JP2014130748A - Light guide plate and surface light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a directional characteristic of light transmitted through an emission optical pattern the same as a directional characteristic of a deflection pattern provided at a light guide plate, in the light guide plate having a light introduction part.SOLUTION: A light guide plate 33 comprises: a plate-shaped light guide plate body 35; and a wedge-shaped light introduction part 34 integrally molded at an end of the light guide plate body 35. At an upper surface of the light introduction part 34, an inclined surface 38 is formed, and in the light introduction part 34, the thickness becomes gradually thinner from a light incident end surface side toward the light guide plate body 35. On a light emission surface 39 of the light guide plate body 35, a plurality of emission prisms 40 are formed for changing a directional characteristic of light emitting from the light emission surface 39 in a width direction, and the emission prisms 40 extend in the direction vertical to the light incident end surface 36. A directional characteristic of the light transmitting through the emission prisms 40 and emitting is the same characteristic as the directional characteristic of light reflecting on an opposite surface of the light emission surface 39 and emitting from the light emission surface 39.

Description

  The present invention relates to a light guide plate and a surface light source device. Specifically, the present invention relates to a surface light source device, a light guide plate, and the like for efficiently making light incident on a light guide plate thinner than the height of the light source.

  In recent years, with the thinning of mobile devices incorporating a surface light source device, the surface light source device is also increasingly required to be thin. In order to reduce the thickness of the surface light source device, it is necessary to reduce the thickness of the light guide plate. However, even if the thickness of the flat light guide plate can be reduced, there is a limit to reducing the height of the light source composed of LEDs. Therefore, when a flat light guide plate is used, the height of the light source is larger than the thickness of the end face (light incident end face) of the light guide plate, and the light source is disposed to face the light incident end face of the light guide plate. Protrudes above the upper surface of the light guide plate. When the light source is thus projected above the light guide plate, all the light emitted from the light source does not enter the light incident end face of the light guide plate, and part of it leaks to the outside, resulting in poor light utilization efficiency.

  In order to solve such a problem, a light introducing portion having a thickness larger than that of the light guide plate main body is provided at the end of the flat light guide plate main body, and the light introducing portion is inclined toward the light guide plate main body from the maximum thickness portion. A light guide plate having an inclined surface provided on the upper surface of the light introducing portion may be used. According to such a light guide plate, the thickness of the end face (light incident end face) of the light introduction part is approximately the same as or larger than the height of the light source, so that the light from the light source is efficiently taken into the light introduction part and light introduction is performed. The light taken into the part can be guided to the thin light guide plate body.

  An example of a surface light source device using such a light guide plate is shown in FIG. In the drawing, the direction perpendicular to the light incident end face 16 is taken as the x direction, the direction perpendicular to the light exit face 18 is taken as the z direction, and the direction perpendicular to the x direction and the z direction is taken as the y direction. A surface light source device 11 illustrated in FIG. 1A includes a light source 12 and a light guide plate 13. The light guide plate 13 is formed by integrally forming a wedge-shaped light introducing portion 14 and a flat light guide plate body 15. On the upper surface of the light introducing portion 14, an inclined surface 17 that is inclined from the end on the light incident end surface side toward the light guide plate main body 15 is formed. On the upper surface of the light guide plate body 15, that is, the light emitting surface 18, lenticular lenses 19 extending in the direction (x direction) perpendicular to the light incident end surface 16 are arranged along the width direction (y direction). In the case of the light guide plate 13 having the light-introducing portion 14 having a wedge shape, the cross section perpendicular to the length direction of the lenticular lens 19 (the cross section parallel to the yz plane) is lenticular as shown in FIG. The angle α of the tangent line in contact with the end of the lens 19 is an arc of about 7.5 °. Further, a large number of fine prism-shaped deflection patterns 20 as shown in FIG. 2A are recessed on the lower surface of the light guide plate main body 15, and the length direction of each deflection pattern 20 is the light incident end face. 16 so as to be parallel to 16.

  According to such a surface light source device 11, the light incident into the light introducing portion 14 from the light incident end surface 16 is reflected between the lower surface of the light introducing portion 14 and the inclined surface 17 and guided to the light guide plate body 15. It is burned. Then, the light guided to the light guide plate body 15 is reflected by the deflection pattern 20 provided on the lower surface of the light guide plate 33 and is emitted from the light emitting surface 18. At this time, the light emitted from the light emitting surface 18 is transmitted through the lenticular lens 19, so that the directivity characteristic is narrowed in the width direction of the light guide plate 13. In addition, as a surface light source device having an optical pattern for emission, for example, there is one described in Patent Document 1 (however, no light introducing portion is provided).

  However, when the behavior of light in the surface light source device 11 as described above is examined in detail, the problem becomes clear. FIG. 2A is a perspective view of the prism-shaped deflection pattern 20 provided on the lower surface of the light guide plate. FIG. 2B is a diagram showing the directivity characteristics of the light that is totally reflected by the deflection pattern 20 and emitted from the smooth light emitting surface 18 as seen from the z direction. In the directional characteristic diagram, the light ray direction is represented as a point on the spherical surface. In the directional characteristic diagram, the direction of the light beam is indicated by a gray or black point, and the light ray direction (bright line) having the maximum intensity is represented by a black dot Q (the same applies to the following directional characteristic diagrams).

  When the light exit surface 18 of the light guide plate 13 is smooth (when the lenticular lens 19 is not provided), the direction of the light reflected from the deflection pattern 20 of FIG. As shown in FIG. 2B, the characteristic has a maximum intensity Q in a direction parallel to the zx plane (that is, light is emitted in the x direction when viewed from the z direction).

  However, when the lenticular lens 19 as shown in FIG. 1B is provided on the light exit surface 18, the directivity characteristics of the light transmitted through the lenticular lens 19 and emitted from the light exit surface 18 are as shown in FIG. become. That is, when viewed from the z direction, light is emitted in a direction inclined obliquely with respect to the x direction, and the light intensity becomes maximum in two directions inclined from the x direction across the zx plane. Thus, the directivity has a maximum intensity Q in two diagonal directions, and bright lines are generated in the diagonal direction. The conventional surface light source device 11 has a problem that the appearance of the screen of the liquid crystal display device is deteriorated when used as a backlight of a liquid crystal panel due to such bright lines.

JP 2012-142303 A

  An object of the present invention is to adapt the directivity characteristic of light transmitted through an outgoing optical pattern to the directivity characteristic of a deflection pattern provided on the light guide plate in a light guide plate having a light introducing portion.

  The light guide plate according to the present invention is provided with a light introduction part for confining light incident from an end face, and a thickness smaller than the maximum thickness of the light introduction part, and is continuous with the light introduction part. A light guide plate main body configured to emit light from the light output surface to the outside, and the light introducing portion is thicker than the light guide plate main body on at least one of the light output side surface and the opposite surface. In the light guide plate having an inclined surface inclined from the surface of the large portion toward the end of the light guide plate body, the light exit surface of the light guide plate body has a directivity characteristic of light emitted from the light exit surface. A plurality of emission optical patterns for changing in the width direction of the light guide plate body are formed, each of the emission optical patterns extends in a direction perpendicular to the end face, and is arranged in the width direction of the light emission surface, Output optical pattern Directional characteristics of light transmitted to the exit is, is characterized by being reflected by the opposite surface of the light emitting surface is a similar characteristic and directivity of light emitted from the light emitting surface.

  In the light guide plate according to the present invention, the directivity characteristic of the light transmitted through the output optical pattern is similar to the directivity characteristic of the light reflected from the opposite surface of the light output surface and output from the light output surface. Due to the characteristics, the bright line due to the light transmitted through the outgoing optical pattern becomes inconspicuous.

  In the light guide plate according to the present invention, the outgoing optical pattern may be formed of a curved surface having a cylindrical surface, may have a trapezoidal cross section, or may have a triangular cross section.

  In an embodiment of the light guide plate according to the present invention, a directivity conversion pattern in which ridge lines and valley lines are alternately arranged along the width direction is formed on at least one of the light emitting side surface and the opposite surface. It is characterized by being. According to this embodiment, it is possible to reduce light leakage from the inclined surface by providing the directivity conversion pattern.

  In particular, in this embodiment, the cross section of the directivity conversion pattern cut in parallel with the end face is positioned in front of the light source arranged to face the end face and has the same width as the light source. A portion in the region includes a slope connecting any one of the ridge lines of the directivity conversion pattern and one valley line adjacent to the ridge line, and the ridge line and the other valley line adjacent to the ridge line. It is preferable that the connecting slope is asymmetric with respect to a straight line passing through the ridge line and perpendicular to the light emitting surface, and at least one set of the asymmetric shape portions having different shapes is present on both sides of the light source center.

  Further, in the cross section of the directivity conversion pattern cut in parallel with the end face, in a region located in front of the light source and in a region having a width equal to the light source, on both sides of the light source center Respectively, the sum of the lateral widths of the slopes in which the normals are inclined toward the light source center side when the normals are set to the slopes connecting the adjacent ridge lines and valley lines of the directivity conversion pattern from the inside to the outside, It is desirable that the normal is larger than the sum of the lateral widths of the slopes inclined to the opposite side of the light source center.

  Further, in the cross section of the directivity conversion pattern cut parallel to the end face, the two adjacent slopes are located in front of the light source and in a region having the same width as the light source. It is desirable that the lateral width of the inclined surface in which the normal line is inclined toward the light source center side is larger than or equal to the lateral width of the inclined surface in which the normal line is inclined toward the side opposite to the light source center.

  In another embodiment of the light guide plate according to the present invention, the directivity conversion pattern is an array of pattern elements having a mountain shape or a V-groove shape, and the pattern element has a direction perpendicular to the end face. You may extend in parallel. Alternatively, the pattern elements may be arranged radially. Alternatively, the pattern elements may be aligned in parallel on both sides of the optical axis center, and may be inclined in opposite directions on both sides of the optical center when viewed from a direction perpendicular to the upper surface of the light guide plate body.

  The surface light source device according to the present invention includes the light guide plate according to the present invention and a light source for sending light to the end face of the light introducing portion of the light guide plate. In such a surface light source device, since the light guide plate according to the present invention is used, bright lines in an oblique direction can be suppressed.

  The liquid crystal display device according to the present invention is disposed so as to face the light guide plate according to the present invention, a light source for sending light to the end face of the light introducing portion of the light guide plate, and the light emitting surface of the light guide plate. It features a liquid crystal panel. In such a liquid crystal display device, since the light guide plate according to the present invention is used, the bright lines in the oblique direction can be suppressed, and the appearance of the screen is improved.

  The liquid crystal display device according to the present invention can also be used in mobile devices such as smartphones, tablet computers, electronic book readers, and electronic dictionaries.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. .

FIG. 1A is a perspective view showing a conventional surface light source device. FIG. 1B is an enlarged cross-sectional view of a lenticular lens formed on the surface of the light guide plate in the surface light source device of FIG. FIG. 2A is a perspective view of a deflection pattern formed on the back surface of the light guide plate. FIG. 2B is a simulation diagram showing the emission directivity characteristics of light that is reflected by the deflection pattern and emitted from a smooth light exit surface. FIG. 3 is a simulation diagram showing the emission directivity characteristics of light emitted from the surface of the light guide plate of the surface light source device shown in FIG. FIG. 4A is a perspective view showing the surface light source device according to Embodiment 1 of the present invention. FIG. 4B is an enlarged cross-sectional view of the output prism formed on the surface of the light guide plate in the surface light source device of FIG. FIG. 5 is a simulation diagram illustrating the emission directivity characteristics of light that passes through the emission prism and is emitted from the surface of the light guide plate in the surface light source device of the first embodiment. FIG. 6A is a schematic cross-sectional view showing a liquid crystal display device using a surface light source device. FIG. 6B is a perspective view showing a part of the two prism sheets stacked on the light emitting surface. FIG. 6C is a perspective view showing one deflection pattern provided on the back surface of the light guide plate. FIG. 7A to FIG. 7E are simulation diagrams showing the emission directivity characteristics when the tangent angle is changed from 10 ° to 50 °. 8A to 8C are schematic views showing different cross-sectional shapes of the emission optical pattern. FIG. 9 is a perspective view showing a part of the surface light source device according to Embodiment 2 of the present invention. FIG. 10 is a perspective view of a surface light source device according to Embodiment 3 of the present invention. FIG. 11 is a cross-sectional view of the directivity conversion pattern in front of the light source, and a part thereof is enlarged and shown. FIG. 12A is an operation explanatory diagram of the directivity conversion pattern shown in FIG. FIG. 12B is a schematic cross-sectional view showing different cross-sectional shapes of the directivity conversion pattern shown in FIG. FIG. 13A is a plan view showing another modification of the third embodiment. FIG. 13B is a plan view showing still another modification of the third embodiment. FIG. 14A is a directional characteristic diagram of a simple light guide plate viewed from the x direction. FIG. 14B is a directional characteristic diagram of the light guide plate in which the directivity conversion pattern is formed on the inclined surface, as viewed from the x direction. FIG. 15 is a vector diagram of the outgoing optical pattern with a tangent angle of 7.5 °. FIG. 16A is a vector diagram of an outgoing optical pattern with a tangent angle of 40 °. FIG. 16B is a vector diagram of an outgoing optical pattern with a tangent angle of 50 °. FIG. 17A to FIG. 17D are diagrams for explaining the relationship between a directivity diagram and a vector diagram. FIG. 18 is a perspective view of a surface light source device according to Embodiment 4 of the present invention. FIG. 19 is a front view of a smartphone according to the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention.

(Embodiment 1)
The surface light source device according to Embodiment 1 of the present invention will be described below with reference to FIG. FIG. 4A is a perspective view showing the surface light source device 31 according to Embodiment 1 of the present invention. FIG. 4B is an enlarged cross-sectional view of the output prism 40 (output optical pattern) formed on the surface of the light guide plate of the surface light source device 31. In the following, the direction perpendicular to the light incident end face 36 is defined as the x direction, the direction perpendicular to the light emitting surface 39 is defined as the z direction, and the direction perpendicular to the x direction and the z direction is defined as the y direction.

  The surface light source device 31 includes a light source 32 and a light guide plate 33. The light source 32 incorporates one or a plurality of LEDs, and emits white light from the front light exit window. This light source 32 may be called a point light source.

  The light guide plate 33 is formed by integrally forming a light introducing portion 34 at an end portion of the light guide plate main body 35. The light guide plate 33 is formed of a transparent resin having a high refractive index such as an acrylic resin, a polycarbonate resin (PC), a cycloolefin material, or polymethyl methacrylate (PMMA).

  The light introducing portion 34 has a wedge shape, and the thickness gradually decreases toward the light guide plate main body side. That is, the end portion on the light incident end surface side of the upper surface of the light introducing portion 34 is a horizontal plane 37, and a smooth inclined surface 38 is formed from the end of the horizontal plane 37 to the end of the light guide plate body 35. The inclined surface 38 extends in a band shape from one side surface of the light guide plate 33 to the other side surface, and is inclined downward from the end of the horizontal surface 37 toward the end of the light guide plate body 35.

  The light guide plate body 35 has a flat plate shape in which the front surface and the back surface are parallel. The light guide plate body 35 has a substantially uniform thickness, and the thickness of the light guide plate body 35 is thinner than the maximum thickness of the light introducing portion 34. The light guide plate body 35 occupies most of the area of the light guide plate 33. The upper surface of the light guide plate main body 35 is a light emitting surface 39, and on the surface opposite to the light emitting surface 39, a fine deflection pattern 42 having a conical shape as shown in FIG. 6C or as shown in FIG. A large number of fine prism-shaped deflection patterns 20 are formed. The directivity characteristic of the light reflected from the conical deflection pattern 42 and emitted from the light exit surface 39 as shown in FIG. 6C is obtained when the light exit surface 39 of the light guide plate 33 is smooth (the exit prism 40). 2), the maximum intensity Q is generated in a direction parallel to the zx plane (that is, light is emitted in the x direction when viewed from the z direction). ) In the following description, the deflection pattern is described as the conical deflection pattern 42, but may be a prism-shaped deflection pattern 20. Further, instead of the deflection patterns 42 and 20, a wedge-shaped light guide plate that gradually becomes thinner as the distance from the light source 32 may be used.

  On the light exit surface 39 of the light guide plate body 35, an exit optical pattern, that is, an exit prism 40 extending in a direction (x direction) perpendicular to the light incident end surface 36, extends along the width direction (y direction) of the light guide plate body 35. Are arranged. A cross section (cross section parallel to the yz plane) perpendicular to the length direction (x direction) of the output prism 40 is an isosceles triangle, and a tangent angle α (hereinafter referred to as a tangent angle) in contact with the end of the output prism 40. That is, the angle of the hypotenuse shown in FIG. 4B is 40 ° or more and 50 ° or less.

  In addition, a reflection sheet 41 for reflecting light leaking from the lower surface of the light guide plate 33 and returning it into the light guide plate 33 is disposed on the lower surface of the light guide plate 33.

  Even in the surface light source device 31, the same light behavior as that of the surface light source device 11 shown in FIG. However, in the surface light source device 31, the tangent angle α of the output prism 40 is 40 ° or more and 50 ° or less. Therefore, the directivity characteristic of the light transmitted through the output prism 40 and output from the light output surface 39 has the maximum intensity Q in the direction parallel to the zx plane as shown in FIG. 5 (that is, the x direction as viewed from the z direction). Light is emitted). Therefore, even if the emission prism 40 is provided on the light emission surface 39, light is emitted in the same direction as when the emission prism 40 is not provided, and the emission light is not recognized as a bright line.

  FIG. 6A is a schematic cross-sectional view showing a liquid crystal display device 51 using the surface light source device 31. A reflection sheet 41 is disposed on the lower surface of the light guide plate 33. In addition, two prism sheets 52 and 53 and a diffusion sheet 54 are sequentially stacked on the upper surface of the light emitting surface 39, and a liquid crystal panel 55 is installed thereon. The prism sheets 52 and 53 are obtained by arranging fine prism patterns having a triangular cross section in parallel. As shown in FIG. 6B, the prism sheets 52 and 53 are arranged so that the directions of the prism patterns are orthogonal to each other. Is superimposed on.

  The light L emitted from the light emitting surface 39 in the x direction by being totally reflected by the deflection pattern 42 is transmitted through the two prism sheets 52 and 53 as shown in FIG. They are aligned in a direction perpendicular to the surface 39 and then spread to an appropriate directivity angle by the diffusion sheet 54. As a result, the back surface of the liquid crystal panel 55 can be illuminated from the vertical direction, and the screen of the liquid crystal panel 55 can be clearly seen within an appropriate range with the front surface of the liquid crystal panel 55 as the center.

  Since the surface of the output prism 40 is inclined, a part of the light guided through the light guide plate 33 leaks directly from the output prism 40 even if it is not totally reflected by the deflection pattern 42. However, if the tangent angle of the output prism 40 is 40 ° to 50 °, the light leaking from the output prism 40 is directed in the x direction as shown in FIG. 5, and therefore the same as the output light totally reflected by the deflection pattern 42. As described above, the light is converted into light in a direction perpendicular to the light emitting surface 39 by the prism sheets 52 and 53 and used for illumination. Therefore, according to the liquid crystal display device 51 using the surface light source device 31 of the present embodiment, the appearance of the screen can be improved.

(simulation result)
FIG. 5 is a simulation diagram showing a state in which the emission directivity characteristic of the light emitted from the light emitting surface 39 of the surface light source device 31 is viewed from the z direction. FIG. 5 shows a case where the tangent angle α of the output prism 40 is 50 °. As can be seen from FIG. 5, in the surface light source device 31 of the first embodiment, the light transmitted through the emission prism 40 and emitted from the light emission surface 39 is narrowed in the width direction of the light guide plate 33 and the direction Q of maximum intensity is It faces the x direction. Therefore, the directivity characteristic of the light transmitted through the output prism 40 having a tangent angle α of 50 ° is such that no bright line is generated in two oblique directions as in the lenticular lens 19 having a tangent angle α of 7.5 ° (see FIG. 3). The directional characteristics of the light totally reflected by the deflection pattern 42 (see FIG. 2B) have the same characteristics.

  FIGS. 7A to 7E show the emission directivity characteristics when the tangent angle α of the emission prism 40 is changed to 10 °, 20 °, 30 °, 40 °, and 50 °, respectively. As can be seen from FIGS. 7A to 7E, when the tangent angle α is 10 ° to 30 °, the distribution of the light emission direction is constricted across the x direction, and the emitted light intensity is Locations with maximum light intensity Q are generated in two oblique directions inclined from the x direction, and bright lines are generated. On the other hand, when the tangent angle α is 40 ° to 50 °, the distribution in the light emission direction is gathered in the x direction, and the maximum light intensity Q is generated only in the x direction. Therefore, from this simulation result, it can be seen that if the tangent angle of the output prism 40 is set to 40 ° or more and 50 ° or less, the same directivity characteristic as the light totally reflected by the deflection pattern 42 can be obtained.

(Other cross-sectional shape of outgoing optical pattern)
FIG. 4B shows an outgoing optical pattern having a triangular section, that is, an outgoing prism 40. The outgoing optical pattern is a lenticular lens having a tangent angle α of 40 ° or more and 50 ° or less as shown in FIG. 8A. 56 may be used. 8B may be an emission optical pattern 57 having a trapezoidal cross section with a tangent angle α of 40 ° or more and 50 ° or less, and the tangent angle α as shown in FIG. 8C is 40 ° or more. The outgoing optical pattern 58 having a polygonal cross section of 50 ° or less may be used. The trapezoidal emission optical pattern 57 reflects light that hits a flat surface as indicated by a broken line in FIG. 8B.

(Embodiment 2)
FIG. 9 is a schematic perspective view showing a part of the surface light source device 61 according to Embodiment 2 of the present invention, that is, a part of the light incident end face 36 of the light source 32 and the light guide plate 33. In the surface light source device 61, a diffusion pattern 62 is arranged in a portion of the light incident end face 36 facing the light source 32. The diffusion pattern 62 is, for example, a convex portion such as an arc shape or a prism shape, and extends from the upper end to the lower end of the light incident end surface 36. Further, the diffusion patterns 62 are arranged in the width direction of the light incident end face 36. If the diffusion pattern 62 is provided on the light incident end face 36, the light from the light source 32 can be spread laterally when entering the light guide plate 33 from the light incident end face 36. Can send. Although not shown in FIG. 9, also in this embodiment, the light output surface 39 is provided with an output optical pattern having a tangent angle of 40 ° to 50 °.

(Embodiment 3)
FIG. 10 is a perspective view of a surface light source device 71 according to Embodiment 3 of the present invention. In the surface light source device 71 of the third embodiment, a directivity conversion pattern 72 including a plurality of pattern elements 73 is formed on the inclined surface 38. The pattern element 73 has a chevron shape or a V-groove shape.

  FIG. 11 shows a cross-sectional shape of the directivity conversion pattern 72 formed in the surface light source device 71. That is, FIG. 11 shows an area (in other words, a light source width W) that is located in front of the light source 32 and has a width equal to the light source 32 (light source width W) in the cross section of the directivity conversion pattern 72 cut parallel to the light incident end face 36. , A portion within the area W / 2 from the light source center C to the left and right sides). Here, the light source center C is a plane that passes through the light emission center of the light source 32 and is perpendicular to the light incident end surface 36 and the light emitting surface 39 of the light guide plate 33. The light source width W does not mean the width of the light source 32 package, but the width of the light emitting surface (light exit window). In FIG. 11, the directivity conversion pattern 72 has a symmetrical shape with respect to the light source center C, but is not necessarily symmetrical.

  In the surface light source device 71 of the third embodiment, the directivity conversion pattern 72 has an asymmetric shape in the region of the light source width W in a cross section parallel to the light incident end surface 36. The region outside the light source width W may have the same structure as the region of the light source width W, but since the amount of light and light intensity supplied are small in the region away from the light source 32, the light source width W In particular, the structure of the directivity conversion pattern 72 is not limited.

  In the region of the light source width W in the cross section parallel to the light incident end face 36, most or all of the pattern elements 73 constituting the directivity conversion pattern 72 have an asymmetric shape. That is, a pattern slope 74 a connecting a certain ridge line (maximum point of the cross section) and one valley line (minimum point of the cross section) adjacent to the ridge line, and the other valley line (minimum of the cross section) adjacent to the ridge line and the ridge line. The pattern slope 74b connecting the point) is asymmetrical with respect to a straight line passing through the ridge line and perpendicular to the light emitting surface 39. However, some of the pattern elements 73 (for example, the pattern element at the position of the light source center C) may be symmetrical. Here, the pattern slopes 74a and 74b are surfaces of the directivity conversion pattern 72 located between adjacent ridge lines and valley lines. In the directivity conversion pattern 72 shown in FIG. 11, the pattern slopes 74a and 74b are flat surfaces, but may be curved surfaces or bent surfaces.

  In the light source center C and a region W / 2 to the left from there (hereinafter referred to as the left region of the light source center C), the normal line N extends from the inside of the light guide plate 33 to the outside of the pattern inclined surfaces 74a and 74b. Is the sum of the lateral widths D2 of the pattern slopes 74b in which the normal line N is inclined toward the light source center side (the total value in the left region of the width W / 2 of the lateral width D2 of each pattern slope 74b) is the normal line N2 Is larger than the sum of the lateral widths D1 of the pattern slopes 74a inclined to the opposite side of the light source center (the total value in the left region of the width W / 2 of the width D1 of each pattern slope 74a).

  Similarly, in the light source center C and the area W / 2 on the right side from the light source center C (hereinafter referred to as the right area of the light source center C), the pattern slopes 74a and 74b are directed from the inside of the light guide plate 33 to the outside. When the normal line N is set, the sum of the lateral widths D2 of the pattern slopes 74b inclined toward the light source center side (the total value of the lateral widths D2 of the respective pattern slopes 74b in the right region of the width W / 2) However, the sum of the width D1 of the pattern slope 74a in which the normal N is inclined to the side opposite to the light source center (the total value in the right region of the width W / 2 of the width D1 of each pattern slope 74a) is larger. .

  In order to realize such a configuration, in two adjacent pattern slopes 74a and 74b (pattern elements), the horizontal width D2 of the pattern slope 74b in which the normal line N is inclined toward the light source center side, and the normal line N is the light source. It may be larger than the lateral width D1 of the pattern slope 74a inclined to the opposite side of the center or the same in part. It is only necessary that at least a part of the pattern elements 73 in the region of the light source width W satisfy this condition. It is preferable that as many pattern elements 73 as possible satisfy this condition, but not all pattern elements 73 are required.

  As a different form of the directivity conversion pattern 72 in the third embodiment, as shown in FIG. 12B, the cross section of each pattern element 73 may be symmetrical. FIG. 12B shows the behavior of light emitted from the light emission center 32a in the directivity conversion pattern 72 including the pattern elements 73 having a symmetric cross-sectional shape. In this case, out of the light emitted from the light emission center 32 a, the light emitted forward from the light emission center 32 a is reflected by the directivity conversion pattern 72, so that it is difficult to leak from the inclined surface of the pattern element 73. However, when the pattern element 73 has a symmetric cross-sectional shape, the light emitted obliquely from the light emission center 32a is external from the inclined surface of the pattern element 73 as light L indicated by a broken line in FIG. Easy to leak. That is, as the position incident on the directivity conversion pattern 72 becomes far from the light source center C, the light gradually enters the surface near the surface of the directivity conversion pattern 72 at an angle close to the vertical. Leaks easily and light loss increases.

  On the other hand, in the directivity conversion pattern 72 shown in FIG. 11, in each of the left and right regions of the light source center C, the sum of the lateral widths D2 of the pattern slopes 74b in which the normal line N is inclined toward the light source center side. The sum of the lateral widths D1 of the pattern slopes 74a inclined to the side opposite to the light source center is larger. In particular, in many pattern elements 73, the width D2 of the pattern slope 74b in which the normal line N is inclined toward the light source center side is larger than the width D1 of the pattern slope 74a in which the normal line N is inclined to the side opposite to the light source center. Or it is the same in some pattern elements.

  As a result, as shown in FIG. 12A, the area of the pattern slope 74a on which the light L1 emitted obliquely from the light emission center 32a is incident at an angle close to vertical is a directional conversion pattern ( Compared to the case of FIG. 12 (B)), it becomes narrower and light does not easily leak from the pattern slope 74a. Furthermore, since the inclination angle of the pattern slope 74a in which the normal N is inclined to the side opposite to the light source center C is increased, the pattern slope pattern 74a is incident on the pattern slope 74a as compared with the case where the pattern elements of the directivity conversion pattern are symmetrical. The incident angle of the light L1 is increased, and the light L1 is less likely to leak from the pattern slope 74a. As a result, according to the directivity conversion pattern 72 including the pattern element 73 having an asymmetric cross section as shown in FIG. 12A, the directivity including the pattern element 73 having a symmetrical cross section as shown in FIG. Compared with the conversion pattern 72, light leakage from the directivity conversion pattern 72 can be suppressed, and the light use efficiency is improved.

(Modification of Embodiment 3)
In the directivity conversion pattern 72 shown in FIG. 11, pattern elements having the same cross-sectional shape are repeatedly arranged in the left and right regions of the light source center C, but the cross-sectional shape of each pattern element is changed to the light source center C. You may change according to the distance from.

  Further, the pattern slopes 74a and 74b of the directivity conversion pattern 72 are not necessarily flat, and may be curved surfaces or bent surfaces.

  Further, the apex angle ω of the pattern elements 73 shown in FIG. 11 is preferably constant for each pattern element 73. This is because, if the apex angle ω is constant, it is easy to process a molding die for molding the directivity conversion pattern 72.

  The directivity conversion pattern having the cross-sectional shape as in the third embodiment is described in detail in International Application: PCT / JP2012 / 56182. Various variations described in the international application can be applied to the surface light source device 71 of the third embodiment.

  In the surface light source device 71 shown in FIG. 10, the pattern elements 73 are arranged in parallel to each other, but the pattern elements 73 may be inclined with respect to a direction perpendicular to the light incident end face 36. For example, in the surface light source device 76 shown in FIG. 13A, the pattern elements 73 are tilted in opposite directions on the left and right of the light source center, and the pattern elements 73 are arranged in a V shape. In the surface light source device 77 shown in FIG. 13B, the pattern elements 73 are radially arranged around the light source center or a point near the light source center.

(Explanation using vector diagram)
Next, in the case of the surface light source device 71 in which the directivity conversion pattern 72 is provided on the inclined surface 38 as shown in FIG. 10, if the tangent angle of the emission optical pattern is 40 ° or more and 50 ° or less, from the emission prism 40. The reason why the leaking light is directed in the x direction will be described using a vector diagram. FIG. 14A and FIG. 14B are diagrams in which a directional characteristic diagram (a diagram in which the light beam direction is represented by a point on the spherical surface R) showing the light beam direction in the light guide plate is viewed from the x direction. The inner circle r represents the limit of light leaking from the light emission surface when the emission optical pattern is provided on the light emission surface (hereinafter, this inner circle is referred to as a critical reflection angle circle r). That is, a light ray inside the critical reflection angle circle r (that is, light having an angle smaller than the critical reflection angle with respect to the x direction) is totally reflected by the outgoing optical pattern, but outside the critical reflection angle circle r. (That is, light having an angle larger than the critical reflection angle with respect to the x direction) leaks from the outgoing optical pattern to generate bright lines.

  FIG. 14A shows the directivity characteristics of light incident from the light incident end face in a thin rectangular parallelepiped light guide plate (simple light guide plate) whose front and back surfaces are parallel. In the case of a simple light guide plate, the light incident on the light guide plate is in the circle r of the critical reflection angle, so that even if an output optical pattern is provided on the light guide plate, no light leaks from the output optical pattern, and the bright line Does not occur.

  FIG. 14B shows a light introduction part in the light guide plate 33 in which the light introduction part 34 having a wedge shape is provided at the end of the light guide plate body 35, and the directivity conversion pattern 72 is formed on the inclined surface 38 of the light introduction part 34. The directivity characteristic of the light which passed 34 and was guide | induced to the light-guide plate main body 35 is represented. In the case of such a light guide plate 33, since the light is totally reflected by the directivity conversion pattern 72, the light rays are out of the critical reflection angle circle r in the diagonal region g. Produce.

  FIG. 15 is a vector diagram of the outgoing optical pattern with a tangent angle of 7.5 °. FIG. 16A is a vector diagram of an outgoing optical pattern with a tangent angle of 40 °. FIG. 16B is a vector diagram of an outgoing optical pattern with a tangent angle of 50 °. First, the relationship between the directivity diagram of FIG. 14 and the vector diagram will be described.

  17A is a directional characteristic diagram viewed from the x direction, FIG. 17B is a directional characteristic diagram viewed from the z direction, and FIG. 17C is a directional characteristic diagram viewed from the y direction. Here, a broken-line circle drawn on the surface of the spherical surface R is a circle r having a critical reflection angle. The small concentric spherical surface s inside the spherical surface R is a spherical surface having a radius 1 / n times that of the spherical surface R (n is the refractive index of the light guide plate). For example, if the refractive index n of the light guide plate is 1.59, the radius of the spherical surface R is 1.59 and the radius of the spherical surface s is 1. The vector diagram is a cut surface obtained by cutting the directional characteristic diagram of FIG. 17A along a plane passing through the circle r having a critical reflection angle. That is, the vector diagram obtained from FIGS. 17A to 17C is as shown in FIG. In the vector diagram, a region outside the circle r having a critical reflection angle, that is, a region where light leaks out from the outgoing optical pattern is shown on the outer circle R (r). For example, in the case of a light guide plate having a directivity conversion pattern provided on an inclined surface, light leaks in a diagonal direction as shown in FIG. 14 (B), and therefore, on a circle R (r) outside the vector diagram. As shown in FIG. 17D, a region g is indicated by a thick line.

  In this way, in the vector diagram, the direction of the light beam transmitted through the output optical pattern and output to the outside is represented by a region on the inner circle s. For example, in the case of transmitting an outgoing optical pattern having a tangent angle of 7.5 °, the light in the region D1 on the outer circle R (r) is the region on the inner circle s as shown in FIG. Move to D2. As a result, the light transmitted through the emission optical pattern is separated and emitted in a direction inclined from the x direction. Therefore, the directivity characteristic of the light emitted from the outgoing optical pattern is as shown in FIG.

  On the other hand, when the transmission optical pattern with a tangent angle of 40 ° is transmitted, the degree of light refraction is larger than when the transmission optical pattern with a tangent angle of 7.5 ° is transmitted. The light in the region D1 above (r) moves to the region D2 above the inner circle s as shown in FIG. That is, the region D2 that has been separated to the left and right is bonded to become one. As a result, the light that passes through the emission optical pattern is emitted in the x direction.

  Further, in the case of transmitting the outgoing optical pattern having a tangent angle of 50 °, the light in the region D1 on the outer circle R (r) is on the inner circle s as shown in FIG. Move to region D2. That is, the left and right regions D2 overlap to become one. As a result, the light that passes through the emission optical pattern is emitted in the x direction. Therefore, the directivity characteristic of the light emitted from the outgoing optical pattern is as shown in FIG. Therefore, the tangent angle α of the outgoing optical pattern may be set to 40 ° or more and 50 ° or less. However, since the shapes of the directivity conversion pattern 72 and the diffusion pattern 62 are optimally designed as appropriate according to the type of the light source and the like, the directivity characteristics of the light guided to the light guide plate body 35 have a certain width depending on the design shape. become. Therefore, the tangent angle α may be 40 ° or less or 50 ° or more.

(Embodiment 4)
FIG. 18 is a perspective view showing a surface light source device 81 according to Embodiment 4 of the present invention. In the surface light source device 81, a plurality of light sources 32 are used for one light guide plate 33. That is, a plurality of light sources 32 are arranged at regular pitches so as to face the light incident end face 36 of the light guide plate 33. An output optical pattern such as an output prism 40 is formed on the light output surface 39 of the light guide plate body 35. According to the fourth embodiment, a surface light source device having a large illumination area can be manufactured. The light guide plate structure that is the basis of the surface light source device 81 may be any of the light guide plates of the above embodiments.

(Embodiment 5)
FIG. 19 is a plan view of a mobile device using the surface light source device or the liquid crystal display device of the present invention, that is, a smartphone 91, and includes a liquid crystal display device 92 with a touch panel on the front. If the surface light source device of the present invention is used for such a smartphone 91, eyeball-like light emission and bright lines are less likely to occur, so the quality of the display screen is improved. The surface light source device of the present invention can be applied to mobile devices such as tablet computers, electronic dictionaries, and electronic book readers in addition to mobile phones such as smartphones.

31, 61, 71, 76, 77, 81 Surface light source device 32 Light source 33 Light guide plate 34 Light introducing portion 35 Light guide plate main body 36 Light incident end surface 38 Inclined surface 39 Light exit surface 40 Emitting prism 42 Deflection pattern 51 Liquid crystal display device 56 Lenticular Lens 57, 58 Output optical pattern 62 Diffusion pattern 72 Directivity conversion pattern 73 Pattern element 91 Smartphone

Claims (14)

A light introduction part for confining light incident from the end face;
A light guide plate main body that is provided to be continuous with the light introducing portion with a thickness smaller than the maximum thickness of the light introducing portion and to allow incident light to be emitted from the light emitting surface to the outside;
The light introduction part has an inclined surface inclined toward the end of the light guide plate body from the surface of the portion having a larger thickness than the light guide plate body on at least one of the light emitting side surface and the opposite surface. Having a light guide plate,
On the light exit surface of the light guide plate body, a plurality of output optical patterns for changing the directivity characteristics of light exiting from the light exit surface in the width direction of the light guide plate body are formed.
The emission optical patterns each extend in a direction perpendicular to the end surface, and are arranged in the width direction of the light emission surface,
The directivity characteristic of the light transmitted through the emission optical pattern is similar to the directivity characteristic of the light reflected from the opposite surface of the light emission surface and emitted from the light emission surface. Light guide plate.   The light guide plate according to claim 1, wherein a surface of the outgoing optical pattern is configured by a cylindrical curved surface.   The light guide plate according to claim 1, wherein a cross section of the outgoing optical pattern is formed in a trapezoidal shape.   The light guide plate according to claim 1, wherein the outgoing optical pattern has a triangular cross section.   The directivity conversion pattern in which ridge lines and valley lines are alternately arranged along the width direction is formed on at least one of the light emission side surface and the opposite surface thereof. The light guide plate described.   Of the cross section of the directivity conversion pattern cut in parallel with the end face, a portion located in front of the light source disposed to face the end face and in a region having a width equal to the light source is A slope connecting one of the ridge lines of the directivity conversion pattern and one valley line adjacent to the ridge line, and a slope connecting the ridge line and the other valley line adjacent to the ridge line, The light guide plate according to claim 5, wherein the light guide plate is asymmetric with respect to a straight line perpendicular to the light exit surface, and at least one set of the asymmetric shape portions having different shapes is present on both sides of the light source center. . Of the cross section of the directivity conversion pattern cut parallel to the end face, in a portion located in front of the light source and in a region having the same width as the light source,
In the regions on both sides of the center of the light source, the slope in which the normal line is inclined toward the light source center side when a normal is made to the slope connecting the adjacent ridge line and valley line of the directivity conversion pattern from the inside to the outside. The light guide plate according to claim 6, wherein a total sum of lateral widths of the light guides is larger than a sum of lateral widths of slopes whose normals are inclined to the side opposite to the light source center. Of the cross section of the directivity conversion pattern cut parallel to the end face, in a portion located in front of the light source and in a region having the same width as the light source,
The two adjacent slopes are such that the width of the slope whose normal is inclined toward the light source center is greater than or equal to the width of the slope whose normal is inclined opposite to the light source center. The surface light source device according to claim 7, wherein the surface light source device is characterized.   2. The directivity conversion pattern is an array of pattern elements having a mountain shape or a V-groove shape, and the pattern elements extend in parallel with a direction perpendicular to the end face. The light guide plate described in 1.   The light guide plate according to claim 1, wherein the directivity conversion pattern is an array of pattern elements having a mountain shape or a V-groove shape, and the pattern elements are radially arranged.   The directivity conversion pattern is an array of pattern elements having a mountain shape or V-groove shape, and the pattern elements are aligned in parallel on both sides of the center of the optical axis and perpendicular to the upper surface of the light guide plate body. The light guide plate according to claim 1, wherein the light guide plates are inclined in opposite directions on both sides of the optical center when viewed from a different direction. The light guide plate according to any one of claims 1 to 11,
A light source for sending light to the end face of the light introducing portion in the light guide plate;
A surface light source device. The light guide plate according to any one of claims 1 to 11,
A light source for sending light to the end face of the light introducing portion in the light guide plate;
A liquid crystal panel disposed to face the light exit surface of the light guide plate;
A liquid crystal display device.   A mobile device comprising the liquid crystal display device according to claim 13.

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