JPH02232832A - Information recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having a high reflectivity and large modulation degree by providing a dyestuff recording layer and a reflecting layer on a substrate and specifying the thickness of the recording layer within the specific range of the optical path length corresponding to the max. value of the reflectivity of the recording medium. CONSTITUTION:The recording layer contg. dyestuff to allow writing and reading of information is provided on the substrate and the reflecting layer consisting of a metal is provided on this recording layer. This recording layer is formed to the thickness equal to the optical path length within + or -10% range of the optical path length corresponding to the max. value of the reflectivity of the recording medium. The reflectivity changes with a change in the optical path length and has plural max. values. The max. value of the reflectivity decreases as the thickness increases but on the contrary, the modulation degree increases and the fluctuation in the reflectivity decreases by an increase in the thickness. The thickness of the recording layer suitable to the desired performance of the recording medium is selected in this way, by which the recording medium having the high reflectivity and the large modulation degree is obtd.

Description

Detailed Description of the Invention [Field of the Invention] The present invention relates to an information recording medium having a recording layer containing a dye and a metal reflective layer on which information can be written and/or read using a high energy density laser beam. It is related to. [Technical Background of the Invention] In recent years, information recording media that use high energy density beams such as laser light have been developed and put into practical use.
This information recording medium is called an optical disk, and is used as a video disk, an audio disk, a large-capacity still image file, a large-capacity computer disk, etc. The basic structure of an optical disk is made of glass, synthetic resin, etc. A disk-shaped substrate consisting of Bi, Sn, etc.
, a metal or metalloid such as In, Te, etc.; or a recording layer made of a cyanine-based, gold-am-based, or quinone-based dye. Note that an intermediate layer made of a polymeric substance is usually provided on the surface of the substrate on the side where the R layer is provided, from the viewpoint of improving the flatness of the substrate, improving the adhesive force with the recording layer, or improving the sensitivity of the optical disc. It is often provided. In addition, for the purpose of improving the durability of the information recording medium, a protective layer is provided on the recording layer, or a recording layer is provided on at least one of the two disc-shaped substrates as a disk structure. ,
An air sandwich structure has been proposed in which these two substrates are joined via a ring-shaped inner spacer and a ring-shaped outer spacer so that the recording layer is located inside and a space is formed. In optical discs provided with such a protective layer or optical discs with an air sandwich structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate.
This has the advantage that the recording layer will not be physically or chemically damaged, or dust will not adhere to its surface, which will impede information recording and reproduction. Writing and reading information to and from an optical disc is usually performed by the following method. Information is written by irradiating the optical disc with a laser beam, and the irradiated portion of the recording layer absorbs the light, causing a local temperature rise and causing physical or chemical changes (for example,
Information is recorded by generating pits (formation of pits) and changing their optical properties. Information is also read by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected or transmitted light that corresponds to changes in the optical characteristics of the recording layer. The above-mentioned recording materials are used to form the recording layer of such information recording media. Sea urchin metals and pigments are known. Information recording media using dyes have advantages in the characteristics of the recording medium itself, such as higher sensitivity compared to recording materials such as metals, as well as manufacturing advantages in that the recording layer can be easily formed by a coating method. It has great advantages. However, recording layers made of dyes generally have low reflectance.
Another drawback is that it is difficult to obtain a high C/N. An information recording medium has been proposed in which a light-absorbing and reflective dye film having a film thickness set to maximize reflectance is provided on a substrate (Japanese Unexamined Patent Publication No. 60-239947). However, the reflectance of this information recording medium is not fully satisfactory. Therefore, the recording layer uses a dye that is advantageous in terms of productivity, has high reflectance, and has small reflectance fluctuations.
It is desired to propose an information recording medium in which the recorded signal has a high C/N. [Object of the invention] The present invention provides an information recording medium that has a dye recording layer and a reflective layer on a substrate, has high reflectance, small reflectance fluctuation, and has a high modulation degree and C/N value of a recorded signal. The purpose is to provide [Summary of the Invention] The present invention provides an information storage system in which a recording layer containing a dye that allows information to be written and/or read by a laser beam, and a reflective layer made of metal are provided in this order on a disc-shaped substrate. An information recording medium, characterized in that the thickness of the recording layer is such that the optical path length is within ±10% of the optical path length at which the reflectance of the information recording medium becomes maximum. It is in. Preferred embodiments of the information recording medium of the present invention are as follows. l) The information recording medium, wherein the dye is at least one type of dye selected from cyanine dyes, azulenium dyes, and squarylium dyes. 2) The information recording medium, wherein the dye recording layer contains 0.001 to 0.1 mole part of a metal complex dye based on 1 mole part of the dye. 3) The above coloring information! The thickness of one layer is such that the optical path length is within ±10% of the optical path length corresponding to any one of the maximum values from the maximum to the fourth maximum value of the reflectance of the information recording medium. The above information recording medium is characterized in that: 4) The above information recording medium, wherein the material of the plastic substrate is polycarbonate, polyolefin, or cell cast polymethyl methacrylate. 5) The metal is Au. Ag. Cu, Pt, Cr, Ti
, AM, and stainless steel. 6) The layer thickness of the reflective layer is 100 to 3
000 or more. [Detailed Description of the Invention] The information recording medium of the present invention has a basic configuration in which a dye recording layer and a metal reflective layer are provided in this order on a disc-shaped substrate. The disc-shaped substrate in the present invention can be arbitrarily selected from various resin materials used as substrates for conventional information recording media. In terms of substrate optical properties, flatness, workability, handling, stability over time, and manufacturing costs, examples of substrate materials include acrylic resins such as cell cast polymethyl methacrylate and injection molded polymethyl methacrylate; Examples include vinyl chloride resins such as vinyl chloride and vinyl chloride copolymers; epoxy resins: polycarbonate resins, amorphous polyolefins, and polyesters. Preferably polycarbonate,
Mention may be made of polyolefins and cell-cast polymethyl methacrylate. “An undercoat layer may be provided on the surface of the substrate on which the recording layer is provided for the purpose of improving flatness, improving adhesive strength, improving the solvent resistance of the substrate, and preventing deterioration of the recording layer. Examples of materials for the undercoat layer include polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, styrene/maleic anhydride copolymer, polyvinyl alcohol, N-methylolacrylamide, styrene/sulfonic acid copolymer, and styrene fist. Vinyltoluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride,
High molecular substances such as chlorinated polyolefin, polyester, polyimide, vinyl acetate-vinyl chloride copolymer, ethylene Φ vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate; organic materials such as silane coupling agents; and inorganic oxides (S i02.Al2 03
etc.) and inorganic substances such as inorganic fluoride (MgF2). The undercoat layer can be formed by, for example, preparing a coating solution by dissolving or dispersing the above substances in a suitable solvent, and then applying this coating solution to the substrate surface by a coating method such as spin coating, dip coating, or extrusion coating. It can be formed by The layer thickness of the undercoat layer is generally 0.005 to 20
It is in the range of μm, preferably 0. The range is from Ol to 10Bm. Furthermore, a pregroup layer and/or a prebit layer may be provided on the substrate (or undercoat layer) for the purpose of forming tracking grooves or unevenness representing information such as address signals. The material for the pregroup layer etc. is at least one monomer selected from monoesters, diesters, triesters and tetraesters of acrylic acid (
or oligomer) and a photopolymerization initiator. The pregroup layer is formed by first coating a mixture of the above-mentioned acrylic ester and polymerization initiator on a precisely made matrix (stamper), and then placing the substrate on top of this coating layer. The liquid layer is cured by irradiating ultraviolet rays through the substrate or matrix, and the substrate and liquid phase are fixed together.
Next. By peeling the X plate from the matrix, a substrate with a pregroup layer is obtained. The thickness of the pregroup layer is generally in the range of 0.05 to 100 pm, preferably in the range of 0.1 to 50 pm. As in the present invention,
If the substrate material is plastic, pregroups and/or prepits may be provided directly on the substrate by injection molding or extrusion molding. A recording layer containing a dye on which information can be written and/or read by laser light is provided on the substrate (or pregroup layer, etc.). The dye used in the present invention is not particularly limited, and any dye may be used. For example, cyanine dyes, phthalocyanine dyes, pyrylium/thiopyrylium dyes, azulenium dyes, squarylium dyes, metal complex dyes such as Ni and Or, naphthoquinone dyes, anthraquinone dyes, indophenol dyes, and indoaniline dyes. Examples include dyes, triphenylmethane dyes, triallylmethane dyes, aluminum-based ●diimmonium dyes, and nitroso compounds. Preferably, cyanine dyes,
Examples include azulenium pigments and squarylium pigments. Among these, semiconductor lasers that emit near-infrared light have been put into practical use as recording and reproducing lasers.
A dye that has a high absorption rate for light in the near-infrared region of 700 to 900 nm is preferable. Note that these dyes may be used alone or as a mixture of two or more. Furthermore, when a cyanine dye is used, it is preferable to use the above-mentioned metal complex dye or aminium dye or diimmonium dye as a quencher. In this case, it is preferable to contain 0.001 to 0.1 mole part of a metal complex dye or the like as a quencher based on 1 mole part of the total dye. The recording layer can be formed by dissolving the dye and, if desired, a binder in a solvent to prepare a coating solution, then applying this coating solution to the surface of the substrate to form a coating film, and then drying it. can. Examples of solvents for preparing the above dye coating solution include esters such as ethyl acetate, butyl acetate, and cellosolp acetate, ketones such as methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone, and carbonized halides such as dichloromethane, 1,2-dichloroethane, and chloroform. Hydrogen, ethers such as tetrahydrofuran, ethyl ether, and dioxane, alcohols such as ethanol, n-propanol, impropanol, and n-butanol, and amino acids such as dimethylformamide.
Examples include fluorinated solvents such as 2,3,3-tetrafluoropropanol. Note that these non-hydrocarbon organic solvents may contain hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, as long as the amount is within 50% by volume. ．． The coating solution also contains antioxidants, UV absorbers, plasticizers,
Various additives such as lubricants may be added depending on the purpose. When a binder is used, examples of the binder include cellulose derivatives such as gelatin, nitrocellulose, and cellulose acetate; natural organic polymeric substances such as dextran, rosin, and rubber; and carbonized materials such as polyethylene, polypropylene, polystyrene, and polyisobutylene. Hydrogen resins, polyvinyl chloride, polyvinylidene chloride, polyvinyl chloride, vinyl resins such as polyvinyl acetate copolymers, acrylic resins such as polymethyl acrylate, polymethyl methacrylate,
Synthetic organic polymeric substances include polyvinyl alcohol, chlorinated polyolefin, epoxy resin, butyral resin, rubber derivatives, and initial condensation products of thermosetting resins such as phenol/formaldehyde resin. Application methods include spray method, spin coating method, dip method, roll coating method, blade coating method, doctor roll method, and screen printing method. In order to form a good alignment state of the dye, it is preferable to use the subin coating method. When a binder is used as a material for the recording layer, the ratio of dye to binder is generally o. oi ~ 99% (ffif
ft ratio), preferably in the range of 1.0 to 95% (weight ratio). In the information recording medium of the present invention, a reflective layer made of metal is further provided on the dye recording layer. By providing a reflective layer, it is possible to obtain the effect of improving reflectance, improving S/N during information reproduction, and improving sensitivity during recording. Materials for the reflective layer include Mg, Se, Y, Ti, and Zr.
, Hf, V, Nb, Ta, Cr, MoW, Mn. Re,
Fe, Co. Ni. Ru. Rh, Pd, I r, Pt,
Cu, Ag. Au, Zn, Cd. An, Ga. In. S
i. Ge, Te. Pb. Po. Sn. Mention may be made of metals and metalloids such as Bi. Furthermore, it may be made of an alloy such as stainless steel. In the present invention, the temperature is 400°
High thermal conductivity at K, at least 10 w/m*k
It is preferable that a reflective layer made of one of the above metals is provided. This allows the heat generated when the dye recording layer is irradiated with laser light to be rapidly conducted to the reflective layer. Among these, Au, Ag. Cu. Pt. Particularly preferred are An, Cr, Ni and stainless steel. These substances may be used alone, in combination of two or more, or as an alloy. The reflective layer can be formed on the recording layer by, for example, vapor deposition, sputtering, or ion plating of the above-mentioned light reflective material. The thickness of the reflective layer is generally in the range of 100 to 3,000 thick, particularly preferably in the range of 500 to 2,000 thick. In the information recording medium of the present invention, the film thickness of the recording layer is within ± the optical path length corresponding to the maximum reflectance of the information recording medium.
It has a # characteristic in that the thickness is such that the optical path length is within the range of 10%. FIG. 1 is a diagram showing an example of the relationship between the reflectance of an information recording medium and the optical path length of the recording layer. In FIG. 1, the reflectance of the information recording medium of Example 1 is determined by the measurement wave fi 7 8 0
It shows the reflectance in nm, and the optical path length is the product of the light passage distance of the recording layer and the absolute refractive index. As shown in Figure 1, as the optical path length changes, the reflectance changes and shows multiple maximum values. That is, the optical path length PI. P2, P3. --Respective maximum reflectance value Rsax in life 1. Rmax
2, R@JX3, ●● is shown. The maximum value of reflectance is Rm
It gradually decreases from axl to Rsax3.
In the present invention, the thickness of the recording layer is determined by the optical path length P1.
, P2, P3. The value should be within ±lθ% of either value of ●●●. By setting the thickness of the recording layer as described above, the reflectance of the information recording medium can be increased and the degree of modulation can be increased. In addition, since the optical path length is set near the maximum value of the reflectance, changes in reflectance caused by changes in the optical path length of the recording layer can be reduced, and reflections caused by variations in the film thickness of the recording layer of the information recording medium can be minimized. It is possible to reduce fluctuations in the rate. The optical path length of the recording layer corresponding to the maximum value of reflectance and the relationship between the optical path length and film thickness of the recording layer are determined by the types of materials forming the substrate, recording layer, reflective layer, and other layers of the information recording medium; The film thickness of the recording layer cannot be unambiguously determined because it varies depending on the formation conditions of the recording layer and/or reflective layer, the wavelength of the laser beam used for writing and/or reading information, etc. The optimal recording layer thickness can be determined by considering various points. If the optical path length PI corresponding to Rsaxl, where the maximum reflectance value is the maximum value, is selected as the optical path length for determining the film thickness of the recording layer, an information recording medium with the maximum reflectance can be obtained. ．． Furthermore, when selecting the optical path length P2 corresponding to Rmax2, which has the second largest reflectance maximum value, the reflectance decreases slightly compared to the case where the optical path length P1 is selected, but the film thickness increases. Therefore, the modulation degree increases and the reflectance fluctuation decreases. The same tendency as above occurs when other optical path lengths are selected. Therefore, in the information recording medium of the present invention, the optical path length at the point where the arbitrary reflectance is maximum is selected so as to obtain the optimal information recording medium according to the desired performance of the information recording medium, and ±lθ%
A recording layer is provided with a film thickness that provides an optical path length within the range of . In the present invention, the reflectance maximum value is ±1 of the optical path length corresponding to any of the maximum values from the maximum to the fourth magnitude.
It is preferable for the recording layer to have a film thickness that provides an optical path length within the range of 0% in terms of balance of reflectance, modulation degree, etc. The information recording medium of the present invention may further include a protective layer on the reflective layer for the purpose of physically and chemically protecting the recording layer and the entire information recording medium. Further, this protective layer may be provided on the side of the substrate where the recording layer is not provided in order to improve scratch resistance and moisture resistance. Examples of materials used for the protective layer include inorganic materials such as Sin, Si02, SiN4, MgF2, and Sn02.
etc. can be mentioned. Further, examples of the organic substance include thermoplastic resins, thermosetting resins, UV-curable resins, etc., and preferably UV-curable resins. In the present invention, remarkable effects can be obtained when the above-mentioned substance is applied by coating. This is particularly effective when the above organic substances are applied by coating. That is, it can also be formed by dissolving thermoplastic resin, thermosetting resin, etc. in a suitable solvent to prepare a coating solution, then applying this coating solution and drying.
In the case of V-curable resin, a coating solution was prepared either as it is or by dissolving it in an appropriate solvent.
UV-curable resins that can also be formed by curing by irradiation with UV light include (meth)acrylate oligomers such as urethane (meth)acrylate, epoxy (meth)acrylate, and polyester (meth)acrylate. , monomers such as (meth)acrylic acid esters, etc. Further, conventional UV curable resins such as photopolymerization initiators can be used. Various additives such as antistatic agents, antioxidants, and UV absorbers may also be added to these coating solutions depending on the purpose. In the present invention. It is preferable to use UV curable resin. The thickness of the protective layer is generally in the range of 0.1-100 gm. In addition to the above, the protective layer can be formed, for example, by laminating a film obtained by plastic extrusion onto the dye recording layer via an adhesive layer.
Alternatively, it may be provided by methods such as vacuum deposition, sputtering, and coating. Examples and comparative examples of the present invention are listed below. However, these examples do not limit the present invention. [Example 1] Dye (A) with the following structural formula: n-C4Hg Cl 04- n-C4Hp
A dye recording layer coating solution was prepared by adding 0.01 mol % of dye (B) having the following structural formula to the above dye and dissolving it in 2,2,3.3-tetrafluoroprobanol. Disc-shaped polygon board with tracking guide (outer diameter: 130 mm, inner diameter = 15 mm, thickness:
1.2mm. Track pitch: 1.6 JLm, group depth 2800 mm) Coating solution E was applied at a rotational speed of 50 orpm by the Subin coating method, and then dried at a rotational speed of 2000 rpm for 1 minute. A recording layer was formed. On the recording layer formed as in L.
A reflective layer with a thickness of 1300 mm was formed by evaporating U. A UV curable resin (product name: UV3070, manufactured by Three Pond Co., Ltd.) is applied as a protective layer on the above reflective layer by spin coating at a rotational speed of 1500 rpm, and then cured by irradiating ultraviolet rays with a high-pressure mercury lamp. A protective layer with a thickness of 17 mm was formed. In the method described in L, the concentration of the dye (A) in the dye recording layer coating solution is changed to prepare a substrate, a dye recording layer, a reflective layer, and a 4M recording layer having recording layers of various thicknesses.
An information recording medium consisting of The reflectance (measurement wavelength: 780
nm) and optical path length [2, plotted to obtain the graph shown in Figure 1. From Figure 1, find the optical path length PI (1300 again) corresponding to R*axl, which is the maximum reflectance value, and
An information recording medium (sample 1) having a recording layer with a film thickness corresponding to (1300 mm) was manufactured by adjusting the concentration of the dye (A) in the dye recording layer coating liquid to 2.75% by weight in the above method. ．． The C/N of sample 1 was determined by the following evaluation method.
When the reflectance and reflectance (Rf) were measured, it was found that C/N = 55 dB and reflectance = 78%. [Comparative Example 1] In Example 1, the concentration of the dye (A) in the dye recording layer coating liquid was changed to 2. Example 1 (sample 1) except that it was changed to .00% by weight
In the same manner as above, an information recording medium (comparative sample 1) having a recording layer with a thickness of 900 mm was manufactured. When the C/N and reflectance (R f) of comparative sample 1 were measured, the C/N was 52 dB and the reflectance was 7i%. [Evaluation of information recording medium] (1) Sensitivity test The information recording medium was rotated at a linear velocity of 5 m/sec, and
．． Information was written by forming a bubble using a 5 MHz (pulse width 200 ngec) semiconductor laser. Next, a spectrum analyzer (TR417
2: Measured the laser output at which the ratio of the output level of carrier to noise (C/N ratio) is maximum and the CZN ratio opposite thereto (RBW = 30 KHZ) using a C/N ratio (manufactured by Takeda Riken).
．． (2) Optical property test Specular reflectance was measured using a transmittance/reflectance measurement device manufactured by Mizojiri Optical Co., Ltd. The light source is a halogen lamp, and the wavelength used is 780 nm. The spot diameter was 1 mm. [Effects of the Invention] The information recording medium of the present invention has a recording layer containing a dye having the thickness specified above, and a reflective layer made of metal thereon. There is. Therefore, the reflectance is high, the modulation degree and the C/N value are large, and the film thickness of the recording layer at the time of manufacture is small.
It has the remarkable effect of minimizing fluctuations in reflectance due to glare.

[Brief explanation of the drawing]

FIG. 1 is a diagram plotting the reflectance and optical path length measured for various information recording media obtained in Example 1. Raax: Maximum reflectance value, P: Optical path length corresponding to the maximum reflectance value. Patent applicant Fuji Photo Film Co., Ltd. Agent Patent attorney Yasushi Yanagawa Procedural amendment

Claims (1)

[Claims] 1. An information recording medium in which a recording layer containing a dye on which information can be written and/or read by a laser beam and a reflective layer made of metal are provided in this order on a disk-shaped substrate, An information recording medium characterized in that the thickness of the recording layer is such that the optical path length is within ±10% of the optical path length corresponding to the maximum value of the reflectance of the information recording medium.