JPH02277069A - Optical recording medium consisting of ferroelectric high polymer - Google Patents

Abstract

PURPOSE:To assure the sensitive reaction even with low-energy semiconductor laser light by incorporating a specific phthalocyanine compd. into a ferroelectric high-polymer material forming a recording layer. CONSTITUTION:The recording layer 1 consisting of a vinylidene polymer film or the like is provided via a lower electrode 4 consisting of an ITO film, etc., on a substrate 2 consisting of glass, etc. and an upper electrode 3 consisting of an Al film or the like is formed on the layer 1. The phthalocyanine compd. (A) which has absorption spectra in a near IR region and is soluble in an org. medium is incorporated into the layer 1. Such a compd. expressed in formula is preferably used for this component A. In the formula, one or more of R'1 to R'8 denote F, SZ; Z denotes 1 to 4C alkyl, prescribed phenyl, etc.; M denotes Cu, Zn, etc.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a reversible optical recording medium using a ferroelectric polymer material as a recording layer for use in optical memories, optical sensors, pyroelectric sensors, displays, etc. .

[Prior Art] Recording media using ferroelectric polymer materials have already been disclosed in various documents and publications, but the recording methods can be specifically classified into the following three types. .

First, the first method is JP-A-59-215096.5
As disclosed in No. 9-215097.61-105792, information is recorded by applying an electric field to any part using crossed electrodes and performing polarization processing, and then a light beam is irradiated to create a pyroelectric current. This method attempts to reproduce information based on the presence or absence of occurrence.

The second method is also published in Japanese Patent Application Laid-Open No. 59-21509.
(+, 59-215097, etc., information is recorded by depolarizing the polarization of an arbitrary part in a sample that has been subjected to polarization treatment in advance,
Similar to the first method, this method attempts to reproduce information based on the presence or absence of pyroelectric current when a light beam weaker than that used during recording is irradiated. However, the response during reproduction by this method is different from the first method, and the portion where the pyroelectric current does not occur becomes the recorded bit.

Furthermore, the third method is IEEE Trans.

ElecLr, Ins, 1El-21, 539, (1
98B) and polymer processing 35.418. (1988), the coercive electric field of the dielectric hysteresis curve that a ferroelectric material exhibits when an alternating current electric field is applied increases by 11
4. Taking advantage of the property that polarization decreases, a light beam is directed at any part of the sample while applying a weak reverse electric field that does not reverse the polarization at room temperature to a sample that has been polarized in advance. Information is recorded by increasing the temperature of the light irradiated part to near the Curie point and reversing the polarization of the light irradiated part. Phase difference (positive/negative)
This is a method for reproducing information recorded by.

[Problem to be solved by the invention] Comparing the above three methods, it is found that the amount of residual polarization at room temperature is
If we convert the magnitude of the pyroelectric current, which is the reproduced signal, into a change in the amount of polarization, the maximum Pr in the first and second methods is 2Pr in the third method. A current corresponding to The third method is considered to be the most desirable because it has major drawbacks in use as a reversible optical memory.

However, the optimal configuration of the sample when using the third method has not been established, and in particular, since this method uses irradiated light to record and reproduce heat, the absorption efficiency of the irradiated light is important. Currently, conventional optical recording media with a recording layer consisting of a single film of ferroelectric polymer (especially vinylidene polymer...hereinafter abbreviated as PVD polymer) have low sensitivity due to their high light transmittance. However, since the output power is low and a high-output laser must be used, there are problems in terms of practicality and productivity.

The recording light source for optical recording systems is compact, lightweight,
Due to demands for higher density, cost, etc., semiconductor lasers are generally used. Furthermore, semiconductor lasers used in optical recording systems generally have a relatively long oscillation wavelength, near near-infrared, from the viewpoint of stability and reliability.

Furthermore, as disclosed in JP-A No. 53-46638, an invention has been proposed in which a dye having absorption near the wavelength of semiconductor laser light is dispersed in a ferroelectric polymer optical recording medium. If recording is performed by the third method using a general dye such as the one described above, the dye will be exposed to a harsh environment of high heat and high voltage during recording, and it will be necessary to use it repeatedly. As a result, a fading phenomenon occurred due to the dissociation and decomposition of dye molecules, and the optical recording medium could not be put into practical use.

[Problems to be Solved by the Invention] As described above, this type of optical recording medium is subjected to the effects of heat and electric fields caused by laser light during recording, so it is exposed to extremely harsh environments compared to other heat mode optical memories. It will be done. Ionic dyes are not suitable as dyes that can withstand such harsh environments. For example, it has been found that when a cyanine dye, which is a cationic dye, is used as a laser light absorbing agent, dissociation, decomposition, etc. occur due to the action of heat and electric field, and the ability to absorb semiconductor laser light is likely to be lost due to fading.

Therefore, the present invention aims to provide a highly practical optical recording medium that reacts extremely sensitively to low-energy semiconductor laser light and can perform a series of operations such as writing, reading, and erasing. be.

[Means for Solving the Problems] According to the present invention, the above object is an optical recording medium using a ferroelectric polymer as a recording material, which is heated by light irradiation from a light source such as a semiconductor laser beam. In an optical recording medium that records information by utilizing the property that the polarization of the polarized portion is selectively reversed by a reverse electric field applied from the outside,
The ferroelectric polymer material forming the recording layer of the optical recording medium or a separate layer in contact with the recording layer has an absorption spectrum in a near-infrared absorption wavelength range that efficiently absorbs the irradiated light, and This is achieved using a ferroelectric polymer optical recording medium containing a phthalocyanine compound soluble in organic solvents.

According to the present invention, in the ferroelectric polymer recording medium,
The recording layer is made of a ferroelectric polymer material, such as PVDtir.
formed by coalescence, has excellent heat resistance and voltage resistance in the recording layer or in a separate layer in contact with the recording layer, has an absorption spectrum in the semiconductor laser oscillation wavelength range, preferably in the near-infrared absorption wavelength range, and Contains a phthalocyanine compound that is soluble in organic solvents as a light absorber, so it has high absorption rate and heat conversion efficiency for irradiated light, and is effective against low power irradiated light such as semiconductor laser light. Provided is a highly practical rewritable optical recording medium that reacts extremely sharply, can perform a series of writing, reading, and erasing operations, and can withstand repeated use.

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 optical recording medium of the present invention in which the phthalocyanine compound is dispersed in the recording layer. 1 in this figure is the recording layer of the optical recording medium, which is a portion made of a PVD polymer film in which the phthalocyanine compound is dispersed. Further, 2 is a substrate that supports the recording layer, 3 is an upper electrode, and 4 is a lower electrode.

In the present invention, the PVD polymer in the recording layer is a part that exhibits ferroelectricity, which can be called the basis of the recording medium, so the light absorber added therein interferes with the ferroelectricity of the PVD polymer. The following characteristics are required as appropriate to ensure that:

1) It has absorption in the vicinity of the wavelength of irradiated light, especially semiconductor laser light; 2) It does not constitute a salt or the like with anions, cations, or pairs of these ions in its molecules, and is electrostatically neutral; 3) be soluble in a solvent that dissolves the PVD polymer; 4) have excellent electrical resistance; 5) be thermally stable; 5) be compatible with the PVD polymer; As shown in the above structural formula, the phthalocyanine compound satisfies condition 2 above. Furthermore, it is known that phthalocyanine compounds are excellent among organic dyes and pigments in terms of conditions 4 and 5 above. However, the reasons why such stable dyes have not been utilized to date include the following problems.

■Because it was poorly soluble or insoluble in organic solvents.

■There was almost no absorption in the vicinity of 800 rv, which is the semiconductor laser oscillation wavelength range.

Therefore, the use of porphyrin compounds is not suggested in the above-mentioned publication (Japanese Unexamined Patent Publication No. 63-46638).

However, after extensive research, the present researchers discovered a dye that overcomes the above problems and satisfies conditions 1) to 5) above.
This led to the present invention.

That is, the dye used in the present invention has the following general formula (1)
The phthalocyanine compound represented by and (II) has an absorption wavelength in the semiconductor laser oscillation wavelength range, preferably in the near-infrared range, and is soluble in an organic solvent.

[In formula (1), at least one of R''1 to R-8 is F or SZ (where Z is substituted with an alkyl group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a halogen) (optionally phenyl or naphthyl group), and M is (u, Zn, Co, Ni, InX, Tie.

or 5nX2, (where X represents a halogen atom)
represents. ] Represent. ] For example, compound No. having the following structural formula, PC
The absorption spectra of -001 and PC-002 in N,N-dimethylformamide solutions are ++'' as shown in Figures 2 and 3.

[In formula (II), R1 to R4 are 5Z (Z is 1 to 2 carbon atoms
0 linear alkyl group) or NPQ (P and Q are each H or -CH2CHCH20R).

H (here, Ro represents H1 alkyl group, alkenyl group, or aryl group), M represents VO, Tie, or InX (here, X represents a halogen atom), and unlike conventional phthalocyanine compounds, its absorption wavelength It is clear that the region extends to the semiconductor laser oscillation wavelength. Furthermore, Figures 4 and 5
As shown in the figure, the absorption spectrum of the film obtained by dissolving the lid and cyanine compound in the PVD polymer shifts to a broader wavelength side than the peak of the absorption spectrum of the solution due to the interaction, and the peak of the absorption spectrum of the solution shifts to the longer wavelength side due to the interaction. The favorable result of matching has also been obtained.

Previously, the present inventors developed Polymer Preprint
, Japan 36 (8), 24771987, due to the ferroelectric behavior of a PVD polymer with one dye added, the dye molecules do not mix into the crystalline layer of the PVD polymer, but are included in its amorphous layer. However, in the case of the phthalocyanine compound, the above model also applies, and an alternating current electric field higher than the coercive electric field is applied to a sample formed by dissolving the phthalocyanine compound in a PVD polymer. As a result, a typical rectangular D-E hysteresis curve as shown in Figure 6.7 is obtained,
It was confirmed that the phthalocyanine compound did not inhibit the ferroelectricity of the PVD polymer. For comparison, the absorption spectrum of a cyanine dye having the following structural formula in a methyl ethyl ketone solution and the DE hysteresis curve of a sample dissolved in a PVD polymer to form a film are shown in Figures 8 and 9.

Although the C113C113 absorption spectrum extends to a long wavelength region, the DE hysteresis curve is rounded, which indicates that the ferroelectricity of the PVD polymer is inhibited.

If the electric field is further applied, the dye dissociates and the color fades.

The phthalocyanine compounds represented by the structural formulas of general formulas (1) and (n) used in the present invention are, for example,
-298974, Japanese Patent Application No. 62-134953, Japanese Patent Application No. 63-65806, and Japanese Patent Application No. 63-21383.
It can be synthesized by the method described in No. 0.

Next, other materials constituting the optical recording medium of the present invention will also be explained.

Various compounds have been reported for the ferroelectric polymer material constituting the recording layer, but in this recording medium, it is desirable to use a material that has ferroelectric properties and exhibits a rectangular shape in dielectric hysteresis measurements. Vinylidene fluoride, vinylidene fluoride and ethylene trifluoride copolymer, vinylidene fluoride and ethylene tetrafluoride copolymer, vinylidene fluoride and vinyl fluoride copolymer, vinylidene fluoride and ethylene tetrafluoride and hexafluoride Among them, vinylidene fluoride and ethylene trifluoride copolymers [hereinafter referred to as P (VDF-T)
r F E)] is most preferred.

The PVD polymer film of this recording layer can be formed by a solution coating method such as dip coating, spray coating, spinner coating, blade coating, roller coating, curtain coating, or the like. Among these methods, methods such as dip coating, spinner coating, and roller coating are preferable from the standpoint that an ultra-thin film can be obtained on soil that forms a PVD polymer film with a uniform thickness.

Furthermore, the recording layer of the present invention can also be provided by a vacuum deposition method.

In order for the ferroelectric polymer recording medium of the present invention to function as an optical memory, it is desirable that at least one of the electrodes sandwiching the recording layer 1 be as transparent as possible to irradiated light. It is preferable to employ a transparent electrode or a semi-transparent electrode. Of course, the substrate 2 and the upper electrode 3
Both may be transparent, or only the upper electrode 3 may be transparent.

The transparent electrode employed in the present invention includes vapor deposition, CVD, and sputtering films of tin-doped indium oxide (ITO), tin oxide, undoped indium oxide, zinc oxide, etc., and the semitransparent electrode includes gold, platinum, silver, copper,
Examples include vapor deposition, CVD, and sputtering films of various metals such as lead, zinc, aluminum, nickel, tantalum, titanium, cobalt, niobium, palladium, tin, chromium, and germanium, but the present invention is not particularly limited to these. isn't it.

Support materials for these electrodes include polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate, polyamide,
Various plastics such as polyimide, polyolefin, acrylic resin, phenol resin, epoxy resin, and the above derivatives, glass, quartz plate, ceramic, etc. are suitable, but like the electrode, it is desirable that they are transparent to irradiated light, and the electrode Although it is preferable that the material also serves as insulation from the electrode, the present invention is not particularly limited thereto, as is the case with the electrode.

The irradiation light source is a semiconductor laser (L
D) is considered optimal. Although the direction of irradiation of the LD light is not horizontal from either the upper or lower electrode side, it is desirable that at least the electrode on the light source side is transparent to the irradiated light.

The present invention utilizes PV, which has until now had poor light absorption and heat conversion efficiency.
Adding a phthalocyanine compound to a polymer film not only improves the light absorption heat conversion efficiency, but also does not impede the ferroelectricity of a ferroelectric polymer optical recording medium that uses the phthalocyanine-added film as a recording layer. , it is possible to improve the sensitivity as well.

[Example] EXAMPLES The present invention will be explained in further detail by way of Examples below.

Example I Synthesis of PC-001 Synthesis was carried out according to Example 1 of Japanese Patent Application No. 63-213830.

The thus obtained phthalocyanine compound (PC-
001), P (VDF-TrFE) copolymer (VD
F/T r F E-65/25 unit molar ratio) in tetrahydrofuran (THF) solution with 3% of the copolymer.
mm% was added to prepare a recording layer coating solution. Then thickness 1
．． It was coated onto a 2 mm ITO-deposited glass substrate by a spin code method so that the film thickness after drying was 2 μm. 6
After vacuum decompression at 0°C for 10 minutes, annealing treatment was performed at 140°C for 1 hour, and aluminum was further steamed as an upper electrode.
A ferroelectric polymer optical recording medium was created.

From the upper electrode side, the recording medium created in this way is
A poling process was performed by applying a DC electric field of 00V. Next, while applying +50 V to the upper electrode, the oscillation wavelength was set to 711.
Irradiation light intensity 12mW using a 0nm semiconductor laser,
Information was recorded by heating several locations in the recording layer from the lower electrode side with a spot diameter of 5 μm. After that, the semiconductor laser light intensity was weakened to 2 mW, and the recording layer was irradiated with the semiconductor laser again while chopping at 15 KHz, and the pyroelectric current generated between the electrodes was measured to evaluate the memory characteristics.
It was found that the /N ratio was about 31 dB and the CZN ratio reached 50 dB.

Example 2 Synthesis of PC-002 Synthesis was carried out according to Reference Example 1, Reference Example 2 and Example 1 of Japanese Patent Application No. 81-29894.

The thus obtained phthalocyanine compound (PC-
A ferroelectric polymer optical recording medium was prepared in exactly the same manner as in Example 1 using 002). A DC electric field of 1200 V was applied to the prepared recording medium from the upper electrode side to perform a poling process. Next, while applying +50V to the upper electrode, information was recorded by heating several locations in the recording layer from the lower electrode side using a semiconductor laser with an oscillation wavelength of 780 nm at an irradiation light intensity of 15 mW and a spot diameter of 5 μm. After that, the semiconductor laser light intensity was weakened to 3 mW, and the recording layer was again irradiated with the semiconductor laser light while chopping at 15 KIIz, and the pyroelectric current generated between the electrodes was measured to evaluate the memory characteristics. It was found that the C/N ratio reached 33 dB and 51 dB.

Examples 3 to 8 Japanese Patent Application No. 1987-298974, Japanese Patent Application No. 1982-13495
No. 3, Tokugan Sho (No. i3-051106 or Tokugan Sho 8)
A phthalocyanine compound (PC-003, pc-o
.

4, PC-005, PC-006, pc-o.

7, PC-008) was synthesized. A ferroelectric polymer recording medium was prepared in the same manner as in Example 1 using each of the phthalocyanine compounds thus obtained as a light absorber. The memory characteristics of the thus prepared recording medium were evaluated under the same conditions as in Example 1. Furthermore, the absorption spectrum of the recording layer was determined by 4-1, and λ11. I asked for The results are shown in Table-1.

Table-1 Example 3 // 4 // 5 〃　　6 Compound no.

C-003 C-004 C-005 C-006 -8Ca H+r 5C4H9 N112 =N112 Substitution position 2 4th position 4th position 4th position 3rd position CI+3 Example 9 Using the sample used in Example 2, firstly, the upper part of this sample was A DC electric field of 200 V was applied from the electrode side, and the poling process was performed again to erase the recorded information.

This recording-reproducing-erasing was regarded as one cycle, and when an experiment was conducted by repeating the above cycle under the same conditions as in Example 2, the C/N of the reproduced signal after 50 cycles and after 100 cycles was No change was observed at 51 dB.

Therefore, it was found that this memory sample could be stably repeated at least 100 times by the above-mentioned repetitive operation.

[Effects of the Invention] As explained above, according to the configuration of the present invention, it responds sharply even to low irradiation intensity such as semiconductor laser light, allows writing, reading, and erasing, and can be used repeatedly. It is possible to obtain a highly reliable optical recording medium that can withstand even high temperatures.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the basic structure of the ferroelectric polymer optical recording medium of the present invention, Fig. 2.3 is a graph showing the solution absorption spectrum of the phthalocyanine compound used in the present invention, Fig. 4.5 The figure is a graph showing the absorption spectrum of the recording layer of the present invention. Figure 6.7 is a graph showing the DE hysteresis curve of the recording layer of the ferroelectric polymer optical recording medium of the present invention. Figure 8 is a cyanine dye. FIG. 9 is a graph showing a DE hysteresis curve of a film in which cyanine dye is dissolved in P (VDF/TrFE).

Claims (3)

[Claims] (1) An optical recording medium that uses a ferroelectric polymer as a recording material, and uses the property that the polarization of a portion heated by light irradiation is selectively reversed by an externally applied reverse electric field. In an optical recording medium for recording, the ferroelectric polymer material forming the recording layer of the optical recording medium or a separate layer in contact with the recording layer has an absorption spectrum in the near-infrared absorption wavelength range, and A ferroelectric polymer recording medium characterized by containing a phthalocyanine compound soluble in an organic medium. (2) The ferroelectric polymer recording medium according to claim (1), wherein the phthalocyanine compound is represented by the following general formula (I). ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) [In formula (I), at least one of R_1' to R_8' is F or SZ (here, Z is an alkyl group having 1 to 4 carbon atoms, or a carbon represents a phenyl group or naphthyl group which may be substituted with an alkyl group of numbers 1 to 4 or a halogen), M is Cu, Zn, Co, Ni, InX, TiO or SnX_2 (here, X is a halogen atom) ). ] (3) The ferroelectric polymer optical recording medium according to claim (1), wherein the phthalocyanine compound is represented by the following general formula (II). ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (II) [In formula (II), R_1" to R_4" are SZ (Z represents a straight-chain alkyl group having 1 to 20 carbon atoms) or NPQ (P,
Each Q is H or ▲ there is a mathematical formula, chemical formula, table, etc. ▼ (here R_0 is H
, indicates an alkyl group, alkenyl group or aryl group)
and M represents VO, TiO or InX (where X represents a halogen atom). ]