JPH0230588A - Stabilization of recording and erasing states - Google Patents

Abstract

PURPOSE:To prevent erroneous recording and erroneous erasing and besides, to obtain excellent durability against repetitive recording and erasing by a method wherein recording information is fixed by fading light absorbing pigment. CONSTITUTION:An Al reflecting film 8 is established on a glass substrate 9. A polymer liquid crystal and a light absorbing pigment expressed by a structural formula II are applied thereon and are heated and dried to prepare an optical recording medium 3. Then, ultraviolet laser beam is repetitively irradiated onto a specific area of a recording layer 2 with a laser 16, and the light absorbing pigment in this area is faded. Though light reflectance is increased by decrease of light absorbing intensity in this area after fading, since it is not varied exceeding a level of a photodiode identifying a recording state and an erasing state, information can be reproduced. Further, though recording light or erasing light is applied to a light fading area, light dispersion intensity of polymer liquid crystal in the recording layer is varied, and recording or erasing can not be performed. Furthermore, though recording and erasing are repetitively performed in an unfixed recording layer area, a reproductive contrast ratio is not varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for fixing recorded information in a specific area of a rewritable optical recording medium.

[Prior Art] Conventionally, rewritable optical recording media use phase change technology such as TeOx,
Optical recording media with a recording layer made of an inorganic material such as magneto-optical material, and optical recording media with a recording layer made of an organic material such as a photochromic material, liquid crystal, or phase-separated polymer are known.

Although it is possible to erase records on these rewritable optical recording media, there is still the possibility of erroneous recording or erasure.
There were problems with the protection of recorded information.

In addition, when the recorded information is, for example, several bit strings on a recording layer, bits obtained by recording (hereinafter referred to as "recorded state") and bits that remain unrecorded or are erased (hereinafter referred to as "recorded state") are included. Protection is becoming necessary for both states of the bit (referred to as the "erased state").

Therefore, recording, reproduction, or A method has been proposed for forming a recording area in which the optical characteristics of the recording layer are not changed by the erasing means.

Examples of this method include: (1) providing a change in the shape of bits or holes on the recording layer; (2) when the recording layer contains an organic material, polymerizing or crosslinking the recording layer to fix its structure, etc. There is.

[Problems to be Solved by the Invention] However, the above-described conventional method for fixing recorded information has the following drawbacks.

In the immobilization method using the shape change of the recording layer as in (2), the optical transmittance or optical reflectance of the recording layer is used to detect the recorded information, so it is difficult to detect whether the recorded or non-recorded state is The drawback was that only one state could be fixed.

Furthermore, in the immobilization method of polymerizing or crosslinking a specific region of the recording layer as in (2), it is necessary to newly add a compound to cause such a chemical reaction in the recording layer.
Such additives cause deterioration of the repeated durability or recording and erasing characteristics of the optical recording medium.

The present invention has been made in order to improve the drawbacks of the prior art, and has a recording layer containing a material whose light transmittance or light reflectance changes reversibly and a light-absorbing dye. In optical recording media, it is possible to improve the recording and erasing conditions by selectively and locally fading the light-absorbing pigment, and preventing erroneous recording and erasing of recorded information, in addition to having excellent durability for repeated recording and erasing. The purpose of this invention is to provide an immobilization method.

[Means for Solving the Problems] That is, the present invention provides a recording layer containing a material whose light transmittance or light reflectance can be changed reversibly and whose optical properties can be maintained, and a light-absorbing dye. A method for fixing recording and erasing states on a rewritable optical recording medium comprising: fixing optical properties of a recording layer by fading a light-absorbing dye; be.

The present invention will be explained in detail below.

In the present invention, a material (hereinafter referred to as
Examples of the recording material include inorganic materials that undergo a crystal-amorphous phase change such as TeOx, liquid crystals, phase-separated polymers, and the like.

Among these recording materials, in the present invention, it is preferable to use polymeric materials such as polymeric liquid crystals and phase-separated polymers.

Compared to phase-changing inorganic materials such as TeOx-based materials and organic compounds such as low-molecular liquid crystals, polymeric materials can be used to form the recording layer more easily, and are more stable against oxidation, photodegradation, etc. , optical recording media with excellent environmental stability and durability for recording and reproduction can be produced at low cost. In addition, polymeric materials have good compatibility with additives such as light-absorbing dyes, and blending of polymeric materials with one another is possible, allowing the creation of a wide variety of optical recording media.

Phase-separated polymers and polymeric liquid crystals can reversibly change their light reflectance and light transmittance depending on whether they are rapidly cooled or slowly cooled after heating, or whether or not an electric field or magnetic field is applied after heating. Moreover, since it has the property of being maintained at a constant temperature, it can be used as a recording layer of a rewritable optical recording medium.

Examples of phase-separated polymers include systems in which two or more types of amorphous polymers are mixed, and these change into a compatible state and a phase-separated state depending on the temperature. In a phase-separated state, a system is separated into micro regions having a specific polymer composition, and if the refractive index of light of each composition is different, the light will be strongly scattered at the interface of the micro regions. Therefore, the phase separation state is a light scattering state. On the other hand, in a compatible state, no such interface exists and light is not scattered. The phase-separated state and the compatible state can be distinguished, for example, by detecting light reflectance or light transmittance, depending on their respective light scattering characteristics.

In addition, due to the change pattern of compatibility-phase separation due to temperature, these phase-separated polymers have L CST (Lowe
r Cr1tical 5solution Tempe
rate) type and UC3T (lJpper Cr1t
ical 5solution Temperature
) The former shows a phase-separated state on the high temperature side and a compatible state on the low temperature side, and the latter shows the opposite. I.J.
The CS T type includes, for example, polystyrene-polyisolatene type, polystyrene-polyphtadiene type, polypropylene oxide polyphtadiene type, etc.;
Type T includes, but is not limited to, polyvinyl chloride-polymethacrylate-〇-hexyl system, styrene acrylonitrile copolymer-polymethyl methacrylate system, polyvinylidene fluoride-polyacrylic methyl methacrylate system, etc. It's not a thing.

In addition, by slowly cooling these phase-separated polymers after heating, the state of compatibility or phase separation on the high temperature side changes to the state on the low temperature side. Because it has the characteristic of retaining its state even after cooling, it can be applied to optical recording media, including rewritable media.

On the other hand, polymer liquid crystals are thermotropic liquid crystals, and nematic, smectic, or cholesteric types can be used as the intermediate phase. Polymer thermotropic liquid crystals have the advantage of not only being able to form a thin film but also being easier to maintain a recording state than low molecular weight liquid crystals.

For example, polymer thermotropic liquid crystals (hereinafter simply referred to as polymer liquid crystals) that can be used in the present invention are classified into the following two types.

■Mesogen groups, or relatively rigid and long atomic groups, or those connected by flexible structures.

■Having a mesogen group or a relatively rigid and long atomic group in the side chain.

These polymer liquid crystals can be used in combination with several different types of polymer liquid crystals. It is also possible to use a mixture of a polymer liquid crystal and a low molecular liquid crystal, or a mixture of a polymer liquid crystal and a polymer.

Specific examples of polymer liquid crystals are shown below, but the invention is not limited to these.

Me R: 0CR3゜R: 0(:3)1゜R: CN Since these polymer liquid crystals have the characteristic of maintaining their structural state at temperatures below the glass transition point, for example, the following recording modes can be used. It is possible.

l13 is maintained in a polydomain state consisting of a large number of domains (domains). Next, recording is performed by heating the polymeric liquid crystal to a temperature higher than the temperature at which it exhibits the isokitic phase, and then rapidly cooling it to below the glass transition point to maintain the polymeric liquid crystal in the isokitic phase state.

In the recording mode (2), the polymer liquid crystal is first maintained in a liquid crystal phase or a monodomain state consisting of a single domain using an electric field or the like. Next, recording is performed by heating the polymeric liquid crystal above its glass transition point and then cooling it to maintain the liquid crystal phase in a polydomain state.

In both of these recording modes (1) and (2), the recording state can be changed by slow cooling after heating or by a combination of heating and electric field application.
Since it is possible to return to the initial state, it can be used as a rewritable optical recording medium. Therefore, it is also possible to reverse each state of first non-scattering and light scattering to set the recording mode.

In the present invention, additives such as antioxidants and nucleating agents may be added to the recording material.

In the present invention, a light-absorbing dye is added to the recording layer. The light-absorbing dye absorbs recording light and erasing light to change the light transmittance or light reflectance of the recording material in the recording layer. This most often occurs because the optical energy absorbed by the light-absorbing dye is converted into heat, resulting in local heating of the recording layer. This is the preferred method for simplifying the process.

Furthermore, when a light-absorbing dye is irradiated with a certain type of light, particularly light with a high quantum energy, that is, with a short wavelength such as ultraviolet light, it may be decomposed and discolored by a photodecomposition reaction.

At this time, part of the absorbed light heats the recording layer in the same way as above, but by adjusting the amount of irradiation light and keeping a balance with the heat dissipation of the recording layer, it is possible to heat the recording layer without substantially heating it. It is possible to perform bleaching of light-absorbing dyes. Therefore,
It is possible to bleach the light-absorbing dye without changing the optical properties of the recording material in the recording layer.

In addition, other methods for fading light-absorbing dyes include, for example,
It is possible to use the chemical action of onge etc.

In the present invention, the recording light, the reproduction light, and the erasing light are as follows, considering their coherent property, monochromaticity, linearity, etc.
Laser light is preferred.

Furthermore, a semiconductor laser is preferable from the viewpoint of compactness and economic efficiency of the light source. The oscillation wavelength of semiconductor lasers is from red to
Examples of light-absorbing dyes that have absorption in the near-infrared wavelength range include the following.

\ / +・ ＼ / (Note) However, n is a positive integer, R is an aromatic cyamine residue, A is an aromatic tetracarboxylic acid residue, and a and b are each independently 0 or 1 to is an integer of 50, and a+b is an integer of 1 to 100.

Note that if He--Ne laser light, Ar ion laser light, etc. are used, light-absorbing dyes having absorption at the respective wavelengths can be used. In particular, when adding it to a polymeric liquid crystal, it is preferable to use a dichroic dye from the viewpoint of compatibility.

However, in the present invention, a cyanine dye such as D-4 is preferable in consideration of the fading property of the light absorption dye.

On the other hand, in the present invention, methods for fading these light-absorbing dyes include irradiating them with light that has a shorter wavelength than recording light or erasing light, that is, has a higher quantum energy, and is mainly irradiated with ultraviolet light. It will be done. It is preferable that the ultraviolet light is a laser beam, similar to recording and erasing light, etc., and it may be a laser beam with an oscillation wavelength in the ultraviolet region, or a laser beam with an oscillation wavelength in a long wavelength region can be emitted by a lower nonlinear optical element. Light obtained by converting into higher harmonics may also be used.

Here, it is necessary to optimize the intensity and repeated irradiation period of the light irradiated to discolor the light-absorbing dye so that the optical properties of the recording material do not change due to the light irradiation.

In order to reproduce recorded information, weak light is irradiated so as not to change the optical properties of the recording material, and the light transmittance or light reflectance of the recording layer is detected. Preferably, the reproduction light is also a laser light. If the wavelength of the reproducing light is the same as that of the recording light or erasing light, the light absorption intensity of the recording layer in the photobleached area decreases, and the amount of detected light also changes. Therefore, it is necessary to set the recording state and erasing state and the detected light level so that they do not change before and after photobleaching.When using light of a wavelength different from the recording light or erasing light as the reproduction light, it is necessary to It is preferable that the absorption intensity is smaller than the absorption intensity of the light-absorbing dye or the absorption intensity at the recording light or erasing light wavelength, and it is more preferable that there is almost no absorption at the reproduction light wavelength. In such a case, the detected light amount level of the reproduction light is not easily affected by the fading.

Further, when detecting the difference in scattering intensity using reproduction light, it is preferable to use light with a shorter wavelength than the recording light or erasing light as the reproduction light in order to improve contrast.

In addition, in the present invention, it is possible to fix each bit in either the recorded state or the erased state by fading the light-absorbing dye. It is possible to perform not only fixation of areas (which may consist of . These fixings can be performed on a specific area or the entire area on the recording layer.

Next, an example of the recording/reproducing method of the present invention will be described.

FIG. 1 shows the element configuration of the optical recording medium. In FIG. 1, 1 is a substrate, and 2 is a recording layer containing a polymeric material and a light-absorbing dye.

A polymer composition containing a polymer material whose light scattering state can be reversibly changed and which can maintain that state and a light color absorbing dye is coated on a substrate. Next, the entire surface of the recording layer is heated and then slowly cooled to fix it in a light scattering state.

The optical recording medium thus obtained is recorded, reproduced, and erased using an apparatus having the configuration shown in FIG.

In FIG. 2, 3 is an optical recording medium, 4 is a laser light source,
5 and 5a are lenses, and 15 is a half mirror 6 which is a reproduction light detection device.

The optical recording medium 3 is irradiated with recording laser pulse light from the laser light source 4, and the recording layer is heated and then rapidly cooled to reduce the light scattering intensity. Next, the laser light from the laser light source 4 is lowered in output and irradiated onto the optical recording medium 3, and the recording is reproduced by detecting the difference in the light scattering intensity of the recording layer based on the amount of transmitted light.

In addition, the spot diameter of the laser beam from the laser light source 4 is increased and the laser beam is irradiated onto the optical recording medium to heat the recording layer and then slowly cool it, and the light scattering intensity is increased again to erase the recording. .

Next, a specific area on the recording layer other than the erased area is irradiated with ultraviolet light from the laser light source 4a to fade the light-absorbing dye.

When similar reproduction was performed on the photobleached area, there was no change in the reproduced information before and after photobleaching, and even when irradiated with recording light or erasing light, the optical characteristics of this area did not change, indicating that the information was fixed. It is possible to perform conversion.

[Examples] Example 1 An optical recording medium (hereinafter referred to as an optical card) having the configuration shown in FIG. 3 was produced.

First of all, the size is 1mm with bleed roots.
An AI1 reflective film 8 is provided on a thick glass substrate 9, and 100 parts by weight of a polymer liquid crystal represented by the following structural formula (I) is placed thereon, and (I) a light absorbing film represented by the following structural formula (11) A solution prepared by dissolving 1 part by weight of the coloring matter C211510C2H5 (II) in 500 parts by weight of dichloroethane was applied onto Spinco-1 by a method. 1) The recording layer 2 is dried by heating at 0°C and then slowly cooled to room temperature.
The polymer liquid crystal inside was maintained in a nematic phase polydomain state (light scattering state).

FIG. 3 shows a configuration diagram of the optical cart obtained as described above.

Next, recording, reproducing, erasing, and forming a fixed recording area on this optical cart were carried out using the apparatus shown in FIG. 4.

A semiconductor laser 10 with a maximum input of 83 [1 nm] is used as a laser light source. Laser light from the semiconductor laser 1o passes through a 174-wavelength plate 13, is focused by a lens 5, and is irradiated onto the recording layer of the optical cart with an appropriate spot diameter.

The reflected light from the A2 reflective film passes through the lens 5 and the 174-wave plate 13 again, is separated from the incident light by the polarizing beam splitter, and is detected by the photodiode 12.

In order to form a rewritable record on the optical cart, the output of the semiconductor laser light is 8 mW, and about 1
Irradiation was performed with a spot diameter of wl11. At this time, the polymeric liquid crystal in the recording layer is heated to a temperature range in which it exhibits the iso-kissed phase and then rapidly cooled, so that it is maintained in the iso-kissed phase state and the scattering intensity of light decreases, making it possible to perform recording.

To play back the recording on the optical cart, the output of the semiconductor laser is reduced to 0.
．． Irradiation was performed at 2 mW, and the AI! This was done by detecting the intensity of reflected light from the reflective film using a photo-taper.The reproduction contrast ratio was 1.2.
There was.

■o: Reflected light intensity I of non-recorded area (high light scattering intensity):
This is the reflected light intensity of the recording section (low light scattering intensity).

The records thus obtained on the optical cart can be erased using the following method.

The output of semiconductor laser light was 1.5 mW, and the recording layer was irradiated with a spot diameter of about 1.3 pm onto the recording section.

At this time, the polymeric liquid crystal in the recording area is heated to a temperature range that exhibits an isotonic phase and then slowly cooled, so it is maintained in a nematic phase polydomain state, and the light scattering intensity increases, causing erasure. did it.

Next, the light-absorbing dye in a specific area on the recording layer of the optical cart excluding the erased area was bleached using the following method to fix the recorded information.

Input by He-Cd laser 16 max 325n
A specific region of the recording layer was repeatedly irradiated 10 times with ultraviolet laser light having a power of 0.1 m and an output of 0.1 mW, and the light-absorbing dye in this region was bleached. At this time,
The recording layer was not substantially heated and the light scattering intensity of the recording material remained unchanged. After fading, the light absorption intensity in this area decreased and the light reflectance increased, or as shown in Figure 7, the level of the phototiode that distinguishes between the recorded state and the erased state does not change. , it has been possible to reproduce information. The reproduction contrast ratio was 0.9.

Further, even when the above-mentioned recording light or erasing light was irradiated onto the photobleached area, the light scattering intensity of the polymer liquid crystal in the recording layer did not change, and recording or erasing could not be performed.

Furthermore, in the unfixed recording layer area, there was no change in the reproduction contrast ratio even after repeated recording and erasing 103 times.

Example 2 Using an optical cart having the same configuration as in Example 1, recording, reproducing, erasing, and recording were performed using a device (FIG. 5) in which a He-Ne laser 17 for reproduction was added to the device shown in FIG. Information was fixed.

There is almost no difference in the reproduction contrast ratio before and after photobleaching.
1.1, and even if recording and erasing techniques were performed on the area fixed by photobleaching, its optical properties did not change. In addition, the unfixed recording layer area is 103
Even after repeated recording and erasing, there was no change in the reproduction contrast ratio.

Example 3 An optical card having the same configuration as in Example 1 was used, and as shown in FIG.
The fundamental wave of n■) is converted into the third harmonic (input a
mW ), and the obtained third harmonic was irradiated onto the optical cart in the same manner as in Example 1, thereby bleaching the light-absorbing dye in the recording layer and fixing the recorded information.

Recording, reproduction, and erasing were carried out in the same manner as in Example 1, and the reproduction contrast ratio was 1.2 before photobleaching and 0.00 after photobleaching.
9, and even if recording and erasing techniques were performed on the area fixed by photobleaching, its optical properties did not change.

Furthermore, even if recording and erasing were repeated 103 times in the unfixed recording layer area, there was no change in the reproduction contrast ratio.

[Effects of the Invention] The present invention provides a rewritable optical recording medium having a recording layer containing a material whose light transmittance or light reflectance is reversibly changed and whose optical properties can be maintained, and a light-absorbing dye. By fading the light-absorbing dye and fixing recorded information, it is possible to prevent erroneous recording and erasing, and to obtain excellent durability against repeated recording and erasing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an optical recording medium used in the present invention; FIG. 2 is a block diagram showing an example of a device used for recording, reproducing, erasing, and fixing recorded information according to the present invention; 3 is a block diagram of the optical recording medium of Examples 1 and 2.3, FIG. 4 is a block diagram showing a device used for recording, reproducing, erasing, and fixing recorded information in Example 1, and FIG. FIG. 6 is a configuration diagram showing a device used for recording, reproducing, erasing, and fixing recorded information in Example 2, and FIG. 6 is a configuration diagram showing a device used for recording, reproducing, erasing, and fixing recorded information in Example 3. FIG. 7 and FIG. 7 are graphs showing the relationship between the recording state and erasing state of the light-absorbing dye before and after fading and the amount of detected light in each example. 1... Substrate 2... Recording layer 3... Optical recording medium 4... Laser light source 5.5a... Lens 6... Photodetector 7... xY stage 8
...A4 reflective film 9...Glass substrate lO...
Semiconductor laser 11...Polarizing beam splitter 12...Photodiode 13...1/4 wavelength plate 14...Filter 1
5- Half mirror-16-He-Cd laser 17-
He-Ne laser 18-YAG laser 19
...KDP nonlinear optical element 20...filter

Claims (10)

[Claims] (1) Recording and erasing conditions on a rewritable optical recording medium having a recording layer containing a material whose light transmittance or light reflectance changes reversibly and which can maintain its optical properties and a light-absorbing dye A method for fixing recording and erasing states, the method comprising fixing the optical properties of a recording layer by fading a light-absorbing dye. (2) The immobilization method according to claim 1, wherein the reversible change in light transmittance or light reflectance is a reversible change in light scattering intensity. (3) The immobilization method according to claim 1, wherein the material whose light transmittance or light reflectance changes reversibly and whose optical properties can be maintained contains a polymeric material. (4) The immobilization method according to claim 3, wherein the polymer material is a phase-separated polymer or a polymer liquid crystal. (5) Recording, reproduction, and erasing of a rewritable optical recording medium include the step of irradiating the recording layer with a reproduction light of a laser beam, and the reproduction light has a different wavelength from both the recording light and the erasing light, and the reproduction light 2. The immobilization method according to claim 1, wherein the absorption intensity of the light-absorbing dye at a wavelength is smaller than the absorption intensity of the light-absorbing dye at a recording light wavelength and an erasing light wavelength. (6) The immobilization method according to claim 1, wherein the color fading of the light-absorbing dye is performed by irradiating the recording layer with bleaching light. (7) The immobilization method according to claim 6, wherein the fading light has a wavelength component different from any of the recording light, reproduction light, and erasing light. (8) The immobilization method according to claim 6, wherein the fading light includes light in the ultraviolet wavelength range. (9) The immobilization method according to claim 6, wherein the bleaching light is laser light. (10) The immobilization method according to claim 6, wherein the bleaching light is a high-order harmonic obtained by a nonlinear optical element.