Flexible display device

1. A flexible display device, comprising:

a flexible display panel that comprises a folding area in which a folding axis is defined and a peripheral area disposed on opposing sides of the folding area; and

a window member overlapping the folding area and the peripheral area, the window member comprising:

a first base layer having a first modulus of elasticity disposed on a surface of the flexible display panel; and

a second base layer disposed on the first base layer in a direction in which the first base layer is disposed on the surface of the flexible display panel and having a second modulus of elasticity that is higher than the first modulus of elasticity,

wherein the first base layer has a first portion that overlaps the folding area, and a second portion that overlaps the peripheral area, the first portion of the first base layer is thicker than the second portion of the first base layer,

wherein the first base layer is continuous within the folding area and the peripheral area,

wherein the second base layer has a first portion that overlaps the folding area, and a second portion that overlaps the peripheral area, the first portion of the second base layer being thinner than the second portion of the second base layer,

wherein the window member comprises a transparent material,

wherein the first base layer is disposed closer to the flexible display panel than the second base layer,

wherein the first base layer and the second base layer are flat in the peripheral area and have uniform thicknesses in the peripheral area, and

wherein a minimum thickness of the first base layer is less than a minimum thickness of the second base layer.

2. The flexible display device of claim 1 , wherein the window member has a substantially constant thickness within the folding area and the peripheral area.

3. The flexible display device of claim 2 , wherein the thickness of the window member is in a range of about 20 micrometers to about 300 micrometers.

4. The flexible display device of claim 1 , wherein:

a first portion of the second base layer overlaps the folding area; and

the thickness of the first portion of the first base layer is about 80% to about 120% of the thickness of the first portion of the second base layer.

5. The flexible display device of claim 4 , wherein:

a second portion of the second base layer overlaps the peripheral area; and

the thickness of the second portion of the first base layer is about 2% to about 20% of the thickness of the second portion of the second base layer.

6. The flexible display device of claim 5 , wherein the first base layer is disposed closer to the flexible display panel than the second base layer.

7. The flexible display device of claim 1 , wherein a width of the first portion of the first base layer, taken in a direction substantially perpendicular to the folding axis, is equal to or smaller than a width of the folding area, taken in the direction substantially perpendicular to the folding axis.

8. The flexible display device of claim 7 , wherein the first portion of the first base layer has a uniform thickness.

9. The flexible display device of claim 7 , wherein the first portion of the first base layer has a curved cross section taken along the direction substantially perpendicular to the folding axis.

10. The flexible display device of claim 7 , wherein the first portion of the first base layer comprises a protrusion having a trapezoidal cross section, taken in the direction substantially perpendicular to the folding axis.

11. The flexible display device of claim 1 , wherein the window member further comprises an adhesive layer attaching the first base layer and the second base layer, and wherein the adhesive layer comprises at least one of an acrylic based resin and a silicon based resin.

12. The flexible display device of claim 1 , further comprising a touch screen and a polarizing plate, disposed between the flexible display panel and the window member.

13. The flexible display device of claim 1 , wherein the window member further comprises a third base layer attached to the first base layer or the second base layer, the third base layer having a modulus of elasticity different from the modulus of elasticity of the first base layer.

14. A flexible display device, comprising:

a flexible display panel that comprises a folding area in which a folding axis is defined and a peripheral area disposed on opposing sides of the folding area; and

a window member overlapping the folding area and the peripheral area, and comprising a first base layer disposed on a surface of the flexible display panel, a second base layer disposed on the first base layer in a direction in which the first base layer is disposed on the flexible display panel, and a third base layer disposed on the second base layer in a direction in which the second base layer is disposed on the first base layer,

wherein the first base layer has the lowest modulus of elasticity among the base layers, has a first portion that overlaps the folding area, and has a second portion that overlaps the peripheral area, the first portion of the first base layer is thicker than the second portion of the first base layer,

wherein the first base layer is continuous within the folding area and the peripheral area,

wherein the third base layer has the highest modulus of elasticity among the base layers, has a first portion that overlaps the folding area, and has a second portion that overlaps the peripheral area, the first portion of the third layer being thinner than the second portion of the third base layer,

wherein a border between the first portion of the second base layer and the first portion of the third base layer is planar,

wherein the window member comprises a transparent material, and

wherein the first base layer and the second base layer are flat in the peripheral area and have uniform thicknesses in the peripheral area.

15. The flexible display device of claim 14 , wherein the first base layer is disposed closer to the flexible display panel than the second and third base layers.

16. The flexible display device of claim 15 , wherein the third base layer is disposed further from the display panel than the first and second base layers.

17. The flexible display device of claim 16 , wherein:

the second base layer has a first portion that overlaps the folding area, and has a second portion that overlaps the peripheral area;

the thickness of the first portion of the second base layer is greater than the thickness of the second portion of the third base layer; and

the second base layer is disposed between the first base layer and the third base layer.