KR20230087845A - Polyamide-imide-based film, preparation method thereof, and cover window and display device comprising the same - Google Patents

Abstract

In an embodiment, provided are a polyamide-imide-based film wherein the content of a nitrogen (N) element in the film is 6 to 7.5 wt% based on the sum of the weight of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film, so that uniform quality and excellent mechanical and optical properties can be achieved, a manufacturing method thereof, and a cover window and a display device comprising the same.

Description

Polyamide-imide-based film, manufacturing method thereof, and cover window and display device including the same

Embodiments relate to a polyamide-imide-based film, a manufacturing method thereof, and a cover window and a display device including the same.

Polyimide-based resins such as poly(amide-imide) (PAI) have excellent friction, heat, and chemical resistance, and are used for primary electrical insulation materials, coatings, adhesives, resins for extrusion, and heat-resistant paints. , heat-resistant plates, heat-resistant adhesives, heat-resistant fibers and heat-resistant films.

Polyimide is used in various fields. For example, polyimide is made in the form of a powder and used as a coating agent for metal or magnet wire, etc., and is mixed with other additives depending on the use. In addition, polyimide is used together with fluoropolymers as paints for decoration and corrosion prevention, and serves to adhere fluoropolymers to metal substrates. In addition, polyimide is used to coat kitchen utensils, is used as a membrane used for gas separation due to its heat and chemical resistance, and is a device that filters contaminants such as carbon dioxide, hydrogen sulfide and impurities in natural gas wells. is also used

Recently, a polyimide-based film having excellent optical, mechanical, and thermal properties at a lower price has been developed by forming a film of polyimide. Such polyimide-based films can be applied to display materials such as organic light-emitting diodes (OLEDs) or liquid-crystal displays (LCDs), and are antireflection films, compensation films, or retardation films when phase difference properties are realized. Applicable to film.

When such a polyimide-based film is immersed in a solvent in the post-process, the optical properties are deteriorated, or when applied to a cover window or display device, the quality of the film is non-uniform, resulting in a decrease in the quality reliability and product yield of the final product. there was.

Therefore, while solving the above problems, there is a continuous increase in demand for developing a film with less variation in film quality, excellent mechanical properties, optical properties, and solvent resistance.

Embodiments are intended to provide a polyamide-imide-based film having uniform quality and excellent mechanical properties, optical properties, and solvent resistance properties, a manufacturing method thereof, and a cover window and a display device including the same.

In the polyamide-imide-based film according to an embodiment, the content of nitrogen (N) elements in the film is based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film. 6 to 7.5% by weight.

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

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

A method for preparing a polyamide-imide-based film according to an embodiment includes preparing a polyamide-imide-based polymer solution by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent; preparing a gel sheet by casting and then drying the solution; and heat-treating the gel sheet, wherein the heat-treating the gel sheet includes heat-treating through a first heater, a second heater, and a third heater spaced apart in a TD direction of the gel sheet; Let T _HC be the temperature of the first heater corresponding to the center of the gel sheet, and T _HN and T _HS be the temperatures of the second and third heaters corresponding to both ends of the gel sheet, respectively. , the T _HN and the T _HS are higher than the T _HC .

The polyamide-imide-based film according to embodiments has a certain level of nitrogen (N) element based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film. By having a content value, there is little variation in physical properties in the TD direction, so that the quality in the width direction is uniform, and excellent mechanical properties, optical properties, and solvent resistance properties can be obtained.

After manufacturing the polyamide-imide-based film, post-processes such as laminating a functional layer for imparting functions such as anti-fingerprint, anti-static, anti-scattering, and improved adhesion are performed. In this post-process, when additional heat treatment is performed, non-uniformity in film quality may be amplified and the defect rate of the final product may increase, so the uniform quality of the polyamide-imide-based film itself is an important management factor.

Accordingly, in the case of the polyamide-imide-based film according to the embodiment, the nitrogen (N) element content value is controlled within a specific range, thereby improving quality reliability and product quality of final products such as a cover window for a display device to which the film is applied or a display device. yield can be improved.

In addition, there are cases in which the film is exposed to solvents during post-processing. In the case of films with low solvent resistance, there is a risk of deterioration in optical and mechanical properties, such as a rapid increase in haze after immersion in a solvent. It is advantageous.

1 is a schematic exploded view of a display device according to an exemplary embodiment.
2 is a schematic perspective view of a display device according to an exemplary embodiment.
3 is a schematic cross-sectional view of a display device according to an exemplary embodiment.
4 is a schematic flowchart of a method for manufacturing a polyamide-imide-based film according to an embodiment.
5 is a plan view schematically illustrating a step of passing a heater in a method for manufacturing a polyamide-imide-based film according to an embodiment.
6 is a perspective view schematically illustrating a heater mounting portion and a gel sheet in a step of passing a heater in a method of manufacturing a polyamide-imide-based film according to an embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, implementations may be implemented in many different forms and are not limited to the implementations described herein.

In the present specification, when each film, window, panel, or layer is described as being formed “on” or “under” each film, window, panel, or layer, (on)" and "under" include both formed "directly" or "indirectly". In addition, the criteria for the top/bottom of each component will be described based on the drawings. The size of each component in the drawings may be exaggerated for description, and does not mean a size actually applied. Also, like reference numerals designate like elements throughout the specification.

In this specification, when a certain component is said to "include", this means that it may further include other components, not excluding other components, unless otherwise stated.

In this specification, a singular expression is interpreted as a meaning including a singular number or a plurality interpreted in context unless otherwise specified.

In addition, it should be understood that all numbers and expressions representing amounts of components, reaction conditions, etc. described in this specification are modified by the term “about” in all cases unless otherwise specified.

In this specification, terms such as first and second are used to describe various components, and the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another.

In addition, unless otherwise specified, “substituted” in this specification means deuterium, -F, -Cl, -Br, -I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, Hydrazone group, ester group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted alicyclic group means substituted with one or more substituents selected from the group consisting of a group, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group, and the above-listed substituents are linked to each other can form a ring.

Polyamide-imide film

In the embodiment, the content of nitrogen (N) elements based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film satisfies a specific level, thereby improving physical properties in the TD direction. Provided is a polyamide-imide-based film having uniform quality with little variation and excellent mechanical properties, optical properties, and solvent resistance.

In the polyamide-imide-based film according to the embodiment, the content of the nitrogen (N) element in the film is the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film. It is 6 to 7.5% by weight on a basis.

Specifically, the content of the nitrogen (N) element in the film based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film of the polyamide-imide-based film is 6 6.1 wt% or more, 6.2 wt% or more, or 6.3 wt% or more, and may be 7.5 wt% or less, 7.4 wt% or less, 7.3 wt% or less, or 7 wt% or less.

More specifically, the content of nitrogen (N) element in the film based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film of the polyamide-imide-based film 6 to 7.3 wt%, 6 to 7 wt%, 6.3 to 7.5 wt%, 6.3 to 7.3 wt%, or 6.3 to 7 wt%, but is not limited thereto.

The carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elemental contents were measured using an element analysis (EA), for example, Model Flash2000 (Thermo Fisher Scientific, Germany). can be a value Alternatively, the content of each element may be a value measured by nuclear magnetic resonance (NMR).

The content of the nitrogen (N) element in the polyamide-imide-based film may be 4 to 7% by weight based on the total weight of the film.

Specifically, based on the total weight of the polyamide-imide-based film, the content of the nitrogen (N) element in the film is 4% by weight or more, 4.2% by weight or more, 4.4% by weight or more, 4.6% by weight or more, 4.8% by weight or more, 5% by weight or more 5.2 wt% or more, 7 wt% or less, 6.8 wt% or less, 6.6 wt% or less, 6.4 wt% or less, 6.2 wt% or less, 6 wt% or less, or 5.8 wt% or less.

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

The content of the nitrogen (N) element in the polyamide-imide-based film may be 8 to 12 parts by weight based on 100 parts by weight of the carbon (C) element in the film.

Specifically, the content of the nitrogen (N) element in the film is 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 relative to 100 parts by weight of the carbon (C) element in the polyamide-imide-based film. , 8.8 parts by weight or more or 9 parts by weight or more, 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 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.

More specifically, the content of the nitrogen (N) element in the film is 8 to 11.2 parts by weight, 8 to 11 parts by weight, 8 to 10.6 parts by weight, relative to 100 parts by weight of the carbon (C) element in the polyamide-imide-based film. It may be 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.

The sum of nitrogen (N) and hydrogen (H) elements in the polyamide-imide-based film may be 6 to 9% by weight based on the total weight of the film.

Specifically, based on the total weight of the polyamide-imide-based film, the sum of the contents of nitrogen (N) and hydrogen (H) elements in the film is 6% by weight or more, 6.2% by weight or more, 6.4% by weight or more, or 6.6% by weight or more. , 6.8 wt% or more, 7 wt% or more, 7.2 wt% or more, or 7.4 wt% or more, and 9 wt% or less, 8.8 wt% or less, 8.6 wt% or less, 8.4 wt% or less, 8.2 wt% or less, or 8 wt% % or less.

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

As the element content of the polyamide-imide-based film according to the embodiment satisfies the above range, the quality deviation in the TD direction is significantly reduced, and the haze change amount is below a certain level after being immersed in a solvent mainly used in post-processing, etc. Excellent solvent resistance.

On the other hand, when the element content in the polyamide-imide-based film according to the embodiment is out of the above-described range, the haze change amount is large after being immersed in a solvent, and the optical properties are deteriorated after going through a post-process, etc., and the TD direction of the film will be described later. The quality deviation is also large, which not only lowers the quality of the film itself, but also directly leads to a product with a high defect rate when applying post-processing.

The content of the carbon (C) element in the polyamide-imide-based film may be 53 to 60% by weight based on the total weight of the film.

Specifically, based on the total weight of the polyamide-imide-based film, the content of the carbon (C) element in the film is 53% by weight or more, 54% by weight or more, 55% by weight or more, 55.5% by weight or more, 56% by weight or more, or 56.5% by weight or more. It may be greater than or equal to 60% by weight, less than or equal to 59.5%, less than or equal to 59% by weight or less than or equal to 58.5% by weight.

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

The content of the hydrogen (H) element in the polyamide-imide-based film may be 1.5 to 3.5% by weight based on the total weight of the film.

Specifically, based on the total weight of the polyamide-imide-based film, the content of the hydrogen (H) element in the film may be 1.5% by weight or more, 1.8% by weight or more, or 2.1% by weight or more, and 3.5% by weight or less, 3.2% by weight or less. , 3 wt% or less, or 2.8 wt% or less.

More specifically, based on the total weight of the polyamide-imide-based film, the content of the hydrogen (H) element in the film is 1.8 to 3.5% by weight, 1.8 to 3% by weight, 1.8 to 2.8% by weight, 2.1 to 3% by weight, or 2.1% by weight. to 2.8% by weight, but is not limited thereto.

The content of the oxygen (O) element in the polyamide-imide-based film may be 15 to 19% by weight based on the total weight of the film.

Specifically, based on the total weight of the polyamide-imide-based film, the content of the oxygen (O) element in the film may be 15 wt% or more, 15.5 wt% or more, 16 wt% or more, or 16.5 wt% or more, and 19 wt% or less , 18.5 wt% or less, or 18 wt% or less.

More specifically, based on the total weight of the polyamide-imide-based film, the content of the oxygen (O) element in the film may be 15.5 to 18.5% by weight, 15.5 to 18% by weight, 16 to 18.5% by weight, or 16 to 18% by weight. However, it is not limited thereto.

The sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the polyamide-imide-based film may be 80 to 85% by weight based on the total weight of the film.

Specifically, based on the total weight of the polyamide-imide-based film, the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film is 80% by weight or more and 80.5% by weight or more. , 81 wt% or more or 81.5 wt% or more, and may be 85 wt% or less, 84.5 wt% or less, or 84 wt% or less.

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

The film includes an N region, a C region, and an S region, which are three partitioned regions in the TD direction. In the film, when the width of the N region is wN, the width of the C region is wC, and the width of the S region is wS, the width of the film is equal to the sum of wN, wC, and wS.

When the transmittance of the polyamide-imide-based film according to the embodiment was measured at a total of 6 points by randomly selecting 2 points in each of the N region, C region, and S region partitioned in the TD direction, the average value of the transmittance was 80 % or more, and the variation rate of transmittance may be 0.5% or less.

Specifically, the average value of the transmittance of the polyamide-imide-based film is 82% or more, 84% or more, 86% or more, 88% or more, or 89% or more, and the transmittance deviation rate is 0.4% or less, 0.3% or less, It may be 0.25% or less, 0.2% or less or 0.15% or less.

When haze is measured at a total of 6 points by randomly selecting 2 points in each of the N region, C region, and S region of the polyamide-imide-based film according to the embodiment divided in the TD direction, the average haze value is 1 % or less, and the haze variation rate may be 10% or less.

Specifically, the average haze value of the polyamide-imide-based film is 0.7% or less, 0.5% or less, or 0.4% or less, and the haze variation rate is 9.5% or less, 9% or less, 8.5% or less, 8% or less, or It may be 7.5% or less.

When the yellowness of the polyamide-imide-based film according to the embodiment is measured at a total of six points by randomly selecting two points in each of the N region, C region, and S region partitioned in the TD direction, the average yellowness value is 5 or less, and the yellowness variation rate is 10% or less.

Specifically, the average value of yellowness of the polyamide-imide-based film may be 4.5 or less, 4 or less, or 3.5 or less, and the yellowness variation rate may be 8% or less, 7% or less, or 6% or less.

When the modulus of the polyamide-imide-based film according to the embodiment was measured at a total of six points by randomly selecting two points in each of the N region, C region, and S region partitioned in the TD direction, the average value of the modulus was 5 GPa or more, and the modulus variation rate is 10% or less.

Specifically, the polyamide-imide-based film may have an average modulus value of 5.5 GPa or more or 6 GPa or more, and a modulus variation ratio of 7% or less, 5% or less, 4% or less, or 3% or less.

When the average value and deviation rate related to transmittance, haze, yellowness, and/or modulus of the polyamide-imide-based film according to the embodiment are in the above range, not only the physical properties themselves are excellent, but also the width direction (TD direction) of the film ), there is little variation in the main physical properties, so there is little quality variation when cutting into the required shape or size when applying the post-process after film production, improving product yield and being economical.

On the other hand, if the average value or deviation rate related to transmittance, haze, yellowness and/or modulus of the polyamide-imide-based film according to the embodiment is out of the above range, it means that the quality is slightly different for each position of the film. Therefore, many defects may occur when applied to the product. In particular, when commercializing the film, it may be subjected to harsh conditions such as additional heat treatment, and in this process, non-uniform quality may be further amplified.

In some embodiments, the polyamide-imide-based 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 based on a thickness of 50 μm. In addition, the thickness variation rate may be 5% or less, 4% or less, 3% or less, or 2.5% or less, but is not limited thereto.

The thickness deviation and deviation rate are the average of the thickness values measured at a total of six points by selecting two random points in each of the N region, C region, and S region partitioned in the TD direction of the film, their deviation, and a deviation rate. In this case, the polyamide-imide-based film has a uniform thickness so that optical properties and mechanical properties can be uniformly displayed at each point.

When the haze is measured after the polyamide-imide-based film is immersed in MIBK for 5 seconds and dried at 80 °C for 3 minutes, the haze change amount (ΔHz _M ) may be 0.2% or less.

Specifically, the haze change amount (ΔHz _M ) of the polyamide-imide-based film after MIBK immersion may be 0.19% or less, 0.18% or less, 0.17% or less, 0.15% or less, or 0.12% or less, but is not limited thereto.

The ΔHz _M (%) is a value of Hz _M - Hz ₀ , wherein Hz ₀ represents the initial haze (%) of the film, and Hz _M is 3 seconds at 80 ° C. It represents the haze (%) measured after drying for minutes.

When the haze is measured after immersing the polyamide-imide-based film in IPA for 5 seconds and drying at 80 °C for 3 minutes, the haze change (ΔHz _I ) may be 0.1% or less.

Specifically, the haze change amount (ΔHz _I ) of the polyamide-imide-based film after IPA immersion may be 0.08% or less, 0.06% or less, or 0.05% or less, but is not limited thereto.

The ΔHz _I (%) is a value of Hz _I - Hz ₀ , wherein Hz ₀ represents the initial haze (%) of the film, and Hz _I is 3 seconds at 80 ° C. It represents the haze (%) measured after drying for minutes.

The polyamide-imide-based film was immersed in MIBK for 5 seconds, dried at 80 ° C. for 3 minutes, and the haze change (ΔHz _M ) when the haze was measured and the polyamide-imide-based film was immersed in IPA for 5 seconds Then, the average value (ΔHz _AVG ) of the haze change amount (ΔHz _I ) when the haze is measured after drying at 80 ° C. for 3 minutes may be 0.15% or less.

Specifically, the average value of haze variation (ΔHz _AVG ) of the polyamide-imide-based film may be 0.13% or less, 0.11% or less, or 0.1% or less, but is not limited thereto.

The average value of the haze variation (ΔHz _AVG ) may be a criterion for determining the solvent resistance of the film.

The polyamide-imide-based film may have a compressive strength of 0.4 kgf/μm or more. Specifically, the compressive strength may be 0.45 kgf/μm or more or 0.46 kgf/μm or more, but is not limited thereto.

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

The surface hardness of the polyamide-imide-based film may be greater than or equal to HB. Specifically, the surface hardness may be H or more or 2H or more, but is not limited thereto.

The polyamide-imide-based film may have a tensile strength of 15 kgf/mm ² or more. Specifically, the tensile strength may be 18 kgf/mm ² or more, 20 kgf/mm ² or more, 21 kgf/mm ² or more, or 22 kgf/mm ² or more, but is not limited thereto.

The polyamide-imide-based film may have an elongation of 15% or more. Specifically, the elongation may be 16% or more, 17% or more, or 18% or more, but is not limited thereto.

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

As for the number of times of folding, bending and unfolding the film so that the radius of curvature of the film is 3 mm is performed once.

When the polyamide-imide-based film satisfies the number of times of folding within the above-described range, it can be usefully applied to a foldable display device or a flexible display device.

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

When the surface roughness of the polyamide-imide-based film satisfies the above range, it may be advantageous to implement a luminance condition or texture that is advantageous for application to a display device.

The residual solvent content in the polyamide-imide-based film may be 1,500 ppm or less. For example, the content of the residual solvent may be 1,200 ppm or less, 1,000 ppm or less, 800 ppm or less, 500 ppm or less, or 300 ppm or less, but is not limited thereto.

The residual solvent refers to the amount of the solvent remaining in the finally produced film without being volatilized during film production.

When the content of the residual solvent in the polyamide-imide-based film exceeds the above range, the durability of the film may be deteriorated and the quality variation of the film may be affected. In particular, since it affects the mechanical strength, it may adversely affect the post-processing of the film, and by accelerating the hygroscopicity of the film, optical properties, solvent resistance, and heat resistance properties may also be deteriorated in addition to mechanical properties.

A polyamide-imide-based film according to an embodiment includes a polyamide-imide-based polymer, and the polyamide-imide-based polymer may be formed by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

The polyamide-imide-based polymer is a polymer including an imide repeating unit and an amide repeating unit.

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

The diamine compound is a compound that forms a copolymer by imide bonding with the dianhydride compound and amide bonding with the dicarbonyl compound.

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

<Formula 1>

In Formula 1,

E is a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic ring group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic ring group, or a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic ring group , substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, substituted or unsubstituted C ₁ -C ₃₀ alkylene group, substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, substituted or unsubstituted C ₂ -C ₃₀ Alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, It may be selected from -C(CH ₃ ) ₂ - and -C(CF ₃ ) ₂ -.

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

(E) _e of Formula 1 may be selected from the groups represented by Formulas 1-1a to 1-14a, but is not limited thereto.

Specifically, (E) _e of Formula 1 may be selected from the groups represented by Formulas 1-1b to 1-13b below, but is not limited thereto:

More specifically, (E)e in Chemical Formula 1 may be a group represented by Chemical Formula 1-6b or a group represented by Chemical Formula 1-9b.

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

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

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

For example, the diamine compound is 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl having the following structure (2,2'-Bis (trifluoromethyl) -4,4 '-diaminobiphenyl, TFDB), but is not limited thereto.

Since the dianhydride compound has a low birefringence value, it is a compound that can contribute to improving optical properties such as transmittance of the film including the polyamide-imide-based polymer.

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

<Formula 2>

In Formula 2, G is a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aliphatic ring group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaliphatic ring group, or a substituted or unsubstituted tetravalent C ₆ -C ₃₀ An aromatic ring group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaromatic ring group, and the aliphatic ring group, the heteroaliphatic ring group, the aromatic ring group, or the heteroaromatic ring group exists alone or , bonded to each other to form a condensed ring, a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, or a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group , -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) ₂ - and -C(CF ₃ ) ₂ -.

G in Formula 2 may be selected from groups represented by Formulas 2-1a to 2-9a, but is not limited thereto.

For example, G in Chemical Formula 2 may be a group represented by 2-2a, a group represented by Chemical Formula 2-8a, or a group represented by 2-9a.

In one embodiment, the dianhydride compound may include a compound having a fluorine-containing substituent, a compound having a biphenyl group, or a compound having a ketone group.

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

In another embodiment, the dianhydride compound may consist of one single component or two mixed components.

For example, the dianhydride compound is 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (2,2'-Bis- (3,4-dicarboxyphenyl) having the following structure -Dicarboxyphenyl)hexafluoropropane dianhydride, 6FDA) and 1 selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride, BPDA) It may include more than one species, but is not limited thereto.

Polyamic acid may be produced by polymerization of the diamine compound and the dianhydride compound.

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

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

<Formula A>

In Formula A, descriptions of E, G and e are as described above.

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

<Formula A-1>

In Formula A-1, n is an integer from 1 to 400.

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

<Formula 3>

In Formula 3,

J is a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic ring group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic ring group, or a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic ring group , substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, substituted or unsubstituted C ₁ -C ₃₀ alkylene group, substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, substituted or unsubstituted C ₂ -C ₃₀ Alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, It may be selected from -C(CH ₃ ) ₂ - and -C(CF ₃ ) ₂ -.

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

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

(J) _j in Chemical Formula 3 may be selected from the groups represented by Chemical Formulas 3-1a to 3-14a, but is not limited thereto.

Specifically, (J) _j in Chemical Formula 3 may be selected from the groups represented by Chemical Formulas 3-1b to 3-8b, but is not limited thereto:

More specifically, (J) _j in Formula 3 may be a group represented by Formula 3-1b, a group represented by Formula 3-2b, a group represented by 3-3b, or a group represented by 3-8b. there is.

For example, (J) _j in Chemical Formula 3 may be a group represented by Chemical Formula 3-1b or a group represented by Chemical Formula 3-2b.

In one embodiment, the dicarbonyl compound may be used alone or in combination with at least two different dicarbonyl compounds. When two or more dicarbonyl compounds are used, two or more dicarbonyl compounds selected from the groups in which (J) _j in Formula 3 are represented by Formulas 3-1b to 3-8b may be used. there is.

In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound including an aromatic structure.

The dicarbonyl compound is terephthaloyl chloride (TPC) having the following structure, 1,1'-biphenyl-4,4'-dicarbonyl dichloride (1,1'-biphenyl-4 , 4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof, but is not limited thereto.

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

<Formula B>

In Formula B, descriptions of E, J, e and j are as described above.

For example, the diamine compound and the dicarbonyl compound may be polymerized to form amide repeating units represented by Chemical Formulas B-1 and B-2.

Alternatively, the diamine compound and the dicarbonyl compound may be polymerized to form amide repeating units represented by Chemical Formulas B-2 and B-3.

<Formula B-1>

In Formula B-1, x is an integer from 1 to 400.

<Formula B-2>

In Formula B-2, y is an integer from 1 to 400.

<Formula B-3>

In Formula B-3, y is an integer from 1 to 400.

According to one embodiment, the polyamide-imide polymer may include a repeating unit represented by Formula A and a repeating unit represented by Formula B below:

<Formula A>

<Formula B>

In Formulas A and B,

E and J are each independently a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic ring group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic ring group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic ring group, substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, substituted or unsubstituted C ₁ -C ₃₀ alkylene group, substituted or unsubstituted C ₂ -C ₃₀ alkenylene group , a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si( selected from CH ₃ ) ₂ -, -C(CH ₃ ) ₂ - and -C(CF ₃ ) ₂ -;

e and j are independently selected from integers from 1 to 5;

When e is 2 or more, 2 or more E are the same as or different from each other,

When j is 2 or more, 2 or more J are the same as or different from each other,

G is a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aliphatic ring group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaliphatic ring group, or a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aromatic ring group , A substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaromatic ring group, wherein the aliphatic ring group, the heteroaliphatic ring group, the aromatic ring group, or the heteroaromatic ring group exists alone or is joined together to form a condensed ring or form a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, - S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) ₂ - and -C(CF ₃ ) ₂ - are connected by a selected connector.

The polyamide-imide-based polymer may include imide-based repeating units and amide-based repeating units in a molar ratio of 2:98 to 70:30. Specifically, the molar ratio of the imide-based repeating unit and the amide-based repeating unit is 2:98 to 60:40, 2:98 to 55:45, 2:98 to 50:50, 5:95 to 70:30, 5: It may be 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.

When the molar ratio of the imide repeating unit and the amide repeating unit is within the above range, the nitrogen (N) element content in the polyamide-imide-based film can be effectively controlled, and the quality reliability of the film can be increased in conjunction with a characteristic processing method. there is.

In the polyamide-imide-based polymer, the molar ratio of the repeating unit represented by Chemical Formula A and the repeating unit represented by Chemical Formula B may be 2:98 to 70:30. Specifically, the molar ratio of the repeating unit represented by Formula A and the repeating unit represented by Formula B is 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.

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

The filler may include, for example, an oxide, carbonate, or sulfur oxide of a metal or metalloid. For example, the filler may include silica, calcium carbonate, barium sulfate, and the like, but is not limited thereto.

The filler may be included in the form of particles. In addition, the filler is not specially coated on the surface and may be evenly dispersed throughout the film.

By including the filler in the polyamide-imide-based film, the film can secure a wide viewing angle without deterioration of optical properties, improve roughness and winding properties, and also improve driving performance scratches during film production. can improve

The refractive index of the filler may be 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.

When the refractive index of the filler satisfies the above range, birefringence values related to nx, ny, and nz may be appropriately adjusted, and luminance of the film at various angles may be improved.

On the other hand, when the refractive index of the filler is out of the above range, the presence of the film on the film may be visually recognized or the haze may increase due to the filler.

The content of the filler may be 100 ppm to 15,000 ppm based on the total weight of the polyamide-imide-based polymer solid content. Specifically, the content of the filler is 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 based on the total weight of the polyamide-imide polymer solids. ppm, or 300 ppm to 14,000 ppm, but is not limited thereto.

When the content of the filler is out of the above range, the haze of the film increases rapidly, and the fillers agglomerate on the surface of the film, so that a foreign body feeling is visually confirmed, or a problem occurs in driving or winding property is reduced in the production process It can be.

In some embodiments, the blue pigment may be included in an amount of 50 to 5000 ppm based on the total weight of the polyamide-imide-based polymer. Preferably, the blue pigment is present in an amount of 100 to 5000 ppm, 200 to 5000 ppm, 300 to 5000 ppm, 400 to 5000 ppm, 50 to 3000 ppm, 100 to 3000 ppm, based on the total weight of the polyamide-imide polymer. 200 to 3000 ppm, 300 to 3000 ppm, 400 to 3000 ppm, 50 to 2000 ppm, 100 to 2000 ppm, 200 to 2000 ppm, 300 to 2000 ppm, 400 to 2000 ppm, 50 to 1000 ppm, 100 to 1000 ppm, 200 to 1000 ppm, 300 to 1000 ppm, or 400 to 1000 ppm may be included, but is not limited thereto.

The UVA absorber may include an absorber that absorbs electromagnetic waves having a wavelength of 10 to 400 nm used in the art. For example, the UVA absorber may include a benzotriazole-based compound, and the benzotriazole-based compound may include an N-phenolic benzotriazole-based compound. In some embodiments, the N-phenolic benzotriazole-based compound may include N-phenolic benzotriazole in which a phenol group is substituted with an alkyl group having 1 to 10 carbon atoms. The alkyl group may be substituted with two or more, and may be straight-chain, branched or cyclic.

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

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.

The above-described components and physical properties of the polyamide-imide-based film may be combined with each other.

In addition, the content of each of the above-mentioned elements of the polyamide-imide-based film, the content of the nitrogen (N) element in the film, the average value and deviation rate of transmittance / haze / yellowness / modulus, etc. In the manufacturing method of the polyamide-imide-based film to be described later along with the chemical and physical properties of the components constituting the specific process conditions of each step can be integrated and adjusted.

For example, the composition and content of components constituting the polyamide-imide-based film, the type and content of additives, and the heat treatment conditions such as polymerization conditions and thermal gradients in the film manufacturing process are all integrated to obtain elemental content and The average value of each property in the width direction, deviation, and deviation rate can be implemented.

Cover windows for display devices

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

The polyamide-imide-based film has a nitrogen (N) element content of 6 to 7.5 based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film. % by weight.

A detailed description of the polyamide-imide-based film is as described above.

The cover window for the display device may be usefully applied to the display device.

display device

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

The polyamide-imide-based film has a nitrogen (N) element content of 6 to 7.5 based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) elements in the film. % by weight.

A detailed description of the polyamide-imide-based film and the cover window is as described above.

1 is a schematic exploded view of a display device according to an exemplary embodiment. 2 is a schematic perspective view of a display device according to an exemplary embodiment. 3 is a schematic cross-sectional view of a display device according to an exemplary embodiment.

Specifically, in FIGS. 1 to 3 , a display unit 400 and a polyamide-imide-based film 100 having a first surface 101 and a second surface 102 on the display unit 400 and a functional layer 200 A display device in which a cover window 300 including a ) is disposed and an adhesive layer 500 is disposed between the display unit 400 and the cover window 300 is illustrated.

The display unit 400 can display an image and may have a flexible characteristic.

The display unit 400 may be a display panel for displaying an image, and may be, for example, a liquid crystal display panel or an organic light emitting display panel. The organic light emitting display panel may include a front polarizer and an organic EL panel.

The front polarizing plate may be disposed on the front surface of the organic EL panel. Specifically, the front polarizing plate may be attached to a surface of the organic EL panel on which an image is displayed.

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

In addition, an adhesive layer 500 may be included between the display unit 400 and the cover window 300 . The adhesive layer may be an optically transparent adhesive layer, and is not particularly limited.

The cover window 300 may be disposed on the display unit 400 . The cover window may be located outside the display device according to the embodiment to protect the display unit.

The cover window 300 may include a polyamide-imide-based film and a functional layer. The functional layer may be at least one selected from the group consisting of a hard coating, a reflectivity reducing layer, an antifouling layer, and an antiglare layer. The functional layer may be coated on at least one surface of the polyamide-imide-based film.

In the case of the polyamide-imide-based film according to the embodiment, it is simply applied in the form of a film to the outside of the display device without changing the display driving method, color filter inside the panel, or laminated structure to provide uniform thickness, low haze, and high transmittance. And since it is possible to provide a display device having transparency, excessive process change or cost increase is not required, there is also an advantage in that production cost can be reduced.

The polyamide-imide-based film according to the embodiment may have excellent optical properties such as high transmittance, low haze, and low yellowness, and mechanical properties such as modulus and flexibility, and change (deterioration) in optical/mechanical properties even when exposed to ultraviolet rays. can be suppressed.

Specifically, in the case of a polyamide-imide-based film having a nitrogen (N) element content in the above range, almost no deviation in physical properties occurs in the TD direction, so the quality is uniform, and it has excellent mechanical properties, optical properties, and heat resistance properties. can Accordingly, when the polyamide-imide-based film is applied to a cover window for a display device or a display device, quality reliability and product yield of a final product can be improved.

Manufacturing method of polyamide-imide film

One embodiment provides a method for manufacturing a polyamide-imide-based film.

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

A method of manufacturing a polyamide-imide-based film according to some embodiments includes adjusting the viscosity of the polyamide-imide-based polymer solution (S110), aging the polyamide-imide-based polymer (S120), and / or degassing the polyamide-imide-based polymer solution (S130) may be further included.

The polyamide-imide-based film is a film containing a polyamide-imide-based polymer as a main component, and the polyamide-imide-based polymer is a polymer including an imide repeating unit and an amide repeating unit in a predetermined molar ratio as structural units.

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

In one embodiment, the polymer solution may be prepared by simultaneously introducing a diamine compound, a dianhydride compound, and a dicarbonyl compound into an organic solvent and reacting the polymer solution.

In another embodiment, preparing the polymer solution may include preparing a polyamic acid (PAA) solution by first mixing and reacting the diamine compound and the dianhydride compound in a solvent; and forming an amide bond and an imide bond by secondarily mixing and reacting the dicarbonyl compound with the polyamic acid (PAA) solution. The polyamic acid solution is a solution containing polyamic acid.

Alternatively, preparing the polymer solution may include preparing a polyamic acid solution by first mixing and reacting the diamine compound and the dianhydride compound in a solvent; preparing a polyimide (PI) solution by dehydrating the polyamic acid solution; and additionally forming an amide bond by secondarily mixing and reacting the dicarbonyl compound with the polyimide (PI) solution. The polyimide solution is a solution containing a polymer having an imide repeating unit.

In another embodiment, preparing the polymer solution may include preparing a polyamide (PA) solution by first mixing and reacting the diamine compound and the dicarbonyl compound in a solvent; and additionally forming an imide bond by secondarily mixing and reacting the dianhydride compound with the polyamide (PA) solution. The polyamide solution is a solution containing a polymer having an amide repeating unit.

The polymer solution prepared as described above may be a solution containing a polymer including at least one member selected from the group consisting of a polyamic acid (PAA) repeating unit, a polyamide (PA) repeating unit, and a polyimide (PI) repeating unit. .

Alternatively, the polymer included in the polymer solution may include an imide repeating unit derived from polymerization of the diamine compound and the dianhydride compound and an amide derived from polymerization of the diamine compound and the dicarbonyl compound. contains repeating units.

Descriptions of the diamine compound, the dianhydride compound and the dicarbonyl compound are as described above.

The amount of solids included in the polymer solution may be 10% to 30% by weight. Alternatively, the solid content contained in the polymer solution may be 15 wt % to 25 wt %, but is not limited thereto.

When the content of the solids contained in the polymer solution is within the above range, a polyamide-imide-based film can be effectively produced in extrusion and casting processes. In addition, the prepared polyamide-imide-based film exhibits similar thermal properties depending on the direction of the film, and thus may have uniform quality and excellent mechanical properties, optical properties, and heat resistance properties.

In another embodiment, preparing the polymer solution may further include introducing a catalyst.

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

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

When the catalyst is added, the reaction rate can be improved, and the chemical bonding strength between repeating unit structures or within the repeating unit structure can be improved.

In one embodiment, preparing the polymer solution may further include adjusting the viscosity of the polymer solution (S110). The viscosity of the polymer solution is 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, thickness uniformity can be improved by improving the film formability of the polyamide-imide-based film.

Specifically, preparing the polymer solution may include preparing a first polymer solution by simultaneously or sequentially mixing and reacting a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent; and preparing a second polymer solution having a target viscosity by additionally adding the dicarbonyl compound.

In the case of preparing the first polymer solution and preparing the second polymer solution, the viscosities of the prepared polymer solutions are different. For example, the viscosity of the second polymer solution is higher than that of the first polymer solution.

A stirring speed when preparing the first polymer solution and a stirring speed when preparing the second polymer solution may be different. For example, a stirring speed when preparing the first polymer solution may be faster than a stirring speed when preparing the second polymer solution.

In another embodiment, 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.

The pH of the polymer solution can be adjusted by adding a pH adjusting agent, and the pH adjusting agent is not particularly limited, but may include, for example, an amine compound such as alkoxyamine, alkylamine or alkanolamine.

By adjusting the pH of the polymer solution within the above-described range, it is possible to prevent defects in a film prepared from the polymer solution and implement desired optical and mechanical properties in terms of yellowness and modulus.

The pH adjusting agent may be added in an amount of 0.1 mol% to 10 mol% based on the total number of moles of monomers in the polymer solution.

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

In another embodiment, one or more selected from the group consisting of a filler, a blue pigment, and a UVA absorber may be added to the polymer solution.

Details such as the type and content of the filler, blue pigment and UVA absorber are as described above. The filler, blue pigment and/or UVA absorber may be mixed with the polyamide-imide-based polymer in the polymer solution.

The polymer solution may be stored at -20 °C to 20 °C, -20 °C to 10 °C, -20 °C to 5 °C, -20 °C to 0 °C, or 0 °C to 10 °C.

When stored at the above temperature, deterioration of the polymer solution can be prevented, and the moisture content can be reduced to prevent defects in the film produced therefrom.

In some embodiments, the polymer solution or the viscosity-adjusted polymer solution may be aged (S120).

The aging may be performed by leaving the polymer solution at -10 to 10 °C temperature conditions for 24 hours or more. In this case, the polyamide-imide-based polymer or unreacted material contained in the polymer solution may homogenize the polymer solution by completing the reaction or achieving chemical equilibrium, for example, and the polyamide-imide-based film formed therefrom The mechanical and optical properties of can be substantially uniform over the entire area of the film. Preferably, the aging may be performed at -5 to 10 °C, -5 to 5 °C or -3 to 5 °C temperature conditions, but is not limited thereto.

In one embodiment, the step of degassing the polyamide-imide-based polymer solution (S130) may be further included. By removing moisture and reducing impurities in the polymer solution through the degassing, the reaction yield can be increased, and the surface appearance and mechanical properties of the final film can be excellently implemented.

The degassing may include vacuum defoaming or inert gas purging.

The vacuum degassing may be performed for 30 minutes to 3 hours after depressurizing the reactor containing the polymer solution to 0.1 bar to 0.7 bar. By performing vacuum degassing under these conditions, air bubbles inside the polymer solution can be reduced, and as a result, surface defects of the film prepared therefrom can be prevented, and optical properties such as haze can be excellently implemented.

In addition, the purging may be performed by purging the internal pressure of the tank to 1 to 2 atm using an inert gas. By performing the purging under these conditions, the reaction yield can be increased by removing moisture in the polymer solution and reducing impurities, and excellent optical properties such as haze and mechanical properties can be implemented.

The inert gas may be at least one selected from the group consisting of nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), but is not limited thereto. no. Specifically, the inert gas may be nitrogen.

The vacuum defoaming and the inert gas purging may be performed as separate processes.

For example, a process of vacuum degassing may be performed, and then a process of purging with an inert gas may be performed, but is not limited thereto.

By performing the vacuum defoaming and/or the inert gas purging, physical properties of the surface of the polyamide-imide-based film may be improved.

A gel sheet may be prepared by casting the polymer solution (S200).

For example, a gel sheet may be formed by applying, extruding, and/or drying the polymer solution on a support.

In addition, the casting thickness of the polymer solution may be 200㎛ to 700㎛. When the polymer solution is cast in the above thickness range and produced as a final film through drying and heat treatment, appropriate thickness and thickness uniformity can be secured.

As described above, the polymer solution may have a viscosity of 150,000 cps to 500,000 cps at room temperature. By satisfying the above viscosity range, the polymer solution can be cast with a uniform thickness without defects when cast, and a polyamide-imide-based film with a substantially uniform thickness can be formed without local/partial thickness change during the drying process. can

After casting the polymer solution, it is dried at a temperature of 60 ° C to 150 ° C, 70 ° C to 150 ° C, 80 ° C to 150 ° C, or 90 ° C to 150 ° C for 5 minutes to 60 minutes to prepare a gel sheet. can Specifically, a gel sheet may be prepared by drying the polymer solution at a temperature of 90 ° C. to 140 ° C. for 15 minutes to 40 minutes.

During the drying, part or all of the solvent of the polymer solution may be volatilized to prepare the gel sheet.

A polyamide-imide-based film may be formed by heat-treating the dried gel sheet (S300).

Heat treatment of the gel sheet may be performed, for example, through a thermal curing machine.

The heat treatment of the gel sheet includes heat treatment through at least one heater.

In addition, the heat treatment of the gel sheet may further include heat treatment with hot air.

In one embodiment, the heat treatment of the gel sheet comprises heat treatment with hot air; and performing heat treatment through at least one heater.

In one embodiment, when performing the heat treatment step by the hot air, the amount of heat can be imparted evenly. If heat is not evenly distributed, satisfactory surface roughness may not be implemented or surface quality may become non-uniform, and surface energy may be excessively increased or decreased.

Heat treatment by the hot air may be performed for 5 minutes to 200 minutes in the range of 60 ℃ to 500 ℃. Specifically, the heat treatment of the gel sheet may be performed for 10 to 150 minutes while raising the temperature at a rate of 1.5 °C/min to 20 °C/min in the range of 80 °C to 300 °C. More specifically, heat treatment of the gel sheet may be performed in a temperature range of 140 °C to 250 °C.

At this time, the heat treatment start temperature of the gel sheet may be 60 °C or higher. Specifically, the heat treatment start temperature of the gel sheet may be 80 °C to 180 °C. In addition, the maximum temperature during heat treatment may be 200 °C to 500 °C.

In addition, the heat treatment of the gel sheet by hot air may be performed in two or more steps. Specifically, the heat treatment of the gel sheet by hot air may be performed sequentially in a first hot air treatment step and a second hot air treatment step, wherein the temperature in the second hot air treatment step is higher than the temperature in the first hot air treatment step. can be high

In one embodiment, the heat treatment of the gel sheet may include heat treatment using at least one heater, specifically, heat treatment using a plurality of heaters.

As an example, referring to FIGS. 5 and 6 , the plurality of heaters include a first heater HC, a second heater HN, and a third heater spaced apart in the TD direction of the gel sheet (polyamide-imide film). (HS). The first heater HC may be mounted on the heater mounting parts A1 and B1 to correspond to the central part of the gel sheet, and the second heater HN may be mounted on the heater mounting parts A1 and B1 to correspond to either end of the gel sheet. B1), and the third heater HS may be mounted on the heater mounting parts A1 and B1 so as to correspond to the other one of both ends of the gel sheet. That is, the first heater HC may be mounted on the heater mounting parts A1 and B1 to be positioned between the second heater HN and the third heater HS. The heater mounting parts A1 and B1 may be provided to face the gel sheet. As an example, the heater mounting parts A1 and B1 may be spaced apart from the gel sheet and face each other. 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 heater mounting portions A1 and B1 may be disposed along the direction (or longitudinal direction) of the gel sheet (polyamide-imide-based film).

The at least one heater may include an IR heater. However, the type of at least one heater is not limited to the above example and may be variously changed.

Specifically, the plurality of heaters may include IR heaters. More specifically, the first heater, the second heater, and the third heater may include an IR heater.

Heat treatment by the at least one heater may be performed in a temperature range of 300 °C or higher. Specifically, the heat treatment by the at least one heater may be performed at a temperature range of 300 °C to 500 °C for 1 minute to 30 minutes or 1 minute to 20 minutes.

Referring to FIG. 6, the heater mounting portion B1 and the gel sheet B2 are positioned in parallel, and the heater mounting portion B1 is spaced apart from the gel sheet B2 disposed on the belt A3 by a specific distance. is located

The gel sheet B2 includes three partitioned regions (N region, C region, and S region) in the TD direction. In the above three partitioned regions, region C is a region located in the middle of the gel sheet, and region N and S are regions located at the ends of the gel sheet.

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.

Also, with respect to the widths of the three partitioned regions, a width ratio of w1:w2:w3 may be 1:0.5 to 1.5:1. Specifically, in relation to the widths of the three partitioned regions, w1 = w2 = w3.

The heater mounting portion B1 is positioned parallel to the gel sheet B2 at a location spaced apart from the gel sheet B2 by a specific distance, and the region corresponding to the N region of the gel sheet B2 of the heater mounting portion B1 forms the second heater HN. A region of the heater mounting portion B1 corresponding to region C of the gel sheet B2 includes the first heater HC, and a region of the heater mounting portion B1 corresponding to region S of the gel sheet B2 includes a third heater HS.

In one embodiment, in the heat treatment step through the at least one heater, the temperature of the first heater HC is set to T _HC in the heater mounting part where three heaters spaced apart in the TD direction of the gel sheet are located, , when the temperatures of the second heater HN and the third heater HS are T _HN and T _HS , respectively, T _HN and T _HS are higher than T _HC .

In another embodiment, the heat treatment of the gel sheet includes heat treatment through a first heater, a second heater, and a third heater spaced apart in the TD direction of the gel sheet, corresponding to the center of the gel sheet. When the temperature of the first heater is T _HC and the temperatures of the second heater and the third heater corresponding to both ends of the gel sheet are T _HN and T _HS , respectively, the T _HN and T _HS is higher than T _HC .

Specifically, the T _HC is 300 °C to 360 °C, 300 °C to 350 °C, or 310 °C to 350 °C.

The T _HN and T _HS are 310 °C to 420 °C, 330 °C to 420 °C, or 340 °C to 400 °C

The T _HN and T _HS are 2% to 18%, 3% to 18%, 5% to 15%, 8% to 15%, 10% to 20%, or 10% to 15% higher than T _HC .

In the heat treatment step through the at least one heater, by providing the above-described temperature gradient between the heaters, it is possible to control the RC value in a desired range and implement similar thermal characteristics according to the direction of the film. In addition, not only the thermal properties of the film, but also other mechanical/optical properties such as transmittance, haze, yellowness, modulus, etc., hardly deviate in the TD direction of the film, so that a film of uniform quality can be obtained.

Subsequently, after the heat treatment of the gel sheet, a cooling step may be performed while moving the cured film.

The step of cooling the cured film while moving may include a first temperature reduction step of reducing the temperature at a rate of 100 °C/min to 1000 °C/min; and a second temperature reduction step of reducing the temperature at a rate of 40 °C/min to 400 °C/min.

In this case, in detail, the second temperature reduction step is performed after the first temperature reduction step, and the temperature reduction rate of the first temperature reduction step may be faster than that of the second temperature reduction step.

For example, a maximum speed during the first temperature reduction step is faster than a maximum speed during the second temperature reduction step. Alternatively, the lowest speed during the first temperature reduction step is faster than the lowest speed during the second temperature reduction step.

By performing the cooling step of the cured film in multiple steps as described above, the physical properties of the cured film can be further stabilized, and the optical and mechanical properties of the film established during the curing process can be more stably maintained for a long period of time.

In addition, a step of winding the cooled cured film using a winder may be performed.

At this time, the ratio of the moving speed of the gel sheet on the belt during drying to the moving speed of the cured film during winding is 1:0.95 to 1:1.40. Specifically, the ratio of the moving speed may be 1:0.99 to 1:1.20, 1:0.99 to 1:1.10, or 1:1.00 to 1:1.05, but is not limited thereto.

When the ratio of the moving speed is out of the above range, there is a fear that the mechanical properties of the cured film may be damaged, and flexibility and elastic properties may be deteriorated.

In the manufacturing method of the polyamide-imide-based film, the thickness deviation (%) according to the following general formula 1 may be 3% to 30%. Specifically, the thickness deviation (%) may be 5% to 20%, but is not limited thereto.

<Formula 1> Thickness variation (%) = {(M1-M2)/M1} X 100

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

The polyamide-imide-based film is manufactured according to the above-described manufacturing method, so that it exhibits excellent physical properties optically and mechanically, and may have isotropic and uniform quality. Such a polyamide-imide-based film may be applicable to various uses requiring flexibility and transparency. For example, the polyamide-imide-based film may be applied not only to display devices, but also to solar cells, semiconductor devices, and sensors.

Description of the polyamide-imide-based film prepared according to the above-described manufacturing method is as described above.

The above will be described in more detail by the following examples. However, the following examples are only for illustrating the present invention, and the scope of the examples is not limited only to these.

<Example 1>

After filling the organic solvent, dimethylacetamide (DMAc), in a temperature-controlled reactor under a nitrogen atmosphere at 10 ° C, aromatic diamine, 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl (TFMB) was slowly added while dissolving.

Thereafter, as a dianhydride compound, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) was slowly added and stirred for 2 hours.

Then, as a dicarbonyl compound, terephthaloyl chloride (TPC) was added and stirred for 1 hour, and isophthaloyl chloride (IPC) was added and stirred for 1 hour to prepare a polymer solution.

The obtained polymer solution was applied onto a support and dried at a temperature ranging from 90° C. to 140° C. to prepare a gel sheet.

Thereafter, as a first heat treatment step, the gel sheet was treated with hot air at a temperature of 140 °C to 250 °C. Then, as a second heat treatment step of the gel sheet, a step of passing a plurality of heaters with a temperature gradient in the TD direction was performed. At this time, IR heaters (IR heaters with a maximum temperature of 1,200 °C) were used as a plurality of heaters. Specifically, in the heater mounting part where three spaced heaters are located in the TD direction of the film, the temperature of the heater (first heater) located in the middle is set to 330 ° C. (T _HC ), and the two heaters located on both ends of the heater mounting part Set the temperature of the heaters (second heater and third heater) to 379.5 ° C. (T _HN , T _HS , 1.15T _HC ), which is 15% higher than the temperature of the heater located in the middle, and pass through the gel sheet to a thickness of 50 A polyamide-imide film of μm was obtained.

The specific composition and molar ratio of the polyamide-imide-based polymer are as described in Preparation Examples in Table 1 below. In addition, the contents of nitrogen (N), carbon (C), oxygen (O), and hydrogen (H) elements were measured using an elemental analyzer (model name Flash2000 (Thermo Fisher Scientific, Germany)) to determine the content of each element in the prepared film. It was measured, and the content ratio of elements in the film was as shown in Table 2 below.

<Examples 2 and 3 and Comparative Examples 1 to 3>

As shown in Tables 1 and 2 below, the film was prepared in the same manner as in Example 1, except that the temperature of the heater and the temperature gradient in the TD direction were changed in the step of passing the polymer composition and molar ratio, and a plurality of heaters. manufactured.

<Production Example> Composition of the polymer

<Evaluation example>

The physical properties of the films prepared in Examples and Comparative Examples were measured and evaluated as follows, and the results are shown in Table 3 below.

Evaluation Example 1: Film thickness measurement

Using a digital micrometer 547-401 from Mitutoyo Co., Ltd. in Japan, randomly selected two points in each of the N area, C area, and S area, the average value of the thickness values measured at a total of six points, their deviation, and Deviation rates were calculated.

Evaluation Example 2: Transmittance and haze measurement

Light transmittance and haze were measured according to the JIS K 7136 standard using a haze meter NDH-5000W manufactured by Denshoku Kogyo Co., Ltd. in Japan.

Evaluation Example 3: Measurement of yellowness

Yellow index (YI) was measured by a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) under d65, 10° conditions according to ASTM-E313 standard.

Evaluation Example 4: Modulus measurement

Using Instron's universal testing machine UTM 5566A, cut the sample at least 10 cm in the direction orthogonal to the main shrinkage direction and 10 mm in the main shrinkage direction, mount it on clips at 10 cm intervals, and wait until fracture occurs at room temperature. A stress-strain curve was obtained while stretching at a rate of 10 mm/min. In the above stress-strain curve, the slope of the load relative to the initial strain was taken as the modulus (GPa).

Evaluation Example 5: Solvent Resistance Evaluation

After immersing a film sample (5 cm * 15 cm) having N, C, and S regions in a solvent for 5 seconds, drying at 80 ° C. for 3 minutes, and measuring the haze again by the method according to Evaluation Example 2, the three regions The average value of the haze variation (ΔHz) of the film samples was calculated, and the smaller the haze variation, the better the solvent resistance. MIBK or IPA was used as the solvent.

In addition, in relation to the thickness, transmittance, haze, yellowness, and modulus of the above-described film, two random points were selected from each of the N region, C region, and S region of the prepared film, and the values measured at a total of six points were averaged. The values, their deviations, and deviation rates were obtained and listed in Table 3. The deviation ratio is a value calculated by dividing the deviation by the average value and then multiplying by 100.

Referring to Tables 2 and 3, the content of the nitrogen (N) element in the film is 6 to 6 based on the sum of the weights of carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) elements in the film. In the case of the film according to the embodiment adjusted to 7.5% by weight, the reliability of the film quality can be improved by significantly reducing the quality deviation in the TD direction in terms of the main physical properties of the film, such as transmittance, haze, yellowness, and modulus. It was confirmed that the solvent resistance of the film was excellent as the haze change amount was below a certain level after being immersed in a solvent mainly used for the process.

100: polyamide-imide film
101: first side 102: second side
200: functional layer 300: cover window
400: display unit 500: adhesive layer
A1, B1: Heater mounting part
A2, B2: gel sheet
A3: Belt
HN, HC, HS: heater

Claims (15)

The content of nitrogen (N) element in the 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,
Polyamide-imide based film.
According to claim 1,
The content of nitrogen (N) element in the film is 4 to 7% by weight based on the total weight of the film,
Polyamide-imide based film.
According to claim 1,
The content of nitrogen (N) element in the film is 8 to 11 parts by weight relative to 100 parts by weight of carbon (C) element in the film,
Polyamide-imide based film.
According to claim 1,
The sum of the contents of nitrogen (N) and hydrogen (H) elements in the film is 6 to 9% by weight based on the total weight of the film,
Polyamide-imide based film.
According to claim 1,
When the transmittance was measured at a total of six points by selecting two random points in each of the N region, C region, and S region partitioned in the TD direction of the film,
The average value of transmittance is 80% or more,
A polyamide-imide-based film having a transmittance variation rate of 0.3% or less.
According to claim 1,
When the haze was measured at a total of six points by selecting two random points in each of the N region, C region, and S region partitioned in the TD direction of the film,
The average value of haze is 1% or less,
A polyamide-imide-based film having a haze variation rate of 10% or less.
According to claim 1,
When the yellowness of the film was measured at a total of six points by selecting two random points in each of the N region, C region, and S region partitioned in the TD direction,
The average yellowness value is 5 or less,
A polyamide-imide-based film having a yellowness variation rate of 10% or less.
According to claim 1,
When the modulus was measured at a total of 6 points by selecting two random points in each of the N region, C region, and S region partitioned in the TD direction of the film,
The average value of the modulus is 5 GPa or more,
A polyamide-imide-based film having a modulus variation of 10% or less.
According to claim 1,
The film includes a polyamide-imide-based polymer,
The polyamide-imide-based polymer includes imide-based repeating units and amide-based repeating units in a molar ratio of 2:98 to 70:30,
Polyamide-imide based film.
According to claim 1,
After immersing the film in MIBK for 5 seconds, drying it at 80 ° C. for 3 minutes, the haze change (ΔHz _M ) when measuring the haze is 0.2% or less,
Polyamide-imide based film.
According to claim 1,
After immersing the film in IPA for 5 seconds, drying it at 80 ° C. for 3 minutes, the haze change (ΔHz _I ) when measuring the haze is 0.1% or less,
Polyamide-imide based film.
Including a polyamide-imide-based film and a functional layer,
The content of the nitrogen (N) element in the polyamide-imide-based 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. person,
Cover windows for display devices.
display unit; and
A cover window disposed on the display unit; includes,
The cover window includes a polyamide-imide-based film and a functional layer,
The content of the nitrogen (N) element in the polyamide-imide-based 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. person,
display device.
preparing a polyamide-imide-based polymer solution by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound in an organic solvent;
preparing a gel sheet by casting and then drying the solution; and
Including; heat-treating the gel sheet,
The heat treatment of the gel sheet includes heat treatment through a first heater, a second heater, and a third heater spaced apart in the TD direction of the gel sheet,
When the temperature of the first heater corresponding to the center of the gel sheet is T _HC , and the temperatures of the second heater and the third heater corresponding to both ends of the gel sheet are T _HN and T _HS , respectively , The method for producing the polyamide-imide-based film of claim 1, wherein the T _HN and the T _HS are higher than the T _HC .
According to claim 14,
The T _HC is 300 ° C to 360 ° C,
The method for producing a polyamide-imide-based film, wherein the T _HN and the T _HS are 2% to 18% higher than the T _HC .

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