JPH0432818A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce changes in display characteristics due to a change in an observing direction by setting up the refractive index of a phase plate in the thickness direction to a value larger than that in a direction vertical to an optical axis. CONSTITUTION:In a liquid crystal display device constituted of an upper side polarizing plate 1, an upper side substrate 5, liquid crystal molecules 7, a lower side substrate 8, a lower side polarizing plate 10, a backlight 12, and a phase plate 3, the refractive indexes of the phase plate 3 consisting of an optically compensating double refraction substance is anisotropically set up and the refractive index in the thickness direction is set up to a value larger than that in the direction vertical to the optical axis. Since the phase plate consisting of the double refraction substance, coloring of the background part and display part of the twisted nematic field effective type liquid crystal display element can be suppressed, and because the refractive index in the thickness direction of the phase plate 3 is larger than that in the vertical direction to the optical axis, a visual change in the display characteristics can be suppressed and effective display characteristics can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a twisted nematic field effect liquid crystal display device that has excellent time-division drive characteristics and is capable of black-and-white and color display, and is particularly applicable to laptop computers, etc. The present invention relates to a liquid crystal display device suitable for a portable computer called a portable computer.

[Prior Art] Liquid crystal display devices have traditionally been widely used in portable computers such as laptop computers, but in recent years, improvements have been made in the image quality of such liquid crystal display devices. The requirements for increasing the amount of information that can be displayed have become stricter, and the required specifications are also shifting from black and white display to color display.

By the way, one type of liquid crystal display device is a twisted nematic field effect type liquid crystal display device, which has been widely adopted due to its excellent time-division drive characteristics. This caused undesirable coloring in at least one of the background or the display area, making it unsuitable for black and white display.

Therefore, as a conventional technology for a liquid crystal display device for black and white display, as shown in FIG. 2, a first liquid crystal element A for driving,
A combination with a second liquid crystal element B for optical compensation was used.

The prior art shown in FIG. 2 is described in Japanese Patent Publication No. 63-53528, and in this figure, 1 is an upper polarizing plate, 5a, 5b are upper substrates, 7a, 7b are liquid crystal molecules, 8a, 8b is a lower substrate, 10 is a lower polarizing plate, 12 is a backlight, 20 is an upper electrode, and 21 is a lower electrode.

Here, the first liquid crystal element A for driving has the difference between the twist angle and the anisotropy of the refractive index as Δnz, and when the thickness of the liquid crystal layer is d, the product of these is Δn Due to the phase difference determined by -d, interference colors occur and coloring occurs.

Therefore, the second liquid crystal element B for optical compensation gives a twist that rotates in the opposite direction to the first liquid crystal element A, and by configuring it to have the same amount of Δn-d, the number is increased. It is possible to cancel the phase difference and obtain a black and white display without coloring.

Incidentally, related devices of this type include, for example, JP-A-147433, JP-A 179912, JP-A 1-217316, and JP-A 1-257918.
For example, the number etc.

[Ode to be solved by the invention] The above prior art does not take into consideration the fact that the display characteristics change when the viewing direction (angle) of the liquid crystal display surface changes, and when viewed from an oblique direction, There were problems in that the brightness changed and coloring appeared on the display.

An object of the present invention is to provide a liquid crystal display device that exhibits little change in display characteristics due to changes in viewing direction and that can always provide good display characteristics.

[Means to solve the problem]

The above objective is achieved by making the refractive index of a phase plate made of a birefringent material for optical compensation anisotropic and making the refractive index in the thickness direction larger than the refractive index in the direction perpendicular to the optical axis. Ru.

[Function] By providing a phase plate made of a birefringent material, coloring of the background and display areas of a twisted nematic field effect type liquid crystal display element can be suppressed, but at this time, refraction in the thickness direction of the phase plate is suppressed. By making the refractive index larger than the refractive index in the direction perpendicular to the optical axis, changes in display characteristics due to viewing angle can be suppressed, and good display characteristics can be provided.

[Example] Hereinafter, a liquid crystal display device according to the present invention will be explained in detail with reference to the illustrated example.

First, FIG. 1 shows an embodiment of the present invention, in which an upper polarizing plate 1, an upper substrate 5, a liquid crystal molecule 7, a lower substrate 8, a lower polarizing plate 10.
In addition, the backlight 12 and the like are the same as in the conventional example described above.

In FIG. 1, numeral 3 denotes a phase plate, which in this embodiment is made of a birefringent plastic film, which is a polydiacetylene membrane doped with iodine, and 4 denotes its stretching axis.

In such a liquid crystal element, the twist direction and twist angle (twist angle) α of the liquid crystal molecules 7 are determined by the rubbing direction 6 of the upper (electrode) substrate 5, the rubbing direction 9 of the lower (electrode) substrate 8, and the nematic liquid crystal. It is defined by the type and amount of the optically active substance added. The maximum value of this twist angle α is limited to 360 degrees because the lighting state near the threshold is oriented to scatter light, and the lower limit is limited by the contrast. ,1
80 degrees is the limit.

In this embodiment, a display device that can display black and white with sufficient contrast even when the number of scanning lines is 200 or more is specified.
This twist angle α is set to 260 degrees.

Next, in this embodiment, a polarizing plate known in the market, for example, Nitto Denko type G1229DU, is used, and the polarizing axis (or absorption axis) 2 of the upper polarizing plate l and the polarizing axis of the lower polarizing plate 10 are (or absorption axis) 11 and the angle β1
should be approximately 90 degrees or 0 degrees.

Furthermore, the angle β between the polarization axis (or absorption axis) 11 of the lower polarizing plate 10 and the rubbing direction 9 of the lower (electrode) substrate 8,
Considering contrast, brightness, color, etc., it is desirable that β be in the range of 30 degrees to 60 degrees (or 120 degrees to 150 degrees). Therefore, in this example, β
, = 135 degrees, and β1 = 45 degrees.

By the way, the characteristics of the liquid crystal display element according to this example have a remarkable dependence on the above-mentioned product value Δn-d, and from the viewpoint of contrast, brightness, color, etc., 0.4 μm≦Δn-d. When the condition of ≦1.5 μm is satisfied, the best characteristics are exhibited, but when the condition of 0.4 μm≧Δn-d, the transmittance decreases and the brightness is insufficient; This results in a decrease in contrast and, in any case, a decrease in display characteristics.

Further, here, the value of Δn has a dependence on the wavelength of the light used, increasing on the short wavelength side and decreasing on the long wavelength side.

Therefore, in this embodiment, He-Ne laser light (wavelength 6
328 people), and the measured value at a temperature of 25° C. is taken as the value of Δn.

In this example, a nematic liquid crystal whose main components are biphenyl-based liquid crystal and ester cyclohexane-based liquid crystal is used as the liquid crystal.
By adding 0.5% by weight of an optically active substance called 11, Δn=0.083, and therefore,
In this example, Δn-d=o,8.

Next, the phase plate 3, which is a feature of this embodiment, will be explained.

As already explained, this phase plate 3 is provided to obtain optical compensation to suppress the appearance of coloring in either the background area or the display area, and is provided to obtain optical compensation for suppressing the appearance of coloring in either the background area or the display area. The stretching axis 4 is the polarizing axis (or absorption axis) 2 of the upper polarizing plate 1 or the polarizing axis (or absorption axis) of the lower polarizing plate IO. ) The angle made with 11 is 3
It is desirable that the angle be in the range of 0 degrees to 60 degrees (or 120 degrees to 150 degrees), and therefore 135 degrees is selected here.

Next, as shown in FIG. 3, this phase plate 3 extends in the direction of its extension axis (or in the direction perpendicular to the axis Z in its thickness direction, and is included within the thickness of this phase plate). (axis extending in the direction indicating the thickest value among the refractive indices along multiple axes)
is the main optical axis When the refractive index in the direction along the axis Z is nx, each refractive index is nz=1
．． 5878 ny=1.5838 nz=1.5838, and the thickness d is set to d=93.8 μm. Note that this dimension d is 50 to 2
A range of 00/im is suitable.

Next, the effects of this embodiment will be explained with reference to the left-right viewing angle characteristics of the contrast ratio shown in FIG.

In FIG. 4, sample 2 is based on the above embodiment, and sample 3 is based on ny=1,5876 nz=1. ．． 5846 ns-], 5820 d=125 μm.

Comparing Sample 2 and Sample 3, when the contrast ratio when viewed from the front at a viewing angle of 0 degrees is 100%, the contrast ratio from 60 degrees in the left and right direction is 60% in Sample 3, and 2 showed a significant improvement of 80%. This was also true in the vertical direction.

Theoretically, the best characteristics can be obtained when the relationship nz = n r ; (n + t + ny) / 2 is satisfied, but from this condition ±10 to 20% The range is practical.

Sample l in Figure 4 is for the case where nz = 1.5858 nz = 1.5838 nz = 1.5538 d = 93.8 μm, and in this case, the contrast ratio when viewed from the front at a viewing angle of 0 degrees When 100%, the contrast ratio from 6o degrees in the left and right direction is 6 degrees for sample 3.
From 0% sample], an extremely large improvement of 90% was observed.

Note that the phase plate 3 having such n, ) ny can be easily produced by laminating, for example, a polycarbonate film and a polyvinyl alcohol film, each having a different refractive index.

By the way, in the above explanation, the type of backlight e2 is not particularly limited, but it includes light sources such as cold cathode discharge tubes, hot cathode discharge tubes, various types of devices, and cutroluminescence. Needless to say, it may be implemented as an external light utilizing type using a reflector, and an uncolored black and white display can be easily obtained by either method.

FIG. 5 shows a second embodiment of the present invention. In this embodiment, the twist angle of the liquid crystal molecules 7 is 90 degrees to obtain a black and white display. The difference between this embodiment and the embodiment shown in FIG. The other configurations are the same except that they are stacked.

These first and second phase plates 3a and 3b are arranged so that their respective principal optical axes 4a and 4b are orthogonal to each other, thereby improving viewing angle characteristics without changing display colors. In the configuration example, when the contrast ratio when viewed from the front is 100%, the contrast ratio from 60 degrees in the left and right direction is 80% from 60% in sample 3.
A significant improvement of % was observed.

Note that the laminated structure of two phase plates in the embodiment shown in FIG. 5 can be applied not only to the embodiment shown in FIG. can.

At this time, the first and second phase plates 3a and 3b may be arranged not only between the upper polarizing plate 1 and the upper substrate 5, but also between the lower substrate 8 and the lower polarizing plate 10, It may be placed on both sides.

FIG. 6 shows a third embodiment of the present invention, in which a first phase plate 3a is disposed between an upper polarizing plate 1 and an upper substrate 5, and a second phase plate 3b is arranged between a lower substrate 8 and a lower polarizing plate 5. It is placed between the plates 1O, and the other configurations, effects, etc. are the same as the embodiment shown in FIG.

FIG. 7 shows a fourth embodiment of the present invention. This embodiment is characterized by using a ferroelectric liquid crystal for the liquid crystal molecules 7. As shown in the figure, an upper polarizing plate 1, an upper substrate 5, a ferroelectric liquid crystal molecules 7,
A lower substrate 8, a phase plate 3, and a lower polarizing plate 10 are arranged in this order.

The rubbing direction 6 of the upper substrate 5 and the rubbing direction 9 of the lower substrate 8 are the same, and the polarization axes 2 and 11 of each polarizing plate 1 and 10 are set in the directions shown in the figure. Note that the other configurations are the same as the embodiment shown in FIG.

The embodiment shown in FIG. 7 has the advantage that phase correction is easy and the response speed is fast.

Next, as a fifth embodiment of the present invention, an embodiment in which the liquid crystal display device according to the present invention is colored will be described.

Although not particularly shown in the drawings, this embodiment is the same as the embodiment shown in FIG. 1 except that a color stripe filter is provided.

The width of each red, green, and blue pixel in this example is 90 μm.
The electrodes overlap each other, their width and thickness are equal to the electrode spacing and thickness, and the substrate surface is approximately flat. Also,
The space between the electrodes of the substrate without a filter is approximately flattened by providing a black matrix such as chromium or by coating a transparent material such as polyimide.

Figure 8 shows the display color range in this example using CIE chromaticity coordinates, and as is clear from this figure, the color reproducibility range is equivalent to that of commercially available color televisions. It can be seen that

Further, the contrast ratio at this time was 10/1.

In FIG. 8, TPT TV is the characteristic of a liquid crystal television using thin film transistors, and STN is the characteristic of a super twisted nematic liquid crystal display.

Next, a sixth embodiment of the present invention will be described with reference to FIG. 9.

In FIG. 9, a liquid crystal 79 is sandwiched between an upper substrate 5 and a lower substrate 8 made of glass, and an upper polarizing plate 1 is arranged outside the upper glass substrate 5. In FIG.

An upper electrode 20, a lower electrode 21, an upper alignment film 78, and a lower alignment film 80 are provided between each substrate 5.8 and the liquid crystal 79. At this time, the phase plate 3 and the lower polarized light The plate 1o is laminated between the lower electrode 21 and the lower alignment film 80.

Here, as the upper electrode 20, it is necessary to use a transparent electrode such as ITo (indium tin oxide).
The lower electrode 21 does not necessarily have to be transparent; for example, a metal electrode such as chromium, aluminum, or gold is more suitable. In addition.

In the case of using a reflected light display method, it is necessary to provide a reflective plate made of aluminum oxide or the like below this lower electrode 21, but in this case as well, by using the metal electrode described above, an independent reflective plate can be provided. No installation required.

Next, the lower polarizing plate 10 is composed of a polydiacetylene film created as described below.

First, p-3BCMU (compound early winter) (7) 0.5g/Q
A chloroform solution was prepared, and several drops of this solution were added dropwise to a developing tank filled with pure water in an LB (Langmuller Project) membrane forming apparatus to develop it.

Then, after waiting for the chloroform to completely evaporate, the mixture was compressed from two opposing directions at a compression rate of cm2/win to form a monomolecular film with a surface pressure of 20 mN/m.

As described above, all of the oriented organic films made of p-3BCMU created at the air-water interface have a film thickness of about 2OA, and 1. =p-3BCMU (-) has good reproducibility and maintains its own high orientation. Therefore, by repeating this operation 30 times, a polarizing plate is created.

The phase plate 3 is also made of a polydiacetylene film, which allows the display color of the liquid crystal display device to be changed as described above.

Note that the value of the product Δn−d of the difference Δn between the refractive index anisotropy of the phase plate 3 and the thickness d of the liquid crystal layer is 0.4 μm≦Δn from the viewpoint of contrast, brightness, and color. −d≦1
, 5, it is desirable to keep it within the range of czm.

According to the embodiment shown in FIG. 9, a liquid crystal display device with high light transmittance can be easily obtained and can be used as a display device that does not use a backlight.

In this embodiment, the phase plate 3 is arranged between the lower electrode 21 and the lower alignment film 80, but the present invention is not limited to this. It may be in between or even outside the glass substrate.

FIG. 10 shows the mounting state of the liquid crystal display device according to the embodiment of the present invention. In the figure, 61 and 63 are IC drive circuits, and the drive circuit 61 is connected to the upper electrode
0, and the drive circuit 63 is configured to drive the lower electrode 21.

Next, FIG. 11 shows an application example of the present invention, in which the liquid crystal display device according to the present invention is applied to a laptop computer.

In the figure, numerals 74 and 75 are liquid crystal display devices, and here, one of the liquid crystal display devices 74 and 75 uses, for example, a ferroelectric liquid crystal such as DOBAMBC as the liquid crystal. It is made of a material that has an input function, and is made to allow data input by touching it with a light pen or magnetic pen, or by touching it with a finger.

Therefore, according to this embodiment, a laptop computer can be easily made smaller and lighter without requiring a keyboard.

〔Effect of the invention〕

According to the present invention, it is possible to easily provide a liquid crystal display device that exhibits little change in display characteristics due to changes in the viewing direction and always exhibits good display characteristics when applied to both black and white and color displays.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a liquid crystal display device according to the present invention, FIG. 2 is an exploded perspective view showing a conventional example of a liquid crystal display device, and FIG. 3 is an explanatory diagram of a phase plate in the present invention. Figure 4 is a characteristic diagram of the phase plate in the present invention, Figures 5 and 6,
In addition, FIG. 7 is an exploded perspective view showing another embodiment of the present invention, FIG. 8 is a characteristic diagram of one embodiment of the present invention, and FIG. 9 is a cross-sectional view showing still another embodiment of the present invention. 10 is an assembly diagram showing an example of a drive circuit in an embodiment of the present invention,
FIG. 11 is an external view showing an embodiment in which the present invention is applied to a laptop computer. 1, 13, 23, 37, 56, 67, 75... Upper polarizing plate, 2.24.38.51.64... Polarizing axis of upper polarizing plate, 3.25.27.39. 46.81...
... Phase plate, 4.26.28.40.47 ... Extension axis of phase plate, 5.14, ]7.29.41.57.6
8.76... Upper board, 6.30.42.52
．． 65...Rubbing direction of upper substrate, 7.5.1
8.31.43.53.69・・・Liquid crystal (molecule),
8.16.32.44.58.7o184...
Lower substrate, 9.33.45.59...Rubbing direction of lower electrode substrate 10.19.34.48.60.7
2.82...Lower polarizing plate, 11.35.49.
55.66...Polarization axis of lower polarizing plate, 12.2
2.36.50...Backlight, 20,62
．． 77... Upper electrode, 21.71.83...
... lower electrode, 61 ... signal side circuit, 63.
...Scanning side circuit. -CIJ dimension Lr) ■ ■〇- (Stretching axis direction) Viewing angle (degrees) Left-right direction Figure Figure 80: Lower alignment film Figure Figure IE x Figure Figure

Claims (1)

[Claims] 1. In a twisted nematic field-effect liquid crystal display element using a nematic liquid crystal material having positive dielectric anisotropy and added with an optically active substance, the laminated structure of the liquid crystal display element is A phase plate having birefringence at least in part is provided, and the refractive index extends perpendicularly to the axis in the thickness direction of the phase plate and along a plurality of axes included within the thickness of the phase plate. The axis extending in the direction showing the maximum value is the main axis, the refractive index in the direction of this main axis is n_x, and the refractive index in the direction along the axis perpendicular to both this main axis and the axis in the thickness direction is n_
y, and the refractive index in the direction along the axis in the thickness direction is n_z, and the phase plate is configured such that n_x>n_y≧n_z holds true. 2. The liquid crystal display device according to claim 1, wherein the relationship between the refractive index n_x and the refractive index n_y is such that 0.9<n_y/n_x<1.1 is satisfied. . 3. In the invention of claim 1, the relationship between the refractive index n_x, the refractive index n_y, and the refractive index n_z is expressed as n_z≒
A liquid crystal display device characterized in that it is configured so that (n_x+n_y)/2 is satisfied. 4. In the invention of claim 1, the relationship between the refractive index n_x, the refractive index n_y, and the refractive index n_z is 0.8×
A liquid crystal display device configured to satisfy (n_x+n_y)<2.0×n_z<1.2×(n_x+n_y). 5. In the invention of claim 1, the thickness of the phase plate is 6.
A liquid crystal display device characterized in that the liquid crystal display device is configured to have a diameter of 0 μm or more and 200 μm or less. 6. In the invention of claim 1, the thickness of the phase plate is 2.
A liquid crystal display device characterized in that the liquid crystal display device is configured to have a diameter of 50 μm or more and 1000 μm or less. 7. The liquid crystal display device according to claim 1, wherein the phase plate is composed of a laminate of plates made of two or more different materials. 8. A liquid crystal display device according to claim 1, wherein the phase plate is laminated between one substrate constituting the liquid crystal display element and the nematic liquid crystal material. 9. The liquid crystal display device according to claim 8, wherein the phase plate is made of a substantially colorless and transparent plate material made by doping iodine into a polydiacetylene film arranged in a substantially uniaxial direction. . 10. The invention according to claim 1, wherein the phase plate is composed of two films having birefringence, and the main optical axes of these two films are arranged so as to be substantially orthogonal to each other. A liquid crystal display device. 11. The liquid crystal according to claim 1, wherein the main optical axis of the phase plate is substantially orthogonal to one of the polarization axis and absorption axis of the polarizing plate constituting the liquid crystal display element. Display device. 12. The liquid crystal display device according to claim 1, wherein two phase plates are arranged with the liquid crystal display element sandwiched therebetween. 13. A liquid crystal display device according to claim 1, wherein the nematic liquid crystal material is composed of a ferroelectric liquid crystal material.