JP3047002B2 - Recording method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a recording method for reversibly recording and erasing information by irradiating light using a recording medium having a recording layer composed of a polymer liquid crystal.

[Conventional technology]

In recent years, a so-called heat mode recording system for applying information in the form of thermal energy and recording as a change in shape or a change in physical properties of a recording material has been put into practical use. As such a heat mode recording medium, an inorganic recording medium using a metal material mainly containing Te, Bi, Se, Tb, In, or the like, or a polymethine dye such as cyanine, phthalocyanine, naphthalocyanine, and porphyrin Recording media using organic dyes such as macrocyclic azaannulene dyes, naphthoquinone, anthraquinone dyes and dithiol metal complex dyes are known. When heat energy is applied to these recording media by irradiation of condensed laser light or the like, the recording layer at the irradiated portion is melted or evaporated to form holes (pits) and record information. But,
These recording media have no possibility of erasing the recorded information and recording new information again. Accordingly, 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, there is a magneto-optical recording medium using an alloy thin film composed of a rare earth metal such as Gd, Tb, and Dy and a transition metal such as Fe, Ni, and Co. In this method, recording is performed using both heating by laser light irradiation and an externally applied magnetic field, and reproduction is performed by utilizing the difference in the rotation direction of the light oscillation plane depending on the direction of magnetization. Further, information is erased by applying an external magnetic field in a direction opposite to that of the heating by the laser and the recording. However, this magneto-optical recording medium does not have sufficient sensitivity at the time of reproduction and has a poor S / N ratio, deterioration of recording sensitivity due to the effects of oxidation, storage stability of recording, a magnetic field generator installed in the recording device and its surroundings. It has drawbacks such as a problem in the reliability of equipment and the like.

As reversible recording media, Ge, Te, Se, Sb, In, Sn
Those utilizing the phase transition between the crystal and the amorphous of the recording layer composed of an inorganic material thin film containing an element as a main component have an advantage that recording and erasing can be performed in a heat mode only by laser beam irradiation. There are problems with the contrast between the recorded and non-recorded portions and the storage stability of the recorded pits, and they have serious drawbacks, especially regarding the stability of the material such as the oxidation of the recording layer.

As means for solving the above-mentioned disadvantages, JP-A-58-125247 discloses a recording material characterized by reversibly changing the transparent alignment state and opaque random state of a polymer liquid crystal by heat or an electric field. Is disclosed. Also disclosed is a method of recording and erasing by adding a light absorber to a polymer liquid crystal and using a laser beam as a heat source.
Examples of such examples are disclosed in JP-A-59-10390 and JP-A-59-35989.
And No. 60-114823.

[Problems to be solved by the invention]

However, in the case of a recording medium using the above-mentioned polymer liquid crystal as a recording layer, the transfer speed at the time of recording is low due to the low thermal conductivity of the recording layer material, and the erasure is several orders of magnitude slower than at the time of recording. In addition, a third force such as an electric field or a magnetic field must be applied in addition to the heat energy. Considering the use as light energy, there is an advantage that a high S / N ratio is easily exhibited, but the system or It could not be put to practical use in terms of speed.

As described above, the conventional recording method using the polymer liquid crystal has various problems such as recording sensitivity and erasing speed.
In particular, it is desired to increase the recording and erasing speeds of the recording medium and to perform highly reliable recording and erasing with no erasure remaining during erasing.

In view of the above, it is an object of the present invention to provide a recording method in which recording and erasing by changing the alignment state or phase state of a polymer liquid crystal recording layer can be performed quickly and reliably.

[Means for solving the problem]

The present inventors have studied the recording and erasing performance of the polymer liquid crystal recording layer in which the alignment state of the liquid crystal portion is reversibly changed by the heat accompanying the irradiation of the light energy with respect to the above object. It has been found that the above object can be achieved by controlling the range of the portion (recording pit) where the molecular orientation state changes in the inside.

That is, according to the present invention, at least on a substrate, a recording medium comprising a polymer liquid crystal and a recording layer containing a light absorbing agent for performing recording and recording / erasing by causing a reversible change in alignment state or phase change. Then, the recording light is irradiated by irradiating the light beam at a time of 100 μsec or less at one point and changing the orientation state or the phase state of a part of the thickness of the recording layer made of the polymer liquid crystal, thereby forming the electric field. A recording and recording erasing method is provided in which a recording formed by irradiating a beam light without applying an external force such as a magnetic field is erased.

Further, at least on the substrate, a recording layer made of a polymer liquid crystal for performing recording and recording / erasing by causing a reversible change in alignment state or phase change, and an alignment layer for aligning the polymer liquid crystal layer are provided. , And in some cases, a heat insulating layer is provided in order to improve the use efficiency of generated heat,
A recording medium containing a light absorbing agent in at least one of the alignment layer and the heat insulating layer is irradiated with a light beam having a time of 100 μsec or less when passing through one point, and a portion in the thickness direction of the recording layer is irradiated. A recording and recording erasing method characterized by erasing a recording formed by irradiating a beam light without applying an external force such as an electric field or a magnetic field after forming a recording by changing an orientation state or a phase state of the recording. Is provided.

Further, at least on the substrate, a recording layer made of a polymer liquid crystal that performs a reversible change in alignment state or phase change to perform recording and erasing, and further, any one of the recording layer or the recording layer A light beam is applied to a recording medium including a photothermal conversion layer that absorbs irradiation light and converts it into heat adjacent to the surface.
Irradiate for less than 100 μs when passing through a point and record by changing the orientation state or phase state in a part of the thickness of the recording layer.After recording, without applying external force such as electric field and magnetic field A recording and recording erasing method is provided in which a formed recording is erased by irradiating a light beam.

The recording layer made of the polymer liquid crystal used in the present invention is thermally recorded by the reversible change in the orientation state or phase between the molecules,
It can be erased and withstand repeated use. In this method, the change in the orientation state of a thermal molecule means a change in the orientation state of a polymer liquid crystal molecule.For example, a change in a molecular aggregation state such as a smectic-nematic transition, a change in a twist pitch of a cholesteric polymer liquid crystal, and the like. It represents. The phase change means a change between phases such as a liquid crystal phase-isotropic phase transition.
In the present recording medium, the thermally changed region and the non-changed region reproduce information by optical or polarization optical contrast difference detection.

Such a recording method using a polymer liquid crystal is described in conventional literatures and publications (for example, VP shibaev et al., Polymer
Communications, Vol. 24, pp. 363-365, 1983), but the point that polymer liquid crystals thermally change and can be reproduced optically or simply optically by polarized light. Only suggests the possibility of application to a recording medium, and requires the assistance of an electric field and a magnetic field during erasing, and considers the possibility of both reversible and irreversible mode recording on the same recording medium only by light beam irradiation. It was not provided for future practical use.

However, when recording is performed by thermally changing the entire 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 increases, Decrease in recording density due to expansion of recording pits due to diffusion, delay in transfer speed during recording / erasing, or initial alignment state such as erasures remaining in pits after erasure, re-recorded areas, or polarized optical scattering parts And various problems such as the appearance of a third state different from the recording state were studied, and in order to cope with these problems, a recording method of changing a part of the recording layer in the thickness direction by the short-time exposure was found. It was confirmed that by overcoming the above-mentioned problems and improving the transfer speed at the time of recording and erasing, it is possible to perform erasure without erasure.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the configuration of a recording medium used in the present invention.
It has a recording layer 2 made of a polymer liquid crystal on a substrate 1 and an alignment layer 3 for aligning the polymer liquid crystal. In this recording medium, a light absorbing agent that absorbs irradiation light is added to the recording layer 2. Note that a heat insulating layer may be provided between the alignment layer 3 and the substrate 1 as needed.

The recording is performed by irradiating the present recording medium with the condensed beam light, and the light absorbed by the light absorbing agent added to the recording layer 2 is converted into heat. As a result, as shown in FIG. Such a temperature distribution is formed in the recording layer 2, and a part of the temperature distribution is heated to an isotropic transition temperature or higher. Here, the light irradiation is stopped, and the recording layer 2 is rapidly cooled, so that the portion of the layer heated above the isotropic phase transition temperature is kept as it is (isotropic phase state), and only that portion is selected. As a result, the optically different states are obtained, and the recording as shown in FIG. 3 is performed. Here, in FIGS. 2 and 3, (a) shows the case where the transmittance of the irradiation light is about 50%, and (b) shows the temperature distribution and recording when the transmittance has a high absorption of about 20% or less. It indicates the state of the pit. FIGS. 2 and 3 show the case where the light beam is irradiated from the substrate 1 side, but the light beam can also be irradiated from the recording layer 2 side. In this case, FIG.
3B, the heat distribution state and the recording state are reversed.

Thus, in order to heat and record a part of the recording layer 2 in the thickness direction, the recording light irradiation needs to be performed for a short time,
For example, when the thickness of the recording layer 2 is about 1 μm, the irradiation time of the light beam is preferably 100 μsec or less, and more preferably 10 μsec or less. This is because the longer the irradiation time of the recording light is, the larger the area reaching the isotropic transition temperature or higher in the recording layer 2 is, and finally the entire recording layer 2 is changed in the thickness direction and recorded. is there.

Further, the recording formed as described above, by irradiating the recording portion with light under different conditions at the time of recording, for example, heating the recording layer to a liquid crystal phase temperature lower than the isotropic phase transition temperature, By heating for a longer time than at the time of recording, or by heating so that the cooling rate becomes slower, the portion that has been in the isotropic phase state by recording returns to the original orientation state, and the recorded state can be erased.

At this time, according to the recording method of the present invention, the recorded state is such that only a part of the recording layer 2 in the thickness direction changes as shown in FIG. Surrounded by the recording part. On the other hand, as shown in FIG. 4, the recording state of the present invention is faster at the time of erasing than the case where the recording is changed to the isotropic state over the entire recording layer by long-time recording. Easily return to the original orientation state,
In addition, it was found that the data could be completely erased without erasure.
This is considered to be due to the difference in the alignment regulating force from the unrecorded portion around the recording portion and the alignment layer.

As the polymer liquid crystal used in the present invention, known liquid crystals can be used, and those having a mesogen moiety in a main chain or a side chain and having an average molecular weight of 500 or more can be used.

Further, the polymer liquid crystal may be crosslinked, and more preferably a photocrosslinkable liquid crystal.

Hereinafter, specific examples of the polymer liquid crystal used in the present invention will be described. In the following, * indicates an asymmetric carbon atom.

Such high-molecular liquid crystals are usually used alone or as a mixture, and other low-molecular liquid crystals can also be used. The low-molecular liquid crystal added here is intended to improve the recording and erasing characteristics by controlling the viscosity and phase transition temperature of the high-molecular liquid crystal, and those known as nematic, smectic or cholesteric liquid crystals are used. it can.

Using such a polymer liquid crystal, for example, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, butyl acetate, ethyl acetate, methyl acetate,
Carbitol acetate, ester system such as butycarbitol acetate, methyl cellosolve, ethyl cellosolve, ether system such as tetrahydrofuran; or aromatic system such as toluene and xylene; alkyl halide system such as dichloroethane; N, N-dimethylformamide; N-N
-Dissolved in a solution such as dimethylacetamide, alcohol, etc., for example, dip coating, spray coating, spinner coating, blade coating,
It can be formed by applying a solution coating method such as roller coating, curtain coating, wire coating or the like, or in some cases from a molten state by heating.

The light absorbing agent added to the polymer liquid crystal layer forming the recording layer 2 in the present invention is required to have the following properties.

1) Absorption for irradiation light 2) Capability of dissolving polymer liquid crystal 3) Heat and light stability 4) Compatibility with polymer liquid crystal 5) Not hindering the orientation of the polymer liquid crystal. In particular, it is preferable that the above-mentioned conditions 1) and 5) are satisfied. Therefore, before describing this material for a light absorber, if an irradiation light source is described, a semiconductor laser is considered to be most suitable in terms of mass productivity and cost. Therefore, known materials having absorption in the semiconductor laser oscillation wavelength region and usable as a light absorber in the present recording medium can be used, and specific examples thereof include the following. For example, methine-polymethine compounds such as cyanines, pyrylium, squarylium, croconium, azulene, pentamethine,
Indanthrene compounds such as thioindigos, quinone compounds such as anthraquinones and naphthoquinones, metal complex compounds such as dithiols, diamines, phthalocyanines, naphthalocyanines, tetradehydrocholines, indoanilines, and diphenylmethane Compounds, dioxazine compounds, dithiazine compounds, triphenylamine compounds, azo dye compounds, perylene compounds, quinacridone compounds, aminium salt compounds, olefin compounds, and the like.

It is preferable that the light absorbing agent has a higher intrinsic absorption coefficient of the material because a small amount of the light absorbing agent may be added to the recording layer 2. However, when a large amount is added to the recording layer 2, for example, when the transmittance of the recording layer 2 is several percent or less, since the light absorption is almost performed at the interface of the recording layer 2, the generated heat is Before the substrate 2 is heated, it is conducted or radiated through the alignment layer 3 to the substrate 1 or the outside world, and the heat utilization efficiency becomes extremely poor. Further, when the same light source is used, the reproduction light irradiated at the time of reproduction of the present recording medium absorbs the same as the recording light, resulting in a remarkable decrease in the detected light amount, and therefore the S / N ratio or C / N ratio A phenomenon occurs in which the ratio decreases. Therefore, the light transmittance of the recording layer 2 to which the light absorbing agent is added is preferably about 20 to 80%, and more preferably in the range of 30 to 70%.

Explaining other constituent materials constituting the present recording medium, well-known materials can be used as the material of the alignment layer 3, and specifically, polyimide or a precursor thereof such as polyimidic acid, fluororesin, polyvinyl alcohol For example, various organic or inorganic materials such as those subjected to a rubbing treatment and silicon oxide obliquely deposited can be used.

Various known materials can also be used for the material constituting the substrate 1. For example, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol,
Various plastics such as polyvinyl acetate, polyamide, polyimide, polyolefin, acrylic resin, phenolic resin, epoxy resin, fluorine-based resin, and the above-mentioned derivatives, glass, quartz plate, ceramic, and the like can be used.

In the case where the heat insulating layer is provided as shown in FIG. 5, various known materials which have been reported conventionally can be used as the constituent material. Specifically, polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, etc. Various materials such as polycarbonate, polyvinyl alcohol, polyvinyl acetate, polyamide, polyimide, polyolefin, acrylic resin, phenol resin, epoxy resin, fluororesin, and the above-mentioned derivatives, and materials such as glass can be used.

Further, in the configuration of FIG. 1, since the light reflecting layer is not provided, when the light absorbing agent does not have a sufficient reflectance, the reproduction is performed by the transmitted light. However, in the case where it is advantageous to perform the reproduction with the reflected light due to the configuration of the system, the reproduction is performed by providing the light reflection layer in the recording medium. For example, when the reproduction light is incident from the recording layer side, the alignment layer is used. It is sufficient to provide a reflective layer between the substrate 3 and the substrate 1. When light is incident from the substrate side, a reflective layer may be provided on the recording layer 2.

Known materials can be used for the material constituting the reflective layer. For example, gold, platinum, silver, copper, lead, zinc, aluminum, nickel, tantalum, cobalt, chromium, niobium,
Deposition of various metals such as palladium, tin, germanium,
Examples include CVD and sputtering films, but the present invention is not particularly limited to these.

FIG. 5 shows another example of the configuration of a recording medium used in the present invention. A recording layer 2 made of a polymer liquid crystal and an alignment layer 3 for aligning the polymer liquid crystal are provided on a substrate 1. A heat insulating layer 4 is formed between 3 and the substrate 1. When the thickness of the heat insulating layer 4 is sufficiently large and the substrate can be replaced by the film, the substrate 1 can be omitted. Also,
When the thermal conductivity of the alignment layer 3 is low and the film thickness is sufficiently large, the alignment layer 3 and the heat insulating layer 4 can be used together.
In the recording medium of FIG. 1, a light absorbing agent was added to the recording layer 2, but in the recording medium of this configuration example, a light absorbing agent was added to at least one of the alignment layer 3 and the heat insulating layer 4. It is.

The recording operation in this case is almost the same as that in FIG. 1 except that the light absorbed by the light absorbing agent added to the alignment layer 3, the heat insulating layer 4, or both is converted to heat. The erasing operation is the same as in FIG. Further, in the recording medium of this configuration example, the heat generated in the layer containing the light absorbing agent is less likely to escape to the substrate 1 due to the presence of the heat insulating layer 4, and the recording speed is further improved.

In the configuration example of FIG. 5, a light absorbing agent is added to at least one of the alignment layer 3 and the heat insulating layer 4.
From the viewpoint of heat utilization efficiency, the case where the light absorbing agent is added to the alignment layer 3 in contact with the polymer liquid crystal layer is better than the case where the light absorbing agent is added to the heat insulating layer 4. More preferred. In the above configuration, the light to be irradiated may be on the polymer liquid crystal layer side or on the substrate 1 side. However, in consideration of the generated heat distribution, the light is preferably incident from the polymer liquid crystal side.

In the configuration example of FIG. 5, the constituent materials of the substrate 1, the recording layer 2, the alignment layer 3 and the heat insulating layer 4 and the light absorber material added to at least one of the alignment layer 3 and the heat insulating layer 4 are the same as those of FIG. The same thing as an example can be used. When a light absorber is added to the alignment layer 3, a polyimide or a precursor thereof, which can be formed by dissolving in an organic solvent or the like in a manufacturing method and forming a film by a solution coating method, or a precursor thereof, which is subjected to a rubbing treatment, is used. desirable.

FIG. 6 shows still another configuration example of the recording medium used in the present invention, in which recording layers 2a and 2b made of a polymer liquid crystal are provided on a substrate 1, and photothermal conversion is provided between these layers to absorb irradiation light and convert it to heat. It has a layer 5 and an alignment layer 3 for aligning the polymer liquid crystal layer.

In the configuration examples shown in FIGS. 1 and 5, a light absorber is added to the recording layer 2, the alignment layer 3, or the heat insulating layer 4 to absorb the irradiation light and efficiently convert the heat to heat to enable reversible recording. However, the same operation can be performed by the light-to-heat conversion layer 5 provided in the configuration example of FIG. The recording operation in this case is substantially the same as the configuration example in FIGS. 1 and 5 except that the light irradiated by the photothermal conversion layer 5 is converted into heat.
The erasing operation is also the same as in these configuration examples.

When the light-to-heat conversion layer 5 is used, the layer configuration of the recording medium is the sixth.
The configuration is not limited to the one shown in the figure, and for example, a configuration as shown in FIGS. 7 and 8 may be used. In these cases, a different temperature distribution is formed in the recording layer 2 at the time of beam light irradiation than in the configuration example of FIG. 6, and in FIG. 7, the area near the alignment layer 3 has the highest temperature. In the case of FIG. 8, the distribution is such that the uppermost part of the recording layer 2 has the highest temperature. Therefore, in the recording medium having such a configuration, the recording portion is recorded in an area corresponding to the temperature distribution. However, when the recording medium having the above configuration is used, there is a possibility that a defect may appear. For example, in the case of FIG. 7, heat generated in the light-to-heat conversion layer 5 is transmitted to the substrate 1 through the alignment layer 3. In this case, it is expected that the heat utilization efficiency is deteriorated, and in the case of FIG. 8, since the recording portion is far from the alignment layer 3, the alignment control force from the alignment layer 3 is reduced, and the erasing time is reduced. Performance may be degraded. However, the above problem can be easily overcome by adjusting the thickness of the storage layer and selecting the material and thickness of the alignment layer.

The light-to-heat conversion layer 5 can be formed by using a light absorbing agent as described above. In this case, the light-to-heat conversion layer 5 may be formed from a single layer of the light absorbing agent, or may be formed of a resin layer containing the light absorbing agent. It may be formed of a layer to which a light absorber is added.

In the case of the recording medium having the structure shown in FIGS. 6 and 7, it is necessary to align the polymer liquid crystal layer on the alignment layer 3 via the photothermal conversion layer 5. Therefore, in these cases, the light-heat conversion layer 5 needs to be made of a material or a structure that hardly disturbs or hinders the alignment regulating force to the polymer liquid crystal layer above it. Is preferably formed from the same polymer liquid crystal as the recording layer to which is added, or a very thin layer of 0.5 μm or less made of a single light absorber.

In the structure shown in FIGS. 6 to 8, the same materials as those in the above-described configuration example can be used for the constituent materials of the layers other than the light-to-heat conversion layer 5.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 An optically polished glass substrate having a thickness of 1.2 mm was used as a substrate 1, and N containing polyamic acid several wt% was formed on the substrate 1.
Using a methylpyrrolidone solution, a thin film having a thickness of about 1000 ° was applied by spin coating, dried, and dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide. This film was subjected to 10 rubbing treatments under a load of 100 g / m ² to form an orientation layer 3.

Next, on this alignment layer 3, 10 wt.
% And 0.1 wt% of a naphthalocyanine dye represented by the following structural formula (A), a recording layer 2 having a thickness of 1 μm was formed by spin coating using a solution dissolved in tetrahydrofuran. A recording medium was obtained.

In the above formula, R _{1 to} R ₄ are the same or different, a linear or branched alkyl group or halogen, or hydrogen, n is the same or different,
0-6 integer, X ₁ and X ₂ are the same or different, -R, -A
r, -OR, -OAr, -OSi (R) ₃ , -OSi (OR) ₃ , -OS
i (OAr) a group selected from the group consisting of ₃ (where R is C ₁ to
A C ₂₂ linear or branched alkyl group, Ar is a phenyl group, a substituted phenyl group, a benzyl group or a group selected from the group consisting of a substituted benzyl group).

The recording medium was annealed in an oven at 165 ° C. for 30 minutes, and the molecules of the polymer liquid crystal in the recording layer 2 were homogeneously aligned. confirmed. As a result of measuring the transmission spectrum of this recording medium, the transmittance at 780 nm was 57%.

In addition, recording, reproduction,
An erasure experiment was performed.

<Recording> With respect to the recording medium prepared above, an oscillation wavelength of 780 nm,
Using a semiconductor laser beam focused to a beam diameter of 1 μm,
Irradiation was performed from the substrate 1 side at a linear velocity of 1 m / s and a light intensity of 12 mW, and several lines were formed linearly at a pitch of 5 μm to perform recording. When the recorded part of the medium after recording was observed at a diagonal position (stage angle of 45 °) under crossed Nicols with a transmission polarization microscope, the recorded part selectively formed a dark state with respect to the surrounding unrecorded part. In this state, it was found that the isotropic phase portion appeared because it did not depend on the stage angle.

<Reproduction> For the recording medium on which the recording was formed as described above, the light intensity was 4 mW using the semiconductor laser previously used.
Then, scanning was performed perpendicularly to the scanning direction of the recording light from the recording layer side at a linear velocity of 1 m / s. The irradiating light passes through one polarizing plate just before entering the sample like a polarizing microscope,
After passing through the medium and before entering the light receiving element (photomultiplier tube), the light was transmitted through another polarizing plate rotated in the direction perpendicular to the polarizing plate that was transmitted first again. When the response obtained from the light-receiving element was measured with this system, it was found that the reproduced signal could be reproduced at approximately 6 kHz and a duty ratio of 15%, and the S / N ratio was detected at least 24 dB and the C / N ratio was detected at 40 dB or more. did it. The output level of this reproduced signal did not change even if it was reproduced 100 times in succession.

<Erasing> An erasing experiment was performed by using a semiconductor laser beam focused on the recording medium at 5 μm, scanning at a strength of 6 mW and a linear velocity of 100 mm / s in the direction perpendicular to the recording line as in the case of reproduction. .
Observation of this medium with a polarizing microscope confirmed that the portion exposed to the erasing light selectively returned to the original homogeneous alignment state, and that the width was erased over 2.5 μm.

(Example 2) In the same manner as in Example 1, the liquid crystal of No. 30 was used in place of the liquid crystal of No. 33, and a polymethine dye represented by the following structural formula (B) was used as a light absorbing agent. Was used to produce a recording medium. The dye content was 4 wt% based on the polymer liquid crystal.
%.

Next, the performance of this recording medium was evaluated by the same method as in Example 1 under the following conditions.

(I) Recording: beam diameter φ1 μm, intensity 12 mW, linear velocity 3 m / s,
Several straight lines were recorded at a pitch of 5 μm.

(Ii) Reproduction: Beam diameter φ1 μm, intensity 5 mW, linear velocity 3 mW (iii) Erasure: Beam diameter φ5 μm, intensity 5 mW, linear velocity 200 m
The medium after m / s recording was confirmed by the appearance of recording lines similar to those in Example 1 under a polarizing microscope. Similarly, it was confirmed that the recording line could be erased over a width of 3 μm in the medium after erasing. Note that the S / N during reproduction was about 30 dB or more.

Example 3 An optically polished glass plate having a thickness of 1.2 mm was used as a substrate 1, and a 10 μm-thick polyvinylidene fluoride film was formed on the substrate 1 by a casting method to form a heat insulating layer 4. Next, a film having a thickness of 2000 mm was formed on the heat insulating layer 4 by spin coating using an N-methylpyrrolidone solution containing 10 wt% of soluble polyimide and 0.5 wt% of the naphthalocyanine dye represented by the above structural formula (A). After forming and drying at 60 ° C. for 30 minutes, the surface was rubbed 10 times with a load of 100 g / cm ² to provide an alignment layer 3.

Next, a 0.5 μm thick recording layer was formed on the alignment layer 3 by a spin coating method using a solution in which the liquid crystal of No. 33 was dissolved at 10 wt% in tetrahydrofuran.
A recording medium having the configuration shown in FIG. 5 was produced.

The recording medium was annealed in an oven at 165 ° C. for 30 minutes, and the molecules of the polymer liquid crystal in the recording layer 2 were homogeneously aligned. confirmed.

Experiments of recording, reproduction, and erasure were performed on the recording medium in the following manner.

<Recording> Using a semiconductor laser beam having an oscillation wavelength of 780 nm and a beam diameter of 1 μm, a linear velocity of 3 m / s,
Irradiation was performed from the substrate side at a light intensity of 7 mW, and several lines were formed linearly at a pitch of 5 μm to perform recording. When the recorded portion of the medium after recording was observed at a stage angle of 45 ° (diagonal position) under crossed Nicols using a polarizing microscope, the recorded portion was selectively darkened with respect to the surrounding unrecorded portion. It was found that an isotropic phase portion appeared because this state did not depend on the stage angle.

<Reproduction> For the recording medium on which the recording was formed as described above, the light intensity was set to 2 mW using the semiconductor laser used earlier.
Then, scanning was performed from the recording layer 2 side at a linear velocity of 3 m / s perpendicular to the scanning direction of the recording light. At this time, the irradiation light passes through a single polarizing plate immediately before entering the medium as in a polarization microscope, and after passing through the medium, a light receiving element (photomultiplier tube)
The light is transmitted through another polarizing plate that is rotated in the direction perpendicular to the polarizing plate that has been transmitted again before the light is incident on the polarizing plate. When the response obtained from the light receiving element was measured in this state, it was found that the reproduced signal could be reproduced at about 18 kHz and the duty ratio was 15%, and that the S / N ratio could be detected at least at 28 dB or more.

<Erasing> An erasing experiment was performed by scanning the recording medium in the direction perpendicular to the recording line in the same manner as during reproduction at an intensity of 6 mW and a linear velocity of 100 mm / s using a semiconductor laser beam focused at 5 μm. Was. When this medium was observed with a polarizing microscope, it was confirmed that the portion exposed to the erasing light selectively returned to the original homogeneous alignment state, and that the width was erased over 2.5 μm.

(Example 4) An optically polished glass plate having a thickness of 1.2 mm was used as the substrate 1, and N-containing several wt% of polyimidic acid was formed on the substrate 1.
Using methylpyrrolidone solution, spin coating method
A thin film having a thickness of 1000 ° was applied, dried and then dehydrated and condensed at 270 ° C. for 1 hour to form a polyimide. This film was subjected to 10 rubbing treatments under a load of 100 g / cm ² to form an alignment layer 3.

Next, the liquid crystal of No. 33 was made into a 5 wt% tetrahydrofuran solution on the alignment layer 3 and 5,000 μm thick by spin coating.
The recording layer 2b was formed. Thereafter, a thickness of the liquid crystal of No. 33 and a tetrahydrofuran solution containing 0.3 wt% of a naphthalocyanine dye represented by the structural formula (A) are also formed on the recording layer 2b by a spin coating method.
After forming a light-to-heat conversion layer 5 having a thickness of 2000 mm and drying,
The recording layer 2a of 5000 ° was formed by a spin coating method using a tetrahydrofuran solution containing 5 wt% of the liquid crystal of No. 3 to prepare a recording medium having the structure shown in FIG. From a measurement of a transmission spectrum of the recording medium, the transmittance at 780 nm was about 60%. When this recording medium was annealed in an oven at 168 ° C. for 30 minutes, and the molecules of the polymer liquid crystal in the recording layer were homogeneously aligned. Observation by a polarizing microscope confirmed that the molecules had a good alignment.

Next, recording, reproduction,
An erasure experiment was performed.

<Recording> With respect to the recording medium prepared above, an oscillation wavelength of 780 nm,
Using a semiconductor laser beam focused to a beam diameter of 1 μm,
Irradiation was performed from the substrate 1 side at a linear velocity of 3 m / s and a light intensity of 12 mW, and several lines were formed linearly at a pitch of 10 μm to perform recording. When the medium after recording was observed with a transmission polarization microscope under crossed Nicols at a diagonal position (stage angle 45 °),
The recorded part selectively forms a dark state with respect to the surrounding unrecorded part, and since this part is always in a dark state without depending on the stage angle, the isotropic phase part appeared by recording confirmed.

<Reproduction> For the recording medium on which the recording was formed as described above, using the semiconductor laser having the wavelength of 780 nm previously used,
Scanning was performed in a direction perpendicular to the recording line from the recording layer side at a light intensity of 4 mW and a linear velocity of 3 m / s. Irradiation light was transmitted through a pair of polarizing plates assembled orthogonally before and after the sample, and then the amount of light was measured by a light receiving element (photomultiplier tube). From the response, a reproduction signal of the recording medium was obtained. As a result, it was found that reproduction was possible at 18 kHz and a duty ratio of 15%. In addition, this signal is subjected to wavelength analysis with a fast Fourier transform analyzer,
When the C / N ratio was determined, it was found that the signal was reproduced at least at 36 dB or more.

<Erasing> A semiconductor laser beam having a wavelength of 780 nm is focused on this recording medium to 5 μm, and the intensity is 4 mW, and the linear velocity is 100 mm / s. went. Observation of the intersection of the erasing light and the recording line with a polarizing microscope revealed that the portion of the recording line irradiated with the erasing light was 3 μm.
It was confirmed that it was erased over the width and returned to the original homogeneous alignment state.

(Example 5) An alignment layer 3 was formed on a glass substrate 1 under the same conditions as in Example 4, and a solution obtained by dissolving the liquid crystal of No. 30 in 10% by weight in tetrahydrofuran was used on the alignment layer 3. Thus, a recording layer 2 having a thickness of 7,000 ° was formed by a dip coating method. Then, the substrate with the recording layer was annealed at 168 ° C. for 30 minutes to orient the molecules of the polymer liquid crystal of the recording layer 2. Further, a low-polymer polyethylene containing 5% by weight of a phthalocyanine dye represented by the following structural formula (C) was melt-coated on the recording layer 2 to obtain a recording medium having the structure shown in FIG.

The performance of the present recording medium was evaluated using a semiconductor laser having a wavelength of 780 nm under the following conditions. Laser light irradiation was performed from the substrate 1 side.

(I) Recording: beam diameter ψ1 μm, intensity 14 mW, linear velocity 3 m / s
Several straight lines were recorded at a pitch of 5 μm.

(Ii) Reproduction: Beam diameter ψ1 μm, intensity 3 mW, linear velocity 3 m / s (iii) Erasure: Beam diameter ψ5 μm, intensity 6 mW, linear velocity 100 m / s The medium after recording and erasing was observed with a polarizing microscope. It was confirmed that the same change as in Example 4 appeared. The S / N ratio during reproduction was 22 dB or more.

(Example 6) In the same procedure as in Example 4, after the alignment layer 3 was provided on the substrate 1, the liquid crystal of No. 34 was spin-coated to a thickness of 3000.
And a recording layer 2b was provided. A film having a thickness of 600 mm was formed on the recording layer 2b by using a 0.5% by weight solution of a polymethine dye represented by the following structural formula (D) in methyl ethyl keto to form a light-to-heat conversion layer 5. The liquid crystal of No. 34 was applied again to form the recording layer 2a, thereby producing a recording medium having the structure shown in FIG.

The performance of this recording medium was evaluated in the same manner as in Examples 5 and 6 under the following conditions.

(I) Recording: beam diameter φ1 μm, intensity 11 mW, linear velocity 3 m / s (ii) Reproduction: beam diameter φ1 μm, intensity 2 mW, linear velocity 3 m / s (iii) Erasing: beam diameter φ5 μm, intensity 6 mW, linear velocity 50 m / s s As a result, good changes in recording and erasing were confirmed as in Examples 5 and 6, and the S / N ratio due to reflected light was 21 dB.
That was all.

〔The invention's effect〕

According to the present invention, in order to perform recording by changing the orientation state of a part in the thickness direction of the polymer liquid crystal recording layer, not only the transfer speed during recording is improved, but also the changed part during recording is erased. In this case, the original state can be easily returned, so that there is no erasure remaining, the erasing speed is increased, and highly reliable recording and erasing can be performed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a layer structure of a recording medium used in the present invention, FIG. 2 is a sectional view showing a temperature distribution to be formed in a recording layer of the recording medium of FIG. 1, and FIG. FIG. 4 is a cross-sectional view showing an example of a recording state in the invention, FIG. 4 is a cross-sectional view showing an example of a recording state formed over the entire recording layer by long-time irradiation, and FIG. 6 to 8 are cross-sectional views showing still another example of the configuration of the recording medium used in the present invention. DESCRIPTION OF SYMBOLS 1 ... Substrate, 2, 2a, 2b ... Recording layer 3 ... Orientation layer 4 ... Heat insulation layer 5 ... Light-to-heat conversion layer

Continued on the front page (72) Inventor Kyoji Tsutsui 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Masafumi Ota 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh (56) References JP-A-3-137834 (JP, A) JP-A-3-119323 (JP, A) JP-A-4-29884 (JP, A) JP-A-3-138688 (JP, A) JP-A-2-139286 (JP, A) JP-A-2-139285 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (3)

(57) [Claims] A beam is applied to a recording medium comprising a recording layer containing a polymer liquid crystal and a light absorbing agent for recording and recording / erasing by causing a reversible change in orientation state or phase change on at least a substrate. 100 hours for light to pass through one point
Irradiation in microseconds or less and changing the orientation state or phase state in a part of the thickness direction of the recording layer composed of the polymer liquid crystal, and after forming the recording, the beam light is applied without applying external force such as electric field and magnetic field. A recording and a recording / erasing method, wherein a recording formed by irradiating is erased. 2. A recording layer comprising a polymer liquid crystal for performing recording and recording / erasing by causing a reversible change in alignment state or phase change on at least a substrate, and an alignment layer for aligning the polymer liquid crystal layer. In addition, in some cases, a heat insulating layer is provided to improve the utilization efficiency of generated heat, and a recording medium containing a light absorbing agent in at least one of the alignment layer and the heat insulating layer, 1 beam light
Irradiate for less than 100 μs when passing through a point and change the orientation state or phase state in a part of the recording layer in the thickness direction.After forming the recording, the beam is applied without applying external force such as electric field and magnetic field. A recording and recording erasing method, wherein a recording formed by irradiating light is erased. 3. A recording layer made of a polymer liquid crystal which performs recording and erasure by causing a reversible change in alignment state or phase change on at least a substrate, and further comprising any one of the recording layer and the recording layer. A recording medium consisting of a light-to-heat conversion layer, which absorbs irradiation light and converts it to heat, is radiated to the recording medium adjacent to one of the surfaces in a time of 100 μsec or less when the light beam passes through one point, and the thickness direction of the recording layer The recording is performed by changing the orientation state or phase state of a part of the recording, and after forming the recording, the formed recording is erased by irradiating the light beam without applying an external force such as an electric field or a magnetic field. Recording and record erasing method.