KR20010007011A - Light guide plate, surface light source device of side light type, and liquid crystal display - Google Patents

Abstract

PURPOSE: To reduce brightness irregularity in the vicinity of an incoming surface by preventing luminous points of point light sources from being seen from the outgoing surface side, in the case of a light plate, a sidelight surface light source device, and a liquid-crystal display device, using point light sources as primary light sources, in which, for example, light goes out from local luminous areas with relatively intense directivity. CONSTITUTION: A plurality of grooves 12D extending in the thickness direction are formed, at least, in portions of a light guide plate 12 confronting point light sources 7, and they are formed so that the cut depths of the grooves 12D are gradually decreased toward an outgoing surface 12C at least in the vicinity of the outgoing surface 12C.

Description

Light guide plate, side light type surface light source device and liquid crystal display device {LIGHT GUIDE PLATE, SURFACE LIGHT SOURCE DEVICE OF SIDE LIGHT TYPE, AND LIQUID CRYSTAL DISPLAY}

The present invention relates to a light guide plate, a side light type surface light source device and a liquid crystal display device, and more specifically, to a light guide plate improved to be suitable for light input from a point light source, and a side light type using such an improved light guide plate. A surface light source device and a surface light source device are used for illuminating a liquid crystal display panel.

It is already known to illuminate a liquid crystal display panel of a liquid crystal display device by a side light type surface light source device. In general, a side light type surface light source device includes a light guide plate and a primary light source for supplying primary light thereto. Conventionally, rod-shaped fluorescent lamps (cold cathode tubes) have been widely used as primary light sources, but recently, those using point-like light sources such as LEDs (light emitting diodes) and semiconductor lasers (also called laser diodes) have been adopted. .

6 shows an example of a conventional side light type surface light source device using a point light emitting source in an exploded perspective view. 7, the cross-sectional structure cut along the line A-A in FIG.

Referring to the drawing, the side light type surface light source device 1 includes a light guide plate 2, a primary light source 3, and a reflection sheet 4. The light guide plate 2 has a wedge-shaped cross section, and the primary light source 3 is disposed in the vicinity of the side cross section (incident cross section; 2A) on the side of which the thickness is thick, and along the back surface 2B which is one measurement surface. The reflective sheet 4 is disposed. The other measuring surface provides an emitting surface 2C for emitting the output light of the light guide plate. As already known, the light guide plate 2 is comprised from the molded article which consists of translucent materials, such as an acrylic resin.

As the reflective sheet 4, a diffusely reflective sheet member such as a white PET film, or a specularly reflective sheet member such as silver foil is used. The reflective sheet 4 returns the leaked light from the back surface 2B into the light guide plate 2 to prevent loss of light.

Further, for correction of the directivity characteristic of the output light and the like, additional sheets such as a prism sheet and a light diffusion sheet are disposed as necessary along the emission surface 2C. In the case of constituting the liquid crystal display device, a liquid crystal display panel is further disposed on the outside thereof.

The primary light source 3 includes a light emitting portion 7 and its supporting member 8. In this example, four light emitting portions 7 are formed on the support member 8 at equal intervals. Each light emitting part 7 comprises one unit which sealed one or several semiconductor chips (for example, LED) in the rectangular resin package, for example. Wiring for supplying a drive current to the point light emitting element incorporated in each unit (light emitting portion) 7 is provided on a printed board constituting the main portion of the supporting member 8. The light guide plate 2 has protrusions at both ends of the incident end face 2A, and the light emitting part 7 is accommodated between the protrusions so that a constant positional relationship close to the incident end face 2A is maintained.

The light emitting area of each light emitting part 7 is much smaller than the area of the incident end surface 2A even when a plurality of point light emitting elements are used. This is one of the major differences from the case of using a rod-shaped fluorescent lamp. Another difference from the case of using a rod-shaped fluorescent lamp or the like is that the primary light emitted from the light emitting portion 7 using the point light emitting element toward the incident end surface 2A has a considerable directivity. In other words, it is difficult to expect the supply of primary light having a wide angle extension such as a rod-shaped fluorescent lamp.

The two general constraints ("narrow light emitting area" and "relatively strong directivity") of the primary light source 3 using the point light source are of the output light of the light guide plate 2 used in combination with the primary light source 3. It gives a non-negligible effect on uniformity. That is, the primary light having a relatively strong directivity emitted from the narrow light emitting area of each light emitting part 7 is discharged from the emission surface 2C as compared with the primary light emitted diffusely from the wide light emitting area like a rod-shaped fluorescent lamp. It is difficult to be converted into output light which is uniformly emitted.

Therefore, if the incident end surface 2A of the light guide plate 2 is formed flat in the same manner as in the case of using a normal rod-shaped fluorescent lamp, a large luminance deviation (excessively bright area and brightness on the exit surface 2C) Insufficient area). For example, in the area E corresponding to the blank section of the light emitting portion 7, there is a lack of light supply clearly, and a dark portion is formed on the emission surface 2C.

Conventionally, such luminance deviation is alleviated by forming the recessed part 2D in the incident end surface 2A. The recessed portions 2D are formed at positions opposite to the respective light emitting portions 7, and the depth thereof is substantially constant along the thickness direction of the light guide plate 2. Therefore, as shown partially enlarged in FIG. 6 (see symbol B), when the primary light is introduced into the light guide plate 2, the semi-cylindrical surfaces of the recesses 2D function like the concave cylindrical lens surfaces. .

As a result, the light beam group L (broken line) after introduction into the light guide plate 2 is spread and propagated in various directions as compared with the case where the incident end surface 2A is flat (that is, when the recess 2D is not formed). . This alleviates the tendency for the emission from the exit surface 2C to deviate locally. In particular, light is distributed even in the area E, and the appearance of a visible dark portion is prevented.

However, one problem arises when such a solving means (formation of recesses 2D) is employed. That is, as shown by the light ray C in FIG. 7, it is emitted from the light emitting part 7 and obliquely passes through the U-shaped valley (in the air) formed by the recessed part 2D, and is introduced into the light guide plate 2. Light rays which exit to the outside (output side) of the emission surface 2C are generated without having a chance of becoming.

It goes without saying that such direct emission causes the luminance deviation in the vicinity of the incident end surface 2A. For example, when applied to the back irradiation of the liquid crystal display device, the point light source is projected to be visible on the display screen. This is clearly undesired due to a decrease in display quality.

Moreover, since the emission position of the light ray C becomes the edge part of the emission surface 2C, actual emission of the light ray C may be interrupted by the edge member (not shown). However, in that case, a loss occurs by blocking the light beam C, which is also undesirable.

SUMMARY OF THE INVENTION The present invention has been proposed under the above-mentioned background, and an object of the present invention is to provide a liquid crystal display device using a light guide plate, a side light type surface light source device using the same, and a copper surface light source device using the same to improve the liquid crystal panel. It is done.

First, the present invention improves a light guide plate having an incidence end surface for inputting light from a light emitting portion using a point-shaped light emitting element, an output surface for outputting light, and an equilateral back surface on the output surface.

The improved light guide plate includes a plurality of grooves connected in at least a part of the incident cross section in the thickness direction of the light guide plate. This groove is formed so as to reduce the depth as it approaches the exit surface, at least in the vicinity of the exit surface (part near the exit surface). In the typical example, the groove has a form in which a pair of flat inclined surfaces are connected. In addition, it is preferable that the incidence end surface is formed to be limited to the very front of the edge where it meets the exit surface.

A slight deformation can be considered in the transition of the depth of the groove with respect to the thickness direction of the light guide plate. For example, the groove may be formed to be deepest at the position closest to the rear surface of the light guide plate. Moreover, you may be formed so that depth may decrease as it approaches a back surface in the vicinity of the back surface (part near a exit surface side). In the latter case, the grooves are deepest on the incidence section, near the positions equidistant to the back and exit surfaces. In any case, it is preferable that the groove does not extend to the edge where the incident end face and the exit face meet.

When the light guide plate thus improved is placed in parallel with the primary light source having at least one local light emitting unit using the point light emitting element, the side light type surface light source device according to the present invention is constructed. The position at which the groove is formed on the incident end surface of the light guide plate is designed to correspond at least to the local light emitting portion.

Further, when the side light type surface light source device is arranged for illumination of the liquid crystal display panel, the liquid crystal display device according to the present invention is constructed.

According to the present invention, when light is supplied toward the groove of the incidence end face, most of the direct exit course as described above (optical path exiting the exit face without passing through the light guide plate; see ray C in Fig. 7) does not occur. Therefore, the luminance deviation caused by it is prevented. Moreover, when it applies to illumination of the liquid crystal display panel of a liquid crystal display device, the fall of a display quality is prevented.

1 is an exploded perspective view schematically showing the entire arrangement of a side light type surface light source device according to the present invention.

2 is a cross-sectional view taken along a plane parallel to the exit surface of one light emitting portion and a groove formed correspondingly to explain one function of the groove formed in the incident cross section.

3 is a partial cross-sectional view taken along the line F-F in FIG. 1 to explain another function of the groove formed in the incident cross section.

4 is a diagram showing one modification of the depth transition of the groove formed in the incident cross section.

5 is a view showing another modification of the depth transition of the groove formed in the incident cross section.

6 is an exploded perspective view showing an example of a conventional side light type surface light source device using a point light emitting source.

7 is a cross-sectional view illustrating a cross-sectional structure taken along the line A-A of FIG. 6.

"Description of the symbols for the main parts of the drawings"

1, 11: side light type surface light source device 2, 12: light guide plate

2A, 12A: Incident cross section 2B, 12B: Back side

2C, 12C: exit face 2D: recess

3: primary light source 4: reflection sheet

7 light emitting portion 8 support member

12D: groove 13, 14: prism sheet

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described with reference to drawings. In addition, in each figure, in order to understand easily, the dimension, shape, etc. of each element are shown to be exaggerated suitably. In addition, about the element used in common with FIG. 6, FIG. 7, the common code | symbol is attached | subjected and the overlapping description is abbreviate | omitted suitably.

First, referring to FIG. 1, an outline of the entire apparatus of the side light type surface light source device according to the present invention is shown in the same exploded perspective view as in FIG. The side light type surface light source device 11 according to the present invention includes a light guide plate 12, a primary light source 3, a reflection sheet 4, and two prism sheets 13 and 14.

The light guide plate 12 has a wedge-shaped cross section, and the primary light source 3 is disposed in the vicinity of the thicker side end surface (incident cross section; 12A), along the back surface 12B as one measurement surface. The reflective sheet 4 is disposed. The other measuring surface provides an emitting surface 12C for emitting the output light of the light guide plate. The light guide plate 12 is comprised from the molded article which consists of translucent materials, such as acrylic resin (PMMA resin), for example.

Moreover, the light scattering pattern for accelerating emission in many cases is formed in the emission surface 12C as needed. The light scattering pattern is formed by, for example, distributing a small rough surface region, and thereby uniformizing the luminance distribution by changing the density of the rough surface region and the like depending on the location. In some cases, a light scattering pattern may be formed on the back surface 12B.

As the reflective sheet 4, a diffusely reflective sheet member such as a white PET film, or a specularly reflective sheet member such as silver foil is used. The reflective sheet 4 returns the leaked light from the back surface 12B into the light guide plate 12 to prevent light loss.

The prism sheets 13 and 14 are examples of additional sheets arranged to correct the directivity characteristic of the output light.

As shown in FIG. 3 which will be referred to later in detail, a plurality of prism cuts are formed on the outer surface of the prism sheet 13 that extend substantially in parallel with the incident end surface. In contrast, a plurality of prism cuts are formed on the outer surface of the prism sheet 14 that extend substantially perpendicular to the incident end surface. Since the operation of the prism sheet is already known, a detailed description thereof will be omitted.

Instead of or in addition to one or both of the prism sheets 13 and 14, a light diffusion sheet, a protective sheet, or the like may be disposed. In the case of constituting the liquid crystal display device, a liquid crystal display panel (not shown) is further disposed outside thereof. In some cases, the additional sheet may not be disposed at all.

As the primary light source 3, the same ones described with reference to FIGS. 6 and 7 may be employed. That is, the unit light emitting portion 7 formed on the support member 8 at equal intervals seals one or a plurality of semiconductor chips (for example, LEDs) in, for example, a rectangular resin package. It has a structure.

Wiring for supplying a driving current to each point light emitting element is provided on a printed board constituting the main portion of the supporting member 8. The light guide plate 12 has the same protrusions as the light guide plate 2 (see Fig. 6) at both ends of the incident end surface 12A, and the light emitting portion 7 is accommodated between the protrusions and is the incident end surface 12A. The constant positional relationship close to is maintained.

The light emitting area of each light emitting portion 7 is much smaller than the area of the incident end surface 12A even when a plurality of point light emitting elements are used. In addition, the light emitting portion 7 emits primary light having a relatively strong directivity as compared with a rod-shaped fluorescent lamp.

The fact that the surface light source device 11 of the present embodiment is substantially different from the conventional device 1 (FIGS. 6 and 7) is that the light guide plate 12 is used instead of the light guide plate 2. The light guide plate 12 has a structure improved according to the present invention. That is, the groove 12D is formed in the incident end surface 12A at a position corresponding to the light emitting portion 7.

As shown partially enlarged in FIG. 1 (refer to reference D), each groove 12D is connected in the thickness direction of the light guide plate 12, while near the exit surface 12C, the exit surface 12C is close to the exit surface 12C. According to the carved shallowly. In this example, the groove 12D has a deepest part corresponding to the edge (hereinafter referred to as the back side edge) that meets the rear face 12B, and extends from there to just in front of the exit face 12C. The groove 12D does not reach the edge (hereafter referred to as the exit face side edge) that meets the exit face 12C.

In FIG. 2, a cross section cut along a plane parallel to the emission surface 12C is drawn for one light emitting portion 7 and a groove 12D formed correspondingly thereto. The grooves 12D are composed of flat pairs of inclined surfaces, and these inclined surfaces function as refractive surfaces. That is, the light emitted from the point-shaped light emitting region of the light emitting portion 7 is incident and refracted by any of the inclined surfaces of the grooves 12D, as indicated by the numeral L, and its propagation direction is expanded, Diversification.

As a result, light is widely distributed in the light guide plate 12. Therefore, even in the part corresponding to the space | interval part of the light emitting part 7 (part corresponding to code | symbol E in FIG. 6) in the vicinity of the incident cross section 12A, a marked lack of light supply is avoided. In this sense, the groove 12D has a function similar to that of the recess 2D in the prior art (see FIG. 6).

In addition, the groove 12D achieves a function not present in the recess 2D in the prior art (see FIG. 6). In other words, it is possible to suppress the generation of light (see the path of symbol C in Fig. 7) which takes the direct emission course which is a problem in the prior art. This will be described with reference to FIG. 3.

FIG. 3 is a partial cross-sectional view taken along the line F-F in FIG. 1. In FIG. 3, attention is paid to the light beam SO emitted from the light emitting point toward the same direction as the light beam C in FIG. 7. The formation of the some groove 12D shallowly toward the edge from the side near the emission surface 12 has an important meaning in the course of the light ray S0.

That is, since the light beam SO does not exist "a wide valley extending to the edge of the emission surface side", it is inevitable to enter the incident end surface 12A. The incident position of the light beam SO into the incident end surface 12A becomes "an inclined surface of any one groove 12D" or "flat surface". As in the present embodiment, when the groove 12D is interrupted to the front of the exit face side edge substantially (depth reaches zero), the latter (flat surface) tends to become.

In FIG. 3, the light beam SO is incident on the flat surface under the maximum conditions. Light ray S0 is refracted as shown in the light guide plate 12, and becomes light ray S1 inclined at a relatively shallow angle with respect to exit surface 12C. Light ray S1 is directly internally incident at a shallow angle to exit surface 12C.

As is well known in the fundamental theory of optics, total internal reflection or near reflection occurs at internal incidence under such conditions. Therefore, all or most of the light beam S1 becomes the light beam S2, and the light guide plate 12 is sent inward. Even when the light beam SO enters the inclined surface of the groove 12D, the situation does not change very much. In other words, in the cross section shown in Fig. 3, the inclination of the inclined plane is also refracted so as to be shallow at the incidence of the inclined plane, and is introduced into the light guide plate 12, and is immediately internally inclined at the inclined plane 12C. Therefore, the optical path is similar to S1 and S2. As a result, in either case, the direct exit path as indicated by the symbol S3 (broken line) does not occur. Therefore, the situation in which the light emitting portion 7 having a light emitting area much smaller than the incident cross section can be seen as a visible light from the outside of the emission surface 12C is avoided. Such an advantage is also obtained when the present surface light source device is applied to the contrast of the liquid crystal display panel. That is, the liquid crystal display panel illuminated with the output light without such a "noticeable list" improves the luminance uniformity of the display screen.

As described above, a light scattering pattern may be formed on the emission surface 12C. In that case, a part of the light beam S1 easily escapes from the light guide plate 12 in accordance with the light and shade of the light scattering pattern. However, even in that case, it does not cause direct emission like the light beam C.

The above-described embodiments do not imply a limitation of the scope of the present invention. For example, all the following variations are allowed.

(a) First, various deformation | transformation are possible with respect to the transition of the depth of the groove | channel 12D. For example, as shown by the broken line in FIG. 4, the trend which becomes secondary functionally shallow toward an exit surface can also be employ | adopted. Further, as shown by broken lines in FIG. 5, the grooves are gradually deepened from the vicinity of the rear edge to the vicinity of the center portion (equivalent distance to the exit surface side edge and the rear edge) and gradually become shallower from there to the front of the exit surface. You may be.

(b) In the above embodiment, the groove 12D is formed to be limited to the section corresponding to each light emitting portion 7. However, it may be formed over the whole width | variety of the cross section 12A which is not corresponding to the light emission part 7, for example.

(c) In the above embodiment, the groove 12D has a form in which a pair of flat inclined surfaces are connected. However, this is a typical example and does not limit the present invention. For example, the form which connected one pair of curved surfaces is also employable. There is no restriction | limiting in particular also about the profile (cross section shape) of a curved surface. For example, the curved surface which becomes a sine wave may be sufficient as the cross-sectional shape cut along the plane parallel to an exit surface.

(d) The grooves 12D may be subjected to surface treatment such as matting and ink attachment. The process of adding the light diffusing function, such as the matting process or ink attachment, reinforces the light distribution function of the grooves 12D and promotes uniform light output.

(e) There are various modifications to the configuration of the light emitting portion 7. For example, it is also possible to employ a semiconductor chip (LED element) equipped on a print base (support member) without resin sealing. In that case, the outer surface of the semiconductor chip may be covered with a protective film. only. The light emitting portion 7 does not have a wide light emitting area that can correspond to approximately the entire incidence cross section, such as a rod-shaped fluorescent lamp, even when viewed alone or as a whole of the primary light source 3. The light emitting region of the light emitting portion 7 is local in that sense.

(f) In the above embodiment, the primary light supply from the light emitting portion 7 was performed from one end face 12A of the light guide plate 12, but the other end face also formed the same groove as the groove 12D, The light emitting portion may be arranged in close proximity.

(g) The light guide plate 12 in the above embodiment has a wedge-shaped cross section. This does not limit the invention. For example, you may employ | adopt the light guide plate which has a uniform thickness in the whole, and may form a groove | channel in the above-mentioned method in the single cross section or two or more cross sections.

(h) The present invention may be applied to side light type surface light source devices used for applications other than liquid crystal display panel illumination of liquid crystal display devices and light guide plates used therein. For example, the present invention can be widely applied to various lighting devices, side light type surface light source devices formed in display devices, and light guide plates used therein.

As described above, according to the present invention, a plurality of grooves extending in the thickness direction are formed in at least a portion of the light guide plate facing the point light source, and at least in the vicinity of the exit surface, the grooves are gradually reduced as the depth of the groove approaches the exit surface. This makes it possible to reduce the luminance deviation in the vicinity of the incident surface by making the light emitting point of the point light source invisible from the emission surface side.

Claims (15)

A light guide plate having an incidence end surface for inputting light from a light emitting portion using a point-shaped light emitting element, an emission surface for outputting light, and an equilateral back surface on the emission surface, At least a portion of the incident cross section includes a plurality of grooves connected in the thickness direction of the light guide plate, The groove is formed so as to reduce the depth at least in the vicinity of the exit surface as it approaches the exit surface. The light guide plate according to claim 1, wherein the groove has a pair of flat inclined surfaces. The light guide plate according to claim 1 or 2, wherein the groove is formed to be limited to the front of the edge where the incident end face meets the exit face. The light guide plate according to any one of claims 1 to 3, wherein the groove is formed deepest at a position closest to the rear surface. The light guide plate according to any one of claims 1 to 3, wherein the groove is formed so as to decrease the depth as it approaches the rear surface in the vicinity of the rear surface. A side light type surface light source device including a primary light source having at least one local light emitting part using a point light emitting element, and a light guide plate placed side by side in the vicinity of the primary light source, The light guide plate has an incidence cross section for inputting light from the primary light source, an emission surface for outputting light, and an equilateral back surface on the emission surface, A plurality of grooves extending in the thickness direction of the light guide plate are formed at a position corresponding to at least the light emitting portion of the incident end surface. And said groove is formed so as to reduce the depth at least in the vicinity of the exit surface as it approaches the exit surface. 7. The side light type surface light source device according to claim 6, wherein the groove has a pair of flat inclined surfaces. 8. The side light type surface light source device according to claim 6 or 7, wherein the groove is formed to be limited to the front of the edge where the incident end face meets the exit face. The side light type surface light source device according to any one of claims 6 to 8, wherein the groove is formed deepest at a position closest to the rear surface. 9. The side light type surface light source device according to any one of claims 6 to 8, wherein the groove is formed so as to reduce the depth as it approaches the rear surface in the vicinity of the rear surface. A liquid crystal display device for illuminating a liquid crystal display panel using a side light type surface light source device, The side light type surface light source device includes a primary light source having at least one local light emitting unit using a point light emitting element, and a light guide plate placed side by side in the vicinity of the primary light source, The light guide plate has an incidence cross section for inputting light from the primary light source, an emission surface for outputting light, and an equilateral back surface on the emission surface, A plurality of grooves extending in the thickness direction of the light guide plate are formed at a position corresponding to at least the light emitting portion of the incident end surface. And the groove is formed so as to reduce the depth as it approaches the exit surface at least in the vicinity of the exit surface. 12. The liquid crystal display device according to claim 11, wherein the groove has a pair of flat inclined surfaces. The liquid crystal display device according to claim 11 or 12, wherein the groove is formed to be limited to the front of the edge where the incident end face meets the exit face. The liquid crystal display device according to any one of claims 11 to 13, wherein the groove is formed deepest at a position closest to the rear surface. The liquid crystal display device according to any one of claims 11 to 13, wherein the groove is formed so as to decrease the depth as it approaches the rear surface in the vicinity of the rear surface.