JPH0212748B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a single-sided coated steel plate in which corrosion resistance is imparted to the unpainted surface by forming an organic rust-preventing film on the unpainted surface that does not impair weldability, solderability, etc. In recent years, in the fields of home appliances and structural building materials, in order to streamline processes, in-house painting of necessary parts has been abolished, and pre-coating, in which painted steel plates are used to process parts, has become popular. Conventionally, this pre-coating was initially applied to materials that can be used as is, such as colored galvanized iron sheets for roofs and walls, which have a corrosion-resistant and weather-resistant colored film on the front side and a rust-preventive service coating on the back side. It was originally practiced in the field, but recently it has been expanded to include parts that undergo electric welding and soldering. However, with the above-mentioned double-sided coated steel sheet, electric welding and soldering cannot be performed because the coating film becomes an obstacle. For this reason, the coated steel plates used in the field of parts that undergo these processes are single-sided coated steel plates that have a corrosion-resistant and weather-resistant colored coating on the front side and are left unpainted on the back side. However, conventional single-sided coated steel sheets were manufactured using a continuous roll-coat coating line that stopped painting the back side and painted only the front side, so the unpainted back side was treated with phosphate and chromic acid as a pre-painting treatment. Sealing, sometimes chromic acid sealing, was the only thing that had been done. For this reason, the corrosion resistance of the back side was poor, with white rust appearing in a salt spray test for about 48 hours, and the product had the disadvantage of rusting during horizontal handling or storage. In addition, for phosphate-treated products, when phosphate crystals are wound into a coil, they may be transferred to the coating on the front side, or they may be built up on a forming roll during roll forming, and the coating may be removed when forming the painted surface. It also had the disadvantage of being damaged. In order to prevent such adverse effects of phosphate treatment, it may be possible to discontinue treatment of unpainted surfaces, but since phosphate treatment is a spray treatment, it will also cover unpainted surfaces, and the electric weldability of that area may be affected. I become inferior. In view of the above-mentioned drawbacks of conventional single-sided coated steel plates, the present invention provides a single-sided coated steel plate that eliminates these drawbacks. It is characterized by the formation of a sexual film. A conventional method for imparting electrical conductivity to an organic film is to include a conductive powder such as metal powder or carbon powder in the film. However, in this method, the film does not have electrical conductivity unless the film contains about 60% or more of conductive powder. For this reason, the film has a disadvantage in that the processability is inferior to that of ordinary paint films because the resin content as a binder is small. Furthermore, paints containing conductive powder are expensive, and the coating must be thick in order to retain the conductive powder, resulting in a considerable increase in cost.
In addition, during roll forming, etc., there is a problem that the conductive powder falls off and builds up on the forming roll as in the case of the phosphate. The inventors of the present invention have investigated the development of electrically conductive coatings free of such problems and have found that polyethyleneimine or silica sol-polyethyleneimine coatings alone are suitable. Figure 1 of the attached drawings shows a silica sol-polyethyleneimine film formed on one side of a hot-dip galvanized steel plate with a thickness of 0.5 mm, welding current of 7 KA, pressure of 150 kg,
The limit of the weldable film thickness was determined by performing spot welding under the condition of 10 cycles of current application, and as is clear from the figure, the limit is 2.5μ. Similarly, the second
As shown in the figure, almost the same results were obtained when spot welding was performed on a polyethyleneimine film. On the other hand, when investigating the solderability, it was found that all films can be soldered up to 2μ. However, it was found that all films had insufficient corrosion resistance when the thickness was less than 0.1μ. Therefore, the film thickness is preferably 0.1 to 2.5 μm. Since the electrically conductive film must be made thin in order to ensure electrical weldability and solderability, it may not have sufficient corrosion resistance for parts used in corrosive environments. In such cases, it is also possible to interpose a chromate film between the steel sheet base and the above film to improve corrosion resistance. In this case, the chromate film has a total chromium content of 5 to 150.
It is best to use mg/ ^m2 . The conductive film is formed by applying an aqueous solution containing polyethyleneimine or silica sol-polyethyleneimine to the surface of the steel sheet. This coating method may be any known method such as a squeeze roll method or a roll coating method. In the case of silica sol-polyethyleneimine, the aqueous solution concentration is 5-10% of silica sol,
It is preferable to use polyethyleneimine containing 5 to 40%; in the case of polyethyleneimine, it should be 5 to 50%
% is preferable. Drying time after application is 40~
It can be done at 250℃ (achieved plate temperature). In the case of the single-sided coated steel sheet of the present invention, the base sheet may be a cold-rolled steel sheet or a laminated steel sheet. For example, in the case of galvanized steel sheets, conventionally used hot-dip galvanized steel sheets, hot-dip zinc-aluminum galvanized steel sheets, iron-zinc alloyed hot-dip galvanized steel sheets, electrolytic zinc or zinc alloy coated steel sheets, and hot-dip aluminum plated steel sheets. There is no problem even if it is made of steel plate or the like. Next, Table 1 specifically shows the effects of the present invention. The thickness of both plates is 0.5mm.

[Table] The performance investigation in Table 1 was conducted in the following manner. (1) Salt spray test The test was conducted for 720 hours in accordance with JIS Z 2371, and the area ratio of rust was evaluated using the following criteria. Evaluation points Rust occurrence area ratio (%) 5 0 4 1~10 3 11~30 2 31~70 1 71~99 0 100 (2) Humidity test Conducted for 720 hours in a humidity tester at 50℃ and 98%RH ,
It was evaluated using the same criteria as the salt spray test. (3) Weldability test Spot welding is performed using a 35° x 4 mmφ electrode under the conditions of a welding current of 7 KA, a pressing force of 150 Kg, and energization time of 10 cycles, and the tensile strength after welding is 250 Kg/1 spot or more. , Less than 250Kg/1 spot was evaluated as ×. (4) Solderability test A 2mmφ Sb-Pb solder wire was cut into 5mm pieces.
This was placed on a film coated with chloride flux and melted with a soldering iron, and its spread area was evaluated using the following criteria. Evaluation symbol Spread area 〇 6 mmφ or more △ 5 mmφ × less than 5 mmφ As described above, since the single-sided coated steel sheet of the present invention has a corrosion-resistant conductive film formed on the unpainted surface, rust will not occur during horizontal handling or storage. Electric welding is also possible. Furthermore, since the film has solderability, it is possible to connect a ground wire to electrical equipment members by soldering. Furthermore, since the conductive film is not mixed with conductive powder, it has good processability, is inexpensive, and does not have build-up during roll forming.

[Brief explanation of drawings]

Figures 1 and 2 show the relationship between the film thickness, weld tensile strength, and weld failure rate when hot-dip galvanized steel sheets with a silica sol-polyethyleneimine film and a polyethyleneimine film formed on one side, respectively, are spot welded. It is a graph.

Claims (1)

[Scope of Claims] 1. A single-sided coated steel plate in which a corrosion-resistant, weather-resistant colored coating is formed on one side of the steel plate and the other side is unpainted, and the other unpainted side is coated with polyethyleneimine or silica sol-polyethylene. A single-sided coated steel sheet characterized by forming an electrically conductive film of imine. 2. The single-sided coated steel sheet according to claim 1, wherein the conductive film has a thickness of 0.1 to 2.5μ. 3. The single-sided coated steel sheet according to claim 1, characterized in that a chromate film is formed between the steel sheet and the electrically conductive film.