JP2963516B2 - Substrate for optical information recording medium and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for an optical information recording medium for recording and reproducing information by using a laser beam, and a method of manufacturing the same, and more particularly, to a substrate for an optical card medium and the manufacture thereof. It is about the method.

[Prior Art] In recent years, optical discs, magneto-optical discs, optical cards, and the like have been developed as optical information recording media and commercialized. In any optical information recording medium,
In order to increase the recording density, a guide groove (pre-group) for recording / reproducing laser light is usually provided on the substrate surface.

Such an optical information recording medium must have a high recording density in terms of quantity, and qualitatively that the information recorded on the recording medium must be free from errors during reproduction, that is, a good C / N ratio. Is required.

In the case of a read-only type, the quality of this information is affected by the structure of the information replicated on the substrate. For example, in the case of the amplitude type by shading, the signal detected by the three-dimensional shape of the unevenness is affected by the density difference and size in the case of the phase type by unevenness.

Also, in the case of the recordable type, information of a format such as a groove (group) for tracking, an address for data recording management, and a synchronizing signal for writing information is copied on the substrate in advance (hereinafter, referred to as “recording information”). Information including these tracking grooves and format pits is called a preformat).

Conventionally, in order to obtain the pre-format signal, a method of reflected light provided uneven pattern like making a phase difference of lambda _0/4 are known to the substrate.

For example, the recording pit in accordance with the CD such as information, λ _0/4
Signal reproduction is possible by depositing a reflective metal film, such as aluminum or gold, having a uniform reflectivity on the substrate onto which the pattern has been transferred by injection molding using a stamper with an irregular pattern of height I have to. In addition, in the case of an addable type of recording medium, when writing the information, in order for the recording to be performed accurately on the recording track, the irradiation position of the recording light must be constantly positioned on the recording track in the scanning direction and the direction perpendicular thereto. It is necessary to maintain control (this is referred to as auto-tracking, hereinafter abbreviated as AT).
Therefore, it is customary to form a tracking track on a substrate in advance, and to record and reproduce information while performing AT control based on the tracking track. The manner of detecting a tracking signal in such a conventional optical information recording medium will be described below.

FIG. 6 is a schematic diagram showing a cross section including a tracking track of a conventional optical information recording medium. In the figure, 2 is an optically transparent 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 engraved on the transparent 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 evaporation. .

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. 7 is a graph showing the relative ratio of the amount of reflected light due to the phase difference of the optical information recording medium of FIG. 6, and shows 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 interference between the diffracted light by the tracking track portion and the reflected light from a portion other than the tracking track portion, the height of the tracking track is λ / 4n.
(Λ is the wavelength of light, and n is the refractive index of the substrate), the signal intensity becomes maximum when it is an odd multiple, and becomes minimum when it is an even multiple.

 This is exactly the same as the previous CD.

Japanese Patent Publication No. 63-19939 discloses that the inclination angle θ between the wall of the information area and the normal to the record carrier has a value between 30 ° and 65 °, and the depth of the concave shape at that time. 0.27λ ₀ /N~0.427
A record carrier having λ ₀ / N has been proposed (λ ₀ : wavelength of optical radiation beam, N: refractive index of transparent medium). That is, it is difficult to form the wall of the pit or hill vertically, and when the wall of the pit or hill is inclined to facilitate the developing process when manufacturing the master, It is disclosed that a good signal can be obtained when the _{value is} 0.27λ ₀ / N to 0.427λ ₀ / N.

Furthermore, IEICE Transactions J67-C2,219 (1984/2)
“Examination of guide groove shape on optical disk by diffraction 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 cross-sectional shape of the concave preformat of the optical information recording medium, and all of them are uniformly reflective materials such as silver, gold, aluminum, and titanium on a transparent substrate. , Tellurium, tellurium oxide, etc., on an optical information recording medium formed by vacuum evaporation or the like, and all of these signals take into account the phase difference.

However, in the case of an optical information recording medium in which a light reflecting 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 causes the following problems. There was a point. FIG. 4 shows that a tracking track consisting 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 information 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 a transparent or opaque plastic or the like. The optical information recording medium 1 is formed by coating a recording layer 3 on a transparent substrate 2 on which a tracking track 7 and a recording track 12 each having a concave shape are engraved by a known molding technique. A protective member 5 made of a transparent or opaque plastic or the like is adhered to the protective member 5 via an adhesive layer 4.

Information is recorded and reproduced on the recording track 12 while performing AT control based on the tracking track 7. 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, such a coating type optical information recording medium,
As shown in FIG. 4, when the recording layer 3 having light reflectivity is provided by coating on the transparent substrate 2 having the concave tracking track 7, the coating solution is collected in the concave portion, and thus the recording layer 3 having light reflectivity is formed. When the film thickness of the recording track 12 is d ₃ and the film thickness of the tracking track 7 is d ₄ , it is inevitable that d ₃ <d ₄ .

Further, in the recording layer having light reflectivity containing dyes and pigments, when the film thickness is about 100Å to several thousandÅ, the reflectance changes depending on the film thickness, and the conventional depth λ ₀ / 4n or
It was not possible to obtain a maximum signal strength in the preformat of 0.27λ ₀ /N~0.427λ ₀ / N. That is, the reflectance with respect to the coating film thickness of the dye / pigment changes as shown in FIG. 5, for example.

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

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

The graph of FIG. 5 is for a dye of formula (II): n _s = 1.49, n = 2.1, k = 1.0, Is a result calculated using the above equation (1).

Refractive index of the adhesive, was used for n _a = 1.48~1.49.

As is apparent from the results shown in FIG. 5, the reflectance of the dye rapidly rises and shows a maximum at a film thickness of 800 to 1000 °, and then shows a substantially constant value at 2000 ° or more.

As described above, the reflectivity changes depending on the film thickness, and the degree of the change is particularly large near the maximum of 800 ° to 1100 °.

Therefore, when a light-reflective substance is applied to a transparent substrate having a concave tracking track, a signal from the light-reflective substance 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 the reason that the height of the concave tracking track does not become the maximum signal intensity when the height is an odd multiple of λ / 4n.

As a solution to such a problem, for example, Japanese Patent Application Laid-Open No. 60-239947 discloses a method in which a light-absorbing and reflective dye film having a film thickness set to maximize the reflectance is provided on a substrate. An information recording medium that can obtain a stable preformat signal by minimizing the reflectance difference between the concave portion and the convex portion of the preformat and preventing the variation in the reflectance from being added to the phase difference between the concave and convex portions is disclosed. However, this can only be used for certain dyes that exhibit a maximum reflectance and a wide range of film thickness.

To solve this problem, Japanese Patent Application No. 62-179126 discloses that a recording layer is formed so that the reflectance difference between a tracking track concave portion formed on a substrate and other portions is maximized. There has been proposed an optical recording medium that obtains a good preformat signal by defining the size of the concave portion.

This is based on the fact that the reflectance of the concave portion and the reflectance of the other portions are determined by the coating film thickness. For example, in the case of the above-described organic dye, the signal S /
In order to improve the N ratio, it is desirable that the reflectivity of the recording track 12 be as high as possible.
The thickness d of the recording track is preferably about 900 to 1100 °. In order to increase the amplitude of the AT control signal as much as possible, it is preferable that the tracking track 7 has a reflectivity difference (contrast) from the recording track 12 as large as possible. Therefore, from FIG.
It is understood that it is better to set the degree or higher. Incidentally, 2000
Even when the thickness is more than Å, the reflectance does not exceed about 10%, and the dependency of the reflectance on the film thickness is small. Therefore, it is possible to set an arbitrary film thickness of 2,000 Å or more.

Incidentally, the thickness d ₄ of the recording layer having light reflectivity of the concave tracking track portion is determined by the amount accumulated in the concave portion in the coating process. Therefore, the film thickness d ₄ is concave depth d ₁ and the tracking track portion, by changing the width l, varying the amount accumulated in the concave portion, it is possible to control the thickness d ₄ of the tracking tracks 7. As described herein above, 900～1100A the thickness d ₃ of the recording track 12, the thickness d ₄ of the tracking tracks 7 to the above 1500~2000Å the recess of tracking tracks depth d ₁ Is 1800 ~
This requires 2000 mm or more, which is deeper than the depth of 1400 mm set when the preformat signal is obtained due to the phase difference.

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

[Problems to be Solved by the Invention] Further, in an optical card medium in which the width of the pre-groove concave portion is 2 to 3 μm, the track-crossing signal contrast obtained from the difference in reflectance between the recording layer of the convex portion and the concave portion of the pre-groove. The value is represented by the following formula (III).

The value of the track crossing signal contrast is 0.35 or less in the case of only the phase difference of the optical information recording medium shown in FIG. 6 or in the groove shape of the optical information recording medium as shown in FIG. In particular, in the case of an optical card in which dust, scratches, and the like are likely to adhere on the substrate surface, which is an optical path, a track crossing signal contrast of 0.35 is insufficient, and an error easily occurs in automatic tracking or automatic focusing.

To remedy these problems, as shown in FIG.
The wall of the concave portion 11 of the tracking groove of the pre-groove has an angle such that θ = 20 to 40 °, the light is scattered by the slope portion 14 of the pre-groove to reduce the reflectivity of the concave portion of the pre-groove, and Methods for increasing the signal contrast have been proposed.

However, it is relatively difficult to produce a substrate having a pre-groove concave portion of θ = 20 to 40 ° as shown in FIG. 8 without variation in θ, which causes problems such as low mass productivity. I have.

The present invention has been made in order to solve such a problem, and by providing a rim-shaped portion around the periphery of the preformat concave / convex concave portion preformat having an uneven shape,
It is an object of the present invention to provide an optical information recording medium capable of obtaining a better track-to-track signal contrast than the conventionally known substrate.

Another object of the present invention is to provide a method for easily manufacturing an optical information recording medium capable of obtaining good cross-track signal contrast.

[Means for Solving the Problems] That is, the present invention is characterized in that a substrate for an information recording medium having a concave and convex preformat has a rim portion around a concave portion of the concave and convex preformat. This is a substrate for an optical information recording medium.

Further, the present invention is characterized in that after forming a resin into a substrate having a concave and convex preformat, the substrate is subjected to a heat treatment to form a rim portion around the concave portion of the concave and convex preformat. This is a method for manufacturing a substrate for an optical information recording medium.

 Hereinafter, the present invention will be described in detail.

FIG. 1 is a schematic sectional view showing an example of the optical information recording medium substrate of the present invention. In the figure, a substrate for an optical information recording medium of the present invention has a rim-shaped portion 13 formed around a concave portion 11 of a pre-groove of a transparent plastic substrate 2 having a concave-convex preformat on one surface. Things.

The height d ₂ of the rim portion 13, the range of 100~3000Å is preferred. When the recording layer is made of an inorganic compound, the depth d ₁ of the concave portion 11 of the pregroove is preferably λ / 4 × n times (where n is an integer) the wavelength λ of the recording / reproducing laser beam, for example, when λ = 830 nm. Is preferably about d ₁ = 1900 to 2100 °. When the recording layer is a coating type organic dye medium, d ₁ is preferably 2400 to 3300 °.

Line width l ₂ of the pre-groove is 1-1 / 2 times the spot diameter of the recording and reproducing laser light is good. For example, in the case of an optical card or the like, since the spot diameter is about 3 μm, l ₂ = 3.0
~ 2.0 µm is preferred.

Further, the width l ₁ of the concave portion 11 is preferably 2.2 to 0.36 μm.

By the rim-shaped portion 13 provided on the optical information recording medium substrate of the present invention, the tracking laser light is scattered,
As a result, it was found that the same effect as the scattering of light by the inclined surface 14 of the pre-groove in which θ = 20 to 35 ° as shown in FIG. 8 was obtained.

Next, a method for manufacturing an optical information recording medium substrate according to the present invention will be described with reference to FIG. As shown in FIG. 2, a rim-shaped portion 13 was formed around the concave portion 11 of the pre-groove by heat-treating a substrate 22 obtained by casting, hot press molding or injection molding. The substrate 2 of the present invention is obtained.

There are various heat treatment methods, and specific methods are shown below.

In the case of a cast-formed substrate As a cast-formed substrate, polymethyl methacrylate (PMMA), diethylene glycol bisallyl carbonate (CR-39), a PMMA derivative, or the like is used. The substrate 22 having the concave portion 11 of the pregroove is subjected to a heat deformation temperature (ASTM D-
Heat treatment at + 5 ° C to 50 ° C higher than 648). For example, in the case of PMMA, the heat deformation temperature is around 105 ° C,
An appropriate heat treatment temperature is 110 to 150 ° C. The height d ₂ of the rim portion 13 is proportional to the heat treatment temperature. On the other hand, if the heat treatment temperature is set higher than the heat distortion temperature by more than 50 ° C,
The shape of the entire pre-groove changes significantly, making it unsuitable for practical use.

In the case of a hot press-molded substrate As a substrate material, if it is an optically transparent and thermoplastic resin, hot press molding is possible. For example, PMMA,
Polycarbonate (PC), polyvinyl chloride (PV
C), polystyrene (PS), polysulfone (PSU) and the like can be used. When the substrate 22 with a pregroove is formed by hot press molding, the heat treatment temperature is set in the range of (thermal deformation temperature of substrate + 5 ° C.) to (hot press molding temperature).

Usually, in the case of PC, hot press molding is performed at 160 to 170 ° C. Further, since the heat deformation temperature is 120 to 125 ° C., it is preferable to perform the heat treatment at 125 to 170 ° C. When heat treatment is performed at a temperature higher than the hot press molding temperature, the concave portion 11
Disappears.

In the case of injection molding As the substrate material, substantially the same material as in hot press molding can be used. The heat treatment is preferably performed at a temperature of +5 to + 50 ° C., which is the thermal deformation temperature of the substrate.

In any of the above cases, the substrate is easily deformed during the heat treatment, so that the heat treatment is performed by bringing the opposite surface of the pre-groove-attached surface of the plastic substrate 22 with the pre-groove into contact with the mirror glass substrate. Is preferred.

When using the optical information recording medium substrate of the present invention to create an optical card, as the recording layer, Te and TeOx
And a phase change type metal such as an Sb-Te alloy, an In-Te alloy, and a Sb-Te-Ge alloy, or an organic dye recording layer.

Usually, in order to protect the recording layer, a protection member 5 is provided via an adhesive layer 4 as shown in FIG.

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, poly Thermoplastic adhesives such as ether, amino resin (urea resin, melamine resin), phenol resin,
Thermosetting adhesives such as epoxy resin, urethane resin and thermosetting vinyl resin, and rubber-based adhesives such as natural rubber, nitrile rubber, chloro rubber, and silicone rubber are used.
In particular, the hot melt type is a dry process,
This is preferable in consideration 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, a glass plate,
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. In the case of a transmission type reading system, it is necessary to be transparent, and the requirement for birefringence is the same as that for the substrate, and its material 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.

This protective member may be laminated directly on the recording layer 3 in optically close contact with the recording layer 3. Further, if necessary, a so-called air gap type form in which a protective member is provided via an air layer may be used.

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

Embodiment 1 As shown in FIG. 3, the pitch a = 12 μm, l ₁ = 1.7 μm, d ₁
A glass casting mold 6 having a chromium vapor deposition section 8 having a size of = 2700 ° and a glass mirror casting mold 16 are assembled via a spacer 9, and a monomer of methyl methacrylate is introduced into the space from the monomer injection port 13. The resulting mixture was poured into 10 and a polymethyl methacrylate substrate 22 having a thickness b = 0.4 mm was obtained by a monomer casting method.

Next, the substrate 22 is subjected to a heat treatment in a clean oven at 140 ° C. for 10 minutes to obtain a substrate 2 having a rim-shaped portion around the concave portion of the pre-groove as in the substrate shown in FIG. Was. High d ₂ of the rim portion was about 2200 Å. Line width l ₁ is 1.
When set to 7 μm, the line width l ₂ after the heat treatment is 2.4 to ₂ .
It was 5 μm. However, the pregroove depth d ₁ is 2700
Å The pitch of the pregroove was 12 μm.

Example 2 A 0.4 mm thick PC (Teijin Kasei Panlite PC-251) sheet was subjected to hot press molding at 170 ° C. on its surface to obtain a preform having a depth d ₁ = 2700 ° and a line width l ₁ = 1.7 μm. Groove 12μ
It was formed at an m pitch.

When this substrate was subjected to a heat treatment in a clean oven at 150 ° C. for 15 minutes, a substrate 2 having a rim-shaped portion at the periphery of the pregroove could be obtained as in the case of the substrate shown in FIG.

The height d ₂ of the rim portion was 1500 Å. Also, the line width l ₂ is
It was 2.4 μm.

Comparative Example 1 A conventional PMMA substrate as shown in FIG. 4 was prepared by casting.

The depth d _{1 of the} pregroove was 2700 ° and l ₁ was 2.4 μm.

Comparative Example 2 A PMMA substrate as shown in FIG. 8 of the conventional example was prepared by casting.

Pregroove depth d ₁ = 2700 °, l ₁ = 2.4 μm, θ = 3
It was 0 ゜.

Next, in order to evaluate the contrast of the signal of the tracking track obtained from the concave portion of the pre-groove, the pre-groove forming surface of each substrate of Examples 1 and 2 and Comparative Examples 1 and 2 was perpendicular to the concave pre-groove. Wavelength 830nm, power 0.
The performance of the pre-groove of each substrate was compared by traversing a reproduction laser beam of 2 mW. Table 1 shows the results.

From the results in Table 1, it can be seen that the substrate having the rim portion around the concave portion of the pre-groove of the present invention (Examples 1 and 2) is equivalent to or equal to Comparative Example 2 due to the scattering of the reproduction laser light by the rim portion. In the comparative example 1, the pre-groove slope 14 or the rim-shaped portion is obtained.
The contrast is low because 13 is not present.

In a normal optical information recording medium, since the recording layer is provided on the substrate, the pre-groove track crossing signal contrast is further increased by the phase difference and the amplitude difference between the concave groove portion and the convex recording portion of the recording layer. Become.

[Effects of the Invention] As described above, according to the present invention, by providing a rim-shaped portion around a concave portion of a preformat having an uneven shape, a track superior to a conventionally known substrate is provided. Transverse signal contrast can be obtained.

Further, according to the method for manufacturing a substrate of the present invention, the temperature of the heat treatment may be kept constant, and the angle θ may be controlled in order to obtain the pregroove slope 14 as shown in FIG. Can easily manufacture a substrate for an optical information recording medium capable of obtaining good pregroove track signal contrast.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the optical information recording medium substrate of the present invention, FIG. 2 is a schematic view showing an example of the method for manufacturing the optical information recording medium substrate of the present invention, and FIG. FIG. 4 is an explanatory view showing an embodiment of a method for manufacturing a substrate of the present invention, FIG. 4 is an explanatory view of a conventional optical information recording medium, FIG. 5 is a graph showing the correlation between the reflectance and the film thickness of an organic dye thin film, FIG. 6 is an explanatory view of a conventional optical information recording medium using an inorganic reflective layer, FIG. 7 is a graph showing the relative ratio of the amount of reflected light due to the phase difference of the optical information recording medium of FIG. 6, and FIG. FIG. 4 is an explanatory view of an optical information recording medium substrate obtained by improving the conventional substrate shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Optical information recording medium 2 ... Transparent substrate 3 ... Recording layer / light reflection layer 4 ... Adhesive layer 5 ... Protective member 6 ... Casting mold 7 ... Tracking track 8 ... Chrome deposition part 9: Spacer 10: Space 11: Concave part 12: Recording track 13: Rim-shaped part 14: Slope part 15: Wall 16: Mirror surface casting 22: Substrate (unheated)

Claims (2)

(57) [Claims] 1. An optical information recording medium substrate having an uneven preformat having a rim portion around a concave portion of the uneven preformat. 2. The method according to claim 1, wherein the resin is molded into a substrate having an irregular preformat, and then the substrate is heated to form a rim around the concave of the irregular preformat. A method for manufacturing a substrate for an optical information recording medium.