JPH09184925A - Light guide plate device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a dark part at the end part of the light emitting surface of a light guide plate on the side of its light incidence end surface. SOLUTION: This light guide plate 1 has the incidence end surface 1A where light from a light source 2 is made incident as its one end surface, the top surface of the light guide plate 1 is a light emitting surface 1B, and the reverse surface of the light guide plate 1 is a reflecting surface 1C, and the light guide plate 1 decreases in plate thickness gradually with the distance from the light incidence end surface 1A. At the end part of the light emitting surface 1B on the side of the light incidence end surface 1A, a material 10 is provided which is larger in refractive index than the light guide plate 1. A part of light which enters the light guide plate 1 from the light source 2 through the light incidence end surface 1A is made incident on the material 10, diffused and reflected by the surface of the material 10 and inside it, and then emitted to the outside directly from the light projection surface 1B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate device used for a backlight for a liquid crystal display device, a backlight for signs such as advertisements, and a lighting fixture.

[0002]

2. Description of the Related Art A light guide plate device used for a backlight of a liquid crystal display device is, for example, as shown in FIGS.
The light guide plate 31, the light source 32, the reflector 33, the control sheet 34, the reflection plate 35, and the like are included. A transparent resin plate is used for the light guide plate 31, one end surface is a light incident end surface 31A on which light from the light source 32 is incident, an upper surface is a light emitting surface 31B, and a lower surface is a reflecting surface 31C. .

Further, recently, in order to reduce the weight and improve the light output efficiency (light emission efficiency), the light guide plate 31 has a so-called "wedge shape" in which the plate thickness gradually becomes smaller as the distance from the light incident end face 31A increases. Is. By the way, if the light guide plate 31 is an acrylic resin plate, the maximum refraction angle of the light incident from the light incident end face 31A is about 42 °. Therefore, the light incident on the light guide plate 31 is totally reflected once or a plurality of times by the light emitting surface 31B and the reflecting surface 31C, and then, at a refraction angle of about 70 ° from the light emitting surface 31B, as shown in FIG. Is emitted to
As shown in FIG. 5, the traveling direction can be changed by the control sheet 34 to a substantially front direction of the light guide plate device, that is, the liquid crystal display device.

[0004]

Therefore, the light emitting surface 31B is formed.
In the end portion on the light entrance end face 31A side of
The light incident from is rarely emitted directly,
At the above-mentioned end, the light incident from the light incident end surface 1A is almost totally reflected. Therefore, the light incident end surface 3 on the light exit surface 31B is
At the end portion on the 1A side, the amount of emitted light is small, and as shown in FIG. 11, a band-shaped dark portion (luminance unevenness) 37 occurs. The dark portion 37 becomes thinner as it goes away from the light source 32, but as shown in FIG.
Obviously, it is visible, but since it is visible on the liquid crystal screen, there is a problem that the image quality of the liquid crystal screen is degraded.
An object of the present invention is to provide a light guide plate device that can solve the above problems.

[0005]

To achieve the above object, the light guide plate device of the present invention is characterized in that at least one end face of the light guide plate is a light incident end face on which light from a light source is incident. The light guide plate has an upper surface as a light exit surface and a lower surface of the light guide plate as a reflection surface, and the thickness of the light guide plate gradually decreases as the distance from the light incident end surface increases. The point is that a material having a refractive index higher than that of the light guide plate is provided at the end portion on the light end face side.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of an embodiment in which the present invention is applied to a liquid crystal display device (in addition, it can be applied to an advertisement and a lighting fixture) will be described with reference to the drawings of FIGS. . Note that in the following description, "upper and lower" will be referred to as FIG.
2 will be described as a reference, the light guide plate device may be used in an upside-down state of FIG. 1 and FIG.
FIG. 1 shows an edge type light guide plate device, which is mainly composed of a light guide plate 1, a light source 2 arranged on one side of the light guide plate 1, a reflector 3, a control sheet 4, a reflection plate 5, and the like. There is.

As shown in FIG. 2, the light guide plate 1 has a rectangular shape,
Alternatively, it is formed into a substantially rectangular plate shape, and is made of a transparent resin plate such as acrylic, polystyrene, polycarbonate, vinyl chloride, methacrylic resin (for example, polymethylmethacrylate (PMMA)), or a transparent glass plate. The shape of the light guide plate 1 is arbitrary and is not limited to the above shape. In order to improve the light output efficiency, an ink containing titanium oxide, silica or the like, or a diffusing material such as fine particles may be mixed inside the light guide plate 1. The light guide plate 1 has an end face on the light source 2 side as a light incident end face 1A on which light is incident, and has a wedge-shaped cross section, and its plate thickness increases as the distance from the light incident end face 1A, that is, the light source 2 increases. Formed to become gradually smaller,
The weight of the light guide plate 1 is reduced and the light output efficiency (light emission efficiency) is improved. The upper surface (front surface) of the light guide plate 1 is a horizontal light emitting surface (light emitting surface, emission surface) 1B, and the rear surface is an inclined reflecting surface 1C.

The light output surface 1B is a rough surface over the entire surface (or substantially the entire surface), and the maximum height roughness (Rmax), which is the difference between the highest point and the lowest point of the cross-sectional curve, is, for example, about 1.
It is set to be 10 μm. The roughening is performed by matte-finishing (mat finish) by sandblasting, chemical etching or the like, unevenness formation, grain formation, and the like. The light guide plate 1 is molded in the mold by injection molding, casting or the like. At the time of molding, the light guide plate 1 corresponds to the rough surface in the mold in order to simultaneously form a rough surface on the light guide plate 1. The inner surface may be roughened as described above. In addition, the light emitting surface 1B is a mirror surface and the Rmax thereof is 0.3 μm or less, or the Rmax of the light emitting surface 1B is about 0.3 to 1.
It may be set to μm. The "mirror surface" means "a smooth surface that specularly reflects". In addition, the following "rough surface"
The "mirror surface" is defined in the same manner as above, and the "rough surface" described below is processed in the same manner as above.

The reflecting surface 1C is a mirror surface over the entire surface (or substantially the entire surface), and its Rmax is, for example, 0.3 μm.
m or less. In addition, Rmax of the reflecting surface 1C is set to about 0.3 to 1 μm, and further, the reflecting surface 1C is set to Rma.
There may be a rough surface state in which x is about 1 to 10 μm.

Except for the light incident end surface 1A of the light guide plate 3
A light-shielding tape (edge tape, reflection tape) 6 (not shown) is attached to the end faces to prevent light leakage from the three end faces. A linear light source such as a fluorescent lamp or a cold cathode discharge tube (cold cathode tube) is used as the light source 2, but a point light source such as a lamp or an LED may be used side by side. The reflector (reflector, reflective film, reflective cover, reflective plate, light-shielding cover) 3 is made of, for example, a silver vapor deposition film attached to the inner surface of a polyethylene film, and the light of the light source 2 is prevented from leaking to the outside. Cover the outer circumference
doing. The reflector 3 may be formed by forming a white coating layer on the inner surface of a polyethylene film, or the reflector 3 may be a part of a white case that houses (stores) the light guide plate 1.

As shown in FIG. 3, the control sheet 4 changes the traveling direction of the light emitted from the light exit surface 1B of the light guide plate 1 to a substantially front direction of the light guide plate device (liquid crystal display device). It is in contact with (or close to) 1B over the entire surface (or almost the entire surface) and is made of, for example, a transparent resin film such as a polycarbonate film. The control sheet 4 is formed by integrally forming an upper flat plate-shaped main body portion 7 and a plurality of lower control portions (prism portions) 8. The control units 8 are arranged in parallel in a direction from the light incident end surface 1A side of the light guide plate 1 toward the opposite end surface thereof, and have a cross section in the form of an inverted isosceles triangle and project downward.

The reflector 5 is in contact with (or close to) the reflective surface 1C of the light guide plate 1 over the entire surface (or substantially the entire surface). The reflection plate 5 is formed by evaporating aluminum (Al), silver (Ag), or the like on the upper surface of a white film such as polyethylene terephthalate (PET), and the upper surface of the reflection plate 5 is a mirror surface. The reflection plate 5 may be a diffuse reflection plate composed of only the white film.

By the way, a light emitting means for emitting light (light emission) from the end of the light emitting surface 1B of the light guide plate 1 on the light incident end surface 1A side is provided as follows. That is, the substance 10 is provided over the entire surface (substantially the entire surface) of the reflection surface 1C of the light guide plate 1 at the end portion on the light incident end surface 1A side.
The substance 10 is adhered (fixed) to the reflecting surface 1B, and its refractive index is set to be higher (higher) than the refractive index of the light guide plate 1. For example, when the light guide plate 1 is PMMA, The refractive index is set to 1.49 or more. The substance 10 is used as a double-sided tape or as an adhesive (glue), and the reflective surface 1C is used.
Alternatively, the reflection plate 5 may be adhered to the light guide plate 1 with the substance 10.

According to the embodiment configured as described above, in the light guide plate device, the light from the light source 2 is incident (light incident) into the light guide plate 1 from the light incident end surface 1A of the light guide plate 1. The light incident on the inside of the light guide plate 1 has a light emitting surface 1B and a reflecting surface (however,
The part corresponding to substance 10 is excluded. ) 1C, while repeating the total reflection, the light travels inside the light guide plate 1 toward the end face 1D of the light guide plate 1 opposite to the light incident end face 1A. In this case, the upper surface of the reflection plate 5 is a mirror surface and the reflection surface 1 of the light guide plate 1 is
If it is in contact with C, the light incident on the reflecting surface 1C is totally reflected with almost no loss. Therefore, the light output efficiency (light emission efficiency) does not decrease due to the light input / reflection on the reflection surface 1C, and the brightness of the light guide plate device can be improved. If the reflection surface 1C of the light guide plate 1 is a mirror surface, it is possible to further reduce loss when light is reflected on the reflection surface 1C, improve light output efficiency, and improve brightness of the light guide plate device.

By the way, of the light guided to the light exit surface 1B of the light guide plate 1 as described above, the light guided at a critical angle or less is emitted (emits or emits) to the outside. In addition, the light emitting surface 1
Since B is a rough surface, a part of the light guided to the light output surface 1B at a critical angle or more is also diffused on the light output surface 1B and emitted to the outside. When the light guide plate 1 is an acrylic resin plate, the refraction angle of the emitted light with respect to the light emitting surface 1B is about 70.
°. As described above, the traveling direction of the light emitted from the light emitting surface 1B is controlled by the control unit 8 of the control sheet 4 as shown in FIG. 3, and the traveling direction of the light guide plate device (liquid crystal display device) is controlled. It can be changed (or changed in angle) to the front direction.

Further, a part of the light incident on the inside of the light guide plate 1 is
It is incident on the portion of the reflecting surface 1C corresponding to the substance 10. At this time, since the refractive index of the substance 10 is higher than that of the light guide plate 1, the light incident on the reflecting surface 1C is not reflected by the reflecting surface 1C but is incident on the substance 10 and is reflected on the surface of the substance 10 or inside the substance 10. After being diffused and reflected, the light enters the light guide plate 1 again. As described above, the light diffusely reflected on the surface of or inside the substance 10 is incident on the inside of the light guide plate 1. Therefore, a part of this incident light is incident on the end portion of the light exit surface 1B on the light incident end surface 1A side. , Is incident at an angle smaller than the critical angle and is emitted to the outside.
Since the light exit surface 1B is a rough surface, part of the light guided to the light exit surface 1B at a critical angle or more is also diffused on the light exit surface 1B and emitted to the outside.

The light from the light source 2 is the light source 2 of the substance 10.
After being incident on the inside from the end face on the side, a part of the incident light is similar to the above, in the light emitting surface 1B,
The light is emitted to the outside from the end on the light incident end face 1A side. As described above, the traveling direction of the light emitted from the end of the light exit surface 1B on the light entrance end surface 1A side to the outside is also controlled by the control sheet 4 in the same manner as above. As described above, the substance 10 allows the light from the light source 1 to be emitted from the end on the light incident end face 1A side of the light emitting surface 1B, and the amount of light emitted from the end can be made larger than in the conventional case. A band-shaped dark portion (luminance unevenness) does not occur at the end portion, and the image quality of the liquid crystal screen can be improved. In the light guide plate, a square, circular, or linear diffuse reflection portion is formed on the reflection surface of the light guide plate by a dot-shaped gradation pattern whose area gradually increases as the distance from the light incident end surface increases, The present invention can also be applied to a light guide plate device having the above light guide plate.

FIG. 4 shows a first comparative example of the present invention, which is a modification of the light emitting means of the present invention, in which the end of the reflection plate 5 on the side of the light incident end face 1A is the reflection face 1C of the light guide plate 1. And the distance from the reflecting surface 1C increases toward the light incident end surface 1A side.
It is inclined with respect to the reflecting surface 1C. It should be noted that if a corner portion is formed on the base end portion 13A of the separating portion 13, it will cause abnormal light emission, so the base end portion 13A is curved.
Note that the separating portion 13 may have a curved protruding shape downward as shown by a virtual line in FIG.

By the way, in order to maintain a state in which the separating portion 13 of the reflecting plate 5 is separated from the light guide plate 1, a holding portion 15 projects downward at an end portion of the lower surface of the light guide plate 1 on the light incident end face 1A side. Formed integrally with each other.
3, the end portion on the light incident end surface 1A side is adhered.
In order to maintain the state where the separating portion 13 of the reflection plate 5 is separated from the light guide plate 1, a transparent smooth sheet or a satin-like sheet made of PET or the like is interposed between the light guide plate 1 and the reflection plate 5. Good.

According to the first comparative example, the light from the light source 2 passes through the holding portion 15 and is reflected by the separating portion 13 of the reflecting plate 5, or is reflected by the separating portion 13 and the light guide plate 1. After repeating total reflection between the surfaces 1C, the light is incident on the end portion of the light exit surface 1 on the light entrance end surface 1A side, and is emitted to the outside as in the present invention.

FIG. 5 shows a second comparative example of the present invention, in which the reflecting surface 1C of the light guide plate 1 has a rough surface 17 at the light incident end surface 1A side to form a light emitting means. There is.

In the second comparative example, the reflecting surface 1 of the light guide plate 1 is
In C, since the reflection state is different between the rough surface 17 and other portions, there is a problem that the boundary portion between the two is visually recognized. FIG. 6 shows a third comparative example of the present invention, and in order to solve the above problem, the entire reflecting surface 1C of the light guide plate 1 is made a rough surface.

By the way, in the conventional wedge-shaped light guide plate, the reason why a dark portion is generated at the end of the light exit surface on the light entrance end face side is further considered. In the conventional light guide plate, the light exit surface is a horizontal plane. Therefore, even if the light entering the inside of the light guide plate is reflected by the light exit surface, the inclination angle of the reflected light with respect to the horizontal plane does not change. However, since the reflecting surface is inclined by a predetermined angle (for example, θ), every time the light entering the light guide plate is reflected by the reflecting surface, the tilt angle of the reflected light with respect to the horizontal plane is only 2 °. , Becomes big. It is considered that such an optical path difference of the reflected light on the light emitting surface and the reflecting surface causes a dark portion at the end portion on the light incident end surface side of the light emitting surface.

7 and 8 show a fourth comparative example of the present invention, in which both the light emitting surface 1B and the reflecting surface 1C of the light guide plate 1 are inclined with respect to the horizontal plane by the same inclination angle θ, and By eliminating the difference, a dark portion does not occur at the end of the light exit surface 1B on the light entrance end surface 1A side.
The light emitting surface 1B and / or the reflecting surface 1C are subjected to rough surface processing or printing for diffuse reflection as shown in FIG. As a result, the brightness and the uniformity of the brightness are improved, and the boundaries of the lights that are first reflected by the light emitting surface 1B and the reflecting surface 1C are blurred when they are emitted to the outside.

[0025]

As described in detail above, according to the present invention,
A band-shaped dark portion does not occur at the end portion of the light exit surface of the light guide plate on the light entrance end surface side, and the image quality of the liquid crystal screen can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional explanatory view showing an example of an embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a main part of FIG. 1;

FIG. 3 is an enlarged explanatory view of a main part of FIG.

FIG. 4 is a cross-sectional explanatory view showing a first comparative example of the present invention.

FIG. 5 is a cross-sectional explanatory view showing a second comparative example of the present invention.

FIG. 6 is a sectional explanatory view showing a third comparative example of the present invention.

FIG. 7 is a cross-sectional explanatory view showing a fourth comparative example of the present invention.

FIG. 8 is an enlarged explanatory diagram of the light guide plate of FIG.

FIG. 9 is a cross-sectional explanatory view showing a conventional example.

FIG. 10 is an explanatory sectional view showing a conventional example.

FIG. 11 is an explanatory plan view showing a conventional example.

[Explanation of symbols]

 1 Light guide plate 1A Light entrance end face 1B Light exit face 1C Reflective surface 2 Light source 10 Material

Claims (1)

[Claims] 1. At least one end surface of the light guide plate is a light incident end surface on which light from a light source is incident, an upper surface of the light guide plate is a light exit surface, and a lower surface of the light guide plate is a reflection surface. In a light guide plate device in which the plate thickness gradually becomes smaller as the distance from the light entrance end face increases, a material having a refractive index larger than that of the light guide plate is provided at the end of the reflecting surface on the light entrance end face side. Characteristic light guide plate device.