JP2022115823A - Polyimide precursor and polyimide - Google Patents

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

The present invention relates to transparent polyimide precursors and polyimides.

BACKGROUND ART Display devices such as liquid crystal display devices and organic EL devices and touch panels are used as components of various displays, including large displays such as televisions and small displays such as mobile phones, personal computers, and smart phones.
For example, in an organic EL device, a thin film transistor (TFT) is generally formed on a glass substrate, which is a support base material, and electrodes, a light emitting layer and electrodes are sequentially formed thereon. Made in a hermetic seal. Further, the touch panel has a structure in which a first glass substrate on which a first electrode is formed and a second glass substrate on which a second electrode is formed are joined via an insulating layer (dielectric layer). there is

In other words, these constituent members are laminates in which various functional layers such as TFTs, electrodes, and light-emitting layers are formed on glass substrates. By replacing this glass substrate with a resin substrate, it is possible to reduce the thickness, weight, and flexibility of a component using a conventional glass substrate. Utilizing this, it is expected to obtain flexible devices such as flexible displays. On the other hand, since resins are inferior to glass in dimensional stability, transparency, heat resistance, moisture resistance, film strength, etc., various studies have been made.

As such a resin substrate material, polyimide is one of the promising materials due to its excellent heat resistance and dimensional stability. Application to devices is expected.

Transparent polyimide substrates for flexible devices are obtained by using a glass substrate as a supporting base material, forming a transparent polyimide film on this supporting base material, mounting electronic components on the transparent polyimide film, and peeling off the supporting base material. be done.

For example, Patent Document 1 discloses a fluorine-containing polyimide film for flexible devices that is produced by peeling from a carrier substrate, and has 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. Disclose that: However, no consideration has been given to transparency.
Patent document 2 reports a highly transparent polyimide film by using an organic solvent having a light transmittance of 89% or more at 400 nm. However, purifying the solvent not only requires a complicated process, but even if the solvent has a high light transmittance, the resulting polyimide may be colored. , is insufficient to obtain highly transparent polyimides.

JP 2012-040836 A JP 2013-23597 A

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyimide film and its precursor from which a transparent polyimide having low coloration and high transmittance, which is optimal for transparent substrates for flexible devices and laminates for wiring boards, can be obtained.

As a result of intensive studies, the present inventors focused on the polyimide precursor varnish and the organic solvent used in the preparation and production of the polyimide, and found that the low coloring degree (YI) and the color values L*, a*, b* were specified. The inventors have found that a polyimide precursor varnish or polyimide with low coloring and high transmittance can be obtained by using a solvent of the present invention.

That is, the present invention provides a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the yellowness index YI of the organic solvent is 2.0 or less, b* is 1.0 or less, and the polyimide precursor A polyimide precursor varnish characterized in that the body varnish has a yellowness index (YI) of less than 5.0 and a b* of less than 2.0.

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

The present invention is a method for producing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the organic solvent has a yellowness index YI of 2.0 or less and b* of 1.0 or less. is used to obtain a polyimide precursor varnish having a yellowness index YI of less than 5.0 and b* of less than 2.0.

The present invention provides a polyimide obtained by imidizing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the organic solvent has a yellowness YI of 2.0 or less and b* of 1.0 or less. , a polyimide having a yellowness YI (thickness 10 μm equivalent value) of 30 or less and a total light transmittance of 80% or more.

The present invention is a method for producing polyimide by imidizing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the organic solvent has a yellowness index YI of 2.0 or less and b* of 1.0. A polyimide production method characterized by using an organic solvent of 0 or less, obtaining a polyimide having a yellowness index (converted to a thickness of 10 μm) of 30 or less and a total light transmittance of 80% or more.

The present invention provides a flexible device comprising a polyimide layer containing the polyimide described above and a functional layer formed on the polyimide layer.
The present invention provides a wiring substrate laminate comprising a polyimide layer containing the polyimide described above and a metal layer on one or both sides of the polyimide layer.

According to the present invention, attention is paid to the organic solvent used in the preparation and production of the polyimide precursor varnish and polyimide, and a specific solvent is used for yellowness (YI) and color values L *, a *, b *. As a result, it has been possible to provide a polyimide precursor varnish or polyimide with low coloring and high light transmittance.

The polyimide precursor varnish of the present invention contains a polyimide precursor and an organic solvent, the yellowness YI of the organic solvent is 2.0 or less, b * is 1.0 or less, and the optical path length is 1 cm and the light at a wavelength of 400 nm Transmittance is 85% or more.
The present inventors have observed that even when a solvent having a light transmittance of 89% or more is used as an organic solvent, the resulting polyimide precursor and polyimide are colored and have a low light transmittance. It is not enough to obtain a highly transparent polyimide precursor or polyimide, and the inventors have studied the existence of more effective parameters, and arrived at the present invention. Its effective parameters are yellowness (YI), color values L*, a*, b*, and in particular, yellowness YI and color value b* significantly affect the transparency of polyimide precursor varnishes and polyimides. I found out what to do.

In the polyimide precursor varnish of the present invention, the organic solvent must have a yellowness index YI of 2.0 or less and b* of 1.0 or less. The effects of the present invention cannot be exhibited with an organic solvent that does not satisfy the condition for either the yellowness YI value or the b* value.
The yellowness index 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.

Although other color values L* and a* are not essential, as an organic solvent, the color value L* is
It is preferably 90.0 or higher, more preferably 93.0 or higher. In the present invention, even an organic solvent having an L* value of 97.0 or less or 96.0 or less can be suitably used. The organic solvent should be selected from those having a color value a* of preferably -0.10 to -0.80, more preferably -0.20 to -0.70.

The polyimide precursor varnish of the present invention preferably has a light transmittance of 85% or more at an optical path length of 1 cm and a wavelength of 400 nm as an organic solvent, and does not need to have a light transmittance of 89% or more. Even an organic solvent having a light transmittance of less than 89%, less than 88%, or less than 87% can be suitably used. An organic solvent having a light transmittance of less than 89% is preferable because it can be easily produced without complicated purification.

The polyimide precursor varnish of the present invention preferably has a purity of 99.8% or more as an organic solvent, and does not need to have a purity of 99.9% or more. Even an organic solvent with a purity of less than 99.9% can be suitably used. An organic solvent with a purity of less than 99.9% is preferable because it can be produced without complicated purification.

As the organic solvent, various organic solvents used in preparation and production of polyimide precursors and polyimides can be used as long as they satisfy the above-mentioned yellowness index YI and color value. For example, N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylimidazolidinone (DMI ), or γ-butyrolactone (GBL). A mixture of these can also be used.

The polyimide precursor varnish of the present invention has a yellowness index (YI) of less than 5.0 and a b* of 2.0.
Must be less than 0. A desired polyimide cannot be obtained with a polyimide precursor varnish that does not satisfy the condition for either the yellowness YI value or the b* value.
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.

Although the other color values L* and a* are not essential, the polyimide precursor varnish preferably has a color value L* of 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. The polyimide precursor varnish should be selected from those having a color value a* of preferably -2.0 to 2.0, more preferably -1.0 to 1.0.

ここで、Ａは酸二無水物残基を示し、Ｂはジアミン残基を示す。 The polyimide precursor of the present invention has a structural unit represented by the following general formula (1), as long as it has a structural unit derived from an acid dianhydride (A) and a structural unit derived from a diamine (B). Widely applicable.

Here, A represents an acid dianhydride residue and B represents a diamine residue.

Combinations of acid dianhydrides and diamines as raw materials include aromatic dianhydride/aromatic diamine, aromatic dianhydride/aliphatic diamine, aliphatic dianhydride/aromatic diamine, and aliphatic dianhydride. Anhydride/aliphatic diamines are included, but preferably contain an aromatic component. When containing an aliphatic component, it preferably has an alicyclic structure. A combination of an aromatic dianhydride and an aromatic diamine is preferred for applications requiring heat resistance.

Acid dianhydrides include, for example, 4,4′-(2,2′-hexafluoroisopropylidene)diphthalic dianhydride, 4,4′-oxydiphthalic dianhydride, 4,4′-(2, 2'-Hexafluoroisopropylidene)diphthalic dianhydride, naphthalene-2,3,6,7-tetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene- 1,2,6,7-tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′- biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3 ,3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1 ,4,5,8-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexa Hydronaphthalene-1,2,5,6-tetracarboxylic 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 dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2 ,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride anhydride, 3,3′,4,4′-p-terphenyltetracarboxylic dianhydride, 2,2′,3,3′-p-terphenyltetracarboxylic dianhydride, 2,3,3 ',4'-p-terphenyltetracarboxylic 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(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl) i) ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene-4,5,10,11 -tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene-1,2,6, 7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic 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 dianhydride, bis{3,5-di(trifluoromethyl)phenoxy}pyromellitic 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 Anhydride, bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride , 2,2-bis{(4-(3,4-dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride, bis{(trifluoromethyl ) dicarboxy phenoxy}bis(trifluoromethyl)biphenyl dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}diphenyl ether dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)biphenyl dianhydride and the like. A mixture of these may also be used.

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

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′-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 diaminopropyltetramethyldiamine siloxane and the like. A mixture of these may also be used.

Preferably, 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-amino phenyl)benzimidazole.
However, as long as the yellowness index (YI) of the polyimide precursor varnish is less than 5.0 and b* is less than 2.0, it is not limited to these.

In the polyimide precursor varnish of the present invention, for example, structural units derived from a monomer having an ether group in the structure of the polyimide precursor account for 10% or more, more preferably 50% or more of the structural units derived from all monomers. useful for It is also useful for a polyimide precursor in which structural units derived from a monomer having a fluorine atom account for 10% or more, more preferably 50% or more of all monomer-derived structural units. Since polyimide precursors and polyimide films having such structural units are excellent in transparency, when using an organic solvent constituting the present invention (that is, in the case of polyimide precursors, when polyimide precursor varnish is used, polyimide In the case of a film obtained by imidizing the polyimide precursor varnish), a polyimide precursor varnish and a polyimide film having superior transparency can be obtained.
However, as long as the yellowness index (YI) of the polyimide precursor varnish is less than 5.0 and b* is less than 2.0, it is not limited to these.

The polyimide precursor of the present invention can be produced by a known method in which acid dianhydride and diamine are used at a molar ratio of 0.9 to 1.1 and polymerized in an organic solvent. For example, it can be obtained by adding an acid dianhydride and a diamine as raw material monomers to an organic solvent under a nitrogen stream and reacting them at room temperature to 80° C. for several hours to several days.
The organic solvent may be used in an amount of, for example, 200 to 1,500 parts by weight, preferably 300 to 900 parts by weight, per 100 parts by weight of the total amount of monomers.

The polyimide of the present invention is obtained by imidating the polyimide precursor varnish of the present invention. Imidization can be performed by a thermal imidization method or a chemical imidization method. Thermal imidization is performed, for example, by forming a film of a polyimide precursor varnish on a supporting substrate, pre-drying it, and then heat-treating it at a temperature of about room temperature to 450°C. Chemical imidization, for example, adding a known dehydrating agent and / or catalyst to the polyimide precursor varnish (e.g., acetic anhydride as a dehydrating agent, pyridine, isoquinoline, N methylimidazole as a catalyst), for example, at 30 ~ 60 ° C. Chemical dehydration.
Preferred conditions for thermal imidization are illustrated. On any support substrate such as glass, metal, resin, the polyimide precursor composition is formed into a film using an applicator, pre-dried at a temperature of 150 ° C. or less for 2 to 60 minutes, then solvent removal, imidization. For this purpose, heat treatment is usually carried out at a temperature of about room temperature to about 470° C. for about 10 minutes to 20 hours, more preferably about 10 minutes to 4 hours. When a desired polyimide film is obtained, the heat treatment temperature may be up to 280°C. It is also possible to vary the heat treatment temperature between 280° C. and 470° C., depending on the mechanical properties required. More preferably, if the film formation maximum 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. Polyimide is preferable because of its excellent balance of film transmittance and mechanical properties (CTE, tensile strength, tensile elongation, elastic modulus). In chemical imidization, a dehydrating agent and a catalyst are added to a solution of a polyimide precursor composition (also called polyamic acid), and chemical dehydration is carried out at 30 to 60°C. Acetic anhydride is exemplified as a representative dehydrating agent, and pyridine is exemplified as a catalyst. Thermal imidization can be completed in a relatively short time by selecting a combination of acid dianhydride, diamine type, and solvent type, and heat treatment including preheating can be performed within 60 minutes. be. A film may be formed as a polyimide precursor composition solution dissolved in a solvent.

The degree of polymerization of the polyimide precursor and polyimide of the present invention is not particularly limited. ,000 cP. The molecular weight of the polyimide precursor can be determined by the GPC method. As a polyimide precursor, for example, the number average molecular weight (Mn) is in the range of 15,000 to 250,000, and the weight average molecular weight (Mw) is in the range of 30,000 to 800,000. The molecular weights of polyimides are also in the same range as the molecular weights of their polyimide precursors.

The polyimide obtained by imidizing the polyimide precursor of the present invention has a yellowness index of 30 or less, or even 20 or less, in the state of a polyimide film having a thickness of 10 μm as a reference thickness (converted value of 10 μm thickness). The total light transmittance is 80% or more, and can be 85% or more.

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

The polyimide of the present invention also has a low coefficient of thermal expansion (CTE), for example 20 ppm/K or less. As for tensile physical properties, a tensile strength of 100 Mpa or more, a tensile elongation of 5% or more, and an elastic modulus of 10 GPa or less can be expressed.

The polyimide of the present invention can be used as a transparent polyimide for 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 made into a laminate by forming various functional layers on the polyimide layer. Examples of the functional layer include liquid crystal display devices, organic EL display devices, touch panels, liquid crystal display displays, organic EL displays, color filters, display devices such as electronic paper, and components thereof. It is also useful as a wiring board laminate (CCL) having a metal layer on one or both sides of the polyimide layer.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Abbreviations and evaluation methods for materials used in Examples and Comparative Examples are shown.

(Acid dianhydride)
・6FDA: 4,4′-(2,2′-hexafluoroisopropylidene)diphthalic dianhydride ・ODPA: 4,4′-oxydiphthalic dianhydride ・PMDA: pyromellitic anhydride ・CBDA: 1, 2,3,4-Cyclobutanetetracarboxylic dianhydride (diamine)
TFMB: 2,2-bis(trifluoromethyl)benzidine BY16-871: diaminopropyltetramethyldisiloxane (manufactured by Dow Corning Toray, 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 to S10). NMP is N-methyl-2-pyrrolidone. DMAC is N,N-dimethylacetamide.

式（１）において、Ｘ,Ｙ,Ｚは、ＪＩＳ Ｚ ８７２２で規定する試験片の三刺激値である。
三刺激値Ｘ,Ｙ,Ｚから色彩値のＬ*, ａ*, ｂ*を求めた。
ここで、Ｌ*は明るさを表し、０に近いと黒、１００に近いと白を表す。ａ*は緑～赤を表し、マイナスは緑、プラスは赤と表す。ｂ*は青～黄と表し、マイナスは青、プラスは黄と表す。ａ*、ｂ*共に数値が大きいほど強い色を表す。ワニスは固形分10～11wt%の状態に希釈した後測定した。 [Light transmittance of solvent and varnish, yellowness YI, L*, a*, b*]
Measured using a SHIMADZU UV-3600 spectrophotometer, quartz standard cell with 1 cm path length. Using ultrapure water as a blank, the light transmittance of the solvent at 400 nm was measured. Moreover, YI (yellowness index) was calculated based on the formula represented by the following formula (1).

In formula (1), X, Y, and Z are the tristimulus values of the test piece specified by JIS Z8722.
Color values L*, a*, b* were obtained from the tristimulus values X, Y, Z.
Here, L* represents brightness, and when it is close to 0, it represents black, and when it is close to 100, it represents white. a* represents green to red, negative for green and positive for red. b* is expressed as blue-yellow, negative being blue and positive being yellow. The larger the value of both a* and b*, the stronger the color. The varnish was measured after dilution to a solids content of 10-11 wt%.

数式（２）において、「厚み」は、各評価フィルムの実際の厚みである。
三刺激値Ｘ,Ｙ,Ｚからから色彩値のＬ*, ａ*, ｂ*を求めた。 [Light transmittance of film, yellowness index YI, L*, a*, b*]
A polyimide film (50 mm×50 mm) was measured for light transmittance (T@308, T@500) at 308 nm and 500 nm using a SHIMADZU UV-3600 spectrophotometer.
YI (yellowness index) was calculated based on the formula represented by the above formula (1).
A value YI(10) converted to a thickness of 10 μm was calculated by the following formula (2).

In Equation (2), "thickness" is the actual thickness of each evaluation film.
Color values L*, a*, b* were obtained from tristimulus values X, Y, Z.

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

[viscosity]
The viscosity of the polyamic acid solution obtained in Synthesis Example was measured at 25° C. using a cone-plate viscometer with a constant temperature water bath (manufactured by Tokimec).

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

[Coefficient of thermal expansion (CTE)]
A polyimide film (3 mm × 15 mm) is heated from 30 ° C. to 450 ° C. at a constant heating rate (10 ° C./min) while applying a load of 30 mN with a thermomechanical analysis (TMA / SS6100) device, and then, The temperature was lowered from 450.degree.

[Tensile test]
Prepare a test piece of polyimide film (10 mm × 15 mm), Tensilon universal testing machine (Orientec Co., Ltd., RTA-250) at a tensile speed of 10 mm / min according to IPC-TM-650, 2.4.19 A tensile test was performed to calculate the tensile elongation, tensile strength, and elastic modulus.

[purity]
Purity was determined by gas chromatography.

The solvents used are as shown in Table 1 below (S1 to S10).

Example 1
Under a nitrogen stream, 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 is heated at 40 ° C. for 30 minutes to dissolve the contents, and then the solution is stirred at room temperature for 30 hours to perform a polymerization reaction, and a polyimide (PI) precursor varnish having a molecular weight (Mw) of 100,000 or more (viscous solution) V1 was obtained.

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

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

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

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

Example 6
Under a nitrogen stream, 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 is heated at 40° C. for 30 minutes to dissolve the contents, and then the solution is stirred at room temperature for 30 hours to carry out a polymerization reaction, resulting in a polyimide precursor varnish (viscous) having a molecular weight (Mw) of 100,000 or more. solution) V6 was obtained.

Comparative example 1
Under a nitrogen stream, 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 ODPA and 13.10 g PMDA were added. This solution is heated at 40° C. for 30 minutes to dissolve the contents, and then the solution is stirred at room temperature for 30 hours to carry out a polymerization reaction. solution) V7 was obtained.

Examples 7 and 8, Comparative Examples 2-5
A 100 ml separable flask was used in place of the diamine, acid anhydride, and solvent having the composition shown in Table 2, and 68 g of the solvent was used to carry out the polymerization reaction in the same manner as in Example 1. Examples 7 and 8 obtained a polyimide precursor varnish having a molecular weight (Mw) of 100,000 or more, and Comparative Examples 2 to 5 having a molecular weight (Mw) of less than 100,000.

The formulations of Examples 1 to 8 and Comparative Examples 1 to 5 are summarized in Table 2.

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

Further, the polyimide (PI) precursor varnishes obtained in Examples 1 to 8 and Comparative Examples 1 to 5 were polyimideized and their optical properties were evaluated. That is, each PI precursor varnish is added with the same solvent as the solvent used for synthesis, and the solid content is diluted to about 11 ± 1 wt% so that the viscosity is easy to apply. A spin coater was used to coat a 100 μm glass substrate as the polyimide layer so that the thickness of the polyimide layer after imidization was about 10 μm. Subsequently, it was dried by heating at 120° C. for 10 minutes to remove the solvent. Next, in a nitrogen atmosphere, the temperature was raised from room temperature to a temperature range of 350 to 450° C. at a constant temperature elevation rate (3 to 10° C./min), and the temperature was maintained for 1 to 30 minutes. Then, it was returned to room temperature in a nitrogen atmosphere, taken out from the oven, and a polyimide layer was formed on the supporting substrate. After that, the supporting substrate was peeled off to obtain each polyimide (PI) film. The peeling was carried out by making a cut around the formed polyimide layer with a cutter, determining the peeling range, and then peeling it off from the support substrate with tweezers.
Each polyimide (PI) film thus obtained was evaluated for thickness, light transmittance at wavelengths of 308 nm and 500 nm, total light transmittance, CTE, tensile strength, tensile elongation, and elastic modulus. The results are shown in Table 3.

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

Claims (8)

A polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the yellowness index YI of the organic solvent is 2.0 or less, b* is 1.0 or less, and the yellowness index of the polyimide precursor varnish ( A polyimide precursor varnish, characterized in that YI) is less than 5.0 and b* is less than 2.0. 2. The polyimide precursor varnish according to claim 1, wherein the light transmittance of the organic solvent at a wavelength of 400 nm at an optical path length of 1 cm is 85% or more and less than 89%. 1, wherein the organic solvent is selected from the group consisting of N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, dimethylimidazolidinone, and γ-butyrolactone; 3. The polyimide precursor varnish according to claim 1 or 2, which is at least one species. A method for producing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein an organic solvent having a yellowness index YI of 2.0 or less and b* of 1.0 or less is used as the organic solvent, A process for producing a polyimide precursor varnish, characterized in that a polyimide precursor varnish having a yellowness index YI of less than 5.0 and b* of less than 2.0 is obtained. A polyimide obtained by imidizing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the yellowness index YI of the organic solvent is 2.0 or less, b* is 1.0 or less, and the polyimide has a yellow color A polyimide having a degree (thickness equivalent to 10 μm) of 30 or less and a total light transmittance of 80% or more. A method for producing polyimide by imidizing a polyimide precursor varnish containing a polyimide precursor and an organic solvent, wherein the organic solvent has a yellowness index YI of 2.0 or less and b* of 1.0 or less. A process for producing a polyimide, comprising using an organic solvent to obtain a polyimide having a yellowness index YI (converted to a thickness of 10 μm) of 30 or less and a total light transmittance of 80% or more. A flexible device comprising: a polyimide layer containing the polyimide according to claim 5; and a functional layer formed on the polyimide layer. A laminate for a wiring board, comprising a polyimide layer containing the polyimide according to claim 5 and a metal layer on one or both sides of the polyimide layer.