JP2003346508A - Backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent unevenness of a tube due to a bending of a light transmissive diffusion plate 4 by covering an opening 1a of a casing 1 with a sheet or a light collecting sheet 10 under the diffusion plate 4 of a back-light device. <P>SOLUTION: The light collecting sheet or the sheet 10, the light transmissive diffusion plate 4 and a light collecting sheet 9 are placed on the opening 1a of the casing 1 of a back-light device 6 in order to prevent unevenness of the tube due to a convex bending which occurs when a cylindrical light source 3 is turned on and hygroscopicity of the plate 4 changes. <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 backlight device used for a liquid crystal display (LCD), and more particularly, to a backlight device in which tube unevenness generated on an LCD panel is reduced.

[0002]

2. Description of the Related Art LCs used as display devices for electronic devices such as microcomputers and television receivers.
Since D has no light emission, it requires a light source for external irradiation such as a backlight device.

[0003] As such a backlight device, a small-diameter fluorescent tube such as a cold cathode tube or a hot cathode tube is generally used as a cylindrical light source, and the fluorescent tube is arranged on the side surface of a light guide plate. Edge light type, a reflector (hereinafter, referred to as a reflector) and a fluorescent tube are housed in the housing, and a light transmitting diffuser disposed in the housing opening directs light from the fluorescent tube and light from the fluorescent tube. There is known a direct type in which light reflected by a reflection plate is incident and diffused by a light transmission / diffusion plate to emit uniform planar light.

The above direct type or edge light type is L
It is selected according to the required performance of the CD, but the direct type uses the direct light of the fluorescent tube, so the light use efficiency is higher than the edge light type, and high brightness for monitors, television receivers, etc. Suitable for required applications.

FIG. 7A is a plan view showing a conventional direct type backlight device, FIG. 7B is a sectional view taken along the line AA 'of FIG. 7A, and FIG. , (B) is FIG. 7 (A)
8B is a cross-sectional view taken along the line BB ′, and FIG. 8B shows a light amount distribution on the light transmission / diffusion plate.

[0006] A housing 1 serving as a lamp house for a backlight.
Is formed in a trapezoidal box shape having a cross section having an opening 1a on the upper surface, and is integrally molded with a white high-reflection grade molding resin, or is formed by a metal plate or a combination of a metal plate and a molding resin.

A high-reflection paint is applied to the inside of the housing 1 or a high-reflection film material or the like is attached to the housing 1 to form a reflection plate 2 as a reflection surface.
To form

The cylindrical light source 3 such as a fluorescent tube is held at a position spaced from the bottom surface of the housing 1 by about 1 to 2 mm.
(In FIGS. 7A and 7B to FIGS. 8A and 8B,
(Integrated with the side plate), and the number of arrangements is determined by the required luminance.

A backlight device 6 is constructed by assembling the above-described components and disposing a light transmitting / diffusing plate 4 made of milky white acrylic resin or the like on the upper surface so as to cover the opening 1a. The emitted light is either directly or
The light is reflected by the reflection plate 2 inside, reaches the light transmission / diffusion plate 4, and is converted into surface light by the light transmission / diffusion plate 4.

At least one light-collecting sheet 9 is provided on the surface of the light-transmitting / diffusing plate 4 to condense light in a direction normal to the illuminating surface.

An important factor that indicates the superiority of the display quality of the LCD is the uniformity of the brightness of the irradiation surface of the backlight device 6. One of the elements representing the brightness uniformity is tube unevenness. As shown in FIG. 8B, the unevenness of the tube causes the light on the illuminating surface emitted from the light transmission / diffusion plate 4 or the light condensing sheet 9 to have a luminance of 8 above the cylindrical light source 3.
This is represented by a luminance change rate when a is compared with the luminance 8b between the adjacent cylindrical light sources 3 and is defined as (maximum luminance−minimum luminance) / maximum luminance × 100% of the value of the adjacent cylindrical light source.

When there is a luminance change on the illuminating surface of the diffusion plate 4 or the light-gathering sheet 9 of the backlight device, that portion is visually recognized as tube unevenness.

For this reason, the fixing position of the cylindrical light source 3 and the housing 1
It is necessary to carry out a design to minimize the tube unevenness in the structural design such as the shape of the tube.

[0014]

As the light transmission / diffusion plate 4 of the above-described backlight device 6, a thermoplastic optical plastic material such as acryl, polycarbonate, or polystyrene is used. In particular, from the viewpoint of optical performance and transparency. And acrylic resin plates are widely used.

[0015] Acrylic resin has higher optical performance and transparency than other optical materials. However, the acrylic resin has a water absorption of approximately 2.0% as compared with other optical resins. For example, the acrylic resin has a high dimensional change and warpage as compared with the water absorption of 0.4% of polycarbonate, and lacks stability in shape. For this reason, when incorporated in the backlight device, the light transmission / diffusion plate 4 is warped or distorted due to a high-temperature environment, a high-humidity environment, a rapid change in temperature, or the like, causing tube unevenness. As a problem in practical use, there is a possibility that the warped diffusion plate 4 presses the LCD panel portion disposed on the light transmitting diffusion plate 4 to cause a phenomenon that the LCD panel portion becomes uneven or the worst case may damage the panel. there were. In addition, in order to suppress tube unevenness, there is a problem that a pattern printed on the surface of the light transmission / diffusion plate 4 on the side of the cylindrical light source 3 is displaced due to warpage, resulting in uneven brightness.

That is, the light transmission / diffusion plate 4 made of such an acrylic resin continues to absorb moisture even in a normal temperature environment. When the amount of water absorption increases, when the cylindrical light source (hereinafter, referred to as a lamp) 3 of the backlight device 6 is turned on, the temperature inside the housing 1 increases with the elapse of time, and the surface on the lamp 3 side becomes the lamp 3.
Is used as a heat source to start dehumidification first. As a result, the light transmission / diffusion plate 4 on the side of the lamp 3 shrinks, and warps in a convex shape on the opposite side to the lamp 3 as shown by a virtual line in FIG.

In this case, there is a problem that the distance between the diffusion plate 4 and the lamp 3 deviates from the design value to cause tube unevenness.

FIG. 6 is a graph showing the mechanism of warpage of the light transmission / diffusion plate 4 for confirming the dependency of the water absorption / diffusion of the light transmission / diffusion plate 4 made of the above-mentioned acrylic resin. Is the ordinate, and the abscissa is the experimental data in which the lighting time of the lamp 3 is taken. That is, the initial water absorption in the backlight device 6 is 0.4%, 0.5%, 0.6%.
% And 1.15% of the light transmission / diffusion plate 4, and the lamp 3 is turned on at 45 ° C.

A curve 20 in FIG. 6 shows the amount of warpage of the light transmission / diffusion plate 4 when the initial water absorption is 1.15%, a curve 21 shows the amount of warpage when the initial water absorption is 0.6%, and a curve 22 shows the initial water absorption. Rate 0.5
% Shows the amount of warpage, and curve 23 shows the amount of warpage when the initial water absorption is 0.4%. From these, it is shown that the larger the initial water absorption is, the larger the amount of warping of the light transmission / diffusion plate 4 becomes. I have.

Curves 24 to 27 indicated by broken lines show initial water absorption rates of 1.15%, 0.6%, 0.5%, and 0.4%.
Shows the change in the water absorption rate at the time. It can be seen from these curves 24 to 27 that the values are converged to a constant value over time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to minimize the warpage of the light transmission / diffusion plate 4 of the backlight device and to reduce the unevenness of the tube. It is intended to obtain a light device.

[0022]

According to the first aspect of the present invention, at least one cylindrical light source and at least one reflector are disposed in a flat casing having an opening in its upper surface. Opening 1a
A backlight device in which a diffusion plate 4 made of an acrylic resin is disposed on the diffusion plate 4 and a condensing sheet 9 is disposed on the diffusion plate 4, wherein a synthetic resin is provided between the diffusion plate 4 and the opening 1 a of the housing 1. This is a backlight device characterized by having a mold sheet 10 interposed.

According to a second aspect of the present invention, there is provided the backlight device according to the first aspect, wherein the synthetic resin sheet 10 is one of a transparent polyester resin, a polycarbonate resin, and a polyolefin resin. is there.

According to a third aspect of the present invention, there is provided the backlight device according to the first aspect, wherein the synthetic resin sheet 10 is the light-collecting sheet 9.

According to the first to third aspects of the present invention, the diffusion plate 4 damages the LCD panel,
It is possible to obtain a backlight device that can prevent warpage that causes tube unevenness.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a backlight device according to the present invention will be described below in detail with reference to FIGS. FIG.
FIG. 1A is a plan view of a backlight device showing one embodiment of the present invention, FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG.
FIG. 1C is an enlarged view of a portion A in FIG. 1B.

In FIGS. 1A to 1C, a housing 1 serving as a lamp house of a backlight device 6 is formed by applying a reflecting sheet or a reflecting member to a reflecting plate 2 adhered in the housing 1. The light reflector or the housing 1 itself is integrally molded with a white high-reflection grade molding resin. The housing 1 is formed in a box shape with an opening 1a provided at the top.

The left, right, front and rear sides of the housing 1 are trapezoidal in cross section as shown in FIG. 1 (B). On the left and right sides, a cylindrical light source support 5 (not shown) molded of high reflection grade resin is provided. A cylindrical light source (lamp) 3, which is fixed and includes at least one or more cold-cathode tubes or hot-cathode tubes, is mounted at a position about 1 to 2 mm away from the surface of the reflector 2 on the bottom surface of the housing 1. ing.

A light-collecting sheet 10 made of polyester resin or the like is provided so as to cover the opening 1a of the housing 1. Further, the light transmission / diffusion plate 4 and the condensing sheet 9 are provided on the upper surface of the condensing sheet 10 in the same manner as in the conventional configuration, so that the lamp 3
The light emitted from the light collector sheet 9, the light transmitted from the lamp 3, and the light reflected by the lower reflector 2 are incident on the light-collecting sheet 10, the light-transmitting diffuser 4, and the light-collecting sheet 9. The light is converted into planar light to form a planar light source.

At least one or more light-condensing sheets 9 shown in FIG. 1C are disposed on the surface of the light-transmitting / diffusing plate 4 to condense and diffuse light in the normal direction of the illuminating surface to increase brightness. ing.

One light-collecting sheet 9 or 10 is shown in FIG.
As shown in the figure, a bead coat in which a small-diameter bead is coated on the surface of a sheet 9 of about 100 μm of a thermoplastic polyester resin such as PET (polyethylene terephthalate), PBT (polybutylene terephthalate), polycarbonate (PC) resin, polyolefin resin or the like. Layer 9b
And a sticking prevention coat layer 9c for preventing sticking of acrylic resin or the like on the back surface.

The light-collecting sheet 10 disposed on the opening 1a
Is the one in which the sticking prevention coat layer 9c and the bead coat layer 9b shown in FIG.
A single sheet of a T resin, a PBT resin, a PC resin, a polyolefin resin or the like may be used.

In order to correct the deflection 11 of the light-collecting sheet 10, the height of the case 1 is adjusted so that the bottom of the case 1 comes into contact with the lower surface of the light-collecting sheet or sheet 10 in the case 1 of the present invention. Approximately identical pins 16 are erected on the bottom surface of the housing 1.

As shown in FIG. 1A, at least one pin 16 can be provided at an appropriate position in a portion where the bending 11 occurs.

FIG. 2A is a perspective view showing an assembling state of a pin 16 according to another embodiment of the present invention. In FIG. Further, for example, three light-collecting sheets 9 are stacked on the light transmission / diffusion plate 4 with the bead coat layer 9b facing upward, and the opening 1 of the housing 1 is opened.
a.

The reflection plate 2 is fixed to the bottom plate 1b through the opening 1a of the housing 1. The pin 16 is erected on a disk-shaped base 16a, and the shape of the pin 16 is substantially conical, and the tip 20 of the light-collecting sheet or the contact point 20 with the back surface of the sheet 10 has a tip shape of about 1 mm ² so as to make point contact. The height is made of 20 mm polycarbonate which is substantially the same as the height of the housing 1.

In FIG. 2A, through holes 2a through which the bases 16a of the three pins 16 can pass are formed in the reflecting plate 2 in correspondence with the standing positions of the pins 16. A pin 16 is inserted into this through hole 2a.
Is attached to the bottom 1b of the housing 1 via an adhesive applied to the bottom surface of the base 16a and fixed.

FIG. 2B shows the housing 1 of the backlight device 6.
2 (C) is a sectional view taken along the line AA 'in FIG. 2 (B).

FIG. 2B shows a case in which one pin 16 is erected substantially at the center of the housing 1.
(C) The conical pin 1 is integrated with the bottom plate 1b of the housing 1 as shown in FIG.
6 is erected.

According to the backlight device 6 of the present invention as described above, it is left in an environment of 50 ° C. and 80% RH (relative humidity) for 30 hours, and a light-condensing sheet or a single sheet 10 such as a PC is light-transmitted and diffused. FIG. 7 (A) shows a case in which it is arranged below the plate 4 and FIG.
8B, the difference in the water absorption rate between the case where the condensing sheet or the single sheet 10 such as a PC is not provided below the light transmission / diffusion plate 4 as shown in FIGS. In this case, when the sheet or the light condensing sheet 10 is not provided, the water absorption and diffusion rate of the light transmission / diffusion plate 4 is set to 0.1.
It was confirmed that the water absorption ratio of the light transmission / diffusion plate 4 in the case where the sheet or the light condensing sheet 10 was provided was 0.5%, compared to 9%.

That is, under the same conditions, it can be understood that the water absorption of the light transmitting / diffusing plate 4 becomes approximately half only by laying the sheet or the light condensing sheet 10 below the light transmitting / diffusing plate 4.

[Embodiment] The screen size of the LCD is 18 inches, and the lamp 3 has an outer diameter of 3 mm and an inner diameter of 2.4 m.
m, and the distance between the plurality of lamps 3 is 23.
5 mm, the distance between the upper surface of the reflector 2 of the housing 1 and the lamp is 2
mm, and a plurality of pins are erected from the reflection plate 2 to have a height of 28 mm.
A single sheet 10 made of an acrylic resin having a thickness of 0.14 mm is disposed at a position of 0.1 mm, and a light transmission / diffusion plate 4 made of an acrylic resin having a thickness of 2 mm is further superimposed on the sheet 10.
FIG. 7 does not include the sheet 10 under the same conditions as those of the backlight device 6 in which the two light-condensing sheets 9 described in (C) are stacked.
(A) Using the same backlight device 6 as in (B) as a comparative example, an experiment was conducted to confirm the amount of dehumidification of the light transmitting diffusion plate 4 when the lamp was turned on.

Comparative Example 1 FIG. 3 shows a case 1 as a comparative example.
The absolute humidity and the amount of warping are plotted as the lighting time of the lamp 3 elapses.
% Moisture absorption was used.

FIG. 3 shows the absolute humidity (g / m ² ) and the amount of warpage (μm) of the light transmitting / diffusing plate 4 on the vertical axis, and the lighting time (minutes) after the lamp 3 is turned on the horizontal axis. The curve 28a represents the absolute humidity in the housing 1, the curve 29a represents the ambient absolute humidity,
FIG. 30A shows the amount of warpage of the light transmission / diffusion plate 4.

That is, when the light-condensing sheet or sheet 10 is not disposed between the light-transmitting / diffusing plate 4 and the opening 1 a of the housing 1, the heat source of the lamp 3 causes dehumidification from the back of the light-transmitting / diffusing plate 4. It is confirmed that the light transmission diffusion plate is largely warped.

[Embodiment 1] FIG. 4 shows an embodiment of the present invention, in which the absolute humidity and the amount of warpage in the casing 1 are plotted as the lamp 3 lighting time elapses.
Used 0.8% moisture absorption in advance.

FIG. 4 shows the absolute humidity (g / m ² ) and the amount of warpage (μm) of the light transmitting / diffusing plate 4 on the vertical axis, and the lighting time (minutes) after the lamp 3 is turned on the horizontal axis. The curve 28b represents the absolute humidity in the housing 1, the curve 29b represents the ambient absolute humidity,
FIG. 30B shows the amount of warpage of the light transmission / diffusion plate 4.

That is, in the case where the condensing sheet or sheet 10 is disposed between the light transmitting / diffusing plate 4 and the opening 1 a of the housing 1, dehumidification from the back surface of the light transmitting / diffusing plate 4 by the heat source of the lamp 3 does not occur. It is confirmed that the light transmission / diffusion plate does not warp significantly, and the addition of the light-collecting sheet or sheet 10 reduces the absolute humidity in the housing 1 and the amount of warpage of the light transmission / diffusion plate 4. I understand that

[Comparative Example 2] Under the same conditions as in Comparative Example 1, the light transmitting / diffusing plate 4 was collected on the opening 1a of the housing 1 of the backlight device 6 as shown in FIGS. 7 (A) and 7 (B). The light transmitting / diffusing plate 4 is previously fixed at an ambient temperature of 40.
What was left for 33 hours in an atmosphere at 85 ° C. and a relative humidity of 85% RH was used (moisture absorption rate: 0.8%).

In the curve 31 of FIG. 5, the vertical axis represents the amount of warpage (mm) of the light transmission / diffusion plate 4, and the horizontal axis represents the lighting time (minutes) of the lamp 3 (temperature 23 ° C., relative humidity 45 to 65% RH). 2 shows the state of change in the amount of warpage of the conventional light transmission / diffusion plate 4.
It is warped to a convex mountain shape by 5 mm.

[Embodiment 2] As shown in FIGS. 1A to 1C, a light-collecting sheet or sheet 10 is placed on an opening 1a of a housing 1 of a backlight device 6 under the same conditions as those in Embodiment 1. The light-transmitting / diffusing plate 4 was fixed and laminated in the order of the light-collecting sheet 9, and the light-transmitting / diffusing plate 4 was previously left in an atmosphere at an ambient humidity of 50 ° C. and a relative humidity of 80% RH for 20 hours (moisture absorption). Rate 0.
8%).

The curve 32 in FIG. 5 shows the diffusion plate 4 after the lamp 3 of the second embodiment is turned on (temperature 23 ° C., relative humidity 45-65% RH).
The amount of warpage after 1400 minutes is ± 0.5 m
It can be seen that it is within m.

That is, the amount of warpage after 17 hours when there is no sheet is 1.6 mm, whereas the amount of warpage after 17 hours when there is a sheet 10 is 0.2 mm.
A backlight device having a high effect of suppressing the amount of warpage can be obtained only by inserting 0.

A curve 33 in FIG. 5 shows a change curve of the amount of warpage when the light transmission / diffusion plate is dried in advance.

In the backlight device 6 described above, the light-collecting sheet or sheet 10 is made of acrylic resin. However, the use of PC or the like having a smaller water absorption than the acrylic resin sheet can further reduce the amount of warpage. And tube unevenness is almost 0
It shows a value close to%. Also, in this example, the light transmitting diffusion plate 4
The side part is a sheet 1 so that moisture can be dehumidified from the outer side
It is possible to allow the air to enter and exit to some extent without being covered by 0 or the like.

[0056]

According to the backlight device of the present invention, the upper and lower surfaces of the light transmitting / diffusing plate 4 are covered with the condensing sheet 9 and the condensing sheet or sheet 10 so that the lower surface of the light transmitting / diffusing plate 4 can be used by the lamp 3. The dehumidification effect caused by the heating is reduced, and by suppressing the mountain-like warpage of the light transmission / diffusion plate 4, it is possible to prevent the LCD panel portion from being damaged and from causing tube unevenness.

[Brief description of the drawings]

FIG. 1 is a plan view showing one embodiment of a backlight device of the present invention, a cross-sectional view taken along the line AA ′ of FIG. 1 (A), and FIG. 1 (B).
FIG.

FIG. 2 is an assembled perspective view and a plan view showing another embodiment of the backlight device according to the present invention, and a sectional view taken along the line AA ′ of FIG. 2 (B).

FIG. 3 is a curve diagram showing the relationship between the absolute humidity of the backlight device of the comparative example and the warpage of the light transmission / diffusion plate.

FIG. 4 is a curve diagram showing the relationship between the absolute humidity of the backlight device of the present invention and the warpage of the light transmitting diffusion plate.

FIG. 5 is a curve diagram showing the amount of warpage of the light transmitting diffuser when the lamps of the backlight devices of the present invention and the comparative example are turned on.

FIG. 6 is a curve diagram showing the amount of warpage and the dependence on moisture absorption of the light transmission / diffusion plate used in the present invention.

FIG. 7 is a plan view and a side sectional view of a conventional backlight device.

FIG. 8 is a side sectional view and a tube unevenness explanatory view of a conventional backlight device.

[Explanation of symbols]

1 ‥‥ housing, 2 ‥‥ reflector, 3 ‥‥ cylindrical light source (cold cathode tube), 6 ‥‥ backlight device, 9 ‥‥ condenser sheet, 1
0 ‥‥ focusing sheet or sheet, 16 ‥‥ pin

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/1335 520 G02F 1/13357 1/13357 F21Y 103: 00 // F21Y 103: 00 F21S 1/00 E

Claims (3)

[Claims] 1. A flat housing having an opening on an upper surface in a flat case.
A backlight device comprising at least one cylindrical light source and a reflector, a diffusion plate made of acrylic resin disposed at the opening of the housing, and a light-condensing sheet disposed over the diffusion plate. A backlight device comprising a synthetic resin sheet interposed between the diffusion plate and the opening of the housing. 2. The backlight device according to claim 1, wherein the synthetic resin sheet is a transparent polyester resin, a polycarbonate resin, or a polyolefin resin. 3. The backlight device according to claim 1, wherein the synthetic resin sheet is a light-collecting sheet.