JPH03205187A - Erasable optical recording medium and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain an erasable optical recording medium by laminating an expanding layer consisting of a resin showing rubber elasticity at room temp. and a dye and a holding layer consisting of a resin reversibly changing between a high elastic modulus state and a low elastic modulus state and a dye to a substrate. CONSTITUTION:A dye is compounded with urethane (meth)acrylate being a resin showing rubber elasticity at least at room temp. characterized in that Tg is room temp. or lower and elastic modulus at room temp. is 0.001 - 100 kg/mm<2> and elastic recovery is 80% or more and volume expansion coefficient is 1 X 10<-5>/ deg.C or more and the obtained composition is dissolved in a proper solvent to prepare a coating solution. This coating solution is applied to a substrate and, after drying, the coating layer is irradiated with active rays to form an expanding layer. A holding layer consisting of a resin reversibly changing between a vitreous state at room temp. and a rubber state at high temp. and a dye is laminated to the expanding layer to form an erasable optical recording medium.

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 selected polymer elastomer capable of being cured by ultraviolet rays is used as a part of a recording layer made of an organic polymer/dye, 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 Application Laid-Open No. 61-163891.61-26).
8487. 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, Japanese Patent Laid-Open No. 62-90291, 63-62794 and 63-1
91691 publications). However, the recording principle of these recording media is that the dye is exposed to light (often laser light).
This method is based on irreversible changes in the shape of the recording medium (often pit formation) caused by the heat generated by the absorption of heat, making it extremely difficult or impossible to erase records. That is, in the case of a dye-only medium, since recording is performed in the form of pits accompanied by vaporization and dispersion of the dye, it is impossible to erase bits once formed.

Furthermore, in the case of a mixed system of a polymer and a dye, recording is performed by forming pits accompanied by flow deformation of the polymerer, so it is difficult to efficiently erase the recorded pits once formed. In addition, another conventional technology (Japanese Patent Application Laid-Open No. 60-698
46. 63-136337. According to Publications Nos. 63-136338 and 63-164042), the recording/erasing method is composed of 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. Possible media have been proposed. When recording on this medium, laser light is irradiated at the absorption wavelength (λl) of the dye mixed in the expansion layer in advance so that the ml layer forms a bump and the retention layer maintains this shape. In addition, when erasing recorded bumps, the absorption wavelength of the dye mixed in the retention layer in advance is
Laser light irradiation is performed at λ2> to heat the holding layer above its Tg so that it becomes difficult to maintain the bump shape.

In the case of this dual layer medium consisting of dye/polymer, the KM ratio of the expansion layer needs to be high in order to perform recording efficiently, in other words to make the band 1 as high as possible. Furthermore, in order to perform erasing efficiently, it is necessary to have a high elastic recovery rate.

In other words, it is desirable that the elastic force of the holding layer that fixed the bump shape is released by the erasing light irradiation, so that the expansion layer contracts and recovers to its original state, that is, the state before recording.

Conversely, if the expansion layer undergoes plastic deformation or Tg is above room temperature, efficient erasure will not occur.

From this point of view, three-dimensionally crosslinked elastic polymers are preferred as the resin for the expansion layer. However, in order to laminate crosslinked polymers, a post-coating crosslinking process is generally required, and industrially it is necessary to carry out this crosslinking reaction in a short period of time. This becomes an essential requirement for continuous coating on film substrates.

As a result of intensive studies to obtain a resin for the expansion layer that satisfies these requirements, the present inventors found that it has a high elastic recovery rate and a Tg
The inventors have now completed the present invention by discovering that a urethane acrylate-based elastomer whose temperature is below room temperature exhibits desired recording and erasing properties and can be photocured in a short period of time by irradiation with ultraviolet rays.

Summary of the present invention The optical recording medium of the present invention has an expanding layer composed of a resin (P1) exhibiting rubber elasticity at least at room temperature and a dye (D1).
A), a retaining layer consisting of a resin (P2) that can reversibly change from a glass state (high elastic modulus state) at room temperature to a rubber state (low elastic modulus state) at a higher temperature, and a dye (D2).
B) is supported on a substrate.

The Wj tension layer (A>) needs to expand effectively when heated by laser beam irradiation in order to improve the recording properties.It also efficiently erases the bumps generated during recording and restores the original state. High rubber elasticity is required in order to return to the original state.Therefore, the resin (PE) must exhibit high rubber elasticity and must not undergo flow deformation when irradiated with laser light.
In other words, a high elastic recovery rate is required. From this point of view, the resin P in the present invention has the following properties: (1) Tg is below room temperature, and (2) elastic modulus at room temperature is 0.001 to 100 Kg/
mm2, (3) an elastic recovery rate of 80% or more, and (4) a volumetric expansion rate of I x 10-5/°C or more.

The elastic modulus at room temperature is <0. 001~100
Kg/mm2, preferably 0. 01～lOKg/
It is mni2. If it is more than that, the holding layer will not be able to fix the bumps, which is not preferable. Further, if it is less than that, it becomes difficult to pull back the bump when irradiated with erasing light, which is not preferable. The elastic recovery rate is determined by the constant length (
Apply external force (tension) to the sample of 1-0), and
06 It is defined as the ratio of the amount of deformation remaining after the external force is released (L' - L, O) to the amount of deformation 0 when stretched (0.I Lo ). That is,] − (i,' −Lo
)0. I Lo'. 'A material of which 100% is more than 80%, preferably more than 90% is used as the ablation layer. If it is 1' beyond that, it is not possible to completely erase even if the erasing light is irradiated, and an erased residue remains, which is not preferable. The volumetric expansion rate is
1゛・, 10-5/”C or more, preferably I x 10
-',/℃ or higher. The volumetric expansion rate is an important factor for efficiently causing Bun 1 formation. If it is less than this, it is not possible to form a sufficiently large bump, or in other words, it is not possible to obtain a large C,/'N ratio, which is not preferable. Further, Tg needs to be below room temperature.

When Tg is above room temperature, the contraction of the bump due to the erasing light is
The expansion layer resin P used in the present invention is a wide urethane (meth)acrylate that satisfies the above requirements [here, urethane (meth)acrylate refers to urethane acrylate and 7/or urethane methacrylate] as an essential component. Urethane (meth)
As for acrylate, the main chain is linear aliphatic polyether,
Both ends of the polymer are made of oligomers such as aliphatic polyester, polybutadiene, polyisoprene, polychloroprene, etc., and may be connected by reacting diisocyanate with soft segments having hydroxyl groups at both ends. ) It is an acrylate.

As the linear aliphatic polyether, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, copolymers thereof, and the like are preferably used. In addition, linear aliphatic polyesters include diols such as ethylene glycol, tetramethylene glycol, diethylene glycol, adivic acid, sebacic acid,
Polymers and copolymers with dicarboxylic acids such as maleic acid and fumaric acid are preferably used. Poly(ε-caplactone) is also preferably used. Polymers of butadiene, isobrene, chloroprene containing hydroxyl groups at both ends, and copolymers thereof are preferably used as the polymer. .2- and 1.4= bonds may be mixed.

The molecular weight of these polymers is relatively small, 100-50
00, preferably 200 to 3000, and these polymers may be linked by urethane bonds with diisocyanates. Suitably used incyanates include 1.4-phenylene diisocyanate, tolylene diisocyanate, and 4.4-phenylene diisocyanate.
Aromatics such as '-diphenylmethane diisocyanate, 4,4'-oxydiphenylene diisocyanate, 1,4-cyclohexane diisocyanate, tetramethylene diisocyanate, octamethylene diisocyanate,
Alicyclic and aliphatic diisocyanates are preferably used.

Both terminal hydroxyl groups of these soft segments further contain hydroxyl groups by reacting with the diisocyanate (
Combined with meth)acrylate.

Examples of the (meth)acrylate containing a hydroxyl group include monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, trimethylolpropane di(meth)acrylate, and pentaerythritol tri(meth)acrylate. Functional or polyfunctional (meth)acrylates are used.Specifically, these urethane (meth)acrylates are prepared by reacting both terminal hydroxyl groups with an excess molar amount of diisocyanate, and then reacting with a (meth)acrylate containing a hydroxyl group. In addition, T of these urethane (meth)acrylate cured products
Other polyfunctional (meth)acrylates may be used in combination to control g, elastic modulus, etc., or to enhance the curing reaction. Suitably used polyfunctional (meth)acrylates include ethylene di(meth)acrylate, tetramethylene di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa( meth>acrylate, etc. These are used in an amount of 30 parts by weight or less based on the urethane acrylate.

The resin (P2) used in the present invention has the role of fixing and releasing the bumps formed by thermal expansion. Therefore, in order to efficiently perform both functions, the resin (P2) is in a glass state ( The resin must be in a rubber state (low modulus of elasticity) at higher temperatures.Suitable resins include thermoplastic resins such as polymethyl methacrylate resin, polycarbonate resin, and polyamide resin. Resins and their partially crosslinked products, epoxy resins, phenolic resins, melamine resins, epoxy (meth)
Examples include thermosetting resins such as acrylate resins and crosslinked resins. Furthermore, epoxy resins, epoxy (meth)acrylate resins, novolac (meth)acrylate resins, etc. may be cured with ultraviolet light and are preferably used.

In the present invention, these compounds may be used alone or as a mixture of a plurality of them.

In addition, epoxy (meth)acrylate and novolac (meth)acrylate resins are used to increase reactivity, control Tg, improve mechanical properties of the film, and increase compatibility with dyes. Multifunctional (
Meth)acrylate may be used in combination.

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 in the respective oscillation wavelength ranges do not overlap excessively. Furthermore, since reading utilizes light reflection from the medium (surface), 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 dye D
, and D2 include vorimethine pigments, pyrylium pigments, thiavirylium pigments, squalirium pigments, croconium pigments, azulenium pigments, cyanine pigments, and phthalocyanine pigments such as phthalocyanine and naphthalocyanine; Examples include dithiol metal complexes such as dithiol niggel complexes; naphthoquinone and anthraquinone dyes; triphenylmeth>-based dyes; aminium and diimmonium dyes.

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 generally a disk-shaped substrate made of polycarbonate, polymethyl methacrylate, glass, or the like, or a film-shaped substrate made of polyester or the like is used. The dye/resin ratio depends on the absorbance of the dye and the film thickness, but is generally 0.05 to 0.4, preferably 1.0 to Oj.

The thickness of the expansion layer is generally 0.1 to 10 μm, preferably 0.5 to 5.0 μm, and the thickness of the retaining layer is 0.1 to 3.0 μm, preferably Oj to 2.0 μm. is used. 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, 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 getone and cyclohexanone; glymes such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether; ethers such as tetrahydrofuran and dioxane Class; nitromethane,
Mention may be made of acetonitrile and mixtures thereof.

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. The initiator is not particularly limited, but generally includes azobisisobutyronitrile (AIBN), beso-inolever oxide (BPO), cumesy hydroperoxide, dicumyl peroxide, tert-butyl hydroperoxide, Examples include lauroyl peroxide. The heating temperature is generally 50-1
A temperature of 50°C, preferably 70-120°C is employed. On the other hand, in the case of ultraviolet curing, ultraviolet rays are irradiated in the presence of a photoinitiator. Examples of photoinitiators include penzophenone initiators such as penzophenone and Michler's getone; digetone initiators such as benzyl and phenylmethoxydigeton; benzoin initiators such as benzoin ethyl ether and benzyl dimethyl ketal; 2.4-
Thioxanthone initiators such as diethylthioxanthone, quinone initiators such as 2-methylanthraquinone and camphorquinone, and the like are preferably used.

If necessary, it is also possible to use a promoter such as an amine promoter. The amount of initiator used is 0.1 based on the resin.
"lOphr, preferably 0.5 to 5 phr
is used. The ultraviolet rays used are low pressure mercury lamps,
Medium-pressure mercury lamps, high-pressure mercury lamps, metal halide lamps, and the like are preferably used.

Recording, reproduction, and erasing of the thus obtained two-layer medium are performed by irradiating it with two types of laser beams. As the laser used in this case, a helium neon laser, an argon laser, a krypton laser, a ruby laser, a dye laser, a semiconductor laser, etc. are used, but a small and inexpensive semiconductor laser is more preferable. Hereinafter, an example of a medium in which the m-tension layer dye D1 exhibits absorption in the vicinity of g4Qnm 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 8400 m. At this time, the expansion layer mainly absorbs light to form bumps. For reproduction, either a 780nm or 840n+n laser can be used, but a laser with a high reflectance at that wavelength is preferred, and a weak laser beam at that wavelength is irradiated to separate the recorded and unrecorded areas. Reproduction is performed by reading the difference in reflectance between the two. Erase is 780
This is done by irradiating a nanometer laser beam.

According to the present invention, excellent recording and erasing characteristics can be obtained in a recording medium based on the basic principle of reading changes in reflectance due to the shape or disappearance of bumps. At the same time, it has the industrial advantage of being able to form films at low temperatures and high speeds, allowing coating and curing to be carried out without deteriorating the substrate or the dye, and reducing media costs. There is.

Examples Example 1 Urethane acrylate U-122 as expansion layer resin P1
Using A (Shin Nakamura Chemical), 3 phr of Irgacure 907 and 830n+n were added to this resin as a photoinitiator.
Polymethine dye IR-82 as a dye for semiconductor lasers
A coating solution was prepared by adding 10 phr of 0 (Nippon Kayaku) and using methyl ethyl ketone as a solvent. The obtained solution was applied onto a glass substrate, dried, and then irradiated with gQw/cm high-pressure mercury lamp light to perform ultraviolet curing. The thickness of the expansion layer <A) was 3 to 4 μm. Next, epoxy acrylic VR-60 (Showa Kobunshi) was used as the retaining layer resin P2, and 3p of Irgacure 907 was added to this resin.
hr, HIT as dye for 780nm semiconductor laser
Add 10 phr of C and dilute with methyl ethyl getone to create a coating solution for the retention layer (B), and apply this solution to the expansion layer <A).
After coating and drying, it was irradiated with light from a high-pressure mercury lamp at 80 W/cm to perform ultraviolet curing, thereby forming a retaining layer (B). The thickness of the holding layer (B) was approximately 1 μm.

The obtained medium was irradiated with a semiconductor laser beam of 830 nm focused to a diameter of about 1 μm, and writing was performed under conditions of a writing power of 10 mW and a linear velocity of 3 m7 sec. As a result, a clear dome-shaped protrusion (bump) was formed, and when this record was read with the above-mentioned semiconductor laser beam of 1 mW, a C/N of 50 dB was obtained.

Next, the recording was erased by irradiation with 7 mW of 780 nm semiconductor laser light, and it was confirmed that the recording could be erased.

Example 2 A 7=3 blend matrix of urethane acrylate U-122A and U-4HA (both from Shin Nakamura Chemical) was used as the expansion layer resin, and the rest was the same as in Example 1 to produce a recording medium consisting of an expansion layer/retention layer. was disciplined.

Writing and reproduction with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 3 Urethane acrylate U-1084A as expansion layer resin
A recording medium consisting of an expansion layer/'retention layer was prepared in the same manner as in Example 1 using M (Shin Nakamura Kagaku).

Writing and reproduction with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 4 Urethane acrylate TB-3001 as expansion layer resin
A recording medium consisting of an expansion layer/retaining layer was prepared in the same manner as in Example 1, using the same method as in Example 1.

Writing and reproduction with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 5: Width urethane acrylate as expansion layer resin TB-300
1 and TB-3016 (both Shin Nakamura Chemical) 1:
EXAMPLE 1 A recording medium consisting of an expansion layer/retaining layer was prepared in the same manner as in Example 1 except that the Example 1 blend matrix was used.

Writing and reproduction with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 6 An 8:2 blend matrix of urethane acrylate Aronix M-1100 (Toagoi Co., Ltd.) and 1,6-hexanediol diacrylate was used as the expansion layer resin, and the rest was formed on a glass substrate in the same manner as in Example]. Then, 10ph of HNTC was added as a retention layer.
A methyl ethyl getone solution of polymethyl methacrylate containing r was applied and dried to produce a recording medium comprising an expansion layer/retaining layer. The thickness of the holding layer was approximately 1 μm.

Writing and reproduction using an 830 nm semiconductor laser tip and erasing using a 780 nm semiconductor laser beam were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 7 Aronix M-1310 <Toagosei>, which is urethane acrylate, and Ebecryl-2 as expansion layer resins
An expanded layer was formed on a glass substrate in the same manner as in Example 1 using a 7:3 blend matrix of 20 (Daicel/UCB). Next, a methyl ethyl getone solution of polymethyl methacrylate containing 10 phr of HI'1'C was applied as a retention layer and dried to produce a recording medium comprising an expansion layer/retention layer. The thickness of the holding layer was approximately 1 μm.

Writing and reproduction using an 830 nm semiconductor laser beam and erasing using a 780 nm semiconductor laser beam were performed in the same manner as in the example, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 8 Ebec, a urethane acrylate, as the expansion layer resin
ry! An expanded layer was formed on a glass substrate in the same manner as in Example 1 using a 7:3 blend matrix of -230 and Ebecryl-1290 (both Daicel/UCB). Next, a toluene solution of polymethyl methacrylate containing 10 phr of silicon naphthalocyanine having the following structure was applied as a holding layer and dried to produce a recording medium comprising an expansion layer/holding layer. The thickness of the retention layer is approximately ]μm
And so.

Writing and reproduction with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 9 Phot, which is urethane acrylate as the expansion layer resin
An expansion layer was formed on a glass substrate in the same manner as in Example 1 using Omer-6008 (San Nopco). Next, a retention layer was formed thereon in the same manner as in Example 8, thereby producing a recording medium consisting of an expansion layer/retention layer.

Writing and reproduction with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Example 10 A recording medium consisting of an expansion layer/retention layer was prepared using the resin shown in Example 5 as the expansion layer resin and the resin shown in Example 8 as the retention layer.

Writing and reproduction with 830 nm semiconductor laser light and erasing with 78 hm semiconductor laser light were performed in the same manner as in Example 1, and it was confirmed that recording, reproduction, and erasing could be performed.

Physical property data Table 1 summarizes the physical property data of the expanded layer used in the present invention.

Claims (1)

[Claims] (1) An expansion layer (A) consisting of a resin (P_1) exhibiting rubber elasticity at least at room temperature and a dye (D_1), which is in a glass state (high elastic modulus state) at room temperature, and has a higher elasticity than that. Resin that can reversibly change to a rubber state (low elastic modulus state) at temperature (P_2)
and a retention layer (B) consisting of a pigment (D_2) and a dye (D_2) are supported and laminated on a substrate.
However, (1) Tg is below room temperature and (2) elastic modulus at room temperature is 0.001 to 100 Kg/m
m^2, (3) has an elastic recovery rate of 80% or more, and (4) has a volume expansion coefficient of 1 x 10^-^5/°C or more, and is an elastic crosslinked body containing urethane (meth)acrylate as an essential component. An erasable optical recording medium characterized by: (2) After coating the expansion layer (A) described in item 1 above with a mixture containing urethane (meth)acrylate and a pigment,
A method for producing an erasable optical recording medium, which is produced by crosslinking and curing by irradiation with actinic rays.