# Patent

## Title
Compensation film and optical film, and display device

## Abstract

A compensation film includes: a first retardation layer including a polymer; a second retardation layer including a liquid crystal having positive birefringence; and a compensation layer including a liquid crystal having a vertical alignment property, where an angle between slow axes of the first and second retardation layers is in a range of about 85 to about 95 degrees, an entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for wavelengths of 450 nm, 550 nm and 650 nm satisfy the following inequation: Re0(450 nm)<Re0(550 nm)<Re0(650 nm), an in-plane retardation (Re3) of the compensation layer for the incident light having a wavelength of about 550 nm is in a range of about zero to about 50 nm, and a thickness direction retardation (Rth3) of the compensation layer for the incident light is less than zero.

## Background
This application claims priority to Korean Patent Application No. 10-2013-0137144 filed on Nov. 12, 2013, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which are incorporated by reference herein in its entirety.
BACKGROUND
1. Field
Embodiments of the invention relate to a compensation film, an optical film and a display device including the compensation film or the optical film.
2. Description of the Related Art
A flat panel display may be classified into a light-emitting display device that emits light by itself and a non-emissive display device that includes a separate light source and a compensation film such as a retardation film is generally employed for improving the image quality thereof.
In a light emitting display device, for example, an organic light emitting diode (“OLED”) display, the visibility and the contrast ratio may be deteriorated by reflection of the exterior light caused by a metal such as an electrode. To reduce the deterioration in the visibility and the contrast ratio, the linear polarized light is shifted into circularly polarized light using a polarizer and a compensation film, such that reflection of the external light by the OLED display and leakage thereof to the outside may be effectively prevented.
To reduce the reflection of the exterior light, the liquid crystal display (“LCD”), which is a non-emissive display device, changes the linear polarized light into the circularly polarized light to improve the image quality according to the type of the device such as a transparent type, a transflective type or a reflective type, for example.
However, a conventional compensation film is strongly dependent upon the wavelength to the incident light, so such a compensation film may effectively operate for light having a certain wavelength, but the effect thereof may be deteriorated for other wavelengths. In addition, a conventional compensation film may have strong viewing angle dependency.
SUMMARY
One embodiment provides a compensation film with improved the display characteristics by reducing the wavelength dependency and the viewing angle dependency.
Another embodiment provides an optical film including the compensation film.
Yet another embodiment provides a display device including the compensation film.
According to one embodiment, a compensation film includes a first retardation layer including a polymer, a second retardation layer including a liquid crystal having positive birefringence, and a compensation layer including a liquid crystal having a vertical alignment property, where an angle between a slow axis of the first retardation layer and a slow axis of the second retardation layer is about 85 to about 95 degrees, an entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for wavelengths of about 450 nanometers (nm), 550 nm, and 650 nm satisfy Re0(450 nm)<Re0(550 nm)<Re0(650 nm), an in-plane retardation (Re3) of the compensation layer for the incident light having a wavelength of about 550 nm is in a range of about zero (0) to about 50 nm, and a thickness direction retardation (Rth3) of the compensation layer for the incident light having the wavelength of about 550 nm is less than zero (0).
In an embodiment, an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm may be in a range of about 150 nm to about 500 nm, an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm may be in a range of about 100 nm to about 360 nm, and the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm is a value obtained by subtracting in-plane retardation (Re2) of the second retardation layer and in-plane retardation (Re3) of the compensation layer from in-plane retardation (Re1) of the first retardation layer.
In an embodiment, the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm may be in a range of about 120 nm to about 160 nm.
In an embodiment, the first retardation layer may have a short wavelength dispersion of about 0.95 to about 1.05, and the second retardation layer may have a short wavelength dispersion of about 1.05 to about 1.30.
In an embodiment, the first retardation layer may have a long wavelength dispersion of about 0.95 to about 1.05, and the second retardation layer may have a long wavelength dispersion of about 0.80 to about 0.99.
In an embodiment, the compensation film may have a short wavelength dispersion greater than or equal to about 0.7 and less than about 1.0, and the compensation film may have a long wavelength dispersion greater than about 1.0 and less than or equal to about 1.2.
In an embodiment, a thickness direction retardation (Rth1) and an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm may satisfy the following inequation: 1.0≦(Rth1/Re1)+0.5≦1.5, and a thickness direction retardation (Rth2) and an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm may satisfy the following inequation: 0.8≦(Rth2/Re2)+0.5≦1.5.
In an embodiment, an entire thickness direction retardation (Rth0) and the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm may satisfy the following inequation: −1.0≦(Rth0/Re0)+0.5≦1.0.
In an embodiment, the first retardation layer may include a polymer having positive birefringence.
In an embodiment, the first retardation layer may be an elongated polymer layer, and the first retardation layer may have a refractive index simultaneously satisfying the following inequations: nx1≧ny1 and nx1≧nz1, where nx1 denotes a refractive index at the slow axis of the first retardation layer, ny1 denotes a refractive index at a fast axis of the first retardation layer, and nz1 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the first retardation layer.
In an embodiment, the second retardation layer may be an anisotropic liquid crystal layer, and the second retardation layer may have a refractive index simultaneously satisfying the following inequations: nx2≧ny2 and nx2≧nz2, where nx2 denotes a refractive index at the slow axis of the second retardation layer, ny2 denotes a refractive index at a fast axis of the second retardation layer, and nz2 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the second retardation layer.
In an embodiment, the compensation layer may have a refractive index simultaneously satisfying the following inequations: nz3≧nx3 and nz3≧ny3, where nx3 denotes a refractive index at a slow axis of the compensation layer, ny3 denotes a refractive index at a fast axis of the compensation layer, and nz3 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film.
In an embodiment, the compensation film may have a refractive index satisfying the following inequation: nx0>nz0>ny0, where nx0 denotes a refractive index at a slow axis of the compensation film, ny0 denotes a refractive index at a fast axis of the compensation film, and nz0 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film.
In an embodiment, the polymer may include a cycloolefin, a cycloolefin copolymer, or a combination thereof.
In an embodiment, the liquid crystal may be a reactive mesogen liquid crystal.
In an embodiment, the reactive mesogen liquid crystal may include at least one of a rod-shaped aromatic derivative having at least one reactive cross-linking group, propylene glycol 1-methyl, propylene glycol 2-acetate, and a compound represented by P1-A1-(Z1-A2)n-P2, where P1 and P2 independently include acrylate, methacrylate, vinyl, vinyloxy, epoxy, or a combination thereof, A1 and A2 independently include 1,4-phenylene, a naphthalene-2,6-diyl group, or a combination thereof, Z1 includes a single bond, —COO—, —OCO—, or a combination thereof, and n is 0, 1, or 2.
According to another embodiment, an optical film including a polarizer element and an embodiment of the compensation film described above.
According to another embodiment, a display device includes a display panel, a compensation film disposed on a side of the display panel, and a polarizer element disposed on a side of the compensation film, wherein the compensation film includes a first retardation layer including a polymer, a second retardation layer including a liquid crystal having positive birefringence, and a compensation layer including a liquid crystal having a vertical alignment property, where an angle between a slow axis of the first retardation layer and a slow axis of the second retardation layer is in a range of about 85 to about 95 degrees, an entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for wavelengths of about 450 nm, 550 nm, and 650 nm satisfy Re0(450 nm)<Re0(550 nm)<Re0(650 nm), an in-plane retardation (Re3) of the compensation layer for the incident light having a wavelength of about 550 nm is in a range of about zero (0) to about 50 nm, and a thickness direction retardation (Rth3) of the compensation layer for the incident light having the wavelength of about 550 nm is less than zero (0).
In an embodiment, an in-plane retardation (Re1) for the incident light having the wavelength of about 550 nm of the first retardation layer may in a range of be about 150 nm to about 500 nm, an in-plane retardation (Re2) for the incident light having the wavelength of about 550 nm of the second retardation layer may be in a range of about 100 nm to about 360 nm, and the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer, and the compensation layer for the incident light having the wavelength of about 550 nm may be in a range of about 120 nm to about 160 nm.
In an embodiment, the first retardation layer may have a short wavelength dispersion in a range of about 0.95 to about 1.05, the second retardation layer may have a short wavelength dispersion in a range of about 1.05 to about 1.30, the first retardation layer may have a long wavelength dispersion in a range of about 0.95 to about 1.05, the second retardation layer may have a long wavelength dispersion in a range of about 0.80 to about 0.99, the compensation film may have a short wavelength dispersion greater than or equal to about 0.7 and less than about 1.0, and the compensation film may have a long wavelength dispersion greater than about 1.0 and less than or equal to about 1.2.
In an embodiment, a thickness direction retardation (Rth1) and an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm may satisfy the following inequation: 1.0≦(Rth1/Re1)+0.5≦1.5, a thickness direction retardation (Rth2) and an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm may satisfy the following inequation: 0.8≦(Rth2/Re2)+0.5≦1.5, and an entire thickness direction retardation (Rth0) and the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm may satisfy the following inequation 3: −1.0≦(Rth0/Re0)+0.5≦1.0.
In an embodiment, the first retardation layer may include a polymer having positive birefringence.
In an embodiment, the polymer of the first retardation layer may include a cycloolefin, a cycloolefin copolymer, or a combination thereof, and the liquid crystal of the second retardation layer may be a reactive mesogen liquid crystal.
In an embodiment, the display panel may be a liquid crystal panel or an organic light emitting panel.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features of the invention will become more apparent by describing in detailed exemplary embodiments thereof with reference to the accompanying drawings, in which:
FIG. 1 is a cross-sectional view schematically showing an embodiment of a compensation film, according to the invention;
FIG. 2 is a top plan view schematically showing a slow axis of the compensation film shown in FIG. 1;
FIG. 3 is a cross-sectional view schematically showing an embodiment of an optical film, according to the invention;
FIG. 4 is a schematic view showing the anti-reflection principle of an embodiment of an optical film, according to the invention;
FIG. 5 is a cross-sectional view schematically showing an embodiment of an organic light emitting diode (“OLED”) display, according to the invention;
FIG. 6 is a cross-sectional view schematically showing an embodiment of a liquid crystal display (“LCD”) device, according to the invention;
FIG. 7 is a graph showing a reverse wavelength dispersion delay result of a compensation film according to Preparation Example 1; and
FIG. 8 is a graph showing retardation of the compensation films according to Preparation Example 1 and Comparative Preparation Example 1 depending on a viewing angle.



DETAILED DESCRIPTION
The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which various embodiments are shown. This invention may, however, be embodied in many different forms, and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.
It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.
It will be understood that, although the terms “first,” “second,” “third” etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower,” can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.
“About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” can mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the claims.
Hereinafter, an embodiment of a compensation film according to the invention will be described referring to FIG. 1.
FIG. 1 is a cross-sectional view schematically showing an embodiment of a compensation film, according to the invention.
Referring to FIG. 1, an embodiment of the compensation film 100 includes a first retardation layer 110, a second retardation layer 120 and a compensation layer 130.
The first retardation layer 110 may include an elongated polymer layer including a polymer having positive birefringence, the second retardation layer 120 may include an anisotropic liquid crystal layer including a liquid crystal having positive birefringence, and the compensation layer 130 may include an isotropic liquid crystal layer including a liquid crystal having a vertical alignment property. The birefringence (Δn) is a difference found by subtracting the refractive index (no) of light propagating perpendicular to an optical axis from the refractive index (ne) of light propagating parallel to the optical axis, and the first retardation layer 110 and the second retardation layer 120 have substantially the same sign (e.g., positive) of birefringence.
The polymer of the first retardation layer 110 having a positive birefringence may include, for example, a cycloolefin, a cycloolefin copolymer, or a mixture/combination thereof.
The first retardation layer 110 may maintain the positive birefringence after being elongated.
The anisotropic liquid crystal of the second retardation layer 120 may be a monomer, an oligomer, or a polymer having a rigid-rod shape, for example. The anisotropic liquid crystal may be aligned substantially in one direction along the optical axis.
The anisotropic liquid crystal may be a reactive mesogen liquid crystal, and may have, for example, a reactive cross-linking group. The reactive mesogen liquid crystal may include, for example, a rod-shaped aromatic derivative having a reactive cross-linking group, propylene glycol 1-methyl, propylene glycol 2-acetate, a compound represented by P1-A1-(Z1-A2)n-P2, or a combination thereof. Here, P1 and P2 independently include acrylate, methacrylate, vinyl, vinyloxy, epoxy, or a combination thereof, A1 and A2 independently include 1,4-phenylene, naphthalene-2,6-diyl group, or a combination thereof, Z1 includes a single bond, —COO—, —OCO—, or a combination thereof, and n is 0, 1 or 2, but is not limited thereto.
The liquid crystal of compensation layer 130 may be, for example, an in-plane isotropic liquid crystal, and may have a vertical alignment property with respect to a length direction of the film. The in-plane isotropic liquid crystal may have no in-plane retardation (Re) or very low in-plane retardation (Re), which will be described later in detail.
In such an embodiment, the compensation properties may be strengthened by adjusting optical properties of the first retardation layer 110 and the second retardation layer 120, and simultaneously reducing a viewing angle dependency due to the compensation layer 130 to reduce the wavelength dependency and the viewing angle dependency of the compensation film 100.
The first retardation layer 110 and the second retardation layer 120 may each have a forward wavelength dispersion retardation, and the compensation film 100 may have a reverse wavelength dispersion retardation. The forward wavelength dispersion retardation has higher or equal retardation to light having a short wavelength than retardation to light having a long wavelength, and the reverse wavelength dispersion retardation has higher retardation to light having a long wavelength than retardation to light having a short wavelength.
The retardation may be referred to as in-plane retardation (Re), and the in-plane retardation (Re) may be represented by Re=(nx−ny)d. Herein, nx denotes a refractive index in a direction having a highest refractive index in a plane of a film (hereinafter referred to as “slow axis”), ny denotes a refractive index in a direction having a lowest refractive index in a plane of a film (hereinafter referred to as “fast axis”), and d denotes a thickness of film.
The in-plane retardation (Re1) of the first retardation layer 110 may be represented by Re1=(nx1−ny1)d1, the in-plane retardation (Re2) of the second retardation layer 120 may be represented by Re2=(nx2−ny2)d2, the in-plane retardation (Re3) of the compensation layer 130 may be represented by Re3=(nx3−ny3)d3, and the in-plane retardation (Re0) of the compensation film 100 may be represented by Re0=(nx0−ny0)d0. Herein, nx1 denotes a refractive index at the slow axis of the first retardation layer 110, ny1 denotes a refractive index at the fast axis of the first retardation layer 110, d1 denotes a film thickness of the first retardation layer 110, nx2 denotes a refractive index at the slow axis of the second retardation layer 120, ny2 denotes a refractive index at the fast axis of the second retardation layer 120, d2 denotes a film thickness of the second retardation layer 120, nx3 denotes a refractive index at the slow axis of the compensation layer 130, ny3 denotes a refractive index at the fast axis of the compensation layer 130, d3 is a film thickness of the compensation layer 130, nx0 denotes a refractive index at the slow axis of the compensation film 100, ny0 denotes a refractive index at the fast axis of the compensation film 100, and d0 denotes a film thickness of the compensation film 100.
The in-plane retardation (Re0) of the compensation film 100 may be a value obtained by subtracting the in-plane retardation (Re2) of the second retardation layer 120 and the in-plane retardation (Re3) of the compensation layer 130 from the in-plane retardation (Re1) of the first retardation layer 110. As described above, in such an embodiment, the compensation layer 130 includes an in-plane isotropic liquid crystal, and thus has no or little in-plane retardation. Therefore, the in-plane retardation (Re0) of the compensation film 100 may be substantially represented by a difference between the in-plane retardation (Re1) of the first retardation layer 110 and the in-plane retardation (Re2) of the second retardation layer 120, and the in-plane retardation (Re1, Re2) may be provided within a predetermined range by changing a thickness and/or a refractive index at the slow axis and/or the fast axis of the first retardation layer 110 and the second retardation layer 120.
According to an embodiment, the first retardation layer 110 may have in-plane retardation (Re1) in a range of about 150 nanometers (nm) to about 500 nm for the incident light having a wavelength of about 550 nm (hereinafter referred to as “reference wavelength”), the second retardation layer 120 may have in-plane retardation (Re2) in a range of about 100 nm to about for 360 nm for the incident light having the reference wavelength, and the compensation layer 130 may have an in-plane retardation (Re3) in a range of about 0 nm to about 20 nm for the incident light having the reference wavelength. The entire in-plane retardation (Re0) of the first retardation layer 110, the second retardation layer 120 and the compensation layer 130 for the incident light having the reference wavelength may be a value obtained by subtracting the in-plane retardation (Re2) of the second retardation layer 120 and the in-plane retardation (Re3) of the compensation layer 130 from the in-plane retardation (Re1) of the first retardation layer 110. In one embodiment, for example, the compensation film 100 may have the in-plane retardation (Re0) in a range of about 120 nm to about 160 nm for the incident light having the reference wavelength.
As described above, the first retardation layer 110 and the second retardation layer 120 may have higher or equal retardation to light having a short wavelength than retardation to light having a long wavelength. In one embodiment, for example, the in-plane retardation (Re1) of the first retardation layer 110 for 450 nm, 550 nm, and 650 nm wavelengths may satisfy Re1(450 nm)≧Re1(550 nm)≧Re1(650 nm), and the in-plane retardation (Re2) of the second retardation layer 120 may satisfy Re2(450 nm)>Re2(550 nm)>Re2(650 nm).
The changing of the retardation of the short wavelength for the reference wavelength may be referred to as short wavelength dispersion, the short wavelength dispersion of the first retardation layer 110 may be represented by Re1(450 nm)/Re1(550 nm), and the short wavelength dispersion of the second retardation layer 120 may be represented by Re2(450 nm)/Re2(550 nm). In one embodiment, for example, the first retardation layer 110 may have a short wavelength dispersion in a range of about 0.95 to about 1.05, and the second retardation layer 120 may have a short wavelength dispersion in a range of about 1.05 to about 1.30.
The changing of the retardation of the long wavelength for the reference wavelength may be referred to as long wavelength dispersion, the long wavelength dispersion of the first retardation layer 110 may be represented by Re1(650 nm)/Re1(550 nm), and the long wavelength dispersion of the second retardation layer 120 may be represented by Re2(650 nm)/Re2(550 nm). In one embodiment, for example, the first retardation layer 110 may have a long wavelength dispersion in a range of about 0.95 to about 1.05, and the second retardation layer 120 may have a long wavelength dispersion in a range of about 0.80 to about 0.99.
In another embodiment, an angle between the slow axis of the first retardation layer 110 and the slow axis of the second retardation layer 120 may be in a range of about 85 degrees to about 95 degrees.
FIG. 2 is a top plan view schematically showing a slow axis of the compensation film shown in FIG. 1.
Referring to FIG. 2, the angle between the slow axis 115 of the first retardation layer 110 and the slow axis 125 of the second retardation layer 120 may be in a range of about 85 degrees to about 95 degrees, for example, may be in a range of about 87.5 degrees to about 92.5 degrees, or may be about 90 degrees.
When the first retardation layer 110 and the second retardation layer 120 have the in-plane retardation, and also when the angle between the slow axis 115 of the first retardation layer 110 and the slow axis 125 of the second retardation layer 120 is in the range of about 85 degrees to about 95 degrees, the compensation film 100 may have a reverse wavelength dispersion retardation.
As described above, in an embodiment, the in-plane retardation (Re0) of the compensation film 100 for the incident light having the reference wavelength may be a value obtained by subtracting the in-plane retardation (Re2) of the second retardation layer 120 and the in-plane retardation (Re3) of the compensation layer 130 from the in-plane retardation (Re1) of the first retardation layer 110, and may be, for example, in a range of about 120 nm to about 160 nm.
In an embodiment, the in-plane retardation (Re0) of the compensation film 100 for the wavelengths of 450 nm, 550 nm, and 650 nm may satisfy the following inequation: Re0(450 nm)<Re0(550 nm)<Re0(650 nm), such that a reverse wavelength dispersion retardation is provided.
The short wavelength dispersion of the compensation film 100 may be represented by Re0(450 nm)/Re0(550 nm), for example, may be greater than or equal to about 0.7 and less than about 1.0. The compensation film 100 may have short wavelength dispersion in a predetermined range, for example, in a range of about 0.75 to about 0.90, or may be about 0.81.
The long wavelength dispersion of the compensation film 100 may be represented by Re0(650 nm)/Re0(550 nm), for example, may be greater than about 1.0 and less than or equal to about 1.2. The compensation film 100 may have long wavelength dispersion in a predetermined range, for example, in range of about 1.15 to about 1.19, or may be about 1.18.
In an embodiment, the retardation includes thickness direction retardation (Rth) besides the in-plane retardation (Re). The thickness direction retardation (Rth) is retardation generated in a thickness direction of a film, and the thickness direction retardation (Rth1) of the first retardation layer 110 may be represented by Rth1={[(nx1+ny1)/2]−nz1}d1, the thickness direction retardation (Rth2) of the second retardation layer 120 may be represented by Rth2={[(nx2+ny2)/2]−nz2}d2, the thickness direction retardation (Rth3) of the compensation layer 130 may be represented by Rth3={[(nx3+ny3)/2]−nz3}d3, and the thickness direction retardation (Rth0) of the compensation film 100 may be represented by Rth0={[(nx0+ny0)/2]−nz0}d0. Herein nx1 denotes a refractive index at a slow axis of the first retardation layer 110, ny1 denotes a refractive index at a fast axis of the first retardation layer 110, nz1 denotes a refractive index in the direction perpendicular to the slow axis and the fast axis of the first retardation layer 110, nx2 denotes a refractive index at a slow axis of the second retardation layer 120, ny2 denotes a refractive index at a fast axis of the second retardation layer 120, nz2 denotes a refractive index in the direction perpendicular to the slow axis and the fast axis of the second retardation layer 120, nx3 denotes a refractive index at a slow axis of the compensation layer 130, ny3 denotes a refractive index at a fast axis of the compensation layer 130, nz3 denotes a refractive index in the direction perpendicular to the slow axis and the fast axis of the compensation layer 130, nx0 denotes a refractive index at a slow axis of the compensation film 100, ny0 denotes a refractive index at a fast axis of the compensation film 100, and nz0 denotes a refractive index in the direction perpendicular to the slow axis and the fast axis of the compensation film 100.
The thickness direction retardation (Rth0) of the compensation film 100 may be represented by the sum of the thickness direction retardation (Rth1) of the first retardation layer 110, the thickness direction retardation (Rth2) of the second retardation layer 120, and the thickness direction retardation (Rth3) of the compensation layer 130. As the thickness direction retardation (Rth0) of the compensation film 100 is decreased, the viewing angle dependency may be reduced. The thickness direction retardation (Rth3) of the compensation layer 130 for the incident light having the wavelength of about 550 nm may be less than about zero (0), for example, −500 nm≦Rth3<0. The compensation layer 130 offsets the thickness direction retardation (Rth1) of the first retardation layer 110 and the thickness direction retardation (Rth2) of the second retardation layer 120, and reduces the thickness direction retardation (Rth0) of the compensation film 100.
In an embodiment, the thickness direction retardation (Rth1) and the in-plane retardation (Re1) of the first retardation layer 110 for the incident light having a reference wavelength satisfy the following Relationship Inequation 1, and the thickness direction retardation (Rth2) and the in-plane retardation (Re2) of the second retardation layer 120 for the incident light having a reference wavelength satisfy the following Relationship Inequation 2.

1.0≦(Rth1/Re1)+0.5≦1.5  Relationship Inequation 1:

1.0≦(Rth2/Re2)+0.5≦1.5  Relationship Inequation 2:

In an embodiment, the compensation layer 130 may realize the compensation film 100 satisfying the following Relationship Inequation 3 by offsetting the thickness direction retardation (Rth1) of the first retardation layer 110 and the thickness direction retardation (Rth2) of the second retardation layer 120 that satisfy Relationship Inequations 1 and 2.

−1.0≦(Rth0/Re0)+0.5≦1.0  Relationship Inequation 3:

In such an embodiment, the first retardation layer 110 has a refractive index simultaneously satisfying the following Relationship Inequations 4 and 5, and the second retardation layer 120 has a refractive index simultaneously satisfying the following Relationship Inequations 6 and 7.

nx1≧ny1  Relationship Inequation 4:

nx1≧nz1  Relationship Inequation 5:

In Relationship Inequations 4 and 5, nx1 denotes a refractive index at a slow axis of the first retardation layer, ny1 denotes a refractive index at a fast axis of the first retardation layer, and nz1 is a refractive index in the direction perpendicular to the slow axis and the fast axis of the first retardation layer.

nx2≧ny2  Relationship Inequation 6:

nx2≧nz2  Relationship Inequation 7:

In Relationship Inequations 6 and 7, nx2 denotes a refractive index at a slow axis of the second retardation layer, ny2 denotes a refractive index at a fast axis of the second retardation layer, and nz2 denotes a refractive index in the direction perpendicular to the slow axis and the fast axis of the second retardation layer.
In such an embodiment, the compensation layer 130 may have a refractive index satisfying the following Relationship Inequation 8 and a refractive index satisfying the following Relationship Inequations 9 and 10, simultaneously.

nz3≧nx2=ny2  Relationship Inequation 8:

nz2≧nx2  Relationship Inequation 9:

nz2≧ny2  Relationship Inequation 10:

In Relationship Inequations 8 to 10, nx3 denotes a refractive index at a slow axis of the compensation layer, ny3 denotes a refractive index at a fast axis of the compensation layer, and nz3 denotes a refractive index in the direction perpendicular to the slow axis and the fast axis of the compensation layer.
The first retardation layer 110, the second retardation layer 120 and the compensation layer 130 each have a refractive index satisfying the relationship inequations, and thereby the compensation film 100 may have a refractive index satisfying the following Relationship Inequation 11: nx0>nz0>ny0.
In Relationship Inequation 11, nx0 denotes a refractive index at a slow axis of the compensation film, ny0 denotes a refractive index at a fast axis of the compensation film, and nz0 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film.
The compensation film 100 may effectively offset the thickness direction retardation (Rth0) due to the compensation layer 130 and simultaneously provide a λ/4 retardation in the entire visible ray region by assembling the first retardation layer 110 and the second retardation layer 120 and by controlling the optical properties thereof to accomplish the reverse wavelength dispersion delay. Accordingly, in an embodiment, the compensation film 100 may effectively perform the circularly polymerized compensation function and may improve display characteristics of a display device including the compensation film 100.
In an embodiment, as shown in FIG. 1, the compensation layer 130 may be disposed on one side of the second retardation layer 120, but is not limited thereto. In an alternative embodiment, the compensation layer 130 may be positioned on one side of the first retardation layer 110, e.g., between the first and second retardation layers 110 and 120.
The compensation film 100 may further include an adhesion layer (not shown) at between the first retardation layer 110 and the second retardation layer 120, between the first retardation layer 110 and the compensation layer 130, or between the second retardation layer 120 and the compensation layer 130. The adhesion layer may effectively attach layers of the compensation film 110 to each other, and may include or be made of, for example, a pressure sensitive adhesive.
The compensation film 100 may be manufactured by preparing each of the first retardation layer 110, the second retardation layer 120 and the compensation layer 130 as a film and assembling the first retardation layer 110, the second retardation layer 120 and the compensation layer 130, or by coating the second retardation layer 120 on the first retardation layer 110 and then coating the compensation layer 130 on the second retardation layer 120. When preparing the retardation layer 120 and the compensation layer 130 as a film, a liquid crystal solution may be coated on a support layer and irradiated to be cross-linked. The support layer may be, for example, a triacetyl cellulose (“TAC”) film, but is not limited thereto. The compensation film 100 may be formed by, for example, roll-to-roll, spin coating, transferring, and the like, but is not limited thereto.
The compensation film 100 may be provided into an optical film together with a polarizer. The optical film may be, for example, an anti-reflective film.
FIG. 3 is a cross-sectional view schematically showing an embodiment of an optical film, according to the invention.
Referring to FIG. 3, an embodiment of the optical film 300 includes a compensation film 100 and a polarizer 200 disposed on one side of the compensation film 100.
The first retardation layer 110 of the compensation film 100 may be disposed to contact the polarizer 200, the second retardation layer 120 of the compensation film 100 may be disposed to contact the polarizer 200, or the compensation layer 130 of the compensation film 100 may be disposed to contact the polarizer 200.
The polarizer 200 may be disposed on a side where the light enters, and may be a linear polarizer shifting the polarization of incident light into linear polarization. The polarizer 200 may include or be made of, for example, elongated polyvinyl alcohol (“PVA”), and the polarizer 200 may be prepared by a method including, for example, drawing a PVA film, adsorbing iodine or a dichroic dye thereto, and borating and washing the PVA film.
The optical film 300 may further include a protective layer (not shown) on a surface of the polarizer 200. The protective layer may be provided for further reinforcing the functionality or improving the durability of the optical film 300, or for reducing reflection or glare, and for example, may be a TAC film, but is not limited thereto.
The optical film 300 may further include a correction layer (not shown) disposed on a side of the compensation film 100. The correction layer may be, for example, a color shift resistant layer, but is not limited thereto.
The optical film 300 may further include a light blocking layer (not shown) which extends along the edge. The light blocking layer may have a strip shape and be disposed along the circumference of the optical film 300. In one embodiment, for example, the light blocking layer may be disposed between the first retardation layer 110 and the second retardation layer 120 of the compensation film 100. The light blocking layer may include an opaque material, for example, a black material. In one embodiment, for example, the light blocking layer may be made of a black ink.
The optical film 300 may be stacked with a compensation film 100 and a polarizer 200 according to a roll-to-roll method, but is not limited thereto.
FIG. 4 is a schematic view showing the anti-refractive principle of an embodiment of an optical film according to the invention.
Referring to FIG. 4, while the incident unpolarized light entered from the outside is passing through a polarizer 200, the unpolarized light is polarized. Then, the polarized light is shifted into circularly polarized light by passing through the compensation film 100, only a first polarized perpendicular component, which is a polarized perpendicular component of two polarized perpendicular components, is transmitted. While the circularly polarized light is reflected in a display panel 40 including a substrate, an electrode, and so on, the circular polarization direction of the circularly polarized light is changed, and the circular polarization light passes through the compensation film 100 again, such that only a second polarized perpendicular component, which is the other polarized perpendicular component of the two polarized perpendicular components, may be transmitted. As the second polarized perpendicular component is blocked by the polarizer 200, light does not exit to the outside, thereby effectively preventing the external light reflection.
The compensation film 100 and the optical film 200 may be applied to various display devices.
An embodiment of a display device may include a display panel, a compensation film disposed on a side of the display panel, and a polarizer element disposed on a side of the compensation film. The display panel may be a liquid crystal display panel or an organic light emitting display panel, but is not limited thereto.
Hereinafter, an embodiment of a display panel, where the display panel is an organic light emitting diode (“OLED”) display, will be described.
FIG. 5 is a cross-sectional view showing an embodiment of an OLED display, according to the invention.
Referring to FIG. 5, an embodiment of the OLED display includes an organic light emitting panel 400, a compensation film 100 disposed on one side of the organic light emitting diode panel 400, and a polarization device 200 disposed on one side of the compensation film 100.
The organic light emitting diode panel 400 may include a base substrate 410, a lower electrode 420, an organic emission layer 430, an upper electrode 440 and an encapsulation substrate 450.
The base substrate 410 may include or be made of glass or plastic, for example.
One of the lower electrode 420 and the upper electrode 440 may be an anode, and the other of the lower electrode 420 and the upper electrode 440 may be a cathode. The anode is an electrode injected with holes, and may include or be made of a transparent conductive material having a high work function to transmit the emitted light to the outside, for example, indium tin oxide (“ITO”) or indium zinc oxide (“IZO”). The cathode is an electrode injected with electrons, and may be made of a conductive material having a low work function and not affecting the organic material, and may include, for example, aluminum (Al), calcium (Ca), barium (Ba) or a combination thereof.
The organic emission layer 430 includes an organic material which may emit light when applying a voltage to the lower electrode 420 and the upper electrode 440.
An auxiliary layer (not shown) may be further provided between the lower electrode 420 and the organic emission layer 430 and between the upper electrode 440 and the organic emission layer 430. The auxiliary layer is used to balance electrons and holes, and may include a hole transport layer (“HTL”), a hole injection layer (“HIL”), an electron injection layer (“EIL”), and an electron transporting layer (“ETL”).
The encapsulation substrate 450 may include or be made of glass, metal or a polymer, and may seal the lower electrode 420, the organic emission layer 430 and the upper electrode 440 to effectively prevent moisture and/or oxygen inflow from the outside.
The compensation film 100 and the polarizer 200 may be disposed on the side emitting light. In an embodiment, where the OLED display has a bottom emission structure, in which light is emitted at the side of the base substrate 410, the compensation film 100 and the polarizer 200 may be disposed on the exterior side of the base substrate 410. In an alternative embodiment, where the OLED display has a top emission structure, in which light is emitted at the side of the encapsulation substrate 450, the compensation film 100 and the polarizer 200 may be disposed on the exterior side of the encapsulation substrate 450.
The compensation film 100 and the polarizer 200 shown in FIG. 5 are substantially the same as the compensation film 100 and the polarizer 200 of the embodiments shown in FIG. 3, and may functions as an anti-reflective film for effectively preventing light passing through the polarizer 200 from being reflected by a metal such as an electrode of the organic light emitting panel 400 and emitted outside of the display device. In such an embodiment, the compensation film 100 may reduce the viewing angle dependency as described above to improve the side viewing angle as well as the front viewing angle. Accordingly, the display characteristics of the OLED display may be improved.
Hereinafter, an embodiment of a display panel, where the display panel is a liquid crystal display (“LCD”), will be described.
FIG. 6 is a cross-sectional view schematically showing an embodiment of an LCD, according to the invention.
Referring to FIG. 6, an embodiment of the LCD includes a liquid crystal display panel 500, a compensation film 100 disposed on one side of the liquid crystal panel 500, and a polarizer element 200 disposed on one side of the compensation film 100.
The liquid crystal panel 500 may be a twist nematic (“TN”) mode panel, a vertical alignment (“PVA”) mode panel, an in-plane switching (“IPS”) mode panel, an optically compensated bend (“OCB”) mode panel, or the like.
The liquid crystal panel 500 may include a first display panel 510, a second display panel 520, and a liquid crystal layer 530 interposed between the first display panel 510 and the second display panel 520.
In an embodiment, the first display panel 510 may include, for example, a thin film transistor (not shown) disposed on a substrate (not shown) and a first electric field generating electrode (not shown) connected to the thin film transistor, and the second display panel 520 may include, for example, a color filter (not shown) disposed on a substrate (not shown) and a second electric field generating electrode (not shown), but it is not limited thereto. In an alternative embodiment, the color filter may be included in the first display panel 510, while the first electric field generating electrode and the second electric field generating electrode may be disposed on the first display panel 510 together therewith.
The liquid crystal layer 530 may include a plurality of liquid crystal molecules. The liquid crystal molecules may have positive or negative dielectric anisotropy. In an embodiment, where the liquid crystal molecules have positive dielectric anisotropy, the major or longitudinal axes thereof may be aligned substantially parallel to the surface of the first display panel 510 and the second display panel 520 when an electric field is not applied thereto, and the major axes may be aligned substantially perpendicular to the surface of the first display panel 510 and second display panel 520 when an electric field is applied thereto. In an embodiment, where the liquid crystal molecules have negative dielectric anisotropy, the major axes may be aligned substantially perpendicular to the surface of the first display panel 510 and the second display panel 520 when an electric field is not applied thereto, and the major axes may be aligned substantially parallel to the surface of the first display panel 510 and the second display panel 520 when an electric field is applied thereto.
The compensation film 100 and the polarizer 200 are disposed on the outside of the liquid crystal panel 500. In an embodiment, as shown in FIG. 6, the compensation film 100 and the polarizer 200 may be disposed on both the lower part and the upper part of the liquid crystal panel 500, but they are not limited thereto. In an alternative embodiment, the compensation film 100 and the polarizer 200 may be disposed on only one of the lower part and the upper part of liquid crystal panel 500.
Hereinafter, the disclosure will be illustrated in more detail with reference to examples. However, these examples are exemplary, and the disclosure is not limited thereto.
Manufacture of Compensation Film
Preparation Example 1
(1) Preparation of First Retardation Layer (A)
A first retardation layer A having optical properties shown in the following Table 1 is prepared by elongating a 100 micrometer (μm)-thick cycloolefin polymer film (from ZEON Corp.) by 50 to 100% at about 140° C. in a uniaxial direction (using a tensile tester from Instron Co.).
(2) Preparation of Second Retardation Layer (B)
A 60 μm-thick Z-TAC film (from Fujifilm Corp.) is rubbed in one direction and coated with +A plate liquid crystal (RMS03-013C, Merck & Co., Inc.) in a thickness of about 5 μm to about 10 μm, and dried in a drying oven at 60° C. for one minute to remove a coating solvent. Subsequently, ultraviolet (“UV”) rays are radiated thereto at 80 milliwatts per square centimeter (mW/cm2) for 30 seconds in a nitrogen-charged container, so that the liquid crystal molecules are photo-cross-linked to provide a second retardation layer (B) having the optical properties shown in the following Table 1.
(3) Preparation of Compensation Layer (C)
A 60 μm-thick Z-TAC film (from Fujifilm Corp.) is coated with +C plate liquid crystal (RMS03-015, Merck & Co., Inc.) in a thickness of about 15 μm to 30 μm, and dried in a drying oven at 60° C. for 1 minute to remove a coating solvent therein. Subsequently, UV rays are radiated thereto at 80 mW/cm2 for 30 seconds in a nitrogen-charged container, so that the liquid crystal molecules may be cross-linked to form a compensation layer (C) having optical properties shown in the following Table 1.
(4) Assembling First Retardation Layer and Second Retardation Layer (AB)
Subsequently, the first retardation layer is disposed to face the liquid crystal layer of the second retardation layer. Herein, the slow axis of the first retardation layer may be disposed at an angle of about 90 degrees with the slow axis of the second retardation layer. Subsequently, the first and second retardation layers are assembled by transferring the liquid crystal layer to one side of the first retardation layer and removing the Z-TAC film from the second retardation layer.
(5) Assembling of Compensation Layer (ABC)
The second retardation layer of the assembly of the first and second retardation layers is disposed to face the liquid crystal layer of the compensation layer. Subsequently, a compensation film is manufactured by assembling the first and second retardation layers and the compensation layer by transferring the liquid crystal layer of the compensation layer onto one side of the second retardation layer and removing the Z-TAC film.










TABLE 1









Wavelength




dispersion














Re




In-plane Retardation (Re)

(650 nm)/














Re
Re
Re
Re (450 nm)/
Re




(450 nm)
(550 nm)
(650 nm)
Re (550 nm)
(550 nm)
Nz

















A
391
388
396
1.008
0.996
1.08


B
279
249
237
1.122
0.952
0.99








C
Re3 = 6 nm, Rth3 = −347 nm





* Nz = (Rth/Re) + 0.5






Preparation Example 2
A compensation film is manufactured according to the same method as in Preparation Example 1, except for preparing a first retardation layer (A), a second retardation layer (B) and a compensation layer (C) having optical properties shown in the following Table 2.










TABLE 2









Wavelength




dispersion














Re




In-plane Retardation (Re)

(650 nm)/














Re
Re
Re
Re (450 nm)/
Re




(450 nm)
(550 nm)
(650 nm)
Re (550 nm)
(550 nm)
Nz

















A
505
501
499
1.008
0.996
1.07


B
404
360
343
1.122
0.952
1.00








C
Re3 = 5 nm, Rth3 = −465 nm





* Nz = (Rth/Re) + 0.5






Preparation Example 3
A compensation film is manufactured according to the same method as in Preparation Example 1, except for preparing a first retardation layer (A), a second retardation layer (B) and a compensation layer (C) having optical properties shown in the following Table 3.










TABLE 3









Wavelength




dispersion














Re




In-plane Retardation (Re)

(650 nm)/














Re
Re
Re
Re (450 nm)/
Re




(450 nm)
(550 nm)
(650 nm)
Re (550 nm)
(550 nm)
Nz

















A
292
290
289
1.008
0.996
1.07


B
166
148
141
1.122
0.952
1.00








C
Re3 = 5 nm, Rth3 = −239 nm





* Nz = (Rth/Re) + 0.5






Preparation Example 4
A compensation film is manufactured according to the same method as in Preparation Example 1, except for preparing a first retardation layer (A), a second retardation layer (B) and a compensation layer (C) having optical properties shown in the following Table 4.










TABLE 4









Wavelength




dispersion














Re




In-plane Retardation (Re)

(650 nm)/














Re
Re
Re
Re (450 nm)/
Re




(450 nm)
(550 nm)
(650 nm)
Re (550 nm)
(550 nm)
Nz

















A
257
255
254
1.008
0.996
1.07


B
132
118
112
1.122
0.952
0.99








C
Re3 = 5 nm, Rth3= −202 nm





* Nz = (Rth/Re) + 0.5






Comparative Preparation Example 1
A compensation film is manufactured by including a first retardation layer (A) and a second retardation layer (B) without preparing and assembling the compensation layer in Preparation Example 1.
Evaluation 1
The compensation films (ABC) according to Preparation Examples 1 to 4 are evaluated for in-plane retardation, thickness direction retardation and wavelength dispersion. The in-plane retardation, the thickness direction retardation, and the wavelength dispersion are measured using AxoScan equipment (manufactured by Axometrics). The measured wavelength ranges from 400 nm to 700 nm, and the film retardation is measured by adjusting the incident angle from −70 degrees to 70 degrees at an interval of 5 degrees.
The results are shown in Table 5 and FIGS. 7 and 8.
FIG. 7 is a graph showing a reverse wavelength dispersion delay result of the compensation film according to Preparation Example 1, and FIG. 8 is a graph showing retardation of the compensation films according to Preparation Example 1 and Comparative Preparation Example 1 depending on a viewing angle.











TABLE 5









In-plane Retardation (Re)
Wavelength dispersion















Re
Re
Re
Re (450 nm)/
Re (650 nm)/




(450 nm)
(550 nm)
(650 nm)
Re (550 nm)
Re (550 nm)
Nz





Preparation
124
146
155
0.85
1.06
0.51


Example 1


(ABC)


Preparation
101
141
156
0.72
1.11
0.49


Example 2


(ABC)


Preparation
126
142
148
0.89
1.04
0.50


Example 3


(ABC)


Preparation
125
137
142
0.91
1.03
0.52


Example 4


(ABC)





* Nz = [(Rth of a first retardation layer (A) + Rth of a second retardation layer (B) − Rth of a compensation layer (C))/(Re of a first retardation layer (A) − Re of a second retardation layer (B))] + 0.5






Referring to Table 5 and FIGS. 7 and 8, the compensation film according to Preparation Examples 1 to 4 show a reverse wavelength dispersion delay and is in a range of −1.0≦Nz≦1.0, and thus may improve viewing angle dependency.
Manufacture of OLED Display
Example 1
An organic light emitting display panel having a structure in which a glass substrate, a cathode including a metallic electrode material, an organic emission layer including a light emitting material, an anode including a transparent conductive material and an upper substrate are sequentially stacked, is prepared. The compensation film according to Preparation Example 1 and a polarizer (manufactured by Cheil Industries Inc.) are sequentially attached to the upper substrate of the organic light emitting display panel to provide an OLED display.
Comparative Example 1
An OLED display is manufactured in accordance with the same procedure as in Example 1, except using the compensation film according to Comparative Preparation Example 1 instead of the compensation film according to Preparation Example 1.
Evaluation 2
The OLED displays according to Example 1 and Comparative Example 1 are evaluated for reflectance and a color shift at the front. The color shift uses a horizontal axis of an a* value and a vertical axis of a b* value, wherein a positive a* value means red, a negative a* value means green, a positive b* value means yellow, a negative b* value means blue, and as absolute values of a* and b* are higher, the color is darker. The smaller the a*, b* and Δa* b* are, the better the color shift is.
The reflectance and the color shift at the front side are evaluated by supplying light under the conditions of a D65 light source, reflection of 8 degrees, and a light receiving part of 2 degrees, and using a spectrum colorimeter (CM-3600d, manufactured by Konica Minolta).
The results are shown in Table 6.












TABLE 6







Front reflectance (%)
a*
b*
Δa*b*




















Example 1
5.03
0.89
-1.33
1.60


Comparative Example 1
5.17
1.17
-2.18
2.47





*Δa*b* = {square root over (a*2 + b*2)}






Referring to Table 6, the OLED display according to Example 1 shows about 0.14% improved reflectance and a color shift improvement of about 0.87 compared with the OLED display according to Comparative Example 1.
Evaluation 3
The OLED displays according to Example 1 and Comparative Example 1 are evaluated for reflectance and color shift at the side. The reflectance and the color shift at the side are evaluated by EZContrast equipment (manufactured by ELDIM).
The results are shown in Table 7.












TABLE 7







45° side
65° side
45°
65°



reflectance (%)
reflectance (%)
color shift
color shift




















Example 1
8.15
19.97
6.00
7.70


Comparative
11.97
21.99
9.59
10.62


Example 1









Referring to Table 7, the OLED display according to Example 1 has significantly improved side reflectance and color shift compared to the OLED display according to Comparative Example 1. Accordingly, in an exemplary embodiment, as shown in the OLED display according to Example 1, the viewing angle dependency is substantially reduced.
While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

## Claims

1. A compensation film comprising:
a first retardation layer comprising a polymer;
a second retardation layer comprising a liquid crystal having positive birefringence; and
a compensation layer comprising a liquid crystal having a vertical alignment property,
wherein
the first retardation layer includes an elongated polymer layer including the polymer having positive birefringence,
an angle between a slow axis of the first retardation layer and a slow axis of the second retardation layer is in a range of about 85 degrees to about 95 degrees,
an in-plane retardation (Re1) of the first retardation layer satisfies the following inequation: Re1(450 nm)≧Re1(550 nm)≧Re1(650 nm),
an in-plane retardation (Re2) of the second retardation layer satisfies the following inequation: Re2(450 nm)>Re2(550 nm)>Re2(650 nm),
an entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for wavelengths of 450 nm, 550 nm and 650 nm satisfy the following inequation: Re0 (450 nm)<Re0 (550 nm)<Re0 (650 nm),
an in-plane retardation (Re3) of the compensation layer for an incident light having a wavelength of about 550 nm is in a range of about zero to about 50 nm,
a thickness direction retardation (Rth3) of the compensation layer for the incident light having a wavelength of about 550 nm is less than zero,
the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm is a value obtained by subtracting an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm and the in-plane retardation (Re3) of the compensation layer from an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm, and
the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm is in a range of about 120 nm to about 160 nm.

2. The compensation film of claim 1, wherein
the in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm is in a range of about 220 nm to about 500 nm, and
the in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm is in a range of about 100 nm to about 360 nm.

3. The compensation film of claim 1, wherein
the first retardation layer has a short wavelength dispersion in a range of about 0.95 to about 1.05, and
the second retardation layer has a short wavelength dispersion in a range of about 1.05 to about 1.30.

4. The compensation film of claim 1, wherein
the first retardation layer has a long wavelength dispersion in a range of about 0.95 to about 1.05, and
the second retardation layer has a long wavelength dispersion in a range of about 0.80 to about 0.99.

5. The compensation film of claim 1, wherein
the compensation film has a short wavelength dispersion greater than or equal to about 0.7 and less than about 1.0, and
the compensation film has a long wavelength dispersion greater than about 1.0 and less than or equal to about 1.2.

6. The compensation film of claim 1, wherein
a thickness direction retardation (Rth1) and an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm satisfy the following inequation: 1.0≦(Rth1/Re1)+0.5<1.5, and
a thickness direction retardation (Rth2) and an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm satisfy the following inequation: 0.8≦(Rth2/Re2)+0.5<1.5.

7. The compensation film of claim 1, wherein
an entire thickness direction retardation (Rth0) and the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm satisfy the following inequation: −1.0≦(Rth0/Re0)+0.5≦1.0.

8. The compensation film of claim 1, wherein
the first retardation layer has a refractive index simultaneously satisfying the following inequations: nx1≧ny1 and nx1>nz1,
wherein
nx1 denotes a refractive index at the slow axis of the first retardation layer,
ny1 denotes a refractive index at a fast axis of the first retardation layer, and
nz1 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the first retardation layer.

9. The compensation film of claim 1, wherein
the second retardation layer is an anisotropic liquid crystal layer, and
the second retardation layer has a refractive index simultaneously satisfying the following inequations: nx2≧ny2 and nx2≧nz2,
wherein
nx2 denotes a refractive index at the slow axis of the second retardation layer,
ny2 denotes a refractive index at a fast axis of the second retardation layer, and
nz2 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the second retardation layer.

10. The compensation film of claim 1, wherein
the compensation layer has a refractive index satisfying the following inequation: nz3≧nx3=ny3, and a refractive index simultaneously satisfying the following inequations: nz3≧nx3 and nz3≧ny3,
wherein
nX3 denotes a refractive index at a slow axis of the compensation layer,
ny3 denotes a refractive index at a fast axis of the compensation layer, and
nz3 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film.

11. The compensation film of claim 1, wherein
the compensation film has a refractive index satisfying the following inequation: nx0>nz0>ny0,
wherein
nx0 denotes a refractive index at a slow axis of the compensation film,
ny0 denotes a refractive index at a fast axis of the compensation film, and
nz0 denotes a refractive index in a direction perpendicular to the slow axis and the fast axis of the compensation film.

12. The compensation film of claim 1, wherein the polymer comprises a cycloolefin, a cycloolefin copolymer, or a combination thereof.

13. The compensation film of claim 1, wherein the liquid crystal is a reactive mesogen liquid crystal.

14. The compensation film of claim 13, wherein
the reactive mesogen liquid crystal comprises a rod-shaped aromatic derivative having a reactive cross-linking group, propylene glycol 1-methyl, propylene glycol 2-acetate, a compound represented by P1-A1-(Z1-A2)n-P2, or a combination thereof,
wherein P1 and P2 independently include acrylate, methacrylate, vinyl, vinyloxy, epoxy, or a combination thereof,
A1 and A2 independently include 1,4-phenylene, a naphthalene-2,6-diyl group, or a combination thereof,
Z1 includes a single bond, —COO—, —OCO—, or a combination thereof, and
n is 0, 1, or 2.

15. An optical film comprising:
a polarizer element; and
the compensation film of claim 1.

16. A display device, comprising:
a display panel;
a compensation film disposed on a side of the display panel; and
a polarizer element disposed on a side of the compensation film,
wherein the compensation film comprises:
a first retardation layer;
a second retardation layer comprising a liquid crystal having positive birefringence; and
a compensation layer comprising a liquid crystal having a vertical alignment property,
wherein
the first retardation layer includes an elongated polymer layer including a polymer having positive birefringence,
an angle between a slow axis of the first retardation layer and a slow axis of the second retardation layer is about 85 to about 95 degrees,
an in-plane retardation (Re1) of the first retardation layer satisfy the following inequation: Re1(450 nm)≧Re1(550 nm)≧Re1(650 nm),
an in-plane retardation (Re2) of the second retardation layer satisfy the following inequation: Re2(450 nm)>Re2(550 nm)>Re2(650 nm),
an entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for wavelengths of about 450 nm, 550 nm, and 650 nm satisfy the following inequation: Re0 (450 nm)<Re0 (550 nm)<Re0 (650 nm),
an in-plane retardation (Re3) of the compensation layer for an incident light having a wavelength of about 550 nm is in a range of about zero to about 50 nm,
a thickness direction retardation (Rth3) of the compensation layer for the incident light having the wavelength of about 550 nm is less than zero,
the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm is a value obtained by subtracting the in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm and the in-plane retardation (Re3) of the compensation layer from the in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm, and
the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm is in a range of about 120 nm to about 160 nm.

17. The display device of claim 16, wherein
an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm is in a range of about 220 nm to about 500 nm, and
an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm is in a range of about 100 nm to about 360 nm.

18. The display device of claim 16, wherein
the first retardation layer has a short wavelength dispersion in a range of about 0.95 to about 1.05,
the second retardation layer has a short wavelength dispersion in a range of about 1.05 to about 1.30,
the first retardation layer has a long wavelength dispersion in a range of about 0.95 to about 1.05,
the second retardation layer has a long wavelength dispersion in a range of about 0.80 to about 0.99,
the compensation film has a short wavelength dispersion greater than or equal to about 0.7 and less than about 1.0, and
the compensation film has a long wavelength dispersion greater than about 1.0 and less than or equal to about 1.2.

19. The display device of claim 16, wherein
a thickness direction retardation (Rth1) and an in-plane retardation (Re1) of the first retardation layer for the incident light having the wavelength of about 550 nm satisfy the following inequation: 1.0<(Rth1/Re1)+0.5<1.5,
a thickness direction retardation (Rth2) and an in-plane retardation (Re2) of the second retardation layer for the incident light having the wavelength of about 550 nm satisfy the following inequation: 0.8<(Rth2/Re2)+0.5<1.5, and
an entire thickness direction retardation (Rth0) and the entire in-plane retardation (Re0) of the first retardation layer, the second retardation layer and the compensation layer for the incident light having the wavelength of about 550 nm satisfy the following inequation 3: −1.0≦(Rth0/Re0)+0.5<1.0.

20. The display device of claim 16, wherein
the polymer of the first retardation layer comprises a cycloolefin, a cycloolefin copolymer, or a combination thereof, and
the liquid crystal of the second retardation layer is a reactive mesogen liquid crystal.

21. The display device of claim 16, wherein the display panel is a liquid crystal panel or an organic light emitting panel.