JPH02257492A - Ferroelectric high-polymer optical recording medium - Google Patents

Abstract

PURPOSE:To improve light absorption efficiency and to increase sensitivity by dispersing and mixing saturable dyestuffs into a recording layer of a PVD polymer having poor optothermo conversion efficiency. CONSTITUTION:The recording layer 1 of the optical recording medium consists of the vinylidene polymer (PVD polymer) film. A lower electrode 2, a substrate 3 and an upper electrode 4 are provided respectively. The optothermo conversion efficiency of the PVD polymer is improved by incorporating >=1 kinds of the dispersed saturable dyestuffs into the recording layer 1 in such a manner. Most of the saturable dyestuffs belong to polymethyne dyestuffs and the more specific examples of these dyestuffs include perchloric acid 5, 5'-cyclo-1, 1'- diphenylamino-3, 3'-diethyl-1-, 12-ethylene tiatricarboxyanine (IR 140), etc. The optothermo conversion efficiency is improved in this way and the recording medium having the higher sensitivity is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a ferroelectric polymer optically reversible recording medium using a vinylidene polymer (hereinafter simply referred to as a PVD polymer) as a recording layer. be.

[Prior art] Polymer optical memory using PVD polymer as a recording medium is
Already known.

This is a revolutionary optical memory that utilizes the ferroelectric properties of PVD polymers, and its recording principle is based on Japanese Patent Application Laid-Open No. 59-21509.
8 and No. 59-215097, or as disclosed in Polymer Processing 35.418 (198B),
Taking advantage of the property of a ferroelectric polymer material to be polarized by an electric field, a weak reverse electric field less than the coercive electric field was applied to the ferroelectric polymer material, which was polarized in one direction by applying a high electric field. It is possible to write by irradiating and heating an arbitrary part with a light beam and selectively inverting the polarization of only the part irradiated with light, and further reading by using the pyroelectric effect caused by light or heat. It is.

When using such a ferroelectric polymer as an optical memory, the absorption efficiency of the light irradiated onto the memory is an important factor, but PVD polymer films generally have high light transmittance; It requires a laser beam, etc. to output power, which has been a big problem when it comes to practical use.

[Problems to be Solved by the Invention] The present invention aims to solve the problems in the polymer optical memory described above, namely, the efficiency of converting the emitted light energy into thermal energy (hereinafter referred to as photothermal energy). The purpose is to improve the conversion efficiency (abbreviated as "conversion efficiency") and provide a ferroelectric polymer recording medium with higher sensitivity.

[Means for Solving the Problems] The present inventor has been conducting research to improve the light-to-heat conversion efficiency of the above-mentioned PVD polymer, and the PVD polymer layer forming the recording layer of the optical recording medium It has been found that it is effective to disperse a saturated dye therein or to provide a light absorption layer containing a saturated dye in the vicinity of the layer, leading to the present invention.

That is, the present invention provides a ferroelectric polymer optical recording medium having a recording layer made of a vinylidene polymer, in which the recording layer contains one or more saturated dyes dispersed therein;
Alternatively, it is a ferroelectric polymer optical recording medium characterized by having a light absorption layer containing a saturated dye provided near the recording layer.

The configuration of the present invention will be explained below based on the drawings.

FIG. 1 is a structural model diagram of the ferroelectric polymer recording medium of the present invention in which a saturated dye is dispersed in the recording layer.

1 in this figure is a portion made of a PVD polymer film which is the recording layer of the optical recording medium. 2.3 and 4 are a lower electrode, a substrate, and an upper electrode, respectively. Further, FIG. 2 is a structural model diagram when a light absorption layer 5 is provided in the ferroelectric polymer recording medium of the present invention. Figure 3 a, b, c, d
and e are examples showing a structural model in the case where the recording layer and the light absorption layer have a laminated structure in the present invention. That is, the light absorbing layer is located above the recording layer (in the opposite direction to the substrate side) (a
) Alternatively, it may be formed at the lower part (b). here,
The recording layer and the light absorption layer each do not need to be a single layer;
A structure (C) in which a light absorption layer is sandwiched between recording layers, or conversely, a structure (d) in which a recording layer is sandwiched between light absorption layers may be used. Furthermore, a structure (e) in which recording layers and light absorption layers are alternately laminated may also be used. Further, the light absorption layer does not necessarily need to be in contact with the recording layer.

Various compounds have been reported for the PVD polymer constituting the recording layer in the present invention, but in this recording medium, it has ferroelectricity and has a rectangular or 1≠ shape in dielectric hysteresis measurement, and as much as possible. It is desirable to have a similar shape, such as vinylidene difluoride homopolymers and vinylidene difluoride copolymers containing 50% by weight or more of vinylidene difluoride. Examples of the copolymer include copolymers of vinylidene fluoride and ethylene trifluoride, propylene hexafluoride, ethylene trifluoride chloride, and the like.

Also included are polyvinylidene cyanide, vinylidene cyanide, and vinyl acetate copolymers, among which vinylidene fluoride and ethylene trifluoride copolymers below P
(abbreviated as VDF-TrFE)] is most preferred.

The PVD polymer film of the recording layer can be formed by a solution coating method such as dip coating, spray coating, spinner coating, blade coating, roller coating, or curtain coating. Among these methods, dip coating or spinner coating is preferable because the PVD polymer film can be formed to a uniform thickness and an ultra-thin film can be obtained.

The electrodes for detecting the pyroelectric effect induced in the recording layer may be such that at least one of the electrodes on the side where light first enters is transparent or translucent to the incident light. An ITO (Indium Tin Oxide) electrode is known as an example of a transparent electrode. The translucent electrode is made of a thin film of metal such as gold, platinum, silver, tin, copper, lead, zinc, aluminum, nickel, tantalum, titanium, cobalt, niobium, palladium, or tin by vapor deposition, CVD, or sputtering. Examples include electrodes.

The light absorption layer converts the incident light energy into thermal energy and only needs to form a structure that can efficiently transmit this energy to the recording layer.In other words, the light absorption layer can be placed on either side of the recording layer. Alternatively, a cumulative structure sandwiched between the recording layer or a cumulative structure sandwiching the recording layer may be formed.Furthermore, this light absorption layer is not necessarily in contact with the recording layer. It is not necessary, but it is desirable that they are in contact.

The photosensitizer constituting the light absorption layer used in the present invention primarily depends on the irradiation wavelength of the light source since there is limited room for selection of the light source described below. In order to efficiently capture incident light energy, it is desirable to use a photosensitizer that has as large an absorption cross section for incident photons as possible. The preferred value of the absorption cross section in the present invention depends on the power density of the light source used, but generally, taking into account the dissipation of thermal energy from the electrode portion,
It is approximately 1.5 x 10-"cm' or more. Furthermore, it is desirable that the photosensitizer has low conductivity so as not to interfere with the pyroelectric effect induced in the recording layer. As long as these conditions are met, In the field of laser spectroscopy, there are saturated dyes that have been used to improve the shape of laser pulses.Most saturated dyes belong to the polymethine dye class, but this is not always the case. Examples include perchloric acid 5,5°-cyclo-1,1′-diphenylamino-3,3°-diethyl-10,12-ethylenethiatricarbocyanine (IR140), perchloric acid 1,1°,
3.3.3°, 3°-hexamethyl-2°2'-(6,
6°,7.7”-dibenzo)indotricarbocyanine (EDITCP), 3,3°-diethyl-9 iodide
, 11-neopentylenethiatricarbocyanine (DN
TTCI), iodide 1,1°, 3.3,3°, 3°-
Hexamethyl-2,2°-indotricarbocyanine (
BITCI), neocyanine (NCI), iodide t, t
'-diethyl-2,2°-dicarbocyanine (DDCI
), cryptocyanin, iodide 1.1', 3.3.3
', 3°-hexamethyl-2,2°-indodicarbocyanine (HIDCI), diethyl iodide-2,2°-thiadicarbocyanine (DTDCI), 1.3° iodide
-diethyl-4,2-quinolylthiacarbocyanine (D
QTCI), and 3.3°-diethyloxadicarbocyanine iodide (DODCI).

The light absorption layer disperses these dyes in the recording layer, or
It may be formed as a film of the above-mentioned saturated dye itself, or by dispersing it in another suitable polymer film. Polymers that can be used for the latter purpose generally include polymethyl methacrylate (PMMA), polystyrene, polyvinyl alcohol (PVA), polyvinyl butyral, polyamide, polyimide, polycarbonate, polyester, and the like. Which one.

Regardless of the method for producing the light absorption layer, all of the methods listed above regarding the formation of the recording layer can be used.

The linear absorption coefficient of the light absorption layer must generally be about l x 1G 30m-' or more in order to absorb enough energy to induce polarization reversal in the recording layer. On the other hand, if the amount of the saturated dye is too large, the dye may deteriorate and the light-to-heat conversion efficiency may decrease. Furthermore, if the amount of dye is too large when dispersed in the recording layer, the insulation properties of the recording layer will be reduced, which may cause a decrease in the stability of memory signals and an increase in noise components.

The substrate used in the present invention only needs to be transparent to incident light like the electrodes and have insulation properties with respect to adjacent electrodes. Specifically, various plastics and glasses such as polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyviniasate, polyamide, polyimide, acrylic resin, phenol resin, epoxy resin, and derivatives of the above, Examples include quartz plates and ceramics.

It is preferable that the irradiation light source has a high power density and enables a high recording density of the memory of the present invention. A laser is an example of a device that satisfies these conditions. The laser is a solid-state laser (fPJ, ruby laser Nd-YA
G laser, etc.), liquid laser (e.g., dye laser, etc.)
, gas lasers (e.g., He-, Ne lasers, Ar-lasers, Ar" lasers, etc.), and semiconductor lasers. There is no particular restriction on the oscillation wavelength of the laser used in the present invention, and generally, as described above, It is preferable to use a long and short wavelength that can improve the recording density.To this end, a wavelength conversion element having nonlinear optical characteristics may be provided in the optical path of the laser beam in order to obtain a double wave of the laser oscillation wavelength. Specific examples of wavelength conversion elements include lithium niobate,
Crystals such as and KDP (X112 PO4) are known. Among these various demands, in addition to the size and weight reduction and economic efficiency of devices that utilize the optical memory of the present invention,
Judging comprehensively, it is currently desirable to use semiconductor lasers among the various lasers mentioned above. The one currently in practical use is the AI GaAs system (oscillation wavelength: 7g).
0 ns) and GaAs system (oscillation wavelength: 830 ns)
Semiconductor lasers such as the following can be mentioned.

The ferroelectric polymer optical recording medium of the present invention, which is composed of the above-described elements, functions as an optical memory in the following manner. That is, first, a strong electrolyte is applied to the recording layer,
Orienting the polarization of strongly galvanic polymers in one direction (poling process).

Next, the medium is placed in the presence of a weak reverse electric field that is less than the coercive electric field, and a light beam is irradiated onto an arbitrary position on the recording layer. The heat generated only in the area irradiated with light reverses the polarization only in that area. In this way, records are written selectively and locally. This recording is read using the pyroelectric effect caused by light or heat.

The present invention will be specifically explained below with reference to Examples. The present invention is not limited only to these examples.

Example 1 5 vt% saturable dye DNTTCI (absorption cross section at 770 nm σ-2,5X 10-''cm')
A copolymer of vinylidene fluoride and ethylene trifluoride containing ? -P (VDF-TrFE) (VDF of TrFE
A solution with a molar ratio of 317) to a 1 mm thick I
It was coated onto TO glass by a spin code method to a thickness of 1 μm, and after this thin film was allowed to dry, aluminum was vapor-deposited. Next, a voltage of 100 V was applied to the P (VDF-TrFE) thin film to perform a poling process. A semiconductor laser beam (beam radius = 2.5μIl) with an oscillation wavelength of 7g0nm and an irradiation intensity of 1.8a+W was applied to the sample thus obtained in the presence of a reverse electric field of 25V.
Information was written by irradiating the P (VDF-TrFE) layer at several locations through the TO electrode.

Next, it is modulated at 1OkHz and the irradiation intensity is 0.16I.
The recording layer was irradiated with the laser beam reduced to IW, the pyroelectric current generated between the two electrodes was measured, and information was read, and the S/N ratio was 51 dB.

Example 2 Saturable dye HIT CI (σ- at 740 nm
The S/N ratio of the pyroelectric current signal was measured by performing the same operation as in Example 1, except that the pyroelectric current signal was 53 dB.

Comparative Example 1 The same operation as in Example 1 was performed except that P (VDF-TrFE) containing no saturated dye was used, and the pyroelectric current S/N ratio was determined to be 30 dB by DI.

Comparative Example 2 The same operation as in Example 1 was performed except that a metal complex dye represented by the following structural formula (3vt%) was used, and the S/N ratio of the pyroelectric current signal was measured and found to be 45 dB.

Example 3 ■T with a thickness of 1III11 by spin coating
On the O glass, a molar ratio of TrFE to VDF of 3
/7 P (VDF-TrFE) solution with a thickness of 1
It was applied in an amount of μl. Waiting for this thin film to dry, the saturated dye DNTTC1 (absorption cross section at 770 nm a = 2.5X 110-16a') was coated with the same method by spin coating to a thickness of about 0.1 μm. Coated. After degassing and drying, aluminum was deposited as an upper electrode. Next, a voltage of 100 μ was applied to the P (VDF-TrFE) thin film to perform a poling process. The sample thus obtained was placed in the presence of a reverse electric field of 2.5 V, and the oscillation wavelength, irradiation intensity, and beam diameter were
P (VDF
-TrFE) layer was irradiated at several locations to write information.

Next, in order to read this information, the same laser beam modulated at 1 kHz and with the irradiation intensity reduced to 0.18 mW is irradiated onto the recording layer, and the light generated between the upper and lower electrodes is The pyroelectric current was measured. Its S/N ratio is 49d
It was B.

Example 4 The pyroelectric current was measured by carrying out the same operation as in Example 3 except for using the saturated dye HIT CI (σ-4,4X 10-16 cm2 in 740 na + l).
The N ratio was 50 dB.

[Effect] As is clear from the above explanation, according to the structure of the present invention, by dispersing and mixing a saturated dye in a PVD polymer recording layer with poor light-to-heat conversion efficiency, or by dispersing and mixing a saturated dye in the vicinity of the recording layer. By providing a light absorption layer containing a saturated dye, the efficiency can be improved and the sensitivity of a ferroelectric polymer optical recording medium with a recording layer made of a PVD polymer can be increased. It has the remarkable effect of being able to react extremely sensitively to high-power irradiation light and perform a series of operations such as writing, reading, and erasing.

[Brief explanation of drawings]

Figure 1 shows the recording temperature of the ferroelectric polymer recording medium of the present invention.
A diagram illustrating the configuration when a saturated dye is dispersed in a layer,
FIG. 2 is a diagram explaining the structure when a light absorption layer is provided in the same recording medium, and FIGS. Diagram to explain. ■... Recording layer, 2... Lower electrode, 3... Substrate, 4
... Upper electrode, 5... Light absorption layer.

Claims (1)

[Claims] In a ferroelectric polymer optical recording medium having a recording layer made of a vinylidene polymer, the recording layer contains one or more saturated dyes dispersed therein, or a saturated dye provided near the recording layer. A ferroelectric polymer optical recording medium characterized by having a light absorption layer containing a dye.