Polyimide precursor, polyimide, and flexible printed circuit board

Abstract

To provide a polyimide excellent in dielectric characteristics and breaking elongation, and a polyimide precursor for obtaining the polyimide.SOLUTION: A polyimide precursor comprising structural units derived from diamines and structural units derived from tetracarboxylic acid dianhydrides, and containing 10 mol% or more and 80 mol% or less of structural units derived from dimer diamine in relation to all units of the structural units derived from diamines, with a weight average molecular weight of 15,000 or more and 130,000 or less, is provided for use as a base film for flexible printed circuit boards. Also provided are a resin composition containing this polyimide precursor and polyimide obtained using this polyimide precursor.SELECTED DRAWING: None

Description

Technical Field

[0001] One embodiment of the present invention relates to a polyimide precursor, a resin composition, a polyimide, a polyimide molded article, and a flexible printed circuit board (FPC).

Background Art

[0002] Polyimide has excellent heat resistance, mechanical strength, and high chemical resistance, and is thus applied to various uses. In addition, since polyimide exhibits high insulation properties, it is used as an insulating material in electronic or mechanical parts. Because of such properties, polyimide is used as a coating film such as a substrate or a protective film in displays, solar cells, touch panels, organic EL lighting, millimeter-wave radars, and the like.

[0003] In recent years, due to the demands for miniaturization and weight reduction, higher integration and higher frequencies of electronic components have been required, and it has been desired to further improve the dielectric properties of insulating materials in a wide frequency range including high frequencies. Insulation properties can be obtained by lowering the relative permittivity of the material, but in order to reduce the loss of transmission signals, it is also important to lower the dielectric tangent. Since transmission loss becomes more problematic in the high-frequency region, reduction of the dielectric tangent in the high-frequency region is required.

[0004] Patent Document 1 proposes a polyimide film having a low dielectric constant and a low dielectric tangent and exhibiting solvent insolubility, which contains a dimer diamine in an amount of more than 15 mol% and less than 50 mol% based on the total diamine component. Patent Document 2 proposes a polyimide film having a low dielectric constant and a low coefficient of thermal expansion and excellent in rigidity and toughness, which contains a dimer diamine in an amount of 5 mol% or more and 25 mol% or less based on the total diamine component.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In Patent Document 1, when the blending ratio of the dimer diamine is increased, the dielectric properties are improved. However, since the polyimide becomes solvent-soluble, by limiting the upper limit value of the blending ratio of the dimer diamine, an attempt is made to obtain a solvent-insoluble polyimide film. Further, in Patent Document 1, from the viewpoint of a low coefficient of thermal expansion, a laminate plate is provided in which a polyimide containing a dimer diamine is sandwiched between polyimides having a low coefficient of thermal expansion and not containing a dimer diamine. In Patent Document 2, it is disclosed that in order to exhibit appropriate rigidity and toughness, the elongation of the polyimide film is preferably 50% or more and 90% or less. A polyimide film having excellent toughness has excellent coating film formability and has an advantage that it is easy to form a coating film on a curved surface as a coating resin for electric wires or the like. On the other hand, in the conventional technology, when a dimer diamine is used to improve the dielectric properties, the resulting polyimide film does not have sufficient strength. In such a polyimide, it is difficult to achieve a low dielectric constant and a low dielectric tangent and further increase the strength, and there is a problem that the elongation at break cannot be sufficiently obtained in particular.

[0007] One object of the present disclosure is to provide a polyimide excellent in dielectric properties and elongation at break, and a polyimide precursor for obtaining this polyimide. [Means for Solving the Problems]

[0008] Some aspects of the present disclosure are as follows. [1] A polyimide precursor containing a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, containing a structural unit derived from a dimer diamine in an amount of 10 mol% or more and 80 mol% or less based on all the units of the structural unit derived from the diamine, having a weight average molecular weight of 15,000 or more and 130,000 or less, and being for a base film of a flexible printed circuit board. [2] A polyimide precursor containing a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, containing a structural unit derived from a dimer diamine in an amount of 10 mol% or more and less than 50 mol% based on all the units of the structural unit derived from the diamine, and having a weight average molecular weight of more than 50,000 and 130,000 or less. [3] A resin composition containing the polyimide precursor according to [1] or [2]. [4] A polyimide obtained by using the polyimide precursor according to [1] or [2]. [5] A polyimide containing a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, containing a structural unit derived from a dimer diamine in an amount of 5 mol% or more and 80 mol% or less based on all the units of the structural unit derived from the diamine, having an elongation at break of 95% or more, and being for a base film of a high-frequency flexible printed circuit board. [6] A polyimide containing a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, containing a structural unit derived from a dimer diamine in an amount of 5 mol% or more and 80 mol% or less based on all the units of the structural unit derived from the diamine, having an elongation at break of 95% or more, having a glass transition temperature of 200°C or more, and being for a base film of a flexible printed circuit board. [7] A polyimide containing a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, containing a structural unit derived from a dimer diamine in an amount of 10 mol% or more and less than 50 mol% based on all the units of the structural unit derived from the diamine, having an elongation at break of 95% or more, and having a glass transition temperature of 200°C or more. [8] The polyimide according to any one of [4] to [7], having a relative dielectric constant Dk(10 GHz) of 3.3 or less. [9] The polyimide according to any one of [4] to [8], wherein the dielectric loss tangent Df (10 GHz) is 0.003 or less.

[10] The polyimide according to any one of [4] to [9], wherein the glass transition temperature is 300 °C or higher.

[11] A polyimide molded article containing the polyimide according to any one of [4] to

[10] .

[12] A flexible printed circuit board containing the polyimide according to any one of [4] to

[10] .

[13] A flexible printed circuit board containing a base film obtained by using the polyimide according to any one of [4] to

[10] .

[14] A flexible printed circuit board including a base film and a coating film layer formed on the base film, wherein at least the coating film layer is obtained by using the polyimide according to any one of [4] to

[10] .

[15] The flexible printed circuit board according to any one of

[12] to

[14] , which is used for a millimeter-wave radar, a high-frequency antenna, or a high-speed transmission substrate. [Effect of the Invention]

[0009] According to one embodiment, a polyimide excellent in dielectric properties and elongation at break, and a polyimide precursor for obtaining this polyimide can be provided. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited by the following examples.

[0011] (Polyimide Precursor) The polyimide precursor according to an embodiment of the present disclosure is a polyimide precursor obtained by using a diamine and a tetracarboxylic dianhydride, and contains 5 to 80 mol% of a dimer diamine with respect to the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 15,000 to 130,000. In a preferred example, it is a polyimide precursor that includes a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, includes a structural unit derived from a dimer diamine in an amount of 10 mol% or more and 80 mol% or less based on all the units of the structural unit derived from the diamine, has a weight average molecular weight of 15,000 or more and 130,000 or less, and is for a base film of a flexible printed circuit board. In another preferred example, it is a polyimide precursor that includes a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, includes a structural unit derived from a dimer diamine in an amount of 10 mol% or more and less than 50 mol% based on all the units of the structural unit derived from the diamine, and has a weight average molecular weight of more than 50,000 and 130,000 or less. According to these exemplified polyimide precursors, a polyimide excellent in dielectric properties and elongation at break can be provided. This polyimide can be widely applied as a polyimide molded body and is suitable for applications that require high insulation.

[0012] The polyimide formed using this polyimide precursor is considered to be able to achieve a lower dielectric constant due to an increase in free volume by having the skeleton of the dimer diamine. Further, this polyimide is considered to be able to obtain a low dielectric tangent because the introduction of the long-chain structure derived from the dimer diamine reduces the concentration of imide groups and relatively decreases the polar groups.

[0013] Polyimides with a low dielectric constant can be widely used as insulating materials. To reduce transmission loss, it is preferable to have a low dielectric constant and a low dielectric tangent. Since the transmission loss tends to increase as the frequency increases, it is also preferable to have a low dielectric tangent in the high-frequency region. The polyimide obtained using the polyimide precursor of one embodiment can have a low dielectric constant and a low dielectric tangent, and shows such a tendency even in the high-frequency region. Such polyimides can be used in various electronic components and mechanical parts, for example, they can be used in displays, solar cells, touch panels, organic EL lighting, millimeter-wave radars, high-frequency antennas, substrates for high-speed transmission, etc. Among these, they can be preferably used in devices used in the high-frequency region, for example, millimeter-wave radars, high-frequency antennas, substrates for high-speed transmission, etc. A millimeter-wave radar is a radar that transmits millimeter waves to an object, receives the reflected waves from the object, and detects the object. In-vehicle millimeter-wave radars mounted on vehicles, etc., are applied to collision prevention systems, automatic driving systems, etc. In high-frequency antennas, there are requirements for high frequencies and high-speed transmission for high-speed communication in communication devices, etc. When accommodating a high-frequency antenna in a housing in small communication devices, etc., a material with a lower dielectric constant and a lower dielectric tangent is desired. Examples of substrates for high-speed transmission include high-speed transmission cables and high-speed transmission connectors, etc. Since the polyimide precursor of one embodiment has a high weight average molecular weight, the resulting polyimide has a high elongation at break and can be formed into various applications such as films, substrates, and molded articles. This polyimide can be used, for example, in flexible printed circuit boards. Since this polyimide has a high elongation at break, it can be used as a base film for flexible printed circuit boards even if it is a single layer of polyimide. Also, when this polyimide is formed into a film on a substrate, since it is a film with a high elongation at break, damage to the film can be prevented when the substrate with the film formed thereon is bent. For example, it can be used in flexible printed circuit boards such as displays, solar cells, touch panels, organic EL lighting, millimeter wave radars, high frequency antennas, and substrates for high-speed transmission, particularly as a base film for flexible printed circuit boards. Among them, from the perspective that characteristics of having a low dielectric constant and a low dielectric tangent in the high frequency region are required, and further miniaturization and thinning of the device are required, it can be preferably used in high frequency flexible printed circuit boards, specifically high frequency flexible printed circuit boards used in millimeter wave radars, high frequency antennas, substrates for high-speed transmission, etc., particularly as a base film for high frequency flexible printed circuit boards. The high frequency flexible printed circuit board is preferably one that can be used in a frequency range of, for example, 1 GHz or more, 5 GHz or more, or 10 GHz or more. Also, the high frequency flexible printed circuit board for millimeter wave radar is preferably one that can be used in a frequency range of 30 to 300 GHz.

[0014] Since the polyimide precursor of one embodiment has a weight average molecular weight of 15,000 to 130,000, the chemical resistance and water resistance of the resulting polyimide can be enhanced. Polyimide is also a material with excellent heat resistance. For example, in a high-temperature environment or in applications where it comes into contact with chemicals or water, hydrolysis and other forms of degradation can be suppressed in this polyimide, and it can exhibit excellent dielectric properties. Such properties are useful for components used in high-temperature environments, such as electronic components installed near an automobile engine. For example, it is useful in applications where transmission loss in the high-frequency region is a problem, such as in in-vehicle millimeter-wave radars. Since this polyimide has flexibility, by using it for the substrate, protective film, or a combination thereof of an in-vehicle millimeter-wave radar, it can have excellent dielectric properties and can be installed by deforming the base material according to the shape of the vehicle body.

[0015] The polyimide precursor according to one embodiment can be obtained by synthesizing a polyamic acid using a diamine compound and a tetracarboxylic dianhydride compound. This synthesis can be carried out by mixing and polymerizing the diamine compound and the tetracarboxylic dianhydride compound in an organic solvent.

[0016] The polyimide precursor can contain a dimer diamine as a diamine component. The dimer diamine is a compound derived from dimer acid, specifically, a compound derived from dimer acid which is a dimer of unsaturated fatty acids such as oleic acid and linoleic acid. The dimer diamine is, for example, a compound represented by the following general formulas (1) to (4). These dimer diamines may be used alone or in combination of two or more.

[0017]

Chemical formula

[0018]

Chemical formula

[0019] In the above general formulas (1) to (4), m, n, p, and q are integers satisfying m + n = 6 to 17 and p + q = 8 to 19. In general formula (4), the dashed line indicates a single bond or a double bond, and all three dashed lines may all be single bonds, or some or all of them may be double bonds. In general formula (4), x is CH x 2 when the dashed line between them is a single bond and 1 when it is a double bond. The dimer diamine is preferably a compound having a carbocyclic structure, more preferably a compound represented by general formula (4). In the compound represented by general formula (4), it is preferable that the dashed line on the carbocyclic structure is a single bond, both of the dashed lines of the carbon chain are single bonds, or a combination thereof, and it is preferable that all the dashed lines are single bonds. In general formula (4), m + n = 10 to 12, p + q = 10 to 12, or a combination thereof is preferable.

[0020] Examples of commercially available dimer diamines include "PRIAMINE 1075, PRIAMINE 1074" manufactured by Croda Japan Co., Ltd. (both are trade names).

[0021] The polyimide precursor according to one embodiment can contain the dimer diamine in an amount of 5 to 80 mol% based on the diamine component contained in the polyimide precursor.

[0022] From the viewpoint of lowering the relative permittivity and dielectric tangent of the resulting polyimide, the dimer diamine is preferably 5 mol% or more, more preferably 10 mol% or more, still more preferably 20 mol% or more, and still more preferably 25 mol% or more based on the diamine component contained in the polyimide precursor. Regarding the diamine component contained in the polyimide precursor, the dimer diamine is preferably 80 mol% or less, more preferably 50 mol% or less, still more preferably 45 mol% or less, and even more preferably 40 mol% or less, from the viewpoints of the heat resistance, tensile strength, and tensile modulus of the resulting polyimide. From the viewpoint of obtaining high heat resistance, high tensile strength, or high tensile modulus, the proportion of this dimer diamine is preferably 40 mol% or less, more preferably 35 mol% or less, and still more preferably 30 mol% or less.

[0023] For example, regarding the diamine component contained in the polyimide precursor, the dimer diamine is preferably 5 to 80 mol%, more preferably 10 to 80 mol%. Further, it may be 10 to 50 mol% or more than 10 mol% and less than 50 mol%, may be 20 to 40 mol%, or may be 20 to 30 mol%. Within these ranges, the relative permittivity and dielectric loss tangent can be lowered while maintaining various properties.

[0024] Here, the amount of the dimer diamine with respect to the diamine component contained in the polyimide precursor can be determined from the following formula using the molar ratio of the diamine compound introduced into the synthesis system. ((Number of moles of dimer diamine) / (Total number of moles of diamine compound))×100 (mol%)

[0025] The polyimide precursor may contain other diamines other than the dimer diamine as the diamine component of the polyimide precursor. Examples of the other diamines include aromatic diamines, alicyclic diamines, aliphatic diamines, etc., or combinations of two or more of these. By including an aromatic diamine as the diamine component, a decrease in heat resistance can be more effectively prevented.

[0026] In the aromatic diamine, the aromatic ring may be either a monocyclic ring or a polycyclic ring. The polycyclic ring may be a bicyclic ring, a tricyclic ring, a tetracyclic ring, etc., and may be a condensed ring. The aromatic ring may be either an aromatic hydrocarbon ring or an aromatic heterocyclic ring. The aromatic diamine preferably has a monocyclic structure such as a benzene ring, or a bicyclic structure such as biphenyl, diphenylmethane, diphenyl ether, etc. Further, the aromatic diamine may contain substituents such as a nitrogen atom-containing group, a fluorine atom, a sulfonyl group, a sulfo group, an alkyl group, etc.

[0027] Examples of the aromatic diamine include 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, 4,3'-diaminodiphenyl ether, 4,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 3,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diamino-3,3'-diethylbiphenyl, 4,4'-diamino-2,2'-diethylbiphenyl, 4,4'-diamino-3,3'-dimethoxybiphenyl, 4,4'-diamino-2,2'-dimethoxybiphenyl, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 3-aminobenzylamine, 4-aminobenzylamine, tolylenediamine, m-xylylenediamine, p-xylylenediamine, 4,4'-bis(4-aminophenoxy)biphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and the like. Among these, diamines having a benzene ring of 2 to 4 rings, more preferably 2 rings, are preferable. In another aspect, diamines having a phenyl ether structure are preferable. Specifically, 4,4'-diaminodiphenyl ether, 4,3'-diaminodiphenyl ether, 4,4'-bis(4-aminophenoxy)biphenyl, or a combination thereof is preferable, and 4,4'-diaminodiphenyl ether is more preferable.

[0028] In the alicyclic diamine, the alicyclic structure may be any of cycloalkane, cycloalkene, and cycloalkyne, and may be either a monocyclic structure or a polycyclic structure such as bicyclic, tricyclic, or tetracyclic. In the alicyclic diamine, the number of carbon atoms in the alicyclic structure is preferably 3 to 20, more preferably 4 to 12, and even more preferably 6 to 10. This alicyclic structure is preferably cycloalkane, and examples thereof include cycloalkanes such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, and norbornane, and polycyclic structures having two or more of these cycloalkanes. Further, the alicyclic diamine may contain substituents such as nitrogen atom-containing groups, fluorine atoms, sulfonyl groups, sulfo groups, and alkyl groups.

[0029] Examples of the alicyclic diamine include 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(2-methylcyclohexylamine), 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-cyclohexanediamine, 1,4-cyclohexanediamine, isophoronediamine, norbornanediamine, bis(aminomethyl)norbornane, and hydrogenated m-xylylenediamine.

[0030] Examples of the aliphatic diamine include aliphatic diamines having a saturated or unsaturated hydrocarbon group with 4 to 20 carbon atoms, preferably 6 to 10 carbon atoms per molecule, and specific examples include hexamethylenediamine and 2,2,4-trimethylhexamethylenediamine.

[0031] The other diamines described above may be used alone or in combination of two or more. By using a combination of two or more diamine compounds, in a resin composition containing a polyimide precursor, the fluidity can be improved and the coatability can be further improved. This is presumably because when two or more diamine compounds are mixed, the formation of by-products such as hardly soluble salts in the resin composition can be suppressed.

[0032] Examples of the tetracarboxylic dianhydride component of the polyimide precursor include aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, aliphatic tetracarboxylic dianhydrides, etc., or combinations of two or more of these. By including an aromatic tetracarboxylic dianhydride as the tetracarboxylic dianhydride component, a decrease in heat resistance can be further prevented.

[0033] In the aromatic tetracarboxylic dianhydride, the aromatic ring may be either a monocyclic or polycyclic ring. The polycyclic ring may be a bicyclic, tricyclic, tetracyclic, etc. ring and may be a condensed ring. The aromatic ring may be either an aromatic hydrocarbon ring or an aromatic heterocyclic ring. The aromatic tetracarboxylic dianhydride preferably has a monocyclic structure such as a benzene ring or a bicyclic structure such as biphenyl, diphenylmethane, diphenyl ether, etc. Further, the aromatic tetracarboxylic dianhydride may contain substituents such as a nitrogen atom-containing group, a fluorine atom, a sulfonyl group, a sulfo group, an alkyl group, etc.

[0034] Examples of the aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,4'-oxydiphthalic anhydride, 4,4'-sulfonyldiphthalic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,5,6-pyrenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, m-terphenyl-3,3',4,4'-tetracarboxylic dianhydride, 2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis[4-(2,3- or 3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, and the like. Among these, tetracarboxylic dianhydrides having benzene rings of 1 to 2 rings are preferred. For example, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, or a combination thereof is preferred. Among them, tetracarboxylic dianhydrides having a benzene ring of 1 ring are preferred. For example, pyromellitic dianhydride is preferred. In this case, the tetracarboxylic dianhydride having a benzene ring of 1 ring may be 30 mol% or more based on the tetracarboxylic dianhydride component, preferably 50 mol% or more, and may be 80 to 100 mol%. The tetracarboxylic dianhydride having a benzene ring of 1 to 2 rings, more preferably a benzene ring of 1 ring, has a high imide group concentration contributing to the intermolecular orientation and can increase the glass transition temperature.

[0035] In the alicyclic tetracarboxylic dianhydride, the alicyclic structure may be any of cycloalkane, cycloalkene, and cycloalkyne, and may be any of monocyclic structure, polycyclic structures such as bicyclic, tricyclic, and tetracyclic structures. In the alicyclic tetracarboxylic dianhydride, the number of carbon atoms in the alicyclic structure is preferably 3 to 20, more preferably 4 to 12, and even more preferably 6 to 10. Examples of this alicyclic structure include cycloalkanes such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, and cyclododecane, and polycyclic structures having two or more of these cycloalkanes. Further, the alicyclic tetracarboxylic dianhydride may contain substituents such as a nitrogen atom-containing group, a fluorine atom, a sulfonyl group, a sulfo group, and an alkyl group.

[0036] Examples of the alicyclic tetracarboxylic dianhydride include 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride, bicyclo[2.2.2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, and the like.

[0037] Examples of the aliphatic tetracarboxylic dianhydride include aliphatic tetracarboxylic dianhydrides having a saturated or unsaturated hydrocarbon group with 4 to 20 carbon atoms, preferably 6 to 10 carbon atoms per molecule, and specifically include butanetetracarboxylic dianhydride and the like. The above-described tetracarboxylic dianhydrides may be used alone or in combination of two or more.

[0038] In one embodiment, the weight average molecular weight of the polyimide precursor is preferably from 15,000 to 130,000. The weight average molecular weight of the polyimide precursor is more preferably 50,000 or more than 50,000 and 130,000 or less. From the viewpoints of the elongation at break, heat resistance, tensile strength, and tensile modulus of the obtained polyimide, particularly from the viewpoint of the elongation at break, the weight average molecular weight of the polyimide precursor is preferably 15,000 or more, more preferably 30,000 or more, still more preferably 50,000 or more than 50,000, and even more preferably 60,000 or more. Also, within these ranges, the film-forming property can be further improved when forming a paint. From the viewpoints of the elongation at break, heat resistance, tensile strength, and tensile modulus of the obtained polyimide, the weight average molecular weight of the polyimide precursor may be 65,000 or more, 70,000 or more, 75,000 or more, or 80,000 or more. From the viewpoint of suppressing the increase in viscosity, the weight average molecular weight of the polyimide precursor is preferably 130,000 or less, more preferably 100,000 or less. In applications where a lower viscosity is required, it may be 90,000 or less, or 80,000 or less. By suppressing the increase in viscosity, the coating property can be further improved when forming a paint.

[0039] In one embodiment, the number average molecular weight of the polyimide precursor is preferably from 10,000 to 80,000. The number average molecular weight of the polyimide precursor is preferably 10,000 or more, more preferably 20,000 or more, still more preferably 30,000 or more, and even more preferably 40,000 or more from the viewpoints of the elongation at break, heat resistance, tensile strength, and tensile modulus of the obtained polyimide, particularly from the viewpoint of the elongation at break, and also from the viewpoint of the film-forming property when forming a paint. The number average molecular weight of the polyimide precursor is preferably 80,000 or less, more preferably 60,000 or less, still more preferably 55,000 or less, and even more preferably 50,000 or less from the viewpoint of suppressing the increase in viscosity. By suppressing the increase in viscosity, the coating property can be further improved when forming a paint.

[0040] In the present disclosure, the weight average molecular weight (Mw) and number average molecular weight (Mn) of the resin are measured by gel permeation chromatography (GPC) and converted using a calibration curve of standard polystyrene. The calibration curve is approximated by a cubic equation using a set of 5 samples of standard polystyrene (TSK standard POLYSTYRENE [manufactured by Tosoh Corporation, trade name]). The conditions of GPC are as shown below. GPC apparatus: High-speed GPC apparatus HLC-8320GPC (manufactured by Tosoh Corporation, trade name) Detector: Ultraviolet absorption detector UV-8320 (manufactured by Tosoh Corporation, trade name) Column: Gelpack GL-S300MDT-5 (total 2 columns) (manufactured by Showa Denko Materials Co., Ltd., trade name) Eluent: THF / DMF = 1 / 1 (volume ratio) + LiBr (0.06 mol / L) + H 3 PO 4 (0.06 mol / L) Flow rate: 1 mL / min Column size: 8 mm I.D. × 300 mm Sample concentration: 5 mg / 1 mL Injection volume: 5 μL Measurement temperature: 40 °C

[0041] An example of the polyimide precursor contains 5 to 20 mol% of dimer diamine with respect to the diamine component contained in the polyimide precursor and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 3.3 or less, a dielectric loss tangent of 0.005 or less, or both. An example of the polyimide precursor contains 10 to 20 mol% of dimer diamine with respect to the diamine component contained in the polyimide precursor and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 3.0 or less, a dielectric loss tangent of 0.003 or less, or both. Another example of a polyimide precursor contains a dimer diamine in an amount of 20 mol% or more and 50 mol% or less based on the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 2.9 or less, a dielectric tangent of 0.0015 or less, or both. Another example of a polyimide precursor contains a dimer diamine in an amount of 20 mol% or more and 30 mol% or less based on the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 2.9 or less, a dielectric tangent of 0.0015 or less, or both. Another example of a polyimide precursor contains a dimer diamine in an amount of 20 mol% to 80 mol% based on the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 2.9 or less, a dielectric tangent of 0.0015 or less, or both. Still another example of a polyimide precursor contains a dimer diamine in an amount of 30 mol% to 80 mol% based on the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 2.7 or less, a dielectric tangent of 0.0015 or less, or both. Still another example of a polyimide precursor contains a dimer diamine in an amount of 50 mol% to 80 mol% based on the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 60,000 or more. The polyimide obtained using the polyimide precursor of this example has a high elongation at break and can satisfy a relative dielectric constant of 2.7 or less, a dielectric tangent of 0.0015 or less, or both.

[0042] The polyimide precursor according to one embodiment may have the above-described configuration and is not limited to its manufacturing method. Hereinafter, an example of the manufacturing method of the polyimide precursor will be described, but the polyimide precursor according to one embodiment is not limited to being manufactured by the following manufacturing method.

[0043] As one method of the manufacturing method of the polyimide precursor, it can include reacting a diamine compound and a tetracarboxylic dianhydride compound. The diamine compound can include a dimer diamine. In addition to the dimer diamine, the diamine compound may also include other diamines such as aromatic diamines, alicyclic diamines, and aliphatic diamines. The tetracarboxylic dianhydride compound can include aromatic tetracarboxylic dianhydrides, alicyclic tetracarboxylic dianhydrides, aliphatic tetracarboxylic dianhydrides, and the like. Details of the diamine compound and the tetracarboxylic dianhydride compound are as described above. The mixing ratio of the diamine compound and the tetracarboxylic dianhydride compound may be, for example, approximately 1:1 in molar ratio and can be adjusted within the range of 1.00:0.95 to 1.00 to 1.05.

[0044] The reaction between the diamine compound and the tetracarboxylic dianhydride can be carried out by solution polymerization. Examples of the synthesis solvent include polar solvents such as N-methyl-2-pyrrolidone, N,N'-dimethylformamide, γ-butyrolactone, N,N'-dimethylpropyleneurea [1,3-dimethyl-3,4,5,6-tetrahydropyrimidin-2(1H)-one], dimethyl sulfoxide, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, sulfolane, and dimethylacetamide; aromatic hydrocarbon solvents such as xylene and toluene; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. These may be used alone or in combination of two or more.

[0045] The amount of the synthesis solvent used during the reaction is preferably 100 to 600 parts by mass, more preferably 200 to 400 parts by mass, based on 100 parts by mass of the total amount of diamine and tetracarboxylic dianhydride. When the amount of the synthesis solvent used is 100 parts by mass or more, each component can react homogeneously. When the amount of the synthesis solvent used is 600 parts by mass or less, the polymerization reaction can be promoted. Further, when the amount of the synthesis solvent used is small, the resin concentration of the obtained resin composition can be increased, and the coating film can be made thicker during coating.

[0046] The polyimide precursor synthesized by the method described above can have a weight average molecular weight within the above range. For example, the weight average molecular weight can be adjusted by sampling the polyimide precursor during synthesis and continuing the synthesis until the target weight average molecular weight is reached. The number average molecular weight of the polyimide precursor can be adjusted in the same manner as the weight average molecular weight. The reaction temperature is not particularly limited, and the reaction can proceed by mixing the raw materials in the synthesis solvent. For example, it may be 50°C or lower, 40°C or lower, 10°C or higher, or 20°C or higher. From the viewpoint of obtaining a high molecular weight polyimide precursor, the reaction time is preferably 3 hours or more, more preferably 5 hours or more, and even more preferably 8 hours or more. The end point of the reaction can be determined by sampling the reaction product and measuring the weight average molecular weight until the target weight average molecular weight is reached.

[0047] Using the polyimide precursor described above, polyimide can be provided. Since this polyimide has a low dielectric constant and a low dielectric tangent, it can be preferably used for an insulating polyimide molded article. Since this polyimide is obtained by dehydrative ring closure of a high molecular weight polyimide precursor, it is possible to provide a polyimide molded article excellent in elongation at break, heat resistance, tensile strength, and tensile modulus, particularly a polyimide molded article with a high elongation at break. Such a polyimide molded article is useful for various applications that require dielectric properties and elongation at break, and is useful, for example, for application to a flexible printed circuit board.

[0048] (Resin Composition) The resin composition according to one embodiment of the present disclosure is characterized by containing the polyimide precursor according to the above-described one embodiment. In a preferred example, the polyimide precursor is a polyimide precursor obtained using a diamine and a tetracarboxylic dianhydride, and contains 5 to 80 mol% of a dimer diamine with respect to the diamine component contained in the polyimide precursor, and has a weight average molecular weight of 15,000 to 130,000. In another preferred example, it contains a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, contains a structural unit derived from a dimer diamine in an amount of 10 mol% or more and 80 mol% or less with respect to all the units of the structural unit derived from the diamine, and has a weight average molecular weight of 15,000 or more and 130,000 or less. It is a resin composition for a base film of a flexible printed circuit board. In still another preferred example, it contains a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, contains a structural unit derived from a dimer diamine in an amount of 10 mol% or more and less than 50 mol% with respect to all the units of the structural unit derived from the diamine, and has a weight average molecular weight of more than 50,000 and 130,000 or less. It is a resin composition containing a polyimide precursor. Details of the polyimide precursor contained in the resin composition are as described above. This resin composition can contain a solvent together with the polyimide precursor. As the solvent, those mentioned as the synthesis solvent in the above-described method for producing the polyimide precursor can be used. When solution-polymerizing the polyimide precursor, this resin composition may use the mixture of the obtained polyimide precursor and the synthesis solvent as it is. Also, it may be one from which the excess synthesis solvent has been removed from the obtained mixture, or one to which a diluting solvent has been further added. The resin content of this resin composition is preferably 5 to 50% by mass, more preferably 10 to 30% by mass. Within these ranges, it can be adjusted to a more preferable viscosity range as a paint. This resin composition can be preferably used as a resin composition for a flexible printed circuit board.

[0049] The viscosity of the resin composition is preferably 1 to 10 Pa·s, more preferably 1 to 5 Pa·s at 30°C. In the present disclosure, the viscosity is a value measured at 30°C using a No. 3 rotor in a rotational B-type viscometer.

[0050] This resin composition may contain additives as necessary. Examples of the additives include colorants such as pigments and dyes, inorganic fillers, organic fillers, lubricants, and the like. By including a filler with a low dielectric constant in the resin composition, it becomes possible to further lower the dielectric constant of the resulting polyimide molded body. On the other hand, since the polyimide according to one embodiment exhibits a low dielectric constant by itself, it can also be preferably applied to uses where the polyimide molded body does not contain a filler from the viewpoint of flexibility. For example, the filler may be 10% by mass or less, 5% by mass or less, or 1% by mass or less based on the total mass of the polyimide molded body, and the polyimide molded body may not substantially contain a filler.

[0051] (Polyimide) The polyimide according to one embodiment of the present disclosure is characterized in that it is a polyimide obtained using the polyimide precursor according to the above-described one embodiment. The polyimide according to another embodiment of the present disclosure includes a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, and includes a structural unit derived from a dimer diamine in an amount of 5 to 80 mol% based on all the units of the structural unit derived from the diamine, and has an elongation at break of 95% or more. In a preferred example, it includes a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, includes a structural unit derived from a dimer diamine in an amount of 5 mol% or more and 80 mol% or less based on all the units of the structural unit derived from the diamine, has an elongation at break of 95% or more, and is a polyimide for a base film of a high-frequency flexible printed circuit board. In another preferred example, it is a polyimide that includes a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, includes a structural unit derived from a dimeric diamine in an amount of 5 mol% or more and 80 mol% or less based on all the units of the structural unit derived from the diamine, has an elongation at break of 95% or more, a glass transition temperature of 200 °C or more, and is for a base film of a flexible printed circuit board. In yet another preferred example, it is a polyimide that includes a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, includes a structural unit derived from a dimeric diamine in an amount of 10 mol% or more and less than 50 mol% based on all the units of the structural unit derived from the diamine, has an elongation at break of 95% or more, and a glass transition temperature of 200 °C or more. These exemplified polyimides can have a high elongation at break and can have a low dielectric constant and a low dielectric tangent. By using this polyimide, a polyimide molded article excellent in dielectric properties and elongation at break can be provided.

[0052] The polyimide can include a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride. In the polyimide, the structural unit derived from a diamine may be a structural unit derived from a diamine that can be used in the above-described polyimide precursor. In the polyimide, the structural unit derived from a tetracarboxylic dianhydride may be a structural unit derived from a tetracarboxylic dianhydride that can be used in the above-described polyimide precursor. In the polyimide, one or more structural units derived from a diamine may be combined and included, and one or more structural units derived from a tetracarboxylic dianhydride may be combined and included.

[0053] In the polyimide, the structural unit derived from a diamine can include a structural unit derived from a dimeric diamine. In the polyimide, the structural unit derived from a dimeric diamine may be a structural unit derived from a dimeric diamine that can be used in the above-described polyimide precursor. In the polyimide, it can contain structural units derived from dimer diamine in an amount of 5 to 80 mol% based on all the units of the structural units derived from diamine. From the viewpoint of reducing the relative permittivity and dielectric loss tangent of the polyimide, the units derived from dimer diamine are preferably 5 mol% or more, more preferably 10 mol% or more, still more preferably 20 mol% or more, and even more preferably 25 mol% or more based on all the units of the structural units derived from diamine. From the viewpoint of preventing a decrease in the heat resistance, tensile strength, and tensile modulus of elasticity of the polyimide, the units derived from dimer diamine are preferably 80 mol% or less, more preferably 50 mol% or less, still more preferably 45 mol% or less, and even more preferably 40 mol% or less based on all the units of the structural units derived from diamine. From the viewpoint of obtaining high heat resistance, high tensile strength, or high tensile modulus of elasticity, the proportion of this dimer diamine is preferably 40 mol% or less, more preferably 35 mol% or less, and still more preferably 30 mol% or less. From the viewpoint of reducing the relative permittivity and dielectric loss tangent while maintaining various properties, for example, the units derived from dimer diamine are preferably 5 to 80 mol%, more preferably 10 to 80 mol% based on all the units of the structural units derived from diamine. Further, 10 to 50 mol% or more than 10 mol% and less than 50 mol% is preferable, 20 to 40 mol% is more preferable, and it may be 20 to 30 mol%.

[0054] The polyimide preferably has an elongation at break of 95% or more. From the viewpoint of obtaining a molded article having flexibility, the elongation at break of the polyimide is preferably 95% or more, more preferably 100% or more, still more preferably 110% or more, even more preferably 120 mol% or more, and even more preferably 150% or more. By having an elongation at break within these ranges, it can be usefully used for molded articles that require bending stress, such as flexible printed circuit boards. The elongation at break of the polyimide is not particularly limited, but it may be 500% or less, may be 400% or less, and may further be 350% or less. For example, the elongation at break of the polyimide is preferably 95 to 500%, may be 100 to 400%, and may further be 150 to 350%.

[0055] The polyimide preferably has a tensile strength of 10 to 400 MPa. From the perspective of material strength, the tensile strength of the polyimide is preferably 10 MPa or more, more preferably 50 MPa or more, still more preferably 70 MPa or more, and even more preferably 80 MPa or more. The tensile strength of the polyimide is preferably 400 MPa or less, more preferably 300 MPa or less, and may be 200 MPa or less. By having a tensile strength within these ranges, the stretching process during film production can be preferably carried out, and a film excellent in in-plane properties can be obtained by orienting the molecular chains.

[0056] The polyimide preferably has a tensile modulus of 0.1 to 5 GPa. From the perspective of material strength, the tensile modulus of the polyimide is preferably 0.1 GPa or more, more preferably 0.3 GPa or more, and may be 0.5 GPa or more. If it is less than 0.1 GPa, when mounting a semiconductor element, a phenomenon may occur in which the wiring circuit and the semiconductor element sink into the polyimide molded body. The tensile modulus of the polyimide is preferably 5 GPa or less, more preferably 3 GPa or less, still more preferably 2.0 GPa or less, and even more preferably 1.6 GPa or less. By having a tensile modulus within these ranges, problems such as peeling or disconnection due to repulsive force during use in an in-vehicle millimeter-wave radar module or an excessive radius during bending, which requires extra space, can be improved.

[0057] In the present disclosure, the tensile strength of the polyimide is defined as the maximum tensile stress applied during the tensile test when a polyimide test piece with a width of 10 mm, a length of 60 mm, and a thickness of 25 μm is set in a tensile testing machine at a chuck distance of 20 mm and pulled at a speed of 5 mm / min at 25°C. The elongation at break is a value obtained by dividing the amount of elongation of the test piece until it breaks by the chuck distance of 20 mm in a test under the same conditions. The tensile modulus is a value obtained by calculating the Young's modulus (MPa) from the slope of the elastic deformation region at the initial stage of stress rise in a test under the same conditions. Other detailed conditions and calculation methods conform to the international standard ISO527-1:2019. As the tensile testing apparatus, for example, "Autograph AGS-100NG" manufactured by Shimadzu Corporation can be used.

[0058] An example of the polyimide contains 5 to 20 mol% of the structural units derived from the dimer diamine with respect to all the units of the structural units derived from the diamine and has an elongation at break of 95% or more. The polyimide of this example can satisfy a relative permittivity of 3.3 or less, a dielectric loss tangent of 0.005 or less, or both. An example of the polyimide contains 10 to 20 mol% of the structural units derived from the dimer diamine with respect to all the units of the structural units derived from the diamine and has an elongation at break of 95% or more, preferably 100% or more. The polyimide of this example can satisfy a relative permittivity of 3.0 or less, a dielectric loss tangent of 0.003 or less, or both. Another example of the polyimide contains 20 mol% or more and less than 50 mol% or 50 mol% of the structural units derived from the dimer diamine with respect to all the units of the structural units derived from the diamine and has an elongation at break of 95% or more, preferably 150% or more. The polyimide of this example can satisfy a relative permittivity of 2.9 or less, a dielectric loss tangent of 0.0015 or less, or both. Another example of the polyimide contains, based on all units of the structural units derived from diamine, 20 mol% or more and less than 30 mol% or 30 mol% of the structural units derived from dimer diamine, and has an elongation at break of 95% or more, preferably 150% or more. The polyimide of this example can satisfy a relative dielectric constant of 2.9 or less, a dielectric loss tangent of 0.0015 or less, or both. Another example of the polyimide contains 20 mol% to 80 mol% of the structural units derived from dimer diamine based on all units of the structural units derived from diamine, and has an elongation at break of 95% or more, preferably 150% or more. The polyimide of this example can satisfy a relative dielectric constant of 2.9 or less, a dielectric loss tangent of 0.0015 or less, or both. Still another example of the polyimide contains 30 mol% to 80 mol% of the structural units derived from dimer diamine based on all units of the structural units derived from diamine, and has an elongation at break of 95% or more, preferably 150% or more, more preferably 300% or more. The polyimide of this example can satisfy a relative dielectric constant of 2.7 or less, a dielectric loss tangent of 0.0015 or less, or both. Still another example of the polyimide contains 50 mol% to 80 mol% of the structural units derived from dimer diamine based on all units of the structural units derived from diamine, and has an elongation at break of 95% or more, preferably 150% or more, more preferably 300% or more. The polyimide of this example can satisfy a relative dielectric constant of 2.7 or less, a dielectric loss tangent of 0.0015 or less, or both.

[0059] From the viewpoint of heat resistance, the glass transition temperature (Tg) of the polyimide is preferably 200 to 500°C, more preferably 300 to 500°C. From the viewpoint of heat resistance, the glass transition temperature of the polyimide is preferably 200°C or higher, more preferably 250°C or higher, further preferably 300°C or higher, and still more preferably 350°C or higher. In the polyimide containing 5 mol% or more and less than 30 mol% of the structural units derived from dimer diamine based on all units of the structural units derived from diamine, the glass transition temperature is preferably 300 to 500°C, more preferably 350 to 500°C, and further preferably 380 to 500°C. In a polyimide containing a structural unit derived from a dimer diamine in an amount of 30 mol% or more and less than 50 mol% based on all the structural units derived from a diamine, the glass transition temperature is preferably 200 to 500 °C, more preferably 300 to 500 °C, and even more preferably 320 to 500 °C. In a polyimide containing a structural unit derived from a dimer diamine in an amount of 50 mol% or more and 80 mol% or less based on all the structural units derived from a diamine, the glass transition temperature is preferably 200 to 500 °C, more preferably 250 to 500 °C, and even more preferably 300 to 500 °C. In the present disclosure, the glass transition temperature is measured using a thermomechanical analyzer by preparing a sample piece having a width of 4 mm, a length of 25 mm, and a thickness of 25 μm and following the following procedure. First, the sample piece is heated from room temperature (20 °C) to 350 °C at a rate of 10 °C / min in a nitrogen atmosphere under a chuck distance of 10 mm, a load of 10 g, and a tensile mode, held for 30 minutes, and then cooled to 30 °C at a rate of 10 °C / min to remove residual stress. Subsequently, this sample piece is heated and measured at a rate of 10 °C / min from 20 °C to 500 °C in a nitrogen atmosphere under a chuck distance of 10 mm by a tensile method, and the temperature corresponding to the inflection point is determined as the glass transition temperature (°C).

[0060] From the viewpoint of heat resistance, the 5% thermogravimetric temperature (T d5 ) of the polyimide is preferably 200 to 600 °C, and more preferably 300 to 500 °C. In the present disclosure, T d5 is measured in an inert atmosphere at a heating rate of 10 °C per minute in the range from 50 °C to 500 °C, and is the temperature at which 5% of the weight has decreased from the initial stage.

[0061] From the viewpoint of obtaining a polyimide molded body with high insulation, the relative permittivity of the polyimide is preferably 3.3 or less, and more preferably 3.0 or less. Further, the relative permittivity of the polyimide is preferably 2.0 or more and 3.3 or less, and more preferably 2.0 or more and 3.0 or less. More specifically, the relative permittivity of the polyimide is preferably 2.00 to 3.30. From the viewpoint of insulation, the relative permittivity of the polyimide is preferably 3.30 or less, more preferably 3.20 or less, still more preferably 3.00 or less, even more preferably 2.80 or less, and may be 2.60 or less. The relative permittivity of the polyimide is not particularly limited, but may be 2.00 or more from the viewpoints of preventing a decrease in heat resistance, tensile strength, and tensile modulus of elasticity.

[0062] From the viewpoint of obtaining a polyimide molded body with low transmission loss, the dielectric tangent of the polyimide is preferably 0.015 or less, and preferably 0.003 or less. Further, the dielectric tangent of the polyimide is preferably 0.0001 or more and 0.015 or less, and more preferably 0.0005 or more and 0.003 or less. More specifically, from the viewpoint of reducing transmission loss, the dielectric tangent of the polyimide is preferably 0.0150 or less, more preferably 0.0100 or less, and still more preferably 0.0050 or less. Further, for applications with higher insulation properties, the dielectric tangent of the polyimide is preferably 0.0030 or less, more preferably 0.0025 or less, and still more preferably 0.0015 or less. The dielectric tangent of the polyimide is not particularly limited, but may be 0.0001 or more, and may be 0.0005 or more. In the present disclosure, the relative permittivity and dielectric tangent of the polyimide can be determined from the capacitance value and thickness of the sample piece according to the cavity resonator perturbation method. Specifically, the relative permittivity and dielectric tangent can be measured by the cavity resonator method (TE mode) using a sample piece obtained by cutting out polyimide into a size of 60 mm × 60 mm and a thickness of 25 μm. The measurement conditions are a frequency of 10 GHz and a measurement temperature of 25°C.

[0063] The polyimide having the above-described characteristics can be obtained using the above-described polyimide precursor, but is not limited to those obtained by this method. By subjecting a high molecular weight polyimide precursor to dehydration ring closure, a polyimide having the above-described elongation at break can be obtained.

[0064] (Molded Body and Flexible Printed Circuit Board) The polyimide molded article according to one embodiment of the present disclosure is characterized by including the polyimide according to the above-described one embodiment. The polyimide molded article according to another embodiment of the present disclosure is characterized by being formed using the resin composition according to the above-described one embodiment. The polyimide molded article may be a plate-like substrate, a coating film applied to a base material, various shapes that can be molded by a mold, and the like. Further, the flexible printed circuit board (FPC) according to one embodiment of the present disclosure is characterized by including the polyimide according to the above-described one embodiment. The flexible printed circuit board according to another embodiment of the present disclosure is characterized by including a polyimide obtained using the above-described resin composition. Since the polyimide obtained using the polyimide precursor or resin composition of one embodiment has a low dielectric constant and a low dielectric tangent, it can provide a substrate with high insulation when used for a flexible printed circuit board. Further, since the polyimide according to one embodiment has high heat resistance and flexibility, it can be preferably applied to a flexible printed circuit board. Such a flexible printed circuit board is excellent in dielectric characteristics, heat resistance, and elongation at break, and thus is useful for applications to in-vehicle pressure sensors, angle sensors, flexible printed circuit boards for inverter wiring, substrates for millimeter-wave radars such as in-vehicle millimeter-wave radars, and the like. Furthermore, it can be suitably used for high-frequency flexible printed circuit boards, specifically, high-frequency flexible printed circuit boards used for millimeter-wave radars, high-frequency antennas, substrates for high-speed transmission, and the like.

[0065] As an example of the flexible printed circuit board, it includes a base film, and the base film includes the polyimide according to the above-described one embodiment. As another example of the flexible printed circuit board, it includes a base film and a coating film layer formed on the base film, and at least the coating film layer includes the polyimide according to the above-described one embodiment. Specifically, the flexible printed circuit board may include a base film. The base film may be a single layer or a laminate. In the case of a single-layer base film, the polyimide of the above-described embodiment can be used for the base film. In the case of a laminate base film, a resin layer of the polyimide of one embodiment and other resin layers can be used for the base film, or two or more types of the polyimides of the above-described embodiment having different compositions can be used for at least two layers of the base film. Examples of the other resin layers include those formed of polyethylene terephthalate, liquid crystal polymer, polyamideimide, and other polyimides other than the polyimide of one embodiment. Since the polyimide according to one embodiment has a high elongation at break, the base film can be provided by a single layer of polyimide. The flexible printed circuit board may be a single-sided flexible printed circuit board in which a conductive layer such as a copper foil is formed on one surface of the base film, or a double-sided flexible printed circuit board in which conductive layers such as copper foils are formed on both surfaces of the base film. The flexible printed circuit board may include a base film and a coating film layer. The coating film layer may be formed as a protective layer after a conductive layer such as a copper foil is provided on the base film. In this flexible printed circuit board, it is preferable that at least one of the base film and the coating film layer contains the polyimide of one embodiment. The base film having the polyimide of one embodiment is as described above. When the base film is formed of other resin, the coating film layer preferably contains the polyimide of one embodiment. The polyimide of one embodiment may be contained in both the base film and the coating film layer.

[0066] A molded article or a flexible printed circuit board according to an embodiment of the present disclosure contains polyimide, the polyimide contains a structural unit derived from diamine and a structural unit derived from tetracarboxylic dianhydride, and contains a structural unit derived from dimeric diamine in an amount of 5 to 80 mol% based on the total amount of the structural units derived from diamine, and has an elongation at break of 95% or more. Details of the polyimide are as described above. This molded article or flexible printed circuit board may be formed using a resin composition containing the polyimide precursor according to the above embodiment, but is not limited to those produced by this method.

[0067] As an example of a method for producing a plate-shaped or coating film-shaped polyimide molded article, it may include applying a resin composition containing a polyimide precursor and a solvent and heating. The above-mentioned materials can be used for the polyimide precursor, the solvent and the resin composition. According to this method, a polyimide molded article excellent in insulation, heat resistance, strength, hydrolysis resistance, chemical resistance, etc. can be provided. The coating film-shaped polyimide molded article can be obtained by coating a resin composition on a substrate and heating. The substrate may be a rigid substrate such as glass or metal, a flexible substrate such as resin, etc. As the material of the flexible substrate, the polyimide of one embodiment may be used. The substrate-shaped polyimide molded article can be obtained by applying a resin composition to a temporary fixing substrate and heating to form a polyimide resin layer, and then peeling the polyimide resin layer from the temporary fixing substrate. This substrate-shaped polyimide molded article can be used as a flexible printed circuit board. The polyimide molded article may be formed into various shapes by filling a resin composition into a mold and heating.

[0068] As a method for applying the resin composition to the substrate, there may be a method of applying the resin composition to the surface of the substrate, a method of immersing the substrate in the resin composition, etc. For example, there are brush coating, dipping, spin coating, cast coating, blade coating, spray coating, etc.

[0069] The resin composition applied to the substrate can be cured by heating to form a polyimide molded body. The heating temperature is preferably 260°C to 520°C. By the heating temperature being at least this lower limit value, the solvent can be removed from the molded body so that no residual solvent remains, promoting the curing of the molded body and further improving the properties. Also, if a polar solvent remains in the molded body, the resin component may dissolve or swell in the polar solvent, causing the properties of the molded body to deteriorate. By the heating temperature being at most this upper limit value, deterioration of the molded body under heating can be prevented. The heating time is preferably 1 second to 1 hour. In this range, it is possible to ensure that no residual solvent remains in the molded body. Also, by preventing the heating time from becoming excessively long, deterioration of the molded body under heating can be prevented.

[0070] In this specification, a numerical range indicated using "~" indicates a range that includes the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value of a certain stepwise numerical range can be arbitrarily combined with the upper limit value or the lower limit value of another stepwise numerical range. The materials exemplified in this specification can be used alone or in combination of two or more, unless otherwise specified. In this specification, the content of each component in the composition means the total amount of the plurality of substances corresponding to each component in the composition, unless otherwise specified, when there are a plurality of substances corresponding to each component in the composition. The term "step" includes not only an independent step, but also a step in which, even if it cannot be clearly distinguished from other steps, as long as the intended action of that step is achieved.

[0071] Hereinafter, several more embodiments will be exemplified. As one embodiment, there is provided a polyimide precursor obtained by reacting a diamine and a tetracarboxylic dianhydride, the polyimide precursor containing 5 to 80 mol% of a dimer diamine with respect to the diamine component contained in the polyimide precursor, and having a weight average molecular weight of 15,000 to 130,000. A polyimide obtained by curing this polyimide precursor. A resin composition containing this polyimide precursor. A polyimide molded body formed using this resin composition. A flexible substrate having a polyimide formed using this resin composition. As another embodiment, there is provided a polyimide containing a structural unit derived from a diamine and a structural unit derived from a tetracarboxylic dianhydride, the polyimide containing a structural unit derived from a dimer diamine in an amount of 5 to 80 mol% with respect to all the units of the structural unit derived from the diamine, and having an elongation at break of 95% or more. A flexible substrate having this polyimide.

Examples

[0072] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0073] The formulations and evaluation results of the examples are shown in Table 1. (Example 1) As a diamine component, 79.9 g (0.15 mol) of a dimer diamine (trade name “PRIAMINE1075”, Clariant Japan K.K., hereinafter referred to as “DDA”) and 29.9 g (0.15 mol) of 4,4'-diaminodiphenyl ether (hereinafter referred to as “ODA”) were dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 63.9 g (0.29 mol) of pyromellitic dianhydride (hereinafter referred to as “PMDA”) was added thereto as an acid anhydride component and reacted. This reaction was carried out by stirring at 50° C. or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently progressed. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from a dimer diamine at the resin content concentration shown in the table was obtained. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0074] (Example 2) 67.8 g (0.13 mol) of DDA and 38.1 g (0.19 mol) of ODA as diamine components were dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 67.7 g (0.31 mol) of PMDA as an acid anhydride component was added thereto and reacted. This reaction was carried out by stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently proceeded. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from a dimer diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0075] (Example 3) 46.6 g (0.087 mol) of DDA and 52.4 g (0.26 mol) of ODA as diamine components were dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 74.5 g (0.34 mol) of PMDA as an acid anhydride component was added thereto and reacted. This reaction was carried out by stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently proceeded. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from a dimer diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0076] (Example 4) As diamine components, 20.7 g (0.039 mol) of DDA and 69.8 g (0.35 mol) of ODA were dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 82.8 g (0.38 mol) of PMDA as an acid anhydride component was added thereto and reacted. This reaction was carried out by stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently proceeded. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from dimeric diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0077] (Example 5) As diamine components, 10.8 g (0.020 mol) of DDA and 76.5 g (0.38 mol) of ODA were dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 86.0 g (0.40 mol) of PMDA as an acid anhydride component was added thereto and reacted. This reaction was carried out by stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently proceeded. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from dimeric diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0078] (Example 6) As diamine component, 83.8 g (0.42 mol) of ODA was dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 89.4 g (0.41 mol) of PMDA as an acid anhydride component was added thereto and reacted. This reaction was carried out by stirring at 50°C or lower for 3 hours or more. After stirring for 3 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently proceeded. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from dimeric diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0079] (Example 7) As diamine components, 40.5 g (0.076 mol) of DDA and 45.5 g (0.23 mol) of ODA were dissolved in 700.0 g of N-methyl-2-pyrrolidone. To this, 87.3 g (0.30 mol) of 3,3’,4,4’-biphenyltetracarboxylic dianhydride (hereinafter referred to as “s-BPDA”) as an acid anhydride component was added and reacted. This reaction was carried out with stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently progressed. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from a dimer diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0080] (Example 8) As diamine components, 35.5 g (0.066 mol) of DDA and 81.7 g (0.20 mol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter referred to as “BAPP”) were dissolved in 700.0 g of N-methyl-2-pyrrolidone. To this, 56.7 g (0.26 mol) of PMDA as an acid anhydride component was added and reacted. This reaction was carried out with stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently progressed. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from a dimer diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0081] (Example 9) As diamine components, 31.8 g (0.060 mol) of DDA and 73.2 g (0.18 mol) of BAPP were dissolved in 700.0 g of N-methyl-2-pyrrolidone, and 68.6 g (0.23 mol) of s-BPDA as an acid anhydride component was added thereto and reacted. This reaction was carried out with stirring at 50°C or lower for 8 hours or more. After stirring for 8 hours or more, the reaction product was sampled to measure the weight average molecular weight and the number average molecular weight, and the reaction was stopped when the reaction had sufficiently proceeded. After the reaction was stopped, a resin composition containing a polyimide precursor having a structure derived from a dimer diamine was obtained at the resin content concentration shown in the table. When the appearance of this resin composition was visually observed, it was uniform and transparent.

[0082] (Weight average molecular weight and number average molecular weight of the resin composition) The resin composition containing the polyimide precursor of each example was measured by the following procedure. The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by gel permeation chromatography (GPC) and converted using a calibration curve of standard polystyrene. The calibration curve was approximated by a cubic equation using a set of 5 samples of standard polystyrene (TSK standard POLYSTYRENE [manufactured by Tosoh Corporation, trade name]). The conditions of GPC are shown below. GPC apparatus: High-speed GPC apparatus HLC-8320GPC (manufactured by Tosoh Corporation, trade name) Detector: Ultraviolet absorption detector UV-8320 (manufactured by Tosoh Corporation, trade name) Column: Gelpack GL-S300MDT-5 (total 2 columns) (manufactured by Showa Denko Materials Co., Ltd., trade name) Eluent: THF / DMF = 1 / 1 (volume ratio) + LiBr (0.06 mol / L) + H 3 PO 4 (0.06 mol / L) Flow rate: 1 mL / min Column size: 8 mm I.D. × 300 mm Sample concentration: 5 mg / 1 mL Injection volume: 5 μL Measurement temperature: 40°C

[0083] (Fabrication of Films) Films were fabricated according to the following procedure using the resin compositions containing the polyimide precursors of each example. The surface of a commercially available glass substrate was degreased with acetone, and the resin composition was applied using a film applicator with a film thickness adjustment function so that the film thickness after curing would be 25 μm, and pre-dried at 80 °C for 60 minutes using a hot plate. Next, the temperature was raised to 150 °C for 30 minutes, 200 °C for 30 minutes, and 250 °C for 30 minutes using an inert gas oven, and then baked at 350 °C for 1 hour to obtain a polyimide cured film. The cured film was immersed in warm water for about 15 minutes and peeled off from the glass substrate.

[0084] (Relative Permittivity and Dissipation Factor of Films) After cutting out the cured films of each example obtained above to a size of 60 mm × 60 mm and performing a drying treatment at 120 °C for 15 minutes, the dielectric properties (relative permittivity Dk and dissipation factor Df) were measured by the cavity resonator method (TE mode). The apparatus used was "MS46122B" manufactured by Anritsu Corporation. The conditions were a frequency of 10 GHz and a measurement temperature of 25 °C.

[0085] (Tensile Strength, Tensile Elastic Modulus, and Elongation at Break of Films) The tensile strength, tensile elastic modulus, and elongation at break of the films of each example were measured by the following procedure. The cured film obtained above was cut out to a size of 10 mm in width and 60 mm in length to obtain a test sample. A tensile test was performed under the following measurement conditions, and the maximum tensile stress applied during the tensile test was defined as the tensile strength. The elongation at break was calculated by dividing the amount of elongation of the film until breakage by the distance between the chucks of 20 mm. The Young's modulus (MPa) was calculated from the slope of the elastic deformation region at the initial stage of stress rise and defined as the tensile elastic modulus. Other detailed conditions and calculation methods were carried out in accordance with the international standard ISO527-1:2019. Apparatus name: "Autograph AGS-100NG" (trade name) manufactured by Shimadzu Corporation Test speed: 5 mm / min Distance between chucks: 20 mm Test piece size: width 10 mm, length 60 mm Set temperature: room temperature (25 °C)

[0086] (Glass transition temperature of the film) The cured films of each example were cut into pieces with a width of 4 mm and a length of 25 mm to prepare sample pieces, which were measured according to the following procedure. First, the sample pieces were heated from room temperature (20 °C) to 350 °C at a rate of 10 °C / min in a nitrogen atmosphere under a tensile mode with a chuck distance of 10 mm and a load of 10 g, held for 30 minutes, and then cooled to 30 °C at a rate of 10 °C / min to remove the residual stress. Subsequently, using a thermomechanical analyzer (model "TMA7100", manufactured by Hitachi High-Tech Science Corporation, trade name), the sample pieces were heated and measured from 20 °C to 500 °C at a rate of 10 °C / min in a nitrogen atmosphere under a tensile method with a chuck distance of 10 mm, and the temperature corresponding to the inflection point was taken as the glass transition temperature (°C).

[0087]

Table 1

[0088]

Table 2

[0089] As shown in Table 1 and Table 2, in Examples 1 to 5 and 7 to 9, films with low dielectric constant and low dielectric tangent could be obtained using polyimide precursors containing dimer diamine (DDA). It can be seen that the polyimide films of Examples 1 to 5 and 7 to 9 have high elongation at break while having low dielectric constant and low dielectric tangent. Since the polyimide precursors contained in the resin compositions of Examples 1 to 5 and 7 to 9 have a large weight average molecular weight, it can be seen that molded articles with high elongation at break can be produced. It can be seen that the polyimide films of Examples 1 to 5 and 7 to 9 are suitable for films for base films of flexible printed circuit boards, for example. Example 6 is a film prepared using a polyimide precursor not containing dimer diamine, which has a high relative dielectric constant and dielectric tangent, and sufficient dielectric properties could not be obtained, and the elongation at break was also low.

Claims

1. 1. A polyimide precursor for use in a base film of a flexible printed circuit board, the polyimide precursor comprising a diamine-derived structural unit and a tetracarboxylic acid dianhydride-derived structural unit, the diamine-derived structural unit accounting for 10 mol % to 80 mol % of all units of the diamine-derived structural units, and having a weight average molecular weight of 15,000 to 130,000.

2. 1. A polyimide precursor comprising a diamine-derived structural unit and a tetracarboxylic acid dianhydride-derived structural unit, the diamine-derived structural unit accounting for 10 mol % or more and less than 50 mol % of all units of the diamine-derived structural units, and having a weight average molecular weight of more than 50,000 and 130,000 or less.

3. A resin composition comprising the polyimide precursor according to claim 1 or 2.

4. A polyimide obtained by using the polyimide precursor according to claim 1 or 2.

5. A polyimide which contains structural units derived from a diamine and structural units derived from a tetracarboxylic dianhydride, the structural units derived from the dimer diamine accounting for 5 mol % to 80 mol % of all the structural units derived from the diamine, and has a breaking elongation of 95% or more, and is used for a base film of a high-frequency flexible printed circuit board.

6. 1. A polyimide for use in a base film of a flexible printed circuit board, the polyimide comprising structural units derived from a diamine and structural units derived from a tetracarboxylic dianhydride, the structural units derived from a dimer diamine accounting for 5 mol % to 80 mol % of all units of the structural units derived from the diamine, the polyimide having a breaking elongation of 95% or more and a glass transition temperature of 200° C. or more.

7. A polyimide comprising a diamine-derived structural unit and a tetracarboxylic acid dianhydride-derived structural unit, the diamine-derived structural unit accounting for 10 mol % or more and less than 50 mol % of all the diamine-derived structural units, the polyimide having a breaking elongation of 95% or more and a glass transition temperature of 200° C. or more.

8. 8. The polyimide according to claim 4, having a relative dielectric constant Dk (10 GHz) of 3.3 or less.

9. 9. The polyimide according to claim 4, having a dielectric loss tangent Df (10 GHz) of 0.003 or less.

10. 10. The polyimide according to claim 4, which has a glass transition temperature of 300° C. or higher.

11. A polyimide molded article comprising the polyimide according to any one of claims 4 to 10.

12. A flexible printed circuit board comprising the polyimide according to any one of claims 4 to 10.

13. A flexible printed circuit board comprising a base film obtained by using the polyimide according to any one of claims 4 to 10.

14. A flexible printed circuit board comprising a base film and a coating layer formed on the base film, at least the coating layer being obtained using the polyimide according to any one of claims 4 to 10.

15. The flexible printed circuit board according to claim 12, which is used for a millimeter wave radar, a high frequency antenna, or a high speed transmission board.

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