JP3192179B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art In a method in which an extrusion-type coating head is relatively pressed against a supporting web while not supporting a back surface of a running web to apply the web, backup webs 5 and 5 'as shown in FIG. The key is how uniformly the web 6 can be pressed against the slit outlet (lip) of the extrusion type coating head 7 where the paint is discharged while the tension is supplied. To press uniformly is to add a uniform discharge resistance to the coating liquid discharged from the slit, and even if the coating liquid is supplied in a uniform distribution within the slit, if the final discharge resistance is locally different, Since the coating liquid is to be discharged from a portion having a small resistance as a whole, the thickness in the width direction becomes non-uniform. Adding the ejection resistance uniformly means, in other words, how uniformly the web can be stretched.

[0002] It is the lip from which the coating liquid is discharged that the web must be stretched uniformly, but this is also the point where two forces are pressed. Due to the tension of the web, the web presses the ejected coating liquid (which is also the force that wets the coating liquid on the web) and the ejected coating liquid presses the web. The running height is determined. At this time, if the tension is too low, a force for wetting the discharged coating liquid is not generated, and the coating film becomes thin. On the other hand, if the tension is too high, the web undergoes elastic deformation, elongates in the running direction, tries to shrink in the width direction, and becomes wavy when viewed in a cross section in the width direction. In this case, the ejection resistance becomes non-uniform in the width direction, which appears as stripe-shaped thickness unevenness as it is. In other words, it is necessary to optimally set the balance of the force at the lip portion in order to apply the film uniformly in the width direction.

[0003]

Conventionally, the tension is set at a fixed value, and the coating method is a pre-metering type such as a reverse method or a gravure method. The effect of the set tension on the web thickness was small. However, in the method using the extrusion-type coating head, the optimal web condition as described earlier when transferring to the web is used in spite of the pre-metering method in which the total coating thickness is determined by the coating liquid supply amount. If not, the second weighing is performed at the time of transfer, causing a blurring or stripe-like coating defect, resulting in a large variation in quality and a reduction in yield. To make matters worse, the optimal condition of the web depends on the properties of the coating solution, the thickness of the web, the coating speed, and the thickness of the coating film, and when these change, it is necessary to respond quickly by changing the tension. There is a need. In actual production, the web thickness (base film thickness), coating speed, and set film thickness are fixed and production is performed as a series. On the other hand, the viscosity of the coating liquid is obtained by dispersing or dissolving the solid content of the magnetic powder, binder and other additives that the coating material wants to remain as a medium in an organic solvent having a high evaporation rate. The paint is stored in the storage tank of the supply system at the time of application, and is sequentially sent to the application head, and apparently the viscosity change seems to be in equilibrium by adding the used amount. However, organic solvents evaporate and paint viscosity tends to rise, and the liquid level (level) of the paint in the tank where it is stored
Its behavior also fluctuates depending on factors such as the state of stirring, the shape of the tank, and the like. Attempts have been made to control the viscosity change during application to maintain it constant.However, for magnetic paints that show pseudoplastic flow, it is difficult to uniformly mix the solvent for viscosity adjustment, and the desired viscosity can be maintained. It is hard to say that. In addition, there is a disadvantage that workability is deteriorated by adding one step.

Accordingly, an object of the present invention is to produce a magnetic recording medium which is excellent by a coating method capable of obtaining a uniform coating thickness even if the viscosity of the magnetic coating material varies.

[0005]

As a result of various studies to solve the above problems, the viscosity of each coating solution was
It was found that stable application could be performed continuously by inputting the optimum tension in proportion to the change in the data and controlling the computer. The apparatus used in the present invention comprises a viscometer for detecting physical properties of a coating liquid and a control unit main body for controlling tension. Generally, when the coating liquid physical properties (solid content concentration or viscosity) increase, the web thickness decreases, the coating speed increases, and when the set coating thickness is reduced, the tension tends to increase. Control is performed so that the application conditions are optimized with respect to the fluctuation factors. It should be noted that a density meter can be used to detect the properties of the coating solution. This is because there is a correlation between the density of the coating solution and the solid concentration and viscosity of the coating solution.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. (Example 1) Width 5 using the viscosity controller of the application portion tension controller of the present invention.
The base film having a thickness of 20 mm and a thickness of 8 μm was coated with audio coating material A at a coating speed of 300 m / min, and then continuously applied at 5 R (roll) so that the thickness became 5.0 μm. At this time, the optimum tension value of the application portion for each viscosity was input to the application portion tension controller in advance, and in this case, T = 0.714V-25. Here, T is the tension of the application portion [kg / width], V is the viscosity of the paint, and the apparent viscosity at a shear rate of 3000 _s ^-1 (hereinafter referred to as V3000).
As shown in Table 1, the viscosity tended to increase with the lapse of time from the start of coating, the viscosity at the start of coating was 42 cp as evaluated by V3000, and the tension at the coating part at the start of coating was 5 kg / width.

(Comparative Example 1) 5R coating was performed in the same manner as in Example 1 except that the apparatus of the present invention was not operated and was performed manually. At this time, the viscosity V3000 at the start of coating is 42
The cp was the same as in Example 1, and the change in viscosity over time was the same as in Example 1, as shown in Table 1. The set tension was 5 kg / same as at the start of coating in Example 1.
Width. With respect to each roll continuously applied, the width direction of the end portion of the application was measured with an X-ray film thickness meter, and the results are shown in Table 1.

[0008]

[Table 1]

In Example 1, good coating could be performed even if the viscosity of the coating material increased with the passage of time. In Comparative Example 1, however, the set application portion tension deviated from the optimal tension as the viscosity changed, resulting in thickness unevenness. Tended to increase gradually. In Comparative Example 1, the thickness in the width direction of the head portion at the beginning of the application of the first roll was 0.2 μm or less, the same level of thickness unevenness as in Example 1, but the viscosity change increased at the end portion in the same roll. , The thickness unevenness was found to increase.

[0010]

As described above, by coping with the inevitable problem such as an increase in the viscosity of the paint by optimizing the tension of the coating portion as in the present invention, the uniformity can be obtained without sticking to the control of the paint viscosity. Thus, it is possible to obtain a magnetic recording medium with a simple configuration and with less variation in quality.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a coating method used in the present invention.

[Description of Signs] 5, 5 'backup roll 6 support (web) 7 coating nozzle

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masujiro Seki 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Eiichi Watanabe 1-13-1 Nihonbashi, Chuo-ku, Tokyo (72) Inventor Katsumi Onozawa 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDC Corporation (72) Inventor Kazuo Katai 1-13-1 Nihonbashi, Chuo-ku, Tokyo Shares Inside the company (72) Inventor Yuji Iwashita 1-13-1 Nihombashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-2-229571 (JP, A) JP-A-63-242376 (JP, A) JP-A-60-150866 (JP, A) JP-A-3-202171 (JP, A) JP-A-4-35766 (JP, A) JP-A 1-2 03074 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 5/842-5/848 B05C 5/02 B05D 1/26

Claims (2)

(57) [Claims] 1. A method in which an extrusion-type coating head is pressed relatively to a web while not supporting a rear surface of a running web, and a coating liquid is extruded from at least one slit of the coating head to apply the coating liquid to the web. A method for producing a magnetic recording medium, wherein the application is performed while controlling the application portion tension in proportion to a change in the paint viscosity. 2. The manufacturing method according to claim 1, wherein the control of the tension of the coating section is performed by inputting an optimum tension corresponding to the viscosity of the coating liquid and controlling the tension by a computer.