KR100207581B1 - Optical recording medium - Google Patents

Abstract

The present invention discloses an optical recording medium characterized in that a first partial reflection layer, a buffer layer, a second partial reflection layer, a reflection layer and a protective layer are sequentially stacked on a substrate. According to the present invention, an optical recording medium compatible with commercially available CDs can be obtained by having excellent storage stability and good light transmitting characteristics.

Description

Optical recording media

1 is a cross-sectional view showing a conventional optical recording medium,

2 is a cross-sectional view showing an optical recording medium according to the present invention.

* Explanation of symbols for main parts of the drawings

1 substrate 2 metal thin film layer

3: buffer layer 4: reflective layer

5: protective layer 6: second partial reflective layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly, to an optical recording medium compatible with a commercially available compact disc (CD) by having excellent storage stability and good light transmitting characteristics.

The explosive increase in the amount of information in accordance with the advancement of information requires the density, capacity and speed of the recording medium. However, as a conventional magnetic recording method has a limitation in the capacity of the recording medium, a new recording method, the magneto-optical method, has been proposed.

Unlike the magnetic recording method, the magnetization direction is perpendicular to the surface of the recording layer, and the coercivity to maintain the magnetization direction is about 5 to 10 times higher than that of the magnetic medium, making it difficult to switch the magnetization direction. At this time, the magnetization direction is converted by focusing the laser light to 1 µm or less and changing to an external magnetic field direction in a state of heating above the Curie temperature, and information is recorded according to the converted magnetization direction.

In this method, the information recording unit becomes smaller than 1 mu m, has a recording density of 10 to 100 times that of the magnetic recording method, and uses the non-contact recording and reproducing method, which facilitates recording preservation and long life. However, this method has a lot of difficulties in manufacturing because it uses a heavy metal-based magnetic material and requires a vacuum deposition or sputtering device in the manufacturing process. In order to solve these drawbacks, attention has been focused on the development of organic optical recording media.

The organic optical recording medium is classified into a write once read many (WORM) recording type and a rewritable (RW) type which can be erased and rewritten after recording.

The WORM type recording medium is manufactured by first forming a recording layer by coating a mixed composition of a dye and a polymer resin capable of absorbing a laser on the reflective layer, and then forming a protective layer thereon.

The information recording of the WORM type recording medium is performed by condensing a laser to the recording layer within 1 μm, whereby the dye in the recording layer absorbs the laser to generate heat, and the polymer resin is decomposed by the heat generated at this time to form pits. . In addition, reproduction of the information recorded on such a recording medium is performed by reflectance difference between the portion with and without the pit. As described above, in the WORM type recording medium, since the recorded portion is a decomposition form of the polymer, rewriting is impossible after erasing the recording.

RW type recording media are manufactured using a method of forming and erasing bumps or pit, a method using liquid crystal, or a method using phase change, among which a method using bumps is widely used. Such RW type recording media are known from Japanese Patent Laid-Open Nos. 58-199345, 63-74135, JP-A 3-256241, JP-A 3-256242, and JP-A-3-266235.

In the recording of information on the RW type recording medium, when the laser is focused on the recording layer, the organic dye in the recording layer absorbs the laser to generate heat, and the polymer resin is thermally expanded by the generated heat to form bumps. Recording can be performed by holding.

The reproduction of the information on the RW type recording medium is performed by reflecting a relatively weak power laser on the recording layer and reflecting the difference in reflectance between the portion recorded in bump form and the unrecorded portion. At this time, attempts have been made to improve the reflectance by changing the dye itself dispersed in the recording layer, but the limit has been reached.

Information erasing of the RW type recording medium is achieved by returning the recording layer to its original state by restoring force when the laser is focused on the erasing layer and heated to a glass transition temperature T _g or more. However, when the erase process is applied, reliability is poor due to repeated use, and thus it is difficult to apply the erase process.

At present, the disk type is practically used as the optical recording medium of the WORM type. In particular, the fields of data storage discs, recordable audio CDs, photo CDs and the like have been advanced considerably. In order for the optical recording medium to be compatible with the CD, it is required not only to have high reflectance and excellent CNR characteristics, but also to have recording storage stability and high recording sensitivity. As such an optical recording medium compatible with CD, a compact disc (React Disc-Recordable: CD-R) is known. The optical recording medium is manufactured by coating a dye capable of absorbing a laser on a transparent substrate to form a recording layer, and then forming a reflective layer thereon. However, this recording medium has a problem that the pigments used are expensive and the storage stability is poor.

In order to solve the above problems, a new type of recordable compact disk (CD-R) using a light absorbing material instead of a dye and using a metal thin film layer and a buffer layer has emerged.

FIG. 1 shows a schematic structure of the optical recording medium. A metal thin film layer 2 is formed on a substrate 1, and a buffer layer 3, a reflective layer 4, and a protective layer 5 are formed thereon. Laminated sequentially. In the optical recording medium, when the buffer layer 3 is formed between the metal thin film layer 2 and the reflective layer 4 as described above, the metal thin film layer generates heat by the recording light, and the portion deformed by the heat expands into the buffer layer. The scattering and path difference of the recording site are used as a signal.

In the optical recording medium, as described above, a photopitoxy metal thin film layer 2 using a laser absorbs a laser to generate heat and deforms, thereby forming a recording pit. Thus, in order to induce heat generation required for recording, It is essential to form it to a sufficient thickness. However, because of this, the transmittance is lowered, and heat generated during information recording is likely to be transferred to the layer adjacent to the metal thin film layer, that is, the substrate and the buffer layer, which may damage the unrecorded portion. As a result, tracking errors frequently occur.

It is therefore an object of the present invention to provide an optical recording medium compatible with CD by solving the above problems and having good light transmitting characteristics while maintaining the absorption and heat generation efficiency of the metal thin film layer within an appropriate range.

In order to achieve the above object, the present invention provides an optical recording medium in which a first partial reflection layer, a buffer layer, a second partial reflection layer, a reflection layer, and a protective layer are sequentially stacked on a substrate.

The first partial reflection layer is a metal thin film layer, and the second partial reflection layer is a second metal thin film layer or a dye thin film layer composed of organic dyes.

The present invention is characterized in that the metal thin film layer and the partial reflection layer are formed above and below the buffer layer to induce heat generation required for recording, and efficiently utilize the heat generated at this time for information recording.

2 is a diagram showing a schematic structure of an optical recording medium of the present invention. A method of manufacturing the optical recording medium of the present invention will be described with reference to this.

A metal thin film layer 2 is formed on the substrate 1 as a first partial reflection layer, and then a buffer layer 3 is formed thereon. The second partial reflection layer 6 selected from the metal thin film layer or the dye thin film layer is formed thereon, and then the reflective layer 4 and the protective layer 5 are sequentially formed.

As the material for forming the substrate 1, polycarbonate, methyl polymethacrylate, epoxy, polyester, amorphous olefin, etc., which are transparent to a laser beam and have excellent impact strength and can be expanded and deformed by heat, can be used. Among these, polycarbonate or amorphous olefins are preferable.

The metal thin film layer 2 is preferably formed to be thinner than the thickness of the conventional metal thin film layer in order to maintain the transmittance in an appropriate range. Due to this, the amount of heat generated during recording is compensated for by the heat of the partial reflection layer, that is, the second metal thin film layer or the dye thin film layer.

The metal thin film layer is at least one metal or alloy thereof selected from the group consisting of Al, Ni, Pd, Co, Cr, Cu, Pt, Ag, Fe, Ti, Ta, and Tn, which have excellent light absorption properties for light sources in the near infrared region. By using a sputtering method to form a thickness of about 0.1 ~ 10nm. The transmittance of the metal thin film layer thus formed is about 65 to 90%.

The buffer layer 3, which absorbs the deformation of the substrate 1 and the metal thin film layer 2, is easily formed, and is preferably formed of an organic material having appropriate fluidity. The recording buffer layer 3 is spin-coated with a composition containing a polymer resin having a glass transition temperature (T _g ) in the range of 50 to 180 ° C. to form a thickness of about 20 to 150 nm. If the Tg of the buffer layer is 50 degrees C or less here, the storage stability of recording will fall.

As the material for forming the buffer layer 3, a compound selected from vinyl alcohol resin, vinyl acetate resin, acrylic resin, polyester resin, polyether resin, urethane resin, cellulose resin and fatty acid and copolymer thereof may be used.

As the second partial reflection layer 6, as described above, a second metal thin film layer or a dye thin film layer is used. In particular, when the dye thin film layer is used as the second partial reflection layer, the heat generating effect of the recording layer can be greatly increased. Here, as the second partial reflection layer, the metal thin film layer has almost the same characteristics as the above-described metal thin film layer 2, and the thickness is suitably about 1 to 50 nm. In addition, the dye thin film layer is formed to a thickness of 20 ~ 250nm using a near-infrared pigment of cyan (cyannine), phthalocyannine (phthalocyannine) and naphthalocyannine (naphthalocyannine). When cyan dye is used as the dye, it has a maximum extinction coefficient in the region of 650 to 790 nm.

The reflective layer 4 is formed to a thickness of 50 ~ 150nm using a metal selected from Au, Al, Ni, Pd, Cu, Pt, Ag, and Fe.

The protective layer 5 is for protecting the recording medium. The protective layer 5 is formed by spin coating an epoxy- or acrylate-based curable resin having a strong impact strength, a transparent material, and a UV curable material. At this time, the thickness is suitably 10 to 20 mu m.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not necessarily limited thereto.

Example 1

The first aluminum layer having a thickness of about 6 nm was formed on the Zeonex 280 (Xeon, Japan) substrate on which the pregroove was formed by using a sputtering method. Thereafter, a polymethyl methacrylate (PMMA) (Aldrich) having a T _g of about 80 ° C. was coated to a thickness of about 50 nm, thereby forming a buffer layer.

A second aluminum layer having a thickness of about 10 nm was formed as a partial reflection layer on the buffer layer. Au was then deposited to form a reflective layer about 100 nm thick. A protective layer having a thickness of about 15 μm was formed using an acrylic UV curable resin. The transmittances of the first and second aluminum layers formed at this time were about 80%, respectively.

Example 2

The same procedure as in Example 1 was conducted except that the transmittances of the first and second aluminum layers were each adjusted to be about 85%.

Example 3

Except having formed the dye thin film layer as a partial reflection layer, it formed in the same method as Example 1. At this time, the dye thin film layer was formed to a thickness of about 50 nm using a composition obtained by dissolving 0.2 g of NK-3267 (Japanese dye) in 10 ml of methyl cellosolve.

Comparative Example 1

An aluminum layer having a thickness of about (10) nm was formed on a Xeonex 280 (Xeon, Japan) substrate on which pregrooves were formed using a sputtering method. Then, PMMA (Aldrich) was coated on the top to a thickness of about 50 nm to form a buffer layer.

Au was deposited on the recording buffer layer to form a reflective layer having a thickness of about 100 nm, and then a protective layer having a thickness of about 15 μm was formed using an acrylic UV curable resin. The transmittance of the aluminum layer formed at this time was about 50%.

Comparative Example 2

It carried out by the same method as the method of Comparative Example 1, except that the transmittance of the aluminum layer was adjusted to about 60%.

Comparative Example 3

A composition in which 0.5 g of NK-3267 (Japanese dye) was dissolved in 10 ml of methyl cellosolve on the substrate was spin coated to form a recording layer having a thickness of about 5 nm. PMMA (Aldrich) was coated on the top to a thickness of about 50 nm to form a buffer layer. Au was deposited on the buffer layer to form a reflective layer having a thickness of about 10 nm, and then a protective layer having a thickness of about 15 μm was formed using an acrylic UV curable resin.

The CNR of the optical recording medium prepared according to the above Examples and Comparative Examples was measured using Pioneer RPD-1000, Philips 522 and APEXOHMT 300, which are shown in Table 1.

From Table 1, in the case of Example 1-3, the thickness of the metal thin film layer is kept thinner than that of Comparative Example 1-2, so that the transmittance in the metal thin film layer is improved, and heat generated during recording is recorded. It was found that the CNR, which is a recording / reproducing characteristic, is better by being used effectively. In addition, in the case of Example 1-3, unlike the case of Comparative Example 1-3, excellent recording and reproducing characteristics were exhibited with or without the use of a smaller amount of dye.

According to the present invention, the following effects are obtained.

First, since the metal thin film layer, which is the first partial reflection layer, is formed to be thin, the light transmitting property is excellent and the heat generated during recording is minimized to be transferred to the adjacent area, so that the recording and reproduction characteristics are excellent. It can be transmitted to prevent the unrecorded area from being damaged.

Second, since the light-transmitting characteristics of the recording layer are improved, it is possible to replace metal with low cost instead of expensive gold as a material for forming the reflective layer.

Third, not only expensive pigments are used, but the amount of pigments used is not only economically advantageous, but also excellent in storage stability.

Claims (17)

An optical recording medium comprising a first partial reflection layer, a buffer layer, a second partial reflection layer, a reflective layer and a protective layer sequentially stacked on a substrate. The optical recording medium according to claim 1, wherein the second partial reflection layer is a metal thin film layer. The metal thin film layer of claim 2, wherein the metal thin film layer is formed of a metal material selected from the group consisting of Al, Ni, Pd, Co, Cr, Cu, Pt, Ag, Fe, Ti, Ta, Tn, and alloys thereof. Optical recording medium. The optical recording medium according to claim 2, wherein the metal thin film layer has a thickness of 1 to 50 nm. The optical recording medium according to claim 2, wherein the metal thin film layer has a transmittance of 65 to 90%. The optical recording medium according to claim 1, wherein the second partial reflection layer is a dye thin film layer containing an organic pigment. 7. The optical recording medium according to claim 6, wherein the organic pigment is a near infrared absorbing dye selected from the group consisting of cyanine, phthalocyanine and naphthalocyanine. The optical recording medium according to claim 6, wherein the thickness of the dye thin film layer is 20 to 250 nm. The optical recording medium according to claim 1, wherein the buffer layer comprises a polymer resin having a glass transition temperature of 50 to 180 ° C. The optical recording medium according to claim 9, wherein the buffer layer has a thickness of 20 to 150 nm. The optical recording medium according to claim 1, wherein the first partial reflection layer is a metal thin film layer. The method of claim 11, wherein the metal thin film layer is formed of a metal material selected from the group consisting of Al, Ni, Pd, Co, Cr, Cu, Pt, Ag, Fe, Ti, Ta, Tn and alloys thereof. Optical recording medium. The optical recording medium according to claim 11, wherein the metal thin film layer has a thickness of 0.1 nm to 10 nm. The optical recording medium according to claim 11, wherein the metal thin film layer has a transmittance of 65 to 90%. The optical recording medium of claim 1, wherein the reflective layer is formed of a metal material selected from the group consisting of Au, Al, Ni, Cu, Pt, Ag, Fe, and alloys thereof. 16. The optical recording medium according to claim 15, wherein the reflective layer has a thickness of 50 to 150 nm. The optical recording medium according to claim 1, wherein the protective layer has a thickness of 10 to 20 µm.