JP2001210121A - Surface light source device and liquid crystal display using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface light source device for an illumination optical system having high and practical optical property, using an illumination optical system with a directional scattering light source as a light source, which was incomplete in the sense of appearance quality as a backlight source means for a large-scale liquid crystal display, while substantially being effective for high brightness, and to provide a liquid crystal display using the surface light source device. SOLUTION: A light guide body 11 having one surface as a light emission plane 12 is provided with a light extraction mechanism 24. A linear light source 15 is arranged at a side end of the light guide body. A light adjusting sheet 18 which has a prism array 18a in almost triangular prism shape, with peak angles directed to the light emission plane and with ridge lines in parallel to the linear light source is arranged on the light emission plane 12 of the light guide body 11. A plane 14 opposed to the light emission plane of the light guide body is provided with a positively reflective sheet 20 which has a light diffusion part 21 near the linear light source.

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 technique for improving the optical characteristics of the surface light source device. The present invention relates to a liquid crystal display device suitably used as a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, transmissive liquid crystal displays (displays) have been frequently used as monitors for personal computers and display devices such as thin TVs. A planar lighting device or backlight is provided. The backlight is a mechanism for converting a linear light source such as a cold cathode discharge tube into planar light.

[0003] Specifically, a method of arranging a light source immediately below the back surface of a liquid crystal element or a method of installing a light source on a side surface and converting the light into a planar shape using a translucent light guide such as an acrylic plate. A typical method is to obtain a surface light source (side light method), and a mechanism for obtaining desired optical characteristics by disposing an optical element such as a prism array on the light emitting surface.

[0004] The side light system is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 61-99187 and 63-6210.
No. 4 discloses this. 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 that can reduce the backlight, and a liquid crystal display device such as a portable personal computer is preferred. Backlights of the sidelight type are often used.

[0005]

The performance required of these backlights has been increasing in recent years. Particularly, in the case of a stationary personal computer monitor display device and a large-screen thin TV, Generally, a transmission type full color liquid crystal device is used. In this case, from the extremely low light transmittance of the color liquid crystal cell itself,
The brightness value required for the backlight light source is inevitably high.

For this reason, in the above-mentioned backlight of the sidelight system, a sheet made of a prism array or the like is frequently used to secure front luminance by an optical condensing function, or special light having a deflection conversion function. It is generally practiced to effectively use the emitted light rays with a functional sheet, but overuse of these not only causes a large increase in cost but also causes adverse effects such as narrowing of the viewing angle characteristics. The emergence of a technique for providing a surface light source device having high optical characteristics by simple means has been awaited.

As one of the solutions to these problems, Japanese Patent Publication No. Hei 7-27136 and Japanese Patent Publication No. Hei 7-2713
As disclosed in, for example, Japanese Patent Application Laid-Open No. 7-1995, it is effective to use directional scattered light with high luminance generated from a rough surface formed on the surface of the light guide or light scattering fine particles dispersed in the light guide. it is conceivable that.

That is, by using a collimated directional scattered light source as a light source, the light condensing property is further improved, and the amount of light incident on a limited light guide can be effectively directed to the front direction. Therefore, it has been clarified that it is possible to realize a low-cost illumination optical system having a higher illumination efficiency with a simpler configuration.

However, when these illumination optical systems are put to practical use, the luminance distribution, which is the most important quality as a backlight light source for a display device, is extremely poor, although the luminance is relatively secured. Particularly, in the vicinity of the light source, many unfavorable phenomena such as bright lines and dark portions in appearance quality occur, which has greatly hindered practical use as a backlight light source for a large liquid crystal display device.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and is essentially effective for increasing the luminance, but has an appearance quality as a backlight light source means of a large liquid crystal display device. Was unfinished in terms of
It is an object of the present invention to provide a surface light source device as an illumination optical system having more advanced and practical optical characteristics using an illumination optical system using a directional scattering light source as a light source, and a liquid crystal display device using the same.

[0011]

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 as a light emitting surface, a light extraction mechanism provided in the light guide, a linear light source provided at a side end of the light guide, and a light guide. A light control sheet having a substantially triangular prism-shaped prism array formed on the light exit surface of the light body so that a vertex angle is directed toward the light exit surface and a ridge line is parallel to the linear light source; A specular reflection sheet disposed on the surface of the body facing the light exit surface, wherein the reflection sheet is provided with a light diffusing portion near the linear light source.

<Specific Structure of 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 satisfied even when the specific components are as follows. The specific configuration is characterized in that the light diffusing portion provided on the reflection sheet has a gradation pattern in which the occupied area gradually decreases as the distance from the linear light source increases.

Further, in the surface light source device of the present invention, it is preferable that the light diffusing portion composed of the gradation pattern is formed by printing using white ink. At this time, it is preferable that the light diffusing portion printed on the specular reflection sheet is provided over a region within 50 mm from the side end of the light guide located on the linear light source side.

Further, in the surface light source device of the present invention, the light diffusing portion printed on the specular reflection sheet has substantially both ends projecting along side edges of the reflection sheet when the reflection sheet is viewed from the front. It is preferable that the pattern is formed in a U-shaped region. Further, the light extraction mechanism of the light guide can be formed by a dot pattern on a rough surface of a convex projection or a printing pattern of a semi-transparent ink.

Further, in the surface light source device of the present invention, it is preferable that a light transmissive sheet having a haze of 50% or less is disposed between the light exit surface of the light guide and the light control sheet. In that case, it is preferable to provide a gradation-like light-shielding pattern near the linear light source on the light-transmitting sheet. Such a gradation light shielding pattern is
It may be provided near the linear light source on the light emitting surface of the light guide.

In the surface light source device of the present invention having the above-described features, the prism array of the substantially triangular prism provided on the light control sheet has a vertex angle of 45 to 45.
It is preferable to use the one at 75 degrees. Further, it is preferable to use a regular reflection sheet having a reflectance of 90% or more.

The present invention is a liquid crystal display device using the above-mentioned surface light source device as a backlight light source means,
At this time, it is preferable to arrange a linear light source at the side end of the light guide located at the upper or lower part when the liquid crystal display device is used.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface light source device of the present invention and a liquid crystal display device using the same according to the present invention will be described in more detail with reference to the embodiments shown in the drawings. 1 and 2 show a surface light source device 10 according to one embodiment of the present invention.

The surface light source device 10 includes a substrate made of a light-transmitting flat plate, that is, a light guide 11, one surface of the light guide 11 being a light emitting surface 12, and a pair of opposed side ends. Part 1
A linear light source 15 is arranged on one of the three sides along the side end. The linear light source 15 includes a fluorescent tube, an LED,
An array or the like can be used, but is not particularly limited thereto.

The linear light source 15 has excellent luminous efficiency,
It is most preferable to use a cold-cathode tube that can be easily miniaturized. A reflector 16 is provided around the linear light source 15 so that the emitted light can be transmitted to the side end 1 of the light guide 11 with as little waste as possible.
3 is made to be incident.

The material used for the reflector 16 is not particularly limited as long as it has a high light reflectance.
For example, a metal plate having a plate thickness of about 0.2 to 0.4 mm or a flexible white plastic film having a thickness of about 0.1 to 0.25 mm is preferably used.

Here, considering the side light type surface light source device having the above-described basic configuration, the linear light source 1 will be described.
Line-shaped bright portions (bright lines) parallel to the linear light source are likely to be generated in the vicinity of the light source portion where the light source 5 is disposed, but these have a great effect on image quality and the like, and should be removed as much as possible. Is preferred.

The reason why a streak bright portion (bright line) parallel to the linear light source is generated in the vicinity of the light source portion is as shown in FIG. 8 near the side end portion 13 where the linear light source 15 is disposed. In this case, light rays flow from the light exit surface 12 and the surface 14 facing the light exit surface of the light guide 11, and these light components cannot satisfy the total reflection condition based on Snell's law. Therefore, even if the light enters the light guide 11 once, it cannot remain in the light guide 11 and is emitted as the bright line 17.

In particular, an optical system using a prism array having a substantially triangular prism shape whose apex is directed toward the light exit surface 12 of the light guide 11 as a light control sheet disposed on the light exit surface 12 of the light guide 11. In this case, this phenomenon is extremely likely to occur, which is a major reason why a surface light source device using the optical system is not practically used in applications where image quality is extremely important, such as a large liquid crystal display device.

In an optical system using a prism array having a substantially triangular prism shape whose apex is directed toward the light exit surface 12 of the light guide 11, a regular reflection sheet on which Ag or Al is deposited as a reflection sheet is further provided. The luminance performance can be dramatically improved by using.

The reason is that when rough surface patterning or semi-translucent ink patterning is provided on the light guide, which is a highly efficient light extraction means with small scattering loss, the scattered light generated from this light extraction means will This is because, since the light-collecting property is originally high, the use of a specular reflection sheet on which Ag or Al is deposited has little change in directivity, and these characteristics are not lost.

However, although a specular reflection sheet is effective for improving the brightness, the characteristic of the above-mentioned bright line which does not disturb the directivity of the specular reflection sheet is very noticeable. It tends to be easier. In other words, in a configuration in which a prism array having a substantially triangular prism shape whose apex angle is directed to the light emitting surface side of the light guide and a regular reflection sheet typified by Ag or Al is used as the reflection sheet, high luminance can be achieved. Although effective, it is difficult to remove bright lines.

On the other hand, according to the present invention, FIGS.
As in the surface light source device 10 of the embodiment shown in FIG. 1, a prism array 18a having a substantially triangular prism shape having a vertex directed toward the light emitting surface 12 is formed above the light emitting surface 12 of the light guide 11. The light control sheet 18 is disposed between the light control sheet 18 and the light exit surface 12.
Are arranged.

Further, in the surface light source device 10 of the present embodiment,
The reflection sheet 20 is disposed on the surface 14 of the light guide 11 opposite to the light exit surface 12. In the surface light source device according to the present invention, as the reflection sheet 20, a specular reflection material having a large surface reflectance, specifically, an Ag or AL vapor deposition sheet is used. The regular reflection sheet 20 is provided with a gradation-like light diffusing portion 21 near the linear light source 15.

As described above, in the present invention, the light diffusing portion 21 is provided near the linear light source of the specular reflection sheet 20 as in the surface light source device 10 of the embodiment shown in FIGS. The problem that the bright lines become excessively noticeable does not occur. That is, the light component that enters from the surface of the light guide 11 where the area of the light guide 11 is large via the specular reflection sheet 20 to be emitted as the bright line from the linear light source 15 is the light diffusion portion 21
In this case, the directivity is disturbed by the diffuse reflection, so that the intensity of the bright line is reduced.

Moreover, the light diffusing portion 21 is preferably
It is a gradation white pattern.
Since the occupied area of the white pattern gradually decreases as the distance from the area increases, the white pattern portion does not stand out as unnatural unevenness.

Here, when the occupied area is gradually reduced, when a certain area is sampled from the specular reflection sheet 20, the area occupied by the white pattern portion in the area gradually increases as the distance from the linear light source 15 increases. Means configured to decrease. For example, as shown in FIG. 4 in which the portion A in FIG. 3 is enlarged, a circular fine pattern is arranged so that the diameter decreases as the distance from the linear light source 15 increases, and a pattern having a constant area corresponds to the arrangement density. Is representatively such that the pattern is gradually reduced as the distance from the linear light source 15 increases.

Further, a region 2 where patterning is provided
2 is within 80 mm, more preferably 50 m, measured from the side edge where the linear light source is located, as shown by the shadow line in FIG.
m, more preferably within a range of 40 mm.
Further, in the present invention, a specular reflection sheet 20 having a reflectance of 90% or more is used.
In an optical system using, the brightness is extremely likely to be reduced in the vicinity of the electrode of the linear light source 15, which is a major problem in appearance quality as in the above-described bright line.

This is because the output angle distribution characteristic of the light source light does not change in the reflection process of the specular reflection sheet in the reflection process of the reflection sheet. The dark part becomes more conspicuous because of the emitted light rays.

This problem can be solved by enlarging and providing a light diffusing portion in the vicinity of the occurrence of a dark portion, similarly to the problem of the bright line described above.
As shown in FIG. 3, when the reflection sheet 20 is viewed from the front, both end sides of the linear light source 15 are disposed on the side end portions 13 of the linear light source 15.
By patterning in a substantially U-shaped area (shadow line portion) 22 having portions 23a and 23b protruding along side edges corresponding to side edges orthogonal to the above, not only the problem of the bright line but also the vicinity of the electrode occurs. It is possible to obtain an extremely practical optical characteristic in which a dark portion is corrected.

Here, in the surface light source device according to the present invention, the light component, which should be a bright line component and whose intensity is appropriately moderated in the light diffusing portion 21, is a light guide as shown in FIG. A light-shielding pattern 19a is provided in the vicinity of a linear light source on a light-transmitting sheet 19 provided between the light-emitting surface 12 of FIG. 11 and a prism array 18a having a substantially triangular prism shape, and the light-shielding pattern 19a is appropriately adjusted. It can also be used as a light source of a light source device.

That is, in the present invention, the sheet 19 provided with the light-shielding pattern 19a is a light-transmitting sheet, and more specifically, the haze value specified in JIS K6719 is 50% or less, more preferably 40% or less. More preferably, it is 35% or less.

This is a prism array 18a of a substantially triangular prism shape whose apex is directed toward the light emitting surface 12 of the light guide 11.
This is because it is preferable that the light rays incident on the light-transmitting sheet 19 are converged as much as possible, and the light-transmitting sheet 19 used in the present invention is essentially different from the light diffusion sheet generally used in the conventional surface light source device. The functions are different. The same effect can also be achieved by providing a light shielding pattern on the light emitting surface 12 of the light guide 11.

Further, in the surface light source device 10 of the present embodiment,
As described above, the light extraction mechanism 24 (see FIG. 2) for efficiently extracting light from the light guide 11 is provided on the surface 14 of the light guide 11 opposite to the light emission surface 12. In the surface light source device of the present invention, the light extraction mechanism 24
Instead of using a multiple scattering process using a white ink or the like in which titania fine particles or the like are dispersed at a high concentration, a process in which the number of scatterings is relatively small or not used is used.

This is for maximizing the incidence efficiency with respect to the substantially triangular prism-shaped prism array 18a whose apex is directed toward the light exit surface 12 of the light guide 11 while preventing the light amount loss due to multiple scattering. Specifically, these functions are realized by a so-called semi-transmissive light extraction mechanism.

More specifically, as shown in FIG. 6A, a fine rough surface 25 formed on the surface 14 of the light guide 11 opposite to the light exit surface 12, and FIG. As shown in FIG. 6C, a projection 26 protruding from the surface 14 as shown in FIG. 6 or a roughened surface 27 having a rough surface 25 as the surface of the projection 26 protruding from the surface 14 as shown in FIG. Or a mode using semi-translucent ink printing or the like.

Here, the semi-translucent ink is an ink in which fine particles having a different refractive index such as silica fine particles are dispersed in a binder at a low concentration, and when printed on a light guide, the printing is performed. The portion preferably has a light transmittance of 20% or more, more preferably 40% or more.

Further, in the aspect of the projection 26 protruding from the surface 14, the inclined surface is formed by making the cross section as shown in FIGS. 7A and 7B triangular or semicircular. The projection rough surface 27 further includes a projection formed as an element, and further has a roughened surface of the projection protruding from the surface 14.
As shown in FIG. 7 (c), the shape of the projection includes a projection having a semicircular cross section with a rough surface.

From the viewpoint of easy adjustment of luminance unevenness and ease of manufacture, most preferably, a pattern in which patterns of substantially the same shape are arranged, for example, a rough projection surface 27 having a projection amount h of 1 μm to 50 μm is formed in a dot shape. In this case, a pattern (graphicalization) is formed by arranging the patterns in a pattern and forming the pattern (graphicalization), or by printing a semi-transparent ink in the same manner as a dot.

The basic pitch of this pattern is preferably as fine as possible in order to prevent the pattern from being seen and to improve the light use efficiency. More specifically, the basic pitch is 0.5 mm or less, more preferably It is 0.4 mm or less, more preferably 0.3 mm or less.

As an example of the pattern arrangement of the patterning, when the surface 14 facing the light emitting surface 12 of the light guide 11 is viewed from the front, the planar shape is an elliptical shape, a triangular shape, a quadrilateral shape or the like. These dots can be formed by patterning (graphicalizing) each of these dots.

However, the semi-transmissive light extraction mechanism is not limited to a dot shape, and the plane shape when the surface 14 is viewed from the front is patterned into a fine mesh shape or a stripe shape. May be used.

In a preferred mode of use of the surface light source device according to the present invention, a linear light source 15 is disposed on at least one of a pair of opposed side ends 13 of the light guide 11, and the linear light source 15 is provided. Is a mode in which it is arranged in a horizontal direction during use. This is because the viewing angle characteristic generally required for the surface light source device is desirably wide in the horizontal direction, and the viewing angle characteristic of the illumination light obtained in the present invention is such that the linear light source 15 is arranged in the above direction. In this case, it is extremely suitable for satisfying this requirement.

This requirement is particularly large for monitors of personal computers and liquid crystal TVs, and a wide viewing angle characteristic is required in the horizontal direction as represented by the TCO standard. The device is very suitable for this purpose. In this case, it is preferable that the prism array 18a having a substantially triangular prism shape whose vertex is directed toward the light emitting surface 12 of the light guide 11 has a vertex angle of 45 degrees or more and less than 75 degrees.

In a preferred embodiment of the surface light source device according to the present invention, both the light guide 11 and the light control sheet 18 are formed of a resin material. In particular, an acrylic resin, a polycarbonate resin, a polyester resin, or a cyclic polyolefin resin is suitably used, and a group of optical elements formed on the surface of the light control sheet is a known thermosetting represented by an acrylic resin or the like, or Those formed of a photocurable resin are preferred.

In the surface light source device of the present invention, a liquid crystal display 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 to any display unit or It refers to a device that performs display by using a liquid crystal cell, which is an array of optical shutters, driven by changing the alignment state of liquid crystal by applying current and changing light transmittance and reflectance.

More specifically, a transmission type simple matrix driving super twisted nematic mode, a transmission type active matrix driving twisted nematic mode, a transmission type active matrix driving in-plane switching mode, a transmission type active matrix driving multi-domain vertical aligned mode, etc. And a liquid crystal display element.

By constructing a liquid crystal display device using the surface light source device of the present invention as a backlight light source for these liquid crystal display elements, it is possible to obtain a large liquid crystal display while being effective in increasing the luminance. In a surface light source device using a prism array having a regular reflection sheet and an apex directed to the light exit surface side of the light guide as a dimming sheet, an unfinished backlight light source means of the device is used. It is possible to provide an illumination optical system having higher-brightness optical characteristics in which appearance quality is prevented from deteriorating due to dark portions generated near the electrodes.

[0054]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. (Example 1) Basically, a surface light source device having the same structure as that shown in FIGS. 1 and 2 was manufactured. That is, the light guide 1
An acrylic resin having a size of 350.0 × 285.0 mm and a thickness of 5 mm is used as 1 and a linear light source 15 composed of a cold cathode tube is disposed on two long sides (a pair of side end portions of the light guide 11 facing each other). 13 differs from the structure shown in FIG. 1 in that the linear light sources are arranged on both sides). The light extraction mechanism 24 was formed on the light guide 11. The protrusion amount h is 15.0 μm, and a protrusion rough surface dot having an average area of 0.25 mm ² is used.

Further, in order to prevent the bright line from becoming conspicuous, the side end 1 of the light guide 11 where the linear light source 15 is arranged is arranged.
The light extraction mechanism 24 is not provided in the region from 3 to 5 mm. Next, on the surface 14 of the light guide 11 opposite to the light exit surface 12, a regular reflective sheet 20 having a light reflectivity of 95%, on which Ag is deposited, is disposed to make the bright lines inconspicuous. A white circular dot pattern (light diffusive portion 21) was printed on the reflection surface 20 in an area 22 within 25 mm from the vicinity of the linear light source. The circular dot pattern has a maximum diameter of 0.5 mm, and is patterned in a gradation shape so that the area gradually decreases as the distance from the linear light source 15 increases.

Further, in order to prevent a dark portion generated near the electrode of the linear light source 15, the white dot pattern 21 provided near the linear light source of the reflection sheet 20 is raised at the side portion (the rising portion, ie, the rising portion, ie, Overhang portion 23a, 2
3b) is formed in a substantially U-shaped range (region) 22, as shown in FIG.

A light transmissive sheet 19 having a haze of 12% was disposed immediately above the light exit surface 12 of the light guide 11. In the vicinity of the linear light source of the light transmissive sheet 19, a gradation-like light-shielding pattern 19a is provided in order to completely remove the bright line, and the pattern is formed by performing white ink printing over a width of 20 mm. The pattern is such that the light-shielding portion gradually decreases as the distance from F.15 increases.

As the triangular prism array 18a facing the light emitting surface 12 of the light guide 11, a triangular prism array having a prism apex angle of 63 degrees and a pitch of 50 μm is formed on a polyethylene terephthalate base film having a thickness of 180 μm. The ridge line of the triangular brhythm array was parallel to the linear light source.

In the surface light source device of this embodiment, as described above, the light source 15 composed of a cold-cathode tube having a diameter of 2.6 mm is disposed at both of the pair of opposed side ends 13 of the light guide 11. did. The periphery of the light source 15 composed of each cold cathode tube was covered with a reflector 16 composed of a white polyester film. For the lighting, the two cold cathode tubes 15 were independently controlled so that the tube currents became constant, and the lighting was performed using a dedicated inverter unit.

According to the surface light source device constructed as described above, the bright lines are diffused by the gradation white printing pattern 21 having light diffusing property provided near the linear light source of the specular reflection sheet 20, and furthermore, the light transmission is achieved. Sex sheet 1
9 has been removed, so that the side edge 13 is normally removed.
The bright line appearing at a position 7 mm further away was completely removed, and a surface light source device having an extremely wide effective light emitting area and excellent appearance quality was obtained.

(Example 2) 298.0 as the light guide 11
Acrylic resin having a width of 218.0 mm, a thick portion of 2.2 mm, and a thin portion of 0.8 mm and having a wedge shape in which the thickness changes in the short side direction of the above-described shape is used. On the other hand, a linear light source 15 composed of a cold-cathode tube is disposed on the (thick side), and a light extraction mechanism 24 composed of translucent ink patterned so that the area becomes relatively larger as the distance from the linear light source 15 increases. Screen printing was performed on the optical body 11.

In the translucent ink, fine silica particles having an average particle size of 2.7 μm are dispersed. Here, the light extraction mechanism 24 is not provided in a region from the side end 13 where the linear light source 15 is disposed to 3.5 mm.

Next, on the surface 14 of the light guide 11 opposite to the light emitting surface 12, a regular reflective sheet 20 with a light reflectance of 95%, on which Ag is deposited, is disposed near the linear light source on the reflective surface. In order to make the bright lines less noticeable, as in the first embodiment,
25 m from the vicinity of the linear light source on the reflection surface of the reflection sheet 20
A white circular dot pattern was printed in the area within m.
The circular dot pattern has a maximum diameter of 0.5 mm, and is patterned in a gradation shape so that the area gradually decreases as the distance from the linear light source 15 increases.

The haze 1 is provided on the light exit surface 12 of the light guide 11.
A 5% light transmissive sheet 19 was provided. A gradation-like light-shielding pattern 19a is provided near the linear light source of the light-transmitting sheet 19, and the pattern performs white ink printing over a width of 8 mm, and the light-shielding portion gradually decreases as the distance from the linear light source 15 increases. It is a pattern.

As the triangular prism array 18a facing the light emitting surface 12 of the light guide 11, a triangular prism array having a prism apex angle of 65 degrees and a pitch of 50 μm is formed on a polyethylene terephthalate base film having a thickness of 120 μm. The ridge line of the triangular prism array was parallel to the linear light source.

The side end 13 of the light guide 11 has a pipe diameter of 2.0 m.
A light source 15 consisting of a cold cathode tube of m was arranged, and the periphery of the light source 15 consisting of the cold cathode tube was covered with a reflector 16 consisting of a white polyester film. Lighting was performed using a dedicated inverter unit with a constant tube current.

According to the surface light source device having such a configuration, the bright lines are diffused by the gradation white print pattern 21 having light diffusing property provided near the linear light source of the specular reflection sheet 20, and the light transmissivity is further improved. The bright line is removed by the sheet 19 of FIG.
The bright line that appeared at a distance of mm is completely removed,
A surface light source device having an extremely wide effective light emitting area and excellent appearance quality was obtained.

[0068]

As described above, according to the surface light source device of the present invention, while being essentially effective for increasing the luminance,
Difficult to use as a backlight light source means for large liquid crystal display panel devices, while using an illumination optical system that uses directional scattered light as a light source, it has better in-plane luminance distribution quality, It is possible to provide an illumination optical system having high-efficiency optical characteristics in which a phenomenon unfavorable in appearance quality does not occur.

That is, the excellent optical characteristics of the present surface light source device are extremely suitable for a liquid crystal display monitor and a backlight light source for a liquid crystal TV, which are recently increasing in size. Therefore, by using the surface light source device of the present invention as a backlight light source unit of a liquid crystal display device, a high quality liquid crystal display device that contributes to an improvement in the efficiency of the entire display device can be provided.

[Brief description of the drawings]

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

FIG. 2 is a partial cross-sectional view showing a part of the surface light source device shown in FIG. 1 in an enlarged manner.

FIG. 3 is a front view of the reflective sheet, which is a component of the surface light source device shown in FIG. 1, schematically showing a region where a light diffusing portion is formed in the reflective sheet.

FIG. 4 is a partially enlarged view showing a gradation white pattern as a light diffusing portion by partially enlarging a light diffusing portion forming region of the reflection sheet shown in FIG. 3;

FIG. 5 is a front view similar to FIG. 3, showing another example (a substantially U-shaped range having raised portions on both sides) of a light diffusion portion forming region to be patterned on a reflection sheet.

FIG. 6 is a structural explanatory view partially showing various aspects of elements constituting a light extraction mechanism used in the surface light source device of the present invention.

FIG. 7 is a structural explanatory view partially showing various aspects of elements constituting a light extraction mechanism used in the surface light source device of the present invention.

FIG. 8 is a partial cross-sectional view showing how a bright line is generated near a light source in a general surface light source device.

[Explanation of symbols]

Reference Signs List 10 surface light source device 11 light guide 12 light emission surface 13 side end (light incidence surface) 14 surface opposite to light emission surface 15 linear light source (cold cathode tube) 16 reflector 17 light component emitted as bright line 18 Light control sheet 18 Almost triangular prism-shaped prism array 19 Translucent sheet 19a Gradation-like light-shielding pattern 20 Reflective sheet made of regular reflective material 21 Light diffusing portion 22 Light diffusing portion forming region 23a Light diffusing portion forming region 23b Both end rising (overhanging) portions of the light diffusion portion forming region 24B Light rising mechanism 25 Light extraction mechanism 25 Rough surface which is a component of light extraction mechanism 26 Projection which is a component of light extraction mechanism Rough surface of the protrusion, which is a component of the take-out mechanism

Claims (11)

[Claims] 1. A light guide having one surface as a light exit surface, a light extraction mechanism provided on the light guide, a linear light source provided on a side end of the light guide, A dimming sheet on which a substantially triangular prism-shaped prism array is formed on the light emitting surface of the light guide such that a vertex angle is directed toward the light emitting surface and a ridge line is parallel to the linear light source; A specular reflection sheet disposed on the surface of the light guide opposite to the light exit surface, wherein the reflection sheet is provided with a light diffusing portion near the linear light source. A surface light source device characterized by the above-mentioned. 2. The method according to claim 1, wherein the light diffusing portion provided on the reflection sheet has a gradation pattern in which an occupied area gradually decreases as the distance from the linear light source increases. The surface light source device as described in the above. 3. The surface light source device according to claim 2, wherein the light-diffusing portion composed of a gradation pattern is formed by printing using white ink. 4. The light-diffusing portion printed on the specular reflection sheet is provided over an area within 50 mm from a side end of the light guide located on the linear light source side. The surface light source device according to claim 3, wherein: 5. The light-diffusing portion printed on the specularly reflecting sheet has a substantially U-shaped region in which both ends protrude along side edges when the reflecting sheet is viewed from the front. 4. A pattern according to claim 3, wherein the pattern is patterned.
Or the surface light source device according to 4. 6. The light guide of the light guide, wherein the light extraction mechanism is formed by a dot pattern on a rough surface of a projection or a printing pattern of a semi-translucent ink.
The surface light source device according to any one of claims 1 to 5. 7. A light transmissive sheet having a haze of 50% or less is provided between the light exit surface of the light guide and the light control sheet, and the linear light source of the light transmissive sheet is provided. The surface light source device according to any one of claims 1 to 6, wherein a gradation-like light-shielding pattern is provided in the vicinity of. 8. The light-emitting body according to claim 1, wherein a gradation-like light-shielding pattern is provided on the light-emitting surface of the light guide near the linear light source. Surface light source device. 9. The surface light source device according to claim 1, wherein a vertex angle of the substantially triangular prism array provided on the light control sheet is 45 to 75 degrees. . 10. The surface light source device according to claim 1, wherein the specular reflection sheet has a reflectance of 90% or more. 11. A liquid crystal display device using the surface light source device according to claim 1 as backlight light source means.