JP2525366B2 - Optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium capable of recording and reproducing with a light beam. In particular, the present invention relates to a protective film formed on the recording layer for the purpose of improving the storage stability of the recording layer.

[Conventional technology]

Conventionally, as an optical memory material used for an optical disk, a rare earth-transition metal alloy thin film, a thin film of a reducing oxide such as a chalcogen compound utilizing a phase transition from amorphous to crystalline, a heat mode recording medium, and a thermoplastic. Recording media and the like are known. For example, as a magneto-optical recording medium formed of a rare earth-transition metal alloy thin film, MnB
Polycrystalline thin films such as i, MnCuBi, GdCo, GdFe, TbFe, DyFe, GdTb
Amorphous thin films such as Fe, TbDyFe, GdFeCo, TbFeCo, GdTbCo, Gd
Single crystal thin films such as IG are known. Of these thin films, film-forming properties when manufacturing large-area thin films at temperatures near room temperature, writing efficiency for writing signals with small photothermal energy, and reading the written signals with a good S / N ratio Considering the reading efficiency, recently, the amorphous thin film is considered to be excellent as a magneto-optical recording medium. In particular, GdTbFe has a large Kerr rotation angle and a Curie point of around 150 ° C., and is therefore optimal as a magneto-optical recording medium.

However, the amorphous magnetic material generally used in magnetic recording media such as magneto-optical recording media such as GdTbFe has the drawback of poor corrosion resistance. The atmosphere,
When exposed to water vapor, the magnetic properties deteriorate, and eventually it is completely oxidized and becomes transparent.

In order to eliminate such a defect, it has been conventionally proposed to provide an inorganic protective layer such as SiO ₂ or SiO on the optical memory material layer. However, the protective layer of inorganic materials such as SiO and SiO ₂ must be formed by using a vacuum device such as vapor deposition and sputtering, and it takes time to form the film, resulting in enormous equipment investment and labor cost. Therefore, the cost of the recording medium is increased. Further, these inorganic protective films have higher thermal conductivity than organic substances, and a large amount of energy is dissipated to the protective film side during recording on the memory material film, which causes a decrease in writing sensitivity.

Further, it has been attempted to apply an organic resin as a protective film on the recording layer, but the resins conventionally tried have the following problems. First, when an acrylic resin, an epoxy resin, a urethane resin or the like is used as a protective film, a substance affecting the recording layer diffuses from the resin into the recording layer and accelerates the deterioration of the recording layer. If acrylic resin, silicone resin, vinyl chloride, etc. are used as the protective film,
The moisture resistance of the protective film is so poor that it cannot function as a protective film. Further, when the above resin is used, it takes time for the resin to cure after application, which causes an increase in manufacturing cost.

[Problems to be solved by the invention]

The present invention has been made to solve the above problems, and provides an optical recording medium having a corrosion-resistant protective film that can be formed in a short time and by a simple operation, and has a small decrease in writing sensitivity. To aim.

[Means for solving problems]

The present invention is an optical recording medium in which an optical recording layer is provided on a substrate, and a protective film made of a mixture of an ethylene / acrylic acid copolymer and a waxy hydrocarbon is formed on the recording layer. It is an optical recording medium characterized by the above.

In the present invention, as the substrate, glass; plastic such as acrylic resin, polycarbonate resin, epoxy resin or the like is used.

In the present invention, the optical recording layer does not mean only the optical memory material layer, but may be an underlayer, an antireflection layer, and / or a layer above and / or below the optical memory material layer, if necessary.
It also means the entire layer formed by appropriately providing a reflective layer, an interference layer, a protective layer made of a material other than the protective film used in the present invention, and the like.

In order to provide the above-mentioned optical recording layer on the substrate, the above-mentioned layers are sequentially laminated by a layer forming means according to their physical properties, for example, a sputtering method, a vacuum evaporation method or the like.

To form the optical recording medium of the present invention, after providing the recording layer by the above-mentioned method, the protective film containing ethylene / acrylic acid copolymer as a main component is formed thereon.
Since ethylene-acrylic acid copolymer is a thermoplastic resin, if it is melted by heating and coated on the recording layer with a coating means such as roll coater, spraying, printing or spin coating, the recording layer and substrate The copolymer applied by heat conduction to the side instantly cools and solidifies to form a coating film, and the time required for forming a protective film after coating is the same as in the case of the organic resin protective film that has been tried in the past. It is much shorter than time. Furthermore, the ethylene / acrylic acid copolymer film is lower in moisture permeability and gas permeability than organic resin films that have been tried so far, and is therefore preferable from the viewpoint of preventing oxidative deterioration of the recording layer. In addition, the thermal conductivity is SiO, SiO ₂
Since it is lower than dielectrics such as Al and Cu, and metals such as Al and Cu, the dissipation of recording energy during recording is small and the recording sensitivity is improved.

The ethylene / acrylic acid copolymer used in the present invention is a copolymer obtained by using ethylene and acrylic acid as main constituent monomers, and the monomer ratio of ethylene and acrylic acid is in the range of 9: 1 to 6: 4. Is preferably used.

As described above, the ethylene / acrylic acid copolymer alone can form a protective film. However, in the present invention, the moisture permeability of the protective film is further reduced and the viscosity of the melt is reduced to facilitate the coating. In order to do so, a waxy hydrocarbon such as paraffin wax or microcrystalline wax is blended with the copolymer. The preferred blending ratio is from 9: 1 by weight of copolymer: waxy hydrocarbon.
It is in the range of 6: 4. The present invention will be described below with reference to the drawings.

1 to 3 are side sectional views for explaining an example of the structure of a recording medium of the present invention, and FIG. 4 is a similar view regarding a conventional recording medium. In each figure, 1 is a substrate, 2 is a base layer, 3 is an optical memory material layer, 4 is a protective film containing ethylene / acrylic acid copolymer as a main component, 5 is a conventional protective film layer, and 6 is an adhesive. It is a layer.

As shown in FIG. 3, a structure in which two recording layers are bonded with an adhesive so as to face each other, and a so-called air sandwich structure in which two recording layers are bonded via a spacer at that time are also formed on the recording layer. As long as a protective film containing an ethylene / acrylic acid copolymer as a main component is formed, this is an embodiment of the optical recording medium of the present invention.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 A disk-shaped optical recording medium having a schematic side cross section having the structure shown in FIG. 1 was produced by the method described below. A polycarbonate resin substrate 1 having a spiral guide groove on its surface was produced by injection molding, and 900 Å thick SiO was deposited as a base layer 2 on it by vacuum deposition, followed by RF sputtering. The GdTbFeCo optical memory material layer 3 was deposited to 700 Å. On top of that, ethylene
A resin prepared by mixing an acrylic acid copolymer and paraffin wax in a weight ratio of 7: 3 was melted by heating and applied to a thickness of 30 μm with a roll coater. Immediately after the coating film was applied, heat was transferred to the recording layer and the substrate side, and instantaneously cooled and solidified to form the protective film 4. Thus, the optical recording medium of the present invention was obtained.

Example 2 A circular optical recording medium having a schematic side cross section having the structure shown in FIG. 2 was produced by the method described below.

The same procedure as in Example 1 was performed until the optical memory material layer was formed, and SiO was formed thereon as the protective film 5 by the 500Å vacuum deposition method. Then, in the same manner as in Example 1, a 40 μm thick mixed protective film 4 having a weight ratio of ethylene / acrylic acid copolymer and paraffin wax of 6: 4 was formed thereon to form an optical composition of the present invention. A recording medium was obtained. The time required for forming the protective film was about 2 minutes.

For comparison, an optical recording medium having a structure shown in FIG. That is, in this case, the process is carried out in the same manner as in Example 1 until the optical memory material layer is formed, on which SiO is formed as the protective film 5 by the 3000Å vacuum deposition method. In this case, the time required to form the protective film is about 5
It was a minute.

After the two obtained recording media were left in an environmental tester at 45 ° C. and 95% RH for 1000 hours, the degree of deterioration of the recording layers was compared, but there was almost no difference between them.

In the case of the same film thickness, although the resin film has a larger gas and water permeation amount than the SiO film, the above results were obtained when the ethylene / acrylic acid copolymer-wax protective film was used. This is probably because the film was formed thick, but nevertheless, the time required for forming the protective film can be considerably shortened in the case of the present invention as described above, so that its economic effect is extremely large.

Example 3 The optical recording medium of Example 2 was pasted with a rubber-based hot melt adhesive 6 so that the recording layers face each other, and a recording medium having a schematic side cross-section shown in FIG. 3 was produced. Thus, the recording medium having the laminated structure has the same effect as that of the second embodiment.

Although the present invention has been described with reference to the magneto-optical recording medium in each of the above embodiments, the type of recording layer is not limited to this.

〔The invention's effect〕

As described above, when the ethylene / acrylic acid copolymer is used for the protective film, the recording sensitivity is improved as compared with the conventional inorganic protective film, which is advantageous in cost. Further, compared with the organic protective film which has been used conventionally, the recording layer has a high protective performance, is heated and melted and applied, and is solidified when the temperature returns to room temperature, so that the film can be formed in a short time, which is advantageous in terms of cost.

[Brief description of drawings]

1 to 3 and FIG. 4 are side sectional views schematically showing the structures of the present invention and the conventional optical recording medium, respectively. 1 ... Substrate, 2 ... Underlayer, 3 ... Optical memory material layer,
4 ... Protective layer containing ethylene / acrylic acid copolymer as a main component, 5 ... Conventional protective layer, 6 ... Adhesive layer.

Claims (2)

(57) [Claims] 1. An optical recording medium having an optical recording layer provided on a substrate, wherein a protective film made of a mixture of an ethylene / acrylic acid copolymer and a waxy hydrocarbon is formed on the recording layer. An optical recording medium characterized by the following. 2. A mixing ratio of the ethylene / acrylic acid copolymer and the wax-like hydrocarbon in a weight ratio of copolymer: wax-like hydrocarbon in the range of 9: 1 to 6: 4. The optical recording medium according to claim 1.