Foldable display device
A foldable display device includes a display panel, a polarizing member on the display panel, a window on the polarizing member, a first adhesive member between the display panel and the polarizing member, and a second adhesive member between the polarizing member and the window. In a first state, the display panel, the polarizing member, the window, the first adhesive member, and the second adhesive member are bent along a bending axis such that the window is closer to the bending axis than the display panel is. The first and second adhesive members have a storage modulus in a range of about 5×10 4 Pa to about 5×10 5 Pa at about −25° C. The second adhesive member has a storage modulus in a range of about 4.5×10 4 Pa to about 6.5×10 4 Pa at about 60° C. The first adhesive member has a stress-relaxation ratio greater than about 40 and less than about 50.
1. A foldable display device comprising:
a display panel;
a polarizing member on the display panel;
a window on the polarizing member;
a first adhesive member between the display panel and the polarizing member; and
a second adhesive member between the polarizing member and the window,
wherein, in a first state, the display panel, the polarizing member, the window, the first adhesive member, and the second adhesive member are bent along a bending axis such that the window is closer to the bending axis than the display panel is,
wherein each of the first adhesive member and the second adhesive member has a storage modulus in a range of 5×10 4 Pa to 5×10 5 Pa at −25° C.,
wherein the second adhesive member has a storage modulus in a range of 4.5×10 4 Pa to 6.5×10 4 Pa at 60° C.,
wherein the first adhesive member has a stress-relaxation ratio that is greater than 40 and less than 50, the stress-relaxation ratio being defined as
Stress-relaxation ratio (%)=100× G ( t 2)/ G ( t 1),
wherein G(t1) is an initial stress-relaxation modulus measured in a state in which the first adhesive member is 600 μm thick, the initial stress-relaxation modulus being measured with a rheometer in a stress-relaxation test mode when a strain of 25% is removed after being applied using a parallel plate for 100 seconds at 60° C., and G(t 2 ) is a stress-relaxation modulus measured after the strain is applied to the first adhesive member for 300 seconds,
wherein the first adhesive member has a residual strain in a range of 5 to 8 at 60° C., the residual strain being defined as
Residual strain (%)= L 2/ L 1×100, and
wherein L1 is a maximum creep strain for a state in which the first adhesive member is prepared to be 600 μm and when a stress of 2000 Pa is applied to the first adhesive member for 1 hour at 60° C. using a rheometer, and L2 is unrecovered residual recovery strain that remains along with elastic recovery strain that is recovered when the applied stress is removed after achieving the maximum creep strain.
2. The foldable display device of claim 1 , wherein, in a second state, the display panel, the polarizing member, the window, the first adhesive member, and the second adhesive member are unbent.
3. The foldable display device of claim 1 , wherein the first adhesive member has a thickness in a range of 25 μm to 100 μm.
4. The foldable display device of claim 1 , wherein the second adhesive member has a thickness in a range of 25 μm to 100 μm.
5. The foldable display device of claim 1 , wherein the first adhesive member has a peel strength of at least 800 gf/in.
6. The foldable display device of claim 1 , wherein the second adhesive member has a peel strength of at least 800 gf/in.
7. The foldable display device of claim 1 , wherein the first adhesive member comprises a first silicone-based base polymer, a first adhesion imparting agent, and a first cross-linking agent, and
wherein the second adhesive member comprises a second silicone-based base polymer, a second adhesion imparting agent, and a second cross-linking agent.
8. The foldable display device of claim 1 , further comprising:
a protective film below the display panel; and
a third adhesive member between the display panel and the protective film,
wherein, in the first state, the protective film and the third adhesive member are bent along the bending axis and, in a second state, are unbent.
9. The foldable display device of claim 8 , wherein a thickness of the third adhesive member is less than a thickness of each of the first adhesive member and the second adhesive member.
10. The foldable display device of claim 8 , wherein the third adhesive member has a storage modulus in a range of 5×10 4 Pa to 5×10 5 Pa at −25° C.
11. The foldable display device of claim 1 , further comprising a touch sensing unit between the polarizing member and the window,
wherein, in the first state, the touch sensing unit is bent along the bending axis and, in a second state, is unbent.
12. The foldable display device of claim 11 , further comprising a fourth adhesive member between the polarizing member and the touch sensing unit,
wherein, in the first state, the fourth adhesive member is bent along the bending axis and, in a second state, is unbent.
13. The foldable display device of claim 12 , wherein a thickness of the fourth adhesive member is less than a thickness of each of the first adhesive member and the second adhesive member.
14. The foldable display device of claim 12 , wherein the fourth adhesive member has a storage modulus in a range of 5×10 4 Pa to 5×10 5 Pa at −25° C.
15. The foldable display device of claim 11 , wherein the touch sensing unit directly contacts the polarizing member.
16. A foldable display device comprising:
a display panel;
a polarizing member on the display panel;
a window on the polarizing member;
a first adhesive member between the display panel and the polarizing member; and
a second adhesive member between the polarizing member and the window,
wherein, in a first state, the display panel, the polarizing member, the window, the first adhesive member, and the second adhesive member are bent along a bending axis such that the window is closer to the bending axis than the display panel is,
wherein each of the first adhesive member and the second adhesive member has a storage modulus in a range of 5×10 4 Pa to 5×10 5 Pa at −25° C.,
wherein the first adhesive member has a stress-relaxation ratio that is greater than 40 and less than 50, the stress-relaxation ratio being defined as
Stress-relaxation ratio (%)=100× G ( t 2)/ G ( t 1),
wherein G(t1) is an initial stress-relaxation modulus measured in a state in which the first adhesive member is 600 μm thick, the initial stress-relaxation modulus being measured with a rheometer in a stress-relaxation test mode when a strain of 25% is removed after being applied using a parallel plate for 100 seconds at 60° C., and G(t 2 ) is a stress-relaxation modulus measured after the strain is applied to the first adhesive member for 300 seconds,
wherein the first adhesive member has a residual strain in a range of 5 to 8 at 60° C., the residual strain being defined as
Residual strain (%)= L 2/ L 1×100, and
wherein L1 is a maximum creep strain for a state in which the first adhesive member is prepared to be 600 μm and when a stress of 2000 Pa is applied to the first adhesive member for 1 hour at 60° C. using a rheometer, and L2 is unrecovered residual recovery strain that remains along with elastic recovery strain that is recovered when the applied stress is removed after achieving the maximum creep strain.