Polyimide precursors and polyimides

Abstract

To provide a polyimide film and a precursor thereof, from which a transparent polyimide having low coloration and high transmittance, which is optimal for a transparent substrate for a flexible device and a laminate for a wiring substrates, can be obtained.SOLUTION: In a polyimide precursor varnish containing a polyimide precursor and an organic solvent, the organic solvent has a yellowness YI of 2.0 or less and b* of 1.0 or less, and the polyimide precursor varnish has a yellowness (YI) of less than 5.0 and b* of less than 2.0. There is also provided a polyimide thereof.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a transparent polyimide precursor and a polyimide.

Background Art

[0002] Display devices such as liquid crystal display devices and organic EL devices, and touch panels are used as constituent members for various displays, including large displays such as televisions and small displays such as mobile phones, personal computers and smartphones. For example, an organic EL device is generally produced by forming a thin film transistor (TFT) on a glass substrate serving as a support base, further sequentially forming an electrode, a light-emitting layer and another electrode thereon, and hermetically sealing these components with a glass substrate, a multilayer thin film or the like. A touch panel has a configuration in which a first glass substrate having a first electrode formed thereon and a second glass substrate having a second electrode formed thereon are bonded together via an insulating layer (dielectric layer).

[0003] That is, these constituent members are laminates in which various functional layers such as TFTs, electrodes, and light-emitting layers are formed on a glass substrate. By replacing this glass substrate with a resin substrate, the conventional constituent members using a glass substrate can be made thinner, lighter, and flexible. Utilizing this, it is expected to obtain flexible devices such as flexible displays. On the other hand, compared with glass, resins are inferior in dimensional stability, transparency, heat resistance, moisture resistance, film strength and the like, so various studies have been conducted.

[0004] As such a resin substrate material, polyimide is one of the promising materials due to its excellent heat resistance and dimensional stability, and is expected to be applied to flexible devices requiring transparency, such as substrates for organic EL devices, touch panel substrates, and color filter substrates.

[0005] A transparent polyimide substrate for flexible devices is obtained by using a glass substrate as a support base, forming a transparent polyimide film on this support base, then mounting electronic components on the transparent polyimide film, and finally peeling off the support base.

[0006] For example, Patent Document 1 discloses a fluorine-containing polyimide film for flexible devices manufactured by peeling from a carrier substrate, having a glass transition temperature of 300°C or higher, a thermal decomposition temperature of 500°C or higher, and a thermal expansion coefficient of 20 ppm / K or less. However, transparency has not been considered. Patent document 2 reports on the use of an organic solvent with a light transmittance of 89% or more at 400 nm to produce a highly transparent polyimide film. However, this process involves complicated steps to purify the solvent, and even if the solvent has high light transmittance, the resulting polyimide may be discolored. Therefore, simply increasing the light transmittance of the solvent is insufficient to obtain a highly transparent polyimide. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-040836 [Patent Document 2] Japanese Patent Publication No. 2013-23597 [Overview of the project]

[0008] The object of the present invention is to provide a polyimide film and its precursor that can produce a transparent polyimide with low coloration and high transmittance, which is ideal for transparent substrates for flexible devices and laminates for wiring boards.

[0009] As a result of diligent research, the inventors focused on the organic solvents used in the preparation and manufacturing of polyimide precursor varnishes and polyimides, and discovered that by using specific solvents, it is possible to obtain polyimide precursor varnishes and polyimides with low coloration (YI) and high transmittance, thereby completing the present invention.

[0010] In other words, the present invention relates to a polyimide precursor varnish comprising a polyimide precursor and an organic solvent, characterized in that the yellowness YI of the organic solvent is 2.0 or less, and b* is 1.0 or less, and the yellowness (YI) of the polyimide precursor varnish is less than 5.0, and b* is less than 2.0.

[0011] The polyimide precursor varnish of the present invention preferably has a light transmittance of 85% or more and less than 89% at an optical path length of 1 cm and a wavelength of 400 nm in an organic solvent. The polyimide precursor varnish of the present invention preferably contains one or more organic solvents selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylimidazolidinone, and γ-butyrolactone.

[0012] The present invention relates to a method for producing a polyimide precursor varnish comprising a polyimide precursor and an organic solvent, characterized in that the organic solvent used has a yellowness YI of 2.0 or less and a b* of 1.0 or less, and the polyimide precursor varnish obtained has a yellowness YI of less than 5.0 and a b* of less than 2.0.

[0013] The present invention relates to a polyimide obtained by imidizing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, characterized in that the yellowness YI of the organic solvent is 2.0 or less, the b* is 1.0 or less, the yellowness YI of the polyimide (calculated on a thickness of 10 μm) is 30 or less, and the total light transmittance is 80% or more.

[0014] The present invention relates to a method for producing polyimide obtained by imidizing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, characterized in that an organic solvent having a yellowness YI of 2.0 or less and a b* of 1.0 or less is used as the organic solvent, and a polyimide having a yellowness (calculated on a thickness of 10 μm) of 30 or less and a total light transmittance of 80% or more is obtained.

[0015] The present invention is a flexible device characterized by comprising a polyimide layer containing the above-mentioned polyimide and a functional layer formed on the polyimide layer. The present invention is a laminate for a wiring board characterized by having a polyimide layer containing the above-mentioned polyimide, and a metal layer on one or both sides of the polyimide layer.

[0016] According to the present invention, by focusing on the organic solvents used in the preparation and production of polyimide precursor varnishes and polyimides, and by using specific solvents with respect to yellowness (YI) and color values ​​L*, a*, and b*, we have achieved the provision of polyimide precursor varnishes and polyimides with low coloration and high light transmittance. [Modes for carrying out the invention]

[0017] The polyimide precursor varnish of the present invention comprises a polyimide precursor and an organic solvent, wherein the yellowness YI of the organic solvent is 2.0 or less, the b* is 1.0 or less, and the light transmittance at a path length of 1 cm and a wavelength of 400 nm is 85% or more. The inventors observed that even when using an organic solvent with a light transmittance of 89% or more, the resulting polyimide precursors and polyimides were colored and had low light transmittance. This indicated that high light transmittance alone was insufficient to obtain highly transparent polyimide precursors and polyimides, and they investigated the existence of more effective parameters, leading to the present invention. These effective parameters are yellowness (YI) and color values ​​L*, a*, and b*. In particular, they found that yellowness YI and color value b* significantly affect the transparency of polyimide precursor varnish and polyimide.

[0018] In the polyimide precursor varnish of the present invention, it is essential that the organic solvent has a yellowness YI of 2.0 or less and a b* of 1.0 or less. If either the yellowness YI value or the b* value of the organic solvent does not meet these conditions, the effects of the present invention cannot be achieved. The yellowness YI of the organic solvent is preferably 1.90 or less, more preferably 1.50 or less. The b* value is preferably 0.90 or less, more preferably 0.85 or less.

[0019] While other color values ​​L* and a* are not essential, the color value L* is used as an organic solvent. Preferably, the L* value should be 90.0 or higher, more preferably 93.0 or higher. In the present invention, organic solvents with an L* value of 97.0 or lower or 96.0 or lower can also be suitably used. As for the organic solvent, it is preferable to select one with a color value a* of -0.10 to -0.80, more preferably -0.20 to -0.70.

[0020] The polyimide precursor varnish of the present invention preferably uses an organic solvent with a light transmittance of 85% or more at a path length of 1 cm and a wavelength of 400 nm; it is not necessary for the light transmittance to be 89% or more. Organic solvents with a light transmittance of less than 89%, less than 88%, or less than 87% can also be suitably used. Organic solvents with a light transmittance of less than 89% are preferable because they can be easily manufactured without complicated purification.

[0021] The polyimide precursor varnish of the present invention preferably uses an organic solvent with a purity of 99.8% or higher, but it is not necessary for the purity to be 99.9% or higher. Organic solvents with a purity of less than 99.9% can also be suitably used. Organic solvents with a purity of less than 99.9% are preferable because they can be manufactured without complicated purification.

[0022] As the organic solvent, as long as the yellow index YI and color values described above are satisfied, various organic solvents used in the preparation and production of polyimide precursors and polyimides can be used. Examples include N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylimidazolidinone (DMI), and γ-butyrolactone (GBL). These may also be used as a mixture.

[0023] The polyimide precursor varnish of the present invention has a yellowness index (YI) of less than 5.0 and a b* value of 2. It is essential that the value is less than 0. A desired polyimide cannot be obtained from a polyimide precursor varnish in which either one of the yellowness index YI value and the b* value does not satisfy the above condition. The yellowness index YI of the polyimide precursor varnish is preferably 4.00 or less, more preferably 3.00 or less. The b* value is preferably 1.50 or less, more preferably 1.00 or less.

[0024] Although the other color values L* and a* are not essential, as the polyimide precursor varnish, it is preferable to select one having a color value L* of preferably 90.0 or more, more preferably 93.0 or more. In the present invention, even a polyimide precursor varnish having an L* value of 97.0 or less can be suitably used. As the polyimide precursor varnish, it is preferable to select one having a color value a* of preferably -2.0 to 2.0, more preferably -1.0 to 1.0.

[0025] The polyimide precursor of the present invention has a structural unit represented by the following general formula (1), and can be widely applied as long as it has a structural unit derived from an acid dianhydride (A) and a structural unit derived from a diamine (B).

Chemical Formula

[0026] Combinations of acid dianhydrides and diamines as raw materials include aromatic acid dianhydride / aromatic diamine, aromatic acid dianhydride / aliphatic diamine, aliphatic acid dianhydride / aromatic diamine, and aliphatic acid dianhydride / aliphatic diamine, but it is preferable that an aromatic component is included. When an aliphatic component is included, it is preferable that it has an alicyclic structure. For applications requiring heat resistance, a combination of aromatic acid dianhydride and aromatic diamine is preferred.

[0027] Examples of acid dianhydrides include 4,4'-(2,2'-hexafluoroisopropylidene)diphthalic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, 4,4'-(2,2'-hexafluoroisopropylidene)diphthalic acid dianhydride, naphthalene-2,3,6,7-tetracarboxylic acid dianhydride, naphthalene-1,2,5,6-tetracarboxylic acid dianhydride, naphthalene-1,2,6,7-tetracarboxylic acid dianhydride, pyromellitic acid dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, and 2,2',3,3'-biphenyltetracarboxylic acid dianhydride. Dianhydride of naphthalene, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,2',3,3'-benzophenonetetracarboxylic acid dianhydride, 2,3,3',4'-benzophenonetetracarboxylic acid dianhydride, naphthalene-1,2,4,5-tetracarboxylic acid dianhydride, naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, naphthalene-1,2,6,7-tetracarboxylic acid dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6 -Tetracarboxylic acid dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2,3,6,7-tetracarboxylic acid dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic acid dianhydride, 3,3',4,4'-p-terphenyltetracarboxylic acid di Anhydride, 2,2',3,3'-p-terphenyltetracarboxylic acid dianhydride, 2,3,3',4'-p-terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(3,4-Dicarboxyphenyl)ethane dianhydride, perylene-2,3,8,9-tetracarboxylic acid dianhydride, perylene-3,4,9,10-tetracarboxylic acid dianhydride, perylene-4,5,10,11-tetracarboxylic acid dianhydride, perylene-5,6,11,12-tetracarboxylic acid dianhydride, phenanthrene-1,2,7,8-tetracarboxylic acid dianhydride, phenanthrene-1,2,6,7-tetracarboxylic acid dianhydride, phenanthrene-1,2,9,10-tetracarboxylic acid dianhydride, cyclopentane-1,2, 3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, (trifluoromethyl)pyromellitic dianhydride, di(trifluoromethyl)pyromellitic dianhydride, di(heptafluoropropyl)pyromellitic dianhydride, pentafluoroethylpyromellitic dianhydride, bis{3,5-di(trifluoromethyl) Phenoxypyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 2,2',5,5'-tetrakis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether dianhydride, 5,5'-bis(trifluoromethyl)-3,3 ',4,4'-tetracarboxybenzophenone dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}benzene dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}, trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride, 2,2-bis{(4-(3,Examples include 4-dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}bis(trifluoromethyl)biphenyl dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}diphenyl ether dianhydride, and bis(dicarboxyphenoxy)bis(trifluoromethyl)biphenyl dianhydride. Mixtures of these may also be used.

[0028] Preferably, the dianhydride is 4,4'-(2,2'-hexafluoroisopropylidene)diphthalic acid dianhydride (6FDA), 4,4'-oxydiphthalic acid dianhydride (ODPA), pyromellitic acid dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 4,4'-(2,2'-hexafluoroisopropylidene)diphthalic acid dianhydride, or 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride. However, this is not limited to the above, as long as the yellowness (YI) of the polyimide precursor varnish is less than 5.0 and the b* is less than 2.0.

[0029] Examples of diamines include 2,2-bis(trifluoromethyl)benzidine, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, 4,4'-diaminodiphenylpropane, 3,3' -diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, benzidine, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 4,4'-diamino-p-terphenyl, 3,3' Examples include diamino-p-terphenyl, bis(p-β-amino-t-butylphenyl) ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,3-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 5-amino-2-(4-aminophenyl)benzimidazole, or diaminopropyltetramethyldisiloxane. Mixtures of these may also be used.

[0030] Preferably, the compounds are 2,2-bis(trifluoromethyl)benzidine (TFMB), 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4-bis(4-aminophenoxy)benzene, 4,4'-diaminodiphenyl ether, p-phenylenediamine (p-PDA), 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 2,4-toluenediamine, m-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, or 5-amino-2-(4-aminophenyl)benzimidazole. However, this is not limited to the above, as long as the yellowness (YI) of the polyimide precursor varnish is less than 5.0 and the b* is less than 2.0.

[0031] The polyimide precursor varnish of the present invention is useful for polyimide precursors in which, for example, the structural units derived from monomers having ether groups in the structure of the polyimide precursor account for 10% or more, more preferably 50% or more, of the total structural units derived from monomers. It is also useful for polyimide precursors in which the structural units derived from monomers having fluorine atoms account for 10% or more, more preferably 50% or more, of the total structural units derived from monomers. Since polyimide precursors and polyimide films having such structural units have excellent transparency, when the organic solvent constituting the present invention is used (i.e., when a polyimide precursor is used as a polyimide precursor varnish, or when a polyimide film is obtained by imidizing the polyimide precursor varnish), a polyimide precursor varnish and polyimide film with even better transparency can be obtained. However, this is not limited to the above, as long as the yellowness (YI) of the polyimide precursor varnish is less than 5.0 and the b* is less than 2.0.

[0032] The polyimide precursor of the present invention can be produced by known methods of polymerization in an organic solvent using an acidic dianhydride and a diamine in a molar ratio of 0.9 to 1.1. For example, it can be obtained by adding an acidic dianhydride and a diamine as raw material monomers to an organic solvent under a nitrogen atmosphere and reacting them at room temperature to 80°C for several hours to several days. For every 100 parts by weight of monomer, the organic solvent should be used in an amount of, for example, 200 to 1500 parts by weight, preferably 300 to 900 parts by weight.

[0033] The polyimide of the present invention is obtained by imidizing the polyimide precursor varnish of the present invention. Imidization can be carried out by thermal imidization or chemical imidization. Thermal imidization is performed, for example, by forming a film of polyimide precursor varnish on a support substrate, pre-drying it, and then heat-treating it at a temperature of room temperature to about 450°C. Chemical imidization is performed, for example, by adding a known dehydrating agent and / or catalyst to the polyimide precursor varnish (for example, acetic anhydride as a dehydrating agent, and pyridine, isoquinoline, or N-methylimidazole as catalysts), and chemically dehydrating it at, for example, 30 to 60°C. The following are examples of preferred conditions for thermal imidation. A polyimide precursor composition is formed on any support substrate such as glass, metal, or resin using an applicator, pre-dried at a temperature of 150°C or lower for 2 to 60 minutes, and then heat-treated at a temperature of approximately 10 minutes to 20 hours, more preferably 10 minutes to 4 hours, at a temperature of approximately 470°C to room temperature for solvent removal and imidation. If the desired polyimide film can be obtained, the heat treatment temperature may be as low as 280°C. The heat treatment temperature can also be changed between 280°C and 470°C depending on the required mechanical properties. More preferably, if the maximum film formation temperature is 340 to 460°C, the organic solvent constituting the present invention is less likely to adversely affect the transparency of the polyimide precursor varnish and polyimide of the present invention, and as a result, the polyimide of the present invention is preferable because it has an excellent balance of film transmittance and mechanical properties (CTE, tensile strength, tensile elongation, elastic modulus). Chemical imidation involves adding a dehydrating agent and a catalyst to a solution of the polyimide precursor composition (also called polyamic acid) and chemically dehydrating it at 30-60°C. Typical dehydrating agents include acetic anhydride, and typical catalysts include pyridine. Thermal imidation, by selecting the appropriate combination of acid dianhydride or diamine and solvent, can be completed relatively quickly, and the heat treatment, including preheating, can be completed within 60 minutes. The polyimide precursor composition can also be prepared as a film by dissolving it in a solvent.

[0034] The degree of polymerization of the polyimide precursor and polyimide of the present invention is not particularly limited, but for example, the viscosity of the polyimide precursor solution measured by an E-type viscometer is preferably in the range of 500 to 100,000 cP, more preferably in the range of 1,000 to 15,000 cP. The molecular weight of the polyimide precursor can be determined by the GPC method. For example, the polyimide precursor has a number-average molecular weight (Mn) in the range of 15,000 to 250,000 and a weight-average molecular weight (Mw) in the range of 30,000 to 800,000. The molecular weight of the polyimide is also in a similar range to the molecular weight of the polyimide precursor.

[0035] The polyimide obtained by imidizing the polyimide precursor of the present invention, in the state of a polyimide film with a standard thickness of 10 μm (calculated value for a thickness of 10 μm), has a yellowness of 30 or less, and can be 20 or less. The total light transmittance is 80% or more, and can be 85% or more.

[0036] The polyimide of the present invention has a light transmittance of 70% or more at 500 nm, and can reach 83% or more, while having a light transmittance of 1% or less at 308 nm. In the manufacture of flexible devices, by irradiating the flexible substrate with a laser, the support substrate can be peeled off without damaging elements formed on the polyimide film, and the laser lift-off method can be preferably applied. As the supporting substrate, known materials can be used, such as inorganic substrates like glass and metal foil, and heat-resistant resin films such as polyimide.

[0037] The polyimide of the present invention also has a low coefficient of thermal expansion (CTE), for example, 20 ppm / K or less. In terms of tensile properties, it can exhibit a tensile strength of 100 MPa or more, a tensile elongation of 5% or more, and an elastic modulus of 10 GPa or less.

[0038] The polyimide of the present invention can be used as a transparent polyimide in various flexible devices. The polyimide of the present invention is suitable as a polyimide film with a functional layer. The polyimide film may consist of multiple layers of polyimide. The polyimide of the present invention can be formed into a laminate by creating various functional layers on the polyimide layer. Examples of functional layers include liquid crystal display devices, organic EL display devices, touch panels, liquid crystal displays, organic EL displays, color filters, electronic paper, and other display devices, as well as their components. It is also useful as a laminate for wiring boards (CCL) having a metal layer on one or both sides of the polyimide layer. [Examples]

[0039] The present invention will be described in more detail below with reference to examples. The abbreviations and evaluation methods for the materials used in the examples and comparative examples are shown below.

[0040] (acid dianhydride) • FDA: 4,4'-(2,2'-hexafluoroisopropylidene)diphthalic anhydride • ODPA: 4,4'-Oxydiphthalic anhydride • PMDA: Pyromellitic anhydride • CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride (Diamine) • TFMB: 2,2-bis(trifluoromethyl)benzidine • BY16-871: Diaminopropyltetramethyldisiloxane (manufactured by Toray Dow Corning, amine equivalent 125 g / mol) • BAPS: Bis[4-(aminophenoxy)phenyl]sulfone AAPBI: 5-amino-2-(4-aminophenyl)benzimidazole (solvent) As shown in Table 1, solvents with different YI, L*, a*, b*, purity, and light transmittance (T) were used (S1-S10). NMP is N-methyl-2-pyrrolidone. DMAC is N,N-dimethylacetamide.

[0041] [Light transmittance, yellowness YI, L*, a*, b* of solvents and varnishes] Measurements were taken using a SHIMADZU UV-3600 spectrophotometer and a quartz standard cell with a path length of 1 cm. Ultrapure water was used as a blank, and the light transmittance of the solvent at 400 nm was measured. Furthermore, the YI (yellowness) was calculated based on the formula shown in equation (1) below.

number

[0042] [Film light transmittance, yellowness YI, L*, a*, b*] The light transmittance (T@308, T@500) at 308 nm and 500 nm was determined for a polyimide film (50 mm x 50 mm) using a SHIMADZU UV-3600 spectrophotometer. The YI (yellowness) was calculated based on the formula (1) shown above. The value YI(10), converted to a thickness of 10 μm, was calculated using the following formula (2).

number

[0043] [Total light transmittance (TT)] The total light transmittance (TT) of a polyimide film (50mm x 50mm) was measured using a HAZE METER NDH500 manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS K7136.

[0044] [viscosity] Viscosity was measured at 25°C using a cone-plate viscometer with a constant-temperature water bath (manufactured by Tokimec Co., Ltd.) for the polyamic acid solutions obtained in the synthesis examples.

[0045] [Molecular weight Mw] Molecular weight was measured by gel permeation chromatography (Tosoh Corporation, product name: HLC-8220GPC). Polystyrene was used as the standard substance, and N,N-dimethylacetamide was used as the developing solvent.

[0046] [Coefficient of thermal expansion (CTE)] A polyimide film (3mm x 15mm) was heated from 30°C to 450°C at a constant heating rate (10°C / min) while applying a load of 30mN using a thermomechanical analyzer (TMA / SS6100). Then, the temperature was lowered from 450°C, and the coefficient of thermal expansion was measured from the elongation (linear expansion) of the polyimide film during the cooling process from 350°C to 100°C.

[0047] [Tensile test] Test specimens of polyimide film (10 mm x 15 mm) were prepared, and tensile tests were performed using a Tensilon universal testing machine (Orientec Co., Ltd., RTA-250) at a tensile speed of 10 mm / min in accordance with IPC-TM-650, 2.4.19. Tensile elongation, tensile strength, and modulus of elasticity were calculated.

[0048] [purity] Purity was measured using gas chromatography.

[0049] The solvents used are as shown in Table 1 below (S1~S10).

[0050] [Table 1]

[0051] Example 1 Under a nitrogen atmosphere, 78.84 g of TFMB was dissolved in 765 g of solvent S1 in a 1000 ml separable flask. Then, 9.50 g of ODPA and 46.66 g of PMDA were added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding a polyimide (PI) precursor varnish (viscous solution) V1 with a molecular weight (Mw) of 100,000 or more.

[0052] Example 2 Under a nitrogen atmosphere, 169.88 g of TFMB was dissolved in 1700 g of solvent S1 in a 2000 ml separable flask. Then, 49.29 g of ODPA and 80.84 g of PMDA were added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding polyimide (PI) precursor varnish (viscous solution) V2 with a molecular weight (Mw) of 100,000 or more.

[0053] Example 3 Under a nitrogen atmosphere, 8.56 g of TFMB was dissolved in 85 g of solvent S2 in a 100 ml separable flask. Then, 2.07 g of ODPA and 4.37 g of PMDA were added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding polyimide (PI) precursor varnish (viscous solution) V3 with a molecular weight (Mw) of 100,000 or more.

[0054] Example 4 Under a nitrogen atmosphere, 25.48 g of TFMB was dissolved in 255 g of solvent S4 in a 300 ml separable flask. Then, 7.39 g of ODPA and 12.13 g of PMDA were added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding polyimide (PI) precursor varnish (viscous solution) V4 with a molecular weight (Mw) of 100,000 or more.

[0055] Example 5 Under a nitrogen atmosphere, 3.02 g of BY16-871 was dissolved in 70 g of solvent S3 in a 100 ml separable flask. Then, 9.04 g of TFMB was added to this solution. After stirring for 10 minutes, 17.93 g of 6FDA was added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding polyimide precursor varnish (viscous solution) V5 with a molecular weight (Mw) of 100,000 or more.

[0056] Example 6 Under a nitrogen atmosphere, 424.57 g of TFMB was dissolved in 4250 g of solvent S3 in a 5000 ml separable flask. After stirring for 10 minutes, 73.40 g of 6FDA and 252.03 g of PMDA were added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding polyimide precursor varnish (viscous solution) V6 with a molecular weight (Mw) of 100,000 or more.

[0057] Comparative Example 1 Under a nitrogen atmosphere, 25.69 g of TFMB was dissolved in 4250 g of solvent S5 in a 300 ml separable flask. After stirring for 10 minutes, 6.21 g of ODPA and 13.10 g of PMDA were added. This solution was heated at 40°C for 30 minutes to dissolve the contents, and then the solution was stirred at room temperature for 30 hours to carry out the polymerization reaction, yielding polyimide precursor varnish (viscous solution) V7 with a molecular weight (Mw) of less than 100,000.

[0058] Examples 7, 8, Comparative Examples 2-5 Using a 100 ml separable flask and 68 g of solvent, the polymerization reaction was carried out in the same manner as in Example 1, with the diamine, acid anhydride, and solvent replaced with the formulations shown in Table 2. Examples 7 and 8 yielded polyimide precursor varnishes with a molecular weight (Mw) of 100,000 or more, while Comparative Examples 2 to 5 yielded polyimide precursor varnishes with a molecular weight (Mw) of less than 100,000.

[0059] The formulations for Examples 1-8 and Comparative Examples 1-5 are summarized in Table 2. [Table 2]

[0060] The optical properties of the polyimide (PI) precursor varnishes obtained in Examples 1-8 and Comparative Examples 1-5 were evaluated. Each PI precursor varnish was diluted with the same solvent used in its synthesis. The light transmittance of the PI precursor varnish at YI, a*, b*, and 400 nm was then measured using a spectrophotometer. The results are shown in Table 3.

[0061] Furthermore, the polyimide (PI) precursor varnishes obtained in Examples 1-8 and Comparative Examples 1-5 were used to polyimide them, and their optical properties were evaluated. Specifically, each PI precursor varnish was diluted to approximately 11±1 wt% solids by adding the same solvent used in its synthesis, so that the viscosity was suitable for coating. Then, it was coated onto a 100 μm glass substrate using a spin coater so that the thickness of the polyimide layer after imidization was approximately 10 μm. Subsequently, the solvent was removed by heating at 120°C for 10 minutes. Next, the temperature was raised from room temperature to 350-450°C in a nitrogen atmosphere at a constant heating rate (3-10°C / min), and then maintained for 1-30 minutes. After that, the temperature was returned to room temperature in a nitrogen atmosphere, removed from the oven, and the polyimide layer was formed on the support substrate. Finally, the support substrate was peeled off to obtain each polyimide (PI) film. The above delamination was performed by first creating a cut all the way around the formed polyimide layer with a cutter to determine the area to be peeled off, and then peeling it off from the supporting substrate with tweezers. For each of the resulting polyimide (PI) films, the thickness, light transmittance at wavelengths of 308 nm and 500 nm, total light transmittance, as well as the CTE, tensile strength, tensile elongation, and elastic modulus were evaluated. The results are shown in Table 3.

[0062] [Table 3-1] [Table 3-2] [Industrial applicability]

[0063] The polyimide precursor varnish and polyimide of the present invention can be suitably used as transparent materials for flexible devices and laminates for wiring boards.

Claims

1. A polyimide precursor varnish comprising a polyimide precursor and an organic solvent, characterized in that the yellowness YI of the organic solvent is 2.0 or less, and its b* is 1.0 or less, and the yellowness (YI) of the polyimide precursor varnish is less than 5.0, and its b* is less than 2.

0. However, the polyimide precursor does not contain silicon-containing diamine as a raw material monomer.

2. The polyimide precursor varnish according to claim 1, wherein the light transmittance of the organic solvent at a path length of 1 cm and a wavelength of 400 nm is 85% or more and less than 89%.

3. The polyimide precursor varnish according to claim 1 or 2, wherein the organic solvent is one or more selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylimidazolidinone, and γ-butyrolactone.

4. A method for producing a polyimide precursor varnish according to Claim 1, characterized in that an organic solvent having a yellowness YI of 2.0 or less and a b* of 1.0 or less is used as the organic solvent, and a polyimide precursor varnish having a yellowness YI of less than 5.0 and a b* of less than 2.0 is obtained.

5. A polyimide obtained by imidizing the polyimide precursor varnish described in Claim 1, characterized in that the yellowness YI of the organic solvent is 2.0 or less, b* is 1.0 or less, the yellowness of the polyimide (calculated on a thickness of 10 μm) is 30 or less, and the total light transmittance is 80% or more.

6. A method for producing polyimide according to Claim 5, characterized in that an organic solvent having a yellowness YI of 2.0 or less and a b* of 1.0 or less is used as the organic solvent, and a polyimide having a yellowness YI (calculated value for a thickness of 10 μm) of 30 or less and a total light transmittance of 80% or more is obtained.

7. A flexible device comprising a polyimide layer containing the polyimide described in claim 5, and a functional layer formed on the polyimide layer.

8. A laminate for a wiring board, characterized by having a polyimide layer containing the polyimide described in claim 5, and a metal layer on one or both sides of the polyimide layer.

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