JPH06250172A - Back light - Google Patents

Abstract

PURPOSE:To provide the back light which is high in electric power consumption- brightness conversion efficiency and enables the relatively easy control of light directivity by arranging a sheet consisting of a light transparent material having many fine lenses of an a focal system on the light exit surface side of a light transmission plate. CONSTITUTION:The sheet 2 consisting of the light transparent material having the many fine lenses 7 of the a focal system is arranged on the light exit surface side of the light transmission plate 1 of the back light for a panel having the light transmission plate 1 consisting of the light transparent material and a wire-shaped light source 4 in proximity contact with at least one flank of the light transmission plate 1. The material of the lens sheet 2 may be any materials, insofar as these material allow the efficient passage of light and is quart, glass, natural or synthetic resins having light transparentability, etc. The method for formation of the lenses 7 include a method for forming the lenses by die molding using a hot press, casting, chemical treatment and by using a UV curing resin., etc. The many lenses 7 may be formed as well at fine spacings between each other by partial implantation of ions to a flat plate, such as glass substrate.

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, an edge light system is often used 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. In the case of this edge light system, as shown in FIG. 2, one surface of the light guide plate is provided with a light diffusing function, and almost all of the surface is covered with a specular reflection plate or a light diffusing reflection sheet. In many cases, the light guide plate is arranged so as to cover the light emitting surface side thereof with a light diffusion sheet.

Particularly in recent years, the backlight is driven in a battery-like manner, and it is desired to further improve the power consumption-luminance conversion efficiency. The backlight has a plurality of linear prisms on its light emitting surface. The sheet (A) made of a translucent material is arranged so that the prism is on the light emitting surface side (the side opposite to the light guide plate), and directivity is given to the light emitted from the backlight to obtain the light emitting surface method. It has been proposed to increase the brightness in the line direction.

However, since the above-mentioned method uses a sheet having a prism, from the optical principle, almost no light rays of 50 degrees or more are emitted with respect to the direction of the normal line lowered to the light exit surface,
Therefore, the sheet (A) that obtains relatively good light directivity is
Although it has a prism with an apex angle of 90 degrees or more, when the apex angle of the prism is 90 degrees or more, a part of the light beam incident on the sheet (A) from the light guide plate side is a prism because of the optical principle. There was a problem that the light was totally reflected inside and returned to the light guide plate side again. The light beam returned to the light guide plate side was repeatedly refracted, reflected and absorbed in and around the light guide plate, and part of the light beam was returned to the sheet (A), but many light beams were absorbed. In order to reduce the absorbed light rays and further increase the light utilization efficiency, the reflectance and the transmittance of each optical member constituting the backlight may be set to 100%. Is currently unknown.

Therefore, in order to give directivity to the light emitted from the light guide plate, the above-mentioned sheet (A) has been unsatisfactorily used. Further, since the sheet (A) itself has a low light diffusing property, the shape of the element having a light diffusing function provided on the light guide plate is seen through, and another light diffusing sheet is used to conceal the shape. Was generally needed.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a backlight which has a high power consumption-luminance conversion efficiency and whose light directivity can be controlled relatively easily.

[0007]

As a result of various studies on the above points, the inventors of the present invention have found that a large number of apertures are arranged at minute intervals on the light emitting surface side of an edge light type backlight.
By arranging a sheet made of a translucent material having a Cull system lens, the directivity of the light is strengthened without totally reflecting the light rays in the prism as in the sheet (A), and the emitted light is emitted. The present invention has been completed by finding that the backlight has a high power consumption-luminance conversion efficiency in the vicinity of the normal direction on the surface.

That is, the present invention provides a light guide plate made of a translucent material, and a panel backlight having a linear light source near at least one side surface end portion of the light guide plate. The present invention relates to a backlight for a panel in which a sheet made of a translucent material having a large number of afocal-type fine lenses is arranged.
Next, the present invention will be described in more detail with reference to the drawings.

The basic structure of the present invention is the same as that shown in FIGS. That is, a light guide plate having a light diffusion function for emitting light to one surface and a light source at least at one end thereof. A cross-sectional view of one embodiment of the present invention is shown in FIG. In FIG. 1, reference numeral 1 denotes a light guide plate, which may be any substance that allows light to efficiently pass therethrough, and is made of quartz, glass, translucent natural or synthetic resin such as acrylic resin. In the present invention, the portion having the light diffusion function is, for example, the following portion. That is, a surface of the light guide plate having a light diffusing function, a light guide plate itself having a light diffusing function in the light guide plate, a light diffusing sheet surface described later arranged on the light emitting surface side of the light guide plate, or the like.

The method of imparting a light diffusing function to the surface of the light guide plate includes substances having a function of diffusing light, such as silica, barium sulfate, calcium carbonate, titanium white, glass beads, resin beads, and bubbles. A method of printing a light-diffusing substance such as paint or printing ink in a dot shape on one wide surface of the light guide plate by a method such as screen printing, or a method of roughening the surface of the light guide plate in a dot shape. There are methods such as forming small holes or forming small protrusions on the surface of the light guide plate. The light diffusion function may be provided on the side opposite to the light emitting surface of the backlight, or may be provided on the light emitting surface side. An example in which the light guide plate is provided on the side opposite to the light emitting surface is shown in FIG. 3 (6 in the figure indicates a light diffusing substance). In addition, a method of imparting a light diffusing function to the light guide plate is a light guide plate made of a substance having a function of diffusing light, such as silica, barium sulfate, calcium carbonate, titanium white, glass beads, resin beads, and bubbles. There is no particular limitation as long as it is a method in which a substance having a refractive index different from the above is contained as a result when the light guide plate is formed.

In the figure, reference numeral 3 denotes a light reflection sheet, which is a reflection sheet of mirror surface such as silver or aluminum or polyethylene terephthalate (PET) which is provided with light diffusion property by BaSO ₄ , TiO ₂ , bubbles and the like. And is arranged so as to cover almost the entire surface of the light guide plate opposite to the light emitting surface.

Numeral 4 in the drawing is a linear light source, and in a preferred embodiment, it is a mirror-like reflection sheet such as silver or aluminum or PET having a gap (slit) at the end of the light guide plate for allowing light to enter. A light reflector (5 in the figure) formed of a light diffusive reflection sheet with light diffusivity provided by BaSO ₄ , TiO ₂ , bubbles, etc., with a gap of a certain width from the light source surface of the linear light source. And is installed near at least one end face of the light guide plate such that its central axis is substantially parallel to the end face of the light guide plate. This linear light source may be a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, or the like, but a fluorescent tube is preferable, and from the viewpoint of power saving, the lengths of the uniform light emitting parts except the electrode part are close to each other. It is preferable that the length is substantially equal to the length of the end portion of the light guide plate.

FIG. 4 is a perspective view of one embodiment of a sheet (hereinafter abbreviated as a lens sheet) having a large number of fine lenses made of a translucent material used in the present invention, and FIG. 5 is a sectional view thereof. Is. FIG. 6 is a perspective view of another embodiment (linear lens) of the lens sheet used in the present invention,
FIG. 7 is a sectional view of the same. In the figure, 7 is a lens formed on the sheet surface, and 8 is a base film made of the same or different material as the lens material and having a different refractive index from the lens material. 8,
9 is a sectional view of still another embodiment of the lens sheet used in the present invention. FIG. 8 shows an example in which a concave lens and a convex lens are opposed to each other, and FIG. 9 shows a convex lens with an appropriate inclusion, for example, a binder (a substance having a smaller refractive index than the lens substance is preferable).
It is an example of a sheet arranged facing each other through.

The lens sheet used in the present invention, which is made of a translucent material and has a large number of lenses arranged at fine intervals on the same surface, must have a so-called afocal optical function. It is arranged on the light emitting surface side of the light guide plate.
The material of the lens sheet may be any substance that allows light to pass through efficiently, and may be quartz, glass, translucent natural or synthetic resin such as PET, polycarbonate, acrylic resin and the like. The same material is used for the above-mentioned base film, but in the case of an afocal system in which lenses are opposed to each other on both sides of the base film, materials having different refractive indexes for the lens and the base film are used.

The method for forming this lens is not particularly limited, but examples thereof include a die molding process by hot pressing, a mold process, a chemical treatment, and a method using an ultraviolet curable resin. Although a lens may be formed on a sheet made of a translucent material by such a method, a flat plate such as glass may be partially ion-implanted to change the refractive index. A plurality of lenses may be optically provided on the same surface at minute intervals. Further, a lens formed in advance may be integrated with the base film.

The shape of the lens is not particularly limited,
There is a shape in which paraxial rays incident parallel to the optical axis are emitted substantially parallel to the optical axis, for example, a shape in which convex lenses and convex lenses face each other, a shape in which convex lenses and concave lenses face each other, etc. It is essential that the so-called afocal system state is such that the focal point of the lens on the light guide plate side and the focal point of the other lens facing each other substantially coincide with each other. It should be noted that when the ions are partially injected into a flat plate such as glass to change the refractive index, it is difficult to determine the shape of the lens, so paraxial rays incident parallel to the optical axis are reflected on the optical axis. Whether or not the light is emitted in parallel is a criterion for determining whether or not the light is an afocal system.

Lens (center of) on the same surface of the lens sheet
The interval between them is not particularly limited, but it is preferable that the distance is as narrow as not distinguishable by human eyes, and it is 1 μm to 1000 μm, preferably 1 μm to 500 μm. However, when the present invention is used for a liquid crystal display, the pixel of the liquid crystal The pitch is almost equal to or smaller than the pitch (for example, when the liquid crystal pixel pitch is 300 μm, the distance between the lenses is approximately 300 μm).
m or less) is better.

The number of lenses included in a unit area of the lens sheet is determined by the distance between the lenses when the peripheral portion of the bottom surface of the lens is partially in contact. The shape of each lens is preferably the same as long as it is possible from the viewpoint of optical properties in the manufacturing method. The diameter of the lens is regulated to some extent by the distance between the lenses described above, but in order to further enhance the directivity of light, the diameter of the lens is larger (the lenses are substantially in contact with each other as far as the manufacturing method allows). The state) is preferable.

The light emitted from the light source is incident on the light guide plate, and from the light guide plate, the light that has been out of the condition of total reflection due to the light diffusion function is emitted at all angles.

It is a feature of the present invention that the afocal lens sheet is arranged on the light emitting surface side of the light guide plate, but the angular magnification of each lens of the lens sheet used is substantially 1 or less. Is preferred. With this structure, the light beam diffused and reflected by the portion having the light diffusing function becomes a light beam having directivity with respect to the normal direction falling on the light exit surface as shown in FIG. 11 by the lens. . Therefore, it is possible to obtain a state of planar light emission which is a light beam having a strong directivity and which has an optical concealing effect on the shape of the light having a light diffusing function by the action of the lens.

Incidentally, the angular magnification referred to here is a concept generally used in lens design, and as shown in FIG. 12, the angle β formed by the optical axis and the outgoing light ray on the light outgoing surface side of the sheet,
It is the ratio (β / α) of the angle α formed by the optical axis and the incident light beam on the light incident surface side. By controlling this angular magnification (that is, substantially 1 or less in the present invention), directivity can be imparted to the light rays emitted from the light guide plate at any angle. Further, unlike the sheet (A) described above, the light rays entering the sheet (A) from the light guide plate are not totally reflected in the prism, so that the light beam can be efficiently reflected from the light guide plate at any angle. Gives directivity to the light rays that emerge,
In addition, a high brightness backlight can be obtained. Further, since the light ray incident on the afocal lens at the angle (γ) is emitted at the angle (γ × β ÷ α), the directivity of the light ray can be controlled relatively easily by controlling the angular magnification.

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

With the structure of the present invention, the directivity of light appears. That is, when the brightness of the light emitted from the surface is measured substantially in the direction normal to the light emitting surface, the brightness is increased as compared with the case where no lens sheet is arranged, and the light is dropped onto the light emitting surface. The directivity of the above-mentioned light appears because the luminance measured in the same manner from a certain angle with respect to the normal is substantially smaller than the luminance measured in the normal direction. I understand.

The more preferable mode of the present invention will be described in detail. (1) When a plurality of linear lens sheets as shown in FIG. 6 are used, they are arranged so that their linear shapes intersect (preferably orthogonal). Then, the effect of the present invention is further increased.
(2) It is preferable that the light diffusing function as described above is applied to the space of the minute plane where the lens of the transparent sheet is not arranged. With such a state, light rays that have not entered the lens can be diffused and more uniform planar light emission can be achieved.

(3) The lens sheet may be arranged directly on the light emitting surface side of the light guide plate, or may be arranged via a light diffusion layer, for example, a light diffusion sheet (2 in FIG. 2). Even when it is arranged directly on the light exit surface side of the light guide plate, it is preferably arranged via a layer having a smaller refractive index than the lens material, for example, an air layer.

The light diffusion sheet arranged on the light emitting surface side of the light guide plate is usually arranged on the light emitting surface side of the light guide plate through an air layer, and this sheet is made of a substance having a function of diffusing light such as silica. , Barium sulfate, calcium carbonate, titanium white, glass beads, resin beads, etc. are coated on a light-transmissive sheet such as PET, polycarbonate, acrylic, or glass. This light diffusing sheet may be used as necessary, for example, when further improving the uniformity of light.

[0027]

INDUSTRIAL APPLICABILITY The present invention has a high power consumption-luminance conversion efficiency and can be obtained as a backlight in which the directivity of light can be controlled relatively easily.

[0028]

EXAMPLES Next, the present invention will be described in more detail with reference to Comparative Examples and Examples. As shown in FIG. 3, a rectangular light guide plate (made by Asahi Kasei, AC-999, made of polymethylmethacrylate, 210 mm × 155 mm) having a thickness of 4.0 mm is provided at both longitudinal ends.
A cold cathode fluorescent tube (made by Harrison Electric Co., Ltd.) with a diameter of 3.8 mm is arranged, and a silver film having a slit of 4 mm is arranged in an elliptical shape so that the reflection surface faces the light source in the portion in contact with the light guide plate. Then, the light emitted from the slit is arranged to enter the light guide plate from the end portion of the light guide plate. On the other hand, the light diffusing substance formed on the surface of the light guide plate is printed with a paint containing titanium white in a circular dot pattern on the intersections (grids) of the orthogonal lines with a virtual spacing of 1 mm on the light guide plate. The film was formed under the following conditions.

The light diffusing substance has a coverage of 26 at the minimum point.
%, 90 at the maximum point (near the middle of the two fluorescent tubes)
%, And in the middle thereof, printing was performed such that these ratios were sequentially increased. Further, the coverage of the light diffusing substance coated on the grid in a state parallel to the axis of the linear light source is the center on the parallel line, that is, from the longitudinal center of the linear light source to the vertical direction to the linear light source. With respect to the distance from the line on the standing light guide plate surface to the light diffusing substance in the direction toward both ends, 26% at the minimum point, 40% at the maximum point, and these in the middle between these, so that the distance gradually increases. Printing was performed such that the ratio was increased in order.

The surface of the light guide plate on which the light diffusing material was printed was covered with a 0.125 mm thick light diffusing reflection sheet (Melinex 329 manufactured by ICI) via an air layer. Further, one sheet of 0.1 mm thick light diffusing sheet (Tsujimoto Denki Seisakusho D-204) was arranged on the light emitting surface side of the light guide plate through an air layer.

The cold cathode tube is provided with an inverter (TDK CXA).
An alternating voltage of 30 KHz is applied from M-10L), and a constant current (5 mA for one cold cathode tube, a total of 10 for two tubes)
The surface luminance when driven with a current (mA) was measured with a luminance meter (Topcon BM-8) at a viewing angle of 2 degrees with respect to the normal direction to the light emitting surface, and it was 1300 cd / m ² .
At this time, there was almost no directivity of light (Comparative Example 1).

In place of the light diffusing sheet, a sheet made by forming a large number of convex lenses as shown in FIG. 4 on both sides of PET having a thickness of 0.1 mm and made of a transparent UV-curing resin, and the lenses are arranged at the centers of adjacent lenses. When the distance between the lens and the lens center is 140 μm and the lenses are almost in contact with each other, the focal points of the lenses facing each other with the PET in between are substantially equal to each other, and the angular magnification is 0.8.
Of the afocal system of Example 1 and operated under the same conditions and conditions as in Comparative Example 1 except that the measured luminance was 1500 cd /
It was m ² . At this time, the directivity of the light was observed with respect to the direction normal to the light exit surface (Example 1).

In place of the lens sheet, a sheet made by forming a large number of linear convex lenses as shown in FIG. 6 on both sides of PET having a thickness of 0.1 mm with a transparent UV curable resin, the lens is
The distance between adjacent lens centers is 140μ
In a state in which the lenses are substantially in contact with each other at m, the focal points of the lenses facing each other with the PET interposed therebetween are substantially the same, and the afocal system has an angular magnification of 0.8. The brightness measured by the device and conditions was 1600.
It was cd / m ² . At this time, the directivity of the light was observed with respect to the direction normal to the light exit surface (Example 2).

Luminance measured by operating with the same apparatus and conditions as in Comparative Example 1 except that two lens sheets of Example 2 were arranged with an air layer so that their linear convex lenses were orthogonal to each other. Was 2000 cd / m ² . At this time, the directivity of the light was observed with respect to the direction normal to the light exit surface (Example 3).

[Brief description of drawings]

FIG. 1 is a perspective view of a conventional backlight.

FIG. 2 is a sectional view of a conventional backlight.

FIG. 3 is a cross-sectional view of one embodiment of the present invention.

FIG. 4 is a perspective view of an embodiment of a sheet having a lens surface used in the present invention.

FIG. 5 is a sectional view of an embodiment of a sheet having a lens surface used in the present invention.

FIG. 6 is a perspective view of an embodiment of a sheet having a linear lens surface used in the present invention.

FIG. 7 is a cross-sectional view of one embodiment of a sheet having a linear lens surface used in the present invention.

FIG. 8 is a cross-sectional view of another embodiment of the lens-faced sheet of the present invention.

FIG. 9 is a cross-sectional view of another embodiment of the sheet having a lens surface of the present invention.

FIG. 10 is a diagram schematically showing an afocal system.

FIG. 11 is a diagram schematically showing an optical relationship between a light diffusion function and a lens.

FIG. 12 is a diagram schematically showing angular magnification.

[Explanation of symbols]

 1: Light guide plate 2: Light diffusion sheet 3: Mirror surface, light diffusion reflection sheet 4: Light source 5: Reflection cover of light source 6: Portion having light diffusion function 7: Lens 8: Base film 9: Inclusion between lenses

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[Procedure amendment]

[Submission date] June 2, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

However, since the above-mentioned method uses a sheet having a prism, from the optical principle, almost no light rays of 50 degrees or more are emitted with respect to the direction of the normal line lowered to the light exit surface,
Therefore, the sheet (A) that obtains relatively good light directivity is
It has a prism with an apex angle of 90 degrees or more, but when the apex angle of the prism is 90 degrees or more, a light ray incident from the light guide plate side at a specific angle in the sheet (A) from the optical principle. mostly is totally reflected by the prism, there is a problem that is returned to the light guide plate of the. The light beam returned to the light guide plate side was repeatedly refracted, reflected and absorbed in and around the light guide plate, and part of the light beam was returned to the sheet (A), but many light beams were absorbed. In order to reduce the absorbed light rays and further increase the light utilization efficiency, the reflectance and the transmittance of each optical member constituting the backlight are set to 1
It may be set to 00%, but such a substance is not known at present.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

As a result of various studies on the above points, the inventors of the present invention have found that a large number of apertures are arranged at minute intervals on the light emitting surface side of an edge light type backlight.
By arranging the sheet made of a translucent material having a cull-type lens, the directivity of light is strengthened, and the power consumption-luminance conversion efficiency is high in the vicinity of the direction normal to the light exit surface. The present invention has been completed by finding out that it becomes a backlight.

[Procedure amendment]

[Submission date] February 1, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

Incidentally, the angular magnification referred to here is a concept generally used in lens design, and as shown in FIG. 12, the angle β formed by the optical axis and the outgoing light ray on the light outgoing surface side of the sheet,
It is the ratio (β / α) of the angle α formed by the optical axis and the incident light beam on the light incident surface side. By controlling this angular magnification (that is, substantially 1 or less in the present invention), directivity can be imparted to the light rays emitted from the light guide plate at any angle. Further, the above-mentioned sheet - light guide plate mustard as bets (A) - Doo (A), the majority of light rays incident at a specific angle that is as totally reflected in the prism
Since it is not so much, it is possible to efficiently give a directivity to the light rays emitted from the light guide plate at any angle and obtain a high-luminance backlight. Further, since the light ray incident on the afocal lens at the angle (γ) is emitted at the angle (γ × β ÷ α), the directivity of the light ray can be controlled relatively easily by controlling the angular magnification.

Claims (4)

[Claims] 1. A backlight for a panel, comprising a light guide plate made of a translucent material, and a linear light source adjacent to at least one side surface end portion of the light guide plate. A backlight for a panel, characterized in that a sheet made of a translucent material having a large number of fine lenses is arranged. 2. The backlight for a panel according to claim 1, wherein an afocal type sheet in which the angular magnification of each lens is substantially 1 or less is arranged. 3. The backlight for a panel according to claim 1, wherein a sheet having a lens sheet surface provided with a light diffusing function is used. 4. The backlight for a panel according to claim 1, wherein a lens sheet integrated with a light diffusion sheet is used.