Composite film and display device comprising same
In the composite film according to the embodiment, an elastic layer in which its modulus change characteristics with respect to temperature have been adjusted to a certain range is coated onto the opposite side to a hard coating layer; thus, it is possible to enhance the surface hardness and elastic recovery characteristics of the hard coating layer. Thus, it can be advantageously applied as a cover window of a flexible display device.
1 . A composite film, which comprises a base film; a hard coating layer disposed on one side of the base film; and an elastic layer disposed on the other side of the base film,
wherein the ΔE′ value according to the following Equation (1) is 2 to 300:
Δ E′=E′[− 30° C.]/ E′[ 50° C.] (1)
in which E′[−30° C.] is the storage modulus (Pa) of the elastic layer at −30° C., and E′[50° C.] is the storage modulus (Pa) of the elastic layer at 50° C., and
wherein the composite film has an Hy increase (N/mm 2 ) of 2.0 N/mm 2 or more as calculated by the following Equation (2) and a recovery increase of 1.5% or more as calculated by the following Equation (3):
H V increase( N /mm 2 )= H V 1 ( N /mm 2 )− H V 2 ( N /mm 2 ) (2)
Recovery increase(%)=Recovery1(%)−Recovery2(%) (3)
in which H V 1 is the Vickers hardness (H V ) (N/mm 2 ) of the composite film, H V 2 is the Vickers hardness (H V ) (N/mm 2 ) of a film having a layer structure excluding the elastic layer from the composite film,
Recovery1 is the recovery (%) of the composite film, and Recovery2 is the recovery (%) of a film having a layer structure excluding the elastic layer from the composite film,
wherein the composite film has a Vickers hardness (H V ) of 30 N/mm 2 or more when measured for the surface of the hard coating layer by a nanoindentation test according to the ISO 14577-1: 2002 (E) standard and a recovery of 69% or more as calculated by the following equation:
Recovery(%)=[( h max −h p )/ h max ]×100
in which h max is the maximum indentation depth (μm) during which the surface of the hard coating layer is pressed downward for 15 seconds at a force of 30 mN and held for 5 seconds, and hp is the depth (μm) of the indentation that remains unrecovered even after the force is released,
wherein the ratio of the storage modulus of the elastic layer to the storage modulus of the base film (elastic layer/base film) is 0.5 or less at 25° C.,
wherein the elastic layer comprises a UV-curable urethane acrylate-based oligomer having 2 to 8 functional groups, and
wherein the hard coating layer comprises at least one selected from the group consisting of a urethane acrylate-based compound, an acrylic ester-based compound, and an epoxy acrylate-based compound.
2 . The composite film of claim 1 , wherein the storage modulus of the elastic layer is 1×10 9 Pa to 3×10 9 Pa at −30° C. and 1×10 7 Pa to 1×10 8 Pa at 50° C.
3 . The composite film of claim 1 , wherein the thickness of the base film is 40 μm to 200 μm, the thickness of the hard coating layer is 2 μm to 20 μm, and the thickness of the elastic layer is 10 μm to 100 μm.
4 . The composite film of claim 1 , wherein the base film comprises at least one selected from the group consisting of a polymer film or ultra-thin glass (UTG).
5 . A display device, which comprises a display panel; and a cover window disposed on the front side of the display panel,
wherein the cover window comprises a base film; a hard coating layer disposed on one side of the base film; and an elastic layer disposed on the other side of the base film, and
wherein the ΔE′ value according to the following Equation (1) is 2 to 300:
Δ E′=E′[− 30° C.]/ E′[ 50° C.] (1)
in which E′[−30° C.] is the storage modulus (Pa) of the elastic layer at −30° C., and E′[50° C.] is the storage modulus (Pa) of the elastic layer at 50° C., and
wherein the cover window has an Hv increase (N/mm 2 ) of 2.0 N/mm 2 or more as calculated by the following Equation (2) and a recovery increase of 1.5% or more as calculated by the following Equation (3):
H V increase( N /mm 2 )= H V 1( N /mm 2 )− H V 2 ( N /mm 2 ) (2)
Recovery increase(%)=Recovery1(%)−Recovery2(%) (3)
in which H V 1 is the Vickers hardness (H V ) (N/mm 2 ) of the composite film, H V 2 is the Vickers hardness (H V ) (N/mm 2 ) of a film having a layer structure excluding the elastic layer from the composite film,
Recovery1 is the recovery (%) of the composite film, and Recovery2 is the recovery (%) of a film having a layer structure excluding the elastic layer from the composite film,
wherein the composite film has a Vickers hardness (H V ) of 30 N/mm 2 or more when measured for the surface of the hard coating layer by a nanoindentation test according to the ISO 14577-1: 2002 (E) standard and a recovery of 69% or more as calculated by the following equation:
Recovery(%)=[( h max −h p )/ h max ]×100
in which h max is the maximum indentation depth (μm) during which the surface of the hard coating layer is pressed downward for 15 seconds at a force of 30 mN and held for 5 seconds, and hp is the depth (μm) of the indentation that remains unrecovered even after the force is released,
wherein the ratio of the storage modulus of the elastic layer to the storage modulus of the base film (elastic layer/base film) is 0.5 or less at 25° C.,
wherein the elastic layer comprises a UV-curable urethane acrylate-based oligomer having 2 to 8 functional groups, and
wherein the hard coating layer comprises at least one selected from the group consisting of a urethane acrylate-based compound, an acrylic ester-based compound, and an epoxy acrylate-based compound.