JPH08111106A - Backlight - Google Patents

Abstract

PURPOSE: To heighten the power consumption-luminance conversion efficiency of a backlight and also to heighten the brightness thereof by arranging a light transmissive prism sheet, having many rectilinear edges, on the light output plane side of a light transmissive member partly coated with a light diffusing material. CONSTITUTION: A backlight is constructed in such a manner that a cold cathode fluorescent tube 4 is arranged at the end part of a light guide plate 1, a part in contact with the plate 1 is then covered with a cylindrical aluminum reflector 5 having slits and light outputted through the slits can be inputted to the plate 1 therethrough. A light diffusing film (a light diffusing sheet) 2 is then arranged on the light output plane side of the plate 1, and a light diffusing reflector sheet 3 is arranged on the plate 1 on the side of its plane coated with a light diffusing material 6. A sheet processed in such a manner that specified spaces can be left respectively between the mutually adjacent vertical edges of many rectilinear prisms paralleled with one another is then arranged on the light diffusing sheet 2 on the light output plane side of the back light in such a manner that each of the prisms can be turned to the outside of the processed sheet. Sufficient brightness can consequently be obtained by the relatively small-sized backlight, and the power consumptionbrightness conversion efficiency of the backlight can be heightened also in the direction of a normal line drawn down to the output light plane of the backlight.

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 backlight mechanism which is thin and easy to see 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 in which a linear light source such as a fluorescent tube is provided at two opposite ends of a light guide plate is often used. In the case of this edge light method, as shown in FIG. 2 or 4, one surface of the light guide plate is partially covered with a light diffusing substance having a refractive index larger than that of the material of the light guide plate, and almost the entire surface thereof is covered. Many are arranged so as to be covered with a light diffusion reflector.

Particularly, in recent years, since the backlight is driven by a battery, further improvement of 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 dispose a reflection plate having a high reflectance on the surface of the light guide plate that 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 not sufficient, and further improvement is desired.

[0005]

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

[0006]

As a result of various studies on the above points, the inventors of the present invention have found that a linear top edge is formed on the light emitting surface side of a translucent material partially covered with a light diffusing substance. Although a light transmissive prism sheet having a large number of is arranged, the directivity of light becomes stronger, and the power consumption-luminance conversion efficiency is high for the vicinity of the normal direction 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 containing a pigment having a large diffuse reflectance, and the surface is mirror-finished or light-reflected. In a backlight for a panel which is covered with a plate and has a linear light source close to at least one side surface end portion of the light guide plate, a prism having linear vertexes on the same surface at fine intervals A sheet comprising a large number of translucent materials arranged in a substantially parallel state, wherein the sheet is a translucent film and a prism having a straight apex made of a translucent material different from the film is formed on the translucent film. The present invention relates to a backlight for a panel in which one or more sheets are arranged on the light emitting surface side of a light guide plate with a light diffusing sheet so that the top ridge surface is on the outside.

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 the figure, reference numeral 1 denotes a light guide plate, which may be any substance that allows light to pass efficiently, and is made of quartz, glass, translucent natural or synthetic resin such as 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 as compared with the material of the light guide plate, for example, paint containing titanium white, printing ink, or the like.
These are printed in dots on the surface of the light guide plate by a method such as screen printing.

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 portion 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. The linear light source may be a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, or 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 is substantially equal to the length of the end portion of the light guide plate.

The mirror surface or the light reflecting plate, for example, the light diffusing reflecting plate (3 in the figure) is arranged so as to cover almost the entire surface of the light guiding plate coated with the light diffusing substance. It is more preferable to dispose so as to cover almost the entire remaining end face portion, in terms of light utilization efficiency and uniform planar light emission.

Reference numeral 7 is a sheet made of a translucent material (hereinafter simply referred to as a sheet), which has a large number of straight apexes parallel to each other on the same surface at fine intervals. By arranging so that it is on the side opposite to the surface facing the light plate), the directivity of the light emitted from the light emitting surface of the backlight is changed, and the directivity in the vicinity of the normal direction dropped on the light emitting surface is made stronger. It is a thing. It may be arranged such that the linear apex portion is parallel to the central axis of the linear light source,
You may arrange so that it may become a right angle.

In the present invention, one sheet or a plurality of sheets are used. When, for example, two sheets are used, both apical ridges are located outside so that their linear apexes are orthogonal to each other. , The effect of the present invention, that is, the power consumption-luminance conversion efficiency is further increased. If necessary, the sheet and the guide should be arranged so that the dot-shaped pattern of the dot-shaped light diffusing substance (6 in the figure) printed on the light guide plate surface cannot be identified. A light diffusion plate (2 in the figure) may be arranged between the light plate and the light plate. As the light diffusion plate used here, a commercially available light diffusion sheet (film) or the like is used.

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.

The above-mentioned conditions in the present invention will be described in more detail. 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, poly Vinyl chloride, polystyrene, polyamide, polyethylene terephthalate (PE
T) and other polyesters, polyethylene, polypropylene, fiber-based resin glass, and the like.

As shown in FIG. 9, the shape of a prism having straight parallel ridges formed on the light output surface side of the sheet used in the present invention is parallel to each other, as shown in FIG. In this state, the apex ridge (8 in the figure) where the two optical planes intersect is linear, and a large number of linear prisms parallel to each other are present in the same plane at minute intervals (P in the figure). Is. The apex angles of these apexes formed on the sheet have portions of substantially the same shape. This 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 above-mentioned 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 large refractive index (polycarbonate,
When a refractive index n = 1.59) is used, the apex angle is preferably 90 degrees rather than 70 degrees and 120 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, when the light emitted from the planar light-emitting body is substantially concentrated within 45 degrees from the normal direction dropped on the light-emitting surface,
The vertical angle is preferably 100 to 140 degrees.

Further, it is particularly preferable to use the above-mentioned sheet prism in which the hypotenuses from the apex have substantially the same length in order to improve the effect of the present invention. In addition, the distribution state of a large number of linear prisms formed on the sheet makes it difficult for the light emitted from the surface to visually recognize the interval between the linear prisms. The 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 apex ridge and the interval between the apex ridges described above. It is necessary to have a thickness (t1 in the figure) to maintain such a positional relationship, and this t1 is preferably thin in order to reduce the light transmittance and the thickness of the backlight. From the viewpoint of strength, the total thickness of the sheet (T in the figure) is 10 to 3000 μm, preferably 5
0 to 1000 μm is preferable. Further, the linear prisms formed on the same surface should have the same shape more effectively.

The method of forming the sheet used in the present invention is as follows.
For example, a method capable of forming a plurality of linear prisms having substantially the same shape in parallel with each other at fine intervals by a method such as mold forming processing by hot pressing, embossing processing, mold processing, chemical processing, printing, etc. I wish I had it. It should be noted that although a slight sag occurs at the apex for manufacturing reasons, it may be within the range in which the effect of the present invention can be recognized.

In the present invention, a translucent material (for example, an ultraviolet curable resin such as an acrylic resin) different from the base film is formed on the translucent film (sheet) (base film) described above such as printing. What is formed by a method so as to have a large number of linear convex shapes at minute intervals is used.

In a liquid crystal display, the contrast becomes lower as the viewing angle from the normal direction lowered to the display surface becomes larger, so that the brightness in the vicinity of the normal direction is important in practical use. 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 whose light emitting surface side is parallel to each other 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 emitting 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 similarly 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.

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

When the apex angle of the prism is 2α (degrees), the refractive index of the sheet made of a light transmissive material is n, and the refractive index of air is 1, the critical angle θc (degrees) is θc = sin ^−1. (1 / n) 1) ray angle theta ₁ (incident in degrees), when emitted at the angle theta ₆ (degrees) (FIG. _{10 (a)) sinθ 1 =} n × sinθ 2 θ 3 = 90 ° -α _{-θ 2 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 incident at an angle theta ₁ (degrees), the angle theta _{When the} light is emitted at ₈ degrees (FIG. 11B) sin θ ₁ = n × sin θ ₂ θ ₃ = 90 ° −α−θ ₂ θ ₄ = θ ₃ (where θ ₃ > θc) θ ₅ = 2α −θ ₄ n × sin θ ₅ = sin θ ₆ (when θ ₅ ≦ θc) θ ₇ = 90 ° −α−θ ₆ θ ₈ = −θ ₇ By performing such a calculation, a transparent material is formed. Material used for sheet Refractive index, knowing the apex angle of the prism, back from the light exit surface of the light made of a translucent material of light rays exiting sheet - the angle of incidence on the bets can be determined emission angle. Although not shown in FIG. 10, depending on the above conditions, the incident light beam may be reflected twice or more inside the prism or may return to the light emitting surface of the backlight.

For example, when the sheet is made of polycarbonate (refractive index n = 1.59) as shown in FIG. 12 and the apex angle of the prism is 90 degrees, the incident angle is 0.
The light beam incident on the sheet at a time is 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 emitting 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 less light is absorbed inside the backlight, the more The higher the reflectance of light inside the backlight, that is, the more the surface other than the light emitting surface of the backlight is covered with the reflector having high reflectance, the more efficient the backlight becomes.

A light ray incident on the sheet at an incident angle of 30 degrees is emitted from the sheet at an emission angle of 0.5 degree, and a light ray incident on the sheet at an incident angle of 60 degrees is emitted at the emission angle. 25.7
Light is emitted from the sheet at a certain degree. Then, in this case, the light emitted from the light emitting surface of the backlight is substantially most concentrated within an angle of about 40 degrees from the normal direction dropped onto the light emitting surface, and as a result, the light is measured from the normal direction. The brightness is
The number is increased as compared with the case where the sheet is not provided.

Similarly, when the sheet is made of polycarbonate as shown in FIG. 13 and the apex angle of the prism is 120 degrees, the sheet is incident on the sheet at an incident angle of 0 degree. The emitted light is emitted from the sheet at an emission angle of 22.7 degrees,
A light ray that enters the sheet at an incident angle of 30 degrees has an exit angle of 1
A light beam emitted from the sheet at 1.2 degrees and a light beam incident on the sheet at an incident angle of 60 degrees exits from the sheet at an emission angle of 34.8 degrees. Then, the light emitted from the light emitting surface of the backlight in this case is substantially most concentrated within an angle of about 44 degrees from the normal direction dropped onto the light emitting surface, and as a result, the light is 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 emitting body.

[0030]

EFFECTS OF THE INVENTION The present invention is comparatively small in size, can obtain sufficient brightness, and consumes less power in the direction normal to the light exit surface.
It can be used as a backlight with high luminance conversion efficiency.

[0031]

EXAMPLES Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. As shown in FIG. 5 or 6, at the short edge of a rectangular light guide plate (225 mm × 127 mm) (2.0 mm thick) (1 in the figure), a cold cathode fluorescent tube with a thickness of 4.8 mm (Harrison Electric (Normal tube manufactured by Co., Ltd.) (4 in the figure) is placed, and a light diffusion film is laminated on the inner surface of a cylindrical aluminum reflector that has a slit of 2 mm in the part that contacts the light guide plate, and light is emitted from the slit. The light is arranged so as to enter 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) (6 in the figure) coated on the surface of the light guide plate is a circular dot pattern screen-printed at a pitch of 1.2 mm, and is prepared under the following conditions. Used. The plots were made 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) (2 in the figure) was arranged on the light emitting surface side of the light guide plate. Further, a light diffusing reflection plate (3 in the figure) is arranged on the surface side of the light guide plate coated with the light diffusing substance. The surface brightness when an alternating voltage of 30 KHz was applied from the inverter to the cold-cathode tube and it was driven with a constant current, the viewing angle was 2 degrees with the brightness meter (Topcon BM-7), and the normal direction was lowered to the light exit surface On the other hand, when measured at a distance of 40 cm from the light emitting surface to the luminance meter, 192 cd
It was / m ² (Comparative Example 1).

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

Further, the brightness was 15 cd / m as 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 linear prism was inside.
It was ² (Comparative Example 2).

Further, 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 having a prism-shaped protrusion with an apex angle of 70 ° was used. Example 2).

Further, the brightness was 330 cd / m ^{2 as} measured by operating under the same apparatus and conditions as in Example 1 except that the apex angle of the prismatic protrusions was set to 120 ° (Example 3).

A thickness of 50 μm is formed on the light diffusion film.
A number of linear protrusions made of UV curable resin (acrylic resin) on the PET base film by a printing method, the bottom width of the protrusions is 50 μm, and the height of the protrusions from the bottom is 25 μm.
m, the same apparatus as Comparative Example 1 except that one sheet formed so that the interval between the convex portions is 50 μm is arranged on the light emitting surface side of the backlight so that the linear convex portions are on the outside,
Operating under the conditions, the measured luminance was 235 cd / m ² (Example 4).

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 from the inverter to the cold cathode tube at a constant current. With respect to the surface luminance when driven, a luminance meter (Topcon BM-7) has a viewing angle of 2 degrees, and an angle with respect to a normal direction dropped to the light emitting surface from 0 degree to 70 degrees as shown in FIG.
FIG. 15 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 degree up to 40 degrees. 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.

[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 of a sheet used in the present invention.

FIG. 10 is a diagram showing an example of ray tracing.

FIG. 11 is a diagram showing an example of ray tracing.

FIG. 12 is a diagram showing an example in which the prism vertical angle is 90 degrees.

FIG. 13 is a diagram showing an example in which the prism vertical angle is 120 degrees.

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

FIG. 15 is a diagram showing an angular distribution 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 substance 7: Sheet having linear prism 8: Linear apex ridge 9: Vertical angle of prism 10 : Backlight 11: Luminance meter 12: Angle with respect to the direction of the normal line on the light exit surface 13: Normal line on the light exit surface

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[Procedure amendment]

[Submission date] July 4, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a backlight mechanism which is thin and easy to see 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 in which a linear light source such as a fluorescent tube is provided at two opposite ends of a light guide plate is often used. In the case of this edge light method, as shown in FIG. 2 or FIG. 4, one surface of the light guide plate is partially covered with a light diffusing substance having a refractive index higher than that of the material of the light guide plate, and almost the entire surface is covered. Many are arranged so as to be covered with a light diffusion reflector.

Claims (6)

[Claims] 1. A light-diffusing substance containing a pigment having a large diffuse reflectance is partially coated on one wide surface of a light guide plate made of a translucent material, and the surface is covered with a light-reflecting plate. In a backlight for a panel having a linear light source near at least one side surface of a light guide plate, a prism having linear apexes at fine intervals on the same surface, in which apexes are substantially parallel In a sheet made of a light-transmitting material having a large number of the above, the sheet is a light-transmitting film on which a prism having a linear apex is formed by a light-transmitting material different from the film, A backlight for a panel, in which one or more sheets of this sheet are arranged on the light emitting surface side of the light guide plate so that the top ridge surface is on the outside. 2. The backlight according to claim 1, wherein a light guide plate, a light diffusion sheet, and a sheet made of a translucent material are arranged in this order. 3. A plurality of sheets made of a translucent material are used,
The backlight according to claim 1 or 2, wherein the top edges of adjacent sheets are arranged so as to be substantially orthogonal to each other. 4. A seam having an apex with an apex angle of 70 to 150 degrees.
The backlight according to claim 1, wherein the backlight is used. 5. The distance between adjacent apexes is 10 to 1
The backlight according to any one of claims 1 to 4, wherein a sheet having a size of 000 µm is used. 6. The backlight according to claim 1, wherein the light diffusing substance contains silicon dioxide.