JPH0572658B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a confidential optical recording medium that can prevent theft and unauthorized use of recorded information in an optical recording medium.

<Prior art> Optical recording media are made by condensing a high-energy-density light beam such as a laser beam into a microscopic shape, forming holes called recording pits or areas with different reflectance in the medium, and forming holes in the recording pits. This is a recording medium that performs reading by scanning the presence/absence with reproduction light.

In recent years, with advances in laser technology and focus/track servo technology, 1μm to 2μm
It has become possible to write recording pits on 30cm diameter discs and play them back at high speed. In terms of recording density, it is possible to increase the capacity to several gigabytes per disk, so it has an importance as an information recording medium that approaches that of magnetic disks.

<Problems to be Solved by the Invention> However, conventional optical recording media are not provided with any means for protecting the security of recorded information. In other words, track groove information, track number information, and the presence or absence of recording pits recorded on a recording medium can be easily observed using a magnifying means such as a microscope. Therefore, once the master disc is obtained, there is a possibility that the information on the recording medium can be easily reproduced and used as data for a copy to make corrections, thereby making the information illegally used. The present invention was created taking into consideration the confidentiality of information recorded on the optical recording medium as described above, and its purpose is to maintain the confidentiality of recorded information on the optical recording medium.
To provide the world with a security-preserving optical recording medium that can easily prevent theft and unauthorized use of recorded information without interfering with playback.

<Means for Solving the Problems> The first configuration of the confidential optical recording medium of the present invention that achieves the above object is to form pits with different reflectances formed by irradiation with laser light in a specific wavelength range. An optical recording medium that can be read by reproduction light is characterized in that a security layer that absorbs light in a wavelength range other than the specific wavelength range is provided on the surface of the medium, and the reflectance is improved by reproduction light in the near-infrared light range. For optical recording media that can read different pits, the security layer is preferably an organic dye-containing layer that can absorb light outside the near-infrared region, but is not limited to this. Alternatively, the security layer may be an inorganic pigment layer.

It is desirable that the light other than the specific wavelength is in the visible light range. Further, the second configuration of the confidential optical recording medium of the present invention that achieves the above object is an optical recording medium in which pits with different reflectances formed by laser beam irradiation can be read by reproduction light in a specific wavelength range. The medium is characterized in that the substrate is a security-preserving substrate capable of absorbing light in a wavelength range other than the specific wavelength range.

<Function> Ordinary optical recording information records minute pits as information, but these recording pits often have a change in reflectance even for light at wavelengths other than the reproduction light wavelength. Therefore, the recorded pit array can be easily read out and the information can be deciphered by observation using a visible microscope. Therefore,
In the present invention, a security layer that absorbs light in a wavelength range other than the specific wavelength range used for reproduction light is provided on the surface of the medium, or a security-maintaining substrate is used to prevent readout of the recording pit at wavelengths other than the specific wavelength range. This made it difficult. Further, recording and reproduction of optical recording media is usually performed using monochromatic light such as a laser, and a photodiode having sensitivity from the visible light region to the near-infrared region is usually used as the reproduction light receiving section. Therefore, when an optical recording medium is reproduced under a white light source such as indoor light, a white light component enters the light receiving section at a certain ratio, causing so-called background noise. However, in the security optical recording medium according to the present invention, visible light components other than reproduction light are absorbed by the security layer even under white light.In other words, the security layer plays the role of a cut filter, and therefore The reproduction S/N ratio can be increased.

<Examples> Examples of the present invention will be described in detail below.

FIG. 1 shows a first embodiment of the present invention. As shown in the figure, an optical recording material layer 12 is formed on a substrate 11, and a security layer 13 is overcoated thereon. In the recording material layer 12, pits 14 having different reflectances are formed by laser beam irradiation, and certain information is recorded therein. When using near-infrared light such as semiconductor laser light as recording/reproduction light, the security layer 13 absorbs light in a wavelength range other than the near-infrared region and transmits only near-infrared light. It is preferable to use an organic dye-containing layer that allows
The organic dye-containing layer has a content of 100%, that is,
A layer consisting of a single organic dye may also be used.

For optical recording media having the above configuration,
By irradiating the recording material layer 12 with a semiconductor laser beam or the like through the security layer 13, the recording pit 1 is
4 is formed. Further, in order to read out the information in the recording pit 14, the recording material layer 12 is irradiated with a semiconductor laser beam or the like with a weakened optical power through the security layer 13, and the reading is carried out using the reflected light. To read the information in the recording pit 14, the security layer 13
Therefore, it cannot be performed using light outside the specific wavelength range used for recording and reproduction. This is because when a semiconductor laser beam is used as the recording/reproducing light and white light is incident from the security layer 13, near-infrared light whose wavelength range has changed only in the recording pit 14 is reflected. Therefore, depending on the light in the visible range, the recording pit 14
The presence or absence of the data is not observed, and therefore the information in the recording pit 14 is kept confidential. That is, although normal optical recording information is recorded as information using minute pits 14, these recording pits 14 often have a reflectance change even with respect to light other than the reproduction light wavelength.
Therefore, without the security layer 13, the rows of recording pits 14 can be easily read out by observation using a visible light microscope, and the information can be decoded. In addition, such a recording pit 1
4 is often written in the form of a track groove called a series of pre-groups. If the track pitch of the track groove, the track groove, and even the track number can be observed in the visible part, it will become an important clue for deciphering the above information, and the reproduction of confidential records will become easier.

For the above reasons, the security layer 13 that prevents observation of recorded information in the visible portion has an important effect on information security.

Further, such a security layer 13 also has the following side effect. Recording on optical recording media
Reproduction is usually performed using monochromatic light such as a laser, and a photodiode sensitive from the visible light region to the near-infrared region is usually used as the reproduction light receiving section. Therefore,
When an optical recording medium is reproduced under a white light source such as indoor light, a white light component enters the light receiving section at a certain ratio, causing so-called background noise. However, in the security optical recording medium according to the present invention, even under white light, visible light components other than reproduction light are absorbed by the security layer 13. In other words, the security layer 13 plays the role of a cut filter. The S/N ratio of recording and reproduction can be increased.

FIG. 2 shows an example in which the security layer 22 is provided on the substrate side. In FIG. 2, 21 is a substrate, 22 is a security layer, 23 is a recording material, and 24 is a spacer, which is a hollow (air sandwich) type structure of a two-type substrate.

Although FIGS. 1 and 2 show an example in which the security layers 13 and 22 are provided independently, they can also be used in common by being mixed into the substrate, for example. An example of this is shown in FIG. Third
In the figure, 31 indicates a substrate containing an organic dye and inorganic pigment that absorbs light other than recording/reproducing light, and 32 indicates an optical recording material.

Examples of the present invention will be specifically shown below.

Example 1 Au was evaporated to a thickness of 500 Å as a reflective layer on a PMMA substrate, and Te was evaporated to a thickness of 150 Å on top of that to form an optical recording material. The surface showed metallic luster. Finally, add malachite to 10 parts of silicone resin as a security layer.
Two parts of Grin was dissolved in a solvent and spin coated to form a 3000 Å resin layer. As a result, the metallic luster with high reflectance on the surface disappeared, and a dark green resin layer was formed. After recording pits were formed on this medium using a semiconductor laser beam with a wavelength of 830 nm, the pits were observed under a microscope using visible light, but the pits could not be observed because only the dark green reflected light was present. Then the wavelength
When the 830 nm semiconductor laser light was read out by the read head with the optical power weakened, the read light could be read out at the same signal level as in the state without the protective layer.

Example 2 CIDisperse Black on polycarbonate board
2 (CI No. 11255) was vacuum deposited to a thickness of 1000 Å. Almost no light is transmitted through this substrate, and the reflected light when visually observed shows a red-gold metallic luster. On this dye layer, a Te-containing-CS _double polymer film of 120 Å was deposited and formed into a hollow sandwich-like optical recording medium via a spacer. After creating recording pits in this optical recording medium using a semiconductor laser beam with a wavelength of 830 nm, the optical power was weakened and the pits were read out, and as a result, the pits could be read out at the same signal level as without the protective layer.
However, when observing visible light, it was not possible to observe pits because only the golden-red reflected light was visible.

Example 3 Acrylic resin (polymethyl methacrylate) 100
CIPigment Black(1) (CINo.50440)
Five parts of the mixture were kneaded and pelletized to obtain a resin material for injection molding. This was injected into a disk of 30 cm x 1.5 mm ^t for an optical recording medium, and this was used as a substrate. TeO-TeO ₂ oxide was produced on this substrate by co-evaporation at 1100 Å in vacuum to form an optical recording medium. An optical recording material produced on another substrate was placed on top of this optical recording material via a thermosetting resin to produce a double-sided recording type optical disc. Pit writing was performed on each surface using a semiconductor laser with a wavelength of 850 nm, and reproduction was performed using light with weakened power, but it was possible to record and reproduce data with an S/N ratio comparable to or higher than that of a normal substrate. Furthermore, the recording pits were blocked by the dye contained in the substrate and could not be observed with a visible light microscope.

Example 4 On an acrylic (PMMA) substrate, Sn-Te (volume ratio 20/80) was co-deposited with PbF ₂ to form PbF ₂ /Sn-
A dispersion layer with Te of 15/85 is provided and used as an optical recording material. On this surface, a 2500 Å thick Nd-glass layer was formed using magnetron sputtering to serve as an overcoat and security layer. The surface exhibits a deep blue color and near-infrared light is transmitted, so pits can be recorded using a semiconductor laser with a wavelength of 780 nm.
And playback was possible. However, pit observation using visible light was impossible due to the Nd-glass layer.

Example 5 Te-Teflon with a thickness of 700 Å was fabricated by sputtering on a glass substrate. This was used as an optical recording material, and Cd--S was further laminated to a thickness of 3000 Å by vapor deposition as a secret-keeping layer and an overcoat layer. wavelength
Recording and reproduction were performed using a semiconductor laser for recording with a wavelength of 840 nm and a semiconductor laser for reading with a wavelength of 780 nm, and good recording and reproduction could be performed with a decrease of less than 5% due to the Cd-S layer having a wavelength cut-off of 750 nm. However, since the Cd-S layer absorbs visible wavelengths, it is impossible to observe the pits using a microscope, and it has become clear that the Cd-S layer has the ability to maintain the confidentiality of the pits.

Example 6 Te is deposited to a thickness of 150 Å on a polycarbonate substrate to form an optical recording layer. Next, after crushing KRS-5 (mixed crystal of TlBr and TlI), PMMA was prepared using tetrahydrofuran.
THF solution (PMMA/THF=8/92: weight ratio)
A deep red KRS-5 dispersed PMMA solution (PMMA/KRS=70/30 weight ratio) was prepared by kneading the mixture.
This PMMA solution was spin-coated on the Te vapor-deposited film to form a 3000 Å thick security layer and overcoat layer. When pits were recorded and reproduced on this medium using a semiconductor laser with a wavelength of 830 nm, the recording and reproduction signals attenuated to about 30%. To remove this,
After crushing KRS-5, use a mesh sieve to obtain an average particle size of 150 Å to 200 Å, and then
When a PMMA-dispersed spin-coated film was used, the reproduction signal of the semiconductor laser was attenuated by about 85%. Visible light is PMMA containing KRS-5 powder
Due to this, visible light observation of the recording pit was impossible, and the confidentiality of the medium was maintained.

<Effects of the invention> As specifically explained above based on the examples,
The security type optical recording medium according to the present invention can prevent information theft and unauthorized use by simply providing a security layer on a normal optical recording medium.

Furthermore, even when the recording medium is played back under external light such as indoor light, in order to cut out light other than the recording and playback light, light of other wavelengths that reach the playback light receiver is cut out. The S/N ratio of light can also be improved.

In addition, if a security layer with different colors is provided by printing or other means, the company name, logo, usage instructions, etc. can be displayed on the optical recording section, which occupies most of the optical recording medium, reducing the area of the medium. It has advantages that can be used effectively. Therefore, when applied to optical disks and optical cards that record high-density confidential information in a highly information-oriented society, their confidentiality is very effectively exhibited.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 are respectively schematic diagrams of the configuration of a confidential optical recording medium according to an embodiment of the present invention. In the drawing, 11, 21 are substrates, 12, 23, 32
1 is an optical recording material, 13 and 22 are security layers, 14 is a recording pit, 24 is a spacer, 25 is a hollow part, 3
1 is a security type board.

Claims (1)

[Scope of Claims] 1. In an optical recording medium in which pits with different reflectances formed by laser beam irradiation can be read in a specific wavelength range by reproduction light, light in a wavelength range other than the specific wavelength range is absorbed. A security-preserving optical recording medium characterized in that a security-preserving layer is provided on the surface of the medium. 2. For optical recording media that can read pits with different reflectances using reproduction light in the near-infrared region, the security layer is an organic dye-containing layer that can absorb light outside the near-infrared region. A security-preserving optical recording medium according to claim 1, characterized in that: 3. The security-preserving optical recording medium according to claim 1, wherein the security layer is an inorganic pigment layer. 4. The confidential optical recording medium according to claim 1, wherein the light outside the specific wavelength range is light in the visible light range. 5. In an optical recording medium in which pits with different reflectances formed by laser beam irradiation can be read by reproduction light in a specific wavelength range, the substrate is a sensitive material that can absorb light in a wavelength range other than the specific wavelength range. A security-preserving optical recording medium characterized by being a retentive substrate.