JPS6313791A - Optical recording medium - Google Patents

Abstract

PURPOSE:To enhance the weatherability of an optical recording medium, by a method wherein a recording layer consists of cyanine dye and polybutyl metacrylate. CONSTITUTION:Cyanine dye used for a recording layer is so constructed that nitrogen-containing heterocycles are combined with the both ends of a methine chain, as shown by a formula I (wherein (n) represents the natural number of methine chains, R and X<-> respectively represent an alkyl group and an anion such as Cl<->, Br<->, I<->, and ClO4<->). On the other hand, polybutyl, metacrylate is shown by formulas II (poly-tert-butyl metacrylate) and III (poly-iso-butyl metacrylate). The composition ratio of the aforesaid cyanine dye and polybutyl metacrylate is in the range of 25/75<A<75/25 (cyanine dye/polybutyl metacrylate=A). The aforesaid cyanine dye and polybutyl metacrylate are dissolved in a solvent to meet the aforesaid composition, thereafter being coated to a transparent substrate to form a recording layer. As the substrate, a rigid transparent substrate of plastic etc. for a normal optical disk is preferable. As the solvent, a general-purpose solvent of every sort such as methanol and ethanol and a mixed solvent of these are used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium typified by an optical disk, and particularly relates to an improvement of a so-called organic dye-based write-once optical recording medium.

[Summary of the invention]

The present invention aims to improve the light resistance of an optical recording medium in which a recording layer is formed on a substrate by composing the recording layer with a cyanine dye and polybutyl methacrylate. It is something.

[Conventional technology]

Optical recording systems have the characteristics of non-contact recording and playback, are easy to handle, and are resistant to scratches and dust. Since it has the advantage of being ten to several hundred times larger, it is expected to be used for large-capacity files such as code information and image information.

Among these, there is a high level of interest in so-called write-once optical recording media, which allow users to read directly after writing. Research is being actively conducted.

By the way, the recording material used for this type of optical recording medium is required to have appropriate light absorption coefficient and reflectance, and conventionally, TC
A metal or metal alloy thin film such as or Ti, a metal compound thin film such as a Te0X thin film, a silver-lead HJ film, etc. have been employed. However, since these gold BFg films are formed using vacuum thin film forming techniques such as sputtering and vacuum deposition, there are problems in terms of mass production, and the resulting optical recording media are expensive. There were drawbacks.

Under these circumstances, organic dye materials are used as recording materials,
Optical recording media have been proposed in which a recording layer is formed using a coating means. In this way, optical recording media using organic dye materials as recording materials can be said to have high practicality in terms of mass production and product cost, since the recording layer can be coated by means such as a spin code.

There are two types of organic dye-based optical recording media: one in which a reflective film is provided between the substrate and the recording layer and the difference in reflectance on the reflective film is read as 1ε; There is a type that directly reads the rate through a transparent substrate, but the former requires forming a reflective film by a method such as vapor deposition, which reduces the process advantage, and the underlying reflective film has a high heat transfer rate. Therefore, it has drawbacks such as large energy loss and the need to increase the output of the laser for irradiation more than necessary.

Therefore, since dyes with high reflectance appeared due to advances in dye synthesis technology, there has been a rise in the number of dyes containing the above organic dyes! Optical recording media in which the reflectance of three layers can be directly read through a transparent substrate are being actively adopted.

[Problem that the invention seeks to solve]

By the way, the above-mentioned optical recording medium utilizes the fact that the temperature of the recording layer in the irradiated area increases rapidly when the organic dye absorbs laser light. It forms the recording focus. Therefore, the organic dye material used must be able to effectively absorb the laser light in the wavelength range of the laser light,
At the same time, it is required to have properties such as good reflection of laser light in this wavelength range and solubility in an appropriate solvent.

Cyanine dyes have large absorption in the near-infrared region, which is the wavelength range of semiconductor lasers, for example, and also have high reflectance in the near-infrared region, so they are considered promising as recording materials for write-once optical recording media. .

However, cyanine dyes generally have poor light resistance, and when long-term storage of information is assumed, there remains concern about their reliability as optical recording media.

Therefore, the present invention has been proposed to solve the above problems, and provides an optical recording medium that does not deteriorate in light resistance even when stored for a long period of time, has excellent reliability, and is excellent in mass production. The purpose is to

[Means for solving problems]

In order to achieve the above-mentioned object, the present inventors have conducted extensive research and found that a recording layer that combines a cyanine dye and polybutyl methacrylate is capable of reflecting laser light in the hn wavelength range. It has been found that not only the light resistance and light absorption coefficient are high, but also the light resistance does not deteriorate over a long period of time, and the mechanical strength is also high.

The optical recording medium of the present invention has been completed based on the above-mentioned findings, and is characterized by the fact that a recording layer containing a cyanine dye and polybutyl methacrylate is formed on a substrate.
H&.

The cyanine dye used in the recording layer in the present invention is
- Formula (1) (where n represents the number of methine chains and is a natural number,
R hafurkyl group, X- is cz-1Br-+I-+C
Each represents an anion such as lO4-. ),
It has a structure in which nitrogen-containing heterocycles are bonded to both ends of a methine chain. That is, it represents the above-mentioned nitrogen heterocycle, and examples of such nitrogen-containing heterocycle include i)) ii) and the like. Note that these nitrogen-containing heterocycles may have some of their hydrogen atoms substituted with an alkyl group or the like.

Specific examples of such cyanine dyes include, for example: etc.

On the other hand, polybutyl methacrylate used in the recording layer in the present invention has the effect of improving the light resistance of the cyanine dye, and is represented by the following structural formula (■), ([[l)] is used.

(n) (I[I) The above polybutyl methacrylate has good compatibility with cyanine dyes and excellent film-forming ability, so it is uniformly dispersed in the cyanine dyes.

Here, the composition ratio of the cyanine dye and polybutyl methacrylate (cyanine dye/polybutyl methacrylate=A) is preferably in the range of 25/75<A<75/25. That is, when A≦25/75, the light resistance of the recording layer deteriorates significantly, and conversely, when A≧75/25, the reflectance of the recording layer decreases and the C/N characteristics deteriorate, which is not preferable.

In the optical recording medium of the present invention, as shown in FIG.
After the cyanine dye and polybutyl methacrylate are dissolved in a solvent to have the above composition, the transparent substrate (2
) to form recording N(1). To record information signals on the obtained optical recording medium, a transparent substrate (
2) The recording layer (1) is irradiated with laser light focused to a diameter of several μm from the side, melting the polybutyl methacrylate in the irradiated area, and melting, decomposing, and sublimating the cyanine dye to form recording bits. do. Also, during reproduction, laser light of a predetermined wavelength is irradiated from the substrate (2) side in the same way, and the information No. 1ε is read based on the difference in reflectance between the focused area and the space area (the area where the focused area is not formed). The structure is as follows.

The laser light to be irradiated may be appropriately selected depending on the absorption wavelength of the recording material (i.e. cyanine dye), and specifically, semiconductor laser, CO, gas laser, ^r gas laser + tie Ne gas laser, ruby laser,
Examples include dye lasers.

The substrate (2) may be of any type as long as it is used in ordinary optical discs, and preferably is a transparent substrate having rigidity such as a glass substrate or a plastic substrate such as polycarbonate resin.

In addition, methanol and ethanol are used as solvents when coating cyanine dye and polybutyl methacrylate to form a recording layer.

Alcohols such as isopropyl alcohol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, ethers such as ethyl ether, dioxane, and tetrahydrofuran, and ethyl acetate.

Examples include esters such as n-butyl acetate, various general-purpose solvents such as henzene, toluene, xylene, n-hexane, cyclohexane, acetonitrile, dimethylformamide, dimethylsulfoxide, chloroform, and mixed solvents thereof.

Furthermore, as a coating method, usual methods are used, such as spin code method, spray coating method, roll coating method, dipping method, etc. Among them, spin coating method is used because of its excellent uniformity of the coating film obtained. The law is preferred.

[Effect]

The cyanine dye used as the recording material of the optical recording medium of the present invention has a high optical absorption coefficient and reflectance in the wavelength region of laser light, and can obtain good optical recording and reproducing characteristics.

Further, by adding a predetermined amount of polybutyl methacrylate to the cyanine dye, the light resistance of the cyanine dye is significantly improved.

〔Example〕

The present invention will be described below based on specific examples.

First, 1% by weight of each of cyanine dye (manufactured by Nippon Kanko Shiki Co., Ltd., trade name NK-125) and polybutyl methacrylate [poly-tert-butyl methacrylate shown in the structural formula (II) above] was added. After dissolving in methyl ethyl ketone, this? Spin-coating Yong Ya on a glass substrate? The film was coated and dried to prepare an optical recording medium with a recording layer having a thickness of 1000.

The structure of the cyanine dye used in this example is the following formula (I
V).

In the above Example 1, an optical recording medium was produced in the same manner as in the above Example 1 except that poly-1so-butyl methacrylate shown in the structural formula CII+) was used as the polybutyl methacrylate.

Comparison ± For comparison, an optical recording medium was produced in the same manner as in Example 1 except that nitrocellulose was used instead of polybutyl methacrylate.

Next, the above Example 1. The optical recording media obtained in Example 2 and Comparative Example were heated to 100% by using a tungsten lamp.
The recording layer was irradiated with light of 0.00 lux, and the state of deterioration of the absorbance of the recording layer at this time was examined. The results are shown in FIGS. 2 and 3.

As is clear from FIG. 2 and the third article, when the deterioration rate of the comparative example is 1, the deterioration rate of Example 1 is 0.1.
4. It was found that the value of Example 2 was 0.13.

In other words, an optical recording medium in which polybutyl methacrylate is added to a cyanine dye as a recording layer has a life span of 7 to 70% compared to one in which nitrocellulose is added.
It can be expanded more than 8 times.

Therefore, it can be said that an optical recording medium whose recording layer is composed of a cyanine dye and polybutyl methacrylate can maintain reliability of information signals for a long period of time.

Further, a predetermined signal was written on the optical recording medium obtained in the above example at a writing laser light output of 8 d, a linear velocity of 2 m1sec, and a modulation frequency of I M/Hz, and a continuous laser output of 0.21 was written. When the signal was reproduced and the C/N of the reproduced signal was checked, it was found to be 50 dB or more (maximum 55 dB).

As a result, it was found that the optical recording medium of the present invention exhibited recording and reproducing characteristics with little noise and high practicality.

〔Effect of the invention〕

As is clear from the above description, in the optical recording medium of the present invention, since a dispersion system of cyanine dye and polybutyl methacrylate is used in the recording layer, light resistance is significantly improved, and at the same time, C /N is also significantly improved.

Therefore, since the reliability of the information signal can be maintained for a long period of time, an extremely practical optical recording medium can be provided.

In addition, the optical recording medium of the present invention has a recording layer formed by a coating technique that has been widely used in the past, so it is advantageous in terms of mass production and productivity, and it also has the advantage of reducing manufacturing costs. have.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing the structure of an optical recording medium. FIGS. 2 and 3 are characteristic diagrams showing the deterioration rate of the t3 calendar as changes in absorbance over time. 1...Recording layer 2...Substrate

Claims (1)

[Claims] An optical recording medium comprising a recording layer containing a cyanine dye and polybutyl methacrylate formed on a substrate.