JPH05128511A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a magnetic layer wherein no irregularity in a coating operation is caused and its smoothness is excellent by a method wherein a magnetic coating film with which a traveling nonmagnetic support body has been coated is made smooth while it is brought into contact with a flexible sheet whose surface roughness is specific and the magnetic layer is formed. CONSTITUTION:A gravure roll 1 picks up a paint 7 in a coating-liquid pan 6; the paint is filled into surface cells 8; the paint is transferred onto a nonmagnetic support body 4. A backup roll 2 brings the long nonmagnetic support body 4 such as a polyester film or the like into pressure-contact with the surface of the gravure roll 1; the paint which has been filled into the cells 8 on the gravure roll 1 is transferred satisfactorily onto the nonmagnetic support body 4. In addition, in order to make a transferred magnetic coating film smooth, a film smoother 5 whose surface roughness Ra is 10X10<-2> to 4X10<-2>mum and which is composed of a flexible film is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a magnetic recording medium in which a magnetic paint, a back coat paint or the like is applied by a gravure coating method, and more particularly, to an improvement in a surface smoothing method for an undried coating film Is.

[0002]

2. Description of the Related Art Generally, audio tapes and video tapes are coated with a magnetic paint prepared by dispersing and kneading a ferromagnetic powder, a binder, a dispersant, a lubricant, etc. in an organic solvent on a non-magnetic support such as a polyester film. By doing so, the magnetic layer is formed.

To apply these magnetic paints on a non-magnetic support, there have been, for example, a gravure coating method, a reverse roll coating method, a die coating method (extrusion method), etc., among them, high speed and operation. The gravure method is widely used because it is easy to manage and inexpensive.

The gravure coating method uses a coating device consisting of a gravure roll having a cell pattern engraved on the surface thereof and a backup roll for press-bonding the nonmagnetic support to the gravure roll. This is a method of transferring the paint. That is, in order to apply a magnetic coating material onto a non-magnetic support using this device, the non-magnetic support is pressure-bonded to a gravure roll with a backup roll made of an elastic material, and the roll surface is rotated by rotating these rolls. By picking up the paint in the coating liquid pan into each depression (cell) between the adjacent cell walls of the cell pattern engraved in the cell pattern and transferring the paint filled in the cell onto the non-magnetic support Paint is applied.

By the way, when the magnetic coating material is transferred by using a gravure roll, the magnetic coating material is transferred as it is on the non-magnetic support in a cell pattern engraved on the surface of the roll. Since the magnetic layer has an uneven shape, the unevenness needs to be smoothed before drying. Therefore, in the gravure coating method, a film smoother is usually used for smoothing the undried magnetic coating film after transferring the magnetic coating material.

This film smoother is, for example, as shown in Japanese Patent Publication No. 57-49973, attached to a roll, and the surface of the film smoother is brought into sliding contact with the magnetic coating in the state of being attached to the roll. The film is smoothed, or one end thereof is fixed by a holder and the other end is a free end, and the magnetic coating film is slid on the free end to smooth the magnetic coating film. In such a film smoother, it has been attempted to use various materials as constituent materials in order to obtain a higher smoothing effect. For example, a film smoother made of plastic, steel, paper or the like is known. Has been.

[0007]

However, when the above-mentioned film smoother is used to smooth the magnetic coating film, the unevenness of the magnetic coating film is eliminated to some extent, but the surface condition of the magnetic layer formed is When compared with the surface roughness range and the like that are severely restricted from the viewpoint of magnetic characteristics, it cannot be said that the surface is sufficiently smooth, and there is an adverse effect that the characteristics of the manufactured magnetic recording medium become non-uniform. When the present inventors have examined this point, the fact that the magnetic layer is not sufficiently smooth is related to the surface roughness of the film smoother, and the conventionally used film smoother has a surface roughness Ra.
Is too high (for example, 62 to 7 for PET film)
6 × 10 ^-2 μm), which proved to be the cause. Up to now, the surface condition of the film smoother itself has not been paid particular attention and has not been regarded as a problem, but the deterioration of the coating condition, which is considered to be the influence of the film smoother, has been overlooked.

Therefore, the present invention has been proposed in view of such conventional circumstances, and a magnetic recording medium capable of forming a magnetic layer having high smoothness and producing a magnetic recording medium having uniform characteristics can be manufactured. It is intended to provide a manufacturing method.

[0009]

In order to achieve the above object, a method of manufacturing a magnetic recording medium according to the present invention comprises a step of applying a coating material onto a non-magnetic support which continuously runs in a longitudinal direction,
In the method for producing a magnetic recording medium, which comprises a step of bringing the undried coating film formed by applying the coating material into contact with a flexible sheet to smooth the surface of the coating film, the surface roughness of the flexible sheet. Is center line average roughness Ra of 10 × 10 ^-2 to 4
It is characterized in that it is 0 × 10 ⁻² μm.

[0010]

When a flexible sheet is brought into contact with a magnetic coating film or a back coating film coated on a running non-magnetic support to smooth the surface of the coating film to form a magnetic layer, a back coating layer, etc. , The surface roughness R as the flexible sheet
When a having a of 10 × 10 ⁻² to 40 × 10 ⁻² μm is used, a magnetic layer and a back coat layer having excellent smoothness are formed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings.

First, in the present invention, a non-magnetic paint such as a magnetic paint or a back coat paint is applied onto the non-magnetic support. For example, in the case of the former, a magnetic coating film is formed by applying a magnetic coating composed of magnetic powder, a binder, a solvent and the like onto a non-magnetic support. In addition, magnetic powder used in magnetic paint,
As the binder and the solvent, any one may be used as long as it is usually used as a material of a magnetic coating material in a coating type magnetic recording medium, and as the magnetic powder, for example, γ-Fe ₂ O ₃ etc. Oxide magnetic powder of Fe, Co
Examples thereof include metal-based magnetic powders, binders such as polyvinyl chloride-based copolymers and polyurethane resins, and solvents such as methyl ethyl ketone, toluene, and cyclohexanone. Further, a lubricant, an abrasive, a dispersant, etc. may be added to the above magnetic paint.

In the latter case, a back coat paint comprising carbon black, a binder, a solvent and the like is applied to the surface opposite to the magnetic paint to form a back coat layer. As the binder and the solvent, any of those used in magnetic paints can be used.

To apply the above paint, for example, the application device shown in FIG. 1 is used. The coating device is a transfer device 3 including a gravure roll 1 having a cell pattern engraved on its surface and a backup roll 2 for pressing the non-magnetic support 4 onto the gravure roll 1, and a non-magnetic support by the transfer device 3. It has a film smoother 5 for smoothing the paint transferred onto the body 4.

The gravure roll 1 picks up the paint 7 stored in the coating liquid pan 6, fills it in the cells 8 provided on the surface thereof, and transfers it onto the non-magnetic support 4. .. The gravure roll 1 is a cylindrical roll made of Fe or the like having a relatively low hardness, and a large number of the cells 8 are formed on the outer peripheral surface as, for example, quadrangular pyramid-shaped recesses.

The backup roll 2 is made by pressing a long non-magnetic support 4 such as a polyester film onto the surface of the gravure roll 1 to fill the paint filled in the cells 8 provided in the gravure roll 1. Magnetic support 4
For good transfer onto the top, it is made of an elastic roll of rubber or the like. Therefore, the elastic force of this roll causes the non-magnetic support 4 to come into close contact with the cells 8 on the surface of the gravure roll 1, and the paint filled in the cells 8 can be satisfactorily transferred to the non-magnetic support 4. The backup roll 2 is provided so as to face the gravure roll 1 and sends the non-magnetic support 4 in the direction of arrow X in the figure in synchronization with the gravure roll 1.

In the transfer device 3, the coating material picked up from the coating liquid pan 6 and filled in the cells 8 is scraped off at a position close to the gravure roll 1 on the supply side of the nonmagnetic support 4. A doctor blade 12 is provided to keep the amount constant.

Further, in the coating device, the film smoother 5 made of a flexible film for smoothing the magnetic coating film transferred by the transfer device 3 having the above-mentioned structure is provided as the transfer device 3. Is provided on the downstream side of.
That is, the magnetic coating film 14 transferred by the transfer device 3
Since it is transferred as it is with the cell pattern of the gravure roll 1, it has irregularities and cannot be used as a magnetic layer as it is. Therefore, in the above coating apparatus, the film smoother 5 is provided on the downstream side of the transfer apparatus. In addition,
The method of supporting the film smoother 5 is not particularly limited. For example, one end of the film smoother 5 may be fixed to the holder, the other end may be formed as a free end, and the free end may be installed so as to contact the non-magnetic support 4 in the width direction.
In this case, the magnetic coating film 14 is brought into sliding contact with the other end of the film smoother so that the irregularities are leveled and smoothed. Alternatively, the film smoother may be attached to a roll, and the roll to which the film smoother is attached may be installed so as to come into contact with the magnetic coating film so that the axial direction thereof is the width direction of the non-magnetic support. In this case, the magnetic coating film is smoothed by making sliding contact with the outer peripheral surface of the roll to which the film smoother is attached.

Here, in order to form a magnetic layer having high smoothness, the surface roughness Ra of the film smoother 5 is 10 × 1.
It is necessary that the thickness is 0 ⁻² to 40 × 10 ⁻² μm. When the surface roughness Ra is less than 10 × 10 ⁻² , the film smoother 5 and the non-magnetic support are likely to be in close contact with each other, resulting in poor running and vibration, etc., to sufficiently smooth the magnetic coating film. I can't. Further, when the surface roughness Ra of the film smoother 5 exceeds 40 × 10 ⁻² μm, the surface is too rough this time, and the surface of the magnetic coating film becomes rough accordingly, and the magnetic layer is also sufficiently formed. It cannot be smoothed. In addition,
The surface roughness Ra referred to here is the center line average roughness Ra defined in JIS-B0601, and is an index of two-dimensional roughness.

The flexible film constituting the film smoother 5 is not particularly limited, and any film can be used as long as it provides sufficient stiffness as a film smoother and has proper wettability with respect to the magnetic paint. For example, a polyethylene terephthalate film is suitable. Further, the surface roughness Ra of the flexible film is
Can be adjusted to a predetermined surface roughness Ra, for example, by adding a filler component such as silica or organic powder.

The thickness of the film smoother is not particularly limited and is arbitrary, but is usually 30 to 100 μm.
m.

Next, in order to confirm the effect of controlling the surface roughness Ra of the film smoother, in the above-mentioned manufacturing method, the film smoother has a film thickness and a surface roughness Ra shown in Table 1. Instead of the smoother, magnetic recording media (Sample Tape 1 to Sample Tape 5, Comparative Tape 1, Comparative Tape 2) were produced.

[0023]

[Table 1]

Then, the three-dimensional roughness SRa of the magnetic layer of the produced magnetic recording medium was measured and the coating state was evaluated. The results are shown in Table 2.

[0025]

[Table 2]

The surface roughness was measured according to the method specified in JIS. Further, the coating state of the magnetic layer is evaluated by visually observing the presence or absence of coating unevenness. When there is almost no coating unevenness, the surface state is particularly good, ⊚, when the surface state is good, the surface is shown. When the condition is within the practical limit, it is expressed as △, and when the surface condition is practically problematic, it is expressed as ×.

As can be seen from Table 2, in the magnetic tape produced by using the film smoother having the surface roughness Ra deviated from the predetermined range, the SRa of the magnetic layer is high and the coating unevenness occurs. On the other hand, in the magnetic tape produced by using the film smoother having the surface roughness Ra within the predetermined range, the SRa of the magnetic layer is 0.03 to
It can be seen that each of them is as low as 0.02 and is formed with a good coating state.

Therefore, it was found that using a film smoother having a surface roughness Ra within a predetermined range is effective in forming a magnetic layer and a back coat layer having a smooth surface without coating unevenness. It was

The present invention may be applied to other smoothing devices such as a bar smoother in addition to the film smoother. For example, if the outer peripheral surface of the bar smoother has a predetermined surface roughness Ra, a magnetic layer having no coating unevenness and high smoothness is formed as in the case described above.

[0030]

As is apparent from the above description, in the method for manufacturing a magnetic recording medium of the present invention, a flexible film is brought into contact with a magnetic coating film applied on a running non-magnetic support to form a magnetic film. When smoothing the surface of the magnetic coating film to form the magnetic layer,
As the flexible sheet, the surface roughness Ra is 10 × 10 ^-2.
Since the one having a thickness of up to 40 × 10 ^-2 μm is used, a magnetic layer having no coating unevenness and excellent smoothness can be formed.

Therefore, according to the present invention, it is possible to obtain a magnetic recording medium which exhibits a clear image when used for a video tape, and exhibits uniform characteristics without sensitivity unevenness when used as an audio tape. Is possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a smoothing device to which the present invention is applied.

[Explanation of symbols]

 1 ... Gravure roll 2 ... Backup roll 5 ... Film smoother

Claims (1)

[Claims] 1. A step of applying a coating material on a non-magnetic support which continuously runs in the longitudinal direction, and a undried coating film formed by the application of the coating material is brought into contact with a flexible sheet to form a surface of the coating film. In the method of manufacturing a magnetic recording medium, the surface roughness of the flexible sheet is 1 at a center line average roughness Ra.
A method of manufacturing a magnetic recording medium, characterized in that it is 0 × 10 ^-2 to 40 × 10 ^-2 μm.