Composite film and display device including the same

Abstract

In the composite film according to the present application, an elastic layer is coated on opposite sides of the hard coat layer, wherein the change characteristic of the modulus of the elastic layer with respect to temperature has been adjusted to a certain range; thus, the surface hardness and elastic recovery characteristic of the hard coat layer can be improved. Thus, it can be advantageously used as a cover window for a flexible display device.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite film having excellent surface hardness and a display device including the same. BACKGROUND

[0002] With the development of IT devices, display technology continues to develop under the impetus of demand. Curved display and bending display technology has been commercialized. In recent years, in the field of mobile devices which require both large screens and portability, flexible display devices which can be flexibly bent or folded in response to external force are preferred. In particular, foldable display devices, the greatest advantage of which is that they are folded into a small size when not in use to enhance their portability, and unfolded to form a large screen when in use.

[0003] The cover window in the flexible display device needs to be flexible and have recoverability. In addition, in the outward folding type display in which the display is exposed to the outside, not only a flexible characteristic is required, but also protection against external force is required.

[0004] Display devices mainly use a polymer film such as transparent polyimide or polyester or a glass substrate as a cover window thereof. However, the polymer film is easily affected by external scratches, and the glass substrate has a problem of insufficient flexibility.

[0005] To solve this problem, Korean Patent Publication No. 2019-0026611 discloses a hard coat film made by sequentially forming a high bending layer and a high hardness layer on a transparent substrate using a siloxane resin, thereby enhancing scratch resistance and flexibility.

[0006] [Prior Art Document]

[0007] [Patent Document]

[0008] (Patent Document 1) Korean Patent Publication No. 2019-0026611 SUMMARY

[0009] TECHNICAL PROBLEM

[0010] In order to improve the surface hardness of the hard coat layer applied to the cover window of the flexible display device, it is generally attempted to increase the thickness of the hard coat layer (upper coat layer) or change the composition of the hard coat layer. However, in this case, the hard coat layer generally loses its flexible characteristic as its brittleness becomes stronger.

[0011] Therefore, as a result of research by the present inventors, it has been found that when an elastic layer, the change characteristic of the modulus of which with respect to temperature has been adjusted to a certain range, is introduced to the opposite side of the hard coat layer (i.e., the lower side of the base film), the surface hardness and elastic recovery characteristic of the hard coat layer can be improved without increasing the thickness of the hard coat layer or changing the composition of the hard coat layer.

[0012] Accordingly, the embodiments to be described below are aimed at providing a composite film having high surface hardness and elastic recovery force as well as flexible properties, and a display device including the same.

[0013] Solution to the problem

[0014] According to an embodiment, there is provided a composite film including a base film; a hard coat layer disposed on one side of the base film; and an elastic layer disposed on the other side of the base film, wherein a ΔE' value according to Equation (1) below is 300 or less:

[0015] ΔE' = E'[-30℃] / E'[50℃]... (1)

[0016] Here, E'[-30℃] is a storage modulus (Pa) of the elastic layer at -30℃, and E'[50℃] is a storage modulus (Pa) of the elastic layer at 50℃.

[0017] According to another embodiment, there is provided a display device including a display panel; and a cover window disposed on a front side of the display panel, wherein the cover window includes a base film; a hard coat layer disposed on one side of the base film; and an elastic layer disposed on the other side of the base film, and a ΔE' value according to Equation (1) above is 300 or less.

[0018] Advantages of the present invention

[0019] In the composite film according to the present embodiment, the elastic layer is coated on the opposite side (i.e., the lower side of the base film) of the hard coat layer, wherein the change characteristic of the modulus of the elastic layer with respect to temperature has been adjusted to a certain range; thus, it is possible to improve the surface hardness and elastic recovery properties of the hard coat layer.

[0020] Accordingly, the composite film according to the present embodiment, when used as a cover window of a display device, for example, a cover window of an outer folding type device or an inner folding type device in which a display is exposed to the outside as shown in Figure 6a and 6b indicated, can have protection against external force as well as flexible properties. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is an exploded perspective view of a display device according to an embodiment.

[0022] Figure 2 is a sectional view of a composite film (cover window) according to an embodiment.

[0023] Figure 3 is a curve showing the relationship between the storage modulus of different elastic layers and temperature, measured by a dynamic mechanical analyzer (DMA).

[0024] Figure 4 shows a cross-sectional view of the sample before (a) and after (b) the indentation in the nanoindentation test.

[0025] Figure 5 shows a cross-sectional view of the sample when the indenter tip is indented (a) and released (b).

[0026] Figure 6a and 6b shows a flexible display device of an inner folding type and a flexible display device of an outer folding type, respectively.

[0027] <LEGEND DESCRIPTION>

[0028] 1: display device, 1a: flexible display device of an inner folding type, 1b: flexible display device of an outer folding type, 2: indenter, 2a: indenter tip, 2b: marker, 10: composite film (cover window), 10a: sample, 20: display panel, 30: substrate, 40: frame, 100: base film, 200: hard coat layer, 300: elastic layer, F max : maximum test force, A p : contact projected area at the maximum test force, h max : maximum depth at the maximum test force, h p : permanent depth that is not recovered after the test force is released DETAILED DESCRIPTION

[0029] BEST MODE FOR CARRYING OUT THE INVENTION

[0030] Hereinafter, various embodiments and examples will be described in detail with reference to the accompanying drawings.

[0031] In the following description of the embodiments, detailed descriptions of related known configurations or functions will be omitted if it is determined that such detailed descriptions can make the subject matter obscure. Further, the sizes of the respective elements in the drawings can be exaggerated for the purpose of convenience or omission, and they can be different from the actual sizes.

[0032] In the present specification, when a part is described as being formed on another part / below another part or connected or coupled to another part, it encompasses not only a case where the parts are directly formed, connected or coupled to each other, but also a case where the parts are indirectly formed, connected or coupled to each other by another part. Further, it is understood that the reference of the upper / lower position of each part can vary according to the direction of the object of observation.

[0033] In the present specification, the terms referring to the respective components are used to distinguish them from each other without intending to limit the scope of the embodiments. Further, in the present specification, unless otherwise specified in the context, a singular expression is also interpreted to encompass a plural expression.

[0034] In the present specification, the term "comprising" is intended to designate a certain feature, region, step, process, element, and / or component. It does not exclude any other feature, region, step, process, element, and / or component from being added or falling within the scope of the present disclosure, unless otherwise specifically stated.

[0035] In the present specification, the terms first, second, and the like are used to describe various components. But these components should not be limited by these terms. The terms are used to distinguish one element from another.

[0036] The molecular weight of a compound or polymer described in the present specification, for example, number average molecular weight or weight average molecular weight, is a well-known relative mass based on carbon-12. Although its unit is not described, it can be understood as the same numerical value of molar mass (g / mole) if necessary.

[0037] In the present specification, the term "substituted" means that at least one substituent is substituted from the group consisting of deuterium, -F, -Cl, -Br, -I, hydroxyl, cyano, nitro, amino, amidino, hydrazine, hydrazone, ester, ketone, carboxyl, substituted or unsubstituted C1-C 30 alkyl, substituted or unsubstituted C2-C 30 alkenyl, substituted or unsubstituted C2-C 30 alkynyl, substituted or unsubstituted C1-C 30 alkoxy, substituted or unsubstituted C6-C 30 alicyclic organic group, substituted or unsubstituted C4-C 30 heterocyclic group, substituted or unsubstituted C6-C 30 aryl, and substituted or unsubstituted C4-C 30 heteroaryl. Two substituents adjacent to each other can be connected to form a ring.

[0038] Figure 1 is an exploded perspective view of a display device according to an embodiment.

[0039] Referring to Figure 1 , a display device (1) according to an embodiment includes a display panel (20); and a cover window (10) disposed at a front side (observation side) of the display panel (20). Specifically, the display device (1) includes the cover window (10), the display panel (20), a substrate (30), and a frame (40) protecting them. In addition, an adhesive layer can be interposed between the cover window (10) and the display panel (20). For example, the adhesive layer can include an optically transparent adhesive.

[0040] The display device according to an embodiment can be flexible. For example, the display device can be a flexible display device or a foldable display device.

[0041] The display panel (20) can be a liquid crystal display (LCD) panel. Alternatively, the display panel (20) can be an organic light emitting display (OLED) panel. The organic light emitting display device can include a front polarizing plate and an organic light emitting display panel. The front polarizing plate can be disposed at a front side of the organic light emitting display panel. In more detail, the front polarizing plate can be coupled to a side of the organic light emitting display panel on which an image is displayed. The organic light emitting display panel displays an image by self-emission of a pixel unit. The organic light emitting display panel includes an organic light emitting substrate and a driving substrate. The organic light emitting substrate includes a plurality of organic light emitting units corresponding to respective pixels. The organic light emitting units each include a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. The driving substrate is operatively coupled to the organic light emitting substrate. That is, the driving substrate can be coupled to the organic light emitting substrate so as to apply a driving signal such as a driving current. More specifically, the driving substrate can drive the organic light emitting substrate by applying a current to each of the organic light emitting units.

[0042] The composite film according to an embodiment is applied to the display device (1) as a cover window (10). Figure 2 is a cross-sectional view of a cover window (i.e., a composite film according to an embodiment) according to an embodiment Figure 1 of FIG. 1A-A').

[0043] Referring to Figure 2 The cover window (10) according to an embodiment includes a base film (100); and a hard coat layer (200) disposed on one side of the base film (100); and an elastic layer (300) disposed on the other side of the base film.

[0044] Properties of the film

[0045] In the composite film, the elastic layer is coated on the opposite side (i.e., the lower side of the base film) of the hard coat layer, in which the change in modulus with respect to temperature has been adjusted to a certain range; thus, the surface hardness and elastic recovery properties of the hard coat layer can be improved.

[0046] The change in modulus with respect to temperature can be measured by, for example, a dynamic mechanical analyzer (DMA).

[0047] According to an embodiment, the ΔE' value according to Equation (1) below is 300 or less.

[0048] ΔE' = E'[-30℃] / E'[50℃]... (1)

[0049] Here, E'[-30℃] is the storage modulus (Pa) of the elastic layer at -30℃, and E'[50℃] is the storage modulus (Pa) of the elastic layer at 50℃.

[0050] For example, the value of ΔΕ' according to the above equation (1) can be 300 or less, 250 or less, 200 or less, 150 or less, 100 or less, or 50 or less. Further, the value of ΔΕ' according to the above equation (1) can be 1 or more, more than 1, 2 or more, 10 or more, 20 or more, 30 or more, 50 or more, or 100 or more. As a specific example, the value of ΔΕ' according to the above equation (1) can be 2 to 300 or 10 to 200.

[0051] Further, in the elastic layer, the modulus at each temperature can be adjusted within a predetermined range.

[0052] As an example, the storage modulus of the elastic layer at -30°C can be 3 x 10 8 Pa or more, 5 x 10 8 Pa or more, 7 x 10 8 Pa or more, or 1 x 10 9 Pa or more. Further, the storage modulus of the elastic layer at -30°C can be 1 x 10 10 Pa or less, 7 x 10 9 Pa or less, 5 x 10 9 Pa or less, or 3 x 10 9 Pa or less.

[0053] As another example, the storage modulus of the elastic layer at -10°C can be 1 x 10 8 Pa or more, 5 x 10 8 Pa or more, 7 x 10 8 Pa or more, or 1 x 10 9 Pa or more. Further, the storage modulus of the elastic layer at -10°C can be 1 x 10 10 Pa or less, 7 x 10 9 Pa or less, 5 x 10 9 Pa or less, or 3 x 10 9 Pa or less.

[0054] As another example, the storage modulus of the elastic layer at 10°C can be 5 x 10 7 Pa or more, 7 x 10 7 Pa or more, 1 x 10 8 Pa or more, or 3 x 10 8 Pa or more. Further, the storage modulus of the elastic layer at 10°C can be 1 x 10 10 Pa or less, 7 x 10 9 Pa or less, 5 x 10 9 Pa or less, or 3 x 10 9 Pa or less.

[0055] As another example, the storage modulus of the elastic layer at room temperature (25°C) can be 1 x 10 6 Pa or greater, 5 x 10 6 Pa or greater, 7 x 10 6 Pa or greater, or 1 x 10 7 Pa or greater. Further, the storage modulus of the elastic layer at room temperature (25°C) can be 1 x 10 10 Pa or less, 5 x 10 9 Pa or less, 1 x 10 9 Pa or less, or 7 x 10 8 Pa or less.

[0056] As another example, the storage modulus of the elastic layer at 30°C can be 1 x 10 6 Pa or greater, 5 x 10 6 Pa or greater, 7 x 10 6 Pa or greater, or 1 x 10 7 Pa or greater. Further, the storage modulus of the elastic layer at 30°C can be 1 x 10 10 Pa or less, 5 x 10 9 Pa or less, 3 x 10 9 Pa or less, or 1 x 10 9 Pa or less.

[0057] As another example, the storage modulus of the elastic layer at 50°C can be 1 x 10 6 Pa or greater, 5 x 10 6 Pa or greater, 7 x 10 6 Pa or greater, or 1 x 10 7 Pa or greater. Further, the storage modulus of the elastic layer at 50°C can be 1 x 10 9 Pa or less, 5 x 10 8 Pa or less, 3 x 10 8 Pa or less, or 1 x 10 8 Pa or less.

[0058] As another example, the storage modulus of the elastic layer at 70°C can be 5 x 10 5 Pa or greater, 1 x 10 6 Pa or greater, 5 x 10 6 Pa or greater, or 8 x 10 6 Pa or greater. Further, the storage modulus of the elastic layer at 70°C can be 5 x 10 8 Pa or less, 1 x 10 8 Pa or less, 7 x 10 7 Pa or less, or 5 x 10 7 Pa or less.

[0059] As another example, the elastic layer can have a storage modulus at 90 °C of 5 x 10 5 Pa or greater, 1 x 10 6 Pa or greater, 5 x 10 6 Pa or greater, or 7 x 10 6 Pa or greater. Further, the elastic layer can have a storage modulus at 90 °C of 5 x 10 8 Pa or less, 1 x 10 8 Pa or less, 7 x 10 7 Pa or less, or 5 x 10 7 Pa or less.

[0060] As a specific example, the elastic layer can have a storage modulus at -30 °C of 1 x 10 9 Pa to 3 x 10 9 Pa, a storage modulus at -10 °C of 1 x 10 9 Pa to 3 x 10 9 Pa, a storage modulus at 10 °C of 3 x 10 8 Pa to 3 x 10 9 Pa, a storage modulus at 30 °C of 1 x 10 7 Pa to 1 x 10 9 Pa, and a storage modulus at 50 °C of 1 x 10 7 Pa to 1 x 10 8 Pa.

[0061] As another specific example, the elastic layer can have a storage modulus at -30 °C of 1 x 10 9 Pa to 3 x 10 9 Pa, and a storage modulus at 50 °C of 1 x 10 7 Pa to 1 x 10 8 Pa.

[0062] In particular, the storage modulus of the elastic layer can be more differentiated at high temperatures. Specifically, the storage modulus of the elastic layer at 50 °C can be 1 x 10 7 Pa or greater. Further, the storage modulus of the elastic layer at 70 °C can be 5 x 10 6 Pa or greater. Further, the storage modulus of the elastic layer at 90 °C can be 5 x 10 6 Pa or greater.

[0063] The modulus of the elastic layer is lower than the modulus of the base film. As an example, the ratio of the storage modulus of the elastic layer to the storage modulus of the base film (elastic layer / base film) can be 0.9 or less at -30°C, for example, 0.5 to 0.9. As another example, the ratio of the storage modulus of the elastic layer to the storage modulus of the base film (elastic layer / base film) can be 0.5 or less at 25°C, for example, 0.005 to 0.5 or 0.05 to 0.5. As another example, the ratio of the storage modulus of the elastic layer to the storage modulus of the base film (elastic layer / base film) can be 0.1 or less at 50°C, for example, 0.001 to 0.1 or 0.001 to 0.05.

[0064] The composite film according to an embodiment can have a surface hardness suitable for use as a cover window.

[0065] The surface hardness of the composite film can be measured by nanoindentation testing.

[0066] Nanoindentation is an analytical technique in which an indenter having a certain geometry is pressed to a material surface with a small force (load) of μN to mN, and then released to obtain a force-displacement curve, which is analyzed to measure various mechanical properties such as tensile properties, residual stress, and hardness and elastic modulus.

[0067] The indenter tip can be various geometries. For example, it can be a conical, pyramidal, or triangular pyramidal (Berkovich triangle or Vickers triangle), cylindrical flat punch shape, etc.

[0068] Figure 4 (a) before and (b) after indentation in nanoindentation testing of the sample are shown. Figure 5 Cross-sectional views of the sample at the time of indentation (a) and release (b) of the indenter tip are shown.

[0069] Reference Figure 4 and Figure 5 Since a common polymer material is viscoelastic, when the sample (10a) is indented by the tip (2a) of the lower end of the indenter (2), it deforms to a maximum depth (h max ) under a maximum test force (F max ). Thereafter, when the indenter (2) is removed to release the indentation by the indenter tip (2a), the deformed portion recovers due to the elasticity of the polymer, while the remaining portion does not permanently recover, leaving a concave indentation (2b) having a certain depth (h p ).

[0070] In this nanoindentation testing, the stiffness (S), projected contact area (A p ), test force (F), maximum indentation depth (h max ) under the maximum force (F max), and obtain force-displacement curves. Based on these results, the indentation modulus (E) can be calculated. IT ), indentation hardness (H) IT Vickers hardness (H) V Martens hardness (H) M Indentation creep (C) IT ), restoration relationship (η) IT Nanoindentation testing can be performed according to standards such as ISO 14577-1:2002(E).

[0071] Vickers hardness (H) V By indentation hardness (H) IT Multiply by 0.0945 (H) I The hardness (×0.0945) can be calculated and measured according to standards such as ISO 14577-1:2002(E). Plastic properties, such as ductility, malleability, and impact resistance, can be measured using Vickers hardness (H...). V The composite membrane according to one embodiment can have, for example, 20 N / mm². 2 Or higher, 25 N / mm 2 Or higher or 30N / mm 2 Or higher, and 70 N / mm 2 Or lower, 50 N / mm 2 Or lower or 40N / mm 2 or lower Vickers hardness (H) V As a specific example, when the surface of the hard coating is measured by nanoindentation testing according to ISO 14577-1:2002(E) standard, the composite film can exhibit a strength of 30 N / mm². 2 Or higher, more specifically, 35 N / mm 2 Up to 70 N / mm 2 Or 30N / mm 2 Up to 40 N / mm 2 Vickers hardness (H) V ).

[0072] The composite film according to one embodiment has a high Vickers hardness (H). V This can be attributed to the elastic layer. For example, a composite membrane can have a strength of 0.5 N / mm, as calculated by the following equation. 2 or higher (N / mm) 2 Specifically, 1.0 N / mm 2 Or higher, 1.5 N / mm 2 Or higher or 2.0 N / mm 2 Or even higher, to give a more specific example, 1 N / mm 2 Up to 10.0 N / mm 2 Or 1.5 N / mm2 to 5.0 N / mm 2 V increased.

[0073] H V increased (N / mm 2 ) = H V 1 (N / mm 2 ) - H V 2 (N / mm 2 )

[0074] Here, H V 1 is the Vickers hardness (H V ) (N / mm 2 ) of the composite film, and H V 2 is the Vickers hardness (H V ) (N / mm 2 ) of the layered structure film excluding the elastic layer in the composite film.

[0075] Further, the Vickers hardness (H V ) of the surface of the elastic layer (single elastic layer) according to an embodiment can be 0.3 N / mm 2 or more, more specifically, 0.3 N / mm 2 to 5 N / mm 2 or 0.3 N / mm 2 to 3.5 N / mm 2 .

[0076] The indentation hardness (H IT ) is also called plastic hardness, which is a measure of the ability of a material to resist permanent (plastic) deformation under maximum force. From this, plastic properties such as ductility, malleability, and impact resistance can be obtained. Specifically, the indentation hardness (H IT ) is calculated as the value (F max / A p ) of the maximum test force (F max ) divided by the projected contact area (A p ) at the penetration depth. The composite film according to an embodiment can have, for example, 250 N / mm 2 or more, 300 N / mm 2 or more, 310 N / mm 2 or more, 320 N / mm 2 or more, 325 N / mm 2 or more, 327 N / mm 2 or more, 328 N / mm 2 or more, 329 N / mm 2 or more, or 330 N / mm 2 or more, and 700 N / mm​2 Or lower, 500 N / mm 2 Or lower, 400 N / mm 2 Or lower or 350 N / mm 2 or lower indentation hardness (H) IT As a specific example, when the surface of the hard coating is measured by nanoindentation testing according to ISO 14577-1:2002(E) standard, the composite film can exhibit a strength of 327 N / mm². 2 Or higher, more specifically, 327 N / mm 2 Up to 500 N / mm 2 Or 327N / mm 2 Up to 400 N / mm 2 Indentation hardness (H) IT ).

[0077] The high pressure indentation hardness (H) of the composite film according to one embodiment IT This can be attributed to the elastic layer. For example, a composite membrane can have a strength of 5 N / mm, as calculated by the following equation. 2 Or higher, specifically, 10 N / mm 2 Or higher or 15 N / mm 2 Or even higher, for example, 5 N / mm 2 Up to 50 N / mm 2 or 10N / mm 2 Up to 30 N / mm 2 H IT Increase (N / mm) 2 ).

[0078] H IT Increase (N / mm) 2 )=H IT 1 (N / mm) 2 )–H IT 2 (N / mm) 2 )

[0079] Here, H IT 1 is the indentation hardness (H) of the composite film. IT (N / mm) 2 ), H IT 2 is the indentation hardness (H) of the layered structure membrane in the composite membrane that does not contain an elastic layer. IT (N / mm) 2 ).

[0080] Furthermore, according to one embodiment, the indentation hardness (H) of the elastic layer IT It can be 2.5 N / mm 2 Up to 50 N / mm 2 2.5N / mm 2Up to 40 N / mm 2 or 3N / mm 2 Up to 35 N / mm 2 .

[0081] Indentation modulus (E) IT The indentation modulus can be calculated using the Poisson's ratio of the sample and indenter, the modulus of the indenter, and the decreasing modulus of the indentation contact. This can be measured using nanoindentation testing according to standards such as ISO 14577-1:2002(E). Elastic properties such as hardness and abrasion resistance can be obtained from the indentation modulus (E). IT The indentation modulus (E) of the composite film according to one embodiment is obtained. IT The pressure can be, for example, 2,500 MPa or greater, 2,800 MPa or greater, 2,900 MPa or greater, 2,935 MPa or greater, or 2,950 MPa or greater, and 4,000 MPa or less, 3,500 MPa or less, 3,300 MPa or less, or 3,100 MPa or less. As a specific example, when the surface of a hard coating is measured by a nanoindentation test according to ISO 14577-1:2002(E) standard, the composite film can have an indentation modulus (E) of 2,700 MPa or greater, more specifically, 2,700 MPa to 4,000 MPa. IT ).

[0082] Furthermore, according to one embodiment, the indentation modulus (E) of the elastic layer IT The pressure can be 50MPa to 2,000MPa, 100MPa to 1,500MPa, or 1,000MPa to 1,500MPa.

[0083] Restoration relationship (η) IT This can be calculated as the elastic reserve deformation work (W) in the force-depth curve. 弹性 ) and total mechanical work of indentation (W) 总 percentage of (W) 弹性 / W 总 ×100%), this curve is obtained by pressing an indenter into the sample surface and then releasing it, and can be measured according to, for example, ISO 14577-1:2002(E) standard. The recovery relationship (η) of the composite membrane according to one embodiment. IT The percentage of recovery can be, for example, 50% or higher, 55% or higher, 60% or higher, 61% or higher, 62% or higher, or 63% or higher, and 85% or lower, 80% or lower, 75% or lower, or 70% or lower. As a specific example, when the surface of a hard coating is measured by a nanoindentation test according to ISO 14577-1:2002(E), the composite film can have a recovery relationship (η) of 61% or higher, more specifically, 61% to 70% or 61% to 65%.IT )..

[0084] In addition, the recovery ratio (η IT ) of the elastic layer according to an embodiment can be 15% to 45%, 20% to 35%, or 20% to 30%.

[0085] Indentation creep (C IT ) describes further deformation of a material under a constant force. To measure indentation creep (C IT ), an indenter is pressed against a sample with a constant force over a longer period of time (several minutes to several hours). It can be calculated by measuring the increased indentation depth due to the continuous pressing. The indentation creep (C IT ) of the composite film according to an embodiment can be, for example, 3.0% or more, 3.5% or more, 4.0% or more, or 4.3% or more, and 7.0% or less, 6.5% or less, 6.0% or less, 5.0% or less, 4.7% or less, 4.6% or less, or 4.5% or less. As a specific example, the composite film can have an indentation creep (C IT ) of 4.0% or more, more specifically, 4.0% to 5.5% or 4.0% to 5.0% when the surface of the hard coat layer is measured by nanoindentation test according to the ISO 14577-1:2002(E) standard.

[0086] In addition, the indentation creep (C IT ) of the elastic layer according to an embodiment can be 5% to 20%, 5% to 15%, 7% to 15%, or 10% to 13%.

[0087] The recovery ratio can be calculated by the following equation, measured according to the nanoindentation test. The recovery ratio of the composite film according to an embodiment can be, for example, 60% or more, 65% or more, 69% or more, 70% or more, or 71% or more, and 90% or less, 85% or less, 80% or less, or 75% or less. As a specific example, the composite film can have a recovery ratio of 69% or more, more specifically, 70% to 90% or 70% to 80% when the surface of the hard coat layer is measured by nanoindentation test according to the ISO 14577-1:2002(E) standard. The recovery ratio can be calculated by the following equation.

[0088] Recovery ratio (%) = [(h max -h p ) / h max ] x 100

[0089] Here, h max is the maximum indentation depth (μm) of the surface of the hard coat layer when pressed down with a force of 30 mN for 15 seconds and held for 5 seconds, and h pIt is the indentation depth (μm) that cannot be recovered even after the force is released.

[0090] The high recovery rate of the composite membrane according to one embodiment can be attributed to the elastic layer. For example, the composite membrane may have a recovery rate increase of 0.5% or higher, specifically 1.0% or higher, 1.5% or higher, or 1.6% or higher, such as 0.5% to 5%, 0.5% to 3%, or 1% to 3% (%), calculated by the following equation.

[0091] Increase in recovery rate (%) = Recovery rate 1 (%) – Recovery rate 2 (%)

[0092] Here, recovery rate 1 is the recovery rate (%) of the composite membrane, and recovery rate 2 is the recovery rate (%) of the layered structure membrane in the composite membrane that does not contain an elastic layer.

[0093] Furthermore, the recovery rate of the elastic layer according to one embodiment can be 25% to 55%, 30% to 50%, 35% to 50%, or 35% to 45%.

[0094] According to one implementation scheme, H is calculated based on the above equation. V Increase (N / mm) 2 It can be 2.0 N / mm 2 Or greater, and the recovery rate increase (%) calculated according to the above equation can be 1.5% or greater.

[0095] The composite film according to one embodiment can have light transmittance, for example, at least a certain level of average visible light transmittance. Therefore, it is advantageous for use as a cover window in display devices. For example, the film can have a transmittance of 70% or higher, 75% or higher, 80% or higher, 82% or higher, 83% or higher, 85% or higher, or 90% or higher. Meanwhile, there is no particular upper limit to the range of light transmittance of the film. It can be, for example, 100% or lower, 98% or lower, 95% or lower, or 90% or lower. The transmittance can be measured, for example, according to the ASTM D1003 standard.

[0096] Furthermore, the composite film according to one embodiment can have a certain degree of haze or even lower. Therefore, it is advantageous for use as a cover window in display devices. For example, the film can have a haze of 5% or lower, 4% or lower, 3.5% or lower, 3% or lower, 2% or lower, or 1.5% or lower. Meanwhile, there is no particular limitation on the lower limit of the film's haze range. It can be, for example, 0% or higher, 0.5% or higher, or 1% or higher. The haze can be measured, for example, according to the ASTM D1003 standard.

[0097] As a specific example, composite films can have 90% or higher light transmittance and 1.5% or lower haze.

[0098] elastic layer

[0099] The elastic layer is formed on opposite sides of the hard coat layer and functions as an impact resistant layer by controlling the modulus, whereby the surface hardness and recovery rate of the hard coat layer can be improved.

[0100] The elastic layer can include an organic resin. The organic resin can include a curable resin, in particular, a thermosetting resin or a UV curable resin. Accordingly, the elastic layer can be a curable coating. The organic resin can function as a binder. In particular, the organic resin can include an elastomer.

[0101] As an example, the elastic layer can include an acrylate-based binder. The content of the acrylate-based binder can be 30% to 98% by weight, based on the weight of the elastic layer. In particular, the content of the acrylate-based binder can be 40% to 95% or 50% to 90% by weight, based on the weight of the elastic layer.

[0102] As a specific example, the acrylate-based binder can include a urethane acrylate-based compound.

[0103] The urethane acrylate-based compound can include a urethane bond as a repeating unit, and can have a plurality of functional groups.

[0104] The urethane acrylate-based compound can be a compound in which the terminal of a urethane compound formed by the reaction of a diisocyanate compound and a polyol is substituted with an acrylate group. For example, the diisocyanate compound can include at least one of a linear, branched, or alicyclic diisocyanate compound having 4 to 12 carbon atoms and an aromatic diisocyanate compound having 6 to 20 carbon atoms. The polyol contains 2 to 4 hydroxyl (-OH) groups, and can be a linear, branched, or alicyclic polyol compound having 4 to 12 carbon atoms or an aromatic polyol compound having 6 to 20 carbon atoms. The terminal substitution with an acrylate group can be performed by an acrylate compound having a functional group capable of reacting with an isocyanate group (-NCO). For example, an acrylate compound having a hydroxyl group or an amine group can be used, and a hydroxyalkyl acrylate or an aminoalkyl acrylate having 2 to 10 carbon atoms can be used.

[0105] The number of functional groups of the urethane acrylate-based compound can be 1 or more, 2 or more, 3 or more, or 4 or more, and 15 or less, 12 or less, 9 or less, 7 or less, 6 or less, 5 or less, or 4 or less. As a specific example, the number of functional groups of the urethane acrylate-based compound can be 2 to 12, 2 to 10, or 2 to 8.

[0106] The urethane acrylate-based compound can be an oligomer. As a specific example, the elastic layer can include a UV-curable urethane acrylate-based oligomer having 2 to 8 functional groups.

[0107] The weight average molecular weight of the urethane acrylate-based compound can be 1,000 or more, 1,500 or more, 2,000 or more, 2,500 or more, 3,000 or more, 3,500 or more, or 4,000 or more, and 50,000 or less, 30,000 or less, 20,000 or less, 10,000 or less, 7,000 or less, or 5,000 or less.

[0108] The glass transition temperature (Tg) of the urethane acrylate-based compound can be -80℃ or more, -70℃ or more, -60℃ or more, -50℃ or more, -40℃ or more, or -30℃ or more, and 100℃ or less, 90℃ or less, 80℃ or less, 70℃ or less, 60℃ or less, or 50℃ or less. As a specific example, the glass transition temperature (Tg) of the urethane acrylate-based compound can be -80℃ to 100℃, -80℃ to 90℃, -80℃ to 80℃, -80℃ to 70℃, -80℃ to 60℃, -70℃ to 100℃, -70℃ to 90℃, -70℃ to 80℃, -70℃ to 70℃, -70℃ to 60℃, -60℃ to 100℃, -60℃ to 90℃, -60℃ to 80℃, -60℃ to 70℃, -60℃ to 60℃, -50℃ to 100℃, -50℃ to 90℃, -50℃ to 80℃, -50℃ to 70℃, or -50℃ to 60℃.

[0109] The elastic layer can further include a photoinitiator. Examples of the photoinitiator include 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, methylbenzoylformate, α,α-dimethoxy-α-phenylacetophenone, 2-benzoyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenyl phosphine oxide, but are not limited thereto. In addition, examples of the commercially available photoinitiator include Irgacure 184, Irgacure 500, Irgacure 651, Irgacue 369, and Irgacule 379. TM 184, Irgacure TM 500, Irgacure TM 651, Irgacue TM 369, IrgaculeTM 907, Darocur TM 1173, Darocur TM MBF, Irgacute TM 819, Darcur TM TPO, Irgacure KIP 100F TM 907 and Esacure TM KIP 100F. The photoinitiator can be used alone or in combination of two or more different types. For example, the content of the photoinitiator can be 0.01 to 10% by weight based on the total weight of the elastic layer, but is not limited thereto.

[0110] The thickness of the elastic layer can be 2 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more, and 100 μm or less, 80 μm or less, 50 μm or less, or 30 μm or less. For example, the thickness of the elastic layer can be 5 to 100 μm. Specifically, the thickness of the elastic layer can be 10 to 100 μm. More specifically, the thickness of the elastic layer can be 30 to 80 μm.

[0111] As a specific example, the thickness of the base film can be 40 to 200 μm, the thickness of the hard coat layer can be 2 to 20 μm, and the thickness of the elastic layer can be 10 to 100 μm.

[0112] The elastic layer can be formed directly on the surface of the base film. Specifically, there can be no other layer between the elastic layer and the base film. In addition, either one of both sides of the elastic layer can be disposed as an interface between the elastic layer and the base film.

[0113] The elastic layer can be formed by applying an elastic coating composition on the base film, and then drying and curing.

[0114] The elastic coating composition can include additives such as a photoinitiator and a solvent, as well as the above-described acrylate-based binder.

[0115] Examples of the solvent include alcohol-based solvents such as methanol, ethanol, isopropanol, and butanol; alkoxy alcohol-based solvents such as 2-methoxyethanol, 2-ethoxyethanol, and 1-methoxy-2-propanol; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and cyclohexanone; ether-based solvents such as propylene glycol monopropyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, and diethylene glycol-2-ethylhexyl ether; and aromatic solvents such as benzene, toluene, and xylene, which can be used alone or in combination.

[0116] The content of the solvent is not particularly limited, as it can be variously adjusted within a range not impairing the physical properties of the coating composition. The weight ratio of the solid content of the components included in the elastic coating composition to the solvent can be 20:80 to 99:1, 30:70 to 70:30, or 40:60 to 60:40 can be employed. If the content of the solvent is within the above range, the composition can have appropriate flowability and coatability.

[0117] The elastic coating composition can be applied by bar coating, knife coating, roll coating, doctor blade coating, die coating, micro gravure coating, comma coating, slot-die coating, lip coating, solution casting, or the like.

[0118] Thereafter, the solvent included in the elastic coating composition can be removed through a drying step. The drying step can be performed at a temperature of 40°C to 100°C, preferably 40°C to 80°C, 50°C to 100°C, or 50°C to 80°C, for about 1 minute to 20 minutes, preferably 1 minute to 10 minutes, or 1 minute to 5 minutes.

[0119] Thereafter, the elastic layer can be cured by light and / or heat. As an example, the elastic layer can be cured by irradiating ultraviolet light at a dose of 0.5 J / cm 2 to 1.5 J / cm 2 under a nitrogen atmosphere.

[0120] Hard coating layer

[0121] The hard coating layer is disposed on one side of the base film.

[0122] The hard coating layer can have an upper side and a lower side, wherein the lower side can face the base film, and the upper side can be the outermost side exposed to the outside. In addition, the lower side of the hard coating layer can be in direct contact with one side of the base film, or can be bonded to one side of the base film through an additional coating layer.

[0123] As an example, the hard coating layer can be directly formed on one side of the base film. As another example, the hard coating layer can be bonded to one side of the base film through a primer coating layer additionally formed on the surface of the base film.

[0124] The hard coating layer can improve the mechanical properties and / or optical properties of the composite film. In addition, the hard coating layer can further include an anti-glare, anti-fouling, anti-static, or the like function.

[0125] The hard coating layer can include at least one of an organic component, an inorganic component, and an organic-inorganic composite component as a hard coating agent.

[0126] As an example, the hard coating layer can include an organic resin. Specifically, the organic resin can be a curable resin. Accordingly, the hard coating layer can be a curable coating layer. In addition, the organic resin can be an adhesive resin.

[0127] Specifically, the hard coat layer can include at least one selected from the group consisting of urethane acrylate-based compounds, acrylate-based compounds, and epoxy acrylate-based compounds. More specifically, the hard coat layer can include urethane acrylate-based compounds and acrylate-based compounds, but is not limited thereto.

[0128] The urethane acrylate-based compound can include a urethane bond as a repeating unit, and can have a plurality of functional groups.

[0129] The urethane acrylate-based compound can be a compound in which a terminal of a urethane compound formed by reacting a diisocyanate compound with a polyol is substituted with an acrylate group. For example, the diisocyanate compound can include at least one of a linear, branched, or alicyclic diisocyanate compound having 4 to 12 carbon atoms and an aromatic diisocyanate compound having 6 to 20 carbon atoms. The polyol contains 2 to 4 hydroxyl (-OH) groups, and can be a linear, branched, or alicyclic polyol compound having 4 to 12 carbon atoms or an aromatic polyol compound having 6 to 20 carbon atoms. The terminal substitution with the acrylate group can be performed by an acrylate compound having a functional group capable of reacting with an isocyanate group (-NCO). For example, an acrylate compound having a hydroxyl group or an amine group can be used, and a hydroxyalkyl acrylate or an aminoalkyl acrylate having 2 to 10 carbon atoms can be used.

[0130] The number of functional groups of the urethane acrylate-based compound can be 2 or more, 5 or more, 7 or more, or 9 or more, and 18 or less, 15 or less, 12 or less, or 10 or less. As a specific example, the number of functional groups of the urethane acrylate-based compound can be 2 to 18, 5 to 18, or 9 to 15.

[0131] The weight average molecular weight of the urethane acrylate-based compound can be 1,500 or more, 2,500 or more, 3,500 or more, or 5,000 or more, and 50,000 or less, 30,000 or less, 20,000 or less, 10,000 or less, or 7,000 or less.

[0132] The glass transition temperature (Tg) of the urethane acrylate-based compound can be -80℃ to 100℃, -80℃ to 90℃, -80℃ to 80℃, -80℃ to 70℃, -80℃ to 60℃, -70℃ to 100℃, -70℃ to 90℃, -70℃ to 80℃, -70℃ to 70℃, -70℃ to 60℃, -60℃ to 100℃, -60℃ to 90℃, -60℃ to 80℃, -60℃ to 70℃, -60℃ to 60℃, -50℃ to 100℃, -50℃ to 90℃, -50℃ to 80℃, -50℃ to 70℃, or -50℃ to 60℃.

[0133] The acrylate-based compound can be at least one selected from the group consisting of substituted or unsubstituted acrylate and substituted or unsubstituted methacrylate. The acrylate-based compound can include 1 to 10 functional groups.

[0134] Examples of the acrylate-based compound include trimethylolpropane triacrylate (TMPTA), trimethylolpropane ethoxylate triacrylate (TMPEOTA), glyceryl propoxylate triacrylate (GPTA), pentaerythritol tetraacrylate (PETA), and dipentaerythritol hexaacrylate (DPHA), but are not limited thereto.

[0135] The acrylate-based compound can have a weight average molecular weight of 500 to 6,000, 500 to 5,000, 500 to 4,000, 1,000 to 6,000, 1,000 to 5,000, 1,000 to 4,000, 1,500 to 6,000, 1,500 to 5,000, or 1,500 to 4,000. The acrylate-based compound can have an acrylate equivalent weight of 50 g / eq to 300 g / eq, 50 g / eq to 200 g / eq, or 50 g / eq to 150 g / eq.

[0136] The epoxy acrylate-based compound can include 1 to 10 functional groups. Examples of the epoxy acrylate-based compound include a monofunctional epoxy acrylate oligomer having a weight average molecular weight of 100 to 300, a bifunctional epoxy acrylate oligomer having a weight average molecular weight of 250 to 2,000, and a tetrafunctional epoxy acrylate oligomer having a weight average molecular weight of 1,000 to 3,000, but are not limited thereto. The epoxy acrylate-based compound can have an epoxy equivalent weight of 50 g / eq to 300 g / eq, 50 g / eq to 200 g / eq, or 50 g / eq to 150 g / eq.

[0137] The content of the organic resin can be 30% to 100% by weight, based on the total weight of the hard coat layer. Specifically, the content of the organic resin can be 40% to 90% or 50% to 80% by weight, based on the total weight of the hard coat layer.

[0138] The hard coating may further include a photoinitiator. Examples of photoinitiators include, but are not limited to, 1-hydroxy-cyclohexyl-phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, methyl benzoyl carbamate, α,α-dimethoxy-α-phenylacetophenone, 2-benzoyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. Furthermore, examples of commercially available photoinitiators include Irgacure. TM 184. Irgacure TM 500, Irgacure TM 651, Irgacue TM 369. Irgacule TM 907, Darocur TM 1173, Darocur TM MBF, Irgacute TM 819, Darcur TM TPO, Irgacoure TM 907 and Esacure TM KIP 100F. Photoinitiators can be used alone or in combination of two or more different types.

[0139] The hard coating may further include a antifouling agent. For example, the hard coating may include a fluorinated compound. The fluorinated compound may have antifouling properties. Specifically, the fluorinated compound may be an acrylate compound having a perfluoroalkyl group. Specific examples may include, but are not limited to, ethyl perfluorohexyl acrylate.

[0140] The hard coating may further include an antistatic agent. The antistatic agent may include an ionic surfactant. For example, the ionic surfactant may include an ammonium salt or a quaternary alkylammonium salt, which may include a halide, such as a chloride or a bromide.

[0141] Further, the hard coat layer can further include additives such as a surfactant, an ultraviolet absorber, an ultraviolet stabilizer, an anti-yellowing agent, a leveling agent, and a dye to improve color values. For example, the surfactant can be a mono- to di-functional fluoro-based acrylate, a fluoro-based surfactant, or a silicone-based surfactant. The surfactant can be used in a form of dispersion or crosslinking in the hard coat layer. Further, examples of the ultraviolet absorber include benzophenone-based compounds, benzotriazole-based compounds, and triazine-based compounds. Examples of the ultraviolet stabilizer include tetramethylpiperidine and the like. The content of the additives can be variously adjusted within a range not impairing physical properties of the hard coat layer. For example, the content of the additives can be 0.01 to 10% by weight based on the weight of the hard coat layer, but is not limited thereto.

[0142] The thickness of the hard coat layer can be 2 μm or more, 3 μm or more, 5 μm or more, or 10 μm or more, and 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. For example, the thickness of the hard coat layer can be 2 to 20 μm. Specifically, the thickness of the hard coat layer can be 5 to 20 μm. If the thickness of the hard coat layer is too small, it can not have sufficient surface hardness to protect the base film, and thus the durability of the composite film can be deteriorated. If it is too large, the flexibility of the composite film can be deteriorated, and the total thickness of the composite film can be increased, which can be disadvantageous for forming a thin film.

[0143] Accordingly, the hard coat layer can be formed of a hard coat layer composition including at least one of an organic-based composition, an inorganic-based composition, and an organic-inorganic composite composition. For example, the hard coat layer composition can include at least one of an acrylate-based compound, a siloxane-based compound, and a silsesquioxane-based compound. Further, the hard coat layer can further include inorganic particles. As a specific example, the hard coat layer can be formed of a hard coat layer composition including a urethane acrylate-based compound, an acrylate-based compound, and a fluoro-based compound.

[0144] The hard coat layer can be formed by applying a hard coat layer composition on the base film, and then drying and curing.

[0145] The hard coat layer composition can include the above-described organic resin, a photoinitiator, an antifouling agent, an antistatic agent, other additives, and / or a solvent.

[0146] Examples of the solvent include alcohol-based solvents such as methanol, ethanol, isopropanol, and butanol; alkoxy alcohol-based solvents such as 2-methoxyethanol, 2-ethoxyethanol, and 1-methoxy-2-propanol; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and cyclohexanone; ether-based solvents such as propylene glycol monopropyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, and diethylene glycol-2-ethylhexyl ether; and aromatic solvents such as benzene, toluene, and xylene, which can be used alone or in combination.

[0147] The content of the solvent is not particularly limited, as it can be variously adjusted within a range not impairing the physical properties of the hard coat composition. The weight ratio of the solid content of the components included in the hard coat composition to the solvent can be 30:70 to 99:1 or 30:70 to 70:30. If the content of the solvent is within the above range, the composition can have appropriate flowability and coatability.

[0148] The hard coat composition can include 10% to 30% by weight of the organic resin, 0.1% to 5% by weight of the photoinitiator, 0.01% to 2% by weight of the stain-proofing agent, and 0.1% to 10% by weight of the antistatic agent. According to the composition, the mechanical properties and the stain-proofing, antistatic properties of the hard coat can be simultaneously improved.

[0149] The hard coat composition can be coated on the base film by a bar coating method, a knife coating method, a roll coating method, a doctor blade coating method, a die coating method, a micro gravure coating method, a comma coating method, a slot-die coating method, a lip coating method, or a solution casting method, etc.

[0150] Thereafter, the solvent included in the hard coat composition can be removed through a drying step. The drying step can be performed at a temperature of 40°C to 100°C, preferably 40°C to 80°C, 50°C to 100°C, or 50°C to 80°C, for about 1 minute to 20 minutes, preferably 1 minute to 10 minutes, or 1 minute to 5 minutes.

[0151] Thereafter, the hard coat composition can be cured by light and / or heat. As an example, the hard coat composition can be cured by irradiating ultraviolet light at a dose of 0.5 J / cm 2 to 1.5 J / cm 2 .

[0152] Base Film

[0153] The base film serves as a base layer for the hard coat, while imparting mechanical properties to the composite film.

[0154] The base film can be a polymer film or a glass substrate, specifically, a strengthened glass substrate having a thickness of less than about 100 pm. For example, the base film can include at least one selected from the group consisting of a polymer film or an ultra-thin glass (UTG).

[0155] Specifically, the base film can be a polymer film. That is, the base film can include a polymer resin.

[0156] According to an embodiment, the base film includes a polyester resin. For example, the base film can be a transparent polyester base film.

[0157] The polyester base resin can be a homopolymer resin or a copolymer resin in which a diol and a dicarboxylic acid are condensed. Further, the polyester base resin can be a blend resin in which a homopolymer resin or a copolymer resin is mixed.

[0158] Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 2,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, diphenyl carboxylic acid, diphenyloxy ethane dicarboxylic acid, diphenyl sulfonic acid, anthracene dicarboxylic acid, 1,3-cyclopentane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethyl malonic acid, succinic acid, 3,3-diethyl succinic acid, glutaric acid, 2,2-dimethyl glutaric acid, adipic acid, 2-methyl dipropionic acid, trimethyl adipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, decanedicarboxylic acid, and the like.

[0159] Further, examples of the diol include ethylene glycol, propylene glycol, hexanediol, neopentyl glycol, 1,2-cyclohexane dimethanol, 1,4-cyclohexane dimethanol, decanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, bis(4-hydroxyphenyl) sulfone, and the like.

[0160] Preferably, the polyester base resin can be an aromatic polyester base resin having excellent crystallinity. For example, it can have a polyethylene terephthalate (PET) resin as a main component.

[0161] The polyester base film can include the polyester base resin, specifically, the PET resin, in an amount of about 85% or more by weight, more specifically, 90% or more, 95% or more, or 99% or more. As another example, the polyester base film can further include a polyester base resin other than the PET resin. Specifically, the polyester base film can further include polyethylene naphthalate (PEN) resin in an amount of up to about 15% by weight. More specifically, the polyester base film can further include the PEN resin in an amount of about 0.1 to 10% by weight or about 0.1 to 5% by weight.

[0162] The polyester-based film having the above composition has enhanced mechanical properties in terms of increased crystallinity and tensile strength during the process of preparing the polyester-based film by heating, stretching, etc.

[0163] The method of preparing the polyester-based film can include (1) extruding a composition including a polyester resin to obtain an unstretched film; (2) stretching the unstretched film in the longitudinal and transverse directions; and (3) heat-setting the stretched film.

[0164] In the above preparation process, the polyester-based film is prepared by extruding a raw material resin and preheating, stretching, and heat-setting it. In this case, the composition of the polyester resin used as a raw material for the polyester-based film is as described above. In addition, the extrusion can be performed at a temperature of 230°C to 300°C or 250°C to 280°C.

[0165] The polyester-based film is preheated at a certain temperature before stretching. Based on the glass transition temperature (Tg) of the polyester resin, the preheating temperature satisfies the range of Tg+5°C to Tg+50°C, and is determined to also satisfy the range of 70°C to 90°C. Within the above range, the polyester-based film can be soft enough to be easily stretched, and also can effectively prevent the breaking phenomenon during the stretching process.

[0166] The stretching is performed by biaxial stretching. For example, it can be performed in the transverse direction (or the tenter direction, TD) and the longitudinal direction (or the machine direction, MD) by simultaneous biaxial stretching or sequential biaxial stretching. Preferably, it can be performed by the sequential biaxial stretching method of performing stretching in one direction first and then in a direction perpendicular thereto.

[0167] The stretching ratio in the longitudinal direction can be in the range of 2.0 to 5.0, more specifically, 2.8 to 3.5. In addition, the stretching ratio in the transverse direction can be in the range of 2.0 to 5.0, more specifically, 2.9 to 3.7. Preferably, the longitudinal stretching ratio (d1) and the transverse stretching ratio (d2) are similar to each other. Specifically, the ratio (d2 / d1) of the longitudinal stretching ratio (d2) to the transverse stretching ratio (d1) can be 0.5 to 1.0, 0.7 to 1.0, or 0.9 to 1.0. The stretching ratio (d1 and d2) refers to a ratio indicating that the length after stretching is 1.0 times the length before stretching. In addition, the stretching speed can be 6.5 m / min to 8.5 m / min, but is not particularly limited thereto.

[0168] The stretched sheet can be heat-set at 150°C to 250°C, more specifically, 160°C to 230°C. The heat-setting can be performed for 5 seconds to 1 minute, more specifically, for 10 seconds to 45 seconds.

[0169] After the heat-setting starts, the sheet can be relaxed in the longitudinal and / or transverse directions, and the temperature range thereof can be 150°C to 250°C.

[0170] According to another embodiment, the base film includes a polyimide-based resin or a polyamide-based resin. Specifically, the base film can be a transparent polyimide-based or polyamide-based film.

[0171] The polyimide-based resin can be prepared by simultaneously or sequentially reacting reactants including a diamine compound and a dianhydride compound. Specifically, the polyimide-based resin can include a polyimide-based polymer prepared by polymerizing the diamine compound and the dianhydride compound. The polyimide-based resin can include imide repeating units derived from polymerization of the diamine compound and the dianhydride compound. In addition, the polyimide-based resin can be polymerized by further including a dicarbonyl compound. Thus, it can include a polyamide-imide-based polymer further including amide repeating units derived from polymerization of the diamine compound and the dicarbonyl compound.

[0172] The diamine compound is not particularly limited, and for example, it can be an aromatic diamine compound containing an aromatic structure. For example, the diamine compound can be a compound represented by the following Formula 1.

[0173] [Formula 1]

[0174] H2N-(E) e -NH2

[0175] In Formula 1, E is selected from a substituted or unsubstituted divalent C6-C 30 aliphatic cyclic group, a substituted or unsubstituted divalent C4-C 30 aliphatic heterocyclic group, a substituted or unsubstituted divalent C6-C 30 aromatic cyclic group, a substituted or unsubstituted divalent C4-C 30 heteroaromatic cyclic group, a substituted or unsubstituted C1-C 30 alkylene group, a substituted or unsubstituted C2-C 30 alkenylene group, a substituted or unsubstituted C2-C 30 alkynylene group, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-; and e is an integer selected from 1 to 5. When e is 2 or more, E can be the same as or different from each other.

[0176] (E) in Formula 1 e may be selected from groups represented by the following Formulas 1-1a to 1-14a, but is not limited thereto.

[0177]

[0178] Specifically, (E) in Formula 1 e may be selected from groups represented by the following Formulas 1-1b to 1-13b, but is not limited thereto.

[0179]

[0180] More specifically, (E) in the above Formula 1 e may be a group represented by the above Formula 1-6b.

[0181] In an embodiment, the diamine compound can include a compound having a fluorine-containing substituent. Alternatively, the diamine compound can consist of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent can be a fluorinated hydrocarbon group, and specifically can be a trifluoromethyl group. However, it is not limited thereto.

[0182] In an embodiment, a diamine compound can be used as the diamine compound. That is, the diamine compound can consist of a single component.

[0183] For example, the diamine compound can include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) represented by the following formula, but is not limited thereto.

[0184]

[0185] The dianhydride compound has a low birefringence value, and thus it can contribute to enhancement of optical properties such as transmittance of a film including a polyimide-based resin.

[0186] The dianhydride compound is not particularly limited, but it can be an aromatic dianhydride compound containing an aromatic structure. For example, the aromatic dianhydride compound can be a compound represented by the following Formula 2.

[0187] [Formula 2]

[0188]

[0189] In Formula 2, G can be a bonding group selected from a substituted or unsubstituted tetravalent C6-C 30 an aliphatic cyclic group, a substituted or unsubstituted tetravalent C4-C 30 an aliphatic heterocyclic group, a substituted or unsubstituted tetravalent C6-C 30 an aromatic cyclic group, or a substituted or unsubstituted tetravalent C4-C 30 a heteroaromatic cyclic group, wherein the aliphatic cyclic group, the aliphatic heterocyclic group, the aromatic cyclic group, or the heteroaromatic cyclic group can exist individually, be fused to each other to form a condensed ring, or be bonded by a bonding group selected from a substituted or unsubstituted C1-C 30 alkylene, a substituted or unsubstituted C2-C 30 alkenylene, a substituted or unsubstituted C2-C 30 alkynylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-.

[0190] G in the above Formula 2 can be a group represented by Formulae 2-1a to 2-9a below, but is not limited thereto.

[0191]

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

[0193] In one embodiment, the dianhydride compound can include a compound having a fluorine-containing substituent. Alternatively, the dianhydride compound can consist of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent can be a fluorinated hydrocarbon group, and specifically can be a trifluoromethyl group. But it is not limited thereto.

[0194] In another embodiment, the dianhydride compound can consist of a single component or a mixture of two components.

[0195] For example, the dianhydride compound can include 2,2'-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) represented by the following formula, but is not limited thereto.

[0196]

[0197] The diamine compound and the dianhydride compound can be polymerized to form a polyamic acid.

[0198] Subsequently, the polyamic acid can be converted into a polyimide by a dehydration reaction. The polyimide can include a repeating unit represented by the following Formula A.

[0199] [Formula A]

[0200]

[0201] In Formula A, E, G, and e are as described above.

[0202] For example, the polyimide can include a repeating unit represented by the following Formula A-1, but is not limited thereto.

[0203] [Formula A-1]

[0204]

[0205] In Formula A-1, n can be an integer of 1 to 400.

[0206] The dicarbonyl compound is not particularly limited, but it can be, for example, a compound represented by the following Formula 3.

[0207] [Formula 3]

[0208]

[0209] In Formula 3, J is selected from the group consisting of a substituted or unsubstituted divalent C6-C 30 an aliphatic cyclic group, a substituted or unsubstituted divalent C4-C 30 an aliphatic heterocyclic group, a substituted or unsubstituted divalent C6-C 30 an aromatic cyclic group, a substituted or unsubstituted divalent C4-C 30 a heteroaromatic cyclic group, a substituted or unsubstituted C1-C 30 alkylene, a substituted or unsubstituted C2-C 30 alkenylene, a substituted or unsubstituted C2-C 30 alkynylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-; j is selected from an integer of 1 to 5. When j is 2 or more, J can be the same as or different from each other. X is a halogen atom. Specifically, X can be F, Cl, Br, I, or the like. More specifically, X can be Cl, but is not limited thereto.

[0210] (J) in Formula 3 above j may be selected from the group consisting of the groups represented by Formulas 3-1a to 3-14a below, but is not limited thereto.

[0211]

[0212] Specifically, (J) in Formula 3 above j may be selected from the group consisting of the groups represented by Formulas 3-1b to 3-8b below, but is not limited thereto.

[0213]

[0214] More specifically, (J) in Formula 3 j may be a group represented by Formula 3-1b above, a group represented by Formula 3-2b above, or a group represented by Formula 3-3b above.

[0215] In an embodiment, a mixture of at least two different dicarbonyl compounds from each other can be used as the dicarbonyl compound. If two or more dicarbonyl compounds are used, (J) in Formula 3 above j may be selected from at least two dicarbonyl compounds from the group consisting of the groups represented by Formulas 3-1b to 3-8b above.

[0216] In another embodiment, the dicarbonyl compound can be an aromatic dicarbonyl compound including an aromatic structure.

[0217] For example, the dicarbonyl compound can include a first dicarbonyl compound and / or a second dicarbonyl compound different from the first dicarbonyl compound.

[0218] The first dicarbonyl compound and the second dicarbonyl compound can each be an aromatic dicarbonyl compound.

[0219] The first dicarbonyl compound and the second dicarbonyl compound can be different aromatic dicarbonyl compounds from each other, but they are not limited thereto.

[0220] If the first dicarbonyl compound and the second dicarbonyl compound are each an aromatic dicarbonyl compound, they include a benzene ring. Thus, they are helpful in improving the mechanical properties, such as surface hardness and tensile strength, of a film containing the polyamide-imide-based resin produced thereby.

[0221] The dicarbonyl compound can include terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), and 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC) represented by the following formulae, or a combination thereof. But it is not limited thereto.

[0222]

[0223] For example, the first dicarbonyl compound can include BPDC, and the second dicarbonyl compound can include TPC, but they are not limited thereto.

[0224] Specifically, if BPDC is used as the first dicarbonyl compound and TPC is used as the second dicarbonyl compound in a proper combination, a film containing the polyamide-imide-based resin produced thereby can have high oxidation resistance.

[0225] Alternatively, the first dicarbonyl compound can include IPC (isophthaloyl chloride), and the second dicarbonyl compound can include TPC, but they are not limited thereto.

[0226] Specifically, if IPC is used as the first dicarbonyl compound and TPC is used as the second dicarbonyl compound in a proper combination, a film containing the polyamide-imide-based resin produced thereby can have high oxidation resistance while reducing manufacturing costs.

[0227] The diamine compound and the dicarbonyl compound can be polymerized to form a repeating unit represented by the following formula B.

[0228] [Formula B]

[0229]

[0230] In formula B, E, J, e, and j are as described above.

[0231] For example, the diamine compound and the dicarbonyl compound can be polymerized to form amide repeating units represented by the following formulae B-1 and B-2.

[0232] [Formula B-1]

[0233]

[0234] In Formula B-1, x is an integer of 1 to 400.

[0235] [Formula B-2]

[0236]

[0237] In Formula B-2, y is an integer of 1 to 400.

[0238] The thickness of the base film can be 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, or 100 μm or more, and 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less. As a specific example, the thickness of the base film can be 20 μm to 500 μm, more specifically 40 μm to 200 μm or 50 μm to 200 μm.

[0239] The base film can have a certain level of optical properties and mechanical properties.

[0240] The base film can have a haze of 3% or less. For example, the haze of the base film can be 2% or less, 1.5% or less, or 1% or less, but is not limited thereto.

[0241] The base film can have a yellow index (YI) of 5 or less. For example, the yellow index of the base film can be 4 or less, 3.8 or less, 2.8 or less, 2.5 or less, 2.3 or less, or 2.1 or less, but is not limited thereto.

[0242] The base film can have a storage modulus of 1 x 10 9 Pa to 3 x 10 9 Pa. Specifically, the base film can have a storage modulus of 1.5 x 10 9 Pa to 3 x 10 9 Pa, more specifically, 2 x 10 9 Pa to 3 x 10 9 MPa, but is not limited thereto.

[0243] The base film can have a transmittance of 80% or more. For example, the transmittance of the base film can be 85% or more, 88% or more, 89% or more, 80% to 99%, or 85% to 99%, but is not limited thereto.

[0244] The base film can have a compressive strength of 0.4 kgf / μm or more. Specifically, the base film can have a compressive strength of 0.45 kgf / μm or more or 0.46 kgf / μm or more, but is not limited thereto.

[0245] The base film can have a surface hardness of HB or more. Specifically, the surface hardness of the base film can be H or more or 2H or more, but is not limited thereto.

[0246] The base film can have a tensile strength of 15 kgf / mm 2 or more. Specifically, the tensile strength of the base film can 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.

[0247] The base film can have an elongation of 15% or more. Specifically, the elongation of the base film can be 16% or more, 17% or more, or 17.5% or more, but is not limited thereto.

[0248] Mode of the Invention

[0249] The following examples are provided to help understanding and the scope of the practice is not limited thereto.

[0250] Preparation Example: Hard Coat Composition A

[0251] The hard coat composition was prepared by compounding the composition shown in Table 1 below.

[0252] [Table 1]

[0253]

[0254]

[0255] Preparation Example: Elastic Coat Compositions A to E

[0256] Each of the elastic coat compositions A to E was prepared by compounding the composition shown in Table 2 below. In each composition, a urethane acrylate-based oligomer having the functional groups and molecular weight shown in Table 3 below was used as a binder.

[0257] [Table 2]

[0258] Elastic coating composition % by weight Adhesive One of urethane acrylate elastomers A to E 47.6 UV initiator Irgacure 184 and the like 2.4 Solvent Methyl ethyl ketone and methyl isobutyl ketone 50.0

[0259] [Table 3]

[0260] Adhesive type Number of functional groups Molecular weight Elastic coating composition A Urethane acrylate elastomer A 3 2,800 Elastic coating composition B Urethane acrylate elastomer B 5 4,600 Elastic coating composition C Urethane acrylate elastomer C 3 4,000 Elastic coating composition D Urethane acrylate elastomer D 3 22,000 Elastic coating composition E Urethane acrylate elastomer E 3 8,000

[0261] Test Example 1: Modulus (Elastic Layer)

[0262] a. Samples: Elastic coating compositions A through E were coated onto the releasable surface of the releasable membrane to a thickness of 25 μm using Mayer rods. Subsequently, they were heat-treated at 60°C for 2 minutes to dry the solvent in the coating compositions, and then subjected to a nitrogen atmosphere at 1 J / cm². 2 The sample is irradiated with a dose of ultraviolet light and then released from the release surface. The resulting single elastic layer, with a thickness of 25 to 50 μm, is cut into pieces 50 mm long and 10 mm wide to prepare samples.

[0263] b. Equipment: Manufacturer: Hitachi, Product Name: DMA7100

[0264] c. Conditions

[0265] -DMA mode: Tension mode

[0266] - Frequency: 1Hz

[0267] - Double cantilever clamp: The two ends of the sample are clamped at a distance of approximately 20mm.

[0268] - Heating method: from -50℃ to 100℃ at a rate of 5℃ / minute.

[0269] d. Results: Based on the temperatures measured under the above conditions, the storage modulus (Pa) of each sample is shown in Table 4 below. Figure 3 As shown. Furthermore, the following equation, ΔE', was calculated and is shown in Table 5 below. ΔE'=E'[-30℃] / E'[50℃]. Here, E'[-30℃] is the storage modulus (Pa) of the elastic layer at -30℃, and E'[50℃] is the storage modulus (Pa) of the elastic layer at 50℃.

[0270] [Table 4]

[0271]

[0272] [Table 5]

[0273]

[0274] The results above show that the ΔE' of the elastic layers prepared with elastic coating compositions A, B and E respectively is confirmed to be 300 or less, while the ΔE' of the elastic layers prepared with elastic coating compositions C and D respectively is greater than 300.

[0275] Test Example 2: Nanoindentation Test (Elastic Layer)

[0276] a. Samples: A4-sized monolayer elastic layer samples were prepared from elastic coating compositions A to E in the same manner as in part a of Test Example 1 above. These samples were then stored at 25±5°C and 50±5% RH until testing, without any additional pretreatment.

[0277] b. Apparatus and method: Vickers hardness (Hv), indentation hardness (HIT), indentation modulus (EIT), recovery behavior (ηR), and indentation creep (CIT) of the samples were measured using a nanoindenter surface analyzer (FISCHERSCOPE HM2000, FISCHER) according to the standards of ISO 14577-1:2002(E) and 14577-2:2002(E). V ), indentation hardness (HIT), indentation modulus (EIT), recovery behavior (ηR), and indentation creep (CIT) of the samples were measured using a nanoindenter surface analyzer (FISCHERSCOPE HM2000, FISCHER) according to the standards of ISO 14577-1:2002(E) and 14577-2:2002(E). IT ), indentation modulus (EIT), recovery behavior (ηR), and indentation creep (CIT) of the samples were measured using a nanoindenter surface analyzer (FISCHERSCOPE HM2000, FISCHER) according to the standards of ISO 14577-1:2002(E) and 14577-2:2002(E). IT ), indentation modulus (EIT), recovery behavior (ηR), and indentation creep (CIT) of the samples were measured using a nanoindenter surface analyzer (FISCHERSCOPE HM2000, FISCHER) according to the standards of ISO 14577-1:2002(E) and 14577-2:2002(E). IT ), indentation modulus (EIT), recovery behavior (ηR), and indentation creep (CIT) of the samples were measured using a nanoindenter surface analyzer (FISCHERSCOPE HM2000, FISCHER) according to the standards of ISO 14577-1:2002(E) and 14577-2:2002(E). IT ), indentation modulus (EIT), recovery behavior (ηR), and indentation creep (CIT) of the samples were measured using a nanoindenter surface analyzer (FISCHERSCOPE HM2000, FISCHER) according to the standards of ISO 14577-1:2002(E) and 14577-2:2002(E).

[0278] Specifically, the single elastic layer film was placed on a glass test plate (Fischerscope Part no. 600-028) having a thickness of about 3T as a sample holder. Thereafter, a nanoindentation test was performed by pressing the diamond tip downward at a force of 30 mN for 15 seconds and allowing to creep for 5 seconds at room temperature; thereafter, it was lifted upward.

[0279] Further, the recovery rate was calculated by the following equation. Recovery rate (%) = [(h max -h p ) / h max ] x 100. Here, h max is the maximum indentation depth (μm) of the hard coat layer surface when pressed downward at a force of 30 mN for 15 seconds and held for 5 seconds, and h p is the indentation depth (μm) that cannot be recovered even after the force is released.

[0280] c. Results: The results of the nanoindentation test are shown in Table 6 below.

[0281] [Table 6]

[0282]

[0283] Example 1: Preparation of composite film

[0284] Step (1): Formation of hard coat layer

[0285] The hard coat layer composition shown in Table 1 was coated on the upper side of a transparent polyester film (NRF, SKC) having a thickness of 65 μm by a die coating method. Thereafter, it was heat-treated at a temperature of 60°C for 3 minutes to dry the solvent in the coating layer, and cured by irradiating ultraviolet light at a dose of 1 J / cm 2 to prepare a hard coat layer having a thickness of about 5 μm.

[0286] Step (2): Formation of elastic layer

[0287] The elastic coating composition A was coated on the surface opposite to the side on which the hard coating layer had been formed (i.e., the lower side of the polyester film) with a Mayer rod. Thereafter, it was heat-treated at 60°C for 2 minutes to dry the solvent in the coating composition, and irradiated with ultraviolet light at a dose of 1 J / cm 2 under a nitrogen atmosphere.

[0288] As a result, a composite film having a three-layer structure of a hard coating layer (5 μm), a polyester film (65 μm), and an elastic layer (30 μm) was obtained.

[0289] Example 2

[0290] A composite film was prepared in the same manner as in Example 1, except that the elastic layer was coated using the elastic coating composition B.

[0291] Example 3

[0292] A composite film was prepared in the same manner as in Example 1, except that the elastic layer was coated using the elastic coating composition E.

[0293] Comparative Example 1

[0294] A composite film having a two-layer structure of a hard coating layer (5 μm) and a polyester film (65 μm) was prepared in the same manner as in Example 1, except that the elastic layer was not formed.

[0295] Comparative Example 2

[0296] A composite film was prepared in the same manner as in Example 1, except that the elastic layer was coated using the elastic coating composition C.

[0297] Comparative Example 3

[0298] A composite film was prepared in the same manner as in Example 1, except that the elastic layer was coated using the elastic coating composition D.

[0299] Test Example 3: Modulus (base film)

[0300] The storage modulus of the base film (polyester base film) was measured in the same manner as in Test Example 1 in the temperature range of -50°C to 90°C, and as a result, it was shown that the storage modulus gradually decreased from about 2.6 x 10 9 Pa to 1.4 x 10 9 Pa as the temperature increased.

[0301] Test Example 4: Nanoindentation test (hard coating layer of composite film)

[0302] a. Sample: The composite films prepared in the examples and comparative examples were each cut into A4 size. They were stored at 25 ± 5°C and 50 ± 5% RH until the test, without additional pretreatment.

[0303] b. Apparatus and method: The nanoindentation test was performed on the hard coated surface of the composite film samples using the same apparatus and method as in b. of Test Example 2 above.

[0304] c. Results: The results of the nanoindentation test are shown in Table 7 below.

[0305] d. Analysis: The surface hardness of Examples 1 to 3 was compared with that of Comparative Example 1 and is shown in Table 8 below.

[0306] [Table 7]

[0307]

[0308] [Table 8]

[0309]

[0310] From the above results, it can be seen that in the composite films of Examples 1 to 3, in which the elastic layer formed using the elastic coating compositions A, B and E was selectively employed, in which the ratio of the storage modulus with respect to temperature was adjusted to a desired range, the nanoindentation surface hardness properties of the opposite side (hard coat) were excellent.

[0311] Specifically, as shown in Table 8, the composite films of Examples 1 to 3 had enhanced nanoindentation surface hardness properties (H V , recovery rate, H IT , E IT , η IT , C IT and h max ) compared to the composite film of Comparative Example 1, which did not employ an elastic layer.

[0312] Meanwhile, in the composite films of Comparative Examples 2 and 3, which employed an elastic layer, by using the elastic coating compositions C and D, the ratio of the storage modulus with respect to temperature was outside the desired range; thus the nanoindentation surface hardness properties were inferior to those of the composite films of Examples 1 to 3.

Claims

1. A composite film comprising a base film; a hard coat layer provided on one side of the base film; and an elastic layer provided on the other side of the base film, wherein the ΔE' value according to the following equation (1) is 2 to 300: ΔE' = E' [-30℃] / E' [50℃] … (1) wherein E' [-30℃] is the storage modulus Pa of the elastic layer at -30℃, and E' [50℃] is the storage modulus Pa of the elastic layer at 50℃; the recovery rate increase % = recovery rate 1% - recovery rate 2% wherein, recovery rate 1 is the recovery rate % of the composite film, and recovery rate 2 is the recovery rate % of a layered structure film not containing the elastic layer in the composite film, said composite film has a Vickers hardness H 2 of 2.0 N / mm or more V increased N / mm 2 and an increase in recovery of 1.5% or more calculated by the following equation: H V + 1 N / mm 2 = H V 1 N / mm 2 – H V 2 N / mm 2 wherein the elastic layer comprises an ultraviolet-curable urethane acrylate oligomer having 2 to 8 functional groups. wherein H V 1 is the Vickers hardness H V N / mm 2 of the composite film V 2 is the Vickers hardness H V N / mm 2 of the layered structure film without the elastic layer in the composite film, The ratio of the storage modulus of the elastic layer to the storage modulus of the base film at 25℃, elastic layer / base film, is 0.5 or less. The thickness of the base film is 40 to 200 μm, the thickness of the hard coat layer is 2 to 20 μm, and the thickness of the elastic layer is 10 to 100 μm.

2. The composite film of claim 1, wherein, The elastic layer has a storage modulus of 1 x 10 9 Pa to 3 x 10 9 Pa at -30°C, and a storage modulus of 1 x 10 7 Pa to 1 x 10 8 Pa at 50°C.

3. The composite film of claim 1, wherein, The base film comprises at least one selected from the group consisting of a polymer film or an ultrathin glass (UTG).

4. The composite film of claim 1, wherein, The Vickers hardness H of the composite film is 30 N / mm or more when the surface of the hard coat layer is measured by nanoindentation test according to the standard of ISO 14577-1:2002(E) V or more, and the recovery rate calculated by the following equation is 69% or more: 2 or more, and the recovery rate calculated by the following equation is 69% or more: % recovery = [(h max – h p ) / h max ] x 100 wherein h max is the maximum indentation depth in pm when the hard coat layer surface is pressed down with a force of 30 mN for 15 seconds and held for 5 seconds, h p is the indentation depth in pm that cannot be recovered even after the force is released.

5. The composite film of claim 1, wherein, The cover window comprises a base film; a hard coat layer provided on one side of the base film; and an elastic layer provided on the other side of the base film, and 6. The composite film of claim 1, wherein, wherein the ΔE' value according to the following equation (1) is 2 to 300: ΔE' = E' [-30℃] / E' [50℃] … (1) wherein E' [-30℃] is the storage modulus Pa of the elastic layer at -30℃, and E' [50℃] is the storage modulus Pa of the elastic layer at 50℃; 7. A display device comprising a display panel; and a cover window provided on a front side of the display panel, wherein the recovery rate increase % = recovery rate 1% - recovery rate 2% recovery rate 1 is the recovery rate % of the composite film, and recovery rate 2 is the recovery rate % of a layered structure film not containing the elastic layer in the composite film, wherein the elastic layer comprises an ultraviolet-curable urethane acrylate oligomer having 2 to 8 functional groups. ​ said cover window has a Vickers hardness H of 2.0 N / mm 2 or more V increased N / mm 2 and an increase in recovery of 1.5% or more calculated by the following equation: H V N / mm 2 = H V 1 N / mm 2 -H V 2 N / mm 2 ​ wherein H V 1 is the Vickers hardness H V N / mm 2 of the composite film V 2 is the Vickers hardness H V N / mm 2 of the layered structure film without the elastic layer in the composite film ​ ​

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