JPS61118492A - Liquid crystal composition for laser - Google Patents

Abstract

PURPOSE:A liquid crystal composition, obtained by adding a dyestuff having a specific adsorption wavelength to a liquid crystal material having a smectic A-nematic phase transition point, and capable of thermal writing even at a relatively low output of laser beam. CONSTITUTION:A liquid crystal composition obtained by adding (B) a dyestuff having an absorption wavelength close to oscillation wavelength of GaAlAs semiconductor laser to (A) a liquid crystal material having smectic A-nematic phase transition point. Preferred examples of the above-mentioned composition include a mixture of 3wt% dyestuff expressed by the formula with a liquid crystal material 4-cyano-4'-n-octylcyanobiphenyl, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquid crystal composition for thermal writing using laser light.

(Prior art) The thermo-optic effect of liquid crystals having a smectibuk A-nematibuk phase transition point (TsN) can be used for writing on liquid crystals by using laser light as a heating means, and a light valve (Furube et al., Japan Society of Applied Physics 1982 Autumn Proceedings 28
Research is underway with the aim of applying it to p- to -I+) and input devices (see Nagae et al., Japan Display, 1983 +3-6).

This electrothermo-optic effect is based on the fact that the alignment state of liquid crystals changes due to heating and cooling. A liquid crystal cell is produced in which smectic A liquid crystal is injected between horizontally aligned transparent substrates. When writing, this liquid crystal cell is once heated by a laser beam to a temperature higher than the temperature at which it becomes an isotropic liquid phase.

Subsequently, when a voltage is applied and the mixture is cooled, it assumes a focal conic arrangement and becomes cloudy. This corresponds to the state of random molecular arrangement near the phase transition point being frozen (memory). On the other hand, when cooled without applying a voltage, they form a horizontal array and become transparent.

(Problems to be Solved by the Invention) When thermal writing is performed on a liquid crystal using a laser beam, it is desired to increase the efficiency of heat absorption of the liquid crystal, that is, to increase the efficiency of using the energy of the laser beam.

An object of the present invention is to provide a liquid crystal composition that easily absorbs the energy of laser light.

(Means for Solving the Problems) The liquid crystal composition for laser thermal writing according to the present invention has a liquid crystal material having a smectic A-nematic phase transition point.
A dye having an absorption wavelength close to the oscillation wavelength of the GaALAs semiconductor laser is added.

(Operations and Effects of the Invention) When performing thermal writing using a GaA, iAs semiconductor laser (wavelength 780 ns), the laser light is absorbed by the above dye, so the efficiency of heat absorption by the laser light of the liquid crystal composition is reduced. Go up.

Therefore, thermal writing is possible even if the output of laser light is relatively low.

(Example) The present inventors have discovered that in order to increase the efficiency of heat absorption by laser light in liquid crystals, it is possible to use a dye that has an absorption peak at a wavelength close to the oscillation wavelength of the laser light. Ta.

GaA and IAs enable compact system design
In a semiconductor laser, the oscillation wavelength is 780 ns or more. By using an anthraquinone dye as a dye with an absorption excitation wavelength close to 780+a, relatively low output energy (~1
2 mW), thermal writing became possible.

Writing method Figure 1 schematically shows part B, which was heated to above the smectic-amatic transition point by laser light irradiation and then cooled without applying any voltage, and non-irradiated parts A and C, which were not irradiated with laser light. show. Here, a liquid crystal composition 4 is sealed in a liquid crystal cell in which substrates 1.2 are placed facing each other and bonded together with a sealant 3, and each group 1i, 1.2 has a transparent electrode 5. 6 and an alignment film 7.8 are formed. Note that the liquid crystal composition 4 includes liquid crystal molecules 4a, 4. . . . and dye molecules 4b, 4b, . Non-irradiated areas A and C
In this case, the arrangement is in a disordered focal conic arrangement, so the dye absorption is weak. And you can see scattered light.

On the other hand, in the irradiated part B, the dye absorption is strong because the arrangement is parallel. Therefore, by visual inspection, A, B, C
It becomes possible to identify the contrast of each part of the image.

The writing time per pixel is as shown in Figure 2.
It is defined by the time t required for the liquid crystal to rise above the smectic A-nematic transition point TsN, return to the nematic phase, and become monochalconic.

A difference exists between the capacitance C1 of reading methods A and C and the capacitance C8 of B. In other words, C1 = εk・S/d C3=(ε9+2εk)・S/(3d) Here, εk and εk are the permittivity when the electric field is applied parallel or perpendicular to the molecule, respectively. , S is the pixel area, and d is the thickness of the liquid crystal. Therefore, the written information can be read by reading the capacity (see Nagae et al., cited above).

Elimination method With a voltage applied to the liquid crystal, the temperature of the liquid crystal is raised to smectic A - nematic transition 11 or higher by heating, and then cooled to a smectic state. Heating methods include a method of irradiating a laser beam and a method of using a heater electrode formed on a glass substrate. The former does not require a heater circuit, so the element is simplified. The erased state is a weakly absorbing scattering state.

Next, experimental examples regarding the liquid crystal composition according to the present invention will be explained. The liquid crystal composition is made by adding 31t% of a dye having the structural formula to the liquid crystal material 4-cyano-4'-n-octylanobiphenyl (BDF (Company-24)).
It is a mixture. This liquid crystal material transforms from a crystalline to a smectic A phase at 21.5°C, further transforms to a nematic phase at 33.5°C, and changes to an isotropic liquid phase at 40.5°C. This liquid crystal composition is sealed in a liquid crystal cell.

The glass substrate forming the liquid crystal cell is a float glass having a thickness of 0.7 mm, and a transparent electrode made of indium oxide and a dielectric film made of polyimide are sequentially formed thereon. The polyimide film is subjected to alignment rubbing treatment using a polishing cloth so that the alignment is parallel to each other. Note that the electrode is formed as a dot matrix pattern, but in the case of a simple light valve type that does not require a capacitive reading function, an entire surface pattern of indium may be used.

Using the thus produced liquid crystal cell 11 filled with the liquid crystal composition according to the present invention, thermal writing and reading are performed using an apparatus having the configuration shown in FIG.

At the 31st K1, the G-A4As laser 13 supplied with power by the power source 12 emits laser light 14. The laser beam 14 irradiates the liquid crystal cell II via a glosser 15 and a lens (Olympus LWD MPLAN44) 16. Note that the laser 13 and lens 16 are attached to an adjustment table 17. The light transmitted through the liquid crystal cell II is sent to the photodiode (SPD-102) of the light receiving circuit 18 located approximately 20 cm away from the lens 6.
incident on .

The optical output energy is obtained by reading the voltage drop across a load resistor (10Ω) connected to the photodiode with a voltmeter weight 9. That is, since the sensitivity of the above photodiode is approximately 0.5 A/W, the prior output energy is (V/1G) 10.5 [W].

The table shows the change in the previous output energy when the liquid crystal cell +1 is irradiated with the laser beam 14. Introduction, liquid crystal cell 1
1 from the optical path of the laser beam 14, the laser beam 1
4 is directly irradiated onto the light receiving circuit 18, and then the gloss
After closing the shutter 5 and installing the liquid crystal cell 11 in the optical path, open the shutter = 15 and set the shutter to 0 with reference to when the shutter is open.
The light output energy (expressed as pressure drop) was measured at three time points: seconds later (immediately after opening), 10 seconds later, and 60 seconds later.

As is clear from the values in the table, the optical output energy changes greatly from 1 = 0 to ( = 10 seconds) for the output energy of the laser light of 12-W and 20 mW. In other words, the laser light is absorbed by the dye. On the other hand, when the output energy of the laser beam is 4W, the change in the optical output energy is constant within the error range, and the change can be observed visually. From the above experimental data, it was confirmed that the transmittance changes with respect to a small output energy of 12-W.

The dye used in this example exhibits a pale green color, but a method for increasing the contrast during display is to mix it with other dyes to make it black. For example, it can be mixed with and to make black.゛In addition, liquid crystal materials that exhibit a smectic A-nematic phase transition point include:
In addition, the following compounds can be used, for example.

4-cyano-4'-n-nonyldiphenyl, 4-cyano-4'-n-undecylbiphenyl, 4-cyano-4°
-n-octyloxybiphenyl, 4-cyano-4°-n
-Nojimachiquinobiphenyl.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a liquid crystal cell showing changes in the liquid crystal composition due to laser light irradiation. FIG. 2 is a graph showing temperature changes during thermal writing. FIG. 3 is a block diagram of an experimental apparatus for transmitting laser light through a liquid crystal cell. 11...Liquid crystal cell, 12...Power supply, +3
...GaA, 9As laser, 14...Laser light, 15...Shutter, +6...Lens, 17...Adjustment stand,...18...Light receiving circuit, 19...Voltmeter. Patent applicant: Sharp Corporation representative
Lawyer Patent Attorney Blue and White Two Idiots Fig. 1 Laser It (GOA7AS χ-780nm) Trouble Iron Hair Hikiton 4d Noyani ・1 ＼ Dai No 1 ＼ 251st Hour Fig. 3

Claims (3)

[Claims] (1) A liquid crystal composition for laser thermal writing, which is obtained by adding a dye having an absorption wavelength close to the oscillation wavelength of a GaAlAs semiconductor laser to a liquid crystal material having a smectic A-nematic phase transition point. (2) In the liquid crystal composition for laser thermal writing described in claim 1, the laser is characterized in that the above-mentioned dye contains a compound having the following structural formula ▲ Numerical formula, chemical formula, table, etc. ▼ Liquid crystal composition for thermal writing. (3) In the liquid crystal composition for laser thermal writing according to claim 2, the above-mentioned dye is the above-mentioned compound and one or more dyes for producing black color by mixing with the compound. A liquid crystal composition for laser thermal writing, comprising: