JPH0316786A - Recording medium and recording method - Google Patents

Abstract

PURPOSE:To provide a recording medium which can record, reproduce and erase information, to record the information in high density at a high speed, and to stably preserve it for a long period by employing thin filmlike crystal of a material having different crystal growing speeds according to directions or a recording layer including it. CONSTITUTION:An opto-thermal conversion layer 3 for absorbing and converting part or all of a light radiated at the time of recording on a board 1 into heat is provided, and a recording layer 2 made of a thin filmlike crystal of a material having different crystal growing speeds according to directions is provided thereon. Heat is applied to such a recording medium to melt the part of the crystal. In a method of partially applying heat, the recording layer absorbs the light to generate heat, or it generates heat by an opto-thermal conversion layer provided separately in case of using a light radiation. In this case, the part becoming the melting point or more of the crystal (central part) is melted, and the direction of the crystal of this part is recorded in a different direction from the crystal therearound. Thus, recording and erasure can be easily conducted by controlling the arrival temperature, cooling temperature of the recording layer, and difference of polarizing characteristics is detected to reproduce at a high speed with high reliability.

Description

[Detailed description of the invention]

[Industrial Field] The present invention relates to a heat mode recording medium and a recording method for recording information by applying heat or irradiating light. This invention relates to a recording method based on reversible changes in crystalline states. [Prior Art] In recent years, so-called heat mode recording systems have been put into practical use, which apply information in the form of thermal energy and record it as a change in shape or physical properties of a recording material. Such heat mode recording media include Te, Bi. Ss%Tb
．． Inorganic recording media using metal materials mainly composed of In, polymethine dyes such as cyanine, macrocyclic azaannulene dyes such as phthalocyanine, naphthalocyanine, volufiline, naphthoquinone, anthraquinone dyes, and dithiol. Recording media using organic dyes such as metal complex dyes are known. When thermal energy is applied to these recording media, such as by irradiation with a focused laser beam, the recording layer in the irradiated area melts or evaporates, forming holes (bits) and recording information. However, these recording media do not have the reversibility of erasing recorded information and recording new information again. With the development of read-only, write-once type heat mode optical recording media as described above, the need for reversible recording media that can be recorded, read, and erased is increasing. As such a reversible recording medium, for example, Gd. Tb,
Rare earth elements such as oy and Fe. There are magneto-optical recording media that use alloy thin films made of transition metals such as Ni and Co. This uses a combination of heating by laser beam irradiation and an externally applied magnetic field to record, and reproduces data by utilizing the difference in the rotational direction of the light vibration plane depending on the direction of magnetization. Information is also erased by heating with a laser and applying an external magnetic field in the opposite direction to that used during recording. However, this magneto-optical recording medium has drawbacks such as insufficient sensitivity during reproduction, poor S/N ratio, and problems with deterioration of recording sensitivity and recording stability due to effects such as oxidation. ing. Furthermore, as reversible recording media, Ge, Te. Se. S
b, In. There is a method that utilizes the phase transition between crystal and non-crystalline materials in a recording layer made of a thin film of an inorganic material containing an element such as Sn as a main component. This recording medium can only be irradiated with laser light.
It has the advantage of being able to record and erase in heat mode, but
It has drawbacks such as insufficient contrast between the recorded and non-recorded areas, insufficient recording stability, and problems with the stability of the material of the recording layer.

[Problem to be solved by the invention]

As described above, recording media and recording methods using conventional recording media have various problems such as recording sensitivity, erasing speed, recording stability, and contrast between recorded and non-recorded areas. In addition, from the standpoint of safety, it is desirable that the recording medium used be made of non-toxic materials. From this viewpoint, the present invention provides a recording medium and a recording method that can record information at high speed and high density using a recording medium that is capable of recording, reproducing, and erasing information, and that can store the information stably for a long period of time. be. [Means for Solving the Problems] For the above-mentioned purposes, the present inventors studied the thermal changes of various materials, and found that a thin film-like crystal whose growth rate varies depending on the long axis of the crystal is used in the recording layer, We discovered that when heat is applied to a part of the material to melt it and recrystallize it, the surrounding crystals crystallize in different directions, and that when this part is reheated to an appropriate temperature and slowly cooled, it returns to its original state. Ta. The recording medium and recording method of the present invention are based on changes in the crystal axis direction of such thin film crystals. That is, the recording medium of the present invention is a recording medium characterized by using a recording layer that is or includes a thin film-like crystal of a material whose crystal growth rate differs depending on the direction, and that the recording layer and the recording layer that are irradiated during recording are The recording medium is characterized in that it also includes a light-to-heat conversion layer that absorbs some or all of the light and converts it into heat. Further, this recording medium is a recording medium in which the recording layer is an organic thin film crystal having optical anisotropy, and is a thin film crystal of a material whose crystal growth rate differs depending on the direction. In addition, the recording method of the present invention involves partially and temporarily melting the thin film crystal by applying heat or irradiating the above-mentioned layer with light, and then recrystallizing the material whose crystal growth rate differs depending on the direction. This is a recording method characterized by recording as a crystal whose direction is different from that of the crystal axes of surrounding crystals. Preferred structural examples of the recording medium of the present invention are shown in FIGS. 1 to 5. Figure 1 shows a recording medium in which a recording layer 2 made of a thin film crystal of a material whose crystal growth rate varies depending on the direction is provided on a substrate 1, and Figure 2 shows a portion of light irradiated onto the substrate 1 during recording. Alternatively, a recording medium is provided with a photothermal conversion layer 3 that absorbs all of the light and converts it into heat (which also serves as a layer that reflects part of the light if necessary), and the recording layer 2 is provided thereon, as shown in FIG. A recording medium on which a recording layer 2 and a light-to-heat conversion layer 3 are sequentially laminated, a fourth
The figure shows a recording medium in which an undercoat layer 4 is provided between the light-to-heat conversion layer 3 and the recording layer 2 of the recording medium shown in FIG. FIG. 5 shows a recording medium in which a protective layer 5 is further provided on the recording layer 2 of the recording medium shown in FIG. The recording layer that characterizes the present invention is made of thin film-like crystals,
The growth rate differs depending on the direction in which the crystal grows. For example, as shown in Figure 6, in a recording medium consisting of a substrate, a light-to-heat conversion layer, and a recording layer, the direction in which the growth rate of the thin film crystals in the recording layer is the highest is oriented uniformly throughout (arrow). belongs to. Therefore, the orientation (direction of the crystal axis) of this thin film crystal is almost the same everywhere. A thin film crystal in such a state can be obtained, for example, by heating a melt of the material between two substrates to form a thin film, cooling the substrates from one direction, and crystallizing the material. In materials where the crystal growth rate differs depending on the direction, the crystallization direction is often preferentially oriented in the direction with the highest growth rate. The recording method of the present invention applies heat to such a recording medium to melt a portion of the thin film crystal. To apply heat locally, for example, a minute heating element such as a thermal head may be brought into contact, or a small spot may be irradiated with focused light. In the case of light irradiation, the recording layer absorbs the light and generates heat, or a separately provided photothermal conversion layer generates heat. If the thin film crystal does not absorb light, a photothermal conversion substance may be included in the recording layer. When heat is applied locally using the above method, a temperature distribution is formed in the thin film-like crystals of the recording layer. For example, when heating is performed by irradiating a laser beam, a temperature distribution is formed in the irradiated area due to the intensity distribution (Gaussian distribution) of the laser beam spot itself and heat conduction to the outside of the spot. Although it is difficult to measure the temperature distribution within a minute spot when laser light is irradiated, a recording medium with the configuration shown in Figure 6 can measure the intensity distribution of the laser light, wavelength, light absorption by each layer, and heat. Considering conduction, the thickness, density,
If the specific heat, thermal conductivity, and refractive index are simulated as the values shown in Table 1 below, for example, the wavelength is 7BOn+*
．． Laser light with a beam diameter of 5 μιφ and an intensity of 4 mV l00
The temperature distribution immediately after μsec irradiation is shown in Figure 7. The temperature distribution has a small temperature difference in the thickness direction of the recording layer, and in the lateral direction, the temperature is highest at the center and decreases toward the periphery. At this time, the part (center part) whose temperature exceeds the melting point of the thin film crystal becomes molten. When the laser beam irradiation is stopped, the heat diffuses and the temperature inside the spot decreases overall. The temperature of the part that was in a molten state at a temperature higher than the melting point becomes lower than the freezing point from the peripheral part, so the range of the molten part becomes smaller, that is, crystallization occurs from the peripheral part of the spot. When the laser beam spot is scanned, it melts in a line and crystallizes from the outside of the line.
When using this heating method, the temperature decreases quickly, so
Crystallization is completed in about several μsoC. When crystallizing at high speed in this way, crystallization preferentially orients the direction of the highest growth rate to be the crystal growth direction, that is, from the outside to the center of the irradiated area, and as a result, the direction of the crystal in this area changes. is recorded in a direction different from that of the surrounding crystals. This situation is, for example, as shown in Figure 8. Recorded portions with different directions of crystal axes, which are formed by partially applying heat to a thin film crystal for a short time, can be detected by optical means. In particular, if the thin film crystal has optical anisotropy, the recorded portion can be observed with clear contrast using a polarized light microscope, and the recorded information can be easily read and reproduced using polarized light. ．． Specifically, in reproduction, focused polarized light (laser light) is incident on a recording medium, and the recording medium is placed so that the reflected or transmitted light is transmitted in a direction of vibration perpendicular to the direction of vibration of the incident light. This can be done by detecting the intensity of light through a polarizer. The intensity of the light used for reproduction is sufficiently weaker than the light used for recording and erasing, so that the temperature of the recording layer does not rise to the recording temperature and erasing temperature. The part recorded as a change in the crystal axis direction in this way is
It can also be erased by heating and cooling under conditions different from those used for recording. For example, after heating and melting the area that includes the recording part of a crystalline thin film, if you cool it slowly instead of rapidly as you would during recording, it will crystallize in the same direction as the crystals outside the melted part, and as a result, the recording will not be possible. will be deleted. Furthermore, depending on the type of material of the thin film crystal, it may be possible to erase it by heating it to a temperature lower than the melting temperature. This temperature is a temperature at which the recording layer does not completely melt, but is at a temperature that allows sufficient thermal movement of molecules. The erasing temperature range varies depending on the material and purity of the recording layer. The erasure of records can be confirmed by increasing the temperature of the recording medium while observing it with a polarizing microscope. As the material used for the recording layer of the recording medium of the present invention, any material can be used as long as it can form a thin film crystal having crystal growth axes with different growth rates. When detecting a portion recorded as a change in the crystal axis direction by a difference in polarization characteristics as described above, it is preferable that this thin film crystal has optical anisotropy. Specific examples of such materials include, for example, organic materials such as fatty acids or fatty acid derivatives, benzoic acid derivatives, or organic materials with a melting point of 50
Examples include, but are not limited to, n-alkanes with a temperature of ℃ or higher. The fatty acid or fatty acid derivative as used in the present invention specifically refers to saturated or unsaturated mono- or dicarboxylic acids, their esters, amides, anilides, hydrazides, ureides, anhydrides, or fatty acid salts such as ammonium salts or metal salts. means. In this case, esters include esters with compounds having two or more hydroxy groups, such as mono-, di- or triglycerides. Further, these may be substituted with a halogen, a hydroxy group, an acyl group, an acyloxy group, or a substituted or unsubstituted aryl group. These saturated or unsaturated fatty acids may be straight-chain or branched, and unsaturated fatty acids may have one double or triple bond,
It is also possible to have two or more. The number of carbon atoms in the hydrocarbon chain in these fatty acids is preferably 10 or more. Specific examples of saturated fatty acids include undecanoic acid, lauric acid, myristic acid, pentadecanoic acid, balmitic acid, heptadecanoic acid, stearic acid, nanodecanoic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melisic acid. Examples of unsaturated fatty acids include oleic acid, elaidic acid, linoleic acid, sorbic acid, and stearolic acid. Specific examples of esters include methyl ester, ethyl ester, hexyl ester,
These include octyl ester, decyl ester, dodecyl ester, tetradecyl ester, stearyl ester, eicosyl ester, and docosyl ester. Further, examples of metal salts include metal salts of these fatty acids such as sodium, potassium, magnesium, calcium, nickel, cobalt, zinc, cadmium, and aluminum. Further, the benzoic acid derivatives referred to in the present invention specifically include benzoic acids represented by the following general formulas (!) to (IV), and their esters, amides, anilides, and the like. In addition, salts such as optionally substituted hydrazides, ureidos, anhydrides, metal salts, and ammonium salts are included. In addition to the compound represented by the general formula (n), esters include esters of aliphatic hydrocarbon compounds with polyhydric alcohols or aromatic hydrocarbons having a plurality of hydroxy groups. It. Examples of substituents for R, R2, R, and other benzoic acid derivatives in the general formula include hydrogen, alkyl groups,
It is an aryl group such as an alkoxy group, a phenyl group, a biphenyl group, a naphthyl group, an anthranyl group, and in addition to these, R is an acyl group, an acyloxy group, a halogen, a nitro group, a hydroxy group, a cyano group, a carboxyl group, and their esters. , a carbamoyl group that may be substituted, a sulfo group and its ester or alkyl group, a phenyl group, and an amino group that may be substituted with a substituted phenyl group. In addition, the above alkyl group, alkoxy group,
The aryl group may be substituted with the same substituents as R. In addition, alkyl groups and alkoxy groups may be linear or specialized, and those with two or more carbon atoms may contain one or more unsaturated bonds in the carbon chain. Good too. Furthermore, the n-alkane derivatives referred to in the present invention include compounds containing one or more double bonds or triple bonds in the carbon chain, compounds in which one or more hydrogen atoms are substituted with halogen atoms, and terminal It is a compound in which a benzene ring which may be substituted with an alkyl group or an alkoxy group is bonded to the carbon atom. Specifically, for example, tetracosane, pentacosane, hexacosane, heptacosane,
n- such as octacosane, nonacosane, triacontane, dotriacontane, tetratriacontane, hexatriacontane, octatriacontane, tetracontane, etc.
There are alkanes and mixtures containing these as main components, so-called paraffins and paraffin waxes. Examples of derivatives include l-hexacosene, l-heptacocene, 1-octacocene, 1-triacontene, 1-tetratriacontene, 1-hexatriacontene. 1-octatriacontene, l-tetracontene, docosylbenzene, tetracosylbenzene, hexacosylbenzene, octacosylbenzene, triacontylbenzene, tritriacontylbenzene, tetratriacontylbenzene, hexatriacontyl Examples include benzene, 1,18-dibromooctadecane, 1,20-dibromoeicosane, and 1,22-dibromodocosane. The recording layer material used preferably has a melting point of 50 to 20
0°C, particularly preferably in the range of 60 to 150°C. If it is lower than this, there will be problems with recording preservation, and if it is higher, the energy required for recording will increase and the recording speed will be slow. In the recording layer of the recording medium of the present invention, one type or a mixture of two or more of these materials can be used. Further, the recording layer in the present invention contains thin film-like crystals mainly composed of these materials, but resins other than these may be used as necessary to form the layer. Examples of the resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer, polychloride vinylidene, vinylidene chloride-acrylonitrile copolymer,
Examples include polyester, polyamide, polyacrylate, polymethacrylate, polycarbonate, polyurethane, and silicone resin. When a resin is used in the recording layer, the weight ratio of the resin to the recording layer material 1 in the entire recording layer is preferably 3 or less, particularly 1 or less. As the substrate of the recording medium of the present invention, for example, a glass plate,
A metal plate or a plastic plate such as polymethyl methacrylate or polycarbonate can be used. In addition, when a photothermal conversion layer is provided and recording is performed by light irradiation,
The photothermal conversion layer may be provided with a layer of metal or metalloid, such as platinum, titanium, silicon, chromium, nickel, germanium, or aluminum. In addition, dyes that absorb the irradiated light, such as azo dyes, cyanine dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, naphthalocyanine dyes, squarylium dyes, dithiol complex dyes, and azulenium dyes, are also available. It may also be a layer of pigment, etc. Furthermore, these photothermal conversion substances may be directly contained in the recording layer instead of in the photothermal conversion layer. Additionally, both may be used in combination to improve recording sensitivity. The undercoat layer 4 includes, for example, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-acrylate copolymer, polyvinylidene chloride, polyester, polyamide, polyimide, polycarbonate, polyester, polyurethane, acrylic resin, silicone resin, etc. can be used. Further, for the protective layer 5, these resins or a glass plate may be used. When using a glass plate, these resin layers may be provided for the same purpose as the undercoat layer, or a surface modification material such as silane-based or titanate-based surface treatment may be used to improve the properties of the glass surface. It may be treated with a chemical. [Effects of the Invention] The recording medium and recording method of the present invention do not make holes in the recording layer or change the surface shape of the recording layer, but only change the crystal state of the thin film crystal. By appropriately controlling the temperature reached and the cooling temperature of the recording layer, recording and erasing can be easily performed. Since recording can be detected as a difference in polarization characteristics, the contrast between recorded and non-recorded areas is high, allowing for high-speed and reliable reproduction. In addition, since the recording part is in a stable crystalline state like the non-recording part, recorded information can be stored for a long period of time. [Example] The present invention will now be explained in more detail with reference to Examples. Example 1 A chromium layer serving as a light reflection layer and a light-to-heat conversion layer was provided on an optically polished glass plate by vacuum deposition. The thickness was approximately 900 pieces. On the other hand, on one side of the glass plate (thickness 0.1+mm) that will serve as the protective layer, a gap material of about 1 μm in diameter is used as a gap material.
A small amount of Otori's silica particles were attached. After heating both of them in a constant temperature bath at 100°C, apply behenic acid (manufactured by Sigma) on the chromium layer of the glass substrate at the same temperature.
(purity of 99% or higher) was placed on top and melted. Next, the protective glass plate was gently placed over the behenic acid melt from one end with the side with the gap material facing down, and the melt was spread over the entire surface and sandwiched. Furthermore, a load was applied uniformly from above the glass plate, and the substrate was cooled from one end to slowly crystallize behenic acid from one direction, forming a thin film of crystals. Through the above operations, a recording layer (0.8 μm thick
) and a protective layer made of glass having a thickness of about 0.1 a+m was formed thereon. Here, in order to investigate the state of behenic acid crystals in the recording layer, the glass plate of the protective layer of a similarly prepared recording medium was peeled off and X-ray diffraction was measured. As shown in Fig. 9, only the diffraction lines based on the long-plane spacing (48.3 persons) of the behenic acid C-type crystals appeared, and this crystal thin film showed that the a-axis and b-axis were aligned with respect to the substrate. It shows that they are oriented almost parallel, with the C axis rising. The recording medium produced as described above was irradiated in a straight line with a semiconductor laser beam having a wavelength of 780 nm and condensed to a diameter of 5 μm, which was continuously turned on so that the intensity was 10+mV at the surface of the recording medium. At this time, the scanning speed was 100 mm/sec. When this recording medium was observed under crossed nicols using a reflective polarizing microscope, dark line-shaped recorded areas were visible within the bright non-recorded areas. Further, when the recording medium was rotated by 45 degrees from this state, the brightness and darkness were reversed, and a bright line-shaped recorded portion was observed in the dark non-recorded portion. This indicates that the crystal orientation of the recording area is different from the crystal orientation of the surrounding non-recording area. Next, record using a polarizing microscope. As I raised the temperature of the recording medium at a rate of 2 degrees Celsius, the records began to disappear at around 60 degrees Celsius.
At 75°C, it disappears completely, and it has been found that the record can be erased by cooling from this temperature. Furthermore, since the behenic acid crystals in the non-recording area melt at about 79°C, it was confirmed that this record was erased at a temperature lower than the melting point of the thin film crystal itself. Example 2 Stearic acid (
Example 1 except that Sigma (purity: 99% or higher) was used.
Similarly, a recording layer (with a thickness of about 0.8
μm) and a thickness of approx. A recording medium with a protective layer made of Hōichi glass was created. This recording medium was scanned with a laser beam in the same manner as in Example 1. However, the irradiation intensity was 8 mW on the surface of the recording medium, and after 6 irradiations, the same recording as in the case of behenic acid in Example 1 was observed using a polarizing microscope. It was also found that when the temperature of the recording medium was increased at a rate of 2°C/min while performing tR using a polarizing microscope, the recording completely disappeared at 67°C, and that the recording could be erased by cooling from this temperature. Ta. Since the stearic acid crystal in the non-recording area melts at about 69°C, it was confirmed that this record is erased at a temperature lower than the melting point of the thin film crystal itself. Example 3 As in Example 1, a glass substrate on which chromium was vacuum-deposited was prepared. A polyimide resin solution (manufactured by Japan Goui Rubber Co., Ltd.: JIB-1) was applied on this chromium layer, and
After drying for a while, a polyimide layer with a thickness of about 0.1 μm was provided. On the other hand, a glass plate with a thickness of about 0.1 μm is prepared as a protective layer, a polyimide layer with a thickness of about 0.1 μm is provided on one side of the glass plate, and a gap material with a diameter of about
A small amount of μmaro silica particles was attached. Both of these at a temperature of 1
After heating in a constant temperature bath at 40°C, a small amount of 4-hexadecyloxybenzoic acid was placed on the polyimide layer on the glass substrate at the same temperature and melted. Next, one glass plate was gently placed over the melt from one end with the side to which the gap material was attached facing down, and the melt was spread and sandwiched throughout. Furthermore, a load was applied uniformly from above the covered glass plate, and the substrate was cooled from one end to slowly crystallize from one direction. Through the above operations, the chromium layer, the polyimide layer, the recording layer (approximately 0.8 μm thick) consisting of a thin crystalline film of 4-hexadecyloxybenzoic acid with almost uniform orientation, the polyimide layer, and the glass are laminated on the substrate in that order. A record of what happened. I got the recording medium. This recording medium was scanned with a laser beam in the same manner as in Example 1. However, the irradiation intensity was set to 12IllI1 on the recording medium surface. After irradiation, the same records as in Example 1 were confirmed when observed with a polarizing microscope. Furthermore, if the temperature of the recording medium is increased at a rate of 2°C/min while observing it with a polarizing microscope, 8°C
It was found that the records disappear completely at 0°C, and that the records can be erased by cooling from this temperature. Since the crystal thin film in the non-recording area melts at about 5° C., it was confirmed that this recording is erased at a temperature lower than the melting point of the thin film crystal itself. Table-1

[Brief explanation of drawings]

Figures 1 to 5 are cross-sectional views of the recording medium of the present invention, in which 1 is a substrate, 2 is a recording layer made of crystals with different growth rates or thin film crystals with long axes, and 3 is a photothermal conversion layer. , 4 indicates an undercoat layer, and 5 indicates a protective layer. FIG. 6 is a diagram showing an example of the crystal axis direction of the thin film crystal of the recording layer, and FIG. 7 is a diagram showing an example of the temperature distribution formed when the recording medium in FIG. 6 is irradiated with a laser beam. It is. Further, FIG. 8 is a diagram showing an example of the crystal axis direction of the recorded portion and non-recorded portion formed when the recording medium of FIG. 6 is irradiated with a laser beam, when viewed from above. FIG. 9 is an X-ray diffraction diagram of the recording layer when a thin film crystal of behenic acid is used for the recording layer. Fig. 7 5μmφ

Claims (4)

[Claims] (1) A recording medium comprising a recording layer made of or containing thin film-like crystals of a material whose crystal growth rate varies depending on the direction. (2) It has a recording layer that is made of or includes a photothermal conversion layer that absorbs some or all of the light irradiated during recording and converts it into heat, and a thin film crystal of a material whose crystal growth rate varies depending on the direction. A recording medium characterized by: (3) The recording medium according to claim (1) or (2), wherein the thin film crystal of a material whose crystal growth rate differs depending on the direction is an organic thin film crystal having optical anisotropy. (4) The thin film crystal is partially and temporarily melted by applying heat or irradiating the recording medium according to any one of claims (1) to (3) with light, and then recrystallized. A recording method characterized by recording a crystal in a direction different from that of surrounding crystals.