KR20030055378A - The backlight unit of liquid crystal display - Google Patents

Abstract

PURPOSE: A backlight unit is provided to reduce the number of conventional prism sheets and prevent moire. CONSTITUTION: A light source generates light. A light guide plate changes the light from the light source to a backlight unit. A prism sheet(41) is located on the light guide plate. The curvatures of prisms are large in the center and small in both sides. More than one prisms in a projecting face of the prism sheet are formed in a concentric circle.

Description

Backlight unit of liquid crystal display {TH BACKLIGHT UNIT OF LIQUID CRYSTAL DISPLAY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit of a liquid crystal display device, and more particularly to a backlight unit of a liquid crystal display device which can reduce the number of optical components and the number of processes.

Typically, a liquid crystal display (hereinafter referred to as "LCD") is a plurality of liquid crystal cells arranged in a matrix form and a plurality of control switches for switching the video signal to be supplied to each of these liquid crystal cells The amount of light transmitted from the backlight unit is adjusted by the configured liquid crystal panel to display a desired image on the screen.

Referring to FIG. 1, a conventional backlight unit includes a lamp 1 for generating light, a lamp housing 3 installed to surround the lamp 1, and light incident from the lamp 1 as a planar light source. The light guide plate 5 to be converted, the reflector 7 positioned below the light guide plate 5 to reflect the light traveling toward the lower surface and the side surface of the light guide plate 5 toward the upper surface, and light passing through the light guide plate 5 are diffused. A diffusion sheet 9 and first and second prism sheets 11 and 13 for adjusting a traveling direction of light via the diffusion sheet 9.

The liquid crystal panel is positioned on the backlight unit. The liquid crystal panel includes an upper substrate 21 having a color filter, a common electrode and an upper alignment layer, a lower substrate 17 formed of a thin film transistor array (TFT), a pixel electrode, and a lower alignment layer; It consists of a liquid crystal 19 injected into the internal space between the upper substrate 21 and the lower substrate 17.

The cold cathode fluorescent lamp is mainly used as the lamp 1 of the backlight unit, and the light generated by the lamp 1 is incident on the light guide plate 5 through an incident surface existing on the side of the light guide plate 5. The lamp housing 3 has a reflecting surface on its inner surface to reflect light from the lamp 1 toward the incident surface of the light guide plate 5. The light guide plate 5 has an inclined back surface and an exit surface that is horizontal, and is made such that the incidence surface and the exit surface of the light guide plate 5 form a right angle. The rear side of the light guide plate 5 is provided so that the reflecting plate 7 faces. The light guide plate 5 allows the light incident from the lamp 1 to reach a distance far from the lamp 1. The light guide plate 5 is generally formed of an acrylic resin (PMMA) having high strength and not easily being deformed or broken and having good transmittance. The reflector 7 serves to reduce light loss by reflecting light incident to itself through the back of the light guide plate 5 toward the light guide plate 5. When the light from the lamp 1 is incident on the light guide plate 5, it is reflected at a predetermined inclination angle from the rear surface which is the inclined surface and uniformly proceeds toward the exit surface. At this time, the light propagated to the lower surface and the side surface of the light guide plate 5 is reflected by the reflector 7 and proceeds toward the exit surface. Light emitted through the exit surface of the light guide plate 5 is diffused to the entire area by the diffusion sheet 9. On the other hand, when the light incident on the liquid crystal panel is vertical, the light efficiency is increased. To this end, it is preferable to stack two prism sheets so that the traveling angle of the light emitted from the light guide plate 5 is perpendicular to the liquid crystal panel.

The first and second prism sheets 11 and 13 are formed in the form of a plurality of prism bars having hills and valleys. As shown in FIG. 2, the two prism sheets 11 and 13 are arranged such that the two prism array directions are perpendicular to each other. In the first and second prism sheets 11 and 13, the x and y directions of light are directed in the z direction, that is, the direction perpendicular to the liquid crystal panel so that light incident from the light guide plate 5 is incident on the upper liquid crystal panel. It changes the path of light. In other words, when the peaks and valleys of the prism are directed in the x direction, the light passing through the first prism sheet 11 enters only the y component of the light perpendicular to the z direction, that is, the liquid crystal panel. . At this time, the optical path of the x component does not change. Similarly, as shown in FIG. 3, when the prism peaks and valleys of the second prism sheet 13 face the y direction, the light passing through the second prism sheet 13 passes through the peaks and valleys of the prism. While being converted in the z direction, it is incident perpendicularly to the liquid crystal panel. At this time, the path of the y component of the incident light does not change.

Since the light passing through the prism sheet is a vector amount, the x, y and z components of the light are independent of each other. Accordingly, as shown in FIG. 4, in the prism of the acid and valley in the x direction to deflect the light of the y component, the light of the x component is not affected, and only the light of the y component is refracted by the refractive index, so that the light is reflected in the z direction. Furnace will change.

The light generated from the backlight unit is incident on the liquid crystal panel.

In the liquid crystal panel, the liquid crystal 19 is driven by the voltage difference between the common electrode of the upper substrate 21 and the pixel electrode of the lower substrate 17 to selectively transmit light from the backlight unit to display an image.

The backlight unit is shown in FIG. 5 when looking at the traveling angle of light from the light source to the liquid crystal panel.

Referring to FIG. 5, the light generated from the light source is emitted about 60 to 80 degrees while passing through the light guide plate 5, and the emission angle of the light is reduced to 40 to 50 degrees while passing through the diffuser plate 9. Subsequently, it can be seen that the emission angle of the light becomes perpendicular while passing through the first and second prism sheets 11 and 13.

In addition, it can be seen that the light passing through the light guide plate 5 is mostly diffused in the x direction. This means that the size of the x component among the components of the light is larger than the size of the y component. Therefore, the degree of deflection of the first prism sheet 11 which deflects the y component of light in the z direction is small, and the degree of deflection of the second prism sheet 13 which deflects the x component of light in the z direction is large. As a result, it can be seen that the first prism sheet 11 has a lower light efficiency than the second prism sheet 13 due to the degree of light deflection of the two prism sheets 11 and 13.

As described above, when the prism sheet is used, a large amount of light is absorbed and reflected by the prism sheet. In addition, according to the trend of large screen, light weight, and high quality of LCD, it is necessary to reduce the number of optical components used in the backlight unit. However, two prism sheets must be used in order to inject light perpendicularly to the liquid crystal panel in the backlight unit. In other words, there is an urgent need for improvements to reduce the weight and thickness of the backlight unit.

Accordingly, an object of the present invention is to provide a backlight unit of a liquid crystal display device which can improve light efficiency and reduce the number of optical components.

1 is a cross-sectional view showing a backlight unit of a conventional liquid crystal display device.

FIG. 2 is a view showing a prism sheet shown in FIG. 1. FIG.

3 is a view showing an optical path via a prism sheet shown in FIG.

4 shows independence of x and y components of light;

5 is a view showing a change in the emission angle of light via the components of the backlight unit shown in FIG.

6 is a cross-sectional view illustrating a backlight unit of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 7 is a view showing a prism sheet shown in FIG. 6. FIG.

FIG. 8 is a view showing another example of the prism sheet shown in FIG. 7. FIG.

9 shows the principle of the circle shown in FIG. 8;

10 illustrates a prism sheet having a plurality of concentric circles.

11 shows a prism sheet having concentric circles of a semicircle.

<Description of Symbols for Main Parts of Drawings>

1, 31: lamp 3, 33: lamp housing

5, 35: LGP 7, 37: Reflector

9, 39: diffusion sheet 11, 13, 41: prism sheet

17, 43: lower substrate 19, 45: liquid crystal

21, 47: upper substrate

In order to achieve the above object, the backlight unit of the liquid crystal display according to the present invention includes a light source for generating light, a light guide plate for converting light from the light source to a surface light source, and a prism having an acid and a valley located on the light guide plate. And a prism sheet formed such that the curvature is larger at the center of the exit surface and smaller at both sides.

Other objects and features of the present invention other than the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

6 to 11 will be described with respect to preferred embodiments of the present invention.

6 and 7, the backlight unit according to the embodiment of the present invention has a prism shape in which the exit surface has curved peaks and valleys, and a prism sheet 41 having a greater curvature of the prism at the center than the periphery. Characterized in that.

The backlight unit includes a lamp 31 for generating light, a lamp housing 33 installed to surround the lamp 31, a light guide plate 35 for converting light incident from the lamp 31 into a planar light source, A reflector plate 37 positioned below the light guide plate 35 to reflect light traveling toward the lower surface and the side surface of the light guide plate 35 toward the upper surface, a diffusion sheet 39 for diffusing light passing through the light guide plate 35; It consists of a prism sheet 41 positioned on the diffusion sheet 39.

The liquid crystal panel is positioned on the backlight unit. The liquid crystal panel includes an upper substrate 47 having a color filter, a common electrode, and an upper alignment layer, a lower substrate 43 formed of a TFT array, a pixel electrode, and a lower alignment layer, and between the upper substrate 47 and the lower substrate 43. It consists of a liquid crystal 45 injected into the inner space of the.

A cold cathode fluorescent lamp is mainly used as the lamp 31 of the backlight unit, and the light generated by the lamp 31 is incident on the light guide plate 35 through an incident surface existing on the side of the light guide plate 35. The lamp housing 33 has a reflecting surface on its inner surface to reflect light from the lamp 31 toward the incident surface of the light guide plate 35. The light guide plate 35 has an inclined rear surface and a plane exit surface. The light guide plate 35 allows the light incident from the lamp 31 to reach a distance far from the lamp 31. The light guide plate 35 is generally formed of an acrylic resin (PMMA) having high strength and not easily being deformed or broken and having good transmittance.

The rear side of the light guide plate 35 is provided so that the reflecting plate 37 faces. The reflecting plate 37 serves to reduce light loss by reflecting light incident to itself through the rear surface of the light guide plate 35 toward the light guide plate 35. When the light from the lamp 31 is incident on the light guide plate 35, the light is reflected at a predetermined inclination angle from the rear surface which is an inclined surface and uniformly travels toward the exit surface. At this time, the light propagated to the lower surface and the side surface of the light guide plate 35 is reflected by the reflecting plate 37 to travel toward the exit surface. Light emitted through the exit surface of the light guide plate 35 is uniformly diffused to the entire area by the diffusion sheet 39.

The prism sheet 41 collects the light diffused from the diffusion sheet 39 and allows the prism sheet 41 to enter the liquid crystal panel vertically. A plurality of prisms having a curvature are formed on the exit surface of the prism sheet 41. A prism having a large curvature is formed at the center of the prism sheet 41, while a prism having a small curvature is formed at the periphery, that is, at the end of the prism sheet 41. As shown in FIG. 7, when the prism directions of the peaks and valleys of the prism sheet 41 face the y direction, the radius of curvature of the prism is large in the center portion of the prism sheet 41, so that the light of the x component is deflected in the z direction. . By the way, since the curvature of the both ends of the prism sheet 41 is smaller than the curvature of a center prism, the light intensity of a y component is deflected to z direction. That is, the prism sheet 41 of the present invention deflects the x component of the light in the z direction at the center portion and the y component of the light in the z direction at both peripheral portions.

As shown in FIG. 8, the prism sheet 41 having such curvature may have a prism formed in a circular shape around a single concentric circle. As shown in Fig. 9, in the circular shape, the size of the x and y components of the light is the same, and the light of the x and y parts is simultaneously changed. Based on this fact, the prism sheet 41 having the concentric prism according to the present invention deflects all incident light in any direction in the z direction. In other words, since the prism is formed in a circular shape, the prism sheet 41 may enter both the x component and the y component of the light incident on the prism sheet 41 in the z direction, that is, in the vertical direction of the liquid crystal panel. Accordingly, the number of optical components required for the backlight unit can be reduced by using only one prism sheet without the need of using two prism sheets conventionally. In addition, the amount of light lost can be reduced by reducing the use of two prism sheets. The prism sheet 41 described above may have a plurality of concentric circles of the prism, as shown in FIGS. 10 and 11, and may have a semi-circular shape.

As described above, the backlight unit of the liquid crystal display according to the present invention includes a prism sheet which is formed such that the curvature of the prism having peaks and valleys is larger at the center of the exit surface and smaller at both sides. The prism sheet may be formed in the form of a prism having peaks and valleys along concentric circles. The backlight unit of the liquid crystal display according to the present invention can reduce the amount of light absorbed or reflected by the prism sheet by reducing the number of conventional prism sheets. Accordingly, the light efficiency can be improved. In addition, the backlight unit of the liquid crystal display device according to the present invention can reduce the number of optical components because the number of prism sheets can be reduced as compared with the conventional. Furthermore. By reducing the number of optical components, not only the cost of optical components can be reduced but also the moiré phenomenon can be prevented.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (3)

A light source for generating light, A light guide plate for converting light from the light source into a surface light source; And a prism sheet positioned above the light guide plate and formed such that the curvature of the prism having peaks and valleys is larger at the center of the exit surface and smaller at both sides. The method of claim 1, The prism formed on the exit surface of the prism sheet is formed in the form of at least one concentric circle backlight unit of the liquid crystal display device. The method of claim 2, And the prism is formed in the shape of a semicircle concentric circle.