JPS5991187A - Liquid crystal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to liquid crystal devices, particularly to light-transmissive liquid crystal bodies for photoelectric display devices.

BACKGROUND OF THE INVENTION There are various applications where it is desirable to modulate a beam of light to form an image based on information provided as an electrical signal. An example of this is when television images or data generated by a computer are projected onto a screen. LCD is selective light book! Since it has 11 characteristics, it can be said that it is a suitable material for image projection devices.

Conventional projection devices using liquid crystal light modulators include (1)
(2) where the liquid crystal is addressed indirectly, and (2) where the cell is addressed directly using a router or an electron beam.
There are different types. An example of the former is the paper by G. Greenberg et al. [PhotoactivatedBire
fringent Liquid Crystal L
light Valve for Color Symbo
logic Display J (IEEE Tran
s, Elec.

Dev,, VOI, Ii'jD-22, NO, 9,
1975, p. 775),
Reflective twisted nematic liquid crystal cell and paper by J.P.
quid Crystal Te1evisionDi
spray J (Proceedings of t
he IEEEJvol, 55°NO, 12, 1968
2146)) There is a reflective nematic cell disclosed by K. Direct address cells described in the literature include etch and
j La5er-Addressed by Dewaei et al.
Liquid Crystal Project
n Displays J (SID Proceedi
ngs, Vol. 19. No. 1. 1978, p. 1) smectic light valves and J. Hansen et al.'s "1" 1quid Crystal Media f
or Electron Beam Recording
J (IEEE Trans, EIec, Div,
, Vol, ED-15, No. 11. 1968 No. 8
There is an electron beam addressed element that uses a cholesteric liquid crystal thin film to generate multiple images using reflected light (p. 96).

All of the optical modulators described above have drawbacks in one or more of the characteristics necessary to display high resolution, high contrast projected images in real time. Using a direct electron beam for addressing is conceptually very attractive because it allows the use of technology that is already highly advanced in cathode ray tubes (CRTs). For higher efficiency and lower cost, direct projection systems have many advantages over conventional reflective elements. Furthermore, for high switching speeds and improved display contrast, the use of nematic liquid crystals in optical modulators appears to be preferable to the conventional use of smectic or cholesteric liquid crystals.

Many compounds have already been reported and are available as materials that can be used to produce nematic liquid crystals. As an example, 4,4'-bls (trans-
4-alklcyclohexyl)-bipheny
There is ls.

The 4th Annual Conference on Liquid Crystals and Ordered Fluids was held in Vegas, Nevada, USA in April 1982.
A paper by Andensink et al. submitted to a symposium on
of Some Hydrocarbons, J.
In addition to these compounds, 4-(trans-4-alky
lcyclohexyl)-alkylbenzene
s and 4-trans-4-alklcyclohexy
l-4-alkylbiphenyls have been described. Also, Liquid Crystals and Ordered Fluids Vol. 1.2 (New York, 1974), p. 617, [5table Low Melting
Atogens of Po5tive Diele
ctric Anisotropy for Displ
ay Devices J has cyanovia z near t
, the compound has been described.

Other nematic liquid crystals include the paper by Earl Hahard et al. [Development Dual-Fre.
quencyAddressable Liquid
Crystals J.

It has been found that a liquid crystal material with an unusual combination of properties is particularly suitable as an electron beam addressed liquid crystal cell for use in modulated transmitted light in projection display devices. This characteristic is a combination of low dielectric anisotropy (ΔG) and high birefringence (Δn). Furthermore, the material must have a low viscosity over a wide temperature range and at room temperature.

OBJECTS OF THE INVENTION One of the objects of the present invention is to provide a liquid crystal suitable for use as a modulated light transmission coupler in a cell between a polarizer and an analyzer in a light transmission path. be.

Another object of the present invention is to provide a liquid crystal suitable for use in thin cells such as CRTs that can be directly addressed with an electron beam.

Yet another object of the present invention is to obtain high birefringence (bi refr
ingence=Δn), low dielectric anisotropy (dielec
tric anisotropy=ΔC) and low viscosity over a wide temperature range and at room temperature.

These and other objects will become apparent from the following description with reference to the accompanying drawings.

SUMMARY OF THE INVENTION A nematic liquid crystal body according to the invention having the preferred combination of properties described above is characterized by one or more cyanobiphenyl (cyanobiphenyl = C
B) a compound (wherein R is an alkyl group having 10 or less carbon atoms, which are directly connected) and one or more phenylschiff* hexf y (phenylcyclohexane =
PCH) compound, (where R is an alkyl group having 10 or less carbon atoms,
directly connected) and one or more shuttleless compounds represented by the following chemical formula:

In the lever, n has 1 to 4 dimensions, and R and R' have 10 carbon atoms.
the same or different alkyl groups up to and including directly connected.

By using such a liquid crystal, a light-transmissive twisted nematic liquid crystal optical pulp with high contrast and high resolution can be produced. Also, due to its low dielectric anisotropy, this liquid crystal is particularly suitable for use in display devices in which twisted nematic liquid crystal cells are directly addressed by an electron beam, and images are generated based on information provided by electrical signals. Obtainable.

In such devices, an electron beam creates a charge image on the surface of the cell, which turns selected areas of the liquid crystal within the cell on in a pattern corresponding to the charge image created by the electron gun. Polarized light passes through the on-region of the liquid crystal cell without change, but is rotated when passing through the off-region of the liquid crystal. Therefore, when light traveling away from the cell passes through the analyzer, all light except for the light that has passed through the selected area of the liquid crystal is blocked.

The light emerging from the analyzer then becomes an image corresponding to the charge image written on the surface of the electron beam cell.

In the twisted nematic liquid crystal cell of this embodiment, the molecules of the liquid crystal are oriented such that plane-polarized light passing through the cell rotates by 906 rotations unless an electric field is applied. When a sufficient electric field is applied to the cell, polarized light passes through the cell unchanged.

An example of a useful application of this property is the “sliding” liquid crystal cell.
Alternatively, there is the production of a light projection display device that acts as a filter and operates similarly to a photo slide in a common projector. In this approximation, the slide is a liquid crystal cell with an electrode arrangement that applies voltage to selected areas of the liquid crystal. This cell is placed between the polarizer and the analyzer in the light transmission path. Polarized light passes through the "on" portion of the liquid crystal cell substantially unchanged, and light passing through the "off" region of the cell undergoes a 90 degree rotation. The analyzer blocks this rotated light from passing through, and the light that passes through the analyzer is one of the cells.
An image corresponding to the area will be projected.

The thickness of the cell, which affects the sharpness of the projected image, is limited by the birefringence (Δn)K of the liquid crystal. A mixture having a relatively high birefringence is preferred, and a clear image can be obtained using a thin cell without producing polychromatic colors due to birefringence. Many liquid crystals have sufficiently high birefringence, for example Δn) 0.15
It is.

A liquid crystal having a high birefringence of about Δn=0.16 is a nematic compound containing the following eutectic mixture.

At least one selected from the first group represented by the chemical formula
Two cyanobi heptagonal compounds. Here, R has 1 carbon atom
0 or less and is a directly linked alkyl group.

At least one selected from the second group represented by the chemical formula
phenylcyclohexane compound. Here, R is a directly chained alkyl group having 10 or less carbon atoms.

This liquid crystal has a Δn suitable for using the cell as a modulated light transmission coupler between a polarizer and an analyzer, but it is
It has a relatively high C11 (permittivity measured parallel to the director of the molecule) of 6.

Generally, substances with high birefringence tend to have high dielectric anisotropy (ΔG). This means that the voltage required to switch the liquid crystal into the "on" state is relatively low for common liquid crystals with high Δn.

A high ΔC does not pose any problem when the liquid crystal is used in a liquid crystal cell where a voltage is directly applied to a fixed cell electrode, but a liquid crystal with a high C11 is not suitable for certain applications. It's profit. For example, the above-mentioned liquid crystal with C11□=r is unsuitable for use in a display device K in which the liquid crystal cells are addressed by fixed electron beams as shown in FIGS. 1 and 4.

Figure 1 shows an electron beam addressed type liquid crystal optical pulp, consisting of a liquid crystal cell αQ having a front surface 02+ and a rear surface Q41, and a writing electron gun Qe that guides a thin electron beam to a selected position on the rear surface 0 of this cell 00). The electron beam changes the potential of the selected region. Furthermore, one or more irradiation electron guns aυ are provided, which apply a wide, unfocused electron beam to the entire back surface I of cell a,
The charge image formed there is erased. Collector (collection)
Electrode C) 0) is the secondary electron emitted from the back surface of cell a0 (141 outer periphery, cell back surface Q4) or the back surface (1
The electrons reflected from 41 are collected. The six writing electron guns A, the irradiation electron gun CI, and the collecting electrode (2) are housed at least partially in a tube that forms part of the back surface of the liquid crystal cell, creating a substantially vacuum state, and these electrodes are placed at one point. It is placed outside the field of view of the liquid crystal observation window (screen) indicated by the chain line. As a result, light entering the screen from the back surface a4 of the liquid crystal cell 00 and exiting from the front surface az can be passed through the liquid crystal cell 00 without any interference and can be modulated thereby.

The face plate CI of the liquid crystal cell itself is a transparent dielectric! 41
1-1 This is preferably, but not necessarily limited to, glass; its faceplate) CI!
One side of 41 is the front surface of the liquid crystal cell (t2).The transparent face plate electrode (A) is formed on the other surface of 241, that is, the back surface (281), and is preferably made of indium-tin oxide using conventional techniques. It is a thin film of alloy (ITO).The target plate of transparent dielectric material has a transparent electrode (a).
D is determined by the spacer C321, and the back surface (outer surface) of the target plate (to) constitutes the back surface 04 of the liquid crystal cell. The gap between the transparent face plate electrode (20) and the target plate C (1) is filled with a layer of nematic liquid crystal C (41).

The liquid crystal body 131 is prevented from digging by a seal C351 of epoxy compound or other suitable material extending from the periphery of the cell 00) to the periphery. The surface of target layer C31 in contact with vIe and liquid crystal layer (9) should be properly treated so that it has a parallel (uniform) boundary alignment, that is, the alignment of the two planes is at right angles, and the inside of the nematic liquid crystal is so that it has a 90° twist.

The collector of this light valve has an electrode (a) that collects the secondary emitted electrons and repelled irradiation electron gun electrons from the back surface Q4) of the dielectric target plate (1), and also collects the light passing through this liquid crystal cell (a). 5 so that the potential image can be written on the back surface I of the target dielectric plate (101) by passing through it without any interference. The target plate (2) of this cell (a) is circular.From this, the collector electrode is placed out of the field of view of the window of the cell (QO) shown by the dashed line, and the cell a (Make the electric field regarding the collector ■ around 11 sufficiently uniform.

To explain the operation, the irradiation gun continuously supplies electron clouds to the entire back surface I of the target plate in order to maintain the same potential vfgVc as the normal irradiation gun 00 cathode on the back surface α4 of the target plate. The back area of the irradiation gun (U8 and the same potential Vfg repels the irradiated electrons, and the back area with a more positive potential than Vfg attracts the irradiation gun electrons until that area reaches vfg, and excess free electrons are attracted to the collector (a) .

The target plate (2) and the electrode (A) form a capacitor together with the liquid crystal C24 which is a dielectric. Typically, this irradiation gun cand is electrically connected to a transparent electrode @, and the transparent electrode (2G) and the back side of the target gloss are usually at the same potential vfg.
and maintains the liquid crystal in an off or unbiased state.

However, under certain conditions, a bias may be applied between the cells, in which case the cathode of the irradiation gun and the electrode (a) are not connected.

The cathode 061 of the writing gun operates at a high potential of, for example, 4.5 KV with respect to the potential vfgK of the irradiation gun, and the cathode 061 of the writing gun operates at a high potential of, for example, 4.5 KV with respect to the potential vfgK of the irradiation gun. 1 Crossover voltage■ Cr1 or higher energy is applied to the writing electron beam to the back surface of target 01 (14
), it emits more electrons than is absorbed, as shown by the characteristic curve in FIG.

As a result, the target dielectric region bombarded with write electron gun electrons will develop a voltage across the dielectric liquid crystal C24+ between that region and the more negative electrode (2G), causing that portion of the liquid crystal to Switch. The collector @ forms the return path for write and irradiation electrons. To perform this function, the collector must be at a positive potential with respect to the write and fire gun cathodes. In addition, without stabilizing the region bombarded by the writing gun beam to the collector potential Vco1, the irradiation gun a8
To recover to , the collector potential is @1 of the target OC
Crossover potential vC "1, that is, secondary electron emission ratio δ is 1
This allows the optical pulp to be used for high speed write and refresh operations rather than as a storage device.

Next, FIG. 3 will be explained. When the region α4 on the back surface of the target (2) is bombarded with the write electron beam, the potential in that region begins to rise toward the collector potential VcolK, but cannot exceed this. Since the collector potential is very below, the irradiation gun electrons are absorbed more than the emitted secondary electrons, and after the write gun current in that region is stopped, the potential in that region is lowered to fg. This allows the writing gun to write a potential image on the target, and then the irradiation gun (IIDK
The data can be erased using the write gun 00 and then written again using the write gun 00. This image is coupled to a liquid crystal, which modulates the light passing through it in accordance with the potential image.

FIG. 4 shows the writing gun 161. Irradiation gun a8 and collector electrode (
A projection device having an exhaust chamber including a), that is, a tube (g) is shown. Liquid crystal cell A [has one on the front of the chamber (to) and one on its back (one
41 facing inward and sealing. The entrance window, which is preferably an aperture covered by a planographic plate of transparent material, is located at the rear (to) K of the chamber (to), and the writing gun (161) is located off the axis of the chamber;
The field of view from the entrance window to the liquid crystal cell Qo is kept unobstructed. A first polarizer (40) is placed behind the entrance window to polarize the light incident on the entrance window.

A second polarizer, or analyzer 121, is placed in front of cell a1 to block all light from passing through, but light in the selected polarization direction passes through it without being attenuated. It can be made from a polarizer and an analyzer (4δ is a commercially available polarizer) K.

The intensity of light passing through the analyzer (421) from a particular area of the liquid crystal cell is determined by the writing gun, since the intensity of the output light from the analyzer (421) is a function of the relative polarization direction of the analyzer and the light incident on it. It depends on the extent of the "on" K-switched region.As a result, the polarization modulation produced by the twisted nematic liquid crystal cell is converted by the polarizer and analyzer into an intensity modulation of the light beam (41). By matching the polarization direction of the photons with that of the polarizer, the intensity of the ultimately obtained image increases according to the intensity of the writing gun electrons. By varying the intensity of the writing gun electron beam, the image intensity decreases as the intensity of the writing gun electron beam increases.

A lens (44J) is used to guide the light from a light source such as a lamp (481) as a light beam through the window of the liquid crystal cell A from the entrance window.Other lens decoys direct the image focus created by the liquid crystal to the screen. Air is applied to the writing gun Oe, which includes a manual deflection plate 63 and a horizontal deflection plate eiη, connected to an observation surface such as the surface of the electron beam, and which deflects the writing electron beam onto the target crocodile beam (A). Displays the image determined by the input signal on the screen□
to be projected.

In a display device that uses an electron beam to write a charge image on the cell surface, the liquid crystal must have a low dielectric anisotropy of, for example, El, (13). The composition of the liquid crystal is very important because the writing beam current and voltage that switch at the speed required for integral monochrome TV image display are significantly reduced.As the beam voltage and current are reduced, the deflection plates (all, 63) The voltage to be applied is reduced, and as a result, the required power, device size, weight, and working capacity are reduced to practical levels.

A low C11 liquid crystal is obtained by adding a third group of compounds to the eutectic mixture described above. This third group includes compounds represented by the following formula.

Here, n is an integer of 1 to 4, R and R are both alkyl groups having 10 or less carbon atoms, and are tangentially linked, and they may be the same or different. An example of such a compound contains two phenyl groups as given by the following formula.

It is necessary to contain 5 to 40% by weight of the third group of compounds. Unexpectedly, these compounds significantly reduce the dielectric anisotropy without significantly changing the birefringence of the final liquid crystal. In order to create a liquid crystal that contains the largest amount of Group 3 compounds and has a wide operating temperature range, several different compounds from Group 3 are used simultaneously, and multiple compounds are combined with one or both of Group 1 and Group 2. It may be advantageous to form an original eutectic mixture consisting of a combination of compounds.

When a compound from the third group is added to a eutectic mixture of compounds from the first and second groups, the birefringence (Δn) changes slightly, but its dielectric anisotropy (ΔC) decreases dramatically. I will do it. An added effect of this is that the temperature range of the liquid crystal with the third group compound is wider than the temperature range of the eutectic mixture before its addition.

In many cases, it is necessary to add substances of the fourth group to lower the melting point of the liquid crystal to a usable range.

A particularly suitable compound for this purpose is represented by the following formula.

Here, R and R may be the same or different (both are directly linked alkyl groups with 10 or less carbon atoms. When this compound is used, the birefringence and dielectric anisotropy are significantly affected. Although this is not the case, the temperature range of the liquid crystal appears to be narrower.Therefore, it is preferable to keep the amount of the fourth group compound to a minimum of less than about 20% by weight.

Furthermore, compounds of the fifth group can be added to reduce excessive viscosity and increase the operating temperature range of the liquid crystal according to the invention. A particularly suitable compound for this purpose is represented by the formula:

Here, R and R' may be the same or different, and both are directly linked alkyl groups having 10 or less carbon atoms.

When the compounds of the formulas '(■) and (V) are used in a liquid crystal, the effect is that more of the compound of the formula (Otori) is dissolved. However, the amounts of compounds of formula (IT) and (V) used should be minimized. Otherwise, if the proportion of the compound of formula (1) decreases too much, an undesirable situation will occur in which the birefringence index decreases.

〔example〕

The liquid crystal cell can be composed of commercially available materials listed below.

Table-1 2nd group 3rd group 4th group 5th group *Manufactured by BDH Pharmaceuticals, Ltd
In each case, a eutectic mixture is first prepared by combining appropriate amounts of one or more compounds selected from the first and second groups. Next, a substantially nonpolar Group 3 compound is added to this eutectic mixture to lower the ΔC. In some cases, compounds of the fourth group are added to lower the melting point. Further, a compound of the fifth group may be added to the eutectic mixture to reduce the viscosity of the liquid crystal.

In this way, various liquid crystal materials are made, and their birefringence (
Tests were made for Δn), dielectric anisotropy (ΔC), melting point (mp) and clearing point (Cp). A list of successful liquid crystal materials is listed in Table-2. Other compounds tested were:
It was excluded from Table 2 because it was smectic, crystallized, or too viscous to be used at room temperature. ■Each liquid crystal listed in Table 2 was tested using a fixed electrode cell. All liquid crystal elements worked, but for the liquid crystal element in Example 3, 1
1 was 13.0 or more, which was not suitable. Considering all factors, the liquid crystal of Example 7 is particularly good because it has a very high Δn, a very low ΔC, and a wide temperature range. The liquid crystal of Example 1 was tested using the electron beam addressed liquid crystal cell described above. Satisfactory projection of black and white Ten Vision images with a wavelength of 0.6 μm was obtained. The cell used here has a separation D = 10 μm, a write gun beam current of 14.7 μm, and a beam width of 4.4 mils (0,1 μm).
113), tense mica was used as the target. The experimental results are as follows.

Display switching speed: 25m5 Contrast ratio: 59:1 Resolution: 8.9 lines/III Writing speed: 16 imsAlthough the preferred embodiments of the present invention have been described above, the present invention should not be limited to only such embodiments; It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention.

Effects of the Invention According to the liquid crystal element of the present invention, low dielectric anisotropy, high birefringence, and a wide temperature range can be obtained by combining special compounds. Further, by adjusting the mixing ratio of the compounds used, these characteristics can be selected to the optimum values for a given purpose. Therefore, the liquid crystal body of the present invention is particularly preferred for use in an electron beam addressed projection type image display device to obtain images with high switching speed and high contrast ratio.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an optical pulp using the liquid crystal element of the present invention, Figure 2 is a secondary electron emission characteristic curve diagram of an example of an electron beam target used in the optical pulp of Figure 1, and Figure 3 is a diagram of the target. FIG. 4 shows a waveform diagram of the potential change in the written area and the writing gun current, and FIG. 4 shows a block diagram of the light valve of FIG. 1 used in the projection device.

Claims (1)

[Scope of Claims] 1. A liquid crystal body comprising a mixture containing a cyanobiphenyl compound, a phenylcyclohexane compound, and a substantially nonpolar compound each represented by the following general formula. Here, R and R' are an alkyl group having 10 or less carbon atoms, may be the same or different, and are an integer from n to 4. 2. C3HII as R of the above cyanobiphenyl compound
and C? H1fi was used, C3H and CBHII were used as R of the above phenylcyclohexane compound, and C and H□ were used as R and R' of the above nonpolar compound, respectively. and C3Hy, n=2. The shrimp liquid crystal body according to claim 1. 3. The weight ratio of the sum of the cyanobiphenyl compound and phenylcyclohexane compound to the nonpolar compound is approximately 3.
:A liquid crystal body according to claim 2 selected in item 1.