CN111936581A

CN111936581A - Varnish containing transparent polyimide-based polymer and solvent

Info

Publication number: CN111936581A
Application number: CN201980021181.7A
Authority: CN
Inventors: 杉山纮子; 池内淳一; 西村友美; 宫本皓史; 林志成; 吕奇明; 李宗铭
Original assignee: Sumitomo Chemical Co Ltd; Industrial Technology Research Institute ITRI
Current assignee: Sumitomo Chemical Co Ltd; Industrial Technology Research Institute ITRI
Priority date: 2018-03-28
Filing date: 2019-03-27
Publication date: 2020-11-13
Also published as: KR20210005607A; TW201942272A; JPWO2019189483A1; WO2019189483A1

Abstract

The present invention provides a varnish comprising a transparent polyimide polymer and a solvent, wherein the integral value of a peak derived from a peroxide detected by chemiluminescence detection liquid chromatography is 70 ten thousand or less, and when a film comprising the transparent polyimide polymer and having a thickness of 50 to 80 μm is produced from the varnish, the film is produced according to Japanese Industrial Standard (JIS) K7105: the total light transmittance of the film measured in 1981 was 80% or more.

Description

Varnish containing transparent polyimide-based polymer and solvent

Technical Field

The present invention relates to a varnish containing a transparent polyimide-based polymer and a solvent.

Background

In recent years, polyimide polymer films have been used as functional films for providing functions to image display devices such as televisions, personal computers, smart phones, tablet computers, and electronic paper. In particular, a functional film used in a display portion of an electronic device such as a display or a touch panel in the image display device is required to have high transparency.

As a method for producing such a polyimide-based polymer film, the following methods are known: the varnish is produced by applying a varnish containing a polyimide-based polymer and a solvent to a substrate to form a coating film, and drying the coating film. For example, patent document 1 describes a method for producing a film using a varnish containing a polyamide imide resin and butyl acetate.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-174905

Disclosure of Invention

Problems to be solved by the invention

However, in the case of producing a varnish after long-term storage after production of the varnish, or in the case of producing a varnish after long-term storage of a solvent used for the varnish, the varnish itself may be colored to deteriorate the transparency of the resulting polyimide-based polymer film. As a solution to recover the transparency, there is a method of purifying the varnish, for example, a method of taking out the polyimide-based polymer from the colored varnish by precipitation or the like and dissolving the polymer in a solvent again, but this method is disadvantageous in terms of cost.

Thus, it is difficult to obtain a varnish having high transparency for a long period of time.

The present invention has been made in view of the above problems, and an object thereof is to provide a varnish having high transparency over a long period of time.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems, and as a result, have completed the present invention. That is, the present invention includes the following embodiments.

[1] A varnish comprising a transparent polyimide-based polymer and a solvent, wherein,

the integrated value of the peak derived from peroxide detected by the chemiluminescence detection liquid chromatography is 70 ten thousand or less,

when a film containing the transparent polyimide polymer is produced from the varnish to a thickness of 50 to 80 μm, the thickness is measured in accordance with Japanese Industrial Standards (JIS) K7105: the total light transmittance of the film measured in 1981 was 80% or more.

[2] The varnish according to [1], wherein when a film made of a transparent polyimide-based polymer having a thickness of 80 μm is produced from the varnish, the film is produced according to Japanese Industrial Standard (JIS) K7105: the total light transmittance of the film measured in 1981 was 80% or more.

[3] A varnish comprising a transparent polyimide-based polymer and a solvent, wherein,

the varnish has a peroxide value of 2.5mg/kg or less as measured by a method according to Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96,

[4] A varnish comprising a transparent polyimide-based polymer and a solvent, wherein,

the peroxide value of the aforementioned solvent detected by the method according to Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96 is 20mg/kg or less,

[5] The varnish according to any one of [1] to [4], wherein the total light transmittance is 90% or more.

[6] The varnish according to any one of [1] to [5], wherein the solvent contains at least 2 kinds of esters.

[7] The varnish according to any one of [1] to [6], wherein the weight average molecular weight of the transparent polyimide polymer in terms of polystyrene is 20 ten thousand or more.

[8] An optical film comprising the varnish according to any one of [1] to [7 ].

[9] The optical film according to [8], which is a film for a front panel of a flexible display device.

[10] A flexible display device comprising the optical film according to [8] or [9 ].

[11] The flexible display device according to [10], further comprising a touch sensor.

[12] The flexible display device according to [10] or [11], further comprising a polarizing plate.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a varnish having high transparency over a long period of time (for example, 3 months or longer) can be provided.

Detailed Description

< varnish >

The varnish of the present invention comprises a transparent polyimide polymer and a solvent,

Further, the varnish of the present invention comprises a transparent polyimide polymer and a solvent,

[1. integral value of peak derived from peroxide ]

The integrated value of the peak derived from peroxide was detected by adding luminol solution to the solvent for preparing the varnish and performing chemiluminescence detection liquid chromatography.

In this specification, the peroxide functions as an oxidizing agent for the luminol reaction in a solvent-luminol solution system. The peak from peroxide comprises the peak of luminescence generated by reaction of peroxide with luminol. The integral value of the peak derived from the peroxide can be measured by, for example, the method described in examples.

The following description will discuss a case where the integrated value of the peak derived from peroxide is 70 ten thousand or less.

When the solvent is 1 solvent, the integral value of the peroxide-derived peak of 1 solvent is 70 ten thousand or less.

When the solvent is a mixed solvent including 2 solvents and the integrated value of one solvent of the 2 solvents in the mixed solvent is much larger than that of the other solvent (for example, 20 times or more larger), it can be determined that the integrated value of one solvent is dominant. In this case, the integral value of the peroxide-derived peak in one solvent is 70 ten thousand or less.

When the integrated value of the peak derived from the peroxide is 70 ten thousand or less, the concentration of the peroxide dissolved in the solvent in the varnish is extremely low, and therefore the reaction rate of the peroxide with the transparent polyimide-based polymer or the like becomes extremely low, and the transparent polyimide-based polymer in the varnish is less likely to be oxidized with the peroxide over time. In this case, since the solvent and the transparent polyimide-based polymer are less likely to deteriorate with time, a varnish having high transparency even after long-term storage (for example, 3 months or more) of the solvent and the varnish can be provided.

From the viewpoint of maintaining high transparency for a further long period of time, the integral value of the peak derived from the peroxide is preferably 50 ten thousand or less, more preferably 35 ten thousand or less, further preferably 10 ten thousand or less, and particularly preferably 5 ten thousand or less.

As means for adjusting the integrated value of the peak derived from the peroxide to 70 ten thousand or less, for example, means for reducing the concentration of the peroxide in the varnish (more specifically, means for inhibiting the generation of the peroxide in the varnish, etc.) can be mentioned. It is considered that the peroxide in the varnish is mainly generated by a reaction of solvent molecules in the varnish with dissolved oxygen (oxidation reaction of the solvent molecules). Therefore, examples of the means for suppressing the peroxide in the varnish include a means for lowering the concentration of dissolved oxygen in the varnish and a means for selecting a solvent type which does not easily react with oxygen to generate a peroxide. Examples of means for reducing the dissolved oxygen concentration in the varnish include: a means for bubbling a solvent with an inert gas (more specifically, a rare gas such as argon or neon, nitrogen, or the like) to replace dissolved oxygen in the solvent with the inert gas; and means for reducing the oxygen concentration of the gas phase in contact with the solvent by setting the atmosphere to be a reduced pressure atmosphere or an inert gas atmosphere. From the viewpoint of sufficiently replacing dissolved oxygen and reducing the cost, the time for the bubbling treatment is preferably 10 minutes or more and 1 hour or less, for example. For example, in the case where the bubbling treatment is performed on a mixed solvent containing two esters, the bubbling treatment may be performed on at least one of these solvents before mixing the two solvents. The bubbling treatment may be performed on the mixed solvent after mixing the two solvents. In addition, the varnish may be subjected to bubbling treatment after the varnish is prepared. The solvent is described later.

When the solvent is a mixed solvent containing 2 or more solvents, the varnish can be evaluated by using the sum (weighted average) of the products of the integrated values of the solvents and the mass ratios of the solvents in the varnish as an integrated value of the varnish (converted integrated value of the varnish). In this case, the converted integrated value of the varnish is preferably 35 ten thousand or less, more preferably 25 ten thousand or less, still more preferably 18 ten thousand or less, particularly preferably 5 ten thousand or less, and very particularly preferably 2.5 ten thousand or less.

[2. peroxide number ]

The peroxide value may be determined according to or in accordance with the Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96. In the measurement of the peroxide value, a solvent used for preparing a varnish (a solvent before preparing a varnish) or a varnish may be used as a measurement target.

(2-1. in the case where the object to be measured is a solvent)

In the case where the object to be measured is a solvent used for the preparation of a varnish, the peroxide value is measured according to the aforementioned peroxide test method JPI-5S-46-96. First, a solvent to be measured is dissolved in toluene. Next, a potassium iodide solution was added to a solvent dissolved in toluene, and the iodine released at this time was titrated with a sodium thiosulfate standard solution, whereby the iodine concentration was determined. In the present specification, the peroxide functions as an oxidizing agent for potassium iodide in a system of a toluene solution of potassium iodide to be measured. The peroxide value of the solvent can be measured by, for example, the method described in examples.

The case where the peroxide value of the solvent is 20mg/kg will be described below.

When the solvent is 1 solvent, the peroxide value of 1 solvent is 20mg/kg or less.

When the solvent is a mixed solvent including 2 solvents and the peroxide value of one of the 2 solvents in the mixed solvent is much larger than the peroxide value of the other solvent (for example, 20 times or more larger), it can be determined that the peroxide value of one solvent is dominant. In this case, the peroxide value of one of them is 20 mg/kg.

When the measurement target is the above-mentioned solvent, the peroxide value is 20mg/kg or less. It is considered that when the peroxide value is 20mg/kg or less, the concentration of the peroxide dissolved in the solvent in the varnish is sufficiently low, and therefore the reaction rate of the peroxide with the transparent polyimide-based polymer or the like becomes extremely low, and the transparent polyimide-based polymer in the varnish is less likely to be oxidized with the peroxide over time. In this case, since the solvent and the transparent polyimide-based polymer are less likely to deteriorate with time, a varnish having high transparency even after long-term storage (for example, 3 months or more) of the solvent can be provided. By producing an optical film using such a varnish having high transparency, an optical film having high transparency can be obtained.

From the viewpoint of further maintaining high transparency of the varnish for a long period of time, the peroxide value is preferably 15mg/kg or less, more preferably 10mg/kg or less, still more preferably 5mg/kg or less, and particularly preferably less than 1 mg/kg.

When the solvent is a mixed solvent containing 2 or more solvents, the varnish can be evaluated by taking the sum (weighted average) of the products of the peroxide values of the respective solvents and the mass ratios of the respective solvents in the varnish as the peroxide value of the varnish (converted peroxide value of the varnish). In this case, the peroxide value in terms of varnish is preferably 10mg/kg or less, more preferably 7.5mg/kg or less, still more preferably 5mg/kg or less, particularly preferably 2.5mg/kg or less, and very particularly preferably less than 0.5 mg/kg.

(2-2. in the case where the measurement object is varnish)

When the measurement object is a varnish, the peroxide value is measured in accordance with the above JPI-5S-46-96. The peroxide value was measured by the same method as in the case where the measurement target was a solvent, except that the measurement target was changed from a solvent to a varnish, the mass of the measurement target was changed, and the measurement target was diluted with a solvent. The peroxide value of the varnish can be measured by, for example, the method described in examples.

When the measurement target was a varnish, the peroxide value was 2.5 mg/kg. When the peroxide value is 2.5mg/kg or less, a varnish having high transparency can be provided even after long-term storage of the varnish for the same reason as in the case where the measurement target is a solvent. By producing an optical film using such a varnish having high transparency, an optical film having high transparency can be obtained.

When the peroxide value is 2.5mg/kg or less, the transparent polyimide-based polymer in the optical film is less likely to deteriorate with time for the same reason as in the case where the measurement target is varnish, and therefore an optical film having high transparency can be obtained.

From the viewpoint of further maintaining high transparency of the varnish for a long period of time, the peroxide value of the varnish is preferably 2.0mg/kg or less, more preferably 1.5mg/kg or less, still more preferably 1.1mg/kg or less, and particularly preferably less than 1 mg/kg.

[3. Total light transmittance ]

The transparent polyimide polymer film having a thickness of 50 to 80 μm has a total light transmittance of preferably 80% or more, more preferably 82% or more, further preferably 85% or more, further more preferably 88% or more, particularly preferably 90% or more, further particularly preferably 91% or more, and particularly preferably 92% or more. When the transmittance is in the above range, for example, in the case of a display device in which a film formed of the varnish of the present invention and an EL element are combined, the EL element can be driven with less power for obtaining the same luminance as in the case of a film having a low transmittance, and therefore, the present invention can contribute to power saving. In order to ensure high transparency of the film, the varnish used in the formation of the film is preferably transparent for a long period of time. The varnish is transparent for a long period of time, and can be confirmed by an accelerated test in which the varnish is stored at 50 ℃ for 1 week, for example.

The total light transmittance of the transparent polyimide-based polymer film can be measured, for example, using a haze meter in accordance with JIS K7105: 1981.

The thickness of the transparent polyimide-based polymer film can be measured, for example, using a micrometer.

When the thickness of the transparent polyimide-based polymer film is not more than 80 μm, the total light transmittance of the film is measured by using a haze meter as described above, and the obtained total light transmittance is converted into a total light transmittance of 80 μm.

The conversion of the total light transmittance can be performed as follows using Lambert-Beer's law, for example. Here, the total light transmittance Tt to be measured with a thickness of 50 μm₅₀The method of converting the total light transmittance into 80 μm will be described.

In the formula (A), the compound represented by the formula (A),

T＝e^-ax...(A)

[ in the formula (A), T represents transmittance, x represents optical path length, and α represents absorption constant ]

Total light transmittance Tt₅₀The transmittance T was substituted, and the film thickness 50 μm was substituted for the optical path x. As a result, the absorption constant α was obtained. Next, in the formula (A), 80 μm was substituted into x, and the absorption constant α obtained previously was substituted, whereby the total light transmittance Tt at a thickness of 80 μm was obtained₈₀(total light transmittance converted to 80 μm).

[4. solvent ]

The solvent preferably has not only the basic characteristics as a varnish composition but also high transparency over a long period of time. The former is the following characteristic: the transparent polyimide polymer is dissolved or dispersed, and the viscosity of the varnish is adjusted to a viscosity suitable for coating. The latter is for example the following characteristic: the solvent molecule is not easy to react with oxygen or even react with oxygen, the peroxide with high reaction activity is not easy to generate; and the characteristic of not being easy to dissolve oxygen.

From the viewpoint of satisfying such characteristics, examples of the solvent include an aprotic polar solvent (more specifically, N-dimethylacetamide (hereinafter, sometimes referred to as DMAc) and dimethylsulfoxide), and a carboxylic acid ester (more specifically, an acetic acid ester and a cyclic carboxylic acid ester). Examples of the acetate include butyl acetate (hereinafter, sometimes referred to as butyl acetate), amyl acetate, and isoamyl acetate. As the cyclic carboxylic acid ester, for example, γ -butyrolactone (hereinafter, sometimes referred to as GBL) is exemplified. These solvents may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

Among these solvents, from the viewpoint of further improving 2 kinds of characteristics, at least 1 kind of solvent selected from the group consisting of GBL, DMAc, butyl acetate, amyl acetate and isoamyl acetate is preferable, and at least 2 or more kinds of esters selected from the above solvents are more preferable. Examples of the combination of the at least 2 or more esters include GBL and DMAc, GBL and butyl acetate, GBL and amyl acetate, GBL and isoamyl acetate, DMAc and butyl acetate, DMAc and amyl acetate, DMAc and isoamyl acetate, butyl acetate and amyl acetate, butyl acetate and isoamyl acetate, amyl acetate and isoamyl acetate, GBL and DMAc and butyl acetate, GBL and DMAc and amyl acetate, GBL and DMAc and isoamyl acetate, GBL and butyl acetate and amyl acetate, GBL and butyl acetate and isoamyl acetate, GBL and amyl acetate and isoamyl acetate, DMAc and butyl acetate and amyl acetate, DMAc and butyl acetate and isoamyl acetate, DMAc and amyl acetate, butyl acetate and isoamyl acetate, DMAc and butyl acetate and amyl acetate, DMAc and amyl acetate, GBL and DMAc and butyl acetate, butyl acetate and isoamyl acetate, GBL and DMAc and isoamyl acetate, and GBL and isoamyl acetate, DMAc and DMAc, GBL and butyl acetate and isoamyl acetate, DMAc and butyl acetate and isoamyl acetate, and GBL and DMAc and butyl acetate and isoamyl acetate, preferably, GBL and butyl acetate, GBL and amyl acetate, GBL and isoamyl acetate, butyl acetate and amyl acetate, butyl acetate and isoamyl acetate, amyl acetate and isoamyl acetate, GBL and butyl acetate and amyl acetate, GBL and butyl acetate and isoamyl acetate, GBL and amyl acetate and isoamyl acetate, and GBL and butyl acetate and amyl acetate and isoamyl acetate, more preferably, GBL and butyl acetate, GBL and isoamyl acetate, GBL and butyl acetate and isoamyl acetate, GBL and amyl acetate and isoamyl acetate, GBL and butyl acetate and isoamyl acetate, GBL and amyl acetate and isoamyl acetate, GBL and isoamyl acetate, and isoamyl acetate, And GBL in combination with butyl acetate and amyl acetate and isoamyl acetate.

In the case of a mixed solvent containing 2 kinds of solvents, the mixing ratio (mass ratio) thereof is preferably 1: 9-9: 1, more preferably 2: 8-8: 2. in the case of a mixed solvent containing 3 kinds of solvents, the mixing ratio (mass ratio) thereof is preferably 1 to 8: 1-8: 1 to 8, more preferably 2 to 7: 2-7: 2 to 7.

When 2 or more solvents are contained, the content of 1 solvent out of the 2 or more solvents is usually 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and usually 90% by mass or less, preferably 80% by mass or less, more preferably 70% by mass or less, and further preferably 60% by mass or less, based on the total amount of the solvents.

[5. transparent polyimide-based Polymer ]

(transparent polyimide-based Polymer obtained by polymerization and imidization)

Examples of the transparent polyimide-based polymer include polyimide and polyamideimide, and the transparent polyimide-based polymer includes polyimide, polyamideimide, and derivatives thereof. In the present specification, polyimide means a polymer containing a repeating structural unit containing an imide group. The polyamideimide is a polymer containing a repeating unit containing both an imide group and an amide group.

The transparent polyimide-based polymer preferably mainly contains a repeating structural unit represented by formula (10) from the viewpoint of transparency of the transparent polyimide-based polymer film. The repeating structural unit represented by the formula (10) is preferably 40 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, particularly preferably 90 mol% or more, and particularly more preferably 98 mol% or more of the total repeating structural units of the transparent polyimide-based polymer. The repeating structural unit represented by formula (10) may be 100 mol%. In the formula (10), G is a 4-valent organic group and A is a 2-valent organic group. The transparent polyimide-based polymer may contain 2 or more kinds of repeating structural units represented by formula (10) different in G and/or a.

[ chemical formula 1]

The transparent polyimide-based polymer may further include 1 or more of the repeating structural units represented by formula (11), formula (12), and formula (13) within a range that does not impair various physical properties of the obtained transparent polyimide-based polymer film.

[ chemical formula 2]

In formulas (10) and (11), G and G¹Represents a 4-valent organic group, preferably an organic group which may be substituted by a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G and G¹Examples of the group include groups represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28), and formula (29), and a chain hydrocarbon group having 4-valent carbon atoms of 6 or less. Wherein X in the formulae (20) to (29) represents a connecting bond, and Z in the formula (26) represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-Ar-、-SO₂-、-CO-、-O-Ar-O-、-Ar-O-Ar-、-Ar-CH₂-Ar-、-Ar-C(CH₃)₂-Ar-or-Ar-SO₂-Ar-. Ar represents an arylene group having 6 to 20 carbon atoms (more specifically, a phenylene group or the like) which may be substituted with a fluorine atom. G and G from the viewpoint of suppressing the yellowness index of the resulting film¹Preferably, the compound represents a group represented by formula (20) to formula (27).

[ chemical formula 3]

In formula (12), G²Represents a 3-valent organic group, preferably an organic group which may be substituted by a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G²Examples of the 3-valent organic group represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28), and the formula (29) include a group in which 1 of the connecting bonds of the groups represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28), and the formula (29) is substituted with a hydrogen atom.

In formula (13), G³Represents a 2-valent organic group, preferably an organic group which may be substituted by a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G³Examples of the 2-valent organic group represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28), and the formula (29) include a group in which non-adjacent 2 of the connecting bonds of the groups are each replaced by a hydrogen atom, and a 2-valent chain hydrocarbon group having 6 or less carbon atoms.

A, A in formulae (10) to (13)¹、A²And A³Each represents a 2-valent organic group, preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As A, A¹、A²And A³Examples thereof include groups represented by the following formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), formula (36), formula (37) and formula (38); a group in which these groups are substituted with a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms.

Formula (30) to formula (38) 'represents a bond, and formula (34) to formula (36)' represents Z¹、Z²And Z³Each independently represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or-CO-. 1 example is: z¹And Z³is-O-and Z²represents-CH₂-、-C(CH₃)₂-、-C(CF₃)₂-or-SO₂-。Z¹And Z²And Z²And Z³Each preferably being meta with respect to the ringOr para.

[ chemical formula 4]

The repeating structural units represented by the formulae (10) and (11) are generally derived from diamines and tetracarboxylic acid compounds. The repeating structural unit represented by formula (12) is generally derived from diamine and tricarboxylic acid compounds. The repeating structural unit represented by formula (13) is generally derived from a diamine and a dicarboxylic acid compound. These carboxylic acid compounds (tetracarboxylic acid compound, tricarboxylic acid compound, and dicarboxylic acid compound) may be carboxylic acid compound analogs (more specifically, carboxylic acid anhydride, alkanoyl halide, and the like).

(tetracarboxylic acid Compound)

Examples of the tetracarboxylic acid compound include an aromatic tetracarboxylic acid compound such as an aromatic tetracarboxylic acid dianhydride, and an aliphatic tetracarboxylic acid compound such as an aliphatic tetracarboxylic acid dianhydride. These tetracarboxylic acid compounds can be used alone in 1 kind, or can be used in combination with 2 or more kinds. The tetracarboxylic acid compound may be a tetracarboxylic acid dianhydride, and may be a tetracarboxylic acid compound analog such as a tetracarboxylic acid chloride compound.

Examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides, and condensed polycyclic aromatic tetracarboxylic dianhydrides.

Examples of the non-condensed polycyclic aromatic tetracarboxylic acid dianhydride include 4,4 '-oxydiphthalic anhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic acid dianhydride, 2', 3,3 '-benzophenonetetracarboxylic acid dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic acid dianhydride, 2', 3,3 '-biphenyltetracarboxylic acid dianhydride, 3, 3', 4,4 '-diphenylsulfonetetracarboxylic acid dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic acid dianhydride (hereinafter, sometimes referred to as "6 FDA"), "4, 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4 '- (p-phenylenedioxy) diphthalic dianhydride, and 4, 4' - (m-phenylenedioxy) diphthalic dianhydride.

Further, as the condensed polycyclic aromatic tetracarboxylic dianhydride, for example, 2,3,6, 7-naphthalene tetracarboxylic dianhydride can be mentioned.

Preferred examples of the aromatic tetracarboxylic acid dianhydride include 4,4 '-oxydiphthalic anhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic acid dianhydride, 2', 3,3 '-benzophenonetetracarboxylic acid dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic acid dianhydride, 2', 3,3 '-biphenyltetracarboxylic acid dianhydride, 3, 3', 4,4 '-diphenylsulfonetetracarboxylic acid dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride, 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4 '- (p-phenylenedioxy) diphthalic dianhydride, and 4, 4' - (m-phenylenedioxy) diphthalic dianhydride. These aromatic tetracarboxylic dianhydrides may be used alone in 1 kind or in combination of 2 or more kinds.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic and acyclic aliphatic tetracarboxylic dianhydrides. In the present specification, the cyclic aliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure. Examples of the cyclic aliphatic tetracarboxylic acid dianhydride include cycloalkanetetracarboxylic acid dianhydrides such as 1,2,4, 5-cyclohexanetetracarboxylic acid dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic acid dianhydride and 1,2,3, 4-cyclopentanetetracarboxylic acid dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic acid dianhydride, dicyclohexyl-3, 3 ', 4, 4' -tetracarboxylic acid dianhydride, and positional isomers thereof. These cyclic aliphatic tetracarboxylic dianhydrides may be used alone in 1 kind or in combination of 2 or more kinds. Examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3, 4-butanetetracarboxylic acid dianhydride and 1,2,3, 4-pentanedicarboxylic acid dianhydride. These acyclic aliphatic tetracarboxylic dianhydrides may be used alone in 1 kind, or in combination of 2 or more kinds.

From the viewpoint of further improving the transparency of the transparent polyimide-based polymer film, the tetracarboxylic acid compound is preferably alicyclic tetracarboxylic acid dianhydride or non-condensed polycyclic aromatic tetracarboxylic acid dianhydride, and more preferably 3,3 ', 4,4 ' -biphenyltetracarboxylic acid dianhydride, 2 ', 3,3 ' -biphenyltetracarboxylic acid dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 4,4 ' - (hexafluoroisopropylidene) diphthalic acid dianhydride (6 FDA). These preferred tetracarboxylic acid compounds may be used alone in 1 kind, or may be used in combination with 2 or more kinds.

(tricarboxylic acid compound and dicarboxylic acid compound)

The raw material monomers may further comprise tricarboxylic acid compounds and/or dicarboxylic acid compounds.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and acid chloride compounds and acid anhydrides which are analogues thereof. These tricarboxylic acid compounds may be used alone in 1 kind, or may be used in combination with 2 or more kinds. Examples of the tricarboxylic acid compound include anhydrides of 1,2, 4-benzenetricarboxylic acid; 2,3, 6-naphthalene tricarboxylic acid-2, 3-anhydride; phthalic anhydride and benzoic acid via a single bond, -CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or phenylene groups.

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and acid chloride compounds and acid anhydrides which are analogues thereof. These dicarboxylic acid compounds can be used alone in 1 kind, or can be used in combination with 2 or more kinds. Examples of the dicarboxylic acid compound include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4, 4' -biphenyldicarboxylic acid; 3, 3' -biphenyldicarboxylic acid; terephthaloyl dichloride (terephthaloyl chloride (TPC)); 4, 4' -oxybis (benzoyl chloride) (OBBC); dicarboxylic acid compound of chain hydrocarbon with carbon number less than 8 and 2 benzoic acidper-CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or phenylene groups.

The proportion of the tetracarboxylic acid compound is preferably 40 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, further more preferably 90 mol% or more, and particularly preferably 98 mol% or more, based on the total amount of the tetracarboxylic acid compound, the tricarboxylic acid compound, and the dicarboxylic acid compound.

(diamine)

Examples of the diamine include an aliphatic diamine, an aromatic diamine, and a mixture thereof. In the present specification, the term "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and may contain an aliphatic group or other substituent in a part of the structure. The aromatic ring may be a monocyclic ring or a condensed ring. Examples of the aromatic ring include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Among the aromatic rings, a benzene ring is preferable. In the present specification, the term "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituent in a part of the structure.

Examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylenediamine and cyclic aliphatic diamines such as 1, 3-bis (aminomethyl) cyclohexane, 1, 4-bis (aminomethyl) cyclohexane, norbornanediamine and 4, 4' -diaminodicyclohexylmethane. These aliphatic diamines may be used alone in 1 kind, or may be used in combination with 2 or more kinds.

Examples of the aromatic diamine include aromatic diamines having 1 aromatic ring such as p-phenylenediamine, m-phenylenediamine, 2, 4-tolylenediamine, m-xylylenediamine, p-xylylenediamine, and 1, 5-diaminonaphthalene, and 2, 6-diaminonaphthalene, 4 '-diaminodiphenylmethane, 4' -diaminodiphenylpropane, 4 '-diaminodiphenyl ether, 3' -diaminodiphenyl ether, 4 '-diaminodiphenyl sulfone, 3' -diaminodiphenyl sulfone, 1, 4-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, 4 '-diaminodiphenyl sulfone, 4' -diaminodiphenyl sulfone, and the like, Bis [4- (4-aminophenoxy) phenyl ] sulfone, bis [4- (3-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2 '-dimethylbenzidine, 2' -bis (trifluoromethyl) -4,4 '-diaminobiphenyl (hereinafter, sometimes referred to as TFMB), 4' -bis (4-aminophenoxy) biphenyl, 9-bis (4-aminophenyl) fluorene, 9-bis (4-amino-3-methylphenyl) fluorene, 9-bis (4-amino-3-chlorophenyl) fluorene, and 9, 9-bis (4-amino-3-fluorophenyl) fluorene having 2 or more Aromatic diamines of aromatic rings. These aromatic diamines may be used alone in 1 kind, or may be used in combination with 2 or more kinds.

The diamine may have a fluorine-based substituent. Examples of the fluorine-based substituent include a C1-5 perfluoroalkyl group such as a trifluoromethyl group, and a fluorine group.

Among the diamines, 1 or more selected from the group consisting of aromatic diamines having a biphenyl structure is preferably used from the viewpoint of high transparency and low coloring property. More preferably, 1 or more selected from the group consisting of 2,2 ' -dimethylbenzidine, 2 ' -bis (trifluoromethyl) benzidine (TFMB), and 4,4 ' -bis (4-aminophenoxy) biphenyl are used.

The diamine is preferably a diamine having a biphenyl structure and a fluorine-based substituent. Examples of the diamine having a biphenyl structure and a fluorine-based substituent include 2,2 '-bis (trifluoromethyl) -4, 4' -diaminobiphenyl (TFMB).

The molar ratio of the diamine to the carboxylic acid compound such as the tetracarboxylic acid compound in the raw material monomer can be appropriately adjusted within a range of preferably 0.9 mol or more and 1.1 mol or less of the tetracarboxylic acid with respect to 1.00 mol of the diamine. In order to exhibit high folding resistance, the transparent polyimide-based polymer to be obtained is preferably high in molecular weight, and therefore the amount of tetracarboxylic acid is more preferably 0.98 mol% or more and 1.02 mol% or less, and still more preferably 0.99 mol% or more and 1.01 mol% or less, based on 1.00 mol of diamine.

In addition, from the viewpoint of suppressing the yellowness index of the obtained transparent polyimide-based polymer film, the proportion of amino groups in the obtained polymer terminals is preferably low, and the amount of the carboxylic acid compound such as a tetracarboxylic acid compound is preferably 1.00 mol or more relative to 1.00 mol of the diamine.

The amount of fluorine in the obtained transparent polyimide-based polymer can be adjusted by adjusting the number of fluorine in the molecule of the diamine and the carboxylic acid compound (for example, tetracarboxylic acid compound) so that the amount of fluorine is preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 10% by mass or more, and particularly preferably 20% by mass or more, based on the mass of the transparent polyimide-based polymer. Since the raw material cost tends to be higher as the fluorine content is higher, the upper limit of the fluorine content is preferably 40 mass% or less. The fluorine-based substituent may be present in either one of the diamine and the carboxylic acid compound, or may be present in both of them. The YI value may be particularly reduced by including a fluorine-based substituent.

(weight average molecular weight in terms of polystyrene)

The weight average molecular weight of the transparent polyimide-based polymer in terms of polystyrene is preferably 20 ten thousand or more, and more preferably 20 ten thousand or more and 50 ten thousand or less. When the weight average molecular weight in terms of polystyrene is within the above range, the transparent polyimide polymer film obtained from the varnish of the present invention can have high flexibility and can have a moderate viscosity of the varnish, thereby having good processability. The weight average molecular weight in terms of polystyrene can be measured by a Gel Permeation Chromatography (GPC) method.

[6. additives ]

The varnish of the present invention may further contain an additive within a range not impairing the transparency. Examples of the additive include inorganic particles, an ultraviolet absorber, an antioxidant, a mold release agent, a stabilizer, a colorant, a flame retardant, a lubricant, a thickener, and a leveling agent.

[ defoaming Properties of varnish ]

The varnish is preferably excellent in defoaming property because handling in the coating step becomes easy. The defoaming property can be adjusted by adjusting the combination, ratio, and viscosity of the resin and the solvent. In the case of a polyimide-based resin, when an acetate solvent (ethyl acetate, butyl acetate, amyl acetate, isoamyl acetate) or the like is used as the solvent, defoaming tends to be more favorable.

[7. method for producing varnish ]

The varnish production method includes, for example, the following steps: a polymerization step of polymerizing a raw material monomer for a transparent polyimide polymer in a solvent A to obtain a precursor of the transparent polyimide polymer; an imidization step of imidizing the transparent polyimide polymer precursor in a solvent A containing a tertiary amine to obtain a transparent polyimide polymer solution; and a dilution step of diluting the transparent polyimide polymer solution with a solvent B to prepare a varnish. The varnish production step may further include a varnish removal step of removing the varnish from the reaction vessel. The imidization step may be performed in a reduced pressure atmosphere.

After the imidization step, the polyimide polymer solution may be brought into contact with a poor solvent for solute polyimide polymer, the polyimide polymer may be taken out as a solid, and the solid may be redissolved in a good solvent to prepare a varnish; alternatively, the redissolved solution may be further diluted with solvent B to prepare a varnish.

(polymerization Process)

In the polymerization step, a raw material monomer of the transparent polyimide polymer is polymerized in a solvent a to obtain a transparent polyimide polymer precursor. The amount of the raw material monomer in the entire liquid including the raw material monomer and the solvent a may be 3 to 60% by mass, and preferably 10 to 60% by mass. When the amount of the raw material monomer is large, the polymerization rate tends to be high, and the molecular weight can be increased. In addition, the polymerization time tends to be shortened, and coloring of the transparent polyimide-based polymer tends to be suppressed. If the amount of the raw material monomer is too large, the viscosity of the polymer or the solution containing the polymer tends to be high, and therefore, there are cases where: the stirring is difficult, or the polymer adheres to the reaction vessel, the stirring blade, or the like, and the yield is lowered. As the solvent a, any of the solvents listed above can be used.

The order of mixing the components of the raw material monomer and the solvent a is not particularly limited, and all of them may be mixed simultaneously or may be mixed separately, and it is preferable to add the carboxylic acid compound after mixing at least a part of the diamine with the solvent. The diamine and the carboxylic acid compound may be added in portions, or may be added in stages for each compound.

By sufficiently stirring the raw material monomer in the polymerization reaction solution, the polymerization of the raw material monomer can be promoted, and the transparent polyimide-based polymer precursor can be formed. The reaction solution can be heated to about 40-90 ℃ as required. The imidization step described later may be performed simultaneously with the polymerization step of the raw material monomer. In this case, the reaction solution may be further heated to a high temperature according to the imidization conditions described later.

The reaction time of the polymerization may be, for example, 24 hours or less, 1 hour or less, or 1 to 24 hours.

In the step of polymerizing the transparent polyimide-based polymer precursor, the reaction solution may contain a tertiary amine. In this case, the tertiary amine may be added before the diamine is mixed with the solvent a, may be added after the mixing, or may be added after the diamine, the solvent and the carboxylic acid compound are mixed.

In addition, the solvent may be diluted with a part of the solvent used in advance and then added to the reaction solution.

[ Tertiary amines ]

The tertiary amine may function as a polymerization catalyst for the raw material monomer in the solvent a in the polymerization step or as an imidization catalyst for the transparent polyimide polymer precursor in the solvent a in the imidization step.

Examples of the tertiary amine include tertiary amines represented by the formula (D) (hereinafter, sometimes referred to as tertiary amines D).

[ chemical formula 5]

In the formula (d), R_1DIs a trivalent aliphatic hydrocarbon group having 8 to 15 carbon atoms.

Examples of the tertiary amine D include 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2, 4-dimethylpyridine, 2,4, 6-trimethylpyridine, 3, 4-cyclopentenopyridine, 5,6,7, 8-tetrahydroisoquinoline, and isoquinoline.

When the imidization step is performed in a reduced pressure atmosphere, the boiling point of the tertiary amine is preferably 120 ℃ or higher, more preferably 140 ℃ or higher, still more preferably 170 ℃ or higher, and particularly preferably 200 ℃ or higher. The upper limit of the boiling point of the tertiary amine is not particularly limited, and is usually 350 ℃ or lower. When the boiling point of the tertiary amine is in the above range, the amount of the tertiary amine removed outside the system tends to be suppressed when water is distilled off under reduced pressure, and therefore, this is preferable.

(imidization step)

Next, in the imidization step, the transparent polyimide polymer precursor is imidized in a solvent a containing a tertiary amine to obtain a transparent polyimide polymer solution. More specifically, the reaction solution containing the tertiary amine may be heated under a reduced pressure atmosphere to promote imidization of the transparent polyimide-based polymer precursor, to form polyimide, and to remove by-produced water or the like by distillation. It is preferable that the transparent polyimide-based polymer precursor in the solvent A is imidized in the reaction vessel in which the polymerization is carried out. The tertiary amine may be added during or before the polymerization step of polymerizing the raw material monomer to produce the transparent polyimide-based polymer precursor as described above, or may be added after the step of producing the transparent polyimide-based polymer precursor. Alternatively, chemical imidization may be performed in a state other than a reduced pressure atmosphere by adding acetic anhydride together with a tertiary amine.

The formation reaction of the transparent polyimide polymer precursor and the imidization reaction can be carried out simultaneously. In this case, the bond of the amide group may be cleaved by water generated in the imidization reaction, and the molecular weight of the obtained transparent polyimide polymer may be lowered. The folding resistance of a film obtained from a varnish containing such a transparent polyimide-based polymer may be reduced. By rapidly removing water from the reaction solution by reducing the pressure in the imidization step, the cleavage reaction of the amide group can be suppressed, and the molecular weight of the obtained transparent polyimide-based polymer can be increased. Therefore, particularly in the case where the formation reaction of the transparent polyimide-based polymer precursor and the imidization reaction are simultaneously performed, the imidization step is performed in a reduced-pressure atmosphere, and thus the following tendency is exhibited: even if a film is directly produced from a varnish containing a transparent polyimide polymer without a purification step, high folding resistance can be imparted to the film.

In the transparent polyimide-based polymer solution, the amount of the tertiary amine added is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.2 parts by mass or more, per 100 parts by mass of the raw material monomer, from the viewpoint of improving the folding resistance. On the other hand, for the purpose of suppressing the coloration of the film, the amount of the tertiary amine to be added is preferably small. The amount of the tertiary amine added is preferably 15 parts by mass or less, more preferably 10 parts by mass or less, further preferably 5 parts by mass or less, further more preferably 2 parts by mass or less, particularly preferably 1 part by mass or less, further particularly preferably 0.7 parts by mass or less, and particularly preferably 0.3 parts by mass or less.

The temperature in the imidization step is preferably 100 ℃ to 250 ℃, more preferably 150 ℃ to 210 ℃. When chemical imidization is performed by adding acetic anhydride and a tertiary amine at the same time, the temperature is preferably 20 to 100 ℃, more preferably 40 to 80 ℃.

When the reduced pressure atmosphere is formed in the imidization step, the pressure is preferably 730mmHg or less, more preferably 700mmHg or less, and still more preferably 675mmHg or less. The pressure in the imidization step may be, for example, 350mmHg or more, or 500mmHg or more. Depending on the vapor pressure of the solvent at the temperature of the imidization step, it may be preferable to perform the imidization under a pressure of 400mmHg or more in order to improve the stability of the reaction. For the same reason, it is sometimes more preferable to carry out the treatment under 600 mmHg.

When the pressure in the imidization step is set to be near the saturated vapor pressure of the solvent in the imidization step, YI tends to be easily suppressed. Preferably within 50mmHg of the saturated vapor pressure.

The heating time is, for example, 1 to 24 hours, preferably 1 to 12 hours, more preferably 2 to 9 hours, further preferably 2 to 8 hours, further preferably 2 to 6 hours, and particularly preferably 2 to 5 hours. Stirring is preferably carried out during heating.

As the reaction time increases, the molecular weight increases, but the yellow color of the transparent polyimide polymer tends to be more easily increased. On the other hand, when the reaction time is short, the molecular weight of the transparent polyimide polymer tends to be low, and the yellow color of the transparent polyimide polymer tends to be weak.

The imidization step is preferably performed in a reduced-pressure atmosphere from the viewpoint of suppressing a decrease in transparency of the transparent polyimide-based polymer film. When the imidization step is carried out under a reduced pressure atmosphere, it is considered that the concentration of oxygen in a gas phase in contact with a liquid phase containing the solvent a in the reaction vessel is low, and therefore, the dissolution of oxygen into the solvent a is reduced, and the concentration of peroxide in the transparent polyimide-based polymer solution is reduced. In the production method, the imidization step by heating the reaction solution in a reduced pressure atmosphere may be performed in a state where the oxygen concentration in the gas phase of the reaction vessel is low, and the oxygen concentration may be made low from the time when the raw material monomer is charged before the heating in a reduced pressure atmosphere. The oxygen concentration is preferably 0.02% or less, and more preferably 0.01% or less. Since the oxygen concentration is particularly a cause of coloring when heated at high temperature, it is preferable to set the oxygen concentration to 0.02% or less when the temperature of the reaction solution is 130 ℃ or higher, for example. Since oxygen is not substantially generated in the synthesis of the precursor and the imidization of the precursor, the oxygen concentration in the gas phase in the imidization step can be reduced by, for example, replacing the inside of the reaction vessel with nitrogen gas before charging the raw materials to lower the oxygen concentration in the gas phase. The oxygen concentration in the imidization step can be determined by, for example, analyzing the oxygen concentration in the gas removed from the reaction vessel when the inside of the reaction vessel is depressurized. When the measurement of the oxygen concentration during reduced pressure is difficult, the oxygen concentration can be measured by sampling the gas phase before and after reduced pressure. For the purpose of reducing the oxygen concentration in the same manner as in the reduced pressure atmosphere, the imidization step may be performed in an inert gas atmosphere instead of the reduced pressure atmosphere.

The pressure was returned to atmospheric pressure after heating, and the mixture was cooled to obtain a transparent polyimide polymer solution.

As another method for suppressing the decrease in transparency of the transparent polyimide-based polymer, acetic anhydride may be added together with a tertiary amine to perform chemical imidization at a relatively low temperature. In this case, since moisture generated by the imidization reaction is removed by the reaction with acetic anhydride, it is possible to remove moisture without reducing the pressure.

If necessary, the transparent polyimide polymer may be taken out from the imidized transparent polyimide polymer solution once, and then redissolved in a solvent for use in the subsequent dilution step.

Examples of the removal method include the following methods: a poor solvent for the transparent polyimide polymer is added to the imidized transparent polyimide polymer solution to precipitate the transparent polyimide polymer, and then the mixture is filtered and taken out.

(dilution step)

Next, in the dilution step, the transparent polyimide-based polymer or a solution thereof is diluted with the solvent B to prepare a varnish. More specifically, the concentration of the transparent polyimide polymer is adjusted by further adding a solvent B to the obtained transparent polyimide polymer or a solution thereof, thereby obtaining a varnish. The solid content concentration in the varnish is preferably 5 to 25% by mass.

When a film is formed from a varnish, a transparent polyimide polymer film in which one of the main components described below is a transparent polyimide polymer can be easily obtained when the varnish contains the transparent polyimide polymer in an amount of 30 mass% or more based on the total amount of solid components in the varnish. The concentration of the transparent polyimide-based polymer is preferably 10% by mass or more, and more preferably 13% by mass or more, based on the total mass of the varnish.

The dilution may be performed in the reaction vessel, or may be performed on the solution recovered from the reaction vessel.

When the solvent B is added to the imidized transparent polyimide polymer solvent in the reaction vessel to dilute the concentration of the transparent polyimide polymer in the reaction vessel, the amount of the polymer remaining in the reaction vessel in the subsequent removal step can be reduced, and the yield of the polymer can be improved. In addition, when the amount of the polymer remaining in the reaction vessel is reduced, the coloration (e.g., yellow color) of the transparent polyimide-based polymer obtained in the subsequent polymerization and imidization repeated step using the reaction vessel is improved.

As the solvent B for dilution, any of the solvents mentioned above can be used. The solvent B and the solvent a may be the same kind as each other or different kinds from each other. By appropriately selecting a solvent having high solubility in the polyimide-based resin as the solvent B for dilution, the recovery rate of the transparent polyimide-based polymer from the reaction vessel is improved.

It is also possible to carry out multiple dilutions in the reaction vessel using a plurality of solvents B of different types.

(varnish removing step)

Next, in the varnish removal step, the varnish is removed from the reaction vessel. The varnish taken out can be used in a film forming step described later.

[8. method for producing transparent polyimide Polymer film ]

An example of a method for producing a transparent polyimide-based polymer film using a varnish will be described. A varnish is cast on a substrate to form a coating film, and the solvent is removed from the coating film by means of pressure reduction, drying, and heating, and the coating film is peeled off from the substrate. Thus, a transparent polyimide polymer film was obtained.

Casting may be performed on a resin substrate, a stainless steel belt, or a glass substrate using a roll-to-roll, batch (batch) manner. Examples of the resin substrate include PET, PEN, polyimide, and polyamideimide. Among these resin substrates, PET is preferable from the viewpoint of adhesion to a film and cost.

In the method for producing a transparent polyimide-based polymer film of the present invention, a certain amount of organic solvent is volatilized by passing a coating film through a dryer (which brings heated gas into contact with the surface of the coating film) or the like, and the coating film can be peeled off from a support as a self-supporting film. The temperature for the application may be adjusted depending on the substrate used, and when a resin substrate is used, the temperature is usually not higher than the glass transition temperature of the resin substrate. Generally, the heating may be carried out at an appropriate temperature of 50 to 300 ℃, and the heating temperature may be adjusted in multiple stages or may be provided with a temperature gradient. It is also preferable to carry out the reaction under an inert atmosphere or under reduced pressure as appropriate.

The peeled transparent polyimide polymer film may be further heated at 80 to 300 ℃ as required.

< optical film >

The optical film of the present invention is formed from the aforementioned varnish. The transparent polyimide-based polymer film described above is useful as an optical film, for example, a front panel of a display device, particularly a front panel (window film) of a flexible display device. The flexible display device includes, for example, a flexible functional layer and an optical film that functions as a front panel by being laminated with the flexible functional layer. That is, the front panel of the flexible display device is arranged on the viewing side above the flexible functional layer. The front panel has the function of protecting the flexible functional layer.

Examples of the display device include wearable devices such as televisions, smart phones, mobile phones, car navigation systems, tablet computers, portable game machines, electronic papers, indicators, bulletin boards, clocks, and smartwatches. As the flexible display device, any display device having a flexible property can be cited, and among them, a foldable display device and a rollable display device can be cited.

< Flexible display device >

The flexible display device of the present invention includes the optical film. The optical film of the present invention is preferably used as a front panel in a flexible display device, and the front panel is sometimes referred to as a window film. The flexible display device includes a laminate for flexible display device and an organic EL display panel, and the laminate for flexible display device is disposed on the viewing side of the organic EL display panel and is configured to be bendable. The laminate for a flexible display device may contain a window film, a polarizing plate (preferably a circularly polarizing plate), and a touch sensor, and the lamination order thereof is arbitrary, but it is preferable that the window film, the polarizing plate, and the touch sensor are laminated in this order from the viewing side, or the window film, the touch sensor, and the polarizing plate are laminated in this order. When the polarizing plate is present on the viewing side of the touch sensor, the pattern of the touch sensor is not easily recognized, and visibility of the display image is improved, which is preferable. The members may be laminated using an adhesive, a bonding agent, or the like. Further, the liquid crystal display device may further include a light-shielding pattern formed on at least one surface of any one of the window film, the polarizing plate, and the touch sensor.

[ polarizing plate ]

The flexible display device of the present invention may further include a polarizing plate, preferably a circular polarizing plate. The circularly polarizing plate is a functional layer having a function of transmitting only a right-handed or left-handed circularly polarized light component by laminating a λ/4 phase difference plate on a linearly polarizing plate. For example, can be used for: the external light is converted into right-handed circularly polarized light, the external light which is reflected by the organic EL panel and becomes left-handed circularly polarized light is blocked, and only the light emitting component of the organic EL is transmitted, thereby suppressing the influence of the reflected light and making it easy to view an image. In order to realize the circularly polarized light function, the absorption axis of the linear polarizer and the slow axis of the λ/4 phase difference plate must be 45 ° in theory, but in practical use, 45 ± 10 °. The linear polarizing plate and the λ/4 phase difference plate do not necessarily have to be stacked adjacent to each other, and the relationship between the absorption axis and the slow axis may be satisfied in the above range. It is preferable to realize completely circularly polarized light at the full wavelength, but this is not necessarily required in practical use, and thus the circularly polarizing plate in the present invention also includes an elliptically polarizing plate. It is also preferable to further laminate a λ/4 retardation film on the viewing side of the linear polarizing plate to convert the emitted light into circularly polarized light, thereby improving visibility in a state where the polarized sunglasses are worn.

The linear polarizing plate is a functional layer having the following functions: light vibrating in the direction of the transmission axis passes through but polarized light of the vibration component perpendicular thereto is blocked. The linear polarizing plate may be a single linear polarizer or a linear polarizer and a protective film attached to at least one surface of the linear polarizer. The thickness of the linearly polarizing plate may be 200 μm or less, and preferably 0.5 to 100 μm. When the thickness is within the above range, the flexibility tends not to be easily lowered.

The linear polarizer may be a film type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (PVA) based film. The polarizing performance can be exhibited by adsorbing a dichroic dye such as iodine onto a PVA-based film that has been stretched and oriented, or by stretching the film in a state where the dichroic dye is adsorbed onto PVA to orient the dichroic dye. The film-type polarizer may be produced by steps such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying. The stretching and dyeing step may be performed by a PVA film alone, or may be performed in a state of being laminated with another film such as polyethylene terephthalate. The thickness of the PVA film to be used is preferably 10 to 100 μm, and the stretch ratio is preferably 2 to 10 times.

In addition, as another example of the polarizer, a liquid crystal coating type polarizer formed by coating a liquid crystal polarizing composition may be used. The liquid crystal polarizing composition may include a liquid crystal compound and a dichroic pigment compound. The liquid crystalline compound is preferably used as long as it has a property of exhibiting a liquid crystal state, and particularly, it can exhibit high polarizing performance when it has a high-order alignment state such as smectic state. Further, it is also preferable that the liquid crystalline compound has a polymerizable functional group.

The dichroic pigment is a pigment which exhibits dichroism by being aligned with the liquid crystal compound, and the dichroic pigment itself may have liquid crystallinity or may have a polymerizable functional group. Any of the compounds in the liquid crystal polarizing composition has a polymerizable functional group.

The liquid crystal polarizing composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like.

The liquid crystal polarizing layer is manufactured by the following method: the liquid crystal polarizing composition is coated on an alignment film to form a liquid crystal polarizing layer.

The liquid crystal polarizing layer can be formed to a thin thickness as compared to a film type polarizer. The thickness of the liquid crystal polarizing layer may be preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.

The alignment film can be produced, for example, by: the alignment film-forming composition is applied to a substrate and is imparted with alignment properties by rubbing, polarized light irradiation, or the like. The alignment film-forming composition may contain a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, and the like in addition to the alignment agent. Examples of the orientation agent include polyvinyl alcohols, polyacrylates, polyamide acids, and polyimides. In the case of applying photo-alignment, an alignment agent containing a cinnamate group (cinnamate group) is preferably used. The weight average molecular weight of the polymer used as the orientation agent may be about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000nm, more preferably 10 to 500nm, from the viewpoint of alignment control force. The liquid crystal polarizing layer may be laminated by being peeled off from the substrate and then transferred, or the substrate may be directly laminated. The substrate preferably functions as a protective film, a retardation plate, or a transparent substrate for a window.

As the protective film, any transparent polymer film may be used, and materials and additives used for the transparent base material may be used. Preferred are cellulose-based films, olefin-based films, acrylic films, and polyester-based films. The coating-type protective film may be one obtained by applying and curing a cationically curable composition such as an epoxy resin or a radically curable composition such as an acrylate. If necessary, a plasticizer, an ultraviolet absorber, an infrared absorber, a colorant (such as a pigment or a dye), a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, or the like may be contained. The thickness of the protective film may be 200 μm or less, preferably 1 to 100 μm. When the thickness of the protective film is within the above range, the flexibility of the protective film is not easily lowered. The protective film may also function as a transparent base material for the window.

The λ/4 phase difference plate is a film that imparts a phase difference of λ/4 in a direction (in-plane direction of the film) orthogonal to the traveling direction of incident light. The λ/4 retardation plate may be a stretched retardation plate produced by stretching a polymer film such as a cellulose film, an olefin film, or a polycarbonate film. If necessary, a retardation adjuster, a plasticizer, an ultraviolet absorber, an infrared absorber, a colorant (such as a pigment or a dye), a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, or the like may be contained. The thickness of the stretched retardation film may be 200 μm or less, preferably 1 to 100 μm. When the thickness is within the above range, the flexibility of the film tends not to be easily reduced.

Further, another example of the λ/4 retardation plate may be a liquid crystal coating type retardation plate formed by coating a liquid crystal composition. The liquid crystal composition comprises a liquid crystalline compound having the following properties: showing nematic, cholesteric, smectic, and the like liquid crystal states. Any compound including a liquid crystalline compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal coating type retardation plate may further contain an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like. The liquid crystal coated retardation plate can be produced by: similarly to the above-mentioned liquid crystal polarizing layer, a liquid crystal composition is applied onto an alignment film and cured to form a liquid crystal retardation layer. The liquid crystal coating type retardation plate can be formed to a smaller thickness than the stretching type retardation plate. The thickness of the liquid crystal polarizing layer may be usually 0.5 to 10 μm, preferably 1 to 5 μm. The liquid crystal-coated retardation plate may be laminated by being peeled off from a substrate and then transferred, or the substrate may be directly laminated. The substrate preferably functions as a protective film, a retardation plate, or a transparent substrate for a window.

Generally, the following materials are more: the shorter the wavelength, the greater the birefringence; the longer the wavelength, the less birefringence is exhibited. In this case, since a phase difference of λ/4 cannot be realized in all visible light regions, it is often designed as follows: lambda/4 at a high visibility of around 560nm, and an in-plane retardation of 100 to 180nm (preferably 130 to 150 nm). The use of an inverse dispersion λ/4 phase difference plate using a material having a birefringence wavelength dispersion characteristic opposite to that of the usual one is preferable because it can improve visibility. As such a material, the material described in japanese patent application laid-open No. 2007-232873 and the like is preferably used also in the case of a stretched phase difference plate, and the material described in japanese patent application laid-open No. 2010-30979 is preferably used also in the case of a liquid crystal coated phase difference plate.

As another method, a technique is also known in which a broadband λ/4 phase difference plate is obtained by combining a λ/2 phase difference plate (japanese patent application laid-open No. h 10-90521). The λ/2 phase difference plate is also manufactured by the same material method as the λ/4 phase difference plate. The combination of the stretching type retardation plate and the liquid crystal coating type retardation plate is arbitrary, and the use of the liquid crystal coating type retardation plate is preferable because the thickness can be reduced.

For the circularly polarizing plate, a method of laminating a positive C plate is also known in order to improve visibility in an oblique direction (japanese patent application laid-open No. 2014-224837). The positive C plate may be a liquid crystal coated retardation plate or a stretched retardation plate. The phase difference in the thickness direction is usually from-200 to-20 nm, preferably from-140 to-40 nm.

[ touch sensor ]

The flexible display device of the present invention may further include a touch sensor. The touch sensor serves as an input means. As the touch sensor, various types such as a resistive film type, a surface acoustic wave type, an infrared ray type, an electromagnetic induction type, and a capacitance type have been proposed, and any type may be used. Among them, the electrostatic capacitance system is preferable. The capacitive touch sensor can be divided into an active region and an inactive region located in an outer peripheral portion of the active region. The active region is a region corresponding to a region (display portion) on the display panel where a screen is displayed, and is a region where a user's touch is sensed, and the inactive region is a region corresponding to a region (non-display portion) on the display device where a screen is not displayed. The touch sensor may include: a substrate having flexible properties; a sensing pattern formed on the active region of the substrate; and each sensing line formed in the inactive region of the substrate and used for connecting the sensing pattern with an external driving circuit through a pad (pad) part. As the substrate having the flexible property, the same material as the transparent substrate of the window can be used. The substrate of the touch sensor preferably has a toughness of 2,000 MPa% or more in terms of suppressing cracks in the touch sensor. The toughness may be more preferably 2,000 to 30,000 MPa%. Here, toughness is defined as: in a Stress (MPa) -strain (%) curve (Stress-strain curve) obtained by a tensile test of a polymer material, the area of the lower portion of the curve up to the failure point is determined.

The sensing pattern may include a 1 st pattern formed in a 1 st direction and a 2 nd pattern formed in a 2 nd direction. The 1 st pattern and the 2 nd pattern are arranged in different directions from each other. The 1 st pattern and the 2 nd pattern are formed in the same layer, and in order to sense a touch location, the patterns must be electrically connected. The 1 st pattern is a form in which the unit patterns are connected to each other via a terminal, but the 2 nd pattern has a structure in which the unit patterns are separated from each other in an island form, and therefore, in order to electrically connect the 2 nd pattern, a separate bridge electrode is required. The sensing pattern may use a known transparent electrode material. Examples thereof include Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Zinc Tin Oxide (IZTO), Indium Gallium Zinc Oxide (IGZO), Cadmium Tin Oxide (CTO), PEDOT (poly (3, 4-ethylenedioxythiophene)), Carbon Nanotubes (CNTs), graphene, and metal wires, and these may be used alone or in a mixture of two or more. ITO may be preferably used. The metal used for the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, selenium, and chromium. These may be used alone or in combination of two or more.

The bridge electrode may be formed on the insulating layer with an insulating layer interposed therebetween on the sensing pattern, and the bridge electrode may be formed on the substrate, on which the insulating layer and the sensing pattern may be formed. The bridge electrode may be formed of the same material as the sensor pattern, or may be formed of a metal such as molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of two or more of these metals. Since the 1 st pattern and the 2 nd pattern must be electrically insulated, an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer may be formed only between the contact of the 1 st pattern and the bridge electrode, or may be formed in a structure of a layer covering the sensing pattern. In the latter case, the bridge electrode may be connected with the 2 nd pattern via a contact hole formed in the insulating layer. In the touch sensor, as means for appropriately compensating for a difference in transmittance between a pattern region where a pattern is formed and a non-pattern region where no pattern is formed (specifically, a difference in transmittance due to a difference in refractive index in these regions), an optical adjustment layer may be further included between the substrate and the electrode, and the optical adjustment layer may include an inorganic insulating substance or an organic insulating substance. The optical adjustment layer can be formed by applying a photocurable composition containing a photocurable organic binder and a solvent onto a substrate. The photocurable composition may further comprise inorganic particles. The inorganic particles can increase the refractive index of the optical adjustment layer.

The photocurable organic binder may include a copolymer of monomers such as an acrylate monomer, a styrene monomer, and a carboxylic acid monomer. The photocurable organic binder may be a copolymer containing different repeating units such as an epoxy group-containing repeating unit, an acrylate repeating unit, and a carboxylic acid repeating unit.

The inorganic particles may include, for example, zirconia particles, titania particles, alumina particles, and the like. The photocurable composition may further contain various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing assistant.

[ adhesive layer ]

The layers (window, polarizing plate, touch sensor) forming the laminate for a flexible display device and the film members (linear polarizing plate, λ/4 phase difference plate, etc.) constituting the layers may be bonded together with an adhesive. As the adhesive, a commonly used adhesive such as an aqueous adhesive, an organic solvent adhesive, a solventless adhesive, a solid adhesive, a solvent volatile adhesive, a moisture curable adhesive, a heat curable adhesive, an anaerobic curable adhesive, an active energy ray curable adhesive, a curing agent hybrid adhesive, a hot melt adhesive, a pressure sensitive adhesive (adhesive), a remoistenable adhesive, or the like can be used. Among them, an aqueous solvent-volatile adhesive, an active energy ray-curable adhesive, and a pressure-sensitive adhesive are preferably used. The thickness of the adhesive layer can be adjusted as appropriate according to the required adhesive strength, and is, for example, 0.01 to 500. mu.m, preferably 0.1 to 300. mu.m. The laminate for a flexible display device may have a plurality of adhesive layers, and the thickness of each adhesive layer and the type of adhesive used may be the same or different.

The aqueous solvent-volatile adhesive may be a polyvinyl alcohol polymer, a water-soluble polymer such as starch, or a water-dispersed polymer such as an ethylene-vinyl acetate emulsion or a styrene-butadiene emulsion. In addition to water and the main agent polymer, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent, and the like may be added. In the case of bonding with the aqueous solvent volatile adhesive, adhesiveness can be provided by injecting the aqueous solvent volatile adhesive between the layers to be bonded, bonding the layers to be bonded, and then drying the layers. The thickness of the adhesive layer when the aqueous solvent-volatile adhesive is used may be usually 0.01 to 10 μm, and preferably 0.1 to 1 μm. When the aqueous solvent volatile adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the adhesive may be the same or different.

The active energy ray-curable adhesive can be formed by curing an active energy ray-curable composition containing a reactive material capable of forming an adhesive layer by irradiation with an active energy ray. The active energy ray-curable composition may contain at least one polymer selected from the group consisting of a radically polymerizable compound and a cationically polymerizable compound, as in the case of the hard coat composition. The radical polymerizable compound may be the same kind of compound as used in the hard coat composition, as used in the hard coat composition. The radical polymerizable compound used in the adhesive layer is preferably a compound having an acryloyl group. In order to reduce the viscosity of the adhesive composition, it is also preferable to include a monofunctional compound.

The cationic polymerizable compound may be the same kind of compound as used in the hard coat composition, as used in the hard coat composition. The cationic polymerizable compound used in the active energy ray-curable composition is particularly preferably an epoxy compound. To reduce the viscosity of the adhesive composition, it is also preferable to include a monofunctional compound as a reactive diluent.

The active energy ray composition may further contain a polymerization initiator. The polymerization initiator may be selected appropriately from a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, and the like. These polymerization initiators are decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations, and radical polymerization and cationic polymerization are carried out. An initiator capable of initiating at least either of radical polymerization and cationic polymerization by irradiation with active energy rays, which is described in the description of the hard coat composition, can be used.

The active energy ray-curable composition may further contain an ion scavenger, an antioxidant, a chain transfer agent, an adhesion-imparting agent, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, an antifoaming agent, an additive, and a solvent. In the case of bonding with the active energy ray-curable adhesive, the bonding can be performed by: the active energy ray-curable composition is applied to either or both of the adhesive layers, and then the adhesive layers are bonded to each other, and either or both of the adhesive layers are cured by irradiation with active energy rays. The thickness of the adhesive layer when the active energy ray-curable adhesive is used may be usually 0.01 to 20 μm, and preferably 0.1 to 10 μm. When the active energy ray-curable adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the adhesive used may be the same or different.

The adhesive may be classified into an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, and the like, depending on the base polymer. The binder may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, an adhesion-imparting agent, a plasticizer, a dye, a pigment, an inorganic filler, and the like in addition to the main polymer. The adhesive layer (adhesive layer) is formed by dissolving and dispersing the components constituting the adhesive in a solvent to obtain an adhesive composition, applying the adhesive composition to a substrate, and then drying the adhesive composition. The adhesive layer may be formed directly or by transferring an adhesive layer formed on another substrate. A release film is also preferably used to cover the pressure-sensitive adhesive surface before bonding. The thickness of the adhesive layer when the adhesive is used may be usually 1 to 500. mu.m, preferably 2 to 300. mu.m. When the above-mentioned adhesive is used for forming a plurality of layers, the thickness of each layer and the kind of the adhesive used may be the same or different.

[ light-shielding pattern ]

The light shielding pattern may be applied as at least a part of a bezel (bezel) or a housing of the flexible display device. The wiring disposed at the edge of the flexible display device is shielded by the light shielding pattern and is not easily recognized, thereby improving visibility of an image. The light-shielding pattern may be in the form of a single layer or a plurality of layers. The color of the light-shielding pattern is not particularly limited, and may have various colors such as black, white, metallic color, and the like. The light-shielding pattern may be formed of a pigment for color development, and a polymer such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or silicone. They may also be used alone or in the form of a mixture of two or more. The light-shielding pattern can be formed by various methods such as printing, photolithography, and inkjet. The thickness of the light-shielding pattern is usually 1 to 100 μm, preferably 2 to 50 μm. Further, it is also preferable to provide a shape such as an inclination in the thickness direction of the light-shielding pattern.

Examples

The present invention will be described in further detail below with reference to examples. In the examples, "%" and "part(s)" refer to% by mass and part(s) by mass unless otherwise specified. First, the evaluation method will be explained.

<1 > production of polyimide varnish and production of polyimide film >

(example 1)

(1) Preparation of polyimide solution

0.5 part by mass of isoquinoline as a catalyst (tertiary amine) was charged into a reaction vessel under a nitrogen atmosphere. The reaction vessel is connected with a vacuum pump provided with a solvent catcher and a filter and is arranged in an oil bath. Next, 305.58 parts by mass of γ -butyrolactone (GBL) as solvent a and 104.43 parts by mass of 2,2 '-bis (trifluoromethyl) -4, 4' -diaminobiphenyl (TFMB) as diamine were further charged into the reaction vessel, and the contents in the reaction vessel were stirred and completely dissolved. Further, 145.59 parts by mass of 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA) as a tetracarboxylic dianhydride was charged into the reaction vessel, and then the temperature was raised by an oil bath while stirring the contents in the reaction vessel. The molar ratio of added TFMB to 6FDA (6 FDA: TFMB) was 1.00: 0.995, the concentration of the raw material monomer was 45 mass%. The amount of the tertiary amine was 0.2 parts by mass with respect to 100 parts by mass of the raw material monomer. When the internal temperature in the reaction vessel reached 120 ℃, the pressure in the reaction vessel was reduced to 400mmHg, and the internal temperature was further increased to 180 ℃. After the internal temperature reached 180 ℃, further heating and stirring were carried out for 5.5 hours, then the pressure was returned to atmospheric pressure, and cooling was carried out to 170 ℃ to obtain a polyimide solution. The oxygen concentration in the reaction vessel before and after the pressure reduction was confirmed to be less than 0.01%. GBL was added at 170 ℃ to form a uniform solution having a solid content of polyimide of 40 mass%, to obtain a polyimide solution. The integral value and the peroxide value of the peroxide-derived peak of GBL are extremely small relative to the integral value and the peroxide value of the diluent solvent, respectively, and can be ignored. Therefore, it was judged that the dilution solvent is dominant in the integral value and the peroxide value among all the solvents in the varnish, and the examples and comparative examples were compared with each other based on the integral value and the peroxide value of the dilution solvent.

(2) Production of varnish

N, N-dimethylacetamide (DMAc) as a diluting solvent (solvent B) was subjected to bubbling treatment with nitrogen gas for 30 minutes. The integrated value of the peroxide-derived peak in DMAc after the bubbling treatment was 31 ten thousand. In addition, the peroxide value of DMAc after bubbling treatment, as measured according to Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96, was less than 1 mg/kg. DMAc subjected to bubbling treatment was added to the polyimide solution obtained in the above (1) at 155 ℃ to prepare a uniform solution containing 20 mass% of the solid content of the polyimide, which was taken out from the reaction vessel to obtain a varnish. The mass ratio of solvent in the resulting varnish (DMAc: GBL) was about 5: 3. the reduced peroxide number of the resulting varnish was less than 1 mg/kg.

Similarly, the mass ratio of the solvent in the varnishes prepared in example 2 and comparative examples 1 to 3 (solvent other than GBL: GBL) was also about 5: 3.

(3) production of polyimide film

To 200.00 parts by mass of the varnish prepared in the above (2), DMAc prepared in (2) was added to prepare a 15 mass% solution, which was cast on a PET (polyethylene terephthalate) film, and then heated at 50 ℃ for 30 minutes and then at 140 ℃ for 10 minutes to form a coating film on PET. The obtained coating film was peeled off from PET and further heated at 200 ℃ for 40 minutes to obtain a polyimide film having a thickness of 80 μm.

(example 2)

(1) Preparation of the varnish

A varnish was obtained in the same manner as in the method for producing a varnish of example 1, except that the temperature of the bubbling diluted solvent was changed from 155 ℃ to 130 ℃ from DMAc to butyl acetate. Butyl acetate subjected to bubbling treatment was obtained by bubbling butyl acetate with nitrogen gas for 30 minutes. The integrated value of the peak derived from the peroxide in the butyl acetate subjected to the bubbling treatment was 9 ten thousand. Further, the peroxide value of butyl acetate subjected to bubbling treatment as measured by Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96 was less than 1 mg/kg.

(2) Production of polyimide film

A polyimide film having a thickness of 80 μm was obtained in the same manner as in the production method of example 1, except that the varnish prepared in example 1(2) was changed to the varnish prepared in example 2 (1). The reduced peroxide value of the varnish prepared was less than 1 mg/kg.

Comparative example 1

(1) Preparation of the varnish

A varnish was obtained in the same manner as in the method for producing a varnish of example 1, except that the bubbling-treated dilution solvent was changed from DMAc to cyclopentanone (hereinafter, also referred to as CP) and the temperature of the bubbling-treated dilution solvent was changed from 155 ℃. The cyclopentanone subjected to the bubbling treatment was obtained by bubbling the cyclopentanone with nitrogen gas for 30 minutes. The integrated value of the peak derived from peroxide in cyclopentanone subjected to the bubbling treatment was 74 ten thousand. Furthermore, the peroxide value of cyclopentanone subjected to the bubbling treatment, as measured by the Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96, was 21 mg/kg.

(2) Production of polyimide film

A polyimide film having a thickness of 80 μm was obtained in the same manner as in example 1 except that the varnish prepared in example 1(2) was changed to the varnish prepared in comparative example 1 (1). The peroxide value of the varnish thus prepared was 11mg/kg in terms of peroxide value.

Comparative example 2

(1) Preparation of the varnish

A varnish was obtained in the same manner as in the production method of comparative example 1, except that the dilution solvent was changed from cyclopentanone subjected to bubbling treatment to cyclopentanone not subjected to bubbling treatment. The integral value of the peak derived from peroxide in cyclopentanone was 1137 ten thousand. Further, the peroxide value of cyclopentanone to which no bubbling treatment was applied was 57mg/kg, as measured by the Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96.

(2) Production of polyimide film

A polyimide film having a thickness of 80 μm was obtained in the same manner as in the production method of example 1 except that the varnish prepared in example 1(2) was changed to the varnish prepared in comparative example 2 (1). The peroxide value of the varnish thus prepared was 29mg/kg in terms of conversion.

Comparative example 3

(1) Preparation of the varnish

A varnish was obtained in the same manner as in the method for producing a varnish of example 1, except that the bubbling-treated dilution solvent was changed from DMAc to methyl isobutyl ketone (MIBK), and the temperature of the bubbling-treated dilution solvent was changed from 155 ℃ to 130 ℃. The MIBK subjected to the bubbling treatment was obtained by bubbling the MIBK with nitrogen gas for 30 minutes. The integrated value of the peak derived from the peroxide in the MIBK subjected to the bubbling treatment was 452 ten thousand. The peroxide value of MIBK subjected to bubbling treatment as measured by Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96 was 102 mg/kg.

(2) Production of polyimide film

A polyimide film having a thickness of 80 μm was obtained in the same manner as in the production method of example 1 except that the varnish prepared in example 1(2) was changed to the varnish prepared in comparative example 3 (1). The peroxide value of the varnish thus prepared was 51mg/kg in terms of conversion.

<2 > production of Polyamide-imide varnish and production of Polyamide-imide film

(example 3)

(1) Synthesis of polyamideimide A

In a reaction vessel equipped with a sufficiently dried stirrer and a thermometer, nitrogen gas was conducted to replace the inside of the vessel with nitrogen gas. Into the reaction vessel, 250.00 parts by mass of 2,2 '-bis (trifluoromethyl) -4, 4' -diaminobiphenyl (TFMB) and 8,520 parts by mass of DMAc were charged, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 104.57 parts by mass of 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA) was added to the flask to carry out a reaction.

Then, 23.16 parts by mass of 4, 4' -oxybis (benzoyl chloride) (OBBC) and 95.62 parts by mass of terephthaloyl chloride (TPC) were added to the mixture to carry out a reaction.

Next, 168.23 parts by mass of acetic anhydride was added thereto, and after stirring for 15 minutes, 51.14 parts by mass of 4-methylpyridine was added thereto, and the reaction vessel was heated to 70 ℃ and further stirred for 3 hours to obtain a reaction solution.

The obtained reaction solution was cooled, and 12,781 parts by mass of methanol was added, followed by dropwise addition of 6,390 parts by mass of ion-exchanged water, thereby precipitating a white solid. The precipitated white solid was collected by centrifugal filtration and washed with methanol to obtain a wet cake containing a polyamideimide resin. The obtained wet cake was dried under reduced pressure at 80 ℃ to obtain polyamideimide A.

(2) Preparation of the varnish

The foregoing polyamideimide a was added to a mixture of GBL and DMAc in 9: 1 (mass ratio) was mixed in a solvent to prepare a polyamideimide varnish B having a concentration of 8.7 mass%.

The peroxide value of the polyamideimide varnish B, measured according to Petroleum institute Standard kerosene peroxide value test method JPI-5S-46-96, was 2.0 mg/kg.

The GBL and DMAc were used as solvents after 1 week of unsealing.

The integrated value of the peroxide-derived peak in DMAc was 46 ten thousand.

Further, the peroxide value in GBL measured according to Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96 was less than 1mg/kg, and the peroxide value in DMAc was 13 mg/kg.

(3) Production of polyamideimide film

The obtained polyamideimide varnish B was applied to a smooth surface of a polyester substrate (trade name "a 4100", manufactured by toyobo co., ltd.) using an applicator in the same manner as in example 3 so that the thickness of the self-supporting film became 55 μm, dried at 50 ℃ for 30 minutes, and then dried at 140 ℃ for 15 minutes, and the obtained coating film was peeled off from the polyester substrate to obtain a self-supporting film. The obtained self-supporting film was fixed to a metal frame, and further annealed at 200 ℃ under the atmosphere to obtain a polyamideimide film (substrate) having a thickness of 50 μm.

(example 4)

(1) Preparation of the varnish

The polyamideimide a obtained in example 3 was added to a mixture of GBL and butyl acetate in a ratio of 9: 1 (mass ratio) was mixed in a solvent to prepare a polyamideimide varnish C having a concentration of 8.9 mass%.

The peroxide value of the polyamideimide varnish C, determined according to the Petroleum institute Standard kerosene peroxide value test method JPI-5S-46-96, is less than 1 mg/kg.

The GBL and butyl acetate are solvents that have been used for 1 week or more after the unsealing.

The integral value of the peak derived from peroxide in butyl acetate was 3.5 ten thousand.

Furthermore, the peroxide value in GBL measured according to Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96 was less than 1mg/kg, and the peroxide value in butyl acetate was less than 1 mg/kg.

(2) Production of polyamideimide film

A film having a thickness of 50 μm was obtained in the same manner as in the film production method of example 3, except that the polyamideimide varnish C was used.

Comparative example 4

(1) Preparation of the varnish

The polyamideimide a obtained in the foregoing example 3 was added to a mixture of GBL and cyclopentanone in a weight ratio of 9: 1 (mass ratio) in a solvent, to prepare a polyamideimide varnish D having a concentration of 9.0 mass%.

The peroxide value of the polyamideimide varnish D, measured according to Petroleum institute Standard kerosene peroxide value test method JPI-5S-46-96, was 2.6 mg/kg.

The GBL and cyclopentanone are solvents that have been opened for 1 week or more.

The integrated value of the fluorescence spectrum derived from peroxide in cyclopentanone was 1,173 ten thousand.

Furthermore, the peroxide value in GBL measured according to Petroleum institute standard kerosene peroxide value test method JPI-5S-46-96 was less than 1mg/kg, and the peroxide value in butyl acetate was 57 mg/kg.

(2) Production of polyamideimide film

A film having a thickness of 50 μm was obtained in the same manner as in the film production method of example 3, except that the polyamideimide varnish D was used.

<3. measuring method and calculating method >

(1) Method for calculating integral value of peak derived from peroxide

(1-1) measurement of chemiluminescence by liquid chromatography

The peak from peroxide contained in the solvent was determined using a chemiluminescence detection liquid chromatography.

(measurement conditions)

Column: l-column2 ODS (5 μm, 4.6 mm. phi. times.250 mm) manufactured by chemical substance evaluation research mechanism

Protection of the column: sumika Chemical Analysis Service, Ltd., SUMIPAX (registered trademark) Filter PG-ODSs (for Analysis)

Column temperature: 40 deg.C

Mobile phase A: water (W)

Mobile phase B: acetonitrile

Liquid conveying of mobile phase: the concentration gradient was controlled by changing the mixing ratio of mobile phase a and mobile phase B as follows.

Time after injection (minutes); 0 to 9090 to 100

Mobile phase a (vol%); 90 → 00

Mobile phase B (vol%); 10 → 100100

Flow rate: 1.0 mL/min

Injection amount: 5 μ L

A detector: chemiluminescence detector (product of Nippon spectral Co., Ltd. "CL 2027 type)

Temperature of the flow cell: 55 deg.C

RESPONSE speed (RESPONSE): standard (STD)

GAIN (GAIN): 100

Attenuation (ATTEN): 1

Post-addition solution: luminol liquid

Post-addition flow rate: 0.1 mL/min

(1-2) method of calculating integral value

Peaks in the chemiluminescence chromatogram are integrated, and when there are a plurality of peaks, the integrated value is obtained in total.

(2) Method of measuring peroxide number (when the object to be measured is a solvent)

The peroxide value of the solvent was measured according to the peroxide value test method of kerosene standard from the institute of Petroleum JPI-5S-46-49. In this test, peroxide (expressed as ROOH in the following reaction formula) was mixed with a potassium iodide solution to reduce the peroxide, and then free iodine was titrated with a sodium thiosulfate standard solution to calculate a peroxide value in mg/kg (ppm). The reaction is based on the following formula.

2KI+ROOH+H₂O→I₂+2KOH+ROH

I₂+2Na₂S₂O₃→Na₂S₄O₆+2NaI

(2-1) measurement method

(preliminary experiments)

The peroxide number was measured as shown in Table 1, and there was an appropriate sample quality based on the obtained peroxide number.

[ Table 1]

Peroxide number (mg/kg)	Weighing of sample (g)
		0～10	50±5
11～30	10±1
		31～50	5±0.5
51～100	3±0.3
		101～	1±0.1

First, a preliminary experiment is performed to determine the appropriate mass of the sample. The inside of the 200mL Erlenmeyer flask was purged with nitrogen for about 3 minutes. A sample (solvent) 1g was taken into a conical flask and accurately weighed with a balance. Toluene 25mL was added and the liquid was vigorously aerated with nitrogen for about 1 minute. 20mL of an acetic acid solution (prepared by mixing 4mL of JIS K8180 [ hydrochloric acid (reagent) ] and 996mL of JIS K8355 [ acetic acid (reagent) ] was added while keeping nitrogen gas flow.

The gas outflow rate was slowly adjusted so as to be 1 bubble/1 second, and 2mL of an aqueous potassium iodide solution (1.2g/mL) was added. The erlenmeyer flask was shaken vigorously for 30 seconds. After the flask was allowed to stand for 5 minutes, 100mL of water was added. The potential difference titration was carried out using 0.005mol/L sodium thiosulfate standard solution to determine the amount of the sodium thiosulfate standard solution required for the titration of the sample. A blank test was performed in the same manner as described above except that 1g of the sample was changed to 0g, that is, the sample was not used, before the measurement, to obtain the amount of the sodium thiosulfate standard solution (blank amount) required for the blank test.

The peroxide value was calculated from the amount of the 2 sodium thiosulfate standard solutions obtained by the following equation.

PON＝[(A-B)M×1000×8]/m

PON: peroxide number (mg/kg)

A: amount of sodium thiosulfate standard solution (mL) required for titration of sample

B: amount of sodium thiosulfate Standard solution required for blank test (mL)

M: molarity (mol/L) of sodium thiosulfate Standard solution

m: weighing of sample (g)

(this test)

The test was carried out in the same manner with the mass of the sample described in table 1 corresponding to the obtained value of the peroxide value. This gives the peroxide value.

(3) Method of measuring peroxide number (in the case where the measurement target is varnish)

The peroxide value of the varnish was measured according to the Petroleum institute standard kerosene peroxide value test method JPI-5S-46-49.

The inside of the 200mL Erlenmeyer flask was purged with nitrogen for about 3 minutes to replace it. A sample (varnish) 1g was taken in a conical flask and accurately weighed with a balance. DMAc (manufactured by FUJIFILM Wako Pure Chemical Corporation, super-dehydrated grade, unopened product) was added in an amount of 25mL to dissolve the DMAc, and 25mL of toluene was further added dropwise thereto, and nitrogen gas was vigorously introduced into the liquid for about 1 minute. 20mL of an acetic acid solution (prepared by mixing 4mL of JIS K8180 [ hydrochloric acid (reagent) ] and 996mL of JIS K8355 [ acetic acid (reagent) ] was added while keeping nitrogen gas flow.

From the amount of the obtained 2 sodium thiosulfate standard solutions, the peroxide value was calculated by the formula described in (2) the method for measuring the peroxide value (in the case where the measurement target is a solvent).

Incidentally, the peroxide value of DMAc (available from FUJIFILM Wako Pure Chemical Corporation, super-dehydrated grade, unopened product) used was 0.0 mg/kg.

The peroxide value of the varnish was measured in the same manner as in (2) the method for measuring the peroxide value (in the case where the measurement target was a solvent), except that the measurement target was changed from the solvent to the varnish, and the mass of the measurement sample was changed from the mass shown in table 1 to 1g, and the measurement sample was dissolved in DMAc 25mL to carry out the measurement without carrying out the preliminary test.

The latter modification, that is, the modification in which the mass of the measurement sample is reduced as compared with the ordinary one and diluted with DMAc, is to suppress the following problems. When the mass of the measurement sample is large, precipitates are generated and adhere to the electrodes of the measurement device, and as a result, the potential may become unstable.

(converted peroxide number)

The converted peroxide value of the varnish was calculated by weighted average using the peroxide value of the solvent used in the varnish preparation and the mass ratio of the solvent in the varnish.

(3) Measurement of imidization ratio

The imidization ratios of the polyimide resins and the polyamideimide resins used in examples and comparative examples were measured by NMR and calculated using signals derived from the partial structures represented by formula (10). The imidization ratio was calculated from the measurement conditions and the obtained results as follows.

[ chemical formula 6]

(method of preparing measurement sample)

A large excess of methanol as a poor solvent was added to the varnishes obtained in examples 1 to 2 and comparative examples 1 to 3, and the resultant was precipitated and dried by reprecipitation to dissolve the obtained resin in deuterated dimethyl sulfoxide (DMSO-d)₆) A2 mass% solution was prepared and used as a measurement sample.

The polyamideimide resin (polyamideimide A) obtained in example 3 was dissolved in deuteriumDimethyl sulfoxide (DMSO-d)₆) A2 mass% solution was prepared and used as a measurement sample.

(measurement conditions of NMR)

A measuring device: 600MHz NMR apparatus (AVANCE 600, Bruker Co., Ltd.)

Temperature of the sample: 303K

The determination method comprises the following steps:¹H-NMR、HSQC

(method of calculating imidization ratio of polyimide resin)

Obtained by using a solution containing a polyimide resin as a measurement sample¹In the H-NMR spectrum, the integral value of the signal from the proton (A) in the formula (10) is represented as Int_AAnd the integral value of the signal from the proton (B) is denoted as Int_B. From these values, the imidization ratio (%) was determined by the following formula (NMR-1). When the signals from the proton (a) and the proton (B) overlap with the signals from the other structures, the intensities of the signals at the portions where the signals do not overlap are integrated, and the original signal intensity is obtained from the area ratio of the portions, thereby calculating the imidization ratio.

[ mathematical formula 1]

Imidization rate (%) < 100 × (1-Int)_B/Int_A) (NMR-1)

(method of calculating imidization ratio of Polyamide-imide resin)

Obtained from a measurement sample containing a polyamideimide resin¹In the H-NMR spectrum, the integral value of the benzene proton C derived from the structure unchanged before and after imidization and not affected by the structure derived from the amic acid structure remaining in the polyamideimide resin among the observed benzene protons is denoted as Int_C. In addition, let Int denote the integral value of benzene proton D in the observed benzene protons, which is derived from a structure that does not change before and after imidization and is influenced by a structure derived from the amic acid structure remaining in the polyamideimide resin_D. According to the obtained Int_CAnd Int_DThe β value is obtained by the following equation.

β＝Int_D/Int_C

Then, the β value of the above formula and the imidization ratio of the polyimide resin of the above formula were obtained for a plurality of polyamide-imide resins, and the following relational expression was obtained from these results.

Imidization ratio (%) ═ kxbeta +100

In the above relation, k is a constant.

Substituting β into the relational expression gives the imidization ratio (%) of the polyamide-imide resin.

(4) Thickness measurement

The thickness of the transparent polyimide-based polymer film was measured using a digital thickness meter (Mitutoyo Corporation, model 547-401).

(5) Measurement of Total light transmittance (Tt) and Haze (Haze)

According to JIS K7105: 1981, the total light transmittance Tt of the transparent polyimide polymer films obtained in examples and comparative examples was measured by a haze meter (Suga Test Instruments co., ltd., "fully automatic direct haze computer HGM-2 DP").

(6) Determination of weight average molecular weight in terms of polystyrene

Gel Permeation Chromatography (GPC) measurement

(6-1) pretreatment method

The sample was dissolved in gamma-butyrolactone (GBL) to prepare a 20% solution, which was diluted 100-fold with DMF eluent, and the solution was filtered through a 0.45 μm membrane filter to obtain a measurement solution.

(6-2) measurement conditions

Column: TSKgel SuperAWM-Hx2 + SuperAW2500 x 1

(6.0 mmI.D.. times.150 mm. times.3 pieces)

Eluent: DMF solution containing 10mmol/L lithium bromide

Flow rate: 0.6 mL/min

A detector: RI detector

Column temperature: 40 deg.C

Injection amount: 20 μ L

Molecular weight standard: standard polystyrene

<4. evaluation method >

(1) Of varnishes b^*Method of measurement of

B of the varnishes obtained in examples and comparative examples was measured using an ultraviolet-visible near-infrared spectrophotometer ("V-670" manufactured by Nippon spectral Co., Ltd.)^*And (4) carrying out measurement. The varnish was filled in a quartz cuvette having an optical path of 1cm, which was set under ultraviolet-visible near-infrared spectrophotometry. Irradiating white light with a wavelength of 300 to 800nm, and measuring transmittance to obtain b^*The value is obtained. B is obtained^*As initial b^*(b before storage)^*)。

(2) Varnish storage test: Δ b^*Is calculated by

The varnishes obtained in examples 1 to 2 and comparative examples 1 to 3 were stored at 60 ℃ for 2 weeks. The varnishes obtained in examples 3 to 4 and comparative example 3 were stored at 50 ℃ for 1 week. Measurement of b of stored varnish^*B after storage^*. According to the initial b^*And b after storage^*To obtain a difference (Δ b)^*)。

(3) Calculation of yellow index (YI value) of film

The yellowness Index (Yellow Index: YI value) of each of the transparent polyimide polymer films obtained in examples and comparative examples was measured using an ultraviolet-visible near-infrared spectrophotometer ("V-670", manufactured by Nippon spectral Co., Ltd.). The background measurement was performed in the absence of the sample, and then the polyimide film was placed on a sample holder, and the transmittance with respect to light having a wavelength of 300 to 800nm was measured to obtain the tristimulus value (X, Y, Z). The YI value was calculated from the tristimulus values based on the following formula. The obtained YI value was set as an initial YI value (YI value before storage).

YI＝100×(1.2769X-1.0592Z)/Y

(4) Varnish storage test: calculation of the Δ YI value

The varnishes obtained in examples 1 to 2 and comparative examples 1 to 3 were stored at 60 ℃ for 2 weeks. The varnishes obtained in examples 3 to 4 and comparative example 4 were stored at 50 ℃ for 1 week. The YI value of a film obtained by forming a film from the varnish after storage was measured by the same method as the initial YI value, and used as the YI value after storage. The difference (Δ YI) is obtained from the initial YI value and the YI value after storage.

(5) Defoaming property

The varnishes obtained in examples and comparative examples were intensively stirred to be mixed with bubbles throughout, and then filled in clean glass bottles having a diameter of 7cm and a depth of 15cm, respectively, until full, and left to stand at room temperature (25 ℃) for 8 hours. Thereafter, the presence or absence of bubbles on the varnish surface was visually confirmed. Based on the results of visual observation, the defoaming property of the varnish was evaluated in accordance with the following criteria.

(evaluation criteria)

A (good): no layer of bubbles of 3cm or more remained on the surface of the varnish.

B (poor): a layer of bubbles of 3cm or more remained on the surface of the varnish.

[ Table 2]

The varnish of examples 1 to 2 contains a transparent polyimide polymer and a solvent. The polyimide films produced from the varnishes of examples 1 to 2 had a total light transmittance of 90% or more.

The solvent used in the preparation of the varnishes of examples 1 to 2 had an integrated value of peaks derived from peroxide of 70 ten thousand or less. The solvent has a peroxide value of 20mg/kg or less.

Delta b of varnish of examples 1 to 2^*Are all 0.0.

The solvent used in the preparation of the varnishes of comparative examples 1 to 3 had an integrated value of peaks derived from peroxide of more than 70 ten thousand. The solvent peroxide value is more than 20 mg/kg.

Delta b of varnishes of comparative examples 1 to 3^*19.0, 22.1, and 10.8, respectively.

As is clear from the above, the varnishes of examples 1 to 2 had Δ b values larger than those of comparative examples 1 to 3^*Small, high transparency for a long time.

[ Table 3]

The varnish of examples 3 to 4 contains a transparent polyimide polymer and a solvent. The polyamideimide films produced from the varnishes of examples 3 to 4 had a total light transmittance of 80% or more.

The solvents used in the preparation of the varnishes of examples 3 to 4 all had an integrated value of peaks derived from peroxide of 70 ten thousand or less, and all had peroxide values of 20mg/kg or less. Furthermore, the peroxide numbers of the varnishes of examples 3 to 4 were all 2.5mg/kg or less.

Delta b of varnishes of examples 3 to 4^*All are 1.5 or less.

The solvent used in the preparation of the varnish of comparative example 4 had an integrated value of peaks derived from peroxide exceeding 70 ten thousand, and the peroxide value of the solvent exceeded 20 mg/kg. The varnish of comparative example 4 had a peroxide value exceeding 2.5 mg/kg.

Delta b of the varnish of comparative example 4^*It was 23.4.

As is clear from the above, the varnishes of examples 3 to 4 had Δ b values larger than that of comparative example 4^*Small, high transparency for a long time.

Claims

1. A varnish comprising a transparent polyimide-based polymer and a solvent, wherein,

when a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm is produced from the varnish, the film is produced according to Japanese Industrial Standard (JIS) K7105: the total light transmittance of the film measured in 1981 was 80% or more.

2. The varnish according to claim 1, wherein when a film made of a transparent polyimide-based polymer having a thickness of 80 μm is produced from the varnish, the thickness of the film is adjusted in accordance with Japanese Industrial Standard (JIS) K7105: the total light transmittance of the film measured in 1981 was 80% or more.

3. A varnish comprising a transparent polyimide-based polymer and a solvent, wherein,

4. A varnish comprising a transparent polyimide-based polymer and a solvent, wherein,

the solvent has a peroxide value of 20mg/kg or less as measured by the method according to the peroxide value test method of kerosene standard in the institute of Petroleum JPI-5S-46-96,

5. The varnish according to any one of claims 1 to 4, wherein when a film made of a varnish and having a thickness of 80 μm and comprising a transparent polyimide-based polymer is formed, the total light transmittance is 90% or more.

6. The varnish of any one of claims 1 to 5 wherein the solvent comprises at least 2 esters.

7. The varnish according to any one of claims 1 to 6, wherein the weight average molecular weight of the transparent polyimide polymer in terms of polystyrene is 20 ten thousand or more.

8. An optical film formed from the varnish recited in any one of claims 1 to 7.

9. The optical film according to claim 8, which is a film for a front panel of a flexible display device.

10. A flexible display device provided with the optical film according to claim 8 or 9.

11. The flexible display device of claim 10, further provided with a touch sensor.

12. The flexible display device according to claim 10 or 11, further comprising a polarizing plate.