JPH0915552A - Liquid crystal display panel - Google Patents

Abstract

PURPOSE: To provide a liquid crystal display panel with which the image display of high image quality is made possible by suppressing the increase in the pixel capacitance corresponding to widening of pixel areas and narrowing of cell gaps. CONSTITUTION: This liquid crystal display panel is composed at least of a liquid crystal cell 9 formed by holding a liquid crystal layer 8 between a pair of transparent substrates 1, 1' respectively having transparent electrodes 3, 3' and oriented films 4, 4' formed to cover these transparent electrodes and a pair of polarizing plates 1, 1' laminated across this liquid crystal cell 9. The twist angle of the liquid crystal molecules constituting the liquid crystal layer 8 by the oriented films 4, 4' is specified to 180 to 270 deg., the sheet resistance value of the transparent electrodes 3, 3' to <=8Ωand the ratio Δε/d between the dielectric constant anisotropy Δε of the liquid crystals constituting the liquid crystal layer 8 and the spacing (d) between a pair of the transparent substrates 1, 1' to <=1.3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display panel, and more particularly to a super twisted nematic type liquid crystal display panel capable of displaying a high quality image by reducing a shadowing level.

[0002]

2. Description of the Related Art A liquid crystal display device, which has recently been widely used as a television receiver, a monitor of a personal computer, and other display devices, is a liquid crystal in which a liquid crystal layer is sandwiched between a pair of transparent substrates on which electrodes and various films are formed. It is configured by molding a driving circuit board, an illumination light source, etc. on a liquid crystal display panel in which a polarizing plate and a reflecting plate are laminated on a cell.

In this type of liquid crystal display panel, the liquid crystal molecules of the liquid crystal layer sandwiched in the gap (cell gap) between the pair of transparent substrates are twisted by the rubbing direction of the alignment film to give a twist angle. It is roughly classified into a simple matrix type in which one pixel is formed at the intersection of transparent electrodes and an active matrix type in which a non-linear element (switching element) is arranged for each pixel.

Among them, the simple matrix type has a simple structure and is easy to manufacture, so that the cost is lower than that of the active matrix type, while nematic liquid crystal is used for the liquid crystal layer.
Since the twisted nematic type in which the molecular direction is twisted by about 90 ° is used, there is a problem that the response speed cannot be increased.

In order to improve this, a so-called super twisted nematic type (hereinafter referred to as STN type) has been proposed in which the twist angle of liquid crystal molecules is set to 180 ° or more and which can also be used for displaying moving images, and present simple matrix type liquid crystal display. It has become the mainstream of panels.

As a prior art of a liquid crystal display device using this type of simple matrix type liquid crystal display panel, for example, Japanese Patent Publication No. 51-13666 can be cited.

[0007]

In recent years, the screen size of display devices has been increasing, and liquid crystal display devices are no exception. When the display area of the STN type liquid crystal display panel is increased, the pixel capacity increases with an increase in the pixel area, the drive waveform is distorted, so-called shadowing (crosstalk) occurs, and image quality deteriorates.

As measures against the image quality deterioration due to this shadowing, it is possible to deal with it in the drive circuit and to reduce the resistance value of the transparent electrode.
Since the design and altitude of (1) require a circuit configuration, conventionally, it was general to lower the sheet resistance of the transparent electrode.

However, the pixel capacity increases due to a large screen size and a narrow gap for achieving high-speed response, which causes a large distortion of the drive waveform. The ing level cannot be reduced.

A liquid crystal material having a dielectric anisotropy (Δε) of 7 or less is disclosed in JP-A-5-40242 for the purpose of reducing the shadowing level. No specific proposals have been made regarding values or cell gaps.

As described above, the sheet resistance of the transparent electrode is reduced as a measure for improving the shadowing level other than that by the drive circuit in the conventional STN type liquid crystal display panel, because the pixel area is enlarged and the high speed response is achieved. It is difficult to reduce the shadowing level only by lowering the sheet resistance of the transparent electrode because the pixel capacitance increases due to the narrow cell gap and the distortion generated in the drive voltage waveform increases.

An object of the present invention is to solve the above-mentioned problems of the prior art and to suppress the increase of the pixel capacity corresponding to the expansion of the pixel area and the narrowing of the cell gap, thereby making it possible to display a high quality image on the liquid crystal display panel. To provide.

[0013]

In order to clarify the constitution of the present invention for achieving the above object, the reference numerals of the embodiments will be added and described.

That is, the first invention according to claim 1 is a pair of transparent substrates 1, 1 ′ having transparent electrodes 3, 3 ′ and alignment films 4, 4 ′ formed to cover the transparent electrodes, respectively. A liquid crystal cell 9 in which a liquid crystal layer 8 is sandwiched between
A pair of polarizing plates 1, 1 ′ stacked with the liquid crystal cell 9 sandwiched therebetween
In a liquid crystal display panel at least composed of
The twist angle of the liquid crystal molecules forming the liquid crystal layer 8 by the alignment films 4 and 4 is 180 ° to 270 °, the transparent electrode 3 and
The sheet resistance value of 3 ′ is 8Ω or less, and the ratio Δε / d of the dielectric anisotropy Δε of the liquid crystal forming the liquid crystal layer 8 and the gap d between the pair of transparent substrates 1 and 1 ′ is 1.3 or less. It is characterized by

A second aspect of the present invention is characterized in that a color display is made possible by forming color filter layers of a plurality of colors on one of the pair of transparent substrates.

The structure of the present invention is not limited to a so-called transmissive liquid crystal display panel in which a liquid crystal cell is composed of a pair of transparent substrates, but a reflective liquid crystal display in which a reflector is installed on one of the pair of substrates. It can also be applied to panels.

[0017]

Since the liquid crystal constituting the liquid crystal display panel is a capacitive load and is driven through an electrode having a finite resistance, the driving voltage waveform applied to the actual liquid crystal is distorted. .

Particularly, when the liquid crystal display panel becomes large in size, high in definition, or has a narrow gap, the capacitance of the liquid crystal and the wiring resistance of the transparent electrode increase, and the distortion of the drive waveform is remarkable due to the increase of the frequency of the drive voltage waveform. become. This drive waveform distortion is considered to be a major cause of shadowing.

In order to reduce the distortion of the drive waveform and improve the display quality, it is necessary to reduce the capacity of the liquid crystal layer which is a load capacity component.

The capacitance C of the liquid crystal layer is expressed by the following equation (1).

C = ε · (S / d) (1) where ε is the dielectric constant of the liquid crystal, S is the pixel area (electrode area), and d is the cell gap. .

It can be seen from the above equation (1) that the capacitance C can be reduced by decreasing the dielectric constant ε of the liquid crystal and the pixel area S and increasing the cell gap d.

However, the pixel area S cannot be arbitrarily polarized because it satisfies the customer's required specifications.
Eventually, by defining ε / d to be a certain value or less as in the configuration of the first aspect of the present invention, the increase of the capacitance C is suppressed and the distortion of the drive waveform that causes shadowing is reduced. .

The second invention is a structure for color display, and by providing a color filter in the first invention, a high-quality color display in which shadowing is suppressed can be obtained. .

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view for explaining the structure of an embodiment of a liquid crystal display panel according to the present invention, in which 1,1 'is a polarizing plate, 2 and 2'are transparent substrates, and 3 and 3'are transparent. electrode,
4, 4'is an alignment film, 5 is a color filter layer, 6 is a seal, 7 is a spacer, 8 is a liquid crystal layer, and 9 is a liquid crystal cell.

In the figure, the liquid crystal cell 9 has a liquid crystal layer 8 between a pair of transparent substrates 1 and 1'having transparent electrodes 3 and 3'and alignment films 4 and 4'formed to cover the transparent electrodes. And a pair of polarizing plates 1, 1 ′ are laminated with the liquid crystal element 9 sandwiched therebetween to form a liquid crystal display panel.

The twist angle of the liquid crystal molecules constituting the liquid crystal layer is
The orientation films 4 and 4 are arranged at 240 ° in the respective rubbing directions. The twist angle is 180 ° to 27
It may be in the range of 0 °.

The sheet resistance of the transparent electrodes 3 and 3'is 8 Ω or less, the thickness of the liquid crystal layer sandwiched between the pair of transparent substrates 2 and 2 ', that is, the cell gap d is 6.0 μm, and the liquid crystal layer is the same. The dielectric constant anisotropy Δε of the liquid crystal constituting No. 8 is 6.2, and therefore the ratio Δε / d of the dielectric anisotropy Δε to the cell gap d is 1.03. It should be noted that this Δε / d should be 1.3 or less for the reason described later.

FIG. 2 shows application to the liquid crystal layer when the ratio Δε / d of the dielectric anisotropy Δε of the liquid crystal forming the liquid crystal layer and the cell gap d exceeds 1.3 and 1.3 or less. FIG. 6 is an explanatory diagram of a driving characteristic comparing the relationship between the voltage (V) to be applied and the electrostatic capacitance C, the curve of a is a liquid crystal cell in which Δε / d is 1.3 or less according to the invention, and the curve of b is 1. Each driving characteristic of the liquid crystal cell exceeding 3 is shown.

From the above-mentioned comparative explanatory diagram, Δε / d is set to 1.
It can be seen that the capacitance C of the liquid crystal, which is a cause of shadowing, is reduced by setting it to 3 or less.

FIG. 3 is a result of qualitative visual evaluation of the shadowing level when the values of the resistance value of the transparent electrode, the liquid crystal dielectric anisotropy Δε and the cell gap d ratio Δε / d are changed. FIG. 4 is an explanatory diagram of the transparent electrode, the resistance value of the transparent electrode is shown by sheet resistance □ / cm ² , and the shadowing level is evaluated by relative evaluation.

In the figure, although a slight improvement can be seen only by lowering the resistance value of the transparent electrode, the allowable level is reached when Δε / d is 1.3 or less.

As described above, in this embodiment, by setting the ratio Δε / d of the dielectric anisotropy Δε of the liquid crystal to the cell gap d to be 1.3 or less, the capacity of the liquid crystal layer is lower than that of the conventional one. Can be realized.

Therefore, the load capacitance of the drive circuit is reduced, the distortion of the drive voltage waveform that causes shadowing is reduced, and uniform and high-quality image display is possible.

In this embodiment, the cell gap is 6 μm.
However, even if the cell gap is further narrowed in order to realize a high-speed response in the future, or conversely, when the cell gap is widened, by defining the above Δε / d, the same and even A liquid crystal display panel capable of displaying a high quality image can be obtained.

In this embodiment, a liquid crystal display panel provided with a color filter has been described as an example, but a so-called monochrome liquid crystal display panel having no color filter has the same effect, and the higher the contrast ratio is, the higher the effect is. The effect is remarkable.

FIG. 4 is a developed perspective view for explaining an example of the structure of the entire liquid crystal display device using the liquid crystal display panel according to the present invention. 10 is a liquid crystal display panel, 10a and 10b are drive circuit boards, and 11 is a light guide plate. , 12 is a reflection plate, 13 is a diffusion plate,
14 is a lamp (cold cathode fluorescent lamp), 14a is a lamp reflector, 14b is a lamp cover, 15 is an intermediate frame, 1
6 is an upper frame, 16a is a cut and raised piece, 16b is a nail, 17
Is a lower frame, 17a is a nail receiver, 18 is a spacer, 19 is an adhesive tape, 20a, 20b, 21a and 21b are cutout portions, and 22a and 22b are cutout portions.

In the figure, the liquid crystal display panel 10 is set on an intermediate frame 15 in which a light guide assembly including a light guide plate 11, a reflection plate 12, a diffusion plate 13 and the like and a backlight including a lamp 14 are laminated on the lower surface thereof. The upper frame 16 and the lower frame 17 are sandwiched and fixed.

Cut and raised piece 1 formed on the upper frame 10
6a contacts a ground pad formed on the drive circuit boards 10a and 10b, and the claw 16b engages with a claw receiver 17a formed on the lower frame 17 to fix the upper frame 16 and the lower frame 17.

The upper frame 16 and the liquid crystal panel 10 are fixed with an adhesive tape 19. Cutouts 20a, 2
0b is provided at a position symmetrical to a line orthogonal to the center of the backlight, and the cutouts 21a and 21b are provided in the longitudinal direction of the lamp 14. Further, notches 22a and 22b are provided in the lower portions of both ends of the lamp 14.

The upper frame 16 is made of a steel plate having a thickness of 0.8 mm, for example, and the lower frame 17 is made of a steel plate or an aluminum having a considerable thickness of, for example, 0.5 mm.

The liquid crystal display device is clamped and fixed by the upper frame 16 and the lower frame 17 in the order shown in FIG. The lamp 14 is installed on one end side of the intermediate frame 15, and the emitted light is directed to the light guide assembly side of the backlight by the lamp reflector 14a. The lamp cover 14b installed on the liquid crystal panel 10 side of the lamp 14 prevents upward light leakage.

The spacer 18 is interposed between the light guide assembly installed in the recess formed in the intermediate frame 15 and the liquid crystal panel 10 to define the display area.

As described above, the upper frame 16 is made of a stainless thin plate and the lower frame 17 is made of an aluminum thin plate. Then, the lamp 14 of the lower frame 17
At least a pair of cutouts 20a, 20b are provided at positions symmetrical to a line orthogonal to the central portion of the lamp 14 over at least the area of the liquid crystal panel 10 in the direction orthogonal to the lamp 14, and the length of the lamp 14 is directly below the lamp 14. At least two cutouts 21a, 21b provided in the direction
And the notch 2 provided at the lower part of both ends of the lamp 14.
2a and 22b are formed.

According to the above structure, the liquid crystal display device can be made thin and lightweight without lowering its rigidity, and at the center of the lamp 14 at least in the direction orthogonal to the lamp 14 over the region of the liquid crystal panel 10. Cutout portions 20a, 20b provided at positions symmetrical to a line orthogonal to
Immediately below the lamp 14, cutouts 21a and 21b provided in the longitudinal direction of the lamp 14 and cutouts 22a and 22b provided at lower portions of both ends of the lamp 14 improve heat dissipation effect, and the liquid crystal panel 10 has A uniform temperature distribution is formed on the entire surface to prevent display unevenness.

Since the lamp 14 is driven at a high frequency, a current flows from the lamp 14 to the lower frame 17 via the stray capacitance between the lower frame 17 and the lamp 14. This current is called “leakage current”, but the amount of current that contributes to the lighting of the lamp 14 is reduced by the amount of “leakage current”, resulting in a decrease in brightness.

Further, the lamp 14 generates heat when it is turned on for a long time, and the temperature in the vicinity thereof rises with respect to the outside air. Therefore, unless some measures are taken, the heat directly affects the liquid crystal panel 10, The temperature distribution of the liquid crystal panel cannot be made uniform. Therefore, in the above-described embodiment, the cutout portion is provided to prevent the deterioration of the brightness due to the "leakage current" and to make the temperature distribution of the liquid crystal panel uniform, thereby preventing the occurrence of the display unevenness.

By adopting the structure described in the above embodiment as the liquid crystal display panel of the liquid crystal display device having such a structure, it is possible to reduce the shadowing level and display a high quality image.

FIG. 5 is a perspective view showing an example in which the liquid crystal display device using the liquid crystal display panel according to the present invention is used in the display portion of a laptop personal computer, and 30 is a liquid crystal using the liquid crystal display panel of this embodiment. Display device, 31 is a display unit, 32
Reference numerals a, 32b and 32c are brightness and contrast and other manual adjusting means, 33 is a personal computer main body, and 34 is a keyboard.

FIG. 6 is a schematic block diagram of the control system for the laptop personal computer shown in FIG. 5. Reference numeral 35 is a drive circuit, 36 is a control circuit, and 37 is a microprocessor unit, both of which are composed of LSI.

In the figure, the display information from the microprocessor unit 37 is converted into various drive waveforms by the control circuit 36 and supplied to the drive circuit 35 of the liquid crystal display device 30 to perform the required display.

As shown in the above embodiments, by using the liquid crystal display panel of the present invention, it is possible to provide a high quality liquid crystal display device without any wing.

[0054]

As described above, according to the present invention,
The resistance value of the transparent electrode is set to a predetermined value or less, and the dielectric constant anisotropy Δε of the liquid crystal and the gap d between the pair of transparent substrates 1 and 1 '.
By providing the ratio Δε / d to a predetermined value or less, it is possible to provide a liquid crystal display panel capable of displaying a high quality image by suppressing an increase in pixel area and an increase in pixel capacity corresponding to a narrow cell gap. can do.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating the structure of an embodiment of a liquid crystal display panel according to the present invention.

FIG. 2 is a voltage applied to the liquid crystal layer when the ratio Δε / d of the dielectric anisotropy Δε of the liquid crystal forming the liquid crystal layer and the cell gap d exceeds 1.3 and 1.3 or less. It is explanatory drawing of the drive characteristic which compared the relationship of (V) and the electrostatic capacitance C.

FIG. 3 is an explanation of the results of a qualitative visual evaluation of the shadowing level when each value of the resistance value of the transparent electrode and the ratio Δε / d of the liquid crystal dielectric anisotropy Δε and the cell gap d is changed. It is a figure.

FIG. 4 is a developed perspective view illustrating a structural example of the entire liquid crystal display device using the liquid crystal display panel according to the present invention.

FIG. 5 is a perspective view showing an example in which a liquid crystal display device using a liquid crystal display panel according to the present invention is used in a display unit of a laptop personal computer.

6 is a schematic block diagram of a control system of the laptop computer of FIG.

[Explanation of symbols]

 1, 1'Polarizer 2, 2'Transparent substrate 3,3 'Transparent electrode 4,4' Alignment film 5 Color filter layer 6 Seal 7 Spacer 8 Liquid crystal layer 9 Liquid crystal cell 10 Liquid crystal display panel 10a, 10b Driving circuit board 11 Conductor Light plate 12 Reflector plate 13 Diffuser plate 14 Lamp (cold cathode fluorescent lamp) 14a Lamp reflector 14b Lamp cover 15 Intermediate frame 16 Upper frame 16a Cut and raised piece 16b Claw 17 Lower frame 17a Claw receiver 18 Spacer 19 Adhesive tape 20a, 20b, 21a , 21b Cutout parts 22a, 22b Cutout part 30 Liquid crystal display device using the liquid crystal display panel of this embodiment 31 Display parts 32a, 32b, 32c Manual adjustment means 33 Personal computer body 34 Keyboard 35 Drive circuit 36 Control circuit 37 Microprocessor unit .

Claims (2)

[Claims] 1. A liquid crystal cell having a liquid crystal layer sandwiched between a pair of transparent substrates each having a transparent electrode and an alignment film formed so as to cover the transparent electrode, and a pair of liquid crystal cells laminated with the liquid crystal cell sandwiched therebetween. In a liquid crystal display panel including at least a polarizing plate, a twist angle of liquid crystal molecules constituting the liquid crystal layer by the alignment film is 180 ° to 270 °, a sheet resistance value of the transparent electrode is 8Ω or less, and the liquid crystal A liquid crystal display panel, wherein a ratio Δε / d of the dielectric anisotropy Δε and the gap d between the pair of transparent substrates is 1.3 or less. 2. A liquid crystal display panel according to claim 1, wherein color filter layers of a plurality of colors are formed on one of the pair of transparent substrates.