JP5267692B2 - Light guide plate and liquid crystal display device - Google Patents

Description

  The present invention relates to a light guide plate and a liquid crystal display device. Specifically, the present invention relates to a light guide plate used for a backlight or the like, and also relates to a liquid crystal display device using the light guide plate for a surface light source device such as a backlight.

  As a surface light source device used as a backlight of a liquid crystal panel, there is one disclosed in Patent Document 1. The surface light source device disclosed in Patent Document 1 is shown in FIG.

  In this surface light source device, a corner portion of a rectangular light guide plate 11 is cut obliquely, or an edge of the light guide plate 11 is cut into a V-groove to form an inclined surface 12 that is inclined obliquely. A light source 13 with high directivity is disposed opposite to the light source 12. In Patent Document 1, such a configuration prevents bright unevenness and dark unevenness from occurring alternately on the surface of the light guide plate even when a highly directional light source is used.

  However, in a backlight (surface light source device) used for a liquid crystal panel such as a mobile phone, the size and aspect ratio of the light emitting surface are different depending on each model. Furthermore, even if the light emitting surface has the same size, in general, the light emitting surface is actually slightly different in size. (For example, even if the size is the same 3 inches, the dimensions of the light emitting surface are slightly different depending on the model of the mobile phone.)

  Therefore, in the backlight for such applications, not only when the light emitting surface size is different, but also when the light emitting surface size is the same, the light guide plate must be used each time when designing individual models. It was necessary to optimize the dimensions and the arrangement of the light sources. Further, if the arrangement of the light sources is changed, the optical pattern provided on the back surface of the light guide plate has to be redesigned so that the light emission luminance becomes uniform. Therefore, when manufacturing backlights of different sizes, it has been necessary to redesign the light guide plate with enormous costs and time.

  In addition, the light guide plate of the backlight is a resin molded product, and is usually manufactured by injection molding, so even if the light guide plate's outer dimensions and light emitting surface size are slightly different, a dedicated mold is produced each time. There is a need. In addition, when a new molding die is produced, the density and shape of the optical pattern formed on the die piece on the back surface of the light guide plate must be adjusted each time so that uniform light emission luminance can be obtained. . Therefore, enormous labor and time are required for mold production, and enormous costs are required.

JP 2002-82625 A

  The present invention has been made in view of such technical problems, and the object is to prepare an original light guide plate and cut the original light guide plate according to the application. It is related with the light guide plate which can obtain the light guide plate of the size according to a request | requirement, and also made it possible to equalize the luminance distribution of the light emission surface. Furthermore, the present invention relates to a liquid crystal display device using this light guide plate for a surface light source device.

  The light guide plate according to the present invention is effective when it is scheduled to be used by cutting one side surface or both side surfaces, and is arranged with a light incident surface facing a plurality of point light sources arranged in a row. A light guide plate designed in advance so as to obtain uniform brightness in the light emitting area, and a plurality of errors from the uniform brightness in the effective light emitting area caused by cutting one side or both side faces. The distance of the light incident surface or the angle of the light incident surface with respect to a point light source located at the end of the point light source is modified by making it different from that before cutting.

  In the light guide plate of the present invention, a light guide plate having an arbitrary size smaller than the original light guide plate can be easily produced by cutting the original light guide plate. In other words, if there is an original light guide plate, it is possible to easily produce light guide plates of various sizes simply by changing the cut-out shape from the original light guide plate without producing a new light guide plate mold. . In addition, although the original light guide plate is cut to an arbitrary size, the distance of the light incident surface or the angle of the light incident surface with respect to the point light source located at the end of the plurality of point light sources is different from that before the cut. By making it, the luminance distribution on the light emitting surface of the cut light guide plate can be made uniform. Therefore, the delivery time of the light guide plate can be shortened and the cost of the light guide plate can be reduced. Furthermore, it becomes possible to flexibly cope with design changes at the product development stage. In addition, backlights of various sizes can be manufactured with one type of light guide plate as a base, and backlights with uniform brightness can be obtained.

  In an embodiment of the light guide plate according to the present invention, the distance between the point light source located at the end and the light incident surface differs according to the distance from the point light source located at the end to the side surface close to the point light source. It is characterized by that. According to this embodiment, it is possible to control the direction of the light incident on the point where the distance between the point light source located at the end and the light incident surface is different, and the luminance distribution on the light emitting surface can be made uniform.

  In another embodiment of the light guide plate according to the present invention, a distance between the point light source located at the end and the light incident surface is a point light source that is not located at the end of the plurality of point light sources, and the light incident surface. It is characterized by being larger than the distance. According to such an embodiment, since the brightness of the corner portion of the light emitting surface can be lowered, the distance between the end point light source and the side surface of the light guide plate (hereinafter referred to as the overhang distance) is the light incident surface processed. This is effective when the distance is shorter than the overhang distance (hereinafter referred to as the appropriate overhang distance) when a uniform luminance distribution is obtained when the straight line is straight.

  In another embodiment of the light guide plate according to the present invention, the distance between the point light source located at the end and the light incident surface is a point light source that is not located at the end of the plurality of point light sources and the light incident surface. It is characterized by being smaller than the distance. According to this embodiment, the brightness of the corner portion of the light emitting surface can be increased, which is effective when the overhang distance is longer than the appropriate overhang distance.

  Yet another embodiment of the light guide plate according to the present invention is characterized in that the distance between the point light source located at the end and the light incident surface increases as the distance from the side surface close to the point light source increases. According to such an embodiment, the brightness of the corner portion of the light emitting surface can be lowered, which is effective when the overhang distance is shorter than the appropriate overhang distance.

  Yet another embodiment of the light guide plate according to the present invention is characterized in that the distance between the point light source located at the end and the light incident surface becomes smaller as approaching the side surface close to the point light source. According to this embodiment, the brightness of the corner portion of the light emitting surface can be increased, which is effective when the overhang distance is longer than the appropriate overhang distance.

  In another embodiment of the light guide plate according to the present invention, the position where the distance between the point light source located at the end and the light incident surface starts to change is the position of the point light source located at the end of the light incident surface. It is characterized by being in a region facing the light emitting surface. According to this embodiment, a part of the light emitted from the end point light source can be used as a normal point light source, and the other light can be used for luminance unevenness adjustment.

  In another embodiment of the light guide plate according to the present invention, the position where the distance between the point light source located at the end and the light incident surface starts to change is the position of the point light source located at the end of the light incident surface. It is characterized by being located farther from the side surface closer to the point light source than the region facing the light emitting surface. According to such an embodiment, all of the light emitted from the end point light source can be used for luminance unevenness adjustment, and the effect of brightness unevenness adjustment is enhanced.

  Still another embodiment of the light guide plate according to the present invention is characterized in that the plurality of point light sources are all directed in the same direction and arranged along the same straight line. According to such an embodiment, control of light emitted from each point light source is facilitated.

  In another embodiment of the light guide plate according to the present invention, the angle when the upper surface and the lower surface of the light incident surface are viewed from the point light source in a cross section perpendicular to the light incident surface and the light output surface is the point light source. The distance between the point light source located at the end and the light incident surface is determined so as to be narrower than the spread angle of the light emitted from the light source. According to such an embodiment, the amount of light incident on the light guide plate is reduced at this location and the brightness can be suppressed. Therefore, this embodiment is effective when the overhang distance is shorter than the appropriate overhang distance.

  Still another embodiment of the light guide plate according to the present invention is characterized in that the light guide plate is cut into a desired dimension by a punching method. According to such an embodiment, it is possible to perform a cut for adjusting the dimensions of the light guide plate and a process such as a light incident surface for making the luminance uniform at a time, and the mass productivity of the light guide plate is improved.

  A liquid crystal display device according to the present invention includes a light source plate according to the present invention, a surface light source device having a plurality of point light sources arranged in a row so as to face the light incident surface of the light guide plate, and the surface light source device. And a liquid crystal panel disposed on the light emitting surface side.

  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. 1 is a plan view of a surface light source device described in Patent Document 1. FIG. FIG. 2 is a schematic cross-sectional view showing the surface light source device according to Embodiment 1 of the present invention. FIG. 3 is an exploded perspective view of the surface light source device of the first embodiment. FIG. 4 is a plan view showing the arrangement of the light guide plate and the point light source used in the surface light source device of Embodiment 1, and shows the light guide plate from which light guide plates having different sizes are produced. FIG. 5 is a plan view showing an example of cutting with the light guide plate shown in FIG. FIG. 6 is a plan view showing another cutting example of the light guide plate shown in FIG. FIGS. 7A, 7B, and 7C are diagrams for explaining the reason why the corner portion on the light incident surface side is obliquely cut in the light guide plate of FIG. FIG. 8 is a diagram for explaining the action of the inclined surface provided on the light guide plate. FIG. 9 is a diagram for explaining another action of the inclined surface provided on the light guide plate. FIG. 10 is a diagram for explaining a method of creating a database for determining the inclination angle of the inclined surface. FIG. 11 is a diagram showing a database for determining the inclination angle of the inclined surface. FIG. 12A is a diagram for explaining a different cutting method for the corner portion on the light incident surface side. FIG. 12B is a diagram for comparing and explaining the operational effects of the cutting method of FIG. FIG. 13 is a plan view of a light guide plate provided with an inversely inclined surface. FIG. 14 is a plan view of a light guide plate provided with depressions. Fig.15 (a) is a figure explaining the position from which an inclined surface differs. FIG. 15B is a diagram for explaining different positions of the reversely inclined surface. FIG. 16A is a plan view of a light guide plate according to another embodiment of the present invention. FIG.16 (b) is a side view of the light-guide plate of another embodiment. 17 is a partially broken perspective view of the light guide plate shown in FIG. 18A and 18B are a plan view and a side view of light guide plates having different widths, which are produced based on the light guide plate of FIG. FIG. 19 is a plan view of another light guide plate having a different width, which is manufactured based on the light guide plate of FIG. 16. FIG. 20 is a plan view showing a different usage example of the light guide plate shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

(Configuration of surface light source device)
First, a basic configuration of the surface light source device 21 according to the present invention will be described with reference to FIGS. 2 and 3. FIG. 2 is a partially cutaway sectional view of the surface light source device 21. FIG. 3 is an exploded perspective view of the surface light source device 21.

  As shown in FIG. 3, the surface light source device 21 includes a reflecting plate 22, a frame 23, a light guide plate 24, a plurality of point light sources 25, a flexible printed circuit board 26, a diffusion plate 27, two prism sheets 28a and 28b, a light shield. It consists of tape 29 and the like.

  As shown in FIG. 2, in the point light source 25 (light emitting element), the surface excluding the front surface of the resin 34 containing the phosphor is covered with a white resin 35. Therefore, when the blue light emitting LED chip 33 emits light, the light emitted from the LED chip 33 is emitted to the outside from the front surface (light emitting window) of the resin 34 while being converted into pseudo white light. A part of the light emitted from the LED chip 33 is reflected at the interface between the transparent resin 34 and the white resin 35 and then emitted from the front surface of the transparent resin 34 to the outside.

  These point light sources 25 are mounted on the lower surface of the flexible printed circuit board 26 and are arranged in a line at a constant pitch.

  The light guide plate 24 is formed into a plate shape using a light-transmitting resin having a high refractive index, such as polycarbonate resin or polymethyl methacrylate (PMMA) resin. A light incident surface 31 for introducing light into the light guide plate 24 is formed on the end surface of the light guide plate 24. A large number of fine deflection patterns 30 (diffusion means) are formed on the lower surface of the light guide plate 24 to totally reflect the light guided through the light guide plate 24 and to emit the light upward from the upper surface (light emitting surface 32).

  Thus, the light emitted from the light source 25 is introduced into the light guide plate 24 from the light incident surface 31, and repeats total reflection between the upper surface (light output surface 32) and the lower surface of the light guide plate 24. Is guided. Then, the light totally reflected or diffused by the deflection pattern 30 in the middle of the light guide is emitted from the light emitting surface 32 to the outside.

  The frame 23 is obtained by cutting a resin sheet having the same thickness as that of the light guide plate 24, and has an opening 36 for positioning the light guide plate 24. In addition, recesses 37 for positioning the point light source 25 mounted on the lower surface of the flexible printed circuit board 26 are provided at the end of the opening 36 at the same pitch as the point light source 25.

  The reflection plate 22 is made of a material having a high reflectance such as a white sheet or a metal foil. The reflection plate 22 reflects light leaking from the lower surface of the light guide plate 24 and re-enters the light guide plate 24 to improve the light utilization efficiency.

  As shown in FIG. 2, the upper surface of the outer peripheral portion of the reflecting plate 22 is bonded to the lower surface of the frame 23 by a double-sided adhesive tape 39a. Then, the light guide plate 24 is placed in the opening 36 of the frame 23, and the point light source 25 is placed and positioned in each recess 37 so that the front surface of each point light source 25 faces the light incident surface 31 of the light guide plate 24. The lower surface of the flexible printed circuit board 26 is bonded to the upper surface of the frame 23 and the upper surface of the end portion of the light guide plate 24 by an adhesive tape 39b. Accordingly, the end portion of the light guide plate 24 is sandwiched and held between the reflection plate 22 and the flexible printed board 26.

  Further, the diffusion plate 27 and the two prism sheets 28 a and 28 b are placed on the light emitting surface 32 of the light guide plate 24, and the edges are pressed by the light shielding tape 29. The prism sheets 28a and 28b are obtained by arranging linear prism patterns having a triangular cross section on the surface in parallel at a constant pitch, but the prism sheets 28a and 28b are overlapped so that the arrangement directions of the patterns are orthogonal to each other. Yes. The light shielding tape 29 is a black adhesive tape, and a window 38 is opened in the light shielding tape 29 in order to expose the prism sheet 28b and the like. The light shielding tape 29 is attached to the upper surface of the flexible printed circuit board 26 and the edge of the prism sheet 28 b, and the diffusion plate 27 and the prism sheets 28 a and 28 b are held by the light shielding tape 29.

  The surface light source device 21 is characterized in that it can be resized and used according to the applicable model and the required size. That is, the surface light source device 21 is designed as a large size. Alternatively, it is designed as the maximum size expected. When a surface light source device 21 having a smaller size is required, the light guide plate 24 is cut to the required size. Further, the reflecting plate 22, the light guide plate 24, the diffusion plate 27, and the prism sheets 28 a and 28 b are also cut according to the size of the light guide plate 24. Or you may cut out from each large format raw material sheet. The frame 23 and the light shielding tape 29 may be cut from the raw material sheet according to the size of the light guide plate 24 or the like by, for example, a numerically controlled cutting device. Note that the flexible printed circuit board 26 on which the point light source 25 is mounted may have a different number of point light sources 25 in stock, or may be manufactured after receiving an order.

  Among the members described above, the reflecting plate 22, the diffusing plate 27, the prism sheets 28a and 28b, etc. are used without being affected by their respective optical characteristics even if they are cut to an appropriate size. However, in the case of the light guide plate 24, the deflection pattern 30 and the like are designed according to the size of the light guide plate 24 and the pitch of the point light sources 25 so that uniform light emission luminance can be obtained. Therefore, in the case of the light guide plate 24, luminance unevenness may occur if the light guide plate 24 is cut into an arbitrary size. Therefore, in the surface light source device 21 of the present invention, when the light guide plate 24 is cut and its size is changed, the light source plate 24 is cut as follows.

(Configuration of light guide plate and cutting method)
FIG. 4 shows an original light guide plate 24 that is set to a large size so that it can be cut and used. In the light guide plate 24, a band-shaped region along the light incident surface 31 is an unused region 41 that is not used as a light emitting surface, and a region excluding the unused region 41 on the upper surface of the light guide plate 24 is a light emitting surface 42. (Effective light emission region).

  The light guide plate 24 is designed and adjusted so that the light emission luminance in the light emitting surface 42 becomes uniform when the point light sources 25 are arranged at a constant pitch P so as to face the light incident surface 31. . Accordingly, the deflection pattern 30 may be repeated in the width direction of the light guide plate 24 at the same pitch as the pitch P of the point light sources 25. When a diffusion pattern (not shown) for diffusing the light incident on the light guide plate 24 to widen the directivity is provided on the light incident surface 31, these patterns are also formed at the same pitch P as the point light source 25. Provided. Therefore, when the light guide plate 24 is cut, the number of point light sources 25 to be used may be reduced. However, the position where the point light sources 25 are installed must be the same as that before the cut even after the light guide plate 24 is cut.

  For example, in the example shown in FIG. 4, the size of the light emitting surface 42 is the light guide plate 24 having a width of 50 mm and a length of 58 mm, and eight point light sources 25 are arranged along the light incident surface 31 with a pitch P of 6 mm. It is designed so that the luminance distribution of the light emitting surface 42 is uniform when arranged. The light guide plate 24 has a rectangular shape, and its width W is 50 mm. Therefore, the distance Q between the end point light source 25 and the side surface of the light guide plate 24 is 4 mm. The length D of the unused area 41 is 5 mm, and the length L of the light emitting surface 42 is 58 mm.

  The distance measured in the direction parallel to the light incident surface 31 from the center of the end point light source 25 to the side surface of the light guide plate 24 (hereinafter referred to as the overhang distance) remains rectangular in the original light guide plate 24. Thus, the light emission luminance of the entire light emitting surface 42 is determined to be uniform. This overhang distance in the initial light guide plate is referred to as an appropriate overhang distance Q. The appropriate overhang distance Q varies depending on the pitch P and directivity of the point light source 25, the pattern shape and arrangement of the deflection pattern 30, etc., but an optimal value can be experimentally determined in advance. Although the overhang distance may be different on the left and right, the left and right overhang distances are assumed to be equal in the following.

  In the first embodiment, when the corner portion of the light guide plate 24 is rectangular, the overhang distance is ½ of the pitch P of the point light source 25 (that is, 3 mm), as shown in FIG. Region G becomes too bright. This is because the end point light source 25 and the side surface of the light guide plate 24 are close to each other as shown in FIG. 7B, and the amount of light source light reflected by the side surface of the light guide plate 24 is large. Therefore, in this case, the overhang distance is set to a certain value larger than P / 2 (that is, an appropriate overhang distance Q. Although it is set to 4 mm in the explanation example, this value also varies depending on the deflection pattern 30 or the like). As shown in FIG. 7A, the luminance on the light emitting surface 42 can be made uniform. In FIG. 7, the intensity (light quantity) of light emitted in each direction is represented by the thickness of the arrow.

  5 and 6 are the light guide plate 24 of FIG. 4 cut along a cut line C indicated by a two-dot chain line. In the case of FIG. 5, the width of the light guide plate 24 is shortened by an integral multiple of the pitch P of the point light sources 25 (for example, the width is W−2P = 38 mm), and the length of the light emitting surface 42 is L1 = 52 mm. It has become. In the case of FIG. 5, since the overhang distance is also equal to the appropriate overhang distance Q, the light emission luminance of the light emitting surface 42 is uniform even when the corner portion is used in a rectangular shape.

  On the other hand, FIG. 6 shows a case where the light guide plate 24 of FIG. 4 is cut to an arbitrary width. For example, in the light guide plate 24 of FIG. 6, the number of point light sources 25 is six, the width W1 of the light guide plate 24 is 36 mm, and the length of the light emitting surface 42 is L2 = 52 mm. Accordingly, the overhang distance A of the light guide plate 24 is 3 mm. However, when the light guide plate 24 is cut to an arbitrary width, if the corner portion remains rectangular, the corner portion of the light emitting surface 42 becomes too bright or dark and uneven brightness occurs on the light emitting surface 42.

(When the overhang distance after cutting is shorter than the appropriate overhang distance Q)
When the light guide plate 24 is simply cut and the overhang distance becomes shorter than the proper overhang distance Q, the corner portion of the light emitting surface 42 becomes too bright. For example, when the overhang distance is A = 3 mm, it is as described in FIG. Therefore, in this embodiment, when the overhang distance is shorter than the appropriate overhang distance Q, the corner portion of the light guide plate 24 is cut obliquely at a position facing the light source 25 at the end as shown in FIG. In this way, the inclined surface 43 is formed and the inclination angle θ of the inclined surface 43 is adjusted so that luminance unevenness does not occur in the corner portion of the light emitting surface 42. The inclined surface 43 is inclined so as to become farther from the extended line of the light incident surface 31 as it goes toward the side end surface of the light guide plate 24. In addition, the inclination angle θ is an angle formed between the extension line of the light incident surface 31 and the inclined surface 43.

FIG. 8 and FIG. 9 are diagrams for explaining the reason why the luminance distribution can be made uniform by suppressing the light intensity at the corner portion of the light emitting surface 42 by providing the inclined surface 43. The first reason is that, as indicated by an arrow in FIG. 8, the light emitted from the point light source 25 is transmitted through the inclined surface 43, so that the light beam direction is bent toward the inside of the light guide plate 24. For example, as shown in FIG. 8, if the inclination angle of the inclined surface 43 is θ, the light emitted perpendicularly from the point light source 25 is α = arcsin [with respect to the normal of the inclined surface 43 according to Snell's law. (1 / n) sinθ]
It can be bent in a direction that makes an angle of Here, n is the refractive index of the light guide plate 24, and since n> 1, α <θ. Therefore, the light traveling toward the corner portion of the light emitting surface 42 is bent inward, and as a result, the luminance at the corner portion of the light emitting surface 42 is suppressed and luminance unevenness hardly occurs.

  The second reason is that when the inclined surface 43 is formed, a space is generated between the light emitting surface of the point light source 25 and the light guide plate 24. That is, if a space (gap) is created between the light emitting surface of the point light source 25 and the inclined surface 43 by providing the inclined surface 43, one of the light emitted from the point light source 25 is shown in FIG. The portion does not directly enter the light guide plate 24 and is absorbed by the flexible printed circuit board 26 and the double-sided adhesive tape 39 b or reflected by the reflecting plate 22 and then absorbed by the light shielding tape 29. As a result, the amount of light incident on the corner portion of the light emitting surface 42 is reduced, the luminance is suppressed, and luminance unevenness is less likely to occur.

  In order to make the luminance uniform, it is necessary to optimize the inclination angle θ of the inclined surface 43. The optimum inclination angle θ can be determined experimentally. In addition, if the relationship between the inclination angle θ of the inclined surface 43 and the luminance level at the corner of the light emitting surface 42 is stored in advance as a database, the inclination angle θ can be determined immediately.

  More specifically, the database may be created as follows. First, as shown in FIG. 10, a light guide plate 24 having an inclined surface 43 with a certain inclination angle θ is produced. At this time, the overhang distance X is set larger than the appropriate overhang distance Q. Then, the brightness of the corner portion (predetermined R region shown in FIG. 10) is measured each time the side surface of the light guide plate 24 is cut and the overhang distance X is gradually shortened. Further, the brightness of the R region is measured while changing the overhang distance X again with respect to the inclined surface 43 of each inclination angle θ while varying the inclination angle θ while keeping the starting point S of the inclined surface 43 fixed. Even when there is no inclined surface 43 (when θ = 0 °), the relationship between the overhang distance X and the brightness of the R region is obtained.

  If the measurement as described above is performed, as shown in FIG. 11, a database representing the relationship between the overhang distance X with the inclination angle θ as a parameter and the brightness of the R region is obtained. However, in FIG. 11, normalization is performed so that the brightness when the inclined surface 43 does not exist (θ = 0 °) and the overhang distance X is equal to the appropriate overhang distance Q is “1”.

  If such a database is prepared, the inclination angle can be easily determined as follows. For example, it is assumed that the protruding distance X of the light guide plate 24 after cutting is A (= 3 mm). When the inclined surface 43 is not provided, the inclination angle θ = 0 °. Therefore, according to FIG. 11, the brightness (ratio) of the R region is 1.1, and the brightness is increased by 10%. . Therefore, if the inclined surface 43 is not provided, the corner portion of the light emitting surface 42 becomes too bright, so that it is necessary to reduce this brightness to 1.0 in order to keep the brightness unchanged from that before cutting. . For that purpose, the brightness moves to a point of 1.0 along the straight line of the overhang distance X = A in FIG. 11, and the value of the inclination angle θ at that time is read. In the case of FIG. 11, the inclination angle θ when the overhang distance is A and the brightness is 1.0 is 5 °. Therefore, when the light guide plate 24 is cut, the inclined surface has an inclination angle θ of 5 °. 43 may be produced.

(Other methods of suppressing brightness)
In addition, when the overhang distance X is shorter than the appropriate overhang distance Q, the method of suppressing the brightness of the corner portion of the light emitting surface 42 is not limited to the single inclined surface 43 as described above. In general, the distance between the light source 25 at the end and the light incident surface 31 only needs to increase as it approaches the side surface of the light guide plate 24.

  For example, as shown in FIG. 12A, the corner portion of the light guide plate 24 may be composed of a plurality of inclined surfaces 43 having different inclination angles. As shown in FIG. 12B, when there is only one inclined surface 43, the light totally reflected by the inclined surface 43 is reflected in the same direction, but a plurality of inclined surfaces 43 having different inclination angles are received. Then, as shown in FIG. 12A, the direction of the totally reflected light is scattered, so that the effect of suppressing the brightness of the corner portion of the light emitting surface 42 is enhanced. It can also be said that one inclined surface 43 is provided facing the light source 25 at the end, and an inclined surface (43) is also provided on the side surface of the light guide plate 24 so as to be continuous with the inclined surface 43. .

  Moreover, the corner part of the light-guide plate 24 may be made into a polygonal shape, and you may make it curve in a substantially circular arc shape by a curved surface. Alternatively, although not shown, a plurality of small inclined surfaces 43 may be continuously formed in a sawtooth shape at a position facing the light source 25 at the end. Further, as can be seen from the description of FIG. 9, the gap between the end point light source 25 and the light guide plate 24 may be simply made wider than the others.

(When the overhang distance after cutting is longer than the appropriate overhang distance Q)
When the light guide plate 24 is simply cut, when the overhang distance is longer than the appropriate overhang distance Q, the corner portion of the light emitting surface 42 becomes darker than before. For example, when the proper overhang distance Q is 4 mm and the overhang distance is B = 5 mm, the corner portion becomes dark.

  When the overhang distance is longer than the appropriate overhang distance Q, as shown in FIG. 13, the vicinity of the light incident surface 31 of the light guide plate 24 is cut obliquely at a position facing the point light source 25 at the end, and the reverse inclined surface. 44, and adjusting the inclination angle of the reverse inclined surface 44, luminance unevenness is prevented from occurring in the corner portion of the light emitting surface 42. The reverse inclined surface 44 is inclined so as to become farther from the extended line of the light incident surface 31 toward the center line of the light guide plate 24.

  If such a reverse inclined surface 44 is provided, as indicated by an arrow in FIG. 13, the light emitted from the end point light source 25 is directed toward the corner portion of the light emitting surface 42 when passing through the reverse inclined surface 44. It is bent, the light intensity at the corner increases, the brightness increases, and the luminance unevenness is eliminated. The method for optimizing the inclination angle of the reverse inclined surface 44 may be the same as when the overhang distance is shorter than the appropriate overhang distance Q.

  Note that when the overhang distance X is longer than the appropriate overhang distance Q, the method of compensating for the decrease in the brightness of the corner portion of the light emitting surface 42 is not limited to the single reverse inclined surface 44 as described above. Generally, the distance between the light source 25 at the end and the light incident surface 31 only needs to be reduced as the side of the light guide plate 24 is approached.

  FIG. 14 shows another countermeasure when the overhang distance after cutting is longer than the appropriate overhang distance Q. In the light guide plate 24 shown in FIG. 14, the trapezoidal depression 45 is formed in a region excluding both ends of the light incident surface 31, so that the distance between the point light sources 25 at both ends is short and the other point light sources. The distance 25 from the light incident surface 31 is relatively long. As described with reference to FIG. 9, when the gap between the point light source 25 and the light incident surface 31 is widened, light leaks and the amount of light decreases at that point, so that the corner portion becomes relatively bright and light emission occurs. The luminance unevenness of the surface 42 is eliminated. In order to adjust the light amount according to the overhang distance, the depth of the dent 45 and the angles of the inclined surfaces at both ends of the dent 45 may be adjusted.

  According to such a structure, the corners of the light guide plate 24 can be kept in a rectangular shape, so that the mechanical holding of the light guide plate by the frame 23 can be performed firmly.

  In contrast to the form shown in FIG. 14, when the overhang distance after cutting is shorter than the proper overhang distance Q, both ends of the light incident surface 31 are formed by forming trapezoidal convex portions. The point light source 25 may have a long distance from the light incident surface 31, and the other point light sources 25 may have a short distance from the light incident surface 31.

  As a method of cutting the light guide plate 24 into a desired size, when the light guide plate 24 is thin, the light guide plate 24 can be cut out with a general push cutting blade. In addition, if the die of the push cutting blade is produced, the inclined surface 43, the reverse inclined surface 44, the depression 45, etc. can be cut simultaneously with the cutting of the light guide plate 24. Therefore, it can cut at once and mass productivity improves. In addition, if it is a small number, it can be cut out with a cutter or the like.

  Moreover, although the inclined surface 43 and the reverse inclined surface 44 demonstrated so far were provided in the range wider than the width | variety of the point light source 25 of an edge, as shown to Fig.15 (a) or FIG.15 (b), an edge is shown. The inclined surface 43 or the reverse inclined surface 44 may start from the middle of the point light source 25. Alternatively, the distance between the end point light source 25 and the light incident surface 31 may change from the middle of the end point light source 25. In this way, the portion of the end point light source 25 that does not face the inclined surface 43 or 44 is used as a normal point light source, and the portion that faces the inclined surface 43 or 44 adjusts brightness unevenness. Can be used for.

(Another embodiment)
FIG. 16 is a plan view showing a light guide plate 24 according to another embodiment of the present invention. The light guide plate 24 also has a plurality of light sources 25 arranged in a line at a constant pitch P (for example, 6 mm) so as to face the light incident surface 31. In the non-use region 41 of the light guide plate 24, the edge region on the light incident surface 31 side is a thick portion 52 having a large thickness, and the region adjacent to the light emitting surface 42 is a thin portion 53 having the same thickness as the light emitting surface 42. It has become. Further, between the thick portion 52 and the thin portion 53, a directivity conversion portion 54 (structure) is provided at a position corresponding to each light source 25. As shown in FIG. 17, the directivity converting portion 54 is a step portion connecting the thick portion 52 and the thin portion 53, and has a shape that is ½ of the frustoconical outer peripheral surface. A large number of fine V-grooves 51 are formed radially. In this light guide plate 24 (before cutting), the proper overhang distance Q is ½ of the pitch P, and is designed so as not to have uneven brightness.

  In the light guide plate 24 having such a directivity conversion unit 54, since the thick part 52 faces the light source 25, the height (thickness) of the light incident surface 31 is increased, and the light from the light source 25 is efficiently used. It can be well taken into the light guide plate 24. On the other hand, the thickness of the light guide plate 24 can be reduced in the region of the light emitting surface 42 where the liquid crystal panel and the like are stacked. As described above, if the light incident side is thick and the light guide plate is thin from the middle, light easily leaks to the outside at the stepped portion, and the light use efficiency is lowered. Therefore, the leakage of light can be reduced by changing the directivity of the light incident on the directivity converting unit 54. The function of the directivity conversion unit 54 is disclosed in International Publication WO2008 / 153024 (PCT / JP2008 / 060610).

  FIG. 18 shows the light guide plate 24 shown in FIG. 16 with both sides cut, and is cut so that the overhang distance is larger than the appropriate overhang distance Q (for example, 4 mm). In addition, a reverse inclined surface 44 is formed on the light incident surface 31 of the light guide plate 24 at a position facing the light source 25 at the end. Then, by optimizing the inclination angle of the reverse inclined surface 44, the light emitted from the light source 25 at the end is sent to the vicinity of the corner of the light guide plate 24, and the luminance of the light guide plate 24 is made uniform. In the actual fabrication example, when B = 4 mm and the luminance unevenness was eliminated, the luminance of 90% of the luminance of the original light guide plate 24 in FIG. 16 could be achieved.

  FIG. 19 shows the light guide plate 24 of FIG. 16 cut so that the overhang distance is smaller than the appropriate overhang distance Q. In addition, the inclined surface 43 is formed by obliquely cutting the corner portion of the light guide plate 24. Then, by optimizing the inclination angle of the inclined surface 43, the light emitted from the light source 25 at the end is totally reflected by the inclined surface 43 to be guided in a necessary direction, and the luminance of the light guide plate 24 is made uniform. In the actual fabrication example, when B = 4 mm and the luminance unevenness was eliminated, the luminance of 92% of the luminance of the original light guide plate 24 in FIG. 16 could be achieved.

(Modification)
In FIG. 20A, the directivity conversion unit 54 is provided at a constant pitch P (for example, 6 mm), and the light sources 25 are designed to be arranged at a pitch several times that (or the directivity conversion unit 54). Can also be said to be provided at a pitch ½ of the pitch of the light source 25). For example, in FIG. 20A, every other light source 25 is omitted from the array of directivity converters 54, and the light sources 25 are arrayed at a pitch of 2P (for example, 12 mm). However, the density of the deflection patterns 30 is increased between the light sources 25 in order to prevent luminance unevenness due to the reduction in the number of the light sources 25. As a result, uniform light emission luminance is maintained. In this light guide plate 24, the proper overhang distance Q is equal to P (for example, Q = 6 mm).

  The light guide plate 24 shown in FIG. 20B is obtained by obtaining a light guide plate having a slightly smaller size based on the light guide plate 24 as shown in FIG. This light guide plate is cut so that the overhang distance is A = 2Q / 3 (for example, 4 mm). And the corner part of the light-guide plate 24 is cut in the position facing the light source 25 of an end, the inclined surface 43 is formed, and uniform light emission is maintained by optimizing the inclination angle of the inclined surface 43. FIG.

  Although not shown in the figure, even in such a form, even when cutting so that the overhang distance is larger than the appropriate overhang distance Q, uniform light emission luminance can be obtained by providing, for example, the reverse inclined surface 44 or the like. .

DESCRIPTION OF SYMBOLS 21 Surface light source device 24 Light guide plate 25 Point light source 31 Light incident surface 32 Light output surface 33 LED chip 41 Non-use area 42 Light emitting surface 43 Inclined surface 44 Reverse inclined surface 45 Depression θ Inclined angle of inclined surface X Overhang distance Q Proper overhang distance

Claims (12)

Uniform brightness is obtained in the effective light-emitting area when one side or both side surfaces are planned to be used, and the light incident surface faces a plurality of point light sources arranged in a row. It is a light guide plate designed to be uniform in advance,
An error from the uniform luminance in the effective light emitting region caused by cutting one side surface or both side surfaces is calculated as a distance of the light incident surface with respect to a point light source located at an end of the plurality of point light sources or the light incident. A light guide plate that is modified by making the angle of the surface different from that before cutting.   The distance between the point light source located at the end and the light incident surface is varied according to the distance from the point light source located at the end to the side surface close to the point light source. The light guide plate described.   The distance between the point light source located at the end and the light incident surface is larger than the distance between the point light source not located at the end of the plurality of point light sources and the light incident surface. The light guide plate according to 1.   The distance between the point light source located at the end and the light incident surface is smaller than the distance between the point light source not located at the end of the plurality of point light sources and the light incident surface. The light guide plate according to 1.   2. The light guide plate according to claim 1, wherein a distance between the point light source located at the end and the light incident surface increases as the distance from the side surface close to the point light source increases.   2. The light guide plate according to claim 1, wherein a distance between the point light source located at an end and the light incident surface decreases as the side surface approaches the point light source.   The position where the distance between the point light source located at the end and the light incident surface starts to change is in a region of the light incident surface facing the light emitting surface of the point light source located at the end. The light guide plate according to claim 1.   The position where the distance between the point light source located at the end and the light incident surface begins to change is a side surface of the light incident surface that is closer to the point light source than the region facing the light emitting surface of the point light source located at the end. The light guide plate according to claim 1, wherein the light guide plate is located far from the light guide plate.   The light guide plate according to claim 1, wherein the plurality of point light sources are all oriented in the same direction and along the same straight line.   In a cross section perpendicular to the light incident surface and the light emitting surface, an angle when the upper surface and the lower surface of the light incident surface are viewed from the point light source is narrower than a spread angle of the light emitted from the point light source. The light guide plate according to claim 1, wherein a distance between the point light source located at an end and the light incident surface is determined.   The light guide plate according to claim 1, wherein the light guide plate is cut into a desired dimension by a punching method. A surface light source device comprising: the light guide plate according to claim 1; and a plurality of point light sources arranged in a row so as to face the light incident surface of the light guide plate;
A liquid crystal panel disposed on the light emitting surface side of the surface light source device;
A liquid crystal display device.

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