Polyamide-imide film

Abstract

The present invention provides a polyamide-imide film having excellent birefringence value uniformity and capable of providing excellent display quality.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of Korean Patent Application No. 10-2019-0090066 filed on July 25, 2019, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The following invention relates to a polyamideimide film. More specifically, the following invention relates to a polyamideimide film having excellent optical properties such as visibility, an optical material including the polyamideimide film, and a display device including the polyamideimide film. Background Art

[0004] In recent years, various display technologies such as liquid crystal displays and organic light-emitting displays have been proposed as optical technologies have rapidly developed. Polymer materials used in displays require further advanced characteristics. For example, in the case of liquid crystal displays, with the push for thinning, lightening, and expansion of screen area, wider viewing angles, higher contrast, suppression of image color changes depending on viewing angles, and uniform display are particularly important.

[0005] Generally, a liquid crystal display has a structure in which polarizers are installed on both sides of a liquid crystal cell, and the orientation of the liquid crystal cell changes depending on whether the driving circuit is applied to an electric field. In addition, the characteristics of the transmitted light from the polarizer change accordingly to achieve visualization of the light. Here, the optical path and birefringence change according to the incident angle of the incident light, which is caused by the fact that the liquid crystal is an anisotropic material with two different refractive indices.

[0006] Due to this characteristic, the liquid crystal display has a different contrast ratio, which is a measure of the clarity of an image observed according to a viewing angle, and causes a grayscale inversion phenomenon, etc., which deteriorates visibility. In addition, a polarizer is also applied to an organic light emitting display to improve visibility through reflection, and therefore, the importance of birefringence of a polymer film applied to the organic light emitting display becomes important.

[0007] In order to overcome these problems, an optical compensation film for compensating for optical retardation generated by a display device is used, and optical films such as various protective films are used together therewith.

[0008] Here, as a material of the optical compensation film used, various polymers such as polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), maleimide-based copolymers, and cellulose-based polymers are known in the art.

[0009] Among them, polyimide, which is a polymer having relatively low crystallinity and an amorphous structure and has excellent transparency, heat resistance, chemical resistance, mechanical physical properties, electrical properties, dimensional stability, etc., is being developed and used.

[0010] However, since polyimide has a benzene ring having a high content of polarization, it has a high optical anisotropy (birefringence value) even under a small orientation effect. Generally, stress is generated during film processing, and orientation of polymer chains is generated by the transmitted stress. Therefore, when a small stress difference is generated over the entire area of ​​the film, it is difficult to achieve a uniform birefringence value over the entire area of ​​the film.

[0011] Therefore, when an optical film having a high birefringence value and a non-uniform birefringence value is applied to a device such as a display using a polarizer, a problem of distortion of the optical design of the display occurs. Therefore, there is a need to manufacture a polyamideimide film to solve this problem. Summary of the invention

[0012] Embodiments of the present invention are directed to providing a polyamideimide film having a low in-plane birefringence value and excellent in-plane birefringence value uniformity, and an optical material including the same.

[0013] In particular, embodiments of the present invention are directed to providing a high-quality display device having excellent visibility with uniform image quality and high contrast by including a polyamide-imide film.

[0014] In one general aspect, the photoelastic coefficient of the polyamideimide film in the transverse direction is less than 2.0×10 -8 m 2 / N, and has an in-plane birefringence value (Δn in ) satisfies the wavelength dispersion of the following equations 1 and 2:

[0015] [Equation 1]

[0016] 1.0<Δn in (450nm) / Δn in (550nm)<1.3

[0017] [Equation 2]

[0018] 0.7<Δn in (650nm) / Δn in (550nm)<1.0

[0019] in

[0020] Δn in (450nm), Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm, 550nm and 650nm, respectively.

[0021] The polyamide-imide film according to the exemplary embodiment of the present invention may have a birefringence value (Δn th ) satisfies the wavelength dispersion of the following equations 3 and 4:

[0022] [Equation 3]

[0023] 0.9<Δn th (450nm) / Δn th (550nm)<1.3

[0024] [Equation 4]

[0025] 0.7<Δn th (650nm) / Δn th (550nm)<0.9

[0026] in

[0027] Δn th (450nm), Δn th (550nm) and Δn th (650 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

[0028] The polyamide-imide film according to the exemplary embodiment of the present invention may satisfy the following Relationship 5:

[0029] [Equation 5]

[0030] 1.0<Δn th (450nm) / Δn th (550nm)<1.25

[0031] in

[0032] Δn th (450nm) and Δn th (550 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 450 nm and 550 nm, respectively.

[0033] The polyamide-imide film according to the exemplary embodiment of the present invention may satisfy the following Relationship 6:

[0034] [Equation 6]

[0035] 0.72<Δn th (650nm) / Δn th (550nm)<0.87

[0036] in

[0037] Δn th (550nm) and Δn th (650 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 550 nm and 650 nm, respectively.

[0038] According to an exemplary embodiment of the present invention, an in-plane birefringence value at a wavelength of 550 nm may be 0.1 times or less of a birefringence value in a thickness direction at a wavelength of 550 nm.

[0039] The in-plane retardation value within the plane according to the exemplary embodiment of the present invention may have a uniformity of 10% or less with respect to an area of ​​15 cm×15 cm.

[0040] The polyamide-imide film according to the exemplary embodiment of the present invention may have a 1.5×10 -8 m 2 / N or less lateral photoelastic coefficient.

[0041] The polyamide-imide film according to the exemplary embodiment of the present invention may satisfy the following Relationship 7:

[0042] [Equation 7]

[0043] 1.1<Δn in (450nm) / Δn in (550nm)<1.25

[0044] in

[0045] Δn in (450nm) and Δn in (550nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm and 550nm, respectively.

[0046] The polyamide-imide film according to the exemplary embodiment of the present invention may satisfy the following Relationship 8:

[0047] [Equation 8]

[0048] 0.72<Δn in (650nm) / Δn in (550nm)<0.9

[0049] in

[0050] Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 550nm and 650nm, respectively.

[0051] Other features and aspects will become apparent from the following detailed description. DETAILED DESCRIPTION

[0052] Hereinafter, the present invention will be described in more detail with reference to specific examples and exemplary embodiments. However, the following specific examples or exemplary embodiments are mentioned only for describing the present invention in detail, the present invention is not limited thereto, and can be implemented in various forms.

[0053] In addition, unless otherwise defined, all technical terms and scientific terms have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein are only used to effectively describe certain specific examples and are not intended to limit the present invention.

[0054] Throughout the specification of describing the present invention, unless explicitly described to the contrary, “comprising” any elements will be understood to mean also including other elements rather than excluding any other elements.

[0055] In addition, singular forms used in the specification and the appended claims are intended to include plural forms as well, unless the context indicates otherwise.

[0056] In this specification, “in-plane birefringence (Δn in )" has the same meaning as the in-plane birefringence and refers to the value of nx-ny when the refractive indices in the slow axis direction (x-axis) and the fast axis direction (y-axis) of the film are nx and ny, respectively. The birefringence in the thickness direction (Δn in )” has the same meaning as the out-of-plane birefringence, and when nz is the refractive index in the thickness direction (z-axis), the birefringence in the thickness direction refers to the value of nz-(nx+ny) / 2.

[0057] Here, the slow axis direction refers to the direction of the higher refractive index of two refractive indexes in a medium plane, and the fast axis direction refers to the direction of the lower refractive index of two refractive indexes in the medium plane.

[0058] In this specification, "delay" refers to a phase difference between two electric field components due to a speed difference in a medium of the two electric field components orthogonal to an electromagnetic wave propagating through the medium.

[0059] In the present specification, the "orientation angle" refers to an angle formed by a slow axis in the longitudinal direction (machine direction, MD (machine direction)) of a film.

[0060] In this specification, "photoelasticity" is defined by the phenomenon that when a load is applied to a solid, the relative positions of molecules inside the object change, and the change in molecular arrangement causes a difference in refractive index to produce birefringence.

[0061] Conventional polyamideimide films have excellent mechanical and thermal properties, thereby achieving excellent durability, dimensional stability, etc. as optical films, but due to the optical property that the birefringence value changes even under a weak external force, conventional polyamideimide films are difficult to have birefringence uniformity over the entire area of ​​the film. Therefore, the present inventors have found that it is possible to provide a polyamideimide film of excellent quality with a wide viewing angle and uniform birefringence and retardation, and an optical material including the polyamideimide film, to provide a display device with excellent optical performance, thereby completing the present invention.

[0062] In order to achieve the above object, the photoelastic coefficient of the polyamide-imide film in the transverse direction of the present invention is less than 2.0×10 -8 m 2 / N, and has an in-plane birefringence value (Δn in ) satisfies the wavelength dispersion of the following equations 1 and 2:

[0063] [Equation 1]

[0064] 1.0<Δn in (450nm) / Δn in (550nm)<1.3

[0065] [Equation 2]

[0066] 0.7<Δn in (650nm) / Δn in (550nm)<1.0

[0067] in

[0068] Δn in (450nm), Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm, 550nm and 650nm, respectively.

[0069] The polyamide-imide film according to the present invention satisfies all of the above-mentioned photoelastic coefficients, birefringence values, and wavelength dispersion, thereby preventing delay non-uniformity due to stress, thereby achieving uniform display quality. In addition, when the polyamide-imide film is provided as a display device, excellent image quality with a wide viewing angle and high contrast can be provided, and the mura phenomenon (mura phenomenon) of color spots (stain) caused by color non-uniformity due to improved visibility does not occur.

[0070] The polyamide-imide film according to the present invention has a thickness of less than 2.0×10 -8 m 2 / N in the lateral direction. Preferably, the photoelastic coefficient may be 1.5×10 -8 m 2 / N or less. Specifically, the lower limit may be 1.0×10 -12 , preferably 1.0×10 -12 to 1.5×10 -8 m 2 / N.

[0071] The polyamide-imide film according to the present invention may have an in-plane birefringence value (Δn in ) satisfies the wavelength dispersion of the following equations 1 and 2:

[0072] [Equation 1]

[0073] 1.0<Δn in (450nm) / Δn in (550nm)<1.3

[0074] [Equation 2]

[0075] 0.7<Δn in (650nm) / Δn in (550nm)<1.0

[0076] in

[0077] Δn in (450nm), Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm, 550nm and 650nm, respectively. The polyamideimide film satisfies the above-mentioned photoelastic coefficient and wavelength dispersion at the same time, thereby greatly reducing the optical changes caused by external forces, thereby having excellent reliability, and achieving a uniform birefringence value throughout the film, and having excellent uniformity, so it is an excellent optical material. At the same time, the polyamideimide film provides a wide viewing angle, thereby ensuring excellent visibility with high image quality.

[0078] Since the polyamide-imide film according to the present invention satisfies both the above-mentioned photoelastic coefficient and wavelength dispersibility, both birefringence uniformity and high image quality due to a wide viewing angle can be improved.

[0079] According to an exemplary embodiment of the present invention, the photoelastic coefficient in the longitudinal direction (MD) and the photoelastic coefficient in the transverse direction (TD) may be different from each other. Specifically, the ratio of the photoelastic coefficient in the longitudinal direction to the photoelastic coefficient in the transverse direction may be 1.05 or more, but is not limited thereto. When the photoelastic coefficient is different depending on the direction, when the film is applied to a material of a photoreactive sensor or the like, the sensitivity range may be widened.

[0080] According to an exemplary embodiment of the present invention, in order to achieve better display quality, preferably, the polyamide-imide film may have an in-plane birefringence value (Δn in ) satisfies the wavelength dispersion of the following relation 7:

[0081] [Equation 7]

[0082] 1.1<Δn in (450nm) / Δn in (550nm)<1.25

[0083] in

[0084] Δn in (450nm) and Δn in (550nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm and 550nm, respectively.

[0085] According to an exemplary embodiment of the present invention, in order to achieve better display quality, the polyamide-imide film may have an in-plane birefringence value (Δn in ) satisfies the wavelength dispersion of the following relation 8:

[0086] [Equation 8]

[0087] 0.72<Δn in (650nm) / Δn in (550nm)<0.9

[0088] in

[0089] Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 550nm and 650nm, respectively.

[0090] According to an exemplary embodiment of the present invention, the polyamide-imide film may have a birefringence value (Δnth ) satisfies the wavelength dispersion of the following equations 3 and 4:

[0091] [Equation 3]

[0092] 0.9<Δn th (450nm) / Δn th (550nm)<1.3

[0093] [Equation 4]

[0094] 0.7<Δn th (650nm) / Δn th (550nm)<0.9

[0095] in

[0096] Δn th (450nm), Δn th (550nm) and Δn th (650 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

[0097] According to an exemplary embodiment of the present invention, in order to achieve a more uniform birefringence value as a whole and ensure a wide viewing angle, preferably, the polyamide-imide film may have a birefringence value (Δn th ) satisfies the wavelength dispersion of the following relation 5:

[0098] [Equation 5]

[0099] 1.0<Δn th (450nm) / Δn th (550nm)<1.25

[0100] in

[0101] Δn th (450nm) and Δn th (550 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 450 nm and 550 nm, respectively.

[0102] According to an exemplary embodiment of the present invention, in order to achieve a more uniform birefringence value as a whole and ensure a wide viewing angle, preferably, the polyamide-imide film may have a birefringence value (Δn th ) satisfies the wavelength dispersion of the following equation 6:

[0103] [Equation 6]

[0104] 0.72<Δn th (650nm) / Δnth (550nm)<0.87

[0105] in

[0106] Δn th (550nm) and Δn th (650 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 550 nm and 650 nm, respectively.

[0107] When the above-mentioned wavelength dispersibility is satisfied, orientation in the thickness direction may be performed to control the in-plane birefringence value and retardation, and thus the birefringence value and retardation uniformity may be further improved by the orientation effect over the entire area of ​​the film.

[0108] According to an exemplary embodiment of the present invention, the in-plane birefringence value can be less than 0.1 times of the birefringence value in the thickness direction. The in-plane birefringence value can be preferably less than 0.09 times, more preferably less than 0.08 times. Specifically, the in-plane birefringence value at a wavelength of 550nm can be 0.01 to 0.1 times, preferably 0.01 to 0.09 times, of the birefringence value in the thickness direction at a wavelength of 550nm. As described above, when the in-plane birefringence value at a wavelength of 550nm is significantly lower than the birefringence value in the thickness direction, the birefringence value can be uniform over the entire area of ​​the film, and significantly improved delay can be achieved only by a low stretch ratio. In addition, a high-quality display that can ensure excellent viewing angles and does not appear stains can be provided.

[0109] According to the exemplary embodiment of the present invention, the retardation value obtained by multiplying the birefringence value depending on the wavelength dispersion by the thickness of the film also shows the above-mentioned tendency.

[0110] According to an exemplary embodiment of the present invention, the retardation value in the thickness direction (R th ) may be 1000 to 10000. When the film has the retardation value as described above, visibility may be significantly improved, which is excellent in providing excellent display quality.

[0111] According to an exemplary embodiment of the present invention, the in-plane retardation value in the plane may have a uniformity of 10% or less relative to an area of ​​15 cm×15 cm. The uniformity may preferably be 9% or less, and more preferably 8% or less. Specifically, the uniformity may be 0.01% to 10%, preferably 0.1% to 9%, and more preferably 0.1% to 8%. The polyamide-imide film having the above uniformity has excellent light uniformity, and when provided for a display, prevents the formation of uneven portions in a screen display to ensure high reliability.

[0112] According to an exemplary embodiment of the present invention, the polyimide-based film is derived from a monomer mixture including dianhydride, diamine and aromatic diacid chloride to provide a polyamide-imide film including a polymerized polyamide-imide resin. There is no particular limitation on dianhydride, diamine and aromatic diacid chloride as long as they are commonly used materials known in the art.

[0113] According to an exemplary embodiment of the present invention, the diamine is, for example, any one or a mixture of two or more selected from aliphatic diamines, aromatic diamines, and the like.

[0114] More specifically, the aromatic diamine is not greatly limited, but, for example, may be any one selected from bistrifluoromethylbenzidine (TFDB), bis(3-aminophenyl)sulfone (3DDS), bis(4-aminophenyl)sulfone (4DDS), diaminophenyl ether, o-phenylenediamine (o-PDA), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), oxydiphenylamine (ODA), methylenedianiline (MDA), bisaminophenylhexafluoropropane (HFDA), 1,3-bis(4-aminophenoxy)benzene (TPE-R), and the like, or a mixture of two or more thereof.

[0115] The aliphatic diamine is not particularly limited, but, for example, may be any one selected from 1,4-diaminocyclohexane, 1,4-cyclohexanebis(methylamine), 4,4'-diaminodicyclohexylmethane (MCA), 4,4'-methylenebis(2-methylcyclohexylamine) (MMCA), ethylenediamine (EN), 1,3-diaminopropane (13DAP), tetramethylenediamine, 1,6-hexamethylenediamine (16DAH), 1,12-diaminododecane (112DAD), and the like, or a mixture of two or more thereof.

[0116] According to an exemplary embodiment of the present invention, the dianhydride may be any one or a mixture of two or more selected from aliphatic dianhydrides, aromatic dianhydrides, and the like.

[0117] More specifically, according to an exemplary embodiment of the present invention, the aromatic dianhydride is not greatly restricted, for example, it can be any one selected from 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA), 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (ODPA), bis(dicarboxyphenoxy)diphenylsulfur dianhydride (BDSDA), etc., or a mixture of two or more thereof, but is not limited thereto.

[0118] There is no great restriction on the aliphatic dianhydride. For example, any one or a mixture of two or more selected from 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 5-(2,5-dioxytetrahydrofuranyl)-3-methylcyclohexene-1,2-dicarboxylic dianhydride (DOCDA), bicyclooctene-2,3,5,6-tetracarboxylic dianhydride (BODA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA), 1,2,4-tricarboxy-3-methylcarboxycyclopentane dianhydride, 1,2,3,4-tetracarboxycyclopentane dianhydride, etc. can be used.

[0119] According to an exemplary embodiment, 5 to 80 moles, preferably 10 to 70 moles of dianhydride may be included based on 100 moles of the diamine to be copolymerized.

[0120] When the dianhydride is included within the above range, a polyamideimide film having excellent visibility and optical properties may be provided.

[0121] According to an exemplary embodiment of the present invention, the aromatic diacyl chloride is not too limited, and for example, it may include any one or a mixture of two or more selected from terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), 1,1'-biphenyl-4,4'-dicarboxylic acid chloride (BPC), 1,4-naphthalene dicarboxylic acid chloride (1,4-NaDC), 2,6-naphthalene dicarboxylic acid chloride (2,6-NaDC), 1,5-naphthalene dicarboxylic acid chloride (1,5-NaDC), etc. Preferably, the aromatic diacyl chloride includes any one or two or more selected from terephthaloyl chloride, isophthaloyl chloride, etc.

[0122] In addition, when the aromatic diacid chloride is used, it is not limited to the compounds exemplified above, and it may be used in combination with other acyl halide compounds, but it is preferred to use the aromatic diacid chloride alone.

[0123] According to an exemplary embodiment, 20 to 95 moles, preferably 30 to 90 moles of the aromatic diacid chloride may be included based on 100 moles of the diamine to be copolymerized.

[0124] The polyamide-imide film produced from the above composition can have excellent mechanical properties and heat resistance, can provide excellent display quality even at high temperatures, and provide optical properties that maintain high transparency. In addition, the film can have more uniform birefringence values ​​and retardation values, and has an extremely wide viewing angle and excellent quality at various angles.

[0125] According to an exemplary embodiment of the present invention, a polyamide-imide film can be produced by adjusting the drying temperature and time in the first drying process after the solution casting process. For example, drying can be performed at a drying temperature of 80°C for 3 minutes. Preferably, drying can be performed at a temperature of 80°C to 160°C for 3 to 15 minutes. Specifically, drying can be performed at a point temperature in the range of 80°C to 160°C, or drying can be performed at a first temperature and then at a second temperature, but the method is not particularly limited as long as the temperature and time conditions are met. When the film is dried as described above, a wide viewing angle can be provided, a high contrast can be achieved, and visibility can be improved to provide excellent image quality.

[0126] According to an exemplary embodiment of the present invention, the polyamide-imide film may be subjected to a stretching treatment. Relative to each direction of the transverse direction (TD) and the longitudinal direction (MD) of the polyamide-imide film before stretching, it may be stretched by 1-30%. Preferably, it may be stretched by 1-20%. When stretched as described above, the dimensional stability of the polyamide-imide film may be improved, and a film with better quality may be provided.

[0127] According to an exemplary embodiment of the present invention, stretching can be performed with a stretching ratio (ratio of transverse / longitudinal elongation) of less than 1.5 according to TD and MD. Specifically, the stretching ratio can be 0.8 to 1.5, preferably 0.9 to 1.4, and more preferably 0.9 to 1.35. When the stretching ratio is as described above, stress can be used to prevent delay unevenness to achieve uniform display quality. Preferably, stretching can be performed simultaneously with secondary drying. Specifically, stretching can be performed in a tentering machine or the like that allows a secondary drying process to be performed simultaneously with stretching. Therefore, when the stretching and secondary drying processes are performed simultaneously, compared with the case where only stretching or only the secondary drying process is performed, an excellent display quality with better light uniformity and almost no uneven portions formed on the screen display can be achieved.

[0128] According to an exemplary embodiment of the present invention, the stretching process performed simultaneously with the secondary drying process can provide one or more, preferably two or more, more preferably three or more, and most preferably four or more stretching regions obtained due to different drying conditions and stretching conditions during the above process. Specifically, when three or more stretching regions are formed, secondary drying and stretching are performed while the film is moved to each region, ensuring a wide viewing angle while significantly reducing fine unevenness on the surface, and can provide excellent image quality.

[0129] More specifically, the stretching process can be performed to produce a film by adjusting the drying temperature and elongation of three or more stretching areas. For example, in a stretching process performed in three or more areas, while stretching, the drying temperature of the first area can be 140 to 210°C, the drying temperature of the second area can be 150 to 250°C, and the drying temperature of the third area can be 180 to 300°C. Preferably, the drying temperature of the first area can be 140 to 200°C, the drying temperature of the second area can be 160 to 240°C, and the drying temperature of the third area can be 190 to 280°C. Here, in the stretching process, stretching and secondary drying are performed when the film passes through the first area to the third area in sequence. When the drying temperature during stretching is set, Relationships 1 and 2 can be satisfied, the birefringence value and the delay uniformity are excellent, and an excellent viewing angle is ensured to provide a high-quality display.

[0130] Preferably, as another exemplary embodiment, a stretching process can be performed to produce a film by adjusting the drying temperature and elongation of four or more stretching regions. For example, in a stretching process performed in four or more regions, while stretching, the drying temperature of the first region can be 140 to 210°C, the drying temperature of the second region can be 150 to 250°C, the drying temperature of the third region can be 180 to 300°C, and the drying temperature of the fourth region can be 200 to 280°C. Preferably, the drying temperature of the first region can be 140 to 200°C, the drying temperature of the second region can be 160 to 240°C, the drying temperature of the third region can be 190 to 280°C, and the drying temperature of the fourth region can be 200 to 270°C. Here, in the stretching process, the film is stretched and dried twice while passing through the first region to the fourth region in sequence. When the drying temperature during stretching is set, Relationship 1 and Relationship 2 can be satisfied, and a high image quality with high definition and no image distortion can be provided.

[0131] More preferably, in order to improve the uniformity of delay over the entire region of the film, the third region or higher regions in the first region to the fourth region may have successively increasing drying temperatures. More preferably, when the film passes through the third region and enters the fourth region, the drying temperature may be the same or reduced.

[0132] According to an exemplary embodiment of the present invention, the stretching process performed simultaneously with the secondary drying process can be performed for a total of 1 to 20 minutes, preferably 5 to 20 minutes, and more preferably 7.5 to 15 minutes, but is not limited thereto. Specifically, when the number of regions for the stretching process is three or more, the drying process can be performed for 1 to 10 minutes, preferably 1 to 6 minutes, in each region, but is not limited thereto.

[0133] According to an exemplary embodiment of the present invention, when the number of regions of the stretching process is three or more, the following Formula 1 and Formula 2 may be satisfied:

[0134] [Formula 1]

[0135] 5≤T2-T1≤50

[0136] [Formula 2]

[0137] 5≤T3-T2≤100

[0138] in

[0139] T1 is the drying temperature (°C) of the first zone in the stretching process of the polyamideimide film, T2 is the drying temperature (°C) of the second zone in the stretching process of the polyamideimide film, and T3 is the drying temperature (°C) of the third zone in the stretching process of the polyamideimide film.

[0140] Preferably, Formula 1 may satisfy 10 to 35 and Formula 2 may satisfy 5 to 80.

[0141] As another exemplary embodiment, in the case of four or more regions, the stretching process may satisfy Formula 1 and Formula 2, and satisfy the following Formula 3:

[0142] [Formula 3]

[0143] -80≤T4-T3≤50

[0144] in

[0145] T3 is the drying temperature (° C.) of the third zone in the stretching process of the polyamide-imide film, and T4 is the drying temperature (° C.) of the fourth zone in the stretching process of the polyamide-imide film.

[0146] Preferably, the above Formula 3 may satisfy -70 to 5, more preferably -70 to 0.

[0147] As described above, when the secondary drying temperature in the stretching process satisfies Equations 1 and 2 or Equations 1 to 3, Relationships 1 and 2 can be satisfied, the in-plane birefringence value can have a much lower value than the birefringence value in the thickness direction, which value can be uniform over the entire area of ​​the film, and an excellent viewing angle can be ensured to provide high-quality display.

[0148] According to an exemplary embodiment of the present invention, the polyamide-imide film may have a thickness of 20 to 200 μm. The thickness of the transparent film is preferably 20 to 150 μm, more preferably 20 to 100 μm. When the film has the above thickness, Relational Formulas 1 and 2 can be satisfied, the uniformity and delay of the birefringence value are excellent, a high contrast ratio due to a high viewing angle can be achieved, and the distortion phenomenon of the image can be suppressed by high definition.

[0149] Another embodiment of the present invention is an optical material including the above-mentioned polyamideimide film.

[0150] The polyamideimide film according to the present invention is an excellent optical material that can provide excellent image quality having good birefringence value and retardation uniformity, achieving high contrast due to a high viewing angle to have high definition, and having no image distortion phenomenon.

[0151] The polyamide-imide film according to the present invention can be applied to a wide range of fields, such as heat-resistant advanced materials, such as automotive materials, aviation materials and spacecraft materials; electronic materials such as insulating coating materials, insulating films, semiconductors and electrode protective films of TFT-LCD, but is preferably used as an optical material in display fields such as liquid crystal display devices.

[0152] Specifically, the polyamideimide film can be applied to the display field as various optical materials selected from cover window films, protective films, retardation films, diffusion films, flexible substrates, sealants, polarizers, touch panel substrates, and the like.

[0153] Another embodiment of the present invention is a polarizer including the above-mentioned polyamideimide film.

[0154] When the polyamide-imide film is included as described above, a polarizer that ensures a wide viewing angle and achieves high image quality can be provided.

[0155] According to the exemplary embodiment of the present invention, the polarizer may be implemented in various shapes, such as a linear polarizer or a circular polarizer, without being limited to a specific shape.

[0156] According to the exemplary embodiment of the present invention, the polarizer can be used in various fields. For example, the polarizer can be used in mobile communication terminals, smart phones, other mobile devices, display devices, electronic blackboards, outdoor electronic displays, and various displays.

[0157] Another embodiment of the present invention is a display device comprising the above-mentioned polarizer or the above-mentioned optical material. When the display device comprises the polyamide-imide film, excellent visibility can be achieved. In addition, even in the case where light is emitted from the display panel not only in the vertical direction but also in all directions, excellent image quality can be achieved compared with a conventional display device, and visibility can be significantly improved.

[0158] According to the exemplary embodiment of the present invention, there is no particular limitation on the display device as long as it belongs to a field requiring excellent optical performance, and the display device can be applied to a field selected from a liquid crystal display, an organic EL display, an electronic paper, etc. In addition, a display panel can be provided according to the application field. Specifically, for example, the display device may include any one or two or more selected from various image display devices such as a liquid crystal display device, an electroluminescent display device, a plasma display device, and a field emission display device, but is not limited thereto.

[0159] The polyamideimide film according to the present invention, the optical material including the polyamideimide film, and the display device including the polyamideimide film will be described in detail by way of examples. However, the following examples are mentioned only for describing the present invention in detail, and the present invention is not limited thereto and can be implemented in various forms.

[0160] In addition, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The terms used herein are only used to effectively describe certain exemplary embodiments and are not intended to limit the present invention.

[0161] Furthermore, unless otherwise specified, the unit of the added materials herein may be % by weight.

[0162] The physical properties of the present invention are measured as follows:

[0163] (1) Photoelastic coefficient

[0164] The photoelasticity is obtained by measuring the delay change of the stretched part relative to the stress generated when the sample is stretched using a Microtest Tensile Stage (MicrotestTensile Stage) available from Deben. The photoelastic coefficient is obtained by the following steps: the sample is cut into a size of 2 cm × 7 cm, the sample is placed at the bottom of the thin jaws of the stretching stage, the sample is covered with thick jaws and fixed with screws, and then the photoelasticity is measured; at this time, the film is tightly fixed, and after the fixing is completed, the distance between the closed jaws is fixed to 20 mm, after which the sample is slowly stretched, and the in-plane birefringence value (Δn) when it increases by 1% to 3% is calculated. in ) to record the photoelastic coefficient. When the stresses generated when stretched by 1% and 3% are called σ1 and σ2 respectively and the in-plane birefringence at this time is called Δn1 and Δn2, the photoelastic coefficient is defined as follows:

[0165] [Δn2-Δn1] / [σ2-σ1]

[0166] (2) Measurement of birefringence and retardation values

[0167] Birefringence value: measured using an Axoscan device available from Axometrics. The birefringence value was obtained by measuring the values ​​of light at wavelengths of 450 nm, 550 nm, and 650 nm. In-plane birefringence (Δn in ) and the birefringence in the thickness direction (Δn th ) is calculated by the following formula:

[0168] Δn in =nx-ny

[0169] (Δn in : in-plane birefringence, nx: refractive index of the slow axis, ny: refractive index of the fast axis)

[0170] Δn th =nz-(nx+ny) / 2

[0171] (Δn th : birefringence in the thickness direction, nx: refractive index of the slow axis, ny: refractive index of the fast axis, nz: refractive index in the thickness direction)

[0172] Retardation: An Axoscan instrument available from Axometrics was used. Retardation was measured for each angle of incidence (θ) and is characterized by detecting with a polarization state analyzer (PSA) how certain linear polarizations generated by a polarization state generator (PSG) change when passing through the film under test.

[0173] (3) Measurement of uniformity of in-plane retardation values

[0174] The uniformity of in-plane retardation is measured using an Axoscan device available from Axometrics equipped with an XY-Mapping Stage. Here, R in value and orientation angle, and the object of uniformity to be measured is R in The sample size during measurement was 15 cm×15 cm, and 100 points of 10EA×10EA were used as measurement points for measurement. The uniformity (%) was determined as follows.

[0175] As the retardation value, R measured using the XY-stage was used as is. in Value, when R in The maximum value is R max , R in The minimum value of R min , the average value is R ave When the uniformity is defined as {(R max -R min ) / (R ave ×2)}×100.

[0176] (4) Evaluation of final film quality

[0177] To evaluate the quality of the final film, when a display combining a polarizer and the manufactured optical film was visually observed at a viewing angle of 165° C., the display was determined to be OK or NG depending on whether a color change occurred and whether image stain was observed.

[0178] (5) Residual solvent content

[0179] As for the residual solvent content, the value obtained by subtracting the weight A370 at 370° C. from the weight A150 at 150° C. using TGA (Discovery, available from TA) was determined as the residual solvent content in the film. Here, the measurement conditions involved increasing the temperature to 400° C. at a temperature increase rate of 30° C. / min, and measuring the weight change in the 150° C. to 370° C. section.

[0180] [Preparation Example 1]

[0181] [Molar ratio of TFMB:6FDA:TPC = 100:14:86]

[0182] Dimethylacetamide (DMAc) and 2,2'-bis(trifluoromethyl)benzidine (TFMB) were added to the reactor under a nitrogen atmosphere and stirred thoroughly, and then 4,4'-hexafluoroisopropyldiphthalic anhydride (6FDA) was added thereto and stirred thoroughly until the reactants dissolved. After that, terephthaloyl chloride (TPC) was added and stirred for 6 hours to dissolve and react, thereby preparing a polyamic acid resin composition. Here, the amount of each monomer was TFMB:6FDA:TPC=100:14:86 in a molar ratio, and the temperature of the reactor was maintained at 30°C. The viscosity of the polyamic acid resin composition finally obtained was 33,000cps. Subsequently, pyridine and acetic anhydride were added to the polyamic acid resin composition at 2.5 times the total amount of dianhydride introduced, and stirred at 60°C for 1 hour to prepare a polymerization solution 1.

[0183] Thereafter, the polymer solution 1 was precipitated in an excess of methanol and filtered to obtain a solid component, which was vacuum dried at 50° C. for more than 6 hours to obtain polyamideimide. The weight average molecular weight of the finally obtained polyamideimide was 106,000 g / mol.

[0184] [Preparation Example 2]

[0185] [Molar ratio of TFMB:CBDA:IPC = 100:60:40]

[0186] Dimethylacetamide (DMAc) and 2,2'-bis(trifluoromethyl)benzidine (TFMB) were added to the reactor under a nitrogen atmosphere and stirred thoroughly, and then 4,4'-cyclobutanetetracarboxylic dianhydride (CBDA) was added thereto and stirred thoroughly until the reactants dissolved. After that, isophthaloyl chloride (IPC) was added and stirred for 6 hours to dissolve and react, thereby preparing a polyamic acid resin composition. Here, the amount of each monomer was TFMB:CBDA:IPC=100:60:40 in a molar ratio, and the temperature of the reactor was maintained at 30°C. The viscosity of the polyamic acid resin composition finally obtained was 90,000cps. Subsequently, pyridine and acetic anhydride were added to the polyamic acid resin composition at 2.5 times the total amount of dianhydride introduced, and stirred at 60°C for 1 hour to prepare a polymerization solution 2.

[0187] Thereafter, the polymer solution 2 was precipitated in an excess of methanol and filtered to obtain a solid component, which was vacuum dried at 50° C. for more than 6 hours to obtain polyamideimide. The weight average molecular weight of the finally obtained polyamideimide was 310,000 g / mol.

[0188] [Preparation Example 3]

[0189] [Molar ratio of TFMB:CBDA:IPC = 100:40:60]

[0190] Dimethylacetamide (DMAc) and 2,2'-bis(trifluoromethyl)benzidine (TFMB) were added to the reactor under a nitrogen atmosphere and stirred thoroughly, and then 4,4'-cyclobutanetetracarboxylic dianhydride (CBDA) was added thereto and stirred thoroughly until the reactants dissolved. After that, isophthaloyl chloride (IPC) was added and stirred for 6 hours to dissolve and react, thereby preparing a polyamic acid resin composition. Here, the amount of each monomer was TFMB:CBDA:IPC=100:40:60 in a molar ratio, and the temperature of the reactor was maintained at 30°C. The viscosity of the polyamic acid resin composition finally obtained was 68,000cps. Subsequently, pyridine and acetic anhydride were added to the polyamic acid resin composition at 2.5 times the total amount of dianhydride introduced, and stirred at 60°C for 1 hour to prepare a polymerization solution 3.

[0191] Thereafter, the polymer solution 3 was precipitated in an excess of methanol and filtered to obtain a solid component, which was vacuum dried at 50° C. for more than 6 hours to obtain polyamideimide. The weight average molecular weight of the finally obtained polyamideimide was 180,000 g / mol.

[0192] [Example 1]

[0193] The polymerized solution 1 was cast on a Yellow PI (Upilex-S125 obtained from Ube) film using a slot die at room temperature and dried in a drying oven at 140° C. for 7 minutes to obtain an initial dry film having a thickness of 70 μm and a width of 300 mm. The film was subjected to the stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 1.9 wt %.

[0194] [Example 2]

[0195] At room temperature, the polymerized solution 1 was cast on a glass substrate using an applicator and dried under the following conditions: 90° C. (2 minutes)-120° C. (3 minutes)-140° C. (2 minutes) to obtain an initial dry film having a thickness of 72 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 2.3 wt%.

[0196] [Example 3]

[0197] The polymerized solution 1 was cast on a yellow PI film using a slot die at 40° C. and dried in a drying oven at 140° C. for 7 minutes to obtain an initial dry film having a thickness of 73 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 2.0 wt%.

[0198] [Example 4]

[0199] The polymerized solution 2 was cast on a yellow PI film using a slot die at room temperature and dried in a drying oven at 140° C. for 7 minutes to obtain an initial dry film having a thickness of 68 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 1.78 wt%.

[0200] [Example 5]

[0201] At room temperature, the polymerized solution 2 was cast on a glass substrate using an applicator and dried under the following conditions: 90° C. (2 minutes)-120° C. (3 minutes)-140° C. (2 minutes) to obtain an initial dry film having a thickness of 69 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 2.2 wt%.

[0202] [Example 6]

[0203] The polymerized solution 2 was cast on a yellow PI film using a slot die at 40° C. and dried in a drying oven at 140° C. for 7 minutes to obtain an initial dry film having a thickness of 71 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 2.1 wt %.

[0204] [Example 7]

[0205] The polymerized solution 3 was cast on a yellow PI film using a slot die at room temperature and dried in a drying oven at 140° C. for 7 minutes to obtain an initial dry film having a thickness of 67 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 1.8 wt%.

[0206] [Example 8]

[0207] The polymerized solution 3 was cast on a yellow PI film using a slot die at 40° C. and dried in a drying oven at 140° C. for 7 minutes to obtain an initial dry film having a thickness of 70 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 2.1 wt %.

[0208] [Comparative Example 1]

[0209] An initial dry film was prepared in the same manner as in Example 1, and then secondary drying and stretching were performed in the manner shown in the following Table 1 to prepare a film having a residual solvent content of 2.1 wt %.

[0210] [Comparative Example 2]

[0211] An initial dry film was prepared in the same manner as in Example 2, and then secondary drying and stretching were performed in the manner shown in the following Table 1 to prepare a film having a residual solvent content of 2.3 wt %.

[0212] [Comparative Example 3]

[0213] An initial dry film was prepared in the same manner as in Example 3, and then secondary drying and stretching were performed in the manner shown in the following Table 1 to prepare a film having a residual solvent content of 3.5 wt %.

[0214] [Comparative Example 4]

[0215] The polymerized solution 2 was cast on a glass substrate using an applicator at room temperature and dried at 120° C. for 20 minutes to obtain an initial dry film having a thickness of 64 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 1.85 wt%.

[0216] [Comparative Example 5]

[0217] The polymerized solution 3 was cast on a yellow PI film using an applicator at room temperature and dried at 140° C. for 2 minutes to obtain an initial dry film having a thickness of 78 μm and a width of 300 mm. The film was subjected to the secondary drying and stretching conditions shown in Table 1 to prepare a transparent PAI film having a residual solvent content of 2.1 wt%.

[0218] [Comparative Example 6]

[0219] An initial dry film was prepared in the same manner as in Example 4, and then secondary dried and stretched in the manner shown in the following Table 1 to prepare a transparent PAI film having a residual solvent content of 1.98 wt %.

[0220] Specifically, in Examples 1 to 8 and Comparative Examples 1 to 6, the secondary drying conditions and the stretching conditions are as shown in Table 1 below, and the production is performed by simultaneously drying and stretching in a tenter, and then, the optical properties of the transparent PAI film are specifically described as shown in Tables 2 and 3 below. Here, the numerical value (%) described as the stretching condition in Table 1 below represents the ratio (%) of the maximum film width of each region relative to the width when entering the first region.

[0221] [Table 1]

[0222]

[0223]

[0224] 100%: Based on the transverse direction (TD) when entering the first region.

[0225] [Table 2]

[0226]

[0227]

[0228] [Table 3]

[0229] <![CDATA[R in Uniformity (%)]]> Final quality assessment Example 1 5.0 qualified Example 2 3.0 qualified Example 3 4.5 qualified Example 4 7.0 qualified Example 5 4.0 qualified Example 6 8.5 qualified Example 7 6.5 qualified Example 8 9.5 qualified Comparative Example 1 6.3 Failure Comparative Example 2 12.5 Failure Comparative Example 3 10.6 Failure Comparative Example 4 11.2 Failure Comparative Example 5 12.5 Failure Comparative Example 6 13.8 Failure

[0230] As shown in Table 2 above, it was confirmed that the polyamideimide film according to the present invention satisfies Relationship 1 and Relationship 2, and satisfies Relationship 1 to Relationship 4, thereby providing a high-quality display having a uniform birefringence value and retardation as shown in Table 3. Specifically, it was confirmed that the polyamideimide film has high clarity and is an excellent optical material that can prevent image distortion. In addition, this can be achieved by adjusting the drying temperature of each region in the stretching process.

[0231] Therefore, the polyamideimide film according to the present invention has an in-plane birefringence value much lower than that in the thickness direction, thereby having a uniform value over the entire area of ​​the film, and is an excellent optical material that can provide high-quality display.

[0232] The polyamideimide film according to the present invention can achieve a uniform birefringence value over the entire area of ​​the film while having a low birefringence value.

[0233] In addition, the polyamide-imide film according to the present invention can provide excellent display quality even under a high-temperature and high-humidity environment.

[0234] In addition, the optical material including the polyamideimide film according to the present invention has significantly reduced changes in optical properties caused by external force, thereby having high reliability.

[0235] In addition, a display device including the polyamideimide film according to the present invention may provide high image quality with a wide viewing angle.

[0236] In addition, a display device including the polyamideimide film according to the present invention has excellent screen contrast and uniform display image quality.

[0237] In the above, although the present invention is described by specific matter and specific exemplary embodiments, they are provided only to help the overall understanding of the present invention. Therefore, the present invention is not limited to the exemplary embodiments, and those skilled in the art to which the present invention belongs can make various modifications and changes according to the description.

[0238] Therefore, the spirit of the present invention should not be limited to the above-described exemplary embodiments, and the appended claims and all modifications equivalent or equivalent to the claims are within the scope and spirit of the present invention.

Claims

1. A polyamide-imide film having a photoelastic coefficient in the transverse direction of less than 2.0×10 -8 m 2 / N, and has an in-plane birefringence value Δn in The wavelength dispersion that satisfies the following equations 1 and 2: [Equation 1] 1.0<Δn in (450nm) / Δn in (550nm)<1.3 [Equation 2] 0.7<Δn in (650nm) / Δn in (550nm)<1.0 in Δn in (450nm), Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm, 550nm and 650nm, respectively. in, The polyamide-imide film is dried in a first drying process, and is stretched and dried simultaneously in three or more stretching zones in a second drying process, The polyamideimide film is derived from a monomer mixture including dianhydride, diamine and aromatic diacid chloride, wherein the diamine is 2,2'-bis(trifluoromethyl)benzidine, the dianhydride is 4,4'-hexafluoroisopropylidene diphthalic anhydride or 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and the aromatic diacid chloride is terephthaloyl chloride or isophthaloyl chloride.

2. The polyamide-imide film according to claim 1, wherein The polyamide-imide film has a birefringence value Δn in the thickness direction. th The wavelength dispersion that satisfies the following equations 3 and 4: [Equation 3] 0.9<Δn th (450nm) / Δn th (550nm)<1.3 [Equation 4] 0.7<Δn th (650nm) / Δn th (550nm)<0.9 in Δn th (450nm), Δn th (550nm) and Δn th (650 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 450 nm, 550 nm, and 650 nm, respectively.

3. The polyamide-imide film according to claim 2, wherein The polyamide-imide film satisfies the following relational formula 5: [Equation 5] 1.0<Δn th (450nm) / Δn th (550nm)<1.25 in Δn th (450nm) and Δn th (550 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 450 nm and 550 nm, respectively.

4. The polyamide-imide film according to claim 2, wherein The polyamide-imide film satisfies the following relational formula 6: [Equation 6] 0.72<Δn th (650nm) / Δn th (550nm)<0.87 in Δn th (550nm) and Δn th (650 nm) are birefringence values ​​in the thickness direction of the film measured at wavelengths of 550 nm and 650 nm, respectively.

5. The polyamide-imide film according to claim 1, wherein The in-plane birefringence value at a wavelength of 550 nm is 0.1 times or less the birefringence value in the thickness direction at a wavelength of 550 nm.

6. The polyamide-imide film according to claim 1, wherein The uniformity of the in-plane retardation value within the plane relative to an area of ​​15 cm×15 cm of the film is 10% or less.

7. The polyamide-imide film according to claim 1, wherein The lateral photoelastic coefficient is 1.5×10 - 8 m 2 / N or less.

8. The polyamide-imide film according to claim 1, wherein The polyamide-imide film satisfies the following relation 7: [Equation 7] 1.1<Δn in (450nm) / Δn in (550nm)<1.25 in Δn in (450nm) and Δn in (550nm) are the in-plane birefringence values ​​measured at wavelengths of 450nm and 550nm, respectively.

9. The polyamide-imide film according to claim 1, wherein The polyamide-imide film satisfies the following relational formula 8: [Equation 8] 0.72<Δn in (650nm) / Δn in (550nm)<0.9 in Δn in (550nm) and Δn in (650nm) are the in-plane birefringence values ​​measured at wavelengths of 550nm and 650nm, respectively.

10. The polyamideimide film of claim 1, wherein the second drying process is performed in three or more zones, the drying temperature of the first zone is 140 to 210°C, the drying temperature of the second zone is 150 to 250°C, and the drying temperature of the third zone is 180 to 300°C.

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