JPS61291073A - Method for smoothing low viscosity coating film - Google Patents

Abstract

PURPOSE:To obtain a coating film having a uniform thickness by removing the irregularity of a scoreline or scraping-off, in a method for coating a mag netic recording medium, by using a smoother having a specific structure. CONSTITUTION:A smoother 21, which is equipped with a recessed part 24 having a uniform depth twice or more a predetermined coating thickness at the central part thereof and has guide surfaces 25, 26 to which mirror surface finishing was applied at both ends thereof, is arrangd in the vicinity of the downstream side of a coating apparatus such as a gravure roll applying a coating solution with viscosity of 1-1,000cps to a film. The film coated with the coating solution is transferred in a state contacted with the smoother 21 under pressure, the coating solution is uniformly applied to the part having the gap width D between the recessed part 24 and the mirror surfaces 25, 26. The length of the aforementioned gap width D is pref. about 8mum when a paint with viscosity of 50cps was used and the total thickness of the smoother 21 is pref. about 2-5mm.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for smoothing a low viscosity coating film for back coating or top coating of magnetic recording media.

(b) Conventional technology Gravure roll coating of high viscosity paint, such as magnetic paint, on a PET (polyethylene terephthalate) web;
In order to eliminate gravure patterns, uneven coating thickness, vertical stripes, etc. that occur on the surface of the coating film when applied using methods such as reverse roll coating and knife coating, and to smoothen the coating film.
A method of smoothing the surface of the coating film by heating the coating film with a heating roll in advance to lower its viscosity and then bringing a flexible blade into contact with it is described, for example, in Japanese Patent Publication No. 54-259.
It belongs to the publicly known publication No. 47.

Further, the cross-sectional shape in the running direction of the web has a radius of curvature of 10R to 100R at a portion where it first contacts the coating film,
A method of performing smoothing using a solid smoother having an edge shape with a downstream end of 150° or less under certain conditions is known, for example, as disclosed in Japanese Patent Application Laid-Open No. 54-8646.

However, the above smoothers are all 3600 C! such as magnetic paint! PE paint with high viscosity like PS
Good results are obtained when forming a fairly thick film on T-film, but when the film has good fluidity, such as when applying a very thin layer of low viscosity paint such as a back coat agent, Use of the above-mentioned smoother not only causes vertical streaks but also has the disadvantage of causing uneven coating, making it impractical.

(c) Problems to be Solved by the Invention As mentioned above, the present invention aims to remove smoothing unevenness such as vertical streaks and scraping when a known smoothing device is applied to a low-viscosity coating film. This is the purpose.

2) Measures to solve the problem: Near the downstream of a coating device such as a gravure roll that applies a low-viscosity coating liquid onto the magnetic coating film on the web, a depth of at least twice the prescribed coating thickness is placed in the central part. A smoother having a uniform concave portion and mirror-finished guide surfaces on both edges is disposed, and the directly cut web coated with the paint is transferred while being pressed against the smoother with uniform pressure.

(Low viscosity coating methods such as those applied with a gravure roll for Hakui leave unevenness such as gravure stripes on the tape, but the smoother scrapes off some of the protrusions and smooths out the entire surface of the tape.) Low viscosity paint can be applied smoothly over a wide range.

(F) Example Backcoat Application System FIG. 1 shows a schematic diagram of a backcoat application system in which the present invention is implemented.

In this figure, the PET tape (2) (medium 120ff, pore size 10 mm) wound with magnetic paint is wound around the supply roller (1), the guide roller (3) and the dancer roller (4).
) and a guide roller (4r) to the gravure coating device port 0. Immediately downstream of the gravure coating device 0, a smoother device holder, which is the gist of the present invention, is arranged.

After smoothing, the tape is gradually dried in an infrared dryer■ and then moved to the dancer roller (5) and three guide rollers F61.
The winding roller (9) is guided through f71 and (8) to the winding roller (9) as a protective coated magnetic tape.
It is wound up.

The main parts of the gravure coating device opening 0 and the smoother device decoration are shown enlarged in FIG.

The gravure roller (111) rotates while a part of it is immersed in back coating agent 0 in the back coating agent tank (121), and a fixed amount of back coating agent (141) measured by a doctor blade αj is coated on the circumferential surface. While the tape (2) is being held and transferred together with the backing roller 051, P
A low viscosity back coating agent 041 is applied to the back side of the magnetic coating film forming surface of the ET tape.

The term "low viscosity" used herein refers to the viscosity of the magnetic paint (
3600CPS) and 10000CPS)
Applicable to viscosities below PS.

The back coated tape (2) is smoother (21
The coating film on the tape guided by the smoother CB is leveled by the shape of the smoother CB and the tape pressure applied mainly to the guide surface of the smoother 211 by the guide roller 221 (2).

In the first embodiment, the smoother device is composed of a smoother +211 and a pair of press-contact rollers. Said smoother Q11
is as shown in the perspective view in Figure 3, with a recess of a fixed depth in the center and mirror-finished guide surfaces (251) at both ends.
It is a stainless steel member with a

The depth D of the recess (support) depends on the viscosity of the back coating agent, the gravure inclination of the gravure roll, the pitch and depth of the gravure groove, but is at least as large as the desired coating thickness (after drying). sufficient depth is required. (See Table 1) Furthermore, the width of the recess in the longitudinal direction of the tape cannot be made too long in order to obtain the effect of scraping off the back coat agent and the smoothing effect.

Incidentally, the conditions in the first embodiment are as follows.

Tape Width 120ff%a Thickness 10 (including magnetic coating thickness) Back coat Viscosity 500PS Gravure roll Gravure angle 45 Gravure groove pitch 11 DC (V groove) Gravure groove depth 30;
2 Hasmusu Depth of the recess 8 Width of the recess
112 Shoulder Inside the shoulder recess 5 seconds (longitudinal direction of the tape) As a result of experiments using each of the above conditions as parameters, the depth of the smoother is less than the depth of the gravure groove for low viscosity paints below IDDOCPS, and the width is 2 to 2. It turned out that it was desirable to have five horses.

In the second embodiment, the same smoother 2n as in the first embodiment was used, and - backing rollers C were used in place of the pair of pressing rollers t2'1I23. This roller is made of synthetic rubber, has a sufficiently large diameter, and is set so that its curved surface, together with the elasticity of the rubber, makes sufficient contact with the width of the smoother (21). This embodiment is particularly effective when the coating film thickness is large.

In the third embodiment, the smoother has a cylindrical shape as shown in FIG.
It is equipped with Guide circumferential surface (four (6) diameters and small diameter portion θ[
The difference between the depth D of the smoother tpt+ in the first and second embodiments is the same as the depth D of the smoother tpt+ in the first and second embodiments, but it is desirable to finish the circumferential surface of the small diameter part to a finish of 0.28 (mirror finish or higher), and at least the diameter It is desirable that φ is 1o%φ or more.

(c) is a packing roll made of synthetic rubber.

According to the method of the present invention, the tape (
2) Back coat agent (7
) is moderately scraped off with smoother + 21) and leveled to 0
5 (Fig. 7), so that when no smoother is provided, the coating is applied over almost the entire surface of the tape as shown in Fig. 8 (B), compared to Fig. 8 (A), which shows the relationship between the thickness of the film and the coating thickness. Since the magnetic tape is made into a flat thread, a magnetic tape with good running performance etc. can be obtained.

Using the depth D of the smoother (21) as a variable under the conditions of the first embodiment described above, the thickness of the coating film when back coated is applied to several tapes using the same smoother is measured, and the results are as follows. It is.

1. The above coating thickness represents the actual coating thickness after drying with a solvent such as toluene.

(g) Effects According to the present invention, even when a very thin coating of extremely low viscosity such as a back coat or top coat agent is applied onto a magnetic recording medium, a uniform and smooth coating film can be formed. .

[Brief explanation of the drawings] Figure 1 is a schematic diagram of the coating system, Figure 2 is a side view of the main parts,
Fig. 3 is a perspective view of the smoother of the first embodiment, Fig. 4 is a sectional view showing the relationship between the smoother and the packing roll, Fig. 5 is a perspective view of the smoother of the third embodiment, and Fig. 6 is the third embodiment. FIG. 7 is a perspective view showing a schematic diagram of the smoothing process, and FIG. 8 is a diagram showing the relationship between distance in the width direction of the film and coating thickness. Mouth D... Gravure roll, (13... Doctor blade, Q5)... Packing roll, Co., Ltd.... Smoosa, @ωyama Yamauchi roller 匈... Packing roll, 0 vessel... Back coat agent. -〇i-p4 t Normalized+ku0 mouth machine-〇

Claims (1)

[Claims] (1) Near the downstream of a coating device such as a gravure roll that applies a coating liquid with a viscosity of 1 to 1000 CPS onto a web, a uniform recess with a depth several times the predetermined dry coating thickness or more is provided in the center, A method for smoothing a low-viscosity coating film, characterized in that a smoother having mirror-finished guide surfaces on both edges is disposed, and the web immediately after the coating has been applied to the smoother is transferred while being pressed against the smoother with uniform pressure. .