JP2005135670A - Liquid crystal display device, backlight device - Google Patents

Abstract

An object of the present invention is to reduce the deflection of a diffusion plate, improve the image quality of a liquid crystal display screen, and achieve uniform display.
The diffusing plate 1 and the housing 2 are fitted together with appropriate play in consideration of the amount of thermal expansion between the projections 21 and 22 and the holes 11a and 12a at the upper edge of the screen. The diffusion plate 1 has a structure that is suspended from the upper edge of the screen. Further, the pulling means 5 is constituted by a weight suspended by a hole provided in the lower edge of the screen of the diffusion plate 1. Due to the gravity based on the weight 5, a tension T acts on the diffusion plate 1 in the in-plane direction, and display unevenness can be prevented.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device typified by a liquid crystal television or a liquid crystal monitor, or a backlight device used for a liquid crystal display device.

  Since display devices and various electronic devices using the display devices can be reduced in power consumption and thinned, liquid crystal display devices are actively used. As one of elemental technologies in a liquid crystal display device, there is a technology for preventing image display unevenness due to deformation of a diffusion plate. In this regard, by using diffusion plates having different diffusion material densities on the front surface and the back surface, even when the liquid crystal display device is placed vertically, the technology of reducing the warpage of the diffusion plate in the direction of pressing the liquid crystal panel (See, for example, Patent Document 1).

  Further, a technique for reducing the warpage of the diffusion plate toward the liquid crystal panel and maintaining the image quality by simultaneously providing the fluorescent tube holding device with a function of suppressing the warpage of the diffusion plate is also disclosed (for example, Patent Document 2). reference). As described above, since the warpage of the diffusion plate becomes a factor of deteriorating the display quality of the liquid crystal screen, a design that fully considers this point is required.

  By the way, most liquid crystal display devices are used in a vertical orientation (a state in which a display surface and an installation surface having a vertical line in the normal direction are arranged in a vertical direction). Therefore, as shown in FIG. 4, a configuration in which the diffusion plate 1 is suspended from the upper side of the screen by the locking pieces 21 and 22 of the housing 2 is generally used. Due to the structure in which the diffusion plate is suspended, it is possible to prevent the diffusion plate from being bent. For example, when the liquid crystal display device is erected without suspending the diffusion plate, the diffusion plate is supported by being hit against the casing at the lower end portion, so that bending occurs due to its own weight. That is, the hanging structure is an essential structure particularly in a large liquid crystal display device.

JP 2002-116704 A JP-A-6-273760

  However, in the apparatus shown in FIG. 4, even when the diffusion plate 1 is simply suspended from the upper side, the display device cannot be suspended as designed only by tilting slightly with respect to the vertical direction. There is a problem that warping may occur. That is, in a structure in which the diffusion plate 1 is simply suspended, as shown in FIG. 5, when the display device is inclined, the diffusion plate is also inclined, and is in a state of hitting a peripheral optical member or holding member. At this time, the diffusion plate 1 is subjected to stress in the thickness direction due to the gravity of the diffusion plate itself and the drags R1 and R2 received from the place where the diffusion plate is in contact with each member. There is a problem that the diffusion plate 1 warps in either direction.

When the diffusion plate warps, the following problems occur.
1) Color spots on the liquid crystal screen The cause of the color spots on the liquid crystal screen is that the optical characteristics (transmittance, birefringence characteristics, etc.) of the polarizing plate of the liquid crystal panel 4 easily change depending on the ambient temperature. This is caused by the fact that the optical characteristics of the polarizing plate of the panel 4 are easily affected by heat and that the diffusion plate 1 is warped so as to come into contact with the liquid crystal panel 4 side. A specific state of the diffusion plate 1 over time is shown in FIG.

  When the liquid crystal display screen is tilted in the downward direction, the diffusing plate 1 having the suspension structure is not locked on the lower side of the screen, so that it touches the liquid crystal panel 4 on the lower side of the screen and It hits the housing 2 on the upper side. Therefore, the diffuser plate 1 receives the drag forces R1 and R2 from the hit portions at the top and bottom (the upper side has the structure of the locking pieces 21 and 22, but the drag R1 remains unchanged). .

  Further, due to the gravity applied to the entire diffusion plate 1, the diffusion plate 1 also receives a force G1 in its thickness direction. Accordingly, at this time, the force applied in the thickness direction of the diffusion plate 1 becomes the three components R1, R2, and G1. For R1 and R2, only the upper and lower sides of the diffuser plate are applied with force, so the middle part of the diffuser plate 1 receives the force of only the gravity component G1. Thus, the phenomenon that the diffusion plate 1 made of a plastic material warps to the liquid crystal panel 4 side particularly at a high temperature due to the non-uniform force applied in the thickness direction of the entire diffusion plate 1. To do. Accordingly, the diffusion plate 1 directly contacts the local area A1 of the liquid crystal panel 4 via the optical sheet, and as a result, only the local area A1 has a different temperature environment and heat transfer environment from other parts. Problems such as color spots on the liquid crystal panel occur.

2) Luminance unevenness due to lamp image on liquid crystal screen The phenomenon that the lamp image is reflected on the screen is likely to occur when the diffusion plate is arranged near the fluorescent tube. That is, the causal relationship with the warpage of the diffuser plate is likely to occur when the diffuser plate warps on the fluorescent lamp side. FIG. 6 shows the change with time and will be described below.

  Contrary to the situation shown in FIG. 5, when the liquid crystal screen is tilted slightly upward as shown in FIG. 6, the diffusion plate 1 hits the housing 2 on the upper side and the lower side of the screen. At the top and bottom of the plate 1, drag forces R 1 and R 2 from the hit portions are received. Further, due to the gravity applied to the entire diffusion plate 1, the diffusion plate 1 also receives a force G1 in its thickness direction component.

  Therefore, at this time, the force applied in the thickness direction of the diffusion plate 1 becomes three components R1, R2, and G1, but R1 and R2 apply force only to the upper side and the lower side of the diffusion plate 1. Therefore, the middle part of the diffusing plate 1 receives only the force due to the gravity component G1. Accordingly, since the force applied in the thickness direction of the diffusion plate 1 is non-uniform across the entire surface, the diffusion plate 1 bends in the same manner as described above. In this case, since the diffusion plate 1 bends toward the fluorescent tube 3 side, the lamp is placed in the region A2 where the distance between the diffusion plate 1 and the fluorescent tube 3 is close beyond the design range assumed by the designer. Since the image is brightly reflected on the diffusion plate, uneven brightness tends to occur on the screen.

  The two phenomena described above have a great influence on the screen display quality particularly in a large-screen display device. However, if the position of the diffusing plate 1 is completely fixed, it is not a good idea because a design that takes into account the thermal expansion phenomenon of the diffusing plate 1 and other optical sheets is necessary, which is contrary to the technology of hanging the diffusing plate in the first place. It will be based on thought.

  An object of the present invention is to prevent the diffusion plate from warping or bending when the liquid crystal display device is tilted with respect to the vertical direction. Furthermore, it is possible to eliminate problems such as display unevenness on the screen due to the warp phenomenon without imposing an unnecessary load on the diffusion plate.

  According to one aspect of the present invention, a backlight including a light source, a housing that houses the light source, the housing having an opening on one surface thereof, and a diffusion plate disposed at a position that closes the opening. There is provided a backlight device characterized by comprising suspension means for suspending the diffusion plate on the upper side and tension means for pulling the diffusion plate on the lower side. By having the suspension means that can be suspended on the upper side of the screen and the tension means that receives the tension on the lower side of the screen, the diffusion plate can be prevented from bending.

  Further, the backlight device includes a light source, a casing that houses the light source, and has a housing having an opening on one surface thereof, and a diffusion plate disposed at a position that closes the opening. There is provided a backlight device provided with a pulling means for pulling the plate in at least one of the vertical direction, the horizontal direction, and the diagonal direction. By providing a pulling means that causes the diffusion plate to be subjected to a pulling action in at least one of the upper and lower directions, the left and right, or the oblique direction of the screen, the deflection of the diffusion plate can be reduced.

  It is preferable that the suspending means or the pulling means is made of an elastically deformable material. By using an elastic material for the suspending means or the pulling means of the diffusion plate, the deflection can be reduced without applying more stress than necessary to the diffusion plate.

  Alternatively, it is preferable that at least one of the suspension means and the tension means is made of a material having a shape memory function with respect to temperature. The deflection can be reduced only when necessary without applying stress to the diffusion plate except when necessary. The shape memory function is a function that exerts the action of the hanging means pulling the diffusion plate upward or the pulling means pulling the diffusion plate downward as the temperature rises when the light source is turned on. Preferably there is. Thereby, the bending of a diffusion plate can be reduced only at the time of backlight lighting. The shape of the suspension means or the tension means is preferably formed by any one of a spiral winding structure, a pipe-like piping structure, and a thin plate winding structure in which a thin plate is wound. In addition, it is preferable that the shape memory function causes a force acting in a direction to suppress the deformation to act according to the deformation with respect to a change in an external condition such as heat or humidity of the diffusion plate. For example, when the diffusion plate extends as the temperature rises, it is preferable that a force that pulls the diffusion plate by the shape memory function works so as to reduce bending due to the extension.

The suspension structure includes a first hole formed in one of the diffusion plate and the housing and a locking means provided at a position corresponding to the hole. Is preferred. The tensile structure includes a second hole formed in either the diffusion plate or the housing,
It is preferable to include an elastic locking means provided at a position corresponding to the hole. The first hole is preferably provided on the upper side of the diffusion plate or the casing.

  It is preferable that the second hole is provided in at least one of the upper side or the lower side of the diffusion plate or the casing. It is preferable that the elastic locking means is a means that is inserted into the second hole and biases in the direction of pulling the diffusion plate.

    The pulling means is preferably configured so that the pulling force can be changed. For example, if the weight of the weight or the compression force of the compression spring can be changed, it can be adjusted to a preferable tensile force according to the use environment or the surrounding environment.

  According to the backlight device of the present invention, an appropriate tension can be applied in the in-plane direction of the diffusion plate at least when the display device is turned on, and the deflection of the diffusion plate can be reduced. Further, by using a temperature-dependent shape memory material for the pulling means, it is possible to prevent the diffusion plate from extending at least during the display period without applying stress to the diffusion plate except when necessary. By using the backlight device in which the deflection of the diffusion plate is reduced, the image quality of the liquid crystal display screen can be improved and the display can be made uniform.

  In this specification, the deflection of the diffusion plate is mainly intended for the deflection that occurs in a situation where the display screen is set up vertically with respect to the installation surface (vertical placement).

  A configuration example of a backlight device according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1A is a perspective view showing an example of the configuration of the liquid crystal display device according to the present embodiment. FIG. 1B is a side sectional view. As shown in FIGS. 1A and 1B, the liquid crystal display device according to the present embodiment includes a diffusion plate 1, a housing 2, a fluorescent tube 3, a liquid crystal panel 4, and a tension means 5 as main components. Further, the diffusion plate 1 and the housing 2 are diffused by fitting them with appropriate play in consideration of the amount of thermal expansion between the projections 21 and 22 and the holes 11a and 12a at the upper edge of the screen. The plate 1 has a structure that is suspended from the upper edge of the screen.

  The pulling means 5 in the present embodiment is configured by a weight that is hung from and suspended from holes 11b and 12b provided in the lower edge of the screen of the diffusion plate 1. Due to the gravity of the weight, a tension T acts in the in-plane direction of the diffusion plate 1, and warping and bending of the diffusion plate 1 can be prevented. In addition, the tension | tensile_strength means 5 provided in the diffusion plate 1 in this Embodiment is not limited to the thing by the tension | tensile_strength using a weight. For example, a structure using the restoring force of an elastic body may be used.

  More specifically, as shown in FIG. 1C, a bottom plate portion 8a, a rising portion 8b rising from the bottom plate portion 8a in a substantially vertical direction, and a U-shaped cross section in the vicinity of the tip portion 8c of the rising portion 8b. It is also possible to use a locking tool 8 having a shape such that the tip bends in the direction of the bottom plate portion 8a. The U-shaped inner surface of the locking tool 8 is in contact with the lower end edges of the holes 11b and 12b formed in the diffusion plate 1. Further, a coil-shaped compression spring 7 is disposed between the upper surface of the bottom plate portion 8a and the bottom plate portion 2b of the housing 2 and on the rising portion 8b.

  In the above structure, the compression spring 7 urges the bottom plate portion 2b of the casing 2 in the upward direction, and as a result pulls the diffusion plate 1 in the direction of pressing down the lower end of the inner edge of the opening 11 of the diffusion plate 1. That is, an elastic locking structure is formed, which is a structure in which the diffusion plate 1 is pulled downward by the restoring force of the compression spring 7.

  The structure shown in FIG. 1 (d) has a cross section in the vicinity of the bottom plate portion 9a disposed below the bottom plate portion 2b of the housing 2, the rising portion 9b rising from the bottom plate portion 9a in a substantially vertical direction, and the tip portion of the rising portion 9b. A first tip portion 9c extending obliquely downward as viewed, and a second tip portion 9d having a width slightly wider than the thickness of the diffusion plate 1 and extending substantially in parallel and downward with the rising portion 9b. A locking member (leaf spring) 9 having a leaf spring structure is used. In the above structure, the leaf spring 9 biases the bottom plate portion 2b of the housing 2 in the upward direction, and as a result, pulls the diffusion plate 1 in the direction of pressing down the inner edge lower end of the opening 11 of the diffusion plate 1 downward. That is, a leaf spring locking structure is formed that pulls the diffusion plate 1 downward by using the restoring force of the leaf spring 9 that attempts to return to an angle smaller than the current angle. When the above structure is used, since the tension means 5 has a function of fixing the housing 2 and the diffusion plate 1 as compared with the structure of FIG. .

  In the case of the structure shown in FIG. 1C or FIG. 1D, a locking structure may be provided both below and above the diffusion plate 1. By providing the locking structure below and above, for example, even when the entire liquid crystal device is installed upside down, it is possible to effectively prevent the diffusion plate from warping. Moreover, the pulling effect can be increased by pulling the deflection of the diffusion plate 1 from above and below. In the structure of FIG. 1C, for example, when the diffusion plate 1 extends due to a temperature rise, the compression spring also thermally expands, so that a force for autonomously pulling the diffusion plate downward acts. Can be suppressed. At this time, when the rising portion 8b is made of a material having a smaller thermal expansion coefficient than the compression spring 7, the above function is effectively exhibited.

  FIG. 2 is a diagram showing a configuration example of a liquid crystal display device according to the second embodiment of the present invention. 2A is a perspective view, and FIG. 2B is a side sectional view. As shown in FIGS. 2A and 2B, the liquid crystal display device according to the present embodiment is similar to the liquid crystal display device according to the first embodiment in that the diffusion plate 1, the housing 2, the fluorescent tube 3, The liquid crystal panel 4 and the pulling means 5 are main components. Similar to the structure shown in FIG. 1, the diffusion plate 1 and the housing 2 have a lower limit temperature and an upper limit temperature in the normal use range between the projections 21 and 22 and the holes 11 a and 12 a at the upper edge of the screen. The diffusion plate 1 is suspended from the upper edge of the screen by adopting a structure that fits with appropriate play in consideration of the amount of thermal expansion therebetween.

  The pulling means 5 in the present embodiment is provided at a position corresponding to each of the holes 11 b and 12 b provided in the lower edge portion of the diffusion plate 1 and the holes 11 b and 12 b of the bottom plate portion 2 b of the housing 2. It has the latching structure which each provided the wire 6 of the spiral winding structure which connects the hole parts 2c and 2c. Thereby, the diffusing plate 1 and the housing 2 are locked while maintaining a certain degree of elasticity both in the vertical direction and in the horizontal direction, and have a flexible configuration.

  Next, a liquid crystal display device according to a modification of the present embodiment will be described. The locking structure of the liquid crystal display device according to this modification is characterized in that, in the structure shown in FIG. 2, the wire 6 having a spiral winding structure is formed of a material having a shape memory function. The wire 6 has a shape memory function particularly related to temperature.

  According to the above structure, when the temperature of the wire 6 reaches a certain level or more, the wire 6 itself automatically strengthens its function as a spiral winding structure, and the diffusion plate 1 faces downward on the display screen. Receives tensile force. Further, the temperature control of the wire 6 may be configured to automatically react with heat generated in the display device (for example, heat generated from the fluorescent tube 3 or a power source). By using the wire 6 having such characteristics, the diffusion plate 1 can receive a strong pulling force in the lower direction of the screen only when the liquid crystal display device is lit. Therefore, at least the deflection of the diffusion plate when the liquid crystal display device is lit. Can be reduced. Further, when the liquid crystal display device is not lit, it is possible to suppress stress deformation particularly when a plastic such as an acrylic material is used as the diffusion plate material by preventing tension from acting on the diffusion plate.

  The outline of the characteristics of the liquid crystal display device according to the second embodiment of the present invention and the modifications thereof has been described above. More specifically, the size, shape, etc. of the spiral winding structure of the wire 6 are the diffusion plate 1. What is necessary is just to design appropriately so that appropriate tension may be applied to. In addition, as an example of the wire having shape memory with respect to such a temperature, a commercially available NiTi alloy (for example, Furukawa NT alloy (manufactured by Furukawa Electric Co., Ltd.)) or the like can be used. However, if a material having a shape memory function with respect to temperature is used, the material is not limited to metal.

  It is only necessary to use a material having a shape memory function with respect to temperature, and to have a material and shape that can positively pull the diffusion plate according to a temperature change. When using such a material, the scope of the present invention It shall be within. In addition, although the spiral winding structure of the wire 6 was shown as a typical example of the tension | pulling means in this Embodiment, structures other than the spiral winding structure using a linear body may be sufficient. For example, a structure in which a corresponding hole is locked by a pipe-like piping structure or a thin plate winding structure in which a thin plate is wound may be used.

  Next, a liquid crystal display device according to a third embodiment of the present invention will be described with reference to the drawings. 3A and 3B are diagrams showing a configuration example of the liquid crystal display device according to the present embodiment. FIG. 3A is a perspective view and FIG. 3B is a side sectional view. As shown in FIGS. 3A and 3B, the liquid crystal display device according to the present embodiment includes a diffusion plate 1, a housing 2, a fluorescent tube 3, a liquid crystal panel 4, and a tension means 5 as main components. In the liquid crystal display device according to the present embodiment, holes 11a, 12a and 11b, 12b provided in the upper and lower edges of diffusion plate 1 and housing 2 are connected as tension means 5, respectively. It has the wire 6 of the winding structure provided in this way. By passing the wire 6 having a winding structure through the respective holes of the diffusion plate 1 and the housing 2, the diffusion plate 1 and the housing 2 are flexibly coupled.

  In addition, as a raw material of the wire 6, it is preferable to use the raw material which has a shape memory function with respect to temperature as mentioned above. With this structure, the diffusing plate 1 is subjected to a tensile action at both the upper edge and the lower edge of the screen. With respect to reducing the deflection of the diffusing plate 1, the structure according to the second embodiment is used. It is the same. In the example shown in FIG. 3, the shape memory material is used as the pulling means at the top and bottom of the screen. However, the pulling means is not limited to this, as shown in FIGS. 1 (c) and 1 (d). An elastic locking structure or a leaf spring locking structure may be used.

  The configuration according to the present embodiment is also effective for warping of the diffusion plate due to causes other than heat (for example, humidity). That is, the present invention is effective not only for bending in the screen vertical direction (surface thickness direction) but also for screen horizontal direction (in-plane direction).

  That is, according to the liquid crystal display device according to the embodiment of the present invention, by providing the tension means for pulling the diffusion plate in the in-plane direction with the thickness direction of the diffusion plate as a normal line regardless of the cause of the bending, It becomes possible to reduce bending. Therefore, the pulling direction of the pulling means is not limited to the vertical direction of the screen, and it is also within the scope of the present invention to provide similar pulling means that pulls in the lateral direction or oblique direction of the diffusion plate.

  The present invention is particularly effective for large liquid crystal display devices. It is also effective for a liquid crystal display device having a structure in which the screen rotates in the plane.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structural example of the liquid crystal display device by the 1st Embodiment of this invention, Fig.1 (a) is a perspective view, FIG.1 (b) is a sectional side view. FIG.1 (c) and FIG.1 (d) are the modifications, and are the figures which expanded a part of FIG.1 (b). It is a figure which shows the structural example of the liquid crystal display device by the 2nd Embodiment of this invention, Fig.2 (a) is a perspective view, FIG.2 (b) is a sectional side view. It is a figure which shows the structural example of the liquid crystal display device by the 3rd Embodiment of this invention, Fig.3 (a) is a perspective view, FIG.3 (b) is a sectional side view. It is a perspective view which shows the structural example of the conventional liquid crystal display device. It is a 1st schematic diagram which shows the time-dependent change of the curvature of the diffusion plate in the conventional liquid crystal display device. It is a 2nd schematic diagram which shows the time-dependent change of the curvature of the diffusion plate in the conventional liquid crystal display device.

Explanation of symbols

1: diffusion plate, 2: housing, 3: fluorescent tube, 4: liquid crystal panel, 5: tension means, 6: wire,
7: Spring, 8: Locking body, 9: Leaf spring, 11a, 11b, 12a, 12b: Hole, G: Gravity, G1, G2: Decomposition component of gravity, R1, R2: Drag, A1: Color stain generation part , A2: Brightness unevenness caused by the lamp image.

Claims (14)

A backlight device having a light source, a housing that houses the light source and having an opening on one surface thereof, and a diffusion plate disposed at a position that closes the opening,
A backlight device comprising: suspension means for suspending the diffusion plate from the housing on the upper side; and tension means for pulling the diffusion plate on the lower side. A backlight device having a light source, a housing that houses the light source and having an opening on one surface thereof, and a diffusion plate disposed at a position that closes the opening,
A backlight device comprising a tension unit that pulls the diffusion plate in at least one of an up-down direction, a left-right direction, and an oblique direction.   The backlight device according to claim 1 or 2, wherein at least one of the suspending means and the pulling means is formed of a material that can be elastically deformed.   The backlight device according to claim 1 or 3, wherein at least one of the suspending means or the pulling means is made of a material having a shape memory function relating to temperature.   The shape memory function is a function that exerts the action of the hanging means pulling the diffusion plate upward or the pulling means pulling the diffusion plate downward as the temperature rises when the light source is turned on. The backlight device according to claim 4, wherein the backlight device is provided.   The shape of the suspension means or the tension means includes any one of a spiral winding structure, a pipe-like piping structure, and a thin plate winding structure in which a thin plate is wound. The backlight device according to any one of 5 to 5. The hanging structure is
A first hole formed in either the diffusion plate or the housing;
7. The backlight device according to claim 1, further comprising a locking unit provided at a position corresponding to the first hole of the casing or the diffusion plate. 8.   The backlight device according to claim 7, wherein the first hole is provided on an upper side of the diffusion plate or the casing. The pulling structure is
A second hole formed in either the diffusion plate or the housing;
9. The structure according to claim 1, comprising elastic locking means provided at a position corresponding to the second hole of the casing or the diffusion plate. 10. The backlight device described.   The backlight device according to claim 9, wherein the second hole is provided in at least one of the upper side and the lower side of the diffusion plate or the casing.   11. The backlight device according to claim 9, wherein the elastic locking means is a means that is inserted into the second hole and biases the diffusion plate in a pulling direction.   The backlight device according to any one of claims 8 to 11, wherein the locking means is locked with play with respect to the first hole.   The backlight device according to any one of claims 1 to 12, wherein the pulling means can change its pulling force. The backlight device according to any one of claims 1 to 13,
A liquid crystal display device comprising a liquid crystal panel illuminated by the backlight device.

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