JPH04294190A - Record medium and method for erasing record - Google Patents

Abstract

PURPOSE:To make erasing speed fast in a record medium or a recording method utilizing phase change of a record layer and change of crystal state so as to realize recording and erasure having high reliability and no erasure miss. CONSTITUTION:On a support body 1, a first photothermal converting layer 2 which absorbs irradiation light to convert into heat, a recording layer 3 consisting of a crystal organic thin film whose crystal state changes reversibly with heat, and a second photothermal converting layer 4 which absorbs the irradiation light to convert into heat are layered in the above-mentioned order. Since the photothermal converting layers 2 and 4 are provided on both sides of the recording layer 3, heat accumulating effect for the recording layer 3 becomes higher, and records can be erased assuredly without causing erasure miss by irradiating erasure light for a short time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat mode recording medium for recording and erasing information using heat applied by light irradiation, and a recording erasing method.

0002

2. Description of the Related Art In recent years, so-called heat mode recording systems have been put into practical use, in which information is applied in the form of thermal energy and recorded as changes in the shape or physical properties of a recording material. Such heat mode recording media include Te, Bi
, Se, Tb, In, etc., or polymethine dyes such as cyanine, macrocyclic azaannulene dyes such as phthalocyanine, naphthalocyanine, and porphyrin, naphthoquinone, and anthraquinone dyes. Recording media using organic dyes such as dyes and dithiol metal complex dyes are known. When thermal energy is applied to these recording media, such as by irradiation with focused laser light, the recording layer in the irradiated area melts or evaporates, forming holes (pits) and recording information. However, these recording media do not have the reversibility of erasing recorded information and recording new information again.

With the development of read-only, write-once type heat mode optical recording media as described above, the need for reversible recording media that can be recorded, read, and erased is increasing.

[0004] As such a reversible recording medium, for example, G
There are magneto-optical recording media that use alloy thin films made of rare earth metals such as d, Tb, and Dy and transition metals such as Fe, Ni, and Co. This uses a combination of heating by laser beam irradiation and an externally applied magnetic field to record, and reproduces data by utilizing the difference in the rotational direction of the light vibration plane depending on the direction of magnetization. Furthermore, information is erased by heating with a laser and by applying an external magnetic field in the opposite direction to that used during recording. However, this magneto-optical recording medium has drawbacks such as insufficient sensitivity during reproduction and a poor S/N ratio, and problems such as deterioration of recording sensitivity and recording stability due to effects such as oxidation. There is.

[0005] Also, as reversible recording media, Ge, Te,
There is a method that utilizes the crystal-amorphous phase transition of a recording layer made of a thin film of an inorganic material mainly composed of elements such as Se, Sb, In, and Sn. This recording medium has the advantage of being able to record and erase information in heat mode using only laser light irradiation, but there are issues with the contrast between the recorded and non-recorded areas, the lack of recording stability, and the stability of the material of the recording layer. It has drawbacks such as problems.

[0006]

As described above, conventional recording media and recording methods still have various problems such as recording sensitivity, erasing speed, recording stability, and recording contrast. In particular, for recording media or recording methods that utilize phase transitions or changes in the crystalline state of the recording layer, it is desired that the erasing speed be increased and that highly reliable recording and erasing can be performed without leaving any unerased data during erasing. There is.

From this point of view, the present invention provides a recording medium and a recording erasing method in which recording is performed by changing the crystalline state or phase change of the recording layer, and erasing of recording is ensured.

[0008]

[Means for Solving the Problems] For the above-mentioned purposes, the present inventors investigated recording and erasing information on a recording layer whose crystalline state reversibly changes due to heat accompanying light irradiation.
We have discovered that the above objectives can be achieved by appropriately combining the recording layer and photothermal conversion layer that make up the recording medium, and by appropriately selecting these combinations and the conditions of the light beam during recording and erasing. .

That is, the recording medium of the present invention includes, on a support, at least a first light-to-heat conversion layer that absorbs irradiated light and converts it into heat, and a crystalline organic thin film that reversibly changes its crystalline state by heat. A recording layer consisting of a recording layer and a second photothermal conversion layer that absorbs irradiated light and converts it into heat are sequentially laminated.

[0010] The second photothermal conversion layer is preferably made of a layer having a relatively higher absorbance for light irradiated during erasing than for light irradiated during recording.

[0011] Furthermore, it is preferable that at least one of the two light-to-heat converting layers is comprised of a resin layer containing a light absorber.

Furthermore, the recording erasing method of the present invention erases the recording by irradiating the above-mentioned recording medium, which has been recorded by irradiating light, with light having a wavelength distribution different from that of the light irradiated during recording.

The recording layer of the recording medium used in the present invention performs recording and erasing by reversible changes in the crystal state and reversible changes between phases, and can be used repeatedly. This change in crystal state includes structural changes and phase transitions of crystals, such as reversible crystal transitions between crystal forms, reversible phase transitions between crystalline and amorphous forms, and crystalline changes. reversible change in the degree of chemical orientation, reversible change in the degree of molecular orientation, reversible change in crystal orientation, i.e. reversible change in crystal axis direction, reversible change in molecular orientation, or reversible change in crystal grain size. difference,
These include reversible changes in the size of crystal domains, which occur singly or in combination in the recording layer. These changes are due to the heat applied during recording or erasing,
Alternatively, the temperature of the recording layer is once raised by the heat generated by light irradiation, and the temperature of the recording layer increases through the melt phase or liquid crystal phase.
In cases where the state changes from a non-recorded state to a recorded state or from a recorded state to an erased state (same as a non-recorded state), when a transition between states occurs directly due to temperature rise without going through the melt phase or liquid crystal phase, There are cases where the transition occurs via an amorphous state.

[0014] Examples of the materials of the recording layer on which such recording and erasing are performed include the following. Phthalocyanine materials such as copper phthalocyanine and magnesium phthalocyanine are examples of materials that utilize the crystal-crystal and crystal-amorphous transitions of organic materials. Furthermore, those that utilize reversible changes in the crystalline state of organic thin film crystals include, for example, fatty acids or fatty acid derivatives, benzoic acid derivatives, and n-alkanes or their derivatives having a melting point of 50° C. or higher.

[0015] The fatty acid or fatty acid derivative as used in the present invention specifically refers to saturated or unsaturated mono- or dicarboxylic acids or their esters, amides, anilides, hydrazides, ureides, anhydrides, or ammonium salts or metal salts. Fatty acid salts mean. In this case, esters include esters with compounds having two or more hydroxy groups, such as mono-, di- or triglycerides. Further, these may be substituted with a halogen, a hydroxy group, an acyl group, an acyloxy group, or a substituted or unsubstituted aryl group. These saturated or unsaturated fatty acids may be linear or branched, and the unsaturated fatty acids may have one double bond or triple bond, or two or more. The number of carbon atoms in the hydrocarbon chain in these fatty acids is preferably 10 or more.

[0016] Specific examples of saturated fatty acids include, for example:
undecanoic acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid,
Examples of unsaturated fatty acids include nanodecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melisic acid. Examples of unsaturated fatty acids include oleic acid, elaidic acid, linoleic acid, sorbic acid, and stearolic acid. . Specific examples of esters include methyl esters, ethyl esters, hexyl esters, octyl esters, decyl esters, dodecyl esters, tetradecyl esters, stearyl esters, eicosyl esters, and docosyl esters of these fatty acids. Further, examples of metal salts include metal salts of these fatty acids such as sodium, potassium, magnesium, calcium, nickel, cobalt, zinc, cadmium, and aluminum.

[0017] Furthermore, the benzoic acid derivatives referred to in the present invention include:
Specifically, benzoic acid represented by (I) to (IV) in the following general formula 1, and its esters, amides, anilides, etc. are included. In addition, salts such as optionally substituted hydrazides, ureidos, anhydrides, metal salts, and ammonium salts are included. In addition to the compound represented by the general formula (II), esters include esters of aliphatic hydrocarbon compounds with polyhydric alcohols or aromatic hydrocarbons having a plurality of hydroxy groups.

[0018]

embedded image Substituents for R1, R2, R3 and other benzoic acid derivatives in the general formula include, for example, hydrogen, an alkyl group,
An aryl group such as an alkoxy group, a phenyl group, a biphenyl group, a naphthyl group, an anthranyl group, and R1 is an aryl group such as an acyl group, an acyloxy group, a halogen, a nitro group, a hydroxy group, a cyano group, a carboxyl group, and esters thereof; Examples include a carbamoyl group which may be substituted, a sulfo group and its ester or alkyl group, a phenyl group, and an amino group which may be substituted with a substituted phenyl group. In addition, the above alkyl groups, alkoxy groups,
The aryl group may be substituted with the same substituent as R1. In addition, the alkyl group and alkoxy group may be linear or branched, and if they have two or more carbon atoms, they may contain one or more unsaturated bonds in the carbon chain. Good too. Furthermore, the n-alkane derivatives used in the present invention include compounds containing one or more double bonds or triple bonds in the carbon chain, compounds in which one or more hydrogen atoms are substituted with halogen atoms, and terminal It is a compound in which a benzene ring which may be substituted with an alkyl group or an alkoxy group is bonded to the carbon atom. Specifically, for example, tetracosane, pentacosane, hexacosane, heptacosane,
n- such as octacosane, nonacosane, triacontane, dotriacontane, tetratriacontane, hexatriacontane, octatriacontane, tetracontane, etc.
There are alkanes or mixtures containing these as main components, so-called paraffins and paraffin waxes. Further, as derivatives, 1-hexacocene, 1-heptacocene, 1-octacosene, 1-triacontene, 1-tetratriacontene, 1-hexatriacontene, 1-octatriacontene, 1-tetracontene, docosylbenzene, tetracontene, Cosylbenzene, hexacosylbenzene, octacosylbenzene, triacontylbenzene, tritriacontylbenzene, tetratriacontylbenzene, hexatriacontylbenzene, 1,18-dibromooctadecane, 1,20-dibrome Examples include eicosane and 1,22-dibromdocosane.

Basically, the recording medium of the present invention, as shown in FIG. The recording layer 3 is transparent and undergoes a reversible crystal state or phase change due to heat, and further has a second light-to-heat conversion layer 4 thereon. In FIG. 2, a protective layer 5 is further provided on these layers. The second photothermal conversion layer is a layer that absorbs a part of the irradiated light and converts it into heat, and mainly transmits the other light. Further, the first photothermal conversion layer is a layer that absorbs a part of the irradiated light and converts it into heat, and when performing reproduction using reflected light, it is a layer that mainly reflects other light, When a transmission layer is used for reproduction, the layer mainly reflects other light. Further, this layer has no large difference in the degree of light absorption for either recording light or erasing light, and serves as a photothermal conversion layer for both types of light.

It is preferable that the second light-to-heat conversion layer is formed of a layer having a relatively higher absorbance with respect to the light irradiated during erasing than with respect to the light irradiated during recording. In this case, the second photothermal conversion layer has small light absorption at the wavelength of the recording light and transmits most of the light, and has a large light absorption at the wavelength of the erasing light, absorbs a part of the erasing light, and generates heat. The remaining light is mainly transmitted. That is, it does not act as a photothermal conversion layer for recording light, but acts as a photothermal conversion layer for erasing light.

Recording is carried out by irradiating a small beam of light while blinking it according to the information. When light irradiation is performed, a portion of the light incident on the recording medium is absorbed by the second light-to-heat conversion layer and converted into heat. The light that has passed through the second photothermal conversion layer also passes through the recording layer, and is partially absorbed and converted into heat by the first photothermal conversion layer. When the first photothermal conversion layer reflects most of the other light, the reflected light enters the second photothermal conversion layer again, a portion of which is absorbed and converted into heat, and the remaining light is transmitted. The heat generated in the first and second photothermal conversion layers is transmitted to the recording layer located therebetween, and the temperature of the recording layer increases. At this time, when the recording temperature of the recording layer reaches a temperature higher than the temperature at which the crystal state changes, and then the light irradiation stops and the temperature decreases, a record is formed at that portion. For example, if this crystal state change occurs via the molten state, when the temperature of the part above the melting point cools and crystallizes, the crystal state differs from the initial crystal state (the state of the surrounding non-recording part). It solidifies into a state and becomes a record. Further, the recording does not need to change in the entire thickness direction of the recording layer, and may be formed in a portion of the layer to such an extent that it can be identified as a recording during reproduction. Erasing occurs when the crystalline state becomes the same as the surrounding crystalline state, but at this time, it is better to record data when only a part of the layer changes than when the entire thickness direction changes due to the surrounding crystalline state. This makes it easier for the regulatory power to operate from the source, making it easier to eliminate.

[0022] When using a recording medium in which the second photothermal conversion layer has a relatively higher absorbance for the light irradiated during erasing than for the light irradiated during recording, the first photothermal conversion layer in contact with the recording layer The recording light is absorbed by the photothermal conversion layer, and the heat generated here is transmitted to the recording layer to perform recording.
If the irradiation time is sufficiently short, only the portion of the recording layer close to the first photothermal conversion layer will be heated, recording will be formed only in this portion, and this will be more advantageous for erasing.

Recording is performed at a temperature higher than the recording temperature (for example, higher than the melting point)
It is not necessary to heat the recording layer with a uniform temperature distribution, and only a portion of the recording layer (for example, near the light-to-heat conversion layer) needs to be heated, so it is possible to perform the heating with light irradiation for a very short period of time. be able to. On the other hand, erasing occurs by being reheated to a phase transition temperature, liquid crystal temperature, rearrangement temperature, etc. lower than the recording temperature, and must be uniformly heated within a certain temperature range. These temperature ranges are from several degrees Celsius to several tens of degrees Celsius, and in order for the heat generated in the photothermal conversion layer by light irradiation to be conducted to the recording layer and the recorded area to fall within this range, the erasing light must be An irradiation time longer than the light irradiation time is required. In particular, in a structure in which the recording layer is in contact with one photothermal conversion layer, the temperature distribution is largely uneven because heat is transmitted only from one side, and it is necessary to irradiate for a longer time to achieve uniform heating. Since the recording medium of the present invention has photothermal conversion layers on both sides of the recording layer, a portion of the incident erasing light is absorbed by the second photothermal conversion layer, and a portion of the remaining light is absorbed by the first photothermal conversion layer. Absorbed. Furthermore, a portion of the light reflected there is absorbed again by the second photothermal conversion layer. Therefore, heat is transmitted from both photothermal conversion layers provided on both sides of the recording layer, making it easier to obtain a uniform temperature distribution, and erasing can be achieved with a shorter irradiation time than in the case where the photothermal conversion layer is provided on one side. The light absorption ratio of the first light-to-heat conversion layer and the second light-to-heat conversion layer needs to be determined in consideration of the overall configuration of the recording medium, the thermophysical properties of the materials used, and the temperature distribution determined by the light irradiation conditions.

Furthermore, when a recording medium is used in which the photothermal conversion layer has a relatively higher absorbance for the light irradiated during erasing than for the light irradiated during recording, it has a higher absorbance for the erasing light. Both the first and second photothermal conversion layers are active. That is, a portion of the incident erasing light is absorbed by the second photothermal conversion layer, and a portion of the remaining light is absorbed by the second photothermal conversion layer. Further, a portion of the reflected light is again absorbed by the second photothermal conversion layer. Therefore, in this case as well, erasing can be achieved with a shorter irradiation time than in a case where a photothermal conversion layer is provided on only one side.

The first light-to-heat conversion layer of the recording medium used in the present invention may be a layer of a metal or metalloid such as platinum, titanium, silicon, chromium, nickel, germanium, or aluminum, and converts a portion of the light into It can also be used as a reflective layer.

The second photothermal conversion layer needs to absorb part of the extinguished light and transmit the rest, so for example, a resin layer containing a light absorber can be used. Examples of light absorbers include azo dyes, cyanine dyes,
naphthoquinone pigments, anthraquinone pigments, squarylium pigments, phthalocyanine pigments, naphthalocyanine pigments, naphthoquinone pigments, porphyrin pigments,
Indigo dyes, dithiol complex dyes, azulenium dyes, quinone imine dyes, quinone dimine dyes, etc. can be used, and the light absorber is selected depending on the wavelength of the light used for recording and erasing. Examples of the resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. , polyvinylidene chloride, vinylidene chloride-acrylonitrile copolymer, polyester, polyamide, polyacrylate, polymethacrylate, polycarbonate, polyurethane, silicone resin,
Heat treatment of polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polyetherimide, polyimide, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyarylate, unsaturated polyester resin, etc. Examples include heat or ultraviolet curing resins such as plastic resins and epoxy resins, which are selected depending on the degree of temperature rise of the layer during recording and erasing.

[0027] The substrate may be a commonly used glass plate or a plastic plate made of acrylic resin, polycarbonate resin, or the like. As the protective layer, a layer transparent to recording light, reproduction light, and erasing light, such as glass or resin, can be used.

In the present invention, when the second photothermal conversion layer is formed of a layer that has a relatively higher absorbance for the light irradiated during erasing than for the light irradiated during recording, most of the recording light is transmitted. Since it is necessary to absorb a portion of the erasing light, a resin layer containing a light absorbing agent that absorbs more erasing light than recording light can be used. In this case, the light absorber is selected depending on the wavelength distribution of recording light and erasing light. As the light absorbent and resin, those mentioned above can be used.

In the present invention, two light sources with different wavelength distributions are used for the recording medium as described above, and one is used as recording light and the other is used as erasing light. Furthermore, during reproduction, either light source can be used, but in terms of light utilization efficiency, it is preferable to use recording light with a weakened intensity. It is preferable to use a laser beam such as a semiconductor laser or a He-Ne laser as the light source, and lasers having two different oscillation wavelengths may be selected from the relationship with the absorption spectrum of the second photothermal conversion layer.

[0030]

[Examples] The present invention will be explained in more detail with reference to Examples below.

Example 1 A phthalocyanine dye represented by the following structural formula 2 was added to a tetrahydrofuran solution of vinylidene fluoride-trifluoroethylene copolymer in an amount of 3% by weight based on the resin, and the mixture was placed on a glass plate with a thickness of about 0.1 mm. The film was applied by spin coating to a dry film thickness of 0.4 μm to form a second light-to-heat conversion layer. The absorption spectrum of this film was as shown in FIG. 3, and the maximum absorption wavelength was 783 nm.

[0032]

[Chemical 2]

On the other hand, a diameter of 4 inches (10
1.6 mm), on a 1.2 mm thick glass disk,
A Cr vapor deposited film with a thickness of about 1000 Å was provided. This Cr layer is the first photothermal conversion layer. Temperature 9 of this glass disk
The Cr layer was placed on a hot plate controlled at 0° C., and a small amount of stearic acid (manufactured by NOF Corporation, purity 99.9%) was placed thereon and melted. A glass plate provided with a second light-to-heat conversion layer was placed over the melt facing downward, and the melt was spread uniformly over the entire surface and sandwiched therebetween. Next, the disk was moved slowly on the hot plate and removed from the hot plate. The temperature of the disk decreased from the part removed from the hot plate, and crystallization started from this part and gradually spread in one direction until the entire disk became crystallized.

While rotating the recording medium composed of the substrate, the first photothermal conversion layer, the recording layer, the second photothermal conversion layer, and the protective layer prepared in this way at 900 RPM, a beam of light having a wavelength of 830 nm condensed to a diameter of 1 μm was emitted. Semiconductor laser light was irradiated with an intensity of 5 mW on the surface of the recording medium. After the irradiation, the recording medium was observed under crossed nicols using a reflective polarizing microscope, and a line-shaped recording with a width of about 1 μm was observed with clear contrast in the area irradiated with the laser beam.

Next, a semiconductor laser beam (wavelength 780 nm) focused to a diameter of 5 μm is applied to the recording medium on which this recording was performed.
was irradiated at an irradiation intensity of 3.5 mW and a linear velocity of 200 mm/sec so as to overlap the recorded portion. After the irradiation, observation was made in the same manner as before, and it was found that in the area scanned by the erasing light beam, the recording had been erased in a band shape with a width of about 3 μm.

Comparative Example 1 A recording medium was prepared in the same manner as in Example 1 except that the second light-to-heat conversion layer was not provided, and recording and erasing were performed in the same manner, but the recording could not be completely erased. . Even when the intensity of the erasing light was changed, complete erasure was not possible. However, when the scanning speed of the erasing light was set to 100 mm/sec, erasing was possible with irradiation with an intensity of 2.5 mW.

From the above results, in the absence of the second photothermal conversion layer, erasing cannot be achieved unless the linear velocity is slowed and the irradiation time is increased so that the entire recording layer is heated to a uniform temperature. In contrast, in the examples of the present invention, heat is transmitted from the photothermal conversion layers provided on both sides of the recording layer, so it has been confirmed that even if the irradiation time is short, it can be heated uniformly and complete erasing can be performed. Ta.

Example 3 A recording medium was prepared in the same manner as in Example 1 except that the material for the recording layer was changed from stearic acid to behenic acid (manufactured by NOF Corporation, purity 99.8%). Recording medium at 900 RPM
While rotating with
The semiconductor laser beam was irradiated with an intensity of 8 mW. When observed with a polarizing microscope, a clear line-shaped record with a width of about 1 μm was observed in the laser beam irradiated area.

Next, a semiconductor laser beam (wavelength 780 nm) focused to a diameter of 5 μm is applied to the recording medium on which this recording was performed.
was irradiated at an irradiation intensity of 4.0 mW and a linear velocity of 200 mm/sec so as to overlap the recorded portion. After irradiation, similar observation revealed that in the area scanned by the erasing light beam, the recording had been erased in a band shape with a width of about 2.5 μm.

Comparative Example 3 A recording medium was prepared in the same manner as in Example 3 except that the second light-to-heat conversion layer was not provided, and recording and erasing were performed in the same manner. cannot be erased, and in order to erase the record, the scanning line speed of the erasing light must be increased to 100 mm.
It was necessary to set it to /sec.

[0041]

[Effects of the Invention] According to the recording medium and record erasing method of the present invention, records formed by changing the crystalline state due to heat can be easily and reliably erased without leaving any residue, and can be erased at high speed. become. Therefore, highly reliable information recording and erasing can be realized even after repeated use.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic configuration of a recording medium used in the present invention.

FIG. 2 is a sectional view showing another basic configuration of a recording medium used in the present invention.

FIG. 3 is a diagram showing an example of an absorption spectrum of a second light-to-heat conversion layer made of a light absorber and a resin.

[Explanation of symbols]

1 board 2
First photothermal conversion layer 3 Recording layer
4 Second light-to-heat conversion layer 5 Protective layer

Claims (4)

[Claims] 1. On a support, at least a first photothermal conversion layer that absorbs irradiated light and converts it into heat, a recording layer consisting of a crystalline organic thin film whose crystal state changes reversibly by heat, and irradiated light. A recording medium comprising a second photothermal conversion layer that absorbs and converts light into heat, which are sequentially laminated. 2. The recording medium according to claim 1, wherein the second light-to-heat conversion layer is made of a layer having a relatively higher absorbance for light irradiated during erasing than for light irradiated during recording. . 3. The recording medium according to claim 1, wherein at least one of the two light-to-heat conversion layers is a resin layer containing a light absorber. 4. Erasing the recording by irradiating the recording medium according to any one of claims 1 to 3, which is recorded by irradiating light with light having a wavelength distribution different from that of the light irradiated at the time of recording. A record erasing method characterized by: