JP2004271871A - Light guide plate, surface light source device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To decrease the number of parts and to brightly illuminate a liquid crystal display panel. <P>SOLUTION: The liquid crystal display device 1 has such a structure that a LED 8 is disposed in the entrance face 12 side formed by cutting out the corner portion of a light guide plate 2, the light from the LED 8 propagates through the light guide plate 2 and while the light propagates, the light exiting from the exit face 3 of the light guide plate 2 is converged near to the normal direction of the exit face 3 of the light guide plate 2 by a prism sheet 4 disposed opposing to the exit face 3 of the light guide plate 2; and the converged light is used to illuminate a liquid crystal display panel 5. The optical axis direction of the LED 8 is approximately aligned to the direction of the transmission axis direction of a polarizing member 10 disposed in the light guide plate 2 side of the liquid crystal display panel 5. The back face 6 of the light guide plate 2 is provided with fine grooves 13 as a polarization converting means to convert the S-polarized component into the P-polarized component. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light guide plate of a surface light source device for illuminating a liquid crystal display panel of a mobile phone, a portable terminal device, an electronic dictionary, various electronic devices, a personal computer and the like from the back side, and a surface light source device using the light guide plate. And a liquid crystal display device that illuminates a liquid crystal display panel with the surface light source device.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a liquid crystal display device widely used in a mobile phone, a personal computer, and the like is a surface light source that illuminates a liquid crystal display panel from the back side in order to reduce the weight and thickness of the liquid crystal display and improve portability and usability. You are using equipment. This surface light source device allows light from a light source to enter the inside of a light guide plate and, in the process of the incident light propagating through the inside of the light guide plate, transmits light whose incident angle with respect to the emission surface of the light guide plate is less than the critical angle. Out of the light exit surface.
[0003]
As is generally known, in such a liquid crystal display device, a polarizing member of a liquid crystal display panel transmits only a specific linearly polarized light component (for example, a P-polarized light component) and transmits another linearly polarized light component (for example, an S-polarized light component). Component). However, the illuminating light generated by the surface light source device used in the liquid crystal display device is a non-biased ordinary light, so that about half of the light energy is absorbed by the polarizing member of the liquid crystal display panel, and the liquid crystal is It is known that light energy effectively used for illumination of a display panel is reduced to about half.
[0004]
As a result, the present applicant disposes a polarization separation element between the light guide plate and the liquid crystal display panel, arranges a polarization conversion element on the back surface side of the light guide plate, and uses the polarization separation element to illuminate a predetermined polarization plane. While selectively transmitting light, reflects light of a polarization plane orthogonal to the light of the predetermined polarization plane, and of the reflected light, light that has re-entered the light guide plate, and light that has exited from the back surface of the light guide plate. Have already devised a surface light source device in which the polarization conversion element converts the polarization into light having a predetermined polarization plane and returns the light into the light guide plate, thereby increasing the energy effectively used for illumination of the liquid crystal display panel. (Patent Document 1).
[0005]
In addition, the present applicant has a polarizing beam splitter that selectively transmits illumination light having a predetermined polarization plane and reflects light having a polarization plane orthogonal to the predetermined polarization plane, between the light guide plate and the liquid crystal display panel. In addition to the arrangement, the light reflected by the polarization splitting element and re-entered into the light guide plate is polarization-converted by the projections formed on the back surface of the light guide plate, thereby increasing the light energy effectively used for illumination of the liquid crystal display panel. Such a surface light source device has already been devised (Patent Document 2).
[0006]
[Patent Document 1]
JP-A-9-138406 (paragraphs 0036 to 0038, see FIG. 2)
[Patent Document 2]
JP-A-11-142849 (paragraphs 0053, 0059, 0060, see FIG. 1).
[0007]
The conventional surface light source devices disclosed in Patent Literatures 1 and 2 emit a large amount of light having a predetermined polarization plane that selectively passes through a polarizing member of a liquid crystal display panel, thereby increasing the display luminance of the liquid crystal display panel, and making it bright and easy to see. It exhibits excellent lighting performance of being able to display an image.
[0008]
[Problems to be solved by the invention]
However, the conventional surface light source device disclosed in Patent Literature 1 includes a polarization splitting element and a polarization conversion element as separate members in addition to the light guide plate. Was likely to occur.
[0009]
In Patent Document 2 described above, polarization conversion is performed by a projection formed on the back surface of the light guide plate, and the risk of light loss is smaller than that in Patent Document 1, but the polarization separation element does not. Since it is arranged separately from the optical plate, there is a possibility that light loss may occur due to the arrangement of the polarization separation element.
[0010]
Therefore, an object of the present invention is to illuminate a liquid crystal display panel brightly with a smaller number of components than in the related art by devising the shape of the light guide plate and the arrangement of the light source.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, light from a light source propagates in the light guide plate, and light emitted from an emission surface of the light guide plate in the process of the propagation is arranged to face the emission surface of the light guide plate. The present invention relates to a surface light source device which is deflected by a light control member toward a normal direction of the light exit surface of the light guide plate and illuminates a liquid crystal display panel with the deflected light. In the surface light source device according to the present invention, the light source is disposed at a corner of the light guide plate, and an optical axis direction of the light source substantially coincides with a light transmission axis direction of the polarizing member on the light guide plate side of the liquid crystal display panel. It is characterized by having
[0012]
According to a second aspect of the present invention, in the surface light source device according to the first aspect, a plurality of grooves extending substantially in the same direction as the optical axis direction are formed in parallel on a surface of the light guide plate opposite to the light exit surface. It is characterized by being formed.
[0013]
The invention of claim 3 relates to a liquid crystal display device comprising the surface light source device according to the invention of claim 1 or 2, and a liquid crystal display panel illuminated by the surface light source device.
[0014]
According to a fourth aspect of the present invention, there is provided a light guide plate in which light from a light source is incident on the inside, the light incident on the inside is emitted from an emission surface in a process of propagation, and the emitted light illuminates a liquid crystal display panel. It is about. In the light guide plate of the present invention, the light source is disposed at a corner portion, and an optical axis direction of the light source substantially coincides with a light transmission axis direction of a polarizing member on a surface opposite to the emission surface of the liquid crystal display panel. It is characterized by:
[0015]
According to a fifth aspect of the present invention, in the light guide plate according to the fourth aspect of the present invention, a large number of grooves extending substantially in the same direction as the optical axis direction are formed on a surface opposite to the light exit surface. I have.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
1 to 3 show a liquid crystal display device 1 according to a first embodiment of the present invention. FIG. 1 is an exploded perspective view of the liquid crystal display device 1. FIG. 2 is a plan view of the liquid crystal display device 1 in which a liquid crystal display panel and a light control member, which will be described later, are indicated by two-dot chain lines. FIG. 3 is a cross-sectional view of the liquid crystal display device 1 taken along the line Aa-Aa in FIG.
[0018]
(Schematic configuration of liquid crystal display device)
As shown in these drawings, in the liquid crystal display device 1, the light control member 4 and the liquid crystal display panel 5 are sequentially superimposed on the light exit surface 3 side of the light guide plate 2, and the rear surface of the light guide plate 2 (the opposite side to the light exit surface 3). The reflection member 7 is disposed so as to face the surface 6). An LED (light emitting diode) 8 as a light source is arranged at one corner of the light guide plate 2. Here, the polarizing member 10 on the light guide plate 2 side of the liquid crystal display panel 5 is formed to be inclined such that the direction of the light transmission axis L1 is substantially diagonal to the liquid crystal display panel 5 having a rectangular shape. Can be transmitted. In these figures, the light guide plate 2, the LED 8, the reflection member 7, and the light control member 4 constitute a surface light source device 11 that illuminates the liquid crystal display panel 5 from the back side.
[0019]
(Light guide plate)
The light guide plate 2 is formed using a material having excellent light transmittance, such as polycarbonate (PC), polymethyl methacrylate (PMMA), and a cycloolefin resin material. As shown in FIG. 2, the light guide plate 2 has a substantially rectangular planar shape (emission surface shape), and is formed in a substantially wedge-shaped cross-section such that its thickness becomes thinner as the distance from the LED 8 increases. (See FIG. 3). The light guide plate 2 is inclined so that the rear surface 6 approaches the emission surface 3 as the distance from the LED 8 increases.
[0020]
At one corner of the light guide plate 2, an incident surface 12 for taking in light from the LED 8 is formed so as to be notched. The light incident surface 12 of the light guide plate 2 is formed so as to be substantially perpendicular to one diagonal L2 of the light exit surface 3. The LED 8 is disposed so as to face the incident surface 12 of the light guide plate 2. The LED 8 is arranged so that its optical axis is substantially orthogonal to the incident surface 12 of the light guide plate 2, and substantially matches the direction of the light transmission axis L 1 of the light guide plate side polarizing member 10 of the liquid crystal display panel 5. ing. That is, the optical axis of the LED 8 matches the diagonal line L2 on the emission surface 3 of the light guide plate 2. Therefore, in the following description, the optical axis of the LED 8 will be represented by a diagonal code L2.
[0021]
On the back surface 6 of the light guide plate 2, fine grooves 13 are formed as polarization conversion means for converting the S-polarized light component into the P-polarized light component. As shown in FIGS. 4, 5 and 7, the fine groove 13 is formed so as to extend in a direction substantially perpendicular to the incident surface 12 (a direction substantially along the optical axis L2 of the LED 8). A plurality is formed continuously in a direction substantially orthogonal to the axis L2. The cross-sectional shape of the fine groove 13 changes little by little as it approaches the LED 8 at a position near the incident surface 12.
[0022]
More specifically, the fine grooves 13 include two types of first fine grooves 13A and second fine grooves 13B having different cross-sectional shapes, and the first fine grooves 13A and the second fine grooves 13B are connected to each other. They are formed alternately on the back surface 6 of the light plate 2 (see FIG. 5). Then, the first fine groove 13A and the second fine groove 13B are located at positions more distant from the LED 8 than the diagonal line L3 and along the line AA as shown in FIGS. In the section shown by cutting, the cross-sectional shapes of the first fine groove 13A and the second fine groove 13B are all substantially triangular. In addition, in both the fine grooves 13A and 13B, first, the first fine groove 13A is located at a position closer to the LED 8 than the diagonal line L3 and in a cross section cut along the line BB at a position near the diagonal line L3. Are formed so as to have a substantially arc-shaped cross section, and the groove depth is gradually reduced from the cross section along the CC line to the cross section along the EE line (as the LED 8 approaches). I have.
[0023]
On the other hand, the second fine groove 13B is located at a position closer to the LED 8 than the diagonal line L3, and in a cross section cut along the line BB at a position near the diagonal line L3, along the line AA described above. It is formed in a substantially triangular cross-section similar to the cross-sectional shape shown by cutting. In addition, the second fine groove 13B is formed in an arc shape substantially similar to the cross-sectional shape of the first fine groove 13A in a cross section cut along the line CC closer to the LED 8 than the line BB. ing. The second fine groove 13B has a groove depth which is made shallower than the adjacent first fine groove 13A more steeply than that of the adjacent first fine groove 13A. It is formed in an arc shape with a shallow depth. Further, the depth of the second fine groove 13B is made shallower as approaching the LED 8, the groove 13 is cut up between the DD line and the EE line, and cut along the EE line. In the cross section shown, the projection is deformed into a projection slightly projecting in an arc shape. Note that the projecting portion that protrudes slightly in an arc shape is not a groove, but will be treated as a part of the second fine groove 13A for convenience of explanation. Further, the first fine groove 13A and the second fine groove 13B described above are smoothly deformed from a cross-sectional shape shown along a line AA to a cross-sectional shape shown along a line EE. Is formed. Further, in the light guide plate 2 of the present embodiment, the first fine groove 13A and the second fine groove 13B both gradually decrease the depth of each groove by gradually increasing the radius of curvature of the arc without changing the groove pitch. It is made to let.
[0024]
As described above, by forming the first fine groove 13A and the second fine groove 13B, in the vicinity of the LED 8, light from the LED 8 propagates in the width direction of the light guide plate 2 (the direction orthogonal to the plate thickness direction). The light from the LED 8 is guided in such a manner that the light from the LED 8 is reflected in multiple directions by a curved surface that is convex inside the light guide plate 2 so that the light from the LED 8 is not obstructed by the first fine groove 13A and the second fine groove 13B. The light can be widely propagated inside the light plate 2. As a result, in the light guide plate 2 of the present embodiment, it is possible to increase the brightness of a portion where a dark portion is likely to be generated at the end in the width direction of the light guide plate 2 (for example, near both ends of the diagonal line L3 in FIG. 4). As a result, the brightness of the light emitted from the light guide plate 2 can be made uniform. On the other hand, in a portion away from the LED 8 by a certain distance or more, the light condensing function by the first fine groove 13A and the second fine groove 13B is sufficiently exhibited, and the light from the LED 8 can be efficiently emitted. Thereby, the luminance of the light emitted from the light exit surface 3 of the light guide plate 2 is made uniform, and the luminance of the emitted light is increased.
[0025]
When the light from the LED 8 enters the inside from the incident surface 12, the light guide plate 2 having such a shape reflects the incident light on the emission surface 3 and the back surface (reflection surface) 6 while the wedge-shaped tip 14 side. It is designed to propagate toward. Then, in the process of propagating light inside the light guide plate 2, light whose incident angle with respect to the emission surface 3 of the light guide plate 2 is equal to or smaller than the critical angle is emitted from the emission surface 3 of the light guide plate 2.
[0026]
It is known from the measured data that the intensity distribution of the light emitted from the light guide plate 2 is the strongest in the vicinity of approximately 70 degrees with respect to the normal direction of the emission surface 3 of the light guide plate 2. Here, assuming that the refractive index of the light guide plate 2 is 1.5, the angle at which the light emitted most from the light exit surface 3 of the light guide plate 2 enters the light exit surface 3 of the light guide plate 2 is about 39 degrees. The incident angle of 39 degrees is a value close to the Brewster's angle (about 34 degrees) at the interface between the light guide plate 2 and the air. Among the light incident on the light exit surface 3 at the incident angle (about 39 degrees) close to the Brewster angle, the ratio of the light emitted from the light exit surface 3 and the light reflected by the light exit surface 3 is as shown in FIG. , Can be easily calculated from a graph showing the relationship between the incident angle θ1 and the reflectance.
[0027]
Considering the known data in FIG. 13 (for example, see FIG. 4.7 on page 94 of “Applied Optics” (published on Dec. 10, 2001) issued by Ohm Co., Ltd.), the light guide plate 2 FIG. 6 shows the propagation state of the light inside. As shown in FIG. 6, of the light propagating inside the light guide plate 2, the light incident on the exit surface 3 of the light guide plate 2 at about 39 degrees has a P-polarized component of 100% and an S-polarized component. Is 100%, which is an unbiased light. However, the light emitted from the emission surface 3 of the light guide plate 2 into the air has a P-polarized component of 95.7% and an S-polarized component of 70.5%. On the other hand, the light reflected by the light exit surface 3 of the light guide plate 2 has a P-polarized component of 4.3% and an S-polarized component of 29.5%. That is, nearly 90% of the reflected light is an S-polarized component. Therefore, if the S-polarized light component is converted into a P-polarized light component and the converted light is incident on the light exit surface 3, the ratio of light emitted from the light exit surface 3 increases, and the light is reflected on the light exit surface 3. The proportion of light emitted is reduced. That is, the emission of light from the emission surface 3 of the light guide plate 2 is promoted, and a large amount of P-polarized light is emitted. Therefore, in the present embodiment, as shown in FIG. 8, the light is reflected on the emission surface 3 side by the slopes 15 and 16 between the first fine groove 13A and the second fine groove 13B formed on the back surface 6 of the light guide plate 2. The reflected light is internally reflected twice to cause disturbance in the polarization state of the light, twist the polarization plane of the S-polarized light, and convert a part of the polarization component of the light from the S-polarization component to the P-polarization component (S -P conversion).
[0028]
As described above, from the emission surface 3 of the light guide plate 2, the optical axis direction (the diagonal line L2 direction) substantially matches the light transmission axis L1 direction of the polarizing member 10 on the light guide plate 2 side of the liquid crystal display panel 5, and Directional light is emitted such that the maximum intensity of the light is directed in a direction inclined by about 70 degrees with respect to the normal direction of the emission surface 3. The light emitted from the light exit surface 3 of the light guide plate 2 has its traveling direction normal to the light exit surface 3 of the light guide plate 2 while its polarization state is substantially maintained by a prism sheet 4 as a light control member described later. That is, the light is converted into directional light that is close to the direction. Here, since the polarizing member 10 on the light guide plate 2 side of the liquid crystal display panel 5 transmits a P-polarized component which is a specific linearly polarized light component, the light guide plate 2 of the present embodiment is connected to the liquid crystal display device. When used as a component of the liquid crystal display panel 1, the ratio of the light emitted from the light guide plate 2 that is effectively used as illumination light for the liquid crystal display panel 5 increases, and the illumination brightness of the liquid crystal display panel 5 is increased. 5 can be easily viewed.
[0029]
(Light control member)
As shown in FIG. 1, the prism sheet 4 as a light control member is formed of a plastic material having excellent light transmittance (for example, PET, PMMA, PC), and is substantially the same as the emission surface 3 of the light guide plate 2. Is formed. In the prism sheet 4, a plurality of fine prism protrusions 17 extending in a direction orthogonal to the fine grooves 13 of the light guide plate 2 are formed in parallel on the surface of the light guide plate 2 facing the emission surface 3. The prism projections 17 of the prism sheet 4 have a substantially triangular cross-sectional shape, and function to deflect the light emitted from the light guide plate 2 substantially toward the normal direction of the emission surface 3 of the light guide plate 2.
[0030]
(Reflective member)
As shown in FIG. 1, the reflection member 7 is, for example, a PET sheet excellent in light reflectivity formed by mixing a white pigment or a film on which a metal excellent in light reflectivity such as aluminum is deposited. The light guide plate 2 is formed in a planar shape substantially similar to the back surface 6 of the rectangular light guide plate 2. The reflecting member 7 functions to reflect light emitted from the back surface 6 side of the light guide plate 2 and return the light to the inside of the light guide plate 2. The reflection member 7 may be configured such that the inside of the housing in which the light guide plate 2 is housed is a surface having excellent light reflectivity (whitened surface), and the housing itself having the light reflection function is the reflection member.
[0031]
(Effects of the present embodiment)
FIG. 9 to FIG. 12 are diagrams for explaining the effect of the liquid crystal display device 1 according to the present embodiment. 9 and 10 show the results of measuring the luminance of the display screen of the liquid crystal display device 1 according to the present embodiment, and show the optical axis (L2) direction of the LED 8 and the polarization member 10 of the liquid crystal display panel 5. FIG. The brightness of the display screen of the liquid crystal display panel 5 when the direction of the light transmission axis L1 is matched is measured. 11 to 12 are arranged such that the direction of the light transmission axis L1 of the polarizing member 10 of the liquid crystal display panel 5 is orthogonal to the direction of the optical axis L2 of the LED 8 of the surface light source device 11 according to the present embodiment. 4 shows a result of measuring the luminance of the display screen of the liquid crystal display device 1 in the case.
[0032]
As is clear from the comparison of these figures, according to the present embodiment shown in FIGS. 9 and 10, the brightness of the central portion is increased by 15% as compared with the cases shown in FIGS. There was also a 15% increase in average luminance. From these results, by making the direction of the optical axis L2 of the LED 8 coincide with the direction of the light transmission axis L1 of the polarizing member 10 on the light guide plate 2 side of the liquid crystal display panel 5, the light from the light guide plate 2 is effectively used as illumination light. It is understood that the ratio increases and the display screen of the liquid crystal display panel 5 can be brightened.
[0033]
As is clear from the above, in the liquid crystal display device 1 of the present embodiment, the direction of the optical axis L2 of the LED 8 is substantially the same as the direction of the light transmission axis L1 of the polarizing member 10 located on the light guide plate 2 side of the liquid crystal display panel 5. Since a large amount of specific linearly polarized light (P-polarized light component) that matches and transmits through the polarizing member 10 on the light guide plate 2 side of the liquid crystal display panel 5 is emitted from the light guide plate 2, Light used as illumination light increases, the display luminance of the screen of the liquid crystal display panel 5 is high, and the screen of the liquid crystal display panel 5 is easy to see.
[0034]
Further, according to the present embodiment, the prism sheet 4 as a light control member is disposed between the emission surface 3 of the light guide plate 2 and the liquid crystal display panel 5, and the light emitted from the light guide plate 2 is Since the light is deflected toward the normal direction of the light exit surface 3, it is possible to illuminate the liquid crystal display panel 5 more brightly in combination with the effect of the present embodiment.
[0035]
Further, according to the present embodiment, the fine grooves 13 as the polarization conversion means are integrally formed on the back surface 6 side of the light guide plate 2, and the polarization conversion means is separately provided in addition to the light guide plate 2. Since the structure is not such a structure, the number of parts of the surface light source device 11 and the liquid crystal display device 1 including the surface light source device 11 can be reduced, and the thickness and weight can be reduced, and the product price can be reduced. Can be achieved.
[0036]
In the present embodiment, the direction of the optical axis (L2) substantially matches the direction of the light transmission axis L1 of the polarizing member 10 on the light guide plate 2 side of the liquid crystal display panel 5. As a result, in the present embodiment, as shown in FIG. 2, the direction of the optical axis (L2) is set to be substantially diagonal to the light guide plate 2 having a substantially square planar shape.
However, when the direction of the diagonal line L2 of the light guide plate 2 is shifted from the direction of the light transmission axis L1 of the liquid crystal display panel 1 on the light guide plate 2 side, the direction of the optical axis is shifted with respect to the diagonal line L2 of the light guide plate 2. You may.
[0037]
In the present embodiment, the light guide plate 2 has a wedge-shaped cross section along the optical axis direction. However, the present invention is not limited to this, and the light guide plate 2 may have the same thickness. . Further, in FIG. 2, the light guide plate 2 has an additional incident surface separately formed at a corner portion of the light guide plate 2 facing the incident surface 12, and an LED is arranged so as to face the additional incident surface. Light from a plurality of LEDs may be incident.
[0038]
[Second embodiment]
14 to 16 show a liquid crystal display device 1 according to a second embodiment of the present invention. FIG. 14 is an exploded perspective view of the liquid crystal display device. FIG. 15 is a cross-sectional view showing the liquid crystal display device cut along the optical axis direction. FIG. 16 is a cross-sectional view of the light guide plate shown in FIG. 15 and is a view for explaining the shape of the light guide plate on the emission surface side. FIG. 17 is a perspective view schematically showing the appearance of the light guide plate, and is a diagram for explaining emission light characteristics. In the liquid crystal display device 1, the same components as those of the liquid crystal display device 1 according to the above-described first embodiment are denoted by the same reference numerals, and the description will be the same as that of the above-described first embodiment. Is omitted and described in detail.
[0039]
As shown in these drawings, the light exit surface 3 of the light guide plate 2 used in the liquid crystal display device 1 according to the present embodiment extends in a direction substantially orthogonal to the optical axis direction and extends in the optical axis direction. A plurality of protrusions 28 are formed along the line. The protrusion 28 has a substantially triangular cross-sectional shape along the optical axis direction, and includes a first inclined surface 30 that is gently inclined so as to decrease the thickness of the light guide plate 2 as the distance from the incident surface 12 increases. And a second inclined surface 31 that sharply inclines in a direction opposite to the first inclined surface 30 from an end of the first inclined surface 30.
[0040]
As shown in FIG. 16, the first inclined surface 30 of the projection 28 emits light from the light exit surface 3 side of the light guide plate 2 in the light traveling inside the light guide plate 2 in a direction away from the incident surface 12. Light other than light is reflected, but light is reflected at an angle twice as large as the inclination angle θa, that is, at an angle larger by 2θa, as compared with the case where the light is reflected at the emission surface 3 that is not inclined. become. As a result, the angle of incidence of light that is reflected on the back surface 6 after being reflected on the first inclined surface 30 and that is incident on the other first inclined surface 30 after reflected on the exit surface 3 that is not inclined The angle of incidence of the light reflected on the back surface 6 and subsequently incident on the non-inclined exit surface 3 is smaller than that of the case where the light is emitted from the non-inclined exit surface 3. As described above, the first inclined surface 30 of the light guide plate 2 serves as an emission promotion function surface for promoting emission of light.
[0041]
Further, as long as the pitch between the projections 28 is the same, the larger the inclination angle θb of the second inclined surface 31 of the projection 28 is, the larger the area ratio of the first inclined surface 30 on the exit surface 3 side is. As a result, the emission promoting function of the first inclined surface 30 is further increased. However, by setting the inclination angle θb of the second inclined surface 31 to an appropriate angle, the second inclined surface 31 reflects light that is reflected on the front end 14 side of the light guide plate 2 facing the incident surface 12 and travels toward the incident surface 3 side. It functions as an emission promoting function surface.
[0042]
Here, the above-described inclination angle θa of the first inclined surface 30 is determined in the range of 0.1 ° to 5 °, and is usually determined to be about 1 °. Further, the inclination angle θb of the second inclined surface 31 is determined in the range of 10 ° to 90 °, and is usually determined to be about 45 °.
[0043]
According to the present embodiment having such a configuration, light is reflected twice on the slopes 15 and 16 formed between the first fine groove 13A and the second fine groove 13B formed on the back surface 6 of the light guide plate 2. , The light polarization state is disturbed, a part of the S-polarized light component of the light is converted into a P-polarized light component (SP conversion), and the light reflected by the slopes 15 and 16 is emitted. Is promoted by the first inclined surface 30 or the second inclined surface 31, and the light emitted from the exit surface 3 is directed in the optical axis direction. As a result, the liquid crystal display device 1 of the present embodiment can efficiently transmit the light emitted from the light guide plate 2 through the light transmission axis L1 of the polarizing member 10 of the liquid crystal display panel 5, and Light absorption by the polarizing member 10 is reduced to enable high-brightness and easy-to-view screen display.
[0044]
In the liquid crystal display device 1 of the present embodiment, light emitted from the light exit surface 3 of the light guide plate 2 in the optical axis direction is applied to the light exit surface 3 of the light guide plate 2 by a prism sheet 4 as a light control member. It is designed to convert toward the line direction. For example, as shown in FIG. 17, in the cross section along the optical axis of the light exit surface 3 of the light guide plate 2, the main exit direction of the light exiting from the first inclined surface 30 is 70 ° clockwise from the normal direction. (−θ = 70 °). The traveling direction of the light in the main emission direction of 70 ° is converted by the prism sheet 4 toward the normal direction. As a result, according to the present embodiment, the liquid crystal display panel 5 is efficiently illuminated.
[0045]
[Third Embodiment]
FIGS. 18 and 19 show a light guide plate 2 of a liquid crystal display device 1 according to a third embodiment of the present invention. FIG. 18 is an external perspective view of the light guide plate 2. FIG. 19 is a sectional view showing the light guide plate 2 of FIG. 18 cut along the optical axis (L2). In this light guide plate 2, the same components as those of the light guide plate 2 of the liquid crystal display device 1 according to the above-described first embodiment are denoted by the same reference numerals, and the description of the above-described first embodiment will be omitted. A detailed description will be omitted, omitting a duplicate description.
[0046]
In the light guide plate 2 according to the present embodiment, the projection 28 formed of the first inclined surface 30 and the second inclined surface 31 is provided in a predetermined range from the entrance surface 12 of the exit surface 3 of the light guide plate 2 (for example, the entrance surface 3). (Where L = 20T, where T is the plate thickness). By forming in this manner, the brightness balance of the outgoing light in the entire area of the outgoing surface 3 is adjusted, and the brightness distribution of the illuminating light matches the image display form, thereby enabling a bright and easy-to-view screen display.
[0047]
[Fourth Embodiment]
FIGS. 20 to 23 show a light guide plate 2 of a liquid crystal display device 1 according to a fourth embodiment of the present invention. FIG. 20 is an external perspective view of the light guide plate 2. FIG. 21 is a cross-sectional view of the light guide plate 2 taken along a line CC of FIG.
FIG. 22 is a diagram for explaining in detail the shape of the light guide plate 2 on the emission surface 3 side. FIG. 23 is a view for explaining the cross-sectional shapes D1-D1 to D4-D4 of FIG. In this light guide plate 2, the same components as those of the light guide plate 2 of the liquid crystal display device 1 according to the above-described first embodiment are denoted by the same reference numerals, and the description of the above-described first embodiment will be omitted. A detailed description will be omitted, omitting a duplicate description.
[0048]
As shown in these figures, the light exit surface 3 of the light guide plate 2 according to the present embodiment is within a predetermined range from the incident surface 12 (for example, when the plate thickness of the incident surface is T, L = 20T). In the figure, a plurality of prism grooves 32 extending in a direction substantially perpendicular to the incident surface 12 are formed continuously in a direction parallel to the incident surface 12. The prism groove 32 has a substantially arc-shaped cross section parallel to the incident surface 12, and is formed so that its depth gradually decreases as the distance from the incident surface 12 increases, as shown in detail in FIGS. 22 and 23. In addition, it is configured to cut up at a position separated from the incident surface 12 by a predetermined distance L. A projection 28 composed of a first inclined surface 30 and a second inclined surface 31 serving as an emission promoting function surface is provided in the entire area of the emission surface 3 where the prism groove 32 is not formed in the extending direction of the prism groove 32. Are formed so as to be substantially orthogonal.
[0049]
In such a light guide plate 2, the prism groove 32 on the exit surface 3 side diffuses light emitted from the inside of the light guide plate 2 (light reflected by the fine grooves 13 on the back surface 6 and having directivity), and the incident surface 12 A bright line (a linearly abnormally bright portion that is generated substantially parallel to the incident surface 12) that is likely to occur in the vicinity is suppressed. Moreover, the prism groove 32 on the exit surface 3 side has a groove depth that decreases as the distance from the entrance surface 12 decreases, and the light diffusion function decreases as the distance from the entrance surface 12 increases. The light is strongly diffused near 12 and the light diffusion is suppressed in a portion far from the incident surface 12 where the bright line is less likely to occur. Then, the projection 28 composed of the first inclined surface 30 and the second inclined surface 31 which are the emission promoting function surfaces of the emission surface 3 of the light guide plate 2 is reflected by the fine grooves 13 on the back surface 6 and has directivity. Promotes light emission. As a result, the light guide plate 2 of the present embodiment can suppress the occurrence of bright lines that degrade the illumination quality, increase the emission light luminance, and enable bright and easy-to-view image display.
[0050]
Further, in the light guide plate 2 of the present embodiment, the light from the LEDs 8 in the width direction (the thickness direction) of the light guide plate 2 near the incident surface 12 is formed by making the cross-sectional shape of the prism groove 32 substantially arc-shaped. The light from the LED 8 can be reflected in multiple directions by the curved surface that is convex inside the light guide plate 2 while preventing the light from propagating in the orthogonal direction) from being hindered by the prism groove 32. The light can be widely propagated inside the light guide plate 2. Note that a light guide plate (not shown) in which the cross-sectional shape of the prism groove 32 has a substantially triangular cross-section even in the vicinity of the LED 8 tends to hinder the propagation of light from the LED 8 due to the inclined surface forming the cross-sectional shape. Compared to the light guide plate 2 of the embodiment, it is difficult to propagate light from the LED 8 widely in the width direction of the light guide plate.
[0051]
[Other Modifications]
In the above-described second to fourth embodiments, the mode in which the predetermined distance L from the incident surface 12 is set to 20T has been exemplified. However, the present invention is not limited to this, and the size of the exit surface 3 of the light guide plate 2 and the light source It is preferable to set the predetermined distance L to an optimal size according to the type and the like.
[0052]
【The invention's effect】
As described above, according to the present invention, the direction of the optical axis of the light source substantially coincides with the direction of the light transmission axis of the polarizing member of the liquid crystal display panel, and the polarizing member of the liquid crystal display panel is polarized by the polarization conversion means formed on the back side of the light guide plate. Since the emission of the specific linearly polarized light component to be transmitted is promoted, and the light emitted from the light guide plate can be efficiently used as the illumination light for the liquid crystal display panel, the illumination brightness of the liquid crystal display panel can be improved.
[0053]
Further, according to the present invention, since the polarization conversion means is formed on the back side of the light guide plate and the polarization conversion means is not arranged separately from the light guide plate, the surface light source device and the liquid crystal display having the surface light source device The number of parts of the device can be reduced, the device can be made thinner and lighter, and the price can be reduced.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a liquid crystal display device according to a first embodiment of the present invention.
FIG. 2 is a plan view of the liquid crystal display device, in which a liquid crystal display panel and a light control member are indicated by a two-dot chain line.
FIG. 3 is a cross-sectional view of the liquid crystal display device taken along the line Aa-Aa in FIG. 2;
FIG. 4 is a plan view of the light guide plate according to the first embodiment of the present invention.
5A is a cross-sectional view taken along the line AA of FIG. 4, FIG. 5B is a cross-sectional view taken along the line BB of FIG. 4, FIG. 5C is a cross-sectional view taken along line CC of FIG. 4, FIG. 5D is a cross-sectional view taken along line DD of FIG. 4, and FIG. 5) is a cross-sectional view taken along line EE in FIG.
FIG. 6 is a diagram for explaining a propagation state of light inside the light guide plate, and is a side view showing a part of the light guide plate in an enlarged manner.
FIG. 7A is a cross-sectional view of the light guide plate cut along a first fine groove, and FIG. 7B is a cross-sectional view of the light guide plate cut along a second fine groove. FIG.
FIG. 8 is a diagram schematically showing the progress of light reflected by the slope on the back surface of the light guide plate.
FIG. 9 is a diagram three-dimensionally showing a luminance measurement result of the display screen of the liquid crystal display panel when the optical axis of the light guide plate and the light transmission axis of the polarizing member of the liquid crystal display panel are matched.
FIG. 10 is a plan view illustrating a luminance measurement result of the display screen of the liquid crystal display panel when the optical axis of the light guide plate and the light transmission axis of the polarizing member of the liquid crystal display panel are matched.
FIG. 11 is a diagram three-dimensionally showing a luminance measurement result of the display screen of the liquid crystal display panel when the optical axis of the light guide plate is orthogonal to the light transmission axis of the polarizing member of the liquid crystal display panel.
FIG. 12 is a plan view showing a luminance measurement result of the display screen of the liquid crystal display panel when the optical axis of the light guide plate is orthogonal to the light transmission axis of the polarizing member of the liquid crystal display panel.
FIG. 13 shows the relationship between the angle of incidence (θ1) of light on the exit surface of the light guide plate and the reflectivity when light is emitted from the inside of the light guide plate (refractive index n = 1.5) to the atmosphere. FIG.
FIG. 14 is an exploded perspective view of a liquid crystal display device according to a second embodiment of the present invention.
FIG. 15 is a cross-sectional view illustrating a liquid crystal display device according to a second embodiment of the present invention, cut along the optical axis direction.
FIG. 16 is a cross-sectional view of the light guide plate shown in FIG. 15, illustrating the shape of the light guide plate on the exit surface side.
FIG. 17 is a perspective view schematically showing the appearance of the light guide plate, and is a diagram for explaining the emission light characteristics.
FIG. 18 is an external perspective view showing a light guide plate of a liquid crystal display device according to a third embodiment of the present invention.
19 is a sectional view showing the light guide plate of FIG. 18 cut along the optical axis L2.
FIG. 20 is an external perspective view showing a light guide plate of a liquid crystal display device according to a fourth embodiment of the present invention.
21 is a sectional view showing the light guide plate of FIG. 20 cut along the optical axis L2.
FIG. 22 is a diagram for explaining in detail an emission surface shape of the light guide plate of FIG. 21;
23 (a) is a prism groove shape on the exit surface side in a section D1-D1 in FIG. 22 (a), and FIG. 23 (b) is a prism groove shape on the exit surface side in a section D2-D2 in FIG. 22 (a). FIG. 23 (c) shows the prism groove shape on the exit surface side in the section D3-D3 in FIG. 22 (a), and FIG. 23 (d) shows the prism groove shape on the exit surface side in the section D4-D4 in FIG. 22 (a). It has a prism groove shape.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Liquid crystal display device, 2 ... Light guide plate, 3 ... Outgoing surface, 5 ... Liquid crystal display panel, 6 ... Back surface (surface opposite to the outgoing surface), 10 ... Polarizing member, 11 ... Surface Light source device, 12: incident surface (side surface), 13: fine groove (polarization conversion means), 20: projection (polarization conversion means, L1: light transmission axis, L2: optical axis)

Claims (5)

The light from the light source propagates in the light guide plate, and in the process of the propagation, the light emitted from the light exit surface of the light guide plate is disposed at the light control member arranged to face the light exit surface of the light guide plate. In the surface light source device, which is deflected near the normal direction of the emission surface and illuminates the liquid crystal display panel with the deflected light,
The surface light source device, wherein the light source is disposed at a corner of the light guide plate, and an optical axis direction of the light source substantially matches a light transmission axis direction of a polarizing member on the light guide plate side of the liquid crystal display panel. 2. The surface light source device according to claim 1, wherein a plurality of grooves extending substantially in the same direction as the optical axis direction are formed in parallel on a surface of the light guide plate opposite to the light exit surface. 3. A liquid crystal display device comprising: the surface light source device according to claim 1; and a liquid crystal display panel illuminated by the surface light source device. In the light guide plate, the light from the light source is made incident on the inside, and the light incident on the inside is emitted from the emission surface in the process of propagation, and the liquid crystal display panel is illuminated with the emitted light.
A light guide plate, wherein the light source is disposed at a corner portion, and an optical axis direction of the light source substantially coincides with a light transmission axis direction of a polarizing member on a surface side of the liquid crystal display panel facing the emission surface. 5. The light guide plate according to claim 4, wherein a number of grooves extending in substantially the same direction as the optical axis direction are formed in parallel on a surface opposite to the light exit surface.

Images