JP2555050B2 - Phase change optical recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an organic optical recording medium that can be additionally written with a semiconductor laser and can be erased as necessary.

BACKGROUND OF THE INVENTION Conventionally, as a write-once high-density optical recording method using a semiconductor laser, for example, a low-melting-point metal thin film such as tellurium is irradiated with laser light to form pits, and optical changes such as reflectance are changed. How to read is known. However, these media have fatal defects such as corrosiveness and toxicity. From this point of view, recently, a recording medium using an organic dye instead of the low melting point metal has been proposed. These utilize the property that a dye absorbs laser energy to cause sublimation, thermal decomposition, and the like to form a pit. However, there are generally very few dyes that exhibit absorption in the semiconductor laser oscillation wavelength range (near infrared region near 800 nm) and are thermally and environmentally stable. Moreover, dyes that absorb in the near-infrared region not only have poor solubility in organic solvents and are difficult to apply, but it is difficult to obtain a coating film with sufficient strength, and in order to obtain a strong homogeneous film, vapor deposition, etc. Although it is possible to form a film by the method described above, it has a defect that it is easily decomposed and difficult because it is an organic substance. In addition, pit formation by sublimation and thermal decomposition requires a large amount of energy, so that it is difficult to record with a small semiconductor laser with low output, and even if recording is possible, the sensitivity is low.

In general, among the organic dyes that include these problems, phthalocyanines are extremely stable both thermally and environmentally, and are resistant to vapor deposition and the like, and exhibit absorption in the near infrared depending on the type, It is known that it exhibits a crystalline polymorphism and causes a phase transition upon heating. For example, JP-A-60-483
In JP-A-96, a recording medium utilizing the fact that aluminum phthalocyanine, tin phthalocyanine, and germanium phthalocyanine are oxidized by irradiation with a semiconductor laser (oscillation wavelength: 830 nm) to change the absorption spectrum,
In the 60-154098 publication, metal-free phthalocyanine, copper phthalocyanine, cobalt phthalocyanine, and aluminum phthalocyanine chloride show absorption at 550 to 700 nm, and the crystalline form changes from α to β by irradiation with helium neon laser (oscillation wavelength 632.4 nm). A recording medium that utilizes the change to

However, in the former case, since the recorded record cannot be reversibly erased because it utilizes an irreversible oxidation reaction, there is a defect that the recording requires high energy. The latter case is a gas ether because the absorption wavelength range of the medium is 550 to 700 nm.
Suitable for recording with He-Ne laser (oscillation wavelength range 633 nm), but not suitable for recording with small semiconductor laser. Therefore, it is not suitable for an optical recording system that requires small size and light weight.

As a result of intensive studies in view of the above problems, the present inventors have found that magnesium phthalocyanine treated with a specific solvent has a crystal system different from both α-type and β-type, and is in the vicinity of 820 nm which is extremely close to the semiconductor laser oscillation wavelength range. In addition to exhibiting the maximum absorption wavelength (λmax), the present invention has reached the present invention by finding a surprising property that it easily undergoes a phase transition by heating and returns to the original state by a solvent.

[Object of the Invention] In view of the problems of the prior art, an object of the present invention is that recording is possible with a small semiconductor laser, and erasing is possible if necessary.
It is to provide an optical recording medium with high sensitivity, non-toxicity, and stability.

[Outline of the Invention] The recording principle of this medium is as follows. When the recording layer is irradiated with a semiconductor laser beam, the phthalocyanine aggregate in the recording layer efficiently absorbs the laser beam and a crystal phase change occurs due to the absorbed light energy. Then, the difference in transmittance between the changed portion (recording portion) and the unchanged portion (non-recording portion) is read by a weak semiconductor laser beam. Depending on the structure of the medium, transmissive reading is possible as shown in FIG. 1, and reflective reading is possible by providing a reflective layer behind the recording layer as shown in FIG.

In the present invention, the maximum absorption wavelength (λma
The thin film of the magnesium phthalocyanine crystal phase having x) is obtained by forming a thin film of magnesium phthalocyanine on a substrate by a vapor deposition method or a sputtering method, and then treating it with a specific organic solvent. As the organic solvent, halogenated hydrocarbons such as chloroform, methylene chloride, carbon tetrachloride, dichloroethane, dibromoethane and tetrachloroethylene are preferably used. The thin film before solvent treatment is AMHor, ROLoutfy, Thin So
As reported in lid Films, 106 291-301 (1983), it is an α-type crystal and shows λmax at 695 and 640 nm. Nguyen Chan Kae, Masao Aizawa, Journal of the Chemical Society of Japan 19
86 (3) β-type crystals are 6 as reported in p393-401.
Λ max at 80 and 625 nm. On the other hand, the thin film treated with the organic solvent is ROLoutfy, AMHor, G. Dipaola-B.
aranyi, CKHsiao, J.Imag.Sci., 29 (3) 116-121 (198
As shown in 5), it is a crystalline phase that is neither α-type nor β-type, and shows λmax at about 820 nm. The thin film used in the present invention has a strong absorption in the semiconductor laser oscillation wavelength range.
A thin film of 05 to 1.0 μm is suitable.

As the substrate used in the present invention, in addition to glass and metal, films and plates of organic polymer materials such as polyester, polycarbonate, polymethylmethacrylate, polyvinyl chloride, epoxy resin, polyimide resin, and cellulosic resin are suitable. Used for. Further, when reading using reflected light, it is necessary to provide a reflective layer. As the reflective layer, a metal having a high reflectance in the laser oscillation wavelength region such as Al, Cr, Au, Pt, Sn, Ag, Bi is preferable.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to this.

Example 1 A magnesium phthalocyanine thin film having a thin film of 0.18 μm was formed on a glass substrate by vacuum vapor deposition to obtain a strong blue transparent homogeneous film. This was immersed in chloroform at room temperature for 10 minutes and dried to prepare a medium. The coating film obtained was heated at 150 ° C. for 5 minutes. FIG. 3 shows visible spectra before the solvent treatment, after the solvent treatment, and after the heating. As is clear from the figure, the spectrum of the coating film before solvent treatment is
It showed λmax at 692 and 638 nm and showed α-type crystals. The spectrum of the coating film after solvent treatment is different from that before treatment,
It showed a strong absorption at 820 nm with an absorbance of 2.2. On the other hand, in the absorption spectrum of the coating film after the heat treatment, the absorption peak at 820 nm disappeared at all. After heat treatment, the coating was immersed in chloroform and the absorption at 820 nm was completely recovered, indicating that it was reversible.

When the X-ray diffraction spectrum of the coating film after the solvent treatment was measured, it was found to be crystals as shown in FIG.
Then, the coating film was observed under a microscope at a magnification of 400 times and found to be uniform, and the crystals were extremely fine.

Next, FIG. 5 shows changes with time in absorbance at 820 nm when the coating film after the chloroform treatment was heated at various temperatures.

As is clear from the figure, the absorbance decreased sharply when heated at 150 ° C. In other words, the transmittance increased sharply. On the other hand, at 100 ° C, there was almost no change in 1 hour, and at 80 ° C, there was no change even after standing for 100 hours. This indicates that this phase transition has a very sensitive temperature threshold, above which it changes very quickly, but below that it is very unlikely. That is, even if the semiconductor laser light having a weaker power than the semiconductor laser light used for recording is read as in general, it does not affect the unrecorded area at all, so that the high S / N ratio Is obtained.

A semiconductor laser (wavelength: 2 μm, power: 20 mW)
By writing at 830 nm), the transmissivity of the irradiated part increased remarkably compared with the unirradiated part.

Example 2 A 0.18 nm thick magnesium phthalocyanine thin film was formed on a glass substrate by vacuum evaporation. Then, this thin film is treated with dichloromethane, dichloroethane, dibromoethane,
Either trichloroethylene or carbon tetrachloride at room temperature
It was immersed for 10 minutes and dried to prepare a medium. The absorption spectra before and after the solvent treatment are shown in FIG. As is clear from the figure,
In each of the halogen-based solvents, a peak was shown near 820 nm. It was found that this peak disappeared completely by heat treatment at 150 ° C for 10 minutes.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structural example of a transmissive medium of the present invention, wherein 1 is a recording layer and 2 is a substrate. FIG. 2 is a cross-sectional view showing a structural example of a reflective medium, in which 3 is a reflective layer, 4 is a recording layer, and 5 is a transparent substrate. FIG. 3 shows visible absorption spectra of the medium of Example 1 before and after the solvent treatment and after heating. A in the figure
Correspond to spectra before solvent treatment, b after solvent treatment, and c after heat treatment of b, respectively. FIG. 4 shows the X-ray diffraction spectrum of the coating film after the solvent treatment. FIG. 5 shows changes with time in absorbance at 820 nm when the coating film after the solvent treatment was heated at various temperatures. FIG. 6 shows visible absorption spectra of the medium of Example 2 before and after the solvent treatment. In the figure, a corresponds to the spectrum before treatment with a solvent, b to dichloroethane, c to dibromoethane, d to dichloromethane, e to tetrachloroethylene, and f to the spectrum after treatment with carbon tetrachloride, respectively.

Claims (1)

(57) [Claims] 1. A phase change type optical recording medium which is mainly composed of a magnesium phthalocyanine crystal phase having a maximum absorption wavelength (λmax) at 800 to 850 nm.