JP7728898B2 - Polyamic acid composition and transparent polyimide film using the same - Google Patents

Description

The present invention relates to a polyamic acid composition containing a terminal monomer having a specific structure, a polyamic acid formed using the polyamic acid composition, and a transparent polyimide film.

Polyimide (PI) is generally produced by solution polymerization of an aromatic acid dianhydride and an aromatic diamine or aromatic diisocyanate to prepare a polyamic acid derivative, and then
Polyimide resins are highly heat-resistant resins produced by cyclization dehydration at high temperatures and imidization. Such polyimide resins are insoluble and infusible, and have excellent thermal oxidation resistance, heat resistance, radiation resistance, and other properties.
Due to its excellent low-temperature properties and chemical resistance, it is used in a wide range of fields, including advanced heat-resistant materials such as automotive materials, aviation and spacecraft materials, and electronic materials such as insulating coating agents, insulating films, semiconductors, and LCD electrode protective films.

However, polyimide (PI) resins are colored brown or yellow due to the high density of aromatic rings and have low transmittance in the visible light region, making them unsuitable for use in fields requiring transparency. Recently, colorless and transparent polyimide films have been developed, but these have a higher coefficient of thermal expansion (CTE) than existing polyimide resins and lower solvent resistance.
Therefore, when colorless and transparent polyimides are used for substrates, optical coatings, and films, they are prone to warping and distortion due to their high thermal expansion coefficient. Therefore, to be used as a display material, it is necessary to ensure that the polyimide film has excellent optical and mechanical properties.

Consequently, there is a need for polyamic acid-forming compositions that exhibit high transparency, low yellowness, and excellent mechanical properties.

The present invention has been devised to solve the above-mentioned problems, and aims to provide a polyamic acid composition containing a monomer having a specific chemical structure that can cap the ends of polyamic acid.

The present invention also provides a polyamic acid formed from the above-mentioned polyamic acid composition and including a terminal-capped structure, and a polymerizable compound obtained by imidizing the polyamic acid,
The object of the present invention is to provide a transparent polyimide film that can simultaneously achieve excellent optical and mechanical properties.

In order to achieve the above object, the present invention provides a polyamic acid composition comprising a polyamic acid and a compound represented by the following Chemical Formula 1 or 2:

(In the above Chemical Formulas 1 and 2,
rings A and B are the same or different and are each independently selected from the group consisting of a C ₃ to C ₃₀ monocyclic aliphatic ring, a C ₃ to C ₃₀ polycyclic aliphatic ring, a C ₆ to C ₃₀ monocyclic aromatic ring, and a C ₆ to C ₃₀ polycyclic aromatic ring;
The monocyclic aliphatic ring, polycyclic aliphatic ring, monocyclic aromatic ring, and polycyclic aromatic ring of rings A and B are substituted or unsubstituted with one or more substituents selected from the group consisting of halogen, cyano group, _C1 - _C10 alkyl group, and _C1 - _C10 haloalkyl group.

The present invention also provides a polyamic acid formed using the above-described polyamic acid composition.

Furthermore, the present invention provides a transparent polyimide film formed by imidizing the above-mentioned polyamic acid composition.

The polyamic acid composition according to the present invention uses a terminal monomer having a specific chemical structure together with a polyamic acid, thereby enabling the production of a transparent polyimide film having a linear structure, high light transmittance, and low yellowness, without deteriorating its excellent mechanical properties.

Such transparent polyimide films have excellent optical and mechanical properties, and are therefore
It can be applied to various fields such as flexible display substrates, cover substrates, protective films, etc.

The effects of the present invention are not limited to the above description, and various other effects are included in the present specification.

The present invention will be described in detail below. However, these are merely examples of the present invention, and the present invention is not limited by these examples, but is defined by the scope of the claims set forth in this specification.

<Polyamic Acid Composition>
The polyamic acid composition of the present invention is a precursor composition for forming a polyamic acid (specifically, an end-capped polyamic acid) for producing a transparent polyimide film, and is characterized by including a compound represented by Chemical Formula 1 or Chemical Formula 2.

Specifically, the polyamic acid composition includes (a) a polyamic acid (hereinafter referred to as a "first polyamic acid") and (b) a compound represented by Chemical Formula 1 or Chemical Formula 2.

The compound represented by Chemical Formula 1 or Chemical Formula 2 is a terminal monomer capable of capping at least one of both ends of a first polyamic acid, and has a halogen element (
The first polyamic acid contains at least one of the following: an electron-withdrawing group (EWG) such as an alkyl group (F, Cl, Br, I), a cyano group (—CN) or a haloalkyl group (for example, _—CF 3 ), an alkyl group, or an aliphatic ring compound structure.
By bonding together, the optical, mechanical, and thermal properties of the polyimide can be improved.

Generally, polyimide films are not colorless but dark brown in color, which is due to the imide (im
CTC (Charge Transfer Complement) of π electrons present in the chain
However, in the present invention, the inclusion of the compound of Formula 1 or Formula 2 not only removes unreacted materials but also restricts the movement of π electrons or inhibits the formation of a π electron resonance structure, thereby making it possible to produce a polyimide having high light transmittance and low yellowness without deteriorating its excellent mechanical properties.

In particular, the compound of Formula 1 or Formula 2 has a halogen element (F, Cl, Br) in the molecule.
, I) or an electron-withdrawing group (EWG) such as a cyano group (—CN) or a haloalkyl group (for example, —CF ₃ ), restricts the movement of π electrons, thereby forming a CT-Complex (Ch
In addition, the ion exchange transfer complex (ESC) effect is suppressed.
Or, when the compound of formula 2 contains an aliphatic ring moiety and an alkyl group in the molecule, π
Since the formation of an electron resonance structure can be inhibited, the CT-Complex effect is suppressed. In this way, the present invention not only removes unreacted substances at the polyamic acid or polyimide terminals, but also suppresses the CT-Complex effect, thereby improving the optical properties of the polyimide.

Furthermore, the polyamic acid composition of the present invention may contain phenyl-based, amide-based
When a monomer such as a cycloaliphatic or cycloaliphatic monomer is used, polyamic acids and polyimides having a linear rigid structure can be formed. Such polyamic acids and polyimides are less susceptible to decomposition by heat or light and are more stable against external impacts, and therefore have excellent optical, thermal, and mechanical properties (modulus and strength).

Furthermore, the polyamic acid composition of the present invention is a polyamic acid composition containing a cardo-based, ether-based,
When a monomer such as a mer-based or sulfone-based monomer is used, polyamic acid and polyimide having a highly flexible structure can be formed.
Such polyamic acid and polyimide have excellent restoring force due to their high flexural properties,
It is more stable to folding and therefore has excellent optical, thermal and mechanical properties before the yield point.

The polyamic acid composition of the present invention contains the compound represented by Chemical Formula 1 or Chemical Formula 2.

In particular, when the first polyamic acid in the polyamic acid composition of the present invention contains more moieties derived from an acid dianhydride than from a diamine, the polyamic acid composition of the present invention may contain the compound represented by Formula 1. In this case,
The content of the compound represented by the chemical formula 1 is about 0.
The total dianhydride content can range from 0.1 to 10 mole %, where total dianhydride refers to the one or more dianhydrides used to form the first polyamic acid.

In addition, when the first polyamic acid in the polyamic acid composition of the present invention contains more moieties derived from diamine than moieties derived from acid dianhydride, the polyamic acid composition of the present invention can contain a compound represented by Chemical Formula 2. In this case,
The content of the compound represented by the formula 2 is about 0.0% by mole based on 100% by mole of the total diamines.
It can range from 1 to 10 mole percent, where total diamine means the one or more diamines used to form the first polyamic acid.

In the compounds of Chemical Formula 1 and Chemical Formula 2, rings A and B are the same or different and each independently represent a C ₃ to C ₃₀ monocyclic aliphatic ring, a C ₃ to C ₃₀ polycyclic aliphatic ring,
It is selected from the group consisting of a C ₆ to C ₃₀ monocyclic aromatic ring and a C ₆ to C ₃₀ polycyclic aromatic ring, and specifically, a C ₃ to C ₂₀ monocyclic aliphatic ring, a C ₃ to C ₂₀ polycyclic aliphatic ring, a C ₆ to C ₂
The aromatic rings are selected from the group consisting of C6- _C20 monocyclic aromatic rings, _C6 - _C20 polycyclic aromatic rings, and C6-C20 monocyclic aromatic rings. In this case, the rings in the polycyclic rings may be the same or different. For example, rings A and B may be the same or different and each independently be a benzene ring or a cyclohexane ring.

The monocyclic aliphatic ring, polycyclic aliphatic ring, monocyclic aromatic ring, and polycyclic aromatic ring of the rings A and B each independently represent a halogen, a cyano group, a C ₁ to C ₁₀ alkyl group, or a C ₁ to C ₁₀
and haloalkyl groups. As an example, the monocyclic aliphatic ring, polycyclic aliphatic ring, monocyclic aromatic ring, and polycyclic aromatic ring of rings A and B are each independently selected from the group consisting of halogen, cyano group, —CH ₃ , and —CF ₃ .

In particular, when the rings A and B are monocyclic aliphatic rings or polycyclic aliphatic rings, any hydrogen atom in each ring may be substituted with a C ₁ to C ₁₀ alkyl group. In this case, the compound of Chemical Formula 1 or Chemical Formula 2 can inhibit the formation of a π-electron resonance structure and form a CT-Complex (Chain
The ion exchange transfer complex (EOC) effect is suppressed.

Furthermore, when rings A and B are monocyclic aromatic rings or polycyclic aromatic rings, any hydrogen atom in each ring may be substituted with one or more substituents selected from the group consisting of halogen, cyano group, and _C1 - _C10 haloalkyl group. In this case, the compound of Chemical Formula 1 or Chemical Formula 2 restricts the movement of π electrons, thereby suppressing the CT-Complex effect.

The compound represented by Chemical Formula 1 may be embodied as compounds represented by the following Chemical Formula 1a and Chemical Formula 1b, but is not limited thereto.

In the above formula 1a,
a is an integer from 0 to 5,
Here, when a is 0, it means that hydrogen is not substituted with the substituent R ₁₁ , and a
is an integer of 1 to 5, one or more R ₁₁ are the same or different and each independently selected from the group consisting of halogen, cyano group, C ₁ to C ₁₀ alkyl group, and C ₁ to C ₁₀ haloalkyl group, preferably selected from the group consisting of halogen, cyano group, and C ₁ to C ₁₀ haloalkyl group, more preferably selected from the group consisting of F, cyano group, and —CF ₃ .

In the above Chemical Formula 1b,
b is an integer from 0 to 5;
Here, when b is 0, it means that hydrogen is not substituted with the substituent R ₁₂ , and b
is an integer of 1 to 5, one or more R ₁₂ are the same or different and each independently selected from the group consisting of halogen, a cyano group, a C ₁ to C ₁₀ alkyl group, and a C ₁ to C ₁₀ haloalkyl group, preferably selected from the group consisting of a C ₁ to C ₁₀ alkyl group, and more preferably a methyl group (—CH ₃ ).

More specifically, the compound represented by the formula 1 is represented by the following formula 1a-1 or 1b
The compounds may be embodied in, but are not limited to, compounds represented by formula (I).

The compound represented by Chemical Formula 2 may be embodied as a compound represented by the following Chemical Formula 2a or 2b, but is not limited thereto.

In the above Chemical Formula 2a,
c is an integer from 0 to 4;
Here, when c is 0, it means that hydrogen is not substituted with the substituent R ₁₃ , and c
is an integer of 1 to 4, one or more R ₁₃ are the same or different and each independently selected from the group consisting of halogen, cyano group, C ₁ to C ₁₀ alkyl group, and C ₁ to C ₁₀ haloalkyl group, preferably selected from the group consisting of halogen, cyano group, and C ₁ to C ₁₀ haloalkyl group, more preferably selected from the group consisting of F, cyano group, and —CF ₃ .

In the above Chemical Formula 2b,
d is an integer from 0 to 4,
Here, when d is 0, it means that hydrogen is not substituted with the substituent R ₁₄ , and d
is an integer of 1 to 4, one or more R ₁₄ are the same or different and each independently selected from the group consisting of halogen, cyano group, C ₁ to C ₁₀ alkyl group, and C ₁ to C ₁₀ haloalkyl group, preferably selected from the group consisting of C ₁ to C ₁₀ alkyl group, more preferably -CH ₃ .

More specifically, the compound represented by the formula 2 can be represented by the following formulas 2a-1 and 2b-
The compound may be embodied in, but is not limited to, a compound represented by formula 1 or formula 2b-2.

The polyamic acid composition of the present invention contains a first polyamic acid.
The polyamic acid is obtained by solution polymerization of a first polyamic acid-forming composition containing one or more diamines and one or more acid dianhydrides, and is reactive due to the presence of an unreacted substance at at least one of both ends of the first polyamic acid.

Specifically, the first polyamic acid may include a repeating unit represented by the following Chemical Formula 3:

In the above Chemical Formula 3,
Ar ₁ is a divalent organic group derived from an alicyclic diamine or an aromatic diamine, and a plurality of Ar _1s are the same or different,
Ar ₂ is a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride, and multiple Ar _2s may be the same or different.
For example, the first polyamic acid may include a repeating unit represented by the following Chemical Formula 4 or Chemical Formula 5.

In Chemical Formula 4 and Chemical Formula 5,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represent a divalent organic group derived from an alicyclic diamine or an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that n1+n2≧1;
m1 and m2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that m1+m2≧1.
In the above Chemical Formulas 3 to 5, Ar ₁ and Ar 2 are derived from an alicyclic or aromatic diamine.
_{Ar 11} to Ar ₁₅ can each independently be embodied by a moiety represented by Formula A:

In the above chemical formula A,
Ring Cy1 and ring Cy2 are the same or different and each independently represent a C ₄ to C ₂₀ monocyclic aliphatic ring, a C ₄ to C ₂₀ polycyclic aliphatic ring, a C ₆ to C ₂₀ monocyclic aromatic ring, or a C ₆ to C 20 polycyclic aliphatic ring.
selected from the group consisting of ₂₀ polycyclic aromatic rings;
The aliphatic ring and aromatic ring of the ring Cy1 and the ring Cy2 each independently represent a C ₁ to C ₂₀
and C ₁ -C ₂₀ haloalkyl groups;
x is 0 or 1;
Y is a single bond, —O—, —S—, —S(═O) ₂ —, —C(═O)—, or —C(═O)N.
H—, a C ₁ to C ₆ alkylene group, a C ₆ to C ₂₀ arylene group,
is selected from the group consisting of
W is a C ₁ -C ₂₀ alkylene group, a C ₁ -C ₂₀ haloalkylene group, and —SO ₂
-, preferably -(CH) ₂ -, -C(CH ₃ ) ₂ -, -C(
It is selected from the group consisting of —CF ₃ ) ₂ —, and —SO ₂ —.

In the above chemical formula A, Y can be selected from the group of substituents represented by the following structural formulas:

In the above Chemical Formulas 3 to 5, Ar ₂ and A 3 are derived from an alicyclic or aromatic acid dianhydride.
r ₂₁ to Ar ₂₅ each independently represent a C ₄ to C ₂₀ tetravalent monocyclic aliphatic ring group _;
is selected from the group consisting of a _C20 tetravalent polycyclic aliphatic ring group, a _C6 to _C40 tetravalent monocyclic aromatic ring group, and a _C6 to _C40 monocyclic tetravalent aromatic ring;
In this case, when Ar ₂ and Ar ₂₁ to Ar ₂₅ each represent a plurality of ring groups, the plurality of ring groups may be the same or different, and each ring group may be -C(=O)-, -C(=O)NH-, -C(
═O)—O—, —S(═O) ₂ —, —S—, —O—, a C ₁ to C ₆ alkylene group, and C
They may or may not be linked to each other by one or more linking groups selected from the group consisting of ₁ to _C6 haloalkylene groups.

Specifically, Ar ₂ and Ar ₂₁ to Ar ₂₅ can each independently be selected from the group of substituents represented by the following structural formulas.

The weight average molecular weight of the first polyamic acid according to the present invention is about 1,000 to 300,000.
0 g/mol.

The first polyamic acid is formed from a first polyamic acid-forming composition containing one or more diamines and one or more acid dianhydrides.

For example, the first polyamic acid can be obtained by dissolving one or more diamines in a solvent, and then adding one or more acid dianhydrides thereto and allowing them to react.

In the first polyamic acid-forming composition, the one or more diamines may be any compound having a diamine structure in the molecule without any particular limitation. For example,
Examples of the diamine compound include aromatic, alicyclic, or aliphatic compounds having a diamine structure. Specifically, the diamine compound may be a non-fluorinated aromatic diamine, a fluorinated aromatic diamine having a fluorine substituent introduced therein, a sulfone-based diamine, a hydroxy-based diamine, an ether-based diamine, an alicyclic diamine, or the like known in the art, which may be used alone or in combination of two or more.

Usable diamines include, for example, oxydianiline (ODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFDB), 2,
2'-dimethylbenzidine (m-Tolidine), 2,2'-bis(trifluoromethyl)-4,3'-diaminobiphenyl (2,2'-bis(trifluoromethyl)
2,2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl (2,2'-bis(trifluoromethyl)-4,3'-diaminobiphenyl)
ethyl)-5,5'-diaminobiphenyl), 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether
uromethyl)-4,4'-diaminodiphenyl etehr, 6
-FODA), bisaminohydroxyphenyl hexafluoropropane (DBOH), bisaminophenoxyphenyl hexafluoropropane (4BDAF), bisaminophenoxyphenyl propane (6HMDA), bisaminophenoxydiphenyl sulfone (DB
SDA), bis(4-aminophenyl)sulfone (4,4'-DDS), bis(3-aminophenyl)sulfone (3,3'-DDS), sulfonyldiphthalic anhydride (SO2DP
A), 4,4'-oxydianiline (4,4'-ODA), bis(carboxyphenyl)
Examples of the cyclohexane-1,4-diamine include, but are not limited to, dimethylsilane, cyclohexane-1,4-diamine, 4,4'-methylenedicyclohexaneamine, 4,4'-methylenebis(2-methylcyclohexaneamine), etc. These may be used alone or in combination of two or more.

In consideration of high transparency, high glass transition temperature, and low yellowness, the fluorinated diamine is preferably 2,2'-bis(trifluoromethyl)-4,4-dimethylaminopropanediamine, which can induce linear polymerization.
As the sulfone-based diamine, bis(4-aminophenyl)sulfone (4,4'-DDS) can be used, and as the hydroxy-based diamine, 2,2-bis(3-amino-4
-methylphenyl)-hexafluoropropane (2,2'-bis(3-amino-4
-methylphenyl) -hexafluoropropane, BIS-AT-
AF) can be used. As the ether-based diamine, 2,2'-bis(
trifluoromethyl)-4,4'-diaminophenyl ether (6-FODA), oxydianiline (ODA), or the like can be used.

Examples of diamines include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFDB), 2,2'-dimethyldibenzidine (m-Tol
idine), 2,2'-bis(trifluoromethyl)-4,3'-diaminobiphenyl (2,2'-bis(trifluoromethyl)-4,3'-diaminobiphenyl
iphenyl), 2,2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl (2,2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl
2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (2,2'-bis(trifluoromethyl)-4,4'-d
The present invention may include one or more selected from the group consisting of: ammonium nitrate, ...

In the first polyamic acid-forming composition, the one or more acid dianhydrides have, in the molecule,
Any compound having an acid dianhydride structure and well-known in the art may be used without particular limitation. Specifically, fluorinated aromatic acid dianhydrides, non-fluorinated aromatic acid dianhydrides, alicyclic acid dianhydrides, and the like well-known in the art may be used alone or in combination of two or more thereof.

The fluorinated aromatic acid dianhydride is not particularly limited as long as it is an aromatic acid anhydride into which a fluorine-containing substituent (e.g., F, —CH ₃ , etc.) has been introduced. For example, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanoic acid dianhydride (2,2-bis(3,4-d
icarboxyphenyl)hexafluoroporopane dianhydr
Ride, 6-FDA), 4-(trifluoromethyl)pyromellitic dianhydride (4-(
trifluoromethyl) pyromellitic dianhyride,
Examples of such compounds include, but are not limited to, 6-FDA and 4-TFPMDA. These compounds may be used alone or in combination of two or more. In particular, 6-FDA is a compound that is highly suitable for clarification because it has a high ability to restrict the formation of charge transfer complexes (CTCs) between and within molecular chains.

The non-fluorinated acid dianhydride is not particularly limited as long as it is an aromatic acid dianhydride to which no fluorine substituent has been introduced. For example, pyromellitic dianhydride (pyromellitic
c dianhydride, PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-biphenyl tetracarboxylic dianhydride
c acid dianhydride (BPDA), 4,4'-bisphenol A dianhydride (4,4'-bisphenol A dianhydride (BPADA), benzophenonetetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (OD
PA), etc. These may be used alone or in combination of two or more.

The alicyclic acid dianhydride is not particularly limited as long as it has an aliphatic ring instead of an aromatic ring and also has an acid dianhydride structure.
Examples include, but are not limited to, cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), bicyclo[2,2,2]-7-octene-2,3,5,6-tetracarboxylic dianhydride (BCDA), etc. These may be used alone or in combination of two or more.

Examples of the acid dianhydride include pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanoic dianhydride (2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanoic dianhydride), and
nyl) hexafluoropropane dianhyride, 6-FDA),
4,4'-bisphenol A dianhydride
hydride, BPADA), 4-(trifluoromethyl)pyromellitic dianhydride (
4-(trifluoromethyl)pyromellitic dianhydr
ide, 4-TFPMDA), cyclobutanetetracarboxylic dianhydride (CBDA), 1
, 2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), and bicyclo[
2,2,2]-7-octene-2,3,5,6-tetracarboxylic dianhydride (BCDA)
The compound may be one or more selected from the group consisting of:

In the first polyamic acid-forming composition of the present invention, the ratio (b/a) of the number of moles (b) of the acid dianhydride to the number of moles (a) of the diamine can be in the range of 0.7 to 1.3, preferably 0.8 to 1.2, and more preferably 0.9 to 1.1.

Here, when the first polyamic acid-forming composition contains more acid dianhydride than diamine, for example, when the ratio (b/a) of the number of moles of acid dianhydride (b) to the number of moles of diamine (a) is greater than about 1.0 and less than about 1.3, specifically greater than about 1.0 and less than about 1.2, more specifically greater than about 1.0 and less than about 1.1, the polyamic acid composition of the present invention may contain the compound represented by Chemical Formula 1. In this case, the content of the compound represented by Chemical Formula 1 may be in the range of about 0.01 to 10 mol % relative to 100 mol % of the total acid dianhydride.

Furthermore, when the first polyamic acid-forming composition contains more diamine than acid dianhydride, for example, when the ratio (b/a) of the number of moles of acid dianhydride (b) to the number of moles of diamine (a) is about 0.7 or more and less than 1.0, specifically about 0.8 or more and less than 1.0, more specifically about 0.9 or more and less than 1.0, the polyamic acid composition of the present invention may contain the compound represented by Chemical Formula 2. In this case, the content of the compound represented by Chemical Formula 2 may be in the range of about 0.01 to 10 mol % relative to 100 mol % of the total diamine.

The first polyamic acid-forming composition may include a solvent for solution polymerization of the monomers.

As the solvent that can be used in the present invention, organic solvents known in the art can be used without limitation, and examples thereof include, but are not limited to, m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl acetate, and dimethyl phthalate (DMP). These can be used alone or in combination of two or more. In addition, low-boiling point solvents such as tetrahydrofuran (THF) and chloroform, or solvents such as γ-butyrolactone can also be used.

In the first polyamic acid-forming composition, the content of the solvent is not particularly limited,
The solvent may be the remainder to adjust the total amount of the first polyamic acid-forming composition to 100% by weight. However, in the present invention, in order to obtain an appropriate molecular weight and viscosity of the first polyamic acid-forming composition, the content of the solvent may be about 50 to 95% by weight, specifically about 70 to 90% by weight, based on the total amount of the first polyamic acid-forming composition.
In the first polyamic acid-forming composition of the present invention, the total content of the one or more diamines and the one or more acid dianhydrides may be about 5 to 50 wt %, specifically about 10 to 30 wt %.

The composition of the first polyamic acid-forming composition is not particularly limited, and may be, for example, 2.5 to 25.0% by weight of one or more diamines relative to the total weight of the first polyamic acid composition (100% by weight).
0% by weight of one or more acid dianhydrides, about 2.5-25.0% by weight of the total composition, and
The balance of the polyamic acid-forming composition of the present invention may contain, but is not limited to, about 30 to 70 wt % of one or more acid dianhydrides and 30 to 70 wt % of one or more diamines relative to 100 wt % of the total solids.

The first polyamic acid-forming composition having the above-described structure has a viscosity of about 1,000 to 400
When the viscosity of the first polyamic acid-forming composition is within the above range, it is easy to control the thickness during coating of the polyamic acid composition of the present invention, and a uniform coating surface can be obtained.

Furthermore, the first polyamic acid-forming composition may further contain at least one additive known in the art, if necessary, within a range that does not significantly impair the objects and effects of the present invention. Examples of such additives include plasticizers, antioxidants, flame retardants, dispersants,
Examples of the additives include viscosity modifiers, leveling agents, etc. The additives are added in amounts appropriately adjusted within the ranges known in the art.

The polyamic acid composition of the present invention is prepared by using the first polyamic acid-forming composition,
After forming a first polyamic acid having at least one reactive end, the compound of Formula 1 or Formula 2 is added to a solution containing the first polyamic acid.

As an example, the polyamic acid composition includes a first polyamic acid and the compound of Chemical Formula 1. In this case, the first polyamic acid includes one or more diamine components and one or more acid dianhydrides, and the ratio of diamine (a) to acid dianhydride (b) is about 1:1 or more to 1:1.
The polyamic acid composition of the present invention is formed from a polyamic acid-forming composition containing a molar ratio of 0.1 to 0.3, and contains anhydride moieties at both ends. The polyamic acid composition of the present invention can maintain excellent mechanical properties and improve optical properties.

In another example, the polyamic acid composition includes a first polyamic acid and a polyamic acid represented by Formula 2.
In this case, the first polyamic acid contains one or more diamine components and one or more acid dianhydrides, and the diamine (a) and the acid dianhydride (b) are mixed in a ratio of about 0.7
The polyamic acid composition of the present invention is formed from a polyamic acid-forming composition containing amine moieties at both ends in a molar ratio of at least 1:1 to less than 1:1. The polyamic acid composition of the present invention can maintain excellent mechanical properties and improve optical properties.

The polyamic acid composition as described above has a viscosity of about 1,000 to 500,000 cp.
The polyamic acid composition of the present invention may have a viscosity of about 5,000 to 100,000 cps, preferably about 5,000 to 100,000 cps, in which case the thickness of the coating can be easily controlled and a uniform coating surface can be obtained.

<Polyamic acid>
The present invention provides a polyamic acid formed from the polyamic acid composition. The polyamic acid of the present invention has at least one end terminated as reactive. Therefore, when the polyamic acid of the present invention is subjected to an imide ring-closure reaction, a transparent polyimide having a linear structure and excellent mechanical and optical properties can be obtained.

Specifically, the polyamic acid is represented by the following chemical formula 6 or 7.

In Chemical Formula 6 and Chemical Formula 7,
PAA is a polyamic acid (hereinafter referred to as "first polyamic acid") derived from a solution polymerization reaction of one or more diamines and one or more acid dianhydrides, or a derivative thereof;
multiple rings A are the same or different;
multiple rings B are the same or different,
Rings A and B are defined as in Chemical Formula 1 and Chemical Formula 2.

In Formulae 6 and 7, PAA may be a group derived from a polyamic acid represented by Formula 8 or 9, but is not limited thereto.

In Chemical Formula 8 and Chemical Formula 9,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represent a divalent organic group derived from an alicyclic diamine or an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that n1+n2≧1;
m1 and m2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that m1+m2≧1.

In the above Chemical Formula 8 and Chemical Formula 9, Ar ₁₁ to Ar 12 are derived from an alicyclic or aromatic diamine.
Specific explanations regarding Ar ₁₅ and Ar ₂₁ to Ar ₂₅ derived from an alicyclic or aromatic acid dianhydride are the same as those in Chemical Formula 4 and Chemical Formula 5, respectively, and therefore will not be repeated.

In a preferred embodiment of the present invention, the polyamic acid may be embodied as a polyamic acid represented by any one of the following Formulas 10 to 13, but is not limited thereto.

In the above Chemical Formulas 10 to 13,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represent a divalent organic group derived from an alicyclic diamine or an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that n1+n2≧1;
m1 and m2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that m1+m2≧1.

a and b are each an integer from 0 to 5, c and d are each an integer from 0 to 4,
R ₁₁ to R ₁₄ are the same or different and each independently represent a halogen, a cyano group, a C ₁
The alkyl group is selected from the group consisting of C 1 -C ₁₀ alkyl groups, and C ₁ -C ₁₀ haloalkyl groups.

In the above Chemical Formulas 10 to 13, Ar ₁₁ derived from an alicyclic or aromatic diamine
Specific explanations regarding Ar ₁₅ to Ar ₁₆ and Ar 21 to Ar ₂₅ derived from an alicyclic or aromatic acid dianhydride are the same as those in Chemical Formula 4 and Chemical Formula 5, respectively, and therefore will not be repeated.

<Transparent polyimide film>
The present invention also provides a transparent polyimide film prepared by imidizing the polyamic acid composition, in which the reactivity of at least one of both ends is terminated, resulting in a polyimide film having excellent mechanical and optical properties and a linear structure.

Specifically, the polyimide of the transparent polyimide film is represented by the following formula 14 or formula 1:
5 is shown.

In Formula 14 and Formula 15, PI is a group derived from a polyimide formed by imidizing a polyamic acid or a derivative thereof derived from a reaction between a diamine and an acid dianhydride;
multiple rings A are the same or different;
multiple rings B are the same or different,
Rings A and B are defined as in Chemical Formula 1 and Chemical Formula 2, respectively.

In Formula 14 and Formula 15, PI is a polymer moiety containing an imide ring, and is a random copolymer well known in the art.
The polymer may be in the form of a copolymer or a block copolymer.

Specifically, in Formula 14 and Formula 15, PI may be a group derived from polyimide represented by Formula 16 and Formula 17 below, but is not limited thereto.

In the above Chemical Formula 16 and Chemical Formula 17,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represent a divalent organic group derived from an alicyclic diamine or an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that n1+n2≧1;
m1 and m2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that m1+m2≧1.

In the above Chemical Formula 16 and Chemical Formula 17, Ar ₁ derived from an alicyclic or aromatic diamine
Specific explanations regarding _{Ar 1} to Ar ₁₅ and Ar ₂₁ to Ar ₂₅ derived from an alicyclic or aromatic acid dianhydride are the same as those in Chemical Formula 4 and Chemical Formula 5, respectively, and therefore will not be repeated.

In a preferred embodiment of the present invention, the polyimide may be embodied as a polyimide represented by any one of the following Chemical Formulas 18 to 21, but is not limited thereto.

In the above Chemical Formulas 18 to 21,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represent a divalent organic group derived from an alicyclic diamine or an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that n1+n2≧1;
m1 and m2 each represent an integer of 1 or greater, specifically an integer of 1 to 10,000, more specifically an integer of 1 to 1,000, provided that m1+m2≧1;
a and b are each an integer from 0 to 5, c and d are each an integer from 0 to 4,
R ₁₁ to R ₁₄ are the same or different and each independently represent a halogen, a cyano group, C
The alkyl group is selected from the group consisting of _{C 1} to C ₁₀ alkyl groups, and C ₁ to C ₁₀ haloalkyl groups.

In the above Chemical Formulas 18 to 21, Ar ₁₁ derived from an alicyclic or aromatic diamine
Specific explanations regarding Ar ₁₅ to Ar ₁₆ and Ar 21 to Ar ₂₅ derived from an alicyclic or aromatic acid dianhydride are the same as those in Chemical Formula 4 and Chemical Formula 5, respectively, and therefore will not be repeated.

As described above, in the present invention, the structural formulas of polyamic acids and polyimide resins using the same have been described in detail using Chemical Formula 6 to Chemical Formula 21. However, the present invention is not limited to the above structural formulas, and there are no particular limitations on the structure and form of polyamic acids and polyimide resins, and they may be variously modified as long as they contain a terminal monomer represented by Chemical Formula 1 or Chemical Formula 2 of the present invention and the reactivity of either one of the terminals is capped.

The polyimide film according to the present invention can be produced by subjecting a transparent polyamic acid composition (for example, a polyamic acid-containing solution) to an exothermic solution polymerization reaction according to a conventional method well known in the art.

For example, the polyamic acid composition is coated (cast) on a support, and then the temperature is gradually increased within a range of about 30 to 350° C., and the imide ring-closing reaction (i
In this case, it is preferable to carry out the reaction under an inert atmosphere such as argon or nitrogen.

The coating method may be any method known in the art, without limitation. For example, spin coating, dip coating, etc.
The transparent polyamic acid composition can be coated one or more times to form a colorless and transparent polyimide layer having a thickness of several hundred nanometers to several tens of micrometers.

In the method for producing a polyimide film according to the present invention, the imidization method used in the step of casting a polymerized polyamic acid on a support and imidizing it may be a thermal imidization method, a chemical imidization method, or a combination of the thermal imidization method and the chemical imidization method.

In the thermal imidization method, the polyamic acid composition is cast on a support and heated for 30 to 400
This method involves gradually increasing the temperature within the range of 0.5 to 10 degrees Celsius for 1 to 10 hours to obtain a polyimide film.

The chemical imidization method is a method in which a dehydrating agent, such as an acid anhydride such as acetic anhydride, and an imidization catalyst, such as an amine, such as isoquinoline, β-picoline, or pyridine, are added to a polyamic acid composition. When the thermal imidization method or the thermal imidization method is used in combination with the chemical imidization method, the heating conditions for the polyamic acid composition may vary depending on the type of polyamic acid composition, the thickness of the polyimide film to be produced, and the like.

To explain in more detail an example of producing a polyimide film using the thermal imidization method and the chemical imidization method in combination, a dehydrating agent and an imidization catalyst are added to a polyamic acid composition, the mixture is cast on a support, and then heated at 80 to 300°C, preferably 150 to 250°C, to activate the dehydrating agent and the imidization catalyst, thereby partially curing and drying the mixture, and a polyimide film is obtained.

The thickness of the polyimide film thus formed is not particularly limited and may be appropriately adjusted depending on the application field, and may be, for example, in the range of about 10 to 150 μm, preferably about 10 to 80 μm.

The transparent polyimide resin film according to the present invention can be applied in various fields, and specifically, is used as a substrate or a protective film for flexible displays, etc. In order to be used in displays, etc., it is basically necessary for the film to have high transparency, low yellowness index, and excellent mechanical properties at the same time. Specifically, when the film thickness is 10 μm, the film is required to have a light transmittance of 88% or more at 550 nm and a yellowness index of 7 or less at 550 nm. In addition, the film is required to have a thickness of 10 μm, and a thickness of 10 μm when used in thin film transistors (TFTs).
To ensure reliability in the deposition process, the polyimide on the support (glass substrate) must have sufficient adhesive strength to prevent it from peeling off from the glass substrate during the process.

In fact, the polyimide film of the present invention, which is produced by imidizing a polyamic acid composition, exhibits high transparency, low yellowness, and simultaneously has high tensile strength and elastic modulus. More specifically, the polyimide film satisfies the physical properties (i) to (iv) described below: (i) a light transmittance of 88% or more at a wavelength of 550 nm; (ii) a light transmittance of 88% or more at a wavelength of 550 nm; and (iii) a light transmittance of 88% or more at a wavelength of 550 nm according to ASTM E31
(iii) the yellow index according to the JIS No. 3 standard is 3.5 or less;
The material satisfies the physical property requirements of (iv) a tensile strength of 100 MPa or more in accordance with ISO 527-3 standard and (iv) a modulus of elasticity of 3.5 GPa or more.

The transparent polyimide film of the present invention having the above-described physical properties is particularly useful in fields requiring high transparency and mechanical properties, for example, but not limited to, flexible display substrates such as organic light-emitting diode (OLED) displays, liquid crystal display (LCD) displays, TFT substrates, flexible printed circuit boards, flexible OLED surface lighting substrates, and substrate materials for electronic paper, as well as cover substrates and/or protective films.

The present invention will be described in detail below with reference to specific examples. The examples described below are merely illustrative examples to aid in understanding the present invention, and are not intended to limit the scope of the present invention.

[Example 1]
1-1. Preparation of polyamic acid composition In a 500 ml three-necked round-bottom flask, 163 ml of N,N-dimethylacetamide (DMAc) was added.
After charging 568 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), 15.0 g (100 mol%) was added.
After adding the TFDB, the TFDB was stirred for 1 hour to completely dissolve it.
,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) 11.025 g (
80 mol%), and 2.761 g (1
After 1 hour, 0.158 g (1 mol %) of a compound of Formula 2b-2 was added to the reactor and cooled to 30° C. to dissolve the compound.

1-2. Preparation of Transparent Polyimide Film The transparent polyamic acid composition obtained in Example 1-1 was coated on a glass plate for LCD using a bar coater, and then heated in a convection oven in a nitrogen atmosphere at 80°C for 30 minutes, 150°C for 30 minutes, 200°C for 1 hour, and 300°C for 1 hour.
The temperature was gradually increased stepwise while drying and imidization were carried out to produce a transparent polyimide film (imidization rate: 85% or more, film thickness: 52 μm). Next, the polyimide film was separated from the glass plate.

[Example 2]
2-1. Preparation of polyamic acid composition After 162.814 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (100 mol %) of TFDB was added, followed by stirring for 1 hour.
The TFDB was stirred to completely dissolve. Next, 11.025 g (
After 1 hour, 0.472 g (3 mol%) of the compound of Formula 2b-2 was added to the reactor.
1%) was added, and then the mixture was cooled to 30°C to dissolve.

2-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 2-1 was used instead of the polyamic acid composition used in Example 1-2.

[Comparative Example 1]
1-1. Preparation of polyamic acid composition After 163.945 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (100 mol %) of TFDB was added, followed by stirring for 1 hour.
The TFDB was stirred to completely dissolve. Next, 11.025 g (
80 mol %) and 2.906 g of ODPA (17 mol %) were added successively, and then the mixture was cooled to 30° C. to dissolve the mixture.

1-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Comparative Example 1-1 was used instead of the polyamic acid composition used in Example 1-2.

[Example 3]
3-1. Preparation of polyamic acid composition After 158.971 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (100 mol%) of 2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenyl ether (6FODA) was added, followed by stirring for 1 hour.
The 6FODA was stirred until completely dissolved. Next, cyclobutane-1,2,
5.249 g (60 mol%) of 3,4-tetracarboxylic dianhydride (CBDA), and 2
,2-bis(3,4-dicarboxyphenyl)hexafluoropropanoic dianhydride (6F
After 1 hour, 0.15 g (1 mol %) of the compound of Formula 2b-2 was added to the reactor, and the temperature was increased to 30° C.
The mixture was cooled to rt and dissolved.

3-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 3-1 was used instead of the polyamic acid composition used in Example 1-2.

[Example 4]
4-1. Preparation of Polyamic Acid Composition After 157.575 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50°C, and 15.0 g (100 mol%) of 6FODA was added. The 6FODA was then stirred for 1 hour to completely dissolve. Next, 5.249 g of CBDA was added to the reactor.
(60 mol%) and 7.333 g (37 mol%) of 6FDA were added in turn and reacted. After 1 hour, 0.450 g (3 mol%) of the compound of formula 2b-2 was added to the reactor.
1%) was added, and then the mixture was cooled to 30°C to dissolve.

4-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 4-1 was used instead of the polyamic acid composition used in Example 1-2.

[Comparative Example 2]
2-1. Preparation of Polyamic Acid Composition After 159.668 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50°C, and 15.0 g (100 mol%) of 6FODA was added. The 6FODA was then stirred for 1 hour to completely dissolve. Next, 5.249 g of CBDA was added to the reactor.
(60 mol %) and 7.927 g of 6FDA (40 mol %) were added successively, and then the mixture was cooled to 30° C. to dissolve.

2-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Comparative Example 2-1 was used instead of the polyamic acid composition used in Example 1-2.

[Example 5]
5-1. Preparation of polyamic acid composition 374.284 g of DMAc was charged into a 500 ml three-necked round-bottom flask, and the temperature of the reactor was raised to 50°C. 15.0 g (60 mol%) of TFDB and 10.2 g of 6FODA were added.
37 g (39 mol%) of BPADA was added sequentially to the reactor and stirred to dissolve the mixture. 40.634 g (100 mol%) of BPADA was then added to the reactor and reacted. After 1 hour, 0.358 g (1 mol%) of the compound of the following formula 1a-1 was added to the reactor.
After adding the above, the mixture was cooled to 30°C and dissolved.

5-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 5-1 was used instead of the polyamic acid composition used in Example 1-2.

[Example 6]
6-1. Preparation of polyamic acid composition 373.336 g of DMAc was charged into a 500 ml three-necked round-bottom flask, and the temperature of the reactor was raised to 50° C., and 15.0 g (60 mol %) of TFDB and 9.71 g of 6FODA were added.
2 g (37 mol %) of each of the above was added in turn, and then the mixture was stirred to dissolve.
40.634 g (100 mol%) of BPADA was added to the reactor and reacted. After 1 hour, 1.074 g (3 mol%) of the compound of Formula 1a-1 was added to the reactor and cooled to 30°C to dissolve.

6-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 6-1 was used instead of the polyamic acid composition used in Example 1-2.

[Comparative Example 3]
3-1. Preparation of polyamic acid composition After 374.758 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (60 mol%) of TFDB and 10.5 g of 6FODA were added.
0 g (40 mol %) of TFDB and 6FODA were added sequentially, and then the mixture was stirred for 1 hour to completely dissolve the TFDB and 6FODA. Next, 40.634 g (100 mol %) of BPADA was added to the reactor.
1%) was added, and then the mixture was cooled to 30°C to dissolve.

3-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Comparative Example 3-1 was used instead of the polyamic acid composition used in Example 1-2.

[Example 7]
7-1. Preparation of polyamic acid composition After 730.514 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (40 mol %) of m-Tolidine and 6FO were added.
35.040 g (59 mol%) of 6FDA was added sequentially and dissolved by stirring. Next, 78.469 g (100 mol%) of 6FDA was added to the reactor and reacted. After 1 hour, 0.810 g (1 mol%) of the compound of Formula 1a-1 was added to the reactor.
1%) was added, and then the mixture was cooled to 30°C to dissolve.

7-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 7-1 was used instead of the polyamic acid composition used in Example 1-2.

[Example 8]
8-1. Preparation of polyamic acid composition After 728.370 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (40 mol %) of m-Tolidine and 6FO were added.
33.853 g (57 mol%) of 6FDA was added to the reactor and dissolved by stirring. 78.469 g (100 mol%) of 6FDA was then added to the reactor and reacted. After 1 hour, 2.428 g (3 mol%) of the compound of formula 1a-1 was added to the reactor.
1%) was added, and then the mixture was cooled to 30°C to dissolve.

8-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Example 8-1 was used instead of the polyamic acid composition used in Example 1-2.

[Comparative Example 4]
4-1. Preparation of polyamic acid composition After 731.587 g of DMAc was charged into a 500 ml three-necked round-bottom flask, the temperature of the reactor was raised to 50° C., and 15.0 g (40 mol %) of m-Tolidine and 6FO were added.
35.634 g (60 mol%) of TFDB and 6FODA were added sequentially, and then the TFDB and 6FODA were stirred for 1 hour to completely dissolve them.
(100 mol %) was added, and then the mixture was cooled to 30° C. to dissolve the compound.

4-2. Production of Transparent Polyimide Film A colorless and transparent polyimide film was produced in the same manner as in Example 1-2, except that the polyamic acid composition obtained in Comparative Example 4-1 was used instead of the polyamic acid composition used in Example 1-2.

For reference, the compositions of the polyamic acid compositions produced in Examples 1 to 8 and Comparative Examples 1 to 4 of the present application are as shown in Tables 1 and 2. The unit of the content of each monomer is mol.
%, where diamine monomers are based on the total number of moles of diamine, dianhydride monomers are based on the total number of moles of dianhydride, and terminal monomers are based on the total number of moles of diamine or dianhydride, 100 mol %.

[Physical property evaluation]
The polyimide films produced in the above Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated for physical properties by the methods described below, and the results are shown in Table 3 below.

(1) Measurement of Light Transmittance Measurement was carried out at a wavelength of 550 nm using a UV-Vis NIR spectrophotometer (Shimadzu, model number: UV-3150).

(2) Measurement of yellowness: Using a spectrophotometer (Konica Minolta, model number: CM-3700d), the yellowness was measured according to ASTM E3
Measurements were made in accordance with the 13th standard.

(3) Measurement of Tensile Strength and Elastic Modulus Using a UTM (manufactured by Instron, model number: 5942), the tensile strength (MPa) and elastic modulus (GPa) were measured in accordance with ISO 527-3 standard.

Experimental results showed that the colorless and transparent polyimide films of the present invention containing the compound of Formula 1 or Formula 2 as a terminal monomer maintained similar modulus and tensile strength to the polyimide films of Comparative Examples 1 to 4 that did not contain a terminal monomer, while exhibiting superior light transmittance and yellowness index compared to the polyimide films of Comparative Examples 1 to 4 (see Table 3). Specifically, in the present invention, the yellowness index and light transmittance were improved without a decrease in modulus and tensile strength due to the content of the terminal monomer of Formula 1 or Formula 2. In particular, the light transmittance increased by about 2% and the yellowness index decreased by about 15% compared to the polyimide film that did not contain a terminal monomer.

From the above results, it can be seen that the polyamic acid composition of the present invention is suitable for flexible displays (F1
It was confirmed that the film can be used as a substrate and a protective film for a flexible display.

Claims (7)

a polyamic acid formed from a first polyamic acid-forming composition comprising one or more diamines selected from the group consisting of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,3'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl, bis(4-aminophenyl)sulfone, 2,2-bis(3-amino-4-methylphenyl)-hexafluoropropane, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, and oxydianiline, and one or more acid dianhydrides, wherein the ratio (b/a) of the number of moles of the acid dianhydride (b) to the number of moles of the diamine (a) is greater than 1.0 and 1.3 or less; and a compound represented by the following chemical formula 1:
A transparent polyimide film for a flexible display substrate formed by imidizing a polyamic acid composition comprising:
(i) a light transmittance of 88% or more at a wavelength of 550 nm;
(ii) a yellow index according to ASTM E313 of 3.5 or less;
(iii) The tensile strength according to the ISO 527-3 standard is 100 MPa or more;
(iv) the elastic modulus is 3.5 GPa or more;
The polyimide of the transparent polyimide film is a polymer represented by the following chemical formula 14 :
( In the above Chemical Formula 1 ,
Ring A is selected from the group consisting of C ₃ to C ₃₀ monocyclic aliphatic rings and C ₄ to C ₃₀ polycyclic aliphatic rings;
The monocyclic aliphatic ring and the polycyclic aliphatic ring of the ring A are substituted or unsubstituted with one or more substituents selected from the group consisting of halogen, a cyano group, a _C1 - _C10 alkyl group, and a _C1 - _C10 haloalkyl group.
(In the above Chemical Formula 14,
PI is a group derived from a polyimide formed by imidizing a polyamic acid or a derivative thereof derived from a reaction between a diamine and an acid dianhydride,
multiple rings A are the same or different;
Ring A is selected from the group consisting of C ₃ to C ₃₀ monocyclic aliphatic rings and C ₄ to C ₃₀ polycyclic aliphatic rings;
The monocyclic aliphatic ring and the polycyclic aliphatic ring of the ring A are substituted or unsubstituted with one or more substituents selected from the group consisting of halogen, a cyano group, a _C1 -C10 _alkyl group, and a C1 _- C10 _haloalkyl group. 2. The transparent polyimide film for a flexible display substrate according to claim 1, wherein the compound represented by Chemical Formula 1 is a compound represented by Chemical Formula 1b:
(In the above chemical formula 1b,
b is an integer from 0 to 5,
R ₁₂ are the same or different and each independently selected from the group consisting of halogen, cyano, C ₁ -C ₁₀ alkyl, and C ₁ -C ₁₀ haloalkyl. The transparent polyimide film for flexible display substrates according to claim 1, wherein the content of the compound represented by Chemical Formula 1 is in the range of 0.01 to 10 mol % relative to 100 mol % of the total acid dianhydride. 2. The transparent polyimide film for a flexible display substrate according to claim 1, wherein the polyamic acid comprises a repeating unit represented by the following Chemical Formula 3:
(In the above Chemical Formula 3,
Ar ₁ is a divalent organic group derived from an aromatic diamine, and a plurality of Ar _1s are the same or different,
_Ar2 is a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride, and multiple _Ar2s are the same or different. 2. The transparent polyimide film for a flexible display substrate according to claim 1, wherein the polyamic acid comprises a repeating unit represented by the following Formula 4 or Formula 5:
(In the above Chemical Formula 4 and Chemical Formula 5,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represents a divalent organic group derived from an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 are each an integer of 1 or more, provided that n1 + n2 ≧ 1;
m1 and m2 are each an integer of 1 or greater, provided that m1+m2≧1. 2. The transparent polyimide film for a flexible display substrate according to claim 1 , wherein PI is a group derived from polyimide represented by the following Chemical Formulas 16 and 17:
(In the above Chemical Formula 16 and Chemical Formula 17,
Ar ₁₁ to Ar ₁₅ are the same or different and each independently represents a divalent organic group derived from an aromatic diamine;
Ar ₂₁ to Ar ₂₅ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 are each an integer of 1 or more, provided that n1 + n2 ≧ 1;
m1 and m2 are each an integer of 1 or greater, provided that m1+m2≧1. 2. The transparent polyimide film for a flexible display substrate according to claim 1, wherein the polyimide of the transparent polyimide film is a polymer represented by any one of the following chemical formulas:
(In the above Chemical Formula 19,
Ar ₁₁ and Ar ₁₂ are the same or different and each independently represent a divalent organic group derived from an aromatic diamine;
Ar ₂₁ to Ar ₂₃ are the same or different and each independently represent a tetravalent organic group derived from an alicyclic acid dianhydride or an aromatic acid dianhydride;
n1 and n2 are each an integer of 1 or more, provided that n1 + n2 ≧ 1;
b is an integer from 0 to 5;
R ₁₂ is selected from the group consisting of halogen, cyano, C ₁ -C ₁₀ alkyl, and C ₁ -C ₁₀ haloalkyl.