JPS6339632B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid crystal display element, and particularly to a liquid crystal display element that uses a rubbing alignment film to enable driving of liquid crystal at 1.5V. In general, methods for forming an alignment film that aligns liquid crystal molecules parallel to a substrate surface include an oblique evaporation method and a rubbing method. The former oblique deposition method is a method in which, for example, SIO is deposited from an oblique direction with respect to the substrate surface, and the tilt angle of the liquid crystal molecules with respect to the substrate surface varies depending on the film formation conditions.
It is usually controllable within the range of 0 to 30 degrees. In addition, the latter rubbing method is a method in which the substrate surface is rubbed in one direction with a cloth, etc. In this case, the tilt angle is not affected by the film formation conditions and can usually be formed at an angle in the range of 2 to 3 degrees. It is. On the other hand, most of the TN type liquid crystal display elements currently used in wristwatches are driven by 3V.
However, in order to drive at 3V, methods such as using two 1.5V batteries or using one battery and providing a booster circuit are adopted, and either method requires extra space. However, it also has disadvantages such as complicating the circuit. On the other hand, compared to 3V drive, 1.5V drive eliminates the need for a booster circuit, simplifies the drive circuit, and significantly reduces power consumption, so the battery capacity can be small, making the battery even smaller and thinner. It takes shape. In this way, the 1.5V of the liquid crystal display element
The drive system is a great advantage in making display devices smaller and thinner, and it also has a great effect on reducing costs, such as by significantly reducing the number of parts. However, 1.5V
Driving has not been put into practical use at all in liquid crystal display elements using current rubbing alignment films, and has only been put into practical use in some liquid crystal display elements using obliquely vapor-deposited alignment films. This is because there are currently almost no liquid crystal materials that can be driven at 1.5V, and the threshold voltage of a TN type liquid crystal display element increases as the tilt angle becomes smaller, so the rubbing method with a small tilt angle requires extremely low voltage drive. This is because it becomes difficult. Therefore, the present invention uses a rubbed alignment film.
The objective is to provide a liquid crystal display element that can be driven at a low voltage of 1.5V or less. In order to achieve such an object, the present invention provides a liquid crystal using a rubbing alignment film by adding 0.05 to 0.25 wt% of at least one type of long-chain alkylamine having 12 to 20 carbon atoms to the liquid crystal. This effectively reduces the threshold voltage of the display element. The present invention will be explained in detail below using Examples. Example 1 When a liquid crystal composed of the following composition was sealed in a TN type liquid crystal cell configured by forming rubbing alignment films on the opposing surfaces of translucent substrates arranged oppositely, 25
The threshold voltage at °C was 1.20V. On the other hand, 0 to 0.30wt of cetylamine was added to the above liquid crystal as a long chain alkylamine with 12 to 20 carbon atoms.
The threshold voltage of each liquid crystal display element when added by varying 0.05wt% within the range of 0.05wt% is shown in Table 1 below.
The values shown in are obtained. Similarly, when n-tetradecylamine or n-octadecylamine is added as a long-chain alkylamine, a threshold voltage equivalent to that of cetylamine can be obtained. The threshold voltage was 1.06V or 1.07V.

【table】

[Table] Therefore, as is clear from Table 1 above, by adding a long-chain alkylamine, as the amount added increases, the threshold voltage becomes lower than that of the conventional one.
It was possible to gradually reduce the voltage to 1.20V. Therefore, the amount of long-chain alkylamine added should be reduced to 0.1wt.
By adding % or more, it was possible to lower the threshold voltage by about 0.1 V or more, and it was possible to drive the liquid crystal at 1.5 V without lowering its clearing point. Example ₂ TN-132 (Hoffmann-La Roche
The threshold voltage of a liquid crystal display element constructed by enclosing a liquid crystal display device (manufactured by Sekisui Chemical Co., Ltd.) is 1.0V, so it can be driven at 1.5V. However, the threshold voltage in a liquid crystal cell with a rubbing alignment film is 1.20V,
1.5V drive is virtually impossible. When a liquid crystal obtained by adding 0.2wt% of n-pentadecylamine as a long-chain alkylamine to liquid crystal TN-132 is sealed in a rubbing alignment film cell, the threshold voltage becomes
The voltage was 1.05V, and characteristics that enabled 1.5V drive were obtained. Generally, it is well known to add isotropic compounds to liquid crystals to reduce their threshold voltage, but in order to obtain a sufficient effect, several
It is necessary to add wt% or more than ten wt%. As a result, there was a drawback that the clearing point of the liquid crystal was significantly lowered. However, with the long-chain alkylamine of the present invention, a sufficient effect was obtained even when added in a small amount of 0.1 wt% or more, and 1.5V driving was possible without lowering the clearing point of the liquid crystal. Furthermore, according to experiments conducted by the inventors, it has been found that if the amount of long-chain alkylamine added is within the range of 0.05 to 0.25 wt%, 1.5V drive can be effectively achieved. However, if the amount added is less than 0.05wt%, 1.5V drive becomes unstable or impossible, and if it exceeds 0.25wt%, long-chain alkylamine precipitates, making 1.5V drive impossible. At the same time, the clearing point of the liquid crystal is lowered, and the display quality is lowered. Therefore, the amount added is 0.1
Very good effects can be obtained within the range of ~0.2wt%. In the above examples, cetylamine, n-
Tetradecylamine, n-octadecylamine,
Although the case where one type of n-pentadecylamine is added has been described, the present invention is not limited to this, but it is possible to add multiple types and the total addition amount is within the range of 0.05 to 0.25 wt%. If,
Exactly the same effect as described above can be obtained. As explained above, the present invention provides that the liquid crystal sealed in a liquid crystal cell equipped with a rubbing alignment film has a carbon number of 12 to 20.
By adding at least one type of long-chain alkylamine, it is extremely easy to drive a liquid crystal display element to 1.5V without deteriorating display quality, making the liquid crystal display element smaller and thinner. and can be provided at low cost. Furthermore, since a sufficient effect can be obtained by adding a very small amount of long-chain alkylamine to the liquid crystal, the manufacturing process can be simplified and extremely excellent effects such as 1.5V drive can be obtained.

Claims (1)

[Claims] 1. Two translucent substrates arranged to face each other,
In a TN type liquid crystal display element comprising a liquid crystal sealed between the two substrates and a rubbing alignment film formed on the liquid crystal interface of the two substrates, a long chain alkyl having 12 to 20 carbon atoms is contained in the liquid crystal. A TN type liquid crystal display element characterized in that at least one type of amine is added. 2. The TN according to claim 1, wherein the amount added is in the range of 0.05 to 0.25 wt%.
type liquid crystal display element.