JPH07161039A - Recording and reproducing method for optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording and reproducing method for an optical recording medium excellent in nondestructive recording property, durability and stability. CONSTITUTION:The optical recording medium has a recording layer produced by dissolving and dispersing a photochromic compd. in a polymer liquid crystal. Information is recorded by irradiating the medium with light l1 in the absorption wavelength region lambda1 of the photochromic compd. while applying an electric field E1 to inverse the optical polarity of the photochromic compd. Information is erased by irradiating the recording medium with light l2 in the absorption wavelength region lambda2 of the photochromic compd. having inverted optical polarity while applying an electric field E2 in the opposite direction to the electric field E1 so that the photochromic compd. showing the inverted optical polarity is again inverted. Then information is reproduced by irradiating the recording medium with light l3 in a wavelength region lambda3 except for the absorption wavelength regions lambda1, lambda2 to detect the anisotropy of the refractive index of the polymer liquid crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing method using an optical recording medium, and more particularly to a stable and high-density optical recording medium reading method using a photochromic compound.

[0002]

2. Description of the Related Art Conventionally, as a rewritable optical recording medium, a method utilizing a photochromic compound has been proposed in Japanese Patent Laid-Open No. 2-190827. However, in the conventional method, the wavelength range of the light used for reading the information is also the wavelength range of the light for erasing the information at the same time, so that there is a practical problem that the information is destroyed. For this reason, a method of using a change in optical rotation in a long wavelength range where physical properties other than the absorbance of the photochromic compound do not change (Japanese Patent Laid-Open No. 1-24653) or a refractive index anisotropy is generated and used. A method for reading out light in the long wavelength region without photoabsorption of photochromic compounds (The 58th Annual Meeting of the Chemical Society of Japan, 1989)
Proceedings of Annual Lecture 31H30) etc. have been proposed.

Further, it has been attempted to obtain a larger change between the recording portion and the non-recording portion by forming a composite with a liquid crystal material. For example, a method in which a photochromic compound is mixed with a liquid crystal material and the cholesteric liquid crystal phase is changed by photoisomerization, or a compound whose structure is largely changed by the photochromic reaction is mixed with the liquid crystal material and a circular dichroism spectrum due to photoisomerization is obtained. Methods and the like using changes have been proposed.

However, even in the method of combining the liquid crystal material and the photochromic compound, the liquid crystal flows with the passage of time, the information becomes unclear, and there is a problem in the thermal stability and the repeated durability of the recording layer.

In order to prevent deterioration over time due to the fluidity of the liquid crystal, a method of using a polymer liquid crystal as a liquid crystal material or a method of fixing a photochromic compound on a substrate and photoisomerizing the photochromic compound on the substrate are used. A method for changing the alignment state of liquid crystal has been proposed (Japanese Patent Laid-Open No. 1-22).
51344 publication). However, even in these methods, there is a problem that it is difficult to completely erase the memory.

As described above, the optical recording medium using the photochromic compound has various problems and has not been put into practical use.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. An object of the present invention is to provide a recording / reproducing method which is excellent in non-destructive readability, durability and stability in an optical recording medium.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventor caused a photopolarization inversion in a photochromic compound by applying an electric field to a polymer liquid crystal in which a photochromic compound is dissolved and dispersed, It has been found that light in a wavelength range different from the light absorption wavelength range of the photochromic compound is modulated by the change in the refractive index anisotropy of the polymer liquid crystal film caused by the photoanisotropic reaction of the photochromic compound. It has been found that, by utilizing this reduction, if information is read out with light of a specific wavelength, nondestructive writing and reproduction with excellent repeatability are realized, and the present invention is completed. Came to.

That is, according to the present invention, an optical recording medium having a recording layer in which a photochromic compound is dissolved and dispersed in a polymer liquid crystal is irradiated with light l ₁ in the light absorption wavelength region λ ₁ of the photochromic compound. By applying an electric field E ₁ , the photochromic compound undergoes optical polarization reversal to record information, and light l in the light absorption wavelength range λ ₂ of the photochromic compound subjected to optical polarization reversal.
_{A step} of irradiating the recording medium with ₂ and applying an electric field E ₂ opposite to the electric field E ₁ to the recording medium, thereby re-optically inverting the photo-polarized photochromic compound to erase information. And the light absorption wavelength range λ ₁
And light l ₃ in the wavelength region lambda ₃ other than lambda ₂ by irradiating the recording medium, an optical recording medium and a step of reproducing the information by detecting the refractive index anisotropy of the liquid crystal polymer Recording and reproducing method.

The present invention will be described in detail below.

The optical recording medium according to the present invention preferably has a structure in which a polymer liquid crystal film in which a photochromic compound is dissolved and dispersed is sandwiched between at least two substrates. A recording medium in which one of the two substrates is a transparent electrode is particularly suitable. An alignment film may be provided between the polymer liquid crystal film and the substrate. Further, a light reflecting layer may be provided on the outside of one substrate.

FIG. 1 shows an example of an optical recording medium according to the present invention. In FIG. 1, 1 and 4 are glass substrates,
2 is a PVA rubbing film, 3 is a polymer liquid crystal film, 5 is a spacer, and 6 is a cell.

As the substrate material, glass, polycarbonate, polymethylmethacrylate, olefin resin or the like can be used.

The thickness of the polymer liquid crystal film is 0.1 μm to 50 μm.
The range of μm is preferable, and particularly preferably 1 μm to 20 μm.
The range is m. When the alignment film is provided, its thickness is preferably in the range of 0.001 μm to 10 μm.

The recording layer of the optical recording medium according to the present invention comprises:
The polymer liquid crystal contains at least a photochromic compound, and its structure is a structure in which the polymer liquid crystal and the photochromic compound are covalently bonded (1).
And a structure (2) in which the photochromic compound is dispersed in the polymer liquid crystal.

The polymer liquid crystal is a polymer having mesogenic molecules exhibiting liquid crystallinity in a side chain as a pendant via a predetermined alkyl spacer, and like the low molecular liquid crystal, a nematic phase, a smectic phase, a cholesteric phase, or the like. It forms various liquid crystal phases.

The recording layer having the structure (1) is prepared by copolymerizing a liquid crystal monomer having an addition polymerization property and a photochromic monomer having an addition polymerization property, or an unsaturated double bond is added to a reactive polymer such as reactive silicone. It can be obtained by an addition reaction of the liquid crystal compound having and the photochromic compound having a double bond.

Examples of the liquid crystal monomer having addition polymerization property include biphenyl type, cyclohexylbenzene type,
For each liquid crystal molecule such as azoxybenzene type, phenylpyrimidine type, biphenylbenzoate type, terphenyl type,
It has a structure in which an acrylic acid ester or a methacrylic acid ester is bonded through an appropriate alkyl spacer.

Examples of the method of polymerizing the liquid crystal monomer having the addition polymerization property and the photochromic monomer having the addition polymerization property include a method of copolymerizing by ordinary radical polymerization or ionic polymerization.

In the present invention, the photochromic compound contained in the liquid crystal is preferably in the range of 0.1 to 50% by weight, more preferably 1 to 20% by weight in terms of monomer unit.
Is the range. The ratio of the photochromic compound is 0.
If it is lower than 1% by weight, the desired change in refractive index anisotropy of the polymer liquid crystal due to photoisomerization of the photochromic compound cannot be obtained, and if it is higher than 50% by weight, liquid crystallinity is remarkably increased. And it becomes difficult to form an optical recording medium.

The above-mentioned molecular weight of the liquid crystal polymer (weight average)
Average molecular weight) is generally 1.0 × 10 ³ ~ 1.0 x 10⁶ 
Selected from the range, more preferably 1.0 × 10³ ~
5.0 x 10^Four Is the range.

A material having a Tg (glass transition point) of 50 ° C. or lower is preferable because it exhibits high modulation efficiency.

Next, the recording layer having the structure (2) will be described. Examples of the polymer liquid crystal include cyanobiphenyl, cyanophenylbenzoate, and cyanophenyl (4-phenylbenzoate) structures having a positive dielectric anisotropy, or methoxybiphenyl, methoxyphenylbenzoate, and methoxyphenyl having a negative dielectric anisotropy. A polymer liquid crystal having a (4-phenylbenzoate) structure or the like and having a main chain structure of polyacrylate type, polymethacrylic type, polyether type, polyester type, polysiloxane type or the like can be generally used.

Examples of the photochromic compound dispersed in the polymer liquid crystal include spiropyran derivatives, spirooxazine derivatives, azobenzene derivatives, fulkyd derivatives, diarylethene derivatives, triarylmethane derivatives and indigo derivatives. Particularly preferred are fulgide derivatives and diarylethene derivative compounds, which are photon-mode photochromic compounds that do not cause thermal isomerization.

The amount of the photochromic compound contained in the recording layer of the structure (2) depends on the desired physical properties,
The range of 0.1 to 50% by weight is preferable, and the range of 1 to 20% by weight is more preferable. If it is less than 0.1% by weight, the desired change in the refractive index anisotropy due to photoisomerization of the photochromic compound cannot be obtained, and if it is more than 50% by weight, the liquid crystallinity is remarkably lowered and It becomes difficult to form it as a recording medium.

In the present invention, various weather resistance stabilizers such as antioxidants represented by hindered amines and hindered phenols may be added to the recording layer for the purpose of improving durability. The addition amount of these is preferably in the range of 0.01 to 5% by weight based on the total weight.

Further, by increasing the change in the refractive index anisotropy of the polymer liquid crystal due to the photoisomerization of the photochromic compound,
A low molecular weight liquid crystal material may be mixed with the recording layer for the purpose of increasing the response speed or expanding the operating temperature range. As a result, the effects of lowering the viscosity and improving the change in the anisotropy of the refractive index occur.

Next, a method of manufacturing the optical recording medium according to the present invention will be described.

First, a solution containing an alignment film material is applied onto a substrate by a spin coating method, a bar coating method, a doctor blade method or the like and dried to form an alignment film. This alignment film is rubbed by rubbing it in one direction with a cloth or paper.

Next, the raw material for forming the recording layer is dissolved or heated and melted in an appropriate solvent and applied on the above-mentioned alignment film to form the recording layer. On the liquid crystal film, another substrate provided with an alignment film is placed so as to oppose the alignment film of the liquid crystal device, and pressure bonding is performed under reduced pressure to produce an optical recording medium.

Next, a recording / reproducing method for the optical recording medium of the present invention will be described.

The structure of the photochromic compound in the polymer liquid crystal when no information is recorded is called structure A, and the structure when information is recorded is called structure B. Information is recorded by irradiating light having a wavelength λ _A absorbed by the photochromic compound of structure A, applying an electric field, and causing the photochromic compound to undergo optical polarization reversal in structure B. To read information, the structure A and the structure B irradiate the recording medium with linearly polarized light having a wavelength λ _C , which the photochromic compound does not absorb, the linearly polarized light transmits or reflects through the optical recording medium, and then passes through the analyzer. This is done by reading out the difference in light intensity. Information is erased by irradiating light having a wavelength λ _B absorbed by the photochromic compound of structure B while applying an electric field opposite to that at the time of recording to change the photochromic compound to structure A.

The preferred range of the applied electric field is 1
The range of 000 V / cm to 100,000 V / cm is preferable, and the range of 2,000 V / cm to 50,000 V / cm is particularly preferable.
The range is cm. Below 1000 V / cm, a sufficient optical polarization reversal effect due to the electric field cannot be obtained, and 100000 V
If it is / cm or more, the power consumption of the recording / reproducing system device using the medium increases, which is not preferable. Suitable optical path difference Δ
By selecting n _{d, it} is possible to set the maximum or minimum transmittance at the wavelength at which the information is read in the initial state before writing the information.

As an optical memory material, a thermally stable photochromic component is dispersed in a polymer liquid crystal in a recording layer,
While applying an electric field, photoisomerization of the photochromic component writes performed portion of the information, the polarization orientation state is changed by inversion, the optical path difference [Delta] n _d is changed, changes the wavelength showing the maximum or minimum transmittance To do. Therefore, when the recording layer film thickness d is set such that the transmittance in the initial state is minimized, the transmittance of the portion where the information is written increases, and the recording can be read as a change in the transmittance. . In addition, this change in transmittance is due to photoisomerization by irradiating light while applying an electric field opposite to that at the time of recording,
It can be reversibly generated due to optical polarization reversal.

[0035]

The present invention will be described in more detail with reference to the following examples.

Example 1 As a polymer liquid crystal, a polymer of a biphenyl acrylate monomer was used. The weight average molecular weight of this polymer liquid crystal is about 4.0 × 10 ⁴ . The cell was manufactured by first applying a 5 wt% PVA aqueous solution to two glass substrates by a spin coating method and rubbing the same. The thickness of this rubbing film (alignment film) was 0.05 μm.

Then, 5 wt.% Of furylfulgide as a photochromic compound was formed on one of the glass substrates. A THF solution mixed with the polymer liquid crystal at a concentration of 10% was applied. The thickness of the polymer liquid crystal film was 0.5 μm. After drying, thickness 10
A resin spacer of μm was dispersed, another glass substrate was overlaid, the temperature was raised, and pressure was applied. The cells formed by crimping are
It was annealed at 100 ° C. for 30 minutes for uniaxial orientation, and this was used as an optical recording medium.

Example 2 The procedure of Example 1 was repeated except that a polymer of phenylbenzoate-based acrylic acid ester monomer was used as the polymer liquid crystal and a polymerizable spirooxazine compound was used as the photochromic compound. A recording medium was created.

Example 3 An optical recording medium was prepared in the same manner as in Example 1 except that a polymer of cyclohexylbenzene acrylic acid ester monomer was used as the polymer liquid crystal and a polymerizable fulgide compound was used as the photochromic compound. Created.

Example 4 Optical recording was carried out in the same manner as in Example 1 except that a polymer of an azoxybenzene-based methacrylic acid ester monomer was used as the polymer liquid crystal and a polymerizable spirooxazine compound was used as the photochromic compound. Created the medium.

Example 5 A polymer of azomethine acrylate monomer was used as the polymer liquid crystal, and a polymerizable spirooxazine compound was used as the photochromic compound.
An optical recording medium was prepared in the same manner as in Example 1.

Example 6 An optical recording medium was prepared in the same manner as in Example 1 except that a polymer of phenylpyrimidine acrylate monomer was used as the polymer liquid crystal and spirooxazine was used as the photochromic compound. .

Example 7 An optical recording medium was prepared in the same manner as in Example 1 except that a polymer of biphenylbenzoate-based acrylic acid ester monomer was used as the polymer liquid crystal and spirooxazine was used as the photochromic compound.

Example 8 An optical recording medium was prepared in the same manner as in Example 1 except that a polymer of cyclohexylbiphenyl acrylate monomer was used as the polymer liquid crystal and a polymerizable fulgide compound was used as the photochromic compound. did.

Example 9 An optical recording medium was prepared in the same manner as in Example 1 except that a polymer of terphenyl methacrylic acid ester monomer was used as the polymer liquid crystal and a fulgide compound was used as the photochromic compound. .

Information was written in and read out from each of the above recording media. Information was written by ultraviolet rays, and the transmitted light before and after irradiation was measured. UV rays (λ
= 365 nm), maximum absorption was exhibited at λ = 510 nm, and the absorption edge was 620 nm. At this time, writing was performed by applying an electric field (+5000 V / cm) to the medium.

The memory was erased by applying a reverse electric field (-5000 V / cm) to that during writing while irradiating with white light. The above recording and reproduction could be reversibly repeated.

The photochromic compound of Example 1 undergoes isomerization before and after irradiation with ultraviolet rays. The difference spectrum obtained by subtracting the spectrum before isomerization from the spectrum after isomerization is 600.
There was no change in the wavelength region below nm. The change in spectrum before and after irradiation with ultraviolet rays is shown in FIG. This change is reversible and could be erased by irradiating white light and applying a reverse electric field (-5000 V / cm) to that during writing, but erasing information by irradiating with reading light (λ = 780 nm) It didn't happen.

Each medium of this example was irradiated with ultraviolet rays and white light every 5 minutes to repeatedly evaluate durability (measurement wavelength λ.
= 760 nm, measurement temperature 25 ° C., parallel Nicols, orientation angle and polarization plane angle 45 °). FIG. 3 shows changes in transmitted light when recording and reading are performed alternately under parallel Nicols. No erasure of information occurred in this example.

The response speed, which is defined as the time required to change from 10% to 90% of the variation of the transmission intensity of the light λ _C (780 nm) shown above, is as fast as about 100 msec and is excellent in repeated stability. Was there.

Comparative Example 1 Polymethylmethacrylate (P
MMA) and 5 wt.% Of furylfulgide as a photochromic compound in PMMA. T formulated at a concentration of
The HF solution is applied on a glass substrate, dried, and the thickness is 0.5.
It was made to be μm. This was used as an optical recording medium.

Next, using the medium of Comparative Example 1 described above, writing was performed by irradiating with ultraviolet rays (λ = 365 nm), and at this time, writing was performed by applying an electric field (+5000 V / cm) to the medium. The difference spectrum before and after the ultraviolet irradiation is 63 out of the absorption wavelength range of the photochromic compound (fulgide).
Only about 2% change in transmitted light was exhibited in the wavelength range of 0 nm to 830 nm. Also, the response time is 500 ms
The value was as large as ec.

Comparative Example 2 Recording and reproduction were performed using the medium of Example 1 without applying an electric field during writing and erasing. In this case, 630
Only about a 2% change in transmitted light was exhibited in the wavelength range of nm to 830 nm. Also, the response time is 500 mse
The value was as large as c.

Comparative Example 3 Using the medium of Example 1, an electric field (+5000 V / cm) was applied during writing without light irradiation, and an electric field (-5000 V / cm) opposite to that during writing was applied during erasing. Meanwhile, recording and reproduction were performed.

Recording and reproduction were impossible because the transmitted light did not change in the wavelength range of 630 nm to 830 nm.

[0056]

The recording / reproducing method of the present invention is excellent in non-destructive readability, repetitive durability, and thermal stability of the recording layer, and is capable of high-density recording in the photon mode. It has an excellent effect.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an optical recording medium of the present invention.

FIG. 2 is a graph showing transmitted light spectra before and after ultraviolet irradiation in an optical recording medium in which an alignment direction is set at an angle of 45 ° with a polarization plane under crossed Nicols.

FIG. 3 is a graph showing a change in transmitted light of an optical recording medium when recording and reading are performed alternately under parallel Nicols.

[Explanation of symbols]

 1,4 Glass substrate 2 PVA rubbing film 3 Uniaxially oriented polymer liquid crystal 5 Spacer 6 cell

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G11B 7/24 516 7215-5D 11/08 9075-5D // B41M 5/26

Claims (1)

[Claims] 1. An optical recording medium having a recording layer in which a photochromic compound is dissolved and dispersed in a polymer liquid crystal,
A step of irradiating the light l ₁ in the light absorption wavelength region λ ₁ of the photochromic compound and applying an electric field E ₁ to cause optical polarization reversal of the photochromic compound to record information, and the photochromic inversion of the optical polarization. Irradiating the recording medium with light l ₂ in the light absorption wavelength region λ ₂ of the compound,
A step of applying an electric field E ₂ opposite to the electric field E ₁ to the recording medium to re-optically reverse the photo-polarized photochromic compound to erase information, and the optical absorption wavelength range λ ₁ and light l ₃ in the wavelength region lambda ₃ other than lambda ₂ by irradiating the recording medium, the optical recording medium and a step of reproducing the information by detecting the refractive index anisotropy of the liquid crystal polymer Recording and playback method.