JPS59122574A - Liquid crystal for thermal-recording liquid crystal elements - Google Patents

Abstract

PURPOSE:A liquid crystal composition for thermal-recording liquid crystal elements that is obtained by using, as a major component, a mixture composed of specific amounts of a substance which is represented by a specific formula and another substance of another formula, thus giving displays of high contrast with a very bright tone. CONSTITUTION:The objective liquid crystal composition is composed of a combination of the substance of formula I and 25-50wt% of the substance of formula II, as a major component, when necessary, dichromic dyes, optically active substances and so on. USE:Direct-viewing type display elements, light bulb elements used in projection type display units, recording elements.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal material used in a thermal writing liquid crystal element that utilizes the thermo-optic effect of liquid crystal.

When a thin layer of cholesteric liquid crystal or smectic liquid crystal, which exhibits a transparent liquid crystal structure, is partially heated and rapidly cooled, that area transitions to an opaque liquid crystal structure that generally scatters light, a phenomenon known as the thermo-optic effect of liquid crystals. There is. In addition, several liquid crystal devices have been proposed that take advantage of this phenomenon and write information by applying a temperature change to a portion of the liquid crystal cell to make that portion opaque. For example, a direct-view display element in which an image is written and the image is viewed directly, a light pulp element used for a projection display in which the written image is projected and viewed, and the information that has been inserted is read electrically or optically. type of recording element, etc. There are also several methods for writing Yu@i, such as irradiating a laser source to cause a temperature rise in the irradiated area, and using Joule heat generation in a resistor to generate a warm armpit rise r. It has been known. In the following, for the sake of simplicity, we will talk about the liquid crystal light pulp element used in projection display devices, in which an image is written by irradiating the liquid crystal cell with a laser source, and the written image is enlarged and projected using a separate optical system. This will be explained using a case as an example.

Initially, the general formula CnH2n+ was used for thermal writing liquid crystal light pulp.
A so-called Schiff base liquid crystal material represented by 1-o-N=HC-σCN was used.

This is because no liquid crystal material other than thick base-based materials has been found that exhibits a smectic phase at the operating temperature of liquid crystal light pulp, that is, around room temperature, and has an appropriate phase transition temperature. Here, the appropriate phase transition temperature is related to the temperature Tc at which the liquid crystal transitions to an isotropic liquid phase, and Tc.
If c is too high, the temperature rise required for writing will increase,
There are disadvantages in terms of power consumption and writing speed, and if Tc is too low, the liquid crystal temperature in the steady state after writing is close to the phase transition temperature Tc, which causes a decrease in the degree of orientational order of liquid crystal molecules. This causes an inconvenience such as a decrease in contrast. Regarding such Schiff base-based liquid crystal materials, Taylor et al. of Bell Laboratories reported in the Journal of Applied
This is reported in Fix, Vol. 45, No. 10. However, it is widely known that Schiff base-based liquid crystal materials are prone to hydrolysis, and therefore thermal writing liquid crystal devices using this type of liquid crystal material have short lifespans and lack reliability, especially in terms of moisture resistance. There is. Therefore, subsequent attempts were made to improve liquid crystal materials, and a chemically stable biphenyl liquid crystal material represented by the general formula R-G-G-CN (where 几 represents an alkyl group or an alkoxy group) was created. The company's company is R()(toC).
The structure of N is C3H17s C9H19's Cl0
H21~C11) 123°C3H17U, (?9H1
A report was published in "The Fixtures and Chemistry Op Liquid" published by Plenum Publishing that a mixed liquid crystal consisting of three components selected from some of the 90 liquid crystal materials is optimal for use in thermal writing liquid crystal light pulp. ·crystal·
Published on pages 219 to 239 of "Devices".

Mata, Thomson, C.N. Dubois, Anal de Physique, Volume 3 (1978), 131
On page 138, R-C (in the structure to C, 几 is C8H17, C9Hts, on C3 (701C8H170
% C3H17C (JU, C9H19COO)
Comparatively examining mixed liquid crystals consisting of components selected from some of the liquid crystal materials used in
It has been reported that a mixed liquid crystal consisting of three components, ilc and coo, is optimal for use in a thermal writing liquid crystal light valve. In this way, improvements have been made in liquid crystal materials, and the shortcomings of early thick basic liquid crystals, such as short lifespan and low reliability, have been overcome. However, even when using the known liquid crystal materials as described above, display performance such as brightness and contrast of the display screen remains unsatisfactory! We have carefully studied the relationship between the transition temperature of J quality and display performance, and have conducted discussions on many liquid crystal materials.
The present invention was achieved by discovering a crystalline material that allows the center of an element with an island-shaped surface, which could not be obtained in the past, to be concentrated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal material for a thermal writing liquid crystal device having unreliable performance.

The liquid crystal material for a thermal writing liquid crystal element of the present invention uses a thermal writing liquid crystal element trap in which information is written by partially applying heat to the liquid crystal material, and is represented by the chemical formula e8Fi17Sitoku←C. It is similar in that it is a mixed liquid crystal containing as main components a substance represented by the chemical formula 〇to) 121 (J-o-oLCN) and 25 to 50 weight percent of a substance represented by the chemical formula 〇to) 121 (J-o-oLCN).

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

The diagram shows the chemical formula 〇5H1y-4Σ (HCN (hereinafter referred to as ucb)) and the chemical formula Ctol (2t (J-◎
FIG. 2 is a diagram showing the results of measuring the phase transition temperature of mixed liquid crystals prepared by mixing a substance represented by @xCN (hereinafter referred to as DUCB) in various proportions. The transition temperature between the smectic liquid crystal phase and the solid phase differs depending on whether it is measured while increasing the temperature or when it is measured while decreasing the temperature. In liquid crystals, it is sufficiently low and is not necessary for the explanation of the present invention, so only a part of it is shown by a dotted line. A liquid crystal cell with a normal structure was created using mixed liquid crystals with various mixing ratios shown in the figure, and when writing was performed by irradiating laser light, the phase transition temperature to the liquid phase was 60°C or less, indicating that the smectic liquid crystal Extremely high-quality writing is performed in a liquid crystal cell using a mixed liquid crystal with a phase-nematic crystal phase transition temperature of 44°C or higher, that is, a mixed liquid crystal with a DOCH mixing ratio of 25 to 50% by weight. When the image was enlarged and displayed using a projection optical system, an extremely bright screen with excellent contrast was obtained. As an example, in a liquid crystal cell using a mixed liquid crystal consisting of 60 weight percent OeB and 40 weight percent I) UCB, 300
When an image written by irradiating an argon laser beam with a light intensity of mW for 1 μs per point was projected onto a screen with a screen gain of 6.4 using a xenon lamp with a light intensity of IKW, the brightness was 1 oort. -1, a contrast of 7:1 was obtained.

On the other hand, good writing could not be performed under the same conditions in a liquid crystal cell using a mixed liquid crystal whose phase transition temperature to a liquid phase exceeds 60° C., that is, a mixed liquid crystal in which the mixing ratio of DUCB exceeds 50% by weight of gold. This is thought to be because the phase transition temperature to the liquid phase is too high, so even laser irradiation does not cause a complete phase transition to the liquid phase. Of course, the quality of the written image can be improved by increasing the laser light intensity or lengthening the irradiation time, but this causes significant disadvantages in terms of equipment price, power consumption, writing speed, etc., and overall performance is not good (L) A liquid crystal cell using a mixed liquid crystal containing OCB at a mixing ratio of less than 25% by weight could not project a bright screen. This is because when projecting using a xenon lamp with a light intensity of I KW, the temperature of the liquid crystal cell increases significantly due to the projection light irradiation, and the liquid crystal material enters a nematic liquid crystal phase or a state close to it, making it inoperable. So, the source of the xenon lamp - due to the fact that it cannot be made large.

In addition, even when the projection light is not irradiated, if the temperature of the liquid crystal material is close to the phase transition temperature, the degree of orientation order of the liquid crystal molecules decreases, and the difference between the transparent state and the original scattering state becomes small, resulting in a decrease in contrast, etc. cause problems. Of course, improvements can be made by cooling and controlling the temperature of the liquid crystal cell, but this results in the inconvenience of high costs and is not desirable in terms of overall performance and cost performance. As a conventional example, when writing was written to a liquid crystal cell using only OCB under the same conditions as in the above-mentioned embodiment and the projection display was performed, the brightness was 4.
The contrast was 5:1 at 0ft-L.

Further, even when conventional mixed liquid crystals other than OCB and DOCB were used, performance comparable to that obtained when only OCB was used was obtained.

In the above, we will take as an example the case of a liquid crystal display device used in a projection display device in which an image is written by irradiating a liquid crystal cell with a laser beam, and the written image is enlarged and projected using a separate optical system for viewing. υAlthough the present invention has been described, the thermal writing liquid crystal element of the present invention has superior performance even when thermal writing is performed by other means or when used as a direct-view display element, recording element, or other element. Needless to say. Furthermore, it goes without saying that the thermal writing liquid crystal element of the present invention has excellent performance even when the liquid crystal substance contains dichroic dyes, optically active VI substances, and other additives.

As explained above, according to the present invention, a thermal writing liquid crystal element having superior performance can be obtained.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between the mixing ratio of mixed liquid crystals and the phase transition temperature for explaining the present invention. Representative Patent Attorney Hakubi

Claims (1)

[Claims] Chemical formula Cs ) (17-G-G-C: The chemical formula Cl0H2 with 25 to 50 percent mass
A liquid crystal material for a thermal writing liquid crystal element, characterized in that it contains a substance represented by 10 (HΣC) as a main component.