WO2023013401A1

WO2023013401A1 - Polyamic acid composition and polyimide composition, polyimide film, and display panel substrate

Info

Publication number: WO2023013401A1
Application number: PCT/JP2022/028046
Authority: WO
Inventors: 健一福川; 穣久宗; 達宣浦上; 佳広坂田
Original assignee: 三井化学株式会社
Priority date: 2021-08-06
Filing date: 2022-07-19
Publication date: 2023-02-09
Also published as: JPWO2023013401A1; TW202321349A

Abstract

A polyamic acid composition according to the present disclosure contains a polyamic acid. A tetracarboxylic acid dianhydride constituting the polyamic acid contains a compound represented by formula (a1) and a compound represented by formula (a2) and/or a compound represented by formula (a3), and a diamine constituting the polyamic acid contains a compound represented by formula (b1). The content of the compound represented by formula (a1) is 10 mol% or more relative to the total amount of acid dianhydrides, and the combined amount of the compounds represented by formulas (a1) and (a2) is 30-80 mol% relative to the total amount of the acid dianhydrides.　[Compound 1] [Compound 2] [Compound 3] [Compound 4]

Description

Polyamic acid composition and polyimide composition, polyimide film, and display panel substrate

The present disclosure relates to polyamic acid compositions and polyimide compositions, polyimide films, and display panel substrates.

Conventionally, in displays such as liquid crystal display elements and organic EL display elements, inorganic glass, which is a transparent material, is used for panel substrates and the like. However, inorganic glass has a high specific gravity (weight) and low flexibility and impact resistance. Therefore, application of a polyimide film, which is excellent in lightness, impact resistance, workability and flexibility, to a panel substrate of a display device has been studied.

Here, the panel substrate of the display device is required to have high transparency. In addition, the panel substrate may be heated in the process of forming elements such as thin film transistors and transparent electrodes on the panel substrate. Therefore, the panel substrate is also required to have high heat resistance.

As a polyimide film used as such a panel substrate, for example, the diamine contains 2,2-bis(trifluoromethyl)benzidine (TFMB), and the tetracarboxylic dianhydride contains 3,3',4,4' Polyimide films derived from polyamic acids including -biphenyltetracarboxylic dianhydride (BPDA) and 9,9′-bis(3,4′-dicarboxyphenyl)fluoric dianhydride (BPAF) have been proposed. (For example, Patent Document 1). A polyimide film obtained from a polyamic acid in which the diamine contains 2,2-bistrifluoromethylbenzidine (TFMB) and the tetracarboxylic dianhydride contains pyromellitic dianhydride (PMDA) has also been proposed. (For example, Patent Document 2).

Also known as low-CTE polyimides are polyimides derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA) and 2,2-bis(trifluoromethyl)benzidine (TFMB). (For example, Non-Patent Document 1).

WO2019/188265 JP 2019-178269 A

In recent years, in the process of forming elements on a panel substrate, when the panel substrate is heated, it suppresses the warping of the substrate and the destruction of the elements due to the difference in thermal expansion coefficient between the inorganic material (of the element) and the polyimide film. Therefore, low thermal expansion is required more than ever.

However, the polyimide film of Patent Document 1 did not have sufficiently low thermal expansion. Although the polyimide film of Patent Document 2 has low thermal expansion, pyromellitic dianhydride (PMDA) tends to cause coloration and tends to increase the b ^* value. In addition, excellent flexibility (bending resistance) is also required in order to meet the application as a flexible substrate. Although the polyimide film of Non-Patent Document 1 exhibits low thermal expansion, it has low bending resistance, and the b ^* value sometimes increases depending on the thermal imide temperature.

The present disclosure has been made in view of such circumstances, a polyamic acid composition capable of imparting a polyimide film having both sufficiently low thermal expansion and bending resistance without increasing the b ^* value, and An object of the present invention is to provide a polyimide composition. Another object of the present invention is to provide a polyimide film and a display panel substrate using the polyimide composition.

[1] The polyamic acid composition of the present disclosure contains a polyamic acid, the polyamic acid contains a structural unit derived from a tetracarboxylic dianhydride and a structural unit derived from a diamine, and the tetracarboxylic acid di The anhydride includes a compound represented by formula (a1) and a compound represented by formula (a2) and/or a compound represented by formula (a3),

(In formula (a1),
R ¹ and R ² are each independently an alkyl group having 1 to 4 carbon atoms,
m and n are each an integer of 0 to 2, and m+n is 3 or less)

(In formula (a3),
R ³ and R ⁴ are each independently an alkyl group having 1 to 4 carbon atoms,
o and p are each an integer of 0 to 3, and o+p is 3 or less)
The diamine contains a compound represented by formula (b1),

The content of the compound represented by the formula (a1) is 10 mol% or more with respect to the total amount of the tetracarboxylic dianhydride, and the compound represented by the formula (a1) and the formula (a2) The total amount of the represented compounds is 30-80 mol % relative to the total amount of said tetracarboxylic dianhydride.
[2] The polyamic acid composition according to [1], wherein the tetracarboxylic dianhydride contains the compound represented by the formula (a3).
[3] The polyamic acid according to [1] or [2], wherein the content of the compound represented by the formula (a3) is 10 to 70 mol% with respect to the total amount of the tetracarboxylic dianhydride. Composition.
[4] The polyamic acid according to any one of [1] to [3], wherein the content of the compound represented by the formula (a1) is higher than the content of the compound represented by the formula (a2). Composition.
[5] The content of the compound represented by the formula (a1) is 30 to 80 mol% with respect to the total amount of the tetracarboxylic dianhydride, according to any one of [1] to [4] polyamic acid composition.
[6] The total amount of the compound represented by the formula (a2) and the compound represented by the formula (a3) is 10 to 70 mol% with respect to the total amount of the tetracarboxylic dianhydride, [ 1] The polyamic acid composition according to any one of [5].
[7] The tetracarboxylic dianhydride further includes a compound represented by formula (a4), or

The diamine further comprises a compound represented by formula (b2),

(In formulas (a4) and (b2),
R ⁵ , R ⁶ , R ⁷ and R ⁸ are each independently an alkyl group having 1 to 4 carbon atoms,
q, r, s and t are each an integer from 0 to 3, and q+r and s+t are each 3 or less)
The polyamic acid composition according to any one of [1] to [6].
[8] The total amount of the compound represented by the formula (a4) and the compound represented by the formula (b2) is 0.5 to 15 mol% with respect to the total of the diamine and the tetracarboxylic dianhydride. The polyamic acid composition according to [7].
[9] The polyamic acid composition according to any one of [1] to [8], wherein the content of the compound represented by formula (b1) is 80 mol% or more relative to the total amount of the diamine.
[10] When the polyamic acid composition is thermally imidized at 350° C. to form a polyimide film having a thickness of 10 μm, the b ^* value in the L ^* a ^* b ^* color system is 8.0 or less. The polyamic acid composition according to any one of to [9].
[11] The polyamic acid composition is thermally imidized at 350° C. to form a polyimide film having a thickness of 10 μm. The polyamic acid composition according to any one of [1] to [9].

[12] The polyimide composition of the present disclosure includes a polyimide, the polyimide includes a structural unit derived from a tetracarboxylic dianhydride and a structural unit derived from a diamine, and the tetracarboxylic dianhydride is , a compound represented by formula (a1) and a compound represented by formula (a2) and/or a compound represented by formula (a3),

The content of the compound represented by the formula (a1) is 10 mol% or more with respect to the total amount of the tetracarboxylic dianhydride, and the compound represented by the formula (a1) and the formula (a2) The total amount of the represented compounds is 30-80 mol % relative to the total amount of said tetracarboxylic dianhydride.

[13] The polyimide composition according to [12], wherein the tetracarboxylic dianhydride contains the compound represented by the formula (a3).
[14] The polyimide composition according to [12] or [13], wherein the content of the compound represented by the formula (a3) is 10 to 70 mol% with respect to the total amount of the tetracarboxylic dianhydride. thing.
[15] The content of the compound represented by the formula (a1) is higher than the content of the compound represented by the formula (a2), [12] to [14] The polyimide composition according to any one of thing.
[16] The content of the compound represented by the formula (a1) is 30 to 80 mol% relative to the total amount of the tetracarboxylic dianhydride, according to any one of [12] to [15] polyimide composition.
[17] The total amount of the compound represented by the formula (a2) and the compound represented by the formula (a3) is 10 to 70 mol% with respect to the total amount of the tetracarboxylic dianhydride, [ 12] The polyimide composition according to any one of [16].
[18] The tetracarboxylic dianhydride further includes a compound represented by formula (a4), or

The diamine further comprises a compound represented by formula (b2),

(In formulas (a4) and (b2),
R ⁵ , R ⁶ , R ⁷ and R ⁸ are each independently an alkyl group having 1 to 4 carbon atoms,
q, r, s and t are each an integer from 0 to 3, and q+r and s+t are each 3 or less)
[12] The polyimide composition according to any one of [17].
[19] The total amount of the compound represented by the formula (a4) and the compound represented by the formula (b2) is 0.5 to 15 mol% with respect to the sum of the diamine and the tetracarboxylic dianhydride. The polyimide composition according to [18].
[20] The polyimide composition according to any one of [12] to [19], wherein the content of the compound represented by formula (b1) is 80 mol% or more relative to the total amount of the diamine.
[21] The polyimide composition according to any one of [12] to [20], which has a linear thermal expansion coefficient of −10 to 30 ppm/K at 100 to 350° C. when formed into a film.
[22] The polyimide composition according to any one of [12] to [21], which, when formed into a film, has a thickness-direction birefringence Δn of 0.19 or less at a wavelength of 633 nm.
[23] comprising the polyimide composition according to any one of [12] to [22],
polyimide film.
[24] The polyimide film according to [23], which has a folding endurance of 10,000 or more in an MIT folding endurance test measured according to JIS P8115.
[25] The polyimide film according to [23] or [24], which has a b ^* value of 16 or less in the L ^* a ^* b ^* color system.
[26] A display panel substrate comprising the polyimide film according to any one of [23] to [25].

According to the present disclosure, it is possible to provide a polyamic acid composition and a polyimide composition capable of imparting a polyimide film having both sufficiently low thermal expansion and bending resistance while suppressing an increase in the b ^* value. A polyimide film and a display panel substrate using the polyimide composition can also be provided.

In this specification, a numerical range represented using "~" means a range that includes the numerical values before and after "~" as lower and upper limits, respectively. In the numerical ranges described stepwise in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described stepwise.

The present inventors have found that by containing the compound represented by the formula (a1) as a tetracarboxylic dianhydride, while suppressing the coloring of the resulting polyimide film (without increasing the b ^* value), It has been found that the CTE can be lowered.

Although this mechanism is not clear, it can be considered as follows. Since the naphthalene ring has a rigid structure and tends to increase the orientation, the CTE of the film can be easily lowered. In addition, the benzene ring easily absorbs light due to the formation of an intermolecular charge transfer complex accompanying the donor-acceptor with two adjacent acid dianhydride sites, and 1,4,5,8-naphthalenetetracarboxylic acid Dianhydrides and condensed rings in which three or more benzene rings are condensed (for example, 3,4,9,10-perylenetetracarboxylic dianhydride, etc.) have a structure similar to a dye compound, and the π electrons in the molecule Since the conjugated system is extended, it is easy to absorb light. On the other hand, the naphthalene ring is less likely to form an intermolecular charge-transfer complex associated with the donor/acceptor that causes light absorption, and is less likely to cause coloration because the π-electron conjugation in the molecule does not spread much. .

As described above, the compound represented by formula (a1) can contribute to lowering the CTE while suppressing coloration, but the bending resistance of the film is likely to be impaired. In contrast, the present inventors have found that by further including at least one of the compound represented by formula (a2) and the compound represented by formula (a3), bending resistance can be ensured while maintaining a low CTE.

That is, a compound represented by formula (a1), a tetracarboxylic dianhydride containing a compound represented by formula (a2) and/or a compound represented by formula (a3), and a specific diamine (TFMB ) can provide a polyimide film that can achieve both low CTE and high bending resistance while suppressing coloration (while having transparency). The configuration of the present disclosure will be described in detail below.

1. Polyamic Acid Composition The polyamic acid composition of the present disclosure contains a polyamic acid and may optionally further contain other optional ingredients such as a solvent.

1-1. Polyamic acid Polyamic acid contains structural units derived from tetracarboxylic dianhydride and structural units derived from diamine.

[Tetracarboxylic dianhydride]
The tetracarboxylic dianhydride includes a compound represented by formula (a1) and a compound represented by formula (a2) and/or a compound represented by formula (a3).

In formula (a1), R ¹ and R ² are each independently an alkyl group having 1 to 4 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 or 2. m and n are each an integer of 0 to 2, and m+n is 3 or less. From the viewpoint of easily lowering the CTE, it is preferable that the orientation (molecular linearity) is high, and m and n are preferably 0.

The compound represented by formula (a1) and the compound represented by formula (a2) can lower the CTE of the polyimide film. In particular, the compound represented by formula (a2) can lower the CTE without coloring the resulting polyimide film (without increasing the b ^* value) than the compound represented by formula (a1). .

Examples of the compound represented by formula (a1) include 2,3,6,7-naphthalenetetracarboxylic dianhydride (NTCDA) and those partially substituted with alkyl groups. 3,6,7-Naphthalenetetracarboxylic dianhydride (NTCDA) is preferred. Examples of compounds represented by formula (a2) include pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylic acid, PMDA).

In formula (a3), R ³ and R ⁴ are each independently an alkyl group having 1 to 4 carbon atoms. The number of carbon atoms in the alkyl group is preferably 1 or 2. o and p are each an integer from 0 to 3, and o+p is 3 or less.

The compound represented by formula (a3) can increase the bending resistance of the polyimide film. Examples of compounds represented by formula (b1) include compounds represented by formula (a3-1) and compounds represented by formula (a3-2).

Examples of compounds represented by formula (a3-1) include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA). Examples of compounds represented by formula (a3-2) include 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA). Among them, the compound represented by formula (a3-1) is preferred, and 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) is more preferred, from the viewpoint of increasing bending resistance. In addition, from the viewpoint of lowering the birefringence Δn, the compound represented by the formula (a3-2) is preferable, and 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) is more preferable. preferable.

Among them, from the viewpoint of further lowering the CTE while increasing the bending resistance of the film, the tetracarboxylic dianhydride preferably contains a compound represented by the formula (a1) and a compound represented by the formula (a3). , a compound represented by formula (a2). That is, the compound represented by formula (a2) can have intermediate properties between the compound represented by formula (a1) and the compound represented by formula (a3).

The content of the compound represented by formula (a1) is preferably 10 mol % or more relative to the total amount of the tetracarboxylic dianhydride. When the content of the compound represented by the formula (a1) is 10 mol % or more, it is possible to suppress the coloring of the polyimide film and lower the b ^* value while lowering the CTE. From the same point of view, the content of the compound represented by formula (a1) is more preferably 30 to 80 mol% with respect to the total amount of tetracarboxylic dianhydride, and 40 to 65 mol%. is more preferred.

The content of the compound represented by formula (a1) is preferably larger than that of the compound represented by formula (a2) from the viewpoint of further lowering the CTE while suppressing the coloration of the film. Specifically, the ratio of the content of the compound represented by formula (a1) to the total amount of the compound represented by formula (a1) and the compound represented by formula (a2) (a1/(a1+a2)) is preferably 0.5 to 1.0, more preferably 0.6 to 1.0.

The amount of the compound represented by formula (a3) is preferably 10 mol % or more relative to the total amount of the tetracarboxylic dianhydride. That is, the compound represented by formula (a3) has a slightly non-planar structure. Therefore, in addition to the compound represented by the formula (a1), when 10 mol% or more of the compound represented by the formula (a3) is further included, the resulting polyimide structure derived from the compound represented by the formula (a1) The intermolecular interaction between the unit and the structural unit derived from the compound represented by formula (a3) tends to moderately weaken. As a result, the coloring and b ^* value of the polyimide film can be further reduced, and the bending performance of the film can be further improved. From the same point of view, the compound represented by formula (a3) is preferably 10 to 70 mol%, more preferably 20 to 65 mol%, relative to the total amount of tetracarboxylic dianhydride. , 30 to 60 mol %.

The total amount (a1+a2) of the compound represented by formula (a1) and the compound represented by formula (a2) is preferably 30 to 80 mol% relative to the total amount of tetracarboxylic dianhydride. When the total amount is 30 mol % or more, the CTE of the film can be sufficiently lowered, and when it is 80 mol % or less, the bending resistance of the film is hardly impaired. From the same point of view, the above total amount is more preferably 30 to 70 mol %, more preferably 40 to 65 mol %, relative to the total amount of tetracarboxylic dianhydride.

The total amount (a2+a3) of the compound represented by the formula (a2) and the compound represented by the formula (a3) is preferably 10 to 80 mol% with respect to the total amount of the tetracarboxylic dianhydride. . When the total amount is 10 mol% or more, the bending resistance of the film tends to be increased, and when it is 80 mol% or less, an excessive increase in CTE can be suppressed. From the same point of view, the total amount is more preferably 10 to 70 mol%, more preferably 23 to 60 mol%, and 40 to 60 mol% with respect to the total amount of tetracarboxylic dianhydride. is particularly preferred.

From the viewpoint of further increasing the bending resistance of the film, the total amount (a1+a2) of the compound represented by the formula (a1) and the compound represented by the formula (a2), the compound represented by the formula (a2) and the compound represented by the formula (a3) ) is preferably 4 or less, preferably 2 or less, more preferably 1 or less, and particularly preferably 0.9 or less. From the viewpoint of further lowering the CTE of the resulting film, (a1 + a2) / (a2 + a3) is preferably 0.4 or more, preferably 0.6 or more, and more preferably 0.8 or more. Preferably, it is more preferably 1 or more. From these viewpoints, (a1+a2)/(a2+a3) is preferably 0.4 to 4, more preferably 0.4 to 2, still more preferably 0.4 to 1, further preferably 0.6 to 1, and 0 0.6 to 0.9 are particularly preferred.

The tetracarboxylic dianhydride preferably further contains a compound represented by formula (a4).

R ⁵ and R ⁶ in formula (a4) each independently represent an optionally substituted alkyl group having 1 to 4 carbon atoms or a fluorine atom. The number of carbon atoms in the alkyl group is preferably 1 or 2. Examples of substituents that the alkyl group may have include a fluorine atom and the like. q and r each represent an integer of 0 to 3; However, q+r is 3 or less.

The compound represented by formula (a4) can not only impart high transparency and heat resistance when formed into a film, but also reduce the birefringence Δn of the film. The compound represented by formula (a4) is preferably 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF).

The content of the compound represented by the formula (a4) is the total amount of the tetracarboxylic anhydride having a fluorene skeleton and the diamine (the total amount of the compound represented by the formula (a4) and the compound represented by the formula (b2) amount) is preferably set within the range described later.

The tetracarboxylic dianhydride may further contain other tetracarboxylic dianhydrides other than the above, as long as the effects of the present disclosure are not impaired. Examples of other tetracarboxylic dianhydrides include aromatic tetracarboxylic dianhydrides other than those mentioned above, alicyclic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic dianhydrides. The content of other tetracarboxylic dianhydrides can be 10 mol % or less with respect to the total amount of tetracarboxylic dianhydrides.

[Diamine]
Diamines include compounds represented by formula (b1).

The compound represented by formula (b1) is 2,2'-bis(trifluoromethyl)benzidine (TFMB). The compound can impart high transparency and low b ^* value when made into a film.

The diamine preferably further contains a compound represented by the formula (b2), for example, from the viewpoint of increasing the heat resistance of the film or reducing the birefringence Δn.

R ⁷ and R ⁸ in formula (b2) each independently represent an optionally substituted alkyl group having 1 to 4 carbon atoms or a fluorine atom. The number of carbon atoms in the alkyl group is preferably 1 or 2. Examples of substituents that the alkyl group may have include a fluorine atom and the like. s and t each represents an integer of 0 to 3; However, s+t is 3 or less.

Examples of compounds represented by formula (b2) include 9,9-bis(4-aminophenyl)fluorene (BAFL), 9,9-bis(4-amino-3-methylphenyl)fluorene (FFDA), 9,9-bis(aminofluorophenyl)fluorene is included.

The content of the compound represented by formula (b1) is preferably 80 mol % or more with respect to the total amount of diamine. When the content of the compound represented by the formula (b1) is 80 mol% or more, it is easy to suppress the coloration of the film (easy to lower the b ^* value). From the same point of view, the content of the compound represented by formula (b1) is preferably 90 mol % or more, and may be 100 mol %.

The content of the compound represented by the formula (b2) is such that the total amount of the compound represented by the formula (a4) and the compound represented by the formula (b2) (the content of the component having a fluorene skeleton) is equal to the diamine and It is set to be 0 to 15 mol %, preferably 0.5 to 15 mol %, based on the total amount of tetracarboxylic dianhydride. When the total amount is 0.15 mol % or more, the birefringence Δn tends to be lowered, and when it is 15 mol % or less, an increase in CTE is easily suppressed. From the same point of view, the above total amount is more preferably 2 to 8 mol %.

The diamine may further contain diamines other than the above as long as the effects of the present disclosure are not impaired. Examples of other diamines include bis(3-aminophenyl)sulfone (3,3-DAS), 4,4′-diaminodiphenylsulfone (4,4-DAS), 1,5-diaminonaphthalene (15DAN), 4,4′-diaminobenzanilide (DABA), m-diaminobenzene (MDA) and other aromatic diamines other than the above, 1,2-cyclohexanediamine (DACH) and 1,3-bis(aminomethyl)cyclohexane, Included are cycloaliphatic diamines such as 1,4-bis(aminomethyl)cyclohexane, and aliphatic diamines such as ethylenediamine and hexamethylenediamine. The content of other diamines can be 10 mol % or less with respect to the total amount of diamines.

[Physical properties]
Although the intrinsic viscosity (η) of the polyamic acid is not particularly limited, it is preferably 0.3 to 2.0 dL/g, more preferably 0.6 to 1.6 dL/g. When the intrinsic viscosity (η) of the polyamic acid varnish is within the above range, it is easy to achieve both coatability and film formability.

The intrinsic viscosity (η) of polyamic acid can be adjusted by adjusting the amount ratio (molar ratio) of tetracarboxylic dianhydride and diamine when preparing polyamic acid. For example, when the acid dianhydride/diamine ratio is equimolar, the intrinsic viscosity (η) tends to increase. The intrinsic viscosity (η) is a value measured at 25° C. with an Ubbelohde viscosity tube when the polyamic acid concentration in N-methyl-2-pyrrolidone (NMP) is 0.5 g/dL.

1-2. Other Components The polyamic acid composition of the present disclosure may, if necessary, further contain components other than the polyamic acid described above.

For example, the polyamic acid composition may further contain a solvent. The solvent may be a solvent used for preparing the polyamic acid composition described later, and is not particularly limited as long as it can dissolve the diamine component and the tetracarboxylic dianhydride component described above. For example, an aprotic polar solvent, an alcoholic solvent, or the like can be used.

Examples of aprotic polar solvents include N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), 1,3-dimethyl-2-imidazolidinone (DMI), N,N- Amide solvents such as dimethylformamide (DMF), N,N-diethylformamide (DEF), hexamethylphosphoramide (HMPA); dimethylsulfoxide; and 2-methoxyethanol, 2-ethoxyethanol, 2-(methoxymethoxy) ethoxyethanol, 2-isopropoxyethanol, 2-butoxyethanol, tetrahydrofurfuryl alcohol, diethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monoethyl ether, tetraethylene glycol, 1 - methoxy-2-propanol, 1-ethoxy-2-propanol, dipropylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, polyethylene glycol, polypropylene glycol, tetrahydrofuran, dioxane, 1, Ether solvents such as 2-dimethoxyethane, diethylene glycol dimethyl ether and diethylene glycol diethyl ether are included.

Examples of alcoholic solvents include methanol, ethanol, 1-propanol, 2-propanol, tert-butyl alcohol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1 ,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 2-butene-1,4-diol, 2-methyl-2,4-pentanediol, 1,2,6-hexanetriol, Diacetone alcohol and the like are included.

These solvents may contain only one type, or may be a combination of two or more types. Among them, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone (DMI) or a mixed solvent thereof is preferable.

The polyamic acid content (resin concentration of the polyamic acid composition) is not particularly limited, but from the viewpoint of coatability, it is 5 to 30% by mass, preferably 10 to 25% by mass, based on the total amount of the polyamic acid composition. can be The resin concentration of the polyamic acid composition may be the same as the solution concentration during preparation of the polyamic acid composition.

1-3. Physical Properties A film (polyimide film) obtained by imidating the polyamic acid composition of the present disclosure is inhibited from being colored and has good bending resistance.

(L ^* a ^* b * b ^* ^value in color system)
The b ^* value in the L ^* a ^* b ^* color system of a polyimide film having a thickness of 10 μm obtained by thermally imidizing a polyamic acid composition at 350° C. is preferably 8.0 or less, more preferably 6.0 or less. , and more preferably 4.0 or less. The b ^* value represents the yellowness of the film, and a smaller value indicates less yellowness. Therefore, the lower limit of the b ^* value is usually about 1.0, preferably 0. A polyimide film having a b ^* value of 8.0 or less is less colored and has excellent transparency, and is suitable for optical films, ie, panel substrates for various display devices.

The b ^* value is obtained by thermally curing (imidizing) the polyamic acid composition at 350 ° C. The b ^* value of a polyimide film having a thickness of 10 μm is measured by a colorimeter (for example, Suga Test Instruments Co., Ltd. tristimulus value direct reading type measurement It is the value when measured using a colorimeter (Colour Cute CC-i model) in transmission mode (when using the above equipment, transmission mode is set to 0°di).

The b ^* value can be adjusted by the monomer composition of the polyamic acid. For example, if the content ratio of the compound (TFMB) represented by the formula (b1) in the diamine is increased, or the content ratio of the compound (PMDA) represented by the formula (a2) in the acid anhydride is decreased, , b ^* values tend to be small.

(bending resistance)
A polyimide film having a thickness of 10 μm obtained by thermally imidizing a polyamic acid composition at 350° C. has a folding endurance in the MIT folding endurance test of, for example, preferably 10,000 times or more, and preferably 40,000 times or more. is more preferable, 100,000 times or more is more preferable, and 200,000 times or more is even more preferable.

The MIT folding endurance test can be performed by the following procedure.
A polyimide film (10 μm thick) is cut into a shape of 120 mm long×15 mm wide to obtain a test piece. One end of this test piece is set in an MIT folding endurance tester (307 type) manufactured by Yasuda Seiki Seisakusho, and the other end is held, with a curvature radius of 0.38 mm, a load of 0.5 kg, and a bending accuracy of 270 degrees (left and right 135 degrees). degree) and the bending speed is 175 times/min. The measurement conditions can be as described in Examples below. The thickness of the polyimide film is not restricted to 9 to 12 μm depending on the thickness of the film.

Bending resistance can be adjusted by the monomer composition of polyimide. For example, among the acid dianhydrides, the total amount (a2 + a3) of the compound represented by the formula (a2) and the compound represented by the formula (a3) is increased (or (a1 + a2) / (a2 + a3) is decreased) When the content of the compound represented by the formula (a3) is increased, the bending resistance tends to increase.

2. Method for Producing Polyamic Acid Composition The polyamic acid composition can be obtained by reacting a tetracarboxylic dianhydride component and a diamine component in a solvent. The types of solvent, tetracarboxylic dianhydride component, and diamine component to be used and their quantitative ratios are as described above.

The reaction for obtaining the polyamic acid composition is preferably carried out by heating the above tetracarboxylic dianhydride and diamine in a solvent at a relatively low temperature (a temperature at which imidization does not occur). . Specifically, the temperature at which imidization does not occur can be 5 to 120°C, more preferably 25 to 80°C. Moreover, the reaction is preferably carried out in an environment in which an imidization catalyst (for example, triethylamine, etc.) is substantially absent.

The content of the tetracarboxylic dianhydride and the diamine in the solution (solution concentration) is not particularly limited, but from the viewpoint of promoting intermolecular cross-linking during imidization, it is preferably high, and the coating properties are not impaired. From the viewpoint of making The concentration of the solution can be 5 to 30% by mass, preferably 10 to 25% by mass, from the viewpoint of coatability.

The above reaction (polymerization reaction) can be performed by a known method. For example, a container equipped with a stirrer and a nitrogen inlet tube is prepared, and the solvent is introduced into the container which is purged with nitrogen. Then, diamine is added so that the final polyamic acid concentration falls within the above range, and the temperature is adjusted and stirred. A predetermined amount of tetracarboxylic dianhydride is added to the solution. Then, the mixture is stirred for about 1 to 50 hours while adjusting the temperature.

It should be noted that, in the above reaction, it is preferable not to perform concentration (concentration by Dean Stark) for removing the generated water. This is to prevent the imidization reaction from proceeding.

When performing the above reaction, the ratio (y/x) of the total molar amount x of the diamine and the total molar amount y of the tetracarboxylic dianhydride is, for example, 0.9 to 1.1, preferably 0.95 to 1.05.

3. Polyimide Composition The polyimide composition of the present disclosure includes a specific polyimide obtained by imidating the polyamic acid contained in the polyamic acid composition.

3-1. Polyimide The polyimide is obtained by imidizing the polyamic acid, and includes structural units derived from the tetracarboxylic dianhydride and structural units derived from the diamine. Polyimide compositions (eg, polyimide films) containing such polyimides have reduced coloration (low b ^* values), low CTE, and good bending resistance.

The polyimide composition may be in the form of powder, pellets, or film. Among them, a film is preferable from the viewpoint of ease of use as a display substrate.

3-2. Physical Properties of Polyimide Composition As described above, the polyimide composition and the polyimide film containing the same have little coloration, low CTE, and good bending resistance. Specifically, the polyimide composition and the polyimide film containing it preferably satisfy one or more of the following physical properties.

(1) Optical properties (total light transmittance)
The total light transmittance (Total Transmittance: TT) of the polyimide film depends on the thermal imidization conditions (especially the heating temperature), but is for example 80% or more, preferably 85% or more, more preferably 87% or more, and more preferably 89% or more. The upper limit of the total light transmittance is preferably 100%, but usually about 92% or 90%. A polyimide film having such a high total light transmittance is suitable for optical films, ie, panel substrates (transparent substrates) for various display devices. The total light transmittance (TT) indicates the average transmittance in the entire wavelength range (300 to 830 nm) of D65, which is a standard light source. From the viewpoint of further improving visibility, the transmittance at a wavelength of 450 nm (T@450 nm) is preferably 60% or more, more preferably 75% or more.

The total light transmittance of the polyimide film is measured with light source D65 according to JIS-K7361-1. The light transmittance at a wavelength of 450 nm can be obtained by measuring the UV-visible spectrum in the wavelength range of 300 to 800 nm and calculating the transmittance of light at a wavelength of 450 nm as T@450 nm.

The total light transmittance of the polyimide film and the transmittance at a wavelength of 450 nm can be adjusted by the monomer composition of the polyimide. For example, when the content ratio of the compound represented by the formula (b1) (TFMB) in the diamine or the content ratio of the compound represented by the formula (a4) in the acid anhydride (for example, BPAF) is high, the total light transmission efficiency and transmittance at a wavelength of 450 nm tend to be high.

(b ^* value)
The b ^* value in the L ^* a ^* b ^* color system of a polyimide film (e.g., a polyimide film having a thickness of 10 μm) is preferably 16.0 or less, more preferably 8.0 or less, still more preferably 6.0 or less, especially Preferably it is 4.0 or less. The lower limit of the b ^* value is usually about 1.0, preferably 0. A polyimide film having a b ^* value of 16.0 or less, preferably 8.0 or less is less colored and has excellent transparency, and is suitable for optical films, ie, panel substrates for various display devices. The method for measuring and adjusting the b ^* value is as described above. The thickness of the polyimide film is not restricted to 9 to 12 μm depending on the thickness of the film.

(Birefringence Δn in thickness direction)
The thickness direction birefringence Δn of the polyimide film at a wavelength of 633 nm is not particularly limited, but is preferably 0.19 or less, more preferably 0.1 or less. When the birefringence Δn is within the above range, when the polyimide film is used as a display substrate, the image displayed on the display device is less likely to be distorted, and the display characteristics can be improved.

The birefringence Δn in the thickness direction can be measured by the following method.
Using a Metricon prism coupler (model 2010), a laser beam with a wavelength of 633 nm is incident on the sample through a coupling prism, and the refractive index (nTE) in TE polarized light and the refractive index (nTM) in TM polarized light are measured, Subtract nTM from nTE to calculate birefringence.

The birefringence Δn in the thickness direction can be adjusted by the monomer composition of polyimide. For example, if the total amount of the compound represented by the formula (a4) and the compound represented by the formula (b2) with respect to the total of the tetracarboxylic dianhydride and the diamine constituting the polyimide (a component containing a fluorene skeleton) is large, The birefringence Δn of the polyimide film tends to be low. This is probably because the many aromatic rings of the compound containing a fluorene skeleton show different orientations and tend to act in a direction that cancels out the optical anisotropy.

(2) Thermophysical properties (Glass transition temperature (Tg))
The glass transition temperature (Tg) of the polyimide film is preferably 370°C or higher, more preferably 400°C or higher. When the Tg of the polyimide film is 370° C. or higher, the film can be applied to substrates for TFT arrays and the like. Specifically, the Tg of the polyimide film is preferably 350° C. or higher when used for manufacturing a TFT array using IGZO (an oxide semiconductor composed of indium, gallium, zinc, and oxygen), and 390° C. It is more preferably 400° C. or higher when used for manufacturing a TFT array using low-temperature polysilicon. If the Tg is within this range, the display device can be used even under the working environment during fabrication of each TFT array, and a highly reliable display device can be easily obtained. Although the upper limit of the Tg of the polyimide film is not particularly limited, it can be, for example, about 500° C. from the viewpoint of moldability.

Using a dynamic viscoelasticity apparatus (RSA-III manufactured by TA Instruments), a sample with a width of 5 mm and a length of 20 mm was measured in a nitrogen atmosphere at a temperature of 25 to 450 ° C., a heating rate of 3 ° C./min, a frequency of 1 Hz, The dynamic viscoelasticity is measured under the measurement condition of an initial load of 5.0 kg/cm ² per cross-sectional area, and the loss tangent (value obtained by dividing the loss elastic modulus by the storage elastic modulus, tan δ) is obtained. Also, the temperature at which tan δ shows the maximum value above the firing temperature is defined as the glass transition temperature.

(Coefficient of linear thermal expansion (CTE))
The coefficient of linear thermal expansion (CTE) of the polyimide film depends on the thermal imidization conditions (especially the heating temperature), but is preferably -10 to 50 ppm/K, more preferably -10 to 30 ppm/K. It is preferably -5 to 20 ppm/K, and particularly preferably 0 to 10 ppm/K. When the coefficient of linear thermal expansion is within the above range, the polyimide film is less likely to deform even at high temperatures when used as a panel substrate for various display devices, and warping due to the high temperature environment in the process of forming electric elements on the substrate. It is easy to suppress misalignment and breakage of electric elements due to thermal deformation such as, and it is easy to stack various elements.

A coefficient of linear thermal expansion (CTE) can be measured by the following method.
After attaching the test piece to a thermomechanical analyzer (TMA), the temperature was raised from room temperature to 300°C at a rate of 5°C/min under a nitrogen atmosphere under a load of 100mN (1st run), and then to 50°C or less. The temperature is lowered to remove the residual stress accumulated in the test piece, and the temperature is again raised to 450 ° C. at 5 ° C./min (2nd run). coefficient (CTE).

The coefficient of linear thermal expansion (CTE) can be adjusted by the monomer composition of polyimide (or its precursor polyamic acid). For example, among the acid dianhydrides, the total amount (a1 + a2) (or (a1 + a2) / (a2 + a3)) of the compound represented by the formula (a1) and the compound represented by the formula (a2) is increased, or the formula When the content of the compound represented by (a1) is increased, the CTE tends to be lowered.

(3) Mechanical properties (tensile strength)
The tensile strength of the polyimide film is preferably 160 MPa or more, for example. The tensile elongation is preferably 4-15%, for example.

Tensile strength and tensile elongation can be measured by the following procedures.
A dumbbell-shaped punched test piece is prepared from the polyimide film and measured with a tensile tester (EZ-S, manufactured by Shimadzu Corporation) under the conditions of a marked line width of 5 mm, a sample length of 30 mm, and a tensile speed of 30 mm/min. From the obtained stress-strain curve, the strength and elongation at the breaking point are defined as tensile strength and tensile elongation, respectively, and the average values of five measurements are determined as tensile strength TS and tensile elongation EL.

(bending resistance)
The number of folding endurance of the polyimide film in the MIT folding endurance test is, for example, preferably 10,000 times or more, more preferably 40,000 times or more, further preferably 100,000 times or more, and 200,000 times. It is more preferable that it is above. A film having a folding endurance number in the above range in the MIT folding endurance test has high flexibility and is therefore suitable as a flexible display substrate. The method of the MIT folding endurance test and the method of adjusting the bending endurance are as described above.

(4) Thickness The thickness of the polyimide film is not particularly limited, and is appropriately selected according to the use of the film. The thickness of the polyimide film is, for example, 1-100 μm, preferably 5-50 μm, more preferably 5-20 μm.

(5) Applications The polyimide film of the present disclosure has high transparency, low CTE, and high bending resistance. Therefore, it is suitable for substrates for electronic devices. Examples of substrates for electronic devices include transparent substrates (display panel substrates) for display devices such as touch panels, liquid crystal displays, and organic EL displays; and substrates for mounting sensors for fingerprint authentication and face authentication. For example, for substrate applications where sensors for fingerprint authentication and face authentication are mounted, it is required to have flexibility, high transparency that does not block the light that is the object of measurement, and little coloring. heat resistance (low CTE) is required. The polyimide film of the present disclosure is also suitable for such uses.

4. Method for producing polyimide film The polyimide film of the present disclosure includes: 1) a step of applying the polyamic acid composition of the present disclosure to a substrate to form a coating film; ) is obtained through the step of

Regarding step 1) (varnish application) The varnish containing the polyamic acid and solvent is applied to the surface of various substrates to form a coating film.

The base material to which the varnish is applied is not particularly limited as long as it has solvent resistance and heat resistance. Any substrate can be used as long as the obtained polyimide film can be easily peeled off, and a flexible substrate such as a glass plate, a metal film, or a heat-resistant polymer film is preferable.

Examples of flexible substrates made of metals include copper, aluminum, stainless steel, iron, silver, palladium, nickel, chromium, molybdenum, tungsten, zirconium, gold, cobalt, titanium, tantalum, zinc, lead, tin, silicon, bismuth. , indium, or alloys thereof. The metal foil surface may be coated with a release agent.

Examples of flexible substrates made of heat-resistant polymer films include polyimide films, aramid films, polyetheretherketone films, and polyethersulfone films. The flexible base material made of a heat-resistant polymer film may contain a releasing agent or an antistatic agent, or may be coated with a releasing agent or an antistatic agent. The base material is preferably a polyimide film because it has good film releasability and high heat resistance and solvent resistance.

The shape of the substrate is appropriately selected according to the shape of the polyimide film to be produced, and may be in the form of a single leaf sheet or in the form of an elongated sheet. The thickness of the substrate is preferably 5-150 μm, more preferably 10-70 μm. When the thickness of the substrate is 5 μm or more, the substrate is less likely to wrinkle or split during application of the varnish.

The method of applying the varnish to the substrate is not particularly limited as long as it can be applied with a uniform thickness. Examples of coating methods include methods using a die coater, a comma coater, a roll coater, a gravure coater, a curtain coater, a spray coater, a lip coater and the like.

Regarding step 2) (imidation of polyamic acid) Next, the coating film of the polyamic acid composition is heated to imidize (ring-close) the polyamic acid.

Specifically, the coating film of the varnish is heated while increasing the temperature from 150°C or lower to over 200°C, thereby imidizing the polyamic acid while removing the solvent in the coating film. After the temperature is raised to a predetermined temperature, the material is heated at that temperature for a predetermined time.

Generally, the temperature at which polyamic acid imidates is 150-200°C. Therefore, when the temperature of the coating film is rapidly raised to 200° C. or higher, the polyamic acid on the coating film surface is imidized before the solvent volatilizes from the coating film. As a result, the solvent remaining in the coating film causes air bubbles or irregularities on the surface of the coating film. Therefore, it is preferable to gradually raise the temperature of the coating film in the temperature range of 150 to 200°C. Specifically, the temperature increase rate in the temperature range of 150 to 200° C. is preferably 0.25 to 50° C./min, more preferably 1 to 40° C./min, and 2 to 30° C./min. It is more preferable that

The temperature may be raised continuously or stepwise (sequentially), but it is preferable to raise the temperature continuously from the viewpoint of suppressing appearance defects of the resulting polyimide film. In addition, the rate of temperature increase may be constant over the entire temperature range described above, or may be changed in the middle.

An example of a method of heating a single-leaf coating film while raising the temperature is to raise the temperature inside the oven. In this case, the heating rate is adjusted by setting the oven. Further, when heating a long coating film while increasing the temperature, for example, a plurality of heating furnaces for heating the coating film are arranged along the conveying (moving) direction of the substrate; Vary for each heating furnace. For example, the temperature of each heating furnace may be increased along the moving direction of the substrate. In this case, the heating rate is adjusted by the conveying speed of the substrate.

As described above, it is preferable to heat at a constant temperature for a certain period of time after raising the temperature. Although the heating temperature is not particularly limited, it is preferably a temperature at which the amount of solvent in the film is 0.5% by mass or less. For example, the solvent can be easily removed by making the temperature higher than the Tg of polyimide. Specifically, the heating temperature is preferably 250° C. or higher, more preferably 300° C. or higher, still more preferably 340° C. or higher, and may be 400° C. or higher. The heating time can usually be about 0.5 to 2 hours. This is because by increasing the heating temperature, damage to the device due to outgassing remaining in the film system or stress change can be suppressed even if the device is exposed to high temperatures in the subsequent device fabrication process. For example, in the case of TFTs for display substrates, if the TFT device type is the low temperature polysilicon (LTPS) type, a higher process temperature (e.g., 400°C or higher) is required compared to conventional amorphous silicon or IGZO types. There is Even after such a high-temperature thermal history, damage to the device can be reduced.

Polyimide is easily oxidized when heated at a temperature exceeding 200°C. When polyimide is oxidized, the obtained polyimide film turns yellow and the total light transmittance of the polyimide film decreases. Therefore, in the temperature range exceeding 200° C., it is preferable to (i) use an inert gas atmosphere as the heating atmosphere, or (ii) reduce the pressure of the heating atmosphere.

(i) When the heating atmosphere is an inert gas atmosphere, the oxidation reaction of polyimide is suppressed. The type of inert gas is not particularly limited, and may be argon gas, nitrogen gas, or carbon dioxide gas. In addition, the oxygen concentration in the temperature range exceeding 200 ° C. is preferably 1% by volume or less, more preferably 0.1% by volume (1000 ppm) or less, and 0.01% by volume (100 ppm) or less. is more preferred. The oxygen concentration in the atmosphere is measured by a commercially available oxygen concentration meter (for example, a zirconia oxygen concentration meter).

(ii) The oxidation reaction of polyimide is also suppressed by reducing the pressure of the heating atmosphere. When reducing the pressure of the heating atmosphere, the pressure in the atmosphere is preferably 15 kPa or less, more preferably 5 kPa or less, and even more preferably 1 kPa or less. When the heating atmosphere is decompressed, the coating film is heated in a decompression oven or the like.

After imidization (ring closure) of polyamic acid, a polyimide film is obtained by peeling off the base material.

Hereinafter, the present disclosure will be described in more detail with examples. However, the scope of the disclosure is not limited thereby.

1. Materials Tetracarboxylic dianhydrides and diamines used in Examples and Comparative Examples are as follows.

[Tetracarboxylic dianhydride]
NTCDA: 2,3,6,7-naphthalenetetracarboxylic dianhydride PMDA: pyromellitic dianhydride BPAF: fluorenylidene bisphthalic anhydride s-BPDA: 3,3',4,4'-biphenyltetra Carboxylic acid dianhydride

[Diamine]
TFMB: 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl BAFL: 9,9-bis(4-aminophenyl)fluorene

2. test 1
2-1. Preparation of varnish (Preparation of polyamic acid varnishes 1 to 15)
A flask equipped with a thermometer, a condenser, a nitrogen inlet tube and a stirrer was charged with the diamine and N-methyl-2-pyrrolidinone (NMP) from Table 1 (the weight of NMP was previously added so that the total concentration of all monomers was 20% by mass). calculated) was added and stirred under a nitrogen atmosphere to form a uniform solution. A predetermined amount of the corresponding tetracarboxylic acid dianhydride in Table 1 was added to the solution as powder, stirred at room temperature for 30 minutes, and then the solution temperature was raised to 85 to 90 ° C. for 1 hour. After stirring for a period of time, a uniform solution was obtained. Thereafter, the mixture was cooled to room temperature, and stirring was continued overnight at room temperature to obtain a pale yellow viscous polyamic acid varnish (polyamic acid concentration: 15% by mass).

(Intrinsic viscosity η)
The intrinsic viscosity η of the obtained varnish was measured with an Ubbelohde viscosity tube at a polymer concentration of 0.5 g/dL, NMP, and 25°C.

Table 1 shows the preparation conditions and physical properties of the polyamic acid varnish.

2-2. Preparation of polyimide film (Preparation of polyimide films 1 to 15)
The polyamic acid varnish prepared above was applied onto a glass substrate with a doctor blade to form a coating film of the varnish. The laminate consisting of the substrate and the varnish coating was placed in an inert oven. After that, the oxygen concentration in the inert oven was controlled to 100 ppm or less, and the atmosphere in the oven was heated from 50°C to 350°C over 2 hours and 30 minutes (heating rate: 2°C/min). held for time. After heating, the sample was naturally cooled under an inert atmosphere and then immersed in distilled water to peel off a polyimide film having a thickness of 9 to 12 μm from the substrate.

2-3. Evaluation For the prepared polyimide film, (1) thermal properties (linear thermal expansion coefficient (CTE) and tan δ), (2) optical properties (total light transmittance, b ^* value, birefringence Δn), (3) mechanical properties (Tensile strength, elongation and MIT folding endurance) were measured by the following methods.

(1) Thermophysical properties (tan δ of DMA (dynamic viscoelasticity measurement))
Using RSA-III manufactured by TA Instruments, a sample with a width of 5 mm and a length of 20 mm was measured in a nitrogen atmosphere at a temperature of 25 to 450 ° C., a temperature increase rate of 3 ° C./min, a frequency of 1 Hz, and an initial load per cross-sectional area. The dynamic viscoelasticity was measured under the measurement condition of 0 kg/cm ² to obtain the loss tangent (value obtained by dividing the loss elastic modulus by the storage elastic modulus, tan δ).

(Coefficient of linear thermal expansion (CTE))
After attaching a test piece (width 5 mm, length 20 mm) to the TMA device, under a nitrogen atmosphere, with a load of 100 mN, the temperature was raised once from room temperature to 300 ° C. at 5 ° C./min (1st run), then 50 After removing the residual stress accumulated in the test piece by lowering the temperature to ℃ or less, and raising the temperature again at 5 ℃ / min to 450 ℃ (2nd run), the TMA elongation ratio in the temperature range of 100 to 350 ℃, The coefficient of linear thermal expansion (CTE) was used.
A CTE of 35 ppm/K or less was judged to be acceptable.

(2) Optical properties (total light transmittance)
The total light transmittance (TT) of the obtained polyimide film was measured with a light source D65 according to JIS-K7361 using a haze meter NDH2000 manufactured by Nippon Denshoku Industries.

(Light transmittance at a wavelength of 450 nm)
Using Multi spec-1500 manufactured by Shimadzu Corporation, UV-visible spectrum measurement in the wavelength range of 300 to 800 nm was performed, and the transmittance of light with a wavelength of 450 nm was obtained as T@450 nm.

(b ^* value)
For the obtained polyimide film, a tristimulus value direct-reading colorimeter (Colour Cute i CC-i type) manufactured by Suga Test Instruments Co., Ltd. is used, and the b ^* value in the L ^* a ^* b ^* color system, which is an indicator of yellowness. was measured in transmission mode 0° di.
If the b ^* value was 8 or less, it was judged to be within the allowable range.

(Birefringence Δn)
Using a Metricon prism coupler (model 2010), a laser beam with a wavelength of 633 nm is incident on the sample through a coupling prism, and the refractive index (nTE) in TE polarized light and the refractive index (nTM) in TM polarized light are measured, Birefringence was calculated by subtracting nTM from nTE.

(3) Mechanical properties (tensile strength, tensile elongation)
A dumbbell-shaped punched test piece was prepared from the obtained polyimide film, and measured with a tensile tester (EZ-S, manufactured by Shimadzu Corporation) under the conditions of a marked line width of 5 mm, a sample length of 30 mm, and a tensile speed of 30 mm/min. gone. From the obtained stress-strain curve, the strength and elongation at the breaking point were defined as tensile strength (TS) and tensile elongation (EL), respectively, and the average value of five measurements was adopted.

(MIT folding endurance (bending endurance))
The polyimide film prepared above was cut into a shape of length 120 mm×width 15 mm to obtain a test piece.
One end of this test piece is set in an MIT folding endurance tester (307 type) manufactured by Yasuda Seiki Seisakusho, and the other end is held, with a curvature radius of 0.38 mm, a load of 0.5 kg, and a bending angle of 270 degrees (left and right 135 degree), and the bending rate was 175 times/minute, and the number of times until breakage was measured. The measurement conditions were as follows.
(Measurement condition)
Bending radius: R = 0.38 mm
Load: 0.5kgf
Bending angle: 270° (left and right 135°)
Bending speed: 175 times/min Number of tests: n = 3
In addition, at the time of the test, the bending of the test piece to one side was counted as one time. Three test pieces were tested, and the arithmetic mean value of these test results was rounded to the nearest two digits to obtain the folding endurance measurement result. Moreover, the upper limit of the folding endurance measurement result was set to 1,000,000 times.
If the number of times until breakage was 10,000 times or more, it was judged to be acceptable.

Table 2 shows the evaluation results of polyimide films 1 to 15.

As shown in Table 2, polyamic acid containing TFMB as a diamine, NTCDA (a1) and BPDA (a3) as tetracarboxylic dianhydrides, and the total amount of NTCDA and PMDA (a1 + a2) is within a predetermined range. It can be seen that the polyimide films obtained from varnishes 2, 3 and 5-15 can achieve both low CTE and high flexibility while maintaining a low b ^* value.

In contrast, polyimide films obtained from polyamic acid varnishes 1 and 15, in which the tetracarboxylic dianhydride contains NTCDA (a1) but does not contain both PMDA (a2) and BPDA (a3), have poor flexibility. I understand. It is also found that the polyimide film obtained from the polyamic acid varnish 13 in which the tetracarboxylic dianhydride is composed only of PMDA (a2) has poor flexibility. Moreover, it can be seen that the polyimide film obtained from the polyamic acid varnish 4 in which the tetracarboxylic dianhydride does not contain BPDA (a3) has poor flexibility.

3. test 2
3-1. Preparation of polyimide film Using the polyamic acid varnish shown in Table 3, a glass substrate (non-alkali glass, OA11 made by NEG, thickness 0.5 mm) was spin-coated and placed in an inert oven (manufactured by Koyo Thermo Systems, model INH21CD). ) is used to adjust the oxygen concentration in the chamber to 20 ppm or less, and the glass substrate and the polyimide resin having a thickness shown in Table 3 or 4 are baked under the following conditions A) or B). A laminate of membranes (polyimide films) was produced.
Condition A) The temperature was raised from 50°C to 430°C at a temperature elevation rate of 2°C/min, and the temperature was maintained at 430°C for 30 minutes. Condition B) The temperature was raised from 50°C to 450°C at a temperature elevation rate of 2°C/min. Hold at 450°C for 30 minutes

3-2. Evaluation (1) Thermophysical properties, (2) Optical properties and (3) Mechanical properties The obtained laminate was immersed in distilled water, and the polyimide film was peeled off from the glass substrate. (1) Thermophysical properties (CTE and tan δ), (2) Optical properties (T @ 450 nm, total light transmittance, b ^* value), (3) Mechanical properties (tensile strength, tensile elongation, tensile Elastic modulus and MIT folding endurance) were measured in the same manner as above.

Table 3 shows the evaluation results of the polyimide film produced under condition A), and Table 4 shows the evaluation result of the polyimide film produced under condition B). In Tables 3 and 4, "-" indicates unmeasured.

As shown in Tables 3 and 4, TFMB as a diamine, NTCDA (a1) and BPDA (a3) as tetracarboxylic dianhydrides, and the total amount of NTCDA and PMDA (a1 + a2) is within a predetermined range The polyimide films obtained from polyamic acid varnishes 5, 6, 8, 15 (examples) had lower b ^* values than the polyimide films obtained from polyamic acid varnish 1 (comparative example), and polyamic acid varnish 15 (comparative It can be seen that the CTE is lower than that of the polyimide film obtained from Example). Among them, the polyimide film obtained from polyamic acid varnish 6 had an MIT folding endurance of more than 1,000,000 times, showing excellent flexibility.

4. test 3
Some of the laminates obtained under the condition A) were evaluated for the LLO peel test and the properties after the LLO peel test.

(1) LLO peeling test Using the glass substrate side of the laminate obtained under the above condition A), a UV solid-state laser peeling device (LSL40F manufactured by Optopia, wavelength: 355 nm, beam size: 45 mm × 0.4 mm, depth of focus: ±1 mm, laser repetition: 20 Hz, beam overlap: 50%).

(2) Properties after LLO Peeling The film after LLO peeling was subjected to UV-visible spectrum measurement in the wavelength range of 300 to 800 nm using Multi spec-1500 manufactured by Shimadzu Corporation. Then, the average transmittance (Tavg.%) converted to a thickness of 10 μm at a wavelength of 390 to 800 nm before and after LLO peeling was applied to the following formula to obtain the rate of change before and after LLO peeling.
Change rate (%) = {(Tavg.% after LLO peeling) - (Tavg.% before LLO peeling) / (Tavg.% before LLO peeling)} × 100
Note that the Tavg. % was calculated in the same manner as above using Multi spec-1500 manufactured by Shimadzu Corporation for the polyimide film produced in the evaluation of 3-2 above.

Furthermore, the mechanical properties (tensile strength, tensile elongation and tensile modulus) of the film after LLO peeling were measured in the same manner as above.

These evaluation results are shown in Table 5.

In the LLO peeling test, it was found that any polyimide film can be peeled off with an irradiation energy of 135 to 150 mJ/cm ² .
In addition, although there was concern about damage to the polyimide film due to laser irradiation, as shown in Table 5, no significant decrease in the rate of change in average transmittance of the film after LLO peeling was observed. Furthermore, as shown by comparing Tables 5 and 3, no significant deterioration in mechanical properties was observed in the tensile test. These results also confirmed that good LLO resistance was exhibited.

This application claims priority based on Japanese Patent Application No. 2021-130236 filed on August 6, 2021. All contents described in the specification of the application are incorporated herein by reference.

The polyamic acid compositions of the present disclosure can impart polyimide films with both sufficiently low thermal expansion and bending resistance without increasing the b ^* value. Such films are applicable to substrates for various electronic devices.

Claims

A polyamic acid composition containing a polyamic acid,
The polyamic acid includes a structural unit derived from a tetracarboxylic dianhydride and a structural unit derived from a diamine,
The tetracarboxylic dianhydride is
a compound represented by formula (a1);
a compound represented by formula (a2) and/or a compound represented by formula (a3);
including

(In formula (a1),
R 1 and R 2 are each independently an alkyl group having 1 to 4 carbon atoms,
m and n are each an integer of 0 to 2, and m+n is 3 or less)

(In formula (a3),
R 3 and R 4 are each independently an alkyl group having 1 to 4 carbon atoms,
o and p are each an integer of 0 to 3, and o+p is 3 or less)
The diamine contains a compound represented by formula (b1),

The content of the compound represented by the formula (a1) is 10 mol% or more with respect to the total amount of the tetracarboxylic dianhydride,
The total amount of the compound represented by the formula (a1) and the compound represented by the formula (a2) is 30 to 80 mol% with respect to the total amount of the tetracarboxylic dianhydride.
A polyamic acid composition.
The tetracarboxylic dianhydride contains the compound represented by the formula (a3),
The polyamic acid composition according to claim 1.
The content of the compound represented by the formula (a3) is 10 to 70 mol% with respect to the total amount of the tetracarboxylic dianhydride.
3. The polyamic acid composition according to claim 2.
The content of the compound represented by the formula (a1) is greater than the content of the compound represented by the formula (a2).
The polyamic acid composition according to claim 1.
The content of the compound represented by the formula (a1) is 30 to 80 mol% with respect to the total amount of the tetracarboxylic dianhydride.
The polyamic acid composition according to claim 1.
The total amount of the compound represented by the formula (a2) and the compound represented by the formula (a3) is 10 to 70 mol% with respect to the total amount of the tetracarboxylic dianhydride.
The polyamic acid composition according to claim 1.
The tetracarboxylic dianhydride further comprises a compound represented by formula (a4), or

The diamine further comprises a compound represented by formula (b2),

(In formulas (a4) and (b2),
R 5 , R 6 , R 7 and R 8 are each independently an alkyl group having 1 to 4 carbon atoms,
q, r, s and t are each an integer from 0 to 3, and q+r and s+t are each 3 or less)
The polyamic acid composition according to claim 1.
The total amount of the compound represented by the formula (a4) and the compound represented by the formula (b2) is 0.5 to 15 mol% with respect to the total of the diamine and the tetracarboxylic dianhydride.
The polyamic acid composition according to claim 7.
The content of the compound represented by the formula (b1) is 80 mol% or more with respect to the total amount of the diamine.
The polyamic acid composition according to claim 1.
When the polyamic acid composition is thermally imidized at 350 ° C. to form a polyimide film having a thickness of 10 μm, the b * value in the L * a * b * color system is 8.0 or less.
Polyamic acid composition according to any one of claims 1 to 9.
When the polyamic acid composition is thermally imidized at 350° C. to form a polyimide film having a thickness of 10 μm, the folding endurance in the MIT folding endurance test measured in accordance with JIS P8115 is 10,000 times or more.
Polyamic acid composition according to any one of claims 1 to 9.
A polyimide composition comprising a polyimide,
The polyimide includes a structural unit derived from a tetracarboxylic dianhydride and a structural unit derived from a diamine,
The tetracarboxylic dianhydride is
a compound represented by formula (a1);
a compound represented by formula (a2) and/or a compound represented by formula (a3);
including

(In formula (a1),
R 1 and R 2 are each independently an alkyl group having 1 to 4 carbon atoms,
m and n are each an integer of 0 to 2, and m+n is 3 or less)

(In formula (a3),
R 3 and R 4 are each independently an alkyl group having 1 to 4 carbon atoms,
o and p are each an integer of 0 to 3, and o+p is 3 or less)
The diamine contains a compound represented by formula (b1),

The content of the compound represented by the formula (a1) is 10 mol% or more with respect to the total amount of the tetracarboxylic dianhydride,
The total amount of the compound represented by the formula (a1) and the compound represented by the formula (a2) is 30 to 80 mol% with respect to the total amount of the tetracarboxylic dianhydride.
Polyimide composition.
The linear thermal expansion coefficient at 100 to 350 ° C. when made into a film is -10 to 30 ppm / K.
13. The polyimide composition of claim 12.
When made into a film, the birefringence Δn in the thickness direction at a wavelength of 633 nm is 0.19 or less.
14. The polyimide composition according to claim 12 or 13.
comprising the polyimide composition of claim 12 or 13,
polyimide film.
The folding endurance number of the MIT folding endurance test measured in accordance with JIS P8115 is 10,000 times or more.
The polyimide film according to claim 15.
The b * value in the L * a * b * color system is 16 or less,
The polyimide film according to claim 15.
comprising the polyimide film of claim 17,
display panel substrate.