JPH05307772A - Optical disk - Google Patents

Abstract

PURPOSE:To provide an optical disk in which the max. value of the tilt during a secular change in the warp state satisfies ISO standard, even when the temp. and humidity in the use environment of the optical disk are remarkably changed. CONSTITUTION:An optical recording layer is formed on one main surface of a resin base plate and also the surface of the optical recording layer side is bent in a recessed form such that the max. value of the tilt stipulated by ISO standard is 0.5-3mrad. Hence even when the use environment (temp. and humidity) of the optical disk remarkably changes, the max. value of the tilt be restrained to be less than 5mrad which is stipulated by ISO standard. and the optical disk which is easy in tracking, low cross talk and superior in reliability, is provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an optical disk having an optical recording layer formed on a resin substrate.

[0002]

2. Description of the Related Art At present, a read-only type optical disc for recording information such as a CD-ROM, a write-once type optical disc capable of writing information only once, and a rewritable type optical disc capable of rewriting information. Have been developed and are being put to practical use.

As a substrate material for such an optical disc,
Although glass or resin is generally used, resin is more preferably used than glass because it is easy to process and copy and is advantageous in terms of material cost. An optical disc using such a resin as a substrate material usually has at least an optical recording layer formed on one surface of a resin substrate, and in order to protect this optical recording layer from external scratches, corrosion due to moisture, etc. A resin protective layer made of an ultraviolet curable resin or a thermosetting resin is formed on the optical recording layer.

[0004]

By the way, an optical disc having a so-called single-plate structure in which an optical recording layer is formed on the one main surface side of the above-mentioned resin substrate is used as a resin in accordance with changes in temperature and humidity of the operating environment. Since the substrate absorbs moisture or dries, the warped state (tilt) of the optical disk changes reversibly with time. This is because, for example, when the optical disk is brought into a relatively dry environment, the water content of the resin substrate gradually decreases to the equilibrium value of the water content in the dry state (drying).
This is because the warpage state of the resin substrate also changes with time so that the optical recording layer side becomes convex until the resin substrate reaches a peak of warpage after a certain period of time and reaches an equilibrium value after a while.

Therefore, in order to prevent such a change in warp as much as possible, an optical disk having a structure in which thin plates having at least rigidity are bonded with an adhesive or the like, or a transparent inorganic material on the read side of the resin substrate is used. It has been proposed to form a film and thereby prevent the infiltration of water (see, for example, JP-A-3-34140).

However, the optical disk having the above-mentioned bonded structure requires an additional bonding step, which complicates the structure and manufacturing process, which is a problem. In addition, in the case of coating with an inorganic film, problems such as cracks and peeling easily occur because the difference in linear expansion coefficient between the inorganic film and the resin substrate is large.

According to the ISO (International Organization for Standardization) standards,
Operating conditions (temperature; 5 to 50 ° C, relative humidity; 3 to 85% RH (absolute humidity; 1 to 30g / m3)) and storage conditions (temperature; -10 to 50 ° C, relative humidity; ^{3 to} 90% RH The maximum value of tilt in (Absolute humidity; 1 to 30 g / m ³ )) is set to 5 mrad or less, and if this standard is not met, tracking becomes difficult and crosstalk becomes large, causing problems. ..

Therefore, the present invention focuses on the above problems,
It is an object of the present invention to provide an optical disk in which the maximum tilt value in the middle of the temporal change of the warp state satisfies the ISO standard even if the temperature and humidity in the environment where the optical disk is used changes significantly.

[0009]

In order to solve the above-mentioned problems, the optical disk of the present invention has an optical recording layer formed on one principal surface of a resin substrate and the surface on the optical recording layer side conforms to the ISO standard. It is characterized by being curved in a concave shape so that the maximum value of the specified tilt is 0.5 to 3 mrad.

[0010]

EXAMPLES Examples of the present invention will be described in detail below. In FIG. 1, 1 is a polycarbonate resin substrate,
2 is an optical recording layer, 3 is a resin protective layer which is a first protective layer, and 4 is a hard coat layer which is a second protective layer. Here, the optical recording layer 2 is a first dielectric layer of amorphous yttrium sialon (100 nm) using a magnetron sputtering device.
Thickness 2a, amorphous Gd-Dy-Fe based magneto-optical recording layer (20 nm thickness) 2b, amorphous yttrium sialon second layer
A dielectric layer (thickness of 30 nm) 2c and a reflective layer of metallic aluminum (thickness of 100 nm) 2d are sequentially laminated. Also,
Each of the resin protective layer 3 and the hard coat layer 4 is formed by applying a urethane acrylate-based or acrylic ester-based ultraviolet curable resin by a spin coating method and curing it.

Next, by combining the thicknesses of the resin protective layer 3 and the hard coat layer 4, optical disks A to I having different initial warp angles (tilts) were produced. As shown in FIG. 2, the tilt in the concave state on the optical recording layer side was defined as (+), and the tilt in the convex state was defined as (−).

Regarding each of the above optical disks, the ISO standard
The tilt change was investigated under the operating environment conditions of Draft 2nd CD 10090. Here, the following two conditions are adopted as the evaluation conditions of the above standard. Condition 1: The optical disc is left in an environment of 33.5 ° C, 90% RH for 1 week, and then put in an environment of 55 ° C, 29% RH (this condition is to observe tilt change due to rapid temperature change,
Absolute humidity in the environment is almost the same). Condition 2: The optical disc is left in an environment of -10 ° C for 1 week and then put in an environment of 33.5 ° C, 90% RH (this condition is to observe tilt change due to abrupt temperature and humidity changes). With respect to the above conditions 1 and 2, the tilt was measured for the standing time immediately after the optical disc was loaded, and the change over time was examined.

[0013]

[Table 1]

An example of the change with time is shown in FIG. 3, which corresponds to the conditions 1 and 2 for the optical disc D.
3 shows changes in the minimum value and the maximum value of the tilt with respect to time. As is clear from FIG. 3, under the condition 1, the tilt shows a change in which a peak of a convex state appears with respect to the optical recording layer with the passage of time, whereas under the condition 2, the tilt appears concave with respect to the optical recording layer. Shows the change in which the peak of the state appears. As described above, the tilt change tendencies are different between the conditions 1 and 2, but the optical disc environment
The absolute value of the tilt became maximum when the standing time immediately after being put in was about 200 min, and the maximum tilt value at that time was −4.6 mrad in condition 1 and +3.0 mrad in condition 2.

It was found that the other Examples A to C and E to I show almost the same temporal change as the optical disc D, and as is clear from Table 1, the maximum value of the tilt is the optical discs C, D and E. , F was less than 5 mrad (absolute value) of the ISO standard, and a good result was obtained. On the other hand, the optical discs A and B are under the condition 2, and the optical discs G, H, and I are
In condition 1, the maximum tilt is 5 mr of the ISO standard.
Exceeded ad (absolute value). That is, the initial value of tilt is +
For optical discs larger than 3 mrad, the maximum tilt value is at least +5 mrad at least in Condition 2 and does not meet the ISO standard, and for optical discs with an initial tilt value of +0.4 mrad or less, the maximum tilt value is at least under Condition 1. It was larger than -5.0 mrad and did not meet the ISO standard.
Also, the maximum tilt value is +0.5 to +3 as the initial value.
If it is mrad, it has been found that the ISO standard is completely cleared. According to the above-mentioned optical disc, it is possible to provide an optical disc having good mechanical characteristics, a stable tracking state, and small crosstalk and excellent reliability. It turned out to be expected.

In this embodiment, the initial value of the tilt was changed mainly by changing the thickness of the protective resin layer and the hard coat layer, but changing the thickness of these resin layers is not the only method. The tilt can be controlled over time depending on the film forming conditions of the optical recording layer 2, the initial warp state of the substrate, and the like, and the tilt can be appropriately changed and implemented without departing from the scope of the present invention.

Further, various materials other than the above can be used for the substrate and each layer constituting the optical disk. That is, various resins such as epoxy resin, acrylic resin, polyester resin, and amorphous polyolefin resin can be used as the substrate. Further, as the resin protective layer and the hard coat layer, various ultraviolet curable resins or thermosetting resins such as acrylic ester type, urethane acrylate type, epoxy type, polyester type, acrylic type can be used. In addition, for the first and second dielectric layers, silicon nitride, aluminum nitride, titanium nitride, silicon carbide,
Materials such as cadmium sulfide, zinc sulfide, magnesium fluoride, cadmium oxide, bismuth oxide, and silicon oxide may be used alone or in combination. In addition, Gd-Tb-Fe and Tb-Fe-C are also included in the magneto-optical recording layer.
o, Dy-Fe-Co, Gd-Tb-Dy-Fe, Gd
-Tb-Fe-Co, Tb-Dy-Fe-Co, Gd-
Dy-Fe-Co, Nd-Gd-Dy-Fe, Nd-G
Various amorphous magnetic alloys of transition metal-rare earth metal type such as d-Dy-Fe and Nd-Gd-Dy-Fe-Co type can be used. Furthermore, in the reflection layer, Cr, Ti, Cu,
Materials in which Ag, Au, SUS, etc. are used alone or in combination can be used.

[0018]

As described above, in the optical disc of the present invention, the optical recording layer is formed on the one main surface side of the resin substrate, the optical recording layer side is concave, and the maximum tilt value is 0.5 to 0.5. 3 mr
It is ad.

As a result, even if the operating environment (temperature / humidity) of the optical disk changes significantly, the maximum tilt value can be suppressed to 5 mrad or less, which is the ISO standard, and tracking is easy and reliability of crosstalk is small. It is possible to provide an extremely excellent optical disc.

The predetermined concave shape on the optical recording layer side can be easily realized by, for example, the thickness of the protective resin layer provided on the reading surface side or the back surface side of the resin substrate. It is possible to form a transparent inorganic film on the read-out surface side to prevent problems such as cracks as much as possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an optical disc according to an embodiment of the present invention.

2A and 2B are cross-sectional views showing warped states (concave and convex) of an optical disc, respectively.

FIG. 3 is a graph showing an example of changes over time due to changes in the usage environment of the optical disc.

[Explanation of symbols]

1 ... Substrate 2 ... Optical recording layer 3 ... Resin protective layer 4 ... Hard coat layer

Claims (1)

[Claims] 1. An optical recording layer is formed on one main surface of a resin substrate, and the surface on the optical recording layer side is concavely curved so that the maximum tilt value specified in the ISO standard is 0.5 to 3 mrad. An optical disc characterized in that