JP2806991B2 - Rewritable optical recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for efficiently recording optical information and erasing recorded pits by a change in shape when heated, and stabilizing recording / erasing and repeated irradiation of reproducing light. High recording media.

Background Art and Problems There have been proposed many organic optical recording media that can reproduce and erase recording and can be applied. For example, JP-A-59-
No. 5448 discloses an erasable optical recording medium comprising a mixture of a polymer and a dye. In this medium, recording is based on pit formation due to flow deformation of the polymer, and erasing is based on the principle of closing the pits by re-melting the raised polymer around the pits generated during recording. Therefore, it is difficult to completely recover the polymer once flowing out, and it is inevitable that erasure remains.
This erasure residue is accumulated as recording and erasure are repeated. Therefore, high repetition durability cannot be obtained by this method. In addition, it is necessary to irradiate a laser beam of high energy in order to use the melting / fluid deformation of the polymer for recording / erasing. As a result, the dye contained in the medium is liable to undergo photochemical deterioration and thermal deterioration, and the disadvantage of repeated use cannot be avoided from this point.

According to JP-A-57-27790 and JP-A-60-253036, an erasable optical recording medium comprising a pit-forming recording layer and an overcoat layer provided thereon is proposed. I have. In this medium, pits are formed by the flow deformation of the recording layer, and the recording is performed by the expansion of the overcoat layer.
However, since the overcoat layer has a high softening temperature, it is necessary to irradiate a laser beam having a relatively strong output for a long time at the time of erasing, as in the case of the above-mentioned recording medium, which is not practical.

According to another proposal (Japanese Patent Application Laid-Open No. 60-69846), an expansion layer made of rubber which is heated and expanded by irradiation with a laser beam to form a dome-shaped projection (bump), and a resin which maintains this shape A recording / erasable medium (bump forming type recording medium) basically composed of a holding layer composed of a recording layer has been proposed. When recording on this medium,
Absorption wavelength (λ ₁ ) of the dye previously mixed in the expansion layer
Laser light irradiation is performed in the vicinity, so that the expansion layer forms a bump by thermal expansion, and the holding layer can maintain this shape. When erasing recorded bumps, laser light irradiation is performed near the maximum absorption wavelength (λ ₂ ) of the dye mixed in the holding layer, and the holding layer is exposed to the Tg.
The above heating is performed to make it difficult to maintain the bump shape. According to the recording method, although the shape of the medium changes during recording / erasing, it is advantageous in repetition characteristics because it does not involve flow deformation. Further, since recording / erasing involves a change in shape but does not involve melting / fluid deformation of the polymer, it is not necessary to irradiate a high energy laser beam. Therefore, the dyes used are in a state of being less likely to deteriorate as compared with the pit type medium. However,
It goes without saying that in order to obtain a medium requiring a high degree of repetition durability, it is necessary to use a dye having high durability. On the other hand, phthalocyanine and naphthalocyanine dyes as near infrared dyes having high durability have been proposed for recording / read-only recording media. There are two major problems in applying these dyes to bump-forming dual-layer media. One is the problem of compatibility with the resin used.
That is, since these dyes were used in the form of depositing or coating only the dye on the substrate, compatibility with the resin was not a problem. On the other hand, in the case of a bump-forming type two-layer medium, compatibility is important for using any of the layers in a mixed system with a resin. Another is the problem of dye association. That is, these dyes show sharp absorption characteristics in a solution, but cause association of the dyes in a polymer matrix, resulting in broadening of absorption. In the case of the recording / reproducing-only medium, the sharpness of the absorption does not matter as long as the medium exhibits high absorbance in the oscillation wavelength range of the semiconductor laser used. On the other hand, in the case of the bump-forming type two-layer medium, it is desirable that the absorption of the dye used for the expansion layer and the absorption of the dye used for the holding layer do not overlap. Therefore, the absorption of the dye used must be sharp.

In view of these circumstances, the present inventor has conducted intensive studies on an optical recording medium that is soluble in an organic solvent, can be coated, and is capable of recording, reproducing, and erasing. By using one or more dyes selected from a lophthalocyanine derivative and a phthalocyanine derivative as dyes for a recording medium, it was found that an optical recording medium without the above-mentioned problems could be obtained, and the present invention was completed. It has arrived.

SUMMARY OF THE INVENTION The optical recording medium of the present invention comprises, on a substrate, an expansion layer (A) comprising a resin (P ₁ ) exhibiting rubber elasticity at least at room temperature and a dye (D ₁ ) having absorption in the near infrared region. Supports a holding layer (B) composed of a resin (P ₂ ) capable of reversibly changing to a glass state at room temperature and a rubber state at a higher temperature and a dye (D ₂ ) having absorption in the near infrared region. Do it.

The order of the expansion layer (A) and the holding layer (B) with respect to the substrate is appropriately changed according to the laser incidence method.

The expansion layer (A) is required to expand effectively when heated by laser light irradiation in order to improve the recording characteristics. In order to efficiently erase the bumps generated by recording and return to the original state, high rubber elasticity is required. Therefore, it is necessary that the resin (P ₁ ) has high rubber elasticity and does not undergo flow deformation due to laser beam irradiation. 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 and olefin-based rubbers And urethane-based thermoplastic elastomers; amine-crosslinkable, isocyanate-crosslinkable, and ultraviolet-crosslinkable elastomers.

The resin (P ₂ ) used in the present invention has a role of fixing a bump (recording) generated by thermal expansion at the time of recording and allowing release of the bump at the time of erasing. Therefore,
In order to perform both actions effectively, at room temperature,
The resin must be in a rubbery state at high temperatures. Suitable resins include thermoplastic resins such as polymethyl methacrylate resin, polycarbonate resin, and polyamide resin and their partially crosslinked products, epoxy resins, phenol resins, melamine resins, epoxy (meth) acrylate resins, and novolak (meth) resins. Thermosetting resins (crosslinked resins) such as acrylate resins and polyfunctional (meth) acrylate resins are exemplified. Further, an epoxy resin, an epoxy (meth) acrylate resin, a novolak (meth) acrylate resin, and a polyfunctional (meth) acrylate resin may be cured by ultraviolet rays and are preferably used.

Dye D ₁ and D _2, in each recording process and erasing process serves to replace the heat by efficiently absorbing a laser beam. Therefore, a dye that matches the oscillation wavelength range of the recording laser and the erasing laser is selected. Then, it is preferable that both laser beams are selectively absorbed and their absorption intensities do not excessively overlap. Further, a dye having an absorption peak in the near infrared is preferable since a laser currently used in the field of optical recording is a semiconductor laser. In addition, reading uses the light reflection of the medium (surface),
It is required that the light reflectance of the medium surface is high. In this respect, the dye D ₂ preferably has a high reflectivity, of course in order to perform the absorption characteristics efficiently, the dye should be chosen to be uniformly dispersed in the respective resins.

Examples of the dye D ₂ for use in the present invention from this point of view,
High reflectance, light resistance, has heat resistance, is soluble in an organic solvent, and is preferably used which is compatible well with resin P _2. In addition, these dyes can be found in the resin in the near infrared, sometimes
Those exhibiting relatively sharp absorption at 750 to 850 nm are preferred. Dyes having such properties include naphthalocyanine dyes, phthalocyanine dyes and naphthalophthalocyanine dyes. Naphthalocyanines preferably used include naphthalocyanine derivatives containing silicon represented by the following formula [I] as a central metal, "Wherein Y ₁ and Y ₂ are the same or different, and oxygen, nitrogen,
Represents an alkyloxy group having 5 to 25 carbon atoms which may contain silicon, an alkenyloxy group, an aralkyloxy group, an aryloxy group, an alkylsiloxy group, an alkoxysiloxy group, or an aryloxysiloxy group. R _{1 to} R ₄ are the same or different and represent a hydrogen atom, a linear or branched alkyl group or a halogen, and n is the same or different and represents an integer of 0 to 6. ].
Among the naphthalocyanine dyes represented by the formulas [I] and [II], when the substituents Y ₁ , Y ₂ and R _{1 to} R ₄ are selected from the following, they are most preferably used in the present invention. Can be

1), suitable Y ₁ , Y ₂ : 2) Suitable R _{1 to} R ₄ : -C _{m ′} H _{2m ′ + 1} (m ′ = 1 to 12) These dyes have bulky substituents, so that the dyes cannot be close to each other. . In other words, the meeting is suppressed. At the same time, since the bulky substituent has a higher affinity for the resin, it associates with the resin rather than the association between the dyes, so that broadening of the absorption spectrum based on the association between the dyes is suppressed. Therefore, the broadening is not only based on the molecular structure of the dye, but also on the matrix resin P ₂
Also depends.

Another suitably used naphthalocyanine is a nucleus-substituted naphthalocyanine. A specific example is shown in the following equation.

In the formula, R _{5 to} R ₈ represent a linear or branched alkyl group having 4 to 12 carbon atoms, and R _{9 to} R ₁₂ represent a linear or branched alkyl group having 1 to 18 carbon atoms. A, b, c, d represent 0 or 1, and a, b, c, d are not all zero at the same time, and M is a metal and a metal oxide or halide. Among the above-mentioned naphthalocyanines, those which can be preferably used in the present invention are those in which R _{5 to} R ₈ and R _{9 to} R ₁₂ are linear or branched alkyl groups having 4 to ₁₂ carbon atoms. In addition, when the central metal M is Cu, Pt, Co, VO, Mn, Zn,
Ni and the like. The absorption properties of these naphthalocyanines are mainly governed by the type of central metal. Further, the compatibility and association with the resin are controlled by the nuclear substituent. That is, the association is suppressed by the steric hindrance of the bulky nuclear substituent. Also in this case, the association property depends on the type of the resin, so the type of the dye should be selected in consideration of the resin.

The following formula shows specific examples of the phthalocyanine dye used in the present invention.

[Wherein R _{13 to} R ₁₆ are the same or different and are a hydrogen atom, a nitro group substituted at least one on each benzene nucleus, a halogen group,
A phenyl group or a fused benzene ring, M is a hydrogen atom,
Indicates a metal oxide or a metal halide. ]. Among the phthalocyanines that are particularly preferably used in the present invention, those in which R is a linear or branched alkyl group having 4 to 12 carbon atoms, and the central metal M is
Examples include those selected from Cu, Pt, Co, VO, Mn, Zn, Ni, and the like.

On the other hand, naphthalophthalocyanine, which is the union of phthalocyanine and naphthalocyanine, is also suitably used. These have a disordered structure because the skeleton is a mixture of part of the naphthalocyanine skeleton and part of the phthalocyanine skeleton,
As the solubility increases and the symmetry of the molecule is lost, association becomes difficult. Preferred examples of such dyes are shown below.

[Wherein, R _{17 to} R ₂₀ represent a linear or branched alkyl group having 1 to 18 carbon atoms and may be the same or different. M represents a metal and a metal oxide or a metal halide. Among the above-mentioned phthalonaphthalocyanines, those particularly preferably used in the present invention include those in which R is a straight-chain or branched alkyl group having 4 to 12 carbon atoms, and wherein the central metal M is Cu, Pt, Co, One selected from VO, Mn, Zn, Ni and the like can be mentioned.

Above-mentioned dye, 5 to 30% by weight relative to the resin (P _2), is used in addition 10% to 25%. If the pigment content is less than 5% by weight, the reflectance on the medium surface will be low, and it will be difficult to reproduce the recorded signal. On the other hand, if the dye content exceeds 50% by weight, the mechanical strength of the coating film is weakened, and the durability of record retention and repetition of record erasure is reduced.

Examples of the dye D ₁ used in the present invention, there is provided a near infrared absorbing dye Do attend organic solvent, is preferably used which is compatible well with resin P _2. Preferable examples include polymethine dyes, pyrylium dyes, thiapyrylium dyes, squalilium dyes, croconium dyes, cyanine dyes such as azurenium dyes; phthalocyanine dyes such as phthalocyanine and naphthalocyanine; phenylenedithiol metal complexes and phenylene Diamine metal complex dyes; naphthoquinone and anthraquinone dyes; triphenylmethane dyes; aminium and diimmonium dyes. Among these, from the viewpoint of light resistance and heat resistance,
The naphthalocyanine dye, phthalocyanine dye,
In addition to the naphthalophthalocyanine dye, phenylenedithiol (the following formula [III]) and phenylenediamine metal complex (the following formula [IV]) are particularly preferable. Specific exemplary compounds as the metal complex are as follows.

[Wherein, Z _{1 to} Z ₈ each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 8 carbon atoms. X is-
Represents S- or -NH-. ] These dyes, 5-30 wt% relative to the resin P _1,
Preferably, it is used by adding 10 to 25% by weight. If the added amount of the dye is less than 5% by weight, the recording sensitivity is lowered, which is not preferable. When the pigment content is 30% by weight or more, the mechanical strength of the coating film is reduced.

The substrate used in the present invention has excellent solvent resistance,
Any material that is optically uniform and has high surface smoothness can be used. Examples of substrates having such properties include epoxy resins, polycarbonate resins, glass, polymethyl methacrylate and poly-4-methylpentene-1.
And the like.

These resins used in the present invention are applied and cured on a substrate after being mixed with a dye. The film thickness of the expansion layer (A) is generally 0.5 to 10 μm, preferably 1.0 to 5.0 μm.
m is used, and the thickness of the holding layer is 0.1 to 3.0 μm, preferably 0.3 to 2.0 μm. Since the recording characteristics and erasing characteristics of the recording medium greatly affect the degree of absorption of laser light in each layer, it is necessary to select these film thicknesses in consideration of the absorbance and concentration of the dye. Further, the reflection characteristic of the medium is not based solely on the surface reflection of the holding layer, but also contributes to the effect of interference with the reflected light between the respective layers. Therefore, the thicknesses of the holding layer and the expansion layer should be selected so as to maximize the interference effect.

The coating method is not particularly limited, but a spin coating method, a casting method, a bar coating method, a doctor knife method, a gravure coating method, or the like is used. Further, when a crosslinked resin is used as the resin for the expansion layer and the holding layer, curing is required. As the curing method, a thermal curing method, an ultraviolet curing method, and an electron beam irradiation method are used. As the thermosetting method, three-dimensional cross-linking is usually performed by heating in the presence of a radical initiator. On the other hand, in the case of the ultraviolet curing method, it is performed by irradiating ultraviolet rays in the presence of a photoinitiator.

The recording method, reproduction and erasure of the double-layer medium thus obtained are performed by irradiating two kinds of laser beams. As a laser used at this time, a helium neon laser, an argon laser, a semiconductor laser, or the like is used, and a small and inexpensive semiconductor laser is more preferable. Hereinafter, the expansion layer dye D ₁ represents the absorption in the vicinity of 840 nm, retention layer dye D ₂ is described as an example media exhibiting absorption in 780nm vicinity. The record is 78
This is performed by irradiating a laser beam of 0 nm. Generally, recording is performed by irradiating a laser beam of 5 to 30 mW, preferably 7 to 20 mW for 5 to 0.1 μsec. For reproduction, continuous laser light of 0.5 to 3 mW, preferably 0.7 to 2.0 mW is applied. Erasing is
A continuous laser beam of 1 to 20 mW, preferably 3 to 12 mW is applied.

According to the present invention, excellent durability can be obtained in a recording medium whose fundamental principle is to read a change in reflectance due to the formation and disappearance of bumps.

Hereinafter, the present invention will be described in more detail with reference to Examples.

<Example> Example 1 Polyisocyanate [trade name: Coronate L] was added to a liquid chloroprene rubber having a hydroxyl group at a molecular chain terminal [number average molecular weight: 5,100, trade name FH-050, (Denki Kagaku Kogyo)].
(Nippon Urethane Industry)] = hydroxyl group / isocyanate group =
The mixture was mixed to 0.5 and diluted 5-fold with chloroform. In this solution, 10 parts by weight of a soluble vanadyl phthalocyanine [trade name: IRD-1001 (Yamamoto Chemical Synthesis)] with respect to the solid content is dissolved, and the obtained solution is applied on a glass substrate. Let dry. Thereafter, the coating film was subjected to a heat treatment at 120 ° C. for 1 hour in a drier to carry out a crosslinking reaction of the polymer. A film having a thickness of about 1 μm was formed by applying a 5 wt% solution of toluene in which 10 wt% of tri-n-hexylsilicon naphthalocyanine was dissolved in PMMA in advance on the thus obtained film. The surface reflectance of the obtained two-layered medium was 12% at 840 nm. The obtained double-layered medium was loaded into a dynamic evaluation machine having a rotating mechanism, and while rotating at 1800 rpm, a semiconductor laser beam having an oscillation wavelength of 830 nm and a top output of 10 mW was irradiated as a 1 MHz pulse signal, and the medium surface was irradiated. The formation of a clear bump (bump) having a diameter of 1.5 μm was observed. Subsequently, when this recording spot was irradiated with a semiconductor laser beam having an oscillation wavelength of 780 nm and a head output of 7 mW as continuous light, the bumps 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 could be a recordable / erasable optical information medium. In addition, even after the repeated test of this recording and erasing 10 ^four times, bump-forming ability was still good.

Comparative Example 1 In Example 1, a film was formed using a cyanine dye (Nippon Kosaku Dye NK-215) instead of using tri-n-hexyl silicon naphthalocyanine and using methyl ethyl ketone as a casting solvent. When the obtained double-layered medium was continuously irradiated with an erasing laser beam having an oscillation wavelength of 780 nm and an intensity of 1 mW at 1800 rpm, the reflectance was significantly reduced from 12% to 7% after 25 minutes. Also, the same concentration of cyanine dye as above
When a film obtained by applying a mixed solution of / PMMA on a glass plate was irradiated with a xenon lamp at 500 W, discoloration of the dye was observed after 100 hours.

From the above, it was clarified that the above-mentioned decrease in the reflectance was caused by the fire of the dye.

Comparative Example 2 In Example 1, a polymethine dye (Nippon Kayaku, IR-82) was used instead of using vanadyloxynaphthalocyanine.
Using 0), a film was formed in the same manner. A reading laser beam having an oscillation wavelength of 830 nm and an intensity of 1.0 mW was applied to the obtained two-layered medium for 1800 hours.
Upon continuous irradiation at rpm, bump formation became impossible after 2 hours. From this fact, it has been clarified that the above dyes do not have sufficient body laser light properties under the conditions of the present invention.

Example 2 A two-layer medium was prepared in the same manner as in Example 1, except that a nickel dithiol complex cyanine dye (Mitsui Toatsu Fine, PA-1001) was used instead of vanadyloxynaphthalocyanine. This medium has an oscillation wavelength of 83 as in the first embodiment.
When a recording laser beam of 0 nm and an intensity of 10 mW was irradiated at 2 MHz at 1800 rpm under a rotation speed, bump formation was clearly observed. In addition, this bump emits 780 nm, 7 mW laser light for 2 μS
It could be erased by continuous irradiation.

Example 3 Instead of using a crosslinked polyurethane in Example 1, a polyurethane containing an acrylate group at a molecular chain terminal [trade name: Photocurable resin 3052C (ThreeBond)] was used, and a soluble vanadyl phthalocyanine [IRD-100] was used.
1 (Yamamoto Chemical Synthesis)] was added to obtain a 5% chloroform solution. The coating solvent was evaporated on a glass substrate, and the obtained coating film was irradiated with a high-pressure mercury lamp under a nitrogen atmosphere for 10 minutes to crosslink the polymer. The same holding layer as in Example 1 was applied to this to obtain a two-layered medium. This was irradiated at 1800 rpm with a semiconductor laser light having an oscillation wavelength of 830 nm and a head output of 10 mW as a 1 MHz pulse signal in the same manner as in Example 1, and a clear bump (bump) having a diameter of 1.3 μm was formed on the medium surface. Formation was observed. Subsequently, the same laser beam (output 7mW) was applied to this recording spot for 1800r.
Upon continuous irradiation for 10 μs at pm, the bumps had disappeared to such an extent that they could not be confirmed by microscopic observation.

Example 4 In Example 1, instead of using PMMA, a 5 wt% chloroform solution of an equivalent mixture of an epoxy resin (Epicoat 828, Shell Chemical) and an alicyclic bifunctional amine (Epomate-002, Shell Chemical) was used. After applying, 100
Crosslinking was carried out by heat treatment in an oven at 10 ° C. for 10 minutes. The obtained two-layer medium was irradiated with a semiconductor laser beam having an oscillation wavelength of 830 nm and a head output of 10 mW as a 1 MHz pulse signal under the same conditions as in Example 1, and the medium surface was 1.4 μm in diameter.
The formation of a distinct ridge (bump) of m was observed. Subsequently, when this recording spot was irradiated with continuous light having an oscillation wavelength of 780 nm and an output of 7 mW, the bumps 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 could be an optical information recording medium capable of recording and erasing.

Continuation of the front page (72) Inventor Kaoru Iwata 4-2-2 Asahigaoka, Hino-shi, Tokyo Teijin Limited Tokyo Research Center (56) References JP-A-63-136337 (JP, A) JP-A-60 -69846 (JP, A) JP-A-2-5250 (JP, A) JP-A-2-18938 (JP, A) JP-A-3-124490 (JP, A) JP-A-3-126580 (JP, A) (58) Fields surveyed (Int. Cl. ⁶ , DB name) B41M 5/26

Claims (4)

(57) [Claims] An expansive layer (A) comprising a resin (P ₁ ) exhibiting rubber elasticity at least at room temperature and a dye (D ₁ ) having absorption in the near infrared region on a substrate, and a glassy state at room temperature. Optical recording that supports a holding layer (B) composed of a resin (P ₂ ) capable of reversibly changing to a rubbery state at a higher temperature and a dye (D ₂ ) having absorption in the near infrared region. In the medium, (a) the dyes D ₁ and D ₂ are near-infrared absorbing dyes which are soluble in an organic solvent and whose absorption wavelength ranges do not completely overlap each other, and (b) at least _{one of the} dyes D _{1 and} D ₂ One is at least one dye selected from the group consisting of naphthalocyanine dyes, naphthalophthalocyanine dyes and phthalocyanine dyes. (C) Dye D ₂ in the holding layer (B) is 5 to 30% by weight. % Included,
And, it has been adjusted thickness (d) retaining layer retaining layer and the content of the dye D ₂ and D ₁ so that the reflectance is 5% or more of (B) (B) and expansion layer (A) An optical recording medium characterized by the above-mentioned. 2. The dye according to claim 1, wherein at least _one of the dyes D ₁ or D ₂ has the following formula: "Wherein Y ₁ and Y ₂ are the same or different, and oxygen, nitrogen,
Represents an alkyloxy group having 5 to 25 carbon atoms which may contain silicon, an alkenyloxy group, an aralkyloxy group, an aryloxy group, an alkylsiloxy group, an alkoxysiloxy group, or an aryloxysiloxy group. R _{1 to} R ₄ are the same or different and represent a hydrogen atom, a linear or branched alkyl group or a halogen, and n is the same or different and represents an integer of 0 to 6. Or the following formula: In the formula, R _{5 to} R ₈ represent a linear or branched alkyl group having 4 to 12 carbon atoms, and R _{9 to} R ₁₂ represent a linear or branched alkyl group having 1 to 12 carbon atoms. A, b, c, d represent 0 or 1, and a, b, c, d are not all zero at the same time, and M is a metal and a metal oxide or halide. Represents. "
A naphthalocyanine dye represented by the formula:
The optical recording medium according to the item. Wherein at least one of the dye D ₁ or D ₂ of the first term describes, soluble phthalocyanine dye in an organic solvent, from naphtha b phthalocyanine dyes, and phenylenedithiol and phenylenediamine metal complex dyes 3. The optical recording medium according to claim 1, wherein the optical recording medium is one or more selected dyes. 4. The method according to claim 1, wherein the dye (D ₁ ) is contained in the expansion layer (A) in an amount of 5 to 30% by weight. Optical recording medium.