JPS6363145A - Optical recording medium - Google Patents

Abstract

PURPOSE:To permit high-speed erasure without decreasing recording sensitivity by providing a layer consisting of a heat insulating material between a good conductor which is a heat generating source for induction heating and recording material. CONSTITUTION:This recording is constituted of at least a substrate, the record ing material, the heat insulating material, and the good conductor. The good conductor is provided in the recording medium and the heat insulating material is provided between said conductor and the recording material. The recording material is heated by laser light 11 but the escape of the heat from the record ing material to the good conductor at the time of recording is prevented by the layer of the heat insulating material; therefore, the recording sensitivity is not impaired. As to the erasure, on the other hand, heating over a wide range is infeasible with only the laser light, but the heating of the good conduc tor over a wide range is made possible by the eddy current generated with a change in magnetic flux and the erasure is speeded up. Since the recording material is indirectly heated from the inside of the substrate, the partial erasure and rewriting are obviated and the need for heating the substrate is eliminated as compared to the laser light 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium for optically recording and reproducing information.

[Conventional technology]

Devices that use laser light focused on the submicron order to record information at high density on a recording medium and play it back can record large amounts of information such as video and audio, and will be useful in the future information society. It is expected that it will become an indispensable device. For example, "Nikkei Electronics J
There is an optical disk device (known as 1984°3.26). Optical disk devices include (1) playback-only type, (2)
There are three types: write-once type and (3) rewritable type, and read-only type and write-once type have almost reached the stage of practical use.

On the other hand, there is still no established method for rewritable formats.
Research and development of rewritable optical disks using phase change materials and the like is actively underway. Optical discs using phase change materials currently being researched use a method of erasing data using laser light.

[Problem that the invention seeks to solve]

In the case of optical discs that utilize the above-mentioned phase change, the erasing sensitivity is generally slower than the recording sensitivity, so it has been necessary to use a method of irradiating an elongated beam for erasing or a method of slowing the rotation speed.

In addition, because the erasing temperature is higher than or close to the heat-resistant temperature of the substrate, although it can be erased by heating it for a long time in a thermostatic oven, it actually cannot be erased. When adding , there was a problem in that the temperature of the medium during recording was prevented from rising due to the good conductor with high thermal conductivity, resulting in a decrease in sensitivity.

An object of the present invention is to provide an optical recording medium that enables high-speed erasing without reducing recording sensitivity.

[Means for solving problems]

The present invention enables high-speed erasing without reducing recording sensitivity by providing a layer of heat insulating material between a good conductor, which is a heat source for induction heating, and a recording material.

[Effect]

That is, although the recording material is heated by the laser beam, the heat insulating material layer prevents heat from escaping from the recording material to the good conductor during recording, so that recording sensitivity is not impaired. On the other hand, for erasing, it is not possible to heat a wide range with laser light alone, but a good conductor can be heated over a wide range due to eddy currents accompanying changes in magnetic flux, making it possible to speed up erasing. Furthermore, since the recording material is indirectly heated from inside the substrate, there is no unerasure or rewriting compared to laser light, and there is no need to heat the substrate.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, 10 is a recording medium for optical memory, which includes at least a substrate,
It consists of a recording material, a heat insulating material, and a good conductor. The insulating material used here is a material that is highly sensitive to electromagnetic waves such as lasers, and is a material that is highly sensitive to electromagnetic waves such as lasers.
Recording materials using crystalline-amorphous phase change, such as the recording material disclosed in No. 6897, or Japanese Patent Application Laid-Open No. 166-1983
487 and JP-A-60-180887, etc., which are organic memory materials using dyes and polymers, are characterized by: (1) high-speed recording but slow erasing; (2) Is the erase temperature higher than the heat resistant temperature of the substrate (120 to 150 C for plastic substrates)?

Therefore, during erasing, a technique is required to heat the recording material from the inside of the substrate, that is, without heating the substrate, and to continue heating the recording material for a certain period of time. Induction heating using a high frequency magnetic field is a suitable acceleration means for this purpose. According to this method, only the good conductor can be heated without heating the insulator. In the present invention, a good conductor is provided inside the recording medium, and a heat insulating material is provided between the good conductor and the recording material. When a change in magnetic flux is applied to this recording medium from the outside, the recording material can be indirectly heated by heat generated by eddy current loss generated in a good conductor.

Further, in order to prevent deterioration of recording sensitivity due to the influence of a good conductor with high thermal conductivity, which causes a rise in temperature of the recording material during recording, a heat insulating material is provided between the good conductor and the recording material.

Figure 2 specifically shows the effect of the heat insulating material. In the figure, 10 represents a recording medium, 11 represents a recording spot, 12 represents a laser beam, and 13 represents heat conduction from the recording spot to a good conductor. FIG. 2(a) shows the case where a recording laser beam is irradiated onto a recording medium with a film structure that does not include a heat insulating material.
Figure (b) shows the case where a heat insulating material is included.As is clear from Figure 0, in a film configuration that does not include a heat insulating material, heat conduction from the recording spot to a good conductor is greater than in the case where a heat insulating material is included. , the temperature rise of the recording spot becomes pure.

FIG. 3 shows the change in recording spot temperature over time during recording. In the figure, α and β rays are shown in Figure 2 (a) and (b), respectively.
) represents the temperature change of the recording medium with the film configuration. Also γ
The line shows the case of a recording medium with a normal film structure that does not contain a good conductor.

tz * tx + and t8 are the recording times in each case. As explained in FIG. 2, when a heat insulating material is not included, the heat conduction from the recording spot to the good conductor is greater than when it is included, so the temperature rise during recording is slower. If the time when the recording spot temperature reaches the recording temperature is the recording time, as shown in the figure.

tx>ti≧t8. However, by changing the material and film thickness of the heat insulating material, the β rays can be freely set between α rays and γ rays. In other words, if you increase the thickness of the insulation material or choose a material with low thermal conductivity, β rays will approach γ rays, and if you decrease the thickness of the insulation material or choose a material with high thermal conductivity, β rays will approach γ rays.
The line approaches the alpha line. At this time, the recording time t2 is tl and t8
The recording sensitivity can be freely set within this range.

FIG. 4 shows the temperature distribution inside the recording medium during recording and erasing. 10 in FIG. 1 represents the recording medium. Fourth
FIG. 4(a) shows the temperature distribution during recording, and FIG. 4(b) shows the temperature distribution during erasing. θ1 and θ2 are recording and erasing temperatures, respectively. The recording time and erasing time of the recording material are respectively tw and te, and the half width of the temperature distribution in the film thickness direction during recording and erasing is λ1. Let it be λ0.

Generally, since tw<to, the thickness λ and the thickness λ· as shown in the figure are set.Therefore, the film thickness λ of the heat insulating material between the recording material and the good conductor is set to be λ, <λ×λ6. As a result, during recording, heat conduction from the recording material to the good conductor is reduced, so that the recording sensitivity does not decrease as explained in Figure 3, and during erasing, heat is sufficiently conducted from the good conductor heated by the eddy current to the recording film. It becomes erasable. Furthermore, compared to the case where the recording material is directly heated and erased using a laser or the like, when the recording material is heated indirectly by the method of the present invention, the temperature distribution within the recording material becomes uniform and rewriting is prevented. The recording material can be completely erased.

This effect is facilitated by an insulating material between the recording material and the good conductor.

The film structure shown in FIG. 1 explained above shows the minimum film structure for carrying out the present invention, and when used as an optical memory medium, in addition to these films, a film for forming grooves and a film for optical 6 Important elements of the present invention in which an absorbing film, a protective film to prevent deterioration of the recording material, and a heat insulating film to protect the substrate and groove forming film from the heat of the recording material film are often added. A good conductor film is included in at least one layer of the film, and a heat insulating film is included between the recording material film and the good conductor film.

Next, a specific magnetic flux generation method will be explained.

The magnetic flux generator 20 in FIG. 5 includes a coil 22.degree. switch 24. Power supply 26. It is composed of a variable resistor 28.

When switch 24 is turned on, current flows through coil 22 and magnetic flux H is generated. If the positions of this magnetic flux generator 20 and the disk 10 vary relative to each other, eddy electric lacquering will occur on the conductor of the disk 1o. Further, the variable resistor 28 is used to control the strength of the magnetic flux H, and can be adjusted according to the sensitivity of the recording medium.

FIG. 6 shows the configuration of an optical disk device suitable for carrying out the present invention, in which an optical disk 1o is rotated by a motor 30. As shown in FIG. Currently, optical disk devices have been developed that use a constant one-rotation speed method and a constant circumferential speed method, but either of these methods will be used here. In a normal optical disk device with such a configuration, information or data is recorded, reproduced, and erased by the optical head 40 controlled by the signal processing system 150, but the present system is further characterized by magnetic flux generation. This is because a container 20 is added.

That is, as explained with reference to FIG. 5, a magnetic field is generated by the magnetic flux generator 20, eddy currents are generated within the optical disk 10, and the disk is heated.

In this way, the recording medium in the disk reaches the erase temperature θ2
When this point is reached, the information or data recorded on the disc will be erased. Further, this magnetic flux generator N20 can also be used to improve recording sensitivity. That is,
When heating the recording medium with eddy current, heating it to the highest possible temperature below the erase temperature 02 will reduce the heating burden on the optical head 40 and shorten the time required to reach the recording temperature θl. Although the example is shown in which the head 20 is located on the opposite side to the head 40, it is of course possible to install the head 20 on the same side. Furthermore, as shown in FIG. 7(a), there is an override recording system in which recording is performed while erasing by arranging the positional relationship between the eddy current generating section and the optical laser spot as shown in the figure with respect to the rotational direction of the disk. can be realized. That is, as shown in FIG. 7(b), although the temperature rises due to eddy current, the amount of eddy current generation is controlled so that the time of 02 or more is slightly less than the erasing time. Therefore, when the temperature laser is not irradiated, the temperature decreases like alpha rays, and when it is irradiated, the temperature can be maintained like beta rays, making it possible to erase. In addition, the intensity of the laser can be further increased like a γ ray to reach the recording temperature θ↓ for recording. In this way, the feature of this system is that recording and erasing can be performed only by laser intensity modulation.

〔Effect of the invention〕

According to the present invention, since the recording material can be heated from the inside of the substrate, it is possible to heat a wide range without overheating the substrate, so it is possible to achieve faster erasing, and there is also a heat insulating material between the recording material and a good conductor. Therefore, it is possible to avoid reducing the recording sensitivity.

[Brief explanation of drawings]

FIG. 1 is a film configuration diagram of a recording medium according to an embodiment of the present invention, and FIG.
1! l is a schematic diagram showing heat conduction from the spot during recording,
Figure 3 is a temperature change diagram of a recording spot, Figure 4 is a temperature distribution diagram during recording and erasing, Figure 5 is a diagram of a magnetic flux generator for implementing the present invention, and Figure 6 is a diagram for implementing the present invention. A system diagram of a preferred optical disk device and FIG. 7 show a system diagram of an override system. 10... Recording medium, 11... Recording spot, 12.
...Laser light, 13...Heat conduction, 20...Magnetic flux generator, 22...Coil, 24...Switch, 26...
・Power supply, 28... Variable resistor, 30... Motor, 4
0... Optical head. to---i I now have 21 tombs of 17, 2 figures (α) (b) Time 4th figure on the left side of the left side of the mouth

Claims (1)

[Claims] 1. An optical recording medium that has a good conductor inside and erases memory contents by induction heating the good conductor using a high-frequency magnetic field, characterized in that a heat insulating material is added between the good conductor and the recording material.