JPH0980430A - Surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive surface light source device capable of obtaining high luminance with less reflection loss by forming a silicone oxide layer as an antireflection film on the incident plane and/or the outgoing plane of at least either of a light transmission plate and a diffusion plate. SOLUTION: The light generated by the linear light source 4 is made incident on the light transmission plate 2 from the side face of the plate 2. The incident light passes through the light transmission plate 2, the light passes through the plate 2 while partly outgoing from the outgoing plane side, then, the light advances toward a side face opposite to the linear light source 4, then, the light is emitted on the whole outgoing plane. After the light outgoing from the plate 2 is diffused by the diffusing plate body 1, the light is condensed by a prism sheet 5, then, the liquid crystal display screen is irradiated with the light. In this case, the silicone oxide layer is installed on the rear side of the diffusing plate body 1. When the light outgoing from the plate 2 passes through the diffusing plate body 1, the reflection loss of the light with a specified wavelength corresponding to the film thickness is suppressed by the presence of the silicone oxide layer, then, the light transmission efficiency is enhanced as much as the suppression of the loss. Thus, the high luminance is obtained, and in the case of requiring the same luminance, the device is used at a low power.

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 for a backlight of a liquid crystal display or the like.

[0002]

2. Description of the Related Art Conventionally, a thin display device using a liquid crystal such as a personal computer, a word processor, a liquid crystal television, etc. does not emit light from the liquid crystal itself, so that a backlight for illuminating the liquid crystal display screen from the back side is used. There is. Since this backlight needs to uniformly illuminate the entire liquid crystal display screen, a light guide plate system using a light guide plate is generally adopted. As shown in FIG. 3, the light guide plate type surface light source device includes a light guide plate 21, light sources 20 arranged on both side surfaces of the light guide plate 21, and a rear surface side of the light guide plate 21. The light guide plate 21 is provided with a reflection plate 22 for reflecting light that is going to be emitted from the back surface, and a diffusion plate 26. The diffusion plate 26 diffuses the light emitted from the emission light surface of the light guide plate 21, and makes the diffusion plate body 23 uniform in the brightness of the irradiation surface.
And the light-condensing sheet 24 disposed on the diffuser plate body 23 so that the light passing through the diffuser plate body 23 is collected in the front direction.
It is composed of The light-condensing sheet 24 is used as a single sheet or two sheets. In this device, the light source 20
Light is incident from the side surface of the light guide plate 21, the incident light is uniformly propagated to the entire light guide plate 21 and emitted from the entire emission light surface, and is diffused by the diffuser plate body 23 and condensed by the condensing sheet 24. After that, a liquid crystal display screen (not shown) arranged above the diffusion plate 26 is uniformly illuminated.
Further, when it is not necessary to make it thin like a vehicle-mounted display device, as shown in FIG.
A direct type device provided on the surface facing the outgoing light surface of 1a may also be used. In FIGS. 3 and 4, 25, 2
Reference numeral 5a is a reflection cover that reflects the light of the light sources 20, 20a toward the light guide plates 21, 21a.

In order to increase the brightness of the outgoing light surface of such a surface light source device and reduce the power consumption of the device itself, the light guide plate 2 is used.
A material having a high light transmittance is used for each member that transmits light, such as 1, 21a and the diffusion plate 26, and the light loss is suppressed as much as possible.

[0004]

However, in the above surface light source device, the reflection loss in which a part of the light to be transmitted is reflected on the surface of each member such as the light guide plate 21 and the diffusing plate 26 through which light is transmitted is avoided. I can't. Therefore, there is a problem that the light transmission efficiency is poor and high brightness cannot be obtained. Therefore, as a means for reducing the reflection loss, a liquid crystal display device disclosed in Japanese Patent Laid-Open No. 5-297366 has been proposed. That is, the liquid crystal display plate includes a liquid crystal display plate, a light guide plate, a light source for making light incident on the light guide plate, and a diffusion sheet for making the brightness of the irradiation surface of the light guide plate uniform. By forming a fluorine compound layer such as a transparent fluorine resin on at least one light transmission interface of the light guide plate and the diffusion sheet, reflection loss is reduced and light transmission efficiency is improved. However, although this can suppress the reflection loss to some extent, there is a problem that the cost is very high because an expensive solvent-soluble fluororesin is used to form the fluorine compound layer. Further, since the fluorine compound layer is easily charged,
There is also a problem that foreign matter adheres to the surface and the light transmittance is rather lowered.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an inexpensive surface light source device capable of obtaining high brightness with almost no reflection loss.

[0006]

In order to achieve the above object, a surface light source device of the present invention includes a transparent light guide plate, a light source for allowing light to enter from a part of the light guide plate, and an exit of the light guide plate. What is claimed is: 1. A surface light source device, comprising: a diffusion plate disposed on a light emitting surface side and diffusing light emitted from an emission light surface, wherein at least one of the light guide plate and the diffusion plate has an incident light surface and / or an emission light surface A silicon oxide layer serving as an antireflection film is formed.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION That is, the inventors of the present invention have conducted a series of studies for the purpose of obtaining a surface light source device having a small reflection loss and a high light utilization efficiency. Attention was paid to the fact that reflection loss is reduced by forming a silicon oxide layer serving as an antireflection layer on the surface of a member through which is transmitted. As a result of further research, they have found that the silicon oxide layer does not become charged like the conventional fluorine compound layer, and reached the present invention.

Next, the present invention will be described in detail.

The surface light source device of the present invention comprises a transparent light guide plate, a light source for allowing light to enter from a part of the light guide plate, and a diffuser plate arranged on the outgoing light surface side of the light guide plate. There is. Then, a silicon oxide layer is formed on at least one of the incident light surface and / or the exit light surface of the light guide plate and the diffusion plate, and the silicon oxide layer serves as an antireflection film to prevent surface reflection at the light transmitting interface. It was designed to be suppressed. In the present invention, the diffuser plate is composed only of a diffuser plate body for diffusing the light emitted from the light guide plate, the diffuser plate body, and the diffuser plate body provided on the surface side of the diffuser plate body. And a case where the sheet is formed of a light-condensing sheet that condenses light that has passed through.

As a material of the light guide plate used in the surface light source device, a material having high transparency is preferably used. For example,
Various materials such as acrylic resin, methacrylic resin, polyester resin, polycarbonate, polystyrene are used, but not limited thereto. Further, the shape is not limited to the plate shape, and can be formed in a desired shape such as a rectangular parallelepiped shape.

As the diffuser plate body constituting the above-mentioned diffuser plate, it is preferable to use a transparent resin substrate on which a diffusion layer of spherical fine particles for diffusing transmitted light is formed. As a material of the resin substrate, a material having high transparency is preferable, and examples thereof include polyethylene terephthalate, polycarbonate, polystyrene, acrylic resin, methacrylic resin and the like, but the material is not limited to these and various materials can be used. Of these, polyethylene terephthalate is most preferably used because it has few impurities, high transparency, and is inexpensive. The thickness of the resin substrate of the diffuser plate body is preferably set to 50 to 150 μm. The spherical fine particle diffusion layer is formed, for example, by applying a solution in which spherical fine particles are dispersed in a resin binder onto the surface of a resin substrate and drying the solution. As the resin binder, various resins such as acrylic resin, polyester resin, and silicone resin are used, but the resin binder is not particularly limited. As the spherical fine particles, transparent ones are used and various materials such as acrylic resin, urethane resin, styrene resin and silica are used. The spherical fine particles have an average particle size of 5 to 5.
70 μm is preferably used, but more preferably 2
Those having a thickness of 0 to 50 μm are used. That is, if the particle size is too small, a sufficient light diffusion effect cannot be obtained, and if the particle size is too large, dot-like spots are visible on the irradiation surface. By using, as the diffuser plate body, a transparent resin substrate on which a transparent spherical fine particle diffusion layer is formed, the spherical fine particles act as a kind of lens and have an effective light diffusion effect. Can be made.

The main body of the diffusion plate is not limited to the one in which the diffusion layer of spherical fine particles is formed on the transparent resin substrate as described above, and a resin sheet containing a light diffusing agent dispersed therein may be used. A resin sheet having irregularities formed on the surface thereof, or a milky white resin sheet or porous sheet may be used.

Further, the light-condensing sheet that can form a diffuser plate together with the diffuser plate body has, for example, prismatic or wave-like unevenness on its surface in order to collect outgoing light passing through the diffuser plate body in the front direction. Are formed in a line. Then, one or two sheets are arranged on the front surface side of the diffusion plate body.

According to the present invention, the light guide plate, the diffusion plate body,
A silicon oxide layer is formed on at least one of the incident light surface and / or the exit light surface of the light collecting sheet.

As a method for forming the above-mentioned silicon oxide layer on the surface of each member, there are sputter deposition method, vacuum deposition method, CV method.
Various methods such as the D method and the sol-gel method are performed. Among these, the sol-gel method is to obtain a silicon oxide layer by applying a sol solution composed of silica or the like to form a dry gel, and heating the dry gel to dehydration-condensate. Most suitable. In particular, the photo-assisted sol-gel method of curing the produced film by irradiating it with ultraviolet rays after low-temperature drying is more preferable because the processing temperature is low. As a method for applying the sol solution in the sol-gel method, various methods such as dipping method, spray coating, and spin coating are performed. In particular, spin coating involves rotating a sheet-shaped member and applying the sol solution to the surface thereof. Is applied dropwise evenly by centrifugal force, which is suitable from the viewpoint of the uniformity of the coating film.

When the film thickness (T) of the silicon oxide layer formed as described above satisfies the following equation, a specific wavelength (λ)
It is possible to suppress the reflection loss of light and improve the transmission efficiency accordingly. Where X is the refractive index of silicon oxide,
n is a positive odd number (1, 3, 5, 7 ...). As a result, surface reflection is prevented, light utilization efficiency is improved, and high brightness can be obtained. In addition, as compared with the conventional fluorine compound layer, charging hardly occurs.

[Formula 1] T = λ ÷ 4 ÷ X × n

Next, the present invention will be described with reference to the drawings.

The surface light source device of the present invention is used, for example, as a backlight of a liquid crystal display device as shown in FIG. That is, in the figure, 2 is a light guide plate, 4 is a linear light source such as a cold cathode tube which allows light to enter from the side surface of the light guide plate 2,
Reference numeral 3 denotes a reflecting plate which is arranged on the back surface side of the light guide plate 2 and reflects the light which is going to be emitted from the back surface of the light guide plate 2. Reference numeral 10 denotes a diffusing plate, which is provided on the outgoing light surface side of the light guide plate 2 and a diffusing plate main body 1 is provided on the outgoing light surface side of the diffusing plate body 1 to have a light collecting function or the like. It is composed of a prism sheet (condensing sheet) 5. Reference numeral 9 is a reflection cover that reflects the light beam of the linear light source 4 and makes it enter from the side surface of the light guide plate 2. As shown in FIG. 2, the diffusion plate body 1 has a transparent resin substrate 7 on which a silicon oxide layer 8 is formed on the back surface, and a binder 6a and spherical fine particles 6b on the surface.
And a fine particle diffusion layer 6 is formed.

In the above structure, the light generated by the linear light source 4 enters the light guide plate 2 from the side surface of the light guide plate 2. At this time, light may be directly incident from the linear light source 4 or may be light reflected by the reflection cover 9. The incident light passes through the inside of the light guide plate 2, and a part of the incident light exits from the exit light surface side, passes through the inside of the light guide plate 2, and advances toward the side surface opposite to the side surface where the linear light source 4 is provided. To do. This allows
The entire emission light surface emits light. Light emitted from the light emitting surface of the light guide plate 2 is diffused by the diffuser plate body 1 and then condensed by the prism sheet 5 to illuminate a liquid crystal display screen (not shown). At this time, when passing through the diffuser plate body 1, the presence of the silicon oxide layer 8 provided on the back surface of the diffuser plate body 1 suppresses the reflection loss of light of a specific wavelength according to the film thickness (T). Therefore, the light transmission efficiency is increased accordingly. Therefore, high brightness can be obtained, and if the brightness is the same as the conventional one, it can be used with low power.

Further, as described above, when the light guide plate 2 is formed in a plate shape and the line light source 4 is provided on one of the four side surfaces, the line light source 4 is not provided. On the other three sides, it is desirable to dispose the same reflection plate 3 as that disposed on the back surface. By doing so, the light guide plate 2
The light leakage from the side surface of the is eliminated, and the light utilization efficiency is further improved.

In the above surface light source device, the light guide plate 2 is formed in a plate shape, but the present invention is not limited to this and can be formed in a desired light guide body shape such as a rectangular parallelepiped. The light source used is not limited to the linear light source 4, and may be a point light source, and a desired light source can be used. Further, the position of the light source is not limited to one place, but may be provided at a plurality of places. Further, although the surface light source device is applied to a backlight for illuminating a liquid crystal display, it is not limited to this, and can be applied to all other surface light source devices including a direct type surface light source device. .

[0022]

As described above, according to the surface light source device of the present invention, the surface reflection is suppressed by the silicon oxide layer and there is almost no reflection loss, so that high brightness can be obtained. Moreover,
Unlike the conventional fluorine compound layer, since it is not charged, foreign matter does not adhere. Further, unlike the conventional case, an expensive solvent-soluble fluororesin is not used and an inexpensive silicon oxide layer is formed, so that the apparatus itself becomes inexpensive. Further, when the diffusion plate body is composed of a transparent resin substrate and a diffusion layer of transparent spherical fine particles formed on the surface of the resin substrate,
The spherical fine particles act as a kind of lens, and an effective light diffusion effect can be obtained. Moreover, when the resin substrate forming the diffusion plate body is made of polyethylene terephthalate, the material is inexpensive and the manufacturing cost of the device itself can be further reduced.

Next, examples will be described together with comparative examples.

[0024]

Example 1 First, in order to form a silicon oxide layer by the sol-gel method, tetraethoxysilane, water, ethanol, and nitric acid were used in a molar ratio of 1: 12: 45: 0.
25 parts were mixed to obtain a sol solution. Then, the sol solution was applied to the outgoing light surface of the transparent acrylic light guide plate by spin coating (250 rpm, 40 seconds) and dried at 60 ° C. for 5 minutes, and then a light (ultraviolet ray) having a wavelength of 245 nm was applied for 5 minutes. Irradiate and cure, thickness 1000
A Å silicon oxide layer was formed. In the obtained light guide plate,
Almost no foreign matter was attached due to electrification. The obtained light guide plate was incorporated into the surface light source device shown in FIG. 1 and the front luminance was measured. As a result, it was 1810 cd / m ² .

[0025]

Example 2 A substrate made of PET (polyethylene terephthalate) (trade name: Lumirror T56, manufactured by Toray Industries, thickness 75 μ)
m), first, on one side (incident light surface) of Example 1
The same sol solution as above was applied under the same conditions, dried and cured to form a silicon oxide layer having a thickness of 1000Å. Next, a polyester binder with an average particle size of 50 μm
80 parts by weight of the acrylic spherical fine particles (trade name: MBX-50, manufactured by Sekisui Chemical Co., Ltd.) were dispersed in 100 parts by weight of the binder to prepare a solution. The fine particle dispersion solution was applied to the emission light surface of the PET substrate and dried at 120 ° C. for 3 minutes to form a fine particle diffusion layer, thereby forming a diffusion plate body. The obtained diffuser plate body,
Almost no foreign matter was attached due to electrification. Further, this diffuser plate body was incorporated into the surface light source device shown in FIG. 1 and the front luminance was measured. As a result, it was 1812 cd / m ² .

[0026]

Example 3 Two prism sheets were prepared, and the sol solution similar to that in Example 1 was applied to the incident light surfaces of these prism sheets under the same conditions, followed by drying and curing treatment to obtain a thickness of 10
A 00Å silicon oxide layer was formed. The obtained prism sheet had almost no foreign matter attached due to charging. The prism sheet was incorporated into the surface light source device shown in FIG. 1 and the front luminance was measured. As a result, 1850 cd
/ M ² .

[0027]

[Comparative Example 1] As a comparative example, a light guide plate, a diffuser plate body, and a prism sheet which are not subjected to surface antireflection treatment such as a silicon oxide layer are used, and these are incorporated into the surface light source device shown in FIG. As a result of measuring the front luminance in the same manner as in Examples 1 to 3, it was 1760 cd / m ² .

[0028]

Comparative Example 2 Further, as a surface antireflection treatment, a light guide plate having a fluororesin layer formed on the outgoing light surface was formed. First,
Solvent-soluble fluoropolymer (Product name: CYTOP CTX
-102A, manufactured by Asahi Glass Co., Ltd.) having a concentration of 2% by weight was prepared. The fluoropolymer solution was applied by spin coating (1500 rpm, 10 seconds) to the outgoing light surface of the transparent acrylic light guide plate and dried at 100 ° C for 30 minutes, and then a fluororesin layer with a thickness of 1000 Å was formed. It was The resulting light guide plate was significantly charged with foreign matter due to charging. In addition, as a result of measuring the front luminance by incorporating this light guide plate into the surface light source device shown in FIG.
m ² .

From the above results, according to the surface light source device of the present invention, there is almost no adhesion of foreign matter due to electrification, and much higher brightness can be obtained than the surface light source device using the untreated member. Recognize. Moreover, high brightness can be obtained regardless of whether the silicon oxide layer is formed on the light transmitting surface of any of the light guide plate, the diffusion plate body, and the light-condensing sheet. In particular, the silicon oxide layer is formed on the two prism sheets. It is understood that higher brightness can be obtained in the case of

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a surface light source device of the present invention.

FIG. 2 is a cross-sectional view showing a diffusion plate body.

FIG. 3 is an explanatory diagram showing a conventional example.

FIG. 4 is an explanatory diagram showing another conventional example.

[Explanation of symbols]

 2 light guide plate 4 line light source 10 diffuser plate

Claims (6)

[Claims] 1. A transparent light guide plate, a light source for allowing light to enter from a part of the light guide plate, and a diffuser plate disposed on the exit light surface side of the light guide plate for diffusing light emitted from the exit light surface. A surface light source device comprising: a light guide plate and / or a diffusion plate, wherein a silicon oxide layer serving as an antireflection film is formed on an incident light surface and / or an outgoing light surface of at least one of the light guide plate and the diffusion plate. Light source device. 2. The surface light source device according to claim 1, wherein the diffusing plate comprises a diffusing plate body for diffusing light and a light collecting sheet for collecting the light transmitted through the diffusing plate body. 3. The surface light source device according to claim 2, wherein a silicon oxide layer is formed on at least one surface of the diffusion plate body. 4. The surface light source device according to claim 3, wherein the diffuser plate main body comprises a transparent resin substrate and a transparent spherical fine particle diffusion layer formed on the surface of the resin substrate. 5. The surface light source device according to claim 4, wherein the fine particles have an average particle diameter of 5 to 70 μm. 6. The surface light source device according to claim 4, wherein the resin substrate is made of polyethylene terephthalate.