KR20020018219A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to prevent the puckering of sheets due to the contact between the sheets by forming contact preventing layers serving as a diffusion layer at both surfaces of a reflection polarization layer, thereby minimizing the defects of back light assembly due to the sheet rejects. CONSTITUTION: A liquid crystal display includes a back light assembly(23) having a light source(20) for generating light, a light guiding plate(24) mounted at a side of the light source and uniformly projecting light generated from the light source toward an LCD panel, a condensing element(30) mounted around the LCD panel of the light guiding plate and formed of a plurality of prism for condensing luminous flux of the incident light perpendicular to the LCD panel plane, a contact preventing element(34,38) mounted around the LCD panel of the condensing element for minimizing a contact area between sheets, and a reflection polarization element(36) for realizing a high luminance by repeating polarization transmission and reflection of the incident light from the light condensing element, and the LCD panel(50) formed on the back light assembly.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of improving the brightness of the liquid crystal display device and minimizing the defective rate of each sheet constituting the backlight assembly.

In general, a liquid crystal display device applies a voltage to a specific molecular array of liquid crystals and converts the same into another molecular array, and changes optical characteristics such as birefringence, photoreactivity, dichroism, and light scattering characteristics of the liquid crystal cell that emit light by the molecular arrangement. It is a display using modulation of the light by a liquid crystal cell by converting into a visual change.

The liquid crystal display device is largely divided into TN (Twisted Nematic) and STN (Super-Twisted Nematic) methods, and due to the difference in driving method, an active matrix display method using a switching element and a TN liquid crystal and a passive matrix using STN liquid crystal There is a passive matrix display method.

The big difference between these two methods is that the active matrix display method is used for TFT-LCD, which drives the LCD using the TFT as a switch, and the passive matrix display method does not use transistors, thus requiring a complicated circuit. Do not

Since the liquid crystal display is a passive optical device that does not emit light by itself, an image is displayed by using a backlight assembly attached to the rear surface of the liquid crystal panel.

Recently, various structures have been developed for slimming and lightening to secure the competitiveness of the product. In particular, in view of the fact that the liquid crystal display device is mainly used in portable computers and the like, the weight reduction is treated more heavily.

In particular, the role and function of the backlight assembly have emerged as an important problem in the liquid crystal display device. Since the size and the light efficiency of the liquid crystal display device vary depending on the structure of the backlight assembly, the mechanical and optical characteristics of the overall liquid crystal display device are different. Because it is affected a lot.

Typically, a backlight assembly of a liquid crystal display device is divided into a lamp unit and a light guide unit, and the light guide unit includes a reflector, a light guide plate, a diffusion sheet, two light collecting sheets, and a protective plate.

However, there is a problem in that the backlight assembly for the liquid crystal display device having the above-described structure cannot secure a wide viewing angle.

That is, the conventional backlight assembly for a small liquid crystal display uses two light collecting sheets in order to secure high front luminance. However, when two light collecting sheets are used in this manner, the backlight assembly for the small liquid crystal display device is perpendicular to the plane of the LCD panel. The light collecting property is increased, but the viewing angle is narrowed.

Therefore, a single light collecting sheet is used for a backlight assembly of a large liquid crystal display device requiring a wide viewing angle, and recently, a liquid crystal display device employing a reflective polarizing sheet capable of maintaining high luminance while using a single light collecting sheet is used. Backlight assembly has been developed.

A liquid crystal display device employing the above-mentioned reflective polarizing sheet is disclosed in US Pat. No. 6,025,897.

FIG. 1 is a view schematically showing a liquid crystal display device employing the conventional reflective polarizing sheet, and FIG. 2 is a cross-sectional view of the device of FIG. 1 taken along lines A ₁ -A ₂ .

1 and 2, the liquid crystal display includes a lamp unit 3, a light guide unit 18, and an LCD panel 15.

The lamp unit 3 comprises a lamp 1 for generating light and a lamp reflector 2 surrounding the lamp 1.

A cold cathode tube is mainly used as the lamp 1, and the light generated by the lamp 1 is incident through the side surface of the light guide plate 4.

The lamp reflector 2 improves the efficiency of the light generated by the lamp by reflecting the light generated from the lamp 1 toward the side of the light guide plate 4.

The light guide unit 3 is formed with a reflective plate 6, a light guide plate 4, a diffusion sheet 8, a light collecting sheet 10, a reflective polarizing sheet 12, and a protective sheet 14.

The light guide plate 4 is formed of a plastic-based transparent material such as acrylic to form a panel having an inclined lower surface and a horizontal upper surface (or alternatively, an inclined upper surface and a horizontal lower surface), so that the lamp 1 The light generated from the light is directed toward the LCD panel 15 seated at the upper portion via the upper surface of the light guide plate 4. Accordingly, various patterns such as fine dot patterns are printed and formed on the lower surface of the light guide plate 4 to convert the traveling direction of the light generated from the lamp 1 toward the LCD panel.

A reflecting plate 6 is formed on a lower surface of the light guide plate 4, and the diffusion sheet 8, the light collecting sheet 10, the reflective polarizing sheet 12, and the protective sheet 14 are disposed on the upper surface of the light guide plate 4. ) Are sequentially stacked.

The reflecting plate 6 reflects light, which is generated from the lamp 1 and proceeds to the lower surface of the light guide plate 4, not reflected by the fine dot pattern to the upper surface of the light guide plate 4 again. In addition, the optical loss of light incident on the LCD panel 15 is reduced, and at the same time, the uniformity of light transmitted to the upper surface of the light guide plate 4 is improved. As such, the light guide plate 4 and the reflection plate 6 guide the light generated from the lamp 1 toward the upper surface of the light guide plate 4.

At this time, the light passing through the upper surface of the light guide plate 4 includes not only light emitted perpendicularly to the upper surface, but also light emitted obliquely at various angles.

The diffusion sheet 8 located between the light guide plate 4 and the light collecting sheet 10 prevents partial concentration of light by dispersing light incident from the light guide plate 4. In order to perform such a role, an upper surface and a lower surface of the diffusion sheet 8, that is, a surface 8a adjacent to the LCD panel 15 of the diffusion sheet 8 and a surface adjacent to the light guide plate 4 are provided. A large number of beads are formed in 8b, respectively.

The light collecting sheet 10 has a triangular prism-shaped prism formed on an upper surface thereof, and serves to condense the light diffused from the diffusion sheet 8, and thus the light collecting sheet 10 The light passing through is substantially perpendicular to the plane of the LCD panel 15.

The reflective polarizing sheet 12 formed on the light collecting sheet 10 includes a plurality of reflective polarizing layers having a polarization axis in a predetermined direction.

The reflective polarizing sheet 12 adjusts the light incident from the light collecting sheet 10 to have high luminance through repeated polarization transmission and reflection processes.

The protective sheet 14 formed on the reflective polarizing sheet 12 not only serves to protect the surface of the reflective polarizing sheet 12, but also serves to diffuse light in order to uniformize the distribution of the light. Perform.

Therefore, a plurality of beads are formed on the upper and lower surfaces of the protective sheet 14, and diffuses light incident from the light collecting sheet 10 and the reflective polarizing sheet 14.

The LCD panel 15 is seated on the protective sheet 14 of the light guide unit 3.

That is, according to the backlight assembly structure of the conventional liquid crystal display device described above, one light collecting sheet is used to secure a wide viewing angle, and a reflective polarizing sheet is used to secure high luminance.

However, according to the above-described conventional liquid crystal display device, in using the above-mentioned reflective polarizing sheet, the lower surface of the reflective polarizing sheet, that is, the surface adjacent to the condensing sheet is closer to the mirror surface, so that the contact surface is in contact with the condensing sheet. Since it becomes wider, it is easy to generate static electricity, and at the same time, the prism constituting the light collecting sheet has a sharp shape at the top thereof, and when the reflective polarizing sheet is in contact with the light collecting sheet. There is a problem that the adhesion between the two sheets due to the static electricity is difficult to assemble.

In addition, there is a problem that the movement of each sheet occurs due to the difference in expansion ratio between the two sheets due to heat generated in the backlight assembly during the reliability test or operation after assembly.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of minimizing the defective rate of sheets used in the backlight assembly of the liquid crystal display device and at the same time reducing the thickness of the liquid crystal display device.

1 is a perspective view schematically showing the conventional liquid crystal display device described above.

FIG. 2 is a cross-sectional view of the device of FIG. 1 taken along line A ₁ -A _2. FIG.

3 is a perspective view schematically illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a cross-sectional view taken along the line B1-B2 of the apparatus of FIG.

5 is a cross-sectional view illustrating a reflective polarizing sheet according to the present invention.

<Explanation of symbols for main parts of the drawings>

20: lamp 22: lamp reflector

23: lamp unit 24: light guide plate

26: reflector 28: diffusion sheet

30: light collecting sheet 34: first adhesion preventing layer

36: reflective polarizing layer 38: second adhesion preventing layer

40: reflective polarizing sheet 42: light guide unit

50: LCD panel

In order to achieve the above object, the present invention is a light source for generating light, iii) a light guide plate formed on one side of the light source, and uniformly incident light generated from the light source toward the LCD panel, c) the A light converging means comprising a plurality of prisms provided on the LCD panel side of the light guide plate and condensing the luminous flux of light incident from the light guide plate in a direction perpendicular to the plane of the LCD panel; and d) the LCD panel of the light converging means. It is provided on the side, including a contact preventing means for minimizing the adhesion area between the sheets, the backlight having reflective polarization means for adjusting the light incident from the light collecting means to have a high brightness through the repeated polarization transmission and reflection process And an LCD panel formed on the backlight assembly. to provide.

According to the present invention, by forming a reflective polarizing member having an adhesion preventing member for minimizing the adhesion area between sheets, it is possible to minimize the failure rate of each sheet, and also to reduce the number of sheets used, The reduction of cost through shortening and the reduction of defective rate that can occur throughout the backlight assembly can improve product yield.

Hereinafter, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a view schematically illustrating a backlight assembly structure of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a cross-sectional view of the apparatus of FIG. 3 taken along lines A ₁ -A ₂ .

3 and 4, a liquid crystal display according to the present invention includes an LCD panel 50 and a backlight assembly having a lamp unit 23 and a light guide unit 42. do.

The lamp unit 23 includes a lamp 20 for generating light and a lamp reflector 22 surrounding the lamp 20.

A cold cathode tube is mainly used as the lamp 20, and the light generated by the lamp 20 is incident on the light guide plate 24 of the light guide unit 42. The lamp reflector 22 is formed to surround the lamp, and serves to reflect the light generated from the lamp 20 to the light guide plate 24.

The light guide unit 42 includes the light guide plate 24. The reflective plate 26 is formed under the light guide plate 24. A diffusion sheet 28 is provided on the light guide plate 24, that is, on the LCD panel side of the light guide plate 24. The light collecting sheet 30 and the reflective polarizing sheet 40 are sequentially stacked on the diffusion sheet 28 in the direction of the LCD panel 50.

The LCD panel 50 is seated on the light guide unit 35.

The light guide plate 24 is formed of a plastic-based transparent material such as acrylic to form a panel having an inclined lower surface and a horizontal upper surface. The light guide plate 24 may be formed to have a wedge shape, or may be formed to have a planar shape when the lamp unit 23 is formed on both sides of the light guide plate 24.

The lamp unit 23 is formed on one side of the light guide plate 24, and the light generated from the lamp 20 enters the light guide plate 24 and proceeds to the diffusion sheet 28 stacked on the light guide plate. Be sure to

A dot pattern (not shown) which reflects the light generated from the lamp on the lower surface of the light guide plate 24 and enters the light toward the diffusion sheet 28 stacked on the upper surface of the light guide plate 24. Various patterns such as may be printed and formed.

The reflecting plate 26 is provided below the light guide plate 24, and the reflecting plate 26 again transmits light that is not reflected toward the diffusion sheet 28 by the dot pattern of the light guide plate 24. It serves to reflect toward the diffusion sheet 28.

The light reflected by the dot pattern of the light guide plate 24 and the reflecting plate 26 and incident on the diffusion sheet 28 proceeds in a form of a predetermined angular range with respect to the horizontal plane of the diffusion sheet 28. .

The diffusion sheet 28 stacked on the light guide plate 24 uniforms the light distribution of the dot pattern of the light guide plate 24 and the light reflected from the reflection plate 26, and the light guide plate 24 of the diffusion sheet 28 is uniform. Beads are formed on the surface 28b adjacent to the surface 28a and the surface 28a adjacent to the light collecting sheet 30, respectively.

In this case, the diffusion sheet 28 may be selectively formed.

That is, since a plurality of beads are formed in the reflective polarizing sheet 40 to serve as the diffusion sheet 28, the diffusion sheet 28 may be omitted.

On the diffusion sheet 28, a light condensing sheet 30, which condenses the light beam of light diffused from the diffusion sheet 28 in a direction perpendicular to the plane of the LCD panel 50, is stacked. In the light collecting sheet 30, a plurality of triangular prisms 30a are arranged on the upper surface of the transparent sheet side by side in a predetermined direction.

Preferably, the top of the prisms 30a of the light collecting sheet 30, that is, the portion on which the LCD panel 50 of the prisms 30a is seated is formed to have a round shape.

As such, when the tops of the prisms 30a are formed in a round shape, scratches are generated by friction between the conventional tops of the sharp prisms and the reflective polarizing sheet stacked on the prisms. Can be prevented.

Experimentally, it can be seen that the prisms according to the present invention have a hardness of about HB while the tops of the conventional tops have sharp edges of 6B or less, while the hardness is about HB.

In addition, conventional prismatic sharp prism has a problem that the charge is concentrated on the top portion, when stacking another sheet on the prism, a lot of static electricity generated, but the top portion according to the present invention to use a round prism If so, the static electricity generated between the light collecting sheet and the sheet stacked on the light collecting sheet may be minimized.

On the light collecting sheet 30, a reflective polarization sheet 40 is formed to control the light collected from the light collecting sheet 30 to have a high directionality through repeated polarization transmission and reflection processes.

The reflective polarizing sheet 40 includes an adhesion preventing member and a reflective polarizing layer 36.

This will be described with reference to the drawings.

5 is a cross-sectional view illustrating a reflective polarizing sheet of a liquid crystal display according to the present invention.

Referring to FIG. 5, the reflective polarizing sheet 40 includes a reflective polarizing layer 36 formed of a plurality of polarizing layers having a polarization axis in a predetermined direction and an adhesion preventing member for minimizing the adhesion area between sheets.

The reflective polarization layer 36 passes the light collected by the light collecting sheet 30 and has incident light having the same direction as the polarization axis of the plurality of polarization layers, and reflects light having a different direction from the polarization axis.

That is, among the light incident on the first polarization layer adjacent to the light collecting sheet 3, a component of light coinciding with the polarization axis of the first polarization layer passes through the first polarization layer and is a second polarization on the first polarization layer. The incident light is incident on the layer, and the components of the reflected light having a different direction from the polarization axis of the first polarization layer are reflected below the first polarization layer.

The components of the reflected light are reflected and the phase is changed at the same time, is reflected back from the lower portion of the first polarization layer to be incident again to the first polarization layer, the polarization axis of the first polarization layer in the same manner as described above A component of light having the same directionality as is transmitted. As the recycling process is repeated, the luminance of light emitted from the reflective polarizing sheet may be improved.

The adhesion preventing member may include a first adhesion preventing layer 34 formed on a surface adjacent to the light collecting sheet of the reflective polarization layer 36 and a second formation formed on a surface adjacent to the light collecting sheet 30 of the reflective polarization layer 36. The adhesion preventing layer 38 is included.

The first and second adhesion preventing layers 34 and 38 are formed by dispersing acrylic beads 34a and 38a in a polycarbonate resin.

Preferably, the first and second adhesion preventing layers 34 and 38 are attached to the reflective polarizing layer 36 by using an adhesive, thereby manufacturing the integral reflective polarizing sheet 40.

The acrylic beads 34a and 38a are formed on the surface adjacent to the light collecting sheet 30 of the first adhesion layer 34 and the surface adjacent to the LCD panel 50 of the second adhesion layer 38, respectively. do.

In this case, a transparent material such as polyester may be used as the resin.

In the first and second adhesion layer 34, 38, the content of the acrylic beads (34a, 38a) is preferably about 10 to 50% by weight based on the total amount of the adhesion layer.

When the content of the acrylic beads is less than 10% by weight, the diffusion rate is lowered to generate a moire phenomenon, when the content of the acrylic beads exceeds 50% by weight there is a problem that the front brightness is lowered.

Therefore, the first adhesion preventing layer 34 minimizes the area in which the reflective polarizing sheet 40 and the light collecting sheet 30 are in close contact with each other. Thus, assembling is difficult due to the adhesion between the two sheets, or between the two sheets. It serves to prevent the occurrence of wicking of the sheet due to the difference in expansion rate.

In addition, the first adhesion preventing layer 34 also serves to diffuse the light collected from the light collecting sheet 30.

In addition, the second adhesion preventing layer 38 serves to minimize the adhesion area between the LCD panel 50 and the reflective polarization sheet 40, and protects the surface of the reflective polarization layer 36. By acting as a conventional protective sheet to partially diffuse the light incident from the reflective polarization layer 36 to ensure a wide viewing angle, the light transmitted through the reflective polarization layer with the pixels of the LCD panel Moiré phenomenon in which a wave pattern is generated on the screen by interference can be prevented.

Therefore, as described above, by forming the first and second adhesion preventing layers 34 and 38 integrally with the reflective polarizing layer 36 to diffuse light, the role of the reflective polarizing layer and the role of the protective sheet. Since it can be performed as one sheet, it is possible to minimize the number of sheets used in the backlight assembly, thereby minimizing the thickness and weight of the entire liquid crystal display device, thereby reducing the weight and thickness of the liquid crystal display device It can be achieved easily.

The LCD panel is mounted on the reflective polarizing sheet 40.

According to the present invention, each of the reflective polarizing layers used in the backlight assembly of the liquid crystal display device has a contact preventing layer which minimizes the adhesion area between the sheets and serves as a diffusion layer which partially diffuses the light incident from the bottom. Since it is possible to prevent the sheet drift due to the adhesion between the sheets, it is possible to minimize the defect of the backlight assembly due to the defect of the sheet, it is possible to greatly reduce the cost and manufacturing yield.

In addition, by integrally forming the reflective polarizing layer and the first and second adhesion preventing layers that diffuse light in order to secure a wide viewing angle, the role of the reflective polarizing layer, the protective sheet and the diffusion layer can be performed as one sheet. Since the number of sheets used in the backlight assembly can be minimized, the thickness and weight of the entire liquid crystal display device can be minimized, thereby making it possible to easily reduce the weight and thickness of the liquid crystal display device.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and modified within the scope of the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be understood that this can be changed.

Claims (9)

a) a light source for generating light, iii) a light guide plate formed on one side of the light source, for uniformly inciding light generated from the light source toward the LCD panel, c) provided on the LCD panel side of the light guide plate, and A light collecting means made up of a plurality of prisms for condensing the light flux of the light incident from the light guide plate in a direction perpendicular to the plane of the LCD panel, and d) provided on the LCD panel side of the light collecting means, minimizing the adhesion area between sheets. A backlight assembly including a reflection preventing means for adjusting the light incident from the light collecting means to have high luminance through repetitive polarization transmission and reflection processes; And And a LCD panel formed on the backlight assembly. The liquid crystal display device of claim 1, wherein the reflective polarization means comprises a reflective polarization layer configured to repeatedly adjust the light collected from the light converging means to have high luminance through a polarization transmission and reflection process. 3. The contact preventing layer of claim 2, wherein the adhesion preventing means is formed on a surface of the reflective polarizing layer adjacent to the light collecting means and minimizes an area of contact with the light collecting means and diffuses the light collected from the light collecting means. And a second adhesion preventing layer formed on a surface of the reflective polarization layer adjacent to the LCD panel to minimize the adhesion area with the LCD panel and to diffuse the polarized light from the reflective polarization layer. 4. The plurality of beads of claim 3, wherein the first adhesion preventing layer uniformly diffuses the light incident from the light collecting means and minimizes an area in which the light collecting means and the reflective polarizing layer are in close contact with each other. Liquid crystal display comprising a. 4. The plurality of beads of claim 3, wherein the second adhesion preventing layer uniformly diffuses light incident from the reflective polarization layer and minimizes an area between the reflective polarization layer and the LCD panel. 5. Liquid crystal display comprising a. 6. The liquid crystal display device according to claim 4 or 5, wherein the plurality of beads are formed on a surface adjacent to the light collecting means of the first adhesion layer and on a surface adjacent to the LCD panel of the second adhesion layer. The liquid crystal display device according to claim 4 or 5, wherein the content of the plurality of beads is 10 to 50% by weight based on the total amount of the first and second adhesion preventing layers. The liquid crystal display device according to claim 1, wherein the device further comprises diffusion means which is provided on the LCD panel side of the light guide plate and diffuses the light beam distribution of the incident light to be uniform. The liquid crystal display of claim 1, wherein the tops of the prisms have a round shape.