JP2000098328A - Optical recording medium and optical recording/reading method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make recordable information writably by a digital system with an inexpensive and a safe org. material used as an optical recording layer. SOLUTION: This optical recording medium 1 is provided with an optical recording layer 4 through an intermediate layer 3 on a supporter 2 consisting of glass or quartz. The layer 4 contains an org. low molecular cholesteric liq. crystalline compd. as a main component, which has a different spectrum corresponding to a heating temp. in case cooling rapidly after heating at a temp. of higher than or equal to a liq. crystal phase transfer temp. The information of a fixed reflect spectrum is recorded in each bit by irradiating the optical recording layer 4 with a light beam, and further the information is read by detecting a reflectivity in each recorded bit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly to an optical recording medium capable of digitally recording and reading information in a digital manner using a liquid crystal composition, and optical recording / reading on the medium. About the method.

[0002]

2. Description of the Related Art Conventionally, as an optical recording medium on which information can be rewritten digitally, an optical recording medium using an inorganic material has two needs.
Broadly classified into types. One is a magneto-optical type using the thermomagnetic effect, and the other is a phase change type utilizing a difference in reflectance due to a change in a crystalline-amorphous phase, for example. The phase change type includes, besides the crystalline-amorphous phase change of TeOx,
_{2. A} thin film using a semiconductor-metal phase transition and a styrene oligomer, and a SmS film using a metal-semiconductor phase transition and a change between crystals have been proposed.

However, in recent years, with the widespread use of various information terminal devices, higher-density recording has been demanded for optical recording media, and new recording media, such as those using organic materials, which are different from conventional ones, have been developed. Materials are being considered.

[0004] As an optical recording medium in which the recording layer is made of an organic material, one using an organic dye is known. That is, information is recorded by forming holes (bits) by melting the organic dye layer with heat, developed by Kodak Company. However, an optical recording medium using an organic dye is a write-once type and has a problem that it cannot be freely rewritten. Further, there is no known optical recording medium that can perform high-density recording and can freely set the recording density. Not been.

Accordingly, an object of the present invention is to use an organic material as an optical recording layer and to freely write and erase information.
It is an object of the present invention to provide a new and useful optical recording medium of a digital system in which recording density can be freely set and high-density recording is possible.
It is a further object of the present invention to provide an optical recording / reading method that is optimal for the optical recording medium.

[0006]

In order to achieve the above objects, the optical recording medium according to the present invention has an optical recording layer provided on a support with an intermediate layer interposed therebetween. When the material is heated to a temperature higher than the liquid crystal phase transition temperature and rapidly cooled, the organic low-molecular-weight cholesteric liquid crystalline compound having a different reflection spectrum according to the heating temperature is used as a main component.

In the present invention, the organic low-molecular-weight cholesteric liquid crystalline compound used as an optical recording material is solidified in a state of emitting a predetermined reflected light by heating and rapidly cooling to a predetermined temperature, and information is recorded bit by bit. Is done. Then, information can be read by detecting the reflectance of each recorded bit. Further, the liquid crystal compound is heated to a predetermined temperature or higher and then rapidly cooled / slowly cooled to be in a transparent / scattered state, thereby erasing the record.

As described above, according to the present invention, information can be freely written and erased, and the organic material used is inexpensive and safe. Further, since this kind of organic material emits a reflection spectrum according to the energy (for example, wavelength) of the recording light, not only on / off binary information but also multi-valued and high-density recording can be performed, and The recording density can be freely set. In the optical recording medium according to the present invention, since the liquid crystal compound is used as a digital optical memory, the thickness of the optical recording layer is 0.1 to 10 μm, more preferably 0.1 to 10 μm.
To 7 μm, more preferably 0.2 to 5 μm.

The optical recording layer may contain a plurality of organic low-molecular cholesteric liquid crystal compounds. By using a plurality of types of organic low-molecular-weight cholesteric liquid crystal compounds, it becomes easy to adjust the variable width of the selective reflection wavelength and the temperature control width.

For recording / reading multi-valued information, a plurality of light beams having different energies may be irradiated and recorded, and each reflectance may be read by a plurality of detectors.

Further, in the optical recording medium according to the present invention, the optical recording layer may be formed of a composite film of a low-molecular cholesteric liquid crystal compound and a polymer resin. With such a composite film, the mechanical strength of the optical recording layer is increased, and the medium is more resistant to bending and friction. Further, a protective layer may be provided on the optical recording layer. With this protective layer, the optical recording layer is mechanically or chemically protected from the outside.

The material of the protective layer is not particularly limited as long as it is transparent, and various materials can be used. For example, it can be formed by a known method such as a coating method using a transparent resin or an organic compound material. The thickness of the protective layer can be, for example, 10 nm to 5 μm.

The intermediate layer provided between the optical recording layer and the support may be formed of a resin or the like, and may have a function of bonding the optical recording layer and the support. Further, an intermediate layer may be formed of metal or the like to reflect light incident from the optical recording layer side, or an organic pigment such as a phthalocyanine pigment or an inorganic pigment such as carbon black may be dispersed in a resin or the like. An intermediate layer may be formed to absorb light incident from the optical recording layer side. The intermediate layer can be formed by a vapor deposition method, a coating method, or the like. The thickness of the intermediate layer is 10 nm to 500 nm in the case of vapor deposition, and 100 nm in the case of coating.
About 10 to about 10 μm.

When the liquid crystal exhibits a cholesteric phase, the surface of the support is preferably substantially flat in order to direct the helical axis in a direction perpendicular to the surface of the support, and glass or quartz is used as the material of the support. Are suitable. In this case, the intermediate layer preferably has a smooth surface in contact with the optical recording layer. If the direction of the helical axis of the liquid crystal is well aligned in the direction perpendicular to the surface of the support, high reflectivity can be obtained, and S
/ N ratio increases. Further, it is preferable that the intermediate layer be provided with a light absorbing property or a light reflecting property.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an optical recording medium and an optical recording / reading method according to the present invention will be described below with reference to the accompanying drawings. In each of the embodiments described below, specific substance names are described. However, this is only one example, and the present invention is not limited to these substances. It is possible to use the following materials.

(First Embodiment, see FIG. 1) In FIG. 1, an optical recording medium 1 is composed of a support 2, an intermediate layer 3, and an optical recording layer 4 from below. The support 2 is quartz, and the intermediate layer 3 is formed by vacuum-depositing Au on the support 2 to a thickness of 200 nm. The optical recording layer 4 is a liquid crystal layer containing an organic low-molecular cholesteric liquid crystal compound as a main component. Specifically, a liquid crystalline compound represented by the following chemical structural formula (A) was vacuum-deposited on the intermediate layer 3 to form an optical recording layer 4 having a thickness of about 1 μm.

[0017]

Embedded image

In the optical recording medium 1 having the above configuration, 8
When heated to 7 to 115 ° C., the liquid crystalline compound exhibits a cholesteric phase in which the helical axis is directed perpendicular to the intermediate layer 3 and reflects light having a specific wavelength according to the temperature. About 87
° C, green at about 95 ° C, blue at about 115 ° C,
By quenching from those temperatures, it solidifies in its reflective state. Further, if the mixture is heated to about 119 ° C. or higher and rapidly cooled, it becomes a transparent state, and if it is gradually cooled, it becomes a cloudy scattering state.

(Second Embodiment, see FIG. 2) In FIG. 2, the optical recording medium 1 comprises a support 2, an intermediate layer 3, and an optical recording layer 41 from below. The support 2 and the intermediate layer 3 are made of the same material as in the first embodiment. Optical recording layer 4
Reference numeral 1 denotes a composite film of an organic low-molecular cholesteric liquid crystal compound and a polymer resin, and a liquid crystal composition 41a and a resin film 4
1b.

Specifically, the liquid crystal compound represented by the chemical structural formula (A) is combined with a photopolymerization initiator DAROCUR117.
3 (manufactured by Ciba Geigy) and an aromatic ring-containing bifunctional acrylate R712 (manufactured by Nippon Kayaku Co., Ltd.) to which 3 wt% was added were mixed at a weight ratio of 8: 2 to prepare a liquid crystal composition.
After spin-coating this liquid crystal composition on the intermediate layer 3, 1
By irradiating 5 mW / cm ² ultraviolet rays for 5 minutes,
A composite film (optical recording layer 41) having a thickness of 2 μm was formed.

In the optical recording medium 1 having the above configuration, 9
When heated to 0 to 120 ° C., the liquid crystal compound exhibits a cholesteric phase in which the helical axis is directed perpendicular to the intermediate layer 3 and reflects light having a specific wavelength according to the temperature. About 90
° C, green at about 98 ° C, blue at about 120 ° C,
By quenching from those temperatures, it solidifies in its reflective state. Further, after heating to about 125 ° C. or higher, the material becomes transparent when rapidly cooled, and becomes opaque when slowly cooled.

In FIG. 3, the optical recording medium 1 comprises a support 2, an intermediate layer 3, an optical recording layer 41, and a protective layer 5 from below. Support 2
The intermediate layer 3 is made of the same material as that of the first embodiment.
The optical recording layer 41 is formed by the same material and the same manufacturing method as in the second embodiment. Further, a solution obtained by diluting 100 parts by weight of a urethane acrylate-based ultraviolet curable resin (manufactured by Dainippon Ink and Chemicals, Inc .: Unidick C7-157) with 50 parts by weight of ethyl acetate is applied onto the optical recording layer 41, and 15 mW / c is applied.
By irradiating ultraviolet rays of m ² for 5 minutes, the thickness of 1 μm
Was formed.

In the optical recording medium 1 having the above configuration, 8
When heated to 7 to 115 ° C., the liquid crystalline compound exhibits a cholesteric phase in which the helical axis is directed perpendicular to the intermediate layer 3 and reflects light having a specific wavelength according to the temperature. About 87
° C, green at about 95 ° C, blue at about 115 ° C,
By quenching from those temperatures, it solidifies in its reflective state. Further, after heating to about 119 ° C. or higher, the material becomes transparent when rapidly cooled, and becomes opaque when cooled slowly.

(Fourth Embodiment, see FIG. 4) In FIG. 4, the optical recording medium 1 is composed of a support 2, an intermediate layer 3, an optical recording layer 4, and a protective layer 5 from below. The support 2 is made of quartz, and the intermediate layer 3 is made of a metal-free phthalocyanine pigment.
It is formed by vacuum evaporation on the support 2 to a thickness of 00 nm. For the optical recording layer 4, the liquid crystalline compound represented by the chemical structural formula (A) was vacuum-deposited on the intermediate layer 3 to a thickness of 200 nm. The protective layer 5 is made of parylene having a thickness of 50 nm.
It was formed thereon by a thermal CVD method.

In the optical recording medium 1 having the above configuration, 8
When heated to 7 to 115 ° C., the liquid crystalline compound exhibits a cholesteric phase in which the helical axis is directed perpendicular to the intermediate layer 3 and reflects light having a specific wavelength according to the temperature. About 87
° C, green at about 95 ° C, blue at about 115 ° C,
By quenching from those temperatures, it solidifies in its reflective state. Further, after heating to about 119 ° C. or higher, the material becomes transparent when rapidly cooled, and becomes opaque when cooled slowly.

(Refer to the fifth embodiment, FIG. 4) The optical recording medium 1 of the fifth embodiment has a sectional structure shown in FIG. 4 in structure, and the support 2 is made of glass. As the intermediate layer 3, a copolymerized nylon resin (CM800 manufactured by Toray Industries, Inc.)
An isopropyl alcohol solution in which carbon black was dispersed in 0) was applied on the support 2 and dried to form a 5 μm-thick film.

The optical recording layer 4 is prepared by mixing and dissolving 9 parts by weight of the liquid crystal compound represented by the chemical formula (A) and 1 part by weight of the liquid crystal compound represented by the following chemical formula (B) in 500 parts by weight of toluene. This solution was spin-coated on the intermediate layer 3 and dried by heating to form a film having a thickness of 1 μm. Further, on the optical recording layer 41, a urethane acrylate-based ultraviolet curable resin (Dainippon Ink Chemical Co., Ltd .: Unidick C7-15)
7) A solution obtained by diluting 100 parts by weight with 50 parts by weight of ethyl acetate was applied, and irradiated with 15 mW / cm ² ultraviolet rays for 5 minutes to form a protective layer 5 having a thickness of 1 μm.

[0028]

Embedded image

In the optical recording medium 1 having the above configuration, 5
When heated to 5 to 100 ° C., the liquid crystal compound exhibits a cholesteric phase in which the helical axis is oriented perpendicular to the intermediate layer 3 and reflects light having a specific wavelength according to the temperature. About 55
It shows red at about 80 ° C., green at about 80 ° C. and blue at about 95 ° C., and solidifies in its reflection state by quenching from those temperatures. After heating to about 118 ° C or higher,
It becomes a transparent state when it is rapidly cooled, and it becomes a cloudy scattering state when it is gradually cooled.

(Optical recording / reading device, see FIGS. 5 and 6)
FIG. 5 shows a first example of the optical recording / reading device. This device modulates a semiconductor laser 31 by a drive circuit 33,
The emitted infrared light beam is condensed on the optical recording medium 1 via the collimator lens 32, and information is written bit by bit, on and off. The written information is read by detecting the reflectance from the optical recording layer one bit at a time by a detector 35 composed of a combination of a light emitting element and a light receiving element.

FIG. 6 shows a second example of an optical recording / reading apparatus for recording information in multiple values. This device is blue,
Semiconductor lasers 31b, 3 for writing green and red
1g and 31r are modulated by the drive circuit 33, and the light beams emitted from each of them are collimated by the collimator lenses 32b and 3r.
The light is condensed on the optical recording medium 1 via 2g and 32r, and information is written bit by bit. Each semiconductor laser 31b, 31
g, 31r emit light beams having different energies (wavelengths), and raise the temperature at the focal point to a predetermined value. For example, the portion irradiated by the semiconductor laser 31g is about 95% in the optical recording medium 1 of the first embodiment.
When heated to ° C., it shows a green reflection state with a wavelength of 520 nm, and is solidified in the reflection state by rapid cooling by rotation. In this manner, the written information is transmitted to three detectors 35 each composed of a combination of a light emitting element and a light receiving element.
Reading is performed by detecting the reflectance from the optical recording layer one bit at a time at b, 35g, and 35r.

In any of the devices, the optical recording medium 1 is driven to rotate in one direction, and the writing unit and the detector are moved in the radial direction of the optical recording medium 1 as in a normal magnetic disk or optical disk. Writing and reading are performed.

Further, even in the apparatus shown in FIG. 5, multi-value information can be recorded by controlling the emission energy of one semiconductor laser. However, as shown in FIG. 6, it is easier to control the energy by recording three colors by using three semiconductor lasers. Further, it is also possible to read multi-value information with one detector.

(Performance evaluation, see FIG. 7) Here, the first
Each of the optical recording media obtained in the fifth to fifth embodiments was subjected to a performance evaluation test by a process described below. FIG. 7 is an explanatory view of the test apparatus, and shows the optical recording medium 1 of the first embodiment. E is a light beam light emitting element, R is a light receiving element composed of a photodiode, and S is a slit.
Note that a spectral reflectance can be measured by using a multi-spectrophotometer as the light receiving element. A heated / quenched recording portion 4r is formed in the optical recording layer 4 of the sample.
The reflected light amount of the unrecorded portion 4ur was measured and compared.

Here, the evaluation process will be described. (1) As light beam scanning light sources for recording information,
For the optical recording medium of the third embodiment, the wavelength 1319n
m, a YAG laser with an output of 0.1 kW was used, and a wavelength of 825 nm was used for the optical recording media of the fourth and fifth embodiments.
Using a semiconductor laser having an output of 100 mW, the beam diameter is reduced to 1 μm, and irradiation is performed for about 1 ms to form the recording section 4r.

(2) The reflected light amounts of the recorded portion 4r and the unrecorded portion 4ur are measured. (3) When each optical recording medium is heated to about 50 ° C. by a heater, the YAG laser is used for the first to third embodiments, and the YAG laser is used for the fourth and fifth embodiments. Each of the semiconductor lasers is irradiated with a slightly wider beam diameter to the recording portion 4r, and then rapidly cooled to a transparent state. The irradiation time is about 1 ms. The erasing may be performed by gradually cooling after heating to the liquid crystal phase transition temperature to change to the cloudy scattering state. (4) Recorded part 4r and unrecorded part 4ur after erasing information
Is measured.

In the above process, the output of the recording light beam is converted to a reflection wavelength of green (around 530 nm) or blue (460).
(near nm). The measurement results are shown in Table 1 below.

[0038]

[Table 1]

The numerical values shown in Table 1 are reflected light amount ratios, and the reflected light amounts in the first to third embodiments are the light receiving amount of the unrecorded portion 4ur when the light receiving amount of the light receiving element R of the recording portion 4r is 1. The amount of light received by the element R is expressed as a ratio. 4th, 5th
The reflection light amount ratio of the embodiment is the light receiving element R of the unrecorded portion 4ur.
Is a ratio of the amount of light received by the recording unit 4r when the amount of light received is 1.

(Other Embodiments) The optical recording medium and the optical recording / reading method according to the present invention are not limited to the above embodiments, but can be variously modified within the scope of the invention. In particular, various low-molecular-weight cholesteric liquid crystal compounds constituting the optical recording layer may be used in addition to those shown in the chemical structural formulas (A) and (B).
As a device for recording / reading information, it goes without saying that a device other than those shown in FIGS. 5 and 6 can be used.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing an optical recording medium according to a second embodiment of the present invention.

FIG. 3 is a sectional view showing an optical recording medium according to a third embodiment of the present invention.

FIG. 4 is a sectional view showing an optical recording medium according to fourth and fifth embodiments of the present invention.

FIG. 5 is a schematic perspective view showing a first example of an optical recording / reading device.

FIG. 6 is a schematic perspective view showing a second example of the optical recording / reading device.

FIG. 7 is an explanatory diagram of a performance evaluation test of the optical recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical recording medium 2 ... Base layer 3 ... Intermediate layer 4 ... Optical recording layer 5 ... Protective layer 31 ... Semiconductor laser 35 ... Detector 41 ... Optical recording layer (composite film)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) G11B 7/24 516 B41M 5/26 Y 522 102 (72) Inventor Kiyofumi Hashimoto Azuchi-cho, Chuo-ku, Osaka-shi, Osaka No. 2-313 Osaka International Building Minolta Co., Ltd. F-term (reference) 2H088 EA62 GA03 HA24 HA28 MA20 2H111 EA04 EA12 EA23 EA31 EA32 EA43 FA01 FA11 FA12 FA14 FA15 FA16 FB50 FB59 GA02 5D029 JA04 JB11 JB15 CC09 A09 DD02 FF11 KK03 KK06 KK12 KK14

Claims (12)

[Claims] 1. A support, an optical recording layer mainly composed of an organic low-molecular-weight cholesteric liquid crystalline compound having a different reflection spectrum according to the heating temperature when heated to a temperature higher than the liquid crystal phase transition temperature and rapidly cooled; And an intermediate layer provided between the optical recording layer and the optical recording layer. 2. The optical recording medium according to claim 1, wherein the optical recording layer comprises a composite film of an organic low-molecular cholesteric liquid crystal compound and a polymer resin. 3. The optical recording medium according to claim 1, wherein a protective layer is provided on the optical recording layer. 4. The optical recording medium according to claim 1, wherein an intermediate layer having a smooth surface in contact with the optical recording layer is provided between the support and the optical recording layer. The optical recording medium according to the above. 5. The optical recording layer has a thickness of 0.1 to 10 μm.
Claim 1, Claim 2, Claim 3 characterized by the following.
Or the optical recording medium according to claim 4. 6. The optical recording medium according to claim 1, wherein said optical recording layer has a thickness of 0.1 to 7 μm. 7. The optical recording layer contains a plurality of organic low-molecular-weight cholesteric liquid crystal compounds in the optical recording layer. Optical recording medium. 8. The optical recording layer according to claim 1, wherein the optical recording layer is formed by evaporating an organic low-molecular cholesteric liquid crystal compound. The optical recording medium according to claim 5, 6, or 7. 9. An optical recording medium according to claim 1, wherein said optical recording medium is irradiated with a light beam to record information of a predetermined reflection spectrum for each bit and to detect a reflectance of each recorded bit. An optical recording / reading method characterized by reading information by reading. 10. The optical recording / reading method according to claim 9, wherein the recorded information is erased by heating the optical recording layer above a liquid crystal phase transition temperature. 11. The optical recording / reading method according to claim 9, wherein information is recorded by irradiating a plurality of light beams having different energies. 12. The optical recording / reading method according to claim 11, wherein the detection of the reflectance is performed by a plurality of detectors.