JPH02131987A - Recording medium - Google Patents

Abstract

PURPOSE:To provide excellent recording sensitivity, recording speed, satisfactory recording stability, high speed erasure of recorded information by providing a recording layer which contains a thin filmlike crystal containing fatty acid or fatty acid derivative as a main ingredient or a layer containing its thin filmlike crystal. CONSTITUTION:A substrate 1 formed with an optothermal conversion layer 3 is covered with a glass plate or a resin film corresponding to a protective layer 5 for holding a gap responsive to the thickness of a necessary recording layer 2. The whole substrate formed with the gap is intruded into a constant- temperature oven, held at a temperature higher than the melting point of a material used for the layer 2, the melted material is placed at the end of the gap, and impregnated to the gap. When the obtained melted liquid layer is gradually cooled and crystallized, a thin filmlike crystal of the layer 2 is formed between the layers 3 and 5. The recording medium of this invention is made of the thin filmlike crystal which contains fatty acid or fatty acid derivative as a main ingredient or has a recording layer containing it, and utilizes the fact that the crystal state of the crystal is reversibly changed by the application of heat.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a high-density recording medium that utilizes a reversible change in crystalline state due to the application of thermal energy.

[Prior art]

In recent years, so-called heat mode recording systems have been put into practical use, which convert information given by light into thermal energy and record it as a change in the shape or physical properties of a recording material. Such heat mode recording media include inorganic recording media using metal materials whose main components are 7e, Bi, Se, Tb, In, etc.;
Recording media are known that use organic dyes such as polymethine dyes such as cyanine, macrocyclic azaannulene dyes such as phthalocyanine, naphthalocyanine, and vorifylline, naphthoquinone, anthraquinone dyes, and dithiol metalloid dyes. 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, creating holes (pits).
It is used to form and record 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, played back, and erased is increasing. As such a reversible recording medium, for example, rare earth elements such as Gd, Tb, Dy and F
There is a magneto-optical recording medium that uses an alloy thin film made of transition metals such as e, Ni, and Co. This uses a combination of heating by laser beam irradiation and an externally applied magnetic field to record, and reproduces by utilizing the difference in the rotational direction of the light vibration plane depending on the direction of magnetization. Furthermore, information is erased by heating with a laser and by applying an external magnetic field in the opposite direction to that used during recording. However, this magneto-optical recording medium has drawbacks such as insufficient sensitivity during reproduction and a poor S/R ratio, as well as problems with deterioration of recording sensitivity and recording stability due to effects such as oxidation. There is.

Also, as reversible recording media, Go, Te, Ss, Sb, I
There is a method that utilizes the crystal-amorphous phase transition of a recording layer made of a thin film of an inorganic material mainly composed of elements such as n 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 the contrast between recorded and non-recorded areas and recording stability are not sufficient.
It has drawbacks such as problems with the safety of the material of the recording layer. On the other hand, JP-A-54-119377, JP-A-55
-1541911. 63-39378, 63-41
Publication No. 186 discloses a thermal recording material comprising a resin matrix material and an organic low-molecular substance present in the matrix material in the form of fine particles dispersed therein. When this recording material is heated above a certain temperature and cooled, it becomes cloudy (light-shielding state).
When heated to a certain temperature range and then cooled, it becomes transparent, and recording is performed by this reversible change in light-shielding properties. However, even if the contrast caused by this light-shielding property is clear in the case of records that are large enough to be observed with the naked eye, microscopically magnifying the recorded areas formed by small changes in the number of 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 these particles is no longer small enough to cause such scattering. In order to compensate for this, it is possible to make the recording layer much thicker than the size of the recording, but by heating the thick recording layer uniformly throughout the thickness direction, it is possible to create a small recording area. It is practically difficult to form. Therefore, it cannot be applied to recording media that perform high-density recording. In addition, as an erasable recording medium using an organic material, for example, JP-A-58-199343 discloses an organometallic complex bis(1-p-n-alkylphenylbutane-1
．． 3-dionato) (■) and organic polymer mixture, JP-A-1986
No. 3-15793 discloses a mixture of crystalline and immature thermoplastic resins, JP-A-63-95993 and JP-A-96748 disclose a crystalline aromatic vinylene sulfide polymer, and JP-A No. 63-279440 discloses a crystalline aromatic vinylene sulfide polymer. is a sulfur-containing polymer, and JP-A No. 63-128993 discloses a sulfur containing polymer,
2,2] Octane quaternary salt, Japanese Patent Application Laid-Open No. 63-259851 discloses a recording medium that utilizes the crystalline-amorphous transition or change in the degree of orientation of stretched and oriented polymers or liquid crystalline polymers. There is. However, all of these have slow recording speeds or slow erasing speeds, making them difficult to put into practical use.

[Problem to be solved by the invention]

As described above, conventional recording media have various problems such as recording stability, recording sensitivity, erasing speed, and contrast between recorded and non-recorded areas. Furthermore, from the standpoint of safety, it is desirable that the recording medium be made of non-toxic materials. From this viewpoint, the present invention provides a recording medium on which information can be recorded, reproduced, and recorded information can be erased, and which can be used repeatedly. We also provide recording media that have excellent recording sensitivity and recording speed, good recording stability, high contrast between recorded and non-recorded areas, can record information at high density, and can erase recorded information at high speed. It is something to do. Furthermore, the present invention provides a non-toxic and highly safe recording medium. [Means for Solving the Problems] As a result of studying the thermal changes of various organic materials for the above-mentioned purposes, the present inventors found that when thin film crystals of fatty acids or fat V derivatives are used in the recording layer, It was discovered that the crystalline state of the part to which heat was applied changes. We also discovered that this changed area could be restored to its original state by being reheated to an appropriate temperature. The present invention is based on the thermal reversible change of such fatty acid or fatty acid derivative thin film crystals.

That is, the recording medium of the present invention is a recording medium having a recording layer on a substrate, in which the recording layer is a thin film crystal whose main component is a fatty acid or a fatty acid derivative, or a layer containing the thin film crystal. It is characterized by Further, the recording medium of the present invention has a recording layer made of or containing the above-mentioned thin film crystal, and a light-heat exchange layer that absorbs part or all of the light irradiated during recording and converts it into heat. This is a characteristic feature.

Furthermore, in the above two configurations, the recording medium of the present invention contains a photothermal conversion substance that absorbs part or all of the light irradiated during recording and converts it into heat in the recording layer containing a fatty acid or a fatty acid derivative. It is characterized by this. The recording medium of the present invention will be explained in detail below. Does the recording layer of the recording medium of the present invention consist of thin film crystals containing fatty acids or fatty acid derivatives as a main component? In detail, the fatty acid or fatty acid derivative referred to here refers to saturated or unsaturated mono- or dicarboxylic acids or their esters, amides, anilides, hydrazides, ureides, anhydrides, or ammonium salts or fatty acid salts such as metal salts; esters are
Includes esters with compounds having more than one hydroxyl group, 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 unsaturated fatty acids may have one double or triple bond or two or more. The carbon number of these saturated or unsaturated fatty acids is preferably 10 or more. Specific examples of saturated fatty acids include undecanoic acid, lauric acid, myristic acid, pentadecanoic acid, panolemitic acid,
Examples of unsaturated fatty acids include heptadecanoic acid, stearic acid, nanodecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melisic acid.
Examples include oleic acid, elaidic acid, linoleic acid, sorbic acid, and stearolic acid. Specific examples of esters include methyl esters, ethyl esters, hexyl esters, octyl esters, decyl esters, dodecyl esters, tetradecyl esters, stearyl esters, eicosyl esters, and docosyl esters of these fatty acids.

Examples of metal salts include sodium, potassium, magnesium, calcium,
There are metal salts such as nickel, nickel, zinc, cadmium, and aluminum.

The fatty acid or fatty acid derivative used preferably has a melting point in the range of 50-200°C, particularly 60-150°C. If it is lower than this, there will be a problem with the preservation of the record, and if it is higher, the energy required for recording will increase and the recording speed will be slow. In the recording layer of the recording medium of the present invention, one type or a mixture of two or more of these fatty acids or fatty acid derivatives can be used. Further, the recording layer in the present invention is made of or contains thin film-like crystals mainly composed of these fatty acids or fatty acid derivatives, but in addition to this, resins may be used as necessary to form the layer. be able to. Examples of the JtA 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, and polyvinyl chloride-vinyl acetate copolymer. Examples include vinylidene chloride, vinylidene chloride-acrylonitrile copolymer, polyester, polyamide, polyacrylate, polymethacrylate, polycarbonate, polyurethane, and silicone resin. When a resin is used in the recording layer, the weight ratio of the resin to 1 part fatty acid or fatty acid derivative in the entire recording layer is 3 or less, especially 1 part by weight.
It is preferable that it is below.

Substrates used in the recording medium of 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 reproduction light. When reading by reflected light, a film of a metal or semimetal such as platinum, titanium, silicon, chromium, nickel, germanium, or aluminum is provided as a reflective layer, if necessary. The recording medium of the present invention performs recording by applying heat to the recording layer, but when using light such as a laser beam as a method of applying heat, one part of the irradiated light is used in accordance with the information to be recorded. Either it is necessary to provide a light-to-heat conversion layer that absorbs some or all of the light and convert it into heat, or it is necessary to include a substance in the recording layer that absorbs light and converts it into heat. As the light-to-heat conversion layer, a metal or semimetal film similar to the reflective layer may be provided, and therefore, this layer can also be used as the reflective layer. The photothermal conversion layer also contains dyes that absorb the irradiated light, such as azo dyes, cyanine dyes, naphthoquinone dyes, anthraquinone dyes, squarylium dyes, phthalocyanine dyes, naphthalocyanine dyes, porphyrin dyes, Indigo dyes, dithiol complex dyes, azulenium dyes, quinoneimine dyes,
It may be a layer containing a quinone diimine dye, etc., and is selected depending on the wavelength of the light used for recording. On the other hand, as the substance to be contained in the recording layer that absorbs light and converts it into heat, various dyes can be used to be contained in the light-to-heat conversion layer, and the material is selected depending on the wavelength of the light used for recording. The recording medium of the present invention has a recording layer made of or containing a thin film crystal mainly composed of a fatty acid or a fatty acid derivative on a substrate, and the recording layer is a layer whose crystal state changes upon application of heat. Figures 1 to 5 show examples of the configurations of commonly used recording media, although their configurations are not specified. In FIG. 1, 1 is a substrate, and 2 is a recording layer consisting of or containing a thin film-like crystal whose main component is a fatty acid or a fatty acid derivative. FIG. 2 shows a photothermal conversion layer 3 between the substrate 1 and the recording layer 2 shown in FIG. 1, which absorbs part or all of light, converts it into heat, and reflects part of the light as necessary
It has been established. In FIG. 3, a recording layer 2 is provided on a substrate 1, and a photothermal conversion layer 3 is provided thereon. In FIG. 4, an undercoat layer 4 is provided below the recording layer 2 of FIG. 2 for the purpose of improving the film quality of the recording layer 2, for example.
Further, FIG. 5 shows a structure in which a protective layer 5 is provided on the recording layer 2 of FIG. 4.

For the undercoat 94, various resins can be used, such as the resins that may be used when forming the recording layer 2 described above. The protective layer 5 may also be made of these resins, or may be made of a glass plate. 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 undercoat M, or a surface treatment agent such as silane or It may be treated in advance with a titanate-based surface treatment agent. In order to manufacture the recording medium of the present invention, a light-to-heat conversion layer 3 is formed on the substrate 1 as necessary using, for example, the metal or metalloid as described above, by means such as vapor deposition, sputtering, or plating. Recording layer 2 is formed on top. For example, there are the following methods for forming the recording layer 2. First, a glass plate or resin film corresponding to the protective layer 5 is covered over the substrate l provided with the light-to-heat conversion layer 3, keeping a gap corresponding to the required thickness of the recording layer 2. In order to create a gap, a spacer layer may be provided around the area where the recording layer 2 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 photothermal conversion N3 side. Alternatively, it may be attached to the protective layer 5 side. Place the entire substrate with gaps formed in this way in a constant temperature bath or place it on a hot plate, keep it at a temperature higher than the melting point of the material used for recording/f12, place the molten material at the end of the gap, and place the molten material between the gaps. Let it soak in. When the obtained melt layer is slowly cooled and crystallized, a film is formed between the photothermal conversion layer 3 and the protective layer 5.
Thin film crystals of layer 2 can be formed. At this time, in order to maintain the gap interval constant, pressure may be applied using a weight or the like until crystallization. Additionally, these operations may be performed under reduced pressure to prevent air bubbles from entering. Further, as another manufacturing method, for example, the material forming the recording layer 2 may be mixed with a suitable organic solvent such as tetrahydrofuran or methyl ethyl ketone. Dissolve in methyl isobutyl ketone, chloroform, carbon chloride, etc., spin coat method,
A layer of uniform thickness is formed on the light-to-heat conversion layer 3 by coating and drying by a blade coating method, dip coating method, or the like, or by a vapor deposition method. If necessary, apply a resin dissolved in an appropriate solvent on top of this. Next, 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 of the recording layer 2, and then slowly cooled to crystallize and form the thin film crystals of the recording layer 2. Form. Recording layer 2
In addition, various methods such as the Langmuir-Prodgett method can be used to form the . When a photothermal conversion substance is included in the recording layer 2, the dye may be simultaneously dissolved in a solution of the material of the recording layer 2, or dispersed and applied.

When forming the light-to-heat conversion layer 3, which absorbs part or all of the light irradiated during recording or erasing and converts it into heat, using the dye described above, it is formed by a method such as vapor deposition or sputtering. It may also be formed by applying a solution dissolved or dispersed in a solvent.

In this case, a binding resin may be used if necessary. If a light-reflecting layer is required, a vapor-deposited metal film may be provided separately. Furthermore, the thickness of the recording layer 2 that is made of or contains thin film-like crystals mainly composed of fatty acids or fatty acid derivatives is as follows:
There is no particular limitation, but usually 10 to 10. ，
Preferably, the number is about 10 to 51 people. The thickness of the photothermal conversion layer 3 is determined in an appropriate range depending on the wavelength and intensity of the light used for recording and the type of material used, but it is generally between 50 and 5 pcm.
It is about m. The recording medium of the present invention has a recording layer consisting of or containing thin film crystals mainly composed of fatty acids or fatty acid derivatives, and the crystal state of the thin film crystals is reversibly changed by application of heat. It takes advantage of this fact. Various methods can be considered for recording information, that is, applying heat, but in order to perform high-density recording, the most preferable method is to use focused laser light irradiation. In this case, it is necessary to provide the recording medium with the aforementioned photothermal conversion 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.

During recording, the photothermal conversion layer or photothermal conversion material absorbs light and generates heat in the area irradiated with the laser beam, and the recording layer made of film-like crystals of fatty acids or fatty acid derivatives or containing the same is instantaneously heated. When the laser beam irradiation stops, the material cools down rapidly, forming recording pits (the pits here are not holes, but areas recorded as changes in the crystal state in the thin film crystal). At this time, in the recording layer, a part of the thin film crystal, that is, a part that is instantaneously heated by the heat transmitted from the light-to-heat conversion layer (substance) generated by short-term laser beam irradiation,
A temperature is reached at which the crystal completely melts. However, when the laser light irradiation stops, the heat diffuses, and this part is instantly cooled and assimilated (crystallized). The crystalline state of the portion where heat melting and then cooling crystallization occur instantaneously in this manner is different from that of the portion to which no heat is applied, that is, the crystalline state of the surrounding non-recording portion.

Examples of changes in the crystal state include (1) changes in the size and morphology of crystal grains, (2) changes in the direction of crystal axes or molecular orientation, and (3) changes in crystal ellipsoidal structure. .

Before recording is performed, the recording layer is a thin film of crystals with a substantially uniform thickness and oriented in a substantially uniform direction. Among these changes, (1) change in the size and form of crystal grains means, for example, that the recording part in a thin film crystal becomes a collection of small 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 direction of the crystal axis or the change in the direction of the molecular arrangement in (2) means, for example, that the crystals are basically the same, but the direction in which the crystals are oriented, that is, the direction of the crystal axis, is different. 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 (3) refers to the crystallization of the recording area to a different crystalline state from the surrounding non-recording area, and this includes cases where the regularity of the molecular arrangement is greatly disturbed or This includes cases where the range in which it has properties is very narrow and it changes to an amorphous state. These changes in the crystal state are caused by the local application of short-term heat to the thin convergent crystal, i.e., the rapid cooling from the molten state caused by short-term light irradiation. The speed mainly depends on the time of light irradiation. Since it is difficult to measure temperature changes in minute areas irradiated with focused laser light, we consider the intensity distribution of the laser light, light absorption and heat conduction, and measure the thickness of each layer, light absorption characteristics, and If we simulate the temperature change of the recording layer using the thermal properties such as conductivity and specific heat as shown in Table 1, we can see that, for example, the change in temperature 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 for the faster the cooling rate, the more fine the material becomes. It is also related to the state of molecular orientation; 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, which may result 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. ．． Such a change in the orientation direction due to recording may be caused by, for example, XA! of the recording layer. This can be confirmed by measuring diffraction. 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 the laser beam varies greatly depending on the distance from the photothermal conversion layer and the distance from the center of the beam, and crystallization occurs differently in each location. occurs, so the condition is not necessarily uniform. Therefore, (1
), (2), and (3) are compounded in various forms depending on the position even within one recording section.

Table 1 Laser light wavelength: 830 nm In order to more specifically explain the change in crystalline state caused by such recording, we will explain the case where 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: chromium-deposited film, protective H: vinyl chloride-vinyl acetate copolymer) made of stearic acid thin film crystals formed as described above when unrecorded is stearin. It is a C-type crystal of acid, and its 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 r+=2.3, 4, 5, 7, 8, 9, 10, 12) is observed. on the other hand. On this recording layer, a semiconductor laser beam with a wavelength of 830 nm and a beam diameter of 1 praφ is continuously illuminated at a linear velocity of 3,500 to 40,001 m/see and an intensity of 5+ sW on the medium surface, so that the recording line is illuminated over the entire surface in a spiral shape without leaving any gaps between recording lines. After recording, in the X-ray diffraction diagram determined by 4Ig (Fig. 7), a clear diffraction line appears at 21.6° in addition to the diffraction line of stearic acid C-type long plane spacing that appeared before recording. . This diffraction line is due to the short plane spacing (4. IL person) of the C-type crystal, which means that the a-axis and b-axis were oriented almost parallel to the substrate when unrecorded, but the laser beam After irradiation, the orientation direction of the crystal changed, indicating that a structure in which the C axis was oriented parallel to the substrate was formed, at least in part.

The recorded state can be confirmed using optical observation means such as a microscope or a polarizing microscope. In particular, such a change in the crystal state is often accompanied by a change in polarization characteristics, which can often be clearly observed as a contrast between light and dark or a difference in color tone under crossed Nicol conditions using a polarizing microscope. Therefore, in order to reproduce (read) recorded information, focused polarized light is incident on the recording medium, and the reflected or transmitted light is placed so that the light in the vibration direction perpendicular to the vibration direction of the incident light is transmitted. The intensity of the light used for reproduction is sufficiently weakened compared to the light used for recording and erasing, so that the temperature of the recording layer does not rise to the erasing temperature. do. In this way, heat is applied to a part of the thin film crystal mainly composed of fatty acids or fatty acid derivatives in the recording layer, and the information recorded as a change in the crystal state is instantaneously melted and recrystallized. is lower than the temperature at the time of recording,
This is a temperature at which the crystal thin film of the recording layer does not melt, but 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 forming the recording layer. The erasure of this record can be confirmed by increasing the temperature of the recording layer while observing it with a polarizing microscope. For example, if a dark recorded area is formed in a non-recorded area that appears uniformly bright, the recorded area will begin to chip at a certain temperature or higher.
In a temperature range of approximately 5 to 20° C., all of the recorded portion disappears, and the entire state becomes the same as the non-recorded portion. If you raise the temperature further. The field of view becomes completely dark as the crystal thin film of the recording layer melts. Therefore, when the molecules in the tiny recording area formed in a thin film crystal with a changed crystal state reach a state where they can undergo sufficient thermal movement, they begin to arrange in the same way as the molecules in the surrounding non-recording area. , by returning from that temperature to room temperature, the whole becomes a uniform thin film state crystal and disappears. Specifically, erasing can be done by heating the entire recording medium to the above temperature range and cooling it to erase the entire recording,
It is also possible to erase only a portion of the recorded information by locally heating and cooling the recorded bit portion or a slightly wider area 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 pit area may be adjusted to fall within the erasing temperature range, and irradiation may be repeated. At this time, the recording bit part (the part whose crystal state has changed) of the thin film crystal of the recording layer is heated to the erasing temperature, and when it is cooled, the crystal state is the same as the surrounding non-recording part. The state returns and the recorded pits are erased. This erased state, like the recorded state, can be confirmed by optical observation means such as an m-microscope or a polarizing microscope. The recording medium of the present invention basically does not use heat to make holes in the recording layer or change the surface shape of the recording Jd, but instead to use heat to form holes in the recording layer or change the surface shape of the recording layer Jd, the recording medium contains the thin film-like crystals forming the recording layer or the IIa layer. Recording is performed by changing the crystalline Ill of a portion of a thin film crystal, and the difference between the formed recorded portion and non-recorded portion is detected as, for example, a difference in polarization characteristics. In this respect, the recording medium of the present invention is significantly different from conventional recording media. For example, this is based on a completely different phenomenon from the recording medium described in the prior art section, in which organic low-molecular compounds exist in a dispersed state in a resin matrix, and the light-shielding property changes depending on the heating temperature. In other words, in the recording medium of this example, the organic low-molecular-weight compound exists in the form of fine particles in the recording layer, and the recording section itself is also formed by a large number of fine particles, and the recording is caused by differences in light-shielding properties based on the scattering of light due to the dispersed state of these fine particles. In contrast, in the recording medium of the present invention, the fatty acid or fatty acid derivative exists as a thin film crystal, and the recording is formed as a change in the crystal state in a part of the thin film crystal, resulting in changes in optical properties. It detects the difference. Therefore, the difference between the two banks is obvious. [Effects of the Invention] Recording and erasing on the recording medium of the present invention is basically based on the difference in temperature reached by thin film crystals of fatty acids or fatty acid derivatives that form the recording layer, and this is due to the difference in temperature achieved by the thin film crystals of fatty acids or fatty acid derivatives that form the recording layer. Can be adjusted. Also, since recording and erasing can be performed at high speed, recording is performed while erasing. So-called overwriting is possible. Further, this recording and erasing can be performed repeatedly and stably. Furthermore, since the recording section is in a stable state like the non-recording section, recorded information can be stored stably for a long period of time. [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A chromium layer serving as a light reflection layer and 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 ml) and a thickness of 1.2 mm.
The thickness was approximately 900 people. On this chromium layer, vinyl chloride-vinyl acetate copolymer (Union Carbide Co., Ltd. 1%
A 5 wt % tetrahydrofuran solution of VY}IH) was applied and dried to form a resin layer with a thickness of approximately 0.2 μm.
Next, a low % tetrahydrofuran solution of stearic acid (manufactured by Sigma, purity 99% or higher) 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 heat treated at 90°C for about 2 minutes and then slowly cooled. Through the above operations, a recording layer (thickness approximately O.S.) consisting of thin film-like crystals of stearic acid oriented almost uniformly on the chromium layer, and a protective layer made of vinyl chloride-vinyl acetate copolymer on top of the recording layer (approximately O.S. thickness) are formed on the chromium layer. A layer (approximately 0.6 mm thick) was formed. While rotating the thus prepared recording medium at 90 ORPM, it was irradiated with semiconductor laser light with a wavelength of 830 nm focused on a diameter of 14 under the following conditions (1) and (2) to form a spiral record. At this time, the linear velocity in the recording direction of the recorded portion on the disk is approximately 350
0-4000mm/see. Irradiation conditions (1) Lighting conditions: Two frequencies: 200K}lz, duty ratio: 50% Intensity on the recording medium surface: 5 V Recording line spacing: Approximately 3.54 (center distance) (2) Lighting conditions: Continuously lit recording medium Intensity in plane: 5Ilw Distance between recording lines: approx. 1 [(center distance) When the recording medium irradiated with laser light under the conditions (1) above is observed w4 in the orthogonal Nicol state using a reflective polarizing microscope, the recording layer It was observed with clear contrast that a line-shaped recorded portion with a width of about 1 pa was formed in the laser beam irradiated area. However, this recording section cannot be recorded with a normal optical microscope. It was almost impossible to confirm. Figure 8 shows a photograph of an example observed using a polarizing microscope. The recording layer of the recorded recording medium is stripped from the chromium layer,
The surface (the surface that was in contact with the chromium layer) was examined using a scanning electron microscope! When observed, the area irradiated with the laser beam was a collection of small plate-shaped crystals. When a recording medium irradiated with laser light under the conditions (2) above was similarly observed using a polarizing microscope, it was found that recording was performed over the entire irradiated area of the recording medium with almost no gaps. The 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 6 shows the X-ray diffraction before recording, and Figure 7 shows the X-ray diffraction after recording. From FIG. 6, 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 as shown in Figure 7, a diffraction line (2 0 = 21.6'') based on the short plane spacing appears, and a structure in which the C axis is oriented parallel to the substrate is formed in the recording part of the recording layer. Next, the temperature of the recording medium recorded under the conditions (1) was raised from room temperature at a rate of 1°C/min while observing it under a polarizing microscope. .

Then, the recording section that was visible with clear contrast changed to 6
It started to disappear at about 0℃, and at about 68℃ it became completely the same brightness as the surrounding area and disappeared. Moreover, no change was observed in the state of the surrounding non-recording area up to this temperature. As the temperature continued to rise further, the field of view became completely dark from one end to 69.4°C, and quickly spread to the entire area, indicating that the crystal thin film of the recording layer had completely melted at this temperature. Next, on the recording medium recorded under the conditions (1), a semiconductor laser beam with a wavelength of 780 nm focused to a diameter of 5 Ija was applied to the recording medium at an intensity of 1. 5mV, 2mw and 3
Continuously lights up at 1l, line speed 50mm/see
It was scanned in a straight line at a speed of When this recording medium was observed with a polarizing microscope, it was found that the 9th
As shown in the photo in the figure, the irradiation intensity was too strong in the area irradiated with 2Ilw and 3mW intensities, so in the center of the beam, the thin film-like crystals reached a temperature higher than the melting temperature, and a new line-shaped record was formed. It was done. However, at the edge of this line, that is, at the area scanned by the peripheral part of the beam, the recorded area previously recorded by the Igφ laser beam was erased. On the other hand, in the area irradiated with an intensity of 1.5 mW, the area recorded by the previous 1, cowφ laser beam was erased in a band shape with a width of about 2.5 mm. based on the above results. It was confirmed that the recording layer entered the erasing temperature range by irradiation with an intensity of 1.51, and erasing was performed.

Example 2 A glass disk having chromium J as a light-to-heat conversion layer was prepared in the same manner as that used in Example 1. In addition, a small amount of silica particles with a diameter of about 14 mm was attached as a gap material to one side of a 0.1 mm thick glass plate to serve as a protective layer. After heating both in a thermostat at 100°C, apply behenic acid (manufactured by Sigma;
(purity of 99% or higher) was placed on top and melted. Next, one glass plate was gently placed over the behenic acid melt from one end with the side with the gap material facing down, and the melt was spread over the entire surface and sandwiched. Furthermore, a load was applied uniformly over the covered glass plate, and the temperature of the thermostat was slowly lowered to crystallize the behenic acid into a thin film of crystals. By the above operations, a recording layer (about 0.8 Il thick
a) and a protective layer made of glass with a thickness of 0.1 mm was formed thereon. The recording medium created in this way is rotated at 90 ORPM, and a semiconductor laser beam with a wavelength of 830 nm focused to a diameter of 1 is heated at a linear velocity of 3500 to 4000 mm/see.
It was irradiated in a spiral pattern. The irradiation conditions at this time were the two conditions (1) and (2) as in Example 1. However, in (1), the irradiation intensity is 3, 4, 5, 6,
8, 10, 12mν, and in (2) it was 8■V. When observing the state of the recording recorded under irradiation condition (1) using a reflective polarizing microscope in the orthogonal Nicol state, there is a clear contrast that shows that recording has been made with an intensity of 41 or higher in the laser beam irradiated area of the recording layer. It was recognized in In addition, as the intensity of the irradiated laser beam increases, the width of the recorded part, that is, the part where the crystal state has changed due to melting and recrystallization, becomes wider.
．． When observing the recorded portion using a polarizing microscope (8 lines), when the same portion was rotated on the sample stage, a reversal was observed in the contrast of brightness between the non-recorded portion and the recorded portion. That is, at a certain angle, the recorded area appeared dark compared to the bright non-recorded area, but when the same area was rotated by 45 degrees, a bright recorded area was detected within the dark non-recorded area. A polarized light micrograph of the area recorded at an intensity of 8 mV is shown in Figure 10 (a
) and (b). Note that (a) and (b) are observations of the same part rotated by 45 degrees. Next, as in Example 1, when the temperature of the recording medium was increased while observing the recorded area with a polarizing microscope, the recorded area that had been visible with clear contrast began to disappear at around 60°C.
It was completely erased at about 77°C. Further, at this temperature, no change was observed in the non-recording area, and when the temperature rose to 79.5°C, the entire crystal thin film melted. Next, two behenic acid recording media prepared under similar conditions were prepared, and one of them was coated with the above (
Laser light was irradiated under the conditions of 2). When this recording medium was observed using a polarizing microscope, it was found that recording was performed over the entire irradiated area of the recording medium with almost no gaps.

The glass plates of the protective layers of these two recording media were peeled off, and the X-ray diffraction of the fully recorded recording layer and the unrecorded recording layer was measured to compare the crystalline state. Furthermore, the recording medium on which the entire surface had been recorded was heated to 75° C. at a rate of 1° C./min, then returned to room temperature, and X-ray diffraction was measured in a state in which most of the recording had been erased. Figure 12 shows before recording, Figure 13 shows after recording, and 14 shows
The figure shows the X-ray diffraction pattern after erasure. These results show that the molecular orientation partially changes after recording, but almost returns to its original state after erasing. Furthermore, as in Example 1, a laser beam of 51 Rφ was continuously lit at 2.5, 2, and 1.5 mW, respectively, on the recording medium recorded with a laser beam of 1 cape φ under the conditions of (1) above. After scanning at a linear speed of 50 mm/see so as to overlap the recorded part, the first part was observed using a polarizing microscope.
As shown in the photo in Figure 1. The area irradiated with 2o+V was erased in a band shape about 3 squares wide. In addition, at 2.5 mW or more, the intensity was too high and a new line-shaped record was created, and erasure was observed at the edge of the line. 5mW
However, the recording section was only slightly thinner.

Example 3 A glass substrate (5 cm x
5cm, thickness 1.21cm), a chromium layer as a light-to-heat conversion layer, on top of which behenic acid, a recording layer of thin film crystal, and further a glass SR! We created a recording medium consisting of: However, the thickness of the recording layer was approximately 0.6 microns.

A semiconductor laser beam with a wavelength of 780n+* is focused on this recording medium to a diameter of 5 tones, and the intensity at the recording medium surface is 7.10.14.
The light was turned on continuously so that the output power was 200 mm/sec, and scanning was performed in a straight line at a linear speed of 200 mm/sec. When this recording medium was observed under a polarizing microscope, clear recording was observed as shown in the photograph in Figure 15(a). Further, when this part was viewed by rotating the sample stage by 45 degrees, it was observed that the brightness of the non-recorded part and the recorded part was reversed, as shown in the photograph in FIG. 15(b).

Regarding the recording medium created in the same way, the strength was set to 1 to 2 m.
The entire surface of the recording medium was irradiated almost without gaps under the same conditions as above. The thickness of the WI retaining layer of this recording medium is 0.
Peel off the 1+lml glass plate from the recording layer and
Linear diffraction was measured. For comparison, a similarly prepared recording medium was not irradiated with laser light, the glass plate of the protective layer was removed, and X-ray diffraction was measured. Comparing the X-ray diffraction before recording (Figure 16) and after recording over the entire surface (Figure 17), both show that the long-plane spacing of the C-type crystals of behenic acid (48.
The diffraction lines based on 3 people) can be clearly seen. On the other hand, the change in the short surface interval due to recording is different from that in Example 2, which uses a similar recording medium but has a shorter irradiation time. However, when observed using a polarizing microscope, the contrast between the non-recorded area and the recorded area is clear, so it can be seen that the way the orientation direction changes due to recording is different between this irradiation condition and the case of Example 2 (Example The difference in irradiation conditions between 2 and 2 is the difference in irradiation time based on the difference in beam diameter and linear velocity: approximately 0.25 μsec in Example 2 and approximately 100 μsec in Example 3.
c).

Example 4 A glass disk having a chromium layer similar to that in Example 1 was prepared. A polyimide resin solution (manufactured by Japan Synthetic Rubber Co., Ltd.: JIB-1) was applied on this chromium layer, and
After drying for a while, a polyimide layer with a thickness of about 0.1 μl was provided. On the other hand, a polyimide layer with a thickness of about 0.1 μm was similarly provided on one side of the glass with a thickness of 0.1 m+a to serve as a protective layer, and a small amount of silica particles with a diameter of about 1 μm was attached on top of it as a gap material. . Place both of these in a thermostatic chamber, and
The recording layer material shown in Example 2 was melted and sandwiched in the same manner as in Example 2. The temperature at this time was 10 to 20°C higher than the melting point of each material. After spreading the melt over the entire surface,
A load was applied uniformly onto the glass plate of the protective layer, and the temperature of the thermostatic chamber was slowly lowered to crystallize the material of the recording layer. By the above operations, recording media having recording layers made of thin film crystals of each material listed in Table 2 were created.

The recording medium thus prepared was irradiated with semiconductor laser light focused to a diameter of 1 mm under the same conditions as in Example 2.
However, the intensity of the recording light was as shown in Table 2. When each recording medium was observed under a polarizing microscope, it was confirmed that records similar to those of the recording media of Examples 1 and 2 were formed. Table 2 Example 5 A glass disk having the same chromium layer as in Example 1 was prepared. On this chromium layer, 5wt of vinyl chloride-vinyl acetate copolymer (manufactured by Union Carbide: νY118) was applied.
% tetrahydrofuran solution and dried to a thickness of approximately 0.
．． 2. A resin layer was provided. Next, a naphthalocyanine dye (the following structural formula) was dissolved on top of this in a 10 vt% tetrahydrofuran solution of stearic acid (manufactured by Sigma, purity 99% or higher) based on the stearic acid. The liquid was applied and dried at 45°C.

Furthermore, a 5 wt % tetrahydrofuran solution of the same vinyl chloride-vinyl acetate copolymer as above was applied on top of it.
Dry at ℃. After heat-treating this disk at 90°C for about 2 minutes, it is slowly cooled to form a recording layer and a protective layer made of thin film-like crystals of stearic acid containing a naphthalocyanine dye with almost uniform orientation on the chromium layer. did. The thus produced recording medium was irradiated with semiconductor laser light (830n resistance) focused to a diameter of 14 in the same manner as in the case of irradiation condition (1) of Example 1 except that the intensity was 3V. When the portion of the recording medium irradiated with the laser beam was observed with a polarizing microscope, the recorded portion could be seen with clear contrast as in Example 1.

[Brief explanation of the drawing]

1 to 5 are cross-sectional views of the recording medium of the present invention, in which 1 is a substrate, 2 is a layer of fatty acid or fatty acid derivative,
3 is a photothermal conversion layer, 4 is an undercoat layer, and 5 is a protection Jr! is shown. Figure 6 is an X-ray diffraction diagram of a recording medium with a thin film crystal of stearic acid as its recording layer in an unrecorded state, and Figure 7 is an X-ray diffraction diagram of the same recording medium after recording. Also, FIG. 8 shows I! on this recording medium! This is a polarizing micrograph of a portion recorded by 4φ laser beam irradiation, and FIG. 9 shows a 51Rφ laser beam in this recording section.
This is a polarized light micrograph of a recording medium that has been partially erased by being irradiated with multiple laser beams. Figures 10 (a) and (b) are polarized light micrographs of a portion recorded by irradiating a recording medium with a thin film-like crystal of behenic acid as a recording layer with a laser beam of l - φ; (b)
is an observation of the same part rotated 45 degrees. Moreover, FIG. 11 is a polarized light micrograph of a recording medium in which the recording portion was irradiated with a 5-φ laser beam to partially erase the recording portion. Furthermore, FIGS. 12, 13, and 14 are X-ray diffraction diagrams of the behenic acid recording medium in an unrecorded state, after recording, and after erasing, respectively. Furthermore, FIGS. 15(a) and (b)
) is a recording medium with a thin film crystal of behenic acid as a recording layer.
This is a polarized light micrograph of a portion of the door φ recorded by irradiating it with a laser beam, and (.) and (b) are images of the same portion rotated by 45 degrees. Moreover, FIG. 16 and FIG. 17 are the X-ray diffraction diagrams of this recording medium in an unrecorded state and after recording, respectively. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 >++ l QQ (i ji, collapse φI, }) Light irradiation X1000 Figure 10 (a) × Sawa... (L>) Figure 15 (a) x,)mi,1 (b) x5oa

Claims (3)

[Claims] (1) A recording medium having a recording layer on a substrate, characterized in that the recording layer is a thin film crystal whose main component is a fatty acid or a fatty acid derivative, or a layer containing the thin film crystal. . (2) The recording medium according to claim (1), further comprising a photothermal conversion layer that absorbs some or all of the light irradiated during recording and converts it into heat. (3) The recording according to claim (1) or (2), characterized in that the recording layer contains a photothermal conversion substance that absorbs part or all of the light irradiated during recording and converts it into heat. Medium.