JPH0240128A - Perpendicular magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a perpendicular magnetic recording medium, in particular, to a perpendicular magnetic recording medium, in which fine particles are dispersed in primary particles, and a uniform unevenness is imparted to the surface of a magnetic recording layer, thereby achieving excellent durability and electromagnetic properties. The present invention relates to a perpendicular magnetic recording medium that also has conversion characteristics.

[Prior Art] In recent years, development of metal thin film magnetic recording media in which metal magnetic thin films are formed using thin film deposition methods such as vacuum evaporation, sputtering, and plating has been extremely active. This type of media has a closed-packed magnetic recording layer that significantly improves electromagnetic conversion characteristics compared to coated media, and is therefore expected to bring about major advances in magnetic recording technology in general.

Among these, co-based alloy perpendicular magnetic recording media such as CoCr are expected to have advantages as thin metal film media as well as perpendicular recording methods, and are attracting the interest of many researchers as high-density recording media. .

To summarize recent research reports, although perpendicularly magnetized films using these thin film deposition methods have excellent electromagnetic conversion properties, they are significantly inferior in running durability compared to coated media, and research is still ongoing, especially regarding Go-Or alloy magnetic recording layers. It can be said that there is a lot of room for

In order to improve the running durability of these CO-based alloy thin film perpendicular magnetic recording media, the following methods, for example, have been studied.

The first is research into modifying the surface of the magnetic recording layer, which can be roughly divided into two types: those that provide a protective function and those that provide a lubricating function, each with 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.

[Problems to be Solved by the Invention] In the second method, the inventors developed a flexible medium (tape) using a GoCr-containing Cr directly magnetized film.

In the process of considering the practical use of floppy disks, etc., we discovered the following problems. That is, as is conventionally known, in Goer alloys, the substrate is heated when forming the magnetic recording layer in order to improve the magnetic properties. Therefore, a heat-resistant plastic film such as polyimide film, polyamide film, polyimide amide film, polyetherimide film, polysulfone film, etc. is used for the substrate of the flexible medium. The required heat resistance is that the glass transition point is at least 200°C or higher, preferably 250°C.
That's all there is to it. When the surface of these heat-resistant films is roughened and a GoCr-containing Cr film is formed, for example, by sputtering, the surface of the magnetic thin film becomes a rough surface reflecting the irregularities of the surface of the base film. It is well known that these roughened films contribute to the running durability of the medium, and the gist thereof is disclosed in, for example, Japanese Patent Application Laid-Open No. 127523/1983.

The method of roughening the surface of a plastic film is to mix protrusion-forming particles into the raw material in a solution state before forming it into a film, or to apply a dilute solution containing protrusion-forming particles after forming the film, so that the particles protrude when dried. There are methods to form fine wrinkles, methods to make use of catalyst residues or precipitates of soluble catalysts, and methods to make use of the crystallization process when stretching an extruded product to form a film. The latter two methods are mainly used to make PET film smoother, and utilize the unique process characteristics of PET. Heat-resistant films made of polyimide, polyamide, etc. are formed by casting, so the former two methods are appropriate, but in terms of process simplification, formation of protrusions by protruding filler is advantageous and is a low-cost industrial method. Suitable for production. The present invention relates to an improved CO-based perpendicular magnetic recording medium using a heat-resistant film in which protrusions are formed by a fine particle filler.

The inventors prototyped a film by mixing various protrusion-shaped particles mainly consisting of inorganic fine particles in an imide, amide, etc. plastic film, then formed a CoCr alloy magnetic layer by sputtering and evaluated the media function. The fine particles used were TiO2゜ZrO2, 5i02, Ba
It is SO4, etc., and its particle size is 100 to 1000A. As a result, simply mixing these inorganic ultrafine particles will not function by dispersing the fine particles down to the primary particles, and several to hundreds of particles will always aggregate and form protrusions between particles. found. Fine particles that function only as aggregates have the following problems when used in magnetic media for high-density recording.

(1) Since it is difficult to completely control the aggregation process, protrusions of various heights are formed.

The only part of the protrusion that actually functions in terms of defining the state of contact with the head is the highest part, and most of the protrusions do not function effectively.

(2) As a result of (1) above, the height of the protrusion that functions effectively cannot be controlled, and the spacing between the head and the medium 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. For example, when we manufactured a polyimide film filled with protrusions using conventional technology, sputtered a CoCr alloy thin film on it, and evaluated the tape, we found that only 1% of the total number of protrusions could be seen under a scanning electron microscope. It turned out to be insufficient.

(4) If there are agglomerates of fine particles in close proximity, they tend to shadow each other during the formation of the magnetic layer, which affects the growth process of the columnar crystals of the Goer alloy and causes abnormal growth of protrusions.

(5) It is not possible to sufficiently prevent coarse protrusions that are far from the actual desired height, and dropouts caused by the film frequently occur.

These problems are serious deficiencies in realizing CoCr alloy thin film media with heat-resistant plastic films. In order to roughen the surface of a heat-resistant film made of imide, amide, etc. produced by the casting method with embedded protrusion-forming particles and produce a CoCr alloy thin film medium, the dispersion state of the particles must be sufficiently controlled. .

As a result of cross-sectional observation, it was found that the protrusions formed with the filler by the conventional method had shapes as shown in FIGS. 1(a) and 1(b) as a result of aggregation of the protrusion-forming particles. Generally, both types coexist in the same film, but the ratio of their existence probability is strongly influenced by the dispersion state of the fine particles and the drying conditions during film production.

Figure 1 (a) shows that the polyamic acid precursor film is gradually annealed, and during solvent removal and imidization, protrusion of protrusions occurs.
This is common when the polyamic acid precursor film is rapidly heated to cause the desolvation reaction and imidization to proceed simultaneously and rapidly. In the figure, 11 is the surface of the polyimide film, and 12 is a protrusion-forming filler. Generally, in type (a), it is difficult to accurately control the protrusion height, and the protrusion height has a wide distribution.

Therefore, problems (1), (2), (3), and (5) above occur. On the other hand, in the type (b), abnormal growth of protrusions is likely to occur during the formation of the CoCr magnetic layer, resulting in the problem (4).

If there is a planar aggregation of protrusions as shown in (b), when forming a CoCr magnetic layer, Co
Abnormal growth of Cr crystal grains occurs, and the surface of the magnetic layer becomes rough. Although this mechanism has not been fully elucidated, it is presumed that when crystal grains grow using protrusions on the film surface as nuclei, adjacent columnar crystal grains overlap and become coarser during the growth process. Experience has shown that the surface protrusions of the base film aggregate in a planar manner, and the more oblique the angle of incidence of the CoCr vapor-deposited particles on the substrate, the stronger this tendency is. When such a phenomenon is noticeable, the roughness of the polyimide film substrate surface and the Coa
The roughness of the t film-forming surface no longer matches, and the latter is rougher. Abnormally grown protrusions become a spacing factor,
In addition to impairing the electromagnetic conversion characteristics, particularly large particles can also become a dropout factor, significantly reducing the overall performance of the tape. Such a state of agglomeration of planar protrusions cannot be clearly seen by measuring the height of the protrusions on the film surface, but rather by observing the distribution of the protrusions using a high-resolution electron microscope.

In any case, if the filler fine particles are aggregated, a highly functional film cannot be obtained regardless of the drying method.

In order to impart irregularities to the medium surface using such a method, it is necessary to improve the dispersion state of the filler in order to improve the performance of the perpendicular recording medium.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a perpendicular magnetic recording medium that is excellent in both durability and electromagnetic conversion characteristics.

[Means for solving the problem] and [Action] The present invention has the following features:
A perpendicular magnetic recording medium in which a perpendicular magnetic recording layer is formed by a thin film deposition method on a support containing fine particles, the support having 111112 minute protrusions caused by the fine particles on the surface of the support.
The fine protrusions have an average of 105 to 108 per particle, most of the fine particles are dispersed in primary particles, and the height distribution of the fine protrusions is as follows: Ho, 0+≦(1+σ)d HO,l ≧200A Hl ≧0.35d It is characterized by satisfying the following. However, d is the average grain size of the fine particles, σ is the deviation of the fine particle diameter, HQ, 01 is the height of fine protrusions corresponding to 0.01% of the number of fine protrusions from the highest, H
O and I are the heights of fine protrusions corresponding to 0.1% of the number of fine protrusions from the highest, and Hl is the height of fine protrusions corresponding to 1% of the number of fine protrusions from the highest.

By using the present invention, it is possible to obtain a perpendicular magnetic recording medium that is excellent in both electromagnetic conversion characteristics and running durability, and at the same time, it is possible to manufacture a medium that is superior to conventional media in terms of dropout and mass production yield.

Furthermore, since the present invention is a surface roughening technology that omits the step of roughening the surface by coating, which is a part of PUT or the like, it is possible to reduce the cost of manufacturing the media.

The key points in producing the heat-resistant film used in the present invention are the method of mixing and dispersing the fine particles into the film raw material and the drying conditions after casting. As a dispersion method, it is effective to pre-treat the surface of the fine particles with a coupling agent to improve the affinity with the organic material, and to perform initial dispersion at a high viscosity.

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 preferably heat resistant and has a glass transition point of 200°C or higher.

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

The protrusions on the surface of the support are formed by dispersing fine particles in a raw material solution for the support. Heat-resistant films such as polyimide and polyamide are formed by a casting method, so protrusion-forming particles are mixed into a raw material in a solution state before being formed into a film (filling method).

The fine particles used in the present invention include element No. n of the periodic table.
, III, IV groups and other transition metal elements, oxides, nitrides, carbides, salts, and inorganic particles made of simple elements are preferred. Specifically, MgO, ZnO.

Aj! 203. SiO+, TiO2, TiN, Z
rN, VN, SiC, Tie.

NbC, MO2C, WC, MgCCh, GaCO3,
CaSO4, BaSO4, Gu, Ag, Au, Z
n, Aj), Fe, Go, 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.
The one is good.

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 gutter, resulting in a decrease in output and an increase in dropout.

Furthermore, it is necessary that there be an average of 105 to 108 fine protrusions per l2. If it is less than 10 5 pieces/11 m 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 108 particles/mm2, the amount of particles mixed becomes excessive, causing agglomeration of particles and the formation of coarse protrusions.

The magnetic recording layer formed on the support is a metal thin film type, especially a ferromagnetic alloy film 2 mainly composed of Fe, Co, and Ni.
A perpendicular magnetic recording layer of a ferromagnetic oxide film or a ferromagnetic nitride film is preferred. 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 metal foil method.

Among them, a Cr-based magnetic recording layer formed by vacuum evaporation or sputtering, especially a Go-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! ,
In some cases, a thin film of Ge, Cr, Ti, SiO2, etc., or a high magnetic permeability layer such as a Fe-Ni film, a Go-Zr film, etc., is 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, Ap203, 5i02, Si3 are added on the magnetic recording layer to improve corrosion resistance, wear resistance, and lubricity.
N4.

No, old inorganic protective layer, or fluororesin.

An organic lubricating layer such as fatty acid ester or stearic acid may be formed. In the case of the Go-Or film, the Go 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.

Hereinafter, the present invention will be explained in detail based on examples.

[Examples] Example 1 An example of a perpendicular magnetic recording medium in which an aromatic polyimide film is mixed with Si02 fine particles to form irregularities and a CaCr alloy thin film is attached by sputtering will be described.

In a cylindrical polymerization tank, 7 moles of 3.3',4.4'-biphenyltetracarboxylic dianhydride (BPDA), 3 moles of pyromellitic dianhydride (PMD'A), and 6 moles of paraphenylenediamine (PPD). 4 moles of diaminodiphenyl ether (DADE), 10 moles of N-methylpyrrolidone
kg was added at the same time, and the mixture was stirred at 50°C under normal pressure for 44 hours to carry out condensation polymerization. In this polymerization solution, a polyamic acid having a copolymerization composition of 33% by weight, consisting of a total of four components, the above-mentioned two tetracarboxylic acid components and two diamine components, is produced. The solution in this state had extremely viscous properties, and its rotational viscosity was about 25,000 cp.

This solution was transferred to a Ni-Goo equipped with a heating device, and 35 g of 5i02 fine particles adjusted to an average particle size of 400A (catalysts and chemical industry type, trade name 08CAL) were added to the same solution, and heated to 50°C.
During initial dispersion, the particles were kneaded for 24 hours to obtain uniform particles with small deviations in particle size. Furthermore, the Si02 fine particles were surface-treated with a coupling agent before being added to the polyamic acid solution. In this surface treatment, the Si02 fine particles were ultrasonically cleaned with methanol and then acetone, and then added to a dilute solution of a coupling agent, stirred for 6 hours, and then separated and dried at 80°C. Generally, silane-based coupling agents are effective, but in particular, since the heat treatment temperature in the film manufacturing process is continuously high, it is desirable to use a heat-resistant coupling agent having a benzene ring structure. For example, it is preferable that the structural formula is represented by the following formula.

The solution after dispersion was transferred to a sand mill equipped with a heating device, and 9.8 kg of N-methylpyrrolidone heated to 50° C. was gradually added to dilute the solution to a solid content concentration of 20%, followed by stirring. Thereafter, dispersion was performed in a sand mill for 24 hours. In this state, the rotational viscosity of the solution was 4000 cp. Since the amount of 5i02 particles added is small with respect to the total amount of the solution, the amount of SiO2 particles added, particle size, etc. have no effect on the solution viscosity. The obtained solution was cast using a casting apparatus as shown in Fig. 2,
A film was formed. In Fig. 2, 21 is a container for supplying the raw material solution;
22 is a die that determines the coating thickness, 23 is a casting drum, 24 is a free roll, 25a, 25b, 25
C is a high temperature furnace consisting of three zones, and 28 is a winding roll. In this example, the die 22 was adjusted so that the wet coating thickness was 60 pm and the dry film thickness was 10 pm. Further, the casting drum was heated to 170° C., and the film thickness when peeled from the casting drum was about 20 #Lm. This semi-dry film is further heated at 420°C in two zones, high-temperature furnaces 25a and 25b.
The imidization and desolvation reactions are completed. In this embodiment, no heating is performed in zone 25c. The height distribution of protrusions caused by Si02 particles depends to some extent on the drying conditions during film formation. In the apparatus shown in FIG. 2, drying on the casting drum is mainly a desolvation reaction, and imidization of the polyamic acid proceeds at the same time as desolvation in the high-temperature furnace. The shape of the protrusion is mainly formed by 5i0 by solvent removal.
7 This is the high-temperature furnace side where surface protrusion of fine particles and shape fixation by imidization proceed simultaneously. In general, the higher the temperature and the faster the temperature, the more prominent the projections tend to be.

A magnetic recording medium was manufactured by sputtering a CaCr alloy magnetic layer thereon using a polyimide film having a thickness of 10 ILm obtained by the method described above. Figure 3 shows the sputtering equipment 1! Indicates the abbreviation.

In Fig. 3, 31 is a raw polyimide film slit to a width of 100 mm, 32 is a rotating drum heated to 150°C, 33 is a film wound up after forming a magnetic layer, and 34 is a CoCr alloy target (Gr 20% ), 3
5 is a vacuum chamber, and 38 is a free roll.

The vacuum chamber 35 is divided vertically by a partition wall 37, 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 Ar pressure in the lower chamber is 0.
50pa, RF power 2KW, film formation rate approx. 20
This was done with 0OA/win. Further, the incident angle is limited by a mask 38. The thickness of the formed film is approximately 0.3511 m, and the magnetic properties are 4 W Ms = 4500 Gauss, He”
-1200 oersted, He''=700 oersted.

The film on which the CoCr magnetic layer was formed was further developed in Japanese Patent Application Laid-Open No.
- co by the method disclosed in No. 19Ei424.
The oxide film was made into a protective film by applying a thick acid of approximately 100 A, and a back coat made of a polyester binder with carbon particles added thereto was applied to a thickness of 0.5 ILm, and then cut into a width of 8 mm.

The surface roughness of the manufactured Coat alloy thin film magnetic tape is:
Measured by shadowing method. Because the protrusions formed are extremely low, a few hundred amps, and their density is dense, conventional stylus-based surface roughness measurement methods such as Christetub cannot trace individual protrusions, making it difficult to accurately trace individual protrusions. This is because the roughness cannot be grasped. What is the shadowing method?
As shown in Figure (a), a heavy metal with high secondary electron generation efficiency, such as an Au-Pd alloy, is used as an evaporation source 41, and is thinly evaporated diagonally onto a sample 42, which is the rough surface to be measured, and as shown in Figure (b). This method involves observing the length of the shadow from directly above using a high-resolution electron microscope such as a low-acceleration FE-3EX. If the deposition incident angle θ is 85° and the Au-Pd film thickness is IOA, the height of each protrusion can be measured with an accuracy of approximately 8%. FIG. 5 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 10,000 g B 2 or more was measured. Note that Hitachi S-800 was used as the FE-SEX. When the surface of the polyimide film was measured using a similar method, it was found that the distribution of protrusion heights hardly changed before and after the CoCr magnetic layer was formed.

In addition, the protrusion density was determined by randomly taking 10 photographs at 3000x magnification using the low-acceleration FE-3EX mentioned above, and a total of approximately 10,000 μm.
The number of protrusions present in an area equivalent to 2 was counted and converted to a protrusion density per unit area (mm2).

In addition, the planar agglomeration state of the protruding particles is the same as that of the low acceleration FE-3E.
Judgment was made by observing with X at a magnification of about 3000 times. The observation area was set to a size of 7000βM2, and the number of coarse protrusions aggregated in a planar manner was counted, and when the frequency exceeded 0.01% of the total number of protrusions, it was judged that the dispersion state was poor.

Example 2 A magnetic tape was manufactured that differed from Example 1 above only in the drying conditions during polyimide film manufacturing. 40 high temperature furnace 25a
0°C, 25b and 25c were set at 370°C, Example 1
The reaction progressed at a slower rate compared to . The methods for forming the CoCT alloy magnetic layer, CO oxide protective film, back coat, etc. on the polyimide film were exactly the same as in Example 1 above.

FIG. 6 shows the results of measuring the surface roughness of the magnetic tape in this example using the shadowing method described above. Since the maximum height of the protrusions is determined by the filler particle size, it is the same as in Example 1, but the height of the protrusions is reduced overall. This is because the speed of the desolvation reaction and imidization reaction in the furnace was slowed down, and the amount of protrusion of the protrusions was reduced.

Example 3 High temperature furnace 25a, 25b, 25c all zones at 370°C
Other than that, it was the same as in Example 1 above. FIG. 7 shows the surface roughness of the magnetic tape in this example.

Comparative Example 1 High temperature furnace 25a, 25b, 25c all zones 350'
C! The procedure was the same as in Example 1 except that it was closed. FIG. 8 shows the surface roughness of the magnetic tape of this example.

Comparative Example 2 High temperature furnace 25a, 25b, 25c all zones 330'
The procedure was the same as in Example 1 except that C was used. FIG. 9 shows the surface roughness of the magnetic tape of this example.

Example 4 The same procedure as in Example 1 was carried out, except that the average particle size of the Si02 fine particles added was set to eooA.

Example 5 The same procedure as in Example 1 was carried out except that the average particle size of the Si02 fine particles added was 60 (lA).

Comparative Example 3 The same procedure as in Example 1 was carried out except that the average particle size of the 5i02 fine particles added was 20OA.

Comparative Example 4 The same procedure as in Example 1 was carried out except that the average particle size of the 5i02 fine particles added was 100OA.

Comparative Example 5 The same procedure as in Example 1 was carried out except that the average particle size of the 5i02 fine particles added was 120A.

Comparative Example 6 In Example 1, the 5i02 fine particles were not treated with a coupling agent and the initial dispersion in a high viscosity state was omitted, that is, BPDA 7 mol, PMDA 3 mol, PP06 mol, DADE 4 mol, N- At the same time, 19.8 kg of methylpyrrolidone was added, and the mixture was heated at 50°C under normal pressure.
Stir for 4 hours to prepare a 20% polyamic acid solution. 5i02 fine particles having an average particle size of 400 A were added to this after washing, and the solution dispersed in a sand mill was used for casting. CoCr alloy magnetic layer, Go oxide protective film,
The method for forming the back coat is the same as in Example 1 above.

FIG. 10 shows the protrusion height distribution of this comparative example magnetic tape measured by the shadowing method described above. This comparative tape has a large number of bundled protrusions that are taller than the particle size of the filler used. On the other hand, it has been confirmed that the protrusion height distribution on the surface of the polyimide film used in this comparative example is almost the same as in Example 1, and the roughness on the film-formed surface is caused by CoCr crystals generated from planar agglomerated protrusions. Due to abnormal grain growth. In addition.

In the film of this comparative example, the area of each protrusion is large, and the absolute number of protrusions is one order of magnitude smaller than that of Example 1.

Comparative Example 7 The drying conditions were changed in Comparative Example 6, and the high temperature furnace 25a
, 25b, and 25c were set at 350°C, and the solvent removal and imidization reactions were allowed to proceed slowly. In this case, a particle group in which several to tens of 5i02 particles aggregated functions as one giant filler, and protrusions higher than the filler diameter already appear on the surface of the polyimide film, and as they are, the Goer film forming surface reflected in roughness. The methods for forming the GoOr magnetic layer, CO oxide protective film, and back coat are the same as in Example 1. FIG. 11 shows the surface roughness measured by the shadowing method of the magnetic tape of this comparative example.

Comparative Example 8 In Comparative Example 7, Ti with an average particle size of 150A was used as a filler.
A magnetic tape was manufactured in the same manner except that 02 was used.

Looking at the cross section of the magnetic tape, it was found that hundreds of Ti02 particles formed a cluster of aggregated particles. According to shadowing measurements, the protrusion height was actually higher than that of Comparative Example 7 despite the use of particles with a small particle size. This makes it clear that in the state where agglomeration occurs, the diameter of the primary particles does not really matter, but rather the size between the aggregated particles and the drying conditions determine the properties of the protrusions.

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 four points: dropout, still life, and repeated durability. The results of the evaluation measurements are shown in Table 1.

In addition, the projection height corresponding to 0.01% of the total number of projections is Ho, o+, the projection height corresponding to 0.1% is HO, I, and the projection height corresponding to 1% is Hl. Then, if the protrusion height distribution curve is f (h), IC:, 1
It is expressed as f(h)dh/f: f(h)dh=o, ool.

Although the embodiment of the 8 mm video tape has been described above, the magnetic recording medium of the present invention can also be used as a video flop disk.

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 the spacing loss caused by Ho, 0+ or even larger protrusions.

For films with poor particle dispersion, Ho
, 0+ ≧(l+σ)d, and the aggregate determines the luminance signal output. However, d is the particle size of the fine particles, and σ is the deviation of the particle size. In such a state 7a+, the spacing loss is too large and the original performance of the perpendicular magnetization film cannot be utilized. Furthermore, particles having an extremely large particle size also bring about similar results.

Fine particles having an average particle diameter of 1000A or more are unsuitable for the present invention.

(2) Methyl durability life will be improved if the number of protrusions is large and the heights are uniform. This is presumed to be because the head load is distributed and wear and tear on the medium is reduced. The number of protrusions must be 105/mm2 or more, and in order for the heads of the protrusions to be aligned, it is necessary that a large number of fine particles protrude a considerable portion of their particle size, and mathematically, H1≧0.
35d, more preferably H1≧0.5d.

In the case of still playback, coarse protrusions with a low abundance ratio are quickly scraped off, so protrusions with a height around H1 function effectively, and when the protrusions are aligned, at least half the diameter of the fine particles. This is because there are many protruding protrusions.

(3) Good cycling durability is obtained when HO,I≧200A, more preferably HO,I≧250A. In order to obtain this value with dispersed fine particles, the fine particles must have a certain size, although it depends on the drying conditions. Generally speaking, it is preferable to use fine particles having a particle size of at least 150A, preferably 225A or more.

(4) Dropout was defined as a drop in output level of 18 dB and a duration of 15 p, s. Dropouts are significantly more common in situations where there are agglomerates of fine particles. Therefore, the condition without agglomeration, HO,Ol≦(l+σ)d, is essential, and more preferably Ho,0+≦0.8d. The cause of dropouts is a problem in practice, even if the probability is so small that it cannot be easily detected with microscopic observation, so rather than expressing it numerically as above, it is better to scan a large area of the sample and find out the number of aggregates. It is a good idea to check if it exists. The above conditions regarding H0.01 are necessary but not sufficient.

(Hereinafter, blank space) The present invention relates to a polyimide film, Si02 fine particles, C
The combination is not limited to oCr magnetic layers. In addition to polyimide, heat-resistant films such as polyamide, polyimide amide, polyetherimide, and polysulfone have sufficient heat resistance to satisfy the magnetic properties of the Goer alloy magnetic layer, and inorganic fine particles for fillers include TiO2, Zr
O2, HfO2, Sin, BaSO4°Ca5G4.
There are powders of many oxides, sulfides, carbonates, carbides, and nitrides such as CaCO3. By using an appropriate dispersion method, coupling agent, and dispersant for the combination of a film polymer and an inorganic fine particle filler, the effects of the filler-secondary particle dispersed film of the present invention can be obtained.

In addition, in the CO-based alloy perpendicularly magnetized film, other than CoCr, CoR
E, CoV, CoW, GoPt, etc. are being considered, and it goes without saying that such alloy compositions can also be used. Furthermore, if the thickness of the film is made a little thicker, it can immediately be applied to flexible disks such as floppy disks and video floppies.

In the case of disk media, there is no evaluation item equivalent to durability against repeated running, but instead a high durability of about 107 to 108 times is required for still life. Therefore, under the above conditions, I
While O,I≧20OA is not necessarily required, Hl
The conditions for H1≧0.42 need to be stricter.
d, more preferably H1≧0.55d.

Further, since media for digital memory (currently data floppies in particular) have stricter conditions for dropout than media for video, the present invention, which has an improved state of particle dispersion, is particularly effective.

Furthermore, the method for forming the magnetic layer is not limited to sputtering, but may also include vacuum evaporation, ion blating, and the like. The present invention has similar effects even in a so-called perpendicular two-layer medium in which the magnetic layer has a soft magnetic underlayer such as permalloy under a ferromagnetic layer. Furthermore, the perpendicularly magnetized film referred to in the present invention is effective even if some in-plane component is mixed in the crystal growth direction due to an oblique vapor deposition component, etc., as long as abnormal growth of protrusions does not occur.

[Effects of the Invention] As explained above, according to the present invention, fine particles for forming protrusions are mixed into a heat-resistant film made of polyimide or the like formed by a casting method and dispersed into primary particles, and then dried by an appropriate drying method. By adjusting the protrusion amount of the protrusions on the support, it is possible to obtain a magnetic recording medium that has excellent electromagnetic conversion characteristics and running durability, and has less dropout.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of protrusion-forming particles, Figure 2 is an explanatory diagram of the casting apparatus, Figure 3 is a schematic diagram of the sputtering apparatus, Figure 4 is a diagram of the principle of the shadowing method, and Figures 5 to 11. is a protrusion height distribution diagram on the magnetic tape surface in Examples and Comparative Examples. 11... Polyimide film surface, 12... Fine particles for forming protrusions.

Claims (1)

[Scope of Claims] 1) A perpendicular magnetic recording medium in which a perpendicular magnetic recording layer is formed by a thin film deposition method on a support containing fine particles, wherein fine protrusions caused by the fine particles are formed on the surface of the support with a diameter of 1 mm^.
2, most of the fine particles are dispersed in primary particles, and the height distribution of the fine protrusions is H_0_. _0_1≦(1+σ)d H_0_. A perpendicular magnetic recording medium characterized by satisfying the following conditions:_1≧200Å H_1≧0.35d. (However, d is the average particle diameter of the particles, σ is the deviation of the particle diameter, H
＿0＿． _0_1 is the height of fine protrusions corresponding to 0.01% of the number of fine protrusions from the highest, H_0_. _1 is the height of microprotrusions corresponding to 0.1% of the number of microprotrusions from the highest, H_1
is the height of fine protrusions corresponding to 1% of the number of fine protrusions from the highest. )