Polyamide-imide film, method for producing the same, and cover window and display device including the same

Abstract

To provide a polyamide-imide-based film which is excellent in mechanical properties, optical properties, and the suitability for post-processing, a process for preparing the same, and a cover window and a display device each comprising the same.SOLUTION: The present invention provides a polyamide-imide-based film with a TGA weight loss area value (TDA) of 0.01% min / °C or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present embodiment relates to a polyamide-imide film, a method for producing the same, and a cover window and a display device including the same.

Background Art

[0002] Polyimide resins such as poly(amide-imide) (PAI) are excellent in friction, heat, and chemical resistance, and are applied to primary electrical insulators, coating agents, adhesives, extrusion resins, heat-resistant paints, heat-resistant plates, heat-resistant adhesives, heat-resistant fibers, and heat-resistant films.

[0003] Polyimide is utilized in various fields. For example, polyimide is made into a powder and used as a coating agent for metals or magnet wires, and is used by mixing with other additives according to the application. Also, polyimide is used as a paint for decoration and corrosion prevention together with a fluoropolymer, and plays a role in adhering the fluoropolymer to a metal substrate. Further, polyimide is also used for coating kitchen cooking utensils, has characteristics of heat resistance and chemical resistance, is also used as a membrane for gas separation, and is also used in a device for filtering contaminants such as carbon dioxide, hydrogen sulfide, and impurities in a natural gas well.

[0004] Recently, by forming polyimide into a film, a polyimide film that is cheaper and has excellent optical, mechanical, and thermal properties has been developed. Such a polyimide film is applicable to display materials such as organic light-emitting diodes (OLEDs) or liquid-crystal displays (LCDs), and is applicable to an antireflection film, a compensation film, or a retardation film when realizing retardation physical properties.

[0005] When a functional layer such as a hard coating layer is laminated on such a polyimide film, there has been a problem that the functional layer peels off from the film or the mechanical / optical properties of the film deteriorate when immersed in a solvent during subsequent processes. Therefore, the demand for the development of films excellent in mechanical properties, optical properties, and post-processability has been continuously increasing.

Summary of the Invention

Problems to be Solved by the Invention

[0006] An embodiment aims to provide a polyamide-imide film excellent in mechanical properties, optical properties, and post-processability, a method for producing the same, and a cover window and a display device including the same.

Means for Solving the Problems

[0007] The polyamide-imide film according to one embodiment has a TGA weight loss area value (TDA) of 0.01%·min / °C or less.

[0008] The cover window for a display device according to another embodiment includes a polyamide-imide film and a functional layer, and the polyamide-imide film has a TGA weight loss area value (TDA) of 0.01%·min / °C or less.

[0009] The display device according to still another embodiment includes a display unit and a cover window disposed on the display unit, the cover window includes a polyamide-imide film and a functional layer, and the TGA weight loss area value (TDA) of the polyamide-imide film is 0.01%·min / °C or less.

[0010] The method for producing the polyamide-imide film according to one embodiment includes polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound on an organic solvent to prepare a polyamide-imide polymer solution, casting the solution to produce a gel sheet, and heat-treating the gel sheet.

Effects of the Invention

[0011] By controlling the TGA weight loss area value (TDA) of the polyamide-imide film according to the realization example to 0.01%·min / °C or less, it is excellent not only in optical and mechanical properties but also in post-process properties such as adhesion to the functional layer and solvent resistance.

[0012] After manufacturing the polyamide-imide film, post-processes such as a process of laminating a functional layer for imparting functions such as fingerprint resistance, antistatic property, anti-scattering property, and improvement of adhesion and / or a process of immersing in a solvent will be carried out.

[0013] After going through such post-processes, there is a risk that the optical and mechanical properties will deteriorate, such as the functional layer peeling off from the film or the haze increasing rapidly after solvent immersion. Therefore, post-process properties such as the content controllability of the film and the adhesion of the functional layer play an important role in the quality reliability of the final product.

[0014] Therefore, in the case of the polyamide-imide film according to the realization example, by controlling the TGA weight loss area value (TDA) within a specific range, the quality reliability and product yield of the final product such as a cover window for a display device or a display device to which the film is applied can be improved.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, implementation examples will be described in detail with reference to the accompanying drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the invention. However, the implementation examples can be realized in various different forms and are not limited to the implementation examples described in this specification.

[0017] In this specification, when each film, window, panel, or layer, etc. is described as being formed "on" or "under" each film, window, panel, or layer, etc., "on" and "under" include all those formed "directly" or "indirectly" via other components. Also, the reference for above / below each component is described with reference to the drawings. Note that the size of each component in the drawings may be exaggerated for the purpose of explanation and does not mean the actual size applied. Also, throughout the specification, the same reference numerals refer to the same components.

[0018] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated, it does not exclude other components but may further include other components.

[0019] In this specification, singular expressions are interpreted to include singular or plural as interpreted in the context, unless otherwise specifically explained.

[0020] Also, all numbers and expressions representing amounts of components, reaction conditions, etc. described in this specification should be understood to be modified by the term "about" in all cases, unless otherwise specified.

[0021] In this specification, terms such as first, second, etc. are used to describe various components, and the components should not be limited by the terms. The terms are only used to distinguish one component from another.

[0022] Also, in this specification, "substituted" means substituted with one or more substituents selected from the group consisting of deuterium, -F, -Cl, -Br, -I, hydroxyl group, cyano group, nitro group, amino group, amidino group, hydrazine group, 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 organic group, substituted or unsubstituted heterocyclic group, substituted or unsubstituted aryl group, and substituted or unsubstituted heteroaryl group, unless otherwise specified, and the listed substituents may be bonded to each other to form a ring.

[0023] [Polyamide-imide film] The examples provide a polyamide-imide film that is excellent in post-process properties such as heat resistance, yellowness, solvent resistance, and adhesion of the functional layer by satisfying a specific level of the TGA weight loss area value (TDA) of the film.

[0024] The polyamide-imide film according to the examples has a TGA weight loss area value (TDA) of 0.01%·min / °C or less.

[0025] Specifically, the TGA weight loss area value (TDA) of the polyamide-imide film is 0.009%·min / °C or less, 0.008%·min / °C or less, 0.007%·min / °C or less, 0.006%·min / °C or less, 0.005%·min / °C or less, 0.004%·min / °C or less, 0.003%·min / °C or less, 0.0022%·min / °C or less, or 0.002%·min / °C or less, and may be 0.0001%·min / °C or more, 0.0002%·min / °C or more, 0.0003%·min / °C or more, 0.0004%·min / °C or more, 0.0005%·min / °C or more, 0.0006%·min / °C or more, 0.0007%·min / °C or more, 0.0008%·min / °C or more, 0.0009%·min / °C or more, or 0.001%·min / °C or more.

[0026] More specifically, the TGA weight loss area value (TDA) of the polyamide-imide film may be 0.0001 - 0.01%·min / °C, 0.0001 - 0.008%·min / °C, 0.0001 - 0.006%·min / °C, 0.0001 - 0.004%·min / °C, 0.0001 - 0.003%·min / °C, 0.0001 - 0.0022%·min / °C, 0.0001 - 0.002%·min / °C, 0.0005 - 0.01%·min / °C, 0.0005 - 0.008%·min / °C, 0.0005 - 0.006%·min / °C, 0.0005 - 0.004%·min / °C, 0.0005 - 0.003%·min / °C, 0.0005 - 0.0022%·min / °C, 0.0005 - 0.002·min / °C, 0.0008 - 0.01%·min / °C, 0.0008 - 0.008%·min / °C, 0.0008 - 0.006%·min / °C, 0.0008 - 0.004%·min / °C, 0.0008 - 0.003%·min / °C, 0.0008 - 0.0022%·min / °C, 0.0008 - 0.002%·min / °C, 0.001 - 0.01%·min / °C, 0.001 - 0.008%·min / °C, 0.001 - 0.006%·min / °C, 0.001 - 0.004%·min / °C, 0.001 - 0.003 min / °C, 0.001 - 0.0022%·min / °C, or 0.001 - 0.002%·min / °C, but is not limited thereto.

[0027] During TGA analysis, the primary weight loss temperature (Tw) refers to the temperature at which the weight loss change rate is the highest within the temperature range of 270°C to 330°C. Also, in the graph of the weight loss change rate (y-axis) against temperature (x-axis), the area of the section to which the primary weight loss temperature (Tw) belongs among the area between the graph and the straight line connecting the point corresponding to the temperature of (Tw - 30)°C and the point corresponding to the temperature of (Tw + 30)°C is defined as the TGA weight loss area value (TDA).

[0028] The TGA analysis can be performed using a thermal gravimetric analyzer TGA Q500 model from TA Instruments, taking 2 g of the measurement sample of the polyamide-imide film and heating it at a rate of 10°C / min in the range of 25°C to 700°C.

[0029] By controlling the TGA weight loss area value (TDA) of the polyamide-imide film within the aforementioned range, not only are the optical and mechanical properties excellent, but also the adhesion to the functional layer is improved during post-processing such as the functional layer lamination process, and the phenomenon of delamination between layers can be significantly reduced when applied to products. Furthermore, since the physical properties do not deteriorate even after immersion in solvents mainly used in subsequent processes, it has excellent solvent resistance.

[0030] On the other hand, when the TGA weight loss area value (TDA) of the polyamide-imide film is outside the aforementioned range, the adhesion to the functional layer is low, the optical properties such as yellowness deteriorate after solvent immersion, not only does the quality reliability of the film decrease, but it can also lead to products with a high defect rate during the manufacture of products using the film.

[0031] The primary weight loss temperature (Tw) by the TGA analysis of the polyamide-imide film can be 285°C or higher.

[0032] Specifically, the primary weight loss temperature (Tw) of the polyamide-imide film by TGA analysis is 290°C or higher, 293°C or higher, 295°C or higher, 298°C or higher, or 300°C or higher, and can be 330°C or lower, 325°C or lower, 320°C or lower, 315°C or lower, 312°C or lower, 310°C or lower, or 308°C or lower.

[0033] More specifically, the primary weight loss temperature (Tw) of the polyamide-imide film by TGA analysis can be 280°C to 330°C, 280°C to 320°C, 280°C to 315°C, 280°C to 310°C, 290°C to 330°C, 290°C to 320°C, 290°C to 315°C, 290°C to 310°C, 295°C to 330°C, 295°C to 320°C, 295°C to 315°C, or 295°C to 310°C, but is not limited thereto.

[0034] When the primary weight loss temperature (Tw) of the polyamide-imide film satisfies the above range, post-processing properties such as the adhesion of the functional layer and solvent resistance can be improved.

[0035] In one implementation example, the 1% weight loss temperature (Td1) of the polyamide-imide film by TGA analysis can be 290°C or higher.

[0036] Specifically, the 1% weight loss temperature (Td1) of the polyamide-imide film by TGA analysis is 295°C or higher, 300°C or higher, 305°C or higher, or 310°C or higher, and can be 360°C or lower, 355°C or lower, 350°C or lower, 345°C or lower, or 340°C or lower.

[0037] More specifically, the 1% weight loss temperature (Td1) of the polyamide-imide film by TGA analysis can be 280°C to 360°C, 280°C to 350°C, 280°C to 345°C, 280°C to 340°C, 290°C to 360°C, 290°C to 350°C, 290°C to 345°C, 290°C to 340°C, 300°C to 360°C, 300°C to 350°C, 300°C to 345°C, 300°C to 340°C, 310°C to 360°C, 310°C to 350°C, 310°C to 345°C, or 310°C to 340°C, but is not limited thereto.

[0038] For example, the 1% weight loss temperature (Td1) may mean the temperature at which 1% weight loss occurs when 2 g of a measurement sample of the polyamide-imide film is taken and analyzed while heating at a rate of 10 °C / min in the range of 25 °C to 700 °C using a thermal gravimetric analysis TGA Q500 model from TA Instruments.

[0039] In one implementation example, the 5% weight loss temperature (Td5) by TGA analysis of the polyamide-imide film may be 400 °C or higher.

[0040] Specifically, the 5% weight loss temperature (Td5) by TGA analysis of the polyamide-imide film is 405 °C or higher, 410 °C or higher, 415 °C or higher, 420 °C or higher, 425 °C or higher, or 430 °C or higher, and may be 470 °C or lower, 460 °C or lower, 455 °C or lower, 450 °C or lower, 445 °C or lower, or 440 °C or lower.

[0041] More specifically, the 5% weight loss temperature (Td5) by TGA analysis of the polyamide-imide film is 400 °C to 470 °C, 400 °C to 460 °C, 400 °C to 450 °C, 400 °C to 440 °C, 410 °C to 470 °C, 410 °C to 460 °C, 410 °C to 450 °C, 410 °C to 440 °C, 420 °C to 470 °C, 420 °C to 460 °C, 420 °C to 450 °C, 420 °C to 440 °C, 430 °C to 470 °C, 430 °C to 460 °C, 430 °C to 450 °C, or 430 °C to 440 °C, but is not limited thereto.

[0042] For example, the 5% weight loss temperature (Td5) may mean the temperature at which 5% weight loss occurs when 2 g of a measurement sample of the polyamide-imide film is taken and analyzed while heating at a rate of 10 °C / min in the range of 25 °C to 700 °C using a thermal gravimetric analysis TGA Q500 model from TA Instruments.

[0043] When the 1% weight loss temperature (Td1) and 5% weight loss temperature (Td5) of the polyamide-imide film satisfy the previous range, the residual solvent content in the film is low, and the optical and mechanical properties of the film can be improved.

[0044] The polyamide-imide film can have a functional layer adhesion of 4B or more, or 5B.

[0045] The functional layer can be one or more selected from the group consisting of, but not limited to, a hard coating layer, a reflectance reduction layer, an antifouling layer, and an antiglare layer.

[0046] In one implementation example, a primer layer can be further included between the functional layer and the polyamide-imide film.

[0047] Specifically, the polyamide-imide film can have a hard coating layer adhesion of 4B or more. More specifically, the polyamide-imide film can have a hard coating layer adhesion of 5B.

[0048] For example, the hard coating layer adhesion is obtained by applying a primer layer composition to the polyamide-imide film to form a primer layer with a thickness of 0.1 μm, applying a hard coating layer composition on the primer layer to form a hard coating layer with a thickness of 5 μm, then cutting the surface of the hard coating layer into a grid pattern at regular intervals based on the ASTM D 3359 (Method B) standard, sticking a tape (Nitto Tape 50B) on it and peeling it off, and measuring the degree to which flakes in the grid unit are generated on the surface.

[0049] At this time, the hard coating layer can contain at least one of an organic component, an inorganic component, and an organic-inorganic composite component as a hard coating agent. As an example, the hard coating layer can contain an organic resin. Specifically, the organic resin can be a curable resin. Thereby, the hard coating layer can be a curable coating layer.

[0050] Specifically, the hard coating layer may contain one or more selected from the group consisting of urethane acrylate compounds, acrylic ester compounds, and epoxy acrylate compounds. More specifically, the hard coating layer may contain a urethane acrylate compound and an acrylic ester compound.

[0051] The amount of haze change (ΔHz M ) when the polyamide-imide film is immersed in MIBK for 5 seconds, dried at 80°C for 3 minutes, and then the haze is measured may be 0.5% or less.

[0052] Specifically, the amount of haze change (ΔHz M ) after the polyamide-imide film is immersed in MIBK may be 0.4% or less, 0.3% or less, 0.2% or less, 0.15% or less, or 0.1% or less, but is not limited thereto.

[0053] The ΔHz M (%) is the value of Hz M -Hz 0 The Hz 0 represents the initial haze (%) of the film, and the Hz M represents the haze (%) measured after the film is immersed in the MIBK solvent for 5 seconds and dried at 80°C for 3 minutes.

[0054] The amount of haze change (ΔHz I ) when the polyamide-imide film is immersed in IPA for 5 seconds, dried at 80°C for 3 minutes, and then the haze is measured may be 0.3% or less.

[0055] Specifically, the amount of haze change (ΔHz I ) after the polyamide-imide film is immersed in IPA may be 0.2% or less, 0.15% or less, 0.1% or less, or 0.08% or less, but is not limited thereto.

[0056] The ΔHz I(%) is Hz I -Hz 0 is the value of, and the Hz 0 represents the initial haze (%) of the film, and Hz I represents the haze (%) measured after immersing the film in an IPA solvent for 5 seconds and then drying it at 80°C for 3 minutes.

[0057] When the polyamide-imide film is immersed in MIBK for 5 seconds and then dried at 80°C for 3 minutes and the haze is measured, the haze change amount (ΔHz M ), and when the polyamide-imide film is immersed in IPA for 5 seconds and then dried at 80°C for 3 minutes and the haze is measured, the haze change amount (ΔHz I ) average value (ΔHz AVG ) can be 0.4% or less.

[0058] Specifically, the average value (ΔHz AVG ) of the haze change amount of the polyamide-imide film can be 0.3% or less, 0.2% or less, 0.15% or less, 0.12% or less, 0.1% or less, 0.09% or less, or 0.08% or less, but is not limited thereto.

[0059] The average value (ΔHz AVG ) of the haze change amount can be a measure for judging the tolerance of the film.

[0060] In one embodiment, the polyamide-imide film can have a surface tension of 40 dyn / cm or more on the first surface.

[0061] Specifically, the polyamide-imide film has a surface tension of 43 dyn / cm or more, 45 dyn / cm or more, 46 dyn / cm or more, or 47 dyn / cm or more on the first surface, and can be 55 dyn / cm or less, 53 dyn / cm or less, 52 dyn / cm or less, 51 dyn / cm or less, or 50 dyn / cm or less.

[0062] In one implementation example, the first surface may be the air surface of the film. The air surface means the surface that does not contact the support used in the formation of the polyamide-imide film. Specifically, in the method for manufacturing the film, the air surface may mean the surface that does not contact the belt on which the polyamide-imide polymer solution is cast and dried.

[0063] In one implementation example, the surface tension of the second surface of the polyamide-imide film may be 40 dyn / cm or more.

[0064] Specifically, the surface tension of the second surface of the polyamide-imide film may be 43 dyn / cm or more, 45 dyn / cm or more, 46 dyn / cm or more, or 47 dyn / cm or more, and may be 55 dyn / cm or less, 53 dyn / cm or less, 52 dyn / cm or less, 51 dyn / cm or less, or 50 dyn / cm or less.

[0065] In one implementation example, the second surface may be the belt surface of the film. The belt surface means the surface that contacts the support used in the formation of the polyamide-imide film. Specifically, in the method for manufacturing the film, the belt surface may mean the surface that contacts the belt on which the polyamide-imide polymer solution is cast and dried.

[0066] According to an implementation example, the modulus of the polyamide-imide film is 5 GPa or more. Specifically, the modulus may be 5.5 GPa or more, 5.7 GPa or more, or 6 GPa or more.

[0067] The transmittance of the polyamide-imide film may be 80% or more. For example, the transmittance may be 85% or more, 88% or more, and may be 100% or less, or 99% or less.

[0068] The haze of the polyamide-imide film is 1% or less. Specifically, the haze can be 0.8% or less, 0.7% or less, 0.6% or less, or 0.5% or less, but is not limited thereto.

[0069] The transmittance and / or haze of the film can be values measured in the visible light wavelength range (400 nm to 700 nm). Specifically, the transmittance of the film can be the total light transmittance measured in the visible light wavelength range.

[0070] The yellowness index (YI) of the polyamide-imide film is 5 or less. For example, the yellowness index can be 4.5 or less, 4.0 or less, or 3.5 or less, but is not limited thereto.

[0071] In an implementation example, the polyamide-imide film can have a thickness deviation of 3 μm or less, or 2 μm or less based on a thickness of 50 μm. Also, the thickness deviation rate can be 5% or less, 4% or less, or 3% or less, but is not limited thereto.

[0072] In one implementation example, the polyamide-imide film can have a modulus of 5 GPa or more, a transmittance of 80% or more, a haze of 1% or less, and a yellowness index of 5 or less based on a film thickness of 50 μm, but is not limited thereto.

[0073] The compressive strength of the polyamide-imide film can be 0.4 kgf / μm or more. Specifically, the compressive strength can be 0.45 kgf / μm or more, or 0.46 kgf / μm or more, but is not limited thereto.

[0074] When the polyamide-imide film is perforated at a speed of 10 mm / min using a 2.5 mm spherical chip in the UTM compression mode, the maximum perforation diameter (mm) including cracks is 60 mm or less. Specifically, the maximum perforation diameter can be 5 mm to 60 mm, 10 mm to 60 mm, 15 mm to 60 mm, 20 mm to 60 mm, 25 mm to 60 mm, or 25 mm to 58 mm, but is not limited thereto.

[0075] The surface hardness of the polyamide-imide film can be HB or higher. Specifically, the surface hardness can be H or higher, or 2H or higher, but is not limited thereto.

[0076] The polyamide-imide film can have a tensile strength of 15 kgf / mm 2 or higher. Specifically, the tensile strength can be 18 kgf / mm 2 or higher, 20 kgf / mm 2 or higher, 21 kgf / mm 2 or higher, or 22 kgf / mm 2 or higher, but is not limited thereto.

[0077] The polyamide-imide film can have an elongation rate of 15% or higher. Specifically, the elongation rate can be 16% or higher, 17% or higher, or 18% or higher, but is not limited thereto.

[0078] When the polyamide-imide film is folded so that the radius of curvature becomes 3 mm based on a thickness of 50 μm, the number of folding times before breaking can be 200,000 times or more.

[0079] The number of folding times is defined as one cycle of bending and unfolding the film so that the radius of curvature becomes 3 mm.

[0080] By satisfying the number of folding times within the above range, the polyamide-imide film can be usefully applied to a foldable display device or a flexible display device.

[0081] The surface roughness of the polyamide-imide film can be 0.01 μm to 0.07 μm. Specifically, the surface roughness can be 0.01 μm to 0.07 μm or 0.01 μm to 0.06 μm, but is not limited thereto.

[0082] By satisfying the above range for the surface roughness of the polyamide-imide film, it can be advantageous for realizing advantageous luminance conditions and texture for application to a display device.

[0083] The content of the residual solvent in the polyamide-imide film can be 1500 ppm or less. For example, the content of the residual solvent can be 1200 ppm or less, 1000 ppm or less, 800 ppm or less, 500 ppm or less, or 300 ppm or less, but is not limited thereto.

[0084] The residual solvent means the amount of the solvent that does not volatilize during film production and finally remains in the produced film.

[0085] When the content of the residual solvent in the polyamide-imide film exceeds the above range, the durability of the film may decrease, and it may also affect the quality variation of the film. In particular, since it affects the mechanical strength, it has an adverse effect during the post-processing of the film, accelerates the water absorption of the film, and may also reduce the optical properties, solvent resistance, and heat resistance characteristics in addition to the mechanical properties.

[0086] The polyamide-imide film according to the implementation example contains a polyamide-imide polymer, and the polyamide-imide polymer can be formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

[0087] The polyamide-imide polymer is a polymer containing an imide repeating unit and an amide repeating unit.

[0088] Specifically, the polyamide-imide polymer may include an imide repeating unit derived from the polymerization of a diamine compound and a dianhydride compound, and an amide repeating unit derived from the polymerization of the diamine compound and a dicarbonyl compound.

[0089] The diamine compound forms a copolymer by forming an imide bond with the dianhydride compound and an amide bond with the dicarbonyl compound.

[0090] The diamine compound is not particularly limited, and for example, it can be an aromatic diamine compound containing an aromatic structure. For example, the diamine compound can be a compound represented by the following Chemical Formula 1.

[0091] JPEG0007688814000001.jpg1968In the Chemical Formula 1, E is a substituted or unsubstituted divalent C 6 -C 30 alicyclic group, a substituted or unsubstituted divalent C 4 -C 30 heteroalicyclic group, a substituted or unsubstituted divalent C 6 -C 30 aromatic ring group, a substituted or unsubstituted divalent C 4 -C 30 aromatic heterocyclic 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 -, -C(CH 3 ) 2 -, and -C(CF 3 ) 2 - and can be selected from among them.

[0092] e is selected from integers from 1 to 5, and when e is 2 or more, E can be the same as or different from each other.

[0093] JPEG0007688814000002.jpg113163

[0094] JPEG0007688814000003.jpg113163

[0095] More specifically, the (E) in Chemical Formula 1 e may be a group represented by Chemical Formula 1-6b or a group represented by Chemical Formula 1-9b.

[0096] In one implementation example, the diamine compound may include a compound having a fluorine-containing substituent or a compound having an ether group (-O-).

[0097] The diamine compound may consist of a compound having a fluorine-containing substituent. At this time, the fluorine-containing substituent is a fluorinated hydrocarbon group, and specifically may be a trifluoromethyl group, but is not limited thereto.

[0098] In some implementation examples, the diamine compound may include one type of diamine compound. That is, the diamine compound may consist of a single component.

[0099] JPEG0007688814000004.jpg81163

[0100] Since the dianhydride compound has a low birefringence value, it is a compound that can contribute to the improvement of optical properties such as the transparency of a film containing the polyamide-imide polymer.

[0101] JPEG0007688814000005.jpg78163

[0102] In Chemical Formula 2, G is a substituted or unsubstituted tetravalent C 6 -C 30 alicyclic group, a substituted or unsubstituted tetravalent C 4 -C 30 heteroalicyclic group, a substituted or unsubstituted tetravalent C 6 -C 30 aromatic ring group, a substituted or unsubstituted tetravalent C 4 -C 30It is an aromatic heterocyclic group, and the alicyclic group, the heteroalicyclic group, the aromatic ring group, or the aromatic heterocyclic group exists alone, is bonded to each other to form a condensed ring, or is a 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 - and is bonded by a linking group selected from the following.

[0103] JPEG0007688814000006.jpg112163

[0104] For example, G in Chemical Formula 2 may be a group represented by Chemical Formula 2-2a, a group represented by Chemical Formula 2-8a, or a group represented by Chemical Formula 2-9a.

[0105] 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.

[0106] The fluorine-containing substituent is a fluorinated hydrocarbon group, and specifically may be a trifluoromethyl group, but is not limited thereto.

[0107] In other embodiments, the dianhydride compound may consist of one single component or two mixed components.

[0108] JPEG0007688814000007.jpg147164

[0109] The diamine compound and the dianhydride compound can polymerize to form a polyamic acid.

[0110] Subsequently, the polyamic acid can be converted into a polyimide by a dehydration reaction, and the polyimide contains imide repeating units.

[0111] JPEG0007688814000008.jpg64160

[0112] For example, the polyimide may contain, but is not limited to, a repeating unit represented by the following chemical formula A-1.

[0113] JPEG0007688814000009.jpg63147

[0114] JPEG0007688814000010.jpg55163

[0115] In the chemical formula 3, J is a substituted or unsubstituted divalent C 6 -C 30 alicyclic group, a substituted or unsubstituted divalent C 4 -C 30 heteroalicyclic group, a substituted or unsubstituted divalent C 6 -C 30 aromatic ring group, a substituted or unsubstituted divalent C 4 -C 30 aromatic heterocyclic 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 -, -C(CH 3 ) 2 -, and -C(CF 3 ) 2 and can be selected from.

[0116] j is selected from integers from 1 to 5, and when j is 2 or more, Js may be the same as or different from each other. X is a halogen atom. Specifically, X may be F, Cl, Br, I, etc. More specifically, X may be Cl, but is not limited thereto.

[0117] JPEG0007688814000011.jpg121162

[0118] JPEG0007688814000012.jpg96162

[0119] More specifically, (J) in Chemical Formula 3 j may be a group represented by Chemical Formula 3-1b, a group represented by Chemical Formula 3-2b, a group represented by 3-3b, or a group represented by 3-8b.

[0120] For example, (J) in Chemical Formula 3 j may be a group represented by Chemical Formula 3-1b or a group represented by Chemical Formula 3-2b.

[0121] In one embodiment, the dicarbonyl compound may be used alone as one kind of dicarbonyl compound, or at least two different kinds of dicarbonyl compounds may be mixed and used. When two or more kinds of dicarbonyl compounds are used, the dicarbonyl compounds may be two or more selected from the groups represented by (J) in Chemical Formula 3 j which are represented by Chemical Formulas 3-1b to 3-8b.

[0122] In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound containing an aromatic structure.

[0123] JPEG0007688814000013.jpg154163

[0124] JPEG0007688814000014.jpg80163

[0125] For example, the diamine compound and the dicarbonyl compound may polymerize to form amide repeating units represented by Chemical Formulas B-1 and B-2.

[0126] Alternatively, the diamine compound and the dicarbonyl compound may polymerize to form amide repeating units represented by Chemical Formulas B-2 and B-3.

[0127] JPEG0007688814000015.jpg55112For Chemical Formula B-1, x is an integer from 1 to 400.

[0128] JPEG0007688814000016.jpg55107

[0129] JPEG0007688814000017.jpg55107

[0130] According to one implementation example, the polyamide-imide polymer may include a repeating unit represented by the following Chemical Formula A and a repeating unit represented by the following Chemical Formula B.

[0131] JPEG0007688814000018.jpg6194

[0132] JPEG0007688814000019.jpg4685

[0133] Among Chemical Formulas A and B, E and J are each independently a substituted or unsubstituted divalent C 6 -C 30 alicyclic group, a substituted or unsubstituted divalent C 4 -C 30 heteroalicyclic group, a substituted or unsubstituted divalent C 6 -C 30 aromatic ring group, a substituted or unsubstituted divalent C 4 -C 30 aromatic heterocyclic group, a substituted or unsubstituted C 1 -C 30 alkylene group, a substituted or unsubstituted C 2 -C30 an 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 (-), and is selected from among; e and j are each independently selected from the integers 1 to 5, when e is 2 or more, two or more Es are the same as or different from each other, when j is 2 or more, two or more Js are the same as or different from each other, G is a substituted or unsubstituted tetravalent C 6 -C 30 alicyclic group, a substituted or unsubstituted tetravalent C 4 -C 30 heteroalicyclic group, a substituted or unsubstituted tetravalent C 6 -C 30 aromatic ring group, a substituted or unsubstituted tetravalent C 4 -C 30 aromatic heterocyclic group, and the alicyclic group, the heteroalicyclic group, the aromatic ring group, or the aromatic heterocyclic group may exist alone, be bonded to each other to form a condensed ring, or be bonded by a linking group selected from among 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 (-).

[0134] The polyamide-imide polymer may contain imide repeating units and amide repeating units in a molar ratio of 2:98 to 70:30. Specifically, the molar ratio of the imide repeating units to the amide repeating units may be 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 5:95 to 70:30, 5:95 to 60:40, 5:95 to 55:45, 5:95 to 50:50, or 10:90 to 40:60, but is not limited thereto.

[0135] When the molar ratio of the imide repeating unit to the amide repeating unit is within the above range, TGA characteristics such as the TGA weight loss area value (TDA) of the polyamide-imide film can be effectively controlled, and combined with a characteristic process method, the quality reliability of the film can be improved.

[0136] In the polyamide-imide polymer, the molar ratio of the repeating unit represented by the chemical formula A and the repeating unit represented by the chemical formula B may be 2:98 to 70:30. Specifically, the molar ratio of the repeating unit represented by the chemical formula A and the repeating unit represented by the chemical formula B may be 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 5:95 to 70:30, 5:95 to 60:40, 5:95 to 55:45, 5:95 to 50:50, or 10:90 to 40:60, but is not limited thereto.

[0137] The polyamide-imide film according to the implementation example may further contain one or more selected from the group consisting of a filler, a blue pigment, and a UVA absorber in addition to the polyamide-imide polymer.

[0138] The filler may include, for example, oxides, carbonates, sulfates of metals or metalloids. For example, the filler may include silica, calcium carbonate, barium sulfate, etc., but is not limited thereto.

[0139] The filler may be contained in a particulate form. Further, the filler is in a state where no special coating treatment is performed on its surface and is uniformly dispersed throughout the film.

[0140] By the polyamide-imide film containing the filler, the film can secure a wide viewing angle without deterioration of optical properties, can improve roughness and winding property, and can improve the running property scratch improvement effect during film production.

[0141] The refractive index of the filler may be 1.55 to 1.75. Specifically, the refractive index of the filler may be 1.60 to 1.75, 1.60 to 1.70, 1.60 to 1.68, or 1.62 to 1.65, but is not limited thereto.

[0142] By the refractive index of the filler satisfying the above range, the birefringence value related to the refractive index in the x direction (nx), refractive index in the y direction (ny), and refractive index in the z direction (nz) of the film is appropriately adjusted, and the luminance at various angles of the film can be improved.

[0143] On the other hand, when the refractive index of the filler is out of the above range, problems such as the presence of the filler being visually observed on the film or the haze increasing due to the filler may occur.

[0144] The content of the filler may be 100 ppm to 15000 ppm based on the total weight of the polyamide-imide polymer solid content. Specifically, the content of the filler may be 100 ppm to 14500 ppm, 100 ppm to 14200 ppm, 200 ppm to 14500 ppm, 200 ppm to 14200 ppm, 250 ppm to 14100 ppm, or 300 ppm to 14000 ppm based on the total weight of the polyamide-imide polymer solid content, but is not limited thereto.

[0145] When the content of the filler is outside the above range, the haze of the film increases rapidly, aggregation of the fillers occurs on the film surface, a foreign object feeling can be visually confirmed, problems can occur in running during the production process, and the winding property may deteriorate.

[0146] In some embodiments, the blue pigment may be contained in an amount of 50 ppm to 5000 ppm based on the total weight of the polyamide-imide polymer. Preferably, the blue pigment may be contained in an amount of 100 ppm to 5000 ppm, 200 ppm to 5000 ppm, 300 ppm to 5000 ppm, 400 ppm to 5000 ppm, 50 ppm to 3000 ppm, 100 ppm to 3000 ppm, 200 ppm to 3000 ppm, 300 ppm to 3000 ppm, 400 ppm to 3000 ppm, 50 ppm to 2000 ppm, 100 ppm to 2000 ppm, 200 ppm to 2000 ppm, 300 ppm to 2000 ppm, 400 to 2000 ppm, 50 ppm to 1000 ppm, 100 ppm to 1000 ppm, 200 ppm to 1000 ppm, 300 to 1000 ppm, or 400 ppm to 1000 ppm based on the total weight of the polyamide-imide polymer, but is not limited thereto.

[0147] The UVA absorber may include an absorber that absorbs electromagnetic waves having a wavelength of 10 nm to 400 nm used in the art. For example, the UVA absorber includes a benzotriazole-based compound, and the benzotriazole-based compound may include an N-phenolic benzotriazole-based compound. In some embodiments, the N-phenolic benzotriazole-based compound may include N-phenolic benzotriazole in which the phenol group is substituted with an alkyl group having 1 to 10 carbon atoms. The alkyl group may be substituted with two or more and may be linear, branched, or cyclic.

[0148] In one implementation example, the UVA absorber may be contained in an amount of 0.1% to 10% by weight based on the total weight of the polyamide-imide polymer. Preferably, the UVA absorber is contained in an amount of 0.1% to 5% by weight, 0.1% to 3% by weight, 0.1% to 2% by weight, 0.5% to 10% by weight, 0.5% to 5% by weight, 0.5% to 3% by weight, 0.5% to 2% by weight, 1% to 10% by weight, 1% to 5% by weight, 1% to 3% by weight, or 1% to 2% by weight based on the total weight of the polyamide-imide polymer, but is not limited thereto.

[0149] The physical properties of the aforementioned polyamide-imide film are based on a thickness of 40 μm to 80 μm. For example, each physical property of the polyamide-imide film is based on a thickness of 50 μm.

[0150] The characteristics regarding the constituent components and physical properties of the aforementioned polyamide-imide film can be combined with each other.

[0151] Also, the aforementioned TGA weight loss area value (TDA), primary weight loss temperature (Tw), 1% weight loss temperature (Td1), and / or 5% weight loss temperature (Td5) of the polyamide-imide film, etc., together with the chemical and physical properties of the components forming the polyamide-imide film, can be comprehensively adjusted according to the specific process conditions at each stage in the manufacturing method of the polyamide-imide film described below.

[0152] For example, the composition and content of the components forming the polyamide-imide film, the content of the residual solvent, the polymerization conditions in the film manufacturing process, the heat treatment conditions such as the heat treatment stage and the cooling stage, etc., all are combined, and physical properties such as the TGA weight loss area value (TDA) and the primary weight loss temperature (Tw) within the target range can be realized.

[0153] [Cover Window for Display Device] A cover window for a display device according to one implementation example includes a polyamide-imide film and a functional layer.

[0154] The polyamide-imide film has a TGA weight loss area value (TDA) of 0.01%·min / °C or less.

[0155] Specific descriptions of the polyamide-imide film are as described above.

[0156] The cover window for the display device can be usefully applied to the display device.

[0157] [Display device] A display device according to one embodiment includes a display unit and a cover window disposed on the display unit, and the cover window includes a polyamide-imide film and a functional layer.

[0158] The polyamide-imide film has a TGA weight loss area value (TDA) of 0.01%·min / °C or less.

[0159] Specific descriptions of the polyamide-imide film and the cover window are as described above.

[0160] FIG. 1 is a schematic exploded view of a display device according to one embodiment. FIG. 2 is a schematic perspective view of a display device according to one embodiment. FIG. 3 is a schematic cross-sectional view of a display device according to one embodiment.

[0161] Specifically, FIGS. 1 to 3 illustrate a display device in which a display unit 400, a polyamide-imide film 100 having a first surface 101 and a second surface 102 on the display unit 400, and a cover window 300 including a functional layer 200 are disposed, and an adhesive layer 500 is disposed between the display unit 400 and the cover window 300.

[0162] The display unit 400 can display an image and can have flexible characteristics.

[0163] The display unit 400 may be a display panel for displaying an image, and for example, may be a liquid crystal display panel or an organic electroluminescence display panel. The organic electroluminescence display panel may include a front polarizing plate and an organic EL panel.

[0164] 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 the surface of the organic EL panel on which an image is displayed.

[0165] The organic EL panel may display an image by self-luminescence in pixel units. The organic EL panel may include an organic EL substrate and a driving substrate. The organic EL substrate may include a plurality of organic electroluminescence units respectively corresponding to pixels. 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 drivingly connected to the organic EL substrate. That is, the driving substrate is connected so as to be able to apply a driving signal such as a driving current to the organic EL substrate, thereby applying a current to each of the organic electroluminescence units to drive the organic EL substrate.

[0166] Also, 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.

[0167] The cover window 300 may be disposed on the display unit 400. The cover window is located on the outer periphery of the display device according to the embodiment and may protect the display unit.

[0168] The cover window 300 may include a polyamide-imide film and a functional layer. The functional layer may be one or more selected from the group consisting of a hard coating layer, a reflectance reduction layer, an antifouling layer, and an antiglare layer. The functional layer may be coated on at least one surface of the polyamide-imide film. Specific descriptions regarding the functional layer and the hard coating layer are as described above.

[0169] In the case of the polyamide-imide film according to the implementation example, without changing the display driving method, the color filter inside the panel, the laminated structure, etc., it can be easily applied in film form outside the display device to provide a display device having a uniform thickness, low haze, high transmittance, and transparency. Since it does not require excessive process changes or cost increases, there is also an advantage that production costs can be reduced.

[0170] The polyamide-imide film according to the implementation example can have excellent optical properties such as high transmittance, low haze, and low yellowness, and mechanical properties such as modulus and flexibility, and the change (deterioration) of optical / mechanical properties can be suppressed even when exposed to ultraviolet rays.

[0171] Specifically, in the case of a polyamide-imide film in which the TGA weight loss area value (TDA) is within the range of the previous art, it is excellent not only in optical and mechanical properties but also in post-process properties such as the adhesion of the functional layer and solvent resistance. As a result, the quality and physical properties of the film do not deteriorate even after passing through the post-process. When the polyamide-imide film is applied to a cover window for a display device or a display device, the quality reliability and product yield of the final product can be improved.

[0172] [Manufacturing Method of Polyamide-Imide Film] One implementation example provides a method for manufacturing a polyamide-imide film.

[0173] The manufacturing method of the polyamide-imide film according to one implementation example includes a step (S100) of polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide polymer solution, a step (S200) of casting the solution to produce a gel sheet, and a step (S300) of heat-treating the gel sheet (see FIG. 4).

[0174] The manufacturing method of a polyamide-imide film according to one implementation example may further include a step (S110) of adjusting the viscosity of the polyamide-imide polymer solution, a step (S120) of aging the polyamide-imide polymer solution, and / or a step (S130) of degassing the polyamide-imide polymer solution.

[0175] The polyamide-imide film is a film mainly composed of a polyamide-imide polymer, and the polyamide-imide polymer is a polymer containing an imide repeating unit and an amide repeating unit as structural units in a predetermined molar ratio.

[0176] In the manufacturing method of the polyamide-imide film, the polymer solution for preparing the polyamide-imide polymer can be prepared by simultaneously or sequentially mixing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent in a reactor and reacting the mixture (S100).

[0177] In one implementation example, the polymer solution can be prepared by simultaneously introducing and reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound into an organic solvent.

[0178] In another implementation example, the step of preparing the polymer solution may include a step of first mixing and reacting the diamine compound and the dianhydride compound in a solvent to prepare a polyamic acid (PAA) solution, and a step of secondarily mixing and reacting the dicarbonyl compound with the polyamic acid (PAA) solution to form amide bonds and imide bonds. The polyamic acid solution is a solution containing a polymer having amic acid repeating units.

[0179] 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 secondarily mixing and reacting the dicarbonyl compound with the polyimide (PI) solution to additionally form an amide bond. The polyimide solution is a solution containing a polymer having an imide repeating unit.

[0180] 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; and secondarily mixing and reacting the dianhydride compound with the polyamide (PA) solution to additionally form an imide bond. The polyamide solution is a solution containing a polymer having an amide repeating unit.

[0181] The polymer solution thus prepared may be a solution containing a polymer including one or more selected from the group consisting of polyamic acid (PAA) repeating units, polyamide (PA) repeating units, and polyimide (PI) repeating units.

[0182] Alternatively, the polymer contained in the polymer solution includes an imide repeating unit derived from the polymerization of the diamine compound and the dianhydride compound, and an amide repeating unit derived from the polymerization of the diamine compound and the dicarbonyl compound.

[0183] The descriptions of the diamine compound, dianhydride compound, and dicarbonyl compound are as described above.

[0184] The content of the solid component contained in the polymer solution may be 10 wt% to 30 wt%. Alternatively, the content of the solid component contained in the polymer solution may be 15 wt% to 25 wt%, but is not limited thereto.

[0185] When the content of the solid component contained in the polymer solution is within the above range, a polyamide-imide film can be effectively produced in the extrusion and casting steps. Further, the produced polyamide-imide film can exhibit similar thermal properties depending on the direction of the film, have uniform quality, and have excellent mechanical properties, optical properties, and heat resistance properties.

[0186] In another implementation example, the step of preparing the polymer solution may further include a step of adding a catalyst.

[0187] At this time, the catalyst may include, but is not limited to, one or more selected from the group consisting of beta picoline, acetic anhydride, isoquinoline (IQ), and pyridine-based compounds.

[0188] Based on 1 mole of the polyamic acid, the catalyst may be added in an amount of 0.01 molar equivalent to 0.5 molar equivalent, 0.01 molar equivalent to 0.4 molar equivalent, or 0.01 molar equivalent to 0.3 molar equivalent, but is not limited thereto.

[0189] When the catalyst is added, the reaction rate can be improved, and the chemical bonding force between repeating unit structures or within the repeating unit structure can be improved.

[0190] In one implementation example, the step of preparing the polymer solution may further include a step (S110) of adjusting the viscosity of the polymer solution. The viscosity of the polymer solution may be adjusted to 80,000 cps to 500,000 cps, 100,000 cps to 500,000 cps, 150,000 cps to 500,000 cps, 150,000 cps to 450,000 cps, 200,000 cps to 450,000 cps, 200,000 cps to 400,000 cps, 200,000 cps to 350,000 cps, or 250,000 cps to 350,000 cps based on normal temperature. In this case, by improving the film-forming property of the polyamide-imide film, the thickness uniformity can be improved.

[0191] Specifically, the step of preparing the polymer solution may include a step of simultaneously or sequentially mixing and reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a first polymer solution, and a step of further adding the dicarbonyl compound to prepare a second polymer solution having a target viscosity.

[0192] In the case of the step of preparing the first polymer solution and the step of preparing the second polymer solution, the viscosities of the prepared polymer solutions are different. For example, the viscosity of the second polymer solution is higher than that of the first polymer solution.

[0193] The stirring speed when preparing the first polymer solution may be different from the stirring speed when preparing the second polymer solution. For example, the stirring speed when preparing the first polymer solution may be faster than the stirring speed when preparing the second polymer solution.

[0194] In another embodiment, the step of preparing the polymer solution may further include a step of adjusting the pH of the polymer solution. In this step, the pH of the polymer solution is adjusted to 4 to 7, and for example, it may be adjusted to 4.5 to 7.

[0195] The pH of the polymer solution is adjusted by adding a pH adjuster. The pH adjuster is not particularly limited, and may include, for example, amine compounds such as alkoxyamine, alkylamine, or alkanolamine.

[0196] By adjusting the pH of the polymer solution within the aforementioned range, the occurrence of defects in the film produced from the polymer solution can be prevented, and the desired optical and mechanical properties can be achieved in terms of yellowness and modulus.

[0197] The pH adjuster may be added in an amount of 0.1 mol% to 10 mol% based on the total number of moles of monomers in the polymer solution.

[0198] In one implementation example, the organic solvent may be one or more selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), m-cresol, tetrahydrofuran (THF), and chloroform. The organic solvent used in the polymer solution may be dimethylacetamide (DMAc), but is not limited thereto.

[0199] In other implementation examples, one or more selected from the group consisting of a filler, a blue pigment, and a UVA absorber may be added to the polymer solution.

[0200] Specific details such as the types and contents of the filler, blue pigment, and UVA absorber are as described above. The filler, blue pigment, and / or UVA absorber may be mixed with the polyamide-imide polymer in the polymer solution.

[0201] The polymer solution can be stored at -20°C to 20°C, -20°C to 10°C, -20°C to 5°C, -20°C to 0°C, or 0°C to 10°C.

[0202] When stored at the above temperature, deterioration of the polymer solution can be prevented, the water content can be reduced, and defects in the film produced thereby can be prevented.

[0203] In some implementation examples, the polymer solution or the viscosity-adjusted polymer solution may be aged (S120).

[0204] The aging can be carried out by allowing the polymer solution to stand under temperature conditions of -10 to 10°C for 24 hours or more. In this case, the polyamide-imide polymer or unreacted substances contained in the polymer solution, for example, by finishing the reaction or achieving chemical equilibrium, the polymer solution is homogenized, and the mechanical and optical properties of the polyamide-imide film formed thereby can be substantially uniform over the entire film area. Preferably, the aging can be carried out under temperature conditions of -5 to 10°C, -5 to 5°C or -3 to 5°C, but is not limited thereto.

[0205] In one embodiment, it may further include the step (S130) of degassing the polyamide-imide polymer solution. By removing moisture in the polymer solution and reducing impurities through the degassing, the reaction yield can be increased, and excellent surface appearance and mechanical properties of the final film can be realized.

[0206] The degassing may include vacuum degassing or inert gas purging. The vacuum degassing can be carried out for 30 minutes to 3 hours after reducing the pressure of the reactor containing the polymer solution to 0.1 bar to 0.7 bar. By performing vacuum degassing under such conditions, the bubbles inside the polymer solution can be reduced, and as a result, surface defects of the film produced thereby can be prevented, and excellent optical properties such as haze can be realized.

[0207] Also, the purging can be carried out by a method of purging the internal pressure of the tank with an inert gas at 1 atm to 2 atm. By performing the purging under such conditions, moisture inside the polymer solution can be removed and impurities can be reduced, thereby increasing the reaction yield, and excellent optical properties such as haze and excellent mechanical properties can be realized.

[0208] 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 not limited thereto. Specifically, the inert gas may be nitrogen.

[0209] The vacuum degassing and the inert gas purge may be performed in separate steps. For example, a step of vacuum degassing may be performed, and thereafter, a step of purging with an inert gas may be performed, but is not limited thereto.

[0210] By performing the vacuum degassing and / or the inert gas purge, the physical properties of the surface of the produced polyamide-imide film can be improved.

[0211] The polymer solution may be cast to produce a gel sheet (S200). For example, the polymer solution may be applied and extruded on a support to form a gel sheet.

[0212] Also, the casting thickness of the polymer solution may be 200 μm to 700 μm. By casting the polymer solution within this thickness range, appropriate thickness and thickness uniformity can be ensured when it is manufactured as the final film through heat treatment.

[0213] As described above, the viscosity of the polymer solution may be 150,000 cps to 500,000 cps at room temperature. By satisfying this viscosity range, when the polymer solution is cast, it can be cast into a uniform thickness without defects, and in the subsequent heat treatment process, a polyamide-imide film with a substantially uniform thickness can be formed without local / partial thickness changes.

[0214] The gel sheet may be heat-treated to form a polyamide-imide film (S300). The heat treatment of the gel sheet may be performed, for example, by a heat curing device.

[0215] The step of heat-treating the gel sheet may include two or more heat-treatment steps and two or more cooling steps. For example, the step of heat-treating the gel sheet may include three or more heat-treatment steps and three or more cooling steps.

[0216] In one implementation example, the step of heat-treating the gel sheet may include a first heat-treatment step, a second heat-treatment step, and a third heat-treatment step. Specifically, the step of heat-treating the gel sheet may include a first heat-treatment step, a second heat-treatment step, a third heat-treatment step, a first cooling step, a second cooling step, and a third cooling step. More specifically, the step of heat-treating the gel sheet may sequentially perform a first heat-treatment step (S310), a first cooling step (S320), a second heat-treatment step (S330), a third heat-treatment step (S340), a second cooling step (S350), and a third cooling step (S360) (see FIG. 5).

[0217] In the first heat-treatment step, the gel sheet obtained by casting the polymer solution may be heat-treated at a temperature of 60°C to 150°C, 70°C to 150°C, 80°C to 150°C, or 90°C to 150°C for 5 minutes to 60 minutes. Specifically, the gel sheet may be heat-treated at a temperature of 90°C to 140°C for 10 minutes to 30 minutes.

[0218] During the first heat-treatment step, a part or all of the solvent of the gel sheet may be volatilized, and the gel sheet may be dried.

[0219] In some implementation examples, the first heat-treatment step may be performed while moving on a belt, but is not limited thereto.

[0220] The first cooling step may be performed after the first heat-treatment step. Specifically, in the first cooling step, the gel sheet may be cooled at a temperature of 10°C to 70°C, 15°C to 60°C, 15°C to 50°C, or 15°C to 40°C for 5 minutes to 60 minutes. Specifically, the gel sheet may be cooled at a temperature of 15°C to 35°C for 5 minutes to 30 minutes.

[0221] The second heat treatment stage can be performed after the first cooling stage. Specifically, the second heat treatment stage can be performed by hot air treatment.

[0222] In one implementation example, when the step of heat treating with the hot air is performed, the heat quantity can be evenly applied. If the heat quantity is not evenly distributed, a satisfactory surface roughness may not be achieved, or the surface quality may become non-uniform, and the surface energy may excessively increase or decrease.

[0223] The heat treatment with the hot air can be performed in the range of 60°C to 500°C for 5 minutes to 200 minutes. Specifically, the heat treatment of the gel sheet can be performed for 5 minutes to 100 minutes while increasing the temperature at a rate of 1.5°C / min to 20°C / min in the range of 80°C to 350°C. More specifically, the heat treatment of the gel sheet can be performed in the temperature range of 140°C to 300°C.

[0224] At this time, the starting temperature of the heat treatment of the gel sheet with the hot air can be 60°C or higher. Specifically, the starting temperature of the heat treatment of the gel sheet can be 80°C to 180°C. Also, the maximum temperature during the heat treatment can be 200°C to 500°C.

[0225] Also, the heat treatment of the gel sheet with the hot air can be performed in two or more stages. Specifically, the heat treatment of the gel sheet with the hot air is sequentially performed in a first hot air treatment stage and a second hot air treatment stage, and the temperature in the second hot air treatment stage can be higher than the temperature in the first hot air treatment stage.

[0226] In one implementation example, the step of heat treating the gel sheet can include a third heat treatment stage of heat treating with at least one heater, specifically, a step of heat treating with a plurality of heaters after the second heat treatment stage.

[0227] The plurality of heaters can include a plurality of heaters spaced apart in the width direction (TD direction) of the gel sheet. The plurality of heaters are mounted on a heater mounting portion, and two or more of the heater mounting portions can be arranged along the traveling direction (MD direction) of the gel sheet.

[0228] The at least one heater may include an IR heater. However, the type of the at least one heater is not limited to the above example and can be variously changed. Specifically, the plurality of heaters may include an IR heater.

[0229] The heat treatment by the at least one heater can be performed in a temperature range of 250°C or higher. Specifically, the heat treatment by the at least one heater can be performed for 1 minute to 30 minutes, or 1 minute to 20 minutes in a temperature range of 250°C to 400°C.

[0230] The temperature described in the heat treatment by the heater is the temperature in the heat treatment apparatus where the gel sheet is present, and corresponds to the temperature measured by a temperature sensing sensor located in the third heat treatment section in the heat treatment apparatus.

[0231] The second cooling stage can be performed after the third heat treatment stage. In the second cooling stage, the gel sheet can be cooled at a temperature of 30°C to 150°C, 30°C to 120°C, 50°C to 120°C, or 70°C to 120°C for 1 minute to 60 minutes. Specifically, the gel sheet can be cooled at a temperature of 70°C to 100°C for 2 minutes to 30 minutes.

[0232] In one implementation example, the second cooling stage may further include a first temperature reduction stage of reducing the temperature at a rate of 100°C / min to 1000°C / min.

[0233] The third cooling stage can be performed after the second cooling stage. In the third cooling stage, the gel sheet can be cooled at a temperature of 10°C to 70°C, 15°C to 60°C, 15°C to 50°C, or 15°C to 40°C for 1 minute to 60 minutes. Specifically, the gel sheet can be cooled at a temperature of 15°C to 35°C for 2 minutes to 30 minutes.

[0234] In one implementation example, the third cooling stage may further include a second temperature reduction stage of reducing the temperature at a rate of 40°C / min to 400°C / min.

[0235] At this time, specifically, the second temperature reduction stage is performed after the first temperature reduction stage, and the temperature reduction rate in the first temperature reduction stage may be faster than the temperature reduction rate in the second temperature reduction stage.

[0236] For example, the maximum speed during the first temperature reduction stage is faster than the maximum speed during the second temperature reduction stage. Or, the minimum speed during the first temperature reduction stage is faster than the minimum speed during the second temperature reduction stage.

[0237] By performing the cooling stage of the cured film in such multiple stages, the physical properties of the cured film can be further stabilized, and the optical and mechanical physical properties of the film established during the curing process can be more stably maintained for a long time.

[0238] When the heat treatment of the gel sheet is performed while satisfying the temperature, time, and process procedure of the heat treatment stage and the cooling stage, efficient drying and curing are performed, the residual solvent in the film is minimized, and physical properties such as the target range of the TGA weight loss area value (TDA), the primary weight loss temperature (Tw), and the 1% weight loss temperature (Td1) can be controlled. Furthermore, not only the optical and mechanical properties of the film manufactured by the manufacturing method, but also the post-process properties such as the functional layer adhesion and solvent resistance are excellent.

[0239] The temperature of the second cooling stage and the temperature of the third cooling stage may be different. The temperature of the second cooling stage may be higher than the temperature of the third cooling stage, but is not limited thereto.

[0240] In one implementation example, the temperature of the second cooling stage may be 20°C to 100°C, 40°C to 80°C, or 50°C to 80°C higher than the temperature of the third cooling stage.

[0241] Also, a step of winding the cooled cured film by a winder may be performed.

[0242] At this time, on the belt during drying, the ratio of the moving speed of the gel sheet to the moving speed of the cured film during winding is 1:0.95 to 1:1.40. Specifically, the ratio of the moving speeds 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.

[0243] If the ratio of the moving speeds is outside the above range, the mechanical properties of the cured film may be impaired, and the flexibility and elastic properties may decrease.

[0244] In the method for producing 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} × 100 In the general formula 1, M1 is the thickness (μm) of the gel sheet, and M2 is the thickness (μm) of the cooled cured film during winding.

[0245] By being produced based on the above-described production method, the polyamide-imide film not only exhibits excellent optical and mechanical properties, but may also have post-process properties such as excellent functional layer adhesion and solvent resistance. Such a polyamide-imide film may be applicable to various applications that require transparency. For example, the polyamide-imide film may be applied not only to display devices, but also to solar cells, semiconductor elements, sensors, and the like.

[0246] The description of the polyamide-imide film produced by the production method described above is as described above.

[0247] (Example) The above content will be further described in detail by the following examples. Note that the following examples are only for illustrating the present invention, and the scope of the examples is not limited only thereto.

[0248] (Example 1) After filling a reactor capable of temperature adjustment with dimethylacetamide (DMAc), which is an organic solvent, under a nitrogen atmosphere at 10°C, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), which is an aromatic diamine, was gradually added and dissolved while being added.

[0249] Thereafter, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanedianhydride (6-FDA), which is a dianhydride compound, was gradually added and stirred for 2 hours.

[0250] Then, terephthaloyl chloride (TPC) was added as a dicarbonyl compound and stirred for 1 hour, and isophthaloyl chloride (IPC) was added and stirred for 1 hour to prepare a polymer solution.

[0251] The obtained polymer solution was applied onto a support to form a gel sheet.

[0252] Thereafter, as a first heat treatment step, the gel sheet was heat-treated with hot air at a temperature of 140°C for 15 minutes to dry the gel sheet, and as a first cooling step, it was cooled at a temperature of 35°C for 5 minutes. Next, as a second heat treatment step of the gel sheet, the gel sheet was heat-treated with hot air at a temperature of 275°C for 5 minutes. As a third heat treatment step of the gel sheet, the gel sheet was passed through an IR heater while adjusting the temperature so that the temperature measured by a temperature sensing sensor within the heat treatment section reached 280°C. Subsequently, after cooling at a temperature of 100°C for 3 minutes as a second cooling step, and then cooling at a temperature of 30°C for 3 minutes as a third cooling step, a polyamide-imide-based film with a thickness of 50 μm was obtained.

[0253] The specific composition and molar ratio of the polyamide-imide-based polymer are as described in the production examples in Table 1 below.

[0254] (Examples 2, 3 and Comparative Examples 1 to 3) As shown in Table 1 and Table 2 below, films were produced in the same manner as in Example 1, except that the composition and molar ratio of the polymer, the temperature and time of each heat treatment stage and cooling stage during the gel sheet heat treatment were different. (Production Example: Composition of Polymer)

[0255] JPEG0007688814000020.jpg52155

[0256] JPEG0007688814000021.jpg117155

[0257] (Evaluation Example) For the films produced in the above Examples and Comparative Examples, physical properties were measured and evaluated as follows, and the results are shown in Table 3 below.

[0258] (Evaluation Example 1: Film Thickness Measurement) Using a digital micrometer 547-401 from Mitutoyo Corporation, Japan, the thicknesses at five locations at arbitrary positions were measured, and the average value was taken as the thickness.

[0259] (Evaluation Example 2: Transmittance and Haze Measurement) Using a haze meter NDH-5000W from Nippon Denshoku Industries Co., Ltd., Japan, the light transmittance and haze were measured based on the JIS K 7136 standard.

[0260] (Evaluation Example 3: Yellowness Measurement) The yellowness (Yellow Index, YI) was measured by a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) under the conditions of d65 and 10°, according to the ASTM-E313 standard.

[0261] (Evaluation Example 4: Modulus Measurement) Using the Instron universal testing machine UTM5566A, samples were cut to a length of 10 cm or more in a direction perpendicular to the main shrinkage direction and 10 mm in the main shrinkage direction, attached to clips at 10 cm intervals, and then stretched at a speed of 10 mm / min at room temperature until breakage occurred to obtain a stress-strain curve. In the stress-strain curve, the slope of the load with respect to the initial deformation was taken as the modulus (GPa).

[0262] (Evaluation Example 5: Surface Tension Measurement) Using the Mobile Surface Analyzer from Kruss, Germany, based on German Industrial Standard (DIN 55660), the surface tensions of the air side and belt side of the film were measured respectively.

[0263] (Evaluation Example 6: TGA Analysis of Film) For the TGA analysis, 2 g of the measurement sample of the polyamide-imide-based film was taken using the thermal gravimetric analysis TGA Q500 model from TA Instruments, and analyzed while heating at a rate of 10 °C / min in the range of 25 °C to 700 °C.

[0264] The primary weight loss temperature (Tw) was determined as the temperature at which the rate of weight loss change was the largest in the temperature range of 270 °C to 330 °C. In the graph of the rate of weight loss change (y-axis) against temperature (x-axis), the area of the section to which the primary weight loss temperature (Tw) belongs among the area between the graph and the straight line connecting the point corresponding to the temperature of (Tw - 30) °C and the point corresponding to the temperature of (Tw + 30) °C was taken as the TGA weight loss area value (TDA).

[0265] Also, the 1% weight loss temperature (Td1) and 5% weight loss temperature (Td5) were determined as the temperatures at which 1% weight loss and 5% weight loss occurred respectively during the TGA analysis.

[0266] (Evaluation Example 7: Evaluation of Adhesion of Hard Coating Layer) A polyester resin (PLASCOAT 446, Mutual Chemical Industry Co., Ltd., Japan) and a polyurethane resin (solid content: 28% by weight, H-15, Daiichi Kogyo Seiyaku Co., Ltd., Japan) were mixed at a weight ratio of 7:3 (solid content weight ratio), and a solution in which water (H 2 O) and isopropyl alcohol (IPA) were mixed at 85:15 parts by weight was added. After stirring at room temperature for 30 minutes, a primer layer composition was prepared.

[0267] Furthermore, 54.32 parts by weight of a urethane acrylate oligomer (PU2050, Miwon Specialty Chemical Co., Ltd.), 23.28 parts by weight of a polyfunctional acrylate monomer (M300, Miwon Specialty Chemical Co., Ltd.), 19.4 parts by weight of a silica sol (MA-ST, Nissan Chemical Industries, Ltd.) in which silica fine particles with a particle size of 10 nm to 15 nm were dispersed at 30% by weight in methanol, and 3 parts by weight of a photoinitiator (I-184, BASF) were added to prepare a hard coating layer composition.

[0268] The primer layer composition was applied to a polyamide-imide film sample to form a primer layer with a thickness of 0.1 μm, and the hard coating layer composition was applied onto the primer layer to form a hard coating layer with a thickness of 5 μm.

[0269] Thereafter, the adhesion between the film sample and the hard coating layer was evaluated by a cross-cut test. After cutting the surface of the hard coating layer into a lattice pattern at regular intervals based on the ASTM D 3359 (Method B) standard, a tape (Nitto Tape 50B) was pasted onto it and peeled off to check the degree to which flakes in lattice units were generated on the surface. Grades were assigned from 0B to 5B according to the following criteria, and the case of 5B was evaluated as the most excellent (see Figure 6). - 5B: The cut surface is clean and the squares of the lattice are not separated (0% of the lattice area) - 4B: Small pieces of the coating are separated at the intersections (less than 5% of the lattice area) - 3B: Small pieces of the coating are separated along the corners and at the intersections of the cut portions (5% - 15% of the lattice area) - 2B: The edge of the cross-section of the coating and a part of the square are separated (15% - 35% of the grid area) - 1B: The coating is largely peeled off along the edge of the cross-section and the square is separated (35% - 65% of the grid area) - 0B: The degree of peeling of the coating and separation of the square becomes more serious (more than 65% of the grid area)

[0270] (Evaluation Example 8: Solvent Resistance Evaluation) After immersing the film sample (5 cm × 15 cm) in the solvent for 5 seconds, it was dried at 80°C for 3 minutes, and the haze was measured again by the method according to Evaluation Example 2. The less the change in haze, the better the solvent resistance was evaluated. As the solvent, MIBK or IPA was used.

[0271] JPEG0007688814000022.jpg22190

[0272] Referring to Table 2 and Table 3, in the case of the film according to the examples where the TGA weight loss area value (TDA) was controlled to 0.01%·min / °C or less, not only the optical properties such as transmittance, haze, and yellowness, and the mechanical properties such as modulus, but also the hard coating adhesion was excellent. After immersion in the solvent mainly used in the subsequent process etc., by showing that the change in haze was below a specific level, Solvent resistance it was also confirmed to be excellent.

Explanation of Reference Signs

[0273] 100: Polyamide-imide film 101: First surface 102: Second surface 200: Functional layer 300: Cover window 400: Display part 500: Adhesive layer

Claims

Claim 1: A polyamide-imide film, wherein the TGA weight loss area value (TDA) by the following analysis method is 0.01% / min / °C or less, wherein the haze change amount (ΔHz M) when measuring the haze after immersing the polyamide-imide film in MIBK for 5 seconds, drying at 80°C for 3 minutes, is 0.2% or less, wherein the haze change amount (ΔHz I) when measuring the haze after immersing the polyamide-imide film in IPA for 5 seconds, drying at 80°C for 3 minutes, is 0.1% or less, a polyamide-imide film. [Analysis method] When performing TGA analysis while heating a polyamide-imide film at a rate of 10°C / min in the range of 25°C to 700°C, when the primary weight loss temperature (Tw) is defined as the temperature with the largest weight loss change rate in the temperature range of 270°C to 330°C, in the graph of the weight loss change rate (y-axis) against temperature (x-axis), the area between the straight line connecting the point corresponding to the temperature of (Tw - 30)°C and the point corresponding to the temperature of (Tw + 30)°C, and the area of the section to which the primary weight loss temperature (Tw) belongs among the areas between the graphs is defined as the TGA weight loss area value (TDA). Claim 2 wherein the primary weight loss temperature (Tw) by TGA analysis of the polyamide-imide film is 290°C or higher, wherein the 1% weight loss temperature (Td1) by TGA analysis of the polyamide-imide film is 300°C or higher, wherein the 5% weight loss temperature (Td5) by TGA analysis of the polyamide-imide film is 420°C or higher, the polyamide-imide film according to Claim 1. Claim 3 wherein the hard coating adhesion of the polyamide-imide film is 5B, the polyamide-imide film according to Claim 1. Claim 4 wherein the polyamide-imide film contains a polyamide-imide polymer, wherein the polyamide-imide polymer contains imide-based repeating units and amide-based repeating units in a molar ratio of 2:98 to 70:30, the polyamide-imide film according to Claim 1. Claim 5 wherein the surface tension of the first surface of the polyamide-imide film is 40 dyn / cm or higher, the polyamide-imide film according to Claim 1. Claim 6 Based on a thickness of 50 μm of the polyamide-imide film, the modulus is 5 GPa or higher, the transmittance is 80% or higher, the haze is 1% or less, the yellowness is 5 or less, the polyamide-imide film according to Claim 1.

7. A cover window for a display device, comprising a polyamide-imide film and a functional layer, wherein the TGA weight loss area value (TDA) by the following analysis method in the polyamide-imide film is 0.01%·min / °C or less, wherein the haze change amount (ΔHz M) when haze is measured after immersing the polyamide-imide film in MIBK for 5 seconds, drying at 80°C for 3 minutes, is 0.2% or less, and wherein the haze change amount (ΔHz I) when haze is measured after immersing the polyamide-imide film in IPA for 5 seconds, drying at 80°C for 3 minutes, is 0.1% or less. [Analysis method] When performing TGA analysis while heating a polyamide-imide film at a rate of 10°C / min in the range of 25°C to 700°C, when the primary weight loss temperature (Tw) is defined as the temperature with the largest weight loss change rate in the temperature range of 270°C to 330°C, in the graph of the weight loss change rate (y-axis) against temperature (x-axis), the area of the section to which the primary weight loss temperature (Tw) belongs among the area between the straight line connecting the point corresponding to the temperature of (Tw - 30)°C and the point corresponding to the temperature of (Tw + 30)°C and the graph is defined as the TGA weight loss area value (TDA).

8. A display device, comprising: a display unit; and a cover window disposed on the display unit, wherein the cover window comprises a polyamide-imide film and a functional layer, wherein the TGA weight loss area value (TDA) by the following analysis method in the polyamide-imide film is 0.01%·min / °C or less, wherein the haze change amount (ΔHz M) when haze is measured after immersing the polyamide-imide film in MIBK for 5 seconds, drying at 80°C for 3 minutes, is 0.2% or less, and wherein the haze change amount (ΔHz I) when haze is measured after immersing the polyamide-imide film in IPA for 5 seconds, drying at 80°C for 3 minutes, is 0.1% or less. [Analysis method] When performing TGA analysis while heating a polyamide-imide film at a rate of 10 °C / min in the range of 25 °C to 700 °C, when the primary weight loss temperature (Tw) is defined as the temperature at which the weight loss change rate is the largest in the temperature range of 270 °C to 330 °C, in the graph of the weight loss change rate (y-axis) against temperature (x-axis), the area of the section to which the primary weight loss temperature (Tw) belongs among the area between the straight line connecting the point corresponding to the temperature of (Tw - 30) °C and the point corresponding to the temperature of (Tw + 30) °C and the graph is defined as the TGA weight loss area value (TDA).

9. A step of polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound on an organic solvent to prepare a polyamide-imide polymer solution; A step of casting the polyamide-imide polymer solution to produce a gel sheet; A step of heat-treating the gel sheet, The step of heat-treating the gel sheet sequentially performs a first heat-treatment step, a first cooling step, a second heat-treatment step, a third heat-treatment step, a second cooling step, and a third cooling step, In the first heat-treatment step, the gel sheet cast from the polymer solution is heat-treated at 60 °C to 150 °C, In the first cooling step, the gel sheet is cooled at 10 °C to 70 °C, In the second heat-treatment step, it is performed at 60 °C to 500 °C, In the third heat-treatment step, the heat-treatment by at least one heater is performed at 250 °C to 400 °C, In the second cooling step, the gel sheet is cooled at 30 °C to 150 °C, In the third cooling step, the gel sheet is cooled at 10 °C to 70 °C, The method for producing a polyamide-imide film according to claim 1.

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