JPH0319064Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) This invention relates to a rewritable optical recording medium that performs recording in heat mode.

(Prior art) In recent years, in the field of information processing, with the rapid increase in the amount and variety of information, conventional magnetic memory is becoming insufficient as a general recording method, and the I tend to want to. Therefore, as an alternative to the conventional recording method, an optical recording method using an optical recording medium is being considered.

As an example of a medium used in such an optical recording method,
There are metal thin films or metal-containing polymer materials.
Since this is a writing method that uses a laser beam to melt and evaporate the medium in the recording area to create a hole, it is impossible to erase or rewrite the recording.

On the other hand, a magneto-optical material is known as a first example of this rewritable optical recording medium. This performs reading using the magnetic force effect, but since this effect is small, the read S/N is very poor. Also, it is difficult to produce a homogeneous medium. A second example is the use of amorphous chalcogenide for photodarkening, but this material is sensitive to photodarkening at short wavelengths, and there are significant limitations on the wavelengths that can be used. As a third example, a medium that combines a thermoplastic polymer and a photoconductor is known, but it requires corona discharge and whole surface heating during recording, which is not convenient.
Also, the sensitive wavelength is limited by the photoconductor.

As described above, conventional optical recording media have many problems and drawbacks, such as many of them being non-rewritable, and those that are rewritable having insufficient characteristics. This is the reality.

(Purpose and structure of the invention) Therefore, the inventors of the present invention conducted numerous tests and studies to solve these drawbacks, and as a result, they arrived at the present invention. The present invention consists of forming a reflective layer, a light-absorbing layer, and a thermoplastic layer in this order on a substrate made of conductive glass such as Nesa Glass that can generate heat when energized, and also incorporating a light-absorbing material into the thermoplastic layer. It is an optical recording medium characterized by significantly improved optical recording properties that allow repeated erasing and rewriting, and in which the substrate is a conductive glass substrate such as Nesa glass, and records can be erased by applying electricity to the substrate and generating heat. The purpose is to realize a medium that can perform this well.

(Example) An example of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the optical recording medium of the present invention, in which 1 is a transparent substrate made of Nesa glass, 4 is a reflective layer, 2 is a light absorption layer formed thereon, and 3 is a transparent substrate made of Nesa glass. This is a thermoplastic layer formed on the light absorption layer 2 and mixed with a light absorption material. As the reflective layer 4, for example, a vapor-deposited film of aluminum is used. Further, as the light absorption layer 2, a vapor deposited film of copper phthalocyanine or a carbon black coating film is used,
As the thermoplastic layer 3, a light-absorbing material was mixed into polystyrene dissolved in a solvent, and a film having a thickness of about 1 μm was formed by spin coating. Here, the light-absorbing material to be mixed needs to be uniformly distributed within the film during film formation. In this example, a dye obtained by melt-mixing crystal violet lactone and propyl gallate at a weight ratio of 1:1 was mixed as a light-absorbing material in an amount of 20% by weight of the entire film.
The molecular weight of the polystyrene used here is 1500.
~5000.

Recording is performed on this medium in heat mode. That is, when irradiated with an Ar laser beam at an output of 4 mW or less and an irradiation time of 2 mS, it was possible to write micro pits with a diameter of about 1 μm. Furthermore, by heating the entire medium to a temperature higher than the glass transition temperature of polystyrene, recording pits could be erased, and rewriting could be performed after cooling. Moreover, in this example, approximately 500 or more erases and
We confirmed that it has sufficient performance to withstand rewriting. It was possible to read out pits based on differences in light absorption, refractive index, reflectance, etc.

The light absorption layer in the present invention is preferably one that has a large absorption coefficient at the writing wavelength and is resistant to heat during writing and erasing, and includes copper phthalocyanine, carbon black, other metal phthalocyanines, various pigments, etc. . For the thermoplastic layer, it is desirable to use a thermoplastic material that is sufficiently hard at the recording temperature (room temperature, etc.), has a relatively low glass transition temperature, is sufficiently soft above the glass transition temperature, and easily undergoes plastic flow deformation. . In addition to the above-mentioned polystyrene, examples include rosin ester, acrylic resin,
Polymers such as polyethylene are available, and those with relatively low molecular weight and approximately monodisperse molecular weight distribution have good properties. The molecular weight of the above polymer is suitably 1500 to 5000. If the molecular weight is too low, it will be soft at room temperature and recording cannot be maintained stably. On the other hand, if it is too high, the erase/rewrite repetition characteristics will deteriorate. The light-absorbing material mixed into the thermoplastic layer must be uniformly distributed within the thermoplastic material without agglomeration, have a large absorption coefficient at the writing wavelength, and be sufficient to withstand the thermal cycle associated with writing and erasing. Preferably something stable. There are many such materials other than those used in this example, such as dyes.

Next, the writing and erasing principles of this optical recording medium will be described. FIG. 2a shows the state before writing, in which 1 is a transparent substrate, 4 is a reflective layer, 2 is a light absorption layer, and 3 is a thermoplastic layer mixed with a light absorption material. As shown in Figure b, when the laser beam 5 is irradiated, the directly incident laser beam 5 and the reflected light of the laser beam 5 by the reflective layer 4 are transferred to the light absorbing layer 2 and the thermoplastic layer 3.
The light-absorbing material inside absorbs the light, causing a rapid rise in temperature. As a result, the temperature of the thermoplastic layer 3 also rises to a temperature equal to or higher than the glass transition temperature, and the thermoplastic layer 3 is softened and a depression is formed as shown in c in the same figure. it is,
After irradiation, the temperature immediately returns to room temperature, and the dents remain stable at room temperature. The depressions (writing pits) thus formed can be detected by differences in light absorption, refractive index, and surface reflection. Further, by forming the reflective layer 4 between the substrate 1 and the light absorption layer 2, it is possible to detect the difference in reflected light. Here, if the laser power is too large, the thermoplastic layer 3 or the light absorption layer 2
destruction occurs, and the erasure described below becomes impossible. For erasing, the entire thermoplastic layer 3 is softened by heating as shown in FIG. The heating method is resistance heating by passing an electric current from an external power source (not shown) through the transparent substrate 1 made of conductive glass such as Nesa glass which can generate heat when energized. The heat generated by the substrate 1 due to this energization heats the entire medium, and as a result, the entire surface of the thermoplastic layer 3 is uniformly heated and softened (plastic flow deformation), and its surface becomes flat, erasing the recording. It can be done.

(Effects of the Invention) As is clear from the above description, the optical recording medium of the present invention enables extremely minute recording using laser beam irradiation and heating as the recording method. In addition, the medium of the present invention uses conductive glass as the substrate, and the thermoplastic layer is softened (plastic flow deformation) by applying electricity to the substrate to generate heat, thereby erasing records. It can be done well. Furthermore, the medium of the present invention has the following effects by mixing a light-absorbing material into the thermoplastic layer and further forming a reflective layer and a light-absorbing layer as an underlying layer. That is, if there is only one thermoplastic layer and no light-absorbing material is mixed in, most of the laser beam will pass through the thermoplastic layer, and the temperature of the thermoplastic layer will not rise and writing will not be possible. On the other hand, by mixing a light-absorbing material, the laser beam is absorbed and the irradiated area is heated to enable writing. This writing sensitivity increases by increasing the proportion of light-absorbing material mixed in;
If the amount exceeds 20% by weight, the repeatability characteristics will deteriorate. i.e. hardening of the thermoplastic layer ←→
This increases the possibility that unevenness due to repeated softening and segregation of the light-absorbing material will occur. Incorporating too much light-absorbing material into the thermoplastic layer will defeat the purpose of using a low-molecular-weight, monodisperse thermoplastic material. Therefore, in this invention, the amount of light-absorbing material in the thermoplastic layer is reduced to 20% by weight or less to prevent repeated deterioration of characteristics, and by separately forming a reflective layer and a light-absorbing layer underneath, the light-absorbing material in the thermoplastic layer is reduced to 20% by weight or less, which improves sensitivity and high-speed writing. The sex is also excellent. In other words, the three-layer structure provides excellent sensitivity, high-speed writing, and repeatability. In addition, the medium has extremely advantageous features such as being able to be formed by a method such as coating and being extremely low in cost and easy to increase in size. Furthermore, by using a polymer with a molecular weight of 1,500 to 5,000 and a substantially monodisperse molecular weight distribution in the thermoplastic layer, the present invention realizes a medium with excellent repeatability of recording and erasing, recording sensitivity, and writing speed. In addition, by using the three-layer structure as described above and reducing the amount of light-absorbing material in the thermoplastic layer, the performance can be further improved as described above. Furthermore, since erasability is good as described above, rewriting can be performed satisfactorily.

Therefore, the optical recording medium of the present invention enables repeated writing and erasing with high repeatability using the highly demanding laser beam recording method.
It can be used as a high-density recording medium that can replace conventional magnetic recording.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the optical recording medium of this invention, and FIGS. 2A to 2D are explanatory diagrams illustrating the operating principle of the embodiment. DESCRIPTION OF SYMBOLS 1...Transparent substrate, 2...Light absorption layer, 3...Thermoplastic layer, 4...Reflection layer, 5...Laser light.

Claims (1)

[Scope of utility model registration request] An optical recording medium that is rewritable and performs recording in a heat mode by irradiating a laser beam light of a predetermined wavelength, the medium having a reflective layer on a substrate made of conductive glass that can generate heat when energized. a light absorption layer made of a light absorption material with a large absorption coefficient at the writing wavelength and a molecular weight of 1500 to 5000;
and a thermoplastic layer made of a polymer having a substantially monodisperse molecular weight distribution in this order, and further comprising a small amount of the light-absorbing material mixed into the thermoplastic layer.