JPH0520712A - Recording medium, recording method and recorder - Google Patents

Abstract

PURPOSE:To provide the recording system which can easily attain the recording and many-valued recording of both reverisible and irreversible modes by only the control of the energy of light for irradiation by using the recording medium having a high-polymer liquid crystal recording film. CONSTITUTION:An optothermal conversion layer 4, an oriented layer 3 and the recording layer 2 consisting of the high-polymer liquid crystal which executes recording and erasing by causing a change or phase transition in a reversible orientation state are formed on a substrate 1. The material which is changed in the orientation state or phase state in a part in its thickness direction when irradiated with light for a short period of time is used for the recording layer 2. The size of the recording pits formed in the thickness direction of the recording layer 2 is changed in multiple stages, by which the many-valued recording is executed. The recording of both reversible and irreversible modes is executed by the recording pits over the entire part of the thickness direction and the recording pits in a part in the thickness direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a recording medium having a recording layer made of a polymer liquid crystal, and a recording medium and a recording method for reversibly recording / erasing information by heating or irradiating light, and a recording method therefor. Related to the recording device. More specifically, the present invention relates to a recording / erasing method in a recording medium applicable to an optical recording medium such as an optical disk, an optical card, an optical tape, a thermal recording medium, or a display medium such as a display. The present invention relates to a new recording method that enables multi-valued recording and a new recording method that enables multi-mode recording capable of recording both reversible mode and irreversible mode of information by a simple operation.

[0002]

2. Description of the Related Art In recent years, a so-called heat mode recording system has been put into practical use in which information is applied in the form of thermal energy and recorded as a change in shape or a change in physical properties of a recording material.
As such a heat mode recording medium, Te, B
An inorganic recording medium using a metal material containing i, Se, Tb, In, etc. as a main component, or a polymethine dye such as cyanine, a macrocyclic azaannulene dye such as phthalocyanine, naphthalocyanine, and porphyrin, naphthoquinone, anthraquinone Recording media using organic dyes such as dyes and dithiol metal complex dyes are known.
When heat energy is applied to these recording media by irradiation of condensed laser light, the recording layer in the irradiated portion is melted or evaporated to form holes (pits) and information is recorded. However, these recording media have no possibility of erasing recorded information and recording new information again.

Therefore, with the development of such a read-only, write-once, heat mode optical recording system, the need for a reversible recording medium capable of recording, reproducing, and erasing is increasing. As such a reversible recording medium, for example, Gd, T
There is a magneto-optical recording medium using an alloy thin film made of a rare earth metal such as b or Dy and a transition metal such as Fe, Ni or Co. In this, recording is performed by using heating by irradiation of laser light and an externally applied magnetic field in combination, and reproduction is performed by utilizing the difference in the rotation direction of the vibrating surface of light depending on the direction of magnetization. Information is erased by heating with laser light irradiation and applying an external magnetic field in the opposite direction to that at the time of recording. But,
This magneto-optical recording medium has low sensitivity during reproduction, a poor S / N ratio, deterioration of recording sensitivity due to the influence of oxidation and the like, storage stability of recording, magnetic field generators and peripheral devices provided in the recording device, etc. It has drawbacks such as reliability problems.

As reversible recording media, Ge, Te,
The one utilizing the phase transition between the crystal and the amorphous of the recording layer composed of an inorganic material thin film containing elements such as Se, Sb, In and Sn as a main component records and erases in a heat mode only by laser irradiation. However, there are problems with the contrast between the recorded and unrecorded areas and the storage stability of the recording pits.
In particular, it has serious drawbacks regarding the stability of the material such as oxidation of the recording layer.

As a means for solving the above drawbacks, Japanese Patent Laid-Open No. 58-58
Japanese Patent Publication No. 125247 discloses a recording material characterized in that a transparent alignment state and an opaque random state of a polymer liquid crystal are reversibly changed by heat or an electric field.
There is also disclosed a method of recording and erasing by using a laser light as a heat source by adding a light absorber to a polymer liquid crystal, and examples of such a method are disclosed in JP-A-59-10390 and JP-A-59-10390.
Examples thereof include those described in JP-A-59-35989 and JP-A-60-114823.

Further, a report on a heat mode recording medium having both performances of a reversible recording medium and a write-once type recording medium is disclosed in JP-A-2-48987 and 2-89229, which comprises an indium-based inorganic recording layer. It is reported as a shape change type recording medium. This recording medium is such that upon irradiation with strong energy, holes (holes) are formed, resulting in irreversible recording, and upon irradiation with relatively weak energy, reversible pits with a changed shape are formed. However, this recording medium has a problem in the contrast between the recorded portion and the unrecorded portion and the storage stability of the recording pits, and particularly has a defect regarding the material stability such as the oxidation of the recording layer. However, there are many problems in terms of productivity, such as requiring an air gap above the recording layer.

[0007]

In the case of a recording medium using the above-mentioned polymer liquid crystal as a recording layer, the transfer rate at the time of recording is slow due to the low thermal conductivity of the recording layer material, and the erasing is faster than the recording. In addition to the thermal energy, a third force such as an electric field / magnetic field must be applied because it becomes more than several orders of magnitude slower. Considering its use as an optical memory, recording with a high S / N ratio is easy. Despite its advantages, it could not be put to practical use in terms of system or speed.

Further, according to the conventional recording method, since the detection is carried out by the presence or absence of transmitted light or reflected light in the two states of the alignment state and the random state, the recording signal is low level (O) and saturation level (a). The memory density is limited to 10 ⁸ bit / cm ² , and the memory density is still insufficient in consideration of future increase in capacity and high speed of the computer.

Further, Japanese Patent Laid-Open No. 63-26647 discloses a recording medium using a ferroelectric liquid crystal (FLCP). However, this ferroelectric liquid crystal recording medium is often used with a positive dielectric anisotropy in terms of response, so that its orientation direction is a component (homeotropic orientation) that is oriented perpendicular to the recording film surface. Component) becomes stronger. In addition, 2 due to switching of the alignment direction of the liquid crystal part
It is known that the difference in the birefringence between the oriented and unoriented states is larger than the difference in the birefringence between the states, and the system is composed of an orthoscope from the viewpoint of mass productivity and cost. Considering the above, it is clear that a high S / N ratio can be easily obtained in the recording layer material by orienting it in parallel with the recording film surface (homogeneous orientation). However,
When a ferroelectric liquid crystal recording medium having a negative dielectric anisotropy is used, a homogeneous alignment property appears, but its response is not much different from that of a normal liquid crystal, and rather its structure is special. In addition, there is a situation that it is not cost effective and has not been put to practical use.

As a method for overcoming the above-mentioned memory density limit, a multiple recording method for writing a plurality of signals in a single recording spot is being studied, and one of them is high density light by photochemical hole burning (PHB). Memory is reported. However, the PHB method requires keeping the memory film at an extremely low temperature of several K to several tens of K, and there are many problems to be solved as an optical information recording system, and it has not been put to practical use.

In view of the above circumstances, the present invention provides a recording medium, a recording method, and a recording apparatus in which recording and erasing can be performed at high speed and reliably by changing the alignment state or phase state of a polymer liquid crystal recording layer. To aim. Further, the present invention is
A recording medium that enables multiple recording and achieves high density recording,
An object of the present invention is to provide a recording method and a recording device.
A further object of the present invention is to provide a recording medium, a recording method, and a recording apparatus that can easily achieve recording in both reversible and irreversible modes by a simple operation of changing the irradiation condition of a recording light beam.

[0012]

For the above-mentioned purpose, the inventors of the present invention recorded and erased on a polymer liquid crystal recording layer in which the alignment state of the liquid crystal site was reversibly changed by heat accompanying the irradiation of light energy. As a result of examining the performance, by appropriately selecting the light irradiation conditions at the time of recording and erasing and controlling the size in the film thickness direction of the portion (recording pit) where the molecular orientation state changes in the recording layer, It was found that the purpose of can be achieved.

That is, according to the present invention, at least a recording layer made of a polymer liquid crystal that causes reversible change of orientation state or phase change on a substrate for recording and erasing and an alignment layer for orienting the polymer liquid crystal. And a recording layer characterized in that the recording layer has a partially changed orientation state or phase state in the thickness direction thereof by light irradiation for a short time. In this recording medium, it is also possible to perform so-called multiple recording in which a plurality of pieces of information are input to one recording pit by controlling the size of the changed portion by irradiating the recording light beam with the intensity of the recording light beam modulated. .

Further, according to the present invention, at least a recording layer made of a polymer liquid crystal for performing recording and erasing by causing a reversible change in orientation state or phase change on the substrate and an alignment layer for orienting the polymer liquid crystal. And a recording medium characterized in that the recording layer is such that the orientation state or phase state of a part or all of the recording layer in the thickness direction is changed by light irradiation. This recording medium performs reversible recording by changing the orientation state or phase state of a part of the molecule in the thickness direction of the recording layer, and changes the orientation state or phase state of a molecule in the whole part of the recording layer in the thickness direction. It is also possible to perform irreversible recording by doing so and to perform so-called multi-mode recording in which both are input on a single recording medium. In this multi-mode recording, since no physical change of the recording layer such as formation of holes as in the above-mentioned indium-based phase change recording medium does not occur, an air gap or the like is not required and the productivity is high. Become.

Further, according to the present invention, the product (retardation) of the birefringence in the film thickness direction and the film thickness (retardation) in the initial alignment state of the polymer liquid crystal constituting the recording layer in the above structure is 25 to 7.
A recording medium is provided which is in the range of 50 nm. When this recording medium is used, recording is performed so that the change in the reproducing light amount due to the change in the retardation in the film thickness direction of the recording layer increases after recording rather than before recording, and the recording pit is subjected to external force. It is possible to perform recording / erasing for completely erasing without applying a voltage.

Further, according to the present invention, there is provided a recording method using a recording medium having a recording layer made of a polymer liquid crystal which undergoes reversible change in orientation state or phase change as described above.

Further, according to the present invention, signal processing means for converting an input signal into a signal of at least three stages or more,
A light beam output means for outputting a light beam at the time of recording, and a light beam modulation means for causing the light beam output means to output a light beam having an intensity of several steps are provided. Provided is a recording device characterized by recording information by forming the information.

The recording layer composed of a polymer liquid crystal used in the present invention is capable of recording and erasing by thermal orientation of molecules or reversible change between phases and enduring repeated use. In this method, the change in the thermal alignment state of the molecule means the change in the alignment state of the high-molecular liquid crystal molecules. To represent. The phase change is, for example, a liquid crystal phase.
-It means a change between phases such as isotropic phase transition. In this recording medium, information is reproduced between the thermally changed area and the unchanged area by detecting the optical or polarization optical contrast difference.

A recording method using such a polymer liquid crystal is disclosed in conventional literatures, publications, etc. (eg VP Shibaev et al.
Written, Polymer Communications, Volume 24, Pages 363-365,
In 1983), a number of reports were made, but it was suggested that the polymer liquid crystal is thermally changed and can be applied to a recording medium from the viewpoint that it can be reproduced optically by polarization or simply optically. However, the possibility of reversible / irreversible mode recording by irradiating only the light beam on the same recording medium has not been studied, because it requires the assistance of an electric field and a magnetic field during erasing, and it is provided for future practical use. It was difficult to do.

However, when the present invention thermally changes all or most of the recording layer in the film thickness direction as in the conventional method, the contrast ratio between the recorded portion and the unrecorded portion becomes large. However, there is a decrease in the recording density due to the expansion of recording pits due to thermal diffusion, a delay in the transfer speed during recording / erasing, or a portion remaining in the pit after erasing, a re-recorded portion, or a polarization optical scattering portion. Various problems such as the appearance of a third state different from the initial orientation state and the recording state were examined, and a recording method for changing a part of the thickness direction of the recording layer by short-time exposure was found in order to address these problems. By using the means for controlling the size of the recording pits by modulating the intensity of irradiation light, the polymer liquid crystal memory can easily perform multi-valued recording to overcome the above-mentioned problems, and to realize multiplex recording. It was found that the recording is possible.

Here, the control of the size of the recording pit in the present invention specifically refers to the state as shown in FIG. That is, when the intensity of the recording light beam is low, the recording pits are formed small at the boundary between the recording layer and the alignment layer as shown in (a), and when the intensity is high, as shown in (b). It means that the recording pit reaches the inside of the recording layer more than (a). At this time, if the orientation state of the original polymer liquid crystal is homogeneous orientation, through a pair of orthogonal polarizing plates, the change in the optical path length of the polarized light, that is, the change in the amount of transmitted light or reflected light due to the change in retardation. Can be detected as

That is, when the recording pits are formed as shown in FIG. 1, the optical path length of the polarized light in the film thickness direction is unrecorded portion> portion in the state of FIG. 1 (a)> FIG. 1 (b). It becomes shorter in order of the part of the state. At this time, information can be reproduced by detecting a change in the amount of polarized transmitted light or reflected light under crossed Nicols. According to the previous report, the relationship between the retardation R and the reproduction light amount I is expressed by the following equation (1). I = I ₀ sin ₂ (πR / λ) (1) where I ₀ is the incident light amount and λ is the incident light wavelength. Therefore, when the retardation R is very small, I is proportional to the polarization optical path length, and becomes smaller in the order of the unrecorded portion> the portion in the state of FIG. 1 (a)> the portion in the state of FIG. 1 (b). In a certain range, it is also possible to control the reproduction light amount in the order of unrecorded portion <portion in state (a) of FIG. 1 <portion in state (b) of FIG. For example, when the film thickness is about 2 μm and the birefringence is about 0.20, the former case, the film thickness is about 3 μm.
The latter case occurs when the birefringence is about 0.20 at m. Either case can be adopted in the present invention.
By the way, comparing the former case with the latter case, it is easier to judge the latter case than the former case between the two states of (a) and (b), and further, when considering the conventional optical recording system. The advantage that the detection system is simpler when the amount of reproduction light is increased after recording than before recording, and the system itself becomes easier after all. Therefore, as a result of studying the conditions capable of achieving such a recording state, the present inventors have found that the above state is realized when the retardation R value is in the range of 25 to 750 nm. In this case, although the film thickness of the recording layer is related to the medium structure, it is preferable that the film thickness of the reflective recording medium is approximately 0.5 to 2.5 μm and that of the transmissive recording medium is twice that. Further, the birefringence index is difficult to be specified unconditionally because it also depends on the structure and alignment state of the mesogenic site of the polymer liquid crystal, but a range of about 0.05 to 0.30 is preferable.

When the irradiation energy of the recording beam light is sufficiently large as in the conventional method, the entire portion in the film thickness direction of the recording layer is thermally changed, and thus the light is applied without applying an electric field or a magnetic field. It was confirmed that the beam was not erased only by irradiation, and on the other hand, when the irradiation energy of the recording light beam was relatively small, part of the recording layer in the thickness direction changed,
We have found that it can be erased only by irradiation with a light beam, and that the polymer liquid crystal memory can easily perform multimode recording.

Here, the multi-mode recording in the present invention is to control the size of the recording pits according to the irradiation condition of the recording light, and specifically, by the difference of the recording light intensities as shown in FIG. Forming the two states of a) and b). In other words, if the intensity of the recording beam light is low, (a)
As described above, the recording pit is formed in the recording layer, and its upper end does not reach the surface layer portion of the recording layer. However, when the strength is high, it means that the recording pit is formed larger than that in (a) as shown in (b) and the state of the polymer liquid crystal changes over the entire film thickness of the recording light irradiation portion. At this time, if the original alignment state of the polymer liquid crystal layer is a homogeneous alignment, through a pair of orthogonal polarizing plates, the change of the optical path length of the polarized light, that is, the amount of transmitted light or reflected light due to the change of retardation It is also possible to detect it as a change, and it is also possible to discriminate between reversible and irreversible two states and to make multi-valued recording.

According to the present invention, also in the multi-mode recording, the value of the retardation R is set to 2 as in the multi-valued recording.
By setting the thickness in the range of 5 to 750 nm, it is possible to realize a recording medium in which the reproduction light amount increases after recording as compared with before recording.
In this case, in addition to the above-mentioned advantages, the unrecorded state is temporarily set to 0,
By associating the (a) state with + K and the (b) state with -K such as -K, it is possible to design a system that can more easily process complex operations and the like compared to the conventional system. .

The present invention will be described in detail below with reference to the drawings. As shown in FIG. 3, the recording medium used in the present invention comprises a recording layer 2 made of polymer liquid crystal on a substrate 1, an alignment layer 3 for orienting the polymer liquid crystal layer, and a photothermal conversion layer 4 for absorbing a light beam. It is possible to omit the photothermal conversion layer 4 by adding a light absorbing agent such as a dye that absorbs a light beam to the recording layer 2 or the alignment layer 3 based on the constitution.

First, a recording method in which the orientation state or phase state of a part in the thickness direction is changed by light irradiation for a short time in the above structure will be described. When the recording medium is irradiated with the condensed beam light, the light absorbed in the photothermal conversion layer 4 is converted into heat, and as a result, a temperature distribution as shown in FIG. 4 is formed in the recording layer 2, A part of the temperature inside is heated above the isotropic transition temperature (isotropic point). By stopping the light irradiation and quenching the recording layer 2 here, the portion heated in the layer above the isotropic phase transition temperature is retained as it is (isotropic phase state), and only that portion is selected. Then, the states become different from each other in terms of polarization optics, and recording as shown in FIG. 5 is performed.

Recording by short-time exposure in the present invention means scanning of the light beam applied to the recording medium at a speed such that the exposure time per point is several ms or less, and more specifically. From the standpoint of view, it is desirable to be several tens of μs or less. When the exposure time is extremely short, such as several nanoseconds or less, the recording layer 2 is not heated above the isotropic phase transition temperature and recording pits are not formed. Further, when the time is extremely long, the portion heated above the isotropic phase transition temperature diffuses and the entire film thickness becomes an isotropic state as shown in FIG.

In the recording formed as described above, for example, the recording layer is heated to a liquid crystal temperature lower than the isotropic phase transition temperature by irradiating the recording portion with light under a condition different from that at the time of recording. Or heating for a longer time than when recording,
It can be erased by heating so that the cooling rate becomes slow. That is, by such heating, the recording pits held in the isotropic state are reheated, and when the viscosity of the minute area including the recording pits is reduced and the molecules in the area are allowed to undergo molecular motion, The liquid crystal molecules in the random state are re-aligned under the influence of the alignment control force from the surrounding polymer liquid crystal molecules and the alignment layer, thereby erasing. The temperature at which this molecular reorientation occurs is preferably a few degrees Celsius to several tens of degrees Celsius lower than the isotropic phase transition temperature, but at least the entire recording pit should be in this temperature range in order to perform complete erasure without erasure. It needs to be heated to enter. Further, it is preferable that the temperature gradually changes during erasing. Therefore, by irradiating with a power lower than that at the time of recording and a relatively longer time than that at the time of recording, it becomes possible to surely perform erasing. At this time, for example, if the intensity is weakened for the same irradiation time as during recording, the entire recording pit cannot be heated uniformly, and if only the irradiation time is increased, the deep part in the film thickness direction is heated to a high temperature. After all, it will be re-recorded.

The layer structure of the recording medium used in the present invention is not limited to that shown in FIG. 3, and a photothermal conversion layer 4 may be provided in the central portion of the recording layer 2 as shown in FIG. 7, for example. In this case, a temperature distribution different from that shown in FIG. 4 is formed in the recording layer 2 when the beam light is irradiated, and in the case of FIG. 7, the center portion of the recording layer has the highest temperature distribution. Therefore, in the recording medium having these configurations, the recording portion is recorded in each area according to the temperature distribution. However, in the case of using the recording medium having the above-mentioned configuration, there may be some inconveniences,
For example, in the case of FIG. 7, since the recording portion is farther from the alignment layer 3 than in the configuration of FIG. 3, the alignment regulating force from the alignment layer 3 may be reduced, and the performance at the time of erasing may be deteriorated. However, the above-mentioned problems are also caused by the adjustment of the recording layer thickness and the material of the alignment layer,
It can be easily overcome by selecting the film thickness, rubbing method, etc., and further selecting the constitution and material of the photothermal conversion layer.

The method of recording by changing the orientation state or the phase state of a part of the recording layer in the thickness direction by the irradiation for a short time has been described above with reference to FIG. According to the method, the intensity of the recording light beam is modulated and applied to the recording medium having the same structure as that of FIG. 3 and the size of the recording pit formed in accordance with the intensity of the recording beam is different in the multiple levels. It is also possible to perform multi-valued recording in which the recording is performed and the difference is detected by the difference in the amount of transmitted light or the reflected light or the phase difference.

Furthermore, as described above, according to the present invention, the recording medium having the same structure as that of FIG. Is a reversible recording pit that is erasable by light or heat due to a partial change in the thickness direction of the recording layer and a recording pit due to a change in the entire thickness direction of the recording layer It is also possible to perform so-called multi-mode recording in which an irreversible recording pit that is not easily erased by heat is formed for recording, and the pit is detected by a light amount difference or phase difference of transmitted light or reflected light.

Known polymer liquid crystals can be used in the present invention, but those having a mesogen moiety in the main chain or side chain and an average molecular weight of 500 or more can be used. Further, the polymer liquid crystal may be crosslinked, and more preferably a photocrosslinking type.

Specific examples of the polymer liquid crystal used in the present invention will be given below. In the following, * indicates an asymmetric carbon atom.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

[0040]

[Table 6]

[0041]

[Table 7]

[0042]

[Table 8]

[0043]

[Table 9]

[0044]

[Table 10]

[0045]

[Table 11]

[0046]

[Table 12]

Such polymer liquid crystals are usually used alone or as a mixture, and it is also possible to use other low molecular liquid crystals in addition. The low-molecular liquid crystal added here is for the purpose of improving the recording characteristics and the erasing characteristics by controlling the viscosity and phase transition temperature of the high-molecular liquid crystal, and a known nematic, smectic or cholesteric liquid crystal is used. it can.

Using such a polymer liquid crystal, for example, a ketone system such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc., an ester system such as butyl acetate, ethyl acetate, methyl acetate, carbitol acetate, butyl carbitol acetate, methyl, etc. Dissolve in ether type such as cellosolve, ethyl cellosolve, tetrahydrofuran, aromatic type such as toluene and xylene, halogenated alkyl type such as dichloroethane, N, N-dimethylformamide, N-N-dimethylacetamide, alcohol type, etc. For example, solution coating methods such as dip coating, spray coating, spinner coating, blade coating, roller coating, curtain coating and wire coating, and in some cases melting by heating. It can be formed by coating from the state.

As the material for forming the photothermal conversion layer 4 used in the present invention, known materials can be used, and specifically, the following materials are exemplified. For example, as organic materials, methine / polymethine compounds such as cyanines, pyryliums, squaryliums, croconiums, azulenes and pentamethines, indanthrene compounds such as thioindigos, quinones such as anthraquinones and naphthoquinones. Compounds, dithiols, diamines, phthalocyanines, naphthalocyanines, tetrahydrocholines, metal complex compounds such as indoanilines, diphenylmethane compounds, dioxazine compounds, dithiazine compounds, triphenylamine compounds, azo dyes Examples include dye groups having absorption in the visible or near-infrared region of system compounds, and the inorganic materials include, for example, gold, platinum,
Examples of the vapor deposition of various metals such as silver, copper, lead, zinc, aluminum, nickel, tantalum, cobalt, chromium, germanium, niobium, palladium, tin, CVD, sputtering film, etc., the present invention is not limited thereto. Not something.

When the above-mentioned inorganic material and some organic materials are used, the photothermal conversion layer 4 can also be used as a reflection layer. Therefore, when reproducing information, the reproduction light is reflected from the recording layer side and the reflected light is reflected. Can be adopted. When the reflectance of the photothermal conversion layer 4 is low, the method of detecting information by the transmitted light of the recording layer 2 is easily adopted, and thus the reproducing light may be incident from either side of the recording layer 2 and the substrate 1.

Other constituent materials constituting the present recording medium will be described. Known materials can be used as the material of the alignment layer 3. Specifically, a rubbing treatment is performed on polyimide or its precursor polyamic acid. It is possible to use those subjected to the above, or those obtained by oblique vapor deposition of silicon oxide or the like.

Various known materials can be used as the material for the substrate 1. For example, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate, polyamide, polyimide, polyolefin. It is possible to use various plastics such as acrylic resin, phenol resin, epoxy resin, fluorine resin, and the above derivatives, glass, quartz plate, ceramics, and the like.

Next, the information recording apparatus according to the present invention will be described. FIG. 8 is a schematic configuration diagram showing an information recording apparatus according to an embodiment of the present invention. The information signal processing device 10 drives the light source drive circuit 11 by binarizing the input information signal and distinguishing between the reversible / irreversible recording mode and the erasing mode according to the type of the information signal. The light source drive circuit 11 drives the light source 12 in response to the signal from the information signal processing circuit 10 and outputs a recording light beam from the light source 12. The light source 12 irradiates a recording medium with a recording laser beam, and a semiconductor laser (L
D) or He-Ne laser can be used, but LD is preferable in terms of cost and configuration. The light beam emitted from the light source 12 is collimated by the shaping lens 13.
After that, an optical system at the time of recording and at the time of erasing is selected by a mirror 16 directly below the shaping lens 13, and first at the time of recording, it passes through the objective lens 14 and is condensed on a recording medium 30 which is rotationally driven by a motor 28. As a result, the state of the irradiated portion changes, and reversible / irreversible recording pits are formed according to the intensity of the irradiated light modulated and output by the light source 12.

Further, the objective lens 15 is an optical system used when outputting the erasing light beam. The light beam output from the light source 12 is collimated by the shaping lens 13 and then passed through the objective lens 15 by the mirror 16 for recording. The information recording medium 30 is focused and irradiated under an irradiation condition different from the time. The mirror 16 is a motor 17 and a motor driver circuit 1
Controlled by the information signal processing circuit 10 via 8.

On the other hand, the reproduction of information is performed by the reproduction light beam from the light source 20, the reproduction light beam emitted from the light source 20 is collimated by the shaping lens 21, passes through the beam splitter 22, and is linearly formed by the wave plate 23. Alternatively, after being converted into circularly polarized light, the information recording medium 30 is irradiated through the objective lens 24. This reproducing light beam is used for the recording medium 3
The light is reflected at 0, passes through the objective lens 24 and the wave plate 23, passes through the beam splitter 22, and is guided to the detector 26 through the condenser lens 25. This detector 26
Is a photoelectric conversion element such as a photodiode,
The reproduction information from the recording medium 30 is detected, output to the reproduction signal processing device 27, and output as a reproduction signal. In addition,
The detection signal from the detector 26 is also fed back to the control device 29 via the reproduction signal processing device 27, and this control device 29 performs focusing control and tracking control of the objective lenses 14, 15, 24.

Although an example of a device for performing multi-mode recording has been described above, orientation of a portion of the recording layer in the thickness direction of the recording layer is performed by irradiating laser light for a short time without distinguishing between the reversible mode and the irreversible mode. The information recording apparatus for a recording medium according to claim 1, wherein the recording light intensity is adjusted so that the state or the phase state changes, and the mechanism for changing the recording light power in several steps is provided. An information recording device for the recording medium described in 2 can be configured.

[0057]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

Example 1 An optically polished glass plate having a thickness of 1.2 mm was used as a substrate 1, and a chromium film having a thickness of about 900 Å was vapor-deposited on the substrate 1 to provide a photothermal conversion layer 4. Then, an N-methylpyrrolidone solution containing several% by weight of polyamic acid was formed thereon by a spin coating method to a thickness of about 1000Å, and then 90 ° C.
After drying at 270 ° C., dehydration condensation was performed at 270 ° C. for 1 hour to form a polyimide. Apply 10g to this film under a load of 100g / cm ^2.
The rubbing process was performed once to form the alignment layer 3. Then, on the alignment layer 3, the above-mentioned No. The recording layer 2 having a thickness of 0.5 μm was also formed by a spin coating method using a solution of 33 of the liquid crystal dissolved in tetrahydrofuran in an amount of 10% by weight.
Then, a recording medium having the structure shown in FIG. 3 was produced.

When this recording medium was annealed at 170 ° C. for 30 minutes to orient the molecules of the polymer liquid crystal of the recording layer 2 in a homogeneous orientation, it was confirmed by polarization microscope observation that the orientation was good.

<Recording> Recording was linearly formed on the recording medium prepared above using a semiconductor laser beam having an oscillation wavelength of 780 nm and a beam diameter of 1 μm at a linear velocity of 3 m / s and a light intensity of 10 mW. Observation of the recorded part under a crossed Nicols at a stage angle of 45 ° (diagonal position) using a polarization microscope revealed that the recorded part selectively formed a dark state and had a clear contrast with the unrecorded part. Was found to have.

<Reproduction> With respect to the recording medium on which the recording is formed as described above, the light intensity of the semiconductor laser light is lowered to 1 mW, and the linear velocity is set to 3 m / s to be perpendicular to the recording line. Using a system that can scan and detect the reflected light with a pin photodiode, one polarizing plate is provided before the semiconductor laser light is incident on the recording layer and one after it is reflected. It was installed so that the azimuths were orthogonal. When the response obtained from the light receiving element in this state was measured, it was found that a clear output difference was obtained between the unrecorded portion and the recorded portion, and it was possible to detect with an S / N ratio conversion of at least 30 dB or more.

<Erase> When this recording medium was heated on a hot stage heated to 170 ° C. for 30 seconds and then rapidly cooled, it was confirmed by a polarization microscope that the recording line was completely erased.

An intensity of 6 m is obtained by using a semiconductor laser beam focused on a beam diameter of 5 μm on the recording medium after the recording.
Scanning was performed in the direction perpendicular to the recording line in the same manner as in reproduction at W and a linear velocity of 50 mm / s, and partial erasing was attempted. When the recording medium was observed with a polarizing microscope, it was confirmed that part of the recording line was erased over a width of 2.5 μm.

Example 2 As a substrate 1, an optically polished glass plate having a thickness of 50 × 50 (mm ² ) and a thickness of 1.2 mm was used, and a chromium vapor deposition film having a thickness of about 900 Å was provided on the substrate 1 to perform photothermal conversion. It was Layer 4.
Then, a solution of N-methylpyrrolidone containing several wt% of polyimic acid is spin-coated thereon for about 10
A thin film having a thickness of 00Å was applied, dried, and dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide. 100g on this membrane
The alignment layer 3 was formed by performing rubbing treatment 10 times with a load of / cm ² .

Next, on the alignment layer 3, the above-mentioned No. Three
The liquid crystal of 3 was used as a 5 wt% tetrahydrofuran solution, and the recording layer 2 of 5000 Å was formed by spin coating, and then 1
Annealing treatment was performed at 70 ° C. for 30 minutes to align the liquid crystal molecules, and then rapidly cooled to prepare a recording medium.

When this recording medium was observed under a crossed Nicols using a polarization microscope, a clear difference in light and shade was produced depending on the stage angle, and the molecules of the polymer liquid crystal were homogeneously aligned with respect to the substrate surface. It was confirmed.

Next, using this recording medium, recording / erasing / reproducing experiments were conducted in the following procedure.

<Recording> An oscillation wavelength of 78 is applied to this recording medium.
Using a semiconductor laser beam focused at 0 nm and a beam diameter of 1 μm, the intensity was changed to 16, 12, 8 mW at a linear velocity of 4 m / s, and several lines were recorded linearly for each intensity at a pitch of 10 μm. . When the recording medium was observed at a diagonal position (stage angle of 45 °) under a crossed Nicols using a reflection type polarization microscope, the recorded portion selectively formed a dark state unlike the surrounding unrecorded portion. . Since this portion is always in the dark state regardless of the stage angle, it was confirmed that the isotropic portion appeared in the recording layer by the above operation.

<Reproduction> Using the above recorded medium, the intensity of the semiconductor laser beam used for recording was 3 mW and the linear velocity was 4 m.
/ S was scanned from the recording layer side in the direction perpendicular to the recording line. The irradiation light passed through the polarizer before entering the medium, was reflected from the medium, passed through the analyzer, and was allowed to measure the amount of light by the light receiving element (photomultiplier tube). Each signal is shown in Table 1 according to the response from this light receiving element.
It turns out that it can be regenerated like 3.

[0070]

[Table 13]

From the above results, the reproduction signal of the present recording medium depends on the recording light intensity, and the higher the recording light intensity, the wider the width of the recorded line and the greater the difference in brightness from the unrecorded portion. I understood.

<Erase> A wavelength of 780 is applied to the recording medium.
An erasing light was scanned from the substrate side at a linear velocity of 200 mm / s at a linear velocity of 200 mm / s in the same manner as the reproducing light and erasing light perpendicular to the recording line using a beam obtained by concentrating a semiconductor laser light of 5 nm to 5 μm. When the intersection of the erasing light and the recording line was observed under a crossed Nicols with a polarizing microscope, the recording light intensity was 12 mW and 8
It was confirmed that the recording line was erased over the width of 2 μm in the portion recorded at mW and returned to the original homogeneous alignment state. However, in the portion recorded at 16 mW, although the recording line was thin, it was not completely erased.

Comparative Example 1 After the recording medium used in Example 1 was annealed again at 170 ° C. for 30 minutes to initialize it, recording and erasing experiments were conducted under the following conditions. Recording conditions Beam diameter: 1 μmφ Beam intensity: 1.6 mW Linear velocity: 3 m / s Erase beam diameter: 5 μmφ Beam intensity: 6 mW Linear velocity: 50 mm / s

When the line after recording was observed, it was found that a line thicker than that in the example was formed. When erasing was performed on this, it was found that the line after erasing was almost unchanged, and the recording line could not be completely erased because there was a portion that was slightly thinner than after recording.

Comparative Example 2 Using the medium used in Example 2, a semiconductor laser beam having a wavelength of 780 nm and a beam diameter of 5 μm was scanned at a linear velocity of 4 m / s and an intensity of 16 to 4 mW by the same operation as in the same example. did. When this medium was observed with a polarization microscope in the same manner as in Example 2, no change was observed in the recording line and erasure was impossible.

Comparative Example 3 Under the same conditions as in Comparative Example 2, the beam diameter of the erasing light was changed to that in Example 2.
When the same operation as in Comparative Example 2 was performed after condensing the light to a diameter of 1 μm in the same manner as above, a new line was drawn perpendicularly to the recording line at the intensity of 8 to 16 mW and re-recording was performed. or,
No polarization optical change was observed on the medium at an intensity of 7 to 1 mW.

Example 3 An optically polished Pyrex glass having a thickness of 1.2 mm was used as a substrate 1, and a chromium film having a thickness of about 900 Å was vapor-deposited on the substrate 1 to provide a photothermal conversion layer 4. A N-methylpyrrolidone solution containing several% by weight of a polyamic acid was spin-coated on this to form a thin film having a thickness of about 100 nm, which was then dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide. 100g / c on this film
The alignment layer 3 was formed by rubbing 10 times under a load of m ² . Then, on the alignment layer 3, the No. A liquid crystal of 33 was dissolved in tetrahydrofuran in an amount of about 10% by weight, and a wet gap of 10 μm was obtained by a blade coating method.
To form a recording layer 2 having a thickness of 300 nm on the alignment layer 3 and subjected to an alignment treatment in an oven at 170 ° C. for 30 minutes,
A recording medium having the structure shown in FIG. 3 was produced. When this recording medium was observed under a crossed Nicols using a polarization microscope,
It was confirmed that the mesogen moiety of the present polymer liquid crystal had a good homogeneous orientation with respect to the substrate, because it showed a large difference in brightness depending on the stage angle.

Next, as a light beam output means, a wavelength of 780n
m, a semiconductor laser (LD) with a rated output intensity of 35 mW, and an optical system for focusing this on the sample surface to φ1 μm, and a semiconductor laser drive circuit as a light beam modulating means, for reversible and irreversible information. According to two pieces of information, the intensity on the sample surface is set to 8 mW in the reversible mode and 16 mW in the irreversible mode according to two pieces of information. Modulation was performed, and the recording beam light was irradiated from the substrate side of 250 ns.

Using this recording medium, the beam light intensity on the sample surface of the recording apparatus was lowered to 2 mW, and the reflectance was measured from the recording layer side through a pair of polarizing plates under continuous lighting (CW). The result is as follows.

[0080]

[Table 14]

Further, with respect to the present recording medium, a wavelength of 780n
LD with a rated output intensity of 35 mW on the sample surface of φ5
When erasing light was irradiated from the substrate side at a continuous lighting (CW) with a focus on μm, a beam light intensity on the sample surface of 8 mW, and a linear velocity of 200 mm / s, the portion recorded with 8 mW of the above recording pits was completely erased. It was confirmed that it was possible, but 1
The portion recorded at 5 mW could not be erased even though the erasing light velocity was reduced to 20 mm / s and scanning was performed several times.

Example 4 Optically polished Pyrex glass having a thickness of 1.2 mm was used as the substrate 1, and a chromium film having a thickness of about 900 Å was vapor-deposited on the substrate 1 to provide the photothermal conversion layer 4. A N-methylpyrrolidone solution containing several% by weight of a polyamic acid was spin-coated on this to form a thin film having a thickness of about 100 nm, which was then dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide. 100g / c on this film
The alignment layer 3 was formed by rubbing 10 times under a load of m ² . Then, on the alignment layer, the No. A solution of 33 liquid crystal of about 10% by weight in tetrahydrofuran was spin-coated on the alignment layer 3 to a thickness of 1.2.
The recording layer 2 having a thickness of μm is formed, and the recording layer 2 is heated in an oven at 170 ° C. for 30 minutes.
The recording medium having the structure shown in FIG. When this recording medium was observed under a crossed Nicols using a polarization microscope, it showed a large difference in brightness depending on the stage angle, so that the mesogen portion of the present polymer liquid crystal had a good homogeneous orientation with respect to the substrate. Was confirmed.

Next, a wavelength of 780n is used as a light beam output means.
m, a semiconductor laser (LD) having a rated output intensity of 35 mW, and an optical system for focusing this on a sample surface to φ5 μm, and a semiconductor laser drive circuit as a light beam modulating means, which has five types depending on five kinds of information. Using a recording device having a signal output means for generating a step output signal,
The intensity on the sample surface is set to 0 mW, 12 according to the 5 information.
The recording beam was irradiated from the substrate side of 25 μs after being modulated in 5 steps of mW, 13 mW, 14 mW, and 15 mW. By irradiating the laser beam based on this signal, information of five different levels was recorded. Using this sample, the beam light intensity on the sample surface of the recording apparatus was lowered to 2 mW, and the reflectance was measured from the recording layer side through a pair of polarizing plates under continuous lighting (CW). Was obtained.

[0084]

[Table 15] It was also confirmed that the recording pits could be completely erased by subjecting the recording medium to the orientation treatment again at 170 ° C. for 30 minutes in the oven.

Example 5 Optically polished borosilicate glass having a thickness of 1.2 mm was used as the substrate 1.
Then, a chromium film having a thickness of about 1000 Å was vapor-deposited on the substrate 1 to form the photothermal conversion layer 4. Then, an N-methylpyrrolidone solution containing several% by weight of polyamic acid was applied thereon by spin coating to form a thin film of about 500 nm. This was dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide, allowed to cool at room temperature, and rubbed with a load of 100 g / cm ² for 10 times to form an alignment layer 3.
Then, on the alignment layer 3, the No. A liquid crystal of 33 was dissolved in a tetrahydrofuran solution in an amount of 10% by weight, and a thickness of about 1.6 μm was obtained by spin coating as in the alignment layer.
After forming recording layer 2 of
The recording medium having the structure shown in FIG.

When this recording medium was observed under a crossed Nicols using a polarizing microscope, a clear difference in brightness was exhibited depending on the stage angle. Therefore, the polymer liquid crystal recording film showed a good homogeneous alignment with the substrate. It was confirmed that Further, the retardation of this recording medium was measured by a microspectroscopic system, and it was about 190 nm at a wavelength of 780 nm.

Next, a semiconductor laser (LD) having a wavelength of 780 nm and a rated output intensity of 35 mW is used as a light source, and an optical system for condensing this beam light to φ5 μm on the sample surface, and an LD drive circuit as a means for modulating the beam light. And a recording apparatus having a motor and a motor drive for moving the recording medium at a constant speed are used, the laser light intensity is modulated in five stages according to five kinds of information, and 100 mm / Recording light was irradiated under the conditions shown in Table 16 at a scanning speed of s and a duty ratio of 50%.

[0088]

[Table 16]

Using this recording medium, the beam light intensity of the recording apparatus was lowered to 3 mW, and the amount of reflected light at the recording portion was changed from the recording layer side through a pair of polarizing plates orthogonal to each other during continuous lighting (CW). Upon measurement, the results shown in Table 16 were obtained.

When the recording medium was irradiated with erasing light from the substrate side by continuous lighting (CW) at a laser beam intensity of 6 mW and a scanning speed of 0.64 mm / s in the recording apparatus,
It was confirmed that the recording pits could be almost completely erased.

Example 6 An optically polished Pyrex glass having a thickness of 1.2 mm was used as a substrate 1, and a chromium film having a thickness of about 1000 Å was vapor-deposited on the substrate 1 to provide a photothermal conversion layer 4. Then, an N-methylpyrrolidone solution containing several% by weight of polyamic acid was applied thereon by spin coating to form a thin film of about 500 nm. This was dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide, allowed to cool at room temperature, and then 100 g / cm 2 was added to this film.
^A rubbing treatment was applied 10 times with a load of ² to form an alignment layer 3. Then, on the alignment layer 3, the No. The liquid crystal of No. 33 was dissolved in a tetrahydrofuran solution in an amount of 10% by weight, and a thickness of about 1.
After forming the recording layer 2 of 6 μm, 170 ° C. in an oven
Was subjected to an alignment treatment for 30 minutes to prepare a recording medium having the structure shown in FIG.

When this recording medium was observed under a crossed Nicols using a polarizing microscope, a clear difference in brightness was exhibited depending on the stage angle. Therefore, the polymer liquid crystal recording film showed a good homogeneous alignment with the substrate. It was confirmed that Further, the retardation of this recording medium was measured by a microspectroscopic system, and it was about 190 nm at a wavelength of 780 nm.

Next, a semiconductor laser (LD) having a wavelength of 780 nm and a rated output intensity of 35 mW is used as a light source, and an optical system for condensing this beam light to φ5 μm on the sample surface, and an LD drive circuit as a means for modulating the beam light. And a recording device having a motor and a motor drive for moving the recording medium at a constant speed are used, the laser light intensity is modulated in three stages according to three kinds of information, and 100 mm / Recording light was irradiated under the conditions of Table 17 at a scanning speed of s and a duty ratio of 50%.

[0094]

[Table 17]

Using this recording medium, the beam light intensity of the above recording apparatus was lowered to 3 mW, and the amount of reflected light of the recording portion from the recording layer side through the pair of polarizing plates orthogonal to each other during continuous lighting (CW). Was measured, and the results shown in Table 17 were obtained.

When the recording medium was irradiated with erasing light by continuous lighting (CW) from the substrate side with a laser light intensity of 6 mW and a scanning speed of 0.64 mm / s in the recording apparatus, the recording pits were formed. It was confirmed by a polarization microscope that the reversible recording could be erased almost completely, whereas the irreversible recording could not be erased with almost no change.

[0097]

According to the present invention, since recording is performed by changing the orientation state of a part of the polymer liquid crystal recording layer in the thickness direction, not only the transfer rate at the time of recording is improved but also recording is performed. Since the changed portion of is easy to return to the original state at the time of erasing, there is no unerased portion, the erasing speed is increased, and highly reliable recording and erasing can be performed. Further, according to the present invention, multi-value recording becomes possible by simply controlling the magnitude of the alignment state change or phase state change in the film thickness direction of the polymer liquid crystal layer in multiple steps, and the recording density is dramatically increased. Can be improved. Further according to the invention,
It is possible to easily control the range of the alignment state change or the phase change of the polymer liquid crystal layer in the film thickness direction, and perform two types of recording, reversible and irreversible, with a single recording medium.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of control of a recording pit size according to the present invention.

FIG. 2 is an explanatory diagram of control of the size of a recording pit in the present invention.

FIG. 3 is a cross-sectional view showing a layer configuration example of a recording medium used in the present invention.

4 is a cross-sectional view showing a temperature distribution to be formed in a recording layer of the recording medium of FIG.

FIG. 5 is a sectional view showing an example of a recording state in the present invention.

FIG. 6 is a cross-sectional view showing an example of a recording state formed over the entire recording layer by long-time irradiation.

FIG. 7 is a cross-sectional view showing another layer configuration example of the recording medium used in the present invention.

FIG. 8 is a schematic diagram showing a configuration example of an information recording apparatus according to the present invention.

[Explanation of symbols]

1 substrate 2 recording layer 3 alignment layer 4 photothermal conversion layer 10 information signal processing device 11 light source drive circuit 12, 20 light source 13, 21 shaping lens 14, 15, 24 objective lens 16 mirror 22 beam splitter 23 wavelength plate 25 condensing lens 26 Detector 27 Playback signal processing device 29 Control device 30 Information recording medium

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical indication location G11B 7/24 521 7215-5D (72) Inventor Kaoru Teramura 1-3-6 Nakamagome, Ota-ku, Tokyo Stocks Inside Ricoh Company (72) Inventor Masafumi Ota 1-3-6 Nakamagome Ota-ku, Tokyo Inside Ricoh Company Ltd.

Claims (9)

[Claims] 1. A recording layer comprising a polymer liquid crystal for recording and erasing by causing a reversible change of orientation state or phase change on at least a substrate, and an alignment layer for orienting the polymer liquid crystal. The layer is a recording medium characterized in that the orientation state or phase state of a part of the layer in the thickness direction is changed by light irradiation for a short time. 2. The recording layer is capable of forming recording pits having at least two multi-step sizes by irradiating an intensity-modulated recording light beam. recoding media. 3. A recording layer comprising a polymer liquid crystal for recording and erasing by causing a reversible change of orientation state or phase change on at least a substrate, and an alignment layer for orienting the polymer liquid crystal, A layer is a recording medium characterized in that the orientation state or phase state of a part or the whole of the layer in the thickness direction is changed by light irradiation. 4. The recording layer is capable of forming recording pits having a size of at least two steps or more by irradiating an intensity-modulated recording light beam, and is partially formed in the thickness direction of the recording layer. The recording pits formed on the recording layer are erasable reversible recording pits, and the recording pits formed on the entire thickness direction of the recording layer are irreversible recording pits that are not easily erased. The recording medium according to claim 3. 5. The product (retardation) of the birefringence in the film thickness direction and the film thickness (retardation) in the initial alignment state of the polymer liquid crystal constituting the recording layer is in the range of 25 to 750 nm. The recording medium according to any one of 1 to 4. 6. The recording medium according to claim 1, 2 or 5, wherein recording is performed by changing the orientation state or phase state of a part of the recording layer in the thickness direction by light irradiation for a short time. How to record. 7. The recording medium according to claim 3, 4 or 5, wherein recording is performed by changing the orientation state or phase state of a part or all of the recording layer in the thickness direction by light irradiation. How to record. 8. When erasing, the recording pits are heated to a liquid crystal phase temperature range by exposing the recording medium with a lower power than that for recording and for a longer time than a light irradiation time for recording. The recording method according to claim 6 or 7, which is characterized in that. 9. A signal processing means for converting an input signal into a signal having at least three steps or more, a light beam output means for outputting a light beam at the time of recording, and a light beam having several steps of intensity from the light beam output means. 6. A recording method, comprising: a light beam modulating means for outputting the information; and recording information by forming recording pits of multi-step size on the recording medium according to any one of claims 1 to 5. apparatus.