JP2003297120A - Direct backlight and diffusion plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a diffusion plate from warping, while maintaining lightweight and light emitting quality. <P>SOLUTION: A direct backlight has a lamp 3 located on the back 8 side of a diffusion plate 4, the front 14 of which is an emitting surface, where a rib section 10 with a screen structure is formed on at least either of the front 14 and the back 8 of the diffusion plate 4, recess parts 12 are formed in areas corresponding meshes of the rib section 10 so that the thickness of the recess parts 12 is less than the rib section 10, and the mesh size of the rib section 10 is minute to a degree that unevenness of light emitting is not caused substantially by the difference between the thickness of the diffusion plate 4 at the recess parts 12 and the thickness of the diffusion plate 4 at the rib section 10. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct type backlight and a diffusion plate.

[0002]

2. Description of the Related Art In recent years, a direct type backlight is increasingly used as a large planar light emitting device having a size of more than 15 inches. Since the direct type backlight has a lamp arranged on the back surface side of a diffusion plate, the interior of the backlight is hollow. Therefore, as compared with the side type backlight in which the lamp is arranged on the side portion of the light guide plate, the direct type backlight is lightweight even if the size is increased, and is suitable for the size increase.

[0003]

However, if the direct type backlight is simply increased in size, there is a problem that the diffusion plate is warped and the emission quality is deteriorated due to uneven emission.
In other words, the direct type backlight has a structure in which only the peripheral edge of the diffusion plate is supported by the support frame and the inside has a hollow structure, so that the vicinity of the central portion of the diffusion plate is liable to be sunk and bent. Moreover, in order to reduce the weight, an organic polymer material such as acrylic or polycarbonate, which has a lower specific gravity than glass or the like, is used as the material of the diffusion plate, and the material is likely to be deformed. When the diffuser plate is warped, the distance between the lamp and the diffuser plate is not uniform in the plane, causing unevenness of light emission and lowering the light emission quality.

Therefore, it is conceivable to increase the rigidity of the diffusion plate by increasing the thickness of the diffusion plate to prevent the diffusion plate from warping. However, if the diffuser plate is simply thickened, the weight of the diffuser plate increases and the lightness which is an advantage of the direct type backlight is lost. In addition, if the diffuser plate is made thicker, the amount of light absorbed by the diffuser plate increases, so that the diffuser plate becomes darker and the high brightness required for the backlight is lost.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the diffusion plate from warping while maintaining the lightness and the light emitting quality.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a direct type backlight in which a lamp is arranged on the back surface side of a diffusion plate having a light emitting surface, and at least one of the front surface and the back surface of the diffusion plate is provided. Is formed with a mesh rib portion, and a concave portion is formed in a region corresponding to the mesh of the rib portion so as to have a smaller thickness than the rib portion. The thickness of the diffusion plate in the concave portion and the diffusion in the rib portion are formed. It is characterized in that the mesh of the rib portion is so small that the unevenness of light emission due to the difference from the thickness of the plate does not substantially occur on the light emitting surface.

According to this structure, since the diffusion plate is reinforced by the rib portion, the warp can be reduced. Moreover, since the rib portion has a mesh shape and the concave portion is formed in the area corresponding to the mesh, the diffusion plate is thin at the concave portion, and even if the rib portion is provided, the diffusion plate can be reduced in weight. As a result, the brightness of the recess is not significantly reduced. Further, since the mesh of the rib portion is fine, even if unevenness in the thickness of the diffusion plate occurs due to the presence of the rib portion and the concave portion, human eyes cannot recognize the uneven light emission, and substantially uneven light emission occurs. Absent. More specifically,
The recess preferably has a maximum diameter of 3 mm or less.

Further, in the present invention, it is preferable that the rib portion is formed in a non-lattice shape. When the rib portions are formed in a grid pattern, the rib portions are formed in a straight line shape and the recesses are arranged in a straight line shape to form a regular pattern. Human eyes
Since a regular pattern has a property that it is easy to discriminate even if it is fine, if the rib portion is formed in a grid pattern, even if it is fine, streak-like light emission unevenness becomes conspicuous. Therefore, by making the rib portion non-lattice-shaped, it is possible to effectively prevent uneven light emission. Specifically, it is preferable to form the rib portion in a honeycomb shape.

Further, in the present invention, it is preferable that the rib portion and the concave portion are formed on the back surface which is a surface on the lamp side and not formed on the surface which is a light emitting surface. Even if the rib portion and the concave portion are formed on the surface, the warp can be prevented, but if the rib portion and the concave portion are formed on the surface serving as the light emitting surface, the light emission quality is likely to deteriorate. On the other hand, if ribs and recesses are formed on the back surface, the unevenness of light emission is reduced due to the diffusion action of the diffusion plate while the light from the lamp is transmitted from the back surface to the front surface of the diffusion plate, and the emission quality is degraded. Is prevented.

Moreover, an optical sheet for improving the optical characteristics of the light emitting surface such as a lens sheet or a diffusion sheet may be placed on the surface of the diffusion plate, but the optical sheet is placed on the surface of the diffusion plate. Then, the optical sheet comes into contact with the diffuser plate (a range of the rib portion) and a part not in contact with the diffuser plate (a region of the concave portion), which rather deteriorates the emission quality. On the other hand, by placing the optical sheet on the surface of the diffuser plate, which is flat because the ribs and the recesses are not formed, it is possible to prevent the degradation of light emission quality.

Further, in the diffusion plate according to the present invention, a net-shaped rib portion is formed on at least one surface of the diffusion plate front surface and the diffusion plate back surface, and the mesh portion of the rib portion is formed in the area described above. The recess is formed to have a thickness smaller than that of the rib portion, and the unevenness of light emission due to the difference between the thickness of the diffusion plate in the recess and the thickness of the diffusion plate in the rib portion does not substantially occur on the light emitting surface. The mesh of the rib portion is minute.

When this diffusing plate is used for a direct type backlight, the diffusing plate is reinforced by the rib portion, so that the warp can be reduced. Moreover, since the rib portion has a mesh shape and the concave portion is formed in the area corresponding to the mesh, the diffusion plate is thin at the concave portion, and even if the rib portion is provided, the diffusion plate can be reduced in weight. As a result, the brightness of the recess is not significantly reduced.
Further, since the mesh of the rib portion is fine, even if there are rib portions and concave portions having different thicknesses, the human eyes cannot recognize the uneven light emission, and the uneven light emission does not substantially occur.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a direct type backlight 1 used in a liquid crystal display device. In this direct type backlight 1, a plurality of lamps 3 are installed on a bottom surface 2a of a box-shaped casing 2 having an upper opening, and a diffusion plate 4 is attached to an upper opening of the casing 2. On the surface of the diffusion plate 4, a lens sheet and a diffusion sheet are placed as the optical sheet 5. Also, the casing 2 has
An inverter is provided as a lighting device 6 for lighting the lamp 3.

The lamp 3 is a linear light source, and is specifically constituted by a cold cathode tube. Each lamp 3
It is located behind the diffuser plate 4. The light emitted from the lamp 3 is directly or reflected on the reflection surface formed on the bottom surface 2a of the casing 2, passes through the diffusion plate 4 and the optical sheet 5, and is irradiated from the back to a liquid crystal panel (not shown).

The diffusion plate 4 is made of a resin such as white transparent acrylic or polycarbonate and is molded by injection molding or the like. The diffusing plate 4 has a diffusing action of diffusing the light from the lamp 3, and converts the light from the plurality of linear light sources 3 into planar light. The diffusion plate 4 has a rectangular shape as shown in FIG. 2, and is attached so that the peripheral edge thereof is supported by the casing 2. The interior of the backlight surrounded by the casing 2 and the diffusion plate 4 is hollow.

As shown in FIGS. 2 and 3, a net-shaped rib portion 10 is formed on the entire rear surface 8 of the diffusion plate 4 on the lamp 3 side.
Are formed so as to project in the thickness direction of the diffusion plate. Further, a region corresponding to the mesh of the mesh rib portion 10 is a concave portion 12 recessed in the diffusion plate thickness direction with respect to the rib portion 10. Such a shape of the back surface 8 of the diffusion plate is formed when the diffusion plate 4 is molded. That is, the rib portion 10 is provided integrally with the diffusion plate 3.

Since the rib portion 10 is formed, the diffusion plate 4 can be reinforced as compared with the case where the rib portion 10 is not provided. Therefore, even if the inside of the backlight is hollow, it is possible to reduce the warp such that the center of the diffusion plate 4 hangs, and it is possible to prevent the deterioration of the light emission quality. Moreover, since the rib portion 10 is formed in a mesh shape on the back surface 8 of the diffusion plate and is only partially present, even if the rib portion 10 is formed, the weight of the diffusion plate 4 as a whole does not increase so much. .

Here, the total thickness of the diffusion plate 4 including the rib portion 10 is x, the depth of the recess 12 (= the height of the rib portion 10) is y,
The thickness of the diffusion plate 4 in the range of the recess 12 is z. Note that x
= Y + z is established. At this time, recess depth (rib height)
It is preferable to set y to about 10 to 100% of the plate thickness z. That is, by suppressing the rib height y to the same level as the plate thickness z, it is possible to suppress an increase in weight of the diffusion plate 4. More preferably, the rib height y is 50 to 8 of the plate thickness z.
It can be 0%. More specifically, the rib portion 10
The total thickness x of the diffuser plate 4 including
It is preferably m, and more preferably 2 to 4 mm. Even if the diffusion plate 4 is made thin, the rib portion 10 still exists,
Warpage can be effectively prevented.

Depth of concave portion 12 (= height of rib portion 10) y
Is preferably 3 mm or less so as not to increase the unevenness of light emission, and 2 mm for proper reinforcement of the diffusion plate 4.
It is more preferable that the degree is.

In the present embodiment shown in FIGS. 2 and 3, the rib portion 10 is formed as a honeycomb mesh pattern, and each recess 12 is hexagonal. The maximum diameter (distance between facing apexes) S1 of the hexagonal recess 12 is set to 3 mm or less. In addition, the maximum outer diameter S2 of the hexagonal frame-shaped portion existing around one hexagonal recess 12 of the rib portion 10 is set to 4 mm or less. As described above, the mesh of the mesh rib portion 10 is fine. Note that in FIG. 2, the size of the mesh of the rib portion 10 is drawn larger than the size of the entire diffusion plate 4 for easy understanding of the drawing.

At the portion where the rib portion 10 is formed, the diffuser plate 4 is thick and absorbs much light from the lamp 3. On the other hand, in the portion where the concave portion 12 is formed, the diffusion plate 4 is thin, and the absorption of light from the lamp 3 is small. Therefore, of the light emitted from the diffuser plate surface 14 serving as the light emitting surface, the light emitted from the region in which the rib portion 10 is formed and the light emitted from the region in which the concave portion 12 is formed have strictly different brightness. In contrast, the rib portion 10 is darker.

However, since the mesh is so fine that the difference between the bright area and the dark area cannot be discerned by human eyes,
Substantially no uneven light emission occurs, and good light emission quality is obtained. Moreover, the rib portion 10 and the concave portion 12 are the back surface 8 of the diffusion plate 4.
Therefore, even when light passes from the back surface 8 of the diffusing plate to the front surface side 14 of the diffusing plate, slight unevenness in light emission caused by the diffusing action of the diffusing plate 4 is reduced.

Further, since the rib portion 10 is formed as a narrow strip having a width of about 0.5 mm, the area of the dark region in the plane of the diffuser plate 4 is small, and the decrease in brightness is small. The width of the rib portion 10 can be set in the range of, for example, about 0.1 mm to 1 mm. The width of the rib 10 is 1 mm
By setting the following, the rib portion 10 becomes inconspicuous and 0.
By setting the thickness to 1 mm or more, necessary strength can be secured. Further, by making the rib portion 10 thinner and making the area occupied by the recess 12 larger than the area occupied by the rib portion 10 in the plane of the diffusion plate 4, brightness can be secured.

Further, in this embodiment, the mesh rib portion 10 is used.
Since the honeycomb pattern is adopted as the above, the straight line portion is short and it is inconspicuous, and uneven light emission can be suppressed. Diffuser 4
The surface 14 is a flat surface in which neither the rib 10 nor the recess 12 is formed. When unevenness is formed on the surface 14, a portion that comes into contact with the optical sheet and a portion that does not come into contact with the optical sheet are formed, which causes unevenness in light emission. It doesn't cause it.

The shapes of the rib portion 10 and the concave portion 12 are not limited to those shown in FIGS. 2 and 3, and various shapes can be adopted. 4 to 7 show modifications regarding the shapes of the rib portion 10 and the concave portion 12.

In the first modification shown in FIG. 4, the rib portion 10 is used.
Are formed in a grid pattern in which vertical stripes and horizontal stripes are orthogonal to each other, and the recesses 12 are quadrangular. Even if a lattice pattern is adopted as the mesh pattern of the rib portion 10, the diffusion plate 4 can be reinforced. However, when the grid-shaped rib portion 10 is used, the rib portion 10 is formed in a linear shape, and the concave portions 12 are arranged in a linear shape, so that a regular pattern is formed. Since the human eye has a property that it is easy to discriminate even if it is a regular pattern even if it is fine, if the rib portion is formed in a grid pattern, even if it is fine, streak-like light emission unevenness tends to stand out. From this point of view, the non-lattice-shaped rib portion 10 shown in FIGS. 2, 3, and 5 to 7 is preferable.

In the second modification shown in FIG. 5, the recesses 12 are quadrangular as in the first modification, but the recesses 12 are arranged in a staggered pattern, so that the first modification is different from the first modification. The linearity of the pattern is reduced and streak-like uneven light emission is less noticeable.

FIG. 6 shows a third modification. Recess 1
The shapes of 2 do not have to be unified, for example,
As shown in FIG. 6, concave portions having different shapes such as an octagonal concave portion 12a and a square concave portion 12b may be mixed.

FIG. 7 shows a fourth modification. Recess 1
The sizes of 2 do not have to be unified, and for example, as shown in FIG. 7, recesses having different sizes may be mixed such as a large circular recess 12c and a small circular recess 12d. . The rib portion 10 is a portion other than the concave portions 12c and 12d.

The present invention is not limited to the above embodiment. For example, the rib portion may be formed not on the back surface of the diffuser plate but on the front surface or both surfaces. The shape of the recess may be a polygon such as a triangle or a pentagon, an ellipse, or any other shape other than those described above.
The shape of the rib portion can be appropriately set according to the shape of the concave portion. Further, the direct type backlight of the present invention is used not only for liquid crystal display devices but also as various light emitting devices such as a light emitting device for signboards, a light box for seeing negatives of photographs, and a Schaukasten for seeing X-ray photographs. Available.

[0031]

According to the present invention, the rib is reinforced by the rib portion, so that the warp can be reduced. Moreover, since the rib portion has a mesh shape and the concave portion is formed in the area corresponding to the mesh, the diffusion plate is thin at the concave portion, and even if the rib portion is provided, the diffusion plate can be reduced in weight. As a result, the brightness of the recess is not significantly reduced. Further, since the mesh of the rib portion is fine, even if unevenness in the thickness of the diffusion plate occurs due to the presence of the rib portion and the concave portion, human eyes cannot recognize the uneven light emission, and substantially uneven light emission occurs. Absent.

Further, when the rib portions are formed in a grid pattern, uneven light emission can be effectively prevented. Further, when the rib portion and the concave portion are formed on the back surface that is the surface on the lamp side and not formed on the front surface that is the light emitting surface, the light from the lamp transmits from the back surface to the front surface of the diffusion plate. In the meantime, unevenness of light emission is reduced by the diffusion action of the diffusion plate, and deterioration of light emission quality is prevented.

Moreover, by placing the optical sheet on the surface of the diffuser plate which is flat due to the absence of the ribs and recesses, the emission quality is degraded even if the optical sheet is placed on the surface of the diffuser plate. Can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a direct type backlight.

FIG. 2 is a rear view of the diffusion plate.

FIG. 3A is an enlarged view of a portion X in FIG.
(B) is the sectional view on the AA line of (a).

FIG. 4 is an enlarged plan view of a first modification of the diffusion plate.

FIG. 5 is an enlarged plan view of a second modification of the diffusion plate.

FIG. 6 is an enlarged plan view of a third modification of the diffusion plate.

FIG. 7 is an enlarged plan view of a fourth modification of the diffusion plate.

[Explanation of symbols]

1 Direct type backlight 3 lamps 4 diffuser 5 Optical sheet 8 back side 10 Rib part 12 recess 14 surface S1 concave maximum diameter

Claims (7)

[Claims] 1. A direct type backlight in which a lamp is arranged on the back surface side of a diffusion plate whose front surface is a light emitting surface, wherein a net-like rib portion is provided on at least one of the front surface and the back surface of the diffusion plate. A recess is formed in a region corresponding to the mesh of the rib portion so as to have a thickness smaller than that of the rib portion, and light is emitted due to a difference between the thickness of the diffusion plate in the recess and the thickness of the diffusion plate in the rib portion. A direct-type backlight in which the mesh of the rib portion is so small that unevenness does not substantially occur on the light emitting surface. 2. The direct type backlight according to claim 1, wherein the recess has a maximum diameter of 3 mm or less. 3. The direct type backlight according to claim 1, wherein the rib portion is formed in a non-lattice shape. 4. The direct type backlight according to claim 1, wherein the rib portion is formed in a honeycomb shape. 5. The direct type backlight according to claim 1, wherein the rib portion and the concave portion are formed on the back surface and are not formed on a surface which is a light emitting surface. 6. The direct type backlight according to claim 5, wherein the rib and recess are not formed so that the optical sheet is placed on a flat diffusion plate surface. 7. A mesh-shaped rib portion is formed on at least one surface of the diffuser plate front surface and the diffuser plate rear surface, and a thickness of the mesh portion of the rib portion is smaller than that of the rib portion. A concave portion is formed in the concave portion, and the mesh of the rib portion is so small that the unevenness of light emission due to the difference between the thickness of the diffuser plate in the concave portion and the thickness of the diffuser plate in the rib portion does not substantially occur on the light emitting surface. Diffusion plate characterized by that.