JP2007329099A - Surface light source device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device of which the thickness can be reduced by preventing generation of moire fringes, and to provide a liquid crystal display device including it. <P>SOLUTION: In the surface light source device 20, light emitted from a light source 1 passes through the inside of a light guide plate 2, and an irregular pattern 3 formed at a predetermined pitch reflects the light to be emitted from a light emission surface 2a of the light guide plate 2 in a predetermined direction. A reflecting plate 4 reflects light, which leaks from the light guide plate 2 to the side opposite to the light emission surface 2a, toward the light guide plate 2. Because an optical branching layer 6 partly transmits and partly reflects light emitted from the light emission surface 2a in a predetermined direction, light with an emission pattern of which the unevenness due to the pitches of the irregular pattern 3 is smoothed is incident on a prism sheet 5 even if the light guide plate 2 is thin. The prism sheet 5 corrects the incident light so as to be in the normal direction of the light guide plate and emits the light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface light source device and a liquid crystal display device using the same.

  A liquid crystal display device widely used in personal computers, mobile phones, and the like usually includes a light source device because the liquid crystal material does not emit light. In particular, in a liquid crystal display device when mounted on a mobile device, a thin light guide plate and a light source such as a light emitting diode (LED) or a fluorescent tube disposed on a side portion of the light guide plate in order to reduce the thickness and weight. And a light extraction unit that emits light, which is emitted from the light source and incident from the side portion of the light guide plate, and guided through the light guide plate while repeating total reflection, to the liquid crystal display panel side. Is generally used.

  As the light extraction means, a diffusion pattern by dot printing of diffuse reflection ink or an uneven pattern such as a prism formed on the light guide plate is used. When a higher brightness is required, an uneven pattern is often used.

  As a conventional typical surface light source device, a surface light source device 200, which is an example in which a concavo-convex pattern is formed on the surface of a light guide plate as light extraction means, is shown in a perspective view in FIG. Further, the cross sections taken along the broken lines X1, X2, and X3 in FIG. 8 all have the same configuration, and the cross sectional view is shown in FIG.

  This conventional example is referred to as a first conventional example.

  As can be seen from FIGS. 8 and 9, the surface light source device 200 of the first conventional example includes a light source 30, which is a plurality of LEDs, a light guide plate 31 made of a transparent material such as acrylic, and light emission from the light guide plate 31. The concave / convex pattern 32 formed on the surface 31b facing the surface 31a, the reflecting plate 33 disposed on the surface 31b side where the concave / convex pattern 32 of the light guide plate 31 is formed, and the prism disposed outside the light emitting surface 31a. The sheet 34 is configured. The light sources 30 are provided on the side of the light guide plate 31.

  Light emitted from the light source 30 and guided to the inside of the light guide plate 31 from the light incident surface 31c which is one side surface of the light guide plate 31 travels inside the light guide plate 31 while repeating total reflection. Of the light reflected by the concavo-convex pattern 32 when guided, the light traveling at an angle smaller than the critical angle of the light exit surface 31a exits from the light exit surface 31a to the outside. The light emitted to the outside from the light emitting surface 31a is changed in the traveling direction in a direction close to the normal direction of the emitting surface by refraction and reflection by the prism sheet 34, and illuminates the liquid crystal panel.

  Since the surface light source device 200 of the first conventional example is a thin surface light source device that emits light uniformly in a plane, it is used as a light source device of many liquid crystal display devices.

  As another surface light source device, FIG. 10 is a perspective view showing a surface light source device 300 which is an example in which a concavo-convex pattern as light extraction means and prisms of a prism sheet are formed concentrically around a light source. .

  This is called a second conventional example. The second conventional example is described in Patent Document 1, for example.

  In the surface light source device 300 of the second conventional example, the concave / convex pattern 32 which is a light extraction means provided on the light guide plate 31 and the prism of the prism sheet 34 are formed concentrically around the light source 30. The configuration is the same as that of the surface light source device 200 of the first conventional example. In FIG. 10, the cross sections taken along the broken lines X1, X2, and X3 along the radial direction of the concentric circles have the same configuration as that of FIG.

  In the surface light source device 300, since most of the light emitted from the light source 30 is perpendicularly incident on the concave and convex pattern 32 and the prism of the prism sheet 34, the light is easily emitted efficiently in the normal direction of the emission surface, and is substantially parallel light. A surface light source device close to can be realized.

  A liquid crystal panel for displaying an image is laminated on the light exit surface side of the prism sheet 34 of the surface light source devices 200 and 300 of the first conventional example and the second conventional example. In the liquid crystal panel, a microlens that collects output light of the surface light source device in the opening may be formed as in the technique described in Patent Document 2, for example.

  An example of this is shown in FIG.

  In FIG. 11, a liquid crystal panel 41 having a microlens 44 is laminated on the light emitting surface side of the surface light source device 40.

  The liquid crystal panel 41 includes a transmission opening 42 that transmits light defined by a transparent electrode, and a light shielding unit 43 that is defined mainly by a metal electrode such as a TFT or a signal line. The microlens 44 is formed on the one substrate on the surface light source device 40 side of the liquid crystal panel 41 so as to correspond to each transmission opening 42. In this conventional technique, the light emitted from the surface light source device 40, that is, the light incident on the microlens 44 is preferably light close to parallel light from the viewpoint of light collection efficiency.

As a method of forming the transmissive openings of the liquid crystal panel and the arrangement of the micro lenses, as shown in FIG. 12, one lenticular lens called a lenticular lens is associated with one row of the transmissive openings 51. There are various arrangement examples, such as those arranged in a manner as shown in FIG. 13 or FIG. In FIG. 12, a rectangular transmission opening 51 is provided in each picture element partitioned by the light shielding layers 53 and 54, and one micro is formed in each row formed by the transmission opening 51 in the horizontal direction on the paper surface. A lens 52 is disposed. In FIG. 13, three circular transmission openings 51 are provided in each picture element partitioned by the light shielding layers 53 and 54, and one microlens 52 is disposed in each transmission opening 51. In FIG. 14, one circular transmission opening 51 is provided in each picture element partitioned by the light shielding layers 53 and 54, and one microlens 52 is disposed in each transmission opening 51. The microlenses 52 in FIG. 14 are arranged in a staggered manner.
Japanese Patent No. 3151830 (Registration: January 26, 2001, International Publication (WO 98/19105): May 7, 1998) JP 2005-62741 A (publication: March 10, 2005) Japanese Patent No. 3521940 (Registration: February 20, 2004, Publication (Japanese Patent Laid-Open No. 7-49496): February 21, 1995)

  In particular, liquid crystal display devices for mobile use have been studied to reduce the thickness of members used for liquid crystal panels and surface light source devices in view of increasing portability and design from the viewpoint of portability. As the resin molding technology has been improved, the light guide plate has also been made thinner. As a result, it has been found that moire fringes are generated on the display screen, and the display is significantly impaired.

  The principle will be briefly described.

  FIG. 15 is a cross-sectional view of the previous surface light source device when the light guide plate 31 is thick (for example, 0.8 mm). The member numbers correspond to those in FIGS.

  In general, the pixel pitch of the liquid crystal panel 41 is about 50 μm, the pitch of the prism sheet 34 is about 15 μm, and the pitch of the uneven pattern 32 of the light guide plate 31 is about 50 μm to 100 μm.

  The light that has been guided through the light guide plate 31 and reflected by the concave / convex pattern 32 serving as the light extraction means is emitted from the exit surface of the light guide plate 31 with a certain spread angle, and enters the prism sheet 34. When the light guide plate 31 is thick, the light emitted from the light guide plate 31 is uniformly incident on the surface of the prism sheet 34, so that the light that is refracted and reflected by the prism sheet 34 and enters the liquid crystal panel 41 is the prism sheet 34. It is striped at a pitch equal to 15 μm. The stripes with a pitch of 15 μm are sufficiently smaller than the pixel pitch of 50 μm of the liquid crystal panel 41 and therefore do not cause moiré fringes.

  FIG. 16 is a cross-sectional view of a surface light source device realized by recent improvements in resin molding technology when the light guide plate 31 is thin (for example, 0.4 mm). The member numbers correspond to those in FIGS.

  The pixel pitch and prism pitch are the same as in the example where the light guide plate 31 is thick. As in the case where the light guide plate 31 is thick, the light guided through the light guide plate 31 and reflected by the concave / convex pattern 32 serving as the light extraction means is emitted from the exit surface of the light guide plate 31 with a certain spread angle. , Enters the prism sheet 34.

  Unlike the case where the light guide plate 31 is thick, when the light guide plate 31 is thin, since the distance between the light extraction means and the prism sheet 34 is short, the light emitted from the light guide plate 31 is not uniform within the plane of the prism sheet 34. Incident. Therefore, the light that is refracted and reflected by the prism sheet 34 and enters the liquid crystal panel 41 is striped at a pitch close to 50 μm to 100 μm of the concave / convex pattern 32 that is a light extraction means. The stripes having a pitch of 50 μm to 100 μm cause the moire stripes to occur, and the display is remarkably impaired because the pitch is close to the pixel pitch of 50 μm of the liquid crystal panel 41.

  Here, the moire fringes will be described in more detail with reference to FIG. 17 which is an enlarged view of a sectional view of the surface light source device.

  An uneven pattern 32 (32a, 32b) is formed on the light guide plate 31 having a thickness d, and the interval between adjacent uneven patterns 32a and 32b (pitch of the uneven pattern 32) is assumed to be p. In order to make the in-plane luminance distribution uniform, the concavo-convex pattern 32 is basically different in pitch and shape in the plane, but here, for simplicity, the in-plane distribution is not considered, and the average in the plane The explanation is advanced using values.

  When the light 60 guided through the light guide plate 31 with a certain spread angle is reflected by the concave / convex pattern 32a or 32b, the traveling direction changes. Of the light whose traveling direction has changed, light incident on the light emitting surface 31a at an angle smaller than the critical angle θ2 of the light emitting surface 31a of the light guide plate 31 is emitted to the outside of the light guide plate 31. Of the light whose traveling direction has changed, light incident on the light emitting surface 31a at an angle larger than the critical angle θ2 of the light emitting surface 31a of the light guide plate 31 is totally reflected and continues to be guided.

  Although the light emitted from the light emitting surface 31a to the outside of the light guide plate 31 depends on the shape of the concavo-convex pattern 32, in general, the intensity becomes maximum at an angle close to the critical angle θ2, and gradually decreases as the angle decreases. The intensity is attenuated.

  When the size of the uneven pattern 32 is sufficiently smaller than the thickness of the light guide plate 31 and the angle at which the light intensity attenuates to the extent that the shading can be recognized is θ1, the pitch of the uneven pattern 32 is reflected in the output pattern of the emitted light. The condition where the moire fringes occur is that the point where the straight line having the inclination θ2 passing through the concave / convex pattern 32a and the straight line having the inclination θ1 passing through the concave / convex pattern 32b intersect with each other outside the light exit surface 31a of the light guide plate 31, that is, It is on the prism sheet 34 side.

In other words, the boundary conditions for generating moire fringes are expressed as follows.
p / d = tan (θ2) −tan (θ1)
In an actual configuration, the light emitted from the light emitting surface 31a is refracted and then enters the prism sheet 34. Therefore, the conditions for overlapping the light emitted to the outside of the light guide plate 31 are slightly different. Is arranged in the vicinity of the light guide plate 31 and has almost no influence.

  When acrylic, which is a general resin material, is used for the light guide plate 31, θ2 is about 42 °. Further, if the attenuation factor of the light intensity at which the light and shade can be recognized is 20%, θ1 is about 35 °. At this time, when calculated from the above equation, p / d = 0.2. When the pitch p of the uneven pattern 32 is 100 μm, the boundary condition for generating moire fringes is that the thickness d of the light guide plate 31 is d = 0.5 mm. It is.

  That is, moire fringes are not generated when the thickness d of the light guide plate 31 is 0.5 mm or more, but moire fringes are generated when the thickness d is 0.5 mm or less.

  While the demand for thinning the liquid crystal display device is increasing, limiting the thickness of the light guide plate 31 is a big problem, and a structure in which moire fringes are not generated even when the liquid crystal display device is thinned is desired.

  As a method for solving this problem, a method of reducing the pitch p of the concavo-convex pattern 32 can be easily considered. It is extremely difficult to form.

  As another method, as shown in FIG. 18, a method of easily arranging the diffusion layer 35 between the liquid crystal panel 41 and the prism sheet 34 is conceivable, but only the front luminance of the surface light source device is reduced. However, since the parallelism of light is lowered, the light condensing efficiency is lowered particularly in a liquid crystal display device provided with a microlens, which is not preferable for display and cannot be said to be in a state where thinning is possible.

  In view of the above-described problems, an object of the present invention is to provide a surface light source device capable of reducing the thickness by preventing generation of moire fringes and a liquid crystal display device including the surface light source device.

  In order to solve the above problems, the surface light source device of the present invention reflects a light source, a light guide plate that introduces light emitted from the light source and travels inside, and reflects light that travels inside the light guide plate. Light extraction means formed at a predetermined pitch so as to be emitted in a predetermined direction from the light emission surface of the light guide plate, and a part of the light emitted in the predetermined direction from the light emission surface of the light guide plate is transmitted. A light branching layer that partially reflects the light branching layer, and a correction unit that corrects light incident through the light branching layer in a direction close to the normal direction of the light guide plate and emits the light to the side opposite to the light guide plate side. And a light reflecting layer provided on the side opposite to the light branching layer side of the light guide plate so as to reflect light leaking from the light guide plate to the light guide plate side, and from the correction means The light after being emitted is output light.

  According to the above invention, the light emitted from the light source and introduced into the light guide plate travels inside the light guide plate, and the light extraction means formed at a predetermined pitch reflects this light to emit light from the light guide plate. The light is emitted from the surface in a predetermined direction. Since the light reflecting layer is provided on the side opposite to the light branching layer side of the light guide plate so as to reflect the light leaking from the light guide plate to the light guide plate side, it leaks from the light guide plate to the side opposite to the light emitting surface. The emitted light is reflected to the light guide plate side, and this light is contributed to the light emitted from the light emitting surface. Since the light branching layer partially transmits and reflects part of the light emitted from the light emitting surface of the light guide plate in a predetermined direction, even if the light guide plate is thin, it is caused by the pitch of the light extraction means. Light in a state in which the density of the emission pattern is relaxed enters the correction means. The correcting means corrects the light incident through the light branching layer in a direction close to the normal direction of the light guide plate and emits the light to the side opposite to the light guide plate side. The light emitted from the correction means becomes output light of the surface light source device.

  Therefore, even when the output light of the surface light source device having such a configuration is irradiated on the liquid crystal panel, the incident light to the correcting means in the surface light source device has a uniform intensity distribution due to the light branching layer. Moire fringes that harm the display do not occur. In addition, this surface light source device does not require a diffusion layer, and since the parallelism of light does not change, the front luminance of the surface light source device is not reduced.

  As described above, there is an effect that it is possible to provide a surface light source device that can reduce the thickness by preventing the generation of moire fringes.

  In order to solve the above problems, the surface light source device of the present invention is characterized in that the light source includes one or a plurality of point light sources.

  According to the above invention, by using a small and thin point light source typified by a light emitting diode, light source light can be efficiently incident on a thin light guide plate. There is an effect that can be done. Furthermore, by using a plurality of point light sources, light can be uniformly incident on a relatively large light guide plate, so that it can be applied to a medium-sized liquid crystal slightly larger than a mobile phone. .

  In the surface light source device of the present invention, in order to solve the above-described problem, the light source is one point light source composed of one or a plurality of light emitters, and the light extraction means is substantially centered on the point light source. It is formed as a pattern extending in a direction orthogonal to the radial direction of the circle, and the pattern is arranged at the predetermined pitch in the radial direction of the circle.

  According to the above invention, the light emitted from the light source as one point light source and guided while totally reflecting the inside of the light guide plate can be changed in the traveling direction by the light extraction means, thereby having uniform intensity. As light having a distribution, there is an effect that the light is emitted at an angle close to parallel to the light emission surface.

  In order to solve the above problems, the surface light source device of the present invention satisfies p / d> 0.2 where p is the predetermined pitch of the light extraction means and d is the thickness of the light guide plate. It is characterized by that.

  According to the above invention, it is possible to prevent the generation of moire fringes with respect to a light guide plate having a typical configuration in which moire fringes have been generated.

  In order to solve the above problems, the surface light source device of the present invention is characterized in that the thickness of the light guide plate is 0.5 mm or less.

  According to the above invention, when the predetermined pitch of the light extraction means is set to 100 μm near the lower limit that can avoid the difficulty of formation, the conventional light guide plate having a typical thickness in which moire fringes are generated. As a result, it is possible to satisfactorily prevent the generation of moire fringes.

  In order to solve the above problems, the surface light source device of the present invention is characterized in that the light branch layer is made of a half mirror.

  According to said invention, there exists an effect that the setting of the transmittance | permeability and reflectance of a light branch layer becomes easy by comprising a light branch layer with a half mirror.

  In order to solve the above problems, the surface light source device of the present invention is characterized in that the light branching layer is composed of a polarization separation layer.

  According to the above invention, by configuring the light branching layer as a polarization separation layer, it is possible to control the transmittance and the reflectance of the light branching layer according to the polarization state of the light emitted from the light guide plate. Play.

  In the surface light source device of the present invention, in order to solve the above problems, the light source is one point light source composed of one or a plurality of light emitters, and the transmission axis of the polarization separation layer is substantially the same as the point light source. It is characterized by the radial direction of the circle with the center.

  According to the above invention, since the light source is a single point light source and the transmission axis of the polarization separation layer is in the radial direction of a circle with the point light source as the center, the transmittance of the polarization separation layer is improved. There is an effect that the light use efficiency of the surface light source device becomes higher.

  In order to solve the above problems, the surface light source device of the present invention is characterized in that an antireflection layer is formed on the polarization separation layer.

  According to the invention, since the antireflection layer is formed on the polarization separation layer, the transmittance of the polarization separation layer is improved.

  In the surface light source device of the present invention, in order to solve the above problems, the light source is one point light source composed of one or a plurality of light emitters, and the transmission axis of the polarization separation layer is substantially the same as the point light source. It is characterized in that the direction is perpendicular to the radial direction of the center circle.

  According to the above invention, the light source is a single point light source, the antireflection layer is formed on the polarization separation layer, and the transmission axis of the polarization separation layer is in the radial direction of a circle whose center is the point light source. Therefore, the transmittance of the light branching layer is improved, and the light use efficiency of the surface light source device is further improved.

  In order to solve the above problems, the surface light source device of the present invention is characterized in that a retardation film is disposed between the light branch layer and the reflector.

  According to the above invention, by changing the polarization direction of the light reflected by the polarization separation layer as the light branching layer by the retardation film, the light is reflected by the light reflection layer and reenters the polarization separation layer. In this case, there is an effect that the light can be efficiently transmitted through the polarization separation layer.

  In the surface light source device of the present invention, in order to solve the above-described problem, the retardation film satisfies a ¼ wavelength condition, and a slow axis is disposed to be inclined by 45 ° from the light transmission axis of the polarization separation layer. It is characterized by being.

  According to the above invention, since the retardation film satisfies the ¼ wavelength condition and the slow axis is inclined 45 ° from the transmission axis of the polarization separation layer, it is reflected by the polarization separation layer and transmitted through the retardation film. In addition, since the polarization direction of the light reflected by the light reflection layer and again transmitted through the retardation film is parallel to the transmission axis of the polarization separation layer, the light is transmitted through the polarization separation layer very efficiently. There is an effect that can be.

  In order to solve the above problems, the liquid crystal display device of the present invention is characterized in that a liquid crystal panel is laminated on the correction means side of the surface light source device.

  According to said invention, there exists an effect that the liquid crystal display device which prevented generation | occurrence | production of a moire fringe and enabled thickness reduction can be provided.

  In the liquid crystal display device of the present invention, in order to solve the above problems, one microlens for condensing the output light of the surface light source device is formed for each transmission aperture formed in the liquid crystal panel. It is characterized by.

  According to the above invention, since the output light of the surface light source device can be efficiently condensed on each transmission opening formed in the liquid crystal panel by the microlens, the liquid crystal panel efficiently outputs the output light of the surface light source device. There is an effect that it can be used for display well.

  In the liquid crystal display device of the present invention, in order to solve the above-described problem, a plurality of transmission openings formed in the liquid crystal panel form one or more columns, and the output light of the surface light source device is output for each column. One condensing microlens is formed.

  According to the above invention, since the output light of the surface light source device can be efficiently condensed on each transmission opening formed in the liquid crystal panel by the microlens, the liquid crystal panel efficiently outputs the output light of the surface light source device. There is an effect that it can be used for display well.

  As described above, the surface light source device of the present invention reflects the light source, the light guide plate that introduces light emitted from the light source and travels inside, and reflects the light that travels inside the light guide plate. Light extraction means formed at a predetermined pitch so as to be emitted in a predetermined direction from the light emission surface of the light, and part of the light emitted in the predetermined direction from the light emission surface of the light guide plate is transmitted and partially A light branching layer that reflects the light, and a correction unit that corrects light incident through the light branching layer in a direction close to the normal direction of the light guide plate and emits the light to the opposite side of the light guide plate; A light reflecting layer provided on a side opposite to the light branching layer side of the light guide plate so as to reflect light leaking from the light guide plate to the light guide plate side, and emitted from the correction means The later light is output light.

  As described above, there is an effect that it is possible to provide a surface light source device that can reduce the thickness by preventing the generation of moire fringes.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings referred to below, the number of prisms is reduced for the sake of simplicity, but a larger number of prisms are formed on an actual light guide plate.

[First embodiment]
An embodiment of the present invention will be described with reference to FIGS. 1 to 7 as follows.

  A cross-sectional view of the liquid crystal display device 100 according to the present embodiment is shown in FIG. Moreover, the perspective view of the surface light source device 20 used for this embodiment is shown in FIG.

  As shown in FIG. 1, the liquid crystal display device 100 according to the first embodiment includes a laminate of a liquid crystal panel 10 and a surface light source device 20.

  The liquid crystal panel 10 includes a substrate on which switching elements such as TFTs, signal lines, and pixel electrodes are formed at a pitch of 50 μm (referred to as a TFT substrate), and a substrate on which pixel electrodes and RGB color filters are periodically formed. (Referred to as a CF substrate) is a structure in which a liquid crystal layer is sandwiched between the transparent opening 11 defined by a transparent electrode and light mainly defined by a metal electrode such as a TFT or a signal line. A light shielding portion 12. The microlens 13 is formed on the surface of the TFT substrate on the surface light source device 20 side so as to correspond to the transmission opening 11 on a one-to-one basis.

  The arrangement method of the transmissive aperture 11 and the microlens 13 is the staggered arrangement shown in FIG. 14 described in the background art, but other arrangements as shown in FIG. 13 may be used. -Like microlenses may be arranged corresponding to one row of transmission openings.

  The microlens 13 can be formed by a known method. Specifically, for example, it is formed by the steps described below.

  First, a mold master in which the desired shape of the microlens 13 is precisely formed is prepared. An ultraviolet curable resin is sealed between the mold master and the TFT substrate of the liquid crystal panel 10. Subsequently, the encapsulated resin is irradiated with ultraviolet rays and cured. After completely curing the UV curable resin, the mold is gently peeled off.

  If the above method is used, the microlens 13 having high optical characteristics can be easily manufactured with high mass productivity. As the material of the microlens 13, an ultraviolet curable resin having high transparency in a completely cured state and low birefringence is preferably used. In addition to the above method, for example, an ion exchange method, a photolithography method, a heat dripping method, or the like is used.

  Further, on the front and back surfaces of the liquid crystal panel 10 thus prepared, a polarizing plate (not shown), a retardation film for viewing angle compensation, and the like are arranged.

  The surface light source device 20 includes a light source 1, a light guide plate 2, a reflection plate 4, a prism sheet 5, and a light branching layer 6. The reflection plate 4, the light guide plate 2, the light branching layer 6, and the prism sheet 5 are laminated in this order.

  The light source 1 is disposed on the side of the light guide plate 2. As the light source 1, a light source having a sufficiently narrow width as compared with the width dimension of the light guide plate 2 is used. For example, a light emitting diode (LED) can be used. Thereby, the light source 1 becomes one point light source for the light guide plate 2. If the light source 1 can be arranged with a sufficiently small width compared to the width dimension of the light guide plate 2, a plurality of light emitters are arranged in addition to one light emitter to form one light source. Even those arranged can be used as point light sources. For example, this corresponds to an LED lamp in which two LED chips are mounted in one LED lamp, or a case where two LED lamps are arranged close to each other.

  By using a small and thin point light source typified by a light emitting diode, light source light can be efficiently incident on the thin light guide plate 2, so that the thin surface light source device 20 can be provided.

  The light guide plate 2 is made of a transparent material such as acrylic. In the present embodiment, the light guide plate 2 is created by injection molding. The light guide plate 2 is a substantially rectangular flat plate, and a light incident surface 2c is formed at an end portion. The light source 1 is disposed outside the light incident surface 2c. Further, the thickness of the peripheral portion of the light incident surface 2c may be increased so that the light emitted from the light source can be taken into the interior efficiently. In that case, the region connecting the portions having different thicknesses of the light guide plate 2 has a shape that draws a gentle curve so as not to disturb the light guide. The surface of the light guide plate 2 on the light branching layer 6 side is a light emitting surface 2a.

  In addition, an uneven pattern (light extraction means) 3 is formed on the surface 2 b of the light guide plate 2 that faces the light exit surface 2 a. In this embodiment, the shape of the concavo-convex pattern 3 is created in advance in an injection mold, and the concavo-convex pattern 3 is formed simultaneously with the injection molding of the light guide plate 2. The light guide plate 2 has a thickness of 0.4 mm.

  As shown in FIG. 2, the reflection surface of the uneven pattern 3 is formed so as to extend in the X direction orthogonal to the Y direction that is the radial direction of a circle centering on the light source 1 that is a point light source. In other words, the concavo-convex pattern 3 is constituted by a groove extending in the X direction. Thereby, the light guided while totally reflecting the inside of the light guide plate 2 is emitted at an angle close to parallel to the surface of the light emitting surface 2 a by changing the traveling direction by the concave-convex pattern 3. Although the uneven pattern 3 is provided as a part of the light guide plate 2, the light extraction means may be provided separately from the light guide plate 2.

  Light emitted at an angle close to parallel to the surface of the light exit surface 2a is corrected by the prism sheet 5 in the normal direction of the light guide plate 2, that is, the normal direction of the light exit surface 2a. Further, in order to obtain in-plane uniformity of the light intensity, the distance between the adjacent uneven patterns 3 is shortened as the distance from the light source 1 increases. Specifically, the pitch of the concavo-convex pattern 3 was 50 μm to 100 μm.

  As the prism sheet (correcting means) 5, a thin transparent sheet on which a large number of prisms are resin-molded was used. Such a sheet can be easily produced by the 2P method using a mold. The prisms of the prism sheet 5 are also arranged concentrically around the light source 1 that is a point light source, similarly to the concave-convex pattern 3 of the light guide plate 2. The prism is formed on the surface of the prism sheet 5 on the light guide plate 2 side. The prism pitch of the prism sheet 5 is 15 μm, and the inclination angle of the prism is defined so that the light emitted from the light guide plate 2 is efficiently corrected in the normal direction of the light guide plate 2. The prism sheet 5 emits the light whose direction is corrected in this way to the side opposite to the light guide plate 2 side. The prism sheet 5 is not necessarily limited to correcting incident light in the normal direction of the light guide plate 2, but may be any material that corrects incident light in a direction close to the normal direction of the light guide plate 2.

  The light emitted from the prism sheet 5 becomes output light from the surface light source device 20. When a light irradiation target such as a liquid crystal panel is directly connected to the prism sheet 5, the emitted light of the prism sheet 5 becomes the output light of the surface light source device 20 as it is. When there is a prism sheet 5 that is further connected as a member of the surface light source device 20, the light after passing through those members becomes the output light of the surface light source device 20.

  The reflection plate (light reflection layer) 4 is provided on the side opposite to the light branching layer 6 side of the light guide plate 2 so that the light leaking from the light guide plate 2 is reflected to the light guide plate 2 side. Accordingly, the reflecting plate 4 reflects light leaking from the surface 2b opposite to the light emitting surface 2a of the light guide plate 2 toward the light guiding plate 2 and contributes to the light emitted from the light emitting surface 2a. Let The reflecting plate 4 is a thin sheet on which a metal thin film or a dielectric multilayer film is formed, and it is preferable that the reflecting plate 4 has little diffusion and high reflectance. The reflection plate 4 is disposed outside the surface 2b on which the concave / convex pattern 3 of the light guide plate 2 is formed. The actual occupation area of the concave / convex pattern 3 is smaller than the total area of the light guide plate 2, and the interface reflectance at the concave / convex pattern 3 is about 4% (for light guided through the light guide plate 2). Therefore, the light reflected by the reflecting plate 4 occupies most of the light emitted from the light emitting surface 2 a of the light guide plate 2.

  The light branching layer 6 transmits a part of the light emitted from the light emitting surface 2a of the light guide plate 2 and reflects a part thereof. In the present embodiment, a half mirror is used as the light branching layer 6. The half mirror can be created by forming a thin metal film such as silver or aluminum or a dielectric multilayer film on a thin transparent sheet so as to be in a semitransparent state.

  The transmittance of the half mirror can be freely changed according to the design of the concave / convex pattern 3 and the prism sheet 5 because the transmittance and reflectance of the half mirror can be easily set. A transmittance of about 50% is preferable.

  In the present embodiment, the half mirror has a uniform transmittance in the plane, but the transmittance may be non-uniform in the plane. For example, FIG. 3 shows an example in which the in-plane region of the half mirror is divided into 5 parts in length and breadth and the transmittance is changed for each grid. In the half mirror of the figure, the transmittance near the center is the highest, and decreases toward the periphery. By increasing the transmittance near the center in this way, the light transmitted near the center increases, so that the luminance near the center can be improved.

  As another design, it is also possible to increase the transmittance as the distance from the light source 1 is reduced, thereby reducing the light leaking from the terminal portion of the light guide plate 2 and creating a surface light source device with high light utilization efficiency. .

  Such a half mirror with non-uniform transmittance in the plane can be formed by, for example, mask vapor deposition.

  Another example of the light branching layer 6 includes a reflective layer in which an opening is formed on a mirror surface having a high reflectance. Various shapes such as a round shape, a square shape, and a line shape are conceivable as the opening shape. However, in order to prevent moire fringes, the pitch between the adjacent openings is sufficient compared to the pixel pitch of the liquid crystal panel 10. Must be small. Moreover, it is good also as a nonuniform shape, arrangement | positioning, and the transmittance | permeability in a surface.

  Still another example of the light branching layer 6 includes a polarization splitting layer. The polarization separation layer refers to a polarization selective reflection film having a function of selectively transmitting polarized light in a predetermined axis direction and reflecting other polarized light, represented by a product name DBEF manufactured by 3M, for example. If the polarization separation layer is used, the transmittance and reflectance of the light branching layer 6 can be controlled in accordance with the polarization state of the light emitted from the light guide plate 2.

  4 and 5 are cross-sectional views when the polarization splitting layer 7 is used as the light branching layer 6.

  As the direction of the transmission axis of the polarization separation layer 7, when the X direction and the Y direction used in FIG. 2 are used, in FIG. 4, the transmission axis is the Y direction, and in FIG. 5, the transmission axis is the X direction. is there.

  4 and 5, the light reflected by the polarization separation layer 7 is efficiently transmitted through the polarization separation layer 7 when reflected by the reflection plate 4 and re-enters the polarization separation layer 7. The retardation film 8 is laminated on the surface of the reflection plate 4 on the light guide plate 2 side. As the polarization separation layer 7, DBEF manufactured by 3M Company was used.

  The retardation film 8 may be disposed between the polarization separation layer 7 and the reflection plate 4, and the same effect can be obtained even when disposed between the polarization separation layer 7 and the light guide plate 2. The retardation film 8 is not always necessary.

  The retardation film 8 is transparent, the retardation satisfies a quarter wavelength condition (more specifically, the retardation value is about 140 nm), and the slow axis is inclined by 45 ° from the transmission axis of the polarization separation layer. It is preferable. In this case, the polarization direction of the light reflected by the polarization separation layer 7 and transmitted through the retardation film 8, reflected by the reflection plate 4 and transmitted through the retardation film 8 again is the transmission axis of the polarization separation layer 7. Since they are parallel, light is transmitted through the polarization splitting layer 7 very efficiently. Further, when birefringence occurs inside the light guide plate 2 when the light guide plate 2 is molded, it is preferable to set the phase difference in consideration thereof.

  Table 1 shows the results of measuring the transmittance of the polarization separation layer 7 when the transmission axis of the polarization separation layer 7 is the X direction or the Y direction.

  Table 1 shows the result of measuring the transmittance of the polarization separating layer 7 when light emitted from the light guide plate 2 is assumed and non-polarized light is incident from the 70 ° direction. When the transmission axis was in the X direction, the transmittance was 22%, and when the transmission axis was in the Y direction, the transmittance was 33%. That is, it is preferable to set the transmission axis of the polarization separation layer 7 in the Y direction because the transmittance is improved and the light use efficiency of the surface light source device 20 is higher.

  Table 1 also shows the same results when an antireflection layer is formed on the front and back surfaces of the polarization separation layer 7. When the antireflection layer is formed, the light reflection on the surface of the polarization separation layer 7 is reduced, so that the transmittance is increased. As the antireflection layer, a moth-eye structure having a fine structure was used. When the antireflection layer was formed, the transmittance was 42% when the transmission axis was in the X direction, and the transmittance was 33% when the transmission axis was in the Y direction.

  That is, when the antireflection layer is formed, the transmittance of the light branching layer 6 is improved and the light use efficiency of the surface light source device 20 is higher when the transmission axis of the polarization separation layer 7 is in the X direction. This result shows that surface reflection is very large especially for light in the X direction in the case of oblique incidence. This is a result that can be easily inferred from Fresnel's law.

  As the antireflection layer, a multilayer film deposited may be used. In that case, it is preferable to determine the respective film thicknesses so that the surface reflectance becomes the lowest at an oblique angle such as the 70 ° direction.

  As the polarization separation layer 7, a layer utilizing selective reflection of a spiral structure, a wire grid polarizer, or the like can be used.

  As still another light branching layer, for example, a transparent substrate or another liquid crystal panel can be used.

  In the surface light source device 20 having the above-described configuration, the light branching layer 6 partially transmits and partially reflects the light emitted from the light emitting surface 2a of the light guide plate 2, as shown in FIG. Although the light plate 2 is thin, light in a state in which the density of the emission pattern due to the pitch of the uneven pattern 3 of the light guide plate 2 is relaxed enters the prism sheet 5. When the liquid crystal panel 10 and the surface light source device 20 created by the above method are stacked to form the liquid crystal display device 100, the light incident on the prism sheet 5 in the surface light source device 20 has a uniform intensity by the light branching layer 6. Since it has a distribution, moire fringes that impair the display were not generated even though the light guide plate 2 was thin.

  Further, the surface light source device 20 does not require a diffusion layer, and since the parallelism of light does not change, the front luminance of the surface light source device does not decrease, and even if the microlens 13 is provided, the light collection effect is reduced. I never did.

  Further, when the polarization separation layer 7 is used as the light branching layer 6, the liquid crystal display device 100 is arranged such that the transmission axis of the polarization separation layer 7 and the transmission axis of the polarizing plate installed in the liquid crystal panel 10 are aligned. The brightness of the display was improved by 1.5 times, resulting in a bright display.

  Here, the relationship between the pitch p of the uneven pattern 3 of the light guide plate 2 and the thickness d of the light guide plate 2 and the effect of the surface light source device 20 will be described. As can be seen from the description of the background art, when acrylic, which is a general resin material, is used for the light guide plate 31 and the attenuation factor of light intensity that can be recognized by light and shade is 20%, in such a conventional typical configuration, Moire fringes were generated at p / d> 0.2. However, according to the surface light source device 20 of the present embodiment, it is possible to prevent the occurrence of moire fringes even when p / d> 0.2. Further, since it is extremely difficult to form the pitch p at 50 μm or less, when 100 μm near the general lower limit is set as the pitch p, p / d> 0.2 is d ≦ 0.5 mm. Thus, generation of moire fringes can be satisfactorily prevented by the thin light guide plate 2 having a thickness of 0.5 mm or less.

  As a comparative example, a liquid crystal display device was produced by laminating a surface light source device having the same configuration as that of the first embodiment except that the light branching layer 6 was not arranged, and a liquid crystal display panel. did.

[Second Embodiment]
Another embodiment of the present invention will be described below with reference to FIG. In addition, about the member of the same code | symbol as the member demonstrated in said 1st embodiment, it shall have the same function unless there is particular notice.

  FIG. 7 is a perspective view of the surface light source device 120 according to the present embodiment. The cross-sectional view of the surface light source device 120 is the same as FIG.

  The surface light source device 120 forms the uneven pattern 3 and the prism of the prism sheet 5 so as to be parallel to the light incident surface 2c of the light guide plate 2, and the light source 1 used in the first embodiment is connected to the light incident surface 2c. The configuration is the same as that of the surface light source device 20 of the first embodiment except that a plurality (three in this case) are arranged in the direction orthogonal to the thickness direction along the light incident surface 2c.

  As a result of laminating the liquid crystal panel 10 and the surface light source device 120 created by the above method, the moire fringes that impair the display, although the pixel pitch of the liquid crystal panel 10 and the pitch of the concavo-convex pattern 3 of the light guide plate 2 are close to each other. Did not occur.

  In the case where the polarization separation layer 7 is used as the light branching layer 6, if the transmission axis of the polarization separation layer 7 and the transmission axis of the polarizing plate installed in the liquid crystal panel 10 are arranged to coincide, The brightness was improved by a factor of 1.5, resulting in a bright display.

  In the present embodiment, more light sources 1 than three light sources can be used. Further, a linear light source such as a fluorescent tube can be used as the light source 1.

  As in the present embodiment, when the light source 1 is composed of a pseudo-line light source composed of an assembly of a plurality of point light sources or the line light source itself, light can be uniformly incident on a relatively large light guide plate 2. The surface light source device 120 can also be applied to a medium-sized liquid crystal that is slightly larger than a mobile phone.

  Each embodiment has been described above.

  By the way, Patent Document 3 describes an example in which a light branching layer made of a multilayer structure is disposed between a light guide plate and a correcting means.

  However, this configuration is intended to improve the luminance of the liquid crystal display device by using the light emitted from the surface light source device as polarized light, and does not describe moire fringes generated due to the thinness of the light guide plate.

  Further, this configuration is specialized for a linear light source, and a surface light source device formed concentrically around the light source is not described, but a liquid crystal display device having a microlens that requires more parallel light Can not be used.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can be particularly suitably used for a liquid crystal display device mounted on a portable device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, showing an embodiment of the present invention, is a cross-sectional view showing a main configuration of a liquid crystal display device. It is a perspective view which shows the structure of the surface light source device used for the liquid crystal display device of FIG. It is a perspective view which shows the in-plane distribution of the transmittance | permeability at the time of comprising a light branch layer with a half mirror. It is sectional drawing which shows the direction of the 1st transmission axis at the time of comprising a light branch layer with a polarization separation layer. It is sectional drawing which shows the direction of the 2nd transmission axis at the time of comprising a light branch layer with a polarization separation layer. It is sectional drawing which shows the state of the output light of the surface light source device in the liquid crystal display device of FIG. FIG. 24, showing another embodiment of the present invention, is a cross-sectional view illustrating a configuration of a main part of a liquid crystal display device. It is a perspective view which shows a prior art and shows the principal part structure of a surface light source device. It is sectional drawing which shows the structure of the surface light source device of FIG. It is a perspective view which shows a prior art and shows the principal part structure of the surface light source device which used the light source as the point light source. It is sectional drawing which shows the structure of the liquid crystal display device with which the liquid crystal panel provided with the micro lens was laminated | stacked. It is the top view and sectional drawing which show the 1st structural example of a micro lens. It is a top view which shows the 2nd structural example of a micro lens. It is a top view which shows the 3rd structural example of a micro lens. It is sectional drawing which shows the structure of the liquid crystal display device provided with the surface light source device which has a thick light-guide plate. It is sectional drawing which shows the structure of the liquid crystal display device provided with the surface light source device which has a thin light-guide plate. It is sectional drawing which shows the relationship between the dimension of a light-guide plate, and generation | occurrence | production of a moire fringe. It is sectional drawing which shows the structure of the liquid crystal display device provided with the surface light source device which has a diffused layer.

Explanation of symbols

1 Light source (point light source)
2 Light guide plate 2a Light exit surface 3 Uneven pattern (light extraction means)
4 Reflector (light reflection layer)
5 Prism sheet (correction means)
6 Light branching layer 7 Polarization separation layer (light branching layer)
8 Retardation film 10 Liquid crystal panel 11 Transmission opening 13 Microlens 20 Surface light source device 100, 120
Liquid crystal display

Claims (15)

A light source;
A light guide plate that introduces light emitted from the light source and advances the light internally;
Light extraction means formed at a predetermined pitch so as to reflect the light traveling inside the light guide plate and emit it in a predetermined direction from the light output surface of the light guide plate;
A light branching layer that transmits a part of the light emitted in the predetermined direction from the light emitting surface of the light guide plate and reflects a part thereof;
Correcting means that corrects light incident through the light branch layer in a direction close to the normal direction of the light guide plate and emits the light to the side opposite to the light guide plate side;
A light reflecting layer provided on the side opposite to the light branching layer side of the light guide plate so as to reflect light leaking from the light guide plate to the light guide plate side;
With
A surface light source device characterized in that the light emitted from the correcting means is output light.   The surface light source device according to claim 1, wherein the light source includes one or a plurality of point light sources. The light source is one point light source composed of one or a plurality of light emitters,
The light extraction means is formed as a pattern extending in a direction orthogonal to a radial direction of a circle having the point light source substantially at the center, and the pattern is arranged at the predetermined pitch in the radial direction of the circle. The surface light source device according to claim 1, wherein the surface light source device is a device. When the predetermined pitch of the light extraction means is p and the thickness of the light guide plate is d,
p / d> 0.2
The surface light source device according to claim 1, wherein:   The surface light source device according to claim 1, wherein a thickness of the light guide plate is 0.5 mm or less.   The surface light source device according to claim 1, wherein the light branching layer includes a half mirror.   The surface light source device according to claim 1, wherein the light branching layer includes a polarization separation layer. The light source is one point light source composed of one or a plurality of light emitters,
The surface light source device according to claim 7, wherein a transmission axis of the polarization separation layer is a radial direction of a circle substantially centered on the point light source.   The surface light source device according to claim 7, wherein an antireflection layer is formed on the polarization separation layer. The light source is one point light source composed of one or a plurality of light emitters,
10. The surface light source device according to claim 9, wherein a transmission axis of the polarization separation layer is a direction orthogonal to a radial direction of a circle having the point light source substantially in the center.   The surface light source device according to claim 7, wherein a retardation film is disposed between the light branching layer and the reflecting plate.   The surface light source device according to claim 11, wherein the retardation film satisfies a ¼ wavelength condition, and a slow axis is disposed to be inclined by 45 ° from a light transmission axis of the polarization separation layer.   12. A liquid crystal display device, wherein a liquid crystal panel is laminated on the correction means side of the surface light source device according to any one of claims 1 to 11.   14. The liquid crystal display device according to claim 13, wherein one microlens that collects output light of the surface light source device is formed for each transmissive opening formed in the liquid crystal panel.   The plurality of transmission openings formed in the liquid crystal panel form one or more rows, and one microlens for condensing output light of the surface light source device is formed for each row. The liquid crystal display device according to claim 13.

Images