JP5147297B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a direct type backlight unit used in a liquid crystal display device.

As a liquid crystal panel used for a liquid crystal display device, a simple matrix type and an active matrix type using a TFT (Thin Film Transistor) are known. However, since such a liquid crystal panel is not a self-luminous type, a separate illumination light source is necessary to visualize an image formed on the liquid crystal panel.
Accordingly, the liquid crystal display device includes a liquid crystal display panel in which a drain driver and a gate driver are arranged in the periphery, and a backlight unit that irradiates the liquid crystal display panel (hereinafter, the backlight unit is referred to as BLU).

The BLU includes a side light type BLU and a direct type BLU.
In recent years, liquid crystal display devices have become larger and have larger screens. In such large-sized and large-screen liquid crystal display devices, direct type BLUs that provide high brightness are suitable.
Note that liquid crystal display devices that employ a direct-type BLU are described in, for example, Patent Document 1 and Patent Document 2.

JP 2006-259750 A Japanese Patent Laid-Open No. 11-084377

The direct type BLU has one or a plurality of linear light sources (for example, cold cathode fluorescent lamps), an optical member including a diffuser plate on which light emitted from the linear light sources is incident, and a linear light source. A reflector (reflecting member) having a reflecting surface that reflects light irradiated to the side opposite to the liquid crystal display panel to the liquid crystal display panel side is provided.
In recent years, there is an increasing demand for thinning a liquid crystal display device having a large screen.
However, in order to reduce the thickness of a large-screen liquid crystal display device, it is necessary to reduce the thickness of the direct type BLU. When the direct type BLU is thinned, that is, when the distance between the optical member and the reflector is shortened, there is a problem that the luminance distribution becomes nonuniform on the display surface of the liquid crystal display panel. The non-uniform luminance distribution is particularly noticeable on the end face of the liquid crystal display panel, and a decrease in luminance on both end faces in the longitudinal direction of the linear light source has become a problem.
An object of the present invention is to solve the above-described problems and provide a liquid crystal display device in which luminance attenuation at both ends in the longitudinal direction of a linear light source is small.

In order to achieve the above object, the backlight unit of the liquid crystal display device of the present invention inclines at least the inner surface of the side wall of the frame in both end regions of the linear light source toward the outside of the frame.
That is, the present invention provides a liquid crystal display device comprising a liquid crystal panel and a backlight unit that is installed on the back surface of the liquid crystal panel and emits illumination light. A frame having a side wall rising in the direction of the liquid crystal panel, a linear light source extending in a direction parallel to one of the pair of side walls at the inner bottom of the frame, and interposed between the linear light source and the liquid crystal panel At least an inner side of a pair of side walls in a direction orthogonal to the linear light source, and a reflecting surface inclined in a direction opening from the bottom toward the direction opposite to the liquid crystal panel direction.

Preferably, the backlight unit in the liquid crystal display device has two or more reflecting surfaces having different inclination angles for each side wall in a direction orthogonal to the linear light source.
Further, another backlight unit in the liquid crystal display device has a reflecting surface inclined on both sides of the electrode portion of the linear light source.
Further, another backlight unit in the liquid crystal display device is characterized in that a side wall in a direction orthogonal to the linear light source is constituted by at least one curved reflecting surface.
Further, another backlight unit in the liquid crystal display device is characterized in that a side wall in a direction orthogonal to the linear light source is constituted by a plurality of step-like reflecting surfaces.
Another backlight unit in the liquid crystal display device is characterized in that a side wall in a direction orthogonal to the linear light source is composed of a plurality of reflecting surfaces whose inclination angles gradually increase from the bottom of the frame.
Another backlight unit in the liquid crystal display device is characterized in that a side wall in a direction orthogonal to the linear light source is composed of a plurality of reflecting surfaces whose inclination angles gradually decrease from the bottom of the frame.

  According to the present invention, in a thinned liquid crystal display device, it is possible to reduce the decrease in luminance of the liquid crystal display panel at both ends in the longitudinal direction of the linear light source and improve the light emission quality. In addition, the frame can be narrowed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a configuration example of a liquid crystal display device including a direct type backlight. FIG. 1A is a developed perspective view showing only the backlight, and FIG. 1B is a view perpendicular to a linear light source for explaining a state in which the backlight of FIG. 1A is incorporated in a liquid crystal panel. FIG. 1C is a partial sectional view showing a partial sectional view in a direction parallel to the linear light source of FIG.

As shown in FIG. 1A, a direct type backlight 1 includes a frame 2 having side walls 2b and 2c rising from a pair of opposing parallel edges of a rectangular bottom plate 2a in a liquid crystal panel direction, and the frame 2 A linear light source 3 attached to extend in a direction parallel to one of the pair of side walls 2b at the inner bottom of the bottom plate 2a, and a light diffusion plate 4 interposed between the linear light source 3 and the liquid crystal panel. I have.
The linear light source 3 is, for example, a cold cathode fluorescent lamp. In FIG. 1A, the two linear light sources 3 are installed along the bottom surface 2a in parallel with the other side walls 2b so that the two are hung on the side walls 2c.

A state in which the backlight 1 is installed on the back surface of the liquid crystal panel 5 is shown in FIGS. The liquid crystal panel 5 is configured by sandwiching a liquid crystal layer 5e between two transparent substrates (glass plates) 5a and 5b and laminating polarizing plates 5c and 5d on the upper surface thereof. The liquid crystal panel may be either a simple matrix type or an active matrix type, and other light compensation films and the like may be laminated depending on the type.
The direction of the arrow A indicates the effective display area of the liquid crystal panel 5 of the liquid crystal display device.

  As shown in FIG. 1B, at least the inner surface of the linear light source 3 and the bottom plate 2a of the frame 2 and the side wall 2b parallel to the longitudinal direction of the linear light source 3 is a reflective surface. Is reflected in the direction of the liquid crystal panel 5 to efficiently use the light.

On the other hand, as shown in FIG. 1C, the linear light source 3 has electrodes 3a for applying a voltage at both ends, and no light is emitted from the electrode 3a. Accordingly, it is inevitable that the luminance of the end portion of the liquid crystal panel is reduced to some extent as compared with the central portion. However, the effective display area of the liquid crystal display panel 5 is within the range of the arrow A. That is, the effective display area extends up to the upper part of the electrode 3. If the electrode 3a is arranged outside the effective display area, this problem may be solved. However, in recent years, in addition to thinning, there is an increasing demand for a narrower frame. As the liquid crystal display device becomes thinner and narrower, the electrode 3a must be disposed inside the effective display area.
In order to cover this, at least the inner surface of the side wall 2c of the frame 2 perpendicular to the linear light source 3 has a reflective surface as in the case of FIG. The light from the light source 3 is reflected in the direction of the liquid crystal panel 5 to provide a reflector that efficiently uses the light.

  FIG. 2 is a diagram for explaining the luminance distribution near the end of the effective display area of the left side wall 2c of FIG. FIG. 2A is a schematic cross-sectional view showing the relative positions of the line light source 3 and its electrode 3a, and the left side wall 2c and the bottom plate 2a. FIG. 2B is a graph for explaining the qualitative relationship between the luminance levels of the liquid crystal panel 5 in the direction parallel to the line light source 3 of FIG. The horizontal axis is the position in the direction parallel to the linear light source 3 from the end d0 of the effective display area toward the inside of the effective display area, and the vertical axis is the luminance level. Moreover, FIG.2 (c) shows the relationship between an applicable position and the electrode 3a of the line light source 3 on the graph upper part for reference. Moreover, it is the schematic which shows that the left side wall 2c and the baseplate 2a are the reflectors which have the inclination by angle (theta). However, in the present invention, the side wall in the direction perpendicular to the linear light source is referred to as a reflector, and is distinguished from other reflecting surfaces.

In the graph of FIG. 2B, it can be seen that the luminance level P decreases from the inside of the effective display area toward the end d0. That is, there is almost no decrease in the luminance P from the inside of the liquid crystal panel 5 to the electrode 3a, and the decrease in the luminance P becomes remarkable from the position d1 (luminance P1) of the electrode 3a. It has become. In addition, if the side wall 2c does not have a reflecting function as a reflector, it has been found that the luminance P0 at the effective display region end d0 further decreases and becomes almost zero.
As shown in FIG. 2, the side wall 2c has a tilt angle θ with respect to the bottom plate 2a and is a reflecting surface to constitute a reflector. In the effective display area above the electrode 3a portion where the line light source 3 does not emit light. Although we tried to reduce the brightness level, it is still not enough.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 3 is a view for explaining an embodiment of the reflector according to the present invention. The configuration is the same as that of FIG. 2, and the side wall 2c0 is different from the shape of the side wall 2c.
In the embodiment of FIG. 3, the reflecting surface of the side wall 2c0 is a reflector having at least two or more different inclination angles, or a reflector having at least two or more reflecting surfaces.
That is, as shown in the side wall 2c0 of FIG. 3 (a) or (c), the reflector of the embodiment of FIG. 3 has at least two different inclination angles or has at least two inclined surfaces. The inclined surfaces are the two inclined surfaces f1 and f2 that constitute the reflector of the side wall 2c0 shown in FIG. For example, there are three inclined surfaces, of which two upper and lower surfaces have the same inclination angle, and one of the inner surfaces is a reflector different in configuration from the upper and lower surfaces. The broken line portion in FIG. 3 (b) is a reproduction of the luminance level shown in FIG. 2, and the solid line portion is the luminance level in the configuration of FIG. 3 (a) or FIG. 3 (c). According to the present embodiment, as shown in FIG. 3B, the luminance level at the effective display region end d0 increases to P0 ′.

In the embodiment of FIG. 3, the height at which the tilt angle of the reflector changes is lower than the axial center 3x of the line light source 3. However, there are cases where the axial center 3x of the line light source 3 is higher than this. Further, the height above the tube or the height below the tube may be used as a reference in consideration of the tube diameter of the linear light source 3 without using the height of the axial center 3x as a reference.
In any case, the boundary between the bottom plate 2a and the side wall 2c0 is inside the electrode 3a.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 4 is a view for explaining an embodiment of the reflector of the present invention.
FIG. 4 is a diagram simply showing the shape of the bottom plate 2a and the reflector of the present invention from the lateral direction, similarly to FIG. 2 (c) or FIG. 3 (c). The alternate long and short dash line is the center 3x of the line light source 3.

The reflector (side wall) of FIG. 4 is an embodiment having four inclined surfaces. Further, the inclined surfaces h1 to h4 are formed by curved lines (not shown), for example, strings inscribed by parabolas. Accordingly, the inclination angles of the inclined surfaces h1 to h4,..., Hn have the following relationship. That is,
θh1 <θh2 <θh3 <θh4 <... <θhn (1)
It is.

If the number of inclined surfaces is infinite, a curve is obtained. Accordingly, the inclined surface constituting the side wall (reflector) of the present invention includes a curved line.
In addition, curves such as parabola are upside down, and the relationship between the tilt angles is
θh1>θh2>θh3>θh4>...> θhn Equation (2)
(See FIG. 5). In this case, it is constituted by a string circumscribing a curve such as a parabola.
Further, it is not necessary to use one curve as a base, and a plurality of curves having the same or different forms may be used.

Moreover, you may process so that it may become smooth, such as taking the edge of the corner part of the junction part of each inclined surface, and comprising with a curve.
Furthermore, the curve may be divided at a predetermined ratio to form stepped side walls.
In addition, although the division | segmentation structure of an inclined surface may be equal in both a height direction and a horizontal direction, it is normal that it differs. For example, when the angle between the tangent line of the curve and the bottom plate 2a is small, the division ratio may be increased.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 5 is a view for explaining an embodiment of the reflector of the present invention.
FIG. 5 is a diagram simply showing the shape of the bottom plate 2a and the reflector of the present invention from the lateral direction, similarly to FIG. 2 (c) or FIG. 3 (c). The alternate long and short dash line is the center 3x of the line light source 3.
FIG. 5 shows an embodiment in which curves such as parabola are upside down with respect to FIG. That is, the relationship between the tilt angles is
θm1>θm2>θm3>θm4>...> θmn... Equation (3)
It is.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 6 is a view for explaining an embodiment of the reflector of the present invention.
FIG. 6 is a diagram simply showing the shape of the bottom plate 2a and the reflector of the present invention from the lateral direction, similarly to FIG. 2 (c) or FIG. 3 (c).
As shown in FIG. 6, in the case of a reflector having three or more inclined surfaces, the inclined surfaces q0,..., Qk, qk + 1, qk + 2,. ..., Qn (n and k are natural numbers, 0 ≦ k <n), there is the following relationship. That is,
θk <θk + 1 and θk + 1> θk + 2 (4)
Or
θk> θk + 1 and θk + 1 <θk + 2 (5)
That is, in the embodiment of FIG. 4 or FIG. 5, the inclination angle of the reflecting surface constituting the reflector is either simply increased or simply decreased as it goes upward.
However, as in the embodiment of FIG. 6, the inclination angles of the reflecting surfaces constituting the reflector are not simply reduced gradually or increased gradually, but are combined with irregular inclination angles. Therefore, the reflector is uneven.
Moreover, you may process so that it may become smooth, such as taking the edge of the uneven | corrugated | grooved part of the connection part of each reflective surface, and comprising with a curve.

Furthermore, other embodiments of the present invention will be described below. Each of the above-described embodiments is a reflector constituted by a plurality of inclined angles or a plurality of inclined reflecting surfaces with respect to the longitudinal direction of the linear light source. However, in another embodiment of the present invention, the shape of the side surface of the linear light source is inclined.
FIG. 7 is a diagram showing a reflector portion of the above-described embodiment of FIG. 4 as viewed from above. For convenience of explanation, the liquid crystal panel portion is omitted for convenience. Further, only the two linear light sources and the left end are shown.
FIG. 7 is a schematic view of the reflector shape shown in FIG. 4 as viewed from above. The inclined surfaces h1 to h4 rise from the bottom plate 2a and reach the liquid crystal panel surface. H0 is a portion in contact with the frame portion (outside the effective display area) of the liquid crystal panel surface.

Next, another embodiment of the present invention will be described with reference to FIGS. 8 and 9 are diagrams for explaining an embodiment of the reflector of the present invention.
The embodiment shown in FIGS. 8 and 9 reflects in the direction perpendicular to the longitudinal direction of the linear light source, whereas the embodiment described above has a reflector structure that is inclined so as to reflect in the longitudinal direction of the linear light source. It is so inclined.

8, a triangular pillar-shaped reflector in parallel between two linear light sources 3 arranged side by side in parallel in is provided on the side wall 2c. In FIG. 8, for convenience, the two linear light sources, the bottom plate 2a, and the reflector b1 are shown only halfway. Moreover, the number of the linear light sources 3 and the number of the reflectors b1 can be provided arbitrarily. Further, the length of the reflector b1 may be up to the other end (not shown) or may be halfway.

FIG. 9 shows a reflector structure in which, for example, the inclined surface of the embodiment of FIG. 4 is further inclined in a direction parallel to the linear light source 3.
By providing such an inclination, light from the light source is efficiently reflected not only in the longitudinal direction of the linear light source but also in the direction perpendicular to the longitudinal direction of the linear light source. Level further increases.
In FIG. 9, only one linear light source is drawn so that the structure of the reflector b <b> 2 can be easily understood, but it goes without saying that a similar linear light source 3 exists on the left side. Similarly, the linear light source 3 and the bottom plate 2a are shown only halfway.
Moreover, the number of the linear light sources 3 and the number of the reflectors b2 can be arbitrarily provided. Further, the length of the reflector b2 may be up to the other end (not shown) or may be halfway.

As described above, according to the embodiment shown in FIGS. 4 to 9, the luminance level on the end side of the effective display area is close to the internal luminance level, so that the decrease in luminance at the end portion of the liquid crystal panel is reduced. be able to.
That is, in the thinned liquid crystal display device, it is possible to reduce the decrease in luminance of the liquid crystal display panel at both ends in the longitudinal direction of the linear light source and to improve the light emission quality. Furthermore, it is possible to narrow the frame.

In the embodiment described above, the shape of the reflector is the same for all the liquid crystal panels. However, the central portion and both end portions of the liquid crystal panel may have different shapes with respect to the direction perpendicular to the axial direction of the linear light source. Further, the shape of the reflector may be changed alternately or in a predetermined order.
Further, in the above-described embodiment, the reflecting surface of the reflector is usually subjected to a mirror finish or a surface treatment so as to have a gloss in order to increase the reflection efficiency. However, the brightness level distribution of the liquid crystal panel may be made more uniform by roughening the surface with means such as a blaster and diffusing the light with light reflection. In that case, after the surface is roughened, a reflective film may be formed to increase the reflectance.

  As mentioned above, although this invention was demonstrated by the Example, these embodiment is an Example of this invention, Comprising: This invention is not limited only to these embodiment. The present invention is not limited to the embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention as long as it has ordinary knowledge in the technical field to which the present invention belongs.

The schematic diagram explaining the structural example of the liquid crystal display device provided with the direct type | mold backlight. The figure for demonstrating the luminance distribution near the effective display area edge part of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention. The figure for demonstrating one Example of the reflector of this invention.

Explanation of symbols

  1: Backlight, 2: Frame, 2a: Bottom plate of frame, 2b: Side wall of frame, 2c, 2c0: Side wall of frame, 3: Linear light source, 3a: Linear light source electrode, 3x: Axis center of linear light source 4: Light diffusion plate, 5: Liquid crystal panel, A: Effective display area.

Claims (3)

In a liquid crystal display device comprising a liquid crystal panel and a backlight unit that is installed on the back surface of the liquid crystal panel and emits illumination light,
The backlight unit includes a frame having side walls that rise in the direction of the liquid crystal panel from each pair of opposite parallel edges at the bottom, a linear light source that extends in a direction parallel to one of the pair of side walls, A light diffusing plate interposed between the linear light source and the liquid crystal panel;
A pair of side walls in a direction perpendicular to the longitudinal direction of the linear light source is inclined in a direction to open from the bottom toward the liquid crystal panel,
A liquid crystal display characterized in that at least one curved reflection surface is provided on the inner surface of each of the inclined side walls, and the inclination angle of the reflection surface gradually decreases from the bottom of the frame toward the liquid crystal panel. apparatus. In a liquid crystal display device comprising a liquid crystal panel and a backlight unit that is installed on the back surface of the liquid crystal panel and emits illumination light,
The backlight unit includes a frame having side walls that rise in the direction of the liquid crystal panel from each pair of opposite parallel edges at the bottom, a linear light source that extends in a direction parallel to one of the pair of side walls, A light diffusing plate interposed between the linear light source and the liquid crystal panel;
A pair of side walls in a direction perpendicular to the longitudinal direction of the linear light source is inclined in a direction to open from the bottom toward the liquid crystal panel,
A liquid crystal display device comprising a plurality of step-like reflecting surfaces provided on the inner surface of each of the inclined side walls. 3. The liquid crystal display device according to claim 1 , wherein each of the inclined side walls is orthogonal to a longitudinal direction of the linear light source between the plurality of linear light sources. A liquid crystal display device comprising a triangular prism-shaped reflector having a triangular cross section and extending in a direction parallel to a longitudinal direction of the linear light source.

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