JPS61177440A - Liquid crystal display element and its production - Google Patents

Abstract

PURPOSE:To prevent the generation of uneven display by using polyimide films each having the thickness ranging 20-100Angstrom as the oriented org. films to be formed on the opposed surfaces of two sheets of electrode substrates. CONSTITUTION:Dot electrodes 3 and a common electrode 4 consisting of transparent conductive films are deposited and formed to respective prescribed pattern sizes on the opposed surfaces of the upper and lower substrates 1, 2 consisting of, for example, light transparent glass plates. The polyimide is deposited and formed on the electrodes 3, 4 and thereafter the oriented org. films 5 subjected to a rubbing treatment on the surface are formed on the electrodes 3, 4. The substrates 1 and 2 are spaced at a prescribed distance from each other and the peripheral part thereof is sealed by a sealant 6 contg. spacers to form a liquid crystal cell. A liquid crystal 7 is sealed therein. The effect of high stability is obtd. by maintaining the film thickness with in the 20-100Angstrom range. The generation of the uneven display arising from the dependency of the liquid crystal on the frequency of the threshold voltage is thus prevented.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a liquid crystal display element suitable for preventing the occurrence of display unevenness due to large fluctuations in the threshold voltage of the liquid crystal on the low frequency side, and a method for manufacturing the same. be.

[Background of the invention]

In recent years, liquid crystal display elements have been used in watches, calculators, cameras, etc. due to their thinness and low power consumption.
The scope of use of wall-mounted devices is expanding to include measuring instruments, information display devices for automobiles, and even televisions in the future. We are in a situation where we have to overcome hurdles.

When such liquid crystal display elements are used in watches, calculators, etc., a small display area is sufficient, but as technology advances, υ
As it has become possible to gradually increase the display area, liquid crystal display elements of approximately A4 size have come to be required in the information industry field. In order to display such a large screen, the number of dots must be 128 (
vertical) x 480 (horizontal) or 200 (vertical) x 640 (
horizontal) type is required. Furthermore, in order to drive these, in the case of 128 dots, the duty is 1/64,
In the case of 200 dots, it is common to drive at a duty of 1/100.

However, when the duty becomes high, the margin during time division inevitably becomes narrower, resulting in a problem in that the display quality deteriorates significantly.

In other words, when driving a liquid crystal display element in a time-division manner, a voltage averaging method is generally used as a driving method, and this method involves
One method inverts the polarity and converts to AC within one frame time (the time it takes to scan all the scanning lines once) (hereinafter referred to as A method), and the other method inverts the polarity and converts to AC in two frame times (hereinafter referred to as B method). There are two types of methods. These drive systems are discussed in detail, for example, in the August 16, 1980 issue of Nikkei Electronics, pages 150 to 174.

The time-division driving method for liquid crystal display elements is also described in the above-mentioned literature, but as the number of time divisions increases, the B-method driving is mainly used.

However, the lowest driving frequency in B-method driving is half the frame frequency, and there are cases where driving is performed at an extremely low frequency. On the other hand, in a liquid crystal display element, as shown in Figure 1, the voltage-transmittance characteristic □□□
The voltage at which the transmittance is 9 (l) when viewed in the 25°C direction, that is, the threshold voltage vth of the liquid crystal, has frequency dependence as shown in Figure 2, and the threshold voltage vth of the liquid crystal
If th fluctuates greatly on the low frequency side, the above-mentioned B
When method driving is used, depending on the lighting pattern, display unevenness with severe shading appears. For example, if the liquid crystal has a characteristic that the threshold voltage vth decreases on the low frequency side as shown in FIG. 2, the signal electrode Y1.
Y Goose, Y1. ~Y1? and scanning electrode Xl.

When a voltage is selectively applied between x, , The display color of the illuminated dots (D) in the array groups CI and Cs is also light, but it is darker than the non-lit dots E in the dot array groups CL, C, and the display is colored pale black just like the shape. state. This is Todd array group AI
+ A meaning The frequency component of the driving voltage applied to the liquid crystal of the line in the A1 portion is the dot array group C1+C! Therefore, when considering the frequency characteristics of the threshold voltage of the liquid crystal shown in Fig. 2, when considering the threshold voltage as a reference, the dot array group AI + A2 v
A substantially large driving voltage is applied to the A3 portion as well as the dot array group CI rC: Therefore, the dot array group A, Am, and the A portion are the dot array group CI, A phenomenon occurs in which the non-lit dots E and the other dots C and E also light up black. That is, in FIG. 2, for the potential difference v1 t "! between the driving voltage Vie applied to the liquid crystal and the threshold voltage vth at that frequency, Vt>Vs, and the dot array group Al r At j
A substantially large drive voltage is applied to the dot array groups C1 and C in the portion Am, and to the dot array group AI.

The portions Am and A will be lit blacker than the portions cl and c of the dot array group.

This phenomenon occurs because the driving frequency range gradually expands as the duty number increases. For example, in the case of "/64 duty" (3011 to 1.
92KHz) and 100 duty (30Hz~3K
It is necessary to drive within a frequency range up to about 100 Hz.

FIG. 4 shows the fluctuation of the threshold voltage Vth at each driving frequency divided by the threshold voltage Vth (500 Hz) at the center frequency (500 Hz) of the normal driving frequency range, and is shown as a circle. As shown in the figure, since liquid crystal display elements generally exhibit changes in threshold voltage vth depending on the driving frequency, as the driving frequency range becomes wider, the difference between the maximum threshold voltage and the minimum threshold voltage increases. This causes display unevenness.

On the other hand, as the duty of the drive system becomes higher, the difference between the voltage applied to the lighting dot (D) and the voltage applied to the non-lighting dot E becomes smaller, that is, the margin (tolerance)
becomes smaller. During low-duty driving, the area of non-lit dots can be almost ignored, and only appears to be lit when the liquid crystal display element is tilted in the viewing direction.
However, in the case of high-duty drive, the tolerance becomes extremely small, so crosstalk appears over the entire display surface even when the LCD screen is viewed from the front, and this crosstalk display The desired dot is lit on the screen. For this reason, if the threshold voltages differ between adjacent dot arrays, it will be more clearly visible.

[Purpose of the invention]

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a liquid crystal display element that prevents the occurrence of display unevenness caused by the frequency dependence of a threshold voltage, and a method for manufacturing the same. It's about doing.

[Summary of the invention]

In order to achieve such an object, the present invention uses a polyimide film with a film thickness in the range of 20 to 100X as an organic alignment film formed on each opposing surface of two electrode substrates arranged oppositely. It is something.

[Embodiments of the invention]

Next, the present invention will be explained in detail using the drawings.

FIG. 5 is a sectional view of essential parts showing an embodiment of a liquid crystal display element according to the present invention. In the figure, dot electrodes 3 are formed from transparent conductive films on the opposing surfaces of upper and lower substrates 1 and 2 made of transparent glass plates. Common electrodes 4 are deposited and formed with predetermined pattern dimensions, and these electrodes 3,
4 is coated with polyimide, such as polyimide isoindoquinazolinedione (for example, Hitachi Chemical's trade name PIQ).
), an organic alignment film 5 is formed on the surface thereof by rubbing. Then, a liquid crystal cell is formed by separating the upper and lower substrates 1 and 2 by a predetermined distance from each other and sealing their peripheral parts with a sealing material 6 containing a spacer. RO-TN-
132 (trade name) liquid crystal T is sealed.

On the other hand, as a conventional organic alignment film, for example, polyimide isoindoquinazolinedione is coated to a thickness of about several hundred thick, and then the surface is rubbed to form a liquid crystal cell, as shown in Table 1 below. When encapsulating various commonly used liquid crystal materials, most of the materials have the above-mentioned VT
h (30Hρ/vth (500H!) is 0.97 or less. Generally, vth (30Hz)/vth
(500Hz) is 0.97 or more, there is no practical problem, and preferably, if it is 0.98 or more, display unevenness can be completely ignored. Therefore, these materials shown in Table 1 were almost unusable.

Therefore, in the liquid crystal display element according to the present invention, the thickness of the organic alignment film 5 shown in FIG. 5 is approximately 250λ as shown in FIG.
Form the following various values and vth(a.

The film thickness at which HE )/vth (500Hz) was 0.97 or more was determined. As a result, the thickness of the organic alignment film 5 was reduced to about 1
It became clear that it had to be formed to a thickness of 00A or less. In this case, the liquid crystal material used is Vth (30Hz) /
It is the E liquid crystal with the smallest Vth (500Hz). Similarly, as a result of encapsulating various liquid crystal materials shown in Table 1 (into an element with an organic alignment film of 100 A), Vth
(30Hz)/Vth(500Hz) falls within the range of 0.98 to 1.0 in the normal frequency range, and drive frequency 3
The fluctuation of the threshold voltage in the range of 0 to 5001 it is approximately 2
I was able to keep it below .

In addition, in the above-mentioned embodiment, the case where the film thickness of the organic alignment film 15 was about 1001 was explained, but the present invention is not limited to this, and if the film thickness is less than 20X, the liquid crystal Orientation deterioration is likely to occur, and if the film thickness is set to 100λ or more, the frequency range is expanded and display unevenness is likely to occur. Therefore, the film thickness of is 20~1O
A range of OX is preferable, and by setting the range to 20 to 50, a highly stable effect can be obtained.

Next, a method for manufacturing a liquid crystal display element according to the present invention will be explained.

First, the υ dot electrode 3 is placed on the surface of the upper substrate l by a normal means.
After forming, on the dot electrode 3 forming surface of the upper substrate 1, 0.2 to 0.3% by weight of polyimide isoindoquinazolinedione dissolved in NMP (N-methylpyrrolidone) is applied.
Add the solution dropwise and heat on a spinner at 3200-3800r, p
Spin coat with lm. Next, add 200 to 300
A polyimide film is produced by baking at 0° C. for about 1 to 2 hours. It is also formed on the lower substrate 2 in the same manner as described above.

Next, the surfaces of the polyimide isoindoquinazoline dione films formed on both electrode substrates 1 and 2 are rubbed in the respective directions, and then a sealing material 6 is applied to the peripheral area of either of the substrates 1 and 2. 3.4 electrodes each.
A liquid crystal cell is formed by adhering the two sides facing each other.

〔Effect of the invention〕

As explained above, according to the present invention, the organic alignment film formed on the opposing surfaces of two electrode substrates has a film thickness of 20 to 100λ.
By providing a polyimide film in the range of 20 to 30, it is possible to prevent display unevenness caused by the frequency dependence of the threshold voltage of the liquid crystal, and thus a liquid crystal display element with high quality and reliability can be obtained. Further, according to the method for manufacturing an organic alignment film according to the present invention, an organic alignment film can be formed extremely easily.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between transmittance and voltage when driving a liquid crystal display element in a time-division manner, Figure 2 is a diagram showing the frequency dependence of the threshold voltage of the liquid crystal, and Figure 3 is a diagram showing the relationship between the transmittance and voltage when the liquid crystal display element is driven in a time-division manner. FIG. 4 is a diagram illustrating the driving frequency range of the liquid crystal display element, and FIG. 5 is a diagram illustrating an embodiment of the liquid crystal display element according to the present invention. Figure 6 shows the Vth (30Hz)/Vth (500Hz) with respect to the film thickness of the organic alignment film.
FIG. DESCRIPTION OF SYMBOLS 1... Fist upper substrate, 2φ, fist, lower substrate, 3φ... Dot electrode, 4, Ass main electrode, 5e... Organic alignment film, 6... Seal material, T... Agent Patent Attorney Small
Katsu Kawa O'-2-Figure 1 Figure 2 fIi Autumn f (Hz) Figure 3 Separate! History (Hz)

Claims (1)

[Claims] 1. In a liquid crystal display element in which an organic alignment film is provided on each opposing surface of two electrode substrates arranged oppositely, and a liquid crystal is sealed between the electrode substrates, as the organic alignment film. Film thickness is 20~
A liquid crystal display element characterized by using a polyimide film having a thickness of 100 Å. 2. In a liquid crystal display element in which an organic alignment film is provided on each opposing surface of two electrode substrates arranged oppositely, and a liquid crystal is sealed between the electrode substrates, the organic alignment film is formed by disposing a polyimide solution on the electrode substrates. A method for manufacturing a liquid crystal display element, which comprises spinning and baking the liquid crystal display element.