JPS62241146A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve recording sensitivity and tracking performance by setting the average layer thickness of an intermediate coating layer consisting of a chlorinated polyolefin within a prescribed range. CONSTITUTION:This information recording medium is constituted of a substrate 11, the intermediate coating layer 12 provided thereon and a recording layer 13. Writing and reading out of information are executed by the laser light past the substrate 11 in the stage of use. The chlorinated polyolefin is used as the material of the layer 12 on pregrooves and the average layer thickness is set within a 50-1,000Angstrom range. A high heat insulating characteristic is thus provided and therefore, the sensitivity of the recording medium is improved even if the layer 12 is provided in the form of a thin layer on the pregrooves. Tracking accuracy is improved by determining the distance (a) from the bottom of the pregrooves and the surface of the layer 12 covering the peak of the side walls, the refractive index of the substrate 11 and laser light wavelength in such a manner as to satisfy prescribed conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention provides a method for writing and/or reading information using a high energy density laser beam.
This invention relates to an information recording medium. More specifically, the present invention relates to an improvement in an information recording medium having a guide groove for tracking.

[3? Technical Background] In recent years, information recording media that use high energy density beams such as laser light have been developed and put into practical use. This information recording medium is called an optical disk, and is used as a video disk, an audio disk, a large-capacity still image file, a large-capacity computer disk memory, and the like.

The basic structure of an optical disk is a disk-shaped substrate made of glass, synthetic resin, etc., and Bi, Sn, etc.
, a recording layer made of a metal or semimetal such as In, Te, etc.

In addition, as a disk rear structure to protect the recording layer,
A recording layer is provided on at least one of the two disk-shaped substrates, and the two substrates are connected with a ring-shaped inner spacer so that the recording layer is located inside and a space is formed. An air sandwich structure has been proposed in which the air sandwich structure is joined via a shaped outer spacer. In optical discs with such an air sandwich structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate. This has the advantage that there is no possibility that the recording or reproduction of information will be hindered by dust or dust adhering to its surface.

Writing and reading information to and from an optical disc is usually performed by the following method.

Information is written by irradiating this optical disc with a laser beam, and the irradiated portion of the recording layer absorbs the light, causing a local temperature rise, causing physical or chemical changes (for example, the formation of pits). information is recorded by changing its optical properties. Information is also read by irradiating the optical disc with a laser beam, and the information is reproduced by detecting reflected or transmitted light depending on changes in the optical characteristics of the recording layer.

As described above, writing and reading information on an optical disk is usually performed by irradiating a laser beam onto a predetermined location on the disk surface. On the other hand, since there is a strong desire to increase the amount of information recorded on optical discs, efforts are being made to increase the density of recording sites such as pits. And, due to the increase in the density of such recording sites,
Because it is difficult to irradiate a laser beam to the correct predetermined position, recently, in order to guide the laser beam so that it accurately follows the planned irradiation position (generally called tracking), the method shown in Figure 1 of the attached drawings is used. A tracking guide groove (also called a pregroove) having a cross-sectional shape as shown in FIG. 1 is increasingly provided on the disk surface.

In order to improve the tracking accuracy of an optical disc, it is desirable that the dimensions of the pregroove be constant. In particular, if the pregroove depth is not constant, the magnitude of the tracking error signal will vary depending on the location, resulting in a negative impact on the reading device. affect

For example, poor tracking phenomena such as crosstalk and track skipping become more likely to occur, and the quality of the reproduced signal deteriorates.

Furthermore, it has been known to provide an intermediate layer made of a polymeric material (for example, a heat insulating layer, a sensitivity enhancement layer (gas generation layer)) between the substrate and the recording layer for the purpose of increasing recording sensitivity. .

The intermediate layer is formed by a coating method such as a spin cord method using a coating liquid in which a polymeric substance such as polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, nitrocellulose, polyvinyl chloride, or polyethylene is dissolved in a solvent. commonly formed.

In order to improve the tracking characteristics of an information recording medium, the present applicant has developed a method for writing information using a laser and adding an intermediate coating layer to a tracking guide groove cut by +iQ on the surface of a disc-shaped substrate. / or the distance between the intermediate coating layer that covers the bottom of the guide groove and the intermediate coating layer that covers the top of the side wall of the guide groove in an information recording medium consisting of a recording layer where reading is Iir (F) a)
However, for the refractive index (n) of the substrate and the wavelength (λ) of the laser beam used to write information to or read information from the recording medium, the conditions in F are: [ (2m+1) λ/8n]X0.9≦a≦[(2m
+1) λ/8nlX1.1 [However, 1m is 0 or l
A patent application has already been filed for an information recording medium characterized by satisfying the following integers.
No. 2284). According to this information recording medium, tracking failure phenomena such as crosstalk and track skipping are less likely to occur compared to conventional information recording media with the same type of pregroove, so data can be recorded and reproduced stably, and C/N1t (Ratio of output level of carrier and noise)
It is possible to "direct"

[Objective of the Invention] According to the research of the present inventor, when an intermediate layer is deposited by a coating method on the surface of a substrate provided with a pregroove, a difference occurs in the thickness of the intermediate layer at the bottom of the pregroove and the top of the sidewall. Furthermore, it has been found that the thickness of the intermediate layer is non-uniform between the inner peripheral edge and the outer peripheral edge of the substrate.

That is, the thickness of the intermediate layer formed on the pregroove using a coating method such as a spin-coating method tends to be thicker at the bottom of the pregroove and thinner at the top of the sidewall. Moreover, the layer thickness of the intermediate layer tends to change from the inner peripheral edge side to the outer peripheral edge side of the substrate depending on the direction of application. Therefore, if a pre-groove is provided on the substrate surface, it is difficult to uniformly apply the intermediate layer to the entire surface, and the depth of the pre-groove is partially shallower than the predetermined depth. It was a trend.

Therefore, the main object of the present invention is to provide an information recording medium with high recording sensitivity and improved tracking characteristics.

[Summary of the Invention] The present invention is characterized in that a recording layer B is provided on a tracking guide groove provided on the surface of a substrate, through an intermediate coating layer, in which information can be read and/or read by a laser. In the information recording medium, the intermediate coating layer is made of chlorinated polyolefin, and the intermediate coating! The present invention provides an information recording medium characterized in that the average layer thickness of the rN layer is within the range of 50 to 1000X.

[Effects of the Invention] As a result of further research on information recording media, the present inventor found that when chlorinated polyolefin is used as the material for the intermediate layer, the intermediate layer has high heat insulation properties even if the layer thickness is reduced. ,
Therefore, it is possible to significantly increase the MO sensitivity,
At the same time, we discovered that it is possible to reduce non-uniformity in the depth of the pregroove and improve tracking characteristics.
This has led to the present invention.

That is, in the present invention, the chlorinated polyolefin layer, which is the intermediate coating layer, has high lfr#I characteristics even in a thin layer with an average layer thickness of 50 to 1000 mm, so it is possible to form good pits in the recording layer. Can be easily molded. As a result, a high C/N ratio can be obtained with a low laser output, and recording sensitivity can be increased.

Furthermore, by making the chlorinated polyolefin layer thinner, an intermediate layer having a more uniform layer thickness can be formed (tTLfl), and as a result, the depth of the pregroove can be made constant. Therefore, tracking failure phenomena such as crosstalk and track skipping can be prevented, and C/N
The ratio can be increased.

Therefore, the information recording medium of the present invention has higher recording sensitivity and markedly improved tracking performance than conventional pregrooved information recording media.

[Detailed Description of the Invention] A typical example of the information recording medium of the present invention is schematically shown in FIG. 1 of the accompanying drawings.

In FIG. 1, the information recording body 11 is composed of a substrate 11, an intermediate coating layer 12 and a recording layer 13 provided thereon. In addition, in Fig. 1, [a] is the guide groove (
is the distance between the surface of the intermediate coating layer covering the bottom of the pre-groove (pre-groove) and the surface of the intermediate coating layer covering the top of the side wall of the guide groove, [bl is the depth of the guide groove provided on the substrate] be.

Guide groove (pre-groove) of the substrate of the information recording medium of the present invention
The shape of the pregroove is not particularly different from conventionally known pregrooves, and therefore, there is no particular restriction on the shape of the pregroove.

When using the information recording medium of the present invention, the I-i
Writing and reading are performed by laser light passing through the substrate. That is, in the embodiment shown in FIG.
Laser light is irradiated from the tip side.

The information recording medium of the present invention can be manufactured, for example, by the following method.

The pregrooved substrate can be manufactured by, for example, molding a plastic material such as polycarbonate resin or polyacrylic resin, or by laminating a resin layer having pregrooves on an f-plane substrate such as a plastic plate or a glass plate. These methods are already generally known. The depth of the pregroove of the undeveloped IJJ (corresponding to bl in FIG. 1) is preferably within the range of 800 to 1200X.

Next, an intermediate coating layer, which is a characteristic feature of the present invention, is provided on the pregroove.

As the material for the intermediate coating layer of the present invention, chlorinated polyolefin is used.

The chlorinated polyolefin generally has a chlorination rate of 30% or more, preferably 50% or more, 1-1, particularly preferably 1! within the range of 50 to 70%. ! It has a prime rate. Among these chlorinated polyolefins, chlorinated polyethylene and chlorinated polypropylene are particularly preferred in terms of thermal stability and solubility.

The intermediate coating layer may be provided by dissolving the above-mentioned chlorinated polyolefin in a solvent and applying a coating solution of WtAl, and then applying this coating solution onto the pregroove.

As a solvent for dissolving chlorinated polyolefin,
Toluene, xylene, ethyl acetate, butyl acetate, cellosolve acetate, methyl ethyl ketone, 1,2-dichloroethane, methyl isobutyl ketone, cyclohexane,
Cyclohexanone.

Tetrahydrofuran, ethyl ether, dioxane, etc. can be mentioned.

What is the concentration of chlorinated polyolefin in the coating solution?

It is preferably within the range of 0.1 to O,jfiψ%. If the concentration of the chlorinated polyolefin is lower than 0.1% by weight, recording sensitivity may not be sufficiently improved. Also, 0
．． If it is more than 4% by weight, the coating liquid may have a high viscosity and it may be difficult to apply it uniformly, and the sensitivity of the recording medium may become partially non-uniform.

It is also possible to further add various additives such as plasticizers and lubricants to these coating solutions depending on the purpose.

Examples of the coating method include a spray method, a spin code method, a dip method, a roll coat method, a blade coat method, and a screen printing method.

An intermediate coating layer can be formed on the pregroove by coating the coating liquid on the pregroove to form a coating film and then drying it. The layer thickness (average layer thickness) of the intermediate coating 4f layer is preferably in the range of 50 to 1000, particularly preferably in the range of 100 to 400.

In particular, when a spin code method is used as a coating method, it is generally difficult to uniformly form an intermediate coating layer on the pregroove, but it is preferable to form a thin layer with an average layer thickness in the range of 50 to 1000 Å. This makes it possible to obtain a uniform intermediate coating layer. Furthermore, even if the intermediate coating layer is as thin as described above and is provided in the blur groove, it has high lfr thermal properties, and therefore can increase the sensitivity of the recording medium.

The error in the layer thickness of the intermediate coating layer is about 10% in normal coating operations, preferably within 5%, taking into consideration the reproducibility of the coating film thickness.

Further, the depth of the pregroove preferably satisfies the following conditions. That is, the distance I between the surface of the intermediate coating layer covering the bottom of the pregroove shown in FIG. 1 and the surface of the intermediate coating layer covering the top of the side wall of the pregroove.
ll (a) with respect to the refractive index (n) of the substrate and the wavelength (input) of the laser light used when writing information to or reading information from the recording medium: [(2m+1) λ/8n]X0.9≦a≦[(2m
+1)λ/8n]X1.1, more preferably.

[(2m+i)λ/8n]xo, 95≦a≦[(2m+
1) λ/8n]X1.05 [However, m is an integer of 0 or 1 or more. ] satisfies the condition.

By providing the intermediate coating layer on the pregroove according to the above conditions, it is possible to significantly improve tracking accuracy compared to conventional information recording media with the same type of pregroove.

For details such as the dimensions of the pre-groove provided with the intermediate Pa Ai layer, please refer to the above-mentioned Japanese Patent Application No. 1983 filed by the applicant.
-228417.

Next, a recording layer is provided on the intermediate coating layer.

Examples of materials used for the recording layer include Te, Zn, I
Metals such as n, Sn, Zr, An, Cu, Au; Bi, A
Metalloids such as S and Sb; semiconductors such as Ge and Si; and alloys thereof, or combinations thereof. In addition, sulfides, oxides of these metals or metalloids,
Compounds such as borides, silicon compounds, carbides and nitrides; and mixtures of these compounds with metals can also be used in the recording layer.

The recording layer can be formed on the intermediate coating layer using the above recording material by a method such as vapor deposition, sputtering, or ion blasting. The recording layer may be a single layer or a multilayer, but its layer thickness is generally in the range of 100 to 5500X in view of the optical density required for optical information recording.

Since the recording layer is provided via an intermediate coating layer, good bits can be easily formed in the recording layer due to the high 1lr8# property of the intermediate coating layer.

This allows a high C/N ratio with low laser power. Furthermore, gas is generated from the irradiated portion of the intermediate coating layer, making it easier to form pits, and C/N
It becomes possible to make the ratio even higher.

In addition, the back side of the substrate (the side opposite to the side where the Q layer is provided)
IIG made of an inorganic substance such as silicon dioxide, tin oxide, or magnesium fluoride may be provided on the surface of the substrate by vacuum deposition, sputtering, etc. in order to improve scratch resistance, moisture resistance, and the like.

In this way, an information recording medium having a basic structure in which the substrate, the chlorinated polyethylene layer, and the recording layer are laminated in this order can be manufactured.

Note that although the manufacturing of the information recording medium according to the present invention has been mainly explained using an example of a type consisting of a single substrate, the information recording medium of the present invention may have any configuration according to known techniques. In other words, a type of information recording medium manufactured by laminating two information recording media each made of a single substrate as described above, and a protective layer (resin layer, protective Various configurations can be taken, such as a type of information recording medium in which a plate (such as a plate) is formed, and an air sandwich type information recording medium.

Next, Examples and Comparative Examples of the present invention will be described.

[Example 1] Disc-shaped polycarbonate resin substrate provided with pregrooves by injection molding [outer diameter: 130 mm, inner diameter: 15 mm,
Thickness: 1.2mm, group depth b) in Figure 1: 1
Spin a coating solution containing chlorinated polyethylene [0.2% chlorinated polyethylene dissolved in a mixed solvent of methyl ethyl ketone and cyclohexane (10:100, volume ratio)] on the group surface with a track pitch of 1-6 gml. It was coated using a coater and then dried to form a chlorinated polyethylene layer having an average layer thickness of 250X.

The resulting chlorinated polyethylene layer had a layer thickness of 300X in four parts (corresponding to the bottom of the pregroove), and a layer thickness of 200X in the convex part (corresponding to the top of the pregroove side wall).

Further, the distance fa (a in FIG. 1) between the bottom surfaces of the four parts of the chlorinated polyethylene layer and the top surfaces of the convex portions was 900X (90 nm).

Next, on the chlorinated polyethylene layer described above, In, Au and GeS were each added in a weight ratio of 66%.

Co-deposited at a ratio of 12% and 22% to a thickness of 300
A recording layer of angstroms was formed.

In this way, an optical disk having the structure shown in FIG. 1, consisting of a substrate, a chlorinated polyethylene layer, and a recording layer in this order, was manufactured.

[Comparative Example 1] An optical disc consisting of the substrate and QB was manufactured in the same manner as in Example 1 except that the chlorinated polyethylene layer was not provided on the pregroove surface of the substrate.

[Comparative Example 2] A nitrocellulose-containing coating solution [methyl cellosolve/butanol/improper tool mixed solution (12:8:80,
Nitrocellulose dissolved in an amount of 0.25% (volume ratio)] was applied using a spin coater, and then dried to form an intermediate coating layer having an average layer thickness of 300X.

Four parts of the resulting intermediate coating layer (corresponding to the bottom of the pregroove)
The distance (a in FIG. 1) between the bottom surface of the convex portion and the top surface of the convex portion (corresponding to the top of the pregroove side wall) was 900 nm (90 nm).

Next, a recording layer made of In, Au, and GeS was formed on the intermediate coating layer by the same method as in Example 1.

In this way, an optical disc consisting of a plate, an intermediate coating layer, and a recording layer was manufactured in this order.

[Evaluation of optical disc] Tracking performance and C/N of each optical disc obtained
The ratio was evaluated.

(1) Tracking performance reading laser beam wavelength (λ) 830 nm (in vacuum)
The tracking performance was evaluated by changing the number of revolutions using a laser power of 0.8 mW. The evaluation criteria were as follows: A for cases in which no all-round tracking loss occurred, B for cases in which at least a small amount of tracking loss occurred, and C for cases in which a large amount of tracking loss occurred.

The results obtained are summarized in Table 1.

Table 1 Rotation speed (rpm) Example I A AA Comparative example I A B C2A
B C As is clear from the results shown in Table 1, the optical disk of the present invention (Example 1) in which the intermediate coating layer is a chlorinated polyethylene layer does not lose tracking even at a high speed of 1800 rpm. This did not occur at all, and the tracking performance was extremely good. On the other hand, for comparison, those without an intermediate coating layer (Comparative Example 1) and those with an intermediate coating layer made of nitrocellulose (Comparative Example 2) were particularly
Tracking loss occurred during high rpm rotation.

(2) After writing 1001 data of (2,7) RLL code (pit length lILm, pit period 1.5 lm) at C/N ratio linear speed: 5 m/sec, linear speed: 5 m/s. The C/N ratio was determined by performing frequency analysis on the reproduced signal using a spectrum analyzer. The setting conditions of the spectrum analyzer are a resolution bandwidth of 30 KHz, a video bandwidth of 100 Hz, and an Ml transmission frequency of 3.3 MHz.

The measurement results are shown in FIG. 2. That is, the optical disc of the present invention (Example 1) in which the intermediate coating layer was made of a chlorinated polyethylene layer was
It showed a stable and high C/N ratio than B.

On the other hand, for comparison, the sensitivity was lower in the case without the intermediate coating layer (Comparative Example 1) compared to Example 1, and in the case where the intermediate coating layer was made of nitrocellulose (Comparative Example 2)
In the range where the write power exceeds 6.5 mW, I;
At high speeds, I was unable to take any measurements because the car went off track.

Furthermore, in the optical disc of Example 1, the maximum value of the C/N ratio was 53 dB at a writing power of 6.5 mW;
The maximum C/N ratio of 11 discs in the optical disc of Comparative Example I was 51 dB at a writing power of 7.5 mW, and that of Comparative Example 2
The optical disc had a power output of 51 dB at 6°5 mW.

Therefore, the C/N of the optical disc manufactured in Example 1
It was clear that the ratio was superior to that of the optical discs of Comparative Example 1 and Comparative Example 2 manufactured by the conventional method.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of a pregroove type information recording medium having an intermediate coating layer. The 21st m is a graph showing the C/N ratio of the optical disc of Example 1 and the optical discs of Comparative Examples 1 and 2. 12: Intermediate coating layer; 13: Recording layer; Distance from coating layer surface, b nibble group depth

Claims (1)

[Claims] 1. An information recording medium in which a recording layer on which information can be written and/or read by a laser is provided on a tracking guide groove provided on the surface of a substrate via an intermediate coating layer. , the intermediate coating layer is made of chlorinated polyolefin, and the average layer thickness of the intermediate coating layer is 50 to 50.
An information recording medium characterized by being within a range of 1000 Å. 2. The information recording medium according to claim 1, wherein the average layer thickness of the intermediate coating layer is within the range of 100 to 400 Å. 3. The information recording medium according to claim 1, wherein the chlorinated polyolefin is chlorinated polyethylene or chlorinated polypropylene. 4. The distance (a) between the surface of the intermediate coating layer covering the bottom of the guide groove and the surface of the intermediate coating layer coating the top of the side wall of the guide groove is determined by the refractive index (n) of the substrate and the distance The following conditions for the wavelength (λ) of the laser light used when writing information to or reading information from the recording medium: [(2m+1)λ/8n]×0.9≦a The information recording medium according to claim 1, which satisfies ≦[(2m+1)λ/8n]×1.1 [where m is an integer of 0 or 1 or more]. 5. The distance (a) between the surface of the intermediate coating layer covering the bottom of the guide groove and the surface of the intermediate coating layer coating the top of the side wall of the guide groove is determined by the refractive index (n) of the substrate and the distance The following conditions for the wavelength (λ) of the laser beam: [(2m+1)λ/8n]×0.95≦a≦[(2m+1)λ/8n]×1.05 [However, m is 0 or 1 5. The information recording medium according to claim 4, wherein the information recording medium satisfies the following integer.