JPS62202346A - Optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the intrusion of oxygen, moisture, etc., into a recording film and to improve durability by making the thickness of auxiliary films larger than the thickness of guide grooves. CONSTITUTION:A protective film 7, recording film 3, protective film 8, adhesive layer 5 and another substrate 6 are successively laminated on a substrate 1 having the guide grooves and the thicknesses of the protective films 7, 8 are formed larger than the thicknesses of the guide grooves. The direct contact of the substrate 1 or the adhesive layer 5 and the recording film 3 is obviated and the intrusion of the oxygen and moisture into the recording film 3 from the side end thereof through the substrate 1, the adhesive layer 5, etc., is prevented by setting the thicknesses of the protective films 7, 8 in the above- mentioned manner. The preventive effect acts effectively not only after the completion of production of an optical recording medium but also during the film formation of the recording film 3, etc. The gas generated from the substrate 1 in the stage of the film formation is also effectively shut off. The corrosion resistance of the optical recording medium is thereby improved and the recording medium is made to withstand long-term use.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical recording medium on which recording and reproduction can be performed using a light beam.

[Conventional technology]

Conventionally, optical memory recording films have been developed on substrates such as glass, acrylic resin, polycarbonate resin, and epoxy resin, utilizing magneto-optical effects, photochromism, phase transition from amorphous to crystalline, deformation of shape memory alloys, etc. formed,
Optical recording media are known.

Although stiff recording media are required to have a long lifespan, this has not always been possible. For example, when an amorphous material is used as a recording film, one of the factors that shortens the lifetime is crystallization of the film. However, it is known that this problem can be solved by increasing the crystallization temperature.

It has become clear that another factor that shortens the lifespan is corrosion of the recording film due to moisture and oxygen in the environment. The main countermeasures can be broadly classified into two methods. One method is to suppress deterioration by improving the recording film itself, and the other is to protect the recording film with a protective film.

As a method of suppressing deterioration by improving the recording film itself, if the film is made of organic material, there is a method of changing some of the functional groups or changing the polarity by changing the number of carbon atoms. In the case of metal alloys, methods include changing the alloy composition or adding additives.However, in either case, sensitive records,
In many cases, the reproduction characteristics cannot be maintained and these characteristics deteriorate. In this case, a method of blocking moisture, oxygen, etc. from the outside using a protective film can be used as an effective method. However, even the conventionally known method of improving durability using a protective film is not necessarily satisfactory, and there is still room for improvement.

The present invention is based on the inventor's research on the mechanism of corrosion occurrence and progression in various optical recording media including recording media made of rare earth-transition metal alloys whose recording film deteriorates even when exposed to trace amounts of moisture or oxygen. It was completed as a result of intensive research, and its purpose is to provide an optical recording medium that has improved corrosion resistance and can withstand long-term use.

(Means for Solving the Problems) The present invention, which can achieve the above-mentioned object, includes an auxiliary film made of an inorganic material exhibiting corrosion resistance, and an optically The optical recording medium is characterized in that the thickness of the auxiliary layer is greater than the depth of the guide groove in an optical recording medium formed by sequentially laminating recording films for recording and reproduction.

Before explaining the details of the optical recording medium of the present invention,
First, the knowledge obtained regarding the relationship between the structure of conventional optical recording media and the mechanism of corrosion occurrence and progression will be explained. FIG. 2 shows a typical example of a conventional optical recording medium, which has a structure in which a protective film 2, a recording film 3, a protective film 11@4, an adhesive layer 5, and another substrate 6 are laminated on a substrate 1. .

As shown in this figure, in order to perform high-density and accurate recording, optical recording media generally have a transparent substrate 1.
A guide groove is provided. The depth of the guide groove is determined from the viewpoint of obtaining an efficient tracking signal, for example, when performing high-density recording using autofocus and autotracking, assuming that the refractive index of the substrate 1 is n and the wavelength of the reproduction light is λ. It is common to use λ/8n (Formula 1).

Generally, it is practically advantageous to use a semiconductor laser with a wavelength of around λ=830 nm as a light source for an optical recording medium using a light beam, and as a material for a transparent substrate, a material with a refractive index of 1. Since glass, acrylic resin, polycarbonate resin, etc. around 5 is usually used, the depth of the guide groove is about 700 to 800 according to formula 1.

In conventional optical recording media, ^tN, TiN, Si3N4 are formed on the substrate 1 on which guide grooves of this depth are formed.
, ZnS, Si[: , Tic, SiO
A protection layer 11i2 made of various corrosion-resistant materials such as , TiO2, etc. is laminated to a thickness of approximately 178 to 374 mm, which is the depth of the guide groove.

It has been found that in such optical recording media, even if the protective film 2 is made of a material with a particularly high ability to block oxygen, etc., and is formed densely, the magnetic properties etc. gradually deteriorate and there is a limit to the durability. did. The inventor believes that this result occurs because the recording film 3 is effectively protected from oxygen and moisture traveling in the direction of arrow A in FIG. 2, but is not protected from oxygen and moisture traveling in the direction of arrow B. We have come to believe that oxidation and deterioration by these oxygens and the like is one of the major causes.

Furthermore, the characteristics of optical recording media deteriorate not only due to oxygen and moisture entering from the outside of the optical recording medium, but also due to the formation of the protective film 2 and recording film 3 on the substrate, which are usually exposed to high temperatures. This may also be due to degassing from 1.
This was discovered through detailed investigation of the initial characteristics of optical recording media.

FIG. 1 shows one embodiment of the optical recording medium of the present invention, which was completed based on the above findings. This optical recording medium has a structure in which a protective film 7, a recording film 3, a protective film 8, an adhesive layer 5, and another substrate 6 are sequentially laminated on a substrate 1 having a guide groove. The difference from the medium is that the thickness of the protective film 7.8 is thicker than the depth of the guide groove. Protective film 7.8
By setting the thickness of
Intrusion from the side edges of the recording film 3 via the adhesive layer 5 or the like can be prevented. This prevention effect is effective not only after the completion of manufacturing the optical recording medium but also during the formation of the recording film 3 and the like, and can effectively block gas generated from the substrate 1 during film formation. Therefore, the optical recording medium of the present invention exhibits excellent corrosion resistance and can withstand long-term use.

In the optical recording medium of the present invention, the film interposed between the substrate and the recording film to prevent direct contact between the substrate and the recording film is an auxiliary film other than the recording film, such as a protective film, and as a result, the recording film is protected from oxygen, moisture, etc. As long as the film is made of an inorganic material that can protect against corrosion, that is, provide corrosion resistance, it may be a film that also performs various other functions, or it may have a multilayer structure. Such auxiliary films include 8u, Ag, Cu,
Reflective film composed of H1, SiO, 5i02, II
Examples include an antireflection film made of N or the like.

The present invention is applicable to various types of optical recording media, such as optical recording media having a recording film formed by coating a solvent containing dye or fine magnetic particles, or an air sandwich structure, or a structure in which a 1ζ plate is provided only on one side. It is widely applicable to various recording media and is very effective. In particular, when applied to RT users, the substrate and solvent do not come into contact with each other, suppressing deterioration of the substrate material due to the solvent, and providing the effect of widening the range of choices for solvents and base materials. can.

As described above, the present invention has a wide range of applications, including oxidation,
As an optical recording medium, that is, a recording film that is prone to corrosion due to moisture, etc., (a) a magneto-optical recording film that exhibits a magneto-optical effect, such as a rare earth-transition metal amorphous thin film, or (b) a phase change recording film. It is particularly effective when applied to a recording medium using a film to be used, for example, a tellurium-based film or a laminated film of antimony/selenium and bismuth/tellurium. Among them, TbFe, GdTbFc, TbFe(
:o, GdTbFeC.

It is very effective when applied to recording media using rare earth-transition metal amorphous thin films such as. Further, the present invention uses a substrate made of a plastic material such as acrylic resin or polycarbonate resin, or a flat plate of a transparent inorganic material such as glass coated with a plastic such as ultraviolet curing resin. It is particularly effective when applied to recording media.

〔Example〕

EXAMPLES The present invention will be specifically described below with reference to Examples.

Example 1 First, a polycarbonate substrate on which guide grooves were transferred and formed was produced by injection molding using a stamper having grooves for forming guide grooves with a depth of 700 mm. Various films shown below were sequentially formed on this substrate by RF sputtering. .

Material Nobusaho J舊Il! 2(A) SiO 1000 person recording layer
GdTbFeCo 1000 people protection 11 ([1)
One more layer on the completed Si0 100QA laminate.
Two polycarbonate substrates are bonded together using adhesive,
An optical disc according to the present invention was created.

Example 2 Protective films (A) and (13) were each coated with a thickness of 1000 mm.
An optical disc was produced in the same manner as in Example 1 except that iN was used instead.

Comparative Example 18, IB, 2 The thickness of the protective films (A) and (B) of Example 1 were both 50
0 people (Comparative Example 18) or 200 people (Comparative Example 1B)
A 2 Ml optical disc was prepared in the same manner as in Example 1 except that . Protective films (A) and (B) of Example 2
An optical disc (Comparative Example 2) was produced in the same manner as in Example 2, except that the knob size was changed to 150 people.

A durability test was conducted on each of the optical discs of Examples 1 and 2, Comparative Example 1, IB, and 2 by a method of examining the coercive force after being left at a temperature of 60° C. and a humidity of 90% for 1000 hours. The results are shown in Table 1. From these results, it is clear that the optical disc according to the present invention has improved durability.

Examples 3 to 7 EL and Comparative Examples 3 to 7 Optical discs according to the present invention and corresponding conventional types were produced in the same manner as in Example 1, except that the protective films (8) and (B) were films as shown in Table 1. created an optical disc. A durability test similar to that described above was conducted for each optical disc.

The results are also shown in Table 1.

Although the degree of durability improvement varies depending on the structure and material of the protective film, if the thickness of the protective layer is equal to or greater than the depth of the guide groove,
Improvement in durability is recognized.

Example 8 The following films were laminated on the same polycarbonate resin substrate as used in Example 1 by RF sputtering.

Material Thickness Protective film 5i0100OA // Z n 5 300 person recording layer G
dTbFeCo 150 people interference layer ZnS
300 people // Si0 600 people Reflection layer to 1
500 people protective layer Si0 1000 people Another polycarbonate substrate was bonded to the completed laminate using an adhesive to produce an optical disc according to the present invention.

Example 9, IO1 Comparative Example 8.9.10 An optical disc according to the present invention (Example 9.10) was prepared in the same manner as in Example 8 except that the layer structure was as shown in Table 2.
Conventional type optical discs (Comparative Examples 8, 9, and 10) were prepared, and each optical disc was subjected to the same durability test as in - above. The results are also shown in Table 2. Table 2 also confirms the excellent durability of the optical disc of the present invention.

Examples If to 14 The present invention was carried out in the same manner as in Example 5.8 except that in each of Examples 5.8, the polycarbonate resin substrate was replaced with an acrylic resin substrate having guide grooves of the same depth. Such optical discs were created (Example 11 and +2 in order)
.

Example 5.8, except that in each of Examples 5.8, the polycarbonate resin substrate was replaced by a substrate with an ultraviolet curable resin (epoxy acrylate) layer on glass, having guide grooves of the same depth. Embodiments 13 and 14 in the order in which optical discs according to the present invention are prepared in the same manner as in Embodiment 8)
.

Durability tests were conducted on each optical disc.

The result was as follows.

Examples 11, 13... Almost the same coercive force (60.9) as in Example 5 was obtained.

Examples 12, 14... Substantially the same coercive force as in Example 8 (bed 0.9) was obtained.

The fact that almost the same values were obtained even when the substrate was changed indicates that the decrease in magnetic properties was due to moisture and oxygen taken into the film during the growth process, rather than moisture and oxygen entering from the outside during the durability test. It is estimated to be.

Table 2 (Effects of the Invention) As explained in detail above, the optical recording medium of the present invention in which the thickness of the auxiliary film is thicker than the depth of the guide groove prevents oxygen, moisture, etc. from entering the recording film from the substrate. Even optical recording media with transition metal-rare earth amorphous recording films, which were extremely susceptible to corrosion, have improved durability and can withstand longer-term use. Ta.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the optical recording medium of the present invention, and FIG. 2 is a schematic sectional view of a conventional optical recording medium. 1.6: Substrate 2.4.7.8: Protective film 3: Recording film 5: Adhesive layer

Claims (1)

[Claims] 1) An auxiliary film made of an inorganic material exhibiting corrosion resistance and a recording film for optical recording and reproduction are sequentially laminated on a transparent substrate having a guide groove. An optical recording medium characterized in that the thickness of the auxiliary film is greater than the depth of the guide groove. 2) The optical system according to claim 1, wherein a second auxiliary film thicker than the depth of the guide groove is laminated on a surface of the recording film that is not in contact with the auxiliary film. recording medium.