Optical film

Abstract

The present invention relates to an optical film, a polarizing plate including the same, and a display device. The exemplary optical film may have a desired wavelength dispersion characteristic using positive and negative uniaxial retardation films satisfying a predetermined condition. In addition, the optical film has a desired wavelength dispersion characteristic, and thus may be utilized in various fields requiring delicate control of optical properties. For example, the optical film can be useful in the polarizing plate used to prevent reflection and ensure visibility in the display device.

Claims

1. A polarizing plate, comprising: a linear polarizer; and an optical film, comprising: a positive uniaxial retardation film satisfying General Formula 1 and having a positive in-plane retardation value; and a negative uniaxial retardation film satisfying General Formula 1 and having a negative in-plane retardation value, which are stacked, wherein the positive uniaxial retardation film and the negative uniaxial retardation film are disposed to have an angle of 5 to 5 degrees between slow axis of each film, wherein the light absorbing axis of the linear polarizer is disposed to have an angle of 40 to 50 degrees with the optical axis of the positive uniaxial retardation film, wherein the value of an in-plane retardation is defined by General Formula 2, and wherein the in-plane retardations of the uniaxial retardation films satisfy Formulas 1 to 3:
n.sub.xn.sub.yn.sub.z[General Formula 1]
Rin=d(neno)[General Formula 2]
|R.sub.1()|>|R.sub.2()|[Formula 1]
R.sub.1(450)/R.sub.1(550)<R.sub.2(450)/R.sub.2(550)[Formula 2]
|R(450)|<|R(650)|[Formula 3] where in General Formula 1, n.sub.x, n.sub.y, and n.sub.z are refractive indexes of a retardation film in x, y, and z directions, respectively; in General Formula 2, Rin is a value of in-plane retardation, d is a thickness of the retardation film, ne is an extraordinary refractive index, no is an ordinary refractive index, the extraordinary refractive index refers to a refractive index in an x axis direction, and the ordinary refractive index refers to a refractive index in a y direction; in Formula 1, |R.sub.1()| is an absolute value of an in-plane retardation of any one of the positive and negative uniaxial films with respect to light with a wavelength of nm, |R.sub.2()| is an absolute value of an in-plane retardation of the other one of the positive and negative uniaxial films with respect to light with a wavelength of nm, and is a wavelength of 450, 550, or 650 nm; in Formula 2, R.sub.1(450) and R.sub.1(550) are in-plane retardation values of one of the positive and negative uniaxial films, which has a higher absolute value of in-plane retardation, with respect to light with wavelengths of 450 and 550 nm, respectively, and R.sub.2(450) and R.sub.2(550) are in-plane retardation values of the other one of the positive and negative uniaxial films, which has a lower absolute value of in-plane retardation, with respect to light with wavelengths of 450 and 550 nm; in Formula 3, |R(450)| is an absolute value of the sum of R.sub.1(450) and R.sub.2(450), and |R(650)| is an absolute value of the sum of R.sub.1(650) and R.sub.2(650).

2. The optical film according to claim 1, wherein the in-plane retardations of the uniaxial retardation films satisfy Formula 4:
0.81R(450)/R(550)0.99[Formula 4] where R(450) is the sum of R.sub.1(450) and R.sub.2(450), and R(550) is the sum of R.sub.1(550) and R.sub.2(550).

3. The optical film according to claim 1, wherein the in-plane retardations of the uniaxial retardation films satisfy Formula 5:
1.01R(650)/R(550)1.19[Formula 5] where R(550) is the sum of R.sub.1(550) and R.sub.2(550), R(650) is the sum of R.sub.1(650) and R.sub.2(650), the R.sub.1(650) is an in-plane retardation value of one of the positive and negative uniaxial films, which has a higher absolute value, with respect to light with a wavelength of 650 nm, and R.sub.2(650) is an in-plane retardation value of the other one of the positive and negative uniaxial films, which has a lower absolute value, with respect to light with a wavelength of 650 nm.

4. The optical film according to claim 1, wherein the positive uniaxial retardation film has a normal wavelength dispersion characteristic, and the negative uniaxial retardation film has a normal, flat, or reverse wavelength dispersion characteristic.

5. The optical film according to claim 1, wherein the positive uniaxial retardation film has a flat wavelength dispersion characteristic, and the negative uniaxial retardation film has a normal or reverse wavelength dispersion characteristic.

6. The optical film according to claim 1, wherein the positive uniaxial retardation film has a reverse wavelength dispersion characteristic, and the negative uniaxial retardation film has a normal, flat, or reverse wavelength dispersion characteristic.

7. The optical film according to claim 1, wherein the sum of R.sub.1(550) and R.sub.2(550) is in the range of 110 to 220 nm or in the range of 110 to 220 nm.

8. The optical film according to claim 1, wherein the positive uniaxial retardation film has an in-plane retardation in the range of 95 to 145 nm or in the range of 200 to 290 nm, with respect to light with a wavelength of 550 nm.

9. The optical film according to claim 1, wherein the negative uniaxial retardation film has an in-plane retardation in the range of 220 to 290 nm or in the range of 95 to 145 nm, with respect to light with a wavelength of 550 nm.

10. The optical film according to claim 1, wherein the positive uniaxial retardation film is a liquid crystal film including a stick-type liquid crystal compound or an optical anisotropic polymer film.

11. The optical film according to claim 1, wherein the negative uniaxial retardation film is a liquid crystal film including a discotic liquid crystal compound or a cholesteric liquid crystal compound or an optical anisotropic polymer film.

12. A display device comprising the polarizing plate of claim 1.

13. The display device according to claim 12, which is a reflective liquid crystal display, a semi-transparent reflective liquid crystal display, or an organic light emitting device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of an exemplary optical film;

(2) FIG. 2 is a diagram for describing x, y, and z axes of a retardation film;

(3) FIG. 3 is a graph for describing a wavelength dispersion characteristic of the retardation film;

(4) FIG. 4 is a diagram for describing an optical axis of the exemplary retardation film;

(5) FIG. 5 is a schematic diagram of an exemplary polarizing plate;

(6) FIG. 6 is a diagram for describing the relationship between the optical axis of the exemplary retardation film and a light absorbing axis of a linear polarizer;

(7) FIG. 7 shows light leakage intensity of an optical film of Example 1;

(8) FIG. 8 shows light leakage intensity of an optical film of Example 2;

(9) FIG. 9 shows light leakage intensity of an optical film of Comparative Example 1;

(10) FIG. 10 shows light leakage intensity of an optical film of Comparative Example 2;

(11) FIG. 11 shows light leakage intensity of an optical film of Comparative Example 3; and

(12) FIG. 12 shows light leakage intensity of an optical film of Comparative Example 4.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(13) Hereinafter, an optical film will be described with reference to Examples in detail. However, the scope of the optical film is not limited to the following Examples.

(14) Hereinafter, a retardation value and light leakage intensity in Examples and Comparative Examples were measured by the following method.

(15) 1. Measurement of in-Plane or Thickness-Direction Retardation Value

(16) In-plane or thickness-direction retardation value of a retardation film, a stacked film, or an optical film was measured using an Axoscan tool (Axomatrics) capable of measuring 16 Muller matrixes. Particularly, 16 Muller matrixes were obtained according to the manual of the manufacturer using the Axoscan tool, and thereby a retardation value was extracted.

(17) 2. Measurement of Light Leakage Intensity

(18) Light leakage intensity was evaluated by attaching an optical film of Example or Comparative Example on one surface of PVA (Poly vinyl alcohol) polarizer, measuring a reflectivity at a tilt angle of 50 degrees using a spectrometer (N&K), and measuring an intensity of light leaked from a PVA polarizer at every azimuthal angle. The light leakage intensity was defined with an arbitrary unit (AU) using the maximum brightness at every azimuthal angle as a control.

Example 1

(19) An optical film of Example 1 was manufactured by stacking a positive uniaxial retardation film having an in-plane retardation value of 262.5 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 250 nm with respect to light with a wavelength of 550 nm and an in-plane retardation value of 237.5 nm with respect to light with a wavelength of 650 nm, and a negative uniaxial retardation film having an in-plane retardation value of 120 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 100 nm with respect to light with a wavelength of 550 nm, and an in-plane retardation value of 80 nm with respect to light with a wavelength of 650 nm for optical axes thereof to be arranged in parallel.

(20) In addition, a polarizing plate was manufactured by attaching a positive uniaxial retardation film of the optical film to a PVA polarizer, and an intensity of light leaked from the PVA polarizer was measured at every azimuthal angle while irradiating light toward the optical film. In the manufacture of the polarizing plate, the polarizing plate was attached to the positive uniaxial retardation film so that a light absorbing axis of the PVA polarizer and a slow axis of the positive uniaxial retardation film form an angle of about 45 degrees counterclockwise when the optical film was observed on a side of the polarizer. Results of measuring the light leakage intensity of the optical film of Example 1 are shown in FIG. 7

Example 2

(21) An optical film of Example 2 was manufactured by stacking a positive uniaxial retardation film having an in-plane retardation value of 125 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 100 nm with respect to light with a wavelength of 550 nm and an in-plane retardation value of 75 nm with respect to light with a wavelength of 650 nm, and a negative uniaxial retardation film having an in-plane retardation value of 270 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 250 nm with respect to light with a wavelength of 550 nm, and an in-plane retardation value of 230 nm with respect to light with a wavelength of 650 nm for optical axes thereof to be arranged in parallel.

(22) In addition, a polarizing plate was manufactured by attaching a positive uniaxial retardation film of the optical film to a PVA polarizer, and an intensity of light leaked from the PVA polarizer was measured at every azimuthal angle while irradiating light toward the optical film. In the manufacture of the polarizing plate, the polarizing plate was attached to the positive uniaxial retardation film so that a light absorbing axis of the PVA polarizer and a slow axis of the positive uniaxial retardation film form an angle of about 45 degrees counterclockwise when the optical film was observed on a side of the polarizer. Results of measuring the light leakage intensity of the optical film of Example 2 are shown in FIG. 8.

Comparative Example 1

(23) An optical film of Comparative Example 1 was manufactured by stacking a positive uniaxial retardation film having an in-plane retardation value of 100 nm with respect to light with a wavelength of 550 nm, and a negative biaxial retardation film having an in-plane retardation value of 250 nm with respect to light with a wavelength of 550 nm and a thickness-direction retardation value of 60 nm with respect to light with a wavelength of 550 nm for optical axes thereof to be arranged in parallel.

(24) In addition, a polarizing plate was manufactured by attaching a positive uniaxial retardation film of the optical film to a PVA polarizer, and an intensity of light leaked from the PVA polarizer was measured at every azimuthal angle while irradiating light toward the optical film. In the manufacture of the polarizing plate, the polarizing plate was attached to the positive uniaxial retardation film so that a light absorbing axis of the PVA polarizer and a slow axis of the positive uniaxial retardation film form an angle of about 45 degrees counterclockwise when the optical film was observed on a side of the polarizer. Results of measuring the light leakage intensity of the optical film of Comparative Example 1 are shown in FIG. 9.

Comparative Example 2

(25) An optical film of Comparative Example 2 was manufactured by stacking a negative biaxial retardation film having an in-plane retardation value 250 nm with respect to light with a wavelength of 550 nm and a thickness-direction retardation value of 60 nm with respect to light with a wavelength of 550 nm, and a negative biaxial retardation film having an in-plane retardation value of 250 nm with respect to light with a wavelength of 550 nm and a thickness-direction retardation value of 60 nm with respect to light with a wavelength of 550 nm for optical axes thereof to be arranged in parallel.

(26) In addition, a polarizing plate was manufactured by attaching a positive uniaxial retardation film of the optical film to a PVA polarizer, and an intensity of light leaked from the PVA polarizer was measured at every azimuthal angle while irradiating light toward the optical film. In the manufacture of the polarizing plate, the polarizing plate was attached to the positive uniaxial retardation film so that a light absorbing axis of the PVA polarizer and a slow axis of the positive uniaxial retardation film form an angle of about 45 degrees counterclockwise when the optical film was observed on a side of the polarizer. Results of measuring the light leakage intensity of the optical film of Comparative Example 2 are shown in FIG. 10.

Comparative Example 3

(27) An optical film of Comparative Example 3 was manufactured by stacking a positive uniaxial retardation film having an in-plane retardation value of 300 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 250 nm with respect to light with a wavelength of 550 nm and an in-plane retardation value of 225 nm with respect to light with a wavelength of 650 nm, and a negative uniaxial retardation film having an in-plane retardation value of 120 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 100 nm with respect to light with a wavelength of 550 nm, and an in-plane retardation value of 90 nm with respect to light with a wavelength of 650 nm for optical axes thereof to be arranged in parallel.

(28) In addition, a polarizing plate was manufactured by attaching a positive uniaxial retardation film of the optical film to a PVA polarizer, and an intensity of light leaked from the PVA polarizer was measured at every azimuthal angle while irradiating light toward the optical film. In the manufacture of the polarizing plate, the polarizing plate was attached to the positive uniaxial retardation film so that a light absorbing axis of the PVA polarizer and a slow axis of the positive uniaxial retardation film form an angle of about 45 degrees counterclockwise when the optical film was observed on a side of the polarizer. Results of measuring the light leakage intensity of the optical film of Comparative Example 3 are shown in FIG. 11.

Comparative Example 4

(29) An optical film of Comparative Example 4 was manufactured by stacking a positive uniaxial retardation film having an in-plane retardation value of 340 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 250 nm with respect to light with a wavelength of 550 nm and an in-plane retardation value of 225 nm with respect to light with a wavelength of 650 nm, and a negative uniaxial retardation film having an in-plane retardation value of 120 nm with respect to light with a wavelength of 450 nm, an in-plane retardation value of 100 nm with respect to light with a wavelength of 550 nm, and an in-plane retardation value of 90 nm with respect to light with a wavelength of 650 nm for optical axes thereof to be arranged in parallel.

(30) In addition, a polarizing plate was manufactured by attaching a positive uniaxial retardation film of the optical film to a PVA polarizer, and an intensity of light leaked from the PVA polarizer was measured at every azimuthal angle while irradiating light toward the optical film. In the manufacture of the polarizing plate, the polarizing plate was attached to the positive uniaxial retardation film so that a light absorbing axis of the PVA polarizer and a slow axis of the positive uniaxial retardation film form an angle of about 45 degrees counterclockwise when the optical film was observed on a side of the polarizer. Results of measuring the light leakage intensity of the optical film of Comparative Example 4 are shown in FIG. 12.

EXPLANATION OF MARKS

(31) 1: Optical Film 101: Positive Uniaxial Retardation Film 102: Negative Uniaxial Retardation Film 100: Retardation Film 2: Polarizer Plate 201: Linear Polarizer