JP2995681B2 - recoding media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-density recording medium utilizing a reversible change in a crystalline state by application of thermal energy.

(Prior art)

In recent years, a so-called heat mode recording system, which converts information given by light into a form of thermal energy and applies it to record as a change in shape or a change in physical properties of a recording material, has been put into practical use. As such a heat mode recording medium, an inorganic recording medium using a metal material mainly containing Te, Bi, Se, Tb, In, or a polymethine dye such as cyanine, phthalocyanine, naphthalocyanine, Recording media using organic dyes such as macrocyclic azaannulene dyes such as porphyrin, naphthoquinone, atraquinone dyes, and dithiol metal complex dyes are known. When heat energy is applied to these recording media by irradiation of condensed laser light or the like, the recording layer at the irradiated portion is melted or evaporated to form holes (pits) and record information. However, these recording media are
It does not have the reversibility of erasing recorded information and recording new information again.

With the development of the read-only, write-once heat mode optical recording medium as described above, the need for a reversible recording medium capable of recording, reproducing, and erasing is increasing.

As such a reversible recording medium, for example, there is a magneto-optical recording medium using an alloy thin film composed of a rare earth element such as Gd, Tb, and Dy and a transition metal such as Fe, Ni, and Co. In this method, recording is performed using both heating by laser light irradiation and an externally applied magnetic field, and reproduction is performed by utilizing the difference in the rotation direction of the light oscillation plane depending on the direction of magnetization. Further, information is erased by applying an external magnetic field in a direction opposite to that of the heating by the laser and the recording. However, this magneto-optical recording medium has drawbacks such as insufficient sensitivity at the time of reproduction and a poor S / N ratio, and deterioration of recording sensitivity and problems in recording stability due to the effects of oxidation and the like. ing.

Further, there is a reversible recording medium utilizing a phase transition between a crystal and an amorphous of a recording layer composed of an inorganic material thin film mainly composed of elements such as Ge, Te, Se, Sb, In and Sn. This recording medium has the advantage that recording and erasing can be performed in heat mode only by irradiating a laser beam, but there are problems with the contrast between the recorded and non-recorded areas, insufficient recording stability, and the safety of the material of the recording layer. There are disadvantages such as there is.

On the other hand, JP-A-54-119377, JP-A-55-154198, JP-A-63-3937
8, JP-A-63-41186 discloses a heat recording material comprising a resin matrix material and an organic low-molecular substance existing in a fine particle dispersed state in the matrix material. When this recording material is heated to a certain temperature or more and cooled, it becomes cloudy (light-shielded state), and when it is heated and cooled to a certain temperature range, it becomes transparent, and recording is performed by the reversible change of this light-shielding property. However, even if the contrast due to this light-shielding property is clear when recording is large enough to be visually observed, a recording portion formed by changing a small portion of about several μm is microscopically enlarged. In contrast, when the image is observed, the contrast is low enough that the image cannot be confirmed as a record. In the recording layer, the light scattering property changes depending on the state of the fine particles of the organic low-molecular substance in the matrix, but when the size of the recording portion becomes about several μm, the size of the recording portion becomes large. On the other hand, the size of the fine particles is no longer small enough to cause such scattering. To compensate for this, it is conceivable to make the thickness of the recording layer much larger than the size of the recording.However, such a thick recording layer is uniformly heated in the thickness direction over the entire recording layer. Is substantially difficult to form. Therefore, it cannot be applied to a recording medium that performs 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-pn-alkylphenylbutane-1,3-dionato) (II) And an organic polymer mixture, JP-A-63-15793
JP-A-63-95993 and JP-A-96748 disclose crystalline aromatic vinylene sulfide polymer, and JP-A-63-279440 discloses a mixture of crystalline and amorphous thermoplastic resin. Sulfur polymers, diazabicyclo [2,2,2] octane quaternary salt disclosed in JP-A-63-128993, and crystals of stretch-oriented polymers and liquid crystalline polymers described in JP-A-63-259851. A recording medium using a crystal transition or a change in the degree of orientation is shown. However, these are all slow in recording speed or erasing speed, and are difficult to put to practical use.

[Problems to be solved by the invention]

As described above, the conventional recording medium has various problems such as recording stability, recording sensitivity, erasing speed, and contrast between a recorded portion and a non-recorded portion. It is desirable that the recording medium is made of a non-toxic material from the viewpoint of safety.

From such a viewpoint, the present invention provides a recording medium that can record and reproduce information and erase recorded information and that can be used repeatedly. It also provides a recording medium with excellent recording sensitivity and recording speed, good recording stability, high contrast between recorded and non-recorded parts, capable of recording information at high density, and erasing recorded information at high speed. Is what you do. Further, the present invention provides a highly safe recording medium without toxicity.

[Means for solving the problem]

The present inventors have studied the thermal change of various organic materials for the above purpose, and found that when a thin film crystal of a fatty acid or a fatty acid derivative is used for the recording layer, the crystal state of the portion to which heat is applied changes. I found to do. It has also been found that this changed portion returns to its original state by being reheated to an appropriate temperature. The present invention is based on the thermal reversible change of such a fatty acid or fatty acid derivative thin film crystal.

That is, the recording medium of the present invention has a recording layer on a substrate, records by reversibly changing the crystal state of a part of the recording layer, and then detects the recording by a change in the polarization characteristics of the part. Wherein the recording layer is a thin-film crystal of a fatty acid or a fatty acid derivative or a layer containing the thin-film crystal.

Further, the recording medium of the present invention comprises 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. It is a feature.

Further, the recording medium of the present invention, in the above two constitutions, contains a photothermal conversion substance which absorbs a part or all of the light irradiated at the time of recording and converts it into heat in a recording layer containing a fatty acid or a fatty acid derivative. It is characterized by the following.

 Hereinafter, the recording medium of the present invention will be described in detail.

The recording layer of the recording medium of the present invention is composed of or contains a thin-film crystal containing a fatty acid or a fatty acid derivative as a main component. Unsaturated mono- or dicarboxylic acids or their esters, amides, anilides,
It is a hydrazide, ureide, anhydride, or a fatty acid salt such as an ammonium salt or a metal salt, and the ester includes an ester with a compound having two or more hydroxyl groups, for example, a mono-, di-, or triglyceride. Further, these may be substituted by 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 may have two or more double bonds. These saturated or unsaturated fatty acids preferably have 10 or more carbon atoms.

Specific examples of the saturated fatty acids include, for example, undecanoic acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nanodecanoic acid, arachinic acid, behenic acid, lignoceric acid, serotinic acid, montanic acid, melysin Examples of the unsaturated fatty acids include oleic acid, elaidic acid, linoleic acid, sorbic acid, and stearic acid. Specific examples of the ester include, for example, methyl ester, ethyl ester, hexyl ester, octyl ester, decyl ester, dodecyl ester, tetradecyl ester, stearyl ester, eicosyl ester, docosyl ester of these fatty acids.

Examples of metal salts include metal salts of these fatty acids such as sodium, potassium, magnesium, calcium, nickel, cobalt, zinc, cadmium, and aluminum.

The fatty acid or fatty acid derivative to be used preferably has a melting point of 50 to 200 ° C, particularly preferably 60 to 150 ° C. If it is lower than this, there is a problem in the storage stability of the recording, and if it is higher than this, the energy required for recording increases, and the recording speed decreases.

One or more of these fatty acids or fatty acid derivatives may be used in the recording layer of the recording medium of the present invention. Further, the recording layer in the present invention is made of or includes a thin-film crystal containing these fatty acids or fatty acid derivatives as a main component. In addition to this, a resin is used as necessary in forming the layer. be able to. Examples of the resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. , Polyvinylidene chloride, vinylidene chloride-acrylonitrile copolymer, polyester, polyamide, polyacrylate, polymethacrylate, polycarbonate,
Examples include polyurethane and silicone resin. When a resin is used in the recording layer, the weight ratio of the resin to the fatty acid or fatty acid derivative 1 in the entire recording layer is preferably 3 or less, particularly preferably 1 or less.

Examples of the substrate used for the recording medium of the present invention include a glass plate, a metal plate, and a plastic plate such as polymethyl methacrylate and polycarbonate. However, when recording is read by transmitted light after information recording, it is necessary to use a substrate that transmits reproduction light as the substrate. When reading with reflected light, if necessary, for example, platinum,
Titanium, silicon, chromium, nickel, germanium,
A reflective layer is formed by providing a metal or semimetal film such as aluminum.

The recording medium of the present invention is to record by applying heat to the recording layer. However, when light such as laser light is used as a method of applying heat, one of the light irradiated according to the information to be recorded is used. It is necessary to provide a light-to-heat conversion layer that absorbs part or all of the light and converts it to heat, or to include a substance that absorbs light and converts it to heat in the recording layer. As the light-to-heat conversion layer, a metal or metalloid film similar to the above-mentioned reflection layer may be provided, and therefore, this layer can also be used as the reflection layer. The light-heat conversion layer is a dye that absorbs irradiated light, such as an azo dye, a cyanine dye, a naphthoquinone dye, an anthraquinone dye, a squarylium dye, a phthalocyanine dye, a naphthalocyanine dye, a porphyrin dye, and an indigo dye. It may be a layer containing a dye, a dithiol complex dye, an azurenium dye, a quinone imine dye, a quinone diimine dye, or the like, and is selected according to the wavelength of light used for recording. On the other hand, as the substance that absorbs light contained in the recording layer and converts it into heat, various dyes contained in the above-mentioned light-to-heat conversion layer can be used, and are selected according to the wavelength of light used for recording.

The recording medium of the present invention is composed of a thin-film crystal mainly composed of a fatty acid or a fatty acid derivative on a substrate, or has a recording layer containing the same, and the recording layer changes its crystalline state by application of heat. Is characterized in that,
Although their configurations are not specified, examples of the configuration of a recording medium that is usually used are shown in FIGS. In FIG. 1, reference numeral 1 denotes a substrate, and reference numeral 2 denotes a recording layer made of or containing a thin film crystal mainly containing 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 the light, converts it to heat, and reflects part of the light as necessary. It is provided. FIG. 3 shows a recording layer 2 provided on a substrate 1 and a photothermal conversion layer 3 provided thereon. FIG. 4 shows a structure in which an undercoat layer 4 for the purpose of improving the film quality of the recording layer 2, for example, is provided under the recording layer 2 of FIG.
FIG. 5 shows a case where a protective layer 5 is provided on the recording layer 2 of FIG.

For the undercoat layer 4, various resins such as the examples of the resins that may be used when the recording layer 2 is formed can be used. Similarly, these resins may be used for the protective layer 5 or a glass plate may be used. When a glass plate is used, 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 such as a silane-based or It may be previously treated with a titanate-based surface treatment agent.

In order to manufacture the recording medium of the present invention, the light-to-heat conversion layer 3 is formed on the substrate 1 as necessary using, for example, the above-mentioned metal or metalloid by means of vapor deposition, sputtering or plating. The recording layer 2 is formed thereon.

The method for forming the recording layer 2 includes, for example, the following method. First, a glass plate or a resin film corresponding to the protective layer 5 is covered on the substrate 1 provided with the light-to-heat conversion layer 3 while maintaining a gap corresponding to the required thickness of the recording layer 2. In order to form a gap, a spacer layer may be provided around the portion where the recording layer 2 is to be formed, or a gap material having a small and uniform diameter, such as silica particles or polystyrene beads, may be previously coated on the light-to-heat conversion layer 3. It may be attached to the side or the protective layer 5 side. The entire substrate with the gap formed in this way is placed in a thermostat or placed on a hot plate, kept at a temperature higher than the melting point of the material used for the recording layer 2, and the molten material is placed at the end of the gap.
Soak between gaps. When the obtained melt layer is slowly cooled and crystallized, a thin film crystal of the recording layer 2 can be formed between the light-to-heat conversion layer 3 and the protective layer 5. At this time, in order to maintain the gap interval constant, pressure may be applied with a weight or the like until crystallization. These operations may be performed under reduced pressure to prevent air bubbles from entering.

As another manufacturing method, for example, a material for forming the recording layer 2 is dissolved in an appropriate organic solvent such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, etc., and spin coating, blade coating, dip coating, A layer having a uniform thickness is formed on the photothermal conversion layer 3 by coating and drying by a coating method or the like, or by a vapor deposition method. If necessary, a resin dissolved in a suitable solvent is applied thereon. Next, this is placed in a thermostat or placed on a hot plate, heated to a temperature equal to or higher than the melting point of the material of the recording layer 2 and then slowly cooled to crystallize, thereby forming a thin film crystal of the recording layer 2. Form. Various other methods such as the Langmuir-Blodgett method can be used for forming the recording layer 2.

When a light-to-heat conversion substance is contained in the recording layer 2, for example, the above-mentioned dye may be simultaneously dissolved in a solution of the material of the recording layer 2 or dispersed and applied.

When the light-to-heat conversion layer 3 that absorbs part or all of the light irradiated at the time of recording or erasure and converts the light into heat is formed using a dye as described above, it may be formed by a method such as vapor deposition or sputtering, It may be formed by applying a liquid dissolved or dispersed in a solvent. In this case, a binder resin may be used if necessary. If a light reflecting layer is required, a metal deposition film may be separately provided.

Further, the film thickness of the recording layer 2 which is made of or contains a thin film crystal mainly containing a fatty acid or a fatty acid derivative is not particularly limited, but is usually 10 to 10 μm,
It is preferably about 10 ° to 5 μm. An appropriate range for the thickness of the light-to-heat conversion layer 3 is determined by the wavelength and intensity of light used for recording and the type of material used, but is generally about 50 to 5 μm.
It is about.

The recording medium of the present invention is made of a thin-film crystal containing a fatty acid or a fatty acid derivative as a main component or has a recording layer containing the thin-film crystal, and the crystal state of the thin-film crystal changes reversibly by application of heat. It is to take advantage of that. Various methods are conceivable for recording information, that is, applying heat, but a method using irradiation of a focused laser beam is most preferable for performing high-density recording. In this case, the recording medium needs to be provided with the above-described light-to-heat conversion layer that absorbs light and converts it to heat, or it is necessary to add a substance that absorbs light and converts it to heat in the recording layer.

At the time of recording, the laser light irradiation part generates heat by the light-to-heat conversion layer or the light-to-heat conversion material absorbing light, and the recording layer composed of a thin film of a fatty acid or a fatty acid derivative or containing the same is instantaneously heated, When the light irradiation stops, the film is rapidly cooled, and recording pits (here, pits are not holes but portions that are recorded as changes in the crystal state in the thin film crystal) are formed.

At this time, in the recording layer, a part of the thin film crystal, that is, a part which is instantaneously heated by the heat transmitted from the photothermal conversion layer (material) generated by the short-time irradiation of the laser beam, is completely melted. Reach the temperature. However, when the laser beam irradiation stops, the heat diffuses, and this portion is instantaneously cooled and solidified (crystallized). As described above, the crystal state of the portion that has been instantaneously heated, melted, and cooled is different from the state of the portion to which heat is not applied, that is, the crystal state of the surrounding non-recording portion.

The 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 a crystal axis, or a change in the orientation direction of molecules, and (3) a change in the crystal structure. The recording layer before the recording is performed is a thin-film crystal having a substantially uniform thickness and arranged in a substantially uniform direction. Among these changes, the change in the crystal grain size and morphology in (1) is, for example, a case where a recording portion in a thin film crystal is a set of small divided crystals. This change in state can be confirmed by observing the peeled recording layer with, for example, a scanning electron microscope. Also (2)
The change in the crystal axis direction or the change in the molecular orientation direction means, for example, that the crystal structure is basically the same, but the crystal is oriented in a different direction, that is, the crystal axis direction is different, or Although not so clear, it is basically a set of molecules with some orientation, and the overall orientation direction is different from the surrounding non-recording part. The change in the crystal structure in (3) means that the recorded portion has crystallized into a crystal state different from that of the surrounding non-recorded portion. The range of properties is very narrow, including the case of changing to an amorphous state.

These changes in the crystalline state are due to the partial short-time application of heat to the thin-film crystal, that is, rapid cooling from the molten state caused by short-time light irradiation. It depends on the time of light irradiation. Since it is difficult to measure the temperature change of the minute part irradiated by the focused laser light, the thickness of each layer, light absorption characteristics, heat When thermal characteristics such as conductivity and specific heat are set to the values shown in Table 1, and the temperature change of the recording layer is simulated, for example, the time required for cooling from 80 ° C. to 60 ° C. is as follows.
About 1.7 μsec at 0 μsec, about 15 n at irradiation time of 0.25 μsec
sec, and the difference between the cooling rates is very large. Therefore, the change in the crystal state caused by light irradiation (heat application) for a short time also changes depending on the irradiation time and is not constant.
For example, in microcrystallization, there is a tendency that the higher the cooling rate, the finer the crystal. Also, it is related to the orientation state of the molecules, and generally, the higher the cooling rate, the more the orientation disorder tends to increase, and the range in which the molecules take a regular arrangement is narrowed.
The crystallinity may be low. However, even under such conditions, some orientation state exists at least partially, and the recording method of the present invention is characterized by the fact that the orientation of the recording portion is different from the orientation direction of the surrounding non-recording portion. . Such a change in the orientation direction due to the recording can be confirmed, for example, by measuring the X-ray diffraction of the recording layer. In addition, the above (1) caused by recording,
The changes in the crystal states of (2) and (3) occur in combination rather than separately. Also, inside the melted part of the recording layer irradiated with the laser light,
Depending on the distance from the light-to-heat conversion layer and the distance from the center of the beam, the attained temperature and the cooling rate greatly differ, and different crystallization occurs in each place, so that the state is not always uniform. Therefore, the changes in the crystalline state of (1), (2), and (3) occur in various forms depending on the position, even within one recording unit.

In order to more specifically explain such a change in crystal state due to recording, a case where stearic acid, which is a typical fatty acid, is used as a material of a recording layer will be described. The unrecorded crystalline state of the recording layer (substrate: glass, light-to-heat conversion layer: chromium vapor-deposited film, protective layer: vinyl chloride-vinyl acetate copolymer) composed of the stearic acid thin film crystal formed as described above is as follows: A C-type crystal of stearic acid,
The axis and the b axis are oriented substantially parallel to the substrate. This is because the X-ray diffraction pattern of this recording layer (FIG. 6) shows that the diffraction line (39.8 °) due to the long plane spacing (39.8 °) of the stearic acid C-type crystal (however,
n = 2, 3, 4, 5, 7, 8, 9, 10, 12). On the other hand, a wavelength of 830 nm and a beam diameter of 1
An X-ray diffraction diagram of a μmφ semiconductor laser beam was continuously lit at a linear velocity of 3500 to 4000 mm / sec at an intensity of 5 mW on the medium surface, and the entire surface was recorded in a spiral shape with no space between recording lines. In FIG. 7), a clear diffraction line at 21.6 ° newly appears in addition to the diffraction line of the stearic acid C-type long plane spacing which had appeared at the time of unrecording. This diffraction line is due to the short plane spacing (4.11 °) of the C-type crystal, which means that the a-axis and b-axis were oriented almost parallel to the substrate when not recorded, but after laser irradiation. Changes the crystal orientation,
This shows that a structure in which the c-axis is oriented parallel to the substrate is formed at least partially.

The recorded state can be confirmed by an optical observation means such as a microscope and a polarizing microscope. Especially,
Such a change in crystal state often accompanies a change in polarization characteristics, and can often be clearly observed as a contrast between light and dark or a difference in color tone under crossed Nicols using a polarizing microscope. Therefore, when reproducing (reading) the recorded information, the focused polarized light is made incident on the recording medium, and the reflected or transmitted light is arranged so as to transmit the light in the vibration direction orthogonal to the vibration direction of the light having the incident light. This can be done by detecting the intensity of light through the polarizer placed. The intensity of the light used for reproduction is sufficiently weaker than the light used for recording and erasing, and is set so that the temperature of the recording layer does not rise to the erasing temperature.

By applying heat to a part of the thin-film crystal mainly composed of a fatty acid or a fatty acid derivative in the recording layer and instantaneously melting and recrystallizing the information, the information recorded as a change in the crystalline state is recorded on the recording layer. Is a temperature lower than the temperature at the time of recording, and is a temperature at which the crystalline thin film of the recording layer does not melt. However, erasing can be performed by heating to a temperature at which molecules can perform sufficient thermal motion. The erasable temperature range varies depending on the material, purity and the like of the recording layer, but exists at a temperature lower than the melting point of the thin film crystal forming the recording layer. The erasure of this recording can be confirmed by increasing the temperature of the recording layer while observing with a polarizing microscope. For example, if a dark recording portion is formed in a non-recording portion that looks uniformly bright, the recording portion starts to be chipped at a certain temperature or higher, and the recording portion completely disappears in a temperature range of about 5 to 20 ° C. , The whole becomes the same state as the non-recording part. When the temperature is further increased, the field of view becomes completely dark because the crystalline thin film of the recording layer melts. Therefore, when the molecules of the micro-recorded part with the changed crystalline state formed in the thin-film crystal are in a state where they can be moved sufficiently by heat, they will take the same arrangement as the molecules of the surrounding non-recorded part. When the temperature returns from the temperature to room temperature, the whole becomes a uniform thin film state crystal and is erased.

Specifically, the entire recording medium can be erased by heating and cooling the entire recording medium to the above-mentioned temperature range, and the entire recording can be erased. Alternatively, the recording pit portion or a slightly wider range can be locally heated and cooled to the erasing temperature. Thereby, it is also possible to erase only a part of the recorded information. In the latter case, the intensity of the laser beam irradiated at the time of recording may be reduced, the temperature of the recording pit portion may be adjusted to be within the erasing temperature range, and the laser beam may be irradiated repeatedly. At this time, the recording pit portion (the portion where the crystal state has changed) of the thin film crystal of the recording layer is heated to the erasing temperature once, and when cooled, the crystal state is changed to the original state, that is, the same crystal as the surrounding non-recording portion. Returning to the state, the recording pit is erased. This erased state can be confirmed by an optical observation means such as a microscope and a polarizing microscope similarly to the recorded state.

The recording medium of the present invention basically does not make a hole in the recording layer by heat or change the surface shape of the recording layer, but a thin film crystal forming the recording layer or a thin film contained in the recording layer. The recording is performed by changing the crystal state of a part of the crystalline crystal, and the difference between the formed recorded portion and the 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 the conventional recording medium. For example, this is based on a completely different phenomenon from a recording medium in which an organic low-molecular compound is present in a dispersed state in a resin matrix described in the section of the prior art 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 compound is present in the recording layer in the form of fine particles, and the recording portion itself is also formed by a large number of fine particles. On the other hand, in the recording medium of the present invention, the fatty acid or the fatty acid derivative is present as a thin film crystal, and the recording is formed on a part of the thin film crystal as a change in the crystal state, and as a result, the optical properties are reduced. The difference is detected. Therefore, the difference between the two is clear.

〔The invention's effect〕

Recording and erasing of the recording medium of the present invention are basically based on the difference in the temperature at which the thin-film crystals of the fatty acid or fatty acid derivative forming the recording layer reach, and this can be adjusted by the intensity of the laser light to be irradiated. Further, since both recording and erasing can be performed at high speed, so-called overwriting (overwriting) in which recording is performed while erasing is possible. Further, this recording and erasing can be repeatedly performed stably. Further, since the recording unit is in a stable state like the non-recording unit, the recorded information can be stably stored for a long period of time.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 Optically polished 4 inch (101.6 mm) diameter, 1.2 mm thick
A chromium layer as a light reflection layer and a light-to-heat conversion layer was provided on the glass disk of No. 1 by vacuum evaporation. About 90 thickness
It was 0Å. 5 wt% of a vinyl chloride-vinyl acetate copolymer (VYHH, manufactured by Union Carbide Co.)
Apply a tetrahydrofuran solution and dry to a thickness of about 0.2
A μm resin layer was provided. Next, a 10 wt% tetrahydrofuran solution of stearic acid (manufactured by Sigma, purity: 99% or more) was applied onto the resin layer, and dried at 45 ° C. 5% by weight of the same vinyl chloride-vinyl acetate copolymer
A tetrahydrofuran solution was applied and dried at 45 ° C. This disk was heat-treated at 90 ° C. for about 2 minutes and then gradually cooled.
By the above operation, a recording layer (thickness of about 0.8 μm) consisting of a thin crystal of stearic acid having a substantially uniform orientation on the chromium layer was obtained.
μm), and a protective layer (thickness: about 0.6 μm) made of a vinyl chloride-vinyl acetate copolymer was formed thereon.

While rotating the recording medium thus produced at 900 RPM, a semiconductor laser light having a wavelength of 830 nm condensed to a diameter of 1 μm was irradiated under the following conditions (1) and (2) to form a spiral recording. At this time, the linear velocity in the recording direction at the recorded part on the disc is about 3500 to 4000 mm
/ sec.

Irradiation condition (1) Lighting condition: frequency 200KHz, duty ratio
50% Intensity on recording medium surface: 5 mW Recording line interval: about 3.5 μm (center-to-center) (2) Lighting condition: continuous lighting Intensity on recording medium surface: 5 mW Recording line interval: about 1 μm (center-to-center) When the recording medium irradiated with the laser beam under the condition (1) is observed in a crossed Nicols state using a reflection polarization microscope, a line-shaped recording portion having a width of about 1 μm is formed in the laser beam irradiated portion of the recording layer. , With clear contrast. However, this recording portion could hardly be confirmed by ordinary optical microscope observation. An example observed with a polarizing microscope is shown in a photograph in FIG.

When the recording layer of the recorded recording medium was peeled from the chromium layer and its surface (the surface in contact with the chromium layer) was observed with a scanning electron microscope, the portion irradiated with the laser light was a collection of small plate-like crystals. Was.

When the recording medium irradiated with the laser beam under the condition (2) was similarly observed using a polarizing microscope, it was found that the recording was almost completely performed over the entire irradiation range of the recording medium. With respect to the recording medium on which the entire recording was performed, the X-ray diffraction of the same portion before and after the recording was measured. FIG. 6 shows the X-ray diffraction before recording, and FIG. 7 shows the X-ray diffraction after recording. From FIG. 6, before recording, only a diffraction line based on the long surface spacing of the stearic acid C-type crystal was observed, and the structure was such that the a and b axes were oriented in parallel. However, after the recording in FIG. 7, the diffraction line based on the short surface interval (2θ = 21.6 °)
Appears, indicating that a structure in which the c-axis is oriented parallel to the substrate is formed in the recording portion of the recording layer.

Next, the temperature of the recording medium was changed from room temperature to 1 while observing the recording medium recorded under the condition (1) with a polarizing microscope.
The temperature was increased at a rate of ° C / min. Then, the recording part that had been seen with a clear contrast began to disappear from around 60 ° C,
At about 68 ° C, the brightness was completely the same as the surroundings, and the image was erased. In addition, up to this temperature, the surrounding non-recording part state
No change was noted. 69.4 ° C when the temperature is further increased
Thus, it became clear that the crystal thin film of the recording layer was completely melted at this temperature at this temperature.

Next, on the recording medium recorded under the condition (1), a semiconductor laser beam having a wavelength of 780 nm condensed to a diameter of 5 μm is continuously lit so that the intensity on the recording medium surface becomes 1.5 mW, 2 mW and 3 mW, Scanning was performed linearly at a linear speed of 50 mm / sec so as to overlap the previous recording portion. Observation of this recording medium with a polarizing microscope revealed that, as shown in the photograph of FIG. 9, the portions irradiated at 2 mW and 3 mW overlapped with each other had an excessively high irradiation intensity. The temperature became higher than the melting temperature, and a new line-shaped record was formed. However, at the edge portion of this line, that is, at the portion scanned by the periphery of the beam, the recording portion previously recorded with the laser light of 1 μmφ was erased. On the other hand, in the portion irradiated with 1.5 mW of overlapped intensity, the recording portion by the previous 1 μmφ laser beam was erased in a band shape with a width of about 2.5 μm. From the above results, it was confirmed that the recording layer entered the erasing temperature range by irradiating with the intensity of 1.5 mW, and erasing was performed.

Example 2 A glass disk having a chromium layer as a light-to-heat conversion layer was prepared in the same manner as in Example 1. Further, a minute amount of silica particles having a diameter of about 1 μm was adhered as a gap material to one surface of a glass plate having a thickness of 0.1 mm serving as a protective layer. After heating both in a constant temperature bath at 100 ° C, behenic acid (Sigma: Purity) was placed on the chromium layer of the glass disk at the same temperature.
(99% or more) was melted in a small amount. Next, one glass plate was gently covered from one end on a melt of behenic acid with the surface to which the gap material was attached facing down, and the melt was spread over the entire surface and sandwiched. Further, a uniform load was applied from above the covered glass plate, the temperature of the thermostat was slowly lowered, and behenic acid was crystallized to form a thin film crystal. By the above operations, a recording layer (about 0.8 μm thick) consisting of thin crystals of behenic acid with a substantially uniform orientation on the chromium layer and a protective layer consisting of glass with a thickness of 0.1 mm are formed on it. Was done.

The recording medium thus produced was rotated at 900 RPM, and a semiconductor laser beam having a wavelength of 830 nm, which was condensed to a diameter of 1 μm, was irradiated spirally at a linear velocity of 3500 to 4000 mm / sec. The irradiation conditions at this time are the same as in the case of the first embodiment.
Two conditions (1) and (2) were set. However, the irradiation intensity was set to 3,4,5,6,8,10,12mW in (1), and 8 in (2).
mW.

Observation of the recorded state under the irradiation condition (1) in a crossed Nicols state using a reflection polarization microscope revealed that recording was possible at a laser beam irradiated portion of the recording layer at an intensity of 4 mW or more with clear contrast. Was done. In addition, as the intensity of the irradiated laser beam increases, the width of the recording portion, that is, the portion where the crystal state has changed due to melting and recrystallization increases, and the width is about 0.4 μm at 4 mW and about 1.8 μm at 12 mW.
m.

In observing the recorded portion with a polarizing microscope, when the same portion was rotated on the sample stage, the contrast between the non-recorded portion and the recorded portion was reversed. That is, when the recording portion appeared dark at a certain angle with respect to the bright non-recording portion, when the same portion was rotated by 45 °, a bright recording portion was observed in the dark non-recording portion. Polarization micrographs of the portion recorded at an intensity of 8 mW are shown in FIGS. 10 (a) and (b). (A) and (b) are obtained by observing the same part rotated by 45 °.

Next, as in Example 1, when the temperature of the recording medium was increased while observing the recording portion with a polarizing microscope, the recording portion that had been seen with clear contrast began to disappear from about 60 ° C.
It was completely erased at about 77 ° C. At this temperature, no change was observed in the non-recording portion, and when the temperature rose to 79.5 ° C., the entire crystalline thin film melted.

Next, two behenic acid recording media prepared under the same conditions were prepared, and one of them was irradiated with laser light under the condition (2). When the recording medium was observed with a polarizing microscope, it was found that the recording was almost completely performed over the entire irradiation range of the recording medium. The glass plates of the protective layers of these two recording media were peeled off, and the crystal states were compared by measuring the X-ray diffraction of the recording layer on the entire surface and the unrecorded recording layer. Further, the recording medium on which the entire surface is recorded is moved at a rate of 1 ° C./min
After the temperature was raised to 75 ° C., the temperature was returned to room temperature, and X-ray diffraction in a state where the recording was almost erased was measured. Before recording in Figure 12,
FIG. 13 shows an X-ray diffraction diagram after recording and FIG. 14 shows an X-ray diffraction diagram after erasure.
From these, it can be seen that the molecular orientation partially changed after recording, and almost returned after erasure.

Further, on the recording medium recorded with the laser light of 1 μmφ under the condition of the above (1), the laser light of 5 μmφ is continuously turned on at 2.5, 2, and 1.5 mW, respectively, as in Example 1, and the linear velocity is 50 mm. After scanning at a speed of / sec so as to overlap the recording portion, observation with a polarizing microscope revealed that the portion irradiated at 2 mW was erased in a band shape with a width of about 3 μm as shown in the photograph of FIG. Further, at 2.5 mW or more, the intensity was too high, so that a new line-shaped recording could be performed. Erasure was observed at the edge of the line, and at 1.5 mW, the recording portion was only slightly thin.

Example 3 In exactly the same manner as in Example 2, a glass substrate (5 cm × 5 cm,
A recording medium comprising a chromium layer as a light-to-heat conversion layer, a behenic acid, a thin-film crystal recording layer on the chromium layer, and a glass protective layer on the chromium layer was prepared. However, the thickness of the recording layer was about 0.6 μm.

Semiconductor laser light having a wavelength of 780 nm focused on the recording medium to a diameter of 5 μm was continuously lit so that the intensity was 7, 10, and 14 mW on the surface of the recording medium, and linearly scanned at a linear speed of 200 mm / sec.
Observation of the recording medium with a polarizing microscope revealed clear recording as shown in the photograph of FIG. 15 (a). When this part is observed by rotating the sample stage by 45 °,
As shown in the photograph of FIG. 2B, the reversal of light and dark between the non-recorded portion and the recorded portion was observed.

The recording medium prepared in the same manner was irradiated with almost no gap on the entire surface of the recording medium under the same conditions as above with the intensity set to 12 mW. A glass plate having a thickness of 0.1 mm as a protective layer of the recording medium was peeled off from the recording layer, and the X-ray diffraction of the recording layer was measured. For comparison, a recording medium similarly prepared was not irradiated with a laser beam, the glass plate of the protective layer was peeled off as it was, and X-ray diffraction was measured. When the X-ray diffractions before recording (FIG. 16) and after the entire recording (FIG. 17) are compared, in each case, a diffraction line based on the long plane interval (48.3 °) of the C-type crystal of behenic acid is clearly observed. On the other hand, the change of the portion of the short surface interval due to the recording is different from that of the second embodiment in which the irradiation time is short while using the same recording medium. However, when observed with a polarizing microscope, the contrast between the non-recorded portion and the recorded portion is clear, and thus it can be seen that the method of changing the orientation direction by recording differs between this irradiation condition and Example 2. The difference between the irradiation conditions and Example 2 is the difference in irradiation time based on the difference between the beam diameter and the linear velocity: about 0.25 μsec in Example 2, and about 100 μsec in Example 3.

Example 4 A glass disk having the same chromium layer as in Example 1 was prepared. A polyimide resin solution (JIB-1 manufactured by Nippon Synthetic Rubber Co., Ltd.) was applied on the chromium layer, and dried at a temperature of 150 ° C. for 1 hour to form a polyimide layer having a thickness of about 0.1 μm. On the other hand, a polyimide layer having a thickness of about 0.1 μm was similarly provided on one side of glass having a thickness of 0.1 mm serving as a protective layer, and a minute amount of silica particles having a diameter of about 1 μm was adhered thereon as a gap material. Both were put in a thermostat, and the materials of the recording layer shown in Table 2 were 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 uniform load was applied from above the glass plate of the protective layer, and the temperature of the thermostat was slowly lowered to crystallize the material of the recording layer. By the above operation, a recording medium having a thin film crystal of each material shown in Table 2 as a recording layer was prepared.

The recording medium thus produced was irradiated with a semiconductor laser beam condensed to a diameter of 1 μm under the same conditions as in Example 2. However, the recording light intensity was as shown in Table-2. Observation with a polarizing microscope of each recording medium confirmed that recordings similar to those of the recording media of Examples 1 and 2 were formed.

Example 5 A glass disk having the same chromium layer as in Example 1 was prepared. A 5 wt% tetrahydrofuran solution of a vinyl chloride-vinyl acetate copolymer (VYHH, manufactured by Union Carbide Co.) was applied on the chromium layer and dried to form a resin layer having a thickness of about 0.2 μm. Next, a solution prepared by dissolving 3 wt% of a naphthalocyanine-based dye (the following structural formula) with respect to stearic acid in a 10 wt% tetrahydrofuran solution of stearic acid (manufactured by Sigma, purity: 99% or more) is applied thereon. Dried at 45 ° C. Further, a 5 wt% tetrahydrofuran solution of the same vinyl chloride-vinyl acetate copolymer as described above was applied thereon.
Dried at 5 ° C. This disk is heat-treated at 90 ° C for about 2 minutes, and then gradually cooled to form a recording layer and a protective layer consisting of a thin crystal of stearic acid containing a naphthalocyanine dye having a nearly uniform orientation on the chromium layer. did.

The recording medium produced in this manner was irradiated with a semiconductor laser beam (830 nm) focused to a diameter of 1 μm in the same manner as in the irradiation condition (1) of Example 1 except that the intensity was 3 mW. When the laser light irradiated portion of this recording medium was observed with a polarizing microscope, the recorded portion could be observed with a clear contrast as in Example 1.

[Brief description of the drawings]

1 to 5 are cross-sectional views of a recording medium of the present invention, in which 1 is a substrate, 2 is a recording layer of a fatty acid or a fatty acid derivative,
Reference numeral 3 denotes a light-to-heat conversion layer, 4 denotes an undercoat layer, and 5 denotes a protective layer. FIG. 6 is an unrecorded X-ray diffraction pattern of a recording medium having a thin film of stearic acid as a recording layer, and FIG. 7 is an X-ray diffraction pattern of the same recording medium after recording. FIG. 8 is a polarization microscope photograph of a portion recorded on the recording medium by irradiating a laser beam of 1 μmφ, and FIG.
4 is a polarization microscope photograph of a recording medium partially erased by overlappingly irradiating the laser light. FIGS. 10 (a) and (b) are polarization micrographs of a portion where a recording medium having a thin layer crystal of behenic acid as a recording layer was irradiated with a laser beam of 1 μmφ and recorded, and (a) and (b)
Is the same part rotated 45 ° and observed. Also,
FIG. 11 is a polarization microscope photograph of a recording medium in which a laser beam of 5 μmφ has been superposedly irradiated on the recording portion and partially erased. FIGS. 12, 13, and 14 are X-ray diffraction diagrams of a behenic acid recording medium in an unrecorded state, after recording, and after erasing, respectively. Further, FIGS. 15 (a) and 15 (b) are polarization microscope photographs of a portion where a recording medium having a thin layer crystal of behenic acid as a recording layer was irradiated with a laser beam of 5 μmφ and recorded.
And (b) are observations of the same part rotated 45 °. FIG. 16 and FIG. 17 are an X-ray diffraction diagram of the recording medium in an unrecorded state and after recording, respectively.

──────────────────────────────────────────────────続 き Continued on the front page (72) Ryohei Miyake 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-54-149617 (JP, A) JP-A-57-38190 (JP, A) JP-A-58-104794 (JP, A) JP-A-64-14077 (JP, A) JP-A-62-107448 (JP, A) JP-A-54-5447 (JP, A) JP-A-64-19532 (JP, A) JP-A-63-130380 (JP, A) JP-A-62-268689 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB Name) B41M 5/26

Claims (3)

(57) [Claims] 1. A recording medium having a recording layer on a substrate, recording by reversibly changing a crystal state of a part of the recording layer, and detecting the recording by a change in a polarization characteristic of the part. Wherein the recording layer is a thin-film crystal of a fatty acid or a fatty acid derivative or a layer containing the thin-film crystal. 2. A recording medium according to claim 1, further comprising a light-to-heat conversion layer for absorbing a part or all of the light irradiated during recording and converting the light into heat. 3. The recording layer according to claim 1, wherein the recording layer contains a photothermal conversion material which absorbs part or all of the light irradiated during recording and converts the light into heat. Recording medium.