JPH04209346A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To prevent flaw on a medium by forming a magneto-optical recording layer, protective layer, and lubricating layer on a disk substrate and constituting this lubricating layer of a polymer material comprising perfluoropolyether having an isocyanate group at its end. CONSTITUTION:On a glass substrate, there is provided a magneto-optical recording layer having 150-1000Angstrom thickness, on which a protective layer is formed to have 100-2000Angstrom thickness and 1.4-2.5 refractive index in order to improve the interference effect. Then a dense lubricating layer essentially comprising polymerized perfluoroether having an isocyanate group as the end group. This perfluoropolyether having an isocyanate group as the end group has a skelton structure expressed by formula I. The average mol.wt. of this perfluoropolyether is 1000-10000, preferably. When the mol.wt. is larger than this range, the proportion of isocyanate groups decreases and enough polymn. is hardly effected. Thereby, flaw due to collision of a head on the medium can be prevented.

Description

[Detailed description of the invention]

[00011

[Field of Industrial Application] The present invention relates to a magneto-optical recording medium that performs recording and reproduction using a flying magnetic head. [0002] [Prior Art] A magnetic field modulation type magneto-optical recording method using a floating magnetic helarad has been proposed as a magneto-optical method that allows overwriting (ISOM'87 Proceedings, P1
49~). Compared to the conventional magnetic field modulation recording method using a fixed head, this method allows the distance between the head and the medium to be reduced by an order of magnitude, and it is possible to generate a larger magnetic field. In particular, the difference in magnetic field strength is remarkable in the ability to generate a magnetic field at high frequencies (IMHz or higher). [0003]

[Problems to be Solved by the Invention] However, as the distance between the head and the medium becomes smaller, the probability of collision between the head and the medium increases, causing scratches on the medium (head) and reducing the reliability of the medium. There's a problem. In the above-mentioned document (ISOM'87 Proceedings, P149~), the medium is overcoated with a resin layer several tens of micrometers thick to ensure reliability, but collision between the head and the medium cannot be avoided, and as a result, the overcoat Peeling of the coating layer generates dust, which causes serious problems in the system. [0004] Furthermore, in the magnetic field modulation method using the above-mentioned floating magnetic head, recording and reproduction can be performed from both sides. Therefore,
A method (hereinafter sometimes referred to as an air incident method) has been proposed in which an optical head is incorporated into a floating magnetic head and laser light is incident from the floating magnetic head side, thereby allowing recording and reproduction from both sides. (EP341
829). In this method, problems such as interference and scattering of laser light can be avoided and the overcoat layer can be used with a thickness of several tens of micrometers. [0005]

SUMMARY OF THE INVENTION The above problems are solved by the magneto-optical recording medium of the present invention. That is, the present invention provides a magneto-optical medium used in a magneto-optical recording method for recording and reproducing using a floating magnetic head, which comprises forming at least a magneto-optical recording layer, a protective layer, and a lubricant layer on a disk substrate. The present invention resides in a magneto-optical recording medium characterized in that the lubricating layer is composed mainly of a polymerized monomer of perfluoropolyether having an isocyanate group at its end. [0006] This effect is particularly remarkable in a magneto-optical recording medium in which recording and reproduction are performed by entering a laser beam from the floating magnetic head side. The present invention will be explained in detail below. [00071 In the present invention, the disk substrate includes:
There is no particular restriction, and usually a glass substrate with pregrooves formed with an ultraviolet curable resin (hereinafter sometimes referred to as 2P glass) is used, but other materials include ceramic substrates such as glass, and resin substrates such as polycarbonate. , a metal substrate such as an aluminum alloy, etc. can also be used. [0008] As the magneto-optical recording layer, for example, TbF
Amorphous magnetic alloys of rare earth elements and transition metals such as TbFeCo, TbCo, and DyFeCo are used. A single layer may be used as the magneto-optical recording layer, or GdFe
Two or more recording layers may be stacked, such as C○/TbFeCo. The thickness of the recording layer is preferably about 150 to 1000 mm. [0009] The protective layer provided on the magneto-optical recording layer includes Sio2, A1203, Ta205. T
Metal oxides such as iC2, metal nitrides such as 513N4, T
Inorganic carbides such as iC and SiC, and mixtures thereof,
A composite compound such as Al-Ta-0 is used. The protective layer is formed for the purpose of preventing moisture permeation, reducing noise by reducing reflectance due to interference effects, and preventing wear and tear caused by physical contact (sliding) with the flying head. In order to obtain sufficient interference effect, the refractive index n should be 1.4~
2.5, and in order to improve wear resistance, a Vickers hardness of 1000 kg/mm2 or more is suitable. The film thickness is preferably about 100 to 200 OA. [00101] A feature of the present invention is that a lubricating layer consisting of a dense layer mainly composed of a polymerized perfluoropolyether having isocyanate groups as terminal groups is provided on the surface of the protective layer. A perfluoroether having an isocyanate group at a terminal group has, for example, a skeleton structure represented by the following general formula. [0011] or [0012] The isocyanate group is bonded to the terminal end of the above-mentioned skeleton structure, for example, via a urethane bond or an amide bond. Furthermore, in order to increase the reactivity of the isocyanate group, it is also possible to use an isocyanate group directly connected to a benzene ring by acting on a tolylene diisocyanate group or the like. The average molecular weight of the perfluoroether having an isocyanate group at the end group synthesized in this way is preferably about 1,000 to 10,000. When the molecular weight is larger than this, the ratio of isocyanate groups to the perfluoroether skeleton decreases, making it difficult to cause sufficient polymerization. [0013] In order to control the reaction of the isocyanate groups and make the polymerization more satisfactory, it is effective to form a lubricating layer by the following manufacturing method. That is, this is a manufacturing method in which a coating solution containing a perfluoroether having an isocyanate group blocked by a blocking agent as a terminal group is applied, the blocking agent is then dissociated, and the isocyanate group is polymerized. [0014] Any compound may be used as the blocking agent as long as it binds to isocyanate groups but dissociates upon heating to generate isocyanate groups again. However, if the temperature for dissociation is high, There is a risk that the fluoropolyether itself will be decomposed. Therefore, monofunctional blocking agents used in the production of ordinary blocked isocyanates, ie, alcohols, phenols, lactams, oximes, etc., are used as blocking agents. Examples of alcohols include isopropyl alcohol, t-butyl alcohol, cumyl alcohol, and the like. Examples of phenols include phenol, cresol, xylenol, alkylphenol, nitrophenol, halogenated phenol, and the like. [0015] Examples of lactams include ε-caprolactam, 6-valerolactam, γ-butyrolactam, β-
Examples include propiolactam. Examples of oximes include formamide oxime, methyl ethyl ketoxime, acetaldoxime, acetoxime, diacetylmonoxime, cyclohexanone oxime, benzophenone oxime, and the like. Among these, particularly preferred blocking agents are methyl ethyl ketoxime, phenol, and cresol because their dissociation temperature is not too high and they are easy to handle. [0016] The above-mentioned perfluoropolyether having a blocked isocyanate group as a terminal group is dissolved and diluted in an appropriate solvent such as Freon 113 and used as a coating liquid. [0017] The method of applying the coating liquid to the surface of the protective layer is as follows:
A spin code method, a dipping method, a spray method, a wipe method, etc. can be employed as appropriate. The amount of coating is not particularly limited, but from the viewpoint of lubricating performance, the thickness of the perfluoropolyether having a blocked isocyanate group as a terminal group is preferably 2OA or more. The blocking agent can be easily dissociated by heat treatment at a temperature appropriately selected depending on the type of blocking agent, according to a conventional method. [0018] Note that the dissociated blocking agent is preferably volatilized and removed from the system, but a part of it may remain in the system as long as it does not significantly inhibit the polymerization of isocyanate groups. do not have. Due to the dissociation of the blocking agent, the isocyanate groups absorb moisture in the air and cause a polymerization reaction (self-curing) called moisture curing to form a dense layer. [0019] A second protective layer may be provided between the disk substrate and the magneto-optical recording layer. The second protective layer is SiO
2. Metal oxides such as A1203, Ta205, Tio2, metal nitrides such as 513N4, TiC, Si
Inorganic carbides such as C, and mixtures thereof, Al-Ta
A complex compound such as -0 is used. The second protective layer is formed for the purpose of preventing moisture permeation from the disk substrate. [00201 A reflective layer may be provided together with the magneto-optical recording layer and the protective layer. The reflective layer may be made of any material as long as it has a high reflectance, but since Au, Ag, and Pt are expensive and Cu is prone to corrosion, a thin film of AI or A1 alloy is preferable. Especially for AI, Ta, Ti, Zr, V, Pt, M
An alloy to which 15 at% or less of O, Cr, Pd, etc. is added provides good characteristics in both the C/N ratio and sensitivity. The thickness of the reflective layer is preferably 250 to 500. The reflective layer is provided between the magneto-optical recording layer and the protective layer, but in the case of the air-injected method, the reflective layer is provided between the magneto-optical recording layer and the disk substrate (or the second protective layer if there is a second protective layer). provided in between. [0021] An interference layer may be provided between the reflective layer and the magneto-optical recording layer for the purpose of lowering the reflectance and noise by utilizing the interference effect. The interference layer is S iO:: , A h
Metal oxides such as 03, Ta205, TiC2 and Si
: Metal nitrides such as +N4, inorganic carbides such as TiC and SiC, mixtures thereof, and composite compounds such as Al-Ta-0 are used. The film thickness is preferably 50 to 500 mm. [0022]

According to the present invention as described above, a magneto-optical medium which is mainly composed of perfluoroether and has a dense layer that exhibits good lubrication properties with a small frictional force between it and a floating magnetic head, especially an air-in A magneto-optical recording medium is provided which exhibits sufficient recording and reproducing characteristics using the Shibushito method. [0023]

EXAMPLES The present invention will be explained in detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. [0024] Example 1 (a) A perfluoropolyether having an isocyanate group as a terminal group (trade name DISOC, manufactured by Enmonte) was blocked with methyl ethyl ketoxime. The reaction was carried out at room temperature using an excess of methyl ethyl ketoxime (equivalent ratio 1.2). [0025] 2 g of the above reactant was added to 1 liter of Freon 1
13 to prepare a coating solution. [0026] (b) Sputter silicon nitride onto a 2P glass substrate at 700A, Tbz: +Fe59CO
s to 1000A, and silicon nitride to 100OA.
The above coating solution was applied on a magneto-optical recording disk with a diameter of 5.25 inches, which had been prepared for 130 days.
C. for 20 minutes to dissociate and volatilize the blocking agent, and to sufficiently cure the isocyanate groups with moisture. [0027] When a contact start/stop (hereinafter abbreviated as C8S) test was conducted to check durability using a floating magnetic head, the initial coefficient of dynamic friction was 0°2, and after 5000 cycles of C3S, it was 0. It was 4. [0028] Also, when this disc was recorded and played back using the air incident method, the bit length was 0. 8
A C/N ratio of 48 dB was obtained in μm, and no influence of the lubricant layer was observed. Note that this measurement was performed using light modulation recording with a transparent glass substrate attached to the lubricant side. Comparative example 1
A C8S test was conducted in the same manner as in Example 1 using a disk similar to Example 1 but without a lubricating layer. The initial dynamic friction coefficient was 1.3, and after 17 C3S tests, the C8S test was stopped due to overload.

[Procedural amendment]

[Submission date] February 12, 1991

[Procedural amendment 1]

[Name of item to be amended] Specification

[Correction target item name] 0004 [Correction method] Change

[Correction details]

[0004] Further, in the magnetic field modulation method using the above-mentioned floating magnetic head, recording and reproduction cannot be performed from both sides. Therefore, a method (hereinafter sometimes referred to as the air incident method) has been proposed that allows recording and reproduction from both sides by incorporating an optical head into a floating magnetic head and injecting laser light from the floating magnetic head side. . (EP
341829). In this method, an overcoat layer having a thickness of several tens of micrometers cannot be used due to problems such as interference and scattering of laser light.

Claims (1)

[Claims] 1. A magneto-optical recording medium used in a magneto-optical recording method for recording and reproducing using a floating magnetic head, which comprises forming at least a magneto-optical recording layer, a protective layer, and a lubricant layer on a disk substrate. 1. A magneto-optical recording medium characterized in that the lubricating layer consists of a layer mainly composed of a polymer obtained by polymerizing perfluoropolyether having an isocyanate group at the end.