JP3133417B2 - 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, and more particularly to a method for manufacturing a magnetic recording medium having a magnetic coating film having a uniform coating thickness.

[0002]

2. Description of the Related Art In a method in which an extrusion-type coating head is relatively pressed against a web while the rear surface of the running web is not supported, the extrusion is performed between backup rolls 2 and 2 as shown in FIG. The force generated by the discharge pressure ΔP of the coating liquid (magnetic paint) discharged from the slit of the die coating head 3 and the application angle θ of the web 1 and the web tension T set for transferring the paint, F = T · sin θ
When the balance is obtained, the transfer of the paint becomes stable and uniform application can be achieved. Although detailed studies are underway, it is estimated that when the coating is performed using a flat blade type applicator, the wet film thickness is almost half of the gap of the flat blade type applicator. (See FIG. 2). In this case, the paint flows naturally so as to have a wet film thickness of 1/2 with respect to the set gap, and converges on the stable wet film thickness. In the case of a coating method using an extrusion-type coating head, the final wet film thickness _hw is determined according to the supply flow rate and the coating speed, but it corresponds to the gap of the flat blade applicator described above, that is, The height h ₁ of the liquid sandwiched between the lip, which is the exit of the slit from which the coating liquid is discharged, and the web varies depending on the balance between ΔP and F. It is presumed that the above theory is applied, that is, stabilization occurs under the condition of h _w = (１ ／) h ₁ (see FIG. 3).

The direct factors that determine the liquid height h ₁ are:
Although ΔP and F are the same as described above, when the coating liquid is supplied at a constant flow rate, ΔP is determined by following the gap (fluid height) of the transition part, and eventually the fluid height is h
_The factor for changing ₁ is governed by the force F that the web tries to push, that is, the tension T or the approach angle θ of the web. However, when the angle of entry of the web is changed to be adjusted, the web (base film) is liable to be scraped when the angle is increased, and the transfer of the paint becomes difficult even when the tension T is increased when the angle is increased. Also becomes noticeable. For such a reason, it is considered that it is appropriate to adjust the tension T while keeping the angle of entry at an angle that satisfies the two conditions of scraping and displacement and keeping the angle constant.

[0004]

If the coating is performed by such an adjusting method, a rough paint can be applied. In any case, however, the web relies on adjusting the tension T in order to secure a stable transition, so that the web is more or less deformed (widthwise waving phenomenon). For paints having poor transferability, the force F for transfer can be increased by increasing the tension T to shift to the applicable zone, but at the same time, the deformation of the web is large, and ΔP in that state is small, and the deformation of the web is small. If a pressure sufficient to push back is not generated, thickness unevenness in the width direction occurs due to deformation of the web, and as a result, a problem such as a decrease in yield or a variation in characteristics due to the thickness unevenness has occurred.

[0005]

Various studies have been made to solve the above-mentioned problems, and as a result of analyzing data on the flow of the coating liquid, the flow of the coating liquid suitable for the above-mentioned coating method was found to be the flow of Ostwald. Equation: (Shear stress) = k ·
Although for the coating solution n when fitted to (shear rate) ⁿ takes 0.4 above values were performed good coating 0.4
It was also found that those having a flow rate of less than 1.0 showed remarkable deformation of the web due to a large tension and caused a problem due to uneven thickness in the form of stripes.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Details will be shown in Examples and Comparative Examples. The flow of the coating solution was measured using a cone plate type viscometer (cone angle 0.5 °, cone diameter 4 cm, maximum shear rate 4000).
s ^-1 ).

(Example 1) A coating liquid A (magnetic coating material in which acicular γ-Fe ₂ O ₃ powder is dispersed) having a flow index n = 0.62 was used, and the thickness after drying was 3 mm on a 14 mm base with a width of 500 mm The coating was performed at 300 m / min.

(Example 2) Coating is performed under the same conditions as in Example 1 using a coating liquid B (magnetic coating material in which acicular γ-Fe ₂ O ₃ powder is dispersed) having a flow index n = 0.51. Was.

Example 3 An application was performed under the same conditions as in Example 1 by using a coating liquid C (magnetic coating material in which needle-like iron powder was dispersed) having a flow index n = 0.44.

[0010] (Example 4) Te with <br/> to indicate to the coating solution flow index n = 0.33 of Comparative Example 1, myristic acid relative magnetic powder as an additive 10w
When t% was added, the flow index became n = 0.41,
Using this coating liquid as F, coating was performed under the same conditions as in Example 1.

(Comparative Example 1) An application was performed under the same conditions as in Example 1 by using a coating liquid D (magnetic coating material in which needle-like iron powder was dispersed) having a flow index n = 0.33.

(Comparative Example 2) The coating was performed under the same conditions as in Example 1 by using a coating liquid E (magnetic coating material in which needle-like iron powder was dispersed) having a flow index n = 0.32.

Comparative Example 3 A coating composition was prepared by removing sorbitan monostearate added as a dispersant from the composition of the coating composition C having a flow index n = 0.44.
n = 0.39, and the coating liquid was G, and coating was performed under the same conditions as in Example 1. Table 1 shows the results.

[0014]

[Table 1] The thickness unevenness is the thickness difference (μm) in the width direction, and the number of defects is
It is indicated by the number of reels that are out of specification when cut at 1/2 inch width.

[0015]

As described above, the flow index n of the paint is 0.
For paints of 4 or more, good and stable application could be performed, but for paints in which n is less than 0.4,
Deformation of the base film appeared as thickness unevenness as it was, resulting in a stripe-shaped coated surface. In Comparative Example 1, 3 defects occurred, and in Comparative Example 2, 4 defects occurred.

[Brief description of the drawings]

FIG. 1 is a side view illustrating an extrusion coating apparatus used in the present invention.

FIG. 2 is an explanatory diagram of a flat blade applicator.

FIG. 3 is a side view illustrating a liquid height h ₁ and a wet coating thickness h _w .

[Explanation of symbols]

Reference Signs List 1 web (base film) 2 backup roll 3 extrusion type coating head 4 flat blade applicator g gap h _W wet coating thickness h ₁ liquid height

Continued on the front page (72) Inventor Masujiro Seki 1-13-1 Nihonbashi TDC Corporation, Chuo-ku, Tokyo (72) Inventor Eiichi Watanabe 1-13-1 Nihonbashi 1-chome Nihonbashi, Chuo-ku, Tokyo Inside (72) Inventor Katsumi Onozawa 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Kazuo Katai 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation ( 72) Inventor Yuji Iwashita 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-2-229571 (JP, A) JP-A-2-79218 (JP, A) ( 58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 5/848

Claims (1)

(57) [Claims] 1. A method in which an extrusion-type coating head is relatively pressed against a web without supporting a back surface of a running web, and a coating solution is extruded from at least one slit of the coating head to apply the coating liquid to a support. Wherein, when the flow of the coating liquid to be applied is applied to the Ostwald's flow equation: (shear stress) = k · (shear speed) ⁿ , a coating liquid having an index n of 0.4 or more is used. Of manufacturing a magnetic recording medium.