JP3004288B2 - Erasable optical recording medium and manufacturing method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an erasable optical recording medium utilizing shape change upon heating and a method for manufacturing the same. More specifically, the present invention relates to an optical recording medium and a method for producing the same, wherein a selected polymer that can be cured with actinic rays such as ultraviolet rays is used for a part of a recording layer composed of an organic polymer / dye. .

Background Art and Problems There have been proposed many optical recording media using organic dyes (for example, Japanese Patent Application Laid-Open No. 61-163891, 61-268487, 62-5819).
1, 62-122787, 62-39286 and 63-72594). Also, many optical recording media using a combination of an organic dye and an organic polymer have been proposed (see, for example, JP-A-62-90291, 63-62794 and 63-191691). However, the principle of recording in these recording media is that the irreversible shape change of the recording medium due to heat generated by the dye absorbing light (mostly laser light) (in many cases,
Pit formation), it was extremely difficult or impossible to erase the record. That is, in the case of a dye-only medium, recording is performed by forming pits accompanied by vaporization and separation of the dye, so that it is impossible to erase pits once formed. Further, in the case of a mixed system of a polymer and a dye, since recording is performed by forming pits due to the flow deformation of the polymer, it has been difficult to efficiently erase once formed recording pits. Further, other prior arts (JP-A-60-69846, 63-136337, 63-136338 and
JP-A-164042), a recordable / erasable medium comprising an expansion layer which is heated and expanded by irradiation with a laser beam to form a dome-shaped projection (bump), and a holding layer which retains this shape. Has been proposed. When recording on this medium, laser light irradiation is performed at the absorption wavelength (λ ₁ ) of the dye previously mixed in the expansion layer to form a bump on the expansion layer. Then, the holding layer is also deformed according to this shape. However, when the laser beam is irradiated, the holding layer is rapidly cooled and solidified, and this shape can be maintained. Next, when erasing the recorded bumps, the holding layer is irradiated with a laser beam at the absorption wavelength (λ ₂ ) of the dye previously mixed in the holding layer, and the holding layer is heated to a temperature equal to or higher than its Tg. If the heating is not performed, it becomes difficult to maintain the bump shape due to the restoring force of the expansion layer.

In the case of this two-layered medium composed of a dye / polymer, recording can be performed efficiently, in other words, in order to make the bumps as high as possible, the Tg of the polymer in the holding layer should be as high as possible. Then, the holding layer is in a glassy state with a high degree of thermal expansion. On the other hand, in order to perform erasing efficiently, it is better that the Tg of the holding layer is low. Moreover, in order to obtain an erasable medium, it is not preferable that the holding layer undergoes irreversible deformation by laser beam irradiation, that is, flow deformation of the polymer. From such a viewpoint, a three-dimensional crosslinked polymer is preferable as the resin for the holding layer. However, in order to laminate a crosslinked polymer, a curing process after coating is generally required, and industrially, it is necessary to perform this curing in a short time. This is an essential requirement for continuous coating on a film substrate.

The present inventors have conducted intensive studies to obtain a resin for a holding layer that satisfies these contradictory requirements, and as a result, a polymer having a specific structure has desired thermal characteristics and is irradiated with ultraviolet light in a short time. The present invention was found to cure and reached the present invention.

SUMMARY OF THE INVENTION The optical recording medium of the present invention comprises an expansion layer (A) comprising a resin (P ₁ ) and a dye (D ₁ ) exhibiting rubber elasticity at least at room temperature, and a glassy state (high elastic state) at room temperature. A supporting layer (B) made of a resin (P ₂ ) and a dye (D ₂ ) which can be reversibly changed to a rubber state at a higher temperature is supported by a substrate. Note that the relationship between the expansion layer (A) and the holding layer (B) with respect to the substrate can be appropriately changed according to the laser incident direction.

The expansion layer (A) needs to expand effectively when heated by laser irradiation in order to enhance the recording characteristics. In order to efficiently erase the bumps generated by recording and return to the original state, high rubber elasticity is required at the time of erasing. Therefore, it is necessary that the resin (P ₁ ) has high rubber elasticity and does not undergo flow deformation by laser beam irradiation. Suitable resins include natural rubber; styrene-butadiene rubber, butadiene rubber,
Isoprene rubber, nitrile rubber, chloroprene rubber, butyl rubber, ethylene-propylene rubber, urethane rubber,
Synthetic rubbers such as silicone rubber; styrene-based, olefin-based, urethane-based thermoplastic elastomers; and amine-crosslinked, isocyanate-crosslinked, and ultraviolet-crosslinkable elastomers.

Dye D ₁ and D ₂ absorbs efficiently the laser beam in each recording process and erasing process serves to convert into heat. Therefore, a dye having an absorption that matches the oscillation wavelength range of the recording laser and the erasing laser is selected. Then, it is preferable that the absorption intensities in the respective oscillation wavelength ranges do not excessively overlap so that both laser beams can be selectively absorbed. Further, a dye having an absorption peak in the near infrared is preferable since a laser currently used in the field of optical recording is a semiconductor laser. In addition, reading uses the light reflection of the medium, so that the light reflectance of the holding layer is required to be high. In this respect, the dye D ₂ preferably has a high reflectivity. Of course, for efficient absorption properties, the dyes should be selected to be uniformly dispersed in each resin. Suitable dyes D ₁ and D _2, cyanine dyes, pyrylium dyes, thiapyrylium dyes, squarylium dyes, croconium dyes, polymethine dyes such as azulenium dyes; phthalocyanine pigments such as phthalocyanine and naphthalocyanine; Dithiol metal medium; naphthoquinone, anthraquinone dye; triphenylmethane dye; aminium;
And diimmonium dyes. A plurality of these dyes may be used as a mixture.

In the present invention, the resin (P ₂ ) used for the holding layer (B) fixes bumps generated by the thermal expansion of the expansion layer (A) by laser beam irradiation during recording, and releases the bumps during erasing. It is responsible for the function that allows. Therefore, in order to effectively perform both functions, the resin must be in a rubber state at a high temperature and a glass state at a normal temperature, that is, a resin having a high elasticity. That is,
At a high temperature, the elastic modulus is required to be low in order to form a bump with the thermal expansion of the expansion layer (A). At room temperature, a high tensile modulus is required to fix the bump against the contraction force of the expansion layer (A), and it is required to be 80 kg / mm ² or more, preferably 100 kg / mm ² or more. Below this, the shape of the bump cannot be sufficiently maintained, and the recording characteristics and the recording stability deteriorate. Further, for efficient recording and erasing, the temperature at which the glass state changes to the rubber state (glass transition temperature Tg) is also important. In that sense,
The transition temperature is 60 to 150 ° C, preferably 70 to 120 ° C. Below this, the height of the formed bump is low, which is not preferable in recording characteristics, and is also not preferable in recording stability. Above this, unerased residues remain at the time of erasing, which is not preferable. As the resin P ₂ for use in the present invention is an epoxy (meth) acrylate, epoxy novolac (meth) acrylate. These resins are
A coating film having a desired Tg can be obtained by crosslinking with actinic rays, heat, or the like.

Epoxy (meth) acrylate has the following general formula: In the formula, Y is an alkylene group having 1 to 5 carbon atoms, R is a (meth) acryloyl group, and n is an integer of 1 to 20. In the formula, Y is a methylene group, 2,2-
Epoxy acrylate, which is a propylene group, is preferable because it has a high Tg and can improve the recording characteristics without causing a decrease in the erasing characteristics. On the other hand, epoxy novolac acrylate has the following general formula "Where R is (R 'is a methyl group or a hydrogen atom), and m is a carbon number of 1-20.
And X is a hydrogen atom or a methyl group. "
It is a compound shown by these. In addition, acrylate is preferred because it has higher reactivity than methacrylate.

In the present invention, these compounds may be used alone or as a mixture of two or more. Further, other polyfunctional acrylates may be used in combination within a range of 30% by weight or less without impairing the purpose of the present invention. This is effective in increasing the reactivity, controlling the Tg, increasing the mechanical properties of the film, and increasing the compatibility with the dye. Suitable polyfunctional (meth) acrylates include ethylene di (meth) acrylate, tetramethylene di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, and dipentaerythritol hexa (meth) acrylate. A) acrylates and polyfunctional urethane acrylates.

These resins used in the present invention are applied and cured on a substrate after being mixed with a dye. The substrate to be used is not particularly limited, but a disk-shaped substrate such as polycarbonate, polymethyl methacrylate, or glass, or a film-shaped substrate such as polyester is generally used. Dye /
Although the ratio of the resin depends on the absorbance and the film thickness of the dye, it is generally 0.05 to 0.4 (wt / wt), preferably 0.1 to 0.3 (wt / w).
t). 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 holding layer is 0.1 to 10 μm.
To 3.0 μm, preferably 0.3 to 2.0 μm. The coating method is not particularly limited, but a spin coating method, a casting method, a bar coating method, a doctor knife method, a gravure coating method, or the like is used. Suitable solvents used at that time include
Aliphatic hydrocarbons such as hexane, heptane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; alcohols such as methanol, ethanol and butanol; haloalkanes such as chloroform and methylene chloride; ethyl acetate and butyl acetate Esters; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; glymes such as ethylene glycol monomethyl ether and ethylene glycol monobutyl ether; ethers such as tetrahydrofuran and diquine; nitromethane; acetonitrile; and mixtures thereof.

As the curing method, a thermal curing method, an ultraviolet curing method, and an electron beam irradiation method are used. In the case of heat curing, three-dimensional crosslinking is usually performed by heating in the presence of a radical initiator. The initiator is not particularly limited, but is generally azobisisobutyronitroli (AIBN), benzoyl peroxide (BPO),
Cumene hydroperoxide, tert-butyl hydroperoxide, lauroyl peroxide and the like. The heating temperature is generally 50 to 150 ° C, preferably 70 to 120 ° C. Above that, the substrate and the dye deteriorate, which is not preferable. The curing time is generally from 5 minutes to 10 hours, preferably 10 minutes.
It is performed in a range of minutes to 5 hours.

On the other hand, in the case of the ultraviolet curing method, it is performed by irradiating ultraviolet rays in the presence of a photoinitiator. Examples of the photoinitiator include benzophenone initiators such as benzophenone and Michler's ketone; diketone initiators such as benzyl and phenylmethoxydiketone; benzoin ethyl ether;
Benzoin based initiators such as benzyl dimethyl ketal;
Thioxanthone-based initiators such as 2,4-diethylthioxanthone and quinone-based initiators such as 2-methylanthraquinone and camphorquinone are preferably used. If necessary, an accelerator such as an amine accelerator may be used in combination. As the ultraviolet rays to be used, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, and the like are suitably used. The power of the light source is 1 mW / cm ^{2 to} 1 kW / cm ² . The irradiation time depends on the power of the light source and the photoreaction speed, but is carried out for 1 second to 1 hour, preferably for 10 seconds to 10 minutes.

The recording method, reproduction and erasure of the thus obtained two-layer medium are performed by irradiating two kinds of laser beams. As a laser used at this time, a helium neon laser, an argon laser, a semiconductor laser, or the like is used, and a small and inexpensive semiconductor laser is more preferable. Hereinafter, the expanding layer dye D ₁ shows absorption around 840 nm, and the retaining layer dye D ₂ has a wavelength of 780 nm.
A description will be given by taking a medium exhibiting absorption in the vicinity as an example. The record is
Irradiation with 840 nm laser light is performed. At this time, the expansion layer mainly absorbs light to form a bump.
Reproduction is performed by irradiating a weak laser beam of 840 nm and reading a difference in reflectance between a recorded portion and an unrecorded portion.
Erasing is performed by irradiating 780 nm laser light. Generally, the recording is 5-30 mW, preferably 7-20 mW.
Irradiate for 5 to 0.1 microseconds with a power of mW. Reproduction is 0.5-3mW,
Preferably, irradiation is performed at a power of 0.7 to 2.0 mW for 5 to 0.1 μsec. Erasing is performed at a power of 1 to 20 mW, preferably 3 to 12 mW.
Irradiate for 0.1-20 seconds.

According to the present invention, excellent recording / erasing characteristics can be obtained in a recording medium whose fundamental principle is to read the change in reflectance due to the formation and disappearance of bumps. At the same time, since the film can be formed at a low temperature and at a high speed, there is an industrial advantage that coating and curing can be performed without deteriorating the substrate and the dye used, and the medium cost is reduced.

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

Example 1 BP obtained by adding 1 phr of benzyl methoxy ketal (BDMK) and 1 phr of azobisisobutyronitrile (AIBN) to a bisphenol A type epoxy acrylate resin (hereinafter abbreviated as BP-1) represented by the following structural formula. -1 chloroform solution on glass plate by bar coating method
It was applied to 100 μm, irradiated with ultraviolet light, and then cured by heating in an oven at 80 ° C. for 1 hour. The thin film was peeled from the glass plate, and the tensile modulus was measured with an Instron 4302 (Inston Ron Co.). At room temperature, 176 kg / mm ² , 120
At 0 ° C, it was 0.5 kg / mm ² . The glass transition point is 72 ℃
Met.

NK ester obtained by adding 10 phr of a polymethine dye IR820 represented by the following structural formula and 2 phr of Irgacure 907 (Ciba Geigy) to NK ester U-122A (Shin Nakamura Chemical Industry Co., Ltd.) which is a urethane acrylate A U-122A methyl ethyl ketone (MEK) solution was applied on a glass substrate to a thickness of 3 μm by a bar coating method, and irradiated with ultraviolet light to form an expansion layer. A chloroform solution of BP-1 to which BR-1 was added with 10 phr of a cyanine dye NK-125 having the following structure (Nippon Kosoku Dye Co., Ltd.) and 1 phr of BDMK was cast on the expanded layer, dried, and nitrogen atmosphere was added. Irradiation with ultraviolet light was performed below to form a 0.8 μm holding layer.

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

Example 2 An epoxy acrylate represented by the following structural formula (hereinafter BP)
BP-2 MEK solution containing 1 phr of benzyldimethoxyketal (BDMK) and 1 phr of azobisisobutyronitrile (AIBN) applied to a glass plate to a thickness of 100 μm by a bar coating method. Then, the mixture was irradiated with ultraviolet light and heated in an oven at 80 ° C. for 1 hour to be cured. Peeling the thin film from the glass plate at normal temperature was measured by a tensile modulus Instron 4302 (Instron Co.) was 149 kg / mm ^2, at 120 ℃ 3.2Kg / mm ^2. The glass transition point was 70 ° C.

MEK of NK ester U-122A obtained by adding 10 phr of IR820 and 2 phr of Irgacure 907 (Ciba Geigy) to NK ester U-122A (Shin-Nakamura Chemical Co., Ltd.)
The solution was applied on a glass substrate by a bar coating method to a thickness of 3 μm.
And irradiating it with ultraviolet light to form an expansion layer. 10 phr NK-125 and 1 phr BDMK for BR-2
The MEK solution of BP-2 to which was added was cast on the expansion layer, dried, and irradiated with ultraviolet light under a nitrogen atmosphere to form a holding layer. When this two-layer medium was irradiated with laser light having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, formation of a bump having a diameter of 1 μm was recognized. When the laser beam having a wavelength of 780 nm and 7 mW was defocused and irradiated to the bump for 10 μs, the bump disappeared within the range of microscopic observation.

Example 3 Bisphenol F type epoxy acrylate of the following structural formula (hereinafter abbreviated as BP-3) was added with 1 phr of benzyldimethoxy ketal (BDMK) and 1 phr of azobisisobutyronitrile (AIBN). The chloroform solution was applied to a thickness of 100 μm on a glass plate by a bar coating method, irradiated with ultraviolet light, and cured by heating in an oven at 80 ° C. for 1 hour. The thin film was peeled off from the glass plate, and the tensile modulus was measured by Instron 4302 (Instron) to be 102 kg / mm ² at room temperature and 3.2 kg / mm ² at 120 ° C. The glass transition point was 78 ° C.

MEK of NK ester U-122A obtained by adding 10 phr of IR820 and 2 phr of Irgacure 907 (Ciba Geigy) to NK ester U-122A (Shin-Nakamura Chemical Co., Ltd.)
The solution was applied on a glass substrate by a bar coating method to a thickness of 3 μm.
And irradiating it with ultraviolet light to form an expansion layer. 10 phr NK-125 and 1 phr BDMK for BR-3
A chloroform solution of BP-3 to which was added was cast on the expansion layer, dried, and irradiated with ultraviolet light under a nitrogen atmosphere to form a holding layer. Wavelength 840nm, 10mW, pulse width 5μ
When a laser beam was irradiated for 2 seconds, formation of a bump having a diameter of 1 μm was recognized. When the laser beam having a wavelength of 780 nm and 7 mW was defocused and irradiated to the bump for 10 μs, the bump disappeared within the range of microscopic observation.

Example 4 A 100 μm film was prepared in the same manner as in Example 1 by using VR77 (Showa Kogaku Co., Ltd.) instead of BP-1 in Example 1, and the tensile modulus was 140 kg / mm ² and the glass transition was The point was 71 ° C. Further, in the same manner as in Example 1, a two-layer medium composed of the expansion layer / holding layer was formed. When this two-layer medium was irradiated with laser light having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, formation of a bump having a diameter of 1 μm was recognized. When the laser beam having a wavelength of 780 nm and 7 mW was defocused and irradiated to the bump for 10 μs, the bump disappeared within the range of microscopic observation.

Example 5 In the same manner as in Example 1 except that VR90 (Showa Kogaku Co., Ltd.) was used in place of BP-1 in Example 1, a two-layer medium composed of an expansion layer and a holding layer was formed. The wavelength of 840 nm, 1
When a laser beam of 0 mW and a pulse width of 5 μs was irradiated, the formation of a bump having a diameter of 1 μm was recognized. When the laser beam having a wavelength of 780 nm and 7 mW was defocused and irradiated to the bump for 10 μs, the bump disappeared within the range of microscopic observation.

Example 6 An epoxy novolac acrylate (hereinafter abbreviated as BP-4) having the following structure was used in place of BP-1 in Example 1,
When a film of m was prepared in the same manner as in Example 1, the tensile elastic modulus was 210 kg / mm ² and the glass transition point was 115 ° C.
Further, in the same manner as in Example 1, a two-layer medium composed of the expansion layer / holding layer was formed. When this two-layer medium was irradiated with laser light having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, formation of a bump having a diameter of 1 μm was recognized. Wavelength 780 nm, 7
When the laser beam of mW was defocused and irradiated for 10 μs, the bumps disappeared within the range of microscopic observation.

Example 7 In the same manner as in Example 1, a two-layer medium composed of an expansion layer and a holding layer was formed using a naphthalocyanine dye having the following structure in place of NK125 of Example 1.

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

Example 8 A chloroprene FHO50 having a hydroxyl group at a terminal (Electrochemical Industry Co., Ltd.) and coronate L, which is a polyfunctional isocyanate, were mixed so that the amount of hydroxyl group and the amount of isocyanate became equal, and 10 phr of IRD1001 (Yamamoto Kasei Co., Ltd.), and applied to a thickness of 3 μm by a bar coating method.
An expansion layer was formed by heating and curing at 1 ° C. for 1 hour. A chloroform solution of BP-1 to which BR-1 was added with 10 phr of NK-125 and 1 phr of BDMK was cast on the expansion layer,
It was dried and irradiated with ultraviolet light under a nitrogen atmosphere to form a 0.8 μm holding layer. When this two-layer medium was irradiated with laser light having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, formation of a bump having a diameter of 1 μm was recognized. Wavelength 780nm, 7mW
When defocused and irradiated for 10 microseconds,
The bump disappeared within the scope of microscopic observation.

Example 9 ECHO-302 (Echo Range and Laboratory) was used in place of BP-4 of Example 6 to form a two-layer medium composed of an expansion layer and a holding layer in the same manner as in Example 1. This 2
When the layer medium was irradiated with laser light having a wavelength of 840 nm, 10 mW, and a pulse width of 5 μs, formation of a bump having a diameter of 1 μm was recognized. When the laser beam having a wavelength of 780 nm and 7 mW was defocused and irradiated to the bump for 10 μs, the bump 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 fundamental principle is to read the change in reflectance due to the formation and disappearance of bumps. At the same time, since the film can be formed at a low temperature and at a high speed, coating and effects can be performed without deteriorating the substrate and the dye used, and there is an industrial advantage that the medium cost is reduced.

Continuation of front page (72) Inventor Kaoru Iwata 4-2-2 Asahigaoka, Hino-shi, Tokyo Teijin Limited Tokyo Research Center (56) References JP-A-63-136337 (JP, A) JP-A-2 -189738 (JP, A) JP-A-60-69846 (JP, A) JP-A-63-164042 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (2)

(57) [Claims] 1. A resin exhibiting rubber elasticity at least at room temperature (P ₁ )
The dye (D ₁₎ consisting of an expansion layer (A), a glass state (high elastic state) at room temperature, the resin capable of reversibly changed to the rubber state at higher temperatures (P ₂₎ and dye (D ₂ ) and the holding layer (B) and the optical recording medium comprising supporting the substrate as a recording layer consisting of the transition temperature of the resin P ₂ from (a) a glass state to a rubber state 60 to 150
(B) an elasticity at room temperature of 80 kg / mm ² or more, which is mainly composed of a cured product of epoxy (meth) acrylate and / or epoxy novolak (meth) acrylate. Optical recording medium. 2. The method according to claim 1, wherein the retaining layer is cured by applying a mixture containing an epoxy (meth) acrylate and / or an epoxy novolak (meth) acrylate and a dye, and then irradiating the mixture with an actinic ray. A method for producing an erasable optical recording medium, characterized by being formed by: