JP2632920B2 - Recording method, recording medium and recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable recording method, a recording medium for the rewritable recording medium, and a recording / reproducing apparatus for the rewritable recording medium, and more particularly, to a chiral smectic C phase having a spiral structure as a recording layer. The present invention relates to a device using molecular liquid crystals.

[Conventional technology]

At present, the optical storage system has been put to practical use as having a large capacity and excellent random access. There are a wide variety of methods, and digital audio disks (CDs) and laser video disks (LDs) have been put into practical use for playback only. As a type capable of optical recording, a write-once optical disk (WO) and an optical card (OC) are known, and there are a type using a phase change of a metal thin film and a type using pit formation of an organic dye.

Further, research on a rewritable optical disk has been promoted, and practical use of a device using a magneto-optical effect and a device using a phase change are being attempted. Among them, a polymer liquid crystal has also been proposed as an information recording medium (JP-A-59-10930, JP-A-59-35989, and JP-A-62-154340).
Among them, there has been proposed a recording method in which the helical pitch of the cholesteric polymer liquid crystal is changed or the light reflectance is changed in multiple levels by forming a pit in a non-aligned state (Japanese Patent Laid-Open No. Sho 62). No. 107448, the same year 62-
No. 12937). In addition to the information recording medium, a display device using a polymer liquid crystal has been proposed (Japanese Patent Laid-Open No. 62-27-1987).
No. 8529, and No. 62-278530).

[Problems to be solved by the invention]

However, the above conventional example has various disadvantages when used in a rewritable information storage medium or a display device.
A recording medium using a phase change medium or a magneto-optical recording medium has drawbacks in terms of production cost, production time, and production equipment because it is necessary to make a thin film by techniques such as vapor deposition and spatter. Furthermore, phase change media have the disadvantage of being toxic due to the use of chalcogenite compounds such as Te. Further, in a magneto-optical recording medium, the recording state is read out by detecting the rotation of the polarization plane due to the Kerr effect and the Faraday effect accompanying the spin inversion using the spin inversion, and the rotation angle is as small as 1 ° or less. Therefore, there is a disadvantage that the optical system and the electric system are complicated. Therefore, the above method is not suitable for display.

On the other hand, information storage media and display devices using a polymer liquid crystal as an optical modulation layer can be manufactured at low cost and have excellent recording contrast.
It is expected as a device. However, the medium, method, and apparatus using the polymer liquid crystal described in the above-mentioned conventional example have a drawback that the writing and erasing speeds are low, and are not suitable for high-speed recording, overwriting, and the like.

On the other hand, it is known that a low molecular ferroelectric liquid crystal (hereinafter, FLC) has a helical structure when sealed in a cell thickness of usually several tens μm or more and subjected to horizontal alignment treatment. This occurs because the orientation direction of the molecules in each layer of the smectic phase shifts on a cone having an inclination angle with respect to the normal of the layer of the smectic phase (FIG. 2 (a)). It is known that when an electric field is applied thereto, the dipole moment of each molecule is arranged along the electric field, and the helical structure can be dissolved (FIG. 2 (b)).

It has been proposed to realize a display element by using the fact that the amount of transmitted light changes with such a change in molecular arrangement (K. Yoshince, KGBalakrishnan, T. Uemoto, Y. Iwa
saki and Y. Inuishi, Jpn. J. Appl. Phys., 17 , 597 (197
8)). In such a display element, by applying an electric field between the electrodes, it is possible to respond from the helical structure to the non-helical structure at a high speed of several hundred μsec.

However, the change in the helical structure due to the electric field using the FLC is effective only when an electric field is applied. However, the helical structure is restored as soon as the electric field is removed. Become. Further, since the electric field application portion is determined by the electrode area, it has been difficult to increase the density as an information storage medium.

[Means for solving the problem (and action)]

According to the present invention, in a recording medium using a polymer liquid crystal layer having a helical structure in a chiral smectic C phase as an optical modulation layer, the helical structure is controlled,
The recording state can be realized by selecting a pitch, a spiral turning direction, or a non-helical structure. As a result, information storage media and display media can be manufactured at low cost by simple methods such as spin coating and coating, and at the same time, spiral and non-helical structures can be selected at high speed, their writing conditions can be stably maintained, and high contrast can be achieved. It became possible to play.

The helical structure in the polymer liquid crystal having a chiral smectic C phase results from twisting of the mesogen portion in each smectic layer. However, the helical structure is more stabilized because the mesogens are linked by a covalent bond. Since light is scattered in accordance with the period (helical pitch) of the helical structure, it is desirable to control the helical pitch in accordance with the wavelength of the writing light or the reading light.

The helical pitch changes depending on the chemical structure of the polymer liquid crystal, and can be set to an arbitrary range. Furthermore, by controlling the temperature in the chiral smectic C phase,
The helical pitch changes according to the temperature, and can be fixed by rapidly cooling to a temperature below the glass transition point of the polymer liquid crystal.

On the other hand, selective scattering by a helical structure has wavelength dependence, and colorization can be performed by selective scattering in the vicinity of visible light. For this purpose, it is desirable that the central axis of the helical structure is horizontal to the substrate so that the angle dependence is reduced.

The helical structure can be clockwise or counterclockwise by controlling the chemical structure, temperature, and the like. When these are irradiated with circularly polarized light, only circularly polarized light rotating in the same direction is selectively reflected. In particular, when the rotation direction of the helical structure changes from clockwise to counterclockwise depending on the temperature, high contrast can be obtained by rapidly cooling the glass to below the glass transition point and fixing the rotation direction.

When the glass transition point is much higher than room temperature, the spiral structure of the chiral smectic C phase and the glassy state of the Iso phase,
A recording state and a non-recording state can be obtained by selecting another liquid crystal phase such as a smectic A phase non-helical structure or a non-helical structure of a chiral smectic C phase.

For this purpose, the temperature is raised to the phase selected by the heating means,
Quenching is used. Alternatively, the temperature is raised by one step, cooled to the (liquid crystal) phase to be used, and then fixed by rapid cooling. At this time, the molecular arrangement can be changed by applying an electric or magnetic field, and an electric field is particularly suitable for obtaining a non-helical structure of the chiral smectic C phase.

The following are examples of the polymer liquid crystal used in the present invention.

(In the following formulas (1) to (13), 15> n ≧ 1) (In the following formulas (14) to (17), p = 5 to 1000, p1 + p2 = 5
10001000, q = 1１〜16, q1 = 1１〜16, q2 = 1１〜16. ) (In the following formulas (18) to (46), * indicates an asymmetric carbon center,
n = 5 to 1000. ) In order to have a good helical structure in the chiral smectic C phase in the above polymer liquid crystal, the structure of the flexible chain is important. For this, an alkyl chain, an alkylene chain, a poly (alkyloxy) chain, an allyl chain, a methacryl chain, or the like is used. Particularly preferably, poly (dimethylsiloxane) is used as a flexible chain.

Various optically active groups such as a 2-methylbutyl group, a 1-methylpropyl group, a 1-methyl-heptyl group, and a cholesterol group are used, and those having a structure with large steric hindrance tend to have a small helical pitch.

Polymer liquid crystals that do not have optically active groups must be used by mixing with compounds having optically active groups, and in particular, mixed with low-molecular ferroelectric liquid crystals and used as the polymer liquid crystal layer of the present invention. Is preferred. Examples of the low-molecular ferroelectric liquid crystal are as follows.

Further, when writing and erasing are performed by laser light or the like, sensitivity is improved by providing a laser light absorbing layer or adding a laser light absorbing compound to the polymer liquid crystal layer. Examples of the laser light absorbing compound to be added to the polymer liquid crystal layer include the following.

Further, a deterioration preventing agent such as an ultraviolet absorber and an antioxidant, a nucleating agent, and a fluorescent dye may be mixed and used.

Although it is necessary to orient the obtained polymer liquid crystal layer, the recording medium of the present invention can provide a high contrast without being completely orientated. In order to realize a helical structure and a non-helical structure using the response by an electric field in the chiral smectic C phase, it is necessary to perform horizontal alignment. For horizontal alignment, an organic polymer such as PVA or PI or a deposited film of SiO ₂ or the like can be used as an alignment film, and rubbing treatment can further impart uniaxiality. Also, good orientation can be obtained by shearing, stretching and the like.

In the present invention, since the helical structure in the chiral smectic C phase is used as a recording state, when the amount of reflected light with respect to light having a specific wavelength is measured, the amount of reflected light may change continuously in accordance with the change in helical pitch. all right. Thus, if the holding temperature of the polymer liquid crystal layer is controlled, and the spiral pitch is selected and then fixed by cooling, a continuous reflected light quantity is obtained as a recording state, which is effective for multi-value recording.

On the other hand, the ratio of the helical structure can be controlled by an interface or an external field, and the helical structure can also be used for multi-value recording. For this reason, gradation display can be performed relatively easily.

Example 1 A polyamic acid solution was spin-coated on a glass substrate 1 having a transparent electrode 2 and baked at 300 ° C. to obtain a polyimide alignment film 3. Next, 0.5 wt% of the dye represented by Formula III was dissolved in a mixture of the polymer liquid crystals (I) and (II) having the following structure at a ratio of 2: 1.

The glass substrate 1 and aluminum were mixed with the polymer liquid crystal composition.
Insert between glass substrate 1 'with 5000Å
C. and pressed. The thickness of the polymer liquid crystal layer 4 of the obtained storage medium was about 50 μm. Next, when gradually cooled from 120 ° C., a periodic structure due to a helical structure was observed at 60 ° C. by a reflection type polarizing microscope.

Embodiment 2 FIG. 1 shows an embodiment of the present invention.

The laser light generated from the laser light source 7 is applied to an optical modulator 9.
The light was modulated by the signal of the modulation signal generator 10 and linearly polarized by the polarization beam splitter 11. This is a quarter-wave plate 1
2 was converted into circularly polarized light, and the light was irradiated onto the recording medium prepared in Example 1 through the condenser lens 13.

FIG. 3 is an enlarged view of the recording medium when the recording medium is irradiated with a laser, focusing on the recording medium. The laser power on the board was 2 mW. The reflectivity was about 20%. By rotating the polarizing beam splitter 11 by 90 °, the linearly polarized light was rotated by 90 °, and similarly passed through a quarter-wave plate to obtain reverse-rotated circularly polarized light. Similarly, when the light was irradiated onto the medium through the condenser lens 13, the reflectance was 35%.

Next, when a DC voltage of 100 V was applied from the voltage modulator 15 to the recording medium, the reflectance became 50% in about 200 msec. The laser beam was stopped and reproduction was performed again with a laser power of 0.5 mW, but the reflectance did not change.

Embodiment 3 FIG. 5 shows a display device of the present invention.

The polymer liquid crystal composition used in Example 1 was heated to 120 ° C. and coated with a roll coater on a substrate on which a transparent ITO electrode was sputtered on a PET film. Further, the surface was coated with a 5 μm amide imide film and pressure-bonded, and both ends were adhered to obtain an endless film 19. Drive roller 20
While maintaining the temperature at 80 ° C. with the sheet heater 21 to form a helical structure. The laser light modulated by the semiconductor laser 22 was irradiated onto the light, and the light was scanned in one direction by the polygon mirror 23. When an image was formed and recorded on the medium 19 through the f-θ lens 24, an image with good contrast was obtained.

Embodiment 4 FIG. 4 shows a recording / reproducing apparatus of the present invention using a heating element head.

A mixture of the polymer compounds (I) and (II) used in Example 1 at a ratio of 2: 1 was applied to a glass substrate on which an ITO transparent electrode 30 was formed on a glass substrate 1 to a thickness of about 30 μm, and the temperature was reduced from 120 ° C. It was cooled slowly (4 layers). An ultraviolet-curable fluorine-based resin protective layer 18 was applied thereon to a thickness of 2 μm and cured by irradiating ultraviolet rays. The heating element head 6 was brought into contact with the medium, a current was applied, and a 200 V bias voltage was further applied between the lower electrode 30 and the heating element head 6. When the non-helical structure was recorded by turning off the current and cooling, a display with a contrast of 2: 1 was obtained. Further, the display sandwiched between the two polarizing plates provided a display having a contrast of 10: 1, and could be stably maintained at room temperature.

〔The invention's effect〕

As described above, in the chiral smectic C phase, by using a recording medium having a polymer liquid crystal layer having a helical concept as an optical modulation layer, and using a recording method for controlling the helical structure and the non-helical structure, It is possible to obtain a recording / reproducing apparatus which can be made large-area, high-definition, and high-contrast at low cost and has a high recording / erasing speed.

[Brief description of the drawings]

FIG. 1 shows a recording / reproducing apparatus according to the present invention. FIG. 2 is a model of a helical structure and a non-helical structure in a chiral smectic C phase. FIG. 3 is an example of a recording medium of the present invention. FIG. 4 is another example of a recording medium of the present invention. 1,1 '... substrate 2 ... transparent electrode 3 ... alignment film 4 ... polymer liquid crystal layer 5 ... reflection layer (electrode) 6 ... thermal head 7 ... laser light source 8 ... collimator Lens 9 Optical modulator 10 Modulated signal generator 11 Polarized beam splitter 12 Quarter-wave plate 13 Condenser lens 14 Actuator 15 Voltage modulator 16 Medium drive Apparatus 17 Detector 18 Protective film 19 Display medium 20 Drive / heat treatment roller 21 Surface heater 22 Semiconductor laser 23 Polygon mirror 24 f-θ lens 25 Transparent Electrode 26 Electrode 27 Lighting 28 Black body 29 Internal mirror 30 Electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuzo Kaneko 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Akihiro Mori 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside the Company (72) Inventor Kayoshi Toshida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shunichi Onishi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Takeo Eguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-62-89929 (JP, A) JP-A-63-72784 (JP, A) JP-A-62-266521 (JP, A) JP-A-62-112295 (JP, A) Koji Okano and Shunsuke Kobayashi "Basic Liquid Crystal" (Showa 9-9-25) Baifukan 165 lines 5 to 10

Claims (12)

(57) [Claims] 1. Recording by selectively generating a helical structure and a non-helical structure in a chiral smectic C phase of a polymer liquid crystal layer having a chiral smectic C phase above the glass transition point of the polymer liquid crystal layer. Form the state,
A recording method, wherein the recording state is maintained below a glass transition point of the polymer liquid crystal layer. 2. The recording method according to claim 1, wherein said polymer liquid crystal layer is horizontally aligned. 3. A recording medium characterized by having a polymer liquid crystal in a chiral smectic C phase in either a helical structure or a non-helical structure and maintaining such a state below the glass transition point as a recording layer. . 4. A means for eliminating a helical structure in a chiral smectic C phase, a means for controlling a helical pitch of a chiral smectic C phase by temperature control, a means for fixing the helical pitch by quenching, and a reflection for incident light. Recording means for reproducing a recording by reading light. 5. The recording apparatus according to claim 4, wherein said incident light is circularly polarized light. 6. A recording medium comprising a polymer liquid crystal in a chiral smectic C phase in a state of either a helical structure or a non-helical structure and maintaining such a state at a glass transition point or lower as a recording layer. And a means for forming a recording state by selectively generating either a helical structure or a non-helical structure in the chiral smectic C phase in the recording layer. 7. A helical structure and a non-helical structure in a chiral smectic C phase of a polymer liquid crystal layer comprising a polymer liquid crystal having a chiral smectic C phase and having no optically active group and a compound having an optically active group. Wherein a recording state is formed by selectively generating a temperature above the glass transition point of the polymer liquid crystal layer, and the recording state is maintained below the glass transition point of the polymer liquid crystal layer. . 8. The recording method according to claim 7, wherein said polymer liquid crystal layer is horizontally aligned. 9. The recording method according to claim 7, wherein the compound having an optically active group is a low-molecular ferroelectric liquid crystal. 10. A chiral smectic C phase comprising a polymer liquid crystal having no optically active group and a compound having an optically active group, and having a helical structure or a non-helical structure. A recording medium having a polymer liquid crystal layer held below as a recording layer. 11. The recording medium according to claim 10, wherein the compound having an optically active group is a low-molecular ferroelectric liquid crystal. 12. A chiral smectic C phase comprising a polymer liquid crystal having no optically active group and a compound having an optically active group, and having a helical structure or a non-helical structure. A recording medium having a polymer liquid crystal layer retained below as a recording layer, and selectively causing either a helical structure or a non-helical structure in the chiral smectic C phase in the recording layer. Means for forming a recording state by means of a recording device.