Prism sheet, method for making the same and liquid crystal display device using the same

A liquid crystal display device comprising:

• a liquid crystal display panel;
• a plurality of lamps;
• a light diffusion plate, the liquid crystal display panel and the light diffusion plate stacked above the lamps in that order;
• and
• a prism sheet disposed on the light diffusion plate, the prism sheet includes a transparent main body having a surface, a plurality of first elongated micro-protrusions and second elongated micro-protrusions protruding from the surface of the main body respectively,
• wherein each of the first elongated micro-protrusions extends along a first direction, each of the second elongated micro-protrusions extends along a second direction that intersects with the first direction, widths and heights of each of the first elongated micro-protrusions vary along the first direction, and widths and heights of each of the second elongated micro-protrusions vary along the second direction.

A method for making a prism sheet, comprising:

• providing a cutting device, the cutting device comprising a cutter, a table plate, and a control unit, the table plate controlled to move up and down by the control unit, the cutter having a blade that is rotated along its center axis;
• providing a mold insert preform on the table plate, the mold insert preform having a flat surface;
• the cutter with the rotating blade being moved to etch the flat surface of the mold insert preform along a first direction, at the same time, the table plate being driven to move up and down by the control unit in a first predetermined manner, thereby a first elongated depression being formed in the flat surface, wherein widths and sizes of the first elongated depression vary according to the first predetermined manner;
• repeating the step of forming the first elongated depression to form a plurality of first elongated depressions in the flat surface;
• the cutter with the rotating blade being moved to etch the flat surface of the mold insert preform along a second direction, at the same time, the table plate being driven to move up and down by the control unit according to a second predetermined manner, thereby a second elongated depression being formed in the flat surface, wherein widths and sizes of the second elongated depression vary according to the second predetermined manner, the second elongated depression intersecting with the first elongated depressions;
• repeating the step of forming the second elongated depression to form a plurality of second elongated depressions in the flat surface, thereby a mold insert is achieved;
• using the mold insert to form the prism sheet by injection molding method.