JP2784939B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium, particularly to a heat mode optical recording medium.

<Prior Art> An optical recording medium has a feature that the recording medium does not wear and deteriorate because the recording and reading heads are not in contact with the medium. For this reason, various optical recording media have been studied for development.

Among such optical recording media, heat mode optical recording media have been actively developed in that development processing in a dark room is unnecessary.

This heat mode optical recording medium is an optical recording medium that uses recording light as heat. As an example, a small hole called a pit is formed by melting or removing a part of the medium with recording light such as a laser. There is a pit formation type in which writing is performed by forming a pit, information is recorded by the pits, and the pits are detected and read out by a reading light. Most of such pit formation type media, particularly those using a semiconductor laser capable of downsizing the device as a light source, have a recording layer mainly made of a material mainly composed of Te.

In recent years, Te-based materials are harmful, and it is necessary to increase the sensitivity, and it is necessary to lower the manufacturing cost. Practical use of a medium using a system recording layer is in progress.

Representative examples of such a dye include indolenine-based cyanine dyes (JP-A-59-24692).

However, in the case of indolenine-based cyanine dyes, reproduction degradation occurs due to repeated irradiation of reproduction light. In addition, light degradation occurs in storage in a bright room.

For these reasons, the present inventors have proposed a method of adding a quencher in order to prevent decolorization (reproduction deterioration) due to reproduction light and to improve the storage stability in a bright room (Japanese Patent Application Laid-Open No. 59-1984).
No. 55794, No. 59-55795).

However, since the addition of a quencher alone is not sufficient in terms of stability and the like, the present inventors have further proposed that the quencher be ion-bonded to a dye and used as a conjugate. Kaisho 60-118748, 60-118749
No.).

However, this conjugate must be obtained by reacting a quencher anion with a dye cation, and synthesis is often difficult and complicated. In addition, it is relatively difficult to dissolve a sufficient concentration in a solvent that does not attack polycarbonate (PC) commonly used as a substrate, such as an alcohol-based substrate.

In view of the above, the present inventor has proposed to improve this point by adding a quencher function in a cyanine dye (Japanese Patent Application Laid-Open Nos. 61-16891 and 61-1).
No. 6894).

<Problems to be Solved by the Invention> The above-mentioned dyes provided with a quencher function are:
It is a reaction product of a compound having a sulfonic acid group, a carboxylic acid group, a sulfonic acid group or a carboxylic acid group directly or via an appropriate linking group with a transition metal salt such as Ni.

However, in the proposal of the above publication, a sulfonic acid group is linked to the nitrogen in the aromatic ring of the cyanine dye skeleton via an alkylene group, an arylene group or the like.

Such a material has an advantage that it is easy in terms of synthesis, but it has been found that the deterioration of reproduction is not sufficiently prevented and that there is a problem in the storage stability in a bright room.

Further, in JP-A-61-243445, cyanine dye skeleton of an aromatic ring to ^{_{CH 2 3 SO 3 - (Ni}} 2+) 1/2 (m is 1-8)
Is disclosed, but has the same problems as described above and is insufficient.

Further, JP-A-60-124289 discloses a nickel salt of a cyanine dye having an SO ₃ ^- group.

However, this molecule has acid anions such as ClO ₄ ⁻ and Br ^{− in the} molecule because SO ₃ ⁻ (Ni) _1/2 is bonded to the cyanine dye skeleton. For this reason, the stability is lacking due to the presence of the acid anion, and the quencher effect is also insufficient. Even the experimental results of the publication show that only an insufficient effect of preventing deterioration of reproduction and storage stability in a bright room.

The present invention provides an optical recording medium having a recording layer containing a cyanine dye, in which prevention of reproduction deterioration is sufficient, excellent in storage stability in a bright room, chemically stable, and having sufficient solubility in a mild solvent such as alcohol. The purpose is to provide.

<Means for Solving the Problems> In order to achieve the above object, the present invention has the following configurations (1) and (2).

(1) An optical recording medium having a recording layer containing a cyanine dye represented by the following formula (I) on a substrate.

Formula (I) D _ye SO ₃ ⁻ ) _m · (m−1) / 2 · M ^{2+ wherein} D _ye is a cyanine dye cation having an indolenine ring which may have a condensed ring as an aromatic ring Represents a residue, M represents Ni, Co, Pt or Pd, and m represents an integer of 2 or more.

In addition, at least two SO ₃ ^— are directly bonded to respective ring-constituting carbon atoms of the pair of aromatic rings. (2) the aromatic ring is a 2-indolenin ring and / or a 2- (4,5-benzo) indolenin ring, and the SO ₃
^- an optical recording medium described in (1) which is directly bonded to the 6-position of 2-India renin ring 5-position and 2- (4,5-benzo) indolenine ring.

<Operation> The optical recording medium of the present invention irradiates recording light in a pulse shape while running or rotating. At this time, heat is generated by the cyanine dye in the recording layer, so that the cyanine dye melts to form pits.

The pits thus formed are read out by detecting reproduction light, particularly reflected light, while the medium is running or rotating.

In this case, recording and reproduction are performed from the substrate side through the substrate.

Note that a semiconductor laser is preferably used as the recording or reproducing light from the viewpoint of miniaturizing the device.

The indolenine-based cyanine dye of the present invention has no acid anion, and further has a sulfonic acid group directly bonded to a ring-constituting carbon atom other than a heteroatom in the aromatic ring of the dye skeleton, and the sulfonic acid group (SO ₃ ^-) one, but in the ring N ⁺
And neutralized in a charged manner, and another SO ₃ ^- and a divalent ion such as nickel are salt-formed.

For this reason, it is excellent in stability, sufficiently prevented from being degraded by regeneration, improved in storage in a bright room, and has sufficient solubility in mild solvents such as alcohol.

<Specific Configuration> Hereinafter, a specific configuration of the present invention will be described in detail.

Indolenine cyanine dyes of the present invention, m number of SO ₃ ^- has, of which at least two, coupled directly to a ring-constituting carbon atoms excluding endocyclic hetero atom of the aromatic ring of the dye skeleton. And one of these SO ₃ ^- is an aromatic ring
Neutralization with N ⁺ is performed, and the remaining (m−1) SO ₃ ⁻ and the divalent ion form a salt.

The number m of such SO ₃ ⁻ may be at least 2, and is usually 2 to 8, particularly 2 to 6, and more preferably 2 to 4.

In this case, more specifically, SO ₃ ^— directly bonded to the ring-constituting carbon atoms of the aromatic rings at both ends is generally 1 to ₃ per ring.
About 2 to 2 in the molecule, especially 2 or 4.
In addition, SO ₃ ^- is a ring-forming nitrogen atom or a ring-forming carbon atom of an aromatic ring, via an alkylene group or the like, and has one to one ring.
Two or more bonds may be formed, and these are usually preferably in the form of a salt with M ²⁺ .

The cyanine dye of the present invention has no acid anion in the molecule.

By using an indolenine-based cyanine dye having such a structure, light stability and stability are increased, and the effects of the present invention can be obtained.

Such an effect is achieved when SO ₃ ^- is directly bonded to the ring-constituting carbon atom of the aromatic ring of the dye skeleton, and this SO ₃ ^- and M 2 ⁺ form a salt, and further, an acid anion is not present. It is obtained only by using it.

Accordingly, those acid anion remains, SO ₃ such as a carboxylic acid group ^- those having other than acid groups, SO ₃ ^- those not linked directly to the ring-constituting carbon atoms of the aromatic ring, metal ions other than M ²⁺ For example, the effect of the present invention cannot be obtained in the case of the combination.

As such a cyanine dye, a dye represented by the following formula (II) is preferable.

Formula (II) In the above formula (II), Z ₁ and Z ₃ together with C and N each represent a pyrrole ring, an oxazole ring, an imidazole ring, a thiazole ring,
Represents a group of atoms necessary to complete a selenazole ring, a pyridine ring or an indolenine ring, for example, S, Se, O,
N, —CH ＝ CH— and the like.

In addition, these rings include an aromatic ring (for example, a benzene ring,
Naphthalene ring, phenanthrene ring, quinoxaline ring, etc.)
May be condensed.

However, at least one aromatic ring is an indolenine ring in terms of reflectance and sensitivity.

Also, p ≧ 1, q ≧ 1, usually p and q are 1 or 2. That is, each of the pair of aromatic rings, at least one, usually 1 or 2 at a time of SO ₃ ^- are directly bonded.

The SO ₃ ^- may have other substituents on the site of a possible substitution on the ring except for the substitution site.

Examples of such a substituent include an alkyl group, an aryl group, a heterocyclic residue, a halogen atom, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an alkylcarbonyl group, an arylcarbonyl group, an alkyloxycarbonyl group, and an aryloxycarbonyl. Group, alkylcarbonyloxy group, arylcarbonyloxy group, alkylamide group, arylamide group, alkylcarbamoyl group, arylcarbamoyl group, alkylamino group, arylamino group, carboxylic acid group, alkylsulfonyl group, arylsulfonyl group, alkylsulfone Various substituents such as an amide group, an arylsulfonamide group, an alkylsulfamoyl group, an arylsulfamoyl group, a cyano group, and a nitro group may be used.

R ₁ and R ₂ are an alkyl group, an aryl group,
Represents an alkenyl group, particularly preferably an alkyl group.

These groups may further have a substituent, such a substituent as an alkylcarbonyloxy group, an alkylamide group, an alkylsulfonamide group, an alkoxycarbonyl group, an alkylamino group, an alkylcarbamoyl group, It may be any of an alkylsulfamoyl group, a hydroxyl group, a halogen atom, a carboxylic acid group, and a carboxylate group.

Incidentally, m is SO ₃ as said ^- a number of, when m> 2, SO ₃ ^-, in addition to those directly attached to an aromatic ring-constituting carbon atoms, those that bind to a substituent attached to an aromatic ring Or may be included in R ₁ , R ₂ , R _{3 and the} like.

Therefore, normally p + q = m, but p + q + n = m
(N ≧ 1, especially n = 2 or 4).

Further, in some cases, there may be a sulfonate group bonded to a metal other than the above M ²⁺ .

L represents a polymethine linking group for forming a cyanine dye, and specific examples include the following.

Here, Y represents a hydrogen atom or a monovalent group. In this case, examples of the monovalent group include a lower alkyl group such as a methyl group, a lower alkoxy group such as a methoxy group, a dimethylamino group, a diphenylamino group, a methylphenylamino group, a morpholino group, an imidazolidine group, and an ethoxycarbonylpiperazine group. It is preferable that the compound is an alkylcarbonyloxy group such as an acetoxy group, an alkylthio group such as a methylthio group, a cyano group, a nitro group, or a halogen atom such as Br or Cl.

R ₈ and R ₉ each represent a hydrogen atom or a lower alkyl group such as a methyl group.

 Then, 1 is 0 or 1.

The bonding site in the aromatic ring completed by Z ₁ or Z _{2 of} L is the 2-position (that is, the position of the C atom) or the 3-position, but is preferably the 2-position.

Also, M is Ni, Co, Pt or Pd,
The plurality may be used.

Incidentally, those cyanine dyes of the present invention, optionally, the EG ^2-like from the reaction solvent such as ethylene glycol in the synthesis (EG) is coordinated to Ni ²⁺ or the like in addition to the cyanine dye cation It may be.

Further, the ring completed with Z ₁ and Z ₂ is preferably as described above, and particularly, both are a 2-indolenin ring, a 2- (4,5-benzo) indolenin ring,
It is preferably a (5,6-benzo) indolenin ring or a 2-dibenzoindolenin ring.

In such a case, it is particularly preferable that both aromatic rings have 2-
Of an indolenine ring, the 5-position and 5 '
Those having SO ₃ ^— at the − position are preferred.

Preferred examples of the cyanine dye in the invention include the following.

The content of such a cyanine dye depends on the entire recording layer.
The content should be 50 to 100 wt%, preferably 80 to 100 wt%.

With such a content, the effect of the present invention is further enhanced.

In order to obtain such a cyanine dye, a raw material cyanine dye combined with a normal acid anion and a salt of Ni, Co, Pd, Pt,
Such as chloride, bromide, especially _{NiCl 2, NiBr 2, CoCl 2} , PdC
l ₂ , chloroplatinic acid or the like may be reacted.

As a raw material cyanine dye, SO ₃ ^- may be used at a predetermined site, and its Na salt or alkylammonium salt may be used. This may be easily mixed with an aqueous solution such as NiCl ₂ to precipitate the desired product. Obtainable.

Alternatively, in some cases, the raw material cyanine dye is dissolved in a predetermined solvent, for example, ethylene glycol, or a mixture of ethylene glycol and a ketone-based, aromatic-based, alcohol-based solvent, or the like, and heated to an equivalent amount of NiCl ₂ or the like. By performing the isolation, a cyanine dye having a quencher function as a reaction product is obtained.

At this time, ethylene glycol may coordinate. The isolation of the reaction product is usually performed by distilling off the solvent. Alternatively, precipitation may be carried out by adding a hydrocarbon-based solvent or water, and the 44th Annual Meeting of the Chemical Society of Japan, 3M24, Proceedings P628 (198
1) and the 47th Annual Meeting of the Spring Meeting 4038 Proceedings, P1421 (1983).

The reaction product of the starting cyanine dye and the Ni salt, etc.,
It has a visible ultraviolet absorption spectrum that is almost the same as the absorption spectrum of the starting cyanine dye itself, and the presence of Ni and the like is confirmed.

Further, the cyanine dye of the present invention obtains a salt which is more soluble than the target Ni salt or the like, for example, a salt of Na, K, NH ₄ or the like, and dissolves it in an appropriate solvent to obtain a coating solution. After forming a layer as a recording layer in the optical recording medium, the coating film can be obtained by immersing the coating film in a solution such as NiCl ₂ and performing salt exchange.

When such a method is employed, coatability is improved, and a good coating film can be obtained.

The recording layer in the optical recording medium of the present invention may contain other dyes in addition to the cyanine dye.

As such a dye, any of various known cyanine dyes may be used, and for example, JP-A-61-16891
And No. 61-16894.

In addition, the recording layer may further contain a quencher, a conjugate of a quencher anion and a dye cation, a resin, and the like.

These are described in detail in JP-A-61-16891 and JP-A-61-16891.
-16894.

Further, the recording layer may contain various additives disclosed in the above publication.

The thickness of the recording layer in the present invention may be 0.05 to 0.5 μm, preferably 0.07 to 0.15 μm.

In the present invention, the recording layer may be formed by a conventional method, and may be applied on a substrate using a predetermined solvent and dried.

In addition, as a solvent used for coating, for example, alcohols such as methanol and ethanol, methyl cellosolve,
A cellosolve such as ethyl cellosolve, diacetone alcohol or water, or a mixture thereof may be used.

The material of the substrate on which such a recording layer is formed is not particularly limited as long as it is substantially transparent to writing light and reading light, and may be any of various resins and glass.

Examples of such a resin include polymethyl methacrylate, acrylic resin, epoxy resin, polycarbonate resin, polysulfone resin, polyethersulfone, polyolefin, and methylpentene polymer.

The shape of the substrate may be any of a tape, a drum, a belt, and the like, depending on the use.

Further, the substrate may usually have a tracking groove or the like.

In the present invention, the substrate may have a base layer formed thereon. Various top protective layers, half mirror layers, and the like can be provided on the recording layer as needed.

The optical recording medium of the present invention may have the above-mentioned recording layer on one surface of such a substrate, or may have the recording layers on both surfaces thereof. Further, two recording layers are applied on one surface of the substrate, and they are opposed to each other with a predetermined gap so that the recording layers face each other.
A so-called air-sandwich structure can be used, which is sealed to prevent dust and scratches.

Alternatively, an adhesive structure in which a reflective layer is closely adhered and laminated on the recording layer may be used.

<Example> Hereinafter, the present invention will be described specifically with reference to examples.

Example 1 A recording layer was provided on a polycarbonate resin substrate having a diameter of 13 cm.

The recording layer was formed by dissolving the exemplary compound (1) described in the text as a cyanine dye in methanol to form a 2 wt% solution, and applying this to a thickness of 0.08 μm by spin coating to form a layer.

The optical recording medium thus manufactured is referred to as Sample No. 1.

 The synthesis of the exemplary compound (1) was performed as follows.

0.002 mol of the starting cyanine dye (NK-3298) having the following structure and 0.02 mol of NiCl ₂ (10 times the amount of the starting cyanine dye) were dissolved in 50 ml of water and reacted at 80 ° C. for 1 hour.

Thereafter, the mixture was left at room temperature, and the precipitated crystals were collected, washed with acetone and dried to obtain a product.

The resulting product showed almost the same absorption spectrum as the original dye, confirming the presence of Ni.

Samples No. 2 and No. 3 were prepared in the same manner except that the cyanine dye in the recording layer in Sample No. 1 was changed to Exemplified Compound (2) or (3) described in the text.
And

In addition, the exemplified compounds (2) and (3) are both sampled.
It was synthesized according to Exemplified Compound (1) in No. 1.

Separately, the raw material cyanine dye (Na salt) in Sample No. 1 was dissolved in methanol on the substrate used in Sample No. 1, and a 1.8 wt% solution was formed to a thickness of 0.07 μm by spin coating. By coating, a recording layer was formed.

Thereafter, this recording layer was immersed in an aqueous solution of NiCl ₂ (25 ° C.) for 30 seconds to convert it into a Ni salt, which was used as an exemplary compound (1), washed with pure water, and dried to obtain a sample of the present invention. This is designated as Sample No. 4.

A sample was prepared in the same manner as in Sample No. 1, except that the cyanine dye of the recording layer in the recording layer was replaced with a cyanine dye (A) having a carboxylic acid group having the following structure and a Na salt exchanged with a Ni salt. This is designated as Sample No. 5.

Further, in Sample No. 1, a cyanine dye (B) having SO ₃ ^{− in} which the cyanine dye in the recording layer was bonded to the aromatic ring of the cyanine dye skeleton via a linking group having the following structure, and a Na salt was exchanged for a Ni salt, A sample was prepared in the same manner except that (C) was replaced.

 These are designated as sample Nos. 6 and 7.

Also, in Sample No. 1, the cyanine dye in the recording layer was changed to the Na salt [NK-1967 cyanine dye (D)] corresponding to Exemplified Compound (1) instead of Exemplified Compound (1). Was prepared.

 This is designated as Sample No. 8.

Recording was performed on the sample Nos. 1 to 7 thus produced from the back side of the substrate using a semiconductor laser (830 nm or 780 nm), respectively. In this case, the rotation speed of the substrate is
The light-collecting unit output was 1800 rpm, the recording frequency was 500 kHz, and the recording frequency was 500 kHz.

Then, at 780 nm, the output of the light-collecting part: 0.2 mW as the reproduction light, the reflected light through the substrate is detected, and a spectrum analyzer manufactured by Hewlett-Packard Company is used.
The S / N ratio was measured at z.

In addition, after irradiating a 0.2 mW laser reproduction beam as a pulse of 1 kHz width and 3 kHz in a stationary state for 5 minutes (reproduction deterioration),
After irradiation with a xenon lamp of 1.5 kW and a distance of 20 cm for 20 hours (light room storage stability), the change (%) in the sum of the reflectance and the absorptance from the back side of the substrate was measured.

 Table 1 shows the results.

From the results shown in Table 1, the effect of the present invention is clear.

<Effect of the Invention> According to the present invention, reproduction deterioration can be sufficiently prevented, and the light room storage stability is improved.

 And its chemical stability is very high.

Further, the cyanine dye constituting the recording layer has a sufficient solubility in a mild solvent such as alcohol, and is advantageous for forming a coating film.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41M 5/26

Claims (2)

(57) [Claims] 1. An optical recording medium having a recording layer containing a cyanine dye represented by the following formula (I) on a substrate. Formula (I) D _ye SO ₃ ⁻ ) _m · (m−1) / 2 · M ^{2+ wherein} D _ye is a cyanine dye cation having an indolenine ring which may have a condensed ring as an aromatic ring Represents a residue, M represents Ni, Co, Pt or Pd, and m represents an integer of 2 or more. Also, at least two SO ₃ ^- are each
Directly bond to each ring-constituting carbon atom of the pair of aromatic rings. ] 2. The method according to claim 1, wherein the aromatic ring is a 2-indolenin ring and / or
Or a 2- (4,5-benzo) indolenin ring,
The SO ₃ ^- is the 5-position of the 2-indolenin ring and 2- (4,
The optical recording medium according to claim 1, which is directly bonded to the 6-position of the 5-benzo) indolenin ring.