JPH07116617B2 - Rust prevention method for exposed base metal end face of surface treated steel sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a rust preventive method for an exposed end surface of a surface-treated steel sheet in which a base metal portion is exposed by processing such as bending, drilling, and pressing.

(Prior Art and Problems Thereof) Post-painting and post-plating have been performed on home electric appliances, but in recent years, so-called surface-treated steel sheets that have been pre-plated or painted on the surface of the steel sheet--zinc or zinc Processes are being actively omitted by substituting alloy-plated steel plates, aluminum-plated steel plates, and pre-coated steel plates. In this case, the flat surface portion and the processed surface where the surface-treated coating remains can exhibit sufficient corrosion resistance by selecting an appropriate steel plate. However, in many cases, a cutting portion occurs in the processing, and it is necessary to handle the end face portion with care. That is, as shown in FIG. 1, the cut end surface portion of the surface-treated steel sheet has a (drip surface), b (shear surface), c (fracture surface), and d (burr). The sagging and sheared surfaces are covered by the surface treatment film that flows in, but the fractured surface often exposes the base metal. Corrosion of the exposed portion depends on the covering of the surface-treated coating and the use environment, but may cause rusting.

When the plate thickness is thin, the area of c (fracture surface) in Fig. 1 is small, so it is not a practical problem in many cases. However, when the plate thickness is thick, red rust is conspicuous. It was customary to cover the exposure of the base metal by rust treatment or punching at the time of processing, devising the shape of the die. However, these methods are in contradiction with the target process saving, and the appearance of the finished surface is likely to be non-uniform, so that improvement is required.

The present invention intends to further reduce costs by simultaneously performing the two steps of degreasing → repairing when rust-proofing the exposed base iron end surface after processing in such a surface-treated steel sheet. To do.

(Means for Solving Problems) In order to solve the above problems, the present invention uses an alkaline degreasing liquid having a rust-preventive film-forming component, and thus performs degreasing after processing without reducing degreasing ability. , An anticorrosion film (chemical conversion film or plating film) is to be formed on the exposed end face of the base metal, and the components contained as the anticorrosion film formation are Ni complex compound, chelate compound, or condensed phosphorus. An acid compound and a metal ion having two or more valences, or a nitrate or a nitrite compound.

As the degreasing method, well-known means such as spraying, dipping, electrolytic degreasing can be used.

As the degreasing agent, an aqueous solution of caustic soda, sodium silicate or sodium phosphate can be used, and a surfactant may be contained if necessary. When forming a plated coating film, a weak alkaline type degreasing agent having a pH of 8 to 12 can be generally used.

The degreasing conditions also do not need to be special, and therefore, for example, a commercially available alkaline degreasing agent for non-ferrous metals (concentration 10 to 30 g /
) For about 30 to 60 seconds at a temperature of 40 to 80 ° C,
Alternatively, it can be performed by immersing it in this.

In the case of electrolytic degreasing, the above-mentioned caustic soda, sodium carbonate, sodium orthosilicate, sodium phosphate or a solution obtained by adding a surfactant to an aqueous solution of these can be used.

As described above, there are some additives added as the rust-preventive film forming component.
The specific examples are as follows.

(I) Ni complex compound Examples of substances belonging to this are nickel citrate,
There are EDTA-Ni, nickel tartrate, nickel oxalate, etc.,
The addition amount is 1 to 50 grams, preferably about 5 to 30 grams per alkaline degreasing liquid. If it is out of this range, that is, if it is less than 1 gram, the rust prevention effect is insufficient,
If it exceeds 50 g, the surface-treated surface is adversely affected, the precipitation of nickel hydroxide and the degreasing power are reduced, and thus both are not preferable.

Ni forms an anticorrosion plating film, which requires that it does not precipitate in alkaline degreasing, which is achieved by taking the form of a complex compound. For this reason, the Ni complex compound was adopted as one of the additive components.

As an example of an alkaline degreasing liquid containing a Ni complex compound, a commercially available alkaline degreasing agent (for example, trade name Fine Cleaner FC
4326) 20g / liquid with nickel citrate 20g / added, and if the exposed end surface of the steel sheet to be treated is immersed in this at 60 ° C for 60 seconds, no red rust is observed even after one year indoors. .

(Ii) Chelate compound This was selected as a means for forming a poorly water-soluble chelate film on the Fe surface, and suitable chelating agents include tannic acid, hydroxybenzotriazole (HBT), chain-like and There are cyclic oxycarboxylic acids, phenols, and amines.

The addition amount is generally 1 to 50 g, preferably 5 to 30 g per 1 alkali degreasing liquid. If it is less than 1 g, the film formation necessary for rust prevention is insufficient, and if it exceeds 50 g, it will not adversely affect the surface treatment film and degreasing. It is not preferable because the ability is reduced.

As a specific example, the commercially available alkaline degreasing agent FC4326 20 g /
There is a liquid containing 20 g of hydroxybenzotriazole added, which is used as a weak alkali. 60 ℃ under spray conditions,
When sprayed for 30 seconds, red rust did not occur for 2 years in a normal indoor exposure test. Good results were also obtained when a degreasing solution containing 10 g of tannic acid was used.

(Iii) A condensed phosphate compound comprising a condensed phosphoric acid compound and a metal ion having a valence of 2 or more.

Examples of the condensed phosphoric acid compound include phytic acid, sodium tripolyphosphate, heavy phosphate, sodium hexametaphosphate, and the like. As divalent or higher valent metal ions (represented as Me), Mg ²⁺ , Ca ²⁺ , Zn ^{2 There are +} , Al ³⁺ , Ni ²⁺ , Co ²⁺ , Cr ³⁺ , Sn ^2+, etc., but the condensed phosphate compound composed of these metal ions and the condensed phosphate compound forms a coordination bond. Therefore, it is difficult to settle in alkali, so it is used as a portion for forming an anticorrosion film.

The addition amount is 1 to 50 g / degreaser, preferably 5 to 30
1 g of divalent metal ion (Me) to g / of condensed phosphoric acid compound
It is ~ 25g /. When Me is more than 25 g /, solubilization is difficult and precipitation easily occurs, which is not preferable.

In addition, nitrate may be added in order to accelerate the formation of the rust preventive film. As a specific example, phytic acid 20g / and calcium phytate 20g / (calcium 1.2g /)
Painted steel plate (1.0 m
When m) was treated with a spray at 60 ° C for 30 seconds, no red rust was observed in normal indoor exposure in the home after about 2 years.

(Iv) Nitrate, nitrite, sodium nitrate, ammonium nitrate, zinc nitrate, sodium nitrite, ammonium nitrite, zinc nitrite and the like.

When these substances are contained in the alkaline degreasing liquid, they simultaneously form an oxide on the surface of the ground iron to passivate the iron and passivate the iron, so that these substances meet the intended purpose.

The amount of addition is 1 to 50 g, preferably 5 to 30 g, per degreasing liquid, and if it is less than 1 g, the rust preventive property is insufficient, and if it exceeds 50 g, the degreasing ability decreases, which is not preferable.

As a specific example, an electrogalvanized steel sheet coated with a degreasing solution obtained by adding 20 g / sodium nitrate to the degreasing solution of 20 g / of the above-mentioned fine cleaner was spray degreased and the rust preventive power of its end face was examined. The treated product did not show rust after about one year. Similarly, the case of 5 g of sodium nitrite / added degreasing solution was also good.

(Example) As a steel plate to be treated, an organic resin film of about 1 micron and 3
After cutting a 1.0 mm thick surface-treated steel sheet with a micron galvanized coating and punching with a punch, add the additives shown in the table below to a commercially available alkaline degreaser (fine cleaner).
The liquid added to FC4326) was used for degreasing and simultaneous formation of a rust preventive film.

The degreasing liquid has a concentration of 20 g / and a concentration of 60 ° C, and the treatment is spraying.
It took 30 seconds.

The treated steel sheet is exposed to the inside of the factory building where the temperature is not controlled and to the ordinary living room according to the home environment, and the exposed portion of the base metal on the end face is regularly observed. The degree of occurrence was evaluated.

(Effect) When the method of the present invention is used, by using a degreasing agent containing a rust preventive film-forming component, at the same time as degreasing,
A rustproof coating can be formed on the exposed end surface of the base metal, and the range of alternatives to surface-treated steel sheets can be expanded.

[Brief description of drawings]

 FIG. 1 is a cross-sectional configuration diagram of a cut surface of a surface-treated steel sheet.

Claims (1)

[Claims] 1. A surface-treated steel sheet having a base metal portion exposed by processing, an alkaline degreasing liquid containing a Ni complex compound, an alkaline degreasing liquid containing a chelate compound, or a condensed phosphoric acid compound and a metal ion having a valence of 2 or more. By treating with an alkaline degreasing solution containing a condensed phosphate compound consisting of or with an alkaline degreasing solution containing a nitrate or a nitrite compound, simultaneously with degreasing, it is possible to form an anticorrosive film on the exposed base iron surface. The feature is a method of rust prevention of the exposed base metal end surface of the surface-treated steel sheet.