JP2641049B2 - Optical information recording medium and recording method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rewritable optical information recording medium and a recording method thereof.

[Conventional technology]

As a rewritable optical recording medium, a magneto-optical recording medium, a phase transition type optical recording medium, and the like have been known.

The former magneto-optical recording medium has a recording layer of TbFe, GdFeCo
Recording and erasing are performed using a thin film of an amorphous alloy of a rare earth element such as a transition metal and a transition metal and utilizing the magnetic Kerr effect in the recording layer. With this type of optical recording medium, a high C / N value is difficult to obtain because the difference in light intensity obtained during reproduction is small.

The latter phase-change optical recording medium is known to utilize a phase change between a crystal such as a Te-based compound and an amorphous phase. However, as a more excellent stability, a liquid crystal solid phase and a nematic phase are used. Utilizing a reversible phase transition has been proposed. This has a structure in which a liquid crystal 1 is sealed between transparent electrodes 5 and 6 formed on the surfaces of transparent substrates 3 and 4, for example, as shown in FIG. 3 (JP-A-59-104624).

However, the optical information recording medium utilizing such a phase transition of the liquid crystal requires the transparent electrodes 5 and 6 for applying an electric field to the liquid crystal 1. At the time of recording, a contact must be brought into contact with an optical information recording medium rotating at a high speed, and a voltage must be applied to the transparent electrodes 5 and 6 through the contact.
Therefore, a relatively complicated structure and recording method must be adopted.

On the other hand, while applying a magnetic field to the liquid crystal, by irradiating a laser beam to the liquid crystal, the liquid crystal partially undergoes a phase transition to record information, and while applying a magnetic field to the liquid crystal from a direction different from the recording time,
An optical recording method of a phase transition type optical information recording medium in which information is erased by partially irradiating a liquid crystal by irradiating a laser beam thereto has already been proposed. When optical recording of this type is used, a transparent electrode for applying an electric field to the liquid crystal is not required.

[Problems to be solved by the invention]

However, in the conventional optical recording method of the phase-change optical information recording medium using a magnetic field, a high C / N value cannot be obtained, and the deterioration of the C / N value after repeatedly performing recording and erasing is large. There was a problem that.

The present invention solves the above-mentioned problems in the conventional rewritable optical information recording medium utilizing the phase transition of the liquid crystal, achieves a high C / N value, and also reduces deterioration of the C / N value after repeated reproduction. It is an object to provide a small optical information recording medium and a recording method thereof.

[Means for solving the problem]

The structure of the present invention will be described with reference to the reference numerals in the drawings. The optical information recording medium according to the first invention has a transition temperature of 15
The recording layer 12 is formed of liquid crystal exceeding 0 ° C. and lower than the temperature at the time of laser beam irradiation.

The recording method according to the second invention has a transition temperature of 150
A method of recording or erasing data on or from the recording layer 12 by irradiating the recording layer 12 with a laser beam having a temperature exceeding 100 ° C. while forming a magnetic field perpendicular to or parallel to the surface of the recording layer 12 at the irradiated location. It is.

[Action]

The transition temperature of the recording layer 12 is required to be sufficiently higher than room temperature in order to maintain the recorded state at room temperature.However, the present inventor has found that the C / N value and the C / N value after repeated reproduction are different. In terms of deterioration, the inventors have found that the transition temperature of the recording layer 12 is an important factor. That is, as described later, the recording temperature is set to a temperature exceeding 150 ° C. and the recording layer 12 is irradiated with a laser beam while applying a magnetic field perpendicularly to the surface of the recording layer 12 to perform recording. By applying a magnetic field in parallel to the surface of the layer 12 for erasing, it was confirmed that a high C / N value was obtained, and the decrease after repeated reproduction was extremely low. Specifically, a C / N value as high as 40 dB or more is obtained, and the decrease after repeated reproduction is 2 dB or less.

On the other hand, when the transition temperature of the recording layer 12 is 150 ° C. or lower, it is difficult to obtain a high C / N value, and the C / N value upon repeated reproduction is greatly deteriorated. Specifically, when the transition temperature of the recording layer 12 is about 80 ° C., the C / N value is as low as 35 dB, and the deterioration after repeated reproduction is as large as 10 dB.

〔Example〕

 Next, an embodiment of the present invention will be described.

(Example 1) 2% by weight of dianylsalbenzidine represented by the following chemical formula (a), which is a high-temperature liquid crystal, and an indole cyanine dye, which is a laser absorbing dye represented by the following chemical formula (b): 0.5% by weight was dissolved in diacetone alcohol.

This solution was applied to the surface of a polymethyl methacrylate substrate having a diameter of 130 mm and a thickness of 1.2 mm by a spinner method, passed through a magnetic field of 10 KOe so that the substrate cut the magnetic field vertically, dried, and dried to form a 70 nm thick recording layer. Formed. Further, a commercially available Lumiflon (manufactured by Asahi Glass Co., Ltd.) was applied thereon by a spinner method to produce an optical information recording medium.

As shown in FIG. 1, the magnetic poles of the electromagnets a and b were opposed at an interval of 2 μm, and these magnetic poles were used as the same magnetic pole to form a so-called combined magnetic pole. As a result, the recording layer
A semiconductor laser beam having a wavelength of 830 nm, an incident power of 10 mW, and a spot diameter of 1 μm is irradiated from the substrate 11 side while applying a vertical magnetic field of 1000 Oe to the surface of the substrate 12 at a linear velocity of 1.4 m / sec and a recording frequency of 500 KH.
Recorded with z.

Next, a wavelength of 830 nm and an incident power were applied to this optical information recording medium.
Irradiate 0.3mW laser light, measure C / N value of reproduction signal,
The results are shown in Table 1. Further, repeating the playback 10 ⁵ times, obtains a reduction in C / N value according to Table 1 The results
It was shown to.

Then, as shown in FIG. 2, the opposite magnetic poles are set to different magnetic poles, and while applying a parallel magnetic field of 1000 Oe to the surface of the recording layer 12, a wavelength of 830 nm, an incident power of 10 mW,
The above record was erased by irradiating a semiconductor laser beam having a spot diameter of 1 μm.

(Example 2) Optical information recording was performed in the same manner as in Example 1, except that 2% by weight of tetramethylbenzophenazine and 0.5% by weight of copper phthalocyanine were used instead of dianilsalbenzidine and indole cyanine dye. Made a medium.

In the same manner recorded in the optical information recording medium, by reproducing it, the initial C / N value and 10 ⁵ times after regeneration
The reduction of C / N value was determined, and these are shown in Table 1.

(Example 3) An optical information recording medium was produced in the same manner as in Example 1 except that dianylsalbenzidine derivative represented by the following chemical formula was used in the same amount instead of dianylsalbenzidine.

In the same manner recorded in the optical information recording medium, by reproducing it, the initial C / N value and 10 ⁵ times after regeneration
The decrease in C / N value was determined, and these are shown in Table 1.

Example 4 An optical information recording medium was produced in the same manner as in Example 2 except that tetramethylbenzophenazine was used in the same amount as dimethyltriphenylene represented by the following chemical formula.

In the same manner recorded in the optical information recording medium, by reproducing it, the initial C / N value and 10 ⁵ times after regeneration
The decrease in C / N value was determined, and these are shown in Table 1.

Comparative Example In Example 1, the same amount of pn-heptanoxybenzylideneaminobiphenyl iodine-substituted compound represented by the following chemical formula was used in place of dianilsalbenzidine, and an optical information recording medium was similarly produced. made.

In the same manner recorded in the optical information recording medium, by reproducing it, the initial C / N value and 10 ⁵ times after regeneration
The decrease in C / N value was determined, and these are shown in Table 1.

As described above, the transition temperature of the liquid crystal forming the recording layer 12 needs to be sufficiently higher than the normal temperature, and particularly, 150 ° C.
It is necessary to exceed This is because the transition temperature of the liquid crystal is
At a temperature of 150 ° C. or lower, a high C / N value is hardly obtained, and the deterioration of the C / N value upon repeated reproduction is large. Incidentally, while the transition temperature of the liquid crystal forming the recording layer 12 in the comparative example was 79 ° C., in Examples 1 to 4,
Exceeds ° C. And the latter C / N value is 40dB or more, 1
0 Degradation after ⁵ times playback is 2dB or less, whereas the former C / N
The value was 37 dB, and the deterioration after 10 reproductions of ⁵ times was 10 dB.

〔The invention's effect〕

As described above, in the optical information recording medium and the recording method according to the present invention, unlike the conventional optical information recording medium using a liquid crystal and the recording method, it is not necessary to apply an electric field to the liquid crystal. There is no need to sandwich layers,
It is not necessary to contact the optical information recording medium with a contact at the time of recording. In addition, an optical information recording medium having a high C / N value and having a small deterioration of the C / N value after repeated reproduction can be provided and a recording method thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conceptual diagram of an optical information recording medium and an optical recording method according to an embodiment of the present invention, and FIG. FIG. 3 is a longitudinal sectional view showing a conventional example of an optical information recording medium. 11 ... substrate, 12 ... recording layer

Claims (2)

(57) [Claims] In an optical information recording medium having a rewritable recording layer formed on a substrate, the recording layer is formed of liquid crystal having a transition temperature exceeding 150 ° C. or higher and lower than the temperature at the time of laser beam irradiation. An optical information recording medium characterized by being performed. 2. A method for recording on an optical information recording medium having a rewritable recording layer 12 formed on a substrate 11, wherein the upper recording layer 12 having a transition temperature exceeding 150.degree. A magnetic field perpendicular to or parallel to the surface of the recording layer 12.