JP2002116704A - Backlight device and method for assembling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the warpage of a light diffusing plate used for a backlight. SOLUTION: In the backlight device 7 in which the diffusing plate 5 is arranged on one side of a reflector 3 at a specified interval and fluorescent tubes 4 is arranged between the reflector 3 and the diffusing plate 5 as light sources, the diffusing plate 5 is made of an acrylic resin plate manufactured with a casting method and the resin plate is arranged so that its light-density side surface faces the reflector 3, thus the resin plate is warped toward the reflector 3.

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 as a light source of an LCD (Liquid Crystal Display Panel) which is frequently used for various display elements, display devices of electronic equipment, and the like.
In particular, the present invention relates to improvement of a direct type backlight device.

[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. It is known that such a backlight device includes a direct type and a sidelight type depending on the setting of a light source.

FIG. 9 is an exploded perspective view of a conventional direct-type backlight device, in which a box-shaped lamp housing 1 provided with an opening 1d in the front surface of a rectangular shape has left and right sides. Have fluorescent tube supports 2L and 2R, and these fluorescent tube supports 2L and 2R are made of white high-reflection grade molding resin. AA ′ in FIG.
As shown in FIG. 10A, which is a cross section along the cross-sectional direction, the reflective plate 3 made of a polyester white high-reflection film is fixed. The reflecting plate 3 is bent so that its upper and lower ends or, if necessary, its left and right end portions are inclined as shown in FIG. 10 (A), so that its cross section becomes substantially U-shaped. A plurality of fluorescent tubes 4 serving as a light source of the LCD panel are arranged side by side between the left and right fluorescent tube support bases 2L and 2L in the housing 1.

The reflecting plate 3 is configured to reflect the light from the plurality of fluorescent tubes 4 to the opening (upper side) 1d side of the housing 1 with high reflectance.

In the above description, the case where the housing 1 is formed of resin and the reflection plate 3 such as a reflection sheet is disposed on the inner surface of the housing 1 has been described. However, the housing 1 is formed of metal and the inner surface of the housing 1 is formed. Those coated with a high-reflection paint are often used.

The fluorescent tube 4 is selected to have a relatively small diameter of about 2 to 5 mm, and the fluorescent tube supports 2L and 2R are used to fix the fluorescent tube 4 at a position close to the bottom surface of the reflector 3. It supports the end of the tube 4. Fluorescent tube 4 used
Is appropriately selected according to the required luminance.

By disposing a light diffusion plate 5 made of a milky white acrylic resin or the like so as to cover the opening 1d on the front surface of the housing 1, the light emitted from the fluorescent tube 4 can be directly or fluorescently emitted. The light reflected by the lower reflector 3 from the tube 4 is incident on the diffuser 5 to be converted into planar light in the diffuser 5 to form a planar light source.

At least one light-collecting sheet 6 is adhered to the surface of the diffusion plate 5 to condense light in the normal direction of the illuminating surface and increase the brightness. Further, gradation printing for controlling luminance unevenness may be performed on the back surface of the diffusion plate 5 in some cases.

On the upper surface of the light-condensing sheet 6, an LCD housing, which is an LCD panel unit 8 in which LCs, polarizing plates, color filters and the like are integrated between glass substrates, is mounted to constitute an LCD display device. I have.

[0010]

The diffusing plate 5 used in the above-mentioned backlight device 7 is made of a thermoplastic optical plastic material (acryl, polycarbonate, polystyrene, etc.), and particularly from the viewpoint of optical performance and transparency. , Acrylic resin plate is widely selected.

As an acrylic resin plate manufacturing method, there are an extrusion method in which a material is heated and pressurized into a fluidized state and continuous extrusion molding from a die, and a cast (casting) manufacturing method. Since it does not need to be fluidized, it has higher heat resistance and mechanical properties than those made by the extrusion method. In addition, the cast method does not cause internal distortion, and thus has high optical performance. For this reason, it is desirable to use a resin plate manufactured by the casting method as a diffusion plate of a backlight for LCD.

Acrylic resin has higher optical performance and transparency than other optical materials. However, the acrylic resin has a higher water absorption rate than other optical resins, causing dimensional changes and warpage, and lacks stability in shape. For this reason, when incorporated in the backlight device, the diffuser plate 5 is warped or distorted due to a high temperature environment, a high humidity environment, a sudden change in temperature, or the like. As a problem in actual use, the warped diffusion plate 5 presses the LCD panel unit 8 and
There is a possibility that a phenomenon that causes unevenness in the CD panel section 8 or a worst case may damage the panel. In addition, there is also a problem that the printing pattern is displaced due to warpage and luminance unevenness occurs.

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 diffusion plate 5 of the backlight device and prevent the LCD panel from being damaged by the warpage. A backlight device and a method for assembling the same are to be obtained.

[0014]

According to the first aspect of the present invention, a diffusing plate 5 is disposed so as to cover an opening 1d of a casing 1, and a light source and a reflecting plate 3 are disposed in the casing 1 immediately below. A backlight device 7 of a system, in which a diffusion plate 5 is formed by a casting method,
The surface of the diffusion plate 5 where the density of the diffusing agent is high is positioned above the diffusion plate 5 covering the opening 1 d, and the surface of the diffusion plate where the density of the diffusing agent is low is arranged so as to face the reflection plate 3 in the housing 1. The backlight device is characterized by being provided.

The present invention according to claim 1 utilizes the fact that a layer having a low density and a layer having a high density are formed when a diffusion plate 5 made of an acrylic resin plate is produced by a casting method. When the side where the density of the diffusing agent is low is the front side and the side where the density is high is the back side, the surface is directed to the reflection plate 3 side, so that the diffusion plate 5 can be prevented from warping to the LCD panel section 8 side. .

According to a second aspect of the present invention, at least one spacer pin 9 extends from the bottom surface of the housing 1 to the diffusion plate 5.
The backlight device according to claim 1, wherein the backlight device is provided upright.

According to the second aspect of the present invention, the LCD panel is formed by warping the diffusion plate 5 toward the inside of the housing 1.
A backlight device capable of adjusting the amount of warpage and the position of warpage without damaging the panel can be obtained.

The present invention according to claim 3 is characterized in that the diffusion plate 5 is warped only inward of the housing 1 and abuts against the tip of the spacer pin 9 to regulate the warpage of the diffusion plate 5. Item 7 is a backlight device according to Item 2.

According to the third aspect of the present invention, it is possible to restrict the warpage of the diffusion plate.

According to a fourth aspect of the present invention, there is provided a process for irradiating light to an upper surface or a lower surface of a diffusion plate 5 manufactured by a casting method to detect a state of density of a diffusing agent in the diffusion plate. A process of arranging and assembling a surface having a low agent density so as to face the reflecting plate 3 and the light source 4 provided in the housing 1.

According to the present invention, the warping direction of the diffusion plate 5 is deflected toward the inside of the housing 1 so that L
A method of assembling a backlight device that does not damage the CD panel section 8 can be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a backlight device according to the present invention will be described below with reference to FIGS.

FIG. 1 is a perspective view of a backlight device according to the present invention, in which a part is cut away, FIG. 2 is a partially enlarged sectional view of a portion C in FIG. 3, and FIG. FIG. 4 is a partially enlarged cross-sectional view for explaining the configuration of the present invention corresponding to FIG. 2, and FIG. 5 is FIG. 1 for explaining the operation of the present invention corresponding to FIG.
6 and 7 are explanatory views of a method for manufacturing a diffusion plate used in the backlight device of the present invention, and FIG. 8 is a perspective view showing another configuration of the backlight device of the present invention. It is.

In FIG. 1, portions corresponding to those in FIG. 9 are denoted by the same reference numerals, and redundant description is omitted. In the figure, a casing 1 is formed by bending a metal plate such as aluminum having a screen size of 460 mm in a diagonal dimension so as to have a U-shape in cross section.
b, a reflective plate 3 made of a polyester reflective film is adhered to the inner surface thereof, and a fluorescent tube support 2L made of a rectangular parallelepiped white high-reflection grade molding resin is provided on the left and right ends of the housing 1.
And 2R are fixed to the side portions 1a and 1b between the bent pieces of the housing 1, and a plurality of fluorescent tubes 4 having a diameter φ of about 3 mm and a tube length of about 365 mm are juxtaposed between the fluorescent tube support bases 2L and 2R. In this case, the fluorescent tube 4 is fixed at a position spaced from the reflector 3 by about 1 to 2 mm, thereby forming the housing 1 as a lamp housing having an opening 1d on the front surface.

The light diffusing plate 5 is fixed so as to cover the opening 1d of the casing 1 so as to cover the fluorescent tube support bases 2L and 2R and the upper ends of the bent side portions 1a and 1b of the casing 1. In this case, the distance between the reflection surface of the reflection plate 3 and the diffusion plate 5 is 20 mm.
The thickness of the diffusion plate 5 is 2 mm, and the total light transmittance is 5
0% is selected, and two first and second light-collecting sheets 6a and 6b are adhered to the upper surface of the diffusion plate 5 as light-collecting sheets 6 to condense light in the normal direction of the illumination surface. are doing. In the backlight device 7 of the present invention, the above-mentioned diffusion plate is formed by a casting method.

FIGS. 6 and 7 show this casting method.
This will be described with reference to FIG. FIG. 6 shows a process of one embodiment in which the diffusion plate 5 is obtained by a casting method using an acrylic resin, and a curing agent or a catalyst is added to methyl methacrylate (MMA monomer) which is a raw material of the diffusion plate. The monomer 10 is subjected to prepolymerization such as bulk polymerization to obtain a liquid syrup 11, and a monomer or prepolymer obtained by mixing and stirring a white pigment (Tospearl manufactured by Toshiba Silicone Co., Ltd.) as a diffusing agent (coloring agent) 12. It is poured into a fastener 13 with a gasket 15 interposed between two glass plates 14,
After a plurality of fasteners 13 are placed on the mount 18 of the polymerization tank 17 and heat treatment is performed, the plate material obtained by the release
3 is cut into a predetermined shape after attaching, and the diffusion plate 5 is obtained.

FIG. 7 shows a process of another embodiment in which the diffusion plate 5 is obtained by a casting method using an acrylic resin. FIG. 7 shows a case where the diffusion plate 5 is obtained by a sol-bend casting method. A diffusion agent (coloring agent) 12 composed of a white pigment is mixed into a syrup 11 obtained by prepolymerizing a monomer 10 containing a catalyst in an MMA monomer and stirred. The concentrated solution is cast on the surface of the endless belt 30, a polymerization treatment is performed in a polymerization zone 32, a solvent is evaporated in a heat treatment zone 33, a heat treatment is performed, and a plate material obtained by cooling in a cooling zone 34 is subjected to an inspection process 36. After sticking the protective paper 37, the diffusion plate 5 having a predetermined size is obtained via the cutter 38.

The problem of the diffusion plate obtained by the above-mentioned casting method will be described with reference to FIGS. FIG. 4 shows an enlarged cross-sectional view similar to the part C in FIG. 3, but the diffusion plate 5 placed on the housing 1 is mixed with the syrup by the diffusion agent 12 of the white pigment in the production process by the casting method. Even if sufficient stirring is performed, gravity is applied while the liquid syrup 11 is cast on the fastener 13 or the stainless steel belt 30. In this case, the specific gravity of the MMA monomer serving as the base material is 1.19,
The silicone-based white pigment used for Tospearl (trade name, Toshiba Silicone Co., Ltd.) as the diffusing agent 12 has a specific gravity as high as 1.32. 14, and the MMA monomer having a low specific gravity floats on the upper side, and as a whole, as shown in the enlarged view of part B in FIG. It was found that the first layer having a high density of the diffusing agent and the second layer having a low density of the diffusing agent were separated.

In order to detect such a first layer and a second layer, it is possible to easily discriminate the density by irradiating strong light on the upper and lower sides of the diffusion plate 5 and to determine the density of the second layer (diffusion agent density is lower). It was also found that the (sparse) portion was much thinner than the first layer (dense agent density) portion.

The diffusion plate 5 of the above-described casting method is shown in FIG.
When the fluorescent plate 4 is turned on and actually driven as shown in FIG. 5, the diffuser plate 5 is substantially in the center position of the housing 1 as shown by a dashed line in FIG. , A tendency to warp upward.

In this case, the LC provided in front of the diffusion plate 5
There is a possibility that the D panel section 8 is pressed to cause unevenness in the LCD panel section 8 or to damage the LCD panel section 8 in the worst case.

Therefore, in the backlight device 7 of the present invention, as shown in FIG. 2 which is an enlarged view of a portion C in FIG. Reflector 3
Alternatively, the first layer 5a having a high density of the diffusing agent is fixed to the housing 1 with the surface of the first layer 5a having a high density of the diffusing agent facing the upper side of the opening 1d of the tube 1, that is, the side facing the LCD panel section 8. To do so.

As described above, the backlight device 7 provided with the diffuser plate 5 has the diffuser plate 5 substantially at the center position of the housing 1 at the time of actual driving with the fluorescent tube 4 turned on as shown by the dashed line in FIG. Case 1
Was found to warp into a valley-like concave shape inside. That is, it was confirmed that the diffusion plate had a warp, and the side where the density of the diffusing agent was low tended to warp in a mountain shape. As a mechanism, the difference in diffusing agent density is reflected in the difference in linear expansion coefficient,
It is expected that a portion having a low density of the diffusing agent has a higher coefficient of linear expansion than a portion having a high density, and that a portion having a low density of the diffusing agent has a larger expansion than a portion having a high density, so that warpage is expected to occur.

If the direction of warping of the diffusion plate is limited and the diffusion plate 5 is warped concavely, the possibility of unevenness or breakage of the LCD panel disposed on the front surface of the housing 1 is eliminated.

Further, as shown in the perspective views of FIGS. 3 and 6, a spacer pin 9 for regulating the amount of warpage when the diffuser plate 5 warps in a valley shape is erected from the housing 1b, whereby the diffuser plate 5 Can be regulated to reduce the amount of warpage.

The spacer pins 9 may be erected integrally with or separately from the housing 1. The shape of the spacer pins 9 is substantially conical and the contact surface with the back surface of the diffusion plate 5 is in point contact. It can be formed into chips.

The backlight device 7 in which the first layer 5a shown in FIG. 4 and FIG.
When a rated current of 35 W is applied to the fluorescent tube 4 in a high-temperature environment of 0 ° C., the diffusion plate 5 has a convex shape of 1 m at the center as shown in FIG.
m warpage.

However, as shown in FIGS. 2 and 3, when the second layer 5b of the diffuser plate 5 is on the lower side and the first layer 5a is on the upper side, the backlight device 7 is operated at a rated current of 35 W in a high temperature environment of 50 ° C. Is applied to the fluorescent tube 4, the center warp of the diffusion plate 5 becomes a valley-like warp as shown in FIG. 3, and the warp of the valley is 1 mm and L
One that does not press the CD panel portion 8 is obtained.

Further, as shown in FIGS. 3 and 6, a polycarbonate spacer pin 9 having a height of approximately 20 mm, which is substantially the same as the height of the housing 1, is mounted on the reflector 3 having the same structure as described above. When energizing the fluorescent tube 4 in a high-temperature environment, it was confirmed that the diffusion plate 5 did not sink into the housing 1 by the spacer pins 9, and a backlight device 7 in which the diffusion plate 5 was not warped was obtained.

In order to assemble the backlight device of the present invention, the diffuser plate 5 formed by the casting method described with reference to FIGS. 6 and 7 is cut into a predetermined diffuser shape to diffuse high-intensity light such as a halogen lamp. The upper surface or the lower surface of the plate 5 is irradiated with a first layer having a high density of the diffusing agent and a second layer having a low density of the diffusing agent.
The layers are detected, and in the assembly process of the backlight device, the opening 1d of the housing 1 in which the reflecting plate 3 and the fluorescent tube 4 are incorporated.
The diffusion plate 5 may be placed so that the second layer of the diffusion plate 5 comes to the side, and the diffusion plate 5 may be fixed to the housing 1 by a predetermined method.

[0041]

According to the backlight device and the method for assembling the backlight device of the present invention, a layer having a low diffusion agent density and a layer dense when a diffusion plate made of an acrylic resin plate is produced by a casting method are formed. By taking advantage of the fact that the diffuser plate does not warp to the LCD panel side by setting the surface to face the reflector side when the dense side is the front side and the dense side is the back side. . Also, according to the present invention, by diffusing the diffusion plate toward the inside of the housing, the diffusion plate can be
Without the problems caused by pressing the panel,
It is possible to obtain a backlight device in which the amount of warpage and the position of the warp can be adjusted and the warpage can be regulated. Further, according to the present invention, it is possible to obtain a method of assembling a backlight device in which the direction of warpage of the diffusion plate 5 is deflected toward the inside of the housing 1 so that a problem caused by the diffusion plate pressing the LCD panel does not occur. .

[Brief description of the drawings]

FIG. 1 is a perspective view in which a part of a backlight device of the present invention is cut away.

FIG. 2 is a partially enlarged sectional view of a portion C in FIG. 3;

FIG. 3 is a sectional view taken along the line DD ′ of FIG. 1;

FIG. 4 is a partially enlarged cross-sectional view for explaining a configuration of the present invention corresponding to FIG. 2;

FIG. 5 is a sectional view taken along the line DD ′ of FIG. 1 for explaining the operation of the present invention corresponding to FIG. 3;

FIG. 6 is an explanatory diagram of a method for manufacturing a diffusion plate used in the backlight device of the present invention.

FIG. 7 is an explanatory diagram of another method for manufacturing a diffusion plate used in the backlight device of the present invention.

FIG. 8 is a perspective view showing another configuration of the backlight device of the present invention.

FIG. 9 is an exploded perspective view of a conventional backlight device.

10 is a sectional view taken along the line AA 'of FIG. 1A and FIG.
It is the A section enlarged view of B.

[Explanation of symbols]

1 ‥‥ housing, 1d ‥‥ opening, 2L, 2R left and right fluorescent tube support, 3 ‥‥ reflector, 4 ‥‥ fluorescent tube, 5 ‥‥ diffuser,
5a ‥‥ first layer, 5b ‥‥ second layer

Claims (4)

[Claims] 1. A diffusion plate is arranged so as to cover an opening of a housing,
A backlight device of a direct type in which a light source and a reflection plate are provided in the housing, wherein the diffusion plate is formed by a casting method, and a surface of the diffusion plate where a diffusion agent density is high covers the opening. A backlight device, comprising a diffuser having a diffuser density lower than a surface of the diffuser and facing the reflector in the housing. 2. The backlight device according to claim 1, wherein at least one or more spacer pins are erected from a bottom surface of the housing in a direction of the diffusion plate. 3. The backlight device according to claim 2, wherein the diffusion plate is warped only in the inward direction of the housing and abutted against the tip of the spacer pin to regulate the warpage of the diffusion plate. 4. A process for irradiating an upper surface or a lower surface of a diffusion plate produced by a casting method with light to detect a state of diffusion agent density of the diffusion plate, And assembling the backlight unit so as to face the reflector and the light source provided in the backlight unit.