JPH02257444A - Information recording medium and recording/reproducing method - Google Patents

Abstract

PURPOSE:To obtain a preformat signal of uniformity and less variation by forming a cross-sectional shape into a trapezoidal shape with a longer upper base than a lower base, having an angle made by an oblique side of the trapezoid and a plane of an information recording medium at <=35 deg. and making the depth of a recessed part more than lambda/4n. CONSTITUTION:A recessed tracking track 7 has its cross section in the trapezoidal shape with the longer upper base than the lower base, and this trapezoid is regulated by the angle theta made with the oblique side of this trapezoid and the plane of the information recording medium 1, the height of the trapezoid, i.e. the depth (d) of the recessed part, and moreover its width (l). By forming the angle theta as <=35 deg., and also forming the depth (d) of the recessed part deeper than lambda/4n which is a depth of making a phase difference of normal reflecting light max., the preformat signal of high contrast can be obtained (N.B. lambda: wavelength of optical emission beam and (n): refractive index). By this method, the good preformat signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an information recording medium for recording and/or reproducing information using light, and particularly to an information recording medium from which a good preformat signal can be obtained.

[Conventional technology]

In recent years, electronic file systems using compact disks and write-once disks, erasable magneto-optical materials,
BACKGROUND ART Commercialization and research and development of optical information recording and reproducing devices such as optical disk systems using phase change materials are actively being carried out. Recently, optical card systems using portable optical recording media, such as card-shaped optical recording media (hereinafter referred to as optical cards), have also attracted attention.

Optical cards are characterized by being easy to carry due to their shape, and having a larger information capacity than disks for their area (in the case of disks, no information is recorded in the center).

These optical recording media include audio compact discs (hereinafter abbreviated as CDs) and video discs.

There are read-only types such as CD-ROMs that are intended for mass dissemination of information, write-once types that allow additional information to be written for the purpose of information files, and rewritable types. Qualitatively, such optical recording media have a high recording density, and qualitatively, the information recorded on the recording medium must be error-free when reproduced, that is, C/N.
good performance is required.

In the case of read-only types, the quality of the information is affected by the structure of the information reproduced on the substrate.

For example, in the case of an amplitude type recording medium in which information is recorded using an optical density difference and reproduction is performed based on the amplitude difference, the density difference and size, and the information recording is performed using unevenness and the In the case of a phase-type recording medium that performs reproduction using a phase difference, the detected signal is affected by the three-dimensional shape of its unevenness.

Also, in the case of the write-once type, in order to write information, information such as tracking grooves (groups), addresses for data recording management, and format information such as synchronization signals are copied on the board in advance (hereinafter referred to as , these tracking grooves,
Information including formatting pits is called preformat).

Conventionally, in order to obtain this preformat signal, the reflected light on the board was λ. A method of providing a concavo-convex pattern with a depth or height that creates a phase difference of /4 is known.

For example, for CDs, the recording pits are λ depending on the information.

Using a stamper with a concavo-convex pattern with a height of /4, the pattern is transferred to a substrate by injection molding, and aluminum having a reflectance of -
Signal reproduction is made possible by depositing a reflective metal film such as gold.

In addition, in the case of write-once type recording media, in order to write information accurately on the recording track, it is necessary to keep the irradiation position of the recording light constantly on the recording track in the scanning direction and in the direction perpendicular to it. Control (this is called auto-tracking, hereinafter abbreviated as AT) is required.

Therefore, it is customary to previously form a tracking track such as a track groove on the substrate as described above, and to record and reproduce information while performing AT sub-control relying on this tracking track. The manner in which tracking signals are detected in such a conventional optical recording medium will be described below.

FIG. 5 shows a schematic diagram of a cross section including a tracking track of a conventional optical recording medium. In the figure, 2 is an optically transparent substrate made of plastic or the like, 3 is a recording layer made of, for example, tellurium oxide, and 5 is a protective member.

A tracking track 7 having an uneven shape is previously formed on the substrate 2 by a known molding technique, and a recording layer 3 is laminated to a uniform thickness on the surface of the tracking track 7 by means such as vacuum deposition.

Light for recording/reproducing information or for AT sub-control enters from the direction of arrow A in the figure. As is well known, in order to obtain a good AT control signal, the height (depth) of the tracking track 7 must be accurately controlled. Figure 6 is a graph showing the relationship between the height of the tracking track and the intensity of reflected light reaching the AT control signal detection system. When detecting a signal using this method, the signal strength is maximum when the height of the tracking track is an odd multiple of λ/4n (λ is the wavelength of the light, and n is the refractive index of the substrate), and is minimum when it is an even multiple. .

This is exactly the same as the case with the previous CD.

By the way, in Japanese Patent Publication No. 63-19939, the angle of inclination between the wall of the information area and the normal to the record carrier is 30° to 6.
It has one value between 5° and the height (depth) of the information area is between 0.27λo/N and 0.427λ. /N, where λ0 is the wavelength of the optical radiation beam in free space and N is the refractive index of the substrate.

In other words, it is difficult to form the walls of pits or hills vertically by the development process, and when the walls of the pits or hills are sloped to facilitate the development process when manufacturing the master, it is difficult to form the walls of the pits or hills vertically. Depth or height of convex part 0.27λo/N~0
．． 427λ. It is stated that a good signal can be obtained by setting the value to /N nanometers.

Furthermore, IEICE Transactions J67-C2, 219 (19
84/2) "Studying the shape of guide grooves on optical disks using diffracted light analysis" reported that the angle between the wall of the track groove and the plane of the optical disk has a wide tolerance (the effect on the signal is small). has been done.

As described above, various studies have been conducted on the cross-sectional shape of the preformat of optical recording media and the relationship between the signals.
These all relate to optical recording media in which a reflective material such as silver, gold, aluminum, titanium, etc. is uniformly formed on a transparent substrate by vacuum deposition, etc., and detection of signals from these optical recording media is based on the phase difference of the reflected light. This is done using the .

However, in the case of a base material 6 medium in which a light reflective layer is formed by coating, the following problems arise when using a substrate made with consideration given to obtaining a preformat signal by the phase difference of reflected light as described above. there were. Figure 3 shows that a tracking track consisting of a concave groove is formed on an optically transparent substrate, a solution containing a light reflective dye and pigment is applied to the surface including the track, and then the solution is dried. 1 is a schematic diagram showing a cross-sectional structure in a direction transverse to a tracking track of an optical recording medium 1 on which a recording layer is formed. In the figure, 2 is a transparent substrate made of plastic or the like, 3 is a recording layer having light reflection properties, 4 is an adhesive layer, and 5 is a protective member made of transparent or opaque plastic or the like.

Information is recorded and reproduced by scanning the recording track 12 with the laser head while performing AT control based on the tracking track 11 and irradiating the recording track with a laser beam. At this time, the light beam used for recording and reproducing information enters from the direction indicated by arrow A in the figure.

By the way, in such a coating type optical recording medium, when the light reflective layer 3 is provided by coating on the transparent substrate 2 having the concave tracking track 11, the light reflective layer 3 accumulates in the concave portions, as shown in FIG. The film thickness is the film thickness of the recording track 12 by dz
) The film thickness of the racking track portion 11 is d, then d2
It is inevitable that <d.

In addition, in the case of a light reflecting layer containing dyes and pigments, when the film thickness is about 100 to several thousand films, the reflectance changes depending on the film thickness, and the conventional depth λ. The maximum signal strength could not be obtained with the /4 preformat.

That is, the reflectance with respect to the coating film thickness of the dye and pigment is, for example,
It changes as shown in Figure 1.

Note that the reflectance (R) of the recording layer can be calculated using the following equation (1).

''' n5+n* δ=4πdn*/λ n5 is the refractive index of the transparent substrate, n is the refractive index of the adhesive layer, n
Wood represents the complex refractive index of the dye layer (taking into consideration the influence of absorption), d represents the thickness of the dye layer, and λ represents the wavelength of light used for recording and reproduction. Also, it is expressed as n*=n-ki, where n is the refractive index of the dye layer,
k is the extinction coefficient.

The graph in Figure 4-1 is for a dye represented by the following structural formula, where n5==1.49. n &=1.49, n=2
．． 1°k=1.0, so n'=2.1-1. oi
(i=v”””T).

This is the result of calculation using the above equation (1) with λ=830 nm.

104e As is clear from the results in Figure 4-1, the reflectance of the dye rises rapidly and reaches a maximum when the film thickness is 800 to 1000 nm, and then remains almost constant at 2000 Å or more. .

In this way, the reflectance changes depending on the film thickness, especially the 8
The degree of change is large near the maximum of 00 to 1100 people.

Therefore, when a light-reflecting material is coated on a transparent substrate having concave tracking tracks, the signal from there will not only be due to the phase difference due to the concavities and convexities (but also include a large factor of reflectance (amplitude) in addition to the phase difference). This is considered to be the reason why a tracking signal with high contrast cannot be obtained when the height of the concave tracking is an odd multiple of λ/4n described above.

In order to solve these problems, for example, Japanese Patent Laid-Open No. 60-239947 discloses a method in which a light-absorbing and reflective dye film is provided on a substrate with a film thickness set to maximize the reflectance. discloses an information recording medium that can obtain a stable preformat signal by minimizing the difference in reflectance between concave and convex portions of a preformat, and by preventing fluctuations in reflectance from being added to the phase difference between the concave and convex portions. However, this method can only be used for specific dyes that have a wide range of film thicknesses that exhibit maximum reflectance.

In addition, in order to solve this problem, the present applicant has
No. 179126 discloses a method for obtaining a good preformat signal by specifying the dimensions of the recess so that the recording layer is formed such that the difference in reflectance between the tracking track recess formed on the substrate and the other parts is maximized. We are proposing recording media.

This takes advantage of the fact that the reflectance of the concave part and the reflectance of other parts are determined by the film thickness.For example, in the case of the organic dye mentioned above, the S/N ratio of the signal is explained using Figure 3. In order to improve the reflectance of the recording track 12, it is desirable to make the reflectance of the recording track 12 as high as possible. Therefore, for this purpose, the film thickness d2 of the recording track is preferably about 800 to 1100 mm. Further, in order to increase the amplitude of the AT control signal as much as possible, it is preferable that the tracking track section 11 has a reflectance difference (contrast) as large as possible with respect to the recording track. Therefore, from FIG. 4, the film thickness d is set to 15
It turns out that the number of people should be around 00 to 2,000 people.

Note that even at a thickness of 2000 Å or more, the reflectance does not exceed about 10%, and the dependence of the reflectance on the film thickness is small, so it is possible to set the film thickness to any desired thickness of 2000 Å or more.

Incidentally, the film thickness d1 of the light reflective layer in the concave tracking track portion is determined by the amount accumulated in the concave portion during the coating process. Therefore, the film thickness d of the tracking track 11 can be controlled by changing the depth d and width l of the concave tracking track portion to change the amount accumulated in the concave portion. As explained above, in order to make the film thickness d2 of the recording track 900 to 1100 Å and the film thickness d of the tracking track 11 1500 to 2000 Å or more, the depth d of the recess of the tracking track must be
is required to be 1800 to 2000 Å or more, which is deeper than the 1400 depth set when obtaining the preformat signal due to the above-mentioned phase difference.

In this way, when applying a reflective material to a substrate having a concave tracking track, the depth of the concave portion is
4n (where λ is the wavelength of the reproduction light, n is the refractive index of the substrate), but by improving the depth of the recess in consideration of the accumulation of the coating liquid, the contrast of the preformatted signal is excellent. However, it was still not completely satisfactory.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems.When forming a light reflective layer by coating on a transparent substrate, the coating liquid accumulates in the preformat recesses, resulting in a uniform thickness. The purpose of this is to provide an information recording medium that can obtain a better preformat signal than conventional ones.

Another object of the present invention is to provide an information recording medium that can obtain a preformatted signal that is better and more uniform than conventional ones.

[Means for solving problems]

The information recording medium of the present invention has a light reflecting layer provided by coating on an information recording medium substrate having a concavo-convex preformat, in which the cross-sectional shape of the concave portion of the concave-convex preformat is longer than the length of the upper base. The preformat recess has a trapezoidal shape whose length is longer than the length of the bottom, the angle θ between the oblique side of the trapezoid and the plane of the information recording medium is 35° or less, and the depth d of the preformat recess is λ/4n. It is also characterized by its deep depth.

That is, the present invention is applicable to an information recording medium in which a preformat is likely to be read by both the difference in reflectance caused by the difference in film thickness between the concave and convex portions of a light reflecting layer formed by wet coating, and the phase difference due to the concavity and convexity. In the preformat recess, e
After discovering that the film shape and film thickness of the light-reflecting layer around the dge area greatly contribute to the acquisition of high-contrast preformat signals, we conducted various studies based on this finding.
As mentioned above, by making the cross-sectional shape of the preformat recess trapezoidal, making the depth deeper than λ/4n, and making the angle θ between the oblique side and the plane 35° or less, a preformat signal with higher contrast can be obtained. This is what was obtained. The reason for this is not clear, but it is thought that the gentle depressions formed on the surface of the coated light-reflecting layer and the oblique side of the preformat recess having an angle of 35" or less work synergistically to obtain a preformat signal with high contrast. .

Furthermore, since the light reflecting layer is formed through a coating and drying process so that the recording track 11 is continuously formed up to the tracking track 12 as shown in FIG. 2, it is thought that a uniform preformat signal can be obtained.

Furthermore, the trapezoidal shape allows the coating liquid of the light reflective layer to accumulate in the preformat recesses in a very uniform manner, and as a result, it is thought that a more stable and uniform preformat signal can be obtained than in the past.

Next, the present invention will be explained in detail using figures.

FIGS. 1 and 2 are schematic cross-sectional views showing embodiments of the optical recording medium of the present invention. In FIG. 1, l is a transparent substrate, on the surface of which a concave preformat, specifically a tracking track 7, is formed. transparent substrate l
A light reflecting layer 3 is formed by coating on the preformat forming surface, and a protective member 5 is adhered via an adhesive layer 4.

FIG. 2 is an enlarged cross-sectional view of the optical recording medium according to the present invention shown in FIG. In FIG. 2, 12 is a concave tracking track formed on the substrate, and 11 is a recording track on which information is recorded.

As shown in FIG. 2, the concave tracking track of the present invention has a trapezoidal cross-sectional shape in which the length of the upper base is longer than the length of the lower base. This trapezoid is defined by the angle [θ] between the hypotenuse of the trapezoid and the plane of the information recording medium, the height of the trapezoid, that is, the depth of the recess (dl), and the width (fl).

In the present invention, the angle [θ] is formed to be 35° or less, and the depth (d) of the recess is usually deeper than λ/4n, which is the depth at which the phase difference of reflected light is maximum. By doing so, a preformatted signal with high contrast can be obtained, which is preferable. Specifically, the depth of the preformat recess is n = 1.49 using a beam of λ = 830 mm.
When using polymethyl methacrylate as the substrate, it is preferable that the depth of the recess is deeper than about 1,400 mm, and when using a beam with λ = 830 mm and using polycarbonate with n = 1.58 as the substrate. Preferably, the depth of the recess is greater than about 1320 mm. As a result, a light reflecting layer having a thickness exhibiting substantially the lowest reflectance is formed in the recessed portion.

By the way, it has been found that these angle [θ], depth (d), width (f), and contrast of the preformat signal exhibit a correlation. A schematic diagram thereof is shown in FIG.

In FIG. 7, the vertical axis shows the contrast of the track crossing signal, and the horizontal axis shows the correlation between the depth (d) and the width [l] using the angle θ. However, Dl and D2 represent one value of the depth d of the recess, and Dl>D2.

Also, L2 represents one value of the width l of the recess, and L2
shall be.

As can be seen from FIG. 7, the contrast increases as the depth Cd) increases. On the other hand, when [θ] is constant, if d is made shallow, the slope of the straight line becomes small (this means that if a tracking signal that is as uniform as possible is to be obtained, the tolerance of the value of angle [θ] becomes larger.

For example, in Figure 7, the contrast is 0.4 to 0.45.
When obtaining a value in the range of 1-L2, the allowable range of [θ] at the depth of D2 is about 28° to about 3
2°, and when D2 is about 210 to 28°da, the smaller the value is, the wider it becomes. Therefore, when considering the machining accuracy of the slope of the preformat, it is preferable that the tolerance range of [θ] be wide, and high contrast can be achieved. The value of (d) is 15 to obtain
00 to 3,700 people, particularly 2,000 to 3,000 people, and more preferably 2,500 to 3,000 people.

Furthermore, as shown in FIG. 7, when the angle [θ] is 35° or less, the contrast of the track crossing signal increases as the angle [θ] becomes smaller, but when θ=15° or more, especially 20°
When the angle is ˜30°, a preformat recess having a slope of angle [θ] can be stably formed. Considering this point, the angle θ is 35° or less, particularly preferably 15° or more and 35°.
The angle is preferably 20° or more and 30° or less.

Also, the width [l] of the tracking track depends on the optical system of the recording/reproducing device, and the width! is preferably in the range of 0.5<1<1.5 with respect to the beam spot diameter [φ]. For example, in the case of an optical disk, the beam spot diameter [φ] is 1 to 2 μm, and in the case of an optical card, [φ] = 3 μm.
It is m.

On the other hand, as shown in Figure 7, the width of the tracking track [
It can be seen that the smaller the value of β], the higher the contrast can be obtained.

Considering these, in the case of optical discs, l is 0.5 to 3
μm1, especially 0.5 to 1.0 μm, more preferably 0.5 to 0.
The thickness is preferably 8 μm. By reducing l, the contrast is improved, the recording density is also improved, and the recording capacity can be increased. In addition, in the case of portable information recording media such as optical cards, where the spot diameter [φ] is set large to prevent dust and scratches, l is 1.5 to 1.5.
4.5μm1 especially 1.8~3.5μm1 even 2~3μm
It is preferable to form it in m.

A light reflecting layer 3 is formed by wet coating on a substrate on which a preformat having such a shape is formed.

As shown in FIG. 2, the light reflecting layer 3 is formed continuously from the recording track 11 to the recessed portion 12, which is a slope and a tracking track, by using the groove shape of the present invention.

This light reflecting layer is required to have a predetermined reflectance in order to reliably read the preformat information formed on the substrate. The value is determined depending on the relationship with the reproducing device, but in order to perform highly accurate reproduction without being affected by dust, scratches, etc. on the substrate surface, it is preferable that at least the recording track portion has a reflectance of 15% or more.

Materials for such a light reflecting layer include whether the information recording medium of the present invention is a ROM type that only reads information formed on the substrate as a preformat, or a tracking track or address pit formed on the substrate as a preformat. Although it depends on whether it is a type that allows new information to be additionally written using, etc., it is preferable that the reflectance differs depending on the film thickness in any case.

In the case of the former ROM type, metal fine particles dispersed in a binder or heat-resistant dyes and pigments are used, and in the latter type, ROMs that both absorb and reflect recording and reproducing light are used. Preferably, dyes and pigments conventionally known as optical recording materials, such as cyanine-based, squalium-based, phthalocyanine-based, tetradehydrocholine-based, polymethine-based, naphthoquinone-based dyes and pigments, and organometallic rust materials such as benzenedithiol nickel complexes are preferably used. can be preferably used.

Furthermore, in the latter case, a light reflecting layer may be provided by coating only the preformat portion, and the portion where additional writing is to be performed may be a vapor deposited metal film.

Organic solvents that can be used when coating the light-reflecting layer vary depending on whether the dye is in a dispersed or dissolved state, such as methanol, ethanol, isopropanol, diacetone alcohol, etc. Examples include alcohol-based solvents, ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone, as well as amide-based, ether-based, ester-based, aliphatic halogenated hydrocarbon-based, aromatic, and aliphatic hydrocarbon-based solvents. In particular, alcohol solvents are preferred because they do not attack the substrate during coating of the light reflective layer.

In FIG. 2, recording track ll of the information recording medium of the present invention
In order to obtain a good preformat signal with high contrast, the film thickness d2 of the light reflection layer is preferably applied to a film thickness that exhibits substantially the highest reflectance of the light reflection layer. This film thickness d2 is determined by the optical constant n (refractive index) and k (extinction coefficient) of the recording layer used, but in the case of dyes and pigments, it is usually applied by 400 to 1500 coats. On the other hand, the film thickness d of the concave portion of the concave preformat is preferably such that the difference in reflectance between the recording tracks described above is as thick as possible (so that the film thickness exhibits the lowest reflectance), and is usually 120 mm.
0 Å or more, particularly preferably 1500 to 3000 people. In the present invention, the depth d of the concave preformat is formed to be deeper than λ/4n, particularly 1.07 to 2.7 times, and more preferably about 1.4 to 2.2 times, λ/4n. By setting the film thickness of d2 within the above range, d! The film thickness is 1200 Å
The above is formed.

The specific film thickness is determined by the optical constant n1k specific to the material of the light reflective layer. For example, the above n=2.1, k=1.0
In the case of a polymethine dye having the following structural formula (1), the film thickness dependence of reflectance changes as shown in Figure 4-1.

Structural formula [1] Therefore, when using this material, it is preferable that the film thickness d2 of the recording track portion is 900±100 mm.
At this time, a signal showing good contrast is expected when the film thickness d1 of the concave tracking track portion is 1800 to 2000, which indicates the minimum reflectance. For this purpose, the depth d of the concave tracking track portion should be set to 2000~
By setting the number of people to 3,000, preferably 2,300 to 2,700, particularly 2,500 to 2,700, the above d1
= A value of 1800 to 2000 people is secured.

In addition to this, in the present invention, the cross-sectional shape of the concave preformat is a trapezoid whose upper base is longer than the lower base, and the angle θ between the oblique side and the plane of the information recording medium is 35' or less.
A particularly good preformat signal could be obtained by setting the value to '~30'.

Incidentally, in the present invention, as a method for forming a concave preformat on a transparent substrate, an injection method, a combination method, a cast molding method, a 2P method, etc. are used using a preformed mold.

Further, the transparent substrate is required to have high transmittance for information recording and 10R reproduction light, and substrates made of glass, ceramic, acrylic resin, vinyl chloride resin, polystyrene resin, polycarbonate resin, etc. are used.

Furthermore, when providing a light reflective layer on a concave preformat substrate by wet coating, a solution or dispersion of the light reflective layer material can be applied by roll coating, Meyer bar coating, air knife coating, calendar coating, dip coating, spraying, etc. Apply using the following method.

By the way, the solubility of the light-reflecting layer material liquid is determined by the dye and solvent used, and based on this, the solid content concentration and viscosity of the coating liquid are determined in order to obtain the film thickness that maximizes the reflectance.

For example, when diacetone alcohol is used as a solvent using dyes as shown in the structural formulas [I] and [IL], the concentration of the dye is 1 to 5 wt%, particularly 2 to 4 wt%.
is preferable, and the viscosity is preferably 2 to 20 cps.

Particularly preferred is 2 to 8 cps.

Furthermore, as for the drying conditions of the coating film, it is preferable that the solvent of the coating solution is applied while evaporating, and the process of leveling the film is controlled so that a coating film is uniformly formed in the preformat recesses. Specifically, for example, Gently blow clean air at room temperature onto the applied surface to dry it. In this case, the flow rate of clean air is 1-5 m/min, especially 2.5 m/min.
~3.5 m/min is preferred, and the drying time is preferably 10 seconds to 2 minutes, particularly 20 to 40 seconds.

The transparent substrate on which the light reflection layer is formed in this manner is laminated with a protective member, for example, via an adhesive.

In the present invention, the adhesive layer may include conventionally known adhesives, such as vinyl acetate, acrylic esters, vinyl chloride, polymers and copolymers of vinyl monomers such as ethylene, acrylic acid, and acrylamide, polyamides, polyesters, and polyethers. Thermoplastic adhesives such as amino resins (urea resin, melamine resin), phenolic resins, epoxy resins, urethane resins, chemical adhesives such as thermosetting vinyl resins, natural rubber, nitrile rubber, chloroprene process, This is preferable when considering mass and continuous production.

The protective member has the purpose of mechanically protecting the recording layer 3, and can be made of plastic, metal, ceramics, glass plate, paper, or a composite material thereof.

Further, the protective member itself may be transparent or opaque, as long as it satisfies the above-mentioned purpose.

Rather, these are determined by the optical information reading method; if it is a transmission type reading method, it must be transparent, and the requirements for birefringence are the same as for the substrate, so the material used is naturally limited. .

In the case of a reflective reading method, the protective layer may be opaque and its material can be selected from a wide range of materials.

This protective member may be laminated on the optical recording layer in direct optical contact with the recording layer 3. Alternatively, a so-called air gap type configuration may be used in which a protective member is provided via an air layer if necessary.

As explained above, the cross-sectional shape of the concave preformat formed on the substrate of the information recording medium provided with the light reflective layer by wet coating is a trapezoidal shape in which the upper base is longer than the lower base, and the hypotenuse of the trapezoid and the information recording medium By setting the angle between the planes to be 356 or less, it is possible to obtain a particularly excellent preformat signal that is uniform and has little variation.

In addition, in the present invention, scratches and dust are easily attached to the surface (in order to prevent tracking errors caused by this, the optical spot diameter for recording and reproduction is designed to be large, and the width of the tracking track is formed to be large according to the spot diameter. The present invention is particularly suitable for use in portable information recording media because it is possible to obtain a preformatted signal with high contrast even in the case of portable information recording media.

In the present invention, the cross-sectional shape of the concavo-convex preformat and the film thickness of the recording layer are set from a photo taken by cutting the created optical card in the direction perpendicular to the tracking track and taking the cross-section with an SEM (3000x magnification). did.

Further, an optical card recording/reproducing machine (manufactured by Canon) was used to measure the contrast.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 As a transparent substrate, length 10 cm x width 10 cm x thickness 0.4
mm polymethyl methacrylate substrate (n=1.49)
A concave preformat was engraved by hot pressing. The preformat is group 3 for AT.
Tracking tracks (groups) of μm were formed at a pitch of 12 μm, and 2560 recording areas and tracking tracks were provided.

At this time, the shape of the AT group of the tracking track has a groove width of 3 μm, a depth of d=2500 people, and a group angle θ=25°.

The following structural formula [! ]2 as drying conditions
Clean air at 3° C. was blown onto the coated surface for 20 seconds at a flow rate of 3 m/min.

The optical constant of this dye is n=2.1. = 1.0, and the thickness dependence of the reflectance is as shown in Figure 4-1.

From this figure, the film thickness of each light reflective layer is set as the dry film thickness in the recording area d 2 = 1000 layers, and in this case, the film thickness in the tracking track (group) d = 1800
The depth of the group was set to d = 2,500 people so that the number of people in the group was 2,500 people. The substrate on which the recording layer was formed was a hot melt adhesive based on ethylene vinyl acetate copolymer, and the protective material was
．． A polymethine dye represented by Acryzo4e with a 35mm logo printed is dissolved in diacetone alcohol and applied as a 3wt% solution onto the substrate using a roll coater.The diacetone alcohol solvent is evaporated and exposed to light. A reflective layer 3 was formed.

A tracking track crossing signal is measured as an AT control signal for the optical card. The optical system for reproduction is 830n.
The evaluation was made by the contrast when a 3 μm diameter semiconductor laser was focused on a 3 μm diameter spot and the distance between the recording track and the tracking track was crossed.

Examples 2 to 4 In Example 1, the group angle θ was set to 30° and 15°.
An optical card was prepared in the same manner as in Example 1, except that the angle was 12°, and the contrast was measured when crossing between the recording track and the tracking track.

Example 5 The cross-sectional shape of the uneven preformat and the angle of the slope [θ]
A polymethine dye represented by the structural formula [I] was coated on this substrate in the same manner as in Example 1, with a depth [dl] of 25° and a depth [dl] of 2000, to form a light reflective layer and produce an optical card. did. However, the film thickness d2 of the light-reflecting layer on the preformat convex portion was 1,000 layers, and the film thickness d of the preformat concave portion was 1,600 layers.

The contrast of the track crossing signal of the optical card thus prepared was measured in the same manner as in Example 1.

Example 6 The cross-sectional shape of a concavo-convex preformat to be formed on a polymethyl methacrylate substrate was prepared such that the slope angle [θ] was 25° and the depth [dl was 1500 mm.
] A polymethine dye represented by the formula was applied in the same manner as in Example 1 to form a light reflective layer and an optical card was produced. However, the film thickness (d2) of the light reflective layer on the preformat convex portion is 8
00 people, and at this time, the film thickness d2 of the preformat recess is
There were 1,200 people.

The contrast of the track crossing signal of the optical card thus prepared was measured in the same manner as in Example 1.

Comparative Example 1 (1) Group angle θ is 40. . (2) The angle θ of the tracking track group was set to 90.
°, and the depth is 1 which corresponds to λ/4n of the phase difference type.
An optical card was prepared in the same manner as in Example 1, except that the number of participants was 400. (3) θ was set to 906, and the depth of the group was set to a value considering the thickness of the coating liquid of the light reflective layer, that is, 2500 participants. The rest was an optical card made in the same manner as in Example 1. (4) Example 1 except that θ=25° and the depth of the group was 1400 people corresponding to λ/4n where the phase difference was maximum.
The contrast was measured for an optical card prepared in the same manner as above, and for each of the above optical cards.

The above results are shown in Table-1.

Table Example 7 A dye having the following structural formula [■] was used as a light-reflecting layer material.

Structural Formula [1] FIG. 4-2 is a graph showing the relationship between the film thickness and reflectance of the light-reflecting layer when the organic dye represented by the above-mentioned Structural Formula [II] is used. The refractive index n of the above dye is expressed as =o,8 with an extinction coefficient of 3.0, and the graph was calculated using the above-mentioned equation (1) using the constant.

From the graph, the reflectance has a maximum value of 26% when the dye layer thickness is around 600 to 700 layers, and a minimum value of 1 when the dye layer thickness is around 1300 to 1400 layers.
Get 0%. Further, it can be seen that the reflectance is approximately constant at 14% at a thickness of 3000 Å or more.

Therefore, the coating is applied so that the film thickness (d2) is 600 films on the recording track, and the group depth is set to 3,000 films so that the film thickness d1 on the tracking track (group) is 1,300 films. =25°.

In this example, the coating liquid for the light-reflecting layer was used with the above structural formula [
■] 3wt% of the dye shown in diacetone alcohol
The dissolved one was used.

Furthermore, the light reflecting layer coated on the substrate was dried by blowing clean air at 23° C. onto the coated surface for 30 seconds at a flow rate of 3.5 m/min.

In other respects, an optical card was prepared in the same manner as in Example 1, and evaluated in the same manner as in Example 1.

Examples 8 to 1O Optical power cords were prepared in the same manner as in Example 7 except that θ was changed to 30', 15°, and 116.

The contrast of this optical card when crossing between the recording track and the tracking track was measured.

Example 11 The cross-sectional shape of the concavo-convex preformat was made such that the slope angle [θ] was 25 degrees and the depth (d) was 2000 mm. On this substrate, the dye represented by the structural formula [11] was applied as in Example 7. A light reflective layer was formed by coating in the same manner to produce an optical card. However, the film thickness d2 of the light reflective layer on the preformat convex portion is 60
In this case, the film thickness d of the preformat recess is 12
There were 00 people.

The contrast of the track crossing signal of the optical card thus prepared was measured in the same manner as in Example 7.

Example 12 The cross-sectional shape of the uneven BRIFO° mud is the angle of the slope [θ]
= 20°, depth (dl = 1500 people) A dye represented by the structural formula [II] was applied onto a human substrate in the same manner as in Example 7 to form a light reflective layer, thereby producing an optical card.

However, the film thickness (d2) of the light reflective layer on the preformat convex part
was 600 people, and the film thickness d2 of the preformat recess at this time was 1100 people.

The contrast of the track crossing signal of this optical card was measured.

Comparative Example 2 (1) An optical card was produced in the same manner as in Example 7 except that the angle θ was 40°.

(2) Set the angle θ of the tracking track group to 90
'', and the depth is 1, which corresponds to λ/4n of the phase difference type.
An optical card was prepared in the same manner as in Example 7, except that the number of participants was 400. (3) θ was set to 906, and the depth of the group was set to a value considering the thickness of the coating liquid of the light reflective layer, that is, 3000 participants. The optical card was otherwise made in the same manner as in Example 7. (4) The same as in Example 7 except that θ = 20° and the group depth was 1400 people, which corresponds to λ/4n where the phase difference is maximum. Contrast measurements were made for optical cards prepared in the same manner and for each of the above optical cards.

The above results are shown in Table 2.

As can be seen from Tables 1 and 2, according to the present invention, it was possible to obtain preformatted signals that always had good contrast and little variation, and stable tracking could be performed.

On the other hand, in Comparative Examples, the contrast of the preformat signal is low, and in Comparative Example 1 (3), (4) and Comparative Example 2 (3), (4), preformat signals with partially high contrast are obtained. The variation was large, making it impossible to perform stable tracking.

〔Effect of the invention〕

As explained above, the cross-sectional shape of the concave preformat formed on the substrate of the information recording medium provided with the light reflective layer by wet coating is trapezoidal with the upper base longer than the lower base, and the hypotenuse of the trapezoid and information recording. The angle formed by the plane of the medium is 35° or less,
Moreover, by making the depth of the preformat recess deeper than λ/4n, it was possible to obtain a particularly excellent preformat signal that was uniform and with little variation, and to perform stable tracking.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing the cross-sectional structure of an information recording medium according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing the cross-sectional structure of a conventional optical recording medium. Figure 2 is a graph showing the relationship between the film thickness of the light reflective layer and reflectance, Figure 5 is a schematic diagram showing the cross-sectional structure of a conventional optical recording medium, and Figure 6 is the height of the tracking track and detection of the AT control signal. It is a graph showing the relationship between the intensity of reflected light reaching the system. FIG. 7 is a schematic diagram showing the correlation between the angle [θ] of the cross section of the concavo-convex preformat, the depth [d], and the width [l] of the concave portion, and the contrast value of the preformat signal. 1... Information recording medium 2... Transparent substrate 3... Light reflective layer 4... Adhesive layer 5... Protective member 6.11... Recording track 7.12... Tracking track A ...Recording and reproducing light Figure 6 Track skin 1;

Claims (19)

[Claims] (1) In an information recording medium that has a light reflecting layer provided by wet coating on a substrate for an information recording medium having an uneven preformat, and can perform at least recording or reproduction using an optical radiation beam, the unevenness The preformat recess has a trapezoidal cross-sectional shape in which the length of the upper base is longer than the length of the lower base, and the angle θ between the oblique side of the trapezoid and the plane of the information recording medium is 35° or less, and An information recording medium characterized in that the depth d is deeper than λ/4n. (where λ: optical radiation beam wavelength, n: refractive index of the substrate) (2) The information recording medium according to claim 1, wherein the thickness of the light reflecting layer is different between the concave portions and the convex portions of the concavo-convex preformat. (3) The light reflecting layer is an organic dye The information recording medium according to claim 1, comprising: (4) The information recording medium according to claim 1, wherein the angle [θ] between the oblique side of the preformat recess and the plane of the information recording medium is 15° or more and 35° or less. (5) The information recording medium according to claim 4, wherein the angle [θ] between the slope of the preformat recess and the plane of the information recording medium is 20° or more and 30° or less. (6) The information recording medium according to claim 2, wherein the thickness of the light reflecting layer in the concave portion of the preformat is greater than the thickness of the convex portion of the preformat. (7) The thickness of the light-reflecting layer at the convex portions of the preformat is such that the film thickness exhibits the substantially maximum reflectance, and the thickness of the film at the concave portions of the preformat is the thickness that exhibits the substantially lowest reflectance. The information recording medium according to claim 6. (8) The information recording medium according to claim 1, wherein the preformat recess has a depth of 1500 Å or more and 3700 Å or less. (9) The information recording medium according to claim 8, wherein the preformat recess has a depth of 2000 Å or more and 3000 Å or less. (10) The information recording medium according to claim 9, wherein the preformat recess has a depth of 2500 Å or more and 3000 Å or less. (11) Claim 3 wherein the organic dye is a polymethine dye.
information recording medium. (12) having a light reflecting layer provided by wet coating on an information recording medium substrate having an uneven preformat;
The cross-sectional shape of the recessed portion of the uneven preformat is a trapezoid in which the length of the upper base is longer than the length of the lower base, and the angle θ between the hypotenuse of the trapezoid and the plane of the information recording medium is 35° or less, and A recording/reproducing method characterized in that at least information is recorded or information is reproduced by irradiating an information recording medium with a preformat recess depth d deeper than λ/4n with an optical radiation beam having a wavelength λ. (13) The recording/reproducing method according to claim 12, wherein the angle [θ] between the oblique side of the preformat recess of the information recording medium and the plane of the information recording medium is 15° or more and 35° or less. (14) The recording/reproducing method according to claim 12, wherein the angle [θ] formed by the oblique side of the preformat recess of the information recording medium and the plane of the information recording medium is 20° or more and 30° or less. (15) The recording/reproducing method according to claim 12, wherein the thickness of the light reflecting layer in the concave portion of the preformat is greater than the thickness in the convex portion of the preformat. (16) The thickness of the light reflecting layer of the information recording medium at the convex portions of the preformat is the thickness that exhibits the substantially maximum reflectance, and the thickness at the concave portions of the preformat is the thickness that exhibits the substantially lowest reflectance. 13. The recording/reproducing method according to claim 12, wherein the recording/reproducing method has a thickness. (17) The recording/reproducing method according to claim 12, wherein the preformat recess of the information recording medium has a depth of 2000 Å or more and 3000 Å or less. (18) The recording/reproducing method according to claim 12, wherein the depth of the preformat recess of the information recording medium is 2000 Å or more and 3000 Å or less. (19) The recording/reproducing method according to claim 12, wherein the preformat recess of the information recording medium has a depth of 2500 Å or more and 3000 Å or less.