JPS6331861B2 - - Google Patents

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. More specifically, 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. Prior Art In optical recording media, there is no contact between the medium and the writing or reading head, so the recording medium does not deteriorate due to wear and tear.
For this reason, development research on various optical recording media is being conducted. 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 a laser beam to form a small hole called a pit. It records information. However, with conventional heat mode optical recording media,
There are disadvantages in that information recorded as pits cannot be erased, and written information cannot be corrected or rewritten, or it is difficult. To explain this situation more specifically, one of the conventionally known heat mode optical recording media has a recording layer made of nitrocellulose and a light absorbent. For example, a laser beam of 1 μm is applied to such a medium as a recording light.
When irradiated as a minute spot of about φ, the irradiated area becomes extremely hot in a short time, the nitrocellulose ignites and disappears, and 1-bit information is recorded as a minute hole. However, recorded information cannot be erased from such media. On the other hand, heat mode optical recording media are also known in which the recording layer is a layer made of tellurium or tellurium-selenium-arsenic. However, in this case as well, since the pits are formed by melting a metalloid with a high melting point, it is extremely difficult to restore the recorded pits. Further, JP-A-55-161690 describes a heat mode optical recording medium having a recording layer made of a light-absorbing dye and a thermoplastic resin on a reflective substrate. In this medium, the recording layer is thinned to about 0.01 to 0.2 μm, and the resin in the irradiated area is melted and moved by laser light irradiation, or the light-absorbing dye in the irradiated area is moved laterally. Then, the reflective substrate is exposed and pits are formed. However, even in this case, it is difficult to return the light-absorbing dye that has once moved or to backfill and flatten the small holes that have once reached the bottom of the layer. Therefore, the publication does not disclose or suggest that this medium is capable of erasing and rewriting recorded information. In contrast, using a medium in which thermoplastic is coated on a conductor, a charge is uniformly applied to the thermoplastic layer, a part of the thermoplastic is melted by laser light irradiation, and the change in volume generates electricity. A recording method is known in which a change in the attraction force is generated to obtain pits due to surface irregularities corresponding to laser beam irradiation. In this method, by reheating the medium, the surface unevenness returns to a flat surface and the recorded information can be erased, but it requires a corona discharger, etc., complicates the mechanism of the writing device, and consumes the device. There are disadvantages such as increased power consumption. 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 Further, in the invention of this application, when writing information, the shape of the peripheral portion of the pit formed is good, and good recording is performed.
A second object of the present invention is to provide an optical recording medium that can be read with an extremely high S/N ratio, and a method for writing and erasing information using such a medium. Furthermore, we aim to provide a medium and method that can withstand repeated erasing and rewriting many times.
This is the third purpose. Other objects of the invention of this application will become clear from the following description. The present inventors conducted various studies for this purpose and found that when a recording layer is formed by incorporating a light-absorbing dye or pigment into polypropylene with a number average molecular weight of 400 to 10,000, erasing and rewriting are possible. The inventors have discovered that a recording pit can be read out with an extremely high S/N ratio, and that it 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, forming recording pits. In the optical recording medium to be formed, the thermoplastic resin is made of polypropylene with a number average molecular weight of 400 to 10,000, and the layer contains 0.002 to 10 parts by weight of a light-absorbing dye or pigment per 1 part by weight of polypropylene. This is an optical recording medium characterized by the following. Further, the second invention includes a light-absorbing dye or pigment and polypropylene having a number average molecular weight of 400 to 10,000 on the substrate, and the light-absorbing dye or pigment is contained in 0.002 to 10 parts by weight per 1 part by weight of the polypropylene. An optical recording medium having a layer is irradiated with recording light to melt and soften the layer to form a recording pit, and at this time, a layer containing both the polypropylene and a light-absorbing dye or pigment remains at the bottom of the recording pit. The method for writing and erasing information is characterized in that the recording pit is heated to flatten the layer, thereby erasing information. . Specific Structure of the Invention Hereinafter, 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 with a number average molecular weight of 400 to 10,000. As a thermoplastic resin, this polypropylene is
It softens or melts, deforms, and forms recording pits. In this case, the average molecular weight of polypropylene is 400
Below this, the polypropylene is liquid or has a softening point too low to be usable. On the other hand, if the average molecular weight exceeds 10,000, erasing and rewriting are possible, but the shape of the recording pits, especially in the peripheral area, 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 can be erased and rewritten many times.
Moreover, at that time, there is little deterioration in S/N. When the average molecular weight is 500 to 6000, such effects become 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 a thermal decomposition product of high molecular weight polypropylene, a direct polymerization product of propylene,
It is easily obtained as a by-product during the production of high molecular weight polypropylene, or 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 pigment or amount exhibits a large light absorption rate with respect to recording light and is intended to enable temperature rise in the irradiated area. Therefore, various known dyes and pigments such as carbon black can be used depending on the wavelength of the recording light. On the other hand, the content ratio of polypropylene and light-absorbing dye or pigment contained in the recording layer is generally 0.002 to 10 parts by weight of polypropylene.
It can be selected within a wide range of parts by weight. If this amount is less than 0.002 parts by weight, recording sensitivity decreases. Furthermore, if it exceeds 10 parts by weight, the bottom of the recording bit may reach the bottom of the recording layer, making erasing difficult.
Characteristics deteriorate due to repeated recording and erasing. Such a recording layer is coated on a substrate using various known methods such as a spinner or a coater.
The thickness is generally 0.05 μm to 1 mm. Note that such a recording layer may contain other additives in addition to the above-mentioned polypropylene and light-absorbing dye or pigment. Examples of such additives include various oligomers and polymers. In this case, the polymer or oligomer is contained in an amount of approximately 30% by weight or less based on the polypropylene to improve adhesion to the support, improve coatability, and change the softening temperature. can. 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, polymethacrylic resin, polyacrylic resin, polycarbonate resin,
It is preferable to use various resins such as phenol resin, epoxy resin, diallyl phthalate resin, unsaturated polyester resin, and polyimide resin. No matter which of these is used, the recording pits will not reach the bottom of the recording layer, and the effects of the present invention will be achieved.
Further, the shape and dimensions can be varied depending on the intended use, such as a disk, tape, belt, or drum. In this case, the medium of this application may have the above-mentioned recording layer on one side of such a substrate, or may have recording layers on both sides thereof. Also, two substrates with recording layers coated on one side are used, and the recording layers are placed facing each other with a predetermined gap between them, and they are sealed tightly to prevent dust and scratches. You can also avoid it. It is also possible to provide the above-mentioned substrate with a subbing layer such as a metallic reflective layer or various resin layers, if necessary, and to provide a recording layer on this subbing layer. Writing and erasing information using the optical recording medium of this application configured as described above may be performed as follows. First, recording light is irradiated. As the recording light, various types of lasers can be condensed and various outputs can be used. In addition, the scanning conditions, pulse width, focusing conditions, etc. of the laser beam can be changed widely.
Under the irradiation conditions of W and a normal pulse width of about 20 to 1000 nsec, the recording pits do not reach the bottom of the recording layer, and the effects of the present invention are realized. By irradiating the recording light, 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 at the irradiated portions. In this case, the recording pit does not reach the bottom of the recording layer, and a layer containing polypropylene and a light-absorbing dye or pigment remains at the bottom of the pit. As a result of forming such pits, erasure, which will be described later, becomes possible. And, with 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 surrounding portion, so that a high S/N ratio can be obtained during reading. In this case, the average molecular weight is
When compared with the case of using polypropylene exceeding 10,000, an extremely high S/N ratio can be obtained. On the other hand, information recorded in this way can be erased by reheating the medium. At this time, the surface, which was once recorded and turned into uneven pits, remelts and returns to a flat surface. As mentioned above, this is
This is because polypropylene and light-absorbing dyes or pigments remain at the bottom of the pit during recording. That is, the polypropylene is melted and softened by reheating during erasing, and the medium surface returns to a flat surface. When heating is carried out by light irradiation, the light-absorbing dye or pigment makes it possible to raise the temperature, causing the polypropylene to melt and soften. 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 pit 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, so the number of repetitions increases. However, erasing and writing can always be performed reliably and efficiently. Specific Effects of the Invention According to the optical recording medium and information writing and erasing method of this application, once written information can be easily and reliably erased. Furthermore, the shape of the recording pits in which information is written 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 to 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, as shown in the Examples below. Furthermore, since erasing is always performed stably, information can be written in a sufficiently stable manner even if erasing and rewriting are repeated many times. The present inventors conducted various experiments to confirm the effects of the present invention. An example is shown below. Example As polypropylene, one with a number average molecular weight of 800 obtained by thermal decomposition of high molecular weight polypropylene was used,
In addition, as a dye, copper-phthalocyanine-based oleosol Fast Blue EL (manufactured by Sumitomo Chemical Co., Ltd.) was used, and 3 g of this polypropylene and 0.3 g of the dye were used.
Dissolve g in 50ml of toluene by heating, and add this to 150mmφ,
On a 1.2 mm thick glass substrate, using a spinner method,
A layer was coated to a thickness of 1.0 μm to obtain medium A. Separately, using polypropylene having a number average molecular weight of 1500 obtained in the same manner as above, a medium B having a 1.0 μm thick recording layer was obtained in exactly the same manner as above. Furthermore, polypropylene is added to Viscoel 660−
P (manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight
3000) and Viscol 550-P (same as above, number average molecular weight 4000) were used, and media C and D having recording layers with a thickness of 1.0 .mu.m were obtained in exactly the same manner as the medium A described above, except that the media were changed to Viscoel 550-P (same as above, number average molecular weight 4000). On the other hand, comparative media E and F, each having a recording layer of 1.0μ thickness, were prepared using Viscoel 330-P (number average molecular weight 15,000) manufactured by Sanyo Chemical Industries, Ltd. and polypropylene with a number average molecular weight 150,000. I got it. For each medium A to F obtained in this way, 10 mW
A He-Ne laser was focused to 1 μm using an objective lens with an NA (numerical aperture) of 0.55, and irradiated as a 500 nsec pulse. As a result, the surface of the recording layer of media A to F has a diameter
In the 2 μm recorded portion, a pit was formed with a convex 0.4 μm width at the periphery and a concave inner center. In both cases, the bottom of the pit did not reach the bottom of the layer, and polypropylene and dye were present. Note that in media A to D, the periphery of the pit showed a smooth shape, whereas in media E,
F had a poor shape around the pit. Next, a 1 mW He--Ne laser was focused to 1 μΦ using the same optical system as above, and the reflected light was detected with a photodiode, and its S/N ratio was calculated. In this case, the amplifier system used was one with a normal 10 MHz band, and the RMS value (effective value) was used as the noise. The results are shown in Table 1.

【table】

[Table] From the results shown in Table 1, it can be seen that the optical recording medium of the invention of this application allows information to be read out with an extremely good S/N ratio. Note that when the media A to D were erased using an infrared heater and writing and erasing were repeated, the above-mentioned S/N ratio hardly changed. In addition, when reading through transmitted light was performed on media A to F, the results were exactly the same as those in Table 1 above. In the above media A to F, the content ratio of the dye was 0.1 part by weight per 1 part by weight of polypropylene, but for comparison, the content ratio of the dye was 0.001 part by weight and
A medium of 20 parts by weight was prepared. With 0.001 parts by weight, no bits are formed and 20
Parts by weight were difficult to erase.

Claims (1)

[Scope of 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 pits. In the recording medium, the thermoplastic resin is
1. An optical recording medium comprising polypropylene having a number average molecular weight of 400 to 10,000, wherein the layer contains 0.002 to 10 parts by weight of a light-absorbing dye or pigment per 1 part by weight of polypropylene. 2. The optical recording medium according to claim 1, which has a number average molecular weight of 500 to 6,000. 3. An optical recording medium having a layer on a substrate containing a light-absorbing dye or pigment and polypropylene having a number average molecular weight of 400 to 10,000, and containing 0.002 to 10 parts by weight of the light-absorbing dye or pigment per 1 part by weight of the polypropylene. The layer is then irradiated with recording light to melt and soften the layer to form a recording pit. At this time, a layer containing both the polypropylene and a light-absorbing dye or pigment remains at the bottom of the recording pit. A method for writing and erasing information, characterized in that writing is performed, while the recording pits are heated to flatten the layer, thereby erasing information. 4. The method for writing and erasing information according to claim 3, wherein the number average molecular weight is 500 to 6000.