JPH10319242A - Light guide plate - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a screen in which most of the light emitted from each position of a light guide plate is directed toward the center, so that a person who is watching the screen at the center of the screen can easily see the peripheral portion. SOLUTION: The light guide plate 11 (12) for emitting light from an emission surface (diffusion prism surface 11a (12a)) provided with a large number of fine diffusion grooves in parallel, wherein the groove surface of the diffusion groove is: The cross-sectional shape in the direction orthogonal to the diffusion groove is formed by equilateral triangles b00 and b01 having an obtuse apex at the central part b0, and an edge b2.
In b20, the side b20 corresponding to the groove surface forming an inclination that bends most of the emitted light toward the central portion at an acute angle is the side corresponding to the inclined groove surface that does not emit most of the emitted light toward the central portion. b2
A light guide plate 11 (12) formed by two sides of a saw-shaped triangle longer than 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a light guide plate for emitting light taken in from the outside through a diffusion prism surface. Light guide plate of the present invention, for example, a liquid crystal backlight device,
It is used for a backlight device or the like for viewing radiographs.

[0002]

2. Description of the Related Art FIG. 4A shows a backlight device for a liquid crystal display. The illustrated device includes a light guide plate P10, a long light source (fluorescent lamp) 21 provided along one end surface of the light guide plate P10, and a diffusion plate 40 provided on the light exit surface P10a side of the light guide plate P10. And the lens film 30 provided on the diffusion plate 40. The light guide plate P10 is made of plastic such as acrylic or polycarbonate, and has a wedge shape that gradually narrows from an end face facing the light source 21 to an end face on the opposite side. That is, the surface P10c opposite to the light exit surface P10a is tapered. In addition, dot printing is performed on the opposite surface P10c, thereby increasing the emission efficiency.

[0003] Light taken into the light guide plate P10 from the light source 21 is repeatedly scattered and reflected inside the light guide plate P10, and is emitted from the light emission surface P10a. A diffusion plate 40 is provided on the light emitting surface P10a so that uniform luminance can be obtained. Further, a lens film 30 composed of two lens sheets is provided on the diffusion plate 40, thereby improving the directivity. A large number of fine prisms (not shown) having a triangular cross section are formed in parallel on each lens sheet 30, and the arrangement directions of the prisms of both sheets are orthogonal to each other. Both seats are provided.

Japanese Patent Laid-Open Publication No. Hei 8-254616 discloses FIG.
As shown in (b), a scattering pattern (not shown) is formed on the back surface (tapered surface) P11c of the wedge-shaped transparent substrate, and a large number of fine V-shaped grooves having a depth of 25 μm are formed on the front surface (outgoing surface) P11a. (Groove whose cross section is an equilateral triangle) 5
An edge light panel P11 for a liquid crystal backlight is disclosed, which is formed at a pitch of 0 μm to form a diffusion prism surface, thereby improving the luminance of light incident from the light source 21. That is, the lens film 30 of the apparatus shown in FIG.
A light guide plate P11 which does not require the diffusion plate 40 is disclosed.
In FIG. 4B, the diffusion groove P11b is shown in an enlarged manner than the others.

[0005]

In the backlight device shown in FIG. 4 and the edge light panel disclosed in JP-A-8-254616, most of the light emitted from the emission surface P10a (P11a), that is, the surface of the diffusion prism is emitted. Go perpendicular to the surface. In other words, most of the backlight emitted from the peripheral portion of the panel is not directed to a person viewing the panel on a vertical line at the center of the liquid crystal panel. For this reason, there is a problem that it becomes difficult for the person to visually recognize the peripheral portion of the screen. Such a problem becomes more remarkable as the screen becomes larger.

According to the present invention, most of the light emitted from each position including the edge of the light guide plate is directed in the direction perpendicular to the center of the screen of a liquid crystal panel or the like, so that the light is viewed at the center of the screen. An object is to provide a screen that is easy for humans to see.

[0007]

According to a first aspect of the present invention, light taken in from the outside is diffused on a diffusion prism surface having a large number of fine diffusion grooves or diffusion ridges provided substantially in parallel, and the light is diffused from an emission surface. The light guide plate for emitting light, wherein the cross-sectional shape of the diffusion groove or the diffusion ridge is a saw-shaped edge of the prism surface so as to direct the light at the edge of the output surface to the center of the output surface. A light guide plate characterized by the following. According to a second aspect of the present invention, in the configuration of the first aspect, the shape of the diffusion groove or the diffusion ridge at the center of the prism surface is substantially an isosceles triangle, and the vertex angle becomes sharper toward the edge. A light guide plate having a shape.

According to a third aspect of the present invention, in the configuration of the second aspect, the shape of the diffusion groove or the diffusion ridge from the center of the prism surface to the edge is changed stepwise. It is a light plate. According to a fourth aspect of the present invention, there is provided the light guide plate according to the second aspect, wherein the shape of the diffusion groove or the diffusion ridge from the center of the prism surface to the edge is continuously changed. .

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the light guide plate has a light incident surface on a side surface, a light exit surface on an upper surface, and a light exit surface on a lower surface. With a tapered light reflecting surface approaching the light emitting surface as
The light guide plate is characterized in that the cross section has a wedge shape, and the diffusion groove or the diffusion ridge is arranged on the light emitting surface or the light reflecting surface substantially in parallel with the incident light.

According to a sixth aspect of the present invention, in any one of the first to fourth aspects, the light guide plate has a light incident surface on a lower surface and a light emission surface on an upper surface, and The ridge is a light guide plate that is disposed on the light exit surface or the light reflection surface.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows two types of light guide plates 11, 12 according to an embodiment. The two types of light guide plates 11 and 12 are made of acrylic resin, polycarbonate resin, or the like, and their size is 190 mm × 260 mm. In each case, a large number of fine diffusion grooves (prisms) are formed in parallel on the emission surfaces 11a and 12a, thereby forming a diffusion prism surface.

As shown in FIG. 1C, the light guide plate 11 has a wedge shape in which the surface 11c opposite to the diffusion prism surface 11a, which is the exit surface, approaches the exit surface 11a as the distance from the light source 21 increases. The structure is such that light taken in from 21 is emitted upward from the emission surface 11a on the opposite surface 11c.
For this reason, the opposite surface 11c is provided with dot printing (or an Al reflection film) for enhancing the emission efficiency from the emission surface 11a. The thickness is 3 mm at the left end and 1.2 mm at the right end in the figure.

As shown in FIG. 1D, the light guide plate 12 has a diffusion prism surface 12a as an exit surface and an opposite surface 12c.
Are formed in a parallel plate shape so that light taken in from a surface emitting light source 22 provided on the opposite surface 12c side is emitted from an emission surface 12a. The thickness is 3 mm.

As shown in FIG. 1B, a large number of fine diffusion grooves are formed in parallel on each of the light emitting surfaces 11a and 12a of the light guide plate 11 and the light guide plate 12. The diffusion groove is cut in a direction perpendicular to the diffusion groove (the line AA in FIG. 3A), and the cross-sectional shape of the groove surface is the shape of the isosceles triangular equilateral sides b00 and b01 at the center part b0. Make At the edge b2, a side b20 corresponding to a groove surface that forms a slope that bends most of the emitted light toward the center (a slope that decreases as the distance from the center b0 decreases) causes most of the emitted light toward the center. A side corresponding to a groove surface that forms a slope that does not emit light (a slope that increases as the distance from the center part b0 increases / a slope that is perpendicular to the emission surfaces 11a and 12a / an overhang slope).
It is longer than b21 and has a sawtooth triangular shape with two acute sides.

Most of the light emitted from the groove surface having a slope that decreases as the distance from the central portion b0 decreases is bent toward the central portion b0. Also, most of the light emitted from the groove surface that forms a slope that rises / vertically slopes / overhangs as it moves away from the center part b0 is not bent in the direction of the center part b0, but is bent outward in the direction opposite to the center part b0. Or not emitted.

That is, in the light guide plate 11, the light that is horizontally incident from the side light source 21 is directed upward in the vertical direction by the effect of dot printing on the opposite surface 11c. Also, light guide plate
In 12, the light incident from the lower surface light source 22 goes upward in the vertical direction. That is, in each of the light guide plates 11 and 12, most of the light that is incident from the outside and travels inside the light guide plate and reaches the emission surfaces 11a and 12a is directed upward.

For this reason, the light that reaches the central portion b0 of the exit surface where the cross-sectional shape of the groove surface is the shape of the equilateral sides b00 and b01 of an isosceles triangle, as shown in FIG. When the light is emitted from the inclined surface b00, most of the light is bent to the left, and when the light is emitted from the downwardly inclined surface b10, most of the light is bent to the right. From above.

The light reaching the light-emitting surface edge b1 (b2), whose cross-sectional shape is a two-sided sawtooth triangular shape having an acute vertex angle, is as shown in FIG. 3 (b). In the case where the light is emitted from the inclined surface b10 (b20) that goes down as the distance from the central portion b0 is increased (the light is emitted from the long side portion), most of the light is bent toward the central portion b0. Also, almost no light is emitted from the vertical inclined surface b11 (b21), which is the short side portion. The same applies to the case where the short side portion is an overhanging surface (not shown). In the case where the short side portion is an inclined surface (not shown) that rises away from the central portion b0, most of the emitted light is in the central portion b0. It is bent in the opposite direction (outward) without being bent in the direction. As a result, most of the light emitted from the emission surface edge b1 (b2) is bent in the direction of the central portion b0.

As described above, since the diffusion grooves on the light exit surfaces 11a and 12a are formed, the light emitted from the light guide plate 11 and the light guide plate 12
In the central part b0, it goes upward, and in the edge part b1 (b2), it goes in the direction of the central part b0. As a result, for a person viewing the liquid crystal screen or the X-ray photograph disposed thereon with the light guide plates 11 and 12 as backlights on a perpendicular line to the central portion b0, the edges become bright and easy to see. In FIG. 1B, the triangular shape which is the cross-sectional shape of the diffusion groove from the center to the edge, such as the center b0 to the middle b1 to the edge b2, is represented by three.
Although it is changed in stages, it may be changed in two stages, in multiple stages of four or more stages, or continuously.

When the shape of the triangle is changed in three steps as shown in the figure, the number of blocks in the case where the light guide plates 11 and 12 are divided by the shape of the diffusion groove is five blocks. A stamper for forming a light guide plate by an injection molding method can be formed by three types of cutting tools. That is, the number of bytes is about half of the number of blocks.

The depth of the diffusion groove shown in FIG.
5 μm. The vertex angle of the isosceles triangle at the center b0 is 90 °, the vertex angle of the saw-shaped triangle at the middle b1 is 70 °, and the edge b2
Has an apex angle of 55 °. Note that a preferable range of the depth of the diffusion groove is about 10 μm to 300 μm. When the thickness is less than 10 μm, the influence of interference appears,
If it is more than m, the groove is easily visible.

The base angle of the prism of the diffusion groove is θ (FIG. 3)
(B)), the distance between the person and the screen is h, the distance between the diffusion groove and the center of the light guide plate is 1 (ell), and the refractive index of the light guide plate is n.
Then, it may be set so that a large amount of light is emitted in the direction of tan ^-1 (h / l). Therefore,

## EQU1 ## nsin (θ) = sin (φ)

The base angle θ may be set as follows: tan ⁻¹ (h / l) = θ + (90−φ)

FIG. 2 shows a modification of the light guide plate 11. FIG. 11A shows a light guide plate A11 in which a scattering pattern concave groove A11d is formed on the back surface (an opposite surface A11c of the emission surface A11a), and FIG. 12B shows a light guide plate in which a scattering pattern concave groove B11d is formed on the emission surface B11a. B1
1 In any case, diffusion grooves A11b and B11b are formed on the emission surfaces A11a and B11a. The shape of the diffusion grooves A11b and B11b and the transition of the deformation thereof (the shape is changed from an isosceles triangle to a sawtooth triangle from the center b0 to the edge b2), the depth and the pitch are as described above. This is the same as the case of the light guide plate 11. Thus, instead of dot printing, the concave groove A1
1d, B11d as the scattering pattern, opposite surface A11c or emission surface B1
Also in the case where the light guide plate 1a is formed, the light emitted from the edge b2 and the intermediate part b1 can be bent in the direction of the central part b0, similarly to the light guide plate 11 described above. Incidentally, in the case of any of the light guide plates A11 and B11 in FIG.
An Al reflection film is formed on the opposite surfaces A11c and B11c of the emission surfaces A11A and B11a.

The concave grooves A11d and B11d of the scattering pattern are parallel to the end face facing the light source 21 and are parallel to the light source 21 as shown in FIG.
The pitch becomes narrower as the distance from the distance increases, and finally the pitch becomes a continuous pitch. Thus the concave groove
The formation of A11d and B11d makes it possible to efficiently turn the light incident from the light source 21 into the light guide plates A11 and B11 upward and direct the light toward the emission surfaces A11a and B11a with reference to FIGS. I will explain. FIG. 5 and FIG.
This is the same as the light guide plate A11 in FIG.

The concave groove A11d is a cross section when cut in a direction perpendicular to the concave groove A11d, and has a bottom width of 50 μm and a vertex angle of 150 °. Further, the width of the flat portion between the adjacent concave grooves A11d is 0.5 mm on the end side close to the light source 21, and monotonically narrows toward the opposite end, and at the opposite end. It is continuous (there is no flat portion between adjacent concave grooves A11d).

As shown in FIG. 6A, when there is no concave groove on the back surface 11c, most of the light entering the light source 21 in the horizontal direction repeats total reflection inside the light guide 11 and repeats the light source 21. The light is emitted from the vicinity of the opposite end. For this reason, uniform light cannot be emitted from the entire exit surface 11a.

As shown in FIG. 6B, when the zigzag grooves are formed at equal pitches on the back surface C11c, most of the light entering the light source 21 in the horizontal direction is reflected by the zigzag grooves near the light source 21. Then, the light is emitted from the vicinity of the end on the light source 21 side. For this reason, uniform light cannot be emitted from the entire exit surface C11a.

As shown in FIG. 6 (c), a prism array (an array in which the pitch is wider at the end closer to the light source 21 and the pitch becomes narrower toward the opposite end) is formed on the exit surface D11a. Since the emitted light is emitted in a direction away from the light source 21, a lens that corrects the emitted light and points upward is required.

As shown in FIG. 6D, when the concave groove A11d is formed on the back surface A11c as in the example of FIG.
In an area where A11d is sparse (area near the light source 21), most of the light that has entered the light source 21 in the horizontal direction repeats total internal reflection inside the light guide 11 and proceeds to the right in the figure, and the concave groove As A11d increases, the amount of upward light increases, and most of the light is upward near the opposite end. As a result, uniform light can be emitted from the entire exit surface A11a. Since there is no deviation in the direction of the emitted light, a correction lens as in the case of FIG. 6C is unnecessary.

Although the light guide plate has a diffusion groove in the above-described embodiment, the same effect can be obtained when a similar diffusion groove is formed in the lens film 30 (see FIG. 4). Further, the light guide plate described in the above embodiment is combined with the diffusion plate 30 and the lens film 40 shown in FIG.
Further, a high-performance backlight device may be configured.

In the above embodiment, the diffusion grooves are arranged on the light emitting surface. However, the diffusion grooves may be arranged on the opposite surfaces 11c and 12c. In this case, in the configuration of the opposite surface 11c, as described above, it is necessary to set the saw shape so that the light is not directed by refraction but directed toward the center by reflection. Further, in the above-described embodiment, the diffusion groove is described as an example of the means for providing diffusion. However, a projection may be provided instead of the groove to direct light. As described above, various modifications can be made to the embodiment of the present invention within the scope of the technical idea of the present invention.

The light guide plate according to the present invention is used not only as a backlight for a liquid crystal display panel, but also for irradiating a display panel from the back, and is not limited to a backlight. It is also applicable to those that do. For example, the present invention can be widely applied to a display device for backing up a transparent film and used for a conference, a display device for backing up an X-ray film, an emergency light, a guide light, a light scattering cover of a fluorescent light, and the like.

[0033]

According to the present invention, among the many fine diffusion grooves or diffusion ridges provided on the diffusion prism surface of the light guide plate,
By making the cross section of the edge of the prism surface into a sawtooth shape, the light at the edge of the light emitting surface of the light guide plate is directed to the center of the light emitting surface. Most can be directed toward the center of the light guide plate. For this reason, it is possible to provide a screen that is easy to see at the peripheral portion for a person who is watching the screen near the center of the screen irradiated from behind with the light emitted from the light guide plate of the present invention.

[Brief description of the drawings]

FIG. 1 schematically shows light guide plates 11 and 12 of an embodiment,
(A) is a common top view of the light guide plates 11 and 12, and (b) is (a)
(C) is a sectional view taken along the line BB of (a) regarding the light guide plate 11, and (d) is a sectional view taken along the line BB of the light guide plate 12.
FIG. 4 is a cross-sectional view taken along line B.

FIG. 2A is a schematic perspective view of a light guide plate A11 in which a scattering pattern is formed on the back surface (the surface opposite to the diffusion prism surface) of the light guide plate 11 in FIG. 1, and a scattering pattern is formed on the surface (diffusion prism surface). The schematic perspective view of the light guide plate B11 (b).

FIG. 3 is an explanatory diagram (a) showing the direction of light emitted from groove surfaces b00 and b01 near the center b0 (FIG. 1 (b)) of the diffusion prism surface.
FIG. 4B is an explanatory diagram showing the direction of light emitted from the groove surfaces b10 and b11 near the non-center b1 (b2), and FIG.

FIG. 4 is a schematic perspective view of a conventional backlight device (a).
And a schematic perspective view of a conventional edge light panel (b).

FIG. 5 shows a scattering pattern (groove) A1 on the back surface A11c of the emission surface A11a.
(A) a schematic perspective view of a light guide plate A11 having 1d;
(B) of FIG.

FIG. 6 shows the scattering and reflection of light inside the light guide plate, and (a)
Is the light guide 11 (when there is no scattering pattern on the back surface), (b)
Is a light guide C11 (when a scattering pattern having an equal pitch is formed), (c) is a light guide D11 (when a scattering pattern is formed at a non-equal pitch on the surface), and (d) is a light guide. Body A11 (when scattering patterns are formed on the back surface at unequal pitch)
Is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Light guide 12 Light guide 21 Light source (long shape) 22 Light source (surface light source)

Claims (6)

[Claims] 1. A light guide plate for diffusing light taken in from the outside on a diffusion prism surface having a large number of fine diffusion grooves or diffusion ridges provided substantially in parallel and emitting the light from an exit surface, wherein the diffusion groove is provided. Alternatively, a cross-sectional shape of the diffusion ridge is a light guide plate in which an edge of the prism surface is saw-shaped so as to direct light at an edge of the emission surface to the center of the emission surface. 2. The diffusion groove or diffusion ridge at the center of the prism surface has a substantially isosceles triangular shape, and has a sawtooth shape having a sharp apex angle toward the edge. A light guide plate characterized by the above-mentioned. 3. The light guide plate according to claim 2, wherein the shape of the diffusion groove or the diffusion ridge from the center of the prism surface to the edge changes gradually. 4. The light guide plate according to claim 2, wherein the shape of the diffusion groove or the diffusion ridge from the center of the prism surface toward the edge changes continuously. 5. The light guide plate according to claim 1, wherein the light guide plate has a light incident surface on a side surface, a light exit surface on an upper surface, and a light exit surface closer to the lower surface as the distance from the light incident surface increases. Having a tapered light reflecting surface, the cross section has a wedge-shaped shape, and the diffusion groove or the diffusion ridge is arranged on the light emitting surface or the light reflecting surface, almost in parallel to the incident light. A light guide plate characterized by the above-mentioned. 6. The light guide plate according to claim 1, wherein the light guide plate has a light incident surface on a lower surface and a light emission surface on an upper surface, and the diffusion groove or the diffusion ridge is a light emission surface. A light guide plate which is arranged on a surface or a light reflecting surface.