JPH0652576A - Optical recording disk and its manufacture - Google Patents

Abstract

PURPOSE:To improve the recording and reproducing characteristics of an optical recording disk by forming a substrate protective layer by applying ultraviolet curing resin paint having surface tension smaller than the critical surface tension of a transparent substrate to the surface of the transparent substrate. CONSTITUTION:A substrate protective layer 4 is formed by applying ultraviolet curing resin paint to the surface of a transparent substrate 1 to a film thickness of 3-10mum by spin coating and hardening the paint. In order to make the surface of the substrate protective layer smooth without recessed nor projecting section, ultraviolet curing resin paint having surface tension r1 which is smaller than the critical surface tension gammaC of the substrate 1 is used as the paint to be applied to the surface of the substrate 1. Therefore, the surface of the layer 4 which becomes the incident surface of laser light can be made smooth and the recording and reproducing characteristics of this optical recording disk can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording disk and a method for manufacturing the same, and more particularly to improvement of an ultraviolet curable resin used as a material for a substrate protective layer.

[0002]

2. Description of the Related Art Conventionally, as optical recording discs for recording / reproducing information by irradiating laser light, magneto-optical discs, various write-once optical discs, digital audio discs (so-called compact discs), optical video discs (so-called lasers). Discs) have been put to practical use.

In each of these optical recording disks, a recording portion made of a functional film such as a recording layer and a reflecting layer is formed on a transparent substrate, and a laser beam is irradiated from the side opposite to the recording portion side for signal recording and recording. And / or playback is performed.

As the recording layer, a perpendicular magnetic film having magneto-optical characteristics (Kerr effect or Faraday effect), for example, a rare earth-transition metal amorphous alloy film such as a TbFeCo alloy thin film is formed as the recording layer. In the write-once optical disc, a low melting point metal thin film, a phase change film, a film containing an organic dye, etc. are formed. Further, as the reflective layer, an Al reflective film is generally formed because it has a high reflectance and is a thermally good conductor.

Further, as a transparent substrate on which these functional films are formed, a polycarbonate substrate which has low water absorption and excellent dimensional stability against changes in humidity is used.

[0006] Here, this polycarbonate substrate is easily charged and dust is adsorbed, and is relatively soft (pencil hardness B to HB), so that it is easily scratched. Therefore, in these optical recording discs, the surface of the transparent substrate that is exposed to the outside, that is, the surface opposite to the side on which the recording portion is formed, protects the substrate from dust adsorption and scratches. Layers are provided. The substrate protective layer has a film thickness of 3 to 10 formed by spin coating an acrylic ultraviolet curing resin coating, for example.
It is formed by coating and curing so as to have a thickness of μm.

[0007]

By the way, in the above-mentioned optical recording disk, as described above, a signal is recorded / reproduced by irradiating a laser beam from the side opposite to the recording section side, and the laser beam is emitted from the substrate. It will be directly incident on the protective layer. Therefore, the surface property of the substrate protective layer has a great influence on the recording / reproducing characteristics, and in order to obtain good recording / reproducing characteristics, it is important that the substrate protective layer is formed with good surface properties without unevenness. Become.

However, when an ultraviolet curable resin coating material which has been used for a substrate protective layer has been applied to the surface of a transparent substrate, the wettability is insufficient and the resin is not uniformly applied, resulting in many coating irregularities. In addition, it is often the case that impurities such as silicone oil are mixed in the ultraviolet curable resin paint, but the surface tension of such silicone oil is 2
If there is a mixture of about 0 dyne / cm,
As a result, a so-called repellency phenomenon occurs, and a minute defect portion where the resin is not applied occurs. For this reason, the formed substrate protective layer has irregularities due to these surface defects, and the surface property is deteriorated.

Therefore, the present invention has been proposed in view of such a conventional situation, and an optical recording disk having a good surface property, in which the substrate protective film has no unevenness caused by coating unevenness and cissing, and It is an object to provide a manufacturing method thereof.

[0010]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies, and as a result, when the UV-curable resin coating which has been conventionally used is applied to the substrate protective layer, it occurs. The surface tension (25 dyne / cm) of the above ultraviolet curable resin coating material is the critical surface tension of the transparent substrate (polycarbonate substrate: 25 dyne / c).
This is because there is no difference between m) and the use of an ultraviolet curable resin paint whose surface tension is smaller than the critical surface tension of the transparent substrate prevents uneven coating and repellency and provides good surface properties. The inventors have come to the finding that a substrate protective layer having a can be formed.

The present invention has been completed based on these findings. That is, the optical recording disk of the present invention has at least an optical recording layer formed on one main surface of a transparent substrate, and a substrate protective layer made of an ultraviolet curable resin on one main surface opposite to the optical recording layer. In the optical recording disk, the surface tension of the substrate protective layer is smaller than the critical surface tension of the transparent substrate.

Further, the transparent substrate is a polycarbonate substrate. Furthermore, in the method for producing an optical recording disk of the present invention, in forming a substrate protective layer by applying an ultraviolet curable resin coating on one main surface of the transparent substrate opposite to the side on which the optical recording layer is formed, The ultraviolet-curable resin coating material having a surface tension smaller than the critical surface tension of the transparent substrate is used.

Further, the present invention is characterized in that a polycarbonate substrate is used as the transparent substrate.

[0014]

[Function] When an ultraviolet curable resin coating material having a surface tension smaller than the critical surface tension of the transparent substrate is applied to the surface of the transparent substrate,
The ultraviolet curable resin coating material spreads evenly on the surface of the transparent substrate. Even if impurities such as silicon oil having a surface tension of about 20 dyne / cm are mixed in the ultraviolet curable resin coating material, repelling does not occur. Therefore, a substrate protective layer having a good surface property is formed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described with reference to the drawings. The present embodiment is an example in which the present invention is applied to a magneto-optical disk.

In the magneto-optical disk of this embodiment, as shown in FIG. 1, a recording part 2 is laminated on one main surface of a transparent substrate 1, and a recording part protection layer 3 is further provided on the recording part 2 and a transparent substrate. 1 is provided with a substrate protective layer 4 on one main surface opposite to the recording portion side, a magnetic field is applied from the recording portion protective layer 3 side, and laser light is emitted from the substrate protective layer 4 side. Recording and reproduction of a signal are performed by irradiating.

The transparent substrate 1 is a disk-shaped transparent substrate having a thickness of about several millimeters, and its material is a plastic material such as acrylic resin, polycarbonate resin, polyolefin resin, epoxy resin, glass, or the like. Also used.

The substrate protective layer 4 is provided in order to prevent the transparent substrate 1 from adsorbing dust and scratching, and the surface of the transparent substrate 1 is coated with an ultraviolet curable resin coating in a thickness of 3 to 10 μm.
It is formed by spin-coating and curing so that the thickness becomes m.

Here, in the present invention, in order to make the surface of this substrate protective layer, which is the incident surface of the laser beam, in a good state without unevenness, the surface tension γ _L of the transparent substrate is the ultraviolet curable resin coating material. A material having a critical surface tension smaller than γ _C shall be used.

That is, the surface property of the substrate protective layer is deteriorated mainly by the occurrence of coating unevenness and cissing when the ultraviolet curable resin coating material is applied. Therefore, in order to form a substrate protective layer having good surface properties, it is necessary to use an ultraviolet curable resin coating material having a high wettability on a transparent substrate so as to prevent such coating unevenness and repelling.

Here, the wettability of the liquid when the liquid is placed on the solid surface depends on the surface tension γ _{L of the} liquid and the critical surface tension γ _C of the solid, and when γ _L <γ _C The placed liquid spreads very thinly and evenly over the surface of the solid over time. This is also the case when spin-coating the UV-curable resin coating on the transparent substrate surface, and the UV-curable resin coating is transparent when the surface tension γ _L of the UV-curing resin coating is smaller than the critical surface tension γ _{C of the} transparent substrate. It exhibits a good wetting property on the surface of the substrate and provides a substrate protective layer having a good surface property without causing coating unevenness and cissing.

The above ultraviolet curable resin coating composition has a difference γ _C − between its surface tension γ _L and the critical surface tension γ _C of the transparent substrate.
The larger γ _{L, the} higher the wetting property, which is preferable for preventing the occurrence of surface defects, but if the surface tension γ _L is too small, it will be difficult to handle as a paint, so the lower limit of the surface tension γ _L is It is preferable to set in consideration of such points. For example, when a polycarbonate substrate (critical surface tension γ _C : 25 dyne / cm) is used as the transparent substrate, the surface tension γ _L is 20 to 24 dyne / c.
m UV curable resin coating is suitable.

In addition, when spin-coating a UV-curable resin coating material, the viscosity of the coating material as well as the surface tension affects its surface property, and the fluidity is increased by reducing the viscosity to a certain extent, resulting in leveling (unevenness). In this case, the coating material flows into the uneven portion and becomes flat), which is advantageous in preventing the occurrence of surface defects. However, when the viscosity is too low, it is still difficult to handle. Therefore, the viscosity of the UV curable resin paint is 10
~ 100 cps, preferably 30-100 cps
More preferably, it is ps.

In Table 1, acrylic UV-curable resin coatings having different surface tensions γ _L and viscosities η are respectively used for polycarbonate substrates having a diameter of 3.5 inches (critical surface tension γ _C : 25
The results of examining the number of occurrence of surface defects such as coating unevenness and cissing when a film having a film thickness of 5 μm on dyne / cm) are shown. The number of samples is 17.

[0025]

[Table 1]

As shown in Table 1, when an ultraviolet curable resin paint having an appropriate surface tension γ _L and viscosity η is used (Experimental Example 2)
On the substrate, a substrate protective layer having good surface properties without forming surface defects is formed.

As the above ultraviolet curable resin paint,
For example, an acrylic ultraviolet curable resin paint or the like is used which has a surface tension adjusted by adding a surface tension adjusting agent to the ultraviolet curable resin paint usually used for the protective layer in this type of magneto-optical disk.

On the other hand, the substrate protective layer 4 of the transparent substrate 1
The recording portion 2 formed on the one main surface on the side opposite to the side has a four-layer structure including a recording magnetic layer 5, dielectric layers 6, 7 and a reflective layer 8, and has a first dielectric layer on the transparent substrate 1. The body layer 6, the recording magnetic layer 5, the second dielectric layer 7, and the reflective layer 8 are laminated in this order.

Of these, the first dielectric layer 6 and the second dielectric layer 6
For the dielectric layer 7, an oxide, a nitride, or the like can be used, but a nitride is more preferable because oxygen in the dielectric may adversely affect the recording magnetic layer 5, and oxygen and moisture can be used. Silicon nitride, aluminum nitride, or the like is preferable as a substance that does not transmit the laser light and can sufficiently transmit the used laser light.

The recording magnetic layer 5 is an amorphous magnetic thin film having a direction of easy magnetization in a direction perpendicular to the film surface, and is excellent in magneto-optical characteristics and has a large coercive force at room temperature. It is desirable to have a Curie point near 200 ° C. As a recording material satisfying such conditions, a rare earth-transition metal alloy amorphous thin film and the like can be mentioned, and among them, a TbFeCo type amorphous thin film is preferable. An additional element such as Cr may be added to the recording magnetic layer 5 for the purpose of improving the corrosion resistance.

The reflective layer 8 is preferably formed of a film having a high reflectance that reflects 70% or more of the laser light at the boundary with the second dielectric layer 7, and a nonmagnetic metal vapor deposition film is suitable. . In addition, it is desirable that this reflective layer be a good thermal conductor, and in consideration of availability, film formation, and the like,
Aluminum is suitable.

Each of these layers 5, 6, 7 and 8 is formed by a so-called vapor phase plating technique such as vapor deposition or sputtering. At this time, the film thickness of each layer can be set arbitrarily, but is usually set to several hundreds to several thousands Å. These film thicknesses are preferably determined not only by considering the optical properties of each layer alone, but also by considering the effect of combination. this is,
For example, when the film thickness of the recording magnetic layer 5 is smaller than the wavelength of the laser light, the laser light causes multiple interference with the light transmitted through the recording magnetic layer 5 and reflected at the boundary between the layers, and the recording magnetic property is changed by the combination of the film thicknesses. This is because the effective optical and magneto-optical characteristics of the layer 5 greatly vary.

The recording part protective layer 3 formed on the recording part 2 is provided to protect the recording part 2 from corrosion due to impact or contact with an external environment. It is formed by spin-coating an ultraviolet curable resin coating on the surface of the upper reflective layer 8 so as to have a film thickness of 3 to 5 μm and curing it.

When forming the recording portion protective layer 3, as in the case of the substrate protective layer 4, the surface tension γ _L of the ultraviolet curable resin coating is higher than the critical surface tension γ _{C of the} reflecting layer serving as the formation surface. If a small one is used, there is no surface defect such as unevenness and cissing and a recording portion protective layer having a high protective effect is formed. For example, the critical surface tension of an Al reflective film is
54 dyne / cm from immediately after formation to 1 hour,
Decreases with time and 37 dyne / cm after 30 days
However, an ultraviolet curable resin coating material having a surface tension smaller than the critical surface tension of the Al reflective layer during the formation of the recording portion protective layer (usually within 1 hour after the formation of the Al reflective film) may be used. The viscosity of the ultraviolet curable resin coating material is also preferably 30 to 100 cps, like the above-mentioned substrate protective film.

As such a UV-curable resin coating material, as in the case of the substrate protective layer, an acrylic UV-curable resin coating material or the like whose surface tension is adjusted by adding a surface tension adjusting agent is used.

[0036]

As is apparent from the above description, in the present invention, the substrate protective layer is formed by applying the ultraviolet curable resin paint whose surface tension is smaller than the critical surface tension of the transparent substrate on the surface of the transparent substrate. Therefore, the surface of the substrate protective layer which becomes the laser light incident surface can be made in a good state without unevenness, and the recording / reproducing characteristics of the optical recording disk can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of essential parts showing an example of an optical recording disk of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent substrate 2 ... Recording part 3 ... Recording part protection layer 4 ... Substrate protection layer

Claims (4)

[Claims] 1. An optical recording disk comprising at least an optical recording layer formed on one main surface of a transparent substrate, and a substrate protective layer made of an ultraviolet curable resin formed on one main surface opposite to the optical recording layer. An optical recording disk, wherein the surface tension of the substrate protective layer is smaller than the critical surface tension of the transparent substrate. 2. The optical recording disk according to claim 1, wherein the transparent substrate is a polycarbonate substrate. 3. When forming a substrate protective layer by applying a UV curable resin coating on one main surface of the transparent substrate opposite to the side on which the optical recording layer is formed, the surface tension of the UV curable resin coating is reduced. A method for manufacturing an optical recording disk, characterized in that a transparent substrate having a surface tension smaller than the critical surface tension is used. 4. The method of manufacturing an optical recording disk according to claim 3, wherein a polycarbonate substrate is used as the transparent substrate.