JP2890760B2 - Optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium used for an optical disk or the like as a high-density recording medium for recording information such as data and images.

2. Description of the Related Art Conventionally, a photochromic substance has been known as a material that causes a reversible color change.

Among the photochromic substances, spiropyran, which is an organic compound exhibiting a photoring-opening reaction, has been most frequently studied, and many spiropyrans have been published to date.

For example, when the following colorless spiropyran is irradiated with ultraviolet light, it changes to merocyanine and exhibits a red color. This merocyanine returns to the original spiropyran upon irradiation with visible light.

As an application of this photochromic substance, there is a rewritable optical recording medium.

The optical recording medium is initialized by applying spiropyran onto a disk and setting the entire surface to a colored state by ultraviolet rays.
Recording can be performed by converging and irradiating this medium with laser light having a wavelength suitable for changing from a colored body to a colorless body. In addition, the spot can be initialized again by irradiating ultraviolet rays.

Problems to be Solved by the Invention In a photochromic material, a colorless or colored body is generally thermally unstable. For example, the above spiropyran compound has low stability of the colored body.

To overcome this low stability, for example,
-224413 proposes to improve the stability of a colored body by forming an association of a compound having an alkyl chain introduced into a spiropyran skeleton in an LB film.

However, not all compounds in which an alkyl chain has been introduced into the spiropyran skeleton can form an aggregate.In many spiropyrans, it is difficult to form an aggregate, and since the colored body is unstable, it can be used as an optical recording medium. Did not.

Accordingly, an object of the present invention is to provide an optical recording medium having a photochromic substance that is stable against light.

Means for Solving the Problems An optical recording medium is formed by mixing a photochromic substance having a chemical structure represented by the following general formula, which is difficult to form an aggregate, with an ionic surfactant and a nonionic surfactant. I do.

Wherein R ₁ is an alkyl group having 8 to 30 carbon atoms, R ₂ is hydrogen, a methoxy group or CH ₂ OCOC _n H _{2n + 1} (n = 1 to 3)
0), X represents either a halogen or a nitro group, and Y represents hydrogen, a halogen or a nitro group.

Effect According to the present invention, spiropyran is formed by the interaction between the long alkyl chain of the surfactant and the long alkyl chain of the spiropyran substance and the ability of the surfactant to form a self-assembled aggregated state. A molecular sequence that facilitates coalescence is formed.

The ionic surfactant stabilizes the ionized state of the spiropyran-colored merocyanine, and the nonionic surfactant stabilizes the order of the assembled state. These effects are different from the effect of imparting surface activity by salt formation as in the ion complex method.

By irradiation with ultraviolet light or ultraviolet light in a heated atmosphere, the colored merocyanine of spiropyran forms an aggregate and the light stability is improved.

Examples Examples of the present invention will be described below.

The used photochromic substances are spiropyrans A to D represented by the following chemical structural formulas.

These molecules have a long-chain alkyl group, and can produce a uniform cast film, and can produce a stable LB film by itself or by mixing with octadecane or with stearic acid. .

However, the colored merocyanine was a monomer and did not form an aggregate.

Therefore, the coloring state was unstable, and it was impossible to use it as an optical recording medium.

Therefore, the following quaternary dioctadecyldimethylammonium was used as the cationic surfactant of the present invention.

As the anionic surfactant, a sulfonate-based surfactant F shown below was used.

Further, as a nonionic surfactant, methyl stearate of the following linear saturated fatty acid ester was used.

CH ₃ (CH ₂ ) ₁₆ COOCH ₃ Surfactant G The stabilization of the colored state due to the formation of the aggregate depends on the mixing ratio of the three components of the photochromic substance, the ionic surfactant and the nonionic surfactant. It can be realized without.

However, in order to obtain a sufficient optical density for the recording layer of the optical recording medium, the mixing ratio of the photochromic substance, the ionic surfactant and the nonionic surfactant is 1: 1.
0.5 pairs (0.5-10) to 1-4 pairs (0.5-10) are desirable.

Example 1 Spiropyran A, surfactant E and surfactant G
Was dissolved in methyl alcohol / benzene at a ratio of 1: 1 to 2 to prepare a sample for development.

The aqueous phase was pure water obtained by distilling ion-exchanged water once, and the water temperature was 20 ° C.

The formation of the monomolecular film at the air-water interface was performed at a compression speed of 10 mm / min.

After that, the surface pressure is 25mN / m and the cumulative speed is 10m / min by LB method.
Under the conditions described above, nine layers were accumulated on the quartz plate substrate.

The LB film thus produced was colorless immediately after the accumulation as shown by the broken line in FIG. 1, and was colored blue-green as shown by the solid line in FIG.

From this absorption spectrum, it was confirmed that a sharp J-aggregate having a maximum wavelength of 650 nm was formed.

This colored body was stable with no change in absorbance at all with the passage of time in a dark place.

 An optical recording medium was formed using this thin film as a recording layer.

Irradiation of a red semiconductor laser with a wavelength of 670 nm results in about 1
A recording bit having a diameter of μm could be formed.

Further, by irradiating the recording state with ultraviolet rays at 35 ° C., erasing could be performed, and repetition of recording / erasing was confirmed.

Comparative Example 1 Spiropyran A and octadecane were dissolved in benzene at a ratio of 1: 3 to prepare a developing sample.

The aqueous phase was pure water obtained by distilling ion-exchanged water once, and the water temperature was 20 ° C.

The formation of the monomolecular film at the air-water interface was performed at a compression speed of 10 mm / min.

After that, the surface pressure is 25mN / m and the cumulative speed is 10mm / min by LB method.
Under the conditions described above, seven layers were accumulated on a quartz plate substrate.

The LB film thus produced was colorless immediately after the accumulation as shown by the broken line in FIG. 2, and was colored blue as shown by the solid line in FIG.

The absorption was a broad spectrum with a maximum wavelength of about 610 nm, and no J-aggregate was formed.

This colored body had a decrease in absorbance in a few minutes when left in a dark place, and could not be used as an optical recording medium because it was unstable to light.

Example 2 Spiropyran B, Surfactant F and Surfactant G
Was dissolved in methyl alcohol / benzene at a ratio of 1: 2: 2 to prepare a casting solution.

A film was formed from this solution using a casting method by spin coating.

 Spin speed was 2000 rpm for 20 seconds.

The thin film thus produced was initially colorless as shown by the broken line in FIG. 3, but was colored blue-green with an absorption maximum wavelength of 650 nm as shown by the solid line in FIG. An aggregate was formed, showing good stability of the colored product.

Using this thin film as an optical recording medium, recording and erasing could be performed using irradiation of a red semiconductor laser having a wavelength of 670 nm and irradiation of a third harmonic (wavelength of 352 nm) of a Nd: YAG laser in a 40 ° C. atmosphere.

Comparative Example 2 Spiropyran B and surfactant F were dissolved in methyl alcohol / benzene at a ratio of 1: 3 to prepare a casting solution.

A film was formed from this solution using a casting method by spin coating.

 Spin speed was 2000 rpm for 20 seconds.

The thin film thus produced was colorless immediately after accumulation as shown by the broken line in FIG. 4, and was colored blue as shown by the solid line in FIG. The spectrum was broad at a wavelength of about 612 nm, and no J-aggregate was formed.

Further, in the colored state, the absorbance was reduced in a few minutes in a dark place, and it could not be used as an optical recording medium due to instability.

Example 3 Spiropyran C, Surfactant E and Surfactant G
Are mixed at a ratio of 1: 1 to 3 to form a recording layer by the LB method, and the absorption maximum wavelength of the colored body by the J-aggregate is about 645 nm.
Met.

Further, spiropyran D is similarly mixed with surfactant E and surfactant G at a ratio of 1: 1 to 5 to form a recording layer by the LB method. It was about 640 nm.

Both optical recording media using spiropyran could be recorded by an excimer laser-excited dye laser with an oscillation wavelength corresponding to each absorption maximum wavelength, and could be erased by excimer laser irradiation in a 35 ° C atmosphere. .

Effect of the Invention Due to the optical recording medium comprising a mixture of a photochromic substance, an ionic surfactant and a nonionic surfactant having a chemical structure represented by the following general formula of the present invention, optical recording due to unstable colored body It has become possible to apply a photochromic substance that cannot be used as a medium to a rewritable optical recording medium.

Wherein R ₁ is an alkyl group having 8 to 30 carbon atoms, R ₂ is hydrogen, a methoxy group or CH ₂ OCOC _n H _{2n + 1} (n = 1 to 3)
0), X represents either a halogen or a nitro group, and Y represents hydrogen, a halogen or a nitro group.

[Brief description of the drawings]

1 and 3 are absorption spectrum diagrams of a recording layer of one embodiment of the optical recording medium of the present invention, and FIGS. 2 and 4 are absorption spectrum diagrams of a recording layer of a conventional optical recording medium.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiji Ando 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-846 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) B41M 5/26 G11B 7/24

Claims (5)

(57) [Claims] 1. An optical recording medium comprising a mixture of a photochromic substance having a chemical structure represented by the following general formula, an ionic surfactant and a nonionic surfactant. Wherein R ₁ is an alkyl group having 8 to 30 carbon atoms, R ₂ is hydrogen, a methoxy group or CH ₂ OCOC _n H _{2n + 1} (n = 1 to 30)
X is either a halogen or a nitro group, Y is
Represents any one of hydrogen, halogen, and a nitro group. 2. The ionic surfactant is a cationic surfactant of an amine having an alkyl chain or an ammonium having an alkyl chain, wherein at least one of the alkyl chains has 8 to 30 carbon atoms. The optical recording medium according to claim 1, wherein 3. The ionic surfactant is an anionic surfactant of a carboxylic acid, a sulfonic acid or a salt thereof, and has at least one alkyl chain having 8 to 30 carbon atoms. The optical recording medium according to claim 1, wherein 4. The optical recording medium according to claim 1, wherein the nonionic surfactant is a linear saturated fatty acid ester. 5. The optical recording medium according to claim 1, wherein the halogen is bromine.