JPS6079090A - Liquid crystal - Google Patents

Abstract

PURPOSE:To provide a triphenylene (deriv.)-contg. liquid crystal which develops a smectic phase and shows an improved resolution, etc. when used for a liquid crystal light bulb which inputs information by utilizing an electrothermal optical effect of the liquid crystal. CONSTITUTION:The liquid crystal is prepd. by adding less than 10mol% triphenylene of the formula or deriv. thereof to a liquid crystal which develops a smectic phase (e.g. n-octylcyano-biphenyl or n-decyloxycyanobiphenyl). The liquid crystal 7 is placed between a transparent electrode 3 and a mirror layer 6 of a liquid crystal light bulb consisting of glass plates 1 and 2, transparent In2O electrodes 3 and 4 for application of erasing voltage and a light absorbing layer 5 which absorbs eraser beam and convert it into heat, a projected light reflecting mirror layer 6 which enlarges and projects image information in the light bulb for display, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid crystal used in a display device or a recording device, which utilizes the electrothermo-optic effect of liquid crystal.

When cholesteric liquid crystal or smectic liquid crystal that exhibits a transparent liquid crystal structure is heated and rapidly cooled, it generally transitions to an opaque liquid crystal structure that scatters light, and if a voltage is applied during cooling, the initial transparent liquid crystal structure changes. This is well known as the electrothermal optical effect of liquid crystals. Also, this current fi
1. Several methods have been proposed for incorporating information into a liquid crystal cell by applying a partial temperature change to the liquid crystal cell to make the area opaque. Although such a liquid crystal can be used for various purposes such as an optical recording medium, the case where it is used as a display element will be described below for the sake of simplicity. In one method, images and writing are performed by irradiating a liquid crystal cell with a laser beam and causing a rise in temperature at the irradiated portion.

Only the portion becomes light-scattering, and an image can be written on a transparent background using light-scattering pixels. -This image is enlarged and projected using the optical system for full projection, so there are 4 images.

This method allows the laser beam to be focused narrowly! It is possible to display a near + density display, and by selecting an optical blur for projection that is 1 inch smaller, a brighter and thicker screen display is possible, which is attracting attention. In this case, a liquid crystal cell with a single layer of scattered crystal held in gold is called a liquid crystal light cell.

Thermal writing type liquid crystal light pulp, which allows information to be written with high resolution and bright projection-type display on a large screen, has the disadvantage that the display contrast is not always sufficient, but efforts have been made to improve this. Several laws have been proposed. A typical method is to add a certain kind of dopant to the liquid crystal material used for liquid crystal light pulp. Examples of effective dopants are given in the paper by et al. However, as they also state in this paper, the mechanism by which the dopant gives the display contrast (K shadow w) of liquid crystal light pulp is not clear, and the effectiveness of the same dopant differs when the liquid crystal is smectic liquid crystal and cholesteric liquid crystal. The only way to select an effective dopant was to conduct experiments and measure contrast ratios. the result.

No necessarily effective dopant has yet been found, and the contrast obtained by adding a dopant, which Taylor et al. reported in the above-mentioned paper, is at most 18=1.
This is not necessarily sufficient in practical terms.

When the present invention is used in a display device, the quotient is 19'? Hoe degree.

The objective is to provide a liquid crystal display with a large screen, brightness, and a high contrast ratio.

As a result of conducting experiments on a large number of dopants, the inventor of the present invention discovered a correspondence relationship between the figure of merit β and the display contrast of a certain Inno1 related to dopants, and was thus able to develop the present invention. Below, the correspondence between the sensitivity index β and β and the display contrast CR will be explained. FIG. 1 is a representative example of the results of measuring the four-time transition temperature of a liquid crystal material by varying the amount of dopant added. In Figure 1, x
It represents the molar ratio of til--band, where ■ represents an isotropic liquid phase, N represents a nematic liquid crystal phase, and I+N represents a region where both phases coexist. In FIG. 1, the regions where the snoctic liquid crystal phase and solid phase exist are omitted for the sake of simplicity. Furthermore, in the case of a mixed liquid crystal with a cholesteric liquid crystal, which will be described later, the above-mentioned nematic liquid crystal phase may be replaced with a cholesteric liquid crystal phase.

The figure of merit β corresponds to the rate of decrease in the phase transition temperature of the liquid crystal material due to the addition of a dopant, and is expressed as β-[1-(r/
Tc) )/X. Here, Tc is the phase transition temperature of the liquid crystal material to the isotropic liquid phase when X=O. 1st
In the figure, the value of β exists for both the phase transition temperature of N+I and ■ and the phase transition temperature of N and N+I, and for all of them, β1. It is expressed as βゞ. As a result of measuring β1 and βゞ (in some cases, the two coincide) for a large number of dopants, it was found that the values are larger when the geometric shape of the dopant molecule is extremely different from that of the liquid crystal molecule. I was able to find it. In addition, we created a laser-heat-written liquid crystal 2-item with a normal structure using these dopane-doped smectic liquid crystals, and irradiated it with argon laser light to achieve the electro-thermo-optical effect of the smectic liquid crystal. When all the image information writing experiments based on the above were carried out, it was found that the larger the value of β and the addition of dopant If, the larger the display contrast (CR) was able to write information. Figure 2 shows an example of experimental results, showing that the display contrast obtained when dopant with different β values was added to biphenyl-based mixed liquid crystal by adding 0.1 mol percent to the display contrast obtained when no dopant was added at all. β1 of the normalized contrast normalized by . This tendency is β1. This was true for both βゞ, and the same was true for mixed liquid crystals other than binoenyl.

In this way, the present inventor found a figure of merit for the dopant that corresponds to the contrast on the surface of the liquid crystal light pulp, and based on this empirical rule, found a dopant that overcomes the problem of display contrast, which was a drawback of the conventional liquid crystal light pulp. This is a redundant version of the present invention.

That is, the liquid crystal of the present invention is used in a liquid crystal light valve of a type that performs cool/cool writing using the electrothermal optical effect of the liquid crystal, and contains 10 mol percent or less of triphenylene or its +A>8 form. It is characterized by being a liquid crystal exhibiting a smectic phase metal.

The present invention will be described in detail below with reference to Examples. Third
The figure is a cross-sectional view showing the structure of a liquid crystal light node according to an embodiment of the present invention. In FIG. Indium oxide transparent electrode for voltage application, 5
In this embodiment, it is a cadmium telluride (CdTe) film that selectively heats all parts of the liquid crystal material and absorbs a writing laser beam for writing information and converts it into heat. Reference numeral 6 denotes a mirror layer that reflects projection light for enlarging and projecting image information written on the liquid crystal light valve, and is an aluminum (Az) film in this embodiment. 7 is a layer of smectic liquid crystal material doped with dopants. Also,
Reference numerals 8 and 9 are light beams added for explanation, 8 is a laser beam for writing, and 9 is a white light for projection.

Example 1 A liquid crystal light valve having the structure shown in FIG. 3 was created by using normal octyl cyanobiphenyl as the smectic liquid crystal and adding 43 mol percent of triphenylene, which is represented by the structural formula, for the liquid crystal material layer 7. . The argon laser light is used as the laser light 8 for this liquid crystal light valve KfF with a sight of 200mW.
When irradiated and scanned at a scanning speed of 8 m/sec, the liquid crystal material in the entire irradiated area was in a light scattering state, and image information could be written in the light scattering state compared to the transparent state in the non-irradiated area. .

The light from the xenon lamp with an output level of 1 was irradiated onto the liquid crystal light valve in which all the image information had been written as projection light 9, and the light reflected by the mirror layer 6 of the liquid crystal light valve was projected onto the screen to form an image of 100. This/period's high-resolution image is 100ftL on a large screen with a total width of 2.6m and a crystalline size of 26m.
It was possible to project images at a brightness of Further, when the display contrast ratio was measured on this projection surface, it was 18:1. In addition, when the β value of triphenylene was measured separately, it was β−βゞ=0.168.

Example 2 A liquid crystal light/cruise with the same structure as in Example 1 was prepared except that the amount of triphenylene added was 8.1 mol percent, and image information was written and projected under the same conditions as in Example 1 to obtain a display contrast. When I measured it, it was 19:1.

Example 3 As a smectic liquid crystal, a mixed liquid crystal (hereinafter referred to as mixed liquid crystal N5) was prepared by mixing normal octylcyanobiphenyl and normal decyloxycyanobiphenyl in a total weight ratio of 60:40.
It is written as P4. ) was used, except that a liquid crystal light valve having the same structure as in Example 1 was prepared, image information was written and projected under the same conditions as in Example 1, and the display contrast was measured to be 20:1.

Example 4 A liquid crystal light valve having the same structure as Example 1 was created, except that N5P4'i was used as the smectic liquid crystal, and a material to which 54 mol percent of dodecahydrotriphenylene, represented by the structural formula, was added was used for the product material layer 7. Image information was written and projected under the same conditions as in Example 1, and the display contrast was determined to be 22:1. In addition, β of dodecano-hydrotriphenylene is separately added.
When all the values were measured, βI=0.481. βゞ−0,7
It was 19.

Example 5 A liquid crystal liquid crystal compound having the same structure as in Example 1 was prepared except that the addition of triphenylene was 10.5 mol percent, and both images were obtained under the same conditions as in Example 1.
Write and project on lψ and check the display contrast)
The ratio was 12:1.

Example 6 Example 1 except that N5P4 was used as the smectic liquid crystal, 2.7 mol percent of paraterphenyl represented by the structural formula was added thereto, and the same material was used for the liquid crystal material layer 7.
A liquid crystal light valve having the same structure was prepared, image information was written and projected under the same conditions as in Example 1, and the display contrast was measured to be 10:1. In addition, when the β value of paraterphenyl was separately measured, β1−βN
=0.035.

Example 7 A liquid crystal light valve having the same structure as Example 1 except that normal octyl cyanobiphenyl without dopants was used as the liquid crystal material layer 7 (corresponding to β-〇) was fabricated.
Image information was written and projected under the same conditions as in Example 1, and the display contrast ratio was measured to be 8:1.

Example 8 A liquid crystal light valve having the same structure as Example 1 was created except that N5Pd without dopant (k) addition was used as the liquid crystal material layer 7 (corresponding to β-0), and image information was obtained under the same conditions as Example 1. When the display contrast was measured for all lines of writing and projection, it was 1o:1.

From the above examples, compared to Examples 7 and 8 in which a smectic liquid crystal without dopant 1 was added, triphenylene with a dopant of 10 mol percent or less (Example 1.2.3) or dodecahydrotriphenylene, a triphenylene derivative, It can be seen that an exceptionally good display contrast is obtained in the liquid crystal light valve using the smectic liquid crystal containing (Example 4). The β value of both dohanto and triphenylene is β1-βゞ-o16
8, dodecahydrotriphenylene is β”=0.481
゜βN=0.719, but on the other hand, in the case of Example 6 in which paraterphenyl having a small β value of β1-βゞ-0,035, which is almost zero, was used as a dopant, the display contrast was It is almost the same as when no dopant is added. Further, even in the case of Example 5 in which the amount of triphenylene added exceeded 10 molversene, the effect of the dopant was hardly obtained in terms of display contrast. It has been revealed that a liquid crystal light valve using a smectic liquid crystal containing triphenylene or a triphenylene derivative selected as a dopant with a large figure of merit β can achieve a display with particularly high contrast. Note that the structure of the liquid crystal light valve schematically illustrated in FIG. 3 is one example. For example, when the light absorption layer 5 uses long wavelength light such as a YAG laser as the writing laser light, the indium oxide transparent electrode 4 is used as the light absorption layer 5. Alternatively, the mirror layer 6 can be omitted if the liquid crystal light valve is used as a transmissive type rather than a reflective type. Further, in FIG. 2, the electrode 4 for applying the erase voltage can be omitted by replacing it with an aluminum film 6.

As described above, the essential structure of the liquid crystal light valve of the present invention is that the liquid crystal used in the liquid crystal material layer is a smectic liquid crystal containing 10 mol percent or less of triphenylene or its derivatives. These examples are not intended to limit the invention in its entirety. It goes without saying that the smectic liquid crystal may be any liquid crystal that has a smectic phase, and may also be a mixed liquid crystal with nematic liquid crystal or cholesteric liquid crystal.

As explained above, according to the present invention, high angle t (Q degrees,
1 (1) is a liquid crystal light valve that can display a large screen, brightness, and particularly high contrast ratio.

[Brief explanation of the drawing]

FIGS. 1 and 2 illustrate the phase diagram of a liquid crystal material of /b and the dependence of the normalized contrast on the 1.-Bant figure of merit to explain the present invention. The third column is a cross section M showing the structure of the liquid crystal light valve 1-7 of an embodiment of the present invention, in which 1.2 is a glass substrate, 3 and 4 are transparent electrodes, 5 is a light absorption layer, and 6 is the mirror layer, 7 is the laser beam for writing in the lfV crystal material layer 14, and 9 is the projection light. 2-/8 ] 2 4 5

Claims (1)

[Claims] A liquid crystal used in a liquid crystal light valve that writes information using the electrothermo-optic effect of the liquid crystal, characterized by being a liquid crystal exhibiting a smectic phase containing 10 mol percent or less of triphenylene or its derivatives. LCD.