WO2008093930A1

WO2008093930A1 - Light guide panel for lcd back light unit and lcd back light unit thereby

Info

Publication number: WO2008093930A1
Application number: PCT/KR2007/006551
Authority: WO
Inventors: Seong Hoon Lee; Man Suk Kim; O Yong Jeong; Chul Goo Chi
Original assignee: Cheil Industries Inc.
Priority date: 2007-01-29
Filing date: 2007-12-14
Publication date: 2008-08-07
Also published as: TWI402542B; KR100781328B1; TW200839329A

Abstract

Disclosed are a light guide plate for an LCD backlight unit where prisms are formed only on the rear side to improve brightness and uniformity of light, and an LCD backlight unit using the same. The light guide plate includes a lateral side for receiving incident light, a front side connected to the lateral side for emitting light to an outside, and a rear side for reflecting light. The rear side is formed with a stripe pattern and at least one cross-prism on a portion where the stripe pattern is not formed. The stripe pattern has a width that increases with an increase in distance from the lateral side, and has a main prism formed therein.

Description

[DESCRIPTION] [Invention Title]

LIGHT GUIDE PANEL FOR LCD BACK LIGHT UNIT AND LCD BACK LIGHT UNIT THEREBY

[Technical Field]

The present invention relates to a light guide plate for an LCD backlight unit and an LCD backlight unit using the same.

[Background Art]

Since a liquid crystal display is not an emissive device, it must have a backlight unit as a light source for emitting light. Then, images and the like are displayed on a liquid crystal panel having liquid crystals arranged in a predetermined pattern by adjusting a transmittance amount of light emitted from the backlight unit

The backlight unit of the liquid crystal display generally includes a diffusion sheet and/or a prism sheet to improve uniformity and brightness of light through uniform distribution of light. Therefore, there is a need of a backlight unit which can provide plane light with high brightness and uniformity on the front panel of the liquid crystal display while ensuring excellent visibility without using the diffusion sheet or the prism sheet.

[Disclosure] [Technical Problem]

The present invention has been made in view of the above problems, and an aspect of the present invention is to provide a light guide plate for LCD backlight units that can ensure high brightness, excellent uniformity and visibility of light on the overall surface of an LCD panel. [Technical Solution]

In accordance with an aspect of the present invention, a light guide plate includes a lateral side for receiving incident light, a front side connected to the lateral side for emitting light to an outside, and a rear side for reflecting light, wherein the rear side is formed with a stripe pattern and at least one cross-prism on a portion where the stripe pattern is not formed, the stripe pattern having a width increasing with an increase in distance from the lateral side, and including a main prism formed therein.

[Advantageous Effects]

According to the present invention, the light guide plate for an LCD uniformly increases not only the amount of light reaching an LCD panel, but also the amount of light progressing perpendicular thereto, thereby ensuring excellent brightness, uniformity, and visibility, as compared to conventional LCDs employing the conventional light guide plate. Further, it can be found that the light guide plate of the invention provides a remarkably improved brightness, as compared to a conventional light guide plate having the cross-prism formed on the front side.

Accordingly, in manufacturing the backlight unit, the light guide plate of the invention allows elimination of one or both of the diffusion sheet and the prism sheet, which are used for the conventional backlight unit, thereby reducing manufacturing costs of the backlight unit.

[Description of Drawings]

Figs. 1 and 2 are perspective views of a rear side of a light guide plate for an LCD backlight unit according to one embodiment of the present invention;

Figs. 3 and 4 are cross-sectional views of the light guide plate for the LCD backlight unit according to one embodiment of the present invention;

Fig. 5 is enlarged cross-sectional views of vertex angles of cross-prisms of the light guide plate for the LCD backlight unit according to one embodiment of the present invention;

Fig. 6 is an enlarged cross-sectional view illustrating a configuration of main prisms of the light guide plate for the LCD backlight unit according to one embodiment of the present invention;

Fig. 7 is a perspective view of a light guide plate having a front prism according to another embodiment of the present invention; and

Figs. 8 to 10 are perspective views illustrating a variety of examples of a cross-sectional shape of the front prism.

[Best Mode]

Figs. 1 and 2 are perspective views of a rear side of a light guide plate for an LCD backlight unit according to one embodiment of the present invention.

As shown in Fig. 1 , the light guide plate may have one or more cross-prisms

340 formed only on a portion of the rear side where a stripe pattern 320 is not formed. Alternatively, as shown in Fig. 2, the light guide plate may have the cross-prisms 340 formed on the overall the rear side excluding the area where the stripe pattern 320 is formed.

According to one embodiment of the invention, the light guide plate for the LCD backlight unit is generally made of a transparent acryl material, which is not likely to be broken or deformed, and which has a high strength, light weight and high transmittance of visible light. The light guide plate includes a main body 300, the stripe pattern 320, in which a plurality of main prisms 322 are arranged, and the cross-prisms 340 disposed on the rest of the rear side where the stripe pattern 320 is not formed. Preferably, the cross-prisms 340 and the main prisms 322 define an angle of

60-120 degrees therebetween in the longitudinal direction.

The main body 300 includes a lateral side 301 for receiving incident light, a front side 303 that is connected to the lateral side 201 and faces an LCD panel (not shown), and the rear side 305 that is connected to the lateral side 301 and faces the front side 303.

The term "lateral side 301" means lexically a side surface of an object, but is defined herein as a surface through which light emitted from a light source 306 enters the light guide plate. In Fig. 3, the lateral side 301 is the surface adjacent to the light source 306.

Although the front side 303 is a planar surface in this embodiment, it may have a front prism formed over the surface thereof as shown in Figs. 7 to 10.

Stripes are formed at constant intervals on the rear side 305 in the transverse and longitudinal directions, and will be defined as the stripe pattern 320.

Here, the stripe pattern 320 may indicate a single stripe or an aggregate of stripes formed on the rear side 305.

Further, the width of the stripe pattern 320 indicates a width (w) in a direction perpendicular to an incidence direction of light. As shown in the figures, the width (w) of the stripe pattern 320 increases with an increase in distance from the lateral side 301 through which light enters. This is based on the fact that the farther the distance from the lateral side 301, the less the amount of light arrives. Accordingly, the stripe pattern 320 serving to refract and reflect light increases in size to improve refractivity and reflectivity of light, irrespective of the less amount of arriving light.

The stripe pattern 320 is constituted by a plurality of main prisms 322 arranged perpendicular to the direction of light entering the light guide plate from the light source.

The stripe pattern 320 is formed on the rear side 305, and the cross-prisms 340 are formed on the portion of the rear side where the stripe pattern 320 is not formed.

The cross-prisms 340 are disposed perpendicular to the main prisms 322. In other words, the cross-prisms 340 are formed to have a longitudinal direction, which is parallel to the direction of light entering the light guide plate from the light source. Figs. 3 and 4 are cross-sectional views of the light guide plate for the LCD backlight unit according to one embodiment of the present invention.

As shown in Figs. 3 and 4, the main prisms 322 and the cross-prisms 340 are perpendicular to one another, and have different heights.

The main prisms 322 may be formed higher than the cross-prisms 340 as shown in Fig. 3. Alternatively, the cross-prisms 340 may be formed higher than the main prisms 322 as shown in Fig. 4.

Fig. 5 is enlarged cross-sectional views of vertex angles of cross-prisms of the light guide plate for the LCD backlight unit according to one embodiment of the present invention. The vertical angels are given as 80°, 90°, 100°, 110°, 120°, 130°, and 140° from the left, and each prism has a pitch of 25 /an.

Fig. 6 is an enlarged cross-sectional view illustrating a configuration of main prisms of the light guide plate for the LCD backlight unit according to one embodiment of the present invention. The left prism has a radius of curvature of zero, the middle one has a positive radius of curvature, and the right one has a negative radius of curvature.

[Mode for Invention]

Next, the present invention will be described with reference to examples to show that, when the light guide plate according to one embodiment of the invention is employed for an LCD backlight unit, it exhibits improved brightness, uniformity, and visibility of light.

It should be noted that description of matter apparent to those skilled in the art will be omitted herein.

Examples to demonstrate advantageous effects of the present invention will be described in the following.

1. Examples and Comparative Examples <Example 1-1> A stripe pattern with a pattern pitch of 430 μm was formed on the rear side of a wedge type light guide plate of 288.8 x 217.7 x 2.4 (start) x 0.8 mm (end) in width (W) x length (L) x thickness (T), and main prisms having a height of 14.25μm, a pitch of 25/ffii and an interior angle of 82.5 degrees were formed in the stripe pattern.

Further, cross-prisms having a pitch of 25, urn, a height of 10.49^m, and an interior angle of 100 degrees were formed on an area of the rear side where the stripe pattern was not formed, and were disposed perpendicular to the main prisms. The front side of the light guide plate was in a specular state.

The same conditions as in the example 1-1 were given except that the vertex angle of the cross-prisms was modified by 10 degrees to be from 110 to 170 degrees. Modified factors of Examples 1-2 to 1-8 are shown in Table 1.

Table 1

EX: Example

A stripe pattern with a pattern pitch of 430 μm was formed on the rear side of a wedge type light guide plate of 288.8 x 217.7 x 2.4 (start) x 0.8 mm (end) in width (W) x length (L) x thickness (T), and main prisms having a height of 14.25/mi, a pitch of 25/Λn and an interior angle of 82.5 degrees were formed in the stripe pattern.

<Example 2-l> A stripe pattern with a pattern pitch of 430 im was formed on the rear side of a wedge type light guide plate of 288.8 x 217.7 x 2.4 (start) x 0.8 mm (end) in width (W) x length (L) x thickness (T), and main prisms having a height of 14.25/zm, a pitch of 25,«m and an interior angle of 82.5 degrees were formed in the stripe pattern.

Here, the prism had a radius of curvature of (+) 0.1R at each side (here, the radius of curvature is provided as a millimeter unit).

Further, cross-prisms having a pitch of 25//m, a height of 8.75,αm, and an interior angle of 110 degrees were formed on an area of the rear side where the stripe pattern was not formed, and were disposed perpendicular to the main prisms. The front side of the light guide plate was in a specular state.

The same conditions as in the example 2-1 were given except that an R value, that is, the radius of curvature at the side of the prism, was modified by 0.1 to be from (+) 0.4 to (-) 0.4. Modified factors of Examples 2-2 to 2-8 are shown in Table 2.

Table 2

CR: Radius of curvature, EX: Example

A stripe pattern with a pattern pitch of 430 μm was formed on the rear side of a wedge type light guide plate of 288.8 x 217.7 x 2.4 (start) x 0.8 mm (end) in width (W) x length (L) x thickness (T), and main prisms having a height of 14.25/an, a pitch of 25/ΛII and an interior angle of 82.5 degrees were formed in the stripe pattern. Further, cross-prisms having a pitch of 25/an, a height of 8.75//m, and an interior angle of 110 degrees were formed on an area of the rear side where the stripe pattern was not formed, and were disposed perpendicular to the main prisms. The front side of the light guide plate was in a specular state.

2. Result analysis Table 3

BR: Brightness, EX: Example, CE: Comparative Example

Table 3 shows results of brightness measurement with respect to Examples 1- 1 to 1-8 and Comparative Example 1.

As can be seen from Table 3, the inventive examples generally exhibit a higher central brightness than the comparative examples. In particular, Example 1-2 has the highest brightness, and excellent brightness compared with the comparative examples is obtained when the cross-prisms have an interior angle of 100 to 160 degrees as in Examples 1-1 to 1-6.

Table 4

CR: Radius of Curvature, BR: Brightness, EX: Example, CE: Comparative Example

Table 4 shows results of brightness measurement with respect to Examples 2- 1 to 2-8 and Comparative Example 2. Example 2-3 has the highest brightness, and central brightness rapidly reduces from Examples 2-1 and 2-5 to 2-8, as compared with Comparative Example 2. As can be seen from Table 4, the inventive examples, where the main prisms have a radius curvature of (+) R, exhibit a higher central brightness than the comparative examples, and in particular, excellent brightness compared with the comparative examples is obtained when the main prisms have the R values in Examples 2-2 to 2-4.

In view of ratio of pitch to radius of curvature of the main prisms, it is desirable that the main prisms have a groove or reverse-groove shape having a ratio of pitch to radius of curvature in the range of 1 : 1 to 1 :30.

When the light guide plate (see Fig. 2) described above in the examples is applied to the LCD, the backlight unit provides an effect of using a prism sheet even in the case of not using the prism sheet, which is typically used in a conventional LCD backlight unit.

That is, when using the light guide plate according to the inventive examples, it is possible to eliminate one or two optical sheets, which are necessarily used for the conventional backlight unit.

Fig. 7 is a perspective view to illustrate a light guide plate which has front prisms according to another embodiment of the present invention.

In this embodiment, the front side 303 is formed with the front prisms 360, each of which has a predetermined cross-sectional shape, and serves to make uniform diffraction, refraction, and diffusion of light exiting through the main body 300 of the light guide plate.

As in the embodiment shown in Fig. 2, a stripe pattern 320 and one or more cross-prisms 340 are formed on the rear side 305.

The front prisms 360 are formed on the overall surface of the front side 303 without being separated from each other, and disposed to have a longitudinal direction coincident to the direction where light is emitted from the light source.

In Fig. 7, a vertical cross-sectional shape of the front prisms 360 is a triangular shape, but may be modified in various shapes.

In particular, when the front prism 360 has a triangular cross-section, it preferably has a vertex angle in the range of 70-100 degrees. Figs. 8 to 10 are perspective views illustrating a variety of examples of a cross-sectional shape of the front prism 360.

As shown in Fig. 8, the front prisms 360 may be formed to have separation planes therebetween. The reason of disposing the front prisms 360 not closely but at constant intervals (d) is that this configuration can improve uniformity and visibility of light.

That is, when the light prisms 360 diffract, refract and diffuse light emitted from the main body 300 in a direction inclined to the LCD panel (not shown) that faces the light guide plate 310, such a configuration of the front prisms 360 being disposed at constant intervals (d) to define planes (that is, spaces between the prisms on the front side) therebetween can allow the light to progress perpendicular to the LCD panel (not shown) through these planes, thereby improving the uniformity of light reaching the LCD panel (not shown)

As shown in Fig. 9, the front prisms 360 may have a vertical cross-section of a trapezoid shape. Alternatively, as shown in Fig. 10, the front prisms 360 may have a vertical cross-section of a reverse groove shape that has a predetermined radius of curvature at each side.

In the front prisms 360 having the trapezoidal cross-section as shown in Fig. 9, light progresses perpendicular to the LCD panel (not shown) through planes (A) formed on top of the respective trapezoidal front prisms 360.

In the front prisms 360 having the reverse groove-shaped vertical cross- section as shown in Fig. 10, the front prisms 360 preferably have a radius of curvature in the range of 0.01-1.0 mm at each side.

An area ratio of the front prisms 360 to the separation planes between the front prisms 360 on the front side 303 of the main body 300 is preferably in the range of 1:0.5 to 1:10.

Further, in Figs. 9 to 10, a ratio of height (h2) to width (w2) of the front prisms 360 is preferably in the range of 0.3-0.6. If the ratio is less than 0.3, a horizontal viewing angle increases excessively, thereby reducing the brightness. If the ratio is more than 0.6, the horizontal viewing angle decreases excessively, providing unsatisfactory optical properties.

Claims

[CLAIMS]

[Claim 1 ] A light guide plate for an LCD backlight unit, comprising a lateral side for receiving incident light, a front side connected to the lateral side for emitting light to an outside, and a rear side for reflecting light, wherein the rear side is formed with a stripe pattern and at least one cross- prism on a portion where the stripe pattern is not formed, the stripe pattern having a width increasing with an increase in distance from the lateral side, and including a main prism formed therein.

[Claim 2] The light guide plate according to claim 1, wherein an angle of

60-120 degrees is defined between longitudinal directions of the cross-prism and the main prism.

[Claim 3] The light guide plate according to claim 1, wherein the main prism in the stripe pattern has a longitudinal direction perpendicular to a direction where light enters the light guide plate from the light source.

[Claim 4] The light guide plate according to claim 1, wherein the cross-prism is perpendicular to the main prism.

[Claim 5] The light guide plate according to claim 1, wherein the main prism in the stripe pattern is formed higher than the cross-prism.

[Claim 6] The light guide plate according to claim 1, wherein the cross-prism is formed higher than the main prism in the stripe pattern.

[Claim 7] The light guide plate according to claim 1, wherein the cross-prism and the main prism have a cross-sectional shape selected from a triangular shape, a trapezoidal shape, a groove or reverse-groove shape having a predetermined radius of curvature at each side, and a combination thereof.

[Claim 8] The light guide plate according to claim 7, wherein the cross-prism has the triangular cross-sectional shape, and the triangular cross-sectional shape has a vertex angle of 100-160 degrees.

[Claim 9] The light guide plate according to claim 7, wherein the main prism has the triangular cross-sectional shape, and the triangular cross-sectional shape has a vertex angle of 70-100 degrees.

[Claim 10] The light guide plate according to claim 7, wherein the main prism has the groove or reverse groove cross-sectional shape, of which ratio of pitch to radius of curvature is in the range of 1 : 1-1 :30.

[Claim 11 ] The light guide plate according to claim 1, wherein the front side is formed with front prisms having a predetermined cross-sectional shape.

[Claim 12] The light guide plate according to claim 11, wherein the front prisms have a longitudinal direction perpendicular to a longitudinal direction of the main prism.

[Claim 13] The light guide plate according to claim 11, wherein the front prisms have a cross-sectional shape selected from a triangular shape, a trapezoidal shape, a groove or reverse-groove shape having a predetermined radius of curvature at each side, and a combination thereof.

[Claim 14] The light guide plate according to claim 11, wherein the front prisms are disposed to have a predetermined separation plane therebetween.

[Claim 15] The light guide plate according to claim 14, wherein a ratio of the front prisms to the separation plane is in the range of 1:0.5 to 1:10 in view of surface area.

[Claim 16] The light guide plate according to claim 11, wherein a ratio of height to width of the front prisms is in the range of 0.3-0.6.

[Claim 17] A backlight unit for a liquid crystal display, comprising: the light guide plate according to claim 1 ; and a light source disposed at one side of the light guide plate.

[Claim 18] A liquid crystal display, comprising: the light guide plate according to claim 1 ; and a light source disposed at one side of the light guide plate.