JPS61197675A - Image recording method - Google Patents

Abstract

PURPOSE:To provide a method of recording an image by widening a temperature range in which an image can remain stored, by using a liquid crystal containing a 4'-alkyl-4-fluorobiphenyl and successively practicing specific means to the liquid crystal. CONSTITUTION:A method of recording image information characterized by using a liquid crystal element comprising a liquid crystal which exhibits a thermooptical effect and held between upper and lower substrates, means for heting the liquid crystal element from the outside, means for giving a corona discharge and means for locally heating with a laser beam and successively practing the means to the liquid crystal element. The liquid crystal to be used includes a liquid crystal containing a 4'-alkyl-4-fluorobiphenyl of the formula (wherein R is a 1-10C alkyl). Examples of 4'-alkyl-4-fluorobiphenyl used include 4'-pentyl-4-fluorobiphenyl and 4'-propyl-4-fluorobiphenyl.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image recording method, and particularly to a simple image recording method using a rewritable medium.

In recent years, there has been an increase in demand for the use of rewritable media for single-image recording, but conventional technology has some practical problems.For example, display devices are often used to make offices paperless. However, display devices using CRTs and the like have a problem in that it is difficult to display texts in high definition, and one image cannot be stored as an image for a long period of time. Furthermore, since hard copy images produced by so-called printers cannot be rewritten, there is a problem in that the amount of paper used increases. On the other hand, although cards such as cash cards and credit cards are widely used, there is also a demand for recording amounts and other information on these cards. Although it is possible to meet these demands by using a flat display device, for example, the device has disadvantages such as requiring a power source and having a complicated structure.

The present invention has been made in view of the above-mentioned drawbacks of the prior art. It is an object of the present invention to provide an image recording method that can make the handling of images practical.

[Means for Solving the Problems] The present invention makes the surface of the liquid crystal element transparent by means of heating the entire liquid crystal element in which a liquid crystal exhibiting a thermo-optical effect is sandwiched between substrates and by means of applying corona charging. Next, image information is written by locally heating means using laser light.

The liquid crystal used in the present invention is preferably a mixed liquid crystal of nematic liquid crystal and cholesteric liquid crystal, or a smectic liquid crystal having a nematic phase. A liquid crystal containing 4'-argyl-4-fluorobiphenyl represented by ), which represents an alkyl group having 1 to 10, is used. Examples of compounds represented by the above general formula include 4'-pentyl-4-fluorobiphenyl, 4'-propyl-4-fluorobiphenyl, etc., and all compounds in which R has 1 to 10 carbon atoms can be used alone. Alternatively, it can be used as a mixture or in combination with other liquid crystal materials.

[Function 1] The operating principle will be explained when a smectic liquid crystal is used as a liquid crystal exhibiting a thermo-optic effect.

When the liquid crystal layer is heated, the orientation state of the liquid crystal molecules becomes an isotropic liquid phase state. Thereafter, during the cooling process, the liquid crystal layer changes from a monoisotropic liquid phase state to a nematic phase and a smectic A phase, and its alignment state is stabilized in the smectic A phase. When the state in the liquid crystal layer passes through the nematic phase, when an electric field is applied, the molecular alignment in the liquid crystal layer becomes vertically aligned due to the effect of slow cooling of the liquid crystal and the alignment effect caused by the electric field, making it optically transparent. It becomes a state. On the other hand, in the cooling process,
When no voltage is applied, the molecular arrangement within the liquid crystal layer is rapidly cooled while remaining in a random state of an isotropic liquid phase, resulting in an optically cloudy state.

The liquid crystal containing the compound represented by the above general formula exhibits a smectic phase at room temperature, has a low melting point, and has a low viscosity in the liquid crystal state. For this reason,
In the image recording method of the present invention, the operating temperature and operating threshold voltage can be set low, making it extremely easy to write and erase information to the liquid crystal element.

[Example] An example of the image recording method of the present invention will be described below with reference to FIGS. 1 and 2.

Example 1 FIG. 1 is a configuration diagram showing an example of a liquid crystal element used in the present invention. In the figure, 1 and 3 are glass plate substrates. In this example, the thickness of the substrate 1 is 50IL11, and the substrate 3 is
The thickness of the substrate was 1 inch, and the inner surface of each was subjected to vertical alignment treatment, so that the space between the upper and lower substrates had a thickness of 20 islands. Between these two substrates, 4'-propylfluorobiphenyl, which exhibits a smectic A phase at room temperature, and a dye represented by the formula rwK-27?2J (Japanese photosensitive dye type), which has absorption at the wavelength of laser light, were mixed. A liquid crystal element 4 was obtained by encapsulating the material. By mixing a dye having the above properties into the liquid crystal 2, a laser with relatively low output can be used.

A method of recording an image on this liquid crystal element 4 will be explained next. Second
Each recording process on the liquid crystal element 4 is shown in FIGS.

FIG. 2(a) is a diagram showing the heating process. Here, the liquid crystal element 4 is sent in the direction of the arrow by a belt 20, and the liquid crystal element 4 is heated to an isotropic liquid phase by a power source 10 and a resistance wire or a heating lamp 5. do.

FIG. 2(b) is a diagram showing the electric field application process by the corona charger 6. Here, 20V/10 is applied to the liquid crystal 2 of the liquid crystal element 4 sent by the belt 21 in the direction of the arrow.
Apply an electric field of the same magnitude as p. In this case, while an electric field is applied to the liquid crystal 2, the liquid crystal layer needs to be cooled through an isotropic liquid phase to a smectic phase, so it is desirable that the charging width be relatively wide. As time passes, the image display surface of the liquid crystal element 4 becomes transparent.

FIG. 2(C) is a diagram showing a writing process using laser light. In FIG. 2(C), the liquid crystal element 4 sent in the direction of the arrow by the belt 22 is moved by the semiconductor laser 7.
The laser beam is emitted from the laser beam, polarized by the polygon mirror 8 in a direction perpendicular to the display surface, and further focused by the f-0 lens 9, and is rapidly heated at point A. This local heating changes the liquid crystal 2 from a smectic phase to an isotropic liquid phase, but since no electric field is applied in this process, the liquid crystal 2 is rapidly cooled and becomes cloudy. That is,
The selected surface portion of the liquid crystal element 4 is as follows.

It is locally heated by the laser beam and becomes cloudy,
An optical density difference is generated between the heated area and the non-heated area, and image information is recorded.

In this example, in the heating process, heat is applied so that the temperature at which the liquid crystal 2 becomes an isotropic liquid crystal phase is 43°C or higher, and then in the electric field application process, the corona charger 6 is heated to about 40°C.
When an electric field with an electric field strength of 30 V/20 JL was applied, the display surface of the liquid crystal element 4 became transparent. Furthermore, in the thermal writing process, the liquid crystal 2 described above is heated to 43 degrees Celsius again.
As described above, as a result of performing local heating with a 1G+sw GaAl1As laser beam (wavelength 780 nm) focused to a diameter of 20 ILm, a good cloudy image with sufficient contrast could be obtained. In this case, any image can be obtained by modulating the current applied to the semiconductor laser 7 according to the output image.

Furthermore, the cloudy image thus obtained had good memory properties even at room temperature, and the memory properties did not change even with changes in temperature or body temperature when handled by hand.

Example 2 In writing with laser light, a combination of a gas laser and an AO modulation element can also be used. In this case, it is desirable to mix in the liquid crystal material a dye that absorbs at the wavelength of the laser light used, as described above.

1) Using a He-Me laser (833 nm),
r'1l in the same mixed liquid crystal as used in the above example.
As a result of writing using a mixture of the dye shown in "-27" (BDH Trading Company name), a good white image could be obtained in the previous section.

2) Using Ar' L/- laser (488 nm),
Writing was performed using the same liquid crystal mixture as in 1) above, mixed with a dye represented by the formula "rc24s" (manufactured by Nippon Kanko Shiki), and as a result, a good image of white on a red background could be obtained.

The above 2s! Currently, gas lasers of this kind can provide higher output than semiconductor lasers, so they can record at faster speeds than when using semiconductor lasers.

In addition, as another example, PET can be used instead of the glass substrate.
When formed using a substrate such as (polyethylene terephthalate), a flexible recording medium could be obtained.

[Effects of the Invention] In the present invention, a liquid crystal exhibiting a thermo-optic effect is used as an image information recording medium, and an image is recorded by the thermo-optic effect, which saves image information more easily than conventional methods. , can be easily rewritten. Moreover, the recording medium of the present invention requires less heat to be applied during image recording.
This is an energy-saving recording method, and the medium can be handled at room temperature after recording, making it extremely practical.

Furthermore, since the compound of the general formula shown in the present invention has high mutual solubility with other conventionally known liquid crystal substances, it is possible to obtain a wide range of liquid crystal mixtures, and it is possible to obtain liquid crystal elements having desired characteristics. can. Therefore, the design of the image recording process becomes extremely easy.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of a liquid crystal element used in the present invention, and FIGS. 2(a) to (C) are explanatory diagrams of each recording process in an embodiment of the image recording method according to the present invention. be. 1.3...Substrate, 2...Liquid crystal, 4...Liquid crystal element. 5... Heat lamp, 6... Corona charger, 7...
semiconductor laser, 8... polygon mirror, 9... f-0 lens, 10
...Power supply, 2G, 21.22...Belt.

Claims (1)

[Scope of Claims] A liquid crystal element comprising a liquid crystal exhibiting a thermo-optical effect sandwiched between upper and lower substrates, means for heating the liquid crystal element from the outside, means for applying corona charging, and means for locally heating the liquid crystal element with laser light. In an image display method characterized in that image information is recorded by sequentially applying these means to the liquid crystal element, the liquid crystal used in the liquid crystal element has a general formula: ▲A mathematical formula, a chemical formula, a table, etc. ▼ (However, in the above formula, R represents an alkyl group having 1 to 10 carbon atoms.) An image recording method characterized by containing a 4'-alkyl-4-fluorobiphenyl represented by the following formula.