JP2005228402A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium of high preservability capable of maintaining characteristics such as jitters. <P>SOLUTION: The optical recording medium, which is provided with at least a recording layer containing organic dye and a light transmission layer on a supporting body, is provided with an intermediate layer substantially containing no sulfur between the recording layer and the light transmission layer. It is preferable that the content of sulfur in the intermediate layer is ≤1 mass%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical recording medium, and more particularly to a write-once optical recording medium containing an organic dye in a recording layer.

  With the start of digital high-definition broadcasting, further increase in the amount of image data is expected, and accordingly, a high capacity and a high data transfer speed are required for recording media (see, for example, Patent Document 1). ). When trying to record digital high-definition broadcasts at home, it is said that DVD ± R already has insufficient capacity, and development of next-generation DVDs has been actively conducted. As an example, a Blu-ray disc recorder that can record and play back BS digital high-definition broadcasts for 2 hours is on the market.

A recording medium for this Blu-ray disc recorder was also released at the same time, which was a medium having a phase change recording layer. The manufacture of the phase change medium requires a large vacuum film forming apparatus or the layer structure is complicated. In view of this point, development of a write-once Blu-ray disc medium using an organic dye is underway in order to manufacture a recording medium at a lower cost even in the next-generation DVD system including the Blu-ray disc. When the method of forming a film of organic dye by spin coating is employed, there is an advantage that manufacturing equipment that has been used in the manufacture of CD-R and DVD-R can be continuously used.
On the other hand, write-once Blu-ray disc media are also required to have high storage stability like conventional CD-R and DVD-R.

By the way, the write-once type Blu-ray disc medium has a configuration in which, for example, a reflective layer, a recording layer, and a transparent sheet are laminated in this order on a substrate. The said transparent sheet is bonded together via an adhesive, for example. In order to prevent the pressure-sensitive adhesive from affecting the recording layer, an intermediate layer is usually provided. In consideration of optical characteristics, film forming speed, use record in a phase change optical disk medium, etc., it has been proposed to use a material containing sulfur for the intermediate layer. However, when sulfur is contained in the intermediate layer, there is a problem that the sulfur and a metal (for example, Ag) constituting the reflective layer react with each other to form sulfides and reduce the storage stability.
In the conventional CD-R and DVD-R, no adhesive is used for bonding, and thus the intermediate layer as described above is not necessary.
Japanese Patent Laid-Open No. 11-120617

  In view of the above, an object of the present invention is to solve the above problems. That is, an object of the present invention is to provide an optical recording medium with high storage stability that can maintain good characteristics such as jitter.

The above problems are solved by the present invention described below.
That is, the present invention is an optical recording medium comprising, on a support, at least a recording layer containing an organic dye, and a light transmission layer,
An optical recording medium comprising an intermediate layer substantially free of sulfur between the recording layer and the light transmission layer.
The sulfur content in the intermediate layer is preferably 1% by mass or less.

  Since the optical recording medium of the present invention can maintain good characteristics such as jitter, it can exhibit high storage stability.

  The optical recording medium of the present invention includes at least a recording layer containing an organic dye and a light transmission layer on a support. An intermediate layer substantially not containing sulfur is provided between the recording layer and the light transmission layer.

  By not containing sulfur substantially in the intermediate layer, it is possible to prevent alteration of the metal constituting the reflective layer (formation of sulfide) while suppressing the influence of the pressure-sensitive adhesive used when forming the light transmission layer. As a result, high storage stability can be exhibited while maintaining good characteristics such as jitter.

  Here, “substantially containing no sulfur” means that the content of sulfur in the intermediate layer is 1% by mass or less in consideration of the case where sulfur is contained as an inevitable impurity. Is 0.8% by mass or less, more preferably 0.5% by mass or less, and still more preferably 0% by mass. By setting the content to 1% by mass or less, it is possible to prevent sulfur and the metal component of the reflective layer from reacting to generate sulfide.

  The sulfur content can be measured, for example, by fluorescent X-ray measurement. Specifically, after forming the intermediate layer directly on the substrate, the sulfur content can be obtained by performing the fluorescent X-ray measurement.

  What is necessary is just to use the material which does not contain sulfur which is mentioned later as a method which does not contain sulfur substantially. In addition, when sulfur is included as an inevitable impurity, there is no problem as long as the sulfur content corresponds to the amount not substantially contained.

  As the material constituting the intermediate layer, various materials can be used as long as they do not contain sulfur. For example, Mg, Al, La, Li, Na, Ca, Nd, Ce, Pb, Na—Al, Zr, Hf, Si, Ta, Y, Mg, Th, Sn, La, In, Nd, Sb, Ce, Ti, Bi, Gd, In-Sn, In-Zn, Cr, Al, Ti, Au, Au alloy , Ag, an Ag alloy, Pt, Zn, Se, and the like, and examples thereof include fluorides, oxides, nitrides, and the like containing one or more of these.

  Among these, it is preferable to use a material containing Zn or an oxide thereof. In addition to Zn or its oxide, oxides (other oxides) such as Al and Ga may be contained. When using ZnO and including other components, the mass ratio of ZnO to another oxide (ZnO: other oxide) is preferably 95: 5 to 5:95, and 90:10: It is more preferable that it is 50:50, and it is further more preferable that it is 80: 20-60: 40. By setting it to 95: 5 to 5:95, it becomes possible to improve the light transmittance in a short wavelength region.

The thickness of the intermediate layer is preferably 1 to 100 nm, more preferably 1 to 50 nm, and even more preferably 1.5 to 20 nm.
By setting the thickness of the intermediate layer to 1 to 100 nm, sufficient separation ability between the organic dye of the recording layer and the adhesive layer can be obtained, and deformation to the adhesive layer side during signal recording can be suppressed.

The intermediate layer can be formed by sputtering, for example.
The pressure during film formation is preferably 1 × 10 ⁻² to 1 × 10 ⁻⁵ torr, and the rate (sputtering rate) is preferably 1 to 10 nm / sec. Ar or the like can be used as the type of gas, and the gas flow rate is preferably 1 to 50 sccm (1 to 50 ml / min). The sputtering power is preferably 0.5 to 8 kW, more preferably 0.7 to 7 kW, and even more preferably 1 to 5 kW.

  When the film is formed by the RF sputtering method, the tuning (matching) is adjusted so that the REF with respect to the FWD is 10% or less, preferably 5% or less, more preferably 2.5% or less. In the case of oxides and nitrides, these gases may be mixed in a sputtering gas to form a film by reactive sputtering.

A preferred layer structure of the optical recording medium of the present invention is as follows: (intermediate layer), reflective layer, (intermediate layer), recording layer, intermediate layer, adhesive layer, light transmission layer, (hard coat layer) on the substrate in this order. This is a configuration provided. In addition, other layers may be provided between the layers for the purpose of improving adhesiveness, recording characteristics, storage stability, and the like. Further, in the above configuration, the layer described in parentheses means a layer formed as necessary.
Hereinafter, the substrate and other layers of the optical recording medium of the present invention will be described using the optical recording medium as a specific example. The present invention is not limited to these.

(substrate)
Specific examples of substrate materials include glass; acrylic resins such as polycarbonate and polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers; epoxy resins; amorphous polyolefins; polyesters; metals such as aluminum; These may be used together if desired.
Among the above materials, polycarbonate and amorphous polyolefin are preferable, and polycarbonate is particularly preferable from the viewpoints of moisture resistance, dimensional stability, and low cost. Further, the thickness of the substrate (the average thickness of the region where the recording layer is formed) is preferably in the range of 1.1 ± 0.3 mm.

  On the substrate, a guide groove for tracking or an unevenness representing information such as an address signal (the convex portion of the substrate is called an on-groove and the concave portion is called an in-groove. Here, “on-groove” is sometimes called “groove”. .) Is formed. In order to achieve a higher recording density, it is preferable to use a substrate on which grooves having a narrower track pitch are formed as compared with CD-R and DVD-R.

The track pitch of the groove is preferably in the range of 300 to 360 nm. More preferably, the range is 310 to 340 nm.
Moreover, it is preferable to make the depth (groove depth) of a groove into the range of 20-50 nm. By setting it as such a range, it becomes possible to prevent the molding from becoming difficult while preventing the tracking error signal from becoming small and making tracking difficult. More preferably, it is 25-40 nm.

  The half width of the on-groove is preferably in the range of 50 to 200 nm. By setting this range, it is possible to reduce jitter while preventing a tracking error from being lowered. More preferably, the range is 70 to 190 nm, and still more preferably 90 to 180 nm.

An undercoat layer may be formed on the surface of the substrate on the side where a reflective layer, which will be described later, is provided for the purpose of improving flatness and adhesion.
Examples of the material for the undercoat layer include polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, styrene / maleic anhydride copolymer, polyvinyl alcohol, N-methylol acrylamide, styrene / vinyl toluene copolymer, and chloro. Polymer materials such as sulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate, etc .; silane coupling Surface modifiers such as agents;
The undercoat layer is formed by dissolving or dispersing the above materials in an appropriate solvent to prepare a coating solution, and then applying this coating solution to the substrate surface by a coating method such as spin coating, dip coating, or extrusion coating. can do. The thickness of the undercoat layer is generally in the range of 0.005 to 20 μm, and preferably in the range of 0.01 to 10 μm.

(Reflective layer)
For the reflective layer, a light reflective material having a high reflectance with respect to the laser beam is used. The reflectance is preferably 70% or more.
As a light reflecting material having high reflectance, 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, Bi, and other metals and semi-metals or stainless steel. These light reflecting materials may be used alone, or may be used in combination of two or more kinds or as an alloy. Among these, Cr, Ni, Pt, Cu, Ag, Au, Al, and stainless steel are preferable. Particularly preferred is Au, Ag, Al or an alloy thereof, and most preferred is Ag or an alloy containing Ag as a main component (Ag: 50% by mass or more).

  The reflective layer can be formed on the substrate, for example, by vapor deposition, sputtering or ion plating of the light reflective material. The thickness of the reflective layer is generally in the range of 10 to 300 nm and preferably in the range of 50 to 200 nm.

(Recording layer)
The recording layer is a layer formed on the reflective layer and capable of recording information with a laser beam having a wavelength of 500 nm or less, and is a dye type containing an organic dye.
Specific examples of the organic dye include a cyanine dye, an oxonol dye, a metal complex dye, an azo dye, and a phthalocyanine dye.

Examples of the organic dye include JP-A-4-74690, JP-A-8-127174, JP-A-11-53758, JP-A-11-334204, JP-A-11-334205, and JP-A-11-334206. 11-334207, JP-A 2000-43423, 2000-108513, 2000-158818, and the like are preferably used.
Furthermore, organic compounds such as triazole compounds, triazine compounds, cyanine compounds, merocyanine compounds, aminobutadiene compounds, phthalocyanine compounds, cinnamic acid compounds, viologen compounds, azo compounds, oxonol benzoxazole compounds, and benzotriazole compounds can also be used as recording layer materials. Preferably used. Among these compounds, cyanine compounds, aminobutadiene compounds, benzotriazole compounds, and phthalocyanine compounds are particularly preferable.

  The recording layer is prepared by dissolving a recording substance, which is an organic dye, in a suitable solvent together with a binder and the like, and then coating the coating liquid on the reflective layer formed on the substrate surface. After forming, it is formed by drying. The concentration of the recording substance in the coating solution is generally in the range of 0.01 to 15% by mass, preferably in the range of 0.1 to 10% by mass, more preferably in the range of 0.5 to 5% by mass, and most preferably. Is in the range of 0.5-3 mass%.

Examples of the solvent for the coating solution include esters such as butyl acetate, ethyl lactate and cellosolve acetate; ketones such as methyl ethyl ketone, cyclohexanone and methyl isobutyl ketone; chlorinated hydrocarbons such as dichloromethane, 1,2-dichloroethane and chloroform; dimethylformamide and the like Amides; Hydrocarbons such as methylcyclohexane; Ethers such as tetrahydrofuran, ethyl ether, dioxane; Alcohols such as ethanol, n-propanol, isopropanol, n-butanol diacetone alcohol; 2,2,3,3-tetrafluoropropanol, etc. Fluorinated solvents; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether; That.
The above solvents can be used alone or in combination of two or more in consideration of the solubility of the recording material used. Various additives such as an antioxidant, a UV absorber, a plasticizer, and a lubricant may be further added to the coating solution depending on the purpose.

  When a binder is used, examples of the binder include natural organic polymer materials such as gelatin, cellulose derivatives, dextran, rosin, and rubber; hydrocarbon resins such as polyethylene, polypropylene, polystyrene, and polyisobutylene; Vinyl resins such as vinyl, polyvinylidene chloride, polyvinyl chloride / polyvinyl acetate copolymer, acrylic resins such as polymethyl acrylate and polymethyl methacrylate, polyvinyl alcohol, chlorinated polyethylene, epoxy resin, butyral resin, rubber And synthetic organic polymers such as initial condensates of thermosetting resins such as derivatives and phenol / formaldehyde resins. When a binder is used in combination as a material for the recording layer, the amount of binder used is generally in the range of 0.01 times to 50 times (mass ratio), preferably 0.1 times the recording substance. The amount is in the range of 5 to 5 times (mass ratio). The concentration of the recording substance in the coating solution thus prepared is generally in the range of 0.01 to 10% by mass, preferably in the range of 0.1 to 5% by mass.

  Examples of the coating method include a spray method, a spin coating method, a dip method, a roll coating method, a blade coating method, a doctor roll method, and a screen printing method. The recording layer may be a single layer or a multilayer. The recording layer generally has a thickness in the range of 20 to 500 nm, preferably in the range of 30 to 300 nm, and more preferably in the range of 50 to 100 nm.

The recording layer can contain various anti-fading agents in order to improve the light resistance of the recording layer.
As the antifading agent, a singlet oxygen quencher is generally used. As the singlet oxygen quencher, those described in publications such as known patent specifications can be used.
Specific examples thereof include JP-A Nos. 58-175893, 59-81194, 60-18387, 60-19586, 60-19587, and 60-35054. 60-36190, 60-36191, 60-44554, 60-44555, 60-44389, 60-44390, 60-54892, JP-A-60-47069, JP-A-63-209995, JP-A-4-25492, JP-B-1-38680, JP-A-6-26028, etc., German Patent 350399, and Japan Examples include those described in Chemical Society Journal, October 1992, page 1141.

  The amount of the anti-fading agent such as the singlet oxygen quencher used is usually in the range of 0.1 to 50% by mass, preferably in the range of 0.5 to 45% by mass, based on the amount of the organic dye. More preferably, it is the range of 3-40 mass%, Most preferably, it is the range of 5-25 mass%.

(Middle layer)
The intermediate layer is formed on the recording layer by the method described above using the material substantially not containing sulfur as described above. It is essential that the intermediate layer is formed between the recording layer and the light transmission layer, and in addition, at least one of “between the substrate and the reflective layer” and “between the reflective layer and the recording layer”. It may be formed.

(Light transmission layer)
The light transmission layer is formed to prevent the inside of the optical recording medium from being contaminated, scratched, impacted, or to prevent moisture from entering. The material is not particularly limited as long as it is a transparent material, but a transparent sheet made of polycarbonate, cellulose triacetate, or the like, preferably provided with an adhesive on at least one surface.
Note that “transparent” means that the recording light and the reproduction light are transmitted (transmittance: 90% or more).

A hard coat layer may be formed on the surface of the transparent sheet opposite to the surface to which the adhesive is applied in order to prevent the transparent sheet from being damaged. In order to form such a transparent sheet on the recording layer, it is preferable to carry out as follows.
First, a radiation curable resin coating solution is continuously applied to one surface of a transparent sheet wound in a roll shape. A coating film formed by coating is continuously irradiated with radiation and cured to provide a hard coat layer on the transparent sheet. Thereafter, an adhesive layer made of an adhesive is continuously provided on the other surface of the cover film, and a transparent sheet provided with the hard coat layer and the adhesive layer is punched into a predetermined shape (disk shape). Using the adhesive layer of the disc-shaped transparent sheet as a bonding surface, the transparent sheet is provided on the recording layer to form a light transmission layer. In addition, the bonding method of a transparent sheet, etc. are merely examples, and various methods can be applied.

  The thickness of the transparent sheet is preferably in the range of 0.03 to 0.15 mm, and more preferably in the range of 0.05 to 0.12 mm. By setting it as such a range, there exists an advantage that handling becomes easy and a coma aberration can be suppressed.

  As the pressure-sensitive adhesive, acrylic-based, rubber-based, or silicon-based pressure-sensitive adhesives can be used, but acrylic-based pressure-sensitive adhesives are preferable from the viewpoints of transparency and durability. As such an acrylic pressure-sensitive adhesive, 2-ethylhexyl acrylate, n-butyl acrylate and the like are the main components, and in order to improve cohesion, short-chain alkyl acrylates and methacrylates such as methyl acrylate, ethyl acrylate, and methyl methacrylate are used. And acrylic acid, methacrylic acid, acrylamide derivatives, maleic acid, hydroxylethyl acrylate, glycidyl acrylate, and the like, which can be crosslinking points with the crosslinking agent, are preferably used. The glass transition temperature (Tg) and the crosslinking density can be changed by appropriately adjusting the mixing ratio and type of the main component, the short chain component, and the component for adding a crosslinking point. In addition, the commercially available transparent sheet to which the adhesive was previously provided can also be used.

The radiation curable resin used for the hard coat layer may be any resin that can be cured by radiation irradiation, and more specifically, a resin having two or more radiation-functional double bonds in the molecule. It is preferable that
Examples thereof include acrylic acid esters, acrylamides, methacrylic acid esters, methacrylic acid amides, allyl compounds, vinyl ethers, vinyl esters and the like. Among them, preferred are bifunctional or higher acrylate compounds and methacrylate compounds.

Next, a method for recording information on an optical recording medium and a method for reproducing recorded information according to the present invention will be described.
Information is recorded on the optical recording medium, for example, as follows.
First, while rotating the optical recording medium at a constant linear velocity, 350 to 500 nm (preferably 400 to 440 nm) laser light for recording is irradiated from the transparent sheet side (opposite side of the substrate). By this laser light irradiation, the recording layer absorbs the light and the temperature rises locally, causing a physical or chemical change (for example, generation of pits) and changing its optical characteristics. Information is recorded by this change in optical characteristics.

Examples of the laser light source having an oscillation wavelength of 350 to 500 nm include a blue-violet semiconductor laser having an oscillation wavelength in the range of 390 to 415 nm, a blue-violet SHG laser having a central oscillation wavelength of about 430 nm, and the like.
In order to increase the recording density, the numerical aperture (NA) of the objective lens used for the pickup is preferably 0.7 or more, and more preferably 0.80 or more.

  On the other hand, the recorded information is reproduced by rotating the optical recording medium at the same constant linear velocity as described above, and irradiating the transparent sheet side with laser light having a wavelength equal to or less than that of the laser used for information recording. And it can carry out by detecting the reflected light.

(Example 1)
A substrate having a thickness of 1.1 mm was formed by injection molding using a polycarbonate resin (Panlite AD5503) manufactured by Teijin Chemicals Limited. The groove track pitch of the substrate was 320 nm, the half width of the on-groove portion was 120 nm, and the groove depth was 35 nm.

  On this substrate, a reflective layer is formed to a thickness of 100 nm by a vacuum film forming method using a target composed of Ag: 98.1 parts by mass, Pd: 0.9 parts by mass, and Cu: 1.0 parts by mass. did. The input power was 2 kW and the Ar flow rate was 5 sccm.

  The organic dye represented by the following chemical formula was weighed and dissolved so as to have a ratio of 2.5 g to 100 ml of TFP. The solution was irradiated with ultrasonic waves for 2 hours to dissolve the pigment, then left in an environment of 23 ° C. and 50% for 0.5 hours or longer, and filtered through a 0.2 μm filter. Using this solution, a recording layer having a thickness of 140 nm was formed on the reflective layer by spin coating. Then, it heat-processed for 1 hour in 80 degreeC clean oven.

After the heat treatment, an intermediate layer having a thickness of 7 nm was formed by a vacuum film formation method using a target composed of 70 parts by mass of ZnO and 30 parts by mass of Ga ₂ O ₃ . The input power was 2 kW, the Ar flow rate was 50 sccm, and RF tuning was optimized. As a result, REF = 40 with respect to FWD = 2000.

  After forming the intermediate layer, a polycarbonate film (thickness: 80 μm) having an adhesive layer having a thickness of 20 μm formed on one surface was bonded to prepare an optical recording medium.

  The produced optical recording medium was set in a DDU-1000 (manufactured by Pulstec Industrial Co., Ltd.) equipped with a laser optical system having a wavelength of 403 nm and NA = 0.85, and 1-7 modulation was performed with a power of 5.5 mW. Random signals (2T to 8T) were recorded and reproduced with a power of 0.35 mW to evaluate jitter. At this time, the linear velocity was 5.28 m / s, and the laser emission pattern during recording was optimized. Jitter was measured using a conventional equalizer. The results are shown in Table 1 below.

  In addition, after the produced optical recording medium was stored in an environment of 80 ° C. and 85% for 96 hours, the recorded track jitter was measured under the same conditions as before storage, and compared with the jitter before storage (change in archival jitter). ). The results are shown in Table 1 below.

Further, after storage, jitter was evaluated for a new unrecorded track in the same manner as before storage, and compared with the jitter evaluated before storage (shelf jitter change).
The sample after storage was observed with a differential interference microscope at a magnification of 100 times, and the presence or absence of black spot-like defects (sulfides) was observed. The results are shown in Table 1 below.

(Example 2)
An optical recording medium was prepared and evaluated in the same manner as in Example 1 except that a target composed of ZnO: 70 parts by mass and A1 ₂ O ₃ : 30 parts by mass was used at the time of forming the intermediate layer.

(Example 3)
An optical recording medium was prepared and evaluated in the same manner as in Example 1 except that a target made of Si was used at the time of forming the intermediate layer. At this time, the input power was 2 kW, the Ar flow rate was 50 sccm, and the film was formed by DC sputtering. Others were the same as in Example 1.

(Comparative Example 1)
An optical recording medium was prepared and evaluated in the same manner as in Example 1 except that a target comprising ZnS: 80 parts by mass and SiO ₂ : 20 parts by mass was used during the formation of the intermediate layer.

  In addition, when the fluorescent X-ray measurement was performed about each optical recording medium (laminated body) after forming an intermediate | middle layer, in the optical recording medium of Examples 1-3, sulfur content is 1 mass% or less. On the other hand, the optical recording medium of Comparative Example 1 was 25% by mass.

  From Table 1 above, in all of the optical recording media of Examples 1 to 3, no black spots due to silver sulfide were observed, and good jitter values were maintained under various storage conditions.

Claims (2)

An optical recording medium comprising, on a support, at least a recording layer containing an organic dye, and a light transmission layer,
An optical recording medium comprising an intermediate layer substantially free of sulfur between the recording layer and the light transmission layer. The optical recording medium according to claim 1, wherein the content of sulfur in the intermediate layer is 1% by mass or less.