JPS6192454A - Optical recording method - Google Patents

Abstract

PURPOSE:To attain high-density recording by forming optical isotropy to a recording medium in the reading direction, applying an electric field to the recording part in a direction with a tile angle in the read direction, irradiating the light for heating the medium thereby decreasing a recording unit area. CONSTITUTION:An organic amorphous compound is used as the recording medium, where an anisotropy is caused in the refractive index by applying an electric field to orient a dipole and the orientation relax temperature of the radial causing the dipole is >=40 deg.C. In recording, electrodes 2a, 2b are provided in a direction having a tile angle theta to the read direction L of the recording medium L, an electric field is applied to a direction with a tilt in the reading direction and a ray T is irradiated. In reading the recording, orthogonal polarizers 3a, 3b are placed at both sides of the recording medium 1, and the ray L is received by an analyzer 4 through the polarizer 3a, the recording medium and the polarizer 3b. In erasing the recording, the entire recording medium 1 is heated to the orientation relax temperature of the polar radical or the orientation is relaxed by irradiating the light on the erased part only.

Description

DETAILED DESCRIPTION OF THE INVENTION (Objective) The present invention relates to a recording method that is excellent for optical recording that can be recorded and read out optically.

(Background of the Invention) There are two types of optical recording: methods that utilize the photon effect and methods that utilize the thermal effect. The present invention relates to a recording method that utilizes thermal effects. Thermal effects that have been studied so far for optical recording include solid phase/vapor phase transition, amorphous/crystalline transition, metal/semiconductor transition, and magnetic transition. From the perspective of recording methods, solid phase/vapor phase transition is a method of creating holes in the recording layer using heat, while amorphous/crystal transition and metal/semiconductor transition are methods that change the refractive index of the recording layer before and after the transition. This is a recording method that uses changes in light, reflectance, and light absorption coefficient.

Magnetic transition is a recording method that utilizes the difference in the rotational direction of the vibration plane of light depending on the magnetization direction of the magnetic material forming the recording layer.

The present invention utilizes the presence or absence of refractive index anisotropy in the dipole orientation state and disordered state.

Examples of methods that have been studied in the past to utilize orientation of dipoles by an electric field include liquid crystal displays and polarization treatments that impart piezoelectricity or pyroelectricity to a ferroelectric substance. The latter method involves orienting dipoles through polarization treatment in order to impart pressure properties and pyroelectricity, and cannot be used for optical recording.

The former optically utilizes the change in orientation caused by an electric field, but in order to use it for recording, it is necessary to continue applying an electric field, so it is used exclusively for display purposes.

The present inventors have arrived at the present invention as a result of intensive research aimed at utilizing the orientation of dipoles caused by an electric field and the anisotropy of the refractive index associated therewith for optical recording.

If you put something that is optically isotropic when viewed from the viewing direction between crossed polarizers and the light passes through it, you won't see anything, but when you look from the viewing direction, you can put something that is optically anisotropic between crossed polarizers. It is generally known that if the major axis or minor axis of the refractive index ellipsoid does not coincide with the axis of the orthogonal polarizer, part of the light will be transmitted.

It is also generally known that in the case of low molecular weight liquid crystals, molecules are oriented by an electric field and exhibit optical anisotropy.

This phenomenon is used in liquid crystal displays, but in order to use it in displays, it is usually only necessary to be able to control the orientation of a region larger than 0.1 mm x 0.1 mm, which is fine enough to be used for recording. No attempt has been made to control the orientation of this portion, nor has there been any attempt to freeze and fix this orientation.

The orientation and change of dipoles contained in ordinary materials that are not liquid crystals due to electric fields has been studied as a dielectric relaxation phenomenon, but nothing has been studied in relation to optical properties.

Usually, such research uses a film sample and conducts experiments with electrodes attached to both sides of the film, so optical measurements cannot be performed unless the electrodes are removed, and when viewed from the direction perpendicular to the film surface, This is thought to be due to the lack of optical anisotropy.

When trying to utilize the orientation of dipoles caused by an electric field for optical recording, it is not enough to simply orient the dipoles by the electric field and thereby produce optical anisotropy; it is also necessary to be able to record with high density and high speed. is necessary.

(Summary of the Invention) The present invention provides an organic amorphous compound that produces anisotropy in the refractive index by orienting dipoles by an electric field, and in which the orientation relaxation temperature of the group that produces the dipole is 40°C or higher. is used as a recording medium, and after making the recording medium optically isotropic with respect to the reading direction, an electric field is applied to the recording part in a direction at an angle with respect to the reading direction, and the temperature is increased by irradiating light. This optical recording method is characterized by aligning the dipoles in a direction oblique to the reading direction, and then cooling and solidifying the recording unit area. It is possible to record data, and it is also possible to repeatedly record and erase data at high speed.

(Detailed Description of the Invention) The recording material that can be used in the present invention includes a dipole whose direction can be easily changed by an electric field at the recording temperature, and the optical anisotropy caused by the orientation of the dipole is does not relax at least below 40°C, preferably below 50°C;
An organic amorphous compound whose glass transition temperature is 50°C or higher, preferably 60°C or higher is used.

Among such organic amorphous compounds, there are polymer compounds that have polar groups in the main chain or side chains and have a large dipole moment. ) as (・yo aromatic ring, heterocycle, -CN, -
COO)l, (COO)nM (M is a metal element), etc. can be used.

Such materials include various oligomers, polymers, σ
IJ includes polycarbonate, polystyrene, styrene, etc.
Examples include acrylonitrile copolymer and polyacrylonitrile.

Further, even if a substance having a low-molecular dipole that is oriented along with the orientation of the dipole in this wonderful substance is included, it is sufficient if the substance has the above-mentioned temperature characteristics as a whole.

In order to convert light into heat when irradiated with light, a substance that absorbs light at the wavelength used for recording is dissolved in the recording layer at an appropriate concentration, or it is placed in the recording layer to absorb light and generate heat. It is necessary to provide a layer to change the Such a recording layer may be formed on the substrate by coating or the like.

A recording medium is produced by molding these organic amorphous compounds into a disc, tape, or line, or by coating the surface of another base material.

Before recording, the recording medium is processed to become optically isotropic with respect to the reading direction, similar to the erasing operation.

The reading direction means the direction of light irradiated when reading a record, and means the direction of the light beam in FIG. 2.

Therefore, having optical isotropy with respect to the reading direction means that it is optically isotropic when viewed from the direction of the light beam in Figure 1, and the light beam does not exhibit birefringence. do.

To make the recording medium optically isotropic in the reading direction, the dipole orientation can be erased by heating the recording medium to a temperature higher than the orientation relaxation temperature of the polar groups, or the recording medium can be made optically isotropic in the reading direction. This can be done by increasing the temperature while applying an electric field in the same direction as the reading direction and aligning the dipoles in one direction.

The recording medium made isotropic with respect to the reading direction is rapidly cooled and fixed.

For recording, as shown in FIG. 1, electrodes 2a and 2b are provided in a direction having an inclination angle θ with respect to the reading direction of the recording medium 1, and an electric field is applied in a direction inclined with respect to the reading direction. irradiate.

As a result, the temperature of the part irradiated with the light beam T rises to a temperature higher than the orientation relaxation temperature of the polar group in the organic amorphous compound,
The applied electric field orients the dipoles of the organic compound in that direction. If this is then rapidly cooled, the orientation of the dipoles is fixed and the record is preserved.

The inclination angle θ of the electric field is 5° or more, preferably 10° or more.

Further, the temperature of the portion where the dipole is irradiated with the light beam is heated to a temperature higher than the temperature at which the orientation of the polar groups of the organic compound is relaxed in the recording state, preferably higher than the glass transition point of the organic compound.

In order to read the records recorded in this way, as shown in FIG.
By receiving light through the analyzer 4 through b, it is possible to read the record based on changes in the intensity of the transmitted light caused by the presence or absence of dipole orientation or the difference in the direction of orientation, and it is also possible to use reflected light.

The polarization direction of the incident light for reading needs to be shifted by 5 degrees or more from the direction in which the electric field is applied to the recording surface, and most preferably at an angle of 45 degrees. The direction of the polarizer 3b on the analyzer 4 side needs to be orthogonal to this polarization direction. The recording light does not need to be polarized.

When erasing a record, the entire recording medium 1 is heated to a temperature higher than the orientation relaxation temperature of the polar group, or light is applied only to the erased portion to relax the orientation so that the recording medium 1 is optically equidistant in the reading direction. Directional.

It can also be erased by directing the dipoles in the reading direction by exposing them to light and applying a direct rise in the reading direction.

Example Thin films of five types of polymers, polystyrene, styrene-acrylonitrile copolymer, polyacrylonitrile, polycarbonate, and polymethyl methacrylate, were formed on a substrate, and an electric field was applied at an angle of 30 to 60 degrees to the normal to the film surface. The temperature was raised to a temperature between the glass transition temperature (Tg) and Tg-1 to 25°C, and then cooled.

The strength of the applied electric field is 1000 Kv for polystyrene.
/σ, 900 Kv/cm for styrene-acrylonitrile copolymer and polymethyl methacrylate,
1900 KV/crns for polyacrylonitrile
In the case of polycarbonate, it is 880 K'i/an. In this way, the ratio of the brightness of transmitted light between orthogonal polarizers was determined for the part with refractive index anisotropy and the part without anisotropy, and it was 9.5 for polystyrene.
times, 3.8 times for styrene-acrylonitrile copolymer
2.0 times for polyacrylonitrile, dlo for polycarbonate, 2 times, and 1 for polymethyl methacrylate.
．． It was three times as much. Those having a phenyl group or phenylene group in the main chain or side chain are relatively low voltage and have a large light intensity ratio, so they are easy to use, but Ike ones can also be used satisfactorily. The material that has optical anisotropy in this way is
・When we officially raised the temperature to above Tg, we were able to eliminate optical anisotropy only in the heated portion. It was also possible to eliminate optical anisotropy by heating the entire portion that had optical anisotropy. Furthermore, we were able to repeat these steps with good reproducibility.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the method of recording on a recording medium,
The figure is an explanatory diagram showing a reading method. 1: Recording medium 2 / Electrode L reading direction Patent applicant Mitsubishi Yuka Co., Ltd. Agent Patent attorney Hidetoshi Furukawa (+e<'I Tarino Figure 1 Figure 2

Claims (1)

[Claims] The recording medium is an organic amorphous compound that produces anisotropy in the refractive index by orienting the dipoles by an electric field and has an orientation relaxation temperature of 40° C. or higher for the group that produces the dipoles. After making it optically isotropic with respect to the reading direction, the recording section is made to be optically isotropic in the reading direction by applying an electric field in a direction at an angle to the reading direction and irradiating light to raise the temperature. An optical recording method characterized by orienting dipoles in a direction tilted to the opposite direction, and then cooling and solidifying the dipoles.