JP2652279B2 - Information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium capable of recording and / or reproducing information by a laser beam.

[0002]

2. Description of the Related Art In recent years, information recording media using high energy density beams such as laser beams have been developed and put into practical use. This information recording medium is called an optical disk, and can be used as a video disk, an audio disk, 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.

[0003] Reading information from a compact disc is as follows.
This is performed by irradiating a laser beam while rotating the disk. 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. The compact disc for reproduction only is designed to read (reproduce) the CD while rotating it at a constant linear speed of 1.2 to 1.4 m / sec based on the CD standard.
mm and a signal surface outer diameter of 116 mm, it is required to have a maximum recording time of about 74 minutes at a track pitch of 1.6 μm.

[0004] In addition, D in which writing (recording) of information is possible is performed.
A RAW (Direct Read After Write) type information recording medium has also been developed and partially put into practical use. Such a D
The RAW type information recording medium (optical disk) has a disc-shaped transparent substrate made of plastic, glass, or the like, and a recording material made of a metal or semimetal such as Bi, Sn, In, Te, etc. provided thereon. And a recording layer comprising a dye. Recording of information on an optical disc is performed, for example, by
This is performed by irradiating the laser beam onto the optical disk, and 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 a chemical change such as a phase change. Information is recorded by changing 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.

[0005] 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.

Further, there has been proposed an information recording medium in which a ROM area in which pits are previously formed on a substrate is provided on the inner peripheral side of the above-described recordable area (Japanese Patent Laid-Open No. 2-4).
2652). In this information recording medium,
The laser light absorbing layer made of a dye is provided only in the recordable area, and the laser light absorbing layer made of the dye is not provided in the ROM area where the prepits are formed. The reason is,
This is because, if a laser light absorbing layer made of a dye is provided in the area where the pre-pits are formed, the modulation degree of the pre-pit signal becomes small and information in the ROM area cannot be reproduced practically.

The inventor of the present invention has proposed that the optical film thickness of the light absorbing layer in the pit portion of the pre-pit region and the optical film thickness of the light absorbing layer in the inter-pit region can be obtained even if the light absorbing layer made of a dye is provided in the pre-pit region. Is λ / 8 (where λ is the wavelength of the reproducing laser beam)
It has been found that by providing a light absorbing layer as described below, a pre-pit signal can be reproduced with a high degree of modulation, and a patent application has already been filed for an information recording medium having a light absorbing layer containing a dye in both the pre-pit region and the pre-groove region. (See Japanese Patent Application No. 2-191257). In this information recording medium, even in the pre-groove region, the difference between the optical film thickness of the groove bottom portion and the optical film thickness of the land portion of the light absorbing layer containing the dye is λ / 8 (where λ is (Wavelength of laser light) or less, and even if the depth of the pre-groove is reduced, the depth of the groove on the surface of the light absorbing layer can be made sufficiently large. After recording the information, a reproduced signal having a high modulation degree can be obtained.

When a light absorbing layer containing a dye is provided only in the pre-groove region, the optical thickness at the bottom of the groove of the light absorbing layer is larger than the optical thickness at the land, so that the depth of the groove is small. Generally, it is formed to have a range of 40 to 400 nm. However, when the light absorbing layer containing a dye is provided in both the pre-groove region and the pre-pit region as described above, the groove is formed in order to increase the reflectance. Is preferably reduced to a depth in the range of 15 to 60 nm.

By the way, the substrate of the information recording medium as described above is generally made of an acrylic resin such as polymethyl methacrylate in view of the optical characteristics of the substrate, flatness, workability, handleability, stability over time, and manufacturing cost. Manufactured by injection molding a polyvinyl chloride resin such as polyvinyl chloride or a vinyl chloride copolymer; an epoxy resin; a polycarbonate resin; a thermoplastic resin such as amorphous polyolefin or polyester.

That is, a stamper in which a spiral or concentric ridge corresponding to a groove (groove) in a pre-groove area or a pit (hole) in a pre-pit area of a substrate of an information recording medium is formed is placed in a cavity of an injection molding machine. Then, the substrate resin is injection-molded, whereby the substrate on which the ridges of the stamper are transferred and grooves or pits are formed is manufactured.

In general, a stamper is formed by forming a photoresist layer on a cleaned original glass plate that is optically completely flat, exposing it to a laser beam to record an information signal, and then performing a development process to form a fine uneven pattern. Is formed. Next, a conductive thin film is formed on the surface on which the fine uneven pattern is formed by vacuum evaporation, sputtering, electroless plating, or the like, and the conductive thin film is subjected to nickel electroforming, and is manufactured by performing back surface polishing and inner and outer diameter processing. You.

By the way, as described above, in the pre-groove region, when the difference between the optical film thickness at the groove bottom and the optical film at the land of the light absorbing layer containing a dye is reduced,
The optical film thickness at the bottom of the groove becomes smaller, and the degree of reflection of the shape of the bottom of the groove on the surface of the light absorption layer, that is, the interface between the light absorption layer and the reflection layer, increases. The influence of noise on the information reproduction performance of the information recording medium increases, and the C / N of the information recording medium tends to decrease. In the case where the groove depth is increased and the optical thickness at the bottom of the groove is much larger than the optical thickness at the land as in the conventional case, when the groove at the bottom of the substrate is shaped into the surface shape of the light absorbing layer. Although the influence of the shape was small, it would not have been considered in particular, but in that case, as described above, the reflectance and the degree of modulation of the reproduced signal were small, and the light absorption layer could not be provided in the prepit portion.

[0013]

After recording information by irradiating a laser beam, the degree of modulation and the reflectance are high, and the C / N ratio is high.
A reproduction signal having a high value can be obtained, and an information recording medium having good tracking characteristics is provided.

An information recording medium in which a light-absorbing layer containing a dye is also formed in a pre-pit formation region provided together with the pre-groove formation region, and a reproduction signal satisfying the CD standard can be obtained from the pre-pit formation region. I will provide a.

[0015]

SUMMARY OF THE INVENTION The present invention provides a dye capable of recording information by irradiating a laser beam on a disk-shaped resin substrate on which a pregroove is formed to form pits for reproduction. An information recording medium provided with a light absorbing layer containing: and a reflective layer made of metal on the light absorbing layer, wherein the center line average roughness (Ra) of the groove bottom of the pre-groove of the substrate is 0.001 μm or less, and the difference between the optical film thickness of the light absorbing layer at the bottom of the groove and the optical film thickness of the light absorbing layer at the land is λ / 8 (where λ is the wavelength of the reproducing laser beam). ) An information recording medium characterized by the following.

In this specification, the center line average roughness (R
a) represents the measurement length in the direction of the center line of the roughness curve as L, the center line as the X axis, the direction of the vertical magnification as the Y axis, and the roughness curve as y = f (x), (1) [See Kenji Sato, "Introduction to Surface Engineering" (published by Yokendo)].

[0017]

(Equation 1)

Preferred embodiments of the information recording medium of the present invention are as follows. (1) The center line average roughness (R
The above-mentioned information recording medium, wherein a) is 0.0005 μm or less.

(2) The substrate is obtained by contacting a pre-groove forming surface of a resin substrate having a pre-groove formed by injection molding with a processing solution containing a solvent capable of dissolving the substrate. The information recording medium described above, which is a substrate.

(3) The substrate is formed by forming a photoresist layer on an original glass plate, exposing it to a spiral or annular laser beam, and developing it to form ridges.
The information recording medium as described above, which is a resin substrate manufactured by injection molding using a stamper manufactured by post-baking at the above temperature and then electroforming.

(4) The pre-groove is 0.2 to 1.4.
The information recording medium as described above, which has a half-value width of μm and a depth of 5 to 70 nm.

(5) 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 /
16 (where λ is the wavelength of the reproducing laser beam) or less.

(6) Pre-pits are further formed on the substrate, and the light-absorbing layer is also provided in the pre-pit formation region. The optical film thickness of the light-absorbing layer in the pit portion and the optical absorption of the light-absorbing layer in the inter-pit portion are provided. The information recording medium as described above, wherein the difference from the target film thickness is λ / 8 (where λ is the wavelength of the reproducing laser beam), preferably λ / 16 or less.

(7) The pre-pit has a size of 0.2 to 1.4 μm.
The information recording medium according to claim 1, wherein the information recording medium has a half width of m and a depth of 60 to 300 nm.

(8) The information recording medium as described above, wherein the depth of the pre-groove is shorter than the depth of the pre-pit by λ / 16 or more in terms of an optical path length.

(9) The information recording medium as described above, wherein a protective layer is further formed on the reflective layer.

In the information recording medium of the present invention, a light absorbing layer containing a dye and a reflective layer made of a metal are provided in this order on a resin substrate on which a pre-groove (and optionally a pre-groove) is formed. It has a basic configuration.

The material of the disc-shaped substrate in the present invention can be arbitrarily selected from various resin materials used as substrates of conventional information recording media. Substrate materials include acrylic resins such as polymethyl methacrylate; polyvinyl chloride, and vinyl chloride copolymer in view of the optical characteristics, flatness, workability, handleability, stability over time, and manufacturing cost of the substrate. And the like; a vinyl chloride resin such as an epoxy resin; a polycarbonate resin; an amorphous polyolefin and a polyester. Preferably, polycarbonate, polyolefin, and polymethyl methacrylate can be mentioned.

In the present invention, a pre-groove (tracking groove) is formed on the surface of the substrate 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 the groove depth is in the range of 15 to 60 nm and the half width of the groove is 0.3 to 0.7 μm. Is most preferably in the range of 20 to 50 nm and the half width of the groove is 0.35 to 0.6 μm. Grooves may be wobbled for addressing or linear velocity control.

The substrate as described above can be manufactured by using a precision stamper (mother) and injection molding a resin material for the substrate.

In the information recording medium of the present invention, the center line average roughness (Ra) of the groove bottom of the substrate is 0.0.
It is characterized in that it is not more than 01 μm, preferably not more than 0.0005 μm. The center line average roughness of the groove bottom can be determined, for example, by using a scanning tunneling microscope and determining an roughness curve according to the above-described equation (1).

The resin substrate having the center line average roughness at the bottom of the groove as described above may be formed, for example, by using a solvent capable of dissolving the pregroove forming surface of the resin substrate having the pregroove formed by injection molding. It can be manufactured by a method of contacting with a processing solution containing the same. When the groove bottom of the substrate comes into contact with the treatment liquid, the convex portion of the groove bottom is preferentially dissolved, and as a result, the groove bottom becomes smooth and the center line average roughness becomes small.

The treatment liquid used in this method is not particularly limited as long as it contains a solvent capable of dissolving the substrate. However, if the dissolving power of the processing liquid in the substrate resin is too large, when the processing liquid is brought into contact with the substrate, the dissolution of the substrate proceeds rapidly in a short time, and the depth of the groove increases, or the half-width of the groove increases. And the land portion may be relatively thin, or in a severe case, a defective portion may be formed in the land portion. Therefore, in order to easily and stably produce a substrate having a small center line average roughness at the bottom of the groove with a wide allowable range of control conditions and good reproducibility, the processing solution is exposed to the substrate resin at a contact temperature. Solvent power
Preferably not too large.

The appropriate value of the dissolving power of the treatment liquid to the substrate resin cannot be determined uniformly because it varies depending on the method of bringing the treatment liquid into contact with the substrate. In the case where the processing liquid is supplied onto the substrate and the processing liquid is brought into contact with the substrate, the dissolving power of the processing liquid with respect to the substrate resin (in this specification, represented by the saturation solubility of the substrate resin in the processing liquid) )
However, a treatment liquid having a concentration of 0.01 to 10 g / ml is preferable.

The specific substance of the treatment liquid varies depending on the type of the material of the resin substrate, and cannot be uniformly specified. The processing liquid may be a single solvent having the above-mentioned dissolving power, but as understood from the value of the above-mentioned dissolving power, the dissolving power of the above-mentioned processing liquid in the substrate resin is relatively small. Therefore, it is generally preferable that the treatment liquid is a mixture of a poor solvent for the substrate resin and a good solvent (generally, a smaller amount than the poor solvent) for the substrate resin. When such a mixed solvent is used, an optimum processing solution can be prepared by changing the ratio of the good solvent and the poor solvent according to the state of the groove bottom of the substrate to be processed and the processing conditions. There is also an advantage.

The above-mentioned single solvent, good solvent and poor solvent suitable for a specific substrate resin can be easily selected by those skilled in the art by referring to the literature or experimentally. For example, when using polycarbonate as the resin for the substrate, as a preferable good solvent, for example, dichloroethane, trichloroethane, tetrachloroethane, toluene, xylene, acetone and the like can be mentioned, and as a preferable poor solvent, for example, ethanol, methanol, Examples thereof include n-propanol, cyclohexane, fluorine alcohol, hexane, octane, ethyl cellosolve, methyl cellosolve, and ethyl ether.

Another method for manufacturing a resin substrate having a center line average roughness at the bottom of the groove as described above is to form a photoresist layer on a glass substrate and expose it to a spiral or annular laser beam. A method in which a ridge is formed by developing, post-baked at a temperature of 105 ° C. or higher, and then a substrate resin material is injection molded using a stamper manufactured by electroforming. The above stamper is a stamper manufactured by a conventional method except that post-baking after development processing is performed at a temperature of 105 ° C. or higher. Conventionally, the post-baking has been performed at a temperature of 80 to 90 ° C. for about 20 minutes.
By using a stamper manufactured at a temperature of not less than ° C., it became possible to manufacture a resin substrate having good smoothness at the groove bottom as described above. The post-baking is preferably performed at a temperature of 105 to 150 ° C. for 20 minutes to 10 hours.

A resin substrate manufactured by using such a stamper may be used as it is as a substrate of the information recording medium of the present invention, or after being treated with the above-described processing liquid, the information substrate of the present invention may be used. It may be used as a substrate of a recording medium.

In the present invention, prepits (ROM areas) in which information such as various application software and address signals are recorded in advance may be formed on the substrate surface. 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 preferably 0.2 to 1.4 μm, more preferably the pit depth is in the range of 70 to 250 nm, and the pit half width is 0.3 to 1.0 μm. Most preferably, it is in the range of 90 to 200 nm and the half width of the pit is 0.4 to 0.7 μm.

When a prepit is formed, the depth of the pregroove is expressed by an optical path length λ / 16 (where λ is the wavelength of the laser beam for reproduction and is described below). Is the same or shorter), more preferably λ / 14 or more, more preferably λ / 14 or more.
It is particularly preferable that the length be 12 or more. The reason is that if the depth of the pre-groove is made 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.

The substrate on which the pre-pits are formed together with the pre-grooves is formed by adding the pre-pits.
It can be manufactured in the same manner as when manufacturing a substrate on which only a pre-groove is formed.

A coating solution for forming a light-absorbing layer using a coating solution containing a resin such as an acrylic resin, a styrene resin, a polyolefin resin, or a polyamide resin on the substrate on which the pregroove is formed. A solvent-resistant layer may be provided for protection from the solvent therein.

A light absorbing layer containing a dye is provided on the substrate (or the solvent resistant 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, azurenium dyes, squarylium dyes, Ni, Cr
Such as metal complex dyes, naphthoquinone dyes, anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallylmethane dyes, aminium dyes, diimmonium dyes,
Nitroso dyes, leuco dyes, croconium dyes,
And the like.

These dyes are known as Light Once (WO)
Not limited to the type, it may be a rewritable (RW) type (or reversible type).

Among these dyes, a dye having a high absorptance to light in the near infrared region of 700 to 900 nm is used because a semiconductor laser that emits near-infrared light is practically used as a recording / reproducing laser. Is preferred.

In particular, a cyanine dye, an azurenium dye and a squarylium dye are preferred, and among the cyanine dyes, a naphthoindolenine dye and an imidazoquinoxaline dye are preferred.

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, a metal complex salt dye or the like is used as a quencher in an amount of 0.0
It is preferable to contain it in a proportion of from 01 to 0.3 mol.

The information recording medium of the present invention is characterized in that the difference between the optical thickness at the groove bottom of the light absorbing layer and the optical thickness at the land is λ / 8 or less. Also,
When the information recording medium of the present invention further has a pre-pit on the substrate, the difference between the optical thickness of the pit portion of the light absorbing layer and the optical thickness of the portion between the pits is λ / 8 or less. It is characterized by.

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 sectional view schematically showing a part of a 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 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.

In FIG. 3, a light absorbing layer 32 made of a dye is formed on the surface of a substrate 31 made of plastic.
A reflection layer 33 made of metal is formed on the light absorption 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 a spin coating method and drying the solution. The thickness t ₆ of the light absorbing layer 32 at the groove bottom 36 of the pre-groove 34
Is the thickness t ₅ of the light absorbing layer 32 on the land 35 of the substrate 31.
Is bigger than. As a result, the depth of the groove shape on the contact surface of the light absorption layer 32 with the reflection layer 33 is
4 is smaller than the depth d ₃ , and when recording pits are formed in the pre-groove 34 by irradiating a laser beam for recording information, an upper portion of the groove of the light absorbing layer 32 (corresponding to a land portion of the substrate) is formed. There is a problem that the modulation degree of the recording pit becomes small because the phase difference between the portion and the bottom becomes small. 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 a plastic.
A reflection layer 13 made of metal is formed on the light absorption layer 12. A pregroove 14 is formed on the substrate 11. The light absorbing layer 12 is a light absorbing layer forming solution having a specific property as described above prepared by dissolving a dye in a solvent,
It is formed by spin coating and drying. Groove bottom 1 of pregroove 14
6, the optical film thickness (n _r · t ₂ ) of the light absorbing layer 12 (however,
n _r is the refractive index of the light absorbing layer, and t ₂ is the groove bottom 1
6 is a thickness of the light absorbing layer 12), an optical film thickness of the light absorbing layer 12 of the land portion 15 of the substrate _{11 (n r · t 1)} ( where, n _r is the refractive index of the light absorbing layer Yes, t ₁ is land 1
5 is the film thickness of the light absorbing layer 12). As a result, the light absorption layer 12
The depth of the groove at the contact surface with the reflective layer 13 is the same as the depth d ₁ of the groove 14 or smaller by about λ / 8 or less in optical film thickness. The phase difference between the recording pit and the recording pit is large. Further, by setting the difference between n _r · 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 n _r · t ₁ and n _r · t ₂ is
It is preferably λ / 11 or less, more preferably λ / 13 or less, even more preferably λ / 16 or less.

The ratio of the reflectance of the groove bottom to the reflectance of the mirror is 70% or more, particularly 80% or more.
More preferably, it is 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 a plastic.
A reflection layer 23 made of metal is formed on the light absorption 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 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 ₄ ) of the light absorbing layer 22 in the pit 26 of the prepit 24 (where n _r is the refractive index of the light absorbing layer, and t ₄ is the refractive index of the light absorbing layer 22 in the pit 26). Thickness) and the optical thickness (n _r · t ₃ ) of the light absorbing layer 22 in the inter-pit portion 25 of the substrate 21 (where n _r is the refractive index of the light absorbing layer, and t ₃ is the pit). (The thickness of the light absorption layer 22 in the intervening portion 25) is not more than λ / 8. As a result, the depth of the hole at the contact surface of the light absorption layer 22 with the reflection layer 23 is the same as the depth d ₂ of the pit 24 or smaller than the optical thickness by 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 pit formation region of the substrate, it becomes possible to reproduce the pits of the substrate with a high degree of modulation.

The difference between the above n _r · t ₃ and n _r · t ₄ is
It is preferably λ / 11 or less, more preferably λ / 13 or less, even more preferably λ / 16 or less.

In the information recording medium of the present invention, a reflective layer is further formed on the above-described light absorbing layer. The effect is similarly exerted in an information recording medium in 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 larger than the depth d ₂ of the pit portion by the optical path length (n · d: n is the refractive index of the substrate). , Where d is a depth dimension).
In particular, it is preferably smaller than λ / 14 or more, more preferably smaller than λ / 12 or more.

The light absorbing layer has a thickness of 40 to 400 nm, particularly 60 to 30 nm, between the land and the pit.
It is preferably 0 nm, more preferably 80 to 250 nm.

The difference between the optical thickness of the light absorbing layer having a specific optical thickness in the information recording medium of the present invention, ie, 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, and 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 in the pit portion is λ / 8.
The following light absorbing layer can be formed by the following method.

That is, a dye solution prepared by dissolving a dye in a solvent on a disk-shaped substrate on which pregrooves or prepits and pregrooves are formed. A dye solution having a concentration limit of 99 to 20%, defined as the ratio of the volume of the dye suspension solution to the original volume of the dye solution when the precipitation of the dye is started by evaporating the solvent, is spin-coated. The light absorbing layer having the above-mentioned optical thickness can be formed by applying a coating method and forming a coating film, followed by drying.

The above-mentioned dye solution used in the above-mentioned light-absorbing layer forming method has a specific property, that is,
A dye solution having a concentration limit of 99 to 20%. 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 dye solution application temperature,
It is defined as meaning the ratio of the dye solution 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) at the time when the dye precipitation starts is 90% of the volume of the original dye solution. Is referred to as a 90% dye solution.

Therefore, the concentration limit of the dye solution (hereinafter referred to as the limit)
Concentration )), the combination of the dye and the solvent (single solvent or mixed solvent), the type and ratio when the solvent is a combination of two or more solvents, the concentration of the dye in the dye solution,
It changes depending on the application temperature and the like. Therefore, a dye solution having a specific concentration limit cannot be uniformly determined for a specific dye.However, preparing a dye solution having a desired concentration limit by variously changing the above conditions is
Those skilled in the art can easily do this.

The dye solution used in the above-described method for forming a light absorbing layer is a dye solution having a concentration limit of 99 to 20%, and a concentration limit of 99 to 30%, particularly 95 to 40%.
More preferably, the dye solution is 90 to 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 above-mentioned dye solution is as long as it satisfies the concentration limit of the dye solution.
It may be a single solvent or a mixed solvent of two or more solvents. When the solvent is a mixed solvent, a good solvent for the dye to be used (preferably, a solvent capable of dissolving 2% by weight or more of the dye to be used at the coating temperature of the dye solution)
And a poor solvent for the dye to be used (preferably, a solvent that does not dissolve the dye to be used at 2% by weight or more 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 solvents such as acetic acid. Acid solvents; ethyl acetate, butyl acetate, amyl acetate,
Ester solvents such as ethylene glycol monoethyl ether acetate and cellosolve acetate; acetone, methyl ethyl ketone, methyl isobutyl ketone;
Ketone solvents such as cyclohexanone; halogenated hydrocarbon solvents such as dichloromethane, 1,2-dichloroethane, chloroform, methylchloroform, trichlene, carbon tetrachloride, tetrachloroethylene; tetrahydrofuran, ethyl ether, isopropyl ether, dioxane; Ether solvents such as diglyme; ethanol, n-propanol, isopropanol, n-butanol, amyl alcohol, diacetone alcohol, ethylene glycol monomethyl ether,
Alcohol solvents such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether and benzyl alcohol; amide solvents such as dimethylformamide; fluorinated alcohols such as 2,2,3,3-tetrafluoropropanol, and fluorine substitution Examples include fluorine-based solvents such as ketone, fluorine-substituted ester, fluorine-substituted amide, fluorine-substituted ether, fluorine-substituted aromatic hydrocarbon, and fluorine-substituted aliphatic hydrocarbon.

In the formation of the light absorbing layer, the dye solution is not particularly limited as long as the dye solution satisfies the concentration limit. The concentration of the dye in the dye solution is 0.5 to 15% by weight, preferably 1 to 10% by weight, more preferably 1.5 to 8% by weight in order to form a light absorbing layer having a large thickness. Is preferred. Various additives such as an antioxidant, a UV absorber, a plasticizer, and a lubricant may be added to the dye solution according to the purpose.

When a binder is used, the binder may be
For example, gelatin, nitrocellulose, cellulose derivatives such as cellulose acetate, dextran, rosin, natural organic high molecular substances such as rubber; and hydrocarbon resins such as polyethylene, polypropylene, polystyrene, polyisobutylene, polyvinyl chloride, polyvinylidene chloride, Vinyl resins such as polyvinyl chloride / polyvinyl acetate copolymer, acrylic resins such as polymethyl acrylate and polymethyl methacrylate, polyvinyl alcohol, chlorinated polyolefin, epoxy resin, butyral resin, rubber derivatives, phenol / formaldehyde resin And the like. Synthetic organic polymer substances such as an initial condensate of a thermosetting resin.

When the above-mentioned dye solution is applied onto a substrate by a spin coating method, it can be performed using a device and a method known per se. The above-mentioned dye solution is generally used at 0 to 100 ° C, particularly at 5 to 80 ° C, more particularly at 10 to 60 ° C.
It is preferred to apply at a temperature of ° C. The rotation speed of the substrate is
When applying a dye solution, generally 10 to 1000 r.p.
m., particularly preferably 100 to 500 rpm.
When drying the dye coating, generally 300 to 10,000
rpm, especially 500-7000 rpm, more particularly 700
It is preferable to set it to 4000 rpm.

A reflective layer is further provided on the light absorbing layer of the information recording medium of the present invention. Be, as a material of the reflection layer,
B, C, Sc, Rb, Sr, As, Os, Tl, At,
Fr, Ra, Mg, Se, Y, Ti, Zr, Hf, V,
Nb, Ta, Cr, Mo, W, Mn, Re, Fe, C
o, Ni, Ru, Rh, Pd, Ir, Pt, Cu, A
g, Au, Zn, Cd, Al, Ga, In, Si, G
Metals and metalloids such as e, Te, Pb, Po, Sn, Bi, and Sb can be mentioned. Among them, C and A
u, Zn, Cu, 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 of 10 to 300 nm, preferably 40 to 200 nm.

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

On this reflective layer, a protective layer may be provided for the purpose of physically and chemically protecting the entire information recording medium, especially 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 and Mg.
F ₂ and SnO ₂ can be exemplified. 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 coating solution is prepared as it is or dissolved in an appropriate solvent, and then the coating solution is applied and cured by irradiation with UV light to form a protective layer. 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 a photopolymerization initiator. Ordinary UV-curable resins such as described above can be used. Various additives such as an antistatic agent, an antioxidant, and a UV absorber may be added to these coating solutions according to the purpose. It is preferable to use a UV curable resin as the material of the protective layer.

The thickness of the protective layer is generally 0.1 to 100 μm.
m, preferably in the range of 0.5 to 20 μm.

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

Recording of information on the information recording medium of the present invention
The information recording medium is moved at a constant linear velocity (preferably 1.2 to 2.8 m
/ Sec, particularly preferably 1.2 to 1.4 m / sec), while irradiating a laser beam from the substrate side to the bottom of the pre-groove to form a pit for reproduction in the light absorbing layer on the groove. It is performed by forming and recording signals. It is preferable to record a CD format EFM signal as the signal in order to obtain 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 pits after the above-described recording are such that the substrate and / or the dye generate heat when irradiated with a laser beam, and melt, evaporate, sublime, deform or change in quality, thereby forming a convex, wavy, or 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 recording a CD format signal or the like at a constant linear speed on the information recording medium of the present invention by the above recording method, it is possible to obtain excellent recording / reproducing characteristics such as signal modulation and reproduction C / N. In addition, the tracking property at the time of recording, particularly the tracking property by the push-pull method is excellent. Further, 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. Further R
In the case of the information recording medium of the present invention provided with the OM area,
Even in the ROM area, it is possible to obtain a reproduced signal having a high modulation degree satisfying the CD standard.

[0082]

EXAMPLES Examples and comparative examples of the present invention will be described below. However, these examples do not limit the present invention.

Example 1 A pre-pit (half-width of pit: 0.6 μm, pit depth: 130 nm) in which an EFM signal was recorded was formed in an area having a diameter of 46 mm to 80 mm, and a pre-pit was formed in an area having a diameter of 80 nm to 118 mm. Groove (track pitch: 1.6 μm, half width of groove:
A disk-shaped polycarbonate substrate (outer diameter: 120 mm, inner diameter: 15 mm, thickness: 1.2 mm) on which 0.5 μm and groove depth: 60 nm was formed was prepared. Scanning tunneling microscope (UNISOKU, US
M-101) and the center line average roughness (Ra) of the groove bottom determined by the above equation (1) is 2
× 10 ⁻³ μm.

The substrate was kept at 23 ° C.
A mixed solution (23 ° C.) of 95 parts by weight of 2,2,3,3-tetrafluoropropanol and 5 parts by weight of dichloroethane is applied by a spin coating method at a substrate rotation speed of 1000 rpm for 10 seconds, and then the same rotation is performed. The surface of the substrate was treated by drying for 30 seconds. The dissolving power of the mixed solution at 23 ° C. for the polycarbonate is as follows:
It was 2 g / ml. In addition, obtained in the same manner as above,
The center line average roughness of the bottom of the groove of the processed substrate (R
a) was 0.5 × 10 ⁻³ μm.

On the other hand, a dye (A) having the following structural formula (A) 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%.

[0086]

Embedded image

This dye solution was maintained at 23 ° C., and the dye solution was applied onto the substrate at 23 ° C. by a spin coating method at a substrate rotation speed of 200 rpm for 4 seconds, and then at a rotation speed of 700 rpm for 30 seconds. After drying for 2 seconds, a light absorbing layer was formed.

480 W, target-substrate distance 95 mm, gas pressure 2 Pa, rate 2
Under the condition of nm / sec, Au was subjected to DC sputtering to form a reflective layer made of Au having a thickness of 100 nm.

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

Thus, an information recording medium comprising the substrate, the dye recording layer, the reflection layer and the protective layer was manufactured.

In the obtained information recording medium, in the pre-groove formation region, the optical film thickness of the light absorbing layer at the bottom of the groove, the optical film thickness of the light absorbing layer at the land, and the C / N value were determined by forming the pre-pit. In the 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 1
The 1T modulation was measured by the following evaluation method. Table 1 shows the evaluation results.

[Example 2] In Example 1, 90 parts by weight of 2,2,3,3-tetrafluoropropanol and methyl ethyl ketone 1 were used to treat the surface of the substrate.
The surface of the substrate was treated in the same manner as in Example 1 except that the mixed treatment solution with 0 parts by weight was used (the dissolving power for polycarbonate at 23 ° C. was 3 g / ml). The center line average roughness of the bottom of the groove of the processed substrate (R
a) was 0.4 × 10 ⁻³ μm.

An information recording medium comprising a substrate, a dye recording layer, a reflective layer, and a protective layer was manufactured in the same manner as in Example 1 except that the substrate treated as described above was used.

Example 1 of the obtained information recording medium
The evaluation was performed in the same manner as in the above. Table 1 shows the evaluation results.

Comparative Example 1 Information recording comprising a substrate, a dye recording layer, a reflective layer and a protective layer was performed in the same manner as in Example 1 except that the surface treatment of the substrate was not performed with the treatment liquid. The media was manufactured.

Example 1 of the obtained information recording medium
The evaluation was performed in the same manner as in the above. Table 1 shows the evaluation results.

Comparative Example 2 In Example 1, the treatment liquid for treating the surface of the substrate was prepared by mixing 70 parts by weight of 2,2,3,3-tetrafluoropropanol and 30 parts by weight of dichloroethane ( The surface of the substrate was treated in the same manner as in Example 1 except that the dissolving power for polycarbonate at 23 ° C. was changed to 12 g / ml). Center line average roughness (Ra) of groove bottom of processed substrate
Was 0.2 × 10 ⁻³ μm.

An information recording medium comprising a substrate, a dye recording layer, a reflective layer, and a protective layer was manufactured in the same manner as in Example 1 except that the substrate treated as described above was used.

Example 1 of the obtained information recording medium
The evaluation was performed in the same manner as in the above. Table 1 shows the evaluation results.

Example 3 A pre-pit and a pre-groove were laser-cut on a glass disk provided with a photoresist layer (manufactured by Shipley, MP1350J, film thickness: 120 nm) and developed.
Post-baking was performed at 20 ° C. for 1 hour, and nickel plating was performed by a conventional method to produce a stamper.

Using the stamper thus produced, polycarbonate was injection-molded, and the diameter was set to 46 mm.
A pre-pit (half-width of pit: 0.6 μm, depth of pit: 130 n) in which an EFM signal is recorded in an area of 80 mm
m) is formed, and a pre-groove (track pitch: 1.6 μm, half width of groove: 0.5 μm, groove depth: 60 nm) is formed in a region having a diameter of 80 nm to 118 mm (outer diameter). : 120mm, inner diameter: 15
mm, thickness: 1.2 mm). The center line average roughness (Ra) of the groove bottom of this substrate is 0.7 × 10
^-3 μm.

An information recording medium comprising a substrate, a dye recording layer, a reflective layer and a protective layer was manufactured in the same manner as in Example 1 except that the above substrate was used.

Example 1 of the obtained information recording medium
The evaluation was performed in the same manner as in the above. Table 1 shows the evaluation results.

Comparative Example 3 Example 3 was the same as Example 3 except that the post-baking conditions of the developed photoresist layer in the process of manufacturing the stamper were changed to a temperature of 100 ° C. and a time of 30 minutes. A stamper was manufactured in the same manner.

A polycarbonate substrate was manufactured by injection molding in the same manner as in Example 3 except that the stamper thus manufactured was used. The center line average roughness (Ra) of the groove bottom of this substrate was 2 × 10 ⁻³ μm.

An information recording medium comprising a substrate, a dye recording layer, a reflective layer and a protective layer was manufactured in the same manner as in Example 1 except that the above substrate was used.

Example 1 for the obtained information recording medium
The evaluation was performed in the same manner as in the above. Table 1 shows the evaluation results.

[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 an EFM encoder (KEN-WOO).
Using D), EFM recording was performed on the bottom of the pregroove at a laser power (recording power) of 6 mW and a constant linear velocity of 1.3 m / sec.

(1) Optical Thickness of Light Absorbing Layer at Bottom of Groove The absolute 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.). Was determined from the results of measuring the reflectance, transmittance, and absolute film thickness of the separately formed dye thin film, 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 obtained in the same manner as in the above 1).

(3) C / N of Groove Area Information recorded under the above conditions is read at a reproduction power of 0.5 m
W, reproduced under the conditions of a constant linear velocity of 1.3 m / sec, and a spectrum analyzer (RBW: 10 kHz, VBW: 100 k)
Hz) and the ratio of the carrier and noise output levels (C /
N) was measured.

(4) Optical film thickness of light absorbing layer in pit portion The optical film thickness was obtained in the same manner as in the above method 1).

(5) Optical film thickness of light absorption layer between pits The optical film thickness was obtained in the same manner as in the above method 1).

(6) 11T modulation degree The recording length 11 of the recorded CD format signal
With respect to the DC reproduced signal of T, the signal strength of the signal portion and the mirror portion (the portion with no signal) was measured, and the modulation factor (C) was obtained by the following equation. C = [(SH−SL) / SH] × 100 (SH: maximum signal strength, SL: minimum signal strength)

[0115]

[Table 1]

As is clear from Table 1, the information recording medium of the embodiment has a C-groove in the pre-groove forming area (information recording area).
/ N is large, the modulation degree is large in the pre-pit formation area (ROM area), and the performance is excellent.

On the other hand, the information recording medium of the comparative example is
Although the degree of modulation in the pre-pit formation area (ROM area) is almost the same as that of the information recording medium of the embodiment, the C / N in the pre-groove formation area is extremely small.

[0118]

According to the information recording medium of the present invention, after recording information in a groove forming area by irradiating a laser beam,
In the case where N, modulation degree and reflectance are high and pre-pits are additionally formed, a reproduced signal having high modulation degree can be obtained even if a light absorption layer is formed in the pre-pit formation region. It is an excellent information recording medium.

[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 one 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.

[Explanation of symbols]

 11, 21, 31 Substrate 12, 22, 32 Light absorbing layer 13, 23, 33 Reflective layer 14, 34 Pre-groove 24 Pre-pit 15, 35 Land 25 Inter-pit 16, 36 Groove bottom 26 Pit

Claims (1)

(57) [Claims] A light absorbing layer containing a dye capable of recording information by irradiating a laser beam to form pits for reproduction is provided on a disk-shaped resin substrate on which a pregroove is formed. An information recording medium further comprising a reflective layer made of metal provided on the light absorbing layer, wherein a center line average roughness (Ra) of a groove bottom of the pregroove of the substrate is 0.001 μm or less; and Wherein 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 (where λ is the wavelength of the reproducing laser beam) or less. Information recording medium.