JPH05323319A - Back light - Google Patents

Abstract

PURPOSE:To obtain the back light which has high electric power to brightness conversion efficiency, provides high brightness and has the directivity of the brightness by disposing >=1 sheets of sheets consisting of a specific light transparent material on the light exit surface side in the state that the peak ridges thereof parallel with the lateral direction of the panel. CONSTITUTION:A wire-shaped light source 4 is coated with a light reflector 5 having a spacing for incidence of light at the end of a light transmission plate in the state of having a spacing of a certain width from the light source surface of the wire-shaped light source 4 and is so installed that the central axis thereof is nearly parallel with the end face of the light transmission plate in proximity to the end face in a part of the light transmission plate. The light directional sheet 7 consisting of the light transparent material has the many straight peak ridges or projecting peak ridges 14 parallel with each other at fine intervals in the parallel state on the same plane and is, therefore, so disposed on the light exit surface side of the light transmission plate that the peak ridge surfaces exist on the outer side. This sheet 7 is so disposed that its peak ridges are paralleled with the lateral direction of the back light, i.e., the lateral direction when the sheet is disposed to face the display device using light transmission plate at the time of disposing the sheet on the light exit surface side of the light transmission plate.

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 or book type word processor, a computer or the like. For such a backlight, a one-lamp 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-lamp type edge light system is often used in which a linear light source such as a fluorescent tube is provided at two opposite ends of a light guide plate. In the case of this edge light system, as shown in FIG. 2 or 4, on one surface of the light guide plate,
In many cases, a light diffusing substance having a refractive index higher than that of the light guide plate material is usually partially covered, and the entire surface is covered with a light diffusing reflector.

Particularly, in recent years, since the backlight is driven by a battery, further improvement in power consumption-luminance conversion efficiency is desired, and a light reflector for covering the linear light source is provided with a reflector having a high reflectance. It has been proposed to dispose the light guide plate or to arrange a reflective plate having a high reflectance on the surface of the light guide plate which is partially covered with the light diffusing substance.

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

Further, as described above, not only the brightness conversion efficiency but also the range of good contrast of the liquid crystal display device is limited, and the word processor of the personal user is limited.
From the viewpoint of confidentiality, the display of a computer, a computer, or the like has been required to have a directivity of luminance so that it cannot be seen by a person diagonally behind. That is, it is a display device in which the brightness from a certain direction of the display device is further increased.

[0006]

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

[0007]

Means for Solving the Problems As a result of various investigations on the above points, the present inventors have found that a straight top edge or a convex portion is formed on the light emitting surface side of a light-transmissive material having a light diffusing property. A backlight in which a light-transmitting sheet having a large number of ridges is arranged in a certain direction has a stronger light directivity, and is substantially liquid crystal display in the vicinity of the normal direction dropped to the light exit surface. It has been found that the backlight has high power consumption-luminance conversion efficiency in a range where the device has a good contrast.

That is, according to the present invention, one wide surface of a light guide plate made of a translucent material is made to be light diffusive, and the surface is covered with a mirror surface or a light diffusive reflection plate, and at least one side surface end portion of the light guide plate is covered with the light diffusion plate. In a backlight for a panel having a linear light source close to, a prism or linear convex ridges having linear ridges at minute intervals on the same surface are provided on the light exit surface side of the light guide plate. In a state where the top edge is parallel to the left and right direction of the panel, that is, when the display device using the sheet is faced in a horizontal direction. The present invention relates to a panel backlight in which one or more sheets are arranged on the light emitting surface side in a parallel state.

Next, the present invention will be described in detail with reference to the drawings. FIG. 5 is a perspective view of an embodiment of an edge light system 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 an embodiment of an edge light system having light sources at two ends of the light guide plate, and FIG. 8 is a sectional view thereof.

In FIG. 1, reference numeral 1 denotes a light guide plate, which may be any substance that allows light to efficiently pass therethrough, and may be quartz, glass, translucent natural or synthetic resin such as acrylic resin. To impart light diffusivity to one surface of the light guide plate, for example, a paint having a high refractive index and a large diffuse reflectance as compared with the material of the light guide plate, for example, a paint containing titanium white, a printing ink. A light diffusing substance (6 in the figure) such as is printed in dots on the surface of the light guide plate by a method such as screen printing. In addition, light diffusivity may be imparted by roughening the surface of the light guide plate, forming small holes, or providing small protrusions.

Reference numeral 4 is a linear light source, and in a preferred embodiment,
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 is covered. It is installed close to the one end face so that its central axis is substantially parallel to the end face 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. However, a fluorescent tube is preferable, and from the viewpoint of power saving, the length of the uniform light emitting portion excluding the electrode portion is close to each other. It is preferable that the length of the end portion of the light guide plate is substantially equal.

The mirror surface or the light diffusing reflection plate (3 in the figure) is arranged so as to cover the entire surface of the light guide plate coated with the light diffusing substance, but the remaining end face portion of the light guide plate which is not in close proximity to the linear light source. It is more preferable to dispose so as to cover almost the entire surface of the above in terms of light utilization efficiency and uniform planar light emission.

Reference numeral 7 denotes a light directing sheet (hereinafter simply referred to as a sheet) made of a translucent material, which is parallel to each other at a fine interval on the same plane and has a straight top or a ridge as shown in FIG. 1
0 has a large number of convex top ridges in parallel with each other, and is arranged on the light exit surface side of the light guide plate so that the top ridge surface is on the outside (opposite side to the surface facing the light guide plate).

According to the present invention, when such a sheet is arranged on the light exit surface side of the light guide plate, the apex is parallel to the left and right direction of the backlight, that is, the left and right direction when facing the display device using the same. The feature is that they are arranged as follows.

By arranging the sheets in this way,
By changing the directivity of the light emitted from the light emitting surface of the backlight, it is possible to further increase the directivity in the vicinity of the normal direction dropped to the light emitting surface and in the range where the liquid crystal display device has a good contrast.

Generally, the range of good contrast of a liquid crystal display device is wider in the left-right direction than in the up-down direction. Therefore, by arranging the sheet in the above-described direction, it is possible to change the directivity of the light emitted from the light emitting surface of the backlight so that the horizontal direction is wider than the vertical direction. When the good contrast range of the liquid crystal display device used is wider in the vertical direction than in the horizontal direction, when the sheet is arranged on the light emitting surface side of the light guide plate, the top edge is the vertical direction of the backlight, That is, it goes without saying that they are arranged so as to be parallel to the vertical direction when facing a display device using this.

In order to make it difficult to identify the pattern of the light diffusing substance (6 in the figure) provided on the surface of the light guide plate, if necessary, a space between the sheet and the light guide plate is provided. A light diffusing plate (2 in the figure) may be arranged on the outside of the sheet, or may be arranged outside the sheet. Such arrangement is preferable in terms of protection of the structure of the sheet. However, since it is necessary that the sheet and the light guide plate do not come into optical contact with each other (for example, through an air layer), if the light diffusion plate is not arranged between the sheet and the light guide plate, It is necessary to slightly roughen the surface of the sheet facing the light guide plate or to dispose a spacer-like element to prevent optical contact.

As described above, the present invention is characterized in that a sheet made of a translucent material having a shape satisfying a certain condition is arranged on the light emitting surface side of the backlight. More specifically, the above-mentioned sheet (7 in the figure) is not particularly limited as long as it is made of a translucent material. For example, methacrylic acid ester, polycarbonate, polyvinyl chloride, polystyrene, polyamide, polyester,
Examples thereof include polyethylene, polypropylene, fibrous resin, glass and the like.

FIG. 9 shows an example of the shape of the straight apexes parallel to each other formed on the light emitting surface side of the sheet used in the present invention.
As shown in, a so-called prism shape having two or more optical planes, the apex ridge (8 in the figure) where the two optical planes intersect is linear, and a fine interval (in the same plane) ( In P) in the figure, there are many linear prisms parallel to each other. The apex angles of these apexes formed on the sheet have portions of substantially the same shape, which means that the apex angles have substantially the same angle when cut under the same conditions centering on the apex. Means that.

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

As another example of the sheet used in the present invention, the shape of the apex is convex with an arc (14 in FIG. 10),
There is a so-called kamaboko type sheet.

The distribution of a large number of apexes formed on the sheet makes it difficult for the light emitted from the surface to visually recognize the intervals between them. It is preferably from about 1000 μm. The thickness of the apex of the sheet (t _{2 in} FIG. 9) is determined by the size of the apex or arc of the apex and the interval between the apex and the apex, but a large number of linear apexes For maintaining the positional relationship in which the elements are parallel to each other with a fine interval (t _{1 in} FIG. 9)
Required a, this t ₁ is thinner is better for the thickness of the light transmittance and the backlight, the sheet - the reasons and intensity on bets manufacturing point, the sheet - the total thickness of the bets ( (T in FIG. 9)
Is 10 to 3000 μm, preferably 50 to 1000 μm
Is good. Further, it is preferable that the linear ridges formed on the same surface have the same shape more effectively.

The method of molding the sheet used in the present invention is not particularly limited, and for example, mold molding by hot pressing, embossing, mold processing, a method of using an ultraviolet curable resin on a base film, chemical Any method can be used as long as it can be formed by a method such as a treatment so as to have a large number of substantially linear ridges in parallel with each other at fine intervals.
It should be noted that some sagging occurs on the apex for manufacturing reasons,
It may be within the range where the effect of the present invention is recognized.

In a liquid crystal display, the contrast becomes lower as the angle viewed from the direction of the normal line lowered on the display surface becomes lower. Therefore, practically, the luminance in the vicinity of the direction of the normal line is important. Further, since the viewfinder can be seen only from the normal direction dropped on the display surface, practically, the brightness in the vicinity of the normal direction is important.

In the present invention, as described above, when a sheet having a large number of linear prisms parallel to each other on the light emitting surface side at fine intervals is arranged on the light emitting surface of the backlight, the directivity of light appears. .. That is, when the brightness of the light emitted from the surface is measured in the direction of the normal line lowered to the light output surface,
Compared to the case where the sheet is not provided, the brightness is increased, an angle with respect to the normal line lowered to the light exit surface,
For example, the luminance measured in the same way from the direction of 40 degrees has a larger reduction rate than the luminance measured in the normal direction (for example, almost 50% of the luminance measured in the normal direction).
It is understood that the above-mentioned light directivity appears.

[0026]

INDUSTRIAL APPLICABILITY The present invention can be used as a backlight which is relatively small in size, has a sufficient luminance, and has a large power consumption-luminance conversion efficiency in the range where the contrast of the liquid crystal display device is good.

Comparative Examples 1 and 2, Examples 1 to 3 Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. 2.0 mm thick rectangular light guide plate (225 mm
X 127 mm) at the short end of a cold cathode fluorescent tube with a thickness of 4.8 mm (Normal tube manufactured by Harrison Electric Co., Ltd.)
And a light diffusing film on the inner surface of a cylindrical aluminum reflector with a 2 mm slit in the part that contacts the light guide plate.
It is 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 (coating containing titanium white) coated on the surface of the light guide plate was a circular dot pattern screen-printed at a pitch of 1.2 mm, and was prepared and used under the following conditions. It was plotted so that the coverage of the light diffusing substance was 6% at the minimum point (cold cathode fluorescent tube side), 80% at the maximum point, and these ratios were sequentially increased in the middle.

Further, one light diffusion film (Tsujimoto Denki Seisakusho D-204) was arranged on the light exit surface side of the light guide plate. The surface luminance when an alternating voltage of 30 KHz is applied from the inverter to the cold-cathode tube and driven at a constant current, the viewing angle is 2 degrees with the luminance meter (Topcon BM-7), and the normal direction is lowered to the light emitting surface. On the other hand, when measured at a distance of 40 cm from the light emitting surface to the luminance meter, it was 192 cd / m ² (Comparative Example 1).

On the light diffusing film, a large number of commercially available linear prisms made of polycarbonate and having parallel apex angles of 90 ° are parallel to each other. A sheet with a thickness of 360 μm processed to have an interval of 350 μm so that the straight apex is perpendicular to the central axis of the light source and the prism is on the outside so that the prism is outside. Comparative Example 1 except that it is arranged
Operated with the same equipment and conditions as above, the measured brightness was 307
It was cd / m ² (Example 1).

Further, the brightness was measured by operating under the same apparatus and conditions as in Example 1 except that one linear prism was placed on the light emitting surface side of the backlight so that the prism was inside.
It was 50 cd / m ² (Comparative Example 2). Furthermore, the brightness was 245 cd / m ^{2 as} measured by operating under the same apparatus and conditions as in Example 1 except that a linear prism in which the apex angle of the prismatic projection was 70 degrees was used (Example 2 ). Further, Example 1 was repeated except that the apex angle of the prism-shaped protrusion was 100 degrees.
Operated with the same equipment and conditions as the above, the measured brightness was 290
It was cd / m ² (Example 3). Further, the apex angle of the prism-shaped projection has a strong light directivity up to 90 degrees, but the peak of the light directivity is in a split state having a large peak other than the normal direction. ..

Next, in order to examine the light distribution characteristics of the backlight, in Comparative Example 1, Example 1, Example 2 and Example 3, an alternating voltage of 30 KHz was applied to the cold cathode tube from the inverter. The surface luminance when driven with a constant current at a viewing angle of 2 degrees by a luminance meter (Topcon BM-7), and the angle with respect to the normal direction lowered to the light emitting surface as shown in FIG. The distance from the light emitting surface to the luminance meter is set to 40 degrees by changing from 0 degree to 70 degrees (that is, in the direction perpendicular to the straight apex).
The luminance values measured in cm are shown in FIG. Similarly, in order to investigate the light distribution characteristics of the backlight, in Comparative Example 1, Example 1, Example 2 and Example 3, a constant voltage was applied to the cold cathode tube by applying an alternating voltage of 30 KHz from the inverter. With respect to the surface luminance when driven by an electric current, a luminance meter (Topcon BM-7) has a viewing angle of 2 degrees, and an angle with respect to a normal direction lowered to the light emitting surface as shown in FIG. FIG. 13 shows the value of luminance when measured at a distance of 40 cm from the light emitting surface to the luminance meter by changing the angle from 0 degree to 70 degrees in the direction parallel to the linear apex). From this figure, it can be seen that when the backlight of the present invention is used, the brightness is increased and the directivity of light is remarkable.

Example 4 Instead of a sheet having a large number of linear prisms, a large number of linear convexes made of a UV-curing resin were formed on a film by a printing method on a polyethylene terephthalate base film having a thickness of 50 μm. The diameter of the bottom of the protrusion is 50 μm,
The measurement was performed by operating with the same apparatus and conditions as in Example 1 except that a sheet formed so that the height from the bottom surface to the convex portion was 25 μm and the interval between the convex portions was 50 μm was used. The brightness was 235 cd / m ² .

[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-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 an 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 an 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 showing an example of a sheet used in the present invention.

FIG. 10 is a perspective view showing an example of a sheet used in the present invention.

FIG. 11 is a conceptual diagram of a measuring method used in the present invention.

FIG. 12 is a diagram showing an angular distribution of emitted light brightness (vertical direction).

FIG. 13 is a view showing an angular distribution (left-right direction) of emitted light brightness.

[Explanation of symbols]

 1: Light guide plate 2: Light diffusing plate 3: Reflecting plate 4: Linear light source 5: Reflector 6: Light diffusing material 7: Sheet with linear prism 8: Linear apex ridge 9: Vertical angle of prism 10 : Backlight 11: Luminance meter 12: Angle with respect to the normal direction lowered to the light emitting surface 13: Normal line lowered to the light emitting surface 14: Crest of convex portion

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[Procedure amendment]

[Submission date] August 21, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

[0030] More luminance linear prisms is that the same apparatus except except that disposed one on the light exit surface side of the backlight as in Example 1 so that the inside condition, in manipulating was measured 1
It was 5 cd / m ² (Comparative Example 2). Furthermore, the brightness was 245 cd / m ^{2 as} measured by operating under the same apparatus and conditions as in Example 1 except that a linear prism in which the apex angle of the prismatic projection was 70 degrees was used (Example 2 ). Further, the luminance was measured at 290 c by operating under the same apparatus and conditions as in Example 1 except that the apex angle of the prism-shaped protrusion was 100 degrees.
It was d / m ² (Example 3). Further, although the apex angle of the prism-shaped protrusions has a strong light directivity up to 90 degrees, the peak of the light directivity was in a split state having a large peak other than the normal direction.

Claims (2)

[Claims] 1. A wide surface of a light guide plate made of a light-transmitting material is made to be light diffusive, and the surface is covered with a mirror surface or a light diffusive / reflecting plate, and is close to at least one side surface end portion of the light guide plate. In a panel backlight having a linear light source, on the light exit surface side of the light guide plate, prisms or linear convex ridges having linear ridges at fine intervals on the same surface are substantially parallel to the ridges. In the backlight for a panel, one or more sheets made of a translucent material are arranged on the light emitting surface side in a state where the top edges are parallel to each other in the horizontal direction of the panel. 2. The distance between adjacent apexes is 10 to 10.
The backlight for a panel according to claim 1, wherein a sheet having a thickness of 1000 μm is used.