JPH03121890A - Erasable optical recording medium - Google Patents

Abstract

PURPOSE:To enhance the stability to recording, erasure and the repeated irradiation with reproducing light by containing an aluminum and/or diimonium compound in a recording layer composed of polymer/dye. CONSTITUTION:An expansible layer A consisting of a resin P1 showing rubber elasticity at room temp. and a dye D1 showing absorption in a near infrared region and a holding layer B consisting of a resin P2 showing a glass state at room temp. and capable of reversibly changing to a rubbery state at high temp. and a dye D2 showing absorption in a near infrared region are supported on a substrate. An aluminum and/or diimonium compound is contained in one of the expansible layer A and/or the holding layer B. The expansible layer A is effectively expanded when it is heated by the irradiation with laser beam to enhance recording characteristics. The resin P1 to be used shows high rubber elasticity and generates no flow deformation by the irradiation with laser beam. The resin P2 plays a role fixing recording formed by thermal expansion at the time of recording and permitting the release of fixing at the time of erasure and the dyes D1, D2 plays a role efficiently absorbing laser beam in both recording and erasing processes to convert the same to heat.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an erasable optical recording medium that utilizes shape change upon heating. More specifically, the present invention relates to an optical recording medium with improved stability against repeated irradiation with recording, erasing and reproducing light, characterized in that the recording layer composed of polymer 7/dye contains an aminium and/or diimonium compound. .

BACKGROUND TECHNOLOGY AND PROBLEMS Conventionally, many organic optical recording media have been proposed that allow recording to be reproduced and erased and that can be coated. For example, JP-A-59
According to Japanese Patent No. 5448, an erasable optical recording medium made of a mixed system of a polymer and a dye is disclosed. In this medium, recording is based on the formation of pits due to flowing deformation of the polymer, and erasing is based on the principle of remelting the raised polymer around the pits generated during recording to close the pits. Therefore, it is difficult to completely restore the polymer once it has flowed out, and it is inevitable that some residue will be left behind. This erased residue is accumulated as recording and erasing are repeated. Therefore, high repeat durability cannot be obtained with this method. Furthermore, since recording and erasing utilize the melting and fluid deformation of the polymer, it is necessary to irradiate it with a high-energy laser beam.

As a result, photochemical deterioration and thermal deterioration of the dye contained in the medium are likely to occur, and from this point as well, repeated use is unavoidably disadvantageous.

Also, JP-A-57-27790 and JP-A-60-253
According to each publication No. 036, an erasable optical recording medium comprising a pit-forming recording layer and an overcoat layer provided thereon is proposed. In this medium, recording is performed by forming 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 it with a relatively strong laser beam for a long time when erasing, similar to the above-mentioned recording media, making it impractical. .

According to yet another proposal (Japanese Unexamined Patent Publication No. 60-69846), an expansion layer that is heated and stretched by laser beam irradiation to form a dome-shaped protrusion (bump) and a retaining layer that maintains this shape are used. A recordable/erasable medium has been proposed.When recording on this medium, a laser beam is irradiated with the absorption wavelength (λ1) of the dye mixed in the expansion layer in advance, and bumps are created in the expansion layer. In addition, when erasing recorded bumps, laser light is irradiated with the absorption wavelength (λ2) of the dye mixed in the retention layer in advance, so that the retention layer can maintain this shape. If the layer is heated above its glass transition temperature (Tg), it becomes difficult to maintain the bump shape.According to this recording method, the shape of the medium changes during recording and erasing, but there is no flow deformation. It is advantageous in terms of repeatability.Also, recording and erasing involve changes in shape but do not involve melting or fluidization of the polymer, so there is no need to irradiate high-energy laser light.Therefore, the dyes used are also similar to those described above. It is in a situation where it is less susceptible to deterioration compared to pit-type media.However, it goes without saying that in order to obtain a medium that requires a high degree of repeated durability, it is necessary to use a highly durable dye. .

In the field of optical recording media for recording and reproduction, several dyes have been proposed from the viewpoint of durability. For example, phthalocyanine and naphthalocyanine are representative stable near-infrared dyes. On the other hand, a mixed dye in which an aminium or diimonium compound is added to a polymethine dye has also been proposed (Japanese Unexamined Patent Publication No. 1989-19389163-67187.63-
299989.63-226642 and 6438490
(Japanese Patent Application Laid-open No. 113482/1999).

In this system, aminium and diimonium compounds improve the stability of polymethine dyes against photodegradation. However, there are two major problems in applying these dyes to bumped bilayer media. One is the problem of compatibility with the resin used. In other words, in conventional recording/reading-only recording media, only dyes and complexes were deposited or coated on the substrate.
Compatibility with the resin was not an issue. On the other hand, in the case of a bump-forming two-layer medium, compatibility is important because both layers are used in a mixed system with a resin. Another issue is the stabilization ability within the polymer matrix. - Pigment deterioration is said to be based on the following mechanism.

(1) The dye absorbs light and is excited.

(2) Singlet oxygen is generated by the excited dye exchanging energy with oxygen.

(3) The generated -single oxygen degrades the dye.

Therefore, in order to prevent photodeterioration of the dye, it is sufficient to absorb the energy of the dye in the excited state to bring the dye to the ground state, or to quench the -single oxygen. Therefore, the stabilization mechanism of the aminium or diimonium compound is a quencher of singlet oxygen that functions as an energy transfer agent (quencher) for the dye in the excited state.
Even if it is to function as a chemical, its concentration is extremely important.

In conventional recording/reading-only media, aminium or diimonium compounds are present in extremely high concentrations because no matrix resin is used. Therefore, whichever mechanism causes the quenching effect, it is expected that the quenching effect will be extremely high. On the other hand, in the case of a bump-forming two-layer medium, the effect cannot necessarily be expected because the particles are dispersed in the matrix resin.

However, as a result of a detailed study on the quenching effect of aminium and diimonium compounds within the matrix resin, the present inventors found that if these compounds are molecularly dispersed within the matrix resin at a certain concentration or higher, polymethine can be quenched even in a resin-type medium. We have discovered that photodeterioration of pigments can be prevented.

As a result of intensive studies to apply this knowledge to a bump-forming two-layer medium, it was possible to stabilize the dye without impairing the mechanical properties required for the medium, and the present invention was completed.

Summary of the Invention The optical recording medium of the present invention includes, on a substrate, an expansion layer (A) comprising a resin <P1) exhibiting rubber elasticity at least at room temperature and a dye <DI) exhibiting absorption in the near-infrared region; A resin (P2) that exhibits a glass state (high elasticity state) at room temperature and can reversibly change to a rubber state (low elasticity state) at higher temperatures.
) and a dye (D2) that absorbs in the near-infrared region are supported.The arrangement of the expansion layer (A) and the retention layer (B) with respect to the substrate depends on the direction of laser incidence. 0 method is also taken into consideration.Then, at least one of the expansion layer A and/or the retention layer B contains an aminium and/or diimmonium compound [the aminium or diimmonium compound contained in the expansion layer (A) is CI, the retention layer is It is called C2].

The expansion layer <A> needs to expand effectively when heated by laser beam 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 (P1) must exhibit high rubber elasticity and must not undergo flow deformation due to laser beam irradiation. Suitable resins include natural rubber styrene-butadiene rubber, butadiene rubber, isoprene rubber, nitrile rubber, chloroprene rubber, butyl rubber,
Synthetic rubbers such as ethylene-propylene rubber, urethane rubber, and silicone rubber; styrene-based, olefin-based, and urethane-based thermoplastic elastomers; amine-crosslinked, isocyanate-crosslinked, and UV-crosslinked elastomers.

The resin (P2) used in the present invention has the role of fixing bumps generated by thermal expansion during recording (recording) and allowing them to be released during erasing. Therefore, in order to effectively perform both functions, the resin must be able to reversibly change from a glass state (high elasticity state) at room temperature to a rubber state (low elastic modulus state) in at least one region higher than that. be. Suitable resins include thermoplastic resins such as polymethyl methacrylate resins, polycarbonate resins, and polyamide resins, and partially crosslinked products thereof, epoxy resins, phenol resins, melamine resins, epoxy (meth)acrylate resins, and novolac (meth) resins. Acrylate resin, polyfunctional (meth)acrylate resin [Note: (
Examples of meth)acrylate include thermosetting resins (crosslinked resins) such as methacrylate and methacrylate. In addition, epoxy resin, epoxy (meth) acrylate resin, novolac (meth) acrylate resin,
Polyfunctional (meth)acrylate resins may be cured with ultraviolet light and are preferably used.

The dyes D1 and D2 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. Furthermore, since reading utilizes light reflection from the medium, the holding 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 D2 include:
Polymethine dyes such as cyanine dyes, pyrylium dyes, thiapyrylium dyes, squalirium dyes, croconium 3 dyes, and azulenium dyes; phthalocyanine dyes such as phthalocyanine and naphthalocyanine; naphthoquinone and anthraquinone dyes; triphenylmethane dyes Examples include dyes.

The dye D1 described above is 5 to 3
If the dye content is less than 5 phr, preferably 1 (1-25 phr), the recording sensitivity will be low, and if the dye content is 30 phr or more, the mechanical strength of the coating will be reduced.

Aminium and 'diimonium compounds used in the present invention have the following general formulas [E], [II], [II[
].

], 4 14 arylene groups, especially beniX, i)-7X.

A quinoid group having 6 to 14 carbon atoms, which may be substituted with a halogen or an alkoxyl group, in particular, A is a quinoid group with 6 to 14 carbon atoms, which may be substituted with an alkyl group, a halogen, or an alkoxyl group; ~5 Xe represents an anion. From R1 to the corner, the number of carbon atoms is 1--
8 represents a substituted or unsubstituted alkyl group, and the substituents from R1 to R1 may be the same or different.

Xe is a chloride ion, bromide ion, iodide ion, perchlorate ion, nitrate ion, benzenesulfonate ion, methyl nitrate ion, ethyl nitrate ion, propyl sulfate ion, tetrafluoroborate ion, tetrafluoroborate ion, Phenylphorotate ion, hexafluorophosphate ion, benzenesulfinate ion, acetate ion, trifluoroacetate ion, propionacetate ion, benzoate ion, oxalate ion, succinate ion, Malonate ion, oleate ion, stearate ion, citrate ion, -hydrogen diphosphate ion, dihydrogen-phosphate ion, pentachlorostannate ion, chlorosulfonate ion, fluorosulfone salt ion, trifluoromethanesulfonate ion, hexafluoroarsenate ion, hexafluoroantimonate ion,
Represents hexachloroantimonate ion, molybdate ion, tungstate ion, titanate ion, zirconate ion, etc.

Furthermore, particularly preferred anions include metal complex anions. The metal complex anion used in the present invention has a bond unit represented by the following general formula, which has a bond unit selected from 87 H, OH, and NH2 on both carbon atoms forming a C-C double bond. Examples include chelate metal complexes of a metal and a compound having an m structure in which one or two types of groups are bonded.

"In the formula, X and Y represent S, O, NH or NH2, and M
does not represent a metal. Examples of such compounds include orthobenzenedithiols,
Catechols, orthophenylenediamines, orthoaminophenols, orthoaminobenzenethiols,
Examples include orthomercaptophenols and 1,2-ethylenedithiol derivatives. As metals, Ni,
Examples include Co, Cu, Pd, and Pt, and Ni is particularly preferably used. These compounds may contain various substituents to increase their solubility.

These aminium and diimonium compounds 8 are present in an amount of 5 to 30 phr, preferably 10 to 2 phr, relative to the resin.
5 phr added. If the quencher content is less than 5 phr, the quenching ability decreases, which is undesirable. Furthermore, if the quencher content exceeds 30 phr, the mechanical strength of the coating film decreases, making it impossible to retain or erase records satisfactorily. In particular, when added to the expansion layer, if the amount added is too high, the elastic modulus decreases, resulting in a decrease in C/N. Furthermore, if more than necessary is added to the retention layer, the recording retention ability will be significantly reduced.

For the same reason, there is also a limit on the total amount of the dye and the quencher. If only to suppress the deterioration of the dye, the quencher concentration should be as high as possible, but in order not to impair the mechanical properties of the expansion layer and the retention layer, the total amount of the dye and quencher should be adjusted based on the resin. The amount is 40 phr or less, preferably 30 phr or less.

Further, the dye and the aminium or diimonium compound used in the present invention must be uniformly mixed with the resin of each layer. 1゜9 In other words, the molecules must be dispersed.

These pigments are mixed with a resin and then applied onto a substrate and cured. Any substrate can be used as long as it has excellent solvent resistance, optical uniformity, and high surface smoothness. Examples of substrates having such characteristics include disk-shaped substrates made of polycarbonate, polymethyl methacrylate, poly-4-methylpentene 1 resin, glass, and the like, and film-shaped substrates made of polyester. The thickness of the expansion layer is generally 0.5 to 10 μm, preferably 0.5 to 10 μm.
．． 5 to 5.0 μm is used, and the thickness of the retaining layer is 0.1 to 5.0 μm.
3.0 μm, preferably Oj to 2.0 μm is used. Since the recording characteristics and erasing characteristics of the recording medium are greatly influenced by the degree of laser light absorption of each layer, the thicknesses of these layers must be selected taking into consideration the absorbance and concentration of the dye.

Further, the reflection characteristics of the medium are not simply based on the surface reflection of the holding layer, but also contribute to the interference effect with reflected light from each layer. Therefore, the thicknesses of the retention layer and the expansion layer should be selected to maximize the interference effect.

0 The coating method 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. 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 curing method, and an electron beam irradiation method are used. In the case of thermosetting, three-dimensional crosslinking and curing is usually carried out by heating in the coexistence of a radical initiator. On the other hand, in the case of ultraviolet curing, ultraviolet rays are irradiated in the presence of a photoinitiator.

Recording, reproduction, and erasing of the thus obtained two-layer medium are performed by irradiating it with two types of laser beams. 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 780 nm.

At this time, the expansion layer mainly absorbs light and forms a bump. 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.

According to the present invention, excellent durability can be obtained in a recording medium based on the basic principle of reading changes in reflectance due to the formation and disappearance of bumps.

The present invention will be explained in more detail in Examples below.

<Example> Example 1 Polymethyl methacrylate (P
MMA), 10 phr of a polymethine dye having the following structural formula 1 and 2.5 or 5 phr of an aminium compound having the following structural formula 2 were added to the resin, and chloroform was used as a solvent to obtain a uniform coating film. 600 to the obtained membrane
The film was irradiated with xenon lamp light with an intensity of 80 mW/cJ that cut out light below nm for 40 hours, and the residual rate of the dye in the film was measured based on changes in the absorption spectrum.

Example 3 An aminium compound represented by the following structural formula 4 was used in place of the aminium compound of Example 1, a coating film was formed in the same manner as in Example 1, and the light resistance of the dye was evaluated.

Example 2 Instead of the aminium compound of Example 1, the following structural formula 3
A coating film was formed in the same manner as in Example 1 using the diimonium compound represented by the following formula, and the light resistance of the dye was evaluated.

3 4 Example 5 An aminium compound having the following structural formula 6 was used instead of the aminium compound of Example 4, and a coating film was formed in the same manner as in Example 1, and the light resistance of the dye was evaluated.

Comparative Example 1 A coating film was formed in Example 1 without adding the aminium compound, and the light resistance of the dye was evaluated.

Example 4 A cyanine dye represented by the following structural formula 5 was used instead of the polymethine dye of Example 1, and a coating film was formed in the same manner as in Example 1, and the light resistance of the dye was evaluated.

Example 6 A coating film was formed in the same manner as in Example 1 except that the diimonium compound of structural formula 3 was used instead of the aminium compound of Example 4, and the light resistance of the dye was evaluated.

Comparative example 2 No aminium compound was added in Example 46 5 Form a coating on the surface and evaluate the lightfastness of the pigment.

Example 7 A cyanine dye represented by the following structural formula 7 was used instead of the polymethine dye in Example 7, and a coating film was formed in the same manner as in Example 1, and the light resistance of the dye was evaluated.

Example 8 Instead of the aminium compound of Example 7, the following structural formula 8
A coating film was formed in the same manner as in Example 1 using the diimonium compound represented by the following formula, and the light resistance of the dye was evaluated.

7 Example 6 A diimonium compound of structural formula 3 was used instead of the aminium compound of Example 4, and a coating film was formed in the same manner as in Example 1-, and the light resistance of the dye was evaluated.

Comparative Example 3 A coating film was formed in Example 7 without adding the aminium compound, and the light resistance of the dye was evaluated.

Example 9 In place of the polymethine dye of Example 1, a cyanine dye represented by the following structural formula was used, and the rest was similar to Example] to form a coating film, and the light resistance of the dye was evaluated.

Table Example 10 A diimonium compound represented by structural formula 3 was used in place of the aminium compound of Example 9, and a coating film was formed in the same manner as in Example C, and the light resistance of the dye was evaluated.

Comparative Example 4 A coating film was formed in Example 9 without adding the aminium compound, and the light resistance of the dye was evaluated.

The results of Examples 1 to 0 are summarized in Table 1, and the results of Comparative Examples 1 to 4 are summarized in Table 2.

Table 2 90 Example 11 Urethane acrylate as expansion layer resin? -U122A
(Shin Nakamura Chemical), 10 phr of a polymethine dye of structural formula 1 as a dye for the expanding layer, 5 phr of a diimonium compound of structural formula 3, 3 phr of Irgacure 907 as a photoinitiator, and methyl ethyl ketone as a solvent were added to this resin. dilute it as a liquid to create a coating solution with a uniform expansion layer. After coating and drying the obtained solution on a glass substrate, it was irradiated with light from a high-pressure mercury lamp of 80 W/cm to photo-crosslink the resin and create an expansion layer.

The thickness of the expansion layer was 3.4 μm. Next, on this expansion layer, 1 cyanine dye of structural formula 5 was added as a dye for the retention layer.
A methyl ethyl ketone solution of polymethyl methacrylate containing 0 phr and 5 phr of the aminium compound of structural formula 2 was coated to a thickness of about 18 μm to prepare a recording medium consisting of an expansion layer/retention layer.

830 nm narrowed to approximately IJLT+i diameter to the obtained medium.
When irradiated with semiconductor laser light of 10 mW, IMHz, and linear velocity of 3 m/sec, clear bumps (dome-shaped protrusions) were formed, confirming that recording could be performed1. When this recording was read with a 1 mW 830 nm semiconductor laser beam, a C/N of 50 clB was obtained, and it was confirmed that reproduction could be performed.

Furthermore, this recorded signal hardly deteriorated even after 105 reproductions. Also, in this medium, 780 nm
When irradiated with semiconductor laser light, it was confirmed that records could be erased.

Comparative Example 5 A recording medium similar to Example 11 was prepared without adding the aminium and diimonium compounds.

Example 11. When the recording was reproduced using a semiconductor laser beam at 8300 m in the same manner as above, the recorded signal was 10
When regenerated more than 4 times, it decreased significantly.

Example 2 A recording medium consisting of an expansion layer/retention layer was prepared in the same manner as in Example 11 except that a cyanine dye of structural formula 9 was used instead of the retention layer dye of Example 11.

When recording, reproducing, and erasing were performed in the same manner as in Example 11, it was confirmed that recording, reproducing, and erasing could be performed. Further, this recorded signal hardly decreased even after 105 times of reproduction.

Comparative Example 6 A recording medium similar to Example 12 was prepared without adding the aminium and diimonium compounds.

When the recording was reproduced using 830 nm semiconductor laser light in the same manner as in Example 11, the recorded signal was 104 nm.
When playing more than that, it decreased significantly.

Claims (1)

[Scope of Claims] (1) An expanding layer (A) consisting of a resin (P_1) exhibiting rubber elasticity at least at room temperature and a dye (D_1) having absorption in the near-infrared region; state),
A retaining layer (B) consisting of a resin (P_2) that can reversibly change to a rubber state (low elasticity state) at a higher temperature and a dye (D_2) that absorbs in the near-infrared region is placed on a substrate. In the optical recording medium supported, (1) the dyes D_1 and D_2 have different maximum absorptions in the near-infrared region, and (2) the dyes D_1 and D_2 are supported by the corresponding resin P_
1 and P_2, and (3) at least one of the expansion layer A and the retention layer B contains an aminium and/or diimonium compound as a stabilizer, and 5 to 30 phr uniformly dispersed in the corresponding resin. and (4) the total amount of the dye and the stabilizer is 40% of the resin.
1. An erasable optical recording medium characterized in that it has a phr or less. (2) The erasable optical recording medium according to claim 1, wherein the aminium and diimonium compounds have absorption in the same or substantially the same region as the dye contained in the layer containing them. (3) The aminium or diimonium compound described in item 1 above has the following general formula [I], [II], [III] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [ I ] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼[II] ▲Mathematical formulas, chemical formulas, tables, etc.▼[III] (In the formula, A represents an arylene group having 6 to 14 carbon atoms, which may be substituted with an alkyl group, halogen, and/or alkoxyl group. In the formula, B represents a quinoid group having 6 to 14 carbon atoms, which may be substituted with an alkyl group, halogen and/or alkoxyl group, and X^■ represents an anion. R_1 to R_8 are the same or different. , number of carbon atoms: 1
Claim 1 or 2, characterized in that the compound is a compound represented by (representing a substituted or unsubstituted alkyl group of -8)
Erasable optical recording medium as described. (4) The arylene group has a mathematical formula, chemical formula, table, etc.▼, ▲ has a mathematical formula, chemical formula, table, etc.▼, ▲ has a mathematical formula, chemical formula, table, etc.▼ or ▲ has a mathematical formula, chemical formula, table, etc.▼ , and the quinoid group has ▲mathematical formula, chemical formula, table, etc.▼, ▲mathematical formula, chemical formula,
There are tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼
4. The erasable optical recording medium according to claim 3, which is ▲contains mathematical formulas, chemical formulas, tables, etc.▼.