JPH03293194A - Method for erasing record - Google Patents

Abstract

PURPOSE:To certainly erase recording by the change of the crystal state or phase of a recording layer by forming recording to a recording medium, wherein a photothermal converting layer absorbing recording light to convert the same to heat and a recording layer substantially transparent to recording light and reversibly generating the change of a crystal state or phase by heat to perform recording and erasure are provided on a substrate, by the short-time irradiation with light and erasing the same by the irradiation with light applied for a time longer than that at the time of recording. CONSTITUTION:A photothermal converting layer 2 absorbing recording light to convert the same to heat is provided on a substrate 1 and a recording layer 3 substantially transparent to recording light and generating the reversible change of a crystal state or phase by heat and a protective layer 4 are provided thereon. Next, semiconductor laser beam is condensed to the recording medium thus formed in a diameter of 5mum so that the intensity on the recording medium becomes 2mW and scanning is linearly applied so as to be superposed on a recording part. The linear speed at this time is set to 50mm/sec and the irradiation time of one point of the recording medium is set to 100musec. After irradiation, when the recording medium is observed by a polarization microscope in the same way as that before irradiation, recording is erased in the scanning part due to erasing beam in a strip shape with width of about 3mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for erasing records on a heat mode reversible recording medium, which records and erases information using heat added by light irradiation.

[Conventional technology]

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, Di, Se, T
b. An inorganic recording medium using a metal material whose main component is In, or polymethine dyes such as cyanine, macrocyclic azaannulene dyes such as phthalocyanine, naphthalocyanine, and porphyrin, naphthoquinone, anthraquinone dyes, and dithiol. Recording media using organic dyes such as 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.

Examples of such reversible recording media include Gd, Tb, D
There are magneto-optical recording media that use alloy thin films made of rare earth metals such as y 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, poor S/N ratio, and problems with deterioration of recording sensitivity and recording stability due to effects such as oxidation. There is.

In addition, as a reversible recording medium, Ge, Te, Se,
There is one 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 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.

[Problem to be solved by the invention]

In this way, conventional recording methods have problems with recording sensitivity, erasing speed,
Various problems remain, such as recording stability and recording consistency. In particular, in recording media 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 recording and erasing can be performed with high reliability without leaving any unerased data during erasing.

From this point of view, the present invention provides an erasing method that reliably erases records by changing the crystal state of the recording layer or by changing the phase.

[Means to solve the problem]

With the above objectives in mind, the present inventors investigated the recording and erasing of a recording layer whose crystalline state reversibly changes due to the heat accompanying light energy irradiation, and found that the light irradiation time during recording and erasing was It has been found that the above objectives can be achieved by adjusting the .

That is, the recording erasing method of the present invention includes a photothermal conversion layer that absorbs recording light and converts it into heat, and a photothermal conversion layer that is substantially transparent to the recording light and has a reversible crystal state change or A record formed by irradiating light for a short time on a recording medium having a recording layer that performs recording and erasing by causing a phase change is erased by irradiating light for a longer time than during recording.

The recording layer of the recording medium used in the present invention performs recording and erasing by reversible changes in the crystalline state and reversible changes in phase, 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 degree of
Reversible change in molecular orientation, reversible change in crystal orientation, reversible change in crystal axis direction, reversible change in molecular orientation, or change in crystal grain size or crystal domain size. There are reversible changes, which occur singly or in combination in the recording layer. These changes occur when the temperature of the recording layer rises due to heat applied during recording or erasing, or heat generated by light irradiation, and changes from an unrecorded state to a recorded state or through a melt phase or liquid crystal phase. There are cases where the recorded state changes to the erased state (same as the unrecorded state), cases where 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.

Examples of recording media on which such recording and erasing are performed include the following. For example, there are phthalocyanine materials such as copper phthalocyanine and magnesium phthalocyanine that utilize the crystal-to-crystal and crystal-to-amorphous transitions of organic materials. There are polymer liquid crystal materials and low molecular liquid crystal materials that utilize . In the case of liquid crystal materials, electric or magnetic fields may be used to form the alignment state.

Furthermore, those that utilize reversible changes in the crystalline state of organic thin film crystals include fatty acids or fatty acid derivatives, benzoic quasi-derivatives, and n-alkanes or their derivatives having a melting point of 50° C. or higher.

In the present invention, fatty acids or fatty acid derivatives include saturated or unsaturated mono- or dicarboxylic acids, their esters, amides, anilides, hydrazides, ureides, anhydrides, or fatty acid salts such as ammonium salts or metal salts. means. 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 straight-chain or branched, and unsaturated fatty acids may have one double or triple bond,
It may have two or more. The number of carbon atoms in the hydrocarbon chain in these fatty acids is preferably 10 or more.

Specific examples of saturated fatty acids include undecanoic acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nanodecanoic acid, arachidic acid, behenic acid, 7-lignoceric acid, cerotic acid, and montanic acid. Examples of unsaturated fatty acids include oleic acid, elaidic acid, linoleic acid, sorbic acid, and stearolic acid. Also, specific examples of esters include:
For example, methyl esters, ethyl esters, hexyl esters, octyl esters, decyl esters, dodecyl esters, tetradecyl esters,
These include stearyl ester, eicosyl ester, and tocosyl ester. Further, examples of metal salts include metal salts of these fatty acids such as sodium, potassium, magnesium, calcium, nickel, cobalt, zinc, cadmium, and aluminum.

Further, the benzoic acid derivatives referred to in the present invention specifically include benzoic acids represented by the following general formulas (I) to (IV), and their esters, amides, anilides, and the like. 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 (n), esters include esters of aliphatic hydrocarbon compounds with polyhydric alcohols or aromatic hydrocarbons having a plurality of hydroxy groups.

3 Substituents for R□, R2, R1 and other benzoic acid derivatives in the general formula include, for example, hydrogen, an alkyl group,
Aryl groups such as alkoxy groups, phenyl groups, biphenyl groups, naphthyl groups, and anthranyl groups, and R groups include acyl groups, acyloxy groups, halogens, nitro groups, hydroxy groups, cyano groups, carboxyl groups, and esters thereof. , a carbamoyl group that may be substituted, a sulfo group and its ester or alkyl group, a phenyl group, and an amino group that 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, n-alkanes such as tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, todriacontane, tetratriacontane, hexatriacontane, octatriacontane, tetracontane, etc. or those containing these as main components There is a mixture called paraffin and paraffin wax. Further, as derivatives, 1-hexacosene, 1-heptacosene, ■-octacosene, 1-triacontin, 1-tetradriacontin, ]-hexatriacontin, ■=niophtatriacontin 1-tetracontin, tocosylbenzene , tetracontinzene,
Hexacosylbenzene, ophtacosylbenzene, 1-liacontylbenzene, tri-1-liacontylbenzene,
Tetratriacontylbenzene, hexa-1-liacontylbenzene, 1. ]8-Dibromooctadecane, 1゜2
Examples include 0-dibromoeicosane and 1,22-dibromotocosane.

The recording medium used in the present invention basically has a photothermal conversion layer 2 on a substrate 1, which absorbs recording light and converts it into heat, as shown in FIG. The recording layer 3 is completely transparent and has a recording layer 3 and a protective layer 4 that undergo a reversible crystal state change or phase change due to heat. Recording is performed by illuminating a small beam of light that blinks according to the information. Light is converted into heat in the recording medium, and the heat changes the recording layer for recording.

When the recording medium of FIG. 1 is irradiated with light for a short period of time, no heat is generated in the recording layer because the protective layer and the recording layer are substantially transparent to the recording light and do not absorb the light. Most of the recording light is absorbed by the photothermal conversion layer below, and heat is generated here. This heat is transmitted to the recording layer in contact with the photothermal conversion layer, causing the recording layer to change. Since the recording light is irradiated for a short time, once the irradiation stops, the heat is quickly diffused and the device is cooled. Since the organic thin film crystal and polymer liquid crystal layers that form the recording layer have low thermal conductivity, the heat from the photothermal conversion layer is not transmitted to the entire thickness of the recording layer in a short period of time, and when the light irradiation is finished, the second The temperature distribution shown in the figure is formed, and only the lower part of the recording layer close to the photothermal conversion layer is heated once, and then cooled down immediately. A change in the crystal state occurs and is recorded only in the area shown by . For example, if this change in crystalline state occurs via a molten state, only the part near the photothermal conversion layer that has reached a temperature above the melting point will melt, and when it crystallizes by subsequent cooling, it will return to the initial state. In other words, it solidifies into a state different from the surrounding crystalline state and becomes a record.

The recording part does not necessarily have to be formed only in a part of the recording layer in the thickness direction, but if it is formed only in a part, the area around the recording part remains unchanged against rearrangement and reorientation during erasing. Since it is subject to the regulating force of the part, it can be easily erased.

To record by heating only a portion of the recording layer in this way, rather than the recording layer itself absorbing light and generating heat, the recording layer and the photothermal conversion layer that absorbs light and generates heat are separated.
And it is preferable that they are in contact with each other. In order to perform high-density recording, the recording layer must be thin, but in order for the recording layer to absorb light and have only a portion of it reach a high temperature, the absorbance must be extremely high. Light must be absorbed only near the surface of the recording layer.

The material of the recording layer does not necessarily have such a high absorbance, and in boat fishing it is often mixed with a dye that absorbs the recording light. However, this can also have a negative effect on the formation and change of the crystalline state of the recording material.

Since the recording medium described above has a transparent recording layer and a light-to-heat conversion layer separated, it is easy to partially heat the recording layer. As mentioned above, it is desirable that the recording layer and the photothermal conversion layer are in direct contact with each other. It is also possible to provide an alignment film. However, in this case as well, in order to locally heat the layers, these layers should be as thin as possible, preferably 1 pm or less.

The recording layer of the recording medium used in the present invention undergoes a transition between delivery and crystal, a phase transition between crystalline and amorphous, a change in the orientation state, and a change in the orientation direction depending on the amount of heat applied or the temperature reached. This is a layer that occurs reversibly. For example, when a recording layer made of thin film crystals is heated and melted by light irradiation and then rapidly cooled, that part becomes amorphous and becomes fixed, or the crystal orientation changes and becomes fixed, and information is recorded. . Next, when the recording layer is heated by irradiating it with light of a different intensity than that used during recording, it is rearranged or reoriented, returns to the crystalline state and orientation state before recording, and is erased.

In the erasing method of the present invention, light irradiation is performed for a longer time than during recording. Records formed by changes in the crystal state or orientation state involve heating part or all of the recording layer to a temperature above the melting point of the recording layer or above the isotropic point. Erasing of records is performed by heating to a phase transition temperature, liquid crystal temperature, or rearrangement temperature lower than these temperatures. The temperature range in which these changes (erasing) occur is between several degrees Celsius and several tens of degrees Celsius, but in order to completely erase records, the recorded portion formed on the recording layer must be uniformly kept within this temperature range. must be made to enter. During recording, it is easier to erase a recording by changing only a portion of the recording layer than by forming the recording over the entire thickness, so a strong laser beam is used to irradiate the recording layer for a short period of time. Since recording may be performed at a temperature equal to or higher than the melting point or isotropic point of the recording layer, the temperature distribution may be steep in the thickness direction of the recording layer. However, during erasing, when laser light is irradiated, it must be uniformly heated over a fairly narrow temperature range, so it is necessary to form a gentle temperature distribution. Such a temperature distribution 5 can be achieved by irradiating laser light for a longer time than during recording. If the irradiation intensity is simply lowered for the same irradiation time as during recording, part of the recorded area will fall within the erasing temperature range, but the entire area will not be within the erase temperature range. If the irradiation time is made longer, the heat generated in the photothermal conversion layer reaches the upper part of the recording layer, and the temperature becomes uniform in the thickness direction of the layer, so that the entire recording part can be brought into the erasing temperature range. Therefore, the entire recorded portion can be completely erased without leaving any trace, and
Re-recording by erasing light will not occur even if the temperature partially reaches above the recording temperature.

Appropriate irradiation times during recording and erasing vary depending on various factors. For example, it varies depending on the layer structure of the recording medium, the materials of the recording layer, light-to-heat conversion layer, protective layer, etc., the thickness of each layer, thermal properties such as thermal conductivity and specific heat, recording temperature, erasing temperature and its range, etc. For the recording medium, the irradiation time during recording and erasing must be determined by taking into account the irradiation time, the temperature reached, the temperature distribution, the temperature distribution during the cooling process, the cooling rate, etc. Therefore, it is not possible to regulate the irradiation time during recording and erasing within a certain range for all recording media, but in particular for layers made of organic materials with relatively low thermal conductivity, the irradiation time during erasing is longer than that during recording. Unless the time is increased, the recorded area cannot be uniformly brought into the erasing temperature range. To give a specific example of the irradiation time during recording and erasing for recording of fatty acids and benzoic acid derivatives given as examples of recording layer materials, for example, the irradiation time during recording is 1μ.
sec or less is preferable for recording on a portion of the recording layer, and during erasing, 10 μsec or more is preferable in order to uniformly bring the recorded portion to the erasing temperature.

The light-to-heat conversion layer of the recording medium used in the present invention may be a layer of metal or semimetal such as platinum, titanium, silicon, chromium, nickel, germanium, aluminum, etc., and can also be used as a reflective layer that reflects part of the light. can do. Further, the substrate may be a glass plate used for boat fishing, 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.

〔Example〕

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

Example 1 A photothermal conversion layer, C
The r layer was provided by vacuum evaporation. The thickness was approximately 950 people. This substrate was placed on a hot plate controlled at a temperature of 90°C with the Cr layer on top, and behenic acid (
A small amount of A) manufactured by Sigma Corporation: purity 99'' was placed and melted. A glass plate with a thickness of approximately 0.1 mm was placed over the behenic acid melt.
The melt was spread uniformly over the entire surface and sandwiched. Next, this disk was slowly moved over the hot plate and removed from the hot plate. The temperature of the disk decreased from the part removed from the hot plate, and the behenic acid melt layer began to crystallize from this part, gradually spreading in one direction and crystallizing the entire disk. After peeling off the glass plate, a 1 (he%) aqueous solution of polyvinyl alcohol was coated on this crystal film. Through the above operations, a recording layer consisting of thin film-like crystals of stearic acid oriented in a substantially --like direction was formed on the Cr layer. (thickness: about 0.6 pm), and a protective layer made of polyvinyl alcohol (about 3.0 m thick) was formed thereon.

While rotating the thus prepared recording medium at 90 ORPM, a semiconductor laser beam of wavelength 830 nm focused to one tone in diameter was turned on so that the intensity at the surface of the recording medium was 51, and was irradiated in a spiral manner. At this time, the linear velocity in the recording direction of the recorded portion on the disk is approximately 3.5
00-4,000 mm/see, and the time during which one point on the recording medium is irradiated is approximately 0.25 μsec.

When a recording medium irradiated with recording light is observed in a crossed nicol state using a reflective polarizing microscope, a line-shaped recording part with a width of about 1/a is formed in the laser light irradiated part of the recording layer with clear contrast. I was able to observe it. However, this recording area was barely visible under a normal optical microscope.

Next, the recorded recording medium was illuminated with a semiconductor laser beam focused on a diameter of 5 capes so that the intensity on the recording medium was 2 m, and was scanned in a straight line so as to overlap the recorded portion.

The linear velocity at this time was 50III/sec, and the irradiation time at one point on the recording medium was 100 μsec. After the irradiation, observation using a polarizing microscope as before revealed that the recording had been erased in a band shape about 3 μm wide in the area scanned by the erasing light beam.

On the other hand, the intensity was set to 2+n for each recorded recording medium.
Laser light with a diameter of 1 μm was irradiated in the same manner as during recording, except that four types of light were used: lJ, 2.5+nl+l, 3d, and 4mW, overlapping with the previous recording. As a result, it was found that at 2.5d or less, the previous record does not change at all and cannot be erased, and at 3+++W or more, a new record similar to the previous record (the line becomes thinner) is formed and overlaps with the previous record. It was found that the recorded state of the recorded areas did not change and could not be erased with the same irradiation time as during recording.

Since it is not actually possible to measure the temperature distribution that occurs in the recording layer when laser light is irradiated, we consider the intensity distribution of the laser light, the light absorption and heat conduction of each layer of the recording medium, and
The thermal properties such as thickness, light absorption property, thermal conductivity, and specific heat of each layer were set to the values shown in Table 1, and the temperature distribution in the recording layer was determined by simulation. Figure 4 shows the temperature distribution when the irradiation time is 0.25 μsec and the recording intensity is 4 mV.
The case of mW is shown in FIG. Irradiation time is 0.25μse
At c, the interval between the isotherms is narrow in the thickness direction, forming a steep temperature distribution, and at 100 μsec, there is almost no temperature difference in the thickness direction, forming a gentle temperature distribution. I understand.

From the above results, it was found that if the irradiation time is the same as that used for recording, erasing cannot be performed because the recorded area cannot be heated uniformly, but if the erasing time is longer than that, the entire area can be heated uniformly, so erasing is possible.

Table - Loser light emission: 830 nm 0 Example 2 Stearic acid (manufactured by Sigma, purity 9) was used instead of behenic acid.
A recording medium was produced in the same manner as in Example 1 except that 9%) was used.

While rotating the recording medium at 90 ORPM,
Semiconductor laser light with a wavelength of 830 nm focused on
III+1 and recorded as in Example 1. The recording was clearly visible under a polarized light microscope.

Next, in the same manner as in Example 1, an erasing light beam having a diameter of 5 μm was irradiated so as to overlap with the recording. Erasing light intensity 1.5
When +nW was used, the previous recorded area could be erased in a band shape with a width of about 3 μm.

On the other hand, the strength of the recorded recording medium is 1.5 m, 2n+l+
Laser light with a diameter of 1 μm was irradiated in the same manner as in the recording except that the four types were used: l, 2°5+nll, and 3n+w. As a result, it was found that with 2II1w or less, the previous record does not change at all and cannot be erased.
, 5 mW or more, a new record similar to the previous record was formed, and there was no change in the area that overlapped with the previous record, indicating that erasure could not be achieved with this irradiation time.

〔Effect of the invention〕

According to the record erasing method of the present invention, records formed by a change in crystalline state or phase due to heat can be easily and reliably erased without leaving any traces, resulting in high reliability even in repeated use. It is possible to erase records of information.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the basic structure of a recording medium used in the present invention, in which 1 is a substrate, 2 is a light-to-heat conversion layer, 3 is a recording layer, and 4 is a protective layer. FIG. 2 is a diagram showing the temperature distribution formed in the recording layer during laser beam irradiation. FIG. 3 is a diagram showing a changing portion 5 in the recording layer formed in accordance with the temperature distribution shown in FIG. Figure 4 shows the irradiation time of 0.2 determined from simulation.
FIG. 5 is a diagram showing the temperature distribution formed in the recording layer when the irradiation time is 5 μsec, and FIG. 5 is a diagram showing the temperature distribution when the irradiation time is 100 μsec.

Claims (2)

[Claims] (1) On the substrate, there is a photothermal conversion layer that absorbs recording light and converts it into heat, and a photothermal conversion layer that is substantially transparent to the recording light and causes a reversible crystal state change or phase change by heat to record and erase. 1. A method for erasing a record, which comprises erasing a record formed by irradiating a recording medium with a recording layer for a short period of time by irradiating it with light for a longer time than during recording. (2) The method for erasing a record according to claim 1, wherein the recording medium is a layer containing a thin film crystal of a fatty acid or a fatty acid derivative, a benzoic acid derivative, an n-alkane, or a derivative thereof.