JPS63241736A - Information recording disk - Google Patents

Abstract

PURPOSE:To execute information recording by providing a high-polymer liquid crystal layer between a pair of disk substrates and rotating one disk around the central axis relative to the other. CONSTITUTION:A high-polymer liquid crystal A expressed by the formula is dissolved in dichloroethane and the soln. is spin-coated on a glass disk 1 having 130mm outside diameter, 15mm inside diameter and 1.2mm thickness and is dried to form the ferroelectric high-polymer liquid crystal film having 0.05-5mum thickness thereon. Such disks are superposed on each other via an Al conductive film 3 and are heated to 120 deg.C to convert the liquid crystal layer 2 to an isotropic state. The disks are slowly cooled down to 100 deg.C at 2 deg.C/min. While the lower substrate is fixed, only the upper substrate is rotated about 30 deg. around the center and thereafter, the substrates are cooled down to a room temp. The liquid crystal layer is uniformly and uniaxially oriented in the circumferential direction. The orientation is disturbed when the recording part of such recording medium is irradiated with 830nm laser. Sufficient contrast is obtd. in the writing and reading out characteristics of this medium so that the good medium is obtd. The medium has excellent environmental resistance as well.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an information recording disk using a polymeric liquid crystal that is recorded using light or heat.

[Conventional technology]

In recent years, development of high recording density recording media using light or heat has been actively conducted. One known example is one that utilizes phase transitions in liquid crystals. Among these, when the liquid crystal is a polymer liquid crystal, there is an advantage that a recording medium with excellent phase stability in the recording portion can be obtained. In order to perform high-density, high-contrast recording on a recording medium using this polymeric liquid crystal layer while taking advantage of the excellent phase stability of the recording part, uniform orientation control is first required as a pretreatment of the liquid crystal layer. need to be done. For example, the orientation methods include a rubbing method, an oblique evaporation method, a method of applying shear stress by sandwiching two substrates, a method of causing a slow phase transition while applying a magnetic field, and a method of orientation using a spacer edge.

[Problems to be Solved by the Invention] However, such an orientation control method is not suitable for obtaining a uniform orientation with high reproducibility and reliability in a large area recording element.

Further, from the viewpoint of use as a recording medium, it is preferable that the medium has a disk shape. (If writing, reading, and erasing can be performed while rotating at high speed around the center, it is advantageous in terms of information transfer speed and shortening of access time.) However, in order to obtain such a disk-shaped liquid crystal recording medium, To achieve this, it is necessary to make the thickness uniform in the circumferential direction and to control the uniaxial alignment of the liquid crystal layer, that is, to align it in a uniform direction.

However, with conventional orientation control methods, it is difficult to achieve such -axis orientation with a uniform thickness.

The present invention has been made in view of the above-mentioned drawbacks, and its purpose is to provide a polymeric liquid crystal layer that is uniaxially aligned in the circumferential direction between a pair of disk substrates, is uniform, and has a high contrast ratio. An object of the present invention is to provide a liquid crystal recording disk that is extremely simple to manufacture.

[Means and effects for solving the problem] According to the present invention, a polymer liquid crystal layer is provided between a pair of disk-shaped substrates, and one substrate is rotated in the circumferential direction about the center with respect to the other substrate. The present invention provides an information recording disk in which the thickness of the polymer liquid crystal layer is uniform, which is obtained by uniaxially aligning the polymer liquid crystal layer along the circumferential direction by the shear stress of the polymer liquid crystal layer.

A schematic diagram of a cross section of the disk of the present invention is shown in FIG.

In the figure, reference numeral 1 indicates a substrate, 2 indicates a polymer liquid crystal layer, and 3 indicates a conductive film. The polymer liquid crystal used in the present invention is a thermotropic liquid crystal, and nematic, smectic, and cholesteric types can be used as the intermediate phase. Polymer thermotropic liquid crystals have the advantage of not only being able to form a thin film but also being easier to maintain a recording state than low molecular weight liquid crystals.

For example, polymer thermotropic liquid crystals that can be used in the present invention are classified into the following two types.

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

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

Specific examples of these polymeric thermotropic liquid crystals are shown in Table 1.

Table 1 0 0 υ
LI L; H3H3 Polymer liquid crystals can be used in combination with several different types of polymer liquid crystals. It is also possible to use a mixture of a polymer liquid crystal and a low molecular liquid crystal, in which case the weight ratio to the polymer liquid crystal is preferably 5 or less. Polymer liquid crystals may contain, if necessary, ordinary polymers (such as olefin resins, acrylic resins, polystyrene resins, polyester resins, polyurethane resins, polycarbonate resins, etc.), oligomers, various plasticizers, various stabilizers, and quenchers. etc. may be contained.

To make the polymer liquid crystal into a thin film, for example, the polymer liquid crystal material is sandwiched between a pair of disk substrates made of glass or plastic and then heated and pressure molded, or the polymer liquid crystal material is placed on the disk substrate using a spin cord or the like. A method such as dipping coating is used. Alternatively, a method may be used in which a polymeric liquid crystal material is dissolved in a solvent and applied onto a substrate and then dried to form a thin film. Furthermore, dyes that absorb light in a specific wavelength range, such as dichroic dyes and infrared absorbing dyes shown below, may be added to these polymeric liquid crystals.

In order to uniformly uniaxially align the liquid crystal thin film in the circumferential direction of the substrate, a polymer liquid crystal layer 2 is placed between a pair of upper and lower substrates 1 as shown in FIG. This is accomplished by displacing one substrate relative to the other substrate in the circumferential direction to generate shear stress in the circumferential direction. Preferably, the rotation is performed in one direction, and the rotation angle is 2.
Alternatively, the polymer liquid crystal layer can be oriented by about 3 degrees, but it is more preferable to rotate it by about 30 degrees to 180 degrees in order to achieve the purpose of making the layer thickness uniform.

Moreover, the rotational angular velocity is more preferably 10 to 20 degrees/second.

By these methods, the polymer liquid crystal layer can be uniaxially aligned in the circumferential direction, and the thickness of the layer can also be made uniform. However, by providing ring-shaped spacers of arbitrary thickness on the inner and outer circumferences, the thickness of the polymer liquid crystal layer can be made more uniform. The thickness of the polymer liquid crystal layer is 0.
A range of 0.05 μm to 5 μm is preferable from the viewpoint of recording and reading performance.

Further, in the present invention, the temperature of the polymer liquid crystal layer is once heated to an isotropic layer, and the polymer liquid crystal layer is oriented in a nematic, smectic or cholesteric phase within a range of 7 g or more. As the disk-shaped substrate, plastics such as acrylic resin, polycarbonate resin, epoxy resin, and epoxy acrylate resin, ceramics such as glass, and metals are used. For recording with laser light, it is preferable to use an optically transparent substrate. Further, the substrate may be provided with a guide groove for tracking.

Furthermore, a disk configuration that allows application of an electric field for recording and reading can also be used.

(This corresponds to the configuration shown in FIG. 2 as an embodiment of the present invention.) Hereinafter, embodiments of the present invention will be described in detail.

<Example 1> Outer diameter 130 mm, inner diameter 15 mm, thickness 1.
On a 2 mm disk-shaped glass substrate, the following polymeric liquid crystal (A) was dissolved in dichloroethane and applied with a spinner, and after drying, a liquid crystal film with a thickness of 2 μm was formed.

Glass substrates each having a reflective film (aluminum vapor deposited film) formed thereon were stacked on each other with the reflective film facing down. 12 of the above disk media
Heat to 0°C to bring the liquid crystal layer into an isotropic state. It was gradually cooled at a rate of 2° C. per minute, and when the temperature decreased to 100° C., the lower substrate was fixed, and only the upper substrate was rotated about 30° around the center.

The temperature was further lowered and cooled to room temperature.

The liquid crystal layer of the obtained disk was uniformly uniaxially aligned in the circumferential direction of the disk.

When the recording portion of this recording medium was irradiated with a recording power of 15 mW using an 830 nm semiconductor laser 6 as shown in FIG. 3, the orientation of the irradiated portion was disturbed and a scattering state occurred. Next, reproduction was performed with a readout power of 1.5 mW, the reproduction light was measured with a photodetector 7, and the contra 8B→signal intensity of the recording section) was calculated.

<Example 2> The following dyes were added to the polymer liquid crystal (A) of Example 1 in O,
A recording disk was produced in exactly the same manner as in Example 1, with a liquid crystal layer having 1 wt% dissolved therein. The medium was recorded and reproduced, and the contrast ratio was measured.

<Example 3> Using a polymer liquid crystal represented by the following structural formula (
Polymer liquid crystal B) A film with a thickness of 2 μm was formed on a glass disk substrate by the spin code method. A disk medium was created in exactly the same manner as in Example 1, and the disk medium was
℃, and when it cools down to 110℃, fix the lower substrate, and rotate only the upper substrate about 1° with the center as the axis.
Rotated 80 degrees.

Recording and reproduction were carried out in the same manner as in Example 1, and the contrast ratio was measured.

<Example 4> The dye used in Example 2 was added to the polymer liquid crystal (B) at 0.
A liquid crystal layer containing 1 wt % dissolved was formed to a thickness of 2 μm, and a disk medium was similarly produced. The medium was recorded and reproduced, and the contrast ratio was measured.

<Example 5> ITO was deposited as a transparent electrode layer on a disk-shaped glass substrate.

1. 0.1 wt% of the dye used in Example 2 was added to the ferroelectric polymer liquid crystal shown below. It was dissolved in 1.2-trichloroethane and applied on the above-mentioned substrate using a spinner, and after drying, a polymer film with a thickness of 3 μm was formed.

n is approximately 20. Further, a glass substrate on which an electrode layer and reflection layer (aluminum vapor deposited film) was formed on the polymer film was laminated with the electrode layer on the lower side. Its cross-sectional configuration is shown in FIG.

The above-mentioned laminate was heated to 90°C, and then slowly cooled (2°C/min) in the smectic A phase, with the lower substrate fixed at 90° with only the upper substrate as the center.
It was rotated slowly (angular velocity about 10°/5ec). Thereafter, it was slowly cooled to form a smectic A phase, and a voltage was applied between the electrodes to align the polarization direction in a certain direction to produce an information recording medium. In this recording medium, while applying a reverse electric field between the transparent electrode (ITO) and the Af electrode, the recording area was heated by irradiating it from the transparent electrode side with an 830 nm semiconductor laser at a recording power of 1.5 mW. Recording was performed by reversing the direction of spontaneous polarization.

Next, a laser beam is irradiated through the polarizer with a reproduction output of 0.15 mW without applying an electric field, and the reflected light contains a difference in birefringence due to the difference in the direction of polarization, so the intensity of the light incident on the photodetector is measured. Then, the contrast ratio was calculated.

Furthermore, by applying a forward electric field to the ITO-Al type O- again and irradiating it with a laser power of 1.8 mW, the recorded portion or the entire surface could be erased.

The measured contrast ratios are shown in Table 2 below.

Table 2 The above disk was also tested under high temperature and humidification (60°C, 90%RH).
Even after being left for 3000 hours, the contrast ratio hardly changed.

[Effects of the Invention] (1) In a disk-shaped recording medium, it has become possible to easily and uniformly control the alignment of the polymer liquid crystal layer uniaxially in the circumferential direction.

■Writing and reading characteristics of the obtained disk medium are as follows.
A sufficient contrast ratio was obtained.

■Disk media has excellent environmental resistance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the structure of an information recording disk according to the present invention and the orientation method of polymer liquid crystal. FIG. 2 is a partial schematic diagram of a cross section of a disk according to the present invention. FIG. 3 is a diagram of the optical system configuration for recording and reproducing the disk. The figure is an explanatory diagram of Example 5. Symbols 1 is a substrate, 2 is a polymeric liquid crystal layer 3 is a conductive film, 4 is a disk, 5 is a beam splitter 1, 6 is a semiconductor laser 7 is a photodetector, 8 is a glass substrate, 9 is a transparent electrode layer, IO is an electrode Indicates a layer and reflective layer. □22'

Claims (4)

[Claims] (1) having a polymer liquid crystal layer between a pair of disk-shaped substrates;
1. An information recording disk characterized in that it is obtained by rotating one substrate about the center with respect to the other substrate and orienting the polymer liquid crystal layer along the circumferential direction by the shear stress of the polymer liquid crystal layer. (2) The information recording disk according to claim 1, wherein the polymer liquid crystal layer described above is a ferroelectric polymer liquid crystal. (3) The information recording disk according to claim 1, wherein the rotation angle of the rotation is in the range of 30° to 180°. (4) The information recording disk according to claim 1, wherein the polymer liquid crystal layer has a layer thickness in a range of 0.05 μm to 5 μm.