JP3284217B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal cell, and more particularly to a liquid crystal display device having a structure in which a transmission type liquid crystal display device using an active matrix type liquid crystal cell is illuminated with a backlight from the back.

[0002]

2. Description of the Related Art Recently, a liquid crystal display device having a thin and easy-to-see backlight mechanism has been used as a display device such as a laptop or book type word processor or computer. In such a backlight, as shown in FIG. 1, a line such as a fluorescent tube having a slit-shaped light reflector having substantially the same shape as one end of the light guide plate is provided at one end of a light-transmitting light guide plate. An edge light system having a shape light source is often used. In the case of this edge light system, as shown in FIG. 2, one surface of the light guide plate is partially covered with a light diffusing substance, and the surface other than the light incident surface and the light exit surface is a specular reflection plate or a light diffuse reflection surface. In many cases, the light guide plate is covered with a light diffusing plate, and the light guide plate is arranged so that the entire light emitting surface emits light uniformly.

Recently, the backlight is driven by a battery, and further improvement in power consumption-luminance conversion efficiency is desired. In particular, in an active matrix type liquid crystal cell, the aperture ratio is low due to its structure, and the light transmittance is also low. Therefore, the shape of the light reflector covering the linear light source can be optimized, It has been proposed to use a high-reflectivity material for the reflector or to provide a high-reflectance reflector on a surface other than the light entrance surface and the light exit surface of the light guide plate.

However, in any of the above-mentioned methods, although the power consumption-luminance conversion efficiency is improved, it is still insufficient, and further improvement is desired.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transmission type liquid crystal display device using a matrix type liquid crystal cell, in which the luminance measured from the liquid crystal display surface side when illuminating from the back surface is high and the power consumption is low. -To provide a liquid crystal display device using a backlight with high luminance conversion efficiency.

[0006]

The present inventors have conducted various studies on the above-mentioned points, and in particular, have studied the backlight used therein, and as a result, have found that a liquid crystal display device in which edge-light type backlights are stacked. In one, a light diffusion function corresponding to the pixels of the matrix type liquid crystal cell to be used is formed, for example, in a dot shape on one wide surface of a light guide plate made of a translucent material, and the dots of the backlight are formed of the liquid crystal. By arranging this on the back surface of the liquid crystal cell so as to be superimposed on the pixels of the cell matrix, the display device having high power consumption-luminance conversion efficiency described above was found, and the present invention was completed.

That is, according to the present invention, in a liquid crystal display device in which a matrix type liquid crystal cell and a backlight are laminated, light diffusion corresponding to pixels of the matrix type liquid crystal cell is performed on one wide surface of a light guide plate made of a light transmitting material. A function is formed, a surface opposite to the light emitting surface is covered with a mirror surface or a light diffuse reflection plate, and a backlight having a linear light source close to at least one side end of the light guide plate is used. Liquid crystal display device. Next, the present invention will be described in more detail with reference to the drawings.

FIG. 3 is a perspective view of one embodiment of the present invention, and FIG. 4 is a sectional view. In the figure, reference numeral 1 denotes a light guide plate, which may be any substance that can efficiently transmit light, such as glass, quartz,
Translucent natural or synthetic resins, such as acrylic resins. Note that the liquid crystal display device is often used under different temperature and humidity conditions than when it was manufactured, but the liquid crystal display device was described above between the light guide plate material and the material of the substrate in contact with the opening of the matrix type liquid crystal cell. When a shape shift occurs due to temperature and humidity conditions, the light diffusion function of the light guide plate does not correspond to the pixels of the matrix type liquid crystal cell (that is, shifts), and a partial decrease in luminance or a moire phenomenon may occur. .

In order to avoid such a phenomenon, according to the present invention, the temperature expansion coefficient and the humidity expansion coefficient of the light guide plate material are made substantially equal to the temperature expansion coefficient and the humidity expansion coefficient of the substrate material. preferable. For example, when the material of the substrate is glass, the material of the light guide plate is also glass. Note that these coefficients are based on values measured by a normal method such as JIS standard.

Reference numeral 2 denotes a light diffusing plate which scatters light emitted from the surface of the light guide plate and allows the light to pass therethrough. The light diffusing plate may be arranged as necessary, but the light diffusing effect is so strong that the entire light emitting surface is uniform. When the surface light emission is started, the effect of the present invention may decrease.

The light diffusing function (6 in the figure) to be applied to the light guide plate is only required to have a function of guiding a light beam that has been repeatedly totally reflected in the light guide plate to the outside of the light guide plate without total reflection, and the method of providing the light diffusion plate is particularly limited. Although not, for example, a method such as applying a light diffusing substance to the light guide plate surface, a method of roughening the light guide plate surface, a concave, convex, a method of processing into a lens shape and the like,
It may be applied to any of the wide surfaces of the light guide plate. More effectively, most of the light emitted from the light guide plate provided with the light diffusing function is concentrated near the normal direction to the wide surface of the light guide plate (that is, most of the light emitted from the light guide plate). Is applied to the opening of the matrix type liquid crystal cell), and a method of coating the light guide plate with a light diffusing substance is particularly preferable.

The method of forming a light diffusing function by processing into a rough surface, a concave shape, a convex shape, or a lens shape is not particularly limited. For example, there are methods such as injection molding, hot pressing, chemical treatment, etching, and ultraviolet curing resin. .

The material of the light diffusing substance applied to the surface of the light guide plate is not particularly limited, and is, for example, a paint containing a resin bead such as titanium white, silica, barium sulfate, glass bead, acryl, printing ink, or the like. These are preferably coated on the light guide plate surface in a dot shape by a method such as screen printing, offset printing, flexographic printing, intaglio printing, but the printing method is not particularly limited. At this time, the shape of the covering portion may be any of a circle and a square. Also, it is preferable that each of the sizes is such that most of the light diffused in that portion irradiates the pixels of the liquid crystal cell.

The present invention is characterized in that a backlight in which the light diffusion function described above is formed on a light guide plate surface corresponding to the pixels of the matrix type liquid crystal cell is used. In the present invention, the light diffusion function formed on the light guide plate surface of the backlight has a pitch substantially equal to the pixel pitch of the matrix type liquid crystal cell, and is partially formed in a matrix in the same arrangement as the cell pixel arrangement. It was done. The light guide plate with the light diffusion function formed under such conditions is arranged so that the matrix of the light diffusion function overlaps the matrix of the liquid crystal cell, so that the light diffusion function exists corresponding to the pixels of the matrix type liquid crystal cell. State.

When the light guide plate and the liquid crystal cell are stacked, if they are stacked in close contact with each other, the entire surface of the light emitting surface shines, making it difficult to adjust the required luminance. Therefore, an intervening substance such as a spacer is placed between these surfaces. It is preferable to arrange and laminate at least so as to form, for example, a monolayer of air.

The state of formation of the light diffusing substance formed on the light guide plate surface of the backlight used in the present invention must correspond to that of the matrix type liquid crystal cell, but the light diffusing function is formed uniformly. Is also a preferred embodiment. That is, the haze value on the light emitting surface of the light guide plate (JIS-K7105)
The light diffusion function is formed in such a state that the light diffusion function (when measured in accordance with JIS) shows a constant value. In the present invention, it is preferable that the haze value shows the above-mentioned constant value in the range of 0.5 to 50%, and the one in which the haze value is out of this range has a uniform luminance on the light emitting surface of the light guide plate. It is not preferable in obtaining.

With such a configuration, the entire light exit surface of the light guide plate does not uniformly emit light, but has a pitch equal to the pixel pitch of the matrix type liquid crystal cell and the same arrangement as the cell pixel arrangement. Can emit light in a matrix, and the luminance can be made uniform.

The mirror surface or the light diffusion reflector (3 in the figure) is arranged so that the surface facing the light emitting surface is covered with the mirror surface or the light diffusion reflector. In addition, if the four side end portions of the light guide plate are arranged so as to cover the side end portions other than the light entrance surface with a specular reflection plate or a light diffusion reflection plate, the luminance is further improved, but the linear light source is formed of a light guide plate. When arranged only on one side end, if a specular reflection plate or a light diffusion reflection plate is arranged on one side end of the light guide plate opposite to one side end of the light guide plate on which the linear light source is arranged,
Not only the luminance is further improved, but also the luminance of the light diffusion function provided on the light guide plate surface becomes more uniform.

Reference numeral 4 denotes a linear light source.
A light reflector 5 having a gap (slit) for allowing light to enter the end of the light guide plate is covered with a gap of a certain width from the light source surface of the linear light source, and at least the light guide plate The light guide plate is installed near the one end surface so that the central axis thereof is substantially parallel to the end surface of the light guide plate. Examples of the linear light source include a fluorescent tube, a tungsten incandescent tube, an optical rod, an LED array, and the like, but a fluorescent tube is preferable. It is preferable that the length of the light guide plate is substantially equal to the length of the end portion.

FIG. 5 is a diagram showing an example of the structure of an active matrix type liquid crystal cell. Here, TFT (Thin
-Film Transistor type panel structure will be described. 7 is a glass substrate, a transparent pixel electrode (8 in the figure) and a TFT forming a matrix circuit portion.
(9 in the figure), scanning lines (10 in the figure), signal lines (1 in the figure)
1) is formed. In addition, a glass substrate (1 in the figure)
2), a black matrix layer (14 in the figure) having an opening (13 in the figure) facing the pixel electrode is formed, and a transparent common electrode (1 in the figure) is formed at a position facing the pixel electrode.
5) is formed. Liquid crystal (16 in the figure) is sealed in the gap between the opposing pixel electrode and the common electrode.
Pixels are formed by the opening area of the black matrix layer. Then, a voltage is applied to the pixel according to the signal by the matrix circuit unit. Incidentally, a polarizing plate (not shown) is arranged outside the glass substrate (7, 12 in the figure).

Since the area of the pixel of the active matrix type liquid crystal cell corresponds to the area of the opening of the black matrix layer, the light from the backlight must pass through this opening. Will not be used. For example, assuming that the aperture ratio of a TFT active matrix type liquid crystal panel having a pixel pitch of about 0.3 mm is about 40%, only about 40% of the light emitted from a backlight whose surface is uniformly emitted passes through the opening. Can not. However, as shown in FIG. 6, the light diffusion function provided to the light guide plate of the backlight is formed in correspondence with the pixels of the matrix type liquid crystal cell, and the matrix of the light diffusion function provided to the light guide plate is overlapped with the matrix of the liquid crystal cell. In addition, the backlight is arranged on the back of the liquid crystal cell, and the matrix-type light diffusion function provided on the light guide plate emits light in the form of dots, so that most of the light emitted from the backlight can be opened through the opening of the matrix type liquid crystal cell. Can be passed.

Although the main part of the present invention has such a structure, it is more preferable to have the following structure.

1) The light diffusion function to be applied to the light guide plate of the backlight used in the present invention is to form dots, that is, dots, and the dots have a dot pitch equal to the pixel pitch of the matrix type liquid crystal cell. There is no particular limitation as long as it is partially formed in a matrix, but any of a circle and a square as described above may be used. These are formed on the light guide plate in the same arrangement as the pixel arrangement of the matrix type liquid crystal cell to be used, for example, in a triangle type (FIG. 7), a mosaic type (FIG. 8) or a stripe type. Further, in the formation state of the light diffusion function, it is preferable that the formation ratio on the light guide plate surface is substantially equal to the aperture ratio of the matrix type liquid crystal cell. The term "formation ratio" as used herein refers to the ratio of the formation area of the light diffusion function applied per unit area of the light guide plate surface.

2) In order to make the brightness of each dot more uniform, if the formation rate of the light diffusing material on the light guide plate surface must be smaller than the aperture ratio of the matrix type liquid crystal cell, A diffusion sheet is arranged on the light emitting surface of the light guide plate so that light emitted from each dot is appropriately diffused by passing through the light diffusion sheet and passes through the entire opening of the matrix type liquid crystal cell. Is preferred.

[0025]

The present invention is a liquid crystal display device which is relatively small, has sufficient luminance, and has a large power consumption-luminance conversion efficiency.

[0026]

Next, the present invention will be described in more detail with reference to Comparative Examples and Examples.

Examples 1-4 Comparative Examples 1-2 Acrylic resin having a thickness of 2 mm as shown in FIG. 4 (linear expansion coefficient: 6 × 10 ⁻⁵ cm / cm · ° C. ASTM D696)
A cold cathode fluorescent tube (normal tube manufactured by Harrison Electric Co., Ltd.) having a diameter of 4.8 mm is arranged at the short end of a rectangular light guide plate (225 mm × 127 mm) made of The inner surface of a cylindrical aluminum reflector with a slit of 2 mm is covered with a light diffusion film laminated on it.
The light emitted from the slit was arranged so as to enter the light guide plate from the end of the light guide plate. On the other hand, the light diffusing substance (paint containing silica) to be coated on the light guide plate surface has a square dot pattern with a dot pitch (0.3 mm) equal to the pixel pitch of the matrix type liquid crystal cell and the pixel arrangement of the liquid crystal cell. Offset printing was performed in the same arrangement (mosaic type), and the coating was performed so that the light diffusion material coverage was constant at 10%. When the light guide plate was measured according to JIS-K7105, the haze value was 2%. Further, the light diffusion sheet was disposed on the light emitting surface of the light guide plate, and the end portions of the four side surfaces of the light guide plate other than the light incident surface were covered with the reflector. Further, the light guide plate and the liquid crystal cell were configured to be laminated via an air layer.

When a 30 KHz alternating voltage is applied from an inverter to a cold cathode tube and driven at a constant current, the brightness on the dot is measured by a luminance meter (Topcon BM-8) at a viewing angle of 0.2 ° and a light emission. 400c when measured at a distance of 12mm from the surface to the luminance meter (the tip of the attachment lens hardware)
d / m ² (Example 1). The light emission state at this time was a state in which each printed dot emitted light uniformly.

Further, the dot matrix of the light diffusing substance provided on the light guide plate is made of a matrix type liquid crystal cell (the material of the substrate in contact with the opening is glass. Linear expansion coefficient: 4 × 10 ^-6 cm / c)
The backlight is arranged on the back of the liquid crystal cell so as to be superimposed on the dot matrix of m. ° C. ASTM D696), and the surface luminance when driven at a constant current by applying an alternating voltage of 30 KHz from the inverter to the cold cathode tube. Was measured with a luminance meter (Topcon BM-8) at a viewing angle of 2 degrees and a distance of 400 mm from the light-emitting surface to the luminance meter (without using an attachment).
Was 76 cd / m ² (Example 2). However, with the change in temperature and humidity, the dot matrix of the light diffusing substance and the dot matrix of the liquid crystal cell were displaced, and a partial decrease in luminance and a moire phenomenon were observed.

Next, a backlight was arranged on the back surface of the liquid crystal cell in the same manner as in Example 2 except that rough dots were formed on the light guide plate by hot pressing. The measured luminance was 60 cd / m ² (Example 3). However, with a change in temperature and humidity, a deviation occurred between the dot matrix of the rough surface dots and the dot matrix of the liquid crystal cell, and a partial decrease in luminance and a moire phenomenon were observed.

Next, the light guide plate is made of glass (linear expansion coefficient:
A backlight was placed on the back surface of the liquid crystal cell in the same manner as in Example 2 except that the brightness was changed to 4 × 10 ⁻⁶ cm / cm · ° C. (ASTM D696). The drop and the moire phenomenon were not observed.
(Example 4) Next, the light diffusing substance (paint containing silica) coated on the light guide plate surface made of acrylic resin was obtained by screen printing circular dot patterns at a pitch of 1.2 mm.
The light-diffusing substance was coated so that the coverage was 9% at the minimum point, 80% at the maximum point, and the ratio was gradually increased in the middle. The haze value when the light guide plate was measured according to JIS-K7105 was 1.9 at the minimum point.
% And 58% at the highest point. Further, two light diffusion sheets are arranged on the light emitting surface of the light guide plate so that the printed dots are not visually recognized, and the three side edges other than the light incident surface of the four side edges of the light guide plate are reflected by the reflector. Covered.

The surface luminance when a 30 KHz alternating voltage was applied to the cold-cathode tube at a constant current by applying an alternating voltage from the inverter was measured by a luminance meter (Topcon BM-8) at a viewing angle of 2 degrees, and from the light-emitting surface to a luminance meter. It was 182 cd / m ² when measured at a distance of 400 mm (without using an attachment) (Comparative Example 1). At this time, dots printed in a uniform light emission state were not visually recognized. Also,
The backlight is placed on the back of the liquid crystal cell,
The luminance of the surface when driven at a constant current by applying an alternating voltage of 30 KHz from the inverter is measured by a luminance meter (Topcon BM-
According to 8), when measured at a viewing angle of 2 degrees and a distance of 400 mm from the light emitting surface to the luminance meter (without using an attachment), it was 23 cd / m ² (Comparative Example 2).

[Brief description of the drawings]

FIG. 1 is a perspective view of a backlight.

FIG. 2 is a cross-sectional view of a backlight.

FIG. 3 is a perspective view of a backlight according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a backlight according to an embodiment of the present invention.

FIG. 5 illustrates an example of the structure of an active matrix liquid crystal cell.

FIG. 6 is a layout diagram of a backlight according to an embodiment of the present invention.

FIG. 7 is a diagram showing an example of a dot arrangement method.

FIG. 8 is a diagram showing an example of a dot arrangement method.

[Explanation of symbols]

 1: light guide plate 2: light diffusion sheet 3: specular reflection plate or light diffusion projection plate 4: linear light source 5: light reflector 6: light diffusion material 7: glass substrate 8: transparent pixel electrode 9: TFT 10 : Scanning line 11: signal line 12: glass substrate 13: opening 14: black matrix layer 15: common electrode 16: liquid crystal 17: matrix circuit section

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/3357

Claims (4)

(57) [Claims] 1. A liquid crystal display device in which a matrix type liquid crystal cell and a backlight are stacked, a haze value at a light exit surface of the light guide plate is 0.5 to 50 on one wide surface of the light guide plate made of a light transmitting material. % And a pitch equal to the pixel pitch of the matrix-type liquid crystal cell, and with the same arrangement as the pixel arrangement of the matrix-type liquid crystal cell , the light diffusion function and the formation rate of the matrix
The light guide plate is formed in a dot shape so as to be smaller than the aperture ratio of the liquid crystal cell, and a light diffusion sheet is formed on the light exit surface of the light guide plate.
While disposing the light, the surface opposite to the light emitting surface is covered with a mirror surface or a light diffuse reflection plate, and a backlight having a linear light source close to the end of at least one side of the light guide plate is used, A liquid crystal display device in which a light diffusing function formed in a dot shape of the backlight and a pixel of the liquid crystal cell are arranged so as to overlap. 2. The liquid crystal display device according to claim 1, wherein the light diffusing function is formed of one selected from a light diffusing substance, a rough surface, a concave shape, a convex shape, and a lens shape. 3. The liquid crystal display device according to claim 1, wherein the light guide plate material and the material of the substrate in contact with the opening of the matrix type liquid crystal cell have substantially equal expansion coefficients. 4. The liquid crystal display device according to claim 1, wherein an active matrix type liquid crystal cell is used.