JPS5814335A - Optical recording medium and information writing and erasing method - Google Patents

Abstract

PURPOSE:To write, read, and erase information reversibly, by providing an optical recording layer, where optical absorbing coloring matters are mixed in polypropylene having a specific number average molecular weight, in the optical recording medium of the heat mode. CONSTITUTION:Polypropylene having a high molecular weight is decomposed thermally to obtain polypropylene having a number average molecular weight of 400-10,000. The mixture where 0.002-10pts.wt. optical absorbing coloring matters or pigment is mixed in 1pt.wt. this polypropylene is dispersed in toluene to form a thin film on a glass disc, thus obtaining an optical recording medium of the heat mode. The He-Ne laser of 10mW is condensed to this optical recording medium to write information by providing a minute ruggedness on the surface. The same weak laser of 1mW is condensed to read information. In case of erasing, the film surface is made flat by heating of an infrared heater. The film surface is changed correctly by heat reversibly, thus obtaining a high-S/N and contactless optical recording material.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The invention of this application relates to an optical recording medium and a method for writing and erasing information [1]. More particularly, the present invention relates to a heat mode optical recording medium in which recorded information can be erased and rewritten, and a writing and erasing method thereof.

In conventional optical recording media, since the medium and the writing or reading head are not in contact with each other, the recording medium does not suffer from wear and tear, and for this reason, research and development of various optical recording media are being carried out.

Among such optical recording media, heat mode optical recording media are being actively developed because they do not require image processing in a darkroom.

This heat mode optical recording medium is an optical recording medium that uses recording light as heat, and a part of the medium is melted or removed using laser light to form small holes called pits. It records information.

However, conventional heat mode optical recording media have drawbacks in that information recorded as pits cannot be erased, and written information cannot be corrected or rewritten, or it is difficult.

This situation will be explained more specifically in 1i: Then, one of the conventionally known heat mode optical recording media has a recording layer made of nitrocellulose and a light absorbent.

When such a medium is irradiated with a laser beam as recording light, for example, with a minute spot of about 1μ/φ,
The irradiated area becomes extremely hot in a short time, the nitrocellulose ignites and disappears, and 1-bit information is recorded as a tiny hole. But 1. Recorded information cannot be erased from such media.

On the other hand, heat mode optical recording media having a recording layer made of tellurium or tellurium selenium-arsenic are also known. However, in this case as well, since the pits are formed by melting metalloids with a high melting point, it is extremely difficult to restore the recorded pits.

Furthermore, Japanese Patent Application Laid-Open No. 55-161690,
A heat mode optical recording medium is described that has a recording layer consisting of a light-absorbing dye and a thermoplastic resin on a reflective substrate. This medium has a recording layer with a thickness of about 0.01 to 0.2μ.
Then, by irradiating the resin with laser light, the resin in the irradiated area is melted and moved, or the light-absorbing dye in the irradiated area is moved laterally, exposing the reflective substrate and forming pits. It is something to do.

However, even in this case, it is difficult to return the light-absorbing pigment that has once moved or to backfill and flatten the small hole that has once reached the layer. Therefore, the publication does not disclose or suggest that this medium is capable of erasing and rewriting recorded information.

On the other hand, using a medium in which thermoplastic is coated on a conductor, a charge is uniformly applied to the thermoplastic snack layer, a part of the thermoplastic is melted by laser light irradiation, and the volume change causes electricity to be generated. A recording method is known in which a change in attraction force is caused to produce pits due to surface irregularities corresponding to laser beam irradiation. In this method, when the medium is reheated, the unevenness on the surface returns to flatness and the recorded information can be erased, but it requires a corona discharger, etc., and the mechanism of the writing device becomes complicated. There are disadvantages such as increased power consumption.

Summer Purpose of the Invention The invention of this application was made in view of the above circumstances, and provides a heat mode optical recording medium that can be erased and rewritten, and a method for writing and erasing information using such a medium. Its main purpose is to provide. In addition, the invention of this application provides that when information is written, the shape of the peripheral portion of the pit formed is good, and good recording is performed, and therefore, the light beam that can be read with an extremely high S/N ratio is provided. A second object thereof is to provide a recording medium and a method for writing and erasing information using such a medium. A third object of the present invention is to provide a medium and method that can withstand repeated erasing and rewriting many times. Other objects of the invention of this application will become obvious from the following description.The present inventors have extensively studied these objects and found that the number average molecular weight is 400~lo, o o 6. When a recording layer is formed by incorporating a light-absorbing dye or pigment into polypropylene, an erasable and rewritable medium is realized.
Moreover, it was discovered that the recorded pits can be read out with an extremely high S/N ratio, and can withstand repeated erasing and rewriting many times, leading to the invention of this application.

That is, the first invention of this application is formed by forming a layer containing a thermoplastic resin and a light-absorbing dye or pigment on a substrate, and when irradiated with recording light, the layer melts and softens to form recording pits. In the optical recording medium on which the thermoplastic resin is formed, the thermoplastic resin is made of polypropylene having a number average molecular weight of 400 to 10,000, and a layer containing both the thermoplastic resin and a light-absorbing dye or pigment remains at the bottom of the recording bit. This is an optical recording medium characterized by being configured to.

Further, the second invention is to irradiate recording light onto an optical recording medium having scraps containing a light-absorbing dye or pigment and polyglopylene having a number average molecular weight of 400 to 10,000 on a substrate to melt the layer. It softens to form a recording pit, and at that time, a layer containing both the polypropylene resin and a light-absorbing dye or pigment remains at the bottom of the recording pit, and information is written using this layer. This method of writing and erasing information is characterized in that heating is performed to flatten the layer, thereby erasing information.

■Specific structure of the invention Below, the specific structure of the invention of this application will be explained in detail.

The optical recording medium in this application has a recording layer provided on a substrate.

The recording layer contains polypropylene having a number average molecular weight of 400 to 10,000. This polypropylene is a thermoplastic resin that softens or melts and deforms as the temperature rises in the area irradiated with recording light to form recording pits.

In this case, the average molecular weight of polypropylene is less than 400 and 11
In No. 1, the polypropylene is liquid or has a softening point too low to be usable. On the other hand, the average molecular weight is 10
,000, erasing and rewriting are possible, but the shape of the recording pits, especially the peripheral portions, becomes defective due to laser irradiation, and the S/N ratio during reading becomes poor. Furthermore, when erasing and rewriting are repeated many times, this S/N ratio deteriorates each time.

On the other hand, when the number average molecular weight is 400 to 10,000, recording pits with an extremely high S/N ratio can be obtained, and they can be erased and rewritten many times, without degrading the S/N. few. And the average molecular weight is 500~
6,000, this effect becomes even more excellent.

In this case, as long as the polypropylene has such an average molecular weight, there is no problem as long as the molecular weight distribution is within a common sense range.

Such polypropylene is easily obtained as a thermal decomposition product of high molecular weight polypropylene, a direct polymerization product of propylene, a by-product during the production of high molecular weight polypropylene, etc.
Alternatively, a commercially available product may be used.

On the other hand, the recording layer contains such polypropylene as well as a light-absorbing dye or pigment.

This light-absorbing dye or at exhibits a large light absorption rate with respect to the recording light and is used to enable temperature rise in the irradiated area.

Therefore, depending on the wavelength of the recording light, various known dyes and pigments such as carbon black/white can be used.

On the other hand, the content ratio of polypropylene and light-absorbing dye or pigment contained in the recording layer is generally based on 1 part by weight of polynolopylene.

It can be selected from a wide range of about 0.002 to 1G parts by weight.

Such a recording layer is deposited on the substrate by various known methods such as a spinner or a coater. Generally, the thickness is 0.05 μm to 1 μm.

Note that such a recording layer may contain other additives in addition to the above-mentioned polypropylene and light-absorbing dye or pigment.

An example of such an additive is a woodcutter oligomer or polymer. In this case, the polymer or oligomer is contained in polypropylene in an amount of approximately 30% by weight or less to improve adhesion to the support, improve coating properties, and change the softening temperature. be able to.

In addition, various plasticizers, surfactants, antistatic agents, lubricants,
Flame retardants, ultraviolet absorbers, antioxidants, stabilizers, dispersants, etc. can be included.

On the other hand, the substrate on which such a recording layer is provided and supported is not particularly limited, and various materials can be used for the substrate. However, in terms of thermal conductivity, various types of glass, various ceramics, or various resins such as polymethacrylic resin, polyacrylic resin, polycarbonate resin, phenol resin, epoxy resin, diallyl phthalate resin, unsaturated polyester resin, and polyimide resin are generally used. It is preferable to use the following. In addition, the shape and dimensions vary depending on the application, such as discs, tapes, belts, etc.
It can be made of various types such as a drum.

In this case, the medium of this application may have the above-mentioned recording layer on one surface of such a substrate, or may have recording layers on both surfaces thereof. Alternatively, two substrates each having a recording layer coated on one side are used, and the recording layers are placed facing each other with a predetermined gap between them, and the substrate is sealed to prevent dust and scratches. You can also do this.

Note that the above-mentioned substrate may be provided with a subbing layer such as a metal reflective layer or various resin layers, if necessary, and a recording layer may be provided on this subbing layer.

Using the optical recording medium of this application configured in this way,
Writing and erasing information may be performed as follows.

First, recording light is irradiated. The recording light is used by condensing each Hinoki laser, and various outputs can be used. Furthermore, the scanning conditions, pulse duration, focusing conditions, etc. of the laser beam can be varied widely.

Then, by such recording light irradiation, the polypropylene in the recording layer is melted and softened, and minute recording pits corresponding to the irradiated light are formed on the surface of the recording layer in the irradiated portion. In this case, the recording pits do not reach the stratification of the recording layer, and a layer containing polypropylene and a light-absorbing dye or pigment remains at the bottom of the bit. As a result of forming such pits, erasing, which will be described later, becomes possible. In the medium of this application, pits with an extremely good shape can be obtained.

On the other hand, in order to read the information written on the medium from the pits formed in this way, a readout laser beam with lower power than the recording beam is used, which is focused and scanned to generate transmitted or reflected light. Detect any output of light.

At this time, as described above, the pits formed in the medium of this application have a good shape, especially the shape of the peripheral portion, so that a high S/N ratio can be obtained during reading. In this case, when compared with the case of using polypropylene with an average molecular weight of over 10,000, an extremely high S/N ratio can be obtained.
All you have to do is reheat the medium. At this time, the surface, which was once recorded as uneven pits, melts again and returns to a flat surface. As heating for erasing, any of laser light irradiation, heating with various heaters, infrared lamp irradiation, etc. may be used.

[When such erasing and writing are repeated, the bit always shows a good shape and reading with a high S/N ratio is performed, and the surface always returns to a flat surface after erasing.
Even if the number of repetitions increases, erasing and writing can always be performed reliably and satisfactorily.

V. Specific Effects of the Invention According to the optical storage medium and the information writing and erasing method of this application, once written information can be easily and reliably erased. Furthermore, the shape of the recording pit written as information is extremely good, and a high S/N ratio can be obtained whether transmitted light or reflected light is used for reading. In this case, when compared with the case where polypropylene having an average molecular weight of more than 10,000 is used, an extremely large improvement in the S/N ratio is observed in K, as shown in the experimental examples described later. Furthermore, since erasure is always performed stably,
Even if erasing and rewriting are repeated many times, information can be written in a sufficiently stable manner.

The present inventors conducted various experiments to confirm the effects of the present invention. An example is shown below.

Experimental Example Polypropylene with a number average molecular weight of 800 obtained by thermal decomposition of high molecular weight polypropylene was used, and copper-phthalocyanine-based oleosole Fast Blue EL (manufactured by Sumitomo Chemical Co., Ltd.) was used as the dye. 3f and dye 0.32 were heated and dissolved in toluene at 5°, and this was coated onto a glass substrate of 150 mm diameter and 1.2 mm thick using a spinner method to form a scratch thickness of 1.0 μm. I got it.

Separately, it was obtained in the same manner as above.

Using polypropylene having a number average molecular weight of 1,500, a medium B having a recording layer with a thickness of 1.0 μm was obtained in exactly the same manner as above.

Furthermore, polypropylene was added to Viscole 660-P (manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight a, ooo) and Viscole 550-P (same as above, number average molecular weight 4,0
00), instead of Shichiriki, 1 is exactly the same as the above medium A.
．． Media C and D having recording layers with a thickness of 0 μm were obtained.

On the other hand, a comparative sample with a recording layer of 1.0μ thickness was prepared using Viscoel 330-P (number average molecular weight 15,000) manufactured by Sanyo Chemical Industries, Ltd. and poly-10-pyrene with a number average molecular weight 150,000. Media E and F were obtained.

For each of the media A and F obtained in this way, 10 mW of He
-New laser was focused on an objective lens tlμ- with NA (numerical aperture) of 0.55, and irradiated as a pulse of 50 Q Sec.

As a result, a bit is formed on the surface of the recording layer of media A-F, with a 0.4μ scratch width on the periphery being convex at the 2μ-diameter recording portion and a concave center on the inside. Ta. In this case, in both cases the bit bottom did not reach stratification and polypropylene and dye were present. In addition, medium A-
In D, the peripheral part of the bit had a smooth shape, whereas in media E and F, the shape of the peripheral part of the bit was poor.

Next, a 1 mW He-Nev laser was focused to 1 μΦ using the same optical system as above, and the reflected light was detected by a photodiode, and its S/N ratio was calculated. In this case, as an amplifier system.

A normal 10P&1Z imperial one was used, and the RMS value (effective value) was used as the noise.

The results are shown in Table 1.

Table 1 A 800 55 B 1,500 51 C3,00048 D 4.000 47 g 15.000 16 F 150.000 15 From the results shown in Table 1, the optical recording medium produced by this application is extremely It can be seen that information can be read out with a good S/N ratio.

Note that when media A and L) were erased using an infrared heater, and after repeated storage and erasing, the above S/
The N ratio hardly changed.

In addition, when reading through transmitted light was performed on media A to F, results completely similar to those of the above fit were obtained.

Agent Patent Attorney Yo Ishii

Claims (1)

[Claims] 1. A layer containing a thermoplastic resin and a light-absorbing dye or pigment is formed on a substrate, and upon irradiation with recording light, the layer is melted and softened to form recording bits. In the optical recording medium, the thermoplastic resin has a number average molecular weight of 400 to 1.
0,000 poly-10 pyrene, and is configured such that a layer containing both a thermoplastic resin and a light-absorbing dye or pigment remains at the bottom of the recording pit.
optical recording media. 2. The optical recording medium according to claim 1, wherein the average molecular weight of 2a is 500 to 6.000. 3. Optical recording medium K having a layer containing a light-absorbing dye or pigment and polyglopyrene having a number average molecular weight of 400 to 10,000 on a substrate, irradiated with recording light to melt and soften the layer to form a recording bit. At that time, a layer containing both the polypropylene and a light-absorbing dye or pigment remains on the bottom of the recording bit, and information is written using this layer.Meanwhile, the recording bit is heated to A method for writing and erasing information, characterized by flattening a layer and thereby erasing information. 4. The information writing and erasing method according to claim 3, wherein the number average molecular cap is 500 to 6,000.