KR19980022575A - Recordable optical disc - Google Patents

Abstract

The present invention relates to a recordable optical disc. In a recordable optical disc, a metal thin film, a strained layer, a reflective film, and a protective film are sequentially formed on a substrate on which a valley is formed, wherein the strained layer is azobisisobutyronitrile, dibenzoyl peroxide, diiso At least one degradable substance selected from the group consisting of butyl peroxide, t-butyl peracetate, dicumyl peroxide, lauryl peroxide, di-sec-butylperoxydicarbonate and methylethylketone peroxide and having a refractive index of 1.8 or more The recordable optical disc reflectance and CNR, which are characterized by including organic materials, are large, so that the reproduction characteristics are excellent as well as the recording sensitivity is excellent.

Description

Recordable optical disc

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recordable optical disc, and more particularly, to a recordable optical disc having excellent reproduction characteristics and recording sensitivity, and having a simple structure.

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 a difficulty in increasing its capacity, an optical disc using a new recording method has emerged.

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

Information recorded on such an optical disc is required to be reproduced (CD compatibility) in a CD-ROM drive of a ROM-type medium during reproduction. To this end, optical discs require more than 65% reflectivity and 47dB CNR (Carrier to Noise Ratio) according to the standardization standard of red books.

In a recordable optical disc, recording is reproduced in accordance with reflectance change due to physical deformation, phase change, magnetic property change, etc. before and after recording. Therefore, in order to have CD compatibility, optical discs require long-term storage and high recording sensitivity in addition to high reflectance and high CNR.

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 disc in which a photosensitive oxy metal thin film absorbs heat by 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 disc has the disadvantage of having a stable recording pit but not having a high reflectance of 65% or more because the metal thin film acts as a reflective film and a light absorbing layer.

U.S. Patent No. 4,990,388 discloses a method of manufacturing an optical disc 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 (FIG. 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.

Meanwhile, in Korean Patent Application No. 95-50705, a metal thin film 52, a strained layer 53 including an easily deformable organic polymer, a reflective film 54, and a protective film 55 are sequentially formed on a substrate 51. An optical disc is disclosed. Here, the strained layer is made of a polymeric material. However, there is a problem that the deformation layer made of a polymer has poor deformation force and poor recording sensitivity.

The technical problem to be solved by the present invention is to solve the above problems and to provide a recordable optical disc having not only excellent reproduction characteristics but also excellent recording sensitivity.

1 to 6 are schematic cross-sectional views of optical discs manufactured according to a conventional method.

7 is a schematic cross-sectional view of an optical disc manufactured according to an embodiment of the present invention.

8 is a graph showing a change in reflectance according to the thickness of the buffer layer.

9 is a graph showing a change in CNR according to a change in recording power during recording on an optical disc.

Explanation of symbols for main parts of the drawings

61,71.Board

62,72.Metal Membrane

63,73.Deformation layer

64,74.

65,75.Shield

In the present invention, a metal thin film, a strained layer, a reflective film, and a protective film are sequentially formed on a substrate on which a bone is formed in order to achieve the above object, wherein the strained layer is azobisisobutyronitrile. At least one selected from the group consisting of dibenzoyl peroxide, diisobutyl peroxide, t-butyl peracetate, dicumyl peroxide, lauryl peroxide, di-sec-butylperoxydicarbonate and methylethylketone peroxide There is provided a recordable optical disc comprising a decomposable substance and an organic substance having a refractive index of 1.8 or more.

The optical disc of the present invention is characterized in that the deforming layer contains a decomposable substance having high reactivity when irradiated with light, and the recording layer has superior recording characteristics as compared with an optical disc made of a polymeric material.

7 is a schematic cross-sectional view of an optical disk according to an embodiment of the present invention. As can be seen from Fig. 7, the optical disc of the present invention has the same structure as the conventional optical disc (Fig. 6), and the recording and reproducing principle is similar. That is, when recording to an optical disk using a laser, the focused laser heats the metal thin film layer 62 and the heat is transferred to the substrate 61 so that the substrate 61 expands and deforms and the metal thin film is caused by the force. The 62 and the deformation layer 63 are to be deformed together. The recorded portion is deformed by the substrate, the metal thin film, and the deformable layer, so that the reflectance is lowered compared to the unrecorded portion, resulting in a difference in reflectance between the recorded portion and the unrecorded portion, and recording and reproduction are performed according to the difference in reflectance. Referring to FIGS. 7 and 8, the principle of decreasing the reflectance of the recorded portion is as follows.

First, the reflectance of the recording site is lowered by the dispersion of incident light in the recording site. Since the substrate 71 and the metal thin film 72 are deformed by the recording laser as shown in FIG. 8, a combination of the deformation at the interface between the substrate and the metal thin film and the deformation at the interface between the deformation layer 73 and the reflective layer 74 The incident light is dispersed by this. Therefore, the reflectance of the recording portion is lower than that of the unrecorded portion where there is no dispersion of incident light.

Second, when the recording light is irradiated so that the metal thin film 72 absorbs light and the absorption region is locally heated to increase the temperature rapidly, the substrate 71, the metal thin film 72, and the strained layer 73 are damaged by heat. As these optical properties are altered, the difference between the unrecorded portion and the optical path is large, resulting in a decrease in reflectance.

Third, the reflectance of the recording site due to the extinction interference of the reflected light a reflected at the interface between the substrate 71 and the metal thin film 72 and the reflected light b reflected at the interface between the strained layer 73 and the reflective film 74. Is lowered. Referring to FIG. 8, the thickness d1 of the strained layer is a size that may cause constructive interference between the reflected light b reflected from the reflective film 74 and the reflected light c reflected from the metal thin film 72. However, when the recording laser is focused, the substrate 71 and the metal thin film 72 expand in the direction of the strained layer 73 so that the thickness d2 of the strained layer becomes small, so that extinction interference occurs. Therefore, while light irradiation, constructive interference occurs in the unrecorded portion, while in the recorder, the reflectance decreases due to extinction interference.

In the present invention, the reflective film 74 is provided on the strained layer 73, and the thickness of the strained layer is increased so that the reflected light b reflected by the reflective film 74 and the reflected light c reflected by the metal thin film 72 become constructive interference. By adjusting, high reflectance of 65% or more is achieved. It is possible to maximize the deformation effect by adjusting the degree of deformation of the deformation layer by adding or not adding a pyrolysis compound to the deformation layer as necessary. Pyrolysis of the components contained in the strained layer may induce a change in the interface between the strained layer and the reflective layer, thereby obtaining a high CNR.

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

In the present invention, the substrate 71 is made of a material that maintains transparency to the laser, has excellent impact strength, and can be easily expanded and deformed at a temperature of 80 to 200 ° C. Materials satisfying these properties include polycarbonate, polymethyl methacrylate, epoxy resin, polyester, amorphous polyolefin, and the like, and the heat deformation temperature is preferably 100 to 200 ° C. 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. As for the thickness of a board | substrate, 0.3-1.5 mm is suitable.

The metal thin film 72 serves as a heating layer that absorbs and generates heat of the recording laser, and serves as a partial mirror that 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 72 preferably has a transmittance of 95 to 5% and an absorption of 5 to 95%. As for thickness, 10-300 GPa is preferable. This is because if the thickness exceeds 300 mm, the recording effect is deteriorated for the following reason. That is, if the thickness is too large, the substrate is difficult to expand during recording, so that the deformation of the recording site is small, or the decrease in reflectance decrease due to the change of the thickness of the deformation layer during recording is low, resulting in low contrast or scattering. This is because it may be difficult to obtain reflectance. On the other hand, if the thickness is less than 10 GPa, the amount of heat generated by light absorption during recording may be small, which may make it difficult to deform the substrate.

As for the thermal conductivity of the metal thin film 72, 4 (W / cm * degreeC) or less is suitable. If it exceeds 4 (W / cm · ℃), the heat generated when recording with the laser is rapidly conducted to the surroundings, making it difficult for the thin film to be heated above the required temperature. Because there is.

In addition, the coefficient of linear expansion is preferably 3 × 10 −6 / ° C. or more. If it is less than the above range, it is because cracking of the metal thin film occurs due to expansion due to deformation of the substrate during recording, so that a uniform recording signal cannot be obtained.

Metal thin film materials satisfying these conditions are gold, aluminum, chromium, aluminum / titanium, copper, nickel, platinum, silver, tantalum or alloys thereof, and the method of forming them is vacuum deposition, electron beam (E-beam) method, sputtering. Law, etc.

The strained layer 73 is deformed according to the deformation of the substrate 71 and the metal thin film 72, and serves to maximize the change in reflectance by changing the shape of the interface between the strained layer and the reflective film. Thus, the strained layer material is used which can be easily deformed by heat transfer from the metal thin film or absorption of its own light energy. The thickness of the strained layer is preferably 50 to 1000 nm.

As a material which can be used for the strained layer 73, there exists an organic substance with refractive index 1.8 or more. As an organic substance having a refractive index of 1.8 or more, aromatic compounds, aliphatic compounds, amides, esters, ureas, sulfides, hydroxy compounds, and the like can be used alone or in combination. In particular, preferred organics are pigments. For example, the dye may be an atraquinone dye, a dioxadine dye, a triphenodithiazine dye, a phenanthrene dye, a cyanine dye, Phthalocyanine pigments, merocyanine pigments, pyrylium pigments, xanthine pigments, triphenylmethane pigments, croconium pigments, azo (azo) pigments, indigoid pigments, methine pigments, azulene pigments, squaria pigments, sulfide pigments, metal dithiolates (methal) dithiolate) dyes and the like can be used alone or in combination.

The pigment | dye as mentioned above or the organic substance with refractive index 1.8 or more can be used in mixture with a polymeric resin. Preferred polymers include vinyl alcohol resin, vinyl acetate resin, acrylate resin, polyester resin, polyether resin, polystyrene resin, urethane resin, cellulose resin, fatty acid resin and the like.

Further, according to the present invention, in order to improve recording sensitivity, a decomposable material which is easily decomposed by heat and which can induce deformation of other materials is further included. Such materials include 2,2'-azobisisobutyronitrile [2,2'-azobis (isobutyronitrile)], dibenzoyl peroxide, diisobutyl peroxide, t-butyl peroxide Acetate (t-butyl peracetate), dicumyl peroxide, lauryl peroxide, di-sec-butylperoxydicarbonate, methylethylketone peroxide peroxide). In the present invention, the compounding weight ratio of the decomposable substance and the organic material having a refractive index of 1.8 or more is 1:99 to 30:70, and the compounding weight ratio of the decomposable substance and the polymer substance is 3: 1 to 1:10. The weight ratio is preferably 3: 1 to 1:10.

In the present invention, the formation of the strained layer is carried out in a conventional manner except for the composition thereof. For example, the above-described strained layer material may be dissolved in an organic solvent, and then spin coated onto the metal reflective film 72. The organic solvent is not particularly limited as long as the organic solvent is excellent in solubility of the strained layer material without damaging the substrate.

The reflective film 74 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 kPa. In addition, a conventional method such as an electron beam method or a sputtering method can be used for the formation method.

Another component of the protective film 75 is to protect other components of the optical disk, and is made of a material having a large impact strength and transparency 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 74 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

Nickel was vacuum-deposited on a 1.2 mm-thick polycarbonate substrate on which a valley having a depth of 170 nm, a width of 0.07 μm, and a track pitch of 1.6 μm was formed to form a nickel thin film layer having a thickness of 5 nm. In a separate vessel, 0.8 g of phthalocyanine-based dye (S 04, Photosensitive Pigment, Japan) and 0.1 g of azobisisobutyronitrile were dissolved in 10 ml of diacetone alcohol. On the nickel thin film layer, the resulting solution was spin coated at 2000 rpm to form a strained layer. The SEM photograph showed that the strained layer had a thickness of 220 nm. The substrate was placed in an oven and dried at 40 ° C. for 4 hours. Aluminum was vacuum-deposited on the strained layer to form a 1000 Å 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 manufactured according to the present invention was measured to be 74%. A 720 kHz signal was recorded at a speed of 1.3 m / sec with a power of 8 mW, and then reproduced by using a 0.7 mW laser. The CNR of the reproduced signal was 61 dB. In order to determine the recording characteristics at high speed, the recording characteristics were measured by the same method as the recording speed of 1.3 m / sec except that the recording speed was 2.6 m / sec. a). In addition, information was recorded using a Pioneer RPD-1000 compact disc recorder, and then reproduced using a Philips compact disc player Mark II, and the recording characteristics were evaluated using CD-CAPS. The item satisfies the CD specification.

Example 2

An optical disc was manufactured in the same manner as in Example 1, except that dibenzoylperoxide was used instead of azobisisobutyronitrile. The reflectance and CNR of the fabricated optical disc were measured, which were excellent as 71% and 56dB, respectively.

Comparative Example 1

An optical disc was produced in the same manner as in Example 1, except that azobisisobutyronitrile was not added. The recording speed is 2.6 m / sec, and other conditions are shown in Fig. 9 by measuring the recording characteristics by the same method as in Example 1 (curve b), which shows that the recording characteristics at high speed are higher than that of the optical disc manufactured according to the present invention. Not good.

As can be seen from the above, the recordable optical disc of the present invention has the advantage that the reflectance and the CNR are large, so that not only the reproduction characteristics are excellent but also the recording sensitivity is excellent.

Claims (12)

In a recordable optical disc, a metal thin film, a strained layer, a reflective film, and a protective film are sequentially formed on a substrate on which a valley is formed. The modifying layer is azobisisobutyronitrile, dibenzoyl peroxide, diisobutyl peroxide, t-butyl peracetate, dicumyl peroxide, lauryl peroxide, di-sec-butylperoxydicarbonate and methylethyl A recordable optical disc comprising at least one degradable material selected from the group consisting of ketone peroxide and an organic material having a refractive index of 1.8 or more. 2. The recordable optical disc according to claim 1, wherein the metal thin film is made of a metal having a k value of 1 or more, which is an imaginary part of the birefringence coefficient. The recordable optical disc according to claim 1, wherein the metal thin film has a thickness of 10 to 300 microseconds. 2. The recordable optical disc of claim 1, wherein the metal thin film is at least one selected from the group consisting of gold, aluminum, silver, platinum, copper, chromium, nickel, titanium, and tantalum. 2. The recordable optical disc according to claim 1, wherein a blending weight ratio of the decomposable substance and the organic substance having a refractive index of 1.8 or more is 1:99 to 30:70. The recordable optical disc according to claim 1, wherein the organic material having a refractive index of 1.8 or more is at least one selected from the group consisting of aromatic compounds, aliphatic compounds, amides, esters, ureas, sulfides and hydroxy compounds. The organic material of claim 1, wherein the organic material having a refractive index of 1.8 or more is an atlaquinone dye, a dioxadine dye, a triphenodithiazine dye, a phenanthrene dye, a cyanine dye, a phthalocyanine dye, a merocyanine dye, or a pyryllium-based dye As dyes, xanthine dyes, trienyl methane dyes, croconium dyes, azo dyes, indigo dye dyes, methine dyes, azulene dyes, squaraine dyes, sulfide dyes and metal dithiolate dyes At least one pigment selected from the group consisting of a recordable optical disc. 2. The recordable optical disc of claim 1, wherein the strained layer further comprises a polymer material. 9. A recordable optical disc according to claim 8, wherein the compounding weight ratio of the decomposable substance and the polymer substance is 3: 1 to 1:10. According to claim 8, wherein the polymer material is a vinyl alcohol resin, vinyl acetate resin, acrylate resin, polyester resin, polyether resin, polystyrene resin, urethane resin, cellulose resin and fatty acid group And at least one selected from the drawings. 2. The recordable optical disc according to claim 1, wherein the strained layer has a thickness of 50 to 1000 nm. 2. The recordable optical disc of claim 1, wherein the reflective film is made of at least one selected from the group consisting of gold, aluminum, silver, chromium, copper, titanium, and tantalum.