JPH0419639A - Optical record and display material - Google Patents

Abstract

PURPOSE:To stabilize the optical record and display material against external light and to enable high-speed writing and erasing by constituting it from a twisted nematic liquid crystal layer, treated so as to arrange liquid crystals in parallel, outer and light-polarizing layers set on both sides of the liquid crystal layer, and a recording layer made of a photochromic compound arranged on the inside of these 3 layers. CONSTITUTION:The optical record and display material is formed by arranging successively from the incident side of light the outer light-polarizing layer 1, the liquid crystal layer 2, the inner light-polarizing layer 3, and the recording layer 4 made of the thermally stable photochromic compound, and both of the layers 1, 3 are arranged so as to have the same light-polarizing direction and transmit only the light having the same polarized face. The liquid crystal layer 2 is made of the twisted nematic liquid crystal treated so as to be arranged in parallel and rotates the incident light by a prescribed angle and emits it, therefore, when the liquid crystal state is maintained, the incident light from the layer 2 is interrupted by the layer 3, thus permitting the external light to be shielded and record or erasion of the record to be executed both at high-speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to optically controlled recording and display materials.

[Prior Art] The functions of recording and display materials controlled by light are in three types: read-only, write and read, and write, read and erase. Among these, what will become mainstream in the future are recording and display materials of the type that can be written, read and erased. This type of optical recording display material uses a technique using so-called photochromism, or a technique that combines phase change of liquid crystal and photochromism.

The technique using photochromism utilizes the fact that the absorption spectrum unique to a substance is changed by photoexcitation to develop a new absorption spectrum.

For example, if the spectrum shown in FIG. 6(a) becomes the spectrum shown in FIG. 6(b) due to optical excitation, then λ
Focusing on 1, it is on before optical excitation (FIG. 6(a)) and off after optical excitation (FIG. 6(b)), and can be used for recording and display. From this spectrum shown in Fig. 6(a),
If optical excitation to the spectrum shown in FIG. 6(b) is a write operation, then optical excitation from the spectrum shown in FIG. 6(0)) to the spectrum shown in FIG. 6(a) is an erase operation.

Conventionally, compounds with such characteristics are shown in Figure 7 (
Stilbene, fulgide and diallylethenic anhydride shown in a) and (C), Figure 8 (a) and (
There were compounds such as azobenzene and stilbene shown in b).

The technology that combines liquid crystal and photochromism utilizes the fact that a change in the three-dimensional structure caused by light irradiation is transmitted to the liquid crystal to destroy its inherent performance as a liquid crystal.

For example, suppose that azobenzene shown in FIG. 8(a) is mixed or bonded to the liquid crystal phase. At this time, when azobenzene is not irradiated with excitation light, as shown in FIG. 9(a), the structure of abbenzene 31 is similar to that of liquid crystal 32, so the monitor light g is in a light transmitting state. It has become. In addition, when azobenzene 31 is irradiated with excitation light, FIG.
), the azobenzene 31 undergoes a structural change and destroys the structure of the liquid crystal 32, so that the monitor light g is scattered at the destroyed portion and becomes opaque.

In this case, if the light transmission state is turned on, the light non-transmission state is turned off, and the erasing operation is to return the azobenzene that has undergone a structural change to its original structure using a different wavelength.

[Problem to be solved by the invention]

The conventional optical recording medium described above had the following drawbacks.

The first drawback is that it is unstable against external light and requires considerable effort to maintain records.

In other words, if the irradiation light for writing is ultraviolet light, the erasing light is visible light (if the irradiation light for writing is visible light, the erasing light is ultraviolet light), so external light is needed to maintain records. must be completely blocked. In particular, when using a floppy disk as a recording medium, it seems possible to block external light with a 3.5-inch disk, but since the shutter for recording operations can be easily opened, it is difficult to use such a device under external light. If you do this, your records will be easily erased. Although such drawbacks are unique to this technology, the reality is that the problem has not been solved from the disk case.

Furthermore, with the recent advances in FA,
It cannot be used for recording and display materials, such as so-called programmable tags, which are used in environments where they are constantly exposed to external light.

The second drawback is a lack of thermal stability.

That is, azobenzene and stilbene shown in FIGS. 8(a) and 8(b) return from the cis state to the original trans state within several hours to several days at room temperature.

Therefore, in the photochromism method, fulgide and diallylethenic anhydride shown in FIG. 7(b) (C) have been proposed as photochromic compounds.

In addition, with technology that combines photochromism and liquid crystal,
Liquid crystal surrounds the cis pair to prevent it from returning to the trans form, but the fact that this effect is sufficient means that structural changes such as azobenzene are less likely to occur due to light irradiation. Erasing could not be performed quickly.

Furthermore, in order to facilitate photoisomerization from the trans form to the cis form, it was necessary to heat the liquid crystal in advance to the temperature at which it would become isotropic.

Furthermore, if for some reason it was placed in an environment at a temperature higher than that at which it becomes isotropic, the previous records would disappear.

Furthermore, the liquid crystal itself has the disadvantage that its liquid crystal properties are destroyed by heat.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide an optical recording and display material that is stable against external light and that can be written and erased at high speed.

[Means for Solving the Problems] The present invention has been made to achieve the above objects, and
By actively incorporating the property of heat that destroys liquid crystallinity, a polarizing layer is provided on both sides of the liquid crystal layer, and by applying heat to the liquid crystal layer, the liquid crystallinity is destroyed, allowing external light to be blocked or transmitted freely. This is how it was done.

That is, the optical recording and display material of the present invention comprises a twisted nematic liquid crystal layer subjected to parallel alignment treatment, and outer and It is characterized by having an inner polarizing layer and a recording layer made of a photochromic compound disposed inside the inner polarizing layer.

The basic layer structure of the optical recording and display material of the present invention will be explained based on FIG.

FIG. 1(a) is a perspective view of each layer separated, and FIG. 1(b) is a sectional view of each layer separated.

In these figures, the upper side in the figures is the light incident side, and an outer polarizing layer 1, a liquid crystal layer 2, an inner polarizing layer 3, and a recording layer 4 are provided in this order from the upper side in the figures.

The outer polarizing layer and the inner polarizing layer are arranged so as to have the same polarization direction, that is, only light having the same polarization plane is transmitted. A polarizing film, a polarizing plate, etc. are used for this polarizing layer. Further, a protective layer can be provided on the outside of the outer polarizing layer (on the light incident side).

The liquid crystal layer is formed of twisted nematic liquid crystal subjected to parallel alignment processing, and rotates the incident light by a predetermined angle and emits it. Therefore, when the liquid crystal state is maintained, the light incident from the outer polarizing layer is rotated, so that the light transmitted through the liquid crystal layer is blocked by the inner polarizing layer.

This rotation angle is preferably 90 degrees.

Furthermore, when this liquid crystal layer is heated by laser light or the like, its liquid crystallinity is destroyed and it becomes isotropic as a normal liquid. Therefore, at this time, the light incident from the outer polarizing layer is passed through once without rotating the optical plane by m times, so that the light emitted from the liquid crystal layer passes through the inner polarizing layer and reaches the recording layer.

That is, the liquid crystal layer may be one that rotates incident light and emits it under the environmental temperature in which it is used, and outputs incident light as it is without rotating it in a heated state.

In such a liquid crystal layer, for example, 4-cyano-
4'-pentoxybiphenyl is mentioned.

The recording layer may be made of any thermally stable photochromic compound, and may be polymerized and coated and fixed onto the substrate, or may be encapsulated in another binder.

To read the records on the recording layer, either transmitted light or reflected light may be used.

That is, when using transmitted light, the substrate itself coated with a recording layer made of a photochromic compound is made of a light-transmitting material, such as glass or polycarbonate, and
It is made of a material that can transmit the monitor light for reading, and the transmitted monitor light is read by a light receiver placed below.

In addition, when using reflected light, the substrate coated with a recording layer made of a photochromic compound is made of a material that reflects light, or a reflective layer is provided at the bottom of the substrate that can transmit light, and the reflected light is is read by a receiver placed above.

It is preferable that a heat absorption layer is disposed between the recording layer and the inner polarizing layer or between the inner polarizing layer and the liquid crystal layer. This heat absorption layer absorbs the heat of the laser light that excites the liquid crystal, and prevents it from adversely affecting the recording layer. This heat absorbing layer protects the recording layer more completely.

[Function] In the optical recording display material of the present invention, the outer polarizing layer converts external light into coherent light and makes it incident on the liquid crystal layer, and the liquid crystal layer rotates the coherent light incident from the outer polarizing layer by a predetermined angle. Or let it pass through as is. The inner polarizing layer blocks light that has entered from the liquid crystal layer and has been rotated by a predetermined angle, or allows light that has entered from the liquid crystal layer to pass therethrough. Recording or erasing of recording is performed on the recording layer by light incident from the inner polarizing layer.

[Example] An example of the optical recording and display material according to the present invention is shown in FIGS.
Figures (a) (b) (C) (d) (e) and Figure 7 (
The explanation will be based on b).

Figure 2 is a cross-sectional view of each layer of the optical recording and display material separated;
Figures (a), (b), (c), (a) and (e) are cross-sectional views showing the operation of the optical recording and display material (7), and Figure 7 (b) is a view showing the structure of the photochromic compound.

In FIG. 2, the upper side of the figure is the light incident side, and the lower side of the figure is the anti-light incident side. Then, from the light incident side, a protective layer 11, an outer polarizing layer 12, a liquid crystal cell 13, a liquid crystal layer 14,
A liquid crystal cell 15, an inner polarizing layer 16, a heat absorbing layer 17, a recording layer 18, and a light reflecting layer or a light transmitting layer 19 are arranged in this order.

The protective layer 11 is for preventing scratches and stains on the outer polarizing film.

The outer and inner polarizing layers 12.16 have a thickness of 0.5 mm
A polarizing film (HN-42HE manufactured by Nihon Polaroid Co., Ltd.) is used, and these polarizing layers 12 and 16 are arranged so as to polarize light in the same direction.

The liquid crystal layer 14 and the liquid crystal cell 13.15 are formed of unidirectionally processed (parallel processed) glass having a thickness of 10-. A liquid crystal layer 14 is formed in which -4'-pentoxybiphenyl (manufactured by Merck & Co., Ltd.) is sealed in a liquid crystal state and arranged in parallel in liquid crystal cells 13 and 15.

The heat absorption layer 17 is arranged to protect the recording layer from damage caused by a thermal laser.

The recording layer 18 uses fulgide as a photochromic compound, which does not lose its liquid crystallinity within the environmental temperature at which a thermally stable one-light recording display material is used.
10 parts of this fulgide is dissolved in 100 parts of MMA (methyl methacrylate) and 30 parts of styrene, followed by 0.5 parts of MEKPO (methyl ethyl ketone peroxide), mixed well, and then coated on a quartz plate. Then, it was made into a thickness of 3 to 5 nm using a spin coater, and then left in an oven at 50"C for 5 hours to form a film of MMAO copolymer. This copolymer film became the recording layer 18, and the quartz plate serves as a reflective layer 19. This quartz plate is coated with an Ag vapor-deposited film for light reflection.

Next, the operation is shown in Figure 3 (a) (b) (c) (a) (e).
The explanation will be based on.

The operation of blocking external light will be explained.

When the optical recording and display material is left in a state where nothing special is done, external light a passes through the outer polarizing layer 12 and becomes coherent light, and then passes through the liquid crystal cell 13, as shown in FIG. 3(a). and enters the liquid crystal layer 14. The external light a that has entered the liquid crystal layer 14 is output with its polarization direction rotated by a predetermined angle, passes through the liquid crystal cell 15, and reaches the inner polarizing layer 16. However, since the external light a has a polarization direction different from that of the inner polarizing layer 16, it cannot enter the inner polarized light N16 and is blocked.

Therefore, the external light a does not reach the recording layer 18.

Next, the operation of transmitting external light will be explained.

First, as shown in FIG. 3('b), a laser beam is irradiated with a wavelength that does not excite the spectrum of the photochromic compound in the recording layer 18, but which provides heat sufficient to cause a phase change in the liquid crystal. Then, the liquid crystallinity of the liquid crystal phase 14 is destroyed, and the liquid crystal phase 14 becomes an equal phase, forming a transparent window 20. Therefore, the coherent light incident from the outer polarizing layer 12 passes through the liquid phase layer 14 as it is without being rotated, so it matches the polarization direction of the inner polarizing layer 16 and passes through the inner polarizing layer 16, and the recording layer 17 can reach up to.

In addition, if the absorption spectrum of the photochromic compound is as shown in Figure 6 (a) and (b), the thermal laser beam will
It is necessary that the wavelength is 73 or more.

Then, recording, erasing, and reading operations are performed in a state where external light can pass through.

To perform recording, as shown in FIG.
0 to the recording layer 18, and the recording section 2
form 1. At this time, if the absorption spectrum of the photochromic compound is as shown in FIG. 6(a), the recording laser beam C has a wavelength of λl.

For erasing, similarly to recording, light with a wavelength of λ2 is irradiated to erase the recording portion 21 formed on the recording layer 18.

To perform reading, as shown in Figure 3(d), λ1
or λ2, a weak laser beam d that does not change the photochromic compound of the recording layer 18 is irradiated. For example, in the case of a wavelength of λ1, the laser beam d passes through the recording section 21, is reflected by the reflective layer 19, and is taken into the detector 22, so that the presence or absence of recording becomes clear. In addition, in the case of the wavelength λ2, the laser beam d is absorbed by the recording section 21, and therefore, if the reflection intensity is measured, the reflection will conversely decrease, and the presence or absence of recording will become clear.

FIG. 3(e) is a cross-sectional view when reading is performed by measuring transmitted light. In this case, a transmitting layer 23 is provided in place of the reflective layer, and external light is transmitted from the recording layer 18 through the transmitting layer 23. In addition to measuring the laser beam d emitted by the detector 22,
This is the same as when using reflected light.

FIG. 5 is an exploded sectional view of another embodiment of the optical recording and display material of the present invention.

The optical recording and display material shown in this figure is the same as the embodiment shown in FIG. 2, except that the heat absorption layer 17 is disposed between the liquid crystal cell 15 and the inner polarizing layer 16.

That is, in this figure, the upper side of the figure is the light incident side, and the lower side of the figure is the anti-light incident side. A cell 15, a heat absorbing layer 17, an inner polarizing layer 16, a recording layer 18, and a light reflecting layer 19 are arranged in this order.

The test results of the performance of the optical recording and display materials as described above will be explained.

Test ② When the optical recording and display material shown in FIG. 2 without the heat absorption layer 17 was measured using a visible and ultraviolet spectrophotometer, the transmitted light intensity was approximately O in the measurement wavelength range of 200 to 700 nm. It was confirmed that external light was blocked.

Next, a 1000d He-Ne laser and a 20m dye laser (λ = 450nm) were coaxially irradiated for 0.5 seconds, and after 1 minute, a 10100O He-Ne laser and a 0.1
Irradiate with mW dye laser (λ = 355 nm),
Monochromator (λ-355nm) installed at the rear of the cell
When the light was received by the photocell through the laser beam (setting), the transmitted intensity was 30% of the transmitted intensity of the 0.1 mW dye laser measured in a blank state. Therefore, it was confirmed that the records were erased.

Test ■ After exposing the same optical recording and display material as in Test I under the sun for 100 hours, the same inspection as in Test ■ was conducted, and it was confirmed that the material worked without any abnormality.

Test ■ A glass plate coated with Ag vapor deposition was used as the reflective layer 19, and the same light irradiation as in Test I was applied to the recording medium at an angle of 60°, and the reflected light was received by a photocell via a monochromator. As a result, although a decrease of about 20% was observed compared to transmitted light, it was possible to sufficiently detect the presence or absence of recording.

Test (2) Using the optical recording and display material shown in FIG. 2, the same tests as Tests (2) and (2) were conducted, and similar results were obtained.

[Effects of the Invention] As described above, according to the present invention, by sandwiching the Rice) 2-machine liquid crystal layer between two polarizing layers, external light is blocked,
By making the liquid crystal layer isotropic using a thermal laser or the like only when necessary, each lightning related to the record is transmitted through, which prevents the record from disappearing at an undesirable time and maintains the record stably. be able to.

[Brief explanation of the drawing]

1(a) and 1(b) are an exploded perspective view and a sectional view showing the basic structure of the optical recording and display material of the present invention, and FIG. 2 is an exploded sectional view of an embodiment of the optical recording and display material of the present invention. Figure 3 (a)
(b), (C), (d), and (e) are cross-sectional views showing the same operation as above, Fig. 4 is a structural formula showing the structure of liquid crystal, and Fig. 5 is an exploded view of another embodiment of the optical recording display material of the present invention. Cross-sectional view, Fig. 6(a) (
b) is a spectrum diagram showing the principle of optical recording; Fig. 7(a)
(b) (C) is a structural formula showing the structure of a photochromic compound, Figure 8 is a structural formula showing the structure of a liquid crystal, and Figure 9 (
Figures a) and (b) are schematic diagrams showing the principle of a technology that combines photochromism and liquid crystal phase change.

Claims (6)

[Claims] (1) A twisted nematic liquid crystal layer processed in parallel alignment, outer and inner polarizing layers arranged on both sides of the liquid crystal layer with their polarization directions so as not to transmit light, and the inner polarizing layer. An optical recording display material characterized by having a recording layer made of a photochromic compound disposed inside. (2) The optical recording display material according to claim (1), wherein a reflective layer is arranged inside the recording layer. (3) The optical recording and display material according to claim (1), wherein a transparent layer is arranged inside the recording layer. (4) The optical recording and display material according to claim (1), (2) or (3), wherein a heat absorption layer is disposed between the recording layer and the inner polarizing layer. (5) The optical recording and display material according to claim (1), (2) or (3), wherein a heat absorption layer is disposed between the inner polarizing layer and the liquid crystal layer. (6) The optical recording and display material according to claim (1), (2), (3), (4) or (5), wherein a protective layer is disposed on the light incident side of the outer polarizing layer.