JP2012084196A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a recording quality by suppressing fluctuation in transmittance to an inner-side recording layer caused by difference in recorded/unrecorded state of a near-side recording layer in a multilayered optical recording medium in which the near-side recording layer has three or more recording layers.SOLUTION: As recording layers other than an innermost recording layer, a transmittance increase layer where the transmittance increases after recording, and a transmittance decrease layer where the transmittance decreases after recording are provided. This configuration can suppress the transmittance fluctuation in at least the innermost recording layer caused by the difference between the recorded/unrecorded state of the near-side recording layer. Consequently, at least in the innermost recording layer, the fluctuation in a laser power caused by the difference between the recorded/unrecorded state of the near-side recording layer can be suppressed so as to improve the recording quality.

Description

  The present invention relates to an optical recording medium in which information is recorded / reproduced by light irradiation.

JP 2010-19202025 A

  As optical recording media on which information is recorded / reproduced by light irradiation, so-called optical disc recording media (simply optical discs) such as CD (Compact Disc), DVD (Digital Versatile Disc), BD (Blu-ray Disc: registered trademark), etc. Also called).

  Such an optical disc has been proposed to have two recording layers in order to increase the information recording capacity. For example, a DVD or BD is of a type called DL (Dual Layer).

  In recent years, a multilayer optical disc having three or more recording layers has also been proposed (see, for example, Patent Document 1).

  Here, in an optical disc having a plurality of recording layers, the recording layer on the near side reaches the back recording layer depending on whether the recording layer on the near side that is close to the laser light incident surface is in a recording state or an unrecorded state. Therefore, a difference occurs in the power of the laser beam. This is because the transmittance of the recording layer changes between the recorded state and the unrecorded state.

  For example, in the case of a two-layer optical disc such as a DL type BD, the recording layer on the front side is only one layer, and therefore the laser power fluctuation in the recording layer on the back side due to the recording / unrecording is slight. It will be a thing. For this reason, in the case of a two-layer optical disc, the change in recording quality in the recording layer on the back side depending on whether recording on the recording layer on the front side / non-recording is small.

  However, in the case of a multilayer optical disc having three or more recording layers, the number of recording layers on the front side is two or more, and the power fluctuation in the recording layer on the back side increases accordingly. That is, when there are a plurality of recording layers on the front side, the transmittance with respect to the laser light reaching the recording layer on the back side is a combination (integration) of the transmittances of the recording layers on the front side. Therefore, the power fluctuation in the recording layer on the back side becomes large.

  Therefore, in the case of a multi-layer optical disc, the difference in recording quality of the recording layer on the back side accompanying the recording / non-recording of the front recording layer becomes large, and it is difficult to stabilize the recording quality. turn into.

Therefore, in the present invention, the optical recording medium is configured as follows.
That is, the optical recording medium of the present invention has three or more recording layers, and the transmittance increases after recording as a recording layer other than the outermost recording layer farthest from the recording light incident side. An ascending layer and a transmittance lowering layer in which the transmittance decreases after recording are provided.

  As described above, the optical recording medium of the present invention is provided with the transmittance increasing layer and the transmittance decreasing layer as the recording layer other than the outermost recording layer. As a result, it is possible to suppress the transmittance fluctuation associated with the recording / non-recording of the recording layer on the front side at least for the outermost recording layer.

  As described above, according to the present invention, it is possible to suppress the transmittance fluctuation associated with the recording / non-recording of the recording layer on the near side of at least the innermost recording layer. As a result, at least the outermost recording layer can suppress the variation in laser power accompanying the above variation in transmittance, thereby improving the recording quality.

  Further, according to the present invention, there is an advantage that the restriction to be imposed on the power margin can be relaxed, and the degree of freedom in designing the optical system can be improved correspondingly.

  Furthermore, according to the present invention, it is possible to use a material that could not be used because the transmittance change after recording is excessive in the past by combining the direction of the change.

1 is a cross-sectional structure diagram of an optical recording medium (in the case of a three-layer structure) according to an embodiment. 1 is a cross-sectional structure diagram of an optical recording medium (in the case of a four-layer structure) according to an embodiment. It is the figure which showed the example of the combination of the transmittance | permeability raise layer in the case of 3 layer structure, and the transmittance | permeability fall layer. It is the figure which showed the example of the combination of the transmittance | permeability raise layer in the case of 4 layer structure, and the transmittance | permeability fall layer. It is a figure for demonstrating the effect which the optical recording medium of embodiment shows.

Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described.
The description will be given in the following order.

<1. Optical Recording Medium of Embodiment>
[1-1. Example of cross-sectional structure]
[1-2. Example of combination of transmittance increasing layer and transmittance decreasing layer]
<2. Comparison of synthetic transmittance>
<3. Summary>
<4. Modification>

<1. Optical Recording Medium of Embodiment>
[1-1. Example of cross-sectional structure]

1 and 2 are diagrams showing a cross-sectional structure of the optical recording medium according to the embodiment. FIG. 1 shows a cross-sectional structure in the case of a three-layer structure having three recording layers, and FIG. 2 shows a recording layer. Each shows a cross-sectional structure in the case of a four-layer structure having four layers.

  Here, the optical recording medium of the embodiment is a disk-shaped optical recording medium. The optical recording medium is a general term for recording media on which information is recorded / reproduced by light irradiation.

First, in FIGS. 1 and 2, the direction in which the laser beam for recording / reproduction is irradiated onto the optical recording medium is indicated by an arrow Li.
As can be seen with reference to this arrow Li, laser light is incident on the optical recording medium shown in FIGS. 1 and 2 from the cover layer 1 side.
The cover layer 1 is made of a resin such as polycarbonate, for example, and is provided to protect the recording layer L formed on the back side.
Hereinafter, the side on which the laser light incident surface is formed is referred to as the front side, and the opposite side is referred to as the back side.

The optical recording medium shown in FIG. 1 includes three recording layers L.
Hereinafter, the number of the recording layer L is assigned in order from the farthest side (the heel side) to the near side (the near side) from the laser light incident surface. That is, the outermost recording layer L becomes the recording layer L0 and then the recording layer L1 and the recording layer L2 in order from the front side to the front side.

The recording layer L0 is formed on the substrate 3. The substrate 3 is made of a resin such as polycarbonate.
An intermediate layer 2 made of an adhesive material such as an ultraviolet curable resin is formed between the recording layer L0 and the recording layer L1, and the intermediate layer is also formed between the recording layer L1 and the recording layer L2. 2 is formed. Further, the cover layer 1 is formed on the front side of the recording layer L2.

Although illustration is omitted, the recording layer L is actually formed with a groove (continuous groove) for guiding the irradiation position of the laser beam.
For this reason, the substrate 3 is actually formed by injection molding using a stamper formed so as to have an uneven cross-sectional shape corresponding to the shape of the groove, and the recording layer L0 is the shape of the stamper on the substrate 3. Is laminated on the side to which the toner is transferred (that is, the transfer surface of the groove).
In addition, as the recording layer L1, an ultraviolet curable resin as a material for forming the intermediate layer 2 is applied on the recording layer L0 laminated as described above by, for example, a spin coating method, and the stamper is pressed thereon. Then, the ultraviolet curable resin is cured by ultraviolet irradiation to form an intermediate layer 2 having a concave-convex cross-sectional shape as a groove, and then laminated thereon. As a result, a groove is also formed in the recording layer L1.
The recording layer L2 is formed in the same manner as the recording layer L1. In other words, an ultraviolet curing tree as a material for forming the intermediate layer 2 is applied on the recording layer L1 laminated as described above, and an ultraviolet curing treatment is performed in a state where the stamper is pressed on the recording layer L1. A shaped intermediate layer 2 is formed and laminated thereon.

Here, the recording layer L is made of a material on which a recording mark (that is, a portion having a reflectance different from that of another portion) is formed in response to laser light irradiation with a predetermined power.
The recording layer L only needs to be configured so that at least a recording mark can be formed, and is not limited to a so-called write-once type / rewritable type.

2 is obtained by adding one set of the intermediate layer 2 and the recording film L to the three-layer structure of FIG.
Specifically, a set of the recording layer L3 and the intermediate layer 2 is added between the recording layer L2 and the cover layer 1 shown in FIG. In this case, the recording layer L3 is formed to be bonded via the recording layer L2 and the intermediate layer 2, and the cover layer 1 is formed on the front side of the recording layer L3.

[1-2. Example of combination of transmittance increasing layer and transmittance decreasing layer]

In the present embodiment, for a multilayer optical recording medium having three or more recording layers L as shown in FIGS. 1 and 2, the depths associated with the recording / unrecorded state of the recording layer L on the front side as described above are described. In order to suppress the transmittance fluctuation with respect to the recording layer L on the side, a transmittance increasing layer in which the transmittance increases after recording and a transmittance decreasing layer in which the transmittance decreases after recording other than the outermost recording layer L The recording layer is provided as a recording layer.

3 and 4 are examples of combinations of transmittance increasing layers and transmittance decreasing layers in the case of a three-layer structure, and examples of combinations of transmittance increasing layers and transmittance decreasing layers in the case of a four-layer structure. Show.
Here, hereinafter, the difference between the transmittance before recording of the recording layer L and the transmittance after recording (change amount of the transmittance before and after recording) is represented by “ΔT”.
Accordingly, the transmittance increasing layer is also referred to as “recording layer L with ΔT> 0”, and the transmittance decreasing layer is also referred to as “recording layer L with ΔT <0”.
3 and 4, the cover layer 1 and the intermediate layer 2 are omitted for convenience of illustration.

First, in the case of a three-layer structure, two examples of combinations shown in FIGS. 3A and 3B are conceivable.
Specifically, FIG. 3A shows the recording layer L1 on the far side of the recording layers L other than the outermost recording layer L0 as the recording layer L (transmittance lowering layer) with ΔT <0, and the front side. The recording layer L2 is a recording layer L (transmittance increasing layer) with ΔT> 0.

  On the other hand, FIG. 3B shows the recording layer L1 as a recording layer L with ΔT> 0 and the recording layer L2 as a recording layer L with ΔT <0.

  As shown in the example of FIG. 3, by adopting a configuration in which the transmittance decreasing layer and the transmittance increasing layer are alternately provided, the transmission to the outermost recording layer L0 depending on whether recording is performed or not recorded on the front recording layer. Rate fluctuations can be minimized.

In the case of the four-layer structure shown in FIG. 4, six examples of combinations shown in FIGS. 4 (a) to 4 (f) are conceivable.
Specifically, FIG. 4A shows the recording layers L1 and L3 other than the outermost recording layer L0, where the recording layer L1 and the recording layer L3 are ΔT <0 and the recording layer L2 is ΔT> 0. In this example, the recording layer L is used.
FIG. 4B shows an example in which the recording layer L1 and the recording layer L3 are set as a recording layer L with ΔT> 0, and the recording layer L2 is set as a recording layer L with ΔT <0.

In the example shown in FIGS. 4A and 4B, recording layers L with ΔT <0 and recording layers L with ΔT> 0 are alternately provided.
As described above, when the total number of recording layers L is four, the configuration in which the transmittance lowering layers and the transmittance increasing layers are alternately provided is the front recording layer L0 with respect to the outermost recording layer L0. Thus, the variation in transmittance depending on whether recording / unrecording is minimized, and the recording layer L1 can also minimize the variation in transmittance depending on recording / unrecording of the front recording layer.

  4C shows the recording layer L1 and the recording layer L2 as a recording layer L with ΔT <0, and the recording layer L3 as a recording layer L with ΔT> 0. FIG. The layer L1 and the recording layer L2 are the recording layer L with ΔT> 0, and the recording layer L3 is the recording layer L with ΔT <0.

  4E shows the recording layer L2 and the recording layer L3 as a recording layer L with ΔT <0, and the recording layer L1 as a recording layer L with ΔT> 0. FIG. 4F shows the recording layer. L2 and the recording layer L3 are recording layers L with ΔT> 0, and the recording layer L1 is a recording layer L with ΔT <0.

In each example shown in FIG. 4 including the examples of FIGS. 4A and 4B, the total number of recording layers L is an even number (that is, the number of layers excluding the uppermost recording layer L0 is an odd number). In this case, the difference between the number of transmittance increasing layers and the number of transmittance decreasing layers is set to 1.
Thereby, when the total number of the recording layers L is an even number, it is possible to minimize the variation in transmittance with respect to at least the outermost recording layer L0.

  Here, the transmittance increasing layer due to ΔT> 0 and the transmittance decreasing layer due to ΔT <0 can be realized, for example, by giving a difference in material and structure of the recording layer L. Alternatively, it can be realized by adjusting the thickness of the recording layer L.

For the sake of confirmation, the outermost recording layer L0 has no effect on the recording performance of the other recording layers L before and after the recording, so it is either a transmittance increasing layer or a transmittance decreasing. It doesn't matter whether it is a layer or not. Alternatively, it is also possible to select a recording layer L whose transmittance does not change before and after recording.

<2. Comparison of synthetic transmittance>

Here, if the absolute value of the transmittance change amount ΔT before and after recording is α, the transmittance change rate with respect to the outermost recording layer L0 due to the recording / non-recording of the front recording layer in the case of the three-layer structure. RT is when the front two layers are all the recording layer L with ΔT> 0 (RT_ [ALL +]), and when both the front two layers are the recording layer L with ΔT <0 (RT_ [ALL−]) ), Each of the cases where the front two layers are a mixture of the recording layer L of ΔT> 0 and the recording layer L of ΔT <0 (RT _ [+ −]) is expressed as follows.

RT_ [ALL +] = (1 + α) * (1 + α)

RT_ [ALL-] = (1-α) * (1-α)

RT _ [+-] = (1 + α) * (1-α)

Similarly, if the absolute value of ΔT is α, the transmittance change rate RT with respect to the outermost recording layer L0 due to the recording / non-recording of the front recording layer in the case of the four-layer structure is the front side 3 When all the layers are the recording layer L with ΔT> 0 (RT_ [ALL +]), when all the three front layers are the recording layer L with ΔT <0 (RT_ [ALL−]), the three front layers When the number of recording layers L with ΔT> 0 = 2 and the number of recording layers L with ΔT <0 = 1 (RT _ [+ − +]), the number of recording layers L with ΔT> 0 in the front three layers = 1 and the number of recording layers L with ΔT <0 = 2 (RT _ [− + −]) are expressed as follows.

RT_ [ALL +] = (1 + α) * (1 + α) * (1 + α)

RT_ [ALL-] = (1-α) * (1-α) * (1-α)

RT _ [+ − +] = (1 + α) * (1-α) * (1 + α)

RT _ [− + −] = (1−α) * (1 + α) * (1−α)

FIG. 5 is a diagram for explaining the effect exhibited by the optical recording medium according to the embodiment, and shows the calculation result of the transmittance change rate RT when α = 0.03.
FIG. 5A shows the calculation results of RT_ [ALL +], RT_ [ALL−], RT _ [+ −] in the case of the three-layer structure, and FIG. 5B shows RT_ [ALL in the case of the four-layer structure. The calculation results of ALL +], RT_ [ALL−], RT _ [+ − +], and RT _ [− + −] are shown.

As shown in FIG. 5A, in the case of a three-layer structure, RT_ [ALL +] = 1.06 and RT_ [ALL −] = 0.94. In contrast, RT _ [+ −], that is, RT in the case of providing a transmittance increasing layer and a transmittance decreasing layer is 1.00.
From this result, it can be seen that according to the configuration example shown in FIG. 3, the variation in transmittance depending on whether recording is performed or not recorded on the front recording layer with respect to the last recording layer L0 can be reduced to 0 (minimum).

In FIG. 5B, RT_ [ALL +] and RT_ [ALL-] in the case of a four-layer structure are 1.09 and 0.91, respectively. On the other hand, RT _ [+ − +], RT _ [− + −] (that is, RT when the difference between the number of transmittance increasing layers and the number of transmittance decreasing layers is 1 in a four-layer structure) is They are 1.03 and 0.97, respectively.
From this result, according to the configuration example shown in FIG. 4, the front side relative to the outermost recording layer L0 is compared with the case where at least the front side recording layer is the recording layer L having the same transmittance change characteristics. It can be seen that the variation in the transmittance depending on whether the recording layer is recorded or not recorded can be suppressed.
As described above, when the total number of the recording layers L is an even number, the difference between the number of the transmittance increasing layers and the number of the transmittance decreasing layers is set to be 1, so that the maximum Variation in transmittance with respect to the recording layer L0 can be minimized.

<3. Summary>

As described above, in the present embodiment, the transmittance increasing layer and the transmittance decreasing layer are provided as the recording layers L other than the outermost recording layer L0. As a result, at least for the outermost recording layer L0, it is possible to suppress the transmittance fluctuation accompanying the recording / non-recording of the recording layer L on the front side. As a result, at least the outermost recording layer L0 can suppress the fluctuation of the laser power due to the fluctuation of the transmittance, thereby improving the recording quality.

  In addition, according to the optical recording medium as such an embodiment, there is an advantage that the restriction to be imposed on the power margin can be relaxed, and the degree of freedom in designing the optical system can be improved correspondingly.

Furthermore, according to the optical recording medium of the present embodiment, it is possible to use a material that could not be used because the transmittance change after recording is excessive, by combining the direction of the change.

<4. Modification>

Here, the present invention should not be limited to the specific examples described above.
For example, in the description so far, only the case where the total number of the recording layers L is 3 or 4 has been illustrated, but of course, the present invention can be suitably applied to the case where the recording layers L are 5 or more.
When the number of recording layers L is 5 or more and the total number of recording layers L is an odd number (that is, when the number of layers excluding the uppermost recording layer L0 is an even number), the transmittance increases. The same number of layers and transmittance lowering layers are provided. As a result, the transmittance variation with respect to at least the outermost recording layer L0 can be minimized. Also in this case, by alternately providing the transmittance increasing layer and the transmittance decreasing layer, the recording layer L other than the outermost recording layer L0 is separately recorded / unrecorded in the recording layer L on the front side. The transmittance variation can be minimized.

  Further, when the recording layer L is 5 or more and the total number of the recording layers L is an even number (that is, when the number of layers excluding the uppermost recording layer L0 is an odd number), the transmittance increasing layer. By making the difference between the number of layers and the number of transmittance lowering layers be 1, it is possible to minimize the transmittance variation with respect to at least the outermost recording layer L0. Also in this case, by alternately providing the transmittance increasing layer and the transmittance decreasing layer, the recording layer L other than the outermost recording layer L0 is associated with recording / unrecording of the recording layer L on the front side. The transmittance variation can be minimized.

  The present invention can also be suitably applied to an optical recording medium having a shape other than a disk shape.

  1 cover layer, 2 intermediate layer, 3 substrate, L0 to L4 recording layer

Claims (6)

A recording layer having three or more recording layers and a recording layer other than the outermost recording layer farthest from the recording light incident side, a transmittance increasing layer that increases the transmittance after recording, and a transmittance that decreases after recording An optical recording medium provided with a transmittance lowering layer. The optical recording medium according to claim 1, wherein the total number of recording layers is an odd number, and the same number of the transmittance increasing layers and the transmittance decreasing layers are provided in a portion excluding the outermost recording layer. The total number of recording layers is an even number, and a difference between the number of the transmittance increasing layers and the number of the transmittance decreasing layers in a portion excluding the outermost recording layer is set to 1. Optical recording media.   The optical recording medium according to claim 1, wherein the transmittance increasing layer and the transmittance decreasing layer are alternately formed.   The optical recording medium according to claim 1, wherein the total number of recording layers is three.   The optical recording medium according to claim 1, wherein the total number of recording layers is four.

Images