JP3030792B2 - 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 of a laptop or book type word processor or computer. Such a backlight has a one-light type 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, and as shown in FIG. A two-light type edge light system in which a linear light source such as a fluorescent tube is provided at two opposing ends of an optical light guide plate is often used. For this edge light system, as shown in FIG. 2 or FIG. 4, a light diffusing material having a refractive index greater than the light guide plate material on one surface of the light guide plate is partially coated, substantially the entire surface of the surface Are often arranged so as to be covered with a light diffusion reflector.

In particular, recently, the backlight is driven by a battery, and further improvement in power consumption-luminance conversion efficiency is desired. Therefore, a reflector having a high reflectivity is used for a light reflector covering a linear light source. It has been proposed to provide a light guide plate or a reflector having a high reflectance on a surface of a 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 a linear top ridge is formed on the light exit surface side of a translucent material partially coated with a light diffusing substance. Are arranged, but the directivity of light becomes stronger, and the above-mentioned back-up with high power consumption-luminance conversion efficiency is provided in the vicinity of the normal direction which is substantially dropped on the light emitting surface. I found it to be a light.

That is, according to the present invention, one wide surface of a light guide plate made of a translucent material is partially coated with a light diffusing substance having a higher refractive index than that of the light guide plate material, and the surface is mirror-finished or light reflected. In a panel backlight, which is covered with a plate and has a linear light source adjacent to at least one side end of the light guide plate, the light guide plate has a linear ridge at a fine interval on the same surface on a light emitting surface side. prisms with is a sheet made of a transparent material having a large number in a state in which the top ridge is substantially parallel to the top edge surface is on the outside, related to one or more the arranged panel backlight light exit surface side It is. Next, the present invention will be described in detail with reference to the drawings. FIG. 5 is a perspective view of one embodiment of an edge light type having a light source at one end of a light guide plate, and FIG. 6 is a sectional view thereof. Similarly, FIG. 7 is a perspective view of one embodiment of an edge light type having light sources at two ends of a light guide plate, and FIG. 8 is a cross-sectional view thereof.

In FIG. 1, reference numeral 1 denotes a light guide plate, which may be any substance that can efficiently transmit light, such as quartz, glass, or a translucent natural or synthetic resin such as an acrylic resin. The light diffusing substance (6 in the figure) applied to the light guide plate is a pigment having a high refractive index and a large diffuse reflectance compared to the material of the light guide plate, for example, a paint containing titanium white, a printing ink, or the like.
These are printed in dot form on the light guide plate surface by a method such as screen printing.

Reference numeral 4 denotes a linear light source.
A light reflector 5 having a gap (slit) for allowing light to enter the end of the light guide plate is covered with a gap of a certain width from the light source surface of the linear light source, and at least the light guide plate The light guide plate is installed near the one end surface so that the central axis thereof is substantially parallel to the end surface of the light guide plate. Examples of the linear light source include a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, and the like, but a fluorescent tube is preferable. It is preferable that the length of the light guide plate is substantially equal to the length of the end portion.

A mirror surface or a light reflecting plate, for example, a light diffusing reflecting plate (3 in the figure) is disposed so as to cover almost the entire surface of the light guiding plate coated with the light diffusing substance. Arranging so as to cover almost the entire remaining end face portion that is not performed is further advantageous in that light utilization efficiency and uniform planar light emission are obtained.

Reference numeral 7 denotes a sheet (hereinafter simply referred to as a sheet) made of a light-transmitting material, which has a large number of straight top ridges parallel to each other at minute intervals on the same surface, and whose top ridge surface is outside (to the light guide plate). By arranging it so that it is on the opposite side to the opposite surface), it changes the directivity of the light emitted from the light emitting surface of the backlight, and makes the directivity closer to the normal direction dropped on the light emitting surface stronger. is there. The linear top ridge may be arranged so as to be parallel to the central axis of the linear light source,
They may be arranged at right angles.

In the present invention, one or more sheets are used. For example, when two sheets are used, the top ridge surfaces of both sheets are outside so that the straight top ridges are orthogonal to each other. The effect of the present invention is further increased by superimposing. The dot-shaped light diffusing substance printed on the light guide plate surface (6 in the figure)
If necessary, a light diffusing plate (2 in the figure) may be disposed between the sheet and the light guide plate so that the dot pattern cannot be identified.

As described above, the present invention is characterized in that a sheet made of a translucent material having a shape satisfying certain conditions is arranged on the light emitting surface side of the backlight.

The conditions in the present invention will be described in more detail. The sheet (7 in the figure) is not particularly limited as long as it is made of a light-transmitting material. Examples of the sheet include methacrylate, polycarbonate, polyvinyl chloride, and polystyrene. , Polyamide, polyethylene terephthalate (PE
T) and the like, polyester, polyethylene, polypropylene, cellulose resin glass and the like.

In the sheet used in the present invention, the shape of the prism formed on the light exit surface side and having linear top ridges parallel to each other is a so-called prism shape having two or more optical planes as shown in FIG. The top ridge (8 in the figure) where the two optical planes intersect is linear, and a large number of linear prisms parallel to each other at minute intervals (P in the figure) are present in the same plane. It is. The apex angles of these ridges formed on the sheet have substantially the same shape, which means that the apex angles have substantially the same angle when cut under the same conditions around the vertex. Means that.

In the present invention, the apex angle (9 in the figure) of the top ridge of the sheet is preferably 70 to 150 degrees. The more preferable angle range of the apex angle depends on the refractive index of the material of the sheet to be used and the light distribution characteristics of the planar light emitter to be used. For example, a material having a large refractive index (polycarbonate,
When the refractive index n = 1.59) is used, the apex angle is preferably 90 degrees rather than 70 degrees, and 120 degrees is more preferable than 90 degrees.
When the angle exceeds 50 degrees, the effect of the present invention decreases,
For example, when the light emitted from the planar light emitter is substantially concentrated within 45 degrees from the normal direction dropped on the light emitting surface,
The apex angle is preferably 100 to 140 degrees.

It is particularly preferable to use prisms of the sheet having substantially the same length of the oblique sides from the vertices in order to improve the effect of the present invention. In addition, the distribution state of the large number of linear prisms formed on the sheet is such that the light emitted from the surface makes it difficult for the interval between the linear prisms to be visually recognized. Ridge spacing is 10-100
It is preferably 0 μm. The thickness (t2 in the figure) of the linear prism portion of the sheet is determined by the apex angle of the top ridge and the interval between the top ridges. A thickness (t1 in the figure) is required to maintain a proper positional relationship, and it is better that this thickness is thinner in order to reduce the light transmittance and the thickness of the backlight. From the viewpoint of strength and strength, the total thickness (T in the figure) of the sheet is 10 to 3000 μm, preferably 5 to 3000 μm.
0 to 1000 μm is good. Further, the linear prisms formed on the same surface preferably have the same shape more effectively.

The method of forming the sheet used in the present invention is not particularly limited, and for example, a linear prism having substantially the same shape by a method such as die molding by hot pressing, embossing, mold processing, chemical treatment, or the like. Any method can be used as long as it can be formed so as to have a large number of in parallel with each other at minute intervals. In addition, a slight droop occurs on the top ridge for manufacturing reasons, but it may be within a range where the effects of the present invention can be recognized.

In a liquid crystal display, the contrast becomes lower as the angle of viewing from the normal direction dropped on the display surface becomes larger, so that the luminance near the normal direction is regarded as important in practical use. Further, since the viewfinder is viewed only from the normal direction lowered onto the display surface, the luminance near the normal direction is regarded as important in practical use.

In the present invention, as described above, when a sheet having a large number of linear prisms parallel to each other at a minute interval on the light emitting surface side is arranged on the light emitting surface of the backlight, light directivity appears. . That is, when measuring the luminance of light emitted from the surface in the normal direction substantially lowered to the light emitting surface,
Brightness is increased as compared with the case where the sheet is not arranged, and a certain angle with respect to a normal line dropped on the light emitting surface;
For example, the luminance measured in the same direction from the direction of 40 degrees has a decreasing rate that is substantially larger than the luminance measured in the normal direction (for example, approximately 50% of the luminance measured in the normal direction).
%), It can be seen that the above-described directivity of light appears.

Next, the operation of the present invention will be described in more detail with reference to the drawings. FIG. 10 is a view showing an example of ray tracing of a ray incident on a cross section of an arbitrary prism of a sheet from an arbitrary point when a sheet having a linear prism is used in the present invention.

Assuming that the apex angle of the prism is 2α (degree), the refractive index of a sheet made of a translucent material is n, and the refractive index of air is 1, the critical angle θc (degree) is θc = sin ^−1. (1 / n) 1) beam is incident at an angle theta ₁ (degrees), when emitted at the angle theta ₆ (degrees) (Fig. _{10) sinθ 1 = n × sinθ} 2 θ 3 = 90 ° -α-θ 2 incident n × sinθ ₃ = sinθ ₄ (provided that when the _{θ 3 ≦ θc) θ 5 =} 90 ° -α-θ 4 θ 6 = θ 5 2) beams are at an angle theta ₁ (degrees), the angle theta ₈ (degrees )) (FIG. 11) sin θ ₁ = n × sin θ ₂ θ ₃ = 90 ° −α−θ ₂ θ ₄ = θ ₃ (when θ ₃ > θc) θ ₅ = 2α−θ ₄ n × sin θ ₅ = sin [theta by ₆ (provided that when θ ₅ ≦ θc) by performing _{θ 7 = 90 ° -α-θ} 6 θ 8 = -θ 7 such calculations, translucent If the refractive index of the material used for the sheet made of the material and the apex angle of the prism are known, the emission angle can be determined from the angle of incidence of the light emitted from the light emitting surface of the backlight on the sheet made of the transparent material. Can be done. Although not shown in FIG. 10, depending on the above conditions, the incident light may be reflected inside the prism twice or more, or may return to the light exit surface of the backlight.

For example, as shown in FIG. 12, when the sheet is made of polycarbonate (refractive index n = 1.59) and the vertex angle of the prism is 90 degrees, the incident angle is 0 °.
The light rays incident on the sheet at a time are totally reflected inside the prism and returned to the backlight. The light rays returned to the backlight are partially absorbed inside the backlight, partially reflected, and emitted again from the light exit surface of the backlight.

Therefore, when the light emitted from the backlight is totally reflected inside the prism of the sheet and returned to the backlight again, the light absorption inside the backlight is reduced, and The higher the reflectivity of light inside the backlight, that is, the more the surface other than the light exit surface of the backlight is covered with the high-reflectance reflector, the more efficient the backlight.

Light rays incident on the sheet at an incident angle of 30 degrees exit the sheet at an exit angle of 0.5 degrees, and light rays incident on the sheet at an incident angle of 60 degrees are exit angles. 25.7
The light is emitted from the sheet at a given temperature. The light emitted from the light emitting surface of the backlight in this case is substantially concentrated most within an angle of approximately 40 degrees from the normal direction dropped on the light emitting surface, and as a result, measured from the normal direction. Brightness is
It increases compared to the case where the sheet is not provided.

Similarly, as shown in FIG. 13, when the sheet is made of polycarbonate and the apex angle of the prism is 120 degrees, the light is incident on the sheet at an incident angle of 0 degree. The emitted light exits the sheet at an exit angle of 22.7 degrees,
A light beam incident on the sheet at an incident angle of 30 degrees has an output angle of 1
Light emitted from the sheet at 1.2 degrees and incident on the sheet at an incident angle of 60 degrees exits the sheet at an output angle of 34.8 degrees. In this case, the light emitted from the light emitting surface of the backlight is substantially concentrated at an angle from the normal direction dropped to the light emitting surface substantially within approximately 44 degrees, and as a result, measured from the normal direction. The brightness increases as compared with the case where the sheet is not provided.

As described above, by controlling the apex angle of the prism of the sheet, it is possible to control the directivity of the light emitted from the light emitting surface of the planar light emitter.

[0028]

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.

[0029]

Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. 5 or thickness 2.0mm as shown in 6 rectangular light guide plate (225 mm × 127 mm) to the end of the short hand (in FIG. 1), cold cathode fluorescent tubes of the thickness of diameter 4.8 mm (Harrison Denki ( Normal tube manufactured by Co., Ltd.) (4 in the figure) is placed, and the inner surface of a cylindrical aluminum reflector having a slit of 2 mm at the portion in contact with the light guide plate is covered with a light diffusion film laminated on the inner surface. The light guide plate was arranged so as to enter the light guide plate from the end. On the other hand, a light-diffusing substance (paint containing titanium white) coating on the light guide plate surface (6 in the figure)
Is obtained by screen-printing a circular dot pattern at a pitch of 1.2 mm, and was prepared and used under the following conditions.
The point where the light diffusion substance coverage is the minimum (cold cathode fluorescent tube side)
6%, 80% at the maximum point, and these ratios were gradually increased in the middle.

Further, one light diffusion film (D-204, Tsujimoto Electric Co., Ltd.) (2 in the figure) was disposed on the light exit surface side of the light guide plate. In addition, light is diffused on the light guide plate
A reflector (3 in the figure) was arranged. The surface luminance when driving the cold cathode tube at a constant current by applying an alternating voltage of 30 KHz from the inverter to the normal direction dropped to the light emitting surface at a viewing angle of 2 degrees by a luminance meter (Topcon BM-7). When measured at a distance of 40 cm from the light emitting surface to the luminance meter, 19
It was ² cd / m ² (Comparative Example 1).

On the light-diffusing film, there are a large number of commercially available straight prisms each made of polycarbonate and having an apex angle of 90 ° parallel to each other, and the distance between adjacent top ridges of the straight prisms. The same apparatus, conditions, and conditions as those of Comparative Example 1 except that one sheet having a thickness of 360 μm processed so as to have an interval of 350 μm was arranged on the light emitting surface side of the backlight so that the linear prism was on the outside. The measured luminance was 307 cd / m ² (Example 1).

Furthermore luminance linear prisms other than arranged one to the light exit surface side of the backlight so that the inside of the actual Example 1 the same equipment and conditions, in manipulating and measured 15cd
/ M ² (Comparative Example 2). Further, the same operation and the same conditions as in Example 1 were performed except that a linear prism having a vertical angle of the prism-shaped protrusion of 70 degrees was used.
It was 45 cd / m ² (Example 2). Further, the same operation and the same conditions as in Example 1 were performed except that the vertex angle of the prism-shaped protrusion was set to 120 degrees, and the measured luminance was 330 cd / m.
² (Example 3).

Next, in order to examine the light distribution characteristics of the backlight, in Comparative Example 1, Example 1 and Example 2, an alternating voltage of 30 KHz was applied to the cold cathode tube from the inverter at a constant current. The surface luminance at the time of driving 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 lowered to the light exit surface as shown in FIG.
Change to 0 degree, distance from light emitting surface to luminance meter 40cm
FIG. 15 shows the values of the luminance when measured in the above. 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 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-light type 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 perspective view of one embodiment of the present invention.

FIG. 6 is a cross-sectional view of one embodiment of the present invention.

FIG. 7 is a perspective view of one embodiment of the present invention.

FIG. 8 is a cross-sectional view of one embodiment of the present invention.

FIG. 9 is a perspective view of a sheet used in the present invention.

FIG. 10 illustrates an example of ray tracing.

FIG. 11 is a diagram illustrating an example of ray tracing;

FIG. 12 is a diagram showing an example in the case of a prism apex angle of 90 degrees.

FIG. 13 is a diagram showing an example in the case of a prism apex angle of 120 degrees.

FIG. 14 is a conceptual diagram of a measurement method used in the present invention.

FIG. 15 is a diagram showing an angular distribution of emission light luminance;

[Explanation of symbols]

 1: light guide plate 2: light diffusion plate 3: reflection plate 4: linear light source 5: reflector 6: light diffusion material 7: sheet having a linear prism 8: linear top ridge 9: apex angle of prism 10 : Backlight 11: Luminance meter 12: Angle with respect to the normal direction dropped on the light emitting surface 13: Normal dropped on the light emitting surface

Claims (2)

(57) [Claims] 1. A light guide plate made of a translucent material is partially covered with a light diffusing substance having a higher refractive index than that of the light guide plate material, and the surface is covered with a mirror surface or a light reflection plate. ,
In a panel backlight having a linear light source adjacent to at least one side end of the light guide plate, a vertex angle of 70 to 1 is formed on the same surface on a light emitting surface side of the light guide plate at fine intervals.
A prism made of a light-transmitting material having a large number of prisms having a 50-degree linear top ridge in a state where the top ridges are substantially parallel to each other,
At least two sheets close to the light exit surface so that the top ridge is on the outside
Panel backlight with the top edge of the sheet to be placed almost orthogonal . 2. The distance between adjacent top ridges is 10
The panel backlight according to claim 1, wherein a sheet having a thickness of from 1000 to 1000 µm is used.