JP2000292787A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a surface light source device without picture display unevenness by improving its frontal brightness utilizing scattered light obtained through a light guide mechanism composed of a rough surface or the like with high brightness and high directivity and preventing a moire pattern from being generated by interference with a periodic optical path such as a liquid crystal element. SOLUTION: A light source 12 is arranged on at least one or both out of a pair of side edge parts, of a light transmission body 11 of which the one surface 11a is made to be a light-emitting surface and besides light guide mechanisms 14, 15, 16,... are formed on the other surface 11c confronted therewith, placed opposite to each other. The light source 12 is covered with a reflector 13 so as to make the light, emitted from the light source 12, incident on the inside of the light transmission body from the end face of the side edge part. A dimmer sheet 17 is arranged on the upper side of the light-emitting surface 11a of the light transmission body 11, and at the same time, a first diffusion means 20 which make exit light from the light-emitting surface 11a of the light transmission body 11 diffuse and make it incident on the dimmer sheet 17 and a second diffusion means 21 which make the light transmitted by the dimmer sheet 17 still more diffuse are arranged. A material with 5-70% haze value is used as the first diffusion means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface light source device,
More specifically, the present invention relates to a technique for mainly improving the performance of preventing display unevenness of an image in a surface light source device suitably used as a backlight of a liquid crystal display device or the like.

[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 latter case of the sidelight system, a mechanism for obtaining desired optical characteristics by arranging an optical element such as a prism array on the light emitting surface of the light guide has been adopted.

[0004] That is, a conventional sidelight type backlight (surface light source device) comprises a cold cathode discharge tube or the like at one end 1b of a light guide 1 made of an acrylic plate or the like as shown in FIG. A tubular light source 2 is provided, and this is
And a diffusion plate 4 is disposed on the light exit surface 1a of the light guide 1, a prism sheet 5 having an apex angle of about 90 degrees is disposed thereon, and another diffusion plate is further disposed thereon. On the other hand, on the surface 1c opposite to the light emitting surface 1a, a dot-like scattering / reflecting portion 7 made of white ink is formed by a printing technique, and foamed polyethylene terephthalate or diffuse reflection is formed close to the surface 1c. The reflection sheet 8 made of a conductive material is arranged.

[0005] The conventional surface light source device configured as described above has a problem that the luminance value is low due to its structural characteristics. However, recently, the performance required for such a backlight is in the direction of becoming more and more sophisticated,
In a portable personal computer or a TV monitor using a color liquid crystal display device, the extremely low light transmittance of the color liquid crystal cell itself inevitably requires a high luminance value for a backlight light source.

[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 to disperse high-luminance highly directional scattered light generated from a rough surface as disclosed in Japanese Patent Application Laid-Open No. 6-18879. It is an attempt to use.

[0008]

However, when such a surface light source device using directional scattered light is used as a backlight of a display device such as a word processor or a personal computer, the front luminance is relatively sufficiently ensured. However, there is a problem that display unevenness is likely to appear in an image on the display device.

[0009] Such display unevenness of an image reduces the commercial value of a surface light source device used for a liquid crystal backlight, an illuminator, and the like, and its prevention has been a major issue. It is considered that such display unevenness of an image occurs due to the following reasons. That is, when a large number of rough dots are formed on the light guide at a constant pitch in order to increase the brightness, the light reflected by these rough dots and emitted from the light exit surface of the light guide plate has a constant periodicity. It becomes a ray.

On the other hand, a liquid crystal element arranged on such a surface light source device typically has a mode in which tens or hundreds of thousands of transistors are arranged in an array as is well known in the art. There is a typical configuration in which a black matrix is provided on this substrate to improve the contrast of the liquid crystal display.

However, when a light beam having a periodic regularity, that is, a wavefront whose position is aligned, enters a light path having a periodicity such as a black matrix, interference is caused and a moire pattern is generated. When such a moiré pattern appears, an image displayed on the display device becomes display unevenness. Therefore, in order to cancel out the periodicity of the light beam emitted from the surface light source device, the modes shown in FIGS. 5 and 6 are generally used.

The surface light source device shown in FIG.
a is a light emitting surface, and a large number of rough surface dots 14, 1
The light guide 11 in which 5, 16,... Are formed at a constant pitch
A tubular light source 12 is disposed at one of the pair of side ends 11 b of the light guide 11, and light emitted from the light source 12 is transmitted from the end face of the side end 11 b into the light guide 11. The light source 12 is configured to be covered with a reflector 13 so as to be incident.

Above the light emitting surface 11a of the light guide 11,
The apex is directed toward the light exit surface 11a and the tubular light source 12
A dimming sheet 17 made of a prism array is provided so that the prism and the generatrix of each prism are parallel to each other. And
The light reflected by the large number of rough surface dots 14, 15, 16,... Formed on the other surface 11c of the light guide 11
1a is a light beam having a periodicity, and the light guide 1
The diffusion plate 18 is arranged on the one light emitting surface 11a to cancel the periodicity. In particular, when the reflection sheet 19 is formed of a specular reflection material such as an Ag vapor-deposited film, the phases of the emitted light beams are likely to be uniform.
It is essential to remove the periodicity due to

However, in this surface light source device, immediately before the light enters the prism array 17 which is a light control sheet, the diffusion plate 18
Is arranged, the scattered light having sharp directivity reflected by the rough surface dots is spread, and is incident on the prism array 17. In the prism array 17 used in this surface light source device, the prism is directed toward the light emitting surface side of the light guide 11 and the aperture angle (ratio) is substantially narrow (the vertex angle is 50 to 80 degrees) in order to increase the luminance. ) Has been. Therefore, there is a problem in that the light component which is deflected in the front direction by the prism array 17 is reduced, so that the luminance is reduced.

Further, as another method for canceling the periodicity of the light beam emitted from the surface light source device, a configuration shown in FIG. 6 has been proposed. In this surface light source device, the diffusion plate 18 is disposed above the prism array 17, and the other configuration is substantially the same as the surface light source device shown in FIG. In the case of such a surface light source device, since the liquid crystal element is mounted immediately above the diffusion plate 18, the distance between the diffusion plate 18 and the liquid crystal element is reduced.

When the distance between the diffusion plate 18 and the liquid crystal element is short, the traveling direction of the outgoing light beam is changed by the forward scattering by the diffusion plate in the very vicinity of the diffusion plate 18, but the phase is sufficiently disturbed. Since the dot pattern is not in the state of the dot, the periodicity of the dot pattern is not sufficiently canceled, causing interference with the black matrix of the liquid crystal element, etc.
As a result, there is a problem that a moiré pattern can be recognized. For this reason, there is a long-awaited need for a technique capable of providing a surface light source device that achieves both improvement in front luminance and prevention of image display unevenness by simple means.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and a high luminance and high directivity scattered light obtained by a light extraction mechanism composed of a rough surface or the like is used. Another object of the present invention is to provide a surface light source device which prevents a moiré pattern caused by interference with a periodic light path by a liquid crystal element or the like and has no image display unevenness.

[0018]

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 surface light source device of the present invention includes a light guide having one surface serving as a light exit surface, and a light extraction mechanism formed on the other surface facing the one surface, and at least one pair of the light guides facing the light guide. A light source provided at one or both of the side ends of the light guide, a reflector covering the light source so that light emitted from the light source is incident on the inside of the light guide from the end face of the side end, and a light guide of the light guide. A light control sheet disposed above the light output surface, and first diffusion means for diffusing light emitted from the light output surface of the light guide and causing the light to enter the light control sheet;
A second diffuser for further diffusing the light passing through the light control sheet, wherein the first diffuser has a haze amount of 5 to 7;
It is characterized by using 0%. The haze amount (%) means scattered light transmittance (Td) / total light transmittance (Tr) measured using an integrating sphere light transmittance measuring device according to JIS K6719.

<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 components are that the light source is composed of a tubular light source, and that the dimming sheet is composed of a prism array,
The prism array is arranged so that a vertex is directed toward the light exit surface of the light guide and the tubular light source and the generatrix of each prism are parallel to each other.

Further, in the surface light source device of the present invention, the first diffusing means can be constituted by the first diffuser disposed between the light exit surface of the light guide and the light control sheet.
Can be constituted by a second diffuser arranged above the light control sheet. Alternatively, the first diffusing means may be a rough surface formed on the light emitting surface of the light guide, and the second diffusing means may be a rough surface formed on the upper surface of the light control sheet. With this configuration, the number of parts can be reduced.

Further, in the surface light source device of the present invention, it is preferable that the light extraction mechanism is formed with a rough surface. In this case, the rough surface serving as the light extraction mechanism may be formed in a large number of dots, and each rough surface dot may be formed so that its area or arrangement density gradually increases as the distance from the light source increases.

According to the surface light source device of the present invention configured as described above, the light beam entering the inside of the light guide from the light source installed at the side end of the light guide is defined by the light emission surface according to a conventional method. The light is reflected toward the light emitting surface by the light extracting mechanism provided on the opposite surface, and emitted from the light emitting surface. The light beam emitted from the light emitting surface is diffused by the first diffusing means.

This first diffusion means has a small haze amount,
Therefore, the degree of light diffusion, that is, the half-value angle of the angular distribution of the emitted light does not become so large. Thereby, the loss of the amount of light incident on the light control sheet composed of the prism array having a substantially small opening angle with the apex angle directed toward the light emitting surface 11a is small,
There is no significant decrease in the brightness value. Next, the light beam redirected by the light control sheet is again diffused by passing through the second diffusion means. The amount of haze of the second diffusing means is larger than that of the first diffusing means, and therefore, is diffused relatively large.

The light beam which has completely lost its periodicity is
Even when the light passes through the liquid crystal element disposed above the second diffusing means, no interference phenomenon occurs, so that no moiré pattern is generated and no image display unevenness occurs. In addition, the light beams having the same phase and scattered by the light extraction mechanism formed on the light guide and exiting from the light exit surface pass through the first diffusing unit and reach the second diffusing unit before reaching the second diffusing unit. Therefore, the same effect can be obtained even if the practical haze amount is made smaller than using a single diffusion unit, so that the final light loss is also small,
Therefore, a sufficient luminance value is secured, and a bright image can be displayed.

[0025]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a surface light source device according to the present invention. FIG. 1 shows a surface light source device 10 according to a first embodiment of the present invention. The surface light source device 10 according to this embodiment includes a light guide 11 having one surface 11a serving as a light emitting surface, and a light source 12 is provided at one of a pair of opposed side ends 11b.

As the light source 12, a fluorescent tube, an LED array or the like can be used, but it is not particularly limited to these light sources. As the light source 12 used in the surface light source device 10 of the present invention, it is most preferable to use a cold cathode tube having excellent light source luminance.

The surface light source device 10 of the embodiment shown in FIG.
As a typical example, is a so-called one-lamp type in which one cold-cathode tube is provided as a light source 12 only at one (light incident end) 11b of a pair of opposed side ends. . But,
In addition to such a configuration, a so-called two-lamp type, in which one cold-cathode tube is provided as a light source 12 at both of a pair of opposed side ends of the light guide 11, four sides of the light guide 11 A four-lamp type in which a cold cathode tube is provided as a light source 12 at all ends, or
It is also possible to use a lamp in which a cold cathode tube of a lamp is provided at one or both side end portions of the light guide 11 facing each other.

A reflector 13 is provided around each light source 12 so that the emitted light can be transmitted to the light guide 1 with as little waste as possible.
It is configured to be incident on one light incident end 11b. The reflector 13 includes a light source 12 disposed inside.
The shape is not particularly limited as long as it can effectively reflect the light from the light source and enter the light guide 11 from the opening, and various shapes can be used.

Further, the light guide 11 is provided with various light extraction mechanisms. Particularly, in the surface light source device of the present invention, a high intensity caused by a rough surface disclosed in Japanese Patent Application Laid-Open No. Hei 6-18879. It is most preferable to use a scattered light having excellent directivity as a light extraction mechanism.

For example, when scattered light is extracted by 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.

In the surface light source device 10 shown in FIG.
The rough dots 14, 15, 16,... Provided on the surface 11c facing the light emitting surface 11a are typical examples thereof.
It is formed of a predetermined pattern, for example, a pattern arranged vertically and horizontally at a predetermined interval from each other. .. Are configured such that the area of each dot increases as the distance from the light source 12 increases, and the amount of light emitted on the light emitting surface 11a becomes as uniform as possible over the entire surface. It has been like that.

Further, from the viewpoint of uniforming the luminance distribution on the light emitting surface, that is, the light emitting surface 11a, the arrangement density of rough surface dots having the same area or different areas may be increased as the distance from the light source increases. The same effect can be obtained.

In the surface light source device 10, the rough surface dots 1
The light extraction mechanism constituting 4, 15, 16,... Includes a reflection sheet 19 disposed on the entire surface in proximity to the surface on which the rough dots are formed. This reflection sheet 1
9 is preferably made of an ortho-emissive material such as silver.

The surface light source device 10 according to the present embodiment comprises a triangular prism array having, for example, an apex angle of 60 to 70 degrees, with the apex angled toward the light exit surface 11a, and the light source 12 and the generatrix of each prism are parallel. The light control sheet 17 further includes a light control sheet 17 arranged so as to change the direction of the emitted light.

A first diffuser (diffusion plate) 20 as first diffusion means is provided between the light exit surface 11 a of the light guide 11 and the light control sheet 17, and furthermore, a light control sheet 17 is provided. A second diffuser 21 as a second diffusing means is disposed above the second diffuser. When the surface light source device 10 configured as described above is used as a backlight of a display device, a liquid crystal element (LCD) 22 is mounted above the second diffuser 21.

As the first diffuser 19, one having a haze amount of about 5 to 70%, preferably 10 to 50%, more preferably 15 to 35% is used. As the second diffuser, a haze amount appropriately selected according to the required performance of the surface light source device 10 can be used.

According to the surface light source device 10 configured as described above, the light beam from the light source 12 incident from the one end 11b propagates in the light guide 11 according to the total reflection condition based on Snell's law. This light beam is applied to the rough dots 14, 1
When reaching the light extraction mechanism composed of 5, 16,..., A scattering phenomenon occurs, and the light rays are emitted without staying in the light guide 11 any longer.

At this time, there are a light beam directly emitted from the light guide 11 and a light beam emitted through reflection by a reflection sheet 19 provided on a surface 11c of the light guide 11 which is opposed to the light emission surface 11a. However, in any case, as is clear from the light scattering state explanatory diagram schematically shown in FIG. 2, scattered light 14A, 15A, having high intensity and high directivity due to rough surface dots 14, 15, 16,. 16A, the direction of the outgoing light beam largely deviates from the normal direction of the light emitting surface 11a, and the half-value angle is narrow.

The light rays thus emitted are diffused to some extent by the first diffuser 20, as shown by reference numerals 14B, 15B, 16B,... In FIG. You. The light beam whose periodicity has been canceled by the first diffuser 20 is transmitted to the light exit surface 11a.
The angle is changed by the light control sheet 17 composed of a triangular prism array arranged so that the light source 12 and the generatrix of each prism are parallel to each other, and the luminance peak position is determined by the method of the light exit surface 11a. Pointed in line direction.

Next, the light beam which is deflected by the light control sheet 17 and whose luminance peak position is directed in the normal direction of the light emitting surface 11a is reflected by the second diffuser 21 in FIG. As shown by..., The light is diffused to enlarge the viewing angle, and is incident on the LCD 22.

The first diffuser 20 for canceling out the periodicity is disposed between the light emitting surface 11a of the light guide 11 and the light control sheet 17 to secure an optical path at a sufficient distance from the LCD 22. As a result, the periodicity of the dot pattern formed of the rough surface of the light beam incident on the light control sheet 17 can be almost completely canceled out.
It does not cause interference with the CD black matrix or the like, and as a result, the occurrence of moiré patterns can be almost completely prevented.

As a result, the light guide 1 is used as a light extraction mechanism.
1, rough surface dots 14, 15, 1 formed on the other surface 11c.
6. Even if scattered light having high directivity is generated by using, the interference phenomenon does not occur, thereby obtaining an image having a simple structure, a high luminance value and no display unevenness. Can be provided.

Next, a second embodiment of the surface light source device of the present invention will be described. In the surface light source device 30 of this embodiment, as shown in FIG. 3, the first diffusing means is constituted by the rough surface 31 formed on the light emitting surface 11a of the light guide 11, and the second diffusing means is further provided. The light control sheet 17 includes a rough surface 32 formed on the upper surface of a downwardly facing prism array.

Except for these components, the configuration is substantially the same as the surface light source device 10 of the embodiment shown in FIG. 1, and the same or corresponding components are denoted by the same reference numerals in FIG. The description is omitted.

As described above, the light guide 1 is used as the first diffusion means.
When the rough surface 31 is formed on the first light emitting surface 11a and the rough surface 32 is formed on the surface of the downward prism array as the second diffusing means, the surface light source device 10 of the first embodiment shown in FIG. Compared with this, the number of parts can be reduced, which can reduce manufacturing costs and improve productivity.

Regarding the light control sheet 17 disposed on the light exit surface 11a of the light guide 11, in addition to the prism having a triangular cross section, a prism having a polygonal cross section, a prism having a top curved surface, a cylindrical lenticular lens, A light control sheet formed of a group of pyramids having a polygonal cross section, a microlens array, a diffractive optical element array, or the like and having a shape designed to satisfy the above-described functions can also be suitably used.

In a preferred embodiment of the surface light source device of the present invention, each of the light guide 11 and the light control sheet 17 is 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.

The surface light source device 10 of the present invention described above,
In the embodiment of No. 30, since undesired bright lines and dark lines are likely to be generated in the vicinity of the light incident end 11b of the light guide 11, FIG.
As shown in FIG. 2, a light shielding portion 3 is provided on an optical functional sheet such as a prism array 17 disposed above the light guide 11.
It is preferable to shield by attaching 3 or the like.

[0050]

As described above, according to the surface light source device of the present invention, a liquid crystal element is mounted while utilizing scattered light with high luminance and high directivity generated from a rough surface as a light extraction mechanism. It is possible to provide a surface light source device with a simple structure and easy production, in which display unevenness of an image due to interference generated in the case is prevented. 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 fragmentary sectional view schematically showing a surface light source device according to a first embodiment of the present invention.

FIG. 2 is a configuration explanatory view schematically showing a light scattering state in the surface light source device shown in FIG.

FIG. 3 is a fragmentary sectional view schematically showing a surface light source device according to a second embodiment of the present invention.

FIG. 4 is a partial cross-sectional view schematically showing the surface light source device in a state where the light source is shielded by attaching a light shielding portion to an optical functional sheet in order to hide a bright line or a dark line in the surface light source device of the present invention.

FIG. 5 is a partial cross-sectional view schematically showing one surface light source device proposed to solve the drawbacks of the conventional surface light source device.

FIG. 6 is a partial cross-sectional view schematically illustrating another surface light source device proposed to solve a disadvantage of the conventional surface light source device.

FIG. 7 is a cross-sectional view schematically showing a conventional typical surface light source device.

[Explanation of symbols]

 Reference Signs List 10 surface light source device 11 light guide 11a light emitting surface of light guide 11b one end of light guide (light incident end) 11c surface opposite to light emitting surface of light guide 12 light source 13 reflector 14 coarse Surface dot (light extraction mechanism) 15 Rough surface dot (light extraction mechanism) 16 Rough surface dot (light extraction mechanism) 17 Light control sheet (prism array) 20 First diffuser (first diffuser) 21 Second diffuser (Second diffusion unit) 22 Liquid crystal element (LCD) 30 Surface light source device 31 Rough surface as first diffusion unit 32 Rough surface as second diffusion unit

Claims (5)

[Claims] 1. A light guide having one surface serving as a light exit surface and having a light extraction mechanism formed on the other surface facing the one surface, and a light guide having at least a pair of side ends facing the light guide. A light source disposed on one or both of the light source, a reflector covering the light source so that light emitted from the light source is incident on the inside of the light guide from the end face of the side end portion, and a reflector covering the light source; A light control sheet disposed above a light output surface, first diffusion means for diffusing light emitted from the light output surface of the light guide and causing the light to enter the light control sheet; and And a second diffusing means for further diffusing the transmitted light, wherein the first diffusing means has a haze of 5 to 70%. 2. The light source comprises a tubular light source, and the light control sheet comprises a prism array. The prism array has a vertex directed toward the light exit surface of the light guide and the tubular light source. The surface light source device according to claim 1, wherein the surface light source device is arranged so that the and the generatrix of each prism are parallel to each other. 3. The first diffuser comprises a first diffuser disposed between the light exit surface of the light guide and the light control sheet, and the second diffuser comprises:
3. The light emitting device according to claim 1, further comprising a second diffuser disposed above the light control sheet.
A surface light source device according to claim 1. 4. The light guide according to claim 1, wherein the first diffuser is formed by a rough surface formed on the light exit surface of the light guide,
3. The light diffusing means according to claim 1, wherein the light control sheet is constituted by a rough surface formed on an upper surface of the light control sheet.
A surface light source device according to claim 1. 5. The surface light source device according to claim 1, wherein the light extraction mechanism is formed with a rough surface.