JP2957651B2 - Information recording medium and method of manufacturing the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an information recording medium on which information can be recorded and / or reproduced by a laser beam, and a method for manufacturing the same.

[Technical Background of the Invention] In recent years, information recording media using a beam of high energy density such as laser light have been developed and put into practical use. This information recording medium is called an optical disk,
It can be used as a disk, an audio disk, and also a large-capacity still image file and a disk memory for a large-capacity computer. Among these information recording media, compact discs (CDs) are widely used for audio reproduction of music and the like. A compact disc is used only for reproducing information consisting of a series of pits formed on a substrate at the time of manufacture. That is, a compact disc is manufactured by molding a suitable plastic material to form pits in a spiral shape, and then forming a metal layer as a reflective layer on the surface thereof. Thus, the compact disc is a recording medium exclusively for reproduction.

Reading information from a compact disc is performed by irradiating a laser beam while rotating the disc. The information is reproduced by detecting a change in the amount of reflected light due to the presence or absence of pits on the disk. Read-only compact discs are designed to read (play) a CD while rotating at a constant linear speed of 1.2 to 1.4 m / s based on the CD standard. Within a range of 116 mm, it is required to have a maximum recording time of about 74 minutes at a track pitch of 1.6 μm.

As mentioned above, audio CDs are now widely used. Accordingly, commercially available CD players used for reproducing audio CDs are widely and generally used, so that mass production reduces the price and improves the performance.

In addition, DRAW (Direct
A read-after-write type information recording medium has also been developed and partially put into practical use. Such a DRAW-type information recording medium (optical disk) has, as its basic structure, a disc-shaped transparent substrate made of plastic, glass, or the like, and a metal or semi-metal such as Bi, Sn, In, or Te provided thereon. And a recording layer composed of a dye. Recording of information on an optical disk is performed, for example, by irradiating the optical disk with a laser beam. As a result, the irradiated portion of the recording layer absorbs the light and locally rises in temperature, resulting in a physical change such as pit formation or the like. Information is recorded by causing a chemical change, such as a phase change, to change its optical properties.
Reading (reproduction) of information from the optical disk is also performed by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected light or transmitted light corresponding to a change in the optical characteristics of the recording layer. You.

Irradiation of a laser beam for recording and reproducing information on the optical disk is usually performed at a predetermined position on the disk surface. In order to guide the laser beam and accurately follow the expected irradiation position (generally called tracking), a tracking guide (pre-groove) of a concave groove is generally provided on the surface of the substrate.

By the way, the recording layer containing a dye is generally formed by applying a solution containing a dye on a substrate on which a pre-groove is formed and drying it. In this case, the thickness of the dye recording layer at the bottom of the groove is the land portion. Of the dye recording layer. Therefore, the depth of the groove on the surface of the dye recording layer formed by reflecting the shape of the pre-groove groove of the substrate becomes shallower than the depth of the pre-groove groove of the substrate. When recording pits are formed on the surface of the dye recording layer, the phase difference between the top of the groove on the surface of the dye recording layer (the portion reflecting the land portion of the substrate) and the bottom of the groove is small, so that the modulation degree of the recording pit is small. There is a problem.

For this purpose, it is conceivable to increase the degree of modulation of the recording pits by increasing the depth of the pregroove of the substrate and relatively increasing the depth of the groove formed on the surface of the dye recording layer. In such a case, the reflectivity generally tends to decrease, and the reflectivity may be insufficient because reproduction is performed using a general CD player.

When the thickness of the dye recording layer at the bottom of the groove of the substrate and the thickness of the dye recording layer at the land become almost the same, the depth of the pre-groove on the substrate can be reduced. And an information recording medium having a large reflectance.

A ROM area in which pits are formed in advance on the substrate;
There has been proposed an information recording medium having a recordable area in which pits for data reproduction are formed by irradiation with a laser beam (see JP-A-2-42652). In this information recording medium, a laser absorption layer made of a dye is provided only in a recordable area, and a laser absorption layer made of a dye is not provided in a ROM area where prepits are formed. The reason is that, if a laser absorbing layer made of a dye is provided in the area where the prepits are formed, the modulation degree of the prepit signal becomes small and information in the ROM area cannot be reproduced practically.

That is, the laser absorption layer composed of a dye is generally formed by applying and drying a solution of the dye,
When the dye solution is applied to the pre-pit formation region, the film thickness of the laser absorbing layer in the pit portion (hole portion) is changed between the pit portions (pits and pits) similarly to the case of applying the dye solution to the pre-groove formation region. (Corresponding to the land portion), the thickness of the laser absorption layer is larger than the thickness of the laser absorption layer. Therefore, the depth of the hole on the surface of the laser absorption layer formed by reflecting the shape of the pit portion of the substrate. This is because the depth is smaller than the depth of the pit on the substrate, and the phase difference between the pit portion and the inter-pit portion is reduced, so that the modulation degree of the pre-pit is reduced.

However, as described in JP-A-2-42652, in an information recording medium in which a dye layer is not provided in a pre-pit portion (ROM area) but is provided only in a recordable area, the dye layer is provided. It is difficult to form the boundary with good reproducibility at the boundary between the colored portion and the portion where the dye layer is not provided, or the film thickness tends to be uneven at the edge of the dye layer. There is a problem that eccentricity of the annular dye layer easily occurs. Furthermore, in practice, RO
Only an information recording medium divided into two areas, the M area and the recordable area on the outer peripheral side, can be manufactured, and the ROM
A recordable area is additionally provided on the inner circumference side of the area,
It is extremely difficult to provide the M area and the recordable area in a mixed manner, and there is also a problem that application software to be recorded in the ROM area in advance and a method of using the software are limited, which is practically inconvenient.

When the thickness of the dye layer in the pre-pit portion of the substrate and the thickness of the dye layer in the portion between the pits are substantially the same, the phase difference between the pre-pits increases, and the information recording medium has a high degree of modulation of the pre-pits.

Even if a laser light absorbing layer made of a dye is formed in the prepit portion, if the degree of modulation of the prepit is large, the light absorbing layer containing the dye is formed in both the prepit forming area (ROM area) and the pregroove forming area (recordable area). Can be formed, and the above-mentioned problems can be solved.

[Object of the Invention] The present invention provides an information recording medium having good tracking characteristics, which can obtain a reproduction signal having a high degree of modulation and reflectance and satisfying the CD standard after recording information by irradiating a laser beam. The purpose is to provide.

Further, the present invention provides an information recording medium in which a light absorbing layer containing a dye is also formed in a region where a prepit is formed, and a reproduction signal satisfying the CD standard can be obtained from the region where the prepit is formed. The purpose is to provide.

Still another object of the present invention is to provide a method for manufacturing an information recording medium having the above-mentioned excellent features.

[Summary of the Invention] In the present invention, a light absorbing layer containing a dye capable of recording information by irradiating a laser beam to form pits is provided on a disc-shaped substrate on which prepits and pregrooves are formed. An information recording medium further provided with a reflective layer made of metal on the light absorbing layer, wherein the pre-pits are 0.
The half-width in the range of 2 to 1.4 μm and the depth of the pre-groove in the range of 60 to 300 nm are expressed as λ / 16 (where λ is the wavelength of the laser beam for reproduction) in terms of the optical path length. And the difference between the optical film thickness of the light absorbing layer in the pre-pit portion and the optical film thickness of the light absorbing layer in the portion between the pre-pits is λ / 8 (where λ is a reproducing laser Below the wavelength of light)
The difference between the optical thickness of the light absorbing layer at the bottom of the pre-groove and the optical thickness of the light absorbing layer at the land between the pre-grooves is λ.
/ 8 (where λ is the wavelength of the reproducing laser beam) or less.

The present invention also provides a pre-groove and a half-value width in the range of 0.2 to 1.4 μm and a depth of the pre-groove in the range of 60 to 300 nm, λ / 16 (where,
(λ is the wavelength of the laser beam for reproduction) is prepared by dissolving a dye in a solvent in the region including the pregroove and the portion where the prepit is formed on the disk-shaped substrate on which the prepit having a depth deeper than the depth is formed. Dye solution, wherein the ratio of the deposition of the dye suspension solution to the original volume of the dye solution when the precipitation of the dye starts by evaporating the solvent from the dye solution at the application temperature of the dye solution A dye solution whose concentration limit is defined as 99 to 20% is applied by a spin coating method and dried to obtain an optical film thickness of the light absorbing layer in the pre-pit portion and a light absorbing layer in a portion between the pre-pits. The difference from the optical film thickness is not more than λ / 8 (where λ is the wavelength of the reproducing laser beam), and the optical film thickness of the light absorbing layer at the bottom of the pre-groove and the light absorption of the land between the pre-grooves. Difference from optical thickness with layer forming a light absorbing layer having a wavelength equal to or smaller than λ / 8 (where λ is the wavelength of a reproducing laser beam) and then providing a reflective layer made of metal on the light absorbing layer. There is also.

Preferred embodiments of the information recording medium of the present invention are as follows.

1) The difference between the optical thickness of the light absorbing layer at the bottom of the groove and the optical thickness of the light absorbing layer at the land is not more than λ / 16 (where λ is the wavelength of the reproducing laser beam). The above information recording medium characterized by the above-mentioned.

2) The difference between the optical thickness of the light absorbing layer in the pit portion and the optical thickness of the light absorbing layer in the portion between the pits is λ / 16 (where λ is the wavelength of the reproducing laser beam) or less. The above information recording medium characterized by the above-mentioned.

3) The information recording medium, wherein the film thickness of the land portion and the pit portion of the light absorbing layer is 40 to 400 nm.

4) The pregroove has a half width of 0.2 to 1.4 μm,
The above-mentioned information recording medium having a depth of 70 nm.

5) The information recording medium as described above, wherein the ratio of the reflectance of the groove bottom to the reflectance of the mirror portion (the area between the two pre-pits where no signal is recorded) is 70% or more.

6) The information recording medium, wherein a protective layer is further formed on the reflective layer.

Preferred embodiments of the method for manufacturing an information recording medium according to the above basic invention are as follows.

1) The difference between the optical thickness of the light absorbing layer at the bottom of the groove and the optical thickness of the light absorbing layer at the land is not more than λ / 16 (where λ is the wavelength of the reproducing laser beam). A method for manufacturing the above information recording medium.

2) The difference between the optical thickness of the light absorbing layer in the pit portion and the optical thickness of the light absorbing layer in the portion between the pits is λ / 16 (where λ is the wavelength of the reproducing laser beam) or less. A method for manufacturing the information recording medium according to the above.

3) The method for manufacturing an information recording medium, wherein the thickness of the land portion and the portion between the pits of the light absorbing layer is 40 to 400 nm.

4) The pregroove has a half width of 0.2 to 1.4 μm,
The method for producing the information recording medium, wherein the method has a depth of 70 nm.

5) The method for producing an information recording medium, wherein the concentration limit of the dye solution is 90 to 50%.

6) The method for producing an information recording medium, wherein the solvent is a single solvent.

7) The solvent is a good solvent for the dye used (preferably,
A solvent capable of dissolving 2% by weight or more of the dye used at the coating temperature of the dye solution) and a poor solvent of the dye used (which is preferably compatible with the good solvent). (A solvent that does not dissolve in an amount of at least 1% by weight).

8) The concentration of the dye in the dye solution is 0.5 to 15% by weight.
The method for manufacturing an information recording medium according to claim 1, wherein

9) The above dye solution is heated at a temperature of 0 to 100 ° C. to 300 to 10,000
The method for producing the information recording medium, wherein the substrate is dried at a rotation speed of the substrate at rpm.

10) The method of manufacturing an information recording medium, wherein the information recording medium has a ratio of the reflectance of the groove bottom portion to the reflectance of the mirror portion of 70% or more.

11) The method for manufacturing an information recording medium, further comprising forming a protective layer on the reflective layer.

[Effect of the Invention] In the information recording medium of the present invention, the optical thickness of the light-absorbing layer containing the dye has a small difference between the bottom of the groove and the land, so that even if the depth of the pre-groove is reduced, the light is absorbed. The depth of the groove on the surface of the layer is sufficiently large, and after recording the information by irradiating a laser beam, it is possible to obtain a reproduced signal that has a high modulation factor and reflectivity and satisfies the CD standard, and has good tracking characteristics. It is a remarkably excellent information recording medium.

Further, in the information recording medium of the present invention, a light absorbing layer containing a dye is also formed in a region where a prepit is formed, and a reproduction signal satisfying the CD standard can be obtained from the region where the prepit is formed. Therefore, the thickness of the light absorbing layer can be made uniform over the entire surface of the information recording medium,
The ROM area in which the pre-pits are formed and the recordable area in which the pre-groove is formed can be provided at an arbitrary location, for example, by mixing both areas. It is a remarkably excellent information recording medium that can be used for a wide range of applications.

Further, the method for producing an information recording medium of the present invention employs a conventionally employed means except that a coating solution for forming a light absorbing layer having specific properties prepared by controlling the type of solvent and the concentration of dye is used. This is a method for manufacturing an information recording medium having a remarkably excellent effect that an information recording medium having the above-described excellent characteristics can be easily manufactured by using the same.

[Detailed Description of the Invention] The information recording medium of the present invention has a basic configuration in which a light absorbing layer containing a dye and a reflective layer made of a metal are provided in this order on a substrate having prepits and pregrooves.

The material of the disk-shaped substrate in the present invention can be arbitrarily selected from various materials used as a substrate of a conventional information recording medium. In view of the optical characteristics, flatness, workability, handleability, stability over time, and manufacturing cost of the substrate, examples of the substrate material include acrylic resins such as glass and polymethyl methacrylate; polyvinyl chloride and vinyl chloride. Examples include vinyl chloride resins such as polymers; epoxy resins; polycarbonate resins; amorphous polyolefins and polyesters. Preferably, polycarbonate, polyolefin, glass and polymethyl methacrylate can be mentioned.

On the surface of the substrate on which the light absorbing layer is provided, an undercoat layer may be provided for the purpose of improving flatness, improving adhesion, improving solvent resistance of the substrate, and preventing deterioration of the recording layer. . Examples of the material of 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 / vinyl. Toluene copolymer, chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester, polyimide, vinyl acetate / vinyl chloride copolymer, ethylene / vinyl acetate copolymer, polyethylene, polypropylene, polycarbonate, epoxy resin Organic substances such as silane coupling agents and titanate coupling agents; and inorganic dielectrics (SiO ₂ , ZnS, AlN, Si ₃ N)
₄ ) and inorganic fluorides (MgF ₂ ).

Undercoat layer, for example, by dissolving or dispersing the above substance in a suitable solvent to prepare a coating solution, spin coating, dip coating, by coating the substrate surface by a coating method such as extrusion coating Can be formed. The thickness of the undercoat layer is generally in the range of 0.005 to 20 μm, preferably in the range of 0.01 to 10 μm.

In the present invention, a pre-groove (tracking groove) is formed on the surface of the substrate (or the surface of the undercoat layer) in order to perform good tracking during recording or reproduction. The shape of the pre-groove, the depth of the groove half-value width of located and grooves in a range of 5 to 70 nm (d ₁ of the first accompanying figures) (width of the groove in the half of the depth of the depth of the groove) Is preferably 0.2 to 1.4 μm), more preferably a groove having a depth of 15 to 60 nm and a half width of the groove of 0.3 to 0.7 μm, and a groove having a groove depth of 20 to 50 nm. Range and the half width of the groove is
Most preferably 0.35 to 0.6 μm. Grooves may be wobbled for addressing or linear velocity control.

In the present invention, further, pre-pits (ROM areas) in which information such as various application software and address signals are recorded in advance on the substrate surface (or undercoat layer surface).
Are formed. The shape of the pre-pit, the depth of the pit (the width of the pits in half the depth of the depth of the pits) (Figure 2 d ₂ of the appended) is in the range of 60~300nm and half-value width of the pits It is preferable that the pit depth is in the range of 70 to 250 nm and the half width of the pit is 0.3 to 1.0 μm, and the pit depth is in the range of 90 to 200 nm. And the pit half width is 0.4 ~
Most preferably, it is 0.7 μm.

Further, the depth of the pre-groove is preferably shorter than the depth of the pre-pit by λ / 16 (where λ is the wavelength of the reproducing laser beam and is the same in the following description) and is shorter than the depth of the pre-pit. , Λ / 14 or shorter, more preferably λ / 12 or shorter. The reason is,
This is because if the depth of the pre-groove is made to be as large as the depth of the pre-pit at which the degree of modulation is sufficiently large, the reflectance of the pre-groove becomes too low.

When the substrate material is plastic, the pregrooves and prepits may be directly provided on the substrate surface by injection molding or extrusion molding. Also, on the surface of the substrate,
A pre-groove layer for forming the pre-groove and the pre-pit may be provided.

As a material for the pregroove layer, a mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester and tetraester and a photopolymerization initiator can be used.

The pre-groove layer is formed by first applying a mixed solution comprising the above-mentioned acrylate and a polymerization initiator onto a precisely formed master (stamper), and then placing a substrate on the coating solution layer. The liquid layer is cured by irradiating ultraviolet rays through the substrate or the matrix to fix the substrate and the liquid phase. Next, the substrate provided with the pre-groove layer is obtained by peeling the substrate from the matrix. The thickness of the pre-groove layer is generally in the range of 0.1 to 100 μm, preferably
It is in the range of 0.1 to 50 μm.

On the substrate (or pre-groove layer) on which pre-grooves and pre-pits have been formed, a material similar to the material for forming the undercoat layer is used to protect from a solvent in a coating solution for forming a light absorbing layer. May be provided with a solvent resistant layer.

A light-absorbing layer containing a dye is provided on the substrate (or the undercoat layer). By irradiating laser light from the substrate side to form pits for reproduction in the light absorbing layer, information is recorded on the light absorbing layer. Therefore, the light absorbing layer in the region of the substrate where the pre-groove is formed functions as a recording layer.

The dye used in the present invention is not particularly limited, and any dye may be used. For example, cyanine dyes, phthalocyanine dyes, naphthalocyanine dyes,
Pyrylium dyes, thiopyrylium dyes, azulenium dyes, squarylium dyes, metal complex salt dyes such as Ni and Cr, naphthoquinone dyes, anthraquinone dyes, indophenol dyes, indoaniline dyes,
Triphenylmethane dye, triallylmethane dye,
Examples of the dye include an aminium dye, a diimmonium dye, a nitroso dye, a leuco dye, a croconium dye, and the like.

These dyes are not limited to the light once (WO) type,
It may be of a rewritable (RW) type (or reversible type).

Among these dyes, dyes having a high absorptivity to light in the near-infrared region of 700 to 900 nm are preferable in view of the practical use of semiconductor lasers that emit near-infrared light as recording / reproducing lasers.

In particular, cyanine dyes, azulenium dyes, and squarylium dyes are preferable, and among the cyanine dyes, naphthoindolenine dyes and imidazoquinoxaline dyes are preferable.

These dyes may be used alone or as a mixture of two or more. When a cyanine dye is used, the metal complex salt dye, the aminium dye, or the diimmonium dye is preferably used together as a quencher. In this case, it is preferable that a metal complex salt dye or the like is contained as a quencher at a ratio of 0.001 to 0.3 mol based on 1 mol of all dyes.

In the information recording medium of the present invention, the difference between the optical thickness of the groove bottom portion of the light absorbing layer and the optical thickness of the land portion,
λ / 8 or less. Further, the information recording medium of the present invention further has pre-pits on the substrate, and the difference between the optical film thickness of the pit portion of the light absorbing layer and the optical film thickness of the inter-pit portion is λ / 8 or less. There is a feature.

The optical thickness of the light absorbing layer in the information recording medium of the present invention will be described in detail with reference to the attached drawings.

FIG. 1 is a cross-sectional view schematically showing a part of a cross-section in a pre-groove region of an embodiment of the information recording medium of the present invention. FIG. 2 is a cross-sectional view schematically showing a part of a cross-section in a pre-pit region of one embodiment of the information recording medium of the present invention. FIG. 3 shows a conventional information recording medium.
FIG. 4 is a cross-sectional view schematically illustrating a part of a cross-section in a pre-groove region.

In FIG. 3, a light absorbing layer 32 made of a dye is formed on the surface of a substrate 31 made of plastic, and a reflective layer 33 made of a metal is formed on the light absorbing layer 32. A pregroove 34 is formed on the substrate 31. The light absorbing layer 32 is formed by applying a solution for forming a light absorbing layer prepared by dissolving a dye in the solvent by spin coating and drying. The thickness t ₆ of the light absorbing layer 32 at the groove bottom 36 of the pre-groove 34 is the same as the light absorbing layer 32 at the land 35 of the substrate 31.
It is larger than the 32 thickness t ₅ of. As a result, the depth of the groove shape at the contact surface between the reflective layer 33 of the light absorption layer 32 is smaller than the depth d ₃ of the pregroove 34, pregrooves 34 by irradiating a laser beam to record information When a recording bit is formed in the light absorption layer 32, the phase difference between the upper part of the groove of the light absorbing layer 32 (the part corresponding to the land part of the substrate) and the bottom part becomes smaller, so that the modulation degree of the recording pit becomes smaller. Was. To solve this problem, the depth of the groove is increased. However, if the depth of the groove is too large, there arises a problem that the reflectivity of the groove portion decreases.

In FIG. 1, a light absorbing layer 12 made of a dye is formed on the surface of a substrate 11 made of plastic, and a reflective layer 13 made of a metal is formed on the light absorbing layer 12. On the substrate 11, a pre-groove 14 is formed. The light absorbing layer 12 is formed by applying a solution for forming a light absorbing layer having specific properties as described above prepared by dissolving a dye in a solvent by spin coating and drying. The optical film thickness (n _r · t ₂ ) of the light absorbing layer 12 at the groove bottom 16 of the pre-groove 14 (where n _r is the refractive index of the light absorbing layer, and t ₂ is the light absorbing layer 12 at the groove bottom 16). And the substrate 11
( _Nr · t ₁ ) (where n _r is the refractive index of the light absorbing layer, and t ₁ is the film thickness of the light absorbing layer 12 of the land 15) Is formed so as to be λ / 8 or less. As a result, the depth of the groove shape at the contact surface between the reflective layer 13 of the light absorbing layer 12 has become smaller as lambda / 8 or less in the same or optical thickness and depth d ₁ of the groove 14, the light absorption The phase difference between the groove bottom and the land of the layer 12 is large, and the modulation degree of the recording pit is large. And n _r
By setting the difference between t ₁ and n _r · t ₂ as described above, the depth d ₁ of the groove 14 can be reduced, and the reflectivity of the groove portion increases.

The difference between the above n _{rt 1} and n _{rt 2} is preferably λ / 11 or less, more preferably λ / 13 or less,
It is even more preferable that it is λ / 16 or less.

The ratio of the reflectance of the groove bottom to the reflectance of the mirror portion is preferably 70% or more, particularly 80% or more, and more preferably 90% or more. In order to increase the ratio of the reflectance of the groove bottom to the reflectance of the mirror, the difference between the optical path length of the groove and the optical path of the land may be reduced.

In FIG. 2, a light absorbing layer 22 made of a dye is formed on the surface of a substrate 21 made of plastic, and a reflective layer 23 made of a metal is formed on the light absorbing layer 22. The substrate 21 has pre-pits 24 formed thereon. The light absorbing layer 22 is formed by applying a solution for forming a light absorbing layer having a specific property as described above prepared by dissolving a dye in a solvent by spin coating and drying. The optical film thickness of the light absorbing layer 22 in the pit portion 26 of the prepit 24 (n _r
t ₄ ) (where n _r is the refractive index of the light absorbing layer, and t ₄ is the thickness of the light absorbing layer 22 in the pit portion 26) and the light absorbing layer 22 in the inter-pit portion 25 of the substrate 21. Optical film thickness ( _nr · t ₃ ) (where n _r is the refractive index of the light absorbing layer, and t ₃ is the light absorbing layer in the pit portion 25)
22 is formed so as to be λ / 8 or less. As a result, the depth of the hole shape at the contact surface of the light absorbing layer 22 with the reflecting layer 23 is the same as the depth d ₂ of the pit 24 or is smaller than the optical thickness by about λ / 8 or less. The phase difference between the pit portion and the inter-pit portion of the layer 22 is large, and the modulation degree of the pit is large. As a result, even if the light absorption layer is formed in the pre-pit formation region of the substrate, the pits on the substrate can be reproduced with a high degree of modulation.

The difference between the above n _{rt 3} and n _{rt 4} is preferably λ / 11 or less, more preferably λ / 13 or less,
It is even more preferable that it is λ / 16 or less.

The information recording medium of the present invention is one in which a reflective layer is further formed on the light absorbing layer, but the function and effect of the light absorbing layer having the optical film thickness in the specified relationship as described above are as follows. The same applies to an information recording medium on which a reflective layer is not formed.

When both the pre-groove and the pre-pit are formed on the substrate, the depth d _{1 of the} groove is longer than the depth d ₂ of the pit portion, and the optical path length (n · d: n is the refractive index of the substrate, d Is a depth dimension), and is preferably smaller than λ / 16 or more, particularly λ / 14 or more, and more preferably λ / 12 or more.

The light absorbing layer, the land portion and the film thickness of the inter-pit portion, 40 ~ 400nm, particularly 60 ~ 300nm, more particularly 80 ~ 250n
m is preferred.

The light absorbing layer having a specific optical thickness in the information recording medium of the present invention, that is, the difference between the optical thickness of the light absorbing layer at the bottom of the groove and the optical thickness of the light absorbing layer at the land is λ /. 8 or less, the difference between the optical film thickness of the light absorbing layer in the pit portion and the optical film thickness of the light absorbing layer between the pits is λ / 8 or less, the light absorbing layer of the present invention Can be formed.

In the production method of the present invention, the light absorbing layer is formed by dissolving the above-described dye in a solvent to prepare a dye solution, and then applying the dye solution to the surface of the substrate by spin coating to form a coating film. And then drying.

The dye solution used in the production method of the present invention has a specific property, that is, the concentration limit is 99 to 20.
% Dye solution. As used herein, the term "concentration limit" refers to the volume of the dye suspension solution at the time the dye precipitation begins by evaporating the solvent from the dye solution at the application temperature of the dye solution, It is defined as meaning the ratio to the original volume. For example, when the solvent was evaporated while the dye solution in which the dye was dissolved in the solvent was maintained at the application temperature for forming the light absorbing layer, the volume was reduced with the evaporation of the solvent, and the solvent was dissolved in time. The dye precipitates, but the volume of the dye solution (strictly speaking, a dye suspension solution) when the dye precipitation starts,
A dye solution that is 90% of the volume of the original dye solution is called a dye solution having a concentration limit of 90%.

Therefore, the concentration limit of the dye solution (hereinafter sometimes referred to as the limit concentration) is determined by the combination of the dye and the solvent (single solvent or mixed solvent) and the type of the solvent when a combination of two or more solvents is used. It varies depending on the ratio, the concentration of the dye in the dye solution, the coating temperature, and the like. For this reason, a dye solution having a specific concentration limit cannot be uniformly determined for a specific dye.However, a person skilled in the art can prepare a dye solution having a desired concentration limit by changing the above conditions variously. It is easy to do.

The dye solution used in the production method of the present invention is a dye solution having a concentration limit of 99 to 20%.
It is preferred that the dye solution be 〜30%, especially 95-40%, more particularly 90-50%. If the concentration limit of the dye solution is larger than the above range, the thickness of the light absorbing layer becomes non-uniform as a whole, and if the concentration limit is smaller than the above range, the optical thickness of the light absorbing layer between the groove bottom and the land portion. And the difference in the optical film thickness of the light absorbing layer between the pit portion and the inter-pit portion becomes large.

The solvent used for preparing the dye solution may be a single solvent or a mixed solvent of two or more solvents as long as the solvent satisfies the concentration limit of the dye solution. When the solvent is a mixed solvent, a good solvent for the dye to be used (preferably, a solvent capable of dissolving the dye to be used at 2% by weight or more at the coating temperature of the dye solution) and a poor solvent for the dye to be used (preferably, It is preferably a mixture with a solvent which does not dissolve 2% by weight or more of the dye used at the coating temperature of the dye solution. At this time, the good solvent and the poor solvent are compatible, and it is necessary that the evaporation rate of the poor solvent is not higher than the evaporation rate of the good solvent at the application temperature. Generally, as the mixing ratio of the poor solvent increases, the concentration limit increases.

Examples of the solvent include aromatic hydrocarbon solvents such as benzene, toluene, xylene, and ethylbenzene; aliphatic hydrocarbon solvents such as hexane, octane, nonane, and cyclohexane; and organic acid solvents such as acetic acid. Ester solvents such as ethyl acetate, butyl acetate, amyl acetate, ethylene glycol monoethyl ether acetate, cellosolve acetate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone;
Halogenated hydrocarbon solvents such as 1,2-dichloroethane, chloroform, methylchloroform, trichlene, carbon tetrachloride, tetrachloroethylene; ether solvents such as tetrahydrofuran, ethyl ether, isopropyl ether, dioxane, diglyme; ethanol; n-propanol, isopropanol, n-
Alcohol solvents such as butanol, amyl alcohol, diacetone alcohol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and benzyl alcohol; amide solvents such as dimethylformamide; 2,2,3,3 Fluorinated alcohols such as tetrafluoropropanol, fluorinated ketones, fluorinated esters, fluorinated amides, fluorinated ethers,
Fluorinated solvents such as fluorine-substituted aromatic hydrocarbons and fluorine-substituted aliphatic hydrocarbons can be mentioned.
In the production method of the present invention, the dye solution is not particularly limited as long as it satisfies the concentration limit, but for convenience of handling and spin coating, a substrate-like overall uniform film thickness. In order to form a light absorbing layer, the concentration of the dye in the dye solution is preferably 0.5 to 15% by weight, more preferably 1 to 10% by weight, and particularly preferably 1.5 to 8% by weight.

The dye solution further contains an antioxidant, a UV absorber,
Various additives such as a plasticizer and a lubricant may be added according to the purpose.

When a binder is used, examples of the binder include cellulose derivatives such as gelatin, nitrocellulose, and cellulose acetate; natural organic polymer substances such as dextran, rosin, and rubber; and carbonized materials such as polyethylene, polypropylene, polystyrene, and polyisobutylene. Hydrogen resins, polyvinyl chloride, polyvinylidene chloride, vinyl resins such as polyvinyl chloride / polyvinyl acetate copolymer, acrylic resins such as polymethyl acrylate and polymethyl methacrylate,
Synthetic organic polymer substances such as polyvinyl alcohol, chlorinated polyolefin, epoxy resin, butyral resin, rubber derivatives, and initial condensates of thermosetting resins such as phenol / formaldehyde resins can be given.

When applying the above-mentioned dye solution on a substrate by a spin coating method, it can be performed using a device and a method known per se. The above dye solution is generally used in an amount of 0 to 100.
C., preferably 5 to 80.degree. C., more preferably 10 to 60.degree. The number of rotations of the substrate is generally 10 to 1000 rpm when the dye solution is applied, preferably 100 to 500 rpm.When the dye coating is dried, it is generally 300 to 10000 rpm, particularly 500-7000r.pm, especially 7
It is preferably set to 00 to 4000 rpm.

A reflective layer is further provided on the light absorbing layer of the information recording medium of the present invention.

As the material of the reflection layer, Be, B, C, Sc, Rb, Sr, A
s, Os, Tl, At, Fr, Ra, Mg, Se, Y, Ti, Zr, Hf,
V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Co, Ni, Ru, R
h, Pd, Ir, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, S
Metals and metalloids such as i, Ge, Te, Pb, Po, Sn, Bi, and Sb can be mentioned. Among them, C, Au, Zn, C
u, Pt, Al, Ni, In and stainless steel are particularly preferred.
These substances may be used alone, or in combination of two or more kinds or as an alloy.

The reflection layer can be formed on the recording layer by, for example, vapor deposition, sputtering, or ion plating of the above-mentioned light reflective substance. In particular, it is preferable to form the reflective layer by sputtering. The thickness of the reflective layer is generally in the range from 100 to 3000, preferably from 400 to 2000.

When a noble metal reflective layer is provided as a reflective layer,
A metal adhesion layer such as Al or an organic adhesion layer can be provided.

A protective layer may be provided on the reflective layer for the purpose of physically and chemically protecting the entire information recording medium, particularly the light absorbing layer and the reflective layer. Further, this protective layer may be provided on the side of the substrate where the light absorbing layer is not provided in order to enhance the scratch resistance and moisture resistance.

Examples of the material used for the protective layer include inorganic substances such as SiO, SiO ₂ , Si ₃ N ₄ , MgF ₂ , and SnO ₂ . Further, examples of the organic substance include a thermoplastic resin, a thermosetting resin, a UV-curable resin, and the like, and a UV-curable resin is preferable.

The protective layer can be formed by, for example, dissolving a thermoplastic resin, a thermosetting resin, or the like in an appropriate solvent to prepare a coating solution, applying the coating solution, and drying. In the case of a UV-curable resin, a protective layer can be formed by preparing a coating solution as it is or by dissolving it in an appropriate solvent, applying the coating solution, and irradiating with UV light to cure. UV curable resins include oligomers of (meth) acrylates such as urethane (meth) acrylate, epoxy (meth) acrylate and polyester (meth) acrylate, monomers such as (meth) acrylate, and photopolymerization initiator Ordinary UV-curable resins such as can be used. Various additives such as an antistatic agent, an antioxidant and a UV adsorbent may be added to these coating solutions according to the purpose. It is preferable to use a UV curable resin as a material for the protective layer.

The thickness of the protective layer is generally 0.1 to 100 μm, preferably 0.1 to 100 μm.
It is in the range of 5-20 μm.

In addition to the above, the protective layer can be formed by, for example, laminating a film obtained by extrusion of a plastic on the reflective layer via an adhesive layer. Alternatively, it may be provided by a method such as vacuum deposition, sputtering, or coating.

The information is recorded on the information recording medium of the present invention from the substrate side while rotating the information recording medium at a constant linear speed (preferably 1.2 to 2.8 m / sec, particularly preferably 1.2 to 1.4 m / sec). This is performed by irradiating a laser beam to the bottom of the pre-groove to form a pit for reproduction in a light absorbing layer on the groove and recording a signal. EF in CD format as signal
Recording the M signal is preferable for obtaining the effects of the present invention. Generally, a semiconductor laser beam having an oscillation wavelength in the range of 750 to 850 nm is used as the recording light. The information recording medium of the present invention can record with a laser power of 10 mW or less.

The above-mentioned pits after recording are such that the substrate and / or the dye generate heat by irradiation with a laser beam, and melt, evaporate, sublime, deform or change in quality.
This is a form in which a change such as a concave shape occurs, a change occurs in a dye, or a change occurs between a dye and a metal reflective layer.

By the above recording method, by recording a CD format signal and the like at a constant linear speed on the information recording medium of the present invention,
It is possible to obtain excellent recording / reproducing characteristics such as a signal modulation degree and a reproducing C / N. Further, the tracking property at the time of recording, particularly the tracking property by the push-pull method is excellent. Also, since the optical disc of the present invention has a high reflectance,
The recorded CD format signal can be reproduced using a commercially available CD player. In the case of the information recording medium of the present invention further provided with a ROM area, the ROM area also has C
A reproduced signal having a high modulation degree satisfying the D standard can be obtained.

Hereinafter, Examples and Comparative Examples of the present invention will be described. However, these examples do not limit the present invention.

Example 1 (Reference Example) A disc-shaped polycarbonate substrate provided with a pregroove on almost the entire surface (outer diameter: 120 mm, inner diameter: 15 mm, thickness: 1.2 m)
m, track pitch: 1.6 μm, half width of groove: 0.55 μ
m, groove depth: 50 nm).

On the other hand, the following structural formula: Was dissolved in propylene glycol monoethyl ether to prepare a dye solution containing 2.4% by weight of the dye (A). The concentration limit of this dye solution at 23 ° C. was 70%.

The dye solution was maintained at 23 ° C., and the dye solution was spin-coated on the substrate at 23 ° C. by 200 rpm.
After coating at a speed of m. for 4 seconds, it was dried at a rotational speed of 700 rpm for 30 seconds to form a light absorbing layer.

Under the conditions of 480 W, target-substrate distance 95 mm, gas pressure 2 Pa, and rate 2 nm / sec, Au
By C sputtering, a reflective layer made of Au having a thickness of 100 nm was formed.

A UV curable resin (trade name: 3070, manufactured by Three Bond Co.) is applied as a protective layer on the reflective layer by a spin coating method at a rotation speed of 1500 rpm, and then cured by irradiating ultraviolet rays with a high-pressure mercury lamp. Thus, a protective layer having a thickness of 2 μm was formed.

Thus, an information recording medium including the substrate, the dye recording layer, the reflective layer, and the protective layer was manufactured.

For the obtained information recording medium, the optical thickness of the light absorbing layer at the bottom of the groove, the optical thickness of the light absorbing layer at the land,
Mirror reflectance, groove reflectance, groove reflectance after recording, and tracking servo gain were measured by the following evaluation methods. The evaluation results are shown in Table 1.

Example 2 (Reference Example) Example 1 was the same as Example 1, except that the half width of the pre-groove was 0.45 μm and the depth of the groove was 30 nm.
An information recording medium was manufactured by using the same substrate as in Example 1 and sequentially forming a light absorbing layer, a reflective layer and a protective layer on the substrate in the same manner as in Example 1.

The obtained information recording medium was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Comparative Example 1 The same substrate as that used in Example 1 was used, and 2,2,3,3-tetrafluoropropanol was used instead of propylene glycol monoethyl ether as a solvent for preparing a dye solution. A light-absorbing layer was prepared in the same manner as in Example 1 except that a dye solution containing 2.3% by weight of the dye (A) was used (the concentration limit of this dye solution at 23 ° C. was less than 20%). Was formed, and then a reflective layer and a protective layer were sequentially formed on the substrate in the same manner as in Example 1 to manufacture an information recording medium.

The obtained information recording medium was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

Example 3 Prepits (half-width of pit: 0.6 μm, pit depth: 130 nm) in which an EFM signal was recorded were formed in an area having a diameter of 46 mm to 80 mm, and a pregroove (track pitch) was formed in an area having a diameter of 80 mm to 118 mm. : 1.6 μm, groove half width: 0.55 μm,
Disc-shaped polycarbonate substrate (groove depth: 50 nm) formed (outer diameter: 120 mm, inner diameter: 15 mm, thickness: 1.2 mm)
Was prepared.

Using the above substrate, a light absorbing layer, a reflective layer, and a protective layer were sequentially formed on the substrate in the same manner as in Example 1 to manufacture an information recording medium.

In the obtained information recording medium, in the pre-pit formation region, the optical thickness of the light absorbing layer in the pit portion, the optical thickness of the light absorbing layer in the portion between the pits, and the 11T modulation were measured by the following evaluation methods. In the pre-groove formation region, the first embodiment
Each item was evaluated in the same manner as in the above. The evaluation results are shown in Table 1.

Example 4 Using the same substrate as that used in Example 3, the following structural formula was used as a dye solution: Of 2,2,3,3-tetrafluoropropanol and propylene glycol monoethyl ether
A dye solution containing 2.3% by weight of the dye (B) prepared by dissolving in a mixed solvent having a volume ratio of 92: 8 (2 of this dye solution)
A light absorbing layer was formed in the same manner as in Example 3 except that the concentration limit at 3 ° C. was 90%). Then, the reflective layer and the protective layer were formed on the substrate in the same manner as in Example 3. To form an information recording medium.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

[Example 5] Using the same substrate as that used in Example 3, the dye (B) was used as a dye solution, and the volume ratio of 2,2,3,3-tetrafluoropropanol and butanol was 70:30. As in Example 3, except that a dye solution containing 2.3% by weight of the dye (B) prepared by dissolving in a mixed solvent of (a) was used (the concentration limit of this dye solution at 23 ° C. was 90%). Then, a light absorbing layer was formed, and then a reflective layer and a protective layer were sequentially formed on a substrate in the same manner as in Example 3 to manufacture an information recording medium.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Example 6 A light absorbing layer, a reflective layer and a protective layer were implemented using the same substrate as that used in Example 3 except that the pit half width of the prepit was 0.5 μm and the pit depth was 120 nm. An information recording medium was manufactured by sequentially forming on the substrate in the same manner as in Example 3.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

[Example 7] A light absorbing layer, a reflective layer and a protective layer were implemented using the same substrate as that used in Example 3 except that the pit half width of the prepit was 0.5 µm and the pit depth was 90 nm. An information recording medium was manufactured by sequentially forming on the substrate in the same manner as in Example 3.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Example 8 The same substrate as that used in Example 3 was used, and the dye (B) was used as a dye solution in a volume ratio of 90:10 of 2,2,3,3-tetrafluoropropanol and isopropyl ether. 2.3% by weight of dye (B) prepared by dissolving in a mixed solvent
A light-absorbing layer was formed in the same manner as in Example 3 except that the contained dye solution (the concentration limit of this dye solution at 23 ° C. was 80%), and then a reflective layer and a protective layer were formed. An information recording medium was manufactured by sequentially forming on the substrate in the same manner as in Example 3.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Example 9 The same substrate as that used in Example 3 was used, and the dye (B) was used as a dye solution, and a volume of 70:30 of 2,2,3,3-tetrafluoropropanol and diisopropyl ketone was used. 2.3% by weight of dye (B) prepared by dissolving in a mixed solvent
A light-absorbing layer was formed in the same manner as in Example 3 except that the contained dye solution (the concentration limit of this dye solution at 23 ° C. was 65%), and then a reflective layer and a protective layer were formed. An information recording medium was manufactured by sequentially forming on the substrate in the same manner as in Example 3.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

[Example 10] Using the same substrate as that used in Example 3, the dye (B) was used as a dye solution, and the volume ratio of 2,2,3,3-tetrafluoropropanol and acetic acid was 90:10. The same as in Example 3 except that a dye solution containing 2.3% by weight of the dye (B) prepared by dissolving in a mixed solvent of (a concentration limit at 23 ° C. of the dye solution was 60%) was used. Then, a light absorbing layer was formed, and then a reflective layer and a protective layer were sequentially formed on a substrate in the same manner as in Example 3 to manufacture an information recording medium.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

[Example 11] Using the same substrate as that used in Example 3, the dye (B) was used as a dye solution in a volume ratio of 90:10 of 2,2,3,3-tetrafluoropropanol and ethyl cellosolve. A dye solution containing 2.3% by weight of the dye (B) prepared by dissolving the dye solution in a mixed solvent at a specific ratio (the concentration limit of this dye solution at 23 ° C. is
The light absorbing layer was formed in the same manner as in Example 3 except that the light-absorbing layer was used, and the reflective layer and the protective layer were sequentially formed on the substrate in the same manner as in Example 3 to obtain information. A recording medium was manufactured.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Example 12 Using the same substrate as that used in Example 3, the dye (B) was used as a dye solution, and the volume ratio of 2,2,3,3-tetrafluoropropanol to butyl cellosolve was 90:10. A dye solution containing 2.3% by weight of dye (B) prepared by dissolving in a mixed solvent of (a concentration limit of this dye solution at 23 ° C.
The light absorbing layer was formed in the same manner as in Example 3 except that the light-absorbing layer was used, and the reflective layer and the protective layer were sequentially formed on the substrate in the same manner as in Example 3 to obtain information. A recording medium was manufactured.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Example 13 Using the same substrate as that used in Example 3, the dye (B) was used as a dye solution, and a volume of 70:30 of 2,2,3,3-tetrafluoropropanol and isoamyl alcohol was used. 2.3% by weight of dye (B) prepared by dissolving in a mixed solvent
A light-absorbing layer was formed in the same manner as in Example 3 except that the dye solution contained (the concentration limit of this dye solution at 23 ° C. was 55%), and then a reflective layer and a protective layer were formed. An information recording medium was manufactured by sequentially forming on the substrate in the same manner as in Example 3.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

[Example 14] Dye (B) was converted to the following structural formula: An information recording medium was manufactured in the same manner as in Example 4 except that the dye (C) having the following formula was used (the concentration limit of the dye solution at 23 ° C. was 90%).

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Comparative Example 2 The same substrate as that used in Example 3 was used, except that the dye solution was changed to the dye solution used in Comparative Example 1.
Then, a light absorbing layer was formed in the same manner as in Example 1, and then a reflective layer and a protective layer were sequentially formed on the substrate in the same manner as in Example 3 to manufacture an information recording medium.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Comparative Example 3 Using the same base as the substrate used in Example 3, dye (B) was prepared by dissolving dye (B) in 2,2,3,3-tetrafluoropropanol as a dye solution. 2.3% by weight dye solution (the concentration limit of this dye solution at 23 ° C is
(Less than 20%) was used to form a light absorbing layer as in Example 3, and then a reflective layer and a protective layer were sequentially formed on the substrate as in Example 3. An information recording medium was manufactured.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

Comparative Example 4 Using the same substrate as that used in Example 3, the dye (B) was used as a dye solution, and the volume ratio of 2,2,3,3-tetrafluoropropanol and ethanol was 70:30. Example 3 except that a dye solution containing 2.3% by weight of the dye (B) prepared by dissolving in a mixed solvent of (a concentration limit at 23 ° C. of the dye solution was less than 20%) was used. A light absorbing layer was formed in the same manner, and then a reflective layer and a protective layer were sequentially formed on a substrate in the same manner as in Example 3 to manufacture an information recording medium.

The obtained information recording medium was evaluated in the same manner as in Example 3. The evaluation results are shown in Table 1.

[Evaluation of Information Recording Medium] The information recording medium obtained above was used as a disk evaluation device (NA: 0.5, laser wavelength: 780 nm) and EFM encoder (K
Using EN-WOOD), recording was performed on the bottom of the pre-groove at a laser power (recording power) of 6 mW and a constant linear speed of 1.3 m / sec.

1) Optical film thickness of the light absorbing layer at the bottom of the groove The absolute film thickness of the light absorbing layer was measured by observing the cross section with an ultra-high resolution electron microscope (S900, manufactured by Hitachi, Ltd.)
The refractive index of the light absorbing layer, the reflectance of the separately formed dye thin film,
The transmittance and the absolute film thickness were obtained from the measured results, and the optical film thickness was calculated from the absolute film thickness and the refractive index.

2) Optical film thickness of light absorbing layer in land portion It was determined in the same manner as in the above method 1).

3) Mirror reflectance The reflectance was measured using a spectrophotometer (UV130 manufactured by Shimadzu Corporation) with an Al plate having a known reflectance as a reference.

4) Groove reflectivity The reflectivity of the mirror portion was measured using a disk evaluation device as a reference.

5) Groove reflectivity after recording It was determined in the same manner as in the above method 4).

6) Tracking servo gain Disturbance was given by an oscillator, measured by a servo analyzer, and represented by a gain compared to CD.

7) Optical film thickness of light absorbing layer in pit portion It was obtained in the same manner as in the above method 1).

8) Optical film thickness of light absorption layer between pits It was determined in the same manner as in the above method 1).

9) 11T modulation degree CD format signal (EF
The signal strength of the signal portion (pre-pit portion) and the mirror portion (the portion where no signal is recorded between the pre-pits) is measured for the DC reproduction signal having a recording length of 11T in the M signal), and the modulation degree (C) is calculated by the following equation. Determined by

(SH: maximum signal strength (signal strength of mirror unit), SL:
Minimum signal strength (pre-pit signal strength) As is clear from the data shown in Table 1, in the information recording medium according to the embodiment of the present invention, the reflectance in the pre-groove forming area (information recording target area) is a high level sufficient for reading by a CD player. On the other hand, the reflectance of the information recording part is sufficiently low, so that signals with high modulation degree can be read, and the tracking servo gain (TSG) is small, so that the occurrence of tracking errors is sufficiently suppressed. You can see what you can do. Further, since the modulation degree of the pre-pit portion is high, the reading accuracy of the signal recorded in the pre-pit portion in advance is high, and the reliability is improved.

On the other hand, in the information recording medium of the comparative example, the reflectance in the pre-groove forming area (information recording target area) is:
The level is high enough to be read by a CD player, and the reflectivity of the information recording portion is sufficiently low. However,
Since the tracking servo gain (TSG) is drastically reduced, tracking errors frequently occur. Further, since the modulation degree of the pre-pit portion is low, the reading accuracy of the signal recorded in the pre-pit portion is low, and the reliability is not sufficient.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a part of a cross section in a pre-groove region of an embodiment of an information recording medium of the present invention. FIG. 2 is a cross-sectional view schematically showing a part of a cross section in a pre-pit region of an embodiment of the information recording medium of the present invention. FIG. 3 is a cross-sectional view schematically showing a part of a cross-section in a pre-groove region of a conventionally known information recording medium. 11, 21, 31: Substrate, 12, 22, 32: Light absorbing layer, 13, 23, 33: Reflective layer, 14, 34: Pregroove, 24: Prepit, 15, 35: Land, 25: Interpit , 16, 36: groove bottom, 26: pit.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification code FI G11B 7/26 531 G11B 7/26 531 (58) Investigated field (Int.Cl. ⁶ , DB name) G11B 7/24 561 G11B 7/24 563 G11B 7/24 565 G11B 7/24 522

Claims (2)

(57) [Claims] A light absorbing layer containing a dye capable of recording information by forming a pit by irradiating a laser beam on a disc-shaped substrate on which prepits and pregrooves are formed; An information recording medium in which a reflective layer made of a metal is provided on a light absorbing layer, wherein the pre-pits have a diameter of 0.
The half-width in the range of 2 to 1.4 μm and the depth of the pre-groove in the range of 60 to 300 nm are expressed as λ / 16 (where λ is the wavelength of the laser beam for reproduction) in terms of the optical path length. And the difference between the optical film thickness of the light absorbing layer in the pre-pit portion and the optical film thickness of the light absorbing layer in the portion between the pre-pits is λ / 8 (where λ is a reproducing laser Below the wavelength of light)
The difference between the optical thickness of the light absorbing layer at the bottom of the pre-groove and the optical thickness of the light absorbing layer at the land between the pre-grooves is λ.
/ 8 (where λ is the wavelength of the reproduction laser beam) or less. 2. The pre-groove and a half-value width in the range of 0.2 to 1.4 μm and a depth of the pre-groove in the range of 60 to 300 nm, which are expressed by an optical path length, λ / 16 (where λ Is prepared by dissolving a dye in a solvent in a region including the pregroove and the portion where the prepit is formed on the disk-shaped substrate on which the prepit having a depth greater than or equal to the wavelength of the laser beam for reproduction is formed. As a ratio of the deposition of the dye suspension solution to the original volume of the dye solution when precipitation of the dye begins by evaporating the solvent from the dye solution at the application temperature of the dye solution. A dye solution having a defined concentration limit of 99% to 20% is applied by a spin coating method and dried to obtain an optical film thickness of the light absorbing layer in the pre-pit portion and an optical thickness of the light absorbing layer in the pre-pit portion. The difference from the target film thickness is λ / 8 (however, , Λ is the wavelength of the reproducing laser beam) or less, and the difference between the optical thickness of the light absorbing layer at the bottom of the pre-groove and the optical thickness of the light absorbing layer at the land between the pre-grooves is λ /. 8. A method for manufacturing an information recording medium, comprising: forming a light absorbing layer having a wavelength of 8 or less (where λ is the wavelength of a reproducing laser beam) and then providing a reflective layer made of metal on the light absorbing layer.