Polyamic acid, polyamic acid composition, polyimide, polyimide film and printed wiring board

Abstract

To provide a polyamic acid that can form a polyimide exhibiting low dielectric properties and low hygroscopic properties, and a polyamic acid composition, a polyimide, a polyimide film, and a printed circuit board, each produced by using this polyamic acid.SOLUTION: The present invention provides a polyamic acid that is a product from a polyaddition reaction between an ester-type acid dianhydride (A) and at least two diamines (B), wherein a dimer diamine (B1) is contained at a molar ratio of 0.3 or more relative to the total diamine component.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyamic acid capable of forming a polyimide exhibiting low dielectric properties and low moisture absorption, as well as a polyamic acid composition, polyimide, polyimide film, and printed wiring board produced using the same. [Background technology]

[0002] High dielectric strength and heat resistance are required for insulating materials used in mobile communication devices such as smartphones and tablets, as well as in electronic devices such as computers and car navigation systems. Polyimide is a polymer formed by imidizing polyamic acid, which is generally synthesized from acid dianhydride and an aromatic diamine compound. It is widely used as such insulating material due to its excellent heat resistance, mechanical properties, and insulating properties.

[0003] In recent years, development has been underway for high-speed, high-capacity printed wiring boards for next-generation high-frequency wireless applications, enabling high-speed signal transmission through the adoption of circuit boards with multilayer wiring structures. Polyimide is used as the interlayer insulating film in multilayer wiring structures, but typical polyimide has high dielectric properties, such as a dielectric constant, which causes delays in signal transmission and hinders speed increases. Furthermore, a high dielectric constant increases capacitance, which can cause wiring near the insulating film to heat up during high-speed (high-frequency) communications, potentially resulting in failure of the printed wiring board.

[0004] To cope with such high frequencies, there is an increasing demand for polyimides that exhibit low dielectric properties. For example, Patent Document 1 discloses that polyimides prepared using aromatic diamines having specific structures and tetracarboxylic dianhydrides exhibit low dielectric constants and excellent heat resistance.

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

[0006] On the other hand, since polyimides generally have a tendency to absorb water due to the imide group, and their dielectric properties differ greatly between humid and dry states, they are also required to exhibit low dielectric properties even under high humidity conditions. Therefore, it is desirable to form polyamides that exhibit not only low dielectric properties but also low moisture absorption. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-152559 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-298625 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above circumstances, an object of the present invention is to provide a polyamic acid capable of forming a polyimide exhibiting low dielectric properties and low moisture absorption, as well as a polyamic acid composition, polyimide, polyimide film, and printed wiring board produced using the polyamic acid. [Means for solving the problem]

[0009] An embodiment of the present invention is a polyamic acid that is a polyaddition reaction product of (A) an ester-type acid dianhydride and (B) at least two diamines, characterized in that the polyamic acid contains (B1) dimer diamine in a molar ratio of 0.3 or more relative to the total diamine components.

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

[0011] In one embodiment of the present invention, the (B) at least two diamines include (B2) an aromatic diamine.

[0012] Another aspect of the present invention is a polyamic acid composition containing the above polyamic acid and (C) an organic solvent.

[0013] Another aspect of the present invention is a polyimide obtained by imidizing the above polyamic acid.

[0014] Another aspect of the present invention is a polyimide film containing the above polyimide.

[0015] Another aspect of the present invention is a printed wiring board comprising the above-described polyimide film. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a polyamic acid capable of forming a polyimide exhibiting low dielectric properties and low moisture absorption, as well as a polyamic acid composition, a polyimide, a polyimide film, and a printed wiring board produced using the polyamic acid. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described in detail below. The polyamic acid of the present invention is a polyaddition reaction product of (A) an ester-type acid dianhydride and (B) at least two diamines, and contains (B1) a dimer diamine at a molar ratio of 0.3 or more relative to the total diamine components. That is, a polyimide formed using the polyamic acid of the present invention has an ester skeleton and a dimer skeleton, and can achieve low water absorption due to the ester skeleton. Furthermore, low dielectric properties are exhibited due to the dimer skeleton, and the inclusion of a certain amount of dimer diamine as a diamine component can further reduce the dielectric constant and dielectric dissipation factor, thereby achieving the desired low dielectric properties. Furthermore, the dimer skeleton of the polyamide improves heat resistance, allowing the formation of a polyamide with excellent thermal decomposition resistance.

[0018] (A) Ester-type acid dianhydride The polyamic acid of the present invention has, as an acid dianhydride component, a structural unit derived from an ester-type acid dianhydride having an ester bond in the molecule. The polyamic acid has a structural unit derived from an ester-type acid dianhydride, which can impart low water absorption to the resulting polyimide. The acid dianhydride has two acid anhydride groups in one molecule, and is preferably a tetracarboxylic acid dianhydride, more preferably an aromatic tetracarboxylic acid dianhydride. The number of ester bonds in the molecule may be one or more, preferably one to three, and more preferably one or two. The ester-type acid dianhydrides may be used alone or in combination of two or more.

[0019] Such an ester-type acid dianhydride preferably has a structure represented by the following formula (1). In formula (1), Ar represents a substituted or unsubstituted arylene group, and a substituted arylene group means that a hydrogen atom of an unsubstituted arylene group has been substituted with an arbitrary 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.

[0020] [ka]

[0021] Examples of the unsubstituted arylene group in the group Ar include an o-phenylene group, an m-phenylene group, a p-phenylene group, a 2,6-naphthylene group, a 4,4'-biphenylylene group, etc. Among these, a p-phenylene group, a 2,6-naphthylene group, and a 4,4'-biphenylylene group are preferred.

[0022] Examples of optional substituents in the substituted arylene group include alkyl groups having 1 to 8 carbon atoms, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, iodine atoms), and halogenated alkyl groups in which hydrogen atoms of the alkyl groups are substituted with the halogen atoms. Among these substituents, alkyl groups having 1 to 8 carbon atoms are preferred, and methyl groups are more preferred. The number of optional substituents may be one or two or more. When there are two or more substituents, these substituents may be the same or different. Specific examples of the substituted arylene group include 2,2',3,3',5,5'-hexamethyl-4,4'-biphenylylene groups, etc.

[0023] The group Ar is preferably a p-phenylene group, a 2,6-naphthylene group, a 4,4'-biphenylylene group, a methylphenylene group, or a 2,2',3,3',5,5'-hexamethyl-4,4'-biphenylylene group.

[0024] Preferred examples of the ester-type acid dianhydride represented by formula (1) include a compound represented by the following formula (1-1) and a compound (TAHQ) represented by the following formula (1-2), and a compound (TMPBP-TME) represented by the following formula (1-2) is more preferred.

[0025] [ka]

[0026] (B) Diamine The polyamic acid of the present invention has structural units derived from at least two diamines as diamine components, one of which has a structural unit derived from (B1) dimer diamine. Here, dimer diamine refers to an aliphatic diamine in which two terminal carboxylic acid groups (—COOH) of a cyclic or acyclic dimer acid obtained as a dimer of an unsaturated fatty acid are substituted with primary aminomethyl groups (—CH—NH) or amino groups (—NH). The polyamic acid having structural units derived from dimer diamine can impart low dielectric properties to the resulting polyimide. Dimer diamines may be used alone or in combination.

[0027] Dimer acids are dibasic acids obtained by intermolecular polymerization 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, reducing the dimer acids, and then amminating them. Such dimer diamines are preferably diamine compounds obtained by substituting the terminal carboxylic acid groups of dibasic acid compounds having 18 to 54 carbon atoms, preferably 22 to 44 carbon atoms, with primary aminomethyl groups or amino groups.

[0028] Commercially available dimer diamine products include "VERSAMINE (registered trademark) 551" and "VERSAMINE (registered trademark) 552" manufactured by Cognics Japan, and "PRIAMINE (registered trademark) 1073," "PRIAMINE (registered trademark) 1074," and "PRIAMINE (registered trademark) 1075" manufactured by Croda Japan.

[0029] Furthermore, in the polyamic acid of the present invention, the dimer diamine (B1) is contained in a molar ratio of 0.3 or more relative to the total diamine components. By containing the dimer diamine in a molar ratio equal to or greater than a specific value relative to the total diamine components, the resulting polyimide can be endowed with a lower dielectric constant and a lower dielectric loss tangent. The molar ratio of the dimer diamine (B1) relative to the total diamine components is preferably 0.3 or more, and more preferably 0.4 or more.

[0030] The polyamic acid of the present invention may contain (B2) an aromatic diamine as another diamine component. Examples of the aromatic diamine 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, diaminodiphenylsulfone, Examples of aromatic diamines 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)diphenyl sulfone. Among these aromatic diamines, PDA, ODA, and TFMB are preferred, with ODA being more preferred. The aromatic diamines may be used alone or in combination of two or more.

[0031] The molar ratio of the diamine to the ester-type acid dianhydride [(B) / (A)] is not particularly limited, but is preferably 0.90 to 1.10, more preferably 0.95 to 1.05, even more preferably 0.97 to 1.03, and particularly preferably 0.98 to 1.02.

[0032] <Polyamic Acid and Polyamic Acid Composition> (C) Organic solvent The polyamic acid of the present invention can be synthesized by a known general method. For example, a polyamic acid composition (polyamic acid solution) can be obtained by reacting an ester-type acid dianhydride with a diamine in an organic solvent (C). The organic solvent used for the polymerization of the polyamic acid is not particularly limited, as long as it can dissolve the ester-type acid dianhydride and diamine as monomer components and 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 hexamethylphosphoric triamide; ester-based solvents such as γ-butyrolactone; alkyl halide 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 alone or in combination of two or more. From the viewpoint of enhancing the solubility and reactivity of the polyamic acid, the organic solvent is preferably selected from the group consisting of amide solvents, ketone solvents, ester solvents, and ether solvents, and amide solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N'-diethylacetamide, and N-methyl-2-pyrrolidone are preferred.

[0033] The molecular weight of the polyamic acid can be adjusted by adjusting the molar ratio between the total number of moles of the ester-type acid dianhydride components and the total number of moles of the diamine components. The molecular weight (weight average molecular weight) of the polyamic acid is not particularly limited, but is preferably 10,000 or more and 100,000 or less from the viewpoint of solubility in organic solvents. The weight average molecular weight of the polyamic acid can be determined, for example, from a standard polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0034] The synthesis of polyamic acid by the polyaddition reaction of an ester-type acid dianhydride and a diamine is preferably carried out in an inert atmosphere such as argon or nitrogen. The polyaddition reaction proceeds by dissolving the ester-type acid dianhydride and the diamine in an organic solvent and mixing them in an inert atmosphere. The order of addition of the ester-type acid dianhydride and the diamine is not particularly limited. For example, the diamine may be dissolved or dispersed in a slurry form in an organic solvent to form a diamine solution, and the ester-type acid dianhydride may be added to the diamine solution. The ester-type acid dianhydride and the diamine may be added directly to the organic solvent in a solid state, or may be added after being dissolved or dispersed in a slurry form in a separate organic solvent.

[0035] The temperature conditions for the polyaddition reaction are not particularly limited, but from the viewpoint of suppressing a decrease in the molecular weight of the polyamic acid due to depolymerization, the reaction temperature is preferably 100° C. or less, 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 may be set arbitrarily within the range of 1 to 72 hours, and may further be left overnight at room temperature if necessary.

[0036] From the viewpoint of film-forming properties, the viscosity of the solution when preparing the polyamic acid composition of the present invention is preferably 500 mPa·s or more. Furthermore, the concentration of polyamic acid in the polyamic acid composition of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 25% by mass or more. In particular, a polyamic acid concentration of 15% by mass or more can improve productivity when forming a polyimide coating film using polyamic acid. Furthermore, from the viewpoint of sufficiently dissolving the polyamic acid in an organic solvent, the upper limit of the polyamic acid concentration is preferably 50% by mass or less, and even more preferably 30% by mass or less.

[0037] In order to impart processability and various functionalities to the polyamic acid and the polyimide formed using the polyamic acid, various organic or inorganic low-molecular-weight or high-molecular-weight compounds may be blended into the polyamic acid composition. For example, the polyamic acid composition may contain dyes, surfactants, leveling agents, plasticizers, fine particles, sensitizers, silane coupling agents, etc. The fine particles may be either organic or inorganic fine particles, and may have a porous or hollow structure.

[0038] <Polyimide> The method for converting polyamic acid to polyimide is not particularly limited, but polyimide can be produced by dehydrating and cyclizing (imidizing) the polyamic acid obtained as described above. The dehydrating and cyclizing (imidizing) method can be a known method such as thermal imidization, which involves dehydrating and cyclizing by heating, or chemical imidization, which involves chemical cyclization using a known dehydrating and cyclizing catalyst.

[0039] 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, examples of dehydration ring-closing catalysts that can be used include pyridine, triethylamine, and acetic anhydride. In this case, the reaction temperature can be any temperature selected from 20 to 100°C, but is preferably 50°C or less, and the reaction time is preferably 1 to 3 hours. The imidization may be carried out in air, under reduced pressure, or in an inert gas such as nitrogen; however, to obtain a highly transparent polyimide film, it is preferably carried out under reduced pressure or in an inert gas such as nitrogen.

[0040] The molecular weight (weight average molecular weight) of the polyimide is not particularly limited, but is preferably 10,000 or more and 100,000 or less from the viewpoints of the low dielectric properties, solubility in organic solvents, and film-forming properties of the resulting polyimide. The weight average molecular weight of the polyimide can be determined, for example, from a value converted into standard polystyrene by gel permeation chromatography (GPC) measurement.

[0041] <Polyimide film> The polyimide film of the present invention contains the polyimide obtained as described above. The method for producing such a polyimide film is not particularly limited, and examples thereof include a method in which the polyamic acid composition described above is applied to a substrate (e.g., a plastic film such as polyethylene, polypropylene, urethane, polyester, polyethylene terephthalate (PET), or polycarbonate, a glass plate, a stainless steel plate, a copper plate including thin copper foil, or an aluminum plate) to form a film, followed by drying and heating to remove the solvent and dehydration ring-closure (imidization); or a method in which the polyamic acid is converted into a polyimide, the resulting polyimide is dissolved in an organic solvent, the polyimide solution is applied to a film on the substrate, and the solvent is then dried and removed. The method for applying the polyimide to the substrate is not particularly limited, and conventionally known coating methods can be used.

[0042] The thickness of the polyimide film is not particularly limited and can be appropriately selected depending on the application. The thickness of the polyimide film is preferably 10 to 100 μm, more preferably 20 to 50 μm. The thickness of the polyimide film can be easily controlled by appropriately adjusting the solid content concentration of each component in the polyamic acid composition, the coating thickness, and the viscosity.

[0043] <Printed wiring board> The polyimide film of the present invention is suitable for use as a film for various components such as color filters, flexible displays, semiconductor components, and optical members. Because the polyimide film exhibits insulating properties, it is suitable for use as an insulating substrate for printed wiring boards. Furthermore, because the polyimide film is a thin, flexible film that exhibits insulating properties, it is also suitable for use as a base film for flexible circuit boards known as flexible printed wiring boards (FPCs). [Example]

[0044] Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as they do not depart from the spirit of the present invention.

[0045] <Examples 1 to 2, Comparative Examples 1 to 3> An organic solvent containing an aromatic diamine shown in Table 1 below was added to a separable flask in the blending ratio shown in Table 1 below. Next, a dimer diamine and an acid dihydrate shown in Table 1 below were added in this order in the blending ratio shown in Table 1 below. The resulting mixture was stirred at 50 to 80°C for 2 hours and then at room temperature for a further 24 hours to prepare polyamic acid compositions used in Examples 1 and 2 and Comparative Examples 1 to 3. The prepared polyamic acid compositions were applied to substrates using the test piece preparation process described below to prepare test pieces. The prepared test pieces were evaluated for each of the properties shown in Table 1 below. The evaluation results are shown in Table 1. The blending amount of each component shown in Table 1 below is in parts by mass unless otherwise specified.

[0046] [Table 1]

[0047] Details of each component in Table 1 are as follows: (A1) Ester-type acid dianhydride TMPBP-TME: Honshu Chemical Co., Ltd., 2,2',3,3',5,5'-hexamethyl[1,1'-biphenyl]-4,4'-diyl bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (A2) Tetracarboxylic acid dianhydride PMDA: Pyromellitic dianhydride (B1) Dimer diamine PRIAMINE® 1075: Dimer diamine, manufactured by Croda Japan (B2) Aromatic diamine 4,4-ODA: 4,4-oxydianiline (C) Organic solvent NMP: N-methyl-2-pyrrolidone

[0048] <Test piece production process> A PET film substrate (Nichiei Kako Co., Ltd.'s "PET75" low-adhesive sheet for processing: 75 μm thick) was surface-treated (degreased) with isopropyl alcohol, and then the polyamic acid compositions prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were applied to the substrate using a bar coater, followed by pre-drying at 80°C for 30 minutes. After pre-drying, the film was thermally cured by post-curing at 150°C for 1 hour and then at 180°C for 30 minutes, forming a cured coating film (polyimide film) of a predetermined thickness on the substrate, and test specimens were prepared.

[0049] <Evaluation> (1) Dielectric constant and dielectric loss tangent In the test piece preparation process, test pieces were prepared so that the thickness of the cured coating film was 30 μm ± 10 μm. Next, using a network analyzer and cavity resonator manufactured by Key Sight Technologies, the obtained test pieces were cut into samples 50 mm long and 2 mm wide using the cavity resonance method. The dielectric constant and dielectric loss tangent were measured at a measurement temperature of 25°C, a measurement humidity of 50 RH%, and a frequency of 10 GHz. In addition, after heating for 200 hours in an atmosphere at a temperature of 85°C and a humidity of 80 RH%, the dielectric constant and dielectric loss tangent at a frequency of 10 GHz were also measured.

[0050] (2) Elastic modulus In the test piece preparation process, test pieces were prepared so that the thickness of the cured coating film was 50 μm ± 10 μm. The formed cured coating film was then peeled off from the substrate and cut into samples of a predetermined size. The elastic modulus of the samples was measured at a pulling rate of 5 mm / min using an autograph manufactured by Shimazu Corporation.

[0051] (3) Elongation and breaking strength The same samples as those prepared for measuring the elastic modulus were measured for elongation and strength at break using an autograph manufactured by Shimazu Corporation at a pulling rate of 5 mm / min.

[0052] (4) Water absorption rate In the test piece preparation step, the test pieces were prepared so that the thickness of the cured coating film was 30 μm±10 μm. The obtained test pieces were cut into 2-3cm squares, and the samples were immersed in distilled water for 24 hours, then removed and the moisture on the surface was wiped off with a cloth.The samples were then heated to 150°C using a moisture measuring device manufactured by Hiranuma Co., Ltd. using the Karl Fischer method, and the water absorption rate was measured based on the amount of moisture released from the sample.

[0053] (5) Heat decomposition resistance In the test piece preparation process, test pieces were prepared so that the thickness of the cured coating film was 30 μm ± 10 μm. The obtained test pieces were cut into small pieces, and the temperature at which the weight lost 5% in an air atmosphere was measured using a thermogravimetric analyzer (Hitachi High-Tech Science Corporation, thermogravimetric analyzer "STA 7200RV") at a heating rate of 10°C / min was evaluated as the thermal decomposition temperature (Td5) [°C].

[0054] (6) Breakdown voltage In the test piece preparation process, the polyamic acid compositions prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were uniformly applied to a copper-clad laminate (ESPANEX) using a bar coater so that the thickness of the cured coating film was 30 μm±10 μm, and then the above-mentioned thermal curing process from pre-drying to post-cure was carried out to form a cured coating film. Next, the dielectric breakdown voltage of the formed cured coating film was evaluated using a voltage resistance tester manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd. under conditions of a set voltage of 12 kV, a set current of 9999 μA, and a voltage rise rate of 500 V / sec.

[0055] As shown in Table 1, in Examples 1 and 2, which used polyamic acids obtained by polyaddition reaction of ester-type acid dianhydride with diamines containing dimer diamine at a molar ratio of 0.3 or more to the total diamine components, polyimides were produced that had low dielectric constants, dielectric loss tangents, and water absorption coefficients, and thus exhibited low dielectric properties and low moisture absorption.

[0056] On the other hand, in Comparative Example 1, in which tetracarboxylic dianhydride was used as the acid dianhydride instead of an ester-type acid dianhydride, the water absorption rate was higher than in Examples 1 and 2, and it was not possible to prepare a polyimide exhibiting the desired low moisture absorption. Note that, since Comparative Example 1 exhibited high absorbency, the dielectric constant and dielectric loss tangent were not measured after heating for 200 hours in an atmosphere at a temperature of 85°C and a humidity of 80 RH%.

[0057] In Comparative Examples 2 and 3, in which the molar ratio of dimer diamine to the total diamine components was less than 0.3, the dielectric constant and dielectric dissipation factor were both high, and it was not possible to produce polyimides exhibiting the desired low dielectric properties. In particular, Comparative Example 3, which did not contain dimer diamine as a diamine, had a higher dielectric constant and dielectric dissipation factor than Examples 1 and 2 and Comparative Examples 1 and 2. Furthermore, because thermal imidization was not complete, dehydration behavior occurred, weight loss was rapid, and thermal decomposition resistance was poor. Because Comparative Examples 2 and 3 exhibited high dielectric constants and dielectric dissipation factors, their absorbency was not measured. In Comparative Example 2, the dielectric constant and dielectric dissipation factor were not measured after heating for 200 hours in an atmosphere at a temperature of 85°C and a humidity of 80% RH. [Industrial Applicability]

[0058] The polyamic acid of the present invention can form polyimides that exhibit not only good insulating properties and mechanical strength but also low dielectric properties and low moisture absorption. Therefore, polyimide films prepared using such polyimides are highly useful, for example, as insulating substrates for printed wiring boards, particularly as base films for flexible printed wiring boards.

Claims

1. A polyamic acid which is a polyaddition reaction product of (A) an ester-type acid dianhydride and (B) at least two diamines, (B1) dimer diamine is contained in a molar ratio of 0.3 or more relative to the total diamine components, The polyamic acid (A) has an ester-type acid dianhydride having a structure represented by the following formula (1): 【Chemical 1】 (In formula (1), Ar is a substituted 4,4'-biphenylylene group, and the substituent includes an alkyl group having 1 to 8 carbon atoms.)

2. The polyamic acid according to claim 1 , wherein the (B) at least two diamines include (B2) an aromatic diamine.

3. A polyamic acid composition comprising the polyamic acid according to claim 1 or 2 and (C) an organic solvent.

4. A polyimide obtained by imidizing the polyamic acid according to claim 1 or 2.

5. A polyimide film comprising the polyimide according to claim 4.

6. A printed wiring board comprising the polyimide film according to claim 5 .

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