WO2012053753A2

WO2012053753A2 - Liquid crystal display

Info

Publication number: WO2012053753A2
Application number: PCT/KR2011/007342
Authority: WO
Inventors: Young-Jae Lee; Jin Su Kim; Jun Lee; Kyoung Jong Yoo
Original assignee: Lg Innotek Co., Ltd.
Priority date: 2010-10-20
Filing date: 2011-10-05
Publication date: 2012-04-26
Also published as: WO2012053753A3; TWI461795B; KR20120040870A; TW201222084A

Abstract

An LCD including a wire grid polarizer is provided. A liquid crystal panel forming pixels is stacked on a backlight unit, and one or more wire grid polarizers are disposed on top or bottom substrates constituting the liquid crystal panel. The wire grid polarizer includes a first grid layer having one or more first grid patterns on a substrate, and a second grid layer having one or more second grid patterns formed on the first grid patterns. A wire grid polarizer includes a first grid layer having first grid patterns on a substrate, and second grid patterns formed on the first grid patterns, and the wire grid polarizer is disposed on an LCD or a backlight unit, thereby preventing distortion of image and reduction of brightness and achieving high durability.

Description

LIQUID CRYSTAL DISPLAY

The present invention relates to a liquid crystal display (LCD) with a wire grid polarizer.

An LCD is a flat panel display that is widely used in a variety of applications, including mobile phones, notebook computers, monitors, and TVs. The LCD transmits or blocks light by variation in alignment of liquid crystals when an electric signal is applied to each pixel in a liquid crystal panel disposed between two polarizing plates. To operate the LCD, a separate light source is required. The separate light source corresponds to a backlight unit.

In a conventional LCD, a mirror effect is implemented by providing absorptive polarizers on a top substrate and a bottom substrate constituting a thin film transistor (TFT) array of a liquid crystal panel, and attaching reflective polarizing films on the absorptive polarizers. Also, a mirror effect is implemented by providing a translucent mirror on an absorptive polarizer.

However, such a structure is directly exposed to external environment, causing deterioration of durability at high temperature and high humidity. Since the reflective polarizing film is manufactured by stretching or in a stack type, distortion of image such as moir occurs. The use of the absorptive polarizer reduces brightness and is cost-consuming.

In addition, the reliability of the LCD is degraded at high temperature and high humidity, and the use of the absorptive polarizing film and the translucent mirror greatly reduces brightness. Moreover, the addition of processes and the use of special mirror increase production costs.

An aspect of the present invention is directed to an LCD in which a wire grid polarizer includes a first grid layer having first grid patterns on a substrate, and second grid patterns formed on the first grid patterns, and the wire grid polarizer is disposed on an LCD or a backlight unit, thereby preventing distortion of image and reduction of brightness and achieving high durability.

According to an embodiment of the present invention, an absorptive polarizer and a translucent mirror are removed from an LCD, and a wire grid polarizer is disposed on the LCD and a bottom substrate, thereby preventing distortion of image and ensuring high reliability even at high-temperature and high-humidity environment.

According to the present invention, the wire grid polarizer having the first grid layer with the first grid patterns on the base substrate and the second grid layer is disposed only on the LCD, or is disposed on the LCD and the backlight unit, preventing distortion of image and reduction of brightness and ensuring high durability.

Furthermore, the wire grid polarizer provided in the LCD according to the present invention can solve the reduction of reliability caused by high temperature and high humidity. Additional processes are unnecessary, and a manufacturing cost problem can be solved by the use of a special mirror.

The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1 to 3 are conceptual diagrams illustrating the arrangement of a liquid crystal panel, a backlight unit, and a wire grid polarizer in an LCD according to the present invention;

FIG. 4 is a conceptual diagram illustrating a main part of the wire grid polarizer according to the present invention;

FIG. 5 is a conceptual diagram illustrating a main part of the wire grid polarizer according to the present invention; and

FIG. 6 is a diagram illustrating another implementation example of the wire grid polarizer according to the present invention.

The present invention is directed to implement a high-efficiency LCD which is resistant against temperature and humidity environment by the arrangement of a wire grid polarizer on a liquid crystal panel or the outside of a bottom substrate, eliminates distortion of image, and prevents reduction of brightness.

To this end, an LCD according to the present invention includes a liquid crystal panel having a top substrate and a bottom substrate, and one or more wire grid polarizers disposed on the top substrate or the bottom substrate.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Wherever possible, the same reference numerals will be used to refer to the same elements throughout the specification, and a duplicated description thereof will be omitted. It will be understood that although the terms first , second , etc. are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

Referring to FIG. 1, an LCD according to the present invention may include a liquid crystal panel A including a top substrate 9 or a bottom substrate 6, and one or more

wire grid polarizers

100 and 200 disposed on the top substrate or the bottom substrate.

In particular, in this case, the

wire grid polarizers

100 and 200 may include a first grid layer having one or more first grid patterns on the substrate, and second grid patterns formed on the first grid patterns.

Specifically, the LCD according to the present invention has a structure in which the liquid crystal panel A is disposed at an upper portion and a backlight unit B is disposed at a lower portion. The liquid crystal panel A includes liquid crystal LC disposed between the top substrate 9 and the bottom substrate 6, and ITOs 7 and 8 for driving the liquid crystal LC. In particular, a color filter is formed on the top substrate 9, and a TFT array is formed on the bottom substrate 6. The backlight unit B is disposed under the liquid crystal panel A and includes a light guide plate 2 guiding light upward, a reflection sheet 1, a diffusion plate 3, and a brightness enhancement film (BEF) 4.

The conventional LCD implements a mirror effect by providing absorptive polarizers on the bottoms surface of the bottom substrate 6 constituting the TFT array of the liquid crystal panel A and the top surface of the top substrate 9 constituting the color filter array, and attaching reflective polarizing films on the absorptive polarizers. Also, the conventional LCD implements a mirror effect by providing a translucent mirror on an absorptive polarizer. However, according to the present invention, a wire grid polarizer is provided, preventing distortion of image and ensuring high reliability even at high-temperature and high-humidity environment.

According to a preferred embodiment, a first wire grid polarizer 100 may be provided on the liquid crystal panel A. According to another embodiment, a second wire grid polarizer 200 may be further provided between the liquid crystal panel and the backlight unit B. Hereinafter, a structure having both the first wire grid polarizer and the second wire grid polarizer will be described as an example.

In addition, the liquid crystal panel A according to the present invention includes the top substrate 9 and the bottom substrate 6, and the TFT array 7 including ITO may be disposed on the bottom substrate 6. The color filter 8 and the liquid crystal LC are disposed under the top glass substrate 9. Since the general liquid crystal panel is applied to the present invention, detailed description thereof will be omitted. Furthermore, the backlight unit B under the liquid crystal panel A may be implemented with a general backlight unit structure including a light guide plate 2 guiding light upward, a diffusion plate 3, and various brightness enhancement films 4.

FIGS. 2 and 3 illustrate modifications of the structure described above with reference to FIG. 1.

The structure of FIG. 2 is different from the structure of FIG. 1 in that a wire grid polarizer 200 is spaced apart from a bottom substrate 6 and a polarizer P1 is attached to the surface of the bottom substrate.

The structure of FIG. 3 is different from the structure of FIG. 2 in that a polarizer P2 is disposed between a top substrate 9 and a first wire grid polarizer 100, leading to further improvement in the efficiency of the present invention.

As a preferred embodiment of the present invention, the first wire grid polarizer 100 of FIG. 2 according to the present invention may be disposed on the top substrate 9, or the second wire grid polarizer 200 attached to or spaced apart from the bottom surface of the bottom substrate 6 of the liquid crystal panel may be further provided. In this case, the first wire grid polarizer 100 disposed on the top substrate of the liquid crystal panel includes metal patterns with high reflectivity, thereby obtaining an excellent mirror effect. Meanwhile, since grid patterns configured with metal patterns are provided, resistance against high temperature and high humidity is improved.

In addition, in the case where the second wire grid polarizer 200 is disposed, light emitted from a light source is polarized. That is, P-wave is transmitted and S-wave is reflected. The reflected S-wave is reused as P-wave, leading to brightness enhancement.

The structure of the first and second wire grid polarizers according to the present invention will now be described with reference to FIG. 4.

The wire grid polarizer according to the present invention may include a first grid layer 120 having one or more first grid patterns 121 on a substrate 110, and one or more second grid patterns 130 formed of a metal on the first grid patterns 121.

A passivation layer C may be further provided on the second grid patterns 130. The passivation layer C may be formed to cover the entire side and top surfaces of the second grid patterns 130. In the case where the passivation layer C is provided, the TFT array 7 or the like may be provided on the passivation layer C, as described above with reference to FIG. 3.

The first grid layer 120 stacked on the top surface of the substrate 110 is formed of a polymer. It is preferable that the first grid patterns 121 being protrusion patterns having a constant period are formed on the surface of the first grid layer formed of a polymer.

That is, the first grid layer 120 is defined as a layer in which a plurality of first grid patterns 121 being protrusion patterns having a constant period are provided on the surface of a resin layer formed of a polymer. In particular, it is apparent that the first grid layer 120 according to the present invention can be formed of a polymer having a refractive index lower or higher than or equal to that of the substrate, depending on purpose of use.

In addition, it is preferable that the width to height ratio of the first grid pattern 121 ranges from 1:0.2 to 1:5, and it is preferable that the width (w) of the first grid pattern 121 ranges from 10 nm to 200 nm and the height (h1) of the first grid pattern 121 ranges from 10 nm to 500 nm. Furthermore, the period of the first grid pattern may range from 100 nm to 250 nm.

The second grid pattern 130 has a structure in which fine protrusion patterns formed of a metal are arranged at a constant period. In particular, a protrusion structure formed on the top surface of the first grid pattern 121 using deposition may be formed using any one metal selected from aluminum, chromium, silver, copper, nickel, and cobalt, or an alloy thereof. The period refers to a distance between one metal grid pattern (second grid pattern) and an adjacent metal grid pattern (second grid pattern).

In the case of the first wire grid polarizer 100 as shown in FIG. 1, the presence of the second grid pattern formed of a metal such as Al makes it possible to obtain an excellent mirror effect and improve the reliability with respect to high temperature and high humidity.

In addition, the cross section of the second grid pattern 130 may have various shapes, for example, a rectangular shape, a triangular shape, a trapezoidal shape, a parallelogram shape, and a semicircular shape, or may have a metal wire shape that is partially formed on a part of a substrate patterned in a shape of triangle, rectangle, or sinusoidal wave. That is, any metal wire grids may be used as long as they are arranged in one direction at a constant period, regardless of the cross-sectional structure.

In this case, the period may be equal to or less than half the wavelength of light used. Therefore, by forming the grids in the period range of 100 nm to 250 nm, balance of a visible light region is ensured and a white balance is maintained. If the period exceeds 250 nm, red light, green light, and white light are unbalanced.

Furthermore, the wire grid polarizer according to the present invention can adjust transmittance according to the height and width of the two grids (first and second grid patterns). If the grid width is widened at the same pitch, the transmittance is lowered and the polarization extinction ratio is increased. To ensure the maximum polarization efficiency, the polarization characteristic is increased as the pitch is decreased. In the case where the grids are formed at the same distance and same height, the polarization characteristic is improved as the grid width is increased. In this case, it is preferable that the first grid has 0.2-1.5 times the width of the second grid pattern. Furthermore, the width to height ratio of the second grid pattern 130 may range from 1:0.5 to 1:1.5. In particular, a width ratio of the first grid pattern to the second grid pattern may range from 1:0.2 to 1:1.5. Specifically, the width of the second grid pattern may range from 2 nm to 300 nm. In this manner, the polarization characteristic can be maximized.

In addition, in the case where the top surface of the second grid pattern 130 being a metal grid is exposed, the durability can be ensured by forming the passivation layer C using any one selected from PMMA, TAC, PVA, PI, PMMA, PET, PEN, PES, PC, and COP.

In the case where the wire grid polarizer having the above-described structure according to the present invention is disposed on the liquid crystal panel or the outside of the bottom substrate in the LCD, the reflectivity can be improved and the resistance against environment can be increased. Therefore, the brightness can be improved by the wire grid polarizer disposed between the liquid crystal panel and the backlight unit.

Hereinafter, various modifications of the wire grid polarizer disposed in the LCD according to the present invention will be described.

(1) Structure of nano optical pattern formed on bottom of substrate

FIG. 5 illustrates another implementation example of the wire grid polarizer according to the present invention. In the similar manner, the wire grid polarizer includes a first grid layer 120 having one or more first grid patterns 121 on a substrate 110, and one or more second grid patterns 130 formed on the first grid patterns 121. In particular, the wire grid polarizer may further include a polymer layer 140 including a plurality of optical patterns 141 formed on the rear surface of the bottom glass substrate 110. By providing the polymer layer in which the optical patterns are formed on the opposite surface to the substrate in which the metal grid patterns are formed, loss of light upon light incidence can be reduced. Hence, an amount of light transmitted is increased and color coordinates are stabilized.

In this case, it is preferable that the polymer layer 140 formed on the opposite surface to the surface of the substrate where the second grid patterns 130 are formed is provided with a plurality of nano-size patterns. In this case, the polymer layer may use a UV resin or a thermosetting resin; however, the present invention is not limited thereto. It is apparent that a polymer resin having high light transmittance can be applied.

In the optical patterns formed on the surface of the polymer layer 140, protrusion patterns protruding from the top surface of the polymer layer may be arranged regularly or irregularly. The width of the protrusion patterns may range from 10 nm to 200 nm. The optical patterns may have various 3D structures as protrusion patterns. For example, the optical patterns may have various structures, for example, a conical shape, a cylindrical shape, a prismatic shape, or a grating shape, whose vertical cross-sectional shape is rectangular, triangular, or semicircular.

In addition, in the case where the polymer layer is formed on the substrate, the optical patterns may be formed by pressurization using a mold where patterns are formed. More preferably, the polymer layer according to the present invention may be formed of a material having a refractive index lower than that of the substrate. In this manner, a critical angle of incident light L1 is increased, and transmittance can be improved by reducing a surface reflection of a light incidence plane. The presence of the nano-scale optical patterns on the light incidence plane increases the light incidence area, leading to improvement of transmittance. Furthermore, the polymer layer 140 also serves as a passivation layer to protect the substrate 110, leading to increase in scratch resistance of the substrate.

(2) Structure of passivation layer

In addition, unlike the above, FIG. 6 illustrates an implementation example in which a surface treatment layer Y may be formed on the first grid patterns 121 or the second grid patterns 131.

The surface treatment layer Y may be formed on the first grid patterns or the second grid patterns, and the structure of the surface treatment layer Y may be formed by be surface-treated by any one of an atmospheric pressure plasma treatment, a vacuum plasma treatment, a peroxide treatment, a pro-oxidant treatment, an anticorrosive treatment, and a self-assembly monolayer (SAM) coating.

In particular, as illustrated in FIG. 6, in the case where the surface treatment layer Y is formed to cover the whole second grid patterns and the attachment region Z between the first grid patterns 121 and the second grid patterns 131, an oxide film or a similar surface treatment film causing no deformation in the surface of each grid pattern and improving the durability is provided to implement physical properties that do not degrade optical characteristics and improve adhesion between the second grid patterns and the polymer layer of the first grid patterns.

While the invention has been shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Claims

A liquid crystal display comprising:

a liquid crystal panel including a top substrate and a bottom substrate; and

one or more wire grid polarizers disposed on the top substrate or the bottom substrate,

wherein the wire grid polarizers include:

a first grid layer having one or more first grid patterns on a substrate; and

second grid patterns formed on the first grid patterns.
The liquid crystal display of claim 1, wherein the wire grid polarizer is a first wire grid polarizer disposed on the top substrate.
The liquid crystal display of claim 2, wherein the first wire grid polarizer is directly attached to the top surface of the top substrate.
The liquid crystal display of claim 2, further comprising a polarizing plate disposed between the first wire grid polarizer and the top substrate.
The liquid crystal display of claim 2, further comprising a second wire grid polarizer disposed under the bottom substrate.
The liquid crystal display of claim 5, further comprising a polarizing plate disposed between the second wire grid polarizer and the bottom substrate.
The liquid crystal display of claim 5, wherein the second wire grid polarizer is disposed in a structure in which the substrate of the wire grid polarizer is attached to the bottom substrate.
The liquid crystal display of claim 5, wherein the wire grid polarizer includes a passivation layer covering the top surface of the second grid pattern.
The liquid crystal display of claim 8, wherein the passivation layer is formed to cover the entire side and top surfaces of the second grid pattern.
The liquid crystal display of claim 1, wherein the first grid layer is formed of a polymer having the same refractive index as the substrate.
The liquid crystal display of claim 1, wherein the second grid pattern is formed of any one metal selected from aluminum, chromium, silver, copper, nickel, and cobalt, or an alloy thereof.
The liquid crystal display of claim 1, wherein a width to height ratio of the first grid pattern ranges from 1:0.2 to 1:5.
The liquid crystal display of claim 12, wherein a width ratio of the first grid pattern to the second grid pattern ranges from 1:0.2 to 1:1.5.
The liquid crystal display of claim 12, wherein the width of the first grid pattern ranges from 10 nm to 200 nm, and the height of the first grid pattern ranges from 10 nm to 500 nm.
The liquid crystal display of claim 12, wherein the width of the second grid pattern ranges from 2 nm to 300 nm.
The liquid crystal display of claim 12, wherein the period of the first grid pattern ranges from 100 nm to 250 nm.
The liquid crystal display of claim 1, wherein the wire grid polarizer further includes a polymer layer with a plurality of optical patterns formed on the rear surface of the substrate.
The liquid crystal display of claim 1, further comprising a surface treatment layer on the first grid patterns or the second grid patterns of the wire grid polarizer.