JPH03219994A - Optical recording medium and preparation thereof - Google Patents

Abstract

PURPOSE:To prevent the generation of a crack in a plastic substrate and to form a recording layer reduced in thickness irregularity by dissolving an org. dye showing easy solubility to a high b.p. solvent and hard solubility to a low b.p. solvent in the high b.p. solvent to apply the resulting solution to the substrate and subsequently replacing the high b.p. solvent with the low b.p. solvent to dry the coated substrate to form the recording layer. CONSTITUTION:A sheet like substrate 1 is passed between rolls 7 to be coated with high b.p. solvent ink 6 prepared by dissolving an org. dye in a high b.p. solvent and the coated sheet like substrate is immersed in a low b.p. solvent 2 by a cylindrical roll 5. By this immersion, the coated high b.p. solvent ink 3 on the sheet like substrate 1 is subjected to solvent replacement to be formed into low b.p. solvent replaced ink 4 to become a state easy to dry. Thereafter, the coated substrate is naturally dried to form a film. As the high b.p. solvent used in coating at first, one having a b.p. of 100 deg.C or higher is pref. and, for example, an aprotic solvent such as dimethylformamide is designated. As the low. b.p. solvent used in solvent replacement, one having a b.p. of below 80 deg.C is pref. and, for example, and alcoholic solvent such as methanol is recommended.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical recording medium in which information is written and read using light, mainly a semiconductor laser, and in particular an optical recording medium whose recording layer is made of an organic system, and the like. Regarding the manufacturing method.

[Prior Art] Conventionally, optical recording media have a recording layer formed on a transparent substrate having a guide groove for tracking, and a reflective layer, a protective layer,
Various configurations including subbing layers and the like have been proposed, and there are a wide variety of manufacturing methods.

In particular, examples of materials forming the recording layer include Pb,
Many inorganic metals such as Bi, Se, and Te, alloys thereof, and organic dyes having an absorption peak near the recording light wavelength have been proposed, and some of them have been put into practical use. As a method for forming a recording layer from these materials, an inorganic thin film is formed by vacuum deposition, sputtering, or the like.

However, in the method of forming the recording layer, vapor deposition and sprinkling require a vacuum apparatus, which poses problems such as high equipment costs.

On the other hand, organic dyes that have good solubility in solvents can be dissolved or dispersed in a solvent and applied by wet coating methods such as a dipping method, a doctor blade method, and a spinner method, so that a low-cost optical recording medium can be obtained. Conventionally, the solvents used at this time include alcohols such as methanol, ethanol, inpropatol, and diacetone alcohol, ketones such as acetone, methyl ethyl ketone, and cyclohexanone, and also amide, ether, ester, and aliphatic halogen solvents. Examples include carbonated hydrocarbon solvents, aromatic hydrocarbon solvents, and aliphatic hydrocarbon solvents, which are appropriately selected and used depending on the dye used.

By the way, the solvent used for coating the recording layer is preferably a solvent that has a low boiling point, dries quickly, does not attack the substrate, and has good solubility for the dye.

That is, when a high boiling point solvent such as dimethylformamide or toluene is used as a coating solvent, when drying after coating to form a recording layer, it takes time to dry and uneven drying may occur. Coating liquid (hereinafter referred to as ink)
There was a problem that the thickness of the recording layer could not be kept constant due to cross-flow of the ink.Also, since the ink remains on the substrate for a long time, depending on the type of plastic substrate, There was a problem that solvent cracks were likely to occur.

However, there are few currently used coating solvents that satisfy all of the above conditions, and the dyes used in the recording layer are limited to those that have good solubility in these solvents, making the selection range of dyes narrow. Ta.

On the other hand, phthalocyanine dyes, naphthalocyanine dyes, naphthoquinone dyes, anthraquinone dyes, etc., which have high reflectance and are suitable as recording layer materials for optical recording media, are generally soluble only in high-boiling point solvents with good solubility. Therefore, until now, vapor deposition or the like has been used for film formation, and it has been difficult to form a recording layer by directly applying it onto a resin substrate.

[Problem to be solved by the invention] The present invention has been made in view of the above problems, and
By applying an ink containing an organic dye dissolved in a high-boiling point solvent and then replacing the solvent with a low-boiling point solvent, the range of solvent selection is expanded, and at the same time, it is possible to expand the range of solvents that can be selected. The object of the present invention is to provide an optical recording medium and a method for producing the same, in which an organic dye can be deposited by wet coating, which otherwise would have required vacuum evaporation or sputtering using a vacuum process.

Another object of the present invention is to be able to dry the solvent contained in the ink in a short time, to prevent cracks from forming on the plastic substrate, and to form a recording layer with less uneven thickness. It is an object of the present invention to provide an optical recording medium that is highly reliable, has no reflectance unevenness, and a method for manufacturing the same.

[Means for Solving the Problems] That is, the present invention exhibits easy solubility in high boiling point solvents,
An optical recording medium characterized by having a recording layer formed using an organic dye that is poorly soluble in low boiling point solvents,
and a method for producing an optical recording medium having a recording layer formed using an organic dye, in which the organic dye is dissolved in a high-boiling point solvent and applied to a substrate, the high-boiling point solvent is replaced with a low-boiling point solvent, and then dried. This is a method of manufacturing an optical recording medium, which is characterized by forming a film.

The present invention will be explained in detail below.

FIG. 1 is an explanatory diagram showing a typical example of the method for manufacturing an optical recording medium of the present invention. In FIG. 1, the method for manufacturing an optical recording medium of the present invention involves passing a sheet-like substrate 1 through a roll 7, coating it with a high-boiling solvent ink 6 in which an organic dye is dissolved in a high-boiling solvent, and then passing it through a cylindrical roller 5. , the sheet-like substrate 1 is immersed in a low boiling point solvent 2. By this immersion, the high boiling point solvent ink 3 applied to the sheet-like substrate 1 is replaced with the ink 4, which is replaced with a low boiling point solvent, and becomes easier to dry. Solvents with fairly low boiling points result in a dry state that can be eaten by fingers. Thereafter, a film can be formed by air drying.

It is also possible to dissolve the organic dye in a high boiling point solvent, apply it to a sheet-like substrate, dry it to a state that can be eroded with the fingers, and then replace the high boiling point solvent with a low boiling point solvent.

In the present invention, the high boiling point solvent used for the first coating preferably has a boiling point of 100° C. or higher. Examples of the high boiling point solvent include aprotic solvents such as dimethylformamide and dimethyl sulfoxide, toluene,
Examples include aromatic solvents such as xylene, chlorobenzene, and nitrobenzene, and ketone solvents such as cyclohexanone.

On the other hand, the low boiling point solvent used for solvent replacement has a boiling point of 8.
Preferably, the temperature is less than 0°C. Examples include alcohol solvents such as methanol, ether solvents such as methyl ethyl ether, diethyl ether, and isopropyl ether, aliphatic solvents such as n-hexane and n-pentane, and furan solvents such as tetrahydrofuran. .

As the high boiling point solvent, it is preferable to appropriately select and use a solvent that has good solubility for the organic dye. In addition, by replacing the solvent with a low-boiling point solvent, it dries easily (because it becomes easy to dry, so any high-boiling point solvent can be used as long as it is easily soluble in organic dyes, and the solvent can be selected easily). It becomes possible to expand the range.

Further, as the low boiling point solvent used for solvent substitution, it is preferable to appropriately select and use a solvent that has low solubility for the organic dye, and it is preferable to use a solvent that has good compatibility with the above-mentioned high boiling point solvent and can be easily replaced.

The organic dye that forms the organic dye coating of the recording layer is a dye generally known as a near-infrared absorbing dye, which is particularly easily soluble in high-boiling point solvents, and has high solubility in low-boiling point solvents. Those showing low solubility are preferably used. For example, cyanine dyes, merocyanine dyes, croconium dyes, squalium dyes, azulenium dyes, polymethine dyes, biryllium dyes, phthalocyanine dyes,
Examples include naphthalocyanine dyes, naphthoquinone dyes, and anthraquinone dyes, and these dyes can be used alone or in combination.

In particular, in the present invention, organic dyes that have conventionally been difficult to form into films by coating methods as dyes that are poorly soluble in solvents, such as phthalocyanine dyes, naphthalocyanine dyes, naphthoquinone dyes, and anthraquinone dyes, etc. A recording layer can be formed by easily forming a film of the dye by a coating method.

For these dyes, triphenylmethane compounds,
It is also possible to add a stabilizer having the ability to quench singlet oxygen, such as a metal complex or an aminium/diimonium salt compound, or to use it as a combination of a dye and the stabilizer. The addition amount is suitably 1 to 60% by weight, preferably 5 to 40% by weight, and more preferably 10 to 30% by weight based on the total solid content of the recording layer.

In addition to these compounds, a binder may be contained in the recording layer consisting of an organic dye thin film. Examples of the binder include nitrocellulose, cellulose phosphate, cellulose sulfate, cellulose acetate, cellulose propionate,
Cellulose butyrate, cellulose myristate, cellulose parimitate, cellulose acetate/propionate, acetic acid/cellulose
Cellulose esters such as cellulose butyrate, cellulose ethers such as methylcellulose, ethylcellulose, propylcellulose, butylcellulose, vinyl resins such as polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyvinylpyrrolidone, Copolymer resins such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, polymethyl methacrylate, polymethyl acrylate, polybutyl acrylate, polyacrylic acid, polymethacrylic acid, Acrylic resins such as polyacrylamide and polyacrylonitrile, polyesters such as polyethylene terephthalate, poly(4,4'
-isobropylidene diphenylene-1,4-cyclohexylene dimethylene carbonate), poly(ethylenedioxy-3,3'-phenylene thiocarbonate),
Poly(4,4'-isopropylidene diphenylene carbonate coated terephthalate) Poly(4,4'-isopropylidene diphenylene carbonate), Poly(4,4'-isopropylidene diphenylene carbonate)
Polyarylate resins such as 4'-5ec-butylidene diphenylene carbonate), poly(4,4'-isopropylidene diphenylene carbonate-block-oxyethylene), or polyamides, polyimides, epoxy resins, and phenol resins. ,polyethylene,
Polyolefins such as polypropylene and chlorinated polyethylene can be used.

Further, the recording layer may contain surfactants, antistatic agents, stabilizers other than quenchers, dispersible flame retardants, lubricants, plasticizers, and the like.

Further, an undercoat layer may be provided between the recording layer and the substrate, and a protective layer may be provided on the recording layer.

As an undercoat layer, the protective layer should be protected against scratches and
It is used for protection from dust, dirt, etc. and for environmental stability of the recording layer.

The materials used for these are mainly inorganic compounds, metals, or organic polymer compounds. Examples of inorganic compounds include SiO□, MgF2. Sin, TiO□.

Examples of metals include Zn, such as ZnO, TiN, and SiN.

Cu, Ni, All, Cr, Ge, Se,
Cd, etc., and organic polymer compounds such as ionomer resins, polyamide resins, vinyl resins, natural polymers, epoxy resins, and silane coupling agents can be used.

As the substrate, plastics such as polyester, polycarbonate, acrylic resin, polyolefin resin, phenol resin, epoxy resin, polyamide, polyimide, glass, or metals can be used.

Coating methods include dip coating, spray coating, spinner coating, bead coating,
This can be carried out using a coating method such as a wire bar coating method, a blade coating method, a roller coating method, or a curtain coating method.

The film thickness (wet) of the high boiling point solvent ink in which an organic dye is dissolved in a high boiling point solvent applied to the substrate 1 is usually 1000 to 5000 μm, preferably 4000 to 40 #Lm.

Further, the thickness of the recording layer formed by replacing such a high boiling point solvent with a low boiling point solvent is 50 to 1100 p,
Preferably, 200 to 1 μm is appropriate.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 An optical recording medium was produced by the method shown in FIG. Cyanine dye (manufactured by Nippon Kanko Shiki Co., Ltd., product name: NK-2014)
30 parts by weight of dimethyl sulfoxide (DMSO) 1
000 parts by weight to prepare an ink. Thickness 1.2
Ink was applied to a sheet-like substrate having spiral irregularities formed on a long sheet of polymethyl methacrylate (PMMA) using a photopolymer method to a wet film thickness of approximately 1 μm using a roller coating method.

At this time, the feeding speed of the sheet-like substrate was 2 m/min. After the coated surface was dried to a state that could be eroded with the fingers, the coated sheet-like substrate was passed through an ether bath to perform solvent replacement, and then the sheet-like substrate was air-dried while being transported to form a recording layer. .

When we examined the recording layer that was formed, we found that there were 600 people ± 50 people.
A uniform thickness of the human body was obtained. Furthermore, no cracks were observed on the substrate. The results of measuring the reflectance at this time are shown in Table 1.

Table 1 Reflectance by distance from disk center (Note) r indicates the distance from the center of the disc.

A backing material of another PMMA substrate was bonded to the sheet-like substrate thus obtained using a UV-curable resin adhesive via a spacer, and then punched out using a male/female die of a press to obtain an optical disk.

This was rotated at 180 rpm, and writing was performed from the substrate side using a semiconductor laser with a wavelength of 830 nm at a recording power of 8 mW and a recording frequency of 3 MHz. Next, reproduction was performed with a read power of 0.8+nW, and when the C/N ratio was measured by spectrum analysis, a value of 50 dB was obtained.

Comparative Example 1 An optical recording medium was produced in the same manner as in Example 1, except that DMSO was used as the high-boiling solvent coating liquid and no low-boiling solvent was used for solvent replacement. The ink didn't dry just by letting it air dry, and even with forced air, it couldn't dry completely.

Furthermore, since the DMSO solvent existed on the sheet-like substrate for a long time, it became cloudy and could not be used as an optical recording medium.

Example 2 An optical recording medium was produced by the method shown in FIG. An ink was prepared by dissolving 2 parts by weight of a naphthalocyanine dye represented by the following general formula (I) in 1000 parts by weight of m-xylene. Ink was applied to a polycarbonate (PC) long sheet-like substrate with a guide groove engraved with a thickness of 0.4 mm using a roller coating method to a wet film thickness of 3 μm.

At this time, the feeding speed of the sheet-like substrate was 1.6 m/min.
It is. Next, the coated sheet substrate was passed through an n-pentane tank to perform solvent replacement, and then the sheet substrate was air-dried while being transported to form a recording layer.

(I) The formed recording layer had a uniform thickness of 1200±60.

A 0.3 mm thick PC board was bonded to the thus obtained sheet-like substrate via an ethylene-acetate dry film using a hot roll method, and cut into wallet size pieces using a laser to create an optical card. did.

This optical card was mounted on a stage that was driven in the X-Y direction, and a semiconductor laser with an oscillation wavelength of 830 nm was used to
．． Information is written in the Y-axis direction from the 4 mm PC board side with a recording power of 4.0 mW and a recording pulse of 80 μsec, and read with a read power of 0.4 mW, and the signal strength of the recording section is measured. 58 was obtained.

Comparative Example 2 In Example 2, except that m-xylene was used as the high boiling point solvent coating liquid and no low boiling point solvent was used for solvent replacement.
An optical recording medium was produced in the same manner as in Example 2. During air drying of the ink, microcracks were generated on the substrate and it became cloudy, making it impossible to use it as an optical recording medium.

Comparative Example 3 An ink was prepared by dispersing 2 parts by weight of the dye used in Example 2 in 1000 parts by weight of ether. When this was applied to a long polycarbonate sheet-like substrate and dried in the same manner as in Example 2, a uniform recording layer could not be formed.

[Effects of the Invention] As explained above, according to the present invention, after applying an ink in which an organic dye is dissolved in a high boiling point solvent, the solvent is replaced with a low boiling point solvent and dried, thereby making it possible to select a solvent. At the same time as the range has expanded, it has become possible to obtain an optical recording medium having a recording layer formed with an amorphous coating film containing a dye, which could not be used in coating methods due to its poor solubility.

In addition, the solvent contained in the ink can be dried in a short time, preventing cracks on the plastic substrate, and forming a recording layer with less uneven thickness, resulting in high reliability with no uneven reflectance. It became possible to obtain a flexible optical recording medium.

Furthermore, in the continuous manufacturing process of optical recording media, it has become possible to reduce the space required to dry the coating film and the equipment for blowing air.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a typical example of the method for manufacturing an optical recording medium of the present invention. 1... Sheet-like substrate 2... Low boiling point solvent 3... Coated high boiling point solvent ink 4... Ink substituted with low boiling point solvent 5... Cylindrical roll 6... High boiling point Solvent ink 7...roll

Claims (4)

[Claims] (1) In a method for producing an optical recording medium having a recording layer formed using an organic dye, the organic dye is dissolved in a high boiling point solvent and applied to a substrate, and then the high boiling point solvent is replaced with a low boiling point solvent. , drying, and film forming. (2) The high boiling point solvent shows easy solubility for the organic dye,
2. The method for producing an optical recording medium according to claim 1, wherein the low boiling point solvent exhibits poor solubility in organic dyes. (3) A film is formed by dissolving the organic dye in a high boiling point solvent, applying it to the substrate, drying it to a state that can be eroded with the fingers, then replacing the high boiling point solvent with a low boiling point solvent, and drying. 1
Or the method for manufacturing an optical recording medium according to 2. (4) An optical recording medium characterized by having a recording layer formed using an organic dye that is easily soluble in high-boiling point solvents and poorly soluble in low-boiling point solvents.