JP2007048670A - Double-sided light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce show-through effects in a double-sided light emitting device. <P>SOLUTION: In this light emitting device, optical sheets and shading sheets wherein light emitting window regulating light emitting area are laminated in back and front surfaces of a light guide plate where the light source has been arranged at the side part, and the light emitting window comprises a large light emitting window and a small light emitting window formed in a position overlapping with the large light emitting window. The color of the surface on side of the light guide plate of the shading sheet in which the small light emitting window is formed is gray. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light emitting device that emits light from a liquid crystal display panel or the like in a portable telephone or the like.

  In a foldable mobile phone, the main display screen appears when it is opened, but in order to provide information to the user even when it is closed, a sub liquid crystal display panel is provided on the back side of the main liquid crystal display panel. The provided ones are widespread. As these backlights, those in which a surface light emitting device is provided for each of the main and sub liquid crystal display panels, and those in which a double-sided light emitting device is provided as a common backlight have been proposed (patents). References 1 to 3). A device employing a double-sided light emitting device has the advantage of being able to reduce costs and thickness.

JP 2002-287144 A JP 2002-132189 A Japanese Patent Laid-Open No. 2001-290445

  However, in the double-sided light emitting device, the light emission area on the main side and the light emission area on the sub side overlap each other, and thus the light emission area on the sub side may appear when viewed from the main side (show-through).

  Accordingly, an object of the present invention is to reduce show-through in a double-sided light emitting device.

  According to the present invention, an optical sheet and a light shielding sheet having a light exit window for defining a light exit area are respectively laminated on the front and back surfaces of a light guide plate having a light source disposed on the side, and the light exit window is a large light exit. In a double-sided light emitting device comprising a window and a small light-emitting window formed at a position overlapping the large light-emitting window, the light-shielding sheet on which the small light-emitting window is formed is colored gray on the surface on the light guide plate side. A double-sided light emitting device is provided.

  According to the double-sided light emitting device of the present invention, since the color of the surface of the light shielding sheet on which the small light emitting window is formed is gray, the large light emitting window is reflected by the light shielding sheet. Light emitted from the light is suppressed. Therefore, show-through is reduced. Further, since the reflection on the light shielding sheet is not completely regulated, the luminance of the light emitted from the large light exit window is not significantly impaired.

  In the present invention, the light shielding sheet on which the small light exit window is formed is formed by laminating a black sheet and a milky white translucent sheet laminated on the light guide plate side with respect to the black sheet. The following configuration can be adopted. According to this configuration, the color of the surface on the milky white translucent sheet side can be made gray by laminating the black sheet and the milky white translucent sheet. And the said light-shielding sheet from which the density | concentration of gray differs can be obtained simply by preparing multiple types of the said milky-white translucent sheet | seats from which transparency differs.

  In the present invention, it is possible to adopt a configuration in which the gray density is set according to the luminance of the light emitted from the small light exit window. According to this configuration, it is possible to optimize the reduction of show-through.

  Moreover, in this invention, the reflection sheet laminated | stacked in the area | region straddling the boundary of the said light source and the said light-guide plate is provided, and this reflection sheet can employ | adopt the structure arrange | positioned so that it may not overlap with the said large sized light emission window. . According to this configuration, since the light-shielding sheet is gray, it is possible to improve luminance that slightly decreases as a whole without changing the light source.

  In the present invention, it is preferable that the optical sheet is a prism sheet, and a prism crest surface of the prism sheet is on the light guide plate side.

  As described above, according to the present invention, show-through can be reduced in the double-sided light emitting device.

<First Embodiment>
Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded perspective view of a double-sided light emitting device A according to an embodiment of the present invention, and FIG. The surface light emitting device A illuminates a liquid crystal display panel in which the components described below are stacked as shown in FIG. 2A and housed in a frame (not shown).

  The surface light emitting device A includes a light guide plate 1. The light guide plate 1 is made of a rectangular and transparent member, and is formed of, for example, an acrylic resin. A light source 2 for allowing light to enter the light guide plate 1 is disposed on the side of the light guide plate 1. In the present embodiment, a point light source such as an LED is exemplified as the light source 2, but a linear light source such as a cold cathode ray tube may be used. Light from the light source 2 enters the light guide plate 1 from the side surface of the light guide plate 1 and propagates through the light guide plate 1, and part of the light exits from the front surface 1 a and the back surface 1 b, respectively.

  Optical sheets 11 and 21 are laminated on the front surface 1a side and the back surface 1b side of the light guide plate 1, respectively. The optical sheets 11 and 21 are, for example, a prism sheet and a diffusion sheet. In the present embodiment, the front and back surfaces are illustrated one by one, but a plurality of types of optical sheets can be employed. In this document, the sheet includes both a film and a plate. A transflective sheet 3 indicated by a broken line in FIG. 1 can be laminated on either the front surface 1a side or the back surface b side of the light guide plate 1. The transflective sheet 3 is arbitrarily laminated in order to improve the luminance on either the front surface 1a side or the back surface 1b side, and when laminated on the front surface 1a side, the luminance on the back surface 1b side is improved and the luminance on the front surface 1a side is lowered. . Conversely, when laminated on the back surface 1b side, the luminance on the front surface 1a side is improved and the luminance on the back surface 1b side is lowered. In addition, although this embodiment demonstrates the case where the transflective sheet 3 is not provided, it is the same also when provided. Further, when a prism sheet is used as the optical sheets 11 and 21, it is desirable that the prism crest be on the light guide plate 1 side.

  Light shielding sheets 12 and 22 having light exit windows 12a and 22a that define light exit areas of the double-sided light emitting device A are laminated on the outermost layers on the front surface 1a side and the back surface b side of the light guide plate 1, respectively. The light exit window 12a is set to a size corresponding to the liquid crystal display panel on the main side, and constitutes a large light exit window. The light exit window 22a is set to a size corresponding to the sub-side liquid crystal display panel, and constitutes a small light exit window.

  As shown in FIG. 2A, the light exit window 22a is formed at a position overlapping the light exit window 12a in plan view. For this reason, when the double-sided light emitting device A is viewed from the main side, the sub-side light emitting area (light exit window 22a) may emerge (become dark) and show-through may occur. For this reason, in this embodiment, show-through is reduced by setting the color of the light guide plate 1 side surface (hereinafter referred to as an inner surface) of the light shielding sheet 22 to gray. The principle will be described below.

  FIG. 2B is a cross-sectional view of the double-sided light emitting device A. In the figure, for convenience of explanation, the sheets are stacked with a gap, but in actuality, they are stacked densely. Now, the light from the light source 2 propagates through the light guide plate 1 and exits from the front surface 1a and the back surface 1b. Here, since the light exit window 22a is smaller than the light exit window 12a and overlaps, a part of the light emitted from the back surface 1b is reflected by the inner surface of the light shielding sheet 22 (arrow a) and passes through the light guide plate 1 again. Then, light is emitted from the surface 1a. However, since such reflection does not occur in the area of the light exit window 22a, when the double-sided light emitting device A is viewed from the main side, the sub-side light emission area (light exit window 22a) becomes dark and show-through occurs.

  This show-through appears prominently when the luminance on the main side is improved, for example, when the reflectance of the inner surface of the light shielding sheet 22 is set high. When the inner surface of the light shielding sheet 22 is made black, almost no reflected light disappears, so that the show-through is almost eliminated. However, in some cases, the show-through state is reversed (when the double-sided light emitting device A is viewed from the main side, the sub-side emission An area (light emission window 22a) becomes brighter. In addition, the luminance on the main side is significantly reduced. Therefore, in this embodiment, the inner surface of the light shielding sheet 22 is gray, thereby reducing the light reflectance of the inner surface of the light shielding sheet 22 and generating a certain amount of reflected light to ensure a certain amount of luminance on the main side. Show-through can be reduced.

  Thus, in this embodiment, since the color of the inner surface of the light shielding sheet 22 on which the small light exit window 22a is formed is gray, the light reflected from the light shield sheet 22 and emitted from the large light exit window 12a is suppressed. . Therefore, show-through is reduced. Further, since the reflection on the inner surface of the light shielding sheet 22 is not completely restricted, the luminance of the light emitted from the large light exit window 12a is not significantly impaired.

  The gray density on the inner surface of the light shielding sheet 22 is desirably set according to the luminance on the sub side. More preferably, it is set according to the luminance ratio between the luminance on the sub side and the luminance on the main side. When the luminance on the sub side is substantially the same as that on the main side, the density is made higher (closer to black) and the reflectance is relatively lowered. When the brightness ratio on the main side and the sub side are substantially equal, show-through is likely to appear prominently, so prevention of show-through is given priority over the brightness on the main side.

  When the luminance on the sub side is lower than that on the main side, the gray density is made lighter (closer to white) and the reflectance is relatively increased. When the sub-side is low in the luminance ratio between the main side and the sub-side (when the main side has a higher luminance than the main-side and sub-side luminance ratios), the show-through will not be noticeable. Give priority to the brightness on the main side.

  When the luminance on the sub side is higher than that on the main side, the gray density is made lighter (closer to white) and the reflectance is relatively increased. When the luminance ratio between the main side and the sub side is higher than the main side, the show-through does not appear remarkably. In practice, however, the sub side is hardly set to be much brighter than the main side.

  In summary, when making the luminance on the sub side higher than that on the main side, the gray density is made relatively light according to the degree, and also when the luminance on the sub side is made lower than that on the main side Accordingly, it is desirable to make the gray density relatively light in accordance with the above, and to make the gray density relatively high as the luminance approaches between the sub side and the main side.

  The light shielding sheet 22 is made of, for example, a PET film. As a method of setting the inner color to gray, it is desirable to use a gray PET film. However, there are few products with different densities in the market, and since light is transmitted to some extent when it is a single gray color, it is light-shielding. It may be inferior. Therefore, the light shielding sheet 22 is configured by laminating a black sheet 222 and a milky white translucent sheet 221 laminated on the light guide plate 1 side with respect to the black sheet 222 as shown in FIG. It is desirable to do. Examples of the sheets 221 and 222 include a PET film. Then, by preparing a plurality of types of semi-transparent sheets 221 having different transparency, it is possible to easily obtain the light shielding sheets 22 having different gray densities. The translucency of the translucent sheet 221 can be set by, for example, the thickness of the sheet and the amount of milky white pigment mixed in the transparent sheet base material. By stacking with the sheet 222, a gray color having an arbitrary density can be obtained.

Second Embodiment
FIG. 3A is an exploded perspective view of a double-sided light emitting device A ′ according to another embodiment of the present invention, and FIG. 3B is a cross-sectional view of the double-sided light emitting device A ′. In FIG. 3B, as in FIG. 2B described above, the sheets are stacked with a gap for convenience of explanation, but in actuality, they are stacked densely. Moreover, the same code | symbol is attached | subjected about the same structure as the double-sided light-emitting device A mentioned above in each figure, and description is abbreviate | omitted. Only different configurations will be described below.

  The double-sided light emitting device A ′ includes reflection sheets 31 and 32 that are stacked in a region straddling the boundary between the light source 2 and the light guide plate 1 (indicated by a line L2 in FIG. 3B). In the present embodiment, the reflective sheet 31 is laminated on the main side and the reflective sheet 32 is laminated on the sub side, but it is effective if they are laminated on at least one of the main side and the sub side. The reflection sheet 32 is made of, for example, a white PET film or a film in which silver is vapor-deposited on the surface on the light guide plate 1 side serving as a reflection surface, and preferably has a higher reflectivity on the reflection surface.

  Now, since the inner surface of the light shielding sheet 22 is gray, for example, the reflectance of the inner surface is inferior compared with the case where the inner surface is white, so that the light reflected by the inner surface and emitted to the main side is reduced. The luminance on the main side slightly decreases. In the present embodiment, by providing the reflection sheets 31 and 32, the light emitted upward and downward from the light source 2 is reflected by the reflection sheets 31 and 32, and is reflected on the light guide plate 1 as indicated by arrows in FIG. It becomes easy to enter and the brightness | luminance as a whole can be improved. Therefore, the luminance that is slightly reduced by making the inner surface of the light shielding sheet 22 gray can be improved without changing the light source 2 to a high output light source.

  Further, the reflection sheets 31 and 32 are disposed so as not to overlap the large light exit window 12a. In FIG. 3B, the line L1 indicates the position of the edge of the light exit window 12a on the light source 2 side, and the edge of the reflection sheets 31 and 32 opposite to the light source 2 is closer to the light source 2 than the line L1. Is set. In this way, when the double-sided light emitting device A ′ is viewed from the main side, the edges of the reflection sheets 31 and 32 can be prevented from being raised or shaded.

It is a disassembled perspective view of the double-sided light-emitting device A which concerns on one Embodiment of this invention. (A) is a perspective view after lamination | stacking of each structure of the double-sided light-emitting device A, (b) is sectional drawing of the double-sided light-emitting device A, (c) is a figure which shows the structural example of the light shielding sheet 22. FIG. (A) is an exploded perspective view of a double-sided light emitting device A 'according to another embodiment of the present invention, and (b) is a cross-sectional view of the double-sided light emitting device A'.

Explanation of symbols

A, A ′ Double-sided light emitting device 1 Light guide plate 2 Light source 11, 21 Optical sheet 12, 22 Light shielding sheet 31, 32 Reflective sheet

Claims (5)

An optical sheet and a light shielding sheet having a light exit window for defining a light exit area are respectively laminated on the front and back surfaces of a light guide plate having a light source disposed on the side, and the light exit window is a large light exit window and the large light exit window. In a double-sided light emitting device consisting of a small light exit window formed at a position overlapping with the window,
A double-sided light emitting device characterized in that the color of the light-shielding sheet-side surface of the light-shielding sheet on which the small light-emitting window is formed is gray. The light shielding sheet on which the small light exit window is formed,
The double-sided light emitting device according to claim 1, wherein a black sheet and a milky white translucent sheet laminated on the light guide plate side with respect to the black sheet are laminated.   3. The double-sided light emitting device according to claim 1, wherein the gray density is set according to a luminance of light emitted from the small light exit window. 4.   The reflective sheet laminated | stacked in the area | region straddling the boundary of the said light source and the said light-guide plate, This reflective sheet is arrange | positioned so that it may not overlap with the said large sized light emission window. The double-sided light-emitting device in any one.   The double-sided light emitting device according to any one of claims 1 to 4, wherein the optical sheet is a prism sheet, and a prism crest surface of the prism sheet is on the light guide plate side.

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