JPH0451819B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an optical recording/reproducing method. BACKGROUND TECHNOLOGY AND PROBLEMS Conventionally, many optical recording media using organic dyes have been proposed, but the recording principle of these recording media is that the dye absorbs light (often laser light) and generates heat. Changes in the shape of the recording medium due to
Since the method is based on pit formation), it is necessary to provide a spacing layer or the like that can absorb the change, making the structure of the recording medium complicated. Also,
Conventional optical recording media using organic dyes detect changes in the light reflectance and transmittance of the medium after irradiation with light, so the rate of change is usually 10% or more, preferably 15% or more. something is required. Therefore, it is currently difficult to reduce the energy required for recording and shorten the irradiation time. Furthermore, conventional optical recording media involve vaporization and dispersion of dye molecules due to pit formation, and are not reversible. For optical recording media that have these problems,
Recently, recording media that utilize the phase change of inorganic crystals due to thermal mode have been proposed, but because these are inorganic materials, simple film forming methods such as coating and casting cannot be used, and vacuum evaporation and sputtering methods cannot be used. It is necessary to use relatively complicated film-forming methods such as In view of these circumstances, the inventors of the present invention have conducted intensive studies on optical recording media that are soluble in organic solvents, can be coated, have high sensitivity, and are erasable and reproducible. The present inventors have completed the present invention by discovering that a special aggregate of 200 exhibits polarization dichroism in the state of a solid film, and that when this substance is brought into a non-association state by light irradiation, it loses its polarization dichroism. Summary of the present invention An optical recording medium according to the present invention includes a substrate, a recording layer, and optionally a reflective layer and a protective layer, in which the recording layer is an organic dye exhibiting polarization dichroism. It is characterized by being a molecular association. Further, in the recording/reproducing method using the optical recording medium according to the present invention, recording is written by irradiating the recording medium with a laser to change the polarization dichroism of the organic dye molecule association in the recording medium. After performing this, the recording is read by detecting changes in the dichroism ratio or rotation angle of the transmitted or reflected polarized light of the light irradiation section. In the optical recording medium used in the present invention, the lamination order of each layer is 1) substrate - (reflection layer) - recording layer -
(protective layer) and 2) substrate-recording layer-(reflective layer) [However, the layer in parentheses is not essential]. According to the lamination order 2) above, it is also possible to create a structure in which the recording layer is sandwiched between the substrate and the reflective layer and hermetically protected. Of each layer, the layers other than the recording layer must be optically inactive, and in particular must not exhibit optical anisotropy such as birefringence. Examples of organic dye molecules used in the present invention include merocyanine and cyanine dyes represented by the following formulas. These dye molecules are
It is used alone or mixed with other dye molecules or with other film-forming substances, and is a special aggregate (usually J-aggregate or Scheibe
The film is formed to form aggregates (called aggregates). As a method for forming the film, a Langmuir Blossom method or a coating method is used. [In the above formula, A represents S, O, C(CH ₃ ) ₂ or Se, X represents a halogen atom or a perhalogen ion, and R ₁ , R ₂ , R ₃ , R ₄ and R ₅ each represent independently represents an alkyl group having 1 to 25 carbon atoms, R ₆ represents H, an alkyl group having 1 to 4 carbon atoms, or an alkoxyl group having 1 to 4 carbon atoms, and n ₁ and n ₂ are 0
_n3 represents an integer of 1 to 3. ] Among these, the following compounds are preferred from the viewpoint of ease of acquisition.

【table】

[Table] Formation of aggregates by the Langmuir Blosget method is carried out as follows. First, a solution of the cyanine dye, etc. dissolved in an organic solvent is dropped onto the water surface of the aquarium (at this time, other molecules such as hexadecane and stearic acid are mixed to an extent that does not interfere with the formation of J-aggregates). ) Obtain a monolayer. Then,
While compressing this monomolecular film with a constant surface pressure,
The monomolecular film is transferred onto the substrate by vertically immersing the substrate into this film and repeating the pulling operation a desired number of times. In this way, a J-aggregate in which the dye molecules are oriented in the direction of infiltration and withdrawal of the substrate is obtained. It is also possible to form a J-aggregate by a coating method. In particular, in the case of the above-mentioned merocyanine dyes, a single solution of the dye or other matrix materials (such as polymethyl methacrylate, polycarbonate, polyvinyl chloride, By casting a mixed solution of polymer materials (polystyrene, polyvinylidene fluoride, polysulfone, etc.), evaporating the solvent, and immersing it in an alkaline aqueous solution,
J-aggregates are easily generated. At this time, an inorganic material (e.g., mica) or an organic polymer material (e.g.,
By using polyvinylidene fluoride, aromatic polyimide, etc.), the J-aggregates become in-plane oriented on the substrate and exhibit polarization dichroism. It was known that the light absorption spectrum of the J-aggregates formed in this way changes greatly due to changes in the minute aggregation state within the molecule due to heat, but it is believed that the J-aggregates exhibit polarization dichroism in the solid state. Until now, it was not known that this material exhibited optical inactivity due to the heat generated by light irradiation. The basic principle of the present invention is to utilize such characteristics of the J aggregate to read the difference in polarization dichroism or optical rotation between the light-irradiated area and the non-irradiated area. Polarization dichroism as used in the present invention means dichroism of linearly polarized light or circularly polarized light, and the former refers to the dichroism of dyes (aggregates).
The latter can be realized by in-plane orientation of the dye molecules, and the latter can be realized by an optically active dye molecule film or aggregate. When these dyes form a special association state like the J-aggregates mentioned above, the in-plane orientation of the dye molecules is disturbed when the J-aggregates dissociate due to heating such as laser irradiation. If so, the dichroism of linearly polarized light is reduced. In addition, although dye molecules form J-aggregates, if they do not originally exhibit in-plane orientation, the maximum absorption wavelength of J-aggregates ( The optical rotation in the λmax) region decreases. In any of the above cases, the recorded portion written by laser irradiation is distinguished from the non-recorded portion by a change in the dichroic ratio or polarization rotation angle of the transmitted or reflected polarized light. As can be understood from the recording/reading principle, the recording medium of the present invention is reversible and rewritable in principle since it does not involve evaporation or dispersion of the dye in the recording area. In addition, reading records does not detect changes in reflectance or transmittance, as has been the case in the past, but rather detects slight changes in the polarization rotation angle (usually 0.05 to 0.50° is sufficient), so the reading required for writing is The light irradiation energy and time can be significantly reduced. The present invention will be described below with reference to Examples. Example 1 Merocyanine shown below (Nippon Kanko Shiki Co., Ltd.)
Co., Ltd., NK-2733) was dissolved in 25 ml of chloroform, and a 10 ^-4 mol/COCl ₂ aqueous solution (water temperature was 17
(controlled at ℃) 90μ drops onto the surface. then 15
After standing still for minutes, the film on the water surface was compressed at a pressure of 30 mN/m, and 60 layers were accumulated at a speed of 0.8 cm/min using the Langmuir-Blodget method on a glass substrate previously treated with octadecyltrichlorosilane. did. In this way, a thickness of approximately 2100 mm was placed on a glass substrate.
An optical recording layer with a thickness of 1.5 Å was formed. The angle of rotation of the polarized light incident on this optical recording medium was measured using an optical polarimeter (manufactured by JASCO Corporation) and was -8.22°, and when converted into specific optical rotation, it was -1.27×10 ⁷ °, which was extremely high. It was a large value. When this optical recording layer was instantaneously heated by flash light irradiation using a xenon lamp, the incident polarization rotation angle of the recording layer was drastically reduced to -0.90°.
From this, it was confirmed in principle that the recording medium can be used as a method for reading out records by changing the angle of rotation of incident polarized light due to heat. After placing the optically inactivated recording medium in a desiccator adjusted to 100% humidity and leaving it at 20°C for 30 minutes, the incident polarization rotation angle was measured again, and it was found to be -7.37° (relative). Optical rotation: −1.13 × 10 ⁷ °), which was almost the initial value. From this, it was confirmed that the recording medium of the present invention is reversible and, in principle, rewritable. Example 2 Using the optical recording medium reproduced in Example 1, a rhodamine dye laser (oscillation wavelength: 600 ± 10 nm) was generated.
When pulse irradiation was performed at 10 CPS with a diameter of 2.0 μm and a power of 30 mw, the incident polarization rotation angle decreased from −7.37° to −2.27°, confirming that laser recording was possible. Also, the recording sensitivity of this medium is
It was equivalent to 10mj/ ^cm2 . Example 3 100 mg of the merocyanine dye used in Example 1 was
It was dissolved in 10 ml of chloroform, and a film was formed on a clean glass plate by spin coating. The thus obtained recording medium having a dye layer with a thickness of 2600 Å was 1wt%
When immersed in a KOH aqueous solution for 10 seconds, the dye layer changed from red to blue-purple, indicating the formation of J aggregates. When this product was subjected to flash irradiation with a xenon lamp in the same manner as in Example 1, the incident polarization rotation angle was drastically reduced from -6.35° to -0.05°.
From this, the recording medium of this example in which the recording layer is the J-aggregate obtained by the coating method also
It was confirmed in principle that the change in polarization dichroism due to heat can be used as a method for reading out the record, similar to the medium obtained in . Example 4 Using the following cyanine dye instead of the merocyanine dye used in Example 1, a monomolecular film was formed on distilled water, and the film was coated on a glass substrate in the same manner as in Example 1.
Accumulated 60 layers. When the thus obtained recording medium having a dye layer with a thickness of 2200 Å was flash irradiated with a xenon lamp in the same manner as in Example 1, the incident polarization rotation angle was drastically reduced from -4.25° to -0.15°. From this, it has been confirmed in principle that the recording medium can be used as a method for reading out records based on changes in polarization dichroism caused by heat.

Claims (1)

[Claims] 1. Recording and reproduction using an optical recording medium consisting of at least a recording layer and a substrate that have polarization dichroism and whose polarization dichroism can be changed by light irradiation. When performing this, first, the recording medium is irradiated with a laser to change the polarization dichroism of the organic dye molecule aggregate in the recording medium, and then a record is written, and then the transmission or An optical recording/reproducing method, characterized in that recording is read out by detecting changes in the dichroism ratio or polarization rotation angle of reflected polarized light. 2. The optical recording/reproducing method according to claim 1, wherein the recording layer is an aggregate of cyanine or merocyanine dye molecules exhibiting polarization dichroism. 3. The optical recording/reproducing method according to claim 1 or 2, wherein the organic dye molecule association has an absorption band in the visible light to near infrared light region.