WO2008099989A1

WO2008099989A1 - Backlight unit

Info

Publication number: WO2008099989A1
Application number: PCT/KR2007/002612
Authority: WO
Inventors: Kyung-Sik Kim; Seung-Gon Park
Original assignee: INTERNATIONAL DISPLAY SOLUTIONS CO Ltd
Current assignee: INTERNATIONAL DISPLAY SOLUTIONS CO Ltd
Priority date: 2007-02-15
Filing date: 2007-05-30
Publication date: 2008-08-21
Anticipated expiration: 2009-08-15

Abstract

The present invention relates to a backlight unit, and more particularly, to a backlight unit wherein a light incident portion of a light guide plate for guiding the light emitted from an LED of a point light source to a front surface of the backlight unit is machined by laser to secure the visibility (prevention of bright lines, dark lines and light leakage). According to the present invention, there is provided a backlight unit, comprising: a light source; a light guide plate for receiving light emitted from the light source at a side surface of the light guide plate and emitting the light to a front surface of the backlight unit; an optical sheet for diffusing the light exiting from the light guide plate; and a frame for accommodating the light source, the light guide plate and the optical sheet therein, wherein the light source includes LEDs, each of the LEDs is a point light source, and a light incident portion of the light guide plate for receiving the light emitted from the LEDs is machined by laser to be formed in a serration pattern.

Description

BACKLIGHT UNIT

Technical Field

[1] The present invention relates to a backlight unit, and more particularly, to a backlight unit wherein a light incident portion of a light guide plate for guiding the light emitted from an LED of a point light source to a front surface of the backlight unit is machined by laser to secure the visibility (prevention of bright lines, dark lines and light leakage). Background Art

[2] Recently, small and lightweight liquid crystal displays (LCDs) with more powerful performance have been produced by virtue of the technology development of semiconductor industries that have been rapidly developed.

[3] Although cathode ray tubes (CRTs) having been widely used for information display devices so far have many advantages in view of performance or price, the CRTs have many disadvantages in view of miniaturization or portability.

[4] On the contrary, since LCDs have advantages of miniaturization, lightweight, low power consumption and the like, the LCDs have gradually come into the spotlight as an alternative means capable of overcoming the disadvantages of the CRTs. Currently, the LCDs have been built in almost all information processing devices that require display devices.

[5] In general, such an LCD is a display device, in which a specific arrangement of liquid crystal molecules is converted into another arrangement thereof by applying a voltage to the specific arrangement to convert a change in optical characteristics of double refraction, optical rotation, dichroism, light diffusion and the like into a change in visual angle. That is, the LCD is a display device using light changed by a liquid crystal cell.

[6] Recently, various structures for slim and lightweight LCDs have been developed to secure the competitiveness of products. In one of these structures, an LCD panel having array and color filter substrates bonded is stacked on and coupled to a backlight assembly as an optical unit, the LCD panel and the backlight assembly are inserted into a mold frame in order to protect them, and a support frame is then coupled to the mold frame in order to secure the mold frame into which the backlight assemblies are inserted.

[7] Specifically, a conventional backlight unit having a backlight assembly, a mold frame and a support frame will be described below with reference to Fig. 1.

[8] As shown in Fig. 1, a mold frame 2, into which a light guide plate 3 and optical sheets 4 are sequentially inserted, is supported in a state where the mold frame 2 is fitted and inserted into a support frame 1. A plurality of projections 2a are formed on side surfaces of the mold frame 2, while a plurality of grooves Ia are formed in side surfaces of the support frame 1 so that the projections 2a are respectively inserted into the grooves Ia. Meanwhile, the light guide plate 3 receives the light emitted from a light source (not shown) provided on an inner side surface of the mold frame 2.

[9] The backlight unit so configured allows the light emitted from the light source (not shown) to exit to a front surface of the backlight unit through the light guide plate 3. A light receiving element such as an LCD panel will be positioned in front of the backlight unit.

[10] A CCFL, EEFL or the like was used as the light source (not shown) for supplying light to the light guide plate 3. However, an LED has been recently used as the light source. In a case where the LED of a point light source is used as a light source for providing light to a light guide plate, dark lines, light leakage phenomena and the like may be more increased and luminance is easy to lower as compared with a case where the CCFL, EEFL or the like is used. Therefore, in a case where the LED of a point light source is used as a light source for providing light to a light guide plate, there is a problem in that the visibility (prevention of bright lines, dark lines and light leakage) should be secured. Disclosure of Invention Technical Problem

[11] Accordingly, the present invention is conceived to solve the aforementioned problems. An object of the present invention is to provide a backlight unit wherein a light incident portion of a light guide plate for guiding the light emitted from an LED of a point light source to a front surface of the backlight unit is machined by laser to secure the visibility (prevention of bright lines, dark lines and light leakage). Technical Solution

[12] According to an aspect of the present invention for achieving the objects, there is provided a backlight unit, comprising: a light source; a light guide plate for receiving light emitted from the light source at a side surface of the light guide plate and emitting the light to a front surface of the backlight unit; an optical sheet for diffusing the light exiting from the light guide plate; and a frame for accommodating the light source, the light guide plate and the optical sheet therein, wherein the light source includes LEDs, each of the LEDs is a point light source, and a light incident portion of the light guide plate for receiving the light emitted from the LEDs is machined by laser to be formed in a serration pattern.

[13] The serration pattern machined in the light incident portion of the light guide plate may be divided into groove portions machined and not machined by laser, which are alternately formed. [14] An interval between the groove and flat portions is preferably determined depending on a distance between the LEDs and the light incident portion of the light guide plate and a distance between the LEDs. [15] The serration pattern may include any one of a V shape, a regularly concavo-convex shape, an irregularly concavo-convex shape, a prism shape, an embossed shape and a concentric circular shape.

Advantageous Effects

[16] According to a backlight unit of the present invention, since a light incident portion of a light guide plate for guiding the light emitted from an LED of a point light source to a front surface of the backlight unit is machined by laser, there are advantages in that the visibility (prevention of bright lines, dark lines and light leakage) can be secured and thus the quality of the backlight unit can be enhanced. Brief Description of the Drawings

[17] Fig. 1 is an exploded perspective view of a conventional backlight unit;

[18] Fig. 2 is a view showing a layout of a light guide plate and LEDs included in a backlight unit according to the present invention; and

[19] Fig. 3 is an exemplary view showing shapes of a light incident portion of the light guide plate included in the backlight unit according to the present invention. Best Mode for Carrying Out the Invention

[20] Hereinafter, a backlight unit according to preferred embodiment of the present invention will be described with reference to the accompanying drawings.

[21] A general configuration of a backlight unit according to an embodiment of the present invention is similar to the conventional backlight unit shown in Fig. 1. That is, in the backlight unit according to the present invention, a light guide plate 3 and optical sheets 4 are sequentially inserted into a mold frame 2, and the mold frame 2 is supported in a state where the mold frame 2 is fitted and inserted into a support frame 1, as shown in Fig. 1.

[22] A plurality of projections 2a are formed on side surfaces of the mold frame 2, while a plurality of grooves Ia are formed on side surfaces of the support frame 1 so that the projections 2a are respectively inserted into the grooves Ia. Meanwhile, the light guide plate 3 receives the light emitted from a light source (not shown) provided on an inner side surface of the mold frame 2.

[23] The backlight unit of the present invention so configured allows the light emitted from the light source (not shown) to be emitted to a front surface of the backlight unit through the light guide plate 3. A light receiving element such as an LCD panel will be positioned in front of the backlight unit.

[24] In brief, the backlight unit of the present invention includes the light source; the light guide plate for receiving the light emitted from the light source at a side surface of the light guide plate and radiating the light to the front surface of the backlight unit; the optical sheets for diffusing the light emitted from the light guide plate; and the frame for accommodating the light source, the light guide plate and the optical sheets therein.

[25] At this time, in the present invention, the light source comprises LEDs 10, each of which is a point light source, and a light incident portion 3a of the light guide plate 3 for receiving the light emitted from the LEDs 10 is machined by laser to be formed with a serration pattern, as shown in Fig. 2. That is the most important feature of the present invention.

[26] Fig. 2 is a plan view showing the LEDs 10 as a light source and the light guide plate

3 included in an edge type backlight unit employed to the present invention. The LEDs 10 are arranged at a side of the light guide plate 3, so that the light emitted through the light incident portion 3a of the light guide plate 3 is transmitted inside the light guide plate 3.

[27] In the present invention, the LEDs 10 are used as a light source. Further, since visibility should be secured as the LEDs 10 are used, the light incident portion 3a of the light guide plate 3 is machined by laser to be formed with a serration pattern.

[28] As shown in Fig. 2, the serration pattern formed in the light incident portion 3a of the light guide plate 3 is divided into portions which are machined and not machined by laser. That is, the serration pattern is divided into groove portions 3b which are machined by laser and flat portions 3c which are not machined by laser. The groove and flat portions 3b and 3c are alternately formed.

[29] The reason why the groove and flat portions 3b and 3c are alternately formed as described above is as follows.

[30] In a state where the light incident portion 3a of the light guide plate 3 has a mirror surface (a case of no serration pattern), the light emitted from the LEDs 10 is generally moves so that an angle 02 of the moving direction of the light is ranged from 0 to 42 degrees in accordance with Snell's law. Thus, if an interval between the LEDs 10 is 10mm or more, a dark portion cannot be prevented from occurring no matter how a density of the LEDs 10 may be large. This is because an amount of the light moving toward the dark portion between the LEDs 10 is too smaller than that of the light moving straight inside the light guide plate 3.

[31] On the other hand, when the serration is continuously machined in the light incident portions 3a to have a serration angle 01 of 90 degrees (i.e., when only the groove portions 3b are formed without the flat portion), the light is spread so that the angle 02 of the moving direction of the light is generally ranged from 15 to 75 degrees. There occurs a problem in that the front of each LED 10 appears in the form of a dark portion due to the weak light moving straight (in a direction of an angle of 0 to 15 degrees) and hotspots appears between the LEDs 10 due to the strong light moving in a direction of 15 to 40 degrees or so.

[32] Therefore, a structure for solving all the problems described above is suggested in the present invention. That is, the groove portions 3b whih are machined by laser and the flat portions 3c which are not machined by laser are included together in the serration pattern formed in the light incident portion 3a of the light guide plate 3.

[33] An interval between the groove and flat portions 3b and 3c included in the serration pattern formed in the light incident portion 3a of the light guide plate 3 is changed depending on various conditions, so that the groove and flat portions 3b and 3c are machined and shaped. That is, the interval between the groove and flat portions 3b and 3c is determined depending on the distance between the LEDs 10 used as the light source and the light incident portion 3a of the light guide plate 3, the distance between the LEDs 10 and the like. The reason why the interval between the groove and flat portions 3b and 3c is adjusted in such a manner is to satisfy the condition for enhancing the visibility and luminance of the backlight unit.

[34] Meanwhile, the serration pattern formed in the light incident portion 3a of the light guide plate 3 may be machined to have various shapes. That is, serration patterns with various shapes may be formed in the light incident portion 3a of the light guide plate 3 as shown in Fig. 3.

[35] Fig. 3 (a) shows a V-shaped serration pattern which causes the light moving inside a light guide plate to be diffused by the roughness of a machined surface (a light incident portion) due to the reflection/diffusion in V-shaped grooves. Fig. 3 (b) shows a regularly concavo-convex serration pattern which causes the light moving inside a light guide plate to be diffused by the roughness of a machined surface (a light incident portion) due to the refraction/reflection in minute concavo-convex portions. Fig. 3 (c) shows an irregularly concavo-convex serration pattern which causes the light moving inside a light guide plate is diffused due to the refraction/reflection in concavo-convex portions with various shapes. Fig. 3 (d) shows a prism-shaped serration pattern which causes the light moving inside a light guide plate to be diffused by the roughness of a processed surface (a light incident portion) due to the reflection in micro-prisms. Fig. 3 (e) shows an embossed serration pattern which causes the light moving inside a light guide plate to be diffused due to the reflection in hemispherical projections. Fig. 3 (f) shows a concentrically circular serration pattern which causes the light moving inside a light guide plate to be diffused due to the reflection in curved grooves. Fig. 3 (g) shows a side view of the light incident portion 3a of the light guide plate 3 having the serration patterns. [36] Although the present invention has been described in connection with the preferred embodiments, it will be understood by those skilled in the art that various modification and changes can be made thereto without departing from the spirit and scope of the present invention defined by the appended claims.

Claims

[ 1 ] A backlight unit, comprising : a light source; a light guide plate for receiving light emitted from the light source at a side surface of the light guide plate and emitting the light to a front surface of the backlight unit; an optical sheet for diffusing the light exiting from the light guide plate; and a frame for accommodating the light source, the light guide plate and the optical sheet therein, wherein the light source includes LEDs, each of the LEDs is a point light source, and a light incident portion of the light guide plate for receiving the light emitted from the LEDs is machined by laser to be formed in a serration pattern.

[2] The backlight unit as claimed in claim 1, wherein the serration pattern machined in the light incident portion of the light guide plate is divided into portions machined and not machined by laser, which are alternately formed.

[3] The backlight unit as claimed in claim 2, wherein an interval between the groove and flat portions is determined depending on a distance between the LEDs and the light incident portion of the light guide plate and a distance between the LEDs.

[4] The backlight unit as claimed in claim 2, wherein the serration pattern includes any one of a V shape, a regularly concavo-convex shape, an irregularly concavo- convex shape, a prism shape, an embossed shape and a concentric circular shape.