KR20210001902A - Polyamide-imide film, preparation method thereof, and cover window and display device comprising same - Google Patents

Abstract

An embodiment relates to a polyamide-imide film maintaining a certain level or more in mechanical properties even at low temperature conditions and having excellent transparency and folding properties, a method for manufacturing the same, and a cover window and a display device including the same, wherein the polyamide-imide film comprises a polyamide-imide polymer, has a modulus (MO_1) of 5 GPa or more at room temperature conditions, and has 1 to 8% of a dMO value defined in equation 1: dMO (%) = ¦ MO_2 - MO_1 ¦ / MO_1 * 100.

Description

Polyamide-imide film, a manufacturing method thereof, and a cover window and display device including the same TECHNICAL FIELD [0001] POLYAMIDE-IMIDE FILM, PREPARATION METHOD THEREOF, AND COVER WINDOW AND DISPLAY DEVICE COMPRISING SAME}

Embodiments relate to a polyamide-imide film having excellent transparency and folding characteristics, having mechanical properties maintained at a certain level or higher even under low temperature conditions, a manufacturing method thereof, and a cover window and a display device including the same.

Polyimide resins such as poly(amide-imide), PAI) have excellent friction, heat, and chemical resistance, and are primary electrical insulation materials, coatings, adhesives, extrusion resins, and heat-resistant paints. , Heat resistant plate, heat resistant adhesive, heat resistant fiber and heat resistant film.

Polyimide is used in various fields. For example, polyimide is made in powder form and used as a coating agent such as metal or magnet wire, and is mixed with other additives depending on the application. In addition, polyimide is used as a paint for decoration and corrosion prevention along with fluoropolymers, and plays a role in bonding fluoropolymers to metal substrates. In addition, polyimide is also used to coat kitchen utensils, and because of its heat resistance and chemical resistance, it is also used as a membrane for gas separation, and contaminants such as carbon dioxide, hydrogen sulfide and impurities from natural gas wells are also used in filtering equipment. Used.

In recent years, by forming a film of polyimide, a polyimide-based film having excellent optical, mechanical and thermal properties has been developed inexpensively. These polyimide-based film is an organic light emitting diode (OLED; organic light-emitting diode ) or a liquid crystal display (LCD; liquid -crystal display) can be applied to the display material and the like, in the implementation phase properties antireflection film, a compensation film or a retardation Applicable to film.

Such a polyimide-based film has a problem that physical properties are rapidly deteriorated in a low-temperature environment. In order to solve this problem, additives may be introduced, and in this case, optical properties may decrease or compatibility may be poor.

In addition, when the polyimide-based film is applied to a display device, the transparent cover window included in the display device includes a hard coating layer in addition to the polyimide-based film. In the process of forming the hard coating layer, haze increases or adhesive strength decreases. The optical properties may deteriorate.

Therefore, while solving the above problems, while maintaining excellent physical properties even under low temperature conditions, research on the development of a film having excellent mechanical properties and optical properties is continuously required.

An embodiment is to provide a polyamide-imide film having excellent transparency and folding characteristics, having mechanical properties maintained at a certain level or higher even under low temperature conditions, a manufacturing method thereof, and a cover window and a display device including the same.

The polyamide-imide film according to an embodiment includes a polyamide-imide polymer, and a modulus (MO ₁ ) in room temperature conditions is 5 GPa or more, and a dMO value defined in the following formula 1 is 1% to 8%.

<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.

A cover window for a display device according to another embodiment includes a polyamide-imide film and a functional layer, the polyamide-imide film includes a polyamide-imide polymer, and the polyamide-imide film The modulus (MO ₁ ) in the room temperature condition of is 5 GPa or more, and the dMO value defined in the following formula 1 is 1% to 8%.

<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.

A display device according to another embodiment includes: a display unit; And a cover window disposed on the display unit, wherein the cover window includes a polyamide-imide film and a functional layer, the polyamide-imide film includes a polyamide-imide polymer, the The modulus (MO ₁ ) of the polyamide-imide film under room temperature conditions is 5 GPa or more, and the dMO value defined in the following formula 1 is 1% to 8%.

<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.

A method of preparing a polyamide-imide film according to an embodiment includes the steps of polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide polymer solution; Injecting the polymer solution into a tank; Extruding and casting the polymer solution in the tank, followed by drying, to prepare a gel sheet; And heat treating the gel sheet, wherein the heat treatment step of the gel sheet includes at least two hot air treatment steps.

The polyamide-imide film according to the embodiment not only has excellent mechanical properties and optical properties, but can maintain excellent mechanical properties even under harsh conditions at low temperatures.

In particular, since the polyamide-imide film is applied to a cover window for a display device, excellent durability can be maintained even when exposed to an extremely cold environment, and stability and reliability of the display appearance can be secured, thereby improving the quality of the display device. Can be expected.

In addition, since the polyamide-imide film according to the embodiment can implement excellent folding characteristics, it can be usefully applied to a foldable display device or a flexible display device.

1 is a cross-sectional view of a display device according to an exemplary embodiment.
2 is a schematic flowchart of a method of manufacturing a polyamide-imide film according to an embodiment.
3 schematically shows a process equipment of a polyamide-imide film according to an embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement them. However, the implementation may be implemented in a variety of different forms and is not limited to the implementation described herein.

In the case where each film, window, panel, or layer, etc., is described as being formed "on" or "under" of each film, window, panel, or layer, the "top (on)" and "under" include both "directly" or "indirectly" formed. In addition, standards for the top/bottom of each component will be described based on the drawings. The size of each component in the drawings may be exaggerated for the sake of explanation, and does not mean a size that is actually applied. In addition, the same reference numerals refer to the same elements throughout the specification.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In the present specification, the singular expression is interpreted as meaning including the singular or plural, interpreted in context, unless otherwise specified.

In addition, all numbers and expressions representing amounts of components, reaction conditions, and the like described in the present specification are to be understood as being modified by the term "about" in all cases unless otherwise specified.

In the present specification, terms such as first and second are used to describe various components, and the components should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component into another component.

In addition, "substituted" in the present specification means deuterium, -F, -Cl, -Br, -I, hydroxyl group, cyano group, nitro group, amino group, amidino group, hydrazine group, unless otherwise specified, Hydrazone group, ester group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted alicyclic oil It means substituted with one or more substituents selected from the group consisting of a device, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group, and the substituents listed above are connected to each other Can form a ring.

Polyamide -Imide film

The embodiment provides a polyamide-imide film capable of maintaining excellent mechanical properties not only excellent in mechanical properties and optical properties, but also under severe conditions at cryogenic temperatures.

The polyamide-imide film contains a polyamide-imide polymer, has a modulus (MO ₁ ) of 5 GPa or more under room temperature conditions, and a dMO value defined in Equation 1 below is 1% to 8%.

<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.

The MO ₂ may be measured at a temperature within an error range recognized in the art.

After the polyamide-imide film is left in a freezer at about -20° C. for 24 hours, the MO ₂ can be measured.

After the polyamide-imide film is taken out from the freezer, the MO ₂ may be measured in a state where the temperature of the polyamide-imide film does not rise and is within the error range.

For example, after the polyamide-imide film is taken out of the freezer, the MO ₂ may be measured within about 1 minute.

For example, after the polyamide-imide film is taken out from the freezer, the MO ₂ may be measured within about 50 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the MO ₂ may be measured within about 40 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the MO ₂ may be measured within about 30 seconds.

For example, after the polyamide-imide film is taken out of the freezer, the MO ₂ may be measured within about 20 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the MO ₂ may be measured within about 10 seconds.

The error range of the measurement temperature of MO ₂ may be -20°C ± 2°C. The error range of the measurement temperature of MO ₂ may be -20°C ± 1.5°C. The error range of the measurement temperature of MO ₂ may be -20°C ± 1°C. The error range of the measurement temperature of MO ₂ may be -20°C ± 0.5°C.

Specifically, the polyamide-imide film has a dMO value defined in Formula 1 of 1.5% to 8%, 1.5% to 7%, 1.5% to 6%, 1.5% to 5%, 1.5% to 4%, It may be 1.5% to 3.5%, or 2.0% to 3.5%, but is not limited thereto.

Since the dMO value of the polyamide-imide film satisfies the above-described range, a film having strong durability and excellent elasticity, because the amount of change in modulus is small under low temperature conditions, and a cover window and a display device including the same can be implemented. It is particularly advantageous when applied to a foldable display device or a rollable display device.

In particular, when the film is applied to a cover window for a display device and a display device, the display device needs to be used in an extremely cold environment, and it is important to secure mechanical properties above a certain level even in such extreme cold.

If the dMO value is out of the above-described range, the mechanical properties rapidly deteriorate under low temperature conditions and thus the reliability of the display appearance decreases, or when applied to a cover window for a display device, cracks may occur due to misalignment with other layers. Therefore, defects may occur in terms of the stability of the appearance.

In addition, the polyamide-imide film may have a modulus (MO ₁ ) of 5.5 GPa or more, 5.8 GPa or more, 6.0 GPa or more, 6.2 GPa or more, 6.5 GPa or more, or 7.0 GPa or more under room temperature conditions, but is limited thereto. It is not.

The polyamide-imide film has a dTS value of 1% to 20% as defined in Equation 2 below.

<Equation 2>

dTS (%) =

In Equation 2, TS ₁ is the tensile strength of the film under room temperature conditions, and TS ₂ is the tensile strength of the film measured at -20°C.

The TS ₂ may be measured at a temperature within an error range recognized in the art.

After the polyamide-imide film is left in a freezer at about -20°C for 24 hours, the TS ₂ may be measured.

After the polyamide-imide film is taken out from the freezer, the temperature of the polyamide-imide film does not rise, and the TS ₂ may be measured in a state within the error range.

For example, after the polyamide-imide film is taken out from the freezer, the TS ₂ may be measured within about 1 minute.

For example, after the polyamide-imide film is taken out from the freezer, the TS ₂ may be measured within about 50 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the TS ₂ may be measured within about 40 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the TS ₂ may be measured within about 30 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the TS ₂ may be measured within about 20 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the TS ₂ may be measured within about 10 seconds.

The error range of the measurement temperature of TS ₂ may be -20°C ± 2°C. The error range of the measurement temperature of TS ₂ may be -20°C ± 1.5°C. The error range of the measurement temperature of TS ₂ may be -20°C ± 1°C. The error range of the measurement temperature of TS ₂ may be -20°C ± 0.5°C.

Specifically, the polyamide-imide film has a dTS value defined in Formula 2 below of 1.5% to 19%, 1.5% to 18%, 1.5% to 15%, 1.5% to 12%, 1.5% to 10%, Alternatively, it may be 1.5% to 7%, but is not limited thereto.

The polyamide-imide film has a dEL value of 5% to 30% as defined in Equation 3 below.

<Equation 3>

dEL (%) =

In Equation 3, EL ₁ is the elongation at break of the film under room temperature conditions, and EL ₂ is the elongation at break of the film measured at -20°C.

The EL ₂ may be measured at a temperature within an error range recognized in the art.

After the polyamide-imide film is left in a freezer at about -20° C. for 24 hours, the EL ₂ can be measured.

After the polyamide-imide film is taken out from the freezer, the temperature of the polyamide-imide film does not rise, and the EL ₂ can be measured in a state within the error range.

For example, after the polyamide-imide film is taken out from the freezer, the EL ₂ may be measured within about 1 minute.

For example, after the polyamide-imide film is taken out from the freezer, the EL ₂ may be measured within about 50 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the EL ₂ may be measured within about 40 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the EL ₂ may be measured within about 30 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the EL ₂ may be measured within about 20 seconds.

For example, after the polyamide-imide film is taken out from the freezer, the EL ₂ may be measured within about 10 seconds.

The error range of the measurement temperature of EL ₂ may be -20°C ± 2°C. The error range of the measurement temperature of EL ₂ may be -20°C ± 1.5°C. The error range of the measurement temperature of EL ₂ may be -20°C ± 1°C. The error range of the measurement temperature of EL ₂ may be -20°C ± 0.5°C.

Specifically, the polyamide-imide film has a dEL value defined in Formula 3 below 5% to 26%, 10% to 26%, 10% to 20%, 10% to 18%, 10% to 15%, Alternatively, it may be 10% to 12%, but is not limited thereto.

The polyamide-imide film has a tensile strength (TS ₁ ) of 25 Kgf/mm ² or more in room temperature conditions.

Specifically, the TS ₁ is 26 Kgf / mm ² or more, 27 Kgf / mm ² Over, 25 Kgf/mm ² To 50 Kgf/mm ² , 25 Kgf/mm ² To 45 Kgf/mm ² , 25 Kgf/mm ² To 40 Kgf/mm ² , 25 Kgf/mm ² To 35 Kgf/mm ² , 25 Kgf/mm ² To 32 Kgf/mm ² , or 26 Kgf/mm ² to 30 Kgf/mm ² , but is not limited thereto.

The polyamide-imide film has an elongation at break (EL ₁ ) of 18% or more under room temperature conditions.

Specifically, the EL ₁ is 18.5% or more, 19% or more, 18% to 35%, 18% to 32%, 18% to 30%, 18% to 28%, 18% to 25%, or 18% to 20 %, but is not limited thereto.

The polyamide-imide film has a modulus (MO ₂ ) of 5.05 GPa or more of the film at -20°C.

Specifically, the MO ₂ is 5.5 GPa or more, 6.0 GPa or more, 6.5 GPa or more, 7.0 GPa or more, 5.05 GPa to 8.5 GPa, 5.5 GPa to 8.0 GPa, 5.5 GPa to 7.7 GPa, 5.5 GPa to 7.0 GPa, 6.0 GPa to It may be 7.0 GPa, or 6.2 GPa to 6.4 GPa, but is not limited thereto.

The polyamide-imide film has a tensile strength (TS ₂ ) of 22.5 Kgf/mm ² measured at -20° C. That's it.

Specifically, the TS ₂ is 23 Kgf/mm ² or more, 25 Kgf/mm ² or more, 22.5 Kgf/mm ² to 35 Kgf/mm ² , 22.5 Kgf/mm ² to 32 Kgf/mm ² , 25 Kgf/mm ² To 32 Kgf/mm ² , or 26 Kgf/mm ² to 31 Kgf/mm ² , but is not limited thereto.

The polyamide-imide film has an elongation at break (EL ₂ ) of 17% or more as measured at -20°C.

Specifically, the EL ₂ may be 17% to 30%, 17% to 25%, 17% to 24%, or 17% to 22%, but is not limited thereto.

The modulus, the tensile strength, and the elongation at break may be measured by the following method.

A load is applied to the film and stretched at a constant speed. At this time, until the film is broken, a load applied to the film according to the deformation of the film is derived. By the load according to the deformation of the film, the modulus, the tensile strength, and the elongation at break may be obtained.

The modulus, the tensile strength, and the elongation at break may be measured by a universal testing machine (UTM). After the film is cut to a predetermined size, the modulus, the tensile strength, and the elongation at break may be measured by the UTM equipment.

Specifically, the film is cut into a size of 10mm X 150mm by a laser cutting equipment (Hardram's HPT500HJ), and a sample can be prepared. As the sample is stretched at a test speed of 12.5 mm/min of the UTM measuring device, the modulus, the tensile strength, and the elongation at break can be measured.

In the present specification, the room temperature may be 20 to 25 °C, specifically 25 °C.

In a state where the temperature of the film is at room temperature, the modulus, the tensile strength, and the elongation at break may be measured in the same manner as described above.

In addition, after storing the film in a low-temperature environment of -20° C. for 24 hours, the modulus, the tensile strength, and the elongation at break may be measured in the same manner as described above within 1 minute after being taken out of the low-temperature environment.

The polyamide-imide film according to the embodiment may have an elongation reflection modulus (LMo ₁ ) at room temperature according to Equation 4 below of 0.5 GPa or more.

<Equation 4>

LMo ₁ (GPa) = (EL ₁ /100) × Mo ₁

Specifically, the LMo ₁ may be 1.0 GPa or more. The LMo ₁ may be 1.1 GPa or more. The LMo ₁ may be 1.2 GPa or more. The LMo ₁ may be 1.3 GPa or more. The LMo ₁ may be 1.4 GPa or more. The LMo ₁ may be 5 GPa or less.

Since the LMo ₁ has the above value, when applied to a foldable display, the polyamide-imide film according to the embodiment can suppress wrinkles in the foldable portion and at the same time have improved bending durability.

The polyamide-imide film according to the embodiment may have an elongation reflection modulus (LMo ₂ ) at a low temperature of 0.6 GPa or more according to Equation 5 below.

<Equation 5>

LMo ₂ (GPa) = (EL ₂ /100) × Mo ₂

Specifically, the LMo ₂ may be 0.7 GPa or more. The LMo ₂ may be 0.9 GPa or more. The LMo ₂ may be 1.0 GPa or more. The LMo ₂ may be 1.1 GPa or more. The LMo ₂ may be 1.2 GPa or more. The LMo ₂ may be 1.3 GPa or more. The LMo ₂ may be 5 GPa or less.

Since the LMo ₂ has the same value, when applied to a foldable display, the polyamide-imide film according to the embodiment can suppress wrinkles in the foldable portion and at the same time have improved bending durability.

Polyamide-imide film according to an embodiment is a value related to mechanical properties such as dMO value, dTS value, dEL value, MO ₁ value, TS ₁ value, EL ₁ value, MO ₂ value, TS ₂ value, EL ₂ value By satisfying the above-described range, durability is strong in extreme low temperature conditions and there is little deformation of physical properties, so that it can be usefully applied to a display device.

Specifically, when the display device to which the film is applied is used in an extremely cold environment, since there is little change in mechanical properties, stability and reliability of the display appearance can be secured, thereby improving the quality of the display device.

The polyamide-imide film has a residual solvent content of 1,500 ppm or less in the film.

For example, the residual solvent content in the film may be 1,200 ppm or less, 1,000 ppm or less, 800 ppm or less, 700 ppm or less, 600 ppm or less, 500 ppm or less, 400 ppm or less, or 300 ppm or less, but is limited thereto. no.

The residual solvent refers to the amount of the solvent remaining in the finally produced film without volatilization during the production of the polyamide-imide film.

When the content of the residual solvent in the polyamide-imide film exceeds the above range, the durability of the film may be deteriorated under low temperature conditions, and in particular, it may affect the mechanical strength, and thus may affect the post-processing of the film. In addition, when the content of the residual solvent exceeds the above range, the hygroscopicity of the film may be accelerated, thereby deteriorating mechanical or optical properties.

The polyamide-imide film according to an embodiment includes a polyamide-imide polymer, and the polyamide-imide polymer may be formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

The polyamide-imide polymer is a polymer comprising an amide repeat unit and an imide repeat unit.

Specifically, the polyamide-imide polymer is an imide repeating unit derived from polymerization of a diamine compound and a dianhydride compound, and an amide repeating unit derived from polymerization of the diamine compound and a dicarbonyl compound. Includes.

The diamine compound is an imide bonded to the dianhydride compound and an amide bonded to the dicarbonyl compound to form a copolymer.

The diamine compound is not particularly limited, but may be, for example, an aromatic diamine compound having an aromatic structure. For example, the diamine compound may be a compound of Formula 1 below.

<Formula 1>

In Formula 1,

E is a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, It may be selected from -C(CH ₃ ) ₂ -and -C(CF ₃ ) ₂ -.

e is selected from an integer of 1 to 5, and when e is 2 or more, E may be the same or different from each other.

(E) _e of Formula 1 may be selected from the group represented by Formulas 1-1a to 1-14a, but is not limited thereto.

Specifically, (E) _e of Formula 1 may be selected from the group represented by Formulas 1-1b to 1-13b, but is not limited thereto:

More specifically, (E) _e of Formula 1 may be a group represented by Formula 1-6b or a group represented by Formula 1-9b.

In one embodiment, the diamine compound may include a compound having a fluorine-containing substituent or a compound having an ether group (-O-).

The diamine compound may be formed of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent may be a fluorinated hydrocarbon group, and specifically, a trifluoromethyl group, but is not limited thereto.

In another embodiment, as the diamine compound, one type of diamine compound may be used. That is, the diamine compound may consist of a single component.

For example, the diamine compound is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-Bis(trifluoromethyl)-4,4) having the following structure. '-diaminobiphenyl, TFDB), but is not limited thereto.

Since the dianhydride compound has a low birefringence value, the dianhydride compound is a compound capable of contributing to improvement of optical properties such as transmittance of a film containing the polyamide-imide polymer.

The dianhydride compound is not particularly limited, but may be, for example, an aromatic dianhydride compound having an aromatic structure. For example, the aromatic dianhydride compound may be a compound of Formula 2 below.

<Formula 2>

In Formula 2, G is a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aromatic ring group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaromatic ring group, and the aliphatic ring group, the hetero aliphatic ring group, the aromatic ring group or the heteroaromatic ring group is present alone, or , Conjugated to each other to form a condensed ring, or a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group , -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) _2- And -C(CF ₃ ) ₂ -.

G in Formula 2 may be selected from the group represented by Formulas 2-1a to 2-9a, but is not limited thereto.

For example, G in Formula 2 may be a group represented by 2-2a, a group represented by Formula 2-8a, or a group represented by 2-9a.

In one embodiment, the dianhydride compound may include a compound having a fluorine-containing substituent, a compound having a biphenyl group, or a compound having a ketone group.

The dianhydride compound may be formed of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent may be a fluorinated hydrocarbon group, and specifically, a trifluoromethyl group, but is not limited thereto.

In another embodiment, the dianhydride compound may be composed of one single component or a mixture of two components.

For example, the dianhydride compound is 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (2,2'-Bis- (3,4) having the following structure. -Dicarboxyphenyl)hexafluoropropane dianhydride, 6FDA) and 1 selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride, BPDA) It may include more than a species, but is not limited thereto.

The diamine compound and the dianhydride compound may be polymerized to produce polyamic acid.

Subsequently, the polyamic acid may be converted to polyimide through a dehydration reaction, and the polyimide includes an imide repeating unit.

The polyimide may form a repeating unit represented by Formula A below.

<Formula A>

In Formula A, descriptions of E, G and e are as described above.

For example, the polyimide may include a repeating unit represented by Formula A-1 below, but is not limited thereto.

<Formula A-1>

In Formula A-1, n is an integer of 1 to 400.

The dicarbonyl compound is not particularly limited, but may be, for example, a compound represented by the following formula (3).

<Formula 3>

In Chemical Formula 3,

J is a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, It may be selected from -C(CH ₃ ) ₂ -and -C(CF ₃ ) ₂ -.

j is selected from an integer of 1 to 5, and when j is 2 or more, J may be the same or different from each other.

X is a halogen atom. Specifically, X may be F, Cl, Br, I, or the like. More specifically, X may be Cl, but is not limited thereto.

(J) _j of Formula 3 may be selected from the group represented by Formulas 3-1a to 3-14a, but is not limited thereto.

Specifically, (J) _j of Formula 3 may be selected from the group represented by Formulas 3-1b to 3-8b, but is not limited thereto:

More specifically, (J) _j of Formula 3 may be a group represented by Formula 3-1b, a group represented by Formula 3-2b, a group represented by 3-3b, or a group represented by 3-8b. have.

For example, (J) _j in Formula 3 may be a group represented by Formula 3-1b or a group represented by Formula 3-2b.

In one embodiment, the dicarbonyl compound may be used by mixing at least two different dicarbonyl compounds. When two or more types of the dicarbonyl compounds are used, two or more types of dicarbonyl compounds selected from the group represented by (J) _j in Chemical Formula 3 may be used. have.

In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound having an aromatic structure.

For example, the dicarbonyl compound may include a first dicarbonyl compound and/or a second dicarbonyl compound.

Each of the first dicarbonyl compound and the second dicarbonyl compound may be an aromatic dicarbonyl compound.

The first dicarbonyl compound and the second dicarbonyl compound may be different compounds.

For example, the first dicarbonyl compound and the second dicarbonyl compound may be different aromatic dicarbonyl compounds, but are not limited thereto.

When the first dicarbonyl compound and the second dicarbonyl compound are each an aromatic dicarbonyl compound, since it contains a benzene ring, the surface hardness and tensile strength of the film containing the prepared polyamide-imide resin It can contribute to improving mechanical properties such as.

In addition, the first dicarbonyl compound and the second dicarbonyl compound may have a structural isomer relationship with each other.

When the first dicarbonyl compound and the second dicarbonyl compound have a structural isomerism relationship with each other, the polymers are well packed and thus excellent mechanical properties may be implemented.

The dicarbonyl compound is terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (1,1'-biphenyl-4) having the following structure. , 4'-dicarbonyl dichloride, BPDC), isophthaloyl chloride (IPC), or a combination thereof, but is not limited thereto.

For example, the first dicarbonyl compound may include BPDC, and the second dicarbonyl compound may include TPC, but is not limited thereto.

When BPDC as the first dicarbonyl compound and TPC as the second dicarbonyl compound are appropriately used in combination, a film including the prepared polyamide-imide resin may have high oxidation resistance.

Alternatively, the first dicarbonyl compound may include IPC, and the second dicarbonyl compound may include TPC, but the present invention is not limited thereto.

When using in an appropriate combination of IPC as the first dicarbonyl compound and TPC as the second dicarbonyl compound, the prepared polyamide-imide resin may have high oxidation resistance, as well as It is economical because it can reduce costs.

The diamine compound and the dicarbonyl compound may be polymerized to form a repeating unit represented by Formula B below.

<Formula B>

In Formula B, descriptions of E, J, e and j are as described above.

For example, the diamine compound and the dicarbonyl compound may be polymerized to form an amide repeating unit represented by Formulas B-1 and B-2.

Alternatively, the diamine compound and the dicarbonyl compound may be polymerized to form an amide repeating unit represented by Formulas B-2 and B-3.

<Formula B-1>

In Formula B-1, x is an integer of 1 to 400.

<Formula B-2>

Y in Formula B-2 is an integer of 1 to 400.

<Formula B-3>

Y in Formula B-3 is an integer of 1 to 400.

According to one embodiment, the polyamide-imide polymer may include a repeating unit represented by Formula A and a repeating unit represented by Formula B below:

<Formula A>

<Formula B>

In Formulas A and B,

E and J are each independently a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic ring group, substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, substituted or unsubstituted C ₁ -C ₃₀ alkylene group, substituted or unsubstituted C ₂ -C ₃₀ alkenylene group , Substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si( CH ₃ ) ₂ -, -C(CH ₃ ) ₂ -and -C(CF ₃ ) ₂ -is selected from,

e and j are each independently selected from an integer of 1 to 5,

When e is 2 or more, 2 or more E are the same or different from each other,

When j is 2 or more, 2 or more J are the same as or different from each other,

G is a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaromatic cyclic group, and the aliphatic cyclic group, the hetero aliphatic cyclic group, the aromatic cyclic group or the heteroaromatic cyclic group is present alone or condensed with each other Or a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-,- S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) ₂ -and -C(CF ₃ ) It is connected by a connector selected from ₂ -.

In the polyamide-imide polymer, the molar ratio of the imide repeating unit and the amide repeating unit may be 2:98 to 45:55, but is not limited thereto. Specifically, the molar ratio of the imide repeating unit to the amide repeating unit may be 2:98 to 40:60, 2:98 to 35:65, or 3:97 to 35:65, but is not limited thereto.

When the molar ratio of the imide repeating unit and the amide repeating unit is within the above range, optical properties such as transmittance, haze, and yellowness of the polyamide-imide film and mechanical properties such as modulus, tensile strength, and elongation at break are excellent.

In the polyamide-imide polymer, the molar ratio of the repeating unit represented by Formula A and the repeating unit represented by Formula B may be 2:98 to 45:55, but is not limited thereto. Specifically, the molar ratio of the repeating unit represented by Formula A and the repeating unit represented by Formula B may be 2:98 to 40:60, 2:98 to 35:65, or 3:97 to 35:65, It is not limited thereto.

According to another embodiment, the polyamide-imide film may further include a metal salt.

The metal of the metal salt may be at least one selected from Group 1, Group 2, Group 13, and Group 14 metals. For example, the metal of the metal salt may be a metal belonging to Group 1. As another example, the metal of the metal salt may be at least one selected from lithium (Li), sodium (Na), and potassium (K). For example, the metal salt may contain a lithium cation.

The anion of the metal salt may be at least one selected from halogen ions, carbonate ions, nitrate ions, phosphate ions and sulfate ions. In addition, the anion may be a monovalent anion or a divalent anion.

The metal salt may be at least one selected from Li ₂ CO ₃ , LiBr, LiCl, Na ₂ CO ₃ and NaCl. For example, the metal salt may be at least one selected from Li ₂ CO ₃ , LiBr and LiCl.

The number of metal salts contained in the polyamide-imide film may be one or two or more. For example, the number of metal salts included in the polyamide-imide film may be one.

According to an embodiment, the metal salt contained in the polyamide-imide film is preferably Li ₂ CO ₃ or LiCl.

Since the polyamide-imide film contains a metal salt, agglomeration caused by strong attraction between amide repeating units in the polyamide-imide polymer is prevented, and the solubility of the polymer is increased in a solvent to increase the high molecular weight. Polyamide-imide polymers can be formed. As a result, a polyamide-imide film exhibiting excellent mechanical properties, particularly high modulus, even at low temperatures can be implemented.

The content of the metal salt is 0.1 to 2.0 parts by weight based on 100 parts by weight of the solid content of the polyamide-imide polymer.

Specifically, the content of the metal salt is 0.1 to 1.8 parts by weight, 0.1 to 1.6 parts by weight, 0.3 to 1.5 parts by weight, 0.5 to 1.5 parts by weight, 0.5 to 1.2 parts by weight based on 100 parts by weight of the solid content of the polyamide-imide polymer. Parts, or 0.5 to 1.0 parts by weight, but is not limited thereto.

When the content of the metal salt exceeds the above range, the metal salt elutes to the film surface and the aggregated particles become visually visible defects, and the optically cloudy and transparency decreases to achieve the appearance quality as an optical film. There is a problem that it cannot be done.

According to one embodiment, the polyamide-imide film may further include a filler.

The filler may be at least one selected from the group consisting of barium sulfate, silica, and calcium carbonate. When the polyamide-imide film includes the filler, it is possible to improve roughness and windability, as well as improve the effect of improving running scratches during film production.

In addition, the particle diameter of the filler may be 0.01㎛ to 1.0㎛. The particle diameter of the filler is 0.01㎛ or more to less than 1.0㎛, 0.02㎛ to 0.9㎛, 0.05㎛ to 0.9㎛, 0.1㎛ to 0.8㎛, 0.1㎛ to 0.7㎛, 0.1㎛ to 0.6㎛, 0.1㎛ to 0.5㎛ or 0.1 It may be ㎛ to 0.3㎛, but is not limited thereto.

The polyamide-imide film may contain the filler in an amount of 0.01 to 2.5% by weight, based on the total weight of the polyamide-imide film.

According to one embodiment, the transmittance of the polyamide-imide film may be 80% or more. For example, the transmittance may be 85% or more, 88% or more, 80% to 99%, 80% to 99%, 85% to 99%, or 88% to 99%.

The haze of the polyamide-imide film is 1% or less. Specifically, the haze may be 0.8% or less, 0.7% or less, 0.6% or less, or 0.5% or less, but is not limited thereto.

The yellow index of the polyamide-imide film is 4 or less. For example, the yellowness may be 3.8 or less, 3.5 or less, 3.0 or less, or 2.7 or less, but is not limited thereto.

When the polyamide-imide film is folded to have a radius of curvature of 1 mm based on a thickness of 50 μm, the number of folding times before breaking may be 200,000 or more, but is not limited thereto. The number of folding is one that is bent and unfolded so that the radius of curvature of the film is 1 mm.

The compressive strength of the polyamide-imide film is 0.4 kgf/µm or more. Specifically, the compressive strength may be 0.45 kgf/µm or more or 0.46 kgf/µm or more, but is not limited thereto.

When perforating the polyamide-imide film in UTM compression mode at a speed of 10 mm/min using a 2.5 mm spherical tip, the maximum perforation diameter (mm) including cracks is 60 mm or less. Specifically, the maximum perforation diameter may be 5 to 60 mm, 10 to 60 mm, 15 to 60 mm, 20 to 60 mm, 25 to 60 mm, or 25 to 58 mm, but is not limited thereto.

The polyamide-imide film has a surface hardness of HB or higher. Specifically, the surface hardness may be H or more or 2H or more, but is not limited thereto.

The polyamide-imide film according to an embodiment can secure excellent optical properties such as low haze, low yellowness (YI), and high transmittance, as well as excellent folding properties and excellent mechanical properties even in harsh environments at low temperatures. .

Accordingly, it is possible to implement long-term stable mechanical properties for a substrate requiring flexibility in terms of modulus, elongation, tensile properties, and elastic resilience.

The physical properties of the polyamide-imide film described above are based on a thickness of 40 µm to 60 µm. For example, the physical properties of the polyamide-imide film are based on a thickness of 50 μm.

The features of the composition and physical properties of the polyamide-imide film described above may be combined with each other.

For example, the polyamide-imide film may have a transmittance of 80% or more, a haze of 1% or less, and a yellowness of 4 or less, but is not limited thereto.

In addition, the above-described physical properties of the polyamide-imide film are the chemical and physical properties of the components constituting the polyamide-imide film, as well as the process conditions of each step in the method of manufacturing the polyamide-imide film to be described later. Is the result of the synthesis.

Cover for display device window

A cover window for a display device according to an embodiment includes a polyamide-imide film and a functional layer.

The polyamide-imide film contains a polyamide-imide polymer, and the modulus (MO ₁ ) of the polyamide-imide film under room temperature conditions is 5 GPa or more, and the dMO value defined in the following formula 1 is 1% to 8%.

<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.

A detailed description of the polyamide-imide film is as described above.

The cover window for a display device may be usefully applied to a display device.

Display device

A display device according to an embodiment includes a display unit; And a cover window disposed on the display unit, wherein the cover window includes a polyamide-imide film and a functional layer.

The polyamide-imide film contains a polyamide-imide polymer, and the modulus (MO ₁ ) of the polyamide-imide film at room temperature conditions is 5 GPa or more, and the dMO value defined in the following formula 1 is 1% to 8%.

<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.

A detailed description of the polyamide-imide film and the cover window is as described above.

1 is a cross-sectional view of a display device according to an exemplary embodiment.

Specifically, FIG. 1 shows a polyamide-imide film 100 and a functional layer 200 having a first surface 101 and a second surface 102 on the display unit 400 and the display unit 400. A display device in which a cover window 300 including a is disposed and an adhesive layer 500 is disposed between the display unit 400 and the cover window 300 is illustrated.

The display unit 400 may display an image and may have a flexible characteristic.

The display unit 400 may be a display panel for displaying an image, for example, a liquid crystal display panel or an organic light emitting display panel. The organic light emitting display panel may include a front polarizing plate and an organic EL panel.

The front polarizing plate may be disposed on the front surface of the organic EL panel. Specifically, the front polarizing plate may be adhered to a surface on which an image is displayed in the organic EL panel.

The organic EL panel displays an image by self-emission in units of pixels. The organic EL panel may include an organic EL substrate and a driving substrate. The organic EL substrate may include a plurality of organic electroluminescent units each corresponding to a pixel. Specifically, each may include a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. The driving substrate may be driveably coupled to the organic EL substrate. That is, the driving substrate is coupled so as to apply a driving signal such as a driving current to the organic EL substrate, so that current is applied to each of the organic electroluminescent units to drive the organic EL substrate.

In addition, an adhesive layer 500 may be included between the display unit 400 and the cover window 300. The adhesive layer may be an optically transparent adhesive layer, and is not particularly limited.

The cover window 300 is disposed on the display unit 400. The cover window may be positioned at the outermost side of the display device according to the embodiment to protect the display unit.

The cover window 300 may include a polyamide-imide film and a functional layer. The functional layer may be at least one selected from the group consisting of a hard coating, a reflectance reducing layer, an antifouling layer, and an anti-glare layer. The functional layer may be coated on at least one surface of the polyamide-imide film.

In the case of the display device according to the embodiment, since a film having improved mechanical properties is included in a low temperature condition, it is easy to protect the display unit from a low temperature condition.

Polyamide -Method of manufacturing imide film

One embodiment provides a method of manufacturing a polyamide-imide film.

A method of preparing a polyamide-imide film according to an embodiment includes the steps of polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide polymer solution; Injecting the polymer solution into a tank; Extruding and casting the polymer solution in the tank, followed by drying, to prepare a gel sheet; And heat treating the gel sheet, wherein the heat treatment step of the gel sheet includes at least two hot air treatment steps.

Specifically, referring to FIG. 2, in the method of manufacturing a polyamide-imide film according to an embodiment, a diamine compound, a dianhydride compound, and a dicarbonyl compound are simultaneously or sequentially mixed in an organic solvent in a polymerization facility. Mixing and reacting the mixture to prepare a polymer solution (S100); Moving the polymer solution to a tank (S200); Purging using an inert gas (S300); Extruding and casting the polymer solution in the tank on a belt and then drying to prepare a gel-sheet (S400); Manufacturing a cured film by heat treatment while moving the gel-sheet (S500); Cooling while moving the cured film (S600); And winding the cooled cured film using a winder (S700).

The polyamide-imide film is a film mainly composed of a polyamide-imide resin, and the polyamide-imide resin is a resin containing an amide repeating unit and an imide repeating unit as structural units in a predetermined molar ratio.

In the method for producing the polyamide-imide film, the polymer solution for preparing the polyamide-imide resin is a diamine compound, a dianhydride compound, and a dicarbonyl compound simultaneously or It is prepared by sequentially mixing and reacting the mixture (S100).

In one embodiment, the polymer solution may be prepared by reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound simultaneously in an organic solvent.

In another embodiment, the preparing of the polymer solution may include preparing a polyamic acid (PAA) solution by first mixing and reacting the diamine compound and the dianhydride compound in a solvent; And forming an amide bond and an imide bond by secondary mixing and reacting the dicarbonyl compound with the polyamic acid (PAA) solution. The polyamic acid solution is a solution containing polyamic acid.

Alternatively, the step of preparing the polymer solution may include preparing a polyamic acid solution by first mixing and reacting the diamine compound and the dianhydride compound in a solvent; Dehydrating the polyamic acid solution to prepare a polyimide (PI) solution; And forming an amide bond by secondary mixing and reacting the dicarbonyl compound to the polyimide (PI) solution. The polyimide solution is a solution containing a polymer having an imide repeating unit.

In another embodiment, the step of preparing the polymer solution may include preparing a polyamide (PA) solution by first mixing and reacting the diamine compound and the dicarbonyl compound in a solvent; It may include a step of forming an imide bond further by secondary mixing and reacting the dianhydride compound to the polyamide (PA) solution. The polyamide solution is a solution containing a polymer having an amide repeating unit.

The polymer solution prepared as described above may be a solution containing a polymer containing at least one selected from the group consisting of polyamic acid (PAA) repeat units, polyamide (PA) repeat units, and polyimide (PI) repeat units. .

Alternatively, the polymer contained in the polymer solution is an imide repeating unit derived from polymerization of the diamine compound and the dianhydride compound, and an amide derived from polymerization of the diamine compound and the dicarbonyl compound. Includes repeating units.

The solid content contained in the polymer solution may be 10% to 30% by weight. Alternatively, the content of the solid content in the polymer solution may be 15% by weight to 25% by weight, but is not limited thereto.

When the content of the solid content in the polymer solution is within the above range, a polyamide-imide film can be effectively produced in an extrusion and casting process. In addition, the prepared polyamide-imide film may have mechanical properties such as modulus, tensile strength, elongation at break, and optical properties, such as low yellowness, that are hardly degraded even under low temperature conditions.

In one embodiment, before the step of preparing the polymer solution, a step of dissolving a metal salt in an organic solvent may be included.

Description of the type and content of the metal salt is as described above.

In another embodiment, preparing the polymer solution may further include introducing a catalyst.

In this case, the catalyst may include at least one selected from the group consisting of beta picoline, acetic anhydride, isoquinoline (IQ), and pyridine-based compounds, but is not limited thereto.

The catalyst may be added in an amount of 0.01 to 0.5 mole equivalent, 0.01 to 0.4 mole equivalent, or 0.01 to 0.3 mole equivalent based on 1 mole of the polyamic acid, but is not limited thereto.

When the catalyst is added, the reaction rate may be improved, and chemical bonding between or within the repeating unit structure may be improved.

In another embodiment, preparing the polymer solution may further include adjusting the viscosity of the polymer solution.

Specifically, the step of preparing the polymer solution includes: (a) preparing a first polymer solution by simultaneously or sequentially mixing and reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent; (b) measuring the viscosity of the first polymer solution to evaluate whether a target viscosity is reached; And (c) preparing a second polymer solution having a target viscosity by adding the dicarbonyl compound when the viscosity of the first polymer solution does not reach the target viscosity.

The target viscosity may be 100,000 cps to 500,000 cps at room temperature. Specifically, the target viscosity may be 100,000 cps to 400,000 cps, 100,000 cps to 350,000 cps, 100,000 cps to 300,000 cps, 150,000 cps to 300,000 cps, or 150,000 to 250,000 cps at room temperature. However, it is not limited thereto.

In the case of the step of preparing the first polymer solution and the step of preparing the second polymer solution, the viscosity of the prepared polymer solution is different. For example, the viscosity of the second polymer solution is higher than that of the first polymer solution.

The stirring speed when preparing the first polymer solution and the stirring speed when preparing the second polymer solution are different. For example, the stirring speed when preparing the first polymer solution is faster than the stirring speed when preparing the second polymer solution.

In another embodiment, the step of preparing the polymer solution may further include adjusting the pH of the polymer solution. In this step, the pH of the polymer solution may be adjusted to 4 to 7, for example, 4.5 to 7, or 5 to 7.

The pH of the polymer solution may be adjusted by adding a pH adjusting agent, and the pH adjusting agent is not particularly limited, but may include, for example, an amine-based compound such as alkoxyamine, alkylamine or alkanolamine.

By adjusting the pH of the polymer solution to the above range, it is possible to prevent damage to the equipment in the subsequent process, to prevent the occurrence of defects in the film prepared from the polymer solution, and to target optical properties in terms of yellowness and modulus. And mechanical properties.

The pH adjuster may be added in an amount of 0.1 mol% to 10 mol% or 0.1 mol to 7.5 mol% based on the total number of moles of monomers in the polymer solution.

In another embodiment, preparing the polymer solution may further include purging using an inert gas. By removing moisture and reducing impurities through the inert gas purging step, the reaction yield can be increased, and the surface appearance and mechanical properties of the final film can be excellently implemented.

The inert gas may be one or more selected from the group consisting of nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), but is limited thereto. no. Specifically, the inert gas may be nitrogen.

The molar ratio of the dianhydride compound: the dicarbonyl compound used to prepare the polymer solution may be 2:98 to 45:55, for example, 2:98 to 40:60, 2:98 to 35:65 or 3:97 to 35:65. By using the dianhydride compound and the dicarbonyl compound in such a molar ratio, optical properties such as transmittance, haze, yellowness, etc. of the polyamide-imide film prepared from the polymer solution and modulus, tensile strength, elongation at break, etc. It is advantageous to achieve the desired mechanical properties.

remind The description of the diamine compound, the dianhydride compound and the dicarbonyl compound is as described above.

In one embodiment, the organic solvent is dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), m- Cresol (m-cresol), tetrahydrofuran (tetrahydrofuran, THF) and may be one or more selected from the group consisting of chloroform. The organic solvent used in the polymer solution may be dimethylacetamide (DMAc), but is not limited thereto.

Next, after the step of preparing the polymer solution, the polymer solution is moved to a tank (S200).

3 is a schematic diagram of a manufacturing process equipment for the polyamide-imide film according to an embodiment. 3, the above-described polymer solution is prepared in a polymerization facility 10, and the polymer solution thus prepared is transferred and stored in a tank 20.

In this case, after preparing the polymer solution, a step of moving the polymer solution to a tank without a separate process is performed. Specifically, the polymer solution prepared in the polymerization facility is transferred to and stored in the tank as it is without a separate precipitation and re-dissolution process for removing impurities. Conventionally, in order to remove impurities such as hydrochloric acid (HCl) generated during the preparation of the polymer solution, the prepared polymer solution was purified through a separate process to remove impurities, and a process of re-dissolving it in a solvent was performed. . However, in this case, there is a problem that the loss of the active ingredient increases in the process of removing the impurities, and as a result, the yield decreases.

Accordingly, the manufacturing method according to an embodiment minimizes the content of impurities at a source in the manufacturing process of the polymer solution, or even if predetermined impurities are present, they are appropriately controlled in a subsequent process so as not to deteriorate the physical properties of the final film. It has the advantage of producing a film without a separate precipitation or re-dissolution process.

The tank 20 is a place to store the polymer solution before filming it, and its internal temperature may be -20°C to 20°C.

Specifically, the internal temperature may be -20°C to 10°C, -20°C to 5°C, -20°C to 0°C, or 0°C to 10°C, but is not limited thereto.

By controlling the internal temperature of the tank 20 within the above range, it is possible to prevent the polymer solution from being deteriorated during storage, and to reduce the moisture content to prevent defects in the film produced therefrom.

The method of manufacturing the polyamide-imide film may further include performing vacuum defoaming on the polymer solution transferred to the tank 20.

The vacuum defoaming may be performed for 30 minutes to 3 hours after reducing the internal pressure of the tank to 0.1 bar to 0.7 bar. By performing vacuum defoaming under such conditions, air bubbles inside the polymer solution can be reduced, and as a result, surface defects of the film produced therefrom can be prevented, and optical properties such as haze can be excellently implemented.

In addition, the method of manufacturing the polyamide-imide film may further include purging the polymer solution transferred to the tank 20 using an inert gas (S300).

Specifically, the purging is performed by purging the internal pressure of the tank to 1 to 2 atmospheres using an inert gas. By performing nitrogen purging under such conditions, moisture in the polymer solution is removed and impurities are reduced, so that the reaction yield can be increased, and optical properties such as haze and mechanical properties can be excellently implemented.

The inert gas may be one or more selected from the group consisting of nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), but is limited thereto. no. Specifically, the inert gas may be nitrogen.

The vacuum defoaming step and the step of purging the tank using an inert gas are performed as separate processes.

For example, the vacuum degassing step may be performed, and thereafter, the step of purging the tank with an inert gas may be performed, but the present invention is not limited thereto.

By performing the step of vacuum degassing and/or the step of purging the tank using an inert gas, physical properties of the surface of the prepared polyamide-imide film may be improved.

Thereafter, it may further include storing the polymer solution in the tank 20 for 1 to 360 hours. At this time, the internal temperature of the tank may be kept at -20 ℃ to 20 ℃.

The method of manufacturing the polyamide-imide film further includes the step of producing a gel-sheet by casting the polymer solution in the tank 20 and drying it (S400).

The polymer solution may be cast on a casting body such as a casting roll or a casting belt.

Referring to FIG. 2, according to one embodiment, the polymer solution may be applied as a casting body on the casting belt 30 and dried while moving, and may be manufactured as a gel-like sheet.

When the polymer solution is injected onto the belt 30, the injection rate may be 300 g/min to 700 g/min. When the injection rate of the polymer solution satisfies the above range, the gel-sheet may be uniformly formed with an appropriate thickness.

In addition, the casting thickness of the polymer solution may be 200㎛ to 700㎛. When the polymer solution is cast in the above thickness range and then dried and heat treated into a final film, an appropriate thickness and thickness uniformity can be ensured.

As described above, the polymer solution may be 100,000 cps to 500,000 cps at room temperature, for example, 100,000 cps to 400,000 cps, 100,000 cps to 350,000 cps, 150,000 cps to 350,000 cps, or It may be between 150,000 cps and 250,000 cps. By satisfying the viscosity range, when the polymer solution is cast on a belt, it can be cast to a uniform thickness without defects.

After casting the polymer solution, the drying step is performed at a temperature of 80°C to 140°C for 5 to 20 minutes. I can. During the drying, a part or all of the solvent of the polymer solution is volatilized to prepare the gel-sheet.

The moving speed of the gel-sheet on the casting body upon drying may be 0.1 m/min to 15 m/min, for example, 0.5 m/min to 10 m/min, but is not limited thereto.

According to one embodiment, after the step of preparing the gel sheet, the step of fixing the end of the gel sheet may be performed.

In the step of fixing the end of the gel sheet, the gel sheet may be stretched 0.99 to 1.1 times in the MD direction. Specifically, the gel sheet may be stretched 0.99 to 1.08 times, 1.0 to 1.08 times, or 1.01 to 1.08 times in the MD direction, but is not limited thereto.

In addition, in the step of fixing the end of the gel sheet, the gel sheet may be stretched 0.99 to 1.1 times in the TD direction. Specifically, the gel sheet may be stretched 0.99 to 1.08 times, 1.0 to 1.08 times, or 1.01 to 1.08 times in the TD direction, but is not limited thereto.

In addition, the gel sheet may be gradually stretched in the following heat treatment step. Specifically, the gel sheet may be stretched about 1.01 to about 1.08 times in the following heat treatment step.

The manufacturing method of the polyamide-imide film includes the step of preparing a cured film by heat treatment while moving the gel-sheet (S500).

Referring to FIG. 3, the heat treatment of the gel-sheet may be performed by passing through a thermosetting machine 40.

When passing through the thermosetting machine 40, the gel-sheet is subjected to hot air treatment.

When heat treatment by hot air is performed, the amount of heat may be evenly applied. If the amount of heat is not evenly distributed, satisfactory mechanical properties cannot be achieved. In particular, a satisfactory surface roughness cannot be achieved, and in this case, the surface tension may be too high or too low.

According to one embodiment, the heat treatment of the gel-sheet may be performed in two or more steps.

According to another embodiment, the heat treatment may be performed until the content of the residual solvent contained in the film is 1,500 ppm or less.

Specifically, the heat treatment step of the gel sheet is a first hot air treatment step performed for 0.2 to 5 minutes in the range of 80 ℃ to 140 ℃; And a second hot air treatment step performed for 5 minutes to 150 minutes in the range of 160°C to 350°C.

In the heat treatment, the second heat treatment step is performed after the first heat treatment step. At this time, after performing the second heat treatment step, when the content of the organic solvent contained in the gel-sheet exceeds 1,500 ppm, a third heat treatment step may be additionally performed.

By heat treatment under these conditions, the prepared cured film can secure excellent folding properties, optical properties, and excellent mechanical properties even under low temperature.

According to another embodiment, the heat treatment may include passing through an IR heater. The heat treatment by the IR heater may be performed for 1 minute to 30 minutes at a temperature range of 300°C or higher. Specifically, the heat treatment by the IR heater may be performed for 1 minute to 20 minutes at a temperature range of 300 ℃ to 500 ℃.

The manufacturing method of the polyamide-imide film includes cooling while moving the cured film (S600).

3, the cured film is performed after passing through the thermosetting machine 40, and may be performed using a separate cooling chamber (not shown), and an appropriate temperature atmosphere without a separate cooling chamber It can also be carried out by composition.

The step of cooling while moving the cured film may include: a first temperature reduction step of reducing temperature at a rate of 100°C/min to 1000°C/min; And a second temperature reduction step of reducing temperature at a rate of 40°C/min to 400°C/min.

In this case, specifically, the second temperature reduction step is performed after the first temperature reduction step, and the temperature reduction speed of the first temperature reduction step may be faster than the temperature reduction speed of the second temperature reduction step.

For example, a maximum speed during the first temperature reduction step is faster than a maximum speed during the second temperature reduction step. Alternatively, the lowest speed during the first temperature reduction step is faster than the lowest speed during the second temperature reduction step.

By performing the cooling step of the cured film in multiple steps as described above, the physical properties of the cured film can be more stabilized, and the optical properties and mechanical properties of the film established in the curing process can be more stably maintained for a long period of time.

The moving speed of the gel-sheet and the cured film is the same.

The manufacturing method of the polyamide-imide film includes the step of winding the cooled cured film using a winder (S700).

Referring to FIG. 2, the winding of the cooled cured film may be performed using a roll-type winder 50.

At this time, the ratio of the moving speed of the gel-sheet on the belt during drying: the moving speed of the cured film upon winding is 1:0.95 to 1:1.40. Specifically, the ratio of the moving speed may be 1:0.99 to 1:1.20, 1:0.99 to 1:1.10, or 1:1.00 to 1:1.05, but is not limited thereto.

When the ratio of the moving speed is out of the above range, there is a concern that mechanical properties of the cured film may be damaged, and flexibility and elastic properties may be deteriorated.

In the method of manufacturing the polyamide-imide film, the thickness deviation (%) according to the following general formula 1 may be 3% to 30%. Specifically, the thickness deviation (%) may be 5% to 20%, but is not limited thereto.

<General Formula 1> Thickness deviation (%) = {(M1-M2)/M1} X 100

In General Formula 1, M1 is the thickness (µm) of the gel-sheet, and M2 is the thickness (µm) of the cured film cooled during winding.

The polyamide-imide film may exhibit excellent optical and mechanical properties by being prepared according to the above-described manufacturing method. The polyamide-imide film may be applicable to a variety of applications requiring flexibility and transparency. For example, the polyamide-imide film may be applied to solar cells, displays, semiconductor devices, and sensors.

The description of the polyamide-imide film manufactured according to the above-described manufacturing method is as described above.

The above will be described in more detail by the following examples. However, the following examples are for illustrative purposes only, and the scope of the examples is not limited thereto.

< Example >

Example One

After filling dimethylacetamide (DMAc) as an organic solvent in a nitrogen atmosphere at 20° C. in a 1L glass reactor with a temperature controllable double jacket, metal salt (LiCl) is added to the organic solvent based on 100 parts by weight of the following polymer solids: Dissolve parts by weight. Thereafter, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl (2,2'-TFMB) was slowly added and dissolved. Thereafter, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6-FDA) was slowly added and stirred for 1 hour. Then, isophthaloyl chloride (IPC) was added and stirred for 1 hour, terephthaloyl chloride (TPC) was added and stirred for 1 hour to prepare a polymer solution. The obtained polymer solution was applied to a glass plate, dried for the temperature and time of the drying step shown in Table 1, and then the gel sheet was peeled off the glass plate. Thereafter, the end of the gel sheet was fixed to the pin frame, followed by hot air treatment to obtain a polyamide-imide film having a thickness of 50 µm. The hot air treatment was performed by dividing into two steps, and the temperature and time of the first heat treatment step and the second heat treatment step are as shown in Table 1. In addition, the gel sheet was stretched by about 1.03 times during the first heat treatment step.

Regarding the contents of TFMB, 6FDA, TPC and IPC, the number of moles of the dianhydride compound and the dicarbonyl compound are shown in Table 1 based on 100 moles of the diamine compound.

Example 2 to 8 Comparative example 1 and 2

As shown in Table 1 below, a film was prepared in the same manner as in Example 1, except that the type/content/dissolution of the metal salt, the type, content, and process conditions of each reactant were different. The content of the metal salt shown in Table 1 below is based on 100 parts by weight of the polymer solid content in parts by weight of the metal salt.

< Evaluation example >

The following physical properties were measured and evaluated for the films prepared in Examples 1 to 8 and Comparative Examples 1 and 2, and the results are shown in Table 1 below.

Evaluation example 1: Measuring the thickness of the film

Using a digital micrometer 547-401 manufactured by Mitsutoyo, Japan, 5 points were measured in the width direction, and the thickness was measured as an average value.

Evaluation example 2: Measurement of tensile strength

The film was cut into a size of 10mm X 150mm using a laser cutting equipment (Hardram's HPT500HJ), and the same sample was measured three times at a test speed of 12.5 mm/min of a UTM measuring device to measure the tensile strength under room temperature conditions.

In addition, after the film was stored in a low temperature environment of -20°C for 24 hours, it was taken out from the low temperature environment and the tensile strength was measured as described above within 1 minute.

Evaluation example 3: Elongation at break Measure

The film was cut into a size of 10mm X 150mm using a laser cutting equipment (Hardram's HPT500HJ), and the same sample was measured three times at a test speed of 12.5 mm/min of a UTM measuring device, and the elongation at break was measured under room temperature conditions.

In addition, after storing the film in a low temperature environment of -20°C for 24 hours, it was taken out from the low temperature environment and the elongation at break was measured within 1 minute as described above.

Evaluation example 4: Modulus Measure

The film was cut into a size of 10 mm X 150 mm using a laser cutting equipment (Hardram's HPT500HJ), and the same sample was measured three times at a test speed of 12.5 mm/min of a UTM measuring device to measure the modulus under room temperature conditions.

In addition, after storing the film in a low temperature environment of -20°C for 24 hours, it was taken out from the low temperature environment and the modulus was measured as described above within 1 minute.

Evaluation example 5: transmittance and Haze Measure

The light transmittance at 550 nm was measured using a haze meter NDH-5000W manufactured by Denshoku High School in Japan.

Evaluation example 6: Yellowness measurement

Yellow Index (YI) was measured using a CIE colorimeter by a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory).

Evaluation example 7: low temperature Folding evaluation

After manufacturing a multilayer film by interposing an adhesive layer (product name: OCA #8146 from 3M) between the prepared film and the PET substrate, the film is bent so that the radius of curvature is 3 mm, in a low temperature environment of -20°C for 72 hours When unfolded again after standing, the degree of wrinkles was observed with the naked eye. At this time, the case where there was no wrinkle in the naked eye was evaluated as ○, the case where there was a slight wrinkle in the naked eye was evaluated as △, and the case where the wrinkle was easily observed in the naked eye was evaluated as X.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 Furtherance Diamine TFMB 100 TFMB 100 TFMB 100 TFMB 100 TFMB 100 TFMB 100 TFMB 100 TFMB 100 TFMB 100 TFMB 100 Dianhyde
Ride 6FDA 3
6FDA 3
6FDA 7
6FDA 9
6FDA 12
6FDA 15
6FDA 24
6FDA 25
BPDA 10 - 6FDA 50
Dicarbonyl compound TPC 70
IPC 27 TPC 70
IPC 27 TPC 65
IPC 28 TPC 69
IPC 22 TPC 66
IPC 22 TPC 75
IPC 10 TPC 29
BPDC 47 TPC 65 TPC 75
IPC 25 TPC 25
IPC 25 Imide:
Amide 3:97 3:97 7:93 9:91 12:88 15:85 24:76 35:65 0:100 50:50 Metal salt type/content LiCl/1 LiCl / 0.5 - - - - - - LiBr / 1 - Tensile strength (TS ₁ ) Kgf/mm ² 28.45 32.13 29.6 30.7 30.1 27.5 29.61 28.31 24.61 22.62 Low temperature tensile strength (TS ₂ ) Kgf/mm ² 27.78 28.24 30.1 28.6 28 26.1 27.41 22.95 23.2 22.71 dTS % 2.36 12.11 1.69 6.84 6.98 5.09 7.43 18.93 5.73 0.40 Elongation at break (EL ₁ ) % 19.89 23.67 19.2 23.1 23 19.4 27.8 27.81 17 8.9 Low temperature elongation at break (EL ₂ ) % 23.06 17.68 21.5 19 19.5 17.1 21.2 20.6 16.2 11.71 dEL % 15.94 25.31 11.98 17.75 15.22 11.86 23.74 25.93 4.71 31.57 Modulus (MO ₁ ) GPa 7.42 7.43 6.02 5.92 5.54 6.15 6.44 6.65 7.45 4.83 Low temperature modulus (MO ₂ ) GPa 7.57 7.64 6.21 6.03 5.71 6.32 6.55 6.76 7.46 4.87 dMO % 2.02 2.83 3.16 1.86 3.07 2.76 1.71 1.65 0.13 0.83 LMo ₁ GPa 1.476 1.759 1.156 1.368 1.274 1.193 1.790 1.849 1.267 0.430 LMo ₂ GPa 1.746 1.351 1.335 1.146 1.113 1.081 1.389 1.393 1.209 0.570 thickness ㎛ 50 50 50 50 50 50 50 50 50 50 Transmittance % 89 89 89 89.1 89.3 89 89 88.5 88.4 90.8 Haze % 0.47 0.48 0.66 0.52 0.67 0.56 0.46 0.54 2.41 0.41 YI - 2.62 2.65 3.4 2.96 3.12 2.44 2.87 2.7 4.59 1.41 Low temperature folding evaluation
(3R, -20℃,
72 hours) ○ △ ○ ○ ○ ○ ○ △ X X fair
(Temperature
/minute) dry 125/15 125/15 125/15 125/15 115/15 115/15 115/15 115/15 150/20 115/15 1st heat treatment 125/1 125/1 125/1 125/1 115/1 115/1 115/1 115/1 150/1 150/1 2nd heat treatment 225/10 225/10 225/10 225/10 225/10 225/10 225/10 225/10 225/10 225/10

As can be seen in Table 1, it was confirmed that the polyamide-imide films of Examples 1 to 8 satisfies all dMO values of 1% to 8%, so that the modulus value was maintained at a certain level or higher even in a harsh environment at a low temperature. .

When the polyamide-imide film is applied to a cover window for a display device and a display device, it may be used in an extremely cold environment, and it is essential to secure mechanical properties above a certain level even in such extreme cold. Specifically, when the polyamide-imide film is applied to a cover window for a display device and a display device, all dMO values must satisfy 1% to 8% to avoid a problem.

In addition, in addition to the dMO value, the polyamide-imide films of Examples 1 to 8 have dTS value, dEL value, MO ₁ value, TS ₁ value, EL ₁ value, MO ₂ value, TS ₂ value, and EL ₂ value. , All showed excellent results. That is, the polyamide-imide films of Examples 1 to 8 also exhibited high values in mechanical properties such as tensile strength, elongation at break, and modulus at room temperature, and are still excellent after being treated under severe conditions at low temperature for a certain period of time Maintained mechanical properties.

In addition, the polyamide-imide films of Examples 1 to 8 all showed excellent results in low-temperature folding evaluation.

On the other hand, in the case of the films according to Comparative Examples 1 and 2, all of the dMO values exhibited a low value of 1% or less, and when applied to a cover window for a display device, cracks may occur due to misalignment with other layers. In terms of stability, defects may occur. In addition, since the films according to Comparative Examples 1 and 2 did not pass the low-temperature folding evaluation, they are inappropriate to be applied to a foldable display device or a flexible display device.

10 polymerization equipment 20 tank
30: belt 40: thermosetting machine
50: winder
100: polyamide-imide film
101: page 1 102: page 2
200: functional layer 300: cover window
400: display unit 500: adhesive layer

Claims (15)

A polyamide-imide polymer,
Modulus (MO ₁ ) in room temperature conditions is 5 GPa or more,
A polyamide-imide film having a dMO value of 1% to 8% as defined in Formula 1 below:
<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.
The method of claim 1,
DTS value defined in the following formula 2 is 1% to 20%,
DEL value defined in the following formula 3 is 5% to 30%,
Polyamide-imide film:
<Equation 2>
dTS (%) =

<Equation 3>
dEL (%) =

In Equation 2, TS ₁ is the tensile strength of the film under room temperature conditions, and TS ₂ is the tensile strength of the film measured at -20°C,
In Equation 3, EL ₁ is the elongation at break of the film under room temperature conditions, and EL ₂ is the elongation at break of the film measured at -20°C.
The method of claim 1,
The tensile strength (TS ₁ ) of the film at room temperature is 25 Kgf/mm ² or more,
The elongation at break (EL ₁ ) of the film under room temperature conditions is 18% or more, a polyamide-imide film.
The method of claim 1,
The modulus (MO ₂ ) of the film measured at -20°C is 5.05 GPa or more,
The tensile strength (TS ₂ ) of the film measured at -20°C is 22.5 Kgf/mm ² Ideal,
The elongation at break (EL ₂ ) of the film measured at -20°C is 17% or more, a polyamide-imide film.
The method of claim 1,
Modulus (MO ₁ ) in room temperature conditions is 7 GPa or more,
The modulus of the film (MO ₂ ) measured at -20°C is 7 GPa or more, a polyamide-imide film.
The method of claim 1,
A polyamide-imide film further comprising a metal salt.
The method of claim 6,
The content of the metal salt is 0.1 to 2.0 parts by weight, based on 100 parts by weight of the solid content of the polyamide-imide polymer, polyamide-imide film.
The method of claim 1,
The polyamide-imide polymer is a polyamide-imide film comprising a repeating unit represented by the following formula (A) and a repeating unit represented by the following formula (B) in a molar ratio of 2:98 to 45:55:
<Formula A>

<Formula B>

In Formulas A and B,
E and J are each independently a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic ring group, substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, substituted or unsubstituted C ₁ -C ₃₀ alkylene group, substituted or unsubstituted C ₂ -C ₃₀ alkenylene group , Substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si( CH ₃ ) ₂ -, -C(CH ₃ ) ₂ -and -C(CF ₃ ) ₂ -is selected from,
e and j are each independently selected from an integer of 1 to 5,
When e is 2 or more, 2 or more E are the same or different from each other,
When j is 2 or more, 2 or more J are the same as or different from each other,
G is a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaromatic cyclic group, and the aliphatic cyclic group, the hetero aliphatic cyclic group, the aromatic cyclic group or the heteroaromatic cyclic group is present alone or condensed with each other Or a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-,- S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) ₂ -and -C(CF ₃ ) It is connected by a connector selected from ₂ -.
The method of claim 1,
The transmittance of the film is 80% or more,
The haze of the film is 1% or less,
The yellowness of the film is 4 or less, a polyamide-imide film.
Including a polyamide-imide film and a functional layer,
The polyamide-imide film comprises a polyamide-imide polymer,
The polyamide-imide film has a modulus (MO ₁ ) of 5 GPa or more in room temperature conditions,
A cover window for a display device having a dMO value of 1% to 8% as defined in Equation 1:
<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.
A display unit; And
And a cover window disposed on the display unit,
The cover window comprises a polyamide-imide film and a functional layer,
The polyamide-imide film comprises a polyamide-imide polymer,
The polyamide-imide film has a modulus (MO ₁ ) of 5 GPa or more in room temperature conditions,
A display device having a dMO value of 1% to 8% as defined in Equation 1 below:
<Equation 1> dMO (%) =

In Equation 1, MO ₁ is the modulus of the film under room temperature conditions, and MO ₂ is the modulus of the film measured at -20°C.
Polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide polymer solution;
Injecting the polymer solution into a tank;
Extruding and casting the polymer solution in the tank, followed by drying, to prepare a gel sheet; And
Including; heat treatment of the gel sheet;
The heat treatment step of the gel sheet comprises two or more hot air treatment steps,
The method for producing the polyamide-imide film of claim 1.
The method of claim 12,
After the step of preparing the gel sheet, performing the step of fixing the end of the gel sheet,
Method for producing polyamide-imide film.
The method of claim 12,
The drying step is performed for 5 minutes to 20 minutes in the range of 80 ℃ to 140 ℃, polyamide-imide film production method.
The method of claim 12,
The heat treatment step of the gel sheet
A first hot air treatment step performed for 0.2 to 5 minutes in the range of 80°C to 140°C; And
Including, a method for producing a polyamide-imide film; a second hot air treatment step performed for 5 minutes to 150 minutes in the range of 160 ℃ to 350 ℃.

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