JPS5920492A - Surface treated steel sheet having excellent paintability and high corrosion resistance and its production - Google Patents

Abstract

PURPOSE:To obtain a surface-treated steel sheet of which the film coated with a paint contg. a cationic electrodeposition paint is highly watertight, by applying a specific amt. of iron substd. plating an zinc electroplating. CONSTITUTION:The surface of a zinc electroplated steel sheet is subjected to iron substd. plating by a spraying method or dipping method to form a film of 0.5-10g/m<2> having a projecting Fe part existing locally and microscopically on the zinc electroplating layer. When the Zn-Ni plating layer 2 formed on, for example, a base metal Fe 1 is treated with an acidic soln. contg. >= about 5g/l Fe<2+>, the anode reaction of the equation I and the cathode reaction of the equations II, III are effected. As a result, the layer 2 is elutated microscopically by anode reaction and is recessed 2a; furthermore, an Fe 3 part projected by cathode reaction is formed partially on the layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly corrosion-resistant surface-treated steel sheet with excellent paintability and a method for producing the same. This is what we are trying to provide.

Recently, it has become common to use antifreeze agents such as rock salt on roads in winter and in cold regions, and it is highly recommended that cars used under such conditions have stronger anti-rust properties. Furthermore, paint adhesion is an essential requirement for car body exterior panels. For this reason, various comprehensive measures have been taken for filter steel plates used in such applications, and among these, surface-treated steel plates and cationic di-N coating methods are known to be particularly effective. ing.

That is, electrolytic galvanized steel sheets, which have superior properties equivalent to those of cold-rolled steel sheets, have been widely used as surface-treated steel sheets for automobiles, but recently zinc-based alloys 11, which have significantly superior corrosion resistance and weldability, have been widely used. Molded steel sheets have been developed and are being put into practical use, and these surface-treated steel sheets are chemically modified foils.

After processing and painting, the product has comprehensive anti-corrosion performance.However, electrolytic galvanized steel sheets and zinc-based alloys with excellent corrosion resistance in the composition range 'llc plating (91
I-plates (hereinafter collectively referred to as phosphor-based plated steel plates) do not necessarily have sufficient paintability. In particular, the adhesion of the paint film on first-generation lead-based electroplated steel sheets coated with two types of paints, including cationic coatings, clearly decreases in hot water and humid environments, and the adhesion of the paint film on cold-rolled steel sheets decreases significantly. If the car is hit by flying objects such as pebbles while the car is running, the paint film is likely to peel off, causing rust and blisters to form in these areas, resulting in a decrease in the rust prevention ability. However, in a humid environment with warm water, the adhesion of the paint film (hereinafter referred to as watertightness) decreases due to p'ttn,ky (prog
, Coa〆ings 9 (1981)] and Mr. Masuko [Corrosion Prevention Technology J. (1981) No. 2.69
9-704] etc., it is thought that this occurs because the adhesion at the interface between the paint film and the base is broken. However, the adhesive failure at the interface is caused by the adhesion between the paint film and the base forming a water layer of penetrating water. This occurs when the pressure is weaker than the pressure applied, so by increasing the adhesion strength, the water-resistant layer 11 of the coating film is improved.

Furthermore, it is difficult to measure the adhesion force of the paint before adhesive failure occurs due to its high strength, but it is easy to predict that the adhesion force will change by changing the condition of the base. The following five methods are known to improve the water resistance and tightness of coating films.

■ Applied on Zn-Ni alloy plating by Zn-Fn alloy plating with high iron content or h-metsuki chipping [Mr. Sakai et al.: Tetsu-to-Hagane 67 (192 No. 1) 8980.
/Kai Kaisho 57-67195).

(2) Disperse the Cγ hydrate precipitated from 07'F in the plating layer (Japanese Patent Application Laid-Open No. 123395/1983).

0 C-1 and C after chemical conversion treatment? Sealing with a mixture of J' (Jaynes W, Dauis: SA
E'rechnicalPa, perSerigsN
0.8'20336 (Fgh, 1982)).

However, these methods are still unsatisfactory as the following problems still remain. That is, in ■, pure iron plating formed by electroplating or Zn with high iron content
Since F'A alloy joints are hard and brittle, they are susceptible to processing when a continuous film is formed, and in particular, 91M116, which has a large amount of attached Sf bt, has poor workability because '1afi concentration occurs during air plating. In Mafko ■ and ■, C and JII are 1 month old, so it is strictly 7. c. Pollution countermeasures are required, and chemical solutions are not easy to handle. Furthermore, in case (2), the C in the film dissolved in the chemical conversion treatment M (1 solution) upsets the balance of the chemical conversion treatment solution, making normal chemical conversion treatment a waste of time.

The present invention was created after repeated studies and speculations in view of the above-mentioned disadvantages. That is, the present inventors applied a cationic electroplating coating to a zinc-based plating plate (
As a result of intensive research on improving the water-resistant adhesion of the coating film of f-coating, we found that 0.5~1o
rAr? Iron 1? ! We have found that the surface-treated steel sheet of the present invention exhibits significantly superior coating film water resistance and watertightness 7-3. First, zinc-based plating is applied using a normal electroplating method, and then iron-11 plating is performed using a spray method or a dipping method. That is, in this case, the following reaction occurs on the lead-based plating (1).

2 H+-1-2$-+H, ↑ Displacement plating is characterized by the fact that plating occurs even when no external current flows, as shown in the above equation, and therefore, unlike electroplating, the shape of the object to be plated is This does not cause the problem of non-uniform plating thickness distribution due to the formation of areas where current is concentrated, and the plating film thickness is generally uniform from a macroscopic perspective in the areas covered with galvanized plating.

On the other hand, the anode i%ll and cathode part are locally divided +i
lr, so from a microscopic perspective, it differs from an iron film formed by electroplating in that iron is localized at the cathode. It has the effect of softening the hard and brittle properties of
In other words, the deterioration of workability due to the excessive overlaying layer on the edge of the steel sheet, which is seen in electroplating, and the weakness of microscopically continuous coatings in compression processing cannot be improved with displacement plating.

The strength of iron displacement plating on zinc-based electroplating is closely related to the water resistance of the coating film (at 2,0,5v/11? or more, the effect of improving water resistance appears).

1 o y/n again? Securing the iron replacement plating seal '1-a) requires a long process, and such a thick plating h1 is not suitable for an electric plating line that operates at high speed. . Therefore, the above-mentioned iron replacement acetate 112. (1,5f/n1 or more, 10f/
n? The composition of the displacement plating solution and the plating conditions are described below.The iron displacement plating solution consists of a ferrous salt, a buffer, a complexing agent, and a pH adjuster.

Ferrous salts are the source of iron that precipitates, including ferrous chloride,
Ferrous sulfate, ferrous sulfate, ammonium sulfate, and mixtures thereof can be used.

Buffers include sodium acetate, sodium citrate,
If halogen is used, usually 1 to 502μ is added a). Sodium citrate, sodium tartrate, and sodium ascorbate are used as complexing agents, and ammonium chloride and ammonium sulfate are used as complexing agents with ammonium ions. is added, usually 1 to 3009/
can be added. As the pH adjuster, alkalis such as ammonium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, as well as hydrochloric acid, sulfuric acid, and organic acids may be used. It is controlled by the bath temperature, P H1FJ + υ degree, but these parameters need to be set within the following range for practical purposes in the case of iron displacement plating on zinc-based alloy plating. 10 for c or more
If the temperature is below 0°C, the plating rate is too low, and if it is above 100°C, the amount of water evaporated is too large, making it difficult to maintain a constant bath concentration. PH is 1 or more and 5
Therefore, if the pH is less than 1, water and wood formation will be too high. If the P II exceeds 5, the dissolution rate of zinc will be low, and the iron displacement plating rate will be too low. It is necessary that the position is 5 f/ or more; if it is less than this, the cutting speed will be too low for practical use.

If the bath composition and processing conditions of the displacement plating solution are selected as described above, iron displacement plating is possible on a lead-based electroplated steel sheet having a potential less noble than that of iron. Please give me some examples of applicable zinc-based electroplated steel sheets: Zn plating, Z
Examples include n-Ni gold plating, Zn-Fx gold alloy plating, Z-Ct (1-Ct composite plating), Zn Co-WiO plating, and multilayer plating that combines these.

Further, the iron 1a bending process can be applied not only to electroplating but also to hot-dip zinc plating.

The state of the formed splice layer is schematically shown in FIG.
As the above-mentioned displacement plating is performed on the plating layer 2, a reaction as shown in the above-mentioned formula takes place, and the plating layer 2 is partially eluted by the anode reaction on a microscopic scale, resulting in 2α. A protruding portion t2h3 is partially formed on the abutment layer 2 by Cando reaction.

In this way, the amount of localized and protruding h3 portion is 0.5~
As mentioned above, it is 10 f/rl. In some cases, a Zn plating film is formed on the ZnNl plating layer to form a Zn-Ni plating layer 20).
Specific manufacturing examples and examples of the invention which sufficiently ensure surface corrosion characteristics can be implemented or not are described below.

Example 1 A steel plate that had undergone pretreatment consisting of electrolytic degreasing in an alkaline solution and sulfuric acid pickling was electroplated under the plating conditions shown below, and a plating amount of 302"/r1.Ni content was obtained. 12”l
A gold plating film was formed using Ni-based nickel.

Plating solution composition N15Q46I% 0=325 fμZ
++” O4・7Ht O= 175 f/lNσ2
``4 = 609 /'' was obtained as above, and this was followed by displacement plating of iron using the Sdale method.

νIJ replacement plating lead condition may be the following ψ~■7111, but please change the temperature and treatment time! lAI adjustment ◇ ■Displacement plating solution composition F'yC1a°41TtO'= l U (l f /
LNII4C1' = 100f/l C1,g COONa ・3Ht 0=20IP/lC
,H, ((month 1)(COONc)s 21(zo=5
f'/l ■PH H = 4, rfft history = 50 to 80℃ ) Check the water resistance and N&I adhesion after repainting ^T, and then the next ■
Phosphate treatment: Nippon Barker's Bf3UO4 was used and phosphate treatment was performed by dipping method.

■Cationic electrolayer coating Coating film thickness 20 μl 11 constant 1 coat ◇ ■Intermediate coating Melamine alkyd paint 25 μm ○Top coating Melamine alkyd paint 35 μm Corrosion resistance was determined by sealing the back and edges of the test piece with tape, then placing a cross cut on the test painted surface and applying 100
A 0-hour salt water spray test was conducted, and the occurrence of flisters from the cross-cut ill was evaluated based on the following criteria: Maximum bulge width on one side is 4 mm or less = ○ Maximum bulge width on one side is 41 nm: Exceeds = X Water resistant adhesion of the membrane is 3
Tape the back 11■ and νIM side of the coated test piece.
- After that, immerse in pure water at 40°C for 240 hours σ(
Immediately after removing the specimen from the aquarium, cut the base of the 1()0 fish at 2 mm intervals with a sharp knife, and separate the coating film from the base with a laser cutter. We measured the performance and performed one song in total based on the following criteria.

The paint film has not peeled off at all 2Q100
++1 to 9 of pI are removed 11・W2△“ 1
01 hard or above attack i HiC 2 × above and T Koyo 57. cEach test result: E1 adhesion is less than 0.5r/i σ
) The following Table 1 summarizes the comparison examples and the comparison cases of 0.52/di or more.

In other words, according to Table 171, the water tightness of sand with ZnNt gold alloy is poor, but the water tightness of the 8 cases is clearly improved by replacing one piece of iron with 0.5 y A1 or more. ing.

In addition, in the above-mentioned non-invention example 4, ZnN1
The image method of micro-Aussie electron spectroscopy was used to determine whether Fb was distributed in the alloy plating. Figure 3 shows the distribution of Zn. It is clear that the locally distributed and continuous film 'af2.r' is not a problem, and the I and j parts are formed as protrusions.

Example 2 In Example 1, after pretreatment under the same conditions as shown in [6], a plating amount of 25 f/n was applied to a cold rolled steel sheet by changing the electroplating conditions only for the time. , Z with Ni content ratio 12
After forming the n-Ni alloy plating film, 59/n? Form a film on the Zn plate under the following conditions 1.■ Plating solution composition
O= 4tJOjμ1nc14 = 1tJtlf
/1NH4CL = lOW/1 CII, 1COON rt ・:31120=I U
Wμ or Ji'l 5 L -CZn/Zn +Ni
N Mino 2J9 Metsu @ Y Row 1. After 1.1, iron displacement plating is performed using the immersion method under the conditions shown in the following ■~O, and the iron (J
The amount was adjusted by changing the temperature and treatment time.

■1 Replacement liquid composition FδO4・7) & O= 300f/n? (NII,
)2So4= 20f/+JCs Ik (011)
(COONα), ・21120=5 f/L (Ril)
I (= 3, warm expansion = 50~8U @ CO treatment time = 1o
In order to check the corrosion resistance after coating with cation 'E and the water resistance 7N of the flea film after 3 coats, phosphate treatment and cation electrolysis were performed for ~30 seconds under the same conditions as shown in Example 1. One test piece without coating, intermediate coating, and top coating χ was prepared and tested with the same test pieces as shown in Example 1, and according to the same price standard, lIf value 12
7 The results are shown in Table 2 below, and the results show that the product according to the present invention has an iron tIita plating of more than o, sr/- compared to the Zn/Zn-Ni two-layer plating. It was confirmed that the water resistant adhesion of the coating film was improved (7), and the corrosion resistance was also improved.

When using the pressure of the present invention as explained above in Table 2, a surface-treated steel sheet having excellent corrosion resistance and water-resistant adhesion of the coating film is provided,
Also, does it provide a suitable manufacturing method and good durability under the conditions in which it is used as a road anti-icing agent? This invention is industrially very effective because it can be used for automobile bodies (for example, it can provide VT boards, etc.).

[Brief explanation of drawings]

The drawings show the technical content of the present invention, and the first
The figure is a schematic enlarged cross-sectional view showing the state of the plated layer formed by the present invention, and Figure 2 is a cross-sectional view showing the state of the plated layer formed by the present invention.
7) / 'A image is a micrograph at a magnification of 10c + t + (6) / 8I! 3 is a micrograph at a magnification of 10c + t + (6).・However, in Figure 1, there are 16, where 1 is monthly and 2 is Zn-Ni.
The plating layer, 2α is the recessed part due to the 1′i″ replacement,
3 is shown in the air section J'rJ. No. / Yuanqin 2 Peng No. σ Country

Claims (1)

[Claims] 1. 0.5 to 1 U f/n on the zinc-based electroplating layer
? A highly corrosion-resistant surface-treated steel sheet with excellent paintability, characterized by forming a plating film structure having microscopically localized and protruding portions. 2. Production of a highly corrosion-resistant surface-treated steel sheet with excellent paintability by treating a zinc-based electroplated steel sheet with an acidic solution having an Ev concentration of 51% or more to replace iron on the zinc-based electroplated layer. Law.