JPH0795124B2 - Light guide plate for planar light source - Google Patents

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 used as a backlight for various display devices, or a surface light source device for a display such as an illuminated signboard, a light table,
The present invention relates to a light guide plate of a planar light source device such as a viewer. Particularly, the present invention relates to a light guide plate of a planar light source device called an edge light method or a side light method in which a light source is arranged on at least one side end surface of the light guide plate, and particularly to a light guide plate with improved brightness, manufacturing workability, and mass productivity. Involve

[0002]

2. Description of the Related Art As shown in FIG. 4, an edge light type planar light source device includes a transparent resin plate 3, a light source 1 installed on at least one side end surface 3a of the transparent resin plate 3, and a light from the transparent resin plate 3. The diffusion plate 2 is arranged on the emission surface 3b side, and the reflection plate 4 is arranged on the reflection surface 3c side of the transparent resin plate 3 facing the light emission surface 3b. The transparent resin plate 3 guides the incident light 6 from the light source 1 by utilizing the total reflection of the transparent resin plate 3 as shown in FIG.
By providing the light diffusing layer 5 on the light guide plate 3d, the incident angle of the light reaching the light diffusing layer 5 is changed to a critical angle of total reflection or more, and the light is again incident on the transparent resin plate 3 to form the light reflecting plate 4 The light is emitted to the opposite side.

In such an edge light type planar light source device, the amount of light reaching generally decreases as the distance from the light source increases. Therefore, the brightness distribution in the case of the light guide plate having a uniform light diffusion layer on the surface of the transparent resin plate is As shown in FIG. 6, the brightness decreases as the distance from the light source increases. Therefore, it is difficult to obtain a uniform planar light source, and various improvements have been made to obtain a uniform planar light source.

For example, JP-A-51-88042,
Japanese Utility Model Laid-Open No. 62-28306, Japanese Patent Laid-Open No. 63-3370.
No. 3, JP-A-64-57240, the cross section is wedge-shaped so that it becomes thinner as it gets away from the light source, or the light emitting surface is roughened with a continuous inclined surface and the amount of light reaching is made uniform. A light guide plate for obtaining a flat surface light source is disclosed. Further, JP-A-57-128383,
Japanese Utility Model Application Laid-Open No. 64-38621, JP-A-1-24159.
In JP-A-0, the light diffusing layer 7 is formed on the light guide plate 3 so that the light diffusing layer has an area ratio adjusted according to the amount of light reaching the light diffusing layer, and as shown in FIG. A light guide plate adapted to obtain a uniform surface light source.

Further, Japanese Patent Application Laid-Open No. 2-126501 discloses a light guide plate in which the density of a light diffusion layer pattern is limited to improve brightness and uniformity. At present, as the edge light guide plate, a light guide plate having a light diffusion layer is often used so that the area ratio increases as the distance from the light source increases.

[0006]

By the way, in the case of forming a light guide plate having a light diffusion pattern whose area ratio increases as the distance from the light source increases, in the case of the same light source, the light guide distance increases as the light guide distance increases. As the length of the light guide plate becomes longer, the brightness as a planar light source decreases as shown in FIG. Therefore, in the case of the same light source, the longer the length of the light guide plate, the smaller the area ratio of the minimum points or lines of the light diffusion layer on the light source side must be reduced. For example, in an actual edge light type planar light source device, when one cold cathode tube having a diameter of about 4 mm is used as a light source and the thickness of the light guide plate is 2 mm, and the length of the light guide plate is 100 mm, the light diffusion on the light source side is performed. The area ratio of the minimum point of the layer is about 17%, whereas it is about 9% when the length of the light guide plate is 200 mm.

On the other hand, when such a light diffusing layer is formed on a transparent resin plate by silk screen printing which is generally performed at present, if the dots are square, the printing accuracy is stable. The length of one side of the minimum point to be reproduced is about 300 μm, which corresponds to an area ratio of 12.5% when the density of halftone dots is 30 lines / inch, and an area ratio of 40 lines / inch. It corresponds to 22%. If the area ratio is less than this, the reproducibility of halftone dots due to printing will deteriorate, the pattern of the light diffusion layer will vary from one halftone dot to another, and uneven brightness will occur,
The halftone dot area ratio changes depending on the number of printed sheets.

Therefore, as is currently desired, when a large screen edge light type planar light source light guide plate is manufactured by printing, the reproducibility of the minimum point or the minimum line of the light diffusion layer on the light source side is poor, Therefore, there is a problem that the production yield is remarkably reduced. When using a light guide plate having a light diffusion layer formed of dots or lines, light is emitted only from the portion to which the light diffusion layer is attached, so the light guide plate shines in the pattern of the light diffusion layer. It was not seen as a uniform planar light source. Therefore, in order to obtain a uniform planar light source, normally, a diffusion film is used on the light emission surface side of the light guide plate to diffuse the emitted light and blur the pattern of the light diffusion layer on the light guide plate so that it cannot be seen. . Especially when the area ratio of the pattern of the light diffusion layer on the light guide plate is small, the contrast between the light emitting portion and the non-light emitting portion is large, and a diffusion film having high diffusion efficiency is required to blur the pattern. Further, if the density of halftone dots or lines is made coarse in order to improve the reproducibility of halftone dots or linear light diffusion layer patterns by printing and improve the productivity, the contrast becomes even larger, resulting in higher diffusion efficiency. I needed a diffusion film.

However, a diffusion film having a high diffusion efficiency generally has a low light transmittance, and when a diffusion film having a high diffusion efficiency is used, the brightness as a planar light source is lowered. Therefore, in order to obtain a surface light source with high brightness,
The light diffusing layer pattern on the light guide plate preferably has a large area ratio, and the density of the halftone dot or linear light diffusing layer pattern is 20.
In the case of lines / inch or more, the area ratio needs to be 20% or more, more preferably 40% or more. If the density of the light diffusion layer pattern is rough below 20 lines / inch, the area ratio is 30%
The above is preferable.

The present invention has been made in order to solve the above-mentioned drawbacks, and by setting the minimum area ratio of the light diffusion layer pattern on the light guide plate, the diffusion plate having high light transmittance can be used. It is an object of the present invention to provide a light guide plate that can obtain brightness, and another object of the present invention is to eliminate the unevenness of the brightness distribution of the light guide plate due to defective pattern reproducibility due to printing, thereby increasing the productivity of the light guide plate. Is.

[0011]

As a result of research to achieve the above object, the present inventor has found that, in the light guide plate currently manufactured by printing, the haze value of the light diffusing layer is completely zero as described above. Without paying attention, the fact that the light output distribution of the light guide plate was determined by the area ratio distribution of the light diffusion layer on the light guide plate was actually determined by the haze value distribution of the light guide plate. Invented. That is, in the planar light source light guide plate of the present invention, the area ratio increases with distance from the light source on at least one plane orthogonal to the side end surface of the transparent resin plate on which the light source is installed on at least one side end surface. In a planar light source light guide plate having a light diffusion layer having a halftone dot or linear pattern attached thereto, the haze value is 60 or less when the maximum area ratio of the light diffusion layer is 100%, and the minimum of the pattern. The area ratio is 20% or more.

The light guide plate for a planar light source of the present invention has the same structure as the light guide plate for a planar light source 3d shown in FIG. 5, and the transparent substrate used is poly (methyl methacrylate), (meth).
A highly transparent substrate such as an acrylic ester copolymer, polycarbonate, polystyrene, polyvinyl chloride, or glass is used. The ink used is prepared by dispersing a transparent resin and a transparent or white light diffusing material by a known method. As the transparent resin, polymethylmethacrylate, acrylic such as (meth) acrylic acid ester copolymer, styrene, urethane, epoxy, vinyl, polyester, cellulose, polyamide, etc. are used. To be done. Further, as the light diffusing material, it is preferable to use a transparent or white pigment because the coloring becomes deeper with the distance from the light source when it is colored. As the transparent pigment, natural or synthetic silica, glass beads, inorganic pigments such as diamond, acrylic resin, styrene resin,
Organic pigments such as silicone resin and benzoguanamine resin, and natural pigments such as rice starch and cone starch can be used, and white pigments include titanium oxide, zinc oxide, barium sulfate, calcium carbonate, magnesium carbonate, and water. Aluminum oxide, talc, clay and the like can be used. These pigments may be used alone or 2
You may use it in mixture of 2 or more types. If necessary, additives such as a dispersant and a leveling agent can be added to the ink in order to improve dispersibility and coatability.

An ink composed of such a transparent resin and a transparent or white light diffusing material and having a haze value of 60 or less when the area ratio is 100% has a difference depending on the pigment used and the printed film thickness. However, in general printing, the pigment is generally 12% by weight with respect to the resin solid content of 100%.
It is obtained by adding the following. Here, the haze value is 100 as the ratio of diffused light transmittance to total light transmittance.
It has been multiplied by. Further, as shown in FIG. 1, the haze value of a certain portion C on the light guide plate is (the area ratio of the light diffusion layer is 100).
% Of haze value (11) × area ratio of the light diffusion layer in that portion). That is, the area ratio of the light diffusion layer is 100%.
In this case, the area ratio of the light diffusion layer can be arbitrarily determined by controlling the haze value.

When the conventional ink was printed at an area ratio of 100%, the haze values were all 80 or more. Therefore, the area ratio of the small dots of the conventional light diffusion layer may be 10% or less. Therefore, in order to form a light diffusion pattern with a minimum area ratio of 20% or more, more preferably 40% or more, it is sufficient to reduce the haze value of the light diffusion layer in the case of an area ratio of 100%. The light diffusion layer may have a thickness of 60 or less, more preferably 50 or less.

In order to form a planar light source light guide plate from such a substrate, a light diffusion layer pattern is printed on a transparent substrate with an ink prepared so as to obtain a predetermined haze value.
In this case, the printing method is not particularly limited to silk screen printing, and the minimum area ratio of the light diffusion layer should be increased even in offset printing, letterpress printing, etc., which have better image reproducibility than silk screen printing. It is clear that is advantageous as in silk screen printing in terms of productivity and using a diffusion film to blur the light diffusion layer pattern.

[0016]

The present invention provides an edge light type light guide plate,
By controlling the haze value of the ink forming the light diffusion layer on the light guide plate, the light diffusion layer pattern can be arbitrarily set. More specifically, the light diffusing layer pattern is set in a range in which the pattern can be blurred even with a diffusing film having good printing reproducibility and high light transmittance.

[0017]

EXAMPLES Example 1 A transparent substrate having a thickness of 2 mm and a size of 148 mm × 225.
mm acrylic plate (Sumitomo Chemical Co., Ltd .: Sumipex E
001) is prepared, and on one side of this acrylic plate, the density of 20 lines / inch and the density of 20 lines / inch and 5%, 10%, 20%, 30%, 40%, 50% of 40 lines / inch,
A tint chart having an area ratio of 60%, 70%, 80%, 90%, and 95% was silk-screen printed to examine the dot reproducibility by printing. The haze value when this ink was printed at an area ratio of 100% was 85.

Ink composition-Clear ink (Teikoku Ink Mfg. Co., Ltd .: SP-62AU clear: solid content 37.5% by weight) 100 parts by weight-Synthetic silica pigment (Fuji Devison Co., Ltd .: Cyloid 978) 7.5 parts by weight Methyl ethyl ketone 12.5 parts by weight The change in dot reproducibility depending on the number of printed sheets when 60 sheets were continuously printed is shown in FIG. 2 (density 20 lines / inch) and FIG. 3 (density 40 lines / inch). Table 1 shows the variation in the area ratio of each halftone dot in the 60th halftone dot area ratio.

[0019]

[Table 1]

From the above, in the silk screen printing, the density of the halftone dots is 20 lines / area in the area where the stability of the change of the halftone dot reproducibility depending on the number of printed sheets and the stability of the area ratio of each halftone dot are excellent.
It can be seen that the area ratio is 10% or more in the case of inches and the area ratio 20% or more in the case of 40 lines / inch. Example 2 Eight acrylic plates of Example 1 were prepared, and the same ink as that of Example 1 was used on one side thereof at a dot density of 20 lines / inch and 40 lines / inch to obtain 10%, 20%, 30%, A 40% uniform screen was printed. After printing, attach a silver vapor deposition reflective tape to the side surface of the acrylic plate other than the light incident part, and install a cold cathode lamp with a tube diameter of 5.6 mm and a lamp brightness of 17,000 nt at the short side light incident end. The periphery of the plate light incident part was covered with a silver vapor deposition reflector. Further, a white polyester film (Toray Industries, Inc .: Lumirror E-60) is arranged as a reflection plate on the coating surface side of the acrylic plate, and a light diffusion film (Kimoto: D-2 Co., Ltd.) is arranged on the coating surface side.
04) was arranged to produce an edge light type planar light source unit.

In this surface light source device, a visual examination of a halftone dot pattern was conducted through a diffusion film.
In the case of 20 lines / inch, the halftone dot pattern was almost invisible at 30% or more, and the halftone dot pattern was completely invisible at 40% or more. In the case of 40 lines / inch, the halftone dot pattern was almost invisible at 20% or more, and completely invisible at 30% or more.

Example 3 The same ink as in Example 1 was used on one side of the acrylic plate of Example 1 so that the area ratio increases as the distance from the end on the light source side increases, and the dot density is 20 lines / inch, the minimum. A light diffusion layer pattern was printed at a dot area ratio of 8% and a maximum dot area ratio of 30% to obtain a light guide plate A.

Also, on one surface of another acrylic plate similar to that of Example 1, halftone dot density of 20 lines / inch, minimum point so that the area ratio increases with the distance from the end on the light source side with the ink of the following composition. The light diffusion layer pattern was printed at a maximum area ratio of 75% to obtain a light guide plate B. The haze value when this ink was printed at an area ratio of 100% was 34.

Ink composition-Clear ink (Teikoku Ink Mfg. Co., Ltd .: SP-62AU clear: solid content 37.5% by weight) 100 parts by weight-Synthetic silica pigment (Fuji Devison Co., Ltd .: Cyloid 978) 4.2 parts by weight -Methylethylketone 7.0 parts by weight These two light guide plates were attached to the edge light unit of Example 2 and evaluated as a surface light source device, and the results of Table 2 were obtained.

[0025]

[Table 2]

From this result, the brightness distribution of the light guide plate is determined by the distribution of the haze value, and the area ratio of the light diffusion layer is 100%.
It can be seen that by controlling the haze value in the case, the same luminance distribution can be obtained even if the area ratio distribution of the light diffusion layer is changed. Further, it can be seen that by setting the minimum value of the area ratio of the light diffusing layer to 20% or more, the brightness unevenness due to printing unevenness and the pattern visibility through the diffusion film are improved.

Example 4 A light diffusion pattern was formed on one surface of the acrylic plate of Example 1 with a dot density of 20 lines / inch so that the area ratio increases with the ink having the composition shown below as the distance from the end on the light source side increases. Printed. At this time, the area ratio of the minimum point is 20% and the maximum point is 8
It was 0%. When this light guide plate was attached to the edge light unit of Example 2 to form a surface light source device, a uniform surface light source was obtained in which there was no unevenness in brightness due to variations in halftone dot area even in a portion close to the light source and no halftone dot pattern was visible. Was given. The haze value when this ink was printed at an area ratio of 100% was 30.

Ink composition: Clear ink (Teikoku Ink Mfg. Co., Ltd .: SP-62AU clear: solid content 37.5% by weight) 100 parts by weight Synthetic silica pigment (Fuji Davison: Cyloid 978) 3.0 parts by weight Methyl ethyl ketone 5.0 parts by weight Example 5 As a transparent substrate, the thickness is 3 mm, and the size is 150 mm × 210.
mm acrylic plate (Sumitomo Chemical Co., Ltd .: Sumipex E
001) was prepared, and a light diffusion pattern was printed on one surface of the acrylic plate with an ink having the following composition at a dot density of 40 lines / inch so that the area ratio increases as the distance from the end on the light source side increases. . The area ratio of the minimum point at this time is 20%
The maximum score was 70%.

When this light guide plate was attached to the edge light unit of Example 2 to form a surface light source device, there was no brightness unevenness due to variations in the halftone dot area even in the portion close to the light source, and a uniform halftone pattern was not visible. A light source is obtained. The haze value when printing this ink at an area ratio of 100% is 6
It was 0. Ink composition-Clear ink (Teikoku Ink Mfg. Co., Ltd .: SP-62AU clear: solid content 37.5% by weight) 100 parts by weight-Calcium carbonate (Tatsumori Co., Ltd .: Sunlight 700) 5.0 parts by weight-Methyl ethyl ketone 8.3 parts by weight Example 6 A transparent substrate having a thickness of 3 mm and a size of 150 mm × 210
mm acrylic plate (Sumitomo Chemical Co., Ltd .: Sumipex E
001) was prepared, and a light diffusion pattern was printed on one surface of the acrylic plate with an ink having the following composition at a dot density of 40 lines / inch so that the area ratio increases as the distance from the end on the light source side increases. . The area ratio of the minimum point at this time is 40%
The maximum score was 80%.

When this light guide plate was attached to the edge light unit of Example 2 to form a surface light source device, there was no unevenness in brightness due to variations in halftone dot area even in a portion near the light source, and a uniform halftone pattern was not visible. A light source is obtained. The haze value when printing this ink at an area ratio of 100% is 2
It was 5. Ink composition-Clear ink (Teikoku Ink Mfg. Co., Ltd .: SP-62AU clear: solid content 37.5% by weight) 100 parts by weight-Silicone resin pigment (Toshiba Silicone Co., Ltd .: Tospar 130) 2.0 parts by weight-Methyl ethyl ketone 3.3 parts by weight

[0031]

As is apparent from the above description, the light guide plate for a planar light source according to the present invention focuses on the haze value of the light guide plate as a means for controlling the light emission rate. The area ratio of the light diffusion layer can be arbitrarily changed by controlling the haze value when the area ratio is 100%. Therefore, compared with the conventional method of controlling the light emission rate only by the area ratio of the light diffusing layer, the high brightness surface light source which is superior in productivity and can easily blur the halftone dot pattern with the diffusion film having good transmittance. Is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a haze value of a light guide plate for a planar light source according to the present invention.

FIG. 2 is a diagram showing a graph in which a change in halftone dot reproducibility depending on the number of printed sheets is measured when printing up to 60 sheets at a halftone dot density of 20 lines / inch.

FIG. 3 is a diagram showing a graph in which a change in halftone dot reproducibility depending on the number of printed sheets is measured when printing up to 60 sheets at a halftone dot density of 40 lines / inch.

FIG. 4 is a configuration diagram of an edge light type planar light source device of the present invention and a conventional example.

FIG. 5 is a diagram showing the principle of an edge light type planar light source device of the present invention and a conventional example.

FIG. 6 is a diagram showing a relationship between a distance from a light source and a luminance distribution of a conventional edge light type planar light source device.

FIG. 7 is a diagram showing a part of a conventional edge light type planar light source device.

FIG. 8 is a diagram showing a relationship between a distance from a light source and an average brightness of a conventional edge light type planar light source device.

[Explanation of symbols]

 1 ………… light source 3 ………… transparent resin plate 3a ………… side end face 3d ……… light guide plate 5 ………… light diffusion layer

Claims (1)

[Claims] 1. A planar shape obtained by printing a light diffusion layer having a dot or linear pattern on at least one plane orthogonal to the side end surface of a transparent resin plate on which a light source is installed on at least one side end surface. In the light guide plate for a light source, the haze value of the light diffusion layer having an area ratio of 100% is 60 or less, and the minimum area ratio of the pattern is 20% or more.