JP3207875B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium.

[0002]

2. Description of the Related Art In manufacturing a magnetic recording medium, a reverse method or a gravure method is generally used as a coating method. In the reverse method, a smooth coating film can be obtained to a certain extent without using smoothing. However, a three-dimensional coating streak is generated in the longitudinal direction, more or less, due to a complicated relationship with the paint properties. On the other hand, in the gravure method, smoothing is indispensable in order to transfer a gravure pattern and to obtain a uniform and smooth coating film.

[0003] As a conventional smoothing method, a smoothing means such as a base film or a metal is brought into contact with the surface of a coating film to generate a shear stress higher than the yield value of the coating material to obtain a smooth coating film to some extent. ing. However, in this case as well, there are disadvantages such as generation of longitudinal streaks due to unevenness of the contact portion, accuracy of the end portion of the contact portion, and a printed gravure pattern remaining.

On the other hand, in order to increase the recording density of a medium, high coercive force, high saturation magnetic flux density, fine particles, high filling, high orientation, planar smoothing, thinning of the magnetic powder, etc. are performed. ing. However, when the density is increased, the reliability and durability of the medium are reduced, and for example, clogging and dropout of the magnetic head frequently occur, and still characteristics are deteriorated. As a method for improving the reliability and durability, proposals have been made on the type and amount of abrasive added.

Concerning the amount of abrasive added, for example, Japanese Patent Application Laid-Open No. 61-57036 proposes that the density of the abrasive on the surface of the magnetic layer be regulated to 0.25 particles / μm ² or more. I have. However, in the case of a thin magnetic layer for high-density recording having a thickness of about 4 μm or less, if the amount of abrasive is increased by the usual addition method, reliability and durability are improved, but sensitivity and C / N etc. deteriorates,
The wear amount of the magnetic head increases.

On the other hand, Japanese Patent Publication No. 54-14482 discloses that two magnetic layers are laminated, and the abrasive amount of the lower magnetic layer is reduced.
It has been proposed to reduce the amount of the abrasive in the surface magnetic layer to 1/3 or less to improve the head clogging prevention effect and the electromagnetic conversion characteristics. However, in this gazette, as is apparent from the examples, two magnetic layers of 6 μm and 4 μm are laminated to form one layer.
The magnetic layer has a thickness of 0 μm, and a magnetic layer of, for example, 4 μm or less, which is required for high density and long recording, is not considered. That is, it is difficult to form such a thin magnetic layer in a multi-layer structure as described in this publication, and the productivity is extremely poor. The upper layer is 0.6μ
Even if it can be laminated to a thickness of about m, the density of the abrasive in the upper layer is uniform in the thickness direction, maintains a high density in the layer, and the thickness of the upper layer itself is It is too thin, and the processing in the calendar process becomes insufficient. For this reason, the adverse effect on the electromagnetic conversion characteristics is particularly large, and the operation rate is reduced due to a complicated manufacturing process.

As described above, in a high-density medium, there is a contradiction between the improvement of the electromagnetic conversion characteristics and the improvement of the reliability and durability of the medium. Is extremely difficult.

[0008]

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a method of manufacturing a magnetic recording medium having reduced coating defects such as gravure patterns and longitudinal stripes. Another object of the present invention is to manufacture a medium suitable for high-density recording, particularly having a single magnetic layer, exhibiting high electromagnetic conversion characteristics, and exhibiting high reliability and durability. It is to provide a method.

[0009]

This and other objects are achieved by the present invention which is defined below as (1) to (7). (1) While continuously moving the long non-magnetic support, after gravure-coating the coating composition for a magnetic layer containing a magnetic powder and a binder, one surface of the non-magnetic support is
A plurality of unit magnets are arranged so as to be inclined with respect to the moving direction of the non-magnetic support so that the magnetic field component does not coincide with the gravure pattern inclined with respect to the moving direction of the non-magnetic support. Only one magnetic pole is located on one surface side of the body, adjacent magnetic poles are different from each other, and the length direction of the unit magnet is parallel to the non-magnetic support and inclined with the longitudinal direction. The magnetic powder in the coating film is vibrated by repeatedly disposing the magnetic field between the unit magnets, which are arranged in opposition to the non-magnetic support and the tilted unit magnet, at least eight times while alternately reversing the magnetic field. And making the magnetic field in the magnetic layer 500 to 2000 G at an angle between the longitudinal direction of the nonmagnetic support and the magnetic field of 10 to 80 ° to smooth the gravure pattern of the gravure coating. Characteristic magnetic recording medium The method of production. (2) While continuously moving a long non-magnetic support, a coating composition for a magnetic layer containing a magnetic powder and a binder is applied, and a smoothing means is brought into contact with the surface of the coating film. On one side of the magnetic support, a plurality of unit magnets are arranged so as to be inclined with the moving direction of the nonmagnetic support so that the gravure pattern and the magnetic field component that are inclined with respect to the moving direction of the nonmagnetic support do not match, In this unit magnet, only one magnetic pole is located on one surface side of the non-magnetic support, adjacent magnetic poles are different from each other, and the length direction of the unit magnet is parallel to the non-magnetic support and the longitudinal direction thereof. As inclined with respect to the direction, arranged opposite to the non-magnetic support, repeatedly applying the magnetic field between the unit magnet and the direction of movement of the non-magnetic support alternately more than eight times while alternately reversing the magnetic field, Vibrates the magnetic powder in the coating to make it non-magnetic When the angle between the longitudinal direction of the support and the magnetic field is 10 to 80 °, the magnetic field in the magnetic layer is 500 to
The method for producing a magnetic recording medium according to the above (1), wherein the smoothing is performed to 2000 G. (3) While continuously moving the long non-magnetic support, after applying a magnetic layer coating composition containing a magnetic powder, a non-magnetic abrasive having a Mohs hardness of 6 or more, and a binder,
On one side of the non-magnetic support, a plurality of unit magnets are arranged so as to be inclined with respect to the moving direction of the non-magnetic support so that the magnetic field component does not match the gravure pattern inclined with respect to the moving direction of the non-magnetic support. In this unit magnet, only one magnetic pole is located on one surface side of the non-magnetic support, adjacent magnetic poles are different from each other, and the length direction of the unit magnet is parallel to the non-magnetic support. It is disposed opposite to the non-magnetic support so as to be inclined with respect to the longitudinal direction, and the magnetic field between the unit magnets inclined and the direction of movement of the non-magnetic support is alternately reversed and applied repeatedly while applying a magnetic field. Vibrating the magnetic powder inside,
A method for manufacturing a magnetic recording medium, comprising: forming a magnetic layer in the surface layer portion, wherein the non-magnetic abrasive is contained at a higher density than other portions. (4) The thickness of the magnetic layer is 4 μm or less, and the non-magnetic abrasive in the magnetic layer is 5 to 5% of the magnetic powder.
20% by weight, and 0.1% from the surface of the magnetic layer.
The density of the non-magnetic abrasive in the surface layer having a thickness of 6 μm is defined as ρ
_1, when the content density of the non-magnetic abrasive remainder was [rho _2,
The method for producing a magnetic recording medium according to the above (3), wherein ρ ₁ / ρ ₂ is 1.5 or more. (5) The above (3) or (4), wherein the nonmagnetic abrasive has an average particle size of 0.6 μm or less and ρ1 of ₈ to 25%.
3. The method for manufacturing a magnetic recording medium according to claim 1. (6) The plurality of unit magnets are adjacent to each other and have different polarities on the non-magnetic support-facing surfaces, and the length direction of the unit magnets is parallel to the non-magnetic support and inclined with respect to the longitudinal direction. As described above, the method for producing a magnetic recording medium according to any one of the above (3) to (5), wherein the magnetic recording medium is arranged on a side opposite to a coating surface of the nonmagnetic support. (7) The method of manufacturing a magnetic recording medium according to any one of (1) to (6), wherein the magnetic powder is oriented after an external magnetic field is applied by the unit magnet.

(1) While continuously moving a long non-magnetic support, a coating composition for a magnetic layer containing a magnetic powder and a binder is gravure-coated, and then the direction of movement of the non-magnetic support is determined. A method for manufacturing a magnetic recording medium, characterized in that a magnetic powder in a coating film is vibrated by applying a tilted magnetic field repeatedly while inverting it four times or more to smooth the gravure pattern of the gravure coating.

(2) After a long non-magnetic support is continuously moved, a coating composition for a magnetic layer containing a magnetic powder and a binder is applied, and a smoothing means is brought into contact with the surface of the coating. Applying a magnetic field inclined in the direction of movement of the non-magnetic support and inclining four or more times while inverting the magnetic field in the coating film to vibrate the magnetic powder in the coating film and smoothing the longitudinal stripes by the smoothing means. A method for manufacturing a magnetic recording medium.

(3) The plurality of unit magnets are adjacent to each other and have different polarities on the non-magnetic support-facing surface, and the length direction of the unit magnets is inclined with respect to the longitudinal direction of the non-magnetic support. The method of manufacturing a magnetic recording medium according to the above (1) or (2), wherein the magnetic recording medium is disposed so as to face the nonmagnetic support.

(4) A coating composition for a magnetic layer containing a magnetic powder, a nonmagnetic abrasive having a Mohs hardness of 6 or more, and a binder was applied while continuously moving a long nonmagnetic support. Thereafter, a magnetic field inclined in the direction of movement of the non-magnetic support is inverted and applied repeatedly to vibrate the magnetic powder in the coating film, so that the non-magnetic abrasive has a higher density in the surface layer than in other parts. Forming a magnetic layer contained in the magnetic recording medium.

(5) The thickness of the magnetic layer is 4 μm or less, and the magnetic layer contains 5 to 20% by weight of the nonmagnetic abrasive based on the magnetic powder. When the content density of the nonmagnetic abrasive in the surface layer having a thickness of 0.6 μm from the surface is ρ ₁ and the content density of the remaining nonmagnetic abrasive is ρ ₂ , ρ ₁ / ρ ₂ is 1.5 or more. The method for manufacturing a magnetic recording medium according to the above (4).

(6) The non-magnetic abrasive has an average particle size of 0.1.
The method for producing a magnetic recording medium according to (4) or (5), wherein the magnetic recording medium has a thickness of 6 μm or less and ρ1 of ₈ to 25%.

(7) The unit magnets adjacent to each other have different polarities on the nonmagnetic support facing surfaces of adjacent unit magnets, and the length direction of the unit magnets is inclined with respect to the longitudinal direction of the nonmagnetic support. As described above, the method of manufacturing a magnetic recording medium according to any one of the above (4) to (6), wherein the magnetic recording medium is arranged on a side opposite to a coating surface of the nonmagnetic support.

(8) After the above-mentioned external magnetic field is applied, the orientation of the magnetic powder is performed, and only the above (1) or above can extract all applicable process input point information and display it in a list. The method for manufacturing a magnetic recording medium according to any one of the above. (9) The angle between the longitudinal direction of the nonmagnetic support and the magnetic field is 10
The method for manufacturing a magnetic recording medium according to any one of the above (1) to (8), wherein the angle is 80 to 80 °.

[0018]

In the present invention, the repetitive application of the oblique magnetic field while inverting the coating eliminates coating defects such as longitudinal streaks or gravure patterns on the coating surface, improves the surface properties and improves the quality of the coating. Can improve the yield.

Further, by repeatedly applying the oblique magnetic field while reversing the magnetic field, a small amount of the abrasive can be reduced even if the total amount of the abrasive in the magnetic layer is reduced, especially in the case of a thin single-layer magnetic layer. The abrasive content can be continuously reduced from the surface layer toward the support by floating on the surface layer of the layer. As a result, high reliability and durability can be secured, and the high electromagnetic conversion characteristics of the thin high-density recording magnetic layer are maintained. At this time, an oblique reversal magnetic field is applied before orientation,
By moving the magnetic paint and pulling the magnetic powder toward the support, a relatively large amount of abrasive is distributed on the surface, so that the defoaming effect and the orientation effect of the coating film are also exhibited, and the electromagnetic conversion characteristics are further improved. Things.

[0020]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail. In the present invention, on a non-magnetic support, in a binder,
Preferably, an abrasive is added and a magnetic paint in which magnetic powder is dispersed is applied. As the magnetic powder to be used, any of ordinary ones can be used, for example, iron oxide particles such as γ-Fe ₂ O ₃ ,
Co-containing iron oxide particles, such as Co-containing γ-Fe ₂ O ₃ , metal magnetic particles, barium or strontium ferrite particles, CrO _2, etc., may be appropriately selected depending on the purpose, and the coercive force, residual magnetization, ratio The surface area and the like may be appropriately selected depending on the purpose. The magnetic powder to be used is usually in a needle form or a granular form, and is selected depending on the use as a magnetic recording medium.

As the binder used in the present invention, any binder used for ordinary magnetic recording media can be used. For example, a thermoplastic binder, a thermosetting binder, an electron beam curable binder, and the like can be given. The content of the binder per 1 part by weight of the magnetic powder is preferably about 0.1 to 0.3 parts by weight.

In the present invention, it is preferable to use a non-magnetic abrasive having a Mohs hardness of 6 or more as the abrasive. Examples of such non-magnetic abrasives include alumina Al ₂ O ₃ , non-magnetic chromium oxide Cr ₂ O ₃ , silicon carbide SiC, and titanium oxide T
One or more of iO ₂ , silica SiO ₂ , and zirconia ZrO ₂ may be mentioned, and among these, Al ₂ O ₃ , Cr is preferable in terms of abrasive dispersibility or head wear.
Those containing at least one of ₂ O ₃ and SiC are preferred.
The average particle size of these abrasives is 0.6 μm or less, especially 0.1 μm.
It is preferably about 0.4 μm. When the thickness exceeds 0.6 μm, the electromagnetic conversion characteristics are deteriorated, and when the particle size is too small, the durability is insufficient. In addition, in the particle shape of the abrasive,
Various shapes such as a spherical shape and a square shape may be used.
The calculation may be performed by assuming a circle from the projected area of the image.

Such an abrasive is contained in the entire magnetic layer in a total amount of 5 to 20% by weight, particularly 8 to 18% by weight, and more preferably 10 to 18% by weight based on the magnetic powder. The total amount is 5
If the amount is less than the weight percentage, the durability stability decreases. On the other hand, if it exceeds 20% by weight, the electromagnetic conversion characteristics deteriorate.

It is preferable that such an abrasive is usually unevenly distributed in the surface layer portion of the magnetic layer having a single-layer structure. That is, the content density of the abrasive is highest on the surface layer portion and lowest on the support side. And it is preferable to have an inclined region in which the content density changes continuously from the surface layer portion toward the support.

More specifically, ρ ₁ / ρ ₂ is 1.5 or more, more preferably 1.5 or more, where ρ _{1 is} the content density of the surface layer having a thickness of 0.6 μm from the surface and ρ ₂ is the content density of the remaining portion. Is preferably set to 1.5 to 10. ρ ₁ / ρ
_{If 2} is less than 1.5, the effect of the present invention tends to decrease. However, if it is too large, the effect of reinforcing the magnetic layer tends to be insufficient. In this case, the content density is a projected area% of the abrasive occupying a predetermined region of the magnetic layer when a cross-sectional TEM image of the magnetic layer is observed, and depends on the amount of the added abrasive.
[rho ₁ is preferably set to 8-25%, especially 10-20%. tend to durability is decreased [rho ₁ is small, tends to too large, the electromagnetic conversion characteristics decreased.

The content density of the abrasive in the entire magnetic layer is usually about 2 to 8% when the added amount is 5 to 20% by weight. To form a layer, about 25% by weight of an abrasive must be added. And in the case of the magnetic recording medium of the present invention,
The high-density region having a content density of 10 to 20% is generally about 0.3 to 1.0 μm, and it is usually possible to have a slope or transition region in which the density decreases with a continuous gradient on the support side of this region. preferable.

For such a magnetic layer, it is effective to use various known antistatic agents, lubricants, dispersants, and additives for reinforcing the strength of the coating film according to the intended use. The thickness of the magnetic layer is preferably 4 μm or less, particularly about 1.0 to 4.0 μm.

The porosity in the magnetic layer is 7% or less, usually about 2 to 7%. The porosity can be calculated, for example, by comparing the saturation magnetization σ _{S of the} magnetic powder with the residual magnetic flux density Br of the medium, and can also be obtained from the SEM image of the cross section of the magnetic layer. Further, in the present invention, the magnetic layer is usually a single-layer film having the above-mentioned abrasive-containing density profile, but in some cases, a magnetic underlayer may be provided on the support side of the single-layer film. Good. The medium of the present invention may have such a magnetic layer only on one surface of the non-magnetic support, and the external magnetic field application described later may be performed each time the magnetic layer is formed. It may be a so-called double-sided medium.

There is no particular limitation on the non-magnetic support used for the magnetic recording medium of the present invention, and a material selected from various flexible materials and various rigid materials according to the purpose may be used in a predetermined form such as a tape shape according to various standards. The shape and the size may be set. For example,
Examples of the flexible material include polyester such as polyethylene terephthalate. If necessary, a back coat layer or the like may be provided on the opposite side of the underlayer or the magnetic layer of the non-magnetic substrate. The back coat layer is not limited, and may be a known coating type back coat layer containing a conductive filler, various pigments, and the like, or a plasma polymerized film may be used as the back coat layer.

In order to obtain such a magnetic recording medium, first, a magnetic paint having a predetermined composition is prepared as a coating composition for a magnetic layer. Next, this magnetic paint is applied on the long non-magnetic support 3. The application is performed by a reverse method, a gravure method, or the like. Then, if necessary, a smoothing means is brought into contact with the coating film surface.

Next, during the drying, an oblique external magnetic field in which the direction of the magnetic field is continuously reversed is applied. The magnetic field generating means of the external magnetic field applying means used is arbitrary, and examples thereof include a permanent magnet and an electromagnet.

Here, one example of the external magnetic field applying means suitable for the present invention is shown in FIGS. The external magnetic field applying means 5 shown in FIGS. 1 and 2 is configured such that a plurality of unit magnets 4 are provided on the back surface opposite to the application surface of the nonmagnetic support 3 so that adjacent unit magnets have different polarities. It is arranged and configured. The number of unit magnets 4 to be arranged corresponds to the number of magnetic field reversals, and is preferably 4 or more, especially about 8 or more and about 25 or less . If the number of reversals is small, the effect of eliminating surface defects is lost. Further, it is difficult to obtain a predetermined abrasive distribution profile. Also, an excessively large number of inversions is unnecessary, and it is preferable that the surface is not roughened.

Each unit magnet 4 is, as shown in FIG.
Each unit magnet 4 has a length longer than the width of the non-magnetic support of the tape 1, and each unit magnet 4 is arranged parallel to the non-magnetic support and inclined with respect to the transport direction. As a result, an oblique reversal magnetic field indicated by an arrow in the figure is alternately applied to the tape 1. Note that each unit magnet 4 does not necessarily have to have a width wider than the support 3, and it is sufficient that the aggregate of the unit magnets 4 is wider than the support 3 as a whole.

It is extremely difficult to level the paint itself for various coating film defects such as gravure patterns or short and long streak failures such as long streaks. Therefore, in the present invention,
When the coating film itself was vibrated by applying an oblique reversal magnetic field to the magnetic powder from the outside, the surface defect was eliminated.

That is, the external magnetic field applying means 5 is also a non-contact type smoothing means from another viewpoint.
In this case, the magnetic field component of the continuously inverted oblique magnetic field of the NS pole is
Do not match the longitudinal streak or gravure pattern. More specifically, the direction of the magnetic field effective for eliminating coating defects such as longitudinal stripes or the gravure pattern GP shown in FIG. 4 is, as shown by the arrow in FIG. is there. Therefore, when the magnetic field vectors are decomposed, the components are set so that the component force exists in a direction perpendicular to these components. In this case, as shown in FIG. 3, the angle θ between the magnetic field H and the transport direction MD of the nonmagnetic support 3
Is about 10 to 80 °. In this case, 0 ° is a parallel magnetic field, and θ> 0 is an inclined or oblique magnetic field. However, in order to allow a large amount of abrasive to be present near the surface, θ =
Since 0 has already been proposed in Japanese Patent Application No. 1-342988, θ = 0 is excluded in the present invention. θ> 0
As a result, such an effect is increased.

The unit magnets 4 may be arranged adjacent to each other as shown, or may be arranged with a predetermined gap. Further, it is advantageous to use the unit magnets 4 having the same magnetic field strength and size. In this case, the unit magnet 4 to be used is optional as long as a uniform magnetic field is applied in the tape width direction, and may have a size corresponding to a reversal cycle described later. The maximum energy product (BH) max of the unit magnet 4 is preferably about 3.5 to 37 MGOe.
The interval between the tape 1 and the external magnetic field applying means 5 is usually 3 to
It is about 20 mm. In this way, the intensity of the magnetic field in the magnetic layer 2 is preferably 300 G or more, particularly preferably 500 G or more.
~ 2000G.

Using such an external magnetic field applying means 5,
In opposition to this, the tape 1 is transported. As a result, an external magnetic field whose direction of the magnetic field is continuously reversed is applied to the undried magnetic layer 2 as shown in the figure. In this way, every time the direction of the magnetic flux from the unit magnet 4 is reversed, the magnetic powder in the applied magnetic paint swings while inverting, and the magnetic paint also swings, and the magnetic powder is moved by the external magnetic field. It is periodically drawn to the application means side. At this time, the non-magnetic abrasive is relatively densely distributed on the surface of the magnetic layer 2. Moreover,
The surface is smoothed and coating defects are eliminated. Then, the magnetic powder is subjected to a kind of pre-orientation treatment in accordance with such oscillation, so that the degree of orientation is increased and the squareness ratio is improved. At the same time, defoaming is performed with the rocking, and the porosity decreases.

In this case, the number of reversals of the magnetic field is determined by the unit magnet 4
The number is the same as above, and 4 or more, especially 8 as described above
More than about 25 or less . Further, the magnetic field reversal cycle may be generally set to about 50 to 400 times / second.

In such a case, in the illustrated example, an external magnetic field substantially in the longitudinal (conveying) direction of the tape or in a direction inclined thereto is applied from the back side of the support, and this is reversed.
The reason why the magnetic powder is applied from the back side of the support is to swing the magnetic powder on the support side. On the other hand, when acting from the coating film surface, rocking occurs on the coating film surface side, and the abrasive is
Does not float on the surface. From these, unlike the illustrated example, the external magnetic field applying means 5 may be arranged on both the coating surface side and the back surface side of the support 3, but especially when the external magnetic field applying means 5 is arranged only on the back surface side as shown in the illustrated example. It is highly effective in creating a gradient distribution of the abrasive. However, to eliminate surface defects,
Either of them may be on the back side or both.

Next, the tape 1 is conveyed between the magnets 6 for orientation to perform longitudinal orientation. In this case, the magnet for orientation 6 is arranged so as to be separated from the external magnetic field applying means 5 so as not to interfere with the magnet. The magnetism of the magnet for orientation 6 is as follows.
Usually, it is preferable that the polarity is opposite to the polarity of the unit magnet 4 in the last stage of the external magnetic field applying means 5. In this way, the alignment can be performed smoothly. The orientation magnetic field strength in the magnetic layer 2 is preferably about 1500 to 10000 G.

After that, it is cured through a surface smoothing treatment such as calendering. Then, this may be cut into a predetermined size by a slitter or the like to obtain a magnetic tape or the like, or a raw film may be obtained by replacing the alignment process with a random alignment process, and a floppy disk may be obtained by punching the raw material.

[0042]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

Example 1 A magnetic coating material was prepared at the compounding ratio shown below.

100 parts by weight of metal magnetic powder Average major axis: 0.2 μm Average axis ratio: 8 Hc: 1500 Oe σ _S : 130 emu / g Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH manufactured by UCC) 10 parts by weight Polyurethane resin (N-2304 manufactured by Nippon Polyurethane) 10 parts by weight Low molecular weight polyisocyanate compound (Coronate L manufactured by Nippon Polyurethanes) 5 parts by weight Abrasives 3 to 30 parts by weight Stearic acid 0.2 parts by weight Lecithin 0.5 parts by weight Toluene 50 parts by weight Methyl ethyl ketone 50 parts by weight Methyl isobutyl ketone 50 parts by weight

In this case, the abrasive has an average particle size of 0.25 μm.
Of Cr ₂ O ₃ and Al ₂ O ₃ having an average particle diameter of 0.20 μm were mixed at a weight ratio of 1: 1 and used in parts by weight shown in Table 1. This magnetic paint was applied on a 10 μm-thick polyester film by a reverse method, applied with an external magnetic field, oriented, calendered, and then heat-cured.

In this case, the external magnetic field is applied by an external magnetic field applying means 5 having a plurality of unit magnets 4 shown in FIGS.
This was performed using At this time, the magnetic field direction H and the transport direction MD
Is 60 °. Since the length of the unit magnet 4 in the tape transport direction was 20 mm, the length of the unit magnet 4 in the tape transport direction was 40 mm. At this time, the surface magnetic field of each unit magnet was the same. Then, the number of unit magnets was changed, and the magnetic field was inverted at the times shown in Table 1 below. The number of magnetic field reversals is the number of unit magnets. Also, the magnet for orientation 6
Was 4000 G, and the final thickness of the magnetic layer was 3.0 μm.

This was cut into a width of 8 mm by a slitter to prepare a magnetic tape sample. Observing the TEM image of the cross section of the magnetic layer of each sample were determined [rho ₁ and the remainder [rho ₂ of the surface layer portion of 0.6μm from the surface. ρ ₁ and ρ ₂ are
This is the projected area ratio of the abrasive in the cross section. In addition, in Sample Nos. 1 to 4 of the present invention, a range of about 0.2 μm from the position of about 0.2 μm from the surface layer had ρ ₁ as described above, and had an inclined layer below this.

Further, as a comparative tape sample, a lower layer of the magnetic layer was applied, and an upper layer was laminated thereon, thereby preparing Sample No. 13. In this case, the lower layer contained 12.5 parts by weight of the abrasive with respect to 100 parts by weight of the magnetic powder, and the upper layer contained 25 parts by weight of the abrasive. The final thickness of the magnetic layer was 2.4 μm for the lower layer and 0.6 μm for the upper layer.

Table 1 shows the squareness ratio, Br, and porosity (%) of each sample. The porosity was calculated from the residual magnetic flux density Br of the tape. 5MHz of each sample
The RF output at was measured. Note that the RF output was represented by a dB value with respect to the output of Sample No. 11.

Further, still characteristics and head clogging of each sample were evaluated. Still characteristics are normal temperature (23
C., 65% RH), and the output decrease after 2 hours was evaluated according to the following criteria.

◎: RF output decrease less than 1.0 dB ：: 1.0 dB or more and less than 2.0 dB Δ: 2.0 dB or more and less than 3.0 dB ×: 3.0 dB or more

Further, clogging of the head is caused by high temperature and high humidity (40 ° C.).
C., 80% RH), and evaluated according to the following criteria.

A: No more than 100 passes occurred. ：: Occurs when less than 100 and 50 or more △: Occurs when less than 50 and 20 or more X: Occurs when less than 20 passes

Table 1 shows the results.

[0055]

[Table 1]

Table 1 shows the effect of the present invention.

The comparative sample No. 13 had poor calendering workability and a rough surface because the upper layer was thin.
RF output is low. In contrast, the sample No. 1 of the present invention
No. 4 to No. 4 each had good electromagnetic conversion characteristics and durability.

Example 2 Using the same type of magnetic paint for floppy disk as in Example 1, the magnetic coating was dried to a thickness of 2 by the reverse method.
It was applied to a thickness of μm and was brought into contact with a contact-type smoothing device. Thereafter, as shown in FIGS. 1 and 2, θ = 45 °, the number of steps = 7 steps, a switching magnetic field of 1000 G in NS magnetic field strength was applied on the base film, and then the sample was oriented. Was prepared.

Comparative Example 1 A sample was prepared under the same conditions as in Example 1 except that no reversal magnetic field was applied. In this case, 0.1μ
Longitudinal stripes with a depth of m were found.

Example 3 The same magnetic paint as in Example 2 was used, and a magnetic coating film was applied by a gravure reverse method using a 45 ° oblique gravure cylinder, and then θ = 45 ° (gravure pattern) The direction of the magnetic field is at right angles), the number of stages = 10, NS
A switching field of 1000 G was applied on the base film with a magnetic field strength, and then orientation was performed to prepare a sample.

Comparative Example 2 A sample was produced under the same conditions as in Example 3 except that no reversal magnetic field was applied.

The above four samples were punched out to 3.5 inches, used as floppy disks, and measured for high-pass modulation and evaluated for surface condition. Table 2 shows the results. The high-pass modulation is a% value obtained by dividing the average of the high-pass value by the average of the low-pass value and multiplying the result by 100 by dividing the low-pass value and the high-pass value by a low-pass filter after the modulation measurement.

[0063]

[Table 2]

From the results shown in Table 2, the effect of the present invention is clear.

[0065]

According to the present invention, coating defects such as longitudinal stripes and gravure patterns on the coating surface can be eliminated, the surface properties can be improved, the coating quality can be improved, and the yield can be improved. . In addition, high reliability and durability can be secured,
In addition, the high electromagnetic conversion characteristics of the thin magnetic layer for high-density recording can be maintained, and the defoaming effect and the orientation effect of the magnetic coating film can be obtained, so that the electromagnetic conversion characteristics are further improved.

[Brief description of the drawings]

FIG. 1 is a side view for explaining a magnetic recording medium manufacturing method of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is a plan view illustrating a relationship between a magnetic field direction and a transport direction of a nonmagnetic support.

FIG. 4 is a plan view showing a relationship between a gravure pattern and a magnetic field.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tape 2 Magnetic layer 3 Non-magnetic support 4 Unit magnet 5 External magnetic field application means 6 Orientation magnet MD Moving direction GP Gravure pattern H Magnetic field

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kunimasa Mohara 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-61-267932 (JP, A) JP-A-58 JP-A-1441437 (JP, A) JP-A-53-64504 (JP, A) JP-A-58-12132 (JP, A) JP-A-3-295030 (JP, A)

Claims (7)

(57) [Claims] 1. A gravure coating of a coating composition for a magnetic layer containing a magnetic powder and a binder while continuously moving a long non-magnetic support, and then, on one surface side of the non-magnetic support, A plurality of unit magnets are arranged so as to be inclined with respect to the moving direction of the non-magnetic support so that the magnetic field component does not coincide with the gravure pattern inclined with respect to the moving direction of the non-magnetic support. Only one magnetic pole is located on one side of the body, adjacent magnetic poles are different from each other,
The unit magnet is disposed opposite to the non-magnetic support so that the length direction of the unit magnet is parallel to the non-magnetic support and inclined with respect to the longitudinal direction, and the unit magnet is inclined with the moving direction of the non-magnetic support. Repeatedly apply the magnetic field between the unit magnets at least eight times while alternately reversing it,
The magnetic powder in the coating film is vibrated so that the angle between the longitudinal direction of the non-magnetic support and the magnetic field is 10 to 80 °, and the magnetic field in the magnetic layer is 500 to 2000 G. A method for manufacturing a magnetic recording medium, comprising smoothing a gravure pattern. 2. A coating composition for a magnetic layer containing a magnetic powder and a binder is applied while continuously moving a long non-magnetic support, and a smoothing means is brought into contact with the coating film surface. A plurality of unit magnets are arranged on one surface side of the non-magnetic support so as to be inclined with the moving direction of the non-magnetic support so that the magnetic field component does not match the gravure pattern inclined with respect to the moving direction of the non-magnetic support. However, in this unit magnet, only one magnetic pole is located on one surface side of the nonmagnetic support, and adjacent magnetic poles are different from each other,
The unit magnet is disposed opposite to the non-magnetic support so that the length direction of the unit magnet is parallel to the non-magnetic support and inclined with respect to the longitudinal direction, and the unit magnet is inclined with the moving direction of the non-magnetic support. Repeatedly apply the magnetic field between the unit magnets at least eight times while alternately reversing it,
The magnetic powder in the coating film is vibrated so that the magnetic field in the magnetic layer has a magnetic field of 500 to 2000 G at an angle between the longitudinal direction of the non-magnetic support and the magnetic field of 10 to 80 ° and is smoothed. Item 2. The method for manufacturing a magnetic recording medium according to Item 1. 3. A method for coating a magnetic layer coating composition containing a magnetic powder, a nonmagnetic abrasive having a Mohs hardness of 6 or more, and a binder while continuously moving a long nonmagnetic support. A plurality of unit magnets are arranged on one surface side of the non-magnetic support so as to be inclined with respect to the moving direction of the non-magnetic support so that the magnetic field component does not match the gravure pattern inclined with respect to the moving direction of the non-magnetic support. However, in this unit magnet, only one magnetic pole is located on one surface side of the nonmagnetic support, and adjacent magnetic poles are different from each other,
The unit magnet is disposed opposite to the non-magnetic support so that the length direction of the unit magnet is parallel to the non-magnetic support and inclined with respect to the longitudinal direction, and the unit magnet is inclined with the moving direction of the non-magnetic support. A magnetic layer in which the magnetic powder in the coating film vibrates by repeatedly applying the magnetic field between the unit magnets while inverting the magnetic field alternately, and wherein the nonmagnetic abrasive is contained at a higher density than other portions in the surface layer portion Forming a magnetic recording medium. 4. The magnetic layer has a thickness of 4 μm or less,
The magnetic layer contains the nonmagnetic abrasive in an amount of 5 to 20% by weight based on the magnetic powder, and the density of the nonmagnetic abrasive in the surface layer having a thickness of 0.6 μm from the surface of the magnetic layer. the [rho _1, when a _2-containing density [rho nonmagnetic abrasive balance method of manufacturing a magnetic recording medium according to claim 3 ρ ₁ / ρ ₂ is 1.5 or more. 5. The non-magnetic abrasive has an average particle size of 0.6 μm.
Claim m or less [rho ₁ is 8 to 25% 3 or 4
3. The method for manufacturing a magnetic recording medium according to claim 1. 6. A unit magnet according to claim 1, wherein the unit magnets adjacent to each other have different polarities on opposite surfaces of the non-magnetic support, and a length direction of the unit magnet is parallel to the non-magnetic support and a longitudinal direction of the unit magnet. The method for manufacturing a magnetic recording medium according to claim 3, wherein the magnetic recording medium is arranged so as to be inclined on a side opposite to a coating surface of the nonmagnetic support. 7. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic powder is oriented after an external magnetic field is applied by the unit magnet.