JPH03158287A - Recording - Google Patents

Abstract

PURPOSE:To ensure the acceleration of deletion speed and the complete deletion of data when it is required by controlling the range of an area subjected to change in a recording layer where a crystal state changes reversibly due to heat. CONSTITUTION:A recording layer 2 where a crystal state changes reversibly and a protecting layer 3 are provided on a substrate 1. A method of recording data by changing a crystal state in only part of the recording layer in a width direction applies here. For example, when this recording medium is irradiated with light from the protecting layer side, the protecting layer 3 is transparent to the projected light and the recording layer 2 absorbs the light. When the light absorption factor is high, the light is absorbed by only the top of the recording layer 2, so that heat generated there. When the thermal conductivity of the recording layer 2 is comparatively low and time required for light emission, is short the heat diffuses to the surroundings, if the light emission is discontinued, and the layer cools off immediately. Subsequently, only the top 4 of the recording layer where the temperature reaches the level for the occurrence of a change in the crystal state, changes, forming records. In addition, the deletion speed can be accelerated without any undeleted portion as the changed portion during recording is apt to return to its original state during deletion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording method for a heat mode recording medium in which information is recorded by applying heat or irradiating light.

[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, Bi, Se, T
b, inorganic recording media using metal materials mainly composed of In, etc., 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 (bits) 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,
There is a magneto-optical recording medium that uses an alloy thin film made of a rare earth metal such as Dy and a transition metal such as Fe, Ni, or 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, a poor S/N ratio, and problems such as deterioration of recording sensitivity and recording stability due to effects such as magnetization. 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 a heat mode using only laser light irradiation, but it has problems with the contrast between recorded and non-recorded areas, insufficient recording stability, and the stability of the material of the recording layer. It has drawbacks such as problems with sexuality.

[Problem to be solved by the invention]

In this way, conventional recording methods have problems with recording sensitivity, erasing speed,
Various problems remain, including recording stability and recording contrast. In particular, for 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 viewpoint, one object of the present invention is to provide a recording method in which recording and erasing can be performed quickly and reliably by changing the crystalline state or phase change of the recording layer.

[Means to solve the problem]

For the above-mentioned purposes, the present inventors investigated recording and erasing on a recording layer whose crystalline state changes reversibly due to heat accompanying light energy irradiation, and found that the crystalline state in the recording layer changes. It has been found that the above object can be achieved by controlling the range of the parts.

That is, in the recording method of the present invention, light is irradiated onto a recording medium having at least a substrate and a recording layer whose crystal state changes reversibly by heat or whose phase changes to perform recording and erasing. A recording method in which recording is performed by changing the crystal state of a portion in the thickness direction or by changing the phase, and the recording layer is or contains an organic thin film crystal. .

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. a reversible change in the degree of chemical orientation, a reversible change in the degree of molecular orientation, a reversible change in crystal orientation, that is, a reversible change in the crystal axis direction, a reversible change in the direction of molecular orientation, or a reversible change in the orientation of crystal grains. There are reversible changes in the size and size of crystalline domains, and these 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 recorded state via a melt phase or liquid crystal phase. There are cases where the state changes from a state to an erased state (same as an unrecorded state), cases where a transition between states occurs directly due to temperature rise without going through the melt phase or liquid crystal phase, and cases where a transition occurs via an amorphous state. There are cases where you do so.

Examples of recording media on which such recording and erasing are performed include the following. Te-Ge-5b system, Te-Ga-3e-5b system, Te-Ge-3n-0 that utilize the phase transition between crystalline and amorphous inorganic materials.
system, Te-Ge-5n-Au system, In-5s system, In-
5e-Tl system, In-5e-TI-Co system, In-5
b4e system, Te-5s-Go-5b system, etc., and those that utilize crystal-to-crystal transitions such as transition between low temperature phase and high temperature phase, transition between stable phase and metastable phase, etc., include Ag-Zn system, Cu -AQ-Ni system, In-3b-5e system, In-
There are materials such as 5b-Te type. In addition, as a method that utilizes the crystal-crystal and crystal-amorphous transitions of organic materials,
For example, there are phthalocyanine materials such as copper phthalocyanine and magnesium phthalocyanine, and there are polymeric liquid crystal materials and low molecular liquid crystal materials that utilize transition between an oriented state and an isotropic state or an amorphous state. 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, for example, fatty acid or fat rvIvI conductors, benzoic acid derivatives, and n-alkanes or their derivatives having a melting point of 50° C. or higher.

The fatty acid or fatty acid derivative as used in the present invention specifically refers to 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, balmitic acid, heptadecanoic acid, stearic acid, nanodecanoic acid, arachidic acid, behenugly, 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 ester, ethyl ester, hexyl ester,
Examples include octyl ester, decyl ester, 5-dodecyl ester, tetradecyl ester, 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 (1) to (IV), and their esters, amides, anilides, and the like. In addition, hydrazides, ureidos, anhydrides, and metal salts that may be substituted.

Contains salts such as ammonium salts. Moreover, esters include compounds other than those represented by general formula (n).

Polyhydric alcohols or aliphatic hydrocarbon compounds.

Contains esters with aromatic hydrocarbons having multiple hydroxy groups.

3 R1, R,, R, and other substituents of the benzoic acid derivative 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, and the alkyl group and alkoxy group may be linear or branched, and may have 2 or more carbon atoms. The carbon chain may contain one or more unsaturated bonds.

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 and pentacosane.

There are n-alkanes such as hexacosane, heptacosane, octacosane, nonacosane, triacontane, todoriacontane, tetratriacontane, hexatriacontane, octatriacontane, and tetracontane, or mixtures containing these as main components, so-called paraffins and paraffin waxes. . Further, as derivatives, 1-hexacosene,
1-heptacontine, 1-oftacocene, 1-triacontin, 1-tetratriacontin, 1-hexatriacontin, 1-octatriacontin, 1-tetracontin, tocosylbenzene, tetracontanzene, hexacosylbenzene, Oftacosylbenzene, triacontylbenzene, tritriacontylbenzene, tetratriacontylbenzene, hexatriacontylbenzene, 1
．． 18-dibromooctadecane, I.

Examples include 20-dibromoeicosane and 1,22-dibromotocosane.

The recording medium used in the present invention basically has, as shown in FIG. 1, a recording layer 2 and a protective layer 3 on a substrate 1, the crystal state of which can be changed reversibly. As a method for recording by changing the crystalline state of only a portion of the recording layer in the thickness direction, for example, if the change in the crystalline state is caused by heat, it is possible to record by changing the crystalline state of only a portion of the recording layer in the thickness direction. The temperature can be increased by adding heat to the.

Methods of applying heat include, for example, a method in which a thermal head or the like is brought into contact with the recording layer, and a method in which light is irradiated and the heat generated by absorption of the light is utilized.

For information recording media that generally require high recording density,
A method using light irradiation is often used. In either case, during recording, some particles are left in the recording layer as shown in Figs. 2(a) and (b).
, a temperature distribution as shown in (C) must be formed. This temperature distribution depends on the method of applying heat, the amount of heat applied, the time it is applied, and the number of recording layers, substrates, and other records.
Thermal conductivity of the layers that make up the medium.

Determined by thermal properties such as specific heat. In addition, when using light irradiation, consideration must be given to where the light is absorbed and becomes heat.

To explain more specifically, consider the case where a recording medium consisting of a substrate, a recording layer, and a protective layer shown in FIG. 1 is irradiated with light from the protective layer side. The retention layer is transparent to the irradiated light, and the recording layer absorbs the light.

Moreover, if the absorbance is quite high, the light is absorbed only in the upper part of the recording layer, and heat is generated in this part. When the thermal conductivity of this recording layer is relatively low and the time for irradiating light is short (when the time for generating heat is short)
, there is less heat diffusion, and the temperature distribution formed is as shown in Figure 2 (
It will be like a). This temperature distribution is formed for 1w4 when light is irradiated for a short period of time, and when the light irradiation stops, the heat diffuses to the surroundings and is immediately cooled. therefore.

At this point, only the upper part of the recording layer, whose temperature exceeds the temperature that causes the crystal state change, changes and a record is formed (see Figure 3: 4 in the figure).
(The same applies to the following figures). )
. If the change that occurs here is a change that occurs via a molten state, the part that has been melted by light irradiation will, after cooling, be in a state different from its initial state, that is, the state of the surrounding crystal that was not exposed to light irradiation. , becomes a record.

In addition, if the substrate sandwiching the recording layer and the 7I layer have high thermal conductivity or a large heat capacity and the heat of the recording layer can easily escape, light will be absorbed evenly throughout the thickness of the recording layer and heat will be generated. Figure 2 (b)
As shown in FIG. 4, only the central portion of the recording layer has a high temperature, and only the crystalline state in the central portion changes, resulting in recording as shown in FIG.

Next, the protective layer and the recording layer are transparent to the irradiated light, and when the substrate absorbs the light, the upper part of the substrate that is in contact with the recording layer absorbs the light and generates heat. Since this heat is transmitted to the recording layer, the temperature distribution becomes as shown in FIG. 2(C), where the temperature is highest at the part of the recording layer that is in contact with the substrate. The temperature rises deeper into the recording layer as the thermal conductivity of the recording layer increases and as the light irradiation time increases. By shortening the light irradiation time, only a portion of the recording layer on the substrate side can be brought to a temperature higher than the melting temperature of the recording layer or within the phase transition temperature range, and recording is performed as shown in FIG. 5.

Glass plates, acrylic resins, polycarbonate resins, and other plastic plates are often used as substrates.
In the case of such a transparent substrate, a photothermal converter m (5 in FIG. 6) that absorbs light and converts it into heat may be provided between the recording layer and the substrate. The heat generated in the photothermal conversion layer is transmitted to the recording layer and can be recorded as shown in FIG. The photothermal conversion layer may be a layer of metal or semimetal such as platinum, titanium, silicon, chromium, nickel, germanium aluminum, etc., and this layer can also be used as a reflective layer that reflects part of the light.

In the recording layer used in the present invention, crystal-crystal transition, crystalline-amorphous phase transition, change in orientation state, and change in orientation direction occur reversibly depending on the amount of heat applied or the temperature reached. It is a layer. For example, when a recording layer made of a thin film of 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, during recording, if you irradiate light under different conditions to heat it to a temperature lower than the melting temperature, heat it for a longer time than during recording, or irradiate it with a slower cooling rate, the crystalline state will change depending on the recording. The portion where the data has changed returns to the crystalline state before recording, and erasing is performed. At this time, according to the recording method of the present invention, since only a portion of the recording layer in the thickness direction has changed in the recorded state as shown in FIGS. 3 to 5, the surrounding area remains in the original unrecorded state. Comparing the state in which Yuko is surrounded by crystals and the state in which the crystal state of the recording layer changes over the entire layer during recording, as shown in Figure 7, only a portion of the thickness direction changes during erasing. It is easier to return to the original crystalline state due to the regulating force of the crystals around the changed part, and therefore the erasure speed is faster and there is no residue remaining.

As described above, the recording method of the present invention enables highly reliable and high-speed recording and erasing.

〔Example〕

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

Example 1 A chromium (Cr) vapor deposited film with a thickness of approximately 900 mm was provided as a light-to-heat conversion layer on an optically polished glass disk having a diameter of 4 inches (101.6 mm) and a thickness of 1 to 2 mm. A 5 wt % solution of vinyl chloride-vinyl acetate copolymer (Union Carbide Co., Ltd. 1: VYHH) in tetrahydrofuran was applied thereon and dried to form a resin layer with a thickness of about 0.2 mm.

Next, a 10 wt % tetrahydrofuran solution of stearic acid (manufactured by Sigma, purity 99%) was applied onto this resin layer and dried at 45°C. Furthermore, a 5 wt % tetrahydrofuran solution of the same vinyl chloride-vinyl acetate copolymer as above was applied thereon and dried at 45°C. This disk was placed on a hot plate heated to 95° C. and left for 2 minutes, then slowly moved in one direction on the hot plate and removed from the hot plate. At this time, the stearic acid melt layer was crystallized from the part removed from the hot plate, spread in one direction, and was crystallized as a whole. Through the operation of 0 or more, it was finally oriented in a nearly -like direction on the Cr layer. A recording layer (thickness: about 0.81 Ja) made of thin film-like crystals of stearic acid, and a protective layer (thickness: about 0.6 μm) made of vinyl chloride-vinyl acetate copolymer were formed thereon.

While rotating the thus produced recording medium at 90 ORPM, it was irradiated with a semiconductor laser beam having a wavelength of 830 nm focused on a diameter 11 under the following conditions (1) and (2) to form a spiral record. At this time, the linear velocity in the recording direction in the recorded portion of the disk is approximately 3 SO
O=4000mm/see.

Irradiation conditions (1) Lighting conditions: 2 frequencies: 200 KIlz, duty ratio: 50% Intensity on the recording medium surface: 5 mW Recording line spacing: approx. 3° 5 μm (center distance) (2) Lighting conditions: 2 consecutive reading lights on the recording medium surface Intensity: 5 mW Recording line spacing: Approximately ha (center to center) When observing a recording medium irradiated with laser light under the conditions (1) above in a crossed Nicol state using a reflective polarizing microscope, it is noted that
The laser beam irradiation part of the calendar has a width of approximately 1. It is clear that the n line-shaped recorded areas are formed with clear contrast.
I could tell. However, this recording section is a normal optical microscope maf.
In A, it was barely noticeable.

When the recording medium was observed using a polarizing microscope in the same way as the recording medium irradiated with laser light under the conditions (2) above, it was observed that recording was performed over the entire irradiated area of the recording medium with almost no gaps. X-ray diffraction of the same portion of the recording medium on which the entire surface was recorded was measured before and after recording. Figure 8 shows the X-ray diffraction before recording, and Figure 9 shows the X-ray diffraction after recording.
As shown in the figure. From FIG. 8, before recording, only the diffraction lines based on the long-plane distance of the C-type crystal of stearic acid were observed, and the structure was such that the a and b axes were oriented in parallel. However, after recording in Figure 9, the diffraction line (2θ=21.6
'') appears, indicating that a structure in which the C axis is oriented parallel to the substrate is formed in the recording portion of the recording layer.

Next, when the upper protective layer of the recording medium recorded under the condition (2) is peeled off from one end, the stearic acid recording layer is separated into the lower chromium layer side and the upper protective layer side, and the upper part is separated together with the protective layer. Peeled off. X-ray diffraction was measured in the same manner as above for the stearic acid recording layer divided into two parts. Figure 10 shows the X-ray diffraction on the upper protective layer side, and the X-ray diffraction on the lower Cr and lW side.
Line diffraction is shown in FIG. The stearic acid crystal yield on the protective layer side in FIG. 10 matches the X-ray diffraction pattern before recording in FIG. 8, whereas the stearic acid crystal yield on the Cr layer side in FIG. A diffraction line (2θ=21.6°) based on the short plane spacing similar to that which appeared in the subsequent X-ray diffraction of the entire recording layer was observed.

From the above results, it can be concluded that the recording on the stearic acid thin film crystal is due to a change in the orientation direction of the crystal, and that the entire O layer is changed and recorded under these conditions when irradiated with laser light. (It can be seen that only a part of the Cr71 side is changed and recorded.

Since it is not possible to actually measure what kind of temperature distribution is formed in the recording layer when laser light is irradiated, the intensity distribution of the laser light and the light absorption and heat conduction of each layer of the recording medium are taken into account to determine the temperature distribution of each layer. When the temperature distribution in the recording layer was simulated using the thermal characteristics such as thickness, light absorption characteristics, thermal conductivity, and specific heat as shown in Table 1, the results shown in FIG. 12 were obtained. In this recording medium, the laser beam is Cr
It is absorbed only by M and turns into heat, and this heat is transmitted to the recording layer.

Under these conditions, the irradiation time is very short and the thermal conductivity of the recording layer is also low, so only the portion of the recording layer close to the Cr layer will heat up and only this portion will melt. It is thought that as soon as it stops, it cools down, crystallizes again, and records it. This is consistent with the experimental results described above.

Table - Loser light wavelength: 830 nm Next, on the recording medium recorded under the conditions (1), a semiconductor laser beam with a wavelength of 780 nm focused at a diameter of 5 mm was applied to the recording medium with an intensity of 1.51 nm. It lights up continuously so that
Scanning was performed linearly at a linear speed of 50 ma+/see so as to overlap the already formed recording portion.

When this recording medium was observed with a reflective polarizing microscope, it was found that in the area scanned by the 5-line laser beam, the record formed by the 1-μm-diameter laser beam was erased in a band shape with a width of about 2.5 μm.

From the above results, it was found that records formed in a part of the recording layer made of stearic acid crystals in the thickness direction can be erased by irradiating the recording layer with laser light in a layered manner.

Example 2 A Cr layer as a light-to-heat conversion layer was provided by vacuum deposition on an optically polished glass disk having a diameter of 4 inches (101.6 ma+) and a thickness of 1.2 mm. The thickness was approximately 950 people. This substrate was placed on a hot plate whose temperature was controlled to 95° C. with the Cr layer facing upward, and a small amount of behenic acid (manufactured by Sigma, purity 99%) was placed on the top and melted. A glass plate with a thickness of about 0.1o+i was placed over the behenic acid melt, and the melt was spread uniformly over the entire surface and sandwiched. Next, the disk was moved slowly in one direction 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 the crystallization of the behen melt layer started from this part, gradually spreading in one direction and crystallizing the entire disc. A 1 (ht%) aqueous solution of polyvinyl alcohol was coated on this crystal film. Through the above operations, a recording layer (with a thickness of approximately 0.5 h) consisting of thin film-like crystals of stearic acid oriented in a substantially --like direction was formed on the Cr layer. 6μ1
1) and a protective layer (about 0.3 mm thick) made of polyvinyl alcohol was formed thereon.

The thus prepared recording medium was subjected to the irradiation conditions of Example 1 (1.
) Irradiated and recorded in the same way. The recording could be clearly observed using a polarizing microscope.

Next, as in Example 1, a semiconductor laser beam focused to a diameter of 5 μm was continuously turned on with an intensity of 21117,
Scanning was performed in a straight line at a linear speed of 50 mm/see so as to overlap the recorded portion that had already been formed. Afterwards, when observed with a polarizing microscope, the area scanned by the 5-φ laser beam was found to have a record formed by the 1-paφ laser beam.
It was erased in a band shape with a width of about 3μ.

Comparative Example 1 A recording medium having a recording layer made of thin film crystals of stearic acid was prepared in exactly the same manner as in Example 1.

A semiconductor laser beam with a wavelength of 780 nm focused to a diameter of 5 μm is applied to this recording medium with an intensity of 7.10.14 at the surface of the recording medium.
It was lit continuously so that the voltage was mV, and scanning was performed in a straight line at a linear velocity of 200 mm/see. When observing this recording medium with a polarizing microscope, the width is approximately 2 μl at a recording intensity of 7 mW, 10n+W.
A line-shaped record of about 4 μ- and about 5 lines at 14 W could be observed with clear contrast.

Next, as in Example 1, a diameter of 5I was applied to this recording medium.
The laser beam focused on JIa has an intensity of 1 on the recording medium surface.
, continuous lighting at 5mW, linear speed 50mm/s
When scanning was performed at a linear velocity of ee in a direction perpendicular to the previous recording line, the area where the already formed line-shaped recording part intersected with the laser beam irradiated from behind was observed with a polarizing microscope and found to be 10aW. All lines recorded at an intensity of 14aW (no change, not erased), and 7aW
The line recorded at the intensity of 11 was slightly constricted at the intersection, and slight erasure was observed at the periphery of the line. From this result, it was found that the recordings recorded under the recording conditions of Example 1 (1 paφ, linear velocity 3500-4000 mm/5ec) could be completely erased, whereas those recorded under the conditions of this comparative example (5 lines φ, line 'i!l) 200mm/5ec)
It turns out that most of what is recorded cannot be erased.

In order to consider the difference in temperature distribution in the recording layer due to the difference in recording conditions, the temperature distribution formed under the conditions of this comparative example was simulated as in Example 1, and the result was as shown in FIG. Under these conditions, the heat generated in the Cr layer is transmitted to the upper part of the recording layer, reaching the melting temperature or higher throughout the thickness of the recording layer, and the change in crystalline state due to recording is thought to occur throughout the thickness. .

In addition, when the protective layer on the top of the recording medium is peeled off after recording, only the protective layer is peeled off, and when the surface of the crystal film of the remaining recording layer is observed, the recorded area looks like a collection of microcrystals, and the top of the recording layer It showed that heat was being transferred and changes were occurring.

From the above results, it has been found that when the overall crystal state in the thickness direction of the recording layer is changed and recorded, the crystal in the recorded portion is difficult to return to the original crystal, and erasing is difficult.

〔Effect of the invention〕

The recording method of the present invention does not involve making holes in the recording layer or changing the surface shape of the recording layer, but instead changes the crystalline state of a portion of the recording layer in the thickness direction or causes a phase change. Since recording is performed, parts that have changed during recording can easily return to their original state during erasing, so there is no unerased area and the erasing speed is increased, making it possible to perform highly reliable recording and erasing at high speed. .

[Brief explanation of the drawing]

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 recording layer, and 3 is a protective layer. FIG. 2 is a diagram showing the temperature distribution formed in the recording layer during laser beam irradiation. FIGS. 3, 4, and 5 are diagrams showing changing portions 4 in the recording layer formed corresponding to the temperature distributions (a), (b), and (C) shown in FIG. 2, respectively. FIG. 6 is a diagram showing a state in which information is recorded on a recording medium in which a light-to-heat conversion layer 5 is provided on a transparent substrate. FIG. 7 is a diagram showing a state in which recording is formed over the entire thickness of the recording layer. Figure 8 is an X-ray diffraction diagram of an unrecorded recording layer, and Figure 9 is an X-ray diffraction diagram of an unrecorded recording layer.
2 is an X-ray diffraction diagram of a recording layer after recording by irradiating the entire surface with a laser beam. FIG. Figure 10 is an X-ray diffraction diagram of the recording layer on the protective layer side when the recording layer is separated into the protective layer side and the substrate side after full-surface recording, and Figure 11 is an X-ray diffraction diagram of the recording layer on the substrate side. It is a line diffraction diagram. Figure 12 shows the irradiation time 0.
FIG. 13 is a diagram showing the temperature distribution formed in the recording layer when the irradiation time is 25 μsec, and FIG. 13 is a diagram showing the temperature distribution formed in the recording layer when the irradiation time is 25 μsec.

Claims (3)

[Claims] (1) Using a recording medium that has at least a substrate and a recording layer that performs recording and erasing by causing a reversible crystal state change or phase change by heat, the crystal state of a portion of the recording layer in the thickness direction is changed. A recording method characterized by recording by changing the phase or recording by changing the phase. (2) the recording layer is an organic thin film crystal, or
The recording method according to claim 1, wherein a recording medium containing this is used. (3) The recording method according to claim (1), wherein a recording medium is used in which the recording layer is a thin film crystal of a fatty acid or a fatty acid derivative, a benzoic acid derivative, an n-alkane or a derivative thereof, or a layer of polymer liquid crystal. .