JP4622967B2 - Surface light source device - Google Patents

Description

  The present invention relates to an edge light type liquid crystal display device using a light guide plate and a light source, and more particularly to a planar light source device using a light emitting diode (LED) as a light source.

  In a liquid crystal display device widely used as a display device such as a television or a personal computer, light is irradiated from the back surface of the liquid crystal panel using a planar illumination device. FIG. 1 shows a cross-sectional view of an edge light type planar illumination device using a conventional cold cathode tube. Such a planar lighting device includes a main light plate made of a rectangular transmissive material, and a cold cathode tube which is a linear light source arranged to face the side surface of the main light plate. White light from the cold cathode tube incident on the inside from the side surface of the main light guide plate is extracted in a planar shape from the light exit surface of the main light plate while being repeatedly reflected. Here, for example, an acrylic resin or a polycarbonate resin having high transparency is used as a member used for the main light plate. As the light source, many cold cathode tubes and hot cathode tubes having white light are used. Such an edge light type planar light source device is required to have high luminance, and therefore it is important to improve the light utilization efficiency.

  On the other hand, in recent years, the application range has expanded with the improvement of the luminous efficiency of LED elements. Therefore, by using an LED light source as the light source of the planar light source device, the color reproduction range can be improved and mercury-free can be achieved. Therefore, an LED backlight has been developed as a means for realizing higher functionality of the liquid crystal display device. It is becoming active. Since the LED element is a point light source, it has a configuration in which a plurality of LED elements are arranged in series along the side surface of the light guide plate in order to be applied to an edge light type planar light source device that requires a linear light source ( For example, reference 1).

JP 2005-259374 A

A planar light source device using an LED light source is required to have high brightness, low cost, and low power consumption. In order to realize low cost and low power consumption, it is effective to reduce the number of LED elements to be used. However, in order to maintain high luminance, the utilization efficiency of light from the LED elements is improved. Is important. Therefore, the optimization of the optical structure for efficiently taking out the light emitted from the LED element is a problem. In order to improve the color reproduction range, which is an advantage of using an LED light source, a red LED, a green LED, and a blue LED (hereinafter referred to as RGB-LED) are used as LED elements, and these are mixed and whitened. Is most effective. Therefore, it becomes a problem to suppress luminance unevenness and color unevenness of white light from the LED light source on the incident surface of the main light plate.

  Accordingly, in view of the above problems, the present invention reduces optical loss when white light is incident on a light guide plate while having an optical system configuration that suppresses luminance unevenness and color unevenness of white light from an RGB-LED light source. Thus, an object is to provide a planar light source device with high brightness.

In order to solve the above-mentioned problems, the present invention is an edge light type in which a transparent adhesive in which fine particles having a light diffusing function are dispersed inside a transparent adhesive is disposed between the connection surfaces of the main light guide plate and the color mixing light guide plate. In the planar light source device, the transparent adhesive is disposed only on the surface facing the surface on which the LED element is mounted and in the vicinity thereof, and the transparent adhesive, the main light guide plate, and the color mixing light guide plate are connected . .

  According to the planar light source device configured according to the present invention, it is possible to efficiently guide the white light emitted from the RGB-LED elements to the leading light plate while suppressing luminance unevenness. Accordingly, it is possible to provide a planar illumination device with high brightness.

  Embodiments of the planar light source device according to the present invention will be described below.

FIG. 3 is a schematic view of the planar light source device according to claim 1, FIG. 4 is a schematic view shown in FIG. 3, and a cross-sectional view when the center in the thickness direction is viewed from the display direction. The planar light source device includes a main light plate 1, a color mixing light guide plate 12, a light diffusion sheet 13, a transparent adhesive 16, an LED unit 9, and a wiring board 11. The color mixing light guide plate 12 is provided with a plurality of recessed spaces (hereinafter referred to as sealing spaces 14) along the long side direction in order to accommodate the LED units 9. The LED unit 9 is disposed in the sealing space and sealed with a transparent resin material. Here, the LED unit 9 has a configuration in which two or more types of LED elements having different emission wavelengths are mounted on one submount substrate. In the first embodiment, red, blue, and green LED elements are mounted on one unit, and white light is obtained by the principle of the three primary colors of light. Further, in the reflector 15 portion formed on the color mixing light guide plate 12, the light emitted from the LED elements is repeatedly reflected, and a reflection sheet is applied to the outer peripheral portion of the color mixing light guide plate using a general adhesive means such as an adhesive. By connecting, the effect of color mixing in the color mixing light guide plate is enhanced. Here, it is desirable that the main light plate and the color mixing light guide plate are made of acrylic resin or polycarbonate resin having excellent transparency. In the first embodiment, acrylic having excellent light transmittance in the visible light region. Resin was used.

  FIG. 5 shows a luminance distribution on the light exit surface of the light-mixing light guide plate indicated by AA ′ in FIG. 4 when four LED units 9 are arranged in series. The region 20 immediately above the LED unit shown in FIG. 5 is a surface facing the surface on which the LED unit 9 is mounted and a region in the vicinity thereof, and indicates that the luminance is higher than the region between the LED units 9. Yes.

  Therefore, as shown in FIG. 4, in order to make the emitted light with large luminance unevenness from the color mixing light guide plate as shown in FIG. The light guide plate is disposed only on the surface facing each LED unit 9 and the vicinity thereof on the exit surface of the light guide plate, and is not disposed on the surface directly above each LED unit. Thereby, on the emission surface of the color mixing light guide plate, the high-brightness area immediately above where the LED unit 9 is mounted is diffused in all directions by the light diffusion sheet disposed in the area, and no light diffusion sheet is disposed. It is possible to equalize to a level equivalent to the luminance of the area. Therefore, it is possible to reduce the luminance unevenness of the light incident on the main light plate.

  Here, the light diffusion sheet 13 has a configuration in which a base sheet, a light diffusion layer formed on one plane of the base sheet, and a backcoat layer formed on a surface where the light diffusion layer is not formed. . For the base sheet, for example, a colorless and transparent synthetic resin such as polyethylene terephthalate, polyethylene naphthalate, acrylic, polycarbonate, polystyrene, and polyolefin is used. In Example 1, a polyethylene terephthalate is used as a base sheet, and a light diffusion sheet in which a light diffusion layer having a light diffusion function is formed on one plane is used. As a transparent adhesive layer, an alkaline adhesive having a thickness of 50 μm is used. A transparent pressure-sensitive adhesive layer using an agent was used.

The transparent adhesive layer before being bonded to the color mixing light guide plate is protected on both sides by a plastic film. After the transparent adhesive layer is cut to the same size as the light emitting surface of the color mixing light guide plate, only one surface of the protective film is peeled off first. After pasting the surface from which the protective film of the transparent adhesive layer has been peeled off to the light exiting surface of the color mixing light guide plate, using a roller or the like, pressure is applied from the surface to which the protective film of the transparent adhesive layer is bonded, thereby mixing the colors. The air remaining between the light guide plate and the transparent adhesive layer is removed. Subsequently, the protective film on the other surface of the transparent adhesive layer is peeled off, and the surface on which the light diffusion surface of the light diffusion sheet cut to the same size as the incident surface of the color mixing light guide plate is not formed is transparent. Bond with the adhesive layer. The light diffusion sheet is pressurized using a roller or the like to remove the remaining air, and the light diffusion sheet is adhered to the transparent adhesive layer. In the color mixing light guide plate formed as described above, the light diffusion sheet is laminated on the incident surface on the side of the main light guide plate. At this time, the color mixing light guide plate and the main light guide plate are held by the casing of the outer frame in the liquid crystal display device, and therefore, between the main light guide plate and the light diffusion sheet, 0. 1
An air layer with a thickness of mm or less is formed.

  In order to confirm the effect of improving the light utilization efficiency of the planar light source device thus formed, total luminous flux measurement was performed. As a result, when the total luminous flux incident on the main light guide plate when the transparent adhesive layer is not used is 100%, the total luminous flux is obtained by adhering the light diffusion sheet and the color mixing light guide plate with the transparent adhesive layer. Measurement results increasing by 10% to 15% were obtained, confirming the effectiveness of the present invention.

  Usually, when the light diffusing sheet is disposed directly between the main light guide plate and the color mixing light guide plate, a slight air layer is formed on each boundary surface due to the surface roughness and warpage of each member. Therefore, when the light emitted from the LED element reaches the emission surface of the color mixing light guide plate, it reaches at an angle greater than the critical angle due to the refractive index difference between the acrylic resin forming the color mixing light guide plate and the air layer. The light is totally reflected, and the light taken out of the color mixing light guide plate is reduced. Therefore, by connecting the light diffusion sheet and the color mixing light guide plate with a transparent adhesive layer, the refractive index difference is reduced, the total reflection component on the light exit surface of the color mixing light guide plate is suppressed, and more light is mixed. It becomes possible to take out from the light guide plate.

  In addition, although the transparent adhesive used for this invention is what is called a double-sided adhesive tape formed with arbitrary appropriate adhesives or adhesives, it is desirable to use adhesives, such as an acrylic type and a silicone type. In particular, the smaller the refractive index difference between the main light guide plate, the color mixing light guide plate and the transparent adhesive layer, the higher the light utilization efficiency. Therefore, the main light guide plate or color mixing light guide plate is made of acrylic resin, and the transparent adhesive layer is made of acrylic. The highest light utilization efficiency can be obtained when a system adhesive is used. In consideration of the assemblability of the planar light source device, it is preferable to use a transparent adhesive layer having a thickness of 10 μm to 200 μm.

  In Example 1, it is possible to improve the light utilization efficiency by connecting the light diffusion layer of the light diffusion sheet and the main light plate with a transparent adhesive, but the light scattering effect which is the purpose of use of the light diffusion sheet This reduces the brightness unevenness in the surface.

  Therefore, as described in claim 2, Example 2 shown in FIG. 6 is based on the substrate sheet instead of the light diffusion sheet in which the light diffusion layer is formed on one plane of the substrate sheet used in Example 1. It is sectional drawing at the time of using the light diffusion sheet which mixed the microparticles | fine-particles which have a light-diffusion function in it. Other configurations and the effect of reducing luminance unevenness are the same as in the first embodiment.

  By arranging such a light diffusion sheet only on the surface facing the surface on which the LED unit 9 is mounted and in the vicinity thereof, and not on the surface directly above each LED unit, the light exit surface of the color mixing light guide plate Even if the incident surfaces of the main light guide plate are connected to each other by a transparent adhesive layer, the light diffusion sheet has a light diffusion function inside the base sheet, so that the light scattering effect of the light diffusion sheet is maintained. However, it is possible to increase the light use efficiency.

  As described in claim 3, in Example 3 shown in FIG. 7, instead of the light diffusion sheet used in Example 1 and Example 2, fine particles having a light diffusion function are mixed in the transparent adhesive layer. It is sectional drawing at the time of connecting the main light board and the light-guide plate for color mixing by this transparent adhesive layer using the transparent adhesive which was prepared. Other configurations and the effect of reducing luminance unevenness are the same as in the first embodiment.

  By arranging the transparent adhesive layer having such a function only on the surface facing the surface on which the LED unit 9 is mounted and in the vicinity thereof, and not on the surface directly above each LED unit, color mixing is achieved. Since the exit surface of the light guide plate and the entrance surface of the main light plate can be bonded by the transparent pressure-sensitive adhesive layer, it is possible to increase the light use efficiency while maintaining the light scattering effect of the light diffusion sheet.

  The liquid crystal display device according to claim 4 will be described. The light diffusion sheet in which the light diffusion layer is formed on one plane of the base sheet has a thickness of about 0.1 mm to 0.3 mm. Therefore, an air layer exists in the area where the light diffusion sheet is not disposed on the connection surface between the main light guide plate and the color mixing light guide plate in the structure described in the first embodiment, and the light use efficiency is reduced.

  Therefore, as shown in FIG. 8, a concave portion 21 for accommodating the light diffusion sheet is provided on the incident surface of the main light guide plate only on the surface facing the surface on which the LED unit 9 is mounted and in the vicinity thereof. The light diffusion sheet described in Example 1 in which a light diffusion layer having a light diffusion function is formed on one plane is accommodated. As a result, on the exit surface of the color mixing light guide plate, the region where the light diffusion sheet is not disposed and the main light guide plate can be connected using the transparent adhesive layer, so that a uniform luminance distribution is obtained. In addition, a planar light source device with high light utilization efficiency can be realized. In addition, you may provide the recessed part 21 in the light-projection surface of the light-guide plate for color mixing.

  The liquid crystal display device according to claim 5 will be described. A light diffusing sheet in which fine particles having a light diffusing function are mixed in a base sheet has a thickness of about 0.1 mm to 0.3 mm. Therefore, on the connection surface between the main light guide plate and the color mixing light guide plate in the structure described in the second embodiment, an air layer exists in a region where the light diffusion sheet is not disposed, and the light use efficiency is lowered.

  Therefore, as shown in FIG. 9, the incident surface of the main light guide plate is provided with a recess 21 for accommodating the light diffusion sheet only on the surface facing the surface on which the LED unit 9 is mounted and in the vicinity thereof. The light diffusing sheet in which the fine particles having the light diffusing function are mixed in the base material sheet described in Example 2 is accommodated in the concave portion 21, so that the light diffusion is performed on the emission surface of the color mixing light guide plate. The connection area | region of the area | region which has not arrange | positioned the sheet | seat, and the main light guide plate can be connected using a transparent adhesive layer. Therefore, it is possible to realize a planar light source device that can obtain a uniform luminance distribution on the light incident surface of the main light guide plate and has high light utilization efficiency. In addition, you may provide the recessed part 21 in the light-projection surface of the light-guide plate for color mixing.

  As described above, by using the present invention, an LED backlight having a uniform luminance distribution and high light utilization efficiency can be realized. In all the embodiments described above, the LED light source is disposed only on one side of the main light guide plate. However, the light source having the same structure may be provided on both side surfaces of the main light guide plate.

Sectional drawing of the edge light system backlight using the conventional cold cathode tube. Sectional drawing of the edge light system backlight using the conventional LED light source. FIG. 2 is a schematic diagram of an LED backlight according to the first embodiment. Sectional drawing when the center of the thickness direction of FIG. 3 schematic diagram is seen from the display direction. FIG. 5 is a luminance distribution diagram of a light exit surface of the color mixing light guide plate indicated by AA ′ in FIG. 4. Sectional drawing of the LED backlight of the present Example 2. FIG. Sectional drawing of the LED backlight of the present Example 3. FIG. Sectional drawing of the LED backlight of the present Example 4. FIG. Sectional drawing of the LED backlight of the present Example 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Leading light plate, 2 ... Side surface reflection sheet, 3 ... Back surface reflection sheet, 4 ... Light diffusion sheet, 5 ... 1st light-condensing plate, 6 ... 2nd light-condensing plate, 7 ... Cold cathode fluorescent tube, 8, 15 ... Reflector, DESCRIPTION OF SYMBOLS 9 ... LED unit, 10 ... Lens, 11 ... Wiring board, 12 ... Light guide plate for color mixing, 13 ... Light diffusion sheet,
DESCRIPTION OF SYMBOLS 14 ... Sealing space, 16 ... Transparent adhesive, 17 ... Light-diffusion surface, 18 ... Base material sheet, 19 ... Transparent adhesive with a light-diffusion function, 20 ... Area just above LED unit, 21 ... Recessed part, 22 ... Air layer.

Claims (2)

In an edge light type planar light source device in which a transparent adhesive in which fine particles having a light diffusing function are dispersed inside a transparent adhesive is disposed between connection surfaces of a main light plate and a color mixing light guide plate, the transparent adhesive is A planar light source device , which is disposed only on a surface opposite to a surface on which an LED element is mounted and in the vicinity thereof, and the transparent adhesive, a leading light plate, and a color mixing light guide plate are connected. The planar light source device according to claim 1 , wherein the transparent adhesive layer is made of an acrylic adhesive having a thickness of 10 µm to 200 µm .

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