WO2019189483A1

WO2019189483A1 - Varnish containing transparent polyimide-based polymer and solvent

Info

Publication number: WO2019189483A1
Application number: PCT/JP2019/013392
Authority: WO
Inventors: 紘子杉山; 池内　淳一; 友美西村; 皓史宮本; 志成林; 奇明呂; 宗銘李
Original assignee: 住友化学株式会社; 財團法人工業技術研究院
Priority date: 2018-03-28
Filing date: 2019-03-27
Publication date: 2019-10-03
Also published as: TW201942272A; JPWO2019189483A1; CN111936581A; KR20210005607A

Abstract

This varnish comprises a transparent polyimide polymer and a solvent, wherein: the integrated value of a peroxide-derived peak detected by chemical light emission detection liquid chromatography is 700,000 or less; and when a film containing the transparent polyimide polymer and having a thickness of 50-80 μm is produced from the varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standards (JIS) K 7105:1981 is 80% or more.

Description

Varnish containing transparent polyimide polymer and solvent

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

In recent years, polyimide polymer films have been used as functional films for imparting functions to image display devices such as televisions, personal computers, smartphones, tab reds, and electronic paper. In particular, high transparency is required for a functional film used for a display portion of an electronic device such as a display or a touch panel in the image display device.
As a method for producing such a polyimide polymer film, a method is known in which a varnish containing a polyimide polymer and a solvent is applied onto a substrate to form a coating film, and then the coating film is dried. ing. For example, Patent Document 1 describes a method for producing a film using a varnish containing a polyamideimide resin and butyl acetate.

JP2015-174905A

However, when the varnish is produced for a long period of time or when the varnish is produced after the solvent used for the varnish is preserved for a long period of time, the transparency of the polyimide polymer film obtained by coloring the varnish itself decreases. There was a thing. As a countermeasure for restoring transparency, there is a method of purifying varnish, for example, a method of taking out a polyimide polymer from a colored varnish by precipitation or the like and re-dissolving it in a solvent, which is disadvantageous in terms of cost.
Thus, it was difficult for the varnish to have high transparency over 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.

As a result of intensive studies in order to solve the above problems, the present inventors have completed the present invention. That is, the present invention includes the following aspects.
[1] A varnish containing a transparent polyimide polymer and a solvent,
The integral value of the peak derived from the peroxide detected by the chemiluminescence detection liquid chromatography method is 700,000 or less,
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it, varnish.
[2] When a film containing a transparent polyimide polymer having a thickness of 80 μm is produced from varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 is 80% or more. The varnish according to [1].
[3] A varnish containing a transparent polyimide polymer and a solvent,
The peroxide value of the varnish detected by a method in accordance with JPI-5S-46-96 is a peroxide value of 2.5 mg / kg or less.
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it, varnish.
[4] A varnish containing a transparent polyimide polymer and a solvent,
The peroxide value of the solvent detected by the method based on JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, is 20 mg / kg or less,
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured according to Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it, varnish.
[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 two types of esters.
[7] The varnish according to any one of [1] to [6], wherein the transparent polyimide polymer has a polystyrene-reduced weight average molecular weight of 200,000 or more.
[8] An optical film formed from the varnish according to any one of [1] to [7].
[9] The optical film according to [8], which is a film for a front plate 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 including a touch sensor.
[12] The flexible display device according to [10] or [11], further including a polarizing plate.

According to the present invention, it is possible to provide a varnish having high transparency over a long period (for example, 3 months or more).

<Varnish>
The varnish of the present invention is
Including a transparent polyimide polymer and a solvent,
The integral value of the peak derived from the peroxide detected by the chemiluminescence detection liquid chromatography method is 700,000 or less,
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it.
The varnish of the present invention is
Including a transparent polyimide polymer and a solvent,
The peroxide value of the varnish detected by a method in accordance with JPI-5S-46-96 is a peroxide value of 2.5 mg / kg or less.
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it.
The varnish of the present invention is
Including a transparent polyimide polymer and a solvent,
The peroxide value of the solvent detected by the method based on JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, is 20 mg / kg or less,
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it.

[1. Integrated value of peroxide-derived peak]
The integrated value of the peak derived from peroxide is the integrated value of the peak derived from peroxide detected by the chemiluminescence detection liquid chromatographic method by adding the luminol solution to the solvent for preparing the varnish.
In the present specification, the peroxide acts as an oxidizing agent for the luminol reaction in the solvent-luminol liquid system. The peroxide-derived peak includes a luminescence peak generated by the reaction between the peroxide and luminol. The integrated value of the peak derived from peroxide can be measured, for example, by the method described in the examples.

The following explains that the integral value of the peak derived from peroxide is 700,000 or less.
When the solvent is one kind of solvent, it means that the integral value of the peak derived from the peroxide of one kind of solvent is 700,000 or less.
When the solvent is a mixed solvent composed of two kinds of solvents, and the integrated value of one of the two solvents in the mixed solvent is much larger than the integrated value of the other solvent (for example, It can be determined that the integral value of one solvent is dominant. In such a case, it means that the integral value of the peak derived from the peroxide of one solvent is 700,000 or less.

When the integral value of the peak derived from the peroxide is 700,000 or less, the concentration of the peroxide dissolved in the solvent in the varnish is sufficiently low, so the reaction rate between the peroxide and the transparent polyimide polymer is high. It becomes extremely slow, and the transparent polyimide polymer in the varnish is less likely to be oxidized by peroxide over time. In such a case, since the solvent and the transparent polyimide polymer are unlikely to deteriorate with time, a varnish having high transparency can be provided even after long-term storage (for example, 3 months or more) of the solvent and varnish. .
The integral value of the peak derived from the peroxide is preferably 500,000 or less, more preferably 350,000 or less, still more preferably 100,000 or less, particularly preferably 50,000 or less, from the viewpoint of maintaining high transparency over a long period of time. is there.

As a means for adjusting the integral value of the peak derived from the peroxide to 700,000 or less, for example, means for reducing the concentration of peroxide in the varnish (more specifically, generation of peroxide in the varnish is performed. And the like). It is considered that the peroxide in the varnish is generated mainly by the reaction between the solvent molecules in the varnish and dissolved oxygen (oxidation reaction of the solvent molecules). For this reason, as means for inhibiting peroxide in the varnish, for example, means for reducing the dissolved oxygen concentration in the varnish, and means for selecting the type of solvent that hardly reacts with oxygen to generate peroxide. Can be mentioned. As a means for reducing the dissolved oxygen concentration in the varnish, for example, a bubbling process is performed on the solvent with an inert gas (more specifically, a rare gas such as argon gas and neon gas, and nitrogen gas). And means for substituting the dissolved oxygen in the solvent with an inert gas, and means for reducing the oxygen concentration in the gas phase in contact with the solvent under a reduced-pressure atmosphere or an inert gas atmosphere. The time for the bubbling treatment is preferably, for example, 10 minutes or more and 1 hour or less from the viewpoint of sufficiently achieving replacement of dissolved oxygen and reducing the cost. For example, when performing a bubbling process with respect to the mixed solvent containing 2 types of ester, you may perform a bubbling process of at least one of those solvents, before mixing 2 types of solvents. After mixing the two solvents, a bubbling process may be performed on the mixed solvent. Moreover, you may perform a bubbling process with respect to a varnish after preparing a varnish. The solvent will be described later.

When the solvent is a mixed solvent composed of two or more solvents, the sum (weighted average) of the product of the integral value of each solvent and the mass ratio of each solvent in the varnish is the varnish integral value (converted integral value of varnish) ) Varnish may be evaluated. In such a case, the converted integral value of the varnish is preferably 350,000 or less, more preferably 250,000 or less, further preferably 180,000 or less, particularly preferably 50,000 or less, and very particularly preferably 25,000 or less.

[2. Peroxide value]
The peroxide value can be measured according to or based on the Peroxide Value Test Method JPI-5S-46-96 of the Petroleum Institute Standard Kerosene. In the measurement of the peroxide value, a solvent for preparing a varnish (a solvent before preparing the varnish) or a varnish can be used as a measurement target.

(2-1. When the measurement target is a solvent)
When the object to be measured is a solvent for preparing a varnish, the peroxide value is measured according to the peroxide test method JPI-5S-46-96. First, the solvent to be measured is dissolved in toluene. Next, a potassium iodide solution is added to a solvent dissolved in toluene, and iodine released at this time can be determined by titration with a sodium thiosulfate standard solution. In the present specification, the peroxide acts as an oxidizing agent for potassium iodide in the measurement object-toluene solution of potassium iodide. The peroxide value of the solvent can be measured, for example, by the method described in the examples.

The following explains that the peroxide value of the solvent is 20 mg / kg.
When the solvent is one kind of solvent, it means that the peroxide value of one kind of solvent is 20 mg / kg or less.
When the solvent is a mixed solvent composed of two kinds of solvents, and the peroxide value of one of the two solvents in the mixed solvent is much larger than the peroxide number of the other solvent ( For example, it can be determined that the peroxide value of one solvent is dominant. In such a case, it means that one peroxide value is 20 mg / kg.

When the measurement object is the solvent, the peroxide value is 20 mg / kg or less. When the peroxide value is 20 mg / kg or less, since the concentration of the peroxide dissolved in the solvent in the varnish is sufficiently low, the reaction rate between the peroxide and the transparent polyimide polymer is extremely slow, It is believed that the transparent polyimide polymer in the varnish is less likely to be oxidized by the peroxide over time. In such a case, since the solvent and the transparent polyimide polymer are unlikely to deteriorate with time, a varnish having high transparency can be provided even after storage of the solvent for a long period (for example, 3 months or more). By producing an optical film using such a highly transparent varnish, an optical film having high transparency can be obtained.

The peroxide value is preferably 15 mg / kg or less, more preferably 10 mg / kg or less, still more preferably 5 mg / kg or less, particularly preferably less than 1 mg / kg from the viewpoint of maintaining high transparency of the varnish for a longer period of time. is there.
When the solvent is a mixed solvent composed of two or more solvents, the sum of the product of the peroxide value of each solvent and the mass ratio of each solvent in the varnish (weighted average) is the varnish peroxide value Varnish may be evaluated as (oxide value). In such a case, the converted peroxide value of the varnish is preferably 10 mg / kg or less, more preferably 7.5 mg / kg or less, further preferably 5 mg / kg or less, particularly preferably 2.5 mg / kg or less, very particularly preferably. Is less than 0.5 mg / kg.

(2-2. When the object to be measured is varnish)
When the object to be measured is varnish, the peroxide value is measured according to the above-mentioned JPI-5S-46-96. The peroxide value is measured in the same manner as when the measurement target is a solvent, except that the measurement target is changed from a solvent to a varnish, the mass of the measurement target is changed, and the measurement target is diluted with a solvent. The peroxide value of the varnish can be measured, for example, by the method described in the examples.

When the measurement target is varnish, the peroxide value is 2.5 mg / kg. When the peroxide value is 2.5 mg / kg or less, a varnish having high transparency can be provided even after long-term storage of the varnish for the same reason as when the measurement target is a solvent. By producing an optical film using such a highly transparent varnish, an optical film having high transparency can be obtained.
In addition, when the peroxide value is 2.5 mg / kg or less, the transparent polyimide polymer in the optical film is less likely to deteriorate over time for the same reason as when the object to be measured is varnish. Can be obtained.

The peroxide value of the varnish is preferably 2.0 mg / kg or less, more preferably 1.5 mg / kg or less, still more preferably 1.1 mg / kg or less, from the viewpoint of maintaining high transparency of the varnish for a longer period of time. Particularly preferably, it is less than 1 mg / kg.

[3. Total light transmittance]
The total light transmittance of the transparent polyimide polymer film having a thickness of 50 to 80 μm is preferably 80% or more, more preferably 82% or more, still more preferably 85% or more, even more preferably 88% or more, It is particularly preferably 90% or more, further particularly preferably 91% or more, particularly preferably 92% or more. When the transmittance is in the above range, for example, when a display device is produced by combining a film formed from the varnish of the present invention and an EL element, the same as when combined with a film having a low transmittance. Since the EL element can be driven with less power to obtain brightness, it can contribute to power saving. In order to ensure high transparency of the film, the varnish used for forming the film is preferably transparent over a long period of time. Whether the varnish is transparent over a long period of time can be confirmed, for example, by an accelerated test in which the varnish is stored at 50 ° C. for 1 week.

The total light transmittance of the transparent polyimide polymer film can be measured using a haze meter in accordance with JIS K 7105: 1981, for example.
The thickness of the transparent polyimide polymer film can be measured, for example, using a micrometer.

Further, when the thickness of the transparent polyimide polymer film is other than 80 μm, the total light transmittance of the film is measured using a haze meter as described above, and the total light transmittance obtained is 80 μm in thickness. You may convert into total light transmittance.
The total light transmittance can be converted, for example, using the Lambert-Beer law as follows. Here, a method for converting the total light transmittance Tt ₅₀ measured at a thickness of 50 μm into a total light transmittance at 80 μm will be described.
Formula (A)

[In formula (A), T represents transmittance, x represents optical path length, and α represents absorption constant]
The total light transmittance Tt ₅₀ is substituted for the transmittance T, and the film thickness 50 μm is substituted for the optical path length x. As a result, an absorption constant α is obtained. Next, by substituting 80 μm into x and substituting the previously obtained absorption constant α in the formula (A), the total light transmittance Tt ₈₀ (total light transmittance in terms of ₈₀ μm) at a thickness of ₈₀ μm is obtained. It is done.

[4. solvent]
The solvent preferably has high transparency over a long period of time, while having basic characteristics as a composition of the varnish. The former is a characteristic in which a 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, a characteristic that a solvent molecule does not easily react with oxygen, or does not easily generate a peroxide having a high reaction activity even if it reacts with oxygen, and a characteristic that does not readily dissolve oxygen.
From the viewpoint of satisfying such characteristics, examples of the solvent include aprotic polar solvents (more specifically, N, N-dimethylacetamide (hereinafter sometimes referred to as DMAc), dimethyl sulfoxide, and the like). And carboxylic acid esters (more specifically, acetic acid esters, cyclic carboxylic acid esters, and the like). Examples of the acetate include butyl acetate (hereinafter sometimes referred to as vinegar buty), amyl acetate, and isoamyl acetate. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (hereinafter sometimes referred to as GBL). These solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

Among these solvents, from the viewpoint of further improving two characteristics, at least one solvent selected from the group consisting of GBL, DMAc, butyl acetate, amyl acetate, and isoamyl acetate is preferable, and is selected from the above solvents. At least two or more esters are more preferable. Examples of the combination of at least two kinds of 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, and 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 Isoamyl acetate, GBL, amyl acetate and isoamyl acetate, DMAc and butyl acetate and amyl acetate, DMAc and butyl acetate and isoamyl acetate, DMAc and amyl acetate and isoamyl acetate, butyl acetate and amyl acetate and isoamyl acetate, GBL and DMAc and butyl acetate Amyl acetate, GBL and DMAc and butyl acetate and isoamyl acetate, GBL and DMAc and amyl acetate and isoamyl acetate, GBL and butyl acetate and amyl acetate and isoamyl acetate, DMAc and butyl acetate and amyl acetate and isoamyl acetate, and GBL and DMAc and And a combination of butyl acetate, amyl 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, butyl acetate, amyl acetate, GBL, butyl acetate, isoamyl acetate, GBL, amyl acetate, isoamyl acetate, butyl acetate, amyl acetate, isoamyl acetate, and combinations of GBL, butyl acetate, amyl acetate, and isoamyl acetate. More preferred GBL and butyl acetate, GBL and amyl acetate, GBL 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 acetic acid A combination with isoamyl is mentioned.
In the case of a mixed solvent composed of two solvents, the mixing ratio (mass ratio) is preferably 1: 9 to 9: 1, more preferably 2: 8 to 8: 2. In the case of a mixed solvent composed of three solvents, the mixing ratio (mass ratio) is preferably 1 to 8: 1 to 8: 1 to 8, more preferably 2 to 7: 2 to 7: 2 to 7. .
In the case of comprising two or more solvents, the content of one of the two or more solvents is usually 10% by mass or more, preferably 20% by mass or more, more preferably 30%, based on the total amount of the solvent. It is 90 mass% or less normally, Preferably it is 80 mass% or less, More preferably, it is 70 mass% or less, More preferably, it is 60 mass% or less.

[5. Transparent polyimide polymer]
(Transparent polyimide polymer obtained by polymerization and imidization)

Examples of the transparent polyimide polymer include polyimide and polyamideimide, and comprehensively include polyimide, polyamideimide, and derivatives thereof. In this specification, a polyimide means a polymer containing a repeating structural unit containing an imide group. Polyamideimide is a polymer containing a repeating unit containing both an imide group and an amide group.

The transparent polyimide polymer preferably contains mainly a repeating structural unit represented by the formula (10) from the viewpoint of the transparency of the transparent polyimide 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, based on all repeating structural units of the transparent polyimide polymer. % Or more, particularly preferably 90 mol% or more, and still more preferably 98 mol% or more. 100 mol% may be sufficient as the repeating structural unit represented by Formula (10). In Formula (10), G is a tetravalent organic group, and A is a divalent organic group. The transparent polyimide-based polymer may include two or more repeating structural units represented by the formula (10) in which G and / or A are different.

The transparent polyimide polymer is any one of repeating structural units represented by the formula (11), the formula (12) and the formula (13) as long as various physical properties of the obtained transparent polyimide polymer film are not impaired. The above may be further included.

In formula (10) and formula (11), G and G ¹ represent a tetravalent organic group, preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The G and ^{G 1,} for example, formula (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), wherein And groups represented by (28) and formula (29), and chain hydrocarbon groups having 6 or less tetravalent carbon atoms. * The in formula (20) to (29) represents a bond, Z in the formula (26) is a single _{_{bond, -O -, - CH 2 -}} , - CH 2 -CH 2 -, - CH ( CH ₃ ) —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —Ar—, —SO ₂ —, —CO—, —O—Ar—O—, —Ar—O—Ar. _{-, - Ar-CH 2 -Ar} -, - Ar-C (CH 3) represents a 2 -Ar- or _-Ar-SO 2 -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom (more specifically, a phenylene group or the like). From the viewpoint of suppressing the yellowness of the obtained film, G and G ¹ preferably represent groups represented by formulas (20) to (27).

In Formula (12), G ² represents a trivalent organic group, and preferably represents an organic group that may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of the trivalent organic group represented by G ² include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), and formula. (27), a group in which any one of the bonds of the groups represented by formula (28) and formula (29) is replaced by a hydrogen atom, and a trivalent hydrocarbon group having 6 or less carbon atoms. It is done.

In Formula (13), G ³ represents a divalent organic group, and preferably represents an organic group that may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of the divalent organic group represented by G ³ include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), and formula. (27) A group in which two non-adjacent bonds in the groups represented by formula (28) and formula (29) are each replaced by a hydrogen atom, and a divalent chain hydrocarbon having 6 or less carbon atoms Groups.

In the formulas (10) to (13), A, A ¹ , A ² and A ³ all represent a divalent organic group, preferably substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Represents a good organic group. As A, A ¹ , A ² and A ³ , for example, the following formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), formula (36) ), A group represented by formula (37) and formula (38); a group in which they are substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon having 6 or less carbon atoms Groups.
* In Formula (30) to Formula (38) represents a bond, and Z ¹ , Z ² and Z ³ in Formula (34) to Formula (36) are each independently a single bond, —O—, _{_{_{_{-CH 2 -, - CH 2 -CH}}}} 2 -, - CH (CH 3) -, - C (CH 3) 2 -, - C (CF 3) 2 -, - SO 2 - or an -CO-. One example is when Z ¹ and Z ³ are —O— and Z ² is —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ — or —SO ₂ —. To express. Z ¹ and Z ² , and Z ² and Z ³ are each preferably in a meta position or a para position with respect to each ring.

The repeating structural unit represented by the formula (10) and the formula (11) is usually derived from a diamine and a tetracarboxylic acid compound. The repeating structural unit represented by the formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating structural unit represented by the formula (13) is usually derived from a diamine and a dicarboxylic acid compound. These carboxylic acid compounds (tetracarboxylic acid compounds, tricarboxylic acid compounds, and dicarboxylic acid compounds) may be carboxylic acid compound analogs (more specifically, carboxylic acid anhydrides, alkanoyl halides, and the like).

(Tetracarboxylic acid compound)
Examples of the tetracarboxylic acid compound include an aromatic tetracarboxylic acid compound such as an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic acid compound such as an aliphatic tetracarboxylic dianhydride. These tetracarboxylic acid compounds may be used individually by 1 type, and may be used in combination of 2 or more type. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as a tetracarboxylic acid chloride compound in addition to the tetracarboxylic dianhydride.

Examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydride, monocyclic aromatic tetracarboxylic dianhydride, and condensed polycyclic aromatic tetra Carboxylic dianhydrides are mentioned.
Non-condensed polycyclic aromatic tetracarboxylic dianhydrides include, for example, 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2, 2 ', 3,3'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3- Dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (hereinafter referred to as 6FDA) To describe 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4 -Dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3- Dicarboxyphenyl) methane dianhydride, 4,4 ′-(p-phenylenedioxy) diphthalic dianhydride, and 4,4 ′-(m-phenylenedioxy) diphthalic dianhydride.

Examples of the condensed polycyclic aromatic tetracarboxylic dianhydride include 2,3,6,7-naphthalene tetracarboxylic dianhydride.
As the aromatic tetracarboxylic dianhydride, preferably 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3 '-Benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 3,3' , 4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane Anhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride, 1,2-bis (2,3- Dicarboxypheny ) Ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis ( 3,4-dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 4,4 ′-(p -Phenylenedioxy) diphthalic dianhydride and 4,4 '-(m-phenylenedioxy) diphthalic dianhydride. One of these aromatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. In this specification, the cycloaliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure. Examples of the cycloaliphatic tetracarboxylic dianhydride include 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and 1, Cycloalkanetetracarboxylic dianhydrides such as 2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic Examples thereof include acid dianhydride, dicyclohexyl-3,3 ′, 4,4′-tetracarboxylic dianhydride, and regioisomers thereof. One of these cycloaliphatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination. Examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. It is done. One of these acyclic aliphatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination.

From the viewpoint of further improving the transparency of the transparent polyimide polymer film, the tetracarboxylic acid compound is preferably an alicyclic tetracarboxylic dianhydride or a non-condensed polycyclic aromatic tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) More preferred is propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA). These suitable tetracarboxylic acid compounds may be used singly or in combination of two or more.

(Tricarboxylic acid compound and dicarboxylic acid compound)
The raw material monomer may further contain a tricarboxylic acid compound and / or a dicarboxylic acid compound.
Examples of the tricarboxylic acid compound include aromatic tricarboxylic acid, aliphatic tricarboxylic acid, and related acid chloride compounds and acid anhydrides. These tricarboxylic acid compounds may be used individually by 1 type, and may be used in combination of 2 or more type. Examples of the tricarboxylic acid compound include 1,2,4-benzenetricarboxylic acid anhydride; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; phthalic anhydride and benzoic acid having a single bond, Examples include compounds linked by —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —SO ₂ —, or a phenylene group.

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and related acid chloride compounds and acid anhydrides. These dicarboxylic acid compounds may be used individually by 1 type, and may be used in combination of 2 or more type. Examples of the dicarboxylic acid compound include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; terephthalic acid dichloride (terephthaloyl chloride (TPC)); , 4′-oxybis (benzoyl chloride) (OBBC); a dicarboxylic acid compound of a chain hydrocarbon having 8 or less carbon atoms and two benzoic acids are —CH ₂ —, —C (CH ₃ ) ₂ —, —C Examples thereof include compounds linked by (CF ₃ ) ₂ —, —SO ₂ —, or a phenylene group.

The ratio of the tetracarboxylic acid compound to the total of the tetracarboxylic acid compound, tricarboxylic acid compound, and dicarboxylic acid compound is preferably 40 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more, and even more. Preferably it is 90 mol% or more, Most preferably, it is 98 mol% or more.

(Diamine)
Examples of diamines include aliphatic diamines, aromatic diamines, or mixtures thereof. In the present specification, the “aromatic diamine” refers to a diamine in which an amino group is directly bonded to an aromatic ring, and an aliphatic group or other substituent may be included in a part of the structure. The aromatic ring may be a single 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. Of the aromatic rings, a benzene ring is preferable. In the present specification, “aliphatic diamine” means a diamine in which an amino group is directly bonded to an aliphatic group, and an aromatic ring or other substituent may be included in a part of the structure. .

Examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylene diamine, 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, norbornane diamine, and 4, And cycloaliphatic diamines such as 4'-diaminodicyclohexylmethane. These aliphatic diamines may be used alone or in combination of two or more.

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

The diamine can also have a fluorine-based substituent. Examples of the fluorine-based substituent include a perfluoroalkyl group having 1 to 5 carbon atoms such as a trifluoromethyl group and a fluoro group.

Among the diamines, from the viewpoint of high transparency and low colorability, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure. Use one or more selected from the group consisting of 2,2′-dimethylbenzidine, 2,2′-bis (trifluoromethyl) benzidine (TFMB), and 4,4′-bis (4-aminophenoxy) biphenyl Is more preferable.
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′-diaminodiphenyl (TFMB).

The molar ratio between the diamine in the raw material monomer and the carboxylic acid compound such as a tetracarboxylic acid compound is preferably within a range of 0.9 mol to 1.1 mol of the tetracarboxylic acid with respect to 1.00 mol of the diamine. Can be adjusted. In order to develop high folding resistance, it is preferable that the obtained transparent polyimide polymer has a high molecular weight. Therefore, the amount of tetracarboxylic acid is more preferably 0.98 mol with respect to 1.00 mol of diamine. It is more than 1.02 mol, More preferably, it is 0.99 mol% or more and 1.01 mol% or less.
In addition, from the viewpoint of suppressing the yellowness of the obtained transparent polyimide polymer film, it is preferable that the proportion of amino groups in the resulting polymer terminal is low, such as tetracarboxylic acid compound with respect to 1.00 mol of diamine. The amount of the carboxylic acid compound is preferably 1.00 mol or more.

Adjusting the number of fluorine in the molecule of diamine and carboxylic acid compound (for example, tetracarboxylic acid compound), the amount of fluorine in the obtained transparent polyimide polymer is preferably based on the mass of the transparent polyimide polymer. The amount may be 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. Since the raw material cost tends to increase as the proportion of fluorine increases, the upper limit of the amount of fluorine is preferably 40% by mass or less. A fluorine-type substituent may exist in either diamine or a carboxylic acid compound, and may exist in both. By including a fluorine-based substituent, the YI value may be particularly reduced.

(Weight average molecular weight in terms of polystyrene)
The polystyrene equivalent weight average molecular weight of the transparent polyimide polymer is preferably 200,000 or more, more preferably 200,000 or more and 500,000 or less. When the polystyrene-equivalent weight average molecular weight is in the above range, a high flexibility of the transparent polyimide polymer film obtained from the varnish of the present invention can be obtained, and an appropriate viscosity of the varnish can be obtained and good workability can be obtained. It is done. The polystyrene-equivalent weight average molecular weight can be measured using a gel permeation chromatography (GPC) method.

[6. Additive]
The varnish of the present invention may further contain an additive as long as the transparency is not impaired. Examples of the additive include inorganic particles, ultraviolet absorbers, antioxidants, mold release agents, stabilizers, colorants, flame retardants, lubricants, thickeners, and leveling agents.

[Defoaming property of varnish]
It is preferable that the varnish has a good defoaming property because it is easy to handle in the coating process. The defoaming property can be adjusted by adjusting the combination and ratio of resin and solvent and the viscosity. In the case of a polyimide resin, when an acetate solvent (ethyl acetate, butyl acetate, amyl acetate, isoamyl acetate) or the like is used as a solvent, the defoaming property tends to be good.

[7. Manufacturing method of varnish]
The method for producing the varnish includes, for example, a polymerization step in which a raw material monomer of a transparent polyimide polymer is polymerized in a solvent A to obtain a transparent polyimide polymer precursor, and the transparent polyimide in the solvent A containing a tertiary amine. An imidization step of imidizing a polymer precursor 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 manufacturing process of a varnish may further include the varnish extraction process which extracts a varnish from a reaction container. Moreover, you may implement an imidation process in a pressure-reduced atmosphere.
Also, after the imidization step, the polyimide polymer solution is once brought into contact with a poor solvent for the polyimide polymer that is a solute, the polyimide polymer is taken out as a solid content, and the obtained solid content is taken as a good solvent. The varnish may be prepared by re-dissolving the varnish, or the solution obtained by re-dissolution may be further diluted with the solvent B to prepare the varnish.

(Polymerization process)
In the polymerization step, the raw material monomer of the transparent polyimide polymer is polymerized in the solvent A to obtain a transparent polyimide polymer precursor. The amount of the raw material monomer in the total liquid containing the raw material monomer and the solvent A can be 3 to 60% by mass, preferably 10 to 60% by mass. When the amount of the raw material monomer is large, the polymerization rate tends to increase, and the molecular weight can be increased. Further, the polymerization time can be shortened, and the coloring of the transparent polyimide 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, so that it becomes difficult to stir or the polymer adheres to the reaction vessel or the stirring blade and the yield is low. Sometimes it becomes. The solvent A can be the same as those mentioned above.

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

By sufficiently stirring the raw material monomer in the polymerization reaction solution, the polymerization of the raw material monomer is promoted to form a transparent polyimide polymer precursor. If necessary, the reaction solution may be heated to about 40 to 90 ° C. The imidization process described later can also proceed in parallel with the progress of the raw material monomer polymerization process. In this case, the reaction solution may be heated to a higher temperature in accordance with the imidization conditions described later.
The polymerization reaction time can be, for example, 24 hours or less, or 1 hour or less, or 1 to 24 hours.

The reaction solution may contain a tertiary amine during the polymerization step of the transparent polyimide polymer precursor. In this case, the tertiary amine may be added before mixing the diamine and the solvent A, may be added after mixing, or may be added after mixing the diamine, the solvent, and the carboxylic acid compound.
Moreover, after diluting with a part of the solvent to be used, it may be added to the reaction solution.

[Tertiary amine]
The tertiary amine can 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 a tertiary amine represented by the formula (d) (hereinafter sometimes referred to as a tertiary amine D).

In the formula (d), R _1D is 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 ° C. or higher, more preferably 140 ° C. or higher, still more preferably 170 ° C. or higher, and particularly preferably 200 ° C. or higher. Although the upper limit of the boiling point of the tertiary amine is not particularly defined, it is usually 350 ° C. or lower. When the boiling point of the tertiary amine is in the above range, it is preferable because the amount of the tertiary amine removed outside the system tends to be suppressed when water is distilled off under reduced pressure.

(Imidization process)
Subsequently, 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, by heating a reaction solution containing a tertiary amine in a reduced-pressure atmosphere, the imidation of the transparent polyimide polymer precursor is promoted, and water produced as a by-product while producing polyimide is retained. Can be left. It is preferable to imidize the transparent polyimide polymer precursor in the solvent A in the reaction vessel in which the above polymerization is performed. The tertiary amine may be added during or before the polymerization step for polymerizing the raw material monomer to produce a transparent polyimide polymer precursor as described above, but produces a transparent polyimide polymer precursor. It may be added after the process. Further, chemical imidization may be performed without adding a reduced pressure atmosphere by adding acetic anhydride together with a tertiary amine.

The production reaction of the transparent polyimide polymer precursor and the imidization reaction may be performed simultaneously. In that case, the bond of an amide group may be cut | disconnected by the water produced | generated by imidation reaction, and the molecular weight of the transparent polyimide type polymer obtained may become low. A film obtained from a varnish containing such a transparent polyimide polymer may have a low folding resistance. In the imidization step, the pressure in the reaction solution is reduced and water in the reaction solution is quickly removed, so that the cleavage reaction of the amide group can be suppressed and the molecular weight of the resulting transparent polyimide polymer can be increased. Therefore, especially when the production reaction and the imidation reaction of the transparent polyimide polymer precursor proceed simultaneously, the imidization process is performed in a reduced-pressure atmosphere, so that the transparent polyimide polymer is included without going through a purification process. Even if the film is produced directly from the varnish, the film tends to have high folding resistance.

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

The temperature of the imidization step is preferably 100 ° C. or higher and 250 ° C. or lower, more preferably 150 ° C. or higher and 210 ° C. or lower. When acetic anhydride and a tertiary amine are added simultaneously for chemical imidization, the temperature is preferably 20 to 100 ° C., more preferably 40 to 80 ° C.

When the reduced pressure atmosphere is used in the imidization step, the pressure is preferably 730 mmHg or less, more preferably 700 mmHg or less, and even more preferably 675 mmHg or less. The pressure in the imidization step can be, for example, 350 mmHg or more, and may be 500 mmHg or more. Depending on the vapor pressure of the solvent at the temperature of the imidization step, it may be preferable to perform the pressure at 400 mmHg or higher in order to increase the stability of the reaction. For the same reason, it may be more preferable to carry out at 600 mmHg.
If the pressure in the imidization step is set near the saturated vapor pressure of the solvent in the imidization step, YI tends to be suppressed. A pressure within 50 mmHg from the saturated vapor pressure is preferred.

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, even more preferably 2 to 6 hours, and particularly preferably 2 to 5 hours. It is. Stirring is preferred during heating.
When reaction time becomes long, molecular weight will become high, but there exists a tendency for the yellowishness of a transparent polyimide type polymer to become strong easily. 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.

From the viewpoint of suppressing the decrease in transparency of the transparent polyimide polymer film, the imidization step is preferably performed in a reduced-pressure atmosphere. When the imidization step is carried out under a reduced pressure atmosphere, the oxygen concentration in the gas phase contacting the liquid phase containing the solvent A in the reaction vessel is low, so that the dissolution of oxygen into the solvent A is reduced, and the transparent polyimide It is considered that the peroxide concentration in the 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. The oxygen concentration may be low from the time of charging. The oxygen concentration is preferably 0.02% or less, and more preferably 0.01% or less. If the oxygen concentration is high when heated to a high temperature, it causes coloring in particular. For example, when the temperature of the reaction solution is 130 ° C. or higher, the oxygen concentration is preferably 0.02% or lower. In the synthesis of the precursor and the imidization of the precursor, oxygen is not substantially generated. For example, by reducing the oxygen concentration in the gas phase by replacing the inside of the reaction vessel with nitrogen gas before starting the raw material, The oxygen concentration in the gas phase in the conversion step can be reduced. The oxygen concentration in the imidization step can be grasped, for example, by analyzing the oxygen concentration in the gas removed from the reaction vessel when the pressure inside the reaction vessel is reduced. If it is difficult to measure the oxygen concentration during decompression, the oxygen concentration may be measured by sampling the gas phase before and after decompression. For the purpose of lowering the oxygen concentration as in the reduced pressure atmosphere, the imidization step may be performed in an inert gas atmosphere instead of the reduced pressure atmosphere.

After heating, the solution is returned to atmospheric pressure and cooled to obtain a transparent polyimide polymer solution.

As another method for suppressing the decrease in the transparency of the transparent polyimide polymer, acetic anhydride may be added together with the tertiary amine, and chemical imidization may be performed at a lower temperature. In this case, the water generated by the imidization reaction is removed by the reaction with acetic anhydride, so that it is not necessary to remove the water by reducing the pressure.
If necessary, the transparent polyimide polymer may be once taken out from the imidized transparent polyimide polymer solution, and then redissolved in a solvent and used in the next dilution step.
Examples of the extraction method include a method of adding a poor solvent for the transparent polyimide polymer to the imidized transparent polyimide polymer solution to precipitate the transparent polyimide polymer, followed by filtration and extraction. It is done.
(Dilution process)
In the subsequent dilution step, the transparent polyimide polymer or a solution thereof is diluted with the solvent B to prepare a varnish. More specifically, solvent B is further added to the obtained transparent polyimide polymer or a solution thereof to adjust the concentration of the transparent polyimide polymer to obtain a varnish. A suitable solids concentration in the varnish is preferably 5 to 25% by weight.
In addition, when producing a film from a varnish, if the varnish which contains 30 mass% or more of transparent polyimide type polymers with respect to the total amount of the solid content in a varnish is used, one of the main components mentioned later is a transparent polyimide type polymer. A transparent polyimide polymer film can be easily obtained. The concentration of the transparent polyimide polymer is preferably 10% by mass or more, more preferably 13% by mass or more based on the total mass of the varnish.

Dilution can be performed in the reaction vessel, and can also be performed on the solution recovered from the reaction vessel.

In the reaction vessel, when the solvent B is added to the transparent polyimide polymer solvent after imidization to dilute the concentration of the transparent polyimide polymer in the reaction vessel, it remains in the reaction vessel in the next extraction step. The amount of the polymer can be reduced, and the yield of the polymer can be improved. Further, when the amount of the polymer remaining in the reaction vessel is reduced, the coloring (for example, yellow) of the obtained transparent polyimide polymer is improved in the subsequent polymerization and imidation repeating steps using this reaction vessel.

The solvent B for dilution can be the same as those mentioned above. The solvent B and the solvent A may be the same type or different from each other. By appropriately selecting a solvent having high solubility in the polyimide resin as the solvent B for dilution, the recovery rate of the transparent polyimide polymer from the reaction vessel is increased.

The dilution in the reaction vessel can be performed a plurality of times using a plurality of different types of solvents B.

(Varnish extraction process)
Subsequently, in the varnish extraction step, the varnish is extracted from the reaction vessel. The extracted varnish can be used in a film forming process described later.

[8. Method for producing transparent polyimide polymer film]
An example of a method for producing a transparent polyimide polymer film using varnish will be described. A varnish is cast on the base material to form a coating film, and the solvent is removed from the coating film by means such as reduced pressure, drying, and heating, and then peeled off from the base material. Thereby, a transparent polyimide polymer film is obtained.

Casting can be performed on a resin substrate, a stainless steel belt, or a glass substrate by a roll-to-roll or batch method. Examples of the resin base material include PET, PEN, polyimide, and polyamideimide. Of these resin substrates, PET is preferable from the viewpoints of adhesion to the film and cost.

In the method for producing a transparent polyimide polymer film of the present invention, a certain amount of an organic solvent is volatilized by passing the coating film through a dryer that contacts a heated gas with the surface of the coating film, May be peeled off from the support as a self-supporting film. The working temperature is adjusted depending on the substrate used, and when a resin substrate is used, it is generally carried out at or below the glass transition temperature thereof. Usually, the heating may be performed at an appropriate temperature of 50 to 300 ° C., and the heating temperature may be adjusted in multiple stages or a temperature gradient may be provided. It is also suitable to carry out under an inert atmosphere or under reduced pressure as appropriate.

If necessary, the peeled transparent polyimide polymer film may be further heated at 80 to 300 ° C.

<Optical film>
The optical film of the present invention is formed from the varnish. The transparent polyimide polymer film is used as an optical film, and is useful, for example, as a front plate of a display device, particularly as a front plate (window film) of a flexible display device. The flexible display device includes, for example, a flexible functional layer and an optical film that is stacked on the flexible functional layer and functions as a front plate. That is, the front plate of the flexible display device is disposed on the viewing side on the flexible functional layer. This front plate has a function of protecting the flexible functional layer.

Display devices include wearable devices such as televisions, smartphones, mobile phones, car navigation systems, tablet PCs, portable game machines, electronic paper, indicators, bulletin boards, watches, and smart watches. Examples of the flexible display device include all display devices having flexible characteristics, and among them, a foldable display device and a rollable display device that are preferably foldable.

<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 plate in a flexible display device, and the front plate may be referred to as a window film. The flexible display device includes a flexible display device laminate and an organic EL display panel. The flexible display device laminate is arranged on the viewing side with respect to 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 order of stacking thereof is arbitrary, but the window film, the polarizing plate, It is preferable that the touch sensor or window film, the touch sensor, and the polarizing plate are laminated in this order. The presence of a polarizing plate on the viewing side of the touch sensor is preferable because the touch sensor pattern is less visible and the visibility of the display image is improved. Each member can be laminated | stacked using an adhesive agent, an adhesive, etc. Moreover, the light-shielding pattern formed in at least one surface of the any one layer of the said window film, a polarizing plate, and a touch sensor can be comprised.

[Polarizer]
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 or left circularly polarized component by laminating a λ / 4 retardation plate on a linearly polarizing plate. For example, external light is converted into right circularly polarized light, the external light reflected by the organic EL panel and turned into left circularly polarized light is blocked, and only the light emitting component of the organic EL is transmitted to suppress the influence of the reflected light and image Used to make it easier to see. In order to achieve the circular polarization function, the absorption axis of the linearly polarizing plate and the slow axis of the λ / 4 retardation plate need to be 45 ° theoretically, but practically 45 ± 10 °. The linearly polarizing plate and the λ / 4 retardation plate are not necessarily laminated adjacent to each other as long as the relationship between the absorption axis and the slow axis satisfies the above range. Although it is preferable to achieve complete circular polarization at all wavelengths, the circular polarization plate in the present invention includes an elliptical polarization plate because it is not always necessary in practice. It is also preferable to further improve the visibility in a state where polarized sunglasses are applied by laminating a λ / 4 retardation film on the viewing side of the linearly polarizing plate and making the emitted light circularly polarized.

The linear polarizing plate is a functional layer having a function of blocking polarized light having a vibration component perpendicular to the light that is oscillating in the transmission axis direction. The linear polarizing plate may include a linear polarizer alone or a linear polarizer and a protective film attached to at least one surface thereof. The linear polarizing plate may have a thickness of 200 μm or less, preferably 0.5 to 100 μm. When the thickness is in the above range, flexibility tends to be difficult to decrease.
The linear polarizer may be a film-type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (PVA) film. A dichroic dye such as iodine is adsorbed on a PVA-based film oriented by stretching or is stretched in a state of being adsorbed to PVA, whereby the dichroic dye is oriented and exhibits polarizing performance. In the production of the film-type polarizer, other processes such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying may be included. The stretching or dyeing process may be performed by a PVA film alone or in a state where it is laminated with another film such as polyethylene terephthalate. The thickness of the PVA film used is preferably 10 to 100 μm, and the draw ratio is preferably 2 to 10 times.
Furthermore, as another example of the polarizer, a liquid crystal-coated 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 dye compound. The liquid crystalline compound only needs to have the property of exhibiting a liquid crystal state. In particular, the liquid crystalline compound preferably has a higher-order alignment state such as a smectic phase because it can exhibit high polarization performance. The liquid crystal compound preferably has a polymerizable functional group.

The dichroic dye is a dye that is aligned with the liquid crystal compound and exhibits dichroism, and the dichroic dye itself may have liquid crystallinity or have a polymerizable functional group. You can also. Any compound in the liquid crystal polarizing composition has a polymerizable functional group.
The liquid crystal polarizing composition 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 polarizing layer is manufactured by applying a liquid crystal polarizing composition on an alignment film to form a liquid crystal polarizing layer.
The liquid crystal polarizing layer can be formed thinner than a film-type polarizer. The thickness of the liquid crystal polarizing layer may be preferably 0.5 to 10 μm, more preferably 1 to 5 μm.
The alignment film can be produced, for example, by applying an alignment film forming composition on a substrate and imparting alignment 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 aligning agent. Examples of the aligning agent include polyvinyl alcohols, polyacrylates, polyamic acids, and polyimides. When applying photo-alignment, it is preferable to use an aligning agent containing a cinnamate group. The polymer used as the aligning agent may have a weight average molecular weight of about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000 nm, and more preferably 10 to 500 nm, from the viewpoint of alignment regulating force. The liquid crystal polarizing layer can be peeled off from the base material, transferred and laminated, or the base material can be laminated as it is. It is also preferable that the base material plays a role as a transparent base material for a protective film, a retardation plate, or a window.

The protective film may be a transparent polymer film, and materials and additives used for the transparent substrate can be used. A cellulose film, an olefin film, an acrylic film, and a polyester film are preferred. It may be a coating-type protective film obtained by applying and curing a cationic curing composition such as an epoxy resin or a radical curing composition such as an acrylate. If necessary, plasticizers, ultraviolet absorbers, infrared absorbers, colorants such as pigments and dyes, fluorescent brighteners, dispersants, thermal stabilizers, light stabilizers, antistatic agents, antioxidants, lubricants, solvents, etc. May be included. The protective film may have a thickness of 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 difficult to decrease. The protective film can also serve as a transparent substrate of the window.

The λ / 4 phase difference plate is a film that gives 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 manufactured by stretching a polymer film such as a cellulose film, an olefin film, or a polycarbonate film. If necessary, retardation adjusting agents, plasticizers, UV absorbers, infrared absorbers, colorants such as pigments and dyes, fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, antistatic agents, antioxidants Further, it may contain a lubricant, a solvent and the like. The stretchable retardation plate may have a thickness of 200 μm or less, preferably 1 to 100 μm. When the thickness is in the above range, the flexibility of the film tends not to decrease.
Furthermore, as another example of the λ / 4 retardation plate, a liquid crystal coating type retardation plate formed by applying a liquid crystal composition may be used. The liquid crystal composition includes a liquid crystal compound having a property of exhibiting a liquid crystal state such as nematic, cholesteric, and smectic. Any compound including a liquid crystal compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal-coated 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 coating type retardation plate can be produced by coating and curing a liquid crystal composition on an alignment film to form a liquid crystal retardation layer, as described for the liquid crystal polarizing layer. The liquid crystal coated retardation plate can be formed thinner than the stretched 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 coating type retardation plate can be peeled off from the substrate, transferred, and laminated, or the substrate can be laminated as it is. It is also preferable that the base material plays a role as a transparent base material for a protective film, a retardation plate, or a window.

In general, there are many materials that exhibit higher birefringence as the wavelength is shorter and smaller birefringence as the wavelength is longer. In this case, since a phase difference of λ / 4 cannot be achieved in the entire visible light region, an in-plane phase difference of 100 to 180 nm, preferably 130, becomes λ / 4 with respect to the vicinity of 560 nm having high visibility. It is often designed to be ˜150 nm. It is preferable to use a reverse dispersion λ / 4 phase difference plate using a material having birefringence wavelength dispersion characteristics opposite to that of normal, since the visibility can be improved. As such materials, those described in Japanese Patent Application Laid-Open No. 2007-232873 and the like in the case of a stretching type phase difference plate, and those described in Japanese Patent Application Laid-Open No. 2010-30979 in the case of a liquid crystal coating type phase difference plate may be used. preferable.
As another method, a technique for obtaining a broadband λ / 4 phase difference plate by combining with a λ / 2 phase difference plate is also known (Japanese Patent Laid-Open No. 10-90521). The λ / 2 retardation plate is also manufactured by the same material method as the λ / 4 retardation plate. Although the combination of the stretchable retardation plate and the liquid crystal coating type retardation plate is arbitrary, it is preferable to use the liquid crystal coating type retardation plate for both because the thickness can be reduced.
In order to improve the visibility in the oblique direction on the circularly polarizing plate, a method of laminating a positive C plate is also known (Japanese Patent Laid-Open No. 2014-224837). The positive C plate may also be a liquid crystal coated retardation plate or a stretched retardation plate. The retardation in the thickness direction is usually −200 to −20 nm, preferably −140 to −40 nm.

[Touch sensor]
The flexible display device of the present invention may further include a touch sensor. The touch sensor is used as input means. Various types of touch sensors such as a resistive film method, a surface acoustic wave method, an infrared method, an electromagnetic induction method, and a capacitance method have been proposed, and any method may be used. Of these, the electrostatic capacity method is preferable. The capacitive touch sensor is divided into an active region and a non-active region located in an outer portion of the active region. The active area is an area corresponding to an area (display unit) where the screen is displayed on the display panel, and is an area where a user's touch is sensed. This is a region corresponding to the display unit. The touch sensor includes a flexible substrate; a sensing pattern formed in an active region of the substrate; and formed in an inactive region of the substrate and connected to an external driving circuit through the sensing pattern and a pad portion. Each sensing line can be included. As the substrate having flexible characteristics, 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 from the viewpoint of suppressing cracks in the touch sensor. More preferably, the toughness may be 2,000 to 30,000 MPa%. Here, the toughness is defined as the area under the curve up to the fracture point in a stress-strain curve obtained through a tensile test of the polymer material.

The sensing pattern may include a first pattern formed in the first direction and a second pattern formed in the second direction. The first pattern and the second pattern are arranged in different directions. The first pattern and the second pattern are formed in the same layer, and each pattern must be electrically connected in order to sense a touched point. The first pattern is a form in which each unit pattern is connected to each other through a joint, but the second pattern has a structure in which each unit pattern is separated from each other in an island form. A separate bridge electrode is required for connection. A known transparent electrode material can be applied to the sensing pattern. For example, 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-ethylenedithiothiophene)), carbon nanotube (CNT), graphene, metal wire, and the like. These can be used alone or in combination of two or more. Preferably ITO can be used. The metal used for the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, telenium, and chromium. These can be used alone or in admixture of two or more.

The bridge electrode can be formed on the sensing pattern via the insulating layer and on the insulating layer. The bridge electrode is formed on the substrate, and the insulating layer and the sensing pattern can be formed thereon. The bridge electrode may be formed of the same material as the sensing pattern, and is 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. You can also Since the first pattern and the second 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 joint of the first pattern and the bridge electrode, or may be formed in a layer structure covering the sensing pattern. In the latter case, the bridge electrode can be connected to the second pattern via a contact hole formed in the insulating layer. The touch sensor has a transmittance difference between a pattern area where a pattern is formed and a non-pattern area where a pattern is not formed, specifically, a light transmittance induced by a difference in refractive index in these areas. As a means for appropriately compensating for the difference, an optical adjustment layer may be further included between the substrate and the electrode, and the optical adjustment layer may include an inorganic insulating material or an organic insulating material. The optical adjustment layer can be formed by coating a photocurable composition containing a photocurable organic binder and a solvent on a substrate. The photocurable composition may further include inorganic particles. The inorganic particles can increase the refractive index of the optical adjustment layer.
The photocurable organic binder can include, for example, 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 including different repeating units such as an epoxy group-containing repeating unit, an acrylate repeating unit, and a carboxylic acid repeating unit.
Examples of the inorganic particles include zirconia particles, titania particles, and alumina particles. The photocurable composition may further contain additives such as a photopolymerization initiator, a polymerizable monomer, and a curing auxiliary agent.

[Adhesive layer]
Each layer (window, polarizing plate, touch sensor) forming the laminate for a flexible display device and a film member (linear polarizing plate, λ / 4 retardation plate, etc.) constituting each layer can be bonded with an adhesive. Adhesives include water-based adhesives, organic solvent-based adhesives, solvent-free adhesives, solid adhesives, solvent evaporation adhesives, moisture-curing adhesives, heat-curing adhesives, anaerobic-curing adhesives, active Commonly used materials such as energy ray curable adhesives, curing agent mixed adhesives, hot melt adhesives, pressure sensitive adhesives (adhesives), and rewet adhesives can be used. Of these, water-based solvent volatile adhesives, active energy ray-curable adhesives, and pressure-sensitive adhesives are often used. The thickness of the adhesive layer can be appropriately adjusted according to the required adhesive force and the like, and is, for example, 0.01 to 500 μm, preferably 0.1 to 300 μm. There may be a plurality of adhesive layers in the laminate for a flexible display device, but the thickness and the type of adhesive used may be the same or different.

As the water-based solvent-evaporating adhesive, water-soluble polymers such as polyvinyl alcohol polymers and starches, water-dispersed polymers such as ethylene-vinyl acetate emulsions and styrene-butadiene emulsions can be used as the main polymer. In addition to water and the main 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 blended. In the case of bonding with the water-based solvent volatile adhesive, the water-based solvent volatile adhesive can be injected between the layers to be bonded, and the adhesion layer can be bonded, and then dried to provide adhesion. The thickness of the adhesive layer in the case of using the water-based solvent volatile adhesive is usually 0.01 to 10 μm, preferably 0.1 to 1 μm. When the water-based 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 that irradiates active energy rays to form an adhesive layer. The active energy ray-curable composition can contain at least one polymer of a radical polymerizable compound and a cationic polymerizable compound similar to the hard coat composition. The radical polymerizable compound is the same as the hard coat composition, and the same kind as the hard coat composition can be used. As the radical polymerizable compound used for the adhesive layer, a compound having an acryloyl group is preferable. It is also preferable to contain a monofunctional compound in order to lower the viscosity of the adhesive composition.

The cationic polymerizable compound is the same as that of the hard coat composition, and the same kind as that of the hard coat composition can be used. As the cationic polymerizable compound used in the active energy ray-curable composition, an epoxy compound is particularly preferable. It is also preferable to include a monofunctional compound as a reactive diluent in order to lower the viscosity of the adhesive composition.
The active energy ray composition may further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, radicals and cationic polymerization initiators, which can be appropriately selected and used. These polymerization initiators are decomposed by at least one of active energy ray irradiation and heating to generate radicals or cations to advance radical polymerization and cationic polymerization. In the description of the hard coat composition, an initiator capable of initiating at least one of radical polymerization or cationic polymerization by irradiation with active energy rays can be used.

The active energy ray curable composition further includes an ion scavenger, an antioxidant, a chain transfer agent, an adhesion promoter, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, an antifoaming solvent, an additive, a solvent. Can be included. When adhering with the active energy ray curable adhesive, the active energy ray curable composition is applied to either or both of the adherend layers and then bonded, and the active energy ray curable composition is activated through either of the adhering layers or both of the adhering layers. It can be bonded by irradiating with energy rays and curing. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is usually 0.01 to 20 μm, 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 adhesive used may be the same or different.

The pressure-sensitive adhesives are classified into acrylic pressure-sensitive adhesives, urethane pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives and the like according to the main polymer, and any of them can be used. In addition to the main polymer, the adhesive may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a tackifier, a plasticizer, a dye, a pigment, an inorganic filler, and the like. Each component constituting the pressure-sensitive adhesive is dissolved and dispersed in a solvent to obtain a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition is applied onto a substrate and then dried to form a pressure-sensitive adhesive layer (adhesive layer). Is done. The pressure-sensitive adhesive layer may be directly formed, or a layer separately formed on the substrate can be transferred. In order to cover the adhesive surface before bonding, it is also preferred to use a release film. When the pressure-sensitive adhesive is used, the thickness of the adhesive layer may be usually 1 to 500 μm, preferably 2 to 300 μm. When the pressure-sensitive adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the pressure-sensitive adhesive used may be the same or different.

[Shading pattern]
The light shielding pattern can be applied as at least part of a bezel or a housing of the flexible display device. The visibility of the image is improved by concealing the wiring arranged at the edge of the flexible display device by the light-shielding pattern and making it difficult to see. The light shielding pattern may be a single layer or a multilayer. The color of the light-shielding pattern is not particularly limited, and can have various colors such as black, white, and metal color. The light shielding pattern can be formed of a pigment for embodying a color and a polymer such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or silicone. These can be used alone or in a mixture of two or more. The light shielding pattern can be formed by various methods such as printing, lithography, and inkjet. The thickness of the light shielding pattern is usually 1 to 100 μm, preferably 2 to 50 μm. It is also preferable to give a shape such as an inclination in the thickness direction of the light shielding pattern.

Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified, “%” and “parts” in the examples mean mass% and parts by mass. First, the evaluation method will be described.

<1. Manufacture of polyimide varnish and film formation of polyimide film>
Example 1
(1) Preparation of polyimide solution In a nitrogen atmosphere, 0.5 part by mass of isoquinoline as a catalyst (tertiary amine) was charged into a reaction vessel. The reaction vessel was connected to a vacuum pump equipped with a solvent trap and a filter, and was installed in an oil bath. Next, 305.58 parts by mass of γ-butyrolactone (GBL) as solvent A and 2,2′-bis (trifluoromethyl) -4,4′-diaminodiphenyl (TFMB) 104.43 as diamine in the reaction vessel. The contents in the reaction vessel into which the mass part was further added were stirred and completely dissolved. Furthermore, after putting 145.59 parts by mass of 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) as tetracarboxylic dianhydride into the reaction vessel, the contents in the reaction vessel were stirred. Meanwhile, the temperature started to rise in the oil bath. The molar ratio of TFMB to 6FDA (6FDA: TFMB) was 1.00: 0.995, and the concentration of the raw material monomer was 45% by mass. The amount of the tertiary amine relative to 100 parts by mass of the raw material monomer was 0.2 parts by mass. When the internal temperature in the reaction vessel reached 120 ° C, the pressure in the reaction vessel was reduced to 400 mmHg, and then the internal temperature was raised to 180 ° C. After the internal temperature reached 180 ° C., the mixture was further heated and stirred for 5.5 hours and then returned to atmospheric pressure and cooled to 170 ° C. to obtain a polyimide solution. When the oxygen concentration in the reaction vessel was confirmed before and after decompression, it was less than 0.01%. GBL was added at 170 degreeC, and the polyimide solution was obtained as a uniform solution whose solid content of a polyimide is 40 mass%. Note that the integrated value and peroxide value of the peak derived from the peroxide of GBL were very small and negligible with respect to the integrated value and peroxide value of the diluent solvent described later, respectively. For this reason, it was judged that the diluting solvent was dominant in the integral value and the peroxide value in all the solvents in the varnish, and the examples and comparative examples were compared and examined based on the integral value and the peroxide value of the diluting solvent.

(2) Manufacture of varnish N, N-dimethylacetamide (DMAc) as a diluting solvent (solvent B) was bubbled with nitrogen gas for 30 minutes. The integrated value of the peak derived from the peroxide in DMAc after the bubbling treatment was 310,000. In addition, the peroxide value of DMAc after bubbling treatment measured according to the JPO-5S-46-96 peroxide value test method of the Japan Petroleum Institute standard kerosene was less than 1 mg / kg. To the polyimide solution obtained in (1) above, DMAc subjected to bubbling treatment was added at 155 ° C. to obtain a uniform solution having a polyimide solid content of 20% by mass, and taken out from the reaction vessel to obtain a varnish. The mass ratio of the solvent in the obtained varnish (DMAc: GBL) was approximately 5: 3. The converted peroxide value of the obtained varnish was less than 1 mg / kg.
Similarly, the solvent mass ratio (solvents other than GBL: GBL) in the varnishes prepared in Example 2 and Comparative Examples 1 to 3 was also approximately 5: 3.

(3) Film formation of polyimide film DMAc prepared in (2) is added to 200.00 parts by mass of varnish prepared in (2) above to prepare a 15% by mass solution on a PET (polyethylene terephthalate) film. Then, the coating film was formed on PET by heating at 50 ° C. for 30 minutes and then at 140 ° C. for 10 minutes. The obtained coating film was peeled from PET and further heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 80 μm.

(Example 2)
(1) Preparation of varnish Manufacture of the varnish of Example 1 except that the dilution solvent subjected to the bubbling treatment was changed from DMAc to butyl acetate and the temperature of the dilution solvent subjected to the bubbling treatment was changed from 155 ° C to 130 ° C. A varnish was obtained in the same manner as described above. The butyl acetate subjected to the 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 90,000. The peroxide value of butyl acetate subjected to the bubbling treatment measured according to the JPI-5S-46-96 peroxide value test method of the Japan Petroleum Institute standard kerosene was less than 1 mg / kg.

(2) Film formation of polyimide film Except for changing from the varnish prepared in Example 1 (2) to the varnish prepared in Example 2 (1), the production method of Example 1 was used, and the thickness was 80 μm. A polyimide film was obtained. The converted peroxide value of the prepared varnish was less than 1 mg / kg.

(Comparative Example 1)
(1) Preparation of varnish The diluted solvent subjected to the bubbling treatment was changed from DMAc to cyclopentanone (hereinafter sometimes referred to as “CP”), and the temperature of the diluted solvent subjected to the bubbling treatment was changed from 155 ° C. to 130 ° C. A varnish was obtained in the same manner as in the method for producing a varnish of Example 1, except that the change was made. The cyclopentanone subjected to the bubbling treatment was obtained by bubbling cyclopentanone with nitrogen gas for 30 minutes. The integrated value of the peak derived from the peroxide in the cyclopentanone subjected to the bubbling treatment was 740,000. The peroxide value of cyclopentanone subjected to bubbling treatment measured according to the JPI-5S-46-96 peroxide value test method of the Japan Petroleum Institute standard kerosene was 21 mg / kg.

(2) Film formation of polyimide film Except for changing from the varnish prepared in Example 1 (2) to the varnish prepared in Comparative Example 1 (1), the manufacturing method of Example 1 was used, and the thickness was 80 μm. A polyimide film was obtained. The converted peroxide value of the prepared varnish was 11 mg / kg.

(Comparative Example 2)
(1) Preparation of varnish A varnish was obtained in the same manner as in the production method of Comparative Example 1, except that the diluting solvent was changed from cyclopentanone subjected to bubbling treatment to cyclopentanone not subjected to bubbling treatment. The integrated value of the peak derived from the peroxide of cyclopentanone was 11.37 million. Further, the peroxide value of cyclopentanone not subjected to the bubbling treatment, which was measured according to the JPE-5S-46-96 peroxide value test method of the Japan Petroleum Institute standard kerosene, was 57 mg / kg.

(2) Formation of polyimide film 80 μm in thickness 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). A polyimide film was obtained. Moreover, the converted peroxide value of the prepared varnish was 29 mg / kg.

(Comparative Example 3)
(1) Preparation of varnish Examples except that the diluted solvent subjected to the bubbling treatment was changed from DMAc to methyl isobutyl ketone (MIBK), and the temperature of the diluted solvent subjected to the bubbling treatment was changed from 155 ° C to 130 ° C. A varnish was obtained in the same manner as in No. 1 varnish production method. MIBK subjected to bubbling treatment was obtained by bubbling MIBK with nitrogen gas for 30 minutes. The integral value of the peak derived from the peroxide in the MIBK subjected to the bubbling treatment was 45.2 million. In addition, the peroxide value of MIBK subjected to bubbling treatment measured according to the method for testing the peroxide value of the Japan Petroleum Institute standard kerosene JPI-5S-46-96 was 102 mg / kg.

(2) Film formation of polyimide film Except for changing from the varnish prepared in Example 1 (2) to the varnish prepared in Comparative Example 3 (1), the manufacturing method of Example 1 was used, and the thickness was 80 μm. A polyimide film was obtained. Moreover, the converted peroxide value of the prepared varnish was 51 mg / kg.

<2. Manufacture of polyamideimide varnish and film formation of polyamideimide film>
Example 3
(1) Synthesis of Polyamideimide A Nitrogen was passed through a reaction vessel equipped with a sufficiently dried stirrer and thermometer, and the inside of the vessel was replaced with nitrogen. To the reaction vessel, 250.00 parts by mass of 2,2′-bis (trifluoromethyl) -4,4′-diaminodiphenyl (TFMB) and 8,520 parts by mass of DMAc were added, and TFMB was added to DMAc while stirring at room temperature. Dissolved in. Next, 104.57 parts by mass of 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) was added to the flask for reaction.
Subsequently, 23.16 parts by mass of 4,4′-oxybis (benzoyl chloride) (OBBC) and 95.62 parts by mass of terephthaloyl chloride (TPC) were added and reacted.
Next, 168.23 parts by mass of acetic anhydride was added and stirred for 15 minutes, then 51.14 parts by mass of 4-picoline was added, the reaction vessel was heated to 70 ° C., and further stirred for 3 hours to obtain a reaction solution. .
The obtained reaction liquid was cooled, 12,781 parts by mass of methanol was added, and then 6,390 parts by mass of ion-exchanged water was added dropwise to precipitate 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 at 80 ° C. under reduced pressure to obtain polyamideimide A.

(2) Preparation of varnish Polyamideimide varnish B having a concentration of 8.7% by mass was prepared by adding the polyamideimide A to a solvent in which GBL and DMAc were mixed at 9: 1 (mass ratio).
The peroxide value of polyamideimide varnish B measured in accordance with JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, was 2.0 mg / kg.
As the GBL and DMAc, a solvent that has passed for one week or more after opening was used.
The integrated value of the peak derived from the peroxide in DMAc was 460,000.
Further, the peroxide value in GBL measured based on JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, was less than 1 mg / kg, and the peroxide value in DMAc was 13 mg / kg.

(3) Polyamideimide film formation As in Example 3, the obtained polyamideimide varnish B was formed on a smooth surface of a polyester substrate (trade name “A4100”, manufactured by Toyobo Co., Ltd.), and the thickness of the self-supporting film. Was applied using an applicator so as to be 55 μm, dried at 50 ° C. for 30 minutes and then at 140 ° C. for 15 minutes, and then 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 ° C. in the air to obtain a polyamideimide film (base material) having a thickness of 50 μm.

Example 4
(1) Preparation of varnish Polyamideimide A obtained in Example 3 was added to a solvent in which GBL and butyl acetate were mixed at 9: 1 (mass ratio), and polyamideimide varnish C having a concentration of 8.9 mass% was added. Prepared.
The peroxide value of polyamideimide varnish C measured in accordance with JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, was less than 1 mg / kg.
As the GBL and butyl acetate, a solvent having passed for 1 week or more after opening was used.
The integrated value of the peak derived from the peroxide in butyl acetate was 35,000.
In addition, the peroxide value in GBL measured based on JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, was less than 1 mg / kg, and the peroxide value in butyl acetate was less than 1 mg / kg. It was.

(2) Polyamideimide film formation Except for using polyamideimide varnish C, a film having a thickness of 50 μm was obtained in the same manner as in the film production method of Example 3.

(Comparative Example 4)
(1) Preparation of varnish Polyamideimide A obtained in Example 3 in the previous period was added to a solvent in which GBL and cyclopentanone were mixed at a ratio of 9: 1 (mass ratio), and a polyamideimide having a concentration of 9.0 mass%. Varnish D was prepared.
The peroxide value of polyamideimide varnish D measured in accordance with the JPE-5S-46-96 peroxide value test method of Japan Petroleum Institute standard kerosene was 2.6 mg / kg.
For GBL and cyclopentanone, a solvent that has passed for 1 week or more after opening was used.
The integrated value of the fluorescence spectrum derived from peroxide in cyclopentanone was 11.73 million.
In addition, the peroxide value in GBL measured based on the peroxide value test method JPI-5S-46-96 of the Japan Petroleum Institute standard kerosene was less than 1 mg / kg, and the peroxide value in butyl acetate was 57 mg / kg. .

(2) Film formation of polyamideimide film Except for using polyamideimide varnish D, a film having a thickness of 50 µm was obtained in the same manner as the film manufacturing method of Example 3.

<3. Measurement method and calculation method>
(1) Method for calculating integral value of peroxide-derived peak (1-1) Measurement of chemiluminescence detection liquid chromatograph The peak derived from peroxide contained in a solvent is determined using a chemiluminescence detection liquid chromatograph method. It was measured.
(Measurement condition)
Column: Chemical Substance Evaluation Research Organization L-column2 ODS (5 μm, 4.6 mmφ × 250 mm)
Guard column: Sumipax (registered trademark) Filter PG-ODS (for analysis) manufactured by Sumika Chemical Analysis Co., Ltd.
Column temperature: 40 ° C
Mobile phase A: Water mobile phase B: Transfer of acetonitrile mobile phase: The concentration ratio was controlled by changing the mixing ratio of mobile phase A and mobile phase B as follows.
Time after injection (minutes); 0-90 90-100
Mobile phase A (vol%); 90 → 0 0
Mobile phase B (vol%); 10 → 100 100
Flow rate: 1.0 mL / min Injection volume: 5 μL
Detector: Chemiluminescence detector ("CL2027 type" manufactured by JASCO Corporation)
Flow cell temperature: 55 ° C
Response speed (RESPONSE): Standard (STD)
Gain (GAIN): 100
Attenuation (ATTEN): 1
Post addition solution: Luminol solution Post addition flow rate: 0.1 mL / min

(1-2) Calculation method of integral value The peaks of the chemiluminescence chromatogram were integrated, and when there were a plurality of peaks, the total value was obtained as the integrated value.

(2) Method for measuring peroxide value (when measuring object is solvent)
The measurement of the peroxide value of the solvent was carried out based on the method for testing the peroxide value of the Japan Petroleum Institute Standard Kerosene, JPI-5S-46-49. In this test, peroxide (represented as ROOH in the following reaction formula) was mixed with potassium iodide solution to reduce the peroxide, then titrated the released iodine with sodium thiosulfate standard solution, and the peroxide value was determined. Can be calculated as mg / kg (ppm). The reaction is according to the following formula:
_{2KI + ROOH + H 2 O →} I 2 + 2KOH + ROH
_{_{_{_{I 2 + 2Na 2 S 2 O}}}} 3 → Na 2 S 4 O 6 + 2NaI

(2-1) Measurement method (preliminary experiment)
In the measurement of the peroxide value, as shown in Table 1, there is an appropriate sample mass depending on the obtained peroxide value.

First, preliminary experiments were performed to determine the appropriate sample mass. The 200 mL Erlenmeyer flask was purged with nitrogen gas for about 3 minutes and replaced. 1 g of a sample (solvent) was placed in an Erlenmeyer flask and precisely weighed with a balance. 25 mL of toluene was added, and nitrogen gas was vigorously bubbled into the liquid for about 1 minute. 20 mL of acetic acid solution (4 mL of JIS K 8180 [hydrochloric acid (reagent)] mixed with 996 mL of JIS K 8355 [acetic acid (reagent)]) was added while the nitrogen gas was being passed.
The outflow rate of the gas was adjusted so as to be gradually 1 bubble / 1 second, and 2 mL of an aqueous potassium iodide solution (1.2 g / mL) was added. The Erlenmeyer flask was shaken vigorously for 30 seconds. After leaving the Erlenmeyer flask for 5 minutes, 100 mL of water was added. Potentiometric titration was performed with 0.005 mol / L sodium thiosulfate standard solution, and the amount of sodium thiosulfate standard solution required for titration of the sample was determined. Prior to this measurement, the amount of sodium thiosulfate standard solution required for the blank test was determined by performing the blank test in the same procedure as above except that the sample 1 g was changed to 0 g, that is, the sample was not used. (Blank amount) was determined.

From the amount of the obtained two sodium thiosulfate standard solutions, the peroxide value was calculated by the following formula.
PON = [(A−B) M × 1000 × 8] / m
PON: Peroxide value (mg / kg)
A: Amount of sodium thiosulfate standard solution required for titration of sample (mL)
B: Amount of sodium thiosulfate standard solution required for the blank test (mL)
M: molar concentration of sodium thiosulfate standard solution (mol / L)
m: Amount of sample taken (g)

(main exam)
This test was carried out in the same procedure with the mass of the sample shown in Table 1 corresponding to the peroxide value obtained. In this way a peroxide value was obtained.

(3) Peroxide value measurement method (when the measurement target is varnish)
The measurement of the peroxide value of the varnish was carried out according to the peroxide value test method JPI-5S-46-49 of the Japan Petroleum Institute standard kerosene.
The 200 mL Erlenmeyer flask was purged with nitrogen gas for about 3 minutes and replaced. 1 g of a sample (varnish) was placed in an Erlenmeyer flask and precisely weighed with a balance. 25 mL of DMAc (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., ultra-dehydrated grade, unopened product) was added and dissolved, 25 mL of toluene was further added dropwise, and nitrogen gas was vigorously bubbled into the solution for about 1 minute. 20 mL of acetic acid solution (4 mL of JIS K 8180 [hydrochloric acid (reagent)] mixed with 996 mL of JIS K 8355 [acetic acid (reagent)]) was added while the nitrogen gas was being passed.
The outflow rate of the gas was adjusted so as to be gradually 1 bubble / 1 second, and 2 mL of an aqueous potassium iodide solution (1.2 g / mL) was added. The Erlenmeyer flask was shaken vigorously for 30 seconds. After leaving the Erlenmeyer flask for 5 minutes, 100 mL of water was added. Potentiometric titration was performed with 0.005 mol / L sodium thiosulfate standard solution, and the amount of sodium thiosulfate standard solution required for titration of the sample was determined. Prior to this measurement, the amount of sodium thiosulfate standard solution required for the blank test was determined by performing the blank test in the same procedure as above except that the sample 1 g was changed to 0 g, that is, the sample was not used. (Blank amount) was determined.
From the amount of the obtained two sodium thiosulfate standard solutions, the peroxide value was calculated using the formula described in (2) Method for measuring peroxide value (when the measurement target is a solvent).
The peroxide value of DMAc used (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., ultra-dehydrated grade, unopened product) was 0.0 mg / kg.
(2) Except that the measurement object was changed from the solvent to the varnish, the mass of the measurement sample was changed from 1 mass to 1 g without carrying out the preliminary test, and the measurement was further performed by dissolving in 25 mL of DMAc. The peroxide value of the varnish was measured in the same manner as in the method for measuring the peroxide value (when the measurement target is a solvent).
The latter change, that is, the change in which the mass of the measurement sample is made smaller than usual and diluted with DMAc is to suppress the following problems. When the mass of the measurement sample is large, a precipitate is formed and adheres to the electrode of the measurement instrument, and as a result, the potential may become unstable.
(Converted peroxide value)
The converted peroxide value of the varnish was calculated by a weighted average using the value of the peroxide value of the solvent used for producing the varnish and the mass ratio of the solvent in the varnish.

(3) Measurement of imidization rate The imidization rate of the polyimide resin and the polyamideimide resin used in Examples and Comparative Examples was measured by NMR and calculated using a signal derived from the partial structure represented by Formula (10). . The method for calculating the imidization rate from the measurement conditions and the obtained results is as follows.

(Measurement sample preparation method)
Resins obtained by adding a large excess of methanol as a poor solvent to the varnishes obtained in Examples 1 and 2 and Comparative Examples 1 to 3 and precipitating and drying by reprecipitation were obtained as deuterated dimethyl sulfoxide (DMSO). What was dissolved in -d ₆ ) to give a 2% by mass solution was used as a measurement sample.
A measurement sample was prepared by dissolving the polyamideimide resin (polyamideimide A) obtained in Example 3 in deuterated dimethyl sulfoxide (DMSO-d ₆ ) to give a 2 mass% solution.

(NMR measurement conditions)
Measuring apparatus: 600 MHz NMR apparatus (“AVANCE600” manufactured by Bruker)
Sample temperature: 303K
Measurement method: ¹ H-NMR, HSQC

(Calculation method of imidization ratio of polyimide resin)
In the ¹ H-NMR spectrum obtained using the solution containing the polyimide resin as the measurement sample, the integral value of the signal derived from the proton (A) in the formula (10) is represented by Int _A and the integral of the signal derived from the proton (B). The value was Int _B. From these values, the imidization ratio (%) was determined by the following formula (NMR-1). In addition, when signals derived from protons (A) and protons (B) overlap with signals derived from different structures, the intensities of the non-overlapping portions in the signals are integrated, and the original area ratio of the portions is calculated from the area ratio of the portions. The signal intensity was determined and the imidization rate was calculated.

(Calculation method of imidization ratio of polyamide-imide resin)
In the ¹ H-NMR spectrum obtained from the measurement sample containing the polyamide-imide resin, the structure derived from the structure of the observed benzene protons that does not change before and after imidation and derived from the amic acid structure remaining in the polyamide-imide resin The integral value of benzene proton C that is not affected by Int _C was defined as Int _C. Further, the integrated value of benzene protons D, which is derived from a structure that does not change before and after imidization among the observed benzene protons and is influenced by the structure derived from the amic acid structure remaining in the polyamideimide resin, was defined as Int _D. The β value was determined from the obtained Int _C and Int _D by the following formula.
β = Int _D / Int _C
Next, the β value of the above formula and the imidization ratio of the polyimide resin of the above formula were determined for a plurality of polyamideimide resins, and the following correlation formula was obtained from these results.
Imidization rate (%) = k × β + 100
In the above correlation equation, k is a constant.
β was substituted into the correlation equation to obtain the imidization ratio (%) of the polyamideimide resin.

(4) Thickness Measurement The thickness of the transparent polyimide polymer film was measured using a Digimatic Thickness Gauge (product number 547-401 manufactured by Mitutoyo Corporation).

(5) Measurement of total light transmittance (Tt) and Haze The total light transmittance Tt of the transparent polyimide-based polymer films obtained in Examples and Comparative Examples was measured according to JIS K 7105: 1981 as a haze meter (suga It was measured by “Fully Automatic Direct Reading Haze Computer HGM-2DP” manufactured by Tester Co., Ltd.).

(6) Measurement of polystyrene-equivalent weight average molecular weight Gel permeation chromatography (GPC) measurement (6-1) Pretreatment method A sample was dissolved in γ-butyrolactone (GBL) to make a 20% solution, and then 100% with a DMF eluent. Diluted twice and filtered through a 0.45 μm membrane filter was used as a measurement solution.
(6-2) Measurement condition column: TSKgel SuperAWM-H × 2 + SuperAW2500 × 1 (6.0 mm ID × 150 mm × 3)
Eluent: DMF solution containing 10 mmol / L lithium bromide Flow rate: 0.6 mL / min Detector: RI detector Column temperature: 40 ° C.
Injection volume: 20 μL
Molecular weight standard: Standard polystyrene

<4. Evaluation method>
(1) measured with the b ^* of the resulting varnish by b ^* measurement methods Examples and Comparative Examples of the varnish, ultraviolet-visible-near infrared spectrophotometer (manufactured by JASCO Corporation "V-670") did. The varnish was packed in a quartz cell having an optical path length of 1 cm, and this quartz cell was set to ultraviolet visible near infrared spectrophotometry. The transmittance was measured by irradiating white light with a wavelength of 300 to 800 nm to obtain a b ^* value. The resulting ^{b *} was the initial ^{b *} (before storage ^{b *).}

(2) Varnish Storage Test: Calculation of Δb ^* The varnishes obtained in Examples 1-2 and Comparative Examples 1-3 were stored at 60 ° C. for 2 weeks. The varnishes obtained in Examples 3 to 4 and Comparative Example 3 were stored at 50 ° C. for 1 week. The b ^* of the stored varnish was measured to obtain b ^* after storage. From the initial ^{b *} and after storage ^{b *,} to obtain a difference ([Delta] b ^*).

(3) Calculation of yellowness (YI value) of film The yellowness (Yellow Index: YI value) of each of the transparent polyimide polymer films obtained in Examples and Comparative Examples was measured with an ultraviolet-visible near-infrared spectrophotometer. (“V-670” manufactured by JASCO Corporation). After performing background measurement in the absence of a sample, a polyimide film was set on a sample holder, transmittance was measured for light having a wavelength of 300 to 800 nm, and tristimulus values (X, Y, Z) were obtained. . The YI value was calculated from the tristimulus values based on the following formula. The obtained YI value was used as the initial YI value (YI value before storage).
YI = 100 × (1.2769X−1.0592Z) / Y

(4) Varnish Storage Test: Calculation of ΔYI Value The varnishes obtained in Examples 1-2 and Comparative Examples 1-3 were stored at 60 ° C. for 2 weeks. The varnishes obtained in Examples 3 to 4 and Comparative Example 4 were stored at 50 ° C. for 1 week. The YI value of the film obtained by forming the varnish after storage was measured by the same method as the initial YI value, and was defined as the YI value after storage. A difference (ΔYI) was obtained from the initial YI value and the YI value after storage.

(5) Defoaming property The varnishes obtained in the examples and comparative examples were vigorously stirred and filled with bubbles throughout, and then filled into clean glass bottles having a diameter of 7 cm and a depth of 15 cm, respectively, at room temperature. It was left in an environment (25 ° C.) for 8 hours. Thereafter, the presence or absence of bubbles on the varnish surface was visually confirmed. From the result of visual observation, the defoaming property of the varnish was evaluated based on the following criteria.
(Evaluation criteria)
A (good): No foam layer of 3 cm or more remained on the varnish surface.
B (Poor): A foam layer of 3 cm or more remains on the varnish surface.

The varnishes of Examples 1 and 2 contained a transparent polyimide polymer and a solvent. The total light transmittance of the polyimide films prepared from the varnishes of Examples 1 and 2 was 90% or more.
The integral values of the peaks derived from the peroxides of the solvents used in the preparation of the varnishes of Examples 1 and 2 were all 700,000 or less. The peroxide values of the solvents were all 20 mg / kg or less.
The Δb ^* values of the varnishes of Examples 1 and 2 were all 0.0.

The integral value of the peak derived from the peroxide of the solvent used in the preparation of the varnishes of Comparative Examples 1 to 3 exceeded 700,000. In addition, the peroxide values of the solvents all exceeded 20 mg / kg.
The Δb ^* values of the varnishes of Comparative Examples 1 to 3 were 19.0, 22.1, and 10.8, respectively.

From the above, it is clear that the varnishes of Examples 1 and 2 have small Δb ^{* and} high transparency over a long period of time compared to the varnishes of Comparative Examples 1 to 3.

The varnishes of Examples 3 to 4 contained a transparent polyimide polymer and a solvent. The total light transmittance of the polyamideimide films prepared from the varnishes of Examples 3 to 4 was 80% or more.
The integral values of the peaks derived from the peroxides of the solvents used in the preparation of the varnishes of Examples 3 to 4 were all 700,000 or less, and the peroxide values of the solvents were all 20 mg / kg or less. . The peroxide values of the varnishes of Examples 3 to 4 were all 2.5 mg / kg or less.
The Δb ^* values of the varnishes of Examples 3 to 4 were all 1.5 or less.

The integral value of the peak derived from the peroxide of the solvent used for the preparation of the varnish of Comparative Example 4 exceeded 700,000, and the peroxide value of the solvent exceeded 20 mg / kg. Moreover, the peroxide value of the varnish of the comparative example 4 exceeded 2.5 mg / kg.
The Δb ^* of the varnish of Comparative Example 4 was 23.4.

From the above, it is clear that the varnishes of Examples 3 to 4 have a smaller Δb ^{* and} higher transparency over a long period of time than the varnish of Comparative Example 4.

Claims

A varnish containing a transparent polyimide polymer and a solvent,
The integral value of the peak derived from the peroxide detected by the chemiluminescence detection liquid chromatography method is 700,000 or less,
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured according to Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it, varnish.
When a film containing a transparent polyimide polymer having a thickness of 80 μm is prepared from a varnish, the total light transmittance of the film measured in accordance with Japanese Industrial Standard (JIS) K 7105: 1981 is 80% or more. The varnish according to claim 1.
A varnish containing a transparent polyimide polymer and a solvent,
The peroxide value of the varnish detected by a method in accordance with JPI-5S-46-96 is a peroxide value of 2.5 mg / kg or less.
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured according to Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it, varnish.
A varnish containing a transparent polyimide polymer and a solvent,
The peroxide value of the solvent detected by the method based on JPI-5S-46-96, a peroxide value test method of the Japan Petroleum Institute standard kerosene, is 20 mg / kg or less,
When a film containing the transparent polyimide polymer having a thickness of 50 to 80 μm was produced from the varnish, the total light transmittance of the film measured according to Japanese Industrial Standard (JIS) K 7105: 1981 was 80%. That's it, varnish.
The varnish according to any one of claims 1 to 4, wherein the total light transmittance is 90% or more when a film containing a transparent polyimide polymer having a thickness of 80 µm is produced from the varnish.
The varnish according to any one of claims 1 to 5, wherein the solvent contains at least two kinds of esters.
The varnish according to any one of claims 1 to 6, wherein the transparent polyimide polymer has a polystyrene-equivalent weight average molecular weight of 200,000 or more.
An optical film formed from the varnish according to any one of claims 1 to 7.
The optical film according to claim 8, which is a film for a front plate of a flexible display device.
A flexible display device comprising the optical film according to claim 8 or 9.
The flexible display device according to claim 10, further comprising a touch sensor.
The flexible display device according to claim 10, further comprising a polarizing plate.