JPH03225322A - Recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium enabling rapid vanishment with pyroelectric current by successively laminating an electrode, a layer of a ferroelectric substance, a layer of a light absorbing substance, an oriented layer, a recording layer of a high molecular liq. crystal and a transparent electrode on a substrate. CONSTITUTION:An electrode 7, a layer 6 of a ferroelectric substance, a layer 5 of a light absorbing substance, an oriented layer 3, a layer 4 of a high molecular liq. crystal and a transparent electrode 2 are successively laminated on a substrate 1 to form a recording medium. When this medium is irradiated with light having high density energy such as semiconductor laser light from the electrode 2 side in accordance with a recording signal, a record is formed in the irradiated part of the layer 4 by heating to the phase transition temp. In order to vanish this record, a short circuit is caused between the electrodes 2, 7, the temp. of the layer 4 is so regulated as to keep the liq. crystal state by irradiation with light, pyroelectric current is generated by a change of the temp. of the layer 6 due to heat generated by the layer 5 by irradiation with light and an electric field is applied. Rapid vanishment is thus enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rewritable recording medium using polymeric liquid crystal.

[Prior Art] Due to the spread of OA in recent years, the amount of various information data has been increasing steadily. For this reason, optical disk recording devices are being actively developed as a means for storing such information data at high density. However, in order to organize and edit information or access computers, it is essential that the recording material be capable of reversibly recording and erasing information, and from this perspective semiconductors such as chalcogenide or thermal Development of plastic resin as a recording material is underway. However, the above semiconductors have the drawback of being toxic or requiring processes such as vapor deposition, which increases costs, and the above resins use dyes as light absorbers, so the lifespan of the recording material is short or the contrast is poor. There is a problem in that a low and sufficient signal-to-noise ratio cannot be obtained, and so far no one has been found that can be put to practical use.

As a solution to the above problems, Japanese Unexamined Patent Publication No. 58-12
No. 5247 discloses a recording material characterized in that a transparent aligned state and an opaque random state of a polymer liquid crystal can be reversibly changed by heat and an electric field. Here heat can be generated by irradiating the light absorber with laser light, i.e. as a writing means.
Laser light can be used. Such an example is also disclosed in JP-A-60-114823, in which polysiloxane is used as the polymeric liquid crystal.

In order to repeatedly use a recording medium that uses polymeric liquid crystal as a recording material, it is necessary to change the recorded state (generally an opaque random state) to the base state (generally a transparent array state).
need to be returned to. Various methods have been proposed in the past to return from a random state to an arrayed state.
Generally, the polymer liquid crystal is heated to the liquid crystal temperature and an electric field is applied from the outside. Using an external electric field complicates the system, making it more difficult to speed up, override, etc.

[Problems to be Solved by the Invention] The present invention provides heat and heat to the recording layer by passing a pyroelectric current generated from a ferroelectric material between electrodes due to a temperature change due to heat generation in the light-absorbing material layer due to light irradiation. The aim is to provide a recording medium in which recording can be erased by applying an electric field to rearrange polymer liquid crystals.

[Means for Solving the Problems] The structure of the present invention for solving the above problems includes an electrode, a poling-treated ferroelectric material layer, a light-absorbing material layer, an alignment layer, a recording layer consisting of a polymeric liquid crystal, and This recording medium basically has a layered structure in which transparent electrode layers are sequentially laminated.

Specifically, the present invention integrates a pyroelectric material layer that exhibits the property of generating ferroelectric current due to temperature changes, a recording layer made of polymeric liquid crystal, and a light-absorbing material layer, and absorbs light by light irradiation. This is a recording medium that enables recording to be erased by applying an electric field and heat to the recording layer by passing a pyroelectric current generated by temperature changes due to heat generation in the layer between electrodes, and rearranging the polymer liquid crystal. .

Also, if the polarization amount is P1 and the temperature is T, then the pyroelectric constant PY is PY-d
It is expressed as P/dT, and if t is the pyroelectric current, then P-IPXt, so I p = Py XdT/
It becomes dT. That is, the pyroelectric current is determined by the amount of polarization associated with temperature change. A copolymer of vinylidene fluoride and trifluoroethylene, which is a typical ferroelectric substance [
The dielectric hysteresis curve of P(VDF/TrFE)] and the value of EcSPr are shown in Table 1 and FIG. 3 below.

Table 1 To obtain a pyroelectric current from a ferroelectric substance, it is necessary to apply an external electric field to align the direction of polarization, that is, to perform a poling process and to change the temperature by an appropriate method. Poling treatment involves sandwiching a ferroelectric material between electrodes and applying an electric field higher than the coercive field, or applying corona charging with an appropriate charger with an electrode provided on only one side of the ferroelectric material layer to increase the surface potential. This can be done by increasing the coercive field potential to a level higher than the coercive field potential.

To explain the basic layer structure with reference to the drawings, as shown in FIG. A material layer B and an electrode 7 are laminated in this order.

In contrast to the example shown in FIG. 1, FIG. 2 shows an electrode 7, a ferroelectric material layer 6, a light absorbing material layer 5, an alignment layer 3, and
, a polymer liquid crystal layer 4, and a transparent electrode 2 are laminated in this order.

By annealing the recording medium thus produced at a liquid crystal temperature, a uniform alignment state can be obtained.

By locally irradiating this recording medium with high-density energy light such as semiconductor laser light from the transparent electrode side in accordance with the recording signal, the recording medium is heated to a phase transition temperature or clearing point, and then cooled to heat the irradiated area. A difference in light scattering, optical activity, birefringence, or light absorption occurs, and a record is formed.

To erase a record, the transparent electrode and the electrode are short-circuited and light is irradiated to bring the polymer liquid crystal layer to the liquid crystal temperature.The pyroelectric current is generated by the temperature change in the ferroelectric material layer due to the heat generation of the light-absorbing material layer caused by the light irradiation. This is done by generating and applying an electric field.

The polymer liquid crystal used in the present invention can be of any known type, has a liquid crystal group in its main chain or side chain, and has an average molecular weight of 500 or more.

Further, the polymer liquid crystal may be crosslinked.

Furthermore, it is more preferable that the crosslinking is photocrosslinking.

Specific examples of polymer liquid crystals used are listed below.

In addition, In specific examples, * indicates an asymmetric carbon atom.

O2 CR3 (CH2) Support N None N 2) Hs 9? 1-Dc4CN 0 Ichibo◇%CN 1 1←◇()cN 02 (CH2)I CH3 O 0(Co(CH2) ll-C0+ v-C0-0C
H2-CH-C2I35co-beheoc-)o- Such polymeric liquid crystals are usually used alone or in combination, and furthermore, other low-molecular liquid crystals are used.

The purpose of this low-molecular liquid crystal is to control the viscosity, phase transition temperature, etc. of the polymeric liquid crystal to improve recording characteristics and erasing characteristics. Known low-molecular liquid crystals such as nematic, smectic, or cholesteric liquid crystals can be used.

Using such polymeric liquid crystals, for example, ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, esters such as butyl acetate, ethyl acetate, carpitol acetate, butyl carpitol acetate, methyl cellosolve, ethyl cellosolve, tetrahydrofuran, etc. Dissolved in ether type solvents such as toluene, aromatic type such as toluene, xylene, halogenated alkyl type such as dichloroethane, N,N-dimethylformamide, alcohol type, etc., and recorded by coding such as spin code or dip. A medium can be created.

It is also possible to directly fill a recording medium having a cell-type structure.

Depending on the case, the temperature may be raised once and then slowly cooled to form a phase.

At that time, apply an electric field or magnetic field as necessary.

Note that the thickness of the liquid crystal layer is approximately 0.01 to 100 μm.

Furthermore, the polymer liquid crystal layer may contain one or more light-absorbing substances.

The light-absorbing substance is controlled and used with light such as a laser, and in some cases, pleochroic dyes are also used. The light absorption of these light-absorbing materials should be adapted to the wavelength of the laser used.

If the recording/reading process is to be carried out using various laser wavelengths, it is preferable to use a mixture of light-absorbing substances that exhibit high absorption in the wavelength range of the lasers used.

Specific examples are as follows.

(azo dye) for example, -1 H3 (Azulene dye) (phthalocyanine) for example, R-alkyl group In the formula R -n-CtzH2s (naphthalocyanine) or (metal complex) for example, There is.

These substances are used dissolved or dispersed, for example, U
It can contain a V stabilizer, an antioxidant, a softener, etc., and can be formed into a film by casting 1 vapor deposition or the like to form a light-absorbing material layer. Furthermore, Cr, Ge, N15T
A metal material such as is Pt5A1 can be provided by vapor deposition, sputtering, etc. to form a light-absorbing material layer. These metal materials are advantageous because they also act as electrodes.

Let me briefly explain pyroelectric current. When an alternating current electric field is applied to a ferroelectric material, a dielectric hysteresis curve as shown in FIG. 4 is obtained. Here, the point intersecting the X axis is the coercive electric field Ec (
The point that intersects the Y-axis is the residual polarization Pr (the amount of polarization remaining when the electric field is 0).
It is generally defined as Ferroelectric materials generally have a structure in which microcrystals are dispersed in an amorphous state, and such a hysteresis curve is obtained by aligning or reversing the polarization of the entire crystal. Coercive electric field and remanent polarization depend on temperature, become smaller as the temperature increases, and disappear when the Curie temperature is exceeded (for details, see Takeo Furukawa, Kobunshi Kako Vol. 85, No. 9, 1986). Dielectric materials include polyvinylidene fluoride, a copolymer of vinylidene fluoride and trifluoroethylene, a copolymer of vinylidene fluoride and tetrafluoroethylene, polyvinylidene cyanide, etc., and tetrahydrofuran, methyl ethyl ketone, N, N-
A ferroelectric material layer can be obtained by dissolving it in dimethylformamide, N,N-dimethylacetamide, acetone, etc. and forming a film by an appropriate casting method. Furthermore, the film can also be formed by a vacuum evaporation method.

Suitable materials for the alignment layer include organic polymer materials such as polyimide, polyvinyl alcohol, polyamide, and polyvinylidene fluoride, silane coupling agents, and oxides such as SiO.

[Example code] Hereinafter, the present invention will be specifically explained with reference to Examples.

1. ITO (tin-doped indium oxide) was sputtered as an electrode on a 2 mm thick glass substrate, and then a methyl ethyl ketone solution of P (VDF/TrFE) (copolymerization ratio 65/35 (manufactured by Atochem, France)) was sputtered. Prepare
It was applied onto ITO using a spinner and dried at 100° C. to form a ferroelectric material layer with a thickness of 0.5 μm. Next, Cr was deposited to a thickness of 100 OX on the ferroelectric material layer to form a light-absorbing material layer.

This light-absorbing material layer has an electrical resistance (~50Ω/hole) to the extent that it also acts as a conductive layer.

Next, prepare a water/methanol solution of polyvinyl alcohol, and use a spinner to apply it onto the light-absorbing material so that the film thickness after drying is 10%.
00 g/ci+' and rubbed 5 times at a pressure of 100 g/ci+' to form an alignment layer. Next, polymer liquid crystal Lc34 was dissolved in tetrahydrofuran and applied onto the alignment layer using a spinner to provide a polymer liquid crystal layer with a thickness of 2 μm. Next, a film of zinc oxide was formed on the polymer liquid crystal layer by sputtering to provide a transparent electrode layer, thereby producing a recording medium having the structure shown in FIG. 2.

By subjecting this recording medium to annealing treatment at 150° C., the polymeric liquid crystals were oriented, and a recording medium with good orientation was obtained. Next, between the ITO electrode and the Cr layer (light-absorbing material layer),
The ferroelectric material layer was subjected to poling treatment by applying a direct current of v.

A semiconductor laser beam of 780 nm is applied to the recording medium treated in this manner with a spot diameter of about 5 μm and an irradiation intensity of 1, 2
When the laser beam was irradiated from the lμSee substrate side and observed under a polarizing microscope, the orientation of the polymer liquid crystal layer in the portion irradiated with the laser beam was disturbed, and a dark recording area was formed under crossed nicol conditions.

Next, with the zinc oxide transparent electrode layer and the Cr layer short-circuited, a 780 nw semiconductor laser beam was focused from the substrate side to a spot diameter of 5 μm and was irradiated onto the 2 μSee recording area with an irradiation light intensity of 51 W, resulting in disturbances in the recorded area. The original orientation was reoriented and the record was erased.

[Effects of the Invention] As explained above, the recording medium of the present invention can rapidly erase data due to the effect of the electric field produced by the pyroelectric current generated by the temperature change of the ferroelectric material layer.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views showing the structure of a specific example of the recording medium of the present invention. 3 and 4 are graphs for explaining dielectric hysteresis curves. l...Substrate, 2...Transparent electrode, 3...Alignment layer, 4
...Polymer liquid crystal layer, 5...Light-absorbing material layer, B...
- Ferroelectric material layer, 7... electrode. Diagram

Claims (1)

[Claims] (1) A recording medium that basically has a layer structure in which electrodes, a poling-treated ferroelectric material layer, a light-absorbing material layer, an alignment layer, a recording layer made of polymeric liquid crystal, and a transparent electrode layer are sequentially laminated.