JPH07241517A - Coating method by roll coater - Google Patents

Abstract

PURPOSE:To provide a coating method by a roll coater in which uniform film thickness is obtained at a high speed by the roll coating device of a reverse coater system. CONSTITUTION:Continuous coating is performed on the surface of a steel strip by a roll coating device of a two roll-type reverse coater system. Difference of the circumferential velocity of an applicator roll and a pickup roll is set up to at most 70m/min and also rubber hardness of the applicator roll lined by a rubber is regulated to 60-75 in spring hardness (Hs). Thereby a beautiful coating film is formed even in a time of operation at a high line speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method using a roll coater for performing a high-speed and beautiful continuous coating on a belt-shaped material by roll coating in an equipment line for surface-treated steel sheets and the like.

[0002]

2. Description of the Related Art In recent years, a pre-coated steel sheet coated on a raw material before forming, assembling, and the like is directly processed, assembled, and used, and a chemical conversion treatment, painting, and baking process by a user can be omitted, which causes pollution problems. In addition, it has good paint usage efficiency and baking energy efficiency, has high resource and energy saving effects, and is widely used for home appliances, automobiles, and the like.
The material of the pre-coated steel sheet is hot-dip galvanized steel sheet,
To improve the functionality of surface-treated steel sheets such as galvanized steel sheets, cold-rolled steel sheets, and chrome-coated steel sheets, roll coating, curtain flow coating, or electrostatic coating is used to apply resins and paints for corrosion resistance and fingerprint resistance. , With improved lubricity. In coil coating, roll coating is the most common case.

Conventionally, a roll coater type coating device (hereinafter referred to as a roll coating device) has been widely used for continuous coating on a running belt-shaped material such as a steel plate. The roll coating device is generally composed of a pickup roll, an applicator roll, a backup roll that supports the strip-shaped material, and a coating liquid pan. The roll coating apparatus includes a natural coater system in which the rotation direction of the applicator roll is the same as the traveling direction of the strip material, and a reverse coater system in which the rotation direction of the applicator roll is opposite to the traveling direction of the strip material. The natural coater method is less likely to damage the applicator roll than the reverse coater method, so it is suitable for long-term coating and high coating speed. On the other hand, in the natural coater method, the coating liquid is torn between the roll and the band-shaped material, which makes it easy to get roll eyes.
It is necessary to reduce the viscosity of the coating fluid, and it is used for primer coating and backside coating thin film coating. The reversing coater method is used for top coating because it is suitable for obtaining a smooth coating film by eliminating the roll eyes on the coated surface. The reversing coater method allows for thick film coating, but because of this, the viscosity of the coating liquid is relatively high, and if air bubbles are contained in the coating liquid, the bubbles will burst during painting and the unpainted portion will be pulled out. There is.

As shown in FIG. 3, the reverse coater type roll coating apparatus has a pickup roll 1
After applying the coating in the coating liquid pan 5 to the outer periphery and transferring it to the applicator roll 2 having a rubber hardness of 30 to 60 and a rubber lining, the applicator roll 2 has a predetermined film thickness. Then, the applicator roll 2 continuously transfers to the strip-shaped material 4 that moves along the backup roll 3 to form a coating film. This roll coating apparatus is practically used in many industrial fields because the equipment is simple and the control is easy. However, in the roll coating apparatus, when trying to increase the line speed in order to improve the productivity, it is necessary to increase the number of rotations of the pickup roll and the applicator roll as well, and depending on the respective roll peripheral speeds. Painting defects occur. For example, at the contact point between the applicator roll and the pickup roll, air is mixed and bubbles are generated in the coating liquid, and the bubbles are transferred to the applicator roll and transferred to the strip-shaped material and remain in the coating film. It is well known that the appearance of the paint is poor.

As a measure for preventing air from entering between the applicator roll and the pickup roll, it is common to reduce only the peripheral speed of the applicator roll and reduce the amount of pushing between the rolls. Also, as another measure,
A helix nozzle for heaving the coating surface of the coating pan along the longitudinal direction of the coating pan so that the gap just before rolling between the applicator roll and the pickup roll is always filled with the coating liquid over its entire length. A reverse roll coater device (Japanese Unexamined Patent Publication No. Sho 63-11987) equipped with a device provided in a pan (Japanese Patent Laid-Open No. Hei 2-174961) and a device for preliminarily coating a steel sheet in advance in order to improve the coating property of a strip-shaped object.
No. 6) has been proposed.

[0006]

The method of lowering only the peripheral speed of the applicator roll and reducing the indentation amount between the rolls is to reduce the amount of coating liquid on the surface of the applicator roll, resulting in poor lubrication and applicator rolls. Chatter may occur on the roll, causing uneven coating. In addition, JP-A-2-
The apparatus disclosed in Japanese Patent No. 174961 discloses that the coating liquid is violently ejected from a nozzle in order to lift the coating liquid from the liquid surface of the coating liquid pan, thereby disturbing the liquid surface of the coating liquid pan and entraining bubbles and the like. Further, the method of using the precoating apparatus disclosed in JP-A-63-119876 involves spraying a coating liquid prior to coating to precoat, which makes it difficult to make the coating film uniform. As described above, the current roll coating methods still have various problems in forming a uniform coating film at high speed.

An object of the present invention is to provide a coating method using a roll coater which can eliminate coating defects that occur when a reverse coater type roll coating apparatus is operated at high speed and can obtain a uniform film thickness at high speed. .

[0008]

SUMMARY OF THE INVENTION The inventors of the present invention have conducted various experiments on the mechanism of coating defect generation due to the high applicator roll peripheral speed found in conventional roll coaters.
A study was conducted. As a result, when the peripheral speed difference between the applicator roll and the pickup roll exceeds 70 m / min, bubbles are generated due to air inclusion, and the peripheral speed difference between the applicator roll and the pickup roll is 70 m / mi.
When the peripheral speed of the applicator roll is reduced to be n or less, the amount of coating liquid on the surface of the applicator roll is reduced and the lubrication is deteriorated, resulting in chattering of the applicator roll and uneven coating. It was confirmed that the coating thickness becomes thicker when the peripheral speed of the pickup roll is increased.

As a result of further experiments and examinations, the peripheral speed difference between the applicator roll and the pickup roll was 70 m /
Even if it is less than min, the rubber hardness of the rubber-lined applicator roll is 60 to 60 in terms of spring hardness (Hs).
It has been clarified that, by setting the ratio to 75, it is possible to prevent mixing of bubbles generated during high-speed operation, and it is possible to prevent coating unevenness due to chattering of the applicator roll, and arrived at the invention.

That is, according to the present invention, in a method of continuously coating the surface of a steel strip by a two-roll type reverse coater type roll coating device, the peripheral speed difference between the applicator roll and the pickup roll is 70 m / mi.
n or less, and the rubber hardness of the rubber-lined applicator roll is 6 in terms of spring hardness (Hs).
It is a coating method using a roll coater, which is characterized in that it is 0 to 75.

[0011]

In the present invention, by setting the peripheral speed difference between the applicator roll and the pickup roll to be 70 m / min or less, it is possible to prevent the generation of bubbles due to the inclusion of air between the applicator roll and the pickup roll. . Further, by setting the rubber hardness of the rubber-lined applicator roll to be 60 to 75 in terms of spring hardness (Hs), uneven coating due to chattering of the applicator roll due to poor lubrication of the applicator roll surface can be prevented. is there. The spring hardness (Hs) of rubber hardness in the present invention refers to the spring hardness (Hs) in the normal state measured according to the provision of 5.2 of JIS K 6301 (vulcanized rubber physical test method).

In the present invention, the difference in peripheral speed between the applicator roll and the pickup roll is set to 70 m / min or less when the difference in peripheral speed between the applicator roll and the pickup roll is larger than 70 m / min. The coating liquid foams, and the foam is transferred to the applicator roll and transferred to the surface of the steel strip, resulting in poor coating. However, the peripheral speed difference between the applicator roll and the pickup roll is 70 m / mi.
This is because when n is less than or equal to n, bubbles can be prevented from being generated due to the mixing of air between the applicator roll and the pickup roll. That is, when it was observed that the coating liquid was transferred to the foamed steel strip surface at various peripheral velocities of the applicator roll and the pickup roll, as shown in FIG. 1, the applicator roll peripheral velocity-the pickup roll peripheral velocity> 70 m. / Mi
When bubbles are generated in n, and the difference in peripheral speed between the applicator roll and the pickup roll becomes larger, the coating liquid foams and is transferred to the applicator roll. Become.

The rubber hardness of the rubber-lined applicator roll in the present invention is 60 to 75 in terms of spring hardness (Hs), as shown in FIG.
If the spring hardness (Hs) is less than 60, decreasing the peripheral speed of the applicator roll will reduce the amount of coating liquid on the surface of the applicator roll, resulting in poor lubricity, resulting in chattering on the applicator roll and uneven coating. Occurs. When the spring hardness (Hs) is 60 to 75, the contact area between the applicator roll and the surface of the steel strip becomes small even if the coating liquid amount on the surface of the applicator roll is reduced by lowering the peripheral speed of the applicator roll. Therefore, the amount of coating liquid per unit area can be secured. Conversely, the spring hardness (Hs) is 7
If it exceeds 5, the contact areas between the applicator roll and the pick-up roll and between the applicator roll and the steel strip surface become extremely small, so paint breakage occurs and the applicator roll chatters, resulting in a beautiful coating film. Not only that, but also the film thickness becomes too thin. When the rubber hardness is in the range of 60 to 75 in terms of spring hardness (Hs), the film thickness of the coating film may be slightly reduced. By raising the peripheral speed slightly, a predetermined film thickness of the coating film can be secured. The lining rubber of the applicator roll is not particularly limited, but urethane rubber, nitrile butadiene rubber, chloroprene rubber and the like, which have excellent wear resistance, are preferable.

[0014]

Example: An electrogalvanized steel strip having a plate thickness of 0.5 mm and a plate width of 1100 mm, a diameter of 300 mm, a body length of 1600 mm,
Pickup roll consisting of steel roll with surface mesh processing, and spring hardness (Hs) 55 to 7 on steel roll
Using a reverse coater type roll coating device consisting of an applicator roll with an outer diameter of 260 mm and a body length of 1600 mm, which has been applied with a urethane rubber lining of 8 in a thickness of 25 mm and a paint pan, a chromate with a paint viscosity of 3 centipoise and a nonvolatile content of 20% is used. The dispersed resin liquid was continuously coated under various conditions shown in Table 1, the presence or absence of chatter in the applicator roll, and the appearance of the coating film were visually observed to perform a comprehensive coating evaluation. The results are shown in Table 1. The APR in Table 1
Indicates an applicator roll, and PUR indicates a pickup roll. Further, the peripheral speed ratio in Table 1 was determined by the ratio to the line speed, and the peripheral speed difference was calculated by the following formula: Applicator roll peripheral speed-Pickup roll peripheral speed. Further, in Table 1, APR chatter column in Table 1 indicates that there is no chatter, X indicates chatter, that in the coating appearance column indicates that it is good, X indicates that the appearance is poor due to foaming, and that in the comprehensive evaluation column indicates ○.
Indicates good coating, and x indicates poor coating.

[0015]

[Table 1]

As shown in Table 1, in the comparative example in which the rubber hardness of the rubber lining of the applicator roll is 60 or less in spring hardness (Hs), the difference in peripheral speed between the applicator roll and the pickup roll is 70 m / When it was larger than min, the coating appearance was poor due to the generation of bubbles, and when the peripheral speed of the applicator roll was lowered in order to suppress the bubbles, chatter occurred on the applicator roll and uneven coating occurred. On the other hand, the rubber hardness of the rubber lining of the applicator roll is 60 to 75 in terms of spring hardness (Hs),
In the example in which the difference in peripheral speed between the applicator roll and the pickup roll was 70 m / min or less, the applicator roll did not cause chattering, and the appearance of the coating was not deteriorated due to the generation of bubbles.

[0017]

As described above, according to the method of the present invention, the difference in peripheral speed between the applicator roll and the pickup roll of the roll coating device is set to 70 m / min or less, and the lining rubber of the applicator roll is When the hardness is 60 to 75 in terms of spring hardness (Hs), a beautiful coating film can be formed even during operation at high line speed.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the peripheral speed of an applicator roll, the peripheral speed of a pickup roll, and a bubble generation region.

FIG. 2 is a graph showing the relationship between the spring hardness (Hs) of the lining rubber of the applicator roll and the presence or absence of chattering in the applicator roll.

FIG. 3 is a schematic explanatory view of a general reverse roll type roll coating apparatus.

[Explanation of symbols]

 1 Pick-up roll 2 Applicator roll 3 Backup roll 4 Band-shaped material 5 Coating liquid pan

Claims (1)

[Claims] 1. A method of continuously coating the surface of a steel strip with a two-roll type reverse coater type roll coating device, wherein the peripheral speed difference between the applicator roll and the pickup roll is set to 70 m / min or less, and A coating method using a roll coater, wherein the rubber hardness of the rubber-lined applicator roll is 60 to 75 in terms of spring hardness (Hs).