Backlight unit and liquid crystal display device using the same

1. A backlight unit of a liquid crystal display device, comprising:

a light source;

a reflective sheet disposed near a rear surface of the light source;

an optical sheet to direct light emitted from the light source to travel in a direction towards a liquid crystal display panel; and

a cover bottom assembly formed to house the light source, the reflection sheet and the optical sheet,

wherein the cover bottom assembly comprises support side bottoms formed at two short sides of the cover bottom assembly to dispose the optical sheet thereon, and the support side bottom includes a joining part to fix the optical sheet to the support side bottom using a movable body movable on a surface of the optical sheet,

wherein the joining part includes two first projected parts projected from the support side bottom, the projected parts arranged to face each other and a second projected part connected between the ends of the two first projected parts.

2. The backlight unit according to claim 1 , wherein the joining part includes:

an elastic body of which one side is fixed to the second projected part;

a supporting member formed on the other side of the elastic body movable horizontally to compress the elastic body; and

a rotatable body movable horizontally together with the supporting member to hold the optical sheet.

3. The backlight unit according to claim 2 , wherein the rotatable body is cylindrical.

4. The backlight unit according to claim 2 , wherein the rotatable body is formed of a plurality of spheres connected with one pivot.

5. The backlight unit according to claim 4 , wherein the pivot engages a groove at formed at each of the two projected parts to constrain the elastic body to move horizontally.

6. The backlight unit according to claim 2 , wherein the elastic body is a plate spring.

7. The backlight unit according to claim 2 , wherein the elastic body is a spring.

8. The backlight unit according to claim 2 , wherein the second projected part and the two first projected parts facing each other are formed in a ‘[’ shape.

9. The backlight unit according to claim 8 , wherein the supporting member and the rotatable body are movable horizontally between the two first projected parts of the ‘[’ shape.

10. The backlight unit according to claim 2 , wherein a moving distance of the rotatable body is limited by an inclined surface of a guide panel covering the support side bottom.

11. The backlight unit according to claim 10 , wherein the rotatable body is arranged to be rotated by a free movement of the optical sheet, the movement and rotation of the rotatable body to be limited by the inclined surface of the guide panel to prevent an additional free movement of the optical sheet.

12. The backlight unit according to claim 2 , wherein the rotatable body I arranged to be rotated by a free movement of the optical sheet.

13. A liquid crystal display device, comprising:

a backlight unit including a light source; a reflective sheet disposed at a rear surface of the light source; an optical sheet to direct light emitted from the light source towards a liquid crystal display panel; and a cover bottom assembly formed to house the light source, the reflection sheet, and the optical sheet, wherein the cover bottom assembly comprise support side bottoms formed at two short sides of the cover bottom assembly to dispose the optical sheet thereon, and the support side bottom includes a joining part to hold the optical sheet to the support side bottom using a movable body movable horizontally on the optical sheet;

a liquid crystal display panel including an upper substrate having a color filter, a common electrode and a black matrix are formed thereon, a lower substrate on which data lines are formed to cross gate lines and a thin film transistor is formed at crossings of the data line and the gate line, and a liquid crystal formed in a space between the bonded upper and lower substrates; and

a guide panel supporting the liquid crystal display panel to be joined with the support side bottom of the backlight unit,

wherein the joining part includes two first projected parts projected from the support side bottom, the projected parts arranged to face each other and a second projected part connected between the ends of the two first projected parts.

14. The liquid crystal display device according to claim 13 , wherein the joining part of the backlight unit includes:

an elastic body of which one side is fixed to the second projected part;

a supporting member formed on the other side of the elastic body movable horizontally to compress the elastic body; and

a rotatable body movable horizontally together with the supporting member to hold the optical sheet.

15. The liquid crystal display device according to claim 14 , wherein the elastic body is a plate spring.

16. The liquid crystal display device according to claim 14 , wherein the elastic body is a spring.

17. The liquid crystal display device according to claim 14 , wherein a moving distance of the rotatable body is limited by an inclined surface of the guide panel covering the support side bottom.

18. The liquid crystal display device according to claim 17 , wherein the rotatable body is arranged to be rotated and moved by a free movement of the optical sheet, the movement and rotation of the rotatable body limited by an inclined part of the guide panel to prevent an additional free movement of the optical sheet.

19. The liquid crystal display device according to claim 14 , wherein the rotatable body is cylindrical.

20. The liquid crystal display device according to claim 14 , wherein the rotatable body is composed of a plurality of spheres connected to one pivot.