KR102463845B1 - Polyamic acid composition having improved adherent property and trasparent polyimide film using the same - Google Patents

Abstract

The present invention provides a polyamic acid composition comprising a compound having a specific chemical structure as a diamine component, and a polyimide prepared from the composition.
Since the polyamic acid composition according to the present invention provides excellent optical properties, high adhesion properties with a glass substrate, and high thermal properties, a polyimide film using the same can be applied as a flexible display material.

Description

Polyamic acid composition with improved adhesion and polyimide film comprising the same

The present invention relates to a polyamic acid composition having improved adhesion properties on a glass substrate including a diamine-based monomer having a specific chemical structure, and a colorless and transparent polyimide film prepared from the polyamic acid composition and applicable as a flexible display substrate or a protective film.

In general, a flat panel display (FPD) such as a plasma display, a display for a liquid crystal device, a display for an organic light emitting device, etc. uses a glass substrate. As displays using such a glass substrate are gradually reduced in thickness and size, transparent plastic substrates are being studied as replacements for glass substrates.

As a transparent plastic substrate replacing the glass substrate, a substrate using a polyethylene terephthalate (PET) film or a polyether sulfone (PES) film has been developed. The transparent plastic substrate using a polymer resin such as PET or PES has good ductility compared to a glass substrate, but has a low heat resistance because of a low glass transition temperature (Tg). In addition, since the coefficient of thermal expansion (CTE) is higher than that of the glass substrate, there is a problem that deformation occurs easily by a process made at a high temperature during the display manufacturing process (eg, a thin film transistor process of 300° C. or higher). Therefore, the development of a transparent plastic substrate material having high heat resistance and low coefficient of thermal expansion while exhibiting the same transparency as a glass substrate is required, and various studies are being conducted. .

In general, polyimide (PI) has excellent mechanical, chemical, and electrical properties in addition to excellent heat resistance, so it has recently been expanded to coating materials, molding materials, and composite materials including PI. Since the polyimide resin is colored brown or yellow under the influence of a change transfer complex (CTC) and has low transmittance in the visible light region, there is a limitation in exhibiting high transparency like a glass substrate. Therefore, numerous studies are underway to solve these problems. In general, polyimide (PI) resin refers to a high heat-resistant resin produced by solution polymerization of an aromatic dianhydride and an aromatic diamine or an aromatic diisocyanate to prepare a polyamic acid derivative, followed by ring closure dehydration at a high temperature to imidize it.

As the aromatic dianhydride component for preparing the polyimide resin, pyromellitic dianhydride (PMDA) or biphenyltetracarboxylic dianhydride (BPDA) is used, and the aromatic diamine component is 2, 2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), oxydianiline (ODA), p-phenylene diamine (p-PDA), m-methylene diamine (m-MDA) , methylene diamine (MDA), bisaminophenylhexafluoropropane (HFDA), and the like are used. The polyimide made of such a dianhydride or diamine monomer has low or almost no adhesion to the glass substrate, so that the film is separated from the glass substrate during the TFT process. In addition, since the correlation between optical properties and thermal properties is in a trade-off relationship, it is necessary to develop a compound having a suitable component for each property, that is, a monomer for transparent PI. Also, there is a demand for the development of a polyamic acid composition and polyimide film for a transparent plastic substrate having excellent adhesion to a glass substrate and high thermal properties.

In the present invention, when a monomer having a specific structure and a substituent is introduced, optical properties, adhesion properties with a glass substrate, heat resistance properties, and thermal expansion coefficient properties are improved compared to the prior art.

More specifically, in the present invention, it is determined that it is effective to introduce a diamine-based monomer having a specific chemical structure and substituent in order to obtain a polyimide resin having high transparency, high adhesion, and excellent thermal properties, and the content of the diamine monomer is specified By adjusting the range, it aims to prepare a transparent polyamic acid composition and polyimide film that can simultaneously implement low YI (Yellow Index), high light transmittance, high adhesion to a glass substrate, and excellent thermal stability.

In addition, the present invention is a transparent polyamic acid composition applicable to a plastic transparent substrate for a flexible display of LCD and OLED, a TFT substrate, a flexible printed circuit board, a flexible OLED surface lighting substrate, a substrate material for electronic paper, etc. and to provide a polyimide film.

In order to achieve the above object, the present invention is (a) a diamine containing a compound represented by the following formula (1); (b) acid dianhydride; and (c) an organic solvent, wherein the compound represented by Formula 1 provides a polyamic acid composition comprising 10 to 80 mol% based on 100 mol% of the total diamine.

In Formula 1,

,

및

으로 이루어진 군으로부터 선택되며,A is a single bond, or

,

and

is selected from the group consisting of

X ₁ and X ₂ are the same as or different from each other, and are each independently selected from the group consisting of hydrogen, halogen, a C ₁ ~ C ₆ alkyl group, and a C ₁ ~ C ₆ alkyl group in which at least one hydrogen is substituted with a halogen atom, However, at least one of X ₁ and X ₂ is a halogen or a halogen atom-substituted C ₁ ~ C ₆ alkyl group,

A plurality of Y is a hydrogen-bonding functional group, each independently a hydroxyl group,

n is an integer of 1 or 2.

In the present invention, X ₁ and X ₂ may each independently be an electron withdrawing group (EWG) that is F or CF ₃ .

In the present invention, the diamine is a fluorinated first diamine; At least one selected from the group consisting of a sulfone-based second diamine, a hydroxy-based third diamine, an ether-based fourth diamine, and an alicyclic fifth diamine may be further included.

In the present invention, the content of the first fluorinated diamine, the sulfone-based diamine, the hydroxy-based third diamine, the ether-based fourth diamine and the alicyclic fifth diamine is 20 to 90 mol% based on 100 mol% of the total diamine, respectively It can be %.

In the present invention, the acid dianhydride may include at least one selected from the group consisting of a fluorinated aromatic primary acid dianhydride, an alicyclic secondary acid dianhydride, and a non-fluorinated aromatic tertiary acid dianhydride.

In the present invention, the content of at least one compound selected from the group consisting of the first acid dianhydride, the second acid dianhydride and the third acid dianhydride may be 10 to 100 mol% based on 100 mol% of the total acid dianhydride.

In the present invention, the ratio (a/b) of the number of moles of the diamine (a) and the acid dianhydride (b) may be in the range of 0.7 to 1.3.

The present invention also provides a transparent polyimide film prepared by imidizing the above-described polyamic acid composition.

In the present invention, the transparent polyimide film may satisfy the physical property conditions of the following (i) to (vi), more specifically (i) the adhesive force on the glass substrate according to ASTM D 3359 standard is 2B or more, (ii) yellowness according to ASTM E 313-73 standard is 7 or less (based on film thickness of 10 μm), (iii) light transmittance at a wavelength of 550 nm is 89% or more, (iv) glass transition temperature (T _g ) is in the range of 330 to 400 ° C, (v) the coefficient of thermal expansion (CTE) by TMA measurement is in the range of 10 to 60 ppm / ° C, (vi) the retardation in the thickness direction calculated by the following formula (R _th ) is 10 μm in thickness It may be 80 nm to 400 nm as a reference.

Phase difference R _th (nm) = [(n _{x +} n _y ) / 2 - n _z ] ×d

(n _x is the largest refractive index among the in-plane refractive indexes of the polyimide resin film measured with light having a wavelength of 550 nm; n _y is the refractive index perpendicular to n _x among the in-plane refractive indexes of the polyimide resin film measured with light having a wavelength of 550 nm ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 550 nm; d is the thickness of the polyimide film.)

In the present invention, the transparent imide film may be used as a substrate or a protective film for a flexible display.

In the present invention, it is possible to provide a polyamic acid composition having excellent optical properties, thermal properties and adhesion properties with a glass substrate by adopting a diamine monomer having a specific structure and a substituent and adjusting its content to a specific range.

In addition, in the present invention, by imidizing the polyamic acid composition having excellent optical properties, thermal properties and adhesion properties with a glass substrate and applying it as a transparent substrate, a flexible display substrate that exhibits excellent physical properties and product reliability. can

1 is a photograph showing the adhesive force evaluation result (5B) of the polyimide film prepared in Example 1.
2 is a photograph showing the evaluation (0B) of the adhesive force of the polyimide films prepared in Comparative Examples 1 to 8.

Hereinafter, the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims described in the specification.

<Transparent polyamic acid composition>

The transparent polyamic acid composition of the present invention is for preparing a transparent polyimide film, and it is characterized in that it contains the compound represented by Formula 1 as a diamine component.

More specifically, the polyamic acid composition may include (a) a diamine containing the compound of Formula 1; (b) acid dianhydride; and (c) an organic solvent.

The diamine (a) monomer used for preparing the transparent polyamic acid of the present invention includes a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

,

및

으로 이루어진 군으로부터 선택되며,A is a single bond, or

,

and

is selected from the group consisting of

X ₁ and X ₂ are the same as or different from each other, and are each independently selected from the group consisting of hydrogen, halogen, a C ₁ ~ C ₆ alkyl group, and a C ₁ ~ C ₆ alkyl group in which at least one hydrogen is substituted with a halogen atom, However, at least one of X ₁ and X ₂ is a halogen or a halogen atom-substituted C ₁ ~ C ₆ alkyl group,

A plurality of Y is a hydrogen-bonding functional group, each independently a hydroxyl group,

n is an integer of 1 or 2.

Conventional transparent polyimide (colorless polyimide) exhibits low yellowness due to the use of a fluorine-substituted monomer in the compound, but has little or low adhesion to the glass substrate due to the fluorine. Therefore, when manufacturing a display, there is a problem that the film is easily separated from the glass substrate during the Thin Film Transistor (TFT) process. In order to solve this problem, when it is attempted to improve adhesion through chemical bonding such as a silane coupling agent, haze is generated due to refractive index mismatching, thereby reducing optical properties. .

Therefore, in the present invention, in order to simultaneously improve the adhesive properties as well as excellent optical properties, a functional group capable of forming a hydrogen bond with a glass substrate, for example, at least one hydroxy group (-OH), etc. is introduced into the compound of Formula 1 with diamine ( It is characterized in that it is used as a diamine) component.

Since a large number of hydrogen-bonding functional groups such as a hydroxyl group exist on the surface even after the polyimide is cured, it is possible to significantly improve the adhesion properties of the polyimide film through the formation of hydrogen bonding with the glass substrate.

In addition, in the present invention, by introducing at least one electron withdrawing group (EWG) such as fluorine (F) or CF ₃ in Chemical Formula 1, the optical properties and thermal properties described above can be further improved. More specifically, the polyimide film is not colorless but dark brown, because of the Charge Transfer Complex (CTC) of π electrons present in the imide chain. Since -F, -CF ₃ , etc. introduced in Formula 1 are strong electron withdrawing groups, high transparency of polyimide may be exhibited by preventing the CT-Complex from occurring through movement between π electrons.

According to a preferred example of the present invention, X ₁ and X ₂ may be a conventional electron withdrawing group (EWG) known in the art, and each independently fluorine (F) or CF ₃ It is preferable.

In addition, Y may be used without limitation, a conventional hydrogen bonding functional group known in the art. In this case, a plurality of Ys are the same as or different from each other, and it is preferable that they are each independently a hydroxyl group (-OH), and more preferably two hydroxyl groups are introduced.

,

또는

인 것이 바람직하다. Also, A is

,

or

It is preferable to be

The compound represented by Formula 1 according to the present invention may be more specific to any one of the compound groups consisting of the following compounds 1 to 12, but is not particularly limited thereto.

In the present invention, the amount of the diamine monomer represented by Formula 1 is not particularly limited, and for example, may be in the range of 10 to 80 mol% based on 100 mol% of the total acid dianhydride, preferably 20 to 80 mol% can be a range.

Here, it may be used interchangeably, including a conventional diamine compound known in the art.

In the present invention, in addition to the compound of Formula 1 described above, it may be used in combination with a conventional diamine compound known in the art.

In the present invention, the diamine compound mixed with the compound of Formula 1 may be used without particular limitation as long as it has an intramolecular diamine structure. For example, there is an aromatic, alicyclic, or aliphatic compound having a diamine structure.

The diamine that can be used in the present invention has optical properties such as high transmittance, low Y.I, and low haze; thermal properties such as high glass transition temperature (High Tg) and low coefficient of thermal expansion (Low CTE); Considering mechanical properties such as high modulus and high surface hardness, linear structure with fluorinated substituents or sulfone, hydroxy, ether, etc. An appropriate combination of structures containing Accordingly, in the present invention, as the diamine compound, a fluorinated aromatic first diamine, a sulfone-based diamine, a hydroxy-based third diamine, an ether-based fourth diamine, and an alicyclic fifth diamine are used alone as the diamine compound. or a mixture of two or more thereof.

Non-limiting examples of diamine monomers (a) that can be used include oxydianiline (ODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFDB) ), 2,2'-bis (trifluoromethyl) -4,3'-diaminobiphenyl (2,2'-Bis (trifluoromethyl) -4,3'-Diaminobiphenyl), 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'-diaminodiphenyl ether, 6-FODA), bisaminohydroxyphenyl hexafluoropropane (DBOH), bisaminophenoxyphenyl hexafluoro Ropropane (4BDAF), bisaminophenoxyphenylpropane (6HMDA), bisaminophenoxydiphenylsulfone (DBSDA), bis(4-aminophenyl)sulfone (4,4'-DDS), bis(3-aminophenyl) ) sulfone (3,3'-DDS), sulfonyldiphthalic anhydride (SO ₂ DPA), 4,4'-oxydianiline (4,4'-ODA), bis (carboxyphenyl) dimethylsilane, or A form in which one or two or more thereof is mixed is applicable.

Considering high transparency, high glass transition temperature, and low yellowness, the fluorinated primary diamine is 2,2'-bis(trifluoromethyl)-4,4'-dia, which can induce linear polymerization. Preference is given to using minobiphenyl (2,2'-TFDB). In addition, it is preferable to use bis(4-aminophenyl)sulfone (4,4'-DDS) as the sulfone-based second diamine. In addition, the hydroxy-based third diamine is 2,2-bis (3-amino-4-methylphenyl)-hexafluoropropane (2,2-Bis (3-amino-4-methylphenyl)-hexafluoropropane, BIS-AT- AF) is preferred. In addition, it is preferable to use 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6-FODA) or oxydianiline (ODA) as the ether-based fourth diamine.

In the diamine monomer (a) of the present invention, the content of the fluorinated first diamine, sulfone-based second diamine, hydroxy-based diamine, ether-based fourth diamine, alicyclic fifth diamine, etc. is not particularly limited, but each It may be 20 to 90 mol% based on 100 mol% of the total diamine, preferably 20 to 80 mol%.

As the acid dianhydride (b) monomer used for preparing the transparent polyamic acid of the present invention, conventional fluorinated, non-fluorinated, alicyclic, etc. acid dianhydrides known in the art having an intramolecular acid dianhydride structure may be used without limitation. For example, a fluorinated primary acid dianhydride, an alicyclic secondary acid dianhydride, and a non-fluorinated tertiary acid dianhydride may be used alone, or a mixture of two or more thereof may be used.

In the present invention, the fluorinated first acid dianhydride monomer is not particularly limited as long as it is an aromatic acid dianhydride having a fluorine substituent introduced thereto.

For an example of the available fluorinated first dianhydride, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydrid, 6-FDA) and 4-(trifluoromethyl)pyromellitic dianhydride (4-(trifluoromethyl)pyromellitic dianhydride, 4-TFPMDA). These may be used alone or in combination of two or more. Among fluorinated acid dianhydrides, 6-FDA is a very suitable compound for transparency because it has a very high property of limiting the formation of a change transfer complex (CTC) between and within molecular chains.

In addition, the alicyclic secondary acid dianhydride that can be used in the present invention is not particularly limited as long as it is a compound having an acid dianhydride structure while having an alicyclic ring rather than an aromatic ring in the compound.

For an example of the alicyclic second dianhydride usable in the present invention, cyclobutane tetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentane tetracarboxylic dianhydride (CPDA) , bicyclo[2,2,2]-7-octene-2,3,5,6-tetracarboxylic dianhydride (BCDA), or a mixture of one or more thereof, but is not particularly limited thereto. .

The non-fluorinated tertiary acid dianhydride monomer is not particularly limited as long as it is a non-fluorinated aromatic acid dianhydride into which a fluorine substituent is not introduced.

Non-limiting examples of non-fluorinated tertiary acid dianhydride monomers that can be used include Pyromellitic Dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (3, 3',4,4'-Biphenyl tetracarboxylic acid dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), and oxydiphthalic dianhydride (ODPA). These may be used alone, or two or more thereof may be used in combination.

In the present invention, the content of at least one compound selected from the group consisting of the first acid dianhydride, the second acid dianhydride and the third acid dianhydride is not particularly limited. For example, each of these may be 10 to 100 mol% based on 100 mol% of the total acid dianhydride, preferably 10 to 90 mol%, and more preferably 20 to 80 mol%.

According to a preferred example of the present invention, when a fluorinated first acid dianhydride and a non-fluorinated tertiary acid dianhydride are mixed as the acid dianhydride (b), their ratio may be 40 to 90: 10 to 60 mol%.

In addition, according to another preferred example of the present invention, when the fluorinated first acid dianhydride and the alicyclic second acid dianhydride are mixed as the acid dianhydride (b), their use ratio is 30-80: 20-70 mol% ratio. have.

In addition, according to another preferred example of the present invention, when an alicyclic secondary acid dianhydride and a non-fluorinated tertiary acid dianhydride are mixed as the acid dianhydride (b), their use ratio is 30-70: 30-70 mol% ratio can

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

As the solvent (c) for the solution polymerization of the above-mentioned monomers included in the polyamic acid composition of the present invention, an organic solvent known in the art may be used without limitation.

Examples of usable solvents include m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl At least one polar solvent selected from acetate and dimethyl phthalate (DMP) may be used. In addition, a low-boiling solution such as tetrahydrofuran (THF), chloroform, or a solvent such as γ-butyrolactone may be used.

The content of the solvent is not particularly limited, but in order to obtain an appropriate molecular weight and viscosity of the polyamic acid solution, the content of the polymerization solvent (first solvent) is preferably 50 to 95% by weight based on the total weight of the polyamic acid composition. and more preferably in the range of 70 to 90% by weight.

In the present invention, the above-described acid dianhydride and diamine are added to an organic solvent and then reacted to prepare a transparent polyamic acid composition. As an example, including the diamine of Formula 1, at least one diamine component of the first to fifth diamines, and an acid dianhydride, diamine (a) and acid dianhydride (b) to improve glass transition temperature and yellowness A transparent polyamic acid composition may be formed in an equivalent ratio of approximately 1:1.

The composition of the polyamic acid composition is not particularly limited, and for example, based on 100% by weight of the total weight of the polyamic acid composition, 2.5 to 25.0% by weight of acid dianhydride, 2.5 to 25.0% by weight of diamine, and the remaining amount satisfying 100% by weight of the composition It may be composed of an organic solvent. For example, the content of the organic solvent may be 70 to 90% by weight. In addition, based on the solid content of 100% by weight in the present invention, it may be in the range of 30 to 70% by weight of acid dianhydride and 30 to 70% by weight of diamine, but is not particularly limited thereto.

The transparent polyamic acid composition of the present invention may have a viscosity in the range of about 1,000 to 200,000 cps, preferably about 5,000 to 50,000 cps. When the viscosity of the polyamic acid solution falls within the above-mentioned range, it is easy to control the thickness when coating the polyamic acid solution, and the coating surface can be uniformly exhibited.

In addition, the polyamic acid solution of the present invention may contain, if necessary, a small amount of additives such as plasticizers, antioxidants, flame retardants, dispersants, viscosity modifiers, and leveling agents within the range that does not significantly impair the purpose and effect of the present invention. .

<Polyimide Film>

The present invention provides a polyimide film prepared by imidization and heat treatment of the polyamic acid solution described above at a high temperature.

The polyimide resin is a polymer material containing an imide ring, and has excellent heat resistance, chemical resistance, abrasion resistance and electrical properties. In this case, the polyimide resin may be in the form of a random copolymer or a block copolymer.

Meanwhile, in order for the polyimide resin film to be applied to a flexible display, etc., it must have characteristics such as high transparency, low coefficient of thermal expansion, and high glass transition temperature. More specifically, a light transmittance of 89% or more at 550 nm in a film thickness of 10 μm, a yellowness value of 550 nm of 7 or less, and a glass transition temperature (Tg) of 300° C. or more are required. In addition, in order to secure reliability during the TFT deposition process, the polyimide on the support (glass substrate) is required to have an adhesive force that does not peel from the glass substrate during the process.

In fact, the polyimide film of the present invention prepared by imidizing the above-described polyamic acid composition has high transparency, low yellowness, high adhesion to a glass substrate, low coefficient of thermal expansion, and high glass transition temperature (Tg). More specifically, the polyimide film has the following physical property conditions of (i) to (vi), such as (i) an adhesive strength of 2B or more on a glass substrate according to ASTM D 3359 standard, (ii) ASTM E 313-73 standard has a yellowness of 7 or less (based on 10 μm), (iii) a light transmittance of 89% or more at a wavelength of 550 nm, (iv) a glass transition temperature (T _g ) in the range of 330 to 400 ° C, (v) The coefficient of thermal expansion (CTE) by TMA measurement is in the range of 10 to 60 ppm/℃, and (vi) the retardation (R _th ) in the thickness direction calculated by the following formula may be 80 nm to 400 nm based on a thickness of 10 μm.

Phase difference R _th (nm) = [(n _{x +} n _y ) / 2 - n _z ] ×d

(n _x is the largest refractive index among the in-plane refractive indexes of the polyimide resin film measured with light having a wavelength of 550 nm; n _y is the refractive index perpendicular to n _x among the in-plane refractive indexes of the polyimide resin film measured with light having a wavelength of 550 nm ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 550 nm; d is the thickness of the polyimide film.)

The polyimide film according to the present invention may be prepared by exothermic solution polymerization of a transparent polyamic acid solution according to a conventional method known in the art. For example, after coating (casting) the transparent polyamic acid composition on a support, it can be prepared by inducing an imide ring closure reaction (imidazation) for 0.5 to 8 hours while gradually increasing the temperature in the range of 30 to 350 ° C. At this time, it is preferable to react in an inert atmosphere such as argon or nitrogen.

In this case, the coating method may use a conventional method known in the art without limitation, for example, spin coating, dip coating, solvent casting, slot die coating (Slot die coating). ) and may be made by at least one method selected from the group consisting of spray coating. The transparent polyamic acid composition may be coated one or more times so that the colorless and transparent polyimide layer has a thickness of several hundred nm to several tens of μm.

In the polyimide film manufacturing method according to the present invention, the imidization method applied to the imidization step by casting the polymerized polyamic acid to a support is thermal imidization method, chemical imidization method, or thermal imidization method and chemical It can be applied in combination with the imidization method.

The thermal imidization method is a method of obtaining a polyimide film by casting a polyamic acid solution on a support and heating it for 1 to 10 hours while gradually raising the temperature in a temperature range of 30 to 400°C.

In addition, the chemical imidization method is a method of adding a dehydrating agent represented by an acid anhydride such as acetic anhydride and an imidization catalyst represented by amines such as isoquinoline, β-picoline, and pyridine to a polyamic acid solution. When the thermal imidization method or the thermal imidization method is used in combination with the chemical imidization method, the heating conditions of the polyamic acid solution may vary depending on the type of the polyamic acid solution, the thickness of the polyimide film to be prepared, and the like.

More specifically, the polyimide film production example in the case of using the thermal imidization method and the chemical imidization method in combination, the dehydrating agent and the imidization catalyst are added to the polyamic acid solution and cast on the support, then 80 ~ 300 ℃, Preferably, the polyimide film can be obtained after partial curing and drying by heating at 150 to 250° C. to activate the dehydrating agent and imidization catalyst.

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

In the present invention, the transparent polyimide film produced as described above can be used in various fields, and in particular, displays for organic EL devices (OLEDs) requiring high transparency and heat resistance, displays for liquid crystal devices, TFT substrates, and flexible printed circuit boards , a flexible OLED surface lighting substrate, a substrate material for electronic paper, and/or a flexible display substrate and/or protective film.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are only examples to help the understanding of the present invention, and the scope of the present invention is not limited thereto.

[Synthesis of transparent polyamic acid composition and preparation of polyimide film]

[Example 1]

1. Preparation of polyamic acid solution

A 500 mL three-necked round-bottom flask was used as a reactor, and 145.9 g of N,N -dimethylacetamide (hereinafter referred to as DMAc) was charged to the reactor while passing nitrogen at a flow rate of 50 mL/min, and the temperature of the reactor was set to 40°C. After raising the temperature, 20.0 g (41.1 wt %) and 3.53 g (7.3 wt %) of Compound 2 and 4-aminophenylsulfone (hereinafter referred to as 4,4'-DDS) were added, respectively, and stirred for 1 hour to obtain Compound 2 and 4,4'-DDS was completely dissolved. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 18.92 g (38.9 wt %) of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (hereinafter referred to as 6FDA) was added. After that, the mixture was stirred for 2 hours. Finally, 6.19 g (12.7 wt%) of pyromellite dianhydride (hereinafter referred to as PMDA) was added, and then 48.6 g of DMAc was added thereto, followed by reaction at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 24,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

2. Manufacture of transparent polyimide film

After spin-coating the pliamic acid solution on glass for LCD, in a nitrogen atmosphere convection oven at 80°C for 30 minutes, at 150°C for 30 minutes, at 200°C for 1 hour, at 300°C for 1 hour while gradually increasing the temperature stepwise, drying and A transparent polyimide resin film having an imidization rate of 85% or more was prepared by performing an imidation reaction. After that, the polyimide resin film coated on the glass for LCD is left in a bath type ultrasonic device containing distilled water to peel the polyimide film from the glass plate for LCD, and a transparent polyimide film with a thickness of 9 to 12 μm. got Thereafter, the film was left in a vacuum oven at 100° C. to remove moisture present in the polyimide film, and then moisture was removed for about 1 hour to obtain a final polyimide film.

[Example 2]

In Example 1, 190.2 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., and Compound 7 and 2,2-bis (3-amino-4-methylphenyl) hexafluoropropane (hereinafter, BIS-AT- AF) were added 20.0 g (31.5 wt %) and 6.5 g (10.2 wt %), respectively, and stirred for 1 hour to completely dissolve Compound 7 and BIS-AT-AF. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 31.7 g (49.9 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 5.3 g (8.4 wt %) of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (hereinafter referred to as BPDA) was added, and then 63.4 g of DMAc was added thereto and heated at 30°C. The reaction was carried out for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 11,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 3]

In Example 1, 127.3 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and 20.0 g of compound 11 and 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as TFDB) were each added ( 47.1 wt %), 4.4 g (10.3 wt %) were added and stirred for 1 hour to completely dissolve Compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 14.1 g (33.2 wt) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 4.0 g (9.4 wt %) of cyclobutane-1,2,3,4-tetracarboxylic acid dianhydride (hereinafter referred to as CBDA) was added, and then 42.4 g of DMAc was added again, followed by 24 at 30°C. reaction time. After the reaction was completed, a polyamic acid solution having a viscosity of about 10,000 cP at 20% solids was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 4]

In Example 1, 147.1 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 20.0 g (40.7 wt %) and 4.6 g (9.4 wt %) of Compound 2 and TFDB were added respectively for 1 hour. Stirring to completely dissolve compound 2 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 18.9 g (38.5 wt%) of 6FDA was added thereto, followed by stirring for 2 hours. Finally, 5.6 g (11.4 wt %) of CBDA was added, and then 49.0 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 37,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 5]

In Example 1, 169.9 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 2 and 4,4'-DDS were respectively 18.0 g (31.8 wt %) and 8.5 g (15 wt %) was added and stirred for 1 hour to completely dissolve Compound 2 and 4,4'-DDS. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 15.1 g (26.7 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, after adding 15.0 g (26.5 wt%) of BPDA, 56.6 g of DMAc was added again, and the reaction was performed at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 26,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 6]

In Example 1, 166.8 g of DMAc was filled in the reactor, and the temperature of the reactor was raised to 40° C., and then 16.0 g (28.8 wt%) and 13.8 g (24.8 wt%) of Compound 7 and BIS-AT-AF, respectively. Compound 7 and BIS-AT-AF were completely dissolved by stirring for 1 hour. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 19.6 g (35.3 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 6.2 g (11.1 wt %) of PMDA was added, and then 55.6 g of DMAc was added thereto and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 25,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 7]

In Example 1, 159.1 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., 21.0 g (39.6 wt %) and 12.2 g (23 wt %) of compound 11 and TFDB, respectively, were added and stirred for 1 hour. Thus, compound 11 and TFDB were completely dissolved. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 10.4 g (19.6 wt%) of PMDA was added, followed by stirring for 2 hours. Finally, 9.4 g (17.7 wt %) of CBDA was added, and then 53.0 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 31,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 8]

In Example 1, 157.2 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 15.0 g (28.6 wt %) and 9.1 g (17.4 wt %) of Compound 2 and TFDB were added respectively for 1 hour. Compound 2 and TFDB were completely dissolved by stirring. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 25.2 g (48.1 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, after adding 3.1 g (5.9 wt %) of PMDA, 52.4 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 32,000 cP at 20% solids was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 9]

In Example 1, 155.8 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 2 and 4,4'-DDS were respectively 12.5 g (24.1 wt %) and 13.2 g (25.4 wt %) was added and stirred for 1 hour to completely dissolve Compound 2 and 4,4'-DDS. Thereafter, the temperature of the reactor was cooled to 30° C. and then 15.8 g (30.4 wt %) of 6FDA was added thereto, followed by stirring for 2 hours. Finally, after adding 10.4 g (20 wt%) of CBDA, 51.9 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 24,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 10]

In Example 1, 161.5 g of DMAc was filled in the reactor, and the temperature of the reactor was raised to 40° C., and then 10.5 g (19.5 wt %) and 20.4 g (37.8 wt %) of Compound 7 and BIS-AT-AF, respectively. Compound 7 and BIS-AT-AF were completely dissolved by stirring for 1 hour. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 13.8 g (25.6 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 9.2 g (17.1 wt%) of CBDA was added, and then 53.8 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 12,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 11]

In Example 1, 153.7 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 10.5 g (20.5 wt %) and 13.8 g (26.9 wt %) of compound 11 and TFDB were added respectively for 1 hour. Stirring to completely dissolve compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 22.3 g (43.5 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 4.7 g (9.2 wt%) of PMDA was added, and then 51.2 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 19,000 cP at 20% solids was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 12]

In Example 1, 155.5 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 12.5 g (24.1 wt %) and 16.3 g (31.4 wt %) of Compound 5 and TFDB were added thereto, respectively, for 1 hour. Stirring to completely dissolve compound 5 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 17.5 g (33.7 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 5.6 g (10.8 wt%) of PMDA was added, and then 51.8 g of DMAc was added thereto and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 37,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 13]

In Example 1, 155.9 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 10.0 g (19.3 wt %) and 13.6 g (26.2 wt %) of Compound 2 and TFDB were added thereto, respectively, for 1 hour. Stirring to completely dissolve compound 2 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 25.2 g (48.6 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, after adding 3.1 g (6 wt %) of PMDA, 52.0 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 36,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 14]

In Example 1, 160.8 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 15.0 g (27.9 wt%) and 15.9 g (29.6 wt%) of Compound 2 and 4,4′-DDS were respectively added to the reactor. was added and stirred for 1 hour to completely dissolve Compound 2 and 4,4'-DDS. Thereafter, the temperature of the reactor was cooled to 30° C. and then 18.6 g (34.6 wt %) of PMDA was added thereto, followed by stirring for 2 hours. Finally, 4.2 g (7.8 wt %) of 6FDA was added, and then 53.6 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 11,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 15]

In Example 1, 161.1 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and 5.0 g (9.3 wt %) and 25.9 g (48.2 wt %) of Compound 7 and BIS-AT-AF, respectively. Compound 7 and BIS-AT-AF were completely dissolved by stirring for 1 hour. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 13.1 g (24.4 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 9.7 g (18.1 wt%) of PMDA was added, and then 53.7 g of DMAc was added thereto and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 13,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 16]

In Example 1, 165.7 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 6.0 g (10.9 wt %) and 21.0 g (38 wt %) of Compound 11 and TFDB, respectively, were added thereto and for 1 hour. Stirring to completely dissolve compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 21.8 g (39.5 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 6.4 g (11.6 wt%) of CBDA was added, and then 55.2 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 17,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 17]

In Example 1, 153.3 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 5.5 g (10.8 wt %) and 19.1 g (37.4 wt %) of Compound 5 and TFDB were added thereto, respectively, for 1 hour. Stirring to completely dissolve compound 5 and TFDB. Thereafter, the temperature of the reactor was cooled to 30° C. and then 13.3 g (26 wt %) of 6FDA was added thereto, followed by stirring for 2 hours. Finally, after adding 13.2 g (25.8 wt%) of BPDA, 51.1 g of DMAc was added again, and the reaction was performed at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 23,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 18]

In Example 1, 154.5 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., and 5.0 g (9.7 wt %) and 18.2 g (35.3 wt %) of Compound 2 and TFDB, respectively, were added for 1 hour. Stirring to completely dissolve compound 2 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 25.2 g (48.9 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, after adding 3.1 g (6 wt %) of PMDA, 51.5 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 28,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 19]

In Example 1, 157.8 g of DMAc was filled in a reactor, and the temperature of the reactor was increased to 40° C., and then Compound 2, Compound 11, and 4,4'-DDS were respectively 3.4 g (6.5 wt%), 3.5 g (6.7 wt%), and 19.2 g (36.5 wt%) were added and stirred for 1 hour to completely dissolve Compound 2, Compound 11, and 4,4'-DDS. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 22.7 g (43.2 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 3.8 g (7.2 wt %) of CBDA was added, and then 52.6 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 9,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 20]

In Example 1, 160.9 g of DMAc was filled in a reactor, and the temperature of the reactor was increased to 40° C., and then Compound 2, Compound 7, and BIS-AT-AF were respectively 3.1g (5.8 wt%), 2.5g (4.7 wt%) %), and 25.5 g (47.6 wt%) were added and stirred for 1 hour to completely dissolve Compound 2, Compound 7 and BIS-AT-AF. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 12.9 g (24.1 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 9.6 g (17.9 wt%) of PMDA was added, and then 53.6 g of DMAc was added again, followed by reaction at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 8,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 21]

In Example 1, 158.3 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 7, Compound 11, and TFDB were respectively 2.4 g (4.6 wt %), 3.1 g (5.9 wt %), and 21.9 g (41.6 wt%) was added and stirred for 1 hour to completely dissolve Compound 7, Compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 15.2 g (28.8 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 10.1 g (19.2 wt %) of CBDA was added, and then 52.8 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 11,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 22]

In Example 1, 157.2 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 2, Compound 5, and TFDB were each 6.5 g (12.4 wt %), 6.8 g (13 wt %), and 11.8 g (22.5 wt%) was added and stirred for 1 hour to completely dissolve Compound 2, Compound 5 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 23.0 g (43.9 wt%) of 6FDA was added thereto, followed by stirring for 2 hours. Finally, 4.3 g (8.2 wt %) of CBDA was added, and then 52.4 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 13,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

[Example 23]

In Example 1, 160.0 g of DMAc was filled in the reactor, and the temperature of the reactor was increased to 40° C., and then Compound 2, Compound 7 and TFDB were each added to 2.7 g (5.1 wt%), 2.1g (3.9 wt%), and 19.6 g (36.8 wt%) was added and stirred for 1 hour to completely dissolve Compound 2, Compound 7 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 23.8 g (44.7 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 5.0 g (9.4 wt %) of PMDA was added, and then 53.3 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 16,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 24]

In Example 1, 159.9 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 2 and 4,4'-DDS were respectively 3.8 g (7.1 wt %) and 24.1 g (45.2 wt %) was added and stirred for 1 hour to completely dissolve Compound 2 and 4,4'-DDS. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 12.7 g (23.8 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, after adding 12.7 g (23.8 wt %) of CBDA, 53.3 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 14,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 25]

In Example 1, 161.5 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 7 and BIS-AT-AF were respectively 2.4 g (4.5 wt %) and 27.9 g (51.8 wt %) Compound 7 and BIS-AT-AF were completely dissolved by stirring for 1 hour. Thereafter, the temperature of the reactor was cooled to 30° C. and then 20.2 g (37.5 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 3.4 g (6.3 wt %) of CBDA was added, and then 53.8 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 9,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 26]

In Example 1, 159.3 g of DMAc was filled in the reactor and the temperature of the reactor was raised to 40° C., and then 2.8 g (5.3 wt %) and 22.0 g (41.5 wt %) of Compound 11 and TFDB were added thereto, respectively, for 1 hour. Stirring to completely dissolve compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 23.7 g (44.7 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 4.5 g (8.5 wt %) of CBDA was added, and then 53.1 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 17,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 27]

In Example 1, 154.3 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then 2.7 g (5.3 wt %) and 21.1 g (41.1 wt %) of Compound 5 and TFDB were added thereto, respectively, for 1 hour. Stirring to completely dissolve compound 5 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 22.8 g (44.4 wt %) of 6FDA was added, followed by stirring for 2 hours. Finally, 4.8 g (9.3 wt %) of PMDA was added, and then 51.4 g of DMAc was added again, followed by reaction at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 15,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 28]

In Example 1, 157.3 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., and 2.5 g (4.8 wt %) and 20.5 g (39.1 wt %) of Compound 2 and TFDB were added thereto, respectively, for 1 hour. Stirring to completely dissolve compound 2 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 25.2 g (48.1 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 4.2 g (8 wt%) of BPDA was added, and then 52.4 g of DMAc was added thereto and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 31,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 29]

In Example 1, 159.6 g of DMAc was filled in the reactor, and the temperature of the reactor was raised to 40° C., and then Compound 2, Compound 11, and TFDB were each added to 5.1 g (9.6 wt%), 5.3g (10.0 wt%), and 13.9 g (26.1 wt%) was added and stirred for 1 hour to completely dissolve Compound 2, Compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 25.7 g (48.3 wt %) of 6FDA was added, followed by stirring for 2 hours. Finally, 3.2 g (6.0 wt%) of PMDA was added, and then 53.2 g of DMAc was added thereto and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 15,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 30]

In Example 1, 157.9 g of DMAc was filled in the reactor, and the temperature of the reactor was raised to 40° C., and then 5.3 g (10.1 wt %), 6.9 g (13.1 wt %) of compound 7, compound 11 and TFDB, respectively, and 18.2 g (34.6 wt%) was added and stirred for 1 hour to completely dissolve Compound 7, Compound 11 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 11.1 g (21.1 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, after adding 11.1 g (21.1 wt%) of CBDA, 52.6 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 16,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Example 31]

In Example 1, 155.7 g of DMAc was filled in a reactor, and the temperature of the reactor was raised to 40° C., and then Compound 2, Compound 5 and TFDB were each added to 5.3 g (10.2 wt %), 5.5 g (10.6 wt %), and 14.5 g (27.9 wt%) was added and stirred for 1 hour to completely dissolve Compound 2, Compound 5 and TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 20.1 g (38.7 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 6.6 g (12.7 wt%) of PMDA was added, and then 51.9 g of DMAc was added and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 8,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 1]

In Example 1, 158.7 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., 26.0 g (49.1 wt%) of TFDB was added, and the mixture was stirred for 1 hour to completely dissolve TFDB. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 18.0 g (34 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, 8.9 g (16.8 wt %) of PMDA was added, and then 52.9 g of DMAc was added again, followed by reaction at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 110,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 2]

In Example 1, 158.9 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., 30.0 g (56.6 wt%) of TFDB was added, and the mixture was stirred for 1 hour to completely dissolve TFDB. Thereafter, the temperature of the reactor was cooled to 30° C. and then 13.8 g (26 wt %) of BPDA was added thereto, followed by stirring for 2 hours. Finally, 9.2 g (17.4 wt %) of CBDA was added, and then 53.0 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 190,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 3]

In Example 1, 161.0 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., 23.0 g (42.8 wt%) of 4,4'-DDS was added, and 4,4'-DDS was stirred for 1 hour. was completely dissolved. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 20.6 g (38.4 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, after adding 10.1 g (18.8 wt%) of PMDA, 53.7 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 74,000 cP at 20% solids was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 4]

In Example 1, 158.0 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., 26.5 g (50.3 wt %) of 4,4'-DDS was added, and 4,4'-DDS was stirred for 1 hour. was completely dissolved. Thereafter, the temperature of the reactor was cooled to 30° C. and then 15.7 g (29.8 wt %) of BPDA was added thereto, followed by stirring for 2 hours. Finally, after adding 10.5 g (19.9 wt%) of CBDA, 52.7 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 81,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 5]

In Example 1, 157.9 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., 27.5 g (52.2 wt %) of BIS-AT-AF was added, and the mixture was stirred for 1 hour to completely complete BIS-AT-AF. dissolved. Thereafter, the temperature of the reactor was cooled to 30° C. and then 16.9 g (32.1 wt%) of 6FDA was added thereto, followed by stirring for 2 hours. Finally, 8.3 g (15.7 wt %) of PMDA was added, and then 52.6 g of DMAc was added again, followed by reaction at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 45,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 6]

In Example 1, 161.0 g of DMAc was filled in the reactor, the temperature of the reactor was raised to 40° C., 32.0 g (59.6 wt %) of BIS-AT-AF was added, and the mixture was stirred for 1 hour to completely complete BIS-AT-AF. dissolved. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 13.0 g (24.2 wt%) of BPDA was added, followed by stirring for 2 hours. Finally, 8.7 g (16.2 wt%) of CBDA was added, and then 53.7 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 56,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 7]

In Example 1, 159.2 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., and 20.0 g (37.7 wt%) of 4,4'-oxydianiline (hereinafter referred to as 4,4'-ODA) was added and stirred for 1 hour to completely dissolve 4,4'-ODA. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., after which 22.2 g (41.8 wt%) of 6FDA was added, followed by stirring for 2 hours. Finally, after adding 10.9 g (20.5 wt%) of PMDA, 53.1 g of DMAc was added again, followed by reaction at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 44,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

[Comparative Example 8]

In Example 1, 153.5 g of DMAc was filled in a reactor, the temperature of the reactor was raised to 40° C., 23.0 g (44.9 wt%) of 4,4'-ODA was added, and the mixture was stirred for 1 hour to 4,4'-ODA. was completely dissolved. Thereafter, the temperature of the reactor was cooled and maintained at 30° C., and then 16.9 g (33 wt%) of BPDA was added thereto, followed by stirring for 2 hours. Finally, after adding 11.3 g (22.1 wt%) of CBDA, 51.2 g of DMAc was added again and reacted at 30° C. for 24 hours. After the reaction was completed, a polyamic acid solution having a viscosity of about 53,000 cP at 20% solid content was obtained through a glass filter having a pore size of 1 μm in a pressure reducing device.

A transparent polyimide film was prepared in the same manner as in Example 1 using the prepared polyamic acid solution.

The compositions of the polyamic acid compositions prepared in Examples 1 to 31 and Comparative Examples 1 to 8 are shown in Tables 1 and 2 below.

Diamine (mol%) Acid dianhydride (mol%) first monomer second monomer 3rd monomer first monomer second monomer Example 1 Formula 2 (80) - 4,4'-DDS (20) 6-FDA (60) PMDA (40) Example 2 compound 7 (80) - BIS-AT-AF (20) 6-FDA (80) BPDA (20) Example 3 compound 11 (80) - TFDB (20) BPDA (20) CBDA (30) Example 4 compound 2 (80) - TFDB (20) 6-FDA (60) CBDA (40) Example 5 compound 2 (60) - 4,4'-DDS (40) 6-FDA (40) BPDA (60) Example 6 compound 7 (60) - BIS-AT-AF (40) BPDA (70) PMDA (30) Example 7 compound 11 (60) - TFDB (40) PMDA (50) CBPA (50) Example 8 compound 2 (60) - TFDB (40) 6-FDA (80) PMDA (20) Example 9 compound 2 (40) - 4,4'-DDS (60) 6-FDA (40) CBDA (60) Example 10 compound 7 (40) - BIS-AT-AF (60) BPDA (50) CBDA (50) Example 11 compound 11 (40) - TFDB (60) 6-FDA (70) PMDA (30) Example 12 compound 5 (40) - TFDB (60) BPDA (70) PMDA (30) Example 13 compound 2 (40) - TFDB (60) 6-FDA (80) PMDA (20) Example 14 compound 2 (20) - 4,4'-DDS (80) PMDA (40) CBDA (60) Example 15 compound 7 (20) - BIS-AT-AF (80) BPDA (50) PMDA (50) Example 16 compound 11 (20) - TFDB (80) 6-FDA (60) CBDA (40) Example 17 compound 5 (20) - TFDB (80) 6-FDA (40) BPDA (60) Example 18 compound 2 (20) - TFDB (80) 6-FDA (80) PMDA (20) Example 19 compound 2 (10) compound 11 (10) 4,4'-DDS (80) BPDA (80) CBDA (20) Example 20 compound 2 (10) compound 7 (10) BIS-AT-AF (80) BPDA (50) PMDA (50) Example 21 compound 7 (10) compound 11 (10) TFDB (80) 6-FDA (40) CBDA (60) Example 22 compound 2 (10) compound 5 (10) TFDB (80) 6-FDA (70) CBDA (30) Example 23 compound 2 (10) compound 7 (10) TFDB (80) 6-FDA (70) PMDA (30) Example 24 compound 2 (10) - 4,4'-DDS (90) BPDA (40) CBDA (60) Example 25 compound 7 (10) - BIS-AT-AF (90) BPDA (80) CBDA (20) Example 26 compound 11 (10) - TFDB (90) 6-FDA (70) CBDA (30) Example 27 compound 5 (10) - TFDB (90) 6-FDA (70) PMDA (30) Example 28 compound 2 (10) - TFDB (90) 6-FDA (80) BPDA (20) Example 29 compound 2 (20) compound 11 (20) TFDB (60) 6-FDA (80) PMDA (20) Example 30 compound 7 (20) compound 11 (20) TFDB (60) BPDA (40) CBDA (60) Example 31 compound 2 (20) compound 5 (20) TFDB (60) 6-FDA (60) PMDA (40)

Diamine (mol%) Acid dianhydride (mol%) monomer first monomer second monomer Comparative Example 1 TFDB (100) 6-FDA (5) PMDA (50) Comparative Example 2 TFDB (100) BPDA (50) CBDA (50) Comparative Example 3 4,4'-DDS (100) 6-FDA (50) PMDA (50) Comparative Example 4 4,4'-DDS (100) BPDA (50) CBDA (50) Comparative Example 5 BIS-AT-AF (100) 6-FDA (50) PMDA (50) Comparative Example 6 BIS-AT-AF (100) BPDA (50) CBDA (50) Comparative Example 7 4,4'-ODA (100) 6-FDA (50) PMDA (50) Comparative Example 8 4,4'-ODA (100) BPDA (50) CBDA (50)

[Evaluation of physical properties]

The physical properties of the transparent polyimide films prepared in Examples 1 to 31 and Comparative Examples 1 to 8 were evaluated in the following manner, and the results are shown in Table 3 below.

<Method for evaluating physical properties>

1) Film thickness measurement: The thickness was measured with a Mitutoyo Micrometer (Model No. 293-140), and the deviation of the device is Δ0.5% or less.

2) Light transmittance (Transmittance): It was measured at a wavelength of 550 nm using a UV-Vis-NIR Spectrophotometer.

3) Y.I (Yellow Index): Yellowness was measured according to ASTM E313-73 standard using a UV spectrometer (KONICA MINOLTA CM-3700d).

4) Phase difference (R _th ): The vertical phase difference was measured by measuring at an incident angle of 45 degrees using RETS-100 (OTSUKA ELECTRONICS). More specifically, the sample size was 5 cm horizontally and vertically, and the specimen was mounted in a sample holder and fixed at 550 nm using a monochromator, and the thickness direction retardation (R _th ) was measured at an incident angle of 45°.

R _th = [(n _{x +} n _y ) / 2 - n _z ] ×d

Here, n _x is the largest refractive index among in-plane refractive indices, n _y is a refractive index perpendicular to n _x among in-plane refractive indices, n _z is a perpendicular refractive index, and d is the thickness of the polyimide film by converting it to 10 μm. is the calculated value.

5) Glass transition temperature (Tg): DMA (TA Instrument, model name: Q800) was used to measure the glass transition temperature in the range of 30 ~ 400 ℃.

6) Coefficient of Thermal Expansion (CTE): It was measured at 50-350° C. using TMA (TA Instrument, model name: Q400).

7) Adhesion evaluation: evaluated using ASTM D 3359.

After coating a transparent polyamic acid resin with a film thickness of 15 μm or less on a glass substrate, drying and imide ring closure reaction were performed. Then, the peeling state of the polyimide adhesive surface was confirmed.

In this case, 5B indicates that the percentage of peeled polyimide is 0%, 4B indicates that the percentage of peeled polyimide is 5% or less, 3B indicates that the percentage of peeled polyimide is 5 to 15%, and 2B indicates that the percentage of peeled polyimide is 5% or less. 15-35%, 1B shows the case where the percentage of peeled polyimide is 35-65%, and 0B shows the case where the percentage of peeled polyimide is more than 65%, respectively.

For reference, FIG. 1 below is a photograph showing the polyimide film of Example 1 having an adhesion evaluation result of 5B, and FIG. 2 is a photograph showing the polyimide films of Comparative Examples 1 to 8 having an adhesion evaluation result of 0B.

As a result of looking at the results of Table 3, in the case of the films of Examples 1 to 31 in which the diamine monomer of Formula 1 according to the present invention was used, compared with the films of Comparative Examples 1 to 8 that do not include the diamine of Formula 1, It was found that it has excellent optical properties such as increased light transmittance, reduced yellowness, and reduced phase difference, and has excellent heat resistance and thermal expansion coefficient properties due to an increase in glass transition temperature. In particular, it was found that the films of Examples 1 to 31 containing the diamine of Formula 1 had high adhesion properties in contrast to Comparative Examples 1 to 8.

Therefore, it can be seen that the polyimide film of the present invention improves the optical, thermal, and adhesive properties of the conventional polyimide film, and the polyimide film is a colorless and transparent flexible display plastic substrate that will replace the LCD glass substrate when manufacturing a flat panel display. It was confirmed that it can be applied usefully.

Claims (11)

(a) a diamine (A) containing a compound represented by the following formula (1) and a fluorinated primary diamine; a diamine containing at least one diamine compound (B) selected from the group consisting of a sulfone-based second diamine, a hydroxy-based third diamine, an ether-based fourth diamine, and an alicyclic fifth diamine;
(b) an acid dianhydride; and
(c) containing an organic solvent;
The compound (A) represented by Formula 1 is included in the range of 10 to 80 mol% based on 100 mol% of the total diamine,
the fluorinated first diamine; At least one diamine compound (B) selected from the group consisting of a sulfone-based second diamine, a hydroxy-based third diamine, an ether-based fourth diamine, and an alicyclic fifth diamine is 90 to 20 based on 100 mol% of the total diamine included in the mole % range,
The polyamic acid composition, characterized in that the adhesive force of the film formed by imidizing the polyamic acid composition on a glass substrate according to ASTM D 3359 standard is 2B or more.
[Formula 1]

In Formula 1,
A is a single bond, or

,

and

is selected from the group consisting of
X ₁ and X ₂ are the same as or different from each other, and are each independently selected from the group consisting of hydrogen, halogen, a C ₁ ~ C ₆ alkyl group, and a C ₁ ~ C ₆ alkyl group in which at least one hydrogen is substituted with a halogen atom,
A plurality of Y is a hydrogen-bonding functional group, each independently a hydroxyl group,
n is an integer from 0 to 2,
However, the compound of Formula 1 includes at least one hydroxyl group. According to claim 1,
The X ₁ and X ₂ are each independently F or CF ₃ An electron withdrawing group (EWG) of a polyamic acid composition. According to claim 1,
The compound represented by the formula (1) is a polyamic acid composition, characterized in that selected from the group of compounds represented by the following formula.

delete delete According to claim 1,
The acid dianhydride comprises at least one selected from the group consisting of a fluorinated aromatic primary acid dianhydride, an alicyclic secondary acid dianhydride, and a non-fluorinated aromatic tertiary acid dianhydride. 7. The method of claim 6,
The content of at least one compound selected from the group consisting of the first acid dianhydride, the second acid dianhydride and the third acid dianhydride is 10 to 100 mol% based on 100 mol% of the total acid dianhydride. . According to claim 1,
The polyamic acid composition, characterized in that the ratio (a/b) of the number of moles of the diamine (a) and the acid dianhydride (b) is in the range of 0.7 to 1.3. A transparent polyimide film produced by imidizing the polyamic acid composition according to any one of claims 1 to 3 and 6 to 8. 10. The method of claim 9,
Transparent polyimide film, characterized in that it satisfies the physical property conditions of the following (i) to (vi):
(i) The adhesive strength on the glass substrate according to ASTM D 3359 is 2B or more,
(ii) Yellowness according to ASTM E313-73 standard is 7 or less (based on 10㎛),
(iii) a light transmittance of 89% or more at a wavelength of 550 nm;
(iv) the glass transition temperature (T _g ) is in the range of 330 to 400 ℃,
(v) the coefficient of thermal expansion (CTE) by TMA measurement is in the range of 10 to 60 ppm / ℃,
(vi) A transparent polyimide resin film, characterized in that the retardation (R _th ) in the thickness direction calculated by the following formula is 80 nm to 400 nm based on a thickness of 10 μm.
Phase difference R _th (nm) = [(n _{x +} n _y ) / 2 - n _z ] ×d
(n _x is the largest refractive index among the in-plane refractive indexes of the polyimide resin film measured with light having a wavelength of 550 nm; n _y is the refractive index perpendicular to n _x among the in-plane refractive indexes of the polyimide resin film measured with light having a wavelength of 550 nm ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 550 nm; d is the thickness of the polyimide film.) 10. The method of claim 9,
A transparent polyimide film used as a substrate or a protective film for a flexible display.

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