JPS61284582A - Improvement of suitability of steel sheet to phosphating - Google Patents

Abstract

PURPOSE:To improve the suitability of a steel sheet to phosphating simply and stably by anodizing the Fe surface of the steel sheet in an electrically conductive aqueous salt soln. contg. a specified amount of one or more among colloidal SiO2, Fe2O3, SnO2, TiO2, Sb2O3 and CeO2. CONSTITUTION:An electrically conductive aqueous salt soln. contg. one or more among colloidal SiO2, Fe2O3, SnO2, TiO2, Sb2O3 and CeO2 each having 1-100mum particle size is prepd. The Fe surface of a steel sheet is anodized in the salt soln. When the anodized surface is phosphated, very dense phosphate crystals are formed on the surface of the steel sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for improving the phosphate chemical conversion treatment property of the Fe surface of a steel plate.

<Prior art and its problems> Before steel sheets are painted by customers such as automobiles, home appliances, and building materials, chemical conversion treatment with phosphate is performed to improve paint adhesion and post-painting corrosion resistance. During this phosphate treatment, if areas with no crystals called stagnation or uneven coarse crystals are formed, or even if the crystals are uniform but the appearance is uneven, the paint adhesion may be affected. This becomes a serious problem because it impairs later corrosion resistance, uniformity of appearance, etc.

On the other hand, the phosphate chemical treatment properties of the steel plate surface often deteriorate due to various factors during the manufacturing process. In other words, oxides generated during the annealing process or quenching with water after continuous annealing may reduce the chemical activity of the surface, or pickling to remove surface oxides may reduce Mn and other substances on the surface layer. When the chemical conversion treatment property improving component is dissolved or reduced, the chemical conversion treatment property is deteriorated.

In addition, when electroplating is performed on the non-plated side of single-sided plating, most of the plating is done in a pickling bath, so stains may occur due to the accumulation of acid-insoluble substances and the precipitation of impurities.
Alternatively, plating precipitation due to the circulation of plating current may cause deterioration of chemical conversion treatment properties. Further, when the plating is hot-dip plating, the non-plated surface may be oxidized due to the high temperature, or the plating metal may go around, causing deterioration in chemical conversion treatment properties.

Several methods have thus far been proposed as countermeasures against these problems. For example, according to Japanese Patent Publication No. 57-30913 and Japanese Patent Application Laid-open No. 59-107083, the chemical conversion treatment property is improved by rubbing the surface of a steel plate. However, this method cannot be expected to have a drastic effect, and the abrasive material is often worn by the steel plate edge, resulting in uneven processing due to uneven friction and a heavy maintenance burden on the abrasive material. There was a problem.

Also, JP-A-59-129783, JP-A-59-12
In No. 9784, 0.001-0.5g/rn was applied to the surface of the steel plate.
A method of precipitating Sn or Ni-based alloys has been proposed, but it is difficult to precipitate such trace metals uniformly and stably, and if the amount of precipitation is too large, it may actually deteriorate chemical conversion treatment properties. There were times when I was forced to do so.

<Object of the invention> The object of the present invention is to eliminate the drawbacks of the prior art as described above,
The present invention aims to provide a simple, stable and drastic method for improving the phosphate treatment properties of Fe surfaces.

<Structure of the Invention> The present invention provides the Fe surface of a steel plate with colloidal SiO2
, Fe2O:+, 5n02, TiO2,5b20
3, (: One or two or more of c02, 0.01
This is a method for improving the phosphate treatability of a steel sheet, which is characterized by performing electrolytic treatment as an anode in a conductive salt aqueous solution containing at least 10 wL% by weight.

The specific contents of the present invention will be explained in detail below.

The inventors, SiO2, Fe2O:+, 5n02
, TiO2, 5b203, CeO2, and other colloids are added to the bath.We have found that when a steel plate is subjected to anodic electrolysis treatment in a bath containing colloids such as TiO2, 5b203, CeO2, etc., and then subjected to phosphate treatment, very dense chemical crystals can be obtained on the surface of the steel plate.

That is, the thickness 0.8 [II
m 5PCE steel plate as is and 200 gin, p
After anodic electrolytic treatment at 120 C/dm'' in a sodium phosphate bath at 50°C, phosphate treatment was performed using Nippon Paint's Granodin SD 2000 using a dip method. Phosphoric acid Soda bath is colloid-free,
There were four types: 1.5 wt% addition of 5n02 colloid, 1 wL% addition of SiO2 colloid, and 1 wj% addition of Fe2O3 colloid. A scanning electron micrograph of the obtained chemical conversion coating is shown in FIG.

As shown in FIG. 1a, the original plate contains a mixture of coarse crystals, but when electrolyzed in a colloid-free bath, the crystal size becomes fairly uniform as shown in FIG. 1b. This is thought to be because oxides that reduce the chemical activity of the surface are removed by electrolysis. On the other hand, 5n02, S
The chemical crystals of the steel plate electrolyzed in a bath containing colloids such as iO2 and Fe2O3 are shown in Figures 1c, 1d, and 1e.
As shown in the figure, it is much more dense than that obtained by anodic electrolysis using a colloid-free bath electrolyte (see Figure 1b).

When chemical crystals with large sizes are subjected to stress or chipping after painting, the crystals tend to crack or break, causing so-called slip band development. However, the finer the chemically formed crystal, the better it is.

In particular, the effects of colloids shown in Figures 1c, 1d and 1e are TiO2, 5b20:+, Ce02(7)
It was also recognized in colloids. Furthermore, the effect of the colloid was confirmed even when conductive salts added to the electrolytic bath other than phosphates were used, such as Na2504 and NaCJZ.

Table 1 shows the analytical values of Sn on the surface of the steel sheet when the steel sheet was subjected to anodic electrolytic treatment using the 5n02 colloid 1.5 wL% addition bath shown in FIG.

Table 1 From Table 1, it can be seen that when electrolyzing with a 5n02-added bath, the amount of Sn attached increases with the amount of electricity.

Therefore, the reason for the densification of the chemical conversion coating crystals due to anodic electrolysis in the amount of colloid added is considered to be as follows. The acid generated on the surface of the steel sheet through anodic electrolysis removes oxides and contaminants from the surface, creating an active surface. It is thought that colloidal oxides are adsorbed there and become extremely fine crystal nuclei during chemical conversion treatment.

The colloidal oxide in the present invention has a particle size of I to 100.
It means a particulate oxide in the mμ range.

Generally, an oxide sol prepared by dispersing particles having a particle size of 5 to 30 mμ in water is well known as an oxide sol, and it is preferable to use this in the present invention as well.

Further, the amount of colloidal oxide added needs to be 0.01 wL% or more and less than 10 wt%. 0. O1w
If it is less than 10 L%, the improvement effect of the chemical conversion coating is poor;
This is because if it exceeds wL%, the activity of the surface of the steel sheet will be reduced, and the chemical conversion treatment property will be deteriorated, or gelation will occur due to electrolysis, which will cause problems in operation.

The main components of the electrolytic bath are conductive salts, including cations that do not deposit on the cathode during electrolysis, such as Na, K, Li,
NH4, to1. An aqueous solution containing one or more inorganic salts such as Mg is used.

In the present invention, the steel plate must be electrolytically pickled in an electrolytic bath to make the surface clean and active, so it must be treated as an anode.

Since cathodic treatment does not remove or activate surface contaminants, the effect of improving chemical conversion treatment cannot be obtained. The conditions for anodization are not limited to these, but generally include: bath temperature: room temperature to 70°C, bath pH: 1 to 12, salt concentration: 50 to 70°C.
500g/u, current density: 5-200 A/drrr
', electricity i: 20 to soo coulombs/drn', and processing time to be appropriately selected from the range of a few seconds to ten seconds.

The phosphate chemical conversion treatment after the anodic electrolytic treatment may be carried out by any method such as a dipping method or a spray method using various known chemical conversion baths.

The present invention is applicable not only to cold-rolled steel sheets, but also to all Fe surfaces of steel sheets, such as non-plated surfaces such as single-sided electroplating, single-sided hot-dip coating, and molded products such as automobile bodies. be.

<Example> Examples of the present invention will be specifically described below.

E was applied to SP with a thickness of 0.8 m/m manufactured by continuous annealing.
Single-sided Zn-Ni alloy plated steel plate made of steel plate and 5PCD steel plate with a plate thickness of 0.7+n/m (plating conditions: bath-
NiSO4・6820300g/41, ZnSO4・7
t (20160g/ffi, pHL, S, bath temperature 55°C,
Current density 50A/drn2, plating weight ff130g/
Anodic electrolytic treatment was performed on the non-plated surface of the sample (lo'') using a horizontal electrolytic bath under the electrolytic bath and electrolytic conditions shown in Table 2.

For all colloidal oxides, oxide sol manufactured by Nichijo Kagaku was used.

After electrolysis, wash with water, dry, and use Nippon Paint Granogin 5.
Phosphate treatment was performed using 02000, and the chemical appearance of the Fe surface, the amount of chemical conversion coating deposited, and the chemical crystal size were examined.

In addition, after applying cationic electrodeposition coating with a coating thickness of 20μ using Nippon Paint's Power Top U-30,
JIS Z by cross-cutting the coating film and using 5% saline solution
An 800-hour salt spray test was conducted in accordance with 2371, and the blister width at the cross-cut portion was measured.

These results are shown in Table 2 along with the results of comparative examples.

All of the comparative examples that are outside the scope of the present invention have a large chemical crystal size and a large blister width in the salt spray test after painting. On the other hand, all the examples of the present invention exhibit a uniform chemical conversion coating appearance and produce a dense chemical conversion coating.
The corrosion resistance after painting was also excellent.

<Effects of the Invention> The present invention provides colloidal SiO2, Fe2O on the steel plate surface.
3. This is a method of anodic electrolytic treatment using an electrolytic solution containing a predetermined amount of one or more of SnO2, TiO2, 5b203, (:e02), and it is possible to generate a uniform and dense chemical conversion film on the Fe surface. , significantly improves the film adhesion of phosphate conversion coatings and the corrosion resistance after painting.

[Brief explanation of drawings]

FIG. 1 is a scanning electron micrograph (1000x magnification) used as a drawing to show the crystal structure. FIG. 1a is an electron micrograph of an untreated steel plate, and FIG. 1b is an electron micrograph of a steel plate similar to that of FIG. 1a, which was electrolytically treated in a colloid-free bath and then treated with phosphate. Figures 1C, 1d and 1e are each 5n02
Colloid, SiO2:20oid and F(+203
This is an electron micrograph of a steel plate that has been electrolytically treated in a colloid-added bath and then phosphate-treated. Patent attorney Yo Ishii - et al - 1 -: 2 Taku・-:
1. ”::]j Figure 1a Figure 1b Figure 10 Figure 1e

Claims (1)

[Claims] (1) The Fe surface of the steel plate is coated with colloidal SiO_2,
Fe_2O_3, SnO_2, TiO_2, Sb_2O
_3, one or two or more of CeO_2, 0.0
A method for improving the phosphate treatability of a steel sheet, which comprises performing electrolytic treatment as an anode in a conductive salt aqueous solution containing 1 wt% or more and less than 10 wt%.