JPH04255929A - Information recording medium - Google Patents

Abstract

PURPOSE:To obtain an information recording medium with high reflectance by providing at least three absorbing layers having particular refractive index and extinction coefficient easily formed by coating. CONSTITUTION:The information recording medium is provided with light absorbing layers capable of recording information by irradiating a disk-shaped substrate whose surface is formed with a pre-group by a laser beam and forming a pit for reproduction. A first absorbing layer consists of organic substance and has the refractive index of 1.8 or above and the extinction coefficient of 0.5 or below; a second absorbing layer consists of organic substance and has the refractive index of below 1.8 and the extinction coefficient of 0.5 or below; a thrid absorbing layer consists of organic substance and has the refractive index within the range of 1.0 to 4.0 and the extinction coefficient of 1.0 or above. The difference in the optical film thickness of the sum of the first and second layers and that of the land part is lambda/8 or below.

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 using 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 large-capacity computer disk memory.

[0003] DRAW that can write (record) information
(Direct Read After Write
) type information recording media have been developed and some have been put into practical use. The basic structure of such a DRAW type information recording medium (optical disk) is a disc-shaped transparent substrate made of plastic, glass, etc., and Bi, Sn, and I
It has a recording layer made of a metal or semimetal such as n, Te, etc., or a recording layer made of a dye. Information is recorded on an optical disk by, for example, irradiating the optical disk with a laser beam, and the irradiated portion of the recording layer absorbs the light and locally increases in temperature, resulting in physical changes such as pit formation or Information is recorded by causing chemical changes such as phase changes to change its optical properties. Reading (reproducing) information from an optical disc is also performed by irradiating the optical disc with a laser beam, and the information is reproduced by detecting reflected or transmitted light that corresponds to changes in the optical characteristics of the recording layer. Ru.

[0004] Laser beam irradiation for recording and reproducing information on the optical disc is usually performed at a predetermined position on the disc surface. In order to guide the laser beam so that it accurately follows the intended irradiation position (generally referred to as tracking), a grooved tracking guide (pregroove) is generally provided on the surface of the substrate.

By the way, a recording layer containing a dye is generally formed by coating a solution containing a dye on a substrate on which pregrooves are formed and drying it.
The thickness of the dye recording layer at the groove bottom is thicker than the thickness of the dye recording layer at the land. Therefore, the depth of the grooves on the surface of the dye recording layer, which are formed to reflect the shape of the pregroove grooves on the substrate, is shallower than the depth of the pregroove grooves on the substrate. When recording pits are formed on the surface of the dye recording layer, the phase difference between the top of the groove on the surface of the dye recording layer (the part reflecting the land area of the substrate) and the bottom of the groove becomes smaller, so the modulation degree of the recording pit becomes smaller. There is a problem.

[0006] To this end, it is conceivable to increase the modulation degree of the recording pit by increasing the depth of the pregroove of the substrate and making the depth of the groove formed on the surface of the dye recording layer relatively deep. However, in that case, the reflectance generally tends to decrease.

[0007] When the thickness of the dye recording layer at the bottom of the groove of the substrate and the thickness of the dye recording layer at the land portion are approximately the same, the depth of the pregroove of the substrate can be reduced, and these problems can be solved at the same time. The resulting information recording medium has both a large modulation degree and a large reflectance.

[0008] Furthermore, R with pits formed in advance on the substrate
An information recording medium having an OM area and a recordable area in which pits for data reproduction are formed by laser beam irradiation has been proposed (see Japanese Patent Laid-Open No. 2-42652). In this information recording medium, the laser absorption layer made of dye is provided only in the recordable area, and the laser absorption layer made of dye is not provided in the ROM area in which prepits are formed. The reason for this is that if a laser absorption layer made of dye is provided in the region where pre-pits are formed, the degree of modulation of the pre-pit signal becomes small, making it impossible to practically reproduce information in the ROM area.

That is, a laser absorption layer made of a dye is generally formed by applying a dye solution and drying it, and when the dye solution is applied to the pre-pit forming area, the dye solution is applied to the pre-groove forming area. As in the case of coating, the thickness of the laser absorption layer in the pit portion (hole) is the same as the thickness of the laser absorption layer in the inter-pit portion (the area between the pits, which corresponds to the land portion). Therefore, the depth of the hole on the surface of the laser absorption layer, which is formed to reflect the shape of the pit on the substrate, is shallower than the depth of the pit on the substrate, and the distance between the pit and the area between the pits is smaller than the depth of the pit on the substrate. Since the phase difference between the pre-pits and the pre-pits becomes smaller, the degree of modulation of the pre-pits becomes smaller.

However, in an information recording medium in which a dye layer is not provided in the pre-pit area (ROM area) and is provided only in the recordable area, as described in Japanese Patent Application Laid-Open No. 2-42652, It is difficult to form the boundary with good reproducibility at the boundary between the layered part and the part without the dye layer, or the film thickness tends to be uneven at the edge of the dye layer. There are problems such as the tendency for eccentricity of the annular dye layer to occur. Furthermore, in reality, it is only possible to manufacture an information recording medium that is divided into two areas, a ROM area and a recordable area on the outer circumferential side of the ROM area, and an additional recordable area is provided on the inner circumferential side of the ROM area. Also, it is extremely difficult to provide a ROM area and a recordable area in a mixed manner, which limits the application software that can be recorded in advance in the ROM area and how to use it, making it inconvenient in practice. be.

[0011] When the thickness of the dye layer in the pre-pit portions of the substrate and the thickness of the dye layer in the inter-pit portions are approximately the same, the phase difference between the pre-pits becomes large, resulting in an information recording medium in which the degree of modulation of the pre-pits is large.

Even if a laser light absorbing layer made of dye is formed in the pre-pit portion, if the degree of modulation of the pre-pit is large, both the pre-pit forming area (ROM area) and the pre-groove forming area (recordable area) contain the dye. It becomes possible to form a light absorption layer, and the above problems are solved.

[0013] By the way, in a normal DRAW type information recording medium (optical disk), recording is generally performed at a high linear velocity, but a particularly high reflectance is not required. On the other hand, CD-DR records at a slow linear velocity using the CD format signal used in compact discs (CDs).
AW requires high reflectance. In other words, CD-Ds on which information is recorded have a high reflectance.
This provides the great advantage of being able to play RAW on a commercially available CD player.

[0014] As a method for improving the reflectance, it is generally practiced to provide a metal reflective layer on a light absorbing layer containing a dye. Also, EP0 of the European Patent Publication Publication
353393A2 and EP0353394A2 disclose the provision of an enhancement layer between the dye absorbing layer and the metal reflective layer in order to further improve the reflectance. Materials for the enhancement layer include SiO, SiO2, Si
Inorganic materials such as 3 N4 and AlN have been described.

However, when a reflective layer or an enhancement layer is provided on the light absorption layer in order to increase the reflectance of the former,
It is necessary to form the reflective layer and the enhancement layer by a vapor deposition method such as sputtering, which requires expensive equipment.
There are significant manufacturing disadvantages, such as the fact that it takes a long time to form the layers.

[0016]

[Problem to be Solved by the Invention] Can be manufactured by a manufacturing method including a simple film forming step by coating.
An object of the present invention is to provide an information recording medium that can obtain a reproduced signal with a high degree of modulation after recording information by irradiating laser light, has good tracking characteristics, and has a high reflectance.

[0017] Furthermore, it is an object of the present invention to provide an information recording medium in which a light absorption layer containing a dye is also formed in the region where the pre-pits are formed, and in which a reproduced signal with a high degree of modulation can be obtained from the region where the pre-pits are formed. That's true.

[0018]

[Means for Solving the Problems] The present invention provides a dye that can record information by irradiating laser light onto a disc-shaped substrate with pregrooves formed on the surface to form pits for reproduction. The information recording medium is provided with a light absorption layer containing, in order from the substrate side, one or two repeating layer units consisting of a first absorption layer and a second absorption layer, and a third repeating layer unit. and the first absorption layer is a layer made of an organic substance 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 substance and has an extinction coefficient of 0.5 or less. A layer having 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 and has 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 within the range of 1.0 to 4.0 and an extinction coefficient of 1.0 or more, and further comprising a first absorption layer and a second absorption layer of the light absorption layer. Information characterized in that the difference between the total optical thickness of the groove bottom and the land part of the two absorption layers is λ/8 or less (where λ is the wavelength of the reproduction laser beam) It is a recording medium.

Another aspect of the present invention is to produce a dye that can record information by irradiating a laser beam onto a disc-shaped substrate on which pre-pits and pre-grooves are formed to form pits for reproduction. An information recording medium comprising a light absorption layer comprising one or two repeating layer units consisting of a first absorption layer and a second absorption layer and a third absorption layer in order from the substrate side. and the first absorption layer is made of an organic substance and has a refractive index of 1.8 or more and a refractive index of 0.5.
A layer having an extinction coefficient of: , a layer made 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 made of an organic substance and having a refractive index of 1.0 to 4
．． It is a layer having a refractive index within the range of 0 and an extinction coefficient of 1.0 or more, and further, the optical thickness of the pit portion of the total of the first absorption layer and the second absorption layer of the light absorption layer. The difference between the optical film thickness between the pits is λ/8 (where λ is the wavelength of the reproduction laser beam) or less, and the difference between the optical film thickness at the bottom of the groove and the optical film thickness at the land part is The information recording medium is characterized in that it has a wavelength of λ/8 (where λ is the wavelength of a reproduction laser beam) or less.

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

(2) Difference between the refractive index of the third absorption layer and the second absorption layer when the third absorption 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 described above, wherein at least one of the first absorption layer, the second absorption layer, and the third absorption layer has an extinction coefficient of 0.01 or more.

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

(5) The above-mentioned information recording medium, 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 above-mentioned information recording medium is characterized in that it is in the range of.

(7) The organic substance 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 above information recording medium.

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

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

(10) The difference between the optical thickness at the bottom of the groove 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 (however, λ is The above-mentioned information recording medium is characterized in that the wavelength of the information recording medium is equal to or less than the wavelength of a reproduction laser beam.

(11) The difference between the optical thickness of the pit portion and the optical thickness of the inter-pit portion of the total of the first absorption layer and the second absorption layer of the light absorption layer is λ/16 (however, λ is a wavelength of a reproduction laser beam) or less.

(12) The above information recording medium, wherein the light absorption layer has a film thickness of 40 to 400 nm at the land portion and between the pits.

(13) The pregroove is 0.2 to 1.
The information recording medium described above has a half width of 4 μm and a depth of 5 to 80 nm.

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

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

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

(17) The information recording medium 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 described above, further comprising a protective layer formed on the third absorption layer.

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

The present inventors have conducted extensive research in order to obtain an information recording medium that has a layer structure such as an absorbing layer that can be formed by simply coating on a substrate and has a high reflectance, and has developed the present invention. It has been reached.

In the information recording medium of the present invention, a light absorption layer made of an organic substance such as a dye is provided on a substrate, and the light absorption layer consists of a first absorption layer and a second absorption layer in order from the substrate side. consisting of one or two repeating layer units and a third absorption layer, each of these three types of layers having a specified refractive index and extinction coefficient; The difference between the optical film thickness at the bottom of the groove and the optical film thickness at the land part, and the optical film thickness at the pit part if pre-pits are additionally provided, in terms of the total of the layer and the second absorption layer. It has a basic configuration in which the difference from the optical film thickness between the pits is λ/8 (where λ is the wavelength of the reproduction laser beam) or less. Therefore, for example, when the number of repeating layer units is one, the layer structure of the light absorption layer is from the substrate side to the first absorption layer -
If the number of repeating layer units is two, from the substrate side, the order is: second absorption layer - third absorption layer - first absorption layer - second absorption layer - third absorption layer. There are three absorption layers.

The structure of the information recording medium of the present invention will be explained with reference to FIG. 1, which schematically shows a cross-sectional view of an embodiment thereof.

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

The substrate 2 is provided with pregrooves or pregrooves and prepits 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, which indicates the degree of light transmission, is close to 0.

The first absorption layer 3 is made of an organic substance (preferably a dye) and meets the following conditions (I): n1 ≧1.8 and k1 ≦0.5 (I)
(However, n1 is the refractive index of the first absorption layer 3, and k1
is the extinction coefficient of the first absorption layer 3).

The above range is generally 4.0≧n1≧1.
8 and 0≦k1≦0.5, especially 3.8≧n1≧2.
0 and 0≦k1≦0.3, more particularly 3.5≧n1≧2
．． 2 and 0≦k1≦0.2.

[0046] This first absorption layer 3 can be formed using a dye or the like which is generally used as an absorption layer material. That is, it can be formed by applying a coating liquid in which a dye or the like is dissolved in a solvent using a spin coating method or the like (the optical thickness of the groove bottom, land, pit, and inter-pit areas of the light absorption layer is as described above). (The method for forming each absorption layer so that the relationship is as follows will be described later)
. The first absorption layer 3 has a high refractive index (n1) and a low extinction coefficient (k1). Therefore, the difference in 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 (k1) is low, and most of the light other than the reflected light is transmitted.

The second absorption layer 4 is made of an organic substance (preferably a polymer compound) and satisfies the following condition (II): n2 <
1.8 and k2 ≦0.5 (II) (where n2 is the refractive index of the second absorption layer 4, and k2 is the extinction coefficient of the second absorption layer 4). Has the value of the coefficient.

The above range is generally 1.0≦n2<1.
8 and 0≦k2≦0.5, especially 1.0≦n2≦1.
7 and 0≦k2≦0.3, more particularly 1.0≦n2≦1
．． 6 and 0≦k2≦0.1.

The second absorption layer 4 can generally be formed by using a polymer compound or a dye having a low refractive index and applying a coating solution in which these are dissolved in a solvent by spin coating or the like. The second absorption layer 4 has a low refractive index (n2), and due to the difference in refractive index with the first absorption layer 3, light is slightly reflected at the interface between the first absorption layer 3 and the second absorption layer 4. This difference in refractive index is preferably 0.5 or more, particularly preferably 1.0 or more. By making the difference large in this way, it is possible to reduce the amount of scattered light other than reflected light that cannot be detected during recording and reproduction. Since the extinction coefficient (k2) of the second absorption layer 4 is low, most of the light that is not reflected is transmitted. This second absorption layer 4 corresponds to a so-called enhancement layer, and by interposing it between the first absorption layer 3 and the third absorption layer 5, the reflectance can be improved.

The third absorption layer 5 is made of an organic substance (preferably a dye), and the third absorption layer 5 satisfies the following conditions (III).
) or (IV). n3 ≧1.8 and k3 ≦0.5 (II
I ) (where n3 is the refractive index of the third absorption layer 5,
k3 is the extinction coefficient of the third absorption layer 5)

The above range is generally 4.0≧n3≧1.
8 and 0≦k3≦0.5, especially 3.8≧n3≧2.
0 and 0≦k3≦0.3, more particularly 3.5≧n3≧2
．． 2 and 0≦k3≦0.2.

1.0≧n4≧4.0 and k4≧1.0
(IV) (However, n4 is the refractive index of the third absorption layer 5, and k4 is the extinction coefficient of the third absorption layer 5.)

The above range is generally 4.0≧n4≧1.
0 and 1.0≦k4≦10, especially 3.5≧n4≧1
．． 0 and 1.2≦k4≦8.0, more particularly 3.0≧n
It is preferable that 4≧1.0 and 1.5≦k4≦5.0.

This third absorption layer 5 is preferably a layer made of a dye, and even if the layer satisfies condition (III),
Any layer that satisfies condition (IV) may be used.

The third absorption layer 5 can also be formed in the same manner as described above by applying a coating liquid in which a dye or the like is dissolved in a solvent by spin coating 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 similar to the interface between the substrate and the first absorption layer. A large amount of reflected light can be obtained that is equal to or greater than the amount of reflected light at . This is because the refractive index of the second absorption layer 4 is set smaller than the refractive index of the substrate. Like the difference between the first and second absorption layers 4, the difference in refractive index between the second and third absorption layers 5 is preferably 0.5 or more, particularly preferably 1.0 or more. Although the extinction coefficient (k3) is low, as mentioned above, the reflectance is high and the amount of transmitted light is small.

Third absorption layer 5 satisfying the above condition (IV)
Although the refractive index (n4) does not need to be high, it is necessary that the extinction coefficient (k4) be high. That is, since the extinction coefficient is high, almost no laser light from the second absorption layer 4 passes through the third absorption layer 5, and most of the light is reflected, exhibiting a high reflectance.

As described above, although the information recording medium of the present invention is an information recording medium in which the first absorbent layer 3, the second absorbent layer 4, and the third absorbent layer 5 can all be formed by coating, First, it has a reflectance comparable to or higher than the high reflectance that can be obtained only when a metal reflective layer or an enhancement layer is conventionally provided on a dye-absorbing layer by a method other than a coating method such as sputtering. That is, a first absorption layer (corresponding to a normal dye absorption layer) with a high refractive index and a low extinction coefficient, a second absorption layer 4 (corresponding to a normal enhancement layer) having a low refractive index and a very low extinction coefficient, and Adopt a configuration consisting of a third absorption layer 5 (corresponding to a normal reflective layer) that has the same high refractive index and low extinction coefficient as the first absorption layer, or has a high extinction coefficient such as a normal metal. Accordingly, an information recording medium having 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 keeping the refractive index and extinction coefficient within the above ranges, the recording and reproducing characteristics will not be impaired. Furthermore, the information recording medium of the present invention can record long pit signals with extremely small distortion compared to an optical disc having a metal reflective layer on a dye absorption layer.

The information recording medium 1 in FIG. 1(B) has a first absorbent layer 3, a second absorbent layer 4, a first absorbent layer 3, a second absorbent layer 4, and a third absorbent layer 5 on a substrate 2. are formed, and the contents of each layer are the same as those described with respect to FIG. 1(A).

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

The material for the disc-shaped substrate in the present invention can be arbitrarily selected from various materials used as substrates for conventional information recording media. Examples of substrate materials include glass, acrylic resins such as polymethyl methacrylate; polyvinyl chloride, vinyl chloride, etc. Examples include vinyl chloride resins such as polymers; epoxy resins; polycarbonate resins; amorphous polyolefins and polyesters. Preferably polycarbonate, polyolefin,
Mention may be made of glass and polymethyl methacrylate.

[0062] On the surface of the substrate on which the light absorption layer is provided,
An undercoat layer may be provided for the purpose of improving planarity, improving adhesive strength, improving solvent resistance of the substrate, and preventing deterioration of the recording layer. Examples of materials for the undercoat layer include polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, styrene/maleic anhydride copolymer, polyvinyl alcohol, N-methylolacrylamide, styrene/sulfonic acid copolymer, and styrene/maleic anhydride copolymer. Vinyltoluene 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 (SiO2, ZnS,
AlN, Si3 N4, etc.), inorganic fluoride (MgF2
) and other inorganic substances.

[0063] The undercoat layer is prepared by, for example, dissolving or dispersing the above substances in a suitable solvent to prepare a coating solution, and then applying this coating solution to the substrate surface by a coating method such as spin coating, dip coating, or extrusion coating. It can be formed by The layer thickness of the undercoat layer is generally 0.0
in the range of 0.05 to 20 μm, preferably 0.01 to 1
It is in the range of 0 μm.

In the present invention, a pregroove (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 (d1 in the attached Figure 2) 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) is 0. .2 to 1.4 μm is preferable, and it is more preferable that 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. ~50
in the range of nm and the half width of the groove is 0.35 to 0.
．． Most preferred is 6 μm. addressing,
Alternatively, the groove may be wobbled for linear velocity control.

In the present invention, the substrate surface (
Pre-pits (or undercoat layer surface) are pre-recorded with information such as various application software and address signals.
A ROM area) may also be formed. The shape of the pre-pit has a pit depth (d2 in attached Figure 3) of 60~
It is in the range of 300 nm and the half width of the pit (width of the pit at 1/2 the depth of the pit) is 0.2 to 1.
．． Preferably, the pit depth is 4 μm, and the pit depth is 70 to 70 μm.
In the range of 250 nm and the half width of the pit is 0.3~
It is more preferable that the pit depth is 1.0 μm, and the pit depth is in the range of 90 to 200 nm and the half width of the pit is 0.
．． The most preferred is 4 to 0.7 μm.

In addition, when pre-pits are formed, the depth of the pre-grooves is λ/16 in terms of optical path length than the depth of the pre-pits (where λ is the wavelength of the reproduction laser beam, and as described below) The same is true for λ/14 or more, more preferably λ/14 or more;
It is particularly preferred that the length be shorter than 12. The reason for this is that if the depth of the pregroove is made as large as the depth of the prepit where the degree of modulation becomes sufficiently large, the reflectance of the pregroove becomes too low.

When the substrate material is plastic, the pregroove or the pregroove and prepit may be directly provided on the surface of the substrate by injection molding or extrusion molding. Further, a pregroove layer for forming the pregroove or the pregroove and prepit may be provided on the surface of the substrate.

As the 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 pregroove layer is formed by first coating a mixture of the above-mentioned acrylic ester and polymerization initiator on a precisely made matrix (stamper), and then placing the substrate on top of this coating layer. The liquid layer is cured by irradiation with ultraviolet rays through the substrate or the matrix, thereby fixing the substrate and the liquid phase. Next, by peeling the substrate from the mother mold, a substrate provided with a pregroove layer is obtained. 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.

[0069] A solvent in a coating solution for forming a light absorption layer on a substrate (or pregroove layer) on which pregrooves or prepits are formed, using a material similar to that for forming the undercoat layer. A solvent-resistant layer may be provided to protect the material from water.

[0070] A light absorption layer consisting of the first absorption layer, second absorption layer and third absorption layer as described above is provided on the substrate (or undercoat layer). Information is recorded in the light absorption layer by irradiating laser light from the substrate side to form reproduction pits in the light absorption layer. Therefore, the light absorption layer in the region of the substrate where the pregroove is formed functions as a recording layer.

The organic material for the first absorption layer may be any material as long as it has a refractive index and an extinction coefficient that satisfy the above-mentioned condition (I). Generally, dyes are selected from dyes whose maximum absorption wavelength is about 50 to 200 nm shorter than the recording or reproducing 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, azulenium dyes, squalirium dyes, Ni, Cr.
Metal complex dyes such as naphthoquinone dyes, anthraquinone dyes, indophenol dyes, indoaniline dyes, triphenylmethane dyes, triallylmethane dyes, aminium dyes, diimmonium dyes,
Nitroso dyes, leuco dyes, croconium dyes,
and other dyes.

These dyes are light once (WO)
It is not limited to the type, and may be a rewritable (RW) type (or reversible type). Among these dyes, since the use of semiconductor lasers that emit near-infrared light as recording and reproducing lasers has been put into practical use, dyes with a wavelength of 600 to 900 nm are preferred.
A dye having a high absorption rate for light in the near-infrared region is preferable.

These dyes may be used alone or as a mixture of two or more. Furthermore, when a cyanine dye is used, it is preferable to use the above-mentioned metal complex dye, aminium dye, or diimmonium dye together as a quencher. In that case, use a metal complex dye as a quencher at a rate of 0.0% per mole of the total dye.
The content is preferably 0.01 to 0.3 mole.

As the dye used as the material for the first absorption layer, cyanine dyes, azulenium dyes and squarylium dyes are particularly preferable, and among the cyanine dyes, merocyanine dyes, phthalocyanine dyes,
Preferred are naphthalocyanine dyes, naphthoindolenine dyes and imidazoquinoxaline dyes.

In the information recording medium of the present invention, the difference between the optical thickness of the groove bottom and the land of the total of the first absorption layer and the second absorption layer of the light absorption layer is λ. /8
It is characterized by the following: In addition, when the information recording medium of the present invention further has pre-pits on the substrate, the total optical film thickness of the pit portion and the optical thickness of the inter-pit portion of the first absorption layer and the second absorption layer of the light absorption layer. The difference from the target film thickness is λ/8
It is characterized by the following: In order to form a light absorption layer so that the optical thickness of the light absorption layer has the above relationship, it is necessary to It is necessary to form each absorption layer so that the optical thickness satisfies the above conditions.

By the way, when the second absorption layer is made of a polymer compound, the difference between the optical film thickness at the bottom of the groove and the optical film thickness at the land part, and the optical film thickness at the pit part, as described later. There is virtually no difference between the optical film thickness and the optical film thickness between the pits. Therefore, in order to make the above-mentioned difference in optical thickness of the total of the first absorption layer and the second absorption layer of the light absorption layer λ/8 or less, in the case of one first absorption layer, the first absorption layer must be The difference between the optical film thickness at the groove bottom and the land part of one absorption layer, and the difference between the optical film thickness at the pit part and the optical film thickness between the pits, should be λ/8 or less. Bye. In addition, when there are two first absorption layers, the difference between the optical film thickness at the groove bottom and the optical film thickness at the land part, and the optical film thickness at the pit part, of the total of the two first absorption layers. The difference between the film thickness and the optical film thickness between the pits is λ/
It should be 8 or less.

[0078] Therefore, the optical thickness of the first absorption layer of the above-mentioned light absorption layer will be explained in detail with reference to the attached drawings.

FIG. 2 is a cross section schematically showing a part of the cross section in the pregroove region of an intermediate product in which a first absorption layer is formed on a substrate in the manufacturing process of an embodiment of the information recording medium of the present invention. It is a diagram. FIG. 3 is a cross-sectional view schematically showing a part of the pre-pit area of the intermediate product. FIG. 4 is a cross-sectional view schematically showing a part of a pregroove area of a conventionally known information recording medium.

In FIG. 4, a light absorption layer 32 made of a dye is formed on the surface of a substrate 31 made of plastic. A pregroove 33 is formed in the substrate 31. The light-absorbing layer 32 is formed by applying a light-absorbing layer forming solution prepared by dissolving a dye in a solvent using a spin coating method and drying the solution. Pregroove 3
The film thickness t6 of the light absorption layer 32 at the groove bottom 35 of No. 3 is as follows:
It is larger than the film thickness t5 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 absorption layer 32 that comes into contact with the air becomes larger than that of the groove 34.
When the depth d3 becomes smaller than the depth d3, and when recording pits are formed in the pregroove 33 by irradiating laser light to record information, the upper part of the groove of the light absorption layer 32 (the part corresponding to the land part of the substrate) There is a problem in that the modulation degree of the recording pit becomes small because the phase difference between the bottom and the bottom becomes small. To solve this problem, the depth of the groove is increased. However, if the depth of the groove is made too large, a problem arises in that the reflectance of the groove portion decreases.

In FIG. 2, a first absorption layer 12 made of a dye is formed on the surface of a substrate 11 made of plastic. A pregroove 13 is formed in the substrate 11. The first absorption layer 12 is formed by applying a first absorption layer forming solution prepared by dissolving a dye in a solvent and having specific properties as described below by a spin coating method and drying the solution. Optical thickness (nr ・t2) of the first absorption layer 12 on the groove bottom 15 of the pregroove 13
(However, nr is the refractive index of the first absorption layer, and t2 is the thickness of the first absorption layer 12 at the groove bottom 15.)
Optical film thickness (nr ・t1) of the first absorption layer 12 on the land portion 14 of the substrate 11 (where nr is the refractive index of the first absorption layer, and t1 is the film thickness of the first absorption layer 12 on the land portion 14 The difference between the thickness and the thickness is λ/8 or less. As a result, the depth of the groove shape on the outer surface of the first absorption layer 12 that comes into contact with air is the depth d1 of the groove 13.
The first absorption layer 12 has a large phase difference between the groove portion and the land portion, and the degree of modulation of the recording pit is large. Further, by setting the difference between nr·t1 and nr·t2 as described above, it is possible to reduce the depth d1 of the groove 13, and the reflectance of the groove portion increases.

[0082] The difference between nr ・t1 and nr ・t2 above is preferably λ/11 or less, and λ/13
It is more preferably at most λ/16, even more preferably at most λ/16.

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

In FIG. 3, a first absorption layer 22 made of a dye is formed on the surface of a substrate 21 made of plastic. Pre-pits 23 are formed on the substrate 21 . The first absorption layer 22 is prepared by dissolving a dye in a solvent and using a first absorption layer forming solution having specific properties as described below.
It is formed by coating using a spin coating method and drying. The optical thickness (nr ・t4) of the first absorption layer 22 in the pit portion 25 of the pre-pit 23 (however,
nr is the refractive index of the first absorption layer, t4 is the thickness of the first absorption layer 22 in the pit portion 25), and the optical thickness of the first absorption layer 22 in the inter-pit portion 24 of the substrate 21 ( nr・
t3 ) (where nr is the refractive index of the first absorption layer,
t3 is the film thickness of the first absorption layer 22 in the inter-pit portion 24). As a result, the depth of the hole shape on the outer surface of the first absorption layer 22 in contact with the air is the same as the depth d2 of the pit 24, or is as small as λ/8 or less in optical film thickness, and the first absorption layer There is a large phase difference between the pit portions of the layer 22 and the inter-pit portions, and the degree of modulation of the pits is large. As a result, even if the first absorption layer is formed in the pit formation region of the substrate, it is possible to reproduce the pits of the substrate with a high degree of modulation.

The difference between nr ・t3 and nr ・t4 above is preferably λ/11 or less, and λ/13
It is more preferably at most λ/16, even more preferably at most λ/16.

When both pre-grooves and pre-pits are formed on the substrate, the depth d1 of the groove is longer than the depth d2 of the pit portion, the optical path length (n·d: n is the refractive index of the substrate, (d is the depth dimension) is preferably smaller by λ/16 or more, particularly λ/14 or more, and even more particularly λ/12 or more.

[0087] The film thickness of the land part and the part between the pits of the first absorption layer is 10 to 1000 nm, particularly 30 to 1000 nm.
Preferably it is 500 nm, more particularly 40 to 300 nm.

[0088] The first absorption layer having a specific optical thickness as described above, that is, the difference between the optical thickness of the first absorption layer at the groove bottom and the optical thickness of the first absorption layer at the land portion. is λ/8
A dye for forming a first absorption layer which is as follows, and 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 which precipitation of the dye begins by evaporating the solvent from the dye solution at the coating temperature of the dye solution. Defined as meaning the ratio to the original volume. For example, when a dye solution in which a dye is dissolved in a solvent is maintained at the coating temperature for forming the first absorption layer and the solvent is evaporated, the volume decreases as the solvent evaporates, and the solution eventually dissolves. When the dye starts to precipitate, the volume of the dye solution (strictly speaking, it is a dye suspension solution) is 90% of the original dye solution volume. It is called a dye solution with a limit of 90%.

Therefore, the concentration limit of a dye solution depends on the combination of the dye and the solvent (single solvent or mixed solvent), the type and ratio of the combination of two or more solvents, and the concentration of the dye in the dye solution. It varies depending on concentration, coating temperature, etc. For this reason, it is not possible to uniformly determine a dye solution with a specific concentration limit for a specific dye, but those skilled in the art will be able to prepare a dye solution with a desired concentration limit by varying the conditions described above. This can be done easily.

The dye solution used to form the first absorbing layer is a dye solution with a concentration limit of 99 to 20%, but with a concentration limit of 99 to 30%, particularly 95 to 40%, more particularly 90%. Preferably, the dye solution is ~50%. If the concentration limit of the dye solution is larger than the above range, the film thickness of the first absorption layer will become non-uniform as a whole, and if it is smaller than the above range, the optical thickness of the first absorption layer between the groove bottom and the land part will be uneven. The difference in film thickness and the difference in optical thickness of the first absorption layer between the pit portion and the inter-pit portion become large.

[0091] The solvent used for preparing the above dye solution is as long as it satisfies the concentration limit of the dye solution.
A single solvent may be used, or a mixed solvent of two or more types of solvents may be used. When the above-mentioned 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, It is preferably a mixture with a solvent that does not dissolve 2% by weight or more of the dye used at the coating temperature of the dye solution. In this case, it is necessary that the good solvent and the poor solvent are compatible, and that the evaporation rate of the poor solvent is not greater than the evaporation rate of the good solvent at the above coating temperature. Generally, the concentration limit increases as the mixing ratio of the poor solvent increases.

The above solvents 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; ester solvents such as ethyl acetate, butyl acetate, amyl acetate, ethylene glycol monoethyl ether, acetate, cellosolve acetate, etc.; 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-based solvents such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, benzyl alcohol, etc.; amide-based solvents such as dimethylformamide; fluorinated alcohols, fluorinated alcohols such as 2, 2, 3, 3, tetrafluoropropanol, etc. Examples include fluorine-based solvents such as ketones, fluorine-substituted esters, fluorine-substituted amides, fluorine-substituted ethers, fluorine-substituted aromatic hydrocarbons, and fluorine-substituted aliphatic hydrocarbons.

The dye solution is not particularly limited as long as it satisfies the above-mentioned limit concentration, but for convenience of handling and by spin coating, the first absorption layer with a uniform thickness on the entire substrate can be formed. The concentration of the dye in the dye solution is between 0.5 and 14% by weight, especially 1
Preferably it is from 1.5 to 8% by weight, more particularly from 1.5 to 8% by weight.

[0094] The dye solution further contains an antioxidant,
Various additives such as UV absorbers, plasticizers, lubricants, etc. may be added depending on the purpose.

[0095] When using a binder, as a binder,
For example, cellulose derivatives such as gelatin, nitrocellulose, and cellulose acetate, natural organic polymer substances such as dextran, rosin, and rubber; and hydrocarbon resins such as polyethylene, polypropylene, polystyrene, and polyisobutylene, polyvinyl chloride, polyvinylidene chloride, Vinyl resins such as polyvinyl chloride/polyvinyl acetate copolymers, acrylic resins such as polymethyl acrylate and polymethyl methacrylate, polyvinyl alcohol, chlorinated polyolefins, epoxy resins, butyral resins, rubber derivatives, phenol/formaldehyde resins Synthetic organic polymer substances such as initial condensates of thermosetting resins such as

[0096] When applying the above-mentioned dye solution onto a substrate by a spin coating method, it can be carried out using a device and method that are known per se. The dye solution is generally heated at 0 to 100°C, particularly 5 to 80°C, more particularly 10 to 60°C.
Preferably it is applied at a temperature of .degree. The rotation speed of the board is
When applying a dye solution, generally 10 to 1000 r.p.m.
p. m. , especially from 100 to 500 r. p. m. When drying the pigment coating, it is generally 300
~10000r. p. m. , especially 500-7000r.
p. m. , more particularly from 700 to 4000 r. p. m. It is preferable to

A second absorbent layer is provided on the first absorbent layer. Any organic material may be used as the material for the second absorption layer as long as it has a refractive index and an extinction coefficient that satisfy the above-mentioned condition (II).

[0098] Examples of materials satisfying the above formula (II) include polymer compounds. 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, ABS
Resin, acrylic resin such as polymethyl methacrylate, polyvinyl acetate, polycarbonate, polyacetal, chlorinated polyethylene, chlorinated polyether, polyamide, fluororesin, polyphenylene oxide, cellulose acetate resin, cellulose nitrate resin, cellulose acetate butyrate resin Mention may be made of resins, polybutadiene, acrylonitrile resins, polyethylene terephthalate and polybutene.

A dye can also be used as a material for the second absorption layer. Generally, such dyes have a maximum absorption wavelength that is 200 nm longer than the recording or reproducing wavelength of the laser.
Pigments on the short wavelength side of about nm or more, or 100 nm
You can choose from among dyes that are on the longer wavelength side. Preferred are cyanine dyes, merocyanine dyes, phthalocyanine dyes and naphthalocyanine dyes.

When a polymer compound is used as the material for the second absorbent layer, the second absorbent layer can be formed by preparing a solution using the above-mentioned solvent and applying a spin coating method. In this case, unlike the case of forming a dye-containing layer, there is a difference between the optical thickness of the second absorption layer at the groove bottom and the optical thickness of the second absorption layer at the land, and There is substantially no difference between the optical thickness of the second absorption layer and the optical thickness of the second absorption layer between the pits. If a dye is used as the material for the second absorption layer, the second absorption layer should be formed by spin coating using a dye solution with a specific concentration limit as described for the formation of the first absorption layer. Can be done.

[0101] A third absorbent layer is provided on the second absorbent layer. The organic substance of the material of the third absorption layer meets the above conditions (III
) or (IV), any material having refractive index and extinction coefficient values that satisfy (IV) may be used.

As the organic substance satisfying the above formula (III), substantially the same material as that of the first absorption layer can be used.

As the organic substance satisfying the above formula (IV), it is preferable to use a dye whose absorption maximum wavelength is near the laser recording or reproducing wavelength. Preferred are cyanine dyes, merocyanine dyes, phthalocyanine dyes and naphthalocyanine dyes.

[0104] Since the third absorption layer functions as a reflection layer as described above, the difference between the optical thickness at the bottom of the groove and the optical thickness at the land, and the difference in the optical thickness at the pit, as explained for the first absorption layer, It is not necessary to particularly consider reducing the difference between the optical film thickness of the area between the pits and the optical film thickness of the area between the pits. Therefore, it can be formed using conventional dye film forming methods. Of course, it can also be formed by spin coating using a dye solution with a specific concentration limit as described for the formation of the first absorption layer.

[0105] The layer thickness of the first absorption layer, second absorption layer, and third absorption layer is generally in the range of 10 to 1000 nm, respectively, as measured at the land portion or the portion between the pits, and is preferably The range is from 30 to 500 nm, particularly preferably from 40 to 300 nm.

[0106] When a binder is used in combination as a material for the dye layer, it is necessary to make sure that the refractive index and extinction coefficient of the first absorption layer, second absorption layer, and third absorption layer do not deviate from the specified ranges of the present invention. It is necessary to use it. The ratio of dye to binder generally ranges from 0.01 to 99% (by weight), preferably from 1.0 to 95% (by weight).

[0107] The above three layers, the first absorption layer, the second absorption layer and the third absorption layer, are formed by, for example, attaching three nozzles to a spinner used for spin coating, and performing coating and drying operations for forming each layer in order. It can be formed by successive steps. Therefore, the absorption layer can be formed extremely easily on the substrate.

In the information recording medium of the present invention, a protective layer may be provided on the light absorption layer for the purpose of physically and chemically protecting the light absorption layer. Further, this protective layer may be provided on the side of the substrate where the light absorption layer is not provided in order to improve scratch resistance and moisture resistance.

[0109] Examples of materials used for the protective layer include SiO, SiO2, Si3 N4 as inorganic substances.
, MgF2, SnO2, etc. In addition, organic substances include thermoplastic resins, thermosetting resins,
Examples include UV curable resins, preferably UV curable resins.
It is a curable resin.

The protective layer can be formed by, for example, dissolving a thermoplastic resin, a thermosetting resin, or the like in a suitable solvent to prepare a coating solution, and then applying the coating solution and drying it. In the case of a UV curable resin, a protective layer can be formed by applying the coating solution as it is or by dissolving it in an appropriate solvent to prepare a coating solution, and curing it by irradiating it with UV light. UV curable resins include (meth)acrylate oligomers such as urethane (meth)acrylate, epoxy (meth)acrylate, and polyester (meth)acrylate, monomers such as (meth)acrylic acid ester, and a photopolymerization initiator. Ordinary UV curable resins such as those can be used. These coating solutions further contain antistatic agents, antioxidants, and UV
Various additives such as absorbents may be added depending on the purpose. It is preferable to use a UV curable resin as the material for the protective layer.

[0111] The thickness of the protective layer is generally 0.1 to 100μ.
m, preferably in the range of 0.5 to 20 μm.

[0112] It is also possible to form a third absorption layer by mixing the above protective layer forming material with the third absorption layer forming material of the light absorption layer, so that the third absorption layer also serves as a protective layer. .

In addition to the above, the protective layer can be formed, for example, by laminating a film obtained by extrusion of plastic onto the dye recording layer via an adhesive layer. Alternatively, it may be provided by methods such as vacuum deposition, sputtering, and coating.

[0114] Furthermore, two pieces of the information recording medium of the present invention are made to face each other with their light absorption layers facing inside, and a ring-shaped inner spacer is provided so that a space is formed between the two pieces of information recording medium. By joining two information recording media with a ring-shaped outer spacer interposed therebetween, an information recording medium with an air sandwich structure can be obtained. In this air sandwich structure information recording medium, the light absorption layer does not come into direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate. It will not be damaged or have dust attached to its surface, which will prevent information from being recorded or reproduced. One of the information recording media of the air sandwich structure may be a substrate not provided with a light absorption layer (pre-pits may be provided); A protective layer may be provided on the surface of the substrate and/or on the surface of the substrate on which the light absorption layer is not provided.

[0115] The information recording medium of the present invention having the above-mentioned structure has an extremely high reflectance. A reflective layer may also be provided. In this case, even higher reflectance can be obtained, but the advantage that the information recording medium can be manufactured only by coating is lost.

[0116] The light-reflective substance that is the material of the reflective layer is a substance that has 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, Ru
, Rh, Pd, Ir, Pt, Cu, Ag, Au, Zn,
Cd, Al, Ga, In, Si, Ge, Te, Pb, P
Mention may be made of metals and semimetals such as O, Sn, Bi, and Sb. Among these, preferred are Al, A
u, Cr and Ni. These substances may be used alone, or in combination of two or more or as an alloy.

[0117] The reflective layer can be formed on the substrate by, for example, vapor deposition, sputtering, or ion plating of the above-mentioned light reflective material. The thickness of the reflective layer is generally in the range of 10 to 300 nm.

[0118] Recording of information on the information recording medium of the present invention is as follows:
The information recording medium is moved at a constant linear velocity (preferably 1.2 to 2.8 m
/second, preferably 1.2 to 1.4 m/second), a laser beam is irradiated from the substrate side to the bottom of the pre-groove to form reproducing pits in the light absorption layer above the groove. This is done by forming and recording the signal. In order to obtain the effects of the present invention, it is preferable to record a CD format EFM signal as the signal. Generally, a semiconductor laser beam having an oscillation wavelength in the range of 700 to 900 nm is used as the recording light. With the information recording medium of the present invention, recording can be performed with a laser power of 10 mW or less.

[0119] The above-mentioned pits after recording are caused by the substrate and/or the dye being heated by laser beam irradiation and melting, evaporating, sublimating, deforming, or deteriorating, resulting in a convex, wavy, or wavy shape between the substrate and the dye. These include changes such as a concave shape, changes within the dye, and changes between the dye and the metal reflective layer.

When the extinction coefficient of the first absorption layer is close to 0, pits are formed only in the third absorption layer; otherwise, pits are formed in the first absorption layer and pits are formed in the third absorption layer. It is thought that the absorbent layer also deforms. Furthermore, when the energy of the laser is large, pit formation and deformation may also occur in the second absorption layer. Furthermore, when the extinction coefficients of the first and third absorption layers are set to approximately 0 and a dye is used in the second absorption layer, it is possible to record in the second absorption layer. However, it is generally difficult to record only on one layer, and the influence on other layers is unavoidable.

[0121] During recording, tracking control is performed by a push-pull method or the like using the tracking pregroove. Information is recorded in the grooves of the pregroove or in the lands between the grooves.

[0122] Information can be reproduced using a three-beam method, for example, by rotating the recording medium at the same constant linear velocity or constant angular velocity as described above, irradiating semiconductor laser light from the substrate side, and detecting the reflected light. Information can be reproduced while performing tracking control.

[0123] By recording a CD format signal or the like on the information recording medium of the present invention at a constant linear velocity using the above recording method, it is possible to obtain excellent recording and reproducing characteristics such as signal modulation degree and reproduction C/N. Furthermore, the tracking performance during recording, especially the tracking performance by the push-pull method, is excellent. Furthermore, in the case of the information recording medium of the present invention provided with a ROM area, a reproduced signal with a high degree of modulation 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 invention.

[Example 1] Pre-pits (half-width of pits: 0.6 μm, pit depth: 120 nm) in which EFM signals were recorded were formed in an area with a diameter of 46 mm to 80 mm, and pre-pits were formed in an area with a diameter of 80 mm to 118 mm. Groove (track pitch: 1.6 μm, groove half width: 0.5
A disc-shaped polycarbonate substrate (outer diameter: 120 mm, inner diameter: 5 μm, groove depth: 40 nm) was formed.
15 mm, thickness: 1.2 mm, refractive index: 1.58) was prepared.

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

[0127]

[Chemical formula 1]

[0128] In addition, 1,2-polybutadiene (manufactured by Scientific Polymer Products, No. 668)
0.6g, 15cc of cyclohexane and 10cc of n-nonane
A coating solution for forming a second recording layer was prepared by dissolving in a mixed solvent with C. and maintained at 23°C.

Furthermore, the same coating solution as the above-mentioned first absorption layer formation coating solution was prepared as a third absorption layer formation coating solution.

[0130] The first absorption layer forming coating liquid was applied to the pre-pit and pre-groove forming surface of the above substrate at 23°C by spin coating at a substrate rotation speed of 200 rpm. p. m. After coating for 5 seconds at a speed of 1400r. p. m. 30 at
It was dried for a second to form a first absorption layer having the optical thickness shown in Table 1.

[0131] The coating liquid for forming the second absorbent layer was applied onto the first absorbent layer by spin coating at a rotation speed of 1400 r. p. m
．． The coating was applied at a speed of 30 seconds and dried to form a second absorption layer having the optical thickness shown in Table 1.

[0132] On the second absorption layer, a third absorption layer having an optical thickness of 220 nm at the land portion was formed using the above coating liquid for forming the third absorption layer in the same manner as in the formation of the first absorption layer.

In this way, an optical information recording medium (FIG. 1) consisting of a substrate, a first absorption layer, a second absorption layer, and a third absorption layer
(A)) was produced.

Regarding the obtained information recording medium, in the pregroove forming area, 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 part are In the pre-pit formation area, the optical thickness of the first absorption layer and the second absorption layer in the pit area, and the optical thickness of the first absorption layer and the second absorption layer in the area between the pits. , and 11T modulation degree were measured by the following evaluation method. The evaluation results are listed in Table 1.

Note that 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) was formed, and its reflectance and transmittance were measured.) were as follows. First absorption layer [refractive index (n1): 2.6, extinction coefficient (k1): 0
．． 06] Second absorption layer [Refractive index (n2): 1.5, extinction coefficient (k2): 0
] Third absorption layer [refractive index (n3): 2.6, extinction coefficient (k3): 0
．． 06]

[Example 2] In Example 1, the 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 this.

[0137]

[Case 2]

[0138] Regarding the obtained information recording medium, Example 1
The same evaluation items as described in were measured in the same manner. The evaluation results are listed in Table 1.

[0139] The refractive index and extinction coefficient of each absorption layer were as follows. First absorption layer [refractive index (n1): 2.6, extinction coefficient (k1): 0
．． 07] Second absorption layer [refractive index (n2): 1.5, extinction coefficient (k2): 0
] Third absorption layer [refractive index (n3): 2.6, extinction coefficient (k3): 0
．． 07]

[Comparative Example 1] Information was prepared in the same manner as in Example 1, except that the coating liquids prepared as follows were used as the coating liquid for forming the first absorbent layer and the coating liquid for forming the third absorbent layer. A recording medium was manufactured.

Coating liquid for forming the first absorption layer: The above dye (A
) was dissolved in 2,2,3,3-tetrafluoropropanol to prepare a coating solution for forming a first absorption layer containing 2.25% by weight of the dye (A). The limiting concentration of this coating liquid at 23° C. was 10% or less.

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

[0143] Regarding the obtained information recording medium, Example 1
The same evaluation items as described in were measured in the same manner. The evaluation results are listed in Table 1. Note that the refractive index and 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 liquids prepared as follows were used as the coating liquid for forming the first absorbent layer and the coating liquid for forming the third absorbent layer. A recording medium was manufactured.

[0145] Coating liquid for forming the first absorption layer: the above dye (B
) was dissolved in 2,2,3,3-tetrafluoropropanol to prepare a first absorption layer forming coating solution containing 2.25% by weight of the dye (B). The limiting concentration of this coating liquid at 23° C. was 10% or less.

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

[0147] Regarding the obtained information recording medium, Example 1
The same evaluation items as described in were measured in the same manner. The evaluation results are listed in Table 1. Note that the refractive index and 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 subjected to a disc evaluation device (NA: 0.5, laser wavelength: 780 nm) and an EFM encoder (KE
Recording was carried out at the bottom of the pregroove using a laser (recording power) of 4 mW and a constant linear velocity of 1.3 m/sec.

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

2) Optical thickness of absorption layer in land portion 1 above
) was obtained using the same method.

3) Optical thickness of absorption layer in pit portion 1 above
) was obtained using the same method.

4) Optical thickness of absorbing layer between pits This was determined in the same manner as in 1) above.

5) Mirror part reflectance Using an aluminum plate with known reflectance as a reference,
It was measured using a spectrophotometer (UV130 manufactured by Shimadzu Corporation).

6) 11T modulation degree Among the CD format signals recorded above, the recording length is 11
Regarding the DC reproduction signal of T, the signal strength of the signal portion and the mirror portion (portion without signal) was measured, and its modulation degree (C) was determined 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 example had a large reflectance in the pre-groove forming area (information recording area) and a greatly excellent 11T modulation degree in the pre-pit forming area (ROM area). It has performance.

[0157] On the other hand, the information recording medium of the comparative example has the following characteristics:
The reflectance in the pre-groove forming area was comparable to that of the information recording medium of the example, but in the pre-pit forming area (RO
The 11T modulation degree in the M area) was lower than that of the information recording medium of the example.

[0158]

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

[0159] In the information recording medium of the present invention, there is little difference in the optical thickness of the light absorption layer containing the dye between the groove bottom and the land, so even if the depth of the pregroove is made shallow, the optical thickness of the light absorption layer is small. It is an outstanding information recording medium in that the depth of the grooves on the surface is sufficiently large, the sensitivity is high, and a reproduced signal with a high degree of modulation can be obtained after information is recorded by irradiation with a laser beam.

[0160] Furthermore, in the information recording medium of the present invention, a light absorption layer containing a dye is also formed in the region where the pre-pits are formed, and moreover, it is possible to obtain a reproduced signal with a high degree of modulation from the region where the prepits are formed. Therefore, the thickness of the light absorption layer can be made uniform over the entire surface of the information recording medium, and the ROM area where pre-pits are formed and the recordable area where pre-grooves are formed can be separated, for example. It is an outstanding information recording medium that can be installed in any location, such as by mixing both areas, and can be used for a wide range of purposes without any restrictions on the type of application software or how it can be used.

[Brief explanation of the drawing]

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

FIG. 2 is a cross-sectional view schematically showing a part of a cross section in a pregroove area 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 pre-pit area of an embodiment of the information recording medium of the present invention.

FIG. 4 is a sectional view schematically showing a part of a cross section in a pregroove area of a conventionally known information recording medium.

[Explanation of symbols]

1 Information recording medium 2 Board 3 First absorption layer 4 Second absorption layer 5 Third absorption layer 11, 21, 31 Board 12, 22, 32 Absorption layer 13, 33 Pregroove 23 Prepit 14, 34 Land part 24 Between pits 15, 35 Groove bottom 25 Pit part

Claims (2)

[Claims] Claim 1: A light-absorbing layer containing a dye that can record information by irradiating it with laser light to form pits for reproduction is provided on a disc-shaped substrate with pregrooves formed on its surface. An information recording medium comprising:
Consisting of one or two repeating layer units consisting of a first absorbent layer and a second absorbent layer and a third absorbent layer in order from the substrate side,
and the first absorption layer is a layer made of an organic substance and having a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less,
The second absorption layer is a layer made of an organic substance 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 and has a refractive index of 1.8 or more and an extinction coefficient of 0.5 or less, or a layer that is made of an organic material and has a refractive index within the range of 1.0 to 4.0. 1.
It is a layer having an extinction coefficient of 0 or more, and furthermore, the difference between the optical thickness of the groove bottom and the land part of the total of the first absorption layer and the second absorption layer of the light absorption layer is An information recording medium characterized in that it is λ/8 (where λ is the wavelength of a reproduction laser beam) or less. 2. A light absorbing layer containing a dye that can record information by irradiating laser light to form pits for reproduction on a disk-shaped substrate with pre-pits and pre-grooves formed on the surface. An information recording medium provided with
The light absorption layer consists of one or two repeating layer units consisting of a first absorption layer and a second absorption layer and a third absorption layer in order from the substrate side, and the first absorption layer consists of an organic substance. and a layer having 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 substance, and 1.
a layer having a refractive index of less than 8 and an extinction coefficient of 0.5 or less, and the third absorption layer is made of an organic substance, and 1.
a layer having a refractive index of 8 or more and an extinction coefficient of 0.5 or less,
or a layer made of an organic substance and having a refractive index within the range of 1.0 to 4.0 and an extinction coefficient of 1.0 or more, and further comprising a first absorption layer and a second absorption layer of the light absorption layer. The total difference between the optical film thickness at the pit portion and the optical film thickness between the pits is λ/8 (where λ is the wavelength of the reproduction laser beam) or less, and the optical film thickness at the bottom of the groove An information recording medium characterized in that the difference between the optical film thickness of the land portion and the land portion is λ/8 or less (where λ is the wavelength of a reproduction laser beam).