Polyamide-imide based films, their preparation methods, and covering windows and display devices including them.

Abstract

The present invention aims to provide a polyamide-imide-based film, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film, wherein the nitrogen (N) element content in the film is 6% to 7.5% by weight, thus exhibiting uniform quality and excellent mechanical and optical properties. The present invention also discloses a method for preparing the polyamide-imide-based film, as well as a cover window and display device including the polyamide-imide-based film.

Description

Technical Field

[0001] This embodiment relates to a polyamide-imide-based film, a method for preparing the same, and a cover window and display device including the same. Background Technology

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

[0003] Polyimide has applications in various fields. For example, it is made into powder form and used as a coating for metal or magnetic wires. Depending on the application, it can be mixed with other additives. Furthermore, polyimide is used in combination with fluoropolymers as decorative and anti-corrosion paints. It also acts as a binder for fluoropolymers onto metal substrates. In addition, polyimide is used to coat kitchenware, utilizes its heat and chemical resistance as a gas separation membrane, and is used in natural gas wells to filter contaminants such as carbon dioxide, hydrogen sulfide, and other impurities.

[0004] In recent years, polyimide has been developed in the form of films, which are inexpensive and possess excellent optical, mechanical, and thermal properties. These polyimide-based films can be used in display materials such as organic light-emitting diodes (OLEDs) or liquid crystal displays (LCDs), and if delay properties are achieved, they can be used in anti-reflective films, compensation films, and delay films.

[0005] The optical properties of this polyimide-based film deteriorate when it is immersed in a solvent during post-processing or when it is exposed to light such as ultraviolet light. When applied to cover windows or display devices, there are problems with the reliability of the final product and the yield rate due to the non-uniformity of the film's mass in the lateral direction or the directional variation of its physical properties.

[0006] Therefore, there has always been a need to develop a membrane that can solve the above problems while having small quality deviations, isotropy, and excellent mechanical, optical, solvent, and light resistance properties. Summary of the Invention

[0007] Technical issues

[0008] This embodiment aims to provide a polyamide-imide-based film with uniform quality, isotropic properties, and excellent mechanical, optical, solvent, and light resistance properties, a method for preparing the same, and a cover window and display device including the same.

[0009] Solution to the problem

[0010] According to one embodiment of the polyamide-imide-based membrane, the nitrogen (N) content in the membrane is 6 to 7.5% by weight, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the membrane.

[0011] According to another embodiment, a cover window for a display device includes a polyamide-imide film and a functional layer, wherein the nitrogen (N) content in the polyamide-imide film is 6 to 7.5% by weight, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film.

[0012] According to another embodiment of the display device, it includes: a display unit; and a cover window disposed on the display unit, wherein the cover window includes a polyamide-imide film and a functional layer, and the content of nitrogen (N) in the polyamide-imide film is 6 to 7.5% by weight based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film.

[0013] A method for preparing a polyamide-imide-based film according to one embodiment includes polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide-based polymer solution; casting the solution and then drying it to prepare a gel sheet; and heat-treating the gel sheet, wherein the step of heat-treating the gel sheet includes heat-treating the gel sheet by means of a first heater, a second heater, and a third heater spaced apart in the TD direction of the gel sheet, and when the temperature of the first heater corresponding to the center of the gel sheet is T... HC When the temperatures of the second and third heaters corresponding to the two ends of the gel sheet are T, HN and T HS At that time, T HN and T HS Higher than T HC .

[0014] Beneficial effects of the present invention

[0015] Because the polyamide-imide-based film according to the embodiment has a specific level of nitrogen (N) content in the film based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film, its physical properties in the TD direction have almost no deviation, so its mass in the transverse direction is uniform, and it can have excellent mechanical properties, optical properties and solvent resistance.

[0016] Once the polyamide-imide film is prepared, it undergoes post-processing, such as laminating functional layers to impart properties like anti-fingerprint, antistatic, anti-scattering, and enhanced adhesion. During such post-processing, the non-uniformity of the film quality is exacerbated by additional heat treatment, which can increase the defect rate of the final product. Therefore, the uniformity of the polyamide-imide film itself is an important management factor.

[0017] Since the nitrogen (N) content in the polyamide-imide-based film according to one embodiment is controlled within a specific range, the quality reliability and product yield of the final product can be improved, such as the cover window or display device of a display device using the film.

[0018] Furthermore, when the membrane is exposed to solvents during post-processing, membranes with low solvent resistance may suffer from deterioration of optical and mechanical properties, such as a sharp increase in haze after immersion in solvents; therefore, membranes with excellent solvent resistance are advantageous.

[0019] Furthermore, when a film is exposed to light such as ultraviolet light, films with low lightfastness may suffer from deterioration of optical properties, such as a sharp increase in haze due to photoyellowing; therefore, films with excellent lightfastness are advantageous. Attached Figure Description

[0020] Figure 1 This is a schematic exploded view of a display device according to one embodiment;

[0021] Figure 2 It is a schematic perspective view of a display device according to one embodiment;

[0022] Figure 3 This is a schematic cross-sectional view of a display device according to one embodiment;

[0023] Figure 4 This is a schematic flowchart of a method for preparing a polyamide-imide-based film according to one embodiment;

[0024] Figure 5 This is a schematic plan view showing the step of passing a polyamide-imide-based film according to one embodiment through a heater during its preparation process;

[0025] Figure 6 This is a schematic perspective view showing the heater mounting section and gel sheet in the step of passing a polyamide-imide-based film according to one embodiment through a heater during its preparation process. Detailed Implementation

[0026] Best way to carry out the invention

[0027] The embodiments will be described in detail below with reference to the accompanying drawings to enable those skilled in the art to readily implement them. However, these embodiments can be implemented in many different ways and are not limited to those described herein.

[0028] Throughout this specification, when referring to each membrane, window, panel, layer, etc., being formed "above" or "below" another membrane, window, panel, layer, etc., it means not only that one element is directly formed above or below another element, but also that one element is indirectly formed above or below another element, with other elements situated between them. Furthermore, the term "above" or "below" for each element can be found in the accompanying drawings. For ease of description, the dimensions of the various elements in the drawings may be exaggerated and do not represent actual dimensions. Moreover, throughout this specification, the same reference numerals denote the same elements.

[0029] Throughout this specification, when a component is referred to as "comprising" an element, it should be understood that it may include other elements, but not exclude other elements, unless otherwise specifically stated.

[0030] In this specification, the singular expression is interpreted as encompassing the singular or plural as interpreted in the context, unless otherwise stated.

[0031] Furthermore, unless otherwise specified, all figures and expressions relating to the amount of components, reaction conditions, etc., used herein should be understood as being modified by the term “about”.

[0032] The terms first, second, etc., are used herein to describe various elements, and these elements should not be limited by these terms. These terms are used only to distinguish one element from another.

[0033] Furthermore, as used herein, the term "substituted" means substituted by at least one of the following substituents: deuterium, -F, -Cl, -Br, -I, hydroxyl, cyano, nitro, amino, amido, hydrazine, hydrazone, ester, ketone, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alicyclic organogroups, substituted or unsubstituted heterocyclic groups, substituted or unsubstituted aryl, and substituted or unsubstituted heteroaryl. The substituents listed above can be linked together to form a ring.

[0034] Polyamide-imide film

[0035] Since this embodiment is based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the membrane, and satisfies a specific level of nitrogen (N) element content, it can provide a polyamide-imide-based membrane with almost no deviation in physical properties in the TD direction, thus exhibiting uniform quality, isotropy, and excellent mechanical, optical, solvent resistance, and light resistance.

[0036] According to one embodiment of the polyamide-imide-based membrane, the nitrogen (N) content in the membrane is 6 to 7.5% by weight, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the membrane.

[0037] Specifically, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the membrane, the nitrogen (N) content in the polyamide-imide membrane can be 6% or higher, 6.1% or higher, 6.2% or higher, or 6.3% or higher, and 7.5% or lower, 7.4% or lower, 7.3% or lower, or 7% or lower by weight.

[0038] More specifically, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the nitrogen (N) content in the polyamide-imide membrane may be 6% to 7.3%, 6% to 7%, 6.3% to 7.5%, 6.3% to 7.3%, or 6.3% to 7% by weight, but is not limited thereto.

[0039] The content of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) can be values ​​measured using elemental analysis (EA), for example, using a model named Flash2000 (Thermo Fisher Scientific, Germany). Alternatively, the content of each element can be values ​​measured by nuclear magnetic resonance (NMR).

[0040] Based on the total weight of the membrane, the nitrogen (N) content in the polyamide-imide membrane can be from 4% to 7% by weight.

[0041] Specifically, based on the total weight of the membrane, the nitrogen (N) content in the polyamide-imide membrane may be 4% or higher, 4.2% or higher, 4.4% or higher, 4.6% or higher, 4.8% or higher, 5% or higher or 5.2% or higher, and 7% or lower, 6.8% or lower, 6.6% or lower, 6.4% or lower, 6.2% or lower, 6% or lower or 5.8% or lower.

[0042] More specifically, the nitrogen (N) content in the polyamide-imide-based membrane may be 5% to 7%, 5% to 6.2%, 5% to 6%, 5% to 5.8%, 5.2% to 7%, 5.2% to 6.2%, 5.2% to 6%, or 5.2% to 5.8% by weight, but is not limited thereto, based on the total weight of the membrane.

[0043] The nitrogen (N) content in a polyamide-imide membrane can be 8 to 12 parts by weight relative to 100 parts by weight of carbon (C) in the membrane.

[0044] Specifically, relative to 100 parts by weight of carbon (C) in the membrane, the nitrogen (N) content in the polyamide-imide membrane can be 8 parts by weight or more, 8.2 parts by weight or more, 8.4 parts by weight or more, 8.6 parts by weight or more, 8.8 parts by weight or more, or 9 parts by weight or more, as well as 12 parts by weight or less, 11.8 parts by weight or less, 11.6 parts by weight or less, 11.4 parts by weight or less, 11.2 parts by weight or less, 11 parts by weight or less, 10.8 parts by weight or less, 10.6 parts by weight or less, 10.5 parts by weight or less, 10.4 parts by weight or less, 10.2 parts by weight or less, or 10 parts by weight or less.

[0045] More specifically, the nitrogen (N) content in the polyamide-imide membrane may be 8 to 11.2 parts by weight, 8 to 11 parts by weight, 8 to 10.6 parts by weight, 8 to 10 parts by weight, 9 to 12 parts by weight, 9 to 11.2 parts by weight, 9 to 11 parts by weight, 9 to 10.6 parts by weight, or 9 to 10 parts by weight, but is not limited thereto, relative to 100 parts by weight of carbon (C) in the membrane.

[0046] Based on the total weight of the membrane, the sum of nitrogen (N) and hydrogen (H) content in the polyamide-imide membrane can be 6% to 9% by weight.

[0047] Specifically, based on the total weight of the membrane, the sum of the nitrogen (N) and hydrogen (H) elements in the polyamide-imide membrane by weight can be 6% or higher, 6.2% or higher, 6.4% or higher, 6.6% or higher, 6.8% or higher, 7% or higher, 7.2% or higher, or 7.4% or higher, as well as 9% or lower, 8.8% or lower, 8.6% or lower, 8.4% or lower, 8.2% or lower, or 8% or lower.

[0048] More specifically, the sum of nitrogen (N) and hydrogen (H) content in the polyamide-imide membrane, by weight, may be 7% to 9%, 7% to 8.8%, 7% to 8%, 7.4% to 9%, 7.4% to 8.8%, or 7.4% to 8%, but is not limited thereto, based on the total weight of the membrane.

[0049] According to one embodiment, the EC of the polyamide-imide based film... A The value can be 15.9 or greater, EC A Such as the following, etc.

[0050] As defined in Equation 1.

[0051]

[0052] In equation 1,

[0053] C w It is the carbon (C) content (by weight percentage) of the membrane based on the total weight of the membrane.

[0054] O w It is the oxygen (O) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0055] H w It is the content (by weight percentage) of hydrogen (H) in the membrane based on the total weight of the membrane, and

[0056] N w It is the nitrogen (N) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0057] Specifically, the EC of polyamide-imide based films A It can be 16 or greater, 16.2 or greater, 16.4 or greater, 16.6 or greater, or 16.8 or greater, as well as 21 or less, 20.5 or less, 20 or less, 19.5 or less, 19 or less, 18.5 or less, or 18 or less.

[0058] More specifically, the EC of polyamide-imide based films A It can be 15.9 to 20, 15.9 to 19, 15.9 to 18, 16 to 20, 16 to 19 or 16 to 18, but is not limited to these.

[0059] EC of polyamide-imide films B The value can be 15.3 or greater, EC B As defined in Equation 2 below.

[0060]

[0061] In equation 2,

[0062] C w It is the carbon (C) content (by weight percentage) of the membrane based on the total weight of the membrane.

[0063] O w It is the oxygen (O) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0064] H w It is the content (by weight percentage) of hydrogen (H) in the membrane based on the total weight of the membrane, and

[0065] N w It is the nitrogen (N) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0066] Specifically, the EC of polyamide-imide based films B It can be 15.5 or greater, 15.8 or greater, 16 or greater, 16.3 or greater, 16.5 or greater, 16.8 or greater, or 17 or greater, as well as 21 or less, 20.5 or less, 20 or less, 19.5 or less, 19 or less, 18.5 or less, or 18 or less.

[0067] More specifically, the EC of polyamide-imide based films B It can be 15.3 to 20, 15.3 to 19, 15.3 to 18, 16 to 20, 16 to 19, 16 to 18, 16.8 to 20, 16.8 to 19 or 16.8 to 18, but is not limited to these.

[0068] EC of polyamide-imide films C The value can be 14 or greater, EC C As defined in Equation 3 below.

[0069]

[0070] In equation 3,

[0071] C w It is the carbon (C) content (by weight percentage) of the membrane based on the total weight of the membrane.

[0072] O w It is the oxygen (O) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0073] H w It is the content (by weight percentage) of hydrogen (H) in the membrane based on the total weight of the membrane, and

[0074] N w It is the nitrogen (N) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0075] Specifically, the EC of polyamide-imide based films C It can be 14.3 or greater, 14.5 or greater, 14.8 or greater, 15 or greater, 15.3 or greater or 15.5 or greater, and 20 or less, 19.5 or less, 19 or less, 18.5 or less, 18 or less, 17.5 or less, 17 or less or 16.5 or less.

[0076] More specifically, the EC of polyamide-imide based films C It can be 14 to 19, 14 to 18, 14 to 17, 14 to 16.5, 15 to 19, 15 to 18, 15 to 17, 15 to 16.5, 15.3 to 19, 15.3 to 18, 15.3 to 17 or 15.3 to 16.5, but is not limited to these.

[0077] EC of polyamide-imide films D The value can be 10.5 or greater, EC D As defined in Equation 4 below.

[0078]

[0079] In equation 4,

[0080] C w It is the carbon (C) content (by weight percentage) of the membrane based on the total weight of the membrane.

[0081] O w It is the oxygen (O) content (by weight percentage) in the membrane based on the total weight of the membrane, and

[0082] N w It is the nitrogen (N) content (by weight percentage) in the membrane based on the total weight of the membrane.

[0083] Specifically, the EC of polyamide-imide based films D It can be 11 or greater, 11.3 or greater, 11.5 or greater, 11.8 or greater, 12 or greater, 12.2 or greater or 12.3 or greater, and 17 or less, 16.5 or less, 16 or less, 15.5 or less, 15 or less or 14.5 or less.

[0084] More specifically, the EC of polyamide-imide based films D It can be 10.5 to 17, 10.5 to 16, 10.5 to 15, 10.5 to 14.5, 11.5 to 17, 11.5 to 16, 11.5 to 15, 11.5 to 14.5, 12 to 17, 12 to 16, 12 to 15 or 12 to 14.5, but is not limited to these.

[0085] Based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the carbon (C) content in the polyamide-imide membrane can be 66.7% or higher by weight.

[0086] Specifically, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the membrane, the carbon (C) content in the polyamide-imide membrane can be 67% or higher, 67.4% or higher, 67.6% or higher, 68% or higher, 68.4% or higher, 68.6% or higher, or 69% or higher, and 73% or lower, 72.5% or lower, 72% or lower, 71.5% or lower, 71% or lower, 70.5% or lower, or 70% or lower.

[0087] More specifically, based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the membrane, the carbon (C) content in the polyamide-imide membrane may be 66.7% to 72%, 66.7% to 71%, 66.7% to 70%, 67% to 72%, 67% to 71%, 67% to 70%, 68.4% to 72%, 68.4% to 71%, or 68.4% to 70% by weight, but is not limited thereto.

[0088] Since the elemental content of the polyamide-imide-based film according to one embodiment meets the above range, the mass deviation in the TD direction is significantly reduced, it is isotropic, and even after immersing it in a solvent mainly used for post-treatment or exposing it to light for a period of time, the amount of haze change is below a certain level, thus giving the film excellent solvent resistance and light resistance.

[0089] Conversely, if the elemental content of the polyamide-imide-based film according to one embodiment is outside the above range, the haze changes significantly after immersion in a solvent or exposure to ultraviolet light, leading to deterioration of optical performance during post-processing. Furthermore, the quality deviation in the TD direction of the film and / or the quality deviation between the MD and TD directions as described below is large, which deteriorates the quality of the film itself and directly results in a high defect rate of the product during post-processing.

[0090] Based on the total weight of the membrane, the carbon (C) content in the polyamide-imide membrane can be 53% to 60% by weight.

[0091] Specifically, based on the total weight of the membrane, the carbon (C) content in the polyamide-imide membrane can be 53% or higher, 54% or higher, 55% or higher, 55.5% or higher, 56% or higher or 56.5% or higher, and 60% or lower, 59.5% or lower, 59% or lower or 58.5% or lower by weight.

[0092] More specifically, based on the total weight of the membrane, the carbon (C) content in the polyamide-imide membrane may be 55% to 60%, 55% to 59%, 55% to 58.5%, 56% to 60%, 56% to 59%, or 56% to 58.5% by weight, but is not limited thereto.

[0093] Based on the total weight of the membrane, the hydrogen (H) content in the polyamide-imide membrane can be from 1.5% to 3.5% by weight.

[0094] Specifically, based on the total weight of the membrane, the hydrogen (H) content in the polyamide-imide membrane may be 1.5% or higher, 1.8% or higher, or 2.1% or higher by weight, and 3.5% or lower, 3.2% or lower, 3% or lower, or 2.8% or lower by weight.

[0095] More specifically, the hydrogen (H) content in the polyamide-imide-based membrane may be, but is not limited to, 1.8% to 3.5%, 1.8% to 3%, 1.8% to 2.8%, 2.1% to 3%, or 2.1% to 2.8% by weight, based on the total weight of the membrane.

[0096] Based on the total weight of the membrane, the oxygen (O) content in the polyamide-imide membrane can be from 15% to 19% by weight.

[0097] Specifically, based on the total weight of the membrane, the oxygen (O) content in the polyamide-imide membrane may be 15% or higher, 15.5% or higher, 16% or higher, or 16.5% or higher, and 19% or lower, 18.5% or lower, or 18% or lower by weight.

[0098] More specifically, the oxygen (O) content in the polyamide-imide membrane may be, but is not limited to, 15.5% to 18.5%, 15.5% to 18%, 16% to 18.5% or 16% to 18% by weight, based on the total weight of the membrane.

[0099] Based on the total weight of the membrane, the sum of the contents of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) in the polyamide-imide membrane can be 80% to 85% by weight.

[0100] Specifically, based on the total weight of the membrane, the sum of the contents of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) in the polyamide-imide membrane by weight can be 80% or higher, 80.5% or higher, 81% or higher or 81.5% or higher, and 85% or lower, 84.5% or lower or 84% or lower.

[0101] More specifically, based on the total weight of the membrane, the sum of the contents of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) in the polyamide-imide membrane may be 81.5% to 84.5%, 81.5% to 84%, 82% to 84.5% or 82% to 84% by weight, but is not limited thereto.

[0102] The membrane comprises three regions divided along the TD direction: region N, region C, and region S. In the membrane, when the width of region N is wN, the width of region C is wC, and the width of region S is wS, the width of the membrane is equal to the sum of wN, wC, and wS.

[0103] When the transmittance is measured at six points in total, two arbitrary points are selected in each of the regions N, C and S divided in the TD direction of the polyamide-imide film, the average transmittance can be 80 or higher, and the transmittance deviation rate can be 0.5% or lower.

[0104] Specifically, the average transmittance of the polyamide-imide-based film can be 82% or higher, 84% or higher, 86% or higher, 88% or higher, or 89% or higher, and the transmittance deviation rate can be 0.4% or lower, 0.3% or lower, 0.25% or lower, 0.2% or lower, or 0.15% or lower.

[0105] When haze is measured at a total of six points, two arbitrary points are selected in each of the regions N, C, and S divided along the TD direction of the polyamide-imide film, the average haze can be 1% or lower, and the haze deviation rate can be 10% or lower.

[0106] Specifically, the average haze of the polyamide-imide film can be 0.7% or lower, 0.5% or lower, or 0.4% or lower, and the haze deviation rate can be 9.5% or lower, 9% or lower, 8.5% or lower, 8% or lower, or 7.5% or lower.

[0107] When the yellow index is measured at six points in total, two arbitrary points are selected in each of the regions N, C and S divided in the TD direction of the polyamide-imide film, the average value of the yellow index is 5 or lower, and the yellow index deviation rate is 10% or lower.

[0108] Specifically, the average yellow index of the polyamide-imide film can be 4.5 or lower, 4 or lower, or 3.5 or lower, and the deviation rate of the yellow index can be 8% or lower, 7% or lower, or 6% or lower.

[0109] When the modulus is measured at six points in total, two arbitrary points are selected in each of the regions N, C, and S divided along the TD direction of the polyamide-imide film, the average modulus is 5 GPa or greater, and the deviation rate of the modulus is 10% or less.

[0110] Specifically, the average modulus of the polyamide-imide film can be 5.5 GPa or greater or 6 GPa or greater, and the modulus deviation rate can be 7% or lower, 5% or lower, 4% or lower or 3% or lower.

[0111] If the average value and deviation rate related to the transmittance, haze, yellow index and / or modulus of the polyamide-imide film according to one embodiment are within the above range, the physical properties are excellent, and the physical properties of the film do not change much in the transverse (TD direction). Therefore, when the film is cut into the required shape or size for post-processing once it is prepared, there is almost no quality deviation, which increases the product yield and is therefore economical.

[0112] Conversely, if the average value and deviation rate related to the transmittance, haze, yellow index, and / or modulus of the polyamide-imide film according to one embodiment are outside the aforementioned ranges, it means that the quality varies slightly at different locations of the film. Therefore, when applied to a product, this can lead to numerous defects. In particular, when the film is commercially available, it may be subjected to harsh conditions such as additional heat treatment. During this process, the non-uniform quality may be further exacerbated.

[0113] In one embodiment, the R of the polyamide-imide-based film MO The value can be 95% to 105%, R MO As defined in Equation 5 below.

[0114]

[0115] In equation 5,

[0116] MO T The modulus is measured longitudinally along the TD direction of the membrane, and

[0117] MO M The modulus is measured longitudinally along the MD direction of the membrane.

[0118] Specifically, the R of polyamide-imide based films MO The value can be 95% or higher, 96% or higher, 97% or higher, or 98% or higher, and 105% or lower, 104% or lower, 103% or lower, 102% or lower, 101% or lower, or 100% or lower.

[0119] More specifically, the R of polyamide-imide based films MO The values ​​can be 95% to 103%, 95% to 100%, 97% to 105%, 97% to 103%, 97% to 100%, 98% to 105%, 98% to 103%, or 98% to 100%, but are not limited to these.

[0120] The modulus (MO) of the polyamide-imide film is measured with its TD direction as the longitudinal direction. T The modulus can be 5 GPa or greater. Specifically, the modulus can be 5.5 GPa or greater, 5.7 GPa or greater, 6 GPa or greater, or 6.2 GPa or greater. In addition, the modulus can be 10 GPa or less, but is not limited thereto.

[0121] The modulus (MO) of polyamide-imide films is measured with its MD direction as the longitudinal direction. M The modulus can be 5 GPa or greater. Specifically, the modulus can be 5.5 GPa or greater, 5.7 GPa or greater, 6 GPa or greater, or 6.2 GPa or greater. In addition, the modulus can be 10 GPa or less, but is not limited thereto.

[0122] In one embodiment, the R of the polyamide-imide-based film EL The value can be between 90% and 110%, R EL Such as the following, etc.

[0123] As defined in Equation 6.

[0124]

[0125] In equation 6,

[0126] EL T The elongation is measured longitudinally along the TD direction of the membrane, and

[0127] EL M The elongation is measured longitudinally along the MD direction of the membrane.

[0128] Specifically, the R of polyamide-imide based films EL The value can be 90% or higher, 92% or higher, 94% or higher, 96% or higher or 97% or higher, and 110% or lower, 108% or lower, 106% or lower, 104% or lower or 100% or lower.

[0129] More specifically, the R of polyamide-imide based films EL The values ​​can be 90% to 104%, 90% to 100%, 94% to 110%, 94% to 104%, 94% to 100%, 97% to 110%, 97% to 104%, or 97% to 100%, but are not limited to these.

[0130] The elongation (EL) of polyamide-imide films is measured with the TD direction as the longitudinal direction. T The elongation can be 15% to 35%. Specifically, the elongation can be 15% or higher, 17% or higher, 20% or higher, or 22% or higher, and 35% or lower, 32% or lower, 30% or lower, 27% or lower, or 25% or lower. More specifically, the elongation can be 15% to 30%, 15% to 25%, 20% to 35%, 20% to 30%, or 20% to 25%, but is not limited thereto.

[0131] The elongation (EL) of polyamide-imide films is measured longitudinally along the MD direction. M The elongation can be 15% to 35%. Specifically, the elongation can be 15% or higher, 17% or higher, 20% or higher, or 22% or higher, and 35% or lower, 32% or lower, 30% or lower, 27% or lower, or 25% or lower. More specifically, the elongation can be 15% to 30%, 15% to 25%, 20% to 35%, 20% to 30%, or 20% to 25%, but is not limited to these.

[0132] If the modulus and / or elongation of the polyamide-imide-based film according to one embodiment, and their ratio in the TD direction / MD direction, are within the aforementioned ranges, the physical properties themselves are excellent, and the variation in physical properties between the transverse (TD direction) and longitudinal (MD direction) directions is small. Thus, the film is isotropic and its quality reliability is enhanced. Furthermore, when the film is cut into the desired shape or size for post-processing once prepared, there is almost no quality deviation, which increases the product yield and is therefore economical.

[0133] Conversely, if the modulus and / or elongation of the polyamide-imide film according to one embodiment, and their ratio (TD direction / MD direction), are outside the aforementioned range, it means that the quality of the film varies in different directions. Therefore, when applied to products, this can lead to numerous defects. In particular, when the film is commercially available, it may undergo harsh conditions such as additional heat treatment during its post-processing. In this process, the non-uniform quality may be further exacerbated.

[0134] In some embodiments, the polyamide-imide-based film may have 80% or higher transmittance, 1% or lower haze, 5 or lower yellow index, 5 GPa or greater modulus in the MD direction, 5 GPa or greater modulus in the TD direction, 20% to 30% elongation in the MD direction and 20% to 30% elongation in the TD direction, but is not limited thereto.

[0135] The physical properties of polyamide-imide films, such as transmittance, haze, and yellow index, can be the average of values ​​measured at two or more arbitrary points. Specifically, they can be the average of values ​​measured at a total of six points, selected from each of regions N, C, and S of the prepared film.

[0136] In some embodiments, based on a thickness of 50 μm, the polyamide-imide film may have a thickness deviation of 3 μm or less, 2 μm or less, 1.5 μm or less, or 1.2 μm or less. Furthermore, the thickness deviation rate may be 5% or less, 4% or less, 3% or less, or 2.5% or less, but is not limited thereto.

[0137] Thickness deviation and thickness deviation rate refer to the average thickness, deviation, and deviation rate measured at six points (two arbitrary points selected in each of regions N, C, and S) divided along the TD direction of the film. In this case, since the polyamide-imide film has a uniform thickness, its optical and mechanical properties can be uniformly displayed at each point.

[0138] When a polyamide-imide film is immersed in MIBK for 5 seconds and dried at 80°C for 3 minutes, the change in haze (ΔHz) is measured. M It can be 0.2% or lower.

[0139] Specifically, the haze change (ΔHz) of the polyamide-imide film after immersion in MIBK. M The percentage can be 0.19% or lower, 0.18% or lower, 0.17% or lower, 0.15% or lower, or 0.12% or lower, but is not limited to these.

[0140] ΔHz M (%) is Hz M – The value of Hz0, where Hz0 represents the initial haze (%) of the film, Hz M The haze (%) represents the haze measured after immersing the membrane in MIBK solvent for 5 seconds and drying it at 80°C for 3 minutes.

[0141] When a polyamide-imide film is immersed in IPA for 5 seconds and dried at 80°C for 3 minutes, the change in haze (ΔHz) is measured. I It can be 0.1% or lower.

[0142] Specifically, the change in haze (ΔHz) after immersion of the polyamide-imide film in IPA. I It can be 0.08% or lower, 0.06% or lower, or 0.05% or lower, but is not limited to these.

[0143] ΔHz I (%) is HzI – The value of Hz0, where Hz0 represents the initial haze (%) of the film, Hz I The haze (%) represents the haze measured after immersing the membrane in IPA solvent for 5 seconds and drying it at 80°C for 3 minutes.

[0144] The change in haze (ΔHz) of a polyamide-imide film after immersion in MIBK for 5 seconds and drying at 80°C for 3 minutes. M The change in haze (ΔHz) after a polyamide-imide film is immersed in IPA for 5 seconds and dried at 80°C for 3 minutes. I The average value (ΔHz) AVG It can be 0.15% or lower.

[0145] Specifically, the average value of the haze change of the polyamide-imide film (ΔHz) AVG It can be 0.13% or lower, 0.11% or lower, or 0.1% or lower, but is not limited to these.

[0146] The average value of the haze change (ΔHz) AVG It can be used as a measure to determine the solvent resistance of a membrane.

[0147] When the polyamide-imide film is heated by a UV-A lamp (wavelength 340nm) at 60℃ with a frequency of 0.63W / m 2 When irradiated for 72 hours, the change in yellowness index (ΔYI) can be 5 or lower when measuring yellowness.

[0148] Specifically, after the polyamide-imide film is irradiated with ultraviolet light, the change in the yellow index (ΔYI) can be 4.8 or lower, 4.6 or lower, 4.4 or lower, 4.2 or lower, or 4 or lower, but is not limited to these values.

[0149] ΔYI is the value of YI1–YI0, where YI0 represents the initial yellow index of the polyamide-imide film, and YI1 represents the yellow index of the film when exposed to a UV-A lamp (wavelength 340nm) at 60℃ with a wavelength of 0.63W / m. 2 The yellow index was measured 72 hours after irradiation.

[0150] The change in the yellow index (ΔYI) can be used as a measure to determine the lightfastness of a film.

[0151] If the yellow index of the polyamide-imide film according to one embodiment changes within the above range, the appearance will hardly change even when the film is exposed to light such as ultraviolet light; therefore, it can directly lead to a high-quality product.

[0152] The compressive strength of the polyamide-imide-based film can be 0.4 kgf / μm or higher. Specifically, the compressive strength can be 0.45 kgf / μm or higher, or 0.46 kgf / μm or higher, but is not limited to these.

[0153] When perforating a polyamide-imide film using a 2.5-mm spherical tip at a speed of 10 mm / min in UTM compression mode, the maximum diameter (mm) of the perforation, including cracks, is 60 mm or less. Specifically, the maximum diameter of the perforation can be 5 mm to 60 mm, 10 mm to 60 mm, 15 mm to 60 mm, 20 mm to 60 mm, 25 mm to 60 mm, or 25 to 58 mm, but is not limited to these.

[0154] The surface hardness of the polyamide-imide film can be HB or higher. Specifically, the surface hardness can be H or higher, or 2H or higher, but is not limited to these.

[0155] The tensile strength of polyamide-imide based films can reach 15 kgf / mm. 2 Or higher. Specifically, the tensile strength can be 18 kgf / mm. 2 Or higher, 20 kgf / m 2 Or higher, 21 kgf / mm 2 Or higher or 22 kgf / m 2 Or higher, but not limited to this.

[0156] The elongation of the polyamide-imide-based film can be 15% or higher. Specifically, the elongation can be 16% or higher, 17% or higher, or 18% or higher, but is not limited to these.

[0157] When a polyamide-imide film with a thickness of 50 μm is folded to have a radius of curvature of 3 mm, the number of folds before breakage can be 200,000 or more.

[0158] When the membrane is folded to a radius of curvature of 3 mm and then unfolded, the number of folds is counted as 1.

[0159] Since the polyamide-imide-based film has a folding count that meets the above range, it can be advantageously applied to foldable or flexible display devices.

[0160] The surface roughness of the polyamide-imide film can be from 0.01 μm to 0.07 μm. Specifically, the surface roughness can be from 0.01 μm to 0.07 μm or from 0.01 μm to 0.06 μm, but is not limited thereto.

[0161] Since the surface roughness of the polyamide-imide film meets the above-mentioned range, it can help achieve the desired brightness or texture, and thus better apply it to display devices.

[0162] The residual solvent content in the polyamide-imide-based film can be 1,500 ppm or less. For example, the residual solvent content can be 1,200 ppm or less, 1,000 ppm or less, 800 ppm or less, 500 ppm or less, or 300 ppm or less, but is not limited to these.

[0163] Residual solvents refer to solvents that do not evaporate during the membrane production process and remain in the final membrane.

[0164] If the residual solvent content in the polyamide-imide film exceeds the above-mentioned range, the film's durability may deteriorate, potentially affecting quality deviations. In particular, it may adversely impact post-processing of the film due to its effect on mechanical strength. Furthermore, the film's optical properties, lightfastness, heat resistance, and, not to mention mechanical properties, may also deteriorate due to increased moisture absorption.

[0165] According to one embodiment, the polyamide-imide-based film comprises a polyamide-imide-based polymer, which is prepared by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

[0166] Polyamide-imide polymers are polymers containing repeating imide units and repeating amide units.

[0167] Specifically, the polyamide-imide polymer includes imide repeating units derived from the polymerization of diamine compounds and dianhydride compounds, and amide repeating units derived from the polymerization of diamine compounds and dicarbonyl compounds.

[0168] Diamine compounds are compounds that form imide bonds with dianhydride compounds and amide bonds with dicarbonyl compounds, thereby forming copolymers.

[0169] There are no particular limitations on the diamine compound; for example, it can be an aromatic diamine compound containing an aromatic structure. For instance, a diamine compound can be a compound represented by Formula 1.

[0170] [Formula 1]

[0171] H2N-(E) e -NH2

[0172] In Equation 1,

[0173] E can be either self-substituted or unsubstituted divalent C6-C 30 Aliphatic cyclic groups, substituted or unsubstituted divalent C4-C 30 Aliphatic heterocyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring groups, substituted or unsubstituted divalent C4-C 30Heteroaromatic ring groups, substituted or unsubstituted C1-C 30 Alkylene, substituted or unsubstituted C2-C 30 alkenyl, substituted or unsubstituted C2-C 30 Alynyl, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2-.

[0174] e is selected from integers from 1 to 5. When e is 2 or greater, Es can be the same or different from each other.

[0175] In Equation 1, (E) e The groups represented by formulas 1-1a to 1-14a can be selected, but are not limited thereto.

[0176]

[0177] Specifically, (E) in Formula 1 e The groups represented by formulas 1-1b to 1-13b can be selected, but are not limited to these.

[0178]

[0179] More specifically, (E) in Equation 1 e It can be a group represented by formula 1-6b above or a group represented by formula 1-9b above.

[0180] In one embodiment, the diamine compound may include a compound having a fluorinated substituent or a compound having an ether group (-O-).

[0181] Diamine compounds can consist of compounds having fluorinated substituents. In this case, the fluorinated substituent can be a fluorinated hydrocarbon group, and specifically a trifluoromethyl group. However, it is not limited to this.

[0182] In some embodiments, the diamine compound may include a single diamine compound. That is, the diamine compound may consist of a single component.

[0183] For example, diamine compounds may include, but are not limited to, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) represented by the following formula.

[0184]

[0185] Dihydride compounds have low birefringence values, which can help improve the optical properties of films, including polyamide-imide polymers, such as enhancing transmittance.

[0186] There are no particular limitations on the dianhydride compound, but it can be, for example, an aromatic dianhydride compound containing an aromatic structure. For example, an aromatic dianhydride compound can be a compound represented by the following formula 2.

[0187] [Equation 2]

[0188]

[0189] In Equation 2, G can be selected from substituted or unsubstituted tetravalent C6-C. 30 Aliphatic cyclic groups, substituted or unsubstituted tetravalent C4-C 30 Aliphatic heterocyclic groups, substituted or unsubstituted tetravalent C6-C 30 Aromatic ring groups, either substituted or unsubstituted, are tetravalent C4-C. 30 The heterocyclic ring group, wherein the aliphatic ring group, aliphatic heterocyclic group, aromatic ring group or heterocyclic ring group may exist alone, fused together to form a fused ring, or 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 The bonding groups of alkynyl, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2- are bonded together.

[0190] In Formula 2 above, G can be selected from groups represented by Formulas 2-1a to 2-9a below, but is not limited to them.

[0191]

[0192] For example, G in Formula 2 can be a group represented by Formula 2-2a, a group represented by Formula 2-8a, or a group represented by Formula 2-9a.

[0193] In one embodiment, the dianhydride compound may include a compound having a fluorinated substituent, a compound having a biphenyl group, or a compound having a ketone group.

[0194] The fluorinated substituent can be a fluorinated hydrocarbon group, and specifically a trifluoromethyl group. However, it is not limited to this.

[0195] In another embodiment, the dianhydride compound may consist of a single component or a mixture of two components.

[0196] For example, the dianhydride compound may include at least one selected from the group consisting of 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), having the following structure, but not limited thereto.

[0197]

[0198] Diamine compounds and dianhydride compounds can polymerize to form polyamic acid.

[0199] Subsequently, polyamic acid can be converted into polyimide through a dehydration reaction, and the polyimide includes repeating imide units.

[0200] Polyimide can form repeating units represented by the following formula A.

[0201] [Formula A]

[0202]

[0203] In equation A, E, G, and e are as described above.

[0204] For example, polyimide may include repeating units represented by the following formula A-1, but is not limited thereto.

[0205] [Formula A-1]

[0206]

[0207] In equation A-1, n is an integer from 1 to 400.

[0208] There are no particular restrictions on dicarbonyl compounds, but they can be, for example, compounds represented by the following formula 3.

[0209] [Formula 3]

[0210]

[0211] In Equation 3,

[0212] J can be either self-substituted or unsubstituted divalent C6-C 30 Aliphatic cyclic groups, substituted or unsubstituted divalent C4-C 30 Aliphatic heterocyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring groups, substituted or unsubstituted divalent C4-C 30 Heteroaromatic ring groups, substituted or unsubstituted C1-C 30 Alkylene, substituted or unsubstituted C2-C 30 alkenyl, substituted or unsubstituted C2-C 30 Alynyl, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2-.

[0213] j is selected from integers from 1 to 5. When j is 2 or greater, j can be the same or different from each other.

[0214] X is a halogen atom. Specifically, X can be F, Cl, Br, I, etc. More specifically, X can be Cl, but is not limited to this.

[0215] In equation 3 above, (J) j The groups represented by formulas 3-1a to 3-14a can be selected, but are not limited thereto.

[0216]

[0217] Specifically, in equation 3 above, (J) j The groups represented by formulas 3-1b to 3-8b can be selected, but are not limited to these.

[0218]

[0219] More specifically, (J) in Equation 3 j It can be a group represented by formula 3-1b, a group represented by formula 3-2b, a group represented by formula 3-3b, or a group represented by formula 3-8b.

[0220] For example, (J) in equation 3 above j It can be a group represented by formula 3-1b above, or it can be a group represented by formula 3-2b above.

[0221] In one embodiment, a single dicarbonyl compound can be used, or a mixture of at least two different dicarbonyl compounds can be used as the dicarbonyl compound. If two or more dicarbonyl compounds are used, then (J) in Formula 3 above... j At least two dicarbonyl compounds selected from the groups represented by formulas 3-1b to 3-8b above can be used as dicarbonyl compounds.

[0222] In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound containing an aromatic structure.

[0223] The dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloro (BPDC), isophthaloyl chloride (IPC), or combinations thereof, as shown in the following formula. However, it is not limited to these.

[0224]

[0225] Diamine compounds and dicarbonyl compounds can be polymerized to form repeating units represented by the following formula B.

[0226] [Formula B]

[0227]

[0228] In equation B, E, J, e, and j are as described above.

[0229] For example, diamine compounds and dicarbonyl compounds can be polymerized to form amide repeating units represented by the following formulas B-1 and B-2.

[0230] Alternatively, diamine and dicarbonyl compounds can be polymerized to form repeating amide units represented by the following formulas B-2 and B-3.

[0231] [Formula B-1]

[0232]

[0233] In equation B-1, x is an integer from 1 to 400.

[0234] [Formula B-2]

[0235]

[0236] In equation B-2, y is an integer from 1 to 400.

[0237] [Formula B-3]

[0238]

[0239] In equation B-3, y is an integer from 1 to 400.

[0240] According to one embodiment, the polyamide-imide polymer may include repeating units represented by the following formula A and repeating units represented by the following formula B:

[0241] [Formula A]

[0242]

[0243] [Formula B]

[0244]

[0245] In equations A and B,

[0246] E and J are each independently selected from substituted or unsubstituted divalent C6-C. 30 Aliphatic cyclic groups, substituted or unsubstituted divalent C4-C 30 Aliphatic heterocyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring group, substituted or unsubstituted divalent C4-C 30 Heteroaromatic ring groups, substituted or unsubstituted C1-C 30 Alkylene, substituted or unsubstituted C2-C 30 alkenyl, substituted or unsubstituted C2-C 30-Alynyl, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2-,

[0247] e and j are each independently selected from integers from 1 to 5.

[0248] When e is 2 or greater, then two or more E's are the same or different from each other.

[0249] When j is 2 or greater, then two or more J's are either the same or different from each other.

[0250] G is a tetravalent C6-C that is substituted or unsubstituted. 30 Aliphatic cyclic groups, substituted or unsubstituted tetravalent C4-C 30 Aliphatic heterocyclic groups, substituted or unsubstituted tetravalent C6-C 30 Aromatic ring groups, either substituted or unsubstituted, are tetravalent C4-C. 30 The heterocyclic ring group, wherein the aliphatic ring group, aliphatic heterocyclic group, aromatic ring group or heterocyclic ring group may exist alone, fused together to form a fused ring, or 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 The bonding groups of alkynyl, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2- and -C(CF3)2- are bonded together.

[0251] The polyamide-imide polymer may include repeating imide units and repeating amide units in a molar ratio of 2:98 to 70:30. Specifically, the molar ratio of repeating imide units to repeating amide units may be 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 5:95 to 70:30, 5:95 to 60:40, 5:95 to 55:45, 5:95 to 50:50, or 10:90 to 40:60, but is not limited thereto.

[0252] If the molar ratio of imide repeating units to amide repeating units is within the above range, combined with a unique processing method, the nitrogen (N) content in the polyamide-imide-based membrane can be effectively controlled and the membrane quality reliability can be improved.

[0253] In polyamide-imide polymers, the molar ratio of the repeating unit represented by Formula A to the repeating unit represented by Formula B can be from 2:98 to 70:30. Specifically, the molar ratio of the repeating unit represented by Formula A to the repeating unit represented by Formula B can be from 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 5:95 to 70:30, 5:95 to 60:40, 5:95 to 55:45, 5:95 to 50:50, or 10:90 to 40:60, but is not limited thereto.

[0254] In addition to the polyamide-imide polymer, the polyamide-imide film according to one embodiment may also include at least one selected from the group consisting of fillers, blue pigments and UVA absorbers.

[0255] The filler may include, for example, oxides, carbonates, or sulfates of metals or metalloids. For example, the filler may include, but is not limited to, silica, calcium carbonate, barium sulfate, etc.

[0256] The filler can be used in granular form. Furthermore, the filler surface is not specially coated and can be uniformly dispersed throughout the membrane.

[0257] Because polyamide-imide films include fillers, they can ensure a wide viewing angle without degrading optical properties, and can not only improve roughness and rollability, but also improve the effect of mitigating scratches caused by sliding during film preparation.

[0258] The filler may have a refractive index of 1.55 to 1.75. Specifically, the refractive index of the filler may be 1.60 to 1.75, 1.60 to 1.70, 1.60 to 1.68, or 1.62 to 1.65, but is not limited thereto.

[0259] If the refractive index of the filler meets the above range, the birefringence values ​​related to the x-direction refractive index (nx), y-direction refractive index (ny), and z-direction refractive index (nz) can be appropriately adjusted, and the brightness of the film at different angles can be improved.

[0260] Conversely, if the refractive index of the filler is outside the above range, the filler may be clearly visible on the film, or the haze may increase due to the filler.

[0261] The filler content can be from 100 ppm to 15,000 ppm based on the total weight of the solids content of the polyamide-imide polymer. Specifically, the filler content can be from 100 ppm to 14,500 ppm, 100 ppm to 14,200 ppm, 200 ppm to 14,500 ppm, 200 ppm to 14,200 ppm, 250 ppm to 14,100 ppm, or 300 ppm to 14,000 ppm based on the total weight of the solids content of the polyamide-imide polymer, but is not limited thereto.

[0262] If the filler content is outside the above range, the haze of the membrane will increase sharply, and the filler may aggregate on the surface of the membrane, so that a foreign body sensation can be visually observed, or it may cause problems with sliding performance or reduce the rollability during the preparation process.

[0263] In some embodiments, the blue pigment can be used in amounts from 50 ppm to 5,000 ppm based on the total weight of the polyamide-imide polymer. Preferably, the amount of blue pigment used can be 100 ppm to 5,000 ppm, 200 ppm to 5,000 ppm, 300 ppm to 5,000 ppm, 400 ppm to 5,000 ppm, 50 ppm to 3,000 ppm, 100 ppm to 3,000 ppm, 200 ppm to 3,000 ppm, 300 ppm to 3,000 ppm, or 400 ppm to 3,000 ppm based on the total weight of the polyamide-imide polymer. 00ppm, 50ppm to 2,000ppm, 100ppm to 2,000ppm, 200ppm to 2,000ppm, 300ppm to 2,000ppm, 400ppm to 2,000ppm, 50ppm to 1,000ppm, 100ppm to 1,000ppm, 200ppm to 1,000ppm, 300ppm to 1,000ppm or 400ppm to 1,000ppm, but not limited to these.

[0264] UVA absorbers may include absorbers that absorb electromagnetic waves with wavelengths of 10 to 400 nm as used in the art. For example, UVA absorbers may include benzotriazole compounds. Benzotriazole compounds may include N-phenolobenzotriazole compounds. In some embodiments, the N-phenolobenzotriazole compound may include an N-phenolobenzotriazole in which the phenolic group is substituted with an alkyl group having 1 to 10 carbon atoms, which may be substituted with two or more alkyl groups, which may be straight-chain, branched, or cyclic.

[0265] In some embodiments, the UVA absorber may be used in an amount of 0.1% to 10% by weight, based on the total weight of the polyamide-imide polymer. Preferably, the amount of UVA absorber used, by weight, may be 0.1% to 5%, 0.1% to 3%, 0.1% to 2%, 0.5% to 10%, 0.5% to 5%, 0.5% to 3%, 0.5% to 2%, 1% to 10%, 1% to 5%, 1% to 3%, or 1% to 2% relative to the total weight of the polyamide-imide polymer, but is not limited thereto.

[0266] The physical properties of the polyamide-imide-based film described above are based on a thickness of 40 μm to 80 μm. For example, the physical properties of the polyamide-imide-based film are based on a thickness of 50 μm.

[0267] The composition and performance characteristics of the polyamide-imide-based film described above can be combined with each other.

[0268] Furthermore, the content of each element in the polyamide-imide film as described above, the content of nitrogen (N) in the film, and the average and deviation rates of its transmittance, haze, yellow index, and modulus can be adjusted by combining the chemical and physical properties of each component constituting the polyamide-imide film, as well as the specific conditions of each step in the method for preparing the polyamide-imide film as described below.

[0269] For example, the composition and content of the components constituting the polyamide-imide-based film, the type and content of additives, polymerization conditions and heat treatment conditions such as the thermal gradient during film preparation can be combined to achieve the desired range of element content, average value, deviation, and deviation rate of each physical property in the lateral direction.

[0270] Cover window for display device

[0271] According to one embodiment, a cover window for a display device includes a polyamide-imide base film and a functional layer.

[0272] Based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the nitrogen (N) content in the polyamide-imide membrane is 6% to 7.5% by weight.

[0273] According to one embodiment, the EC of the polyamide-imide based film... A The value can be 15.9 or greater, EC A As defined in Equation 1 above.

[0274] Details regarding polyamide-imide-based films are as described above.

[0275] Covering windows for display devices can be advantageously applied to display devices.

[0276] Display device

[0277] A display device according to one embodiment includes a display unit; and a cover window disposed on the display unit, wherein the cover window includes a polyamide-imide base film and a functional layer.

[0278] Based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the nitrogen (N) content in the polyamide-imide membrane is 6% to 7.5% by weight.

[0279] According to one embodiment, the EC of the polyamide-imide based film... A The value can be 15.9 or greater, EC A As defined in Equation 1 above.

[0280] The details of the polyamide-imide film and the cover window are as described above.

[0281] Figure 1 This is a schematic exploded view of a display device according to one embodiment. Figure 2 It is a schematic perspective view of a display device according to one embodiment. Figure 3 This is a schematic cross-sectional view of a display device according to one embodiment.

[0282] Specifically, Figures 1 to 3 A display device is shown, which includes a display unit (400) and a cover window (300) disposed on the display unit (400), wherein the cover window includes a polyamide-imide base film (100) having a first side (101) and a second side (102) and a functional layer (200), and an adhesive layer (500) is inserted between the display unit (400) and the cover window (300).

[0283] The display unit (400) is used to display images and may have flexible characteristics.

[0284] The display unit (400) can be a display panel for displaying images. For example, it can be a liquid crystal display panel or an organic electroluminescent display panel. An organic electroluminescent display panel may include a front polarizer and an organic EL panel.

[0285] The front polarizer can be positioned on the front side of the organic EL panel. Specifically, the front polarizer can be attached to the side of the organic EL panel where the image is displayed.

[0286] Organic EL panels can display images through the self-emission of pixel units. An organic EL panel may include an organic EL substrate and a driving substrate. The organic EL substrate may include multiple organic electroluminescent units, each corresponding to a pixel. Specifically, it may include a cathode, an electron transport layer, a light-emitting layer, a hole transport layer, and an anode. The driving substrate is operatively coupled to the organic EL substrate. That is, the driving substrate can be coupled to the organic EL substrate to apply a driving signal, such as a driving current, so that the driving substrate can drive the organic EL substrate by applying current to the individual organic electroluminescent units.

[0287] Furthermore, an adhesive layer (500) can be inserted between the display unit (400) and the cover window (300). The adhesive layer can be optically transparent, but is not particularly limited thereto.

[0288] A cover window (300) may be provided on the display unit (400). The cover window is located on the outside of the display device, thereby protecting the display unit.

[0289] The cover window (300) may include a polyamide-imide base film and a functional layer. The functional layer may be at least one selected from the group consisting of a hard coating layer, an anti-reflective layer, an anti-fouling layer, and an anti-flare layer. The functional layer may be coated on at least one side of the polyamide-imide base film.

[0290] According to one embodiment, a polyamide-imide-based film can be applied to the exterior of a display device in film form without altering the display driving method, color filters within the panel, or the lamination structure, thereby providing a display device with uniform thickness, low haze, high transmittance, and high transparency. Since no significant process changes or cost increases are required, it helps reduce production costs.

[0291] According to one embodiment, the polyamide-imide-based film can have excellent optical properties in terms of high transmittance, low haze and low yellow index, and can have excellent mechanical properties such as modulus and flexibility, and can suppress changes (deterioration) in its optical and mechanical properties when exposed to ultraviolet light.

[0292] Specifically, polyamide-imide films with nitrogen (N) content within the aforementioned range exhibit minimal variation in physical properties along the TD direction, resulting in uniform quality and excellent mechanical, optical, and heat resistance. Therefore, when polyamide-imide films are applied to the cover window or display device itself, the reliability and yield of the final product can be improved.

[0293] Preparation method of polyamide-imide based film

[0294] One embodiment provides a method for preparing a polyamide-imide-based film.

[0295] A method for preparing a polyamide-imide-based film according to one embodiment includes polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a polyamide-imide-based polymer solution (S100); casting the solution and then drying it to prepare a gel sheet (S200); and heat-treating the gel sheet (S300) (see...). Figure 4 ).

[0296] The method for preparing a polyamide-imide-based membrane according to some embodiments may further include adjusting the viscosity of the polyamide-imide-based polymer solution (S110), aging the polyamide-imide-based polymer solution (S120), and / or degassing the polyamide-imide-based polymer solution (S130).

[0297] Polyamide-imide-based membranes are membranes whose main component is a polyamide-imide-based polymer. A polyamide-imide-based polymer is a resin that comprises repeating imide units and repeating amide units in a specified molar ratio as structural units.

[0298] In the preparation method of polyamide-imide-based film, a polymer solution of polyamide-imide-based polymer can be prepared by simultaneously or sequentially mixing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent in a reactor and reacting the mixture (S100).

[0299] In one embodiment, the polymer solution can be prepared by simultaneously mixing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent and reacting them.

[0300] In another embodiment, the step of preparing the polymer solution may include first mixing a diamine compound and a dianhydride compound in a solvent and reacting them to produce a polyamic acid (PAA) solution; and a second step of mixing the polyamic acid (PAA) solution with a dicarbonyl compound and reacting them to form amide and imide bonds. The polyamic acid solution is a solution comprising polyamic acid.

[0301] Alternatively, the steps for preparing the polymer solution may include first mixing and reacting a diamine compound and a dianhydride compound in a solvent to prepare a polyamic acid solution; dehydrating the polyamic acid solution to obtain a polyimide (PI) solution; and a second step, mixing and reacting the polyimide (PI) solution with a dicarbonyl compound to further form amide bonds. The polyimide solution is a solution comprising a polymer having repeating imide units.

[0302] In another embodiment, the step of preparing the polymer solution may include first mixing and reacting a diamine compound and a dicarbonyl compound in a solvent to produce a polyamide (PA) solution; and a second step of mixing and reacting the polyamide (PA) solution with a dianhydride compound to further form imide bonds. The polyamide solution is a solution comprising a polymer having repeating amide units.

[0303] The polymer solution thus prepared can be a solution comprising a polymer containing at least one selected from the group consisting of polyamic acid (PAA) repeating units, polyamide (PA) repeating units, and polyimide (PI) repeating units.

[0304] Alternatively, the polymer solution may contain polymers comprising repeating imide units derived from the polymerization of diamine and dianhydride compounds and repeating amide units derived from the polymerization of diamine and dicarbonyl compounds.

[0305] Detailed information on diamine compounds, dianhydride compounds, and dicarbonyl compounds is as described above.

[0306] The solid content in the polymer solution may be 10% to 30% by weight. Alternatively, the solid content in the polymer solution may be 15% to 25% by weight, but is not limited thereto.

[0307] If the solid content in the polymer solution is within the above range, polyamide-imide films can be effectively prepared in the extrusion casting step. Furthermore, the polyamide-imide films prepared in this way exhibit similar thermal properties in the film direction, thus possessing uniform quality and excellent mechanical, optical, and heat resistance properties.

[0308] In another embodiment, the step of preparing the polymer solution may further include introducing a catalyst.

[0309] Here, the catalyst may include, but is not limited to, at least one selected from the group consisting of β-methylpyridine, acetic anhydride, isoquinoline (IQ) and pyridyl compounds.

[0310] Based on 1 mole of polyamic acid, the catalyst can be added in amounts of 0.01 to 0.5 molar equivalents, 0.01 to 0.4 molar equivalents, or 0.01 to 0.3 molar equivalents, but is not limited thereto.

[0311] Adding a catalyst can accelerate the reaction rate and enhance the chemical bonding between or within repeating unit structures.

[0312] In one embodiment, the step of preparing the polymer solution may further include adjusting the viscosity of the polymer solution (S110). At room temperature, the viscosity of the polymer solution may be 80,000 cps to 500,000 cps, 100,000 cps to 500,000 cps, 150,000 cps to 500,000 cps, 150,000 cps to 450,000 cps, 200,000 cps to 450,000 cps, 200,000 cps to 400,000 cps, 200,000 cps to 350,000 cps, or 250,000 cps to 350,000 cps. In this case, the film-forming ability of the polyamide-imide film can be improved, thereby enhancing thickness uniformity.

[0313] Specifically, the steps for preparing the polymer solution may include simultaneously or sequentially mixing and reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent to prepare a first polymer solution; and further adding a dicarbonyl compound to prepare a second polymer solution having a target viscosity.

[0314] In the steps of preparing the first polymer solution and the second polymer solution, the polymer solutions have different viscosities. For example, the viscosity of the second polymer solution is higher than that of the first polymer solution.

[0315] In the steps of preparing the first polymer solution and the second polymer solution, the stirring speeds can be different from each other. For example, the stirring speed when preparing the first polymer solution can be faster than the stirring speed when preparing the second polymer solution.

[0316] In yet another embodiment, the step of preparing the polymer solution may further include adjusting the pH of the polymer solution. In this step, the pH of the polymer solution may be adjusted to 4 to 7, for example, 4.5 to 7.

[0317] The pH of the polymer solution can be adjusted by adding a pH adjuster. The pH adjuster is not particularly limited and may include, for example, amine compounds such as alkoxyamines, alkylamines, and alkanolamines.

[0318] By adjusting the pH of the polymer solution to the range described above, defects can be prevented in the film made from the polymer solution, and the desired optical and mechanical properties in terms of yellow index and modulus can be achieved.

[0319] Based on the total number of moles of monomers in the polymer solution, the amount of pH adjuster used can be from 0.1% to 10% in moles.

[0320] In one embodiment, the organic solvent may be at least one selected from the group consisting of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), m-cresol, tetrahydrofuran (THF), and chloroform. The organic solvent used in the polymer solution may be dimethylacetamide (DMAc), but is not limited thereto.

[0321] In another embodiment, at least one selected from the group consisting of fillers, blue pigments, and UVA absorbers can be added to the polymer solution.

[0322] Details regarding the types and amounts of fillers, blue pigments, and UVA absorbers are as described above. The fillers, blue pigments, and UVA absorbers can be mixed with the polyamide-imide polymer in the polymer solution.

[0323] The polymer solution can be stored at temperatures ranging from -20°C to 20°C, -20°C to 10°C, -20°C to 5°C, -20°C to 0°C, or 0°C to 10°C.

[0324] If stored at the above temperature, the degradation of the polymer solution can be prevented and the moisture content reduced, thereby preventing defects in the resulting film.

[0325] In some embodiments, the polymer solution or a polymer solution whose viscosity has been adjusted may be aged (S120).

[0326] Aging can be carried out by placing the polymer solution at a temperature of -10°C to 10°C for 24 hours or longer. In this case, for example, the polyamide-imide polymer or unreacted materials contained in the polymer solution can complete the reaction or reach chemical equilibrium, thereby homogenizing the polymer solution. The mechanical and optical properties of the resulting polyamide-imide film can be substantially uniform over the entire area of ​​the film. Preferably, aging can be carried out at temperatures of -5°C to 10°C, -5°C to 5°C, or -3°C to 5°C, but is not limited thereto.

[0327] In one embodiment, the method may further include degassing the polyamide-imide polymer solution (S130). The degassing step can remove moisture from the polymer solution and reduce impurities, thereby improving the reaction yield and imparting excellent surface appearance and mechanical properties to the final produced membrane.

[0328] Degassing may include vacuum degassing or purging with an inert gas.

[0329] After reducing the internal pressure of the tank containing the polymer solution to 0.1 bar to 0.7 bar, vacuum degassing can be performed for 30 minutes to 3 hours. Vacuum degassing under these conditions reduces air bubbles in the polymer solution. Therefore, surface defects in the resulting film can be prevented, and excellent optical properties such as haze can be achieved.

[0330] Furthermore, purging can be performed by purging the canister with an inert gas at an internal pressure of 1 atm to 2 atm. Purging under these conditions can remove moisture from the polymer solution, reduce impurities, thereby improving reaction yield and obtaining excellent optical and mechanical properties such as haze.

[0331] The 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 inert gas can be nitrogen.

[0332] Vacuum degassing and purging with inert gas can be performed in separate steps.

[0333] For example, a vacuum degassing step can be performed, followed by purging with an inert gas, but this is not the only option.

[0334] Vacuum degassing and / or purging with an inert gas can improve the surface physical properties of the polyamide-imide film thus prepared.

[0335] A polymer solution can be cast to prepare a gel sheet (S200).

[0336] For example, polymer solutions can be extruded, coated, and / or dried on a carrier to form gel sheets.

[0337] Furthermore, the thickness of the polymer solution cast can range from 200 μm to 700 μm. When the polymer solution is cast to a thickness within the above range, the final film produced after drying and heat treatment can have a suitable and uniform thickness.

[0338] As described above, the polymer solution can have a viscosity of 150,000 cps to 500,000 cps at room temperature. Because the viscosity meets the above range, the polymer solution can be cast to a uniform thickness without defects, and a polyamide-imide film with a substantially uniform thickness can be formed without local / partial thickness variations during drying.

[0339] A polymer solution is cast and then dried at temperatures of 60°C to 150°C, 70°C to 150°C, 80°C to 150°C, or 90°C to 150°C for 5 to 60 minutes to prepare a gel sheet. Specifically, the polymer solution is dried at a temperature of 90°C to 140°C for 15 to 40 minutes to prepare a gel sheet.

[0340] The solvent in the polymer solution can be partially or completely evaporated during the drying process to prepare gel sheets.

[0341] The dried gel sheet can be heat-treated to form a polyamide-imide film (S300).

[0342] For example, the heat treatment of gel sheets can be carried out by a heat curing device.

[0343] The steps of heat-treating gel sheets include heat treatment via at least one heater.

[0344] In addition, the heat treatment step of the gel sheet may also include heat treatment with hot air.

[0345] In one embodiment, the step of heat-treating the gel sheet includes heat treatment with hot air; and heat treatment by at least one heater.

[0346] In one embodiment, if hot air is used for heat treatment, heat can be provided uniformly. If the heating is uneven, a satisfactory surface roughness cannot be obtained, or the surface quality may be uneven, and the surface energy may be excessively increased or decreased.

[0347] Hot air heat treatment can be performed for 5 to 200 minutes within a temperature range of 60°C to 500°C. Specifically, the heat treatment of the gel sheet can be performed for 10 to 150 minutes within a temperature range of 80°C to 300°C at a heating rate of 1.5°C / min to 20°C / min. More specifically, the heat treatment of the gel sheet can be performed within a temperature range of 140°C to 250°C.

[0348] In this case, the initial temperature for heat treatment of the gel sheet can be 60°C or higher. Specifically, the initial temperature for heat treatment of the gel sheet can be between 80°C and 180°C. Furthermore, the maximum temperature for heat treatment can be between 200°C and 500°C.

[0349] Furthermore, the heat treatment of the gel sheet can be performed in two or more stages. Specifically, the gel sheet can be heat-treated with hot air sequentially in a first hot air treatment stage and a second hot air treatment stage. The temperature in the second hot air treatment stage can be higher than the temperature in the first hot air treatment stage.

[0350] In one embodiment, the step of heat-treating the gel sheet may include heat treatment by at least one heater, or more specifically, heat treatment by multiple heaters.

[0351] As an example, see Figure 5 and Figure 6The plurality of heaters may include a first heater (HC), a second heater (HN), and a third heater (HS) spaced apart in the TD direction of the gel sheet (polyamide-imide-based film). The first heater (HC) may be mounted on heater mounting portions (A1, B1) corresponding to the center of the gel sheet, the second heater (HN) may be mounted on heater mounting portions (A1, B1) corresponding to either end of the gel sheet, and the third heater (HS) may be mounted on heater mounting portions (A1, B1) corresponding to the other end of the gel sheet. That is, the first heater HC may be mounted on heater mounting portions (A1, B1) and positioned between the second heater (HN) and the third heater (HS). The heater mounting portions (A1, B1) may be configured to face the gel sheet. As an example, the heater mounting portions (A1, B1) may be configured to face and be spaced apart from the gel sheet. Preferably, the distance between the first heater (HC) and the second heater (HN) may be the same as the distance between the first heater (HC) and the third heater (HS). Two or more of the heater mounting sections (A1, B1) may be arranged along the direction of travel (or longitudinally) of the gel sheet (polyamide-imide film).

[0352] At least one heater may include an infrared heater. However, the type of at least one heater is not limited to the examples above and can be varied.

[0353] Specifically, the multiple heaters may include infrared heaters. More specifically, the first heater, the second heater, and the third heater may each include an infrared heater.

[0354] The heat treatment by at least one heater can be carried out in a temperature range of 300°C or higher. Specifically, at least one heater can be used for heat treatment for 1 to 30 minutes or 1 to 20 minutes in a temperature range of 300°C to 500°C.

[0355] Reference Figure 6 The heater mounting part (B1) and the gel sheet (B2) are placed in parallel, and the heater mounting part (B1) is separated from the gel sheet (B2) set on the belt (A3) by a certain distance.

[0356] The gel sheet (B2) comprises three regions (N region, C region, and S region) divided in the TD direction. Among the three divided regions, region C is located in the middle of the gel sheet, while regions N and S are located at the ends of the gel sheet.

[0357] When the width of region N is w1, the width of region C is w2, and the width of region S is w3, the width (w0) of the gel sheet is equal to the sum of w1, w2, and w3.

[0358] Furthermore, the width ratio of the three partitioned regions, w1:w2:w3, can be 1:(0.5 to 1.5):1. Specifically, the widths of the three partitioned regions can satisfy w1 = w2 = w3.

[0359] The heater mounting section (B1) is placed parallel to the gel sheet (B2) and spaced at a specific distance from it. The region in the heater mounting section (B1) corresponding to region N of the gel sheet (B2) includes a second heater (HN), the region in the heater mounting section (B1) corresponding to region C of the gel sheet (B2) includes a first heater (HC), and the region in the heater mounting section (B1) corresponding to region S of the gel sheet (B2) includes a third heater (HS).

[0360] In one embodiment, during the heat treatment step using at least one heater, when the temperature of the first heater (HC) is T HC The temperatures of the second heater (HN) and the third heater (HS) are T, respectively. HN and T HS T HN and T HS Higher than T HC .

[0361] In another embodiment, the step of heat-treating the gel sheet includes heat-treating it by means of a first heater, a second heater, and a third heater spaced apart in the TD direction of the gel sheet, wherein the temperature of the first heater corresponds to T at the center of the gel sheet. HC When the temperatures of the second and third heaters at both ends of the gel sheet are T HN and T HS At that time, T HN and T HS Higher than T HC .

[0362] Specifically, T HC It is 300℃ to 360℃, 300℃ to 350℃, or 310℃ to 350℃.

[0363] T HN and T HS The range is 310°C to 420°C, 330°C to 420°C, or 340°C to 400°C.

[0364] T HN and T HS T HC 2% to 18%, 3% to 18%, 5% to 15%, 8% to 15%, 10% to 20%, or 10% to 15%.

[0365] In the heat treatment step using at least one heater, when a temperature gradient as described above is applied between the heaters, the elemental content ratio can be controlled within a desired range, and similar thermal properties can be achieved in the film direction. Furthermore, the thermal properties of the film, as well as other mechanical and optical properties such as transmittance, haze, yellowness index, and modulus, show almost no deviation in the TD direction of the film. Because its physical properties change very little with direction, a film of uniform quality can be obtained.

[0366] Subsequently, after the heat treatment step of the gel sheet, the step of cooling and curing the film can be carried out while the curing film is being moved.

[0367] The step of cooling the cured film while it is being moved may include a first cooling step of reducing the temperature at a rate of 100°C / min to 1000°C / min and a second cooling step of reducing the temperature at a rate of 40°C / min to 400°C / min.

[0368] In this case, specifically, a second cooling step is performed after the first cooling step. The cooling rate of the first cooling step can be faster than the cooling rate of the second cooling step.

[0369] For example, the maximum rate of the first cooling step is faster than the maximum rate of the second cooling step. Or, the minimum rate of the first cooling step is faster than the minimum rate of the second cooling step.

[0370] If the cooling and curing process is carried out in this multi-stage manner, the physical properties of the cured film can be further stabilized, and the optical and mechanical properties of the film obtained in the curing process can be maintained more stably for a longer period of time.

[0371] In addition, a winding machine can be used to wind the cooled cured film.

[0372] In this case, the ratio of the speed at which the gel sheet moves on the belt during drying to the speed at which the cured film moves during 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, or 1:1.0 to 1:1.05, but is not limited to these.

[0373] If the ratio of moving speeds is outside the above range, the mechanical properties of the cured film may be impaired, and its flexibility and elasticity may deteriorate.

[0374] In the method for preparing polyamide-imide based films, the thickness deviation (%) according to the following relationship 1 can be 3% to 30%. Specifically, the thickness deviation (%) can be 5% to 20%, but is not limited thereto.

[0375] [Formula 1] Thickness deviation (%) = (M1 - M2) / M1 × 100

[0376] In Equation 1, M1 is the thickness of the gel sheet (μm), and M2 is the thickness of the cured film cooled during winding (μm).

[0377] The polyamide-imide-based film prepared by the above method exhibits excellent optical and mechanical properties, as well as uniform quality and isotropy. Polyamide-imide-based films are suitable for various applications requiring flexibility and transparency. For example, they can be used not only in display devices but also in solar cells, semiconductor devices, sensors, and more.

[0378] The details of the polyamide-imide-based membrane prepared by the above-described method are as follows.

[0379] Implementation schemes of the present invention

[0380] The invention will be described in more detail below with reference to the following embodiments. However, these embodiments are illustrative and the scope of the invention is not limited thereto.

[0381] [Example 1]

[0382] Under a nitrogen atmosphere, dimethylacetamide (DMAc) was added as an organic solvent to a temperature-controlled reactor at 10°C. Then, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), an aromatic diamine, was slowly added and dissolved.

[0383] Then, slowly add 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) and stir the mixture for 2 hours.

[0384] Then, terephthaloyl chloride (TPC) as a dicarbonyl compound was added, followed by stirring for 1 hour; isophthaloyl chloride (IPC) was added, followed by stirring for 1 hour, thereby preparing a polymer solution.

[0385] The resulting polymer solution is coated onto a substrate and then dried in a temperature range of 90°C to 140°C to prepare a gel sheet.

[0386] Subsequently, as a first heat treatment step, the gel sheet is treated with hot air at a temperature of 140°C to 250°C. Next, as a second heat treatment step, the gel sheet is passed through multiple heaters in the TD direction with a temperature gradient. Here, infrared heaters (infrared heaters with a maximum temperature of 1200°C) are used as the multiple heaters. Specifically, the gel sheet is passed through the heater mounting portions of three heaters spaced apart in the TD direction of the film to obtain a polyamide-imide film with a thickness of 50 μm. Here, the temperature of the middle heater (the first heater) is set to 330°C. HC The temperature of the two heaters (the second heater and the third heater) located at both ends of the heater mounting section is set to 379.5℃ (T). HN T HS 1.15T HC Its temperature is 15% higher than that of the heater located in the middle.

[0387] The specific composition and molar ratio of the polyamide-imide polymer are described in Table 1 below for the preparation examples. Furthermore, the content of each element in the membrane thus prepared was measured using an elemental analyzer (model name: Flash2000 (Thermo Fisher Scientific, Germany)) to measure the content of nitrogen (N), carbon (C), oxygen (O), and hydrogen (H). The elemental content ratios in the membrane are shown in Tables 2 and 3 below.

[0388] <Examples 2 and 3 and Comparative Examples 1 to 3>

[0389] As shown in Tables 1 and 2 below, the membranes were prepared in the same manner as in Example 1, except that the composition and molar ratio of the polymers, the temperature of the heaters in the multiple heater steps, and the degree of temperature gradient in the TD direction were changed.

[0390] <Preparation Examples> Polymer Composition

[0391] [Table 1]

[0392]

[0393] [Table 2]

[0394]

[0395]

[0396] [Table 3]

[0397]

[0398] <Evaluation Example>

[0399] The membranes prepared in the examples and comparative examples were subjected to the following performance measurements and evaluations. The results are shown in Tables 4 and 5 below.

[0400] Evaluation Example 1: Measurement of Film Thickness

[0401] The thickness was measured at six points in each of the three regions (N, C, and S) using a Mitsutoyo 547-401 digital micrometer to calculate the average thickness, thickness deviation, and thickness deviation rate.

[0402] Evaluation Example 2: Measurement of Transmittance and Haze

[0403] Transmittance and haze were measured using a haze meter NDH-5000W manufactured by Nippon Denshoku Kogyo Co., Ltd., in accordance with JIS K 7136 standard.

[0404] Evaluation Example 3: Measurement of Yellow Index

[0405] The Yellow Index (YI) was measured using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) under d65 and 10° conditions according to ASTM-E313 standard.

[0406] Evaluation Example 4: Measurement of Modulus and Elongation

[0407] A specimen was cut at least 10 cm in the direction perpendicular to the main contraction direction of the membrane, and 10 mm in the main contraction direction. It was fixed in an Instron universal testing machine UTM 5566A with clamps spaced 10 cm apart. The specimen was stretched at 10 mm / min until fracture at room temperature, and stress-strain curves were obtained. The slope of the load relative to the initial strain on the stress-strain curve was taken as the modulus (GPa). Furthermore, the rate of change of the fracture deformation length relative to the initial length was taken as the elongation (%).

[0408] For the measurement of modulus and elongation, measurements were taken with the MD and TD directions of the film as the longitudinal directions, respectively. The value measured in the TD direction as the longitudinal direction was divided by the value measured in the MD direction as the transverse direction, and then multiplied by 100 to obtain the ratio. The respective values ​​(R...) MO and R EL As shown in Table 5 below.

[0409] Evaluation Example 5: Lightfastness Assessment

[0410] Using Q-Lab's QUV / Spray / RP equipment, at 60°C, a UV-A lamp (wavelength 340nm) was used at a rate of 0.63W / m.2 The film was irradiated for 72 hours, and the yellow index was measured again according to the method in Evaluation Example 3 above. The change in the yellow index (ΔYI) was calculated. The smaller the change in the yellow index, the better the lightfastness.

[0411] Evaluation Example 6: Solvent Resistance Evaluation

[0412] A membrane sample (5 cm × 15 cm) with regions N, C, and S was immersed in solvent for 5 seconds, dried at 80°C for 3 minutes, and the haze was measured again according to the method in Evaluation Example 2 above. The average value of the haze change (ΔHz) of the membrane sample in the three regions was calculated. The smaller the haze change, the better the solvent resistance. MIBK or IPA was used as the solvent.

[0413] In addition, the thickness, transmittance, haze, yellow index, and modulus of the prepared membrane were measured at six points in each of regions N, C, and S, with two arbitrary points selected for each region. Their average values, deviations, and deviation rates were calculated, as shown in Table 4. The deviation rate was calculated by dividing the deviation by the average value and then multiplying by 100.

[0414] [Table 4]

[0415]

[0416] [Table 5]

[0417]

[0418] Referring to Tables 4 and 5, for the membrane according to the embodiment, where the nitrogen (N) content in the membrane is 6% to 7.5% by weight based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements, the mass deviation in the TD direction is significantly reduced in terms of the membrane's main physical properties such as transmittance, haze, yellow index, and modulus, and it exhibits isotropy, thereby improving the membrane's quality reliability. Furthermore, even after immersion in solvents primarily used for post-treatment or exposure to light for a certain period, the change in haze remains below a certain level, thus giving the membrane excellent solvent resistance and lightfastness.

[0419] Figure Labels

[0420] 100: Polyamide-imide based film

[0421] 101: First side 102: Second side

[0422] 200: Functional layer; 300: Cover window

[0423] 400: Display unit; 500: Adhesive layer

[0424] A1, B1: Heater mounting section

[0425] A2, B2: Gel sheets

[0426] A3: Belt

[0427] HN, HC, HS: Heater

Claims

1. A polyamide-imide-based film, comprising a polyamide-imide-based polymer prepared from a polydiamine compound, a dianhydride compound, and a dicarbonyl compound, in, The diamine compound includes 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB). The dianhydride compound includes at least one selected from the group consisting of 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA). The dicarbonyl compound includes at least one selected from the group consisting of terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloro (BPDC), and isophthaloyl chloride (IPC). Based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the nitrogen (N) content in the membrane is 6% to 7.3% by weight. Based on the total weight of the membrane, the sum of nitrogen (N) and hydrogen (H) elements in the membrane is 6% to 9% by weight. Based on the total weight of the membrane, the nitrogen (N) content in the membrane is 4% to 7% by weight, and The nitrogen (N) content in the membrane is 8 to 11 parts by weight relative to 100 parts by weight of carbon (C) in the membrane.

2. The polyamide-imide-based film according to claim 1, wherein, Transmittance, haze, yellowness index, and modulus were measured at six points in each of the regions N, C, and S, which were divided along the TD direction of the membrane. The average transmittance is 80% or higher, and the transmittance deviation is 0.3% or lower. The average haze level is 1% or lower, and the haze deviation rate is 10% or lower. The average value of the yellow index is 5% or lower, and the deviation rate of the yellow index is 10% or lower. The average modulus is 5 GPa or greater, and the modulus deviation rate is 10% or less.

3. The polyamide-imide-based film according to claim 1, wherein, The membrane was immersed in MIBK for 5 seconds and dried at 80°C for 3 minutes. Its haze and the change in haze (ΔHz) were measured. M ) is 0.2% or lower, and The membrane was immersed in IPA for 5 seconds and dried at 80°C for 3 minutes. Its haze and the change in haze (ΔHz) were measured. I The percentage is 0.1% or lower.

4. The polyamide-imide-based film according to claim 1, having an EC of 15.9 or greater as defined in Equation 1 below. A Values, such as 15.3 or greater as defined in Equation 2 below. B Values, such as 14 or greater as defined in Equation 3 below. C Values, and EC values ​​of 10.5 or greater as defined in Equation 4 below. D value: [Equation 1] ; [Equation 2] ; [Equation 3] ; [Equation 4] ; In equations 1 to 4, C w It is the weight percentage of carbon (C) in the membrane, based on the total weight of the membrane. O w It is the weight percentage of oxygen (O) in the membrane, based on the total weight of the membrane. H w It is the weight percentage of hydrogen (H) in the membrane based on the total weight of the membrane, and N w It is the weight percentage of nitrogen (N) in the membrane based on the total weight of the membrane.

5. The polyamide-imide-based film according to claim 1, having an R content of 95% to 105% as defined in Equation 5 below. MO The value, and R as defined in Equation 6 below, is 90% to 110%. EL value: [Equation 5] ; [Equation 6] ; In equations 5 and 6, MO T The modulus is measured longitudinally along the TD direction of the membrane. MO M The modulus is measured longitudinally along the MD direction of the membrane. EL T The elongation is measured longitudinally along the TD direction of the membrane, and EL M The elongation is measured longitudinally along the MD direction of the membrane.

6. The polyamide-imide-based film according to claim 1, wherein, The membrane was illuminated by a UV-A lamp with a wavelength of 340 nm at 60°C at a rate of 0.63 W / m. 2 After 72 hours of irradiation, the yellowness was measured, and the change in the yellowness index (ΔYI) was 5 or lower.

7. A cover window for a display device, comprising a polyamide-imide-based film and a functional layer, wherein, The polyamide-imide-based film comprises a polyamide-imide-based polymer prepared from a polydiamine compound, a dianhydride compound, and a dicarbonyl compound. The diamine compound includes 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB). The dianhydride compound includes at least one selected from the group consisting of 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA). The dicarbonyl compound includes at least one selected from the group consisting of terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloro (BPDC), and isophthaloyl chloride (IPC). Based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the nitrogen (N) content in the polyamide-imide membrane is 6% to 7.3% by weight. Based on the total weight of the polyamide-imide membrane, the sum of the nitrogen (N) and hydrogen (H) elements in the membrane is 6% to 9% by weight. Based on the total weight of the membrane, the nitrogen (N) content in the membrane is 4% to 7% by weight, and The nitrogen (N) content in the membrane is 8 to 11 parts by weight relative to 100 parts by weight of carbon (C) in the membrane.

8. A display device comprising a display unit; and a cover window disposed on the display unit. in, The cover window comprises a polyamide-imide-based film and a functional layer, wherein the polyamide-imide-based film comprises a polyamide-imide-based polymer prepared from a polydiamine compound, a dianhydride compound, and a dicarbonyl compound. The diamine compound includes 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB). The dianhydride compound includes at least one selected from the group consisting of 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA). The dicarbonyl compound includes at least one selected from the group consisting of terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloro (BPDC), and isophthaloyl chloride (IPC). Based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the membrane, the nitrogen (N) content in the polyamide-imide membrane is 6% to 7.3% by weight. Based on the total weight of the polyamide-imide membrane, the sum of the nitrogen (N) and hydrogen (H) elements in the membrane is 6% to 9% by weight. Based on the total weight of the membrane, the nitrogen (N) content in the membrane is 4% to 7% by weight, and The nitrogen (N) content in the membrane is 8 to 11 parts by weight relative to 100 parts by weight of carbon (C) in the membrane.

9. A method for preparing a polyamide-imide-based film according to claim 1, comprising: Polymerizing diamine compounds, dianhydride compounds, and dicarbonyl compounds in an organic solvent to prepare polyamide-imide polymer solutions; A casting solution is then dried to prepare a gel sheet; and The gel sheet was heat-treated. The step of heat-treating the gel sheet includes heat-treating it by passing it through a first heater, a second heater, and a third heater spaced apart in the TD direction. The heat treatment step of the gel sheet includes heat treatment with hot air. The hot air heat treatment is carried out for 5 to 200 minutes within a temperature range of 60°C to 500°C. The temperature of the first heater corresponding to the center of the gel sheet is T. HC The temperatures of the second and third heaters corresponding to the two ends of the gel sheet are T and T, respectively. HN and T HS T HN and T HS Higher than T HC ,as well as Among them, T HC It is 300℃ to 360℃, calculated in degrees Celsius, T HN and T HS T HC 10% to 20% higher.

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