JPS6388518A - Thermal image forming device - Google Patents

Abstract

(57) [Abstract] 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 a thermal image forming device, particularly as a thermo-optic conversion element, in which optical rotation of a plane of polarized light passing through a liquid crystal is controlled by the helical pitch of the liquid crystal,
The present invention therefore relates to a thermal imaging device incorporating cholesteric liquid crystals arranged in a temperature-dependent manner as thermo-optic conversion elements.

An example of such an image forming apparatus is "Applied Optics" published in 1979, Vol. 18, No. 2.
It is described on page 607. A case example of such a device utilizing compensated cholesteric liquid crystal mixtures is also described in UK Patent Application No. 8,615,750.

In such a device, the pitch of the liquid crystal helix must assume its natural value at any particular temperature so that the optical rotation due to polarization varies continuously as a function of temperature. Therefore, the total twist of the liquid crystal must also change continuously.

For this purpose, the average direction of the long axes of the liquid crystal molecules, ie the director, must be able to rotate freely at at least one boundary of the liquid crystal adjacent to one of the plates containing the liquid crystal. The ideal liquid crystal alignment for such an image forming device, in which the liquid crystal is enclosed between two parallel plates, is a plane. That is, the liquid crystal director is parallel to the grate at all points. In the plate on which polarized light is incident, it is desirable that the director be parallel to the polarization direction of the light, and in other plates.

The director must be able to rotate freely.

However, obtaining such alignment is difficult. This is because conventional planar alignment tends to give the director a preferred orientation.

[Summary of the invention]

An object of the present invention is to use a presteric device as a thermo-optic conversion element, which fixes the director of the liquid crystal adjacent to one of the two plates confining the liquid crystal in a predetermined orientation, while allowing the director adjacent to the other plate to rotate. An object of the present invention is to provide a thermal image forming device incorporating a liquid crystal.

That is, the present invention provides a thermal image forming apparatus incorporating a cholesteric liquid crystal confined between two opposing surfaces as a thermo-optic conversion element, in which the alignment of the liquid crystal adjacent to one of the opposing surfaces is planar; The present invention provides a thermal image forming apparatus characterized in that the alignment of the liquid crystal in contact with another surface is homeotropic.

Which of the following is an embodiment of the present invention? The accompanying drawings are described for purposes of illustration only.

FIG. 1 is a schematic diagram of the device of the present invention, and FIG. 2 is a graph plotting optical rotation versus temperature characteristics of the device of the present invention.

First, referring to FIG. 1, the thermal image forming apparatus of the present invention is separated by a spacer 8. It consists of a liquid crystal 1 inserted between two plastic thin films 2.3 several microns thick. Each thin film 2.5 has a respective 79 inment J@4.5, which effectively affects the alignment of the liquid crystals adjacent to each layer.

The alignment layer 4 is a planar alignment layer, which is formed by rubbing the plastic thin film 2 in a non-oriented manner, or by applying polyamide or polyvinyl acetate (PVA) to the thin film 2.
It can be obtained by attaching another polymer such as and rubbing this polymer layer. Other planar alignment methods known to those skilled in the art can also be used.

Alignment ffi 3 is a homeotropic alignment layer that can be multiple, monolayer, several molecular layers, or lecithin or organic Schiff/octadecyl-triethoxysilane (OTS).
), e or any other surfactant. The latter is thermostable.

Therefore, it is particularly suitable. Similarly, there are other suitable methods to obtain the required alignment.

Those skilled in the art will know.

Therefore, the direction of the director of the liquid crystal 1 changes in the mixture, as shown in FIG. That is, the alignment layer 4
The director adjacent to is parallel to the plane of the thin film 2 and is at an angle of -or 2 inch. The director adjacent to the alignment layer 5 can thus pivot about its axis perpendicular to the membrane 3. This is because the alignment layer 5 has no effect on this turning.

Adjacent to the thin film 2, the dichroic thrush transmits infrared rays and reflects other wavelengths? -6fc
establish. The angle of the mirror 6 is set so that the light from the light source 7 can be directed toward the thin film 2. lens 9
Using seven.

The light from the light source 7 is made parallel and a fc polarizer 11 is provided to polarize this light in a direction parallel to the direction of the director of the liquid crystal adjacent to the thin film 2. Then, an infrared lens 13 is provided at a position where infrared rays from the field of view can be focused on the liquid crystal. Also.

A chopper 15 is provided to interrupt the incident light beam. A detector 17 such as a TV left camera is provided on the side of the thin film 5, and an analyzer 19 is provided between this detector 17 and the thin film m5. The electrical output of detector 17 is coupled to signal processor 21 . The liquid crystal cell is enclosed within a temperature controlled enclosure 181 which is transparent to infrared radiation from the field of view to be imaged.

The liquid crystal 1 consists of two classes of cholesteric liquid crystals, namely cholesteryl chloride with a right-handed helical structure or twist and cholesteryl myristate with a left-handed helical structure or twist.
A mixture of 1.6:1.0 (weight ratio) is sufficient. Also,
This liquid crystal mixture is. The pitch shows a helical structure that is sensitive to temperature.

Specific compensation temperature TN-4 2. This pitch becomes infinite at 5℃. This is because the right-handed helical structure changes to the left-handed helical structure at this temperature. Carn in 1977
Published by S. brldge Universities Press. 'Liqu' by Chandrasekhar
As shown in Figure 4, 1.5 of 1d Crystal, the optical rotation of the mixture becomes very high with respect to temperature within a range of 1°C of temperature TN.

When using the device, the operator/closure 18 must be heated to a temperature T.
Maintain the temperature at either just above or below N. When infrared light is focused on mixture 1, mixture 1 causes light source 7 to
The polarization direction of the light from the is rotated by an amount that depends on the intensity of the incident infrared radiation. Therefore, since the analyzer 10 is provided between the detector 17 and the thin film S, the pattern of the light rays from the light source 7 which the detector receives also depends on the intensity of the infrared radiation incident on the mixture 1. In this way, an image corresponding to the pattern of infrared radiation incident on the mixture 1 can be formed. In this case, the signal processor 21 outputs an output signal which is used to enhance the contrast of the light pattern incident on the detector 17 by electronic means to form an image.

Because the temperature of the liquid crystal mixture is maintained very close to the temperature TN, the sensitivity of the device to temperature is high, so that the device can detect even small temperature changes within the field of view. The 1°C sensitivity range of liquid crystals is relatively large for such devices, so the required temperature stability of the device is only modest compared to that often required for thermal imaging devices! It's not important. Ambiguity is avoided by maintaining the mixture at a temperature slightly offset from the compensation temperature.

Alternatively, if the mixture 1 is held at its compensation temperature while the chopper 15 is cutting off the incident light from the field of view, the dark field signal of the detector 17 will be independent of the thickness of the liquid crystal mixture 17 and the processing The signal processing by the device 21 is facilitated.

The birefringence of the liquid crystal mixture 17 at the compensation temperature is also very sensitive to temperature. When this is utilized in an image forming apparatus, it becomes possible to optically display the temperature of infrared rays incident on the image forming apparatus.

Many other compensating liquid crystal mixtures are suitable for use in thermal imaging devices according to the present invention. Such a mixture is similar to the above device.

Can be integrated into the same common equipment. An example of such a mixture is a mixture of two biphenyl chiral dopants of the following structural formula in a nematic host. These two types of dopants induce mutually opposite twists within the host.

and another mixture of CB15 from BDH in ZL11132 from Kierck and Zl from Merck.
, l811. FIG. 2 shows the optical rotation of this mixture as a function of temperature and therefore liquid crystal pitch.

The chain line indicates the formula: ρ-2πd/P. However, ρ is optical rotation, d
is the liquid crystal cell thickness for the corresponding total plane alignment, and P is the liquid crystal pitch.

As can be seen from the M2 diagram, changes in director alignment have the effect of reducing the effective float of the cell. Therefore, the slope of the graph becomes smaller. The solid line in FIG. 2 shows the required continuous change in optical rotation depending on pitch and temperature.

The temperature sensitivity of the device of the present invention can be further improved by making one of the cholesteric components near the smectic phase change at the compensation temperature. This increases the temperature-dependent rate of pitch change and therefore the temperature-dependent rate of change of optical rotation.

Although the illustrated device utilizes a compensating liquid crystal device, in accordance with the present invention, the plane and homeotropic alignment of the liquid crystal adjacent each confinement surface is adjusted to compensate for the uncompensated cholesteric component utilized in the thermal imaging device. can also be used.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus of the present invention, and FIG. 2 is a graph plotting optical rotation against temperature characteristics of the apparatus of the present invention. In Figure 1, 2.3 is thin fat, 4.5 is alignment layer,
6 is a dichroic mirror, 7 is a light source, 8 is a spacer, 9 is a lens, 11 is a polarizer, 13 is an infrared lens, 1
7 is a detector, 19 is an analyzer, and 21 is a signal processor. Patent Applicant: The General Electric Company. B, L, C.

Claims (13)

[Claims] (1) In a thermal image forming device incorporating a cholesteric liquid crystal confined between opposing surfaces as a thermodynamic conversion element, the alignment of the liquid crystal adjacent to one side of the surface is planar, and the alignment of the liquid crystal adjacent to the other side of the surface is planar. A thermal image forming device characterized in that liquid crystal alignment is homeotropic. (2) The device according to claim 1, wherein the planar alignment is obtained by non-directionally rubbing the one surface. (3) The device of claim 1, wherein said one surface is a polymer. (4) The device of claim 1, wherein said homeotropic alignment is obtained by said other layer of surfactant. (5) The device according to claim 4, wherein the surfactant is an organosilane octadecyl-triethoxysilane. (6) The liquid crystal is a compensated cholesteric liquid crystal obtained by mixing two types of cholesteric liquid crystals, one of which has a left-handed twist and the other has a right-handed twist; Apparatus according to claim 1, having a composition such that it exhibits an infinite pitch at said compensation temperature and configured to operate with said mixture maintained in the region of said compensation temperature. (7) Claim 6, wherein one of the cholesteric liquid crystals is in the vicinity of a smectic phase change at the compensation temperature.
Equipment described in Section. (8) One of the cholesteric liquid crystals is cholesteryl myristate and the other is cholesteryl chloride,
Apparatus according to claim 6. (9) the mixture is a mixture of two biphenyl chiral dopants in a nematic host, and these dopants exhibit mutually opposite twists within the host;
Apparatus according to claim 6. (10) The above two dopants have the following structural formulas,
Apparatus according to claim 9. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ and ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (11) The above mixture is SLI1132 manufactured by Merck.
CB15 manufactured by BDH and S8 manufactured by Merck
7. The device according to claim 6, wherein the device is a mixture of 11. 12. The method of claim 6, further comprising means for maintaining the mixture at a temperature offset from the compensation temperature in order to avoid ambiguity in the output signal of the device. (13) A chopper is provided for blocking infrared radiation incident on the device, and means are provided for maintaining the mixture at the compensation temperature while the chopper is blocking incoming radiation from the device. The device according to item 6.