KR100224748B1 - An optical recordable and reproducable medium - Google Patents

Abstract

The present invention relates to an optical recording medium capable of recording / reproducing. The recording / reproducing optical recording medium of the present invention, in which an organic expansion layer, a metal thin film, an organic complete layer, a reflective film, and a protective film are sequentially formed on a substrate, has a high reflectivity of 70% or higher and 47 dB of reproductive properties, which are required for CD compatibility. In addition to being satisfactory, there is a recording stability.

Description

Recordable / Playback Optical Recording Media

1 to 5 are schematic cross sectional views of optical recording media produced according to a conventional method.

6 is a schematic cross-sectional view of an optical recording medium according to an embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

51 substrate 52 organic expansion layer

53 metal thin film 54 organic buffer layer

55 reflective film 56 protective film

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recordable / reproducible optical recording medium, and more particularly, to a recordable / reproducible optical recording medium having CD compatibility and recording stability since it exhibits high reflectivity of 70% or more and 47 dB or more.

Currently, the most widely used recording medium is a magnetic recording medium, which utilizes the principle that information is recorded according to the magnetization direction of the magnetic material. Examples of such recording media include video tapes, audio tapes, floppy disks, and the like.

On the other hand, the explosive increase of various kinds of information due to the high degree of informatization of society in general requires high density, large capacity and high speed of the recording medium. However, since the conventional magnetic recording medium has difficulty in increasing its capacity, an optical recording medium using a new recording method has emerged.

Optical recording media are read-only memory (ROM) type that reads and writes only once, depending on whether they can be erased, or write once read many (WORM) type, and can be erased and rewritten after recording. It is divided into erasable type.

On the other hand, the information recorded in such an optical recording medium requires a characteristic (CD compatibility) that can be reproduced by a recording disc (Compact Disc Player: CD-ROM drive) of a ROM type medium at the time of reproduction. For this purpose, the optical recording medium requires 65% daily reflectance and a carrier to neise ratio (CNR) of more than 47 dB according to red books and standardization regulations.

In a recordable optical recording medium, recording is reproduced in accordance with reflectance change due to physical deformation, phase change, magnetic property change, etc. of the recording layer before and after recording. Therefore, in addition to high reflectance and CNR characteristics, long-term storage life and high recording sensitivity characteristics are required for optical recording media to have CD compatibility.

On the other hand, Japanese Patent No. 63-268142 discloses a sensitized layer 2 made of gelatin, casein, polyvinyl alcohol, or the like on a substrate 1, and a metal thin film layer 3 made of chromium, nickel, gold, etc. (50 to 500 kPa) thereon. ), And an optical disk in which a photosensitive oxy metal thin film absorbs heat using a laser to deform the sensitized layer and the metal thin film to form a recording pit (FIG. 1). However, such an optical disk has a disadvantage in that recording pits are exposed and record retention is not good.

U.S. Patent No. 4,973,520 discloses an optical disc on which a three-layer film consisting of a metal thin film 12, a metal oxide film 13 and a metal thin film 14 is formed on a substrate 11 (FIG. 2). However, such an optical disc has excellent recording characteristics with a CNR of 50 dB or more, but has a disadvantage in that recording pits are exposed to the outside, thereby degrading recording retention.

To compensate for this disadvantage, U. S. Patent No. 4,983, 440 discloses a recording layer consisting of two metal thin films 22a and 22b on a substrate 21 and an optical disc on which a protective layer 23 is formed. 3), such a disk has the disadvantage that the reflectance is 20% or less.

In US Patent No. 5,039,558, a recording medium having a metal thin film 32, 32 'and a protective layer 33, 33' formed on a substrate 31, 31 'is sandwiched with an adhesive layer 34 sandwiched therebetween. The method of making is disclosed (FIG. 4). However, such an optical recording medium has a disadvantage in that the recording pits are stable, but the metal thin film does not have a high reflectance of 70% or more by acting as a reflective film and a light absorbing layer.

In addition, US Patent No. 4,990,388 discloses a method of manufacturing an optical recording medium by forming an organic dye layer 42 as a recording layer on a substrate 41, and then forming a reflective film 43 and a protective layer 44. (Figure 5). This recording medium heats and deforms the substrate by absorbing the recording laser in the dye layer during recording, thereby changing the reflectance before and after recording, thereby reproducing the recording signal. The reflectance is 70% or more and the CNR after recording is 47 dB. It is more than CD compatibility. However, such a disc not only has a disadvantage in that the recording layer is weak to heat and light, and an expensive organic dye is expensive, but also has a disadvantage in that productivity is poor due to difficulty in precise thickness control when dissolving the organic dye in an organic solvent.

Accordingly, an object of the present invention is to provide a recording / reproducible optical recording medium having CD compatibility and recording stability since it exhibits high reflectivity of 70% or more and playback characteristics of 47 dB or more.

In order to achieve the above object, the present invention provides a recording / reproducing optical recording medium, characterized in that the organic expansion layer, the metal thin film, the organic buffer layer, the reflective film and the protective film are sequentially formed on the substrate.

6 is a cross-sectional view of an optical recording medium according to an exemplary embodiment of the present invention. An expansion layer 52 including an easily deformable organic material, a metal thin film 53, and a buffer layer including an easily deformable organic material are disposed on a substrate 51. 54, the reflective film 55 and the protective film 56 are sequentially formed.

In terms of its function, when a laser enters the optical recording medium, the focused laser heats the metal thin film, and the generated heat is transferred to the expansion layer and the buffer layer, and the expansion layer expands as the expansion layer expands by the transferred heat. The layer / metal thin film / buffer layer is thermally deformed, whereby the recording of the optical recording medium according to the present invention is carried out according to the principle that the reflectance of the condensed portion is lower than that of the uncondensed portion.

In addition, the optical recording medium of the present invention is made of a multi-layer, the reflectance is changed according to the reinforcement / destructive interference phenomenon of light. Therefore, proper thickness control of each layer is necessary for the optical recording medium to have CD compatibility.

Looking at each component of the optical recording medium according to the present invention in more detail as follows.

In the present invention, the substrate 51 has a thickness of 0.3 to 1.5 mm, is made of a material that maintains transparency to the laser, has excellent impact strength and can be easily expanded and deformed by heat, and preferred materials are polycarbonate, Polymethyl methacrylate, epoxy resin, polyester, amorphous polyolefin and the like. Further, a surface for guiding the incident laser light at the time of recording or reproduction is formed on the surface of the substrate, the depth of which is preferably 40 to 250 mW and the width of 0.3 to 1.2 m.

The expansion layer 52, which is another component of the optical recording medium according to the present invention, should have a low thermal conductivity, a high coefficient of thermal expansion, and a low glass transition temperature compared with the buffer layer 54 so that the expansion efficiency for condensing can be large. As satisfying these conditions, there are rubber or elastomer-based resins, preferably thermoplastic polyester elastomers, thermoplastic polyurethane ultraviolet curable resins, and the like.

The metal thin film 53, which is another component of the optical recording medium according to the present invention, serves as a heating layer that absorbs and generates heat for the recording laser, and serves as a partial mirror which shows a difference in contrast before and after recording. Therefore, the optical property of the metal is preferably 1 or more for the imaginary part k during birefringence because the light absorption rate is low when recording is less than 1 because the deformation of the recording part is small and the recording sensitivity is lowered.

In the present invention, the metal thin film 53 has a thickness of 30 to 300 kPa, a transmittance of 95 to 5%, and a water absorption of about 5 to 95%. In addition, the metal thin film is made of gold, aluminum, chromium, aluminum / titanium, copper, nickel, platinum, silver, or an alloy thereof, and the method of forming the metal thin film includes vacuum deposition, electron beam (E-beam), sputtering, and the like. .

The buffer layer 54, which is another component, is a layer that absorbs deformation of the substrate 51 and the metal thin film 53, and is formed of an organic material that can be easily deformed and has proper fluidity. In addition, the glass transition temperature of the organic material included in the buffer layer is higher than the glass transition temperature of the expanded layer and preferably in the range of 60 to 180 ° C. When the glass transition temperature is less than 60 ° C, record retention is deteriorated. This is because when the temperature exceeds 180 ° C, the strain rate is small and the recording sensitivity may be lowered. Preferred examples of such organic substances include vinyl alcohol resins, vinyl acetate resins, acrylate resins, polyester resins, polyether resins, urethane resins, cellulose resins and fatty acid resins.

According to the present invention, an organic pigment can be included in the buffer layer 54 in order to improve the recording sensitivity of the optical recording medium. In this case, the organic dye included in the buffer layer absorbs a laser and is heated to make it easy to deform the substrate and the metal thin film by recording, thereby improving the recording sensitivity of the optical recording medium.

The buffer that functions as described above is preferably formed by dissolving the above-mentioned materials in an organic solvent, followed by spin coating, in which case the organic solvent should be selected so as not to damage the substrate.

In the present invention, the reflective film 55, which is another component of the optical recording medium, may be made of a metal such as gold, aluminum, copper, chromium, or an alloy thereof, and the thickness thereof is preferably 500 to 1500 mW. Moreover, as for the manufacturing method, the electron beam method or the sputtering method is preferable.

The protective film 56, which is another component of the optical recording medium according to the present invention, is for protecting other components of the optical recording medium. The protective film 56 is made of a material having a large impact strength, a transparent and curable by ultraviolet rays. Preferred examples of such materials include epoxy or acrylate based UV curable resins. In addition, the protective film is preferably formed by spin coating the material on the reflective film 55 and curing with ultraviolet rays.

Hereinafter, the features of the present invention will be described in detail through examples, but the present invention is not necessarily limited thereto.

Example 1

In 200 ml of cyclohexanone, 100 g of a urethane-based thermosetting resin (Morton, Thiokol-Solithane 13) and 7.3 g of a curing agent (Morton, Thiokol-C113-300) were dissolved. The resulting solution was spin coated at 2000 rpm on a 1.0 mm thick polycarbonate substrate having a depth of 170 nm, a width of 0.07 μm, and a track pitch of 1.6 μm, and then thermally cured at 80 ° C. for 4 hours to form an expanded layer. . Aluminum was vacuum-deposited on the formed expansion layer to form a thin film having a thickness of 10 nm. In a separate container, 0.9 g of cyano-biphenyl epoxy amine was dissolved in 10 ml of diacetone alcohol, and then spin-coated at 2000 rpm on the metal thin film. It was 2500 kPa when the thickness of the coating layer in a valley part was measured through the sample. Subsequently, the substrate was placed in a vacuum oven and dried at 40 ° C. for 4 hours to form a buffer layer. Then, aluminum was vacuum-deposited thereon to form a 1000 μm thick reflective film. Finally, an optical disk was manufactured by spin coating the epoxy acrylate UV curable resin and then curing the epoxy acrylate UV curable resin.

Using an evaluation apparatus using a laser of 780 nm, the reflectance of the disk made according to the present invention was measured and found to be 72%. Further, a 720 Hz signal was recorded at a speed of 1.3 m / sec at a power of 8 Hz, and then recorded and reproduced using a 0.7 Hz laser. The CNR of the reproduced signal was 51 dB. The CNR was measured while changing the recording power under these recording conditions, and a CNR of 47 dB or more was obtained at a power of 4 Hz or more.

Example 2

An optical disk was manufactured in the same manner as in Example 1, except that the thickness of the aluminum metal thin film was 7 mm. The optical disc produced had a reflectance of 55%, and the recording performance was evaluated in the same manner as in Example 1 (recording: 1.3 m / sec, 8 Hz, 720 Hz, reproduction: 0.7 Hz). have.

Example 3

An optical disk was manufactured in the same manner as in Example 1, except that the thickness of the aluminum metal thin film was 12 mm. The manufactured optical disc had a reflectance of 70%, and the recording performance was evaluated by the same method as in Example 1 (recording: 1.3 m / sec, 8 Hz, 720 Hz, reproduction: 0.7 Hz), and the CNR was 50 dB. There is this.

As can be seen from the above, the optical recording medium produced according to the present invention not only satisfies the high reflectivity of 70% or more and the reproduction characteristic of 47dB or more, which are conditions necessary for CD compatibility, but also has recording stability.

Claims (7)

An organic expansion layer, a metal thin film, an organic buffer layer, a reflective film, and a protective film are sequentially formed on the substrate, wherein the metal thin film is composed of a metal having a k-value of 1 or more, which is a birefringent imaginary part, and has a thickness of 30 to 300 microseconds. Reproducible optical recording medium. The recording / reproducing optical recording medium according to claim 1, wherein the substrate is provided with a valley for guiding light during recording and reproduction. The recording / reproducing optical recording medium according to claim 1, wherein the metal thin film is formed of at least one selected from the group consisting of gold, aluminum, silver, platinum, copper, chromium, nickel, titanium, and tantalum. The recording / reproducing optical recording medium according to claim 1, wherein the organic expansion layer comprises one selected from the group consisting of thermoplastic polyester elastomer and thermoplastic polyurethane ultraviolet curable resin. The recording / reproducing optical recording medium according to claim 1, wherein the polymer material of the organic buffer layer has a higher glass transition temperature than the polymer material of the organic expansion layer. The method of claim 5, wherein the polymer material is selected from the group consisting of vinyl alcohol resin, vinyl acetate resin, acrylate resin, polyester resin, polyether resin, urethane resin, cellulose resin and fatty acid resin And a recordable / reproducible optical recording medium. 6. The recording / reproducing optical recording medium according to claim 5, wherein the organic buffer layer contains 30% by weight or less of organic dyes with respect to the polymer material.