JP4324006B2 - Surface illumination element - Google Patents

Description

  The present invention relates to a surface illumination element suitable for an edge light type surface illumination device.

  In recent years, edge light type surface illumination devices have been frequently used as illumination means for display devices that are required to be thin, for example, liquid crystal display devices. As shown in FIG. 4, such an edge-light type surface illumination device includes a linear light source 131 that is surrounded by a light reflecting sheet 132 on the light incident surface 121 a of the light guide plate 121. The light diffusing sheet 122 is laminated on the light emitting surface 121b, and the reflecting sheet 123 is disposed on the light reflecting surface 121c of the light guide plate 121.

  However, in such an illuminating device, the light from the light source 131 is diffused over a wide range by the light guide plate 121. Therefore, luminance unevenness tends to occur as the illumination area increases, and in particular, the vicinity of the light source 131 tends to become bright. In particular, bright lines K (lines with high-luminance portions) are generated along the linear light source 131, which makes it difficult to interpret the display. The direct light reflected by the light reflecting surface 121c is also a factor, but the light reflected by the reflecting sheet 132 mainly near the end of the light emitting surface 121b of the light guide plate 121 is light reflecting surface 121c. It has been found that the main factor is to concentrate at a predetermined position.

In order to prevent the generation of the bright line K, the applicant of the present application has proposed that the reflection-reducing member 104 colored in the vicinity of the linear light source is provided on the surface of the light guide plate 121 as shown in FIG. Application No. 6-109982.
JP-A-6-289390

  However, if the color of the reflection reducing member provided in the belt shape is thin, the effect of reducing the bright line is small. On the other hand, if the color is black, the bright line can be reduced, but the boundary of the presence or absence of the reflection reducing member is clear and reflected. It has been found that a black belt-like line appears along the reduction member, thereby degrading the display quality.

  Therefore, an object of the present invention is to provide a surface illumination element suitable for a surface illumination device that can improve display quality with little luminance unevenness.

The surface illumination element of the present invention includes a linear light source, a light guide having a light incident surface disposed close to the linear light source, a light reflecting member surrounding the linear light source, and light of the light guide. A light diffusing sheet disposed on the light emitting surface, wherein an end of the light reflecting member is fixed in contact with the light emitting surface side of the light guide, and the light diffusing sheet. A light absorption layer for suppressing emission lines having a light absorption pattern in which the light absorption rate gradually decreases as the distance from the light incident surface is closer to the surface in contact with the light guide, close to the light incident surface. It is formed.

  In the present invention, since the light absorption layer having the light absorption pattern in which the light absorption rate gradually decreases as the distance from the light incident surface is provided on the surface of the light diffusion sheet that contacts the light guide, the light diffusion sheet is fixed to the light guide. Generation of bright lines caused by light reflected from the end of the light reflecting member can be suppressed, luminance unevenness can be reduced, and the boundary line of the light absorption layer can be made unclear to improve display quality.

  Embodiments of the present invention will be described below with reference to the drawings. The surface illumination device 1 is mainly configured by a surface illumination element 2, a light source 3, and a frame body (not shown) that integrates them, and is disposed on the back surface of a display device such as a liquid crystal display device.

  The surface illumination element 2 includes a light guide 21 made of a transparent and thin resin plate (thickness of about 1 to 4 mm) such as an acrylic resin, a light diffuser 22 laminated on the surface of the light guide 21, And a light reflector 23 laminated on the back surface of the light body 21.

  The light guide 21 has a light incident surface 21a as a side surface facing the light source 3, a light exit surface 21b as a surface that intersects the light incident surface 21a at a substantially right angle, and a back surface that faces the light exit surface 21b as light. The reflecting surface 21c is used. Although only one light guide 21 is shown, it may be formed by stacking a plurality of laminated light-transmitting flat plates, and the back surface constituting the light reflecting surface 21c has a spot-like shape. It is more preferable if coating or unevenness is provided to achieve uniform light scattering.

  The light diffusing body 22 is composed of a light diffusing sheet 22a having a thickness of about 0.1 mm covering almost the entire surface of the light guide 21, and more preferably a plurality of prisms on the light diffusing sheet 22a. The lens sheet 22b may be laminated.

  The light reflector 23 is made of a white sheet or a reflective sheet such as a thin aluminum sheet. In order to enhance the light diffusion and upward directivity effect, an extremely slight air layer is formed between the light reflector 21 and the light guide 21. And is fixed to the end of the light guide.

  The light source 3 includes a linear light source 31 composed of a fluorescent tube or a cold cathode tube arranged in parallel with the light incident surface 21a, and a semi-cylindrical silver deposition surrounding the linear light source 31 in a non-contact manner. Alternatively, a reflective sheet 32 made of aluminum foil is provided. The reflection sheet 32 is fixed by adhering or pressing both ends thereof to the light guide 21.

  A light absorption layer 4 is formed on one or both of the light emitting surface 21 b and the light reflecting surface 21 c of the light guide 21 so as to be close to the light source 31 and suppress the bright line. The light absorption layer 4 has a predetermined pattern having a black color or a color that can easily absorb light (more preferably, a color that facilitates light absorption of the light source 3) in a region or area from one side to the opposite side ( A light absorption pattern 41 that gradually decreases as the distance from the light incident surface increases) is formed by printing or the like. The pattern 41 has, for example, a dot pattern as shown in FIG. 2 (a), a gradient pattern as shown in FIG. 2 (b) so that the light absorption rate gradually decreases as the distance from the light incident surface increases. Although it is formed using a white circle pattern or the like as shown in FIG. 4C, other patterns in which the coloring area gradually decreases can also be adopted.

  The light absorbing layer 4 may be arranged by printing the light absorbing pattern 41 directly on the light emitting surface 21b or the light reflecting surface 21c of the light guide 21 or on the diffusion sheet 22a or the reflecting sheet 23. What has been printed or the like may be disposed in contact with the light emitting surface 21 b or the light reflecting surface 21 c of the light guide 21. Such a light absorption layer 4 does not need to be formed on the entire surface of the light emitting surface 21b and the light reflecting surface 21c of the light guide 21, and the thickness of the light guide 21, the size of the linear light source 31, and the light guide 21. In consideration of the distance between the light incident surface 21a and the like, the light incident surface 21a may be formed in a predetermined range.

  If the light absorption pattern 41 is directly formed on the light emitting surface 21b or the light reflecting surface 21c adjacent to the light incident surface 21a of the light guide 21, the end of the reflection sheet 32 fixed to the light guide 21 is formed. It can be covered with the light absorption pattern 41, and light reflection by the end of the reflection sheet 32 can be effectively prevented to suppress generation of bright lines.

  In addition, the light absorption pattern 41 is formed on the diffusion sheet 22a or the reflection sheet 23, and is disposed adjacent to the light incident surface 21a of the light guide 21 so as to overlap the light emission surface 21b or the light reflection surface 21c. For example, the diffusion sheet 22a and the reflection sheet 23 are thinner than the light guide 21 and have flexibility, so that the printing process and handling are facilitated, and the assembly workability can be improved.

  As a result of arranging the light absorbing layer 4 in this way, the surface luminance is as shown in FIG. 3A, and when nothing is applied as shown in FIG. 3B, as shown in FIG. The brightness near the light incident surface could be flattened as compared with the conventional one in which black solid printing was applied.

  In addition, although the said Example illustrated the case where the generation | occurrence | production of a bright line is prevented and arrange | positioning the light absorption layer 4, it replaces with the light absorption layer 4 as another Example, and is the same even if it uses a narrow light-diffusion sheet. There is an effect. The light diffusing sheet is made of a material having an optical function of diffusing incident light in a random direction, and the upper and lower surfaces of the light guide 21 close to the light source 3, preferably the light guide 21 and the light reflector 23. Is disposed within a predetermined range, for example, a range equivalent to the reflection reducing member 104 shown in FIG. Conventionally, light having a critical angle of 42 degrees or more with respect to the light emitting surface 21c of the light guide 21 made of acrylic resin goes out of the light guide 21 and is reflected by the light reflector 23 to cause bright lines. However, by arranging the light diffusing sheet, this light can be randomly diffused to prevent generation of bright lines.

It is a side view which shows one Example of this invention. (A)-(c) is explanatory drawing which shows the example of a pattern for light absorption of the Example. It is a brightness | luminance characteristic view of the Example. It is a side view which shows a prior art example. It is explanatory drawing which shows the example of the pattern for the conventional light absorption.

Explanation of symbols

2 surface illumination element 21 light guide 21a light incident surface 21b light exit surface 21c light reflection surface 22 light diffuser 23 light reflector 3 light source 31 linear light source 32 reflection sheet 4 light absorption layer 41 pattern for light absorption

Claims (1)

A linear light source;
A light guide whose light incident surface is arranged close to the linear light source;
A light reflecting member surrounding the linear light source ;
A light diffusion sheet disposed on the light exit surface of the light guide;
In a surface illumination element comprising:
The end of the light reflecting member is fixed in contact with the light emitting surface side of the light guide,
On the surface side of the light diffusion sheet in contact with the light guide, a light absorption layer for suppressing emission lines having a light absorption pattern in which the light absorption rate gradually decreases as the distance from the light incident surface increases. A surface illumination element formed near the surface.

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