JPH0562184A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To manufacture a magnetic recording medium in which the thickness of a magnetic coating film is uniform. CONSTITUTION:In a state that the back of a running web is not supported, an extrusion-type coating head is pressed relatively to the web. A coating liquid is extruded from at least one slit in the coating head, and the web is coated with the liquid. When a coating operation is executed continuously at high speed, the speed of the coating operation is lowered when the web is passed through a joint (a spliced part) between rolls, and a feed amount and a tension are adjusted. Thereby, a uniform coating film can be obtained.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In a method in which a running web (support film such as polyester) is stretched between a pair of backup rolls and a magnetic coating material is applied using an extrusion type coating head in the middle of these rolls, the final coating is performed. It is possible to supply and apply only the amount of paint that remains as a film, does not require an excessive amount of supply like the conventional gravure method or roll coating method such as reverse method, and when speeding up,
There are no problems such as the dispersion of paint due to the centrifugal force caused by the rotation of the roll, or the dispersion of paint when it is transferred to the web, so coating can be sped up, productivity is improved, and cost can be reduced. Become.

For speeding up, conventional 300 to 400 m
Was up to about 450/600 m / mi by using the extrusion type coating head.
It is possible to increase the speed by n or more.

[0004]

A problem that arises when the speed is increased is a problem of passing a seam (splice portion) between rolls.
In the coating itself, the speed is equal and the productivity is increased, but the extrusion coating head itself must be moved in order to pass through the splice portion, and the length of the base that passes during this period is the uncoated portion. , Will be a loss.
It is a simple story to increase the coating speed by 1.5 times and spend the same time to pass through the splice portion, but the loss also becomes 1.5 times. Even if productivity is improved by increasing the coating speed, this is unreasonable.

In that case, the time for passing through the splice portion may be shortened, but in order to maintain the slit gap precisely controlled by the extrusion coating head itself, the mechanical strength must be maintained. It is a structure that is considerably heavy in weight, and it is practically difficult to make it less than 1 second due to the weight, even if the movement of a cylinder or the like for movement is to be made faster.

In addition, it is desired that at least about 10 seconds should be taken into consideration when cleaning the paint discharge portion of the extrusion coating head when passing the splice portion between the rolls (wiping the portion where the paint spills when leaving). Is. In this way, the key to achieving high-speed coating is how to solve the two problems of improving productivity by increasing speed and increasing defects at the splice part.

[0007]

In order to solve the contradictory problem described above, an attempt was made to temporarily reduce the speed before and after splicing. However, it is not done simply, and for the slowed down portion and the re-accelerated portion, even if the coating supply amount is adjusted relative to the coating speed, that portion becomes a defective portion due to thickness unevenness in the width direction. Therefore, the yield in the length direction was not improved.

Then, the present inventors further examined the behavior thereof in detail, and found that a certain factor was also changing at the same time. That is, when the coating speed is changed while maintaining a constant coating thickness, the optimum coating part tension value also changes at the same time, so that not only the amount of paint is adjusted relative to the speed but also the coating part tension is changed. You have to control.

The present inventors collected data on the optimum tension value of the coating portion with respect to the change in speed when the coating thickness was constant for each coating material to be coated. This changes the speed as a constant coating thickness and changes the coating part tension within the same speed. The widthwise thickness of the thus prepared sample was measured with a film thickness meter, and the condition where the thickness was most uniform was judged as the optimum tension value of the coating portion. An experiment was conducted by programming these and changing the coating part tension control system so that the coating part tension could be changed according to the actual speed of the coating line.

[0010]

[Explanation of Embodiments] Concretely, the following embodiments will be explained. (Example 1) Using audio paint A, width 520 mm,
The base film having a thickness of 8 μm was dried at a speed of 450 m / min so as to have a coating film thickness of 4.7 μm, and two rolls having a base film length of 5000 m were continuously applied. At this time, the tension of the coating portion was set as follows.

T = 0.036V-3.2 where T is tension [kg / width] and V is coating speed [m / m]
in]. Also, in the roll-to-roll splicing, deceleration is started at the remaining 100 m of the previous roll, and the speed is 200 m / mi at a deceleration acceleration of 0.3 m / s ^2.
decelerating to n, splicing, splicing with an unwinder, and simultaneously moving the extrusion type coating head,
The discharge of the paint was stopped and the lip portion was washed. It took 10 seconds for the coating head to move to the home position, and the discharge of the paint was restarted when the coating head moved to the home position. From the timing of returning to the fixed position, the vehicle traveled at 200 m / min for 4 seconds, and then accelerated at an acceleration rate of 0.3 m / s ² to 450 m / min.
The speed was constant at min. At this time, it took 4 seconds after the paint was discharged again until the flow rate became stable. The amount of coating material supplied in the acceleration / deceleration range was controlled in proportion to the speed so that the coating film thickness was constant.

Comparative Example 1 Coating was performed under the same conditions as in Example 1 except that the tension was set constant at 13 kg / width. At this time as well, until the flow rate stabilizes after the paint is discharged again 4
It took seconds.

(Comparative Example 2) The set tension was set constant at 13 kg / width, and the splice between rolls was made as follows:
As in Example 1, two rolls were continuously applied at a coating speed of 450 m / min without deceleration and acceleration. At this time, the moving time of the extrusion coating head was 10 seconds. Also at this time, it took 4 seconds after the paint was discharged again until the flow rate became stable. The results are shown in Table 1.

[0014]

[Table 1]

In the first embodiment, a loss of 47 m, which corresponds to the travel time of the coating head and the length of time it takes for the coating material to be stabilized after being re-discharged, is comparatively large.
Thickness unevenness in the width direction occurred in the portion where the deceleration started and the portion where the speed became constant at 200 m / min, and an extra 75 m was lost as compared with Example 1.

Further, in Comparative Example 2 in which coating was performed without deceleration, the length of time during which the coating head moved and the time during which the coating material was re-discharged until the coating material became stable, and the equivalent 105
I lost m.

As is clear from the results, the loss length of the material can be shortened by adopting a method of accelerating and decelerating at the splice portion and changing the coating material supply amount and the coating portion tension according to the coating speed.

Claims (1)

[Claims] 1. A method of applying an extrusion-type coating head to a web by pressing the extrusion-type coating head relative to the web while the back surface of the traveling web is not supported, and pushing out the coating solution from at least one slit of the coating head. A method for manufacturing a magnetic recording medium, characterized in that, when coating is performed continuously at a high speed, the coating speed is reduced and the supply amount and tension are adjusted when passing through a joint (splice portion) between rolls.