The present invention relates to cationic antipyrine based azo metal complex dyes for use in optical layers for optical data recording, preferably for optical data recording using a laser with a wavelength from 380 to 650 nm.

The invention further relates to an optical data recording medium capable of recording and reproducing information by laser beam irradiation. Particularly, it relates to a heat mode type optical data recording medium, which employs a cationic antipyrine based azo metal complex dye in the optical layer.

Optical data recording media (optical discs) capable of recording information only once with a laser beam are conventionally known. Such optical discs are also referred to as write-once CDs (CD-Rs) and in a typical structure thereof, a recording layer (optical layer) comprising an organic compound such as an organic dye, a light reflective layer comprising a metal such as gold, and a protective layer made of a resin, are laminated successively, in this order, on a transparent disc-shaped substrate. Information is recorded to a CD-R by irradiating a near-infrared laser beam (usually a laser beam with a wavelength near 780 nm) thereon, in which the irradiated area of the recording layer absorbs the beam. The temperature of the irradiated area increases, causing the optical characteristics of the area to undergo physical or chemical changes (e.g. the formation of pits) and the information is thus recorded.

With regards to reading (reproduction) of information, this is also conducted by irradiating a laser beam with a wavelength identical to that of the recording laser beam. Information reproduction from the CD-R is conducted by detecting the difference of the reflectivity in the recording area between the areas where the optical characteristics have been changed (recorded area) and not changed (unrecorded area).

In recent years, there has been a demand for optical information recording media possessing higher recording density. To meet this demand for greater recording capacity, an optical disc referred to as a write-once digital versatile disc (DVD-R) has

been proposed (for example, see Nikkei New Media special volume "DVD", published in 1995). The DVD-R is configured by appending two discs, each usually formed by laminating a recording layer containing an organic dye, a light reflective layer and a protective layer, in this order, on a transparent disc-shaped substrate in which guide grooves (pre-grooves) for laser beam tracking are formed. The pre-grooves occupy a narrow area of the DVD-R, specifically one-half or less of the DVD-R (0.74-0.8 μm) and the recording layers of the disc are formed towards the inner portion of the disc. The DVD-R can also be configured so that a disc-shaped protective substrate is included with the recording layer formed towards the inner portion of the disc. Information is recorded to and reproduced from the DVD-R by irradiating a visible laser beam thereon (usually a laser beam with a wavelength of about 630 nm to 680 nm), and thus, recording at a density higher than that of a CD-R is possible.

However, considering factors such as the recent spread of networks (e.g. Internet) and the emergence of high definition television (HDTV) broadcasting, cheap and convenient recording media, that are capable of recording image information at even larger capacity are required. While DVD-Rs sufficiently serve as high-capacity recording media at present, demand for larger capacity and higher density has increased.

Blu-ray ^® discs (Blu-ray ^® disc is a standard developed by Hitachi Ltd., LG Electronics Inc., Matsushita Electric Industrial Co. Ltd., Pioneer Corporation, Royal Philips Electronics, Samsung Electronics Co. Ltd., Sharp Corporation, Sony Corporation, Thomson Multimedia) or HD-DVD discs (a standard developed by Toshiba and NEC) are going to be the next milestone in optical recording technology. Its new specification increases the data storage up to 27 GBytes per recording layer for a 12 cm diameter disc. By adopting a blue diode laser with a wavelength of 405 nm (GaN or SHG laser diodes), the pit size and track interval can be further reduced, again increasing the storage capacity by an order of magnitude.

Here also organic dyes have attracted considerable attentions and some solutions have been already proposed in the field of short wavelength diode-laser optical storage. Examples of such media include JP-A Nos. 4-74690, 7-304256, 7-304257, 8-127174, 11-53758, 11-334204, 11-334205, 11-334206, 11-334207, 2000-43423, 2000-108513,

2000-113504, 2000-149320, 2000-158818, and 2000-228028. In the methods described above, information is recorded and reproduced by irradiating a blue laser beam (wavelength: 430 nm, 488 nm) or blue-green laser beam (wavelength: 515 nm) onto an optical disc having a recording layer containing porphyrine compounds, azo dyes, metal azo dyes, quinophthalone dyes, trimethinecyanine dyes, dicyanovinylphenyl skeleton dyes, coumarin compounds and naphthalocyanine compounds.

Unfortunately, the optical discs described in the above patent publications can not obtain the sensitivity required for practical use when recording information by irradiation of a short wavelength laser beam at a wavelength of 380 to 500 nm. Particularly, in the optical discs described in the above patent publications, the recording characteristics actually deteriorated when irradiating a laser beam with a wavelength of 380 to 500 nm.

Amino antipyrylazo dyes of the below general formulae are known for many years (see for example DE 1076078 A and US 2,993,884):

In addition to their uses as classical dyes for textiles or as dyes for copying processes, they are widely used as metallochromic indicators for spectrophotometric determination of metal contents. Extensive studies have been published on such type of complexation reactions and most of the classical aromatic diazo ligands have been investigated and described in the literature (see for example Bezdekova et al; Czech. Collection of Czechoslovak Chemical Communications, 1968, 33, 12, 4178-87 or more recently Shoukry M et al; Synthesis and reactivity in Inorganic and Metal-Organic Chemistry, 1997, 27, 5, 737-750). These azo derivatives behave generally as monobasic tridentate ligands towards metals such as nickel, copper or manganese.

Surprisingly it has now been found, that specific cationic antipyrine based azo metal complex dyes as described below are useful as dye compounds in optical layers for optical data recording media. These products show very interesting recording

characteristics and excellent overall performances when applied in recording media. The cationic antipyrine based azo metal complex dyes possess high light stability, read out stability and sufficient reflectivity to be used on production lines.

The present invention therefore relates to cationic antipyrine based azo metal complex dyes for use in an optical layer comprising cationic antipyrine based azo metal complex dyes as described below and to the use of said optical layers for optical data recording media.

Particularly, the invention relates to a heat mode type optical data recording medium, which employs a cationic antipyrine based azo metal complex dye in the optical layer.

More particularly, the invention relates to a write once read many (WORM) type optical data recording medium capable of recording and reproducing information with radiation of blue laser of preferably 405 nm or a red laser of preferably 650 nm, which employs cationic antipyrine based azo metal complex dye in the optical layer.

The present invention is directed to a dye compound of formula (I)

wherein

M represents a metal atom;

R ₁ is selected from hydrogen, C _1-10 alkyl, C _5-10 cycloalkyl, the alkyl groups being optionally substituted by halogen (Cl, Br, F, I); C _1-10 alkoxy, unsubstituted phenyl or substituted phenyl (with substituents being halogen, C _1-10 alkyl or nitro), unsubstituted benzyl or substituted benzyl (with substituents being halogen, C _1-10 alkyl or nitro), cyano, carboxy or C _1-10 alkyl carboxylate;

R ₂ is selected from C _1-10 alkyl, C _5-10 cycloalkyl, the alkyl groups being substituted by halogen (Cl, Br, F, I);

R ₃ is selected from hydrogen, alkyl, unsubstituted phenyl or substituted phenyl (with substituents being -Cl, -CN, -Br, -CF ₃ , C _1-8 alkyl, chloromethyl, C _1-8 - alkoxymethyl or phenoxymethyl, NO ₂ or sulfonamide);

A is selected from an aromatic cycle unsubstituted or substituted (with substituents being halogen, C _1-10 alkyl, dicyanomethylene, cyano, carboxy, C _1-10 alkyl carboxylate, sulfonamide or nitro), or a heterocycle unsubstituted or substituted

(with substituents being halogen, C _1-10 alkyl, dicyanomethylene, cyano, carboxy, C _1-10 alkyl carboxylate, sulfonamide or nitro);

Y is hydroxyl, amino, carbonamido (RCON) or sulfonamido (RSO ₂ N) wherein R is linear or branched C _1-12 alkyl, trifluoromethyl, chloromethyl, Ci- ₄ -alkoxymethyl or phenoxymethyl (where phenoxy may or may not be substituted by one or two chlorine, methoxy, nitro or Ci-4-alkyl and in the case of two substituents, the substituents may be identical or different) phenylthiomethyl, where phenyl is unsubstituted or substituted by Ci^alkyl; benzyl; phenylethyl; C _3-7 cycloalkyl; phenyl which is unsubstituted or substituted by C _1-2 alkyl, C _1-2 -alkoxy or nitro;

X ^" is selected from ClO ₄ ^" , SbF ₆ ^" , PF ₆ ^" , BF ₄ ^" , TCNQ ^" (Tetracyano-p-quinodimethane),

TCNE ^" (Tetracyanoethylene), Cl ^" , Br ^" , I ^" , Tos ^" (p-Tolysulfonate).

In a preferred aspect, the present invention is directed to a dye compound of formula (I) wherein

M is selected from the group consisting of B, Al, Ga, Co, Cr, Fe, Y; R ₁ is selected from CH ₃ , C ₂ H ₅ , C ₃ H ₇ or unsubstituted phenyl, R ₂ is selected from CH ₃ , C ₂ H ₅ ,

R ₃ is selected from H, CH ₃ , C ₂ H ₅ or unsubstituted phenyl; A is selected from

(2)

wherein R is C _1-4 alkyl or -NH-phenyl; Y is hydroxyl; X ^" is selected from ClO ₄ ^" , SbF ₆ ^" , PF ₆ ^" , BF ₄ ^" , Tos ^" (p-Tolysulfonate).

In a more preferred aspect, the present invention is directed to a dye compound of formula (I) wherein

M is Co;

R ₁ is CH ₃ ;

R ₂ is CH ₃ ;

R ₃ is unsubstituted phenyl;

A is selected from

Y is hydroxyl;

X ^" is selected from ClO ₄ ^" , SbF ₆ ^" , PF ₆ ^" , Tos ^" (p-Tolysulfonate).

An optical layer according to the invention comprises a compound of formula (I) or a mixture of compounds of formula (I).

The optical layers according to the invention comprise a compound of formula (I) or a mixture of such compounds preferably in an amount sufficient to have a substantial influence on the refractive index, for example at least 30% by weight, more preferably at least 60% by weight, most preferably at least 80% by weight.

Further, the invention relates to a method for producing an optical layer, comprising the following steps

(a) providing a substrate (b) dissolving a dye compound or a mixture of dye compounds of formula (I) in an organic solvent to form a solution,

(c) coating the solution (b) on the substrate (a);

(d) evaporating the solvent to form a dye film.

As a substrate, various kinds of materials can be used, for example, glass, polycarbonates, acrylic resins such as polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and polyvinyl chloride copolymers; epoxy resins; amorphous polyolefϊns; polyesters; and metals such as aluminum. Among them, polycarbonates and amorphous polyolefins are preferred, with polycarbonates being particularly preferred in view of the moisture proofness, dimensional stability and low cost.

Optionally a light reflection layer is disposed to the substrate. For to the light reflection layer, a light reflecting material having a high reflectance to laser beam is used. The reflectance is preferably 70% or more. Suitable light reflecting material are selected from metals and semimetals such as Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Si, Ge, Te, Pb, Po, Sn and Bi, or stainless steels. The light reflecting material may be used alone or may be used in a combination of two or more of them, or as an alloy. Among them preferred are Cr, Ni, Pt, Cu, Ag, Au and Al, as well as stainless steels. Particularly preferred are Au, Ag, Al or alloys thereof and most preferred are Au, Ag or alloys thereof.

The light reflection layer can be formed on the substrate, for example, by vapor depositing, sputtering or ion plating. The thickness of the light reflection layer is, generally, within a range of from 10 to 300 nm and, preferably, within a range from 50 to 200 nm.

The optical layer can be formed, for example, by vapor deposition, sputtering, CVD, or solvent coating. The preferred methods are solvent coating or vapor deposition. The

most preferred method is solvent coating.

For solvent coating, the compound of the invention described above is dissolved in a solvent and, optionally, a quencher and/or a binder is added to prepare a coating solution. The coating solution is then coated to the surface of the substrate (or onto the light reflection layer on the substrate) and then dried.

Suitable organic solvents for coating are selected from C _1-8 alcohol , halogen substituted C _1-8 alcohols, C _1-8 ketone, C _1-8 ether, halogen substituted C _1-4 alkane, or amides. Preferred C _1-8 alcohols or halogen substituted C _1-8 alcohols are for example methanol, ethanol, isopropanol, diacetone alcohol (DAA), 2,2,3, 3-tetrafluoropropanol, trichloroethanol, 2-chloroethanol, octafluoropentanol or hexafluorobutanol.

Preferred C _1-8 ketones are for example acetone, methylisobutylketone, methylethylketone, or 3-hydroxy-3-methyl-2-butanone. Preferred halogen substituted C _1-4 alkanes are for example chloroform, dichloromethane or 1-chlorobutane. Preferred amides are for example dimethylformamide or dimethylacetamide.

The coating method is selected from spraying, spin coating, dipping, roll coating, blade coating, and screen printing. The coating temperature is from 10 to 50 ^° C, preferably from 24 to 40 ^° C. and, more preferably, from 25 to 37 ^° C.

The most preferred coating method is spin-coating. The most preferred solvents are 2- methoxyethanol, n-propanol, isopropanol, isobutanol, n-butanol, amyl alcohol or 3- methyl- 1-butanol or preferably fluorinated alcohols, e.g. 2,2,2-trifluoroethanol or 2,2,3, 3-tetrafluoro-l-propanol, octafluoropentanol and mixtures thereof.

The obtained optical layer may be a single layer or a stacked layer and the thickness of the optical layer is, generally, within a range from 20 to 500 nm, more preferably, within a range from 30 to 300 nm, most preferably, within a range from 50 to 100 nm.

An optical data recording medium according to the invention comprises on an optical layer on a substrate capable of recording information by irradiation of a laser beam,

wherein the optical layer contains the compound represented by the general formula (I).

A method for producing an optical recording medium comprising an optical layer according to the invention, comprises the following additional steps

(e) sputtering a metal layer onto the dye layer

(f) applying a second polymer based layer to complete the disc.

A high-density optical recording medium according to the invention therefore preferably is a recordable optical disc comprising: a first substrate, which is a transparent substrate with grooves, a recording layer (optical layer), which is formed on the first substrate surface using the compounds of formula (I), a reflective layer formed on the recording layer, a second substrate, which is a transparent substrate with grooves connected to the reflective layer with an attachment layer.

The use of compounds of formula (I) results in advantageously homogeneous and amorphous films, providing for low-scattering optical layers having a high refractive index. The absorption edge is surprisingly steep even in the solid phase. Further advantages are high light stability in daylight and under laser radiation of low power density with, at the same time, high sensitivity under laser radiation of high power density, uniform script width, high contrast, and also good thermal stability and storage stability.

EXAMPLES

Ligand (1)

A mixture of 31.1 g of 4-aminoantipyrine, 200 ml of water and 48 g of concentrated hydrochloric acid (30%) was gradually admixed with 37.3 ml of sodium nitrite at 0°C;

After 1 hour of reaction at 0°C, the violet-pink diazotization solution was added dropwise to an alkaline solution of 29 g of phenylpyrazolone while maintaining pH at

7.5-9 with sodium hydroxide (30%). The batch was stirred 3 hours then filtered with suction. The precipitate was washed with water and dried. The presscake yielded 58.1 g of dye ligand of the following formula (1 )(99%)

Ligand (2) coupler preparation A mixture of 45.3 g of 2,6-dichloropyridine and 76.4 ml of dimethyl sulphate was stirred at 100° C. for 24 hours. After cooling, the viscous solution was diluted with 90 ml of dimethylformamide, and a solution of 20 g of malononitrile in 30 ml of dimethylformamide and then 77.1 g of triethylamine were added dropwise, while cooling with ice. The mixture was subsequently stirred for 20 hours and 20 g of a yellow product were then filtered off with suction.

The presscake of [l-methyl-6-chloro-2(l)-pyridinylidene] malononitrile so obtained was dropped into 100 ml of water and 100 ml of N-methylpyrrolidone and heated to 80°C for 10 hours and at 90°C for 5 hours, pH=10 being maintained by drop wise addition of 30% strength sodium hydroxide solution via a titrator. After this period, the mixture was diluted with a volume of 400 ml water and brought to pH=l with concentrated hydrochloric acid. The green precipitate formed was filtered off with suction and washed with water. Yield: 9.5 g.

ligand synthesis

A mixture of 20.3 g of 4-amino antipyrine, 300 ml of water and 33 g of concentrated hydrochloric acid (30%) was gradually admixed with 24.8 ml of sodium nitrite at 0°C;

After 1 hour of reaction at 0°C, the violet-pink diazotization solution was added dropwise to an alkaline solution of 17.3 g of 2-(6-Hydroxy-l -methyl- lH-pyridin-2- ylidene)-malononitrile while maintaining pH at 7.5-9 with sodium hydroxide (30%).

The batch was stirred 3 hours then filtered with suction. The precipitate was washed with water and dried. The copper-green presscake yielded 33.2 g of dye of the following formula (2).

EXAMPLES 1-6 cationic metalazo complex synthesis

A solution of 1.2 g of cobalt (II) acetate tetrahydrate in 20 ml acetonitrile is stirred one hour with 0.5 ml of concentrated nitric acid (65%). The violet solution is then added to an acetonitrile solution of 2 equivalents of the ligand as described above. The mixture is stirred for 5 hours at 60°C, cooled down to 20°C and then dropped into a 60 ml aqueous solution of sodium hexafluoroantimonate. After stirring for one hour at ambient temperature, the precipitate is filtered off, washed with water and then dried. Purification can be performed by dissolution of the obtained complexes in solvent, filtration over a short Celite column and evaporation of the filtrate.

TABLE 1

APPLICATION EXAMPLE

0.20 g of the dye obtained from examples 1 to 6 were dissolved in 10 ml of tetrafluoropropanol, and stirred at room temperature for 4 hours. The solution was smoothly filtered with a Teflon filter (having 0,2 μm pore size) and spin coated over a substrate to form a dye layer. The substrate was a polycarbonate substrate with 0.6 mm thickness.

The optical and thermal properties of the cationic antipyrine based azo metal complex dye compounds given in Table 1 were measured respectively with an elipsometer ETA- RT for the dyes dedicated to DVD-R application (red laser) and with an UV-RT elipsometer for the dyes dedicated to blue laser disc application. The dyes show high absorption at the desired wavelengths (between 350 and 460 nm for the blue laser and between 550 nm and 630 nm for the red one). In addition, the shape of the absorption spectra, that still remains critical to the disc reflectivity and formation of clean mark edges, are composed of one major band with a second one forming a shoulder.

More precisely, n values of the refractive index of the dyes were found suitable for the application as recording medium. And moreover, light stabilities were found

comparable to commercial dyes which usually are stabilized with quenchers for the use in optical data recording.

Sharp threshold of thermal decomposition within the required temperature range characterizes the new cationic antipyrine based azo metal complex dyes which are assumed to be desirable for the application in optical layers for optical data recording.

As a conclusion, the cationic antipyrine based azo metal complex dye compounds are within the specifications which are primarily required by the industry for the use of dyes in optical data recording, in particular in the next-generation optical data recording media in the blue laser range.