JP3054771B2 - Recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to recording of information by applying thermal energy and heat mode recording of information by irradiating light, and more particularly, to information based on reversible changes in crystalline state due to heat. And a reversible recording method.

[Conventional technology]

In recent years, a so-called heat mode recording system for applying information in the form of thermal energy and recording 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, anthraquinone 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. But,
These recording media do 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 performs reproduction using polarized light, but the difference between a recorded part and a non-recorded part is small, so that the sensitivity at the time of reproduction is not sufficient and the S / N ratio is poor. It has disadvantages such as deterioration of recording sensitivity and a problem in recording stability due to the influence of oxidation and the like.

As reversible recording media, Ge, Te, Se, Sb, In, Sn
There is a method utilizing a phase transition between a crystal layer and an amorphous layer of a recording layer composed of an inorganic material thin film containing an element as a main component. This recording medium can perform heat mode recording and erasing only by irradiating a laser beam, and reproduces data based on the difference in reflectance. However, since the difference in reflectance between the recording portion and the non-recording portion is small, the reading speed is low. And have left problems with reliability.

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 and cooled to a certain temperature or higher, 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 in light-shielding properties. 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 that the thickness of the recording layer is much thicker than the size of the recording. Forming the recording portion is substantially difficult. Therefore, it cannot be applied to a recording medium that performs high-density recording.

In addition, as erasable recording media using organic materials, for example, Japanese Patent Application Laid-Open No. 58-199343 discloses an organometallic complex bis (1-pn-alkylphenylbutane-1,3-dionato) (II) and an organic metal complex. Molecular mixture, JP-A-63-15793 discloses a mixture of crystalline and amorphous thermoplastic resin, JP-A-63-9599.
3, 96748 has a crystalline aromatic vinylene sulfide polymer,
JP-A-63-279440 discloses a sulfur-containing polymer and JP-A-63-1289.
Reference numeral 93 denotes a diazabicyclo [2,2,2] octane quaternary salt, and JP-A-63-259851 discloses a recording using a stretched oriented polymer or a crystal, amorphous transition or change in the degree of orientation of a liquid crystalline polymer. The method is shown. These are all slow in recording speed or erasing speed, and are difficult to put into practical use.

[Problems to be solved by the invention]

As described above, the recording method using the conventional recording medium leaves various problems in recording sensitivity, erasing speed, recording stability, contrast between a recorded portion and a non-recorded portion, and the like. It is desirable that the recording medium to be used is made of a non-toxic material from the viewpoint of stability.

From such a point of view, the present invention provides a recording method that uses a recording medium on which information can be recorded, reproduced, and erased, records information at high speed and high density, and can stably store the information for a long period of time.

[Means for solving the problem]

The present inventors have studied recording on organic compound crystals for the above purposes, and as a result, when heat is instantaneously applied to a thin film crystal having optical anisotropy, the crystal state partially changes. It has been found that the crystal state returns to the original crystal state by reheating to an appropriate temperature, and that the polarization characteristics change greatly. The recording method of the present invention is based on such a reversible change in the crystalline state.

That is, the recording method of the present invention comprises a recording medium comprising an organic thin film crystal having optical anisotropy or having a recording layer containing the thin film crystal,
After applying heat to melt a part of the thin-film crystal, it is crystallized by quenching, and in this part, a change in the crystal state accompanied by a change in the orientation direction of the molecule is recorded. In addition, heat is applied to a recording medium comprising an organic thin film crystal having optical anisotropy or having a recording layer containing the thin film crystal to melt a part of the thin film crystal, and then quenched. The recording is performed by causing a change in the crystal state accompanied by partial microcrystallization of the thin film crystal in this portion and recording. A recording medium comprising a light-to-heat conversion layer made of a light-to-heat conversion material that absorbs part or all of the heat and converting it to heat, and a recording layer comprising an organic thin film crystal having optical anisotropy, or a recording layer containing the thin film crystal, or The light-to-heat conversion material and the A recording medium consisting of a film-like crystal or having a recording layer containing the photothermal conversion material and the thin-film crystal is irradiated with light, a part of the thin-film crystal is melted, and then crystallized by rapid cooling, In this part, a change in the crystalline state accompanied by a change in the orientation direction of the molecule is generated and recorded, and a part or all of the irradiated light is absorbed and converted into heat. A recording medium comprising a light-to-heat conversion layer made of a light-to-heat conversion material and an organic thin film crystal having optical anisotropy, or a recording layer containing the thin-film crystal, or a light-to-heat conversion material and the thin film crystal Alternatively, a recording medium having a recording layer containing the photothermal conversion substance and the thin film crystal is irradiated with light, a part of the thin film crystal is melted, and then rapidly cooled to crystallize. Partial fine crystals It is characterized in that for recording cause a change in the crystalline state with crystallization.

In the recording method of the present invention, the organic thin film crystal having the above optical anisotropy is mainly composed of a fatty acid or a fatty acid derivative, a benzoic acid derivative or an n-alkane having a melting point of 50 ° C. or more or a derivative thereof. Things.

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

The recording medium used in the recording method of the present invention is provided with a recording layer containing an organic thin film crystal having optical anisotropy. Representative materials for forming such a recording layer include: Examples thereof include fatty acids or fatty acid derivatives, benzoic acid derivatives, n-alkanes having a melting point of 50 ° C. or higher, and derivatives thereof.

The fatty acid or fatty acid derivative used herein specifically refers to a saturated or unsaturated mono- or dicarboxylic acid or an ester, amide, anilide, hydrazide, ureide, anhydride, or fatty acid salt such as an ammonium salt or a metal salt thereof. Yes, esters include esters with compounds having two or more hydroxy groups, such as mono, di or triglycerides. 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, arachiic 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.

In addition, the benzoic acid derivative referred to here specifically includes benzoic acid represented by the following general formula and its ester, amide, anilide and the like. In addition, other optionally substituted hydrazide, ureide or anhydride,
Salts such as metal salts and ammonium salts are included. Also,
The ester includes, in addition to the compound represented by the general formula (II), an ester of an aliphatic hydrocarbon compound with a polyhydric alcohol or an aromatic hydrocarbon having a plurality of hydroxy groups.

Examples of the substituents of R ₁ , R ₂ , R ₃ and other benzoic acid derivatives in the general formula include a hydrogen, an alkyl group, an alkoxy group or a phenyl group, a biphenyl group, a naphthyl group, an aryl group such as an anthranyl group. R ₁ is an acyl group, an acyloxy group, a halogen, a nitro group, a hydroxy group, a cyano group, a carboxyl group and an ester thereof, an optionally substituted carbamoyl group, a sulfo group and an ester thereof, or an alkyl group. Group, a phenyl group, an amino group which may be substituted with a substituted phenyl group, and the like. Further, the above-described alkyl group, alkoxy group, aryl group may be substituted with the same substituents as R _1. The alkyl group and the alkoxy group may be linear or branched, and in the case of those having two or more carbon atoms, the carbon chain may contain one or more unsaturated bonds. Good.

The term “n-alkane derivative” as used herein refers to a compound having one or more double bonds or triple bonds in a carbon chain, a compound in which one or more hydrogen atoms are substituted with a halogen atom, and a terminal. Is a compound in which a benzene ring which may be substituted with an alkyl group or an alkoxy group is bonded to the carbon atom of the above. Specific examples of the n-alkane include, for example, n-alkanes such as tetracosane, pentacosane, hexacosane, peptacosane, octacosane, nonacosan, triacontane, dotriacontane, tetratriacontane, hexatriacontane, octatriacontane, tetracontane and the like. There are mixtures containing these as main components, so-called paraffin and paraffin wax. The derivatives include 1-hexacocene, 1-heptacosene, 1-octacocene, 1-triaconten, 1-tetratriaconten, 1-hexatriaconten, 1-octatriaconten, 1-tetraconten, docosylbenzene, Kosylbenzene, hexacosylbenzene, octakosylbenzene, triacontylbenzene, tritriacontylbenzene, tetratriacontylbenzene, hexatriacontylbenzene, 1,18-dibromooctadecane, 1,20-dibromo Eikosan and 1,22-dibromodokosan.

The material of the recording layer used preferably has a melting point of 50 to 200.
C., preferably in the range of 60 to 150C. If it is lower than this, there is a problem in the storability of the recording, and if it is higher than this, the energy required for recording becomes large, and the recording speed becomes slow.

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

As the substrate of the recording medium used in the present invention, a glass plate,
Examples include a metal plate, 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 the reproduced light. In the case of reading with reflected light, a metal or metalloid layer such as platinum, titanium, silicon, chromium, nickel, germanium, or aluminum is provided as necessary to form a reflective layer that reflects part of light.

In the recording method of the present invention, recording is performed by applying thermal energy to a recording layer of a recording medium in accordance with information to be recorded. It is necessary to provide a layer that absorbs a part 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. This light absorbing layer may be provided with a metal or metalloid layer such as platinum, titanium, silicon, chromium, nickel, germanium, aluminum, etc.
In this case, it can also be used as a reflective layer. The light absorbing 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 naphthoquinone dye, a porphyrin dye, an indigo dye, It may be a layer containing a dithiol complex dye, an azurenium dye, a quinone imine dye, a quinone diimine dye, or the like, and the dye is selected according to the wavelength of light used for recording. These dyes are also used when a light-absorbing substance is contained in the recording layer.

The recording medium used in the present invention is an organic thin film crystal having optical anisotropy or has a recording layer containing the same, and its configuration is not specified, but it is usually used frequently. Configuration example of a recording medium
FIG. 5 to FIG.

FIG. 1 shows a recording medium in which an organic anisotropic crystal having optical anisotropy is formed on a substrate 1 or a recording layer 2 including the same is formed. FIG. A light-absorbing layer 3 (a layer that reflects a part of light, if necessary) that absorbs a part and converts it into heat, and is made of or contains an organic thin film crystal having optical anisotropy FIG. 3 shows a recording medium provided with a recording layer 2, FIG. 3 shows a recording medium provided with a recording layer 2 on a substrate 1, and a light absorbing layer 3 provided thereon, and FIG. 4 shows light absorption of the recording medium shown in FIG. 2. For example, a recording medium having an undercoat layer 4 provided between the layer 3 and the recording layer 2 for the purpose of improving the film quality of the recording layer, etc. FIG. This is a recording medium provided with a protective layer 5.

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, the protective layer 5 may be made of these resins or a glass plate. 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 for improving the properties of the glass surface, for example, a silane-based Or it may be one treated with a titanate-based surface treatment agent.

In order to manufacture the recording medium used in the present invention, the light-to-heat conversion layer 3 is formed on the substrate 1 as necessary by using a metal or metalloid as described above, for example, by 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 provided with the light-to-heat conversion layer 3 while keeping a gap corresponding to the required thickness of the recording layer. In order to form a gap, a spacer layer may be provided around the portion where the recording layer is to be formed, or a gap material having a small and uniform diameter, such as silica particles, polystyrene beads, etc., may be provided in advance on the light-to-heat conversion layer side. Alternatively, it may be attached to the protective layer side. The entire substrate with the gap formed in this way is placed in a thermostat or placed on a hot plate and kept at a temperature higher than the melting point of the material used for the recording layer. Let it go. When the obtained melt layer is gradually cooled and crystallized, a thin film crystal of the recording layer can be formed between the light-to-heat conversion layer 3 and the protective layer 5. At this time, in order to keep the gap interval constant, pressure may be applied by a weight or the like until crystallization. The treatment may be performed under reduced pressure in order to prevent bubbles from entering. As another production method, for example, a material for forming a recording layer is dissolved in an appropriate organic solvent, for example, 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 an appropriate solvent is applied. 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, and then slowly cooled to crystallize to form a thin film crystal of the recording layer. . Various other methods such as the Langmuir-Blodgett method can be used for forming the recording layer.

When a light-to-heat conversion substance is contained in the recording layer, for example, the dye may be dissolved or dispersed in a solution of the material of the recording layer at the same time, or applied.

The thickness of the recording layer is not particularly limited, but is usually 10
Å to 10 μm, preferably about 10 to 5 μm. The appropriate thickness of the layer that absorbs a part of the irradiated light and converts it into heat depends on the wavelength and intensity of the light used for recording and the type of material used, but is generally about 50 ° to 5 μm. .

The recording method of the present invention utilizes a partial and reversible change in crystal state of an organic thin film crystal having optical anisotropy. Recording and erasing of information are performed by applying heat, and various methods can be considered as a method of applying heat.However, in order to record information at a higher density, a method of irradiating a focused laser beam is most preferable. . in this case,
The recording medium must be provided with a layer that absorbs light and converts it to heat, or a substance that absorbs light and converts it to heat needs to be added to the recording layer.

Recording of information is performed as follows. The laser-irradiated portion of the recording layer is made of an organic thin film crystal having optical anisotropy or generates heat by absorption of light by the light-absorbing layer or the light-absorbing substance, or the recording layer containing this is instantaneous. It is heated and cooled rapidly when laser light irradiation stops, and the recording pits (however, the pits do not mean holes or depressions, but the portions recorded as changes in the crystal state in the thin film crystal for convenience) Are called pits).

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 absorbing layer (substance) generated by the short-time laser irradiation,
A temperature is reached at which the crystals are completely melted. 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 is 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 a minute part irradiated by the focused laser light, the thickness of each layer, light absorption characteristics, heat Conductivity,
When the thermal characteristics such as specific heat are set to the values shown in Table 1, and the temperature change of the recording layer is simulated,
The time required to cool to ℃ is 100μs
About 1.7μsec for ec, about 15nsec for irradiation time of 0.25μsec
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. In addition, it is also related to the orientation state of the molecules. Generally, the higher the cooling rate is, the more the orientation disorder tends to be. 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 crystallization occurs under different conditions in each place, so that the state is not always uniform. Therefore, (1), (2),
The change in the crystal state of (3) occurs in a single recording unit, depending on the position and in various forms.

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 °) caused by the long plane spacing (39.8 °) of the stearic acid C-type crystal
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. In particular, such a change in the crystal state often accompanies a change in the 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 performed by detecting the intensity of light through the polarizer. 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.

In this way, information is recorded as a change in crystal state by applying heat to a part of the organic thin film crystal having optical anisotropy in the recording layer and instantaneously melting and recrystallizing,
Although the temperature of the recording layer is lower than the temperature at the time of recording and the recording layer is not completely melted, erasing can be performed by heating to a temperature at which molecules can move sufficiently. 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. This record is erased,
This can be confirmed by increasing the temperature of the recording layer while observing with a polarizing microscope. With a polarizing microscope, the state of the recording part looks like a dark line in, for example, a bright non-recording part, but as the temperature increases, the line starts to be cut off from a certain temperature, and eventually the whole becomes a non-recording part. It becomes the same bright state, and the record is erased when cooled from this temperature. At this erasing temperature, the brightness of the non-recording portion does not change, but when the temperature is further raised to the melting point of the recording layer, the entire field of view becomes completely dark. Therefore, when the molecules of the micro-recorded portion having a changed crystalline state formed in the thin-film crystal become in a state capable of performing sufficient thermal motion, they will take the same arrangement as the molecules of the surrounding non-recorded portion, By returning from that temperature to room temperature, the whole is erased as a uniform thin film crystal.

Specifically, the recording can be erased by heating and cooling the entire recording medium to the above temperature range to erase the entire recording, or to locally record the recording pit portion or a slightly wider range. By heating and cooling to the erasing temperature, it is also possible to erase only 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 method 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. Partially changes the crystal state of the crystal, and the change is not merely a change from crystal to amorphous,
It is recorded as a change including a change in the orientation direction of molecules or a partial microcrystallization, and is erased by restoring the crystal state.The difference between the formed recorded part and the non-recorded part is optically different. It is detected as a difference in polarization characteristics based on anisotropy. In this respect, the recording medium used in 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 method of the present invention, the organic compound exists as a thin film crystal, and the recording is formed as a change in the crystal state on a part of the thin film crystal, and the resulting difference in optical properties is reduced. It is to detect. Therefore, the difference between the two is clear.

〔The invention's effect〕

The recording method of the present invention is basically performed by heating an organic thin film crystal having an optical anisotropy for forming a recording layer to a melting temperature or higher, and erasing is heated to a lower temperature. It is done by doing. Therefore, since recording and erasing can be performed at high speed by adjusting the intensity of the laser beam to be irradiated, so-called overwriting (overwriting) in which recording is performed while erasing is possible. Also,
This recording and erasing can be repeatedly performed stably. Further, since the recording unit is in the same stable state as 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 plane spacing (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 which was repeatedly irradiated with the intensity of 1.5 mW, the recording portion by the laser beam of 1 μmφ 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 rotating the same part by 45 ° and observing it.

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, another recording medium was irradiated with a laser beam 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. After the entire recording, the glass plate of the protective layer of the recording medium was peeled off, and X-ray diffraction was measured. On the other hand, the recording medium prepared in the same manner was not recorded, the protective layer was peeled off, and X-ray diffraction was measured. Further, the temperature of the recording medium after the recording was raised to 75 ° C. at a rate of 1 ° C./min, the temperature was returned to room temperature, and X-ray diffraction in a state where the recording was almost erased was measured. Unrecorded in Fig. 12, after recording in Fig. 13,
The figure shows the 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 recording layer of behenic acid thin film crystal thereon, 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 the recording medium of the present invention, wherein 1 is a substrate, 2 is a recording layer of an organic thin film crystal having optical anisotropy, 3 is a photothermal conversion layer, 4 is The undercoat layer and the reference numeral 5 indicate 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 an image obtained by rotating the same part by 45 °. 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 (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.
(A) and (b) are obtained by rotating the same part by 45 ° and observing it. 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 Company, Ltd. (56) References JP-A-57-117140 (JP, A) JP-A-54-149617 (JP, A) JP-A-61-92453 (JP, A) JP-A-58-199194 (JP, A) JP-A-2-131987 (JP, A) JP-A-2-139286 (JP) JP-A-64-19532 (JP, A) JP-A-61-175088 (JP, A) JP-A-64-14077 (JP, A) JP-A-57-38190 (JP, A) 58-104794 (JP, A) JP-A-54-5447 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (5)

(57) [Claims] 1. A method of applying heat to a recording medium comprising an organic thin film crystal having optical anisotropy or having a recording layer containing the thin film crystal to melt a part of the thin film crystal, followed by rapid cooling. A recording method wherein a crystal state is changed in this portion along with a change in the orientation direction of molecules, and recording is performed. 2. A method comprising: applying heat to a recording medium comprising an organic thin film crystal having optical anisotropy or having a recording layer containing the thin film crystal to melt a part of the thin film crystal; A recording method characterized by causing a change in the crystal state accompanied by partial microcrystallization of a thin film crystal in this portion to perform crystallization. 3. Absorbing part or all of the irradiated light,
A recording medium comprising a light-to-heat conversion layer made of a light-to-heat conversion substance that converts heat and an organic thin film crystal having optical anisotropy or a recording layer containing the thin-film crystal, or the light-to-heat conversion substance and the thin film The recording medium having a recording layer comprising the photothermal conversion material and the thin film crystal, which is composed of a crystal, or is irradiated with light, a part of the thin film crystal is melted, and then crystallized by rapid cooling. A recording method characterized by causing a change in a crystalline state accompanying a change in the orientation direction of a molecule in a portion to perform recording. 4. Absorbing part or all of the irradiated light,
A recording medium comprising a light-to-heat conversion layer made of a light-to-heat conversion substance that converts heat and an organic thin film crystal having optical anisotropy or a recording layer containing the thin-film crystal, or the light-to-heat conversion substance and the thin film The recording medium having a recording layer comprising the photothermal conversion material and the thin film crystal, which is composed of a crystal, or is irradiated with light, a part of the thin film crystal is melted, and then crystallized by rapid cooling. A recording method characterized by causing a change in a crystal state accompanied by partial microcrystallization of a thin film crystal in a portion to perform recording. 5. An organic thin film crystal having optical anisotropy,
The recording method according to any one of claims 1 to 4, wherein the fatty acid, a fatty acid derivative, a benzoic acid derivative, or an n-alkane having a melting point of 50 ° C or higher or a derivative thereof is used as a main component.