JPH04284871A - Method for forming dispersed resin film and apparatus therefor - Google Patents

Abstract

PURPOSE:To obtain a resin coated steel prate having a dispersed resin film formed to the entire surface region thereof at uniform distribution density and excellent in fingerprint resistance, weldability and solderability by preventing that the resin emulsion blown out of a high speed rotary atomizer for electrostatic dispersing painting is carried by the air stream in the periphery of a steel plate to flow in a downstream direction. CONSTITUTION:When a dispersed resin film is formed to the surface of a steel plate P subjected to chromate treatment by electrostatically dispersing the particle droplets E of a resin emulsion on the surface of the steel plate P from an atomizer N rotating at a high speed, the particle droplets E are made easy to flow in the downstream direction by the air stream F generated in the vicinity of the surface of the steel plate P. By applying resistance force G to the particle droplets E in the direction reverse to the direction of the air stream F, the deflection of the particle droplets E is suppressed to deposit the particle droplets E on the steel plate P in distribution density uniform with respect to the lateral direction of the steel plate P. Since the dispersed resin film is formed to the steel plate over the entire surface thereof in uniform distribution density, a highly reliable surface-treated steel plate not locally inferior in fingerprint resistance, weldability or the like is obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a method and apparatus for forming a dispersed resin film having conductivity, weldability, etc. on the surface of a steel sheet in a uniform distribution over the entire surface without impairing fingerprint resistance, corrosion resistance, etc. Regarding.

0002

2. Description of the Related Art Fingerprints are likely to adhere to the surface of a steel plate during handling, causing surface discoloration. Particularly in the case of stainless steel, for which surface appearance is important, interference colors appear on the surface due to fingerprints, which significantly reduces commercial value. In addition, fingerprints attached to steel plates that have been surface-treated such as galvanized
It cannot be easily removed from the surface of the steel plate by wiping it with a cloth.

[0003] In order to remove these fingerprints from the steel plate surface,
A process of cleaning the steel plate with detergents and solvents is used. However, the addition of a cleaning process complicates the production line and reduces productivity. Therefore, fingerprint resistance is imparted by covering the steel plate surface with a chromate film and a resin film.

[0004] Conventional resin films are formed in a relatively large amount so as to cover the entire surface of a steel plate. Therefore, since the formed resin film acts as an insulating layer, weldability, solderability, etc. are deteriorated when electrical products, interior parts, various equipment, etc. are assembled using the resin-coated steel sheet.

In order to satisfy these conflicting demands, the present inventors have developed a method of forming a discontinuous resin film on the surface of a steel plate, and have disclosed the method in Japanese Patent Application Laid-open Nos. 114635-1983 and 1983-1983. -276539 Publication, JP-A-64-11
It is introduced in Publication No. 981, etc. In the newly proposed method, electrostatically charged resin liquid is sprayed from a nozzle that rotates at high speed, and is caused to fly onto the surface of the steel plate using electrical attraction. Here, when adjusting the amount of resin liquid applied to the surface of the steel plate, many droplets adhere to the surface of the steel plate. Next, a discontinuous resin film is formed on the surface of the steel plate by performing baking treatment in a drying oven.

[0006]

[Problem to be Solved by the Invention] When forming a discontinuous resin film on the surface of a steel plate by electrostatic dispersion, a negatively charged atomizer is rotated at high speed, and the resin emulsion is spread from this atomizer as droplets onto the surface of the steel plate. It's flying. However, the steel plate to be painted is sent downstream at a transport speed of about 40 to 70 m/min. Therefore, an air flow accompanying the traveling of the steel plate is generated near the surface of the steel plate.

[0007] When the resin emulsion droplets that fly from the atomizer onto the surface of the steel plate reach the vicinity of the surface of the steel plate, they are swept downstream by the air flow. Therefore, the droplets that reach the surface of the steel sheet have a distribution that deviates from the intended distribution. Due to this deviation, partial density distribution occurs in the distribution density of the droplets. In areas where droplets are densely distributed, bridges are formed between the droplets before baking, making it easier to form a continuous resin film. On the other hand, in locations where the droplets are coarsely distributed, the proportion of exposed metal surfaces increases, making it impossible to obtain the required fingerprint resistance. Furthermore, since the amount of resin film deposited becomes uneven, the surface appearance also deteriorates.

The present invention has been devised to solve these problems, and by offsetting the adverse effects caused by the air flow near the surface of the steel plate with pneumatic or electrostatic repulsive force, the desired effect can be achieved. The purpose of this method is to deposit resin emulsion droplets in a uniformly dispersed form onto the surface of a steel plate, thereby forming a dispersed resin film with a uniform distribution density over the entire surface area.

[0009]

[Means for Solving the Problems] In order to achieve the object, the dispersion resin film forming method of the present invention electrostatically disperses resin emulsion droplets onto the surface of a chromate-treated steel plate from an atomizer rotating at high speed. When forming the dispersed resin film, the method is characterized in that the deflection of the droplets toward the downstream side riding on the air flow accompanying the traveling of the steel plate is canceled out by air pressure or electrical repulsive force.

[0010] In the case of reducing the flow energy of the air flow by using a countercurrent air flow, an electrostatic dispersion coating device through which a chromate-treated steel plate passes, and a high-speed A device is used that includes a pair of rotating atomizers and an air jet nozzle provided at the outlet opening of the electrostatic dispersion coating device. Also,
If the flow energy of the airflow is to be reduced by electrostatic repulsion, a negatively charged auxiliary electrode is used at the exit opening of the electrostatic dispersion coating device.

[0011]

[Operation] The resin emulsion droplets dispersed from the atomizer fly outward in the radial direction due to the centrifugal force given by the high speed rotation of the atomizer. Since it is negatively charged via the atomizer, it is pulled by the positively charged steel plate when grounded. When the steel plate P is stationary, the forces acting on the flying droplets are centrifugal force and electrical attraction force, and are uniform in the circumferential direction around the atomizer N. Therefore, the resin emulsion droplets E adhere to the steel plate P in a dispersed form with a constant radius R, as shown in FIG. 1(a). At this time, so that the distribution density of the droplets E becomes uniform in the width direction of the steel plate P,
The radius R is set larger than the width of the steel plate P.

However, when the steel plate P is running in the transport direction D, an air flow F is generated as the steel plate P moves. The air flow F becomes faster as it approaches the surface of the steel plate P. The resin emulsion droplets E that fly into the atmosphere where the air flow F is generated are pulled by the flow energy of the air flow F and flow downstream. The flow energy of the air flow F becomes particularly large near the exit side of the electrostatic dispersion coating device. As a result, as shown in FIG. 1(b), at the stage when the droplets E reach the surface of the steel plate P, the droplets E are distributed in a state deviated from the intended circumferential distribution. When viewed in the longitudinal direction of the steel plate P, the distribution density of the droplets E becomes uneven due to this deviation. As described above, this density may locally cause insufficient adhesion or continuity of the resin film.

In the present invention, the adverse effects of the air flow F are suppressed by a force G acting in a direction opposite to the conveyance direction D of the steel plate P. This counterforce G is obtained by blowing air in a countercurrent from the outlet side of the electrostatic dispersion coating device or by applying an electrostatic repulsive force to the flying droplets. The droplets E, which try to deviate downstream on the airflow F, are pushed back by the counterforce G. As a result, as shown in FIG. 1(c), the amount of deviation is canceled or reduced, and the droplets E are distributed at a uniform density in the width direction of the steel plate P.

The present invention is implemented, for example, on a manufacturing line as shown in FIG. The steel plate 10 is conveyed from left to right in FIG. A chromate treatment device 20, a drying device 30, a cooling device 40, an electrostatic dispersion coating device 50, and a post-cooling device 60 are arranged along this pass line from the upstream side.

The chromate treatment apparatus 20 has a roll coater 23 immersed in a container 22 placed in a closed chamber 21 . The chromate treatment liquid 24 contained in the container 22 is lifted up by the roll coater 23 and supplied to the steel sheet 10 being passed. A chromate film is formed on the surface of the steel sheet 10 by contact with this chromate treatment liquid. In addition, in FIG. 2, the chromate treatment liquid 24 is supplied to the surface of the steel plate 10 by the roll coater 23, but the chromate treatment liquid can also be supplied by a spray method. In addition, by passing the steel plate 1 through an electrolytic bath,
It is also possible to form a chromate film on the surface of 0.

The steel plate on which the chromate film has been formed is sent to a drying device 30 after excess treatment liquid is removed. The drying device 30 is provided with a hot air supply port 31 and an exhaust port 32, and hot air of 180±20° C. is supplied thereto. While the hot air passes through the inside of the drying furnace 30, which has a high-temperature atmosphere, the chromate treatment liquid remaining on the surface of the steel plate 10 evaporates, and the steel plate 10 is dried. In addition,
As the heating and drying means, a heater, a radiation heating tube, etc. disposed along the pass line of the steel plate 10 may be used.

The steel plate 10 after drying is then passed through a cooling device 40.
sent to. The cooling device 40 is divided into a plurality of chambers 42 to 45 by partition walls 41. and,
Cooling air is supplied to the chambers 42 to 45 by the air supply fan 46. The steel plate 10 is cooled by contacting the cooling air. This air cooling method is a preferable cooling means in order to prevent chromic acid from being leached from the chromate film formed on the surface of the steel plate 10.

Cooling air supplied from the air blowing fan 43 is blown into the cooling device 40 so as to come into countercurrent contact with the steel plate 10 being conveyed, that is, to flow from the chamber 45 on the downstream side to the chamber 42 on the upstream side. It is preferable. However, when cooling air is blown into the most downstream chamber 45, the flow rate of cooling air flowing out from the outlet side of the cooling device 40 increases. Therefore, as shown in the figure, cooling air is blown into the downstream chamber 44 avoiding the most downstream chamber 45. Also, the steel plate 10 leaving the cooling device 40 is 1
It is preferable to control the air cooling conditions so that the temperature is maintained in a range of 40 to 80°C.

The cooled steel plate 10 is sent to an electrostatic dispersion coating device 50. The electrostatic dispersion coating device 50 has a pair of atomizers 52 and 53 arranged opposite to each other on both the upper and lower surfaces of the steel plate 10 passing through the inside of the sealed chamber 51 . The atomizer 52 has a head 54 attached to the tip of a rotating shaft 53, as shown in FIG. A space 55 is circumferentially bored inside the head 54 , and the space 55 communicates with an open space 57 via an atomization hole 56 . The head 54 is charged to a high voltage of about -100 KV by a power supply line 58, and a nozzle 59 supplies the resin liquid to be applied.
The tip faces the space 55. Note that the lower atomizer 53 also has a similar structure.

[0020] These atomizers 52 and 53 cost tens of thousands of rp
When rotating at high speed at speed m, the resin liquid supplied from the nozzle 59 to the space 55 reaches the open space 57 via the atomization hole 56, and is released as droplets in the radial direction by centrifugal force. The droplets emitted from the atomizers 52 and 53 are negatively charged, are pulled by the positively charged steel plate 10 due to grounding, and adhere to the surface of the steel plate 10.

[0021] At this time, a nozzle 51a is provided for blowing air from the exit side of the electrostatic dispersion coating device 50 so as to cancel out the air flow generated by conveying the steel plate 10. The nozzle 51a is arranged at an angle so that air is blown out toward the surface of the steel plate 10. In addition, this airflow
A branch pipe 6 from an air supply fan 64 of a post-cooling device 60 to be described later.
5 and is preferably provided with a flow rate regulating valve so as to generate an air flow in the opposite direction corresponding to the air flow generated on the surface of the steel plate 10. Nozzle 51
The flow rate of the air flow blown out from a is determined by taking into account the air flow generated by conveying the steel plate 10,
It is usually maintained in the range of 3 to 10 Nm3/min.

[0022] When maintaining the amount of resin adhering to the steel plate 10 in the range of 0.1 to 2.0 g/m2 in terms of dry weight,
As shown in FIG. 4, a discontinuous dispersed resin layer 13 is formed on the plating layer 11 and the chromate film 12 formed on the surface of the steel plate 10. The diameter d of each dispersed resin layer 13 is 40 to 150 μm. Here, if the resin adhesion amount 13 is less than 0.1 g/m2, the surface area of the plating layer 11 exposed without being covered with resin becomes large, and the fingerprint resistance decreases. On the other hand, the resin adhesion amount is 2.0g/
When it exceeds m2, bridges are formed between the individual dispersed resin layers 12, and a continuous resin film tends to be formed. In this respect, it is preferable to maintain the resin adhesion amount in the range of 0.1 to 2.0 g/m2.

As the resin liquid, a water-soluble or water-dispersible organic resin emulsion is used. For example, there are organic resin emulsions such as acrylic-silica composite resins or resin emulsions as described above containing 1 to 25% wax, and acrylic-modified polyolefin resins.

The electrostatic dispersion coated steel sheet is then cooled by a post-cooling device 60. Like the cooling device 40, the post-cooling device 60 includes a plurality of chambers 62 and 63 partitioned by a partition wall 61, and cooling air is blown into the chamber 63 on the downstream side from an air supply fan 64. In this process, the dispersed resin layer 12 is dried, and a desired discontinuous resin film is formed on the surface of the steel plate 10.

[0025]

[Example] Example 1: An acrylic-silica resin liquid containing 20% wax was applied to the surface of a steel plate running at a line speed of 70 m/min using the atomizer shown in Figure 2. . An average coating weight of 1.0 g/m2 was applied to a steel plate with the entrance temperature of the electrostatic dispersion coating device 50 set at 100°C.
The resin was electrostatically dispersed under

When air was not blown out from the nozzle 51a in a countercurrent state, resin emulsion droplets adhered to the steel plate 10 with a dense distribution density in the center and a coarse distribution density in the width direction of the steel plate 10. Therefore, the central surface of the steel plate 10 after baking had a film in which a plurality of resin films were interconnected. In addition, the distribution density of the dispersed resin film is small at both ends.
There was a problem with fingerprint resistance.

On the other hand, the flow rate from the nozzle 51a is 7Nm.
When an air flow was blown into the electrostatic dispersion coating device 50 at a rate of 3/min, the distribution density of droplets was 1.3/min in the width direction of the steel plate 10.
It was maintained in the range of 0±0.2 g/m2, and no bridges were detected between the dispersed resin films. In addition, even if the distributed resin film is formed at the smallest distribution density,
It had sufficient fingerprint resistance.

Embodiment 2: Auxiliary electrodes 51c, 51c shown in FIG. 5 were employed as a means for applying a counterforce to the air flow generated as the steel plate 10 is transported. That is, auxiliary electrodes 51c, 51c connected to the negative side of the power source are arranged near the outlet side of the sealed chamber 51, and the atomizer 52,
An electrostatic repulsive force is generated between the negatively charged resin emulsion droplets ejected from the auxiliary electrodes 51c and 51c. These auxiliary electrodes 51c, 51c may be connected to atomizers 52, 53 so that negative charges can be applied from the atomizers 52, 53.

The voltage applied to the auxiliary electrodes 51c, 51c depends on the flow rate of the generated air flow, in other words, the conveyance speed of the steel plate 10, but under normal conditions it is set in the range of 50 to 100 KV. When a negative charge of 70 KV was applied to the auxiliary electrodes 51c and 51c and the resin emulsion was electrostatically dispersed under the same conditions as in Example 1, the dispersed resin film formed on the surface of the steel plate after baking was 1 in the width direction. .0±0.1g/
It was distributed with a variation of m2. Furthermore, no bridges or areas with poor density were detected that interconnected adjacent dispersed resin films.

[0030]

[Effects of the Invention] As explained above, in the present invention, droplets of resin emulsion that try to deviate downstream by riding on the airflow generated by the running of the steel plate are prevented by countercurrent airflow or electrostatic The repulsive force pushes it back upstream. As a result, the resin emulsion that reaches the steel plate surface is
It is distributed with a uniform distribution density in the width direction of the steel plate. As a result, the dispersed resin film after baking becomes a surface layer that has excellent fingerprint resistance over the entire surface of the steel plate and does not function as an insulating layer.

[Brief explanation of the drawing]

[Figure 1] Diagram for explaining the action of the present invention

[Figure 2]
The production line adopted in Example 1 of the present invention is shown.

FIG. 3 shows an atomizer of an electrostatic dispersion coating device.

FIG. 4 shows a dispersed resin layer attached to a chromate-treated plated steel sheet.

FIG. 5 shows a facility configuration that uses electrostatic repulsion to suppress displacement of resin emulsion droplets.

[Explanation of symbols]

10 Steel plate 20 Chromate treatment device 30 Drying device 40 Cooling device 50 Electrostatic dispersion coating device 51a Nozzle

Claims (3)

[Claims] Claim 1: When a dispersed resin film is formed on the surface of a chromate-treated steel plate by electrostatically dispersing resin emulsion droplets from a high-speed rotating atomizer, the particles are dispersed on the downstream side by riding the airflow that accompanies the running of the steel plate. A method for forming a dispersed resin film, characterized in that the deviation of the droplets toward the direction of the droplets is canceled out by air pressure or electrical repulsion. 2. An electrostatic dispersion coating device through which a chromate-treated steel plate passes, a pair of atomizers that are disposed opposite to each other on both upper and lower surfaces of the steel plate and rotate at high speed, and an output of the electrostatic dispersion coating device. and an air jet nozzle provided in the side opening, and the flow energy of the air flow accompanying the traveling of the steel plate is reduced by the air flow jetted toward the upstream side from the air jet nozzle. A device for forming a dispersed resin film. 3. An electrostatic dispersion coating device through which a chromate-treated steel plate passes, a pair of atomizers arranged opposite to each other on both upper and lower surfaces of the steel plate and rotating at high speed, and an output of the electrostatic dispersion coating device. A dispersion resin comprising an auxiliary electrode provided in a side opening and to which a negative charge is applied, and generating an electrostatic repulsive force between the flying droplets and the auxiliary electrode. Film forming device.