Polyamide-imide based film, preparation method thereof, and cover window and display device comprising the same

Abstract

The present invention provides a polyamide-imide-based film, which includes a polyamide-imide-based polymer and has an RC value of 0.96 to 1.03 represented by the following equation 1, so that its quality is uniform and has excellent mechanical properties and optical properties, and also provides a method for preparing the film, and a cover window and a display device including the film. <Equation 1> RC = CTE MD / CTE TD In Equation 1, CTE MD CTE is the average value of the thermal expansion coefficient (ppm / °C) of the film in the MD direction. TD It is the average value of the thermal expansion coefficient (ppm / °C) of the film in the TD direction, and the average value is the average value of the thermal expansion coefficient measured at six points in total, two arbitrary points selected in each of the regions N, C and S divided in the TD direction of the film.

Description

Technical Field

[0001] The present embodiment relates to a polyamide-imide based film, a preparation method thereof, and a cover window and a display device including the same. Background Art

[0002] Polyimide-based resins, such as poly(amide-imide) (PAI), have excellent abrasion resistance, heat resistance, and chemical resistance. Therefore, they are used in applications such as primary electrical insulation, coatings, adhesives, extrusion resins, heat-resistant coatings, heat-resistant sheets, heat-resistant adhesives, heat-resistant fibers, and heat-resistant films.

[0003] Polyimide is used in various fields. For example, polyimide is made into powder form and used as a coating for metal or magnetic wire. It can be mixed with other additives depending on the application. In addition, polyimide is used as a paint for decoration and corrosion protection together with fluoropolymers. It also plays a role in bonding the fluoropolymer to the metal substrate. In addition, polyimide is used to coat kitchenware, used as a gas separation membrane using its heat and chemical resistance, and used in natural gas wells to filter pollutants such as carbon dioxide, hydrogen sulfide, and impurities.

[0004] In recent years, polyimide has been developed in the form of a film that is inexpensive and has excellent optical, mechanical and thermal properties. Such polyimide-based films can be applied to display materials such as organic light-emitting diodes (OLEDs) or liquid crystal displays (LCDs), and can be applied to anti-reflection films, compensation films and retardation films if retardation properties are achieved.

[0005] When such a polyimide-based film is applied to a cover window or a display device, there is a problem in that quality reliability and product yield are deteriorated due to uneven quality of the film in a lateral direction.

[0006] Therefore, while solving the above problems, there has been a need to develop a film that exhibits similar thermal properties in the film direction and is excellent in mechanical and optical properties. Summary of the invention

[0007] Technical issues

[0008] The present embodiment aims to provide a polyamide-imide-based film having uniform quality and excellent mechanical properties, optical properties, and heat resistance, a preparation method thereof, and a cover window and a display device including the same.

[0009] Solution to the problem

[0010] One embodiment provides a polyamide-imide-based film including a polyamide-imide-based polymer and having an RC value of 0.96 to 1.03 as represented by the following Equation 1.

[0011] <Equation 1> RC = CTE MD / CTE TD

[0012] In Equation 1, CTE MD It is the average value of the coefficient of thermal expansion (ppm / ℃) of the film in the MD direction, CTE TD It is the average value of the thermal expansion coefficient (ppm / °C) of the film in the TD direction.

[0013] The average value is an average value of thermal expansion coefficients measured at six points in total, two arbitrary points are selected in each of the region N, the region C, and the region S divided in the TD direction of the film.

[0014] Another embodiment provides a cover window for a display device, including a polyamide-imide based film and a functional layer, wherein the polyamide-imide based film includes a polyamide-imide based polymer and has an RC value of 0.96 to 1.03 as represented by Equation 1 above.

[0015] Yet another embodiment provides a display device comprising a display unit; and a cover window disposed on the display unit, wherein the cover window comprises a polyamide-imide based film and a functional layer, the polyamide-imide based film comprises a polyamide-imide based polymer, and has an RC value of 0.96 to 1.03 as represented by the above equation 1.

[0016] One embodiment provides a method for preparing a polyamide-imide-based film, which includes 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 solution and then drying it to prepare a gel sheet; and heat-treating the gel sheet, wherein the step of heat-treating the gel sheet includes heat-treating the gel sheet by a first heater, a second heater, and a third heater spaced apart in a TD direction of the gel sheet, and when the temperature of the first heater corresponding to the center of the gel sheet is T HC When the temperatures of the second heater and the third heater corresponding to the two ends of the gel sheet are T HN and T HS When T HN and T HS Higher than T HC .

[0017] Beneficial effects of the present invention

[0018] Since the polyamide-imide-based film according to the present embodiment has an RC value within a predetermined range, it exhibits similar thermal properties in a film direction so that its quality is uniform, and it may have excellent mechanical properties, optical properties, and heat resistance.

[0019] Once the polyamide-imide-based film is prepared, it is subjected to post-processing, such as laminating a functional layer to impart functions such as anti-fingerprint, anti-static, anti-scattering, and adhesion enhancement. In such post-processing, when additional heat treatment is performed, the non-uniformity of the film quality is aggravated, which may increase the defect rate of the final product. Therefore, the uniform quality of the polyamide-imide-based film itself is an important management factor.

[0020] Since the RC value of the polyamide-imide-based film is controlled within a specific range, the quality reliability and product yield of a final product to which the film is applied, such as a cover window of a display device or a display device, can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic exploded view of a display device according to an embodiment;

[0022] Figure 2 is a schematic perspective view of a display device according to an embodiment;

[0023] Figure 3 is a schematic cross-sectional view of a display device according to an embodiment;

[0024] Figure 4 is a schematic flow chart of a method for preparing a polyamide-imide based film according to one embodiment;

[0025] Figure 5 is a schematic plan view showing a step of passing a polyamide-imide-based film according to an embodiment through a heater in a preparation process thereof;

[0026] Figure 6 : is a schematic perspective view showing a heater installation part and a gel sheet in a step of passing a polyamide-imide-based film according to an embodiment through a heater in a preparation process thereof. DETAILED DESCRIPTION

[0027] Best Mode for Carrying Out the Invention

[0028] Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention belongs can easily implement them. However, these embodiments can be implemented in many different ways and are not limited to those described here.

[0029] Throughout this specification, when referring to each film, window, panel, layer, etc. formed "on" or "under" another film, window, panel, layer, etc., it means not only that one element is directly formed on or under another element, but also that one element is indirectly formed on or under another element, with other elements interposed therebetween. In addition, the terms "on" or "under" each element may refer to the accompanying drawings. For ease of description, the sizes of the various elements in the accompanying drawings may be exaggerated and do not represent actual sizes. In addition, throughout the specification, the same reference numerals represent the same elements.

[0030] Throughout the specification, when a part is referred to as “comprising” an element, it should be understood that other elements can be included rather than excluded unless specifically stated otherwise.

[0031] In the present specification, a singular expression is construed to include the singular or plural as construed in the context unless otherwise specified.

[0032] Moreover, unless otherwise indicated, all numbers and expressions relating to amounts of components, reaction conditions and the like used herein are to be understood as modified by the term "about".

[0033] The terms first, second, etc. are used herein to describe various elements, and these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

[0034] In addition, the term "substituted" as used herein means substituted by at least one selected from the group consisting of the following substituents: deuterium, -F, -Cl, -Br, -I, hydroxyl, cyano, nitro, amino, amidino, hydrazine, hydrazone, ester, keto, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alicyclic organic, substituted or unsubstituted heterocyclic, substituted or unsubstituted aryl, and substituted or unsubstituted heteroaryl. The substituents listed above may be connected to each other to form a ring.

[0035] Polyamide - Imide-based film

[0036] One embodiment provides a polyamide-imide-based film having an RC value within a predetermined range, so that it exhibits similar thermal properties in a film direction, thereby having uniform quality, and having excellent mechanical properties, optical properties, and heat resistance.

[0037] A polyamide-imide-based film according to an embodiment includes a polyamide-imide-based polymer. The polyamide-imide-based film has an RC value of 0.96 to 1.03 as represented by the following Equation 1.

[0038] <Equation 1> RC = CTE MD / CTE TD

[0039] In Equation 1, CTE MD is the average value of the coefficient of thermal expansion (ppm / °C) in the MD direction of the film, CTE TD is the average value of the thermal expansion coefficient (ppm / °C) in the TD direction of the film. The average value is the average value of the thermal expansion coefficient measured at six points in total, two arbitrary points selected in each of the regions N, C, and S divided in the TD direction of the film.

[0040] The film includes three regions divided in the TD direction, region N, region C, and region S. In the film, when the width of region N is wN, the width of region C is wC, and the width of region S is wS, the width of the film is equal to the sum of wN, wC, and wS.

[0041] Specifically, the RC value of the polyamide-imide based film represented by Equation 1 may be 0.96 or more, 0.97 or more, 0.98 or more, 0.99 or more, or 1.00 or more, and it may be 1.03 or less, or 1.02 or less.

[0042] The coefficient of thermal expansion (CTE) is a value measured in a temperature range of 50° C. to 250° C. based on a sample of a polyamide-imide-based film having a width of 3 mm, a length of 10 mm, and a thickness of 50 μm. MD The CTE is the average value of the coefficient of thermal expansion measured in the longitudinal direction of the film sample with the MD direction of the film as the longitudinal direction. TD It is the average value of the thermal expansion coefficient measured with the TD direction of the film as the longitudinal direction of the film sample.

[0043] The coefficient of thermal expansion is a linear expansion coefficient that represents the change in length of a film that expands with a change in temperature. Its value may vary depending on which direction of the film is the longitudinal direction of the sample being measured. That is, the value of the coefficient of thermal expansion may vary depending on whether the longitudinal direction of the sample being measured is the MD direction or the TD direction of the film.

[0044] The RC value is the ratio of the average value (ppm / °C) of the thermal expansion coefficient of the film in the MD direction to the average value (ppm / °C) of the thermal expansion coefficient of the film in the TD direction. Since the polyamide-imide-based film according to an embodiment has an RC value satisfying the above range, it has a thermal behavior close to isotropic. As the film is closer to isotropic, a more excellent screen quality can be achieved when it is applied to a display device.

[0045] On the other hand, if the RC value of the polyamide-imide based film according to one embodiment is outside the above range, the thermal properties in the film direction are different, and the quality deviation of the film in the TD direction is large as described below, which will reduce the quality of the film itself and directly lead to a high defect rate of the product during post-processing.

[0046] Specifically, CTE MD The CTE is 20ppm / ℃ to 40ppm / ℃. MD It may be 21 ppm / °C or more, 22 ppm / °C or more, or 23 ppm / °C or more, and may be 38 ppm / °C or less, 36 ppm / °C or less, 34 ppm / °C or less, or 33 ppm / °C or less.

[0047] In addition, CTE TD The CTE is 20ppm / ℃ to 40ppm / ℃. TD It may be 21 ppm / °C or higher, 22 ppm / °C or higher, or 23 ppm / °C or higher, and may be 38 ppm / °C or lower, 36 ppm / °C or lower, 34 ppm / °C or lower, 33 ppm / °C or lower, or 32 ppm / °C or lower.

[0048] In one embodiment, CTE MD Can be larger than CTE TD .

[0049] In another embodiment, when the thermal expansion coefficient is measured at six points in total by selecting two arbitrary points in each of the regions N, C, and S divided in the TD direction of the film, the CTE MD and CTE TD The deviation rate is 1% or less.

[0050] Since the RC value of the polyamide-imide-based film according to an embodiment is controlled within the above range, the thermal expansion coefficients of the film in MD and TD directions are similar and the quality deviation in the transverse direction is low, it is possible to ensure quality reliability and improve product yield.

[0051] When the yellowness index is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the polyamide-imide base film, the average value of the yellowness index is 5 or less, and the deviation rate of the yellowness index is 10% or less.

[0052] Specifically, the average value of the yellowness index of the polyamide-imide and the film may be 4.5 or less, 4 or less, or 3.5 or less, and the deviation rate of the yellowness index thereof may be 8% or less, 7% or less, 6% or less, or 5% or less.

[0053] When the modulus is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the polyamide-imide base film, the average value of the modulus is 5 GPa or higher, and the deviation rate of the modulus is 10% or lower.

[0054] Specifically, the polyamide-imide-based film may have an average value of modulus of 5.5 GPa or more, or 6 GPa or more, and a deviation rate of modulus thereof may be 7% or less, 5% or less, 4% or less, or 3.5% or less.

[0055] When the haze is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the polyamide-imide base film, the average value of the haze is 1% or less, and the deviation rate of the haze is 10% or less.

[0056] Specifically, the average value of the haze of the polyamide-imide-based film may be 0.7% or less, 0.5% or less, or 0.4% or less, and the deviation rate of the haze thereof may be 9.5% or less, or 9% or less.

[0057] When the transmittance is measured at a total of six points, two arbitrary points are selected in each of the regions N, C and S divided in the TD direction of the polyamide-imide base film, the average value of the transmittance is 88% or higher, or 88.5% or higher, and the deviation rate of the transmittance is 1% or lower, 0.5% or lower, 0.3% or lower, or 0.2% or lower.

[0058] If the average values ​​and deviation rates related to the yellowness index, modulus, haze and / or transmittance of the polyamide-imide-based film according to one embodiment are within the above ranges, the physical properties are excellent and the quality deviation in the transverse direction (TD direction) is low, so when the film is cut into a desired shape or size for post-processing after its preparation, there is almost no quality deviation, which increases the product yield and is therefore economical.

[0059] On the other hand, if the average values ​​and deviation rates of the yellowness index, modulus, haze and / or transmittance of the polyamide-imide-based film according to an embodiment are outside the above ranges, it means that the quality of the film is different at different locations, albeit slightly. Therefore, when it is applied to a product, there may be many defects. In particular, when the film is commercially used, it may be subjected to harsh conditions such as additional heat treatment. In this process, uneven quality may be further aggravated.

[0060] In some embodiments, the thickness deviation of the polyamide-imide-based film is 3 μm or less, or 2 μm or less based on a thickness of 50 μm. In addition, the thickness deviation rate may be 5% or less, 4% or less, or 3% or less, but is not limited thereto.

[0061] The thickness deviation and the thickness deviation rate may refer to the deviation and the deviation rate of the thickness average value measured at six points in total by selecting two arbitrary points in each of the regions N, C, and S divided in the TD direction of the film. In this case, since the polyamide-imide-based film has a uniform thickness, its optical properties and mechanical properties at each point can be uniformly exhibited.

[0062] The compressive strength of the polyamide-imide-based film may be 0.4 kgf / μm or more, and specifically, the compressive strength may be 0.45 kgf / μm or more, or 0.46 kgf / μm or more, but is not limited thereto.

[0063] When a polyamide-imide-based film is perforated using a 2.5-mm spherical tip at a speed of 10 mm / min in a UTM compression mode, the maximum diameter (mm) of the perforation including cracks is 60 mm or less. Specifically, the maximum diameter of the perforation may be 5 mm to 60 mm, 10 mm to 60 mm, 15 mm to 60 mm, 20 mm to 60 mm, 25 mm to 60 mm, or 25 mm to 58 mm, but is not limited thereto.

[0064] The surface hardness of the polyamide-imide-based film may be HB or higher. Specifically, the surface hardness may be H or higher, or 2H or higher, but is not limited thereto.

[0065] The tensile strength of the polyamide-imide based film can be 15kgf / mm 2 Or higher. Specifically, the tensile strength can be 18kgf / mm 2 or higher, 20kgf / mm 2 or higher, 21kgf / mm 2 or higher, or 22kgf / mm 2 or higher, but not limited thereto.

[0066] The elongation of the polyamide-imide-based film may be 15% or more. Specifically, the elongation may be 16% or more, 17% or more, or 17.5% or more, but is not limited thereto.

[0067] When a polyamide-imide-based film based on a thickness of 50 μm is folded to have a curvature radius of 3 mm, the number of foldings before breaking may be 200,000 or more.

[0068] When the film was folded to a curvature radius of 3 mm and then unfolded, the number of folds was counted as 1.

[0069] Since the number of folding times of the polyamide-imide-based film satisfies the above range, it can be advantageously applied to a foldable display device or a flexible display device.

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

[0071] Since the surface roughness of the polyamide-imide based film satisfies the above range, it can be beneficial to achieve brightness conditions or texture, and it can be better applied to display devices.

[0072] The content of the residual solvent in the polyamide-imide-based film may be 1,500 ppm or less. For example, the content of the residual solvent may be 1,200 ppm or less, 1,000 ppm or less, 800 ppm or less, or 500 ppm or less, but is not limited thereto.

[0073] Residual solvent refers to the solvent that does not volatilize during the membrane production process and remains in the final membrane.

[0074] If the content of the residual solvent in the polyamide-imide-based film exceeds the above range, the durability of the film may be reduced and may have an impact on the quality deviation of the film. In particular, since it affects the mechanical strength, it may have an adverse effect on the post-processing of the film. Due to the accelerated hygroscopicity of the film, the optical properties and heat resistance, not to mention the mechanical properties, may also be deteriorated.

[0075] A polyamide-imide based film according to an embodiment includes a polyamide-imide based polymer prepared by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

[0076] Polyamide-imide based polymers are polymers containing imide repeating units and amide repeating units.

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

[0078] The diamine compound is a compound that forms an imide bond with a dianhydride compound and an amide bond with a dicarbonyl compound, thereby forming a copolymer.

[0079] The diamine compound is not particularly limited, and may be, for example, an aromatic diamine compound containing an aromatic structure. For example, the diamine compound may be a compound represented by Formula 1 below.

[0080] [Formula 1]

[0081] H 2 N——(E) e ——NH 2

[0082] In Formula 1, E can be selected from substituted or unsubstituted divalent C 6 -C 30 Aliphatic cyclic group, substituted or unsubstituted divalent C 4 -C 30 Aliphatic heterocyclic group, substituted or unsubstituted divalent C 6 -C 30 Aromatic ring group, substituted or unsubstituted divalent C 4 -C 30 Heteroaromatic ring group, substituted or unsubstituted C 1 -C 30 Alkylene, substituted or unsubstituted C 2 -C 30 Alkenylene, substituted or unsubstituted C 2 -C 30 Alkyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) 2 -、-Si(CH 3 ) 2 -、-C(CH 3 ) 2 - and -C(CF 3 ) 2 -.

[0083] e is selected from integers of 1 to 5. When e is 2 or more, Es may be the same as or different from each other.

[0084] (E) in Formula 1 e The group may be selected from the groups represented by the following formulae 1-1a to 1-14a, but is not limited thereto.

[0085]

[0086] Specifically, (E) in Formula 1 e The group may be selected from the groups represented by the following formulae 1-1b to 1-13b, but is not limited thereto.

[0087]

[0088] More specifically, (E)e in Formula 1 may be a group represented by the above Formula 1-6b or a group represented by the above Formula 1-9b.

[0089] In one embodiment, the diamine compound may include a compound having a fluorine-containing substituent or a compound having an ether group (—O—).

[0090] The diamine compound may be composed of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent may be a fluorinated hydrocarbon group, and specifically may be a trifluoromethyl group. However, it is not limited thereto.

[0091] In some embodiments, the diamine compound may include one diamine compound. That is, the diamine compound may be composed of a single component.

[0092] For example, the diamine compound may include 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) represented by the following formula, but is not limited thereto.

[0093]

[0094] The dianhydride compound has a low birefringence value, and thus it can contribute to the enhancement of optical properties such as transmittance of a film including the polyamide-imide-based polymer.

[0095] The dianhydride compound is not particularly limited, but it may be, for example, an aromatic dianhydride compound containing an aromatic structure. For example, the aromatic dianhydride compound may be a compound represented by Formula 2 below.

[0096] [Formula 2]

[0097]

[0098] In Formula 2, G can be selected from substituted or unsubstituted tetravalent C 6 -C 30 Aliphatic cyclic group, substituted or unsubstituted tetravalent C 4 -C 30 Aliphatic heterocyclic group, substituted or unsubstituted tetravalent C 6 -C 30 Aromatic ring group or substituted or unsubstituted tetravalent C 4 -C 30 The heteroaromatic ring group, wherein the aliphatic ring group, the aliphatic heterocyclic group, the aromatic ring group or the heteroaromatic ring group can exist alone, be fused to each other to form a fused ring, or be selected from substituted or unsubstituted C 1 -C 30 Alkylene, substituted or unsubstituted C 2 -C 30 Alkenylene, substituted or unsubstituted C 2 -C 30 Alkyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) 2-、-Si(CH 3 ) 2 -、-C(CH 3 ) 2 - and -C(CF 3 ) 2 -bonded with a bonding group.

[0099] G in the above Formula 2 may be selected from the groups represented by the following Formulae 2-1a to 2-9a, but is not limited thereto.

[0100] G in the above Formula 2 may be selected from the groups represented by the following Formulae 2-1a to 2-9a, but is not limited thereto.

[0101]

[0102] For example, G in Formula 2 may be a group represented by the above-mentioned Formula 2-2a, a group represented by the above-mentioned Formula 2-8a, or a group represented by the above-mentioned Formula 2-9a.

[0103] In one embodiment, the dianhydride compound may include a compound having a fluorine-containing substituent, a compound having a biphenyl group, or a compound having a keto group.

[0104] The fluorine-containing substituent may be a fluorinated hydrocarbon group, and specifically may be a trifluoromethyl group, but is not limited thereto.

[0105] In another embodiment, the dianhydride compound may consist of a single component or a mixture of two components.

[0106] For example, the dianhydride compound may include at least one selected from the group consisting of 2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), which has the following structure, but is not limited thereto.

[0107]

[0108] The diamine compound and the dianhydride compound can be polymerized to form a polyamic acid.

[0109] Subsequently, the polyamic acid may be converted into polyimide through a dehydration reaction, and the polyimide includes an imide repeating unit.

[0110] The polyimide may form a repeating unit represented by Formula A below.

[0111] [Formula A]

[0112]

[0113] In formula A, E, G and e are as described above.

[0114] For example, the polyimide may include a repeating unit represented by the following Formula A-1, but is not limited thereto.

[0115] [Formula A-1]

[0116]

[0117] In formula A-1, n is an integer of 1 to 400.

[0118] The dicarbonyl compound is not particularly limited, but it may be, for example, a compound represented by Formula 3 below.

[0119] [Formula 3]

[0120]

[0121] In Formula 3, J can be selected from substituted or unsubstituted divalent C 6 -C 30 Aliphatic cyclic group, substituted or unsubstituted divalent C 4 -C 30 Aliphatic heterocyclic group, substituted or unsubstituted divalent C 6 -C 30 Aromatic ring group, substituted or unsubstituted divalent C 4 -C 30 Heteroaromatic ring group, substituted or unsubstituted C 1 -C 30 Alkylene, substituted or unsubstituted C 2 -C 30 Alkenylene, substituted or unsubstituted C 2 -C 30 Alkyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) 2 -、-Si(CH 3 ) 2 -、-C(CH 3 ) 2 - and -C(CF 3 ) 2 -.

[0122] j is selected from integers of 1 to 5. When j is 2 or more, Js may be the same as or different from each other.

[0123] X is a halogen atom. Specifically, X may be F, Cl, Br, I, etc. More specifically, X may be Cl, but is not limited thereto.

[0124] (J) in the above formula 3 j The group may be selected from the groups represented by the following formulae 3-1a to 3-14a, but is not limited thereto.

[0125]

[0126] Specifically, (J) in the above formula 3 j The group may be selected from the groups represented by the following formulae 3-1b to 3-8b, but is not limited thereto.

[0127]

[0128] More specifically, (J) in Formula 3 j It may be a group represented by the above formula 3-1b, a group represented by the above formula 3-2b, a group represented by the above formula 3-3b, or a group represented by the above formula 3-8b.

[0129] For example, (J) in the above formula 3 j It may be a group represented by the above formula 3-1b or a group represented by the above formula 3-2b.

[0130] In one embodiment, a single dicarbonyl compound may be used alone, or a mixture of at least two different dicarbonyl compounds may be used as the dicarbonyl compound. If two or more dicarbonyl compounds are used, then (J) in the above formula 3 j At least two dicarbonyl compounds selected from the groups represented by the above formulae 3-1b to 3-8b may be used as the dicarbonyl compound.

[0131] In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound comprising an aromatic structure.

[0132] The dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof, as shown in the following formula, but is not limited thereto.

[0133]

[0134] The diamine compound and the dicarbonyl compound may be polymerized to form a repeating unit represented by Formula B below.

[0135] [Formula B]

[0136]

[0137] In Formula B, E, J, e and j are as described above.

[0138] For example, a diamine compound and a dicarbonyl compound may be polymerized to form amide repeating units represented by the following formulae B-1 and B-2.

[0139] Alternatively, the diamine compound and the dicarbonyl compound may be polymerized to form amide repeating units represented by the following formulae B-2 and B-3.

[0140] [Formula B-1]

[0141]

[0142] In Formula B-1, x is an integer of 1 to 400.

[0143] [Formula B-2]

[0144]

[0145] In formula B-2, y is an integer of 1 to 400.

[0146] [Formula B-3]

[0147]

[0148] In formula B-3, y is an integer of 1 to 400.

[0149] According to one embodiment, the polyamide-imide-based polymer may include a repeating unit represented by the following formula A and a repeating unit represented by the following formula B:

[0150] [Formula A]

[0151]

[0152] [Formula B]

[0153]

[0154] In formula A and B, E and J are each independently selected from substituted or unsubstituted divalent C 6 -C 30 Aliphatic cyclic group, substituted or unsubstituted divalent C 4 -C 30 Aliphatic heterocyclic group, substituted or unsubstituted divalent C 6 -C 30 Aromatic ring group, substituted or unsubstituted divalent C 4 -C 30 Heteroaromatic ring group, substituted or unsubstituted C 1 -C 30 Alkylene, substituted or unsubstituted C 2 -C 30 Alkenylene, substituted or unsubstituted C 2 -C 30 Alkyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) 2 -、-Si(CH 3 ) 2 -、-C(CH 3 ) 2- and -C(CF 3 ) 2 -,

[0155] e and j are each independently selected from integers from 1 to 5,

[0156] When e is 2 or more, two or more Es are the same or different from each other,

[0157] When j is 2 or more, two or more Js are the same or different from each other,

[0158] G is a substituted or unsubstituted tetravalent C 6 -C 30 Aliphatic cyclic radical, substituted or unsubstituted tetravalent C 4 -C 30 Aliphatic heterocyclic group, substituted or unsubstituted tetravalent C 6 -C 30 Aromatic ring group, or substituted or unsubstituted tetravalent C 4 -C 30 The heteroaromatic ring group, wherein the aliphatic ring group, the aliphatic heterocyclic group, the aromatic ring group or the heteroaromatic ring group may exist alone, be fused to each other to form a fused ring, or be selected from substituted or unsubstituted C 1 -C 30 Alkylene, substituted or unsubstituted C 2 -C 30 Alkenylene, substituted or unsubstituted C 2 -C 30 Alkyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) 2 -、-Si(CH 3 ) 2 -、-C(CH 3 ) 2 - and -C(CF 3 ) 2 -bonded to a bonding group.

[0159] The polyamide-imide polymer may include imide repeating units and amide repeating units in a molar ratio of 2:98 to 70:30. Specifically, the molar ratio of the imide repeating unit to the amide repeating unit may be 2:98 to 60:40, 5:95 to 60:40, or 5:95 to 55:45, but is not limited thereto.

[0160] If the molar ratio of the imide repeating unit to the amide repeating unit is within the above range, combined with a unique treatment method, the RC value of the polyamide-imide based film can be effectively controlled and the quality reliability of the film can be improved.

[0161] In the polyamide-imide-based polymer, the molar ratio of the repeating unit represented by the above formula A to the repeating unit represented by the above formula B may be 2:98 to 70:30. Specifically, the molar ratio of the repeating unit represented by the above formula A to the repeating unit represented by the above formula B may be 2:98 to 60:40, 5:95 to 60:40, or 5:95 to 55:45, but is not limited thereto.

[0162] The polyamide-imide-based film according to an embodiment may further include at least one selected from the group consisting of a filler, a blue pigment, and a UVA absorber, in addition to the polyamide-imide-based polymer.

[0163] The filler may include, for example, an oxide, carbonate or sulfate of a metal or metalloid. For example, the filler may include silicon dioxide, calcium carbonate, barium sulfate, etc., but is not limited thereto.

[0164] The filler can be used in the form of particles. In addition, the surface of the filler is not specially coated and can be evenly dispersed throughout the film.

[0165] Since the polyamide-imide-based film includes the filler, the film can ensure a wide viewing angle without deteriorating optical properties, and can improve not only roughness and windability but also the improvement effect of scratches caused by sliding during the film preparation process.

[0166] The filler may have a refractive index of 1.55 to 1.75. Specifically, the refractive index of the filler may be 1.60 to 1.75, 1.60 to 1.70, 1.60 to 1.68, or 1.62 to 1.65, but is not limited thereto.

[0167] If the refractive index of the filler satisfies the above range, the birefringence values ​​related to nx, ny, and nz can be properly adjusted, and the brightness of the film at different angles can be improved.

[0168] On the other hand, if the refractive index of the filler is outside the above range, there may be a problem that the filler is visually conspicuous on the film or haze increases due to the filler.

[0169] The content of the filler may be 100 ppm to 15,000 ppm based on the total weight of the solid content of the polyamide-imide-based polymer. Specifically, the content of the filler may be 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 solid content of the polyamide-imide-based polymer, but is not limited thereto.

[0170] If the content of the filler is outside the above range, the haze of the film increases sharply, and the fillers may agglomerate with each other on the surface of the film so that a foreign body feeling may be visually observed, or it may cause a problem in sliding performance or deteriorate windability during the production process.

[0171] The blue pigment may include OP-1300A manufactured by Toyo, but is not limited thereto.

[0172] In some embodiments, the blue pigment may be used in an amount of 50 ppm to 5,000 ppm based on the total weight of the polyamide-imide-based polymer. Preferably, the blue pigment may be used in an amount of 100 ppm to 5,000 ppm, 200 ppm to 5,000 ppm, 300 ppm to 5,000 ppm, 400 ppm to 5,000 ppm, 50 ppm to 3,000 ppm, 100 ppm to 3,000 ppm, 200 ppm to 3,000 ppm, 300 ppm to 3,000 ppm, 400 ppm to 3,000 ppm. 0ppm, 50ppm to 2,000ppm, 100ppm to 2,000ppm, 200ppm to 2,000ppm, 300ppm to 2,000ppm, 400ppm to 2,000ppm, 50ppm to 1,000ppm, 100ppm to 1,000ppm, 200ppm to 1,000ppm, 300ppm to 1,000ppm, or 400ppm to 1,000ppm, but is not limited thereto.

[0173] UVA absorbers may include absorbers that absorb electromagnetic waves with wavelengths of 10nm to 400nm used in the art. For example, UVA absorbers may include benzotriazole-based compounds. Benzotriazole-based compounds may include N-phenolic benzotriazole-based compounds. In some embodiments, N-phenolic benzotriazole-based compounds may include N-phenolic benzotriazoles in which the phenol group is substituted with an alkyl group having 1 to 10 carbon atoms, which may be substituted with two or more alkyl groups, and the alkyl group may be linear, branched or cyclic.

[0174] In some embodiments, based on the total weight of the polyamide-imide polymer, the UVA absorber can be used in an amount of 0.1% to 10% by weight. Preferably, relative to the total weight of the polyamide-imide polymer, the UVA absorber can be used in an amount of 0.1% to 5%, 0.1% to 3%, 0.1% to 2%, 0.5% to 10%, 0.5% to 5%, 0.5% to 3%, 0.5% to 2%, 1% to 10%, 1% to 5%, 1% to 3% or 1% to 2% by weight, but is not limited thereto.

[0175] The physical properties of the polyamide-imide based film described above are based on a thickness of 40 μm to 60 μm. For example, the physical properties of the polyamide-imide based film are based on a thickness of 50 μm.

[0176] The characteristics of the composition and performance of the polyamide-imide-based film as described above may be combined with each other.

[0177] In addition, the RC value, CTE MD and CTE TD The average values ​​and deviation rates of the yellowness index, modulus and haze can be adjusted by combining the chemical and physical properties of the components constituting the polyamide-imide-based film, and the specific conditions of each step in the method for preparing the polyamide-imide-based film as described below.

[0178] For example, the combination and content of each component constituting the polyamide-imide-based film, polymerization conditions and heat treatment conditions during film preparation, etc. are combined to achieve the RC value and the deviation rate of each physical property within the desired range.

[0179] Cover window for display device

[0180] A cover window for a display device according to an embodiment includes a polyamide-imide based film and a functional layer.

[0181] The polyamide-imide-based film includes a polyamide-imide-based polymer and has an RC value of 0.96 to 1.03 as represented by Equation 1 above.

[0182] The details about the polyamide-imide-based film are as described above.

[0183] The cover window for a display device may be advantageously applied to the display device.

[0184] Display device

[0185] A display device according to an embodiment includes a display unit; and a cover window disposed on the display unit, wherein the cover window includes a polyamide-imide-based film and a functional layer.

[0186] The polyamide-imide-based film includes a polyamide-imide-based polymer, and has an RC value of 0.96 to 1.03 as represented by Equation 1 above.

[0187] The details of the polyamide-imide base film and cover window are as described above.

[0188] Figure 1 is a schematic exploded view of a display device according to an embodiment, Figure 2 is a schematic perspective view of a display device according to an embodiment. Figure 3 is a schematic cross-sectional view of a display device according to an embodiment.

[0189] Specifically, Figures 1 to 3 A display device is shown, which includes a display unit (400) and a cover window (300) arranged on the display unit (400), wherein the cover window includes a polyamide-imide base film (100) having a first side (101) and a second side (102) and a functional layer (200), and an adhesive layer (500) is inserted between the display unit (400) and the cover window (300).

[0190] The display unit (400) is used to display an image, and it may have a flexible property.

[0191] The display unit (400) may be a display panel for displaying an image. For example, it may be 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.

[0192] The polarizing plate may be disposed on the front side of the organic EL panel. Specifically, the front polarizing plate may be attached to the side of the organic EL panel where the image is displayed.

[0193] The organic EL panel can display images by self-luminescence of pixel units. 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 of which corresponds to a pixel. Specifically, it may include a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, and an anode. The drive substrate may be operably coupled to the organic EL substrate. That is, the drive substrate may be coupled to the organic EL substrate so as to apply a drive signal such as a drive current, so that the drive substrate can drive the organic EL substrate by applying a current to each organic electroluminescent unit.

[0194] In addition, an adhesive layer (500) may be interposed between the display unit (400) and the cover window (300). The adhesive layer may be an optically transparent adhesive layer, but is not particularly limited.

[0195] A cover window (300) may be provided on the display unit (400). The cover window is located at an outer position of the display device, thereby protecting the display unit.

[0196] The cover window (300) may include a polyamide-imide based film and a functional layer. The functional layer may be at least one selected from the group consisting of a hard coating layer, an anti-reflection layer, an anti-fouling layer, and an anti-glare layer. The functional layer may be coated on at least one side of the polyamide-imide based film.

[0197] The polyamide-imide-based film according to an embodiment can be applied to the outside of a display device in the form of a film without changing a display driving method, a color filter in a panel, or a laminated structure, thereby providing a display device having uniform thickness, low haze, high transmittance, and high transparency. Since neither significant process changes nor cost increases are required, it is beneficial to reduce production costs.

[0198] The polyamide-imide-based film according to one embodiment may have excellent optical properties in terms of high transmittance, low haze, and low yellowness index, and may have excellent mechanical properties such as modulus and flexibility, and when it is exposed to ultraviolet rays, changes (deterioration) in its optical properties and mechanical properties may be suppressed.

[0199] Specifically, the polyamide-imide-based film having an RC value within the above range exhibits similar thermal properties in the film direction, so its quality is uniform and can have excellent mechanical properties, optical properties and heat resistance. Therefore, when the polyamide-imide-based film is applied to a display device or a cover window of a display device, the quality reliability and product yield of the final product can be improved.

[0200] Preparation method of polyamide-imide based film

[0201] One embodiment provides a method for preparing a polyamide-imide based film.

[0202] The method for preparing a polyamide-imide-based film according to an embodiment includes polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide-based polymer solution (S100); casting the solution and then drying it to prepare a gel sheet (S200); and heat-treating the gel sheet (S300) (see Figure 4 ).

[0203] The method of preparing a polyamide-imide based film according to some embodiments may further include adjusting the viscosity of the polyamide-imide based polymer solution ( S110 ), aging the polyamide-imide based polymer solution ( S120 ), and / or degassing the polyamide-imide based polymer solution ( S130 ).

[0204] The polyamide-imide-based film is a film having a polyamide-imide-based polymer as a main component. The polyamide-imide-based polymer is a resin including an imide repeating unit and an amide repeating unit at a predetermined molar ratio as structural units.

[0205] In the method for preparing a polyamide-imide based film, a polymer solution of a polyamide-imide based polymer may be prepared by simultaneously or sequentially mixing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent in a reactor and reacting the mixture ( S100 ).

[0206] In one embodiment, the polymer solution may be prepared by simultaneously mixing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent and reacting them.

[0207] In another embodiment, the step of preparing the polymer solution may include first mixing a diamine compound and a dianhydride compound in a solvent and reacting them to produce a polyamic acid (PAA) solution; and secondly, mixing and reacting the polyamic acid (PAA) solution with a dicarbonyl compound to form an amide bond and an imide bond. The polyamic acid solution is a solution including polyamic acid.

[0208] Alternatively, the step of preparing the polymer solution may include first mixing and reacting a diamine compound and a dianhydride compound in a solvent to prepare a polyamic acid solution; dehydrating the polyamic acid solution to obtain a polyimide (PI) solution; and secondly, mixing and reacting the polyimide (PI) solution with a dicarbonyl compound to further form an amide bond. The polyimide solution is a solution including a polymer having an imide repeating unit.

[0209] In another embodiment, the step of preparing a polymer solution may include first mixing and reacting a diamine compound and a dicarbonyl compound in a solvent to produce a polyamide (PA) solution; and secondly mixing and reacting the polyamide (PA) solution with a dianhydride compound to further form an imide bond. The polyamide solution is a solution including a polymer having an amide repeating unit.

[0210] The polymer solution thus prepared may be a solution including a polymer comprising at least one selected from the group consisting of a polyamic acid (PAA) repeating unit, a polyamide (PA) repeating unit, and a polyimide (PI) repeating unit.

[0211] Alternatively, the polymer contained in the polymer solution includes imide repeating units derived from polymerization of a diamine compound and a dianhydride compound and amide repeating units derived from polymerization of a diamine compound and a dicarbonyl compound.

[0212] The details of the diamine compound, the dianhydride compound and the dicarbonyl compound are as described above.

[0213] The polymer solution may contain 10% to 30% by weight of solids, or 15% to 25% by weight of solids, but is not limited thereto.

[0214] If the solid content contained in the polymer solution is within the above range, the polyamide-imide-based film can be efficiently prepared in the extrusion and casting steps. In addition, the polyamide-imide-based film thus prepared exhibits similar thermal properties in the film direction, so its quality is uniform and can have excellent mechanical properties, optical properties and heat resistance.

[0215] In another embodiment, the step of preparing the polymer solution may further include introducing a catalyst.

[0216] Here, the catalyst may include at least one selected from the group consisting of β-picoline, acetic anhydride, isoquinoline (IQ), and a pyridyl compound, but is not limited thereto.

[0217] The catalyst may be added in an amount of 0.01 mol to 0.5 mol equivalent, 0.01 mol to 0.4 mol equivalent, or 0.01 mol to 0.3 mol equivalent, based on 1 mol of the polyamic acid, but is not limited thereto.

[0218] Further addition of a catalyst can accelerate the reaction rate and enhance the chemical bonding force between or within the repeating unit structures.

[0219] In one embodiment, the step of preparing the polymer solution may further include adjusting the viscosity of the polymer solution (S110). At room temperature, the viscosity of the polymer solution may be 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. In this case, the film-forming ability of the polyamide-imide-based film can be improved, thereby enhancing the thickness uniformity.

[0220] Specifically, the step of preparing the polymer solution may include mixing and reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent simultaneously or sequentially to prepare a first polymer solution; and further adding a dicarbonyl compound to prepare a second polymer solution having a target viscosity.

[0221] In the step of preparing the first polymer solution and the second polymer solution, the polymer solutions have different viscosities from each other. For example, the viscosity of the second polymer solution is higher than the viscosity of the first polymer solution.

[0222] In the steps of preparing the first polymer solution and the second polymer solution, the stirring speeds may be different from each other. For example, the stirring speed when preparing the first polymer solution may be faster than the stirring speed when preparing the second polymer solution.

[0223] In yet another embodiment, the step of preparing the polymer solution may further include adjusting the pH value of the polymer solution. In this step, the pH value of the polymer solution may be adjusted to 4 to 7, such as 4.5 to 7.

[0224] The pH of the polymer solution may be adjusted by adding a pH adjuster. The pH adjuster is not particularly limited, and may include, for example, amine compounds such as alkoxyamines, alkylamines, and alkanolamines.

[0225] By adjusting the pH of the polymer solution to the above range, it is possible to prevent defects from occurring in a film made from the polymer solution and to achieve desired optical and mechanical properties in terms of yellowness index and modulus.

[0226] The pH adjuster may be used in an amount of 0.1% to 10% by mole based on the total moles of the monomers in the polymer solution.

[0227] In one embodiment, the organic solvent may be at least one selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), meta-cresol, tetrahydrofuran (THF) and chloroform. The organic solvent used in the polymer solution may be dimethylacetamide (DMAc), but is not limited thereto.

[0228] In another embodiment, at least one selected from the group consisting of a filler, a blue pigment, and a UVA absorber may be added to the polymer solution.

[0229] The details of the types and contents of the filler, blue pigment and UVA absorber are as described above.The filler, blue pigment and UVA absorber may be mixed with the polyamide-imide based polymer in the polymer solution.

[0230] The polymer solution may be stored at a temperature of -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.

[0231] If stored at the above temperature, it is possible to prevent degradation of the polymer solution and reduce the moisture content, thereby preventing defects in the resulting film.

[0232] In some embodiments, the polymer solution or the polymer solution whose viscosity has been adjusted may be aged ( S120 ).

[0233] Aging can be performed by placing the polymer solution at a temperature of -10°C to 10°C for 24 hours or longer. In this case, for example, the polyamide-imide-based polymer or unreacted material contained in the polymer solution can complete the reaction or reach a chemical equilibrium, thereby homogenizing the polymer solution. The mechanical properties and optical properties of the polyamide-imide-based film thus formed can be substantially uniform over the entire area of ​​the film. Preferably, aging can be performed 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.

[0234] In one embodiment, the method may further include degassing the polyamide-imide polymer solution (S130). The degassing step can remove moisture and reduce impurities in the polymer solution, thereby improving the reaction yield and giving the final produced film excellent surface appearance and mechanical properties.

[0235] Degassing may include vacuum degassing or purging with an inert gas.

[0236] After reducing the internal pressure of the tank containing the polymer solution to 0.1 bar to 0.7 bar, vacuum degassing can be performed for 30 minutes to 3 hours. Vacuum degassing under these conditions can reduce bubbles in the polymer solution. Therefore, surface defects of the film thus manufactured can be prevented and excellent optical properties such as haze can be achieved.

[0237] In addition, purging can be performed by purging the tank with an inert gas at an internal pressure of 1 atm to 2 atm. Purging under these conditions can remove moisture from the polymer solution, reduce impurities, thereby improving the reaction yield, and obtain excellent optical properties such as haze and mechanical properties.

[0238] The inert gas may be at least one selected from the group consisting of nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn), but is not limited thereto. Specifically, the inert gas may be nitrogen.

[0239] Vacuum degassing and purging with inert gas can be performed in separate steps.

[0240] For example, a vacuum degassing step may be performed followed by purging with an inert gas, but is not limited thereto.

[0241] Vacuum degassing and / or purging with an inert gas can improve the surface physical properties of the polyamide-imide-based film prepared therefrom.

[0242] The polymer solution may be cast to prepare a gel sheet ( S200 ).

[0243] For example, the polymer solution may be extruded, coated, and / or dried on a support to form a gel sheet.

[0244] In addition, the casting thickness of the polymer solution may be 200 μm to 700 μm. When the polymer solution is cast to a thickness within the above range, the final film manufactured after drying and heat treatment may have a suitable and uniform thickness.

[0245] As described above, the polymer solution may have a viscosity of 150,000 cps to 500,000 cps at room temperature. Since the viscosity satisfies the above range, the polymer solution can be cast to a uniform thickness without defects and a polyamide-imide-based film having a substantially uniform thickness can be formed without local / partial thickness variation during drying.

[0246] The polymer solution is cast and then dried at 60 to 150° C., 70 to 150° C., 80 to 150° C., or 90 to 150° C. for 5 to 60 minutes to prepare a gel sheet. Specifically, the polymer solution is dried at 90 to 140° C. for 15 to 40 minutes to prepare a gel sheet.

[0247] The solvent of the polymer solution may be partially or completely volatilized during the drying process to prepare a gel sheet.

[0248] The dried gel sheet may be heat-treated to form a polyamide-imide-based film ( S300 ).

[0249] For example, the heat treatment of the gel sheet may be performed by, for example, a heat curing device.

[0250] The step of heat treating the gel sheet includes heat treating by at least one heater.

[0251] Furthermore, the step of heat-treating the gel sheet may further include heat-treating the gel sheet with hot air.

[0252] In one embodiment, the step of heat-treating the gel sheet comprises heat-treating with hot air; and heat-treating by at least one heater.

[0253] In one embodiment, if hot air is used for heat treatment, heat can be provided uniformly. If the heating is not uniform, satisfactory surface roughness cannot be obtained, or the surface quality may be uneven, and the surface energy may be excessively increased or decreased.

[0254] The hot air heat treatment may be performed at a temperature range of 60° C. to 500° C. for 5 to 200 minutes. Specifically, the heat treatment of the gel sheet may be performed at a temperature range of 80° C. to 300° C. at a temperature increase rate of 1.5° C. / min to 20° C. / min for 10 to 150 minutes. More specifically, the heat treatment of the gel sheet may be performed at a temperature range of 140° C. to 250° C.

[0255] In this case, the initial temperature of the heat treatment of the gel sheet may be 60° C. or higher. Specifically, the starting temperature of the heat treatment of the gel sheet may be 80° C. to 180° C. In addition, the maximum temperature of the heat treatment may be 200° C. to 500° C.

[0256] In addition, the heat treatment of the gel sheet can be carried out in two or more stages. Specifically, the gel sheet can be heat treated with hot air in the first hot air treatment stage and the second hot air treatment stage. The temperature in the second hot air treatment stage can be higher than the temperature in the first hot air treatment stage.

[0257] In one embodiment, the step of heat-treating the gel sheet may include heat-treating by at least one heater, specifically, heat-treating by a plurality of heaters.

[0258] As an example, refer to Figure 5 and Figure 6 , the plurality of heaters may include a first heater (HC), a second heater (HN) and a third heater (HS) spaced apart in the TD direction of the gel sheet (polyamide-imide based film). The first heater (HC) may be mounted on the heater mounting portion (A1, B1) to correspond to the center of the gel sheet, the second heater (HN) may be mounted on the heater mounting portion (A1, B1) to correspond to any one of the two ends of the gel sheet, and the third heater (HS) may be mounted on the heater mounting portion (A1, B1) to correspond to the other of the two ends of the gel sheet. That is, the first heater HC may be mounted on the heater mounting portion (A1, B1) to be positioned between the second heater (HN) and the third heater (HS). The heater mounting portion (A1, B1) may be arranged to face the gel sheet. As an example, the heater mounting portion (A1, B1) may be arranged to face the gel sheet and be spaced apart therefrom. Preferably, the distance between the first heater (HC) and the second heater (HN) may be the same as the distance between the first heater (HC) and the third heater (HS). Two or more of the heater mounting parts ( A1 , B1 ) may be disposed along the running direction (or longitudinal direction) of the gel sheet (polyamide-imide-based film).

[0259] The at least one heater may include an infrared heater. However, the type of the at least one heater is not limited to the above example and may be variously modified.

[0260] Specifically, the plurality of heaters may include infrared heaters. More specifically, the first heater, the second heater, and the third heater may each include an infrared heater.

[0261] The heat treatment of the at least one heater may be performed at a temperature range of 300° C. or higher. Specifically, the at least one heater may perform the heat treatment at a temperature range of 300° C. to 500° C. for 1 minute to 30 minutes or 1 minute to 20 minutes.

[0262] Reference Figure 6 The heater mounting portion (B1) and the gel sheet (B2) are placed in parallel, and the heater mounting portion (B1) is spaced a specific distance from the gel sheet (B2) disposed on the belt (A3).

[0263] The gel sheet (B2) includes three regions (N region, C region and S region) divided in the TD direction. Among the three divided regions, region C is a region located in the middle of the gel sheet, and region N and region S are regions located at the ends of the gel sheet.

[0264] When the width of region N is w1, the width of region C is w2, and the width of region S is w3, the width (w0) of the gel sheet is equal to the sum of w1, w2, and w3.

[0265] In addition, for the widths of the three divided regions, a width ratio of w1:w2:w3 may be 1:(0.5 to 1.5): 1. Specifically, the widths of the three divided regions may satisfy w1=w2=w3.

[0266] The heater mounting part (B1) is placed parallel to the gel sheet (B2) and separated from the gel sheet (B2) by a specific distance. The area of ​​the heater mounting part (B1) corresponding to the area N of the gel sheet (B2) includes a second heater (HN), the area of ​​the heater mounting part (B1) corresponding to the area C of the gel sheet (B2) includes a first heater (HC), and the area of ​​the heater mounting part (B1) corresponding to the area S of the gel sheet (B2) includes a third heater (HS).

[0267] In one embodiment, in the step of heat treatment by at least one heater, when the temperature of the first heater (HC) is T HC , the temperatures of the second heater (HN) and the third heater (HS) are T HN and T HS , T HN and T HS Higher than T HC .

[0268] In another embodiment, the step of heat treating the gel sheet includes heat treating the gel sheet by a first heater, a second heater and a third heater spaced apart in the TD direction of the gel sheet, and when the temperature of the first heater corresponds to the center of the gel sheet at T HC , when the temperatures of the second heater and the third heater at the two ends of the gel sheet are T HNand T HS When T HN and T HS Higher than T HC .

[0269] Specifically, T HC It is 300℃ to 360℃, 300℃ to 350℃, or 310℃ to 350℃.

[0270] T HN and T HS 310°C to 420°C, 330°C to 420°C, or 340°C to 400°C.

[0271] T HN and T HS T HC 2% to 18%, 3% to 18%, or 5% to 15% higher.

[0272] In the step of heat treatment by at least one heater, when a temperature gradient as described above is applied between the heaters, the RC value can be controlled within a desired range, and similar thermal properties can be achieved in the film direction. In addition, the thermal properties of the film, as well as other mechanical and optical properties, such as haze, yellowness index, and modulus, have almost no deviation in the TD direction of the film. Therefore, a film of uniform quality can be obtained.

[0273] Subsequently, after the step of heat treating the gel sheet, a step of cooling the solidified film while moving the solidified film may be performed.

[0274] The step of cooling the solidified film while it moves may include a first temperature decreasing step of decreasing the temperature at a rate of 100° C. / min to 1000° C. / min and a second temperature decreasing step of decreasing the temperature at a rate of 40° C. / min to 400° C. / min.

[0275] In this case, specifically, the second temperature reduction step is performed after the first temperature reduction step. The temperature reduction rate of the first temperature reduction step may be faster than the temperature reduction rate of the second temperature reduction step.

[0276] For example, the maximum rate of the first cooling step is faster than the maximum rate of the second cooling step. Alternatively, the minimum rate of the first cooling step is faster than the minimum rate of the second cooling step.

[0277] If the step of cooling the cured film is performed in such a multi-stage manner, the physical properties of the cured film can be further stabilized, and the optical properties and mechanical properties of the film obtained in the curing step can be more stably maintained for a longer period of time.

[0278] Furthermore, a step of winding up the cured film after cooling using a winder may be performed.

[0279] In this case, the ratio of the moving speed of the gel sheet on the belt during drying to the moving speed of the cured film during winding is 1:0.95 to 1:1.40. Specifically, the moving speed ratio may be 1:0.99 to 1:1.20, 1:0.99 to 1:1.10, or 1:1.0 to 1:1.05, but is not limited thereto.

[0280] If the ratio of the moving speeds is outside the above range, the mechanical properties of the cured film may be impaired, and the flexibility and elastic properties may be deteriorated.

[0281] In the method of preparing a polyamide-imide based film, a thickness variation (%) may be 3% to 30% according to the following Relationship 1. Specifically, the thickness variation (%) may be 5% to 20%, but is not limited thereto.

[0282] [Equation 1] Thickness change (%) = (M1-M2) / M2×100

[0283] In Relational Formula 1, M1 is the thickness (μm) of the gel sheet, and M2 is the thickness (μm) of the solidified film cooled during winding.

[0284] The polyamide-imide-based film prepared by the above-mentioned preparation method has excellent optical and mechanical properties, and has uniform quality and isotropy. The polyamide-imide-based film can be applied to various uses requiring flexibility and transparency. For example, the polyamide-imide-based film can be applied not only to display devices, but also to solar cells, semiconductor devices, sensors, etc.

[0285] The details of the polyamide-imide-based film prepared by the above-mentioned method for preparing the polyamide-imide-based film are as described above.

[0286] Embodiments for carrying out the invention

[0287] Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[0288] [Example 1]

[0289] Under a nitrogen atmosphere, dimethylacetamide (DMAc) as an organic solvent was added to a temperature-controllable reactor at 10° C. Then, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) as an aromatic diamine was slowly added thereto and dissolved.

[0290] Then, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) was slowly added, followed by stirring for 2 hours. Subsequently, 3,3',4,4'-biphenyltetracarboxylic dianhydride was slowly added thereto, followed by stirring for 4 hours.

[0291] Then, terephthaloyl chloride (TPC) was added, and the mixture was stirred for 1 hour, thereby preparing a polymer solution.

[0292] The polymer solution thus obtained was coated on a substrate and then dried at a temperature ranging from 90° C. to 140° C. to prepare a gel sheet.

[0293] Thereafter, as a first heat treatment step, the gel sheet was treated with hot air at a temperature of 140°C to 250°C. Next, as a second heat treatment step, a step of passing the gel sheet through a plurality of heaters in the TD direction with a temperature gradient was performed. Here, an infrared heater (an infrared heater with a maximum temperature of 1,200°C) was used as a plurality of heaters. Specifically, the gel sheet was passed through a heater mounting portion of three heaters spaced apart in the TD direction of the film to obtain a polyamide-imide-based film with a thickness of 50 μm. Here, the temperature of the heater (first heater) located in the middle was set to 330°C (T HC ), the temperature of the two heaters (the second heater and the third heater) at both ends of the heater mounting portion is set to 346.5°C (T HN , T HS , 1.05T HC ), which is 5% higher than the temperature of the heater located in the middle.

[0294] The specific composition and molar ratio of the polyamide-imide based polymer are described in the preparation examples in Table 1 below.

[0295] <Examples 2 and 3 and Comparative Examples 1-5>

[0296] As shown in Tables 1 and 2 below, the membranes were prepared in the same manner as in Example 1, except that the composition and molar ratio of the polymers, the temperature of the heaters in the step of passing through multiple heaters, and the degree of temperature gradient in the TD direction were also changed.

[0297] <Preparation Example> Composition of polymer

[0298] [Table 1]

[0299]

[0300] <Evaluation Example>

[0301] The following properties of the films prepared in the examples and comparative examples were measured and evaluated respectively. The results are shown in Table 2 below.

[0302] Evaluation Example 1: Measurement of film thickness

[0303] The thickness was measured at 5 random points using a digital micrometer 547-401 manufactured by Mitutoyo Corporation. Their average value was adopted as the thickness.

[0304] Evaluation Example 2: Measurement of transmittance and haze

[0305] The transmittance and haze were measured using a haze meter NDH-5000W manufactured by Nippon Denshoku Kogyo in accordance with JIS K 7136 standards.

[0306] Evaluation Example 3: Measurement of Yellowness Index

[0307] The yellowness index (YI) was measured according to ASTM-E313 standard under the conditions of d65 and 10 using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory).

[0308] Evaluation Example 4: Measurement of modulus

[0309] The sample was cut at least 10 cm in a direction perpendicular to the main shrinkage direction of the film and 10 cm in the main shrinkage direction. In the universal testing machine UTM 5566A of Instron, it was fixed by a clamp spaced 10 cm apart. The sample was stretched at a speed of 10 mm / min at room temperature until it broke, and a stress-strain curve was obtained. The slope of the load relative to the initial strain on the stress-strain curve was taken as the modulus (GPa).

[0310] Evaluation Example 5: Measurement of Coefficient of Thermal Expansion (CTE)

[0311] Based on a film having a width of 3 mm, a length of 10 mm, and a thickness of 50 μm, the coefficient of thermal expansion (CTE) was measured using a thermal expansion coefficient measuring device (Seiko Exstar 6000 (TMA6100) Model of Seico Inst. (Japan)) according to the following heating conditions. The second scanning value is used for the measurement value of the coefficient of thermal expansion, and the measurement temperature range is 50° C. to 250° C.

[0312] The first scanning condition was as follows: starting from 30 °C, heating to 360 °C at a heating rate of 10 °C / min, and then cooling to 30 °C.

[0313] The second scanning condition was as follows: starting from 30°C and increasing to 360°C at a heating rate of 5°C / min.

[0314] In addition, CTE MD The CTE is the average value of the coefficient of thermal expansion measured in the longitudinal direction of the film.TD It is the average value of the thermal expansion coefficient measured with the TD direction of the film as the longitudinal direction.

[0315] Here, CTE is calculated according to the following Equation 2.

[0316] [Equation 2]

[0317]

[0318] In addition, the thickness, transmittance, haze, yellowness index, modulus and thermal expansion coefficient of the film were measured at six points in total by selecting two arbitrary points on each of the regions N, C and S of the film preparation, and their average values, deviations and deviation rates were calculated and shown in Table 2. The deviation rate is a value calculated by dividing the deviation by the average value and then multiplying by 100.

[0319] [Table 2]

[0320]

[0321]

[0322] See Table 2, according to the RC value (CTE MD / CTE TD In the embodiment where the value) is adjusted to 0.96 to 1.03, the quality deviation of the main physical properties of the film, such as haze, yellowing index, modulus, and thermal expansion coefficient, in the TD direction is significantly reduced, which proves that the reliability of the film quality can be improved.

[0323] Reference numerals

[0324] 100: Polyamide-imide based film

[0325] 101: first side 102: second side

[0326] 200: Functional layer 300: Cover window

[0327] 400: display unit 500: adhesive layer

[0328] A1, B1: Heater installation

[0329] A2, B2: Gel sheet

[0330] A3: Belt

[0331] HN,HC,HS:Heater

Claims

1. A polyamide-imide-based film comprising a polyamide-imide-based polymer and having an RC value of 1.00 to 1.03, wherein the RC value is represented by the following equation 1: <Equation 1> RC = CTE MD / CTE TD In Equation 1, CTE MD CTE is the average value of the thermal expansion coefficient (ppm / °C) of the film in the MD direction. TD is the average value of the thermal expansion coefficient of the film in the TD direction (ppm / °C), and The average value is an average value of the thermal expansion coefficients measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the film; When the haze is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the film, the average value of the haze is 1% or less, and the deviation rate of the haze is 10% or less; The polyamide-imide based polymer is formed by a diamine compound, a dianhydride compound and a dicarbonyl compound.

2. The polyamide-imide based film according to claim 1, wherein CTE MD 20ppm / ℃ to 40ppm / ℃, CTE TD 20ppm / ℃ to 40ppm / ℃.

3. The polyamide-imide based film according to claim 1, wherein When two arbitrary points in total six points are selected in each of the region N, region C, and region S divided in the TD direction of the film to measure the yellowness index and the modulus, the average value of the yellowness index is 5 or less, the deviation rate of the yellowness index is 10% or less, the average value of the modulus is 5 GPa or more, and the deviation rate of the modulus is 10% or less. 4 . The polyamide-imide-based film according to claim 1 , further comprising at least one selected from the group consisting of a filler, a blue pigment, and a UVA absorber.

5. The polyamide-imide based film according to claim 1, wherein The polyamide-imide based polymer includes an imide based repeating unit and an amide based repeating unit in a molar ratio of 2:98 to 70:

30.

6. A cover window for a display device, comprising a polyamide-imide base film and a functional layer, wherein: The polyamide-imide-based film includes a polyamide-imide-based polymer and has an RC value of 1.00 to 1.03, wherein the RC value is represented by the following Equation 1: <Equation 1> RC = CTE MD / CTE TD In Equation 1, CTE MD CTE is the average value of the thermal expansion coefficient (ppm / °C) of the film in the MD direction. TD is the average value of the thermal expansion coefficient of the film in the TD direction (ppm / °C), and The average value is an average value of the thermal expansion coefficients measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the film; When the haze is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the film, the average value of the haze is 1% or less, and the deviation rate of the haze is 10% or less; The polyamide-imide based polymer is formed by a diamine compound, a dianhydride compound and a dicarbonyl compound.

7. A display device comprising a display unit; and a cover window disposed on the display unit, wherein the cover window comprises a polyamide-imide based film and a functional layer, the polyamide-imide based film comprises a polyamide-imide based polymer and has an RC value of 1.00 to 1.03, wherein the RC value is represented by the following equation 1: <Equation 1> RC = CTE MD / CTE TD In Equation 1, CTE MD CTE is the average value of the thermal expansion coefficient (ppm / °C) of the film in the MD direction. TD is the average value of the thermal expansion coefficient of the film in the TD direction (ppm / °C), and The average value is an average value of the thermal expansion coefficients measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the film; When the haze is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided in the TD direction of the film, the average value of the haze is 1% or less, and the deviation rate of the haze is 10% or less; The polyamide-imide based polymer is formed by a diamine compound, a dianhydride compound and a dicarbonyl compound.

8. A method for preparing a polyamide-imide based film as claimed in claim 1, comprising: 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 solution and then drying it to prepare a gel sheet; and The gel sheet is heat treated. The step of heat-treating the gel sheet includes heat-treating the gel sheet by a first heater, a second heater, and a third heater spaced apart in a TD direction of the gel sheet, and When the temperature of the first heater corresponding to the center of the gel sheet is T HC The temperatures of the second heater and the third heater at both ends of the gel sheet are T HN and T HS When T HN and T HS Higher than T HC ; The first heater, the second heater, and the third heater each include an infrared heater, T HC is 300°C to 360°C, and T HN and T HS T HC 2% to 18% higher.

9. The method for preparing a polyamide-imide based film according to claim 8, wherein: The step of heat-treating the gel sheet includes heat-treating with hot air.

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