JP3528261B2 - Backlight for panel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight for a panel which illuminates a transmissive or semi-transmissive panel from the back side.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a thin and easy-to-read backlight mechanism has been used as a display device for a laptop type or notebook type word processor, a computer or the like. . In such a backlight, as shown in FIG. 1, at one end of a light-transmitting light guide plate,
A one-lamp type edge light system in which a linear light source such as a fluorescent tube is provided, and a two-lamp type edge light system in which a linear light source is provided at two opposite ends of a light-transmitting light guide plate as shown in FIG. Often used. In the case of this edge light method, as shown in FIG. 2 or 4, a light diffusing element having a function of diffusing light is formed on one surface of the light guide plate (for example, the refractive index is larger than that of the light guide plate material). (Partially covering the light diffusing substance, roughening the surface of the light guide plate, making holes in the light guide plate, etc.), arranging the light diffuser plate on the light exit surface of the light guide plate, and opposite the light exit surface of the light guide plate. Many are arranged so that the side surface is covered with a reflector.

The light guide plate used for such a backlight is for fixing the light guide plate and the components of the backlight (for example, a light diffusion plate, a light reflection plate, etc.) and a substrate of a transmissive or semi-transmissive panel. It is usual to have a hole or a contact (welding) portion (fixing / holding portion) in its peripheral portion.

In recent years, in particular, laptop and notebook type personal computers and word processors have been remarkably reduced in size and weight, and there is a strong demand for reduction in size and weight of the backlight, which is a component thereof, and the size of the light guide plate. That is, the size is made as close as possible to the size of the area in which planar light emission is performed (the area in which the light diffusing element is formed on the light guide plate, hereinafter referred to as the light emitting portion).

However, the light guide plate is usually used by being fixed to a component as a backlight (for example, a light diffusing plate, a light reflecting plate) or a substrate of a panel, and as a means for this, a screw or a rivet is used. Holes for inserting etc.,
Alternatively, a portion for adhesion or welding is required in addition to the light emitting portion. Therefore, in many cases, protrusions (for example, 7 and 8 in FIG. 5) are formed on the periphery of the light guide plate and used for fixing them.

The light incident on the light guide plate is repeatedly reflected on the inner surface of the light guide plate and travels in a predetermined direction. When the light guide plate has a protruding portion as described above, the light enters the portion, As a result, there is a problem that the brightness in the vicinity of the light emitting portion close to the protrusion becomes small, the brightness of the light emitting portion of the light guide plate including other portions becomes non-uniform, and further the luminous efficiency is lowered.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an edge light type backlight which can be firmly fixed and can obtain a uniform luminance surface.

[0008]

As a result of various studies on the above problems, the inventors of the present invention have found that the light on the light emitting surface near the protrusion of the light guide plate has a function of fixing the light guide plate and the like. It has been found that by changing the diffusion function under certain conditions, it is possible to provide a backlight for a panel in which the luminance distribution of the entire light emitting portion is uniform even if the light emitting region approaches the protruding portion.

That is, according to the present invention, a linear light source is provided on at least one of the side end portions of the light guide plate made of a translucent material, and a light source is provided on one surface of the light guide plate. A light diffusing element having a function of diffusing is formed so that its function becomes larger as the distance from the linear light source increases, and a light diffusing plate is provided on the light emitting surface side of the light guide plate, and light is reflected on the surface side opposite to the light emitting surface. In a panel backlight in which a plate is arranged, a light guide plate having one or more protrusions is used, and a light diffusing element on the surface of the light guide plate close to the protrusions is densely formed at least as compared with the vicinity thereof. For backlights for automobiles.

Next, the present invention will be described in more detail with reference to the drawings. The basic configuration of the present invention is, for example, a perspective view of FIGS.
It is similar to that shown in the sectional view. In the figure, 1 is a light guide plate, which may be any substance that allows light to pass efficiently, such as quartz,
Examples of the material include glass and translucent natural or synthetic resin such as acrylic resin.

The light diffusing element referred to in the present invention means an element having a light diffusing function, and this light diffusing function can be expressed based on the haze value of the light guide plate. For example, the light guide plate having the light diffusing element has a haze value larger than that of the same light guide plate having no light diffusing element. The haze value referred to here is a value measured according to JIS-K7105.

The method of forming the light diffusing element is to print the light diffusing substance in a dot shape directly on the light guide plate surface, to roughen the light guide plate surface, or to provide a large number of small holes on the light guide plate surface. In the figure, the light diffusing function is formed so as to become denser as the distance from the light source increases.
When a light-scattering substance is used for the light guide plate to provide a light-diffusing function, paint or printing ink containing a pigment with a high diffuse reflectance (such as titania) is used, and these are guided by a screen printing method. Dots are printed on the light plate surface.

The mirror surface or the light reflecting plate (3 in the figure) is arranged so as to cover almost the entire surface of the light guide plate opposite to the light emitting surface, and the remaining end face of the light guide plate which is not brought close to the linear light source. It is even better to dispose so as to cover almost the entire surface of the part in terms of light utilization efficiency and uniform planar light emission.

Reference numeral 2 denotes a light diffusing plate which scatters and allows the light emitted from the light guide plate surface to pass therethrough. In the present invention, one or more light diffusing plates are used.

Reference numeral 4 denotes a linear light source (rod-shaped light source), and in a preferred embodiment, a light reflector 5 having a gap (slit) at the end of the light guide plate for allowing light to enter, and the light source surface of the linear light source. It is covered with a gap of a certain width, and is installed close to at least one end face of the light guide plate such that its central axis is substantially parallel to the end face of the light guide plate. The linear light source may be a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, or the like, but a fluorescent tube is preferable, and from the viewpoint of power saving, the length of the uniform light emitting section excluding the electrode section is close to each other. It is preferable that the length is substantially equal to the length of the end portion of the light guide plate.

FIG. 5 shows an example of a light guide plate in which a component as a backlight and a function of fixing to a substrate of a transmissive or semi-transmissive panel are provided outside a light emitting portion. Reference numerals 7 and 8 in the drawing denote other constituent elements of the backlight or projections having holes for inserting and fixing screws or rivets to the substrate of the transmissive or semi-transmissive panel, and 9 in the drawing shows light diffusion. A portion in which an element (6 in the drawing) is formed, that is, a light emitting portion is shown. Reference numeral 10 in the drawing denotes a reflector provided on the outer side (end surface) of the protruding portion. At the protruding portion protruding from the side surface of the light guide plate, the light traveling in the light guide plate becomes complicated due to its shape, and the end face thereof may emit more light than necessary. Therefore,
The above-mentioned reflector (10 in the figure) is effective in preventing light loss in this portion. The reflector may cover at least a portion corresponding to the thickness of the end face around the protrusion.

FIG. 6 and FIG. 7 are schematic views of an embodiment showing the state of the light diffusing element formed in the portion close to the protrusion on the surface of the light guide plate, and 9 indicates the light emitting portion, and in this example, , 11 in FIG. 6 and 12 in FIG. 7 (the portions where the straight lines intersect in the drawing), the light diffusion function is changed from that of the other portions. That is, it is essential in the present invention that the light diffusing function is large (the light diffusing elements are densely formed) as compared with the vicinity thereof. When forming the light diffusing element more densely than in the vicinity of the surroundings, the haze value may be increased by the ratio of (luminance value of peripheral portion / luminance value of dark portion) × dark portion.

A method of increasing the light diffusing function on the surface of the light guide plate in the vicinity of the protruding portion as compared with other portions is, for example,
The light-diffusing element has a function of diffusing light larger than the surrounding area, that is, a side in contact with the light-emitting portion of the projecting portion is the bottom side, and is formed to have a peak in the vertical direction of the light-emitting portion. This is a method of printing the light diffusion material in a dot shape on the inner portion of the formed chevron or roughening the surface of the light guide plate. That is, when printing the light diffusion material in dots,
The covering rate (density) per unit area is made larger than that in the vicinity of the surroundings, and if the method is roughening, the proportion of roughening is also made large.

A guide for the area of the portion (the range shown by 11 in FIG. 6 and 12 in FIG. 7) in the vicinity of the protrusion formed on the light guide plate in the light guide plate surface where the light diffusion elements are densely formed. Is 0.5-of the area of one surface of the protrusion (7, 8).
An area corresponding to 5 times is preferable in order to make the entire brightness uniform. Further, the degree of densely forming the light diffusing elements is such that the density of the light diffusing elements in the vicinity of the protruding portion formed on the light guide plate is at least 1.5 times higher than the density in the vicinity of the periphery thereof. It is also preferable to form the density (coverage) within the range in order to make the entire brightness uniform. Further, depending on the positional relationship with the linear light source, the top of the above-mentioned mountain shape does not always coincide with the center line when the side in contact with the light emitting portion of the protrusion is regarded as the bottom side as shown in FIG.

In the present invention, when the light diffusing elements are made dense, it is preferable that the degree of the light diffusing elements is continuously changed as smoothly as possible, and the density is gradually increased from the peripheral portion where the light diffusing elements are present. Is preferable (therefore, in this case, the density of the light emitting portion of the light guide plate is maximized in the substantially central portion of the portion facing the protrusion).

The present invention is used by installing a transmissive or semi-transmissive display panel such as a liquid crystal panel on the upper surface of the light diffusion plate.

[0022]

Industrial Applicability According to the present invention, an extremely large and uniform light emitting portion can be obtained as compared with the area on the light emitting surface side of the light guide plate, so that the present invention can be used as a backlight which is small in size and light in weight and uniform in planar light emission.

[0023]

EXAMPLES Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. A rectangular light guide plate with a thickness of 3 mm (215 mm
A cold cathode fluorescent tube with a diameter of 3 mm is arranged at the long end of (160 mm), and a light diffusion film is laminated on the inner surface of a cylindrical aluminum reflector having a slit of 3 mm in the portion in contact with the light guide plate. The light source was covered with the light source and arranged so that the light emitted from the slit enters the light guide plate from the end portion of the light guide plate.

On the other hand, the light-diffusing substance (paint containing titanium white) coated on the surface of the light guide plate (the back surface of the light guide plate) was formed by screen-printing circular dot patterns under the following conditions. The light-diffusing material coverage is 6% at the minimum point on the light source side (1.8% in haze value) and 80% at the maximum point at the end of the light guide plate opposite to the light source (haze value). 58%),
In the middle, the plots were made so that these ratios would gradually increase. The size of the light emitting area (light emitting part) is 213 mm ×
It is 157 mm.

Further, one light diffusion film (Tsujimoto Denki Seisakusho D-204) was arranged on the light exit surface side of the light guide plate. A light diffusive reflector was arranged on the surface of the light guide plate other than the light entrance face and the light exit face. At a portion of the side surface of the light guide plate near the cold cathode fluorescent tube, a width of 5.3 mm with a hole having a diameter of 2.5 mm for inserting a screw for fixing the light guide plate as shown in FIG. 6, A 5 mm long protrusion is provided. A similar protrusion having a width of 10 mm and a length of 5 mm is provided at the end of the light guide plate on the opposite side of the cold cathode fluorescent tube. The distance from the end of the light guide plate to the light emitting portion was about 1 mm.

The surface luminance when an alternating voltage of 30 KHz is applied to the cold cathode tube by an inverter and driven by a constant current,
With a luminance meter (Topcon BM-8), the viewing angle is 0.2 degrees, and the distance from the light emitting surface to the luminance meter (attachment lens tip) is 12 mm with respect to the direction normal to the light emitting surface. The result of measurement in the direction is shown in FIG. 9 (a) (the vertical axis represents the luminance ... Relative value, and the horizontal axis represents the distance in the arrow direction.
The dotted line in the figure shows the average luminance of the whole). When the state of planar light emission at this time was visually observed, the luminance of the portion 11 in FIG. 8 was lower than that of the surrounding light emitting portion (9 in the figure) (Comparative Example).

Next, in order to make the light diffusing function of the portion 11 in FIG. 8 larger than that of the vicinity thereof, that is, the diameter of the dot of the light diffusing substance coated on the surface of the light guide plate is 10 to 250 μm.
By changing in the range of, the coverage of this part is 12 to 20%
FIG. 9B shows the results measured by operating under the same apparatus and conditions as those of the comparative example except that the haze value was set to 2.9 to 6.3% (the vertical axis represents luminance ... Relative value, horizontal axis). Indicates the distance in the direction of the arrow. The dotted line in the figure indicates the average luminance of the whole). The area of the portion where the light diffusing function was changed was substantially the same as the area of the projecting portion (7 in the figure, but including the area of the hole portion). Further, the coverage of the portion other than the portion 11 in FIG. 8 was around 12%. Further, similar results were obtained for the portion (12 in the figure) corresponding to the protrusion (8 in the figure) at the end farthest from the light source of the light guide plate shown in FIG. In this case, a reflection plate (10 in the figure) is provided outside the protruding portion, and the coverage is set to 78% (the coverage other than 12 in the drawing is 78 to 100% ... 57 to 90% in haze value). ). In addition, the state of planar light emission at this time was visually observed, and as a result, it was a state of uniform planar light emission (Example).

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a one-light type edge light type backlight.

FIG. 2 is a cross-sectional view showing an example of a one-lamp edge-light type backlight.

FIG. 3 is a perspective view showing an example of a two-light type edge light type backlight.

FIG. 4 is a cross-sectional view showing an example of a two-light type edge light type backlight.

FIG. 5 is a diagram showing a light guide plate having a protrusion.

FIG. 6 is a diagram showing a state of a light diffusing element on a surface of a light guide plate which is close to a protrusion.

FIG. 7 is a diagram showing a state of a light diffusing element on a surface of a light guide plate which is close to a protrusion.

FIG. 8 is a diagram showing a state of a light diffusing element on a surface of a light guide plate which is close to a protrusion.

FIG. 9 is a diagram showing the brightness of the light guide plate surface.

[Explanation of symbols]

1: Light guide plate 2: Light diffusion plate 3: Light reflector 4: Linear light source 5: Light reflector 6: Light diffusion element 7: Protrusion part for contact (melt) wear 8: Protrusion part for welding (melting) 9: Light emitting part 10: Reflector provided outside the protruding portion 11: Range where the light diffusion function is larger than that of the vicinity 12: Range where the light diffusion function is larger than that of the vicinity 13: Brightness measurement direction 14: Brightness measurement direction

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/13-1/141 G02B 6/00 F21V 8/00

Claims (6)

(57) [Claims] 1. A light guide plate made of a translucent material, which has a linear light source adjacent to at least one of the side surface end portions thereof, and has a function of diffusing light on one surface of the light guide plate. A light diffusing element having a function increasing as the distance from the linear light source increases, and a light diffusing plate is arranged on the light emitting surface side of the light guide plate and a light reflecting plate is arranged on the surface side opposite to the light emitting surface. In the backlight for a panel, a light guide plate having one or more protrusions is used, and the light diffusion element on the light guide plate surface close to the protrusion is formed densely at least as compared with the light diffusion elements in the vicinity thereof. Backlight for panel. 2. The backlight according to claim 1, wherein the protruding portion of the light guide plate has a function of fixing the light guide plate. 3. The area of the surface of the light guide plate on which the light diffusing elements are densely formed, in the vicinity of the protrusion formed on the light guide plate, corresponds to 0.5 to 5 times the surface area of one surface of the protrusion. The backlight according to claim 1. Wherein the light diffusing element of the projection vicinity formed on the light guide plate, at least around the vicinity claims 1 to 3 was formed to a density of 1.5 times or less in the range greater than the density of the noise
The backlight for a panel according to item 1 . 5. A panel backlight according to end faces of at least the projecting portion on any one of claims 1 to 4 coated with a light reflecting plate of the light guide plate. 6. The light-diffusing element is selected from a light-diffusing dot-like material, a rough surface, and small holes.
The backlight according to any one of 5 above.