JPH0462275B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to recording information using external energy such as optical energy or thermal energy, and reproducing information using optical changes in the recorded portion. Regarding optical recording media that can be used.

[Conventional technology]

Optical recording media have the characteristic that the recording medium does not wear out or deteriorate because there is no contact between the medium and the writing or reading head.

Furthermore, high-density recording becomes possible by recording using a focused light beam such as a laser beam.
It also has characteristics such as being able to write and read information at high speed and short access time.

Furthermore, recording on such a recording medium can be performed by converting the information to be recorded into an electrical time-series signal and scanning the recording medium with a laser beam whose intensity is modulated according to the signal. This has the advantage that recorded images can be obtained in real time.

Optical recording media having such characteristics include:
MnBi-based polycrystalline materials, Gd-Co, Gd-Tb-Fe
There are magneto-optical recording media using rare earth-transition metal-based amorphous alloys such as . This uses both laser heating and an externally applied magnetic field to record data, and reproduces data by using the difference in the rotational direction of the light vibration plane depending on the direction of magnetization. In particular, perpendicular magneto-optical recording in which magnetization is perpendicular to the optical recording medium allows high-density recording. However, this magneto-optical recording medium
The disadvantage is that the sensitivity during reproduction is poor and the S/N ratio is very poor. Therefore, this poses a major problem in practical use because reading errors are likely to occur.

In addition, Te, Bi, As-Te-
There is a recording medium in which a thin metal film such as Se is irradiated with focused laser light, and the irradiated area is locally evaporated to form pits. For reproduction, the presence or absence of pits is read out using reflected light.

However, this recording medium has problems such as the need for a high power laser beam to record information, and the difficulty in controlling the shape of the pits, which tends to increase the noise level.

Furthermore, optical recording media that utilize the transition from amorphous to crystalline Te-TeO thin film, Se-S
Some methods utilize the photo-blackening phenomenon based on structural changes between metastable states within the amorphous phase of thin films.

However, Te-based media have problems regarding toxicity;
The problem is that the contrast between the recorded area and the unrecorded area is not sufficient. Se-S thin film is
The recording sensitivity is low, and furthermore, the light absorption edge is a relatively short wavelength, and the absorption is small at wavelengths near the absorption edge, and the recording sensitivity for long wavelength light is particularly poor.

Under these circumstances, there is a strong desire to further improve recording sensitivity, increase recording density, improve S/N ratio by increasing optical contrast between recorded and unrecorded areas, and make recording media non-toxic. .

[Problem that the invention seeks to solve]

The present inventors have proposed an optical recording medium that is recorded using external energy such as light or heat and reproduced using optical changes in the recorded portion, which does not have the above-mentioned drawbacks, that is, is non-toxic. We have conducted extensive research to provide an optical recording medium that has good recording sensitivity, high optical contrast between recorded and unrecorded areas, and can record information at high density.

[Means for solving problems]

As a result, it was discovered that an optical recording medium having an optical recording layer made of the following polymer could solve the above problems, and the present invention was achieved.

That is, the present invention relates to an addition polymer (hereinafter referred to as "aromatic vinylene sulfide polymer") of a diethynylbenzene derivative and a benzenedithiol derivative, which has a group represented by the following structural formula () as a repeating unit.
It is abbreviated as ) is used as an optical recording layer.

[R ¹ , R ² , R ³ , and R ⁴ each represent a group selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, and halogen. ] The present invention will be explained in detail below.

(1) Structure and manufacture of optical recording medium The optical recording medium of the present invention is a molded article of an aromatic vinylene sulfide polymer, generally a thin film-like article, preferably a substrate made of an aromatic vinylene sulfide polymer. It is used by forming a thin film.

The substrate used in the present invention may be a transparent plastic substrate such as polymethyl methacrylate or polycarbonate, or a transparent inorganic material substrate such as glass.

The above-mentioned aromatic vinylene sulfide polymer used as an optical recording layer on the substrate can be synthesized by addition polymerization of compounds having structures shown in the following structural formulas () and ().

[R ¹ , R ² , R ³ , and R ⁴ each represent a group selected from hydrogen, an alkyl group having 1 to 12 carbon atoms, and a halogen. ] Examples of compounds represented by the structural formula () are:
p-diethynylbenzene, diethynyltoluene,
Examples include diethynylethylbenzene.

Examples of compounds represented by the structural formula () are:
Examples include p-benzenedithiol, 2-chloro-p-benzenedithiol, and toluene-2,5-dithiol.

As a means of reaction, compounds () and ()
It is preferable to obtain the polymer by irradiating the mixture with actinic rays.

Active rays refer to visible rays, ultraviolet rays, electromagnetic waves such as γ rays, X-rays, electron beams, neutron rays, and the like.

It can also be obtained by adding a radical generator such as benzoyl peroxide to a mixture of compounds () and (). Furthermore, it is also possible to carry out the polymerization in the presence of a trace amount of oxygen.

When forming an aromatic vinylene sulfide polymer thin film on a substrate to obtain the present recording medium, compounds () and () are simultaneously sublimated and vapor-deposited on the substrate,
This can be polymerized by irradiating actinic rays.

Alternatively, a solution of a mixture of compounds () and () is applied onto a substrate by a spin coating method, a blade coating method, a dip method, a casting method, etc., and then dried, and then irradiated with actinic rays to polymerize. It can also be obtained by

Compounds () and () are simultaneously sublimated and vapor-deposited to form a mixed vapor-deposited monomer crystal thin film of compounds () and (), and then irradiated with active light to obtain an aromatic vinylene sulfide polymer crystal thin film. The reason is that when a crystalline thin film of aromatic vinylene sulfide polymer is used as an optical recording layer before recording,
This is a useful thin film formation method.

The thickness of the aromatic vinylene sulfide polymer thin film constituting the optical recording layer is not particularly limited, but is usually 10 to 100 μm.

Further, the above-mentioned aromatic vinylene sulfide polymer used as the optical recording layer of the present invention generally has a number average molecular weight of 300 to 500,000.

The optical recording medium of the present invention is characterized in that it has an addition polymer (aromatic vinylene sulfide polymer) of a diethynylbenzene derivative and a benzenedithiol derivative having the above-mentioned formula () as a repeating unit as a recording layer, Although the structure is not particularly limited, examples of commonly used optical recording media are shown in FIGS. 1a, b, and c.

In the figure a, 1 is a substrate, and 2 is an optical recording layer made of the above-mentioned aromatic vinylene sulfide polymer.

In the figure b, a protective film 3 made of a transparent inorganic material or a resin such as acrylic is provided on the upper surface of the upper recording layer 2 of the recording medium shown in a.

The recording medium shown in c in the figure has a substrate 1 provided on the lower surface of the recording layer 2 via a reflective film 4 made of aluminum, silver, etc., and a protective film 3 formed on the upper surface of the recording layer 2.

(2) Recording method The present inventors discovered that the above-mentioned aromatic vinylene sulfide polymer undergoes a phase transition between crystalline and amorphous by applying external energy such as light energy or thermal energy. did. The optical recording medium of the present invention uses this aromatic vinylene sulfide polymer as an optical recording layer and records information by inducing a phase transition between crystal and amorphous in the optical recording layer by applying external energy.

It is confirmed by X-ray diffraction data that a phase transition between a crystalline phase and an amorphous phase is induced by applying external energy to the aromatic vinylene sulfide polymer thin film used as the optical recording layer. . In other words, as seen in the diffraction diagram of the crystalline phase in Figure 2 and the diffraction diagram of the amorphous phase in Figure 3, the crystalline phase has sharp crystal peaks, whereas the amorphous phase has such sharp crystal peaks. does not have.

For example, in the above equation (), R ¹ = R ² = R ³ = R ⁴ =
The crystal phase of the aromatic vinylene sulfide polymer that is H has a sharp maximum diffraction peak at 2θ = 14 ~ 15°,
Further, in contrast to crystalline peaks at 2θ=28-29°, 42-44°, and 58-60°, the amorphous phase does not have such sharp crystalline peaks at all.

When an extremely thin aromatic vinylene sulfide polymer thin film of, for example, 0.1 μm or less is used as the optical recording layer, the crystal peak of the crystal phase may not be confirmed in X-ray diffraction. However, even in such a case, as long as the crystalline phase and the amorphous phase can be distinguished from each other in the light absorption or light reflectance of the aromatic vinylene sulfide polymer thin film, it can be used as an optical recording layer.

The phase transition between a crystalline phase and an amorphous phase induced by external energy in the aromatic vinylene sulfide polymer used as the optical recording layer is confirmed by the light absorption rate or light reflectance of both.

For example, in the above equation (), R ¹ = R ² = R ³ = R ⁴ = H
The crystalline and amorphous phases of the aromatic vinylene sulfide polymer can be clearly distinguished in the light reflectance or light absorption in the 300-800 nm region.

The terms "crystalline phase" and "amorphous phase" refer to the presence or absence of a crystalline peak in X-ray diffraction.
Furthermore, it is said to represent two phases with different molecular arrangements that can be identified in the light absorption spectrum or light reflection spectrum (a phase with a highly regular molecular arrangement is a crystalline phase, and a phase with a low regularity of molecular arrangement is an amorphous phase). It is also used in a broader sense.

As the external energy used for recording in the present invention, optical energy, thermal energy, electrical energy, mechanical energy, etc. can be used. Among them, optical energy is preferable in the sense that the energy to be applied can be locally narrowed and high-density recording is possible. When using optical energy, it is possible to select between recording using the photon effect of light and recording using heat mode.

When using the photon effect, the wavelength of the light used needs to match the wavelength at which phase transition is induced, but when using the heat mode, there is no need to limit it in particular.

As light sources for applying optical energy, lasers such as various semiconductor lasers, gas lasers, and dye lasers having oscillation wavelengths in the ultraviolet to visible to infrared regions, and various pulse generation lamps such as xenon flash lamps are used.

The optical recording medium of the present invention can exhibit high recording sensitivity by using the aromatic vinylene sulfide polymer represented by the above formula () as the optical recording layer.

For example, in the above equation (), R ¹ = R ² = R ³ = R ⁴ =
The activation energy for the phase transition from the crystalline phase to the amorphous phase due to thermal energy of the aromatic vinylene sulfide polymer, which is H, is estimated to be the following value, and the phase transition from the crystalline phase to the amorphous phase can be achieved with extremely high sensitivity. metastasize.

6.9Kcal/mol (crystalline peak 2θ=14°d=
Taking the diffraction intensity of 7.7〓 as 100, its relative intensity is
34.3 Kcal/mol (activation energy for phase transition in the region where the relative intensity is 90 to 20) 38.9 Kcal/mol (activation energy for phase transition in the region where the above relative intensity is 40 to 0) (activation energy for phase transition in the region) The crystalline phase of the aromatic vinylene sulfide polymer represented by the above formula () is used as the optical recording layer before recording, and external energy is applied to this to create an amorphous state. This method uses an amorphous phase of an aromatic vinylene sulfide polymer expressed by the above formula () as an optical recording layer before recording, and applies external energy to it. There is a method for recording by inducing a phase transition to a crystalline phase by applying external energy, and an amorphous phase of an aromatic vinylene sulfide polymer represented by the above formula () is used as the optical recording layer before recording, and external energy is applied to this. There are two methods of recording: one in which a phase transition to a crystalline phase is induced by applying an electric current, and the other is recording.

Either method is selected depending on the type of aromatic vinylene sulfide polymer represented by the above formula () used as the optical recording layer.

For example, in the above equation (), R ¹ = R ² = R ³ = R ⁴ =
When a H aromatic vinylene sulfide polymer thin film is used as an optical recording layer, the former recording method is usually used for recording.

As described above, the optical recording medium of the present invention uses an aromatic vinylene sulfide polymer thin film for the optical recording layer, and focuses external energy modulated by information, particularly preferably optical energy, onto the optical recording layer. In contrast, information is recorded by inducing phase transition between a crystalline phase and an amorphous phase in an optical recording layer.

In recording information, within one pit,
For example, normal one-dimensional recording in which the crystalline phase and the amorphous phase correspond to 0 and 1 is possible.

Furthermore, intermediate states having various degrees of crystallinity can be set between the above-mentioned crystalline phase and amorphous phase by controlling the degree of external energy such as externally applied optical energy.

For example, in the equation () above, R ¹ = R ² = R ³ = R ⁴ =
An aromatic vinylene sulfide polymer crystal of H is used as an optical recording layer, and ultraviolet light (240~
Figure 4 shows the relationship between the irradiation time and the relative ratio of the diffraction intensity of the crystal peak when irradiating the crystal with a wavelength of 400 nm.

In this way, n intermediate states are set between the reference crystalline layer and the amorphous phase with a degree of crystallinity between the two, and (n+2) arrangements are made to correspond to these intermediate states. Recording is also possible.

Furthermore, aromatic vinylene sulfide polymers having different substituents (R ¹ , R ² , R ³ , R ⁴ ), molecular weights, etc. in the aromatic vinylene sulfide polymer represented by the above formula () By stacking several layers together and recording by selectively inducing a phase transition between the crystalline phase and the amorphous phase of each layer, it is possible to record even more information.

In this way, the optical recording medium of the present invention is capable of recording information at a higher density than ever before.

(3) Reproduction of recording Recorded information is reproduced by utilizing the difference in optical properties between the crystalline phase and the amorphous phase of the aromatic vinylene sulfide polymer thin film used as the optical recording layer.

Normally, reproduction is performed by utilizing the difference in light reflectance or light absorption coefficient between the crystalline phase and the amorphous phase of the aromatic vinylene sulfide polymer thin film.

That is, the optical recording layer on which information is recorded is irradiated with light, and the information is read based on the intensity of the light reflected by the optical recording layer. Information is reproduced by utilizing the difference in light reflectance between recorded and unrecorded areas of the optical recording layer.

Alternatively, the optical recording layer on which information is recorded is irradiated with light, and the information is read based on the intensity of the light absorbed by the optical recording layer. That is, information is reproduced by utilizing the difference in light absorption coefficient between the recorded portion and the unrecorded portion of the optical recording layer.

At this time, the greater the difference in light reflectance or light absorption coefficient between the recorded portion and the unrecorded portion, the greater the S/N ratio during reproduction can be achieved.

The optical recording medium of the present invention can achieve a high S/N ratio during reproduction by selecting an aromatic vinylene sulfide polymer for the optical recording layer.

For example, in the above equation (), R ¹ = R ² = R ³ = R ⁴ =
When an aromatic vinylene sulfide polymer crystal thin film of H is used as an optical recording layer, the optical reflectance of the crystal phase of the optical recording layer is, for example, 50 nm for light with a wavelength of 560 nm.
%, whereas the crystal phase has light energy,
The optical reflectance of the amorphous phase, which undergoes a phase transition by applying external energy such as thermal energy, to light with a wavelength of 560 nm is approximately 70%, and this difference in optical reflectance is used to reproduce recorded information. be able to.

In other words, it is possible to obtain a large S/N ratio when reproducing information, and to suppress read errors to a low level.For reproducing records, crystals of an aromatic vinylene sulfide polymer thin film used as an optical recording layer are used. It is possible to use light having a wavelength that is above the short wavelength end of the light absorption (reflection) spectrum of the phase or amorphous phase and below the long wavelength end of the spectrum.

〔Example〕

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

Example 1 Using a vacuum evaporation apparatus, 0.134 g of an equimolar mixture of p-benzenedithiol and p-diethynylbenzene powder crystals was placed in a boat, and the evaporation chamber was brought to a vacuum of 0.5 Torr by evacuation. 60 more evaporation sources
C. and sublimed for 30 seconds to form a crystalline thin film of a mixed vapor-deposited monomer of p-benzenedithiol and p-diethynylbenzene on the quartz glass substrate. The crystalline thin film of this mixed vapor-deposited monomer was maintained at 60°C and irradiated with ultraviolet rays for 12 minutes using a high-pressure mercury lamp (300w).

The thus obtained p-benzenedithiol and p
- The second X-ray diffraction diagram of the addition polymer (aromatic vinylene sulfide polymer) crystal of diethynylbenzene
Shown in the figure. The maximum diffraction peak is 2θ=14° (d=7.78
Å), and in addition to this, 2θ = 29° (d = 3.90 Å),
Peaks were shown at 2θ = 44° (d = 2.60 Å) and 2θ = 58° (d = 1.95 Å).

Further, the number average molecular weight of the above polymer was found to be 3000 by the copper acetylide method. As a result of measuring the above polymer by elemental analysis, infrared absorption analysis, X-ray diffraction, etc., It was recognized as a crystalline polyadduct of diethynylbenzene and benzenedithiol with a repeating unit of nearly 100% crystallinity.

Thus, an optical recording layer is formed on the quartz glass substrate. An optical recording medium was obtained in which a thin film (thickness: 10.6 μm) of an aromatic vinylene sulfide polymer crystal having repeating units was formed.

This optical recording medium was irradiated with thermal energy to transform the crystalline phase of the aromatic vinylene sulfide used as the optical recording layer into an amorphous phase.

In order to roughly estimate the activation energy of phase transition from crystalline to amorphous phase due to thermal energy, the crystalline phase is
FIG. 5 shows the relative intensity ratio of the crystal peak 2θ=14° (d=7.7 Å) and the holding time at each temperature of 60 to 70°C. From this, we plotted using the Arrhenius equation and roughly estimated the activation energy from the crystalline phase to the amorphous phase.

From this, the activation energy for phase transition from crystalline phase to amorphous phase is 6.9Kcal/mol (crystalline peak 2θ=14°d=
The relative intensity is 100 with the diffraction intensity of 7.7 Å as 100.
Activation energy of phase transition in the region of ~80) 34.3 Kcal/mol (activation energy of phase transition in the region of above relative intensity of 90 to 20) 38.9 Kcal/mol (region of above relative intensity of 40 to 0) The activation energy of the phase transition in

The activation energy of this phase transition is small, and when the transition from a crystalline phase to an amorphous phase due to thermal energy is used for recording, it can be recorded with high sensitivity.

In addition, in Figure 4, ultraviolet light (240 to 400 nm) is applied to the crystal phase.
Irradiation time and crystal peak (2θ=
14, d = 7.7 Å).

In this way, the aromatic vinylene sulfide polymer crystal serving as the optical recording layer of the optical recording medium undergoes a phase transition to an amorphous phase due to thermal energy and optical energy. The X-ray diffraction diagram of the amorphous phase is shown in FIG. 3, and it can be seen that all the crystal peaks seen in the crystalline phase have disappeared.

Furthermore, scanning electron micrographs of replica images of the surfaces of the crystalline phase and the amorphous phase are shown in FIG. There are significant differences in the surface morphology of the crystalline and amorphous phases, and the two can be easily distinguished.

In addition, when we measured the reflectance for 560 nm light using an ultraviolet diffuse reflectance spectrometer for crystalline and amorphous phases (Hitachi 330 spectrometer, attached Hitachi 201-2101 60% integrating sphere), we found that the crystalline phase was about 50%, while the amorphous phase was about 70%. By utilizing this difference in light reflectance between the crystalline phase and the amorphous phase, records can be reproduced favorably.

Further, even when the crystalline phase and amorphous phase described above were left in air at 40° C. for one month, there was no change at all in their X-ray diffraction diagram and light reflectance.

〔Effect of the invention〕

As described above, the optical recording medium of the present invention is non-toxic, has good recording sensitivity, has a large optical contrast between recorded areas and unrecorded areas, and is capable of recording information with high sensitivity. .

[Brief explanation of the drawing]

FIGS. 1a, b, and c are cross-sectional views showing embodiments of the optical recording medium of the present invention, in which 1 is a substrate, 2 is an optical recording layer,
3 is a protective film, and 4 is a reflective film. Figure 2 is an X-ray diffraction diagram of the crystalline phase of the aromatic vinylene sulfide polymer of the present invention obtained in Example 1, and Figure 3 is an X-ray diffraction diagram of the amorphous phase. . FIG. 4 is a graph showing the relationship between the irradiation time and crystal X-ray diffraction peak intensity ratio when the optical recording medium of the present invention obtained in Example 1 is irradiated with ultraviolet light, and FIG. 2 is a graph showing changes in the relative intensity ratio of crystal X-ray diffraction peaks when a recording medium is held at a high temperature. Figure 6 a, b
is a scanning electron microscope magnification (20,000 times) of a replica image of the surface of the recording layer (aromatic vinylene sulfide polymer) of the optical recording medium of the present invention obtained in Example 1.
In the photograph, a is a crystalline phase and b is an amorphous phase.

Claims (1)

[Scope of Claims] 1. An optical recording characterized by using an addition polymer of a diethynylbenzene derivative and a benzenedithiol derivative as an optical recording layer, in which the group represented by the following structural formula () is used as a repeating unit. Medium. [In the formula, R ¹ , R ² , R ³ , R ⁴ are hydrogen,
Represents a group selected from alkyl groups having 1 to 12 carbon atoms and halogens. ]