JPH04294192A - High density recording method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method for recording multilevel information or a plurality of pieces of information on an irradiated area using a recording medium that records information using heat added by light irradiation.

0002

[Prior Art] Conventionally, optical information recording media are recorded by forming pits in a recording layer of a metal thin film or an organic dye thin film using heat generated by light irradiation, and detecting changes in optical characteristics due to the pits. Write-once recording media that reproduce information, magneto-optical recording media that record by reversing the direction of magnetization using heat from light irradiation and an external magnetic field, and reproduce using the magneto-optical effect, or crystal-amorphous thin films of inorganic materials. There are rewritable recording media, such as recording media that record information by a phase transition between two layers and reproduce information by detecting a change in optical characteristics accompanying the phase transition.

[0003] Such recording media are required to have high density and high capacity in order to increase the capacity and high speed processing of information processing devices. However, in the above recording method, only a signal of 0 or 1, which corresponds to the presence or absence of recording, can be recorded in one recording spot. In such one-stage recording, there is a limit to the recording density, and the recording density is insufficient.

[0004] In order to achieve higher density, a multiplex recording method in which a plurality of signals are written in one recording spot is being researched. This includes, for example, photochemical hole burning (
PHB) etc. PHB utilizes the phenomenon that holes are formed in the absorption spectrum of guest molecules existing in the host medium according to the wavelength of the irradiated laser light, and records signals as the presence or absence of holes at multiple wavelength positions within one recording spot. It is possible to perform multiplex recording in the wavelength dimension.

However, PHB has not been put into practical use because it is necessary to maintain the recording layer at a low temperature of several degrees K to several tens of degrees K in order to maintain recording.

[0006]

Further, the present invention has been made in order to realize higher density recording. In order to perform high-density recording, it is necessary to change the signal entering one recording spot from the conventional binary recording of whether or not to record to multilevel recording. If multilevel recording is possible, multiple pieces of information can be recorded in one recording spot, making multiple recording possible. Based on this idea, it is an object of the present invention to provide a recording method that forms multi-stage recording in one recording spot and enables high-density recording.

[0007]

[Means for Solving the Problems] For the above-mentioned purposes, the present inventors investigated recording and erasing on a recording layer whose crystalline state reversibly changes due to heat accompanying light energy irradiation. It has been found that the above object can be achieved by controlling the range of the region in which the crystal state changes in the layer.

The high-density recording method of the present invention is a recording medium in which information is recorded, reproduced, and erased by irradiation with light. A method of recording on a recording medium provided with a recording layer of a crystalline organic thin film that reversibly changes its crystal state by partially changing the recording layer by irradiating light, and in which the recording portion changes in response to an information signal. Recording is performed by changing the size of the area in multiple stages, so that the output by re-irradiation during reproduction becomes a multi-stage output level different from the initial state, that is, the unrecorded state.

The recording layer of the recording medium used in the present invention performs recording and erasing by reversible changes in the crystal state and reversible changes between phases, and can be used repeatedly. This change in crystal state includes structural changes and phase transitions of crystals, such as reversible crystal transitions between crystal forms, reversible phase transitions between crystalline and amorphous forms, and crystalline changes. reversible change in the degree of chemical orientation, reversible change in the degree of molecular orientation, reversible change in crystal orientation, i.e. reversible change in crystal axis direction, reversible change in molecular orientation, or reversible change in crystal grain size. difference,
These include reversible changes in the size of crystal domains, which occur singly or in combination in the recording layer. These changes are due to the heat applied during recording or erasing,
Alternatively, the temperature of the recording layer is once raised by the heat generated by light irradiation, and the temperature of the recording layer increases through the melt phase or liquid crystal phase.
In cases where the state changes from an unrecorded state to a recorded state or from a recorded state to an erased state (same as an unrecorded state), when a transition between states occurs directly due to temperature rise without going through the melt phase or liquid crystal phase, There are cases where the transition occurs via an amorphous state.

[0010] Examples of recording media on which such recording and erasing are performed include the following. Phthalocyanine materials such as copper phthalocyanine and magnesium phthalocyanine are examples of materials that utilize the crystal-crystal and crystal-amorphous transitions of organic materials. moreover,
Those that utilize reversible changes in the crystalline state of organic thin film crystals include, for example, fatty acids or fatty acid derivatives, benzoic acid derivatives, and n-alkanes or their derivatives having a melting point of 50° C. or higher.

[0011] The fatty acid or fatty acid derivative as used in the present invention specifically refers to saturated or unsaturated mono- or dicarboxylic acids or their esters, amides, anilides, hydrazides, ureides, anhydrides, or ammonium salts or metal salts. Fatty acid salts mean. 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 linear or branched, and the unsaturated fatty acids may have one double bond or triple bond, or two or more. The number of carbon atoms in the hydrocarbon chain in these fatty acids is preferably 10 or more.

[0012] Specific examples of saturated fatty acids include, for example:
undecanoic acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid,
Examples of unsaturated fatty acids include 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 esters, ethyl esters, hexyl esters, octyl esters, decyl esters, dodecyl esters, tetradecyl esters, stearyl esters, eicosyl esters, and docosyl esters of these fatty acids. Further, examples of metal salts include metal salts of these fatty acids such as sodium, potassium, magnesium, calcium, nickel, cobalt, zinc, cadmium, and aluminum.

[0013] Furthermore, the benzoic acid derivatives referred to in the present invention include:
Specifically, benzoic acid represented by general formulas (I) to (IV) in Chemical Formula 1 below, and its esters, amides, anilides, etc. are included. 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 (II), esters include esters of aliphatic hydrocarbon compounds with polyhydric alcohols or aromatic hydrocarbons having a plurality of hydroxy groups.

[0014]

embedded image Substituents for R1, R2, R3 and other benzoic acid derivatives in the general formula include, for example, hydrogen, an alkyl group,
An aryl group such as an alkoxy group, a phenyl group, a biphenyl group, a naphthyl group, an anthranyl group, and R1 is an aryl group such as an acyl group, an acyloxy group, a halogen, a nitro group, a hydroxy group, a cyano group, a carboxyl group, and esters thereof; Examples include a carbamoyl group which may be substituted, a sulfo group and its ester or alkyl group, a phenyl group, and an amino group which may be substituted with a substituted phenyl group. In addition, the above alkyl groups, alkoxy groups,
The aryl group may be substituted with the same substituent as R1. In addition, the alkyl group and alkoxy group may be linear or branched, and if they have two or more carbon atoms, they may contain one or more unsaturated bonds in the carbon chain. Good too.

[0015] Further, 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, and compounds in which one or more hydrogen atoms are substituted with halogen atoms. , and a compound in which a benzene ring, which may be substituted with an alkyl group or an alkoxy group, is bonded to the terminal carbon atom. Specifically, for example, tetracosane, pentacosane, hexacosane, heptacosane,
n- such as octacosane, nonacosane, triacontane, dotriacontane, tetratriacontane, hexatriacontane, octatriacontane, tetracontane, etc.
There are alkanes or mixtures containing these as main components, so-called paraffins and paraffin waxes. Further, as derivatives, 1-hexacocene, 1-heptacocene, 1-octacosene, 1-triacontene, 1-tetratriacontene, 1-hexatriacontene, 1-octatriacontene, 1-tetracontene, docosylbenzene, tetracontene, Cosylbenzene, hexacosylbenzene, octacosylbenzene, triacontylbenzene, tritriacontylbenzene, tetratriacontylbenzene, hexatriacontylbenzene, 1,18-dibromooctadecane, 1,20-dibrome Examples include eicosane and 1,22-dibromdocosane.

The recording medium used in the present invention is basically as shown in FIG.
As shown in (a), a photothermal conversion layer 2 that absorbs irradiated light and converts it into heat is provided on a support 1, and a recording layer 3 that causes a reversible crystal state change or phase change due to heat,
Further, as shown in FIG. 1(b), a protective layer 4 is further provided thereon. Recording is performed by irradiating the recording medium with a focused beam of light in a blinking manner according to the information. When light irradiation is performed, the light incident on the recording medium is absorbed by the photothermal conversion layer and converted into heat, and this heat is transmitted to the recording layer, raising the temperature of the recording layer. At this time, when the recording temperature of the recording layer, that is, the temperature at which the crystalline state changes, reaches a temperature higher than that, and then the light irradiation stops and the temperature decreases, a record is formed in that portion. For example, if this crystal state change occurs via a molten state, when the temperature of the part that exceeds the melting point cools and crystallizes, it will be in a state different from the initial crystal state (the state of the surrounding non-recording part). It becomes a record.

[0017] The recording method of the present invention uses a recording medium having the above-mentioned characteristics and performs recording by partially changing the recording layer by irradiating light. The size of the image is changed in multiple stages and recorded.
High-density recording is performed by making the output by the reproduction light irradiation during reproduction have multiple output levels different from the initial state.

In the recording medium described above, the temperature of the recording layer is increased by heat transmitted from the light-to-heat conversion layer adjacent to one side of the recording layer. The range in which the temperature of the recording layer exceeds the recording temperature varies depending on the intensity of the irradiation light and the irradiation time. In general, a metal thin film photothermal conversion layer has higher thermal conductivity than an organic recording layer, so the spread of heat in the photothermal conversion layer determines the size in the film surface direction of the range where the crystal state of the recording layer changes. . Therefore, the stronger the intensity of the irradiation light and the longer the irradiation time, the larger the record formed. FIG. 2 shows an example of the relationship between the irradiation light intensity and the recording size over a certain irradiation time. As shown in the figure, by changing the recording light irradiation conditions in multiple stages according to the information, it is possible to form records with multiple sizes depending on the irradiation conditions.

Records formed in multiple sizes according to information are detected by reproduction light irradiated with a spot of a fixed size. If there is a record that changes in size in multiple stages within the irradiation range of the reproduction light spot, the intensity of the reflected or transmitted light with respect to the reproduction light is taken as the average within the reproduction light spot, so it can be compared with the multi-stage output. Therefore, if the intensity level of the reproduced output is made to correspond to the type of recorded signal, recorded information can be reproduced. Even when recording is detected by changes in birefringence, reproduction can be performed in the same way by using linearly polarized light as the reproduction light and using a polarizer on the detection side.

The light-to-heat conversion layer of the recording medium used in the present invention is
For example, platinum, titanium, silicon, chromium, nickel,
A layer of metal or semimetal such as germanium or aluminum may be used, and can also be used as a reflective layer that reflects part of the light. Furthermore, commonly used plastic plates such as glass plates, acrylic resins, and polycarbonate resins can be used as the substrate. As the protective layer, a layer transparent to recording light, reproduction light, and erasing light, such as glass or resin, can be used.

[0021]

[Examples] The present invention will be explained in more detail with reference to Examples below.

Example 1 A photothermal conversion layer of C was placed on an optically polished glass disk with a diameter of 4 inches (101.6 mm) and a thickness of 1.2 mm.
The r layer was provided by vacuum evaporation. The thickness was approximately 950 Å. This substrate was placed on a hot plate controlled at a temperature of 90°C with the Cr layer on top, and behenic acid (
A small amount of Sigma (purity: 99%) was placed and melted. A glass plate with a thickness of about 0.1 mm was placed over the behenic acid melt, and the melt was spread uniformly over the entire surface and sandwiched between the plates. Next, the disk was moved slowly on the hot plate and removed from the hot plate. The temperature of the disk decreased from the part removed from the hot plate, and the behenic acid melt layer began to crystallize from this part, gradually spreading in one direction and crystallizing the entire disk. After peeling off the glass plate, a 10 wt % aqueous solution of polyvinyl alcohol was applied onto the crystal film. By the above operations, a recording layer (thickness of about 0.6 μm) made of thin film crystals of behenic acid oriented in a substantially uniform direction on the Cr layer, and a protective layer (thickness of about 0.6 μm) made of polyvinyl alcohol on top of the recording layer (thickness of about 0.6 μm) are formed on the Cr layer. .3 μm) was formed.

[0023] The recording medium produced in this way was
While moving at a speed of 000 mm/sec, laser beams with a wavelength of 830 nm focused to a diameter of 1 μm were applied to three laser beams with intensities of 4.0 mW, 6.0 mW, and 8.0 mW, respectively, on the recording medium surface.
Recording was done in stages. When this recording medium was observed under crossed nicols using a reflective polarizing microscope, it was confirmed that a line-shaped record was formed in the area irradiated with the recording light. The thickness of each recording line is 0.6 μm
, 1.2 μm, and 1.9 μm.

Next, the non-recorded area and the area recorded under the above three conditions were irradiated with laser light focused to a diameter of 2 μm, and the reflected light was received by a detector through a polarizer to measure the light intensity. The polarizer allows light that vibrates in a direction perpendicular to the polarization plane of the incident light to pass through, and the relationship between the polarization plane of the incident light and the direction of the recording medium is such that the intensity of the reflected light in the non-recording area is maximized. did. The intensity of reflected light at each part was as follows.

[0025]

[Table 1]

From this result, it was found that if reproduction is performed using polarized light as described above, outputs of different levels can be obtained depending on the recording intensity level.

[0027] Therefore, it was confirmed that by modulating the recording intensity according to the information, multiple levels of recording with different sizes can be formed at one recording position, and that multiple levels of output can be obtained during reproduction.

[0028] In addition, these recordings were performed using an erasing laser beam focused to 5 μmφ at a linear velocity of 100 mm/sec and an intensity of 2.
．． By irradiating with 3 mW, it was possible to completely erase it.

[0029]

According to the recording method of the present invention, multi-stage recording can be easily formed at one recording position and multiplex recording of signals is possible, so that a high-density recording system can be realized.

[Brief explanation of drawings]

FIGS. 1A and 1B are cross-sectional views showing the basic configuration of a recording medium used in the present invention, respectively.

FIG. 2 is a diagram showing the relationship between recording intensity and recording size during recording.

[Explanation of symbols]

Claims (1)

[Claims] 1. A recording medium for recording, reproducing, and erasing information by irradiating light, comprising at least a photothermal conversion layer on a support that absorbs irradiated light and converts it into heat, and a photothermal conversion layer that reversibly changes the crystal state by heat. This is a method of recording by partially changing the recording layer by irradiating light on a recording medium that has a recording layer of a crystalline organic thin film. 1. A high-density recording method, characterized in that the output level is changed to a non-recorded area, and the output level of the reproduction light irradiated during reproduction is set to a multi-step output level that is different from that of a non-recorded area.