JP2005135844A - Optical element and backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device having a structure of reduced sheets, flatly emit light, guided in a light guide plate from a front surface, with uniform brightness. <P>SOLUTION: The optical element 30 is equipped with an optical means 32Am, in which the light from a light source is made incident, and of the incident light, the light traveling with directivity, spreading in a radial shape against the light guiding direction of a light guide plate 10, is polarized into a light having a directivity of traveling in the direction parallel with the light guide direction of the light guide plate 10, and emitted, and the emitted light is made incident on a light incident surface 11 of the light guide plate 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight device of a liquid crystal display (LCD), and more particularly, to an optical element used for significantly reducing the number of parts of the backlight device and a backlight device including the optical element. .

  A backlight unit, which is a backlight device of a liquid crystal display device, is required to be mass-produced with the spread of electronic devices equipped with the liquid crystal display device. The backlight unit is mainly formed by a light source and a light guide plate that guides light emitted from the light source to emit light.

  As the light source, a fluorescent tube, a light emitting diode (LED), or the like is used. In particular, a light emitting diode is often used when the light source is mounted on a miniaturized and thin electronic device.

  In general, as shown in FIG. 15, a backlight unit 100 using light emitting diodes as a light source includes a light guide plate 80, for example, a light source 90 having a plurality of light emitting diodes such as three light emitting diodes 91a, 91b, 91c, a reflective sheet 101, A diffusion sheet 102, a first lens sheet 103, and a second lens sheet 104 are provided.

  The backlight unit 100 is disposed such that the light emitting diodes 91a, 91b, and 91c are in close contact with the light incident surface 81 of the light guide plate 80 at a predetermined pitch, and the light output surfaces 92a, 92b, and 92c are in close contact with each other. The reflection sheet 101 is disposed on the reflection surface 82 side, and the diffusion sheet 102, the first lens sheet 103, and the second lens sheet 104 are disposed in this order on the light emitting surface 83 of the light guide plate 80. 111 are housed and assembled with the reflective sheet 101 facing the inner surface 111A of the frame. In the following description, the light emitting diodes 91a, 91b, 91c are also collectively referred to as the light emitting diode 91.

  Light that has entered the light incident surface 81 of the light guide plate 80 from the light emitting diode 91 is guided while being totally reflected by the inner surfaces of the light reflecting surface 82 and the light emitting surface 83 of the light guide plate 80. The light reflecting surface 82 of the light guide plate 80 is formed with a prism pattern, a dot pattern, and the like for efficiently rising incident light toward the light emitting surface 83. The light incident on the inner surface of the emission surface 83 is emitted from the light emission surface 83.

  Since the light emitted from the light emitting surface 83 has a very large variation in the in-plane light amount distribution, the light is incident on the diffusion sheet 102 and uniformized.

  The light emitted from the diffusion sheet 102 is incident on the first lens sheet 103 and the second lens sheet 104 and deflected so as to be condensed in the normal direction of the light emitting surface 83. The direction components of the light that the first lens sheet 103 and the second lens sheet 104 condense the light that has passed through the diffusion sheet 102 are different.

  One first lens sheet 103 is also called a Y-direction lens sheet. In FIG. 16, the light guide plate 80 including the light emitting diode 91 is arranged on the XY coordinate plane so that the light emitting surface 83 faces the front. The lens sheet collects the light component in the Y-axis direction in the normal direction of the light exit surface 83 when the light guide direction is the X-axis direction. The other second lens sheet 104 is also called an X-direction lens sheet, and is a lens sheet that condenses the light component in the X-axis direction shown in FIG. 16 in the normal direction of the light exit surface 83.

  In this way, the light emitted from the light exit surface 83 of the light guide plate 80 and passing through the diffusion sheet 102 is passed through the first lens sheet 103 and the second lens sheet 104, so that the backlight unit 100 The front luminance can be improved efficiently.

  The reflection sheet 101 disposed on the light reflection surface 82 side of the light guide plate 80 is arranged outside the light reflection surface 82 when the light incident from the light incident surface 81 is guided while being totally reflected in the light guide plate 80. The light that jumps out is reflected and returned to the light guide plate 80 again.

JP 2003-35910 A

  With the demand for downsizing and thinning electronic devices, backlight units mounted on such electronic devices, for example, used for illumination of liquid crystal display devices tend to be thinned. However, as described with reference to FIG. 15, the number of parts of the backlight unit 100 is very large, and among them, the reflection sheet 101, the diffusion sheet 102, the first lens sheet 103, the second lens sheet 104, and the like. It is the situation that four kinds are used.

  Since these sheets each have a thickness of about 0.1 to 0.15 mm, they are at least 0.4 mm or more when they are overlapped, and there is a problem that the backlight unit 100 is prevented from being thinned. .

  However, the functions of any of the above-described sheets are back of the mechanism for emitting light from the light emitting surface 83 while guiding the light incident on the light incident surface 81 of the light guide plate 80 from the light source 90 in this way. All of the light units 100 are essential and indispensable.

  In particular, the diffusion sheet 102, the first lens sheet 103, and the second lens sheet 104 stacked on the light output surface 83 of the light guide plate 80 can be expected to dramatically improve the front luminance, but are very expensive. It is a member.

  Specifically, when the diffusion sheet 102, the first lens sheet 103, and the second lens sheet 104 are incorporated in the backlight unit 100, these three sheets reduce some percentage of the total cost of the backlight unit 100. When high front luminance is required, there is a problem that cost increase is inevitably required.

  Therefore, the present invention has been devised to solve such a problem, and among the sheets constituting the backlight device, the diffusion sheet, the first reflection sheet, and the second reflection sheet are used as the diffusion sheet. An object of the present invention is to provide an optical element for reducing the function of the sheet, the first reflective sheet, and the second reflective sheet without impairing the function, and a backlight device including the optical element.

  In order to achieve the above-mentioned object, an optical element according to the present invention has one side as a light incident surface, and light incident from the light incident surface is a light exit surface that is one main surface and light that is the other main surface. It is an optical element that adjusts the light incident on the light incident surface of the light guide plate that is totally reflected by the reflecting surface and guided by light, and emits light from the light emitting surface, and receives the light emitted from the light source, Of the incident light, the light having directivity that spreads radially with respect to the light guide direction of the light of the light guide plate proceeds in a direction parallel to the light guide direction of the light of the light guide plate. And an optical means for deflecting and emitting the light having a property to enter the light incident surface of the light guide plate.

  In order to achieve the above-described object, a backlight device according to the present invention has one side as a light incident surface, and light incident from the light incident surface is a light exit surface that is one main surface and the other main surface. A light guide plate that is totally reflected by the light reflecting surface and guides light from the light emitting surface, and a plurality of light emitting elements arranged at predetermined intervals in the longitudinal direction of the light incident surface of the light guide plate. A light source, an optical element that receives light emitted from the plurality of light emitting elements of the light source, and is emitted as incident light on the light incident surface of the light guide plate, and disposed on the light reflecting surface side of the light guide plate The light guide plate includes the light source, the optical element, and a frame that holds the reflection sheet. The light guide plate has an X-axis direction as the light incident direction, and the X The direction perpendicular to the axial direction and parallel to the light exit surface is the Y-axis direction. When the normal direction is the direction perpendicular to the X-axis direction and the Y-axis direction, the light incident from the light incident surface is such that the inclination in the X-axis direction approaches zero with respect to the normal direction. The X-axis direction light distribution control means for controlling the light distribution to be emitted from the light exit surface, and the optical element is a light guide direction of the light of the light guide plate out of the incident light. In contrast, light having directivity that spreads radially is deflected to light having directivity that travels in a direction parallel to the light guide direction of the light of the light guide plate, and is emitted. It has an optical means for making it incident on the light incident surface.

  The optical element of the present invention is a light guide direction of light of a light guide plate from light having directivity that spreads light from a light source incident on the light guide plate in a radial direction with respect to the light guide direction of light of the light guide plate. The light is deflected to emit light having directivity that travels in a direction parallel to the light, and is incident on the light incident surface of the light guide plate.

  As a result, light emitted from the light source, which is a point light source, can be vertically incident on the entire light incident surface of the light guide plate, so that uniform light emission from the light guide plate with a certain level of brightness or more can be achieved. It is possible to make it.

  Further, the backlight device of the present invention provides the X-axis direction light distribution control means for converting the light deflected by the optical element into light having directivity that travels in a direction parallel to the light guide direction of the light from the light guide plate. By making the light incident on the light guide plate having the X-axis because light distribution control in the Y-axis direction, light distribution control in the X-axis direction, and light diffusion processing are not required for the light emitted from the light exit surface of the light guide plate Even without using a lens sheet or a diffusion sheet that performs light distribution control in the direction and light distribution control in the Y-axis direction, uniform surface light emission at a certain level or higher is possible.

  Therefore, since such a backlight device can reduce expensive lens sheets and diffusion sheets that have been essential in the past, the device can be thinned and the cost can be significantly reduced.

  The best mode for carrying out the invention of an optical element and a backlight device according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows a backlight unit 40 shown as the best mode for carrying out the present invention. The backlight unit 40 is configured by assembling the light guide plate 10, the light source unit 20, the optical element 30, and the reflection sheet 15 in frames 35 and 36.

  As a material used for the light guide plate 10, a transparent thermoplastic resin such as a methacrylic resin, a styrene resin, or a polycarbonate resin is used in addition to an acrylic resin. For example, the light guide plate 10 is injection-molded using a highly transparent acrylic resin or the like as a material. The light guide plate 10 reflects light incident from the light incident surface 11 in multiple directions by the light reflecting surface 12 which is one main surface of the light guide plate 10, and the reflected light is uniform light from the light emitting surface 13. To be emitted.

  The light reflecting surface 12 is formed with a fine uneven shape, for example, a prism pattern, a dot pattern, etc., and the light that is incident and guided into the light guide plate 10 is efficiently raised in the direction of the light emitting surface 13. Such processing is performed.

  For example, the light reflecting surface 12 is formed with a prism pattern composed of n (n is a natural number) prisms 12An, and the light incident and guided into the light guide plate 10 is efficiently emitted from the light emitting surface 13. Launch in the direction. The prism pattern formed on the light reflecting surface 12 is formed at the time of injection molding of the light guide plate 10 or is formed by direct processing after injection molding (direct cut). The prism pattern 12An will be described later in detail.

  The light guide plate 10 has a wedge shape so that the thickness in the light guide direction of the light that is incident and guided from the light incident surface 11 gradually decreases. However, the present invention is not limited to such a wedge shape. It can also be applied to a light guide plate having a shape.

  As the light source of the light guide plate 10, a light source unit 20 including light emitting diodes (LEDs) 21a, 21b, and 21c arranged in a row at predetermined intervals on the substrate 23 shown in FIG. 1 is used. The light emitting directions of the light emitting diodes 21a, 21b, and 21c are all the same, and the light emitting surfaces are referred to as light emitting surfaces 22a, 22b, and 22c, respectively. In the following description, the light emitting diodes 21a, 21b, and 21c are collectively referred to as the light emitting diode 21, and the light emitting surfaces 22a, 22b, and 22c are also collectively referred to as the light emitting surface 22. The light emitting diode 21 is, for example, a chip type light emitting diode.

  In the backlight unit 40, the light source unit 20 is disposed on the light incident surface 11 side of the light guide plate 10 via the optical element 30, and the reflection sheet 15 is disposed on the light reflecting surface 12 side. The light guide plate 10, the light source unit 20, the optical element 30, and the reflection sheet 15 arranged in this way are the frame 35 and the frame 36 that serve as the casing of the backlight unit 40, and the inner surface of the frame 36. It is assembled on the 36A side so that there is no rattling.

  FIG. 2 shows the light guide plate 10, the light source unit 20, and the optical element 30 included in the backlight unit 40 arranged on the XY coordinate plane so that the light guide direction is the X-axis direction and the light exit surface 13 is the front. FIG. When the light guide plate 10 is arranged on the XY coordinate plane in this way, the light emission direction from the light emission surface 13 is the Z-axis direction.

  Next, the prism 12An formed on the light reflecting surface 12 of the light guide plate 10 will be described.

  FIG. 3 shows a cross-sectional view of the light guide plate 10 taken along the line AA shown in FIG. As shown in FIG. 3, the prism 12An has a cross-sectional shape of a triangle having a base on the light reflecting surface 12 side, the base angle on the light incident surface 11 side of the triangle is an angle α = 50 to 60 °, and the other bottom. The groove is formed on the light reflecting surface 12 with a groove having an angle β in the range of 70 ° to 90 °.

  For example, when the light guide plate 10 is injection-molded, the cross-sectional shape on the inner surface of the cavity of the injection-molding mold that forms the light reflecting surface 12 is the angle α = 50 ° to 60 ° and the angle β = as described above. A plurality of convex portions may be formed so as to form a triangle having a base angle of 70 ° to 90 °.

  1 and 3, the prisms 12An formed on the light reflecting surface 12 are fixed in pitch and the prisms 12An arranged regularly are shown. However, the prisms 12An may be irregularly changed. Further, the pitch can be changed for each adjacent prism 12An. Further, in FIG. 3, the height of the prism 12An, that is, the depth of the groove formed on the light reflecting surface 12 is also described as being constant. However, the present invention is not limited thereto, and the light emitting surface 13 is not limited thereto. In order to effectively start up in the normal direction, all values such as the pitch of the prism 12An and the height of the prism 12An determined by the depth of the groove formed on the light reflecting surface 12 are arbitrarily designed. Can do.

  For example, when the prism 12An is formed at a fixed pitch, the depth of the groove to be manufactured is changed to change the height of the prism 12An or the pitch of the prism 12An is changed. It is also possible to fix the depth of the groove to be fixed and to make the height of the prism 12An constant.

  As shown in FIG. 3, the incident light L1 incident from the light incident surface 11 of the light guide plate 10 enters the prism 12An, and the X-axis direction component is normal to the light emitting surface 13 by the inclined surface S of the prism 12An. The light is split into the deflected light L2 deflected in the direction, the transmitted light L3 traveling in the X-axis direction as the light guide direction, the deflected light L4 emitted outside the light guide plate 10, and the like.

  The deflection angle of the component in the X-axis direction of the deflected light L2 is determined by the angles α and β of the plurality of grooves formed on the light reflecting surface 12 at the time of injection molding, and the angle α = 50 ° -60 ° as shown in FIG. By setting the angle β and the angle β = 70 ° to 90 °, the X-axis direction component of the deflected light L2 is deflected substantially in the normal direction of the light exit surface 13. The transmitted light L3 is incident on another prism 12An located at the rear stage in the light guide direction. The deflected light L4 is emitted to the outside of the light guide plate 10, but is returned again into the light guide plate 10 by the reflection sheet 15 used when the light guide plate 10 is configured as the backlight unit 40.

  As described above, the X-axis direction component of the light incident from the light incident surface 11 and guided through the light guide plate 10 by the prism pattern formed on the light reflecting surface 12 of the light guide plate 10 is light distribution-controlled. The light exit surface 13 is deflected in the normal direction and is raised. Specifically, assuming that the normal of the light exit surface 13 is 0 °, the light guided into the light guide plate 10 forms a groove such that the angle α = 58 ° and the angle β = 90 °, for example. In this case, the prism 12An formed on the light reflecting surface 12 is raised in the range of about 0 ° to 25 ° in the X-axis direction.

  Subsequently, the function of the optical element 30 will be described. Here, when the backlight unit 40 is assembled without adding the optical element 30 as a component, the light emitting surface 22 of each light emitting diode 21 of the light source unit 20 is in close contact with the light incident surface 11 of the light guide plate 10. think about.

  Since each light emitting diode 21 constituting the light source unit 20 functions as a point light source, the light emitted from each light emitting diode 21 has a directivity that spreads radially in the Y-axis direction as shown in FIG. The light enters the light guide plate 10. That is, the light emitted from the light emitting diode 21 and incident from the light incident surface 11 has directivity that spreads radially in the light guiding direction of the light guide plate 10. The light incident in this way becomes deflected light whose X-axis direction component is raised in the normal direction of the light emitting surface 13 as described above by the prism 12An.

  At this time, for example, among the deflected lights L2a to L2g shown in FIG. 4, the deflected lights L2a and L2b and the deflected lights L2f and L2g are incident on the prism 12An at a wide angle from the light emitting diode 21 and deflected. In the axial direction, it has a component that rises in the direction near the normal line of the light emitting surface 13, but in the Y-axis direction, it becomes deflected light having a component that is very inclined from the normal line. End up.

  Therefore, the front luminance of the light emitting surface 13 created by such deflected light becomes non-uniform in which the line-shaped region K running in the X-axis direction shown in FIG. 4 is increased. For example, as shown in FIG. 5, when light is incident on the light incident surface 11 of the light guide plate 10 from the three light emitting diodes 21a, 21b, and 21c included in the light source unit 20 and the light emitting surface 13 is viewed from the front, Line-shaped regions Ka, Kb, and Kc appear in stripes.

  As described above, the light guide plate 10 in which the front luminance of the light output from the light emitting surface 13 becomes high in the line-shaped region functions sufficiently as the light guide plate of the backlight unit of the liquid crystal display device. I can't.

  In the light guide plate 10, the region where the front luminance of the light emitting surface 13 is high in a line shape is generated because the light incident by the light emitting diode 21 has directivity and is incident on the prism 12An. As a result, as described above, even if the prism 12An is deflected in the normal direction in the X-axis direction of the light exit surface 13, light that is not deflected in the normal direction in the Y-axis direction is also emitted.

  Therefore, as shown in FIG. 1, in the backlight unit 40, the optical element 30 is disposed before the light emitted from each light emitting diode 21 of the light source unit 20 is incident on the light incident surface 11 of the light guide plate 10. Light distribution control of light incident on the optical plate 10 is performed.

  As shown in FIG. 1, the optical element 30 has m prisms 32Am (m is a natural number) on a light emitting surface 32 opposite to a light incident surface 31 on which light from each light emitting diode 21 of the light source unit 20 is incident. ) Is formed. The prism 32Am has a triangular prism shape whose longitudinal direction is the Z-axis direction shown in FIG.

  The prism 32Am formed on the light emitting surface 32 of the optical element 30 is a Fresnel lens that is thinned without changing the optical properties of the thick lens by making the continuous lens surface stepped. Yes.

  The prism 32Am formed on the light exit surface 32 is directed to the light incident from the light emitting diode 21 of the light source unit 20 with directivity spreading radially in the Y-axis direction, that is, the light guide direction of the light guide plate 10. As shown in FIG. 6, the light having directivity that spreads radially is deflected to light having directivity that travels in the X-axis direction, that is, in a direction parallel to the light guide direction of the light from the light guide plate 10. Designed. When the optical element 30 having such a prism 32Am is inserted between the light source 20 and the light guide plate 10 and light emitted from the light source 20 is incident on the optical element 30, the light incident surface 11 of the light guide plate 10 is obtained. The light having directivity that travels in the direction parallel to the light guide direction is emitted from the optical element 30 and incident on the entire surface.

  Thereby, the light incident on the light guide plate 10 does not include light that spreads radially in the light guide direction of the light guide plate 10. As a result, when the light is incident on the prism 12An formed on the light reflecting surface 12, the component in the X-axis direction is raised so as to be in the normal direction of the light emitting surface 13 as described above. The front luminance of the light emitted from the light is made uniform over the entire light emitting surface 13.

  Therefore, as described above, of the light incident from the light emitting diode 21 of the light source 20, light having directivity that spreads radially with respect to the light guide direction of the light of the light guide plate 10 is converted into the light of the light guide plate 10. By designing the prism 32Am of the optical element 30 so as to be deflected to light having directivity traveling in a direction parallel to the light guide direction, bright lines appearing in stripes as shown in FIGS. 4 and 5 described above. There is an effect to suppress.

  FIG. 7 shows specific design values of the prism 32Am formed on the light emitting surface 32 of the optical element 30. FIG. This is a simulation result when the thickness of the optical element 30 in the X-axis direction is 6.0 mm and the pitch between the light emitting diodes 21 of the light source 20 is 9.4 mm as shown in FIG.

  The prism 32Am has a directivity in which all light emitted from the light emitting diode 21 with a directivity spreading radially in the Y-axis direction travels in parallel with the X-axis direction, that is, the light guide direction of the light of the light guide plate 10. In order to deflect the light to have, it is necessary to form the prism pattern symmetrically with the axis parallel to the X axis from the center of the light emitting diode 21 as the axis of symmetry.

Therefore, as the light-emitting diode 21b shown in FIG. 8, symmetrically with respect to the center axis of symmetry extending in the X-axis direction from the light-emitting diode 21b, the region _{Y O} in which the upper and lower, each having a width of 4.7 mm, the region _{Y U} A prism pattern is formed. The design value shown in FIG. 7 is the design value of the upper or lower region of the prism patterns formed symmetrically with respect to the symmetry axis extending in the X-axis direction from the center of the light emitting diode 21.

Next, the design value of the prism 32Am shown in FIG. 7 will be specifically described. For example, Figure a state when the design value of the prism 32Am shown in FIG. 7, and a prism pattern of the upper region Y _O symmetry axes extending in the X-axis direction from the center of the light-emitting diode 21b shown in FIG. 8 9 Shown in

As shown in FIG. 9, when the prism 32Am is a prism P _x (x is a natural number), based on the design value of FIG. 7, the region Y _O in the Y-axis direction is 4.7 mm at a pitch of 0.047 mm. , ₁₀₀ prisms P _{1 to} P ₁₀₀ are formed. In FIG. 9, prisms P _{1 to} P ₄ , P ₆₈ , P ₆₉ , P ₉₉ , and P ₁₀₀ are shown as representatives. Each prism P _x has a triangular prism shape that the Z-axis direction shown in FIG. 2 and the longitudinal direction is shown a triangle which becomes the bottom surface in FIG. The apex angle of the triangle serving as the bottom surface, for example, the apex angle A shown in the prism P ₆₈ is an angle of the same magnitude in the prism P _x and is 48 °.

Θ is one of the design values shown in FIG. 7, as shown in the prism P ₆₈ in FIG. 9 shows one of the base angles of the triangle which is a bottom surface of the prism P _x. Since the apex angle is constant as described above, the prism shape is determined by varying the base angle θ. Incidentally, it is shown in Figure 9, the lower region Y _U with respect to the central X-axis symmetry axis extending in the direction from the light-emitting diode 21b, so that the prism patterns of the region Y _O symmetrical are formed.

  Thus, the optical element 30 is formed with the prism 32Am symmetrically with the symmetry axis extending in the X-axis direction from the center of each light emitting diode 21, for example, based on the design value shown in FIG. Light having a directivity that spreads in a radial direction with respect to the light guide direction of the light of the light guide plate 10 and enters the light guide plate 10 in a direction parallel to the light guide direction of the light of the light guide plate 10 Can be deflected to light.

  As a material for forming the optical element 30, in order to efficiently reflect light incident from the light source 20 and guide it efficiently, the refractive index is 1.44 to 1.45 as a lower limit, and a refractive index value higher than this. Will be selected. For example, the acrylic resin used also when forming the light guide plate 10 has a refractive index of 1.49 and is also a material that can be injection molded. Since it is necessary to form the prism 32Am on the light emitting surface 32, the optical element 30 can be easily formed by using this acrylic resin, which can be injection-molded, and can be mass-produced at low cost. Become.

  Next, in order to verify the effect of the optical element 30, the front luminance of the light guide plate 10 when the optical element 30 in which the prism 32Am was formed was used based on the design values shown in FIG. 7 was calculated by simulation. As the light emitting diodes 21a, 21b, and 21c, white light emitting diodes (NSCW-215 series) manufactured by Nichia Corporation are used, and a current of 15 mA is applied.

FIG. 10 shows the luminance distribution of the light exit surface 13 of the light guide plate 10 as a simulation result. As shown in FIG. 10, the luminance distribution of the light emitting surface 13 becomes 5000 cd / ^{m 2} about brightness and a region G1,4000cd / ^{m 2} about brightness and a region G2,3000cd / ^{m 2} about luminance region The distribution is such that three different luminance areas G3 appear. The region G1 is a region where light emitted from each light emitting diode 21 is emitted in parallel with the X axis direction, and the region G2 is the light emitted from the light emitting diode 21 in the Y axis direction. Slightly diffused light is an area that is deflected by the optical element 30 and arrives. The area G3 is light emitted from the light emitting diode 21 that is further diffused in the Y-axis direction than the light that has reached the area G2. Is a region reached by being deflected by the optical element 30.

As shown in FIG. 10, when an optical element 30 having a prism 32Am formed on the light emitting surface 32 is used, the front luminance due to the light emitted from the light emitting surface 13 of the light guide plate 10 is a region having different luminance (region G1). , G2, G3) occurs, but an average luminance of 3000 cd / m ² can be obtained over the entire light exit surface 13 of the light guide plate 10. The front luminance is improved by the direction in which the light having directivity traveling radially with respect to the light guide direction of the light of the light guide plate 10 is parallel to the light guide direction of the light of the light guide plate 10 by the prism 32Am of the optical element 30. It is thought that this is a result of significantly reducing the emission loss from the side surface of the light guide plate 10 due to the light having directivity that advances toward the light, indicating that the light utilization efficiency is very high. Yes.

  Thus, it can be seen that the use of the optical element 30 suppresses luminance unevenness appearing as stripe-like bright lines as described with reference to FIGS. For example, as described above, the light reflecting surface 12 is a triangle whose cross-sectional shape is the base on the light reflecting surface 12 side, and the base angle on the light incident surface 11 side of the triangle is an angle α = 50 ° to 60 °, and the other When a plurality of grooves with a base angle of β = 70 ° to 90 ° are formed and the prism 12An is formed on the light reflecting surface 12, the light in the X-axis direction is effectively raised, and the stripe shape The bright line will appear conspicuously, so that it is particularly effective when the optical element 30 is used.

  Even when a plurality of grooves whose cross-sectional shape is a triangle having an angle α = angle β = 45 °, which is generally used as a conventional technique, is formed on the light reflecting surface 12, the optical element 30 is used. When the light emitting diode 21 which is a point light source is used, luminance unevenness appearing as a stripe-like bright line can be suppressed.

  The difference in luminance distribution between the regions G1, G2, and G3 shown in FIG. 10 is that a cylindrical prism as a diffusion prism is formed on the light incident surface 31 of the optical element 30 in contact with the light emitting surface 22 of the light emitting diode 21 as shown in FIG. It can be controlled by forming a plurality of lenses 31As (S is a natural number) and diffusing light incident on the optical element 30. The light emitted from the light emitting diode 21 and guided through the optical element 30 through the cylindrical lens 31As is diffused with directivity spreading in the Y-axis direction and is incident on the prism 32Am. Therefore, the light incident on the light incident surface 11 of the light guide plate 10 through the cylindrical lens 31As and the prism 32Am is uniformly diffused over the entire light incident surface 11 of the light guide plate 10, and The light is deflected so as to have directivity that travels in a direction parallel to the light guide direction. Thereby, the luminance distribution of the light emitted from the light emitting surface 13 of the light guide plate 10 can be made high luminance and uniform.

  Such a backlight device 40 including the optical element 30 deflects the light emitted from each light emitting diode 21 included in the light source unit 20 into light having directivity parallel to the X axis by the optical element 30. Light distribution control in the Y-axis direction is performed, and the light is incident from the light incident surface 11 of the light guide plate 10. The light incident on the light guide plate 10 is reflected by the light reflecting surface 12 and the reflecting sheet 15 and is emitted from the light emitting surface 13. At this time, the light reflection surface 12 in the light guide plate 10 controls the light distribution of the X-axis direction component of the light incident on the prism 12An, rises in the normal direction of the light reflection surface 13, and is condensed.

  Therefore, in the light guide plate 10, the light whose light distribution is controlled in the Y-axis direction by the optical element 30 is guided in the light guide plate 10 while being raised in the X-axis direction by the prism 12An, and the light exit surface. 13 will be emitted. The light emitted from the light emitting surface 13 is applied to, for example, a liquid crystal display device or the like from the opening 35 </ b> A opened in the frame 35.

  Thus, for example, the backlight unit 40 condenses the light component in the Y-axis direction in the normal direction of the light exit surface 83, which is included in the backlight unit 100 shown in the related art. Since the first lens sheet 103 and the second lens sheet 104 for condensing the light component in the X-axis direction in the normal direction of the light exit surface 83 are not necessary, the cost is significantly reduced and the backlight unit 40 is thin. Can be

  This is because the prism pattern of the prism 32Am formed on the light emitting surface 32 of the optical element 30 deflects the directional light spreading in the Y-axis direction to light parallel to the X-axis direction, that is, the light of the light guide plate 10 Designed to deflect light having directivity that travels in a direction parallel to the light guide direction to control light distribution in the Y-axis direction, and to form a prism 12An on the light reflecting surface 12 of the light guide plate 10 The cross-sectional shape of the groove to be fabricated is such that the light reflecting surface 12 side is the base, the base angle on the light incident surface 11 side is angle α = 50 ° to 60 °, and the other base angle is angle β = 70 ° to 90 °. This is because, by appropriately designing and controlling the light distribution so as to form a certain triangle, it is sufficient to obtain the same front luminance as when a lens sheet is used. Thereby, the backlight unit 40 can acquire sufficient front luminance over the entire light emitting surface 13.

  The prism pattern formed on the light reflecting surface 12 may have a shape other than the prism 12An, and the present invention is not limited to this prism pattern.

  For example, in the case where the prism 12An is formed on the light reflecting surface 12 by forming a groove having a triangular cross-sectional shape, the values of the angle α and the angle β are the angle α = 50 ° to 60 ° and the angle β = The prism pattern may be formed by changing to a value other than 70 ° to 90 °. Further, a prism pattern formed by producing a groove having a cross-sectional shape as shown below may be used.

  For example, the cross-sectional shape of the groove formed in the light reflecting surface 12 is a cross-sectional shape 45 like a trapezoid with a round as shown in FIG. 12, or a cross-sectional shape 46 made up of two triangles as shown in FIG. Alternatively, as shown in FIG. 14, a prism pattern formed by making a cross-sectional shape 47 like a trapezoid with one side having arbitrary irregularities may be used.

  Furthermore, even when a backlight unit is configured using the optical element 30, sheets such as the diffusion sheet 102, the first lens sheet 103, and the second lens sheet 104 described in the related art are appropriately used. The light emitted from the light emitting surface of the light guide plate may be used to adjust the emitted light.

It is a figure for demonstrating the structure of the backlight unit shown as embodiment of this invention. It is a figure for demonstrating the XY coordinate axis set to the light-guide plate with which a backlight unit is provided. It is a figure for demonstrating the some prism formed in the light reflection surface of the light-guide plate with which the backlight unit is provided. In the backlight unit, it is a figure for demonstrating the light radiate | emitted when using only the light-guide plate which formed the prism in the light reflection surface. FIG. 4 is a diagram for explaining a negative effect when only a light guide plate having a prism formed on a light reflecting surface is used in the backlight unit. It is a figure for demonstrating the function which the optical element with which the backlight unit is provided has. It is the figure which showed the design value of the some prism formed in the light-projection surface of an optical element. It is a figure for demonstrating the symmetry with respect to the light emitting diode of the some prism formed in the light-projection surface of an optical element. It is the figure which showed typically the some prism formed based on the design value shown in FIG. It is the figure which showed the simulation result of the front luminance distribution radiate | emitted from a light-guide plate, when a backlight unit is comprised using the optical element which formed the some prism based on the design value shown in FIG. It is a figure for demonstrating the cylindrical lens formed in the light-incidence surface of an optical element. It is the figure which showed an example of the cross-sectional shape of the prism formed in the light reflection surface of a light-guide plate. It is the figure which showed another example of the cross-sectional shape of the prism formed in the light reflection surface of a light-guide plate. It is the figure which showed another example of the cross-sectional shape of the prism formed in the light reflection surface of a light-guide plate. It is a figure for demonstrating the structure of the backlight unit shown as a prior art. It is a figure for demonstrating the XY coordinate axis set to the light-guide plate with which the backlight unit is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light guide plate, 11 Light incident surface, 12 Light reflective surface, 12An (n is a natural number) Prism, 13 Light output surface, 20 Light source part, 30 Optical element, 31 Light incident surface, 32 Light output surface, 32 Am (m is , Natural number) Prism, 40 backlight unit

Claims (9)

One side is a light incident surface, and the light incident from the light incident surface is totally reflected by the light exit surface as one main surface and the light reflection surface as the other main surface, and guided from the light exit surface. An optical element that adjusts light incident on the light incident surface of the light guide plate that emits light,
The light emitted from the light source is incident. Of the incident light, the light having directivity that spreads radially with respect to the light guide direction of the light of the light guide plate is guided by the light of the light guide plate. An optical element comprising: an optical unit that deflects and emits light having directivity that travels in a direction parallel to the light direction and enters the light incident surface of the light guide plate. 2. The optical element according to claim 1, wherein the optical means is a Fresnel lens including a plurality of prisms formed in a longitudinal direction of a light exit surface of the optical element in contact with the light incident surface of the light guide plate. . The optical element according to claim 1, further comprising a diffusion prism that diffuses incident light on a light incident surface of the optical element on which light from the light source is incident. One side is a light incident surface, and the light incident from the light incident surface is totally reflected by the light exit surface as one main surface and the light reflection surface as the other main surface, and guided from the light exit surface. A light guide plate for surface emission;
A light source having a plurality of light emitting elements arranged at predetermined intervals in the longitudinal direction of the light incident surface of the light guide plate;
An optical element that receives light emitted from the plurality of light emitting elements of the light source and emits light as incident light on the light incident surface of the light guide plate;
A reflective sheet disposed on the light reflecting surface side of the light guide plate;
The light guide plate includes the light source, the optical element, and a frame that holds the reflection sheet.
The light guide plate has an incident direction of the light as an X-axis direction, a direction perpendicular to the X-axis direction and parallel to the light emitting surface as a Y-axis direction, and perpendicular to the X-axis direction and the Y-axis direction. When the direction is the normal direction, the light incident from the light incident surface is deflected so that the inclination in the X-axis direction approaches zero with respect to the normal direction, and is emitted from the light emitting surface. X-axis direction light distribution control means for performing light distribution control,
The optical element emits light having directivity that spreads radially in the light guide direction of the light of the light guide plate among the incident light and is parallel to the light guide direction of the light of the light guide plate. A backlight device comprising: an optical unit that deflects and emits light having directivity that travels in any direction, and causes the light to enter the light incident surface of the light guide plate. The optical means of the optical element is a Fresnel lens composed of a plurality of prisms formed in the longitudinal direction of the light emitting surface of the optical element in contact with the light incident surface of the light guide plate. The backlight device described. The backlight device according to claim 4, wherein the optical element has a diffusion prism that diffuses incident light on a light incident surface of the optical element on which light from the light source is incident. The X-axis direction light distribution control means of the light guide plate is a plurality of prisms formed in the X-axis direction on the light reflecting surface and having a longitudinal direction in the Y-axis direction. 4. The backlight device according to 4. The prism is formed by forming a plurality of grooves having a predetermined shape with the Y-axis direction as a longitudinal direction on the light reflecting surface in the X-axis direction,
The groove has a triangular cross-sectional shape with the light reflecting surface side as the base, the base angle α of the triangle on the light incident surface side is α = 50 ° to 60 °, and the other base angle β is β The backlight device according to claim 7, wherein the angle is 70 ° to 90 °. The backlight device according to claim 4, wherein the plurality of light emitting elements included in the light source are light emitting diodes (LEDs).

Images