JPS598353B2 - Composite coated steel plate for highly corrosion-resistant machining with excellent adhesion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coated steel plate, particularly a highly corrosion-resistant composite coated steel plate with excellent adhesion.

In recent years, with the issue of resource and energy conservation, there has been a growing trend towards durability of automobiles, home appliances, building materials, etc., and there has been an active movement towards product development with emphasis on corrosion resistance.

Particularly in automobiles, rock salts are sometimes sprayed to prevent highways from freezing, and automobile bodies are required to have corrosion resistance, especially rust prevention. Generally speaking, in order to simply improve the corrosion resistance of steel sheets, plating treatments such as galvanizing, aluminum plating, tin plating, and zinc-aluminum composite plating, color paint films, vinyl films, and zinc-containing conductive coatings are generally used to improve the corrosion resistance of steel sheets. Surface coating treatments such as films have been applied, but plating alone cannot meet the requirements for high corrosion resistance, and it is necessary to increase the surface coating after plating to improve corrosion resistance. In that case, there are drawbacks similar to those of the coated steel sheet described below. Painted steel sheets have high corrosion resistance, but when subjected to severe forming processes, the paint film is susceptible to peeling damage, and welding is so difficult that it is impossible to weld, except for zinc-containing conductive paint films. However, it had the disadvantage that it could not be used as a processed material for parts that were assembled after being formed (hereinafter referred to as forming plate material).

・In short, surface-treated steel plates that are sufficiently suitable for use as forming plates that require particularly high rust resistance cannot be obtained using conventional technology, and therefore cold-rolled steel plates or galvanized steel plates are used for forming. After assembly, it is necessary to perform base chemical conversion treatment and surface painting again, or when using painted steel sheets, it is necessary to perform partial painting repairs, etc., which complicates the manufacturing process and increases product costs.

Here, a coating composition containing hexavalent chromium and a reducing compound are applied to the surface of a metal substrate, and the substrate is heated at a sufficient temperature and time to volatilize volatile components from the coating composition. an undercoat consisting of a residual substance obtained by depositing a residual substance on the surface, and an electrically conductive material selected from the group consisting of aluminium, copper, cadmium, magnetite, carbon and zinc on the undercoat; A composite coating consisting of a top coat composition consisting of a pigment and a vehicle and a top coat of residual material obtained by firing this has been proposed. The applied coated steel sheet still had issues with adhesion and weldability, and also had drawbacks in that the coating process was complicated.

In addition, unlike the above-mentioned chromate treatment, chemical conversion treatment with metal phosphate, especially iron phosphate, as a base coating for steel sheets allows ultra-thin film treatment, even if the resulting film is amorphous. Therefore, it has excellent adhesion and weldability, so after this treatment, or sometimes after sealing the iron phosphate coating with chromate treatment, zinc powder is applied over these coatings. A composite coated steel sheet was developed in which the conductive paint containing the above-mentioned conductive paint was applied and the paint film was then cured, and although the adhesion and weldability were considerably improved, it was still far from satisfactory.

This invention has superior surface characteristics than the above-mentioned phosphate film-conductive coating composite coated steel sheet, and has a highly corrosion-resistant finish that allows post-forming and assembly treatment and surface painting to be omitted or simplified. This paper proposes a composite coated steel sheet for industrial use.

This invention consists of an alloyed galvanized film made by heat-treating the galvanized steel sheet surface, and a conductive paint film obtained by overlaying this with a conductive paint and then firing it. This paper proposes a highly corrosion-resistant composite coated steel sheet for processing with excellent adhesion.

In this invention, due to the combined effect of the surface protection effect of the conductive coating and the sacrificial corrosion protection effect of the alloyed galvanized coating, salt
It exhibits extremely high corrosion resistance against corrosive environments such as moisture and humidity, and even on partially exposed areas such as scratches in the paint film, welded joints, and end face cuts, the sacrificial corrosion protection effect of alloyed zinc plating is effective. This allows corrosion protection of exposed parts.

Normally, even if a composite coated steel sheet is used in combination with other ordinary steel sheets, surface coating treatments such as base chemical treatment, electrolytic coating, electrostatic coating, and spray coating are applied again, but this invention The conductive coating film has excellent base chemical conversion treatment properties and paintability, so even if surface coating treatment is applied over the conductive coating film, it will not be coated. There is no under-film 5 corrosion blistering that tends to occur under the coating film, and electrochemical corrosion caused by galvanic action that tends to occur on the joint surface between the alloyed galvanized layer and the ordinary steel sheet is sufficiently suppressed. I can do it.

In addition, in the third application of the composite coated steel sheet of this invention to a forming plate material, in addition to the fact that the conductive coating itself has a characteristic that it is difficult to peel off during forming ironing such as press forming and roll forming, It exhibits superior peeling resistance due to its strong adhesion to the plating layer.

Further, the composite coated steel sheet according to the present invention can be easily welded and has excellent adhesive bondability, so that it can be satisfactorily used as a sheet material for forming processing.

This invention will be explained in detail below.

The lower coating of the composite coated steel sheet of the present invention comprises an alloyed galvanized layer, and this galvanizing and alloying may be carried out by conventional methods.

Just to be sure, I will show you an example of the usual procedure. For example, in a continuous hot-dip galvanizing line, the surface of a steel plate is heated and reduced in a continuous heating furnace and then passed through a zinc bath with a basis weight of 45'r/m.
After hot-dip galvanizing (on one side), the plated surface is rapidly heated to 550°C for 10 seconds in an alloy heating furnace to remelt the plated surface, and then rapidly cooled to 400°C for alloying treatment.

At this time, the basis weight of the galvanized film is 5 to 120y/TrL
It is desirable that the value be within the range of .

If the basis weight is less than 5f/'Fi', high corrosion resistance cannot be obtained and the life will be shortened due to corrosion. Moreover, if it exceeds 120'/g, corrosion resistance is good, but peeling tends to occur during molding and weldability deteriorates, which is not preferable. Subsequently, a conductive paint containing zinc powder is applied over the above-mentioned alloyed galvanized layer, but it is necessary to apply the conductive paint to a cured film thickness of 6 to 30 μm. This is because if the film thickness is less than 6 μm, it is difficult to say that corrosion resistance is sufficient.
On the other hand, if it is thicker than 30 μm, peeling will easily occur during processing, resulting in poor workability and weldability. For applying the conductive paint, common coating equipment such as a brush, spray, roll coater, shower coater, etc. can be used.

As the heating drying device for the coating film, a conventional hot air drying oven, an infrared ray oven, or a high frequency induction heating oven can be appropriately selected.

Depending on the type of paint vehicle, ultraviolet irradiation or electron beam irradiation can also be applied. The baking conditions are 2 as the temperature reached by the steel plate.
It is 30-200 seconds at 00-250°C.

The conductive paint used in this invention is generally called a high-concentration zinc powder paint, and its composition is almost the same as that used conventionally as a shot primer for steel structures such as ships and bridges. It is easy to obtain and economically advantageous because it contains as the main conductive component and is used by simply kneading it with a vehicle.

Depending on the type of vehicle, phthalic acid resins, epoxy resins, melamine resins, polyester resins, polyurethane resins, etc. are used for this paint.

Figure 1 shows the relationship between the zinc content in the conductive coating and the time for red rust to occur in the salt spray test.

As is clear from FIG. 1, if the zinc content is less than 30% by weight, red rust is likely to occur and the strength of the coating film after burning is also reduced, resulting in a marked deterioration of the corrosion resistance after processing. Moreover, if it exceeds 90% by weight, the viscosity of the paint will increase, resulting in a difference in the thickness of the paint film and causing a problem that the characteristics of the paint film will vary greatly. In addition, when the organic resin in the coating film decreases, the bond strength becomes weaker, the coating film becomes brittle, and the peeling resistance deteriorates, so that the coating film 1 is more likely to peel off during processing. Therefore, in this invention, the zinc content in the conductive coating film is limited to a range of 30 to 90% by weight.

Note that it is more advantageous in terms of weldability if aluminum powder, copper powder, iron oxide, carbon, or other conductive pigments are blended together with zinc powder. Here, we will discuss samples in which the above-mentioned conductive paint is applied over a steel plate having the alloyed galvanized layer of the present invention as an undercoating, and a steel plate subjected to conventional hot-dip galvanizing or electrogalvanizing. , and compared their corrosion resistance, workability, and weldability.

After degreasing and cleaning a cold-rolled steel sheet that had been treated in a normal process, the following treatment was immediately performed to prepare a sample.

Sample 1: (alloyed galvanized) A cold-rolled steel plate with a thickness of 0.8 m/m was adjusted to a coating weight of 45 f1r/go (one piece deposit) on a continuous hot-dip plating line, and then heated to 550°C and then heated to 550°C. Alloyed hot-dip galvanized steel sheet subjected to alloying treatment.

Sample 2: (Hot-dip galvanizing) A cold-rolled steel plate with a thickness of 0.8 m/m was plated with a coating weight of 459 on a continuous hot-dip galvanizing line.
Hot-dip galvanized steel sheet adjusted to r/go (one side) area weight.

Sample 3: (Electrogalvanizing) A cold-rolled and annealed steel plate with a thickness of 0.8 m/m was plated on a continuous electrolytic galvanizing line with a plating thickness of 45'r/Trl'.
Electrogalvanized steel sheet with (on one side) electrolytically bonded.

On the undercoat prepared as above, an epoxy resin containing 70% by weight of zinc powder was coated to a thickness of 15 μm using a roll coater and heated to 200°C for 60 seconds.
After baking, a coating was formed by cooling.

The test results for each sample are shown in Table 1. Paint film adhesion 1 Weldability 1 Corrosion resistance, paint film adhesion, and weldability were each determined by the following tests.

(1) Corrosion resistance After applying salt water spray (JIS Z237l 5% salt water continuous spray) for 1000 hours, the cross cut portion was peeled off with tape, and the peeling width was evaluated.

(2) Paint film adhesion A de Hupont impact test with a weight of 500' and a center of impact radius of 3/1.6 inch, and an Erichsen test were conducted to determine the minimum drop height and extrusion height at which paint film cracks occur, respectively. I judged it.

(3) Weldable electrode material: Cu-Cr alloy, tip diameter: 4.8mm, pressure: 2
Spot welding was performed at 00 kg, secondary current of 9500 to 11200 A1, and 10 to 20 energization cycles, and judgment was made based on the number of continuous spot welding points.

For samples 2 and 3, in which the undercoat was a hot-dip galvanized film or an electrogalvanized film, the occurrence of pristerning due to underfilm corrosion was significant in the salt spray test, and the conductive coating was damaged, resulting in a significant deterioration in corrosion resistance. However, in the alloyed galvanized film (sample 1), corrosion resistance did not deteriorate due to underfilm corrosion, and high corrosion resistance was obtained due to the combined effect with the conductive coating.

Regarding adhesion, Samples 2 and 3 have smooth plating film surfaces with few minute irregularities, so the adhesion with the upper coating is poor and peeling occurs easily during molding.

However, in sample 1, the adhesion between the lower coating and the upper coating is strong, so the paint film does not easily peel off even after processing. Furthermore, in terms of weldability, sample 1 is superior to samples 2 and 3. When comparing the number of points that can be continuously welded, sample 1
is about twice that of samples 2 and 3.

As mentioned above, the alloyed galvanized film as an undercoat is
It has extremely excellent properties when combined with a conductive coating,
Applying this composite coating to a steel plate significantly improves corrosion resistance, adhesion, and weldability.

The present invention will be explained below in comparison with Examples and Comparative Examples.

Example 1 After continuous annealing and surface reduction treatment of an aluminum-killed cold-rolled steel sheet, hot-dip galvanizing was immediately carried out to give an area weight (both sides) of 45 f/Tft', and the galvanizing was carried out in an alloying furnace for 10 seconds.
Alloying treatment is performed by rapidly heating to 50°C and then rapidly cooling to 400°C.

Apply 15 μm of epoxy resin-based conductive paint with a zinc content of 70% by weight on only one side of the alloyed galvanized layer.
After coating with a roll coater to a film thickness of , it was baked at 200°C for 60 seconds.

Example 2 After continuous annealing and surface reduction treatment of an aluminum killed cold-rolled steel sheet, the area weight (both sides) was immediately reduced to 60 f/m.
Hot-dip galvanizing is carried out so that it becomes 1.
Alloying treatment is performed by rapidly heating to 600°C in 0 seconds and then rapidly cooling to 400°C.

On one side of the alloyed galvanized layer, apply a polyester resin conductive paint with a zinc content of 50% by weight to a thickness of 1.
After coating at 0 .mu.m, it was heated at 200.degree. C. for 60 seconds.

Comparative Example 1 An aluminium-killed cold-rolled steel sheet that had been cold-rolled and then annealed was degreased and washed, and immediately an epoxy resin-based conductive paint with a zinc content of 80% by weight was applied to only one side using a roll coater to a film thickness of 15 μm. Thereafter, it is baked at 200° C. for 60 seconds.

Comparative Example 2 An aluminium-killed cold-rolled steel sheet that had been cold-rolled and annealed was degreased and washed, and then an epoxy resin containing hexavalent chromium ions, a reducing agent, and a thickener was applied to a film thickness of 2 μm using a roll coater for 30 seconds. The zinc content is 80% by weight, superimposed on the chromate film obtained by heat curing to 16"C.
An epoxy resin-based conductive paint was applied using a roll coater to a film thickness of 13 μm, and then baked at 280°C for 60 seconds.

Comparative Example 3 An aluminum killed steel sheet that had been cold rolled and annealed was degreased and washed, and then an iron phosphate chemical conversion treatment liquid was sprayed on the sheet surface at a concentration of 45 pt and a temperature of 65° C. to form an iron phosphate chemical conversion coating.

Immediately heat the chromic acid treatment solution (CrO, 2Of/') to a temperature of 60
Apply by roll coater method at ℃, total chromium 511f/
/ I performed the sealing of Go. Subsequently, the zinc content is 80% by weight.
epoxy resin-based conductive paint was applied with a roll coater to a film thickness of 15 μm, and then heated to 200°C for 60 seconds.
It was burned into. ．． These Examples and Comparative Examples were subjected to corrosion resistance, coating adhesion, and weldability tests similar to those used to examine changes in surface properties due to differences in undercoating, and the results are shown in Table 2.

The method for determining the test results is the same as described above.

In Examples 1 and 2 according to the present invention, the weldability is comparable to that of the comparative example, which originally exhibits excellent properties, but the corrosion resistance and adhesion are significantly improved compared to the comparative example. In the embodiments of the present invention, cold-rolled steel plates are used as the material, but cold-rolled steel plates and steel strips, hot-rolled steel plates and steel strips can also be used as materials to which the present invention can be applied.

As described above, this invention improves surface properties, especially corrosion resistance and adhesion, by simply performing alloying on the galvanized film that is the lower coating of composite coated steel sheets. It can be used with great advantage when considering workability and pollution generation, since it can be used as it is for forming and welding without requiring pretreatment at the customer's end.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the zinc content in the conductive coating film and the red rust generation time in the salt spray test.

Claims (1)

[Claims] 1. A steel sheet with excellent adhesion that has an alloyed galvanized film on the surface of the steel plate and an electrically conductive film with a thickness of 6 to 30 μm containing zinc powder in a range of 30 to 90% by weight. Composite coated steel plate for high corrosion resistance processing.