JPH07171468A - Paint coating device - Google Patents

Abstract

PURPOSE:To easily form a thin coating film having a desirable surface property in the device with a paint discharge groove formed on the coating surface of a paint coating head by forming the coating surface behind the groove with at least two curved surfaces having a different curvature. CONSTITUTION:The magnetic recording medium such as a floppy disk and video disk is produced by coating the surface of a flexible nonmagnetic substrate of polyethylene terephthalate with a magnetic paint or a back coat paint with use of a paint coating head 4. The head 4 is divided into a front head 41 and a back head 42, and a paint discharge groove 43 is formed between the heads. In this case, the back edge face 44 of the back head 42 is divided into the part close to the groove 43 and the part far from the groove in the traveling direction of the web, namely, the curvature of coated surface close to the groove is made larger than that of the part far from the groove.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating material application device, and more particularly to improvement of a coating material application head of a magnetic material application device used for manufacturing a magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of magnetic recording media such as floppy disks and video tapes, various paints such as magnetic paints and back coat paints are applied to the surface of a flexible non-magnetic support such as polyethylene terephthalate. Each layer such as a magnetic layer, a protective layer or a back coat layer is formed. The non-magnetic support as an object to be coated is usually supplied as a long strip-shaped material, and after the above layers are formed on one or both sides of the material, it is cut into a desired shape or die-cut to finish the product. To be

As a method for applying a coating material to a long strip-shaped flexible non-magnetic support (hereinafter referred to as a web), various coating methods such as a roll coating method, a gravure coating method, an extrusion coating method and the like can be used. The method is known. Among them, the extrusion coating method has no coating loss because the coating head sends all the coating liquid that has been sent to the coating head. It is suitable as a method of applying a coating material with a uniform film thickness. As a conventional technique of such an extrusion coating method, for example, JP-A-50-138036 or JP-A-57-84.
The one described in Japanese Patent No. 771 is known.

FIG. 3 is a schematic view showing the outline of the construction of such a conventional extrusion type coating device. In FIG. 3, the web 1 which is the object to be coated is guided by the front guide rolls 2 and the rear guide rolls 3 to keep the track constant, and is running in the direction indicated by the arrow A. The front end of the paint application head 4 is the front head 41.
And a back head 42, and a paint discharge groove 43 is formed between them. Back head 42 coating surface 4
No. 4 is also called a back edge surface because a back edge 45 is formed at the rear end thereof, and is hereinafter referred to as a back edge surface 44.

By pressing the paint coating head 4 having such a structure against the running web 1, the paint discharge groove 4 is formed.
The coating material discharged from 3 is applied to the web 1. At this time, by controlling the pressure of the discharged coating material and the pressing pressure of the coating material application head 4 against the web 1, a coating film having a uniform thickness is formed on the web 1. That is, in the above device, the width of the paint discharge groove 43, the traveling speed of the web 1,
Alternatively, when the discharge pressure of the paint is constant, the thickness of the coating film can be controlled by the pressing pressure of the paint coating head 4 against the web 1.

Further, in the magnetic recording medium, its characteristics are closely related to the surface property of the magnetic layer, so that it is important to control the surface property of the coating film at the time of manufacturing. The surface property of such a coating film can be controlled by adjusting the angle formed by the back edge surface 44 and the running trajectory of the web 1 immediately after coating when the web 1 leaves the back edge surface 44. .

Therefore, in order to obtain a magnetic recording medium provided with a magnetic layer having a good surface property, paint coating heads having back edge surfaces of various shapes have been proposed so far, and good results have been obtained in some cases. Has been obtained.

[0008]

By the way, in recent years, there has been an increasing demand for a large recording capacity and a high recording density for a magnetic recording medium, and in order to meet those demands, many studies have been carried out from various fields, and a magnetic powder has been developed. Improvement of additives and development of new varieties are actively carried out. Therefore, the physical properties of the magnetic paint to be applied have changed compared to conventional ones,
In addition, the thickness of the coating film to be formed is becoming much thinner than in the past. And, with such changes, some inconveniences are occurring.

For example, when a hexagonal ferrite magnetic powder such as Ba ferrite suitable for high recording density is to be highly filled in the magnetic layer, the viscosity of the magnetic coating tends to be higher than that of the conventional one. . Generally, in a coating material coating device, it is unavoidable that the coating material coating head thermally expands due to the circulation of the coating material and the frictional heat between the web and the head, and the width of the coating material discharge groove changes to some extent. Such a change in the width of the paint discharge groove, which was not a problem when forming a relatively thick coating film like the one shown in Fig. Will have a great effect on.

For this reason, it has been difficult to form a thin coating film having a good surface property by using the conventional coating material coating device having the coating material coating head. Then, even when a smooth coating film with improved surface properties is formed, even if it is microscopically smooth, macroscopically undulations of large wavelength occur in the running direction of the web. However, on the contrary, there is an unfavorable phenomenon such as macroscopically flat without waviness but microscopically not smooth. In such a case, the characteristics of the manufactured magnetic recording medium are adversely affected.

From the above, it is not always easy to form a magnetic layer having a desired thickness and a desired surface property in a conventional coating apparatus having a coating head, and a superior coating head has been developed. Was requested.

The present invention has been made in view of the above problems, and is an extrusion type paint coating apparatus equipped with a paint coating head capable of easily forming a thin coating film having a preferable surface property. The purpose is to provide.

[0013]

A coating material application device of the present invention forms a coating material discharge groove on a coating surface of a coating material coating head which is orthogonal to a traveling direction of an object to be coated, and is behind the coating material discharge groove with respect to the traveling direction. In the paint coating device, wherein the coating surface is formed into a curved surface that curves with respect to the running trajectory of the object to be coated, the rear coating surface includes at least two curved surfaces having different curvatures in the running direction. It is characterized by being. It is more preferable that, of at least two curved surfaces having different curvatures with respect to the traveling track, the curved surface closer to the paint discharge groove has a larger curvature than the other curved surface.

[0014]

In the coating material application apparatus of the present invention, the coating material applied to the web to be coated comes into contact with the curved surface on the side close to the coating material discharge groove in the first step so as to eliminate the large swell having a long wavelength. It is roughly smoothed. Next, in the second step, the curved surface on the side far from the paint discharge groove is brought into contact therewith, and at that time, a smoothing action for eliminating fine irregularities is applied. The effect is further improved by increasing the curvature of the curved surface on the side closer to the ejection groove and decreasing the curvature of the curved surface on the far side. In this way, by constructing the back edge surface with a combination of two curved surfaces having different curvatures, and using this as a two-step smoother called a one-step smoother and a two-step smoother,
At the same time that the coating surface is microscopically smoothed, macroscopically, the waviness is effectively removed and smoothed. Therefore, according to the present invention, the smoothing effect on the back edge surface can be further enhanced.

[0015]

EXAMPLES Examples of the present invention will be described below.

EXAMPLE FIG. 1 is a schematic view showing a cross section of an example of a coating material coating head in a coating material coating device of the present invention in a direction orthogonal to a coating material discharge groove.

As shown in FIG. 1, the front end of the paint coating head 4 is divided into a front head 41 and a back head 42, and a paint discharge groove 43 is formed between them. The back edge surface 44 of the back head 42 is bisected into a side closer to the paint discharge groove 43 and a side farther from the running direction of the web 1 (not shown) which is the object to be coated, and both are in the running direction of the web 1. On the other hand, two curved surfaces having different curvatures are curved. Further, the curvature of the curved surface on the side closer to the paint discharge groove is made larger than the curvature of the curved surface on the side distant from it.

When the curved surface has an arc-shaped cross section, the curvature is given as the reciprocal of the radius R. Therefore, as shown in FIG. 1, the radius R ₁ of the curved surface on the side closer to the paint discharge groove is on the far side. It is smaller than the radius R _{2 of the} curved surface. When the present invention is applied to a paint coating head in which the length of the paint discharge groove is 20 mm or more and the cross-sectional shapes of two curved surfaces are both arcuate, R ₁ and R ₂ are 1 mm ≦ R ₁ ≦ 10 mm, 5 mm ≦ <
Particularly preferable results are obtained when R ₂ ≦ 30 mm. .

In FIG. 1, the shapes of the front head 41 and the coating material discharge groove 43 are shown for the sake of easy understanding in describing the constitution of the present invention, and do not limit the present invention.

Embodiment 1 FIG. 2 is a perspective view of an embodiment of a paint coating head of a paint coating device according to the present invention. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals. As shown in FIG. 2, the coating material coating head 4 of the present embodiment is divided into a front head 41 and a back head 42, and a coating material discharge groove 43 is formed between them. The back edge surface 44 of the back head 42 is divided into two curved surfaces, that is, a side 45 near the paint discharge groove and a side 46 far from the paint discharge groove with respect to the running direction of a web (not shown) that is the object to be coated. In this embodiment, the curved surfaces 45 and 46 have radii R ₁ = 5 mm and R, respectively.
_It has an arc shape of ₂ = 15 mm.

The paint application head 4 shown in FIG.
A head connecting member 4 for connecting the front head 41 and the back head 42 so that the width of the paint discharge groove 43 formed between the front head 41 and the back head 42 can be adjusted.
7 is provided. The head connecting member 47 has a substantially U-shaped cross section, and its opening end is fixed to the back head 42 so as to sandwich the side surface in the direction orthogonal to the back edge, and the other end is embedded in the front head 41. It is connected to the front head 41 by a guide pin 48 and an adjustment bolt 49 for adjusting the width of the paint discharge groove. By installing the guide pin 48 and the adjusting bolt 49 and making the front head 41 slidable with respect to the running direction of the web, the width of the paint discharge groove 43 can be adjusted and the thickness of the coating film can be controlled more. It will be even easier.

Further, a cooling device (not shown) can be connected to the paint coating head 4 shown in FIG. 2 via a pipe indicated by reference numeral 50, if necessary. When the cooling device is connected to cool the entire paint application head, thermal expansion of the paint application head due to circulation of the paint and frictional heat between the web and the head is prevented. Therefore, the width of the paint discharge groove is prevented from changing.

Here, in order to investigate the effect of the present invention, a magnetic recording medium coated with a magnetic coating material was manufactured using the coating material coating apparatus of the present embodiment having the above-mentioned structure, and its characteristics were evaluated.

In producing a magnetic recording medium, first, a magnetic coating material having the following composition was prepared by a conventional method.

[Magnetic coating composition] Magnetic powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer 7 parts by weight Polyurethane resin 7 parts by weight Myristic acid 2 parts by weight Butyl stearate 2 parts by weight Alumina (average particle size 0.3 μm) 5 Parts by weight carbon 3 parts by weight organic solvent (methyl ethyl ketone / cyclohexanone = 1
1/1) 230 parts by weight Then, the obtained magnetic coating material was applied onto a PET film having a thickness of 7 μm by using the apparatus of this example to prepare a magnetic recording medium sample 1. Then, the thickness irregularity of the formed magnetic layer and its surface property were examined. The discharge pressure of the paint is 2 kg / cm
^2. The running speed of the film was set to 100 m / min. The surface property of the magnetic layer was evaluated by measuring with a three-dimensional surface roughness meter.

Examples 2 to 4 Paint coating apparatus similar to Example 1 except that the sizes of R ₁ and R ₂ were changed as shown in Table 1 below.
~ 4 configured. Then, magnetic recording medium samples 2 to 4 were produced using them, and evaluated in the same manner as sample 1.

[0027] Comparative Examples 1 to 3 further, as a comparative example of the present invention, the back edge surface, other cross-section consisting of an arc-shaped one curved surface of radius R ₁ of Example 1 similar to the varnish coating device Comparative Example 1 ~ 3 configured. Then, using them, magnetic recording medium samples 5 to 7 are manufactured,
Evaluation was performed in the same manner as in the example.

Table 1 below shows the evaluation results of Samples 1 to 7 produced using the apparatus of the above Examples and Comparative Examples together with the sizes of R ₁ and R ₂ .

[0029]

[Table 1] As is clear from Table 1, when the apparatus of this example was used, a coating film having a desired film thickness and preferable surface properties could be easily obtained as compared with the conventional apparatus.

[0030]

As described above, according to the present invention, in an extrusion type coating material coating device used for coating a magnetic coating material in the production of a magnetic recording medium, for example, the back edge surface of the coating material is set in the running direction of the web. Since two curved surfaces having different curvatures are provided, the back edge surface of one paint application head can act as a smoother having two steps. When the curvature of the curved surface near the paint discharge groove is made larger than that of the other curved surface, the smoothing effect of the back edge surface is further enhanced, and the coating surface is smoothed microscopically and macroscopically. Easy to do.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of a coating material coating head relating to a coating material coating device of the present invention.

FIG. 2 is a perspective view showing the outline of an embodiment of a coating material coating head relating to the coating material coating device of the present invention.

FIG. 3 is a schematic diagram showing an outline of a configuration of a conventional extrusion-type paint coating device.

[Explanation of symbols]

 1 ... Web 2 ... Front guide roll 3 ... Rear guide roll 4 ... Application head 41 ... Front head 42 ... Back head 43 ... Paint discharge groove 44 ... Back edge surface 45 ... … Side near paint discharge groove 46 …… Far away from paint discharge groove 47 …… Head connecting member 48 …… Guide pin 49 …… Adjust bolt 50 …… Cooling pipe

Claims (2)

[Claims] 1. A paint discharge groove that is orthogonal to the running direction of the object to be coated is formed on the coating surface of the paint applying head, and the application surface behind the paint discharging groove with respect to the running direction is the running track of the object to be coated. In the coating material application device which is formed in a curved surface that is curved with respect to the curved surface, the coating material device at the rear side is provided with at least two curved surfaces having different curvatures with respect to the traveling direction. 2. Of at least two curved surfaces having different curvatures with respect to the traveling direction, the curved surface on the side closer to the paint discharge groove has a larger curvature than the other curved surface. Item 1. A paint application device according to item 1.