JP2732942B2 - Photochromic material and rewritable optical recording medium using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a photochromic material and a rewritable optical recording medium using the same. More specifically, novel photochromic materials that can be used as various recording and storage materials, display materials such as displays, photographic printing materials, optical filters, luminometers, masking materials, and rewritable optical recording using the same. Regarding the medium.

[Prior Art and Problems to be Solved by the Invention] Conventionally, as a photochromic material, a photochromic material disclosed in Jun. Seto in "Solid State Physics", 21 , 235-240 (1986) is well known.

A photochromic material is a material that is colored by irradiation with ultraviolet light and is decolorized by irradiation with visible light or heat, and the photochromic compound is dispersed in a solution or a polymer medium, or is supported on the polymer medium by a chemical bond. It is made by things. In particular, it is known that a material made by being supported by a chemical bond can suppress the elution of a photochromic compound from a medium, and can improve the heat stability of a colored body (for example, a collection of polymer papers). (Kobunshi Ronbunshu), 33 , 649 (197
6)).

Further, the side chain type polymer liquid crystal-based photochromic material exhibits photochromism and thermo photochromism, Molecular Crystals And Liquid Crystals, (Mol.Cryst.Liq.Cryst.), 155, 221
~ 230 (1988).

On the other hand, spiropyran containing sulfur has been proposed as having sensitivity in the near infrared region (for example, see Journal
Of Physical Chemistry (J.Phys.Chem.), 7
2, 997 (1968)). This photochromic compound is reversibly colored and decolored in the photon mode.

Among the conventionally known photochromic materials as described above, there is a possibility that a benzothiopyran-based spiropyran compound can be used for a rewritable optical recording medium, and a spiropyran compound containing sulfur matches the wavelength of a semiconductor laser. is there.

However, the above-mentioned spiropyran compound containing sulfur has a drawback that durability against repeated coloring and decoloring is extremely poor, and that the colored body is unstable to heat, and has a serious problem in practical use. is there. Also,
When used for an optical recording material, there is a problem that the recording is destroyed by the reading light because of photon mode recording.

The present invention has been made to solve the above-described problems, and is an inexpensive organic material, which is colored in a photon mode and a heat mode using a light source (for example, a semiconductor laser) in the ultraviolet and near-infrared region. The object is to provide a photochromic material having heat stability capable of repeatedly controlling the decolored state and a rewritable optical recording medium using the same.

[Means for Solving the Problems] The present invention provides a compound represented by the following general formula (I): (In the formula, R ¹ is a hydrogen atom or a methyl group, R ² and R ³ are each a hydrogen atom, a hydroxyl group, a halogen atom, an amino group, a lower alkoxy group or an aryl group, and R ² and R ³ are the same group. And l may be different groups, l is an integer of 1 to 20) and a benzothiopyran-based pyropyranprepolymer represented by the general formula (II): (Wherein, R ⁴ is a hydrogen atom or a methyl group, R ⁵ is a nitrile group, a lower alkoxy group, —OC ₆ H ₁₃ or m is an integer of 1 to 20), and a photochromic material containing a copolymer with a liquid crystal prepolymer and a rewritable optical recording medium using the photochromic material.

[Action] The photochromic material of the present invention is inexpensive and can suppress the thermal isomerization reaction without adversely affecting the photoisomerization reaction. In other words, since it is thermally stable and gives a threshold value to the photoisomerization reaction, coloring and decoloring can be controlled by light intensity, and a semiconductor laser can be used. Therefore, the rewritable recording medium using this can achieve the intended purpose.

[Example] The photochromic material of the present invention contains the following copolymer.

The copolymer has a general formula (I): A benzothiopyran-based spiropyran prepolymer (hereinafter, referred to as a prepolymer (I)) represented by the following general formula (II): (Hereinafter referred to as prepolymer (II)) and a copolymer (hereinafter referred to as copolymer (A)). The copolymer (A) has good thermal stability of the colored body and excellent durability against repeated coloring and decoloring.

The prepolymer (I) is a component for developing photochromism. In the general formula (I), R ¹ is a hydrogen atom or a methyl group, and R ² and R ³ are a hydrogen atom, a hydroxyl group, a halogen atom, an amino group, respectively. , A lower alkoxy group or an aryl group, and R ² and R ³ may be the same group or different groups. Specific examples of the lower alkoxy group and the aryl group include a methoxy group, an ethoxy group, a phenyl group, a tolyl group, a xylyl group, and a naphthyl group. 1 is an integer of 1 to 20, preferably 1 to 6. This is from the experimental results
As the value increases, both the light response speed and the thermal reaction speed tend to increase. When l is greater than 20, the photoresponse speed increases, but the effect of inhibiting the thermal reaction by the mesogen group is weakened. Is no longer suitable for his purpose.

Specific examples of the prepolymer (I) include, for example, And so on.

The method for synthesizing the prepolymer (I) is not particularly limited. For example, the method of S. Arakawa et al. (Chemistry Letters, Chem. Lett., 1905 (198)
5)) and the method of J. Vorborgt et al. (Journal of Polymer Science, Polymer Chemistry Edition (J. Polym. Sci. Poly)
m. Chem. Ed.), 12 , 2511 (1974)).

The prepolymer (II) is a component for stabilizing heat resistance. In the general formula (II), R ⁴ is a hydrogen atom or a methyl group, R ⁵
Is a nitrile group, a lower alkoxy group, -OC ₆ H ₁₃ or And specific examples of the lower alkoxy group include a methoxy group and an ethoxy group. M is an integer of 1 to 20, preferably 1 to 6. m is also l
Similarly to the above, if it is larger than 20, the effect of inhibiting the thermal reaction of the photochromic group by the mesogen group will be weakened, and will not be suitable for the purpose of the present invention.

Specific examples of the prepolymer (II) include, for example, And so on.

The method for synthesizing the prepolymer (II) is not particularly limited. For example, the method of M. Portugall et al. (Makromol. Chem.,
183 , 2311 (1982)).

In the copolymer (A) composed of the prepolymer (I) and the prepolymer (II), the prepolymer (I) and the prepolymer (II) were copolymerized in such a ratio as to show a smectic state or a nematic state. From this point, 1 to 50 parts of the prepolymer (I) is added to 100 parts of the prepolymer (II) (parts by weight, the same applies hereinafter).
Those obtained by using 10 to 30 parts are preferred.

The lengths l and m of the spacers in the prepolymers (I) and (II) may be different, but the groups introduced into the copolymer by the prepolymer (II) containing a mesogen group (hereinafter referred to as Lc ) Is preferably the same from the viewpoint that the photochromic group can be interposed between the photochromic groups.

The degree of polymerization of the copolymer is not limited, but the degree of polymerization affects the temperature range in which liquid crystallinity is exhibited.

The method for producing the copolymer is not particularly limited, and the copolymer can be produced by a commonly used polymerization method.

The resulting copolymer is schematically shown in FIG. In FIG. 1, (1) a main chain formed by copolymerizing prepolymers (I) and (II), (2) a spacer, and (3) a mesogen group introduced by the prepolymer (II). , (4a) are photochromic groups a, (4) which are spiropyran groups introduced by the prepolymer (I).
b) is a photochromic group II which is a group derived from the photochromic group I (4a). Sp is a ring-closing stabilizer and Mer is a ring-opening stabilizer, and Mer is thermally stabilized by the regular orientation of Lc.

The photochromic material of the present invention containing the copolymer (A) gives a threshold value to the photoisomerization reaction, can further suppress the thermal isomerization reaction, and can achieve the intended purpose. Therefore, the coloring and decoloring of the photochromic material of the present invention is changed to a colored state by irradiation with ultraviolet light,
It can be made colorless by strong near infrared rays, strong visible light or heat. This conversion can be repeated many times.
The colored state does not return to a colorless state with relatively weak near-infrared light and visible light.

The rewritable optical recording medium of the present invention uses the above-described photochromic material of the present invention, and usually has a substrate coated with the photochromic material.

Examples of the substrate include a substrate made of glass, ceramic, metal, plastic, or the like, which is generally used for a translucent or light-reflective optical recording medium.

The method for applying the photochromic material to the substrate is not particularly limited. For example, a solution obtained by dissolving the copolymer (A) in a solvent is coated by a spray method, a spin coating method, or the like, dried, heated, A method of coating the melted material and cooling it can be used.

The thickness of the film formed in this manner is usually 0.3 to 3.0 μm from the point of using a recording / reproducing method using a laser beam.
m is preferred.

In the rewritable optical recording medium of the present invention, the film of the photochromic material formed as described above may be subjected to a treatment such as annealing, and furthermore, for example, 0.
A film of aluminum or the like having a thickness of about 02 to 1 μm may be formed by a commonly used method such as a vacuum evaporation method.

For recording information on such a rewritable optical recording medium of the present invention, for example, first, a strong visible light of about 3 to 20 mW is focused on a medium initialized with an ultraviolet wavelength of 380 nm and about 1 J / cm ^2. This can be performed by irradiating the recording portion to make the recording portion colorless.

The recorded information has a wavelength of about 600 to 800 nm,
Reproduction can be performed by determining the presence or absence of coloring of each bit with relatively weak light of about 0.2 to 0.8 mW. The determination of whether or not each bit is colored may be performed using either transmitted light or reflected light.

As a light source for recording, reproducing, or erasing information, a laser, a mercury lamp, a xenon lamp, a metal halide lamp, a halogen lamp, a tungsten lamp, and the like can be used, and an optical filter can be used in combination.

Next, the photochromic material and the recording medium of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

Examples 1 to 5 A benzothiopyran-based spiropyran prepolymer (prepolymer (I)) was synthesized as described below.

That is, 5-nitrothiosalicylaldehyde was converted according to the method of S. Arakawa et al. The benzothiopyran-based spiropyran was then synthesized according to the method of J. (Where k represents 2, 3 or 6).

The liquid crystal prepolymer (prepolymer (II)) is prepared according to the method of M. Portugal et al. (Where j is 2, 3, 4 or 6, R ⁹ is CN or —OCH ₃
Is shown).

Table 1 shows an example of the result of identifying the prepolymer (II).

0.2 mM of the prepolymer (I) and 2 mM of the prepolymer (II) thus obtained were mixed with 2 mol% of AIBN based on the total amount of the prepolymer (I) and the prepolymer (II).
Was used as an initiator to copolymerize in 10 ml of toluene to obtain copolymers 1 to 5 shown in Table 2 (corresponding to Examples 1 to 5, respectively).

3 mg of each of the obtained copolymers (photochromic materials) was placed on a glass plate, melted at 100 ° C., covered with a cover glass, and uniformly spread to prepare a 10 μm-thick test piece.

The obtained five test pieces were irradiated with ultraviolet light (a light from a 500 W xenon lamp passed through an ultraviolet filter (UV-D33S, manufactured by Toshiba Kasei Co., Ltd.)) for 1 minute, immediately after irradiation and in a dark room. The color change of the test piece after storage for 3 months was examined. The test piece before irradiation was yellow. The results are shown in Table 3.

For a test piece (test piece 1) prepared from copolymer 1, an absorbance meter (GP-25 manufactured by Nippon Kogaku Co., Ltd.) was used.
Using 0), the absorption spectra of light before and after irradiation with ultraviolet light at 25 ° C. were examined. Table 2 shows the results. FIG. 2 (a) shows the light absorption spectrum of the test piece before irradiation with ultraviolet light, and FIG. 2 (b) shows the light absorption spectrum of the test piece after irradiation with ultraviolet light.

From FIG. 2, it can be seen that the test piece 1 shows photochromism, the colored body shows an absorption peak at 705 nm, and has absorption in the near infrared region. (Note that λmax of the benzothiopyran-based spiropyran prepolymer is 680 nm, and the absorption peak can be reduced by using the photochromic material of the present invention.
It can be seen that 25 nm has shifted to the longer wavelength side. Further, when the test piece 1 after the ultraviolet irradiation was irradiated with visible light and heat, the spectrum returned to the light absorption spectrum of the test piece 1 before the ultraviolet irradiation, and this could be repeated many times.

The reaction rate [k] of light and thermal decolorization in the test piece 1 was determined from the change over time of the transmitted light of the colored body with respect to light having a wavelength of 680 nm under continuous irradiation of visible light (680 nm). The Arrhenius plot is shown in FIG. In FIG. 3, (c) shows a photo-decolorization reaction process, and (d) and (e) show a thermal decolorization reaction process.

From FIG. 3, it can be seen that the copolymer 1 is in a manic state at 80 ° C. or higher, and in a glassy nematic state below 80 ° C., and at room temperature, the thermal decoloring rate is very slow from the step (e). It is considered that the thermal decoloring process of (e) was due to a process not stabilized by Lc.

Further, the change in absorbance at 680 nm when the irradiation was performed with the intensity of the ultraviolet rays set to the above 5% was measured. The results are shown in FIG.

It can be seen from FIG. 4 that if the ultraviolet light is weak, it does not become a colored body.

The same applies to the intensity of visible light when making a colorless body.

From the results of Examples 1 to 5, the photochromic material of the present invention using the copolymer (A) has photochromic properties, the coloring state is thermally stable, and the coloring / decoloring state indicates light intensity. It can be seen that can be controlled by.

Example 6 1 200 mg of the copolymer obtained in Example 1 was dissolved in 2 ml of tetrahydrofuran, and this was applied by a spin coating method on a 130 mm ^φ non-grooved glass plate. Film thickness after drying is about 1μm
Met. After annealing at 80 ° C. for 10 minutes, an aluminum layer of about 550 ° was formed as a reflective film on the film by a vacuum evaporation method to obtain a rewritable optical recording medium.

Then, the obtained rewritable optical recording medium was irradiated with ultraviolet rays using a black light to develop a color on the entire surface, and a signal was recorded (erased) with a semiconductor laser. The recording conditions are as follows:
780nm wavelength semiconductor laser power 14 ~ 20mW, beam half width 1.3μm, disk linear velocity 3.85m / S, carrier frequency 10
0KHz ~ 1MHz, duty ratio 50%, playback power 1m
W.

FIG. 5 is a sketch drawing of a micrograph showing recording dots when recording with a sweep signal of 14 to 20 mW and a power of 100 kHz to 1 MHz. The recording line width is about 1 μm. The thin part (f) of the white line on the left side of the figure is a part written at 14 mW and 100 kHz, and the right part (g) is a part recorded at 20 mW. 20
The memory at mW, 1 MHz was 27 dB in C / N ratio. When the recording power was 14 mW or less, recording was not possible under the above conditions, and it was found that the recording power had a threshold value. That is, the recording sensitivity was 350 to 500 mJ / cm.

In addition, it was found that about 6000 times of continuous reproduction was possible with a reproduction power of 1 mW. FIG. 6 shows an oscilloscope waveform photograph of the reproduced signal. In the figure, the vertical axis represents the reflection change rate (about 10
% / Div), and the horizontal axis shows the bit length (10 μm / div).

Furthermore, it was confirmed that this recording can be erased by irradiating ultraviolet rays with a reproduction black light, and that recording can be repeated with a semiconductor laser.

As for the stability of record keeping, we have already cleared 150 days at room temperature.

The results of Example 6 show that the rewritable optical recording medium to which the photochromism of the present invention is applied has excellent characteristics.

Note that in Example 6, the reproduction stability can be further stabilized if the conditions are mildly thermally. Further, the substrate used here has no groove, and a high refractive index layer is also provided. Since these are not provided, C / N
The ratio and the recording sensitivity are further improved.

[Effects of the Invention] The photochromic material of the present invention improves the stability of the colored state and gives a threshold value to the photoisomerization reaction, so that the colored / decolored state is extremely easy to control, and various recording / memory materials, It can be used as a display material such as a display, a photographic printing material, an optical filter, a light meter, a masking material and the like.

Further, the rewritable optical recording medium of the present invention is a rewritable optical recording medium that can be rewritten in a photon mode using semiconductor laser light utilizing photochromic characteristics. Also,
In addition to the recording medium, it can be used as, for example, a display device.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a copolymer (A) used for the photochromic material of the present invention, FIG. 2 is a graph showing a spectrum change of the copolymer 1 before and after ultraviolet irradiation,
FIG. 3 is a graph plotted by the Arrhenius equation of the reaction rate of light and thermal decolorization of Copolymer 1, FIG. 4 is a graph showing the time-dependent change in the coloration of Copolymer 1 at low UV intensity, and FIG. FIG. 5 is a sketch drawing of a micrograph showing recording dots of the rewritable optical recording medium of Example 6, and FIG. 6 is Example 6.
3 is an oscilloscope waveform photograph of a reproduction signal of the rewritable optical recording medium of FIG. (Signs in the drawings) (1): Main chain (2): Spacer (3): Mesogen group (4a): Photochromic group I (4b): Photochromic group II

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiko Tsutsumi 8-1-1 Tsukaguchi Honcho, Amagasaki-shi, Hyogo Inside Materials Research Laboratory, Mitsubishi Electric Corporation (72) Inventor Yoshiyuki Nakaki 8-1-1 Tsukaguchi-Honcho, Amagasaki-shi, Hyogo No. 1 Inside Mitsubishi Electric Corporation Industrial System Research Laboratories

Claims (2)

(57) [Claims] 1. A compound of the general formula (I): (Wherein, R ¹ is a hydrogen atom or a methyl group, R ² and R ³ are each a hydrogen atom, a hydroxyl group, a halogen atom, an amino group, a lower alkoxy group or an aryl group, and R ² and R ³ are the same group. And may be different groups, l is 1-20
A benzothiopyran-based spiropyran prepolymer represented by the general formula (II): (Wherein, R ⁴ is a hydrogen atom or a methyl group, R ⁵ is a nitrile group, a lower alkoxy group, —OC ₆ H ₁₃ or m is an integer of 1 to 20), and a photochromic material containing a copolymer with a liquid crystal prepolymer. 2. A rewritable optical recording medium using the photochromic material according to claim 1.