JPH04285178A - Formation of disperse-resin film - Google Patents

Abstract

PURPOSE:To obtain a resin-coated steel sheet excellent in fingerprint resistance, weldability and solderability by baking a disperse resin film with the remaining heat imparted to the steel sheet when a chromate film is heated and dried. CONSTITUTION:A chromated 20 steel sheet 10 is heated and dried 30, and the temp. of the steel sheet 10 being cooled 40 after heating is detected by a thermometer 47. The capacity of the cooler 40 is adjusted based on the detected temp., and the steel sheet is kept at 140-80 deg.C on the inlet side of an electrostatic disperse coating device 50. A resin emulsion is electrostatically dispersed on the steel sheet to form a discontinuous resin film on the surface. The amt. of the resin to be deposited is preferably controlled to 0.1-20g/m<2>. Since the remaining heat of the steel sheet heated to dry its chromate film is utilized to bake the resin film, chromating and resin baking are performed in a continuous line while saving the energy and space.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a dispersed resin film on the surface of a steel plate having electrical conductivity, weldability, etc. without impairing fingerprint resistance, corrosion resistance, etc.

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 developed a method of forming a discontinuous resin film on the surface of a steel plate, and 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 high-speed rotating atomizer, 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, by performing baking treatment in a drying oven, a discontinuous resin film is formed on the surface of the steel plate.

[0006]

[Problem to be solved by the invention] When forming a discontinuous resin film on the surface of a steel plate by electrostatic dispersion, it is necessary to preheat the steel plate to a predetermined temperature in order to improve the amount of resin adhering to the surface of the steel plate. Become. However, if a heating furnace is provided upstream of the electrostatic dispersion coating device for preheating, an area for installing the heating furnace is required, and the equipment load also increases.

[0007] The present invention was devised to solve these problems, and uses residual heat from the drying process that is carried out after chromate treatment to bake the resin, thereby making it possible to coat steel sheets with electrostatic dispersion coating. Omits the heating furnace for preheating,
The aim is to build a production line that is excellent both in terms of equipment and thermoeconomics.

[0008]

[Means for Solving the Problems] In order to achieve the object, the method for forming a dispersed resin film of the present invention heat-dries a chromate-treated steel plate, and in the cooling process after heating,
The present invention is characterized in that a resin emulsion is electrostatically dispersed on the steel plate in a temperature range of 0°C to form a discontinuous resin film on the surface of the steel plate.

[0009] The resin film attached to the steel plate surface has a thickness of 0.1
It is preferable to form the coating with an adhesion amount of ~2.0 g/m2. Further, the steel plate used in the present invention is not subject to any restrictions on the steel type or surface treatment as long as it is preheated after chromate treatment. However, when applied to materials that are plated such as zinc plating or materials where surface appearance is important, such as stainless steel, remarkable effects are exhibited.

0010

[Operation] Formation of a resin film by electrostatic dispersion coating is usually performed following chromate treatment. Further, the chromate treatment involves a step of forming a chromate film by chemical conversion treatment or an electrolytic method, and then heating and drying the surface of the steel sheet. Therefore, when using the residual heat of the steel plate after heating and drying, the preheating process of the steel plate required for electrostatic dispersion coating of resin liquid is omitted, and the chromate treatment and electrostatic dispersion coating can be performed in a continuous line. .

However, it is not possible to form a good dispersed resin film simply by using the residual heat after the chromate treatment. In other words, heating and drying after chromate treatment is performed by raising the temperature of the steel plate to about 160 to 200°C, but when a resin liquid is electrostatically dispersed on a steel plate in such a high temperature range, the resin liquid that has flown onto the surface of the steel plate is Boils instantly. As a result, boiling traces of the resin film remain on the surface of the steel sheet, a so-called powdering phenomenon occurs, and the surface texture of the product deteriorates. Conversely, if a resin liquid is electrostatically dispersed onto a steel plate that has been cooled to near room temperature, the resin liquid adhering to the surface of the steel plate will not dry, making it impossible to form the desired discontinuous resin film.

[0012] According to research conducted by the present inventors, it has been found that it is important for the steel plate to be in a temperature range of 140 to 80°C in order to form the targeted resin film. Although the steel plate temperature varies slightly depending on the amount of resin applied, as long as the steel plate is maintained in the temperature range of 140 to 80°C, a good discontinuous resin film is formed.

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

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. 1, 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.

[0016] 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 downstream chamber 45 to the upstream chamber 42. 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.

A thermometer 47 is provided on the outlet side of the cooling device 40 or on the inlet side of the electrostatic dispersion coating device 50 to detect the temperature of the steel plate 10 leaving the cooling device 40. The steel plate temperature detected by the thermometer 47 is sent to the air blowing fan 46 as a control signal a via an appropriate computing unit. Then, the rotational speed of the air blowing fan 46 is controlled, and cooling air is blown into the cooling device 40 at an air flow rate corresponding to the steel plate temperature. In this way, the steel plate 10 exiting the cooling device 40 is
It is maintained at a temperature range of 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] 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. 3, a discontinuous dispersed resin layer 13 is formed on the plating layer 11 and 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, organic resin emulsions containing 1 to 25% wax in acrylic-silica composite resins, 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.

[0024]

EXAMPLE 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 FIG. Coating amount 0.5g/ on steel plates at various steel plate temperatures.
Fig. 4 shows the results of examining the properties of the resin film when the resin was applied under the conditions of 1.0 g/m2 and 1.0 g/m2.

As is clear from FIG. 4, the adhesion amount is 0.5
g/m2, if the steel plate temperature at the entrance side of the electrostatic dispersion coating device 50 was 70° C. or lower, the resin film exiting the post-cooling device 60 was not dried. Moreover, when the steel plate temperature exceeded 140° C., powdering was detected in the obtained resin film. This is a defect caused by the applied resin boiling due to the steel plate temperature being too high.

[0026] When the adhesion amount was 1.0 g/m2, the steel plate temperature was less than 80°C, and the resin film was in an undried state with poor baking. Also, when the steel plate temperature exceeds 145℃,
Powdering was detected.

However, in any case, the temperature of the steel plate at the entrance side of the electrostatic dispersion coating device 50 is set at 80 to 140°C.
When maintained in the temperature range of °C, a resin film with good baking properties without drying or powdering was formed.

[0028]

Effects of the Invention As explained above, in the present invention, the resin applied discontinuously to the surface of the steel plate is baked by using the preheating given to the steel plate by heating and drying performed after chromate treatment. ing. Therefore, not only can chromate treatment and electrostatic dispersion coating be performed in a continuous line, but the preheating furnace required for electrostatic dispersion coating can be omitted, resulting in energy and space savings, and production. A surface treatment line with excellent properties has been constructed. Further, since the temperature of the steel plate to be electrostatically dispersed coated is maintained at 80 to 140°C, a good resin film is formed without drying or powdering.

[Brief explanation of the drawing]

FIG. 1 shows a manufacturing line to which the present invention is applied.

FIG. 2 shows an atomizer of an electrostatic dispersion coating device.

FIG. 3 shows a dispersed resin layer attached to a chromate-treated plated steel sheet.

FIG. 4 shows the influence of the amount of resin deposited and the temperature of the steel plate on the formed resin film.

[Explanation of symbols]

10 Steel plate 20 Chromate treatment device 30 Drying device 40 Cooling device 50 Electrostatic dispersion coating device 46 Air supply fan

Claims (2)

[Claims] 1. A chromate-treated steel plate is heated and dried, and a resin emulsion is electrostatically dispersed on the steel plate at a temperature of 140 to 80°C during the cooling process after heating, so that a negative continuous resin is applied to the surface of the steel plate. A method for forming a dispersed resin film, the method comprising forming a film. [Claim 2] The resin film according to Claim 1 has a molecular weight of 0.2 to 2
．． A method for forming a dispersed resin film, characterized in that the coating is applied at a coating weight of 0 g/m2.