JPH052134B2 - - Google Patents

Description

Detailed Description of the Invention 3-1 Field of Industrial Application The present invention relates to an optical recording medium, and more particularly, to an optical recording medium on which information is recorded by applying an optical external field.

3-2 Prior Art Optical recording media that utilize changes in optical properties include:
Generally, the following properties are required. (i) The energy required for recording is small and it can be done at high speed; (ii)
(ii) high optical contrast between recorded and unrecorded areas; (iv) rewritable; (v) stable medium that can withstand long-term storage and use; (vi) ) No toxicity or danger, etc.

Optical recording media that have been considered so far include the following. (i) thin films of low melting point metals such as Te and Se and their alloys; (ii) thin films of metal compounds such as TeOx; (iii) thin films of organic materials such as dyes and pigments such as fluorescein and cyanine; and (iv) thin films of photochromic compounds.

In the organic system, many proposals have been made, including a heat mode type using an organic dye and a photon mode type using a photochromic compound. However, this method has drawbacks such as insufficient sensitivity, low contrast, and difficulty in improving the S/N ratio, and lack of stability after recording, so that it is not practically satisfactory. Many proposals have been made for non-organic systems, among which Te
Practical use of write-once optical disk memories using Te-based compounds such as -C and TeOx has begun. Furthermore, recently there has been active development of rewritable optical disk memories that utilize the phase transition between crystalline and amorphous TeOx.

However, for example, when using the phase transition between crystal and amorphous TeOx, the reflectance of the unrecorded area is approximately 15
~20%, and the recording section is about 30-40%. The difference is about 15 to 20%, which is not sufficient. Furthermore, when utilizing such a phase transition, there is a limit to the speed-up of recording. Furthermore, there are problems with the toxicity of Te-based media, and it is desirable to make them less toxic and non-toxic.

In the future, we will develop media with dramatically improved properties (i) to (v) above, and aim to reduce the error rate by increasing capacity, speeding up recording, and essentially improving the S/N ratio. A reduction is strongly desired.

3-3 Purpose It is an object of the present invention to provide an organic optical recording medium in which information is recorded at high speed and with high density by applying an optical external field, and the optical contrast between the recorded portion and the unrecorded portion is large. In the present invention, optical recording is a general term for reading recorded information optically. Therefore, an optical recording medium means a medium recorded in an optically readable state.

3-4 Specific Description of the Invention As a result of intensive technical studies, the present inventors discovered that information can be recorded by utilizing changes in the main chain structure of polydiacetylene due to the application of an optical external field. This led to an invention. The main chain structure of polydiacetylene as used in the present invention has A-type bonds and B-type bonds, and it is presumed that the A-type bonds are acetylene bonds and the B-type bonds are butatriene-type bonds (see Figure 1).
Each type has planar and non-planar configurations.

It is presumed that the present invention mainly involves structural changes between A-type bonds and B-type bonds, and that optical recording occurs when planar and non-planar structures are added to this.

Note that this optical recording medium can be used not only for reading, but also for write-once type and rewritable type.

Below, first, polydiacetylene, second, polydiacetylene thin film, third, changes in main chain structure, fourth, absorption spectrum and reflection spectrum, fifth, external field application, and sixth, recording/reproduction/erasing. Explain.

3-4-1 Polydiacetylene The polydiacetylene used in the present invention is a polymer of diacetylene monomers, and can cause a change in the main chain structure between A-type bonds and B-type bonds by applying an external field. If so, it is not particularly limited. However, diacetylene monomer is a general term for compounds having a conjugated diacetylene bond, and includes various derivatives thereof.

Preferred polydiacetylenes include acids such as carboxylic acid and sulfonic acid, and their esters, amides, and salts; alcohols and their esters such as carboxylic acid, sulfonic acid, isocyanic acid, and carbamic acid in the side chain. It is a polymer of diacetylene monomer. For example, a polymer of diacetylene monomers having the general formula shown below can be used.

CH ₃ (CH ₂ ) _n-1 −C≡C−C≡C−(CH ₂ )
nCOOH RNHOCO(CH ₂ ) _n −C≡C−C≡C−(CH ₂ )
nOCONHR RSO ₃ O(OH ₂ ) _n −C≡C−C≡C−(CH ₂ )
nOSO ₂ R (The substituent R is not particularly limited.) The polydiacetylene used in the present invention may optionally be a copolymer of two or more diacetylene monomers,
Alternatively, it may be a mixture of two or more types of polydiacetylenes. Furthermore, it may be a mixture of polydiacetylene and a low molecular weight or high molecular weight organic substance.

3-4-2 Polydiacetylene thin film The polydiacetylene thin film used in the present invention is formed by the following method. First, a thin film of diacetylene monomer is formed on a substrate by vacuum evaporation, solution coating, or the like, and then polymerized using heat, light, gamma rays, or the like. The film thickness is not particularly limited, but is usually 100 Å to 10 μm.
It is.

〔substrate〕

As the substrate, it is preferable to use one having transparency suitable for the light wave characteristics of the desired light source in order to improve sensitivity. At this time, a transmittance of approximately 90% or more of incident light can be used as a rough standard for transparency. Such substrates include inorganic materials such as glass, polyester, polypropylene, polycarbonate,
Examples include a disc, tape, film, or sheet made of organic materials such as polymers such as polyvinyl chloride, polyamide, polystyrene, and polymethyl methacrylate, or modified polymers, copolymers, and blends thereof.
On the other hand, when recording information by entering information recording light from the opposite side of the substrate, in addition to the above-mentioned transparent substrate, a disc-shaped disk made of an inorganic or organic material to which pigments, dyes, pigments, reinforcing agents, etc. are added, A tape, film, or sheet shape, or a metal plate such as an aluminum alloy can be used as the substrate.

[Vacuum evaporation method]

Vacuum deposition is performed in accordance with a general method as follows. Diacetylene monomer is evaporated by direct heating in a coil or boat made of W, Mo, Ta, etc., or by indirect heating in a crucible made of quartz, alumina, beryllia, etc. At this time, resistance heating, high frequency heating, or the like is used as a heating method to heat the diacetylene monomer to a temperature selected depending on its characteristics, usually above its melting point. Also the pressure is usually 10 ^-3 torr
The following shall apply.

[Coating method]

Spray method from a solution of diacetylene monomer,
Apply to the substrate using a spinner method or the like. The solvent and concentration used at this time are not particularly limited. Considering the uniformity of the thin film, it is desirable to use a solvent with high solubility; typical examples include acetone, ketones such as methyl ethyl ketone, chloroform, halogen compounds such as methylene chloride, esters such as ethyl acetate, dimethylacetamide, Amides such as dimethylformamide and N-methyl-2-pyrrolidone, and nitrites such as acetonitrile.

It is possible to apply known techniques for providing a protective layer on the polydiacetylene thin film of the present invention or bonding two films together.

3-4-3 Changes in main chain structure The main chain structure of polydiacetylene has A-type bonds and B-type bonds.
There are bond structures such as type bonds (Fig. 1), and corresponding to these, the existence of planar and non-planar configurations is presumed. Alternatively, these main chain structures are sometimes called blue type, red type, or yellow type. These main chain structures are fixed by absorption spectra, reflection spectra, resonance Raman spectra, X-ray diffraction, etc. (Gregory
J. Exarhosetal, JACS, 98 481 (1976)).

Conventionally, changes between A-type and B-type bonds have been described using TCDU (poly(5,7-dodecadiyne-1,
12-diol-bis phenyl urethane) single crystal is induced by stress and changes from B-type bond to A-type bond (H.Muller et al., Mol.
Cryst.Liq.Cryst., 45, 313 (1978)), ETCD (poly(5,7-dodecadiine-1,12-diol bis ethyl urethane) single crystal (side chain = -
(CH ₂ ) ₄ -OCONH-C ₂ H ₅ ) has an A-type bond at about 70°C or below, a B-type bond at about 120°C or above, and exhibits thermochronism with hysteresis at an intermediate temperature ( RRChance et al., J. Chem.
Phys., 67, 3616 (1977)).

The present invention provides an optical recording medium in which information is recorded by locally applying an external optical field to a polydiacetylene thin film to cause a change in the main chain structure, for example, a change between A-type bonds and B-type bonds. Related.

In the present invention, the degree of change in the main chain structure can also be changed by controlling the applied external field. For example, the degree of change between the A-type bond and the B-type bond can be changed by controlling the irradiated optical energy. (Figures 6 and 7) If this control method is used, in addition to the usual one-dimensional recording in which A-type bonds and B-type bonds correspond to "0" and "1" within one bit, Multidimensional recording is also possible. For example, multidimensional recording is also possible in which n+2 bond states of A-type bonds, A-B-type mixed bonds (n pieces), and B-type bonds are made to correspond to "n+2 arrays." When n=2, it can be expressed in quaternary notation using an A type bond, an A-B type mixed bond (1), an A-B type mixed bond (2), and a B type bond.

Note that rewriting can also be performed using multidimensionality. For example, in the case of n=2 above, binary recording is performed by assigning the A type bond and A-B type mixed bond (1) to "0" and "1", and the rewriting is performed using the A type bond and the A-B type mixed bond (1). After setting -B type mixed coupling (1) or A-B type mixed coupling (2), writing can be performed again with A-B type mixed coupling (2) or B type coupling.

The recording mechanism will be explained by taking as an example the change between the A-type bond and the B-type bond of polydiacetylene.

The potential energy curve for the A-type bond and B-type bond of polydiacetylene can be assumed as shown in FIG. 2A. Curve g in the figure represents the ground state, curves a and b represent the electronic excited state, ΔEa and ΔEb represent the excitation energy from g→a and g→b, respectively, and ΔE _A
^* and ΔE _B ^* represent the activation energy of the change from A→B and B→A, respectively.

Stable at operating temperature (refers to the temperature of the optical recording medium when storing and reproducing records. The temperature of the energy irradiated area where the change between A-type bond and B-type bond occurs is generally higher than the operating temperature). When polydiacetylene having an A-type bond is irradiated with light having an energy of ΔEb, it is excited from the g state to the b state. B-type coupling in the b state is reached while vibrationally relaxing along the curve b. Next, it returns to the g state again and completes the change to a stable B-type bond (dashed line) at the operating temperature.
Furthermore, by applying an optical external field, the stable and metastable states of the A-type bond and B-type bond are switched through local strain, thereby changing to the B-type bond. Such a process can be used for recording.

Furthermore, if a recording section having stable B-type bonds at the operating temperature is irradiated with light having an energy of ΔEa, g
state is excited to the a state. The A-type bond in the a-state is reached while vibrationally relaxing along the curve a. Next, it returns to the g state again and completes the change to a stable A-type bond (solid line) at the operating temperature. Alternatively, when it is irradiated with thermal energy of ΔE _B ^* or more, or when it is cooled, it changes to an A-type bond (dashed line) along the curve g. Furthermore, by applying an optical external field, the stable and metastable bonds of the B-type bond and the A-type bond are exchanged through local strain, thereby changing to the A-type bond. Such a process can be used to erase records.

In the present invention, when electronically excited state b is used, recording is possible at a much higher speed than when using amorphous/intercrystalline transition.

The present invention is not limited to FIG. 2A. For example, even if the magnitude relationship between the potential energy curves of type A and type B is A>B and A=B, the same explanation can be given by replacing A and B in the above explanation.

3-4-4 Absorption spectrum/reflection spectrum The spectra of A-type bonds and B-type bonds of polydiacetylene in the ultraviolet to near-infrared region have peaks around 638 nm and 535 nm, respectively. The difference is large, about 103 nm, and the overlap between spectra is small. Therefore, A-type bond and B
Changes in optical contrast (absorption coefficient, reflectance) due to changes in type bonding are also extremely large, which is extremely advantageous for improving the S/N ratio in recording and reproduction. The same applies to the reflection spectrum.

Absorption spectra and reflection spectra related to other main chain structures can be similarly measured.

3-4-5 External field application When using optical energy, the wavelength of light for recording needs to provide energy of ΔE _A ^* or more. Preferably, irradiation of 1×10 ⁻¹³ joule/μm ² or more is performed using light with a wavelength of 180 nm to 12 μm.

For reproduction, light in a wavelength range above the short wavelength end of the B-type coupled spectrum and below the long wavelength end of the A-type coupled spectrum is used.
Preferably, it is light in a wavelength range of 350 nm or more and 700 nm or less.

As the erasing light source, light having energy ΔEa shown in FIG. 2A can be used.

Specific light sources include Ar laser, He-Ne
Lasers with oscillation wavelengths in the ultraviolet, visible, and infrared regions, such as lasers, He-Cd lasers, dye lasers, and semiconductor lasers, and various short pulse generating lamps such as xenon flash lamps can be used.

3-4-6 Recording/Reproducing/Erasing Optical information recording/reproducing devices are well known.

Recording is usually performed by modulating and imparting the intensity of light in accordance with the information signal. It is recorded as changes in the optical characteristics of the irradiated area, such as reflectance and absorption coefficient. Light is irradiated on the surface side of the polydiacetylene thin film,
Alternatively, it is possible to do so from either side of the thin film through a transparent substrate.

Reproduction is performed by reflective optical signal reproduction that reads changes in reflectance. It is also possible to perform reproduction by providing a reflective film on the thin film side opposite to the reading side and reading changes in the amount of light from this reflective film. This change in light amount is based on a change in the absorption coefficient (optical density) of the thin film.

Erasing is performed by applying an optical, thermal or mechanical external field. For example, this is performed by light irradiation or temperature change (cooling) of the entire thin film. Light irradiation can be performed either from the front side of the thin film or from the back side through a transparent substrate.

Next, the present invention will be explained with reference to Examples.

3-4-7 Examples Example 1 As a diacetylene monomer, 10,12-diinpentacosacic acid [CH ₃ -(CH ₂ ) ₁₁ -C≡C-C≡C
−(CH ₂ ) ₈ −COOH] was used. A deposited film was produced using a vacuum evaporation apparatus as follows. Approximately 50 mg of diacetylene monomer was placed in a molybdenum boat 2x
It was heated to 80° C. under a vacuum of 10 ^-5 torr and deposited on a 25 mm x 25 mm quartz glass to produce a diacetylene monomer vapor deposited film with a thickness of 1.0 μm.

This vapor-deposited film was irradiated with ultraviolet light (240 to 240 nm) obtained using a high-pressure mercury lamp and a bandpass filter (UV-D33S) at 20 mW/cm ² for 30 minutes.
The monomer was polymerized to form a blue polydiacetylene film. The absorption spectrum and resonance Raman spectrum of this polydiacetylene are shown by line a in FIG. From the spectrum, this polydiacetylene is A
It was a type combination.

The polydiacetylene thin film was then further irradiated with ultraviolet light (240-240 nm). The polydiacetylene irradiated with energy of 3×10 ⁻⁶ Joule/μm ² changed to a B-type bond as shown by line b in FIG. 3. It was found that the change from A-type bond to B-type bond depends on irradiation energy. 7.0×
Change starts from 10 ^-7 Joule/μm ² , 2.6×
It was finished at 10 ^-6 Joule/μm ² (Figure 6). The change in optical density at this time is 1.1 to 0.2 at 640 nm,
It was 0.6 to 1.1 at 552 nm.

When polydiacetylene was scanned and irradiated with a beam of ultraviolet light (240 to 400 nm) with a diameter of 1.0 μm, a clear pattern with a width of approximately 1.0 μm was formed.

Example 2 In the same manner as in Example 1, 10,12-diimpentacosaic acid [CH ₃ -(CH ₂ ) ₁₁ -C≡C-C≡C-
( _CH2 ) ₈ -COOH] was polymerized to form a polydiacetylene thin film. As shown by line a in FIG. 4, this polydiacetylene was A type bond. It was also confirmed that hysteresis was exhibited. However, the temperature was raised and cooled at a rate of 1.0°C/min (Figure 7).

The polydiacetylene thin film was irradiated with Ar laser light (488 nm). Polydiacetylene irradiated with 1×10 ^-6 W/μm ² had a change from A-type bond to B-type bond, as shown by line b in FIG. The change in optical density at this time was 0.52. When a polydiacetylene thin film was scanned and irradiated with an Ar laser beam (5145 Å) with a diameter of 1.0 μm, a clear pattern was formed in which a region approximately 1.0 μm wide was converted into B-type bonds.

3-5 Effects of invention The effects of the present invention are as follows.

(i) Can write (record) at high speed.

(ii) can be recorded in two or multiple dimensions with high density;

Records can be stored stably at room temperature.

(ii) The optical contrast between recorded and unrecorded areas is large.

(iv) Can be rewritten.

(v) Non-toxic.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing an acetylene type bond and a butatriene type bond, Figure 2 is an explanatory diagram showing a potential energy curve and a hysteresis curve, and Figure 3 is an explanatory diagram showing a potential energy curve and a hysteresis curve.
Figure 4 is a light absorption spectrum diagram of the present invention obtained in Example 1 and Example 2, respectively, and Figure 5 is a diagram of the light absorption spectrum of the present invention obtained in Example 1.
Fig. 6 is a graph showing the change from type A to type B due to irradiation energy, and Fig. 7 is a graph showing the change from type A to type B due to heating and its change. It is a graph showing hysteresis.

Claims (1)

[Claims] 1 Forming a diacetylene monomer thin layer on a substrate by vapor deposition or solution coating, and locally applying optical power to the polymerized polydiacetylene thin film to cause local changes in the main chain structure of polydiacetylene. An optical recording medium that records information.