JPH01119374A - Coating film forming method - Google Patents

Abstract

PURPOSE:To eliminate uneven coating due to mesh skipping at high speed coating, by applying a coating fluid on a substrate running continuously by the use of a gravure roll in which the surface roughness has been made approximately uniform over the whole surface. CONSTITUTION:Upon the insertion of a base film 2 between a gravure roll 1 and a back roll 7, the base film is sent out continuously and, at the same time, a coating fluid 3 adhering to the gravure roll 1 is transferred onto the base film 2. Next, the surface of the thus-applied coating fluid is smoothed by a smoother 8 and the coating is dried, thereby forming a predetermined coating layer. The gravure roll 1 is cylindrical and has a large number of helical grooves 5 on its surface. These grooves have been made to have a uniform surface roughness through the steps of super-finishing, finishing by plating, and sandblasting.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a coating film forming method in which a coating film is formed by applying, for example, a magnetic paint or a non-magnetic paint to a support that is continuously running with a gravure roll. It is related to
In particular, it relates to improvements in gravure rolls used.

[Summary of the invention]

In the present invention, when coating a paint onto a support that is continuously running with a gravure roll, the surface roughness of the gravure roll used is made approximately equal over the entire surface, thereby reducing uneven coating especially during high-speed application. This is an attempt to resolve the issue.

[Conventional technology]

For example, the knife coating method, reverse roll coating method, gravure roll coating method, etc. are generally used as a method for coating magnetic tape coatings and related media coatings on a support. Among these, the gravure roll coating method is widely used because it has excellent productivity and operability, is easy to manage, and is advantageous from the viewpoint of manufacturing cost.

The gravure roll coating method described above uses a cylindrical gravure roll that is partially immersed in the paint and has uneven parts (peaks and valleys) formed on its surface, and a gravure roll that is pressed against the gravure roll. A coating film is formed by passing the support between a backup roll that rotates in the opposite direction to the gravure roll as the gravure roll rotates.

That is, in this coating method using a gravure roll, the paint is adhered to and held on the uneven portions of the gravure roll by rotating the gravure roll, and the paint is transferred onto a support such as a base film of a magnetic tape, thereby forming a coating film. This is a method of forming.

[Problems to be solved by the invention] Incidentally, in recent years, in order to improve productivity in the field of coated magnetic recording media, it is necessary to increase speed and yield, and from this point of view as well, the gravure roll coating method has been attracting attention. However, when considering speeding up the coating speed, restrictions on coating speed due to uneven coating have become a major problem.

In other words, a plurality of spiral grooves (so-called helical grooves) are provided on the outer peripheral surface of the gravure roll for applying magnetic paint, etc., but when coating at high speed, the magnetic paint held on the surface of the gravure roll is supported. It may be difficult to transfer it uniformly onto the body surface, causing uneven coating. In particular, when a high viscosity paint is used, the large shearing force applied to the paint has a large effect on the paint adhesion in each helical groove, which tends to cause cavity silane and paint slippage, which can cause problems with transfer and significantly There is a tendency for so-called skipped stitch reduction, in which no coating film is formed, to frequently cause uneven coating.

Alternatively, depending on the type of paint M (the influence of additives such as lubricants), the paint on the peaks of Celmizo may slip,
Cases are often experienced in which it is difficult to transfer the paint smoothly, such as when bubbles are generated in the paint in the valleys.

For these issues, the accuracy of each roll, the amount of nip between the gravure roll and the backup roll.

This problem can be solved to some extent by adjusting the amount of filling in the gravure roll and the excess paint (so-called bead) between the gravure roll and the backup roll, but it cannot be said to be a fundamental solution, and it is necessary to adjust these appropriately. requires considerable skill and know-how.

Therefore, the present invention has been proposed in view of the above-mentioned conventional situation, and it does not cause uneven coating due to skipped stitches even when applied at high speed, and can be applied to a wide range of paints from extremely low viscosity paints to high viscosity paints. The purpose is to provide a coating film forming method applicable to coating.

[Means for solving problems]

The present inventors have conducted extensive research over a long period of time regarding the paint transfer and transfer state on gravure rolls, and have focused on the surface state of gravure rolls.

That is, when manufacturing the gravure roll (10), when the gravure roll material is pressed through rolling with a die and so-called knurling is performed to form helical grooves (11) on the surface, the As shown in Figure 4, scratches or small protrusions (feed marks) (12) occur on the slope (lla) of the groove (11). On the other hand, the top (llb) of the helical groove (11) is flattened because it is finally polished (so-called superfinishing). Therefore, the top (11b) of the mountain part of the helical groove (11) of the gravure roll and the slope (11b) of the groove (11)
In normal gravure rolls, after this rolling and super-finishing, chrome plating is also applied to obtain durability, but the plating surface has a roughness of the base. In fact, when examining the surface roughness of gravure rolls used so far, it was found that at the top of the mountain, the surface roughness is 5. ~10μm (JIS BO60
1), whereas the surface roughness of the slope of the groove reaches 30 to 50 am.

Therefore, we came to the conclusion that there is a large difference in surface tension between the top and slope of the groove, causing the aforementioned uneven coating.

Therefore, the present invention has been completed based on this knowledge, and includes a coating film forming method in which a coating material is applied onto a support that is continuously running with a gravure roll. This is a special feature in that it is approximately equal throughout.

Here, in order to eliminate unevenness in the surface condition and improve paint adhesion, various methods such as honing, brushing, and affinity plating were tried, but all of them resulted in uneven transfer due to the effects of paint slippage, etc. Occurred.

Therefore, in the present invention, fine irregularities are formed over the entire surface of the gravure roll, thereby increasing the surface tension and creating a surface condition with no difference at the top or slope of the helical groove.

Such fine irregularities can be created using fine particle sand (JIS particle size #200 to 600) using, for example, a general sandblasting method.
) can be easily formed by using air pressure to shoot onto a rotating gravure roll. Of course, the method for forming the unevenness is not limited to this, and any method may be used as long as it can eliminate the field marks and form uniform unevenness on any part of the gravure roll. Various etching techniques can also be employed.

In addition, the value of surface roughness may be set appropriately depending on the type of paint used, the thickness of the coating film, etc., but for example, when forming a coating film with a thickness of 1 μm or more, the surface roughness value should be set at 10 points. Average roughness R
1 and 3 to 5 μm, and when forming a coating film with a thickness of less than 1 μm, it is preferably 2 to 3 μm.

The present invention is suitable for application to the production of coated magnetic recording media, and in particular, any support such as polyesters, polyolefins, vinyl chloride, polyamide, acetate, etc. can be used.

The paint to be applied may be either magnetic or non-magnetic, and the binder may be any conventionally known binder, such as vinyl chloride-vinyl acetate copolymer, polyurethane resin, or high-molecular-weight polyester resin. is also available. Any conventionally known solvent can be used, and examples include methyl ethyl ketone, methyl isobutyl ketone, and toluene.

In addition, in the case of magnetic paint, the magnetic powder is r-F.
e, O,, Co coated 1-Fe! In addition to oxide magnetic powders such as O, etc., metal magnetic powders such as Fe-Co and Fe-Co-N1 can also be used.

Furthermore, various additives such as lecithin, carbon, lubricant 9 dispersant, abrasive, etc. may be added to the magnetic paint and non-magnetic paint.

[Effect]

In general, uneven transfer in the gravure roll coating method is
It is a well-known fact that the problem becomes more pronounced as the solid content of the paint increases, as the coating thickness increases, and as the gravure roll has a finer mesh.

The mechanism of paint transfer in the present invention is a microscopic phenomenon and is not necessarily clear, but since the surface roughness of the gravure roll is uniform, the paint is evenly attached even when rotating at high speed, and solid Transfer unevenness is prevented almost regardless of the thickness, coating thickness, or mesh.

In addition, since the peaks of the gravure roll have a rough surface, slips do not occur.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. It goes without saying that the present invention is not limited to the following examples.

First, FIG. 1 shows a schematic configuration of a gravure coating apparatus used in carrying out the present invention.

This gravure coating device has a paint tank (4) filled with liquid paint (3), and is rotatable above the paint tank (4), and has a large number of helical grooves (5) formed on its surface. At the same time, a gravure roll (1) is disposed so that its lower half is located in the paint (3), and the gravure roll (1) is in pressure contact with the gravure roll (1) and rotates as the gravure roll (1) rotates. The main component is a back roll (7) that is rotated in the opposite direction to the roll (1).

The base film (2) is coated using such a gravure coating device.
To apply paint, first, use the gravure roll (1
) in the counterclockwise direction (in the direction of arrow X in the figure) in FIG. 1, and the gravure roll (1 ). Along with this rotational drive, the back roll (7) moves in the clockwise direction in FIG. 1 (arrow Y in the figure).
direction).

Next, the gravure roll (1) and back roll (7)
Insert the base film (2) between the two. As a result, the base film (2) is transferred to these rolls (1),
(7), and at the same time the paint (3) adhering to the gravure roll (1) is transferred.

After that, the coated surface is flattened by a smoother (8),
A predetermined coating film is formed by drying.

Gravure roll (1
) has a cylindrical shape, and a large number of spiral grooves (5) are formed on the surface.

This helical groove (5) is cut by rotating a cylindrical object that will become the gravure roll (1) using a die (not shown) and using a blade provided on the die. It is formed by so-called knurling.

The die used here is smaller than the above-mentioned cylindrical object, and as it is knurled, it is gradually moved in the longitudinal direction (axial direction) of the cylindrical object to create a spiral helical groove (
5) is formed.

After forming the helical grooves (5), the gravure roll (1) is subjected to a superfinishing process, a plating process, and a sandblasting process so that its surface roughness becomes uniform. ing.

The above-mentioned superfinishing process refers to a process in which the tips of the peaks of the helical groove (5) are partially shaved off to make a smooth surface in order to correct irregularities, undulations, and protrusions of the helical groove (5) caused by knurling. The above-mentioned plating finishing step is carried out in order to prevent wear of the material forming the above-mentioned gravure roll (1).

In addition, the sandblasting process performed after the plating finishing process uses fine particle sand powder (JIS particle size #200 to 600).
) onto the rotating gravure roll (1) using air pressure to roughen the surface of the top (5a) and slope (5b) of the helical groove (5), as shown in Figures 2 and 3. This is to make the degrees uniform. By going through this sandblasting process, the top part (5) of the helical groove (5)
a) and a base film (2) that can equalize and increase the surface tension of the slope portion (5b) and that is inserted between the back roll (7) and this gravure roll (1).
This prevents slipping.

In addition, in the above description, the plating process is performed after superfinishing, and then the sandblasting process is performed, but the invention is not limited to this, and for example, the plating process may be performed after the sandblasting process. Furthermore, after these steps, this gravure roll (
1) If there are minute protrusions on the surface, a light superfinishing process may be performed. ) is preferably used.

Next, the present inventors attempted coating under the conditions specifically shown in the following table, and conducted an experiment to determine whether or not uneven coating would occur.

In addition, in the table, each example uses a gravure roll that has been subjected to sandblasting treatment, and each comparative example uses a gravure roll that has not been subjected to sandblasting treatment.

Also, Example 1. Example 2. Comparative example 1. In comparative example 2,
Capacity 1.5 mm 8/inch, width at top (5a) 6
Example 3 using a gravure roll with a helical groove (5) depth of 100 μm and a helical groove pitch of 0.65 μm.
．． Example 4. Comparative example 3. In Comparative Example 4, the capacity was 0.
2 t/inch, width of top (5a) 40 μm, helical groove (helical groove depth 15 μm).

A gravure roll with a helical groove pitch of 0.18 m was used. The surface roughness of the gravure roll used in Examples 1 to 3 was 3 to 4 μm in ten-point average roughness, and the surface roughness of the gravure roll used in Example 4 was approximately 3 to 4 μm in ten-point average roughness. 2
It was set as μm.

On the other hand, in magnetic paint, Co coating - Fe, O, is used as magnetic powder.
A product having a predetermined viscosity was prepared using a vinyl chloride copolymer-polyurethane resin as a binder, methyl ethyl ketone as a solvent, and lecithin as an additive.

The non-magnetic paint was also prepared in the same manner as the magnetic paint except that chromium oxide was used instead of the magnetic powder as the pigment.

The results are shown in the table below. The experimental results in the table were evaluated by visually observing the coating film, and cases where uneven coating occurred are indicated by an X mark, and cases without problems are indicated by an O mark.

(Left below) As is clear from the table based on the above experiment, when coating films are formed in each of the examples to which the present invention is applied, extremely remarkable effects are obtained that are not affected by coating viscosity, solid content, or coating speed. I was able to do that. In particular, 250 m/min in Example 1 and 350 m/min in Example 2.

In Example 4, there was no problem at all even when the coating film was formed at 250 m/min.

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, the surface roughness of the gravure roll is made approximately equal over the entire surface, so that skipping of stitches (paint skip) etc. does not occur when paint is transferred. This makes it possible to eliminate uneven coating even during high-speed coating.

Furthermore, it can be widely applied from low-viscosity paints to high-viscosity paints, and can eliminate slips caused by the effects of additives.

Therefore, according to the present invention, it is possible to speed up coating film formation, improve yield, and improve workability, and it is possible to improve productivity.

The present invention can be applied not only to the field of magnetic recording media but also to the field of printing, etc., and can be said to have great utility value.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of main parts showing an example of the configuration of a gravure coating device used in carrying out the present invention, FIG. 2 is an enlarged perspective view of main parts of a gravure roll used, and FIG. 3 is a gravure coating device. FIG. 4 is a schematic view showing the surface condition of the roll, and is an enlarged perspective view of the main part of a conventional gravure roll. 1... Gravure roll 5... Helical groove

Claims (1)

[Claims] 1. A coating film forming method in which a coating material is applied onto a support continuously traveling by a gravure roll, characterized in that the surface roughness of the gravure roll surface is made substantially equal over the entire surface.