JP5077715B2 - Light guide plate - Google Patents

Description

The present invention relates to a light guide plate, in particular, relates to a light guide plate to illuminate the incident display elements like light from the light source.

  In a liquid crystal display device provided in a mobile phone, a portable information terminal, or the like, a backlight device for illuminating a display unit is used. This backlight device includes a light guide plate disposed on the back surface of a liquid crystal panel as a display unit, and a light source such as a light emitting element (LED) or a cold cathode tube disposed on the side of the light guide plate. . The backlight device having such a configuration has an advantage that the entire device can be thinned because light is incident from the side surface of the light guide plate, so that it is not necessary to arrange a light source in the thickness direction of the light guide plate. .

  Incidentally, in recent years, liquid crystal display devices are often mounted on thin mobile phones, digital cameras, and the like, and the demand for downsizing of backlight devices has become strict. Accordingly, the light guide plate has been made thinner. However, it is difficult to downsize the LED used as the light source to the same extent as the thickness of the light guide plate. However, the light emission characteristics of LEDs are generally low in directivity, and some of the emitted light spreads radially at a wide angle, so it is a problem how to efficiently make the emitted light from the LED enter the thin light guide plate. It has become.

  Here, Patent Document 1 discloses a backlight device provided with a light receiving portion on which an inclined surface is formed that is inclined at an angle of 45 degrees or less upward from the main body portion of the light guide plate. Also disclosed is a technology for reducing the thickness of the backlight device by providing a light-receiving surface inclined substantially at right angles to the inclined surface, and inclining the light-emitting surface of the light source in parallel with the light-receiving surface. Has been.

JP 2003-121840 A

  However, in the former case, the light incident on the inclined surface is not necessarily totally reflected. Therefore, in order to increase the reflectance on the inclined surface, the inclined surface is covered with a reflective film. However, when the reflective film is coated, the manufacturing process of the light guide plate becomes complicated. Further, due to the characteristics of the reflective film, there is a problem that the light utilization efficiency is lowered because a lot of light is absorbed. Furthermore, in the latter case, it can contribute to reducing the thickness of the backlight device. However, in order to further reduce the thickness of the main body of the light guide plate, the number of times of reflection of incident light is increased in the light receiving portion. However, there is a problem that the light utilization efficiency is lowered.

The present invention has been made in view of the problems of the prior art, and provides a light guide plate capable of increasing the light utilization efficiency when light from a light source is incident to illuminate a display element or the like. For the purpose.

The light guide plate according to claim 1 is a light guide plate integrally formed with an incident portion for entering light from a light emitting element and an exit portion for emitting incident light to the outside.
The incident portion is an incident surface for incident light from the light emitting element , a boundary surface that defines a boundary between the incident portion and the emission portion and through which light traveling from the incident portion to the emission portion passes, A top surface and a bottom surface extending in a direction intersecting the incident surface and the boundary surface and facing each other;
One surface of the top surface and the bottom surface is relative to the other surface so that the size of the exit surface in the thickness direction of the light guide plate is smaller than the size of the entrance surface in the thickness direction of the light guide plate. Is inclined,
At least one of the top surface and the bottom surface is provided with a structure having a light leakage reduction shape that suppresses the amount of light emitted from a surface other than the boundary surface among light incident from the incident surface. And
The light leakage reduction shape is emitted from the light emitting element when the plane extending from the incident surface side toward the boundary surface side and extending along the thickness direction of the light guide plate is a virtual plane. When light traveling along a plane is incident on the light leakage reducing shape, the reflected light has a directional component that leaves the virtual plane,
The light leakage reduction shape has a plurality of pairs of inclined surfaces having intersections extending from the incident surface side toward the boundary surface side, and the plurality of pairs of inclined surfaces are in the thickness direction of the light guide plate. As seen from the above, including a pair of inclined surfaces in which an intersection extends along the direction of the normal line of the emission surface of the light emitting element , and inclined surfaces arranged on both sides of the inclined surface pair,
The interval on the incident surface side of the adjacent intersecting portions is smaller than the interval on the boundary surface side,
The exit portion may have a exit surface extending in a direction intersecting with the boundary surface,
When the angle formed by the pair of inclined surfaces at the intersecting portion is β, the following conditional expression (4) is satisfied .
100 ° ≦ β ≦ 170 ° (4)

According to the light guide plate of the present invention , one of the top surface and the bottom surface is such that the size of the exit surface in the thickness direction of the light guide plate is smaller than the size of the entrance surface in the thickness direction of the light guide plate. Since this surface is inclined with respect to the other surface, light from a light source having a thickness larger than that of the light guide plate can be guided well. In addition, when the light emission characteristics of the light source are low, a part of the light emitted from the light source does not satisfy the total reflection condition while repeating the reflection between the top surface and the bottom surface that are inclined to each other. There is a risk of leaking outward from the bottom surface. On the other hand, in the present invention, light leakage is reduced by suppressing the amount of light emitted from a surface other than the boundary surface out of light incident from the incident surface on at least one of the top surface and the bottom surface. Since a structure having a shape is provided, it becomes easy to satisfy the total reflection condition even if light incident from the incident surface is repeatedly reflected by the top surface and the bottom surface that are inclined to each other. Alternatively, the light utilization efficiency can be increased by suppressing light leaking outward from the bottom surface. The “boundary surface” is not a surface exposed to the outside, but a conceptual surface that defines a boundary between the incident portion and the emission portion.

Furthermore, according to the present invention, when the light leakage reduction shape is a virtual plane that extends from the incident surface side toward the boundary surface side and extends along the thickness direction of the light guide plate, Since the light emitted from the light source and traveling along the virtual plane is incident on the light leakage reducing shape, the reflected light has a shape having a directional component so as to be separated from the virtual plane. , It becomes easy to satisfy the total reflection condition.

According to the present invention, the light leakage reduction shape is characterized in that the interval on the incident surface side of the adjacent intersecting portions is smaller than the interval on the exit surface side. It becomes easy to control the traveling direction of the incident light, and it is possible to control various characteristics such as illuminance distribution and luminance distribution on the boundary surface according to the purpose, so illuminance unevenness on the boundary surface is reduced. The

When the angle β formed by the pair of inclined surfaces at the intersecting portion satisfies the conditional expression (4), the light incident on the incident portion can easily satisfy the total reflection condition, so that the light use efficiency can be improved. Compared to the case where there is no light, the light utilization efficiency is about 1.2 times or more. In particular, if β is 170 ° or less, the effect of controlling the traveling direction of the light can be enhanced, and sufficient light utilization efficiency can be obtained. On the other hand, if β is 100 ° or more, the tip portion of each inclined surface becomes a shape that is difficult to be chipped, and manufacturing is easy, and it is difficult for debris and the like to adhere to the light guide plate. Sufficient light utilization efficiency can be obtained. Preferably, if β satisfies the following formula, light utilization efficiency of about 1.3 times or more can be realized as compared with the case where there is no inclined surface.
116 ° ≦ β ≦ 165 ° (4 ′)

ADVANTAGE OF THE INVENTION According to this invention, when the light from a light source injects and illuminates a display element etc., the light- guide plate which can improve the utilization efficiency of light can be provided.

It is sectional drawing of the backlight apparatus containing the light-guide plate concerning this Embodiment. It is the figure which cut | disconnected the backlight apparatus of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is a schematic perspective view of the incident part 4IN. It is a figure for demonstrating the light leakage reduction shape. It is a figure which shows the simulation result which this inventor performed. 6A is a side view of the incident portion 4IN, FIG. 6B is a top view of the incident portion 4IN, and FIG. 6C shows a pair of inclined surfaces 4g and 4h on the exit surface side. It is the enlarged view seen. It is a side view of the incident part concerning the modification of this Embodiment. It is a figure which expands and shows the prism of the incident part concerning the modification of this Embodiment. It is a top view of the incident part concerning the modification of this Embodiment. It is a perspective view of the incident part concerning another embodiment. It is a top view of the incident part shown in FIG. It is a figure which shows the result of the simulation which the inventor performed. It is a side view which shows the light-guide plate 4 concerning this Embodiment. It is a perspective view which shows the light-guide plate 4 concerning another embodiment. It is the figure which looked at embodiment shown in FIG. 14 from the side. It is a graph which shows the result of the simulation which this inventor performed. It is a perspective view which shows the light-guide plate 4 concerning another embodiment. It is the figure which looked at embodiment shown in FIG. 17 from the side. It is a graph which shows the result of the simulation which this inventor performed. It is a side view of the light-guide plate 4 concerning another modification. It is a side view of the light-guide plate 4 concerning another modification.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a cross-sectional view of a backlight device BL including a light guide plate according to the present embodiment. FIG. 2 is a diagram of the backlight device BL of FIG. It is. In FIGS. 1 and 2, an LED 2 and a light guide plate 4 that are three light sources are arranged in the housing 1. The light guide plate 4 made of a transparent resin such as PC or PMMA is integrally formed from a thin plate-shaped emission portion 4OT and an incidence portion 4IN disposed between the LED 2 and the emission portion 4OT. . The incident part 4IN protrudes in a trapezoidal plate shape (see FIG. 2) from the light source side surface of the emission part 4OT. A fine convex portion (or concave portion) 3 is formed on the outgoing surface 4k which is the upper surface of the outgoing portion 4OT. The convex part 3 which is a light scattering part becomes larger (higher) as the distance from the LED 2 is increased, and the arrangement interval thereof is narrowed, so that the light irradiated from the exit surface 4k of the light guide plate 4 is uniformly uniform as a whole. Can be approached. Further, a diffusion plate 5 is disposed on the exit surface 4 k of the light guide plate 4, and a liquid crystal display element 6 is disposed on the upper surface of the diffusion plate 5. Note that the backlight device BL includes an LED 2, a light guide plate 4, and a diffusion plate 5. The LED 2 may be integrally attached to the light guide plate 4.

  1 and 2, the light emitted from the LED 2 is guided into the emission part 4OT by the incident part 4IN of the light guide plate 4, and travels from the emission surface 4k to the lower surface of the liquid crystal display element 6 through the diffusion plate 5. It is designed to irradiate evenly.

  FIG. 3 is a schematic perspective view showing the vicinity of one incident portion 4IN of the light guide plate 4. As shown in FIG. In FIG. 3, the thickness direction of the light guide plate 4 is defined as the vertical direction (Y direction), and the width direction of the light guide plate 4 is defined as the horizontal direction (X direction). The incident portion 4IN includes a top surface 4a, a bottom surface 4b, side surfaces 4c and 4d, and an incident surface 4e intersecting these. Here, as a conceptual boundary between the incident portion 4IN and the emission portion 4OT, a surface defined to be parallel to the incident surface 4e is defined as a boundary surface 4f, but this is not exposed to the outside.

  The incident surface 4e is arranged in contact with or close to the emitting surface 2a of the LED 2 (see FIG. 1). The vertical dimension D1 of the incident surface 4e is larger than the vertical dimension D2 of the boundary surface 4f, and the horizontal dimension L1 of the incident surface 4e is larger than the horizontal dimension L2 of the boundary surface 4f. It is getting smaller. Since it has such a shape, the incident part 4IN can guide the light emitted from the LED 2 to the thin emission part 4OT.

  Further, the incident portion 4IN forms a light leakage reduction shape 4M on the top surface 4a. Here, the vertical dimension D1 of the incident surface 4e represents the vertical dimension on the incident surface 4e side of the incident part 4IN excluding the light leakage reduction shape, and the vertical dimension D2 of the boundary surface 4f is: The vertical dimension on the boundary surface 4f side of the incident portion 4IN excluding the light leakage reduction shape is shown. Next, the light leakage reduction shape according to this embodiment will be described.

  FIG. 4 is a diagram for explaining a light leakage reduction shape. In FIG. 4, a YZ plane (imaginary plane) is defined as a plane orthogonal to the bottom surface 4b of the incident portion 4IN. The YZ plane passes through the center of the LED 2 in the width direction of the light guide plate 4 and extends along the thickness direction of the light guide plate 4. Here, it is assumed that the top surface 4A 'indicated by the dotted line is inclined so as to become narrower toward the boundary surface 4f side with respect to the bottom surface 4b. In such a case, the light that is emitted from the front edge of the YZ plane and travels along the YZ plane satisfies the total reflection condition while the incident angle is small. It is reflected and subsequently reflected by the bottom surface 4b at the point B ′, and does not leave the YZ plane even after reflection. However, since the top surface 4A 'is inclined toward the boundary surface 4f with respect to the bottom surface 4b, the incident angle θ2' at the point B is larger than the incident angle θ1 at the point A. Therefore, if one of the incident angles exceeds the threshold value during repeated reflection, the total reflection condition is lost, and light may leak to the outside through the top surface 4A 'or the bottom surface 4b.

  Here, as a light leakage reduction shape, a configuration is considered in which a top surface 4A that is not only inclined toward the boundary surface 4f side with respect to the bottom surface 4b but also inclined toward the right side surface side is provided (see solid line). ). In the example of FIG. 4, it is assumed that the YZ planes intersect at the intersection positions of the top surfaces 4A 'and 4A. According to such a configuration, the light emitted from the front edge of the YZ plane and traveling along the YZ plane is reflected by the top surface 4A at the point A as shown by the solid arrow, and is subsequently different from the point B ′. Although reflected by the bottom surface 4b at the point B, the point B does not exist in the YZ plane. In other words, the light reflected by the top surface 4A at the point A has an X direction component orthogonal to the YZ plane, proceeds in a direction away from the YZ plane, and enters a point B far from the point B ′. Become. Therefore, when the top surface 4A ′ is used and when the top surface 4A is used, when the incident angle θ1 at the point A is the same, the incident angle θ2 at the point B is equal to the incident angle θ2 at the point B ′. Thus, when the top surface 4A is used, the possibility of satisfying the total reflection condition is increased even when reflection is repeated, compared with the case where the top surface 4A 'is used.

  However, this effect is not limited to light rays incident on the light leakage reduction shape along the YZ plane or along a plane parallel to the YZ plane, that is, incident light rays having only components in the Y direction and the Z direction. . Similar effects can be obtained with respect to incident rays having components in the X direction in addition to the Y and Z directions. That is, a part or all of the Y direction component of the incident light beam is converted into the X direction or the Z direction by the top surface 4A, so that the possibility that the light beam satisfies the total reflection condition is increased.

  Thus, in the light leakage reduction shape, either the top surface 4a or the bottom surface 4b of the incident portion 4IN is uniformly inclined in the direction in which the width in the vertical direction (height direction) of the side surface 4c or 4d becomes narrow. Can only demonstrate its function. Furthermore, in the present embodiment, as shown in FIG. 3, a part of the top surface 4a is deformed, and a plurality of pairs of intersecting long and slender inclined surfaces (referred to as line-like irregularities or prisms) 4g, 4h are provided. Since the intersection (which is called the apex of the prism) 4i of the pair of inclined surfaces 4g and 4h extends from the incident surface 4e toward the boundary surface 4f, the vertical direction of the incident portion 4IN The dimensions can be reduced, which can contribute to the downsizing of the backlight device. In the present embodiment shown in FIGS. 3 to 13, the pair of inclined surfaces 4g and 4h constitute the light leakage reduction shape 4M. Although not shown in some drawings, when a gap surface 4x is formed between a pair of inclined surfaces 4g and 4h as will be described later, the gap surface 4x also has a light leakage reduction shape 4M. In addition, when the tapered surface 4p connected to the pair of inclined surfaces 4g and 4h is formed as described later, the tapered surface 4p is also included in the light leakage reduction shape 4M.

  FIG. 5 is a diagram showing a simulation result performed by the present inventor. 5A shows a state where the incident portion 4IN is projected in the Z-axis direction of FIG. 3, and FIG. 5B shows a state where the incident portion 4IN is projected in the X-axis direction of FIG. . According to FIG. 5, it is understood that the light incident on the incident portion 4IN is directed to the exit surface while being reflected in the order of R1 to R10 between the prism on the top surface 4a and the bottom surface 4b.

Here, a preferable form of the incident portion 4IN will be described. 6A is a side view of a portion of the incident portion 4IN excluding the light leakage reduction shape, FIG. 6B is a top view of the incident portion 4IN, and FIG. 6C is a light leakage. It is the figure which took out only the part of a reduced shape, and is the enlarged view which looked at a pair of inclined surface 4g, 4h toward the boundary surface side. The height dimension on the incident surface 4e is D1, the height direction dimension on the boundary surface 4f is D2, the distance (full length) between the incident surface 4e and the boundary surface 4f is L3, and the incident surface 4e and the top surface 4a. When the angle between the incident surface 4e and the bottom surface 4b is θ2, the smaller one of the angles θ1 and θ2 falls below the upper limit of the following formula (1), It is preferable to reduce the total length L3 of the portion 4IN and to exceed the lower limit value because the total reflection condition is easily satisfied.
70 ° <θ <90 ° (1)

Further, it is preferable that the area of the incident surface 4e is larger than the area of the boundary surface 4f because light can be efficiently distributed. That is, it is preferable to design the incident portion 4IN so that the following expression is established when the width direction dimension of the incident surface 4e is L1 and the width direction dimension of the boundary surface 4f is L2.
L1 × D1 ≦ L2 × D2 (2)

In FIG. 6B, it is preferable that the angle γ formed by the center line of the incident portion 4IN and the apex of the prism having the light leakage reduction shape satisfy the following expression, because the total reflection condition is easily satisfied. The angle γ is effective even at 0 °.
0 ° ≦ γ ≦ 40 ° (3)

The angle β formed by the inclined surfaces 4g and 4h in FIG. 6C is more than the lower limit value of the following expression, so that the total reflection condition can be easily satisfied, and the angle β of the incident portion 4IN is less than the upper limit value. The height can be suppressed.
100 ° ≦ β ≦ 170 ° (4)

  FIG. 7 is a side view of an incident portion according to a modification of the present embodiment. As shown in FIG. 7A, the angle θ1 formed by the top surface 4a of the incident portion 4IN with respect to the incident surface of the incident portion 4IN facing the emission surface of the LED 2, and the bottom surface 4b of the incident portion 4IN. Not only when the angle θ2 is equal, but also as shown in FIG. 7B, the angle θ1 formed by the top surface 4a of the incident portion 4IN with respect to the incident surface of the incident portion 4IN and the bottom surface of the incident portion 4IN. The angle θ2 formed with 4b may be varied. Further, as shown in FIG. 7C, an angle θ1 (or θ2) formed by the top surface 4a (or the bottom surface 4b) of the incident portion 4IN with respect to the incident surface of the incident portion 4IN can be an obtuse angle. .

  FIG. 8 is an enlarged view showing the top surface of the incident portion according to the modification of the present embodiment. As shown in FIG. 8A, the inclined surfaces 4g and 4h may stand up at different angles as shown in FIG. 8B, as well as when they stand up at the same angle with respect to the horizontal plane. Further, as shown in FIG. 8 (c), a plane 4j may be arranged between adjacent prisms, or as shown in FIG. 8 (d), the intersection 4i of the inclined surfaces 4g and 4h may be a plane. good. Furthermore, as shown in FIG. 8E, the surface of the prism may be a curved surface. In such a case, the inclined surfaces 4g and 4h are smoothly connected at the intersection. In addition, the shapes of these modified examples can be configured to appear in the middle of the length direction (depth direction) of the light guide, for example, or can be configured to combine a plurality of shapes by switching from the middle.

  FIG. 9 is a top view of an incident portion according to a modification of the present embodiment. As shown in FIG. 9 (a), the intersection 4i, which is the apex of the prism, extends not only when inclined to both sides with respect to the center line of the incident portion 4IN, but also as shown in FIG. 9 (b). Further, it may extend parallel to the center line of the incident portion 4IN, or may extend in a direction inclined with respect to the center line of the incident portion 4IN, as shown in FIG. Furthermore, as shown in FIG. 9D, the intersecting portions 4i may extend radially, or may extend so as to draw a curve instead of a straight line. Further, as shown in FIGS. 9E and 9F, the side surfaces 4c and 4d of the incident portion 4IN may be curved surfaces. The dotted lines in FIGS. 9B, 9C and 9D represent the valleys (valley ridge lines) of the prism. For example, in FIG. 9A, the valleys of the prism are omitted. .

  FIG. 10 is a perspective view of an incident part according to another embodiment, and FIG. 11 is a top view of the incident part shown in FIG. Similarly, in FIG. 10, the thickness direction of the light guide plate 4 is the vertical direction (Y direction), and the width direction of the light guide plate 4 is the left and right direction (X direction). The incident portion 4IN integrally formed from a transparent resin such as PC, PMMA, or cycloolefin polymer has a top surface 4a, a bottom surface 4b, side surfaces 4c, and 4d, and an incident surface 4e and a boundary surface 4f that intersect these. And have. Here, as a conceptual boundary between the incident portion 4IN and the emission portion 4OT, a surface defined to be parallel to the incident surface 4e is defined as a boundary surface 4f, but this is not exposed to the outside. Furthermore, a part of the top surface 4a is deformed, and a plurality of pairs of a pair of slender inclined surfaces (which are referred to as streaky irregularities or prisms) 4g and 4h are provided, and an intersection of the pair of inclined surfaces 4g and 4h. 4i (this is called the apex of the prism) extends from the incident surface 4e toward the boundary surface 4f. Further, an intersection between adjacent pairs of inclined surfaces 4h and 4g is defined as a valley ridge line 4j.

  The incident surface 4e is arranged in contact with or close to the emitting surface 2a of the LED 2 (see FIG. 1). The vertical dimension D1 on the incident surface 4e side of the side surfaces 4c and 4d is larger than the vertical dimension D2 on the boundary surface 4f side, and the horizontal dimension L1 of the incident surface 4e is equal to the boundary surface 4f. It is smaller than the dimension L2 in the left-right direction. In addition, the interval W1 between the adjacent intersecting portions 4i on the incident surface 4e side is smaller than the interval W2 on the boundary surface 4f side. Further, the number of streaky irregularities on the incident surface 4e side is equal to the number of streaky irregularities on the boundary surface 4f side. In the present embodiment, the dimension of the pair of inclined surfaces 4g and 4h forming the light leakage reduction shape in the thickness direction of the light guide plate 4 gradually increases from the incident surface 4e side toward the boundary surface 4f side. ing.

Here, in FIG. 10, when the angle formed by the pair of inclined surfaces 4g and 4h at the intersecting portion 4i is β, the following conditional expression (4) is satisfied.
100 ° ≦ β ≦ 170 ° (4)

  Since it has such a shape, it becomes easy to control the traveling direction of light incident from the incident surface 4e, and various characteristics such as illuminance distribution and luminance distribution on the boundary surface 4f can be controlled according to the purpose. Therefore, unevenness in illuminance at the boundary surface 4f is reduced. Moreover, since the light incident from the incident surface 4e easily satisfies the total reflection condition, the light use efficiency can be improved.

  FIG. 12 is a diagram showing the results of a simulation performed by the inventor. 12, in the embodiment shown in FIGS. 10 and 11, the angle θ <b> 1 between the incident surface and the top surface is 89.6 ° as an example of a range satisfying 70 ° <θ <b> 1 <90 °, and the refractive index 1. The result of an example in which the apex angle β of the prism having a light leakage reduction shape is changed from 90 ° to 180 ° when the incident portion is configured using the resin material of 525 is shown. The apex angle β of 180 ° means that the prism has no light leakage reduction shape and the top surface is flat. In FIG. 12, the vertical axis represents the light efficiency, and the horizontal axis represents the apex angle β of the prism. According to the results shown in FIG. 12, the light use efficiency of 0.44 or more can be ensured when β is in the range of 100 ° to 170 °. Furthermore, in the range where β is 116 ° or more and 165 ° or less, the light use efficiency can be secured 0.52 or more.

  By the way, depending on the backlight device, there is a case where it is desired to relatively reduce the thickness of the emitting portion 4OT of the light guide plate 4. However, if the thickness of the incident portion 4IN is reduced in accordance with the thickness of the emission portion 4OT, the thickness of the valley portions of the inclined surfaces 4g and 4h becomes almost zero, and the strength of the light guide plate 4 is insufficient in the vicinity of the boundary surface 4f. There is a risk of bending or breakage. In addition, problems such as molding defects due to a decrease in rigidity also occur. Therefore, in order to ensure the strength of the light guide plate 4, the boundary surface 4f side of the incident portion 4IN may be formed so as to protrude from the boundary surface 4f side of the emission portion 4OT.

  In such a case, as shown in FIG. 13, the light traveling in the incident portion 4IN is incident from the side surface to the diffusion plate 5 positioned above the exit portion 4OT from the end surface of the protruding incident portion 4IN. There is a possibility that the intensity distribution of the light emitted from the diffusion plate 5 may be non-uniform. In the following embodiments, such problems can be alleviated or eliminated.

  FIG. 14 is a perspective view showing a light guide plate 4 according to another embodiment. In the present embodiment, when the thickness direction is the vertical direction, the boundary surface of the incident portion 4IN with respect to the maximum thickness T1 on the boundary surface 4f side of the incident portion 4IN (that is, the emission portion 4OT) including the light leakage reduction shape. The thickness T2 of the end portion on the 4f side is thin. Further, the dimension D2 in the height direction on the boundary surface 4f side of the incident portion 4IN is smaller than the thickness T2 on the boundary surface 4f side of the emitting portion 4OT. Therefore, a part of the crest formed by the inclined surfaces 4g and 4h adjacent to the boundary surface 4f protrudes upward from the boundary surface 4f. Note that even if the crests formed by the inclined surfaces 4g and 4h to the intersecting lines 4m and 4n where each of the inclined surfaces 4g and 4h intersects the gap surface 4x (that is, the entire light leakage reduction shape) protrudes from the incident surface 3b. However, in order to obtain the effect of the present invention, it is sufficient that at least a part of the light leakage reducing shape protrudes from the incident surface 3b.

  Furthermore, in the present embodiment, among a plurality of pairs of inclined surfaces, a gap surface 4x that is a plane extending between two inclined surfaces 4h and 4g forming a valley and extending in parallel with the bottom surface 4b. Is provided. Since the gap surface 4x and the intersecting lines 4m and 4n of the two inclined surfaces 4h and 4g intersecting with the gap surface 4x are gradually separated from the incident surface 4e side toward the boundary surface 4f side, the manufacturing is easy. That is, the gap surface 4x has a triangular shape as viewed from above. Further, the gap surface 4x is in contact with the boundary surface 4f but not in contact with the incident surface 4e. Since the gap surface 4x is formed, the dimensions of the inclined surfaces 4g and 4h constituting the light leakage reduction shape in the thickness direction of the light guide plate 3 are gradually increased from the incident surface 4e side to the boundary surface 4f side. After increasing, it gradually decreases (see FIG. 15). Since the angle β formed by the pair of inclined surfaces 4g and 4h is constant over the entire length of the intersecting portion 4i, the manufacture is easy. Other configurations are the same as those in the embodiment shown in FIG. In the present embodiment shown in FIGS. 14 to 16, the pair of inclined surfaces 4g and 4h and the gap surface 4x constitute the light leakage reduction shape 4M.

  FIG. 15 is a side view of the embodiment shown in FIG. According to the present embodiment, a part of the light that passes through the vicinity of the top surface 4a out of the light incident from the incident surface 4e of the incident portion 4IN is totally reflected by the gap surface 4x, whereby the boundary surface 4f. It is designed to pass through. Thereby, the light leaking out of the light guide plate 4 from the end surface adjacent to the boundary surface 4f of the incident portion 4IN can be suppressed.

  FIG. 16 is a graph showing the results of a simulation performed by the present inventors, where the vertical axis represents the light leakage rate, and the horizontal axis represents the incident portion including the light leakage reduction shape with respect to the boundary surface side thickness T2 of the emission portion. Corresponds to the maximum thickness T1 on the boundary surface side. The inventor changed the inclination angle of the gap surface 4x with respect to a horizontal plane (here, a plane parallel to the bottom surface of the light guide plate 4) to 0 °, 0.1 °, 0.2 °, and 0.3 °. As a result, it was found that the light leakage rate increases as T1 / T2 is increased under any condition. In addition, according to another examination result, it is known that the light use efficiency is high when T1 / T2 is in the range of 1.1 to 1.5.

  FIG. 17 is a perspective view showing a light guide plate 4 according to still another embodiment. In the present embodiment, among a plurality of pairs of inclined surfaces, the two inclined surfaces 4g and 4h that form a mountain intersect with each other, and are in contact with the boundary surface 4f and at a predetermined angle with respect to the boundary surface 4f. A tapered surface 4p inclined to the incident surface 4e side is provided. The tapered surface 4p can be formed by scraping a plurality of pairs of inclined surfaces 4g and 4h together by a virtual plane Q inclined at an angle δ with respect to the boundary surface 4f. You may make it mutually differ. In the present embodiment, the maximum thickness T1 of the end portion on the boundary surface 4f side of the incident portion 4IN is equal to the thickness of the end portion on the boundary surface 4f side of the emission portion 4OT. Since the tapered surface 4p is formed, the dimensions of the inclined surfaces 4g and 4h constituting the light leakage reduction shape in the thickness direction of the light guide plate 4 gradually increase from the incident surface 4e side toward the boundary surface 4f side. After that, it gradually becomes smaller (see FIG. 18). The angle β formed by the pair of inclined surfaces 4g and 4h is constant over the entire length of the intersection 4i. Other configurations are the same as those in the embodiment shown in FIG. In the present embodiment shown in FIGS. 17 to 19, the pair of inclined surfaces 4g and 4h and the tapered surface 4p constitute the light leakage reduction shape 4M.

  FIG. 18 is a side view of the embodiment shown in FIG. According to the present embodiment, a part of the light that passes through the vicinity of the top surface 4a out of the light incident from the incident surface 4e of the incident portion 4IN is totally reflected by the tapered surface 4p, whereby the boundary surface 4f. It is designed to pass through. Thereby, more light can be taken in to the emission part 4OT side via the boundary surface 4f.

  FIG. 19 is a graph showing the results of a simulation performed by the present inventor. In (a), the vertical axis represents the light utilization efficiency, and the horizontal axis represents the tapered surface and the boundary surface of the incident portion shown in FIG. In (b), the vertical axis is the light leakage rate, and the horizontal axis is the angle δ between the tapered surface of the incident portion and the boundary surface. As is clear from FIG. 19, it was found that the tapered surface 4p has the lowest light leakage rate and the highest light utilization efficiency in the range of 75 ° to 85 °.

  FIG. 20 is a side view of the light guide plate 4 according to another modification. As shown in FIG. 20, the inclined surfaces 4g and 4h constituting the light leakage reduction shape may be provided on the top surface 4a on the exit surface 4e side of the incident portion 4IN and on the bottom surface 4b on the boundary surface 4f side. . At this time, it is desirable that the inclined surfaces 4g and 4h on the top surface 4a side and the inclined surfaces 4g and 4h on the bottom surface 4b side do not overlap in the vertical direction.

  FIG. 21 is a side view of the light guide plate 4 according to another modification. As shown in FIG. 21A, when the bottom surface 4b of the incident portion 4IN is disposed so as to be inclined with respect to the bottom surface 4s of the emission portion 4OT, the amount of light taken from the boundary surface 4f to the emission portion 4OT side is reduced. And the light utilization efficiency increases.

  On the other hand, as shown in FIG. 21B, when the bottom surface 4b of the incident portion 4IN is arranged on the same plane with respect to the bottom surface 4s of the emission portion 4OT, the assembling property is improved.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, the prism may be provided only on the bottom surface 4b, or may be formed on both the top surface 4a and the bottom surface 4b. Alternatively, the top surface 4a and / or the bottom surface 4b may be planar and a sheet on which a prism is formed may be attached. Further, the incident part 4IN and the emission part 4OT may be separated.

1 housing 2 LED
3 convex portion 4 light guide plate 4IN incident portion 4OT emitting portion 4A, 4A ′, 4a top surface 4b bottom surface 4c, 4d side surface 4e incident surface 4f boundary surface 4g, 4h inclined surface 4i intersecting portion 4k emitting surface 4x gap surface 4p tapered surface 5 Diffuser 6 Liquid crystal display element

Claims (1)

A light guide plate integrally formed with an incident part for incident light from the light emitting element and an outgoing part for emitting incident light to the outside,
The incident portion is an incident surface for incident light from the light emitting element , a boundary surface that defines a boundary between the incident portion and the emission portion and through which light traveling from the incident portion to the emission portion passes, A top surface and a bottom surface extending in a direction intersecting the incident surface and the boundary surface and facing each other;
One surface of the top surface and the bottom surface is relative to the other surface so that the size of the exit surface in the thickness direction of the light guide plate is smaller than the size of the entrance surface in the thickness direction of the light guide plate. Is inclined,
At least one of the top surface and the bottom surface is provided with a structure having a light leakage reduction shape that suppresses the amount of light emitted from a surface other than the boundary surface among light incident from the incident surface. And
The light leakage reduction shape is emitted from the light emitting element when the plane extending from the incident surface side toward the boundary surface side and extending along the thickness direction of the light guide plate is a virtual plane. When light traveling along a plane is incident on the light leakage reducing shape, the reflected light has a directional component that leaves the virtual plane,
The light leakage reduction shape has a plurality of pairs of inclined surfaces having intersections extending from the incident surface side toward the boundary surface side, and the plurality of pairs of inclined surfaces are in the thickness direction of the light guide plate. As seen from the above, including a pair of inclined surfaces in which an intersection extends along the direction of the normal line of the emission surface of the light emitting element , and inclined surfaces arranged on both sides of the inclined surface pair,
The interval on the incident surface side of the adjacent intersecting portions is smaller than the interval on the boundary surface side,
The exit portion may have a exit surface extending in a direction intersecting with the boundary surface,
A light guide plate that satisfies the following conditional expression (4), where β is an angle formed by a pair of inclined surfaces at the intersection .
100 ° ≦ β ≦ 170 ° (4)

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