JPH0944835A - Magnetic recording media - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a magnetic recording medium that achieves both smoothing and low friction of a base film while achieving high productivity at low cost, and that obtains desired electromagnetic conversion characteristics. It is what SOLUTION: An undercoat layer which is a coating film made of a binder 3 having spherical particles 2 is formed on a non-magnetic support 1,
A ferromagnetic metal thin film is applied to this undercoat layer by a vacuum thin film forming technique for a magnetic recording medium. The diameter of the spherical particles 2 is 50 nm or more, or 100 nm or more and 500 nm or less, and the glass transition point Tg of the spherical particles 2 is 140 ° C. or more and 400 ° C. or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called thin film type magnetic recording medium in which a ferromagnetic metal thin film is formed as a magnetic layer on a non-magnetic support by a vacuum thin film forming technique such as vapor deposition or sputtering.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, a powder magnetic material such as an oxide magnetic powder or an alloy magnetic powder is used as a vinyl chloride-vinyl acetate copolymer, a polyester resin,
2. Description of the Related Art A coating type magnetic recording medium prepared by coating a magnetic coating material dispersed in an organic binder such as urethane resin or polyurethane resin on a non-magnetic support and drying it is widely used.

On the other hand, in the field of video tape recorders (VTRs) and the like, there is a strong demand for high-density magnetic recording in order to achieve high image quality, and as a magnetic recording medium corresponding thereto, Co-Ni alloy, C
Non-magnetic support of polyester film, polyamide, polyimide film, etc. for metal magnetic materials such as o-Cr alloys and Co-O based on plating or vacuum thin film forming technology (vacuum evaporation method, sputtering method, ion plating method, etc.) A so-called ferromagnetic metal thin film coating type magnetic recording medium, which is directly deposited on the body as a magnetic layer, has been proposed and has attracted attention.

This ferromagnetic metal thin film type magnetic recording medium is
Not only is it excellent in coercive force, squareness ratio, and electromagnetic conversion characteristics in the short wavelength region, but also because the magnetic layer can be made thin, recording demagnetization and thickness loss during reproduction are extremely small, and
Since there is no need to mix a binder or the like, which is a non-magnetic material, in the magnetic layer, there are various advantages such that the packing density of the magnetic material can be increased.

[0005]

By the way, in a magnetic recording medium for forming a thin film for ferromagnetic magnetic recording by using the above-mentioned vacuum thin film forming technique such as vapor deposition, the base film which is a non-magnetic support has a good electromagnetic conversion property. It is necessary that the surface be extremely smooth in order to obtain the characteristics. However, if it is too smooth, the friction coefficient becomes large, and problems such as an adhesion phenomenon (so-called sticking) occur.

Therefore, in the conventional ferromagnetic metal thin film type magnetic recording medium, SiO 2 is formed on the surface of the base film.
₂ or the like, or an organic material having a relatively high glass transition point Tg for maintaining a high protrusion height in a manufacturing process with high heat load such as vapor deposition, an undercoat layer containing these spherical particles and a binder is formed. It was applied to achieve both the smoothness of the base film and the low friction required for a magnetic recording medium.

However, the inorganic material such as SiO ₂ is high in material cost, which results in high cost. For this reason, an undercoat layer having spherical particles made of an organic material having a relatively high glass transition point Tg is used, but in this case, the surface particles are small and have high friction due to the smoothness, so that mass production of the base film is performed. Sex matters. Therefore, the production of the magnetic recording medium must be expensive.

Particularly, with the recent progress in high-density recording, the demand for magnetic recording media with high electromagnetic conversion characteristics has increased, and metal thin film media, which are essentially advantageous for output at short recording wavelengths, have lower costs. Long-awaited. However, the high cost of manufacturing the magnetic recording medium makes it difficult to realize the high-density recording.

Therefore, the present invention intends to provide a magnetic recording medium which achieves both smoothness and low friction of a base film while achieving high productivity at low cost, and which can obtain desired electromagnetic conversion characteristics. It is what

[0010]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, an undercoat layer containing spherical particles and a binder was formed on a nonmagnetic support. In a magnetic recording medium in which a ferromagnetic metal thin film is formed on a layer by a vacuum thin film forming technique such as vapor deposition, focusing on the manufacturing process and selecting the glass transition point Tg of spherical particles,
The heat load when the ferromagnetic metal thin film is formed by the vacuum thin film forming technology can suppress the surface height of the spherical particles to an appropriate height, which is excellent in productivity and the target electromagnetic field. It has been found that conversion characteristics can be obtained.

Therefore, according to the present invention, an undercoat layer containing spherical particles and a binder is formed on a non-magnetic support, and a ferromagnetic metal thin film is formed on this undercoat layer by a vacuum thin film forming technique. In the medium, the diameter of the spherical particles is 50
The glass transition point Tg of the spherical particles is 1 nm or more and 500 nm or less and the glass transition point Tg of the spherical particles is 140 ° C. or more and 400 ° C. or less.
It is characterized in that the temperature is 40 ° C. or higher and 400 ° C. or lower.

The diameter of the spherical particles is 100 nm or more and 500 nm or less.

Further, it is characterized in that the surface density of the spherical particles is not less than 0.5 million pieces / mm ^{2 and not} more than 20 thousand pieces / mm ² .

In the magnetic recording medium of the present invention, an undercoat layer composed of spherical particles and a binder and a ferromagnetic metal thin film are formed on a non-magnetic support by a vacuum thin film forming technique.

The metal magnetic layer is formed by depositing a ferromagnetic metal material, and the ferromagnetic metal material may be any as long as it is used in a usual vapor deposition tape. May be For example, Fe, Co,
Ferromagnetic metals such as Ni, Fe-Co, Co-Ni, Fe
-Co-Ni, Fe-Cu, Co-Cu, Co-Au,
Co-Pt, Mn-Bi, Mn-Al, Fe-Cr, C
o-Cr, Ni-Cr, Fe-Co-Cr, Co-Ni
Examples include ferromagnetic alloys such as -Cr and Fe-Co-Ni-Cr. The metal magnetic layer may be a single layer film or a multilayer film of these. Further, in the case of a multilayer film, an intermediate layer may be provided in order to improve the adhesive force between the layers and control the coercive force. Further, the vicinity of the surface of the magnetic layer may be an oxide to improve the corrosion resistance and the like.

As means for forming the metal magnetic layer, a vacuum vapor deposition method of heating and evaporating a ferromagnetic metal material under vacuum to deposit it on a non-magnetic support, or ion plating in which the ferromagnetic metal material is evaporated during discharge. A so-called PVD technique such as a sputtering method or a sputtering method in which atoms on the target surface are knocked out by argon ions generated through a glow discharge in an atmosphere containing argon as a main component may be used.

As the non-magnetic support, any of those generally used as a non-magnetic support for this type of magnetic recording medium can be used. For example, polyesters, polyamides, polyolefins can be used. Examples thereof include vinyl resins, polyimides, polyamides and polycarbonates.

Further, the undercoat layer comprises a binder having spherical particles. The spherical particles are preferably organic spherical particles such as polyethylene and polymethylmethacrylate. Examples of the binder include polyester resin, phenol resin, urethane resin and the like.

As described above, the diameter of the spherical particles formed on the base film which is the non-magnetic support is 50 nm or more,
500 nm or less, preferably 100 nm or more,
It is 500 nm or less.

If the diameter of the spherical particles is other than the above, the contact area with the guide roll or the like cannot be reduced during film formation by the vacuum thin film forming technique or during winding into a roll. A good low friction effect cannot be obtained,
Mass productivity of the base film is reduced.

However, the spherical particles have a glass transition point T
It is necessary that g is 140 ° C. or higher and 400 ° C. or lower.

The glass transition point Tg of the spherical particles is 140 ° C.
If it is smaller than the above, the shape of the spherical particles is not maintained due to the heat load when forming the ferromagnetic metal thin film by the vacuum thin film forming technique such as vapor deposition, and the magnetic recording medium cannot be provided with an appropriate surface roughness. It is not possible to impart sufficient durability.

On the other hand, the glass transition point Tg of the spherical particles is 40.
If the temperature is higher than 0 ° C, the shape of the spherical particles is maintained as it is and the surface height becomes high even when the ferromagnetic metal thin film is formed by the vacuum thin film forming technique, so that the surface height of the magnetic recording medium increases. Smoothness is impaired, spacing loss is likely to occur, and this causes deterioration of electromagnetic conversion characteristics.

As described above, according to the present invention, the diameter of the spherical particles is 50 nm or more and 500 nm or less, preferably 100 nm or more and 500 nm or less,
The contact area with the guide rolls can be reduced during film formation by the vacuum thin film forming technology or when wound into a roll, and as a result, a good low friction effect can be obtained even in the state of the base film. , High productivity can be obtained.

Moreover, when the ferromagnetic metal thin film is formed by the vacuum thin film forming technique by selecting the glass transition point Tg of the spherical particles, a high heat load is applied to the surface of the non-magnetic support, and the projections on the surface are formed. Also, the height of the surface becomes low due to the heat load exceeding the glass transition point Tg.

Therefore, the desired electromagnetic conversion characteristics can be obtained by the effect of suppressing the protrusion height of the spherical particles while achieving low cost and high productivity.

[0027]

EXAMPLES Specific examples of the present invention will be described below based on experimental results, but the present invention is not limited to these examples.

In the magnetic recording medium of this embodiment, as shown in FIG. 1, an undercoat layer which is a coating film is formed on a base film 1 which is a non-magnetic support. As the base film 1 which is this non-magnetic support, polyethylene terephthalate (PET) having a thickness of 10 nm was used.

The undercoat layer has spherical particles 2.
The spherical particles 2 are formed on the surface of the base film 1 so as to satisfy the durability required as a magnetic recording medium. In this example, polystyrene was used for the spherical particles 2. As the binder 3, a polyester resin was used.

The height of the spherical particles 2 of this embodiment is 50 nm.
As described above, the thickness is 500 nm or less, and the surface density is 0.5 million pieces / mm ² or more and 20 thousand pieces / mm ² or less. The thickness of the coating film of the binder 3 is 10 nm or more,
It is 100 nm or less.

By the way, as shown in FIG. 2, as a method of manufacturing a so-called ferromagnetic metal thin film coating type magnetic recording medium which is directly deposited as a magnetic layer on a non-magnetic support, a non-rolled roll is used. The base film 1 serving as a magnetic support is unwound and the alloy in the crucible 4 is heated by an electron beam to evaporate to form a vapor deposition film for forming a magnetic layer on the surface of the base film 1 rotated by a roller 6. The film and the winding of the magnetic recording medium are wound via the guide roll 5.

The ferromagnetic metal thin film is formed by a vacuum thin film forming technique such as vapor deposition using a Co--Ni alloy, and by introducing oxygen during the film formation, a magnetic material suitable as a magnetic recording medium. I tried to become. After forming this ferromagnetic metal thin film, a perfluoropolyether lubricant is applied.

In such a manufacturing process, the base film 1 in which the height of the spherical particles 2 is 50 nm or more and 500 nm or less has a large number of particles as projections on the surface and is formed by a vacuum thin film forming technique. Alternatively, the contact area with a guide roll or the like is reduced when the film is wound into a roll, and as a result, even in the state of the base film 1, a good low friction effect is obtained, and high productivity can be obtained.

However, when the non-magnetic support is used as a base film for a metal thin film medium in terms of the height and density of the spherical particles as described above, so-called spacing loss occurs due to surface protrusions. The electromagnetic conversion characteristics that occur are not obtained.

However, according to this embodiment, the spherical particles 2 formed on the base film 1 which is a non-magnetic support have a glass transition point Tg of 200 ° C.

In such a magnetic recording medium, when a ferromagnetic metal thin film is formed by the above vacuum thin film forming technique, a high heat load is applied to the surface of the nonmagnetic support, and the projections on the surface also have a glass transition point Tg. The heat load that is exceeded reduces the height of the surface.

As described above, in this embodiment, attention is paid to the film forming method of the ferromagnetic metal thin film, and this is skillfully utilized.
Therefore, it is possible to provide a magnetic recording medium which is low in cost, good in productivity, and excellent in wear characteristics and electromagnetic conversion characteristics.

Example 2 As in Example 1, the spherical particles 2 are polystyrene and the glass transition point Tg is 200 ° C. However, unlike Example 1, the diameter of the spherical particles 2 is 200 nm, and the surface density of the spherical particles 2 is 20,000 particles / mm ² . Other conditions are the same as in the first embodiment.

Experiments were conducted on the above-mentioned Examples 1 and 2 together with Comparative Examples 1 to 5 which will be described later, and electromagnetic conversion characteristics,
Friction and productivity were evaluated.

According to Examples 1 and 2, when a ferromagnetic metal thin film is formed by a vacuum thin film forming technique such as vapor deposition, a high heat load is applied to the surface of the non-magnetic support, and the projections on the surface also undergo glass transition. A heat load exceeding the point Tg lowers the height of the surface.

In Examples 1 and 2, the height of the spherical particles was lower than that before the magnetic thin film layer was formed due to the heat load in the vacuum thin film forming technique. That is,
The surface height of the projections on the surface was reduced to ½ or less by the heat load exceeding the glass transition point Tg.

Therefore, as in the prior art, spherical particles 2 made of an inorganic material such as SiO ₂ or an organic material having a relatively high glass transition point Tg for maintaining the height of protrusions in a process of high heat load such as vapor deposition. Unlike the case where the material coated on the surface is used as the undercoat layer, friction and the like are increased due to its smoothness, and there is no difficulty in manufacturing the same.

Experiment In this experiment, the above-mentioned Examples 1 and 2 to which the present invention was applied.
Comparative Examples 1 to 5 were prepared to compare the electromagnetic conversion characteristics, friction, and productivity. From the comparison between the two, as will be described later, the glass transition point Tg of the spherical particles 2 and the spherical particles 2
Experiments were carried out by considering the diameter, the surface density of the spherical particles 2, and the like. The results are shown in Tables 1 and 2.

Here, Table 1 shows the productivity of the base film 1 which is a non-magnetic support in the state where the undercoat layer which is the coating film is formed. Each magnetic recording medium shown in Table 2 was prepared by using the good base film 1 of Samples 2 to 4.

[0045]

[Table 1]

Samples 2 to 4 in Table 1 are coated with the spherical particles 2 of Examples 1 and 2 and have a large friction reducing effect because the protrusions on the surface are appropriately large.
Good productivity.

[0047]

[Table 2]

Comparative Example 1 Spherical particles 2 were made of SiO ₂ . The diameter of the spherical particles 2 is 30 nm, and the surface density of the spherical particles 2 is 1.0.
It is 10,000 pieces / mm ² . Other conditions are the same as in the first embodiment.

Comparative Example 2 As in Comparative Example 1, the spherical particles 2 used SiO ₂ . However, since the spherical particles 2 have a diameter of 80 nm,
Has a surface density of 20,000 pieces / mm ² . Other conditions are the same as in the first embodiment.

Comparative Example 3 As in Example 1, the spherical particles 2 were polystyrene and had a glass transition point Tg of 200 ° C. In addition, Example 1
Similarly to the above, the surface density of the spherical particles 2 is 50 thousand / mm ² . However, the diameter of the spherical particles 2 is 600 nm.
Other conditions are the same as in the first embodiment.

Comparative Example 4 The spherical particles 2 were polystyrene, but different from Example 1, a glass transition point Tg of 130 ° C. was used. Further, as in Example 1, the spherical particles 2 have a diameter of 400 nm,
The surface density of the spherical particles 2 is 50 thousand / mm ² . Other conditions are the same as in the first embodiment.

Comparative Example 5 Spherical particles 2 were polystyrene, but unlike Example 1, those having a glass transition point Tg of 500 ° C. were used. Further, as in Example 1, the spherical particles 2 had a diameter of 400 nm, and the spherical particles 2 had a surface density of 50000 particles / mm ² . Other conditions are the same as in the first embodiment.

Experimental Results First, as is clear from Table 1, in Examples 1 and 2, due to the effect of surface smoothing due to the heat load such as the vapor deposition,
The desired electromagnetic conversion characteristics were obtained. In particular, Example 1
Shows a good value of 0 dB. The mass productivity of the base film 1 used at this time is extremely high, and the cost of the base film 1 can be greatly reduced.

These Examples 1 and 2 have glass transition points Tg
A material as low as 200 ° C. is used, and the height of the projections of the spherical particles 2 is appropriately lowered due to the heat load in the vacuum thin film forming technique such as vapor deposition, and good electromagnetic conversion characteristics are obtained.

Therefore, next, Examples 1 and 2 and Comparative Example 1 will be described.
5 to 5, the following experimental results were obtained.

(1) First, the glass transition point T of the spherical particles 2
Consider g.

As is apparent from Table 2, in Comparative Example 4 in which the glass transition point Tg of the spherical particles 2 is as low as 130 °, the mass productivity of the base film 1 is good, but the vacuum thin film forming technique is used on the non-magnetic support. When forming the ferromagnetic metal thin film, a temperature higher than the glass transition point Tg is applied, so that the shape of the particles is not maintained and the friction reduction as a magnetic recording medium cannot be achieved. That is, the diameter of the spherical particles becomes too small.

On the other hand, the glass transition point Tg of the spherical particles 2 is 5
In Comparative Example 5 having a high value of 00 °, even when the ferromagnetic metal thin film is formed on the nonmagnetic support by the vacuum thin film forming technique, the shape of the spherical particles remains unchanged and the height of the particles does not decrease. That is, the diameter of the spherical particles does not become 1/2 or less.

Therefore, the glass transition point Tg of the spherical particles 2 is 140 ° C. or more and 400 ° C. or less, and the diameter of the spherical particles when forming the ferromagnetic metal thin film is 1/2 or less. It turns out that it is preferable to have.

(2) Next, the diameter of the spherical particles 2 will be considered.

In Comparative Example 3, the glass transition point Tg is the same as in Example 1, but the spherical particles 2 have a large diameter of 600 nm, and therefore the electromagnetic conversion characteristics are deteriorated. That is,
The comparative example 3 is good in both the effect of reducing friction and the productivity, but is not preferable because the important electromagnetic conversion characteristics are deteriorated. Therefore, it is understood that the upper limit of the diameter of the spherical particles 2 is preferably 500 nm or less.

On the other hand, the mass productivity of the base film 1 in the case of Comparative Example 1 in which the diameter of the spherical particles 2 is 30 nm is not good. Therefore, the lower limit of the diameter of the spherical particles 2 is 50 nm.
It can be seen that the above is preferable.

Further, the spherical particles 2 of Comparative Example 3 have a diameter of 8
When the thickness is 0 nm, the electromagnetic conversion characteristics are good, but the mass productivity of the base film 1 is not good, which is not preferable. Therefore, it is understood that the diameter of the spherical particles is preferably 100 nm or more.

Therefore, the diameter of the spherical particles is 50 nm or more,
500 nm or less, preferably 100 nm or more,
It can be seen that the thickness is 500 nm or less.

(3) Next, regarding the type of the spherical particles 2, the productivity is poor in Comparative Examples 1 and ₂ in which SiO ₂ which is an inorganic material is used as the spherical particles 2. In Comparative Example 2, although the spherical particles 2 are large and friction and the like are improved, it is not preferable in terms of mass productivity of the base film 1.

[0066] Further (4), the surface density of the spherical particles 2, from the first and second embodiments, it is preferable that there 20,000 pieces / mm ² or less at 0.5 million cells / mm ² or more.

(5) Further, the diameter of the spherical particles 2 is 30 n.
When m, the mass productivity of Comparative Example 1 is not good. Therefore, it is understood that the lower limit of the diameter of the spherical particles 2 is preferably 50 nm or more.

(6) Finally, as is clear from Table 1,
The thickness of the coating film of the binder 3 is 10 nm or more and 10
It is preferably 0 nm or less.

[0069]

As described above, in the magnetic recording medium according to the present invention, the spherical particles have a diameter of 50 nm or more, or 1
Since the thickness is from 00 nm to 500 nm, a large number of particles are maintained on the surface of the base film with an appropriate protrusion height, and a good low friction effect is obtained, so that high productivity can be obtained.

Moreover, the glass transition point Tg of the spherical particles is 1
Since the temperature is 40 ° C. or higher and 400 ° C. or lower, the heat load when the ferromagnetic metal thin film is formed by the vacuum thin film forming technique can appropriately suppress the surface protrusion height of the spherical particles, and the wear characteristics Also, the electromagnetic conversion characteristics can be improved.

Therefore, the magnetic recording medium according to the present invention achieves both the smoothness and the low friction of the base film while achieving the high productivity at a low cost, and moreover, the desired electromagnetic conversion characteristics can be obtained. A recording medium can be provided.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention and is a cross-sectional view schematically showing a state in which an undercoat layer is formed on a base film.

FIG. 2 is a schematic view showing an example of a vapor deposition device.

[Explanation of symbols]

 1 non-magnetic support (base film) 2 spherical particles 3 binder

Front Page Continuation (72) Inventor Shinichi Matsumura 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (3)

[Claims] 1. A magnetic recording medium in which an undercoat layer containing spherical particles and a binder is formed on a non-magnetic support, and a ferromagnetic metal thin film is formed on this undercoat layer by a vacuum thin film forming technique. A magnetic recording medium having a particle diameter of 50 nm or more and 500 nm or less and a glass transition point Tg of spherical particles of 140 ° C. or more and 400 ° C. or less. 2. The spherical particles have a diameter of 100 nm or more and 5
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 00 nm or less. 3. The surface density of the spherical particles is 50 thousand / m.
^2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is m ² or more and 20,000 pieces / mm ² or less.