JPS61289558A - High-density information recording carrier - Google Patents

Abstract

PURPOSE:To prevent the deterioration of functional films and to stabilize the titled carrier for a long period of time by constituting thin inorg. glass film layer of inorg. glass having a specific coefft. of linear expansion. CONSTITUTION:This carrier consists of the thin inorg. glass film layer formed on a transparent plastic substrate and a high-density information recording layer formed threon. the thin inorg. glass film layer is constituted of inorg. glass having 40-70X10<-7>/ deg.C coefft. of linear expansion and the optical disk is constituted of the plastic substrate 1 a protective layer 2, a recording medium layer 3, a surface protective layer 4 and an outside surface protective layer 5. The substrate 1 is preferably made of an acrylic resin, polycarbonate resin and epoxy resin in terms of double refractive index, formability and stability, An optional medium for draw and re-draw is usable for the high-density information recording medium layer 3 and the inorg. glass having the special characteristics is used for the protective layer 2. The inorg. glass layer is also usable for the outside protective layer 4 on the outside surface of the recording layer 3 and is further usable as the outside surface protective layer 5 for the plastic substrate 1. The deterioration of the functional films is thereby prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a high-density information recording carrier used in an optical recording/reproducing device that records/reproduces information using laser light. The present invention relates to a high-density information recording carrier made of plastic that has excellent durability, and further relates to a high-density information recording carrier for magneto-optical recording and reproduction that has excellent magneto-optical properties.

(Prior Art) The most important technical point regarding optical discs at present is how to improve durability, that is, reliability when using a plastic substrate.

In other words, a recording layer formed on a plastic substrate, which has various advantages over a glass substrate, is subject to deterioration or alteration due to moisture or monomer remaining in the plastic substrate, or moisture entering through the plastic substrate. There were drawbacks.

The present inventor proposed a method for solving the above-mentioned drawbacks in %K No. 59-32230 titled "Optical Information Recording Carrier" submitted on February 22, 1980, in which there is no alkali between the plastic substrate and the recording layer. It was proposed to provide a thin film of glass. Although this method dramatically extends the durability of the optical disc and is completely satisfactory, the inventor further developed the above invention and conducted experiments to further improve the durability.
They found even more favorable conditions and completed the present invention.

(Object of the invention) The object of the present invention is to solve the above-mentioned conventional problems.
The object of the present invention is to provide a long-term stable optical information recording carrier by making the plastic substrate glass-like and improving its smoothness, hardness, hygroscopic deformability, and moisture resistance to prevent deterioration of the functional film based on the substrate.

Another object of the present invention is to provide an optical information recording carrier, that is, a high-density information recording carrier, which uses a rare earth-transition metal amorphous alloy as the functional film and has greatly improved magneto-optical properties. be.

(Structure of the Invention) The present invention provides a high-density information recording carrier comprising a transparent plastic substrate, an inorganic glass thin film layer formed on the substrate, and a high-density information recording layer formed on the inorganic glass thin film layer. The present invention relates to a high-density information recording carrier, characterized in that the inorganic glass thin film l- is composed of an inorganic glass having a linear expansion coefficient of 40 to 70×10/°C.

The high-density information recording carrier to which the present invention is applied is described in detail in the aforementioned Japanese Patent Application No. 59-32230 filed by the present applicant, and a summary thereof will be described below.

Figure 1 shows the structure of a general optical disc, which consists of a transparent plastic substrate 1, a protective layer 2, and a recording medium layer 3.
, a surface protection layer 4, and an outer surface protection layer 5 provided as necessary.

The above substrate l can be made of any transparent plastic such as acrylic resin, polycarbonate resin, styrene resin, or epoxy resin, but acrylic resin, polycarbonate resin, and epoxy resin are generally used for reasons of birefringence, moldability, and stability. preferable.

As the high-density information recording medium layer 3, any known medium for DRAW (recordable once) and E-DRAW (write once-erasable) can be used.

Conventionally, the protective layer 2 is 5in2. Although oxides such as TiO2 and organic polymers such as orcasiloxane have been used, the present invention is characterized in that an inorganic glass with special properties is used as the protective layer 2.

The thickness of this inorganic glass layer 2 can be 100 to 2,000XK, and if it is less than 100X, its protective role is insufficient,
2. If it exceeds OOOX, it is not economical and problems such as absorption of laser light occur. This inorganic glass layer 2 is formed by a physical vapor deposition method (P
VD).

As the inorganic glass, glass having a particularly special coefficient of linear expansion, particularly alkali-free glass, is preferable.

This alkali-free glass is commercially available as Corning's code number 7059, and its composition is 5in4.
: 49.9%, BaO: 25.1%, B20. :1
000%, AI, Ol: 10.3%, CaO: 4.3%
It is. However, the above-mentioned inorganic glass of the present invention is not limited to this, and any inorganic glass that can be formed into a thin film by physical vapor deposition may be used.

The inorganic glass layer according to the present invention is not only the protective layer 2 between the plastic substrate 1 and the recording layer 3, but also the recording layer 3.
It can also be used as the outer protective layer 4 of the outer surface of a plastic substrate, and furthermore, it can be used as the outer protective layer 5 of a plastic substrate.

The inorganic glass layer of the present invention is made of conventional SiO,,T
Shows better properties than simple protective films such as iO2, especially moisture absorption resistance.

The best results can be obtained when the present invention is applied to a magneto-optical disk in which the high-density information recording layer is made of a rare earth-transition metal amorphous alloy.

In other words, as the amount of information has increased in recent years, TbFe has been used due to the need for higher density and high-speed access.

An amorphous alloy thin film made of a combination of a rare earth metal such as TbFeCo or GdTbFe and a transition metal has an axis of easy magnetization perpendicular to M-m, and is a high-density information recording medium that can be recorded, reproduced, and erased. Applications of the above-mentioned information recording disks, which are attracting a lot of attention as These are important issues.

Among the factors that pose problems in solving the above problems, the basic factors based on the recording medium include 1. Non-uniformity in film thickness and alloy composition 2. Non-uniformity in magnetic properties 3. Deterioration due to oxidation.

These greatly depend on the cleanliness, smoothness, and scratches of the board.
This is a hindrance to higher performance information recording disks.

By providing the inorganic glass layer 2 according to the present invention between the plastic substrate l and the recording medium layer 3 of the rare earth-transition metal amorphous alloy, the above-mentioned factors 1 to 3 can be solved at once, and magneto-optical recording becomes practical. A carrier (hereinafter referred to as a magneto-optical disk) is obtained.

The magneto-optical recording medium to which the present invention can be applied may be any known rare earth-transition metal amorphous alloy, such as Tb-F
e-based alloy (% Publication No. 57-20691), Dy-F
e-based alloy (Special Publication No. 57-20692), Gd Tb
Fe-based alloy (#I Kaisho 56-126907), Gd-
-Tb Dy-Fe alloy (Japanese Patent Application Laid-Open No. 57-94948), Gd-Co (% Opening No. 54-121719) Tb-
Examples include Fe-Co type. These rare earth-transition metal amorphous layers are preferably formed on the inorganic glass layer of the present invention by a method such as vapor deposition, sputtering, or ion brazing. The thickness of this amorphous layer is generally 50
0 to 1.50 OA.

The composition and thickness of the inorganic glass layer 2 according to the invention are the same as described above.

In other words, research has traditionally focused on forming an amorphous layer on a glass plate.
Although it was possible to form an amorphous layer with perpendicular magnetization on a glass substrate, the technology for stably forming an amorphous layer with perpendicular magnetization on a plastic substrate has not yet been established. That is, in the case of a glass substrate, a Kerr rotation angle of 0.3 degrees or more can be obtained, but in the case of a plastic substrate, a Kerr rotation angle of only about 0.1 degree can be obtained, and in the case of a plastic substrate, a Kerr rotation angle of 0.2 degrees or more can be obtained. Even if something is obtained, long-term stability is poor and reproducibility is poor. Therefore, there has been a strong demand for the establishment of a technique for forming a stable perpendicularly magnetized amorphous material on an easy-to-handle plastic substrate instead of the conventional glass or aluminum substrate.

By forming the above-mentioned inorganic glass layer 2, the present invention provides
A practical magneto-optical disk was created by making the surface of the plastic substrate, on which the amorphous alloy layer could not be stably formed, the same as the glass substrate.

The magneto-optical disk according to the present invention exhibits almost the same C/N ratio as a magneto-optical disk using a conventional glass substrate.

The present invention will be explained below using a magneto-optical disk as an example, but the present invention can be similarly applied to other known DRAW recording media. The reason why we chose magneto-optical recording media as an example is because magneto-optical recording media require much stricter characteristics than DRAW recording media, especially moisture resistance, and even if the magneto-optical recording medium satisfies the requirements, If DRAW
It can be fully applied to recording media for In addition to magneto-optical recording materials, it is clear that the present invention can be applied to any E-DRAW media that requires durability, such as phase change type, shape change type, or form change type.

The linear expansion coefficient of the inorganic glass, which is the first feature of the present invention, is 40 to 70 x 1 in order to improve the BER of the disk.
It is necessary to keep the temperature within the range of o-7/°C. If this value is less than 40XtO-7/℃ and 70X1o-
If it exceeds 7/°C, cracks will occur in the recording layer and the BER will deteriorate.

Generally, the coefficient of linear expansion of inorganic glass can be changed to any value by changing the composition of the glass.

The second feature of the present invention is that the amount of alkali metal in the alkali-free glass is 1 weight factor or less in terms of alkali metal oxide,
Preferably it is 0.8% by weight or less. That is,
Alkali gold W4: Li, Na, K.

It is characterized by being composed of an alkali-free glass containing Rb and Cs in an amount of 1% by weight or less, preferably 0.8% by weight or less, calculated as an alkali metal oxide.

If the amount of alkali metal exceeds 1 in terms of alkali metal oxide, cracks will occur in the recording layer and the record will be destroyed.

The reason for this is not clear, but it is thought that the alkali metal reacts with moisture and monomer passing through the plastic substrate, or with moisture in the outside air, deteriorating the recording layer. It is more preferable that the weight of the alkali metal is less than 0.8 weight in terms of alkali metal oxide, and the smaller the weight is, the more preferable it is, as long as it does not impair the properties of the glass.

However, industrially it is difficult to reduce the alkali metal content to zero, and there is no practical problem if it is 1% by weight or less.

Note that the alkali-free glass of the present invention does not include so-called silicate glass consisting only of SiO□.

That is, although it is well known that 5 in 2 is used alone as a moisture-resistant protective layer, this silicate glass thin film has almost no moisture resistance.

The thickness of the inorganic glass thin film of the present invention is 100 to 2.0ooX
1 is preferable, and if it is less than 100X, the protective role is insufficient, and 2
．． If OOOcA is exceeded, problems such as laser absorption will occur, and it will also be unsuitable.

In the present invention, the high-density information recording layer is made of, for example, TbFeCo.
From rare earth-transition metal amorphous alloys such as r
Although it is particularly suitable for application to optical discs using magneto-optical recording materials, it is also applicable to other high-density recording carriers using recording materials that are subject to deterioration due to monomers in plastics, moisture, and/or moisture from the outside. It is clear that it is applicable to all.

It goes without saying that the protective layer of the inorganic glass thin film of the present invention can also be formed outside the recording layer, that is, on the opposite side to the substrate, to shield the recording layer from the outside air.

The present invention will be explained below using examples.

(Example) As plastic substrates, an acrylic substrate (PMMA) with a thickness of 1.21 mm and a polycarbonate substrate (PC) were prepared. On these substrates, inorganic glass having each composition shown in Table 1 was formed into a thin film of 500A by sputtering using a sputtering device (RF magnetron sputtering device manufactured by Japan Vacuum Technology Co., Ltd.), and then Gd'
A recording layer of 0.12 Tb (1,12 FeO, 76 mm) was formed to a thickness of 1000XK using the above sputtering apparatus,
Further, each of the same inorganic glasses was sputtered thereon by the same method as above to form a thin film layer with a thickness of 1000 Å.

The obtained magneto-optical disk was evaluated by heating the disk at 45℃, 9
BER after maintaining 0RH% for 3θ days (initial lff1
) and C/N change (C/N from initial value
It is expressed as the minimum value (dB).

As seen from Table 1, the linear expansion coefficient is 40 to 70 x lO7
By using inorganic glass with a temperature of °C, it is possible to create an optical disk with a small C/N change rate, and by using alkali-free glass with an alkali metal content of 1% by weight or less in terms of its oxide, the BER can be further improved. do.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an optical disc to which the present invention is applied. (Symbols in the figure) 1: Niblastic substrate, 2: inorganic glass layer, 3: recording layer, 4: surface protective layer, 5: outer surface protective layer. Patent applicant: Daicel Chemical Industries, Ltd. Figure 1

Claims (1)

[Scope of Claims] 1) A high-density information recording carrier comprising a transparent plastic substrate and a high-density information recording layer formed on the substrate via a thin inorganic glass layer, in which the inorganic glass thin film layer linearly expands. A high-density information recording carrier, characterized in that it is made of inorganic glass having a coefficient of 40 to 70 x 10^-^7/°C. 2) The high-density information recording carrier according to claim 1, further characterized in that the alkali-free glass contains an alkali metal in an amount of 1% by weight or less in terms of alkali metal oxide. 3) A high-density information recording carrier according to claim 1 or 2, wherein the high-density information recording layer is made of a magneto-optical recording material.