JPH01102721A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain good head touch by forming a thin film layer having a tensile stress on the 2nd face of a magnetic recording medium formed with an alloy film essentially consisting of Co-Cr on the 1st face of a nonmagnetic base body when the coefft. of thermal expansion of the nonmagnetic base body is smaller than the coefft. of thermal expansion of the alloy film essentially consisting of the Co-Cr. CONSTITUTION:The curling generated in the magnetic recording medium is offset by forming the film 3 having the absolute value of the tensile stress about equal to or larger than the tensile stress of the Co-Cr alloy 2, for example, by forming an inexpensive metal, etc., as a thin film on the opposite side. The recording medium is, therefore, formed thinner as a whole as compared to the dummy formed with the Co-Cr alloys on both faces. The perpendicular magnetic recording medium which is decreased in the rigidity of the medium and has the good head touch is thereby obtd. at the low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to perpendicular magnetic recording media, particularly Go-Cr.
This invention relates to a disc-shaped magnetic recording medium mainly made of alloy.

[Summary of the Disclosure] The present specification and drawings describe a perpendicular magnetic recording medium in which an alloy film mainly composed of Go-Cr is formed on the first surface of a non-magnetic substrate, and the second surface has tensile stress. The present invention discloses a technique for realizing a perpendicular magnetic recording medium that is thin and has low rigidity as a whole and has good head touch by forming a film layer to offset curl.

[Prior art] Perpendicular magnetic recording can dramatically improve recording density compared to the current longitudinal magnetic recording, and in recent years C
Research on perpendicular magnetic recording media centered on o-Cr alloys is being actively conducted. The current general manufacturing method for perpendicular magnetic recording media is sputtering, vacuum deposition, etc. on a base film (e.g., polyester, polyimide, polyamide, polysulfone, etc.).
0% Go-Car alloy film is produced.

However, when forming a film by sputtering or the like, a large amount of heat is applied to the base film, causing thermal expansion of the base film. In addition, in order to improve the magnetic properties of the Go-Cr alloy film, the film is sometimes heat-treated, and as a result,
Similarly, the base film undergoes thermal expansion.

As shown in FIG. 3, C
When the o-Cr alloy film 2 is produced, if the respective thermal expansion coefficients are αfilIl+αCo-Cr, and this relationship is αfi1m<αCo-Cr, sputtering etc. are performed while heating to produce the Go-Cr alloy film. When it is then cooled, the Co--Cr alloy layer shrinks significantly and curves upward in the figure as shown in FIG. 4, resulting in a so-called curled state. When this kind of curl occurs, magnetic recording media such as magnetic tapes suffer from problems such as poor running performance, irregular winding, and poor head touch, and recording media such as magnetic sheets have the drawback of being completely unusable. . Conventionally, as shown in FIG. 5, a fully flexural thin film layer 5 of the same material and thickness is formed on the other side of the polymer film base to prevent this curling.

[Problems to be Solved by the Invention] However, when a Co-Cr alloy film is formed on both the front and back surfaces, the total thickness increases and the rigidity increases, resulting in a problem that it becomes difficult to obtain a good head touch. produce a point. This tendency is especially true when the base film is relatively thick.

Further, since the Go-Cr target is expensive, it is disadvantageous in terms of cost to form a dummy thin film layer thereof on the back surface. Therefore, if a similar effect could be obtained by forming a thin film on the back surface using a thinner and cheaper material, it would be possible to
It can be said that this greatly contributes to lowering the overall cost of -Cr perpendicular magnetic recording media.

The present invention has been made in view of the above-mentioned viewpoint, and an object of the present invention is to provide a Co--Cr perpendicular magnetic recording medium that provides good head touch at a low cost.

[Means for Solving the Problems] The present invention provides a magnetic recording medium in which an alloy film mainly composed of Co--Cr is formed on the first surface of a non-magnetic base, in which the coefficient of thermal expansion of the non-magnetic base is Co. A thin film layer having tensile stress is formed on the second surface when the coefficient of thermal expansion is smaller than that of the alloy film whose main component is -Cr.

[Function] The present invention will be explained in more detail using FIG. 1, which is a schematic diagram thereof. In Figure 1, l is the base film, 2
3 is a Go-Cr alloy film, and 3 is a thin film layer having a tensile stress of an absolute value equal to or higher than that of the Go-Cr alloy film.

Base film l is less than 100 gra, 2 Go-C
In the present invention, the preferred thickness of the r-alloy film is 0.1 gm or more and 2 ILm or less.

Here, the thermal expansion coefficient of the Co-Cr alloy film is 1.1×1O
-5ca+2/'C, so the thermal expansion coefficient of the base film is a fil,<1. I x 10-5cm2
/'O causes the curl state described above. Therefore, by forming a thin film layer on the opposite side of the Go-Cr alloy film having a tensile stress of the same magnitude or greater in absolute value than the Go-Cr alloy film, the curl is offset. This thin film layer with tensile stress is made of, for example, Aρ, Sn, Cu,
In addition to total bending materials such as Zn and alloys containing them as main components, Se.

Metalloids such as Te can be used. These thin film layers are formed by a method such as vacuum deposition.

The thickness of the thin film layer 3 having this tensile stress is appropriately selected,
By forming on the back surface of the Go-Cr alloy film 2, Go
The curl of the magnetic recording medium due to the difference in thermal expansion coefficient between the -Cr alloy film 2 and the base film 1 can be offset. In general, the use of a film with a larger coefficient of thermal expansion α means that curl can be offset with a thinner film and the effect of reducing rigidity can be expected, and the economic benefits are also large.

Furthermore, as shown in Fig. 2, even when a high permeability metal thin film layer such as permalloy is provided between the Go-Cr alloy film and the base film, a film 3 with tensile stress is formed on one side. By doing this, you can offset the curl.

[Examples] The present invention will be described in more detail based on Examples below.

Example 1 Thermal expansion coefficient 0.8 x 1 (15 cm2/℃ thickness 50
Film thickness 0.5 p-ta on polyimide film of gm
A Go-Cr alloy film was formed by sputtering.

The Cr composition is 20%, and the sputtering method is an RF magnetron method. The magnetic properties are Ht = 900 oersted, 4
πMs=4.5KG. In the state where the Co--Cr alloy film was formed on one side, extremely large curls were observed with the Co--Cr alloy film on the inside. When a metal film of Ai) was sputtered on the surface, a flat medium with a film thickness of 0.35 ILm was obtained. If the Aβ metal film is thinner than this, the curl will not be removed sufficiently, and if it is thicker than this, excessive correction will occur.

Example 2 Similarly to Example 1, an AP gold film was formed on the back side of a base film having a Co--Cr alloy film formed on one side by vacuum evaporation. Curl was offset when the APP metal film was 0.22 gm. Even though they are made of the same material, films formed by sputtering and vacuum evaporation have different film stresses, and in general, the film stress tends to be more tensile in the case of vacuum evaporation. Therefore, it can be said that the vacuum evaporation method is more advantageous for forming the thin film layer having tensile stress according to the present invention.

Example 3 Coefficient of thermal expansion 2. OX 10-5cm2/”0 and thickness 30
Go-Cr alloy film 0 on JLm polyamide film
．． 3 pm was formed by sputtering. As a result, extremely large curls were generated with the Co--Cr alloy film inside. When a Se metal film was formed on the back surface by vacuum evaporation, the curl was canceled out with a thickness of 0.18 gm.

The film 3 having tensile stress is not limited to the above embodiment as long as it has an absolute value of tensile stress equal to or greater than that of the Go-Cr alloy film 2.

[Effects of the Invention] As explained above, the present invention prevents curling that occurs in a magnetic recording medium by using a film having an absolute value of tensile stress equal to or greater than that of a Co-Cr alloy, such as an inexpensive metal. This is offset by forming a thin film on the side surface.

Therefore, compared to a dummy Co-Cr alloy film formed on both sides, the perpendicular magnetic recording medium is thinner as a whole, and as a result, the rigidity of the medium is kept low and the head touch is good.
It has the excellent effect of being able to be supplied at low cost.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of the basic configuration of the present invention,
Fig. 3 is an explanatory diagram immediately after forming a Co-Cr alloy film on one side only, Fig. 4 is an explanatory diagram of the curled state after the Co-Cr alloy film is formed and left to cool to room temperature, and Fig. 5 is an explanatory diagram of the curled state after the Co-Cr alloy film is formed. C on both sides
FIG. 3 is a diagram showing a conventional example in which an o-Cr alloy film is formed. l...Nonmagnetic substrate, 2...Go-Cr alloy layer, 3...
...Thin film layer with tensile stress, 4...High magnetic permeability metal thin film layer, 5...Total refraction thin film layer.

Claims (4)

[Claims] (1) In a magnetic recording medium in which an alloy film mainly composed of Co-Cr is formed on the first surface of a non-magnetic base, the coefficient of thermal expansion of the non-magnetic base is the same as that of the alloy mainly composed of Co-Cr. A perpendicular magnetic recording medium characterized in that a thin film layer having a tensile stress is formed on the second surface when the coefficient of expansion is smaller than the coefficient of expansion. (2) The perpendicular magnetic recording medium according to claim 1, wherein the thin film formed on the second surface is a vacuum-deposited metal film. (3) Claims characterized in that a magnetic film with high magnetic permeability is added as an underlayer between the alloy film on the first surface containing Co and Cr as main components and the non-magnetic substrate. 2. The perpendicular magnetic recording medium according to item 1. (4) The perpendicular magnetic recording medium according to claim 3, wherein the thin film formed on the second surface is a vacuum-deposited metal film.