JPH1152380A - Side light type surface light source device and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the utilization efficiency of illumination light and to emit high- grade illumination light by repetitively forming projecting parts on the exit surface of a planar member or the rear surface facing this exit surface and smoothly forming these projecting parts according to the positions on the exit surface or the rear surface. SOLUTION: The very small projecting parts are repetitively formed on the exit surface 12c of the light scattering light transmission plate 12 as shown by an arrow (c) expanding an incident surface 12A side in a direction parallel with the incident surface. The very small projecting parts are so formed by working of metal molds for molding the light guide plate 12 in such a manner that the projecting parts are made successively smoother by the expansion of the radii of the curved surfaces connecting slopes 12E, 12F the nearer the flank side. In addition, the projecting parts are made successively smoother the nearer the incident surface from the front ends of the wedge shapes. As a result, the illumination light emitted to spread outward within the plane parallel with the incident surface 12A is corrected of the directivity so as to face inward and is emitted by the slopes 12E, 12F of the projecting parts repetitively formed in parallel with the incident surface. Then, the directivity of the exit light is corrected in the front surface direction of the exit surface 12c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sidelight type surface light source device and a liquid crystal display device, and more particularly to a sidelight type surface light source device formed such that a plate-like member becomes thinner as the distance from an incident surface increases. Applicable.
According to the present invention, the efficiency of use of illumination light is improved by repeatedly forming protrusions on the emission surface or the back surface opposite to the emission surface of the plate-shaped member and smoothly forming the protrusions according to the position on the emission surface or the back surface. And emits high-quality illumination light.

[0002]

2. Description of the Related Art Conventionally, for example, in a liquid crystal display device,
A liquid crystal display panel is illuminated by a sidelight type surface light source device, thereby reducing the overall shape.

That is, in the sidelight type surface light source device, a primary light source composed of a rod-shaped light source is arranged on a side of a plate-shaped member (that is, composed of a light guide plate), and illumination light emitted from the primary light source is applied to an end face of the light guide plate. More light enters the light guide plate. Further, the sidelight type surface light source device bends the illumination light and emits it from the plane of the light guide plate toward the liquid crystal display panel, whereby the overall shape can be reduced in thickness.

[0004] Such a side light type surface light source device is
A method in which the light guide plate is formed with a substantially uniform thickness,
There is a type in which the thickness of the light guide plate is gradually reduced as the distance from the primary light source increases, and the latter can emit illumination light more efficiently than the former.

FIG. 12 is an exploded perspective view showing an example of the latter sidelight type surface light source device 1, and FIG. 13 is a cross-sectional view of FIG. 12 cut along line AA. In this sidelight type surface light source device 1, a primary light source 3 is arranged on a side of a light scattering light guide plate 2 formed of a light guide plate, and a reflection sheet 4, a light scattering light guide plate 2, and a prism sheet 5 formed of a light control member are sequentially arranged. It is formed by lamination.

The primary light source 3 is formed by surrounding a fluorescent lamp 7 composed of a cold-cathode tube with a reflector 8, and from the opening side of the reflector 8 to the end surface (hereinafter referred to as an incident surface) 2 A of the light-scattering light guide plate 2. Illumination light enters. Here the reflector 8
Is formed of, for example, a sheet material that specularly or irregularly reflects incident light.

The reflection sheet 4 is formed of a sheet-like regular reflection member made of a metal foil or the like or a sheet-shaped irregular reflection member made of a white PET film or the like, and reflects the illumination light leaking from the light scattering light guide plate 2. The light is incident on the light-scattering light guide plate 2, thereby improving the utilization efficiency of the illumination light.

The light-scattering light-guiding plate 2 is a light-scattering light-guiding plate having a wedge-shaped cross section, for example, polymethyl methacrylate (PMM).
Transparent fine particles having a different refractive index from the matrix of A) are uniformly dispersed and mixed. As a result, the light scattering light guide plate 2 receives the illumination light L from the incident surface 2A, which is the end face on the primary light source 3 side, and scatters the illumination light L by the light-transmitting fine particles, and also applies the reflection sheet 4 made of the irregular reflection member. In this case, the illumination is performed while repeatedly reflecting between the reflection sheet 4 side plane (hereinafter referred to as a back surface) 2B and the prism sheet 5 side plane (hereinafter referred to as an exit plane) 2C while partially reflecting the reflection sheet 4. Light L propagates.

During this propagation, the illumination light L has its incident angle with respect to the exit surface 2C reduced every time it is reflected by the back surface 2B, and a component equal to or less than the critical angle with respect to the exit surface 2C is emitted from the exit surface 2C. . The illumination light L emitted from the emission surface 2C is scattered by light-transmitting fine particles inside the light-scattering light guide plate 2, and is emitted as scattered light by being diffusely reflected and propagated by the reflection sheet 4. . However, the illumination light L reflects and propagates on the back surface 2B formed to be inclined in the propagation direction with respect to the emission surface 2C, and emits a component smaller than the critical angle, so that the main emission direction has a wedge-shaped shape. It is formed to be inclined toward the tip. In other words, the light L emitted from the light scattering light guide plate 2 has directivity, whereby the sidelight type surface light source device 1 has directivity.

The prism sheet 5 includes the light scattering light guide plate 2
Is arranged to correct the directivity of the image. That is, the prism sheet 5 is formed of a translucent sheet material such as polycarbonate, and has a prism surface on one side. The prism surface is formed by repeating projections having a triangular cross section extending substantially parallel to one direction.

The prism sheet 5 is provided on the light incident surface 2 of the light guide plate 2.
The prism surface is arranged such that the projections on the prism surface are repeated in a direction orthogonal to A, and the prism surface is opposed to the emission surface 2C. The emission direction is corrected to the front direction of the emission surface 2C. As the prism sheet, a prism sheet having a structure in which prism surfaces are formed on both sides may be used in a stacked state. Thus, in the sidelight type surface light source device 1, the emitted light can be efficiently emitted in the front direction as compared with the sidelight type surface light source device in which the light scattering light guide plate is formed with a substantially uniform plate thickness. It has been done.

[0012]

In such a side light type surface light source device 1, a prism sheet 5 is provided.
It is considered that if the light scattering light guide plate 2 and the light scattering light guide plate 2 are integrated, the utilization efficiency of the illumination light can be further improved and the illumination light can be emitted efficiently.

However, when the prism sheet 5 and the light-scattering light-guiding plate 2 are integrated in this way, as shown by an arrow B, a region having a lower luminance level is observed along the side surface than near the incident surface, and thereby the illumination is performed. There is a problem that light quality is degraded.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above points, and a sidelight type surface light source capable of improving the utilization efficiency of illumination light and emitting high-quality illumination light as compared with the related art. It is intended to propose a device.

[0015]

In order to solve the above-mentioned problems, according to the present invention, illumination light emitted from a predetermined light source is incident on an end face of a plate-like member, and this illumination light is bent to form the plate-like member. The present invention is applied to a sidelight type surface light source device that emits light from an emission surface. In this sidelight type surface light source device,
A projection having a pair of inclined surfaces extending in a direction substantially perpendicular to the end surface is repeatedly formed in a direction substantially parallel to the end surface on the emission surface or on the back surface facing the emission surface to form a plate-like member. At this time, the convex portion is formed smoothly according to the position on the emission surface or the back surface.

Alternatively, the present invention is applied to a similar side light type surface light source device, and the convex portion is formed smoothly as approaching the side surface.

Alternatively, the present invention is applied to a similar side light type surface light source device, and a convex portion is formed smoothly as approaching an end surface.

At this time, the convex portion is smoothly formed as approaching the side surface.

Further, the liquid crystal display panel is illuminated by the side light type surface light source device having the above configuration.

In the sidelight type surface light source device, a projection having a pair of slopes extending in a direction substantially perpendicular to the end face is repeatedly formed on the emission face or the rear face opposite to the emission face in a direction substantially parallel to the end face. Then, if the plate-shaped member is formed, the illumination light can be efficiently emitted by that much. At this time, depending on the position on the emission surface or the back surface, if the convex portion is formed smoothly, according to the smoothness of the convex portion, the illumination light propagating in the extension direction of the convex portion, and distributed to both sides from the convex portion. It is possible to control the ratio between the illumination light and the illumination light emitted from the plate-like member, and consequently to control the ratio between the illumination light reflected inside and the amount of light emitted from each part of the emission surface. Can be controlled.

If the projections are formed smoothly as approaching the side surface, the illumination light propagating in the center of the plate-like member can be distributed to the side surface side, and the amount of light emitted from the side surface can be increased.

Further, by applying the same to the sidelight type surface light source device and forming the convex portion smoothly as approaching the end surface, the illumination light on the end surface side on which the illumination light enters can be changed to the wedge-shaped tip side.
Can be sorted to the side.

At this time, if the convex portion is formed smoothly as approaching the side surface, the illuminating light propagating inside the plate member can be distributed to the side surface side.

Thus, the liquid crystal display panel can be illuminated by these sidelight type surface light source devices to form a high quality display image.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(1) First Embodiment FIG. 2 is an exploded perspective view showing a sidelight type surface light source device according to an embodiment of the present invention when viewed from a wedge-shaped tip end side. The sidelight type surface light source device 10 includes a light scattering light guide plate 12
The primary light source 3 is arranged on the side, and the reflection sheet 11, the light scattering light guide plate 12, and the prism sheet 13 which is a light control member are sequentially laminated and formed by being held in a frame (not shown). In this side light type surface light source device 10,
The same configuration as the side light type surface light source device 1 of FIG.
Corresponding reference numerals are attached and duplicate descriptions are omitted.

Here, this side light type surface light source device 10
In the above, a sheet material made of a regular reflection member on which silver is deposited is applied to the reflection sheet 11 so as to exhibit a high reflectance to illumination light.
The illumination light leaking from B is efficiently returned to the inside of the light-scattering light guide plate 12, and the utilization efficiency of the illumination light is improved.

The light-scattering light guide plate 12 is formed, for example, in a matrix made of polymethyl methacrylate (PMMA).
Transparent fine particles having a different refractive index from the above are uniformly dispersed and mixed to form a wedge-shaped cross section. As a result, the light-scattering light-guiding plate 12 scatters the illumination light L incident from the incident surface 12A with the light-transmitting fine particles, while the back surface 12B and the exit surface 1A.
2C and is repeatedly reflected and propagated, and at this time, a part is emitted from the emission surface 12C.

Further, in the light-scattering light guide plate 12, fine projections are repeatedly formed on the exit surface 2C in a direction parallel to the entrance surface, as shown by partially enlarging the incident surface 12A by an arrow C. You.

Here, the minute projections are formed by connecting a pair of inclined surfaces 12E and 12F extending in a direction orthogonal to the incident surface 12A. Here, the pair of slopes 12E, 12
F is formed to have the same inclination with respect to the emission surface, and the slope 12
The angle α1 formed by E and 12F is selected to be about 60 degrees. The apex angle α1 is 50 degrees to 130 degrees.
Although it is possible to obtain practically usable characteristics by appropriately selecting the temperature within the range, it is preferably in the range of 60 to 110 degrees.

Further, in the light-scattering light guide plate 12, these minute projections are formed, for example, by the sidelight type surface light source device 1.
0 is 1 / compared to the pixel period of the liquid crystal display panel to which
It is formed with a repetition pitch W1 of 50 [μm] smaller than 4 or more.

Further, as shown in FIG. 1, by processing a mold for molding the light-scattering light-guiding plate 12, these minute projections become inclined 12E and 12F near the incident surface as approaching the side surface. The radius of the connecting curved surface expands,
It is formed so as to be smoothed sequentially, and is also formed so as to be sequentially smoothed as it approaches the incident surface from the wedge-shaped tip.

The prism sheet 13 includes the light scattering light guide plate 12
A single-sided prism sheet having a prism surface formed on the side is applied. Here, the prism sheet 13 is formed by curing an acrylic ultraviolet curable resin in a predetermined shape on the surface thereof based on transparent PET.

The prism sheet 13 is formed by repeatedly forming minute projections in a direction orthogonal to the incident surface 12A to form a prism surface, as shown in a partially enlarged side view by an arrow D (FIG. 2). Is done. Here, this minute projection is
The light-scattering light guide plate 12 has a pair of inclined surfaces 13A and 13B extending in parallel with the incident surface 12A. In this embodiment, the pair of inclined surfaces 13A and 13B are directly connected to form a triangular cross section. It has been made.

Here, the inclined surface 13A is used to form a pair of inclined illumination light so that the main illumination light emitted from the light-scattering light guide plate 12 while being inclined toward the wedge-shaped tip is incident at a small incident angle. It is formed with a small inclination β1 with respect to the normal line of the emission surface 12C so as to guide the light to the emission surface 13B without waste. On the other hand, the other inclined surface 13B is formed with a larger inclination β2 than the inclined surface 13A so that the illumination light incident from the inclined surface 13A is totally reflected in the front direction of the emission surface 12C.

That is, the illumination light emitted from the light-scattering light guide plate 12 has a main emission direction inclined approximately 70 degrees toward the wedge-shaped tip direction from the vertical direction, and the illumination light emitted from the light-scattering light guide plate 12 is approximately 20 degrees from the vertical direction.
It is emitted in the range of degrees to 85 degrees. Therefore, after the illumination light in the main emission direction enters from the inclined surface 13A on the incident surface 12A side, it is reflected by the other inclined surface 13B in the front direction of the emission surface 12C, so that the inclination β1 is smaller than the refractive index n of the prism sheet 13; The relationship of β2 is set.

Further, on the premise of this relationship, the inclinations β1 and β2 are set so that the illumination light emitted in the range of 20 to 85 degrees from the vertical direction is emitted along the same path as the illumination light in the main emission direction. Is set. In this embodiment, the angles β1 and β2 are set to 5.6 degrees and 35 degrees, respectively.

Further, in the prism sheet 13, these minute projections are, for example, one pixel in comparison with the pixel period of the liquid crystal display panel to which the sidelight type surface light source device 10 is applied.
It is formed with a repetition pitch W2 of 50 [μm] smaller than / 4.

In the above configuration, the illumination light L emitted from the fluorescent lamp 7 is directly or after being reflected by the reflector 8, then enters the light scattering guide plate 12 from the incident surface 12A, and transmits light. Back surface 1 while being scattered by fine particles
The light is repeatedly reflected between 2B and the exit surface 12C and propagates inside the light scattering light guide plate 12 (see the illumination light L in FIG. 13). At this time, every time the illumination light L is reflected by the back surface 12B, the incident angle with respect to the emission surface 12C decreases, and
A component having a critical angle or less with respect to C is emitted from the emission surface 12C. Further, the illumination light leaking from the back surface 12B of the light scattering light guide plate 12 is reflected by the reflection sheet 11 made of a regular reflection member disposed on the slope side, and is efficiently returned to the inside of the light scattering light guide plate 2, thereby improving the efficiency. The light is well emitted from the emission surface 12C.

When the illumination light L is emitted from the emission surface 12C in this manner, a component having a critical angle or less is emitted from the illumination light propagating from the incidence surface 12A toward the wedge-shaped tip. Thus, when the emission surface is configured by a plane,
The light is emitted with the directivity inclined toward the wedge-shaped tip and with the expanded directivity in the direction along the incident surface 12A.

On the other hand, in this embodiment, the slopes 12E and 12E of the repeatedly formed convex portions are parallel to the incident surface.
By F (FIG. 1), in a plane parallel to the incident surface 12A, the illuminating light emitted so as to spread outward is emitted with its directivity corrected so as to face inward. Thereby, the directivity of the emitted light can be corrected in the direction parallel to the incident surface 12A in the front direction of the exit surface 12C without using the prism sheet 6 (FIG. 12) having the conventional configuration.

Here, the characteristic shown in FIG. 3 is a characteristic of the sidelight type surface light source device having the conventional configuration described above with reference to FIG. 12, and the peak of the luminance level is 3578 [cd].
/ M ² ]. On the other hand, the characteristic shown in FIG. 4 is obtained when the prism-shaped convex portion is formed over the entire exit surface in the configuration described above with reference to FIG. 2, and the slopes 12E and 12F of the convex portion are simply connected directly. Some (ie not a smooth connection but a very small radius of curvature
2E and 12F are connected).

However, as described above, the slopes 12E and 12F
Is simply connected directly to form a convex portion on the exit surface of the light-scattering light guide plate, the difference between the maximum value and the minimum value of the luminance level becomes large. Are observed. In FIG. 4, the maximum value and the minimum value of the luminance level are 498, respectively.
0 [cd / m ² ] and 2654 [cd / m ² ].

Since the prism surface is formed on the exit surface of the light-scattering light guide plate, the illumination light that enters from the incident surface 12A and propagates inside the light-scattering light guide plate 2 hardly propagates to both side surfaces. It is thought that it was. That is, in the conventional sidelight type surface light source device (without forming a prism surface on the emission surface), the illumination light is distributed from the central portion to the side surface by a sufficient amount of light. When a prism surface is formed on the exit surface of the light guide plate, illumination light is repeatedly reflected between the inclined surfaces 12E and 12F and the back surface 12B, and the amount of illumination light propagating in the direction in which the inclined surfaces 12E and 12F extend increases. . Accordingly, the amount of light distributed to the side surface side is reduced by that amount, and a large difference occurs in the luminance level between the central portion and the vicinity of the side surface.

On the other hand, if the slopes 12E and 12F are connected by a curved surface as in this embodiment, the slopes 12E and 12F are smoothed by the convexities determined by the size of the curved surfaces.
Illumination light propagating in the extension direction can be distributed to both sides. Therefore, in the vicinity of the incident surface corresponding to the characteristic of FIG. 4, if the convex portion is formed so as to be gradually smoother as approaching the side surface, the illumination light is distributed to both sides as the closer to the side surface, The amount of emitted light on the side surface can be made uniform. That is, the amount of emitted light on the side surface can be increased.

Further, if the projections are formed so as to be gradually smoother as they approach the entrance surface from the wedge-shaped tip, the amount of light emitted from the wedge-shaped tip increases in the same manner. FIG.
3 shows the characteristics of the sidelight type surface light source device according to the present embodiment in comparison with FIGS. 3 and 4, in which the amount of emitted light is made uniform and the illumination light is emitted with high quality. Recognize. In FIG. 5, the maximum value and the minimum value of the luminance level were 4677 [cd / m ² ] and 3133 [cd / m ² ], respectively.

The illumination light L thus emitted from the emission surface 12C passes through the subsequent prism sheet 13 and illuminates a liquid crystal panel and the like disposed on the front surface of the prism sheet 13. At this time, the illuminating light is directed toward the wedge-shaped tip because the convex portion formed by the pair of inclined surfaces 13A and 13B extending parallel to the incident surface 12A is repeatedly formed on the prism sheet 13 in a direction orthogonal to the incident surface. Outgoing surface 12
After being emitted from C, the light enters the prism sheet 13 via the slope 13A facing the incident surface 12A side of the pair of slopes 13A and 13B, and is guided to the other slope 13B.
Here, the illumination light is totally reflected by the inclined surface 13B, and the directivity of the emitted light is corrected in the front direction of the emission surface 12C in a plane orthogonal to the incident surface 12A.

As described above, the illumination light incident on the prism sheet 13 is positively guided into the prism sheet 13 and emitted in the front direction of the emission surface 12C.
Thereby, the utilization efficiency of the illumination light is improved accordingly.

Further, at this time, the main illuminating light which is emitted from the light scattering light guide plate 12 while being inclined toward the wedge-shaped tip is incident at a small incident angle, and the incident illuminating light is guided to the inclined surface 13B forming a pair without waste. Thus, the slope 13A is set to have a small inclination β1, and the slope 13B is set so that the illumination light incident from the slope 13A is totally reflected in the front direction of the emission surface 12C.
Is set to a large inclination β2, the degree of the multiple reflection of the illumination light is reduced, and the illumination light efficiently transmits through the prism sheet 13, thereby also increasing the amount of emitted light.

Further, since a large number of projections are formed on the emission surface 12C of the light scattering light guide plate 12, the light scattering light guide plate 1
Sticking of the prism sheet to 2 is also effectively avoided.

In correcting the directivity in this way,
Emission surface 12C of light scattering light guide plate 12 and prism sheet 1
Since a large number of convex portions are repeatedly formed on the prism surface of No. 3, microscopic pulsations of the luminance level occur in the repetition direction of the convex portions when viewed microscopically. If the pixel pitch of the liquid crystal display panel is close to the pulsation, so-called moiré occurs, and the quality of the displayed image is significantly deteriorated. That is, in this case, the quality of the emitted light is reduced as viewed from the sidelight type surface light source device.

On the other hand, in this embodiment,
More than 1/4 smaller than the pixel period of the liquid crystal display panel,
Since the convex portions are repeated at the repetition pitches W1 and W2 of 50 [μm], the pulsation of the luminance level can be reduced to the repetition pitch sufficiently separated from the pixel pitch, and the occurrence of moiré correspondingly Can be effectively avoided.

Further, in this embodiment, a pair of slopes 12E, 12E forming a convex portion in the light scattering light guide plate 12 are provided.
F is formed at an equal inclination with respect to the exit surface, and the slope 1
Since the angle α1 formed by 2E and 12F is selected to be about 60 degrees, the utilization efficiency of the illumination light is improved accordingly.

According to the above construction, a prism surface is formed on the exit surface of the light-scattering light-guiding plate, so that the surface becomes smoother in the vicinity of the incident surface as it approaches the side surface, and from the wedge-shaped tip to the entrance surface. By forming this prism surface with minute projections so that it gradually becomes smoother as it gets closer, the illumination light in the central part can be distributed to both side surfaces and the wedge-shaped tip side, so that the utilization efficiency of the illumination light is improved. , And high-quality illumination light can be emitted with a uniform luminance distribution.

(2) Second Embodiment FIG. 6 is an exploded perspective view showing a sidelight type surface light source device according to a second embodiment of the present invention in comparison with FIG. The side light type surface light source device 20 includes a light guide plate 22.
, The primary light source 3 is arranged, and the reflection sheet 11, the light guide plate 22, the light diffusion sheet 24, and the prism sheet 23 are sequentially laminated. In the sidelight type surface light source device 20, the same components as those of the sidelight type surface light source device 10 in FIG. 2 are denoted by the corresponding reference numerals, and the duplicate description will be omitted.

Here, the light guide plate 22 is a plate-like member made of a transparent member, for example, formed by injection-molding acrylic (PMMA resin), and has a wedge-shaped cross section. The light guide plate 22 has light diffusing ink adhered to the back surface thereof, thereby forming the back surface 22B.
A light diffusion surface is formed on the substrate. Thereby, the light guide plate 22 repeatedly reflects between the back surface 22B and the emission surface 22C to propagate the illumination light while scattering the illumination light on the back surface 22B, and at the time of reflection at the back surface 22B and the emission surface 22C, The component below the critical angle is emitted from the back surface 22B and the emission surface 22C.

Further, in the light guide plate 22, fine projections are repeatedly formed on the light exit surface 22C as in the first embodiment. By processing a mold for molding the light guide plate 22, these minute projections are gradually smoothed in the vicinity of the incident surface as they approach the side surface, and gradually as they approach the incident surface from the wedge-shaped tip. It is formed so that Thus, the light guide plate 22 can efficiently emit illumination light with a uniform luminance distribution.

The light diffusion sheet 24 gently diffuses the light emitted from the light guide plate 22 and emits the light.

As the prism sheet 23, a single-sided prism sheet having a prism surface formed on the surface opposite to the light guide plate 22 is used. Here, the prism sheet 23 is made of transparent PE
Based on T, it is formed by curing an acrylic ultraviolet curable resin in a predetermined shape on its surface. In the prism sheet 23, minute projections are repeatedly formed in a direction perpendicular to the incident surface, thereby forming a prism surface. Here, the minute projection has a pair of slopes 23A and 23B extending in parallel with the incident surface of the light guide plate 22, and in this embodiment, the pair of slopes 23A and 23B are directly connected, The cross section is formed in a triangular shape.

As a result, the prism sheet 23 has similar projections repeatedly formed in a direction orthogonal to the direction in which the projections of the light guide plate 22 are repeated, and the projections are inclined from the light guide plate 22 toward the wedge-shaped tip. The directivity of the emitted illumination light L is corrected in the front direction of the emission surface 22C.

Further, in this embodiment, the prism sheet 23 has a pair of slopes 23A and 23B formed so as to have the same inclination with respect to the exit surface, and the angle α2 formed by the slopes 23A and 23B is selected to be about 90 degrees. Has been made. The apex angle α2 can be appropriately selected in the range of 30 ° to 130 ° to obtain practically usable characteristics, but is preferably in the range of 60 ° to 110 °, and more preferably in the range of 80 ° to 100 °.

Further, in the prism sheet 23, these minute projections are, for example, one pixel in comparison with the pixel period of the liquid crystal display panel to which the sidelight type surface light source device 20 is applied.
It is formed with a repetition pitch W2 of 50 [μm] smaller than / 4.

In the configuration shown in FIG. 6, the illumination light incident on the light guide plate 22 is repeatedly reflected between the back surface 22B and the emission surface 22C while being diffused by the light diffusion surface formed on the back surface 22B. A component that propagates through the inside of the optical plate 22 and is smaller than the critical angle with respect to the emission surface 22C is emitted from the emission surface 12C.

At this time, the illumination light L is emitted from the light guide plate 22 with its directivity corrected by the convex portion formed on the emission surface 22C, and is emitted efficiently. In this case, as shown in FIGS. 7 and 8, even in this case, if the prism surface is simply formed on the exit surface of the light guide plate as in the case of FIG. 4, the uniformity of the exit light is extremely deteriorated. Note that FIG.
This is a characteristic of a sidelight type surface light source device having a conventional configuration in which a light diffusion sheet and a prism sheet are stacked on a light guide plate having no prism surface on an emission surface of the light guide plate. The prism sheet has a prism surface facing upward, and the repeating direction of the convex portions is a direction orthogonal to the incident surface. In this case, the maximum value and the minimum value of the luminance level are each 270.
2 [cd / m ² ] and 2393 [cd / m ² ]. FIG. 8 shows a case in which, in the configuration shown in FIG. 6, with respect to the prism-shaped protrusion formed on the emission surface of the light guide plate, the slopes 22E and 22F constituting the protrusion are simply directly connected over the entire surface ( That is, instead of a smooth connection,
In this case, the slopes 22E and 22F are connected with an extremely small radius of curvature), and the maximum value and the minimum value of the luminance level are 3310 [cd / m ² ] and 1690 [c, respectively.
d / m ² ].

On the other hand, in the present embodiment, the fineness is set so as to gradually become smoother in the vicinity of the incident surface as it approaches the side surface, and to become gradually smoother as it approaches the incident surface from the wedge-shaped tip. Due to the repeated formation of the convex portions, the illumination light is distributed by the curved surfaces of the convex portions, and the emitted light is emitted with a uniform luminance distribution. That is, FIG. 9 shows the characteristics of the sidelight type surface light source device according to this embodiment, and the maximum value and the minimum value of the luminance level are 3182 [cd / m ² ] and 18 respectively.
47 [cd / m ² ].

The illumination light emitted with a uniform luminance distribution in this manner is gently scattered by the light diffusion sheet 24 and enters the prism sheet 23, where the directivity is corrected in the front direction of the emission surface 22C. Is done.

According to the configuration shown in FIG. 6, a prism surface is formed on the exit surface of the light guide plate made of a transparent plate-like member, and in the vicinity of the entrance surface, the prism surface is gradually smoothed as approaching the side surface. By forming this prism surface with minute projections so that the surface becomes smoother as it approaches the incident surface from the tip, the same effect as in the first embodiment can be obtained.

(3) Other Embodiments In the above-described embodiment, the case where the convex portion is formed smoothly by changing the curved surface forming the convex portion has been described. However, the present invention is not limited to this. Alternatively, the convex portion may be smoothed by changing the slope of the slope (that is, the slope itself is formed into a curved shape).

In the above-described embodiment, the convex portions are formed so as to be gradually smoothed in the vicinity of the incident surface as approaching the side surface and so as to be gradually smoothed as approaching the incident surface from the wedge-shaped tip. Although the case of forming is described, the present invention is not limited to this, and can be widely applied to a case where a convex portion is formed smoothly according to a position on an emission surface to adjust a luminance distribution.

That is, when the length of the light guide plate and the light-scattering light guide plate (the length in the direction away from the light source) is short, a convex portion is simply formed so as to gradually become smoother as approaching the side surface, and the amount of emitted light is made uniform. Can be When the width of the light guide plate and the light-scattering light guide plate (for example, the length in the direction parallel to the longitudinal direction of the linear light source) is short, or when the light source has a margin, the wedge-shaped tip is simply placed on the incident surface. Protrusions are formed so as to gradually become smoother as approaching, so that the amount of emitted light can be made uniform. Also, corresponding to the emitted light amount distribution in FIG.
As shown in FIG. 10, it is also possible to form the protrusions smoothly along the side surface, and to form the protrusions smoothly at the corners on the tip end side of the wedge, thereby further uniformizing the amount of emitted light.

Further, in the above-described embodiment, the case has been described in which the convex portion is smoothly formed in accordance with the position on the exit surface by processing the light scattering light guide plate and the mold for molding the light guide plate. However, the present invention is not limited to this, and it is also possible to control the transfer characteristics of the shape by setting the molding conditions in the molding process to smoothly form the convex portions according to the position on the emission surface.

Further, in the above-described embodiment, the case where the prism surface is formed on the light-scattering light guide plate and the exit surface of the light guide plate has been described. However, the present invention is not limited to this, and the case where the prism surface is formed on the back surface is described. Also, the present invention can be widely applied to a case where a prism surface is formed on an emission surface and a back surface.

FIG. 11 is an exploded perspective view showing a side light type surface light source device. In this side light type surface light source device 30, a back surface 32B of a light scattering light guide plate 32 is shown.
A prism surface is formed as a light control surface. In the side light type surface light source device 30 shown in FIG.
The same configurations as those of the sidelight type surface light source device 10 described above with reference to FIG. 2 are denoted by the corresponding reference numerals, and redundant description will be omitted.

As shown by an arrow C, the prism surface of the back surface 32B has a pair of convex portions formed by a pair of slopes 32E and 32F repeated along the incident surface similarly to the prism surface formed on the exit surface. The vertices of these convex portions are formed smoothly as approaching the incident surface 32A and approaching the side surface in the same manner as described above with reference to FIG.

As shown in an enlarged manner by an arrow D, the prism sheet 33 has a prism surface as a light control surface on a surface facing the light scattering light guide plate 32 as in the first embodiment. The inclination of a pair of slopes 32E and 32F formed on the back surface of the light scattering light guide plate 32, and the repetition pitch W of the projections
1, the inclination of the pair of slopes 33A and 33B constituting each minute convex portion of the prism sheet 33, and the repetition pitch W2 of the minute convex portion are based on the same concept as in the first embodiment described above. Just set it.

As described above, the back surface 32B of the light-scattering light guide plate 32
The configuration in which the prism surface is formed has almost the same advantages as the configuration in which the prism surface is formed on the exit surface, but since the prism surfaces of the light scattering light guide plate 32 and the prism sheet 33 do not face each other, Further, when assembling the surface light source device, the light scattering light guide plate 32 and the prism surface of the prism sheet 33 are hardly damaged, which is further advantageous in this respect. In this embodiment, the exit surface 32C of the light scattering light guide plate 32 is a smooth surface.
Instead, a light guide plate made of a transparent plate member may be used, and a prism surface may be formed on the back surface of the light guide plate, and a rough surface, a mat surface, or the like may be formed on the emission surface.

In the first and second embodiments, the prism sheets are arranged such that the prism surface faces the light exit surface of the light guide plate or faces away from the light exit surface. However, the present invention is not limited to this, and can be widely applied to a case where a prism sheet is arranged in a direction opposite to the above in each of the above-described embodiments.

Further, in the above-described first embodiment, the case where the prism surface is formed by a pair of inclined surfaces having different inclinations in the prism sheet has been described. However, the present invention is not limited to this, and the present invention is not limited thereto. The present invention can be widely applied to a case where a prism surface is formed by a pair of slopes.

On the contrary, in the second embodiment, the case where the prism surface is formed by a pair of inclined surfaces having the same inclination in the prism sheet has been described, but the present invention is not limited to this, and the present invention is not limited thereto. The present invention can be widely applied to a case where a prism surface is formed by a pair of different slopes.

Further, in the above-described second embodiment, the case where the reflection sheet, the light guide plate, the light diffusion sheet, and the prism sheet are laminated has been described. However, the present invention is not limited to this, and the light diffusion sheet may be replaced with a prism sheet. When it is arranged on the upper surface of the device, it can be widely applied even when it is omitted.

In the above-described embodiment, the case where the reflection sheet is formed by the regular reflection member made of the sheet material on which silver is deposited has been described. However, the present invention is not limited to this.
The present invention can be widely applied to a case where a reflection sheet is formed by various regular reflection members, and further, irregular reflection members such as white PET.

Further, in the above-described second embodiment, the case where the light diffusion surface is formed by printing ink has been described. However, the present invention is not limited to this. Can be widely applied to a case where a light diffusion surface is formed by forming a uniform rough surface, and a case where a light diffusion surface is formed on these surfaces by blasting using a sandpaper or chemical etching.

Further, in the above-described first embodiment, the case where the light scattering light guide plate is formed by mixing translucent fine particles has been described. However, the present invention is not limited to this, and various light scattering light guide plates may be used. The present invention can be widely applied to the case where a light scattering light guide plate is formed by mixing fine particles of the above.

Further, in the above-described embodiment, the case where the illumination light is incident from one end face has been described. However, the present invention is not limited to this, and the sidelight type surface is also configured to receive the illumination light from the other end face. It can be widely applied to light source devices.

In the above-described embodiment, the case where the primary light source is constituted by the fluorescent lamp which is a rod-shaped light source has been described. However, the present invention is not limited to this. Can also be widely applied to the formation of

Further, in the above embodiment, the case where the present invention is applied to the surface light source device of the liquid crystal display device has been described. However, the present invention is not limited to this, and the present invention is not limited to this. It can be widely applied to a surface light source device.

[0087]

As described above, according to the present invention, a projection is repeatedly formed on the emission surface or the back surface opposite to the emission surface of the plate-like member, and the projection is smoothly formed according to the position on the emission surface or the back surface. In this case, the light amount distribution of the illumination light can be adjusted, whereby the utilization efficiency of the illumination light can be improved, and high-quality illumination light can be emitted.

[Brief description of the drawings]

FIG. 1 is a plan view showing an emission surface of a light scattering light guide plate applied to a side light type surface light source device according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing the sidelight type surface light source device according to the first embodiment of the present invention.

FIG. 3 is a characteristic curve diagram showing a light amount distribution of emitted light in a side light type surface light source device having a conventional configuration corresponding to the side light type surface light source device of FIG.

FIG. 4 is a characteristic curve diagram showing a light amount distribution of emitted light when a prism surface is simply formed over the entire exit surface.

FIG. 5 is a characteristic curve diagram showing a light amount distribution of emitted light in the sidelight type surface light source device of FIG.

FIG. 6 is an exploded perspective view showing a sidelight type surface light source device according to a second embodiment of the present invention.

FIG. 7 is a characteristic curve diagram showing a light amount distribution of emitted light in a side light type surface light source device having a conventional configuration corresponding to the side light type surface light source device of FIG.

FIG. 8 is a characteristic curve diagram showing a light amount distribution of emitted light when a prism surface is simply formed over the entire exit surface.

9 is a characteristic curve diagram showing a light amount distribution of outgoing light in the sidelight type surface light source device of FIG.

FIG. 10 is a plan view showing an emission surface of a light-scattering light guide plate applied to a side light type surface light source device according to another embodiment.

FIG. 11 is an exploded perspective view showing a side light type surface light source device in which a prism surface is formed on the back surface of a light guide plate.

FIG. 12 is an exploded perspective view showing a conventional sidelight type surface light source device.

FIG. 13 is a cross-sectional view of FIG. 12 cut along line AA.

[Explanation of symbols]

1, 10, 20, 30 ... side light type surface light source device,
2, 12, 22, 32 ... light scattering light guide plate, 22 ... light guide plate, 2B, 12B, 22B, 32B ... back surface, 2C, 1
2C, 22C, 32C ... Outgoing surface, 5, 6, 13, 2
3, 33 ... Prism sheet

Claims (6)

[Claims] 1. A sidelight-type surface light source device that irradiates illumination light emitted from a predetermined light source from an end surface of a plate member, bends the illumination light, and emits the illumination light from an emission surface of the plate member. The plate-shaped member, a projection having a pair of slopes extending in a direction substantially perpendicular to the end face is repeatedly formed in a direction substantially parallel to the end face, on the emission face or on the back face facing the emission face, The side light type surface light source device, wherein the convex portion is formed smoothly in accordance with a position on the emission surface or the back surface. 2. A sidelight-type surface light source device which irradiates illumination light emitted from a predetermined light source from an end face of a plate member, bends the illumination light and emits the illumination light from an emission surface of the plate member. The plate-shaped member, a projection having a pair of slopes extending in a direction substantially perpendicular to the end face is repeatedly formed in a direction substantially parallel to the end face, on the emission face or on the back face facing the emission face, The side light type surface light source device, wherein the convex portion is formed smoothly as approaching the side surface. 3. A sidelight type surface light source device in which illumination light emitted from a predetermined light source is incident from an end face of a plate member, and the illumination light is bent and emitted from an emission surface of the plate member. The plate-shaped member, a projection having a pair of slopes extending in a direction substantially perpendicular to the end face is repeatedly formed in a direction substantially parallel to the end face, on the emission face or on the back face facing the emission face, The side light type surface light source device, wherein the convex portion is formed smoothly as approaching the end surface. 4. The side light type surface light source device according to claim 3, wherein the convex portion is formed smoothly as the plate member approaches a side surface. 5. A sidelight type surface light source device in which illumination light emitted from a predetermined light source is incident from an end face of a plate-shaped member, and the illumination light is bent and emitted from an emission surface of the plate-shaped member. In the plate-shaped member, a convex portion having a pair of slopes extending in a direction substantially perpendicular to the end surface is repeatedly formed on a back surface facing the emission surface in a direction substantially parallel to the end surface, and approaches the end surface. , The convex portion is formed smoothly, and the convex portion is formed smoothly as approaching the side surface. 6. The first, second, third and fourth aspects of the present invention.
A liquid crystal display device illuminating a liquid crystal display panel with the sidelight type surface light source device according to claim 5.