JP2008091287A - Backlight unit and display device equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit capable of providing emitting directions in two directions; and a display device. <P>SOLUTION: In this edge type backlight unit, a pair of incident surfaces 21a1 and 21a2 are formed on facing side surfaces of a light guide plate 21; light sources 22 are respectively arranged adjacently to the pair of incident surfaces 21a1 and 21a2; a plurality of recessed grooves 21e each forming a symmetrical shape are formed on an emitting surface 21c of the light guide plate 21 or a surface facing to the emitting surface 21c in parallel to an arrangement axis of the light sources 22 respectively arranged adjacently to the pair of incident surfaces 21a1 and 21a2. The backlight unit 20 is composed by arranging a directivity adjustment sheet 25 adjusting directivity on the emitting surface 21c side of the light guide plate 21. This display device 40 is composed by arranging the backlight unit 20 on the back surface of a liquid crystal display panel 30. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  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.

  As one of the prior arts of this backlight unit, an optical sheet for controlling the emission direction has been proposed.

  The optical sheet described in Patent Document 1 below has the shape shown in FIG. FIG. 17 is an enlarged cross-sectional view of the optical sheet disclosed in Patent Document 1. In FIG. 17, the diffused light controlling optical sheet 10 </ b> D is provided with a convex portion 13 having an inclined surface 14 with an inclination angle θ on the opposite surface opposite to the light receiving surface 12 in a parallelogram shape. Yes. Further, a diffusing agent which is fine particles is dispersed in the convex portion 13. According to Patent Document 1, by arranging the diffused light control optical sheet 10D on the light exit surface side of the light guide plate, the light emitted from the light guide plate enters the light receiving surface 12 of the diffuse light control optical sheet 10D, The diffused light is emitted in the direction of arrow C, and the emission direction can be controlled in the direction of arrow C.

JP-A-10-246805

  In addition, backlight units using LEDs have been used in small liquid crystal display devices such as mobile phones. Many backlight units using LEDs have a configuration in which a required number of LEDs 3 are arranged on the side surface of the light guide plate 2 as shown in FIG.

  However, the configuration of the backlight unit described in Patent Document 1 shown in FIG. 17 is configured to have the emission direction in two directions even though the emission direction can be determined as one direction. Absent. For example, the display image is not clearly visible simultaneously from two directions of the driver's seat and the passenger's seat, such as in-car car navigation and liquid crystal television. Furthermore, the optical sheet 10D for diffused light control shown in FIG. 17 is very difficult to manufacture when a sheet-like one is made because the convex portion 13 is inclined.

  Further, in the backlight unit using LEDs, as shown in FIG. 18, since the LEDs 3 have directivity, adjacent LEDs in the vicinity of the incident surface of the light guide plate 2 that collects the light of the LEDs 3. A hot spot (dark part) is generated in the hatched portion indicated by D between the two. The hot spot greatly affects the image quality of the display image. For this reason, it is necessary to enlarge the backlight unit and remove it from the display area of the liquid crystal display panel, or to arrange a large number of LEDs so as not to generate hot spots. This has been a factor in increasing the size of the liquid crystal display device itself including the liquid crystal display panel.

  The present invention has been made in view of the above problems, and is a backlight unit that can be easily manufactured, has directivity in two directions, and whose emission direction can be freely changed, and a display. It is an object to obtain a device and to obtain a small backlight unit and a display device.

  As a means for achieving the above object, the backlight unit according to claim 1 of the present invention is characterized in that the light source is provided close to the entrance surface of the light guide plate having the entrance surface and the exit surface. In the type of backlight unit, a pair of incident surfaces of the light guide plate are provided on opposite side surfaces, the light source is provided close to each of the pair of incident surfaces, and the light guide plate exit surface or the surface facing the exit surface In addition, a plurality of concave grooves or convex portions having a symmetric shape are provided in a streak shape in parallel with the arrangement axis of the light source.

  In addition, the backlight unit according to claim 2 of the present invention is characterized in that the concave groove or convex portion having the symmetrical shape has an isosceles triangle shape or a substantially semicircular shape. is there.

  The backlight unit according to claim 3 of the present invention is characterized in that a directivity adjustment sheet for adjusting directivity is disposed on the light exit surface side of the light guide plate.

  In addition, the backlight unit according to claim 4 of the present invention is characterized in that the directivity adjusting sheet is formed of an optical sheet having a convex shape and parallel ridge lines of the convex part, and the convex of the optical sheet. The portion is directed to the liquid crystal display panel side, and the parallel ridge lines are arranged in parallel with the arrangement axis of the light source.

  Further, the backlight unit according to claim 5 of the present invention is characterized in that the directivity adjusting sheet is formed of an optical sheet having a convex shape and parallel ridge lines of the convex portions, and the convex portion of the optical sheet. The portion is directed to the light guide plate side, and the parallel ridge lines are arranged in parallel with the arrangement axis of the light source.

  The backlight unit according to claim 6 of the present invention is characterized in that the optical sheet is a prism sheet in which the convex shape forms a triangle.

  The backlight unit according to claim 7 of the present invention is characterized in that the optical sheet is a prism sheet in which the convex shape forms a trapezoid.

  Further, the backlight unit according to claim 8 of the present invention is characterized in that the optical sheet is a prism sheet in which the convex shape forms a triangular peak and a valley forms a flat surface. It is.

  According to a ninth aspect of the present invention, the backlight unit is characterized in that the directivity adjusting sheet can adjust the emission direction.

  The backlight unit according to claim 10 of the present invention is characterized in that the adjustment of the emission direction is performed by changing the angle of the apex angle of the triangle or the angle of the trapezoidal slope.

  The backlight unit according to claim 11 of the present invention is characterized in that a diffusion sheet is disposed between the directivity adjusting sheet and the light guide plate.

  The backlight unit according to claim 12 of the present invention is characterized in that the light source is an LED.

  The backlight unit according to claim 13 of the present invention is characterized in that the directivity of light emitted from the backlight unit has a heart shape.

  The display device according to claim 14 of the present invention is characterized in that in the display device including a backlight unit on the back side of the liquid crystal display panel, the backlight unit is set forth in any one of claims 1 to 13. The described backlight unit is used.

  According to the present invention, the following invention effects can be obtained. In the backlight unit of the present invention, a light source is provided close to a pair of opposed incident surfaces, and light from the light source is taken in from both incident surfaces. As a result, the light entering from one incident surface reaches the other incident surface and illuminates the peripheral portion of the other incident surface, and similarly, the light entering from the other incident surface is the peripheral portion of one incident surface. Illuminate. Therefore, since the peripheral portions of the incident surfaces on both sides are illuminated, the hot spot (dark part) that has been observed in the past does not occur. For this reason, compared with the backlight unit of the prior art, the size of the backlight unit can be reduced correspondingly, and the display device can also be reduced in size.

  In addition, light from the light source enters from the incident surfaces on both sides, and both light beams are emitted from the emission surface, so that light having two emission directions is emitted. In general, a light guide plate having a reflecting means such as a prism is approximately 60 ° to the normal line of the exit surface of the light guide plate, depending on the material and shape of the light guide plate in the case of lighting the light source on one side of the light guide plate. Light is emitted in an angle direction of 70 °. For this reason, on the light guide plate having light sources on both sides, light that is emitted in the direction of 60 ° to 70 ° angle with the normal line and light that has two emission directions that are emitted in the direction of −60 ° to −70 ° angle appear. Thereby, the display image of the liquid crystal display device can be visually recognized from two directions.

  In addition, a plurality of symmetrical concave grooves or convex portions are provided in a streak shape parallel to the arrangement axis of the light source on the exit surface of the light guide plate or the surface facing the exit surface. The light from the light source is reflected by the concave grooves provided in parallel and in the form of streaks and guided to the back of the light guide plate. However, since the concave grooves have a symmetrical shape, the light incident from the incident surfaces on both sides The reflection conditions by the concave grooves are also reflected under the same conditions. Further, the light that passes through the concave groove and exits from the exit surface is also emitted under the same conditions. Accordingly, outgoing light emitted in two outgoing directions has the same directivity characteristics. Moreover, the convex part provided in the shape of a stripe brings about the same effect.

  In addition, the concave groove or convex portion having a symmetric shape is an isosceles triangle or a substantially semicircular shape. Since the isosceles triangle and semi-circular shapes are simple, the mold can be easily manufactured and molded. This produces an effect of reducing the manufacturing cost. In addition, the light emitted from the light guide plate is transmitted through this concave groove and the like, but if it has an isosceles triangle shape or a substantially semicircular shape, complicated refraction does not occur in the emitted light, and the light is emitted in a certain direction to some extent. Irradiation is obtained. Also, it acts to reflect incident light from the light source in a uniform direction and guide it to the back of the light guide plate.

  Next, a directivity adjustment sheet is disposed on the light exit surface side of the light guide plate having the above configuration. The directivity adjustment sheet is a sheet for adjusting the light emission direction, and adjusts the light emitted from the light guide plate in a desired emission direction. This directivity adjusting sheet is an optical sheet in which a plurality of convex ridge lines are formed in parallel. Specifically, a prism sheet, a lenticular lens sheet, etc. are mentioned as a suitable thing. In particular, the prism sheet having a triangular convex shape has a simple shape, and a clear directivity in two directions appears. Moreover, since it is easy to manufacture, it can be selected as a more preferable optical sheet. The directivity adjusting sheet made of such an optical sheet is arranged so that the convex part is directed to the liquid crystal display panel side or the convex part is directed to the light guide plate side and the ridge line is parallel to the arrangement axis of the light source. When arranged, the emission direction from the light guide plate can be changed. For example, by changing the angle of the apex angle of the prism sheet, the angle of the emission direction can be changed, and emission light in two directions at a desired angle can be obtained. In addition, a prism sheet having a trapezoidal shape and a prism sheet having a mountain having a triangular shape and a valley having a flat surface can obtain four emission directions. The emitted light in the four directions can be combined into two emitted lights in each direction by adjusting the angle of the apex angle to obtain two broad emitted lights emitted left and right.

  In addition, when a diffusion sheet is disposed between the exit surface of the light guide plate and the directivity adjusting sheet, the exit output direction is changed at the same time as the output output half width is widened by the action of the diffusion sheet. This is presumed that a large number of light having a small emission angle is emitted while the emitted light emitted in two directions from the light guide plate is diffused by the light diffusion action of the diffusion sheet. Thereby, the emission output half width can be widened.

  Moreover, LED is used for a light source. Since it can be driven at a low voltage, it consumes less power and is economical, and since it is small, it can be effectively applied to a portable display device or a small display device.

  As described above, two or four emission directions can be obtained. In particular, the directivity having the output in two directions provides a directional characteristic having a heart shape.

  When the display device including such a backlight unit is applied to, for example, an in-vehicle liquid crystal television or a car navigation system, display images can be viewed from both sides of the driver seat and the passenger seat. Moreover, if it is used by lighting only one of the LEDs, it is possible to obtain an outgoing output only in one direction. The display image can be viewed from two directions or from one direction by switching between both-side lighting and one-side lighting of the LED.

  (First Embodiment) The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below with reference to the drawings. First, a backlight unit and a display device according to a first embodiment of the present invention will be described with reference to FIGS. Here, the figure will be described. FIG. 1 shows a side view of a display device according to a first embodiment of the present invention. FIG. 2 is an enlarged explanatory view illustrating the role of a plurality of symmetrical concave grooves provided on the light exit surface of the light guide plate in FIG. FIG. 3 is a plan view of the directivity adjustment sheet in FIG. 1 and also shows the arrangement relationship with the light source. 4 is a schematic diagram for explaining the directivity of light emitted from the light guide plate in FIG. 1. FIG. 4A is a schematic diagram showing the directivity characteristics of light emitted from the light guide plate, and FIG. FIG. 4 is a schematic diagram showing the emission direction from the light guide plate. 5 is a schematic diagram for explaining the directivity of the emitted light from the directivity adjusting sheet in FIG. 1, and FIG. 5 (a) is a schematic diagram showing the directivity characteristics of the emitted light from the directivity adjusting sheet. FIG. 5B is a schematic diagram showing the emission direction from the directivity adjustment sheet. FIG. 6 is an explanatory diagram for explaining the directivity of the directivity adjustment sheet in FIG. FIG. 7 is a graph showing the directivity characteristics of the backlight unit in FIG. FIG. 8 is an explanatory view schematically showing the operation of another arrangement form of the directivity adjustment sheet.

  As shown in FIG. 1, the display device 40 according to the first embodiment of the present invention includes a backlight unit 20 provided on the back side of the liquid crystal display panel 30. The liquid crystal display panel 30 is an active matrix type liquid crystal display panel using TFT elements, and R (red), G (green), and B (blue) color filters are provided for each pixel provided with the TFT elements. Therefore, a color image is displayed with illumination light from the backlight unit 20.

  The backlight unit 20 has incident surfaces 21a1 and 21a2 on a pair of opposite side surfaces of the light guide plate 21, and a light source 22 is disposed close to the pair of incident surfaces 21a1 and 21a2. The light guide plate 21 has a configuration in which a reflection sheet 23 is provided on the lower surface side and a directivity adjustment sheet 25 is provided on the upper surface side of the light guide plate 21.

  Here, the upper surface of the light guide plate 21 (the surface facing the directivity adjustment sheet 25) forms an exit surface 21c, and the light from the light source 22 collected from the pair of left and right entrance surfaces 21a1 and 21a2 is the exit surface 21c. Exits from. In the first embodiment, as shown in the enlarged view of the portion E in FIG. 1, a plurality of grooves 21e each having an isosceles triangle shape are provided on the emission surface 21c in a line shape. The concave groove 21e approaches the pair of left and right incident surfaces 21a1, 21a2, and is arranged with the arrangement axes of the light source 22 provided in parallel with the incident surfaces 21a1, 21a2 (the A1 axis and the B1 axis shown in FIG. It is provided in parallel with the shaft.

  The specifications of the components constituting the backlight unit 20 will be briefly described. The light guide plate 21 is formed using a resin such as transparent acrylic resin or polycarbonate resin, and has a rectangular flat plate shape. The pair of opposing side surfaces have incident surfaces 21a1 and 21a2, and the exit surface 21c is provided with a plurality of isosceles triangular concave grooves 21e in parallel with the arrangement axes A1 and B1 of the light source 22. The shape of the concave groove 21e is formed by transfer from a mold.

  As shown in FIG. 2, an isosceles triangular concave groove 21 e provided on the exit surface 21 c of the light guide plate 21 allows incident light P <b> 1 and P <b> 2 from the entrance surfaces 21 a 1 and 21 a 2 to go to the back of the light guide plate 21, and It functions to reflect toward the lower surface 21d on the opposite side opposite to the emission surface 21c. Moreover, the light reflected from the lower surface 21d or the reflected light transmitted from the lower surface 21d and reflected from the reflection sheet 23 is also emitted from the emission surface 21c. The concave groove 21e is an isosceles triangle symmetrical so that the condition for reflecting the incident light P1 from the incident surface 21a1 by the concave groove 21e and the condition for reflecting the incident light P2 from the incident surface 21a2 by the concave groove 21e are the same. It has a simple shape. In this way, the directivity characteristics of the outgoing light exiting from the exit face 21c of the light incident from the entrance face 21a1 and the directivity characteristics of the outgoing light exiting from the exit face 21c of the light incident from the entrance face 21a2 are made the same. be able to. In the first embodiment, the symmetric groove 21e is formed in an isosceles triangle shape, but is not limited to an isosceles triangle shape, and a curved surface shape such as a semicircle or a semi-elliptical shape may be used. . Here, a curved surface shape such as a semicircular shape or a semielliptical shape is defined as a substantially semicircular shape. Since isosceles triangles and substantially semicircular shapes are simple in shape, it is possible to obtain a merit that molds can be easily manufactured and parts can be easily formed. In the first embodiment, the concave groove 21e is provided on the emission surface 21c, but there is no problem even if it is provided on the lower surface 21d side. In addition, in the first embodiment, the concave groove 21e having an isosceles triangle is connected in a line shape, but this structure is also a structure in which convex parts having an isosceles triangle are connected in a line shape. . The same effect can be obtained with a configuration in which convex portions are provided instead of the concave grooves. This also achieves the same effect even when the shape is substantially semicircular.

  Next, the light source 22 uses a white LED in the first embodiment. The white LEDs are arranged close to the opposing pair of incident surfaces 21a1, 21a2 of the light guide plate 21 and arranged in parallel with the incident surfaces 21a1, 21a2 (three on the left and right in FIG. 3). The LED has a low driving voltage and is very economical, and since it is small in size, it can be reduced in size without increasing the size of the backlight unit. It can be used as a suitable light source for small display devices and portable devices. The light source 22 is not limited to the LED, and a cold cathode tube or the like can also be used.

  The reflection sheet 23 is provided to reflect the light that has escaped to the lower side of the light guide plate 21 and returned to the liquid crystal display panel 30 side. Further, since the reflected light passes through the light guide plate when returning to the liquid crystal display panel 30, refraction occurs, so that a light diffusion effect is also produced. As the reflective sheet 23, for example, a highly reflective aluminum metal thin plate, a resin sheet provided with an aluminum metal thin film or a silver metal thin film, a resin sheet provided with a white coating film, a molded thin plate formed of a white resin, etc. Can be used.

  The directivity adjustment sheet 25 disposed on the upper surface side of the light guide plate 21 is provided for the purpose of adjusting the emission direction of the light emitted from the light guide plate 21. The directivity adjusting sheet 25 is a convex sheet and an optical sheet in which the ridge lines of the convex portions are parallel is used. In the first embodiment, the optical sheet is provided with a triangular prism 25a. This is a prism sheet in which the apex angle ridge line 25b of the triangular prism 25a is parallel and the prism 25a is continuously provided. Further, the pitch of the triangular prisms 25a is several tens of μm, but in the drawing, it is exaggerated and drawn for easy understanding. As shown in FIG. 3, the prism sheet is arranged so that parallel ridge lines 25b are parallel to the arrangement axes A1 and B1 of the light source 22 arranged close to the incident surfaces 21a1 and 21a2 of the light guide plate 21. . The same is true even if the number of light sources 22 is one on the arrangement axes A1 and B1, and the prism sheet is parallel to the arrangement axis of the cold cathode tubes even when one cold cathode tube is arranged on each of the left and right sides of the light source 22. The ridge line 25b is arranged. Further, the prism sheet is arranged with the apex angle directed toward the liquid crystal display panel 30 side. The directivity adjusting sheet 25 can be manufactured by a sheet extrusion molding method or a hot press molding method.

  Subsequently, the operation and effect of the present embodiment will be described with reference to FIGS. 4 and 5. First, the operation of the light guide plate 21 in which the light source 22 is arranged on the pair of opposed incident surfaces 21a1 and 21a2 shown in FIG. 4 will be described. In FIG. 4B, the light guide plate 21 collects light from the light source 22 arranged on the left and right in the drawing and emits the light from the emission surface 21c in the directions R1 and L1 indicated by arrows. Only a part of the emitted light indicated by the arrows is displayed. Outgoing light emitted in the direction of R1 is emitted from the incident surface 21a2, and indicates an outgoing angle of approximately 60 °. On the other hand, the light emitted in the direction of L1 is emitted from the incident surface 21a1, and indicates a direction in which the emission angle is approximately −60 °. Accordingly, the light from the left light source 22 incident from the incident surface 21a2 is directed in the direction of R1, and the light of the right light source 22 incident from the incident surface 21a1 is directed in the direction of L1 by approximately 60 ° on the opposite side. The light is emitted with a direction of emission.

  With respect to the directivity in these two directions, the directivity characteristic of the outgoing light at the outgoing position O when the outgoing position on the outgoing plane is O is as shown in FIG. Here, how to view FIG. 4A will be briefly described. XX represents the exit surface in the optical waveguide direction, and O represents a certain exit position on the exit surface. The Z axis indicates a vertical axis at the position O, and the direction is determined by setting the Z axis to 0 °. The length m represents the peak of light intensity. The angles at which the peaks of light intensity appear are represented by + γ ° and −γ °. w represents the output half-value width (hereinafter referred to as output width). In FIG. 4A, two directional characteristics, QR1 and QL1, appear in the outgoing light at position O. The emission direction of QR1 is a + γ ° direction, and a peak of intensity m appears. The direction of + γ ° indicates the direction of R1 in FIG. 4B, and is approximately 60 ° as described above. On the other hand, the intensity peak appears in the direction of −γ ° in the emission direction of QL1. The direction of −γ ° indicates the direction of L1 in FIG. 4B, and is approximately −60 ° as described above. Thus, when a light source is arranged on a pair of incident surfaces 21a1 and 21a2 facing the light guide plate 21, emitted light having directivity characteristics in two directions appears.

  Next, the emission direction when the directivity adjustment sheet 25 which is a triangular prism sheet is used will be described with reference to FIG. In FIG. 5B, the light in the direction R1 emitted from the light guide plate 21 is refracted by the prism sheet, which is the directivity adjustment sheet 25, and the optical path is changed in the direction R2. As shown in FIG. 6, the light in the R1 direction incident on the lower surface of the directivity adjusting sheet 25 is refracted at the incident boundary surface on the lower surface of the directivity adjusting sheet 25, and is further emitted from the inclined surface 25d of the prism 25a. The light to be refracted is emitted in the direction of R2. The exit angle in the R2 direction becomes smaller than the exit angle in the R1 direction by 2 degrees of refraction, and changes in a direction in which the exit angle becomes smaller. Similarly, light in the direction L1 emitted from the light guide plate 21 is affected by the lower surface of the directivity adjusting sheet 25 and the inclined surface 25e of the prism 25a, and the optical path is changed in the direction L2. The exit angle in the L2 direction becomes smaller than the exit angle in the L1 direction by 2 degrees of refraction, and changes in a direction in which the exit angle becomes smaller.

  Next, as shown in FIG. 5A, light having two directivity characteristics appears at the output position O as the directivity characteristics of the light emitted from the directivity adjusting sheet 25 in the R2 direction and the L2 direction. The directivity characteristic QR1 appears by light in the emission direction R2, and the directivity characteristic QL2 appears by light in the emission direction L2. In the directivity characteristics of QR1 and QL1 shown in FIG. 5A, the light intensity peaks in the directions of + δ ° and −δ ° by the directivity adjusting sheet 25 as the emission direction. It can be said that the shape formed by these directivity characteristics QR2 and QL2 has a heart shape. Further, the angle δ ° is smaller than the angle γ ° shown in FIG. The angle β ° sandwiched between the two directions of the emitted light having the directivity in these two directions is determined by the apex angle α ° of the vertex 25c of the triangular prism 25a shown in FIG. That is, if the apex angle α ° changes, the angle β ° sandwiched between the two directions changes. Thereby, the angle β ° can be freely adjusted by the apex angle α °. Note that the triangular prism 25a of the directivity adjusting sheet 25 in the first embodiment uses isosceles triangular prisms having the same inclination angles of the inclined surfaces 25d and 25e, and the apex angle α ° is an angle between two emission directions. The angle is such that a peak of light intensity is obtained at (+ δ °, −δ °).

  Here, it demonstrates still in detail using FIG. From FIG. 7, when the left and right light sources 22 are turned on, light intensity peaks appear in the vicinity of + 30 ° and −30 ° (solid curve). When only the right light source is lit, the light intensity peaks near −30 ° (dashed line curve), and when only the left light source is lit, the light intensity peaks near + 30 ° (dashed line curve). From the above, when a prism sheet having a prism apex angle α = 100 ° is used, the emission direction changes in the directions of + 30 ° and −30 °, and the interval between the two emission directions appears narrow. . Compared with the state without the light adjustment sheet (the state shown in FIG. 4), the angle at which the peak of the light intensity appears is about half smaller.

  When the backlight unit 20 having the above-described configuration is provided on the back surface of the liquid crystal display panel 30 to constitute the display device 40, for example, when used in an in-car car navigation system or a liquid crystal television, display images are displayed on the driver seat and the passenger seat. It looks good from both.

  In addition, the display device of the first embodiment is directed in two directions at the same time, but it is also possible to select which direction to direct. For example, in FIG. 5, when only the light source 22 on the incident surface 21a1 side of the light guide plate 21 of the backlight unit 20 is turned on, the emission direction in one direction indicated by the directivity characteristic QL2 appears, and only the light source 22 on the incident surface 21a2 side appears. When is turned on, the emission direction in one direction indicated by the directivity characteristic QR2 appears. In this way, it is possible to selectively change the emission direction.

  In addition, regarding the hot spot (dark part) that has been observed in the prior art, since the light from the light source 22 is collected from the incident surfaces 21a and 121a on both sides of the light guide plate 21, the hot spot generated near the incident surface 21a1 is incident. The hot spot generated in the vicinity of the incident surface 21a2 disappears with the light incident from the incident surface 21a1. As a result, a backlight unit free from hot spots can be obtained. In the prior art, the backlight unit is enlarged and the display device is enlarged so that the hot spot portion does not enter the display area. The display device can be made small.

  In the first embodiment, a triangular prism sheet is used for the directivity adjustment sheet 25. The directivity adjusting sheet 25 is not limited to a prism sheet, and similar effects can be obtained by using a convex lenticular lens sheet. Further, the distance between the two emission directions can be adjusted by changing the radius of curvature of the lenticular lens. Since triangular prism lenses and lenticular lenses have simple shapes, they can be easily manufactured by sheet extrusion molding or hot press molding.

  The backlight unit 20 according to the first embodiment described above has a configuration in which the convex portion of the prism 25a of the directivity adjustment sheet 25 is arranged toward the liquid crystal display panel 30 side. The same result can be obtained even if the configuration is arranged toward the side. FIG. 8 is an explanatory view in which the directivity adjusting sheet 35 is arranged in another form. The apex 35c of the prism 35a forming the triangular shape of the directivity adjusting sheet 35 is disposed toward the light guide plate 21 side. The parallel ridge lines of the prism 35a are arranged in parallel with the arrangement axis of the light source.

  The emitted light L1 emitted from the light guide plate 21 enters the prism 35a of the directivity adjustment sheet 35, undergoes total reflection at the inclined surface 35e of the prism 35a, and is emitted from the directivity adjustment sheet 35 as L7 emitted light. The outgoing light L7 is emitted in a direction in which the outgoing direction rises in angle with respect to the light of L1. Similarly, the outgoing light R1 emitted from the light guide plate 21 undergoes total reflection at the inclined surface 35d of the prism 35a, and is emitted from the directivity adjusting sheet 35 as outgoing light of R7. The emitted light R7 is also emitted in a direction in which the emission direction rises in angle with respect to the light of R1. Thus, outgoing light having two outgoing directions can be obtained from the directivity adjusting sheet 35. Since the inclined surface 35d and the inclined surface 35e of the prism 35a are isosceles triangular inclined surfaces having the same inclination angle, the two emission directions are opposite to each other, and are directed in the same direction as shown in FIG. Characteristics are obtained.

  (Second Embodiment) Next, a backlight unit and a display device according to a second embodiment of the present invention will be described with reference to FIGS. Here, FIG. 9 shows a side view of a display device according to the second embodiment of the present invention. FIG. 10 is a schematic diagram for explaining the directivity of the emitted light from the diffusion sheet in FIG. 9. FIG. 10 (a) is a schematic diagram showing the directivity of the emitted light from the diffusion sheet. b) is a schematic diagram showing the emission direction from the diffusion sheet. 11 is a schematic diagram for explaining the directivity of the emitted light from the directivity adjusting sheet in FIG. 9, and FIG. 11A is a schematic diagram showing the directivity characteristics of the emitted light from the directivity adjusting sheet. FIG. 11B is a schematic diagram showing the emission direction from the directivity adjustment sheet. FIG. 12 is a perspective view showing the emission direction of the display device in FIG. Note that components having the same specifications as the components used in the first embodiment are described with the same reference numerals, but the description is limited to the necessary limit.

  As shown in FIG. 9, the display device 60 according to the second embodiment includes a backlight unit 50 on the back surface of the liquid crystal display panel 30. Since the liquid crystal display device 30 has the same specifications as those of the liquid crystal display panel in the first embodiment, the description of the specifications is omitted here. The backlight unit 50 is provided with a light source 22 in close proximity to a pair of opposing incident surfaces 21 a 1 and 21 a 2 of the light guide plate 21, a reflective sheet 23 is provided on the lower surface side of the light guide plate 21, and the upper surface of the light guide plate 21. The diffusion sheet 54 and the directivity adjustment sheet 25 are laminated on the side.

  Here, in the configuration of the backlight unit 50 of the second embodiment, the diffusion sheet 54 is arranged between the light guide plate 21 and the directivity adjustment sheet 25 in contrast to the configuration of the backlight unit in the first embodiment described above. Only the configuration is different. The light guide plate 21, the light source 22, and the directivity adjustment sheet 25, which are constituent parts, use the same specifications as those of the first embodiment. Therefore, in the second embodiment, description will be made mainly on the operation and effect obtained by providing the diffusion sheet 54.

  Here, the diffusion sheet 54 is made by dispersing silica fine particles in a transparent resin and finishing it into a sheet shape. However, the diffusion sheet 54 is not limited to this, and other well-known ones such as those having fine unevenness on the surface of the resin sheet and finished to a satin finish may be used.

  As described with reference to FIG. 4 in the first embodiment, the directivity characteristic of the light emitted from the emission surface 21c of the light guide plate 21 is emitted by light having emission directions in two directions of approximately + 60 ° and −60 °. To do. As the directivity when the emitted light passes through the diffusion sheet 54, the directivity shown in FIG. Here, the operation and effect of the diffusion sheet 54 will be described while comparing FIG. 4A and FIG. 10A.

  Since the light transmitted through the diffusion sheet 54 is diffused, the light intensity is weaker than the light emitted from the light guide plate 21. In addition, a spread appears in the output width (outgoing output half-value width) due to diffusion. In FIG. 4 (a), the output width is narrow when the hatched area is the output width w of the directivity characteristics QL1 and QR1. On the other hand, in FIG. 10A, the output width of the area of the two directivity characteristics QL3 and QR3 is wider than that of FIG. Thus, the diffused outgoing light has the effect of widening the output range of the directional characteristics. Furthermore, although it is the emission direction of the emitted light, the direction of ± ε ° in FIG. 10A is closer to 0 degree on the Z axis than the direction of ± γ ° in FIG. The direction has changed. This is presumed that light having a small exit angle is emitted while light is diffused. As described above, by providing the diffusion sheet 54, the output width is widened, and the directivity characteristic in which the two emission directions are close to each other as the emission direction rises appears.

  Next, when the emitted light from the diffusion sheet 54 having such directivity passes through the directivity adjusting sheet 25, the directivity shown in FIG. Compared to the directivity characteristics QL2 and QR2 shown in FIG. 5A in the above-described first embodiment in which no diffusion sheet is provided, the output width of the directivity characteristics QL4 and QR4 shown by diagonal lines is widened. The angle of ± θ ° is also smaller than ± δ ° in FIG. 5A, and the two directivity characteristics QL4 and QR4 are brought close to each other to obtain a directivity characteristic having a well-shaped heart shape.

  FIG. 12 shows the directivity characteristics of the display device including the backlight unit 50 configured as described above in a three-dimensional manner. From the liquid crystal display panel 30, the same directional characteristics as those appearing in the backlight unit 50 shown in FIG. Now, in FIG. 12, the emitted light from the display screen position O, when the Z-axis is 0 °, is a direction of Q3 that is + θ ° away from 0 ° toward the x-axis direction, and a direction of Q4 that is −θ ° apart. Directivity appears in the two directions. The directions of Q3 and Q4 are the same as the emission direction appearing in the backlight unit 50. Directional characteristics (S) having a heart shape are obtained by overlapping the directivity characteristics QL4 and QR4 appearing in the backlight unit 50. In addition, since the diffusion sheet 54 is provided, the width of each output appears wide.

  Therefore, since strong light is emitted in the directions of Q3 and Q4, the display image can be seen well from the directions of Q3 and Q4. In addition, since the output width in both the direction of Q3 and the direction of Q4 is wide, even if the position seen in the direction of Q3 or the direction of Q4 is slightly deviated, it is sufficiently clear. A display image comes to be visually recognized.

  Further, since diffused light is emitted from the backlight unit 50, the intensity of the emitted light is small, and a display image with uniform brightness can be obtained.

  Although the directions of Q3 and Q4 are the same as those described in the first embodiment, the emission direction can be freely changed by changing the prism apex angle of the prism sheet which is the directivity adjusting sheet 25. be able to.

  By mounting the backlight unit 50 of the second embodiment on an in-vehicle car navigation system, a liquid crystal television, or the like, the display image can be viewed brightly and clearly from the driver seat and the passenger seat at the same time.

  (Third Embodiment) Next, a backlight unit and a display device according to a third embodiment of the present invention will be described with reference to FIGS. Here, FIG. 13 shows a side view of a display device according to the third embodiment of the present invention. 14 is a schematic diagram for explaining the directivity of the emitted light from the directivity adjustment sheet in FIG. 13, and FIG. 14 (a) is a schematic diagram showing the directivity characteristics of the emitted light from the directivity adjustment sheet. FIG. 14B is a schematic diagram showing the emission direction from the directivity adjustment sheet. FIG. 15 is an explanatory diagram for explaining the operation of the directivity adjustment sheet in FIG. FIG. 16 is a side view showing another shape of the directivity adjusting sheet.

  As shown in FIG. 13, the display device 80 according to the third embodiment includes a backlight unit 70 provided on the back surface of the liquid crystal display panel 30. Here, the backlight unit 70 is provided with a light source 22 close to a pair of opposite incident surfaces 21a1 and 21a2 of the light guide plate 21 and a reflection sheet 23 on the lower surface side of the light guide plate 21. The diffusion plate 54 and the directivity adjustment sheet 75 are laminated on the upper surface side of the optical plate 21. The backlight unit 70 in the third embodiment is different from the backlight unit in the second embodiment described above only in the specification of the directivity adjustment sheet 75, and other components are the same as those in the second embodiment described above. Parts with the same specifications as the component parts in are used. Therefore, the directivity adjustment sheet 75 will be mainly described here, and description of other components will be limited to the necessary limit.

  In the third embodiment, the directivity adjusting sheet 75 is a prism sheet having a prism 75a having a trapezoidal convex shape. The prism sheet of the trapezoidal prism 75a is an isosceles trapezoidal prism having two inclined surfaces 75d and 75e having the same slope angle ψ and a tip having a flat surface 75f as shown in FIG. . The trapezoidal pitch and height are both several tens of μm, but are exaggeratedly drawn in FIGS.

  Since the prism sheet of the trapezoidal prism 75a as described above is used for the directivity adjustment sheet 75, the emitted light of the light source 22 incident from the incident surface 21a1 of the light guide plate 21 is diffused as shown in FIG. When the light passes through the sheet 54 and is emitted from the directivity adjusting sheet 75, outgoing light directed in two directions L6a and L6b appears. Similarly, when the light emitted from the light source 22 incident from the incident surface 21a2 of the light guide plate 21 passes through the diffusion sheet 54 and is emitted from the directivity adjusting sheet 75, the light is directed in two directions R6a and R6b. The light appears. Then, the directivity shown in FIG. 14A appears as the directivity of the emitted light.

  In (a) of FIG. 14, from the position O of the directivity adjustment sheet 75, in the direction on the + side with respect to the Z axis of 0 °, the directivity QR 6 b having the maximum light intensity in the direction of + θ ° Emitted light having two directivity characteristics of the directivity characteristics QR6a that shows the maximum light intensity in the + χ ° direction appears. The outgoing light showing the directivity characteristic QR6b in the + θ ° direction is outgoing light emitted in the direction of R6b in FIG. 14B, and this is indicated by the outgoing light emitted from the inclined surface 75d of the trapezoidal prism 75a. Further, the emitted light indicating the directivity characteristic QR6a in the + χ ° direction is emitted light emitted in the direction of R6a in FIG. 14B, and this is indicated by the emitted light emitted from the flat surface 75f at the tip of the trapezoidal prism 75a. It is. Both the directivity QR6b and the directivity QR6a are obtained by the light emitted from the light guide plate 21 incident from the incident surface 21a2.

  On the other hand, in the direction on the negative side with respect to the Z axis of 0 °, the light intensity is maximum in the direction of −χ ° and that of the directivity characteristic QL6b in which the light intensity is maximum in the direction of −θ °. Outgoing light having two directivity characteristics of the directivity characteristics QL6a appears. The outgoing light indicating the directivity characteristic QL6b in the −θ ° direction is outgoing light emitted in the direction L6b in FIG. 14B, and this is indicated by the outgoing light emitted from the inclined surface 75e of the trapezoidal prism 75a. Further, the emitted light indicating the directivity characteristic QL6a in the -χ ° direction is emitted light emitted in the direction of L6a in FIG. 14B, which is emitted by the emitted light emitted from the flat surface 75f at the tip of the trapezoidal prism 75a. Indicated. Both the directivity characteristics QL6b and the directivity characteristics QL6a are obtained by the light emitted from the light guide plate 21 incident from the incident surface 21a1.

  Next, the reason why the emission directions appear in four directions will be described with reference to FIG. In FIG. 15, outgoing light R5a and R5b indicate the outgoing light from the light guide plate 21 of the light incident from the incident surface 21a2. The outgoing lights L5a and L5b indicate the outgoing light from the light guide plate 21 of the light incident from the incident surface 21a1. The outgoing light R5a is refracted at the boundary surface of the flat surface 75f at the tip of the trapezoidal prism 75a and is emitted in the R6a direction. Further, the outgoing light R5b is refracted at the boundary surface of the inclined surface 75d of the trapezoidal prism 75a and is emitted in the direction of R6b. Here, since the incident angle that is incident on the flat surface 75f is different from the incident angle that is incident on the inclined surface 75d, the exit direction of exit after refraction is different, and the directions of R6a and R6b shown in FIG. The light is emitted in two directions.

  Similarly, the emitted light L5a is refracted at the boundary surface of the flat surface 75f at the tip of the trapezoidal prism 75a and is emitted in the L6a direction. Further, the emitted light L5b is refracted at the boundary surface of the inclined surface 75e of the trapezoidal prism 75a and is emitted in the direction of L6b. Here, since the incident angle that is incident on the flat surface 75f is different from the incident angle that is incident on the inclined surface 75e, the exiting direction after refraction is different, and the direction of L6a and the direction of L6b shown in FIG. The light is emitted in two directions. As described above, the emission direction is divided depending on whether the light enters the flat surface at the tip of the trapezoidal prism 75a or the inclined surface.

  As described above, when a trapezoidal prism sheet is used as the directivity adjustment sheet 75, the emission directions are divided into four directions. Thus, the light travels in four directions, but by adjusting the apex angle of the prism, the light in the L6a direction and the light in the L6b direction are combined, and the light in the R6a direction and the light in the R6b direction is combined. it can. Thereby, it can also be set as a broad broad light emitted in two directions. Also, the use of the diffusion sheet makes the output width (outgoing output half width) wider. Further, the angle in the emission direction can be adjusted by changing the inclination angle ψ ° of the inclined surface of the trapezoidal prism 75a.

  Although the trapezoidal prism sheet is used in the third embodiment, a backlight unit having emission directions in four directions or two directions having a wide emission width can be obtained even when the prism sheet having the shape shown in FIG. 16 is used. Have the same effect.

  The prism sheet of the directivity adjusting sheet 95 shown in FIG. 16 has a plurality of prisms 95a each having a triangular peak, and a trough 95g between adjacent prisms 95a is a prism sheet having a flat surface. Reference numeral 95b denotes a ridge line. The flat surface of the valley 95g has the same function as the flat surface at the tip of the trapezoidal prism.

  In the backlight unit 70 of the third embodiment, the emission direction appears in four directions by simultaneous lighting of the light sources 22 on both sides of the light guide plate 21, but the emission direction appears in two directions on one side by lighting only on one side. It is also possible to obtain four or two emission directions by switching the light sources 22 on both sides simultaneously and one-side lighting.

1 is a side view of a display device according to a first embodiment of the present invention. FIG. 2 is an enlarged explanatory view for explaining the role of a plurality of symmetric grooves provided on the light exit surface of the light guide plate in FIG. 1. It is a top view of the directivity adjustment sheet | seat in FIG. 1, and is the figure which also showed the positional relationship with a light source. 4A and 4B are schematic diagrams for explaining the directivity of light emitted from the light guide plate in FIG. 1. FIG. 4A is a schematic diagram showing directivity characteristics of light emitted from the light guide plate, and FIG. 4B is a light guide plate. It is the schematic diagram which showed the emission direction from. FIG. 5 is a schematic diagram illustrating the directivity of light emitted from the directivity adjustment sheet in FIG. 1, and FIG. 5A is a schematic diagram illustrating the directivity characteristics of light emitted from the directivity adjustment sheet, and FIG. ) Is a schematic diagram showing the emission direction from the directivity adjustment sheet. It is explanatory drawing explaining the directivity of the directivity adjustment sheet | seat in FIG. It is a graph which shows the directivity characteristic of the backlight unit in FIG. It is explanatory drawing which showed typically the effect | action of the other arrangement | positioning form of a directivity adjustment sheet | seat. It is a side view of the display apparatus which concerns on 2nd Embodiment of this invention. FIG. 10A is a schematic diagram illustrating the directivity of light emitted from the diffusion sheet in FIG. 9, FIG. 10A is a schematic diagram illustrating directivity characteristics of light emitted from the diffusion sheet, and FIG. 10B is a diffusion sheet. The schematic diagram which showed the emission direction from the is shown. FIG. 11 is a schematic diagram for explaining the directivity of the emitted light from the directivity adjusting sheet in FIG. 9. FIG. 11A is a schematic diagram showing the directivity characteristics of the emitted light from the directivity adjusting sheet, and FIG. ) Shows a schematic diagram showing the emission direction from the directivity adjustment sheet. FIG. 10 is a perspective view showing an emission direction of the display device in FIG. 9. It is a side view of the display apparatus which concerns on 3rd Embodiment of this invention. FIG. 14A is a schematic diagram for explaining the directivity of the emitted light from the directivity adjusting sheet in FIG. 13. FIG. 14A is a schematic diagram showing the directivity characteristics of the emitted light from the directivity adjusting sheet, and FIG. ) Is a schematic diagram showing the emission direction from the directivity adjustment sheet. It is explanatory drawing explaining the effect | action of the directivity adjustment sheet | seat in FIG. It is the side view which showed the other shape of the directivity adjustment sheet | seat. It is an expanded sectional view which shows one example of the optical sheet for diffused light control of the place shown by patent document 1. FIG. It is explanatory drawing of the hot spot (dark part) which generate | occur | produces in the light-guide plate of the backlight unit in a prior art.

Explanation of symbols

20, 50, 70 Backlight units 21, 31, 41 Light guide plates 21a1, 21a2 Light incident surface 21c Light emission surface 21e Groove 22 Light source 23 Reflective sheets 25, 35, 75, 95 Directional adjustment sheets 25a, 35a, 75a, 95a Prism 25b, 95b Ridge lines 25c, 35c Vertex 30 Liquid crystal display panels 40, 60, 80 Display device 54 Diffusion sheet

Claims (14)

  In an edge light type backlight unit in which a light source is provided close to an incident surface of a light guide plate having an incident surface and an output surface, a pair of incident surfaces of the light guide plate are provided on opposite side surfaces, and the pair of incident surfaces are provided on the pair of incident surfaces. The light source is provided close to each other, and a plurality of symmetrical concave grooves or convex portions are formed in a streak pattern on the exit surface of the light guide plate or on the surface facing the exit surface, and the arrangement axis of the light source A backlight unit characterized by being provided approximately in parallel.   2. The backlight unit according to claim 1, wherein the concave groove or the convex portion having the symmetrical shape has an isosceles triangle shape or a substantially semicircular shape.   3. The backlight unit according to claim 1, wherein a directivity adjustment sheet for adjusting directivity is disposed on an emission surface side of the light guide plate.   The directivity adjusting sheet is formed of an optical sheet having a convex shape and parallel ridge lines of the convex portions, the convex portions of the optical sheet are directed toward the liquid crystal display panel, and the parallel ridge lines are the light sources. 4. The backlight unit according to claim 1, wherein the backlight unit is arranged in parallel to the arrangement axis.   The directivity adjusting sheet is made of an optical sheet having a convex shape and parallel ridge lines of the convex portions, the convex portions of the optical sheet are directed to the light guide plate side, and the parallel ridge lines are the light sources. 4. The backlight unit according to claim 1, wherein the backlight unit is arranged in parallel to the arrangement axis.   The backlight unit according to claim 4, wherein the optical sheet is a prism sheet having a triangular convex shape.   The backlight unit according to claim 4, wherein the optical sheet is a prism sheet having a trapezoidal convex shape.   6. The backlight unit according to claim 4, wherein the optical sheet is a prism sheet whose convex shape forms a triangular peak and whose valley forms a flat surface.   The backlight unit according to any one of claims 3 to 8, wherein the directivity adjusting sheet can adjust an emission direction.   The backlight unit according to any one of claims 6 to 9, wherein the adjustment of the emission direction is performed by changing a vertex angle of a triangle or an angle of a trapezoidal slope.   The backlight unit according to any one of claims 1 to 10, wherein a diffusion sheet is disposed between the directivity adjusting sheet and the light guide plate.   The backlight unit according to claim 1, wherein the light source is an LED.   13. A backlight unit, wherein the directivity of light emitted from the backlight unit according to any one of claims 1 to 6 and claims 9 to 12 has a heart shape.   14. A display device comprising a backlight unit on the back side of a liquid crystal display panel, wherein the backlight unit uses the backlight unit according to any one of claims 1 to 13.

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