JPS5840996B2 - liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using phase transition and accumulation effects of mixed cholesteric liquid crystals.

The phase transition and accumulation effect in a cell filled with mixed cholesteric liquid crystal between vertically aligned electrode substrates is described in the well-known document ``1975 Institute of Electronics and Communication Engineers National Conference Proceedings 1071J. Application to image-type matrix display has been proposed.

The liquid crystal matrix display using this method has advantages such as fast writing speed and image storage effect.5 The driving of this method of liquid crystal matrix display
Similar to the J-X display, a line sequential scanning drive method is used.

In other conventional liquid crystal matrix displays, the scanning time for one scanning electrode, that is, the writing time, is several tens of milliseconds and seven lines, whereas the writing time of this method is generally less than + milliJ seconds/line. And short.

However, until now, the time required for the accumulated surface image to appear after writing, that is, the image fixing time Trp, is as long as several seconds, and thus liquid crystal display using this method has not been put into practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase change accumulation effect type liquid crystal display device with a short image fixing time to the extent suitable for practical use.

According to the present invention, in a phase change/accumulation effect type liquid crystal display device, the liquid crystal composition is composed of alkoxybenzylidene alkylaniline, alkylcyanobiuninyl, and a cholesteric liquid crystal material, and the mixing weight ratio of the cholesteric liquid crystal material is approximately 10%, the mixed weight ratio of alkoxybenzylidene/alkylaniline is 10 to 80%, and the mixed weight ratio of alkylcyanobiphenyl is 5 to 80%.

Next, the present invention will be explained in detail with reference to the drawings.

The image fixing time in a phase transition/accumulation type display of mixed cholesteric liquid crystals is such that the liquid crystal recovers to an almost transparent alignment state after the applied voltage higher than the threshold voltage ■H for transitioning from the cholesteric phase to the vertically aligned nematic phase is removed. This corresponds to the relaxation time Trp.

FIG. 1 shows this relaxation phenomenon as a change in light transmittance.

Trp is defined as the time required for the light transmittance to recover to 70% as shown in the figure, assuming that the light transmittance of the liquid crystal in the completely relaxed and almost transparent alignment state described above is 100φ.

Trp is proportional to about the fourth power of the liquid crystal layer thickness d.

Therefore, in order to shorten Trp, d can be made small, but in terms of manufacturing technology for liquid crystal panels, d is practically limited to about 10 μm.

Trp also depends on the liquid crystal material, but in conventional liquid crystal materials, d is 10 μm and writing speed is 10 m5ec/
In the case below, it took several seconds at most.

Recently, we have found that certain liquid crystal compositions have very short Trp characteristics, and by using this type of liquid crystal composition, image fixing times of 1 second can be achieved without reducing other properties, especially writing speed. The following image storage type liquid crystal display device could be obtained.

This liquid crystal composition is composed of an alkoxybenzylidenealkylaniline cholesteric liquid crystal material and an alkylcyanobiphenyl compound in a mixed weight ratio of 5 to 80%.

Preferably it is selected from 10 to 60 rice cakes.

As alkoxybenzylidenealkylaniline, N
-(p-methoxybenzylidene)-p-n-butylaniline (MBBA), N-(p-ethoxybenzylidene)
-pn-butylaniline (EBBA), N-(p-methoxybenzylidene)-pn-hexylaniline (M
BHA), N-(p-n-butoxybenzylidene)-p
- Methylaniline (BBMA) or the like may be used, but since the cholesteric phase temperature range of the mixed liquid crystal varies depending on the liquid crystal material, it is selected appropriately depending on the application.

Further, as the alkyl cyanobiphenyl, p-n-pentyl-p'-cyanobiphenyl (PCB), p-n-
Hexyl-p'-cyanobiphenyl (HXCB), p
-n-hebutyl-p'-cyanobiphenyl (HPCB)
, p-n-octyl-p'-cyanobiphenyl (OCB
), etc. <Trp characteristics and mixed cholesteric phase temperature range are not much different.

Cholesteric liquid crystal materials include cholesteryl-based materials such as cholesteryl chloride (CC) and cholesteryl chloride (CN), as well as those having a side chain at the alkyl group or alkoxy group at the end of the molecule, such as 4-cyano-4'-( 2-methylbutoxy)biphenyl (CM
BB), and optically active chiral nematics such as P-ethoxyy-(2-methylbutyl)azoxybenzene (EMBAB), there is no significant difference in Trp, and the mixing ratio depends on characteristics such as driving voltage and writing speed. In relation to this, the diameter is generally about 10φ, which is sufficiently small that there is no major difference in the phase temperature range.

Table 1 shows some experimental examples of Trp% properties of such liquid crystal compositions.

The number at the bottom right of each mixed component abbreviation in the mixed liquid crystal composition in the table represents the mixing weight ratio (unit width) of each component.

CMBB: 4-cyano-4'-(2-methylbutoxy)
Biphenyl CC: Cholesteryl chloride *Value at d-10 μm (room temperature) ** Value per line of scanning electrode (room temperature) Table 1 As shown in Table 1, when the weight ratio of the cholesteric liquid crystal material in the mixed liquid crystal is 10φ When the alkylcyanobiphenyl fraction (HXCB, PCB, HPCB) (D weight ratio is within 5 to 72φ, and the weight ratio of the alkoxybenzylidene alkylaniline fraction (MBBA, EBBA) is 1
The Trp in the mixed solution within 8 to 85φ is all short, less than 1 second, which is practical, but it does not contain any alkoxycyanobiphenyl fraction. ■3BA.

I-(PCB90cMBB) which does not contain any CMBBlo and alkoxybenzylidene alkylaniline
A Trp of 1° is long, longer than 2 seconds, and is impractical.

As for the reason for this phenomenon, as a result of investigating the material machining allowance listed in Table 1, we found that the phase state of the mixed liquid crystal made of alkoxybenzylidene alkylaniline, alkylcyanobiphenyl, and cholesteric liquid crystal material has an extremely alkoxy composition. In areas other than benzylidenealkylaniline deficiency or alkylcyanobiphenyl deficiency regions, there is a smectic phase on the lower temperature side than the cholesteric phase, and it has been found that the presence of this smectic phase is associated with short Trp, but there is no strict explanation. is also not well understood.

In addition, in Table 1, the weight ratio of cholesteric liquid crystal material is 10
Although examples have been described for very specific cases, it goes without saying that the mixing ratio does not need to be strictly 10%.
The object of the present invention can be distantly achieved even with a weight ratio of around 10 fb.

In particular, if we are to judge practicality based on the standard of Trp of 1 second or more, the weight ratio of the cholesteric material in the mixed liquid crystal should be about 10, and the weight of alkylcyanobiphenyl should be about 5.
It is desirable to set the weight ratio of alkoxybenzylidene and alkylaniline to 10 to 85, respectively.

That is, when the weight ratio of alkylcyanobiphenyl is less than 5φ or more than 80φ, Trp tends to exceed 1 second, and similarly, when the weight ratio of alkoxybenzylidene/alkylaniline is less than 10 or more than 85, Trp tends to exceed 1 second. This is because the time tends to exceed 1 second.

Next, an example of a liquid crystal display device using the liquid crystal composition as described above will be described with reference to FIG.

FIG. 2 is a schematic cross-sectional view of a phase change/accumulation type liquid crystal display panel which is an embodiment of the present invention.

In the figure, a liquid crystal composition 1 is composed of a pair of electrode substrates 4 having transparent electrodes 2 and 3 made of isodium oxide or the like attached to the inner surfaces thereof;
It is filled between 5 and 5.

The distance between the side substrates 4 and 5, that is, the liquid crystal layer thickness d is kept constant by spacers 6.

The transparent electrodes 2 and 3 are formed in a matrix.

Further, on the inner surface of the side substrate 4.5, a surface treatment agent for vertical alignment,
For example, FS- commercially available from Dainippon Ink and Chemicals
A vertical alignment surface treatment agent with a trade name called 150 is applied.

The liquid crystal composition used in this example was M13BA7oP.
The thickness d of the liquid crystal layer of CB20CC1o is 11 mm.

When a liquid crystal panel with such a configuration was connected to a matrix drive circuit and operated, the image fixing time was 0.7 sec.
, a writing speed of 8.0 m5ec/line, and a contrast of 30:1 were obtained.

Thus, if the image fixing time is about 1 second or less, the phase change/accumulation type liquid crystal display is sufficiently practical.

[Brief explanation of the drawing]

FIG. 1 is a general characteristic diagram for explaining the image fixing time in a phase change accumulation type liquid crystal display. FIG. 2 is a schematic cross-sectional view showing one embodiment of the present invention. 1...Liquid crystal composition, 2,3...Transparent electrode, 4°5...Substrate, 6...Spacer.

Claims (1)

[Claims] 1 In a phase change/accumulation effect type liquid crystal display device in which a mixed cholesteric liquid crystal composition is filled between a pair of transparent electrode substrates subjected to vertical alignment surface treatment, the liquid crystal composition is N-(p
-n-alkoxybenzylizo:/)-p-n-alkylaniline, p-n-alkyl-p'-cyanobiphenyl, and cholesteric liquid crystal material, and the mixing weight ratio of the cholesteric liquid crystal material is about 10. , the mixing weight ratio of the alkoxybenzyritine/alkylaniline is 15
~85, a liquid crystal display device characterized in that the mixing weight ratio of the alkyl cyanobiphenyl is 5 to 80%.