JPH07102739B2 - Optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium which can be recorded by a semiconductor laser or the like.

Conventional technology The arrival of the information age will bring about a dramatic increase in the amount of information.
The diversified and bloated information cannot be effectively used without a large-capacity and quickly accessible memory medium. It can be said that a recordable optical disk is a correct and optimum external memory under such circumstances. Optical discs that can be recorded and played by the user are classified into two types: rewritable and erasable type (hereinafter referred to as E / R disc) and one-time recordable type (hereafter referred to as W / O disc).
Both of these are expected to coexist and develop by making the best use of their respective characteristics. For that purpose, the most important condition is that the latter W / O disk can be mass-produced at low cost. Recently, a coated W / O disk using an organic dye has been attracting attention as one that meets such a purpose. (Reference: Synthetic Organic Chemistry, Vol. 43, p. 334 (1985)) Problems to be Solved by the Invention There are some conditions that must be satisfied as a dye used as a recording film of an optical disk system using a semiconductor laser as a light source. (1) It exhibits a spectral absorption characteristic in the oscillation wavelength band of a semiconductor laser or the like. (2) It has an appropriate reflectance in the above wavelength band. (3) It dissolves in a solvent. As examples of dyes satisfying these conditions, cyanine dyes can be cited as shown in the above-mentioned references. Since naphthoquinone type and phthalocyanine type are not soluble in a solvent, a film cannot be formed by coating, leaving a problem in mass productivity. It has been known that some cyanine dyes have spectral absorption in the infrared region, and many studies have been made as an optical recording material using a semiconductor laser. Some cyanine dyes have excellent characteristics in terms of initial performance such as sensitivity, solubility, reflectance, and spectral absorptivity, but the drawback is that they are faded by external light such as sunlight or used for reproduction. The signal was deteriorated by continuous irradiation of weak light (repeated reproduction), which was insufficient in terms of reliability. Various stabilizers have been investigated to overcome this drawback. (For example, JP-A-59-81194) However, since the main body of the cyanine dye is very unstable, sufficient stability cannot be ensured even after improvement.

Means for Solving the Problems The optical recording medium of the present invention comprises a transparent substrate and at least one component of an iodine or perchloric acid adduct of a squarylium dye represented by the following general formula and formed on the transparent substrate. As the recording film layer.

(Wherein R _{1 to} R ₄ are aryl groups, or R ₁ and R ₂
Or a saturated hydrocarbon ring of 5 to 7 membered ring in which R ₃ and R ₄ are linked, an aromatic hydrocarbon ring, or a hetero ring, and R ₅
And R ₆ are hydrogen, an aryl group or an alkyl group, and Y is an element of Group VI. ) Function The spectral absorption maximum is 700 nm or less in the state of the dye alone before the formation of the adduct, but due to the formation of the adduct, the absorption peak shifts to around 800 nm, and it is possible to record and reproduce with a semiconductor laser or the like. Become. Moreover, it is more stable against external light and repeated reproduction as compared with cyanine dyes.

Examples In the present invention, the following general formula (1) is shown. It has an iodine or perchloric acid adduct of a squarylium dye as an optical recording layer, which is formed on a transparent substrate. In formula (1), R _{1 to} R ₆ are aryl groups, and
R ₁ and R ₂ or R ₃ and R ₄ may be linked to form a 5- to 7-membered hetero ring, an unsaturated hydrocarbon ring, or a saturated hydrocarbon ring. Further, Y in the formula (1) is an element of Group VI, and O, S, Se and Te are suitable among them. That is, it has a structure in which an oxazole, thiazole, selenazole ring or the like is bonded to a squarylium skeleton via a methine group. When these compounds exist in a single state, the spectral absorption peak exists at 600 to 650 nm and recording / reproduction by a semiconductor laser is impossible, but an adduct of the compound represented by the general formula (1) with iodine or perchloric acid. , The spectral absorption peak shifts by a long wavelength of about 200 nm and overlaps with the oscillation wavelength range of the semiconductor laser, which enables recording by the semiconductor laser. The appropriate amount of iodine or perchloric acid added is 0.6 to 1.3 with respect to the compound. Further, the adduct of the general formula (1) is soluble in an organic solvent and can form a uniform film by coating on a transparent substrate. Here, a spin coating method was used so as to be suitable for forming a film on an optical disk. As the transparent substrate, glass, polymethylmethacrylate, polycarbonate, polyamideimide or the like can be used. Further, a groove for tracking servo may be formed on the transparent substrate, and the dye film described in the present invention may be formed thereon. When the solution of the dye may dissolve the transparent substrate, a thin transparent protective film may be previously formed on the substrate. As the transparent protective film, SiO ₂ , SiO, alkylsilane, polysiloxane, etc. are suitable.

Example 1 As shown in the figure, the thickness is 1.2 mm, the depth is 0.06μ, and the width is 0.6μ.
10 nm thick SiO ₂ film on the surface of the track on the substrate 1 made of polymethylmethacrylate (hereinafter referred to as PMMA) in which the grooves (hereinafter referred to as tracks) are spirally formed at 1.6 μ pitch 2 is formed by sputtering.
A methylene chloride solution of the iodine adduct of the compound represented by the following formula (2) was spin-coated on this to form a recording film 3 having a thickness of 60 nm.

While rotating the substrate, the light of a semiconductor laser (hereinafter referred to as LD) focused on a track by a collimating lens having a numerical aperture of 0.5 was irradiated to record a signal of 1 MHz.
The recording power at this time was 4 mW, and the rotation speed was constant at a linear velocity of 3 m / sec. Table 1 shows the characteristics when the recorded signal was reproduced at 0.4 mW. Table 1 also shows the results obtained by performing the repeated reproduction test on the same track and measuring the decrease amount of the reproduced C / N with respect to the initial value after the continuous reproduction of 10 ⁶ times. Also,
Playback after a disc has been left outdoors for one month continuously
The results of measuring the decrease in C / N are also shown in Table 1 as a fading test.

Example 2 Iodine adducts of the compounds represented by the following formulas (3) to (6) were deposited to 60 nm on the PMMA substrate having the same shape as in Example 1 by the same method.
Table 1 shows the results of evaluation of the same items as in Example 1 by preparing an optical disc that was applied thickly to form a recording film.

Comparative Example 1 On a PMMA substrate having the same shape as that of Example 1, a cyanine dye compound represented by the following formula (7) was applied in a thickness of 60 nm by the same method to prepare an optical disc as a recording film, and the same as Example 1. Table 1 shows the results of evaluation of the above items.

Example 3 On a polycarbonate substrate having the same shape as in Example 1, the perchloric acid adducts of the compounds represented by the formulas (2) to (3) were applied to a thickness of 60 nm by the same method to prepare an optical disc as a recording film. Table 2 shows the results of evaluation of the same items as in Example 1.

Comparative Example 2 A PMMA substrate having the same shape as in Example 1 was treated with the same method as the compound represented by the formula (2) without adding an iodine adduct to 60 nm.
Table 2 shows the results of evaluation of the same items as in Example 1 by producing an optical disk having a recording film by applying a thick coating.

EFFECTS OF THE INVENTION As described above, the optical recording medium having the recording film of the iodine or perchloric acid adduct of the squarylium compound according to the present invention has a good initial performance, and further has a continuous repetitive reproduction performance and a light resistance. Are better.

[Brief description of drawings]

The figure is a sectional view for explaining the structure of the optical recording medium of the present invention. 1 ... Transparent substrate, 2 ... Transparent protective film, 3 ... Recording film.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Akira Isomi 1006 Kadoma, Kadoma City, Osaka Prefecture (72) Inventor Toru Tamura 1006 Kadoma, Kadoma City, Osaka Prefecture (56) Reference JP-A-59-190895 ( JP, A)

Claims (2)

[Claims] 1. A transparent substrate, and a recording film layer formed on the transparent substrate and containing, as at least one component, an iodine or perchloric acid adduct of a squarylium dye represented by the following general formula. Characteristic optical recording medium. (Wherein R _{1 to} R ₄ are aryl groups, or R ₁ and R ₂
Or a saturated hydrocarbon ring of 5 to 7 membered ring in which R ₃ and R ₄ are linked, an aromatic hydrocarbon ring, or a hetero ring, and R ₅
And R ₆ are hydrogen, an aryl group or an alkyl group, and Y is an element of Group VI. ) 2. The optical recording medium according to claim 1, wherein the Group VI element in the squarylium dye is any one of oxygen, sulfur, selenium and tellurium.