JP2007123130A - Backlight unit and display device provided with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit which has a high brightness and uniform lightness. <P>SOLUTION: In the backlight having a light guide plate and a light source, the light source 13 is fitted in a corner notched part of the light guide plate 12, a serrated circular prism 12a concentric with the light source as a center is formed on the light guide plate 12. Pitch widths p of the circular prism 12a are kept uniform and inclination angles θ(θ1 to θn) are set bigger as they get away from the light source 13, and depths h (h1 to hn) of the prism are set deeper as they get away from the light source. Furthermore, the inclination angle θ shall be 45° or smaller and an angle β of a valley 12j of the prism 12a shall be 90° or larger. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight unit of a display device or a display device including a backlight unit, and particularly relates to improvement of brightness.

  Liquid crystal display devices have been widely used in personal computers, liquid crystal televisions, electronic notebooks, mobile phones, and other terminal display devices. In order to display a display image of the liquid crystal display device brightly and clearly, a backlight unit is provided on the lower surface side of the liquid crystal display panel. One of the conventional structures of this backlight unit is that shown in FIGS. Hereinafter, the structure of a conventional backlight unit will be described with reference to FIGS. 12 shows a cross-sectional view of the main part of the liquid crystal display device, and FIG. 13 shows an explanatory diagram for explaining the light emission state to the light guide plate according to the number of light sources arranged in FIG. FIG. 14 is a cross-sectional view of the main part of the light guide plate in FIG.

  The backlight unit 8 shown in FIG. 12 is disposed and used on the lower surface side of the liquid crystal display panel 1, and the backlight unit 8 and the liquid crystal display panel 1 constitute a liquid crystal display device 10. The backlight unit 8 includes a light guide plate 2, a light source 3 that is an LED disposed on one side of the light guide plate, a light diffusion sheet 4 disposed on the upper surface side of the light guide plate 2, and the light diffusion sheet 4 The first prism sheet 5 and the second prism sheet 6 provided on the light guide plate 2, and the reflection plate 7 provided on the lower surface side of the light guide plate 2. Here, the first prism sheet 5 and the second prism sheet 6 are prism sheets formed in a straight line, and the first prism sheet 5 and the second prism sheet 6 are linear prisms. It is used by being laminated in a state orthogonal to each other.

  The operation of the backlight unit 8 having the above-described configuration is as follows. The light emitted from the light source 3 that is an LED is guided to the back of the light guide plate 2 by a reflecting means such as a prism provided on the lower surface of the light guide plate 2 and is emitted toward the diffusion sheet 4. The light diffusing sheet 4 diffuses the incident light to make a uniform light quantity distribution state and radiates it toward the first prism sheet 5 and the second prism sheet 6. In the first prism sheet 5 and the second prism sheet 6, the diffused light in the X-axis direction and the light in the Y-axis direction on the plane axis are emitted to the liquid crystal display panel 1 as vertical light. Further, the light emitted through the reflecting means such as a prism provided on the lower surface of the light guide plate 2 and emitted below the light guide plate 2 is reflected by the reflection plate 7 and enters the light guide plate 2 again. In this way, the light of the light source 3 is effectively used to illuminate the display image of the liquid crystal display panel 1 brightly.

  Here, the light source 3 that is an LED is disposed close to one side surface of the light guide plate 2. In FIG. 13A, one light source 3 is disposed at the center of the side surface of the light guide plate 2, and in FIG. 13B, three light sources 3 are disposed on the side surface of the light guide plate 2 at equal intervals. It shows the state. Although LED is used for the light source 3, since the LED has directivity of light emission, its emission angle is limited. In FIG. 13A, when the light guide plate 2 is large, the entire light guide plate 2 cannot be covered with the radiation angle, and the unsightly portion 2f where the amount of light is small and shadow appears appears with a wide area. In order to reduce the area of the unsightly portion 2f, it is necessary to increase the number of LEDs. In FIG. 13B, by using three LEDs, the area of light emission is expanded with adjacent LEDs, and the area of the unsightly portion 2f where the shadow appears is small as shown in the figure. If a large number of LEDs are arranged, the area of the unsightly portion 2f is reduced, and light wraps around almost the entire surface of the light guide plate 2 to brighten the entire surface. Since the structure in which the LEDs are arranged on the side surface of the light guide plate 2 is required to increase the number of LEDs according to the size of the light guide plate 2, the cost of components is increased.

  The light guide plate 2 is made of transparent polycarbonate resin, acrylic resin, or the like, and light reflecting means using a prism is provided on the lower surface thereof as shown in FIG. In FIG. 14, a plurality of prisms 2a having a constant inclination angle θ and a constant pitch p are provided on the lower surface of the light guide plate 2 in parallel with the side surface 2e. The light L emitted from the LED of the light source 3 is reflected by the inclined surface 2b of the prism 2a (this inclined surface 2b is an inclined surface facing the light source 3) and proceeds to the upper surface 2d of the light guide plate 2. If the light L reflected by the inclined surface 2b does not reach the critical angle at the incident angle with the upper surface 2d, it is reflected again from the upper surface 2d and returned into the light guide plate 2. Thus, the scanning of the light in the light guide plate 2 is repeated, and when the critical angle is reached with the upper surface 2d, the light is refracted and emitted from the upper surface 2d. Although light emitted from the prism 2a on the lower surface also appears, it is reflected by the reflecting plate 7 disposed below the light guide plate 2 and returned again into the light guide plate.

  FIG. 15 shows a luminance curve representing how the luminance changes depending on the inclination angle θ of the inclined surface 2b of the prism 2a. m represents the distance from the side surface 2e of the light guide plate 2 on the light source 3 side. From FIG. 15, when the inclination angle θ of the prism is large, the luminance is high from the position of the light incident port of the light guide plate 2 to the middle position, and the luminance is extremely lowered from the middle to the back. That is, when the inclination angle θ of the prism is large, the light does not reach the back of the light guide plate. On the other hand, when the inclination angle θ of the prism is small, the luminance is extremely low from the position of the light entrance to the middle position, and the luminance is high from the middle position to the back position. That is, when the inclination angle θ of the prism is small, a large amount of light gathers in the back, and the amount of light at the entrance is small. Therefore, the prism is formed by setting the tilt angle θ so that the brightness is highest near the center and the brightness is not extremely lowered at the entrance and the back. . However, although the luminance at the center is highest, the luminance difference between the entrance and the innermost portion still occurs, and the uniformity of luminance cannot be eliminated even through the diffusion sheet 4, and the display image is bright. There is a problem that unevenness of thickness appears.

  The present invention has been made in view of the above-described problems, and has an object to obtain a display image that is light and uniform in brightness over the entire surface of the display panel, using fewer light sources.

  As a means for solving the problems, the backlight unit of the present invention is characterized in that the backlight unit is provided on the lower surface side of the display panel and includes a light guide plate and a light source, and the light source is provided at a corner notch of the light guide plate. The light guide plate has a conical circular saw-toothed circular prism centered on the light source, the inclined surface facing the light source of the circular prism is a first inclined surface, and the inclination angle of the first inclined surface is first. Assuming an inclination angle, the circular prism has a constant pitch width, the first inclination angle increases with increasing distance from the light source, and the depth increases with increasing distance from the light source.

  Further, the backlight unit of the present invention is characterized in that in the backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch of the light guide plate, and the light guide plate Has a conical circular saw-toothed circular prism with the light source as the center, and the circular prism has the first inclined surface as the inclined surface facing the light source, and the first inclined angle as the inclined angle of the first inclined surface. The prism has a constant depth, the first inclination angle increases with increasing distance from the light source, and the pitch width decreases with increasing distance from the light source.

  Further, the backlight unit of the present invention is characterized in that in the backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch of the light guide plate, and the light guide plate Has a concentric sawtooth-shaped first circular prism centered on the light source, a second circular prism connected to the first circular prism, and faces the light source of the first circular prism. The slope is defined as the first slope of the first prism, the slope angle of the first slope of the first prism is the first slope angle of the first prism, and the slope facing the light source of the second circular prism is the slope of the second prism. If the inclination angle of the first inclined surface and the first inclined surface of the second prism is the first inclined angle of the second prism, the first circular prism is provided on the light source side. The first inclination angle of the first prism is an inclination angle that emits a part of the light of the light source reflected by the first inclined surface of the first prism to the outside from the upper surface of the light guide plate, and the second prism The circular prism has a constant pitch width, the first tilt angle of the second prism increases as the distance from the light source increases, and the depth increases as the distance from the light source increases.

  Further, the backlight unit of the present invention is characterized in that in the backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch of the light guide plate, and the light guide plate Has a concentric sawtooth-shaped first circular prism centered on the light source, a second circular prism connected to the first circular prism, and faces the light source of the first circular prism. The slope is defined as the first slope of the first prism, the slope angle of the first slope of the first prism is the first slope angle of the first prism, and the slope facing the light source of the second circular prism is the slope of the second prism. If the inclination angle of the first inclined surface and the first inclined surface of the second prism is the first inclined angle of the second prism, the first circular prism is provided on the light source side. The first inclination angle of the first prism is an inclination angle that emits a part of the light of the light source reflected by the first inclined surface of the first prism to the outside from the upper surface of the light guide plate, and the second prism The circular prism has a constant depth, the first tilt angle of the second prism increases with increasing distance from the light source, and the pitch width decreases with increasing distance from the light source.

  The backlight unit of the present invention is characterized in that the first inclination angle is 45 ° or less.

  In addition, the backlight unit according to the present invention is characterized in that the angle of the valley of the circular prism formed by the first slope and the second slope is a slope on the opposite side of the first slope as the second slope. Is 90 ° or more.

  The backlight unit of the present invention is characterized in that the first slope and the second slope are glossy surfaces.

  The backlight unit of the present invention is characterized in that the upper surface of the light guide plate and the end surface of the corner notch are glossy surfaces.

  The backlight unit of the present invention is characterized in that the light source is an LED.

  The display device of the present invention is characterized in that in a display device having a backlight unit on the lower surface side of the display panel, the display panel is brightened and illuminated with uniform brightness using the backlight unit of the present invention. It is characterized by that.

  As an effect of the invention, in the present invention, the light source is disposed in the corner notch of the light guide plate. Even if the radiated light of the light source has directivity, if it is a corner portion, it suffices to illuminate the area range within 90 degrees, so the number of light sources can be reduced, and the effect of cost reduction can be obtained. Further, by arranging the light source in the notch portion of the corner, the light from the light source is collected on the surface and the surface substantially perpendicular to the radiated light from the light source, so that the light lighting efficiency becomes very high. The light guide plate has a concentric circular prism with the light source as the center. In the case of a circular prism, the reflected light reflected by the prism is reflected in the same direction as the traveling direction of the optical axis of the light. Therefore, since the reflected light from the prism spreads radially, a uniform distribution of the amount of reflected light from the prism can be obtained. In the present invention, the circular pitch of the circular prism is constant, the first inclination angle increases as the distance from the light source increases, and the depth increases as the distance from the light source increases. When the first tilt angle of the prism is large, the reflection angle of the light reflected there is small, and the light having a small reflection angle has a large incident angle on the upper surface of the light guide plate. Since light having a large incident angle on the upper surface exceeds the critical angle, it exits from the upper surface and is emitted to the outside. On the other hand, when the first tilt angle of the prism is small, the reflection angle of the light reflected there is large, and the light having a large reflection angle has a small incident angle on the upper surface of the light guide plate. Light having a small incident angle on the upper surface does not reach the critical angle, and therefore is reflected again from the upper surface and returns into the light guide plate. Here, when the relationship of the first tilt angle of the prism near the light source <the first tilt angle of the prism far from the light source is made, the reflected light from the prism near the light source is in the back of the light guide plate (position far from the light source). The reflected light from the prism that is guided in the direction away from the light source is emitted from the surface of the light guide plate. As the first tilt angle increases as the distance from the light source increases, the light reaches the back of the light guide plate, and more light is emitted from the light guide plate at the back. The light intensity distribution becomes uniform. Next, when the depth of the prism is increased as the distance from the light source increases, the area of the first slope can be increased. As the area of the first slope increases, the amount of light incident on the slope increases and the amount of reflected light also increases accordingly. When the depth is constant, the amount of incident light on the first slope decreases as the distance from the light source increases, and the amount of reflected light also decreases. By increasing the depth, it is not necessary to reduce the amount of incident light and the amount of reflected light. This acts to make the light quantity distribution emitted from the light guide plate uniform. Due to the operations and effects as described above, uniform illumination brightness can be obtained over the entire light guide plate.

  Further, in the present invention, the first tilt angle is increased with increasing distance from the light source while the prism depth is constant, and the pitch width is decreased. The effect of increasing the first inclination angle with increasing distance from the light source is as described above. However, when the pitch width is reduced, the length of the first slope is reduced and the area thereof is reduced. The number of increases. As the number of reflected light on one first slope decreases, the number of reflected light increases as a whole, and an increase in reflected light and uniformity can be obtained. As a result, the emitted light quantity distribution can be made uniform, the luminance can be made uniform, and illumination with bright and uniform brightness can be obtained.

  In the present invention, the first prism and the second prism are provided on the light guide plate. The first prism is provided on the light source side, and the first tilt angle of the first prism is increased so that part of the light from the light source is emitted from the light guide plate. In this way, the amount of emitted light increases even in the vicinity of the light source, and the brightness increases. Prevents a decrease in brightness near the light source. The second prism has a constant pitch width, and the first inclination angle increases as the distance from the light source increases, and the depth increases as the distance from the light source increases. Alternatively, the depth is constant, the first inclination angle increases as the distance from the light source increases, and the pitch width decreases as the distance from the light source increases. The operation and effect of this are as described above, and the first prism and the second prism can increase the luminance of the entire light guide plate and at the same time make the luminance uniform.

  Further, by setting the first inclination angle to 45 ° or less, light incident on the first inclined surface at an angle smaller than the critical angle is totally reflected. Then, the light is reflected on the upper surface side of the light guide plate. This produces an effect of reflecting a large amount of light on the upper surface side of the light guide plate.

  Further, by setting the angle of the valley of the prism to 90 ° or more, the mold releasability at the time of injection molding is improved, and the light guide plate can be easily molded.

  In the present invention, the first slope and the second slope of the prism are glossy surfaces. Since light is reflected on the slope, the reflectance is very high when the surface is glossy. Moreover, in this invention, the upper surface of a light-guide plate and the end surface of a corner notch part are a glossy surface. If the upper surface is a glossy surface, the reflectance on the upper surface is increased, and light can be guided toward the back of the light guide plate. Further, when the end surface of the notch portion is a glossy surface, the light from the light source linearly enters the light guide plate and proceeds radially. The light from the light source is used efficiently, and it is effective for uniform brightness.

  Moreover, in this invention, LED is used for a light source. Since it is small and cheap, it can be applied to a small light guide plate and can be miniaturized. It also contributes to cost reduction. In addition, it is economical in terms of power consumption because the drive voltage is low, and it can be suitably used as a backlight light source for a small display panel because it can be made small and bright.

  Further, when the backlight unit of the present invention is used in a display device of a display device, a display image with bright and uniform brightness can be obtained.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. First, the backlight unit according to the first embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 shows a side view of a display device using the backlight unit according to the first embodiment of the present invention, and FIG. 2 is a plan view showing an arrangement state of the light guide plate and the light source in FIG. 3 shows a cross-sectional view taken along line EE in FIG. 4 is an explanatory diagram for explaining the operation of the light guide plate in FIG. 2, and FIG. 5 is a luminance curve diagram showing the luminance state of the light guide plate in FIG.

  As shown in FIG. 1, the backlight unit 18 of the present invention is provided on the lower surface side of the display panel 11 and is provided as a constituent unit of the display device 20. The backlight unit 18 here has a configuration in which a light diffusion sheet 14, a first prism sheet 15, and a second prism sheet 16 are laminated on the upper surface side of the light guide plate 12. The light guide plate 12 is provided with a reflection plate 17 on the lower surface side. Further, a notch is provided in the corner of the light guide plate 12, and a light source 13 serving as an LED is disposed in the corner notch.

  The display panel 11 here uses a liquid crystal display panel, and has a structure in which liquid crystal is sealed in a gap between the upper and lower substrates, and further, polarizing plates are provided on the upper and lower surfaces of the upper and lower substrates. In addition, a plurality of display pixels using thin film transistor (TFT) elements are provided, and red (R), green (G), and blue (B) color filters are sequentially arranged for each pixel. The liquid crystal display panel performs active matrix color display. The light diffusion sheet 14 uses a resin sheet in which silica particles are dispersed. The first prism sheet 15 and the second prism sheet 16 are prism sheets formed in a straight line, and the first prism sheet 15 and the second prism sheet 16 are linear prisms orthogonal to each other. In such a state, it is used by being laminated. Further, the reflecting plate 17 is a plate or sheet, and as the plate, an aluminum metal plate, a brass plate or the like subjected to silver plating or the like is used. As the sheet-like material, a transparent sheet provided with an aluminum metal film or a silver metal film is used. These surfaces are finished with a glossy surface.

  The light guide plate 12 is formed by an injection molding method using a resin having excellent heat resistance, moisture resistance, impact resistance, and chemical resistance, such as polycarbonate resin, polyimide resin, and polyethylene resin. As shown in FIG. 2, a corner notch 12k is provided at a corner (corner) having a rectangular shape, and a light source 13 is disposed at the notch 12k. And the light of the light source 13 is taken in into the light-guide plate 12 from the end surface 12k of the notch part 12k. The light source 13 is a white light emitting LED. As shown in FIGS. 2 and 3, the light guide plate 12 is provided with a plurality of concentric sawtooth circular prisms 12 a (hereinafter simply referred to as prisms) with the light source 13 as the center. As shown in FIG. 2, the prism 12 a is provided with a plurality of ridgelines 12 g of the prism 12 a centering on the light source 13 with the same pitch width. As shown in FIG. 3, the prism 12a has a first slope 12b facing the light source 13, and a second slope 12c on the opposite side. Further, when the inclination angle of the first inclined surface 12 b is the first inclination angle θ, the first inclination angle θ increases as the distance from the light source 13 increases. That is, the first inclination angle θ of the prism 12a has an inclination angle of θ1 at the closest position of the light source 13, then has an inclination angle of θ2, and gradually advances away from the light source 13, θ3,. -It has the inclination | tilt angle of (theta) n (i = 1-n). The inclination angle θ1 <θ2 <.. <θi <.. <θn. Further, these inclination angles θ are smaller than 45 degrees.

  The prisms 12a have a constant pitch width p and are formed at the same interval. Further, the depth h of the prism 12a becomes deeper as the distance from the light source 13 increases. This depth h refers to the depth of the valley 12j formed by the intersection of the first slope 12b and the second slope 12c, and the apex of the prism ridge line 12g and the intersection of the first slope 12b and the second slope 12c. It says the height of. The depth h of the prism 12a has a depth h1 closest to the light source 13, and then has a depth h2. The distance h3,..., Hi,. = 1 to n). The relationship is h1 <h2 <.. <hi <.. <hn. Further, the angle β of the valley 12j formed at the intersection of the first slope 12b and the second slope 12c is 90 ° or more.

  The first slope 12b and the second slope 12c of the prism 12a are finished to be glossy. When the first inclined surface 12b is a glossy surface, the incident light from the light source 13 is well reflected to greatly increase the reflection efficiency. This glossy surface is formed by transfer from a mold that has been mirror-finished during injection molding.

  Further, the upper surface 12d of the light guide plate 12 and the end surface 12e of the corner notch 12k are finished to be glossy. When the upper surface 12d of the light guide plate 12 is a glossy surface, the direct light of the light source 13 incident on the upper surface 12d at an angle not reaching the critical angle and the reflected light from the first inclined surface 12b are reflected at the boundary surface of the upper surface 12d. To the back of the light guide plate 12. That is, light is guided toward the back of the light guide plate 12, and the brightness at the back is increased. Further, if the end face 12e is glossy, the light from the light source 13 enters the light guide plate 12 straightly, and the light utilization efficiency of the light source 13 is greatly enhanced.

  The light source 13 uses an LED. In the first embodiment, white light emitting LEDs are used so that the color display image of the liquid crystal display device appears clearly. If it arrange | positions in the corner notch part 12k of the light-guide plate 12, as shown in FIG. 2, the site | part 12f with a bad appearance where a shadow will appear can be suppressed to a small area. And even the thing of considerable size of the light-guide plate 12 can be used in the directivity area | region of LED. Moreover, since the whole can be illuminated with one LED, the cost can be kept low. Further, by disposing in the corner cutout portion 12k, the unit size can be reduced without increasing the size of the backlight unit itself. Note that the LED to be used is not limited to a white light emitting LED, and it is preferable to select a light emission color according to the specifications of the display panel.

  Next, the effect | action of the light-guide plate 12 which makes said shape is demonstrated using FIG. In the prism 12a according to the first embodiment, the pitch width p is constant, and the first inclination angle θ of the first inclined surface 12b gradually increases as the distance from the light source increases. Further, the depth of the prism 12a is also gradually increased. In the prism 12a at the second position from the light source 13 with the light emitted from the light source 13, if the first slope is 12b2 and the first tilt angle is θ2, the light L2 hitting the first slope 12b2 is the first slope. The upper surface 12d reflects when the angle θ2 is small (because the first inclination angle is set larger as the distance from the light source 13 increases, the first inclination angle θ2 at the position of the second prism from the light source 13 enters the smaller one). Proceed toward. Then, since the incident angle δ2 with the boundary surface is small at the boundary surface of the upper surface 12d, it is reflected again at the boundary surface and returns into the light guide plate 12. Reflection at the boundary surface of the upper surface 12d is determined by the incident angle at that location. When the incident angle is smaller than the critical angle, the light is reflected. When the incident angle is larger than the critical angle, the light is refracted out of the light guide plate and emitted. The incident angle on the boundary surface is determined by the reflection angle at the first inclined surface 12. For example, when the first inclination angle θ2 is small, the reflection angle γ2 at the first inclined surface 12b2 is large. For this reason, the incident angle δ2 with respect to the boundary surface of the upper surface 12d becomes small, and reflection at the boundary surface occurs. Since the prism 12a at a position near the light source 13 has a small first inclination angle θ2, the light from the light source 13 repeats reflection and advances toward the back of the light guide plate 12. Note that there is also light emitted directly from the light source 13 toward the upper surface 12d of the light guide plate 12, and an incident angle incident on the boundary surface of the upper surface 12d appears to reach a critical angle at a position close to the light source 13. The light that has reached the critical angle is directly emitted from the upper surface 12d to the outside of the light guide plate 12.

  In the i-th prism 12a that is considerably deep in the light guide plate 12, the first inclination angle θi of the first slope 12bi is considerably large. Therefore, the light Li incident on the first slope 12bi has a small reflection angle γi when reflected by the first slope 12bi. For this reason, the incident light δi of the light reflected and incident on the boundary surface of the upper surface 12d becomes large, and a lot of light exceeding the critical angle appears. Light exceeding the critical angle exits from the light guide plate 12, and light that does not reach the critical angle is reflected into the light guide plate 12. In the i-th prism 12a, the depth hi of the prism 12a is deeper than the depth of the prism 12a at a position close to the light source 13. For this reason, the length of the first inclined surface 12bi is longer than the first inclined surface 12b of the prism 12a at a position near the light source 13. If the length of the slope is long, the area of the slope increases accordingly, the amount of light incident on the slope increases, and the amount of light reflected by the slope increases. Note that light that enters the first inclined surface 12bi of the prism 12a at an incident angle exceeding the critical angle also appears. Incident light incident at an incident angle exceeding the critical angle passes through the first inclined surface 12bi and travels toward the reflecting plate 17 disposed on the lower surface side of the light guide plate 12. Then, the light is reflected by the reflecting plate 17 and enters the light guide plate 12 again.

  In the n-th prism 12a in the deepest part of the light guide plate 12, the first inclination angle θn of the first slope 12bn is the largest. Therefore, the reflection angle γn of the light Ln incident on the first inclined surface 12bn when reflected by the first inclined surface 12bn becomes small. For this reason, the incident angle δn of the light reflected and incident on the boundary surface of the upper surface 12d becomes large, and a lot of light exceeding the critical angle appears. And the light which radiate | emits outside from the light-guide plate 12 also increases. In the n-th prism 12a, the depth hn of the prism 12a is the deepest. For this reason, the length of the first slope 12bn is the longest, and the area of the slope is also the largest. For this reason, the amount of light incident on the boundary surface of the first slope 12bn is large, and the amount of light reflected on the boundary surface is also large. Light incident on the first inclined surface 12bn of the prism 12a with an incident angle exceeding the critical angle also appears, but incident light incident at an incident angle exceeding the critical angle passes through the first inclined surface 12bn and is reflected. The light travels toward the plate 17 and is reflected by the reflecting plate 17 to enter the light guide plate 12 again.

  Here, the first inclined surface 12b and the second inclined surface 12c of the prism 12a and the upper surface 12d of the light guide plate 12 are finished to be a glossy surface and become a glossy reflecting surface. Further, the inclination angle θ of the first slope 12b is set to 45 ° or less. This 45 ° is a value smaller than the critical angle of the light guide plate made of a resin such as polycarbonate resin, and light incident on the boundary surface of the first inclined surface 12b with an incident angle smaller than the critical angle is totally reflected. Therefore, the first inclined surface 12b reflects a lot of light from the light source 13. Further, the first inclination angle θ increases as the distance from the light source 13 increases. For this reason, the reflection angle (corresponding to γ in FIG. 4) of the light reflected at the boundary surface of the first inclined surface 12b is also gradually reduced. Then, the incident angle (corresponding to δ in FIG. 4) when the reflected light is incident on the boundary surface of the upper surface 12d gradually increases, and more light is incident on the boundary surface of the upper surface 12d beyond the critical angle. Also, the amount of light emitted from the upper surface 12d increases. Further, the depth of the prism 12a gradually increases as the distance from the light source 13 increases. Thereby, since the area of the 1st slope 12b also becomes large sequentially, the light quantity which injects into the boundary surface of the 1st slope 12b increases sequentially, and the reflected light quantity also increases sequentially. Accordingly, the amount of light emitted from the upper surface 12d of the light guide plate 12 is increased even if the light guide plate 12 is located at the back of the light guide plate 12.

  The light emitted from the light source 13 is reflected by the boundary surface of the first inclined surface 12b of the prism 12a. The reflection direction of the reflected light takes the shape of a circular prism in which the prism 12a is concentric with the light source 13 as the center. Therefore, the light travels in the same direction without changing the traveling direction. Therefore, even if the light emitted from the light source 13 in the radial pattern is reflected by the first inclined surface 12b, the light traveling direction does not change and spreads in the radial pattern. Then, it is possible to guide light far away without narrowing the directivity area of the light source 13. This also produces a uniform brightness effect.

  Further, the angle β of the valley 12j formed by the first slope 12b and the second slope 12c of the prism 12a has an angle of 90 ° or more. If the angle β of the valley 12j is 90 ° or more, the mold release property of the light guide plate 12 in the injection molding and the light guide plate 12 is improved, so that the manufacture becomes easy.

  With the above operation, the light from the light source 13 is guided to the back of the light guide plate 12, and the amount of emitted light increases even at the back position, so that the amount of emitted light is made uniform. And the brightness | luminance of the light-guide plate 12 becomes uniform on the whole. FIG. 5 shows a graph depicting the luminance curve of the light guide plate 12. As shown in FIG. 5, a smooth luminance curve is drawn as a whole. It can be seen that the entrance and entrance sides where the light from the light source 13 enters are in a slightly low brightness state, and that the difference between the maximum and minimum brightness is very small and a substantially uniform brightness can be obtained. . Compared with the structure of the light guide plate described in the above prior art, a remarkably uniform brightness can be obtained as a whole.

  Furthermore, the light source 13 uses an LED and is disposed in the corner notch 12k of the light guide plate 12. Since the LED is small, the backlight unit can be reduced in size without increasing the space. Further, since only one LED is required, the cost can be reduced. Further, since the LED has a low driving voltage, it consumes less power and is economical.

  Further, in the display device 20 in which the backlight unit 18 having the light guide plate 12 and the light source 13 is provided on the lower surface side of the liquid crystal display panel 11, the color display image of the display panel is bright, and the color display with uniform brightness. An image is obtained. Further, if the display device 20 including the backlight unit 18 of the present invention is used in a display device, a bright and uniform color display image can be obtained.

  The backlight unit 18 in the first embodiment is composed of the light guide plate 12, the light source 13, the light diffusion sheet 14, the first prism sheet 15, the second prism sheet 16, and the reflection plate 17. The backlight unit of the present invention is not particularly limited to this configuration. For example, it is also possible to delete one prism sheet used and configure it with one prism sheet. It is also possible to configure without using any prism sheet. This prism sheet may be appropriately selected according to the specifications of the display device. In addition, the backlight unit may be configured with a storage frame that has reflection means instead of the reflection plate 17 and holds and stores these components.

  In the first embodiment, a resin sheet in which silica particles are dispersed in the light diffusion sheet 14 is used. However, the sheet is not particularly limited to this specification, and for example, a diffusion sheet having minute irregularities on the surface. Any sheet having a light diffusing function and a light transmitting function, such as a sheet provided with diffusing particles other than silica particles, may be used.

  In the first embodiment, the active matrix type color liquid crystal display panel is used as the display panel. However, the display panel is not limited to the active matrix type color liquid crystal display panel, and may be a monochrome display liquid crystal display panel. The same effect can be obtained.

  Next, a backlight unit according to a second embodiment of the present invention will be described with reference to FIGS. Here, FIG. 6 is a plan view showing the arrangement of the light guide plate and the light source of the backlight unit according to the second embodiment of the present invention, and FIG. 7 is a sectional view taken along line EE in FIG.

  The backlight unit according to the second embodiment of the present invention differs from the configuration of the backlight unit of the first embodiment described above only in the shape of the light guide plate, and the other components are the components in the first embodiment described above. Parts with the same specifications are used. Accordingly, the description will be made mainly with respect to the light guide plate, and description of other components will be kept to a minimum. Further, parts having the same specifications as those used in the first embodiment will be described with the same reference numerals.

  As shown in FIG. 6, the light guide plate 22 is provided with a corner notch 22k at one corner (corner) in the same manner as the light guide plate in the first embodiment described above, and the corner notch 22k has a corner notch. The light source 13 is disposed in the vicinity of the end face 22e of the portion 22k. The light guide plate 22 has a plurality of concentric sawtooth circular prisms 22a (hereinafter simply referred to as prisms) centered on the light source 13 on the lower surface thereof. The light guide plate 22 is formed by an injection molding method using a resin having excellent heat resistance, moisture resistance, impact resistance, and chemical resistance, such as polycarbonate resin, polyimide resin, and polyethylene resin.

  As shown in FIG. 7, the width p of the pitch of the ridge line 22 g of the prism 22 a is gradually narrowed away from the light source 13. That is, the pitch width of the first prism closest to the light source is p1, the pitch width of the second prism is p2, the pitch width of the i-th prism is pi, and the pitch of the innermost prism is When the width is pn, the relationship is p1> p2>...> Pi>...> Pn (i = 1 to n). The prism 22a has a first slope 22b facing the light source 13 and a second slope 22c opposite to the first slope 22b. When the inclination angle of the first inclined surface 22 b is the first inclination angle, the first inclination angle θ increases gradually with increasing distance from the light source 13. That is, the first inclination angle of the first inclined surface 22b of the prism closest to the light source is θ1, the inclination angle of the first inclined surface 22b of the second prism is θ2, and the inclination angle of the first inclined surface 22b of the i-th prism is θi. If the inclination angle of the first slope 22b of the n-th prism located at the innermost position is θn, the relationship is θ1 <θ2 <... <θi <... <θn (i = 1). ~ N). And these 1st inclination-angle (theta) is 45 degrees or less. Further, the depth h of the prism 22a is the same regardless of which prism is taken. The first inclined surface 22b and the second inclined surface 22c of the prism 22a are finished as reflecting surfaces having a glossy surface. Further, the upper surface 22d of the light guide plate 22 and the end surface 22e of the corner notch 22k are also finished with a glossy surface. The angle of the valley 22j formed at the intersection of the first slope 22b and the second slope 22c is 90 ° or more.

  In the light guide plate 22 having such a structure, the prism 22a located near the light source 13 has a small first inclination angle θ of the first inclined surface 22b. Since the reflection angle of light is large and the incident angle of the reflected light to the boundary surface of the upper surface 22d is also small, the light is reflected by the boundary surface of the upper surface 22d and travels toward the back of the light guide plate 22. However, as the distance from the light source 13 increases, the pitch width p of the prism 22a also decreases, and the first inclination angle θ of the first inclined surface 22b also increases, so that the reflection angle of light reflected at the boundary surface of the first inclined surface 22b is increased. Becomes smaller. Further, the incident angle of the reflected light incident on the boundary surface of the upper surface 22d is increased, and a lot of light exceeding the critical angle appears. For this reason, light exceeding the critical angle is refracted out of the light guide plate and emitted. In other words, as described in the first embodiment, when the first inclination angle is increased as the distance from the light source increases, the light from the light source is guided toward the back of the light guide plate 22 and more from the upper surface 22d of the light guide plate 22. Can be emitted. As a result, the effect of uniforming the luminance is obtained.

  The prism 22a has the same prism depth, and the pitch width p gradually decreases as the distance from the light source 13 increases, and the first inclination angle θ of the first inclined surface 22b increases sequentially. Therefore, as the distance from the light source 13 increases, the length of the first inclined surface 22b also decreases gradually, and the area of the inclined surface 22b also decreases. However, the number of the first inclined surfaces 22b increases. For this reason, the amount of light reflected at the boundary surface of one first inclined surface 22b gradually decreases as the distance from the light source 13 increases. On the other hand, the number of first inclined surfaces 22b increases, so that the amount of reflected light also increases as a whole. The light quantity distribution becomes uniform as a whole. Then, the distribution of the amount of light emitted from the light guide plate 22 can be made uniform, and uniform luminance can be obtained.

  The illumination brightness of the light guide plate 22 having the above structure takes a brightness curve similar to the brightness curve shown in FIG. 5 in the first embodiment, and a uniform brightness with little brightness difference is obtained as a whole.

  Next, a backlight unit according to a third embodiment of the present invention will be described with reference to FIGS. Here, FIG. 8 is a plan view showing the arrangement of the light guide plate and the light source used in the backlight unit according to the third embodiment of the present invention, and FIG. 9 is a sectional view taken along line EE in FIG. . FIG. 10 is a luminance curve diagram showing the luminance state of the light guide plate in FIG.

  The backlight unit according to the third embodiment of the present invention is different from the configuration of the backlight unit of the first embodiment only in the shape of the light guide plate, and other components are the components in the first embodiment. Parts with the same specifications are used. Accordingly, the description will be made mainly with respect to the light guide plate, and description of other components will be kept to a minimum. Further, parts having the same specifications as those used in the first embodiment will be described with the same reference numerals.

  As shown in FIG. 8, the light guide plate 32 is provided with a corner notch 32k at one corner (corner) in the same manner as the light guide plate in the first embodiment described above, and the corner notch 32k has a corner notch. The light source 13 is disposed close to the end face 32e of the portion 32k. As shown in FIG. 9, the light guide plate 32 is provided with two types of conical circular saw-toothed circular prisms (hereinafter simply referred to as “prisms”) on the lower surface thereof. The two types of prisms include a first circular prism (hereinafter referred to as a first prism) A1 in a region close to the light source 13, and a second circular prism (hereinafter referred to as a first circular prism) connected to the first prism A1 and away from the light source 13. A2) (referred to as the second prism). In either case, a circular concentric circular prism centering on the light source 13 is formed. In the light guide plate 32 shown in FIG. 8, the ridge line 32g1 of the first prism A1 and the ridge line 32g2 of the second prism A2 are arranged at equal intervals.

  The first prism A1 is composed of a plurality of prisms 32a1, the slope facing the light source 13 of the prism 32a1 is the first slope 32b1 of the first prism, and the slope angle of the first slope 32b1 of the first prism is the first slope of the first prism. Assuming that the tilt angle is one, the first tilt angle of the first prism has the same tilt angle θ1. The first inclination angle θ1 is set to an angle of 45 ° or less. Further, the pitch width p is also provided with the same pitch width, and the depth of the prism 32a1 is also the same depth.

  Next, the second prism A2 is composed of a plurality of prisms 32a2, each inclined surface facing the light source 13 of the plurality of prisms 32a2 is defined as the first inclined surface 32b2 of the second prism, and the inclination angle of the first inclined surface 32b2 is defined as the second inclination angle. Assuming that the first tilt angle of the prism is set, the first tilt angle θ of the second prism gradually increases as the distance from the light source increases. That is, if the inclination angle of the prism 32a2 closest to the light source 13 of the second prism A2 is θ2, the inclination angle of the i-th prism 32a2 is θi, and the inclination angle of the innermost prism 32a2 is θn, then θ2 <. <[Theta] i <.. <[theta] n (i = 2 to n). And all the 1st inclination angles are 45 degrees or less. In addition, the pitch widths of the respective prisms 32a2 of the second prism A2 all have the same dimension, and the same dimension as the pitch width p of the first prism A1. Further, the depth of each of the prisms 32a2 of the second prism A2 is gradually increased as the distance from the light source is increased. That is, assuming that the depth of the prism 32a2 closest to the light source 13 of the second prism A2 is h2, the depth of the i-th prism 32a2 is hi, and the depth of the innermost prism 32a2 is hn, h2 <. The relationship is <hi <.. <hn (i = 2 to n). The specification of the second prism A2 is the same as the specification of the prism in the first embodiment described above.

  Here, the first inclination angle θ1 of the first prism A1 is set to be slightly larger, the light from the light source 13 is reflected at the boundary surface of the first inclined surface 32b1, and the reflected light is reflected on the upper surface 32d of the light guide plate 32. A part of the incident light is emitted to the outside of the light guide plate 32 when entering the boundary surface, and a part of the light is inclined so as to be reflected into the light guide plate 32. That is, the incident light incident on the boundary surface of the first inclined surface 32b1 from the light source 13 has a different incident angle depending on the incident position of the inclined surface. Accordingly, the reflection angles of the light reflected at this boundary surface are also different. The reflected lights having different reflection angles then enter the boundary surface of the upper surface 32d. The incident angles when the reflected lights having different reflection angles are incident on the boundary surface of the upper surface 32d are different incident angles. When the different incident angles are set to be around the critical angle, the incident light incident beyond the critical angle is emitted out of the light guide plate 32. Further, incident light incident at an incident angle that does not reach the critical angle is reflected into the light guide plate 32. Thus, by setting the first inclination angle θ1 of the first inclined surface 32b1 so that the incident angle reflected at the boundary surface of the first inclined surface 32b1 and incident on the boundary surface of the upper surface 32d is around the critical angle, A part of the light of the light source 13 reflected at the boundary surface of the one inclined surface 32 b 1 can be emitted to the outside of the light guide plate 32. The first prism A1 is provided to increase the luminance at a position near the light source 13 of the light guide plate 32. When the light guide plate is configured by only the second prism A2, the luminance at a position near the light source 13 is inevitably lowered as shown in the first embodiment. For this reason, the first prism A1 is provided at a position near the light source 13 to increase the luminance at that position.

  The range in which the first prism A1 is provided may be a width of 5 to 10% with respect to the diagonal length of the light guide plate 32. For example, if the diagonal length is 50 mm, from the end face 32e of the corner notch 32k. It is good to provide in the range of 2.5-5 mm.

  FIG. 10 is a graph depicting the luminance curve of the light guide plate 32 having the prism configuration described above. As shown in FIG. 10, the brightness increases from a1 'to a1 in the region of the first prism A1. And the brightness | luminance difference of Max brightness | luminance and Min brightness | luminance becomes small, and the brightness | luminance curve excellent in the uniformity is obtained. The operation and effect of the second prism A2 is the same as described in the first embodiment, and the description thereof is omitted here.

  The trough angle of the prism 32a1 formed by the first slope 32b1 of the first prism A1 and the second slope 32c1 on the opposite side is set to be 90 ° or more. Similarly, the angle of the valley of the prism 32a2 formed by the first slope 32b2 of the second prism A2 and the second slope 32c2 on the opposite side is set to be 90 ° or more. When the angle is set to 90 ° or more, the releasability of the light guide plate 32 from the mold during injection molding is improved.

  In addition, the first slope 32b1 and the second slope 32c1 in the first prism A1, the first slope 32b2 and the second slope 32c2 in the second prism A2, the upper surface 32d of the light guide plate 32, and the end face 32e of the corner notch 32k. Has a glossy finish. Reflective efficiency is greatly enhanced due to the glossy surface.

  The light guide plate 32 having the above-described configuration is formed by an injection molding method using a resin having excellent heat resistance, moisture resistance, impact resistance, and chemical resistance such as polycarbonate resin, polyimide resin, and polyethylene resin. Glossy surfaces such as slopes and upper surfaces are formed by transfer from a mold.

  When the backlight unit is configured using the light guide plate 32 having the above configuration, a display image in which the brightness is uniform to every corner of the image can be obtained from the display image of the display panel. When the brightness of the illumination is bright and uniform, the color of the color image becomes clear and a beautiful color display image can be obtained.

  In the third embodiment, the pitch width p and depth of the plurality of prisms 32a1 in the first prism A1 are all formed with the same dimensions, but are not limited to the same dimensions. It is good to set appropriately so that uniform luminance can be obtained in view of the obtained luminance situation. In addition, the first tilt angles of the prisms 32a1 in the first prism A1 do not have to be the same, and the respective angles may be slightly changed in view of the obtained luminance.

  Next, a backlight unit according to a fourth embodiment of the present invention will be described with reference to FIG. Here, FIG. 11 shows a cross-sectional view of the main part of the light guide plate used in the backlight unit according to the fourth embodiment of the present invention.

  The backlight unit according to the fourth embodiment of the present invention is different from the configuration of the backlight unit of the first embodiment only in the shape of the light guide plate, and other components are the components in the first embodiment. Parts with the same specifications are used. Accordingly, the description will be made mainly with respect to the light guide plate, and description of other components will be kept to a minimum. Further, parts having the same specifications as those used in the first embodiment will be described with the same reference numerals.

  Although not shown, the light guide plate 42 according to the fourth embodiment is provided with a corner notch at one corner (corner) as in the light guide plate in the first embodiment described above. The light source 13 is disposed in the vicinity of the end face 42e of the notch. Further, the light guide plate 42 is provided with two types of concentric sawtooth circular prisms (hereinafter simply referred to as “prisms”) provided continuously on the lower surface of the light guide plate 42. As shown in FIG. 11, the two types of prisms include a first prism A1 in a region close to the light source 13, and a second prism A2 in a region connected to the first prism A1 and away from the light source 13. In either case, a circular concentric circular prism centering on the light source 13 is formed.

  The first prism A1 is composed of a plurality of prisms 42a1, the slope facing the light source 13 of the prism 42a1 is the first slope 42b1 of the first prism, and the slope angle of the first slope 42b1 of the first prism is the first slope of the first prism. Assuming that the tilt angle is one, the first tilt angle of the first prism has the same tilt angle θ1. The first inclination angle θ1 is set to an angle of 45 ° or less. The pitch width p1 is also set to the same pitch width, and the prism 42a1 has the same depth.

  Next, the second prism A2 is composed of a plurality of prisms 42a2, the slope facing the light source 13 of the prism 42a2 is the first slope 42b2 of the second prism, and the slope angle of the first slope 42b2 is the first slope of the second prism. Assuming the inclination angle, the first inclination angle θ of the second prism gradually increases as the distance from the light source increases. That is, when the inclination angle of the prism 42a2 closest to the light source 13 of the second prism A2 is θ2, the inclination angle of the i-th prism 42a2 is θi, and the inclination angle of the innermost prism 42a2 is θn, θ2 <· · <Θi <·· <θn (i = 2 to n). And all the 1st inclination angles are 45 degrees or less. In addition, the pitch width of each prism 42a2 of the second prism A2 is gradually decreased as the distance from the light source 13 increases. That is, assuming that the pitch width of the first prism 42a2 closest to the light source is p2, the pitch width of the i-th prism 42a2 is pi, and the pitch width of the innermost prism 42a2 is pn, p1> ..> Pi>..> Pn (i = 1 to n). The depth h of each of the plurality of prisms 42a2 is the same depth. The specification of the second prism A2 is the same as that of the light guide plate in the second embodiment described above.

  Here, the first inclination angle θ1 of the first prism in the first prism A1 is set slightly larger, and the light from the light source 13 is reflected by the boundary surface of the first inclined surface 42b1 of the first prism, and the reflected light thereof. When the light enters the boundary surface of the upper surface 42d of the light guide plate 42, a part of the incident light is emitted to the outside of the light guide plate 42, and a part of the light is inclined to reflect the light into the light guide plate 42. That is, the incident angle of the incident light incident on the boundary surface of the first inclined surface 42b1 from the light source 13 differs depending on the incident position of the inclined surface. Accordingly, the reflection angles of the light reflected at this boundary surface are also different. The reflected lights having different reflection angles then enter the boundary surface of the upper surface 42d. The incident angles when the reflected lights having different reflection angles are incident on the boundary surface of the upper surface 42d are different from each other. When the different incident angles are set to be around the critical angle, incident light that has entered beyond the critical angle is emitted out of the light guide plate 42. Further, incident light incident at an incident angle that does not reach the critical angle is reflected into the light guide plate 42. In this way, by setting the first inclination angle θ1 of the first prism so that the incident angle reflected at the boundary surface of the first inclined surface 42b1 and incident on the boundary surface of the upper surface 42d is around the critical angle, the first inclination angle θ1 is set. A part of the light of the light source 13 reflected by the boundary surface of the slope 42b1 can be emitted out of the light guide plate 42. The first prism A1 is provided to increase the luminance at a position near the light source 13 of the light guide plate. When the light guide plate is composed of only the second prism A2, the luminance at a position near the light source 13 is inevitably lowered as shown in the second embodiment. For this reason, the first prism A1 is provided at a position near the light source 13 to increase the luminance at that position.

  The range in which the first prism A1 is provided may be a width of 5 to 10% with respect to the length of the diagonal line of the light guide plate 42. For example, if the diagonal length is 50 mm, it is 2 from the end face 42e of the corner notch. It is good to provide in the range of 5-5 mm.

  The luminance curve of the light guide plate 42 having the above prism configuration is almost the same as the luminance curve shown in FIG. 10 in the third embodiment, and the luminance of the light guide plate at a position close to the light source is obtained. The brightness difference between Max brightness and Min brightness is reduced, and a brightness curve with excellent uniformity is obtained. The operation and effect of the second prism A2 is the same as described in the second embodiment, and the description thereof is omitted here.

  Further, the angle of the valley formed by the first slope 42b1 in the first prism A1 and the second slope 42c1 on the opposite side is set to be 90 ° or more. Similarly, the angle of the valley formed by the first slope 42b2 in the second prism A2 and the second slope 42c2 on the opposite side is set to be 90 ° or more. When the angle is set to 90 ° or more, the releasability of the light guide plate 42 from the mold during injection molding is improved.

  The first slope 42b1 and the second slope 42c1 in the first prism A1, the first slope 42b2 and the second slope 42c2 in the second prism A2, the upper surface 42d of the light guide plate 42, and the end face 42e of the corner notch are Finished with a glossy surface. Reflective efficiency is greatly enhanced due to the glossy surface.

  The light guide plate 42 having the above configuration is formed by an injection molding method using a resin excellent in heat resistance, moisture resistance, impact resistance, and chemical resistance, such as polycarbonate resin, polyimide resin, and polyethylene resin. Glossy surfaces such as slopes and upper surfaces are formed by transfer from a mold.

  When the backlight unit is configured using the light guide plate 42 having the above configuration, brightness that is uniform in every corner of the image can be obtained in the display image of the display panel. When the brightness of the illumination is bright and uniform, the color of the color image becomes clear and a beautiful color display image can be obtained.

  In the fourth embodiment, the pitch width p1 and the depth of the plurality of prisms 42a1 in the first prism A1 are all formed with the same size, but are not limited to the same size. It is good to set appropriately so that uniform luminance can be obtained in view of the obtained luminance situation. Further, the first tilt angles of the first prisms in the first prism A1 do not have to be the same, and the respective angles may be slightly changed in view of the obtained luminance.

  In the above, the structure of the backlight unit of this invention was demonstrated using four embodiment. The configuration of the backlight unit of the present invention not only makes the illumination brightness uniform, but also improves the brightness itself. In a liquid crystal display panel using a light guide plate having a thickness of 0.6 to 1.0 mm and a size of 2.5 to 3 inches, a brightness increase effect of 15% to 20% is obtained. This is because the light of the light source is effectively used for illumination without waste by devising the shape of the prism of the light guide plate.

  When the backlight unit of the present invention is used as a backlight of a display device such as a communication information device such as a mobile phone or a fax machine, various devices, or a display terminal device of the device, the illumination brightness is increased and the brightness of the display image As it increases, an effect of obtaining a display image with uniform brightness is produced.

1 is a side view of a display device using a backlight unit according to a first embodiment of the present invention. It is the top view which showed the arrangement | positioning state of the light-guide plate and light source in FIG. It is EE sectional drawing in FIG. It is explanatory drawing explaining the effect | action of the light-guide plate in FIG. FIG. 3 is a luminance curve diagram illustrating a luminance state of the light guide plate in FIG. 2. It is the top view which showed arrangement | positioning of the light-guide plate and light source of the backlight unit which concern on 2nd Embodiment of this invention. It is EE sectional drawing in FIG. It is the top view which showed arrangement | positioning of the light-guide plate and light source which are used for the backlight unit which concerns on 3rd Embodiment of this invention. It is EE sectional drawing in FIG. FIG. 9 is a luminance curve diagram illustrating a luminance state of the light guide plate in FIG. 8. It is principal part sectional drawing of the light-guide plate used for the backlight unit which concerns on 4th Embodiment of this invention. It is principal part sectional drawing of the conventional liquid crystal display device. It is explanatory drawing explaining the light emission state to the light-guide plate by the arrangement | positioning number of the light sources in FIG. It is principal part sectional drawing of the light-guide plate in FIG. It is a brightness | luminance curve figure showing how brightness | luminance changes with the magnitude | sizes of the inclination-angle of the slope of a prism.

Explanation of symbols

11 Display panels 12, 22, 32, 42 Light guide plates 12a, 22a, 32a1, 32a2, 42a1, 42a2 Circular prisms 12b, 22b, 32b1, 32b2, 42b1, 42b2 First slopes 12c, 22c, 32c1, 32c2, 42c1, 42c2 Second slopes 12d, 22d, 32d, 42d Upper surfaces 12e, 22e, 32e, 42e End surface 12f Poor-looking parts 12g, 22g, 32g1, 32g2 Ridge lines 12j, 22j Valleys 12k, 22k, 32k Corner notch 13 Light source 14 Light diffusion sheet 15 First prism sheet 16 Second prism sheet 17 Reflector 18 Backlight unit 20 Display device A1 First circular prism A2 Second circular prism θ, θ1, θ2, θi, θn First inclination angles p, p1, p2 , Pi, pn Ji width h, h1, h2, hi, hn depth

Claims (10)

In a backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch portion of the light guide plate, and the light guide plate has a sawtooth shape concentrically centered on the light source. When the circular prism has a circular slope, the slope facing the light source of the circular prism is a first slope, and the slope angle of the first slope is a first slope angle, the circular width of the circular prism is constant, The backlight unit is characterized in that the inclination angle increases with increasing distance from the light source, and the depth increases with increasing distance from the light source. In a backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch portion of the light guide plate, and the light guide plate has a sawtooth shape concentrically centered on the light source. When the circular prism has a circular slope, the slope facing the light source of the circular prism is a first slope, and the slope angle of the first slope is a first slope angle, the circular prism has a constant depth, and the first slope The backlight unit is characterized in that the angle increases with increasing distance from the light source, and the pitch width decreases with increasing distance from the light source. In a backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch portion of the light guide plate, and the light guide plate has a sawtooth shape concentrically centered on the light source. A first circular prism, a second circular prism connected to the first circular prism, the inclined surface of the first circular prism facing the light source; the first inclined surface of the first prism; The slope of the first slope of one prism is the first slope of the first prism, the slope of the second circular prism facing the light source is the first slope of the second prism, and the first slope of the second prism Is the first inclination angle of the second prism, the first circular prism is provided on the light source side, and the first inclination angle of the first prism is the first pre-angle. The second circular prism has a constant pitch width, and the second circular prism has a constant pitch width. The backlight unit according to claim 1, wherein the first tilt angle of the prism increases with increasing distance from the light source, and the depth increases with increasing distance from the light source. In a backlight unit provided on the lower surface side of the display panel and having a light guide plate and a light source, the light source is disposed in a corner notch portion of the light guide plate, and the light guide plate has a sawtooth shape concentrically centered on the light source. A first circular prism, a second circular prism connected to the first circular prism, the inclined surface of the first circular prism facing the light source; the first inclined surface of the first prism; The slope of the first slope of one prism is the first slope of the first prism, the slope of the second circular prism facing the light source is the first slope of the second prism, and the first slope of the second prism Is the first inclination angle of the second prism, the first circular prism is provided on the light source side, and the first inclination angle of the first prism is the first pre-angle. The second circular prism has a constant depth, and the second prism has a constant depth. The first tilt angle of the backlight unit increases with increasing distance from the light source, and the pitch width decreases with increasing distance from the light source. The backlight unit according to claim 1, wherein the first inclination angle is 45 ° or less. When the slope on the opposite side of the first slope is a second slope, the angle of the valley of the circular prism formed by the first slope and the second slope is 90 ° or more. Item 6. The backlight unit according to any one of Items 1 to 5. The backlight unit according to any one of claims 1 to 6, wherein the first slope and the second slope are glossy surfaces. 8. The backlight unit according to claim 1, wherein an upper surface of the light guide plate and an end surface of the corner notch are glossy surfaces. 9. The backlight unit according to any one of claims 1 to 4, wherein the light source is an LED. A display device including a backlight unit on a lower surface side of a display panel, wherein the backlight unit uses the backlight unit according to any one of claims 1 to 9 to brighten and uniformly display the display panel. A display device characterized by being illuminated with high brightness.

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