WO2009057845A1

WO2009057845A1 - Light guide plate comprising prism with smooth top

Info

Publication number: WO2009057845A1
Application number: PCT/KR2007/005978
Authority: WO
Inventors: Jae Han Kim; Man Suk Kim; O Yong Jeong; Chul Goo Chi
Original assignee: Cheil Industries Inc.
Priority date: 2007-11-02
Filing date: 2007-11-26
Publication date: 2009-05-07
Also published as: CN101842726A; CN101842726B; KR20090045624A; TW200921165A; KR100968607B1

Abstract

A prism light guide plate for a back light unit of a liquid crystal display device, and more particularly a light guide plate comprising a prism with smooth vertex part, which exists on front or rear surface of the light guide plate, to improve productivity and credibility of the product is provided. The light guide plate includes a main body including side surfaces, upon which light is incident, a front surface and a rear surface connected with the side surfaces, upon which the light exits, and a plurality of prisms provided on the font or rear surface, in which each prism has a rounded corner, where two inclined surfaces meet, or has a smooth vertex part provided with a flat surface at the top, where two inclined surfaces meet.

Description

[DESCRIPTION] [Invention Title]

LIGHT GUIDE PLATE COMPRISING PRISM WITH SMOOTH TOP

[Technical Field]

The present invention relates to a prism light guide plate for a back light unit of a liquid crystal display device, and more particularly to a light guide plate having a prism with smooth top, which exists on front or rear surface of the light guide plate, to improve productivity and credibility of the product.

[Background Art]

In general, a liquid crystal display (hereinafter, referred to simply as a

"LCD") device refers to a device which displays numerals or images through application of an electric field to liquid crystals disposed between two glass substrates, in which the liquid crystals are made of a material having an intermediate phase between a liquid and a solid. Since the LCD device is not a self-luminescent device, it must be provided with a back light unit as a light source to generate light. An image is displayed in such a manner that transmittance of light generated from the back light unit is adjusted in a liquid crystal panel, in which liquid crystals are uniformly arranged.

FIG. 8 is an exploded perspective view showing a back light unit of a conventional LCD device.

As shown in FIG. 8, the conventional LCD back light unit includes a light source 61, a reflection plate 62, a light guide plate 63, a diffusion sheet 64, a prism sheet 65, and a protective sheet 66. The light source 61 serves to emanate light initially in the LCD device. Various types of light source 61 can be used, however the LCD device generally employs a cold cathode fluorescence lamp (CCFL) as the light source 61, which has a low power consumption and emits highly bright white light. The light guide plate 63 is provided below an LCD panel and near one side of the light source 61. The light guide plate 63 serves to convert spot light generated from the light source 61 into plane light and then project the plane light forward to the LCD panel.

The reflection plate 62 is provided on a rear side of the light guide plate 63. The reflection plate 62 serves to reflect light emitted from the light source 61 toward the LCD panel 69 disposed in front of the reflection plate 62.

The diffusion sheet 64 is provided on a front side of the light guide plate 63. The diffusion sheet 64 serves to uniformize light passing through the light guide plate 63. While passing through the diffusion sheet 64, the light is diffused in horizontal and vertical directions, and brightness is rapidly deteriorated. In this regard, the prism sheets 65 are used to refract and concentrate the light, to thereby enhance brightness.

The protective sheet 66 is provided above the prism sheets 65. The protective sheet 66 serves to prevent scratches on the prism sheets 65, and to prevent Moire effect from occurring when using the prism sheets 65 arranged in two layers in the vertical and horizontal directions.

As shown in FIG. 8, the light source 61 is generally provided at one edge of the back light unit 60. As a result, light is not uniformly transmitted through the overall surface of the unit, but rather the edge of the unit tend to be brighter than any other portions of the back light unit. In order to prevent this phenomenon, the light guide plate 63 is used. The light guide plate is generally made of a transparent acrylic resin, which is not easily breakable due to its high strength, and has deformation resistance. The light guide plate is characterized by its light weight and high transmittance of visible light.

In other words, the light guide plate 63 serves to allow light emitted from the light source 61 to be uniformly projected to the overall surface of the light guide plate 63. In practice, however, in a case where the back light unit 60 is disassembled and light is allowed to emit from the light source 61 located at one side of the light guide plate 63, the light is not uniformly projected to the overall surface of the light guide plate 63, but concentrated on both ends of the light guide plate 63. This is because the light guide plate 63 guides the light from the light source 61 to the opposite side of the light guide plate 63.

Thus, the rear surface of the light guide plate 63 is subjected to a specific treatment to cause scattered reflection of light in the light guide plate 63 such that light can be transmitted through the overall surface of the light guide plate 63. Specifically, the rear surface of the light guide plate 63 is formed with a prominence/depression pattern which has a predetermined shape designed in consideration of a distance from the light source 61 and the like. When the prominence/depression pattern is formed on the rear surface of the light guide plate 63, plane light having higher brightness and uniformity is emitted through the overall surface of the light guide panel of the liquid crystal display device. An example of the prominence/depression pattern is a prism form. Such a prism light guide plate is fabricated by preparing a mold of a corresponding pattern, and then injection molding or hot pressing. However, in the fabrication process, many defects have been caused by this prism having a pointed shape. In order to solve these defects, the fabrication process has been improved in various ways. In addition, because of the peculiar shape of the prism, when the product is used as a back light unit, there may be problems that the pointed vertex part of the prism is frictionized with the sheet contacting the prism causing collapsed prism or grinded sheet. [Disclosure] [Technical Problem]

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for fabricating a prism light guide plate by rounding or chamfering the edge of a prism to the extent of not largely deteriorating the brightness, to thereby increasing productivity of a product produced in the same manner as in a conventional production method, and improving credibility of the product.

It is another object of the present invention to provide a back light unit of an LCD device comprising the light guide plate according to the present invention.

[Technical Solution]

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a light guide plate having a prism with a smooth vertex part, comprising a main body including side surfaces, upon which light is incident, a front surface and a rear surface connected with the side surfaces, upon which the light exits, and a plurality of prisms provided on the font or rear surface, wherein each prism has a rounded corner, where two inclined surfaces meet, or has a flat surface provided at the vertex part, where two inclined surfaces meet.

[Advantageous Effects]

The prism light guide plate for an LCD device according to the present invention has effects of not generating deterioration in the brightness and improving productivity and credibility when compared with a conventional light guide plate having a triangular prism with sharp edges. [Description of Drawings]

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a perspective view illustrating a rear surface of a light guide plate comprising a prism with a smooth vertex part according to the present invention;

FIG. 2 is a sectional view illustrating a plurality of prisms each having a smooth vertex according to a first preferred embodiment of the present invention; FIG. 3 is a sectional view illustrating a plurality of prisms each having a smooth vertex according to a second preferred embodiment of the present invention;

FIG. 4 is a sectional view illustrating a plurality of prisms each having a smooth vertex according to a third preferred embodiment of the present invention; FIG. 5 is a graph illustrating distribution and cumulative distribution of amount of light passing through a prism;

FIG. 6 is a table listing partial data of the graph in FIG. 5;

FIG. 7 is a graph comparing the frontal brightness according to an embodiment of the present invention; and FIG. 8 is an exploded perspective view showing a back light unit of a conventional LCD device.

[Best Mode]

The present invention is directed to a light guide plate having a prism with a smooth top, comprising a main body including side surfaces, upon which light is incident, a front surface and a rear surface connected with the side surfaces, upon which the light exits, and a plurality of prisms provided on the font or rear surface, wherein each prism has a rounded corner, where two inclined surfaces meet, or has a flat surface at the vertex part, where two inclined surfaces meet.

[Mode for Invention]

Now, a preferred embodiment of a light guide plate having a prism with a smooth top according to the present invention will be described in detail with reference to the accompanying drawings.

It should be noted that the sizes of components constituting the present invention are exaggerated in the accompanying drawings for the purpose of clarity. Further, terms used in the description are defined in consideration of functions of the present invention. Thus, it should be contemplated that the terms can be varied according to a user or an operator uses.

Therefore, the definition should be based on the overall disclosure of the present invention. FIG. 1 is a perspective view illustrating the rear surface of the light guide plate having a prism with a smooth vertex part according to the present invention.

Referring to FIG. 1, a main body 100 of the light guide plate includes opposite side surfaces 101, upon which light is incident, a front surface 103 connected to the side surfaces 101 and disposed opposite to an LCD panel, and a rear surface 105 connected to the side surfaces 101 and disposed opposite to the front surface 103.

Generally, the term of "side surfaces 101" means side surfaces of an object.

In this specification, however, the side surfaces 101 are defined as the surfaces upon which light emitted from a light source 106 is incident. Therefore, the side surfaces 101 correspond to two surfaces 101 disposed adjacent to the light source

106, respectively, as shown in FIG. 1.

The rear surface 105 is provided with a plurality of main prisms 110 in the longitudinal direction parallel to the longitudinal direction of the light source. The rear surface 105 is also provided with a plurality of supplementary prisms (not shown) in the perpendicular direction to the main prisms. The supplementary prisms (not shown) are provided optionally depending on the characteristics required for the light guide plate. Thus, there are cases where only the main prisms are provided.

As described above, the light guide plate has a plurality of prisms provided on the rear or front surface. Each prism of main prisms, supplementary prisms or front prisms generally has a triangular cross-section. The present invention is not related to the arrangements of the main prisms, supplementary prisms or front prisms provided on the light guide plate, but to a specific cross-sectional shape that corresponds to all the prisms. Therefore, the above-mentioned prisms are collectively referred to as prisms, and their specific cross-sectional structures will be described below. FIG. 2 is a sectional view illustrating a plurality of prisms each having a smooth vertex according to a first preferred embodiment of the present invention.

Referring to FIG. 2, a prism 200 according to the first embodiment of the present invention is characterized by having a rounded top at the vertex part 205.

It may be advantageous in the optical performance to maintain the top of vertex 205, where two inclined surfaces 202 and 204 meet, to have a sharp edge.

However, since the prism is fabricated in fine sizes of several ten micrometers to several hundred micrometers, it is difficult to fabricate the prism vertex part 205 with fine sizes to have a sharp edge.

That is, many defects are generated from being unable to form a uniformed vertex part 205. In addition, even though a pointed vertex may be formed, there is a problem that the top is easily damaged.

The prism 200 is fabricated by hot pressing or injection molding. At this time, the top may be damaged during transformation, or may be collapsed by the friction with the other sheets or abraded by the sheets. The present invention has rounded the top as shown in FIG. 2 to prevent damages on the top and have effects of reducing defects generated during fabrication.

It is preferable that a height (Hl) of the smooth top 205 is formed 1/30 to 1/2 smaller than a height (H2) of the triangular form before the rounding treatment.

When the reduction of the height is less than 1/30, the effect for preventing defects cannot be achieved through the rounding treatment. On the other hand, when the reduction of the height is more than 1/2, the optical performance of the prism is reduced. FIG. 3 is a sectional view illustrating a plurality of prisms each having a smooth vertex according to a second preferred embodiment of the present invention.

As shown in FIG. 3, a prism 300 according to the second preferred embodiment of the present invention is characterized by having a chamfered vertex 305. That is, the top of vertex is provided with a flat surface 306 in a cut form.

The vertex is not chamfered in the process of fabricating the prism, but it is processed using a mold or a hot press in a cut form.

The vertex part 305 is provided with the flat surface 306 to prevent damage to the tip of vertex as in the first preferred embodiment of the present invention, thus has the same effect as the first preferred embodiment.

It is preferable that the height reduction of the prism (H4-H3) by forming the flat surface 306 is limited to a range of 1/30 to 1/2 of the height of the prism.

FIG. 4 is a sectional view illustrating a plurality of prisms each having a smooth vertex according to a third preferred embodiment of the present invention. The third preferred embodiment is a modification of the second preferred embodiment. In this regard, a prism 300 according to the third preferred embodiment of the present invention is characterized by rounding the corners where the flat surface 306 and two inclined surfaces 302 and 304 meet. This is because when the flat surface 306 meets the two surfaces 302 and 304 to form sharp corners again, there are high possibilities that these corners also generate defects.

FIG. 5 is a graph illustrating distribution of amount of light passing through a unit position in a rear surface of a prism, as a function of distribution of cumulative distance from a vertex of the prism. x-axis represents an inclined surface of a prism which is divided into 100 equal parts starting from the vertex of the prism. Here, the left of the graph refers to the vertex part and the right of the graph refers to the lower portion of the prism. The amount of light at each position refers to an amount of light passing through a respective unit position obtained by dividing the inclined surface into 100 equal parts. The cumulative amount of light refers to a cumulative amount of light according to the cumulative distance starting from the vertex part.

FIG. 6 is a table listing partial data of cumulative amount of light according to a height of the prism. The cumulative amount of light passing through about 10% of the prism height is about 7.5%. Thus, when this 10% of the prism is rounded off, about 7.5% of the exit brightness is reduced.

Comparative Example and Experimental Example

A typical conventional prism with pointed vertex (Comparative Example) and a prism of the present invention with chamfered vertex (Experimental Example) were fabricated, and their brightness were measured for comparison.

The prisms of both Comparative Example and Experimental Example had a vertex angle of 82° and the pitch of 50 μm, respectively. The same front prisms are provided on the front surface of a light guide plate in Comparative Example and Experimental Example. In addition, the prism of Experimental Example had the vertex rounded to have a bending radius of 3 μm.

FIG. 7 is a graph illustrating the results of brightness measurement of a conventional light guide plate (Comparative Example) and a light guide plate according to the present invention (Experimental Example). As shown in FIG. 7, the light guide plate of Experimental Example show approximately the same brightness distribution compared with the light guide plate of Comparative Example, with average brightness reduction of about 7%. Although the brightness reduction is not significant, the problems caused by having a pointed vertex can be resolved, to thereby improving the productivity and credibility.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[CLAIMS]

[Claim 1 ] A light guide plate comprising: a main body including side surfaces, upon which light is incident, a front surface and a rear surface connected to the side surfaces, upon which the light exits; and a plurality of prisms provided on the front or rear surface, wherein each prism has a rounded vertex part where two inclined surfaces meet.

[Claim 2] A light guide plate comprising: a main body including side surfaces, upon which light is incident, a front surface and a rear surface connected to the side surfaces, upon which the light exits; and a plurality of prisms provided on the front or rear surface, wherein each prism has a flat surface provided on the vertex part where two inclined surfaces meet.

[Claim 3] The light guide plate according to claim 1 or 2, wherein the prism has a height of 1/30 to 1/2 smaller than a height measured to a point where extended lines of the two inclined surfaces meet.

[Claim 4] The light guide plate according to claim 2, wherein the vertex part has rounded corners where the two inclined surfaces and the flat surface meet.

[Claim 5] A back light unit, comprising a light guide plate of claim 1 or 2.

[Claim 6] A liquid crystal display device, comprising a back light unit of claim 5.