JP4428664B2 - Light guide plate - Google Patents

Description

  The present invention relates to a light guide plate used for illumination means, and more particularly to a light guide plate used for a backlight of a display device such as a liquid crystal display.

  In recent years, light emitting elements such as light emitting diodes (hereinafter referred to as LEDs) have been widely used as light sources for backlights of liquid crystal display devices and illumination units of scanners. It is considered that LEDs and the like are most suitable for downsizing and thinning of such illumination means, leading to cost reduction.

  In such conventional illumination means equipped with light emitting elements such as LEDs as the light source, a light guide plate is used to reduce the number of light emitting elements and obtain uniform illumination intensity, and the light is emitted from the light emitting elements as the light source. There is known a configuration in which light to be incident on a light guide plate and guided in a desired direction.

FIG. 7 is a view showing a configuration of a known backlight unit 110 (see Patent Document 1) for illuminating a liquid crystal panel using such a light guide plate, (a) is a perspective view, and (b) is a side view. is there. In FIG. 7, 101 is an LED as a light source, 102 is a light guide plate, 103 is a prism sheet, 106 is a reflection plate, and 107 is a liquid crystal display plate. The light guide plate 102 has a substantially quadrangular planar shape, and is made of translucent glass or resin. Reference numeral 102 a denotes an upper surface of the light guide plate 102. Reference numeral 102 c denotes a light incident side surface facing the LED 101. Reference numeral 102b denotes a lower surface of the light guide plate 102, which faces the upper surface 102, and a plurality of asymmetric prisms 102b1 are formed. The asymmetric prism 102b1 includes a falling slope 102b11 whose distance from the upper surface 102a increases abruptly as the distance from the light incident side face 102c increases, and a rising slope 102b12 whose distance from the upper face 102a gradually decreases. The three LEDs 101 are held by the holding member 101b and arranged at positions facing the light incident side surface 102c.
Japanese Patent Laid-Open No. 2003-294554

  When a predetermined current is supplied to the LED 101 from a power source (not shown), the LED 101 emits white light or a predetermined color. The light emitted from the LED 101 enters the light incident side surface 102 c of the light guide plate 102, passes through this surface by refraction, and enters the light guide plate 102. The light that has entered the inside is repeatedly reflected between the upper surface 102 a and the lower surface 102 b of the light guide plate as will be described later, and then is transmitted through the upper surface 102 a by refraction and exits the light guide plate 102 and enters the prism sheet 103. Here, the light incident on the prism sheet 103 is specularly reflected in the prism sheet and finally changes its path in the z direction. When the light beam traveling in the z direction is incident on the liquid crystal display plate 107, the direction of light passing through the liquid crystal is idealized, and a clear display is possible.

FIG. 8 is a side view showing an example of a path of light incident on the light guide plate 102 from the LED 101. The light beam emitted from the LED 101 at the exit angle θi is incident on the incident side surface 102c of the light guide plate 102 at the incident angle θi and is transmitted through the surface by refraction. The relationship between the incident angle θi and the refraction exit angle θ at this time If the refractive index of air is 1 and the refractive index of the light guide plate 102 (made of polycarbonate or the like) is n, then according to Snell's law, nsinθ = sinθi,
θ = sin ⁻¹ ((1 / n) sin θi) (1)
It becomes. For example, when the refractive index n of the light guide plate 102 is n = 1.58, and θi = 90 °, θ = sin ⁻¹ (1 / 1.58) = 39.3 ° Therefore, the critical angle θc is θc = 39.3 °.
By the way, since the incident angle θi is actually less than 90 ° at the maximum, the emission angle θ is below the critical angle θc at the maximum from the equation (1). Since the critical angle θc of the light guide plate is generally around 40 °, the emission angle θ does not exceed 40 ° at the maximum. The light beam transmitted through the light incident side surface 102c at the emission angle θ enters the upper surface 102a of the light guide plate 102 at the incident angle θ1. At this time, as can be seen from FIG. 8, since there is a relationship of θ + θ1 = 90 ° and the emission angle θ is 40 ° or less as described above, the incident angle θ1 is 50 ° or more, and a critical angle around 40 °. θc will be exceeded. Therefore, the incident light beam on the upper surface 102a is totally reflected at a reflection angle θ1 of 50 ° or more.

This reflected light is incident on the rising slope 102b12 having an inclination angle of α provided on the lower surface at an incident angle θ2 of θ2 = θ1−α. Here, the inclination angle α is about 1 ° to several degrees. A light ray incident at an incident angle θ2 is reflected by this surface at a reflection angle of θ2, is incident on the upper surface 102a at an incident angle θ3 of θ3 = θ2-α = θ1-2α, and is reflected and reflected at a reflection angle of θ3. The incident light enters the rising slope 102b12 at an incident angle θ4 of θ4 = θ3-α = θ1-3α. In this way, each time the light beam emitted from the upper surface 102a at the reflection angle θ1 first enters the inclined surface 102b12 and the upper surface 102a, the incident angle becomes a value obtained by subtracting α from θ1. That is, when a light beam having a reflection angle θ1 at first is incident for the Nth time after repeated reflection, the incident angle is θN.
θN = θ1-Nα (2)
It becomes. (Here, for the angles θ2, θ3, θ4,... Shown in the figure, the number of incidences N in equation (2) is 1, 2, 3,.

In this way, the incident angle θN decreases, and with respect to the critical angle θc,
θN = θ1-Nα <θc (3)
Then, the incident light passes through the upper surface 102a or the lower inclined surface 102b12 and is emitted to the outside of the light guide plate 2. For example, if θ1 = 52 ° α = 1 ° θc = 40 °,
From the equation (3), N> 12, and it is necessary to repeat the incidence 12 times or more in order to exit to the outside. For this reason, the incident light is not emitted to the outside in the vicinity of the light incident side surface 102c. For example, when the thickness of the light guide plate is 1 mm, the light beam is not emitted to the outside in the range of approximately 3 mm from the light incident side surface 102c, and the normal ray path is to be emitted to the outside in a region farther than this. It is. In the region where the light beam is normally emitted, the emitted light is emitted with no unevenness.

  However, the conventional backlight unit using such a light guide plate (102) has many problems as described below. That is, as shown in the top view of FIG. 9, it is recognized that some bright lines 14 are conspicuous in the region S <b> 1 (3 mm to 4 mm) close to the light incident side surface 102 c of the light guide plate 102. (In FIG. 9, all bright lines are indicated by dark hatching.) S2 is an area where bright lines are not conspicuous. The reason why such a noticeable bright line is generated is considered as follows. As shown in FIG. 10, the emitted light beam reaches from the LED 101 to the edge portion 102d formed by the intersection of the light incident side surface 102c and the upper surface 102a of the light guide plate 102, and enters the light guide plate 102 at the edge portion 102d. At this time, if the edge is not a mirror surface but a rough surface, light is incident on the edge portion in a form of scattering instead of normal refraction. That is, since a plurality of light beams are separated from the edge portion in different directions and transmitted through the light guide plate, the edge portion 102d can be regarded as a secondary light source because it looks as if the edge is shining.

  There may be a case where the incident angle θb of the light from the secondary light source with respect to the rising slope 102b12 of the lower surface 102b is equal to or smaller than the critical angle θc. In this case, as illustrated in the light ray s21, the light is transmitted through the slope 102b12 and reflected. Then, the light is reflected here, enters the light guide plate 102 again, passes through the upper surface 102a, and exits upward. Since this covers a wide range, it does not generate bright lines. Next, when the incident angle θb exceeds the critical angle θc, it is reflected by the rising slope 102b12 and then emitted from the upper surface 102a as exemplified in s22. The number of incidents based on reflection and the like up to this emission has already been reached. As described above, it depends on the difference between the incident angle θb and the critical angle θc, and as this difference increases, the number of incidents increases. This point will be described in more detail with reference to FIG. In FIG. 11, φ1, φ2, φ3, and φ4 are all light beams emitted from the edge portion 102d, and the angle width of each light beam itself is smaller than the inclination angle α of the rising slope 102b12. The emission angle with respect to the upper surface 102a of these light beams is assumed to be φ1 being the smallest, and sequentially increasing by α in the order of φ2, φ3, and φ4.

Here, the emission angles of the light beams φ1, φ2, φ3, and φ4 are θd1, θd2, θd3, and θd4, respectively, and the relationship between the emission angles and the critical angle θc is as follows.
θd1 = 1.5α + θc
θd2 = 2.5α + θc
θd3 = 3.5α + θc
θd4 = 4.5α + θc
.... (4)
Suppose that As shown in FIG. 11, the light beams φ1, φ2, φ3, and φ4 are all incident on the slope 102b12 for the first time, and the incident angles at that time are respectively
θd1-α, θd2-α, θd3-α, θd4-α
However, since both are larger than the critical angle θc according to the equation (4), all of these light beams are reflected on the inclined surface 102b12 and are incident on the upper surface 102a for the second time. Each incident angle is calculated with reference to equation (4).
θd1-2α <θc, θd2-2α> θc, θd3-2α> θc, θd4-α> θc
Thus, only the incident angle θd1-2α of the light beam φ1 is equal to or smaller than the critical angle θc and is emitted from the upper surface 102a with the light beam width b1 as shown in the figure.

The remaining light fluxes φ2, φ3, and φ4 are reflected and incident on the inclined surface 102b12 for the third time, and the incident angle at this time also takes into account the equation (4), respectively.
θd2-3α <θc, θd3-3α> θc, θd4-3α> θc
It becomes. At this time, only the incident angle θd1-3α of the light beam φ2 is equal to or smaller than the critical angle θc, and the light beam φ2 is emitted from the inclined surface 102b12 to the outside with the width b2 of the light beam. Similarly, the light beam φ3 is emitted from the upper surface with the width b3 by the fourth incidence, and the light beam φ4 is emitted from the inclined surface 102b12 to the outside with the width b4 of the light flux by the fifth incidence. In this way, each of the light beams is sequentially emitted to the outside according to the number of times of incidence, but the width of the speed of light when emitted is sequentially increased according to the number of times of incidence,
b1 <b2 <b3 <b4
There is a relationship. This is because even though the angular widths of the light beams φ1, φ2, φ3, and φ4 are the same, the actual width of the light beam increases in proportion to the path length of the light beam, and the number of incidents is large. It is considered that the path length increases as the luminous flux increases, and the actual width of the emitted light increases accordingly. In FIG. 11, the light beam emitted from the lower slope 102b12 is actually reflected by the reflecting plate (106) and enters the light guide plate 2 and then exits from the upper surface 102a. As a result, the light beam exits from the upper surface 102a. It may be handled in the same way.

  When the emitted light beams φ1, φ2, φ3, and φ4 shown in FIG. 11 are considered in correspondence with 14-1, 14-2, 14-3, and 14-4 in the bright lines shown in FIG. 9, they are shown in FIG. The outgoing light of the light flux φ1 having the width b1 is located closest to the light incident side surface 102c and has the narrowest width, and therefore corresponds to the bright line 14-1 shown in FIG. The outgoing light of the light flux φ2 having the width b2 shown in FIG. 11 is located at the second closest position to the light incident side surface 102c, and its width is slightly wider than b1, and therefore corresponds to the bright line 14-2 shown in FIG. In this way, it is considered that the emitted lights of the light beams φ3 and φ4 shown in FIG. 11 sequentially correspond to 14-3 and 14-4 shown in FIG.

  Note that for a light beam having a larger exit angle with respect to the upper surface 102a than the light beam φ4 shown in FIG. 11, the number of incidents until the light exits from the light guide plate 2 further increases as the exit angle increases, and the external It is considered that the position where the light is emitted further away from the light incident side surface 102c, and accordingly, the width of the emitted light beam further increases, and the amount of light per unit area, that is, the luminance, decreases. This coincides with the fact that the width of the bright line shown by the dark hatching in the top view of the light guide plate 102 shown in FIG. 9 becomes wider as the distance from the light incident side surface 102c increases, and the bright line becomes inconspicuous. In this way, the reason why the bright line is conspicuous as shown in FIG. 9 is that the light guide plate 102 has a relatively small number of incidences (1 to 4 times) among the light rays emitted from the edge portion (102d) as shown in FIG. This is considered to be due to the existence of light rays that exit to the outside.

  When such a bright line is generated, a bright and dark stripe pattern is formed, resulting in a backlight unit having a poor appearance. Therefore, an object of the present invention is to prevent the occurrence of bright and dark stripes due to the bright lines in a backlight unit having a light guide plate.

  As a first means for solving the above-mentioned problems, the present invention has an upper surface, a lower surface, and a light incident side surface, and the lower surface has a distance from the upper surface abruptly increasing as the distance from the light incident side surface increases. In the light guide plate in which a plurality of asymmetric prisms each including a second slope whose distance between the first slope and the upper surface gradually decreases, a light beam emitted from an edge portion formed by the light incident side surface and the lower surface on the upper surface. In order to prevent total reflection on the upper surface in the range relatively close to the light incident side surface and incident on the asymmetric prism on the lower surface, a concave symmetric prism having a substantially symmetrical slope in the direction away from the light incident side surface. The light beam emitted from the edge formed by the incident side surface and the lower surface is incident on the falling slope of the symmetric prism at an angle smaller than the critical angle, and the symmetric prism is viewed from the upper incident surface. (If there are multiple symmetric prisms, the symmetric prism located on the farthest side when viewed from the light incident side surface) so that the incident angle of the light incident on the upper surface farther than the critical angle is sufficiently larger than the critical angle. One or a plurality of the above structures are formed.

  As a second means for solving the above-mentioned problems, the present invention has an upper surface, a lower surface, and a light incident side surface, and the lower surface has a distance from the upper surface that suddenly increases as the distance from the light incident side surface increases. A light guide plate in which a plurality of asymmetric prisms each having a first slope and a second slope whose distance from the upper surface gradually decreases is formed, and the position of the asymmetric prism on the lower surface is defined as a light incident side surface of the light guide plate. The light beam emitted from the edge formed by the upper surface is arranged at a necessary distance from the light incident side surface so as to enter the second inclined surface of the asymmetric prism at an angle sufficiently larger than the critical angle, and is separated from the light incident side surface. A concave symmetric prism having a substantially symmetric slope with respect to the direction, and the light emitted from the edge formed by the incident side surface and the upper surface is smaller than the critical angle with respect to the rising slope of the prism. In the light guide plate formed by radiating one or a plurality of light guides in the portion between the light incident side surface and the asymmetric side, an edge portion formed by the light incident side surface and the lower surface on the upper surface of the light guide plate In order to prevent the light emitted from the light from being totally reflected on the upper surface in the range relatively close to the light incident side surface and entering the asymmetric prism on the lower surface, the light beam has a substantially symmetrical slope in the direction away from the light incident side surface. A concave or convex symmetric prism, a light beam emitted from an edge formed by the incident side surface and the lower surface is incident on the falling slope of the symmetric prism at an angle smaller than the critical angle, and on the upper surface, The incident angle of the light beam incident on the upper surface farther from the light incident side surface than the symmetric prism (the symmetric prism located farthest from the light incident side surface when there are a plurality of symmetric prisms) is the critical angle. Those constructed so as to be sufficiently large angle, and characterized in that one or more forms.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the light and dark striped pattern by the conspicuous bright line which may occur at the time of the illumination in the light-guide plate used for a backlight unit can be prevented effectively.

  Hereinafter, an embodiment which is one of the modes for carrying out the present invention will be described with reference to the drawings.

  1A and 1B show a backlight unit 10 using a light guide plate according to the first embodiment, where FIG. 1A is a perspective view and FIG. 1B is a side view. In FIG. 1, 1 is an LED as a light source, 2 is a light guide plate, 3 is a prism sheet, 6 is a reflector, and 7 is a liquid crystal panel. The light guide plate 2 is a plate having a substantially quadrangular planar shape and is made of a light-transmitting resin (polycarbonate or the like). 2 a is the upper surface of the light guide plate 2. Reference numeral 2 c denotes a light incident side surface of the light guide plate 2 facing the LED 1. 2 b is the lower surface of the light guide plate 2. In the lower surface 2b, a parallel plane portion 2bh parallel to the upper surface 2a is provided in the vicinity of the light incident side surface 2c, and a plurality of asymmetric prisms 2bp are formed in a portion connected thereto. The asymmetric prism 2bp has a falling slope 2bp1 whose distance from the upper surface 2a suddenly increases with increasing distance from the light incident side face 2c, and a rising slope 2bp2 whose distance from the upper face 2a gradually decreases.

  The parallel plane 2bh is provided with a concave symmetrical prism 2p that is symmetrical with respect to the x direction (the direction away from the light incident side surface). The symmetric prism 2p has a falling slope 2p1 and a rising slope 2p2. The three-dimensional shape of the symmetrical prism 2p is shown in FIG. 2 (a) as an enlarged view of part A in FIG. 1 (a). As shown in the figure, the apex angle of the symmetric prism 2p is 130 ° or more. The position where the symmetric prism 2p is provided is preferably provided in an area within 3 mm to 4 mm from the light incident side surface 2c. In addition, the inclination angle α of the rising slope 2bp2 of the asymmetric prism shown in FIG. 1C is about 1 ° to several degrees. The thickness of the light guide plate 2 is about 1 mm at a portion close to the light incident side surface 2c. The three LEDs 1 are held by the holding member 1b and are arranged at positions facing the light incident side surface 12c.

  When a predetermined current is supplied to the LED 1 from a power supply (not shown), the LED 1 emits white light or a predetermined color. Of the light emitted from the LED 1, the light incident on the light incident side surface 2 c of the light guide plate 2 as indicated by the dotted line in FIG. Based on the same principle as described with reference to FIG. 8, when the upper surface 2a or the lower surface 2b is first reached, the incident angle (θ1 in FIG. 8) with respect to these surfaces is equal to or greater than the critical angle, and is totally reflected. Then, by repeating the reflection between the upper surface 2a and the lower surface 2b as illustrated by the dotted line in FIG. 1B, the incident angle is decreased by the inclination angle α of the inclined surface every time the reflection is performed as described above, and this is less than the critical angle. When it becomes, it radiates | emits outside by refraction. The light beam that has passed through the upper surface 2 a due to refraction is incident on the prism sheet 3. Here, the light incident on the prism sheet 3 is regularly reflected in the prism sheet, and finally changes its path in the z direction. When the light beam traveling in the z direction is incident on the liquid crystal display plate 7, the direction of light transmitted through the liquid crystal is idealized, and clear display is possible.

  However, in addition to the general light path exemplified by the dotted line, the edge portion D1 shown in FIG. 1B functions as a secondary light source based on the principle already described in the conventional example (see FIG. 10). In FIG. 1B, the path of the light beam from the edge portion D1 is shown by a solid line, and a more detailed description of the path will be given with reference to FIG. In FIG. 3, D1 is an edge portion formed by the light incident side surface 2c and the upper surface 2a of the light guide plate, and D2 is an edge portion formed by the light incident side surface 2c and the lower surface 2b.

  The feature of the present invention relates to the path of the light beam incident on the edge portions D1 and D2 from the LED 1, which will be described below. The case where these parts function as a secondary light source according to the principle already explained by the light incident on the edge parts D1 and D2 will be described. First, the path of light emitted from the edge portion D1 will be described with reference to FIG. The region of light rays emitted from the edge portion D1 is divided into four regions S1, S2, S3 and other regions. The region S1 (hatched hatched region) is a region on the left side of the symmetric prism 2p in the drawing, and in this region, the incident angle with respect to 2bh, which is the lower surface of the light guide plate 2, is less than the critical angle (in this way) The position of the symmetric prism 2p is set.) The light beam in the region S1 passes through the lower surface 2bh and is reflected by the reflecting plate 6, enters the light guide plate 2 again, passes through the upper surface 2a, and exits outside (for example, the light beam s1). The region S2 (the hatched portion of the horizontal line) is a region where the edge portion D1 is stretched with respect to the rising slope 2p2 of the target prism 2p, and light rays in this region have an incident angle with respect to the slope 2p2 equal to or less than the critical angle. The light beam passes through the inclined surface 2p2 and is reflected by the reflecting plate 6, enters the light guide plate 2 again, passes through the upper surface 2a, and exits outside (for example, the light beam s2). Thus, since the light from the reflection plate 6 is continuously emitted from the regions S1 and S2 over the wide range from the upper surface 2a, no bright line is generated.

  Next, the region S3 (vertical hatched portion) is a region in which the edge portion D1 extends over the falling slope 2p1 of the symmetric prism 2p and the subsequent parallel plane 2bh on the right side (in the drawing). Of the light rays in this region, those incident on the falling slope 2p1 are not shown, but are incident at an extremely large incident angle (close to 90 °), and the reflected light is substantially parallel to the upper surface a. a is not reached, and no bright line is produced. Moreover, since the incident angle of the light ray in this region that is incident on the parallel plane 2bh is considerably large, the reflection angle is also quite large (illustrated by the light ray s3), which is considerably beyond the critical angle (for example, 20 ° or more). For this reason, a considerable number of reflections (for example, 20 times) are required to emit the incident angle below the critical angle (the number is less than the actual number in the figure). Therefore, no bright line is generated by this reflected light according to the principle already described in the conventional example. Next, in the region without hatching above the region S3, the light enters the rising slope 2bp2 of the asymmetric prism 2bp with a larger incident angle (illustrated by the light ray s4). Because a considerable number of reflections are required for reasons, no bright lines are generated. As described above, as far as the light emission of the edge portion D1 is concerned, this prevents the occurrence of bright lines as in the prior art.

  In the first embodiment, the parallel plane portion 2bh is provided on the lower surface of the light guide plate, and the symmetric prism 2p is provided on this portion. However, the present invention is not limited to this, and the asymmetric prism 2bp on the lower surface is provided without providing bh on the parallel plane portion. The same effect can be obtained even if a symmetric prism is provided in a part. Further, the number of the symmetric prisms 2p is not limited to one and may be plural.

  Next, the path of light rays emitted from the edge portion D2 will be described with reference to FIG. When the incident angle of the light beam directly incident on the upper surface 2a from the edge portion D2 is equal to or smaller than the critical angle, it is transmitted by refraction and emitted to the outside as illustrated by s5. However, when it is incident on the upper surface 2a at an incident angle slightly exceeding the critical angle, it is emitted to the outside by one or two small reflections as exemplified by s6. In such a case, bright lines are generated according to the principle described in the conventional example.

  Hereinafter, a light guide plate according to a second embodiment of the present invention will be described with reference to the drawings. The second embodiment is improved for preventing the generation of bright lines due to the light emission from the edge portion D2, and FIG. 4 is a diagram showing the shape and action thereof. As shown in FIG. 4, a concave symmetrical prism 2p is also provided on the upper surface 2a of the light guide plate 2. (The three-dimensional structure of the symmetrical prism 2p is shown in FIG. 2C.) The other points are the same as those of the light guide plate 2 shown in FIG. Of the light rays emitted from the edge portion D2, the light rays incident on the upper surface 2a on the left side of the symmetric prism 2p have an incident angle equal to or smaller than the critical angle, and are transmitted by refraction and emitted to the outside as illustrated in s7.

  Next, the light beam incident on the falling surface 2p1 of the symmetric prism 2p becomes the critical angle or less due to the inclination angle of the surface, and is transmitted through this surface by refraction and emitted to the outside as illustrated in s8. Since the light incident on the falling surface 2p1 of the symmetric prism 2p has a very large incident angle with respect to this surface, it is reflected at a large reflection angle close to 90 ° on this surface and the upper surface 2a as illustrated in s9. Therefore, it does not radiate | emit from the upper surface 2a. Next, the light incident on the upper surface 2a on the right side of the symmetric prism 2p has a critical angle that greatly exceeds the critical angle as illustrated in s10. Requires a large number of reflections.

  As described above, the light beam emitted from the edge portion D2 is not emitted to the outside by one or more reflections and a small number of reflections. Therefore, the bright lines are prevented from being generated by the light rays emitted from the edge portion D2 according to the principle already described. That is, according to the second embodiment, it is possible to prevent generation of bright lines due to the light rays emitted from the edge portion D1, and it is also possible to prevent generation of bright lines due to the light rays emitted from the edge portion D2. Generation of bright lines can be completely prevented. FIG. 6 is a top view showing a region of illumination light in the light guide plate 2 according to the second embodiment, and is a region R (shaded region) where the bright line is not conspicuous over the entire region, and the bright line that stands out as in the prior art. Is not allowed at all.

  Hereinafter, a light guide plate according to Example 3 of the present invention will be described with reference to the drawings. The third embodiment is a modification of the second embodiment shown in FIG. 4, and FIG. 5 is a diagram showing its shape and action. As shown in FIG. 5, two convex symmetrical prisms 2p are provided on the upper surface 2a of the light guide plate 2 according to the third embodiment. (The three-dimensional structure of the symmetrical prism 2p is shown in FIG. 2D.) The other points are the same as those of the light guide plate 2 shown in FIG. Here, the position of the left side of the convex symmetric prism 2p on the upper surface 2a is considerably shifted to the left side from the position facing the concave symmetric prism 2p provided on the lower surface 2bh. Of the light rays emitted from the edge portion D2, the light rays incident on the upper surface 2a on the left side of the symmetric prism 2p have an incident angle equal to or smaller than the critical angle, and are transmitted by refraction and emitted to the outside as illustrated in s11. Next, the light beam incident on the rising slope 2p2 of the left symmetric prism 2p is reflected by the prism action of this surface and the falling slope 2p1, and enters the lower surface 2bh at an incident angle equal to or less than the critical angle as illustrated in s12. Then, after passing through this surface and reflected by the reflecting plate 6, it enters the light guide plate 2 again and exits from the upper surface 2a.

  The light beam incident on the falling slope 2p1 of the left symmetric prism is transmitted through this surface and emitted to the outside as illustrated in s13. The light beam incident on the falling slope 2p1 of the right symmetric prism is transmitted through this surface and emitted to the outside as illustrated in s14. Next, since the incident angle of the light beam incident on the right upper surface 2a of the right symmetric prism 2p greatly exceeds the critical angle as illustrated in s15, a large number of light beams are emitted before exiting the light guide plate 2. Requires one reflection.

  As described above, the light beam emitted from the edge portion D2 is not emitted to the outside by one or more reflections and a small number of reflections. Therefore, the bright lines are prevented from being generated by the light rays emitted from the edge portion D2 according to the principle already described. In this way, in the third embodiment as well, similar to the second embodiment shown in FIG. 4, it is possible to prevent the generation of bright lines due to the light rays emitted from the edge portions D1 and D2.

  Next, in the light guide plate 2 as shown in FIGS. 3, 4, and 5, instead of the concave symmetric prism 2 p provided on the parallel plane part 2 bh on the lower surface, this part is shown in FIG. One or a plurality of three-dimensional convex symmetrical prisms may be provided. In this case, although illustration regarding the light path is omitted, generation of bright lines can be prevented with respect to the light rays emitted from the edge portion D1 by the same principle as in the third embodiment shown in FIG.

It is a figure which shows the backlight unit using the light-guide plate which concerns on Example 1 of this invention. It is a figure which shows the three-dimensional shape of the symmetrical prism formed in the light-guide plate etc. which are shown in FIG. It is a figure which shows the shape and effect | action of a light-guide plate shown in FIG. It is a figure which shows the shape and effect | action of a light-guide plate which concern on Example 2 of this invention. It is a figure which shows the shape and effect | action of a light-guide plate which concern on Example 3 of this invention. It is a top view which shows the state of the illumination light of the light-guide plate shown in FIG. It is a figure which shows the backlight unit using the conventional light-guide plate. It is a figure which shows the normal effect | action of the light-guide plate shown in FIG. It is a top view which shows the state of the illumination light of the light-guide plate shown in FIG. It is a figure which shows the abnormal effect | action of the light-guide plate shown in FIG. It is a figure explaining the path | route of the abnormal light of the light-guide plate shown in FIG. 7 in detail.

Explanation of symbols

1 LED
2 light guide plate 2a upper surface 2b lower surface 2c light incident side surface 2bh parallel plane portion 2bp asymmetric prism 2bp1 falling slope 2bp2 rising slope 2p symmetrical prism 3 prism sheet 6 reflector 7 liquid crystal display plate 10 backlight unit D1, D2 edge portion

Claims (2)

A first slope whose distance from the upper surface abruptly increases with increasing distance from the light incident side surface, and a second slope whose distance from the upper surface gradually decreases. In the light guide plate in which a plurality of asymmetric prisms are formed, the light beam emitted from the edge portion formed by the light incident side surface and the lower surface on the upper surface is totally reflected on the upper surface in a range relatively close to the light incident side surface. In order to prevent the light from entering the asymmetric prism, it is a concave symmetric prism having a substantially bilaterally inclined surface in the direction away from the light incident side surface. The light beam emitted from the edge formed by the light beam is incident at an angle smaller than the critical angle, and the symmetric prism as viewed from the light incident side surface on the upper surface (the light incident side surface when there are a plurality of symmetric prisms) One or a plurality of prisms are formed so that the incident angle of the light beam incident on the upper surface on the far side from the symmetric prism located on the farthest side from the viewpoint is a sufficiently larger angle than the critical angle. A light guide plate. A first slope whose distance from the upper surface abruptly increases with increasing distance from the light incident side surface, and a second slope whose distance from the upper surface gradually decreases. A light guide plate in which a plurality of asymmetric prisms are formed, and light rays emitted from an edge portion that forms the position of the asymmetric prism on the lower surface and the light incident side surface of the light guide plate on the upper surface are formed on the second inclined surface of the asymmetric prism. A concave symmetric prism that is arranged at a necessary distance from the light incident side surface so as to be incident at an angle sufficiently larger than the critical angle, and has a substantially symmetrical plane with respect to the direction away from the light incident side surface, A light beam emitted from an edge formed by the light incident side surface and the upper surface is incident on the rising slope of the prism at an angle smaller than the critical angle, between the light incident side surface and the asymmetry. In one or more formed light guide plate comprising a minute,
In the upper surface of the light guide plate, in order to prevent the light emitted from the edge portion formed by the light incident side surface and the lower surface from being totally reflected on the upper surface in a range relatively close to the light incident side surface and entering the asymmetric prism on the lower surface And a concave or convex symmetric prism having a substantially symmetrical slope with respect to the direction away from the light incident side surface, and the light exits from the edge formed by the light incident side surface and the lower surface with respect to the falling slope surface of the symmetric prism. The light beam is incident at an angle smaller than the critical angle, and the symmetric prism is located on the upper surface as viewed from the light incident side surface (if there are a plurality of symmetric prisms, the symmetric prism located on the farthest side as viewed from the light incident side surface) 1) A light guide plate in which one or a plurality of light beams incident on the upper surface on the far side are formed so that the incident angle of the light beam is sufficiently larger than the critical angle.

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