JPH0240130A - perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium having excellent electromagnetic conversion characteristics and traveling durability by forming many fine protrusions on the surface of magnetic recording layer side to have a density of 10<5>-10<4>/mm<2> and specifying the height range of protrusions. CONSTITUTION:Fine protrusions are provided on the surface of magnetic recording layer side of the medium with a density of 10<5>-10<7> per 1mm<2>. Also the statistical distribution of the protrusion height is specified that H0.01, H0.1, H1 which correspond to 0.01%, 0.1%, 1% of the total protrusion from the maximum, respectively, satisfy H0.01<=600Angstrom , H0.1>=200Angstrom , H1>=150Angstrom and H0.1-H1<=150Angstrom . Thereby, the obtained magnetic medium has excellent durability and electromagnetic conversion characteristics.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a perpendicular magnetic recording medium, and in particular, the present invention relates to a perpendicular magnetic recording medium, and in particular, the present invention relates to a perpendicular magnetic recording medium, and in particular, to improve durability and excellent electromagnetic conversion characteristics by limiting the height distribution of fine protrusions on the surface of a magnetic recording layer. The present invention relates to a perpendicular magnetic recording medium that has the following functions.

[Prior Art] A magnetic recording medium in which a ferromagnetic metal thin film 9, 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 of this is CO membranes.

Go-Ni film, Go-Or film, Goo compound film, Ba7
Examples include z-light film. These thin films are highly productive.

It is formed by thin film deposition methods such as vacuum evaporation, sputtering, and ion blating, which have excellent controllability of characteristics.

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, Go
There is much room for research regarding the practical durability of -Or alloy thin film media.

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

First, research into modifying the surface of the magnetic recording layer can be broadly divided into cases in which a protective function is imparted and cases in which a lubricating function is imparted, and each type has its own characteristics in terms of materials and processes.

The second is research into finely roughening the surface of the magnetic recording layer. By providing extremely small protrusions and wrinkles on the surface of the magnetic recording 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.

[Problem to be Solved by the Invention] In the process of investigating the practical use of flexible media (tape, floppy disk, etc.) using a co-C:r 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 a Co--Cr alloy, substrate heating is performed when forming a magnetic recording layer. Therefore, a heat-resistant plastic film such as polyimide film, polyamide film, polyimide amide film, polyetherimide film, polysulfone film, etc. is used as the substrate.

When the surface of these heat-resistant films is roughened and a Go-Cr alloy thin film is formed by, for example, sputtering, the thickness of the magnetic recording layer is extremely 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 consisting mainly of inorganic fine particles into the above-mentioned plastic film to make a prototype film, then formed a Go-Cr alloy magnetic layer by sputtering and evaluated the media function. . The fine particles used were 5i02. It is TiO2゜ZrO2, etc., and its particle size is 100 to 1000A, and the 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 Go-Or alloy thin film media with heat-resistant film supports.

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 plastic film. That is, an object of the present invention is to provide a perpendicular magnetic recording medium that is excellent in both electromagnetic conversion characteristics and running durability.

[Means for solving the problem] and [Action] The present invention has the following features:
A perpendicular magnetic recording medium in which a magnetic recording layer is formed on a support by a thin film deposition method, wherein the perpendicular magnetic recording medium has an average of 105 to 105 minute protrusions per 1 mm2 on the surface of the magnetic recording layer side.
There are 107 microprotrusions, and in the statistical distribution of the heights of the microprotrusions, the protrusion heights corresponding to 0.01%, 0.1%, and 1% from the highest are Ho, o+, Ho, ++ Hl, respectively.
When closed, Ho, 0+ ≦60OA and HO, l
≧20OA and old≧150A and HO,' l -Hl
It is characterized by being ≦15OA.

Hereinafter, the perpendicular magnetic recording medium of the present invention will be explained in detail.

The perpendicular magnetic recording medium of the present invention has a perpendicular magnetic recording layer formed on a plastic support. As the support, polyimide, polyamide, polyimideamide, polysulfone, etc. can be preferably used, and polyimide is particularly preferred from the viewpoint of heat resistance. The support used in the present invention is
A heat-resistant material with a glass transition point of 200° C. or higher is preferable.

Polyimide film is produced by polymerizing diamine and acid dianhydride.
Polyimides that are imidized and molded into a film form are preferably used in the present invention, including para-phenylene diamine (hereinafter abbreviated as PPD) with a diamine component of 30 mol % or more, more preferably 40 to 95 mol %, and 0 to 95 mol %. 70
The acid dianhydride component is biphenyltetracarboxylic dianhydride (BP
(abbreviated as DA) and pyromellitic dianhydride (hereinafter referred to as PMDA)
) is preferable. B.P.D.A.
and PMDA are each 15 to 15% of total acid dianhydride.
85 mol%, preferably 85 to 15 mol%.

A polyimide film consisting of three components (when DADE is 0%) or four components of PPD, DADE, BPDA and PMDA has a coefficient of thermal expansion of 1.0 to 3.0 x 1.
The coefficient of thermal expansion is 0-5 cm/cm/'C, which is close to the coefficient of thermal expansion of the magnetic recording layer formed on this film. Therefore, by changing the blending ratio of the three or four components, a polyimide film with an appropriate coefficient of thermal expansion is selected to alleviate thermal stress during the formation of the magnetic recording layer or warpage of the medium due to changes in environmental temperature. It is possible to produce a magnetic recording medium without curling.

In the magnetic recording medium of the present invention, a large number of fine protrusions are formed on the surface of the magnetic recording layer. These fine projections are formed by making the surface of the support body uneven.

Protrusions on the surface of the support can be formed by forming fine irregularities on a casting belt and transferring these irregularities to the film surface, but it is also possible to form protrusions on the surface of the support by dispersing fine particles in the raw material solution of the support. It is possible to control minute irregularities. Heat-resistant films such as polyimide and polyamide are formed by a casting method, so there is a method of mixing protrusion-forming particles into raw materials in a solution state before forming into a film (injection method), or a method of mixing protrusion-forming particles into a raw material after forming into a film. There is a method of applying a dilute solution containing protrusion-forming particles thereon so that the particles protrude when dried.

The fine particles used in the present invention are those listed in the Periodic Table of Elements
Preferred are oxides, nitrides, carbides, and salts of I, m, and IV group elements and other transition metal elements, as well as inorganic particles made of simple elements. Specifically, MgO, ZnO.

AI! 2Ch, 5i02. TiO2, TiN, Z
rN, VN, SiC, Tie.

NbC, MO2C, We, HgCO3, CaC0:+
, CaSO4, BaSO4, Gu, Ag, Au,
Examples include Zn, Aj), Fe, Co, old, W, and carbon black. 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 1000A.
It is preferable that the particles exist singly or in agglomerated form.

If the height of the fine protrusions formed on the surface of the support film is too low, the slipperiness will decrease and a large number of scratches will occur during the production of recording media and the process of processing them into tapes or sheets. occurs in Furthermore, when the magnetic recording medium is used, running properties deteriorate, the magnetic layer is scraped by the head, causing dropouts, and durability is significantly deteriorated. On the other hand, if the protrusion height is too high, there will be a spacing loss between the medium and the head, resulting in a decrease in output and an increase in dropout.

Furthermore, the average number of microprotrusions is 105 to 10 per mm2.
It is necessary that seven of them exist. If the number is less than 10 5 pieces/mm 2 , the slipperiness of the film decreases, and the runnability and durability during the production of the recording medium or after the recording medium is formed are deteriorated. On the other hand, if it exceeds 107 particles/mm2, the mixed amount of particles becomes excessive, causing agglomeration of particles and the formation of coarse protrusions.

Furthermore, in order to improve durability, it is necessary that the protrusions have the same height. In other words, take the statistical distribution of protrusion heights, and calculate the protrusion heights corresponding to 0.1% and 1% from the highest to H, respectively.
Assuming O, l, and Hl, it is ideal that the HO and old values are close. Actually, when IO,1-H1≦15OA,
Improves durability. Note that when HO,l-H1≧15OA, clogging of the head sometimes occurs. This is thought to be caused by abrasion powder generated when the tall protrusion was scraped.

The height distribution of the microprotrusions can be controlled by the drying conditions during film formation, the type and size of the microparticles, the presence or absence of surface treatment of the microparticles, etc.

The magnetic recording medium of the present invention was evaluated from the viewpoints of brightness signal output, methyl durability life, and repeated durability as follows.

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

Therefore, when HO and Ol are large, the spacing loss is too large and the original performance of the perpendicularly magnetized film cannot be utilized. That is, it is necessary that Ho,01≦600A, more preferably HO,O1≦35OA.

(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, 0+, HO,
l.

This means that the values of Hl are close. Actually, HO,1
-Hl≦15OA, more preferably HO,1-H1
When ≦10OA, good still durability can be obtained. In addition, the protrusion height is H1≧150 A, furthermore H1≧180
A is preferred. In the case of still playback, coarse protrusions with a low probability of existence are quickly removed, so protrusions with a height around H1 function effectively.

(3) In the case of repeated reproduction, the protrusions at heights near HO and I function effectively. Good repeated durability is HO
, l≧200 A, more preferably HO, l≧250
Obtained in A.

The magnetic recording layer formed on the support is preferably a metal thin film type, particularly a perpendicular magnetic recording layer of a ferromagnetic alloy film mainly composed of Fe, Go, or a ferromagnetic oxide film or a ferromagnetic nitride film. . These magnetic recording layers can be formed by physical vapor deposition methods such as vacuum deposition method, ion blating method, sputtering method, etc.
Alternatively, it is formed by the Metsuki method or the like.

Among these, a Cr-based magnetic recording layer formed by vacuum evaporation or sputtering, especially a Co-Cr perpendicular magnetization layer consisting of 15 to 23 wt% Cr and the balance CO, is extremely suitable for high-density recording compared to conventional in-plane magnetization media. Excellent.

At the bottom of these magnetic recording layers, Aj! ,
A thin film of Ge, Cr, Ti, 5i02, etc., or a high magnetic permeability layer such as a Fe-X1 film or a Go-Zr film may be provided as a backing layer of a perpendicularly magnetized film. Further, a thin metal film may be provided on the back surface of the support for the purpose of alleviating curl.

In addition, Aj! is added on the magnetic recording layer to improve corrosion resistance, wear resistance, and lubricity. 203.5i02. Si3N
＋.

Inorganic protective layer such as No, Ni, or fluororesin.

An organic lubricating layer such as fatty acid ester or stearic acid may be formed. In the case of the Co-0r 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 support.

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

Example 1 Diamine component consisting of 80 mol% PPD, 20 mol% DAIIE, 70 mol% BPDA, PMDA
A polyimide film with a thickness of 91 mm was produced using as raw materials an acid dianhydride component consisting of 30 mol % and Si02 particles with an average particle size of 600 A. 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 1
．． 9 x 10-5 cm/Cm/'O, and the tensile elastic constant was 1330 kg/mm2.

A Go-Cr alloy magnetic recording layer was formed on this polyimide film by sputtering to produce a magnetic recording medium.

FIG. 1 shows an outline of the sputtering apparatus. In FIG. 1, 11 is a raw polyimide film slit to a width of 100 mm, 12 is a rotating drum heated to 150°C, 13 is a film wound up after forming a magnetic recording layer, 1
4 is a Go-Gr alloy target (Or20%), 15
The vacuum chamber 116 is a free roll. The vacuum chamber 15 is divided vertically by a partition wall 17, and each divided space is evacuated by an oil diffusion pump (not shown) on the upper side and a cryopump (not shown) on the lower side. The sputtering method is an RF magnetron type, and the At pressure in the lower chamber is 0.50p.
a. RF power 2KW.

The film formation rate was approximately 200OA/win. Also,
The angle of incidence is limited by a mask 18. The formed film thickness is approximately 0.35 gm, and the magnetic properties are 4 πMs = 4500 Gauss.

Hc' = 1200 oersted, Hc' = 700
On the Ørsted Go-Or magnetic recording layer, there is further a
By the method disclosed in No. 24, the CO oxide film was
A protective film is formed with a thickness of 0.00 mm, and a back coat made of a polyester binder with carbon particles added to a thickness of 0.5 mm.
After applying pm, it was cut into 8 mm width.

The surface roughness of the manufactured Go-Or alloy thin film magnetic tape was measured by a shadowing method. Because the number of protrusions formed is extremely small, numbering in the hundreds, and their density is minute, it is not possible to trace individual protrusions using conventional stylus-based surface roughness measurement methods such as Talystep. This is because the exact roughness cannot be determined. In the shadowing method, as shown in Fig. 2(a), a heavy metal with high secondary electron generation efficiency such as Au-Pd is used as an evaporation source 21, and a sample 2 which becomes a rough surface to be measured is used.
In this method, a thin film is deposited diagonally on the 2 (protrusion), and the length of the shadow is observed from directly above using a high-resolution electron microscope such as a low-acceleration FE-3EX, as shown in FIG. 2(b). The deposition incident angle θ is 8
If the angle is 5° and the Au-Pd film thickness is IOA, the height of each protrusion can be measured with an accuracy of ±8%.

FIG. 3 shows the protrusion height distribution on the surface of the magnetic tape of this example measured in this manner. When taking the height distribution, it is preferable to measure as large an area as possible, but in the case of particularly tall protrusions, the probability of their existence is low, so an area of 10,004 m2 or more was measured. The FE-3EX used is 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 Go-Cr magnetic layer.

In addition, the protrusion density was determined by taking 10 photographs at 3000x magnification using the low-acceleration FE-8EW mentioned above, and a total of approximately 10,000 #L.
Count the number of protrusions existing within an area equivalent to I112,
The protrusion density was calculated per unit area (mm2).

Example? The procedure was the same as in Example 1 except that the drying temperature during polyimide film production was lowered. FIG. 4 shows the height distribution of the surface roughness of the magnetic tape in this example.

There was less aggregation of the filler particles than in Example 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the average particle size of the 5i02 fine particles added was 80OA. FIG. 5 shows the height distribution of surface roughness of the magnetic tape of this comparative example.

Comparative Example 2 The same procedure as in Example 2 was carried out except that the average particle size of the 5i02 fine particles added was 80OA. FIG. 6 shows the height distribution of the surface roughness of the magnetic tape in this comparative example.

Example 3 The same procedure as Example 1 was carried out except that the average particle size of the Si02 fine particles added was 45OA. FIG. 7 shows the height distribution of the surface roughness of the magnetic tape in this example.

Example 4 The procedure was the same as in Example 3 except that the amount of 5i02 fine particles added was changed to 1710 as in Example 1.

Example 5 The same procedure as in Example 3 was carried out except that the fine particles of Example 3 that had been surface-treated with a silane coupling agent were used as the Si02 fine particles to be added. FIG. 8 shows the height distribution of the surface roughness of the magnetic tape in this example.

Example 6 The same procedure as Example 5 was carried out except that the drying temperature during polyimide film production was increased. FIG. 9 shows the height distribution of the surface roughness of the magnetic tape in this example.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the fine particles added were Ti02 fine particles with an average particle size of 20OA. FIG. 10 shows the height distribution of the surface roughness of the magnetic tape in this comparative example.

Comparative Example 4 The same procedure as Example 5 was carried out except that the drying temperature during polyimide film production was lowered. FIG. 11 shows the height distribution of the surface roughness of the magnetic tape in this comparative example.

Comparative Example 5 The procedure was the same as in Example 1, except that the fine particles to be added were CaCO3 fine particles with an average particle size of 450A, and the amount added was about 1/100 of that in Example 1.

Comparative Example 6 The fine particles to be added have irregular particle sizes of 100 to 600.
The procedure was the same as in Example 1 except that i02 particles were used and the amount was approximately 1/1000 of that in Example 1.

By the way, when the polyimide film is filled with fine particles, the amount of inorganic fine particles added is ~7 x 106 particles/m as shown in Examples 5 and 6 when the best dispersibility is achieved.
It was found that about m2 is the maximum. If more than this is added, the agglomeration of the filler particles will proceed, and the protrusion density will tend to decrease.

Next, each of the above magnetic tapes was evaluated using a commercially available 8 mm format video deck. 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 shown in Fig. 3, Ho is the protrusion height corresponding to 0.01% of the total number of protrusions on the magnetic tape surface.
, o+, the protrusion height corresponding to 0.1% is HO,I.

If the protrusion height corresponding to 1% is Hl, then the protrusion height distribution curve r(h) is as follows: f(h)dh/J'c: f(h)dh= 0.
0001f:', 1f(h)dh/fn(h)dh=
0.001G” f(h)dh/ f and (h)dh=
It is expressed as 0.01.

Although the embodiment of the 8 mm videotape has been explained above, the magnetic recording medium of the present invention can also be applied to a video floppy disk (e.g.
5 inch φ, 3.5 inch φ.

It can also be used as a 2 inch φ etc.).

(Margins below) [Effects of the Invention] As explained above, the magnetic recording medium of the present invention has a large number of fine protrusions formed on the surface of the magnetic recording layer side, and the density of these protrusions is 105 to 107 pieces/mm2, and the number of protrusions is 0.01% from the highest point when taking the height distribution.

The protrusion heights corresponding to 0.1% and 1% are Ho and o, respectively.
+, )lo, +, H+, then HO, Ol
≦60OA and HO, I≧20OA and H1≧15OA
By setting HO,l-11≦15OA, a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a sputtering apparatus, FIG. 2 is a diagram of the principle of the shadowing method, and FIGS. 3 to 11 are height distribution diagrams of the magnetic tape surface in Examples and Comparative Examples. 11... Support body, 12... Rotating drum,
14... Target, 15... Vacuum chamber 16... Free roll, 17... Partition wall, 21...
Evaporation source, 22...sample (protrusion). (α) (b) Figure 2 Figure 1 Frequency (%) Figure 3 Frequency (Z) Frequency (%) Figure 6 Frequency (/,) Frequency (X) Figure 7 @ Degree (%) Frequency (/ , ) Figure 10 Frequency (Z) @ Degree (X) Figure 11

Claims (1)

[Claims] (1) A perpendicular magnetic recording medium in which a magnetic recording layer is formed on a support by a thin film deposition method, wherein the perpendicular magnetic recording medium has an average of 1 minute protrusion per 1 mm^2 on the surface of the magnetic recording layer side.
There are 0^5 to 10^7, and in the statistical distribution of the height of the microprotrusions, from the highest to 0.01%, 0.1%, 1
The protrusion height corresponding to % is H_0_. ＿0＿１、
H_0_. _1, H_1, H_0_. ＿0＿
1≦600Å and H_0_. _1≧200Å and H_1
≧150 Å and H_0_. A perpendicular magnetic recording medium characterized in that _1-H_1≦150 Å.