JPH03126580A - Erasable optical recording medium - Google Patents

Abstract

PURPOSE:To obtain superior recording/erasing characteristics by a method wherein an expansible layer made of a resin exhibiting rubbery elasticity at room temperature and a coloring matter is laminated on a holding layer made of a resin capable of reversibly turning to a rubbery form at high temperature and a coloring matter. CONSTITUTION:It is required that an expansible layer effectively expands when being heated by a laser beam irradiation and has a high rubbery elasticity for efficiently erasing a bump and returning to the former state. Therefore, it is required that a resin exhibits a high rubbery elasticity and never flow deforms by a laser beam irradiation. A resin used for a holding layer has a role of fixing or releasing a bump caused by a thermal expansion. As the resin, a resin, which is glassy or has a sufficient elasiticity at an ordinary temperature and is rubbery or has a small elasticity at a high temperature, is used: for example, an epoxy resin-cured substance having an elasticity of 80Kg/mm<2> or more at an ordinary temp. and a glass transition temperature of 60-150 deg.C is used. The resin is applied on a substrate and cured after being mixed with a coloring matter.

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 characterized in that a portion of the recording layer made of an organic polymer/dye is a selected polymer and a method for producing the same.

BACKGROUND TECHNOLOGY AND PROBLEMS Conventionally, many optical recording media using organic dyes have been proposed (for example, Japanese Patent Laid-Open No. 61-163891.61-268).
487, 62-56191.62-122787.62
-39286 and 63-72594). In addition, many optical recording media using a combination of an organic dye and an organic polymer have been proposed (for example, JP-A-62-9
0291.63=62794 and 63-191691
91691, the recording principle of these recording media is based on the irreversible change in shape of the recording medium (in most cases, bit formation) caused by the heat generated when the dye absorbs light (often laser light). This made erasure of records extremely difficult or impossible. That is, in the case of a dye-only medium, since recording is performed by forming bits accompanied by vaporization and dispersion of the dye, it is impossible to erase the bits once formed.

Furthermore, in the case of a mixed system of a polymer and a dye, recording is performed by bit formation accompanied by flow deformation of the polymer, so it is difficult to efficiently erase the recording pits once formed. In addition, another conventional technology (Japanese Patent Application Laid-Open No. 60-698
46.63-136337, 63-136338 and 63-164042), an expansion layer that is heated and expanded by laser beam irradiation to form a dome-shaped protrusion (bump), and a retention layer that maintains this shape. A recording/erasable medium consisting of the following has been proposed. When recording on this medium, laser light is irradiated with the absorption wavelength (λ1) of the dye mixed in the expansion layer in advance so that the expansion layer forms a bump and the retention layer maintains this shape. . In addition, when erasing the formed bumps, the absorption wavelength (λ2
), the holding layer is heated above its Tg to make it difficult to maintain the bump shape.

In the case of this dual layer medium consisting of dye/polymer, in order to perform recording efficiently, in other words to make the bump as high as possible, the glass transition temperature (Tg) of the holding layer should be made as high as possible. This is because the holding layer becomes a glass state when the degree of thermal expansion is high. On the other hand, in order to perform erasing efficiently, it is better for the retention layer to have a lower Tg. Furthermore, in order to obtain an erasable medium, it is not preferable that the holding layer undergo irreversible deformation due to laser beam irradiation, that is, flow deformation of the polymer. therefore,
From this point of view, three-dimensionally crosslinked polymers are preferable as the resin for the holding layer. It is preferable that the flow temperature is as high as possible and the melt viscosity is as high as possible. Also, as a matter of course, the holding layer plays the role of maintaining the shape of the bump against the contraction force of the expansion layer. Therefore, high elasticity is required at room temperature.

The inventors of the present invention have conducted intensive studies to obtain a resin for the retention layer that satisfies these requirements, and have found that a cured epoxy resin having a high elastic modulus and a high Tg at room temperature exhibits the desired recording and erasing characteristics. They discovered this and completed the present invention.

Summary of the Invention The optical recording medium of the present invention has an expandable layer (A>) on a substrate, which is composed of a resin (P1) exhibiting rubber elasticity at least at room temperature and a dye (D1), and which is in a glass state at room temperature. It is formed by supporting and laminating a resin (P1) that can reversibly change into a rubber state at high temperature and a retainer/I (B) consisting of a dye (D2).The arrangement of both layers depends on the laser beam incidence method. The selection will be made accordingly.

The expansion layer (A>) is required to expand effectively when heated by laser beam irradiation in order to improve the recording characteristics.The expansion layer (A>) also needs to effectively expand when heated by laser beam irradiation in order to improve the recording characteristics. High rubber elasticity is required in order to restore the elasticity.

Therefore, the resin (P1) must exhibit high rubber elasticity and must not undergo flow deformation due to laser beam irradiation. As the resin suitably used, natural rubber;
Styrene-butadiene rubber, butadiene rubber, isoprene rubber, nitrile rubber, chloroprene rubber, butyl rubber, ethylene-propylene rubber; styrene-based, olefin-based, urethane-based thermoplastic elastomers; amine crosslinked type, incyanate crosslinked type, polyol crosslinked type, ultraviolet rays Examples include crosslinked elastomers.

The resin (P1) used in the present invention plays a role in fixing and releasing bumps generated by thermal expansion.

Therefore, in order to perform both functions efficiently, it must have an elastic modulus sufficient to maintain the glass state, that is, the bump, at room temperature, and a rubber state, that is, the elastic modulus to the extent that it does not impede the thermal expansion of the 8M layer at high temperatures. It is necessary to use a resin with a small size. The resin used in the present invention is a cured epoxy resin having (1) an elastic modulus of 80 Kg/mm2 or more at room temperature, and (2) a glass transition temperature of 60 to 150°C. As mentioned above, the elastic modulus needs to be high in order to fix the bump against the contraction force of the expansion layer, and the tensile elastic modulus is 80 Kg/mm2 or more, preferably 100 Kg/mm2 or more.
A range of mm2 or more is used. If it is less than that, the bump shape cannot be maintained sufficiently. For the reasons mentioned above, the glass transition temperature is 60 to 150°C, preferably 70 to 1
A range of 20°C is used. As a specific epoxy compound, the following general formula: "In the formula, G is a glycidyl group, X is a divalent chain or cyclic hydrocarbon group having 1 to 10 carbon atoms or SO2, and Y is a hydrogen atom or a halogen atom. , n is an integer of θ to 20.” Preferred specific examples include methylene, 2,2-propylene, 1,1-
Examples include epoxy resins such as cyclohexylene and SO2, in which Y is a hydrogen atom or a bromine atom.

n is θ to 20, preferably 0 to 15.

Another epoxy resin includes epoxy novolak represented by the following formula.

"In the formula: G is a glycidyl group, m is an integer of 5 to 20, and R is a hydrogen atom or a methyl group." In the present invention, these epoxy resins may be used alone or as a mixture of two or more. Good too.

The film and curing reactivity of the cured product of the epoxy resin used in the present invention depend on the curing agent.

They are selected in consideration of the type of epoxy resin and the Tg and elastic modulus of the cured product. In addition, compatibility with the dye to be mixed is also an important selection criterion. - Amines and acid anhydrides are used as curing agents for boat fishing.

As the amines, aliphatic and alicyclic aromatic polyamines such as diethylenetriamine, triethylenetetramine, detraethylenepentamine, diaminocyclohexane, methylenedianiline, oxydianiline, and tolylenediamine are preferably used. Also, polyamide amine,
Amines containing heteroatoms such as persamide and diamines containing a spiro ring represented by the following formula are also preferably used.

On the other hand, as acid anhydride curing agents, maleic acid anhydride,
Succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, pyromellitic anhydride, glutaric anhydride, trimellidic anhydride, methylnadecic anhydride , aliphatic, alicyclic, and aromatic acid anhydrides such as chlorendic acid anhydride are preferably used.

The blending ratio of these curing agents is determined according to the epoxy value of the epoxy compound.

The dyes D1 and D2 used in the present invention function to efficiently absorb laser light and convert 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 at each oscillation wavelength do not overlap excessively. Furthermore, since reading utilizes light reflection on the surface of 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 polymethylene dyes such as cyanine dyes, pyrylium dyes, thiapyrylium dyes, squarylium dyes, croconium dyes, and azulenium dyes; phthalocyanine dyes such as phthalocyanine and naphthalocyanine; dithiol nickel. Examples include dithiol metal complexes such as complexes; naphthoquinone and anthraquinone dyes; triphenylmethane dyes; aminium and diimmonium dyes.

Further, even if a plurality of these dyes are used in combination, f14 does not occur.

These resins used in the present invention are mixed with a pigment and then applied onto a substrate and cured. The substrate used is not particularly limited, but -m may be a disk-shaped substrate made of polycarbonate, polymethyl methacrylate, glass, or the like, or a film-shaped substrate made of polyester or the like. The ratio of dye/resin is generally 0.05 to 0.4, preferably 1.0 to 0.3, although it depends on the absorbance of the dye and the film thickness. The thickness of the expansion layer is generally 0.5 to 10 μm, preferably 1.0 to 5.0 μm, and the thickness of the retention layer is 0.5 to 10 μm, preferably 1.0 to 5.0 μm.
．． 1 to 3.0 μm, preferably 0.3 to 2.0 μm is used. 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. 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, methylene chloride, etc. haloalkanes; esters such as ethyl acetate and butyl acetate; acetone, methyl ethyl ketone; ketones such as methyl isobutyl ketone and cyclohexanone; glymes such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether; ethers such as tetrahydrofuran and dioxane; nitromethane,
Mention may be made of acetonitrile and mixtures thereof.

In the case of a crosslinked elastomer used in the expansion layer, it is necessary to crosslink and cure it after coating. As the effect method, a thermosetting method and an ultraviolet curing method are used. In the case of thermosetting, three-dimensional crosslinking and curing is achieved by heating. The heating temperature is generally 50 to 150°C, preferably 70 to 120°C, particularly 80 to 120°C. On the other hand, in the case of ultraviolet curing, ultraviolet rays are irradiated in the presence of a photoinitiator.

Examples of photoinitiators include benzophenone initiators such as benzophenone and Michler's ketone; digetone initiators such as benzyl and phenylmethoxydiketone; benzoin initiators such as benzoin ethyl ether and benzyl dimethyl ketal; and 2,4-diethylthioxanthone. Thioxanthone initiator, 2-methylanthraquinone,
Quinone-based initiators such as camphorquinone are preferably used. As the ultraviolet light to be used, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, etc. are suitably used.

On the other hand, in the case of a retaining layer, heat crosslinking is performed after coating.

Although the heating temperature depends on the type of curing agent, it is generally in the range of 50 to 200°C, preferably 70 to 150°C. If it is more than that, it is not preferable because it causes deterioration of the substrate and the dye. Further, if it is less than that, the curing reaction does not proceed sufficiently, which is not preferable. The curing time for -m is 1 minute to 10 hours, preferably 3 minutes to 5 hours.

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 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. Generally, recording is performed at 5 to 30 mW,
Preferably, the irradiation is performed at a power of 7 to 20 mW for 5 to 0.1 μsec. Regeneration is 0.5-3mW, 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.

According to the present invention, excellent recording and erasing characteristics can be obtained in a recording medium whose basic principle is to read changes in reflectance due to the formation and disappearance of bumps.

Example 1 Epicote 828 (bisphenol A epoxy)
A chloroform solution in which Evomate N-002 with the same functional group equivalent was mixed with oil-based shell epoxy (■) was coated on a glass plate to a thickness of 100 μm using the barcode method.
It was cured by heating at °C for 2 hours. When this thin film was peeled off from the glass plate and its elastic modulus was measured, it was found to be 300 Kg/mm2. Moreover, the glass transition point was 73°C.

Mix chloroprene rubber PH050 (Denki Kagaku Kogyo ■) with a hydroxyl group at the end and Coronate L, a polyfunctional incyanate, so that the amount of hydroxyl groups and the amount of incyanate are equal, and then add 10 phr of IRDlool (Shiraki Kasei ■). was added, applied to a thickness of 3 μm using a barcode method, and heated at 120° C. for 1 hour to cure, thereby forming an expanded layer. 1 for Epicote 828 and Evomate N-002, which were prepared so that the functional group equivalents were equal.
0 phr of TV-IR-2 (Mitsui Toatsu) was added and cast onto the expanded layer, dried, and heated at 80° C. for 3 hours to form a 1 μm thick retaining layer. This two-layer medium has a wavelength of 840 nm and 10
When irradiated with laser light of mW and pulse width of 5 μs, the formation of bumps with a diameter of 1 μm was observed. A laser beam with a wavelength of 780 nm and a power of 7 mW is defocused on this bump.
After irradiation for 0 μs, the bumps disappeared within the range of microscopic observation.

Example 2 Epicote 1007, a bisphenol A epoxy
A chloroform solution in which Evomate N-002 having an equivalent functional group equivalent was mixed with (Oilized Shell Epoxy ■) was coated on a glass plate to a thickness of 100 μm using the barcode method.
Heat at 80'C for 3 hours and harden 1. When this thin film was peeled off from the glass plate and the elastic modulus was measured, it was 290 Kg/mm2.
Met. Moreover, the glass transition point was 96°C.

Chloroprene rubber PH050 (Denki Kagaku Kogyo ■) having a hydroxyl group at the end and Coronate L, a polyfunctional incyanate, were mixed so that the amount of hydroxyl groups and the amount of isocyanate were equal, and then 10 phr of IRDlool (Shiraki Kasei 0 Vermilion) was added. 3μm thick by barcode method.
An expanded layer was formed by applying the mixture to the substrate and heating it at 120°C for 1 hour to cure it. Epicote 1007 and Evomate N-002 mixed so that the functional group equivalents are equal
10 phr of TY-IR-2 (Mitsui Toatsu ■) was added to the mixture, and the mixture was cast onto the expanded layer, dried, and heated at 80°C for 3 hours.
A holding layer of μm was formed. This two-layer medium has a wavelength of 840n.
When a laser beam of 10 mW and a pulse width of 5 μsec was not applied, the formation of bumps with a diameter of 1 μm was observed. When this bump was irradiated with a defocused laser beam of 7 mW and a wavelength of 780 nm for 10 μs, the bump did not disappear within the range of microscopic observation.

Example 3 4.4' instead of Ebomate N-002 in Example 2
- Diaminodiphenylmethane was used. The elastic modulus of this resin at room temperature was 175 Kg/mm2. Moreover, the glass transition point was 105°C. A two-layer medium consisting of a fat-swollen layer/retention layer was formed in the same manner as in Example 2. When this two-layer medium was irradiated with a laser beam having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, the formation of bumps with a diameter of 1 μm was observed. This bump has a wavelength of 780 nm and a wavelength of 7 m.
When the W laser beam was defocused and irradiated for 10 μs, the bumps disappeared within the range of microscopic observation.

Example 4 Epicote 15, a phenolic novolac type epoxy
Trimelidic acid anhydride having the same functional group equivalent was added to 4 (oiled shell epoxy ■), and the mixture was cast onto an expanded layer formed in the same manner as in Example 1, dried, heated at 125°C for 6 hours, and held. Don't form layers. This two-layer medium has a wavelength of 840 nm, 1
When irradiated with laser light of 0 mW and pulse width of 5 μs, the formation of bumps with a diameter of 1 μm was observed. When this bump was irradiated with a defocused laser beam of 7 mW and a wavelength of 780 nm for 10 μs, the bump disappeared within the range of microscopic observation.

Example 5 NK125 (
A two-layer medium consisting of a fat-swollen layer/retaining layer was formed in the same manner as in Example 4 using Japanese photosensitive dye @). When this two-layer medium was irradiated with a laser beam having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, the formation of bumps with a diameter of 1 μm was observed. A defocused laser beam of 7mW with a wavelength of 780nm is irradiated onto this bump for 10μ seconds, and a microscope! F! ! The bump disappeared within the range of my knowledge.

Example 6 A naphthalocyanine dye having the following structure was used in place of TY-IR-2 in Example 1, and a two-layer medium consisting of expanded N/retention layer was formed in the same manner as in Example 1.

When this two-layer medium was irradiated with a laser beam having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μsec, the formation of bumps with a diameter of 1 μm was observed. This bump has a wavelength of 780 nm.
When a 7 mW laser beam was defocused and irradiated for 10 μs, the bumps disappeared within the range of microscopic observation.

Effects of the Invention According to the present invention, excellent recording/erasing characteristics can be obtained in a recording medium whose basic principle is to read changes in reflectance due to the formation and disappearance of bumps.

Claims (1)

[Claims] A resin (P_
1) and a dye (D_1), and a retaining layer consisting of a resin (P_2) that can reversibly change into a glass state at room temperature and a rubber state at a higher temperature and a dye (D_2). In the optical recording medium formed by supporting and laminating (B), the resin P_2 has (1) an elastic modulus of 80 kg at room temperature.
/mm^2 or more, and (2) the glass transition temperature is 60 to 1.
An erasable optical recording medium characterized in that it is an epoxy resin cured at 50°C.