JPH09138970A - Double layer optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent yield from lowering at the time of mass production by filling an adhesive member into a gap having a prescribed height formed by plural projections to be held between a 1st reflecting layer and a 2nd reflecting layer to be stuck together. SOLUTION: Annular projections are formed on a substrate 3 in its inner and outer circumferential parts to be concentric with the substrate at the prescribed height, and they are stuck to a light-transmissive substrate to form a spacer layer 6 (thickness: d). Plural minute projections 5, each in a circular cone or trancated cone or even cylindrical shape at the prescribed height may also be provided in the outer circumferential part of the substrate 10 and yet in such a position surrounding and outside a record holding area. Alternatively, the projection shape may also be a composite shape or a miscellaneous shape. In other words, the shape and quantity of such projections do not matter, provided that when the substrate 10(3) is stuck to the light-transmissive substrate 1, a distance between the reflecting layers 2 and 4 formed on the substrate 10(3) and the light-transmissive substrate 1 respectively should be d, and the projections should be positioned outside and surrounding the information recording area formed by the reflecting layers 2 and 4.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly to a reproducing optical disk in which pits or grooves for carrying information are formed in multiple layers.

[0003]

[0002]

[0004]

2. Description of the Related Art Conventionally, a so-called compact disc (hereinafter referred to as a CD) is known as an optical disc for reproduction.
The CD is a reflective film formed of a disc-shaped substrate having a light-transmitting property and having a predetermined thickness, on one side of which a pit or groove for carrying information is formed, and which is a metal foil so as to cover the pit or groove. Are laminated to form a reflective layer, and an ultraviolet curable resin is spin-coated on the reflective layer to form a protective film having a predetermined thickness. A label is formed on the protective film by a method such as screen printing, and the CD
The information content and other information are displayed visually.

The CD is constructed as described above, and the pit or groove shape transferred from one side of the translucent substrate onto the reflective layer is optically read using an optical pickup or the like to reproduce recorded information. It was

[0006]

In addition, with the recent increase in the density of information, it is required to increase the density of pits or grooves carried by an optical disk, and the pits or grooves are formed in multiple layers to optically read from one side. Optical discs are being considered.

[0007]

As a multilayer optical disc, for example, as shown in FIG. 10, a dual layer optical disc (Dual Layer Disc) is used.
c).

In the double-layered optical disk shown in FIG. 1, pits or grooves for carrying the first information are formed on one surface of a transparent substrate 101 formed by injection molding a transparent synthetic resin and having a predetermined thickness. The pits or grooves are further covered with a reflective layer 102 made of a semitransparent film having a predetermined reflectance and transmittance. Further, a pit or groove that carries the second information is formed on one surface of the substrate 103 having a predetermined thickness, and the pit or groove is covered and closely formed with a reflective layer 104 having a high reflectance. Further, the reflective layers 102 and 104 are attached to each other using a translucent ultraviolet curable resin so as to face each other, and the ultraviolet curable resin is cured to have a predetermined thickness to form a translucent spacer layer. 105 is formed to form a two-layer optical disc.

[0009]

Further, the spacer layer 105 is the reflection layer 10
It is formed by bonding the two substrates on which 2, 104 are formed by a substrate bonding process as shown in FIG. 11, for example. First, in FIG. 11A, a predetermined amount of the ultraviolet curable resin 106 is dropped in a ring shape concentric with the disk on the inner peripheral side on the surface of the substrate 103 on which the reflective layer 104 is formed, and then FIG. In (b), the reflective layer 102 is laminated on the transparent substrate 101, and the substrate 10
When 3 and the transparent substrate 101 are coaxially rotated for a predetermined time, the ultraviolet curable resin 106 is spin-coated between the reflective layers 102 and 104 by a centrifugal force and spreads to a predetermined thickness without a gap. Next, in FIG. 11C, when ultraviolet rays (UV) are irradiated from the transparent substrate 101 side for a predetermined time,
The ultraviolet curable resin 106 is cured to form the spacer layer 105 having a predetermined thickness d.

[0010]

The two-layer optical disc is formed as described above,
As shown in FIG. 10, when reading the first layer (called Layer 0) from the transparent substrate 101 side using an optical pickup (not shown), the reading beam of the optical pickup is focused on the reflective layer 102, The reflected light modulated by the pits or grooves formed on the reflective layer 102 is read. The second layer (called Layer1)
When reading, the reading beam of the optical pickup is transmitted through the reflection layer 102 and focused on the reflection layer 104,
The reflected light modulated by the pits or grooves formed on the reflective layer 104 is read through the reflective layer 102 again.

[0011]

In the two-layer optical disc, the information recorded in the two layers can be appropriately selected and read without turning over both sides of the disc in this way, so that the information can be recorded in two layers by using one optical pickup. Information can be played back instantly.

[0012]

FIG. 12 shows how the light beam emitted from the optical pickup reaches each optical pickup after being reflected by each layer of the two-layer optical disk. As can be seen from FIG. 12, information of Layer 0 is read. In this case, the incident light from the optical pickup is Layer 0 of the disc.
At about 30%, it reaches the optical pickup.

[0013]

When reading the information of Layer 1, about 70% of the incident light from the optical pickup goes to Layer 1 although there is some absorption in the translucent substrate 101 of Layer 0 and the semitransparent reflection film 102. .

[0014]

In Layer 1, about 80% of the light is reflected by the reflective film 104, the reflected light reaches Layer 0 again in the spacer layer, is reflected by Layer 0 again by about 30%, and the light transmitted through Layer 0 is the light. Return to pickup. In this case, when viewed from the optical pickup, L
The reflectances of Layer 0 and Layer 1 are selected so that the reflected light at layer 0 and the reflected light at Layer 1 are almost equal.

[0015]

The spacer layer 105 is the reflective layer 102,
It is formed for the purpose of keeping the interlayer distance of 104 constant, and has a uniform refractive index of light and a large transmittance.

[0016]

When reading a two-layer optical disk, the optical pickup picks up the reflected light from Layer 0 and the Layer.
The reflected light from r1 is reflected, but La
When reading yer0, the focus of the reading beam is set to Layer0, so that
As shown in (a), the light beam with which Layer 1 is irradiated is defocused and greatly spreads.

FIG. 13 shows how the light beam emitted from the optical pickup is defocused on the other reflection layer of the two-layer optical disc when the light beam is focused on one reflection layer.

[0018]

On the other hand, if the spot diameter of the light beam is very large compared to the size of the recorded pit or groove, it will not be modulated by the pit or groove and will only be a DC offset. If the low frequency component is removed by the HPF from the RF signal obtained by converting to, the signal by Layer0 alone can be extracted. Similarly, as shown in FIG.
If the reading beam is focused on r1, only the signal from Layer1 can be extracted.

In this way, in the two-layer optical disc, the information recorded in the two layers can be read by appropriately selecting each layer from one side by using the optical pickup and focusing the light beam.

[0020]

However, the spacer layer has a predetermined width d.
If the width is smaller than the width d ′, as shown in FIG. 13B, when the reading beam is focused on the Layer 0, the light beam irradiated on the Layer 1 does not spread so much, so that the Layer 0 causes When reading a signal, inter-layer crosstalk increases rapidly,
The modulated signal by r1 cannot be ignored. FIG. 14 is a graph showing the relationship between the thickness of the spacer layer and the interlayer crosstalk. Therefore, in the two-layer optical disc,
The thickness d of the spacer layer is practically set to a lower limit of 30 μm to suppress the influence of interlayer crosstalk of each layer read from one side.

[0021]

Here, the optical pickup used for the two-layer optical disc is designed so that a single-layer optical disc can be read, and for example, when the thickness of the translucent substrate reaching the reflective layer of the single-layer optical disc is 0.6 mm. Is set so that the objective lens of the optical pickup is optimally focused by the reflective layer on the translucent substrate having a light beam of 0.6 mm and the aberration becomes zero. Therefore, when reading the information of Layer0 and Layer1 of the two-layer optical disk, respectively,
When the light beam is focused on yer0, the thickness of the transparent substrate 101 affects the aberration, and when focusing the light beam on Layer1, the total thickness of the transparent substrate 101 and the spacer layer 105 is added. Affects the aberration.

[0022]

As shown in FIG. 15, the sum of the thickness of the translucent substrate 101 and the thickness of the spacer layer 105, which reaches the reflection layer read by the light beam, is the thickness when the aberration is 0 (0. 6 mm), the optical aberration (spherical aberration) gradually increases, the light beam cannot be properly focused, and the information of Layer 0 and Layer 1 cannot be read correctly.

Therefore, by forming the thickness of the spacer layer and / or the translucent substrate reaching each reflection layer of the two-layer optical disk within a predetermined range, the aberration of the light beam focused on each reflection layer can be reduced. It is set approximately evenly within the readable range.

[0024]

In FIG. 15, Layer 0 and Layer 0
r1 is evenly displaced from the position corresponding to the reflective layer of the single-layer optical disc through the translucent substrate having a thickness of 0.6 mm, and the aberration when reading each information is the optimum point (that is, aberration 0). It is set to be slightly shifted from. It should be noted that the allowable value of the aberration is such that the position of each reflective layer of the two-layer optical disc with respect to the optical pickup is −50 μm to + at maximum from the position of the reflective layer of the single-layer optical disc having a translucent substrate thickness of 0.6 mm.
If the deviation is within the range of 60 μm, the signal can be normally read in each layer.

[0025]

Now, let us consider the thicknesses of the light-transmissive substrate 101 and the spacer layer 105 constituting the layers Layer 0 and Layer 1 of the two-layer optical disk.

First, in the production of a two-layer optical disc, the thicker the spacer layer, the easier the production.
It is desirable to set the thickness of the translucent substrate to a small value within a range in which yer0 and Layer1 can be read. Here, considering the aberration range in which Layer 0 can be read, as described above, the thickness of the transparent substrate 101 needs to be 0.55 mm at the minimum (0.6 mm to −5 at the maximum).
(Because it is necessary to fit within the range of 0 μm to +60 μm). The transparent substrate 101 is formed by injection molding a transparent polycarbonate resin, for example.
For example, in the case of molding to a thickness of 0.58 mm, variations of about ± 30 μm occur in practice due to fluctuation factors such as molding conditions. Therefore, the center value of the thickness of the transparent substrate 101 is set to 0.58 mm at the minimum.

[0027]

Next, the thickness up to Layer 1 is the thickness of the translucent substrate 101 plus the thickness of the spacer layer 105. If the aberrations in Layer 0 and Layer 1 are set to be equal, the spacer layer The thickness of 105 is set to 0.04 mm.

Here, when the thickness of the transparent substrate 101 varies to the upper limit, the transparent substrate 101 is 0.58 + 0.0.
3 = 0.61 (mm). Therefore, Layer
Considering the aberration range in which 0 can be read, the transparent substrate 1
The maximum value of the sum of the thickness of 01 and the thickness of the spacer layer 105 is 0.61 + 0.05 = 0.66 (mm) at the maximum (must be within a deviation of 0.6 mm to a maximum of −50 μm to +60 μm). The spacer layer 1
The thickness of 05 cannot exceed 0.05 (mm). That is, the spacer layer 105 is formed with a center value of 0.04 mm and a thickness of ± 10 μm.
0 and Layer 1 are not affected by crosstalk, and the information of each layer can be read by uniform aberration within a readable aberration range.

[0029]

However, when the spacer layer is formed by the conventional spin coating method using the above-mentioned UV-curable resin, the viscosity and curing time of the UV-curable resin, the rotation speed and rotation time of the substrate, the substrate surface Since there are many control factors such as physical properties, it is impossible to keep the thickness d within the range of ± 10 μm variation with the lower limit of 30 μm only by dropping it on the reflective layer, and therefore, there is a problem that yield in mass production deteriorates. there were.

[0030]

Further, if there are bubbles or gaps in the spacer layer, the refractive index of the light in that portion will fluctuate greatly, and the diffuse reflection will cause a significant decrease in the transmittance of the light beam, and a marked deterioration in aberration. As a result, the optical pickup cannot correctly read the pits and grooves. Therefore, the UV curable resin used for spin coating is generally subjected to vacuum defoaming treatment or the like in advance, but when the spacer layer is formed by the conventional spin coating method described above, during high-speed spinning (spin-off). Air bubbles from the inner circumference side of the substrate. Most of the entrapped air bubbles escape from the outer peripheral edge during high-speed spinning, but it takes time to bond the substrates, and some air bubbles may remain, resulting in poor mass productivity.

[0031]

Further, if the variation in the thickness of the transparent substrate 101 is strictly controlled, the tolerance of the thickness of the spacer layer 105 may be loosened, but the yield is poor, and the mass productivity is also significantly reduced.

[0032]

[0023]

[0033]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a two-layer structure in which a spacer layer between reflecting layers can be easily formed to have a predetermined thickness and to be optically uniform. An optical disc is provided.

[0034]

[0024]

[0035]

According to the first aspect of the present invention,
A first having a first record holding area carrying a first information
A second substrate having a first reflective layer formed so as to cover the first record holding area on the substrate and a second record holding area carrying second information and having a light transmitting property. The second reflective layer formed so as to cover the upper second record holding area is attached by an adhesive member having a light-transmitting property,
A two-layer optical disc for optically reading the first information or the second information from the substrate side of the first substrate, the first substrate coated with the first reflective layer or the second substrate coated with the second reflective layer. Alternatively, a plurality of protrusions having a predetermined height are provided on the first reflective layer or the second reflective layer, and the adhesive member sandwiches the first reflective layer and the second reflective layer bonded together. The plurality of protrusions are filled in a gap having a predetermined height to form a spacer layer having a height substantially equal to the predetermined height.

[0036]

According to a second aspect of the present invention, in the first aspect of the invention, at least one protrusion of the plurality of protrusions is located at a position inner than the first and second record holding areas of the disc. , Formed in a ring shape substantially concentric with the disk.

[0037]

Further, the invention according to claim 3 is such that the first record holding area on the first substrate having the first record holding area carrying the first information is formed so as to cover the first record holding area. Second reflection holding layer formed on the second substrate having the second reflection holding layer carrying the second information and the second recording holding area carrying the second information and having a light transmitting property. In the two-layer optical disc in which the layer and the layer are attached to each other by a translucent adhesive member to read the first information or the second information from the second substrate side, the adhesive member has a refractive index substantially equal to that of the adhesive member and When a plurality of fine particles having an outer dimension of a predetermined height are mixedly formed and the first reflective layer and the second reflective layer are bonded together, the plurality of fine particles are separated by the first reflective layer and the second reflective layer. It is sandwiched by the second reflective layer and has a predetermined height of a plurality of fine particles. It constituted by forming a spacer layer in pot equal height.

[0038]

[0027]

[0039]

The present invention is constructed as described above.
According to the invention described above, a protrusion having a predetermined height is provided on the substrate or the reflection layer coated with the reflection layer of the two-layer optical disc, and when the reflection layers are bonded by the adhesion member, the adhesive member is The spacer layer between the reflective layers is formed by filling the gap having a predetermined height formed by a plurality of protrusions sandwiched between the reflective layers to form the spacer layer at a height substantially equal to the predetermined height of the protrusions. Can be easily formed with a predetermined thickness.

[0040]

According to a second aspect of the present invention, in the first aspect of the invention, at least one of the plurality of protrusions is located inside the first and second record holding areas of the disc. At the position, because it is formed in a ring shape that is almost concentric with the disc, new air bubbles do not mix into the adhesive member when spin-coating the adhesive member, so the adhesive member is evenly distributed between the reflective layers having a gap of a predetermined height. It is possible to fill the spacer layer, and since the bubbles do not cause a large change in the refractive index in the spacer layer, it is possible to easily form the spacer layer between the reflecting layers with a predetermined thickness and optically uniform.

[0041]

According to the third aspect of the present invention, when the reflective layers of the two-layer optical disk are bonded by the adhesive member, the adhesive member has a refractive index substantially equal to that of the adhesive member and a predetermined height. When a plurality of fine particles having substantially the same outer dimensions are mixedly formed and the respective reflection layers are bonded together, the plurality of fine particles are sandwiched by the respective reflection layers, and the plurality of fine particles have a predetermined height. Since the spacer layers are formed at substantially the same height, the adhesive member filling the reflective layers having a gap of a predetermined height can be formed with a substantially uniform refractive index, and the spacer layers between the reflective layers can be easily formed. In addition, it can be formed to have a predetermined thickness and be optically uniform.

[0042]

[0030]

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, each embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic sectional view showing a main part of a two-layer optical disc according to the first embodiment of the present invention. In the figure, a two-layer optical disc is formed by injection-molding a transparent synthetic resin, for example, a transparent polycarbonate resin, and is formed into a disc shape with a predetermined thickness. A pit or groove that carries the first information forms a recording holding area in the range, and the pit or groove is further covered with a reflective layer 2 made of a semitransparent film having a predetermined reflectance and transmittance. Has been done. The reflective layer 2 is, for example, a thin film obtained by depositing gold (Au) on the transparent substrate 1 by vacuum deposition.

[0044]

Reference numeral 3 is a disk-shaped substrate formed by, for example, heat compression molding or injection molding of synthetic resin, and a pit or groove for carrying the second information is provided in a predetermined range on one surface. A recording holding area is formed, and a reflective layer 4 is formed on the pit or groove with a material having a relatively high reflectance. The reflective layer 4 is, for example, a thin film obtained by adhering aluminum (Al) on the substrate 3 by vacuum vapor deposition.

[0045]

Ring-shaped projections 5a and 5b, which are concentric with the substrate 3 and have a predetermined height, are formed on the inner and outer circumferences on the same side as the surface of the substrate 3 where pits or grooves are formed. Further, 6 is a spacer layer, which is formed by aligning the translucent substrate 1 and the substrate 3 so that the reflective layers 2 and 4 face each other, and thereby the ultraviolet curable resin filled in the gaps obtained by the projections 5a and 5b is filled. It is formed by curing, and the translucent substrate 1 and the substrate 3 are fixed to each other. In addition, the protrusion 5
When the transparent substrate 1 and the substrate 3 are bonded together, a and 5b are projections 5a on the inner circumference side of the record holding areas of the reflective layers 2 and 4, and projections 5b are record holding of the reflective layers 2 and 4. It is provided so as to be located on the outer peripheral side of the region. The two-layer optical disc is configured as described above, and while being rotated at a predetermined speed, the light beam of an optical pickup (not shown) is appropriately irradiated from the transparent substrate side to each reflective layer, and the optical pickup receives information by reflected light. Reading.

[0046]

FIG. 2 is a detailed view of the projection formed on the substrate 3. Protrusions 5a and 5b are formed further on the inner and outer peripheral sides of the recording holding area of the substrate 3 shown in FIG. The cross-sectional shapes of the protrusions 5a and 5b are, for example, as shown in FIGS.
It has a shape as shown in (d) and has a predetermined height h.

[0047]

The protrusions 5a and 5b are formed on the substrate 3 by the following method.

FIG. 3 shows an example of a method for producing the substrate 3. First, a record holding area for carrying the second information is formed on the glass master (FIG. 3 (a)), and the inner and outer circumferences of the record holding section are further formed on the same side as the signal recording surface having the record holding area. The ring-shaped protrusions 7a and 7b having a predetermined height h are formed on the surface by a photoresist process or the like (see FIG. 3).
(B)).

[0049]

Next, a master stamper is formed by electroforming plating (FIG. 3C), and a molding stamper is formed from the master stamper separated from the glass master (FIG. 3D). The stamper for molding has projections 7a, 7
Grooves 8a and 8b corresponding to b are formed. Next, the stamper is attached to the mold of the compression molding machine, and synthetic resin is injection-molded or heat-compression-molded.
By forming a and 5b (FIG. 3 (e)) and taking them out from the mold, the substrate 3 integrally having the projections 5a, 5b having the height h is obtained (FIG. 3 (f)).

[0050]

Further, FIG. 4 shows another example of the method for producing the substrate 3. First, a record holding area for carrying the second information is formed on the glass master (FIG. 4A), and a master stamper is formed on the signal recording surface having the record holding area by electroforming plating ( FIG. 4B). Then, on the master stamper separated from the glass master, in the inner and outer peripheral portions (portions indicated by arrows A and B in FIG. 4C) of the glass master where the record holding area is transferred. Then, additional processing such as cutting is performed to form a ring-shaped groove having a predetermined depth h (not shown) (FIG. 4C).

[0051]

Next, a stamper for molding is prepared from the master stamper having additional grooves formed therein (FIG. 4 (d)). Grooves 8a and 8b having the same shape as the grooves of the master stamper are formed on the molding stamper. Next, when the stamper is attached to the mold of the compression molding machine and the synthetic resin is heated and compression-molded, the protrusions 5a and 5b are formed corresponding to the grooves 8a and 8b (FIG. 4 (e)), and taken out from the mold. As a result, the substrate 3 on which the protrusions 5a and 5b having the height h are integrally formed is obtained (FIG. 4 (f)).

[0052]

Next, how the two-layer optical disc according to the first embodiment of the present invention is formed will be described below with reference to FIG.

First, in FIG. 5A, the substrate 3 is formed by the method described above, and then the reflection layer 4 is formed in advance on the recording holding area (not shown). A predetermined amount of the ultraviolet curable resin 9 is dropped along the outer peripheral side of the protrusion 5a on the inner peripheral side of the substrate 3.

[0054]

Next, referring to FIG. 5B, the reflection layer 2 is previously formed.
The translucent substrate 1 on which is formed is placed above the recording holding area (not shown) transferred onto the substrate 3 so that the reflective layers 2 and 4 sandwich the ultraviolet curable resin 9 therebetween, and the translucent substrate is formed. When 1 and the substrate 3 are coaxially rotated by a predetermined amount, the ultraviolet curable resin 9 is spin-coated in the outer peripheral direction by a centrifugal force. At this time, the translucent substrate 1 is gradually reduced in distance from the substrate 3,
The projections 5a and 5b of the substrate 3 are locked at the tips thereof over the entire circumference,
The distance from the substrate 3 is kept constant (width h).

[0055]

Further, the ultraviolet curable resin 9 is filled in the space formed by the translucent substrate 1 and the substrate 3 and the projections 5a and 5b without any gap, and further rotated at a high speed to obtain an extra ultraviolet curable resin 9 Is shaken off. Also,
At this time, on the inner peripheral side of the substrate 3, the translucent substrate 1 and the protrusions 5a are formed.
Since they are in close contact with each other, air bubbles are not caught from the inner peripheral side of the substrate. Therefore, the ultraviolet curable resin 9 filled in the space formed by the translucent substrate 1, the substrate 3 and the protrusions 5a and 5b does not contain bubbles.

[0056]

Next, referring to FIG. 5C, the transparent substrate 1
When a predetermined amount of ultraviolet rays (UV) is irradiated from above, the ultraviolet curable resin 9 is cured to form a spacer layer 6 having a predetermined thickness d that is substantially equal to the height h of the protrusions 5a and 5b. The spacer layer 6 includes a transparent substrate 1, a reflective layer 2, a substrate 3,
Since the reflection layers 4 are fixed to each other, the reflection layers 2 and 4 can be fixed at a predetermined distance d to form a two-layer optical disc. Further, since the spacer layer 6 does not form bubbles, it does not cause a large change in the refractive index due to bubbles, and is therefore formed optically uniform. A two-layer optical disc is formed by the above.

[0057]

Incidentally, in the first embodiment of the present invention,
A ring-shaped projection concentric with the substrate and having a predetermined height h is formed on the inner and outer peripheral portions of the substrate 3 and is attached to the translucent substrate 1 to form the spacer layer thickness d. As shown in FIG. 3, the outer peripheral portion of the substrate 10 is provided with a plurality of minute projections 5c having a conical shape, a truncated pyramid shape, or a cylindrical shape and having a predetermined height h at the outer peripheral position of the recording holding area. Is also good. The shape of the protrusion is not limited to the above-mentioned shape, and may have a composite shape or an irregular shape.
When 0 is attached to the transparent substrate 1, the distance between the substrate 10 and the reflective layers 2 and 4 formed on the transparent substrate 1 is d.
The same effect can be obtained irrespective of the shape and the number of the recording layers as long as they are formed so as to be located outside the information recording area formed by the reflective layers 2 and 4.

[0058]

Further, in the first embodiment of the present invention,
Although the projections 5a and 5b are provided on the substrate 3, the projections 5a and 5b may be provided on the translucent substrate 1 instead of the substrate 3.

[0059]

Further, as shown in FIG. 7, ring-shaped projections 5d, 5e, 5 having predetermined heights are formed on the inner and outer peripheral portions of the surfaces of the substrate 11 and the transparent substrate 12 which face each other.
It may be configured such that f and 5g are provided and the respective reflection layers are kept at a predetermined distance d by adhering them. As an example, the heights of 5d, 5e, 5f, and 5g are all h /
2, 5d and 5f, and 5e and 5g are laminated to obtain a height of h as a whole, and the distance between the reflective layers is d.
You may form so that it may become.

[0060]

In the first embodiment of the present invention,
Although the protrusions 5a and 5b are integrally formed on the substrate 3, the protrusions do not necessarily have to be integrally formed as long as each reflection layer can be kept at a predetermined distance. For example, on the substrate or the transparent substrate. Alternatively, it may be formed by an additional process such as printing or vapor deposition.

[0061]

Further, in FIG. 6, the protrusion 5c has a conical shape, a truncated cone shape or a cylindrical shape, and is formed by a minute protrusion having a predetermined height h, but as shown in FIGS. 9 (a) to 9 (f). May have a horizontal cross-sectional shape, and by thus forming a substantially convex shape toward the inner peripheral side of the substrate, the ultraviolet curable resin 9 is used to form the reflective layer 2 on the translucent substrate 1, When the reflective layer 4 on the substrate 10 is attached by the above-mentioned spin coating method, even if bubbles are mixed in the ultraviolet curable resin 9, the bubbles move from the inner peripheral side to the outer peripheral side due to the high-speed spin of the substrate. In doing so, the protrusions do not interfere with the movement of the bubbles and retain them in the spacer layer. FIG. 9 is a diagram showing another example of the shape of the protrusion 5c in FIG. 6, and shows a horizontal (parallel to the substrate 10) cross-sectional shape of the protrusion seen from the upper surface of the substrate 10.

[0062]

Next explained is a double-layer optical disc according to the second embodiment of the invention.

FIG. 8 is a diagram showing how a two-layer optical disc according to the second embodiment of the present invention is formed. First, in FIG. 8A, the substrate 14 is peeled off from the master glass stamper prepared by the steps of FIGS. 4A and 4B described above, and the cutting process of FIG. The stamper for molding that was created without was attached to the mold of the compression molding machine and was formed by heat compression molding synthetic resin, and the recording holding area formed on the glass master was transferred onto one side, A record holding area that carries the second information is formed. In addition, the reflective layer 4 is formed in advance on the record holding area that carries the second information. This substrate 14
On the surface on which the reflection layer 4 is formed, a predetermined amount of the ultraviolet curable resin 13 is dropped near the inner peripheral side of the substrate.

[0064]

The ultraviolet-curable resin 13 is a base material 13a mainly composed of urethane acrylate-based, epoxy acrylate-based, ester acrylate-based, melamine acrylate-based materials or polymers thereof, and a predetermined ratio to the base material 13a. It is composed of a plurality of fine particles 13b mixed with each other (for example, about 10% by weight). Fine particles 13b are base 1
It is made of a material having a refractive index relatively close to 3a, and is formed in a shape such that the maximum outer shape does not exceed a predetermined dimension d (for example, 30 μm to 50 μm). The ultraviolet curable resin 13 is preliminarily mixed with a plurality of fine particles 13b in a predetermined ratio (for example, about 10% by weight) with respect to the base material 13a and stirred so as to be uniformly distributed, for example, vacuum defoaming treatment. To remove air bubbles, and has an appropriate viscosity.

[0065]

Next, referring to FIG. 8B, the reflection layer 2 is previously formed.
The translucent substrate 1 on which is formed is placed above a recording holding area (not shown) that is transferred onto the substrate 14 so that the reflective layers 2 and 4 sandwich the ultraviolet curable resin 13, and the translucent substrate is formed. 1
When the substrate 14 is rotated by a predetermined axis coaxially, the ultraviolet curable resin 13 is crushed by the transparent substrate 1 and the substrate 14 and is spin-coated in the outer peripheral direction by the centrifugal force due to the rotation of the substrate. At this time, the translucent substrate 1 is gradually reduced in distance from the substrate 14, and the reflective layers 2 and 4 are locked by sandwiching the plurality of fine particles 13b. Therefore, there is a constant interval between the reflective layers 2 and 4 (the maximum outer diameter d of the plurality of fine particles 13b).
And the ultraviolet curable resin 13 is filled without any gap.

[0066]

Next, referring to FIG. 8C, the transparent substrate 1
When a predetermined amount of ultraviolet rays (UV) is irradiated from above, the ultraviolet curable resin 13 is cured and the spacer layer 15 having the thickness of the maximum outer diameter d of the plurality of fine particles 13b is formed. The spacer layer 15 includes the transparent substrate 1, the reflective layer 2, and the substrate 1.
Since the reflection layer 4 and the reflection layer 4 are fixed to each other, the reflection layers 2 and 4 can be fixed at a predetermined distance d to form a two-layer optical disc. Further, since the base material 13a and the fine particles 13b have similar refractive indexes, the refractive index of light does not fluctuate greatly in the formed spacer layer 15, and therefore, they are formed optically homogeneous. A two-layer optical disc is formed by the above.

[0067]

The UV-curable resin 13 is required to have high transparency in order to efficiently irradiate UV rays and in order for the spacer layer formed after curing to transmit the light beam of the optical pickup without loss. In addition, it is also necessary that the shrinkage rate after curing is small so that internal stress of the substrate is not partially generated during curing and causes birefringence. Therefore, it is desirable to use urethane acrylate having a relatively high transparency and a small shrinkage rate after curing as the base material 13a.

[0068]

When urethane acrylate is mainly used as the base 13a, the fine particles 13b are made of a material having a refractive index close to that of urethane acrylate, such as styrene, acrylic, olefin, vinylbenzene, polycarbonate or silicon dioxide. It is possible to use a material such as a glass-based material, a soda-lime glass-based material, a non-alkali glass-based material, or a polymer thereof.

[0069]

Further, when the transparent substrate 1 is formed by injection molding a polycarbonate resin, the fine particles 13b are made of polycarbonate having the same refractive index so that the transparent substrate 1 and the transparent substrate 1 can be accurately matched. You can

[0070]

If the material of the fine particles 13b is a silicon dioxide-based material, a soda lime glass-based material, an alkali-free glass-based material, or a glass material having a high hardness such as a polymer thereof, the spacer layer formed is Can increase strength,
It is possible to form a two-layer optical disc with less warping, bending, and deformation.

[0071]

In the above-mentioned embodiment, the two-layer optical disc has two layers that can be read from one side of the disc, but by bonding two two-layer optical discs,
A two-layer optical disc in which two layers are read from both sides may be used.

[0072]

[0056]

[0073]

Since the present invention is configured as described above, according to the invention of claim 1, a projection having a predetermined height is formed on the substrate or the reflective layer of the two-layer optical disk coated with the reflective layer. When each reflective layer is attached by an adhesive member, the adhesive member is filled in a gap of a predetermined height formed by a plurality of protrusions sandwiched between the reflective layers, and is approximately equal to the predetermined height of the protrusion. Since the spacer layer is formed at the height, the spacer layer between the reflective layers can be easily formed with a predetermined thickness.

[0074]

According to a second aspect of the present invention, in the first aspect of the invention, at least one of the plurality of protrusions is located inside the first and second record holding areas of the disc. At the position, because it is formed in a ring shape that is almost concentric with the disc, new air bubbles do not mix into the adhesive member when spin-coating the adhesive member, so the adhesive member is evenly distributed between the reflective layers having a gap of a predetermined height. It is possible to fill the spacer layer, and since the bubbles do not cause a large change in the refractive index in the spacer layer, it is possible to easily form the spacer layer between the reflecting layers with a predetermined thickness and optically uniform.

[0075]

According to the third aspect of the present invention, when the reflective layers of the two-layer optical disk are bonded by the adhesive member, the adhesive member has a refractive index and a predetermined height almost equal to those of the adhesive member. When a plurality of fine particles having substantially the same outer dimensions are mixedly formed and the respective reflection layers are bonded together, the plurality of fine particles are sandwiched by the respective reflection layers, and the plurality of fine particles have a predetermined height. Since the spacer layers are formed at substantially the same height, the adhesive member filling the reflective layers having a gap of a predetermined height can be formed with a substantially uniform refractive index, and the spacer layers between the reflective layers can be easily formed. In addition, it can be formed to have a predetermined thickness and be optically uniform.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a main part of a dual-layer optical disc according to a first embodiment of the invention.

FIG. 2 is a detailed view of protrusions formed on the substrate of the dual-layer optical disc according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of a method of manufacturing a substrate of a dual-layer optical disc according to the first embodiment of the present invention.

FIG. 4 is a diagram showing another example of a method of manufacturing the substrate of the dual-layer optical disc in the first embodiment of the invention.

FIG. 5 is a diagram showing how a dual-layer optical disc according to the first embodiment of the present invention is formed.

FIG. 6 is a diagram showing an example of other protrusions of the dual-layer optical disc in the first embodiment of the invention.

FIG. 7 is a diagram showing an example of other protrusions of the dual-layer optical disc in the first embodiment of the invention.

FIG. 8 is a diagram showing how a dual-layer optical disc according to a second embodiment of the present invention is formed.

FIG. 9 is a diagram showing an example of other protrusions of the dual-layer optical disc in the first embodiment of the invention.

FIG. 10 is a schematic cross-sectional view of a main part of a conventional double-layer optical disc.

FIG. 11 is a diagram showing a conventional substrate bonding process for a dual-layer optical disc.

FIG. 12 is a diagram showing how a light beam emitted from an optical pickup in a conventional two-layer optical disc reflects each layer of the two-layer optical disc and reaches the optical pickup again.

FIG. 13 shows a state in which, in a conventional dual-layer optical disc, when a light beam emitted from an optical pickup is focused on one reflective layer of the dual-layer optical disc, it is defocused on the other reflective layer. It is a figure.

FIG. 14 is a graph showing the relationship between spacer layer thickness and interlayer crosstalk in a conventional two-layer optical disc.

FIG. 15 is a graph showing the relationship between the total thickness of the transparent substrate and the spacer layer and the optical aberration (spherical aberration) in the conventional two-layer optical disc.

[Explanation of symbols]

 1 ... Translucent Substrate 2 ... Reflective Layer 3 ... Substrate 4 ... Reflective Layer 5a ... Protrusion 5b ... Protrusion 5c ... Protrusion 5d ... Protrusion 5e ... Protrusion 5f ... Protrusion 5g ... Protrusion 6 ... Spacer layer 7a ... Protrusion 7b ... Protrusion 8a ... Groove 8b ... Groove 9 ... UV curable resin 10 ... Substrate 11 ... Substrate 12 ... Translucent substrate 13 ... UV curable resin 13a ...・ Base material 13b ・ ・ ・ Fine particles 14 ・ ・ ・ ・ ・ ・ Substrate 15 ・ ・ ・ ・ Spacer layer

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 12, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Detailed description of the invention

[Correction method] Change

[Correction contents]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly to a reproducing optical disk in which pits or grooves for carrying information are formed in multiple layers.

[0002]

2. Description of the Related Art Conventionally, a so-called compact disc (hereinafter referred to as a CD) is known as an optical disc for reproduction.
The CD is a reflective film formed of a disc-shaped substrate having a light-transmitting property and having a predetermined thickness, on one surface of which a pit or groove for carrying information is formed, and which is made of a metal foil so as to cover the pit or groove. Are laminated to form a reflective layer, and an ultraviolet curable resin is spin-coated on the reflective layer to form a protective film having a predetermined thickness. A label is formed on the protective film by a method such as screen printing, and the CD
The information content and other information are displayed visually. The CD is configured as described above, and the pit or groove shape transferred from one surface side of the transparent substrate to the reflective layer is optically read by using an optical pickup or the like to reproduce recorded information.

In addition, with the recent increase in the density of information, it is required to increase the density of pits or grooves carried by an optical disk, and the pits or grooves are formed in multiple layers to optically read from one side. Optical discs are being considered.

As a multilayer optical disc, for example, as shown in FIG. 10, a dual layer optical disc (Dual Layer Disc) is used.
c). In the double-layered optical disc shown in FIG. 1, a pit or groove for carrying the first information is formed on one side of a transparent substrate 101 formed by injection molding a transparent synthetic resin and having a predetermined thickness. The pits or grooves are formed by coating a reflective layer 102 made of a semitransparent film having a predetermined reflectance and transmittance. Further, a pit or groove that carries the second information is formed on one surface of the substrate 103 having a predetermined thickness, and the pit or groove is covered and closely formed with a reflective layer 104 having a high reflectance. Further, the reflective layers 102 and 104 are attached to each other using a translucent ultraviolet curable resin so as to face each other, and the ultraviolet curable resin is cured to have a predetermined thickness to form a translucent spacer layer. 105 is formed to form a two-layer optical disc.

Further, the spacer layer 105 is the reflection layer 10
It is formed by bonding the two substrates on which 2, 104 are formed by a substrate bonding process as shown in FIG. 11, for example. First, in FIG. 11A, a predetermined amount of the ultraviolet curable resin 106 is dropped in a ring shape concentric with the disk on the inner peripheral side on the surface of the substrate 103 on which the reflective layer 104 is formed, and then FIG. In (b), the reflective layer 102 is laminated on the transparent substrate 101, and the substrate 10
When 3 and the transparent substrate 101 are coaxially rotated for a predetermined time, the ultraviolet curable resin 106 is spin-coated between the reflective layers 102 and 104 by a centrifugal force and spreads to a predetermined thickness without a gap. Next, in FIG. 11C, when ultraviolet rays (UV) are irradiated from the transparent substrate 101 side for a predetermined time,
The ultraviolet curable resin 106 is cured to form the spacer layer 105 having a predetermined thickness d.

The two-layer optical disc is formed as described above,
As shown in FIG. 10, when reading the first layer (called Layer 0) from the transparent substrate 101 side using an optical pickup (not shown), the reading beam of the optical pickup is focused on the reflective layer 102, The reflected light modulated by the pits or grooves formed on the reflective layer 102 is read. The second layer (called Layer1)
When reading, the reading beam of the optical pickup is transmitted through the reflection layer 102 and focused on the reflection layer 104,
The reflected light modulated by the pits or grooves formed on the reflective layer 104 is read through the reflective layer 102 again.

In the two-layer optical disc, the information recorded in the two layers can be appropriately selected and read without turning over both sides of the disc in this way, so that the information can be recorded in two layers by using one optical pickup. Information can be played back instantly.

FIG. 12 shows how the light beam emitted from the optical pickup reaches each optical pickup after being reflected by each layer of the two-layer optical disk. As can be seen from FIG. 12, information of Layer 0 is read. In this case, the incident light from the optical pickup is Layer 0 of the disc.
At about 30%, it reaches the optical pickup.

When reading the information of Layer 1, about 70% of the incident light from the optical pickup goes to Layer 1 although there is some absorption in the translucent substrate 101 of Layer 0 and the semitransparent reflection film 102. .

In Layer 1, about 80% of the light is reflected by the reflective film 104, the reflected light reaches Layer 0 again in the spacer layer, is reflected by Layer 0 again by about 30%, and the light transmitted through Layer 0 is the light. Return to pickup. In this case, when viewed from the optical pickup, L
The reflectances of Layer 0 and Layer 1 are selected so that the reflected light at layer 0 and the reflected light at Layer 1 are almost equal.

The spacer layer 105 is the reflective layer 102,
It is formed for the purpose of keeping the interlayer distance of 104 constant, and has a uniform refractive index of light and a large transmittance.

When reading a two-layer optical disk, the optical pickup picks up the reflected light from Layer 0 and the Layer.
The reflected light from r1 is reflected, but La
When reading yer0, the focus of the reading beam is set to Layer0, so that
As shown in (a), the light beam with which Layer 1 is irradiated is defocused and greatly spreads. FIG. 13 shows how the light beam emitted from the optical pickup is defocused on the other reflection layer of the two-layer optical disc when the light beam is focused on one reflection layer.

On the other hand, if the spot diameter of the light beam is very large compared to the size of the recorded pit or groove, it will not be modulated by the pit or groove and will only be a DC offset. If the low frequency component is removed by the HPF from the RF signal obtained by converting to, the signal by Layer0 alone can be extracted. Similarly, as shown in FIG.
If the reading beam is focused on r1, only the signal from Layer1 can be extracted. In this way, the two-layer optical disc can read the information recorded on the two layers by appropriately selecting each layer from one side using the optical pickup and focusing the light beam.

However, the spacer layer has a predetermined width d.
If the width is smaller than the width d ′, as shown in FIG. 13B, when the reading beam is focused on the Layer 0, the light beam irradiated on the Layer 1 does not spread so much, so that the Layer 0 causes When reading a signal, inter-layer crosstalk increases rapidly,
The modulated signal by r1 cannot be ignored. FIG. 14 is a graph showing the relationship between the thickness of the spacer layer and the interlayer crosstalk. Therefore, in the two-layer optical disc,
The thickness d of the spacer layer is practically set to a lower limit of 30 μm to suppress the influence of interlayer crosstalk of each layer read from one side.

Here, the optical pickup used for the two-layer optical disc is designed so that a single-layer optical disc can be read, and for example, when the thickness of the translucent substrate reaching the reflective layer of the single-layer optical disc is 0.6 mm. Is set so that the objective lens of the optical pickup is optimally focused by the reflective layer on the translucent substrate having a light beam of 0.6 mm and the aberration becomes zero. Therefore, when reading the information of Layer0 and Layer1 of the two-layer optical disk, respectively,
When the light beam is focused on yer0, the thickness of the transparent substrate 101 affects the aberration, and when focusing the light beam on Layer1, the total thickness of the transparent substrate 101 and the spacer layer 105 is added. Affects the aberration.

As shown in FIG. 15, the sum of the thickness of the translucent substrate 101 and the thickness of the spacer layer 105, which reaches the reflection layer read by the light beam, is the thickness when the aberration is 0 (0. 6 mm), the optical aberration (spherical aberration) gradually increases, the light beam cannot be properly focused, and the information of Layer 0 and Layer 1 cannot be read correctly. Therefore, by forming the spacer layer and / or the translucent substrate to reach the respective reflective layers of the two-layer optical disc within a predetermined range,
The aberrations of the light beam focused on each reflective layer are set to be substantially uniform within a readable range.

In FIG. 15, Layer 0 and Layer 0
r1 is evenly displaced from the position corresponding to the reflective layer of the single-layer optical disc through the translucent substrate having a thickness of 0.6 mm, and the aberration when reading each information is the optimum point (that is, aberration 0). It is set to be slightly shifted from. It should be noted that the allowable value of the aberration is such that the position of each reflective layer of the two-layer optical disc with respect to the optical pickup is −50 μm to + at maximum from the position of the reflective layer of the single-layer optical disc having a translucent substrate thickness of 0.6 mm.
If the deviation is within the range of 60 μm, the signal can be normally read in each layer.

Now, let us consider the thicknesses of the light-transmissive substrate 101 and the spacer layer 105 constituting the layers Layer 0 and Layer 1 of the two-layer optical disk. First, in making a two-layer optical disc, it is easier to make the spacer layer as thick as possible.
It is desirable to set the thickness of the translucent substrate as small as possible within the range where r1 can be read. Here, considering the aberration range in which Layer 0 can be read, the thickness of the translucent substrate 101 needs to be 0.55 mm at a minimum as described above (within the range of 0.6 mm to a maximum of −50 μm to +60 μm). (Because it must fit within the gap). The transparent substrate 101 is formed of, for example, a transparent polycarbonate resin by injection molding. However, when the transparent substrate 101 is molded to a thickness of 0.58 mm, for example, a variation of about ± 30 μm may occur due to a variation factor such as molding conditions. Occur. Therefore,
The central value of the thickness of the transparent substrate 101 is 0.58 m at the minimum.
m.

Next, the thickness up to Layer 1 is the thickness of the translucent substrate 101 plus the thickness of the spacer layer 105. If the aberrations in Layer 0 and Layer 1 are set to be equal, the spacer layer The thickness of 105 is set to 0.04 mm. Here, the transparent substrate 101
When the thickness of the transparent substrate 101 varies to the upper limit, the transparent substrate 101 has a thickness of 0.58 + 0.03 = 0.61 (mm). Therefore, considering the aberration range in which Layer 0 can be read, the maximum value of the total thickness of the transparent substrate 101 and the spacer layer 105 is 0.61 + 0.05 = 0.66.
(Mm) is the limit (0.6 mm to -50 μm at maximum)
The thickness of the spacer layer 105 cannot be formed to exceed 0.05 (mm), because it must fall within the range of +60 μm. That is, the spacer layer 10
5 is formed with a center value of 0.04 mm to ± 10 μm, so that Layer 0 and Layer 1 are not affected by crosstalk, and information of each layer can be read by uniform aberration within a readable aberration range. it can.

However, when the spacer layer is formed by the conventional spin coating method using the above-mentioned UV-curable resin, the viscosity and curing time of the UV-curable resin, the rotation speed and rotation time of the substrate, the substrate surface Since there are many control factors such as physical properties, it is impossible to keep the thickness d within the range of ± 10 μm variation with the lower limit of 30 μm only by dropping it on the reflective layer, and therefore, there is a problem that yield in mass production deteriorates. there were.

Further, if there are bubbles or gaps in the spacer layer, the refractive index of the light in that portion will fluctuate greatly, and the diffuse reflection will cause a significant decrease in the transmittance of the light beam, and a marked deterioration in aberration. As a result, the optical pickup cannot correctly read the pits and grooves. Therefore, the UV curable resin used for spin coating is generally subjected to vacuum defoaming treatment or the like in advance, but when the spacer layer is formed by the conventional spin coating method described above, during high-speed spinning (spin-off). Air bubbles from the inner circumference side of the substrate. Most of the entrapped air bubbles escape from the outer peripheral edge during high-speed spinning, but it takes time to bond the substrates, and some air bubbles may remain, resulting in poor mass productivity.

Further, if the variation in the thickness of the transparent substrate 101 is strictly controlled, the tolerance of the thickness of the spacer layer 105 may be loosened, but the yield is poor, and the mass productivity is also significantly reduced.

[0023]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a two-layer structure in which a spacer layer between reflecting layers can be easily formed to have a predetermined thickness and to be optically uniform. An optical disc is provided.

[0024]

According to the first aspect of the present invention,
A first having a first record holding area carrying a first information
A second substrate having a first reflective layer formed so as to cover the first record holding area on the substrate and a second record holding area carrying second information and having a light transmitting property. The second reflective layer formed so as to cover the upper second record holding area is attached by an adhesive member having a light-transmitting property,
A two-layer optical disc for optically reading the first information or the second information from the substrate side of the first substrate, the first substrate coated with the first reflective layer or the second substrate coated with the second reflective layer. Alternatively, a plurality of protrusions having a predetermined height are provided on the first reflective layer or the second reflective layer, and the adhesive member sandwiches the first reflective layer and the second reflective layer bonded together. The plurality of protrusions are filled in a gap having a predetermined height to form a spacer layer having a height substantially equal to the predetermined height.

According to a second aspect of the present invention, in the first aspect of the invention, at least one protrusion of the plurality of protrusions is located at a position inner than the first and second record holding areas of the disc. , Formed in a ring shape substantially concentric with the disk.

Further, the invention according to claim 3 is such that the first record holding area on the first substrate having the first record holding area carrying the first information is formed so as to cover the first record holding area. Second reflection holding layer formed on the second substrate having the second reflection holding layer carrying the second information and the second recording holding area carrying the second information and having a light transmitting property. In the two-layer optical disc in which the layer and the layer are attached to each other by a translucent adhesive member to read the first information or the second information from the second substrate side, the adhesive member has a refractive index substantially equal to that of the adhesive member and When a plurality of fine particles having an outer dimension of a predetermined height are mixedly formed and the first reflective layer and the second reflective layer are bonded together, the plurality of fine particles are separated by the first reflective layer and the second reflective layer. It is sandwiched by the second reflective layer and has a predetermined height of a plurality of fine particles. It constituted by forming a spacer layer in pot equal height.

[0027]

The present invention is constructed as described above.
According to the invention described above, a protrusion having a predetermined height is provided on the substrate or the reflection layer coated with the reflection layer of the two-layer optical disc, and when the reflection layers are bonded by the adhesion member, the adhesive member is The spacer layer between the reflective layers is formed by filling the gap having a predetermined height formed by a plurality of protrusions sandwiched between the reflective layers to form the spacer layer at a height substantially equal to the predetermined height of the protrusions. Can be easily formed with a predetermined thickness.

According to a second aspect of the present invention, in the first aspect of the invention, at least one of the plurality of protrusions is located inside the first and second record holding areas of the disc. At the position, because it is formed in a ring shape that is almost concentric with the disc, new air bubbles do not mix into the adhesive member when spin-coating the adhesive member, so the adhesive member is evenly distributed between the reflective layers having a gap of a predetermined height. It is possible to fill the spacer layer, and since the bubbles do not cause a large change in the refractive index in the spacer layer, it is possible to easily form the spacer layer between the reflecting layers with a predetermined thickness and optically uniform.

According to the third aspect of the present invention, when the reflective layers of the two-layer optical disk are bonded by the adhesive member, the adhesive member has a refractive index substantially equal to that of the adhesive member and a predetermined height. When a plurality of fine particles having substantially the same outer dimensions are mixedly formed and the respective reflection layers are bonded together, the plurality of fine particles are sandwiched by the respective reflection layers, and the plurality of fine particles have a predetermined height. Since the spacer layers are formed at substantially the same height, the adhesive member filling the reflective layers having a gap of a predetermined height can be formed with a substantially uniform refractive index, and the spacer layers between the reflective layers can be easily formed. In addition, it can be formed to have a predetermined thickness and be optically uniform.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, each embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic sectional view showing a main part of a two-layer optical disc according to the first embodiment of the present invention. In the figure, a two-layer optical disc is formed by injection-molding a transparent synthetic resin, for example, a transparent polycarbonate resin, and is formed into a disc shape with a predetermined thickness. A pit or groove that carries the first information forms a recording holding area in the range, and the pit or groove is further covered with a reflective layer 2 made of a semitransparent film having a predetermined reflectance and transmittance. Has been done. The reflective layer 2 is, for example, a thin film obtained by depositing gold (Au) on the transparent substrate 1 by vacuum deposition.

Reference numeral 3 is a disk-shaped substrate formed by, for example, heat compression molding or injection molding of synthetic resin, and a pit or groove for carrying the second information is provided in a predetermined range on one surface. A recording holding area is formed, and a reflective layer 4 is formed on the pit or groove with a material having a relatively high reflectance. The reflective layer 4 is, for example, a thin film obtained by adhering aluminum (Al) on the substrate 3 by vacuum vapor deposition.

Ring-shaped projections 5a and 5b, which are concentric with the substrate 3 and have a predetermined height, are formed on the inner and outer circumferences on the same side as the surface of the substrate 3 where pits or grooves are formed. Further, 6 is a spacer layer, which is formed by aligning the translucent substrate 1 and the substrate 3 so that the reflective layers 2 and 4 face each other, and thereby the ultraviolet curable resin filled in the gaps obtained by the projections 5a and 5b is filled. It is formed by curing, and the translucent substrate 1 and the substrate 3 are fixed to each other. In addition, the protrusion 5
When the transparent substrate 1 and the substrate 3 are bonded together, a and 5b are projections 5a on the inner circumference side of the record holding areas of the reflective layers 2 and 4, and projections 5b are record holding of the reflective layers 2 and 4. It is provided so as to be located on the outer peripheral side of the region. The two-layer optical disc is configured as described above, and while being rotated at a predetermined speed, the light beam of an optical pickup (not shown) is appropriately irradiated from the transparent substrate side to each reflective layer, and the optical pickup receives information by reflected light. Reading.

FIG. 2 is a detailed view of the projection formed on the substrate 3. Protrusions 5a and 5b are formed further on the inner and outer peripheral sides of the recording holding area of the substrate 3 shown in FIG. The cross-sectional shapes of the protrusions 5a and 5b are, for example, as shown in FIGS.
It has a shape as shown in (d) and has a predetermined height h.

The protrusions 5a and 5b are formed on the substrate 3 by the following method. FIG. 3 shows an example of a method of making the substrate 3. First, a record holding area for carrying the second information is formed on the glass master (FIG. 3 (a)), and the inner and outer circumferences of the record holding section are further formed on the same side as the signal recording surface having the record holding area. The ring-shaped protrusions 7a and 7b having a predetermined height h are formed on the surface by photoresist treatment or the like (see FIG. 3).
(B)).

Next, a master stamper is formed by electroforming plating (FIG. 3C), and a molding stamper is formed from the master stamper separated from the glass master (FIG. 3D). The stamper for molding has projections 7a, 7
Grooves 8a and 8b corresponding to b are formed. Next, the stamper is attached to the mold of the compression molding machine, and synthetic resin is injection-molded or heat-compression-molded.
By forming a and 5b (FIG. 3 (e)) and taking them out from the mold, the substrate 3 integrally having the projections 5a, 5b having the height h is obtained (FIG. 3 (f)).

Further, FIG. 4 shows another example of the method for producing the substrate 3. First, a record holding area for carrying the second information is formed on the glass master (FIG. 4A), and a master stamper is formed on the signal recording surface having the record holding area by electroforming plating ( FIG. 4B). Then, on the master stamper separated from the glass master, in the inner and outer peripheral portions (portions indicated by arrows A and B in FIG. 4C) of the glass master where the record holding area is transferred. Then, additional processing such as cutting is performed to form a ring-shaped groove having a predetermined depth h (not shown) (FIG. 4C).

Next, a stamper for molding is prepared from the master stamper having additional grooves formed therein (FIG. 4 (d)). Grooves 8a and 8b having the same shape as the grooves of the master stamper are formed on the molding stamper. Next, when the stamper is attached to the mold of the compression molding machine and the synthetic resin is heated and compression-molded, the protrusions 5a and 5b are formed corresponding to the grooves 8a and 8b (FIG. 4 (e)), and taken out from the mold. As a result, the substrate 3 on which the protrusions 5a and 5b having the height h are integrally formed is obtained (FIG. 4 (f)).

Next, how the two-layer optical disc according to the first embodiment of the present invention is formed will be described below with reference to FIG. First, in FIG. 5A, the substrate 3 is formed by the method described above, and then, on a recording holding area (not shown),
The reflective layer 4 is formed in advance. A predetermined amount of the ultraviolet curable resin 9 is provided along the outer peripheral side of the protrusion 5a on the inner peripheral side of the substrate 3.
Is dropped.

Next, referring to FIG. 5B, the reflection layer 2 is previously formed.
The translucent substrate 1 on which is formed is placed above the recording holding area (not shown) transferred onto the substrate 3 so that the reflective layers 2 and 4 sandwich the ultraviolet curable resin 9 therebetween, and the translucent substrate is formed. When 1 and the substrate 3 are coaxially rotated by a predetermined amount, the ultraviolet curable resin 9 is spin-coated in the outer peripheral direction by a centrifugal force. At this time, the translucent substrate 1 is gradually reduced in distance from the substrate 3,
The projections 5a and 5b of the substrate 3 are locked at the tips thereof over the entire circumference,
The distance from the substrate 3 is kept constant (width h).

Further, the ultraviolet curable resin 9 is filled in the space formed by the translucent substrate 1 and the substrate 3 and the projections 5a and 5b without any gap, and further rotated at a high speed to obtain an extra ultraviolet curable resin 9 Is shaken off. Also,
At this time, on the inner peripheral side of the substrate 3, the translucent substrate 1 and the protrusions 5a are formed.
Since they are in close contact with each other, air bubbles are not caught from the inner peripheral side of the substrate. Therefore, the ultraviolet curable resin 9 filled in the space formed by the translucent substrate 1, the substrate 3 and the protrusions 5a and 5b does not contain bubbles.

Next, referring to FIG. 5C, the transparent substrate 1
When a predetermined amount of ultraviolet rays (UV) is irradiated from above, the ultraviolet curable resin 9 is cured to form a spacer layer 6 having a predetermined thickness d that is substantially equal to the height h of the protrusions 5a and 5b. The spacer layer 6 includes a transparent substrate 1, a reflective layer 2, a substrate 3,
Since the reflection layers 4 are fixed to each other, the reflection layers 2 and 4 can be fixed at a predetermined distance d to form a two-layer optical disc. Further, since the spacer layer 6 does not form bubbles, it does not cause a large change in the refractive index due to bubbles, and is therefore formed optically uniform. A two-layer optical disc is formed by the above.

Incidentally, in the first embodiment of the present invention,
A ring-shaped projection concentric with the substrate and having a predetermined height h is formed on the inner and outer peripheral portions of the substrate 3 and is attached to the translucent substrate 1 to form the spacer layer thickness d. As shown in FIG. 3, the outer peripheral portion of the substrate 10 is provided with a plurality of minute projections 5c having a conical shape, a truncated pyramid shape, or a cylindrical shape at an outer peripheral position with respect to the recording holding area and having a predetermined height h. Is also good. The shape of the protrusion is not limited to the above-mentioned shape, and may have a composite shape or an irregular shape.
When 0 is attached to the transparent substrate 1, the distance between the substrate 10 and the reflective layers 2 and 4 formed on the transparent substrate 1 is d.
The same effect can be obtained irrespective of the shape and the number of the recording layers as long as they are formed so as to be located outside the information recording area formed by the reflective layers 2 and 4.

Further, in the first embodiment of the present invention,
Although the projections 5a and 5b are provided on the substrate 3, the projections 5a and 5b may be provided on the translucent substrate 1 instead of the substrate 3.

Further, as shown in FIG. 7, ring-shaped projections 5d, 5e, 5 having predetermined heights are formed on the inner and outer peripheral portions of the surfaces of the substrate 11 and the transparent substrate 12 which face each other.
It may be configured such that f and 5g are provided and the respective reflection layers are kept at a predetermined distance d by adhering them. As an example, the heights of 5d, 5e, 5f, and 5g are all h /
2, 5d and 5f, and 5e and 5g are laminated to obtain a height of h as a whole, and the distance between the reflective layers is d.
You may form so that it may become.

In the first embodiment of the present invention,
Although the protrusions 5a and 5b are integrally formed on the substrate 3, the protrusions do not necessarily have to be integrally formed as long as each reflection layer can be kept at a predetermined distance. For example, on the substrate or the transparent substrate. Alternatively, it may be formed by an additional process such as printing or vapor deposition.

Further, in FIG. 6, the protrusion 5c has a conical shape, a truncated cone shape or a cylindrical shape, and is formed by a minute protrusion having a predetermined height h, but as shown in FIGS. 9 (a) to 9 (f). May have a horizontal cross-sectional shape, and by thus forming a substantially convex shape toward the inner peripheral side of the substrate, the ultraviolet curable resin 9 is used to form the reflective layer 2 on the translucent substrate 1, When the reflective layer 4 on the substrate 10 is attached by the above-mentioned spin coating method, even if bubbles are mixed in the ultraviolet curable resin 9, the bubbles move from the inner peripheral side to the outer peripheral side due to the high-speed spin of the substrate. In doing so, the protrusions do not interfere with the movement of the bubbles and retain them in the spacer layer. FIG. 9 is a diagram showing another example of the shape of the protrusion 5c in FIG. 6, and shows a horizontal (parallel to the substrate 10) cross-sectional shape of the protrusion seen from the upper surface of the substrate 10.

Next explained is a double-layer optical disc according to the second embodiment of the invention. FIG. 8 is a diagram showing how a two-layer optical disc according to the second embodiment of the present invention is formed. First, in FIG. 8A, the substrate 14 is peeled off from the master glass stamper prepared by the steps of FIGS. 4A and 4B described above, and the cutting process of FIG. The stamper for molding that was created without was attached to the mold of the compression molding machine and was formed by heat compression molding synthetic resin, and the recording holding area formed on the glass master was transferred onto one side, A record holding area that carries the second information is formed. In addition, the reflective layer 4 is formed in advance on the record holding area that carries the second information. A predetermined amount of the ultraviolet curable resin 13 is dropped on the surface of the substrate 14 on which the reflective layer 4 is formed and near the inner peripheral side of the substrate.

The ultraviolet-curable resin 13 is a base material 13a mainly composed of urethane acrylate-based, epoxy acrylate-based, ester acrylate-based, melamine acrylate-based materials or polymers thereof, and a predetermined ratio to the base material 13a. It is composed of a plurality of fine particles 13b mixed with each other (for example, about 10% by weight). Fine particles 13b are base 1
It is made of a material having a refractive index relatively close to 3a, and is formed in a shape such that the maximum outer shape does not exceed a predetermined dimension d (for example, 30 μm to 50 μm). The ultraviolet curable resin 13 is preliminarily mixed with a plurality of fine particles 13b in a predetermined ratio (for example, about 10% by weight) with respect to the base material 13a and stirred so as to be uniformly distributed, for example, vacuum defoaming treatment. To remove air bubbles, and has an appropriate viscosity.

Next, referring to FIG. 8B, the reflection layer 2 is previously formed.
The translucent substrate 1 on which is formed is placed above a recording holding area (not shown) that is transferred onto the substrate 14 so that the reflective layers 2 and 4 sandwich the ultraviolet curable resin 13, and the translucent substrate is formed. 1
When the substrate 14 is rotated by a predetermined axis coaxially, the ultraviolet curable resin 13 is crushed by the transparent substrate 1 and the substrate 14 and is spin-coated in the outer peripheral direction by the centrifugal force due to the rotation of the substrate. At this time, the translucent substrate 1 is gradually reduced in distance from the substrate 14, and the reflective layers 2 and 4 are locked by sandwiching the plurality of fine particles 13b. Therefore, there is a constant interval between the reflective layers 2 and 4 (the maximum outer diameter d of the plurality of fine particles 13b).
And the ultraviolet curable resin 13 is filled without any gap.

Next, referring to FIG. 8C, the transparent substrate 1
When a predetermined amount of ultraviolet rays (UV) is irradiated from above, the ultraviolet curable resin 13 is cured and the spacer layer 15 having the thickness of the maximum outer diameter d of the plurality of fine particles 13b is formed. The spacer layer 15 includes the transparent substrate 1, the reflective layer 2, and the substrate 1.
Since the reflection layer 4 and the reflection layer 4 are fixed to each other, the reflection layers 2 and 4 can be fixed at a predetermined distance d to form a two-layer optical disc. Further, since the base material 13a and the fine particles 13b have similar refractive indexes, the refractive index of light does not fluctuate greatly in the formed spacer layer 15, and therefore, they are formed optically homogeneous. A two-layer optical disc is formed by the above.

The UV-curable resin 13 is required to have high transparency in order to efficiently irradiate UV rays and in order for the spacer layer formed after curing to transmit the light beam of the optical pickup without loss. In addition, it is also necessary that the shrinkage rate after curing is small so that internal stress of the substrate is not partially generated during curing and causes birefringence. Therefore, it is desirable to use urethane acrylate having a relatively high transparency and a small shrinkage rate after curing as the base material 13a.

When urethane acrylate is mainly used as the base 13a, the fine particles 13b are made of a material having a refractive index close to that of urethane acrylate, such as styrene, acrylic, olefin, vinylbenzene, polycarbonate or silicon dioxide. It is possible to use a material such as a glass-based material, a soda-lime glass-based material, a non-alkali glass-based material, or a polymer thereof.

Further, when the transparent substrate 1 is formed by injection molding a polycarbonate resin, the fine particles 13b are made of polycarbonate having the same refractive index so that the transparent substrate 1 and the transparent substrate 1 can be accurately matched. You can

If the material of the fine particles 13b is a silicon dioxide-based material, a soda lime glass-based material, an alkali-free glass-based material, or a glass material having a high hardness such as a polymer thereof, the spacer layer formed is Can increase strength,
It is possible to form a two-layer optical disc with less warping, bending, and deformation.

In the above-mentioned embodiment, the two-layer optical disc has two layers that can be read from one side of the disc, but by bonding two two-layer optical discs,
A two-layer optical disc in which two layers are read from both sides may be used.

[0056]

Since the present invention is configured as described above, according to the invention of claim 1, a projection having a predetermined height is formed on the substrate or the reflective layer of the two-layer optical disk coated with the reflective layer. When each reflective layer is attached by an adhesive member, the adhesive member is filled in a gap of a predetermined height formed by a plurality of protrusions sandwiched between the reflective layers, and is approximately equal to the predetermined height of the protrusion. Since the spacer layer is formed at the height, the spacer layer between the reflective layers can be easily formed with a predetermined thickness.

According to a second aspect of the present invention, in the first aspect of the invention, at least one of the plurality of protrusions is located inside the first and second record holding areas of the disc. At the position, because it is formed in a ring shape that is almost concentric with the disc, new air bubbles do not mix into the adhesive member when spin-coating the adhesive member, so the adhesive member is evenly distributed between the reflective layers having a gap of a predetermined height. It is possible to fill the spacer layer, and since the bubbles do not cause a large change in the refractive index in the spacer layer, it is possible to easily form the spacer layer between the reflecting layers with a predetermined thickness and optically uniform.

According to the third aspect of the present invention, when the reflective layers of the two-layer optical disk are bonded by the adhesive member, the adhesive member has a refractive index and a predetermined height almost equal to those of the adhesive member. When a plurality of fine particles having substantially the same outer dimensions are mixedly formed and the respective reflection layers are bonded together, the plurality of fine particles are sandwiched by the respective reflection layers, and the plurality of fine particles have a predetermined height. Since the spacer layers are formed at substantially the same height, the adhesive member filling the reflective layers having a gap of a predetermined height can be formed with a substantially uniform refractive index, and the spacer layers between the reflective layers can be easily formed. In addition, it can be formed to have a predetermined thickness and be optically uniform.

Claims (3)

[Claims] 1. A first reflective layer formed to cover the first record holding area on a first substrate having a first record holding area carrying first information, and a second Having a second record holding area for carrying information of
And a second reflective layer formed so as to cover the second record holding area on the substrate, by an adhesive member having a light-transmitting property, from the second substrate side to the first information. Alternatively, in a two-layer optical disc that optically reads the second information, on the first substrate covered by the first reflective layer or on the second substrate covered by the second reflective layer, or A plurality of protrusions having a predetermined height are provided on the first reflective layer or the second reflective layer, and the adhesive member is bonded to the first reflective layer and the second reflective layer. A two-layer optical disc, characterized in that the spacer layer is formed at a height substantially equal to the predetermined height by filling a gap having the predetermined height formed by the plurality of protrusions that are combined and sandwiched. 2. The invention according to claim 1, wherein at least one protrusion of the plurality of protrusions is located at a position inner than the first and second record holding areas of the disc and is substantially adjacent to the disc. A dual-layer optical disc, which is formed in a concentric ring shape. 3. A first reflective layer formed so as to cover the first record holding area on a first substrate having a first record holding area carrying a first information, and a second Having a second record holding area for carrying information of
And a second reflective layer formed so as to cover the second record holding area on the substrate, by an adhesive member having a light-transmitting property, from the second substrate side to the first information. Alternatively, in the two-layer optical disc for reading the second information, the adhesive member is formed by mixing a plurality of fine particles having a refractive index substantially equal to that of the adhesive member and an outer dimension of the predetermined height. When the first reflective layer and the second reflective layer are bonded together, the plurality of fine particles are sandwiched between the first reflective layer and the second reflective layer, and the plurality of fine particles have A two-layer optical disc comprising a spacer layer formed at a height substantially equal to the predetermined height.