JP4299568B2 - Front light unit and liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention mainly relates to a front light unit of a reflective liquid crystal display device.
[0002]
[Prior art]
The reflective liquid crystal display device does not require auxiliary lighting in a bright environment such as outdoors, and has an advantage that power for lighting can be saved. As a method for irradiating the liquid crystal panel with light, a method using a light guide plate is generally used. In particular, a side-site method in which a light source is disposed on one end surface of a light guide plate and light is introduced into the light guide plate can be reduced in thickness and power consumption.
[0003]
[Problems to be solved by the invention]
FIG. 6 shows a liquid crystal display device using a front light unit having a conventional structure. In the figure, 1 is a front light unit, 2 is a light guide plate, 3 is a light source, 4 is a reflector, 8 is an AR film, 10 is a color filter substrate, 11 is a TFT substrate, 12 is a liquid crystal layer, 13 is a polarizing plate, 14 is Each holder frame is shown. The light emitted from the lamp of the light source 3 is reflected directly or by a reflector and incident from the incident end face of the light guide plate 2, and the light totally reflected by the prism surface provided on the upper surface of the light guide plate 2 is provided at the lower part of the light guide plate. The light modulated by the reflective liquid crystal device returns to the light guide plate again and is emitted from the prism surface to display an image.
[0004]
By the way, the reflector 4 is a thin metal plate of about 0.2 to 0.3 mm. When fitting the light guide plate 2 at the end of the reflector 4 as in the conventional example, if the end of the reflector 4 or the light guide plate 2 is warped, there are a portion where the reflector and the light guide plate are in contact with each other, and a portion where a gap is generated. Arise. FIG. 3 shows a cross section of the portion where the gap is generated. The numbers shown in the figure are the same as those shown in FIG. The light reflected by the light source 3 or the reflector 4 leaks directly from the gap (shown by a solid line arrow), or is reflected by the reflector portion projecting on the light guide plate 2 and enters the light guide plate (shown by a dotted arrow). There is a problem that the normal light reflected from the prism surface is superimposed on the light guide plate so that the periphery of the incident end of the light guide plate appears bright.
[0005]
In general, the light guide plate is often manufactured by injection molding or the like, and the corners of the light guide plate are rounded due to the bit shape at the time of mold manufacture. FIG. 4 shows the incident state of light on the light guide plate in the rounded portion. The numbers shown in the figure are the same as those shown in FIG. Of the light incident from the upper corner of the light guide plate, the light shown in the range A is not reflected by the prism surface on the surface of the light guide plate, but is reflected by the reflective liquid crystal and output to the display surface side. Luminance non-uniformity occurs where the periphery of the incident end becomes bright. In addition, among the light incident from the lower corner of the light guide plate, the light shown in the range B is directly output to the display side, and thus is observed as a bright line. And the light other than A and B will be multiple-reflected inside the light guide plate, but since this light is from the portion close to the fitting portion at the corner, it is as a light quantity compared to A and B. Only a small amount propagates through the light guide plate. Accordingly, when the corners are rounded, problems such as uneven brightness, generation of bright lines, and reduction in light amount occur.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-236290
[Means for Solving the Problems]
In order to solve the above problem, the following measures are taken.
In the first invention, the light guide plate is fitted using a housing that is thinner and has a stronger elastic strength than a reflector having a small elastic strength.
Both the reflector and the housing are formed of an elastic member. If the reflector is formed to be wider than the thickness of the light guide plate and the housing is formed to be narrower than the thickness of the light guide plate, the reflector is in contact with the housing. It fits in. That is, the opening of the reflector can be set to the widest range within the range subject to the restrictions of the housing. In addition, since the housing having high elastic strength engages the light guide plate, a gap is less likely to occur than when the reflector is engaged with the light guide plate.
[0008]
According to the second aspect of the present invention, the protrusion is provided in front of the portion of the housing to be engaged with the light guide plate. This protrusion can increase the thickness of the housing to increase the strength, fix the mounting position of the housing to the light guide plate, fix the position of the reflector relative to the housing, and stabilize the position setting of the light source. Since the protrusions cover the rounded corners at the incident end of the light guide plate, they also serve to prevent light from the light source from entering the light guide plate.
[0009]
In the third invention, an elastic member is inserted between the wall of the housing opposite to the light guide plate and the back surface of the reflector.
The elastic member presses the reflector against the projection of the housing, and the position of the reflector and further the position of the light source are fixed.
According to a fourth aspect of the present invention, the portion to be fitted with the light guide plate of the housing and the side surface (first side surface) on the light guide plate side of the projection are subjected to blackening treatment, and the upper surface of the projection is a reflection surface.
[0010]
Reflection at the fitting portion, which is a problem in the present invention, is suppressed, and the upper surface of the protrusion is made a reflective surface, which is equivalent to the reflector extending in the direction of the light guide plate and close to the incident end surface of the light guide plate. The optical coupling efficiency to the optical plate is increased. In addition, by blackening the first side surface of the protrusion, the light returned by reciprocating the light guide plate leaks out from the rounded corner at the incident end of the light guide plate and returns to the light guide plate again. prevent.
[0011]
A fifth invention is a liquid crystal display device in which the front light unit of any one of the first to fourth inventions is installed on the front surface of a reflective liquid crystal panel.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of the present invention. The numbers shown in the figure are the same as those in FIG. In addition, 6 is a projection provided on the housing 5, and 7 is an elastic body.
The reflector 4 is formed by bending an elastic quadrangular metal plate whose one surface is a reflecting surface along a cylinder. At this time, the width of the reflector opening (reflector plate thickening) is formed wider than the thickness of the end portion of the light guide plate.
[0013]
On the other hand, the housing 5 is formed by providing projections 6 in parallel from the ends of two opposing sides of a rectangular metal plate having elasticity, and bending it along a prism. Or you may bend along a cylinder. And the opening width | variety of the bent front-end | tip part is narrower than the thickness of a light-guide plate edge part.
In order to form the projection of the housing, the metal plate before bending is masked on the upper surface of the projection and a step is formed by etching, or a band-shaped metal corresponding to the projection is welded (electrical welding or laser welding). And the top part of a projection part is mirror-finished by grinding | polishing or plating. Further, a black paint is applied to the portion to be fitted with the light guide plate and the first side surface of the protrusion to form a light absorption film.
[0014]
The assembly process of the light source unit is shown in FIG. The numbers in the figure are the same as in FIG. Reference numeral 9 denotes a lamp holder 9. A lamp holder 9 is attached to the light source 3 and is along the concave surface of the reflector 4. The opening of the housing 5 is widened, and the reflector having the elastic body 7 and the light source is inserted through the opening of the housing. When the expansion of the housing opening is stopped, the force that closes the upper and lower sides of the housing suppresses the expansion of the reflector, and the elastic member presses the reflector against the housing opening side. Pressed against the inner side. Then, by making the elastic strength of the housing larger than that of the reflector, the housing is deformed in a direction to close the housing opening. The front light unit is completed by fitting the assembled housing with the light guide plate.
[0015]
FIG. 2 shows a second embodiment of the present invention. The numbers shown in the figure are the same as those in FIGS. As in the conventional example, a film such as an antireflection film or a polarizing plate is attached to the surface of the light guide plate facing the prism surface. In that case, in order to avoid the problem of bonding accuracy and peeling, the film is preferably pasted on the entire surface of the light guide plate. However, when the reflector is fitted with the light guide plate with the film sandwiched as in the conventional example, there is a problem that the transmission characteristics are deteriorated to the depth of the polarizing plate by the ultraviolet rays of the lamp. However, according to FIG. 2, since the light from the light source does not directly enter the polarizing plate, the characteristics are not deteriorated.
[0016]
【The invention's effect】
As described above, according to the present invention, the luminance unevenness caused by the reflected light at the fitting portion and the incident light from the display side edge portion of the light guide plate incident end is reduced, and the liquid crystal side edge portion of the light guide plate incident end is reduced. The generation of bright lines due to can be suppressed. Furthermore, the coupling efficiency between the light source and the light guide plate is increased by arranging the reflector so as to coincide with the upper surface of the protrusion and close to the incident end of the light guide plate.
[Brief description of the drawings]
FIG. 1 is a diagram showing details of a front light unit according to a first embodiment. FIG. 2 is a diagram showing details of a front light unit according to a second embodiment. FIG. 3 is a problem when there is a gap in a fitting portion. [FIG. 4] A diagram showing problems when the angle of the incident end face of the light guide plate is rounded. [FIG. 5] A diagram showing the assembly process of the light source unit. [FIG. 6] A diagram showing a conventional example of a front light unit. Explanation of]
DESCRIPTION OF SYMBOLS 1 Front light unit 2 Light guide plate 3 Light source 4 Reflector 5 Housing 6 Protrusion part 7 Elastic body 8 Film 9 Lamp holder

Claims (3)

In the front light unit, which is disposed on the display side of the liquid crystal display and includes a light guide plate, a light source, a reflector, and a housing that covers the reflector and fits into the light guide plate,
The reflector and the housing are elastic metal plates;
The housing part sandwiches the reflector and engages with the light guide plate, presses the first side surface of the projection provided on the housing part against the incident end of the light guide plate, and the second end surface of the projection part Press the end of the reflector,
An elastic member is provided between the reflector and the housing in order to press the reflector against the second side surface of the protrusion . Top reflecting surface of the projection portion provided in the housing, a front light unit of claim 1, wherein said plane fitted with the first side surface and the light guide plate of the projections, characterized in that a light absorbing surface. A liquid crystal display device comprising a reflective liquid crystal panel and the front light unit according to claim 1 .

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