Polyimide, polyimide film, multilayer wiring board, copper foil with resin, coil structure, magnetic device, and insulated electrical wire

Abstract

The purpose of the present invention is to provide: a polyimide which is capable of forming a polyimide film that exhibits low dielectric properties and low fluidity while exhibiting good film-forming properties and further having excellent embedding properties and adhesion; and a polyimide film, a multilayer wiring board, a copper foil with a resin, a coil structure, and a magnetic device, each of which is produced using the polyimide.　The polyimide has (A) a structure derived from an ester-type acid dianhydride and (B) a structure derived from at least two diamines. The (B) diamines include (B1) a dimeric diamine at a molar ratio of 0.3 or more wherein the number of moles of all diamines is 1.0, and at least one terminal is modified with a maleimide group.

Description

Polyimide, polyimide film, multilayer wiring board, copper foil with resin, coil structure, magnetic device, and insulated wire

[0001] The present invention relates to polyimide, polyimide film, multilayer wiring board, copper foil with resin, coil structure, magnetic device, and insulated wire.

[0002] In recent years, the development of printed wiring boards for next-generation high-frequency wireless with high speed and large capacity has been carried out, and high-speed signal transmission is enabled by adopting a circuit board having a multilayer wiring structure. In the multilayer wiring structure, a prepreg having characteristics such as high insulation, adhesion, and embedding property between wirings is used as an adhesive for each electronic circuit board by combining a glass fiber cloth and an epoxy resin.

[0003] However, epoxy resin usually has high dielectric properties such as dielectric constant, resulting in a large capacitance. Therefore, in use for high-speed communication (high frequency), the wiring near the insulating film generates heat, which may cause failures in the printed wiring board.

[0004] In order to cope with such high frequencies, the demand for polyimide showing high insulation and low dielectric properties is increasing. For example, Patent Document 1 discloses that a polyimide produced using an aromatic diamine having a specific structure and a tetracarboxylic dianhydride shows a low dielectric constant and excellent heat resistance.

[0005] Also, a method of reducing the imide group concentration, reducing the polarity of the whole molecule, and lowering the dielectric constant of polyimide by introducing a fluorene skeleton into the diamine component is known. For example, Patent Document 2 discloses that a polyimide using trimellitic anhydride chloride as an acid anhydride and 9,9-bis(4-aminophenyl)fluorene as a diamine shows high heat resistance and a low relative dielectric constant.

[0006] On the other hand, although polyimide has excellent dielectric properties, it has a high melt viscosity and is difficult to flow, and also has low embedding and adhesion properties because it is an elastomer. Therefore, the development of a polyimide that can form a polyimide film showing not only low dielectric properties but also low fluidity and excellent embedding and adhesion properties is desired.

[0007] Japanese Patent Publication No. 10-152559 Japanese Patent Publication No. 2005-298625

[0008] In view of the above circumstances, the object of the present invention is to provide a polyimide that can form a polyimide film exhibiting low dielectric properties and low fluidity, as well as good film-forming properties, and furthermore, excellent embedding and adhesion properties, and a polyimide film, multilayer wiring board, resin-coated copper foil, coil structure, magnetic device, and insulated wire made using the same.

[0009] An aspect of the present invention is a polyimide having (A) a structure derived from an ester-type acidic dianhydride and (B) a structure derived from at least two diamines, wherein the (B) diamine contains (B1) dimeramine in a molar ratio of 0.3 or more when the total number of moles of diamines is 1.0, and furthermore, at least one terminal is modified with a maleimide group.

[0010] In one embodiment of the present invention, the (A1) ester-type dianhydride has a structure represented by the following formula (1). (In formula (1), Ar represents a substituted or unsubstituted arylene group.)

[0011] Another aspect of the present invention is a polyimide film containing the above-mentioned polyimide.

[0012] Another aspect of the present invention is a multilayer wiring board comprising an insulating layer formed using the above-mentioned polyimide film.

[0013] Another aspect of the present invention is a resin-coated copper foil comprising the polyimide film and a copper foil laminated on the polyimide film.

[0014] Another aspect of the present invention is a coil structure comprising an insulating layer formed using the above-mentioned polyimide film.

[0015] Another aspect of the present invention is a magnetic device comprising an insulating layer formed using the above-mentioned polyimide film.

[0016] Another aspect of the present invention is an insulated wire comprising an insulating layer formed using the above-mentioned polyimide and a wire covered with the insulating layer.

[0017] According to the present invention, it is possible to provide a polyimide that can form a polyimide film exhibiting low dielectric properties and low fluidity, as well as good film-forming properties, and furthermore, excellent embedding and adhesion properties, and a polyimide film, multilayer wiring board, resin-coated copper foil, coil structure, magnetic device, and insulated wire made using the same.

[0018] Embodiments of the present invention will be described in detail below. The polyimide of the present invention has a structure derived from (A) an ester-type acidic dianhydride and a structure derived from (B) at least two diamines, and furthermore, at least one terminal is modified with a maleimide group. In addition, (B) the diamine contains (B1) dimeramine in a molar ratio of 0.3 or more when the total number of moles of diamine is set to 1.0. By including a certain amount of dimeramine as the diamine component, the dielectric constant and dielectric loss tangent can be made lower, and desired low dielectric properties can be achieved. Furthermore, by introducing a low dielectric imide skeleton, modifying the terminals with maleimide groups, and adjusting the molecular weight, a polyimide exhibiting improved embedding properties can be synthesized. Furthermore, by reducing the molecular weight, the melt viscosity can be reduced, and the fluidity and adhesion can be improved.

[0019] (A1) Ester-type acid dianhydride The polyimide of the present invention has a structure derived from an ester-type acid dianhydride having an ester bond in the molecule as an acid dianhydride component. The acid dianhydride has two acid anhydride groups in one molecule, and is preferably a tetracarboxylic dianhydride, and more preferably an aromatic tetracarboxylic dianhydride. There may be one or more ester bonds in the molecule, preferably one to three, and more preferably one or two. The ester-type acid dianhydride may be used alone, or two or more may be used in combination.

[0020] Such ester-type acidic dianhydrides preferably have the structure shown in the following formula (1). In formula (1), Ar represents a substituted or unsubstituted arylene group, and a substituted arylene group means that the hydrogen atoms of an unsubstituted arylene group are substituted with any substituent. The number of carbon atoms in the substituted or unsubstituted arylene group (excluding the number of carbon atoms of the substituent) is preferably 6 to 20, and more preferably 6 to 12.

[0021]

[0022] Examples of unsubstituted arylene groups in the Ar group include o-phenylene, m-phenylene, p-phenylene, 2,6-naphthylene, and 4,4'-biphenylene. Among these, p-phenylene, 2,6-naphthylene, and 4,4'-biphenylene are preferred.

[0023] Examples of substituents on the substituted arylene group include C1-C8 alkyl groups, halogen atoms (fluorine, chlorine, bromine, iodine), and halogenated alkyl groups in which the hydrogen atoms of the alkyl group are substituted with the halogen atoms. Among these substituents, C1-C8 alkyl groups are preferred, and methyl groups are more preferred. The number of substituents may be one or two or more. If there are two or more substituents, they may be the same or different. Specific examples of the substituted arylene group include the 2,2',3,3',5,5'-hexamethyl-4,4'-biphenylylene group.

[0024] Preferred examples of ester-type dianhydrides represented by formula (1) include the compound represented by formula (1-1) below (TAHQ) and the compound represented by formula (1-2) below (TMPBP-TME), with the compound represented by formula (1-2) below being more preferred.

[0025]

[0026] (B) Diamine The polyimide of the present invention has a structure derived from at least two diamines as diamine components, and one of the diamine components has a structure derived from (B1) dimer amine. Here, dimer amine is a cyclic or acyclic dimer acid obtained as a dimer of an unsaturated fatty acid in which two terminal carboxylic acid groups (-COOH) are a primary aminomethyl group (-CH ２ -NH ２ ) or amino group (-NH ２ This refers to an aliphatic diamine substituted with (). By having a polyimide with a structure derived from a dimer amine, low dielectric properties can be imparted to the resulting polyimide. Dimer amines may be used alone or in combination of two or more.

[0027] Dimer acids are dibasic acids obtained by the intermolecular polymerization reaction of unsaturated fatty acids. Aliphatic diamines derived from dimer acids can be obtained by polymerizing unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid to form dimer acids, which are then reduced and aminated. Such dimer amines are preferably diamine compounds 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.

[0028] Commercially available dimeramine products include "Versamin® 551" and "Versamin® 552" from Cognics Japan, and "PRIAMINE® 1073," "PRIAMINE® 1074," and "PRIAMINE® 1075" from Croda Japan.

[0029] In the polyimide, the (B) diamine contains (B1) dimeramine in a molar ratio of 0.3 or more when the total number of moles of diamine is set to 1.0. By including dimeramine in a specific molar ratio or higher relative to the total number of diamine, the resulting polyimide can be given a lower dielectric constant and a lower dielectric loss tangent. The molar ratio of (B1) dimeramine when the total number of moles of diamine is set to 1.0 is preferably 0.5 or more, more preferably 0.60 or more, and even more preferably 0.9 or more.

[0030] The polyimide of the present invention may also contain (B2) aromatic diamines as other diamine components. Examples of aromatic diamines include p-phenylenediamine (PDA), m-phenylenediamine, 4,4'-oxydianiline (ODA), 3,3'-bistrifluoromethyl-4,4'-diaminobiphenyl (TFMB), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis(anilino)ethane, diaminodiphenyl sulfone, Examples include diaminobenzanilide, diaminobenzoate, diaminodiphenyl sulfide, 2,2-bis(p-aminophenyl)propane, 2,2-bis(p-aminophenyl)hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4-bis(p-aminophenoxy)benzene, 4,4'-bis(p-aminophenoxy)biphenyl, diaminoanthraquinone, and 4,4'-bis(3-aminophenoxyphenyl)diphenylsulfone. Among these aromatic diamines, PDA, ODA, and TFMB are preferred, with ODA being more preferred. Aromatic diamines may be used individually or in combination of two or more.

[0031] The molar ratio of diamine to ester-type acidic dianhydride [(B) / (A)] is not particularly limited, but is preferably 0.3 to 2.0, more preferably 0.5 to 1.9, even more preferably 0.75 to 1.8, and particularly preferably 0.75 to 1.7.

[0032] (C) Terminally Modified Maleimide Group The polyimide of the present invention has at least one terminal modified with a maleimide group. Specifically, in a repeating unit of polyimide having (A) a structure derived from an ester-type acid dianhydride and (B) a structure derived from at least two diamines, the terminal is modified via the nitrogen atom (N) of the maleimide group, preferably at least one terminal of the structural portion derived from the diamine is modified with a maleimide group. In such a polyimide structure, only one terminal may be modified with a maleimide group, or both terminals may be modified with a maleimide group. In the polyimide of the present invention, since the reactive group of the maleimide group is introduced at the terminal, it is possible to increase the molecular weight in further reactions.

[0033] From the viewpoint of fluidity and film-forming properties, the molecular weight (weight-average molecular weight) of the polyimide is preferably 50,000 or less, more preferably 40,000 or less, and even more preferably 35,000 or less. Furthermore, from the viewpoint of imparting low dielectric properties to the polyimide, the lower limit of the molecular weight is preferably 5,000 or more. The molecular weight of the polyimide can be determined, for example, from the value converted to standard polystyrene by gel filtration chromatography (GPC) measurement.

[0034] From the viewpoint of low dielectric properties, fluidity, and film-forming properties, the upper limit of the melt viscosity of polyimide is preferably 3000 mPa·s or less, and more preferably 1800 mPa·s or less. Furthermore, from the viewpoint of imparting low dielectric properties to polyimide, the lower limit of the melt viscosity is preferably 1000 mPa·s or more, and more preferably 1000 mPa·s or more. The melt viscosity of polyimide can be measured, for example, using an analytical instrument such as a rheometer.

[0035] <Synthesis of Polyimide> The polyimide of the present invention can be produced by the following steps: (i) A polyamic acid, which is a precursor of polyimide, is synthesized by polyaddition reaction of the above-mentioned ester-type acidic dianhydride with at least two diamines. (ii) The obtained polyamic acid is imidized to synthesize a polyimide with amine-modified ends. (iii) The polyimide with amine-modified ends is reacted with maleic anhydride to add maleic anhydride to the terminal amine. (iv) The polyimide with maleic anhydride added is further imidized to produce a polyimide modified with maleimide groups at the ends.

[0036] (Synthesis of Polyamic Acids) Polyamic acids can be synthesized by known general methods. For example, polyamic acids (polyamic acid solutions) can be obtained by reacting ester-type dianhydrides with diamines in an organic solvent. The organic solvent used for polymerization of polyamic acids is not particularly limited, as long as it can dissolve the ester-type dianhydrides and diamines as monomer components and also dissolve the polyamic acid produced by the polyaddition reaction. Examples of such organic solvents include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and hexamethylphosphate triamide; ester-based solvents such as γ-butyrolactone; alkyl halide-based solvents such as chloroform and methylene chloride; aromatic hydrocarbon-based solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These organic solvents may be used individually or in combination of two or more. From the viewpoint of enhancing the solubility and reactivity of polyamic acid, the organic solvent is preferably selected from the group consisting of amide solvents, aromatic hydrocarbon solvents, ketone solvents, ester solvents, and ether solvents. Amide solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylacetamide, and N-methyl-2-pyrrolidone, and aromatic hydrocarbon solvents such as toluene are preferred.

[0037] The molecular weight of the polyamic acid and the subsequently synthesized polyimide can be adjusted by adjusting the molar ratio of the total moles of the ester-type dianhydride component to the total moles of the diamine component. The molecular weight (weight-average molecular weight) of the polyamic acid is not particularly limited, but it is preferably between 5,000 and 50,000 from the viewpoint of solubility in organic solvents. The weight-average molecular weight of the polyamic acid can be determined, for example, from the value converted to standard polystyrene by gel filtration chromatography (GPC) measurement.

[0038] The synthesis of polyamic acids by the polyaddition reaction of ester-type dianhydrides and diamines is preferably carried out in an inert atmosphere such as argon or nitrogen. In an inert atmosphere, the polyaddition reaction proceeds by dissolving the ester-type dianhydride and diamine in an organic solvent and mixing them. The order of addition of the ester-type dianhydride and diamine is not particularly limited. For example, the diamine may be dissolved in an organic solvent or dispersed in a slurry to form a diamine solution, and the ester-type dianhydride may be added to the diamine solution. The ester-type dianhydride and diamine may be added directly to the organic solvent in a solid state, or they may be added separately dissolved in an organic solvent or dispersed in a slurry.

[0039] The temperature conditions for the polyaddition reaction are not particularly limited, but from the viewpoint of suppressing the decrease in molecular weight of the polyamic acid due to depolymerization, the reaction temperature is preferably 100°C or lower, and from the viewpoint of allowing the polyaddition reaction to proceed appropriately, the reaction temperature is more preferably 20 to 80°C. The reaction time can be arbitrarily set in the range of 1 to 72 hours, and if necessary, it may be left overnight at room temperature.

[0040] When preparing polyamic acid, the viscosity of the polyamic acid solution is preferably 100 mPa·s or more from the viewpoint of imparting good film-forming properties to the resulting polyimide. Further, the solid content (concentration) of polyamic acid in the polyamic acid solution is preferably 10% by mass or more, more preferably 15% by mass or more, and still more preferably 20% by mass or more. In particular, when the concentration of polyamic acid is 30% by mass or more, the productivity in forming a polyimide coating film using polyamic acid can be increased. Also, the upper limit of the concentration of polyamic acid is preferably 40% by mass or less, and more preferably 30% by mass or less from the viewpoint of sufficiently dissolving polyamic acid in an organic solvent.

[0041] In order to impart processing characteristics and various functionalities to polyamic acid, various organic or inorganic low-molecular or high-molecular compounds may be blended into the polyamic acid solution. For example, the polyamic acid composition may contain a dye, a surfactant, a leveling agent, a plasticizer, fine particles, a sensitizer, a silane coupling agent, etc. The fine particles may be either organic fine particles or inorganic fine particles, and may have a porous or hollow structure.

[0042] (Synthesis of polyimide with amine-modified ends) The method for converting the polyamic acid synthesized as described above into polyimide is not particularly limited, but polyimide can be produced by dehydrating and ring-closing (imidizing) the obtained polyamic acid. Known methods such as thermal imidization by dehydrating and ring-closing by heating and chemical imidization by chemically ring-closing using a known dehydrating and ring-closing catalyst can be employed as the method for dehydrating and ring-closing (imidizing).

[0043] In the case of thermal imidization, the heating temperature is preferably 120 to 350°C, more preferably 150 to 250°C. The heating time is preferably 0.5 to 3 hours, more preferably 1 to 2 hours. In the case of chemical imidization, as the dehydration ring-closing catalyst, for example, pyridine, triethylamine, γ-butyrolactone, acetic anhydride, etc. can be used. At this time, the reaction temperature can be any temperature selected from 20 to 100°C, preferably 50°C or lower, and the reaction time is preferably 1 to 3 hours. Among these imidizations, it is preferable to perform chemical imidization. Also, the imidization may be carried out under air, reduced pressure, or in an inert gas such as nitrogen, but in order to obtain a polyimide film with high transparency, it is preferable to carry out the imidization under reduced pressure or in an inert gas such as nitrogen.

[0044] (Addition of maleic anhydride) By the addition reaction of the above-mentioned amine-modified polyimide at the terminal and maleic anhydride, maleic anhydride that has undergone ring-opening is added to the amine at the terminal. The heating temperature of the addition reaction is preferably 50 to 120°C, more preferably 70 to 100°C. Also, the heating time of the addition reaction is preferably 1 to 24 hours, more preferably 3 to 12 hours.

[0045] (Terminal maleimidization) By further imidizing the polyimide to which ring-opened maleic anhydride has been added, a polyimide having a terminal modified with a maleimide group can be synthesized. For the imidization, known methods such as the above-mentioned thermal imidization and chemical imidization can be adopted, and it is preferable to perform chemical imidization. In this way, a polyimide having a maleimide group at the terminal can be produced.

[0046] <Polyimide film> The polyimide film of the present invention contains the polyimide obtained as described above. By applying a solution (composition) containing the polyimide of the present invention onto a substrate and drying and further curing the obtained coating film, a polyimide film provided with a polyimide formed by the activity of the terminal maleimide group can be formed on the substrate. The substrate is not particularly limited, and examples include a polyethylene terephthalate film (PET film), a polyethylene naphthalate film, etc. The surface of the substrate may be subjected to a release treatment.

[0047] The thickness of the polyimide film is not particularly limited, but is preferably 25 μm to 60 μm, and more preferably 30 μm to 50 μm. The thickness of the substrate is not particularly limited, but is preferably 15 μm to 75 μm, and more preferably 25 μm to 50 μm.

[0048] Examples of coating apparatus for applying a polyimide-containing solution onto a substrate include bar coaters, curtain coaters, spray coaters, roll coaters, and screen printing machines. When drying the coated film formed on the substrate, the drying temperature is preferably 50°C to 120°C, and more preferably 80°C to 110°C. The drying time is preferably 180 seconds to 720 seconds, and more preferably 300 seconds to 600 seconds. Furthermore, when thermally curing the coated film after drying, the curing temperature is preferably 150°C to 250°C, and more preferably 180°C to 220°C. The curing time is preferably 180 seconds to 1500 seconds, and more preferably 300 seconds to 1200 seconds.

[0049] <Copper foil with resin> The copper foil with resin of the present invention is obtained by laminating the above-mentioned polyimide film onto copper foil. With such a copper foil with resin, it is possible to build up wiring on a wiring board with the polyimide film as an insulating layer in between. The copper foil may be laminated on one side of the resin film, or it may be laminated on both sides of the resin film with polyimide.

[0050] <Multilayer Wiring Board> The multilayer wiring board of the present invention comprises an insulating layer formed using the polyimide film described above. As an example of manufacturing such a multilayer wiring board, for example, a double-sided copper foil substrate is made by sandwiching the polyimide layer surface of resin-coated copper foil from both sides using the polyimide film described above as a core substrate. Then, a wiring pattern is formed on the copper foil by etching to produce a single-layer wiring board. Furthermore, by appropriately layering the polyimide film and resin-coated copper foil on top of that, a multilayer wiring board can be made in which insulating layers and wiring pattern layers are alternately provided.

[0051] Polyimide is subjected to a heat-curing treatment to form a cured resin layer consisting of a cured polyimide product. Examples of heat-curing treatments include heat-pressing treatment and heat treatment. The heat-curing treatment may be a single-stage treatment or a two-stage or more-stage treatment. The temperature of the heat-curing treatment is preferably 150°C to 250°C, and more preferably 180°C to 200°C. The pressure of the heat-curing treatment is preferably 0.5 MPa to 5.0 MPa, and more preferably 1.1 MPa to 5.0 MPa. The duration of the heat-curing treatment is preferably 0.5 hours to 3 hours, and more preferably 1 hour to 2 hours.

[0052] <Coil Structure> The coil structure of the present invention comprises an insulating layer formed using the polyimide film described above. Such a coil structure can be manufactured by the same method as the multilayer wiring substrate described above. That is, the coil structure can be manufactured by using a wiring substrate having coil-shaped wiring as the material for the multilayer wiring substrate.

[0053] <Magnetic Device> The magnetic device of the present invention comprises an insulating layer formed using the polyimide film described above. Such a magnetic device can be manufactured by the same method as the multilayer wiring substrate described above. By using a wiring substrate having coil-shaped wiring as a single-layer wiring substrate, a coil structure can be manufactured. Then, by providing a known magnetic material such as ferrite on this coil structure, a magnetic device can be manufactured.

[0054] <Insulated Wire> The insulated wire of the present invention comprises an insulating layer formed using the polyimide described above, and a wire covered with the insulating layer. Such an insulated wire can be manufactured by applying a composition containing the polyimide of the present invention onto the wire, drying it in the same manner as described above to form a coating film, and then heat-curing it. For example, copper or aluminum, which have high conductivity, can be used as the material for the wire. The wire may also be plated.

[0055] Next, embodiments of the present invention will be described, but the present invention is not limited to these examples unless it exceeds the spirit of the invention. In the following table, the values ​​of each component are in parts by mass unless otherwise specified.

[0056] <Example 1> 144.2 g of dimeramine ("PRIAMINE® 1075", manufactured by Croda Japan Co., Ltd.), 5.4 g of aromatic diamine (4,4-oxydianiline), 264.8 g of N-methylpyrrolidone (NMP), and 415.8 g of toluene were placed in a separable flask and heated to 70°C to dissolve the diamine. Next, 124.0 g of ester-type acidic dianhydride (TMPBP-TME, manufactured by Honshu Chemical Co., Ltd.) was added, and the mixture was stirred at 70°C for 3 hours. Then, 0.9 g of γ-valerolactone and 1.4 g of pyridine were added, and the mixture was stirred at 150°C for 3 hours. After cooling to 70°C, 20 g of maleic anhydride was added, and the mixture was stirred at 70°C for 3 hours. Subsequently, the mixture was stirred at 150°C for 10 to 24 hours to prepare a polyimide composition having maleimide groups at the ends.

[0057] <Example 2> 118.7 g of dimeramine ("PRIAMINE® 1075", manufactured by Croda Japan Co., Ltd.), 24.7 g of aromatic diamine (4,4-oxydianiline), 297.4 g of NMP, and 392.6 g of toluene were placed in a separable flask and heated to 70°C to dissolve the diamine. Next, 124.0 g of ester-type acidic dianhydride (TMPBP-TME, manufactured by Honshu Chemical Co., Ltd.) was added, and the mixture was stirred at 70°C for 3 hours. Then, 0.9 g of γ-valerolactone and 1.4 g of pyridine were added, and the mixture was stirred at 150°C for 3 hours. After cooling to 70°C, 30 g of maleic anhydride was added, and the mixture was stirred at 70°C for 3 hours. Subsequently, the mixture was stirred at 150°C for 10 to 24 hours to prepare a polyimide composition having maleimide groups at the ends.

[0058] <Comparative Example 1> 120.2 g of dimer amine ("PRIAMINE® 1075", manufactured by Croda Japan Co., Ltd.), 15.0 g of aromatic diamine (4,4-oxydianiline), and 750.8 g of NMP were placed in a separable flask and heated to 50°C to dissolve the diamine. Next, 186.1 g of ester-type acidic dianhydride (TMPBP-TME, manufactured by Honshu Chemical Co., Ltd.) was added, and the mixture was stirred at 50°C for 3.5 hours, and then stirred at room temperature for 24 hours to prepare a polyamic acid composition.

[0059] (Preparation of test specimens) Each composition prepared as described above was coated onto a substrate as follows, and after heat treatment, the substrate was peeled off to prepare test specimens which were cured polyimide products. Substrate: PET film (thickness 38 μm, with release treatment) Coating method: Bar coater DRY film thickness (20 μm to 100 μm) Heat treatment: Drying at 100°C for 10 minutes in a hot air circulating drying oven, then heat curing at 190°C for 20 minutes

[0060] <Evaluation> (1) Film-forming properties The film-forming properties were evaluated for isolation of the cured product of the obtained test specimen from the substrate according to the following criteria.

[0061] ○: Can be isolated without cracks or chips. △: Some cracks occur during isolation. ×: Cracks occur.

[0062] (2) Using a dielectric impedance analyzer ("4291B", manufactured by Hewlett Packard), the cured specimen (thickness: 25 μm, length: 20 mm, width: 20 mm) of the test piece prepared above was used as a sample, and measurements were taken at a measurement temperature of 25°C and a frequency of 1 MHz to determine the dielectric constant at a frequency of 1 MHz.

[0063] (3) Using a melt viscosity rheometer ("HAKKE MARS III", manufactured by Thermo Scientific), the melt viscosity of polyimide was measured using pelletized polyimide as a sample under the conditions of a measurement temperature of 30 to 200°C and a heating rate of 2°C / min.

[0064] (4) Embedding properties The polyimide solution prepared as described above was applied to a PET substrate and dried at 100°C for 10 minutes. The dried polyimide film was vacuum-laminated over another polyimide film (thickness: 25 μm, "Kapton®", manufactured by Toray DuPont) to create a sheet having a polyimide film / polyimide film ("Kapton®") / polyimide film laminated structure. Multiple layers of polyimide film were laminated so that each layer was 50 to 80 μm thick. Printed circuit boards with copper wiring ("FR-4 substrate", thickness: 400 μm, conductor thickness: 35 μm) were placed on both sides of this sheet and vacuum-pressed under the conditions of (i) 150°C, 20 minutes, 0.5 MPa and (ii) 190°C, 60 minutes, 3.3 MPa. The embedding properties were evaluated by observing the cross-section between the copper wirings of this substrate according to the following criteria.

[0065] ○: Polyimide can be filled horizontally along the wiring. ×: Polyimide cannot be filled horizontally along the wiring.

[0066] (5) Adhesion (Peel Strength) The polyimide solution prepared as described above was coated onto a PET substrate to a thickness of 25-35 μm and dried at 100°C for 10 minutes. The dried polyimide film was vacuum laminated onto copper foil at 100°C to produce a sheet with a copper foil / polyimide film / copper foil laminated structure (copper foil thickness: 12 μm). Subsequently, the test specimens were vacuum pressed at (i) 140°C, 10 minutes, 0.5 MPa and (ii) 190°C, 90 minutes, 2.5 MPa. The sheets thus produced were peeled 90° at a speed of 50 mm / min using an Autograph (Shimadzu Corporation) to evaluate their adhesion.

[0067]

[0068] As shown in Table 1, in Examples 1 and 2, which used polyimides having (A) a structure derived from an ester-type dianhydride and (B) a structure derived from at least two diamines, wherein (B) the diamine contains (B1) dimeramine in a molar ratio of 0.3 or more when the total number of moles of diamines is 1.0, and furthermore, at least one terminal is modified with a maleimide group, the obtained polyimides exhibited low dielectric properties and low fluidity, and polyimide films with excellent embedding and adhesion properties were produced. In addition, they could be isolated from the substrate without cracking or chipping, and the film-forming properties were also good.

[0069] On the other hand, in Comparative Example 1, which used a polyimide whose terminals were not modified with maleimide groups, the embedding ability was evaluated as "×", and the peel strength was lower and the adhesion was inferior to that of Examples 1 and 2. Furthermore, it was not possible to obtain a polyimide that exhibited high melt viscosity and low fluidity.

[0070] The polyimide of the present invention exhibits low dielectric properties and low fluidity, as well as good film-forming properties. Furthermore, since polyimide films with excellent embedding and adhesion can be produced using such polyimide, it has high value as a substrate material for high-frequency circuits.

Claims

1. A polyimide having (A) a structure derived from an ester-type dianhydride and (B) a structure derived from at least two diamines, wherein the (B) diamine contains (B1) dimeramine in a molar ratio of 0.3 or more when the total number of moles of diamines is 1.0, and furthermore, at least one terminal is modified with a maleimide group.

2. The polyimide according to claim 1, wherein the (A) ester-type dianhydride has a structure represented by the following formula (1). (In formula (1), Ar represents a substituted or unsubstituted arylene group.) 3. A polyimide film comprising the polyimide described in claim 1 or 2.

4. A multilayer wiring board comprising an insulating layer formed using the polyimide film described in claim 3.

5. A resin-coated copper foil comprising a polyimide film according to claim 3 and a copper foil laminated on the polyimide film.

6. A coil structure comprising an insulating layer formed using the polyimide film described in claim 3.

7. A magnetic device comprising an insulating layer formed using the polyimide film described in claim 3.

8. An insulated electric wire comprising an insulating layer formed using the polyimide described in claim 1 or 2, and an electric wire covered with the insulating layer.

Images