JPH02289924A - Method for reproducing recording - Google Patents

Abstract

PURPOSE:To allow the high-speed and exact reading out of recorded information by making polarized light incident on a recording medium on which crystalline states are partially changed and recorded by applying heat to a thin film-like crystal to melt the crystal, then rapidly cooling the melt. CONSTITUTION:A recording layer 2 contg. the org. thin film-like crystal consisting of, for example, fatty acid or fatty acid deriv. and having optical anisotropy is provided. The heat is applied to such recording medium to melt the thin film-like crystal and thereafter the melt is rapidly cooled to partially change the crystal state and to record the same. The polarized light is made incident to this recording medium and the reflected or transmitted light is passed through a polarizer and is detected. The recording is read out by the intensity difference between the recorded part and the non-recorded part. The contrast of the recorded part and the non-recorded part is high. The reproduction of high reliability and the high-speed reproduction and thus possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] The present invention relates to the reproduction of information recorded by the application of thermal energy or irradiation with light, and more specifically, the reproduction of information recorded as a change in the crystalline state in a crystalline thin film. Regarding playback methods.

[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. Tb
, an inorganic recording medium using a metal material whose main component is In, or a polymethine dye such as cyanine,
Recording media using organic dyes such as macrocyclic azaannulene dyes such as phthalocyanine, naphthalocyanine, and porphyrin, naphthoquinone, anthraquinone dyes, and dithiol metal complex dyes are known. When thermal energy is applied to these recording media, such as by irradiation with a focused laser beam, 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.

As such a reversible recording medium, for example, Gd. Tb,
Rare earth elements such as oy and Fe. Ni. There is a magneto-optical recording medium using an alloy thin film made of a transition metal such as Go. 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, although this magneto-optical recording medium performs reproduction using polarized light, the sensitivity during reproduction is insufficient because the difference between the recorded and non-recorded areas is small.
The recording layer has disadvantages such as a poor /N ratio and problems such as deterioration of recording sensitivity and recording stability due to the effects of oxidation on the recording layer.

Moreover, as a reversible recording medium, Ge. Te. Se.
Sb, In. There is a method that utilizes the phase transition between a crystal and a metal material made of a thin film of an inorganic material containing an element such as Sn as a main component. This recording medium can perform heat mode recording and erasing using only laser light irradiation, and reproduces data based on the difference in reflectance. However, because the difference in reflectance between the recorded and non-recorded areas is small, the readout speed is low. There are still problems with reliability.

On the other hand, JP-A No. 54-119377, No. 55-15419
8. No. 63-39378 and No. 63-41186 disclose thermal recording materials comprising a resin matrix material and an organic low-molecular substance present in the matrix material in a state of fine particle dispersion. When this recording material is heated above a certain temperature and cooled, it becomes cloudy (light-shielding state), and when heated to a certain temperature range and then cooled, it becomes transparent, and recording is performed by reversible changes in this light-shielding property. However, even if the contrast due to this light-shielding property is clear in the case of records that are large enough to be observed with the naked eye, microscopically magnifying recorded areas created by changes in small areas of several micrometers. When observing the recorded image, the contrast becomes so low that it cannot be confirmed as a record. In the recording layer, the scattering properties of light change depending on the state of the matrix of fine particles of organic low-molecular substances. This is because the size of the fine particles is no longer small enough to cause such scattering. In order to compensate for this, it is conceivable to make the recording layer much thicker than the size of the recording. Forming the recording portion is substantially difficult. Therefore, it cannot be applied to a recording medium that performs high-density recording. Further, the above point is the same when erasing recording, and it is difficult to completely erase a minute recording portion without affecting other adjacent recording portions. Therefore, the above method is not particularly suitable for high-density recording and erasing. As described above, the conventional method of reproducing recording using a recording medium has the problem that a sufficient contrast between the recorded portion and the non-recorded portion cannot be obtained.

[Problem to be solved by the invention]

From this perspective, the present invention provides a recording reproducing method that uses a recording medium on which information can be recorded, reproduced, and erased, and that enables high-density recorded information to be read out quickly and accurately. .

[Means to solve the problem]

As a result of studying recording on organic compound crystals for the above-mentioned purposes, the present invention was conceived to show that when heat is instantaneously applied to a thin film-like crystal with optical anisotropy, the crystal state partially changes. They also discovered that by reheating to an appropriate temperature, the crystalline state returns to its original state, and that the polarization properties change significantly as a result. The present invention is based on this reversible change in crystal state.

That is, in the recording reproducing method of the present invention, heat is applied to a recording medium having a recording layer made of or containing an organic thin film crystal having optical anisotropy, thereby forming a thin film crystal. Polarized light is incident on a recording medium whose crystal state has been partially changed by melting and rapid cooling, and the reflected or transmitted light is detected through a polarizer. The recording medium is characterized in that the recording is read out, and the recording medium has optical anisotropy and a photothermal conversion layer that absorbs part or all of the light irradiated during recording and converts it into heat. A recording layer consisting of or containing organic thin film crystals, in which the thin film crystals are irradiated with light to melt and then rapidly cooled to partially change the crystal state for recording. This is a reproduction method in which polarized light is made incident on a recording medium, the reflected or transmitted light is detected through a polarizer, and the recording is read out based on the difference in intensity between recorded and non-recorded areas.

In addition, in the recording reproducing method of the present invention, the change in the crystal state of -1 which occurs in the organic thin film crystal by the application of heat or the irradiation of light causes a change in the orientation direction of the molecules and a partial change in the crystal state of the thin film crystal. This is a recording reproduction method that involves microcrystallization.

Further, in the recording reproducing method of the present invention, the organic film-like crystal having optical anisotropy is a fatty acid or a fatty acid derivative,
The main component is a benzoic acid derivative, an n-alkane having a melting point of 50° C. or higher, or a derivative thereof.

The recording reproduction method of the present invention will be explained in detail below.

The recording medium used in the recording reproducing method of the present invention has a recording-8 single layer containing an organic thin film crystal having optical anisotropy. Examples of the materials include fatty acids or fatty acid derivatives, benzoic acid derivatives, and n-alkanes or derivatives thereof having a melting point of 50° C. or higher.

The fatty acids or fatty acid derivatives used herein are specifically saturated or unsaturated mono- or dicarboxylic acids or their esters, amides, anilides, hydrazides, ureidos, anhydrides, or fatty acid salts such as ammonium b salts or metal salts. and 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 carbon number of these saturated or unsaturated fatty acids is preferably 10 or more -1-.

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, lignoceric acid, cerotic acid, montanic 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,
These include octyl ester, decyl ester, dodecyl ester, tetradecyl ester, stearyl ester, eicosyl ester, and docosyl 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 derivative referred to herein specifically includes benzoic acid represented by the following general formula, and its 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 (If), esters include esters of aliphatic hydrocarbon compounds with polyhydric alcohols or aromatic hydrocarbons having a plurality of hydroxy groups.

i3 Substituents for R1, R2, R3 and other benzoic acid derivatives in the general formula include, for example, hydrogen, an alkyl group, an alkoxy group, or an aryl group such as a phenyl group, a biphenyl group, a naphthyl group, an anthranyl group, etc. , R1
In addition to these, acyl group, acyloxy group, halogen,
Nitro group, hydroxy group, cyano group, carboxyl group and its ester, optionally substituted carbamoyl group, sulfo group and its ester, or alkyl group, phenyl group, amino group optionally substituted with substituted phenyl group, etc. There is. Further, the above alkyl group, alkoxy group, and aryl group may be substituted with the same substituent as R1. In addition, alkyl groups and alkoxy groups 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.

In addition, the n-alkane derivatives mentioned here 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. Specific examples of n-alkanes include, for example,
n- such as tetracosane, pentacosane, hexacosane, peptacontane, 111 octacosane, nonacosane, triacontane, dotriacontane, tetratriacontane, hexatriacontane, octatriacontane, tetracontane, etc.
There are alkanes and mixtures containing these as main components, so-called paraffins and paraffin waxes. In addition, as derivatives, ■-hexacosene, 1-heptacocene, 1-octacosene, 1-triacontene, 1-tetratriacontene, 1-hexatriacontene, 1-octatriacontene, 1-tetracontene, docosylbenzene , tetracosylbenzene, hexacosylbenzene, octacosylbenzene, 1-liacontylbenzene, tritriacontylbenzene, tetratriacontylbenzene, hexatriacontylbenzene, ■,18-dibromooctadecane, 1,20 -Dibromeicosane, 1,22 dibromeidocosane, etc.

The recording layer material used preferably has a melting point of 50 to 20
A temperature in the range of 0°C, particularly 60 to 150°C is preferred.

If it is lower than this, there will be a problem with the storage stability of recording, and if it is higher than this, the energy required for recording will be large and the recording speed will be slow.

In the recording layer of the recording medium used in the present invention, one type or a mixture of two or more of these organic compounds can be used. Further, the recording layer used in the present invention contains thin film-like crystals containing these organic compounds as main components, but resins other than this can be used as necessary to form the layer. 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, vinyl chloride-acrylate copolymer, polychloride Examples include vinylidene, vinylidene chloride-acrylic nitrile copolymer, polyester, polyamide, polyacrylate, polymethacrylate, polycarbonate, polyurethane, and silicone resin. When using a resin in the recording layer, the above organic compound 1 is used throughout the recording layer.
In contrast, the weight ratio of the resin is preferably 3 or less, particularly 1 or less.

Examples of the substrate of the recording medium used in the present invention include glass plates, metal plates, and plastic plates such as polymethyl methacrylate and polycarbonate.

However, if the information is to be read using transmitted light after recording, it is necessary to use a substrate that transmits the reproducing light.

When reading by reflected light, a layer of a metal or semimetal such as platinum, titanium, silicon, chromium, nitride, germanium, or aluminum is provided as necessary to serve as a reflective layer that reflects a portion of the light.

In the recording and reproducing method of the present invention, recording is performed by applying thermal energy to the recording layer of the recording medium according to the information to be recorded. It is necessary to provide a piece of material that absorbs a portion of the irradiated light and convert it into heat, or to include a substance that absorbs light and converts it into heat in the recording Ju. This light-absorbing layer may be, for example, a layer of metal or semimetal such as platinum, titanium, silicon, chromium, nickel, germanium, aluminum, etc., similar to the reflective layer, and in this case, it may also be used as the reflective layer. I can do it. In addition, the light-absorbing layer contains pigments that absorb the irradiated light, such as azo pigments, cyanine pigments, naphthoquinone pigments, anthraquinone pigments, squarylium pigments, phthalocyanine pigments, naphthoquinone pigments, porphyrin pigments,
The layer may contain an indigo dye, a dithiol complex dye, an azulenium dye, a quinone imine dye, a quinone diimine dye, and the like, and the dye is selected depending on the wavelength of the light used for recording. These dyes are also used when a light-absorbing substance is included in the recording layer.

The recording medium used in the present invention is an organic thin film crystal having optical anisotropy, or has a recording layer containing the same, and although its composition is not specified, it is commonly used. Examples of configurations of recording media that can be used are shown in FIGS. 1 to 5.

FIG. 1 shows a recording medium on which a recording layer 2 is formed that is or includes an organic film-like crystal having optical anisotropy; FIG. A light absorption/i13 (layer that reflects part of the light if necessary) is provided to absorb a part of the light and convert it into heat, and the second part is an organic thin film crystal with optical anisotropy, or 3 shows a recording medium provided with a recording layer 2 on a substrate l,
A recording medium having a light absorption layer 3 thereon, FIG. 4 shows a recording medium between the light absorption layer 3 and the recording layer 2 of the recording medium shown in FIG. 2, for example, for the purpose of improving the film quality of the recording layer. A recording medium provided with an undercoat layer 4, FIG. 5 shows the recording layer 2 of the recording medium in FIG.
This is a recording medium in which a protective layer 5 is further provided on 42.

Various resins can be used for the undercoat 14, such as the resins that may be used when forming the layer 2 described above. In addition, these resins may be used for the protective layer 5 as well, or
Alternatively, a glass plate may be used. When using a glass plate, a similar resin layer may be provided on the surface (the surface in contact with the recording layer) for the same purpose as the undercoat layer, or a surface treatment agent that improves the properties of the glass surface, such as a silane-based Alternatively, it may be treated with a titanate surface treatment agent.

In order to manufacture the recording medium used in the present invention, the substrate l
- If necessary, the photothermal conversion layer 3 is formed using, for example, a metal or semimetal as described above, by vapor deposition, sputtering, coating, or the like, and the recording layer 2k is formed thereon.

For example, there are the following methods for forming the record M2. First, a glass plate or resin film corresponding to the protective layer 5 is placed over the substrate provided with the photothermal conversion layer 3, keeping a gap corresponding to the required thickness of the layer. To create a gap, a spacer layer may be provided around the area where the recording layer will be formed, or a gap material having a minute and uniform diameter, such as silica particles or polystyrene beads, may be placed in advance on the side of the light-to-heat conversion layer. Alternatively, it may be attached to the protective layer side. The entire substrate with the gap formed in this way is placed in a constant temperature bath or placed on a hot plate and kept at a temperature higher than the melting point of the material used for the recording layer, and the molten material is placed at the end of the gap and soaked between the gaps. let them get involved. When the obtained melt layer is slowly cooled and crystallized, a thin film-like crystal of the recording layer can be formed between the light-to-heat conversion layer 3 and the protective layer 5. At this time, in order to keep the gap distance constant, pressure may be applied with a weight or the like until crystallization. Further, in order to prevent air bubbles from entering, the reaction may be carried out under reduced pressure. Another manufacturing method is to dissolve the material forming the recording layer in a suitable organic solvent, such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, etc., and apply a spin coating method or blade coating method. A calendar of uniform thickness is formed on the photothermal conversion calendar 3 by coating and drying using a dip coating method or the like, or by a vapor deposition method. A resin dissolved in a suitable solvent is applied thereon as necessary. First, this is placed in a constant temperature bath or placed on a hot plate and heated to a temperature higher than the melting point of the material for the recording layer, and then slowly cooled to crystallize and form the thin film crystals of the recording layer. .

In addition to this, various methods such as the Langmuir-Prodgett method can be used to form the recording layer.

When a photothermal conversion substance is included in the recording layer, the dye may be simultaneously dissolved in a solution of the material of the recording layer, or dispersed and applied.

The thickness of the recording layer is not particularly limited, but is usually 10
It is about 10 people to 10 households, preferably 10 people to 5 μm.

The thickness of the layer that absorbs part of the irradiated light and converts it into heat is
The appropriate range is determined by the wavelength and intensity of the light used for recording and the type of material used, but is approximately 50 to 5 degrees.

Recording in the present invention utilizes a partial and reversible change in the crystal state of an organic thin film crystal having optical anisotropy. Recording and erasing of information is performed by applying heat, and various methods can be considered for applying heat, but in order to record information with higher density, the most preferable method is to use focused laser light irradiation. . In this case, it is necessary to provide the recording medium with a layer that absorbs light and converts it into heat, or to add a substance that absorbs light and converts it into heat into the recording layer.

Information is recorded as follows. The laser beam irradiated portion of the recording layer is a recording layer that is made of or contains an organic thin film crystal in which a light absorption layer or a light absorption substance absorbs light and generates heat, and has an optical anisotropy of -20. is heated instantaneously and cooled rapidly when the laser beam irradiation stops, recording bits (however, pits here do not mean holes or depressions, but areas recorded as changes in the crystal state in a thin film crystal). (referred to as bits for convenience) are formed.

At this time, in the recording layer, a part of the thin film crystal, that is, a part that is instantly heated by the heat transmitted from the light absorption layer (substance) generated by short-term laser beam irradiation, completely melts the crystal. reach the temperature. However, when the laser light irradiation stops, the heat diffuses, and this part is instantly cooled and solidified (crystallized). The crystalline state of the portion where heat melting and cooling crystallization occurs instantaneously in this manner is different from the crystalline state of the portion to which no heat is applied, that is, the crystalline state of the surrounding non-recording portion.

This change in crystal state includes, for example, (1) a change in the size and form of crystal grains, (2) a change in the direction of crystal axes or the orientation of molecules, and (3) a change in crystal structure.

Before recording is performed, the recording layer is a thin film of crystals that are aligned in a substantially uniform direction and have a substantially uniform thickness. Among these changes, (1) a change in the size and form of crystal grains is such that, for example, a recording portion in a thin film crystal becomes a collection of small divided crystals. This change in state can be confirmed by observing the peeled recording layer using, for example, a scanning electron microscope. In addition, the change in the crystal axis direction or the molecular orientation direction in (2) means, for example, that the crystal structure is basically the same, but the direction in which the crystal is oriented, that is, the direction of the crystal axis, is crystallized in a different direction. Or, although it is not as clear as this, it is basically a collection of molecules with some kind of orientation, and the overall orientation direction is different from that of the surrounding non-recording area.

In addition, the change in crystal structure in (3) refers to the crystallization of the recording area to a different crystalline state from the surrounding non-recording area. It also includes cases where the range of crystallization is very narrow and the state changes to an amorphous state.

These changes in the crystal state are caused by the rapid cooling from the molten state caused by the local application of short-term heat to the thin film crystal, that is, by short-term light irradiation, but the cooling rate is mainly due to Depends on the time of light irradiation. Since it is difficult to measure temperature changes in minute areas irradiated with focused laser light, we take into consideration the intensity distribution of the laser light, light absorption, and heat conduction, and measure the thickness of each layer, light absorption characteristics, and heat conduction. If the thermal properties such as conductivity and specific heat are shown in Table 1, and the temperature change of the recording layer is simulated, for example, from 80°C to 6°C.
The time required to cool down to 0°C is the irradiation time of 10
At 0 μsec, it is approximately 1.7 μsec, and the irradiation time is 0.25
In μsec, it is about 15 nsec, and the difference in cooling rate is very large. Therefore, changes in the crystal state caused by short-term light irradiation (heat application) also vary depending on the irradiation time and are not constant. For example, in microcrystalization, there is a tendency that the faster the cooling rate, the more fine the material becomes. It is also related to the orientation state of molecules, and in general, the faster the cooling rate, the more disordered orientation tends to occur, and the range in which molecules are regularly arranged becomes narrower, resulting in a state of low crystallinity. However, even under such conditions, some kind of orientation state exists at least partially, and in the recording method of the present invention, the orientation of this recording area is characterized by being different from the orientation direction of the surrounding non-recording area. . Changes in the orientation direction due to such recording can be confirmed, for example, by measuring X-ray diffraction of the recording layer. Furthermore, the changes in the crystal state (1), (2), and (3) that occur due to recording occur in combination rather than individually. In addition, the temperature and cooling rate of the melted portion of the recording layer that is irradiated with laser light varies greatly depending on the distance from the photothermal conversion layer and the distance from the center of the beam, and each location has different conditions. Because crystallization occurs, the state is not necessarily uniform. therefore,
The changes in the crystalline states (1), (2), and (3) occur in a variety of combinations depending on the position even within one recording section.

Table 1 Laser Light Wavelength = 830 Stops To more specifically explain the change in crystalline state due to such recording, a case will be shown in which stearic acid, a typical fatty acid, is used as the material for the recording layer. The crystal state of the recording layer (substrate: glass, light-to-heat conversion layer: nichrome vapor-deposited film, protective layer: vinyl chloride-vinyl acetate copolymer) made of stearic acid thin film crystals formed as described above when unrecorded is stearic acid. It is a C-type crystal, whose a-axis,
The b-axis is oriented substantially parallel to the substrate. This is the X-ray diffraction diagram of this recording layer (Fig. 6), which shows the diffraction line (however,
This can be seen from the fact that only n = 2.3, 4, 5, 7, 8, 9, 10, 12) was observed. On the other hand, a semiconductor laser beam with a wavelength of 830 nm and a beam diameter of 1 tone φ was applied to this recording layer at a linear velocity of 3500 to 4000 mm/sec and an intensity of 5 at the medium surface.
The measured X-ray diffraction pattern (Fig. 7) after continuous lighting at mIN and recording over the entire surface in a spiral manner without any interval between recording lines shows that the distance between the long planes of stearic acid C type that appeared when no recording was performed was observed. In addition to the diffraction lines, a clear new diffraction line appears at 21.6°. This diffraction line corresponds to the short interval (4
．． ] - 1), and this means that when unrecorded, the +3 axis and b axis were oriented almost parallel to the substrate, but after laser light irradiation, the orientation direction of the crystal changes, It is shown that, at least in part, a structure was formed with the C axis oriented parallel to the substrate.

Since the recorded portion formed in the organic thin film crystal having optical anisotropy is delivered in a different state from the surrounding non-recorded portion, the optical properties, particularly the polarization characteristics, vary greatly. Therefore, the recording section may not be visible at all under a normal optical microscope.
Even if it is hardly visible, if you observe it in a crossed nicol state using a polarizing microscope, you can clearly observe it as a contrast between light and dark or as a difference in color tone.

The recording and reproducing method of the present invention uses polarized light to distinguish recorded areas and non-recorded areas based on the difference in polarization characteristics.

Specifically, in reproduction, polarized light focused on a spot similar to or smaller than that during recording is incident on the recorded recording medium, and the reflected or transmitted light is made to vibrate in a direction different from that of the incident polarized light. This is done by detecting light in the direction of vibration through a polarizer installed so that it passes through, and reading the intensity of the light. The light used for reproduction is, for example, the same laser beam as used for recording, but the intensity is sufficiently weakened so that the temperature of the recording layer does not rise to the recording temperature or the erasing temperature described below. The wavelength of the laser light may be different from that during recording. When laser light is used as reproduction light, it is linearly polarized light, so it can be incident on the recording medium as it is, but when other non-polarized light sources are used, a polarizer is used to convert the laser light into polarized light before it enters the recording medium.

Polarizers that pass reflected light or transmitted light from a recording medium include, for example, a polarizing prism that uses reflection from a transparent body,
Polarizing beam splinter, Nicol prism using birefringence, Glan-Thompson prism
, Wollaston prism
sm), or polarizing filters that utilize dichroism, such as Polaroid (trade name), any of which can be used.

The contrast between the recorded portion and the non-recorded portion changes depending on the relationship between the vibration direction of the polarized light with respect to the recording medium and the angle of the polarizer that passes the reflected or transmitted light.

If the contrast is the ratio of the intensity of reflected light or transmitted light from the recording area and the non-recording area, then the vibration direction and polarization of the incident reproduction light are such that the intensity is 0 or minimum when the recording layer is not present in the optical path. The contrast is often at its maximum when the angle of the beam is 90°, that is, when observed under a polarizing microscope, the state corresponds to crossed Nicols. On the other hand, the intensity of the light from the non-recording portion changes depending on the angle of the vibration direction of the reproducing light with respect to the thin film crystal of the recording medium, and the intensity of the light from the non-recording portion changes, and the maximum and minimum appear alternately every 45 degrees. Furthermore, the recording section may also change in a similar manner. At this time, the maximum and minimum angles of the recorded part and the non-recorded part are different, so at a certain angle the strength of the non-recorded part is greater, but as the angle is shifted, the strength of the recorded part is conversely stronger. In some cases, a reversal of strength may occur. Therefore, the contrast can be maximized by changing the vibration direction of the reproduction light relative to the recording medium while keeping the angle between the vibration direction of the input reproduction light and the polarizer that passes the reflected or transmitted light from the recording medium at 90 degrees. It is preferable to do so. However, the angle between the vibration direction of the reproduction light and the polarizer may not be 90° in some cases. For example, when contrast is defined as the difference in the intensity of light from a recorded area and a non-recorded area, the contrast may become larger if the intensity is shifted from 90' to some extent,
If the intensity of the light should not be too low, it is better to deviate from 90''.

As described above, in the recording reproduction method of the present invention, the relationship between the direction of the thin film crystal of the recording medium, the vibration direction of the reproduction light, and the angle of the polarizer that passes reflected or transmitted light is used to detect recording. The most favorable relationship can be found.

By applying heat to a part of the optically anisotropic organic thin film crystal in the recording layer and instantaneously melting and recrystallizing it, information is recorded as a change in the crystal state. Although the temperature is lower than the temperature at which the recording layer does not completely melt, it can be erased by heating to a temperature at which the molecules can undergo sufficient thermal movement. The temperature range in which erasing is possible varies depending on the material and purity of the recording layer, but
It exists at a temperature lower than the melting point of the thin film crystal that forms the recording layer. The erasure of this record can be confirmed by increasing the temperature of the recording layer while viewing it with a polarizing microscope. With a polarizing microscope, the recorded area looks like a dark line within a bright non-recorded area, but as the temperature is increased, the line begins to disappear at a certain temperature.
Eventually, the entire area will become as bright as the non-recorded area, and if it is cooled from this temperature, the recording will be erased. At this erasing temperature, there is no change in the brightness of the non-recorded area, but when the temperature is further lowered to reach the melting point of the recording layer, the entire visual field becomes completely dark.9 Therefore, the crystals formed in the thin film crystal When the molecules in the minute recording area whose state has changed reach a state where they can undergo sufficient thermal movement, they will adopt an arrangement similar to the molecules in the surrounding non-recording area, and by returning from that temperature to room temperature, the entire structure will change. It becomes a uniform thin film crystal and is erased.

Specifically, recording can be erased by heating the entire recording medium to a temperature range specified in 2 and cooling it, or by heating the entire recording medium to a temperature range specified in 2. It is also possible to erase only part of the recorded information by heating and cooling it to the erasing temperature. In the latter case, the intensity of the laser beam irradiated during recording may be weakened, the temperature of the recorded bit portion may be adjusted to fall within the erasing temperature range, and the irradiation may be repeated. At this time, the recording pit portion of the film-like crystal in the recording layer (the portion where the crystal state has changed) is once heated to the erasing temperature, and when cooled, it returns to its original state, that is, the same as the surrounding non-recording area. It returns to a crystalline state and the recorded pits are erased. This erased state, like the recorded state, can be confirmed by optical observation means such as a microscope or a polarizing microscope.

〔Effect of the invention〕

Recording in the present invention is basically not recorded by making holes in the recording layer using heat, changing the surface shape, or changing the light-shielding property or light-scattering property, but by forming the recording layer. A process in which the crystalline state of a thin film crystal is partially changed, and the change is not simply a change from crystalline to non-crystalline, but is recorded as a change in the orientation of molecules and a change that includes partial microcrystallization. It is. The present invention detects and reproduces the difference between the recorded portion and the non-recorded portion as a difference in polarization characteristics based on optical anisotropy. In this respect, unlike conventional recording and reproducing methods, the contrast between the recorded portion and the non-recorded portion is high, and highly reliable reproduction and faster reproduction are possible.

〔Example〕

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

:32 Example J Optically polished glass substrate (5 x 5 cm, thickness 1.2
1ffl+), a chromium layer which was a light reflection layer and a light-to-heat conversion layer was provided by vacuum deposition. The thickness was approximately 900 people. On the other hand, a glass plate (thickness 0.
Approximately 1 μm in diameter as gassop material on one side of
A fine amount of silica particles was deposited on the surface. both at 1.00℃
After heating the glass substrate in a constant temperature bath, a small amount of dibehenic acid (manufactured by Sigma, purity 99 g or higher) was placed on the glass substrate at the same temperature and melted. Next, the glass plate serving as the protective layer was gently placed over the behenic acid melt from one end with the gap material attached facing down, and the melt was spread over the entire surface and sandwiched. Further, a load was applied uniformly from F to the covered glass plate, and the temperature of the constant temperature bath was slowly lowered to crystallize behenic acid to form film-like crystals. By the above operations, the recording layer (about 0.6 μm thick) made of thin film-like crystals of behenic acid with an almost --like orientation is formed on the chromium layer 7, and the recording layer made of glass with a thickness of 0.1 m is formed on the -F layer. #/Injury formed.

A semiconductor laser beam with a wavelength of 780 nm and a diameter of 5 μm was continuously illuminated on the recording medium thus prepared so that the intensities were 7, 10 and 14n+11 on the surface of the recording medium, and a linear beam was applied at a linear velocity of 200 mn/sec. Five lines were scanned for each. When this recording medium was observed in a crossed nicol state using a polarizing microscope, clear recording was observed as shown in the photograph in FIG. 8 (.). Further, when this part was rotated by 45 degrees and observed, it was observed that the brightness of the recorded area and the non-recorded area were reversed as shown in the photograph in FIG. 8(b).

Next, 5 wavelength 780 light was focused on this recording medium to a diameter of 1 μm.
It was irradiated with a semiconductor laser beam having a wavelength of 1.5 nm and was continuously turned on so that the intensity was 0.51111.1. After the reflected light from the recording medium passed through a polarizer, it was received by a photodiode 1 so that the intensity of the light could be determined. First, a plate was set with only a chromium layer as a reflective layer instead of a recording medium, and the polarizer that passes the reflected light was rotated to make the intensity of the light entering the photodiode at an angle of 0 (i.e. , so that the angle between the vibration direction of the laser beam and the polarization f is 90°)
and fixed it.

Next, the recording medium was moved to the center so that the non-recorded area near the recorded area was irradiated with laser light. In this state, while maintaining the vibration direction of the laser beam and the angle k of the polarizer, the light source and the entire optical system are rotated to change the vibration direction of the incident light on the recording medium, and the intensity of the reflected light to be detected is adjusted. I fixed it at maximum. While maintaining the above-mentioned angular relationship, the recording medium is exposed to the laser beam at a zero angle. 0
The intensity of the reflected light was measured while moving at a speed of 1 mm/min and scanning the laser light in a direction perpendicular to the recording line.

FIG. 9 shows the intensity change of the reflected light at this time. From this result, the ratio of the intensity of the reflected light from the recording line of each intensity to the intensity of the reflected light from the non-recorded portion was determined and evaluated.

We also measured the intensity of the reflected light by scanning exactly the same position with the vibration direction of the laser beam parallel to the direction of the polarizer, and found that the intensity was almost constant between the non-recording area and the recording area. I couldn't tell them apart. The same result was obtained when the light was measured without passing through a polarizer.

From the above results, it can be seen that according to the recording reproduction method of the present invention, the contrast between the recorded portion and the non-recorded portion is high, and recording can be reproduced accurately.

Example 2 Optically polished 4 inch diameter (101.6+nm),
A recording medium was produced in the same manner as in Example 1, except that a glass disk with a thickness of 1.2 nm was used.

This recording medium is rotated at 90 ORPM, and a diameter of 1
Semiconductor laser light with a wavelength of 830 .mu.m was irradiated spirally at a rate of 3500 to 4000 mm/sec.

At this time, the laser beam had a frequency of 200 κHz, a duty ratio of 50%, and an intensity of 8 mW on the medium surface. When this recording medium is observed in a crossed nicol state using a polarizing microscope,
A clear record was enshrined. Furthermore, when the same part was rotated 45 degrees and observed, the brightness and darkness of the recorded and non-recorded areas were reversed. This recorded portion could not be observed with normal optical Ram=36-.

Next, the wavelength of 780n is focused on this recording medium to one tone in diameter.
m semiconductor laser beam with an intensity of 0. The light was continuously turned on and irradiated with a power of 5 mW. At this time, by following the same procedure as in Example 1, the vibration direction of the laser beam and the angle of the polarizer were adjusted to 90°.
”, and the laser beam was made incident so that the intensity of the reflected light from the non-recorded area was maximized. In this state, the laser beam was made perpendicular to the recording line so that the intensity was 0.
Scanning was performed at a speed of 0.01 +n+n/min, and changes in the intensity of reflected light were measured. From this result, the ratio of the intensity of the reflected light from the recorded area to the reflected light from the non-recorded area is calculated as follows:
It became 0.38. Furthermore, if the vibration direction of the laser beam and the direction of the polarizer were parallel to each other and the laser beam was transmitted to exactly the same position, it was not possible to distinguish between the recorded area and the non-recorded area. The same result was obtained when the measurement was performed without passing through a polarizer.

From this, it can be seen that according to the recording and reproducing method of the present invention, the contrast between the recorded portion and the non-recorded portion is high, and recording can be reproduced accurately.

Example 3 A glass disk provided with chromium M'r was prepared in the same manner as in Example 2. On this chromium layer, 5 wt% of vinyl chloride vinyl acetate copolymer (manufactured by Union Carbide: vYHH) was applied.
Apply a tetrahydrofuran solution and dry to a thickness of about 0.
A resin layer of 271111 was provided. Next, a 10Ilt% tetrahydrofuran solution of stearic acid (manufactured by Sigma, purity 99) was applied onto this resin layer and dried at 45°C.Furthermore, the same vinyl chloride-vinyl acetate copolymer as above was applied on top of this. Applying 5 wt% Te1-rahydrofuran solution, 45
Dry at °C. This disk was heat-treated at 90° C. for about 2 minutes and then slowly cooled. Through the above operations, a recording layer (thickness approximately 0.8 μm) consisting of thin film crystals of stearic acid oriented almost uniformly on the chromium layer and a protective layer (about 0.8 μm thick) consisting of vinyl chloride-vinyl acetate copolymer ( Thickness approximately 0.6μII
1) was formed.

This recording medium was irradiated with laser light and recorded in the same manner as in Example 2 except that the irradiation intensity was 5 mW. Similar clear recordings were observed when observed under a polarizing microscope. This recording could not be observed with a normal optical microscope.

Next, when this recording medium was irradiated with laser light and reproduced in the same manner as in Example 2, the ratio of the intensity of the reflected light from the recorded portion to the reflected light from the non-recorded portion was 0.32.

Furthermore, even if the vibration direction of the laser beam and the direction of the polarizer were made parallel to each other and the exact same position was scanned, it was not possible to distinguish between recorded areas and non-recorded areas. The same result was obtained when the measurement was performed without passing through a polarizer.

From this, it can be seen that according to the recording and reproducing method of the present invention, the contrast between the recorded portion and the non-recorded portion is high, and recording can be reproduced accurately.

[Brief explanation of the drawing]

1 to 5 are cross-sectional views of the recording medium used in the present invention, in which 1 is a substrate, 2 is an organic M having optical anisotropy.
Recording layer of film crystal, 3 is photothermal conversion first floor, 4 is sublayer 1-
, 5 indicates a protective layer. FIG. 6 is an X-ray diffraction diagram of a recording medium having a thin film crystal of stearic acid as a recording layer in an unrecorded state, and FIG. 7 is an X-ray diffraction diagram of the same recording medium after recording. FIGS. 8(a) and (b) are polarized light micrographs of a portion recorded by irradiating a 5 μmφ laser beam onto a recording medium having a thin film-like crystal of behenic acid as a recording layer; (a) and (b)
is an observation of the same part rotated 45 degrees. FIG. 9 shows a result of scanning the recorded portion of FIG. 8 with a laser beam of one tone φ and measuring the change in the intensity of the reflected light that passed through the polarizer.

Claims (4)

[Claims] (1) A recording medium that is made of an organic thin film crystal having optical anisotropy or has a recording layer containing the thin film crystal is crystallized by applying heat to melt the film crystal and then rapidly cooling it. A method is characterized in that polarized light is incident on a recording medium on which the state has been partially changed and recorded, the reflected or transmitted light is detected through a polarizer, and the recording is read out based on the difference in intensity between recorded and non-recorded areas. How to play recordings. (2) The above-mentioned recording medium is composed of a light-to-heat conversion layer that absorbs part or all of the light irradiated during recording and converts it into heat, and an organic thin-film crystal having optical anisotropy, or It has a recording layer containing crystals, which is irradiated with light to melt the thin film crystals and then rapidly cooled to partially change the crystal state. A recording playback method that detects reflected or transmitted light through a polarizer and reads the record based on the difference in intensity between recorded and non-recorded areas. (3) A claim that the above-mentioned change in the crystal state that occurs in the organic thin film crystal due to the application of heat or irradiation with light during recording includes a change in the orientation direction of molecules and partial microcrystallization of the thin film crystal. Method for playing back recordings as set forth in item (1) or (2). (4) Claim (1) wherein the organic thin film crystal having optical anisotropy is mainly composed of a fatty acid or a fatty acid derivative, a benzoic acid derivative, or an n-alkane or a derivative thereof having a melting point of 50°C or higher. ), (2) or (3) recording playback method.