KR20010093358A - Optical recording medium - Google Patents

Abstract

PURPOSE: An optical recording medium is provided to prevent damages of an organic pigment layer by forming a heat shielding layer on the organic pigment layer. CONSTITUTION: A pregroove is formed on a substrate(40). The pregroove is used for guiding light when an optical recording medium performs a recording process or a playing process. A reflective layer(41), an organic pigment layer(42), and a protective layer(44) are formed sequentially on the substrate(40). A heat shielding layer(43) is used for protecting the organic pigment layer(42) when the protective layer(44) is formed. The heat shielding layer(43) is formed on the organic pigment layer(42). The heat shielding layer(43) prevents a damage of the pigment used in the organic pigment layer(42). The heat shielding layer(43) protects the pigment of the organic pigment layer(42) from an ultraviolet ray by shielding the ultraviolet ray of 350 or less wavelength.

Description

Optical recording medium

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly, to increase the numerical aperture (NA) of a pick-up lens in order to increase the density of a disk. It relates to an optical recording medium.

Optical recording media are widely used as high density recording media because they have a smaller recording area per recording unit than conventional magnetic recording media. Such optical recording media have a read only memory for reproducing the recorded information, a write once read many for one-time recording, and an erasure for erasing and rewriting after recording. It is classified as Erasable. The recordable optical recording medium reproduces the recording by reflectance change due to physical deformation, phase change, magnetic property change, etc. of the recording layer before and after recording.

CD-R (Compact Disk Recordable), a recordable optical disc, is a medium capable of recording information with a diameter of 12 cm, a board thickness of 1.2 mm, a track pitch of 1.6 µm, and a capacity of 650 MB. In the case of DVD-R (Digital Versatile Disk-Recordable), the wavelength of the laser used is reduced, and the thickness of the substrate is also reduced to 0.6 mm to record 4.7 GB of information. It is possible. However, in order to record HD-TV (High Definition TV) in the future, a recording medium with a capacity of 15-20GB is required to record 2 hours of digital video. The following methods have been proposed to increase the recording density of recording media of the same size and to improve the recording capacity.

First, a pit recording surface is manufactured in a multi-layer, and the recording and reproducing is performed through the interference of the light source using two light sources. However, this has the disadvantage of using two light sources.

Secondly, the recording density is improved by minimizing the area of the pit, which is a recording unit. In other words, in order to increase the recording density, it is necessary to shorten the width of the pit and shorten the track pitch.

The minimum recording pit is proportional to the beam diameter when the laser is focused. The diameter of the focused beam is calculated by the following equation.

Beam diameter = 0.82 × λ / NA

Where? Is the wavelength of the laser used and NA is the numerical aperture of the pickup lens.

In other words, in order to shorten the length of the pit, the wavelength of the laser used or the numerical aperture of the pickup lens should be increased.

In an effort to improve the recording density by reducing the wavelength, the wavelength of the high power laser diode (LD) is continuously shortened to 830 nm, 780 nm, 635-660 nm and 400-430 nm, which is dependent on the development of LD technology.

In addition, the numerical aperture of the pickup lens used is continuously increased to 0.45, 0.50, 0.60 and the like. As the numerical aperture increases, the manufacturing of the lens becomes more difficult, and the working distance between the substrate and the lens is shortened, so that the thickness of the substrate is continuously thinned to 1.2 mm, 0.6 mm and the like.

In Japanese Patent Application Laid-Open No. H10-27,383, as shown in Fig. 1, the substrate 10 having a thickness of 0.6 mm and the lens L1 having a numerical aperture of 0.6 are used to make a minimum pit size of about 0.25 [mu] m to provide an optical recording medium. To improve the recording density. However, there is a disadvantage in that the recording capacity cannot be improved to 15 GB when the recording medium is used.

In US Patent No. 5,838, 646, as shown in Fig. 2, the recording light is incident on the protective layer 23 instead of the substrate 20, and the thickness of the substrate 20 is 0.05-0.6 mm and the numerical aperture of the objective lens L2. Is reduced to 0.55-1.10, and the size of the minimum pit is reduced to about 0.15 mu m to increase the recording capacity to 20 GB or more.

US Patent No. 4,990,388 discloses a recording medium CD-R using a lens L3 having a numerical aperture of 0.5, as shown in FIG. 3, and forming an organic dye layer 31 as a recording layer on a 1.2 mm substrate 30. Doing. The recording medium has a large refractive index of the organic dye of the recording layer, so that the recording is reproduced by the change of the refractive index before and after the recording and the change of the reflectance using the change of the substrate.

However, a problem arises when the recording light is incident on the protective layer as shown in Fig. 2 using the optical recording medium disclosed in US Pat. No. 4,990,388. That is, in the case where the organic dye layer is used as the recording layer, in order to inject the recording light into the protective layer instead of the substrate, the reflective film is deposited on the substrate, and then the organic dye layer (recording layer) and the protective layer are sequentially formed to form a laser. This should be incident as a protective film. At this time, the process of forming a protective layer on the organic pigment layer is carried out by spin coating a protective layer lacquer (Lacquer) on the organic pigment layer and curing with ultraviolet (UV), the organic material is protected during the spin coating process Soluble in the layer monomer, or the organic pigment layer may be physically damaged. In addition, even when the protective layer is coated, in the process of curing the protective layer with ultraviolet rays, the pigment may be damaged by ultraviolet rays, making it difficult to manufacture the disk.

Accordingly, an object of the present invention is to form a heat insulating layer on the organic dye layer to solve the above problems, thereby preventing damage to the organic dye layer that may occur in the process of forming the protective layer and curing the protective layer with ultraviolet rays and recording It is possible to provide a high density optical disc.

1 to 3 show the laminated structure of a conventional optical recording medium and the direction of incidence of laser light during recording and reproduction.

Fig. 4 shows the laminated structure of the optical recording medium and the incident direction of laser light during recording and reproduction according to one embodiment of the present invention.

FIG. 5 is a graph showing a change in transmittance (%) with respect to the wavelength (λ: nm) of light in the heat insulating layer of the optical recording medium according to one embodiment of the present invention.

<Description of Symbols for Major Parts of Drawings>

10, 20, 30, 40 ... substrate 11, 22, 31, 42 ... recording layer

12, 21, 32, 41 ... Reflector 13, 23, 33, 44 ... Protective layer

43. Insulation layer

L1, L2, L3, L4 ... Lens

In order to achieve the above object, the present invention provides a substrate on which a pregroove is formed and a reflective film, an organic pigment layer, a heat insulating layer, and a protective layer, which are sequentially stacked on the substrate, to guide laser light during recording or reproduction. It provides an optical recording medium comprising.

The heat insulating layer preferably has a thickness of 10 to 500 nm, and is preferably made of a material selected from the group consisting of ZnS / SiO 2, TiO 2, TaO 2, SiO 2, SiN, and mixtures thereof.

The substrate has a thickness of 0.5 to 1.1 mm and is preferably made of a material selected from the group consisting of polycarbonate, polymethyl methacrylate, epoxy resin, polyester, and amorphous polyolefin.

The reflective film is preferably made of a metal selected from the group consisting of Ag, Au, Al, Cu and alloys thereof.

The organic dye layer is preferably selected from the group consisting of cyanine dyes, hemiyanine dyes, azo dyes, triphenylmethane dyes, or mixtures thereof.

It is preferable that the thickness of the said protective film is 0.05-0.5 mm.

Hereinafter, the structure and each component layer of the optical recording medium according to the present invention will be described in detail with reference to the accompanying drawings.

4 is a cross-sectional view showing the structure of an optical recording medium according to the present invention. Specifically, the optical recording medium includes a substrate 40 on which guide grooves are formed for guiding light during recording or reproduction, and a reflective film 41 and an organic dye layer 42 sequentially formed on the substrate. ) And a protective film 43. Two disks having the structure described above may be used as a double-sided disk bonded by using an adhesive layer, or one of them may be used by bonding a dummy disk.

As shown in Equation 1, the use of a large numerical aperture pick-up lens is required to increase the density of the disk, and the optical recording medium according to the present invention may solve the optical aberration problem that may occur when using a large numerical aperture lens. The laser beam is made to enter through the protective film, not the substrate. This is represented by the following equation (2).

W ∝ (NA) ³ × d

In Equation 2, W represents optical aberration and d represents the thickness of the laser beam incident layer. That is, since the influence of the optical aberration is relatively increased as the numerical aperture is increased, the thickness of the incident layer is preferably thin to attenuate it.

Therefore, in the present invention, the incident laser light is relatively thinner than the substrate, and the incident laser light is incident through a protective layer that can freely control the thickness thereof in a predetermined range.

According to the optical recording medium of the present invention, the reflectance of the recording portion is lower than that of the unrecorded portion, resulting in a difference in reflectance between the recording portion and the unrecorded portion, and information can be recorded and reproduced according to the difference in reflectance. That is, when the recording light is irradiated and the organic dye layer absorbs the recording light and the temperature of the organic dye layer is increased, the material forming the organic dye layer is decomposed by heat to change the optical properties. Therefore, as scattering occurs due to the optical path difference between the unrecorded portion and the recording portion, the reflectance of the recording portion decreases.

Hereinafter, the characteristic required for each component layer of the optical recording medium according to the present invention will be described in more detail.

The substrate 40 of the optical recording medium according to the present invention is provided with a pregroove for guiding light during recording or reproduction on one surface thereof, and the shape thereof depends on the type and thickness of the organic dye used. The substrate may be made of polycarbonate, polymethyl methacrylate, epoxy resin, polyester, amorphous polyolefin, and the like, and may be injection molded during manufacture. As for the heat distortion temperature of the said resin, 80-200 degreeC is preferable. The thickness of the substrate is 0.5-1.1mm can be appropriately adjusted according to the disk structure design.

The reflecting film 41 is for obtaining high reflectance at the wavelength of light used in recording or reproducing, and is preferably formed of a metal having a high thermal conductivity and a high reflectance so as not to easily cause deformation. As the material of the reflective film, a metal such as Ag, Au, Al, Cu, or an alloy thereof is preferable. In general, the reflective film may be manufactured by vacuum deposition or sputtering. It is preferable that the reflecting film is 10-200 nm in thickness.

The organic dye layer 42 of the optical recording medium according to the present invention serves as a heat generating layer that absorbs the recording laser beam and generates heat, and also serves as a recording layer. The organic dye of the organic dye layer 42 preferably has an appropriate absorption in the wavelength range of the recording laser beam, has a high refractive index, and preferably a pigment that is rapidly decomposed upon heating. For example, cyanine-based dyes, hemiyanine-based dyes, azo-based dyes, triphenylmethane-based dyes, and the like may be used alone or in a mixture.

The organic dye layer 42 is formed by a conventional method using the above-mentioned materials. For example, it is formed by dissolving the aforementioned organic dye layer material in an organic solvent and then spin coating it onto a reflective film. It is preferable that the said organic dye layer is 10-200 nm in thickness.

The heat insulating layer 43, which is a main feature of the optical recording medium according to the present invention, serves to protect the organic dye layer 42 when the protective layer 44 is formed. That is, the pigment used in the organic dye layer 42 may be melted or physically damaged by the protective layer coating solution when the protective layer 44 is formed. Therefore, if the heat insulating layer 43 is formed on the organic dye layer 42 to prevent this, the organic dye layer 42 is separated from the protective layer 44, so that the organic dye is formed during the spin coating of the protective layer 44 Melting in the protective layer monomer, or physical damage to the organic pigment layer can be prevented.

In addition, the organic dye layer 42 may be damaged by ultraviolet (UV) light used to cure the protective layer. When the heat insulation layer 43 is formed on the organic dye layer 42, the organic dye layer 42 is formed. It can block ultraviolet rays of specific wavelengths that can damage them. 5 shows the transmittance of the heat insulation layer 43 with respect to the ultraviolet wavelength. The heat insulating layer 43 blocks ultraviolet rays having a wavelength of 350 nm or less, thereby protecting the dye of the organic dye layer 42 from the ultraviolet rays when the protective layer 44 is cured.

Since the insulating layer 43 serves to protect the organic material during the manufacture of the disc and to transmit the recording and reproduction light, the insulation layer 43 must exhibit high transmittance in the wavelength region of the recording and reproduction light. That is, in FIG. 5, the heat insulation layer 43 exhibits a high transmittance of 70% or more in the wavelength region of the HD-DVD and the DVD recording and reproducing laser beam, in contrast to blocking ultraviolet rays of a specific region used in curing the protective layer. The trend was shown. As the material of the insulating layer 43, ZnS / SiO₂, TaO₂, SiO₂, SiN, and mixtures thereof are preferable. In general, the insulating layer 43 may be formed by vacuum deposition, electron beam (E-beam), or sputtering. The heat insulating layer is preferably in the thickness range of 10 to 500nm.

The protective layer 44 of the optical recording medium according to the present invention serves to protect other constituent layers, especially the organic dye layer, which is the recording layer. A hard resin is suitable for protecting the recording layer, and light is incident through the protective layer during recording and reproduction. Therefore, the thickness of the protective layer should be uniform in consideration of the optical path.

The protective layer is formed according to a conventional method. For example, the impact strength is large and transparent and curable by ultraviolet light, for example, epoxy or acrylate resin. The protective layer is formed by spin coating a UV curable resin on the heat insulating layer 43 and then curing with UV. The thickness of the protective layer is determined by the light used and the numerical aperture of the objective lens, and preferably 0.05-0.5 mm.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are provided to aid the understanding of the present invention and are not intended to be limiting.

<Example 1>

A reflective film was formed by sputtering Ag of 100 nm on a polycarbonate substrate having a thickness of 1.1 mm. The organic pigment layer was formed by spin coating NK 868, a cyanine pigment from Hayashibara, Japan, in 0.15 g / 10 ml TFP solution. After sputtering ZnS / SiO₂ into a 50 nm thick insulating layer, the UV lacquer (Philips 400905) solution was coated and then cured with ultraviolet rays. There was no damage to the organic pigments in the organic pigment layer during the manufacture of the disc, and it was possible to manufacture the disc.

<Example 2>

In Example 1, a disk was prepared in the same manner except that SiN was used instead of ZnS / SiO₂ as the heat insulating layer. In the same manner as in Example 1, there was no damage to the organic pigments in the organic dye layer when the disk was manufactured, and the disks could be manufactured. The change of the transmittance | permeability with respect to the wavelength of the light in the heat insulation layer of the optical recording medium by Example 1 and Example 2 is shown in FIG. That is, high transmittance is shown in the wavelength range of the recording or reproducing light, while low transmittance is shown in the wavelength range of the ultraviolet ray for curing the protective layer which may damage the organic dye layer.

<Comparative Example 1>

In Example 1, except that the heat insulating layer (ZnS / SiO) was not used, a disk was prepared in the same manner. In the coating of UV lacquer, the organic pigment of the organic pigment layer was melted by the lacquer, making it difficult to manufacture a disk.

As described above, the optical recording medium according to the present invention protects the organic dye layer during the process of forming the protective layer by forming an insulating layer between the organic dye layer, which is the recording layer and the protective film, and when the protective layer is cured by ultraviolet rays of a specific wavelength. It was. Therefore, the production of the optical recording medium according to the present invention is facilitated, and the incident of the recording and reproducing laser light through the relatively thin protective layer makes it possible to solve the optical aberration problem caused by the high numerical aperture, resulting in high-density optical Realization of a recording medium is possible.

Claims (8)

An optical recording medium comprising a substrate on which guide bones are formed, and a reflective film layer, an organic dye layer, a heat insulating layer, and a protective layer to which recording light is incident, sequentially formed on the substrate. The optical recording medium of claim 1, wherein the heat insulation layer is made of a material selected from the group consisting of ZnS / SiO2, TiO2, TaO2, SiO2, SiN, and mixtures thereof. The optical recording medium according to claim 1, wherein the heat insulation layer has a thickness of 10 to 500 nm. The optical recording medium according to claim 1, wherein the substrate is made of a material selected from the group consisting of polycarbonate, polymethylmethacrylate, epoxy resin, polyester, and amorphous polyolefin. The optical recording medium according to claim 1, wherein the substrate has a thickness of 0.5 to 1.1 mm. The optical recording medium of claim 1, wherein the reflective film is made of a metal selected from the group consisting of Ag, Au, Al, Cu, and alloys thereof. The method of claim 1, wherein the organic dye layer is selected from the group consisting of cyanine dyes, hemicyanine dyes, azo dyes, triphenylmethane dyes, and mixtures thereof. And an optical recording medium. The optical recording medium according to claim 1, wherein the protective film has a thickness of 0.05 to 0.5 mm.