JP2005044747A - Overhead backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress increase in weight of overhead backlight. <P>SOLUTION: In the overhead backlight where a light source 7 is arranged behind a light diffusion surface member 9, the light diffusion surface member 9 constituted only of a sheet material of less than 1 mm thickness, and the sheet material 9 includes a low transmittance diffusion sheet where the total light transmittance is 10-50%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a direct type backlight.

The direct type backlight is used as a backlight for a liquid crystal display device or the like, and is generally configured by arranging a light source composed of a cold cathode tube behind a diffusion plate. The diffusing plate is formed by kneading a diffusing agent in a synthetic resin material, and diffuses light from a light source to form a substantially uniform light emitting surface. When used for a display device, it is one of the important members for maintaining the quality of the liquid crystal screen.
When a large backlight is required as in a large liquid crystal display device, the volume of the diffusion plate increases and the product weight increases. For example, the weight of the backlight diffuser for a 20-inch screen is 350 g, and the backlight diffuser for a 30-inch screen is 530 g, which is against the demand for weight reduction.
JP-A-7-64084

  The problem to be solved by the present invention is to suppress an increase in the product weight of the direct type backlight.

The present invention relates to a direct type backlight in which a light source is disposed behind a light diffusing surface member, and the light diffusing surface member is composed only of a sheet material having a thickness of less than 1 mm. A low transmittance diffusion sheet having a transmittance of 10 to 50% is included.
The light diffusing surface member is not a diffusing plate having a thickness of several millimeters as in the prior art, but is composed only of a sheet material having a thickness of less than 1 mm.

  In addition, the diffusion sheet used in the conventional backlight is used for increasing the brightness in combination with the diffusion plate (brightness increasing diffusion sheet), and has a relatively high total light transmittance (80 %more than). Therefore, if only the diffusion sheet that has been used in combination with the diffusion plate is used as the light diffusion surface member, the diffusion effect cannot be sufficiently obtained, and the lamp image in which the position directly above the lamp is bright and the space between the lamps is dark remains strong. As a result, good light emission quality cannot be obtained.

  On the other hand, in the present invention, since the low transmittance diffusion sheet having a total light transmittance lower than that of the prior art and 10 to 50% is used, light transmitted through the diffusion sheet is kept low at a position directly above the light source. In addition, the transmitted light is diffused by the light diffusion action of the diffusion sheet. Therefore, the lamp image is improved even with a thin diffusion sheet.

  The low transmittance diffusion sheet preferably has a haze value of 70 to 100%. In this case, the lamp image is further improved.

It is preferable to provide a supporting member that applies tension to and supports the sheet material so that the sheet material does not bend. By pulling and supporting the sheet material, it is possible to prevent the sheet material from being bent even if there is only a thin sheet material without a diffusion plate.
In order to apply tension to the sheet material, the support member includes a frame, and a plurality of tension applying members provided on the frame so as to pull a plurality of portions of the sheet peripheral edge of the sheet material in an out-of-plane direction of the sheet material, It is preferable that it is comprised.

  Further, the present invention provides a direct type backlight in which a light source is disposed behind a light diffusing surface member, wherein the light diffusing surface member is composed only of a sheet material having a thickness of less than 1 mm, and the sheet material is bent. There may be provided a supporting member that applies tension to the sheet material to support it. The light diffusing surface member is not a diffusing plate having a thickness of several millimeters as in the prior art, but is composed only of a sheet material having a thickness of less than 1 mm. In addition, by pulling and supporting the sheet material, it is possible to prevent the sheet material from being bent even if there is only a thin sheet material without a diffusion plate.

  In the direct type backlight in which the light source is disposed behind the light diffusing surface member, the light diffusing surface member is composed only of a sheet material having a thickness of less than 1 mm, and the edge of the sheet material Is provided with a reinforcing frame. The light diffusing surface member is not a diffusing plate having a thickness of several millimeters as in the prior art, but is composed only of a sheet material having a thickness of less than 1 mm. And since the reinforcement frame is provided in the edge part of the thin sheet material, the bending of a sheet material can be prevented.

  According to the present invention, since the light diffusing surface member is thin, an increase in the product weight of the direct type backlight can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 show a direct type backlight 1 according to the first embodiment. The direct type backlight 1 is suitably used as a backlight for a liquid crystal display device. The backlight 1 includes a lower frame 2 serving as a lamp housing and an upper frame 3 attached to the lower frame 2, and the frame of the apparatus is configured by both the frames 2 and 3.

  The lower frame 2 includes a rectangular bottom surface portion 4 and side surface portions 5 erected from each side of the bottom surface portion 4 and is configured as a box-shaped body having an upper surface opening. The lower frame 2 is made of a metal such as aluminum. A light source 7 is disposed inside the lower frame 2, and a linear light source is used as the light source 7. More specifically, the light source 7 is a cold cathode tube lamp. The light source 7 may be a point light source such as an LED.

  Inside the lower frame 2, a plurality of light sources 7 are juxtaposed at a predetermined interval. A light diffusing surface member 9 is disposed in the upper surface opening of the lower frame 2. Light from the light source 7 located behind the light diffusing surface member 9 is applied to the light diffusing surface member 9, and this light diffusing surface member 9 becomes a light emitting surface. The linear or dotted light is diffused by the light diffusing surface member 9, so that the in-plane light intensity becomes substantially uniform and is irradiated onto the liquid crystal panel of the liquid crystal display device. The

  The inner surface of the lower frame 2 (the inner surface 4a of the bottom surface 4 and the inner surface 5a of the side surface if necessary) is a light reflecting surface. Here, the light reflecting surfaces 4a and 5a are diffuse reflecting surfaces, and are located at least behind the light source 7 and reflect light toward the light diffusing surface member 9 side. Specifically, a white reflective sheet is installed on the lower frame inner surfaces 4a and 5a, or white coating is applied to form a diffuse reflection surface.

  As the light diffusion surface member 9, a diffusion sheet is employed. This diffusion sheet is a thin sheet material having a thickness of less than 1 mm. The thickness of the sheet 9 is preferably about 0.1 to 0.8 mm, more preferably 0.1 to 0.3 mm. Specifically, the thickness of the sheet 9 can be about 0.2 mm. Here, as the light diffusion surface member 9, a heavy diffusion plate having a thickness of several millimeters is not used. Therefore, the backlight 1 can be reduced in weight. Further, since the diffusion plate that requires a relatively large amount of resin material is omitted, the material cost can be reduced.

  The diffusion sheet 9 has a low transmittance with a total light transmittance of 10 to 50%. The transmittance is preferably 20 to 40%, specifically about 30%. The diffusion sheet 9 can be formed by applying a diffusing agent to the surface of a base material using a transparent resin such as PET, PC, or acrylic as the base material. Alternatively, it can be formed by kneading a diffusing agent inside the sheet. The low transmittance of the diffusion sheet 9 can be realized by adjusting the amount of the diffusing agent to adjust the amount of light absorbed by the diffusing agent or increasing the reflectance of the sheet surface.

  Moreover, since the diffusion sheet 9 here is for improving the lamp image, the haze value is set to 70 to 100%. Increasing the haze value can be achieved by applying a diffusing agent or making the sheet surface have fine irregularities.

  Since the transmittance of the diffusion sheet 9 is 50% or less, more than half of the light L1 irradiated to the diffusion sheet 9 from the light source 7 is not directly transmitted. That is, the directly transmitted light L2 is suppressed to be lower than the total light amount, and the transmitted light is diffused by the light diffusing action of the diffusion sheet 9. For this reason, it is possible to prevent the position directly above the lamp from becoming very bright, and the lamp image can be relaxed even if the thickness is small as in the case of the conventional diffusion plate.

  Further, a part L3 of the light that does not pass through the diffusion sheet 9 is reflected toward the reflection surface 4a, and finally exits the diffusion sheet 9 by re-reflection by the reflection surfaces 4a and 5a. When the transmittance is lowered by increasing the reflectance of the lamp-side surface 9a of the diffusion sheet 9, most of the light that does not transmit can be reflected light L3, which is efficient.

  As shown in FIG. 3, the reflected light L <b> 3 of the diffusion sheet 9 spreads more than the incident light L <b> 1 of the diffusion sheet 9 due to the diffusion action of the diffusion sheet 9. The spread light L3 is re-reflected by the reflection surface 4a and emitted toward the diffusion sheet 9 while part of the re-reflection light L4 is diffused by the diffusion sheet 9. If the reflection surfaces 4a and 5a are diffuse reflection surfaces, further diffusion effects can be obtained.

In this way, since the amount of light emitted from the light source 7 is directly emitted from the diffusion sheet 9, a large amount of light repeatedly reflects and diffuses in the space inside the lower frame, and is sufficiently spread from the light source 7. Appears on the surface of the diffusion sheet 9 to obtain a light emitting surface with a relaxed lamp image.
That is, even if a thin diffusion sheet is used without a diffusion plate, the lamp image can be relaxed similarly to the diffusion plate by reducing the transmittance, and the backlight 1 can be reduced in weight. Specifically, for a 20-inch liquid crystal display device, a weight reduction of about 300 g could be achieved, and for a 30-inch liquid crystal display device, a weight reduction of about 500 g could be achieved.

  As shown in FIGS. 1 and 2, the periphery of the diffusion sheet 9 is pulled out of the plane by a spring 11 so that the thin diffusion sheet 9 does not bend downward. Specifically, one end of the spring 11 is attached to the corner portion of the rectangular diffusion sheet 9 and the central portion of the long side, and the other end of the spring 11 is the lower frame 2 (the upper portion of the side surface portion 5). Is attached. The diffusion sheet 9 has an attachment hole 12 for attaching one end of the spring 11. The attachment hole 12 and its vicinity (portion pulled by the spring 11) are preferably reinforced by inserting a reinforcing tool such as a round metal fitting in order to prevent the sheet from being torn or stretched. The rectangular diffusion sheet 9 is formed smaller than the rectangular upper surface opening of the lower frame 2, and a spring 11 is disposed in the gap 13 between the periphery of the diffusion sheet 9 and the lower frame side surface portion 5. The

  The spring 11 is a tension applying member that applies tension to the diffusion sheet 9 to apply tension to the sheet 9, and the thin diffusion sheet 9 is prevented from being bent by the spring 11. Moreover, since the spring 11 is attached to the lower frame 2, the diffusion sheet 9 is supported by the lower frame 2 via the spring. As described above, the spring 11 and the lower frame 2 serve as a support member that tensions and supports the diffusion sheet 9. Further, when the sheet 11 is pulled and supported by the spring 11, the sheet 9 can be prevented from being bent even if the sheet 9 expands due to a change with time, and even if the sheet 9 contracts, the extension of the spring 11 can cope. That is, even if the sheet 9 expands and contracts, an appropriate tension is maintained by the spring force.

  The springs 11 are provided at positions facing each other with the center C of the diffusion sheet 9 as a reference, and the diffusion sheet 9 is automatically held at the center of the lower frame 2 which is a fixed support. Thus, the diffusion sheet 9 is automatically centered by the spring 11, and the spring 11 constitutes a centering mechanism. Therefore, even if the diffusion sheet 9 expands and contracts due to heat, water absorption, or the like, the diffusion sheet 9 is automatically centered, and the relative position with respect to the lower frame 2 (light source 7) does not shift much. Therefore, when a lighting curtain (a pattern that reduces the lamp image by printing a pattern that blocks a large amount of light directly above the lamp and blocks a small amount of light between the lamps) is formed on the diffusion sheet 9. The position of the curtain and the position of the light source 7 can be maintained.

Even the conventional diffuser plate has a problem of expansion and contraction due to heat or water absorption. For this reason, the diffuser plate is arranged with play and generates play. When a lighting curtain is applied to such a diffusing plate, the position of the lighting curtain and the position of the light source 7 fluctuate due to the backlash of the diffusing plate, making it difficult to optimally design the position of the lighting curtain.
On the other hand, if the diffusion sheet 9 on which the lighting curtain is formed is automatically centered as in the present embodiment, the position of the lighting curtain and the position of the light source 7 can be kept substantially constant. It is possible to optimally design the position of the lighting curtain, and it is easy to obtain the light emission quality as designed.

As shown in FIGS. 2 and 4, the upper frame 3 attached to the lower frame 2 is provided with a window portion 14 that substantially corresponds to the size of the diffusion sheet 9 or is smaller than the diffusion sheet 9. The window portion 14 is for allowing light from the diffusion sheet 9 serving as a light emitting surface to pass even when the upper frame 3 is placed on the upper opening of the lower frame 2. Here, the window portion 14 is rectangular. It is formed as an upper hole.
The upper frame 3 has a rectangular frame-shaped frame portion 15 around the window portion 14. The frame portion 15 is positioned so as to close the gap 13 between the seat 9 and the lower frame side surface portion 5. Since the frame portion 15 covers the gap 13, it is possible to prevent light from leaking from the gap even if there is the gap 13, and it is possible to prevent a decrease in luminance due to light leakage and deterioration of light emission quality around the light emitting surface. In addition, since the gap 13 is closed, foreign matter can be prevented from entering the backlight through the gap 13, and deterioration of the light emission quality due to foreign matter can be prevented. Further, since the frame portion 15 also covers the tension applying member (spring) 11, the tension applying member 11 can be protected and its operation is stabilized.

A liquid crystal panel is held on the back side 15 a of the frame portion 15, and the liquid crystal screen is disposed on the window portion 14. That is, the upper frame 3 functions as a holder for the liquid crystal panel and serves as a front housing of the liquid crystal display device.
Note that side portions 16 are suspended from the four sides of the upper frame 3, and the side portions 16 of the upper frame 3 are fitted into the lower frame 2, so that both the frames 2 and 3 are integrated. If necessary, the frames 2 and 3 are firmly fixed by fixing means such as screws.
The upper frame also functions as a housing for holding the liquid crystal panel.

  FIG. 5 shows a direct type backlight 1 (excluding the upper frame) according to the second embodiment. Here, optical sheets 20 and 21 other than the low transmittance diffusion sheet are arranged on the low transmittance diffusion sheet 9. The optical sheets 20 and 21 are also sheet materials having a thickness of less than 1 mm. As the optical sheets 20 and 21, a luminance improving diffusion sheet 20 and a lens sheet 21 are provided. The diffusion sheet 20 for improving brightness achieves brightness improvement by converting diffused light emitted from the low transmittance diffusion sheet 9 in the vertical direction by bead coating on the surface of the sheet. The lens sheet 21 is also for improving the brightness, and is condensed by a fine lens to improve the brightness.

These optical sheets 20 and 21 are not simply placed on the low transmittance diffusion sheet 9 but are pulled by the spring 11 in the same manner as the low transmittance diffusion sheet 9. Since the optical sheets 20 and 21 are also pulled, the bending of the sheets 20 and 21 is prevented. The attachment hole 12 to which one end of the spring 11 is attached is formed at the same position of the stacked sheets 9, 20, 21, and is a common attachment hole 12.
In addition, the point which abbreviate | omitted regarding FIG. 5 is the same as that of the backlight 1 shown in FIGS.

6 and 7 show a direct backlight 1 (excluding the upper frame) according to the third embodiment. A rectangular reinforcing frame 30 as a whole is provided at the edge of the low transmittance diffusion sheet 9. The reinforcing frame 30 is for imparting rigidity to the four sides of the sheet 9 that is easily bent so that the sheet 9 is not easily bent. By providing the reinforcing frame 30, the bending can be reduced without applying tension to the sheet 9.
The reinforcement frame 30 is configured in a rectangular shape by arranging rigid members such as synthetic resin on the four sides of the sheet 9. The reinforcing frame 30 is formed as a bar-shaped member having a square cross section (hollow), and each bar-shaped member is fixed to four sides of the sheet 9 with an adhesive or the like. The material used for the reinforcing frame 30 is a material having a thermal expansion coefficient close to that of the sheet 9, so that wrinkles and the like are prevented from occurring in the sheet due to thermal expansion. When the size of the backlight is small (for an 8-inch liquid crystal display device), the thermal expansion coefficient of the reinforcing frame 30 does not need to be considered in particular.

The four reinforcing frames 30, 30, 30, 30 provided on the four sides are arranged separately at the four corners 31 of the sheet 9. Thus, since the rectangular frame 30 is partially interrupted as a whole, it becomes easy to cope with the thermal expansion of the sheet 9.
As shown in FIG. 6, the sheet 9 with the reinforcing frame is installed with the reinforcing frame 30 facing downward so that the reinforcing frame 30 is placed on the lower frame 2.
Note that another optical sheet can be disposed on the sheet 9. The other optical sheet is sandwiched and fixed between the upper frame 3 and the sheet 9.

It is a perspective view of a direct type backlight excluding an upper frame. It is an exploded sectional view of a direct type backlight. It is a conceptual diagram which shows the spreading | diffusion and reflection state of light. It is a perspective view of an upper frame. It is sectional drawing of the direct type | mold backlight (except an upper flame | frame) which concerns on 2nd Embodiment. It is sectional drawing of the direct type | mold backlight (except an upper flame | frame) which concerns on 3rd Embodiment. It is a perspective view of the sheet | seat with a reinforcement frame which concerns on 3rd Embodiment.

Explanation of symbols

1 Direct type backlight 3 Lower frame (frame)
9 Light diffusion surface member (low transmittance diffusion sheet; sheet material)
11 Spring (tensioning member)
20 Optical sheet (sheet material)
21 Optical sheet (sheet material)
30 Reinforcement frame

Claims (6)

In the direct type backlight in which the light source is arranged behind the light diffusing surface member,
The light diffusing surface member is composed only of a sheet material having a thickness of less than 1 mm,
The direct backlight according to claim 1, wherein the sheet material includes a low transmittance diffusion sheet having a total light transmittance of 10 to 50%.   The direct backlight according to claim 1, wherein the low transmittance diffusion sheet has a haze value of 70 to 100%.   The direct type backlight according to claim 1 or 2, further comprising a supporting member that tensions and supports the sheet material so that the sheet material does not bend.   The support member includes a frame and a plurality of tension applying members provided on the frame so as to pull a plurality of locations on the sheet peripheral edge of the sheet material in an out-of-plane direction of the sheet material. The direct type backlight according to claim 3. In the direct type backlight in which the light source is arranged behind the light diffusing surface member,
The light diffusing surface member is composed only of a sheet material having a thickness of less than 1 mm,
A direct type backlight comprising a support member that supports the sheet material by pulling the sheet material so that the sheet material is not bent. In the direct type backlight in which the light source is arranged behind the light diffusing surface member,
The light diffusing surface member is composed only of a sheet material having a thickness of less than 1 mm,
A direct-type backlight having a reinforcing frame provided at an edge of the sheet material.

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