Polyimide films, high-frequency circuit boards, flexible electronic device substrates

Abstract

The present invention provides a polyimide film suitable for circuit board materials and / or display substrate materials, which combines high heat resistance, high-temperature dimensional stability, and low saturated water absorption and / or low water vapor transmission. [Solution] A polyimide film is provided which includes a polyimide obtained by reacting a tetracarboxylic acid component with a diamine component containing 4,4''-diamino-p-terphenyl, wherein the glass transition temperature is higher than 290°C and the coefficient of linear expansion in the temperature range of 50°C to 200°C is 10 ppm / K or less.

Description

Technical Field

[0001] The present invention relates to a polyimide film, and particularly to a polyimide film that can be suitably used for a high-frequency circuit board or a flexible electronic display board, and a polyimide precursor solution for producing the polyimide film.

Background Art

[0002] Polyimide films have excellent heat resistance and mechanical properties, and are widely used as circuit board materials for forming wirings of various electronic devices. In addition, by applying a polyimide precursor solution, which is a raw material of the polyimide film, the application to a flexible electronic device substrate material, which is a substrate for forming electronic elements such as TFTs, is also showing an expanding trend.

[0003] In circuit board materials, with the increasing high-frequency of high-speed signal transmission in electronic devices, in order to reduce transmission loss as much as possible, there is a strong demand for reducing the dielectric constant and dielectric tangent of the substrate material.

[0004] In order to meet such requirements, in Patent Document 1, a polyimide film for a metal laminate and a polyimide metal laminate in which the dielectric constant and dielectric tangent are reduced by using 4,4''-diamino-p-terphenyl (hereinafter also referred to as "DATP") as a diamine component are disclosed.

[0005] In flexible electronic device substrate materials, for the purpose of making displays and the like flexible, polyimide having excellent various physical properties has been studied as an alternative material to glass, which is a conventional device substrate material. However, there is a problem that the linear expansion coefficient is high and the dimensional stability is not sufficient.

[0006] Patent documents 2 to 4 disclose methods for reducing the coefficient of thermal expansion of polyimide using DATP as a diamine component. Specifically, Patent document 2 discloses a resin thin film formation composition obtained by preparing two or more specific polyamic acids using DATP and blending them. Patent document 3 discloses a resin composition for display substrates containing a polyamic acid obtained by polymerizing 3,3'-4,4'-biphenyltetracarboxylic dianhydride and two or more diamines in which DATP is an essential component. Patent document 4 discloses a resin composition for display substrates containing a polyamic acid obtained by polymerizing pyromellitic acid with DATP and p-phenylenediamine. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2018 / 079710 [Patent Document 2] International Publication No. 2016 / 056626 [Patent Document 3] International Publication No. 2015 / 129780 [Patent Document 4] International Publication No. 2014 / 199965 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] While these Patent Documents 1-4 may describe materials that satisfy certain physical properties, such as dielectric loss tangent or coefficient of linear expansion, in practical terms, higher levels of heat resistance and dimensional stability are necessary. Therefore, the main objective of the present invention is to provide a polyimide film that achieves both high heat resistance and dimensional stability, and is highly practical and suitable for industrial production. Another objective is to provide a polyimide film suitable for circuit board materials and / or display substrate materials, which combines high heat resistance, high-temperature dimensional stability, and low saturated water absorption and / or low water vapor transmission. Yet another objective is to provide a polyimide precursor solution with excellent storage stability, for example, in order to manufacture a polyimide film that achieves both high heat resistance and high-temperature dimensional stability and is highly practical. [Means for solving the problem]

[0009] The present invention relates in particular to the following items. 1. A polyimide film comprising a polyimide obtained by reacting a tetracarboxylic acid component with a diamine component containing 4,4''-diamino-p-terphenyl, wherein the glass transition temperature is higher than 290°C and the coefficient of linear expansion in the temperature range of 50°C to 200°C is 10 ppm / K or less. 2. The polyimide film described in [1] above, further comprising a saturated water absorption rate of 1% or less. 3. Furthermore, the water vapor transmission coefficient is 0.1 g·mm / (m 2 The polyimide film described in [1] or [2] above, wherein the time is 24 hours or less. 4. A polyimide film according to any of the above [1] to [3], wherein the coefficient of linear expansion in the temperature range of 50°C to 500°C is -1.0 ppm / K or more and less than 0.5 ppm / K. 5. The polyimide film according to any one of the above [1] to [4], wherein the diamine component is a diamine component containing more than 50 mol% of 4,4''-diamino-p-terphenyl. 6. The polyimide film according to any one of the above [1] to [5], wherein the tetracarboxylic acid component comprises two or more tetracarboxylic acid dianhydrides selected from 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, pyromellitic acid dianhydride, and 4,4'-oxydiphthalic acid dianhydride. 7. The polyimide film according to any one of the above [1] to [6], wherein the tetracarboxylic acid component contains 50 mol% or more of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and further contains one or more tetracarboxylic acid dianhydrides selected from pyromellitic acid dianhydride and 4,4'-oxydiphthalic acid dianhydride. 8. A polyimide precursor solution for producing a polyimide film as described in any of [1] to [7] above. 9. A polyimide film for metal lamination, comprising a metal adhesive layer provided on a polyimide film as described in any of [1] to [7] above. 10. A polyimide metal laminate obtained by laminating a metal layer onto the polyimide film for metal lamination described in [9] above. 11. A high-frequency circuit board using the polyimide metal laminate described in

[10] above. 12. A laminate comprising a polyimide film as described in any of [1] to [7] above and a glass substrate. 13. A flexible electronic device substrate comprising a polyimide film as described in any of [1] to [7] above or a laminate as described in

[12] above. 14. A flexible electronic device substrate having elements on the flexible electronic device substrate described in

[13] above. 15. A method for manufacturing a flexible electronic device as described in

[14] above, comprising: a coating step of coating a carrier substrate with the polyimide precursor solution described in [8] above; a film forming step of heat-treating the carrier substrate coated with the polyimide precursor solution to form a polyimide film; an element forming step of forming an element on the polyimide film; and a peeling step of peeling the polyimide film on which the element is formed from the carrier substrate. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a polyimide film that achieves both high heat resistance and dimensional stability, and is highly practical. Preferably, it is possible to provide a polyimide film suitable for circuit board materials and / or display substrate materials, which combines high heat resistance, high-temperature dimensional stability, and low saturated water absorption and / or low water vapor transmission. Furthermore, it is possible to provide a polyimide precursor composition for realizing these polyimide films. [Modes for carrying out the invention]

[0011] The present invention relates to a polyimide film comprising a polyimide obtained by polymerizing a tetracarboxylic acid component and a diamine component containing 4,4''-diamino-p-terphenyl (DATP), wherein the polyimide film has a glass transition temperature higher than 290°C and a coefficient of linear expansion in the temperature range of 50 to 200°C of 10 ppm / K or less. The following will describe the polyimide film, polyimide precursor composition, circuit board, and flexible device substrate in that order.

[0012] <Polyimide film> The polyimide film of the present invention contains a polyimide obtained by polymerizing a tetracarboxylic acid component and a diamine component, and contains DATP as an essential component as the diamine component. The thickness of the polyimide film is preferably, for example, 1 μm to 500 μm, particularly preferably 5 μm or more and 10 μm or more, and particularly preferably 300 μm or less, 200 μm or less and 100 μm or less. The thickness of the polyimide film may be adjusted as appropriate depending on the application and desired physical properties.

[0013] The tetracarboxylic acid component used in the present invention is not particularly limited, and conventionally known tetracarboxylic acids, their derivatives, and tetracarboxylic anhydrides can be used. However, from the viewpoint of reactivity during polymerization, it is preferable to use tetracarboxylic dianhydrides. Hereinafter, as a representative of the tetracarboxylic acid component, the tetracarboxylic dianhydride will be described, but the tetracarboxylic acid component is not limited to the tetracarboxylic dianhydride.

[0014] The tetracarboxylic dianhydride is not particularly limited, but from the viewpoints of heat resistance and dimensional stability, aromatic tetracarboxylic dianhydrides (a general term for tetracarboxylic dianhydrides having an aromatic group) and alicyclic tetracarboxylic dianhydrides (a general term for tetracarboxylic dianhydrides having an alicyclic structure) are preferable. For example, as the aromatic tetracarboxylic dianhydride, rigid linear aromatic tetracarboxylic dianhydrides such as 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylic dianhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, etc., bent aromatic tetracarboxylic dianhydrides such as 2,3,3',4-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, diphenylsulfonetetracarboxylic dianhydride, m-terphenyltetracarboxylic dianhydride, oxydiphthalic dianhydride, etc., and fluorine-substituted aromatic acid dianhydrides such as 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride can be exemplified. As the alicyclic tetracarboxylic dianhydride, alicyclic acid dianhydrides such as cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, etc. can be preferably mentioned.

[0015] Among the tetracarboxylic dianhydrides, by using 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, oxydiphthalic dianhydride, diphenylsulfone tetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, or m-terphenyltetracarboxylic dianhydride, a polyimide capable of providing a polyimide film with more excellent heat resistance can be obtained. Among these, it is preferable to use 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, or oxydiphthalic dianhydride.

[0016] Among the tetracarboxylic dianhydrides, by using 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, oxydiphthalic dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic dianhydride, diphenylsulfone tetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, m-terphenyltetracarboxylic dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride, or 1,2,4,5-cyclohexanetetracarboxylic dianhydride, a polyimide capable of providing a polyimide film with more excellent dimensional stability can be obtained. Among these, it is preferable to use 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, or 3,3',4,4'-benzophenonetetracarboxylic dianhydride.

[0017] Among the tetracarboxylic dianhydrides mentioned above, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, oxydiphthalic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, diphenylsulfonetetracarboxylic dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride can be used to obtain polyimides that provide polyimides with excellent low water absorption. In particular, it is preferable to use 3,3',4,4'-biphenyltetracarboxylic dianhydride, oxydiphthalic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride, and 1,2,4,5-cyclohexanetetracarboxylic dianhydride.

[0018] Among the tetracarboxylic dianhydrides mentioned above, 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, oxydiphthalic acid dianhydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, diphenylsulfonetetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, and m-terphenyltetracarboxylic dianhydride can be used to obtain polyimides that provide polyimides with a low water vapor permeability coefficient. In particular, 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and oxydiphthalic acid dianhydride are preferred.

[0019] From the viewpoint of the viscosity stability of the polyamic acid, the tetracarboxylic dianhydride preferably includes 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0020] It is preferable to use two or more tetracarboxylic dianhydrides in combination, and particularly preferable to use two or more. By using two or more tetracarboxylic dianhydrides in combination, it is possible to achieve a higher level of both heat resistance and dimensional stability in the polyimide film. In addition, it is possible to obtain a polyimide film with an excellent balance of low water absorption and a low water vapor permeability coefficient.

[0021] When using two or more tetracarboxylic dianhydrides, it is preferable to use at least one selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic acid dianhydride, and oxydiphthalic acid dianhydride from the viewpoint of heat resistance and dimensional stability. Of course, two or more of these may be used in combination. Among these, it is preferable to use at least two selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride, pyromellitic acid dianhydride, and oxydiphthalic acid dianhydride, and it is even more preferable to use 3,3',4,4'-biphenyltetracarboxylic dianhydride as a mixture with other tetracarboxylic dianhydrides, and it is particularly preferable to use 3,3',4,4'-biphenyltetracarboxylic dianhydride as a mixture with at least one selected from pyromellitic acid dianhydride and oxydiphthalic acid dianhydride.

[0022] When 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is used in combination with other tetracarboxylic acid dianhydrides, it is preferable to use 50 mol% or more of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride relative to the total tetracarboxylic acid components, more preferably 60 mol% or more, 90 mol% or less, and even more preferably 80 mol% or less.

[0023] The diamine component used in the present invention contains 4,4''-diamino-p-terphenyl (hereinafter also referred to as "DATP") as an essential component. From the viewpoint of dimensional stability and heat resistance, it is preferable that DATP be present in an amount of 50 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol%, and particularly preferably 100 mol% of the total diamine component.

[0024] In this invention, in order to enhance the functionality of a polyimide film obtained using 4,4''-diamino-p-terphenyl (DATP) as the diamine component or to add other functions, other diamine components can be used in combination. The diamine used in combination is preferably used in an amount of 50 mol% or less, more preferably in an amount of 30 mol% or less, and particularly preferably in an amount of 10 mol% or less, relative to the total diamine component. Furthermore, two or more diamine components other than DATP may be used in combination.

[0025] The diamine components that can be used in combination with DATP are not particularly limited, but examples include 4,4'-diaminodiphenyl ether, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenylmethane, 4,4'-diamino-1,2-diphenylethane, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, m-xylylenediamine, p-xylylenediamine Aromatic diamines having aromatic groups such as n, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-methylenebis(2,6-xylidine), α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 2,2'-dimethyl-4,4'-aminobiphenyl, 3,3'-dimethyl-4,4'-aminobiphenyl, 2,2'-ethylenedianiline, 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-prop Pyrcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, 1,2-diaminocyclohexane, 1,3-diaminocyclobutane, 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, diaminobicycloheptane, diaminomethylbicycloheptane, diaminooxybi Cycloheptane, diaminomethyloxybicycloheptane, isophoronediamine, diaminotricyclodecane, diaminomethyltricyclodecane, bis(aminocyclohexyl)methane, bis(aminocyclohexyl)isopropylidene, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobindan, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobindan, and other alicyclic diamines having an alicyclic structure, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,3,5,6-tetrafluoro-1,4-diaminobenzene, 2,4,5,6-tetrafluoro-1,3-diaminobenzene, 2,3,5,6-tetrafluoro-1,4-benzene(dimethaneamine), 2,2'-difluoro-(1,1'-biphenyl)-4,4'-diamine, 2,2',6,6'-tetrafluoro-(1,1'-biphenyl)-4,4'-diamine, 4,4'-diaminooctafluorobiphenyl, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-oxybis(2,3,5,6-tetrafluoroaniline), 3,3'-bis(trifluoro Suitable examples include fluorine-containing fluorine-based diamines such as methyl)-4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether, 1,4-bis[4-amino-2-(trifluoromethyl)phenoxy]benzene, 2,2-bis[4-[4-amino-2-(trifluoromethyl)phenoxy]hexafluoropropane, 3,5-diaminobenzene trifluoride, and 4,4-diamino-2-(trifluoromethyl)diphenyl ether, as well as ester-bond-containing diamines such as 4-aminophenyl 4-aminobenzoic acid, bis(4-aminophenyl) terephthalate, and bis(4-aminophenyl) biphenyl-4,4'-dicarboxylate bis(4-aminophenyl) ester.

[0026] By using aromatic diamines among the aforementioned diamine components, a polyimide with excellent heat resistance can be obtained. In particular, it is preferable to use 4,4'-diaminodiphenyl ether, 2,2'-dimethylbenzidine, 4,4'-diaminodiphenylmethane, 4,4'-diamino-1,2-diphenylethane, p-phenylenediamine, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0027] By using an alicyclic diamine among the aforementioned diamine components, a polyimide can be obtained that provides a polyimide film with excellent dimensional stability. In particular, it is preferable to use 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, and 1,4-diamino-2-tert-butylcyclohexane.

[0028] Among the aforementioned diamines, polyimides that provide polyimide films with low water absorption can be obtained by using ester-bonded diamines. Among these, 4-aminophenyl 4-aminobenzoate, bis(4-aminophenyl) terephthalate, bis(4-aminophenyl) biphenyl-4,4'-dicarboxylate, and bis(4-aminophenyl) terphenyl-4,4'-dicarboxylate are preferred.

[0029] The polyimide film of the present invention may optionally contain fillers such as fine inorganic fillers or organic fillers. Examples of inorganic fillers include particulate or flattened shapes. Examples of inorganic fillers include particulate inorganic oxide powders such as titanium dioxide powder, silicon dioxide (silica) powder, magnesium oxide powder, aluminum oxide (alumina) powder, and zinc oxide powder; particulate inorganic nitride powders such as silicon nitride powder and titanium nitride powder; particulate inorganic carbide powders such as silicon carbide powder; and particulate inorganic salt powders such as calcium carbonate powder, calcium sulfate powder, and barium sulfate powder. Furthermore, needle-shaped fillers such as strontium carbonate and needle-shaped minerals may also be included. Examples of organic fillers include polyimide particles, silicone particles, and particles of thermosetting resin after thermosetting. Two or more of these fillers may be used in combination. The amount and shape (size, aspect ratio) of the filler can be selected according to the intended use. These fillers can be uniformly dispersed using known methods.

[0030] The amount of filler used can be selected according to the application, but for example, it can be used in a range of 50% by mass or less, preferably 1% by mass or more and 40% by mass or less, based on the weight of the polyimide film.

[0031] The polyimide film of the present invention possesses excellent heat resistance. Specifically, its glass transition temperature is higher than 290°C, preferably 300°C or higher, more preferably 320°C or higher, and particularly preferably 350°C or higher. The upper limit of the glass transition temperature is not particularly limited, but is preferably 600°C or lower. Here, the glass transition temperature of the polyimide film is the peak temperature of tanδ obtained by dynamic viscoelasticity measurement of the polyimide film. In this specification, a glass transition temperature of "above 500°C" means that the glass transition temperature is at a temperature higher than 500°C and cannot be observed by the measuring instrument, or that the decomposition temperature is reached first. Any known measuring instrument can be used for determining the dynamic viscoelasticity.

[0032] The polyimide film of the present invention exhibits excellent dimensional stability. Specifically, the coefficient of linear expansion in the temperature range of 50 to 200°C is 10 ppm / K or less, preferably 9 ppm / K or less, more preferably 8 ppm / K or less, and particularly preferably 6 ppm / K or less. The lower limit of the coefficient of linear expansion in the temperature range of 50 to 200°C is not particularly limited, but is -5 ppm / K or more, preferably -1 ppm / K or more. In addition, it is particularly preferable that the coefficient of linear expansion in the temperature range of 50 to 500°C (also referred to herein as "high-temperature dimensional stability") is less than +0.5 ppm / K and -1.0 ppm / K or more. The coefficient of linear expansion in the temperature range of 50 to 500°C is preferably +0.4 ppm / K or less and -0.95 ppm / K or more, more preferably +0.2 ppm / K or less and -0.8 ppm / K or more. Here, the linear expansion coefficient of polyimide film in the 50-200°C temperature range and the linear expansion coefficient in the 50-500°C temperature range can both be measured using a known TMA measuring device. Specifically, the linear expansion coefficient in the 50-200°C temperature range can be calculated by first heating the polyimide film to 300°C at a heating rate of 20°C / min to mitigate thermal shrinkage during film formation, then allowing it to cool to room temperature, and finally performing secondary heating at a heating rate of 20°C / min. During this process, measurements are taken using a TMA measuring device, and the coefficient can be calculated from the TMA curve from 50°C to 200°C. Furthermore, the coefficient of linear expansion in the temperature range of 50 to 500°C can be calculated by first performing primary heating on the polyimide film at a heating rate of 20°C / min to 500°C to mitigate thermal shrinkage during film formation, then allowing it to cool to room temperature, and finally performing secondary heating at a heating rate of 20°C / min. During this process, the coefficient of linear expansion is measured using a TMA measuring device and calculated from the TMA curve from 50°C to 500°C.

[0033] Furthermore, the polyimide film of the present invention preferably has a saturated water absorption rate of 1.3% by mass or less, more preferably 1.1% by mass or less, and particularly preferably 0.9% by mass or less. The lower limit of the saturated water absorption rate is not particularly limited, but is preferably 0.01% by mass or more. Here, the "saturated water absorption rate" of the polyimide film as used in the present invention is the saturated water absorption rate of the polyimide film with respect to water at 23°C. The method for measuring the saturated water absorption rate is not particularly limited, but for example, a polyimide film with a thickness of 25 μm can be immersed in water at 23°C for 24 hours or more to allow it to absorb saturated water, and the saturated water absorption rate can be calculated from the weight when completely dry and the weight when saturated water is absorbed using the following formula. Saturated water absorption rate (%) = [(weight after saturated water absorption) - (absolutely dry weight)] / (absolutely dry weight) × 100 It is preferable that the saturation water absorption rate of the polyimide film falls within the above range, as this can reduce transmission loss.

[0034] Furthermore, the polyimide film of the invention has a water vapor transmission coefficient of 0.3 g·mm / (m²). 2 It is preferable that it is 24 hours or less, and 0.1 g·mm / (m 2 It is more preferable that it be 24 hours or less, and 0.05 g·mm / (m 2 It is particularly preferable that the water vapor transmission coefficient be less than or equal to 24 hours. The lower limit of the water vapor transmission coefficient is not particularly limited, but is preferably 0.001 g·mm / (m³). 2 The water vapor transmission rate is 24 hours or longer. Here, the water vapor transmission rate of the polyimide film is the value measured at 40°C and 90% relative humidity in accordance with Method B of JIS K7129. The water vapor transmission coefficient is calculated by multiplying the obtained water vapor transmission rate by the film thickness, as shown in the formula below. Water vapor transmission coefficient = Water vapor transmission rate × Film thickness When the water vapor permeability coefficient of the polyimide film falls within the above range, it is preferable because it exhibits excellent dimensional stability and minimal changes in mechanical properties even in humid environments.

[0035] Normally, the physical properties of polyimide films, such as the glass transition temperature and coefficient of thermal expansion, can be independently adjusted using conventionally known methods. However, achieving both properties simultaneously can sometimes require special production conditions, making the overall production process complicated. On the other hand, the polyimide film of the present invention, by selectively using DATP as the diamine component, makes it possible to achieve both properties simultaneously without being heavily dependent on the production process.

[0036] From the viewpoint of glass transition temperature and coefficient of linear expansion, a preferred combination of tetracarboxylic acid and diamine components is a combination in which 10 mol% to 90 mol% of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and 90 mol% to 10 mol% of pyromellitic dianhydride are used as the tetracarboxylic acid component, and DATP is used as the diamine component.

[0037] Furthermore, examples of other preferred combinations of tetracarboxylic acid components and diamine components in the present invention include: (I) a combination in which pyromellitic anhydride is used as the tetracarboxylic acid component in an amount of 10 mol% to 100 mol%, more preferably 90 mol% to 99.5 mol%, and 2,3,3',4-biphenylphenyltetracarboxylic acid dianhydride is used in an amount of 90 to 0 mol%, more preferably 10 mol% to 0.5 mol%, of the total tetracarboxylic acid component, and DATP is used as the diamine component; and (II) a combination in which pyromellitic dianhydride is used as the tetracarboxylic acid component in an amount of 100 mol%, and DATP is used in an amount of 10 mol% to 100 mol%, and metaphenylenediamine is used in an amount of 90 mol% to 0 mol%, of the total diamine component. However, these are merely examples of combinations of tetracarboxylic acid components and diamine components for obtaining a polyimide film having a high glass transition temperature and a low coefficient of thermal expansion, and the above combinations of tetracarboxylic acid components and diamine components do not limit the composition of the polyimide film of the present invention.

[0038] Furthermore, as examples of other preferred combinations of tetracarboxylic acid components and diamine components in the present invention, (I) a combination in which 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is used as the tetracarboxylic acid component in an amount of 50 mol% to 90 mol%, more preferably 80 mol% to 90 mol%, and oxydiphthalic acid dianhydride is used in an amount of 50 mol% to 10 mol%, more preferably 20 mol% to 10 mol%, and DATP is used as the diamine component; (II) a combination in which pyromellitic acid dianhydride is used as the tetracarboxylic acid component in an amount of 70 mol% to 90 mol%, and oxydiphthalic acid dianhydride is used in an amount of 30 to 10 mol%, and DATP is used as the diamine component; (III) a combination in which 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is used as the tetracarboxylic acid component. Examples of combinations include using phenyltetracarboxylic acid dianhydride in an amount of 30 mol% to 60 mol% of the total tetracarboxylic acid components, pyromellitic acid dianhydride in an amount of 20 mol% to 40 mol% of the total tetracarboxylic acid components, and oxydiphthalic acid dianhydride in an amount of 20 to 40 mol% of the total tetracarboxylic acid components, with DATP as the diamine component; and using 3,3',4,4'-biphenyltetracarboxylic acid dianhydride in an amount of 10 mol% to 90 mol%, more preferably 30 mol% to 70 mol%, pyromellitic acid dianhydride in an amount of 90 mol% to 10 mol%, more preferably 70 mol% to 30 mol%, of the total tetracarboxylic acid components as the (IV) tetracarboxylic acid components, with DATP in an amount of 10 mol% to 70 mol%, and p-phenylenediamine in an amount of 90 mol% to 30 mol% of the total diamine components. However, these are merely examples of combinations of tetracarboxylic acid and diamine components for obtaining a polyimide film having a high glass transition temperature and a low coefficient of thermal expansion, and the aforementioned combinations of tetracarboxylic acid and diamine components do not limit the composition of the polyimide film of the present invention.

[0039] For example, in order to provide superior heat resistance and dimensional stability, as well as low saturated water absorption and / or low water vapor transmission, and thereby make it more suitable for use as a circuit board material, the tetracarboxylic acid component can take the following forms, but is not particularly limited to these forms. Firstly, it is preferable to use two types of dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and pyromellitic acid dianhydride, with a molar ratio of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride:pyromellitic acid dianhydride = 10:90 to 80:20, more preferably 20:80 to 60:40, and more preferably 30:70 to 50:50. Secondly, it is preferable to use two types in combination, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and oxydiphthalic acid dianhydride, with a molar ratio of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride:oxydiphthalic acid dianhydride = 95:5 to 40:60, and more preferably 90:10 to 50:50. Thirdly, it is preferable to use two types, pyromellitic dianhydride and oxydiphthalic dianhydride, in combination, with a molar ratio of pyromellitic dianhydride:oxydiphthalic dianhydride = 95:5 to 60:40, and more preferably 90:10 to 70:30. Fourthly, it is preferable to use a combination of three types: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, pyromellitic acid dianhydride, and oxydiphthalic acid dianhydride, with their molar ratio being in the range of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride:pyromellitic acid dianhydride:oxydiphthalic acid dianhydride = 20~60:20~40:20~40.

[0040] Alternatively, in order to provide a polyimide precursor composition that is superior in high temperature dimensional stability (coefficient of linear expansion in the temperature range of 50 to 500°C) in addition to high heat resistance and dimensional stability, and is also superior in viscosity stability, thereby making it more suitable for display substrate material applications, the tetracarboxylic acid component can be in the following forms, but is not particularly limited to these forms. Firstly, it is preferable to use two types of dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and pyromellitic acid dianhydride, with a molar ratio of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride:pyromellitic acid dianhydride = 99.5:0.5 to 95:5, and more preferably 99:1 to 97:3. Secondly, it is preferable to use pyromellitic dianhydride alone. Thirdly, it is preferable to use a combination of three types: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, pyromellitic acid dianhydride, and 2,3,3',4-biphenyltetracarboxylic acid dianhydride, with a molar ratio of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride:pyromellitic acid dianhydride:2,3,3',4-biphenyltetracarboxylic acid dianhydride = 85~95:0.5~2:3~14.5, and more preferably 87~91:0.7~1.5:7.5~12.3.

[0041] <Polyimide precursor solution> The polyimide precursor solution of the present invention is a solution comprising a polyimide precursor having the following chemical formula (I) and / or the following chemical formula (II), obtained by polymerizing the tetracarboxylic acid component and the diamine component, and an organic solvent, and is suitably used for producing the polyimide film of the present invention. [ka] [ka] (In the formula, A is one or more tetravalent organic groups obtained by removing a carboxyl group from a tetracarboxylic acid, and B is one or more divalent organic groups obtained by removing an amino group from a diamine. However, B must include, at least in part, units derived from DATP.)

[0042] Since the aforementioned polyimide precursor solution uses DATP as the diamine component, it can be easily prepared using conventionally known methods. Although not particularly limited, for example, a polyimide precursor solution can be obtained by reacting approximately equimolar amounts of tetracarboxylic dianhydride and a diamine in a solvent at a relatively low temperature of 100°C or below, preferably 80°C or below, so as not to allow the imidation reaction to proceed too far.

[0043] While not particularly limited, the polymerization temperature for obtaining a polyimide precursor solution is usually 25°C or higher and 100°C or lower, preferably 40°C or higher and 80°C or lower, more preferably 50°C or higher and 80°C or lower. The polymerization time is 0.1 hours or higher and 24 hours or lower, preferably 2 hours or higher and 12 hours or lower. By setting the polymerization temperature and polymerization time within the above range, a high molecular weight polyimide precursor solution can be easily obtained with production efficiency. Polymerization can be carried out in an air atmosphere, but is usually suitably carried out in an inert gas atmosphere, preferably nitrogen gas atmosphere. Specifically, the molar ratio of approximately equimolar tetracarboxylic dianhydride and diamine [total tetracarboxylic acid component / total diamine component] is 0.90 or higher and 1.10 or lower, preferably 0.95 or higher and 1.05 or lower, and more preferably greater than 0.98, 1.04 or lower and 1.03 or lower. In this specification, "approximately equimolar" means the molar ratio is in the range of greater than 0.99 to 1.01, and "equomolar" means the significant figures of the molar ratio 1.00.

[0044] A polyimide precursor having chemical formula (I) and / or chemical formula (II) below can be obtained by polymerizing a diamine component and a tetracarboxylic acid component. Typically, a diamine is added to a polymerization apparatus filled with a solvent, and after confirming that the diamine has dissolved, the tetracarboxylic acid component is added. At this time, the tetracarboxylic acid component may be added all at once, in installments, or continuously. By carrying out the imidation reaction in the solvent, the polyimide precursor of the present invention can be obtained in solution, i.e., in a polyimide precursor solution. Thus, the polyimide precursor solution of the present invention does not require the blending of polyimide precursors and can provide a polyimide film with excellent heat resistance and dimensional stability produced in a single polymerization step.

[0045] The solvent used in the polyimide precursor solution of the present invention may be any solvent that is capable of polymerizing the polyimide precursor and in which the polyimide precursor is soluble, and may be either aqueous or organic solvent. The solvent may also be a mixture of two or more solvents, such as a mixed solvent of two or more organic solvents, or a mixed solvent of water and one or more organic solvents. The organic solvent is not particularly limited, but examples include N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, hexamethylphosphorotriamide, 1,2-dimethoxyethane, bis(2-methoxyethyl) ether, 1,2-bis(2-methoxyethoxy)ethane, tetrahydrofuran, bis[2-(2-methoxyethoxy)ethyl] ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethylurea, anisole, m-cresol, phenol, and γ-butyrolactone. The solvent used when polymerizing the polyimide precursor can be used directly as the solvent for the polyimide precursor solution when producing the polyimide film.

[0046] The polyimide precursor is not particularly limited, but it is preferable that its logarithmic viscosity, measured at a temperature of 30°C and a concentration of 0.5 g / 100 mL, is 0.2 or higher, preferably 0.4 or higher, and particularly preferably 0.6 or higher. When the logarithmic viscosity satisfies the above range, a polyimide film with excellent mechanical properties can be obtained.

[0047] The polyimide precursor is not particularly limited, but its weight-average molecular weight Mw is preferably 10,000 or more and 500,000 or less. Particularly preferred are values ​​of 50,000 or more, 70,000 or more, 100,000 or more, 300,000 or less, 200,000 or less, and 150,000 or less. The molecular weight distribution Mw / Mn is preferably 15 or less, more preferably 10 or less, 7 or less, 5 or less, and particularly preferred to be 1.5 or more and 4 or less. When the weight-average molecular weight and molecular weight distribution are within this range, a polyimide film with excellent high-temperature dimensional stability, heat resistance, and mechanical properties can be obtained. Here, the weight-average molecular weight is determined based on a calibration curve obtained from standard polystyrene using a known gel permeation chromatography (GPC) apparatus. The molecular weight distribution is a value calculated using the weight-average molecular weight.

[0048] The polyimide precursor solution is not particularly limited, but the solid content concentration of the polyimide precursor is preferably 5% by mass or more and 45% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and even more preferably more than 10% by mass and 30% by mass or less, relative to the total amount of the polyimide precursor and the solvent. If the solid content concentration is lower than 5% by mass, it may be difficult to increase the thickness of the film, and if it is higher than 45% by mass, the viscosity of the solution may become too high, which may require special film manufacturing equipment.

[0049] Furthermore, the viscosity of the polyimide precursor solution used in the present invention at 30°C is not limited, but is preferably 1000 Pa·sec or less, more preferably 0.5 Pa·sec or more and 500 Pa·sec or less, even more preferably 1 Pa·sec or more and 300 Pa·sec or less, and particularly preferably 2 Pa·sec or more and 200 Pa·sec or less for ease of handling.

[0050] Furthermore, the polyimide precursor solution used in the present invention preferably has excellent viscosity stability from the viewpoint of producing polyimide films stably with high production efficiency. Specifically, this can be expressed as a viscosity change rate, and it is preferable that the viscosity of the polyimide precursor solution after being held at 23°C for 31 days is within ±5%, and more preferably within ±2%, compared to the viscosity of the polyimide precursor solution held at 23°C for 7 days.

[0051] The polyimide precursor solution may optionally contain additives that promote the imidation reaction, such as amine compounds and dehydrating agents, as well as known additives such as organophosphorus-containing compounds, the aforementioned fillers, surfactants, silane coupling agents, and leveling agents.

[0052] Examples of amine compounds include substituted or unsubstituted nitrogen-containing heterocyclic compounds, N-oxide compounds of said nitrogen-containing heterocyclic compounds, substituted or unsubstituted amino acid compounds, aromatic hydrocarbon compounds having a hydroxyl group, or aromatic heterocyclic compounds. Specific examples of imidation catalysts include imidazole derivatives such as 1,2-dimethylimidazole, N-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 5-methylbenzimidazole, and N-benzyl-2-methylimidazole, as well as substituted pyridine derivatives such as isoquinoline, 3,5-dimethylpyridine, 3,4-dimethylpyridine, 2,5-dimethylpyridine, 2,4-dimethylpyridine, and 4-n-propylpyridine. The amount of imidation catalyst used is preferably 0.01 equivalents or more and 2 equivalents or less, particularly 0.02 equivalents or more and 1 equivalent or less, relative to the amide acid units of the polyamic acid. The use of an imidation catalyst can improve the physical properties of the resulting polyimide film, particularly its elongation and edge tear resistance.

[0053] Other amine compounds include aliphatic tertiary amines such as trimethylamine and triethylenediamine, aromatic tertiary amines such as dimethylaniline, and heterocyclic tertiary amines such as isoquinoline, pyridine, α-picoline, and β-picoline, which can be added as needed.

[0054] Examples of dehydrating agents include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride.

[0055] Examples of organophosphorus-containing compounds include phosphate esters such as monocaproyl phosphate, monooctyl phosphate, monolauryl phosphate, monomyristyl phosphate, monocetyl phosphate, monostearyl phosphate, monophosphate of triethylene glycol monotridecyl ether, monophosphate of tetraethylene glycol monolauryl ether, monophosphate of diethylene glycol monostearyl ether, dicaproyl phosphate, dioctyl phosphate, dicapryl phosphate, dilauryl phosphate, dimyristyl phosphate, dicetyl phosphate, distearyl phosphate, diphosphate of tetraethylene glycol mononeopentyl ether, diphosphate of triethylene glycol monotridecyl ether, diphosphate of tetraethylene glycol monolauryl ether, and diphosphate of diethylene glycol monostearyl ether, as well as amine salts of these phosphate esters. Examples of amines include ammonia, monomethylamine, monoethylamine, monopropylamine, monobutylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, monoethanolamine, diethanolamine, and triethanolamine.

[0056] <Method for manufacturing polyimide film> The polyimide film of the present invention can be manufactured by known methods using the polyimide precursor solution. The manufacturing method is not particularly limited, but any of the following manufacturing methods (1) to (4) is preferred. In this specification, "self-supporting film" refers to a film obtained by peeling off the polyimide precursor film from a laminate consisting of a polyimide precursor film obtained by coating a polyimide precursor solution having the structure of chemical formula (I) and / or chemical formula (II) onto a support and drying it, regardless of whether it has been chemically / thermally imidized or subjected to further heat treatment.

[0057] [Manufacturing method (1)] A method for obtaining a polyimide film by coating a polyimide precursor solution containing a polyimide precursor of chemical formula (I) onto a support, drying the resulting laminate of the support and the polyimide precursor film, chemically / thermally imidizing the laminate, and then peeling the polyimide film from the support.

[0058] [Manufacturing method (2)] A method for obtaining a polyimide film by coating a polyimide precursor solution containing a polyimide precursor of chemical formula (I) onto a support, drying it, peeling the polyimide precursor film from the support, fixing this self-supporting film, and then chemically / thermally imidizing it.

[0059] [Manufacturing method (3)] A method for obtaining a polyimide film by coating a polyimide precursor solution containing a polyimide precursor of chemical formula (II) onto a support, drying the resulting laminate of the support and the polyimide precursor film, and then peeling the polyimide film from the support as needed.

[0060] [Manufacturing method (4)] A method for obtaining a polyimide film by coating a polyimide precursor solution containing a polyimide precursor of chemical formula (II) onto a support, drying it, peeling the polyimide precursor film from the support, and then further heating the self-supporting film as needed.

[0061] The laminate of the support and the polyimide precursor film in the above manufacturing methods (1) to (4) is manufactured by coating the support with a polyimide precursor solution and drying the polyimide precursor film formed by drying to a degree that it becomes self-supporting, for example, to the extent that it can be peeled off the support.

[0062] The method for applying the polyimide precursor solution to the support in the above manufacturing methods (1) to (4) is not particularly limited as long as it can form the desired coating film, but known methods such as spin coating, screen printing, bar coating, electrodeposition, saturation, and extrusion molding can be suitably used. Considering the subsequent steps until the polyimide film is formed, such as drying and heating, the thickness of the coating film should be, for example, about 1 μm to 500 μm.

[0063] The drying conditions in the above manufacturing methods (1) to (4) are not particularly limited, but it is preferable to dry in a temperature range of 20°C or higher, 200°C or lower, room temperature (25°C) or higher, 180°C or lower, 30°C or higher, and 150°C or lower. Depending on the heating temperature, drying may take, for example, 1 minute or more, 60 minutes or less, preferably 30 minutes or less, or 20 minutes or less. The heating means is not particularly limited, such as hot air or infrared rays, and may be performed multiple times or with a gradual increase in temperature. These drying conditions may be selected, for example, under an atmosphere such as vacuum, an inert gas such as nitrogen, or air, while considering the properties of the polyimide film.

[0064] In the above manufacturing methods (1) to (4), the support to which the polyimide precursor solution is applied is not particularly limited as long as it can be coated with the polyimide precursor solution and does not affect the subsequent formation of the polyimide precursor film by drying, or the heating, chemical / or thermal imidation reaction, but it is preferable to use glass, metal, plastic substrates, etc.

[0065] Methods (1) and (2) include a step for chemical / or thermal imidation to obtain a polyimide film. Chemical / or thermal imidation may be performed in the state of a laminate of the support and the polyimide precursor film, as in (1), or after peeling the polyimide precursor film from the support to form a self-supporting film, as in (2). Typically, chemical / or thermal imidation can be performed by heat treatment.

[0066] Taking thermal imidation as an example, the maximum heating temperature in the heat treatment is generally 350°C or higher, preferably 450°C or higher, more preferably 490°C or higher, even more preferably 500°C or higher, and particularly preferably 510°C or higher. When the maximum heating temperature is 510°C or higher, the coefficient of linear expansion of the polyimide film can be further reduced. The upper limit of the heat treatment temperature is any temperature at which the properties of the polyimide film do not deteriorate, preferably 600°C or lower, more preferably 550°C or lower. Although the heat treatment can be carried out in an air atmosphere, it is usually suitably carried out in an inert gas atmosphere, preferably nitrogen gas atmosphere. Chemical imidation, depending on the type of additive such as the chemical imidation catalyst, can be performed under milder heat treatment conditions compared to thermal imidation. For example, heat treatment can be carried out in the temperature range of 100°C or higher, 120°C or higher, 150°C or higher, 200°C or higher, 500°C or lower, 450°C or lower, 400°C or lower, and 360°C or lower.

[0067] Furthermore, especially when used as a display substrate material, although not particularly limited, it is desirable to dry it in a temperature range of 50°C to 150°C and then process it at a maximum heating temperature of 150°C to 600°C, preferably 200°C to 550°C, and more preferably 250°C to 500°C.

[0068] Chemical / or thermal imidation heat treatment may be carried out in stages. For example, it is preferable to perform a primary heat treatment at a relatively low temperature of 100°C to 170°C for about 0.5 to 30 minutes, followed by a secondary heat treatment at a temperature above 170°C but below 220°C for about 0.5 to 30 minutes, and then a tertiary heat treatment at a high temperature above 220°C but below 350°C for about 0.5 to 30 minutes, and further a fourth high-temperature heat treatment from 350°C or above to the maximum heating temperature can be performed. It is preferable to carry out the heat treatment continuously. For example, it is preferable to heat treat from a relatively low temperature of 100°C to 170°C to the maximum heating temperature. There are no particular restrictions on the heating rate, but it is preferable to be between 1°C / min and 30°C / min, and particularly preferable to be between 2°C / min and 20°C / min. Within the above range, foaming due to rapid heating can be suppressed, which is preferable.

[0069] In manufacturing method (2), when chemical / or thermal imidation is performed, the self-supporting film can be manufactured while fixing the self-supporting film with a pin tenter, clip, frame, etc., based on known methods.

[0070] Manufacturing methods (3) and (4) include a step of heat treatment. This heat treatment step may be performed in the state of a laminate of the support and the polyimide precursor film, as in (3), or it may be performed after peeling the polyimide precursor film from the support to form a self-supporting film, as in (4). The heat treatment conditions are usually preferably 150°C or higher, 180°C or higher, or 200°C or higher, and more preferably 300°C or lower, 270°C or lower, or 250°C or lower. The heat treatment time can be set appropriately depending on the heating temperature, for example, preferably 1 minute or more, 10 minutes or more, or 20 minutes or more, and more preferably 24 hours or less, 12 hours or less, 1 hour or less, or 30 minutes or less.

[0071] In manufacturing method (4), the self-supporting film can be heat-treated while being fixed, similar to manufacturing method (2).

[0072] As described above, the polyimide film of the present invention contains DATP as a diamine component, and therefore can exhibit excellent dimensional stability without stretching the film. However, depending on the application of the polyimide film, the polyimide film can be oriented by stretching the self-supporting film in the longitudinal direction (so-called MD direction) and / or the transverse direction (so-called TD direction), thereby adding desired physical properties.

[0073] The polyimide film obtained by the present invention has excellent heat resistance and dimensional stability, and can therefore be suitably used, for example, as a heat-resistant layer (core layer) of a metal lamination film in a circuit board such as a high-frequency circuit board. Furthermore, when the polyimide film of the present invention is used for circuit board applications, it is preferable that, in addition to high heat resistance and high-temperature dimensional stability, it also possesses low saturated water absorption and / or low water vapor transmission, from the viewpoint of making it more suitable for circuit board applications.

[0074] The aforementioned metal lamination film generally has a metal adhesive layer on one or both sides of a heat-resistant layer. The metal adhesive layer is a layer used to bond a metal layer to a heat-resistant layer made of the polyimide film of the present invention. As one embodiment of the metal lamination film using the polyimide film of the present invention, for example, a metal lamination film can be exemplified in which a heat-fusible (thermoplastic) polyimide with a Tg of less than 290°C, preferably 250°C or less, and particularly preferably 200°C or less is used as the metal adhesive layer, and this is laminated on one or both sides of the polyimide film of the present invention. As another embodiment, for example, a metal lamination film can be exemplified in which a coating liquid containing a silane coupling agent is applied to one or both sides of the polyimide film of the present invention to form a metal adhesive layer. The coating liquid may be applied to the surface of the heat-fusible polyimide, or a metal lamination film can be exemplified in which a metal adhesive layer is formed using a mixture of the heat-fusible polyimide and the coating liquid.

[0075] Furthermore, the polyimide film of the present invention can be suitably used as a substrate for displays such as touch panels and other displays, as well as for solar cells. As an example, a display substrate using the polyimide film of the present invention will be described. The polyimide film of the present invention has excellent heat resistance and dimensional stability, and is therefore suitably used as a substrate for displays. However, when used as a substrate for displays, it is particularly preferable that the coefficient of linear expansion (i.e., high-temperature dimensional stability) in the temperature range of 50 to 500°C is less than +0.5 ppm / K and -1.0 ppm / K or more, from the viewpoint of making it more suitable for display substrate applications.

[0076] For example, a flexible conductive substrate (flexible electronic device substrate) can be obtained for a display by forming a conductive layer of a conductive material (such as a metal or metal oxide, a conductive organic material, or conductive carbon) on the surface of the polyimide film of the present invention, resulting in a conductive layer / polyimide film laminate or a conductive layer / polyimide film laminate / conductive layer. If necessary, an inorganic layer such as a gas barrier layer for water vapor or oxygen, or a light-adjusting layer may be formed on the surface of the polyimide film by sputtering, vapor deposition, or gel-sol method before forming the conductive layer. In this case, the polyimide film of the present invention may also be used as a laminate by laminating it with a glass substrate.

[0077] Furthermore, circuits are suitably formed in the conductive layer by methods such as photolithography, various printing methods, and inkjet printing.

[0078] The display substrate obtained in this manner has a conductive layer circuit on the surface of a polyimide film composed of the polyimide of the present invention, with a gas barrier layer or inorganic layer interposed as needed. Because this substrate has excellent heat resistance and dimensional stability, it is easy to form fine circuits. Furthermore, if a polyimide film with low water absorption and a low water vapor permeability coefficient is used, it is possible to prevent moisture from penetrating into displays and the like. Therefore, by mounting various elements, this substrate can be suitably used as a display substrate for displays, touch panels, etc., or as a solar cell substrate. [Examples]

[0079] The present invention will be described in more detail below with reference to examples, comparative examples, and reference examples, but the present invention is not limited thereto.

[0080] The measurement method used in the following example is shown below.

[0081] <Glass transition temperature> Using an RSA G2 dynamic viscoelasticity analyzer manufactured by TA INSTRUMENTS, the dynamic viscoelasticity of polyimide films was measured under conditions of a heating rate of 10°C / min and a frequency of 1 Hz. The peak temperature of tanδ was defined as the glass transition temperature. If the tanδ peak was not clearly observed even after heating to 500°C, the glass transition temperature was considered to be "above 500°C". <Coefficient of linear expansion 1> Using an EXSTAR6100 manufactured by SII, polyimide films sampled to a length of 15 mm, width of 3 mm, and thickness of 25 μm were measured in tensile mode, with a load of 4 gf and a heating rate of 20 °C / min. Primary heating was performed up to 300 °C to capture thermal shrinkage during film formation. After cooling to room temperature, secondary heating was performed up to 300 °C at 20 °C / min, and the coefficient of linear expansion was calculated from the TMA curve from 50 °C to 200 °C. <Coefficient of linear expansion 2> Using an EXSTAR6100 manufactured by SII, polyimide films sampled to a length of 15 mm, width of 3 mm, and thickness of 10 μm were measured in tensile mode, with a load of 4 gf and a heating rate of 20 °C / min. Primary heating was performed up to 500 °C to capture thermal shrinkage during film formation. After cooling to room temperature, secondary heating was performed up to 500 °C at 20 °C / min, and the coefficient of linear expansion was calculated from the TMA curve from 50 °C to 500 °C. <Saturated water absorption rate> The saturation water absorption rate was calculated from the weight of the completely dry and saturated water-absorbed polyimide film after immersion in 23°C water for more than 24 hours using the following formula. Saturated water absorption rate (%) = [(weight after saturated water absorption) - (absolutely dry weight)] / (absolutely dry weight) × 100 <Water vapor permeability coefficient> The water vapor transmission rate of polyimide film was measured at 40°C and 90% relative humidity, in accordance with Method B of JIS K7129. The water vapor transmission coefficient was calculated from the measured water vapor transmission rate. Water vapor transmission coefficient = Water vapor transmission rate × Film thickness <Viscosity stability> For polyamic acid solutions, samples were marked with ○ if the viscosity change rate of the solution viscosity after holding at 23°C for 31 days was ±2% or less compared to the viscosity after holding at 23°C for 7 days, samples marked with △ if the change rate was ±5% or less, and all others marked with ×. Viscosity was measured using an E-type viscometer at a measurement temperature of 30°C. <Average molecular weight, molecular weight distribution> The weight-average molecular weight Mw and number-average molecular weight Mn were measured under the following conditions, and the molecular weight distribution Mw / Mn was calculated from the obtained Mw and Mn values. Equipment: Tosoh HLC-8320GPC Column: Tosoh TSKgel Super AWM-H 9um 6.0mm I.D. x 15cm Eluent: NMP (10 mmol / L LiCl, 30 mmol / L phosphoric acid) Measurement temperature: 40℃ Flow rate: 0.5mL / min Detection method: RI Measurement amount: 20μL

[0082] The abbreviations for the compounds used in the following examples are as follows: s-BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride a-BPDA: 2,3,3',4-biphenyltetracarboxylic acid dianhydride PMDA: 1,2,4,5-benzenetetracarboxylic acid dianhydride (pyromellitic dianhydride) ODPA: 4,4'-Oxydiphthalic acid dianhydride PPD: p-phenylenediamine ODA: 4,4'-diaminodiphenyl ether MPD: m-phenylenediamine BAF:9,9-bis(4-aminophenyl)fluorene DATP: 4,4''-diamino-p-terphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene TPE-Q: 1,4-bis(4-aminophenoxy)benzene Bisaniline P: 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene BAPB:4,4'-Bis(4-aminophenoxy)biphenyl BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane DMAc: N,N-dimethylacetamide NMP: N-methyl-2-pyrrolidone

[0083] [Example 1] DMAc was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and then DATP was added as the diamine component. Subsequently, s-BPDA and PMDA were added as tetracarboxylic dianhydride components in equimolar amounts with the diamine component and reacted to obtain a polyamic acid solution with a monomer concentration of 18% by mass and a solution viscosity of 1800 poise at 30°C. The molar ratio of s-BPDA to PMDA was 10:90. The obtained polyamic acid solution was cast as a thin film onto a glass plate, heated in an oven at 120°C for 12 minutes, and peeled off the glass plate to obtain a self-supporting film. The four sides of this self-supporting film were fixed with pin tenters, and it was gradually heated in a heating furnace from 150°C to 450°C (maximum heating temperature was 450°C) to remove the solvent and imide, obtaining a polyimide film with a thickness of 25 μm. The evaluation results are shown in Table 1.

[0084] [Examples 2-22, Comparative Examples 1-4] A polyimide film was obtained in the same manner as in Example 1, except that the type and proportion of the acid anhydride and diamine of the polyamic acid were changed as shown in Table 1. The evaluation results are shown in Tables 1 and 2.

[0085] [Table 1] In Table 1, the amounts of acid anhydrides and diamines in polyamic acids are given in molar amounts, and "-" indicates that the amount was not measured.

[0086] [Table 2] In Table 2, the amounts of acid anhydrides and diamines of polyamic acids are given in molar amounts, and "-" indicates that the amount was not measured.

[0087] When the glass transition temperature and the coefficient of linear expansion in the temperature range of 50°C to 200°C of the obtained polyimide films were evaluated, all of the polyimide films from Examples 1 to 22 exhibited high glass transition temperatures and low coefficients of linear expansion, meaning they possessed high heat resistance and dimensional stability.

[0088] [Example 23] NMP was added to a reaction vessel equipped with a stirrer and a nitrogen inlet tube, and then DATP was added as the diamine component. Subsequently, s-BPDA and PMDA were added as tetracarboxylic dianhydride components in approximately equimolar amounts with the diamine component and reacted to obtain a polyamic acid solution with a monomer concentration of 10% by mass and a solution viscosity of 76.0 poise at 30°C. The molar ratios were s-BPDA:PMDA:DATP, respectively, at 97:3:100. The prepared polyamic acid solution was spin-coated onto an alkali-free glass wafer and heated at 120°C, 150°C, 200°C, and 250°C for 10 minutes each, and at 450°C for 5 minutes to form a 10 μm thick polyimide film, thereby producing a polyimide / glass laminate. The evaluation results of the polyimide film peeled from the glass are shown in Table 3.

[0089] [Examples 24-29, Comparative Example 5, Reference Examples 1-5] A polyimide film was obtained in the same manner as in Example 23, except that the type and proportion of the acid anhydride and diamine of the polyamic acid were changed as shown in Table 3. The evaluation results are shown in Table 3.

[0090] [Table 3] In Table 3, the amounts of acid anhydrides and diamines in polyamic acids are in molar amounts. "-" indicates that the measurement was not performed, and "above 500°C" means that even when the temperature was raised to 500°C and the glass transition temperature was measured, the tanδ peak was not clearly observed.

[0091] When the glass transition temperature and the coefficient of linear expansion in the temperature range of 50°C to 500°C of the obtained polyimide films were evaluated, the polyimide films of Examples 1 to 22 all exhibited high glass transition temperatures and low coefficients of linear expansion, meaning they possessed high heat resistance and high-temperature dimensional stability. Examples 23 to 39 all had a coefficient of linear expansion in the temperature range of 50°C to 200°C that was between -5 ppm / K and 10 ppm / K. Comparative Example 5 and Reference Examples 1 to 5 had a coefficient of linear expansion in the temperature range of 50°C to 500°C that was outside the range of less than +0.5 ppm / K and greater than -1.0 ppm / K, making them unsuitable for display substrate material applications.

[0092] Viscosity stability was measured for Examples 23, 29, Comparative Example 5, and Reference Example 1. The results are shown in Table 4. As is clear from the results in Table 4, the polyimide precursor solution according to the present invention was found to have extremely excellent storage stability. [Table 4]

[0093] Furthermore, when the molecular weight distribution of Examples 1 to 29 was measured, the molecular weight distribution (Mw / Mn) was 5 or less in all cases (in particular, most of Examples 1 to 29 had Mw / Mn = 1.5 or more and 4 or less). Therefore, it can be said that the polyimide precursor solution of the present invention was able to produce a polyimide film with an excellent balance of heat resistance and mechanical strength.

Claims

[Claim 1] A polyimide film comprising a polyimide obtained by reacting a tetracarboxylic acid component with a diamine component containing 4,4''-diamino-p-terphenyl, wherein the polyimide film has a glass transition temperature higher than 290°C and a coefficient of linear expansion of 10 ppm / K or less in the temperature range of 50°C to 200°C.

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