JP2758400B2 - Ferroelectric polymer optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ferroelectric polymer using a vinylidene polymer (hereinafter abbreviated as PVD polymer) useful as a recording layer in optical cards, optical disks, displays, and the like. The present invention relates to a photoreversible recording medium. [Prior art] A polymer optical memory using a PVD polymer as a recording medium
Already known. This is an epoch-making optical memory utilizing the ferroelectricity of a PVD polymer, and its recording principle is disclosed in JP-A-59-215096.
No. 59-215097, or IEEE Trans.Electr.In
S., EI-21, 539, 1986, and Polymer Processing 35 , 418 (1986), a high electric field is applied by utilizing the property that a ferroelectric polymer material is polarized by an electric field. The ferroelectric polymer material polarized in one direction is irradiated with a light beam in a state where a weak reverse electric field equal to or less than the coercive electric field is applied, and selectively heated to selectively irradiate the light irradiated portion. By inverting the polarization, writing can be performed, and reading can be performed using the pyroelectric effect of light or heat. When such a ferroelectric polymer is used as an optical memory, the absorption efficiency with respect to the light applied to the memory is an important factor, but the PVD-based polymer film generally has a high light-transmitting property. Irradiation with high-power laser light causes a large loss, which has been a major problem in practical use. In addition, the recording medium must have electrode layers on both sides of the recording layer in terms of its function.However, no consideration has been given to the electrode material, and the generated heat easily diffuses through the electrodes. It is difficult to raise the temperature of the recording layer
When used as a memory, there is a problem that the S / N ratio and the recording density are reduced. [Purpose] In view of such circumstances, in the present invention, in an optical recording medium made of a PVD-based polymer, at least one of the electrodes sandwiching the recording layer absorbs light in the wavelength region of the semiconductor laser light as a light source. It is an object of the present invention to provide a highly sensitive ferroelectric polymer optical recording medium having a function as a heat source as well as an electrode. [Structure] The present inventors have been conducting research for practical use of the above-mentioned optical recording medium, but by using an electrode material having specific conditions for at least one of the electrode layers of the optical recording medium. A method for improving the light absorption efficiency of the optical recording medium and maintaining the generated heat for a certain period of time was established, and a highly practical ferroelectric polymer recording medium was successfully manufactured. That is, the present invention provides an optical recording medium comprising a PVD-based polymer, wherein a material constituting at least one of a pair of electrodes sandwiching a recording layer composed of the PVD-based polymer is represented by the following conditional expression: A ferroelectric polymer optical recording medium having physical properties satisfying the following. Here, k: thermal conductivity (w · m ⁻¹ · K ⁻¹ ) ρ: density (g · m ^-3 ) c: specific heat (J · g ⁻¹ · K ⁻¹ ) Hereinafter, the configuration of the present invention will be described with reference to the drawings. FIG. 1 is a structural model diagram of a ferroelectric polymer recording medium of the present invention. Reference numeral 1 in this figure denotes a portion composed of a PVD-based polymer film which is a recording layer of the optical recording medium. 2 is a lower electrode, 3
Is an upper electrode. Reference numeral 4 denotes a substrate for supporting the lower electrode 2. The electrode material used in the present invention may be either the upper electrode or the lower electrode in FIG. 1, or both electrodes may be made of the above material. Furthermore, the present inventors have previously reported that a dye can be dispersed in a PVD-based polymer recording layer to improve its light absorption efficiency, but the present invention can also be applied to this case. In this case, it is desirable that the electrode on the incident side of the irradiation light be a transparent electrode and that the other electrode be made of the above-mentioned material. In the present invention, the material constituting the electrode layer preferably has a low thermal conductivity and a relatively high specific heat and density as can be understood from the above formula. Specific examples of metals satisfying this condition include tellurium, bismuth, titanium, niobium, nickel, platinum, antimony, chromium, germanium, silicon, and aluminum. Using the above materials, the electrode layer is formed by an evaporation method, a sputtering method, a CVD method, or the like. Further, a configuration other than the electrode layer will be described. Various compounds have been reported for the PVD-based polymer constituting the recording layer.However, it is desirable that the recording medium has ferroelectricity and has a rectangular shape as measured by dielectric hysteresis, such as vinylidene fluoride. A homopolymer and a vinylidene fluoride copolymer containing at least 50 mol% of vinylidene fluoride. Examples of the copolymer include a copolymer of vinylidene fluoride and ethylene trifluoride, propylene hexafluoride, ethylene trifluoride chloride and the like. Polyvinylidene cyanide, vinylidene cyanide, and vinyl acetate copolymer are also exemplified. Among them, vinylidene fluoride and ethylene trifluoride copolymer (hereinafter abbreviated as P (VDF-TrFE)) are most preferable. 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, and curtain coating. Among them, those obtained by dip coating or spinner coating are preferable from the viewpoint of forming the PVD polymer into a uniform film thickness and obtaining an ultrathin film. To describe other electrode materials employed in the present invention,
As a transparent electrode, tin-doped indium oxide (IT
O), tin oxide, undoped indium oxide, and the like. Translucent electrodes include various metals such as gold, platinum, silver, lead, zinc, aluminum, nickel, tantalum, titanium, cobalt, niobium, palladium, and tin. Examples include vapor deposition, CVD, and sputtering films, but are not particularly limited thereto. As a material of the substrate 4 which is a support of the electrode,
Polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate,
Various plastics such as polyamides, polyimides, polyolefins, acrylic resins, phenolic resins, epoxy resins and the above derivatives and glass, quartz plates, ceramics and the like are preferable, but it is preferable that they are transparent to irradiation light, It is preferable that they also serve as insulation with respect to the above, but the present invention is not limited to these. The irradiation light source is a semiconductor laser (L
D) is considered optimal. The irradiation direction of the LD light may be from either the upper or lower electrode side, but in that case, as described above, it is sometimes desirable that the electrode on the light source side is transparent to the irradiation light. FIG. 2 shows an example in which an undercoat layer 5 is provided on the surface of the lower electrode 2. The undercoat layer 5 is formed by applying or vapor-depositing a surface treating agent on the surface of the lower electrode 2, and the following are mentioned for the purpose. 1) Improvement in adhesion to electrodes 2) Improvement in storage stability of the recording layer 3) Barrier properties of water, gas, solvent, etc. In the above, particularly, the main property is required to be 1. The surface treatment agents used there include hexamethyldisilazane (HMDS), trimethylchlorosilane (TMCS), dimethylchlorosilane (DMCS), and dimethyldichlorosilane (DMDC).
S), bis (trimethylsilyl) acetamide, t-butyldimethylchlorosilane, bis (trimethylsilyl)
Trifluoroacetamide, trimethylsilyldiphenylurea, bistrimethylsilylurea and the like.
It has also been confirmed that a titanium-based coupling agent (anchor coating agent) is effective in addition to the silylating agent. FIG. 3 shows an example in which a protective layer 6 is provided on the upper electrode 3. This protective layer is intended to protect the recording layer from scratches, dust, dirt, etc. and to improve the storage stability of the recording layer. As
It is formed from various polymer materials, silane coupling agents, glass, and the like. Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. Comparative Example 1 A P (VDF-TrFE) film was applied to a thickness of about 1 mm on an ITO vapor-deposited glass by spin coating to a thickness of 1 μm to form a recording layer 1.
Was formed. Gold was used as the upper electrode for this sample. Was deposited, and a voltage of 100 V was applied to the P (VDF-TrFE) film to perform a poling treatment. Further, while applying a reverse electric field of 25 V, using a semiconductor laser having an oscillation wavelength of 830 nm (hereinafter abbreviated as LD), applying P (V
(DF-TrFE) Information was recorded by heating several places in the layer. Thereafter, the LD light intensity is reduced to 0.55 mW, and the P (VDF-TrFE) layer is again irradiated with LD light while chopping at 10 kHz, the pyroelectric current generated between the electrodes is measured, and the recorded information is read out. It turned out that the S / N ratio was 25 dB. Example 1 In the same manner as in the comparative example, a P (VDF-TrFE) film applied to a thickness of 1 μm on an ITO vapor-deposited glass having a thickness of about 1 mm by a spin coating method to form a chromium as an upper electrode. Was deposited to a thickness of about 500 mm. After poling the sample by applying an electric field of 100 V, while applying a reverse electric field of 25 V, a semiconductor laser light having an oscillation wavelength of 830 nm is applied with an intensity of 5.5 mW.
Then, the sample was irradiated from the lower ITO electrode side to heat several places of the sample to record information. When the recorded information was read out in the same manner as in the comparative example, it was found that the S / N ratio was 35 dB. Example 2 Platinum was applied to the upper electrode in the same manner as in the comparative example. Was used to prepare a sample. The S / N ratio of the sample was measured and found to be 39 dB. Example 3 Germanium was added to the upper electrode in the same manner as in the comparative example. A sample was prepared using the method described above, and its S / N ratio was evaluated. Example 4 Tellurium was used for the upper electrode A sample was prepared and evaluated using the same method as in the comparative example, and it was found that the S / N ratio reached 49 dB. Example 5 Bismuth for the upper electrode To prepare a sample in the same manner as in the comparative example below.
Upon evaluation, the S / N ratio was found to be 45 dB. Example 6 Titanium was used for the electrode. To prepare a sample in the same manner as in the comparative example below.
Upon evaluation, the S / N was found to be 44 dB. Example 7 Antimony as upper electrode Was used to prepare and evaluate a sample in the same manner as in the comparative example, and it was found that the S / N ratio was 42 dB. Example 8 Nickel as upper electrode To prepare a sample in the same manner as in the comparative example below.
Upon evaluation, the S / N ratio was found to be 40 dB. Example 9 Niobium as upper electrode To prepare a sample in the same manner as in the comparative example below.
Upon evaluation, the S / N ratio was found to be 40 dB. Example 10 5 wt% of a cyanine dye represented by the following formula was dispersed in a P (VDF-TrFE) solution, and the dispersion was coated on a 1 mm-thick ITO vapor-deposited glass.
The recording layer 1 was formed by spin coating at a thickness of 1 μm. Tellurium as the upper electrode of this sample Was deposited. When this sample was prepared and evaluated by the same operation as in the comparative example, it was found that the S / N ratio reached 55 dB. Example 11 In the same manner as in Comparative Example 1, tin [k / (ρ ·
c) = 5.11 × 10 ⁻⁵ w · m ² · J ⁻¹ ] to prepare a sample. When the S / N ratio of the sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 32 dB. Example 12 In the same manner as in Comparative Example 1, zinc [k / (ρ ·
c) = 5.22 × 10 ⁻⁵ w · m ² · J ⁻¹ ] to prepare a sample. When the S / N ratio of the sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 33 dB. Example 13 In the same manner as in Comparative Example 1, molybdenum [k /
(Ρ · c) = 6.97 × 10 ⁻⁵ w · m ² · J ⁻¹ ] to prepare a sample. When the S / N ratio of the sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 31 dB. Example 14 In the same manner as in Comparative Example 1, tungsten [k /
(Ρ · c) = 8.95 × 10 ⁻⁵ w · m ² · J ⁻¹ ] to prepare a sample. When the S / N ratio of this sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 30 dB. Comparative Example 2 In the same manner as in Comparative Example 1, silver [k / (ρ · c) was applied to the upper electrode.
= 2.30 × 10 ⁻⁴ w · m ² · J ⁻¹ ]. When the S / N ratio of this sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 15 dB. Comparative Example 3 In the same manner as in Comparative Example 1, aluminum [k /
(Ρ · c) = 1.20 × 10 ⁻⁴ w · m ² · J ⁻¹ ] to prepare a sample. When the S / N ratio of the sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 25 dB. Comparative Example 4 Copper [k / (ρ · c)] was applied to the upper electrode in the same manner as in Comparative Example 1.
= 1.48 × 10 ⁻⁴ w · m ² · J ⁻¹ ]. When the S / N ratio of this sample was measured under the same conditions as in Comparative Example 1, it was confirmed to be 22 dB. From the results of the above Examples and Comparative Examples, when the material constituting at least one electrode satisfies k / ρ · c ≦ 1.0 × 10 ⁻⁴ w · m ² / J, the S / N ratio is It is 30 dB or more and can be practically used as a ferroelectric polymer optical recording medium.
Those that do not satisfy the above formula cannot reach 30 dB,
It cannot be used as the same medium. [Effects] As described above, by utilizing the present invention, the light absorption efficiency of the ferroelectric polymer optical recording medium is improved, and the diffusion of the generated heat is reduced, whereby the sensitivity of the optical recording medium is reduced. In response to a low-power irradiation light such as a semiconductor laser, and has a remarkable effect that a series of operations of writing, reading, and erasing can be smoothly performed. Things.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 3 are structural model diagrams of a ferroelectric polymer recording medium of the present invention. 1 ... recording layer, 2 ... lower electrode, 3 ... upper electrode, 4 ...
... substrate, 5 ... undercoat layer, 6 ... protective layer.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shuji Motomura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-1-97923 (JP, A) (58) Surveyed field (Int.Cl. ⁶ , DB name) G11B 9/02 G06K 19/00 K

Claims (1)

(57) [Claims] In an optical recording medium comprising a vinylidene polymer,
A ferroelectric polymer optical recording characterized in that at least one of the pair of electrodes sandwiching the recording layer composed of the vinylidene polymer has physical properties satisfying the following conditional expressions: Medium. Where: k: thermal conductivity (w · m ⁻¹ · K ⁻¹ ) ρ: density (g · m ^-3 ) c: specific heat (J · g ⁻¹ · K ⁻¹ )