Polymer film

Abstract

The present invention relates to a polymer film, the above polymer film comprising: a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin, a haze value (HZ0) before autoclave treatment of 3% or less, and a ΔHZ 24 value of 500% or less represented by Formula 1a.

Description

[0001] This patent application is a divisional application of the patent application with the application date of June 29, 2020, the application number of 202010611676.X, the publication number of CN112225924A, and the invention name of "Polymer film". The invention patent application enters China through the Paris Convention route, and its priority dates are the application date of KR20190078286A of the KR Patent Office on June 28, 2019, the application date of KR20190146804A on November 15, 2019, the application date of KR20190164668A on December 11, 2019, and the application date of KR20200035707A on March 24, 2020. TECHNICAL FIELD

[0002] The present application relates to a polymer film having excellent static bending properties, folding properties, and transparency, and maintaining excellent optical and mechanical properties even at high temperature and high humidity. BACKGROUND

[0003] Polyimide resins such as poly(amide-imide) (PAI) have excellent friction resistance, heat resistance, and chemical resistance, and thus are applied to basic electric insulating materials, paints, adhesives, extrusion resins, heat-resistant paints, heat-resistant boards, heat-resistant adhesives, heat-resistant fibers, and heat-resistant films, etc.

[0004] Polyimides are widely used in various fields. Polyimides are made in powder form and used as coating agents for metals or electromagnetic wires, etc., and can be used in mixture with other additives according to their use. In addition, polyimides are used together with fluorine-containing polymers in decorative and anticorrosive paints, and play a role in bonding the fluorine-containing polymers to metal substrates. In addition, polyimides are also used to coat kitchen utensils, used for gas separation membranes due to their heat and chemical resistance, and also used in filtration devices for filtering pollutants such as carbon dioxide, hydrogen sulfide, and impurities in natural gas wells.

[0005] Currently, polyimides are made into films, and thus polyimide films having low prices and excellent optical, mechanical, and thermal properties are developed. The polyimide films as described above can be applied to display materials such as organic light-emitting diodes (OLEDs) or liquid-crystal displays (LCDs), and when having a retardation property, can be applied to anti-reflection films, compensation films, or phase difference films.

[0006] The polyimide film as described above has a fragile characteristic in that the physical properties are reduced in a high-temperature and high-humidity environment, and thus has a problem in forming a barrier layer. Alternatively, to solve the problem as described above, an additive such as clay having a higher moisture resistance can be introduced, but in this case, there is a problem in that the optical properties are reduced or the compatibility is poor.

[0007] In addition, the polyimide film as described above has a problem in that the recovery is poor when in a state of being continuously bent for a long time. When the polyimide film having poor recovery is applied to a foldable display or the like, there can be a problem in that the screen is deformed.

[0008] Currently, as the development of foldable displays, flexible displays, and the like is becoming more active, there has been a constant need to research how to develop a film having excellent properties in that it can recover its original state as much as possible when flattened after being bent for a long time, and there has been a constant need to research how to develop a film that maintains excellent properties in a high-temperature and high-humidity environment and has excellent mechanical and optical properties. SUMMARY

[0009] An object of the present embodiment is to provide a polymer film having excellent static bending properties, folding properties, and transparency, and maintaining excellent optical properties and mechanical properties even in a high-temperature and high-humidity environment.

[0010] The polymer film according to an embodiment includes a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin, a haze before autoclave treatment (HZ0) of 3% or less, and ΔHZ 24 of 500% or less;

[0011] <Formula 1a>

[0012] In the above Formula 1a,

[0013] HZ0 refers to the haze of the above film before autoclave treatment,

[0014] HZ 24 refers to the haze of the above film after autoclave treatment, and the above autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling with water in an autoclave.

[0015] The polymer film according to another embodiment includes a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin, a modulus before autoclave treatment (MO0) of 5 Gpa or more, and ΔTS 24 of 15% or less;

[0016] <Formula 1b>

[0017] In the above Formula 1b,

[0018] TS0 refers to tensile strength of the above-mentioned film before autoclave treatment,

[0019] TS 24 TS refers to tensile strength of the above-mentioned film after autoclave treatment, and the above-mentioned autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling water in an autoclave.

[0020] The polymer film according to still another embodiment includes: a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin; and butyric acid.

[0021] The polymer film according to the embodiment not only has excellent static bending properties, optical properties, and mechanical properties, but also can maintain excellent optical properties and mechanical properties under severe conditions of high temperature and high humidity.

[0022] In addition, the polymer film according to the embodiment has excellent recovery when it is flattened by releasing the force applied to the film after being bent for a long time, and thus can exhibit a uniform screen state when applied to a foldable display, a flexible display, or the like.

[0023] Further, the polymer film according to the embodiment can be effectively applied to a cover window of a display device, a foldable display device, a rollable display device, or a flexible display device, since it has excellent folding properties. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a cross-sectional view schematically showing a display device according to an embodiment.

[0025] Figure 2 is a schematic view generally showing a flow of a manufacturing method of a polymer film according to an embodiment.

[0026] Figure 3 is a schematic view generally showing a process apparatus of a polymer film according to an embodiment. DETAILED DESCRIPTION

[0027] In order for those skilled in the art to easily practice the present embodiment, a detailed description will be made below with reference to the accompanying drawings. However, the present embodiment can be implemented in various forms, and is not limited only to the embodiments described in the present specification.

[0028] In the present specification, when each film, window, panel, or layer, etc. is described as being provided "on" or "under" each film, window, panel, or layer, etc., "on" and "under" include "directly" or "indirectly via other constituent elements". In addition, the basis of the upper / lower of each constituent element is described by the drawings. The size of each constituent element in the drawings can be exaggerated for the sake of description, but this does not mean that the actual application size. In addition, the same reference numerals refer to the same constituent elements throughout the specification.

[0029] In the present specification, when a component "comprises" a certain constituent element, unless otherwise stated, the component can further include other constituent elements, without excluding other constituent elements.

[0030] In the present specification, unless otherwise stated, a singular expression is interpreted to include singular or plural as interpreted in the context.

[0031] In addition, it should be understood that all numbers and expressions of amounts, ranges, or the like, describing compositions, reaction conditions, and the like, in the present specification are used as approximations, unless otherwise stated.

[0032] In the present specification, the terms first, second, and the like are used to describe various constituent elements, but the above-mentioned constituent elements should not be limited to the above-mentioned terms. The above-mentioned terms are used only to distinguish one constituent element from another.

[0033] In addition, unless otherwise stated, the term "substituted" in the present specification means that at least one substituent is substituted from deuterium, -F, -Cl, -Br, -I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, an ester group, a ketone group, a carboxyl group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alicyclic organic group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group, and the above-mentioned listed substituents can be connected to each other to form a ring.

[0034] Polymer film

[0035] The present embodiment provides a polymer film having excellent static bending properties, folding properties, optical properties, and mechanical properties, and maintaining excellent optical properties and mechanical properties even under high temperature and high humidity.

[0036] The polymer film according to an embodiment includes a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin.

[0037] The haze (HZ0) of the polymer film before autoclave treatment is 3% or less.

[0038] Specifically, the haze (HZ0) of the polymer film before autoclave treatment can be 2.5% or less, 2.0% or less, 1.5% or less, 1.0% or less, 0.8% or less, or 0.6% or less, but is not limited thereto.

[0039] The ΔHZ of the polymer film represented by the following Formula 1a 24 is 500% or less;

[0040] <Formula 1a>

[0041] In the above Formula 1a,

[0042] HZ0 refers to the haze of the film before autoclave treatment,

[0043] HZ 24 refers to the haze of the film after autoclave treatment, and the autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling water in an autoclave. After the film is disposed in the autoclave, the film is not immersed in water, but is treated by water vapor generated from the water.

[0044] Specifically, the ΔHZ of the polymer film represented by the above Formula 1a 24 may be 400% or less, 300% or less, 250% or less, or 200% or less, but is not limited thereto.

[0045] When the haze (HZ0) of the polymer film before autoclave treatment and the ΔHZ of the polymer film represented by the above Formula 1a 24 have values within the above ranges, the film has excellent durability even after being subjected to severe conditions of high temperature and high humidity, and in particular, has less deformation in optical properties, and due to the above characteristics, can be effectively applied to a front panel of a display and a display device.

[0046] The yellowness index (YI0) of the polymer film before autoclave treatment is 3 or less.

[0047] Specifically, the yellowness index (YI0) of the polymer film before autoclave treatment can be 2.8 or less, or 2.7 or less, but is not limited thereto.

[0048] The in-plane retardation (Ro0) of the polymer film before autoclave treatment is 180 nm or less.

[0049] Specifically, the in-plane retardation (Ro0) of the above polymer film before autoclave treatment can be 170 nm or less, 160 nm or less, 150 nm or less, 10 nm to 160 nm, 20 nm to 160 nm, 50 nm to 160 nm, or 80 nm to 150 nm, but is not limited thereto.

[0050] The ΔYI of the above polymer film represented by the following Formula 2a 24 is 30% or less;

[0051] <Formula 2a>

[0052] In the above Formula 2a,

[0053] YI0 refers to the yellowness index of the above film before autoclave treatment,

[0054] YI 24 refers to the yellowness index of the above film after autoclave treatment, and the above autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling water in an autoclave. After the above film is disposed in the autoclave, it is not immersed in water, but is treated by water vapor generated from the water.

[0055] Specifically, the ΔYI of the above polymer film represented by the above Formula 2a 24 may be 25% or less, 20% or less, 15% or less, 10% or less, or 5% or less, but is not limited thereto.

[0056] The ΔRo of the above polymer film represented by the following Formula 3a 24 is 8% or less;

[0057] <Formula 3a>

[0058] In the above Formula 3a,

[0059] Ro0 refers to the in-plane retardation of the above film before autoclave treatment,

[0060] Ro 24 refers to the in-plane retardation of the above film after autoclave treatment, and the above autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling water in an autoclave. After the above film is disposed in the autoclave, it is not immersed in water, but is treated by water vapor generated from the water.

[0061] Specifically, the ΔRo of the above polymer film represented by the above Formula 3a 24 may be 7% or less, 6% or less, 5% or less, or 4.8% or less, but is not limited thereto.

[0062] The haze (Hz) of the above polymer film after 24 hours of autoclaving 24 The concentration is below 3%. The above-mentioned autoclave treatment refers to filling the autoclave with water and treating it at 120°C and 1.2 atm for 24 hours. After the membrane is placed in the autoclave, it is not immersed in water, but can be treated using the steam generated by the water.

[0063] Specifically, the haze (Hz) of the polymer film after 24 hours of autoclave treatment. 24 It can be below 2.5%, below 2.0%, below 1.8%, or below 1.6%, but is not limited to these.

[0064] The yellowness index (YI) of the above polymer film after 24 hours of autoclaving 24 The value is below 3. The above-mentioned autoclave treatment refers to filling the autoclave with water and treating it at 120°C and 1.2 atm for 24 hours. After the membrane is placed in the autoclave, it will not be immersed in water, but will be treated using the steam generated by the water.

[0065] Specifically, the yellowness index (YI) of the polymer film after 24 hours of autoclave treatment. 24 It can be below 2.8 or below 2.7, but it is not limited to these.

[0066] Specifically, if the yellowness index (YI) of the above polymer film after 24 hours of autoclaving is... 24 When the above range is exceeded, the transparency will decrease in high temperature and high humidity environments, therefore the above film is not suitable for front panels or display devices. Moreover, the screen will appear blurry and dark, and to overcome this problem, more power is needed to maintain a brighter display.

[0067] The in-plane phase difference (Ro) of the above polymer film after 24 hours of autoclaving 24 The nanometer size is below 180 nm. The aforementioned autoclave treatment refers to filling the autoclave with water and treating it at 120°C and 1.2 atm for 24 hours. After the membrane is placed in the autoclave, it is not immersed in water, but rather treated using the steam generated by the water.

[0068] Specifically, the in-plane phase difference (Ro) of the polymer film after 24 hours of autoclave treatment is... 24 The range can be below 160nm, below 150nm, below 145nm, 20nm to 160nm, 40nm to 150nm, or 60nm to 145nm, but is not limited to these ranges.

[0069] In particular, the polymer film according to this embodiment has a low ΔHZ 24 Value, ΔYI24 Value and ΔRo 24 Therefore, it can maintain excellent optical properties under harsh conditions of high temperature and high humidity, and is effectively suitable for display devices. Even when using display devices with the above-mentioned polymer film in humid or high-temperature areas, a transparent and clean screen can still be achieved.

[0070] Furthermore, since the polymer film according to this embodiment has HZ0, YI0, Ro0, and HZ within the above-described range... 24 YI 24 Ro 24 ΔHZ 24 Value, ΔYI 24 Value and ΔRo 24 Therefore, it can not only achieve obvious optical properties, but also excellent folding properties, thus making it effective for foldable or flexible display devices.

[0071] The tensile strength (TS0) of the polymer film before autoclave treatment was 20 kgf / mm. 2 above.

[0072] Specifically, the tensile strength (TS0) of the polymer film before autoclave treatment can be 20 kgf / mm². 2 Up to 35Kgf / mm 2 Alternatively, the tensile strength (TS0) of the polymer film before autoclave treatment can be 21 kgf / mm². 2 That's all, but it's not limited to that.

[0073] The elongation at break (EL0) of the polymer film before autoclaving is 15% or more.

[0074] Specifically, the elongation at break (EL0) of the polymer membrane before autoclave treatment can be 15% to 40%. Alternatively, the elongation at break (EL0) of the polymer membrane before autoclave treatment can be 17% or more, 18% or more, 19% or more, or 20% or more, but is not limited to these.

[0075] The modulus (MO0) of the polymer film before autoclave treatment is above 5 GPa.

[0076] Specifically, the modulus (MO0) of the polymer film before autoclave treatment can be from 5 GPa to 10 GPa. Alternatively, the modulus (MO0) of the polymer film before autoclave treatment can be 5.2 GPa or more, 5.3 GPa or more, or 5.5 GPa or more, but is not limited to these.

[0077] The ΔTS of the above polymer film is expressed by the following formula 1b. 24The value is below 15%.

[0078] <Formula 1b>

[0079] In this case, in Equation 1b above, TS0 refers to the tensile strength of the membrane before autoclave treatment, TS 24 This refers to the tensile strength of the membrane after autoclave treatment. Autoclave treatment involves filling the autoclave with water and treating it at 120°C and 1.2 atm for 24 hours. After the membrane is placed in the autoclave, it is not immersed in water but is treated using steam generated from the water.

[0080] Specifically, the aforementioned TS 24 20Kgf / mm 2 above.

[0081] In addition, the ΔTS of the above polymer film 24 The value can be below 12%, below 10%, or below 8.5%, but is not limited to these.

[0082] The ΔEL of the above polymer film is expressed by the following formula 2b. 24 The value is below 30%.

[0083] <Equation 2b>

[0084] At this point, in Equation 2b above, EL0 refers to the elongation at break of the membrane before autoclave treatment, EL 24 This refers to the elongation at break of the membrane after autoclave treatment. Autoclave treatment involves filling the autoclave with water and treating it at 120°C and 1.2 atm for 24 hours. After the membrane is placed in the autoclave, it is not immersed in water but is treated using steam generated from the water.

[0085] Specifically, the EL of the above polymer film 24 It is 15% or more. Or, the above EL 24 It can be 17% to 20%, but it is not limited to that.

[0086] In addition, the ΔEL of the above polymer film 24 The value can be below 28% or below 25%, but it is not limited to these values.

[0087] The ΔMO of the above polymer film is expressed by the following formula 3b. 24 The value is below 15%.

[0088] <Formula 3b>

[0089] At this time, in the above Equation 3b, MO0 refers to the modulus of the film before autoclave treatment, and MO 24 refers to the modulus of the film after autoclave treatment, and the autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling the autoclave with water. After the film is disposed in the autoclave, it is not immersed in water, but is treated by water vapor generated by the water.

[0090] Specifically, the MO 24 is 15% or more. Alternatively, the MO 24 may be 5 Gpa or more, 5.1 Gpa or more, 5.5 Gpa or more, or 6.0 Gpa or more, but is not limited thereto.

[0091] In addition, the ΔMO 24 of the polymer film has a value of 12% or less or 10% or less, but is not limited thereto.

[0092] The ΔSUM 24 of the polymer film has a value of 60% or less. At this time, the ΔSUM 24 is a value representing the sum of ΔTS 24 , ΔEL 24 , and ΔMO 24 .

[0093] Specifically, the ΔSUM 24 of the polymer film can have a value of 50% or less, 40% or less, or 35% or less, but is not limited thereto.

[0094] Since the ΔTS 24 , ΔEL 24 , ΔMO 24 , and ΔSUM 24 of the polymer film satisfy the above ranges, excellent durability of the film under high temperature and high humidity can be obtained, and there is almost no change in physical properties, thereby effectively applying the film to front panels and display devices.

[0095] The ΔTS 72 of the polymer film represented by the following Equation 4b has a value of 60% or less.

[0096] < Equation 4b >

[0097] At this time, in the above Equation 4b, TS0 refers to the tensile strength of the film before autoclave treatment, and TS 72is a tensile strength of the film after autoclave treatment. The autoclave treatment is a treatment in which the film is filled with water in an autoclave, and then treated at a temperature of 120°C and a pressure of 1.2 atm for 72 hours. After the film is disposed in the autoclave, the film is not immersed in water, but is treated by water vapor generated from the water.

[0098] Specifically, the TS 72 is 5 Kgf / mm 2 or more, 8 Kgf / mm 2 or more, or 9 Kgf / mm 2 or more.

[0099] In addition, the ΔTS 72 of the polymer film can be 50% or less, 40% or less, or 30% or less, but is not limited thereto.

[0100] The ΔEL 72 of the polymer film represented by the following Equation 5b is 50% or less.

[0101] < Equation 5b >

[0102] At this time, in the Equation 5b, EL0 is an elongation at break of the film before autoclave treatment, and EL 72 is an elongation at break of the film after autoclave treatment. The autoclave treatment is a treatment in which the film is filled with water in an autoclave, and then treated at a temperature of 120°C and a pressure of 1.2 atm for 72 hours. After the film is disposed in the autoclave, the film is not immersed in water, but is treated by water vapor generated from the water.

[0103] Specifically, the EL 72 is 8% or more, 10% or more, or 12% or more.

[0104] In addition, the ΔEL 72 of the polymer film can be 45% or less or 40% or less, but is not limited thereto.

[0105] The ΔMO 72 of the polymer film represented by the following Equation 6b is 60% or less.

[0106] < Equation 6b >

[0107] At this time, in the Equation 6b, MO0 is a modulus of the film before autoclave treatment, and MO 72is a modulus of the film after autoclave treatment. The autoclave treatment is a treatment at a temperature of 120°C and a pressure of 1.2 atm for 72 hours after filling the autoclave with water. The film is not immersed in water after being disposed in the autoclave, but is treated by water vapor generated from the water.

[0108] Specifically, the MO 72 is 2 GPa or more or 2.5 GPa or more.

[0109] In addition, the ΔMO 72 of the polymer film has a value of 50% or less, 40% or less, 30% or less, or 20% or less, but is not limited thereto.

[0110] The ΔSUM 72 of the polymer film has a value of 160% or less. At this time, the ΔSUM 72 is a value indicating the sum of ΔTS 72 , ΔEL 72 , and ΔMO 72 .

[0111] Specifically, the ΔSUM 72 of the polymer film has a value of 150% or less, 120% or less, 100% or less, or 90% or less, but is not limited thereto.

[0112] Since the ΔTS 72 , ΔEL 72 , ΔMO 72 , and ΔSUM 72 of the polymer film satisfy the above ranges, the polymer film can have excellent durability of the film at high temperature and high humidity, and almost no physical deformation, and thus can be effectively applied to a front panel and a display device.

[0113] The polymer film according to the embodiment, when being folded to have a radius of curvature of 3 mm based on a thickness of 50 μm, has a number of folds before breaking of 100,000 times or more.

[0114] The number of folds is one in which the radius of curvature of the film is 3 mm by bending and unfolding.

[0115] By satisfying the number of folds in the above range, the polymer film can be effectively applied to a foldable display device or a flexible display device.

[0116] The polymer film according to another embodiment, when being folded to have a radius of curvature of 2 mm based on a thickness of 50 μm, has a number of folds before breaking of 200,000 times or more.

[0117] The number of folds is one in which the radius of curvature of the film is 2 mm by bending and unfolding.

[0118] The content of the residual solvent in the polymer film according to the embodiments is 2500 ppm or less, or 1200 ppm or less.

[0119] For example, the content of the residual solvent described above can be 2200 ppm or less, 2000 ppm or less, 1800 ppm or less, 1500 ppm or less, 1000 ppm or less, 800 ppm or less, 500 ppm or less, 1 ppm to 1000 ppm, 1 ppm to 800 ppm, 1 ppm to 500 ppm, 5 ppm to 1000 ppm, 10 ppm to 1000 ppm, or 20 ppm to 1000 ppm, but is not limited thereto.

[0120] The residual solvent described above refers to the amount of solvent that does not evaporate and remains in the film during the film manufacturing process.

[0121] When the content of the residual solvent in the polymer film exceeds the range described above, the durability and optical properties of the film under high temperature and high humidity conditions can be reduced, and in particular, the post-processing of the film can be affected. Specifically, when the content of the residual solvent exceeds the range described above, the hydrolysis of the film can be accelerated to reduce the mechanical and optical properties. In addition, when the content of the residual solvent in the polymer film described above exceeds the range described above, the durability of the film can be reduced, thereby affecting the bending properties such as the static bending properties and folding properties described above.

[0122] The IS value of the polymer film according to the embodiments, which is represented by Equation 7 below, is 5 to 160.

[0123] < Equation 7 >

[0124] In Equation 7 described above, IM refers to the number of moles of the imide repeating unit when the total number of moles of the imide repeating unit and the amide repeating unit in the film is 100, and RS refers to the content (ppm) of the residual solvent in the film.

[0125] For example, the IS value described above can be 5 to 150, 10 to 150, 30 to 150, 50 to 150, 5 to 80, 5 to 60, or 5 to 50, but is not limited thereto.

[0126] When the IS value of the polymer film described above satisfies the range described above, a film having excellent optical properties and durability and excellent folding properties can be achieved even under harsh high temperature and high humidity conditions.

[0127] In particular, when the imide content (IM) is high or the residual solvent content (RS) in the film is high beyond the above range, the long-term durability of the film rapidly decreases. Specifically, when the imide content is too high and the amide content is relatively low, the moisture absorption of the film becomes poor, and thus it can exhibit a fragile property under high humidity conditions.

[0128] The CT value of the above polymer film is 10 or less as represented by the following Formula 8.

[0129] <Formula 8>

[0130] In the above Formula 8,

[0131] HZ0 refers to the haze of the above film before autoclave treatment,

[0132] HZ 24 refers to the haze of the above film after autoclave treatment, and the above autoclave treatment refers to treatment at a temperature of 120°C and a pressure of 1.2 atm for 24 hours after filling the autoclave with water. After the above film is disposed in the autoclave, it is not immersed in water but is treated by water vapor generated by the water.

[0133] In addition, Ro0 refers to the in-plane retardation of the above film before autoclave treatment.

[0134] The above CT can be an index reflecting the heat resistance / humidity resistance of the crystallinity. The higher the crystallinity of the above polymer film, the lower the ΔHZ 24 will generally be. That is, the higher the crystallinity of the above polymer film, the higher the heat resistance / humidity resistance of the above polymer film will be. The higher the crystallinity of the above polymer film, the higher the in-plane retardation (Ro0) will be, and thus the optical properties of the above polymer film will decrease.

[0135] The above polymer film can be manufactured with an appropriate composition and an appropriate process while having the above improved optical properties and improved heat resistance / humidity resistance. For example, the above polymer film has a relatively high amide content, reduces the content of residual solvents, adds a butyric acid additive, and is subjected to a suitable process such as a drying process and a heat treatment process. Thus, the above polymer film can decrease ΔHZ 24 while decreasing the in-plane retardation.

[0136] Thus, the above CT can be 10 or less. The above CT can be 8 or less. The above CT can be 6 or less. The above CT can be 4 or less. The above CT can be 4 or less. The above CT can be 3 or less. The above CT can be 2 or less.

[0137] Because the aforementioned polymer film has a low CT (Coefficient of Thermal Expansion), it can possess improved heat / moisture resistance, as well as improved optical properties. Therefore, the aforementioned polymer film can be effectively applied to displays. Specifically, the aforementioned polymer film can be effectively applied to mobile display devices that are susceptible to harsh external conditions such as moisture and / or heat. In particular, the aforementioned polymer film can be effectively applied to the front panel of a foldable display.

[0138] In addition to the polymer resin described above, the polymer film according to the embodiments may also include butyric acid.

[0139] The polymer membrane according to the embodiments includes a polymer resin and butyric acid. The polymer resin includes a polymer resin selected from the group consisting of polyamide resins and polyimide resins. The polymer membrane includes a polymer resin comprising a plurality of repeating imide units.

[0140] The above-mentioned butyric acid is represented by the following chemical formula T.

[0141] <Chemical Formula T>

[0142]

[0143] Specifically, the butyric acid mentioned above refers to the compound represented by the above chemical formula T, and not to the form in which a portion of the butyric acid is substituted, or the derivatives, salts, anhydrides, etc. of the butyric acid mentioned above.

[0144] The polymer membrane includes butyric acid, and the butyric acid content in the membrane is from 1 ppm to 1200 ppm based on the total weight of the polymer membrane.

[0145] Specifically, the content of butyric acid in the membrane can be 1 ppm to 1000 ppm, 5 ppm to 1000 ppm, 10 ppm to 1000 ppm, 50 ppm to 1000 ppm, 100 ppm to 1000 ppm, 500 ppm to 1000 ppm, 1 ppm to 800 ppm, 1 ppm to 700 ppm, 1 ppm to 500 ppm, 1 ppm to 300 ppm, 10 ppm to 300 ppm, 30 ppm to 300 ppm, or 50 ppm to 270 ppm, but is not limited to these.

[0146] The above content refers to the content of butyric acid that does not volatilize during the membrane production process and is retained in the final membrane.

[0147] When the butyric acid content in the polymer membrane exceeds the above range, some material may be eluted onto the membrane after autoclave treatment, which may cause the membrane haze to increase rapidly.

[0148] The above butyric acid can be residual butyric acid added as a pH adjuster in the process of manufacturing the film, or can be a byproduct generated between different reactions, but is not limited thereto. That is, the butyric acid remaining in the final film can be manufactured by various methods.

[0149] Since the above polymer film has butyric acid remaining therein, when a force applied to the film is released and the film is restored to flat after being maintained in a bent state for a long time, the film has excellent recovery and folding properties, and thus can be effectively applied to a foldable display, a flexible display, a rollable display, or the like.

[0150] When the content of butyric acid remaining in the above polymer film exceeds the above range, the static bending properties or folding properties of the film can be reduced, and the optical properties such as transmittance and yellowness can also be reduced.

[0151] The polymer film according to an embodiment, in a folded state with a curvature radius of 2 mm in a bent state, has an inside angle of 120° or more when a force applied to the film is released after being left to stand at 25℃ for 24 hours, based on a thickness of 50 μm.

[0152] Specifically, the above polymer film, in a folded state with a curvature radius of 2 mm in a bent state, has an inside angle of 125° or more, 130° or more, or 135° or more when a force applied to the film is released after being left to stand at 25℃ for 24 hours, based on a thickness of 50 μm, but is not limited thereto.

[0153] The existing film is easily affected by external pressure, and in particular, is greatly deformed after being maintained in a bent state for a long time, and thus, when applied to a display device, cannot exhibit a uniform screen state, resulting in problems such as screen deformation. Specifically, the existing film, in a folded state with a curvature radius of 2 mm in a bent state, has an inside angle of less than 120° when a force applied to the film is released after being left to stand at 25℃ for 24 hours, based on a thickness of 50 μm, specifically, the inside angle is a value of less than 115°, and has a problem of reduced resistance to static bending.

[0154] On the contrary, the polymer film according to the embodiment has an inside angle of 120° or more according to the above experiment, and thus has superior resilience to the existing film, and when the film having such properties is applied to a post-processing process (for example, when applied to a foldable display or a flexible display), problems such as screen deformation are solved.

[0155] According to another embodiment, the polymer film has a stretch ratio of 1.01 times to 1.15 times in the MD direction.

[0156] Since the stretching ratio of the polymer film according to the embodiment in the MD direction satisfies the above range, when the force applied to the film is released and flatness is recovered after being kept in a bent state for a long time, the film has less deformation and has excellent folding properties, and the film can have excellent physical impact resistance. Specifically, crystallization due to orientation occurs in the film by stretching, so that a film having excellent bending resistance can be obtained.

[0157] If the stretching ratio of the polymer film according to the embodiment in the MD direction exceeds the above range, the recovery properties of the film are sharply decreased, so that it is difficult to achieve the desired physical properties.

[0158] The above-mentioned polyamide resin is a resin including an amide repeating unit. The above-mentioned polyimide resin is a resin including an imide repeating unit.

[0159] In addition, the resin including the above-mentioned imide repeating unit and the above-mentioned amide repeating unit can be referred to as a polyamide resin, and can be referred to as a polyimide-based resin.

[0160] For example, the above-mentioned polymer resin can be a resin including a polyamide resin, a resin including a polyimide resin, or a resin including both a polyamide resin and a polyimide resin.

[0161] The polymer film according to the embodiment includes a polymer resin formed by polymerizing a diamine compound, a dianhydride compound, and an optional dicarbonyl compound.

[0162] As one example, the molar ratio of the above-mentioned dianhydride compound and the above-mentioned dicarbonyl compound is 2:98 to 50:50, 5:95 to 50:50, 10:90 to 50:50, 2:98 to 25:75, 2:98 to 15:85, 20:80 to 100:0, 25:75 to 100:0, 30:70 to 100:0, 40:60 to 100:0, or 50:50 to 100:0.

[0163] When the molar ratio of the above-mentioned dianhydride compound and the above-mentioned dicarbonyl compound is within the above-mentioned range, a film having excellent optical properties and high durability in a high-temperature high-humidity state can be obtained. In addition, when the force applied to the film is released and flatness is recovered after being kept in a bent state for a long time, a transparent film having excellent recovery properties and excellent folding properties can be obtained.

[0164] As another example, the above-mentioned dianhydride compound can consist of one or two or more, and the above-mentioned dicarbonyl compound can consist of zero, one, or two or more.

[0165] The polymer resin includes imide repeating units derived from polymerization of a diamine compound and a dianhydride compound, and amide repeating units derived from polymerization of the diamine compound and a dicarbonyl compound.

[0166] At this time, the polymer resin can include imide repeating units and amide repeating units in a molar ratio of 2:98 to 50:50, 5:95 to 50:50, 10:90 to 50:50, 2:98 to 25:75, 2:98 to 15:85, 20:80:100:0, 25:75:100:0, 30:70:100:0, 40:60:100:0, or 50:50:100:0, but is not limited thereto.

[0167] The diamine compound is a compound that forms a copolymer with the dianhydride compound through an imide bond and with the dicarbonyl compound through an amide bond.

[0168] Although the diamine compound is not specifically limited, it can be, for example, an aromatic diamine compound having an aromatic structure. For example, the diamine compound can be a compound of Chemical Formula 1 below.

[0169] <Chemical Formula 1>

[0170] H2N-(E) e -NH2

[0171] In Chemical Formula 1 above,

[0172] E can be selected from a substituted or unsubstituted divalent C6-C 30 an aliphatic cyclic group, a substituted or unsubstituted divalent C4-C 30 an aliphatic heterocyclic group, a substituted or unsubstituted divalent C6-C 30 an aromatic cyclic group, a substituted or unsubstituted divalent C4-C 30 an aromatic heterocyclic group, a substituted or unsubstituted C1-C 30 an alkylene group, a substituted or unsubstituted C2-C 30 an alkenylene group, a substituted or unsubstituted C2-C 30 an alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-.

[0173] e is an integer selected from 1 to 5, and when e is 2 or more, E can be the same as or different from each other.

[0174] (E) of Chemical Formula 1 above e may be selected from combinations represented by Chemical Formulas 1-1a to 1-14a below, but is not limited thereto.

[0175]

[0176] Specifically, (E) of the above-described Chemical Formula 1 e may be selected from, but not limited to, a group represented by Chemical Formulas 1-1b to 1-13b below.

[0177]

[0178] More specifically, (E) of the above-described Chemical Formula 1 e may be a group represented by the above-described Chemical Formula 1-6b or a group represented by the above-described Chemical Formula 1-9b.

[0179] As one embodiment, the above-described diamine compound can include a compound having a fluorine-containing substituent or a compound having an ether group (-O-).

[0180] The above-described diamine compound can consist of a compound having a fluorine-containing substituent. At this time, the fluorine-containing substituent can be a fluorinated hydrocarbon group, specifically, can be a trifluoromethyl group, but not limited thereto.

[0181] As another embodiment, the above-described diamine compound can use one of diamine compounds. That is, the above-described diamine compound can consist of a single component.

[0182] For example, the above-described diamine compound can include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) having the following structure, but not limited thereto.

[0183]

[0184] In addition, the above-described diamine compound can include TFMB and 4,4'-oxydianiline (ODA), but not limited thereto.

[0185] Since the above-described dianhydride compound has a low birefringence value, it is a compound that can contribute to improving optical properties such as transmittance of a film including a polymer resin. The above-described polymer resin refers to a polymer including an imide repeating unit.

[0186] Although the above-described dianhydride compound is not specifically limited, for example, it can be an aromatic dianhydride compound including an aromatic structure or an alicyclic dianhydride compound including an alicyclic structure.

[0187] For example, the above-described aromatic dianhydride compound can be a compound of the following Chemical Formula 2.

[0188] <Chemical Formula 2>

[0189]

[0190] In the above Chemical Formula 2, G can be selected from the group consisting of a substituted or unsubstituted tetravalent C6-C 30 an aliphatic cyclic group, a substituted or unsubstituted tetravalent C4-C 30 an aliphatic heterocyclic group, a substituted or unsubstituted tetravalent C6-C 30 an aromatic cyclic group, a substituted or unsubstituted tetravalent C4-C 30 an aromatic heterocyclic group, the above aliphatic cyclic group, the above aliphatic heterocyclic group, the above aromatic cyclic group, or the above aromatic heterocyclic group, alone or bonded to each other to form a condensed ring, or connected by a connecting group selected from the group consisting of a substituted or unsubstituted C1-C 30 an alkylene group, a substituted or unsubstituted C2-C 30 an alkenylene group, a substituted or unsubstituted C2-C 30 an alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-.

[0191] G of the above Chemical Formula 2 can be selected from the group represented by the following Chemical Formulas 2-1a to 2-9a, but is not limited thereto.

[0192]

[0193] For example, G of the above Chemical Formula 2 can be the group represented by the above Chemical Formula 2-2a, the group represented by the above Chemical Formula 2-8a, or the group represented by the above Chemical Formula 2-9a.

[0194] In addition, the above alicyclic dianhydride compound can include a cyclobutane structure. Specifically, the above alicyclic dianhydride compound can be CBDA (cyclobutane-1, 2, 3, 4-tetracarboxylic dianhydride), but is not limited thereto.

[0195] As another embodiment, the above dianhydride compound can include a compound having a fluorine-containing substituent, a compound having a biphenyl group, a compound having a keto group, or a compound having a cyclobutane group.

[0196] The above dianhydride compound can consist of a compound having a fluorine-containing substituent. At this time, the fluorine-containing substituent can be a fluorinated hydrocarbon group, specifically a trifluoromethyl group, but is not limited thereto.

[0197] As another embodiment, the above dianhydride compound can consist of one single component or two or more mixed components.

[0198] For example, the above-mentioned dianhydride compound can include 2,2'-Bis-(3,4-Dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) having the following structure, but is not limited thereto.

[0199]

[0200] The above-mentioned dianhydride compound and the above-mentioned diamine compound can be polymerized to produce a polyamic acid.

[0201] Subsequently, the above-mentioned polyamic acid can be converted into a polyimide through a dehydration reaction, and the above-mentioned polyimide includes an imide repeating unit.

[0202] The above-mentioned polyimide can form a repeating unit represented by the following Chemical Formula A.

[0203] <Chemical Formula A>

[0204]

[0205] In Chemical Formula A, the descriptions of E, G, and e are as described above.

[0206] For example, the above-mentioned polyimide can include a repeating unit represented by the following Chemical Formula A-1, but is not limited thereto.

[0207] <Chemical Formula A-1>

[0208]

[0209] n of the above-mentioned Chemical Formula A-1 is an integer of 1 to 400.

[0210] Although the above-mentioned dicarbonyl compound is not specifically limited, for example, it can be a compound of the following Chemical Formula 3.

[0211] <Chemical Formula 3>

[0212]

[0213] In the above-mentioned Chemical Formula 3,

[0214] J can be selected from a substituted or unsubstituted divalent C6-C 30 an aliphatic cyclic group, a substituted or unsubstituted divalent C4-C 30 an aliphatic heterocyclic group, a substituted or unsubstituted divalent C6-C 30 an aromatic cyclic group, a substituted or unsubstituted divalent C4-C 30 an aromatic heterocyclic group, a substituted or unsubstituted C1-C 30alkylene, substituted or unsubstituted C2-C 30 alkenylene, substituted or unsubstituted C2-C 30 alkynylene, -0-, -S-, -C(=0)-, -CH(OH)-, -S(=0)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-.

[0215] j is an integer selected from 1 to 5, and when j is 2 or more, J can be the same as or different from each other.

[0216] X is a halogen atom. Specifically, X can be F, Cl, Br, I, or the like. More specifically, X can be Cl, but is not limited thereto.

[0217] (J) of the above Chemical Formula 3 j may be selected from the group represented by the following Chemical Formulas 3-1a to 3-14a, but is not limited thereto.

[0218]

[0219] Specifically, (J) of the above Chemical Formula 3 j may be selected from the group represented by the following Chemical Formulas 3-1b to 3-8b, but is not limited thereto.

[0220]

[0221] More specifically, (J) of the above Chemical Formula 3 j may be the group represented by the above Chemical Formula 3-1b, the group represented by the above Chemical Formula 3-2b, the group represented by the above Chemical Formula 3-3b, or the group represented by the above Chemical Formula 3-8b.

[0222] As one embodiment, the above dicarbonyl compound can be used by mixing one or at least two kinds of dicarbonyl compounds different from each other. When the above dicarbonyl compound is used by at least two kinds, at least two kinds selected from (J) of the above Chemical Formula 3 j represented by the above Chemical Formulas 3-1b to 3-8b.

[0223] As another embodiment, the above dicarbonyl compound can be an aromatic dicarbonyl compound including an aromatic structure.

[0224] For example, the above dicarbonyl compound can include a first dicarbonyl compound and / or a second dicarbonyl compound.

[0225] The above first dicarbonyl compound and the above second dicarbonyl compound can each be an aromatic dicarbonyl compound.

[0226] The above first dicarbonyl compound and the above second dicarbonyl compound can be different compounds from each other.

[0227] For example, the above-described first dicarbonyl compound and the above-described second dicarbonyl compound can be different aromatic dicarbonyl compounds from each other, but are not limited thereto.

[0228] When the above-described first dicarbonyl compound and the above-described second dicarbonyl compound are each an aromatic dicarbonyl compound, since it includes a benzene ring, it is helpful to improve mechanical properties such as surface hardness and tensile strength of a film including the manufactured polyamide-imide resin.

[0229] The above-described dicarbonyl compound is terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof, but is not limited thereto.

[0230]

[0231] For example, the above-described first dicarbonyl compound can include BPDC, and the above-described second dicarbonyl compound can include TPC, but is not limited thereto.

[0232] When BPDC is used as the above-described first dicarbonyl compound, TPC is used as the above-described second dicarbonyl compound, and they are appropriately combined and used, a film including the manufactured polyamide-imide resin can have high oxidation resistance.

[0233] In addition, the above-described first dicarbonyl compound can include IPC, and the above-described second dicarbonyl compound can include TPC, but is not limited thereto.

[0234] When IPC is used as the above-described first dicarbonyl compound, TPC is used as the above-described second dicarbonyl compound, and they are appropriately combined and used, a film including the manufactured polyamide-imide resin can not only have high oxidation resistance but also reduce costs to have economic efficiency.

[0235] The above-described diamine compound and the above-described dicarbonyl compound can be polymerized to form a repeating unit represented by the following Chemical Formula B.

[0236] <Chemical Formula B>

[0237]

[0238] In the above-described Chemical Formula B, descriptions of E, J, e, and j are as described above.

[0239] For example, the above-described diamine compound and the above-described dicarbonyl compound can be polymerized to form amide repeat units represented by Chemical Formula B-1 and B-2.

[0240] Alternatively, the above-described diamine compound and the above-described dicarbonyl compound can be polymerized to form amide repeat units represented by Chemical Formula B-2 and B-3.

[0241] <Chemical Formula B-1>

[0242]

[0243] x of the above-described Chemical Formula B-1 is an integer of 1 to 400.

[0244] <Chemical Formula B-2>

[0245]

[0246] y of the above-described Chemical Formula B-2 is an integer of 1 to 400.

[0247] <Chemical Formula B-3>

[0248]

[0249] y of the above-described Chemical Formula B-3 is an integer of 1 to 400.

[0250] According to an embodiment, the above-described polymer resin can include repeat units represented by Chemical Formula A below, and can optionally include repeat units represented by Chemical Formula B below.

[0251] <Chemical Formula A>

[0252]

[0253] <Chemical Formula B>

[0254]

[0255] In the above-described Chemical Formulas A and B,

[0256] E and J are each independently selected from the group consisting of a substituted or unsubstituted divalent C6-C 30 aliphatic cyclic group, a substituted or unsubstituted divalent C4-C 30 aliphatic heterocyclic group, a substituted or unsubstituted divalent C6-C 30 aromatic cyclic group, a substituted or unsubstituted divalent C4-C 30 aromatic heterocyclic group, a substituted or unsubstituted C1-C 30 alkylene group, a substituted or unsubstituted C2-C 30 alkenylene group, a substituted or unsubstituted C2-C 30alkylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-,

[0257] e and j are each independently an integer of 1 to 5,

[0258] when e is 2 or more, 2 or more of E are the same or different,

[0259] when j is 2 or more, 2 or more of J are the same or different,

[0260] G can be a tetravalent C6-C 30 aliphatic cyclic group, a tetravalent C4-C 30 aliphatic heterocyclic group, a tetravalent C6-C 30 aromatic cyclic group, a tetravalent C4-C 30 aromatic heterocyclic group, the above aliphatic cyclic group, the above aliphatic heterocyclic group, the above aromatic cyclic group, or the above aromatic heterocyclic group exist individually, or are bonded to each other to form a condensed ring, or are connected by a linking group selected from the group consisting of a substituted or unsubstituted C1-C 30 alkylene, a substituted or unsubstituted C2-C 30 alkenylene, a substituted or unsubstituted C2-C 30 alkynylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-.

[0261] In the above polymer resin, the molar ratio of the repeating unit represented by the above Chemical Formula A to the repeating unit represented by the above Chemical Formula B can be 2:98 to 50:50, 5:95 to 50:50, 10:90 to 50:50, 2:98 to 25:75, 2:98 to 15:85, 20:80 to 100:0, 25:75 to 100:0, 30:70 to 100:0, 40:60 to 100:0, or 50:50 to 100:0, but is not limited thereto.

[0262] When the molar ratio of the repeating unit represented by Chemical Formula A to the repeating unit represented by Chemical Formula B is within the above range, the polymer film has excellent folding properties and optical and mechanical properties under high temperature and high humidity.

[0263] Specifically, the CONH structure present in the repeating unit represented by Chemical Formula B has a high affinity with the OH group, thereby exhibiting excellent moisture absorption to attract moisture, having a sliding property, and making it possible to obtain a film in which the mechanical strength and optical properties are hardly reduced under high temperature and high humidity.

[0264] According to another embodiment, the above-described polymer film can further include a filler.

[0265] The above-described filler can be at least one selected from the group consisting of barium sulfate, silicon dioxide, and calcium carbonate. The above-described polymer film can improve roughness and coiling properties by including the filler, and improve driving scratch resistance during a film manufacturing process.

[0266] In addition, the above-described filler can have a particle diameter of 0.01 μm to 1.0 μm, 0.01 μm or more to less than 1.0 μm. For example, the above-described filler can have a particle diameter of 0.05 μm to 0.9 μm, 0.1 μm to 0.8 μm, 0.1 μm to 0.5 μm, or 0.1 μm to 0.3 μm, but is not limited thereto.

[0267] The above-described polymer film can include the filler in an amount of 0.01 wt% to 3.5 wt%, 0.01 wt% to 3 wt%, or 0.01 wt% to 2.5 wt%, based on the total weight of the polymer film.

[0268] The above-described polymer film can have a transmittance of 80% or more. For example, the above-described transmittance can be 85% or more, 88% or more, 89% or more, 80% to 99%, 85% to 99%, or 88% to 99%.

[0269] The above-described polymer film can have a yellow index of 5 or less. For example, the yellow index can be 4 or less or 3.5 or less, but is not limited thereto.

[0270] The above-described polymer film can have a haze of 2% or less. Specifically, the above-described haze can be 1.8% or less, 1.5% or less, 1% or less, 0.8% or less, or 0.5% or less, but is not limited thereto.

[0271] The above-described polymer film can have a modulus of 4.0 GPa or more, 4.2 GPa or more, 4.5 GPa or more, or 5.0 GPa or more. Specifically, the above-described modulus can be 5.5 GPa or more, 6.0 GPa or more, 6.2 GPa or more, 6.0 GPa to 8.0 GPa, but is not limited thereto.

[0272] The above-described polymer film can have a compression strength of 0.3 kgf / μm or more. Specifically, the above-described compression strength can be 0.4 kgf / μm or more, 0.45 kgf / μm or more, or 0.48 kgf / μm or more, but is not limited thereto.

[0273] When the above polymer film is punched at a speed of 10 mm / min using a 2.5 mm spherical tip in a UTM compression mode, the maximum diameter (mm) of the perforation including a crack is 65 mm or less. Specifically, the maximum diameter of the above perforation can be 60 mm or less, 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.

[0274] The above polymer film has a surface hardness of HB or more. Specifically, the above surface hardness can be H or more or 2H or more, but is not limited thereto.

[0275] The above polymer film has a tensile strength of 14 kgf / mm 2 or more. Specifically, the above tensile strength can be 15 kgf / mm 2 or more, 16 kgf / mm 2 or more, 18 kgf / mm 2 or more, 20 kgf / mm 2 or more, 21 kgf / mm 2 or more, or 22 kgf / mm 2 or more, but is not limited thereto.

[0276] The above polymer film has an elongation of 13% or more. Specifically, the above elongation can be 15% or more, 16% or more, 17% or more, or 17.5% or more, but is not limited thereto.

[0277] The polymer film according to an embodiment has excellent optical properties such as low haze and low yellowness index (YI), and excellent mechanical properties such as high modulus, compression strength, maximum diameter of perforation, surface hardness, tensile strength, elongation, and can ensure excellent folding performance and excellent optical properties and mechanical properties under high temperature and high humidity. Accordingly, it is possible to achieve stable mechanical properties and optical properties for a long time in a device requiring flexibility in modulus, elongation, tensile properties, elastic recovery, and bending resistance.

[0278] The properties of the above polymer film are based on a thickness of 40 μm to 60 μm, or a thickness of 70 μm to 90 μm. For example, the properties of the above polymer film are based on a thickness of 50 μm or a thickness of 80 μm.

[0279] The features of the composition and properties of the above polymer film can be combined with each other.

[0280] In addition, the above properties of the above polymer film, together with the chemical and physical properties of the components constituting the above polymer film, are the result of the comprehensive process conditions of each step in the manufacturing method of the above polymer film described later.

[0281] Front panel for display

[0282] A front panel for display according to an embodiment includes a polymer film and a functional layer.

[0283] The polymer film includes a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin.

[0284] The polymer film according to an embodiment has a haze (HZ0) of 3% or less before autoclave treatment, and a value of ΔHZ represented by Equation 1a below is 500% or less. 24

[0285] The polymer film according to another embodiment has a modulus (MO0) of 5 GPa or more before autoclave treatment, and a value of ΔTS represented by Equation 1b below is 15% or less. 24

[0286] The polymer film according to yet another embodiment includes a polymer resin and butyric acid.

[0287] The polymer film is specifically described as above.

[0288] The front panel can be effectively applied to a display device.

[0289] The polymer film has excellent folding properties, and can maintain excellent optical and mechanical properties under severe conditions of high temperature and high humidity. In particular, the functional layer, in addition to the polymer film, has excellent folding properties, and the front panel can be effectively applied to a foldable display device or a flexible display device.

[0290] Display device

[0291] The display device according to an embodiment includes a display unit, and a front panel disposed on the display unit, wherein the front panel includes a polymer film.

[0292] In addition, the polymer film includes a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin.

[0293] The polymer film according to an embodiment has a haze (HZ0) of 3% or less before autoclave treatment, and a value of ΔHZ represented by Equation 1a below is 500% or less. 24

[0294] The polymer film according to another embodiment has a modulus (MO0) of 5 GPa or more before autoclave treatment, and a value of ΔTS represented by Equation 1b below is 15% or less. 24

[0295] ​​​​The polymer film according to still another embodiment includes a polymer resin and butyric acid.

[0296] The polymer film is described in detail as described above.

[0297] Figure 1 A cross-sectional view of a display device according to an embodiment.

[0298] Specifically, Figure 1 A display device is exemplified, which includes a display unit (400) and a front panel (300) including a polymer film (100) having a first surface (101) and a second surface (102) and a functional layer (200) on the display unit (400). An adhesive layer (500) is further included between the display unit (400) and the front panel (300).

[0299] The display unit (400) can display an image and can have a flexible characteristic.

[0300] The display unit (400) can be a display panel for displaying an image, for example, a liquid crystal display panel or an organic electroluminescent display panel. The organic electroluminescent display panel can include a front polarizing plate and an organic EL panel.

[0301] The front polarizing plate can be disposed on a front surface of the organic EL panel. Specifically, the front polarizing plate can be adhered to a surface of the organic EL panel on which an image is displayed.

[0302] The organic EL panel displays an image by self-emission in units of pixels. The organic EL panel can include an organic EL substrate and a driving substrate. The organic EL substrate can include a plurality of organic electroluminescent units each corresponding to a pixel. Specifically, each can include a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. The driving substrate can be drivingly coupled to the organic EL substrate. That is, the driving substrate is coupled to apply a driving signal such as a driving current to the organic EL substrate, so that the organic EL substrate can be driven by applying a current to each of the organic electroluminescent units.

[0303] In addition, an adhesive layer (500) can be included between the display unit (400) and the front panel (300). The adhesive layer can be an optically transparent adhesive layer, but is not particularly limited thereto.

[0304] The front panel (300) is disposed on the display unit (400). The front panel is the outermost layer of the display device according to an embodiment, thereby protecting the display unit.

[0305] The front panel (300) can include a polymer film and a functional layer. The functional layer can be at least one selected from a hard coat layer, a reflectance reduction layer, an anti-fouling layer, and an anti-glare layer. The functional layer can be coated on at least one surface of the polymer film.

[0306] Method of manufacturing a polymer film

[0307] A method of manufacturing a polymer film is provided as one embodiment.

[0308] A method of manufacturing a polymer film according to one embodiment includes a step of manufacturing a polymer solution including a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin in an organic solvent; a step of moving the polymer solution into a tank; a step of extruding and casting the polymer solution in the tank and drying to manufacture a gel sheet; and a step of heat-treating the gel sheet, the heat-treatment of the gel sheet being performed to 1200 ppm or less of residual solvent.

[0309] A method of manufacturing a polymer film according to another embodiment includes a step of polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent in a polymerization device to manufacture a polymer solution including a polymer resin; a step of moving the polymer solution into a tank; a step of extruding and casting the polymer solution in the tank and drying to manufacture a gel sheet; and a step of heat-treating the gel sheet, the heat-treatment of the gel sheet being performed in the range of 80°C to 500°C for 5 minutes to 180 minutes.

[0310] A method of manufacturing a polymer film according to yet another embodiment includes a step of manufacturing a polymer solution including a polymer resin on an organic solvent; a step of moving the polymer solution into a tank; a step of extruding and casting the polymer solution in the tank and drying to manufacture a gel sheet; and a step of moving the gel sheet and heat-treating to manufacture a cured film.

[0311] Reference Figure 2 As shown in the drawing, a method of manufacturing a polymer film according to one embodiment includes a step (S100) of simultaneously or sequentially mixing a diamine compound, a dianhydride compound, and an optional dicarbonyl compound in an organic solvent in a polymerization device and reacting the mixture to manufacture a polymer solution; a step (S200) of moving the polymer solution into a tank; a step (S300) of purging using an inert gas; a step (S400) of extruding and casting the polymer solution in the tank and drying to manufacture a gel sheet; a step (S500) of moving the gel sheet and heat-treating to manufacture a cured film; a step (S600) of moving the cured film and cooling; and a step (S700) of winding the cooled cured film using a winder.

[0312] The above polymer film is a film in which a polymer resin selected from the group consisting of a polyamide resin and a polyimide resin is a main component.

[0313] In the above method of manufacturing a polymer film, a polymer solution of the above polymer resin is manufactured by simultaneously or sequentially mixing a diamine compound and a dianhydride compound, or a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent in a polymerization apparatus, and reacting the mixture (S100).

[0314] As one embodiment, the above polymer solution can be manufactured by simultaneously injecting a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent and reacting them.

[0315] As another embodiment, the step of manufacturing the above polymer solution can include a step of mixing a diamine compound and a dianhydride compound in a solvent and reacting them to manufacture a polyamic acid solution, and a step of dehydrating the above polyamic acid solution to manufacture a polyimide (PI) solution.

[0316] As still another embodiment, the step of manufacturing the above polymer solution can include a step of initially mixing the above diamine compound and the above dianhydride compound in a solvent and reacting them to manufacture a polyamic acid (PAA) solution, and a step of secondarily mixing a dicarbonyl compound in the above polyamic acid (PAA) solution and reacting it to form amide bonds and imide bonds. The above polyamic acid solution is a solution including polyamic acid.

[0317] Alternatively, the step of manufacturing the above polymer solution can include a step of initially mixing the above diamine compound and the above dianhydride compound in a solvent and reacting them to manufacture a polyamic acid solution, a step of dehydrating the above polyamic acid solution to manufacture a polyimide (PI) solution, and a step of secondarily mixing the above dicarbonyl compound in the above polyimide (PI) solution and reacting it to further form amide bonds. The above polyimide solution is a solution including a polymer having an imide repeating unit.

[0318] As still another embodiment, the step of manufacturing the above polymer solution can include a step of initially mixing the above diamine compound and the above dicarbonyl compound in a solvent and reacting them to manufacture a polyamide (PA) solution, and a step of secondarily mixing the above dianhydride compound in the above polyamide (PA) solution and reacting it to further form imide bonds. The above polyamide solution is a solution including a polymer having an amide repeating unit.

[0319] The polymer solution thus manufactured can be a solution containing a polymer including at least one selected from a polyamide acid (PAA) repeating unit, a polyamide (PA) repeating unit, and a polyimide (PI) repeating unit.

[0320] For example, the polymer included in the polymer solution can include an imide repeating unit derived from polymerization of the diamine compound and the dianhydride compound.

[0321] Alternatively, the polymer included in the polymer solution can include an imide repeating unit derived from polymerization of the diamine compound and the dianhydride compound, and an amide repeating unit derived from polymerization of the diamine compound and the dicarbonyl compound.

[0322] The solid content included in the polymer solution can be 10 to 30 wt%, or 15 to 25 wt%, but is not limited thereto.

[0323] When the solid content included in the polymer solution is within the above range, a polymer film can be effectively manufactured in an extrusion and casting process. In addition, the manufactured polymer film maintains a clean appearance and transparency, and ensures a specific range of optical slip index, maximum static friction coefficient, and kinetic friction coefficient, thereby having excellent anti-blocking properties. Further, it has excellent mechanical properties and optical properties such as low yellowness index, which are hardly degraded even under high temperature and high humidity, and hardly deformed even at a certain load level for a long time, having excellent folding properties.

[0324] As an embodiment, the step of manufacturing the polymer solution can further include a step of adding a catalyst.

[0325] At this time, the catalyst can include at least one selected from betamethyloxy, acetic anhydride, isoquinoline (IQ), and pyridine compounds, but is not limited thereto.

[0326] The catalyst can be added in an amount of 0.01 to 0.4 molar equivalents based on 1 mole of the polyamide acid, but is not limited thereto.

[0327] Alternatively, the catalyst can be added in an amount of 0.01 to 0.3 wt% based on the total weight of the polymer solution. Specifically, the catalyst can be added in an amount of 0.01 to 0.2 wt%, 0.01 to 0.15 wt%, 0.01 to 0.1 wt%, or 0.02 to 0.1 wt% based on the total weight of the polymer solution, but is not limited thereto.

[0328] When the above catalyst is added, the reaction speed can be increased, and the chemical bonding between or within the repeating unit structures can be improved. In addition, by using the above catalyst, a film having a low yellowness index can be manufactured.

[0329] As an embodiment, the step of manufacturing the above polymer solution can further include a step of adding a dehydrating agent.

[0330] At this time, the above dehydrating agent can be acetic anhydride, but is not limited thereto.

[0331] The above dehydrating agent can be added in an amount of 0.01 to 10 wt%, 0.05 to 5 wt%, or 0.05 to 3 wt% based on the total weight of the above polymer solution, but is not limited thereto.

[0332] When the dehydrating agent is added, the effect of obtaining a film having a low yellowness index and haze can be achieved.

[0333] As another embodiment, the step of manufacturing the above polymer solution can further include a step of adjusting the viscosity of the above polymer solution.

[0334] Specifically, the step of manufacturing the above polymer solution includes: (a) a step of simultaneously or sequentially mixing a diamine compound, a dianhydride compound, and an optional dicarbonyl compound in an organic solvent and allowing them to react to manufacture a first polymer solution; (b) a step of measuring the viscosity of the above first polymer solution to evaluate whether a target viscosity is achieved; and (c) a step of, when the viscosity of the above first polymer solution does not achieve the target viscosity, further adding the above dianhydride compound or dicarbonyl compound to manufacture a second polymer solution having the target viscosity.

[0335] The above target viscosity can be 100,000 to 500,000 cps at room temperature. Specifically, the above target viscosity can be 100,000 to 400,000 cps, 100,000 to 350,000 cps, 100,000 to 300,000 cps, 150,000 to 300,000 cps, or 150,000 to 250,000 cps at room temperature, but is not limited thereto.

[0336] In the step of manufacturing the above first polymer solution and the step of manufacturing the above second polymer solution, the polymer solutions manufactured have different viscosities. For example, the viscosity of the above second polymer solution is higher than that of the above first polymer solution.

[0337] The stirring speed when manufacturing the above first polymer solution is different from that when manufacturing the above second polymer solution. For example, the stirring speed when manufacturing the above first polymer solution is faster than that when manufacturing the above second polymer solution.

[0338] As still another embodiment, the step of preparing the above-described polymer solution can further include a step of adjusting the pH of the above-described polymer solution. In this step, the pH of the above-described polymer solution can be adjusted to 4 to 7, for example, can be adjusted to 4.5 to 7, or 4.5 to less than 7, but is not limited thereto.

[0339] The pH of the polymer solution can be adjusted by adding a pH adjuster, although the above-described pH adjuster is not particularly limited, but for example, can include amine compounds such as alkoxy amines, alkyl amines, or alkanol amines, or carboxylic acid compounds such as acetic acid, butyric acid, etc.

[0340] By adjusting the pH of the above-described polymer solution to the above-described range, it is possible to prevent damage to equipment in subsequent processes, prevent defects in the film prepared from the above-described polymer solution, and obtain the desired optical properties and mechanical properties in terms of yellowness index and modulus. In addition, it is possible to improve the recovery and folding properties of the film.

[0341] The amount of the above-described pH adjuster added can be 0.01 to 0.7% by weight, 0.01 to 0.5% by weight, or 0.02 to 0.4% by weight, based on the total weight of the above-described polymer solution, but is not limited thereto.

[0342] Alternatively, the amount of the above-described pH adjuster added can be 0.1 to 10 mol% based on the total number of moles of monomers in the above-described polymer solution.

[0343] Specifically, when a catalyst is added to prepare the polymer solution, chemical imidization or thermal imidization is performed by the catalyst, and by using an appropriate amount, it is possible to prepare a film that is transparent and has a low yellowness index. On the other hand, it is possible that by-products are generated or some properties are reduced during the catalysis, in which case, the reduction in properties can be improved by using a pH adjuster. For example, as the pH adjuster, butyric acid can be used, and the above-described butyric acid can be partially retained in the final film, and when the force applied to the film is released and returned to a flat state after a long time in a bent state, it is possible to obtain a transparent film having excellent recovery and folding properties.

[0344] In many cases, Cl by-products generated from chloride end groups derived from monomers used to prepare the above-described polymer resin or HCl generated during the film preparation process, etc. reduce reactivity, and thus cases in which polymerization in a low molecular weight form occurs are most common. However, by using butyric acid as the above-described pH adjuster, the reactivity of the catalyst is effectively controlled to reduce the amount of polymerization in a low molecular weight form and promote polymerization in a high molecular weight form.

[0345] In addition, low-molecular polymers remaining in the polymer are eluted after autoclave treatment (i.e., after treatment under severe conditions of high temperature and high humidity), resulting in a problem of rapid reduction in optical properties. In addition, existing polymer films have a problem of formation of a barrier layer under an environment of high temperature and high humidity, and an additive such as clay having strong moisture resistance is introduced to solve the problem, which results in a problem of reduction in optical properties or reduction in compatibility.

[0346] On the other hand, as the polymer film according to the embodiment, by adding butyric acid during polymerization, the above-described problems can be solved, and a polymer film having almost no reduction in optical properties and mechanical properties and excellent folding properties can be obtained even after treatment under severe conditions of high temperature and high humidity.

[0347] As another embodiment, the step of manufacturing the above-described polymer solution can further include a step of purging with an inert gas. By the inert gas purging step, moisture can be removed, and impurities can be reduced, the reaction yield can be improved, and a final film having excellent surface appearance and mechanical properties, etc. can be obtained.

[0348] The above-described inert gas can 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 above-described inert gas can be nitrogen.

[0349] The above-described mole ratio of the above-described dianhydride compound and the above-described dicarbonyl compound used to manufacture the above-described polymer solution can be 2:98 to 1:85. For example, the above-described mole ratio can be 3:97 to 15:85, 5:95 to 15:85, 7:93 to 15:85, 2:98 to 25:75, 2:98 to 15:85, 20:80 to 100:0, 25:75 to 100:0, 30:70 to 100:0, 40:60 to 100:0, or 50:50 to 100:0, but is not limited thereto.

[0350] When the above-described dianhydride compound and the above-described dicarbonyl compound are used in the above-described mole ratio, the mechanical properties and optical properties of the polymer film manufactured from the polymer solution are advantageous to achieve a target level.

[0351] The above-described diamine compound, dianhydride compound, and dicarbonyl compound are described above.

[0352] As an embodiment, the organic solvent can be at least one selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), m-cresol, tetrahydrofuran (THF), and chloroform. The organic solvent used in the polymer solution can be dimethylacetamide (DMAc), but is not limited thereto.

[0353] Next, after the step of manufacturing the polymer solution, the polymer solution is moved to a tank (S200).

[0354] Figure 3 A manufacturing process apparatus of the polymer film according to an embodiment is schematically illustrated. Referring to FIG. 1, a polymer solution is manufactured in a polymerization apparatus (10), and the polymer solution thus manufactured is moved to a tank (20) and stored. Figure 3 As illustrated in FIG. 1, the polymer solution is manufactured in the polymerization apparatus (10), and the polymer solution thus manufactured is moved to the tank (20) and stored.

[0355] At this time, after the polymer solution is manufactured, the step of moving the polymer solution to the tank is performed without other processes. Specifically, the polymer solution manufactured in the polymerization apparatus is directly moved to the tank and stored without other precipitation and re-dissolution processes for removing impurities. In the related art, in order to remove impurities such as hydrochloric acid (HCl) generated in the process of manufacturing the polymer solution, the manufactured polymer solution is purified to remove impurities through an additional process, and a process of re-dissolving the same in a solvent is performed. However, in this case, in the process of removing impurities, loss of an active ingredient is increased, and as a result, a problem of a decrease in yield can occur.

[0356] Accordingly, according to the manufacturing method of an embodiment, by minimizing the content of impurities during the process of manufacturing the polymer solution, or even if a small amount of impurities is present, by appropriately controlling the same in a subsequent process, without decreasing the physical properties of a final film, the advantage is that a film can be manufactured without an additional precipitation or re-dissolution process.

[0357] The tank (20) is a place for storing the polymer solution before film formation, and the inside temperature thereof can be -20 to 20°C.

[0358] Specifically, the inside temperature can be -20 to 10°C, -20 to 5°C, -20 to 0°C, or 0 to 10°C, but is not limited thereto.

[0359] By adjusting the internal temperature of the tank (20) to the above range, the above polymer solution can be prevented from deteriorating during storage, and the moisture content can be reduced to prevent defects of the film thus produced.

[0360] The above method of manufacturing a polymer film can further include a step of vacuum degassing the above polymer solution moved into the tank (20).

[0361] After the internal pressure of the tank is reduced to 0.1 bar to 0.7 bar, vacuum degassing can be performed for 30 minutes to 3 hours. By performing vacuum degassing under these conditions, the gas bubbles inside the above polymer solution can be reduced, as a result of which surface defects of the film thus produced can be prevented, and excellent optical properties such as haze can be obtained.

[0362] In addition, the above method of manufacturing a polymer film can further include a step (S300) of purging the above polymer solution moved into the above tank (20) with an inert gas.

[0363] Specifically, the above purging is performed by purging the internal pressure of the above tank to 1 to 2 atmospheres using an inert gas. By performing nitrogen purging under these conditions, the moisture in the above polymer solution is removed, and impurities are reduced to improve the reaction yield, and excellent optical properties such as haze and mechanical properties can be obtained.

[0364] The above inert gas can 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 above inert gas can be nitrogen.

[0365] The above step of vacuum degassing and the above step of purging the above tank with an inert gas are performed as independent processes.

[0366] For example, the above step of vacuum degassing can be performed, and then the above step of purging the above tank with an inert gas can be performed, but is not limited thereto.

[0367] By performing the above step of vacuum degassing and / or the above step of purging the above tank with an inert gas, the properties of the surface of the polymer film thus produced can be improved.

[0368] Thereafter, a step of storing the above polymer solution in the tank (20) for 1 hour to 360 hours can be further included. At this time, the internal temperature of the tank can be maintained at -20°C to 20°C.

[0369] The above method of manufacturing a polymer film includes a step (S400) of extruding and casting the polymer solution in the above tank (20) and drying to manufacture a gel sheet.

[0370] The above polymer solution can be cast in a casting roll or a casting belt or the like.

[0371] Referring to Figure 3 As illustrated, according to an embodiment, the above polymer solution is coated onto a casting belt (30) as a casting body, moved and dried to be manufactured into a sheet in a gel form.

[0372] When the above polymer solution is injected onto the belt (30), the injection speed thereof can be 300 g / min to 700 g / min. When the injection speed of the above polymer solution satisfies the above range, the above gel sheet can be uniformly formed in an appropriate thickness.

[0373] In addition, the casting thickness of the above polymer solution can be 200 μm to 700 μm. When the casting thickness of the above polymer solution satisfies the above thickness range, when it is dried and heat-treated to manufacture a final film, an appropriate thickness and thickness uniformity can be ensured.

[0374] As described above, the above polymer solution can be 100,000 cps to 500,000 cps at normal temperature, for example, 100,000 cps to 400,000 cps, 100,000 cps to 350,000 cps, 150,000 cps to 350,000 cps, or 150,000 cps to 250,000 cps. By satisfying the above viscosity range, the above polymer solution can be cast onto the belt in a uniform thickness without defects.

[0375] After the above polymer solution is cast, it is dried at a temperature of 60°C to 150°C for 5 minutes to 60 minutes to manufacture a gel sheet. Specifically, it can be dried in hot air of 60°C to 120°C for 10 minutes to 50 minutes. For example, the above drying can be performed in hot air of 100°C for 30 minutes.

[0376] During the above drying, the solvent of the above polymer solution is partially or entirely volatilized to manufacture a gel sheet.

[0377] During the above drying, the moving speed of the gel sheet on the casting body can be 0.1 m / min to 15 m / min, for example, 0.5 m / min to 10 m / min, but is not limited thereto.

[0378] The above method of manufacturing a polymer film includes a step (S500) of moving the above gel sheet and heat-treating to manufacture a cured film.

[0379] Referring to Figure 3 As illustrated, the heat-treatment of the above gel sheet can be performed by passing through a heat-curing device (40).

[0380] The heat treatment of the above-described gel sheet is performed in a range of 80°C to 500°C for 5 minutes to 180 minutes. Specifically, the heat treatment of the above-described gel sheet can be performed in a range of 80°C to 500°C while heating at a rate of 2°C / min to 80°C / min for 5 minutes to 150 minutes. More specifically, the heat treatment of the gel sheet can be performed by heating in a temperature range of 80°C to 300°C at a rate of 2°C / min to 80°C / min.

[0381] According to another embodiment, the above-described gel sheet can be subjected to hot air treatment.

[0382] When the heat treatment is performed by hot air, heat can be uniformly provided. If the heat is not uniformly distributed, satisfactory mechanical properties cannot be obtained. Particularly satisfactory surface roughness cannot be obtained, in which case the surface tension can sharply increase or sharply decrease.

[0383] For example, the above-described gel sheet can be subjected to hot air treatment in a temperature range of 200°C to 320°C for 5 minutes to 60 minutes. More specifically, the above-described gel sheet can be subjected to hot air treatment in a temperature range of 250°C to 290°C for 25 minutes to 35 minutes.

[0384] According to still another embodiment, the heat treatment of the above-described gel sheet can be performed in two or more steps.

[0385] According to another embodiment, the above-described heat treatment can be performed such that the content of residual solvent contained in the film is 1200 ppm or less or 1000 ppm or less.

[0386] The above-described heat treatment is performed in a second heat treatment step after performing a first heat treatment step. At this time, when the content of organic solvent contained in the gel sheet exceeds 1000 ppm or 1200 ppm after performing the above-described second heat treatment step, a third heat treatment step can be further performed.

[0387] Specifically, the above-described heat treatment includes a first heat treatment step performed in a range of 60°C to 120°C for 5 minutes to 30 minutes, and a second heat treatment step performed in a range of 150°C to 350°C for 30 minutes to 120 minutes.

[0388] For example, the above-described third heat treatment step can be performed in a range of 200°C to 350°C such that the content of organic solvent contained in the gel sheet is 1200 ppm or less or 1000 ppm or less.

[0389] In addition, in the above-described heat treatment step, the above-described gel sheet can be stretched by 1.01 times to 1.05 times in the MD direction. Between the above-described first heat treatment step and the above-described second heat treatment step, the above-described gel sheet can be stretched by 1.01 times to 1.05 times in the MD direction.

[0390] In the above heat treatment step, the above gel sheet can be stretched by 1.01 to 1.05 times in the TD direction. In the above second heat treatment step, the above gel sheet can be stretched by 1.01 to 1.05 times in the MD direction.

[0391] The above gel sheet can be stretched by 1.01 to 1.05 times in the above MD direction and the above TD direction at the same time. The above gel sheet can be stretched by 1.01 to 1.05 times in the above MD direction, and can be sequentially stretched by 1.01 to 1.05 times in the above TD direction.

[0392] In this condition, heat treatment is performed to cure the above gel sheet to have appropriate surface hardness and modulus, and the cured film prepared has excellent folding properties and optical properties, and has excellent optical and mechanical properties even at high temperature and high humidity, and can ensure excellent properties in recovery when releasing the force applied to the film after maintaining the bent state for a long time.

[0393] The method of manufacturing the above polymer film includes a step of moving the above cured film and performing cooling (S600).

[0394] Referring to Figure 3 As illustrated in the above, the above cured film after passing through the heat curing device (40) can be performed using a separate cooling chamber (not shown), or can be performed without a separate cooling chamber by generating an appropriate temperature atmosphere.

[0395] The step of moving the above cured film and performing cooling can include a first cooling step of cooling at a speed of 100℃ / min to 1000℃ / min, and a second cooling step of cooling at a speed of 40℃ / min to 400℃ / min.

[0396] At this time, specifically, after performing the above first cooling step, the above second cooling step is performed, and the cooling speed of the above first cooling step can be faster than the cooling speed of the above second cooling step.

[0397] For example, the maximum speed in the above first cooling step is faster than the maximum speed in the above second cooling step. Or, the minimum speed in the above first cooling step is faster than the minimum speed in the above second cooling step.

[0398] Since the cooling step of the above cured film is performed in multiple steps, the properties of the above cured film can be made more stable, and the optical properties and mechanical properties of the film obtained in the above curing process can be made more stable for a long time.

[0399] The above gel sheet and the above cured film have the same moving speed.

[0400] The method of manufacturing the polymer film includes a step of winding the cooled and cured film using a winder (S700).

[0401] Referring to Figure 3 As shown in FIG. 1, the winding of the cooled and cured film can use a winder (50) in the form of a roll.

[0402] At this time, in the drying, the ratio of the moving speed of the gel sheet on the belt to the moving speed of the cured film at the time of winding is 1:0.95 to 1:1.40. Specifically, the ratio of the moving speeds can be 1:0.99 to 1:1.20, 1:0.99 to 1:1.10, 1:1.0 to 1:1.05, or 1:1.01 to 1:1.05, but is not limited thereto.

[0403] When the ratio of the moving speeds exceeds the above range, the mechanical properties of the cured film can be deteriorated, and the flexibility and elasticity can be reduced.

[0404] In the method of manufacturing the polymer film, the thickness deviation (%) according to the following Formula 1 can be 3% to 30%. Specifically, the thickness deviation (%) can be 5% to 20%, but is not limited thereto.

[0405] <Formula 1> Thickness deviation (%) = {(M1-M2) / M1} X 100

[0406] In the Formula 1, M1 is the thickness of the gel sheet (μm), and M2 is the thickness of the cooled and cured film at the time of winding (μm).

[0407] The polymer film manufactured according to the manufacturing method as described above can have excellent blocking resistance, optical and mechanical properties. The polymer film can be applicable to various uses requiring flexibility, flexibility, durability, and transparency. For example, in addition to display devices, the polymer film can be applicable to solar cells, semiconductor elements, sensors, etc.

[0408] The polymer film manufactured according to the manufacturing method as described above will be described as above.

[0409] The above will be described in more detail through the following examples. However, the following examples are only for exemplifying the present application, and the scope of the examples is not limited thereto.

[0410] <Example and Evaluation Example>

[0411] Example 1a

[0412] A temperature-controllable double-jacketed 1 L glass reactor was filled with dimethylacetamide (DMAc) as an organic solvent at 20°C under a nitrogen atmosphere, and then 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) (0.2 moles) was slowly added and dissolved. Thereafter, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) (0.1 moles) was slowly added and stirred for 1 hour. Then, terephthaloyl chloride (TPC) (0.1 moles) as a dicarbonyl compound was added and stirred for 1 hour to produce a polymer solution.

[0413] Subsequently, 17 g of acetic anhydride and 4.5 g of isoquinoline as a dehydrating agent and a catalyst were added to the above polymer solution, and then stirred for 1 hour. Thereafter, butanoic acid as a pH adjuster was added and stirred for 2 hours to produce a polymer solution.

[0414] The obtained polymer solution was coated on a glass plate, dried with hot air at 100°C for 30 minutes, peeled off from the glass plate, fixed on a needle frame, and dried at 270°C for 30 minutes to obtain a polymer film having a thickness of 50 μm.

[0415] Examples 2a, 3a, Comparative Examples 1a and 2a

[0416] As shown in Table 1 below, a film was produced in the same manner as in Example 1 except that the type and content of each reactant were changed, and the like.

[0417] For the films produced in Examples 1a to 3a, Comparative Examples 1a and 2a, the physical properties described below were measured and evaluated, and the results are shown in Table 1 below.

[0418] Evaluation Example 1a: Measurement of thickness of film

[0419] A digital micrometer 547-401 by Mitutoyo Corporation was used to measure 5 points in the width direction, and the average value was calculated to measure the thickness.

[0420] Evaluation Example 2a: Measurement of residual solvent content in film

[0421] A thermogravimetric analyzer (DTG-50, manufactured by Shimadzu Corporation) was used to raise the temperature from room temperature to 300°C at a temperature increase rate of 15°C / min in a nitrogen stream, and to maintain the temperature at 300°C for 30 minutes. The total of the mass decreased in the temperature increase process from 150°C to 300°C and the process of maintaining the temperature at 300°C for 30 minutes was divided by the initial mass of the sample to obtain the content of the residual solvent in the film.

[0422] Evaluation Example 3a: Measurement of butanoic acid content in film

[0423] A TD-GC MS analysis method was used to measure the content of butyric acid in the film. Specifically, 0.02 g of the film sample was placed in a sample tube and installed, and then heated at a rate of 10°C / min from 25°C to 300°C. The gas generated by heating by temperature increase was adsorbed onto an adsorption tube (Tenax), which was instantaneously heated (desorbed), separated into components by gas chromatography. The separated components were detected on a mass spectrometer, and the types and contents of the components in the obtained chromatogram were analyzed.

[0424] The content of butyric acid was measured in ppm based on the total weight of the film, and the results are shown in Table 1 below.

[0425] Evaluation Example 4a: Measurement of Transmittance and Haze

[0426] The transmittance at 550 nm was measured using a haze meter NDH-5000W by Nippon Denshoku Industries Co., Ltd.

[0427] Evaluation Example 5a: Measurement of Yellow Index

[0428] The yellow index (YI) was measured according to the spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) using a CIE colorimeter.

[0429] Evaluation Example 6a: Measurement of In-Plane Retardation

[0430] The in-plane retardation (Ro) was measured using a retardation meter (Axoscan manufactured by Axometrics, measurement wavelength 550 nm). In addition, the refractive index, which is basic data of the retardation meter, was measured by an Abbe refractometer (NAR-4T manufactured by Atago, measurement wavelength 589.3 nm).

[0431] Evaluation Example 7a: Autoclave Treatment

[0432] A film having a width of 10 cm, a length of 2 cm, and a thickness of 50 pm was placed in an autoclave and fixed, 2 L of water was filled into the autoclave, and then the autoclave was closed and heated. At this time, the temperature of the autoclave was set to 120°C, the pressure was raised to 1.2 atm, and the treatment was performed for 24 hours. After the set time, the autoclave was automatically closed. After opening the outlet valve, the film was taken out and the corresponding physical properties were measured. The above film was not immersed in water.

[0433] Evaluation Example 8a: Measurement of Flexibility

[0434] The folding was repeated so that the radius of curvature of the film having a thickness of 50 μm was 3 mm (bending and unfolding was counted as one time). After 100,000 times of folding, when deformation of the folded surface was not confirmed by the naked eye, it was indicated by O, and after 100,000 times of folding, when deformation of the folded surface was confirmed by the naked eye, it was indicated by X. The measurement of the number of times of folding was performed using a U-shape folding device of YUASA Co.

[0435] [Table 1]

[0436]

[0437]

[0438] As can be confirmed from Table 1, since the residual solvent content in the polymer films of Examples la to 3a was 1200 ppm or less and the butyric acid content was 1200 ppm or less, excellent optical properties were maintained even when treated under severe conditions of high temperature and high humidity.

[0439] On the other hand, in the case of Comparative Examples la and 2a in which butyric acid was not detected in the film and the content of the residual solvent exceeded 1200 ppm, the low-molecular polymer remaining in the polymer after the autoclave treatment was eluted, and thus the optical properties such as haze, yellowness index, and in-plane retardation were significantly decreased.

[0440] Example 1b

[0441] Into a temperature-adjustable double-jacketed 1 L glass reactor, 585.68 g of dimethylacetamide (DMAc) as an organic solvent was charged under a nitrogen atmosphere at 20°C, and then 0.2 mol of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) was slowly added and dissolved. Thereafter, 0.2 mol of 3,3',4,4'-benzophenonetetracarboxylic acid (BTDA) was slowly added and stirred for 1 hour. Thereafter, 0.06 mol of isophthaloyl dichloride (IPC) was added and stirred for 1 hour, and 0.12 mol of terephthaloyl dichloride (TPC) was added and stirred for 1 hour, to produce a polymer solution. The obtained polymer solution was coated on a glass plate, and dried with hot air at about 80°C for 20 minutes to produce a gel sheet. The gel sheet was peeled from the glass plate and fixed to a needle frame. The gel sheet was stretched by about 1.03 times in a first direction and a second direction perpendicular to the first direction while being fixed to the needle frame. The fixed gel sheet was heat-treated at 270°C for 30 minutes to obtain a polymer film having a thickness of 50 μm.

[0442] As for the contents of TFMB, BTDA, TPC, and IPC, the number of moles of the dianhydride compound and the dicarbonyl compound was shown in Table 2, based on 100 moles of the diamine compound.

[0443] Examples 2b to 6b and Comparative Examples 1b to 3b

[0444] As shown in Table 2 below, the films were produced in the same manner as in Example 1b except that the type, content, and heat treatment time of each reactant were changed.

[0445] For the films produced in Examples 1b to 6b and Comparative Examples 1b to 3b, the physical properties described below were measured and evaluated, and the results are shown in Table 2 below.

[0446] Evaluation Example 1b: Measurement of Thickness of Film

[0447] The thickness was measured using a digital micrometer 547-401 by Mitutoyo Corporation, measuring 5 points in the width direction, and calculating the average value.

[0448] Evaluation Example 2b: Measurement of Residual Solvent in Film

[0449] After taking 0.02 g of the sample to be measured, the amount of residual solvent was measured using a Purge & Trap-GC / MSD device, purging at 30°C for 1 hour, capturing the gas at 300°C for 10 minutes, and performing quantitative and qualitative analysis of the gas to measure the amount of residual solvent.

[0450] Evaluation Example 3b: Measurement of Tensile Strength, Elongation at Break

[0451] Using an Instron universal testing machine UTM 5566A, cut 5 cm or more in the direction orthogonal to the main shrinkage direction of the sample, and cut 10 mm in the main shrinkage direction, install them on the grips at intervals of 10 cm, then extend at a rate of 12.5 mm / min at room temperature until breakage occurs to obtain a stress-strain curve. In the stress-strain curve described above, the tensile strength and elongation at break were measured.

[0452] Evaluation Example 4b: Measurement of Modulus

[0453] Using an Instron universal testing machine UTM 5566A, cut 5 cm or more in the direction orthogonal to the main shrinkage direction of the sample, and cut 10 mm in the main shrinkage direction, install them on the grips at intervals of 5 cm, then extend at a rate of 5 mm / min at room temperature until breakage occurs to obtain a stress-strain curve. In the stress-strain curve, the slope of the load with respect to the initial deformation was taken as the modulus (GPa).

[0454] Evaluation Example 5b: Autoclave Treatment

[0455] A film having a width of 10 cm, a length of 2 cm, and a thickness of 50 μm was placed in an autoclave and fixed, 2 L of water was filled into the autoclave, and then the autoclave was closed and heated. At this time, the temperature of the autoclave was set to 120°C, the pressure was raised to 1.2 atm, and the treatment was performed for 24 hours or 72 hours. After the set time, the autoclave was automatically closed. After opening the outlet valve, the film was taken out and the physical properties were measured. The above film was not immersed in water.

[0456] Evaluation Example 6b: Measurement of Transmittance

[0457] The transmittance at 550 nm was measured using a haze meter NDH-5000W of Nippon Denshoku Industries Co., Ltd.

[0458] Evaluation Example 7b: Measurement of Yellow Index

[0459] The yellow index (YI) was measured according to a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) using a CIE colorimeter.

[0460] Evaluation Example 8b: Measurement of Flexibility

[0461] The folding was repeated so that the radius of curvature of the polymer film having a thickness of 50 μm was 3 mm (bending and unfolding was counted as one time). After 100,000 times of folding, when deformation of the folded surface was not confirmed by the naked eye, O was indicated, and after 100,000 times of folding, when deformation of the folded surface was confirmed by the naked eye, X was indicated. The above number of folding times was measured using a YUASA U-shape folding device.

[0462] [Table 2]

[0463]

[0464]

[0465] From Table 2, it was confirmed that when the polymer films of Examples 1b to 6b were repeatedly folded so that the radius of curvature was 3 mm, the number of folding times before the film was broken was 100,000 times or more.

[0466] In addition, the polymer films of Examples 1b to 6b exhibited excellent yellow index and transmittance in addition to excellent folding properties.

[0467] Furthermore, the polymer films of Examples 1b to 6b exhibited high values in mechanical properties such as tensile strength, elongation at break, modulus, and the like, and maintained excellent mechanical properties even after being treated for a certain time under severe conditions of high temperature and high humidity.

[0468] Example 1c

[0469] Into a temperature-adjustable double-jacketed 1L glass reactor, dimethylacetamide (DMAc) as an organic solvent was charged under a nitrogen atmosphere at 20°C, and then 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) was slowly added and dissolved. Thereafter, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) was slowly added and stirred for 1 hour. Then, terephthaloyl chloride (TPC) was added and stirred for 2 hours.

[0470] Next, pyridine as a catalyst and acetic anhydride as a dehydrating agent were added to the above polymer solution. In addition, butanoic acid as a pH adjuster was added and stirred for 2 hours to produce a polymer solution.

[0471] The obtained polymer solution was coated on a glass plate, and then dried with hot air at 80°C for 30 minutes, and the gel sheet was dried by temperature elevation at a rate of 2°C / min in the temperature range of 80°C to 300°C to obtain a polymer film having a thickness of 50 μm.

[0472] As for the contents of the diamine compound (TFMB), the dianhydride compound (6FDA), and the dicarbonyl compound (TPC), the number of moles of each added is shown in Table 3.

[0473] In addition, as for the catalyst (pyridine) and butanoic acid, the amount of addition was converted to weight% based on the total weight of the above polymer solution, and is shown in Table 3.

[0474] Examples 2c to 5c and Comparative Examples 1c to 3c

[0475] As shown in Table 3 below, a film was produced in the same manner as in Example 1c except that the type and content of each reactant were changed, etc. In addition, Comparative Examples 1c to 3c did not undergo the step of adding butanoic acid.

[0476] For the films produced in Examples 1c to 5c and Comparative Examples 1c to 3c, the following physical properties were measured and evaluated, and the results are shown in Table 3 below.

[0477] Evaluation Example 1c: Measurement of butanoic acid content in the film

[0478] To measure the content of butyric acid in the film, a TD-GC MS analysis method was used. Specifically, 0.02 g of the film sample was placed in a sample tube and installed, and then heated from 25°C to 300°C at a rate of 10°C / min. The gas generated by heating by temperature elevation was adsorbed onto an adsorption tube (Tenax), which was instantaneously heated (desorbed), separated into components by gas chromatography. The separated components were detected on a mass spectrometer, and the types and contents of the components in the obtained chromatogram were analyzed.

[0479] The content of butyric acid was measured in ppm based on the total weight of the film, and the results are shown in Table 3 below.

[0480] Evaluation Example 2c: Strain angle evaluation (static bending test)

[0481] A polymer film having a width of 20 mm, a length of 150 mm, and a thickness of 50 μm was placed in a folded state with a curvature radius of 2 mm at 25°C for 24 hours, and after the force applied to the film was released, the internal angle of the film was measured.

[0482] Evaluation Example 3c: Folding evaluation

[0483] Folding was repeated so that the curvature radius of a polymer film having a thickness of 50 μm was 2 mm (bending and unfolding was counted as one time). The folding speed was set to 60 rpm. If no breakage occurred even if the folding was repeated more than 200,000 times, it was indicated as pass, and if breakage occurred before 200,000 times of folding, it was indicated as fail. The above-mentioned number of folding times was measured using a YUASA U-shape folding device.

[0484] Evaluation Example 4c: Measurement of transmittance

[0485] The transmittance at 550 nm was measured using a haze meter NDH-5000W from Nippon Denshoku Industries Co., Ltd.

[0486] Evaluation Example 5c: Measurement of yellow index

[0487] The yellow index (YI) was measured according to a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) using a CIE colorimeter.

[0488] Evaluation Example 4b: Measurement of modulus

[0489] Using an Instron universal testing machine UTM 5566A, cut 5 cm or more in a direction orthogonal to the main shrinkage direction of the sample, and 10 mm in the main shrinkage direction, mount it on the clip at 5 cm intervals, then extend at a rate of 5 mm / min at room temperature until breakage occurs to obtain a stress-strain curve. In the stress-strain curve, the slope of the load with respect to the initial deformation is taken as the modulus (GPa).

[0490] [Table 3]

[0491]

[0492] As can be confirmed from Table 3, the polymer films of Examples 1c to 5c exhibited excellent results in terms of recovery when returning to a flat state after maintaining a bent state for a long time due to the residual butyric acid in the films. Specifically, the polymer films of Examples 1c to 5c had a strain angle of 120° or more in the static bending test, whereas the polymer films of Comparative Examples 1c to 3c had a strain angle of 115° or less, thus showing a result of reduced resistance to static bending.

[0493] In addition, the polymer films of Examples 1c to 5c, when repeatedly folded so that the radius of curvature was 2 mm, had a folding number of more than 200,000 times before the film was broken, and thus it can be confirmed that they are effectively applicable to foldable displays, flexible displays, and rollable displays, etc. On the other hand, the polymer films of Comparative Examples 1c to 3c, when subjected to the folding test, could not exceed 200,000 times and were broken.

[0494] In addition, the polymer films of Examples 1c to 5c exhibited excellent results in terms of mechanical properties such as modulus and optical properties such as transmittance and yellowness index in addition to static bending properties and folding properties.

[0495] [Explanation of Reference Numerals]

[0496] 10: polymerization apparatus 20: tank

[0497] 30: belt 40: thermal curing device

[0498] 50: winding machine

[0499] 100: polymer film

[0500] 101: first surface 102: second surface

[0501] 200: functional layer 300: front panel

[0502] 400: display unit 500: adhesive layer

Claims

1. A polymer film for a display, characterized by, comprises: a polymer resin formed by polymerizing a diamine compound, a dianhydride compound, and an optional dicarbonyl compound, and butyric acid, the content of the butyric acid in the film is 1 ppm to 1000 ppm based on the total weight of the polymer film, the inner angle of the film is 120° or more when a force applied to the film is released after the film is folded so as to have a curvature radius of 2 mm in a folded state at 25°C for 24 hours.

2. The polymer film for a display according to claim 1, wherein the content of the butyric acid in the film is 1 ppm to 300 ppm based on the total weight of the polymer film.

3. The polymer film for a display according to claim 1, wherein the number of folds before breaking is 200,000 times or more when folded so as to have a curvature radius of 2 mm based on a thickness of 50 μm.

4. The polymer film for a display according to claim 1, wherein the polymer resin comprises repeating units represented by Chemical Formula A and Chemical Formula B at a molar ratio of 10:80 to 100:0: Chemical Formula A ， Chemical Formula B ， in Chemical Formulas A and B, E and J are each independently selected from substituted or unsubstituted divalent C6-C. 30 Aliphatic cyclic group, substituted or unsubstituted divalent C4-C 30 Aliphatic heterocyclic group, substituted or unsubstituted divalent C6-C 30 Aromatic cycloalginate, substituted or unsubstituted divalent C4-C 30 Aromatic heterocyclic groups, substituted or unsubstituted C1-C 30 Alkylene, substituted or unsubstituted C2-C 30 alkenyl, substituted or unsubstituted C2-C 30 Alkyne groups, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2-, e and j are each independently selected from an integer of 1 to 5, two or more E's can be the same or different from each other when e is 2 or more, two or more J's can be the same or different from each other when j is 2 or more, G is selected from tetravalent C6-C, whether substituted or unsubstituted. 30 Aliphatic cyclic group, substituted or unsubstituted tetravalent C4-C 30 Aliphatic heterocyclic group, substituted or unsubstituted tetravalent C6-C 30 Aromatic cyclic groups, substituted or unsubstituted tetravalent C4-C 30 Aromatic heterocyclic groups, aliphatic cyclic groups, aromatic cyclic groups, or aromatic heterocyclic groups may exist alone or be bonded together to form a fused ring, or may be formed by means of substituted or unsubstituted C1-C groups. 30 Alkylene, substituted or unsubstituted C2-C 30 alkenyl, substituted or unsubstituted C2-C 30 It is linked by the linker group among the following: -ynyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2-.

5. The polymer film for a display according to claim 1, wherein the transmittance of the polymer film is 80% or more, the yellowness index of the polymer film is 5 or less, the modulus of the polymer film is 4.0 GPa or more.

6. A front panel for a display, characterized by comprises: a polymer film and a functional layer, the polymer film comprises a polymer resin formed by polymerizing a diamine compound, a dianhydride compound, and an optional dicarbonyl compound, and butyric acid, the content of the butyric acid in the film is 1 ppm to 1000 ppm based on the total weight of the polymer film, the inner angle of the film is 120° or more when a force applied to the film is released after the film is folded so as to have a curvature radius of 2 mm in a folded state at 25°C for 24 hours.

7. A display device, characterized by comprising: comprises: a display unit; and a front panel provided on the display unit, the front panel comprises a polymer film and a functional layer, the polymer film comprises a polymer resin formed by polymerizing a diamine compound, a dianhydride compound, and an optional dicarbonyl compound, and butyric acid, the content of the butyric acid in the film is 1 ppm to 1000 ppm based on the total weight of the polymer film, the inner angle of the film is 120° or more when a force applied to the film is released after the film is folded so as to have a curvature radius of 2 mm in a folded state at 25°C for 24 hours.

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