JP4009263B2 - Backlight device - Google Patents

Description

  The present invention relates to a backlight device used as a light source of a liquid crystal display device such as a liquid crystal television, and more specifically, even if a diffusion plate constituting the backlight device tries to warp due to temperature rise or moisture absorption. The present invention relates to a backlight device capable of obtaining uniform brightness by supporting the optical sheet so that wrinkles do not occur by regulating.

  Conventionally, a backlight device used in a liquid crystal display device such as a liquid crystal television has fluorescent lamps that are light sources arranged at equal intervals in a base plate of a shallow box-like reflector, and a diffusion plate made of an acrylic plate or the like in front of the fluorescent lamp. An optical sheet such as an ITO sheet, a diffusion film, a prism sheet, or a reflective polarizing film is disposed on the front surface. Since these diffusion plates and optical sheets are made of different materials, their respective thermal expansion coefficients are different. Therefore, each time the backlight device is turned on, the temperature rises and expands with different elongation amounts. At this time, if the optical sheets are in close contact with each other, a phenomenon of warping to one side like bimetal occurs and wrinkles occur.

When wrinkles occur, the shadow of the wrinkles is reflected on the liquid crystal panel in front of the wrinkles, resulting in uneven brightness. Conventionally, as a countermeasure, when the irradiation surface of the backlight device is supported vertically, a plurality of pins are provided on the abutting surface of the reflector base plate with which the upper end of the diffusing plate abuts, and a hole is formed at the upper end. The formed diffusion plate and each optical sheet were locked to the pins, and the diffusion plate and each optical sheet were held in a state of being suspended by their own weight. In this state, the optical sheets are held so as to freely expand and contract with each other without applying an external force in the thickness direction to the optical sheets. Moreover, there is a liquid crystal display device described in Patent Document 1 as a technique for holding the end portions of these optical sheets without generating wrinkles.
JP-A-11-281966

  By the way, in the backlight device of a liquid crystal display device, the cause of wrinkling of the optical sheet is influenced by the moisture of the diffusion plate supported on the back surface of the optical sheet, as described above. In other words, the atmosphere in which the backlight device is placed is not completely dry air, but contains an amount of moisture or moisture that increases or decreases depending on the weather of the day, and the moisture is absorbed by the diffusion plate having relatively high water absorption. ing. The amount of moisture absorbed by the diffusion plate varies depending on the humidity of the atmosphere of the day and the temperature of the diffusion plate itself. In particular, when the backlight device starts lighting, a temperature gradient is generated between the front surface side and the back surface side of the diffusion plate, and the amount of moisture absorbed between the front surface side and the back surface side may vary greatly.

As a result, there occurs a phenomenon in which the difference in the amount of swelling that expands by absorbing water between the front surface side and the back surface side of the diffusion plate increases and warps to one side. This phenomenon is also affected by the thermal expansion due to the temperature gradient on the front and back sides of the diffuser, which can lead to complex behavior, but in the normal operating environment, the central part of the diffuser swells forward and reacts. As a result, the peripheral portion of the diffusion plate tends to warp backward. As described above, when the diffusion plate is warped, the optical sheet supported by natural suspension on the front surface of the diffusion plate is sandwiched between the liquid crystal panel disposed on the front surface and freely extends. Can not be. Also, because the periphery of the diffusion plate is warped, part of it is deformed forward and part of it is rearwardly deformed, and the optical sheet supported by the holding metal fitting together with the diffusion plate is pressed against the diffusion plate and can move freely. Disappear.

As a result, the thermally expanded portion of the optical sheet became wrinkled, and a shadow was reflected on the liquid crystal panel on the front surface of the optical sheet, resulting in a problem of uneven brightness. As described above, one factor that causes the warpage of the diffusion plate is that when the diffusion plate repeatedly absorbs and releases moisture due to changes in the relative humidity of the atmosphere, the gradient of the moisture content in the thickness direction in the diffusion plate is small. It can be estimated that the diffusion plate warps due to the difference in the expansion amount corresponding to the difference in the moisture content. As a countermeasure, it is conceivable to correct the warp by fixing the central portion of the diffuser plate that is warped and bulges forward to the light source side of the backlight device. In view of this, the present invention provides a wrinkle of an optical sheet by correcting a warp that occurs at the time of lighting by fixing a diffuser plate, which is a flat surface in the normal state, to the back, that is, to the light source side of the backlight device. The purpose was to stabilize the brightness.

In order to solve the above-mentioned problems, the present invention provides a light source in a housing, a rectangular diffusion plate made of resin in front of the light source, an optical sheet in front of the diffusion plate, and a liquid crystal panel in front of the optical sheet. In the backlight device, the through-hole formed in the diffusion plate, and the engagement of one end engaged with the through-hole and the other end engaged with the planar member installed on the light source side Means. Here, a small screw whose head is thicker than the through hole can be used as the locking means, and the small screw is preferably formed of a transparent material.

  Further, as the locking means, a rod-shaped protrusion in which a spherical portion slightly larger than the through hole is formed at one end and an axial slit is formed in the spherical portion and the other end portion is integrally fixed to the planar member. The rod-shaped protrusions are preferably formed of a transparent material. Further, it is possible to provide the through hole and the locking means in the central portion of the diffusion plate. Further, it is preferable that the locking means be locked at a position slightly bent backward by curving the central portion of the diffusion plate backward.

  As described above, according to the present invention, in the backlight device in which the diffuser plate made of resin is arranged in front of the light source, the diffuser plate is curved when the backlight is turned on, the central portion moves forward, and the periphery moves backward. Even if the diffusing plate is warped, the diffusing plate is locked by the locking means so that the central portion cannot move forward, and thus cannot be warped. As a result, the optical sheet is not pressed by the warp of the diffuser plate to generate wrinkles, and the backlight brightness is stabilized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing a main part of a first embodiment when a backlight device according to the present invention is applied to a liquid crystal display device. In the figure, reference numeral 1 denotes a reflector base plate which is a shallow box-like housing, and a white reflector sheet 2 is laid on the surface thereof. The reflection sheet 2 has mountain-shaped projections 3 formed at regular intervals in the vertical direction, and a lamp clip 4 is fitted so as to straddle the projections 3. A fluorescent tube 5 as a light source is inserted into the lamp clip 4. At the position of the projecting portion 3 of the lamp clip 4, a projection 6 is provided so as to prevent the diffuser plate 7 from curving and retreating due to thermal expansion or the like on the reflection sheet 2 side.

A diffusion plate 7 made of a transparent resin such as acrylic is disposed in front of the reflection sheet 2 and at the tip of the projection 6, and on the front surface thereof, an optical element such as an ITO sheet, a diffusion film, a prism sheet, or a reflective polarizing film. A sheet 8 is disposed. A liquid crystal panel 9 is arranged in front of the optical sheet 8 with an interval. Here, the central portion of the diffusing plate 7 is locked to the reflecting plate base plate 1 side with a transparent countersunk screw 11 made of acrylic so that the diffusing plate 7 is not bent forward due to the influence of temperature change or humidity. . That is, a through-hole 12 is formed from the front side of the diffusion plate 7 at a central portion of the diffusion plate 7 and opposed to an intermediate position of the mountain-shaped protrusion 3 of the reflection sheet 2 and an angle of 90 degrees. Use spot facing.

At the same time, the tapped holes 13 are formed by tapping the reflecting plate base plate 1 and the reflecting sheet 2 at positions facing the through holes 12. Next, a transparent countersunk screw 11 made of acrylic is inserted into the through hole 12 and screwed into the screw hole 13 on the reflection sheet 2 side. At this time, the diffusion plate 7 is held at a position where it is forcibly moved to the reflection sheet 2 side slightly from the position in the free state. This is because when the backlight device is turned on, the central portion of the diffuser plate 7 tends to bend and move forward due to temperature rise and humidity change. In order to prevent this, the light is moved slightly in the opposite direction in advance. Is.

In this way, the diffusion plate 7 is locked to the light source side so as not to move forward, so that the temperature of the diffusion plate 7 rises due to the heat generation of the fluorescent tube 5 when the backlight device is turned on, or the relative humidity of the atmosphere is reduced. When the entire diffuser plate 7 is curved and the central portion is about to move forward, the machine screw 11 prevents the central portion of the diffuser plate 7 from moving forward. As a result, the central portion of the diffusing plate 7 moves forward, the optical sheet 8 is sandwiched between the liquid crystal panel 9 and wrinkles are prevented, and uneven brightness due to wrinkles is eliminated. Will come to be. In addition, it is preferable to apply silicon grease or the like to the contact portion between the through hole 12 of the diffusion plate 7 and the flat screw 11 so that the diffusion plate 7 and the flat screw 11 are in an optically continuous state. .

FIG. 2 is a longitudinal sectional view showing a main part of the second embodiment when the backlight device according to the present invention is applied to a liquid crystal display device. In the figure, reference numeral 1 denotes a reflector base plate which is a shallow box-like housing, and a white reflector sheet 2 is laid on the surface thereof. The reflection sheet 2 has mountain-shaped projections 3 formed at regular intervals in the vertical direction, and a lamp clip 4 is fitted so as to straddle the projections 3. A fluorescent tube 5 as a light source is inserted into the lamp clip 4. A diffusion plate 7 made of a transparent resin such as acrylic is disposed in front of the fluorescent tube 5, and an optical sheet 8 such as an ITO sheet, a diffusion film, a prism sheet, or a reflective polarizing film is disposed on the front surface thereof. A liquid crystal panel 9 is arranged in front of the optical sheet 8 with an interval.

Here, the diffusing plate 7 is locked to the reflecting plate base plate 1 side by the projection 15 projecting from the central portion of the lamp clip 4 so that the diffusing plate 7 does not bend forward due to the influence of temperature change or humidity. did. That is, the projection 15 made of a transparent material is projected from the central portion of the lamp clip 4 at the central portion of the diffuser plate 7 and at the apex of the mountain-shaped projection 3 of the reflection sheet 2. A through hole 16 is formed in the diffusion plate 7. A spherical portion 17 that is slightly thicker than the diameter of the through hole 16 is provided at the tip of the protrusion 15, and a slit 18 is formed at an appropriate depth from the tip of the spherical portion 17 toward the axial base.

With this configuration, when the spherical portion 17 is press-fitted into the through hole 16 of the diffusion plate 7 during assembly of the backlight device, the outer diameter of the spherical portion 17 that narrows the slit 18 and passes through the through hole 16 is reduced. By swelling, the diffusion plate 7 is locked so as not to move forward. At this time, the diffusion plate 7 is held at a position where it is forcibly moved to the reflection sheet 2 side slightly from the position in the free state. This is because when the backlight device is turned on, the central portion of the diffuser plate 7 tends to bend and move forward due to temperature rise and humidity change. In order to prevent this, the light is moved slightly in the opposite direction in advance. Is.

In this way, the diffusion plate 7 is locked to the light source side so as not to move forward, so that the temperature of the diffusion plate 7 rises due to the heat generation of the fluorescent tube 5 when the backlight device is turned on, or the relative humidity of the atmosphere is reduced. When the entire diffuser plate 7 is curved and the central portion is about to move forward, the protrusion 15 prevents the central portion of the diffuser plate 7 from moving forward. As a result, the central portion of the diffusing plate 7 moves forward, the optical sheet 8 is sandwiched between the liquid crystal panel 9 and wrinkles are prevented, and uneven brightness due to wrinkles is eliminated. Will come to be. In the embodiment shown in FIGS. 1 and 2, the diffusion plate 7 is locked at one central portion, but is preferably locked at a plurality of locations.

  The present invention can be used for backlight devices of other display formats besides the backlight device of a liquid crystal display device such as a liquid crystal television.

It is a longitudinal cross-sectional view which shows the principal part of 1st Embodiment of the backlight apparatus which concerns on this invention. It is a longitudinal cross-sectional view which shows the principal part of 2nd Embodiment of the backlight apparatus which concerns on this invention.

Explanation of symbols

1 Reflector base plate

2 Reflective sheet

3 Protruding part

4 Lamp clip

5 Fluorescent tubes

6 Protrusions

7 Diffuser

8 Optical sheet

9 LCD panel

11 Further screw

12 Through hole

13 Screw holes

15 protrusions

16 Through hole

17 Ball

18 slits

Claims (7)

In a backlight device in which a light source is arranged in a housing, a rectangular diffusion plate made of resin is arranged in front of the light source, an optical sheet is arranged in front of the diffusion plate, and a liquid crystal panel is arranged in front of the optical sheet,
A through hole formed in the diffusion plate;
A locking means having one end engaged with the through hole and the other end locked to a planar member installed on the light source side;
A backlight device comprising: The backlight device according to claim 1,
  A backlight device characterized in that a small screw whose head is thicker than the through hole is used as the locking means. The backlight device according to claim 2,
A backlight device, wherein the small screw is made of a transparent material. The backlight device according to claim 1,
As the locking means, a rod-like protrusion having a spherical portion slightly larger than the through-hole formed at one end and an axial slit formed in the spherical portion and the other end fixed integrally with the planar member is used. A backlight device characterized by The backlight device according to claim 4, wherein
A backlight device characterized in that the rod-like projections are made of a transparent material . The backlight device according to any one of claims 1 to 5,
A backlight device, wherein the through hole and the locking means are provided in a central portion of the diffusion plate . The backlight device according to any one of claims 1 to 6,
It said locking means is a backlight apparatus characterized by the locking at a position slightly retracted central portion is curved to the rear of the diffuser.

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