JPH0330871A - Method for coating molten zinc plated steel strip - Google Patents

Abstract

PURPOSE:To apply coating material to the surface of a steel strip during feed without interrupting the supply of the coating material by a method wherein the tip of the orifice part of a slit nozzle is allowed to approach the surface of the steel strip within such a range that said tip of the orifice part of the slit nozzle is not in contact with the surface of the steel plate at an interval of 300mum or less from said surface and the position of said tip is allowed to follow the positional fluctuation of the surface of the steel strip while said interval is always held to an almost constant value. CONSTITUTION:When high viscosity coating material is applied to a molten zinc plated steel strip, the position of the tip of the orifice part of a slit nozzle is allowed to follow the positional fluctuation of the surface of said steel strip and the interval between the surface of the steel strip and the tip of the orifice part of the slit nozzle is set to 300mum or less. In this state, the high viscosity coating material is continuously applied to the surface of the steel plate over the feed width thereof at a set line speed while the tip of the nozzle is held to a non-contact state with respect to the surface of the steel strip and a thin or thick coating film is formed.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention has been developed as an alternative to the roll coating method currently widely used at home and abroad in the manufacturing process of painted hot-dip galvanized steel sheets, and has many advantages. The method relates to a new coating method that uses a paint selected from various paints with different physical properties to a required film thickness that is uniform in the width and length directions of a hot-dip galvanized steel strip and has a good appearance. This is a new method of painting hot-dip galvanized steel strips.

The conventional method for manufacturing painted hot-dip galvanized steel sheets is to apply paint to the surface of the hot-dip galvanized steel strip, which is being conveyed continuously, and then
The paint is dried and cured, and then cut into predetermined lengths to obtain painted hot-dip galvanized steel sheets.

Currently, the coating method used in the manufacturing process of painted hot-dip galvanized steel sheets is carried out by the roll coating method in almost all manufacturing facilities both domestically and internationally.

The roll coating method is a two-roll type or a three-roll type. The paint is transferred from the paint pan to a roll, and the excess paint is rotated by two wooden rolls in the same direction or in the opposite direction to the passing of the plate to adjust the required film thickness. Furthermore, it is a method of coating a hot-dip galvanized steel strip by controlling the film thickness by controlling the circumferential speed ratio of the rolls, pressing pressure, etc.

The paints applied to hot-dip galvanized steel strips are aminoalkyd resin paints, epoxy resin paints, acrylic resin paints, oil-free polyester resin paints, silicone resin paints, fluororesin paints, or salts, in order to meet the quality requirements for various uses. Various resin paints such as bisol paints are used.

However, the roll coating method has the following problems.

(A) The viscosity range of the paint that does not cause problems in the painting process for obtaining a good painted appearance is about 100 to 800 cps. Therefore, in the roll coating method, paints with high viscosity and high solid content cannot be used, and the viscosity of the paint must be adjusted by diluting with a solvent. but.

It is not preferable to use a paint with a low solid content diluted with a solvent from the viewpoint of solvent cost and environmental protection.

(B) In the roll coating method, since the control range of the coating film thickness is about 1 to 30 JLm in terms of the film thickness of the baked layer, it is difficult to obtain a thick film with -1 coating.

(C) The roll surface and paint pan are in contact with the atmosphere.

Therefore, in the roll coating method, the solvent components in the paint evaporate during the coating operation of the steel strip, causing changes in the paint components and viscosity, making it difficult to control the coating film thickness. Furthermore, such roll coating exposed to the atmosphere tends to allow foreign matter to get mixed into the paint, reducing the quality of the paint film.

(D) The end of the steel strip that is continuously threaded will damage the painted rubber roller. Therefore, the roll coating method.

The frequency of roll replacement increases, reducing the operating efficiency of the entire coating equipment.

As a result of repeating various coating experiments to solve the above-mentioned problems of the roll coating method, the present inventors discovered that the slit nozzle coating method can solve the problems described in (A) to CD) above. did. In this slit nozzle coating method, the tip of a slit nozzle, which has an opening that is narrow in the longitudinal direction of the steel strip and extends in the width direction of the steel strip, is fixed close to the surface of the steel strip, and an airtight state that leads to the opening is fixed. The paint is pumped into the paint supply path and then sprayed onto the surface of the steel strip from the slit nozzle opening. In the slit nozzle coating method, first, the paint is pumped with a pump with a small discharge rate, such as a screw feeder, to create an accurate steady flow that matches the line speed (area to be coated per unit time) and the desired film thickness (coating amount). After the supplied amount is sent through the piping to the paint supply path of the slit nozzle body, the flow of paint is spread inside the slit nozzle body with uniform pressure distribution along the width direction of the steel strip, and then from the slit nozzle opening. It is applied to the surface of the steel strip by discharging it. This slit nozzle coating method has the following advantages.

(a) Since the pressurized paint is discharged onto the surface of the steel strip from the slit nozzle opening, it is possible to handle paints with a wide viscosity range (50 to 80,000 cps) from low to high viscosity. Therefore, it becomes possible to use a paint with high viscosity and high solid content, which reduces solvent costs and facilitates environmental protection, and solves the problem described in (A) above of the conventional roll coating method.

(b) By adjusting the amount of paint discharged from the slit nozzle opening, it is possible to obtain a film thickness of up to 300 SLm with one coating. Therefore, it is possible to obtain a thick coating in - times of coating, and the problem described in (B) above of the conventional roll coating method can be solved.

(C) The paint is guided through an airtight paint supply path and does not come into contact with the atmosphere until it reaches the slit nozzle opening.
Therefore, the solvent component in the paint does not evaporate before it is applied to the steel strip, and no foreign matter gets mixed into the paint, solving the problem described in (C) above of the conventional roll coating method. can. Furthermore, since there is no risk of solvent evaporation, the paint can be used at various temperatures, and the viscosity of the paint can be controlled by adjusting the temperature.

(d) In the slit nozzle painting method, the tip of the slit nozzle opening is placed close to the surface of the steel strip and the coating is applied with shearing force, so air bubbles mixed into the coating film can cause wrinkles and wrinkles in the coating film. Does not cause appearance defects, especially when painting with high viscosity and high solids content.
This can be prevented by setting the distance between the steel strip surface and the slit nozzle opening tip to 50 l or less. Further, the problem described in (D) above of the conventional roll coating method can also be solved.

Using the slit nozzle coating method, the highly viscous paint is applied to the surface of the steel strip with a uniform film thickness in the width direction and longitudinal direction of the steel strip,
In addition, in order to paint with a good appearance, the paint must be discharged from the slit nozzle opening as a uniform continuous fluid in the width direction of the opening.According to experiments conducted by the present inventors, the paint must be discharged from the slit nozzle opening in the width direction of the opening. In order to make a paint with a viscosity within the range of 0,000 cps into a thin film with a film thickness of 30 tm or less after baking.

The distance between the steel strip surface and the slit nozzle opening tip is 300 mm.
It was confirmed that by being close to below p ■, it is possible to paint while the discharged paint is a continuous fluid, and a coating film with a uniform thickness in the width and length directions and a good appearance can be obtained. did.

In particular, in order to make a thin film with a film thickness of 3QILm or less with high viscosity paint, and to paint with a small amount of discharge, if the distance is more than 300gm, the fluid tends to become discontinuous.
10 In order to make a thin film, it depends on the line speed (area to be coated per unit time), but it is better to make the distance between the steel strip surface and the slit nozzle opening tip closer to compensate for the reduction in discharge amount. It is easy to form a continuous fluid, and it is easy to obtain a coating film with a good appearance.

However, if the tip of the slit nozzle opening comes into contact with the surface of the steel strip because it is too close, the slit nozzle opening will be damaged by the edge of the steel strip, resulting in streaky appearance defects on the coating film.

Problems to be Solved by the Invention The slit nozzle coating method has the following problems when coating lightweight and smooth materials such as plastic film and paper.
It's relatively easy.

However, according to experiments conducted by the present inventors.

When painting a metal strip such as a hot-dip galvanized steel strip using the slit nozzle coating method, the distance between the steel strip surface and the slit nozzle opening tip is kept close to 3001L or less,
It has been discovered that there are a number of problems that make it difficult to maintain a constant value, such as:

■If the steel strip has a defective shape such as an ear wave or a middle ground, the distance between the steel strip surface and the tip of the slit nozzle opening will change depending on the ear wave or middle ground height.

■When using a reverse-rolled cold-rolled steel sheet as the base plate for hot-dip galvanized steel strip, the top, center, and E
Since there is a difference in the thickness of the original plate at the nd part of about 20 ILm, the interval changes by about 20 ILm in the direction of the threading length.

■Current continuous coating equipment has a drying furnace for baking and curing the coating after roll coating. The steel strip must be held in a non-contact state with rolls or the like until the coating is baked and hardened in the furnace and cooled. Therefore, when painting the roll on the side of the furnace, the backup roll is under a large tension of the steel strip.According to measurements by the inventors, the roll shaft bearing of the backup roll rotates eccentrically due to the tension, causing the roll to The positional fluctuation of the wrapped steel strip is 200~
400 Jj - It was confirmed that it also reaches the intestines.

Even if the bearing part is changed to a metal bearing, fluctuations of 10 to 20g cannot be avoided. In other words, the distance between the tip of the slit nozzle opening and the surface of the steel strip wound around the backup roll changes greatly due to the positional fluctuation of the backup roll. That's what I do.

■When threading continuously through coating equipment, the E+d part of the preceding hot-dip galvanized steel strip and the Top part of the next steel strip are connected by welding or stitching, but the joint is connected to a slit nozzle. When passing the position of the aperture tip, the distance changes rapidly.

In this way, when it is desired to maintain the distance between the steel strip surface and the slit nozzle opening at a substantially constant value of 300 l or less and within a range that does not touch the steel strip surface, there are several problems that hinder this. These problems lead to contact between the tip of the slit nozzle opening and the surface of the steel strip, causing problems similar to those described in (D) above of the conventional roll coating method. Although the slit nozzle coating method originally allows the tip of the slit nozzle opening to approach the surface of the steel strip and apply a high viscosity paint in a thin or thick film, This could not be realized due to defects in the shape of the band's ear waves and the middle ground.

In order to solve this problem, the inventors repeated many more experiments and succeeded in maintaining the distance between the steel strip surface and the slit nozzle opening tip to a constant value without making the slit nozzle opening tip contact the steel strip surface. We have completed the present invention, which can be maintained at

Means for Solving the Problems A method for coating a hot-dip galvanized steel strip according to the present invention (hereinafter referred to as r
The method adopted in the method of the present invention is a coating process in the production of painted hot-dip galvanized steel strip, using a slit nozzle at the tip of the slit nozzle having an opening narrow in the longitudinal direction of the steel strip and extending in the width direction of the steel strip. In this coating method, the paint is brought close to the steel strip surface and the paint under pressure is discharged from the slit nozzle opening onto the steel strip surface. The distance between the steel strip and the tip of the slit nozzle opening is to be maintained at a substantially constant value within a range of 300 layers or less and not in contact with the surface of the steel strip.

Furthermore, a different means adopted by the present invention is that during the painting process in the production of painted hot-dip galvanized steel strip, the continuous strip is wound in the longitudinal direction of the steel strip at a position where it is wound around a backup roll. A coating method in which the tip of a slit nozzle having a narrow opening extending in the width direction of the steel strip is brought close to the surface of the steel strip, and paint under pressure is discharged from the slit nozzle opening onto the surface of the steel strip. The distance between the tip of the slit nozzle opening and the surface of the steel strip does not change significantly due to poor shape, and the distance can be maintained almost constant. Further, it is more effective to arrange a presser roll at a position immediately in front of the slit nozzle opening so as to press the steel strip against the backup roll.

In addition, by applying a certain pressure to the slit nozzle body and pressing the tip of the slit nozzle opening against the steel strip surface, then by discharging the paint from the slit nozzle opening with a constant discharge pressure greater than the pressure, the steel strip surface and slit are Paint by keeping the distance from the nozzle opening tip to a nearly constant value within a range of 300 mm or less and not touching the steel strip surface, and making the position of the slit nozzle opening tip follow the positional fluctuations of the steel strip surface. It is to be. As one of the means for following the slit nozzle, it is possible to freely determine the distance between the steel strip surface and the tip of the slit nozzle opening and keep it constant by regulating the paint discharge pressure that generates the pushing force and reaction force of the slit nozzle. .

In the method of the present invention, the hot-dip galvanized steel strip may be a steel strip, a metal-plated steel strip, a stainless steel strip, an aluminum strip, or another metal strip.

Function The method of the present invention causes the position of the tip of the slit nozzle opening to follow the positional fluctuation of the steel strip surface, and keeps the distance between the steel strip surface and the tip of the slit nozzle opening within a range of 300 mm or less and not in contact with the steel strip surface. The position of the surface of the steel strip is maintained at a nearly constant value, so the position of the surface of the steel strip may vary depending on the selvage of the steel strip, the mid-ground height, the difference in thickness in the longitudinal direction of the hot-dip galvanized steel strip, and/or the eccentric rotation of the backup roll. Even if the distance varies, the distance between the steel strip surface and the slit nozzle opening tip is maintained at a set value of 3004 layers or less without bringing the slit nozzle opening tip into contact with the steel strip surface. Since the distance between the steel strip surface and the tip of the slit nozzle opening is maintained at a set value of 300 g or less, the paint discharged from the slit nozzle opening toward the steel strip surface is transferred to the steel strip being transported at the set line speed. It is applied continuously to the surface of the strip without causing any liquid to run out, forming a thin to thick coating film.

Since the slit nozzle opening tip is close to the steel strip surface, the paint discharged from the slit nozzle opening tip is subjected to shearing force in the gap between the steel strip surface and the slit nozzle opening tip during conveyance. As a result, the coating film coated by the method of the present invention is free from the incorporation of air bubbles into the coating film.
The film has a smooth and beautiful surface without appearance defects such as wrinkles.

Example Next, the method of the present invention will be explained by giving examples.

First Embodiment In the first embodiment, the slit nozzle body is placed outside the position where the steel strip is wound around the backup roll so that it can move forward and backward toward the steel strip. Pressing 5 Next, the paint is discharged from the slit nozzle opening at a constant discharge pressure that is higher than the pressing pressure, thereby separating the slit nozzle opening tip from the steel strip surface and increasing the distance between the steel strip surface and the slit nozzle opening tip. 3001Lm
In this embodiment, the slit nozzle opening tip position follows the positional fluctuation of the steel strip surface by maintaining it at a substantially constant value within a range that does not touch the steel strip surface.
By balancing the pressing force of the pressing means that presses the slit nozzle body and the discharge pressure of the paint discharged from the slit nozzle opening, even if the position of the steel strip surface changes, the steel strip surface and the tip of the slit nozzle opening are The interval can be maintained at an appropriate value, and furthermore, by defining the pressure difference between the two, the interval can be changed to a desired value.

According to experiments conducted by the present inventors, it was easier to obtain a continuous fluid of paint when the spacing was closer to 300 μm or less, especially under conditions where the discharge amount was small to obtain a thin film in the range of 1 to 30 ILm. On the other hand, if the spacing exceeds 300 mm, the fluid in high viscosity paint tends to become discontinuous, and furthermore, when the line speed of the steel strip is high, air is likely to be drawn in between the fluid and the surface of the steel strip. To deal with air entrainment, experiments were conducted with the idea of vacuum degassing on the inlet side where the fluid and steel strip surface come into contact, but stable results could not be obtained.

In the conventional roll coating method, air bubbles in the paint caused by stirring cause appearance defects such as wrinkles and wrinkles.

On the other hand, in the method of the present invention, the tip of the slit nozzle opening is brought close to the surface of the steel strip, so shearing force is applied to the paint to be discharged, so that the appearance defects due to air bubbles do not occur. This was confirmed. In particular, to remove wrinkles and wrinkles caused by air bubbles mixed into paint with high viscosity and high solid content, the distance between the steel strip surface and the tip of the slit nozzle opening should be 50 mm.
This can be prevented by following the steps below.

In addition, it is important to take sufficient care to ensure that the slit nozzle body advances and retreats smoothly and that the resistance on the support sliding surface is reduced. This is a good method that allows the position of the tip of the slit nozzle opening to follow the factors described above, and is inexpensive in terms of equipment and has good workability.

Second Embodiment The second embodiment uses a servo controller that directly detects changes in the distance between the steel strip surface and the tip of the slit nozzle opening using an electrical, optical, or magnetic method, and receives a detection signal. This embodiment is designed to mechanically move the slit nozzle body to maintain the above-mentioned interval at a constant value.This embodiment is capable of controlling the slit nozzle opening tip position with respect to all factors that cause positional fluctuations on the surface of the steel strip. This is a good method that allows you to track the

Third Embodiment In the third embodiment, the slit nozzle body is arranged outside the position where the steel strip is wound around the backup roll so that it can move forward and backward toward the steel strip, and the support portions are fixed to both sides of the slit nozzle body. The tips of the slit nozzles are fitted into grooves provided in the circumferential direction at both ends of the backup roll, and the slit nozzle opening tips follow the positional fluctuations of the rotating backup roll's outer circumferential surface. This embodiment, which involves painting so that the distance from the tip of the opening is a constant value, can effectively follow changes in the distance due to changes in the outer surface position of the eccentrically rotating backup roll. It can be applied to coating steel strips with few thickness changes, ear waves, and inlays.

Other Embodiments The following means can be added to the first to third embodiments.

In the case of a steel strip with a poor shape where the wave height is several inches due to the selvage or middle ground of the steel strip, the distance between the surface of the steel strip and the tip of the nozzle slit opening will change significantly, so the presser roll should be used as a backup. Press it against the roll to lower the wave height, and paint at the position immediately after that.

Further, since the joint portion of the steel strip, such as a weld or a stitcher, is usually about twice or more thick than the steel strip, the distance between the surface of the steel strip and the tip of the slit nozzle opening changes rapidly. In order to avoid this sudden change and to be able to continuously follow the tip of the slit nozzle opening, the joints may be welded together, or various films may be laminated before and after the joint to gradually increase the thickness of the strip. You can change and deal with it. Another method is to detect the position of the joint in advance and temporarily retreat the slit nozzle body with a cylinder or the like when the joint passes through the painting position.
It is also possible to increase the distance between the joint and the tip of the slit nozzle opening. In this case, in order to avoid the formation of unpainted parts on the steel strip and improve the yield, the slit nozzle main body is moved back and forth as short as possible, and the slit nozzle body is moved back and forward instantly.

The above embodiments are applicable not only to the coating method for hot-dip galvanized steel strips, but also to steel strips other than hot-dip galvanized steel strips and various metal-plated steel strips as the material to be coated.

It can also be widely applied to stainless steel strips, aluminum strips, or other metal strips.

Experimental Example The present inventors conducted an experiment to confirm the effectiveness of the method of the present invention and obtained the following results.

(1) Hot-dip galvanized steel strip that is continuously threaded at a line speed of 120 cm/min in a continuous coating facility (plate thickness 0.4 g + × width 91 plate layer 914.80 g 50 l with the tip of the slit nozzle at the entrance side of the drying heating furnace.
An oil-free polyester resin paint (solid content 80%, viscosity 19000 cps at 25°C, white) was applied by discharging it from the slit nozzle opening at a pressure of 6 kg/cs+2.

The gap between the steel strip surface and the slit nozzle opening tip is magnetically detected in Igm units using Magnescale, and the slit nozzle body is made to follow the positional movement of the steel strip surface.
The distance between the steel strip surface and the slit nozzle opening tip is 50±
The coating was carried out so that it was always kept almost constant within the range of 31 Lm. 220℃.

After baking for 30 seconds, the coating thickness was within the range of 13±1 (dry coating thickness) in both the length and width directions of the hot-dip galvanized steel strip, and the coating had a good appearance with no coating defects. I was able to do it.

(2) A molten summer lead-plated steel strip (thickness: 0.35 mm x width: 1214 mm), which is continuously threaded at a line speed of 150 m/min in a continuous coating facility, is wound around a backup roll on the entrance side of the drying and heating furnace. Apply oil-free polyester resin paint (90% solids, viscosity 52,000 cps at 25°C, blue) to the opening of the proverbial gap of 100 l in the width direction of the steel strip using a screw feeder immediately after pressing it with the presser roll. The mixture was fed under pressure to a slit nozzle having a slit nozzle, and was discharged from the slit nozzle opening for coating.

First, a pressure of 4 kg/C was applied to the slit nozzle body using a cylinder to press the slit nozzle opening tip against the steel strip surface, and then to obtain an even larger reaction force.
When the paint was discharged from the opening at a pressure of 8 kg/c layer 2, the tip of the slit nozzle opening was separated from the surface of the steel strip by an interval of 8 l.

When continuous coating was carried out under these conditions, even if the position of the steel strip surface varied due to various factors, the interval could always be kept almost constant within the range of 8 layers ± 2 layers.

After coating, bake at 230°C for 25 seconds and measure the dry film thickness in both the length and width directions of the steel strip.
The coating surface was within the range of (1) and had a good appearance.

As described in detail, the method of the present invention includes: bringing the slit nozzle opening tip close to each other within a range where the distance between the steel strip surface and the slit nozzle opening tip is 300 mm or less and not touching the steel strip surface; Since this interval is always maintained at a substantially constant value and the position of the slit nozzle opening tip follows the positional fluctuation of the steel strip surface, all of the above-mentioned conventional problems can be solved. In other words, the method of the present invention has been put to practical use in continuous coating equipment for hot-dip lead-plated steel strips, which eliminates the disadvantages of the conventional roll coating method: High viscosity, high solid content (low solvent) paints cannot be used. Disadvantages in terms of solvent costs and environmental protection ■ Difficulty in controlling film thickness due to viscosity changes ■ Narrow range of paintable film thickness ■ Contamination of foreign objects into paint due to open type ■ Replacement of coating rolls, etc. The method of the present invention greatly contributes to the progress of manufacturing technology for painted hot-dip galvanized steel strips.

Claims (3)

[Claims] (1) In the painting process of hot-dip galvanized steel strip, the tip of a slit nozzle, which has an opening that is narrow in the longitudinal direction of the steel strip and extends in the width direction of the steel strip, is brought close to the surface of the steel strip and pressure is applied. In a coating method in which paint is discharged onto the steel strip surface from a slit nozzle opening, the position of the slit nozzle opening tip follows the positional fluctuation of the steel strip surface, and the distance between the steel strip surface and the slit nozzle opening tip is 300 μm or less. A method for coating a hot-dip galvanized steel strip, characterized in that the coating is maintained at a substantially constant value within a range that does not touch the surface of the steel strip. (2) An opening that is narrow in the longitudinal direction of the steel strip and extends in the width direction of the steel strip at the position where the continuous steel strip is wound around a backup roll during the coating process of hot-dip galvanized steel strip. In a coating method in which the tip of a slit nozzle with a slit nozzle is brought close to the surface of the steel strip and paint under pressure is discharged from the slit nozzle opening onto the steel strip surface, a certain pressure is applied to the slit nozzle body and the slit nozzle opening The slit nozzle opening tip is separated from the steel strip surface by pressing the tip against the steel strip surface and then discharging the paint with a discharge pressure greater than the pressure, so that the distance between the steel strip surface and the slit nozzle opening tip is 300 μm or less. Coating of a hot-dip galvanized steel strip, characterized in that the coating is maintained at a substantially constant value within a range that does not touch the steel strip surface, and the position of the slit nozzle opening tip follows the positional fluctuation of the steel strip surface. Method. (3) The method for coating a hot-dip galvanized steel strip according to claim 1 or 2, wherein the hot-dip galvanized steel strip is a steel strip, a metal-plated steel strip, a stainless steel strip, an aluminum strip, or another metal strip.