KR100638541B1 - Light guide plate, sidelight type surface light source device and liquid crystal display - Google Patents

Abstract

The side light type surface light source device 2 illuminating the liquid crystal display panel 3 of the liquid crystal display device 1 includes a light guide plate 4, a fluorescent lamp 8, a reflective sheet 6, a prism sheet, and the like. . When the fluorescent lamp 8 is turned on, the emission surface 4C emits light. The exit surface 4C is trimmed shielded (broken line). On the side surface 4G, the projection 4H derived from the gate provided at the time of molding is formed. The formation position of the projection 4H is located on the back surface 4B side than the imaginary line divided into two with respect to the thickness of the light guide plate 4. The back surface 54B is formed with a prism surface composed of a plurality of pairs of slopes 4E and 4F extending substantially perpendicular to the incidence end surface 4A. The strong abnormal light emission generated by dimming the portion where the projection 4H is attached occurs in the narrow region that is trimmed and shielded, and the strong abnormal light emission does not occur in the effective light emitting surface area AR2. The projection 4H is formed so that at least a portion thereof becomes thinner gradually as it moves away from the incident end surface.

Description

Light guide plate, side light type surface light source device and liquid crystal display device {LIGHT GUIDE PLATE, SIDELIGHT TYPE SURFACE LIGHT SOURCE DEVICE AND LIQUID CRYSTAL DISPLAY}

1 is an exploded perspective view showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a side light type surface light source device used in the liquid crystal display of FIG. 1; FIG.

FIG. 3 is a side view illustrating the projection of the light guide plate in the side light type surface light source device shown in FIG. 2. FIG.

4 is a perspective view for explaining the operation of the side light type surface light source device shown in FIG. 2;

Fig. 5 is a side view showing a light guide plate employed in the first modification of the present invention.

Fig. 6 is a side view showing a light guide plate employed in the second modification of the present invention.

7 is a side view showing a light guide plate employed in a third modification of the present invention.

8 is a diagram for explaining the relationship between the occurrence of projections and bright lines.

* Explanation of Signs of Major Parts of Drawings *

1 liquid crystal display 2 side light type surface light source device

3: liquid crystal display panel 4: light guide plate

4A: Incident cross section 4B: Back side

4C: exit surface 4G: side

4H: Protrusion

The present invention relates to a light guide plate, a side light type surface light source device and a display device, and in more detail, a light guide plate that is improved so that this does not adversely affect even if projections derived from the molding process remain on the side surface, and thus the improvement A side light type surface light source device using a light guide plate, and a liquid crystal display device using the same surface light source device for illumination of a liquid crystal display panel. The present invention is applied to, for example, a liquid crystal display device equipped with a personal computer or a vehicle navigation system, a side light type surface light source device and a light guide plate used therein.

It is already known to illuminate a liquid crystal display panel of a liquid crystal display device by a side light type surface light source device. In the side light type surface light source device, since the arrangement in which the primary light source is arranged in parallel to the light guide plate is adopted, it is suitable for thinning the overall shape of the liquid crystal display device equipped with the device.

The light guide plate used in such a side light type light source device includes an incidence end face for inputting light, an output face for outputting light, a back surface opposing the exit face, and a side surface substantially perpendicular to the incidence cross section; And an end face positioned on the side opposite to the incident end face.

The illumination light emitted from the primary light source is introduced into the light guide plate through the incident end surface of the light guide plate and propagated internally so as to be closer to the end face. In the process, internal reflection by the exit surface, the back surface, and the like is repeated. In the internal reflection on the emission surface, part of the light is gradually emitted in accordance with the known optical law in accordance with the relationship between the internal incident angle and the critical angle. As a result, the emission surface is entirely luminous and a surface light source is formed.

Usually, at the time of manufacture of a light guide plate, transparent resin etc. are injection-molded, a transparent plate-shaped member is produced, and then post-processing is performed to a transparent plate-shaped member as needed. As is well known, in injection molding, a gate is formed to inject a material resin into a mold. By use of this gate, projections different from the shape of the mold itself remain on the injection molded article.

Therefore, in actual manufacture of a light guide plate, it becomes a problem at which position a gate is arrange | positioned. For example, when the gate is disposed at a location corresponding to the incident end surface of the light guide plate, protrusions remain on the incident end surface. This projection is naturally cut (gate cut) because it prevents the smooth light incident as an obstacle. However, during gate cut, there are many cases in which a part of the projection remains at the incident end surface, or conversely, a part of the incident end face is cut out.

If such a so-called gate trace is formed on the incident end surface, this causes the optical path to be disturbed, which causes a bright line to appear on the exit surface of the light guide plate. In the actual forming step, it is not uncommon to arrange the light guide plate by arranging the gate at the incidence end face, and therefore, there is a strong demand for solving this problem.

If post-machining is performed carefully after molding to completely eliminate the gate traces remaining on the incidence cross section, the generation of bright lines can be prevented, but this requires a lot of time. In addition, there is a problem that complicated work is forced to avoid problems such as scratches on the light guide plate at the time of post-processing and adhesion of garbage such as cutting powder to the surface of the light guide plate.

In injection molding, however, it is difficult to cut the gate so that no gate traces remain, but it is relatively easy to cut so that the protrusions having a certain protrusion amount are left exactly in the molded article at the time of gate cutting. Such a gate cut process can be performed simultaneously with mold opening of a molding die.

Therefore, even if the projections partially remain on the light guide plate by employing such a technique, it is very advantageous if the projections can be prevented from adversely affecting the quality of the output light from the emission surface by any means.

The reason for this is that post-molding after molding for complete removal of the gate traces becomes unnecessary, and the effort and time required for preparing the light guide plate can be reduced. Also, the gate is formed at a position corresponding to the side surface (one or both of the two side surfaces) that is substantially orthogonal to the incidence end surface of the light guide plate, and the projections left on the same side after molding are then positioned in the frame. It becomes possible to use for this purpose.

However, also in this case, there exists a possibility that the quality of output light may fall by leaving a processus | protrusion on the side surface of a light guide plate. 8 is a diagram for briefly explaining the reason.

As shown in the figure, in the case where the positioning projection is formed on the side (left), the illumination light component reflected at the portion where the projection is attached exhibits a different behavior from other illumination light components, a part of which is localized from the exit surface. It is seen as an enemy. This phenomenon results in the appearance of the stripe-shaped high brightness level region AR1 extending toward the center of the light guide plate at the portion where the projection is attached.

Such an area AR1 tends to be particularly remarkable when a large number of projection lines are formed on the rear surface of the light guide plate, which are substantially orthogonal to the incident end surface. As is already known, this "many projection rows substantially perpendicular to the incidence end face" has a function of strengthening the directivity of the exit face with respect to the plane parallel to the incidence end face of the light guide plate.

As a material of the light guide plate, when a so-called "light scattering light guide" having light scattering ability is employed, the propagation direction is diversified by scattering. However, when the size of the light guide plate or the screen size of the liquid crystal display device is increased to some extent, the scattering ability imparted to the inside of the light guide plate is small because, as already known, there is a request for uniform light emission. As a result, it is impossible to expect sufficient diversification of the propagation direction of the illumination light reflected from the portion where the projection is attached.

If the scattering ability imparted to the inside of the light guide plate is excessively increased in order to prevent bright lines, this time there is a problem that the entire emission surface cannot be made uniformly bright.

The present invention has been proposed under the above background. One object of the present invention is to improve the light guide plate so that it is possible to reduce abnormal light emission due to projections formed on the side surface of the light guide plate even when it is difficult to diversify the propagation direction of the illumination light sufficiently inside.

Still another object of the present invention is to provide a side light type surface light source device in which high quality output light is obtained by equipping the improved light guide plate. Still another object of the present invention is to provide a liquid crystal display device which can obtain high quality display by using the improved side light type surface light source device for illuminating the liquid crystal display panel of the liquid crystal display device. .

The present invention is first applied to a light guide plate having an incident cross section for inputting light, an exit face for outputting light, a back surface opposing the exit face, and a side surface substantially perpendicular to the incident cross section. And according to this invention, the protrusion which protrudes from a side surface is formed in the side surface of a light guide plate at the position closer to the back side than the virtual line which divides the same side into 2 with respect to the thickness direction of a light guide plate.

As a result, even if a part of the illumination light introduced into the light guide plate through the incident end face is directed from the exit surface directly through the part where the projection is attached, the exit position at the part where the projection is attached (on the exit surface) ) Propagates a considerable distance (at least half the thickness of the light guide plate, at least), and the optical path is diversified to some extent. Therefore, even if a bright line region appears on the emission surface in this path, the luminance is suppressed low.

If the projection is formed at the position oriented toward the exit surface side of the light guide plate, the distance from the portion where the projection is located to the exit position (on the exit surface) does not occur in thickness. It may be caused by a strong curved line extending to a position away from (near the center on the incidence section). One reason (first reason) in which the present invention is limited to the position where the projection is formed on the "back side side" lies in this point.

In addition, the light directed to the rear surface through the portion where the projection is attached is partially reflected from the rear surface and then toward the exit surface, and the portion once exits the light guide plate from the rear surface. If there is a reflecting member along the rear surface, it is reflected there, and then returned to the light guide plate, to the exit surface. Therefore, due to the length of the propagation distance to the emission and the diversity of the optical path therebetween, this component also does not cause a strong bright line.

As described above, in order to increase the directivity of the light emitted from the light guide plate, one having a plurality of projection lines having a pair of slopes extending in a direction substantially orthogonal to the incident end surface may be used. In this case, the distance from the light exit surface to the light exit surface can be taken for a long time directly to the exit surface directly through the part where the projection is attached, so that diversification of the optical path can be expected. Even if a bright line region is generated from the vicinity of the edge of the exit surface to the center portion, the luminance is suppressed low and is hardly noticeable.

In addition, the light directed toward the back via the part where the projection is attached is different from the case where the projection does not have a projection on the back. That is, if there is a projection line (a pair of slopes extending perpendicular to the incidence end face) on the back side, the light directed to the back side via the portion where the protrusion is attached is internally reflected by the pair of slopes so that most of the light is directed to the exit face.

What is important here is that since the projections are formed at a position biased to the rear side, the internal incidence into the slope pairs is concentrated in the extremely vicinity of the portion where the projections are attached. As a result, the local strong emission occurs limited to the largest part of the side edge of the exit surface (extreme vicinity of the part where the projection is attached).

Therefore, when the maximum part of the side surface of the exit surface is avoided and used (for example, trimming shielding), most parts including the center portion of the exit surface can be used as an area without generating strong bright lines. Appropriate trimming shielding means can be implemented to shield abnormal light emission near the maximum edge of the exit surface.

In other words, side effects (abnormal luminescence) that occur when a projection row (a pair of slopes extending perpendicular to the incidence section) are formed on the rear surface are oriented to the side of the exit surface by shifting the position at which the projection is formed to the rear side of the light guide plate. It is limited to the portion (corresponding to the very vicinity of the portion where the projection is attached), whereby high practical convenience can be obtained.

If the projections are formed near the exit surface side of the light guide plate, the internal incidence into the pair of slopes formed on the back surface of the light guide plate cannot be ignored even at a position far from the portion where the projections are attached. In that case, there exists a possibility that a fairly strong emission may continue from the side edge of an emission surface toward a center part. Such a situation cannot be dealt with by trimming shielding, which is a practical problem.

In contrast, in the present invention, even in the case where a projection string having a pair of slopes is formed on the rear surface of the light guide plate, such a situation that is difficult to avoid practically can be avoided. Another reason (second reason) in which the present invention is limited to the position where the projection is formed on the "back side side" lies in this point.

Moreover, it is preferable that the protrusion of the side surface of a light guide plate is formed so that thickness may become thin gradually as at least one part moves away from the incident end surface of a light guide plate. In this case, it is considered that the inclined portion occurs in the portion where the projection is attached, and it is difficult for the light passing through it to be concentrated in the linear region on the emission surface.

Next, the present invention is also applied to a side light type surface light source device including a primary light source and a light guide plate. As the light guide plate, the above-described improved light guide plate is adopted.

That is, the light guide plate has an incident cross section for inputting light supplied with the primary light source, an exit surface for outputting light, a back surface opposite to the exit surface, and a side substantially perpendicular to the incident cross section.

And the projection which protrudes from a side surface is formed in the side surface of the light guide plate at the position which approached the back side rather than the virtual line which divides the same side with respect to the thickness direction of a light guide plate. The back surface of the light guide plate may be provided with a plurality of projection lines extending in a direction substantially perpendicular to the incident end surface. For the first and second reasons described above, even in this case, the strong abnormal light emitting region does not extend toward the center of the emission surface.

Moreover, in order to shield abnormal light emission of the maximum part of the edge of an emission surface, appropriate trimming shielding means can be implemented. In addition, it is preferable that the protrusion is formed such that at least a portion thereof becomes thinner gradually as it moves away from the incident end surface of the light guide plate.

When the improved surface light source device is arranged for illumination of the liquid crystal display panel as described above, the display device according to the present invention is obtained. In that case, it goes without saying that the above-mentioned advantages of the light guide plate or the side light type surface light source device are reflected in the liquid crystal display device.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention and its modification are demonstrated with reference to FIGS. In addition, in each drawing, in order to make understanding easy, the dimension, shape, etc. of each element are exaggerated and shown suitably. In addition, about the element which is used in common in several drawing, the common description is abbreviate | omitted suitably and abbreviate | omitted.

(1) Representative Examples

1 and 2, a schematic structure of a liquid crystal display device according to the present invention is shown in an exploded perspective view and a sectional view. In the liquid crystal display device 1 according to the present invention, the side light type surface light source device 2 is disposed in order to illuminate the liquid crystal display panel 3 from behind.

The surface light source device 2 includes a light guide plate 4, a primary light source 5 (cold cathode tube 8 and reflector 9), a reflective sheet 6, and a prism sheet 7. The light guide plate 4 is a translucent member made of acrylic resin (PMMA resin), for example, and has a substantially wedge shaped cross section except for the projection 4H described later. One measurement surface provides the exit surface 4C, and the other measurement surface provides the back surface 4B. The thick end face (minor surface) 4A provides an incident cross section for introducing illumination light supplied from the primary light source 5 into the light guide plate 4.

The cold cathode tube (fluorescent lamp) 8 is arranged on the side of the incident end face 4A, and a reflecting member 9 having specular or diffuse reflection is formed behind the cold cathode tube (fluorescent lamp) 8. All these elements are accommodated and supported in a frame (not shown).

The basic operation of the surface light source device 2 is as already known. That is, when the fluorescent lamp 8 is turned on, the illumination light L is introduced into the light guide plate 4 from the incident end surface 4A. Then, as a general tendency, the illumination light L propagates inside the light guide plate 4 inward (in FIG. 2). However, the light paths therebetween are various, and the internal reflection in the emission surface 4C and the back surface 4B is repeated. A part escapes once out of the light guide plate 4 at the time of internal incidence into the back surface 4B, but most of it is diffusely reflected in the reflective sheet 6 made of, for example, a white PET film, and returned to the light guide plate 4.

In addition, a part escapes out of the light guide plate 4 even when entering the exit surface 4C. This light becomes the output light of the light guide plate 4. The escape (emission) of light from the emission surface 4C or the rear surface 4B occurs in accordance with the well-known optical law. That is, when the internal incidence angle is less than the critical angle, a part of the internal incidence light is emitted from the emission surface 4C (or back surface 4B).

As is already known, the outgoing light from the emitting surface 4C has a directivity inclined so as to be separated from the incident end surface 4A. The prism sheet 6 corrects this directivity and supplies light from a direction substantially perpendicular to the liquid crystal display panel 3. 2, the description of the liquid crystal display panel 3 is omitted.

The directing action of the prism sheet 6 is due to the action of the prism face having a plurality of pairs of slopes as shown in FIG. 2, for example. In this example, these pairs of slopes extend substantially in parallel with the incident end surface 4A. Therefore, the direction light is corrected with respect to the light emitted from the emission surface 4C in the "plane perpendicular to the incident end surface 4A." Details of the operation are already known, and thus description thereof is omitted here.

In addition, there is considerable angular extension of the light emitted from the exit surface 4C in the "plane parallel to the incident end surface 4A" (expansion from the entrance end surface 4A to the left and right upward). In order to improve the light supply to the liquid crystal display panel 3, it is preferable to narrow this angle extension.

As one means for this, the prism surface is formed in the back surface 4B of the light guide plate 4. This prism face is provided with a large number of slope pairs 4E and 4F, as partially enlarged description (arrow B) in FIG. These slope pairs 4E and 4F constitute a large number of projection lines and extend in a direction substantially perpendicular to the incidence end surface 4A. The angle (prism correct angle) which the pair of slopes 4E and 4F make is, for example, about 100 degrees.

The action of such a projection line (prism plane) is already known. That is, when light propagating inside the light guide plate 4 reaches the back surface 4B, it is internally incident on either of the slopes 4E and 4F, and internal reflection occurs. By this internal reflection, the light propagated so as to diverge in the left and right directions when viewed from the incidence end surface 4A is subjected to a direction correction action. As a result, the diverging direction in the left and right directions is attenuated to generate internally propagated light directed toward the emission surface 4C.

When this light is emitted from the emitting surface 4C, the direction of divergence is attenuated with respect to the "surface parallel to the incident end surface 4A". As a result, in this example, the prism surface of the back surface 4B exhibits a direction correction function with respect to the "plane parallel to the incident cross section 4A", and the prism as to the "plane perpendicular to the incident cross section 4A". The sheet 7 exhibits a direction correction function. In addition, it is preferable that the repeat pitch of the pair of slopes (protrusion lines) of the back surface 4B and the prism sheet 7 is minute, for example, approximately 50 m. This is to avoid visual confirmation of the repeat structure.

In addition, so-called light scattering patterns are often formed on the emission surface 4C in order to promote the emission from the emission surface 4C. The light scattering pattern is composed of a plurality of minute light scattering areas formed by suitable roughening treatments such as matt surface treatment, etching to a corresponding mold, and electric discharge machining.

The luminance of the emission surface 4C can be made uniform by changing the distribution density, size, etc. of the micro light scattering area according to the position on the emission surface. The light scattering pattern also has a function of preventing moiré patterns from occurring. This moiré pattern is likely to occur due to the superposition of the fine periodic structure (repetition of the liquid crystal cell, etc.) of the liquid crystal display panel 3 and the repetitive structure of the rear projections 4B or the prism sheet 7 with fine projection lines. . Instead of the light scattering pattern, an emission promoting means such as roughening the entire emission surface 4C may be employed.

1, the exit surface 4C of the light guide plate 4 is trimmed and shielded by the width of about 1-2 mm from the outer periphery (edge) as shown by the broken line quadrangle | corner in FIG. That is, the area AR2 inside the broken line is set in the effective light emitting area, and the irradiation light emitted from this area AR2 is used for illumination of the liquid crystal display panel 3. For trimming shielding, for example, a masking treatment such as adhesion of a light shielding tape, light shielding ink printing, or the like can be used. In particular, the trimming shielding blocks light from the abnormal light emitting region that may occur at the edge maximum portion by the action of the projection 4H described later.

Next, the projection 4H will be described. As described in the description of the prior art, at the time of manufacturing the light guide plate 4, transparent resin or the like is injection molded to form a transparent plate-like member, and then post-processing is performed as necessary. In injection molding, a gate is formed to inject a material resin into a mold. By use of this gate, projections different from the shape of the mold itself remain on the injection molded article.

Referring to FIG. 1, the projection 4H protruding there is partially enlargedly depicted (arrow C) on one of the two side surfaces 4G substantially perpendicular to the incident end surface 4A. This projection 4H is a projection corresponding to the above gate. However, the length (protrusion amount) is shortened by the cutting removal process as needed.

In particular, as shown in FIG. 3, it is most important that the protrusion 4H is formed on the back surface 4B side rather than an imaginary line dividing the side surface 4G in the thickness direction. Needless to say, in order to form the projection 4H at such a position, the gate position during molding may be formed at a position corresponding thereto.

The perspective from the incidence end face 4A is not particularly an absolute condition, but as shown in FIG. 1, it is preferable to be separated from the incidence end face 4A by a suitable distance. However, in the case where the light guide plate 4 has a wedge cross-sectional shape as in the present embodiment, it is a matter of course to form a gate on a relatively thick side (to perform resin injection evenly and smoothly). In this embodiment, in consideration of this point, the projection 4H is formed on a relatively thick side.

In addition, it is preferable that the cross-sectional shape of the projection 4H has a slope (taper surface; 4HD) on the side far from the incident end surface 4A, as indicated in FIG. 3. It is preferable that the inclination angle (the angle formed by the bottom surface 4HB) of the slope (taper surface; 4HD) is slightly smaller than 45 degrees. In addition, as shown, the bottom surface 4HB of the projection 4H is preferably formed to be at the same level as the back surface 4B (exactly, intersection with the side surface 4G).

The side surface 4HA on the side of the incident end surface 4A of the projection 4H is a surface substantially parallel to the incident end surface 4A. The slope (taper surface) 4HD is not parallel to the incident end surface 4A. In the portion where the slope (taper surface) 4HD is formed, the thickness of the projection 4H gradually decreases as it moves away from the incident end surface 4A.

By the way, in general, when projections are formed on the side surface of the light guide plate, the abnormal light emission in the linear form may occur from the vicinity of the base, as described above with reference to FIG. 8 in the description of the prior art (FIG. 8, region ( AR1)). In the present embodiment, by forming the projections 4H as described above, it is assumed that the substantial damage of the abnormal light emission is reduced.

That is, a part of the illumination light L introduced into the light guide plate 4 through the incident end surface 4A was emitted from the emission surface 4C toward the emission surface directly via the portion where the projection 4H is attached. Even if it spreads a considerable distance (at least half of the thickness of the light guide plate 4 at least) from the portion where the projection 4H is attached to the emission position (the exit surface 4C), the optical path is diversified to some extent. do. Therefore, even if a bright line region appears on the emission surface 4C in this path, the luminance is suppressed low.

This is one effect by having the projection 4H formed at the position oriented toward the rear surface 4B of the side surface of the light guide plate. On the other hand, if projections were formed at the `` position biased on the incidence end face 4C side '', the distance from the portion where the projections are attached to the exit position (on the exit face) does not occur in thickness, It may be caused by a strong curved line extending to a position away from the projection (near the center on the incidence section). In this invention, this situation can be avoided.

Next, the light toward the rear surface 4B via the portion where the projection 4H is attached is internally reflected from one of the slopes 4E and 4F of the row of projections on the rear surface 4B, and most of the light is emitted from the exit surface ( 4C). What is important here is that the projection 4H is formed at a position biased toward the rear surface 4B side, so that the internal incidence to the slope pairs is concentrated in the vicinity of the portion where the projection 4H is attached.

As a result, the local strong emission occurs limited to the maximum portion of the side edge of the emission surface 4C (very near the portion where the projection 4H is attached). In the present embodiment, as shown in an enlarged manner in FIG. 4, since the maximum portion of the side edge of the exit surface 4C is trimmed shielded (see dashed line), the strong local emission is shielded thereby, and the liquid crystal display panel 3 ) Is not supplied. Therefore, the influence of this strong local emission does not appear on the display surface and does not impair display quality.

In other words, side effects (abnormal luminescence) that occur when protrusion rows (slope pairs 4E and 4F extending perpendicular to the incidence end surface) are formed on the back surface 4B, and the positions of the projections 4H are formed on the light guide plate 4 By biasing to the back side 4B side of the side), it restrict | limits to the largest part of the side edge of the exit surface 4C, and, thereby, high practical convenience can be obtained.

On the other hand, if the projection 4H is formed near the exit surface 4B side of the light guide plate 4, the internal incidence to the pair of slopes 4E and 4F formed on the back surface 4B is attached to the projection 4H. It can't be ignored even at a significant distance from where it is. Then, there exists a possibility that the very strong emission may continue from the side edge of the emission surface 4 toward the center part. Such a situation is difficult to cope with trimming shielding.

On the other hand, in the present invention, even in the case where the projection lines provided with the pair of slopes 4E and 4F are formed on the back surface 4B of the light guide plate 4, such a situation that is difficult to avoid practically can be avoided.

In addition, in this embodiment, the projection 4H is formed so that the thickness gradually becomes thin as a part thereof moves away from the incident end surface 4A of the light guide plate 4. In this way, it is possible to suppress the bright lines (refer to reference sign AR1 in Fig. 8) that tend to occur on the side far from the incident end surface 4A. This is considered to be because the intersection between the slope 4HD and the side surface 4G is oblique, and therefore, light passing through each point on the intersection is prevented from concentrating on a linear region on the emission surface 4C. . According to the actual examination result, when the angle (theta) in FIG. 3 is set to an angle smaller than 45 degree, the result that especially the line reduction effect is large is obtained.

Further, the bottom 4HB at the same level as the back 4B means that there is no step between the two. Therefore, the light passing through this portion does not contribute to abnormal light emission, which is more preferable for reducing abnormal light emission.

Further, in general, the thinner the light guide plate 4 is, the stronger the local emission occurs at a position closer to the side surface 4G (the maximum portion of the edge), and accordingly, the width of the trimming cutoff can be narrowed. This property is suitable for the recent tendency that a thinner light guide plate is used.

In addition, the thickness of the projection 4H is preferably as thin as possible. This is because the portion extending in the thickness direction of the light guide plate 4 (intersection 4H and side surfaces 4G) among the portions where the projections 4H are attached is shortened, and it is thought that the occurrence of bright lines will be suppressed by that much. Because it becomes.

As described above, according to the present embodiment, a light guide plate having good performance can be produced even if the post-processing such as completely removing the projections 4H derived from the gate is omitted. In addition, these devices can be obtained by using this in a side light type surface light source device or a liquid crystal display device to prevent deterioration of illumination quality and display quality.

(Variation)

The above embodiments are not intended to limit the present invention, and the following modifications can be made, for example.

(a) The cross-sectional shape of the trapezoidal protrusion 4h shown in FIG. 3 is an example to the last. For example, as shown in FIG. 5, as it falls from the incident end surface 4A, you may have a triangular cross section like thickness becoming thin gradually throughout. 6, the cross section may be arc-shaped. In this case, the part which becomes thinner as it moves away from the incident end surface 4A, and the part which becomes thinner as it approaches the incident end surface 4A will coexist. The same coexistence relationship may be employ | adopted as a triangular cross section as shown in FIG.

(b) In the above embodiment, the projection 4H was described as originating from the gate. However, needless to say, the projection 4H does not necessarily need to originate from the gate. That is, the present invention can also be applied to the case where the projections for positioning are intentionally formed on the side surface of the light guide plate in the shape of the entire mold. Of course, it is also conceivable to use a projection derived from the gate as a projection for positioning.

(c) In the said Example, the case where the prism surface was formed in the back surface 4B of the light guide plate 4 was described, but this invention is not limited to this. Even if the prism face is not formed on the back face 4B, the meaning of forming the projection 4H by biasing the back face 4B side sufficiently exists.

That is, as described above, even if the back surface 4B is flat, the intensity of light locally emitted from the light emitting surface 4C toward the light emitting surface 4C directly through the portion where the projection 4H is attached. Is weakened by forming a considerable distance (at least half of the thickness of the light guide plate at least) from the portion where the projection 4H is attached to the emission position (on the exit surface).

Moreover, the light toward the back surface 4B (assuming flatness) via the portion where the projection 4H is attached is directed toward the exit surface 4C after a part is reflected from the back surface 4B, and part of the back surface 4B. Once out of the light guide plate 4. If there is a reflecting member 6 along the back surface 4B, after being reflected there, it is returned to the light guide plate 4 and directed to the emitting surface 4C. Therefore, this component also does not cause strong bright lines depending on the length of the propagation distance to the emission and the diversity of the optical paths.

In addition, the prism surface may be formed in the exit surface 4C instead of the back surface 4B. In this case, abnormal light emission is similarly suppressed.

(d) There are various kinds of additional members arranged along the emission surface 4C, and the prism sheet 7 in the above embodiment is just one example. It is also conceivable to use other additional members such as light diffusion sheets, protective sheets, and the like. In addition, arrangement | positioning of an additional member including the prism sheet 7 may be abbreviate | omitted.

(e) In the above embodiment, the light guide plate was made of transparent resin. However, instead of the transparent resin, a light guide plate having a scattering capability therein may be employed.

(f) Although the light guide plate 4 in the above-mentioned embodiment has a wedge-shaped cross section, this does not limit the present invention. For example, you may employ | adopt the light guide plate which has uniform thickness in the whole.

(e) In the above embodiment, the illumination light is introduced into the light guide plate 4 from one end face 4A. However, the present invention can also be applied to a side light type surface light source device having a configuration in which illumination light is incident from a plurality of cross sections.

(h) In the above embodiment, the fluorescent lamp 8 of the rod-shaped light source is employed as the light source, but a light emitting source of another shape may be employed. For example, an array of a plurality of LEDs (light emitting diodes) may be arranged along the incident end surface 4A.

(i) In the above embodiment, an example in which the side light type surface light source device is applied to the backside irradiation of the liquid crystal display device has been described. However, the present invention is not limited to this.

INDUSTRIAL APPLICABILITY The present invention can be applied to applications other than rear irradiation of liquid crystal display devices, such as side light type surface light source devices required for various lighting devices, display devices and the like and light guide plates used therein.

Claims (12)

A light guide plate having an incidence cross section for inputting light, an outgoing surface for outputting light, a back surface opposing the outgoing surface, and a side surface substantially perpendicular to the incidence cross section, The light guide plate which protrudes from the said side surface is formed in the said side surface at the position of the said back side rather than the imaginary line which divides the said side surface into 2 with respect to the thickness direction of the said light guide plate. The light guide plate according to claim 1, wherein the rear surface is provided with a plurality of projection lines having a pair of slopes extending in a direction substantially perpendicular to the incident end surface. 3. The light guide plate according to claim 2, wherein trimming shielding means for shielding abnormal light emitting regions occurring in the vicinity of the projection is formed on the exit surface. The light guide plate according to any one of claims 1 to 3, wherein the protrusion is formed so that its thickness gradually becomes thin as at least a part thereof moves away from the incident end surface. A side light type surface light source device including a primary light source and a light guide plate, The light guide plate has an incidence cross section for inputting light supplied by the primary light source, an outgoing surface for outputting light, a back surface opposing the outgoing surface, and a side surface substantially perpendicular to the incidence cross section, The side light type surface light source device according to claim 1, wherein projections protruding from the side surface are formed at positions on the rear side of the side face rather than an imaginary line dividing the side surface into two in the thickness direction of the light guide plate. 6. The side light type surface light source device according to claim 5, wherein the rear surface is provided with a plurality of projection lines having a pair of slopes extending in a direction substantially perpendicular to the incident end surface. 7. The side light type surface light source device according to claim 6, wherein trimming shielding means for shielding abnormal light emitting regions occurring in the vicinity of the projection is formed on the exit surface. The side light type surface light source device according to any one of claims 5 to 7, wherein the protrusion is formed so that its thickness gradually becomes thin as at least a part thereof moves away from the incident end surface. A liquid crystal display device for illuminating a liquid crystal display panel using a side light type surface light source device, The surface light source device surface includes a primary light source and a light guide plate, The light guide plate has an incidence cross section for inputting light supplied by the primary light source, an outgoing surface for outputting light, a back side opposite to the outgoing surface, and a side surface substantially perpendicular to the incidence cross section, And a projection protruding from the side surface at a position on the rear side rather than an imaginary line dividing the side surface into two in the thickness direction of the light guide plate. 10. The liquid crystal display device according to claim 9, wherein the rear surface is provided with a plurality of projection lines provided with pairs of slopes extending in a direction substantially perpendicular to the incident end surface. 11. A liquid crystal display device as claimed in claim 10, wherein trimming shielding means for shielding abnormal light emitting regions occurring near said projections is formed in said exit surface. The liquid crystal display device according to any one of claims 9 to 11, wherein the projection is formed so that its thickness gradually becomes thin as at least a portion thereof moves away from the incident end surface.

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