JPH0336517A - Optical recording medium - Google Patents

Abstract

PURPOSE:To shield the intrusion of external light into a photochromic compd. of the lowermost layer and to allow stable optical recording and displaying of information at a high speed with the optical recording medium by using a polarizing film to polarize external light to coherent light in the layer upper than the photochromic compd. layer and using a liquid crystal layer with the orientation to be perpendicular to the polarized light thereof in the next layer. CONSTITUTION:The photochromic compd. layer 10 and a liquid crystal phase 11 which is laminated on the layer 10, is solid within the temp. range at the time of operation and has isotropy at the temp. above the temp. at the time of the operation are provided. The polarizing film 12 is fixed in the polarization direction and is so laminated on the liquid crystal phase 11 that the optical axis thereof intersects nearly orthogonally with the optical axis of the liquid crystal phase 11. The liquid crystal phase 11 is always crossed nicols with the polarizing film 12 of the outermost layer in the case of using the liquid crystal which does not annihilate the liquid crystallinity within the environmental temp. at which the recording medium is used. The polarization of the external light can be shielded within this temp. The accidental annihilation of the record by the photochromic compd. layer 10 of the lowermost layer is prevented in this way and the stable optical recording and displaying of the information at the high speed are executed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to optical recording media.

[Prior Art] There are three functions of optical recording media in which recording and display of information is controlled by light: information can only be read from, information can be written and read, and information can be written and erased.

Among these, the type that will become mainstream in the future is the type that allows writing and reading and erasing.

This type of optical recording medium includes one that uses so-called photochromism technology and one that uses a technology that combines liquid crystal phase change and photochromism.

As shown in FIG. 4, the former technique uses optical excitation to change the characteristic absorption spectrum of the substance constituting the optical recording medium, thereby developing a new absorption spectrum. That is, the spectrum shown at a in the same figure changes to b due to optical excitation.
When the spectrum changes to the one shown in , focusing on the wavelength λ1, it is ON before optical excitation and OFF after optical excitation. As a result, information optical recording is performed. If this state is considered as a write operation, optical excitation from spectrum a to spectrum b becomes information erasing operation.

As a compound that can perform such actions,
Stilbene (A) shown in Table 1 listed at the end of the specification,
Some exhibit the photochromic effect of fulgide (B) and diallylethenic anhydride (C).

On the other hand, the latter technology utilizes the fact that changes in the three-dimensional structure caused by light irradiation are transmitted to the liquid crystal, thereby destroying the properties inherent to the liquid crystal.

As a compound that can perform such actions,
There are compounds whose steric structure changes when irradiated with light, such as azobenzene (A) and stilbene (B) in Table 1 listed at the end of the specification. That is, by mixing or bonding the compounds shown in Table 1 to the liquid crystal phase, the light transmission anisotropy, which is a unique property of the liquid crystal phase 1, causes the liquid crystal phase 1 to have the properties shown in Figure 5 (A) before being irradiated with light. The light 3 in a single direction passes through the polarizing plates 2 that sandwich the liquid crystal phase 1, and as shown in the figure (B), by irradiating this with light, the mixed or bonded substances change their three-dimensional structure, This method takes advantage of the fact that by destroying the liquid crystal phase 1, it becomes opaque to light.

In this case, if the light transmission is turned on, the light non-transmission is turned off, and furthermore, returning the mixed or combined substance at a different wavelength to its original state is erasure.

[Problems to be Solved by the Invention] The first drawback of these technologies is that if the writing irradiation light is ultraviolet light, the erasing light is visible light (the writing irradiation light is visible light). In this case, since the erasing light is ultraviolet light, external light must be blocked in order to preserve the record. Therefore, when considering the form of a floppy disk as a recording medium, 3.
5 inches seems to be able to block out external light. However, since the shutter for recording operations can be easily opened, there is a drawback that recordings can be easily erased if such operations are performed under external light. Such a problem is unique to optical recording media that can be written to, read from, and erased.

A second drawback is that the write/read/erasable optical recording media described above generally lack thermal stability. That is, the compounds shown in Table 1 above return from the cis state to the original trans state within a few days at room temperature. This also applies to compounds A in Table 1 above. In order to overcome this drawback, compounds shown in B and C in Table 1 have been proposed using photochromism technology. However, such compounds cannot overcome the first drawback mentioned above.

Furthermore, in technology using liquid crystals, the liquid crystal incorporates the cis form to prevent it from returning to the trans form. However, when this effect is fully exhibited, it can be said that the compound is less likely to change due to light irradiation. In other words, writing and erasing at high speed is not possible, making it impractical. In other words, the liquid crystal itself has the disadvantage that its liquid crystallinity is destroyed by heat.

The present invention has been made in view of these points, and provides an optical recording medium that can perform high-speed and stable optical recording and display of information.

[2!Means for Solving Problem 1] The present invention includes a photochromic compound layer, a layer laminated on the photochromic compound layer, which is solid within the operating temperature range, and which is solid at a temperature higher than the operating temperature. Light characterized by comprising a liquid crystal phase having isotropy at temperature: IE
x:i medium.

Here, a heat absorption filter may be interposed between the photochromic compound layer and the liquid crystal phase.

The present invention also provides a photochromic compound layer, a polarizing film laminated on the photochromic compound layer and having a fixed polarization direction, and a polarizing film laminated on the polarizing layer and solid within the operating temperature range. An optical recording medium comprising a liquid crystal phase that is isotropic at a temperature higher than the operating temperature and whose optical axis is substantially perpendicular to the optical axis of the polarizing film. .

Here, a heat absorption filter may be interposed between the photochromic compound layer and the polarizing film.

Further, the present invention provides a photochromic compound layer and a liquid crystal phase having isotropy at a temperature of at least 30 degrees Celsius, which is laminated on the liquid crystal phase and arranged such that its optical axis is substantially perpendicular to the optical axis of the liquid crystal phase. together with a polarizing film whose polarization direction is a constant direction;
This is a Koki 1i medium characterized by comprising:

Here, a heat absorption filter may be interposed between the photochromic compound layer and the liquid crystal phase.

In addition, in the optical recording medium of the present invention, a light reflecting layer may be provided directly under the photochromic compound layer.

A device that uses a polarizing film that turns external light into coherent light, and uses a liquid crystal layer in the next layer with an orientation perpendicular to the polarized light to block external light from entering the photochromic compound in the bottom layer. It is.

[Examples] Examples of the present invention will be described below with reference to the drawings.

tJ1 diagram is an explanatory diagram of one embodiment of the present invention.

In the figure, numeral 10 indicates a thermally stable photochromic compound layer for each layer for recording and displaying information. A liquid crystal phase 11, which is an external light blocking layer, is provided on the photochromic compound layer 10. A polarizing film 12 is provided on the liquid crystal phase 11.

Here, the liquid crystal phase 11 is solid within the operating temperature range and is isotropic at temperatures higher than the operating temperature.

Further, the polarized light 812 has a constant polarization direction, and is laminated on the liquid crystal phase 11 such that its optical axis is substantially orthogonal to the optical axis of the liquid crystal phase 11.

In this case, if the recording medium is a product that does not lose its liquid crystallinity within the environmental temperature (operating temperature) in which it is used, the liquid crystal phase 11 will always be in the orthogonal Nicol phase with respect to the outermost layer polarizing film 12. Become. Therefore, within that temperature, the polarization of the external light 14 can be blocked.

Therefore, it is possible to prevent recording by the bottom photochromic compound layer 10 from being lost due to an accident.

Next, the recording operation will be explained with reference to FIG. 1(B). That is, the laser beam is irradiated with a wavelength that is not involved in recording in any way, that is, a wavelength that cannot excite the spectrum of the photochromic compound layer 10 at the bottom layer, and that provides heat that causes a phase change in the liquid crystal phase 11. and liquid crystal phase 11
Let be an isotropic layer. This makes the liquid crystal phase 11 transparent so that the light 15 passing through the polarizing film 12 can be transmitted therethrough. By passing another laser beam that can excite the photochromic compound layer 10 through this window, as shown in FIG.
Record as shown. At this time, if the absorption spectrum of the compound is like the characteristic line a in FIG. 4, the recording laser is λ.

If the spectrum after excitation is as shown in the characteristic line in FIG. 4, the thermal laser only needs to have a wavelength of λ1 or more.

Next, the case of reading will be explained. In the recorded region, the absorption spectrum changes from characteristic line a to characteristic line S in FIG. For this purpose, first, as shown in FIG. 1(D), a window is opened using a thermal laser, and then a weakly output laser beam having a wavelength of λ1 is applied. As a result, the photochromic compound layer 1
The transmitted intensity of the weakly output laser beam 16 that has passed through the laser beam 16 is retained and taken into the detector 17. As a result, it becomes clear whether there is a record or not.

In addition, if it is a laser beam with a weak output of λ2, it will be absorbed by the photochromic compound layer 10, so if the transmitted intensity is measured, the opposite transmitted intensity phenomenon will occur.
You can check whether there are records.

Next, in the case of erasing the record, if a window is similarly opened with a thermal laser and a laser beam having an excitation wavelength of λ2 is irradiated, the spectrum of the recorded area changes from the characteristic line in Figure 4 to the characteristic line a. The absorption spectrum returns. Therefore, it becomes possible to erase records.

Next, an experimental example conducted to confirm the effects of the present invention will be described.

Experimental Example 1 As the lowest photochromic compound layer, 100 parts by weight of a thermally stable compound consisting of fulgitopa vinylanilide (A) shown in Table 1 listed at the end of the specification was added to 30 parts by weight.
0.5 parts by weight of methyl ethyl ketone peroxide (MEKPO) was dissolved in styrene, mixed well, and coated on a quartz plate to form a film with a thickness of 3 to 5 μm using a spin coater. Created. This film is 5
A copolymer film was prepared by leaving it in an oven at 0° C. for 5 hours.

Next, 4-cyano-4'pentoxybiphenyl (B) compound (B) shown in Table 1 was added to the unidirectionally treated glass cell.
By mixing 5CB (manufactured by Merck & Co.) in a liquid crystal state, a liquid crystal phase aligned parallel to the glass surface was formed. The thickness of the glass cell was 5 μm.

As shown in FIG. 2, this glass cell is stacked on the quartz glass plate 10 on which the photochromic compound layer described above is formed, and a polarizing film 12 with a thickness of 30 μm is placed on top of this at right angles to the alignment of the liquid crystal phase 11. The recording medium according to the present invention was obtained by stacking and fixing them together.

This recording medium was subjected to a visible and ultraviolet spectrometer, and the result was 200
In the measurement wavelength of ~700 nm, the transmission intensity is almost 0.
It was confirmed that the outside light was blocked.

Next, the IOW He-Ne laser and the 2W dye laser (λ-355nm) were coaxially irradiated for 0.5 seconds.
After 1 minute, a 10W He-Ne laser and a 0. When the IW dye laser (λ-355 nm) was irradiated and the transmission intensity of the 0.1 W dye laser was measured using a photocell via a monochromator placed at the rear of the cell, it was 95%. Therefore, it was confirmed that the photochromic compound layer was recorded by the 2W laser.

Next, we used an IOW He-Ne laser and a 2W dye laser (
λ-450nm) coaxially, irradiated for 0.5 seconds, and
After a 10W He-Ne laser and a 0. IW dye laser (λ-355 nm) was irradiated, and the light was received by a photocell via a monochromator in the same manner as described above. As a result, the transmission intensity was 30% of that of the blank. Therefore, it was confirmed that the records had disappeared.

Experimental Example 2 After exposing the optical recording medium shown in Experimental Example 1 above to the sun for 100 hours, the same test as in Experimental Example 1 was conducted, and it was confirmed that it operated without any abnormality.

Experimental Example 3 Each cell similar to that shown in Experimental Example 1 above was created,
Light irradiation was performed in the same manner as in Experimental Example 1, with the outermost layer being a liquid crystal phase, the next layer being a polarizing film perpendicular to this layer, and the bottom layer being a photochromic compound cell. As a result, effects exactly similar to those shown in Experimental Example 1 could be obtained.

Experimental Example 4 As a base for a cell similar to that shown in Experimental Example 1 above, a glass cell with Ag vapor deposition was used as shown in FIG.
The recording medium was irradiated with light 21 similar to that shown in Experimental Example 1 at an angle of 60 degrees, and the reflected light 22 was received by a photocell via a monochromator (not shown). As a result, although there was a reduction of about 20% compared to the transmission method,
It was fully possible to detect the presence or absence of records.

As described above, according to the optical recording medium of the present invention, by using a polarizing plate and a liquid crystal arranged in one direction like a rectangular Nicols, external light is normally blocked and only heated when necessary. By setting the crystal phase to an isotropic phase, a recording medium capable of performing a recording operation can be obtained. As a result, it is possible to prevent records from being erased due to unnecessary external light irradiation, and to realize stable record retention.

[Effects of the Invention] As explained above, according to the optical recording medium according to the present invention, information can be optically recorded and displayed at high speed and stably.

No. ■ table stilbene (A) hmm le Gi de (B) diallylethenic anhydride (C) No. ■ table Azobenzene (A) Stilbene (B) No. ■ table Fulgido vinylanilide (A) 4-cyano-4°-hentoxybiphenyl (B)

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of one embodiment of the present invention, Fig. 2 is an explanatory diagram of an experimental example for confirming the effects of the present invention, and Fig. 3 is an explanatory diagram of an example of an experiment for confirming the effects of the present invention. FIG. 4 is a characteristic diagram showing the relationship between absorbance and wavelength, and FIG. 5 is an explanatory diagram showing the drawbacks of conventional optical recording media. DESCRIPTION OF SYMBOLS 10... Photochromic compound layer, 11... Liquid crystal phase, 12... Polarizing film.

Claims (6)

[Claims] (1) Comprising a photochromic compound layer and a liquid crystal phase that is laminated on the photochromic compound layer, is solid within an operating temperature range, and is isotropic at a temperature equal to or higher than the operating temperature. An optical recording medium characterized by: (2) a photochromic compound layer, a polarizing film laminated on the photochromic compound layer and having a fixed polarization direction; and a polarizing film laminated on the polarizing film and solid within the operating temperature range; 1. An optical recording medium comprising a liquid crystal phase that is isotropic at a temperature higher than an operating temperature and whose optical axis is substantially perpendicular to the optical axis of the polarizing film. (3) The optical recording medium according to claim 2, wherein a heat absorption filter is interposed between the photochromic compound layer and the polarizing film. (4) a photochromic compound layer, a liquid crystal phase that is laminated on the photochromic compound layer, is solid within an operating temperature range, and is isotropic at a temperature equal to or higher than the operating temperature; 1. An optical recording medium comprising: a polarizing film laminated on a liquid crystal phase, the optical axis of which is substantially orthogonal to the optical axis of the liquid crystal phase, and whose polarization direction is constant. (5) The optical recording medium according to claim 1 or 4, wherein a heat absorption filter is interposed between the photochromic compound layer and the liquid crystal phase. (6) The optical recording medium according to any one of claims 1 to 5, wherein a light reflective layer is provided directly under the photochromic compound layer.