KR100293233B1 - Pretreatment solution for chromate coating and coating method of electrolytic galvanized iron using the same - Google Patents

Abstract

PURPOSE: A pretreatment solution for chromate coating is provided to remove ZnO from the surface of an electrolytic galvanized iron with a pretreatment solution containing sulfuric acid, nitric acid and CrO prior to forming Zn-Cr-O chromate base coating. CONSTITUTION: The method for forming chromate coating on electrolytic galvanized iron includes: (i) dipping an electrolytic galvanized iron in a pretreatment solution containing CrO 3-10g/L, sulfuric acid 5-20g/L, and nitric acid 10-25g/L at a temperature range of 40 to 50deg.C for 3-10sec; (ii) roll coating the treated electrolytic galvanized iron with a chromate solution.

Description

Pretreatment solution for producing chromate base coating and method for producing coated chromate coating having excellent surface appearance and corrosion resistance

The present invention relates to a pretreatment solution for producing a chromate base coating, and a method for producing a coated chromate coating having excellent surface appearance and corrosion resistance using the same, and more particularly, forming a chromate base coating first using a pretreatment solution and then applying chromate coating. The present invention relates to a method for producing a coated chromate coating having improved surface appearance and corrosion resistance by forming a coating in duplicate by treating with a solution.

The chromate coating treatment is often used to improve the corrosion resistance of a steel plate coated with zinc or the like on its surface. The chromate treatment is classified by a film forming method determined by the treatment solution composition, and the chromate treatment solution is a chromate film formation reaction using a chromate solution containing sulfuric acid, hydrochloric acid, and nitric acid as one or more kinds. The method of forming the film by redox reaction is called reactive chromate treatment, and it is used as the film forming reaction by using an aqueous solution of chromium ion which does not contain the strong acid and to which the colloidal material and the resin in the emulsion state are added. It is called coating type chromate treatment which forms a film using the dehydration condensation reaction between compounds and the intrinsic binding force of the material added to the film composition.

Recently, when the steel sheet is used for home appliances and automobiles, required coating materials include corrosion resistance of the steel sheet, anti-fingerprint (fingerprint resistance), electrical conductivity, surface appearance, weldability, electrical conductivity, water resistance and alkali resistance of the film. It is difficult to satisfy all of the above-described coating demand qualities of steel sheet demands by the reactive chromate treatment which has been conventionally treated, and a treatment technique that satisfies some of the required characteristics by coating chromate treatment. This is known.

However, the above techniques are mainly used for improving physical properties such as corrosion resistance of the coated chromate coating, and the results for surface appearance improvement have not been disclosed. The coating type chromate treatment technology has a disadvantage of inferior surface appearance due to the dark brown color of the film component structure, and is not suitable for home appliances which emphasize the surface appearance mainly because it is mainly used for the coating base.

Accordingly, an object of the present invention is to add Cr ⁶⁺ 0.1-0.5g / L and Cr ³⁺ 0.1-0.2g / L in a solution of CrO 3-10g / L, sulfuric acid 5-20g / L and nitric acid 10-25g / A pretreatment solution for the preparation of chromate backing coatings consisting of L and having a pH of 0.1-2.0 is provided.

It is another object of the present invention to provide a method of forming a chromate coating by immersing it in a pretreatment solution for producing a base coating mainly composed of chromium oxide, sulfuric acid and nitric acid before roll coating the coated steel plate with a coating type chromate solution.

In the first aspect of the present invention,

PH 0.1- consisting of 3-10 g / L CrO, 5-20 g / L sulfuric acid and 10-25 g / L nitric acid added to the solution with Cr ⁶⁺ 0.1-0.5 g / L and Cr ³⁺ 0.1-0.2 g / L A pretreatment solution for producing a chromate backing film of 2.0 is provided.

In the second aspect of the present invention,

Immersing an electrogalvanized steel sheet in a pretreatment solution composed of CrO, sulfuric acid, and nitric acid to form a chromate bar film of Zn-Cr-O principal on the surface;

Roll coating the electrogalvanized steel sheet on which the base film is formed with a coated chromate solution; It provides a method for producing a coated chromate coating excellent in surface appearance and corrosion resistance comprising a.

Hereinafter, the present invention will be described in detail.

The present invention provides a Zn-Cr-O principal by immersing an electrogalvanized steel sheet in a temperature of 40-50 ° C. for 3-10 seconds in a Cr pretreatment solution mainly composed of CrO, sulfuric acid and nitric acid (hereinafter referred to as "pretreatment solution"). The surface appearance of the galvanized steel sheet was improved by improving the surface appearance of the galvanized steel sheet and then immersed in a commercially available coated chromate solution to improve the corrosion resistance.

In the method of the present invention, an electrogalvanized steel sheet having a zinc adhesion of 20 g / m 3 was used as a substrate, and the surface of the steel sheet was present in the form of a film of Zn and ZnO. (b *) was 3-5.

The electrogalvanized steel sheet was added in a solution such that Cr ⁶⁺ 0.1-0.5g / L and Cr ³⁺ 0.1-0.2g / L, preferably Cr ⁶⁺ 0.3g / L and Cr ³⁺ 0.1g / L. It was immersed in a pretreatment solution for preparing a chromate-based coating of a Zn-Cr-O subject having a pH of 0.1-2.0 composed of CrO 3-10 g / L, sulfuric acid 5-20 g / L and nitric acid 10-25 g / L.

Sulfuric acid and nitric acid are strong oxidizing etchants and serve to remove the ZnO film present on the surface of the steel sheet while oxidizing the film of the galvanized steel sheet.

The amount of sulfuric acid and nitric acid settled is preferably 5-20 g / L and 10-25 g / L, respectively, and when the excess amount is added, a desired base film cannot be obtained. PH of this invention obtained by adding the said sulfuric acid and nitric acid is 0.1-2.0, and even if it is pH 2.0 or more, reaction does not occur at all.

When a small amount of CrO is added thereto, Zn ions generated in the ZnO film removed by the etching reaction (ZnO to Zn) by sulfuric acid and nitric acid act as a reducing agent, thereby reducing Cr ⁶⁺ supplied to CrO to Cr ³⁺ while reducing Zn-. When the film forming reaction of Cr takes place and the steel sheet on which the Zn-Cr film is formed is taken out from the immersion liquid, an oxidation reaction with oxygen in the air occurs to form a thin film of Zn-Cr-O type on the base surface of the steel sheet. .

The amount of CrO added to satisfy Cr ⁶⁺ 0.1-0.5g / L and Cr ³⁺ 0.1-0.2g / L in the solution is preferably 3-10g / L, and when added below 3g / L, it is oxidized to sulfuric acid and nitric acid. It is difficult to obtain a Zn-Cr film produced by etching the Zn ²⁺ formed from the ZnO film by reducing the Cr ⁶⁺ in the solution as Cr ³⁺ .

When the CrO is added in an excessive amount of 10 g / L or more, too much chromium ions are inferior in color, thereby reducing the whiteness improvement effect by the Zn-Cr-O base film.

The chromate base coating of the Zn-Cr-O principal exhibits light blue with whiteness (L *) 78-80 and yellowness (b *) -0.7 to 10.

The formed chromate base film of the Zn-Cr-O main body thus formed has improved adhesion between the electrogalvanized layer and the coated chromate film made of Cr (OH) ₃ and Cr ₂ O ₃ to be formed, thereby improving corrosion resistance. The effect of Zn in the chromate base coating of the Zn-Cr-O subject has an effect of improving the surface appearance as the whiteness increases and the yellowness decreases.

As described above, an electrogalvanized steel sheet having an improved surface appearance was treated with a commercially available coated chromate solution.

The coated chromate solution is a commercialized solution based on Cr ⁶⁺ 5-10 g / L, Cr ³⁺ 6-11 g / L, and colloidal silica 5-20 g / L. A chromate coat was prepared in duplicate on the base coat of the -Cr-O subject.

The second formed chromate film is an opaque passivation film having a dark brown color mainly composed of Cr (OH) ₃ and Cr ₂ O ₃ .

In the present invention, before the roll coating treatment of the steel sheet to be treated with the coating type chromate coating solution, the base film is formed by immersing it in the pretreatment solution for preparing the chromate base coating of Zn-Cr-O principal mainly composed of CrO, sulfuric acid and nitric acid. The whiteness of the coated chromate coating can be improved up to 70-75 and the corrosion resistance up to 150 hours or more.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

The adhesion amount, surface appearance, and corrosion resistance of Cr to the electrogalvanized steel sheet according to the method of the present invention were measured as follows.

The surface appearance was measured by using a color difference meter (L *) and yellowness (b *), and the weight was measured by weight loss method. Corrosion resistance was evaluated using the salt spray tester to the time to 5% white rust generator.

Example 1

Changes in Physical Properties of Coated Chromate Coatings with CrO Concentration in Pretreatment Solution

Comparative Example 1

The steel sheet was immersed in the coated chromium mate solution at 40-50 ° C. for 3-10 seconds without undergoing a pretreatment process according to the present invention to form a chromate coating.

Cr adhesion amount, surface appearance and corrosion resistance of the coated steel sheet surface were evaluated and shown in Table 1 below.

Comparative Example 2

10 g of sulfuric acid was used as the pretreatment solution and soaked in the steel sheet for 40-50 ° C. and 3-10 seconds.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate film, and the Cr adhesion amount, surface appearance, and corrosion resistance of the surface were shown in Table 1 below.

Comparative Example 3

20 g of nitric acid was used as the pretreatment solution and soaked in the steel plate for 3-10 seconds at 40-50 ° C.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate film, and the Cr adhesion amount, surface appearance, and corrosion resistance of the surface were shown in Table 1 below.

[Comparative Example 4]

The steel plate was immersed at 40-50 ° C. for 3-10 seconds in a pretreatment solution consisting of 10 g / L sulfuric acid and 20 g / L nitric acid.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate film, and the Cr adhesion amount, surface appearance, and corrosion resistance of the surface were shown in Table 1 below.

Invention Example 5

Zn-Cr-O having 3-5 mg / m 2 of Cr attached to the surface of the steel sheet by immersing the steel sheet at 40-50 ° C. for 3-10 seconds in a pretreatment solution consisting of CrO 3g / L, sulfuric acid 10g / L and nitric acid 20g / L. The main chromium mate base film was formed.

The steel plate on which the base film was formed was roll-coated with a coated chromate solution to form a chromate film, and the Cr ^- adhesion amount, surface appearance, and corrosion resistance of the surface were shown in Table 1 below.

Invention Example 6

Except that 10 g / L CrO was used, the steel sheet was immersed in the same manner as in Inventive Example 5 to form a Zn-Cr-O chromium-based base film having 20-40 mg / m 2 of Cr on the surface of the steel sheet.

The steel sheet on which the base film was formed was roll-coated with a coated chromate solution to form a chromate film, and the Cr adhesion amount, surface appearance, and corrosion resistance of the surface were evaluated and shown in Table 1 below.

Comparative Example 7

Except for using CrO 15g / L, the steel sheet was immersed in the same manner as in Example 5 to form a Zn-Cr-O chromate base film with 50-80mg / ㎡ Cr attached to the surface of the steel sheet.

The steel sheet on which the base film was formed was roll-coated with a coated chromate solution to form a chromate film, and the Cr adhesion amount, surface appearance, and corrosion resistance of the surface were evaluated and shown in Table 1 below.

TABLE 1

As shown in Table 1, when CrO was not added to the pretreatment solution composition (Comparative Example 1-4), even after coating chromate treatment, the whiteness was 65 or less, but the surface appearance was not improved (Inventive Example 5-6 ) The whiteness was improved to 72-77, which is the result of Zn-Cr-O coating according to the pretreatment process.

On the other hand, when more than 15 g / L CrO was added (Comparative Example 7), the weight of the Zn-Cr-O film by pretreatment increased to 50-80 mg / m2 and the total chromate film weight after coating chromate treatment was 150-200 mg. / M², so the film is too thick, the whiteness of the surface appearance is reduced to less than 65.

On the other hand, as the weight of the chromate film increases, the corrosion resistance increases over 250 hours.

This phenomenon is considered to be because the yellowness decreases to -1 to 2 by the formation of the chromate film of the Zn-Cr-O principal by pretreatment.

Therefore, the CrO concentration in the pretreatment solution having the best surface appearance and corrosion resistance at the same time is 3-10 g / L.

Example 2

Changes in Physical Properties of Coated Chromate Coatings According to Changes of Nitric Acid and Sulfuric Acid Concentrations in Pretreatment Solution

Comparative Example 8

The steel plate was immersed at 40-50 ° C. for 3-10 seconds in a pretreatment solution consisting of 5 g / L CrO and 10 mg / L sulfuric acid.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate coating, and the surface Cr adhesion amount, surface appearance, and corrosion resistance were evaluated and shown in Table 2 below.

Comparative Example 9

The same procedure as in Comparative Example 8 was conducted except that 20 mg / L sulfuric acid was used.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate coating, and the surface Cr adhesion amount, surface appearance, and corrosion resistance were evaluated and shown in Table 2 below.

Comparative Example 10

The same procedure as in Comparative Example 8 was conducted except that 20 mg / L nitric acid was used instead of 10 mg / L sulfuric acid.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate coating, and the surface Cr adhesion amount, surface appearance, and corrosion resistance were evaluated and shown in Table 2 below.

Comparative Example 11

The same procedure as in Comparative Example 8 was conducted except that 30 mg / L nitric acid was used instead of 10 mg / L sulfuric acid.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate coating, and the surface Cr adhesion amount, surface appearance, and corrosion resistance were evaluated and shown in Table 2 below.

Invention Example 12

Zn-Cr- having a Cr adhesion amount of 1-3 mg / m 2 on the surface of the steel sheet by immersing the steel sheet at 40-50 ° C. for 3-10 seconds in a pretreatment solution consisting of 5 g / L CrO, 5 g / L sulfuric acid, and 10 g / L nitric acid. O chromate backing film was formed.

The steel sheet on which the base film was formed was roll-coated with a coating type chromate solution to form a chromate film, and the surface Cr adhesion amount, surface appearance, and stone resistance were evaluated and shown in Table 2 below.

[Inventive Example 13]

The same procedure as in Example 12 was carried out except that 20 mg / L instead of 5 mg / L sulfuric acid and 25 mg / L instead of 10 mg / L nitric acid were used.

The steel sheet from which ZnO was removed through the pretreatment process was roll coated with a coated chromate solution to form a chromate coating, and the surface Cr adhesion amount, surface appearance, and corrosion resistance were evaluated and shown in Table 2 below.

TABLE 2

As shown in Table 2, when the nitric acid and sulfuric acid are added independently, the chromate film of the Zn-Cr-O subject by pretreatment is not formed, and thus the surface appearance does not improve more than 65 after the coated chromate treatment.

On the other hand, when the concentration of nitric acid is 10-25 g / L and the concentration of sulfuric acid is 5-20 g / L (Invention Example 12-13), the amount of chromate coating by pretreatment is 1-3 mg / m 2 and the yellowness is -3 to 10 After roll-coating, the coated chromate film was formed, and the whiteness was 75-77. The surface appearance was excellent and the corrosion resistance was also improved to more than 150 hours.

The present invention improved the surface appearance and corrosion resistance together by removing ZnO using a pretreatment solution of sulfuric acid, nitric acid and CrO and preforming the Zn-Cr-O chromate base coating before treatment with the coated chromate solution.

Claims (2)

Chromate consisting of Cr-10 3-10 g / L, sulfuric acid 5-20 g / L and nitric acid 10-25 g / L added to feed Cr ⁶⁺ 0.1-0.5 g / L and Cr ³⁺ 0.1-0.2 g / L Pretreatment solution for blank film preparation CrO 3-10 g / L, sulfuric acid 5-20 g / L and nitric acid 10-25 g / L added to supply Cr ⁶⁺ 0.1-0.5 g / L and Cr ³⁺ 0.1-0.2 g / L in the solution of claim 1 Immersing the galvanized steel sheet in a pretreatment solution for preparing a chromate-based coating film for 3-10 seconds at a temperature of 40-50 ° C to form a chromate-based coating film of Zn-Cr-O subject; And Roll coating the electrogalvanized steel sheet on which the base film is formed with a coated chromate solution; Coating type chromate coating method excellent in surface appearance and corrosion resistance comprising a.