JPS63188818A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain excellent durability and electromagnetic conversion characteristic by using a heat-resistant base film which is limited in the width of the height distribution of fine productions on the surface for a perpendicular magnetic recording medium consisting of Co base such as Co-Cr alloy. CONSTITUTION:A polyimide film of 9mum thickness consisting of an acid dianhydride component and SiO2 particles having 450A average grain size is formed. And a perpendicularly magnetized film consisting of 79wt.% Co and 21wt.% Cr is deposited by evaporation to 0.4mum thereon, by which the film is formed. A Co oxide film is sputtered to 120Angstrom as a protective layer on said film and a back coating layer of about 0.5mum incorporated with carbon particles in a polyester binder is formed on the rear face. The fine projections on the film surface at this time are 10<5>-10<8> pieces per mm<2> in average and the height distribution of said projections is specified to H0.1<600Angstrom , H1>120Angstrom , H10>100Angstrom and is determined to satisfy (H1-H10)<200Angstrom when the projection heights corresponding to 0.1%, 1% and 10% in order of the larger heights are designated as H0.1, H1, H10. The recording medium having the excellent durability and electromagnetic conversion characteristic is thereby obtd.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a CO-based perpendicular magnetic recording medium such as a Co-0r alloy, and in particular to heat resistance with a limited height distribution width of fine protrusions on the surface. The present invention relates to a perpendicular magnetic recording medium that uses E film and has both durability and electromagnetic conversion characteristics.

[Prior Art] A magnetic recording medium in which a ferromagnetic metal thin film, a ferromagnetic oxide thin film, or a ferromagnetic nitride thin film is formed as a magnetic recording layer has excellent characteristics for high-density recording. An example is Co film.

Co-Ni film, Co-Cr film, Co oxide film, B
Examples include a-7x light film. These thin films are formed by thin film deposition methods such as vacuum evaporation, sputtering, and ion blating, which have excellent productivity and controllability of properties.

Although magnetic recording media using these thin film deposition methods have excellent electromagnetic properties, their running durability is significantly inferior to coated media, and it can be said that they have not yet reached the level of practical use. In particular, Co
There is much room for research regarding the practical durability of -Cr alloy thin film media.

In order to improve the running durability of these Co-based gold metal magnetic thin film media, the following two methods have been studied.

The first is research in the direction of modifying the surface of the magnetic layer.
Broadly speaking, there are two types: those that provide a protective film function and those that provide a lubricating function, and each type has its own characteristics in terms of materials and processes.

The second direction is to finely roughen the surface of the magnetic layer.

By providing extremely small protrusions and wrinkles on the surface of the magnetic layer, durability is significantly improved compared to a simple smooth surface. In any case, these techniques result in an increase in spacing loss, so advanced techniques are required to improve durability while maintaining the excellent electromagnetic conversion characteristics of metal magnetic thin films.

[Problems to be Solved by the Invention] In the process of investigating the practical use of flexible media (tape, floppy disc, etc.) using a Co-Cr alloy perpendicular magnetization film in the second method, the inventors discovered the following. We found the following problems. That is, as is conventionally known, in order to improve the magnetic properties of Co-Cr alloys, the substrate is heated during the formation of the magnetic layer. Therefore, the substrate is made of polyimide film, polyamide film, polyimide amide film, or polyetherimide film. , use a heat-resistant plastic film such as polysulfone film. When the surface of these heat-resistant films is roughened and a Co-Cr alloy thin film is formed by, for example, sputtering, the thickness of the magnetic recording layer is very thin compared to conventional coating-type magnetic recording media. The surface becomes a rough surface reflecting the unevenness of the base film surface. These roughened films greatly contribute to the running stability of the medium.

The present inventors mixed various protrusion-forming particles mainly composed of inorganic fine particles into a polyimide film to make a prototype film, then formed a Co--Cr alloy magnetic layer by sputtering, and evaluated the media function. The fine particles used were 5i
02. TiO2, ZrO2, etc., and the particle size is 10
The particle size is 0 to 100 OA, and particles exist singly or in agglomerated form. As a result, it was found that the following problems occur if the unevenness height distribution on the medium surface is not sufficiently controlled.

(1) When there are protrusions of various heights, in the sense of defining the state of contact with the head, the protrusions that actually function are the highest among them, and most of the protrusions do not function effectively.

(2) As a result of (1) above, the height of the protrusion that is effectively functioning cannot be controlled, and the spacing between the medium and the head varies depending on the location. Therefore, the electromagnetic conversion characteristics vary.

(3) As the protrusion that functions effectively is the highest part of the protrusion, the load is concentrated there and the protrusion is chipped.

These problems are serious deficiencies in realizing a Co--Cr alloy thin film medium as a heat-resistant film.

The present invention eliminates the above-mentioned problems of the conventional method by limiting the height and distribution of fine irregularities on the surface of a polyimide film. That is, one object of the present invention is to provide a CO-based alloy perpendicular magnetic recording medium that is excellent in both electromagnetic characteristics and running durability.

[Means for Solving the Problems] and [B] According to the present invention, the number of fine protrusions on the surface is 105 to 108 on average.
mm2, and when the statistical distribution of the heights of microprotrusions is taken, the highest values are 0.1% and 1%.

Letting the protrusion height corresponding to 10% be Hal, Hl, H+o, H(0.1)<600 Å and H1>12OA and HIO>10)>100 Å and H+ −H+o <
A magnetic recording medium is provided in which a ferromagnetic thin film is formed on a polyimide base film, which is characterized by having a diameter of 20 OA.

Polyimide film is produced by polymerizing diamine and acid dianhydride.
The polyimide used in the present invention is polyphenylene diamine (hereinafter abbreviated as PPD) with a diamine component of 30 mol% or more and diaminodiphenyl ether (hereinafter abbreviated as DADE) with a diamine component of 0 to 70 mol%. ), and the acid dianhydride component is biphenyltetracarboxylic dianhydride (hereinafter abbreviated as BPDA).
and pyromellitic dianhydride (hereinafter abbreviated as PMDA).The reason is that PP []
, DADE.

A polyimide film consisting of three or four components of BPDA and PMDA has a thermal expansion coefficient of 1.0 to 3 and an O
X 1O-5c+++/c+a/"0, which is close to the coefficient of thermal expansion of the magnetic recording layer formed on this film. Therefore, thermal stress during formation of the magnetic recording layer or changes in environmental temperature A polyimide film with an appropriate thermal expansion coefficient is used to alleviate the accompanying warping of the medium.
It is possible to select by changing the blending ratio of the three or four components, and it is possible to manufacture a magnetic recording medium without curling.

Surface protrusions can be formed by forming fine irregularities on the casting belt and transferring these irregularities to the film surface, but it is better to disperse fine particles in the polyimide solution to control the fine irregularities. is possible. Heat-resistant films such as polyimide and polyamide are formed by a casting method, so it is possible to mix protrusion-forming particles into raw materials in a solution state before forming the film (injection method), or to add protrusion-forming particles after forming the film. The fine particles of the present invention include oxides of elements No. n, m, rv of the periodic table and other transition metal elements, They are inorganic particles made of nitrides, carbides, salts, and simple elements. Specifically, MgO, ZnO, Ajl'
203,5i02. Ti0z, Tie, ZrN.

VN, Sin, Tie, NbC, MO2C, WC
, MgCO3, CaCO3゜Ca5On, BaSO4
, Cu, Ag, Au, Zr1. AI2. Fe
, Co.

Old, W, carbon black, etc. Furthermore, there are compounds, alloys, etc. of these, and the surfaces of these inorganic particles may be surface-treated with organic groups.

Alternatively, a mixture of multiple types may be used.

The size of these fine particles is 100 to 100)>
It is preferable that particles of 100 Å are present singly or in agglomerated form.

Furthermore, the surface of the film of the present invention has a fine protrusion height of 5
0 to 60)>100 Å. 5) If the thickness is less than 100 Å, the slipperiness will decrease and a large number of scratches will occur during the production of recording media and the process of processing into tapes or sheets. Furthermore, when using a tape or sheet, running properties become poor, the magnetic layer is scraped by the head, causing dropouts, and durability is significantly reduced. on the other hand,
60) If it is higher than 100 Å, there will be a spacing loss between the media and the head, which will reduce the output and increase dropout.

In addition, the average number of microprotrusions is 105 to 1 m+++2.
It is necessary that 108 items exist. 105 pieces/mm2
If it is less than this, the slipperiness of the film decreases, and the runnability and durability at the time of manufacturing the recording medium or after forming the recording medium deteriorate.

On the other hand, if it exceeds 108 particles/mm2, the amount of particles mixed becomes excessive, causing agglomeration of particles and the formation of coarse protrusions.

Furthermore, in order to improve durability, the height of the protrusions must not be too low and the heads of the protrusions must be aligned. That is,
Take the statistical distribution of protrusion height and calculate 1% and 10% from the highest.
Let Ht l HIO be the height of the protrusion corresponding to , respectively. It is thought that the cause is abrasion powder when the insulating protrusion whose values of Hl and HIO are close to each other is shaved.

The CO-based alloy perpendicular magnetic recording medium using the polyimide base film having the above structure has very small spacing loss between the medium and the head, and has excellent electromagnetic conversion characteristics and running durability.

The magnetic recording layer formed on the polyimide film is F
A ferromagnetic alloy film whose main components are e, Co, and old.

It is a ferromagnetic oxide film or a ferromagnetic nitride film.

These magnetic recording layers are formed by a physical vapor deposition method such as a vacuum evaporation method, an ion blasting method, a sputtering method, or a plating method.

Among them, Co-Cr formed by vacuum evaporation or sputtering and consisting of 15 to 23 wt% Cr and the balance Co.
Perpendicular magnetization films are extremely superior to conventional in-plane magnetization media for high-density recording.

Below these magnetic recording layers, thin films such as Aj), Ge, Cr, Ti, 5i02, etc., and perpendicularly magnetized films are used to improve adhesion with the base film, improve crystal orientation, and improve magnetic properties. Fe-Ni film as backing layer.

A high magnetic permeability layer such as a Co--Zr film may also be provided.

Further, a metal thin film may be provided on the back surface of the base for the purpose of mitigating curl.

Further, on the magnetic recording layer, an inorganic protective layer such as AIhO3, SiO2, Si3N4゜No.

An organic lubricating layer such as fatty acid ester or stearic acid may be formed. In the case of the Co--Cr film, the Co oxide layer and the fluororesin lubricating layer are effective in improving durability and reducing friction.

Further, a suitable back coat layer may be formed on the back surface of the base film.

[Example] Hereinafter, the present invention will be described in detail based on examples.

Example 1 Diamine component consisting of 80 mol% PPD, 20 mol% DADE, 70 mol% BPDA, PMDA
A polyimide film with a thickness of 9B was produced using as raw materials an acid dianhydride component consisting of 30 mol % and Si02 particles with an average particle size of inorganic fine particles of 45)>100 Å. When filling the microparticles, an appropriate dispersant was mixed to prevent agglomeration of the microparticles and reduce the number of coarse protrusions. The thermal expansion coefficient of this polyimide film is 9 x lo-5cm/c+w/
'C, tensile strength constant was 830 Kg/mm2.

G containing 79 wt% Co and 21 wt% Cr was deposited on this polyimide film using an electron beam heating continuous evaporation apparatus.

-Cr perpendicular magnetization film deposition rate 0.2 gm/n+in
0.4 gm was formed. The magnetic properties are 4 πMs=4
800 Gauss.

Hc” = 12000c, Hc# = 7000c.

Furthermore, a 12OA CO oxide film was formed as a protective layer on the Co-Cr film by a reactive sputtering method, and on the back side of the base film, a back coat layer containing carbon particles in a polyester binder was formed to a thickness of about 0.5 g.
8III! It was cut to I width. Note that an organic lubricant layer such as a fluororesin or fatty acid ester may be further provided on the protective layer.

The surface roughness of the manufactured Co-Cr alloy thin film magnetic tape was measured by a shadowing method. Because the number of protrusions formed is extremely low, numbering in the hundreds, and the density is dense, shadowing methods used conventionally such as Talystep, etc.
As shown in Figure 1, ha-Pd and low acceleration FE-
This method involves observing the length of the shadow using a high-resolution electron microscope such as 5EM. If the deposition incident angle θ is 85° and the Au and Pd film thicknesses are 1)>100 Å, the height of each protrusion can be measured with an accuracy of ±8%.

FIG. 2 shows the protrusion height distribution on the surface of the magnetic tape of this example measured in this manner. The FE-SEM used was Hitachi S-800. When the surface of the polyimide base film was measured using a similar method, it was found that the distribution of protrusion heights hardly changed before and after the formation of the Co--Cr magnetic layer.

Example 2 On a polyimide film with the same composition as in Example 1, inorganic fine particles average particle size 45)>1 in a polyimide solution with the same composition.
A polyimide film having a total thickness of 9 g+a was fabricated by coating with sufficiently well-dispersed 5i02 of 00 Å. The thermal expansion coefficient, tensile elastic constant, etc. of this polyimide film are the same as in Example 1.

The methods for forming the Co-Cr alloy magnetic layer, Co oxide protective layer, back coat layer, etc. on this polyimide film were the same as in Example 1.

FIG. 3 shows the results of measuring the surface roughness of the magnetic tape of this example by the shadowing method. Compared to Example 1, the inorganic fine particles were well dispersed and the number of high protrusions was reduced. Moreover, the value of HO,l −HIO is also small. It can be said that the state of the surface unevenness of the tape is very close to the gist of the present invention.

Comparative Example 1 A polyimide film having the same composition as in Example 1 and having a thickness of 9 μm was manufactured. This film does not contain 5i02 particles. Other conditions were the same as in Example 1.

FIG. 4 shows the results of measuring the surface roughness of the magnetic tape of this comparative example by the shadowing method. These tape protrusions are mainly caused by defects such as scratches and dust on the film surface. Therefore, the distribution of protrusions also varies depending on the location.

Comparative Example 2 TiO2 particles with inorganic fine particles having irregular particle sizes were dispersed in a polyimide solution having the same composition as in Example 1, and a thickness of 9B was obtained.
polyimide film with an average particle size of 100-50)>10
Manufactured at 0 Å. When the fine particles were loaded inside, the dispersion state was not very good. A magnetic tape was produced under the same conditions as in Example 1.

FIG. 5 shows the results of measuring the surface roughness of the magnetic tape of this comparative example by the shadowing method. The diameter of the filler particles is that of Example 1.
Alternatively, although the protrusions are smaller than those in Example 2, the protrusion heights are distributed even higher. In other words, it can be said that the agglomeration of the filler particles progresses, resulting in a base film with many aggregates. This was also confirmed by surface observation using SEX.

Next, each of the above magnetic tapes was evaluated using an 8 mm format video deck manufactured by Ichisaka. The evaluation items are brightness signal output,
There are three points: still durability life and repeated durability. The results are shown in Table 1. As a result of the evaluation, the following points became clear.

0.1% from the highest of the total number of protrusions on the magnetic tape surface
corresponds to In addition, the protrusion height by the shadowing method is H
If the protrusion height corresponding to O, l, 1% is Hl, and the protrusion height corresponding to 10% is HIO, then the protrusion height distribution curve is f (h), J':, , f (h) dh/Jc:f(h)dh=
It is expressed in 0.001 Haku.

^ (1) The luminance signal output is dominated by the spacing loss caused by HO, I or even larger protrusions.

Therefore, when HO,l is large, the spacing loss is too large and the original performance of the Co-Cr perpendicular magnetization film cannot be utilized, that is, Ho, + < 800 A, more preferably Ho, + < 350 A. It must be.

(2) The still durability life will be improved if the number of protrusions is large and the heads are aligned. This is presumed to be because the load on the head is distributed and wear and tear on the medium is reduced. Also, the protrusion should not be too low. Possible reasons for this are that as wear progresses, the protrusions are low and therefore disappear, resulting in increased wear, or that there is no room for abrasion powder to accumulate.

The number of protrusions is required to be 105/mm2 or more. The heads of the protrusions are aligned, that is, HO, I.

This means that the values of Hl and H'IO are close. In reality, Hl−Hlo <20OA, even better H
+-) (When to <150 A, good still durability is achieved. Also, the protrusion height is HIO>100
A: It is necessary. In the case of still playback, coarse protrusions with a low probability of existence are quickly scraped off, so protrusions with a height near HIO function effectively.

(3) In the case of repeated playback, the protrusions with a height around H1 function effectively. Good repeated durability is Hl>
120 A, even better Hl > 18) > 100 Å
1 is given in

〔Effect of the invention〕

As explained above, according to the present invention, fine protrusions are formed on a polyimide film, the height of the fine protrusions is 5Q to 800 A, and the protrusion density is 105 to 800 A by the shadowing method.
There are 108 pieces/mm2, and if the protrusion heights corresponding to 0.1%, 1%, and 10% from the highest when taking the protrusion height distribution are Ho and 1*Hl + HIO, respectively,
Ha, 1 < 80 OA and Ht > 12) > 100 Å and HIG > 10) > 100 Å and Hl-HIG < 2
00 Co-
A magnetic recording medium having excellent electromagnetic conversion characteristics and running durability can be obtained by forming a directly magnetized film of a Co-based alloy such as a Cr alloy by vacuum evaporation, sputtering, etc. and using it as a magnetic recording medium.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the principle of the shadowing method, and FIGS. 2 to 5 are height distribution diagrams of the magnetic tape surface in Examples and Comparative Examples. l... Evaporation source, 2... Sample (9 sources), Ha,
,...Protrusion height corresponding to 0.1% from the highest in the protrusion distribution, Hl...Protrusion height corresponding to 1% from the highest in the protrusion distribution, HIG...Protrusion height from the highest in the protrusion distribution Protrusion height equivalent to 10%.

Claims (3)

[Claims] (1) A magnetic recording medium in which a ferromagnetic thin film is formed on a base film by a thin film deposition method, in which the surface of the base film has an average of 10^5 to 10 microprotrusions per 1 mm^2.
There are 8 microprotrusions, and in the statistical distribution of the heights of the microprotrusions, the protrusion heights corresponding to 0.1%, 1%, and 10% from the highest are respectively H_(0.1), H_1, and H_( 10)
Then, H_(0.1)<600Å and H_1>1
20 Å and H_(10)>100 Å and H_1-H_(
10) A magnetic recording medium characterized in that <200 Å. (2) The base film contains an aromatic diamine component consisting of at least 30 mol% or more of paraphenylene diamine and 0 to 70 mol% of diaminodiphenyl ether, biphenyltetracarboxylic dianhydride and The magnetism according to claim 1, characterized in that it is made of a polyimide formed from an aromatic polyamic acid solution obtained by copolymerizing a tetracarboxylic acid component consisting of pyromellitic dianhydride. recoding media. (3) At least one layer of the magnetic recording layer is a Co-Cr layer alloy film, and a Co oxide layer is provided on the Co-Cr alloy film, according to claim 1 or 2. The magnetic recording medium described.