JPH03218889A - Erasable optical recording medium - Google Patents

Abstract

PURPOSE:To obtain desired recording and erasing characteristics by using specific polyurethane or urea elastic crosslinked material having Tg of room temp. or lower and specified in the modulus of elasticity, elastic recovery and volume swell at room temp. as the resin constituting an expanding layer. CONSTITUTION:An optical recording medium is constituted by supporting an expanding layer A consisting of a resin P1 showing rubber elasticity at least at room temp. and a holding layer B consisting of a resin P2 capable of reversibly changing between a vitreous state (high modulus-of-elasticity state) at room temp. and a rubber state (low modulus-of-elasticity state) at temp. higher than room temp. on a support. It is necessary that the expanding layer A is effectively expanded when heated by the irradiation with laser beam from an aspect enhancing recording characteristics and high rubber elasticity is required in order to efficiently remove a bump by recording to return the medium to the original state. Therefore, as the resin P1, an elastic crosslinked material having a urethane or urea bond as an essential component having Tg of room temp. or lower, the modulus of elasticity of 0.001-100kg/m<2> at room temp., elastic recovery of 80% or more and volume swell of 1X10<-5>/ deg.C or more is used.

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 consisting of an organic polymer/dye is a selected polymeric elastomer.

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). Furthermore, many optical recording media using a combination of an organic dye and an organic polymer have been proposed. For example, JP-A 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) due to the heat generated by absorption of the recording material, making it extremely difficult or impossible to erase records. That is, in the case of a dye-only medium, since recording is performed by forming pits accompanied by vaporization and scattering of the dye, it has been impossible to erase pits once formed.

In addition, 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 polymer, 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. 63-136338 and 63-164042), a recording medium comprising an expansion layer that is heated and inflated by laser beam irradiation to form a dome-shaped protrusion (bump), and a retention layer that maintains this shape. Erasable media have been proposed. When recording on this medium, laser light is irradiated with a long 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 recorded bumps, the absorption wavelength (
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 two-layer medium consisting of dye/polymer, the expansion rate of the expansion layer must be high in order to perform recording efficiently, in other words to make the bumps 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, the expansion layer may undergo plastic deformation,
If 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.

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
It was discovered that a polyurethane elastomer whose temperature is below room temperature exhibits desired recording and erasing characteristics, and the present invention was completed.

Outline of the present invention The optical recording medium of the present invention includes: - an expansion layer (A>) consisting of a resin (P1) exhibiting rubber elasticity at least at room temperature and a dye (D1); and a glass state (high elastic modulus state) at room temperature. , a retention layer consisting of a resin (P2) that can reversibly change to a rubber state (low elastic modulus state) at a higher temperature and a dye (D2) (
B) is supported on a substrate. The order of support on the substrate can be changed as appropriate depending on the laser incidence method.

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 (P) must exhibit high rubber elasticity and must not undergo flow deformation when irradiated with laser light, in other words, must have a high elastic recovery rate.From this point of view,
The resin P1 in the present invention (1) has a Tg of not more than room temperature, and (2) has an elastic modulus of 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~IOKg/
It is mm2. 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 elastic recovery rate over a certain length (
Apply an external force (tension) to the sample of 10
It is defined as the ratio of the amount of residual deformation (L' - L.) after the external force is released and fS to the amount of deformation (0.ILo) when stretched by %. That is, 1-(L'Lo)/0. IL.
A material having an xl00% of 80% or more, preferably 90% or more is used as the expansion layer. If it is less than that, the eraser cannot be completely erased even if the eraser is irradiated with the eraser light, and erased residue remains, which is not preferable. The volumetric expansion rate is I x 10-5/℃ or more,
Preferably it is I x 10-'/°C or more. The volumetric expansion rate is an important factor for efficient bump formation. If it is less than this, it is not possible to form a sufficiently large bump, 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.

If Tg is above room temperature, the bump may shrink due to erase light or T
Since it is fixed at g, erased residue remains, which is not preferable.

The expansion layer resin P1 used in the present invention is an elastic crosslinked body containing urethane or urea bonds as an essential component and satisfying the above requirements.

The elastic crosslinked body having such a urethane or urea bond as an essential component has the following embodiments.

It is obtained by reacting a precursor having a hydroxyl group at the terminal with a polyfunctional incyanate. Examples of the precursor having a hydroxyl group at the terminal include those whose main chain is a linear aliphatic polyether or aliphatic polyester, and those whose main chain is composed of a diene oligomer such as polybutadiene, polyisoprene, or polychloroprene. Then, these soft segments having hydroxyl groups at both ends are linked by reacting with a polyfunctional incyanate to obtain an elastic crosslinked product.

As the linear aliphatic polyether, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, copolymers thereof, etc. are preferably used. In addition, linear aliphatic polyesters include diols such as ethylene glycol, tetramethylene glycol, diethylene glycol, adipic acid, sebacic acid,
Polymers and copolymers with dicarboxylic acids such as maleic acid and fumaric acid are preferably used. Further, poly(ε-cabrolactone) is also preferably used. Examples of diene oligomers include butadiene, isoprene, and
Polymers of chloroprene and copolymers thereof are preferably used. The molecular weight of these polymers is relatively small <
100 to 5,000, preferably 200 to 3,000 are preferably used. Moreover, these polymers may be linked by urethane bonds using diisocyanate. As the incyanate suitably used, 1.4
-phenylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
4.4'-oxydiphenylene diisocyanate, 1,
Aromatic, alicyclic, and aliphatic diisocyanates such as 4-cyclohexane diisocyanate, tetramethylene diisocyanate, and octamethylene diisocyanate are preferably used.

In addition to the above-mentioned diisocyanates, as the polyfunctional isocyanate used in the crosslinking reaction, polyfunctional isocyanates such as the 123 adduct of trimethylolpropane/tolylene diisocyanate and polymethylene polyphenylene polyisocyanate shown below are also preferred. used.

(2) Crosslinking is carried out by reacting a precursor having an isocyanate terminal with a polyfunctional alcohol or a polyfunctional amine. The precursor having an isocyanate terminal can be obtained by reacting the soft segment having hydroxyl groups at both ends with an excess of the isocyanate.

In addition, polyfunctional alcohols include ethylene glycol,
Diethylene glycol, glycerin, trimethylolpropane, pentaerythritol and the like are preferably used. In addition, polyfunctional amines include diethylenetriamine,
Aliphatic, alicyclic, and aromatic amines such as ditriethylenetetramine, methylene dianiline, oxydianiline, and methylene bis-orthochloroaniline are used.

The resin (P2) used in the present invention has the role of fixing the bumps generated by thermal expansion during recording and allowing them to be released during erasing. Therefore, in order to perform both functions efficiently, it is necessary to Therefore, the resin needs to be in a glass state (high elastic modulus state), and at higher temperatures it becomes a rubber state (low elastic modulus state).Suitable resins include polymethyl methacrylate resin, polycarbonate resin, and polyamide resin. Examples include thermoplastic resins and partially crosslinked products thereof, thermosetting resins (crosslinked resins) such as epoxy resins, phenol resins, melamine resins, and epoxy (meth)acrylate resins.Also, epoxy resins, epoxy (meth)acrylates, etc. Resin, novolac (
For meth)acrylate resins, etc., they 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 resins and novolac (meth)acrylate resins are used to increase reactivity, control Tg, improve the mechanical properties of the film, and improve compatibility with dyes. Multifunctional (
Meta>acrylate [(meth)acrylate refers to acrylate and methacrylate] may be used in combination. Suitably used polyfunctional (meth)acrylate, tetramethylene di(meth)acrylate, tetramethylene(
Examples thereof include meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

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. In addition, since reading utilizes light reflection from the surface of the medium, the holding layer is required to have a high light reflectance. From this point of view,
Preferably, dye D2 has 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 vorimethine dyes, pyrylium dyes, thiapyrylium dyes, squalillium dyes, croconium dyes, azulenium dyes, cyanine dyes, and futacyanine dyes such as futacyanine and naphthalocyanine. Dyes; dithiol metal complexes such as dithiol nickel complexes; naphthoquinone and anthraquinone dyes; triphenylmethane 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 ratio of dye/resin is generally 0.05 to 0.4, preferably 1,θ to 0.3, although it depends on the absorbance of the dye and the film thickness. The thickness of the expansion layer is generally 0.1 to 10 μm, preferably 0.5 to 5.0 μm, and the thickness of the retention layer is 0.1 to 3.0 μm, preferably 0.3 to 2 μm. .0μm
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; getones 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, acetonitrile and mixtures thereof.

The expansion layer is cured by heating at a predetermined temperature for a predetermined time after coating. The heating temperature is generally 5
A temperature range of 0 to 200°C, preferably 70 to 150°C is used. If it is more than that, it is not preferable because it causes deterioration of the substrate and the dye. Moreover, if it is less than that, curing will not proceed sufficiently, which is not preferable. Curing time is generally 5 minutes ~
It is carried out for 10 hours, preferably in the range of 10 minutes to 5 hours.

On the other hand, as a method for curing the holding layer, 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 in the case of (meth)acrylate, it is generally azobisisobutyronitrile (AIBN), penzoyl peroxide (BPO), etc.
, cumene hydroperoxide, dicumyl peroxide,
Examples include radical initiators such as tert-butyl hydroperoxide and lauroyl peroxide. The heating temperature is 5 for one shell.
A temperature of 0 to 150°C, preferably 70 to 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 ketone; diketone 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. If necessary, it is also possible to use a promoter such as an amine promoter. In addition, in the case of epoxy resin,
A photonic cationic polymerization initiator such as ASF6- and PF6- such as diphenylsulfonium and diphenyliodonium salts can also be used. As the ultraviolet light to be used, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, etc. are suitably used. The amount of initiator used is 0. 1 to 10 phr, preferably 0.5 to 5 phr is 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 dye laser, a ruby 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 expansion layer dye D1 exhibits absorption in the vicinity of 840 nm and the retention layer dye D2 exhibits absorption in the vicinity of 780 nm will be described.

Recording is performed by irradiating a laser beam of 840 nm. At this time, the expansion layer mainly absorbs light to form bumps. For reproduction, either a 780 nm or 840 nm laser may be used, but a laser beam having a wavelength with a high reflectance is preferable. Then, reproduction is performed by irradiating a laser beam with a weak wavelength and reading the difference in reflectance between the recorded area and the unrecorded area. Erase is 780
This is done by irradiating with nm laser light.

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.

Examples Example 1 Chloroprene oligomer (F
H-050. Coronate L (Nippon Urethane Kogyo), a polyfunctional incyanate, was added to Denka) to make the isocyanate concentration equimolar to the hydroxyl group concentration, and then 10 phr of soluble vanadyl phthalocyanine (NIR-12) was added to the total solid content. , Yamamoto Kasei). Then, chloroform was added as a solvent to obtain a uniform expanded layer coating solution. The resulting coating solution was applied onto a glass substrate and dried, followed by heat treatment at 120° C. for 1 hour to effect urethane crosslinking, thereby creating an expanded layer on the substrate. The thickness of the expansion layer was 3 to 4 μm. Next, a toluene solution of polymethyl methacrylate containing 10 phr of silicone naphthalocyanine having the structure shown below as a dye for the retention layer was coated and dried on the expansion layer to produce a recording medium comprising the expansion layer/retention layer. The thickness of the holding layer was approximately 1 μm.

R=Si(C6H,) Recording was performed by irradiating the obtained medium with a semiconductor laser beam of 830 nm focused to a diameter of about 1 μm.

Writing was performed by irradiating a laser beam of 10 mW at IMHZ at a linear velocity of 3 m/sec. As a result, it was confirmed that a clear bump (dome-shaped protrusion) was formed. Then, this record was set at 1m at 780nm.
When read with a W semiconductor laser beam, a C/'N of 50 dB was obtained. Next, it was confirmed that the recording was erased when 7 mW of 780 nm semiconductor laser' light was not irradiated.

Example 2 Millione MR- instead of Coronate L in Example 1
100 (Nippon Urethane Kogyo) as the polyfunctional incyanate, and in the same manner as in Example 1, a recording medium consisting of an expansion layer/retaining layer was prepared.

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

Example 3 Nipporan 4043, a polyester elastomer with hydroxyl groups at both ends, was used instead of PH-050 in Example 1.
(Nippon Urethane Kogyo Co., Ltd.), and in the same manner as in Example 1, a recording medium consisting of an expansion layer/retaining layer was prepared.

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

Example 4 Soluble vanadyl phthalocyanine (NIRi2) of Example 3
) instead of IR-820, a vorimethine dye.
(Nippon Kayaku) as the dye for the expansion layer, and in the same manner as in Example 3, a recording medium consisting of an expansion layer/retention layer was prepared.

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

Example 5 Soluble vanadyl phthalocyanine (NIR-1) of Example 1
21, IR-820, a polymethine dye
(Nippon Kayaku) was used as the dye for the expansion layer, and in the same manner as in Example 1, a recording medium consisting of an expansion layer/retention layer was prepared.

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

Example 6 1/2 mol of incyanate methylene bis-orthocroaniline <MBCA) was added as a polyfunctional amine cross-linking agent to Coronae 4076 (Nippon Urethane Kogyo), an elastic prebolimer of isocyanate at both terminals. Next, 10 phr of IR-820 based on the total solid content as a dye for the expansion layer and chloroform as a solvent were added to obtain a uniform expansion layer coating solution. The resulting coating solution was applied onto a glass substrate, dried, and then treated at 120° C. for 2 hours to effect crosslinking through urea bonds. The thickness of the expansion layer is 3 to 4
It was set as μm.

Then, 10 phr of dye for the retention layer is applied onto the expansion layer.
Apply a methyl ethyl ketone solution of polymethyl methacrylate containing HITC (indoline cyanine dye).
This was dried to produce a recording medium consisting of an expansion layer/retaining layer.

The thickness of the holding layer was approximately 1 μm.

When writing was performed by irradiating the obtained medium with a semiconductor laser beam of 830 nm, clear bumps were formed, and it was confirmed that writing could be performed. And this record is 8
Reproduction was possible with 30 nm semiconductor laser light. When the film was then irradiated with 780 nm semiconductor laser light, it was confirmed that the recording was erased.

Example 7 A crosslinked urethane expanded layer was prepared in the same manner as in Example 6 except that pentaerythritol (PET), a polyhydric alcohol, was used as a crosslinker instead of the amine crosslinker in Example 6. Next, 1 is applied as a dye for the retention layer on this expansion layer.
0 phr HITC and 2 phr Ir as photoinitiator
Eboxy acrylate (V
R-60, Showa Kobunshi> was coated from a methyl ethyl getone solution to a film thickness of about 1 μm.

Next, UV curing was performed by irradiation with high-pressure mercury lamp light of 80 W/cm to produce a recording medium consisting of an expansion layer/retaining layer.

As a result of writing and reading with 830 nm semiconductor laser light and erasing with 780 nm semiconductor laser light, it was confirmed that writing, reading, and erasing were possible.

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

table 1 Physical property data of expansion layer resin

Claims (1)

[Claims] A resin (P_1) exhibiting rubber elasticity at least at room temperature and a pigment (
D_1), a resin (P_2) that can reversibly change from a glass state (high elastic modulus state) to a rubber state (low elastic modulus state) at room temperature, and a pigment (D_1); In an optical recording medium formed by supporting and laminating a holding layer (B) consisting of D_2) on a substrate, the resin P_1 has (1) a Tg of not more than room temperature and (2) an elastic modulus of 0 at room temperature. .001 to 100Kg/m
m^2, (3) an elastic recovery rate of 80% or more, and (4) a volumetric expansion coefficient of 1 x 10^-^5/°C or more. Possible optical recording media.