JPH0947715A - Method of coating metal surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating film uniform and good in appearance without unevenness even when the passing speed of a metal belt is made high and the thickness of a coating film is made thin by applying the prescribed quantity of a coating material by a coating material quantitative applicator for applying a coating material with the applied quantity quantitatively being controlled before uniformalizing the thickness of a coating film of the coating material by a gas nozzle. SOLUTION: On the surface of a metal belt 1 traveling, the required quantity of a coating material is applied by a coating material quantitative applicator 2, and using a gas nozzle 3 installed downstream thereof, gas such as air is jetted at suitable pressure according to the coated quantity and the coating condition of the coating material to level the applied coating material, allowing a coating film uniform and good in appearance without unevenness of desired thickness to be obtained. As the coating material quantitative applicator 2, a coating applicator used for a spray coating method, a die coating method, a curtain coating method or a slide coating method can be applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating a metal surface, and more particularly to a method capable of uniformly coating a thin coating film at high speed.

[0002]

2. Description of the Related Art In recent years, for example, in continuous coating on the surface of a metal strip such as a galvanized steel strip, the striping speed of the metal strip is increased to improve productivity, or the coating film is thinned to reduce cost. And studies to save resources are being conducted.

As described above, in order to speed up the passage of the metal strip and to reduce the thickness of the coating film, it is necessary to quantitatively control the coating amount of the coating agent on the surface of the metal strip. is there. As a method for that, a roll coating method,
There are spray coating method, die coating method, curtain coating method, slide coating method and the like.

FIG. 2 shows an example of the roll coating method. In FIG. 2, 1 is a metal strip, 4 is a coating agent, 5 is an applicator roll, 6 is a pickup roll, and 7 is a doctor blade roll. The coating agent 4 is drawn up by the pickup roll 6, the surplus portion is scraped off by the doctor blade roll 7, and transferred to the surface of the metal strip 1 by the applicator roll 5 for coating.

However, in this roll coating method,
There are many factors that determine the coating thickness, such as coating agent concentration, viscosity, surface tension, roll peripheral speed ratio, roll gap, roll surface roughness, and metal strip running speed. Not easy. In practice, when changing the coating film thickness, it is necessary to perform trial coating before coating to confirm that the required coating film thickness has been obtained, which is an obstacle to improving productivity. Also, because the surface roughness of the pickup roll changes over time due to wear of the applicator roll,
The coating amount of the coating agent also changes with time.

On the other hand, in the spray coating method, the die coating method, the curtain coating method, and the slide coating method, the coating film thickness is determined only by the supply amount of the coating agent and the strip speed of the metal strip. Since the film thickness is easily obtained and there are no factors relating to the roll, the coating amount of the coating agent does not change with time. Therefore, in order to increase the speed and reduce the thickness of the coating film, it is preferable to use these methods that are easy to control.

[0007]

However, in the spray coating method, the die coating method, the curtain coating method, and the slide coating method described above, when the speed of passing the metal strip is increased, film breakage due to air entrainment occurs. To do. For example, in the case of die coating method,
As the speed increases, air is entrained in a liquid pool (meniscus) formed between the coating material discharge port and the surface of the metal strip, causing film breakage. Therefore, the literature (KWONG-YA
NG LEE et al; Chem. Eng. Sc
i. 47, 1992), using a coating material having a viscosity of 10 cp, a metal strip having a uniform coating thickness obtained by a die coating method has a strip running speed of at most 50 mpm. In order to prevent coating breakage due to this speedup, for example, Japanese Patent Laid-Open No. 3-238069 proposes a method of sucking air entrained by a suction port installed in front of the coating agent discharge port. However, if we try to increase the speed and reduce the thickness of the wet coating film to a few μm, the amount of meniscus will be considerably small, so even if the entrained air is sucked in, the occurrence of coating film breakage cannot be prevented. .

The present invention has been made in order to solve the above problems, and has a uniform appearance with no coating unevenness even if the speed of passing a metal strip is increased and the thickness of a coating film is reduced. It is an object of the present invention to provide a coating method for a metal surface, which is capable of applying a good coating film.

[0009]

Means for Solving the Problems The above-mentioned problems are solved by applying a predetermined amount of a coating agent by a coating agent quantitative coating device capable of quantitatively controlling the coating amount, and then applying a coating film of the coating agent by a gas nozzle. This is solved by a method for coating a metal surface, which is characterized by uniform thickness.

In order to reduce the thickness of the coating film, after applying a desired amount of coating agent with a coating agent quantitative coating device capable of quantitatively controlling the coating amount, the pressure of the gas ejected from the gas nozzle. The thickness of the coating agent applied to the metal surface can be made uniform by adjusting the. In particular, during coating, even if there is an uncoated portion of the coating agent on the metal surface due to the extremely small coating amount, or if the coating film breaks seen in the die coating method occur, the gas nozzle after coating A uniform coating film can be formed by the leveling action of the ejected gas.

Therefore, even if the speed of passing the metal strip is increased and the thickness of the coating film is reduced, it is possible to apply a coating film having a uniform and good appearance without uneven coating.

The pressure of the gas ejected from the gas nozzle needs to be appropriately adjusted depending on the coating amount of the coating agent on the metal surface and the degree of nonuniformity of the coating state.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an apparatus for coating a metal strip surface, which is an embodiment of the present invention. In FIG. 1, 1 is a metal strip,
Reference numeral 2 is a coating agent quantitative coating device, and 3 is a gas nozzle.

The coating agent is applied to the surface of the running metal strip 1 by the coating agent quantitative coating device 2 in a required amount, and the coating agent is applied by using the gas nozzle 3 installed downstream thereof. By injecting a gas such as air at an appropriate pressure according to the amount and coating state and leveling the applied coating agent, a coating film of the desired coating thickness with a uniform and good appearance without coating unevenness can be obtained. Can be applied.

As the quantitative coating device 2 of the coating agent, a coating agent coating apparatus used in a spray coating method, a die coating method, a curtain coating method and a slide coating method can be applied.

The slit width of the gas nozzle 3 is 0.5 to 2 m.
m is desirable. The distance between the tip of the gas nozzle 3 and the metal surface is preferably 5 to 10 mm. The installation position of the gas nozzle 3 may be slightly downstream of the coating material quantitative coating device 2 so that there is a space in which the coating material that has been dammed to some extent by the gas injection can exist. A position of 100 to 300 mm is desirable from the fixed quantity application device 2 for the agent.

[0017]

[Example] A gap between openings is 0.1 mm and a width is 800 mm
A coating agent having a viscosity of 10 cp and a target coating film thickness of 3 μm and a plate passing speed of 100
Alternatively, it runs at 150 mpm and has a thickness of 0.8 mm and a width of 8
After coating on a 00 mm steel strip, the slit width is 0.5 or 2 mm, and the tip of the nozzle is 5 m from the steel strip surface.
0.13-0.25k by gas nozzle located at m
Air was jetted at a pressure in the range of gf / cm ² to homogenize the coating film. For comparison, a coating film was also applied by a conventional method without using a gas nozzle.

Then, the degree of variation in the coating film thickness was investigated. The results are shown in Table 1. According to the method of the present invention (Nos. 1 to 4), the film thickness of the conventional method (Nos. 5 and 6) shows a large variation of 0 to 6 μm along with the increase of the stripping speed of 100 mpm or more. The coating film thickness is within the target coating film thickness of about 3 μm regardless of the strip passing speed and the nozzle width, and it can be seen that the coating film thickness is extremely uniform.

[0019]

[Table 1]

[0020]

EFFECTS OF THE INVENTION Since the present invention is constructed as described above, even if the speed of passing the metal strip is increased and the thickness of the coating film is reduced, there is no coating unevenness and the appearance is good. It is possible to provide a method for coating a metal surface that can be coated with a simple coating film.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for coating a surface of a metal strip according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a roll coating method.

[Explanation of symbols]

 1 metal strip 2 quantitative coating device for coating agent 3 gas nozzle

Claims (1)

[Claims] 1. A method of applying a predetermined amount of coating agent by a coating agent quantitative coating device capable of quantitatively controlling the coating amount, and then uniformizing the coating film thickness of the coating agent by a gas nozzle. How to paint on the metal surface.