JPH035722A - Liquid crystal electrooptic device - Google Patents

Abstract

PURPOSE:To suppress a decrease in contrast by adding clockwise chiral liquid crystal and counterclockwise chiral liquid crystal in nematic liquid crystal., and determining either clockwise or counter clockwise twist direction, and further adding chiral liquid crystal which is small in HTP, and making fine adjustment for temperature variation. CONSTITUTION:The liquid crystal has the counterclockwise chiral component and clockwise chiral component, the difference between the helical twist power of one chiral liquid crystal component and the helical chiral twist power of the other chiral liquid crystal component is >=0.04, and the variation with temperature is <=0.005. Thus, the chiral liquid crystal which can suppress temperature variation in the difference in HTP between the two kinds of chiral liquid crystal below +0.005 is added. Consequently, the length of the chiral pitch of an STN type liquid crystal electrooptic device is easily adjusted, a defect of the orientation of a rho-less, stripe domain, etc., is eliminated, and defects such as a decrease in contrast and a failure in display due to temperature variation are removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] Heretofore, liquid crystal electro-optical devices called STN type have been quite popular as displays for word processors and the like. This S
T N (Super Twisted Nemat
IC) type liquid crystal electro-optical devices have long been used in watches, calculators, etc.
c) type liquid crystal electro-optical device, the voltage threshold for liquid crystal switching is clear, so the conventional T
It can also be applied to relatively large displays that cannot be used with N-type liquid crystal electro-optical devices.

Now, in general, liquid crystals in STNTN type liquid crystal electro-optical devices produce a twisted state by adding chiral liquid crystal to nematic liquid crystal.If one type of chiral liquid crystal is added to nematic liquid crystal, If the chiral liquid crystal is cloth-wrapped, a liquid crystal that twists to the left can be obtained.

By the way, it is very important to adjust the chiral pitch and cell thickness (thickness of the liquid crystal layer) in the STNTN type liquid crystal electro-optical device.If the chiral pinch is too large relative to the cell thickness, π-less will occur, and if it is too small, striped domain will occur. This alignment defect occurs.

In general, the chiral pinch lengthens as the temperature rises, so even if the chiral pitch length and cell thickness are well adjusted at room temperature and high display quality is obtained, as the temperature rises, the liquid crystal The twist state changes and the display quality, such as a decrease in contrast, deteriorates rapidly. As a countermeasure against this problem, a right-handed chiral and a left-handed chiral are usually added to the nematic liquid crystal. By doing this, the elongation of the chiral pitch due to temperature rise is offset by the cloth wrapping and the left-handed wrapping, and display quality does not deteriorate.

However, in this case, the cancellation of cloth wrapping and left-handed winding naturally occurs even at room temperature, so the chiral pitch at room temperature cannot be increased beyond a certain level, and as a result, the cell thickness cannot be increased beyond a certain level, and the interference between the substrates The yield rate of the process was significantly lowered due to the waste generated.

Furthermore, since it is almost impossible to fine-tune the cancellation of cloth-wound chiral and left-handed chiral, it was necessary to create a chiral liquid crystal material that can cancel out fluctuations in chiral pitch due to temperature changes.

[Structure of the invention]

In order to solve the above-mentioned problems, the present invention provides a liquid crystal electro-optical device in which a liquid crystal is interposed between a pair of substrates and includes a polarizing means for identifying different states of the liquid crystal, in which the liquid crystal has a left-handed chiral component. It contains a right-handed chiral component, and the difference between the helical twist power of one chiral liquid crystal component and the other chiral liquid crystal component is greater than 0.04, and there is no fluctuation due to temperature changes. It is characterized by being within ±0.005.

In the present invention, helical twist power (hereinafter referred to as HTP)
) is defined as follows.

HTP-(P*C) where P is chiral pitch and C is the addition l (wt%) of chiral liquid crystal.

As is clear from the above formula, ) (TP is the reciprocal of the pitch when a certain proportion of chiral liquid crystal is added, that is, it can be said to represent the influence of chiral liquid crystal on nematic liquid crystal to twist the nematic liquid crystal. .

In the present invention, a cloth-wound chiral liquid crystal and a left-handed chiral liquid crystal are added to a nematic liquid crystal. However, the chiral liquid crystals to be added are two types of liquid crystals having a large difference in HTPO. In other words, by using a chiral liquid crystal with a large HTP to determine the twist direction of the entire liquid crystal to cloth-wound or left-handed, and then adding chiral liquid crystals with a small HTP, it is possible to fine-tune the fluctuations in chiral pitch due to temperature changes. , it is possible to minimize fluctuations in chiral pitch due to temperature changes. The inventors have found that this fine adjustment becomes extremely easy by specifically setting the difference in HTP to 0.04 or more.

Furthermore, by adding a chiral liquid crystal that can suppress the fluctuation of the difference in HTP between two types of chiral liquid crystals to within ±0.005, alignment defects will occur in that temperature range. There is no contrast, and the decrease in contrast can be suppressed.

The present invention will be explained below with reference to Examples.

[Example 1] Figure 1(a) shows the H of the left-handed chiral liquid crystal used in this example.
The temperature dependence of TP is shown, and FIG. 1(b) shows the temperature dependence of HTP of the cloth-wound chiral liquid crystal used in this example.

As is clear from the figure, the left-handed chiral liquid crystal used in this example has a larger HTPO value in the range of 0.07 to 0.08 than the cloth-wound chiral liquid crystal, and the temperature change due to the difference in HTP The variation with respect to is also within ±0.005, which is consistent with the gist of the present invention.

Using the liquid crystal obtained by adding these two types of chiral liquid crystal to nematic liquid crystal, 20 liquid crystal cells were manufactured, and by changing the temperature conditions, 12
The contrast was determined for each point and the results are shown in Table 1. However, the numbers not shown in the table are the average values of 20 cells for each measurement point.

Table 2 shows the contrast measurement results when a liquid crystal cell was prepared using the liquid crystal obtained by adding the liquid crystal.

Table 2 Also, as a comparative example, as can be seen from right-handed chiral liquid crystals (a) and (b) having the temperature dependence of HTP as shown in FIGS. 2(a) and (b), respectively, In this case, the difference in HT PO between the two types of chiral liquid crystals used was small.
(approximately 0.01), the adjustment to reduce the fluctuation of chiral pinch due to temperature change was not successful, and alignment defects occurred particularly in the high temperature region, resulting in a sharp drop in contrast.

In addition to this example, experiments were conducted by changing the chiral liquid crystal added to the nematic liquid crystal, but it was also found that if the difference in HTP of the chiral liquid crystal was not at least 0.04, fluctuations in chiral pitch due to temperature changes would occur. It was not possible to sufficiently prevent orientation defects such as π-less and striped domains.

Furthermore, the difference in HTP of the added chiral liquid crystal is 0.0.
Even if it is 4 or more, the fluctuation due to temperature change is ±o,
If the temperature was not within oos, poor orientation occurred at high or low temperatures.

[Effect] As described above, by using the present invention, STN
This makes it easier to adjust the length of the chiral pitch in type liquid crystal electro-optical devices, eliminating alignment defects such as π-less and striped domains. can be overcome.

[Brief explanation of drawings]

Figures 1(a) and (b) and Figures 2(a) and (1)) show the temperature dependence of HTP of chiral liquid crystals. FIG. 3 shows contrast measurement points on the liquid crystal cell. Funeral diagram 1 (α) (shi) Funeral diagram (α) (1))

Claims (1)

[Claims] 1. A liquid crystal electro-optical device having a liquid crystal interposed between a pair of substrates and having a polarizing means for identifying different states of the liquid crystal, wherein the liquid crystal contains a left-handed chiral liquid crystal component and a right-handed chiral liquid crystal component. and the difference between the magnitude of the helical twist power of one chiral liquid crystal component and the magnitude of the helical twist power of the other chiral liquid crystal component is 0.04 or more, and the temperature change of the difference in the magnitude of the helical twist power is 1. A liquid crystal electro-optical device characterized in that a variation relative to that of the liquid crystal is within ±0.005.