JP2010161052A - Light guide plate, and manufacturing method of light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate which has a specific surface roughness and yet has no coloring phenomenon, and to provide a manufacturing method thereof. <P>SOLUTION: The light guide plate 1 receives light from an end face and at least one of an outgoing face and a face opposed to the outgoing face is a light diffusing face (reflecting face 1a) endowed with a light diffusing and reflecting means consisting of random and fine concavo-convex. The concavo-convex has a ten-point average roughness Rz of 0.2 μm or more and 6.5 μm or less, and the light diffusion face is applied with non-volatile transparent liquid of a thickness of 0.001 μm or more and 0.1 μm or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light guide plate for an edge light type backlight used for illumination of a signboard, a liquid crystal display device, etc., and a display device using the same.

In the conventional light guide plate, light diffusing particles or the like are added inside the light guide plate to diffuse and reflect light. In addition, fine grooves are provided by post-processing on the surface of a flat plate having high light transmittance, or reflectors having different areas are provided by printing.
For example, Patent Document 1 describes a light guide whose thickness is reduced as the distance from the light source is increased, and the tilt is adjusted with a reflective surface as a curved surface. Patent Document 2 describes a diffusion plate containing a diffusing agent therein and an example in which a reflective surface is formed by performing mesh-like printing with a gradient in density.
When light diffusing fine particles were added to the inside of the light guide plate, there was no major problem when the light guide distance (distance between the light incident surface and the surface facing the light guide plate) was less than 300 mm. However, when the light guide distance is 300 mm or more, there is a problem that the illuminance on the light emitting surface decreases as the light guide distance increases.
Moreover, the effect of making the illuminance of the light emitting surface uniform is insufficient even when a fine groove is provided by post-processing to finely process the surface of the light guide plate or when a reflector having a different area is provided by printing.

In addition to this, Patent Document 3 discloses a structure in which a fine rough surface portion and a smooth portion are provided on the surface of the light guide, and the area ratio of the rough surface portion is changed. In order to prevent the vicinity of the rough surface portion from being bright and the smooth portion from being dark, a method such as providing a diffusion sheet between the light guide and the display unit or increasing the distance between the light guide and the display unit is used. It is done. However, both of them are contrary to the reduction in thickness and weight of the display device.
Therefore, in order to make the illuminance of the light emitting surface uniform, it is conceivable to provide a fine rough surface portion on the entire surface of the light guide and change the degree of the rough surface. In this case, when the light guide distance becomes long, it is necessary to adjust the degree of the rough surface over a wide range. As a result of various studies on the adjustment of the degree of rough surface, the inventor has found that there is a problem that a coloring phenomenon occurs when a 10-point average roughness Rz has a fine uneven portion of 6.5 μm or less. This coloring phenomenon seems to be due to Rayleigh scattering due to the numerical value of the surface roughness and bluish in the light incident part and yellowish in the position away from the light source. Such a coloring phenomenon is conspicuous when the light guide distance is 300 mm or more. However, the conventional rough surface light scattering type light guide plate has few such light guide distances, and the problem itself has not been revealed.

Japanese Patent Laid-Open No. 2-013925 JP-A-4-145485 Japanese Patent No. 2710465

  An object of the present invention is to provide a light guide plate that does not have a coloring phenomenon even if the light guide plate has a specific surface roughness, and a method for manufacturing the same.

  One aspect of the light guide plate according to the present invention is a light guide plate that enters from an end surface, and at least one of the light exit surface and the surface facing the light exit surface is a light diffusing / reflecting means made of random fine irregularities. A non-volatile transparent having a 10-point average roughness Rz of 0.2 μm or more and 6.5 μm or less and a thickness of 0.001 μm or more and 0.1 μm or less on the light diffusion surface. It is characterized by applying a liquid. A non-volatile transparent liquid is applied to the light diffusing surface of the light guide plate to adjust the degree of roughness. This prevents a reduction in coloration when there are fine irregularities.

  In one embodiment of the light guide plate according to the present invention, the non-volatile transparent liquid is preferably silicone oil, and the distance between the light incident surface and the surface facing the light incident surface is 300 mm or more. Preferably there is.

Furthermore, another aspect of the light guide plate according to the present invention is a light guide plate that enters light from an end surface, and at least one of the light exit surface and the surface facing the light exit surface is light diffusion formed of random fine unevenness. A light diffusing surface provided with a reflecting means, and the unevenness has a 10-point average roughness Rz of 0.2 μm to 6.5 μm and a thickness of 0.001 μm to 0.1 μm on the light diffusing surface. The transparent liquid was applied, and after the coating, the transparent liquid was cured. This makes it possible to prevent a reduction in coloring from occurring when the transparent liquid is used and there are fine irregularities.
The transparent liquid is preferably a silicone rubber liquid (polysiloxane rubber).

  Furthermore, one aspect of a method for manufacturing a light guide plate according to the present invention is a method for manufacturing a light guide plate that enters light from an end face, and has an average of 10 points on at least one of a light output surface and a surface facing the light output surface. A light diffusing surface provided with light diffusing / reflecting means composed of fine irregularities having a roughness Rz of 0.2 μm or more and 6.5 μm or less is formed, and a thickness of 0.001 μm or more and 0.1 μm or less is formed on the light diffusing surface. Apply a non-volatile transparent liquid.

  Further, another aspect of the light guide plate manufacturing method according to the present invention is a light guide plate manufacturing method that enters light from an end surface, and includes 10 points on at least one of the light exit surface and the surface facing the light exit surface. An average roughness Rz of 0.2 μm or more and 6.5 μm or less is formed, and a light diffusion surface provided with light diffusing / reflecting means composed of fine irregularities is formed, and the light diffusion surface has a thickness of 0.001 μm or more and 0.0. A transparent liquid of 1 μm or less is applied, and after the application, the transparent liquid is cured.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a light guide plate which has specific surface roughness, a light guide plate without a coloring phenomenon and its manufacturing method can be provided.

It is sectional drawing which shows an example of the light source device of embodiment of this invention. It is a figure explaining the structure of a light-guide plate. It is the fragmentary figure which expanded the reflective surface of a light-guide plate, (a) is the figure which expanded the cross section of the reflective surface typically, (b) expanded further (a), and a non-volatile liquid apply | coated It is the figure which showed the state performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. In the drawings, components having the same configuration or function and corresponding parts are denoted by the same reference numerals and description thereof is omitted. Further, “10-point average roughness Rz” and “center line average roughness Ra” in the present specification conform to JIS B 0601: 2001.

(Embodiment 1)
An embodiment of an edge light type surface light source device according to the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of a light source device according to an embodiment of the present invention. In FIG. 1, a light source device (surface light source device) includes a light source (linear light source) 4 such as a light guide plate 1, a diffusion film 2, a reflective film 3, a cold cathode tube or LEDs (light-emitting diodes) arranged in a line. A reflection plate 5 surrounding the light source 4 is provided. In FIG. 1, the light source 4 is provided on only one end face of the light guide plate 1, but may be provided on two end faces, or may be provided on three or more end faces. Furthermore, it may be provided in the corner portion. As shown in FIG. 2, the light guide plate 1 has a mirror surface (light exit surface) 1b from which light is emitted and a reflection surface 1a from which light is reflected. The reflection surface 1a has a predetermined surface roughness when the plate is formed. Is given.

Specifically, a light diffusing surface provided with light diffusing / reflecting means composed of random fine irregularities is formed on the reflecting surface 1a. In order to make the luminance of the emission surface uniform, the fine unevenness preferably has a 10-point average roughness Rz of 0.2 μm or more and 6.5 μm or less. Although FIG. 2 shows an example in which the light diffusing surface is formed on the reflecting surface 1a, the light diffusing surface may be formed on the mirror surface 1b, or the reflecting surface 1a and the mirror surface 1b may be formed. A light diffusion surface may be formed on both.
The roughness of the light diffusing surface may vary depending on the location. In order to make the luminance of the emission surface uniform, the fine unevenness of the light diffusion surface may increase as the distance from the light source 4 increases. The light diffusing surface may be formed on a part of the reflecting surface 1a or may be formed on the entire surface. The area where the light diffusing surface is formed may increase as the distance from the light source 4 increases.

  A display device can be configured by using the above-described edge light type surface light source device as a backlight and superimposing a transmissive display element such as a liquid crystal panel or a printed sign on the light emitting surface side.

In order to form a fine shape having a 10-point average roughness Rz of 6.5 μm or less on the surface of the light guide plate 1 as in the present invention, a method of performing a surface roughening process such as sandblasting or polishing can be mentioned. The surface before the roughening treatment may be smooth. After a rough surface is formed in advance by extrusion molding, injection molding, cast molding, or the like, a roughening treatment may be further performed depending on the location or the entire surface.
As the material of the light guide plate 1, inorganic glass or transparent resin can be used, but acrylic resin, polycarbonate resin, styrene resin and the like are preferably employed from the viewpoint of transparency and mechanical properties.

In FIG. 3, the figure which expanded a part of reflective surface 1a of the light-guide plate 1 is shown. FIG. 3A is a schematic enlarged view of the cross section of the reflecting surface 1a. On the surface of the reflecting surface 1a, irregularities having a center line average roughness Ra = 6.5 μm are formed. Here, a non-volatile liquid is applied to the surface of the reflecting surface 1a, but the thickness of the coating is not shown because it is smaller than the surface unevenness.
FIG. 3B shows a further enlarged view, and further shows the portion surrounded by the dotted line of the reflecting surface 1a in FIG. The surface of the reflecting surface 1a has fine irregularities, and it is shown that the nonvolatile liquid 10 is applied to the surface.
As the non-volatile liquid, silicone oil (polysiloxane oil) is preferable because it is environmentally stable and hardly damages the substrate of the light guide plate 1. Alternatively, the non-volatile liquid preferably has high transparency, and preferably has a low viscosity (for example, about 50 Pa · s or less) because it needs to be applied very thinly.

  In order to eliminate the coloring phenomenon while ensuring the surface roughness of the light guide plate necessary for uniform luminance, the application amount of the nonvolatile liquid is important. The coating amount needs to be applied to the surface of the reflective surface 1a with a non-volatile liquid of 0.001 μm or more and 0.1 μm or less. If it is less than this, the coloring phenomenon cannot be sufficiently prevented. If it is larger than this, it is impossible to ensure the surface roughness of the light guide plate necessary for uniform luminance.

  The application amount of the non-volatile liquid may be changed depending on the location of the substrate. You may apply | coat only to a part of board | substrate. For example, it may be applied preferentially to a portion close to the light source 4. When applied only to a portion away from the light source 4, the light traveling in the light guide plate 1 scatters more blue light components near the light source 4, and the light in the light guide plate 1 transmitted to the portion away from the light source 4 is ( It is assumed to be yellowish (as a complementary color). For this reason, when applying only to a part, it is expected that giving priority to a part closer to the light source 4 than to a part far from the light source 4 is effective. Further, the portion closer to the light source is less likely to be colored because the surface roughness is smaller, and it is expected that application to that portion is more effective.

  In the present invention, light diffusing fine particles may be added inside the light guide to such an extent that the effect is not impaired.

  As described above, when the present invention is used, the surface roughness of the light guide plate necessary for uniform luminance is hardly changed, and the surface roughness of a particularly fine light guide plate that causes a coloring phenomenon is smoothed. I can do things. Therefore, it is possible to provide a light guide plate with uniform brightness and no coloring phenomenon.

(Embodiment 2)
In the first embodiment, the case where a non-volatile transparent liquid is used has been described. In the second embodiment, a case where a transparent liquid capable of curing the liquid after being applied to the light guide plate is used will be described. The configuration shown in FIGS. 1 to 3 is the same in the present embodiment, and the description thereof is omitted. Moreover, the manufacturing method of the light-guide plate of this embodiment is the same as Embodiment 1 until the process of apply | coating a transparent liquid except the point using the transparent liquid which can be hardened after application | coating instead of a non-volatile transparent liquid. It is the same. In this embodiment, after applying a transparent liquid, the process of hardening the said transparent liquid is performed.

As the transparent liquid, a liquid having high transparency is preferable, and an uncured silicone rubber liquid (polysiloxane rubber) is preferable from the viewpoint of environmental stability and that the substrate of the light guide plate 1 is hardly damaged. Furthermore, it is preferable that it is low viscosity from the point which needs to apply | coat extremely thinly, for example, it is preferable that it is 50 (Pa * s) or less.
Silicone rubber absorbs moisture in the atmosphere as well as UV-curable, one-component thermosetting, one-component room-temperature curing, two-component thermosetting, and two-component room-temperature curing. A condensation type that cures by heating can be used. Among these, a one-component type thermosetting type and a one-component type room temperature curing type are preferable for convenience.

By using a transparent liquid that can be cured after application, it is possible to further suppress coloring of the light guide plate as compared to the first embodiment. Specifically, as described in Embodiment 1, it has been found that the coloring phenomenon can be improved by applying a transparent liquid to the uneven portion of the light guide plate extremely thinly. However, the liquid adhering to the surface may fall off in the process of handling the light guide plate or adhering to the packing member, and unevenness in brightness or color may be seen in the dropout part, or surrounding members may be contaminated. Another problem occurs.
Then, it can suppress that a transparent liquid falls from a light-guide plate by using the transparent liquid which can be hardened after application | coating instead of a non-volatile transparent liquid. Thereby, even if it is a light guide plate which has specific surface roughness, there is no coloring phenomenon, and the light guide plate which solves the problem resulting from handling, and its manufacturing method can be provided.

(Example)
<Example 1>
A method for manufacturing the light guide plate 1 used in the edge light type surface light source device shown in FIG. 1 will be described below.
First, a light guide plate having a thickness of 8 mm was manufactured by casting using an acrylic resin with a mold having a mirror surface on one side and a uniform embossed surface on the other side.
The embossed surface of the mold was formed by blasting using blast particles having a particle size of about 100 μm.
Next, the surface roughness of the embossed surface of the obtained light guide plate was further adjusted according to the distance from the light source so as to be fine at a position close to the light source and rough at a position far from the light source.

The rough surface after the molding was adjusted as follows.
The part near the light source is polished by reciprocating the surface of the molding surface with No. 100 sandpaper for 50 reciprocations, and further with 50 reciprocating sandpaper for 50 reciprocations. 50 reciprocating polishing with sandpaper.
The part farthest from the light source was 100 reciprocally polished on the surface of the molding surface with No. 100 sandpaper.

  Next, in other parts, the sandpaper count is 100 to # 400 as the place to be polished is farther from the light source, and the number of reciprocations is adjusted to 50 to 200 times or polishing with sandpaper having a large count is performed. A continuous gradation was provided by a method that was not performed. Further, the entire surface was buffed to make the polishing unevenness less noticeable.

Table 1 shows the surface roughness of the diffuse reflection surface in Example 1 obtained as described above. Table 1 shows the position (distance) from the light source and the 10-point average roughness Rz.
[Table 1] Relationship between position from light source and 10-point average roughness Rz

  Next, silicone oil was used as the non-volatile liquid and applied to the diffuse reflection surface 1a. As a coating method, the sponge was wrapped with gauze provided with silicone oil and rubbed by hand. Here, gauze is immersed in silicone oil, but other coating methods may be used. For example, it may be applied using a wiper or the like.

  In order to measure the coating amount of the non-volatile liquid, the weight difference before and after coating can be used. However, when it is very thin as described above, the accuracy may be insufficient. In Example 1, nuclear magnetic resonance spectroscopy (H-NMR method) was applied. Specifically, it can be measured using the measurement method described in JP-A-2006-209036.

  First, a reference solution in which 0.01 g of silicone oil and 5 mL of deuterated chloroform were mixed in advance was prepared. Subsequently, the reference solution was evaluated by nuclear magnetic resonance spectroscopy (H-NMR method). Specifically, the methyl group peak intensity m of silicone oil (peak 0.071 ppm area intensity) and the peak intensity c of deuterated chloroform present in deuterated chloroform (peak 7.24 ppm area intensity). ), And a peak intensity ratio 1 between the peak intensity m and the peak intensity c is calculated. With this peak intensity ratio 1, the weight of the silicone oil present in 5 mL of deuterated chloroform is 0.01 g. We set the standards.

  Similarly, a five-level reference solution was prepared and evaluated in the range of 0.01 to 1 g, and peak intensity ratios of 1 to 5 were obtained.

  Next, the light guide plate of Example 1 coated with silicone oil was cut into a size of 300 mm × 300 mm, and then the silicone oil coated surface of the sheet was washed with 200 mL of hexane, and the hexane solution was distilled off under reduced pressure to remove silicone. Only oil remained. Thereafter, the silicone oil and 5 mL of deuterated chloroform are mixed, and the deuterated chloroform solution in which the silicone oil is mixed is substituted by deuterium present in the methyl group and deuterated chloroform of the silicone oil by H-NMR method. The peak intensity ratio A with no chloroform was evaluated.

  And the silicone oil weight which exists in a sheet | seat surface was evaluated and calculated by contrasting the peak intensity ratio A measured as mentioned above and the peak intensity ratios 1-5 of the reference | standard liquid evaluated beforehand.

  Next, a value obtained by dividing the measured silicone weight by the specific gravity of the silicone oil and further dividing by the sheet area (300 mm × 300 mm) was taken as the thickness of the silicone oil. In this example, the thickness was 0.01 μm.

  The amount of silicone oil contained in the reference solution was increased or decreased according to the amount of coating. In addition, when the coating thickness of the silicone oil was not uniform over the entire surface of the light guide plate, the cutting size was appropriately changed, and the measurement to the same effect was performed.

<Comparative Example 1>
As Comparative Example 1, a light guide plate was prepared in the same manner except that silicone was not applied to the light guide plate prepared in Example 1.

  About the light-guide plate of Example 1 of this invention and the comparative example 1, all produced the edge light type surface light source using the same white LED light source, and evaluated the brightness and the color visually.

  As a result of the evaluation, the surface light source using the light guide plate of the example did not depend on the light guide distance from the light source, maintained uniform brightness, and color unevenness was not particularly noticeable.

  On the other hand, the surface light source using the light guide plate of the comparative example maintained a uniform brightness without depending on the light guide distance from the light source, but was bluish at a position about 100 mm away from the light source and 400 mm from the light source. The distant position was yellowish and the color unevenness was conspicuous.

<Example 2>
The process of manufacturing the light guide plate, that is, the process before applying silicone oil to the diffuse reflection surface 1a was made under the same conditions and processes as in Example 1. Next, an uncured liquid of a one-pack type room temperature curable silicone rubber was used as a transparent liquid and applied to the diffuse reflection surface 1a. As a coating method, the sponge was wrapped with gauze to which a silicone rubber liquid was applied and rubbed by hand. Here, gauze is immersed in a silicone rubber solution, but other coating methods may be used. For example, it may be applied using a wiper or the like.
Thereafter, the rubber liquid was cured by leaving it at room temperature.

<Comparative example 2>
The light guide plate of Example 1 was provided with a location where the transparent liquid was dropped by touching with a finger during handling.

As a result of the evaluation, the surface light source using the light guide plate of Example 2 maintained a uniform brightness regardless of the light guide distance from the light source, and the color unevenness was not particularly noticeable.
On the other hand, although the surface light source using the light guide plate of Comparative Example 1 maintained a uniform brightness without depending on the light guide distance from the light source, it was bluish at a position about 100 mm away from the light source, and from the light source. At a distance of about 400 mm, it was yellowish and the color unevenness was conspicuous.
Further, the surface light source using the light guide plate of Comparative Example 2 was not particularly noticeable in color unevenness, but mottled unevenness in brightness was generated at a position touched with a finger during handling.

  The present invention is not limited to the embodiment and examples described above. Within the scope of the present invention, it is possible to change, add, or convert each element of the above-described embodiment to a content that can be easily considered by those skilled in the art.

DESCRIPTION OF SYMBOLS 1 Light guide plate 1a Reflecting surface 1b Mirror surface (light-emitting surface)
2 Diffusion film 3 Reflective film 4 Light source 5 Reflector 10 Nonvolatile liquid

Claims (7)

A light guide plate that receives light from an end face,
At least one of the light exit surface and the surface facing the light exit surface is a light diffusion surface provided with light diffusion / reflection means composed of random fine irregularities,
The unevenness has a 10-point average roughness Rz of 0.2 μm or more and 6.5 μm or less,
A light guide plate, wherein a non-volatile transparent liquid having a thickness of 0.001 μm to 0.1 μm is applied to the light diffusion surface.   The light guide plate according to claim 1, wherein the non-volatile transparent liquid is silicone oil. A light guide plate that receives light from an end face,
At least one of the light exit surface and the surface facing the light exit surface is a light diffusion surface provided with light diffusion / reflection means composed of random fine irregularities,
The unevenness has a 10-point average roughness Rz of 0.2 μm or more and 6.5 μm or less,
A transparent liquid having a thickness of 0.001 μm or more and 0.1 μm or less is applied to the light diffusion surface,
A light guide plate, wherein the transparent liquid is cured after being applied.   The light guide plate according to claim 4, wherein the transparent liquid is an uncured silicone rubber liquid.   The light guide plate according to any one of claims 1 to 4, wherein a distance between the light incident surface and a surface facing the light incident surface is 300 mm or more. A method of manufacturing a light guide plate that enters from an end surface,
Light diffusion in which at least one of the light exit surface and the surface facing the light exit surface is provided with a light diffusion / reflection means composed of fine irregularities having an average roughness Rz of 10 points of 0.2 μm to 6.5 μm Forming a surface,
A method of manufacturing a light guide plate, wherein a non-volatile transparent liquid having a thickness of 0.001 μm to 0.1 μm is applied to the light diffusion surface. A method of manufacturing a light guide plate that enters from an end surface,
Light diffusion in which at least one of the light exit surface and the surface facing the light exit surface is provided with a light diffusion / reflection means composed of fine irregularities having an average roughness Rz of 10 points of 0.2 μm to 6.5 μm Forming a surface,
A method for producing a light guide plate, wherein a transparent liquid having a thickness of 0.001 μm or more and 0.1 μm or less is applied to the light diffusing surface, and then the transparent liquid is cured.

Images