Optical film, polarizing plate including same, and display device including same
Provided are an optical film, a polarizing plate including same, and a display device including same, the optical film comprising a first layer and second and third layers sequentially formed on the first layer, wherein the first layer and the third layer are each formed directly on the second layer, the first layer is a reverse wavelength dispersive negative A layer, the third layer is a positive C layer, and the ratio of the thickness of the second layer to the thickness of the third layer (the thickness of the second layer/the thickness of the third layer) is about 0.2 to about 2.
1. An optical film comprising:
a first layer; and
second and third layers sequentially formed on the first layer,
wherein each of the first layer and the third layer is directly formed on the second layer, the first layer being a negative dispersion negative A layer, the third layer being a positive C layer, and a thickness ratio of the second layer to the third layer (thickness of the second layer/thickness of the third layer) ranges from about 0.2 to about 2,
wherein the third layer comprises a cellulose ester comprising at least one selected from among cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate.
2. The optical film according to claim 1 , wherein the third layer is a non-crystal layer.
3. The optical film according to claim 1 , wherein the second layer is a non-adhesive layer, a non-bonding layer, or a non-adhesive bonding layer and is formed through erosion of the first layer.
4. The optical film according to claim 1 , wherein the first layer and the second layer comprise the same kind of polymer and have at least one of a different alignment direction of polymers or a different alignment degree of polymers from one another.
5. The optical film according to claim 4 , wherein the first layer has a higher alignment degree of polymers than the second layer.
6. The optical film according to claim 4 , wherein the first layer comprises the polymers aligned in a mono-axial direction or in a bi-axial direction, and the second layer comprises the polymers not in an aligned state.
7. The optical film according to claim 1 , wherein the first layer has an in-plane retardation ratio (Re (450)/Re (550)) of about 0.7 to about 1.0, where Re (550) indicates an in-plane retardation at a wavelength of 550 nm and Re (450) indicates an in-plane retardation at a wavelength of 450 nm.
8. The optical film according to claim 1 , wherein the first layer has an in-plane retardation Re (550) of about 110 nm to about 170 nm at a wavelength of 550 nm.
9. The optical film according to claim 1 , wherein the first layer is formed of at least one selected from among a polycarbonate resin, a cyclic olefin polymer resin, a modified polycarbonate resin, an isosorbide resin, a cellulose resin, a fluorene resin, and a polyester resin.
10. The optical film according to claim 1 , wherein the first layer has an in-plane retardation variation of about 5 nm or more, as represented by Equation 1:
In-plane retardation variation=|Re[0]−Re[1]|, [Equation 1]
wherein Equation 1,
Re[0] is an in-plane retardation Re (unit: nm) of the first layer, as measured on a specimen having a size of 3 cm×3 cm×50 μm at a wavelength of 550 nm, and
Re[1] is an in-plane retardation Re (unit: nm) of the first layer, as measured on the specimen at a wavelength of 550 nm after one drop of methylethylketone is added to the specimen at 25° C. and left for 1 hour.
11. The optical film according to claim 1 , wherein the second layer has a thickness of about 15 μm or less.
12. The optical film according to claim 1 , wherein the third layer has a thickness of about 15 μm or less.
13. The optical film according to claim 1 , wherein a stack of the first layer and the second layer is a negative dispersion negative A layer.
14. The optical film according to claim 1 , wherein a stack of the first layer and the second layer has an in-plane retardation Re (550) of about 110 nm to about 170 nm at a wavelength of 550 nm.
15. The optical film according to claim 1 , wherein a stack of the second layer and the third layer is a positive C layer.
16. The optical film according to claim 1 , wherein, assuming that a machine direction (MD) of the first layer is 0°, the first layer has a slow axis in the range of about −5° to about 5° or about 40° to about 50° with respect to the machine direction (MD) of the first layer.
17. The optical film according to claim 1 , wherein the third layer further comprises a UV absorbent having a maximum absorption wavelength of about 380 nm to about 420 nm.
18. The optical film according to claim 17 , wherein the UV absorbent is present in an amount of about 0.1 wt % to about 2 wt % in the third layer.
19. The optical film according to claim 1 , further comprising: an adhesive layer, a bonding layer, or an adhesive bonding layer on an outermost surface thereof.
20. A polarizing plate comprising: a polarizing film and the optical film according to claim 1 formed on one surface of the polarizing film.
21. The polarizing plate according to claim 20 , wherein the first layer, the second layer, and the third layer are sequentially formed on the polarizing film.
22. The polarizing plate according to claim 20 , comprising: a first protective layer; a polarizer; a second protective layer; the first layer; the second layer; and the third layer sequentially formed in the stated order.
23. The polarizing plate according to claim 20 , comprising: a first protective layer; a polarizer; the first layer; the second layer; and the third layer sequentially formed in the stated order.
24. A display apparatus comprising the optical film according to claim 1 .