Optical sheet having at least, a pattern layer and a core layer composed of light-permeable thermoplastic resins, and manufacturing method thereof

1. An optical sheet, comprising:

at least a pattern layer and a core layer, composed of light-permeable thermoplastic resins for light to pass through, wherein a diffusion or light guiding pattern is formed on the pattern layer and the core layer being on the opposite side of the diffusion or light guiding pattern has a higher viscosity than said pattern layer, wherein said pattern layer and said core layer are composed of polycarbonates, wherein the polycarbonate of the core layer has a viscosity of 3-20 g/10 min and the polycarbonate of the pattern layer has a viscosity of 10-200 g/10 min, and wherein the viscosities are measured at T=300° C./load 1.2 kg and determined according to standard method ISO 1133:1997.

2. The optical sheet according to claim 1 , wherein said pattern layer and said core layer are composed of the same kind of light-permeable thermoplastic resins.

3. The optical sheet according to claim 1 , wherein said pattern layer and said core layer are composed of different kinds of light-permeable thermoplastic resins.

4. The optical sheet according to claim 1 , wherein an emboss pattern is formed on the rear side, opposite of the pattern layer, of said core layer.

5. The optical sheet according to claim 1 , wherein a functional layer is formed the rear side, opposite of the pattern layer, of said core layer.

6. The optical sheet according to claim 5 , wherein said functional layer is a UV-blocking layer.

7. A manufacturing method for an optical sheet according to claim 1 comprising:

a. a co-extrusion process wherein the first raw materials are extruded by a main extruder, and the second raw materials having a lower viscosity than said first raw materials are extruded by a co-extruder;

b a sheet forming process that forms the first and second raw materials, that are completely melted through said co-extrusion process, into a sheet comprising a pattern layer and a core layer through a T-die;

c. a calendering process that forms the diffusion or light guiding pattern, which diffuses lights, on the pattern layer by pressing said sheet by using a calender roll, whose surface has a lower temperature than the glass transition of the first and second raw materials and with a pressing part that is formed around the roll; and

d. a cooling process wherein the optical sheet with the diffusion or light guiding pattern formed on the pattern layer is cooled evenly by use of a guide roll.

8. The optical sheet manufacturing method defined in claim 7 additionally comprising the coextrusion of a functional material layer by a second co-extruder.

9. The optical sheet manufacturing method defined in claim 7 , additionally comprising the formation an emboss pattern on the rear side of said core layer by a supplementary calender roll, around which an emboss pattern is formed, in the process step of calendering c).

10. The optical sheet according to claim 1 , wherein the polycarbonate of the core layer has a viscosity of 5-14 g/10 min.

11. The optical sheet according to claim 1 , wherein the polycarbonate of the pattern layer has a viscosity of 20-80 g/10 min.

12. An optical sheet, comprising:

at least a pattern layer and a core layer, composed of light-permeable thermoplastic resins for light to pass through, wherein a diffusion or light guiding pattern is formed on the pattern layer and the core layer being on the opposite side of the diffusion or light guiding pattern has a higher viscosity than said pattern layer, wherein said pattern layer and said core layer are composed of polycarbonates, wherein the polycarbonate of the core layer has a viscosity of 5-14 g/10 min and the polycarbonate of the pattern layer has a viscosity of 20-80 g/10 min, and wherein the viscosities are measured at T=300° C. / load 1.2 kg and determined according to standard method ISO 1133:1997.