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

Abstract

The present invention provides a polyamide-imide film that exhibits excellent optical properties, mechanical properties, UV blocking properties, and solvent resistance even without containing fluorine atoms, a method for producing the same, and a cover window and display device containing the same. [Solution] A polyamide-imide film is used which contains a polyamide-imide polymer that does not contain fluorine atoms, wherein the polyamide-imide polymer contains imide repeating units, first amide repeating units and second amide repeating units, and when the total of the imide repeating units, the first amide repeating units and the second amide repeating units is 100 mol%, the molar ratio of the imide repeating units is 40 mol% or less, the molar ratio of the first amide repeating units is 70 mol% or less, and the total molar ratio of the first amide repeating units and the second amide repeating units is 60 mol% to 97 mol%.

Description

[Technical Field]

[0001] Examples of implementations relate to polyamide-imide films, methods for manufacturing the same, and cover windows and display devices containing the same. [Background technology]

[0002] Polyimide resins, such as poly(amide-imide) (PAI), exhibit excellent resistance to friction, heat, and chemicals, and are used in primary electrical insulation materials, coatings, adhesives, extrusion resins, heat-resistant paints, heat-resistant plates, heat-resistant adhesives, heat-resistant fibers, and heat-resistant films.

[0003] Polyimide is used in a variety of fields. For example, it is made in powder form and used as a coating agent for metal or magnetic wires, and is mixed with other additives depending on the application. Polyimide is also used to coat kitchen utensils, and due to its heat and chemical resistance, it is used as a membrane for gas separation, and is also used in equipment to filter contaminants such as carbon dioxide, hydrogen sulfide, and impurities in natural gas wells.

[0004] Recently, polyimide films have been developed that are less expensive while possessing excellent optical, mechanical, and thermal properties, by forming polyimides into films. Such polyimide films can be applied to display materials such as organic light-emitting diodes (OLEDs) or liquid crystal displays (LCDs), and can be used as anti-reflective films, compensating films, or phase difference films when achieving phase difference properties.

[0005] However, conventional polyimide-based films, specifically conventional polyamide-imide-based films, have a problem in that the polyamide-imide-based polymer essentially contains fluorine atoms which may be subject to environmental regulations. Accordingly, there is a continuously increasing need for the development of a polyamide-imide-based film having excellent optical properties and mechanical properties even when the polyamide-imide-based polymer does not contain fluorine atoms. Summary of the Invention Problem to be Solved by the Invention

[0006] An embodiment is intended to provide a polyamide-imide-based film excellent in optical properties and mechanical properties, a method for producing the same, and a cover window and a display device including the same. Means for Solving the Problem

[0007] A polyamide-imide-based film according to an embodiment comprises a fluorine atom-free polyamide-imide-based polymer, wherein the polyamide-imide-based polymer comprises an imide-based repeating unit, a first amide-based repeating unit and a second amide-based repeating unit, and when the total of the imide-based repeating unit, the first amide-based repeating unit and the second amide-based repeating unit is 100 mol%, the molar ratio of the imide-based repeating unit is 40 mol% or less, the molar ratio of the first amide-based repeating unit is 70 mol% or less, and the total molar ratio of the first amide-based repeating unit and the second amide-based repeating unit is 60 mol% to 97 mol%.

[0008] According to another implementation, a cover window for a display device includes a polyamide-imide-based film and a functional layer, wherein the polyamide-imide-based film includes a fluorine atom-free polyamide-imide-based polymer, the polyamide-imide-based polymer includes an imide-based repeating unit, a first amide-based repeating unit and a second amide-based repeating unit, when the total of the imide-based repeating unit, the first amide-based repeating unit and the second amide-based repeating unit is 100 mol%, the molar ratio of the imide-based repeating unit is 40 mol% or less, the molar ratio of the first amide-based repeating unit is 70 mol% or less, and the total molar ratio of the first amide-based repeating unit and the second amide-based repeating unit is 60 mol% to 97 mol%.

[0009] According to another implementation, a display device includes a display portion and a cover window disposed on the display portion, wherein the cover window includes a polyamide-imide-based film and a functional layer, the polyamide-imide-based film includes a fluorine atom-free polyamide-imide-based polymer, the polyamide-imide-based polymer includes an imide-based repeating unit, a first amide-based repeating unit and a second amide-based repeating unit, when the total of the imide-based repeating unit, the first amide-based repeating unit and the second amide-based repeating unit is 100 mol%, the molar ratio of the imide-based repeating unit is 40 mol% or less, the molar ratio of the first amide-based repeating unit is 70 mol% or less, and the total molar ratio of the first amide-based repeating unit and the second amide-based repeating unit is 60 mol% to 97 mol%.

[0010] According to one implementation, a method for producing the polyamide-imide-based film includes the steps of: polymerizing a diamine compound, a dianhydride compound and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide-based polymer solution; casting the polymer solution and then drying the same to produce a gel sheet; and heat-treating the gel sheet. Effects of the Invention

[0011] The polyamide-imide film, as demonstrated in this example, readily complies with environmental regulations because the polyamide-imide polymer does not contain fluorine atoms, and possesses excellent optical and mechanical properties.

[0012] Furthermore, the polyamide-imide film used in this example exhibits excellent UV blocking properties. When applied to display devices, it prevents degradation and damage caused by ultraviolet light, maintaining the stable performance of the display device even during long-term use. Moreover, it has excellent solvent resistance, and even if the film is exposed to solvents or other chemicals during subsequent processes, the optical and mechanical properties of the film can be maintained at a certain level or higher. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic exploded view of a display device based on one implementation example. [Figure 2] Figure 2 is a schematic perspective view of a display device based on one implementation example. [Figure 3] Figure 3 is a schematic cross-sectional view of a display device according to one implementation example. [Figure 4] Figure 4 shows a schematic procedure for manufacturing a polyamide-imide film according to one example. [Modes for carrying out the invention]

[0014] Hereinafter, examples of implementations will be described in detail with reference to the accompanying drawings, so that those with ordinary skill in the art to which the present invention pertains can easily carry them out. However, implementations can be realized in various different forms and are not limited to those described herein.

[0015] In this specification, when a film, window, panel, or layer is described as being formed "on" or "under" another film, window, panel, or layer, "on" and "under" include all those formed "directly" or "indirectly" through other components. The criteria for on / under each component are explained based on the drawings. Note that the sizes of components in the drawings may be exaggerated for illustrative purposes and do not represent the actual sizes applied. Throughout the specification, the same reference numeral refers to the same component.

[0016] In this specification, when a part is said to "include" a component, unless otherwise stated, this means that it may include other components rather than excluding them.

[0017] In this specification, unless otherwise specified, singular expressions are interpreted to include singular or plural, as interpreted in the context.

[0018] Furthermore, all figures and expressions describing the amounts of components, reaction conditions, etc., as described herein should be understood to be modified in all cases by the term "approximately" unless otherwise specified.

[0019] In this specification, terms such as "first," "second," etc., are used to describe various components, and such components are not limited to those components. The terms are used solely to distinguish one component from another.

[0020] Furthermore, 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 aforementioned substituents may bond to each other to form a ring.

[0021] [Polyamide-imide film] The realization example provides a polyamide-imide film that is excellent not only in optical properties such as yellowness and haze, and in mechanical properties, but also in UV blocking and solvent resistance.

[0022] The polyamide-imide film according to the implementation example contains a polyamide-imide polymer that does not contain fluorine atoms, and the polyamide-imide polymer contains imide repeating units, first amide repeating units and second amide repeating units, and when the total of the imide repeating units, the first amide repeating units and the second amide repeating units is 100 mol%, the molar ratio of the imide repeating units is 40 mol% or less, the molar ratio of the first amide repeating units is 70 mol% or less, and the total molar ratio of the first amide repeating units and the second amide repeating units is 60 mol% to 97 mol%.

[0023] Specifically, fluorine atoms may not be detected in the polyamide-imide polymer during scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS) analysis. For example, fluorine atoms may not be detected when analyzing a polyamide-imide polymer using SEM-EDS with a Bruker FlatQUAD XFlash150 instrument.

[0024] In one implementation example, the polyamide-imide film does not need to contain substantially no fluorine atoms.

[0025] Specifically, the polyamide-imide film may contain fluorine atoms at a concentration of 500 ppm or less.

[0026] More specifically, the polyamide-imide film may contain fluorine atoms in concentrations of 400 ppm or less, 300 ppm or less, 200 ppm or less, 100 ppm or less, or 50 ppm or less.

[0027] For example, the polyamide-imide film does not have to contain fluorine atoms, but is not limited to that.

[0028] If the polyamide-imide film and / or polyamide-imide polymer in the realized example does not contain fluorine atoms, or contains them within the aforementioned range, it is possible to minimize harmful substances contained in the film and provide an environmentally friendly film, improve chemical stability and extend the film's lifespan, and be free from fluorine-related environmental regulations (PFAS). In this case, the polyamide-imide film in the realized example has excellent optical and mechanical properties even if the polyamide-imide polymer does not contain fluorine atoms.

[0029] In one implementation example, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is set to 100 mol%, the molar ratio of the imide repeating units is 38 mol% or less, 37 mol% or less, 35 mol% or less, 30 mol% or less, 25 mol% or less, or 20 mol% or less, and may be greater than 0 mol%, 1 mol% or more, 2 mol% or more, 3 mol% or more, 5 mol% or more, or 10 mol% or more.

[0030] Specifically, the polyamide-imide film is such that when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is 100 mol%, the molar ratio of the imide repeating units is greater than 0 to 40 mol%, greater than 0 to 38 mol%, greater than 0 to 37 mol%, greater than 0 to 35 mol%, greater than 0 to 30 mol%, greater than 0 to 25 mol%, greater than 0 to 20 mol%, and 1 to 40 mol%, Possible but not limited to 1-38 mol%, 1-37 mol%, 1-35 mol%, 1-30 mol%, 1-25 mol%, 1-20 mol%, 2-38 mol%, 2-37 mol%, 2-35 mol%, 2-30 mol%, 2-25 mol%, 2-20 mol%, 3-35 mol%, 3-30 mol%, 3-25 mol%, 3-20 mol%, 5-30 mol%, 5-25 mol%, 5-20 mol%, 10-25 mol%, or 10-20 mol%.

[0031] In one implementation example, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is set to 100 mol%, the molar ratio of the first amide repeating units may be 69 mol% or less, 67 mol% or less, 65 mol% or less, 63 mol% or less, 60 mol% or less, 40 mol% or less, or 20 mol% or less, and may be greater than 0 mol%, 3 mol% or more, 5 mol% or more, 10 mol% or more, or 15 mol% or more.

[0032] Specifically, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer in the polyamide-imide film is set to 100 mol%, the molar ratio of the first amide repeating units is as follows: greater than 0 to 70 mol%, greater than 0 to 69 mol%, greater than 0 to 67 mol%, greater than 0 to 65 mol%, greater than 0 to 63 mol%, greater than 0 to 60 mol%, greater than 0 to 40 mol%, greater than 0 to 20 mol%, 3 to 70 mol%, 3 to 69 mol%, and 3 to 6 It may be, but is not limited to, 7 mol%, 3-65 mol%, 3-63 mol%, 3-60 mol%, 3-40 mol%, 3-20 mol%, 5-70 mol%, 5-65 mol%, 5-63 mol%, 5-60 mol%, 5-40 mol%, 5-20 mol%, 10-70 mol%, 10-65 mol%, 10-63 mol%, 10-60 mol%, 10-40 mol%, 10-20 mol%, 15-70 mol%, 15-65 mol%, 15-63 mol%, 15-60 mol%, or 15-40 mol%.

[0033] In one implementation example, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is set to 100 mol%, the molar ratio of the second amide repeating units may be 70 mol% or less, 65 mol% or less, 60 mol% or less, 55 mol% or less, 50 mol% or less, 40 mol% or less, or 30 mol% or less, and may be greater than 0 mol%, 5 mol% or more, 10 mol% or more, 15 mol% or more, 20 mol% or more, or 25 mol% or more.

[0034] Specifically, in the polyamide-imide film, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is set to 100 mol%, the molar ratio of the second amide repeating units is greater than 0 to 70 mol%, greater than 0 to 65 mol%, greater than 0 to 60 mol%, greater than 0 to 55 mol%, greater than 0 to 50 mol%, greater than 0 to 40 mol%, greater than 0 to 30 mol%, 10 to 70 mol%, and 10 to 6%. It may be, but is not limited to, 5 mol%, 10-60 mol%, 10-55 mol%, 10-50 mol%, 10-40 mol%, 10-30 mol%, 20-70 mol%, 20-65 mol%, 20-60 mol%, 20-55 mol%, 20-50 mol%, 20-40 mol%, 20-30 mol%, 25-70 mol%, 25-65 mol%, 25-60 mol%, 25-55 mol%, 25-50 mol%, 25-40 mol%, or 25-30 mol%.

[0035] Furthermore, in one implementation example, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is set to 100 mol%, the sum of the molar ratios of the first amide repeating units and the second amide repeating units may be, but are not limited to, 60-95 mol%, 60-93 mol%, 60-90 mol%, 60-85 mol%, 60-80 mol%, 60-75 mol%, 65-97 mol%, 65-95 mol%, 65-93 mol%, 65-90 mol%, 65-85 mol%, 65-80 mol%, 65-75 mol%, 70-97 mol%, 70-95 mol%, 70-93 mol%, 70-90 mol%, or 70-85 mol%.

[0036] If the composition of the polyamide-imide polymer contained in the polyamide-imide film in the example satisfies the above range, the film-forming process during film manufacturing can be carried out appropriately even if the polymer does not contain fluorine atoms. This results in not only excellent optical and mechanical properties, but also a high UV blocking rate and improved optical stability. Therefore, it can be suitably used for protecting electronic components and displays that are sensitive to ultraviolet light. Furthermore, even when exposed to chemicals such as solvents during subsequent processes, the optical and mechanical properties are maintained, making it suitable for various electronic components.

[0037] On the other hand, if the composition of the polyamide-imide polymer contained in the polyamide-imide film does not satisfy the above range, discoloration and deterioration of physical properties due to ultraviolet light may occur, and optical stability may decrease. In addition, if the solvent resistance does not meet the standard, optical and mechanical properties may deteriorate, such as a rapid increase in film haze after immersion in a solvent or contact with a solvent, potentially leading to product quality problems.

[0038] In one implementation example, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units of the polyamide-imide polymer is set to 100 mol%, the molar ratio of the imide repeating units may be 3 to 35 mol%, the molar ratio of the first amide repeating units may be 10 to 70 mol%, and the molar ratio of the second amide repeating units may be 20 to 60 mol%, but is not limited thereto.

[0039] In one implementation example, the polyamide-imide film may have a transmittance of 3% or less at a wavelength of 380 nm, based on a film thickness of 50 μm. Specifically, the polyamide-imide film may have a transmittance of 2.5% or less, 2.3% or less, 2% or less, 1.7% or less, 1.5% or less, 1% or less, 0.7% or less, 0.5% or less, 0.4% or less, 0.35% or less, or 0.3% or less at a wavelength of 380 nm, based on a film thickness of 50 μm.

[0040] For example, the transmittance at the 380 nm wavelength can be measured using a JASCO V-670 ultraviolet-visible-near-infrared spectrophotometer, but is not limited to this.

[0041] If the transmittance of the polyamide-imide film in the implemented example at a wavelength of 380 nm satisfies the aforementioned range, the ultraviolet blocking rate increases, improving the optical stability of the film, and the film can be suitably used to protect electronic components and displays that are sensitive to ultraviolet light. On the other hand, if the transmittance of the polyamide-imide film in the implemented example at a wavelength of 380 nm does not satisfy the aforementioned range, discoloration and deterioration of the material's physical properties due to ultraviolet light may occur.

[0042] In one implementation example, the polyamide-imide film does not need to contain an ultraviolet-blocking material.

[0043] In one implementation example, the polyamide-imide film has a haze change (ΔHz) measured by the following method. M ) may be less than 1%. [Measurement method] A Mayer bar #4 was fixed to the top surface of the 10cm x 10cm cut film (the opposite side of the varnish application plate used during film formation) at the starting point of the coating direction. 2g of methyl ethyl ketone (MEK) solvent was uniformly dropped onto the front of the bar and applied uniformly at a speed of 200mm / min. After drying for 30 seconds in a hot air dryer set to 80°C, the haze (%) of the film was measured. The difference between this haze (%) and the initial haze (%) of the film was defined as the haze change (ΔHz). M )

[0044] Specifically, the aforementioned △Hz M (%) is Hz M -Hz0 is the value of Hz0, where Hz0 indicates the initial haze (%) of the film, and Hz MThis shows the haze (%) of the film measured after fixing a Meyer bar No. 4 to the starting point in the coating direction on the upper surface of the film cut into 10 cm squares (the opposite side of the varnish application plate during film formation), uniformly dropping 2 g of methyl ethyl ketone (MEK) solvent onto the front of the bar, applying it uniformly at a speed of 200 mm / min, and drying it for 30 seconds in a hot air dryer set to 80°C.

[0045] In one implementation example, the polyamide-imide film has a haze change amount (ΔHz) of the film as measured by the measurement method. M ) is 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, or 0.2% or less, and may be 0% or more, 0.01% or more, 0.02% or more, 0.05% or more, or 0.1% or more.

[0046] Specifically, the polyamide-imide film is measured by the haze change amount (ΔHz) of the film according to the measurement method. M ) are 0%~1%, 0%~0.9%, 0%~0.8%, 0%~0.7%, 0%~0.6%, 0%~0.5%, 0%~0.4%, 0%~0.3%, 0%~0.2%, 0.01%~1%, 0.01%~0.9%, 0.01%~0.8%, 0.01%~0.7%, 0.01%~0.6%, 0.01%~0.5%, 0.01%~0.4%, 0.01%~0.3%, 0 The percentages may be, but are not limited to, 0.01%~0.2%, 0.02%~0.7%, 0.02%~0.6%, 0.02%~0.5%, 0.02%~0.4%, 0.02%~0.3%, 0.02%~0.2%, 0.05%~0.7%, 0.05%~0.6%, 0.05%~0.5%, 0.05%~0.4%, 0.05%~0.3%, or 0.05%~0.2%.

[0047] Haze change (ΔHz) of polyamide-imide films based on implementation examples M When the above range is satisfied, the optical and mechanical properties of the film can be maintained at a specific level or higher even when exposed to chemicals such as solvents during subsequent processes, and it has excellent solvent resistance, making it suitable for use in various electronic components.

[0048] On the other hand, the haze change amount (ΔHz of the polyamide-imide-based film according to an embodiment M ) cannot satisfy the above range, there is a risk that optical properties and mechanical properties may degrade, such as a rapid increase in the haze of the film after immersion in a solvent or contact with a solvent. The solvent resistance of the film does not meet the standard, which may cause quality problems of the film or products including the film.

[0049] In one embodiment, based on a film thickness of 50 μm, the modulus of the polyamide-imide-based film may be 5 to 8 GPa, 5 to 7 GPa, 5.4 to 8 GPa, 5.4 to 7 GPa, 6 to 8 GPa, or 6 to 7 GPa, but is not limited thereto.

[0050] The modulus is measured by cutting a sample to a length of 10 cm or more in the direction perpendicular to the main shrinkage direction and 10 mm in the main shrinkage direction, attaching the cut sample to clips spaced 10 cm apart, then stretching the sample at a speed of 10 mm / min at room temperature until fracture occurs to obtain a stress-strain curve. In the obtained stress-strain curve, the slope of the load against initial deformation is taken as the modulus (GPa), which is the measured value. For example, the modulus can be measured using an Instron universal testing machine UTM 5566A, but is not limited thereto.

[0051] When the modulus of the polyamide-imide-based film according to an embodiment satisfies the above range, the mechanical strength and durability of the polyamide-imide-based film are improved, the heat resistance of the film is enhanced, and the film can be suitably used for electronic device components such as cover windows.

[0052] On the other hand, when the modulus of the polyamide-imide-based film according to an embodiment cannot satisfy the above range, the film may be deformed by heat or external force, or the moldability during processing may be degraded.

[0053] In one implementation example, the polyamide-imide film may have a total light transmittance of 78% or more, or 80% or more, as measured in the visible light wavelength range. For example, the total light transmittance may be 82% or more, 84% or more, 85% or more, or 86% or more, and may be 100% or less, 99% or less, 95% or less, 90% or less, 89% or less, or 88% or less.

[0054] In one implementation example, the polyamide-imide film may have a transmittance of 78% or more, or 80% or more, at a wavelength of 550 nm. For example, the transmittance at a wavelength of 550 nm may be 82% or more, 84% or more, 85% or more, or 86% or more, and may be 100% or less, 99% or less, 95% or less, 90% or less, 89% or less, or 88% or less.

[0055] The polyamide-imide film may have a haze of 1% or less. Specifically, the haze may be, but is not limited to, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, or 0.25% or less. The haze of the film may be a value measured in the visible light wavelength range (400 nm to 700 nm).

[0056] The aforementioned transmittance and haze values ​​may be values ​​measured using the NDH-5000W haze meter from Nippon Denshoku Industries Co., Ltd., in accordance with the JIS K 7105 standard.

[0057] The polyamide-imide film may have a yellow index of 5 or less. For example, the yellow index may be 4.8 or less, 4.5 or less, 4.3 or less, 4.2 or less, 4.1 or less, or 4.0 or less, but is not limited to these values.

[0058] The aforementioned yellowness may be a value measured using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) under d65, 10° conditions, in accordance with the ASTM-E313 standard.

[0059] In one implementation example, the polyamide-imide film may have a thickness deviation of 3 μm or less, or 2 μm or less, based on a film thickness of 50 μm. Furthermore, the thickness deviation rate may be, but is not limited to, 5% or less, 4% or less, or 3% or less.

[0060] In one implementation example, the polyamide-imide film may have a modulus of 5 GPa or more, a total light transmittance of 80% or more measured in the visible light wavelength range, a haze of 1% or less, and a yellowness of 5 or less, based on a film thickness of 50 μm, but is not limited to these.

[0061] Specifically, the polyamide-imide film may have, but is not limited to, a modulus of 6 GPa or higher, a total light transmittance of 85% or higher measured in the visible light wavelength range, a haze of 0.5% or lower, and a yellowness of 4.5 or lower, based on a film thickness of 50 μm.

[0062] The polyamide-imide film may have a compressive strength of 0.4 kgf / μm or higher. Specifically, the compressive strength may be 0.45 kgf / μm or higher or 0.46 kgf / μm or higher, but is not limited to these values.

[0063] The polyamide-imide film, when perforated in UTM compression mode using a 2.5 mm spherical tip at a speed of 10 mm / min, has a maximum perforation diameter (mm) including cracks of 60 mm or less. Specifically, the maximum perforation diameter may be, but is not limited to, 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.

[0064] The aforementioned polyamide-imide film may have a pencil hardness of HB or higher on its surface. Specifically, the pencil hardness may be H or higher or 2H or higher, but is not limited to these values.

[0065] The aforementioned polyamide-imide film has a tensile strength of 15 kgf / mm².2 The above is possible. Specifically, the tensile strength is 18 kgf / mm². 2 Above 20 kgf / mm 2 Above, 21kgf / mm 2 or more, or 22 kgf / mm² 2 The above are possible, but not limited to them.

[0066] The polyamide-imide film may have an elongation of 15% or more. Specifically, the elongation may be 16% or more, 17% or more, or 18% or more, but is not limited to these values.

[0067] The aforementioned polyamide-imide film, based on a film thickness of 50 μm, can withstand more than 200,000 folding cycles before breaking when folded to a radius of curvature of 3 mm.

[0068] The number of folding operations is defined as bending the film so that its radius of curvature is 3 mm, and then unfolding it once.

[0069] The polyamide-imide film can be usefully applied to foldable display devices and flexible display devices by satisfying the aforementioned range of folding cycles. Specifically, the polyamide-imide film can be applied to foldable phones, but is not limited thereto.

[0070] The polyamide-imide film may have a surface roughness of 0.01 μm to 0.07 μm. Specifically, the surface roughness may be, but is not limited to, 0.01 μm to 0.06 μm.

[0071] The surface roughness of the polyamide-imide film satisfying the aforementioned range may be advantageous in achieving brightness conditions and textures that are favorable for application to display devices.

[0072] The residual solvent content in the polyamide-imide film may be 2500 ppm or less. Specifically, the residual solvent content may be, but is not limited to, 2200 ppm or less, 2000 ppm or less, 1500 ppm or less, 1200 ppm or less, 1000 ppm or less, 800 ppm or less, 500 ppm or less, or 300 ppm or less.

[0073] The residual solvent refers to the amount of solvent that does not volatilize during film manufacturing and remains in the final manufactured film.

[0074] If the residual solvent content in the polyamide-imide film exceeds the aforementioned range, the film's durability will decrease, potentially affecting variations in film quality. In particular, it will affect the mechanical strength, negatively impacting post-processing of the film, accelerating its water absorption, and potentially degrading not only mechanical properties but also optical properties.

[0075] The polyamide-imide film in the example comprises a polyamide-imide polymer, which can be formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

[0076] The aforementioned polyamide-imide polymer is a polymer containing imide repeating units and amide repeating units.

[0077] Specifically, the polyamide-imide polymer includes imide repeating units derived from the polymerization of a diamine compound and a dianhydride compound, and amide repeating units derived from the polymerization of a diamine compound and a dicarbonyl compound.

[0078] In one example, the polyamide-imide polymer may be a polymer of a diamine compound, a dianhydride compound, and a dicarbonyl compound.

[0079] The diamine compound is a compound that forms a copolymer by forming an imide bond with the dianhydride compound and an amide bond with the dicarbonyl compound.

[0080] The diamine compound is not particularly limited, but may be an aromatic diamine compound containing an aromatic structure. For example, the diamine compound may be a compound represented by the following chemical formula 1.

[0081] [C1] JPEG2026139586000002.jpg863 In the above chemical formula 1, E is a substituted or unsubstituted divalent C6-C 30 Alicyclic group, substituted or unsubstituted divalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring group, substituted or unsubstituted divalent C4-C 30 Aromatic heterocyclic groups, substituted or unsubstituted C1-C 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30 The group can be selected from alkynylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, and -C(CH3)2-.

[0082] e is selected from integers between 1 and 5, and if e is 2 or greater, then any values ​​of E greater than or equal to 2 can be the same or different from each other.

[0083] (E) of the aforementioned chemical formula 1 e The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 1-1a to 1-14a. JPEG2026139586000003.jpg94144

[0084] Specifically, (E) of the above chemical formula 1 e The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 1-1b to 1-13b. JPEG2026139586000004.jpg92138

[0085] More specifically, (E) of the above chemical formula 1 e This can be represented by the chemical formulas 1-7b, but is not limited thereto.

[0086] In one implementation example, the diamine compound may include a compound that does not have a fluorine-containing substituent. Specifically, the diamine compound may consist of a compound that does not have a fluorine-containing substituent.

[0087] In other realizations, the diamine compound may include compounds that do not contain fluorine atoms. Specifically, the diamine compound may consist of compounds that do not contain fluorine atoms.

[0088] In one implementation example, the diamine compound may contain one type of diamine compound. That is, the diamine compound may consist of a single component.

[0089] For example, the diamine compound may include, but is not limited to, 2,2'-dimethylbenzidine (m-Tolidine) having the structure shown below. JPEG2026139586000005.jpg3861

[0090] In one example, the diamine compound may consist of 2,2'-dimethylbenzidine (m-Tolidine), but is not limited thereto.

[0091] Because the dianhydride compound has a low birefringence value, it is a compound that can contribute to improving the optical properties, such as the transmittance, of the film containing the polyamide-imide polymer.

[0092] The aforementioned dianhydride compound is not particularly limited, but may be an aromatic dianhydride compound containing an aromatic structure. For example, the aromatic dianhydride compound may be a compound represented by the following chemical formula 2. [Case 2] JPEG2026139586000006.jpg3959

[0093] In the aforementioned chemical formula 2, G is a substituted or unsubstituted tetravalent C4-C 30 Alicyclic group, substituted or unsubstituted tetravalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted tetravalent C6-C 30 Aromatic ring group, substituted or unsubstituted tetravalent C4-C 30 Aromatic heterocyclic groups, wherein the alicyclic group, the heteroalicyclic group, the aromatic ring group, or the aromatic heterocyclic group exist individually, are bonded to each other to form a fused ring, or are substituted or unsubstituted C1-C 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30 It is bonded by a linking group selected from an alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, and -C(CH3)2-.

[0094] In the above chemical formula 2, G is a substituted or unsubstituted tetravalent C4-C 30 They may also be bonded by alicyclic groups.

[0095] Specifically, G in the above chemical formula 2 may be selected from, but is not limited to, the groups represented by the following chemical formulas 2-1a to 2-9a. JPEG2026139586000007.jpg83142

[0096] For example, G in chemical formula 2 can be represented as 2-2a or 2-8a.

[0097] In one implementation example, the dianhydride compound may include a compound that does not have a fluorine-containing substituent. Specifically, the dianhydride compound may consist of a compound that does not have a fluorine-containing substituent.

[0098] In other realizations, the dianhydride compound may include compounds that do not contain fluorine atoms. Specifically, the dianhydride compound may consist of compounds that do not contain fluorine atoms.

[0099] In other realizations, the dianhydride compound may consist of one single component or a mixture of two components.

[0100] For example, the dianhydride compound may include, but is not limited to, one or more compounds selected from the group consisting of 1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), which have the structures shown below. JPEG2026139586000008.jpg4445JPEG2026139586000009.jpg4150

[0101] Specifically, the dianhydride compound may include 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA).

[0102] In one implementation example, the dianhydride compound may, but is not limited to, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA).

[0103] The diamine compound and the dianhydride compound can polymerize to produce a polyamic acid.

[0104] Next, the polyamic acid can be converted to polyimide by a dehydration reaction, and the polyimide contains imide repeating units.

[0105] The polyimide may contain repeating units represented by the following chemical formula A. [Chemical A] JPEG2026139586000010.jpg4482 In the above chemical formula A, the explanations for E, G, and e are as described above.

[0106] For example, the polyimide may, but is not limited to, a repeating unit represented by the following chemical formula A-1.

[0107] [Chemical A-1] S JPEG2026139586000011.jpg41128 In the above chemical formula A-1, n is an integer from 1 to 400.

[0108] The dicarbonyl compound is not particularly limited, but may be a compound represented by the following chemical formula 3. [C3] JPEG2026139586000012.jpg2757

[0109] In the aforementioned chemical formula 3, J is a substituted or unsubstituted divalent C6-C 30 Alicyclic group, substituted or unsubstituted divalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring group, substituted or unsubstituted divalent C4-C 30 Aromatic heterocyclic groups, substituted or unsubstituted C1-C 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30 The group can be selected from alkynylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, and -C(CH3)2-.

[0110] j is selected from integers between 1 and 5, and if j is 2 or greater, then any values ​​of J greater than or equal to 2 can be the same or different from each other. X can be a halogen atom. Specifically, X can be Cl, Br, I, etc. More specifically, X can be Cl, but is not limited to this.

[0111] (J) of the aforementioned chemical formula 3 j The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 3-1a to 3-14a. JPEG2026139586000013.jpg96145

[0112] Specifically, (J) of the above chemical formula 3 j The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 3-1b to 3-8b. JPEG2026139586000014.jpg73150

[0113] More specifically, (J) of the above chemical formula 3 j This can be represented by the chemical formula 3-1b, the chemical formula 3-2b, the chemical formula 3-3b, or the chemical formula 3-8b.

[0114] For example, (J) of the above chemical formula 3 j This can be represented by the chemical formula 3-1b or the chemical formula 3-2b.

[0115] In one implementation example, the dicarbonyl compound may be used as a single dicarbonyl compound or as a mixture of at least two different dicarbonyl compounds. When two or more dicarbonyl compounds are used, the dicarbonyl compounds are (J) in the chemical formula 3. j Two or more groups selected from the groups represented by the chemical formulas 3-1b to 3-8b may be used.

[0116] In other realizations, the dicarbonyl compound may be an aromatic dicarbonyl compound containing an aromatic structure.

[0117] In one embodiment, the dicarbonyl compound may include a compound that does not contain a fluorine atom. Specifically, the dicarbonyl compound may consist of a compound that does not contain a fluorine atom.

[0118] The dicarbonyl compound may include, but is not limited to, terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof, having the following structures. JPEG2026139586000015.jpg3065JPEG2026139586000016.jpg3081JPEG2026139586000017.jpg3852

[0119] In one example, the dicarbonyl compound may, but is not limited to, terephthaloyl chloride (TPC) and isophthaloyl chloride (IPC).

[0120] The diamine compound and the dicarbonyl compound can polymerize to form a repeating unit represented by the following chemical formula B. [Case B] JPEG2026139586000018.jpg3679 In the above chemical formula B, the explanations for E, J, e, and j are as described above.

[0121] For example, the diamine compound and the dicarbonyl compound can polymerize to form an amide repeating unit represented by the following chemical formulas B-1, B-2, or B-3.

[0122] Alternatively, the diamine compound and the dicarbonyl compound may polymerize to form amide repeating units represented by the following chemical formulas B-2 and B-3.

[0123] [Case B-1] JPEG2026139586000019.jpg34128 In the above chemical formula B-1, x is an integer from 1 to 400.

[0124] [Case B-2] JPEG2026139586000020.jpg35128 In the above chemical formula B-2, y is an integer from 1 to 400.

[0125] [Case B-3] JPEG2026139586000021.jpg3584 In the above chemical formula B-3, y is an integer from 1 to 400.

[0126] In one implementation example, the polyamide-imide polymer is a polymer of a diamine compound, a dianhydride compound, and a dicarbonyl compound, wherein the diamine compound is represented by chemical formula 1, the dianhydride compound is represented by chemical formula 2, and the dicarbonyl compound is represented by chemical formula 3.

[0127] In one implementation example, the polyamide-imide polymer may contain repeating units represented by the following chemical formula A and repeating units represented by the following chemical formula B.

[0128] [Chemical A] JPEG2026139586000022.jpg47128

[0129] [Case B] JPEG2026139586000023.jpg39128

[0130] In the aforementioned chemical formulas A and B, E and J are independently substituted or unsubstituted divalent C6-C 30 Alicyclic group, substituted or unsubstituted divalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring group, substituted or unsubstituted divalent C4-C 30 Aromatic heterocyclic groups, substituted or unsubstituted C1-C 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30Selected from alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, and -C(CH3)2-, e and j are independently selected from integers between 1 and 5. If e is 2 or greater, then 2 or greater E's are either identical or different from each other. If j is 2 or greater, then 2 or greater Js are either identical or different from each other. G is a substituted or unsubstituted tetravalent C4-C 30 Alicyclic group, substituted or unsubstituted tetravalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted tetravalent C6-C 30 Aromatic ring group, substituted or unsubstituted tetravalent C4-C 30 Aromatic heterocyclic groups, wherein the alicyclic group, the heteroalicyclic group, the aromatic ring group, or the aromatic heterocyclic group exists alone, or is bonded to each other to form a fused ring, or is a substituted or unsubstituted C1-C group. 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30 It is bonded by a linking group selected from an alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, and -C(CH3)2-.

[0131] In one example, the diamine compound, the dianhydride compound, and the dicarbonyl compound do not necessarily have to contain a fluorine atom.

[0132] In one example, the diamine compound may include 2,2'-dimethylbenzidine (m-Tolidine), and the dianhydride compound may include 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), but is not limited thereto.

[0133] 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 ratios of the imide repeating units and amide repeating units are 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 2:98 to 45:55, 2:98 to 40:60, 2:98 to 35:65, 2:98 to 30:70, 3:97 to 70:30, 3:97 to 60:40, 3:97 to 55: It could be, but is not limited to, 45, 3:97-50:50, 3:97-45:55, 3:97-40:60, 3:97-30:70, 5:95-70:30, 5:95-60:40, 5:95-55:45, 5:95-50:50, 5:95-40:60, 5:95-30:70, or 10:90-40:60.

[0134] When the molar ratio of the imide-based repeating units to the amide-based repeating units is within the aforementioned range, in conjunction with the characteristic process method, it is possible to improve the quality reliability of the film and achieve excellent optical properties, mechanical properties, and ultraviolet blocking rate.

[0135] In the polyamide-imide polymer, the molar ratio of the repeating unit represented by chemical formula A to the repeating unit represented by chemical formula B may be 2:98 to 70:30. Specifically, the molar ratio of the repeating unit represented by chemical formula A to the repeating unit represented by chemical formula B may be 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 2:98 to 45:55, 2:98 to 40:60, 2:98 to 35:65, 2:98 to 30:70, 3:97 to 70:30, 3:97 to 60:40, 3: It could be, but is not limited to, 97-55:45, 3:97-50:50, 3:97-45:55, 3:97-40:60, 3:97-30:70, 5:95-70:30, 5:95-60:40, 5:95-55:45, 5:95-50:50, 5:95-40:60, 5:95-30:70, or 10:90-40:60.

[0136] In one implementation example, the polyamide-imide polymer may contain one or more amide repeating units. Specifically, the polyamide-imide polymer may contain two or more amide repeating units.

[0137] In one embodiment, the polyamide-imide polymer may include a first amide repeating unit and a second amide repeating unit. The first amide repeating unit may be formed by the reaction of a first dicarbonyl compound and the diamine compound, and the second amide repeating unit may be formed by the reaction of a second dicarbonyl compound and the diamine compound.

[0138] In other realizations, the polyamide-imide polymer may include a first amide repeating unit derived from a first dicarbonyl compound and a second amide repeating unit derived from a second dicarbonyl compound. Specifically, the first amide repeating unit may be derived from the first dicarbonyl compound, and the second amide repeating unit may be derived from the second dicarbonyl compound.

[0139] The first dicarbonyl compound and the second dicarbonyl compound may be different compounds from each other.

[0140] The first dicarbonyl compound and the second dicarbonyl compound may each contain two carbonyl groups. The angle between the two carbonyl groups in the first dicarbonyl compound may be greater than the angle between the two carbonyl groups in the second dicarbonyl compound.

[0141] In the implemented example, the first dicarbonyl compound and the second dicarbonyl compound may be structural isomers of each other.

[0142] The first dicarbonyl compound and the second dicarbonyl compound may each be an aromatic dicarbonyl compound. Specifically, the first dicarbonyl compound and the second dicarbonyl compound may each have one benzene ring (phenyl group).

[0143] For example, the first dicarbonyl compound and the second dicarbonyl compound may be, but are not limited to, different aromatic dicarbonyl compounds.

[0144] Since the first dicarbonyl compound and the second dicarbonyl compound are both aromatic dicarbonyl compounds, they contain a benzene ring, which can contribute to improving the mechanical properties of the film containing the produced polyamide-imide polymer, such as pencil hardness and tensile strength.

[0145] For example, the angle between the two carbonyl groups in the first dicarbonyl compound may be 160° to 180°, and the angle between the two carbonyl groups in the second dicarbonyl compound may be 80° to 140°.

[0146] In one implementation example, the first dicarbonyl compound may contain terephthaloyl chloride (TPC), and the second dicarbonyl compound may contain isophthaloyl chloride (IPC), but is not limited thereto.

[0147] In one implementation example, the first dicarbonyl compound may be terephthaloyl chloride (TPC) and the second dicarbonyl compound may be isophthaloyl chloride (IPC), but is not limited thereto.

[0148] When TPC is used as the first dicarbonyl compound and IPC as the second dicarbonyl compound in an appropriate combination, it contributes to improving the viscosity of the film during polymerization, allowing the film-forming process to be carried out properly. The resulting film containing the polyamide-imide polymer can have high light transmittance, modulus, etc., low haze and yellowness, and improved UV blocking and solvent resistance.

[0149] In one implementation example, the polyamide-imide polymer includes imide repeating units, first amide repeating units, and second amide repeating units, and when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, the molar ratio of the first amide repeating units may be 70 mol% or less. Specifically, when the total of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, the molar ratio of the first amide repeating units may be, but is not limited to, 65 mol% or less, 60 mol% or less, 58 mol% or less, 55 mol% or less, 50 mol% or less, or 40 mol% or less.

[0150] The molar ratio of the first amide repeating unit to the second amide repeating unit may be 21:79 to 79:21. Specifically, the molar ratio of the first amide repeating unit to the second amide repeating unit may be, but is not limited to, 25:75 to 79:21, 30:70 to 79:21, 35:65 to 79:21, 40:60 to 79:21, 21:79 to 75:25, 25:75 to 75:25, 30:70 to 75:25, 35:65 to 75:25, or 40:60 to 75:25.

[0151] By setting the molar ratio of the first amide repeating unit and the second amide repeating unit within the range described above, the physical properties of the polyamide-imide film can be adjusted to the desired range.

[0152] The polyamide-imide film in the example may further contain, in addition to the polyamide-imide polymer, one or more selected from the group consisting of fillers, blue pigments, and UVA absorbers.

[0153] Specifically, the filler may include metal or semi-metallic oxides, carbon oxides, sulfur oxides, etc. For example, the filler may include, but is not limited to, silica, calcium carbonate, barium sulfate, etc.

[0154] The filler may be present in particulate form. Furthermore, the filler is not treated with any special coating on its surface and is uniformly dispersed throughout the entire film.

[0155] By including the filler in the polyamide-imide film, the film can ensure a wide viewing angle without a decrease in optical properties, improve roughness and windability, and also improve runability and scratch resistance during film manufacturing.

[0156] The filler may have a refractive index of 1.55 to 1.75. Specifically, the refractive index of the filler may be, but is not limited to, 1.60 to 1.75, 1.60 to 1.70, 1.60 to 1.68, or 1.62 to 1.65.

[0157] By ensuring that the refractive index of the filler satisfies the aforementioned range, the birefringence values ​​related to the refractive index in the x direction (nx), y direction (ny), and z direction (nz) of the film can be appropriately adjusted, thereby improving the brightness of the film at various angles.

[0158] On the other hand, if the refractive index of the filler falls outside the range, the presence of the filler may be visually confirmed on the film, or a problem may arise where haze increases due to the filler.

[0159] The filler content may range from 100 ppm to 15,000 ppm based on the total weight of the polyamide-imide polymer solids. Specifically, the filler content may range from 100 ppm to 14,500 ppm, 100 ppm to 14,200 ppm, 200 ppm to 14,500 ppm, 200 ppm to 14,200 ppm, 250 ppm to 14,100 ppm, or 300 ppm to 14,000 ppm based on the total weight of the polyamide-imide polymer solids, but is not limited to these ranges.

[0160] If the content of the filler falls outside the range, the haze of the film increases rapidly, and the fillers aggregate on the film surface, which may result in a visible foreign matter texture, or problems with running the film during the production process, or a decrease in winding performance.

[0161] In one example, the content of the blue pigment may be 50 ppm to 5000 ppm relative to the total weight of the polyamide-imide polymer. Preferably, the content of the blue pigment is 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 relative to the total weight of the polyamide-imide polymer. The levels may be, but are not limited to, 3000 ppm, 50 ppm to 2000 ppm, 100 ppm to 2000 ppm, 200 ppm to 2000 ppm, 300 ppm to 2000 ppm, 400 ppm to 2000 ppm, 50 ppm to 1000 ppm, 100 ppm to 1000 ppm, 200 ppm to 1000 ppm, 300 ppm to 1000 ppm, or 400 ppm to 1000 ppm.

[0162] The UVA absorber may include an absorber that absorbs electromagnetic waves with wavelengths of 10 nm to 400 nm used in this field. For example, the UVA absorber may include a benzotriazole compound, and the benzotriazole compound may include an N-phenolic benzotriazole compound. Specifically, the N-phenolic benzotriazole compound may include an 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 atoms and may be linear, branched, or cyclic.

[0163] In one embodiment, the content of the UVA absorber may be 0.1% to 10% by weight relative to the total weight of the polyamide-imide polymer. Preferably, the content of the UVA absorber may be, but is not limited to, 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 relative to the total weight of the polyamide-imide polymer.

[0164] The properties of the polyamide-imide film described above are based on a thickness of 20 μm to 80 μm. For example, the properties of the polyamide-imide film are based on a thickness of 50 μm.

[0165] The thickness of the polyamide-imide film may be between 20 μm and 100 μm. Specifically, the thickness of the polyamide-imide film may be between 20 μm and 80 μm, 20 μm and 60 μm, 20 μm and 50 μm, 25 μm and 100 μm, 25 μm and 80 μm, 25 μm and 60 μm, or 25 μm and 50 μm, but is not limited to these.

[0166] The thickness of the polyamide-imide film can be determined by measuring the thickness at five random locations on the film and taking the average value. Specifically, the thickness of the polyamide-imide film can be determined by measuring the thickness at five random locations using a Mitutoyo Digital Micrometer 547-401 and taking the average value.

[0167] The aforementioned characteristics regarding the components and physical properties of polyamide-imide films can be combined with each other.

[0168] Furthermore, the presence or absence and content of fluorine atoms in the polyamide-imide film and / or polyamide-imide polymer can be adjusted not only according to the type of monomer used in the polymerization process, but also according to additives used in the polymerization process and additives used in subsequent processes.

[0169] Furthermore, the modulus, transmittance, haze, and surface energy of the polyamide-imide film can be adjusted by combining the chemical and physical properties of the components constituting the polyamide-imide film and the specific process conditions at each stage in the manufacturing method of the polyamide-imide film, which will be described later.

[0170] For example, various factors such as the composition and content of the components constituting the polyamide-imide film, the content of residual solvent, the polymerization conditions of the polymer, and the heat treatment conditions such as the heat treatment and cooling stages in the film manufacturing process are combined to achieve the desired range of film properties.

[0171] [Cover window for display device] One example of a cover window for a display device includes a polyamide-imide film and a functional layer.

[0172] The polyamide-imide film comprises a polyamide-imide polymer that does not contain fluorine atoms, and the polyamide-imide polymer comprises imide repeating units, first amide repeating units, and second amide repeating units. When the total of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, the molar ratio of the imide repeating units is 40 mol% or less, the molar ratio of the first amide repeating units is 70 mol% or less, and the total molar ratio of the first amide repeating units and the second amide repeating units is 60 mol% to 97 mol%.

[0173] A detailed explanation of the aforementioned polyamide-imide film is as described above.

[0174] The cover window for the display device can be usefully applied to a display device. Specifically, the cover window for the display device can be usefully applied to a foldable display device, but is not limited thereto.

[0175] [Display device] A display device according to one 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.

[0176] The polyamide-imide film comprises a polyamide-imide polymer that does not contain fluorine atoms, and the polyamide-imide polymer comprises imide repeating units, first amide repeating units, and second amide repeating units. When the total of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, the molar ratio of the imide repeating units is 40 mol% or less, the molar ratio of the first amide repeating units is 70 mol% or less, and the total molar ratio of the first amide repeating units and the second amide repeating units is 60 mol% to 97 mol%.

[0177] A detailed explanation of the polyamide-imide film and cover window is as described above.

[0178] The aforementioned display device may, but is not limited to, a foldable display device.

[0179] Figure 1 is a schematic exploded view of a display device according to one implementation example. Figure 2 is a schematic perspective view of a display device according to one implementation example. Figure 3 is a schematic cross-sectional view of a display device according to one implementation example.

[0180] Specifically, Figures 1 to 3 illustrate a display device in which a display unit 400 and a cover window 300 including a polyamide-imide film 100 having a first surface 101 and a second surface 102 and a functional layer 200 are arranged on the display unit 400, and an adhesive layer 500 is arranged between the display unit 400 and the cover window 300.

[0181] The display unit 400 is capable of displaying an image and may have flexible characteristics.

[0182] The display unit 400 is a display panel for displaying an image, and may be, for example, a liquid crystal display panel or an organic electroluminescent display panel. The organic electroluminescent display panel may include a front polarizing plate and an organic EL panel.

[0183] The front polarizing plate may be placed on the front surface of the organic EL panel. Specifically, the front polarizing plate may be bonded to the surface on which the image is displayed in the organic EL panel.

[0184] The organic EL panel can display an image by self-illumination at the pixel level. The organic EL panel may include an organic EL substrate and a drive 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, an emissive layer, a hole transport layer, and an anode. The drive substrate may be connected to the organic EL substrate in a driving manner. That is, the drive substrate can be connected in such a way that it can apply a drive signal, such as a drive current, to the organic EL substrate, thereby applying current to each of the organic electroluminescent units and driving the organic EL substrate.

[0185] Furthermore, an adhesive layer 500 may be placed between the display unit 400 and the cover window 300. The adhesive layer 500 is not particularly limited as long as it is an optically transparent adhesive layer.

[0186] The cover window 300 may be positioned on the display unit 400. The cover window 300 may be located on the outer casing of the display device according to the embodiment and protect the display unit 400.

[0187] 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 reflectivity reduction 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.

[0188] In the case of polyamide-imide films as demonstrated in the implementation examples, they can be easily applied as a film to the outside of a display device without changing the display driving method, the color filter inside the panel, or the laminated structure. This allows for the provision of a display device with uniform thickness, low haze, high transmittance, and transparency, and has the advantage of reducing production costs because it does not require excessive process changes or cost increases.

[0189] The polyamide-imide films demonstrated in this example can possess excellent optical properties such as high transmittance, low haze, and low yellowness, as well as mechanical properties such as modulus and flexibility. Their superior UV blocking and solvent resistance improve adhesion to other layers, and can also enhance quality uniformity and processability.

[0190] Specifically, in the case of polyamide-imide films as demonstrated in the examples, excellent optical properties, mechanical properties, UV blocking properties, and solvent resistance can be obtained. As a result, when the polyamide-imide film is applied to a cover window for a display device or to a display device, the quality reliability and product yield of the final product can be improved.

[0191] [Method for producing polyamide-imide films] One example of a method for producing a polyamide-imide film includes the steps of: preparing a polyamide-imide polymer solution by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent (S100); producing a gel sheet by casting and drying the polymer solution (S200); and heat-treating the gel sheet (S300) (see Figure 4).

[0192] A method for producing a polyamide-imide film according to one example may further include the steps of adjusting the viscosity of the polyamide-imide polymer solution (S110), aging the polyamide-imide polymer solution (S120), and / or degassing the polyamide-imide polymer solution (S130).

[0193] The polyamide-imide film is a film whose main component is a polyamide-imide polymer, and the polyamide-imide polymer is a polymer that contains imide repeating units and amide repeating units as structural units in a predetermined molar ratio.

[0194] In the method for producing the polyamide-imide film, the polymer solution for preparing the polyamide-imide polymer can be prepared by reacting a mixture obtained by simultaneously or sequentially mixing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent in a reactor (S100).

[0195] In one example, the polymer solution can be prepared by simultaneously adding a diamine compound, a dianhydride compound, and a dicarbonyl compound to an organic solvent and reacting them.

[0196] In other realizations, the step of preparing the polymer solution may include the steps of: first mixing and reacting the diamine compound and the dianhydride compound in an organic solvent to prepare a polyamic acid (PAA) solution; and second mixing and reacting the dicarbonyl compound with the polyamic acid (PAA) solution to form amide and imide bonds. The polyamic acid solution is a solution containing a polymer having amic acid repeating units.

[0197] Furthermore, the steps for preparing the polymer solution may include: preparing a polyamic acid solution by primary mixing and reacting the diamine compound and the dianhydride compound in an organic solvent; preparing a polyimide (PI) solution by dehydrating the polyamic acid solution; and forming additional amide bonds by secondary mixing and reacting the dicarbonyl compound with the polyimide (PI) solution. The polyimide solution is a solution containing a polymer having imide repeating units.

[0198] Furthermore, the step of preparing the polymer solution may include the steps of: first mixing and reacting the diamine compound and the dicarbonyl compound in an organic solvent to prepare a polyamide (PA) solution; and second mixing and reacting the dianhydride compound with the polyamide (PA) solution to form additional imide bonds. The polyamide solution is a solution containing a polymer having amide repeating units.

[0199] The polymer solution prepared in this manner may be a solution containing a polymer comprising one or more repeating units selected from the group consisting of polyamic acid (PAA), polyamide (PA), and polyimide (PI).

[0200] For example, the polymer contained in the polymer solution may include imide repeating units derived from the polymerization of the diamine compound and the dianhydride compound, and amide repeating units derived from the polymerization of the diamine compound and the dicarbonyl compound.

[0201] The descriptions of the diamine compound, the dianhydride compound, and the dicarbonyl compound are as described above.

[0202] The solid content in the polymer solution may be 10% to 30% by weight. Specifically, the solid content in the polymer solution may be 15% to 25% by weight, but is not limited to this.

[0203] When the solid content in the polymer solution is within the specified range, a polyamide-imide film can be effectively manufactured in the extrusion and casting processes. Furthermore, the manufactured polyamide-imide film may have excellent optical properties, UV blocking properties, and solvent resistance.

[0204] In other realizations, the step of preparing the polymer solution may further include the step of adding a catalyst.

[0205] In this case, the catalyst may, but is not limited to, include one or more selected from the group consisting of beta-picoline, anhydride acetate, isoquinoline (IQ), and pyridine compounds.

[0206] The catalyst may be added in amounts of 0.01 to 0.5 molar equivalents, 0.01 to 0.4 molar equivalents, or 0.01 to 0.3 molar equivalents based on 1 mole of polyamic acid, but is not limited to these amounts.

[0207] Adding the catalyst can improve the reaction rate and enhance the chemical bonding strength between or within the repeating unit structures.

[0208] In one embodiment, the step of preparing the polymer solution may further include the step of adjusting the viscosity of the polymer solution (S110). The viscosity of the polymer solution can 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 room temperature. In this case, the film-forming properties of the polyamide-imide film can be improved, and the uniformity of the film thickness can be improved.

[0209] Specifically, the step of preparing the polymer solution may include the steps 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 adding the dicarbonyl compound to prepare a second polymer solution having a target viscosity.

[0210] In the steps of preparing the first polymer solution and the second polymer solution, the viscosities of the prepared polymer solutions may differ. For example, the viscosity of the second polymer solution may be higher than that of the first polymer solution.

[0211] The viscosity of the polymer solution can be measured using the BH-II apparatus of Toki Sangyo Co., Ltd., under constant temperature conditions of 25°C, with the RPM set to 4 and using the No. 4 spindle.

[0212] The stirring speed when preparing the first polymer solution may differ 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.

[0213] In other realizations, the step of preparing the polymer solution may further include the step of adjusting the pH of the polymer solution. In this step, the pH of the polymer solution may be adjusted to 4-7, for example, to 4.5-7.

[0214] The pH of the polymer solution can be adjusted by adding a pH adjusting agent, which is not particularly limited but may include, for example, amine compounds such as alkoxyamines, alkylamines, or alkanolamines.

[0215] By adjusting the pH of the polymer solution within the aforementioned range, defects in the film produced from the polymer solution can be prevented, and the desired optical and mechanical properties in terms of yellowness and modulus can be achieved.

[0216] The pH adjusting agent 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.

[0217] 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. Specifically, the organic solvent used in the polymer solution may be, but is not limited to, dimethylacetamide (DMAc).

[0218] In other implementations, one or more substances selected from the group consisting of fillers, blue pigments, and UVA absorbers may be added to the polymer solution.

[0219] The specific details of the filler, the blue pigment, and the UVA absorber, such as their types and content, are as described above. The filler, the blue pigment, and / or the UVA absorber can be mixed with the polyamide-imide polymer in the polymer solution.

[0220] The polymer solution may 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.

[0221] Storing the polymer solution at the aforementioned temperature prevents deterioration, reduces its water content, and thereby prevents defects in the manufactured film.

[0222] In one embodiment, the step of preparing the polymer solution may further include the step of aging the polymer solution, or the viscosity-adjusted polymer solution (S120).

[0223] The aging process can be carried out by leaving the polymer solution standing at a temperature of -10°C to 10°C for 24 hours or more. In this case, the polymer solution can be homogenized by allowing the polyamide-imide polymer or unreacted material contained in the polymer solution to complete the reaction or reach chemical equilibrium, and the mechanical and optical properties of the resulting polyamide-imide film can be substantially uniform over the entire surface area of ​​the film. Preferably, the aging process can be carried out at a temperature of -5°C to 10°C, -5°C to 5°C, or -3°C to 5°C, but is not limited thereto.

[0224] In one implementation example, the step of preparing the polymer solution may further include the step of degassing the polyamide-imide polymer solution (S130). By removing water from the polymer solution and reducing impurities through degassing, the reaction yield can be increased, and excellent surface appearance and excellent mechanical properties of the final film can be achieved.

[0225] The degassing may include vacuum degassing or inert gas purging. The vacuum degassing can be performed 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 these conditions, air bubbles inside the polymer solution can be reduced, thereby preventing surface defects in the resulting film and achieving excellent optical properties such as haze.

[0226] Furthermore, the purging can be performed by purging the internal pressure of the tank to 1 to 2 atmospheres using an inert gas. By purging under these conditions, water can be removed from the polymer solution, impurities can be reduced, and the reaction yield can be increased, resulting in excellent optical properties such as haze, as well as excellent mechanical properties.

[0227] The inert gas may be, but is not limited to, one or more selected from the group consisting of nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Specifically, the inert gas may be nitrogen.

[0228] The vacuum degassing and the inert gas purging may be carried out by separate processes. For example, a vacuum degassing process may be performed, followed by a purging process with an inert gas, but this is not limited to this.

[0229] The surface properties of the manufactured polyamide-imide film can be improved by performing the vacuum degassing and / or the inert gas purging.

[0230] In the method for producing the polyamide-imide film, a gel sheet can be produced by casting the polymer solution and then drying it (S200). For example, the polymer solution can be coated, extruded, and / or dried on a support to form a gel sheet.

[0231] The casting thickness of the polymer solution can be between 200 μm and 700 μm. By casting the polymer solution within this thickness range, appropriate thickness uniformity can be ensured when the final film is manufactured after drying and heat treatment.

[0232] As mentioned above, the viscosity of the polymer solution can be 100,000 cps to 500,000 cps or 150,000 cps to 500,000 cps at room temperature. By satisfying the viscosity range, the polymer solution can be cast to a uniform thickness without defects when cast, and a polyamide-imide film of substantially uniform thickness can be formed without local / partial thickness changes during the drying process.

[0233] After casting the polymer solution, a gel sheet can be produced by drying it 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 to 60 minutes. Specifically, a gel sheet can be produced by drying the polymer solution at a temperature of 90°C to 140°C for 15 to 40 minutes.

[0234] During the drying process, some or all of the solvent in the polymer solution may evaporate, thereby producing the gel sheet.

[0235] In the method for producing the polyamide-imide film, the dried gel sheet can be heat-treated to form a polyamide-imide film (S300). The heat treatment of the gel sheet can be carried out using a thermosetting apparatus.

[0236] Specifically, the step of heat-treating the gel sheet may include a step of heat-treating it with at least one heater.

[0237] Furthermore, the step of heat-treating the gel sheet may further include a step of heat-treating it with hot air.

[0238] In one implementation example, the step of heat-treating the gel sheet may include a step of heat-treating it with hot air and a step of heat-treating it with at least one heater.

[0239] In one implementation example, when the heat treatment step is performed using hot air, the amount of heat can be applied evenly. If the amount of heat is not distributed uniformly, satisfactory surface roughness may not be achieved, or the surface quality may become uneven, and the surface energy may rise or fall excessively.

[0240] The aforementioned heat treatment with hot air may be carried out at a temperature of 60°C to 500°C for 5 minutes to 200 minutes. Specifically, the heat treatment of the gel sheet may be carried out at a temperature of 80°C to 300°C for 10 minutes to 150 minutes while increasing the temperature at a rate of 1.5°C / min to 20°C / min. More specifically, the heat treatment of the gel sheet may be carried out at a temperature of 140°C to 250°C.

[0241] In this case, the starting temperature for the heat treatment of the gel sheet with hot air may be 60°C or higher. Specifically, the starting temperature for the heat treatment of the gel sheet may be 80°C to 180°C. Furthermore, the maximum temperature during the heat treatment may be 200°C to 500°C.

[0242] The heat treatment of the gel sheet with hot air may be carried out in two or more stages. Specifically, the heat treatment of the gel sheet with hot air may be carried out sequentially in a first hot air treatment stage and a second hot air treatment stage, wherein the temperature in the second hot air treatment stage may be higher than the temperature in the first hot air treatment stage.

[0243] In one embodiment, the step of heat-treating the gel sheet may include a second heat-treating step in which the gel sheet is heat-treated by at least one heater (specifically, by multiple heaters).

[0244] The plurality of heaters may include a plurality of heaters spaced apart in the width direction (TD direction) of the gel sheet. The plurality of heaters are mounted on heater mounting portions, and two or more heater mounting portions may be arranged along the direction of travel of the gel sheet (MD direction).

[0245] The aforementioned at least one heater may include an IR heater. However, the type of the at least one heater is not limited to the examples given above and can be varied in various ways. Specifically, the plurality of heaters may include IR heaters.

[0246] The heat treatment by the at least one heater may be performed at a temperature of 250°C or higher. Specifically, the heat treatment by the at least one heater may be performed at a temperature of 250°C to 400°C for 1 to 30 minutes, or 1 to 20 minutes.

[0247] In the heat treatment using the heater, the temperature is the temperature inside the heat treatment apparatus where the gel sheet is present, and corresponds to the temperature measured by a temperature sensing sensor located in the second heat treatment section within the heat treatment apparatus.

[0248] Next, after the step of heat-treating the gel sheet, a step of cooling the hardened film while moving it may be performed.

[0249] The step of cooling the cured film while moving it may include a first cooling step in which the temperature is reduced at a rate of 100°C / min to 1000°C / min, and a second cooling step in which the temperature is reduced at a rate of 40°C / min to 400°C / min.

[0250] In this case, specifically, the second cooling stage is performed after the first cooling stage, and the cooling rate of the first cooling stage may be faster than the cooling rate of the second cooling stage.

[0251] For example, the maximum rate during said first temperature reduction step can be faster than the maximum rate during said second temperature reduction step. Also, the minimum rate during said first temperature reduction step can be faster than the minimum rate during said second temperature reduction step.

[0252] By performing said cooling step in multiple stages, the physical properties of the cured film can be further stabilized, and the optical properties and mechanical properties of the film established during the curing process can be maintained more stably over a long period of time.

[0253] A step of winding the cooled cured film with a winder may be performed.

[0254] In this case, the ratio of the moving speed of the gel sheet on the belt during winding to the moving speed of the cured film during winding is 1:0.95 to 1:1.40. Specifically, the ratio of said 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.

[0255] If the ratio of said moving speeds deviates from said range, the mechanical properties of said cured film may be impaired, and the flexibility and elastic properties may be degraded.

[0256] In the method for producing said polyamide-imide-based film, the thickness deviation (%) of the film according to General Formula 1 below may be 3% to 30%. Specifically, the thickness deviation (%) of said film may be 5% to 20%, but is not limited thereto. [General Formula 1] Thickness deviation (%) = {(M1-M2) / M1}×100 In General Formula 1, M1 is the thickness (μm) of said gel sheet, and M2 is the thickness (μm) of the cooled cured film during winding.

[0257] The polyamide-imide film produced by the above production method not only exhibits excellent optical and mechanical physical properties, but also can have excellent UV blocking properties and solvent resistance. Such a polyamide-imide film can be applied to various applications that require transparency. For example, the polyamide-imide film can be applied not only to display devices, but also to solar cells, semiconductor elements, sensors and the like. In particular, the polyamide-imide film according to the embodiment does not contain fluorine atoms which may be subject to environmental regulations, so that it can be utilized in more various application fields.

[0258] The description of the polyamide-imide film produced by the production method described above is as stated above.

[0259] (Examples) The above content will be described in further detail by the following examples. It should be noted that the following examples are only for illustrating the present invention, and the scope of the present invention is not limited only thereto.

[0260] (Example 1) A 1L double-jacketed glass reactor with adjustable temperature was charged with 516.0 g of dimethylacetamide (DMAc) under a nitrogen atmosphere at 20°C, then 46.7 g (0.22 mol) of 2,2'-dimethylbenzidine (m-Tolidine) as a diamine compound was gradually added and dissolved. Thereafter, 1.3 g (0.007 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) as a dianhydride compound was gradually added and stirred for 1 hour. Then, 30.8 g (0.152 mol) of terephthaloyl chloride (TPC) as a dicarbonyl compound was added and stirred for 1 hour, and 12.5 g (0.062 mol) of isophthaloyl chloride (IPC) was added and stirred for 1 hour to prepare a polyamide-imide polymer solution. The obtained polymer solution was coated on a glass plate, dried with hot air at 80°C for 30 minutes, peeled off from the glass plate, fixed on a pin frame, and heated at a rate of 2°C / min from 80°C to 300°C, thereby obtaining a polyamide-imide film having a thickness of 50 μm.

[0261] The specific composition and molar ratio of the polyamide-imide polymer are as shown in the manufacturing examples in Table 1 below.

[0262] (Examples 2-6 and Comparative Examples 1-7) As shown in Table 1 below, the film was manufactured in the same manner as in Example 1, except that the composition and molar ratio of the polyamide-imide polymer were different.

[0263] In Comparative Example 2, during the process of adding terephthaloyl chloride (TPC) and stirring for 1 hour, a white powdery precipitate formed in the solution, and further progress was impossible.

[0264] Furthermore, in the case of Comparative Example 4, after polymerization was completed, the viscosity for film production did not rise to the target viscosity, making it impossible to proceed with the film-forming process thereafter. (Manufacturing example: Polymer composition)

[0265] [Table 1]

[0266] (Example of evaluation) The physical properties of the films produced in the examples and comparative examples were measured and evaluated as follows, and the results are shown in Table 2 below.

[0267] (Evaluation example 1: Measuring film thickness) Using a Mitutoyo Japan 547-401 digital micrometer, the thickness was measured at five random locations, and the average value was used to determine the final thickness.

[0268] (Evaluation Example 2: Transmittance and Haze Measurement) Using a NDH-5000W haze meter from Nippon Denshoku Industries Co., Ltd., total light transmittance and haze were measured according to the JIS K 7105 standard.

[0269] (Evaluation example 3: Yellowness measurement) Yellow Index (YI) was measured under conditions of d65 and 10° using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) in accordance with the ASTM-E313 standard.

[0270] (Evaluation Example 4: Modulus Measurement) Using a universal testing machine UTM5566A from Instron, a sample was cut to a dimension of 10 mm in the main shrinkage direction and 10 cm or more in the direction perpendicular to the main shrinkage direction. After mounting the cut sample on clips spaced 10 cm apart, a stress-strain curve was obtained while stretching the sample at a speed of 10 mm / min at room temperature until fracture occurred. In the obtained stress-strain curve, the slope of the load against initial deformation was taken as the modulus (GPa).

[0271] (Evaluation Example 5: Haze change amount (△Hz M ) Measurement) A No. 4 Mayer bar was fixed to the starting end in the coating direction on the upper surface of the 10 cm × 10 cm cut film (the surface opposite the varnish-coated plate during film formation), 2 g of methyl ethyl ketone (MEK) solvent was uniformly dropped in front of the bar, and the solvent was uniformly coated at a speed of 200 mm / min, followed by drying for 30 seconds in a hot air dryer set to 80°C. The difference between the measured haze (%) of the film and the initial haze (%) of the film measured in Evaluation Example 2 above was taken as the haze change amount (△Hz M ).

[0272] (Evaluation Example 6: Transmittance Measurement at a Wavelength of 380 nm) Transmittance at a wavelength of 380 nm was measured using a JASCO UV-Vis-NIR spectrophotometer V-670.

[0273]

Table 2

[0274] Referring to Table 2, it was confirmed that the films according to the examples exhibited excellent optical properties such as transmittance, haze, and yellowness, as well as superior modulus, and also demonstrated excellent solvent resistance and UV blocking properties. [Explanation of Symbols]

[0275] 100: Polyamide-imide film 101: 1st page 102:Second side 200: Functional Layer 300: Cover window 400: Display section 500: Adhesive layer

Claims

1. It contains a polyamide-imide polymer that does not contain fluorine atoms, The polyamide-imide polymer comprises an imide repeating unit, a first amide repeating unit, and a second amide repeating unit. When the sum of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, The molar ratio of the imide repeating units is 40 mol% or less. The molar ratio of the first amide repeating unit is 70 mol% or less. A polyamide-imide film in which the total molar ratio of the first amide repeating unit and the second amide repeating unit is 60 mol% to 97 mol%.

2. When the sum of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, The polyamide-imide film according to claim 1, wherein the molar ratio of the imide repeating units is 3 mol% to 35 mol%.

3. When the sum of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, The polyamide-imide film according to claim 1, wherein the molar ratio of the first amide repeating unit is 10 mol% to 70 mol%.

4. When the sum of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, The polyamide-imide film according to claim 1, wherein the molar ratio of the second amide repeating unit is 20 mol% to 60 mol%.

5. The aforementioned polyamide-imide polymer is a polymer of a diamine compound, a dianhydride compound, and a dicarbonyl compound. The aforementioned diamine compound is represented by the following chemical formula 1, The aforementioned dianhydride compound is represented by the following chemical formula 2, The dicarbonyl compound is represented by the following chemical formula 3, and is the polyamide-imide film according to claim 1: [Chemical formula 1] [Case 2] [Chemical 3] In the above chemical formulas 1 to 3, 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 cyclic 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 -, and -C(CH ３ ) ２ -, and e and j are independently selected from integers between 1 and 5. If e is 2 or more, then 2 or more E's are either the same or different from each other. If j is 2 or more, then the 2 or more Js are either the same or different from each other. G is a tetravalent C, either substituted or unsubstituted. ４ -C ３０ Alicyclic groups, substituted or unsubstituted tetravalent carbon ４ -C ３０ Heteroalicyclic groups, substituted or unsubstituted tetravalent C ６ -C ３０ Aromatic ring group, substituted or unsubstituted tetravalent C ４ -C ３０ Aromatic heterocyclic groups, wherein the alicyclic group, the heteroalicyclic group, the aromatic ring group, or the aromatic heterocyclic group exist individually, are bonded to each other to form a fused ring, or are 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 -, and -C(CH ３ ) ２ - is bonded by a linking group selected from among them, X is a halogen atom.

6. The polyamide-imide film according to claim 5, wherein the diamine compound comprises 2,2'-dimethylbenzidine.

7. The polyamide-imide film according to claim 5, wherein the dianhydride compound comprises 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA).

8. The first amide repeating unit is derived from the first dicarbonyl compound, and the second amide repeating unit is derived from the second dicarbonyl compound. The polyamide-imide film according to claim 1, wherein the angle between the two carbonyl groups in the first dicarbonyl compound is greater than the angle between the two carbonyl groups in the second dicarbonyl compound.

9. The first dicarbonyl compound is terephthaloyl chloride (TPC), The polyamide-imide film according to claim 8, wherein the second dicarbonyl compound is isophthaloyl chloride (IPC).

10. Based on a film thickness of 50 μm, The modulus is 5 GPa or higher. The total light transmittance measured in the visible light wavelength range is 80% or higher. The haze is less than 1%. A polyamide-imide film according to claim 1, wherein the yellowness is 5 or less.

11. Based on a film thickness of 50 μm, The transmittance at a wavelength of 380 nm is 3% or less. Film haze change (ΔHz) Ｍ The polyamide-imide film according to claim 1, wherein the content of ) is 1% or less.

12. It comprises a polyamide-imide film and a functional layer. The polyamide-imide film comprises a polyamide-imide polymer that does not contain fluorine atoms. The polyamide-imide polymer comprises an imide repeating unit, a first amide repeating unit, and a second amide repeating unit. When the sum of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, The molar ratio of the imide repeating units is 40 mol% or less. The molar ratio of the first amide repeating unit is 70 mol% or less. A cover window for a display device, wherein the total molar ratio of the first amide repeating unit and the second amide repeating unit is 60 mol% to 97 mol%.

13. Display unit and The display unit includes a cover window, The cover window includes a polyamide-imide film and a functional layer. The polyamide-imide film comprises a polyamide-imide polymer that does not contain fluorine atoms. The polyamide-imide polymer comprises an imide repeating unit, a first amide repeating unit, and a second amide repeating unit. When the sum of the imide repeating units, the first amide repeating units, and the second amide repeating units is 100 mol%, The molar ratio of the imide repeating units is 40 mol% or less. The molar ratio of the first amide repeating unit is 70 mol% or less. A display device in which the total molar ratio of the first amide repeating unit and the second amide repeating unit is 60 mol% to 97 mol%.

14. The steps include: preparing a polyamide-imide polymer solution by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound on an organic solvent; The steps include: casting the polymer solution and then drying it to produce a gel sheet; A method for producing a polyamide-imide film according to claim 1, comprising the step of heat-treating the gel sheet.

15. The method for producing a polyamide-imide film according to claim 14, wherein the step of preparing the polymer solution includes a step of adjusting the viscosity of the polymer solution to 100,000 cps to 500,000 cps at room temperature.

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