JP2637587B2 - Information recording medium and recording / reproducing method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium for recording and / or reproducing information by light, and more particularly to an information recording medium capable of obtaining a good preformat signal.

[Conventional technology]

In recent years, the commercialization and research and development of optical information recording / reproducing devices such as an electronic file system using a compact disk or a write-once disk, an erasable magneto-optical material, and an optical disk system using a phase change type material have been actively pursued. Is being done. Recently, an optical card system using a portable optical recording medium, for example, an optical recording medium in the form of a card (hereinafter, referred to as an optical card) has attracted attention.

The optical card is characterized in that it can be easily carried in its form, and its information capacity is larger than that of a disc for its area (in the case of a disc, information is not recorded in the center part).

These optical recording media are read-only types, such as compact discs for audio (hereinafter abbreviated as CDs), video-discs, and CD-ROMs, for the purpose of mass distribution of information, and files for information. There are a write-once type in which information can be additionally written and a rewritable type. Such an optical recording medium is required to have a high recording density in terms of quantity and to be qualitatively free from errors, that is, to have a good C / N in reproducing information recorded on the recording medium. Is done.

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

Also, in the case of the appendable type, information of a format such as a groove (group) for tracking, an address for data recording management, and a synchronization signal is previously copied on a substrate in order to write information (hereinafter referred to as a "recording"). The information including the grooves for tracking and the pits for format is called pre-format).

How reflected light to the substrate in order to obtain this Purifuomatsuto signal provided the depth or height of the concavo-convex pattern such as making a phase difference of lambda _0/4 are known in the art.

For example using a stamper having a height of the concavo-convex pattern of the recording pit lambda _0/4 is corresponding to data CD, etc. by Injiekushiyon molding, transfer the pattern to the substrate, it has a uniform reflectivity on the substrate A signal can be reproduced by depositing a reflective metal film such as aluminum or gold.

Further, in the case of a recordable type recording medium, in order to record the information accurately on the recording track, the irradiation position of the recording light is constantly kept on the recording track in the scanning direction and the vertical direction. 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 / reproduce information while performing AT control based on the tracking track. The manner of detecting a tracking signal in such a conventional optical recording medium will be described below.

FIG. 5 is a schematic view 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 tellurium oxide or the like, and 5 is a protective member. A tracking track 7 having an uneven shape is previously engraved on the substrate 2 by a known molding technique, and the recording layer 3 is laminated on the surface of the tracking track 7 to a uniform thickness by means such as vacuum deposition. I have.

Light used for information recording / reproduction or AT control is incident from the direction of arrow A in the figure. As is well known, the height (depth) of the tracking track 7 needs to be accurately controlled in order to obtain a good AT control signal. FIG. 6 is a graph showing the relationship between the height of the tracking track and the intensity of the reflected light reaching the detection system of the AT control signal. The diffracted light by the tracking track and the reflected light from portions other than the tracking track are shown. In the case of detecting a signal using the interference of (1), when the height of the tracking track is an odd multiple of λ / 4n (where λ is the wavelength of light and n is the refractive index of the substrate), the signal intensity is maximized, and the even multiple is obtained. Is the minimum.

 This is exactly the same as the previous CD.

Japanese Patent Publication No. 63-19939 discloses that the inclination angle between the wall of the information area and the normal to the record carrier has one value between 30 ° and 65 °, and the height (depth) of the information area. ) Is 0.27λ ₀
Record carriers have been proposed which have a value between NN / 0.427λ ₀ / N, where λ ₀ is the refractive index of the substrate and the wavelength N of the optical radiation beam in free space.

That is, it is difficult to form the pit or hill wall vertically by the developing process, and when the pit or hill wall is inclined to facilitate the developing process when manufacturing the master, the concave or the concave portion is formed. 0.27λ ₀ /N~0.427λ
It is described that a good signal can be obtained with ₀ / N nanometer.

Furthermore, IEICE Transactions J67-C2,219 (1984/2)
“Examination of guide groove shape on optical disk by diffracted light analysis”
It has been reported that the angle formed between the wall of the track groove and the plane of the optical disk has a large tolerance and little influence on the signal. As described above, various studies have been made on the relationship between the cross-sectional shape of the preform of the optical recording medium and the signal thereof, but all of these methods uniformly apply a reflective material such as silver, gold, aluminum, titanium, or the like to a transparent substrate on a vacuum. With respect to optical recording media formed by vapor deposition or the like, detection of signals from these optical recording media is performed using the phase difference of the reflected light.

However, in the case of an optical recording medium in which a light reflection layer is formed by coating, the use of a substrate made in consideration of obtaining a preformat signal by the phase difference of reflected light as described above has the following problems. Was. FIG. 3 shows that a tracking track composed of a concave groove is formed on an optically transparent substrate, and a solution containing a light-reflective dye or pigment is applied on the surface containing the track, and then the solution is dried. FIG. 2 is a schematic diagram showing a cross-sectional structure in a direction crossing a tracking track of the 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 reflectivity, 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 irradiating a laser beam on the recording track 12 while scanning the recording track 12 while performing AT control with the laser head relying on the tracking track 11. At this time, a light beam used for recording / reproducing information enters from a direction indicated by an arrow A in the figure.

By the way, as shown in FIG. 3, such a coating type optical recording medium accumulates in the concave portion when the light reflective layer 3 is provided on the transparent substrate 2 having the concave tracking track 11 by coating. the film thickness can not be avoided to become a thickness of the recording tracks 12 and d ₂ <d ₁ when the film thickness d ₁ of d ₂ tracking Tora poke unit 11.

In the case of a light reflection layer containing a dye or pigment, the film thickness is 100 mm.
For to several thousands Å thickness on the order of, the reflectance varies with the thickness, it was not possible to obtain a maximum signal intensity in the conventional depth lambda _0/4 of Purifuomatsuto.

That is, the reflectance with respect to the coating film thickness of the dye / pigment is, for example, the fourth
-1 changes as shown in FIG.

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

n _s is the refractive index of the transparent substrate, n _a is the refractive index of the adhesive layer, n ^*
Represents the complex refractive index of the dye layer (considering the effect of absorption), d represents the thickness of the dye layer, and λ represents the wavelength of light used for recording / reproducing.
Also, n ^* = n-ki, where n is the refractive index of the dye layer and k is the extinction coefficient.

The graph of 4-1 diagrams intended dye represented by the following structural _{formula, n s = 1.49, n a} = 1.49, n = 2.1, k = 1.0, thus This is the result of calculation using λ = 830 nm using the above equation (1).

As apparent from the results shown in FIG. 4-1, the reflectance of the dye rapidly rises and shows a maximum when the film thickness is 800 to 1000 °, and then shows a substantially constant value when the film thickness is 2000 ° or more.

As described above, the reflectivity changes depending on the film thickness.
In the vicinity of the maximum of 800 to 1100, the degree of the change is large.

Therefore, when a light-reflective substance is applied to a transparent substrate having a concave tracking track, a signal from the transparent substrate is not only a phase difference due to unevenness but also a factor of reflectance (amplitude) greatly added to the phase difference. This is considered to be a reason that a tracking signal having a high contrast cannot be obtained if the height of the concave tracking is an odd multiple of λ / 4n.

As a solution to such a problem, for example, JP-A-60-239947 discloses a method in which a light-absorbing and reflective dye film having a film thickness set so that the reflectance is maximized is provided on a substrate. There is disclosed an information recording medium capable of obtaining a stable preformat signal by minimizing a reflectance difference between a concave portion and a convex portion of a preform and preventing a variation in reflectance from being added to a phase difference of the unevenness. However, this can only be used for certain dyes that exhibit a maximum reflectance and a wide range of film thickness.

In order to solve this problem, the present applicant has filed Japanese Patent Application No.
No. 179126, a light for obtaining a good preformat signal by defining the size of the concave portion so that the recording layer is formed so that the reflectance difference between the tracking track concave portion formed on the substrate and the other portion is maximized. A recording medium is proposed.

This is based on the fact that the reflectance of the concave portion and the reflectance of the other portions are determined by the film thickness. For example, in the case of the above-described organic dye, the S / N ratio of the signal will be described with reference to FIG. to improve the reflectivity of the recording tracks 12 is desirably as high as possible, hence its thickness d ₂ of the recording tracks is suitably a thickness of about 800～1100A. Also, tracking tigers arrive unit 11 in order to maximize the amplitude of the AT control signal is preferably as large as possible reflectance difference (contrast) between the recording track, thus, the film thickness d ₁ from Figure 4 1500 You can see that it should be about 2000〜. In addition, the reflectance is approx.
Since the reflectance does not exceed 10% and the reflectance has little dependency on the film thickness, it is possible to set the film thickness to an arbitrary film thickness of 2000 mm or more.

Incidentally, the film thickness d ₁ of the concave tracking tiger poke portion of the light reflecting layer is determined by the amount accumulated in the concave portion in the coating process. Therefore, the film thickness d ₁ is and depth d of the concave tracking tigers arrive unit, by changing the width l, varying the amount accumulated in the concave portion, it is possible to control the film thickness d ₁ of the tracking Tora poke 11. Here 900~1100Å the thickness d ₂ of the recording tracks as previously described, in order to tracking tigers arrive 11 the thickness d ₁ 1500～2000A or more, the depth d of the concave portion of the tracking tiger poke 1800 to 2000 mm or more is required, and the depth becomes larger than the depth 1400 mm set when the preformat signal is obtained due to the above-described phase difference.

When a reflective substance is applied to a substrate having a concave tracking track as described above, the depth of the concave
The contrast of the preformat signal is excellent by improving the depth of the concave portion in consideration of the pooling of the coating liquid instead of / 4n (where λ: wavelength of the reproducing light, n: refractive index of the substrate). However, it was still not satisfactory.

[Problems to be solved by the invention]

The present invention has been made in view of the above problems, when forming the light reflecting layer on the transparent substrate by coating, utilizing the fact that the coating liquid remains in the preform concave recess and cannot be applied to a uniform thickness, It is an object of the present invention to provide an information recording medium capable of obtaining a better preformat signal than before.

Another object of the present invention is to provide an information recording medium which can obtain a preform signal which is better and more uniform than before.

[Means for solving the problem]

The information recording medium of the present invention has on its surface an uneven preformat including a tracking track, and the uneven preformat includes a concave portion having a cross-sectional shape in the tracking track transverse direction sandwiched between two convex portions. A projection having a flat bottom, the projection having a flat top, and a light reflection layer provided on the surface of the substrate by wet coating; and at least one of recording and reproduction of information by an optical radiation beam. In the information recording medium capable of performing the following, the reflective layer has different film thicknesses in the concave portion and the convex portion, thereby exhibiting different reflectivities in the concave portion and the convex portion. The cross-sectional shape of the concave portion 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 15 ° or more and 35 ° or less, and Preform The depth d of the concave portion is λ / 4n
(Where λ is the wavelength of the optical radiation beam, and n is the refractive index of the substrate).

Further, the recording and reproducing method of the present invention includes an uneven preformat including a tracking track on the surface, the uneven preformat includes a concave portion having a cross-sectional shape in the tracking track transverse direction sandwiched between two convex portions, The concave portion has a flat bottom portion, and the convex portion has a light reflection layer provided by wet coating on the surface of the substrate having a flat top portion,
The reflective layer has different thicknesses at the concave portion and the convex portion, thereby exhibiting different reflectivities at the concave portion and the convex portion. The information recording medium has an angle θ between the oblique side of the trapezoid and the plane of the information recording medium of 15 ° or more and 35 ° or less, and the depth d of the concave portion is deeper than λ / 4n. Irradiating an optical radiation beam with a wavelength λ to perform at least one of recording and reproduction of information (where n is the refractive index of the substrate).

That is, the present invention relates to an information recording medium in which a preformat is read based on both a difference in reflectance caused by a difference in film pressure between a concave portion and a convex portion of a light reflecting layer formed by wet coating and a phase difference due to unevenness. It was found that the film shape and film thickness of the light reflection layer around the edge of the concave portion greatly contributed to the acquisition of a high-contrast preformat signal. By forming the cross-sectional shape to be trapezoidal and making the depth deeper than λ / 4n and making the angle θ between the hypotenuse and the plane less than 35 °, a pre-format signal with higher contrast can be obtained. Although the reason is not clear, it is considered that the gentle depression formed on the surface of the light reflecting layer formed by coating and the hypotenuse of the preform concave portion having an angle of 35 ° or less are synergistically effective in obtaining a preformat signal having a high contrast.

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

Further, the trapezoidal shape makes it possible for the coating liquid of the light reflecting layer to be very uniformly stored in the preform concave portions, and as a result, a preform signal that is more stable and uniform than before can be obtained.

 Next, the present invention will be described in detail with reference to the drawings.

1 and 2 are schematic sectional views showing an embodiment of the optical recording medium of the present invention. In FIG. 1, reference numeral 1 denotes a transparent substrate, on the surface of which a concave preform, specifically a tracking track 7, is formed. A light reflection layer 3 is formed on the preformated surface of the transparent substrate 1 by coating, 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, reference numeral 12 denotes a concave tracking track formed on a substrate, and reference numeral 11 denotes 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 section whose upper base is longer than the lower base. The trapezoid is defined by the angle [θ] between the oblique side of the trapezoid and the plane of the information recording medium, the height of the trapezoid, ie, the depth [d] of the recess, and the width [l].

In the present invention, the angle [θ] is formed at 35 ° or less, and the depth [d] of the concave portion is formed to be deeper than λ / 4n, which is the depth at which the phase difference of the reflected light is usually maximum. This is preferable because a pre-format signal having a high contrast can be obtained.
Specifically, the depth of the preform recess is, for example, λ = 83.
When polymethyl methacrylate of n = 1.49 is used for the substrate using a beam of 0 nm, the depth of the recess is preferably formed to be deeper than about 1400 °, and a beam of λ = 830 nm and a polycarbonate of n = 1.58 are used. When is used for the substrate, the depth of the concave portion is preferably formed to be deeper than about 1320 °. As a result, a light reflecting layer having a film thickness exhibiting substantially the lowest reflectance is formed in the concave portion.

By the way, these angles [θ], depth [d], width [l]
It was found that the contrast of the preformat signal and the preformat signal showed a correlation. The schematic is shown in FIG.

In FIG. 7, the vertical axis represents the contrast of the cross-track signal,
The horizontal axis shows the correlation between the depth [d] and the width [l] at the angle θ. However D ₁ and D ₂ are the D _1> D ₂ shows one value of the depth d of the concave portion. L ₁ and L ₂ indicate one value of the width l of the concave portion, and L ₁ <L ₂ .

As can be seen from FIG. 7, the contrast increases as the depth [d] increases. On the other hand, if [.theta.] Is constant, if d is made shallow, the slope of the straight line will decrease, and if a tracking signal as uniform as possible is obtained, the tolerance of the value of the angle [.theta.] Will increase.

For example, the case of obtaining a value in the range of 0.4 to 0.45% as a contrast in FIG. 7, l = when L ₂ is at a depth of D ₁ and D ₂ tolerance about 28 ° to the time of D ₁ of the [θ] about 32 °, it is wider when about 21 ° to 28 ° da when D ₂ is small. Therefore, considering the processing accuracy of the preform slope,
It is preferable that the allowable range of [θ] is wider and the value of [d] is 1500 to 3700 °, particularly 2000 to obtain high contrast.
It is preferably between 3000 and 3000, more preferably between 2500 and 3000.

In the region where the angle [θ] is 35 ° or less as shown in FIG. 7, the contrast of the track crossing signal increases as the angle [θ] decreases, but θ = 15 ° or more, particularly 20 ° to 30 °.
In the case of ゜, a preform concave portion having a slope with an angle [θ] can be formed stably. Considering this point, the angle θ
Is formed at 35 ° or less, particularly preferably at 15 ° or more and 35 ° or less, more preferably at 20 ° or more and 30 ° or less.

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

On the other hand, as shown in FIG. 7, the smaller the value of the width [l] of the tracking track, the higher the contrast.

Considering these, in the case of an optical disk, l is 0.5 to 3
μm, particularly preferably 0.5 to 1.0 μm, more preferably 0.5 to 0.8 μm. By reducing l, the contrast is improved and the recording density is also improved, so that the recording capacity can be increased. In the case of a portable information recording medium in which a spot diameter [φ] is set to be large to prevent dust and scratches like an optical card and to prevent the influence, l is 1.5 to 4.5 μm, particularly 1.8
It is preferably formed to a thickness of 3.5 μm, more preferably a thickness of 2-3 μm.

The light reflection layer 3 is formed by wet coating on the substrate on which the preform having such a shape is formed. The light reflecting layer 3 is formed continuously from the recording track 11 to the inclined surface and the concave portion 12 which is a tracking track, as shown in FIG. 2, by the groove shape of the present invention.

The light reflecting layer is required to have a predetermined reflectance in order to reliably read the preformat information formed on the substrate.
Although its value is determined by the relationship with the reproducing apparatus, it is preferable that at least the recording track portion has a reflectance of 15% or more in order to perform high-precision reproduction without being affected by dust or scratches on the substrate surface.

As a material of such a light reflecting layer, the information recording medium of the present invention is a ROM type for reading information formed on a substrate in advance as a preformat or a tracking track or an address pit formed on a substrate as a preformat. It depends on whether it is a type in which new information can be additionally written by utilizing, but in any case, it is preferable that the reflectivity differs depending on the film thickness. In the case of the former ROM type, a material in which metal fine particles are dispersed in a binder or a heat-resistant dye / pigment is used, and in the case of the latter type, a material having both absorption and reflection with respect to recording / reproducing light. Preferably, dyes and pigments conventionally known as optical recording materials, such as cyanine-based, squarium-based, phthalocyanine-based, tetrahydrocholine-based, polymethine-based, naphthoquinone-based dyes and pigments, and organometallic complexes such as benzenedithiol nickel complex. It can be used preferably.

Further, in the latter case, it is also possible to provide a light reflection layer by coating only the preform portion and to use a metal deposition film for the portion to be additionally written.

The organic solvent that can be used when the light reflecting layer is applied depends on whether the dye is in a dispersed state or a dissolved state, and examples thereof include alcohols such as methanol, ethanol, isopropanol, and diacetone alcohol. And ketones such as acetone, methyl ethyl ketone and cyclohexanone, as well as amides, ethers, esters, aliphatic halogenated hydrocarbons, aromatics and aliphatic hydrocarbons. Particularly, an alcohol-based solvent is preferable because it does not attack the substrate when the light reflecting layer is applied.

FIG. 2 shows a recording track 11 of the information recording medium of the present invention.
Thickness d ₂ of the light reflection layer in the preferably applied to a thickness showing substantially the highest reflectance of the light reflecting layer to obtain a high good Purifuomatsuto signal contrast. This film thickness d ₂ is an optical constant n (refractive index) of the recording layer to be used.
Determined by k (extinction coefficient), usually for dyes and pigments
It is applied to 400-1500Å. On the other hand, it is preferably a thickness showing substantially the lowest reflectance as the thickness d ₁ of the concave portion of the concave Purifuomatsuto becomes large as possible a difference in reflectance of the aforementioned recording track, usually 1200Å or more, particularly Fifteen
00-3000 ° is preferred. In the present invention, the depth d of the concave preform is deeper than λ / 4n, particularly 1.07 to 2.7 of λ / 4n.
Times, even the film thickness of d ₁ by a thickness of d ₂ in the above-mentioned range by forming the approximately 1.4-fold to 2.2-fold is formed more than 1200 Å.

The specific film thickness is determined by the optical constants n and k specific to the light reflecting layer material. For example, in the case of the polymethine-based dye of the following structural formula (1) having the values of n = 2.1 and k = 1.0,
The dependency of the reflectance on the film thickness changes as shown in FIG. 4-1.

Structural formula [1] Thus, 1800 Å indicated preferably formed to a thickness d ₂ is 900 ± 100 Å of the recording track portion if the material is used, the time concave tracking Tora poke unit reflectivity film thickness d ₁ is the smallest of A signal showing good contrast is expected when it is Å2000 °. For this purpose, the depth d of the concave tracking track is set to 2000 to 3000 °, preferably 23 mm.
By setting the angle between 00 ° and 2700 °, particularly 2500 ° and 2700 °, the above value of d ₁ = 1800-2000 ° is secured.

In the present invention, in addition to this, the cross-sectional shape of the concave preform is a trapezoid whose upper base is longer than the lower base, the angle θ between the hypotenuse and the plane of the information recording medium is 35 ° or less, and the special loads 20 ° to 30 °. By setting ゜, a particularly good preformat signal could be obtained.

By the way, in the present invention, as a method of forming a concave preform on a transparent substrate, an injection method, a completion method, a casting method, a 2P method, or the like is used using a preformed mold.

In addition, a transparent substrate is required to have a high transmittance to information recording and / or reproducing light, and a substrate made of glass, ceramic, acrylic resin, vinyl chloride resin, polystyrene resin, polycarbonate resin, or the like is used. .

Further, when the light reflecting layer is provided on the substrate of the concave preform by wet coating, the solution or dispersion of the light reflecting layer material is roll-coated, Meyer bar coating, air knife coating, calendar coating, date coating, spraying, etc. Apply by method.

The solubility of the coating solution for the light reflecting layer is determined by the dye and the solvent used, and the solid concentration and the viscosity of the coating solution for obtaining the film thickness with the maximum reflectance are determined based on the solubility.

For example, when diacetone alcohol is used as a solvent using a dye represented by the above structural formulas [I] and [II], the concentration of the dye is preferably 1 to 5 wt%, particularly preferably 2 to 4 wt%, and the viscosity is 2-20 cps, especially 2-8 cps, is preferred.

Further, as a drying condition of the coating film, it is preferable that the process of leveling the coating film while evaporating the solvent of the coating liquid is controlled so that the coating film is uniformly formed in the preform concave portion. Gently blow clean air at room temperature to dry. In this case, the flow rate of the clean air is preferably 1 to 5 m / min, particularly 2.5 to 3.5 m / min, and the drying time is preferably 10 seconds to 2 minutes, particularly preferably 20 to 40 seconds.

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

In the present invention, as the adhesive layer, conventionally known adhesives, for example, polymers and copolymers of vinyl monomers such as vinyl acetate, acrylate, vinyl chloride, ethylene, acrylic acid, acrylamide, polyamide, polyester, polyether Such as thermoplastic adhesives, amino resin (urea resin, melamine resin), phenolic resin, epoxy resin, urethane resin, thermosetting vinyl resin, etc., natural rubber, nitrile rubber, chloroprene rubber, silicon rubber, etc. Rubber adhesive is used. In particular, the hot-melt type is a dry process, which is preferable from the viewpoint of mass production and continuous production.

The protective member has a purpose of mechanically protecting the recording layer 3, and is made of plastic, metal, ceramics, glass plate, or the like.
It is possible to use paper or a composite of these.

The protective member may be transparent or opaque as long as the above-mentioned purpose is satisfied.

These are rather determined by the reading method of optical information, and if it is a transmission type reading method, it is necessary to be transparent, and the requirement for birefringence is also limited to the same as that for the substrate. .

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

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

As described above, the cross-sectional shape of the concave preform formed on the substrate of the information recording medium provided with the light reflection layer by wet coating is changed so that the oblique side of the trapezoid with the trapezoid whose upper base is longer than the lower base and the trapezoidal shape of the information recording medium. By making the angle between the planes equal to or less than 35 °, it is possible to obtain a preform signal which is particularly excellent, uniform and has little variation.

Further, in the present invention, the diameter of the optical spot for recording / reproducing is designed to be large in order to prevent scratching and dust from adhering to the surface and to prevent a tracking error due to the scratch, and the width of the tracking track is increased in accordance with the spot diameter. Even in the case of a portable information recording medium to be formed, a preformat signal with high contrast can be obtained, so that the present invention is particularly suitably used in the case of a portable information recording medium.

In the present invention, the cross-sectional shape of the uneven preform and the thickness of the recording layer are determined by cutting the prepared optical card in a direction perpendicular to the tracking track, and SEM (magnification: 300).
0x) was set from the photograph taken.

An optical card recording / reproducing machine (manufactured by Canon) was used for measuring the contrast.

〔Example〕

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

Example 1 As a transparent substrate, a concave preform was engraved on a polymethyl methacrylate substrate (n = 1.49) of 10 cm long × 10 cm wide × 0.4 mm thick by hot pressing. As a preformat, a 3 μm tracking track (groove), which is an AT groove, was formed with a 12 μm pitch to provide 2560 recording areas and a tracking track.

At this time, the shape of the groove for AT of the tracking track is as follows: groove width; l = 3 μm, depth; d = 2500 °, groove angle θ =
This is a value of 25 ゜.

The following structural formula [I] is used as a material for the light reflecting layer on the transparent substrate having the concave preform. Was dissolved in diacet alcohol and applied as a 3 wt% solution on a substrate by a roll coater. Then, diacetone alcohol as a solvent was volatilized to form a light reflection layer 3. As drying conditions, 23 ° C. clean air was blown onto the coated surface at a flow rate of 3 m / min for 20 seconds.

The optical constants of this dye are n = 2.1 and k = 1.0, and the thickness dependence of the reflectance is as shown in FIG. 4-1.

From this figure, it is assumed that the thickness of each light reflection layer is set to a dry thickness d ₂ = 1000 ° in the recording area, and at this time, the thickness d ₁ = 1800 ° in the tracking track (groove).
The groove was formed at a depth d = 2500 °. The substrate on which the recording layer was formed was a hot-melt adhesive based on ethylene-vinyl acetate copolymer.A protective plate was laminated with a 0.35 mm logo printed acrylic plate, and finally a card size of 86.0
An optical card was cut to 54.0 mm.

A crossing signal of a tracking track is measured as an AT control signal of the optical card. The optical system for reproduction was evaluated by the contrast when a 830 nm semiconductor laser was focused to a spot of 3 μmφ and crossed between the recording track and the tracking track.

Embodiments 2 to 4 When an optical card is prepared and traversed between a recording track and a tracking track in the same manner as in Embodiment 1 except that the groove angle θ is set to 30 °, 15 °, and 12 ° in Embodiment 1. Was measured for contrast.

Example 5 The cross-sectional shape of the uneven preform Matsuo was changed to the angle [θ] of the slope.
25 ° and a depth [d] of 2000 °, a polymethine dye represented by the above structural formula [I] was formed on this substrate in Example 1.
A light reflecting layer was formed in the same manner as described above to prepare an optical card. However, the thickness d ₂ of the light reflection layer on the preform projection is
At this time, the thickness d ₁ of the preform concave portion is 16
It was 00Å.

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

Example 6 The cross-sectional shape of the concave-convex preform formed on a polymethyl methacrylate substrate was set such that the slope angle [θ] was 25 ° and the depth [d] was 1500 °, and the polymethine-based compound represented by the structural formula [I] was formed on the substrate. The dye was applied in the same manner as in Example 1 to form a light reflecting layer, thereby producing an optical card. However, the film thickness (d ₂ ) of the light reflecting layer on the preform protrusion was 800 °, and the film thickness d ₂ of the preform recess was 1200 °.

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

Comparative Example 1 (1) An optical card prepared in the same manner as in Example 1 except that the groove angle θ was set to 40 °, and (2) The groove angle θ of the tracking track was set to 90 °, and the depth was changed. An optical card prepared in the same manner as in Example 1 except that it was set to 1400 ° corresponding to the phase difference type λ / 4n. (3) θ was set to 90 °, and the depth of the groove was considered in consideration of the thickness of the light reflection layer in which the coating liquid for the coating liquid was stored. (4) θ = 25 °, and the depth of the groove was set to 1400 ° corresponding to λ / 4n at which the phase difference becomes maximum. Was an optical card prepared in the same manner as in Example 1. The contrast was measured for each of the above optical cards.

 Table 1 shows the above results.

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

Structural formula [II] FIG. 4-2 is a graph showing the relationship between the thickness of the light reflecting layer and the reflectance when the organic dye represented by the above structural formula [II] is used. The dye has a refractive index n of 3.0 and an extinction coefficient k of 3.0.
= 0.8, and the same graph was calculated using the above equation (1) using the constant. From the graph, the reflectance shows a maximum value of 26% near the dye layer thickness of 600 to 700 ° and a minimum value of 10% near 1300 to 1400 °. In addition, it can be seen that the reflectance is approximately constant at 14% at 3000 mm or more.

Therefore, the film is coated on the recording track so that the film thickness (d ₂ ) becomes 600 °, and at this time, the groove depth 30 is adjusted so that the film thickness d _{1 on the} tracking track (groove) becomes 1300 °.
It was set to 00 °, and further molded to θ = 25 °.

In this example, the coating solution for the light reflecting layer was prepared by adding a dye represented by the above structural formula [II] to diacetone alcohol at 3 wt%.
The dissolved one was used.

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

Otherwise, 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 10 Optical cards were prepared in the same manner as in Example 7 except that θ was changed to 30 °, 15 °, and 11 °. For this optical card, the contrast when crossing between the recording track and the tracking track was measured.

Example 11 The cross-sectional shape of the uneven preform was changed to the angle of the slope [θ].
And the depth [d] was set to 2000 °, and a system dye represented by the above structural formula [II] was coated on the substrate in the same manner as in Example 7 to form a light reflecting layer, thereby producing an optical card. . However the film thickness d ₂ of the light-reflecting layer on Purifuomatsuto convex portion thickness d ₁ of Purifuomatsuto recess when 600Å Toshiko was 1200 Å.

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

Example 12 The cross-sectional shape of the uneven preform was changed to the angle [θ] of the slope.
= 20 °, depth [d] = 1500 °, and a dye represented by the above structural formula [II] was coated on this substrate in the same manner as in Example 7 to form a light reflecting layer, thereby producing an optical card. However, the film thickness (d ₂ ) of the light reflecting layer on the preform protrusion was 600 °, and the film thickness d ₂ of the preform recess at this time was 1100 °.
Met.

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

Comparative Example 2 (1) An optical card was prepared in the same manner as in Example 7, except that the angle of θ was changed to 40 °.

(2) An angle θ of the groove of the tracking track is 90 °, and a depth is 1400 ° corresponding to λ / 4n of the phase difference type.
(3) θ was set to 90 °, and the depth of the groove was set to a value in consideration of the thickness of the light reflection layer where the coating liquid was stored, that is, 3000 °. Optical card prepared in the same manner as in the seventh embodiment. (4) Created in the same manner as in the seventh embodiment, except that θ = 20 ° and the depth of the groove was set to 1400 ° corresponding to λ / 4n at which the phase difference becomes maximum. The contrast was measured for each of the above optical cards and the above optical cards.

 Table 2 shows the above results.

As can be seen from Tables 1 and 2, according to the present invention, it was possible to obtain a preformat signal having good contrast with little variation and stable tracking.

On the other hand, in the comparative example, the contrast of the preformat signal is low, and the comparative examples 1 (3), (4) and 2
In (3) and (4), a preformat signal having a partially high contrast is obtained, but the variation is large.
Stable tracking could not be performed.

〔The invention's effect〕

As described above, the cross-sectional shape of the concave preform formed on the substrate of the information recording medium provided with the light reflection layer by wet coating is changed so that the oblique side of the trapezoid with the trapezoid whose upper base is longer than the lower base and the trapezoidal shape of the information recording medium. By making the angle between the planes equal to or less than 35 ° and making the depth of the preform recesses larger than λ / 4n, it is possible to obtain a preform signal having excellent uniformity and little variation, thereby performing stable tracking. did it.

[Brief description of the drawings]

1 and 2 are schematic views showing a cross-sectional structure of an information recording medium according to an embodiment of the present invention, FIG. 3 is a schematic view showing a cross-sectional structure of a conventional optical recording medium, FIGS. 4-1 and 4 FIG. 2 is a graph showing the relationship between the thickness of the light reflecting layer and the reflectance, FIG. 5 is a schematic diagram showing the cross-sectional structure of a conventional optical recording medium, and FIG. 6 is a diagram showing the height of the tracking track and the AT control signal. It is a graph which shows the relationship of the reflected light intensity which reaches a detection system. FIG. 7 is a schematic diagram showing the correlation between the angle [θ], the depth [d], the width [l] of the concave portion and the contrast value of the preformat signal of the cross section of the concavo-convex preform. DESCRIPTION OF SYMBOLS 1 ... Information recording medium 2 ... Transparent substrate 3 ... Light reflecting layer 4 ... Adhesive layer 5 ... Protective member 6,11 ... Recording track 7,12 ... Tracking track A ... Recording and reproducing light

Claims (15)

(57) [Claims] An uneven preformat including a tracking track is provided on a surface thereof, and the uneven preformat includes a concave portion having a cross section in the tracking track transverse direction sandwiched between two convex portions, and the concave portion has a flat bottom portion. Having a substrate having a flat top and a light reflection layer provided on the surface of the substrate by wet coating, and performing at least one of recording and reproduction of information by an optical radiation beam. In the information recording medium, the reflective layer has a different film thickness between the concave portion and the convex portion, thereby exhibiting different reflectivities between the concave portion and the convex portion. The cross-sectional shape is a trapezoid in which the length of the upper base is longer than the length of the lower base, the angle θ between the hypotenuse of the trapezoid and the plane of the information recording medium is 15 ° or more and 35 ° or less, and the preformat Depth of recess Information recording medium d is equal to or deeper than lambda / 4n (where lambda: wavelength of the optical radiation beam, n: refractive index of the substrate). 2. The information recording medium according to claim 1, wherein the thickness of the light reflection layer in the preformat concave portion is larger than the film thickness in the preformat convex portion. 3. The film thickness of the light reflecting layer at the convex portion of the preformat has substantially the maximum reflectance, and the film thickness at the concave portion of the preformat has a substantially lowest reflectance. 2. The information recording medium according to claim 1, which has a thickness. 4. The preformat concave portion has a depth of 1500-37.
2. The information recording medium according to claim 1, which has a thickness of 00 angstroms. 5. The depth of the preformat recess is 2000-30.
5. The information recording medium according to claim 4, which has a thickness of 00 angstrom. 6. The preformat concave portion has a depth of 2500-30.
6. The information recording medium according to claim 5, which has a thickness of 00 angstrom. 7. The information recording medium according to claim 1, wherein the angle [θ] formed by the slope of the preformat recess and the plane of the information recording medium is not less than 20 ° and not more than 30 °. 8. The method according to claim 1, wherein said light reflecting layer contains an organic dye.
Information recording medium. 9. The information recording medium according to claim 8, wherein said organic dye is a polymethine dye. 10. An uneven preformat including a tracking track is provided on a surface thereof, and the uneven preformat includes a concave portion having a cross-sectional shape in a direction transverse to the tracking track sandwiched between two convex portions, and the concave portion has a flat bottom portion. Has,
The projection has a light reflection layer provided by wet coating on the surface of a substrate having a flat top, and the reflection layer has a different film thickness between the depression and the projection, thereby forming the depression. And the convex portion have different reflectances. The cross-sectional shape of the concave portion is a trapezoid whose upper base is longer than the lower base, and the angle between the oblique side of the trapezoid and the plane of the information recording medium. θ is 15 ° or more and 35 ° or less, and the depth d of the concave portion is greater than λ / 4n.
A recording / reproducing method of information (where n is a refractive index of the substrate), wherein at least one of recording and reproducing of information is performed by irradiating the optical radiation beam of (1). 11. The recording / reproducing method according to claim 10, wherein the thickness of the light reflecting layer in the concave portion of the preformat is larger than the thickness of the light reflecting layer in the convex portion of the preformat. 12. The film thickness of the light reflection layer of the information recording medium at the preformat convex portions is a thickness exhibiting substantially the maximum reflectance, and the film thickness at the preformat concave portions is substantially the lowest. 11. The recording / reproducing method according to claim 10, wherein the recording / reproducing method has a thickness indicating a reflectance. 13. The recording / reproducing method according to claim 10, wherein the depth of the preformat recess of the information recording medium is 2000-3000 Å. 14. The recording / reproducing method according to claim 13, wherein the depth of the preformat recess of the information recording medium is 2500-3000 angstroms. 15. 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 20.
11. The recording / reproducing method according to claim 10, wherein the length is not less than {30}.