KR19980044922A - Method for producing chromate pretreatment for hot dip galvanized steel sheet - Google Patents

Abstract

The present invention relates to a method for producing a chromate pretreatment for hot-dip galvanized steel sheet to improve the corrosion resistance and coating film adhesion after the coating of the chromate treatment by performing the pre-treatment before the chromate treatment of the hot-dip galvanized steel sheet;

It consists of 40-100 g / l by mixing 1 type (s) or 2 or more types of nickel components, such as nickel sulfate, nickel nitrate, and nickel chloride, or the solution containing cobalt component in cobalt salts, such as cobalt sulfate and cobalt nitrate, and a hydrofluoric acid. Or fluorine salt containing sodium, potassium, ammonium, etc., fluorine ion is 50 ~ 90g / ℓ and organic phosphoric acid such as dimethyl phosphite, diethyl phosphite, dipetyl phosphite and the phosphoric acid component is composed of 30 ~ 80g / ℓ It is.

Description

Method for producing chromate pretreatment for hot dip galvanized steel sheet

The present invention relates to a method for producing a chromate pre-treatment for hot-dip galvanized steel sheet to improve the corrosion resistance and coating film adhesion after coating the chromate treatment by performing the pre-treatment before the chromate treatment of the hot-dip galvanized steel sheet.

In general, chromate treatment has been mainly used for temporary rust prevention in order to prevent damage to the steel sheet (white blue and black blue) caused by the corrosion of zinc generated during interpolation after the main galvanization and transportation to demand. It is widely used in non-painting materials for building materials, but in recent years, it is also used in place of phosphate as a coating material.

In particular, in addition to the phosphate solution, it is not only widely used for the management of the chromate solution and the workability during manufacture, but also widely used for the manufacture of high corrosion resistant steel sheet.

Accordingly, coated chromate is generally used for coated steel sheets and for use as a base for hot dip galvanized steel sheets. This is because the solution is simpler to use than the reactive type and the electrolytic type, and the corrosion resistance is very low.

In the case of coated chromate, the quality characteristics are greatly influenced by the adjustment of chromium monovalent and hexavalent, and in the content ratio of chromium trivalent and hexavalent, the amount of trivalent chromium decreases the elution of hexavalent chromium but decreases the corrosion resistance and solution stability. Increasing the content of chromium improves the corrosion resistance, but the secondary adhesion to the top coat is worsened, so it is required to manage the mutually proper content ratio.

However, depending on the use of the solution, the change of the solution occurs over time, and in general, when the coating state of the steel sheet is uneven due to the small amount of chromium coating, the quality characteristics are degraded.

Recently, in order to reduce the size of the sequins during the manufacture of hot-dip galvanized steel sheet, Pb component is not put in the plating bath. Accordingly, as the active point on the surface of the steel sheet decreases during chromate treatment, chromatic adhesion is reduced and coating film adhesion is reduced. It is a factor.

However, in general coating process, the problem is not greatly emphasized, but the existing chromate solution is used, but for a product which strictly requires coating adhesion, etc., an improvement is required.

The present invention has been invented to solve this problem in consideration of the above problems, and before the chromate treatment, the pretreatment is performed to form a metal film on the material surface of the plated steel pipe, and the surface of the galvanized steel sheet is activated to activate the material and the chromate film. The purpose of the present invention is to improve the adhesion of the chromium solution, to improve the uniformity of the chromate solution by smoothing the metal surface, and to improve the corrosion resistance and coating film adhesion.

Features of the present invention having such a purpose are by mixing one or two or more kinds of a solution containing a cobalt component in a nickel component such as nickel sulfate, nickel nitrate, nickel chloride, or cobalt salt such as cobalt sulfate and cobalt nitrate It is composed of 40 ~ 100g / l and hydrofluoric acid or fluorine salt containing sodium, potassium, ammonium, etc., and fluorine ion is 50 ~ 90g / l. Phosphoric acid is composed of organic phosphoric acid such as dimethyl phosphite, diethyl phosphite, dipetyl phosphite, etc. By the component consists of 30 ~ 80g / ℓ.

The present invention is 40 to 100g / by mixing one or two or more of a solution containing a nickel component in nickel salts such as nickel sulfate, nickel nitrate, nickel chloride or cobalt salt in cobalt salts such as cobalt sulfate and cobalt nitrate It is composed of l and hydrofluoric acid or fluorine salt containing sodium, potassium, ammonium, etc., fluorine ion is 50 ~ 90g / l, and phosphoric acid component is 30 ~ with organic phosphoric acid such as dimethyl phosphite, diethyl phosphite, dipetyl phosphite It consists of a solution consisting of 80 g / l.

In addition, the pretreatment solution according to the present invention can be treated by a treatment method such as immersion and spray, and a treatment temperature is provided at a temperature within 30 to 60 ° C. After the treatment, the existing solution is washed with water and dried immediately. After that, a chromate treatment is performed.

The pretreatment solution according to the present invention is composed of nickel / cobalt, fluorine and organophosphate components, and each of these components and contents will be described in detail.

First, nickel salts such as nickel sulfate and salts such as cobalt sulfate are dissolved in water to be 40 to 100 g / l.

At this time, when the concentration of the solution is less than 40g / l, it is difficult to expect the effect of improving the adhesion of the paint due to the small amount of precipitation of the metal components, and if more than 100g / l, the amount of precipitation increases, but it is difficult to expect any more effects as precipitation. As the consumption increases, the consumption of the solution also increases, making the raw unit increase of the solution, which is unnecessary.

In addition, due to the large amount of precipitation of the metal component has a dark color after the coating has a problem that the surface appearance is poor.

In the case of fluorine ions, fluorine or fluorine salt containing sodium, potassium, ammonium, etc., when the fluorine ion is 50 to 90 g / l and the content of the ingredient is 50 g / l or less, the removal function of aluminum oxide on the plating surface is weak and the metal replacement efficiency is reduced. In the case of more than 90g / l is a problem that the plating layer is eluted severely to facilitate the generation of sludge.

When the phosphoric acid component is less than 30g / l using an organic phosphoric acid such as dimethyl phosphite, when the phosphoric acid component is 30g / l or less, the substitution of metal inos and the dissolution of elution aluminum and zinc are not performed well. Excessive elution of aluminum and zinc in the reactor causes a large amount of sludge to be produced.

In addition, when using this solution, it is possible to use by spray and immersion treatment, but it is effective to use a spray treatment method.

This is because the reaction time can be shortened compared to the dipping method during the spray treatment.

The treatment temperature of the solution is preferably 30 ~ 60 ℃, because the reaction occurs very low when less than 30 ℃, the reaction does not proceed faster than 60 ℃ as well as difficult to manage the solution concentration by evaporation of the solution and heat source This is because of the loss.

Hereinafter, the embodiment of the present invention will be described in more detail.

EXAMPLE

Nickel sulfate, cobalt sulfate, hydrofluoric acid, and dimethyl phosphite were dissolved in 1000 mL of deionized water, and then stirred by the respective contents as shown in Table 1 below, followed by sufficiently stirring and heating the temperature of the solution to a constant temperature.

Subsequently, the hot-dip galvanized steel sheet having a sufficiently cleaned zinc plating amount of 50/50 g / m 2, thickness of 0.6 mm and 700 × 150 mm was treated with a spray nozzle at a spray pressure of 1 kg / mm 2 and washed immediately with pure water. And then dried.

The dried specimens were subjected to chromate treatment using a roll coater, and after the chromate treatment, the melamine-alkyd paints were treated with a bar coater to a dry coating thickness of 20 μm and evaluated for coating adhesion and corrosion resistance. Was performed.

The coating film adhesion and corrosion resistance of the steel sheet according to the present invention and the steel sheet treated as a comparative material were evaluated by the following method, and the results are shown in Table 1 below.

TABLE 1

Quality evaluation results according to the change in the amount of each ingredient added

Film adhesion

The coating was spray-treated to give a dry coating thickness of 20 μm using a thermosetting melamine-alkyd paint on the chromate treated specimens, and then cured at 150 ° C. for 25 minutes.

The adhesive evaluation was carried out by a crosscut test (making 100 patterns in the shape of a checkerboard with a thickness of 1 mm) and then examining the peeling state of the coating film using a scotch tape.

(Evaluation standard)

◎: no damage to coating

(Circle): The peeling number of a coating film is two or less

△: peeling number of coating film is less than ten

X: The peeling number of a coating film is ten or more

Corrosion resistance

After the coating treatment was performed in the same manner as the coating-adhesive test specimens, the X-type scribe was performed, followed by a salt spray test for 15 days in accordance with JIS Z 2371, and the size of the blister width generated on one side of the specimen was examined.

(Based on average)

◎: No blister occurrence

○: blister generation width 0.3 mm or less

△: blister generation width 0.3 to 1.0 mm

×: blister generation width 1.0 mm or more

Referring to the results of the invention example and the comparative example of Table 1 as follows.

(Invention example 1-9)

As a result of evaluating coating adhesion and corrosion resistance using a specimen in which a nickel or cobalt metal component was added alone or in a composite solution, and a fluorine and phosphoric acid component was treated in a molten zinc plated steel sheet. Excellent physical properties were shown.

(Comparative Examples 1-10)

When the metal component in the preparation solution is added alone or in combination, it is evaluated to have poor coating film adhesion and corrosion resistance due to less precipitation of metal ions on the steel sheet, and excellent coating film adhesion and corrosion resistance when a large amount is added. However, problems such as unfavorable results in terms of surface appearance such as darkening of the surface color occurred.

In addition, when the fluorine ion addition is lower than the scope of the present invention, there was a tendency that the corrosion resistance is poor due to insufficient reaction, and on the contrary, a large amount of sludge is generated in the case of excess. In the case of free phosphoric acid, the addition effect is not sufficient when it is lower than the range of the invention, which shows a decrease in coating adhesion and poor corrosion resistance. On the contrary, when a large amount is added, a large amount of sludge is generated as well as the corrosion resistance and adhesion thereof are lowered. This occurred.

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Claims (1)

It is composed of 40-100 g / l by mixing one or two or more kinds of nickel components such as nickel sulfate, nickel nitrate and nickel chloride or cobalt components in cobalt salts such as cobalt sulfate and cobalt nitrate. Alternatively, it is a fluorine salt containing sodium, potassium, ammonium, etc., with fluorine ion of 50-90 g / l, organic phosphoric acid such as dimethyl phosphite, diethyl phosphite, dipetyl phosphite, and phosphoric acid component of 30-80 g / l. And controlling the solution configured as described above to a temperature within 30 to 60 ° C. and then pretreating the hot-dip galvanized steel sheet by a solution immersion or spraying method, or the like.