Polyamide film, preparation method thereof, cover window and display device containing the same

Abstract

The present embodiment relates to a polyamide film having excellent optical and mechanical properties, a preparation method thereof, and a cover window and a display device comprising the same. A polyamide film is provided, which comprises a polyamide polymer and has a plastic characteristic value of 18.45 to 19.97% as shown in Formula 1, a preparation method thereof, and a cover window and a display device composed thereof. [Formula 1] Plastic characteristic value (%) = (100-nIT) / (HIT / HM) In Formula 1, nIT, HIT and HM are measured using a nanoindenter according to ISO14577 standard, nIT is elasticity (%), HIT is indentation hardness (N / mm 2 ), HM is the composite hardness (N / mm 2 ).

Description

Technical Field

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

[0002] Polyamide polymers have excellent resistance to friction, heat and chemicals. 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] Polyamide is used in various fields. For example, polyamide is made into powder form and used as a coating for metal or magnetic wire, and it is mixed with other additives according to its application. In addition, polyamide is used as a decorative and anti-corrosion coating together with fluoropolymers. It also plays a role in bonding the fluoropolymer to the metal substrate. In addition, polyamide is used to coat kitchenware, used as a gas separation membrane due to its heat resistance and chemical resistance, and used in natural gas wells to filter pollutants such as carbon dioxide, hydrogen sulfide and impurities.

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

[0005] When such polyamide films are applied to foldable displays, flexible displays, etc., they are required to have optical properties such as transparency and colorlessness as well as mechanical properties such as flexibility and hardness. However, in general, since optical properties and mechanical properties are in a trade-off relationship, improvement of mechanical properties will impair optical properties.

[0006] Therefore, there is a continuous need to develop polyamide membranes with improved mechanical and optical properties. Summary of the invention

[0007] Technical issues

[0008] The present embodiment aims to provide a polyamide film having excellent optical and mechanical properties, and a cover window and a display device including the same.

[0009] The purpose of this embodiment is to provide a method for preparing a polyamide film having excellent optical and mechanical properties.

[0010] Solutions to technical problems

[0011] The polyamide film according to the present embodiment includes a polyamide-based polymer, wherein a plasticity characteristic value represented by the following Formula 1 is 18.45 to 19.97%.

[0012] [Formula 1]

[0013] Plasticity characteristic value (%) = (100 – nIT) / (HIT / HM)

[0014] In formula 1, nIT, HIT and HM are measured by nanoindentation according to ISO14577 standard, nIT is elasticity (%), HIT is indentation hardness (N / mm 2 ), HM is the composite hardness (N / mm 2 )

[0015] The polyamide film according to the present embodiment includes a polyamide-based polymer, wherein an elastic characteristic value represented by the following Formula 2 is 67 to 69.5%.

[0016] [Formula 2]

[0017] Elasticity characteristic value (%) = nIT / {EIT / (EIT+HIT)}

[0018] In Formula 2, nIT, EIT and HIT are measured by nanoindentation according to ISO14577 standard, nIT is elasticity (%), EIT is indentation modulus (GPa), HIT is indentation hardness (N / mm 2 ).

[0019] The polyamide film according to the present embodiment includes a polyamide-based polymer, wherein a second plasticity characteristic value represented by the following Formula 3 is 384 to 416%.

[0020] [Formula 3]

[0021] Second plasticity characteristic value (%) = (1-nIT) / {HIT / (EIT+HIT)}

[0022] In Formula 3, nIT, EIT and HIT are measured by nanoindentation according to ISO14577 standard, nIT is elasticity (%), EIT is indentation modulus (GPa), HIT is indentation hardness (N / mm 2 ).

[0023] The method for preparing a polyamide film according to the present embodiment includes polymerizing a diamine compound and a dicarbonyl compound in an organic solvent to prepare a solution containing a polyamide-based polymer; casting the polymer solution to prepare a gel sheet; and heat-treating the gel sheet.

[0024] The cover window for a display device according to the present embodiment includes a polyamide film and a functional layer, wherein the polyamide film has a plasticity characteristic value of 18.45 to 19.97% as shown in Formula 1 above.

[0025] The display device according to the present embodiment includes a display unit; and a cover window disposed on the display unit, wherein the cover window includes a polyamide film and a functional layer, and the polyamide film has a plasticity characteristic value of 18.45 to 19.97% as shown in Formula 1 above.

[0026] Beneficial Effects of the Invention

[0027] Since the polyamide film described in the embodiment has a plastic characteristic value within a predetermined range, it has excellent optical properties and can improve the mechanical properties of the deep layer and the surface layer. Therefore, a polyamide film with excellent hardness, elasticity and anti-indentation recovery can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic exploded view of a display device according to an embodiment.

[0029] Figure 2 is a schematic perspective view of a display device according to an embodiment.

[0030] Figure 3 is a schematic cross-sectional view of a display device according to an embodiment.

[0031] Figure 4 is a schematic flow chart of a method for preparing a polyamide membrane according to an embodiment.

[0032] Figure 5 is a schematic perspective view showing a nanoindenter head of a nanoindenter for measuring mechanical properties of a polyamide film.

[0033] Best Mode for Carrying Out the Invention

[0034] Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains can easily implement them. However, the embodiments may be implemented in many different ways and are not limited to those described herein.

[0035] In this specification, when it is mentioned that each film, window, panel, layer, etc. is formed "on" or "under" another film, window, panel, layer, etc., this means not only that one element is directly formed on or under another element, but also that one element is indirectly formed on or under another element, with other elements interposed therebetween. In addition, the terms on or under each element may refer to the accompanying drawings. For ease of explanation, the sizes of individual elements in the accompanying drawings may be exaggerated and do not represent actual sizes. In addition, throughout the specification, the same reference numerals refer to the same elements.

[0036] In the present specification, when a component is referred to as “comprising” an element, it should be understood that other elements may be included rather than excluding other elements unless specifically stated otherwise.

[0037] In this specification, unless otherwise specified, an expression in the singular is interpreted as covering the singular or the plural in the context interpretation.

[0038] Moreover, unless otherwise indicated, the numbers and expressions relating to quantities of ingredients, reaction conditions and so forth used herein are to be understood as being modified by the term "about".

[0039] The terms first, second, etc. are used herein to describe various elements, and the elements are not limited by these terms. These terms are only used to distinguish one element from another element.

[0040] In addition, as used herein, the term "substituted" means substituted by at least one substituent selected from the group consisting of deuterium, -F, -Cl, -Br, -I, hydroxyl, cyano, nitro, amino, amidino, hydrazine, hydrazone, ester, keto, carboxyl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, substituted or unsubstituted alkoxy, substituted or unsubstituted alicyclic organic group, substituted or unsubstituted heterocyclic group, substituted or unsubstituted aryl and substituted or unsubstituted heteroaryl. The substituents listed above may be linked to each other to form a ring.

[0041] Polyamide membrane

[0042] The embodiments of the present invention provide a polyamide film which has excellent optical properties in terms of high light transmittance, low haze and low yellowness index, and also has excellent mechanical properties such as modulus, hardness and restoring force.

[0043] According to one embodiment, the polyamide film comprises a polyamide-based polymer.

[0044] The polyamide film has a plasticity characteristic value (or a first plasticity characteristic value) of 18.45 to 19.97% as shown in Formula 1 below:

[0045] [Formula 1]

[0046] Plasticity characteristic value (%) = (100 – nIT) / (HIT / HM)

[0047] In formula 1, nIT, HIT and HM are measured by nanoindentation according to ISO14577 standard, nIT is elasticity (%), HIT is indentation hardness (N / mm 2 ), HM is the composite hardness (N / mm 2 ).

[0048] For example, in a pressure-indentation depth diagram obtained by pressing a film with a nanoindenter and releasing the indentation, nIT (elasticity) can be defined as the percentage of the work of releasing the indentation relative to the sum of the work of the indentation and the work of the indentation release. The work of releasing the indentation may be related to the work of restoring the film deformed by the indentation. In addition, the amount of work of total deformation minus the work of recovery can also be defined as plastic work. The percentage of plastic work to total deformation work can be defined as plasticity. Plasticity can be expressed by the following formula 4.

[0049] [Formula 4]

[0050] Plasticity (%) = (work of total deformation - work of recovery) / (work of total deformation) × 100 = 100 - nIT

[0051] HIT can indicate the indentation hardness at a depth of tens to hundreds of nanometers from the film surface. For example, HIT may be related to the elastic and plastic properties of the film.

[0052] HM is the Martens hardness, which can characterize the composite properties of elasticity and plasticity against indentation.

[0053] Accordingly, the plasticity characteristic value of Formula 1 can be defined as the relationship between plasticity, the plasticity of the film surface, and the composite properties of elasticity and plasticity of the entire film. If the plasticity characteristic value is adjusted to 18.45 to 19.97%, the optical properties such as transmittance, haze, and yellow index of the polyamide film and the mechanical properties such as flexibility, indentation resistance, and indentation recovery can be improved at the same time.

[0054] In some embodiments, the plasticity characteristic value can be 18.45 to 19.95%, 18.45 to 19.93%, 18.5 to 19.97%, 18.5 to 19.95%, 18.5 to 19.93%, 18.7 to 19.97%, 18.7 to 19.95%, 18.7 to 19.93%, 19 to 19.97%, 19 to 19.95%, or 19 to 19.93%. In this case, optical and mechanical properties can be improved.

[0055] In certain embodiments, the polyamide film may have an elasticity characteristic value of 67 to 69.5% as shown in Formula 2 below.

[0056] [Formula 2]

[0057] Elasticity characteristic value (%) = nIT / {EIT / (EIT+HIT)}

[0058] In Formula 2, nIT, EIT and HIT are measured by nanoindentation according to ISO14577 standard, nIT is elasticity (%), EIT is indentation modulus (GPa), HIT is indentation hardness (N / mm 2 ).

[0059] EIT can indicate the modulus at a depth of tens to hundreds of nanometers from the film surface. For example, EIT may be related to elastic properties among elastic and plastic properties of the film.

[0060] Therefore, the elastic characteristic value of formula 2 can be defined as the relationship between the elastic and plastic components of the film surface and the restoring force. If the elastic characteristic value is adjusted to 67 to 69.5%, the optical properties such as transmittance, haze, and yellow index of the polyamide film and the mechanical properties such as flexibility, indentation resistance, and indentation recovery can be improved at the same time.

[0061] Preferably, the elastic characteristic value can be 67 to 69%, 67 to 68.8%, 67.5 to 69.5%, 67.5 to 69%, 67.5 to 68.8%, 68 to 69.5%, 68 to 69%, 68 to 68.8%, 68.2 to 69.5%, 68.2 to 69% or 68.2 to 68.8%.

[0062] In certain embodiments, the polyamide film may have a second plasticity characteristic value of 384 to 416% as shown in Formula 3 below.

[0063] [Formula 3]

[0064] Second plasticity characteristic value (%) = (1-nIT) / {HIT / (EIT+HIT)}

[0065] In Formula 3, nIT, EIT and HIT are measured by nanoindentation according to ISO14577 standard, nIT is elasticity (%), EIT is indentation modulus (GPa), HIT is indentation hardness (N / mm 2 ).

[0066] The second plastic characteristic value of formula 3 can be defined as the relationship between plasticity and the surface elasticity and plastic component of the film. If the second plastic characteristic value is adjusted to 384 to 416%, the optical properties such as transmittance, haze, yellow index and the mechanical properties such as flexibility, indentation resistance and indentation recovery of the polyamide film can be improved at the same time.

[0067] Preferably, the second plasticity characteristic value may be 384 to 412%, 384 to 410%, 388 to 416%, 388 to 412%, 388 to 410%, 390 to 416%, 390 to 412% or 390 to 410%.

[0068] According to one embodiment, the polyamide film may have an x-direction refractive index (n ) of 1.60 to 1.70, 1.61 to 1.69, 1.62 to 1.68, 1.64 to 1.68, 1.64 to 1.66, or 1.64 to 1.65. x ).

[0069] In addition, the polyamide film may have a y-direction refractive index (n ) of 1.60 to 1.70, 1.61 to 1.69, 1.62 to 1.68, 1.63 to 1.68, 1.63 to 1.66, or 1.63 to 1.64. y ).

[0070] Further, the polyamide film may have a z-direction refractive index (n z ).

[0071] If the x-direction refractive index, y-direction refractive index, and z-direction refractive index of the polyamide film are within the above ranges, when the film is applied to a display device, visibility is excellent not only from the front but also from the side, thereby achieving a wide viewing angle.

[0072] According to one embodiment, the polyamide film may have an in-plane retardation (R o Specifically, the in-plane retardation (R o ) may be 700 nm or less, 600 nm or less, 550 nm or less, 100 nm to 800 nm, 200 nm to 800 nm, 200 nm to 700 nm, 300 nm to 700 nm, 300 nm to 600 nm, or 300 nm to 540 nm.

[0073] In addition, according to one embodiment, the polyamide film may have a thickness direction retardation (R th Specifically, the thickness direction retardation (R th ) may be 4,800 nm or less, 4,700 nm or less, 4,650 nm or less, 1,000 nm to 5,000 nm, 1,500 nm to 5,000 nm, 2,000 nm to 5,000 nm, 2,500 nm to 5,000 nm, 3,000 nm to 5,000 nm, 3,500 nm to 5,000 nm, 4,000 nm to 5,000 nm, 3,000 nm to 4,800 nm, 3,000 nm to 4,700 nm, or 4200 nm to 4650 nm.

[0074] Here, the in-plane retardation (R o ) is the anisotropy of the refractive index of the two mutually perpendicular axes on the film (Δn xy =|n x –n y |) multiplied by the film thickness (d) (Δn xy ×d), which is a measure of the degree of optical isotropy and anisotropy.

[0075] In addition, the thickness direction retardation (R th ) is the two birefringence Δn observed in the cross section along the film thickness direction xz (=|n x –n z |) and Δn yz (=|n y –n z The parameter is defined as the product of the average value of |) and the film thickness (d).

[0076] If the in-plane retardation and the thickness-direction retardation of the polyamide film are within the above ranges, when the film is applied to a display device, optical distortion and color distortion can be minimized, and light leakage from the side can be minimized.

[0077] The polyamide film may further include a filler in addition to the polyamide-based polymer.

[0078] The filler may have an average particle size of 60 nm to 180 nm. Specifically, the average particle size of the first filler may be 80 nm to 180 nm, 100 nm to 180 nm, 110 nm to 160 nm, 120 nm to 160 nm, or 130 nm to 150 nm, but is not limited thereto.

[0079] If the average particle size of the filler is within the above range, optical properties are not deteriorated even if a relatively large amount of the filler is used, compared with other inorganic fillers.

[0080] 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.

[0081] If the refractive index of the filler meets the above range, the refractive index of the filler can be appropriately adjusted with n x 、n y 、n z The relevant birefringence value increases the brightness of the film at all angles.

[0082] On the other hand, if the refractive index of the filler is outside the above range, there may occur a problem that the filler is visually noticeable, or haze increases due to the filler.

[0083] The filler may be present in an amount of 100 ppm to 3,000 ppm based on the total weight of the solid content of the polyamide-based polymer. Specifically, the filler may be present in an amount of 100 ppm to 2,500 ppm, 100 ppm to 2,200 ppm, 200 ppm to 2,500 ppm, 200 ppm to 2,200 ppm, 250 ppm to 2,100 ppm, or 300 ppm to 2,000 ppm based on the total weight of the solid content of the polyamide-based polymer, but is not limited thereto.

[0084] If the content of the filler exceeds the above range, the haze of the film may increase sharply, and the fillers may aggregate with each other on the film surface, so that a foreign body feeling may be visually observed, or a problem in sliding performance or reduced windability may be caused during the production process.

[0085] The filler may include, for example, silicon dioxide and barium sulfate, but is not limited thereto.

[0086] The filler can be used in the form of particles. In addition, the filler surface is not specially coated and can be evenly dispersed in the entire film.

[0087] Since the polyamide film includes the filler, the film can ensure a wide viewing angle without deteriorating optical properties.

[0088] The content of the residual solvent in the polyamide film may be 1,500 ppm or less. For example, the content of the residual solvent may be 1,200 ppm or less, 1,000 ppm or less, 800 ppm or less, or 500 ppm or less, but is not limited thereto.

[0089] The residual solvent refers to the solvent that does not volatilize during the membrane preparation process and remains in the final membrane.

[0090] If the content of the residual solvent in the polyamide film exceeds the above range, the durability of the film may be deteriorated and the brightness may be affected.

[0091] According to one embodiment, when a polyamide film having a thickness of 50 μm is folded to have a curvature radius of 3 mm, the number of foldings before breaking is 200,000 or more.

[0092] When the film was folded to a curvature radius of 3 mm and then unfolded, the number of folds was counted as 1.

[0093] When the folding number of the polyamide film meets the above range, it is advantageous for application in a foldable display device or a flexible display device.

[0094] According to one embodiment, the film has a surface roughness of 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.

[0095] If the surface roughness of the polyamide film satisfies the above range, it is advantageous to obtain high brightness even if the angle formed with the normal line of the surface light source becomes large.

[0096] According to one embodiment, the polyamide film comprises a polyamide-based polymer, and the polyamide-based polymer comprises an amide repeating unit, and, optionally, may comprise an imide repeating unit.

[0097] In some embodiments, the polyamide polymer may include an amide repeating unit and an imide repeating unit in a molar ratio of 100:0 to 90:10. In this case, the mechanical properties such as flexibility, mechanical strength, and indentation resistance / resilience of the polyamide film and the optical properties such as transparency, light transmittance, and haze can be improved at the same time. Preferably, the polyamide polymer may include an amide repeating unit and an imide repeating unit in a molar ratio of 99:1 to 97:3 or 99:1 to 95:5.

[0098] In some embodiments, the polyamide-based polymer may be prepared by reacting reactants including a diamine compound and a dicarbonyl compound simultaneously or sequentially. Specifically, the polyamide-based polymer may be prepared by polymerizing a diamine compound and a dicarbonyl compound.

[0099] Alternatively, the polyamide-based polymer is prepared by polymerizing a diamine compound, a dianhydride compound, and a dicarbonyl compound. Here, the polyamide-based polymer may include an imide repeating unit derived from polymerization of a diamine compound and a dianhydride compound and an amide repeating unit derived from polymerization of a diamine compound and a dicarbonyl compound.

[0100] According to one embodiment, the polyamide membrane may include a polyamide-based polymer, wherein the amide bond is formed by polymerization of a diamine compound and a dicarbonyl compound. The polyamide membrane may optionally include a polyamide-imide-based polymer, wherein the imide bond is formed by further polymerization of a dianhydride compound.

[0101] The diamine compound is a compound capable of forming an imide bond with the dianhydride compound and an amide bond with the dicarbonyl compound to form a copolymer.

[0102] The diamine compound is not particularly limited, and may be, for example, an aromatic diamine compound having an aromatic structure. For example, the diamine compound may be a compound represented by the following Formula 1.

[0103] [Formula 1]

[0104] H 2 N-(E) e -NH 2

[0105] In Formula 1, E can be selected from substituted or unsubstituted divalent C 6 -C 30 Alicyclic group, substituted or unsubstituted divalent C 4 -C 30 Aliphatic heterocyclic group, substituted or unsubstituted divalent C 6 -C 30 Aromatic ring group, substituted or unsubstituted divalent C 4 -C 30 Heteroaromatic ring group, substituted or unsubstituted C 1 -C 30 Alkylene, substituted or unsubstituted C 2 -C 30 Alkenylene, substituted or unsubstituted C 2 -C 30 Alkyne, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) 2 -、-Si(CH 3 ) 2 -、-C(CH 3 ) 2 - and -C(CF 3 ) 2 -.

[0106] e is selected from integers of 1 to 5. When e is 2 or more, E's may be the same as or different from each other.

[0107] (E) in Formula 1 e The group may be selected from the groups represented by the following formulae 1-1a to 1-14a, but is not limited thereto.

[0108]

[0109] Specifically, (E) in Formula 1 e The group may be selected from the groups represented by the following formulae 1-1b to 1-13b, but is not limited thereto.

[0110]

[0111] More specifically, (E) in Formula 1 e It may be a group represented by the above formula 1-6b or a group represented by the above formula 1-9b.

[0112] In one embodiment, the diamine compound may include a compound having a fluorine-containing substituent or a compound having an ether group (—O—).

[0113] 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.

[0114] In another embodiment, one diamine compound may be used as the diamine compound. That is, the diamine compound may be composed of a single component.

[0115] For example, the diamine compound may include 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) represented by the following formula, but is not limited thereto.

[0116]

[0117] The dicarbonyl compound is not particularly limited, but it may be, for example, a compound represented by Formula 3 below.

[0118] [Formula 3]

[0119]

[0120] In formula 3,

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

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

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

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

[0125]

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

[0127]

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

[0129] In one embodiment, a mixture of at least two different dicarbonyl compounds can be used as the dicarbonyl compound. If two or more dicarbonyl compounds are used, at least two dicarbonyl compounds can be used, wherein (J) in the above formula 3 j As the dicarbonyl compound, a group selected from the group represented by the above formulae 3-1b to 3-8b.

[0130] In another embodiment, the dicarbonyl compound may be an aromatic dicarbonyl compound including an aromatic structure.

[0131] The dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), isophthaloyl chloride (IPC), or a combination thereof as shown in the following formula, but is not limited thereto. Preferably, TPC and IPC may be used together.

[0132]

[0133]

[0134] In one embodiment, the polyamide-based polymer may include two or more amide repeating units.

[0135] For example, the two or more amide repeating units may include a first amide repeating unit and a second amide repeating unit. The first amide repeating unit may be formed by reacting a first dicarbonyl compound with a diamine compound. The second amide repeating unit may be formed by reacting a second dicarbonyl compound with a diamine compound.

[0136] The first dicarbonyl compound and the second dicarbonyl compound may be different compounds from each other.

[0137] The first dicarbonyl compound and the second dicarbonyl compound may include two carbonyl groups, respectively. An angle between the two carbonyl groups included in the first dicarbonyl compound may be greater than an angle between the two carbonyl groups included in the second dicarbonyl compound.

[0138] In an exemplary embodiment, the first dicarbonyl compound and the second dicarbonyl compound may be structural isomers of each other. Since two dicarbonyl compounds having a structural isomer relationship are used, a polyamide polymer and a film satisfying Formula 1, Formula 2 and / or Formula 3 can be formed, thereby improving the optical and mechanical properties of the polyamide polymer.

[0139] The first dicarbonyl compound and the second dicarbonyl compound may be aromatic dicarbonyl compounds, respectively. In certain embodiments, the first dicarbonyl compound and the second dicarbonyl compound may each have a benzene ring (phenyl).

[0140] For example, the first dicarbonyl compound and the second dicarbonyl compound may be aromatic dicarbonyl compounds different from each other, but are not limited thereto.

[0141] If the first dicarbonyl compound and the second dicarbonyl compound are aromatic dicarbonyl compounds, respectively, they contain a benzene ring, and thus, they can contribute to improving mechanical properties such as surface hardness and tensile strength of a film containing the polyamide-based polymer prepared therefrom.

[0142] For example, the angle between the two carbonyl groups included in the first dicarbonyl compound may be 160° to 180°, and the angle between the two carbonyl groups included in the second dicarbonyl compound may be 80° to 140°.

[0143] For example, the dicarbonyl compound may include the first dicarbonyl compound and / or the second dicarbonyl compound.

[0144] For example, the first dicarbonyl compound may include TPC, and the second dicarbonyl compound may include IPC, but are not limited thereto.

[0145] If TPC is used as the first dicarbonyl compound and IPC is used as the second dicarbonyl compound in a combination, a film containing the polyamide-based resin prepared therefrom can have high oxidation resistance, productivity, light transmittance, transparency, hardness and modulus, low haze, and excellent indentation resistance and recovery.

[0146] The diamine compound and the dicarbonyl compound may be polymerized to form a repeating unit represented by Formula B below.

[0147] [Formula B]

[0148]

[0149] In Formula B, E, J, e and j are as described above.

[0150] For example, the diamine compound and the dicarbonyl compound may be polymerized to form amide repeating units represented by the following Formulas B-1 and B-2.

[0151] [Formula B-1]

[0152]

[0153] In Formula B-1, y is an integer of 1 to 400.

[0154] [Formula B-2]

[0155]

[0156] In formula B-2, y is an integer of 1 to 400.

[0157] In some embodiments, the molar ratio of the first amide repeating unit to the second amide repeating unit may be 25:75 to 75:25. When the molar ratio of the first and second amide repeating units is within the above range, the plasticity characteristic value and the elasticity characteristic value of the polyamide polymer may be adjusted to satisfy the range of formulas 1 to 3. Therefore, the haze, light transmittance, yellow index, modulus, hardness and resilience of the polyamide film may be improved. Preferably, the molar ratio of the first amide repeating unit to the second amide repeating unit may be 30:70 to 75:25, 35:65 to 75:25 or 40:60 to 75:25.

[0158] The dianhydride compound is not particularly limited, but it may include a cyclic dianhydride compound. For example, the dianhydride compound can reduce the birefringence characteristics of the polyamide resin and improve the optical properties such as the light transmittance of the polyamide film.

[0159] In some embodiments, the cyclic dianhydride compound may include an alicyclic dianhydride compound or an aromatic dianhydride compound.

[0160] The alicyclic dianhydride compound can include a compound in which two anhydride groups are substituted in the alicyclic structure. The alicyclic structure can contain 4 to 12 carbons and can be fully saturated or partially unsaturated. Specifically, the alicyclic dianhydride compound can include, for example, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA).

[0161] Aromatic dianhydride compounds can include compounds in which two anhydride groups are substituted on an aromatic ring with 6 to 30 carbon atoms. The aromatic ring can include benzene, condensed rings such as naphthalene or connecting rings such as biphenyl. For example, aromatic dianhydride compounds can include, for example, 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).

[0162] The two anhydride groups in the dianhydride compound can be directly substituted by cyclic hydrocarbon groups or substituted at symmetrical positions of alicyclic or aromatic rings. In this case, the hardness and indentation recovery of the polyamide film can be improved.

[0163] In one embodiment, the dianhydride compound may not contain a fluorine-containing substituent. For example, when the dianhydride compound contains a fluorine group, the plastic component of the film may be excessively increased, thereby reducing the elasticity and restoring force of the indentation.

[0164] For example, the dianhydride compound may include a compound as shown in Formula 2 below.

[0165] [Formula 2]

[0166]

[0167] In Formula 2, G is a substituted or unsubstituted tetravalent C 4 -C 12 Aliphatic cyclic group, substituted or unsubstituted tetravalent C 4 -C 12 Heteroaliphatic cyclic group, substituted or unsubstituted tetravalent C 6 -C 30 Aromatic cyclic group or substituted or unsubstituted tetravalent C 4 -C 30 Heteroaromatic ring groups, wherein the aliphatic ring group, heteroaliphatic ring group, aromatic ring group or heteroaromatic ring group can exist alone, condensed with each other to form a condensed ring, or bonded through a bonding group selected from the following: -O-, -S-, -C(=O)- and -S(=O) 2 -.

[0168] G in the above Formula 2 may be selected from the groups represented by the following Formulae 2-1a to 2-9a, but is not limited thereto.

[0169]

[0170] For example, G in Formula 2 may be a group represented by the above Formula 2-1a or a group represented by the above Formula 2-5a.

[0171] The diamine compound and the dianhydride compound may be polymerized to form an amic acid group.

[0172] Subsequently, the amic acid group is converted into an imide group by a dehydration reaction. In this case, a polyamide-imide polymer including a polyimide segment and a polyamide segment can be formed.

[0173] In some embodiments, the polyamide film has a thickness deviation of 4 μm or less based on a thickness of 50 μm. The thickness deviation may refer to the deviation between the average thickness measured at 10 random positions of the film and the maximum or minimum value. In this case, since the polyamide film has a uniform thickness, its optical properties and mechanical properties at each point may be uniformly presented.

[0174] The polyamide film may have a haze of 1% or less. For example, the haze may be 0.7% or less or 0.5% or less, but is not limited thereto.

[0175] The polyamide film may have a light transmittance of 80% or more, for example, 82% or more, 85% or more, 88% or more, 89% or more, 80% to 99%, 88% to 99% or 89% to 99%, but is not limited thereto.

[0176] The polyamide film may have a yellow index of 3 or less. For example, the yellow index may be 2.8 or less or 2.5 or less, but is not limited thereto.

[0177] The polyamide film may have a modulus of 6 GPa or more. Specifically, the modulus may be 6.3 GPa or more or 6.5 GPa or more, but is not limited thereto.

[0178] The polyamide film may have a compressive strength of 0.4 kgf / μm or more, and specifically, the compressive strength may be 0.45 kgf / μm or more, or 0.46 kgf / μm or more, but is not limited thereto.

[0179] When the polyamide membrane is perforated at a speed of 10 mm / min using a 2.5 mm spherical tip in UTM compression mode, the maximum diameter (mm) of the perforations including cracks may be 60 mm or less. Specifically, the maximum diameter of the perforations may be 5 mm to 60 mm, 10 mm to 60 mm, 15 mm to 60 mm, 20 mm to 60 mm, 25 mm to 60 mm, or 25 mm to 58 mm, but is not limited thereto.

[0180] The surface hardness of the polyamide film may be HB or higher. Specifically, the surface hardness may be H or higher, or 2H or higher, but is not limited thereto.

[0181] The tensile strength of the polyamide film can be 15kgf / mm 2 Specifically, the tensile strength can be 18kgf / mm 2Above, 20kgf / mm 2 Above, 21kgf / mm 2 Above, or 22kgf / mm 2 The above, but not limited to.

[0182] The elongation of the polyamide film is 15% or more. Specifically, the elongation may be 16% or more, 17% or more, or 17.5% or more, but is not limited thereto.

[0183] The polyamide film in one embodiment has excellent optical properties in terms of low haze, low yellowness index, and high light transmittance, as well as excellent mechanical properties such as modulus, hardness, and elasticity.

[0184] The physical properties of the polyamide film described above are based on a thickness of 40 μm to 60 μm. For example, the physical properties of the polyamide film are based on a thickness of 50 μm.

[0185] The features described above with regard to the composition and properties of the polyamide membrane can be combined with one another.

[0186] For example, the polyamide film includes a polyamide-based polymer and has a light transmittance of 80% or more, a haze of 1% or less, and a yellowness index of 3 or less.

[0187] In addition, the properties of the polyamide film and the plasticity and elasticity characteristics of Formulas 1 to 3 are the result of the combination of chemical and physical properties of the components constituting the polyamide film and conditions in each step of the method for preparing the polyamide film as described below.

[0188] For example, the composition and content of the components constituting the polyamide film, the polymerization conditions and heat treatment conditions in the film preparation method, etc. are combined to achieve the plastic characteristic value and / or elastic characteristic value within the desired range.

[0189] Cover window for display device

[0190] According to one embodiment, a cover window for a display device includes a polyamide film and a functional layer.

[0191] The polyamide film includes a polyamide-based polymer and has a plasticity characteristic value of 18.45 to 19.97% as shown in Formula 1 above.

[0192] The details of the polyamide membrane are as described above.

[0193] The cover window for a display device may be advantageously applied to the display device.

[0194] Since the polyamide-based film has a plastic characteristic value and / or an elastic characteristic value within the above range, it has excellent optical and mechanical properties.

[0195] Display device

[0196] According to one embodiment, a display device includes a display unit; and a cover window disposed on the display unit, wherein the cover window includes a polyamide film and a functional layer.

[0197] The polyamide film includes a polyamide-based polymer and has a plasticity characteristic value of 18.45 to 19.97% as shown in Formula 1 above.

[0198] Details of the polyamide film and cover window are as described above.

[0199] Figure 1 is a schematic exploded view of a display device according to an embodiment. Figure 2 is a schematic perspective view of a display device according to an embodiment. Figure 3 is a schematic cross-sectional view of a display device according to an embodiment.

[0200] Specifically, Figures 1 to 3 A display device is shown, comprising a display unit (400) and a cover window (300) arranged on the display unit (400), wherein the cover window comprises a polyamide film (100) having a first surface (101) and a second surface (102) and a functional layer (200), and an adhesive layer (500) is inserted between the display unit (400) and the cover window (300).

[0201] The display unit (400) is used to display images and may have a flexible feature.

[0202] The display unit (400) may be a display panel for displaying an image. For example, it may be a liquid crystal display panel or an organic electroluminescent display panel. The organic electroluminescent display panel may include a front polarizing plate and an organic EL panel.

[0203] The front polarizing plate may be disposed on the front side of the organic EL panel. Specifically, the front polarizing plate may be attached to a side of the organic EL panel on which an image is displayed.

[0204] The organic EL panel displays images through the self-luminescence of pixel units. The organic EL panel may include an organic EL substrate and a drive substrate. The organic EL substrate may include a plurality of organic electroluminescent units, each of which corresponds to a pixel. Specifically, it may include a cathode, an electron transport layer, a light-emitting layer, a hole transport layer and an anode. The drive substrate may be operably coupled to the organic EL substrate. That is, the drive substrate may be coupled to the organic EL substrate to apply a drive signal such as a drive current, so that the drive substrate may drive the organic EL substrate by applying a current to each organic electroluminescent unit.

[0205] In addition, an adhesive layer (500) may be interposed between the display unit (400) and the cover window (300). The adhesive layer may be an optically transparent adhesive layer, but is not particularly limited.

[0206] The cover window (300) may be disposed on the display unit (400). The cover window is located at the outermost position of the display device, thereby protecting the display unit.

[0207] The cover window (300) may include a polyamide film and a functional layer. The functional layer may be at least one selected from a hard coating layer, a reflection reduction layer, an antifouling layer, and an antiglare layer. The functional layer may be coated on at least one side of the polyamide film.

[0208] According to one embodiment, the polyamide film can be applied to the outside of the display device in the form of a film without changing the display driving method, the color filter or the laminated structure inside the panel, thereby providing a display device with uniform thickness, low haze, high light transmittance, and high transparency. Since there is no need to significantly change the process and increase the cost, it can be beneficial to reduce the production cost.

[0209] According to one embodiment, the polyamide film has not only excellent optical properties, such as high light transmittance, low haze, and low yellowness index, but also excellent mechanical properties, such as hardness, modulus, and elasticity.

[0210] Furthermore, according to an embodiment, the polyamide film can minimize optical distortion because it has at most a certain level of in-plane retardation and thickness-direction retardation, and can also reduce light leakage from the side.

[0211] The polyamide film having the plasticity characteristic value and / or the elasticity characteristic value within the above range may have excellent indentation resistance and recovery force as well as high flexibility, and therefore, may have excellent durability and life when applied to a cover window of a touch display device to which pressure is continuously applied by a hand or a stylus.

[0212] Preparation method of polyamide membrane

[0213] One embodiment provides a method for preparing a polyamide membrane.

[0214] According to one embodiment, a method for preparing a polyamide film includes polymerizing a diamine compound and a dicarbonyl compound in an organic solvent to prepare a solution containing a polyamide-based polymer; casting the polymer solution and then drying it to prepare a gel sheet; and heat-treating the gel sheet.

[0215] See also Figure 4 According to one embodiment, the method for preparing a polyamide film includes polymerizing a diamine compound and a dicarbonyl compound in an organic solvent to prepare a solution containing a polyamide polymer (S100); casting the polymer solution to prepare a gel sheet (S200); and heat-treating the gel sheet (S300).

[0216] According to one embodiment, the method for preparing a polyamide film may further include adjusting the viscosity of the polyamide-based polymer solution ( S110 ), aging the polyamide-based polymer solution ( S120 ), and / or degassing the polyamide-based polymer solution ( S130 ).

[0217] The polyamide film is a film with a polyamide polymer as the main component. The polyamide polymer is a resin containing an amide repeating unit as a structural unit. Optionally, the polyamide polymer may contain an imide repeating unit.

[0218] In the method for preparing a polyamide membrane, a polymer solution for preparing a polyamide-based polymer may be prepared by simultaneously or sequentially mixing a diamine compound and a dicarbonyl compound in an organic solvent in a reactor and reacting the mixture ( S100 ).

[0219] In one embodiment, the step of preparing the polymer solution may include mixing and reacting a diamine compound and a dicarbonyl compound in a solvent to produce a polyamide (PA) solution. The polyamide solution is a solution including a polymer having an amide repeating unit.

[0220] In one embodiment, the step of preparing the polymer solution can be performed by using two different dicarbonyl compounds as the dicarbonyl compound. In this case, the two dicarbonyl compounds can be mixed and reacted simultaneously or sequentially. Preferably, the first dicarbonyl compound and the diamine compound can react to form a prepolymer, and the prepolymer and the second dicarbonyl compound can react to form the polyamide-based polymer. In this case, the plastic characteristic value and / or elastic characteristic value of the polyamide-based polymer can be easily adjusted.

[0221] The polymer contained in the polymer solution includes an amide repeating unit derived from polymerization of the diamine compound and the dicarbonyl compound.

[0222] The details of the diamine compound and the dicarbonyl compound are as described above.

[0223] In one embodiment, the method may further include adjusting the viscosity of the polymer solution after the step of preparing the polymer solution (S110). At room temperature, the viscosity of the polymer solution may be 200,000 cps to 350,000 cps. In this case, the film-forming ability of the polyamide film may be improved, thereby improving the thickness uniformity.

[0224] Specifically, the step of preparing the polymer solution may include mixing a diamine compound and a dicarbonyl compound in an organic solvent simultaneously or sequentially to prepare a first polymer solution; and then adding the dicarbonyl compound to prepare a second polymer solution with a target viscosity.

[0225] In the step of preparing the first polymer solution and the second polymer solution, the viscosity of the polymer solutions may be different from each other. For example, the viscosity of the second polymer solution may be higher than the viscosity of the first polymer solution.

[0226] In the steps of preparing the first polymer solution and the second polymer solution, the stirring speeds may be different from each other. For example, the stirring speed when preparing the first polymer solution may be faster than the stirring speed when preparing the second polymer solution.

[0227] In some embodiments, when preparing the first polymer solution, the first dicarbonyl compound and the second dicarbonyl compound may react with the diamine compound in sequence. In this case, a first polymer solution having a viscosity of 10,000 to 150,000 cps may be formed. Preferably, the viscosity of the first polymer solution may be 10,000 to 100,000 cps, 10,000 to 80,000 cps, 10,000 to 60,000 cps, 20,000 to 150,000 cps, 20,000 to 100,000 cps, 20,000 to 80,000 cps, 20,000 to 60,000 cps, 40,000 to 150,000 cps, 40,000 to 100,000 cps, 40,000 to 80,000 cps, or 40,000 to 60,000 cps.

[0228] In some embodiments, the second dicarbonyl compound may further react with the first polymer solution to form a second polymer solution having a viscosity of 200,000 to 350,000 cps. For example, the step of further reacting the second dicarbonyl compound may be used as a viscosity adjustment step.

[0229] By adjusting the viscosity of the polyamide polymer solution through the first polymer solution and the second polymer solution, the plastic characteristic value and the elastic characteristic value within the desired range can be effectively obtained.

[0230] For example, by controlling the addition order and amount of the first dicarbonyl compound and the second dicarbonyl compound, the viscosity, plastic characteristic value and elastic characteristic value of the polymer solution can be adjusted.

[0231] The molar ratio of the first dicarbonyl compound to the second dicarbonyl compound for preparing the polymer solution may be 25:75 to 75:25, preferably 30:70 to 75:25, 35:65 to 75:25 or 40:60 to 75:25.

[0232] By using the first dicarbonyl compound and the second dicarbonyl compound in such a ratio, a polyamide-based polymer having plasticity and elasticity characteristics within the above ranges can be prepared, and the modulus, haze, transmittance, yellowness index, etc. of the polyamide film can be improved.

[0233] In some embodiments, when forming polymer solution (the first polymer solution), dianhydride compound reacts with diamine compound to form polyamic acid or polyimide.Then, polyamic acid or polyimide can react with dicarbonyl compound to form the polymer solution comprising polyamide-imide.In this case, dianhydride compound as above can be used.Based on the total amount of dicarbonyl compound and dianhydride compound, its molar dosage can be 1 to 10%, preferably 1 to 3% or 1 to 5%.In this case, the viscosity of polymer solution, the first polymer solution and the second polymer solution can be adjusted to the required scope, thereby prepare the polyamide film with plasticity characteristic value and / or elasticity characteristic value in the required range.

[0234] In one embodiment, the mixing and reaction of the solvent, the diamine compound and the dicarbonyl compound can be carried out at a temperature of -20 to 25 ° C. If the above temperature range is exceeded, too few or too many polymer nuclei are formed, making it difficult to form a polyamide polymer having the desired plasticity characteristic value and elasticity characteristic value. Therefore, the mechanical properties and optical properties of the polyamide film may deteriorate. In addition, the viscosity of the polymer solution may be less than a predetermined range. Preferably, the mixing and reaction of the diamine compound and the dicarbonyl compound can be carried out at a temperature of -20 to 20 ° C, -20 to 15 ° C, -20 to 10 ° C, -15 to 20 ° C, -15 to 15 ° C, -15 to 10 ° C, -10 to 20 ° C, -10 to 15 ° C, -10 to 10 ° C, -8 to 20 ° C, -8 to 15 ° C, -8 to 10 ° C, -5 to 20 ° C, -5 to 15 ° C or -5 to 10 ° C.

[0235] In one embodiment, the mixing and reaction of the diamine compound and the dianhydride compound can be carried out at a temperature of 0 to 50° C. If the above temperature range is exceeded, too few or too many polymer nuclei are formed, making it difficult to form a polyamide polymer having the desired plasticity characteristic value and elasticity characteristic value. Therefore, the mechanical properties and optical properties of the polyamide film may deteriorate. In addition, the viscosity of the polymer solution may be less than a predetermined range. Preferably, the mixing and reaction of the diamine compound and the dianhydride compound can be carried out at a temperature of 0 to 45° C., 0 to 40° C., 10 to 50° C., 10 to 45° C., 10 to 40° C., 20 to 50° C., 20 to 45° C. or 20 to 40° C.

[0236] The solid content contained in the polymer solution may be 10 wt % to 30 wt %, but is not limited thereto.

[0237] If the solid content contained in the polymer solution is within the above range, a polyamide film can be efficiently manufactured in the casting step. In addition, the polyamide film thus manufactured can have improved mechanical properties such as modulus and optical properties such as a low yellowness index.

[0238] In another embodiment, the step of preparing the polymer solution may further include adjusting the pH value of the polymer solution. In this step, the pH value of the polymer solution may be adjusted to 4 to 7, such as 4.5 to 7.

[0239] The pH of the polymer solution may be adjusted by adding a pH adjuster. The pH adjuster is not particularly limited, for example, an amine compound such as alkoxyamine, alkylamine, and alkanolamine.

[0240] Since the pH value of the polymer solution is adjusted to the above range, it is possible to prevent defects from occurring in a film made from the polymer solution, and to obtain desired optical and mechanical properties in terms of yellowness index and modulus.

[0241] The pH adjuster may be used in an amount of 0.1 mol % to 10 mol % based on the total moles of monomers in the polymer solution.

[0242] In one embodiment, the organic solvent may be at least one selected from 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.

[0243] 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.

[0244] If stored at the above temperature, it is possible to prevent degradation of the polymer solution and reduce the moisture content, thereby preventing defects in a film prepared therefrom.

[0245] In some embodiments, the polymer solution or the polymer solution whose viscosity has been adjusted may be aged ( S120 ).

[0246] The 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 polymer or unreacted material contained in the polymer solution can complete the reaction or reach a chemical equilibrium, thereby homogenizing the polymer solution. The mechanical properties, optical properties and surface energy characteristics of the polyamide film formed therefrom can be substantially uniform over the entire area of ​​the film. Preferably, the aging can be carried out at a temperature of -5°C to 10°C, -5°C to 5°C or -3°C to 5°C.

[0247] In one embodiment, the method may further include degassing the polyamide polymer solution (S130). The degassing step can remove moisture from the polymer solution and reduce impurities, thereby improving the reaction yield and allowing the final prepared film to have excellent surface appearance and mechanical properties.

[0248] The degassing may include vacuum degassing or purging with an inert gas.

[0249] The vacuum degassing can be performed for 30 minutes to 3 hours after the internal pressure of the tank containing the polymer solution is reduced to 0.1 bar to 0.7 bar. Vacuum degassing under these conditions can reduce bubbles in the polymer solution. Therefore, surface defects of the film made therefrom can be prevented and excellent optical properties such as haze can be achieved.

[0250] Specifically, the purging is performed by purging a tank with an internal pressure of 1 to 2 atm with an inert gas. Purging under these conditions can remove moisture from the polymer solution, reduce impurities, thereby increasing the reaction yield, and obtaining excellent optical properties, such as haze, and mechanical properties.

[0251] The inert gas may be at least one selected from nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn), but is not limited thereto. Specifically, the inert gas may be nitrogen.

[0252] The vacuum degassing and the purging with an inert gas may be performed in separate steps, respectively.

[0253] For example, the vacuum degassing step may be performed first, followed by the purging with an inert gas step, but is not limited thereto.

[0254] The vacuum degassing and / or the purging with an inert gas can improve the physical properties of the surface of the polyamide membrane produced thereby.

[0255] Once the solution including the polyamide-based polymer in the organic solvent is prepared as described above, a filler may be added to the solution.

[0256] The filler has an average particle size of 60 nm to 180 nm, a refractive index of 1.55 to 1.75, and a content of 100 ppm to 3,000 ppm based on the total weight of the solid content of the polyamide-based polymer. In addition, the filler may be barium sulfate.

[0257] The details of the filler are as described above.

[0258] The polymer solution may be cast to prepare a gel sheet ( S200 ).

[0259] For example, the polymer solution may be extruded, coated, and / or dried on a support to form a gel sheet.

[0260] In addition, the casting thickness of the polymer solution may be 200 μm to 700 μm. Since the polymer solution is cast to a thickness within the above range, the final film produced after drying and heat treatment may have an appropriate and uniform thickness.

[0261] As described above, the viscosity of the polymer solution at room temperature may be 200,000 cps to 350,000 cps. When the viscosity satisfies the above range, the polymer solution can be cast to a uniform thickness without defects, and a polyamide film having a substantially uniform thickness can be formed without local / partial thickness variations during drying. In addition, a film having the above-mentioned plastic characteristic values ​​and elastic characteristic values ​​can also be produced.

[0262] The polymer solution is cast and then dried at a temperature of 60 to 150° C. for 5 to 60 minutes to prepare a gel sheet. Specifically, the polymer solution is dried at a temperature of 70 to 90° C. for 15 to 40 minutes to prepare a gel sheet.

[0263] The solvent of the polymer solution may be partially or completely volatilized during the drying process to prepare a gel sheet.

[0264] The dried gel sheet may be heat-treated to form a polyamide film (S300).

[0265] The heat treatment of the gel sheet may be performed, for example, by using a thermosetting device.

[0266] The thermosetting device may heat-treat the gel sheet by hot air.

[0267] If the heat treatment is performed with hot air, heat can be supplied evenly. If the heat supply is uneven, satisfactory surface roughness cannot be obtained, which may increase or decrease the surface tension a lot.

[0268] The heat treatment of the gel sheet may be performed at a temperature range of 60°C to 500°C for 5 to 200 minutes. Specifically, the heat treatment of the gel sheet may be performed at a temperature range of 80°C to 300°C at a heating rate of 1.5°C / min to 20°C / min for 10 to 150 minutes.

[0269] In this case, the initial temperature of the heat treatment of the gel sheet may be 60° C. or higher. Specifically, the initial temperature of the heat treatment of the gel sheet may be 80° C. to 180° C.

[0270] In addition, the maximum temperature of the heat treatment may be 300° C. to 500° C. For example, the maximum temperature of the heat treatment may be 350° C. to 500° C., 380° C. to 500° C., 400° C. to 500° C., 410° C. to 480° C., 410° C. to 470° C., or 410° C. to 450° C.

[0271] In one embodiment, the heat treatment of the gel sheet may be performed in two or more steps.

[0272] Specifically, the heat treatment may include a first hot air treatment step performed at a temperature ranging from 60° C. to 120° C. for 5 to 30 minutes; and a second hot air treatment step performed at a temperature ranging from 120° C. to 350° C. for 10 to 120 minutes.

[0273] The heat treatment under these conditions can cure the gel sheet so as to have appropriate surface hardness, modulus, and surface energy, and can simultaneously ensure high light transmittance, low haze, and an appropriate level of gloss of the cured film.

[0274] In one embodiment, the heat treatment may include passing it through an IR heater. The heat treatment by the IR heater may be performed at a temperature range of 300° C. or more for 1 minute to 30 minutes. Specifically, the heat treatment by the IR heater may be performed at a temperature range of 300° C. to 500° C. for 1 minute to 20 minutes.

[0275] The polyamide film prepared by the preparation method can satisfy Formula 1, 2 and / or 3 as described above, and has excellent optical properties and mechanical properties.

[0276] The polyamide film can be applied to various uses that require flexibility, transparency and a certain brightness level. For example, the polyamide film can be applied to solar cells, displays, semiconductor devices, sensors, etc.

[0277] In particular, since the polyamide film has excellent thickness uniformity and optical properties, it is advantageously applied to a cover window of a display device and a display device. Since it has excellent folding properties, it is advantageously applied to a foldable display device or a flexible display device.

[0278] The details of the polyamide membrane prepared by the method for preparing the polyamide membrane are as described above. DETAILED DESCRIPTION

[0279] Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited thereto.

[0280] Examples and Comparative Examples

[0281] At 10° C., under a nitrogen atmosphere, 675 g of dimethylacetamide (DMAc) as an organic solvent was charged into a 1-liter glass reactor equipped with a temperature-controllable double jacket. Then, 64.0 g (0.200 mol) of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) as an aromatic diamine was slowly added thereto and dissolved.

[0282] Subsequently, the temperature in the reactor was raised to 30° C., 1.77 g (0.006 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was slowly added, and the reaction solution was stirred for 2 h.

[0283] The temperature of the reactor was lowered to 10°C, and 30.37 g (0.15 mol) of terephthaloyl chloride (TPC) was slowly added, followed by stirring for 1 hour. Then, 9.13 g (0.05 mol; 94% of the total introduced molar amount) of isophthaloyl chloride (IPC) was added, followed by stirring the mixture for 1 hour, thereby preparing a first polymer solution. The viscosity of the first polymer solution thus prepared was about 50,000 cps.

[0284] Then, 1 ml of a 10 wt% IPC solution in a DMAc solvent was added thereto, and the mixture was subsequently stirred for 30 minutes. This process was repeated, thereby preparing a second polymer solution having a viscosity of 300,000 cps.

[0285] The second polymer solution was left at about 0°C for about a day, and then coated on a glass plate and dried with hot air at 100°C for 30 minutes. The dried polyamide polymer was peeled off the glass plate and fixed on a pin holder, and then heat-treated at a temperature range of 80°C to 300°C at a heating rate of 2°C / min, thereby obtaining a polyamide film with a thickness of 50 μm.

[0286] The introduction order and amount of the diamine compound, dianhydride compound and dicarbonyl compound are described in the following Table 1. The introduction order is described from the top to the bottom of Table 1, starting with the compound added first, and the amount introduced is recorded as the number of moles relative to 100 moles of the diamine compound.

[0287] In Example 2, 1.18 g (0.006 mole) of butane-1,2,3,4-tetraanhydride was used instead of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA). In the comparative examples, the composition of the polymer was changed as shown in Table 1.

[0288] Evaluation example

[0289] The following properties of the films prepared in the examples and comparative examples were measured and evaluated respectively. The results are shown in Table 1 below.

[0290] Evaluation Example 1: Determination of modulus

[0291] The sample was cut off at least 10 cm in the direction perpendicular to the main shrinkage direction of the film, and 10 cm was cut off in the main shrinkage direction. In the universal testing machine UTM 5566A of Instron, it was fixed by a clamp set at an interval of 10 cm. The sample was stretched at a rate of 12.5 mm / min at room temperature until the sample broke, and a stress-strain curve was obtained. The slope of the load relative to the initial strain on the stress-strain curve was used as the modulus (GPa).

[0292] Evaluation Example 2: Measurement of light transmittance and haze

[0293] According to JIS K 7136 standard, light transmittance and haze were measured using a haze meter NDH-5000W manufactured by Nippon Denshoku Industries Co., Ltd.

[0294] Evaluation Example 3: Determination of Yellowness Index

[0295] The yellowness index (YI) was measured using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) at d65 and 10° according to ASTM-E313 standard.

[0296] Evaluation Example 4: Evaluation of Mechanical Properties

[0297] The composite hardness (Martens hardness), indentation hardness (Vickers hardness), indentation hardness, indentation modulus, elasticity and creep of the film samples were measured using FISCHERSCOPE HM2000 from FISCHER. The measurements were carried out in accordance with ISO 14577-1:2015 and 14577-2:2015. Specifically, at room temperature, a pressure of 30 mN was used as follows: Figure 5 A diamond tip of the shape shown presses the membrane down for 20 seconds, holds it for 5 seconds, and then lifts it up again.

[0298] Figure 5 The nanoindenter tip shown may be a modified Vickers indenter. Specifically, in a Vickers indenter having a square bottom and a pyramid shape in which the four corners of the inclined surfaces intersect at one point, two inclined surfaces extend in a direction parallel to one side of the bottom surface (longitudinal direction) and one vertex intersecting one of the inclined surfaces facing the longitudinal direction may be 0.5 μm (L) away from another vertex where the two inclined surfaces facing the width direction intersect the other inclined surface facing the longitudinal direction. In addition, the tip of the indenter (in contact with the sample) may also be rounded so that the radius of curvature (R) is less than 0.2 μm.

[0299] Table 1

[0300]

[0301] Depend on Figure 1 It can be seen that in the film having a first plasticity characteristic value, a second plasticity characteristic value and / or an elasticity characteristic value according to the embodiment, its mechanical properties such as indentation resistance (hardness), recovery force (elasticity), tensile modulus, etc. are enhanced, as well as excellent optical properties such as transmittance, haze, yellowness index, etc.

[0302] <Description of Reference Numerals>

[0303] 100: Polyamide membrane

[0304] 101: First side 102: Second side

[0305] 200: Functional layer 300: Cover window

[0306] 400: display unit 500: adhesive layer.

Claims

1. A polyamide film comprising a polyamide-based polymer, wherein the plasticity characteristic value represented by the following formula 1 is 18.45 to 19.97%; and the elasticity characteristic value represented by the following formula 2 is 67 to 69.5%: [Formula 1] Plasticity characteristic value % = (100 – nIT) / (HIT / HM) [Formula 2] Elasticity characteristic value % = nIT / {EIT / (EIT+HIT)} In equations 1 and 2, nIT, HIT and HM are measured using a nanoindenter according to ISO 14577, nIT is elasticity %, and HIT is indentation hardness N / mm 2 , HM is the composite hardness N / mm 2 , and EIT is the indentation modulus GPa; The polyamide polymer comprises an amide repeating unit and an imide repeating unit in a molar ratio of 99:1 to 95:5; The amide repeating units include a first amide repeating unit derived from a first dicarbonyl compound and a second amide repeating unit derived from a second dicarbonyl compound; the molar ratio of the repeating unit derived from the first dicarbonyl compound to the repeating unit derived from the second dicarbonyl compound is 40:60 to 75:25; The angle between the two carbonyl groups in the first dicarbonyl compound is greater than the angle between the two carbonyl groups in the second dicarbonyl compound; The polyamide film has an in-plane retardation R of 800 nm or less. o The polyamide film has a thickness direction retardation R of less than 5,000 nm. th ; The in-plane retardation R o It is the anisotropy of the refractive index of the two perpendicular axes on the film, Δn xy =|n x –n y |The product of the film thickness d Δn xy ×d defines the parameters; The thickness direction delay R th The two birefringence Δn observed in the cross section along the film thickness direction xz =|n x –n z | and Δn yz =|n y –n z Parameter defined by the product of the average value of | and the film thickness d. 2 . The polyamide film according to claim 1 , having a modulus of 6 GPa or more, a light transmittance of 80% or more, a haze of 1% or less, and a yellowness index of 3 or less based on a film thickness of 50 μm.

3. A polyamide film as claimed in claim 1, comprising a polyamide polymer, wherein: And the second plasticity characteristic value represented by the following formula 3 is 384 to 416%: [Formula 3] Second plasticity characteristic value % = (1 – nIT) / {HIT / (EIT + HIT)} In formula 3, nIT, EIT and HIT are measured by nanoindentation according to ISO14577 standard, nIT is elasticity %, EIT is indentation modulus GPa, HIT is indentation hardness N / mm 2 .

4. A method for preparing a polyamide film as claimed in claim 1, comprising polymerizing a diamine compound and a dicarbonyl compound in an organic solvent to prepare a solution containing a polyamide polymer; casting the polymer solution to prepare a gel sheet; and heat-treating the gel sheet; the step of polymerizing the diamine compound and the dicarbonyl compound comprises: reacting a diamine compound, a first dicarbonyl compound, and a second dicarbonyl compound to form a first polymer solution having a viscosity of 10,000 to 150,000 cps; and reacting the first polymer solution with an additional amount of a second dicarbonyl compound to form a second polymer solution having a viscosity of 200,000 to 350,000 cps; in, The first dicarbonyl compound comprises terephthaloyl chloride; and the second dicarbonyl compound comprises isophthaloyl chloride.

5. The method for preparing a polyamide film according to claim 4, characterized in that: In the step of forming the first polymer solution, the first dicarbonyl compound and the second dicarbonyl compound react with the diamine compound in sequence, and The step of forming the first polymer solution further includes reacting the diamine compound and the dianhydride compound before adding the dicarbonyl compound.

6. A cover window for a display device, comprising a polyamide film and a functional layer, wherein the polyamide film has a plastic characteristic value of 18.45 to 19.97% as shown in the following formula 1; and an elastic characteristic value of 67 to 69.5% as shown in the following formula 2: [Formula 1] Plasticity characteristic value % = (100 – nIT) / (HIT / HM) [Formula 2] Elasticity characteristic value % = nIT / {EIT / (EIT+HIT)} In equations 1 and 2, nIT, HIT and HM are measured using a nanoindenter according to ISO 14577, nIT is elasticity %, and HIT is indentation hardness N / mm 2 , HM is the composite hardness N / mm 2 , and EIT is the indentation modulus GPa; The polyamide film comprises a polyamide-based polymer, wherein the polyamide-based polymer comprises an amide repeating unit and an imide repeating unit in a molar ratio of 99:1 to 95:5; The amide repeating units include a first amide repeating unit derived from a first dicarbonyl compound and a second amide repeating unit derived from a second dicarbonyl compound; The molar ratio of the repeating units derived from the first dicarbonyl compound to the repeating units derived from the second dicarbonyl compound is 40:60 to 75:25; The angle between the two carbonyl groups in the first dicarbonyl compound is greater than the angle between the two carbonyl groups in the second dicarbonyl compound; The polyamide film has an in-plane retardation R of 800 nm or less. o The polyamide film has a thickness direction retardation R of less than 5,000 nm. th ; The in-plane retardation R o It is the anisotropy of the refractive index of the two perpendicular axes on the film, Δn xy =|n x –n y |The product of the film thickness d Δn xy ×d defines the parameters; The thickness direction delay R th The two birefringence Δn observed in the cross section along the film thickness direction xz =|n x –n z | and Δn yz =|n y –n z Parameter defined by the product of the average value of | and the film thickness d.

7. A display device comprising a display unit; and a cover window disposed on the display unit, wherein the cover window comprises a polyamide film and a functional layer, and the polyamide film has a plastic characteristic value of 18.45 to 19.97% as shown in the following formula 1; and an elastic characteristic value of 67 to 69.5% as expressed by the following formula 2: [Formula 1] Plasticity characteristic value % = (100 – nIT) / (HIT / HM) [Formula 2] Elasticity characteristic value % = nIT / {EIT / (EIT+HIT)} In equations 1 and 2, nIT, HIT and HM are measured using a nanoindenter according to ISO 14577, nIT is elasticity %, and HIT is indentation hardness N / mm 2 , HM is the composite hardness N / mm 2 , and EIT is the indentation modulus GPa; The polyamide film comprises a polyamide-based polymer, wherein the polyamide-based polymer comprises an amide repeating unit and an imide repeating unit in a molar ratio of 99:1 to 95:5; The amide repeating units include a first amide repeating unit derived from a first dicarbonyl compound and a second amide repeating unit derived from a second dicarbonyl compound; The molar ratio of the repeating units derived from the first dicarbonyl compound to the repeating units derived from the second dicarbonyl compound is 40:60 to 75:25; The angle between the two carbonyl groups in the first dicarbonyl compound is greater than the angle between the two carbonyl groups in the second dicarbonyl compound; The polyamide film has an in-plane retardation R of 800 nm or less. o The polyamide film has a thickness direction retardation R of less than 5,000 nm. th ; The in-plane retardation R o It is the anisotropy of the refractive index of the two perpendicular axes on the film, Δn xy =|n x –n y |The product of the film thickness d Δn xy ×d defines the parameters; The thickness direction delay R th The two birefringence Δn observed in the cross section along the film thickness direction xz =|n x –n z | and Δn yz =|n y –n z Parameter defined by the product of the average value of | and the film thickness d.

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