JP3284208B2 - Backlight - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a panel backlight for irradiating a transmissive or transflective panel from the back.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a thin and easy-to-see backlight mechanism has been used as a display device such as a laptop or book type word processor or computer. As such a backlight, an edge light system in which a linear light source such as a fluorescent tube is provided at one end of a light-transmitting light guide plate as shown in FIG. 1 is often used. In the case of this edge light method, as shown in FIG. 2, one surface of the light guide plate is partially coated with a light diffusing substance having a higher refractive index than that of the light guide plate material, and almost the entire surface is mirror-reflected. Alternatively, many are arranged so as to be covered with a light diffusion reflector.

In particular, recently, the backlight is driven by a battery, and it is desired to further improve the power consumption-luminance conversion efficiency. Therefore, a reflector having a high reflectance is arranged on the light reflector covering the linear light source. In addition, it has been proposed to provide a high-reflectance reflective plate on the light guide plate partially covered with a light diffusing substance.

However, in any of the above-mentioned methods, although the power consumption-luminance conversion efficiency is improved, it is still insufficient, and further improvement is desired.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight having high power consumption-luminance conversion efficiency and high luminance.

[0006]

As a result of various studies on the above points, the present inventors have found that in an edge light type backlight, at least one light emitting surface is incident on the light emitting surface of the light guide plate. If a film made of a translucent material with a rougher surface than the surface (light guide plate side) is arranged, the light distribution characteristics of the backlight will change, and the directivity of light in the direction of the normal dropped onto the light emitting surface will be stronger. It has been found that a backlight having the above-described power consumption-luminance conversion efficiency is high with respect to the normal direction substantially dropped on the light emitting surface.

That is, according to the present invention, a light diffusing substance having a refractive index value equal to or less than the light refractive index of the light guide plate material is partially coated on one wide surface of the light guide plate made of a light transmissive material. A light-diffusing function is applied to the surface, and the surface is covered with a mirror surface or a light-diffusing reflector, and in a panel backlight having a linear light source adjacent to at least one side end of the light-guiding plate, The present invention relates to a panel backlight in which at least one light-emitting surface is made of a light-transmitting material whose surface is rougher than that of a light-entering surface (light guide plate side).

Next, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention, and FIG. 2 is a view showing an example of an edge light type backlight. In the figure, reference numeral 1 denotes a light guide plate, which may be any substance that allows light to pass therethrough efficiently, such as quartz, glass, or a translucent natural or synthetic resin such as an acrylic resin. Reference numeral 2 denotes a film made of a light-transmitting material whose light exit surface is rougher than the light entrance surface (light guide plate side). The light distribution characteristic of light emitted from the light guide plate is changed, and the normal direction is lowered to the light exit surface. To enhance the directivity to In the present invention, one or a plurality of such films are used, but as can be seen from the embodiments of the present invention, when a plurality of, for example, two, films are used, the luminance is further improved.

The present invention is characterized in that a film made of a light-transmitting material whose light exit surface is rougher than the light incident surface (light guide plate side) is disposed on the light exit surface of the light guide plate.

The above-mentioned conditions in the present invention will be described in more detail. The above-mentioned film (2 in the figure) is made of a light-transmitting material whose light exit surface is rougher than the light entrance surface (light guide plate side). Is not particularly limited as long as it is a light-transmitting material such as acrylic, polycarbonate, glass, or the like. The method of forming a rough surface when the light emitting surface is rough is not particularly limited, and for example, a method of forming a rough surface by a method such as embossing, sand blasting, die molding by hot pressing, or chemical treatment. The light incident surface (light guide plate side) does not need to be particularly consciously roughened, but it is sufficient if the light exit surface is rougher than the light incident surface (light guide plate side) as a result. .

In the present invention, the state of the rough surface is as follows:
For example, as a result of measurement by a method specified in JIS B0601, it can be determined from, for example, 10-point average roughness, center line average roughness, and the like referred to in the same specification.

The condition of the rough surface on the light-emitting surface side of the film made of a translucent material used in the present invention is not particularly limited, and its shape does not need to be particularly regular. However, the rough guide is, for example, when observing the rough surface state on the light-emitting surface side of the film with a microscope with a magnification of 100 times, the surface is formed in an uneven state, and the normal direction descended to the light-emitting surface The step between adjacent concave and convex, or the distance between adjacent concave and concave or convex and convex in the horizontal direction with the light emitting surface is 10 μm to 10
It is a preferable state that it is in the range of 00 μm. The state of the rough surface on the light-emitting surface side of the film used in the present invention will be further described in another expression.In any cross section of the film, the light-emitting surface side has a convex shape, for example, a prism shape or a convex lens shape. It has a similar triangular pyramid shape,
The apex angle of the shape is 40 to 170 degrees, preferably 80 to 1
50 degrees.

In a liquid crystal display, the contrast decreases as the viewing angle increases from the direction of the normal dropped on the display surface. Therefore, the luminance near the direction of the normal is emphasized in practical use. In the present invention, as described above, when a film in which the light exit surface is rougher than the light entrance surface is disposed on the light exit surface of the light guide plate, the luminance of light emitted from the light guide plate is amplified, and the directivity of light is also increased. Is further strengthened. That is, when the luminance of light emitted from the surface is measured in the normal direction substantially lowered to the light exit surface, when the film is not disposed, or when a film whose exit surface is less rough than the entrance surface is disposed. In comparison with the case where the brightness is amplified, the brightness similarly measured from the direction of a certain angle with respect to the normal dropped on the light emitting surface, for example, 60 degrees, is substantially measured in the normal direction. Since the rate of decrease becomes larger than the luminance at the time of performing the measurement (for example, the luminance decreases to approximately 50 to 60% of the luminance measured in the normal direction), the directivity of the light is further enhanced. You can see that. The luminance meter used here is a commercially available luminance meter generally used.

Also, if necessary, the dot-like pattern of the dot-like light diffusing substance (6 in the figure) printed on the light guide plate surface, which will be described later, cannot be discriminated by the human eye. A light diffusion plate may be arranged between the film and the light guide plate.

The light diffusing substance applied to the light guide plate is a pigment having a refractive index equal to or smaller than the material of the light guide plate and having a large diffuse reflectance, for example, a paint containing silica or barium sulfate, a printing ink, or the like. is there. These are printed in dot form on the light guide plate surface by a method such as screen printing. Further, a light guide plate having a light diffusing function by making small holes directly on the surface is used. Mirror or light diffuse reflector (3 in the figure)
Is disposed so as to cover almost the entire surface of the light guide plate coated with the light diffusing substance. Reference numeral 4 denotes a linear light source. In a preferred embodiment, a light reflector 5 having a gap (slit) for allowing light to enter the end of the light guide plate has a gap of a certain width from the light source surface of the linear light source. The light guide plate is installed so that its central axis is substantially parallel to the end surface of the light guide plate.

The linear light source includes a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, and the like. The fluorescent tube is preferable, and the length of the uniform light emitting portion excluding the electrode portion is preferable from the viewpoint of power saving. Is preferably equal to the length of the end of the adjacent light guide plate.

The main part of the present invention has such a structure and is used as a backlight of a panel, especially a liquid crystal panel. In the present invention, it is preferable to adopt the following configuration.

1) The light diffusing substance applied to the light guide plate of the present invention is:
Although the dots are formed in the form of dots, ie, dots, the shape of the dots is not particularly limited, and may be any of a circle, a square, and an intersection line. These are applied on intersections (grids) of orthogonal lines having a certain interval imaginary on the light guide plate, and the interval between the orthogonal lines is preferably 0.5 to 3 mm, more preferably 0.8 to 2 mm. It is appropriately selected according to the thickness of the light guide plate.

Further, it is preferable that the light diffusing substance is coated on the light guide plate at a coverage of 1% to 50% in the vicinity of the linear light source portion and 20% to 100% in a portion farthest from the light source. ,
As the distance from the light source increases, it is preferable to cover the linear light source from the light source such that the coverage gradually increases starting from the coating point on one side end where the linear light source is brought closer. Further, in the vicinity of the end of the light guide plate opposite to the linear light source, the coverage may be equal to or smaller than the previous coverage. The term “coverage” as used herein refers to the ratio of the light scattering substance covering area applied per unit area of the light guide plate surface.

2) In the present invention, more preferably, the above-mentioned increase of the light diffusing material coverage (Y) is increased by 1 to the distance (X) from the linear light source to the light diffusing material on each grid.
7 to 3.5 increases to fall following ranges, namely, the vertical axis Y, when the X in the horizontal axis, Y = lines and Y = aX ^3.5 represented by aX ^1.7 (where a is the guide It is a value obtained from the coverage of the end of the light plate surface, and increases with a value between a line represented by 0 <a ≦ 2), or Y = a ^x (a is the same as described above) 1 <a ≦ 2
).

3) Further, according to the present invention, on the light emitting surface, the coverage of the light diffusing substance coated on the grid in a state parallel to the axis of the linear light source is set at the center (that is, the line) on the parallel line. It is preferable that the coating is formed so that the distance from the center of the shape light source in the longitudinal direction to the light diffusion material in the direction from the line on the light guide plate perpendicular to the linear light source to both ends is gradually increased. The present invention is used by installing an optical display panel such as a liquid crystal panel on the upper surface of the light emitting surface.

[0023]

The present invention is relatively small, can obtain sufficient luminance, and has a low power consumption in the normal direction dropped on the light exit surface.
It can be used as a backlight with high luminance conversion efficiency.

[0024]

Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. A rectangular light guide plate (225 mm × 127 mm) having a thickness of 2.0 mm as shown in FIG.
A cold-cathode fluorescent tube (normal tube manufactured by Harrison Electric Co., Ltd.) having a thickness of 8 mm is arranged, and a light diffusion film is laminated on the inner surface of a cylindrical aluminum reflector having a 2 mm slit at a portion in contact with the light guide plate. It was arranged so that the light emitted from the slit would enter the light guide plate from the end of the light guide plate. On the other hand, the light diffusing substance (paint containing silica) to be coated on the light guide plate surface was obtained by screen printing a circular dot pattern, and was prepared and used under the following conditions. The light diffusion material coverage is 7% at the minimum point and 80% at the maximum point.
%, And in the middle, these ratios are plotted so as to be sequentially increased.

Further, one film made of polycarbonate having a thickness of about 200 μm and having a light exit surface rougher than the light entrance surface (light guide plate side) by embossing was disposed on the light exit surface side of the light guide plate. Regarding the unevenness of the light emitting surface when the film was observed with a microscope having a magnification of 100, the level difference between adjacent concaves and convexes in the normal direction dropped on the light emitting surface was 10 μm or more.
The distance between the concave and the concave or the convex and the convex adjacent to the light emitting surface in the horizontal direction was 10 μm to 800 μm.

The surface (rough surface) of the film was measured for roughness according to JIS B0601. That is, the recording longitudinal magnification is 500 times, the recording lateral magnification is 50 times, and the driving speed is 0.3 mm.
/ Sec, measured under conditions of 5 μmR diamond at the tip of the stylus. The result is that the maximum height (Rmax) of the rough surface is 85 μm,
The 10-point average roughness (Rz) was 60 μm, and the center line average roughness (Ra) was 13 μm. Similarly, a recording vertical magnification of 20
00x, recording lateral magnification 50x, drive speed 0.3mm / sec,
As a result of measuring the roughness of the non-rough surface of the film under the condition of a stylus tip of 5 μmR diamond, Rmax was 12
μm, Rz were 7 μm, and Ra was 1 μm.

The surface luminance when the cold cathode tube was driven at a constant current by applying an alternating voltage of 30 KHz from the inverter was lowered to the light emitting surface at a viewing angle of 2 degrees by a luminance meter (Topcon BM-7). It was 211 cd / m ² when measured at a distance of 40 cm from the light emitting surface to the luminance meter with respect to the normal direction (Example 1).

The same procedure as in Example 1 was carried out except that a normal light-diffusing film (D-204, Tsujimoto Electric Co., Ltd.), which had not been embossed, was placed between the film roughened by the embossing and the light guide plate. Operate on equipment, conditions,
The measured luminance was 210 cd / m ² (Example 2).

The surface roughness of the light-diffusing film of Example 2 was similarly measured at a recording longitudinal magnification of 2,000 and a recording lateral magnification of 50.
As a result of measurement under conditions of double, drive speed of 0.3 mm / sec, and the tip of the stylus at 5 μmR diamond, Rmax was 13 μm, R
z was 9 μm and Ra was 1 μm. Further, Example 1 was repeated except that two films similar to those used in Example 1 were arranged on the light exit surface side of the light guide plate, the light exit surface being rougher than the light entrance surface (light guide plate side). The luminance measured and operated with the same apparatus and conditions was 227 cd / m ² (Example 3).
The same apparatus and conditions as in Example 1 were used, except that one light diffusion film (Tsujimoto Electric Manufacturing Co., Ltd. D-204) was disposed on the light exit surface side of the light guide plate instead of the film roughened by embossing. Operated and measured brightness was 182 cd /
m ² (Comparative Example 1). In addition, the film was roughened by embossing used in Example 1, and the film was operated using the same apparatus and conditions as in Example 1 except that the roughened surface was disposed so as to face the light emitting surface of the light guide plate. And the measured brightness is 17
It was 6 cd / m ² (Comparative Example 2). Further, in Comparative Example 2, the same operation and conditions were used as in Example 1 except that the light diffusion film (Tsujimoto Electric Works D-204) used in Example 2 was placed between the film and the light guide plate. The measured luminance was 174 cd / m ² (Comparative Example 3). Further, the same operation and conditions as in Example 1 were used, except that only two light diffusion films (Tsujimoto D-204) used in Example 2 were arranged on the light exit surface side of the light guide plate. And
The measured luminance was 179 cd / m ² (Comparative Example 4).

Next, in order to examine the light distribution characteristics of the backlight, in Examples 2, 3 and Comparative Examples 1 and 4, an alternating voltage of 30 KHz was applied to the cold cathode tubes from the inverter. The surface luminance when driven at a constant current was measured by a luminance meter (Topcon BM-7) at a viewing angle of 2 degrees, and the angle with respect to the normal direction dropped to the light emitting surface as shown in FIG. FIG. 4 shows the value of the luminance when measured at a distance of 40 cm from the light emitting surface to the luminance meter by changing the luminance to 70 degrees. From this figure, it can be seen that when the backlight of the present invention is used, the luminance increases and the directivity of light is remarkable.

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a backlight according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram of a measurement method used in the present invention.

FIG. 4 is a diagram showing the angular distribution of emitted light luminance in Example 2, Example 3, Comparative Example 1, and Comparative Example 4.

[Explanation of symbols]

1: a light guide plate 2: a film made of a light-transmitting material whose light exit surface is rougher than a light entrance surface (light guide plate side) 3: a specular reflection plate or a light diffusion plate 4: a linear light source 5: a light reflector 6 : Light diffusing substance 7: Backlight according to one embodiment of the present invention 8: Luminance meter 9: Angle with respect to the normal direction dropped on the light emitting surface

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/00 331 F21V 8/00 601 G02F 1/13357

Claims (2)

(57) [Claims] 1. A light guide plate made of a translucent material is partially coated with a light diffusing substance having a refractive index value equal to or less than the light refractive index of the light guide plate material on one wide surface of the light guide plate material, or light diffusing on the same surface. Applying a function, its surface is covered with a mirror surface or a light diffusion reflector, and in a panel backlight having a linear light source close to at least one side end of the light guide plate, the light guide plate has a light exit surface side. The state of the rough surface of the light emitting surface is constituted by irregular irregularities , and when the surface is observed with a microscope having a magnification of 100 times, the step between the adjacent concave and convex is 10 μm to 10 μm.
0 μm, the distance between adjacent dents or dents, or the distance between dents and projections is 10 μm
m to 800 μm, and the number of films made of a light-transmitting material having a rougher surface than the light-entering surface (light guide plate side) is reduced.
With one arranged panel backlight. 2. A light transmitting surface side surface of a film made of a translucent material is rougher than a light incident surface side (light guide plate side).
The state of the rough surface of the light emitting surface is constituted by irregular irregularities , and when the surface is observed with a microscope having a magnification of 100 times, the step between the adjacent concave and convex is 10 μm to 100 μm.
m, the distance between adjacent concaves and concaves or between convexes and convexes is 10 μm or more.
In the range of 800 μm, and when this is disposed on the light exit surface side of the light guide plate, the luminance of light emitted from the light exit surface of the light guide plate is measured from a normal direction substantially lowered to the light exit surface side of the film. The panel backlight according to claim 1, wherein a film that increases the amount of the light is used.