JP2000122054A - Surface light source device and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a liq. crystal display device with a simple and easily productive structure holding satisfactorily a broad angle of visibility property and elevating front brightness with using scattered light having high brightness and high directivity generating from a roughened surface, light scattering particulate or the like. SOLUTION: A surface light source device 10 is provided with one surface of a light emitting surface 15, light sources 12 in at least a pair of side end parts 11a, 11b placed opposite to each other in a light guide body 11 providing a light emitting system, and a light control sheet 17 on the light emitting surface 15. In this case, the angle of visibility distribution of a outgoing light beam 20 obtaining after transmitting the control sheet 17 by an incident light beam from only one side end part 11a is specified to be at a position, in which a peak position of brightness is leaned in an angle more than 5 degree from a normal 21 direction of the light emitting surface 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device and a liquid crystal display device using the same, and more particularly to a viewing angle performance and a front luminance of a surface light source device suitably used as a backlight of a liquid crystal display device or the like. Related to improving technology.

[0002]

2. Description of the Related Art In recent years, a transmissive liquid crystal display (display) device has been frequently used as a display device of a word processor, a personal computer or the like. Such a liquid crystal display device is generally configured by arranging a planar illumination device, that is, a backlight, on the back surface of a liquid crystal element. This backlight has a mechanism for converting a linear light source such as a cold cathode discharge tube into planar light.

[0003] Specifically, a conventional backlight has a light source disposed directly below the back surface of a liquid crystal element, or a light source provided on a side surface thereof, and a surface light source is obtained using a light guide such as an acrylic plate. Is typical (side light method),
In particular, in the case of the latter sidelight method, an optical element such as a prism array is arranged on the light emitting surface of the light guide plate to obtain desired optical characteristics.

[0004] Such a sidelight type backlight is disclosed in, for example, JP-A-61-99187 and JP-A-63-62104, and is already well known. In particular, in order to more effectively bring out the general characteristics of a liquid crystal display device that is lightweight and thin, it is preferable to use a sidelight method in which a backlight can be made thin, and it is suitable for a liquid crystal display device such as a portable personal computer. The backlight of the sidelight type is often used.

[0005]

The performance required of such a backlight has been increasing in recent years, and in particular, a portable personal computer or a TV monitor using a color liquid crystal display device has been developed. Then
Due to the extremely low light transmittance of the color liquid crystal cell itself, the luminance value required for the backlight light source is inevitably high.

[0006] For this reason, in the backlight of the sidelight type, it is inevitable to secure the front luminance by optical condensing action by frequently using a sheet composed of a prism array or the like. However, although the use of a sheet made of a prism array or the like is effective for securing the front luminance, there is a problem in that the viewing angle characteristics are narrowed and the cost is greatly increased.

The most effective solution to such a problem is disclosed in Japanese Unexamined Patent Publication No. 6-18879, which discloses a high-luminance directivity generated from a rough surface or light-scattering fine particles. This is an attempt to use highly scattered light.

However, when these directional scattered lights are used, the front luminance is relatively sufficiently ensured, but the viewing angle characteristics in the direction perpendicular to the long axis of the fluorescent tube as the light source are extremely narrow. Therefore, there is a problem that it becomes a great hindrance to practical application to a liquid crystal display device or the like. Therefore, the appearance of a technology capable of providing a surface light source device having both front luminance and viewing angle characteristics by simpler means has been awaited.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems. The object of the present invention is to utilize a high-intensity highly directional scattered light generated from a rough surface, light-scattering fine particles, etc. An object of the present invention is to provide a surface light source device having a simple structure and easily manufactured, which can maintain a sufficiently wide angular characteristic and increase the front luminance, and a liquid crystal display device using the same.

[0010]

SUMMARY OF THE INVENTION The present invention is a surface light source device, and is configured as follows to solve the above-mentioned technical problem. That is, the present invention provides a light guide having one surface serving as a light emission surface and provided with a light extraction mechanism, a light source provided at least on a pair of opposed side ends of the light guide, In the surface light source device including the light control sheet disposed on the light output surface, the viewing angle distribution of the output light obtained after transmitting through the light control sheet, due to the incident light from only one of the side end portions, has a luminance peak. The position is inclined at least 5 degrees from the normal direction of the light exit surface.

<Additional Configuration in the Present Invention> The surface light source device of the present invention is composed of the above-mentioned essential components. However, the present invention is established even when the components are specifically as follows. The additional component is characterized in that the light extraction mechanism is formed with a rough surface. As a light extraction mechanism,
It is not particularly limited to a rough surface, but a means for generating highly directional scattered light caused by inorganic fine particles or the like dispersed in a light guide may be used.

Also, in the surface light source device of the present invention, a dimming sheet having a substantially prism array shape whose generatrix is parallel to the light source can be used. In this case, the effect of the present invention can be further enhanced.

Further, in the surface light source device of the present invention, the prism array constituting the light control sheet has an apex angle of 55 to 75.
It is preferable that the prism is formed of an isosceles triangular prism. Furthermore, in the surface light source device of the present invention, by the incident light from only one side end, the luminance peak position in the viewing angle distribution of the outgoing light obtained after passing through the light control sheet, and from only the opposite side end. It is characterized in that a similar luminance peak position caused by an incident light beam is separated by 5 degrees or more. Note that the luminance peak position is 1 from the normal direction of the light exit surface.
The effect of the present invention can be obtained most when the position is inclined (shifted) by 0 degrees or more.

Further, the surface light source device according to the present invention is most preferably used for a backlight optical system of a liquid crystal display device. That is, the liquid crystal display device of the present invention can provide a liquid crystal display device having excellent viewing angle characteristics and surface luminance by incorporating the above-mentioned features, that is, components.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a surface light source device and a liquid crystal display device according to the present invention. FIG. 1 shows a surface light source device 10 according to one embodiment of the present invention. The surface light source device 10 according to this embodiment includes a light guide 11 and two light sources 12 arranged on a pair of side ends 11a and 11b facing each other.

These light sources 12 include fluorescent tubes and LEs.
A D array or the like can be used, but is not particularly limited to these light sources. Surface light source device 1 of the present invention
For the light source 12 used for 0, it is most preferable to use a cold cathode tube excellent in light source luminance.

A reflector 13 is provided around each light source 12 so that the emitted light can be transmitted to the light guide 1 as efficiently as possible.
1 is configured to be incident on the side end portions 11a and 11b. By providing the reflector 13 with, for example, a black light absorption band in an overlapping portion of the reflector 13 with the light guide, it is possible to prevent a bright line that is likely to be generated in the vicinity of the light source.

In the surface light source device 10 of the present invention, as described above, a pair of side end portions 11a
At least one light source 12 disposed in each of the light sources 11b is an important component. The surface light source device 10 shown in FIG. 1 is a typical example thereof, and a pair of opposed side end portions 11a and 11b.
This is a so-called two-lamp mode in which one cold cathode tube is provided as a light source 12.

In addition to the above structure, a four-light type or two-light cold cathode tube in which cold cathode tubes as light sources are provided at all four side ends of the light guide 11 may be used. A mode in which two cold-cathode tubes are provided at one end of one side and two cold-cathode tubes are also provided at a side end facing the one side end, and a total of four cold-cathode tubes are used. You can also.

The light guide 11 is provided with various light extraction mechanisms. In the surface light source device of the present invention, in particular,
It is most preferable to use a scattered light having high intensity and excellent directivity caused by a rough surface or light scattering fine particles disclosed in, for example, US Pat.

For example, when scattered light is extracted by using a rough surface as a light extraction mechanism, graining of a gradation pattern or transfer of a dot pattern having a rough surface is effective.
At this time, it is preferable to adjust the degree of the rough surface, the area occupied by the rough surface, and the like to make the luminance distribution uniform. Such uniform luminance on the light emitting surface is one of the characteristics required for the surface light source device.

The rough dots 14a, 14b, 14c... Provided on the surface light source device 10 shown in FIG. 1 are representative examples, and the area of the rough dots increases as the distance from the light source 12 increases. It is configured so that the amount of light emitted onto the light emitting surface 15 is as uniform as possible over the entire surface. Further, from the viewpoint of uniforming the luminance distribution on the light emitting surface, that is, the light emitting surface 15, even if the arrangement density of the rough surface dots having the same area or different areas is increased as the distance from the light source increases, the same applies. The effect can be obtained.

When the scattered light from the rough surface or the light-scattering fine particles alone hinders the adjustment of the viewing angle characteristics and the in-plane luminance distribution, a print pattern of white ink is further formed on the side opposite to the light exit surface. It is possible to use them together. This makes it possible to mix scattered light components with a high viewing angle, so that it is possible to obtain a light extraction mechanism that is more excellent in controllability of illumination light characteristics.

Here, the rough surface dots 14a, 14b, 14
In the light guide 11 having a light extraction mechanism composed of c..., rough surface dots 14a, 14b, and 14c
There is a region where light emission from... Cannot be sufficiently obtained, that is, a dark line generation region. The appearance of the dark line generation area 16 is as follows.
This is because the light emitted from the rough dots 14a, 14b, 14c... Is emitted at a shallow angle that is essentially at an angle of 30 to 50 degrees with respect to the light emitting surface 15.
When a, 14b, 14c,... are present on the surface facing the light exit surface 15, a light emitting area is necessarily obtained near the light source after passing through the light control sheet 17 described later due to the relationship of the light path. Because there is no.

It is conceivable that a cover is provided in the dark line generating area 16 and at least a part of the area is not used as a surface light source. However, in order to prevent such a dark line phenomenon, FIG. As shown in the figure, it is preferable to provide a light extraction mechanism including the rough surface dots 14a, 14b, 14c,.

The surface light source device 10 according to the present embodiment further includes a dimming sheet 17 disposed on the light exit surface 15 of the light guide 11. In the light control sheet 17, the maximum luminance direction of the light emitted from the light control sheet 17 due to the incident light from only one side end 11 a of the light guide 11 is perpendicular to the normal direction of the light output surface 15. It is configured to be shifted (inclined) by 5 degrees or more.

As described above, the light control sheet 17 is used for the light guide 11.
When the incident light from one side end 11a is viewed, the maximum luminance direction of the light emitted from the light control sheet 17 is inclined at least 5 degrees with respect to the normal direction of the light exit surface 15. When both of the two lamps disposed on both side ends are turned on and superimposed on the outgoing light beam due to the light beam incident from the other side end portion 11b opposed thereto, an illumination light characteristic having a wide viewing angle distribution can be obtained. It becomes possible. Such illumination light characteristics are particularly suitable for use in a backlight or the like of a liquid crystal display device.

This situation will be described in more detail with reference to FIG. First, a light beam incident from one side end 11a propagates in the light guide 11 according to a total reflection condition based on Snell's law. This light beam is used as the rough dots 14a, 14b,
When arriving at the light extraction mechanism consisting of 14c..., A scattering phenomenon occurs, and the light rays are emitted without staying in the light guide 11 any longer.

At this time, a light beam directly emitted from the light guide 11, a light beam emitted through reflection by a reflection sheet 19 provided on a surface 18 of the light guide 11 opposed to the light exit surface 15, and the like are provided. However, in any case, rough surface dot 1
In the case of scattered light having high intensity and high directivity due to 4a, 14b, 14c, etc., the direction of the emitted light largely deviates from the normal direction of the light emitting surface 15, and the half-value angle is narrow.

The light beam emitted in this manner is applied to a light control sheet 17 composed of a triangular prism array having an apex angle of 60 to 70 degrees, for example. Are arranged parallel to each other, and the emitted light beam is deflected so that the luminance peak position is directed to the normal direction of the light emitting surface 15, whereby illumination light with high luminance in front can be obtained.

In the surface light source device 10 according to the present invention, the dimming is performed so that the luminance peak of the light ray 20 emitted from the light adjusting sheet 17 is inclined at least 5 degrees from the normal 21 of the light emitting surface 15. The optical parameters of the sheet 17, more specifically, the apex angle of the triangular prism array 17a are adjusted. As a result, the one-side end 11 formed after the light beam incident from the one-side end 11a passes through the light control sheet 17 is formed.
The viewing angle distribution due to the incident light from only a is as shown by the curve S1 in the characteristic diagram shown in FIG.

The above-mentioned optical parameters differ depending on the size of the light guide to be constituted, the method of the light extraction mechanism, and the like, and appropriate values should be set for each. For example, as shown in FIG. 2, a light guide having a size of 12 inches has dot patterns 14a, 14b,...
In the case where is used, it was possible to incline (shift) the luminance peak position (direction) by 6 degrees from the normal direction of the light emitting surface using the triangular prism array 17a having a vertical angle of 63 degrees.

Here, as described above, one side end 11
The viewing angle distribution formed by the incident light only from the side end 11a formed after the light incident from the light transmitting sheet 17 passes through the light control sheet 17 is set such that the luminance peak position is inclined (shifted) from the normal direction. Therefore, the other opposite side end 11
After the light beam incident from b also passes through the light control sheet 17, it forms a viewing angle distribution such as a curve S2 shown in the characteristic diagram of FIG. 3, for example.

Accordingly, the light source 12 disposed at the other end 11b opposite to the light source 12 disposed at the one end 11a
Is turned on at the same time during use, the viewing angle distribution of the emitted light beam becomes illumination light having a high intensity and a wide distribution as shown by a curve S shown in the characteristic diagram of FIG. Thus, it is possible to obtain an illumination light characteristic which is extremely suitable for use in such applications.

Light control sheet 17 used in the present invention
Has a function of changing the direction of the light beam emitted from the light guide 11, and the luminance peak position of the light component incident on the light guide 11 from one side end 11a after passing through the light control sheet 17 ( The direction is not particularly limited as long as it has a function of making the position inclined (displaced) by 5 degrees or more from the normal direction of the light emitting surface 15. At this time, it is preferable that the shape and the arrangement direction of the light control sheet 17 are determined in consideration of the directivity of the emitted light beam 20 according to the light extraction mechanism provided in the light guide 11.

The light extraction mechanism preferably used in the surface light source device of the present invention, which is composed of a rough surface or light scattering fine particles, has an apex angle of 55 to 75 degrees.
It is preferable to arrange a triangular prism array of preferably 55 to 70 degrees, more preferably 60 to 70 degrees, so that the apex angle faces the light emitting surface 15 and the generatrix of the prism is parallel to the light source 12.

Other than the above, the above-mentioned functions of a prism having a polygonal cross section, a prism having a curved top portion, a cylindrical lenticular lens, a group of pyramids having a polygonal cross section, a microlens array, a diffractive optical element array and the like are satisfied. A light control sheet having a shape designed in the above manner can also be suitably used.

In a preferred embodiment of the surface light source device of the present invention, both the light guide 11 and the light control sheet 17 are formed of a resin material. In particular, an acrylic resin, a polycarbonate resin, a polyester resin, or a cyclic polyolefin resin is preferably used, and a group of optical elements formed on the surface of the light control sheet 17 is a known thermosetting represented by an acrylic resin or the like. What is formed with a property or a photocurable resin is preferable.

The light source as the light supply means in the surface light source device of the present invention is not particularly limited, but includes a fluorescent tube (cold cathode tube, hot cathode tube), a tungsten incandescent bulb, an optical rod, an LED array and the like. Representative. In particular,
It is most preferable to use a cold cathode tube as a linear light source that can be easily reduced in size and increased in luminance.

By the way, a liquid crystal display device utilizes an electro-optical effect of liquid crystal molecules, that is, optical anisotropy (refractive index anisotropy), orientation, and the like, and applies an electric field or applies an electric current to an arbitrary display unit. A display that uses a liquid crystal cell, which is an array of optical shutters, driven by changing the alignment state of light and changing the light transmittance and reflectance.

Specifically, there are liquid crystal display elements of a transmission type simple matrix drive super twisted nematic mode, a transmission type active matrix drive twisted nematic mode, and the like. By configuring the liquid crystal display device as above, it is possible to impart characteristics suitable for the liquid crystal display device, such as high luminance, wide viewing angle, low power consumption, and thinness.

[0042]

Next, the surface light source device of the present invention will be described in more detail with reference to preferred embodiments. However, the present invention is not limited to the following embodiments unless departing from the gist thereof. FIG.
FIG. 1 shows an embodiment of the surface light source device of the present invention. A 12-inch, 4 mm thick acrylic resin is used as the light guide 11, and the dot patterns 14a, 14b, 14c,... The light was transferred to the light emitting surface side of the light body 11.

On the surface facing the light exit surface 15, a reflection sheet 19 of 95% light reflectance with silver (Ag) deposited thereon is deposited.
Was arranged. Further, the light control sheet 17 has a thickness of 12
A prism sheet having 0 μm polyethylene terephthalate as a base film and having a prism apex angle of 63 degrees and a pitch of 150 μm is used. A direction in which the prism apical portion faces the light exit surface 15 side and the generatrix of the prism is parallel to the light source 12. It was installed in. A light diffusion sheet 22 having a thickness of 200 μm and a haze of 20% is provided on the prism sheet.

A cold-cathode tube having a diameter of 3 mm is used as the light source 12, and the cold-cathode tubes are disposed on the opposite side ends 11a and 11b, respectively. A reflector made of a film on which silver (Ag) is vapor-deposited is provided. 13 and turned on by applying a voltage via an inverter to obtain a surface light source device 10.

A luminance meter (BM-7, manufactured by Topcom) for the luminance distribution with respect to each emission angle from the center of the surface light source device 10.
It measured using. Table 1 shows the results.

[Table 1]

[0046]

COMPARATIVE EXAMPLE A light control sheet having a prism apex angle of 68 degrees and having a luminance peak position coincident with the normal direction of the light emitting surface due to light emitted from only one light source was used. The luminance distribution was measured using the same members as in the examples.
Table 1 shows the results.

[0047]

As described above, according to the surface light source device of the present invention, the viewing angle characteristics can be improved while utilizing the scattered light having high luminance and high directivity generated from the rough surface or the light scattering fine particles. It is possible to provide a surface light source device which has a simple structure and can be easily produced, which is kept sufficiently wide and has a high front luminance. These features respond to the demand for optical characteristics of illumination light for backlights of liquid crystal display devices, which have recently become more sophisticated.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a surface light source device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a surface light source device according to another embodiment of the present invention in which dark line countermeasures are taken.

FIG. 3 is a characteristic diagram showing a viewing angle distribution of illumination light emitted from the surface light source device of the present invention.

[Explanation of symbols]

Reference Signs List 10 surface light source device 11 light guide 11a one end of light guide 11b other end opposite to light guide 12 light source 13 reflectors 14a, 14b, 14c rough dot pattern (light extraction mechanism) 15 light emission surface Reference Signs List 16 dark line generating region 17 light control sheet 17a triangular prism 18 surface facing light exit surface 15 reflection sheet 20 exit light 21 normal line at light exit surface 22 light diffusion sheet S1 viewing angle only by incident light from one side end Distribution characteristic curve S2 Viewing angle distribution characteristic curve based on only incident light from the other end S3 Viewing angle distribution characteristic curve when two lamps are turned on

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Claims (6)

[Claims] 1. A light guide, one surface of which is a light exit surface and provided with a light extraction mechanism, a light source disposed on at least a pair of opposed side ends of the light guide, and the light In a surface light source device comprising: a light control sheet disposed on an output surface; and an incident light beam from only one of the side end portions, a viewing angle distribution of an output light beam obtained after transmitting through the light control sheet, A surface light source device, wherein a luminance peak position is at a position inclined at least 5 degrees from a normal direction of the light emitting surface. 2. The surface light source device according to claim 1, wherein the light extraction mechanism is formed with a rough surface. 3. The light control sheet according to claim 1, wherein the light control sheet is a substantially prism array light control sheet having a generatrix parallel to the light source.
The surface light source device according to claim 2, wherein a vertex angle portion of the prism faces the light emission surface side. 4. The surface light source device according to claim 3, wherein the prism array constituting the light control sheet comprises an isosceles triangular prism having an apex angle of 55 to 75 degrees. 5. A luminance peak position in a viewing angle distribution of an emitted light beam transmitted through the light control sheet due to an incident light beam from only one side end, and an incident light beam from only the opposite side end. A similar luminance peak position is
The surface light source device according to claim 1, wherein the surface light source device is separated by 5 degrees or more. 6. A liquid crystal display device, wherein the surface light source device according to claim 1 is used for a backlight optical system of a liquid crystal element.