JPH03132391A - Erasable high reflectivity optical recording medium - Google Patents

Abstract

PURPOSE:To reproduce recording with high reflectivity by forming an optical recording medium by providing a recording layer consisting of an expanding layer and a holding layer containing a specific near-infrared absorbing dye on a base material having a layer highly reflective to laser beam. CONSTITUTION:A metal membrane composed of a metal such as Ag, Al, Pt or Au is provided on a substrate (b) composed of polycarbonate or polyethylene terephthalate by vapor deposition to form a layer (a) having high reflectivity to laser beam for reproducing recording. A recording layer (c) being a laminate consisting of an expanding layer (d) and a holding layer (e) capable of being reversibly deformed by the generation of heat accompanied by the irradiation with laser beam is laminated to the layer (a) to obtain an optical recording medium. Different kinds of near-infrared absorbing dyes whose absorbing wavelength regions do not overlap each other perfectly are compounded with the expanding layer (d) and the holding layer (e) and the contents of the dyes and the reflectivities of the recording layer and the reflecting layer are controlled so that the reflectivity of the recording layer to recording reproducing beam becomes 15% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel optical information recording medium and a recording/reproducing and erasing method thereof. More specifically, the present invention relates to a recording medium that can efficiently record optical information and erase each recorded bit by changing its shape when heated, and can reproduce recorded data with high reflectance.

BACKGROUND Techniques and Problems There have been proposed several optical recording media that allow recording to be reproduced and erased and that can be coated.

For example, Japanese Patent Laid-Open No. 59-5448 discloses an erasable optical recording medium made of a mixture of a polymer and a dye. In this medium, recording is performed by bit formation due to the flow deformation of the polymer.
In order to erase a recorded bit once formed, the entire track containing the recorded bit is heated by laser beam irradiation and then slowly cooled to erase it, or the entire surface of the recording medium is heated and slowly cooled to erase it. was necessary, and it was impossible to erase each recorded bit. Also, JP-A-57-277
No. 90 and No. 60-253036 propose an erasable optical recording medium comprising a bit-forming recording layer and an overcoat layer provided thereon. In this medium, recording is performed by formation of pits due to flow deformation of the recording layer and expansion of the overcoat layer. However, since the overcoat layer has a high softening temperature, it is necessary to irradiate a relatively strong output laser beam for a long time when erasing records, which is not practical. According to yet another proposal (Japanese Unexamined Patent Publication No. 60-69846), laser beam irradiation heats and expands the dome-shaped protrusion (bump).
A recordable/erasable medium has been proposed that basically consists of an expansion layer made of rubber that forms a shape, and a retention layer made of resin that maintains this shape. When recording on this medium, laser light is irradiated near the absorption wavelength (λ1) of the dye mixed in the expansion layer in advance, so that the expansion layer forms bumps and the retention layer maintains this shape. do.

In addition, when erasing recorded bumps, laser light is irradiated near the maximum absorption wavelength (λ2) of the dye mixed in the retention layer in advance, and the retention layer is heated above its Tg to maintain the bump shape. make it difficult. According to this disclosed method, it is certainly possible to perform recording and erasure of recording by reducing bumps reversibly, but the following technical problems remain unsolved. That is, a) since an organic dye is used in the recording layer, the reflectance of the medium surface to recording and reproducing light is low, making it difficult to obtain a high C/N ratio; b)
) As a dye used in the resin layer in the recording layer, reflectance,
A dye that has high absorbance, is compatible with the resin layer, and is stable is desired, but dyes that meet all of these required characteristics are extremely limited, and the manufacturing cost is extremely high.C)
When tracking for signal navigation is provided on the media surface,
Problems remain, such as the possibility that the shape of the tracking will be deformed when erasing records.

In view of these circumstances, the inventors of the present invention have conducted intensive studies on optical recording media that are soluble in organic solvents, can be coated, and are capable of recording, reproducing, and erasing, and have found a medium having the layer structure described below. The present invention has been completed by discovering that it can be used as a new optical information recording medium that does not have any problems.

Outline of the present invention The optical recording medium according to the present invention comprises: 1) a layer [al] having high reflectivity for laser beams for recording and reproduction; and a layer provided on the substrate [b]. In an optical recording medium comprising a recording layer tel,
The recording layer EC] is composed of a laminate of an expansion layer [dl] and a retention layer [c] that can be reversibly deformed by heat generated by laser beam irradiation, and the expansion layer and retention layer have an absorption wavelength range. Different near-infrared absorption dyes that do not overlap completely [D1]
and [D21], and the content of the dye, the thickness of the recording layer [c], and the reflective layer [al 2) When recording information by irradiating the recording medium according to item 1 above with a laser beam, 1) the recording layer [c ], the dye contained in the expansion layer [D1
By irradiating a strong laser beam that oscillates at a wavelength [λ11] corresponding to the maximum absorption wavelength of . a step of recording information by forming a part (bump); and ii) a step of reproducing the recording based on the difference in reflectance to recording and reproducing light between the bump recorded in step 1) and the non-recording part. and ii) Once the bumps of the retention layer are formed, the above wavelength [
λ1] is a method for recording, reproducing optical information, and heating and slowly cooling the bumps by irradiating them with a weak laser beam having an oscillation wavelength [λ21] different from the oscillation wavelength [λ1], and erasing information by reducing the number of bumps. This is an erasing method.

The highly reflective layer [al provided on the substrate used in the present invention] consists of a material layer having a reflectance at the interface with air of at least 50%, preferably 60% or more. A metal thin film is preferably used as such a material layer. Specific metals include silver, aluminum, platinum, gold, cobalt, titanium, and nickel. The thickness of these films is preferably 50 nm to 200 nm.

These thin films can be provided by vacuum deposition, sputtering or chemical plating.

The substrate (bl) used in the present invention is not particularly limited as long as it is transparent and optically isotropic. Specific examples include polycarbonate, poly(ethylene terephthalate), poly(methyl methacrylate), and Examples include glass plates.

In the present invention, the expansion layer [dl] needs to expand effectively when heated by laser irradiation in order to improve recording characteristics. High rubber elasticity is required in order to efficiently erase the bumps generated by recording and restore the original state. Therefore, the resin for the expansion layer must exhibit high rubber elasticity and must not undergo flow deformation when irradiated with laser light. Suitable resins include natural rubber; synthetic rubbers such as styrene-butadiene rubber, butadiene rubber, isoprene rubber, nitrile rubber, chloroprene rubber, butyl rubber, ethylene-propylene rubber, urethane rubber, and silicone rubber; styrene-based, olefin-based, Urethane thermoplastic elastomer;
Examples include amine crosslinked, isocyanate crosslinked, and ultraviolet crosslinked elastomers.

The holding layer [e] used in the present invention is capable of forming bumps by thermally expanding with the expansion layer [dl] during recording, and fixing the bumps during the cooling process, and fixing the bumps during erasing. It is responsible for releasing the . Therefore, in order to perform both functions efficiently, the temperature at which the glass state changes to the rubber state (glass transition temperature Tg
) becomes important. In this sense, the resin for the retention layer used in the present invention has an elastic modulus of 80 kg/mm2 or more,
Preferably 100 Kg/am2 or more and Tg 6
It is necessary that the temperature is 0 to 150°C. Specific examples of resins that are suitably used include thermoplastic resins such as polymethyl methacrylate resins, polycarbonate resins, and polyamide resins, and partially crosslinked products thereof, epoxy resins, phenol resins and crosslinked products thereof, melamine resins, and epoxy resins.
meth) acrylate resin, epoxy novolak meth)
Examples include thermosetting resins such as acrylate resins and polyfunctional (meth)acrylate resins. Among these resins,
Epoxy resins, epoxy (meth)acrylate resins, epoxy novolac (meth)acrylate resins, and polyfunctional (meth)acrylate resins may be cured by ultraviolet light and are effectively used.

The coating method for these resins is not particularly limited, but a spin code method, a casting method, a bar code method, a doctor knife method, a gravure coating method, etc. are used.

Suitable solvents used in this case include aliphatic hydrocarbons such as hexane, heptane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; alcohols such as methanol, ethanol and butanol; chloroform and methylene chloride. Haloalkanes such as; esters such as ethyl acetate and butyl acetate; acetone, methyl ethyl ketone; ketones such as methyl isobutyl ketone, cyclohexa, and none; glymes such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether; tetrahydrofuran, dioquine, etc. Mention may be made of ethers, nitromethane, acetonitrile and mixtures thereof. Further, when a crosslinked resin is used as the resin for the expansion layer and the retaining layer, curing is required. As the curing method, a thermosetting method, an ultraviolet ray effect method, and an electron beam irradiation method are used.

As for the thermosetting method, three-dimensional crosslinking and curing is usually carried out by heating in the coexistence of a radical initiator. The temperature of the thermosetting reaction is 50 to 200, depending on the type of resin used.
°C5 preferably 70-150 °C. If it is less than that, the thermosetting reaction will not proceed sufficiently, which is not preferable. On the other hand, if it is more than that, it is not preferable because it causes deterioration of the substrate and the dye. The curing time is generally 5 minutes to 10 hours, preferably 10 minutes to 5 hours. On the other hand, in the case of the ultraviolet effect method, the coating is cured by irradiation with ultraviolet rays after coating. As the irradiation source, a mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, etc. are suitably used. The power of the light source used is 1 mW/- to 1 kW/-. The irradiation time depends on the power of the light source and the photoreaction rate, but is 1 J for 1 second to 1 hour, preferably 10 seconds to 10 minutes. The thickness of the expansion layer is generally 0.1 to 5 μm, preferably 0.4 to 3.0 μm, and the thickness of the retention layer is 0.1 to 5 μm.
1 to 3.0 μm, preferably 0.3 to 2.0 μm is used. The thickness of these films is determined by considering the absorbance and reflectance of the dyes to be combined. In order for the incident light to reach the highly reflective layer provided on the substrate and for the light reflected by the reflective layer to return to the medium surface, at least 10% of the incident light must be
As mentioned above, it is desirable to control the dye concentration and film thickness in the retention layer and the expansion layer so that preferably 15% or more of the dye passes through the two-layer medium consisting of the retention layer and the expansion layer. In addition, the reflectance of the medium is improved by setting the film thickness of the recording layer [cl] so that the reflected light on the medium surface and the multiple reflected light from the highly reflective layer [a] surface strengthen each other through optical interference. is also possible.

The dyes [D1] and [D2] of the present invention play the role of efficiently absorbing laser light and converting it into heat during the recording and erasing processes, respectively. Therefore, a dye is selected that matches the oscillation wavelength range of the recording laser and the erasing laser. In order to selectively absorb both laser beams, it is preferable that the absorption intensities in the respective oscillation wavelength ranges do not overlap excessively. Further, since the laser currently used in the optical recording field is a semiconductor laser, a dye having an absorption peak in the near infrared is preferred. Also,
Since reading utilizes light reflection on the surface of the medium, the retention layer is required to have a high light reflectance.

From this point of view, it is preferable that the dye [D2] has a high reflectance. Of course, for efficient absorption properties, the dyes should be selected to be uniformly dispersed in the respective resin. Suitable dyes [D1] and [D21 include polymethine dyes such as cyanine dyes, biryllium dyes, thiapyrylium dyes, squalillium dyes, croconium dyes, and azulenium dyes; phthalocyanine dyes such as phthalocyanine and naphthalocyanine; ; dithiol metal complexes; naphthoquinone and anthraquinone dyes; triphenylmethane dyes; aminium and diimmonium dyes.

When these dyes are used in combination with the above resins,
The mixing ratio (dye/resin) depends on the absorbance of the dye and the film thickness, but is generally 0.03 to 0.4 wt/wt, preferably 0.05 to 0.3 wt/wt.

An example of the layer structure of the medium suitably used in the present invention is one in which the expansion layer [dl is disposed on the highly reflective substrate [b] directly or with another transparent layer interposed therebetween. This transparent layer may be made of a film-forming polymeric material or may be an inorganic oxide film. These are used to smooth the surface of the substrate or to improve the adhesion between the substrate and the expansion layer. A resin layer [c] is provided on the expanded layer formed as a calyx. Furthermore, a transparent protective layer is provided on the resin [c] if necessary. This protective layer is preferably formed of a thermosetting resin or thermoplastic resin with high surface hardness. Another preferable embodiment of the medium layer structure is that a transparent rubber layer [Jl] with a low elastic modulus is provided on a highly reflective substrate [b], and a resin layer [ej/expansion layer [dl] is provided on top of the transparent rubber layer [Jl]. Layers are provided in sequence.

Furthermore, it is also possible to provide a transparent protective layer on the expansion layer tdl, if necessary. The rubber layer used here [h
] has a room temperature elastic modulus of 0.1 Kg/mm2 or less, preferably 0.1 Kg/mm2 or less. A crosslinked product having an OIKg/mm2 or less is preferable.

Specific examples of such materials include polyurethane acrylate, silicone rubber, polyvinyl acetate and copolymers thereof, polyethylene oxide, and the like. In the medium of this embodiment, the expansion layer is thermally expanded by laser beam irradiation, which induces thermal expansion of the holding layer, and the bumps are held in the rubber layer having a low elastic modulus.

Recording, reproduction, and erasing of the thus obtained two-layer medium are carried out by irradiating it with laser light from two companies. The laser used in this case may be a helium neon laser, an argon laser, a semiconductor laser, etc., but a small and inexpensive semiconductor laser is more preferable. Hereinafter, an example of a medium in which the expansion layer dye D1 exhibits absorption in the vicinity of 840 nm and the retention layer dye D2 exhibits absorption in the vicinity of 780 nm will be described. Recording is performed by irradiating a laser beam of 840 nm.

At this time, the expansion layer mainly absorbs light to form bumps. Reproduction is performed by irradiating a weak laser beam of 840 nm and reading the difference in reflectance between the recorded area and the unrecorded area. Erasing is performed by irradiating with 780 nm laser light. - Recording 5-30 mW,
Preferably, the irradiation is performed at a power of 7 to 20 mW for 5 to 0.1 μsec. Regeneration is 0.5-3 mW, preferably 0.7-2
．． Irradiate for 5 to 0.1 μsec with a power of 0 mW. The erasure is
0.0 with a power of 1-20 mW, preferably 3-12 mW.
Irradiate for 1 to 20 msec.

In the recording medium according to the present invention whose basic principle is to read changes in reflectance due to the formation and disappearance of bumps, excellent recording and erasing characteristics can be obtained. At the same time, since film formation can be performed at low temperatures and high speeds, coating and curing can be performed without causing deterioration of the substrate or the dye used, and the cost of the media is low, which is an industrial advantage.

Hereinafter, the invention will be explained in more detail according to examples.

<Examples> Example 1 Liquid chloroprene rubber having a hydroxyl group at the end of the molecular chain [number average molecular weight: 5,100. Polyisocyanate [trade name: Coronate L (Nippon Urethane Industries)] was mixed with product name PH-050゜ (Denki Kagaku Kogyo) so that the ratio of hydroxyl group/isocyanate group was 1.0, and the mixture was diluted 5 times with chloroform. . 5 phr based on solids content in this solution.
IR-820 (Nippon Kayaku@), a polymethine dye
The resulting solution was applied onto a polyethylene terephthalate film (75 μm) on which aluminum had been deposited in advance to a thickness of 120 nm, and then the solvent was dried. Thereafter, the coating film was heat-treated in a dryer at 120° C. for 1 hour to carry out a crosslinking reaction of the polymer. NK-215 (Japanese Photosensitive Color ■), which is a cyanine dye, and 30 phr of trimellitic acid anhydride were added in advance to the 1.0 μm thick expanded layer film based on the solid content. A 5 wt% solution of MEK dissolved in type epoxy DEN444 (Dow Chemical ■) was applied, and 1
Heat treatment was performed at 25° C. for 3 hours to form a film with a thickness of about 0.6 μm. The transmittance of each layer alone is 55%.
, 35%. The reflectance of the resulting two-layer medium is 2
It was 5%. When this medium was irradiated with a semiconductor laser beam having an oscillation wavelength of 1]t3hm and a leading output power of 10 mW for 1 μsec, the formation of clear bumps with a diameter of 0.8 μm was observed on the medium surface. Subsequently, when this recording spot was irradiated with a semiconductor laser beam having an oscillation wavelength of 780 nm and a leading output power of 5 mW for 7 microseconds, the bumps mentioned above had disappeared to such an extent that they could not be confirmed by microscopic observation. From this result, it was found that the above-mentioned recording medium would be an optical information medium capable of recording and erasing.

Example 2 Liquid chloroprene rubber having a hydroxyl group at the end of the molecular chain [number average molecular l: 5,100. A polyisocyanate [trade name: Coronate L (Japan Urethane Industries)] was mixed with a polyisocyanate [trade name: Coronate L (Japan Urethane Industries)] so that the ratio of hydroxyl groups/isocyanate groups was -1,0, and the mixture was diluted five times with chloroform. In this solution, 10 parts by weight of soluble vanadyl phthalocyanine [trade name: IRD-
1001 (Sansui Chemical Synthesis) was dissolved and the resulting solution was applied onto a polyethylene terephthalate film (75 μm) on which 85 nm of aluminum had been vapor-deposited in advance.
The solvent was dried. After that, the coating film was placed in a dryer for 120 minutes.
A heat treatment was performed at ℃ for 1 hour to perform a crosslinking reaction of the polymer.

A 5 wt % solution of toluene containing 10 wt % tri-n-hexyl silicone naphthalocyanine dissolved in polymethyl methacrylate was applied onto the thus obtained 1.2 μm thick intumescent layer film to give a thickness of approximately 0.0 μm. 7μm
A film with a thickness of . The reflectance of the resulting two-layer medium was 25%. When this medium was irradiated with a semiconductor laser beam having an oscillation wavelength of 830 nm and a leading output power of 10 mW for 1 μs, the formation of clear bumps with a diameter of 2.0 μm was observed on the medium surface. Subsequently, on this recording spot, an oscillation wavelength of 780'nm and a leading output of 5mW are applied.
When irradiated with semiconductor laser light for 7 microseconds, the bumps mentioned above had disappeared to such an extent that they could not be confirmed by microscopic observation. From this result, it was found that the above-mentioned recording medium would be an optical information medium capable of recording and erasing.

Comparative Example 1 Instead of using an aluminum-deposited polyethylene terephthalate (PET) film as the substrate in Example 1,
A medium was similarly prepared using a PET film without aluminum vapor deposition. When the reflectance of this material was measured at 830 nm, it remained at a low value of 8%.

Comparative Example 2 In Example 1, instead of setting the film thicknesses of the retention layer and the expansion layer to 0.6 μm and 1.0 μm, they were set to 5.0 μm and 7.5 μm, and the reflectance of the medium surface was 9. It remained at a low value of .2%.

Example 3 In Example 2, instead of using polymethyl methacrylate, 1,1-cyclohexylene bisphenol-
A - Make a similar two-layer media using polycarbonate. The oscillation wavelength of 830 nm was applied to this medium as in Example 1.
When a recording laser beam with an intensity of 10 mW was irradiated for 1 μsec, clear bump formation was observed. Further, this bump could be erased by irradiating it with a laser beam of 780 nm and 7 mW for 10 μs.

Example 4 In Example 2, instead of using tri-n-hexyl silicon naphthalocyanine, cyanine dye (NK-2
15. Japanese photosensitive dye ■) and nickel dithiol complex (P
Create a medium in the same way using 1=1 salt of A-1001, Mitsui Toatsu Fine ■). The reflectance of this medium was 22%. Further, when this medium was irradiated with a 10 mW laser beam for 1 μs as in Example 1, a bump of 1.6 μm was formed. This bump has a 780nm top output of 5m.
By irradiating W semiconductor laser light for 7 μs,
It disappeared to such an extent that it could not be seen under a microscope. When the recording spot was continuously irradiated with the same laser beam (output mW), the bumps mentioned above had disappeared to such an extent that they could not be confirmed by microscopic observation.

Example 5 A two-layer medium was similarly prepared in Example 2 using polystyrene instead of using polymethyl methacrylate. A semiconductor laser beam with an oscillation wavelength of 830 nm and a leading output of 10 mW was applied to this medium under the same conditions as in Example 1 for 1μ.
When the medium was irradiated for seconds, the formation of clear protuberances (bumps) with a diameter of 1.8 μm was observed on the medium surface. Subsequently, when this recording spot was irradiated with a 780 nm semiconductor laser beam (mW) for 7 μs, the bumps mentioned above had disappeared to such an extent that they could not be confirmed with a microscope.

From this result, it was found that the above-mentioned recording medium could be an optical information recording medium capable of recording and erasing information.

Example 6 In Example 1, instead of providing the expansion layer directly on the reflective substrate, a polyurethane acrylate (Sumitomo Three Bond, T-3016) layer with a thickness of 2 to 3 μm was provided, and this was crosslinked by UV light irradiation. After that, a mixed solution of epoxy resin (DEN-444+ and trimellit anhydride cyanine dye (NR-2181) was applied on this layer to perform a curing reaction, and then the same expansion layer as in Example 1 was formed on the layer. A medium was obtained in the same manner.The reflectance of this medium was 20.5%.
Met. When this medium was irradiated with laser light under the same conditions as in Example 1, a depression with a diameter of 1.6 μm was formed.

When this was irradiated with a 7 mW laser, it was erased to such an extent that it could not be observed with a microscope.

Thus, embodiments of the invention include the following.

1. A substrate [bl] provided with a layer [al] having high reflectivity for laser light for recording and reproduction, and the substrate [b]
In an optical recording medium comprising a recording layer (C1) provided thereon, the recording layer [C] is an expansion layer [(
The expansion layer and the retention layer contain different near-infrared absorbing dyes [D2] and [D2] whose absorption wavelength ranges do not completely overlap. and the content of the dye, the thickness of the recording layer [C], and the reflectance of the reflective layer [al] are adjusted so that the reflective layer of the recording layer accounts for at least 15% or more of the recording and reproducing light. An erasable highly reflective optical recording medium.

The expansion layer [dl] of the recording layer [C] described in item 1 above is placed on the highly reflective substrate [bl directly or with another transparent layer interposed therebetween, and the laminated layer [resin layer fe is provided on the dl]. An optical recording medium characterized by a transparent protective layer being provided on the resin [eJ] as required.

The medium described in item 1 above is a highly reflective substrate [transparent and transparent on bl].
Low elastic modulus resin layer [hl/81 fat layer [e] /It tension layer [
1. An optical recording medium characterized in that the expansion layer [(l) is further provided with a transparent protective layer as required.

An optical recording medium characterized in that the resin [)tl according to item 3 is a thermoplastic low elastic modulus rubber.

On the recording layer [c] described in item 1 above, a second highly reflective layer [
An optical recording medium characterized by being provided with hJ.

2. The optical recording medium according to claim 1, wherein the highly reflective layer [al on the substrate [bl] according to claim 1 is a thin metal film.

The optical information recording medium according to claim 1, wherein the substrate [bl according to claim 1] is a polymer film.

8. The optical information recording medium according to claim 1, wherein a servo track for a recording signal is formed on the substrate [1) according to claim 1 above.

When recording information by irradiating the recording medium described in item 1 above with a laser beam, 1) the wavelength [λ11
By irradiating the irradiated spot with a strong laser beam that oscillates at ii) a step of reproducing the recording based on the difference in the reflectance to the recording and reproducing light between the bumps recorded in the above step) and the non-recording portion, and iii) a step of reproducing the recording based on the differences in the reflectance of the bumps recorded in the above step) and the non-recording portion, and iii) a step of reproducing the recording when the bumps of the retention layer are formed. optical information comprising the step of irradiating a weak laser beam having an oscillation wavelength [λ21 different from the wavelength [^11] to heat and slowly cool the bumps, and erase information by reducing the number of bumps. How to record, play and erase.

Claims (1)

[Claims] 1. Optical recording consisting of a substrate [b] provided with a layer [a] that is highly reflective to laser light for recording and reproduction, and a recording layer [c] provided on the substrate [b] In the medium, the recording layer [c] is composed of a laminate of an expansion layer [d] and a holding layer [e] that can be reversibly deformed by heat generated by laser beam irradiation, and the expansion layer and the holding layer are Different near-infrared absorbing dyes whose absorption wavelength ranges do not completely overlap [D1]
and [D2], and the content of the dye, the thickness of the recording layer [c], and the reflective layer [ An erasable, highly reflective optical recording medium in which the reflectance of a] is adjusted.