JPS621880A - Aftertreatment of metal-plated steel sheet - Google Patents

Abstract

PURPOSE:To form a chromating film excellent in appearance as well as in white rust resistance by applying a chromating solution containing specific amounts of Ti or Mg ions in subjecting the surface of a metal-plated steel sheet to chromate treatment. CONSTITUTION:In subjecting the surface of the steel sheet plated with Zn, Zn alloy or Al to surface treatment by chromating, the chromating solution containing 0.1-1.0g/l Ti ions or 0.07-0.12g/l Mg ions is applied by spraying, dipping or another method, which is capable of forming the chromating film having superior appearance and white rust resistance as compared with the one made by use of a chromating solution containing CrO3 alone.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for post-treatment of metal-plated surface-treated steel sheets such as zinc or zinc alloy plated steel sheets and aluminized steel sheets.

[Prior art]

Conventionally, post-treatment methods for galvanized steel sheets such as hot-dip galvanized steel sheets include spraying,
Apply by dipping, roll coater 1 or electrostatic coating method,
After adjusting the amount of adhesion to a predetermined amount, it was dried to obtain a product. When zinc is exposed to the atmosphere, it reacts with oxygen, carbon dioxide, moisture, etc. in the air, causing white rust (%Ih1te).
Because it is easy to form a unique type of rust called rust, it is treated to improve its corrosion resistance.

The chromate treatment method using a simple CrO3 aqueous solution is classified as a simple unreacted chromate treatment, and since it is simply formed on the zinc surface, the treatment method is easy, and the amount of chromate deposited is usually less than that of Cr.
, can be easily adjusted by changing the concentration. In general, C
Generally speaking, the greater the amount of r adhesion (the amount of chromate adhesion is usually expressed in terms of metal Cr), the better the white rust resistance in salt spray tests, etc., but in a CrO3 single bath, Considering cost and appearance, the amount of Cr deposited cannot be increased unnecessarily, and there is a limit to the improvement in corrosion resistance of this treatment method.

On the other hand, in the chromate treatment of zinc-based post-treatment methods, there is a post-treatment method using anion such as F ion or 5o42- ion as an auxiliary agent as a reactive chromate treatment. A product with a characteristic yellow appearance is obtained, and a product with excellent metallic luster, which is characteristic of zinc metal, cannot be obtained.

In addition, the bath compositions in the post-treatment methods disclosed in the past often contain a mixture of several metal ions, which makes bath management difficult, which causes difficulties in on-site production management. I can't deny it.

[Problem to be solved by the invention]

Currently, in the market, post-treatment methods of various bath compositions are applied for various uses, but Cry.

In the case of single-season baths, white rust often occurs during the storage period for customers after manufacture, especially during the hot and humid rainy season, which often poses a problem. Therefore, the object of the present invention is to develop a post-treatment method that allows easy bath management, improves white rust resistance, and has an excellent appearance.

[Means for solving problems]

As an alternative to such a single Cro3 bath, the present invention provides post-treatment of surface-treated steel sheets such as zinc or zinc alloy plated steel sheets, aluminized steel sheets, etc., in which trace amounts of Ti and Mg ions are added as third elements to the same treatment bath. It's about the method,
The gist of this is that after surface treatment of metal plating is performed on the surface layer of the steel plate, Ti ions of 0.1 to 1.0 g/Q are applied.
, or a CrO3 aqueous solution containing 0.07 to 0.12 g/Q of Mg ions, by spraying, dipping, or roll coater 1.
The present invention aims to provide a post-treatment method for a metal-plated steel sheet in which coating is applied using an electrostatic coating device or the like, and then, if necessary, the coating amount is adjusted using a predetermined adjusting device and then dried.

Hereinafter, the present invention will be described in detail by taking a hot-dip galvanized steel sheet as an example.

The present invention is based on the action of oxidized or hydroxylated Ti, which is extremely stable in a Ti corrosive environment and exhibits excellent composite corrosion resistance even when added in a small amount, and Mg (OH), which is poorly soluble in water and has the same <Mg.
Focusing on the high corrosion resistance of the z-surface film, this method employs a bath in which a trace amount of these elements is added to a CrO3 aqueous solution as a third element.

FIG. 1 shows Cr0. K2T in 15g/Q aqueous solution
i F, 5g/fi (1.0 as Ti'+
g/Q) or M g S O, 7 Hx O0, 8g
/ Q (0.08 g/Ω as Mg2+) was added to a hot-dip galvanized steel plate by immersing it in a post-treatment bath at room temperature, and using a ringer roll, the amount of Cr deposited (in terms of metal Cr) was lomg/rrr. (Single side) Shows the salt water spray test results of adhered products, with salt water spray time on the horizontal axis and white rust occurrence area (%) on the vertical axis.Gelafuchi, K, TiF,
, products with trace amounts of MgSO4・7H,O added are Cr0
．． Shows better white rust resistance than the 15g/Ω single bath.

The numerical limits of the present invention are for Ti ions.

If it is less than 01.0 g/Q, the effect of improving corrosion resistance is insufficient, and if it exceeds 1.0 g/Q, it is not economical due to the unit price of the Ti compound, so the upper limit was set.

On the other hand, if Mg ion is less than 0.07g/Q, Ti
Similar to ion, the corrosion resistance improvement effect is insufficient, and the upper limit of 0.12
g/Q generally refers to M in the form added in the present invention.
For compound g, if the amount exceeds this upper limit, it falls into the category of reactive chromate due to the amount of anions contained, resulting in an appearance with a large amount of adhesion, which is not preferable for the purpose of the present invention, so the upper limit is set at 0.12 g/ I named it Q.

Here, as a source of Ti ions, Na, TiO,..., TiO:it Na, Ti Fsj x2Ti Fs
t(NH4), T i F, etc. are all soluble Ti
On the other hand, the Mg ion source is MgSO4, MgS
Similar soluble Mg compounds such as O4.Hz O, M g S O4.7H20 are employed.

The bath treatment temperature may be room temperature, and no special consideration is required. C
rThe adhesion amount can be adjusted by spraying, dipping, or in the case of a ringer roll, using Cry, or by slightly tightening the aperture compared to a plain bath, or using the Roll Coater 1 electrostatic coating method, etc. In the case of the adhesion method, the respective conventional adjustment methods are followed.

〔Example〕

A steel plate was hot-dip galvanized on a Sendzimir hot-dip galvanizing line, then cooled and solidified.The product was subjected to chromate treatment using the immersion method in a post-treatment bath with the bath composition shown in Table 1, and then the product was subjected to a salt spray test. The area where white rust occurred after 24 hours is shown in Table 1 as the respective results.

As shown in Table 1, the products of the present invention exhibit excellent corrosion resistance.

〔Effect of the invention〕

As a post-treatment of the metal plated steel of the present invention, the area where white rust occurs can be reduced to 1/2 or less compared to the conventional one.

[Brief explanation of drawings]

Figure 1 shows hot-dip galvanized steel sheets coated with various types of Cry. This shows how white rust occurs when salt water is sprayed after treatment in an aqueous solution.

Claims (1)

[Claims] After surface treatment of metal plating on the steel plate, Ti ions 0.1 to 1.0 g/l or Mg ions 0.07 to 0
．． A post-treatment method for metal-plated steel sheets, characterized by applying a CrO_3 aqueous solution containing 12 g/l and drying.