JP2794643B2 - 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 optical information recording medium on which information can be recorded by a laser.

[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.

DRAW capable of writing (recording) information
(Direct Read After Write) type information recording media have been developed and partially put into practical use. Such a DRAW type information recording medium (optical disk) has a disc-shaped transparent substrate made of plastic, glass or the like, and a metal or semi-metal such as Bi, Sn, In, Te, etc. 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. 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.

[0004] 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.

A recording layer containing a dye is generally formed by applying a solution containing a dye on a substrate on which a pregroove is formed and drying the solution.
The thickness of the dye recording layer at the bottom of the groove is larger than the thickness of the dye recording layer at the land. 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 the 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 becomes small, so that the modulation degree of the recording pit becomes 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 to relatively increase the depth of the groove formed on the surface of the dye recording layer. However, in that case, the reflectance generally tends to decrease.

When the thickness of the dye recording layer at the bottom of the groove and the thickness of the dye recording layer at the land become substantially the same, the depth of the pre-groove of the substrate can be reduced, and these problems can be solved simultaneously. The resulting information recording medium has a large degree of modulation and a large reflectance.

[0008] Further, R
There has been proposed an information recording medium having an OM area and a recordable area in which pits for data reproduction are formed by irradiation with laser light (see Japanese Patent Application Laid-Open No. 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 the information in the ROM area cannot be reproduced practically.

That is, the laser absorbing layer made of a dye is generally formed by applying a solution of the dye and drying it. When the dye solution is applied to the pre-pit formation region, the dye solution is applied to the pre-groove formation region. In the same manner as in the case of coating, the thickness of the laser absorption layer in the pit portion (hole portion) is the thickness of the laser absorption layer in the inter-pit portion (a portion between the pits and corresponding to the land portion). Therefore, the depth of the hole on the surface of the laser absorbing layer formed by reflecting the shape of the pit portion of the substrate becomes shallower than the depth of the pit of the substrate, and , The degree of modulation of the pre-pits becomes smaller.

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, a dye is used. At the boundary between the portion where the layer is provided and the portion where the dye layer is not provided,
There are problems that it is difficult to form the boundary with good reproducibility, that the film thickness tends to be uneven at the edge of the dye layer, and that there is a problem that the annular dye layer tends to be eccentric. Further, in practice, only an information recording medium divided into two areas, a ROM area and a recordable area on the outer peripheral side thereof, can be manufactured, and a recordable area is additionally provided on the inner peripheral side of the ROM area. Also, it is extremely difficult to provide a ROM area and a recordable area in a mixed manner, and application software pre-recorded in the ROM area and its use are limited, which is inconvenient in practice. is there.

When the thickness of the dye layer in the pre-pit portion of the substrate is substantially the same as the thickness of the dye layer in the portion between the pits, the phase difference between the pre-pits becomes large, so that an information recording medium having a large pre-pit modulation degree is obtained.

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

On the other hand, a normal DRAW type information recording medium (optical disc) generally performs recording at a high linear velocity, but does not require a particularly high reflectance. On the other hand, a CD-DR that performs recording at a low linear velocity using a CD format signal adopted for a compact disc (CD)
AW requires high reflectance. That is, by having a high reflectance, a CD-D on which information is recorded
A great advantage that RAW can be reproduced by a commercially available CD player is obtained.

As a method of improving the reflectance, a metal reflection layer is generally provided on a light absorbing layer containing a dye. In addition, EP0 of European Patent Publication
353393 A2 and EP 0 353 394 A2 disclose that an enhance layer is provided between the dye absorbing layer and the metal reflective layer in order to further improve the reflectance. Materials for the enhance layer include SiO, SiO ₂ , Si ₃
Inorganic substances such as N ₄ and AlN are described.

However, in the case where a reflection layer or an enhancement layer is provided on the light absorbing layer in order to increase the former reflectance,
It is necessary to form the reflection layer and the enhancement layer by an evaporation method such as sputtering, and the equipment becomes expensive,
It takes a long time to form a layer, and there is a great disadvantage in manufacturing.

[0016]

It can be manufactured by a manufacturing method including a simple film forming step by coating.
It is an object of the present invention to provide an information recording medium which can obtain a reproduced signal having a high modulation degree after recording information by irradiating a laser beam, has good tracking characteristics, and has a high reflectance.

Also, an information recording medium is provided in which a light absorbing layer containing a dye is formed also in a region where a prepit is formed, and a reproduced signal having a high degree of modulation can be obtained from the region where the prepit is formed. That is.

[0018]

According to the present invention, there is provided a dye capable of recording information by irradiating a laser beam on a disk-shaped substrate having a pregroove formed on its surface to form pits for reproduction. an information recording medium where the light absorbing layer is provided containing, light absorbing layer, in order from the substrate side, a pair of the first absorption layer and the two layers a pair of composite absorbent layer made of the second absorbent layer or two sets and a third absorbing layer, and the first absorbing layer is made of an organic substance and has a refractive index of 1.8 or more and 0.5
The second absorption layer is a layer made of an organic material and having a refractive index of less than 1.8 and an extinction coefficient of 0.5 or less, and the third absorption layer is A layer composed of an organic substance and having a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less, or a layer composed of an organic substance and having a refractive index of 1.0 to 1.0.
A layer having a refractive index in the range of 4.0 and an extinction coefficient of 1.0 or more, and furthermore, an optical film at the bottom of the groove, the sum of the first absorption layer and the second absorption layer of the light absorption layer The information recording medium is characterized in that the difference between the thickness and the optical thickness of the land is not more than λ / 8 (where λ is the wavelength of the reproducing laser beam).

In another aspect of the present invention, a dye capable of recording information is formed by irradiating a laser beam on a disk-shaped substrate having prepits and pregrooves formed on its surface to form pits for reproduction. An information recording medium provided with a light-absorbing layer including a light-absorbing layer, wherein the light-absorbing layer is, in order from the substrate side, a two-layer set of a composite absorbing layer composed of a first absorbing layer and a second absorbing layer. of consists of a pair or two pairs and the third absorbent layer, and the first absorbent layer is a layer having and 1.8 or more refractive index made of an organic material and 0.5 below extinction coefficient, the The two absorbing layers are made of organic material and have a refractive index of less than 1.8 and 0.5
A third absorption layer comprising an organic material and having a refractive index of 1.8 or more and a refractive index of 0.5 or more.
A layer having the following extinction coefficient, or a layer made of an organic substance and having a refractive index in the range of 1.0 to 4.0 and an extinction coefficient of 1.0 or more. The difference between the optical film thickness of the pit portion and the optical film thickness of the inter-pit portion of the total of the one absorption layer and the second absorption layer is λ / 8 (where λ is the wavelength of the reproducing laser beam) or less. The difference between the optical film thickness at the groove bottom and the optical film thickness at the land is λ / 8 (where λ
Is the wavelength of the reproducing laser beam) or less.

Preferred embodiments of the information recording medium of the present invention are as follows. (1) The information recording medium as described above, wherein the difference between the refractive index of the first absorbing layer and the refractive index of the second absorbing layer is 0.5 or more.

(2) Difference between the refractive index of the third absorbing layer and the refractive index of the second absorbing layer when the third absorbing layer has a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less. Is 0.5 or more.

(3) The information recording medium as described above, wherein the extinction coefficient of at least one of the first, second and third absorption layers is 0.01 or more.

(4) The information recording medium as described above, wherein the organic substances in the first and third absorption layers are both dyes.

(5) The information recording medium as described above, wherein the organic substance of the second absorption layer is a polymer compound or a dye.

(6) The extinction coefficient of the second absorption layer is 0 to 0.3.
The information recording medium described above, wherein

(7) The organic material of the first absorption layer is at least one selected from indolizine dyes, imidazoquinoxaline dyes, thiazole dyes, indolenine dyes, merocyanine dyes and phthalocyanine dyes. The information recording medium described above.

(8) The organic material of the third absorbing layer is at least one selected from indolizine dyes, imidazoquinoxaline dyes, thiazole dyes, indolenine dyes, merocyanine dyes and phthalocyanine dyes. The information recording medium described above.

(9) The information recording medium as described above, wherein the organic substance of the second absorption layer is a polymer compound.

(10) The difference between the optical thickness at the groove bottom and the optical thickness at the land in the total of the first absorption layer and the second absorption layer of the light absorption layer is λ / 16 (where λ is (The wavelength of a reproduction laser beam) or less.

(11) The difference between the optical film thickness of the pit portion and the optical film thickness of the inter-pit portion in the total of the first absorption layer and the second absorption layer of the light absorption layer is λ / 16 (where λ Is the wavelength of the reproducing laser beam) or less.

(12) The information recording medium as described above, wherein the light absorbing layer has a thickness of 40 to 400 nm at the land and the pit.

(13) When the pre-groove is 0.2-1.
The above-mentioned information recording medium, having a half width of 4 μm and a depth of 5 to 80 nm.

(14) The pre-pit is 0.2 to 1.4.
The information recording medium as described above, which has a half width of μm and a depth of 60 to 300 nm.

(15) 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.

(16) The information recording medium as described above, wherein the reflectance of the mirror portion of the information recording medium is 50% or more.

(17) The information recording medium as described above, wherein the ratio of the reflectance of the groove bottom to the reflectance of the mirror portion is 70% or more.

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

The refractive index and extinction coefficient of each absorption layer of the present invention were measured as follows. A thin film having a thickness of 50 to 150 nm formed on a glass plate by a spin coater method was used as an absorption layer, and the absorption layer was measured at 23 ° C. using light having a wavelength of 780 nm.

The present inventors have conducted intensive studies to obtain an information recording medium having a layer structure such as an absorption layer which can be formed on a substrate only by coating and having a high reflectance. It has been reached.

In the information recording medium of the present invention, a light absorbing layer made of an organic substance such as a dye is provided on a substrate, and the light absorbing layer comprises a first absorbing layer and a second absorbing layer in order from the substrate side. made from a two-layer pair of composite absorbent layer or two sets and a third absorbent layer has a these three kinds of refractive index layers are identified respectively extinction coefficient, further, light The difference between the optical film thickness at the groove bottom and the optical film thickness at the land portion of the sum of the first absorption layer and the second absorption layer of the absorption layer, and the pit portion when pre-pits are additionally provided. Is equal to λ / 8 (where,
(λ is the wavelength of the reproducing laser beam) or less. Thus, the layer structure of the light absorbing layer, for example, the double
If the number of multiplexer absorption layer is set, from the substrate side, the first absorption layer - secondary absorbent layer - a third absorbent layer, when the number of the composite absorbent layer is two sets, from the substrate side, They are a first absorption layer, a second absorption layer, a first absorption layer, a second absorption layer, and a third absorption layer.

The structure of the information recording medium of the present invention will be described with reference to FIG. 1 which schematically shows a sectional view of the embodiment.

In FIG. 1A, the information recording medium 1 is
On a substrate 2, a first absorption layer 3 made of an organic substance, a second absorption layer 4 made of an organic substance, and a third absorption layer 5 made of an organic substance are provided.

The substrate 2 is provided with a pre-groove or a pre-groove and a pre-pit on its surface, and is preferably made of a plastic material. The refractive index of the substrate is generally around 1.6, and the extinction coefficient representing the degree of light transmission is close to zero.

The first absorbing layer 3 is made of an organic substance (preferably a dye) and has the following conditions (I): n ₁ ≧ 1.8 and k ₁ ≦ 0.5 (I) (where n ₁ is the first Is the refractive index of the absorption layer 3, and k ₁ is the extinction coefficient of the first absorption layer 3).

The above range is generally 4.0 ≧ n ₁ ≧ 1.8.
And 0 ≦ k ₁ ≦ 0.5, especially 3.8 ≧ n ₁ ≧ 2.0 and 0 ≦ k ₁ ≦ 0.3, more particularly 3.5 ≧ n ₁ ≧ 2.2 and 0 ≦ k ₁ ≦ 0 .2.

The first absorbing layer 3 can be formed by using a dye generally used as a material for the absorbing layer. That is, it can be formed by applying a coating solution in which a dye or the like is dissolved in a solvent by a spin coating method or the like (the optical film thickness of the groove bottom portion, land portion, pit portion and inter-pit portion of the light absorbing layer is the same as described above). A method of forming each absorption layer so as to satisfy the relationship described later will be described later). The first absorption layer 3 has a high refractive index (n ₁ ) and a low extinction coefficient (k ₁ ). Therefore, the difference in the refractive index between the substrate 2 and the first absorption layer 3 is large, and the reflectance at the interface between the substrate 2 and the first absorption layer 3 is generally about 30 to 40%. The extinction coefficient (k ₁ ) is low, and most light other than reflected light is transmitted.

The second absorbing layer 4 is made of an organic substance (preferably a polymer compound) and has the following condition (II): n ₂ <1.8 and k ₂ ≦ 0.5 (II) (where n ₂ is (The refractive index of the second absorbing layer 4 and k ₂ is the extinction coefficient of the second absorbing layer 4).

The above range is generally 1.0 ≦ n ₂ <1.8.
And 0 ≦ k ₂ ≦ 0.5, especially 1.0 ≦ n ₂ ≦ 1.7 and 0 ≦ k ₂ ≦ 0.3, more particularly 1.0 ≦ n ₂ ≦ 1.6 and 0 ≦ k ₂ ≦ 0. .1 is preferred.

The second absorption layer 4 can be formed by using a polymer compound having a low refractive index, a dye, or the like, and applying a coating solution in which these are dissolved in a solvent by a spin coating method or the like. The refractive index (n ₂ ) of the second absorption layer 4 is low, and light is slightly reflected at the interface between the first absorption layer 3 and the second absorption layer 4 due to the difference in the refractive index between the first absorption layer 3 and the second absorption layer 4. The difference between the refractive indices is preferably 0.5 or more, particularly preferably 1.0 or more. By taking such a large difference, the amount of scattered light other than reflected light that cannot be detected during recording and reproduction can be reduced. Since the extinction coefficient (k ₂ ) of the second absorption layer 4 is low, most of the light not reflected is transmitted. The second absorption layer 4 corresponds to a so-called enhance layer, and includes the first absorption layer 3 and the third absorption layer 5.
, The reflectance can be improved.

The third absorbing layer 5 is made of an organic substance (preferably a dye), and the third absorbing layer 5 meets the following condition (III).
Alternatively, it is a layer made of an organic material having a refractive index and an extinction coefficient that satisfy (IV). n ₃ ≧ 1.8 and k ₃ ≦ 0.5 (III) (where n ₃ is the refractive index of the third absorption layer 5 and k ₃ is the extinction coefficient of the third absorption layer 5)

The above range is generally 4.0 ≧ n ₃ ≧ 1.8.
And 0 ≦ k ₃ ≦ 0.5, especially 3.8 ≧ n ₃ ≧ 2.0 and 0 ≦ k ₃ ≦ 0.3, more particularly 3.5 ≧ n ₃ ≧ 2.2 and 0 ≦ k ₃ ≦ 0. .2.

1.0 ≧ n ₄ ≧ 4.0 and k ₄ ≧ 1.0 (IV) (where n ₄ is the refractive index of the third absorption layer 5 and k ₄ is the extinction of the third absorption layer 5) Decay coefficient)

The above range is generally 4.0 ≧ n ₄ ≧ 1.0
And 1.0 ≦ k ₄ ≦ 10, especially 3.5 ≧ n ₄ ≧ 1.0 and 1.2 ≦ k ₄ ≦ 8.0, more particularly 3.0 ≧ n ₄ ≧ 1.
It is preferable that 0 and 1.5 ≦ k ₄ ≦ 5.0.

The third absorption layer 5 is preferably a layer made of a dye, and may be either a layer satisfying the condition (III) or a layer satisfying the condition (IV).

Similarly to the above, the third absorbing layer 5 can be formed by applying a coating solution in which a dye or the like is dissolved in a solvent by a spin coating method or the like.

The third absorption layer 5 has a higher refractive index than the second absorption layer 4, and the interface between the second absorption layer 4 and the third absorption layer 5 is the interface between the substrate and the first absorption layer. A large amount of reflected light is obtained, which is equal to or larger than the amount of reflected light. This is because the refractive index of the second absorption layer 4 is set smaller than the refractive index of the substrate. The difference between the refractive indices of the second and third absorbing layers 5 is preferably 0.5 or more, particularly preferably 1.0 or more, like the difference between the first and second absorbing layers 4. Although the extinction coefficient (k ₃ ) is low, the reflectance is high as described above, and the amount of transmitted light is small.

The third absorbing layer 5 satisfying the above condition (IV)
The refractive index (n ₄ ) does not have to be high, but the extinction coefficient (k ₄ ) needs to be high. That is, since the extinction coefficient is high, the laser light from the second absorption layer 4 hardly passes through the third absorption layer 5, and most of the light is reflected, and shows a high reflectance.

As described above, the information recording medium of the present invention is an information recording medium in which the first absorption layer 3, the second absorption layer 4, and the third absorption layer 5 can all be formed by coating. Instead, it has a reflectance equal to or higher than the high reflectance obtained only when a metal reflection layer or an enhancement layer is conventionally provided on a dye absorption layer by a method other than a coating method such as sputtering. A first absorption layer having a high refractive index and a low extinction coefficient (corresponding to a normal dye absorption layer), a second absorption layer 4 having a low refractive index and a very low extinction coefficient (corresponding to a normal enhancement layer), and The third absorption layer 5 having the same high refractive index and low extinction coefficient as the first absorption layer or having a high extinction coefficient such as ordinary metal (corresponding to the ordinary reflection layer) is adopted. Thereby, an information recording medium having a high reflectance can be obtained. The reflectance is generally 50% or more, preferably 55% or more,
Particularly preferably 60% or more, and most preferably 65%
% Or more. By setting the refractive index and the extinction coefficient within the above ranges, the recording / reproducing characteristics are not impaired.
Further, the information recording medium of the present invention can record a signal of a long pit with an extremely small distortion as compared with an optical disc having a metal reflection layer on a dye absorption layer.

The information recording medium 1 shown in FIG. 1B has a first absorbing layer 3, a second absorbing layer 4, a first absorbing layer 3, a second absorbing layer 4, and a third absorbing layer 5 on a substrate 2. Is formed, and the contents of each layer are the same as those described with reference to FIG.

Next, the structure, usable materials and manufacturing method of the information recording medium of the present invention will be described in detail.

The material of the disc-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 substrate surface on the side where 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 / methacrylic acid. 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 Polymeric substances such as resins;
Organic substances such as silane coupling agents and titanate coupling agents; and inorganic dielectrics (SiO ₂ , ZnS,
Inorganic substances such as AlN and Si ₃ N ₄ ) and inorganic fluoride (MgF ₂ ) can be mentioned.

The undercoat layer is prepared, for example, by dissolving or dispersing the above substance in an appropriate solvent to prepare a coating solution, and then applying the coating solution to the substrate surface by a coating method such as spin coating, dip coating, or extrusion coating. Can be formed. The thickness of the undercoat layer is generally 0.0
In the range of 0.5 to 20 μm, preferably 0.01 to 1 μm.
The range is 0 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 is such that the groove depth (d _{1 in} FIG. 2 attached) is in the range of 5 to 80 nm and the half width of the groove (the width of the groove at half the depth of the groove). It 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. 20-50n
m and the half width of the groove is 0.35-0.
Most preferably, it is 6 μm. Grooves may be wobbled for addressing or linear velocity control.

In the present invention, pre-pits (ROM areas) in which information such as various application software and address signals are recorded in advance may be formed on the substrate surface (or undercoat layer surface). The shape of the pre-pit is such that the pit depth (d _{2 in} FIG. 3 attached) is 60 to
The half-width of the pit (the width of the pit at half the pit depth) is in the range of 300 to 300 nm;
1.4 μm is preferable and the pit depth is 70 μm.
２５０250 nm and the pit half width is 0.3
More preferably, the pit depth is in the range of 90 to 200 nm and the pit half width is 0.4 to 0.7 μm.

In the case where a prepit is formed, the depth of the pregroove is represented by λ / 16 (where λ is the wavelength of the reproducing laser beam and is expressed by the optical path length, as compared with the depth of the prepit). 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.

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

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 pregroove layer is generally in the range of 0.1 to 100 μm, preferably in the range of 0.1 to 50 μm.

On a substrate (or pre-groove layer) on which pre-grooves or pre-pits are formed, using a material similar to the material for forming the undercoat layer, a solvent in a coating solution for forming a light absorbing layer is used. A solvent-resistant layer may be provided for protection from the solvent.

On the substrate (or undercoat layer), a light absorbing layer including the above-described first absorbing layer, second absorbing layer, and third absorbing layer is provided. 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 organic material of the first absorbing layer may be any organic material having a refractive index and an extinction coefficient satisfying the above condition (I). In general, the wavelength of the absorption maximum is selected from dyes that are 50 to 200 nm shorter than the recording or reproduction wavelength of the laser.

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, the use of a semiconductor laser that oscillates near-infrared light as a recording / reproducing laser has been put to practical use.
Dyes having a high absorptance to light in the near infrared region of the above 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 dye used as the material for the first absorbing layer is preferably a cyanine dye, an azulenium dye or a squarylium dye. Among the cyanine dyes, a merocyanine dye, a phthalocyanine dye,
Naphthalocyanine dyes, naphthoindolenine dyes and imidazoquinoxaline dyes are preferred.

In the information recording medium of the present invention, the difference between the optical thickness at the bottom of the groove and the optical thickness at the land, which is the sum of the first absorption layer and the second absorption layer of the light absorption layer, is λ. / 8
It is characterized by the following. Further, when the information recording medium of the present invention further has a pre-pit on the substrate, the optical film thickness of the pit portion and the optical thickness of the inter-pit portion, which are the total of the first absorption layer and the second absorption layer of the light absorption layer. Λ / 8
It is characterized by the following. In order to form the light absorbing layer so that the optical film thickness of the light absorbing layer has the above relationship, each of the absorbing layers constituting the light absorbing layer, that is, the first absorbing layer and the second absorbing layer It is necessary to form each absorption layer so that the optical film thickness satisfies the above conditions.

When the second absorbing layer is made of a polymer compound, as will be described later, the difference between the optical film thickness at the bottom of the groove and the optical film at the land, and the optical film at the pit, as described later. And the optical film thickness between the pits is not substantially different. Therefore, in order to make the difference in the optical film thickness of the total of the first absorption layer and the second absorption layer of the light absorption layer equal to or smaller than λ / 8, when the number of the first absorption layer is one, The difference between the optical thickness at the groove bottom and the optical thickness at the land and the difference between the optical thickness at the pit and the optical thickness at the inter-pit in one absorption layer are reduced to λ / 8 or less. I just need. When the number of the first absorption layers is two, the difference between the optical thickness of the groove bottom and the optical thickness of the land portion, and the optical thickness of the pit portion, is the total of the two first absorption layers. The difference between the film thickness and the optical film thickness between the pits is λ
/ 8 or less.

Accordingly, the optical thickness of the first absorption layer of the light absorption layer will be described in detail with reference to the accompanying drawings.

FIG. 2 is a cross-sectional view schematically showing a part of a cross-section in a pre-groove region of an intermediate product having a first absorption layer formed on a substrate in a manufacturing process of an embodiment of the information recording medium of the present invention. FIG. FIG. 3 is a cross-sectional view schematically showing a part of a cross-section of the intermediate product in a pre-pit region. FIG. 4 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. 4, a light absorbing layer 32 made of a dye is formed on the surface of a substrate 31 made of plastic. A pregroove 33 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 35 of the pre-groove 33 is
The thickness is larger than the thickness t ₅ of the light absorption layer 32 of the land portion 34 of the substrate 31. As a result, the depth of the groove shape on the outer surface of the light absorbing layer 32 that comes into contact with air becomes smaller than the depth d _{3 of the} groove 34, and is recorded on the pre-groove 33 by irradiating a laser beam for recording information. When the pits are formed, the phase difference between the upper part (the part corresponding to the land part of the substrate) of the groove of the light absorbing layer 32 and the bottom part becomes small, so that there is a problem that the modulation degree of the recording pit 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. 2, a first absorbing layer 12 made of a dye is formed on the surface of a substrate 11 made of plastic. A pregroove 13 is formed on the substrate 11. The first absorption layer 12 is formed by applying a solution for forming a first absorption layer having specific properties as described below, prepared by dissolving a dye in a solvent, by a spin coating method and drying. Optical film thickness (n _r · t ₂ ) of first absorption layer 12 at groove bottom 15 of pre-groove 13
(Where n _r is the refractive index of the first absorbing layer, t ₂ is the thickness of the first absorbing layer 12 at the groove bottom 15) and the optical characteristics of the first absorbing layer 12 of the land 14 of the substrate 11. Target film thickness (n
_r · t ₁ ) (where n _r is the refractive index of the first absorption layer,
t ₁ is a film thickness of the first absorption layer 12 of the land portion 14). As a result, the depth of the groove on the outer surface of the first absorption layer 12 which comes into contact with air is the same as the depth d ₁ of the groove 13 or smaller than the optical thickness by λ / 8 or less. The phase difference between the groove portion and the land portion of the absorption layer 12 is large and the modulation degree of 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 13 can be reduced, and the reflectance 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. 3, a first absorbing layer 22 made of a dye is formed on the surface of a substrate 21 made of plastic. The substrate 21 has pre-pits 23 formed thereon. The first absorbing layer 22 is formed by applying a solution for forming the first absorbing layer having a specific property by a spin coating method and drying it, as described later, prepared by dissolving a dye in a solvent. Pit section 25 of pre-pit 23
Optical thickness (n _r · t ₄ ) of the first absorption layer 22 (where,
n _r is the refractive index of the first absorption layer, and t ₄ is the pit 25
Of the first absorption layer 22) and the optical thickness (n _r · t ₃ ) of the first absorption layer 22 in the inter-pit portion 24 of the substrate 21.
(Where n _r is the refractive index of the first absorption layer, and t ₃ is the thickness of the first absorption layer 22 in the inter-pit portion 24).
It is formed so as to be λ / 8 or less. As a result, the depth of the hole shape on the outer surface of the first absorption layer 22 that comes into contact with the air 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 absorption layer 22 is large, and the modulation degree of the pit is large. As a result, even if the first absorption layer is formed in the pit formation region of the substrate, the pits of the substrate can be reproduced with a high degree of modulation.

The difference between 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.

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 thickness of the land portion and the portion between the pits of the first absorption layer is 10 to 1000 nm, particularly 30 to 1000 nm.
It is preferably 500 nm, more preferably 40 to 300 nm.

The difference between the optical thickness of the first absorbing layer having the specific optical thickness as described above, that is, the optical thickness of the first absorbing layer at the bottom of the groove and the optical thickness of the first absorbing layer at the land portion. Is λ / 8
And a dye for forming the first absorption layer in which the difference between the optical thickness of the first absorption layer in the pit portion and the optical thickness of the first absorption layer in the inter-pit portion is λ / 8 or less. The solution is a dye solution with a concentration limit of 99-20%. 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 application temperature of the dye solution, It is defined as meaning the ratio to the original volume. For example, when the solvent is evaporated while the dye solution in which the dye is dissolved in the solvent is maintained at the application temperature for forming the first absorption layer, the volume decreases with the evaporation of the solvent, and the solvent is eventually dissolved. The dye solution precipitates, and 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. A dye solution with a limit of 90%.

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 to form the first absorption layer is a dye solution having a concentration limit of 99 to 20%, but has a concentration limit of 99 to 30%, particularly 95 to 40%, and more particularly 90 to 90%. It is preferable that the dye solution is ５０50%. If the concentration limit of the dye solution is larger than the above range, the film thickness of the first absorption layer becomes non-uniform as a whole, and if it is smaller than the above range, the optical absorption of the first absorption layer between the groove bottom and the land is reduced. The difference in the film thickness and the difference in the optical film thickness of the first absorption layer between the pit portion and the pit portion are increased.

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,
Ethylene glycol monoethyl ether, acetate,
Ester solvents such as cellosolve acetate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; dichloromethane, 1,2-dichloroethane, chloroform;
Halogenated hydrocarbon solvents such as methyl chloroform, trichlene, carbon tetrachloride, tetrachloroethylene, etc .; 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, benzyl alcohol; amide solvents such as dimethylformamide; 2,2,3,3 - fluorinated alcohols such as tetrafluoropropanol, fluorine-substituted ketone, a fluorine-substituted ester, a fluorine-substituted amide, fluorine-substituted ether , Fluorine-substituted aromatic hydrocarbons,
Fluorinated solvents such as fluorine-substituted aliphatic hydrocarbons and the like can be mentioned.

There is no particular limitation on the dye solution as long as the dye solution satisfies the above-mentioned concentration limit. In order to form the dye, the concentration of the dye in the dye solution is 0.5 to 14% by weight, especially 1%.
It is preferably from 10 to 10% by weight, more preferably from 1.5 to 8% by weight.

The dye solution further contains an antioxidant,
Various additives such as a UV absorber, a plasticizer, and a lubricant may be added 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 carried out using an apparatus 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.

The second absorption layer is provided on the first absorption layer. As the organic substance of the material of the second absorption layer, any substance having a refractive index and an extinction coefficient that satisfy the above condition (II) may be used.

As a material satisfying the above formula (II), a high molecular compound can be mentioned. For example, phenolic resin,
Melamine resin, allyl resin, epoxy resin, polyimide, polyvinyl chloride, polyvinylidene chloride, polyvinyl chloride / polyvinyl acetate copolymer, polyvinylidene fluoride, polyethylene, ethylene / vinyl acetate copolymer, ionomer resin, polypropylene, polybutylene , Polystyrene, acrylonitrile-styrene copolymer, AB
S resin, acrylic resin such as polymethyl methacrylate, polyvinyl acetate, polycarbonate, polyacetal, chlorinated polyethylene, chlorinated polyether, polyamide,
Examples include fluorine resin, polyphenylene oxide, cellulose acetate resin, cellulose nitrate resin, cellulose acetate butyrate resin, polybutadiene, acrylonitrile resin, polyethylene terephthalate, and polybutene.

A dye may be used as a material for the second absorbing layer. Such dyes generally have a wavelength of absorption maximum of 200 or more than the recording or reproducing wavelength of the laser.
Dye on the short wavelength side of about nm or more, or 100 nm
It can be selected from dyes on the longer wavelength side than the extent. Preferred are cyanine dyes, merocyanine dyes, phthalocyanine dyes and naphthalocyanine dyes.

When a polymer compound is used as the material of the second absorbing layer, a solution is prepared using the above-mentioned solvent, and the second absorbing layer can be formed by spin coating. In this case, unlike the case where the dye-containing layer is formed, the difference between the optical thickness of the second absorption layer at the bottom of the groove and the optical thickness of the second absorption layer at the land, and the difference between the optical thickness of the pit and the second absorption layer. There is substantially no difference between the optical thickness of the two absorption layers and the optical thickness of the second absorption layer between the pits. When using a dye as a material for the second absorption layer, use a dye solution having a specific concentration limit as described for the formation of the first absorption layer, and form the second absorption layer by spin coating. Can be.

The third absorbing layer is provided on the second absorbing layer. As the organic material of the material of the third absorption layer, the above-mentioned conditions (III)
Alternatively, any material having a refractive index and an extinction coefficient that satisfy (IV) may be used.

The organic material satisfying the above formula (III) can be substantially the same as the material of the first absorbing layer.

The organic substance satisfying the above formula (IV) includes
Dyes having a wavelength of the absorption maximum near the recording or reproducing wavelength of the laser are preferred. Preferred are cyanine dyes, merocyanine dyes, phthalocyanine dyes and naphthalocyanine dyes.

Since the third absorption layer functions as a reflection layer as described above, as described for the first absorption layer, the difference between the optical thickness at the groove bottom and the optical thickness at the land and the pit portion It is not necessary to particularly consider reducing the difference between the optical film thickness of the pits and the optical film thickness between the pits. Therefore, it can be formed using a conventional dye film forming method. Of course, using dye solutions having specific concentration limits as described for the formation of the first absorbing layer,
It can also be formed by a spin coating method.

The layer thicknesses of the first, second and third absorbing layers are generally in the range of 10 to 1000 nm, as measured at the lands or the pits, and are preferably It is in the range of 30 to 500 nm, particularly preferably in the range of 40 to 300 nm.

When a binder is used in combination as the material of the dye layer, the binder, the first absorption layer, the second absorption layer, and the third absorption layer must be formed so as not to depart from the specific refractive index and extinction coefficient ranges of the present invention. It is necessary to use. The ratio of dye to binder is generally in the range of 0.01-99% (weight ratio), preferably in the range of 1.0-95% (weight ratio).

For the three layers of the first, second and third absorption layers, for example, three nozzles are attached to a spinner used for spin coating, and the operations of coating and drying for forming each layer are sequentially performed. It can be formed by performing it continuously. Therefore, the formation of the absorbing layer on the substrate can be performed very easily.

In the information recording medium of the present invention, a protective layer may be provided on the light absorbing layer for the purpose of physically and chemically protecting the light absorbing 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.

The above-mentioned material for forming the protective layer is mixed with the material for forming the third absorbing layer of the light absorbing layer to form the third absorbing layer, so that the third absorbing layer also functions as the protective layer. .

[0113] 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 light absorbing layer. Alternatively, it may be provided by a method such as vacuum deposition, sputtering, or coating.

The two information recording media of the present invention face each other so that their light absorbing layers are on the inside, and a ring-shaped inner spacer is formed so that a space is formed between the two information recording media. The two information recording media can be joined together with the intermediary of the and the ring-shaped outer spacer to form an information recording medium having an air sandwich structure. In this information recording medium having an air sandwich structure, the light absorbing layer does not come into direct contact with the outside air, and information is recorded and reproduced by laser light transmitted through the substrate. There is no damage or dust adhered to the surface, which does not hinder the recording and reproduction of information. One of the information recording media having the air sandwich structure may be a substrate having no light absorbing layer (prepits may be provided), and the information recording medium may be provided on the light absorbing layer. A protective layer may be provided on the surface of the substrate on which the light absorbing layer is not provided.

The information recording medium of the present invention having the above-mentioned structure has an extremely high reflectance, but is provided on the third absorbing layer or between the third absorbing layer and the protective layer. A reflective layer may be provided. In this case, higher reflectance can be obtained, but the advantage that the information recording medium can be manufactured only by coating is lost.

The light-reflective substance as the material of the reflection layer is a substance having a high reflectance to laser light, and examples thereof include Mg, Se, Y, Ti, Zr, Hf, V, Nb, Ta,
Cr, Mo, W, Mn, Re, Fe, Co, Ni, R
u, Rh, Pd, Ir, Pt, Cu, Ag, Au, Z
n, Cd, Al, Ga, In, Si, Ge, Te, P
Metals and metalloids such as b, Po, Sn, Bi, and Sb can be mentioned. Of these, preferred is A
1, Au, Cr and Ni. 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 substrate by, for example, vapor deposition, sputtering or ion plating of the above-mentioned light reflective substance. The thickness of the reflective layer is generally in the range from 10 to 300 nm.

The 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 700 to 900 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.

[0119] The pits after the above-mentioned recording are formed in such a manner that the substrate and / or the dye are heated by the irradiation of the 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.

When the extinction coefficient of the first absorption layer is close to 0, the pits are formed only in the third absorption layer. Otherwise, the pits are formed in the first absorption layer and the pits are formed in the first absorption layer. It is believed that the absorbing layer also deforms. Also, when the energy of the laser is large, pit formation and deformation may occur in the second absorption layer. Further, when the extinction coefficients of the first and third absorption layers are set to almost 0 and a dye is used for the second absorption layer, it is possible to record on the second absorption layer. However, it is generally difficult to record on only one layer, and the influence on other layers cannot be avoided.

At the time of recording, tracking control is performed by the push-pull method or the like using the tracking pre-groove. Recording of information is performed on the pre-groove grooves or lands between the grooves.

Information is reproduced by, for example, a three-beam method by irradiating a semiconductor laser beam from the substrate side while detecting the reflected light while rotating the recording medium at the same constant linear velocity or constant angular velocity as described above. Information can be reproduced while performing tracking control.

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 a signal modulation degree and a reproducing C / N. In addition, the tracking property at the time of recording, particularly the tracking property by the push-pull method is excellent. Further, in the case of the information recording medium of the present invention provided with a ROM area, a reproduced signal having a high modulation degree can be obtained even in the ROM area.

[0124]

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: 120 nm) in which an EFM signal was recorded was formed in an area of 46 mm to 80 mm in diameter, and a pre-pit was formed in an area of 80 mm to 118 mm in diameter. Groove (track pitch: 1.6 μm, half width of groove:
Disc-shaped polycarbonate substrate (outer diameter: 120 mm, on which 0.55 μm, groove depth: 40 nm) is formed
Inner diameter: 15 mm, thickness: 1.2 mm, refractive index: 1.5
8) was prepared.

On the other hand, the dye (A) having the following structural formula (A) is dissolved in a mixed solvent of 2,2,3,3-tetrafluoropropanol and ethyl cellosolve in a volume ratio of 80:20, A coating solution for forming a first absorption layer containing 2.25% by weight of the dye (A) was prepared and maintained at 23 ° C. The concentration limit of this coating solution at 23 ° C. was 60%.

[0127]

Embedded image

Also, 1,2-polybutadiene (No. 668, manufactured by Scientific Polymer Products)
0.6 g of cyclohexane 15 cc and n-nonane 10 c
c to prepare a coating solution for forming a second absorbent layer, which was maintained at 23 ° C.

Further, the same coating solution for forming the first absorption layer was prepared as the coating solution for forming the third absorption layer.

The coating liquid for forming the first absorption layer was applied to the prepit and pregroove forming surface of the substrate at 23 ° C. by a spin coating method at a substrate rotation speed of 200 rpm for 5 seconds, and then rotated at 1400 rpm. After drying at pm for 30 seconds, a first absorption layer having an optical thickness shown in Table 1 was formed.

On the first absorbing layer, the coating solution for forming the second absorbing layer was applied by a spin coating method at a rotation speed of 1400 rpm for 30 seconds and dried to obtain an optical film having an optical film thickness shown in Table 1. A second absorption layer was formed.

On the second absorbing layer, a third absorbing layer having an optical film thickness of 220 nm on the land was formed in the same manner as the formation of the first absorbing layer using the above-mentioned coating solution for forming the third absorbing layer.

As described above, the optical information recording medium (FIG. 1) comprising the substrate, the first absorption layer, the second absorption layer, and the third absorption layer.
(A)).

In the obtained information recording medium, in the pre-groove formation region, the optical film thickness of the first absorption layer and the second absorption layer at the bottom of the groove, and the optical thickness of the first absorption layer and the second absorption layer at the land portion. In the pre-pit formation region, the film thickness and the mirror part reflectivity are the optical film thickness of the first absorption layer and the second absorption layer in the pit portion, and the optical film thickness of the first absorption layer and the second absorption layer in the inter-pit region. , And 11T modulation were measured by the following evaluation methods. Table 1 shows the evaluation results.

The refractive index and extinction coefficient of each absorption layer (each material was coated as described above and a thin layer (50 to 1
50 nm), and the reflectance and transmittance were measured and determined. First absorption layer [Refractive index (n ₁ ): 2.6, extinction coefficient (k ₁ ): 0.0
6] Second absorption layer [Refractive index (n ₂ ): 1.5, extinction coefficient (k ₂ ): 0] Third absorption layer [Refractive index (n ₃ ): 2.6, extinction coefficient (k ₃₎ ): 0.0
6]

Example 2 In Example 1, Dye A used in the coating solution for forming the first absorption layer and the coating solution for forming the third absorption layer was changed to Dye B having the following structural formula (B). An optical information recording medium was manufactured in the same manner as in Example 1 except for the above.

[0137]

Embedded image

Example 1 of the obtained information recording medium
The same evaluation items as described in the above were measured in the same manner. Table 1 shows the evaluation results.

The refractive index and extinction coefficient of each absorption layer were as follows. First absorption layer [Refractive index (n ₁ ): 2.6, extinction coefficient (k ₁ ): 0.0
7] Second absorbing layer [Refractive index (n ₂ ): 1.5, extinction coefficient (k ₂ ): 0] Third absorbing layer [Refractive index (n ₃ ): 2.6, extinction coefficient (k ₃₎ ): 0.0
7]

Comparative Example 1 Information was prepared in the same manner as in Example 1 except that the coating solutions prepared as described below were used as the coating solution for forming the first absorbing layer and the coating solution for forming the third absorbing layer. A recording medium was manufactured.

Coating solution for forming first absorption layer: The above-mentioned dye (A) is dissolved in 2,2,3,3-tetrafluoropropanol, and the first solution containing 2.25% by weight of dye (A) A coating solution for forming an absorbing layer was prepared. The critical concentration of this coating solution at 23 ° C. was 10% or less.

Coating solution for forming the third absorption layer: The same as the coating solution for forming the first absorption layer.

Example 1 for the obtained information recording medium
The same evaluation items as described in the above were measured in the same manner. Table 1 shows the evaluation results. The refractive index and the extinction coefficient of each absorption layer were the same as in Example 1.

Comparative Example 2 Information was prepared in the same manner as in Example 1 except that the coating solutions prepared as described below were used as the first absorbing layer forming coating solution and the third absorbing layer forming coating solution. A recording medium was manufactured.

Coating solution for forming the first blotting layer: The above-mentioned dye (B) is dissolved in 2,2,3,3-tetrafluoropropanol, and the first dye containing 2.25% by weight of the dye (B) is dissolved. A coating solution for forming an absorbing layer was prepared. The concentration limit of this coating solution at 23 ° C. was 10% or less.

Coating solution for forming third absorbing layer: The same as the above-mentioned coating solution for forming first absorbing layer.

Example 1 of the obtained information recording medium
The same evaluation items as described in the above were measured in the same manner. Table 1 shows the evaluation results. The refractive index and the extinction coefficient of each absorption layer were the same as in Example 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 (KEN-WOO).
Using D), recording was performed on the bottom of the pre-groove at a laser power (recording power) of 4 mW and a linear velocity of 1.3 m / sec during recording.

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

2) Optical film thickness of the absorption layer at the land portion The optical film thickness was obtained in the same manner as in the above method 1).

3) Optical film thickness of absorption layer in pit portion The optical film thickness was obtained in the same manner as in the above method 1).

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

5) Mirror reflectivity Using an aluminum plate having a known reflectivity as a reference,
The measurement was performed using a spectrophotometer (UV130 manufactured by Shimadzu Corporation).

6) 11T modulation degree The recording length of the CD format signal recorded above is 11
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)

[0155]

[Table 1]

As is clear from Table 1, the information recording medium of the embodiment has a high reflectivity in the pre-groove forming area (information recording area) and a large 11T modulation degree in the pre-pit forming area (ROM area). It has performance.

On the other hand, the information recording medium of the comparative example is
Although the reflectivity in the pre-groove formation region was almost the same as that of the information recording medium of the embodiment, the pre-pit formation region (RO
The 11T modulation degree in the (M region) was lower than that of the information recording medium of the example.

[0158]

The information recording medium of the present invention is an information recording medium having three or more absorbing layers having a specific refractive index and extinction coefficient on a substrate, which can be easily formed by coating. By adopting such a configuration, it is possible to obtain an information recording medium having high reflectance while having a great advantage that it can be obtained by a simple manufacturing method.

In the information recording medium of the present invention, the optical film thickness of the light absorbing layer containing the dye is small between the groove bottom and the land. This is an extremely excellent information recording medium in which the depth of the groove on the surface is sufficiently large, the sensitivity is high, and a reproduced signal having a high degree of modulation can be obtained after recording information by irradiating a laser beam.

In the information recording medium of the present invention, a light-absorbing layer containing a dye is also formed in a region where a pre-pit is formed, and a reproduced signal having a high degree of modulation can be obtained from the region where the pre-pit is formed. Therefore, the thickness of the light absorbing layer can be made uniform over the entire surface of the information recording medium, and the ROM area in which the prepits are formed and the recordable area in which the pregroove is formed can be formed, for example. The information recording medium can be provided at an arbitrary place such as a mixture of both areas, and is notably limited in the type and use method of application software, and is a remarkably excellent information recording medium that can be used for a wide range of applications.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a cross section of an embodiment of the information recording medium of the present invention. (A) has three light absorbing layers, and (B) has five light absorbing layers.

FIG. 2 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. 3 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. 4 is a cross-sectional view schematically showing a part of a cross-section in a pre-groove area of a conventionally known information recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Information recording medium 2 Substrate 3 First absorption layer 4 Second absorption layer 5 Third absorption layer 11, 21, 31 Substrate 12, 22, 32 Absorption layer 13, 33 Pregroove 23 Prepit 14, 34 Land portion 24 Inter-pit portion 15, 35 Groove bottom 25 pit

Claims (2)

(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 substrate having a pregroove formed on a surface thereof. An information recording medium comprising the light absorbing layer,
In order from the substrate side, two consisting of the first absorbent layer and a second absorbent layer
It consists of a set of layers a pair of composite absorbent layer or two sets and the third absorbent layer, and the first absorbing layer, and 1.8 or more refractive index made of an organic material and 0.5 following extinction coefficient Wherein the second absorption layer is made of an organic material and has a refractive index of less than 1.8 and an extinction coefficient of 0.5 or less; and the third absorption layer is made of an organic material; A layer having a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less, or a layer made of an organic material and having a refractive index in the range of 1.0 to 4.0;
A layer having an extinction coefficient of 0 or more, and furthermore, the difference between the optical thickness of the groove bottom and the optical thickness of the land in the total of the first absorption layer and the second absorption layer of the light absorption layer. λ
/ 8 (where λ is the wavelength of the reproduction laser beam) or less. 2. A light-absorbing layer containing a dye capable of recording information by irradiating a laser beam on a disk-shaped substrate having prepits and pregrooves formed on its surface to form reproduction pits. An information recording medium provided,
Light absorbing layer, in order from the substrate side and a pair or two pairs and the third absorption layer of the first absorbing layer and the two layers a pair of composite absorbent layer made of the second absorbent layer, and a first absorption The layer is made of an organic material and has a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less, and the second absorption layer is made of an organic material and has a refractive index of less than 1.8 and 0.5. The third absorption layer is made of an organic material and has a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less, or 1. Refractive index in the range of 0-4.0 and 1.
A layer having an extinction coefficient of 0 or more, and further, a difference between the optical film thickness of the pit portion and the optical film thickness of the inter-pit portion of the total of the first and second absorption layers of the light absorption layer. Is λ /
8 (where λ is the wavelength of the laser beam for reproduction) and the difference between the optical film thickness at the bottom of the groove and the optical film at the land is λ / 8 (where λ is the wavelength of the laser beam for reproduction). ) An information recording medium characterized by the following.