JPS6236878B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention utilizes optical recording media, more specifically lasers, and in particular, optical energy with a relatively long wavelength that is compatible with the oscillation wavelength of a semiconductor laser, which allows the recording/reading system to be miniaturized. This invention relates to optical recording media that utilize state changes such as natural melting, evaporation, and sublimation. Conventionally, this type of recording medium has been made of chalcogenite-based amorphous glass (see Japanese Patent Publication No. 54-20136),
Te oxide (see Japanese Patent Publication No. 54-3725), carbon black dispersed self-oxidizing binder (Japanese Patent Publication No. 51
-35144), fluorescein (IEEE,
Spectrum August 1978, p. 20) etc. were used. Chalcogenite amorphous glass is used in the form of a vapor-deposited film as an optical recording material. This material is stable in both the amorphous and crystalline states, but in order to obtain a thin film using methods such as vapor deposition, a manufacturing process is required in which predetermined components are dissolved in a solid solution in vacuum and then rapidly cooled to obtain a uniform raw material. . Furthermore, since there are many kinds of component elements, it is difficult to obtain a raw material with a uniform composition and form a thin film. Furthermore, a thin film of chalcogenite-based amorphous glass has a large initial optical density in an unrecorded state, and has the disadvantage that when the contrast ratio is set high, the readout efficiency is extremely low. Te oxide thin films, which have higher sensitivity than chalcogenite amorphous glasses, are manufactured by vapor-depositing _TeO2 , but the main component forming the thin film is TeOX (X
is assumed to be 0<X<2), and the composition of the thin film changes depending on the deposition conditions, making it quite difficult to manufacture a uniform thin film. Also, the sensitive wavelength range of Te oxide thin film is 350 to 600n.
m, and has the disadvantage that it essentially has no sensitivity when a recording light source is used in a long wavelength region. When a dye-dispersed organic thin film uses a self-oxidizing material such as nitrocellulose as a binder, it has the potential to surpass the above-mentioned inorganic thin film in terms of sensitivity. However, since the medium must be manufactured using a spin coating method from a solution or a casting method, it is very difficult to create a uniform thin film using these methods when increasing the size of an optical recording medium. Furthermore, it is difficult to uniformly disperse absorbers such as dyes and binders in a solution state, and there is a drawback that resolution is poor due to non-uniformity of dispersion of dyes etc. Thin films of fluorescein are obtained by vapor deposition.
It has the same sensitivity resolution as Te oxide. However, since the absorption wavelength is in the visible region of 480 nm, the light source for writing and reading is limited, and it has the disadvantage that it cannot correspond to the oscillation wavelength of semiconductor lasers, which are suitable for downsizing recording and reproducing devices. The vapor deposition of dyes with long absorption wavelengths is easily inferred, but ordinary long wavelength light-absorbing dyes have drawbacks in thermal stability and sublimability, and it is generally difficult to form thin films. (Kyoritsu Zensho Photo Chemistry, p. 62) The present invention was made in view of the above-mentioned current situation, and its purpose is to provide optical recording using a thin film on a substrate of squarylium dye, which has the ability to absorb light in a relatively long wavelength range. Another object of the present invention is to provide an optical recording medium that is excellent in reproducibility of thin film composition and uniformity of thin film. The optical recording medium of the present invention which achieves the above object has a general formula on a substrate.

[Formula] or

It is characterized by providing an organic thin film made of a squarylium dye represented by the formula: (wherein X represents a chromophore). To explain the present invention in detail, in the present invention, the squarylium dye represented by the general formula above that forms an organic thin film is squaric acid (3.4
-dihydroxy-3-cyclobutene-1,2-dione) and a compound having a corresponding chromophore. Next, some specific examples of squarylium dyes used in the present invention are shown in the following table.

【table】

[Table] Squarylium dyes have the ability to absorb light in a relatively long wavelength range, but compared to ordinary dyes, they have excellent storage stability and heat resistance, and have the characteristics of being able to withstand sublimation operations. An example of these dyes having sharp melting and sublimation properties is shown in FIG. In Figure 1, curve 11
is the thermogravimetric change curve of (4)−(a) among the pigments shown in the table.
TG, and shows a significant weight loss at around 280℃. On the other hand, curve 12 is the differential scanning calorimetry curve of the same dye.
DSC, 13 indicates that the dye has a melting point at 312°C, and 14 indicates that the dye decomposes above 370°C. As shown in the figure,
It is clear that this dye is sublimable in a narrow temperature range around 280°C. It also shows that there is a temperature margin between the sublimation and decomposition temperatures, making it possible to easily deposit the film on the substrate and to perform laser recording on the deposited film with good resolution. Therefore, in the present invention, reproducibility of the thin film composition and uniformity of the thin film can be achieved by directly depositing the squarylium dye onto a substrate such as a polyester film, plastics such as Teflon, glass, or metal. Furthermore, squarylium dyes have absorption bands specific to the organic dye depending on their type, so by selecting a squarylium dye according to the type and wavelength of the recording light source, a very large thin film absorption coefficient can be obtained. It is possible to achieve improved sensitivity and improved signal/noise (S/N) ratio compared to conventional materials. Next, the present invention will be described with reference to Examples, but the present invention is not limited thereto in any way. Example 1 500 mg of the dye having the structure shown in Table (1) above was placed in a Mo boat for vapor deposition, evacuated to below 1 x 10 ^-6 mmHg, and then vapor deposited on a Pyrex (registered trademark, hereinafter omitted) substrate. During deposition, the heater is controlled so that the pressure in the vacuum chamber does not rise above 10 ^-5 mmHg. In this way, a Pyrex substrate optical recording medium was produced. When the optical recording medium was irradiated with a He--Ne laser having a wavelength of 632 nm, the exposed area sublimated and the thin film at the exposed area disappeared. Curves 22 and 21 in Figure 2 (1)
This figure shows the transmittance in the visible and near-infrared region before and after irradiation with a He-Ne laser for a medium on which a dye of 0.2 μm is deposited to a thickness of 0.2 μm. It is clear that recording can be performed using a laser having an oscillation wavelength in the 650-750 nm band. Recording sensitivity for He-Ne laser light is approximately 50m
It was J/ ^cm2 . Example 2 The dyes (4)-(a) in the table above were prepared in the same manner as in Example 1.
An optical recording medium was prepared by depositing Al to a thickness of 0.2 μm on a substrate. This was irradiated with a He--Ne laser and the reflected light from the medium was measured. The results are shown in FIG. Curve 32 and curve 31 show the reflection spectra before and after laser irradiation, respectively. Third
As is clear from the figure, even in the reflection mode, there is sufficient contrast between the exposed and unexposed areas. The recording sensitivity was approximately 40 mJ/cm ² . Example 3 In the same manner as in Examples 1 and 2, the dyes (5) to (a) in the table above were deposited on a Pyrex substrate to a thickness of 0.15 μm to prepare an optical recording medium. This was irradiated with an 830 nm semiconductor laser. The transmitted light of the medium was measured and the results are shown in FIG. Curve 42 and curve 41 show the transmittance before and after laser irradiation, respectively. Although the absorption is broader than that of dye (1) and dye (4)-(a), it is clear that recording is possible for light of 830 nm. The recording sensitivity to the semiconductor laser was approximately 50 mJ/cm ² . As is clear from the above examples, the present invention has the following advantages by using squarylium dye. (1) Easy to manufacture Since the composition is a single organic dye, uniform and high-quality thin films can be easily obtained by vapor deposition or other methods.
In addition to glass and metal, media substrate materials include
Plastics, paper, etc. can also be used as substrate materials because vapor deposition is easy and the rise in substrate temperature is small. (2) High sensitivity As shown in the examples, by selecting a dye according to the wavelength of the recording light source, high sensitivity can be achieved regardless of the type of recording light source. In terms of sensitivity, it is a fraction of that of metal thin films and chalcogenite glass, and is equivalent to Te oxide thin films. (3) High contrast ratio When reading records in transmission mode or reflection mode, the contrast ratio before and after exposure is extremely high because the substance on the medium is completely removed. (4) High resolution Organic dyes inherently have low thermal conductivity, and when recording as shown in the examples, the resolution depends on the thermal conductivity of the thin film, but they are excellent in this respect. In addition, as shown in Figure 1, the thermal properties of squarylium dye have very sharp changes, and the threshold for change due to irradiation energy is clear.
It has a resolution of lines/cm or higher. (5) High stability Because the contrast ratio is extremely high, the light energy for reading can be kept small, so it is extremely stable even for long-term use. Furthermore, since the absorption wavelength range is narrower than that of other optical recording media, the stability against light outside the absorption range is particularly excellent.

[Brief explanation of the drawing]

Figure 1 shows the table described in the detailed description of the invention.
(4)-(a) Thermal characteristics diagram of the squarylium dye, Figure 2 shows the optical recording characteristics of the squarylium dye shown in (1) of the same table.
FIG. 3 shows the optical recording characteristics of the squarylium dyes shown in (4)-(a) of the same table, and FIG. 4 shows the optical recording characteristics of the squarylium dyes shown in (5)-(a) of the same table.

Claims (1)

[Claims] 1. An optical recording medium that obtains an optical density change by applying optical or thermal energy,
An optical recording medium characterized in that an organic thin film made of a squarylium dye represented by the general formula [Formula] or [Formula] (wherein X represents a chromophore) is provided on a substrate.