The monoamine compound is obtained by substituting the terminal carboxylic acid group of these monobasic acid compounds with a primary aminomethyl group or an amino group.

The monoamine compound of component (b) is a component that suppresses the increase in molecular weight of the polyimide. During polymerization of the 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 blocking the terminal acid anhydride group and suppressing the increase in molecular weight of the polyamic acid or polyimide.

(c) Amine compounds obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the above-mentioned dimer diamine);
The polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms is a polybasic acid compound mainly composed of a tribasic acid compound having 41 to 80 carbon atoms, which is a by-product during the production of dimer acid. It may also contain a polymerized fatty acid other than dimer acid having 41 to 80 carbon atoms. The amine compound is obtained by substituting the terminal carboxylic acid group of these polybasic acid compounds with a primary aminomethyl group or an amino group.

The amine compound (c) is a component that promotes an increase in the molecular weight of the polyimide. The tri- or higher functional amino group, the main component of which is a triamine derived from trimer acid, reacts with the terminal acid anhydride group of the polyamic acid or polyimide, rapidly increasing the molecular weight of the polyimide. In addition, amine compounds derived from polymerized fatty acids other than dimer acids having 41 to 80 carbon atoms also increase the molecular weight of the polyimide, causing the polyamic acid or polyimide to gel.

When quantifying each component of the above dimer diamine composition by measurement using gel permeation chromatography (GPC), in order to facilitate confirmation of the peak start, peak top, and peak end of each component of the dimer diamine composition, a sample of the dimer diamine composition treated with acetic anhydride and pyridine is used, and cyclohexanone is used as an internal standard substance. Using the sample thus prepared, each component is quantified by the area percentage of the GPC chromatogram. The peak start and peak end of each component are taken as the minimum values of each peak curve, and the area percentage of the chromatogram can be calculated based on this.

In addition, the dimer diamine composition used in the present invention has a total area percentage of components (b) and (c) of 4% or less, preferably less than 4%, in the chromatogram obtained by GPC measurement. By keeping the total area percentage of components (b) and (c) at 4% or less, it is possible to suppress the broadening of the molecular weight distribution of the polyimide.

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 setting it in this range, it is possible to suppress a decrease in the molecular weight of the polyimide, and further to widen the range of the molar ratio of the tetracarboxylic anhydride component and the diamine component. Note that component (b) does not have to be included in the dimer diamine composition.

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 setting it in this range, a sudden increase in the molecular weight of the polyimide can be suppressed, and further, an increase in the dielectric tangent of the resin film over a wide frequency range can be suppressed. Note that component (c) does not have to be included in the dimer diamine composition.

In addition, when the ratio (b/c) of the area percentages of the chromatograms of components (b) and (c) is 1 or more, the molar ratio of the tetracarboxylic anhydride component and the diamine component (tetracarboxylic anhydride component/diamine component) is preferably 0.97 or more and less than 1.0, and such a molar ratio makes it easier to control the molecular weight of the polyimide.

In addition, when the ratio (b/c) of the area percentages of the components (b) and (c) in the chromatogram 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, and by setting such a molar ratio, it becomes easier to control the molecular weight of the polyimide.

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

The dimer diamine composition is preferably purified to reduce the amount of components other than the dimer diamine of component (a). The purification method is not particularly limited, but known methods such as distillation and precipitation purification are suitable. The dimer diamine 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.

Diamine compounds other than aliphatic diamines used in polyimides include aromatic diamine compounds. Specific examples of these 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, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3 -aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)]benzophenone, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane, 3,3'-dimethyl-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, 2,5-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, 1,3-bis(3-aminophenoxy)benzene and other diamine compounds.

Polyimide can be produced by reacting the above tetracarboxylic anhydride component and diamine component in a solvent to produce polyamic acid, which is then heated to close the ring. For example, the tetracarboxylic anhydride component and diamine component are dissolved in approximately equimolar amounts in an organic solvent, and the mixture is stirred at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction, thereby obtaining polyamic acid, which is a precursor of polyimide. In the reaction, the reaction components are dissolved so that the resulting precursor is in the range of 5 to 50% by weight, preferably 10 to 40% by weight, in the organic solvent. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, methylcyclohexane, dioxane, tetrahydrofuran, diglyme, triglyme, 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. The amount of such organic solvents used is not particularly limited, but it is preferable to adjust the amount so that the concentration of the polyamic acid solution obtained by the polymerization reaction is about 5 to 50% by weight.

The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but it can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is also advantageously used because it generally has excellent solvent solubility. The viscosity of the polyamic acid solution is preferably within the range of 500 cps to 100,000 cps. If it is outside this range, defects such as uneven thickness and streaks are likely to occur in the film during coating operations using a coater, etc.

There are no particular limitations on the method for imidizing polyamic acid to form polyimide, and a suitable method is, for example, heat treatment in the solvent at a temperature in the range of 80 to 400°C for 1 to 24 hours. The temperature may be constant, or it may be changed during the process.

In the thermoplastic polyimide of component (A), the dielectric properties, thermal expansion coefficient, tensile modulus, glass transition temperature, etc. can be controlled by selecting the type of the tetracarboxylic anhydride component and diamine component, and the molar ratio of each when two or more types of tetracarboxylic anhydride components or diamine components are used. In addition, in the thermoplastic polyimide of component (A), when the polyimide structural units are multiple, they may be present as blocks or randomly, but it is preferable that they are present randomly.

The imide group concentration of the thermoplastic polyimide of component (A) 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 will be reduced, and the low moisture absorption will be deteriorated due to an increase in polar groups, and Tg and tensile modulus will increase.

The thermoplastic polyimide of component (A) is most preferably a completely imidized structure. However, a part of the polyimide may be an amic acid. The imidization rate can be calculated from the absorbance of the C=O stretch derived from the imide group at 1780 cm ^-1 , based on the benzene ring absorber at about 1015 cm- ¹ , by measuring the infrared absorption spectrum of the polyimide thin film by the single reflection ATR method using a Fourier transform infrared spectrophotometer (commercially available: manufactured by JASCO Corporation, product name: FT/IR620).

<Component (B): Polystyrene elastomer resin>
The polystyrene elastomer resin of component (B) is a copolymer of styrene or a derivative thereof with a conjugated diene compound, including a hydrogenated product thereof. Examples of styrene or a derivative thereof include, but are not limited to, styrene, methylstyrene, butylstyrene, divinylbenzene, vinyltoluene, etc. Examples of conjugated diene compounds include, but are not limited to, butadiene, isoprene, 1,3-pentadiene, etc.
The polystyrene elastomer resin is preferably hydrogenated, since hydrogenation further improves the thermal stability, makes it less susceptible to deterioration such as decomposition and polymerization, and enhances the aliphatic properties, thereby improving compatibility with the thermoplastic polyimide of component (A).

The copolymer structure of the polystyrene elastomer resin of component (B) may be a block structure or a random structure. Preferred examples of polystyrene elastomer resins include 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), but are not limited to these.

The acid value of the polystyrene elastomer resin of the (B) component is 10 mgKOH/g or less, preferably 1 mgKOH/g or less, and more preferably 0 mgKOH/g. By blending a polystyrene elastomer resin with an acid value of 10 mgKOH/g or less into the polyimide composition, the dielectric tangent when the resin film is formed can be reduced and good peel strength can be maintained. On the other hand, if the acid value exceeds 10 mgKOH/g, the dielectric properties deteriorate due to an increase in polar groups, and the compatibility with the (A) component deteriorates, resulting in a decrease in adhesion when the resin film is formed. Therefore, the lower the acid value, the better, and a non-acid-modified one (i.e., an acid value of 0 mgKOH/g) is most suitable as the (B) component of the present invention. In the present invention, since it is possible to develop excellent adhesion when the thermoplastic polyimide of the (A) component contains residues derived from aliphatic diamines, even if a non-acid-modified (i.e., a polystyrene elastomer resin with strong aliphatic properties) is used, the decrease in adhesive strength as feared in Patent Document 1 can be avoided.

The polystyrene elastomer resin of component (B) preferably has a content of styrene units _{[ -CH2CH} ( _C6H5 )-] in the range of 10 to 65% by weight, more preferably 20 to 65% by weight, and most preferably 30 to 60% by weight. If the content of styrene units in the polystyrene elastomer resin is less than 10% by weight, the elastic modulus of the resin decreases and the handling properties as a film deteriorate, whereas if it exceeds 65% by weight, the resin becomes rigid, making it difficult to use as an adhesive, and the rubber component in the polystyrene elastomer resin decreases, leading to deterioration of the dielectric properties.
In addition, by having the content ratio of styrene units within the above range, the proportion of aromatic rings in the resin film is increased, so that when via holes (through holes) and blind via holes are formed by laser processing in the process of manufacturing a circuit board using the resin film, it is possible to increase the absorbency in the ultraviolet region and further improve the laser processability.

The weight average molecular weight of the polystyrene elastomer resin of component (B) is preferably, for example, within the range of 50,000 to 300,000, and more preferably within the range of 80,000 to 270,000. If the weight average molecular weight of component (B) is lower than the above range, the effect of improving the dielectric properties may be reduced, and conversely, if it is higher, the viscosity of the polyimide composition may increase, making it difficult to produce a resin film.

As the polystyrene elastomer resin of component (B), a commercially available product can be appropriately selected and used as long as the acid value is 10 mgKOH/g or less. As such commercially available polystyrene elastomer resins, for example, A1535HU (trade name), G1652MU (trade name), G1726VS (trade name), G1645VS (trade name), FG1901GT (trade name), G1650MU (trade name), G1654HU (trade name), G1730VO (trade name), MD1653MO (trade name), etc. manufactured by KRATON can be preferably used.

[Amount]
The content of the (B) component in the polyimide composition relative to 100 parts by weight of the (A) component is in the range of 10 parts by weight to 100 parts by weight, preferably in the range of 20 parts by weight to 90 parts by weight, and more preferably in the range of 30 parts by weight to 80 parts by weight. If the content of the (B) component relative to 100 parts by weight of the (A) component is less than 10 parts by weight, the effect of lowering the dielectric tangent may not be fully exhibited. On the other hand, if the weight ratio of the (B) component exceeds 100 parts by weight, the adhesiveness when the resin film is formed may decrease, and the solid content concentration in the polyimide composition may become too high, increasing the viscosity and decreasing the handleability.

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

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

Examples of amino compounds for forming crosslinks include (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines. Among these, dihydrazide compounds are preferred. Aliphatic amines other than dihydrazide compounds are prone to form crosslinked structures even at room temperature, which raises concerns about the storage stability of the varnish, while aromatic diamines require high temperatures to form crosslinked structures. In this way, when a dihydrazide compound is used, it is possible to achieve both the storage stability of the varnish and a shortened curing time. Examples of dihydrazide compounds include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide, maleic acid dihydrazide, fumaric acid dihydrazide, diglyceryl ester dihydrazide, ... Dihydrazide compounds such as cholic acid dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, phthalic acid dihydrazide, isophthalic acid dihydrazide, terephthalic acid dihydrazide, 2,6-naphthoedioic acid dihydrazide, 4,4-bisbenzene dihydrazide, 1,4-naphthoic acid dihydrazide, 2,6-pyridine diacid dihydrazide, and itaconic acid dihydrazide are preferred. The above dihydrazide compounds may be used alone or in combination of two or more.

The above amino compounds, such as (I) dihydrazide compounds, (II) aromatic diamines, and (III) aliphatic amines, can also be used in combination of two or more types beyond the scope of the category, such as a combination of (I) and (II), a combination of (I) and (III), or a combination of (I), (II), and (III).

In order to make the mesh-like structure formed by the 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 when 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, crosslinking amino compounds having a molecular weight of 100 to 1,000 are particularly preferred. If the molecular weight of the crosslinking amino compound is less than 90, only one amino group of the crosslinking amino compound will form a C=N bond with a ketone group of the polyimide resin, and the surroundings of the remaining amino groups will be three-dimensionally bulky, making it difficult for the remaining amino groups to form C=N bonds.

When crosslinking the ketone group in the thermoplastic polyimide of component (A) with the crosslinking amino compound, the crosslinking amino compound is added to a resin solution containing component (A) to cause a condensation reaction between the ketone group in the thermoplastic polyimide and the primary amino group of the crosslinking amino compound. This condensation reaction hardens the resin solution to become a hardened product. In this case, the amount of crosslinking amino compound added can be 0.004 mol to 1.5 mol, preferably 0.005 mol to 1.2 mol, more preferably 0.03 mol to 0.9 mol, and most preferably 0.04 mol to 0.6 mol of primary amino groups per 1 mol of ketone groups. If the amount of crosslinking amino compound added is such that the total number of primary amino groups per mole of ketone groups is less than 0.004 moles, crosslinking by the crosslinking amino compound is insufficient, and heat resistance after curing tends to be difficult to achieve. If the amount of crosslinking amino compound added exceeds 1.5 moles, the unreacted crosslinking amino compound acts as a thermoplasticizer, tending to reduce the heat resistance of the adhesive layer.

The conditions of the condensation reaction for crosslinking are not particularly limited as long as the ketone group in the thermoplastic polyimide of component (A) reacts with the primary amino group of the amino compound for crosslinking to form an imine bond (C=N bond). The temperature of the heat condensation is preferably in the range of, for example, 120 to 220°C, more preferably in the range of 140 to 200°C, for the purpose of releasing water produced by condensation out of the system, or for the purpose of simplifying the condensation step when the heat condensation reaction is carried out subsequently after the synthesis of the thermoplastic polyimide of component (A). The reaction time is preferably about 30 minutes to 24 hours. The end point of the reaction can be confirmed by, for example, a Fourier transform infrared spectrophotometer (commercial product: FT/IR620 manufactured by JASCO) by measuring the infrared absorption spectrum, based on the decrease or disappearance of the absorption peak derived from the ketone group in the polyimide resin at around 1670 cm ^-1 , and the appearance of the absorption peak derived from the imine group at around 1635 cm ^-1 .

The thermal condensation of the ketone group of the thermoplastic polyimide of component (A) with the primary amino group of the crosslinking amino compound can be carried out, for example, by the following reaction:
(1) A method in which, following the synthesis (imidization) of the thermoplastic polyimide of component (A), an amino compound for crosslinking is added and heated;
(2) A method in which an excess amount of an amino compound is charged in advance as a diamine component, and following synthesis (imidization) of the thermoplastic polyimide of component (A), the remaining amino compound that is not involved in imidization or amidation is used as a crosslinking amino compound and heated together with the thermoplastic polyimide, or
(3) A method in which the polyimide composition containing the crosslinking amino compound is processed into a predetermined shape (for example, after being applied to a substrate or formed into a film), and then heated;
This can be done by, etc.

The formation of imine bonds has been described as a method for forming a crosslinked structure to impart heat resistance to the thermoplastic polyimide of component (A), but this is not limiting. For example, the thermoplastic polyimide of component (A) can be cured by blending and curing an epoxy resin, an epoxy resin curing agent, or a compound having an unsaturated bond, such as maleimide, activated ester resin, or a resin having a styrene skeleton.

The polyimide composition of the present embodiment may further contain optional components such as inorganic fillers, organic fillers, plasticizers, curing accelerators, coupling agents, pigments, and flame retardants, as necessary, within the scope 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 phosphinates. These may be used alone or in combination of two or more. Other resin components such as epoxy resins, fluororesins, and olefin-based resins may also be added as optional components.

Furthermore, the polyimide composition of the present embodiment may contain a solvent such as an organic solvent. The thermoplastic polyimide of component (A) is soluble in a solvent, and the polystyrene elastomer resin of component (B) also exhibits good solubility in aromatic hydrocarbon solvents such as xylene and toluene, so that the polyimide composition of the present embodiment can be prepared as a polyimide solution (varnish) containing a solvent. As the organic solvent, it is preferable to use a mixed solvent in which one or more selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethylsulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, etc. are mixed with the aromatic hydrocarbon solvent in any ratio.
The content of the solvent is not particularly limited, but it is preferable to adjust the amount used so that the concentration of the polyamic acid or polyimide becomes about 5 to 30% by weight.

[viscosity]
The viscosity of the polyimide composition is preferably within a range of, for example, 3,000 cps to 100,000 cps, and more preferably within a range of 5,000 cps to 50,000 cps, which is a viscosity range that improves the handleability when the polyimide composition is applied and makes it easy to form 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 application by a coater or the like.

[Preparation of polyimide composition]
The polyimide composition can be prepared, for example, by blending a polystyrene elastomer resin into a resin solution of a thermoplastic polyimide prepared using an arbitrary solvent, and mixing them. In this case, in order to uniformly mix the thermoplastic polyimide and the polystyrene elastomer resin, the polystyrene elastomer resin may be mixed in a state of being dissolved in a solvent, or a solvent that has high solubility in the polystyrene elastomer resin may be added.

When an adhesive layer is formed using the polyimide composition of this embodiment, it has excellent flexibility and thermoplasticity. Therefore, it has favorable properties for applications such as adhesive layer materials in FPCs and rigid-flex circuit boards, and adhesives for coverlay films that protect wiring parts.

[Resin film]
The resin film of the present embodiment is a resin film consisting of a single layer or multiple layers including a thermoplastic resin layer, and the thermoplastic resin layer is formed by forming a film using the solid content (the remainder excluding the solvent) of the polyimide composition as a main component.
(A) a thermoplastic polyimide,
and (B) a polystyrene elastomer resin having an acid value of 10 mgKOH/g or less;
and the content of the (B) component relative to 100 parts by weight of the (A) component is within the range of 10 parts by weight or more and 100 parts by weight or less. The resin film of the present embodiment has excellent high-frequency characteristics and excellent adhesiveness (particularly peel strength).

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

(Dielectric constant)
In order to ensure impedance matching when used in a circuit board such as an FPC and to reduce loss of an electric signal, the resin film of the present embodiment has a relative dielectric constant (ε) at 10 GHz after 24 hours of humidity conditioning under constant temperature and humidity conditions of 23° C. and 50% RH of preferably 3.3 or less, more preferably 3.1 or less. If the relative dielectric constant exceeds 3.3, problems such as loss of an electric signal are likely to occur on the transmission path of a high-frequency signal when used in a circuit board such as an FPC.

(Dielectric tangent)
In addition, in order to reduce loss of an electric signal when the resin film of the present embodiment is used in a circuit board such as an FPC, the dielectric loss tangent (Tan δ) at 10 GHz after 24 hours of humidity control under constant temperature and humidity conditions of 23° C. and 50% RH is preferably 0.0020 or less, more preferably 0.0018 or less. If the dielectric loss tangent exceeds 0.0020, problems such as loss of an electric signal are likely to occur on the transmission path of a high-frequency signal when the resin film is used in a circuit board such as an FPC.

(Glass Transition Temperature)
The resin film of the present embodiment preferably has a glass transition temperature (Tg) of 250° C. or less, more preferably in the range of 40° C. or more and 200° C. or less. By making the Tg of the resin film 250° C. or less, thermocompression bonding at a low temperature is possible, so that the internal stress generated during lamination can be alleviated and dimensional change after circuit processing can be suppressed. If the Tg of the resin film exceeds 250° C., the bonding temperature becomes high, and there is a risk of impairing dimensional stability after circuit processing.

(Thickness)
The thickness of the resin film of the present embodiment is preferably, for example, 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, there is a risk of problems such as wrinkles occurring during transportation in the production of the resin film, while if the thickness of the resin film exceeds 125 μm, there is a risk of a decrease in productivity of the resin film.

(Tensile Modulus)
The resin film of the present embodiment preferably has a tensile modulus in the range of 0.1 GPa to 3.0 GPa, more preferably in the range of 0.2 GPa to 2.0 GPa, from the viewpoints of reducing the occurrence of wrinkles, preventing air bubbles from being trapped during lamination, and handling properties.

(Maximum elongation)
From the viewpoints of bendability and crack prevention when applied as an insulating resin layer of an FPC, the resin film of the present embodiment preferably has a maximum elongation within the range of 30% to 200%, and more preferably within the range of 60% to 160%.

The resin film of this embodiment has a low dielectric tangent and excellent adhesion, and is therefore useful as an adhesive layer in coverlay films, circuit boards, multilayer circuit boards, adhesive layers in resin-coated copper foils, bond plies, bonding sheets, etc.

[Laminate]
The laminate according to one embodiment of the present invention has a substrate and an adhesive layer laminated on at least one surface of the substrate, the adhesive layer being made of the above-mentioned resin film. The laminate may also include any layer other than the above. Examples of the substrate in the laminate include substrates made of inorganic materials such as copper foil and glass plate, and substrates made of resin materials such as polyimide film, polyamide film, and polyester film.
Preferred embodiments of the laminate include a coverlay film and a resin-coated copper foil.

[Coverlay film]
The coverlay film, which is one embodiment of the laminate, has a coverlay film material layer as a substrate and an adhesive layer laminated on one side of the coverlay film material layer, the adhesive layer being made of the above-mentioned resin film. Note that the coverlay film may include any layer other than those described above.

The material of the coverlay film material layer is not particularly limited, but may be, for example, a polyimide-based film such as polyimide resin, polyetherimide resin, or polyamideimide resin, a polyamide-based film, or a polyester-based film. Of these, it is preferable to use a polyimide-based film with excellent heat resistance. In addition, the coverlay film material may contain a black pigment to effectively exhibit light-shielding properties, concealing properties, design properties, etc., and may contain optional components such as a matte pigment that suppresses surface gloss, as long as the effect of improving the dielectric properties is not impaired.

The thickness of the coverlay film material layer is not particularly limited, but is preferably within the range of, for example, 5 μm or more and 100 μm or less.
The thickness of the adhesive layer is not particularly limited, but is preferably within the range of 10 μm to 75 μm, for example.

The coverlay film of the present embodiment can be produced by the method exemplified below.
First, as a first method, a varnish-like polyimide composition containing a solvent is applied to one side of a film material layer for a coverlay, and then the composition is dried at a temperature of, for example, 80 to 180° C. to form an adhesive layer, thereby forming a coverlay film having a film material layer for a coverlay and an adhesive layer.

As a second method, a varnish-like polyimide composition containing a solvent is 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 is then thermocompressed to a film material layer for the coverlay at a temperature of, for example, 60 to 220°C to form a coverlay film.

[Copper foil with resin]
The resin-coated copper foil, which is another embodiment of the laminate, is obtained by laminating an adhesive layer on at least one side of a copper foil as a base material, and the adhesive layer is made of the above-mentioned resin film. Note that the resin-coated copper foil of this embodiment may include any layer other than the above.

The thickness of the adhesive layer in the resin-coated copper foil is preferably within the range of 2 to 125 μm, for example, and more preferably within the range of 2 to 100 μm. If the thickness of the adhesive layer is less than the above lower limit, problems such as inability to ensure sufficient adhesion may occur. On the other hand, if the thickness of the adhesive layer exceeds the above upper limit, problems such as reduced dimensional stability may occur. Also, from the viewpoint of lowering the dielectric constant and the dielectric loss tangent, it is preferable that the thickness of the adhesive layer is 3 μm or more.

The material of the copper foil in the resin-coated copper foil is preferably one whose main component is 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 a rolled copper foil or an electrolytic copper foil. In addition, commercially available copper foils can be used as the copper foil.

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, for example, by copper plating, or by laminating a resin film and copper foil by a method such as thermocompression bonding. Furthermore, the resin-coated copper foil may be prepared by casting a coating solution of a polyimide composition onto the copper foil to form an adhesive layer, drying the coating film, and then carrying out the necessary heat treatment.

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

(Second Aspect)
The metal-clad laminate according to another embodiment of the present invention is, for example, a so-called three-layer metal-clad laminate comprising 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, and the adhesive layer is made of the above-mentioned resin film. The three-layer metal-clad laminate may include any layer other than the above. The three-layer metal-clad laminate may have an adhesive layer 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 wiring circuit by etching the metal layer of the three-layer metal-clad laminate.

The insulating resin layer in the three-layer metal-clad laminate is not particularly limited as long as it is made of a resin having electrical insulation properties, and examples thereof include polyimide, epoxy resin, phenolic resin, polyethylene, polypropylene, polytetrafluoroethylene, silicone, ETFE, etc., 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 that it includes a non-thermoplastic polyimide layer.

The thickness of the insulating resin layer in the three-layer metal-clad laminate is preferably within the range of 1 to 125 μm, and more preferably within the range of 5 to 100 μm. If the thickness of the insulating resin layer is less than the above lower limit, problems such as inability to ensure sufficient electrical insulation may occur. On the other hand, if the thickness of the insulating resin layer exceeds the above upper limit, problems such as the metal-clad laminate becoming more susceptible to warping may occur.

The thickness of the adhesive layer in the three-layer metal-clad laminate is preferably in the range of 0.1 to 125 μm, more preferably in the range of 0.3 to 100 μm. In the three-layer metal-clad laminate of the present embodiment, if the thickness of the adhesive layer is less than the above-mentioned lower limit, problems such as insufficient adhesion may occur. On the other hand, if the thickness of the adhesive layer exceeds the above-mentioned upper limit, problems such as reduced dimensional stability may occur. In addition, from the viewpoint of reducing the dielectric constant and 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.
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 setting such a ratio, it is possible to suppress warping of the three-layer metal-clad laminate. Furthermore, the insulating resin layer may contain a filler as necessary. Examples of the filler 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 alone or in combination of two or more.

[Circuit board]
The circuit board according to the embodiment of the present invention is formed by wiring the metal layer of the metal-clad laminate according to any of the above embodiments. One or more metal layers of the metal-clad laminate are patterned by a conventional method to form a wiring layer (conductor circuit layer), thereby manufacturing a circuit board such as an FPC. The circuit board may include a coverlay film that covers the wiring layer.

The following examples are provided to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to these examples. In the following examples, unless otherwise specified, the various measurements and evaluations were performed as follows.

[Measurement of weight average molecular weight (Mw) of polyimide]
The weight average molecular weight was measured by gel permeation chromatography (manufactured by Tosoh Corporation, product name: HLC-8220GPC was used). Polystyrene was used as a standard substance, and tetrahydrofuran (THF) was used as a developing solvent.

[Measurement of storage modulus]
The measurement was carried out using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA-G2).

[Evaluation of dielectric properties]
Using a vector network analyzer (manufactured by Agilent, product name: Vector Network Analyzer E8363C) and an SPDR resonator, the polyimide film (cured polyimide film) was left to stand for 24 hours under conditions of a temperature of 23° C. and a humidity of 50% RH, and then the relative dielectric constant (ε) and dielectric loss tangent (Tan δ) at a frequency of 10 GHz were measured.

[Glass transition temperature (Tg)]
The adhesive sheet was pressed under conditions of temperature: 160°C, pressure: 3.5 MPa, and time: 60 minutes, and cut into test pieces measuring 5 mm x 20 mm. Measurements were performed using a dynamic viscoelasticity measuring device (DMA: manufactured by TA Instruments, product name: RSA-G2) at a heating rate of 4°C/min from 30°C to 200°C and a frequency of 11 Hz, and the temperature at which the change in elastic modulus (tan δ) was maximum was determined as the glass transition temperature.

[Tensile modulus and maximum elongation]
Using a tension tester (Tensilon manufactured by Orientec), a tensile test was carried out at 50 mm/min on a test piece of the resin film (width: 12.7 mm, length: 127 mm) to determine the tensile modulus and maximum elongation at 25°C.

[Solder heat resistance test (dry)]
One of the copper foils of a double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: ESPANEX MB12-25-12UEG) was etched away, and the other copper foil surface and the adhesive sheet were laminated in a manner sandwiched between the copper foils, and pressed under the conditions of temperature: 160°C, pressure: 3.5 MPa, and time: 60 minutes. The test piece with the copper foil was dried at 135°C/60 minutes, and then immersed for 10 seconds in a solder bath set at each evaluation temperature from 260°C to 300°C in 10°C increments, and the adhesion state was observed to confirm the presence or absence of defects such as foaming, swelling, and peeling. The judgment was ◯ (good) when no defects were observed at 280°C, and × (bad) when defects were observed.

[Solder heat resistance test (moisture absorption)]
The copper foil on one side of a double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: ESPANEX MB12-25-12UEG) was etched away, and the other copper foil surface and adhesive sheet were laminated in a manner sandwiched between the copper foils, and pressed under the conditions of temperature: 160°C, pressure: 3.5 MPa, and time: 60 minutes. The test piece with the copper foil was left at 40°C and relative humidity: 90% RH for 72 hours, and then immersed in a solder bath set at each evaluation temperature from 240°C to 300°C in 10°C increments for 10 seconds, and the adhesion state was observed to confirm the presence or absence of defects such as foaming, swelling, and peeling. The judgment was ◯ (good) when no defects were observed at 260°C, and × (bad) when defects were observed.

[Peel strength measurement]
A double-sided copper-clad laminate (manufactured by Nippon Steel Chemical & Material Co., Ltd., trade name: Espanex MB12-25-12UEG) was cut to a width of 50 mm and a length of 100 mm, and then an adhesive sheet was placed on the copper foil side of the sample in which the copper foil on one side had been etched away, and a polyimide film (manufactured by Toray DuPont Co., Ltd., trade name: Kapton 50EN-S) was further laminated on the adhesive sheet, and pressed under conditions of temperature: 160 ° C., pressure: 3.5 MPa, and time: 60 minutes to prepare a laminate. This laminate was cut to a width of 5 mm to prepare a test piece, and a tensile tester (manufactured by Toyo Seiki Seisakusho, trade name: Strograph VE) was used to measure the peel strength between the adhesive layer and the copper foil when the test piece was pulled in the 180 ° direction at a speed of 50 mm / min, and this was taken as the peel strength.

[Method for evaluating film retention]
The adhesive sheet was cut into a test piece 20 mm wide and 20 mm long, folded along the diagonal line to create a crease, and then opened to observe the condition of the film. At this time, the test piece that had no cracks even after folding and opening was rated as "good", and the one with even a partial crack was rated as "no good".

[Method of Evaluating Film Defects]
Polyimide varnish was applied to one side of a release-treated PET film, dried at 100° C. for 5 minutes, and then dried at 120° C. for 10 minutes, and the state of the peeled film was observed. At this time, films without smudges (drag marks) due to aggregates or poor solubility of the elastomer resin were rated as "good," and films with smudges were rated as "no good."

[Acid value]
The acid value is the number of milligrams of potassium hydroxide (KOH) required to neutralize 1 g of sample. It is measured, for example, by the following method. First, the sample is precisely weighed and placed in a 250 mL flask, and 50 mL of ethanol or an equal volume mixture of ethanol and ether is added. The sample is dissolved by heating, and titrated with 0.1 N potassium hydroxide solution while shaking as necessary (indicator: phenolphthalein). The end point of the titration is the point at which the light pink color of the solution persists for 30 seconds. Next, a blank test is performed in the same manner to make corrections, and the acid value is calculated from the following formula.
Acid value = [amount of 0.1 N potassium hydroxide solution consumed (mL) x 5.611] / [amount of sample (g)]

The abbreviations used in the examples represent the following compounds.
BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride DDA: product name: PRIAMINE 1075 manufactured by Croda Japan Co., Ltd., distilled and purified (component a: 99.2% by weight, component b: 0%, component c: 0.8%, amine value: 210 mg KOH/g)
N-12: Dodecanedioic acid dihydrazide NMP: N-methyl-2-pyrrolidone Elastomer resin 1: Manufactured by KRATON, trade name: A1535HU (hydrogenated polystyrene elastomer resin, styrene unit content: 58% by weight, specific gravity: 0.96, no acid value)
Elastomer resin 2: KRATON, product name: G1652MU (hydrogenated polystyrene elastomer resin, styrene unit content: 30% by weight, specific gravity: 0.91, no acid value)
Elastomer resin 3: manufactured by KRATON, product name: G1726VS (hydrogenated polystyrene elastomer resin, styrene unit content: 30% by weight, specific gravity: 0.91, acid value: none)
Elastomer resin 4: KRATON, product name: G1645VS (hydrogenated polystyrene elastomer resin, styrene unit content: 13% by weight, specific gravity: 0.89, no acid value)
Elastomer resin 5: manufactured by KRATON, product name: FG1901GT (hydrogenated polystyrene elastomer resin, styrene unit content: 30% by weight, specific gravity: 0.91, acid value: 10 mgKOH/g)
Elastomer resin 6: manufactured by Asahi Kasei Corporation, product name: Tuftec M1913 (hydrogenated polystyrene elastomer resin, styrene unit content: 30% by weight, specific gravity: 0.91, acid value: 11 mgKOH/g)
Elastomer resin 7: manufactured by Asahi Kasei Corporation, product name: Tuftec M1943 (hydrogenated polystyrene elastomer resin, styrene unit content: 20% by weight, specific gravity: 0.91, acid value: 11 mgKOH/g)
In the above DDA, the "%" of component a, component b, and component c means the area percentage of the chromatogram in GPC measurement. The molecular weight of DDA was calculated by the following formula (1).
Molecular weight = 56.1 × 2 × 1000 / amine value (1)

(Synthesis Example 1)
A polyamic acid solution was prepared by charging 55.51 g of BTDA (0.1721 mol), 94.49 g of DDA (0.1735 mol), 210 g of NMP, and 140 g of xylene into a 1000 ml separable flask and thoroughly mixing for 1 hour at 40° C. This polyamic acid solution was heated to 190° C., heated and stirred for 10 hours, and 125 g of xylene was added to complete the imidization, preparing polyimide solution 1 (solid content: 31 wt %, weight average molecular weight: 80,900, thermoplastic polyimide).

[Example 1]
1.12 g of N-12 and 7.8 g of elastomer resin 1 were mixed with 100 g of the polyimide solution 1 prepared in Synthesis Example 1, and the mixture was diluted with xylene to a solid content of 27% by weight, followed by stirring to prepare polyimide varnish 1a.

[Examples 2 to 8]
Polyimide varnishes 2a to 8a were prepared in the same manner as in Example 1, except that elastomer resins 1, 2, 3, 4, and 5 were used in amounts as shown in Table 1.

Comparative Examples 1 and 2
Polyimide varnishes 9a and 10a were prepared in the same manner as in Example 1, except that elastomer resins 6 and 7 were used in different amounts as shown in Table 1, and the solids concentration of the polyimide varnish was 31% by weight.

Comparative Example 3
A polyimide varnish 11a was prepared in the same manner as in Example 1, except that no elastomer was used and the solids concentration of the polyimide varnish was 31% by weight.

Tables 1 and 2 show the formulations for Examples 1 to 8 and Comparative Examples 1 to 3.

[Example 9]
The 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 an adhesive sheet 1b (thickness: 25 μm).
The various evaluation results for the adhesive sheet 1b are as follows.
Relative dielectric constant: 2.5, dielectric loss tangent: 0.0018, tensile modulus: 0.3 GPa, maximum elongation: 136%, Tg: 41° C., film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.5 kN/m, film defect: good

[Example 10]
An adhesive sheet 2b was prepared in the same manner as in Example 9 using the polyimide varnish 2a.
The various evaluation results of the adhesive sheet 2b are as follows.
Relative dielectric constant: 2.5, dielectric loss tangent: 0.0015, tensile modulus: 0.3 GPa, maximum elongation: 195%, Tg: 43°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.4 kN/m, film defect: good

[Example 11]
An adhesive sheet 3b was prepared in the same manner as in Example 9 using the polyimide varnish 3a.
The various evaluation results of the adhesive sheet 3b are as follows.
Relative dielectric constant: 2.5, dielectric loss tangent: 0.0013, tensile modulus: 0.3 GPa, maximum elongation: 230%, Tg: 42°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.3 kN/m, film defect: good

[Example 12]
An adhesive sheet 4b was prepared in the same manner as in Example 9 using the polyimide varnish 4a.
The various evaluation results of the adhesive sheet 4b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0018, tensile modulus: 0.4 GPa, maximum elongation: 118%, Tg: 40°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.5 kN/m, film defect: good

[Example 13]
An adhesive sheet 5b was prepared in the same manner as in Example 9 using the polyimide varnish 5a.
The various evaluation results of the adhesive sheet 5b are as follows.
Relative dielectric constant: 2.8, dielectric loss tangent: 0.0017, tensile modulus: 0.3 GPa, maximum elongation: 144%, Tg: 40°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.6 kN/m, film defect: good

[Example 14]
An adhesive sheet 6b was prepared in the same manner as in Example 9 using the polyimide varnish 6a.
The various evaluation results of the adhesive sheet 6b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0018, tensile modulus: 0.3 GPa, maximum elongation: 103%, Tg: 42°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.4 kN/m, film defect: good

[Example 15]
An adhesive sheet 7b was prepared in the same manner as in Example 9 using the polyimide varnish 7a.
The various evaluation results of the adhesive sheet 7b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0020, tensile modulus: 0.2 GPa, maximum elongation: 103%, Tg: 41° C., film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.4 kN/m, film defect: good

[Example 16]
An adhesive sheet 8b was prepared in the same manner as in Example 9 using the polyimide varnish 8a.
The various evaluation results of the adhesive sheet 8b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0019, tensile modulus: 0.3 GPa, maximum elongation: 122%, Tg: 41°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.2 kN/m, film defect: good

Comparative Example 4
An adhesive sheet 9b was prepared in the same manner as in Example 9 using the polyimide varnish 9a.
The various evaluation results of the adhesive sheet 9b are as follows.
Relative dielectric constant: 2.8, dielectric loss tangent: 0.0022, tensile modulus: 0.3 GPa, maximum elongation: 201%, Tg: 43°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): x, peel strength: 1.6 kN/m, film defect: bad

Comparative Example 5
An adhesive sheet 10b was prepared in the same manner as in Example 9 using the polyimide varnish 10a.
The various evaluation results of the adhesive sheet 10b are as follows.
Relative dielectric constant: 2.8, dielectric loss tangent: 0.0022, tensile modulus: 0.2 GPa, maximum elongation: 185%, Tg: 41°C, film retention: good, solder heat resistance test (dry): good, solder heat resistance test (moisture absorption): good, peel strength: 1.4 kN/m, film defect: bad

Comparative Example 6
An adhesive sheet 11b was prepared in the same manner as in Example 9 using the polyimide varnish 11a.
The various evaluation results of the adhesive sheet 11b are as follows.
Relative dielectric constant: 2.6, dielectric loss tangent: 0.0021, tensile modulus: 0.5 GPa, maximum elongation: 119%, Tg: 44°C, film retention: good, solder heat resistance test (dry): x, solder heat resistance test (moisture absorption): x, peel strength: 1.0 kN/m, film defect: good

The above results are summarized in Table 3.

As can be seen from Table 3, compared to adhesive sheets 9b and 10b of comparative examples 4 and 5, adhesive sheets 1b to 8b of examples 9 to 16, which contained elastomer resin 1 and elastomer resins 2, 3, 4, and 5, had a dielectric tangent of 0.0020 or less, high peel strength, and no film defects. From these results, it was confirmed that the adhesive sheet as a resin film according to this embodiment can be expected to reduce transmission loss in the high frequency band, for example, around 10 to 20 GHz, and has excellent peel strength while maintaining flexibility and film retention.

As shown in each of the above examples, by adding a hydrogenated polystyrene elastomer resin having an acid value of 10 mg KOH/g or less to a polyimide made from an aliphatic diamine, a clear improvement in dielectric properties was observed, and further an improvement in peel strength was also observed.
Furthermore, it was confirmed that the adhesive sheets obtained in each Example maintained their shape as a film by using a hydrogenated polystyrene elastomer resin having an acid value of 10 mg KOH/g or less in a practical range of blending amount.

These results confirm that the resin film according to this embodiment is suitable for use as a material for circuit boards such as high-frequency compatible FPCs.

Although the embodiment of the present invention has been described in detail above for the purpose of illustration, the present invention is not limited to the above embodiment, and various modifications are possible.

Claims (8)

The following components (A) and (B):
(A) a thermoplastic polyimide, and (B) a polystyrene elastomer resin having an acid value of 10 mgKOH/g or less;
and the content of the (B) component is within the range of 10 parts by weight or more and 100 parts by weight or less relative to 100 parts by weight of the (A) component,
The thermoplastic polyimide is obtained by reacting a tetracarboxylic anhydride component with a diamine component, and contains an aliphatic diamine in an amount of 40 mol % or more relative to the diamine component, and the aliphatic diamine is selected from the group consisting of the following components (a) to (c):
(a) a dimer diamine in which the two terminal carboxylic acid groups of a dimer acid are substituted with a primary aminomethyl group or amino group;
(b) a monoamine compound obtained by substituting a terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group;
(c) Amine compounds obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the above-mentioned dimer diamine);
The dimer diamine composition contains 96% by weight or more of the component (a) in the formula:
The polyimide composition forms, in a film state, a thermoplastic resin layer having a dielectric loss tangent (Tan δ) of 0.0020 or less at 10 GHz as 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. The polyimide composition according to claim 1, wherein the content of styrene units in component (B) is within the range of 10% by weight to 65% by weight. A resin film including a thermoplastic resin layer,
The thermoplastic resin layer comprises the following components (A) and (B):
(A) a thermoplastic polyimide, and (B) a polystyrene elastomer resin having an acid value of 10 mgKOH/g or less;
and a content of the (B) component relative to 100 parts by weight of the (A) component is within a range of 10 parts by weight or more and 100 parts by weight or less, and the thermoplastic resin layer has a dielectric loss tangent (Tan δ) at 10 GHz of 0.0020 or less as 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,
The thermoplastic polyimide is obtained by reacting a tetracarboxylic anhydride component with a diamine component, and contains an aliphatic diamine in an amount of 40 mol % or more relative to the diamine component, and the aliphatic diamine is selected from the group consisting of the following components (a) to (c):
(a) a dimer diamine in which the two terminal carboxylic acid groups of a dimer acid are substituted with a primary aminomethyl group or amino group;
(b) a monoamine compound obtained by substituting a terminal carboxylic acid group of a monobasic acid compound having 10 to 40 carbon atoms with a primary aminomethyl group or an amino group;
(c) Amine compounds obtained by substituting the terminal carboxylic acid group of a polybasic acid compound having a hydrocarbon group having 41 to 80 carbon atoms with a primary aminomethyl group or an amino group (excluding the above-mentioned dimer diamine);
5. A resin film comprising a dimer diamine composition comprising 96% by weight or more of the component (a) described above. A laminate having a substrate and an adhesive layer laminated on at least one surface of the substrate,
A laminate, wherein the adhesive layer is made of the resin film according to claim 3 . A coverlay film having a coverlay film material layer and an adhesive layer laminated on the coverlay film material layer,
A coverlay film, wherein the adhesive layer is made of the resin film according to claim 3 . A resin-coated copper foil in which an adhesive layer and a copper foil are laminated,
A resin-coated copper foil, wherein the adhesive layer is made of the resin film according to claim 3 . A metal-clad laminate having an insulating resin layer and a metal layer laminated on at least one surface of the insulating resin layer,
A metal-clad laminate, wherein at least one of the insulating resin layers is made of the resin film according to claim 3 . A circuit board obtained by wiring the metal layer of the metal-clad laminate according to claim 7 .