JPH0630168B2 - Optical information recording medium - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an information recording medium for optically recording and reproducing information, and more particularly to a double-sided type recording medium formed by bonding two sets of recording mediums together. The present invention relates to an optical information recording medium capable of reducing characteristic deterioration.

BACKGROUND OF THE INVENTION A recording medium for optically recording and reproducing information is formed by forming a recording member whose optical characteristics such as reflectance are changed by heat of a light beam such as laser light on a substrate. . For example, as shown in FIG. 3, the recording medium has a recording member (for example, a chalcogen compound) whose reflectance changes by heat on an optically transparent substrate (for example, glass, acrylic resin, polycarbonate resin, etc.) 1. , An amorphous thin film such as tellurium) 2 are formed.

When the disc is used on both sides, the recording medium configured as described above is bonded to, for example, a similar recording medium by the adhesive layer 3 to form an optical recording medium as shown in FIG.

As a known example in which the double-sided bonding method or the construction of the above optical recording medium is described in detail, Japanese Patent Laid-Open No. 58-6 is available.
536, JP-A-57-66540, and JP-A-58-45633.

However, in the optical recording medium configured as described above, since a part of the incident light is transmitted and reflected from the back surface of the bonding, the ratio of incident light to reflected light (i _R / i _O ) is The ratio becomes larger than the ratio (i _R / i _O ) when the medium is alone, and includes a diffuse reflection component according to the surface state of the recording medium 2 ′ on the back surface,
S / N (signal-to-noise ratio) and C /
No consideration was given to the deterioration of N (carrier-to-noise ratio).

[Object of the Invention]

An object of the present invention is to provide an optical information recording medium having a low noise level, a good S / N and C / N, and excellent recording / reproducing characteristics.

[Outline of Invention]

The deterioration of S / N and C / N of the optical recording medium occurs
Due to the reflection from another laminated recording medium, the above reflection is prevented by mixing a colorant that absorbs light into the adhesive layer, or by using an adhesive that itself absorbs light (for example, black). And the optical interface separation layer of 2 μm or more is provided between the recording member and the adhesive layer to further reduce the noise. It was also found that an optical focus level during recording and reproduction is abnormal due to the lens effect of the air layer generated at the adhesive interface. This focus level abnormality was solved by making the adhesive breathable to facilitate removal of the air layer.

Hereinafter, the lens effect will be described in detail.

When recording or reproducing using an optical recording medium, it is necessary to accurately focus writing or reading light such as laser light on the surface of the recording member. For that purpose, a focusing servo mechanism is usually used.

Hereinafter, an example of the focusing servo mechanism will be described with reference to FIG. Reference numeral 21 is a photodiode including three light receiving elements, and 22 is a four-division photodiode element used for detecting a focus error signal. Reference numeral 23 is a differential amplifier, 25 is a compensation amplifier, 26 is a power amplifier, 27 is a focus motor, and 28 is an objective lens. The return light of the laser light applied to the surface of the recording member (not shown) is applied to the four-division photodiode 22 and converted into an electric signal. The electric signal is output as a focus error signal by the differential amplifier 23, amplified by the compensation amplifier 25 and the power amplifier 26, a current is passed through the focus motor 27, and the objective lens 28 is controlled to operate a focus servo loop.

When the focus servo loop operates normally, the laser beam can always be accurately focused on the surface of the recording member even if the optical recording member moves up and down.

However, the air layer 3 as shown in FIG.
When 1 occurs, the air layer is narrowed by the optical interface separation layer and the adhesive layer, so that the air layer becomes a lens shape and the substrate 1,
1'or recording member 2, 2 ', optical interface separation layer 5,
5 ', the adhesive layer 4, etc. may be deformed like a lens. Therefore, when the lens 32 is used to focus the portion where the air layer is present, the return light may be disturbed by the lens-shaped air layer and / or the deformation.

As a result, it was found that an abnormality occurred in the focus error signal, resulting in an out-of-focus state. FIG. 7 shows an example of an experiment for obtaining the relationship between the focus error signal and the in-focus state.
The recording / reproducing signal level is taken as an index representing the in-focus state, and the focus error signal is obtained by observing the level of the focus error signal terminal 24 shown in FIG.

It was found that the focus error signal was 0.1 Vpp or less in the normal state, but a large focus error signal appeared in the abnormal state, and the recording / reproducing signal level was significantly reduced.

Example of Invention

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a comparative example, and FIG. 2 is a sectional view showing an embodiment of the present invention. In FIG. 1, 1, 1'is a substrate made of an optically transparent acrylic resin, 2 and 2'is a substrate 1,
The recording member 4 provided on the surface 1'and having the reflectance changed by the irradiation of the laser beam is an adhesive layer provided by the present invention. Further, in FIG. 2, reference numerals 5 and 5'indicate optical interface separation layers made of a transparent material provided by the present invention.

In the following embodiments of the present invention, a recording film having a two-layer structure in which a Bi thin film was formed on a Sb ₂ Se ₃ thin film was used as a recording member.

Next, examples according to the present invention and the results thereof will be described.

In the examples of the present invention, a sheet-like adhesive adhesive was used as the adhesive, and the optical interface separation layer was formed by applying a transparent material with a spinner to obtain the results shown in Tables 1 and 2. .

As an adhesive, a carbon black colored black sheet-like adhesive adhesive (thickness 0.1 mm) is formed on the recording member,
Then, another recording member obtained in the same manner was adhered. As a result, the noise was reduced by about 10 dB as compared with the case where an uncolored transparent sheet-shaped adhesive was used.

In Table 1, the noise before bonding is used as a reference, and in Comparative Example 1, by using the bonding structure,
Although the noise was increased by about 17 dB, by using an opaque adhesive as in Comparative Example 2, most of the reproducing laser light that passed through the recording member was absorbed, and extra reflected light did not enter the reproducing light. The noise level has dropped.

However, also in Comparative Example 2, the noise level is increased by about 7 dB as compared with that before the bonding, and the focus error signal level for driving to focus the laser light on the surface of the recording member is abnormal. there were.

That is, for example, a normal focus error signal level is about 0.1 Vpp, whereas a large error signal (focus, error signal) of about 3 Vpp occurs. As described above, this deteriorates the characteristics during recording and reproduction.

Example 1 A transparent ultraviolet curable resin was spin-coated on a recording member as an optical interface separation layer by a spinner and cured by ultraviolet irradiation. Then, in the same manner as in Comparative Example 2, another recording member was bonded using an adhesive.

As a result, the noise when the thickness of the separation layer was 1 μm was about 4 dB lower than that when the separation layer was not provided.

In addition, the noise increase when the thickness of the separation layer is 2 μm, 10 μm, and 30 μm is shown in Example 2, Example 3, and Example 4, respectively.
Is shown in Table 1. From this, the noise decreased as the thickness of the separation layer increased. Therefore, in order to reduce noise, it is preferable to form an optical interface separation layer, and it is more preferable to set the thickness of the separation layer to 2 μm or more.

This can be explained from the design value of the optical lens used for optical recording / reproduction. That is, the depth of focus 1 of the optical lens is l = λ / 2 (NA) ² and, for example, N.V. Using an A0.6 optical lens and substituting the reproduction laser light wavelength λ = 830 nm, the focal depth l
Is about 1 μm. Therefore, noise could be prevented by setting the thickness of the optical interface separation layer to be twice the depth of focus or more.

On the other hand, in Examples 1, 2, 3 and 4, the noise could be reduced, but when it occurred in Comparative Example 2, the foros error signal (about 3 Vpp) was almost the same.

The cause of this focus error signal was considered to be the lens effect due to the air layer that was simultaneously formed when the adhesive sheet was formed on the recording member.

Example 5 As the adhesive, a sheet-shaped black adhesive adhesive having about 0.5 mmφ through holes formed in the sheet surface at about 1 / cm ² was used for the purpose of imparting air permeability.

This adhesive was bonded and formed on a recording member having an optical interface separation layer having a thickness of about 2 μm, and then the recording members obtained in the same manner were bonded and bonded. As a result, when the adhesive with through holes is used, the focus error signal is about 0.1 Vpp.
And it was able to be greatly reduced.

Similarly, the surface density of the through holes is about 2 pieces / cm ² about 0.5.
The focus error signals at the number of pcs / cm ² and about 0.01 / cm ² are shown in Table 2 as Example 6, Example 7 and Example 8, respectively.

As a result, a good focus error signal level was obtained when the surface density of the through holes was 0.5 / cm ² or more.

Further, the noise reduction has the same effect as that described in the first embodiment.

On the other hand, the optical interface separation layer used in the above embodiment can also serve as a protective film of the recording member, and the same effect as this embodiment can be obtained as long as the material separates the interface between the recording member and the adhesive member by 2 μm or more. Is obtained.

In addition, even if the interface separation layer used in the above-mentioned embodiment is laminated on the so-called protective layer, the same effect can be obtained.

〔The invention's effect〕

According to the present invention, since the laser light that has passed through the recording member is absorbed by the adhesive layer and the optical interface separation layer is formed, diffuse reflection at the interface between the recording member and the adhesive layer can be prevented, and thus the noise of the reproduced signal can be reduced. There is. Further, in order to prevent the lens effect of the air layer generated at the interface of the adhesive layer, the use of a breathable adhesive sheet has the effect of reducing the focus error.

[Brief description of drawings]

FIG. 1 is a comparative example of the present invention, FIG. 2 is a cross-sectional view showing an embodiment of the present invention, FIG. 3 is a cross-sectional view of an essential part conceptually showing a recording medium, and FIG. FIG. 5 is a cross-sectional view of a main part conceptually showing an optical recording medium obtained by laminating media.
FIG. 6 is a view used for explaining a focusing servo mechanism used for optical recording / reproducing, FIG. 6 is a sectional view of an essential part conceptually showing an abnormal occurrence of a focus error signal, and FIG. It is a graph which shows a relationship. 1 ... Substrate 2 ... Recording member 3,4 ... Adhesive layer 5 ... Optical interface separation layer 31 ... Air layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-172543 (JP, A) JP-A-56-156941 (JP, A) JP-A-60-164938 (JP, A) Actual development Sho-56- 111447 (JP, U)

Claims (5)

[Claims] 1. A first recording medium in which a recording member whose light reflectance changes by heat is formed on a substrate made of a transparent material, and a second recording medium formed in the same manner. An optical information recording medium formed by bonding together an adhesive made of an opaque material that absorbs light, wherein a transparent layer made of a transparent material is provided between the recording member and the adhesive. Information recording medium. 2. The optical information recording medium according to claim 1, wherein the transparent layer has a thickness that is at least twice the depth of focus of the read light by the objective lens. And an optical information recording medium. 3. The optical information recording medium according to claim 2, wherein the transparent layer has a thickness of 2 μm or more. 4. The optical information recording medium according to claim 1 or 2, wherein the adhesive is a sheet-like adhesive having air permeability. And an optical information recording medium. 5. The optical information recording medium according to claim 4, wherein the adhesive is an adhesive having through holes in a sheet surface. recoding media.