JPS641315B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a novel optical recording medium, in particular an optical recording medium in which a reflective layer coated with a light-absorbing layer is provided on a substrate, and a thin, hard, inert transparent overcoat layer is further applied thereto, and information is recorded thereon. related to information recording bodies. Spong describes an ablative recording method in which a convergent modulated light flux, such as a laser beam, is applied to an optical ablative recording medium. This recording medium consists of a layer of light-reflecting material coated with a light-absorbing material on a substrate, and the thickness of the light-absorbing layer is such that the reflectance is extremely reduced so that the maximum portion of the incident light energy is collected. It is selected so that it can be converted into thermal energy. This thermal energy causes the exposed portions of the light-absorbing material to sublime or melt, thereby exposing the corresponding portions of the light-reflecting layer. During reproduction, the difference in illuminance between the light-absorbing layer and the light-reflecting layer having the lowest reflectance is detected. Research in this area has improved the performance of the materials used, but as an example of this recording medium, a thin film of a light-reflecting material such as aluminum is coated on a thermally insulating substrate with a smooth surface. There is a method in which this aluminum coating is made passivated and then a coating of an organic light-absorbing material such as 4-phenylazo-1-naphthylamine is provided. On the other hand, there is also a light-absorbing layer in which a transparent dielectric layer such as silicon dioxide is deposited on the light-reflecting layer, and a metal thin film is provided on top of the transparent dielectric layer. The most commonly used metal for this is titanium. When an organic dye is used in the light absorbing layer, there remains a problem with the mechanical strength of the dye layer. In order to make the recording medium easier to handle without damaging the dye layer, there is a proposal to provide a protective coating with good mechanical properties. Such an overcoat layer also serves to prolong the life of the recording medium by preventing reaction of the dye layer or metal absorbing layer with the atmosphere. Another problem common to the two types of recording media mentioned above is the effect of surface dust that settles on the media from the surroundings and causes defects or omissions in the signal. These dust particles move under the converging light spot of the recording laser beam and shade that part of the track, preventing the formation of information points for that part of the image signal. When a recorded track portion containing dust particles is reproduced, image defects or omissions due to temporary omission of the information are observed. In the recording medium of the present invention, this dust can be safely removed without causing scratches or other damage to the light absorbing layer. The novel optical recording medium according to the invention consists of a light-reflecting material coated with a light-absorbing material and further overcoated with a thin layer of a hard transparent solid transparent inert material, the protective overcoat being Therefore, the recording medium can be wiped or washed to remove dust particles on the surface without damaging the light-absorbing layer, and the light-absorbing layer is prevented from being chemically attacked by the atmosphere. This invention relates to a recording material used for a recording laser beam that emits light of a predetermined frequency, and this material includes a layer of material that reflects light of the laser frequency and a layer of material that absorbs the light of the laser frequency that covers this layer. A thin transparent inert protective overcoat is provided over the absorbing layer to remove surface contaminant particles by wiping or washing. This overcoat layer can be applied after recording if desired, provided the light absorbing layer is kept clean. The light-reflective material can be applied to an optically smooth, well-adhesive substrate surface. A glass or plastic plate or disk is suitable for this substrate. The reflective layer needs to reflect light of the wavelength used for recording. A thin film of gold approximately 800 Å thick provides a good passive reflective layer, but a thin aluminum film 250-500 Å thick is also sufficient for this purpose; the aluminum film is oxidized to a depth of approximately 30 Å for surface passivation. can do. The light-absorbing layer needs to absorb light at the wavelength used for recording, and it also needs to form an amorphous, adhesive thin film with a thickness that minimizes reflectance, and it also needs to be easily ablated at low temperatures. The holes must be formed with a clear shape and a regular pattern. A thin film of 4-phenylazo-1-naphthylamine obtained by vacuum evaporation of the dye Sudan Black B forms an excellent film, but a thin film of titanium applied over a light-reflecting layer of silicon dioxide does not work. A good light-absorbing layer can be obtained. The material for the overcoat layer according to the invention is preferably hydrophobic and stable to ambient conditions as well as to all solutions used for cleaning the recording medium. In addition, this material is usually amorphous, optically transparent to the wavelength for recording and reproducing, and is suitably a material that does not cause scattering. When recording a signal through this overcoat,
Additionally, the overcoat must not interfere with the formation of the underlying signal elements or substantially affect image quality during reproduction. Therefore, it is desirable that the overcoat material has a sufficiently high melting point and hardness to withstand breakage during recording. Since the organic dyes used in the light-absorbing layer are easily soluble in most organic solvents, the required properties of the overcoat material are that it can form an amorphous coating by solvent-free deposition methods, and also by normal handling. It is desirable to withstand mechanical stress. By carefully adjusting the thickness of the thin protective overcoat,
The non-reflective light absorbing state of the light absorbing layer can be preserved as it was. The thickness of the optically passive non-reflective top layer is mλ/2n, where m is an integer, λ is the wavelength of the recording/reproducing light from the laser, and n is the refractive index of the top layer material at that wavelength. is optimally equal to . Although both organic and inorganic overcoating materials are suitable for use in this invention, inorganic dielectric materials have higher melting points and form harder coatings than organic materials, and are less susceptible to breakage during recording. Additionally, inorganic materials are not attacked by any of the organic solvents typically used to clean discs, and thus provide a slightly more flexible overcoat layer than organic materials. In a preferred embodiment, a disk that has previously been coated with a light-reflecting layer and a light-absorbing layer is provided with an overcoat layer of silicon dioxide (SiO ₂ ) of a suitable thickness. Preferred methods for forming this SiO ₂ layer include electron beam deposition in a high vacuum or reactive glow discharge from a gaseous monomer such as silane. Formed by these two methods
There is no perceptible difference between _{the two} SiO layers. When using resistance heating, SiO _x (1<x<2) is produced,
It has lower strength than _SiO2 . Several organic materials are also recognized as suitable for the overcoat layer of this invention. Sucrose derivatives in which the hydroxyl group of sucrose is substituted with an ester group such as an acetyloxy group or a benzoyloxy group form a good protective overcoat. For example, a benzoic acid sucrose layer formed from sucrose in which six or more hydroxyl groups are substituted with benzoyloxy groups is deposited on the light-absorbing layer of the recording medium. A good overcoat layer can also be obtained by vapor deposition of 8-acetate sucrose. Other materials suitable for the overcoat layer used in this invention include pentaerythritol derivatives of rosin acid.
This material is a low molecular weight (3000-7000) thermoplastic that can be vapor deposited. A pentaerythritol ester of partially or fully hydrogenated rosin acid, with the main rosin acid component being abietic acid and a softening point of approximately 104°C.
Forms a good overcoat layer. A highly cross-linked thin film formed on the surface of the light-absorbing layer by glow discharge or by polymerization of reactive monomers deposited on the surface of the light-absorbing layer also makes a good overcoat. . Suitable such thin films are those produced by exposing a mixture of acetylene and nitrogen (mixing ratio 1:3) or a mixture of argon carrier gas and perfluoroethylcyclohexane to a glow discharge. Even if the method described in US Pat. No. 3,342,754 is used, the general formula A similar highly cross-linked polymeric coating is obtained with repeating units of . However, n is the number of repeating units in the polymer, and R and R' are H or Cl. Next, the present invention will be explained in more detail with reference to the accompanying drawings. FIG. 1 shows a recording medium 24 of the present invention before exposure to a recording beam, showing a substrate 110, a light reflective layer 11
2. Transparent passivation layer 114 thereon, light absorption layer 11
6, an overcoat layer 120 of silicon dioxide or other suitable inorganic or organic material. FIG. 2 shows the recording medium 24 of the present invention after exposure to recording light, with the light absorbing layer 116 being ablated leaving apertures 118 and exposing the passivation layer 114 to light. The overcoat layer 120 remains in place. It is clear that the recording medium after recording, that is, the information recording body, has not only one aperture 118 but a plurality of apertures 118 as shown in FIG. The manner of use of the recording medium of the present invention can be explained in more detail with reference to FIG. During recording, light emitted by a laser 10 is supplied to a modulator 12 where it is modulated according to an input electrical signal source 14. This modulated light is expanded by the recording optical system 16 to increase the diameter of the intensity modulated laser beam to meet the required aperture of the objective lens 18. This expanded modulated laser beam is totally reflected by the polarizing beam splitter 20 and is incident on the objective lens 18 through the beam rotating quarter-wave plate 22 . Furthermore, the modulated recording beam is incident on a recording medium 24 as shown in FIG. 1, ablating a portion of its light-absorbing layer and exposing a portion of its light-reflecting layer. The recording medium 24 is rotated approximately 1800 times by the turntable drive device 26.
It rotates while drawing a vortex track at a speed of 1 minute.
The convergence servo mechanism 28 functions to keep the distance between the objective lens 18 and the surface of the recording medium 24 constant. During reproduction, the path of the recording beam on the recording medium 24 is traced by an unmodulated low-intensity laser beam, that is, a laser beam that does not cause an ablation phenomenon on the recording medium. Then, the reflected light is modulated by the recorded reflection/non-reflection pattern, and the objective lens 18
and returns through the quarter-wave plate 22. This light passes through the 1/4 wavelength plate 22 twice and has its polarization plane rotated by 90 degrees, and is sent to the photodetector 32 by the reproducing optical system 30 through the polarizing beam splitter 20. This photodetector 32 converts the reflected light into an electrical signal corresponding to an input signal and outputs it to an output terminal 34. Tracking servo mechanism 36 monitors the light passing through reproduction optics 30 to ensure that the beam does not go off track during reproduction. The recording medium of this invention has a signal-to-noise ratio of 45 to 50 dB.
It can make high-quality recordings with an average of 48dB, but
Photoinduced thermal recording can be performed on the organic dye layer through the overcoat layer without reducing the signal-to-noise ratio by more than 5 dB. Also surprisingly, when the titanium absorption layer is overlaid with silicon dioxide, the signal-to-noise ratio increases by 3-4 dB. The signal-to-noise ratio is within the range of broadcasting standards, and even recording media with a low signal-to-noise ratio are useful as video records and digitally encoded information records for general consumers. Next, the present invention will be described with reference to Examples, but this does not mean that the present invention is limited to the following description. Example 1 An aluminum layer with a thickness of about 300 Å is deposited on a glass disk with a diameter of 30.5 cm. After the surface of the aluminum layer is oxidized to a depth of about 30 Å to passivate the metal layer, the dye Sudan Black B is applied on top of the aluminum layer. A layer of 4-phenylazo-1-naphthylamine approximately 525 Å thick is deposited by vapor deposition and pyrolysis, and on top of this dye layer a layer approximately 1670 Å thick is deposited.
A silicon dioxide overcoat layer of 1.5 Å was formed by glow discharge of silane. The recording medium obtained in this way can be used at a wavelength of 4880 nm emitted from the argon laser of the apparatus shown in Figure 3.
Exposure to 50 ns pulses of light at Å, the laser power was set to 200-300 mW, and the signal-to-noise ratio
The best recording of 45dB was obtained. No evidence that the silicon dioxide film was destroyed during recording was observed during playback, and microscopic examination at 1000x revealed that there was no change in the thin film during recording.
When an aluminum film was deposited on the silicon dioxide top layer after recording, the diffraction pattern of the recorded signal visible in the film showed that the surface of the silicon dioxide film was slightly oscillated. Example 2 A 800 Å thick layer of gold is deposited on a 30.5 cm diameter disk, and a 400 Å thick layer of 4-phenylazo-1 is placed on top of it.
- After the naphthylamine dye layer had been applied, a silicon dioxide overcoat layer was applied to this dye layer analogously to Example 1. When recording was carried out on this recording medium as in Example 1 and the number of missing pieces per recorded track was measured, the average number of missing pieces per track was 14. Next, this recording medium was placed in a dust chamber for 15 minutes to deposit aluminum oxide particles weighing 12 mg and having a diameter of 5 .mu.m, and the same measurement was carried out, and the average number of missing pieces increased to 150 per track. Next, when this recording medium was spin-cleaned with isopropyl alcohol and measured, the average number decreased to 29 per track. Example 3 After depositing an aluminum layer approximately 300 Å thick on a glass disk with a diameter of 30.5 cm, and depositing a silicon dioxide layer approximately 800 Å thick on top of this aluminum layer,
A titanium absorbing layer approximately 50 Å thick was deposited over the silicon dioxide layer, and a protective layer approximately 3340 Å thick was deposited thereon by electron beam evaporation of silicon dioxide. Recording was carried out in the same manner as in Example 1 on this recording medium and a similar recording medium without a silicon dioxide overcoat. When the power was set at 500 mW, the signal-to-noise ratio for the recording medium without the overcoat was 46 dB and with the silicon dioxide overlayer was 49 dB. For output settings up to 1000 mW, the signal-to-noise ratio for non-topped recording media is up to 46 dB, and for top-attached recording media is up to 46 dB.
It was 50dB hot. Example 4 In Example 2, a sucrose benzoate layer with a thickness of about 1630 Å was deposited over the dye layer instead of the silicon dioxide layer. The benzoic acid sucrose used for this purpose contains approximately 75% or more of the -OH groups in sucrose.

[Formula] is substituted with a group. Recordings were made in the same manner as in Example 1 before and after the application of this benzoic acid sucrose overcoat layer. The objective lens used for this recording was subjected to a cover glass correction of approximately 0.08 mm. When the laser power was set to 250 mW, the signal-to-noise ratio was 43 dB for the recording element before deposition and 40 dB for the recording element after deposition, with the benzoate sucrose overcoat remaining intact. Comparative Example The following overcoat materials were deposited over the organic dye layer of Example 4, but none of these materials formed an amorphous optical quality film.

【table】 [Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the recording medium of the present invention before recording, FIG. 2 is a cross-sectional view of the recording medium of the present invention after recording, and FIG. 3 is an outline of a recording/reproducing method that can use the recording medium of the present invention. It is an illustration. 24...recording medium, 110...substrate, 112...
...Light reflective layer, 114...Transparent passivation layer, 116
... Light absorbing layer, 118 ... Open pores, 120 ... Overcoat layer.

Claims (1)

[Claims] 1. A layer of a light-reflecting material, a layer of a light-absorbing material covering the light-reflecting material, and a layer of a light-absorbing material covering the light-absorbing material so as to be able to remove surface contaminants. a solid transparent hard inert thin protective overcoat of
a saccharide derivative in which a hydroxyl group is substituted with an ester group, a pentaerythritol derivative of rosin acid, and a polymer produced from acetylene or perfluoroethylcyclohexane by glow discharge; Recording medium used for recording with a laser beam emitting light at a desired frequency, characterized in that the thickness of the coating is a function of the wavelength of the laser beam used and also of the refractive index of the coating material at that wavelength. 2 A layer of material that is reflective at the frequency of the light used, and a layer of material that absorbs light at the frequency that covers this light-reflective material layer, and has a row of spaced recesses representing recorded information. a sucrose derivative in which the hydroxyl group is substituted with an ester group; formed of a material selected from the group consisting of a pentaerythritol derivative of rosin acid and a polymer produced by glow discharge from acetylene or perfluoroethylcyclohexane, the thickness of said overcoat layer being as specified above. 1. An information recording medium for use in a reproducing device using a reproducing light beam of a desired frequency, characterized in that the wavelength of the reproducing light is a function of the wavelength of the light and also of the refractive index of the material to be coated at that wavelength.