Liquid crystal composition

Details Liquid crystal composition Liquid crystal composition

1989-07-11

1992-03-10

Maples, John S.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

25229901, C09K 1912, C09K 1952

Patent

active

050947761

DESCRIPTION:

BRIEF SUMMARY
INDUSTRIAL FIELD

The present invention relates to a liquid crystal composition used for liquid crystal display devices of a thermally addressing type utilizing a thermooptical effect, and this liquid crystal composition is characterized by having an extremely narrow nematic phase and also having a low-melting smectic phase.


BACKGROUND ART

In recent years, the development of liquid crystal display elements is remarkable, and these display elements are mostly directed to the application of nematic liquid crystals. On the other hand, liquid crystal displays of different driving modes, utilizing characteristics of other liquid crystal phases have also been intensively researched for practical use, and as one of these devices, there is a thermal writing projection device utilizing a thermooptical effect of a smectic A phase. The mode of such a device can provide a display of a far larger area and a far higher capacity in the number of figures, as compared with a conventional TN mode (twisted nematic mode).
Characteristics required for the liquid crystal materials used in this field include the following:
(1) a wide smectic A phase range (preferably, a smectic A phase range down to 0.degree. to -20.degree. C.),
(2) an extremely narrow nematic phase range,
(3) a high birefringence index,
(4) a small specific heat and a low phase transition energy; and
(5) a large dielectric anisotropy value.
Of these requirements, the items (1), (2) and (3) are considered to be important for improving the quality level of display such as contrast on a projected screen. As to liquid crystal materials having the above-mentioned characteristics, no single compound has yet been found, and hence mixtures of various liquid crystal compounds have now been investigated. Examples of these liquid crystal compounds can be represented by the following general formulae: ##STR5##
Furthermore, examples of compositions of these compounds are set forth in Table 1.


TABLE 1 ______________________________________ Compo- mp SN NI NR sition Compounds (.degree.C.) (.degree.C.) (.degree.C.) (.degree.C.) ______________________________________ a I.sub.8, I.sub.10, I.sub.15 24 73.5 74 0.5 b II.sub.8, II.sub.10 12 37 42 5 c II.sub.8, II.sub.10, V.sub.8 6 53 56 3 d II.sub.8, II.sub.10, IV.sub.9 8 41.5 47 5.5 e II.sub.8, III.sub.10, IV.sub.9 -30 46.8 51.0 3.2 f II.sub.8, II.sub.10, III.sub.10 -32.7 54.7 57.3 2.6 III.sub.12, IV.sub.9, VI.sub.8 ______________________________________
In Table 1, the respective abbreviations have the following meanings:
In the column labelled "Compound" in the table, for example, I.sub.8 means the compound of n=8 of Formula (I), mentioned above.
With regard to the composition a, the nematic range is as extremely narrow as 0.5.degree. C., but the melting point is as high as 24.degree. C., which is in the vicinity of room temperature. Therefore, this composition is difficult for practical use, though it seems to be usable in experiments. On the other hand, with regard to the compositions e and f, the melting points are as low as -30.degree. C. and -32.7.degree. C., respectively, but the nematic ranges are as wide as 3.2.degree. C. and 2.6.degree. C., respectively. Thus these compositions are not always satisfactory.
The nematic range is a factor which has an influence on the writing rate and the display contrast of the display elements, and when the nematic range is wide, the writing rate is low and the contrast also is inferior. That is, when thermal writing is carried out within a wide nematic range, a long cooling time is required in the nematic phase in the step of forming an opaque smectic phase from an isotropic liquid via a nematic phase, which constitutes a factor of retarding the writing rate. Furthermore, when the nematic phase state remains for a long period of time, the liquid crystal is oriented by a substrate subjected to an orientation treatment (vertical orientation or homogeneous orientation), so that no scattered smectic A phase can be obtained, which constitutes

REFERENCES:
patent: 3947375 (1976-03-01), Gray et al.
patent: 4053431 (1977-10-01), Scherrer et al.
patent: 4069167 (1978-01-01), Inukai et al.
patent: 4112239 (1978-09-01), DuBois et al.
patent: 4551264 (1985-11-01), Eidenschink et al.

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