JPS61215542A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the stability and reliability by using a composite body consisting of a compound having a photochromic functional group and a cross- linked polymer having a network structure in which the size of the meshes is nearly equal to or several times the size of the photochromic functional group. CONSTITUTION:The space where photochromic functional groups present in the meshes of a cross-linked polymer can freely move in an ordinary state is limited by restricting the size of the meshes or forming a proper side chain having a smaller size than the meshes. A reversible change between a light energy state and a low energy state is controlled by a steric hindrance effect. When writing or erasure is carried out with said composite body, it is necessary to cause a photochromic reversible change by heating the composite body to a temp. above the softening point. The chain of the cross-linked polymer is softened by the heating, so the steric hindrance effect is eliminated. The low energy state can be changed into the high energy state by irradiating light having the required specified wavelengths while supplying heat energy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is used for optical information recording. The present invention relates to a stable and erasable organic thin film recording medium.

Conventional technology The use of organic thin films with photochromic functions as information recording media has already been proposed (Industrial Materials, Vol. 31, No. 9, pp. 27-31, 1983).
.

Photochromism is A of a certain compound.

It is a phenomenon accompanied by a change in absorption spectrum when a reversible change of A=H occurs between 82 different molecular structures or states. Here, A is a low energy state (stable state), B is a high energy state (unstable state), and the A-+B change is due to light energy.

On the other hand, B4A changes are often caused by thermal energy, light energy (with different wavelengths), and electromagnetic energy.

Now, if the low energy state A of a photochromic compound corresponds to the information erasing state and the high energy state B corresponds to the information recording state, information can be written (recorded) by supplying light energy and erasing information by supplying thermal energy. It is now possible to reversibly improve optical properties (absorbance, refractive index) in both states.

The recorded information can be read by detecting the difference in reflectance and transmittance, and can be used as an erasable/rewritable optical information recording medium.

Problems to be Solved by the Invention However, there is one major problem in putting such photochromic organic compounds into practical use as erasable optical recording media. The question is how to stabilize the high energy (unstable) state B of photochromic compounds at room temperature. The high-energy state of many photochromic organic compounds is unstable, and when left at room temperature, they return to the low-energy (stable) state A in a short or long period of time due to absorption of thermal energy, absorption of visible light, etc. Conventional photochromic organic thin films are made by dispersing such photochromic compounds in polymers.

Alternatively, the photochromic compound is chemically bonded to the side chain position of the polymer chain, but the high energy state of the contained photochromic compound returns to the low energy state when left at room temperature. Namely.

Conventional recording media using photochromic organic thin films lack stability and reliability.

Means for Solving the Problems The photochromic organic thin film recording medium of the present invention uses a compound having a photochromic functional group.

It is composed of a complex with a crosslinked polymer compound having a network structure whose network size is the same or several times the size of the photochromic functional group. In particular, the crosslinked polymer compound is characterized by having a three-dimensional network structure and having side chains smaller than the size of the network.

As described above, in the recording medium of the present invention, by mainly limiting the size of the network formed by the crosslinked polymer, and by appropriately providing side chains smaller than the size of the network, The space in which the photochromic functional group can freely move in a normal state (eg, normal @) is limited. Such free space limitations, ie, steric hindrance effects, suppress the reversible change between high and low energy states of the photochromic compound. This is because photochromic reversible changes, especially cis-trans type, ring-opening-ring-closing type photoisomerization reactions, involve changes in the steric molecular structure, and even if such a steric structural change is attempted, cross-linking will occur. Structural changes do not occur because the polymer chains act as obstacles. That is, no photochromic reversible change occurs. Therefore, in the recording medium having the two configurations of the present invention, the high energy state (for example, corresponding to the written recording state) and the low energy state (for example, corresponding to the erased state) of the photochromic compound can be stably present at room temperature. .

Next, in order to perform writing and erasing on the recording medium of the present invention, it is necessary to cause a photochromic reversible change. For this purpose, the composite according to the invention is heated using a thermal energy supply device.

By raising the temperature above its softening point, the chains of the crosslinked polymer become flexible, the steric hindrance effect is removed, and reversible photochromic changes can occur. That is,
Photochromic conformational changes are possible only when the composite is heated to a temperature above the softening point, and no conformational change occurs again when the composite is cooled to a temperature below the softening point.

A change to a high energy state is possible by simultaneous irradiation with light of a specific wavelength necessary for the change and thermal energy supply (for example, heat ray irradiation such as laser light). On the other hand, a change to a lower energy state is possible by supplying only thermal energy or by simultaneously supplying thermal energy and optical energy having a wavelength longer than the specific wavelength.

As described above, in the recording medium of the present invention, by adjusting the size of the network formed by the crosslinked polymer steel in the composite to the same size as the photochromic functional group, or several times the size of the photochromic functional group, photochromic reversibility can be achieved. The steric hindrance effect that controls the reaction can be expressed below the softening point and canceled above the softening point. Therefore, by setting the softening point to a temperature higher than room temperature (for example, 60°C or higher),
Can be stored stably at room temperature. An erasable recording medium can be obtained.

EXAMPLE The optical recording medium of the photochromic organic thin film of the present invention comprises a compound having a photochromic functional group.

It consists of a complex with a crosslinked polymer compound having a network structure whose network size is the same or several times the size of the photochromic functional group.

Here, the compound having a photochromic functional group is a low molecular compound having the functional group or a high molecular compound having the functional group at the position of a side chain.

The composite of the present invention is one in which these low-molecular or high-molecular compounds are dispersed in a crosslinked high-molecular compound having a network structure. Moreover, the composite of the present invention is as follows.

A photochromic low molecular compound is chemically bonded to the side chain position of a crosslinked polymer compound, or a photochromic polymer compound is crosslinked with a crosslinked polymer compound.

It is desirable that the crosslinked polymer compound has a three-dimensional network structure. This is because the three-dimensional network chains have stable positions within the complex, and can provide a steric hindrance effect more effectively and with better reproducibility when the steric structure of the photochromic functional group changes. Further, it is desirable that the size of the mesh is comparable to the size of the photochromic functional group.

If the mesh size is too large, the mesh chains will not be able to provide a steric hindrance effect on the photochromic functional groups even if the mesh steel is in a rigid state at temperatures below the softening point. The size of the network that can have a steric hindrance effect is up to several times the size of the photochromic functional group. With a mesh size of this size, side chains smaller than the mesh size (
By appropriately providing a crosslinked polymer with, for example, an alkyl group, it is possible to obtain a steric hindrance effect due to the side chain.

On the other hand, if the size of the network is too small, even if the network chains are in a flexible state at a temperature above the softening point, the steric hindrance effect will not be released and the photochromic functional group will not be able to undergo structural changes.

The photochromic functional group of the present invention is preferably a photoisomerizable functional group that undergoes a conformational change.

As such examples, cis-trans type photoisomerization functional groups, ring-opening-ring closure type photoisomerization functional groups, etc. are known. Specific examples of cis-trans photoisomerizable compounds include azobenzene compounds.

Examples of reversible reactions of azobenzene compounds are shown below.

Also.

R Specific examples of ring-opening-ring-closing photoisomerizable compounds include:

These include spiropyran compounds. Examples of reversible reactions of spiropyran compounds are shown below. Regarding stilbenes and fulgides,
The open ring form is an isomer with a lower energy state.

closed ring body (low energy state) open ring body (high energy state) These are all examples of low molecular weight compounds. next.

An example of a polymer compound having a photochromic functional group in a side chain position is shown below. The main chain of these polymer compounds is
such as polyethylene and polypeptides.

In fact, many known polymers can be used.

%-CI (2-G force 1) In order for the crosslinked polymer compound of the present invention to form a network structure, polymerization using a polymerizable monomer or oligomer having at least two or more unsaturated groups is required.

Preferably the body. For example, radiation-polymerizable monomers such as diacrylates and dimethacrylates having two unsaturated groups, triacrylates and trimethacrylates having three unsaturated groups, and tetraacrylates having four unsaturated groups can be used. can. Furthermore, 9 For example, polyethylene glycol dimethacrylate CH2=C(CH3)-Co-(oCH2-CH
2) n-0-C.

The size of the network of the bipolymer can be adjusted by changing the length of two molecules (the number of n in -C(CH3)=CH2). In addition, to form a three-dimensional network structure, it is useful to use trimethacrylate with three unsaturated groups or tetraacrylate with four unsaturated groups, and dimethacrylate with two unsaturated groups. Methacrylate and trimethacrylate with 3 unsaturated groups or 4
The size of the three-dimensional network can also be effectively controlled by changing the blending ratio of tetraacrylate having 2 unsaturated groups. Also, these polymers are 60°
It has a softening point higher than C. For example, polymethyl methacrylate has a softening point above 150°C.

Further, in the recording medium of the present invention, the compound having a photochromic functional group is arranged in such a manner that the compound has a photochromic functional group.

Alternatively, it is characterized by having a regular array structure with respect to the array direction and center of gravity position. This is a method for aligning the orientation of photochromic compounds in a certain direction.

For example, liquid crystal polymerization is useful. When using the liquid crystal polymerization method, after molecularly aligning a mixed liquid crystal consisting of 1, for example, a photochromic compound, a liquid crystal compound, and 9 a polymerizable monomer, 1
It can be polymerized to obtain a solid polymer film with a fixed liquid crystal alignment structure. Here, it is possible to give the photochromic compound itself polymerizability (by introducing an unsaturated group) or liquid crystallinity (by introducing a biphenyl skeleton, phenylcyclohexane skeleton, etc. and designing a rod-shaped molecule). Furthermore, the liquid crystal compound itself can be made to have polymerizability. Next, as a method for regularly arranging photochromic compounds in terms of orientation and center of gravity, there is a Langmire-Projet film polymerization method. The polymer is then polymerized to obtain a solid polymer film having a regularly arranged structure of photochromic functional groups. A photochromic polymer film having such a regular array structure is particularly useful as a highly reliable recording medium with high recording density.

Tramethylolmethanetetraacrylate (C(CH2
-o-Co-CH=CH2) 4) A homogeneous mixture consisting of 25 molti was coated on a transparent glass substrate using a spinner, polymerized with ultraviolet light to create a photochromic polymer thin film with a thickness of 7 μm, and heated at a temperature of 220°C. Annealing was performed to obtain a recording medium.

This recording medium exhibited a low absorbance of 0.05 for visible light with a wavelength of 650 to 600 nm. Next, while irradiating ultraviolet rays, a laser beam having a wavelength of 830 nm was simultaneously irradiated instantaneously to heat a local portion of the recording medium to 220° C., and then rapidly cool it. The local area irradiated with this laser beam has a wavelength of 6
Large absorbance 0 for visible light from 60 to 600 nm
．． It showed 32. A constant temperature and humidity test was conducted on this sample at a temperature of 60°C and a relative humidity of 80% for 5 consecutive hours, but no change in absorbance over time was observed within the measurement error. On the other hand, this sample was only irradiated with a laser beam, and the localized portion was instantaneously heated to a temperature of 220° C. and rapidly cooled. When the absorbance of this local area was measured again, it returned to the low value of 0.06.

As can be seen from the above experiments, the intensity of the laser beam irradiated at the same time as ultraviolet ray irradiation was modulated with the information signal to be recorded, and writing was performed by scanning the beam.

Further, when erasing the recording (local area with absorbance of 0.32), only laser light irradiation was performed. On the other hand, to read the record, the difference between the absorbance o, 32 of the recorded portion and the extinction degree 0.05 was detected using visible light (preferably laser light) with a wavelength of 550 to 650 nm.

Effect of the invention As described above, according to the recording medium of the present invention.

By controlling the reversible change exhibited by photochromic compounds using the steric hindrance effect of crosslinked polymer chains with a network structure, the high-energy state and low-energy state of the photochromic functional group can be stabilized at room temperature, respectively. Stability.

Highly reliable, erasable and rewritable optical information recording becomes possible.

Claims (15)

[Claims] (1) Optical recording of a photochromic organic thin film consisting of a composite of a compound having a photochromic functional group and a crosslinked polymer compound having a network structure whose network size is the same or several times the size of the photochromic functional group. Medium. (2) The compound having the photochromic functional group is
The optical recording medium according to claim 1, which is a low molecular compound having a photochromic functional group. (3) The optical recording medium according to claim 2, wherein the low molecular compound having a photochromic functional group is bonded to the chain of the crosslinked polymer compound as a side chain. (4) The compound having the photochromic functional group is
The optical recording medium according to claim 1, which is a polymer compound having a photochromic functional group at a side chain position. (5) The optical recording according to claim 4, wherein the polymer compound having the photochromic functional group at the side chain position forms a crosslink between the chain thereof and the chain of the crosslinked polymer compound. Medium. (6) The optical recording medium according to claim 1, wherein the crosslinked polymer compound has a three-dimensional network structure. (7) The optical recording medium according to claim 1 or 6, wherein the crosslinked polymer compound has a side chain smaller than the size of the network. (8) The compound having the photochromic functional group is
The optical recording medium according to claim 1, 2, or 4, which has a regular array structure with respect to its orientation. (9) The compound having the photochromic functional group is
The optical recording medium according to claim 1, 2, or 4, which has a regular array structure with respect to its orientation and center of gravity. (10) Claims 1, 2, 3, and 4, wherein the photochromic functional group is a photoisomerization functional group.
The optical recording medium according to item 5, item 8, or item 9. (11) The optical recording medium according to claim 10, wherein the photoisomerization functional group is a cis-trans type isomerization functional group. (12) The optical recording medium according to claim 10, wherein the photoisomerization functional group is a ring-opening-ring-closing isomerization functional group. (13) Claims 1, 3, 5, 6, or 7, wherein the crosslinked polymer compound is a polymer of polymerizable monomers having at least two unsaturated groups. Optical recording medium described in Section 1. (14) A patent in which the above-mentioned crosslinked polymer compound having a three-dimensional network structure is a copolymer of a polymerizable monomer having two unsaturated groups and a polymerizable monomer having three or four unsaturated groups. The optical recording medium according to claim 6. (15) The optical recording medium according to claim 1, wherein the composite has a softening point of 60°C or higher.