KR960007775B1 - Chromate solution of controlling an eruption of a chrome and the method for making c chromate steel plate using the same - Google Patents

Abstract

The chromate solution is prepared by (A) forming a chromium solution having 10-40 g/l chromium component at 0.3-0.7 chromium reduction ratio and (B) adding 3.0-25.0 g/l phosphoric acid, 1.0-5.0 g/l fluorine, 3.0-15.0 g/l silica and 0.05-3.0 wt% silane coupling agent. And the chromate steel plate is produced by coating a steel plate with the obtained chromate solution and drying it at 120-200 deg.C. The coated steel plate has good corrosion resistance, good surface appearance and prevents chromium from dissolving.

Description

Chromate solution in which chromium elution is suppressed and method for producing chromate steel plate using this solution

1 is a graph showing the relationship between the steel plate temperature and the corrosion resistance of the chromate steel sheet using the solution of the present invention.

2 is a graph showing the relationship between the temperature of the steel sheet of the chromate steel sheet using the solution of the present invention and chromium elution.

The present invention relates to a chromate solution in which chromium elution is suppressed and a method for producing a chromate steel sheet using the solution. More specifically, a chromate solution and a solution in which the chromium elution of the chromate film is suppressed is excellent in corrosion resistance, beautiful surface appearance. It relates to a method for producing a chromate steel sheet using.

Recently, the use of zinc and zinc-based alloy plated steel sheet is increasing to improve the corrosion resistance of the steel sheet, and phosphate treatment and chromate treatment are performed as pretreatment to prevent white rust generation of the galvanized layer. The chromate is performed by various methods for the purpose of corrosion resistance.

Chromate coating that shows corrosion resistance is mainly composed of soluble hexavalent chromium and insoluble trivalent chromium. Hexavalent chromium is self-repairing function, denseness of coating, and trivalent chromium is extracted by corrosion barrier effect. , Chromate film formation reaction is divided into typical, reactive, coating type, etc. by the treatment method according to the solution composition, and shows the characteristic difference accordingly.

In the case of electrolytic chromate, the amount of chromium deposition can be precisely controlled by controlling the amount of electricity, while there is a disadvantage in that corrosion is poor due to the occurrence of microcracks in the coating. It decreases the life of the solution due to aging of the solution, such as the decrease of free acidity in the solution, which makes it difficult to control the amount of chromium deposition, which causes chromium waste water pollution by water washing after chromate treatment, and the corrosion barrier according to the chromate coating component. There is a disadvantage that the effect is weak enough corrosion resistance.

On the other hand, the coated chromate is formed by simply coating the solution on the steel sheet rather than the reaction of the film formation with the solution and the material to be treated. There is no pollution problem by chrome waste water.

However, since the coated chromate coexists in the solution simultaneously with hexavalent chromium and trivalent chromium, the corrosion barrier effect is superior to other treatment methods, but the self-repair effect is relatively low. Uniform surface appearance uniformity is required.

Recently, the development of high-performance surface-treated steel sheet has been actively promoted, and the development of post-treatment processes such as treating various organic composite resins on such coated films has been accelerated, and the organic composite resin treatment method is also changed from a conventional solvent type to a water-soluble type. With the development, the necessity of suppressing the dissolution of chromium in the chromium film by the post-treatment process has emerged to secure excellent corrosion resistance. Accordingly, the present invention provides a chromate solution and a method for producing a chromate steel plate using the chromate solution, which is excellent in corrosion resistance, surface appearance and coating film adhesion, and in particular, chromium elution is suppressed by controlling the proper components and contents of the chromate solution. I would like to, but its purpose is.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the chromate solution, the chromium component is 10-40 g / l, and the chromium solution has a chromium reduction ratio of 0.3-0.7. The phosphoric acid: 3.0-25.0 g / l, fluorine: 1.0-5.0 g / l, and silica: 3.0 -15.0 g / l and a silane coupling agent: 0.05-3.0% by weight of the chromium elution is suppressed, characterized in that the composition is added.

In addition, the present invention is a method for producing a chromate steel sheet, after applying the chromate solution according to the present invention to a galvanized steel sheet, and then dried at a steel plate temperature of 120-200 ^° C. It is related with the manufacturing method of the chromate steel plate in which elution is suppressed.

Hereinafter, the chromate solution according to the present invention will be described in detail.

The chromate solution according to the present invention is based on chromic anhydride, and an appropriate amount of trivalent chromium ions are present in the solution as a reducing agent. Phosphoric acid, silica, and fluorine compounds are added thereto, and chromium elution inhibitor, corrosion resistance, and film adhesion are improved. It is the solution which contained the silane coupling agent for the objective.

In more detail, in the solution of the present invention, one or two or more selected from hexavalent chromium compounds such as chromic anhydride, sodium chromium, potassium chromium, and ammonium chromium are added to make the chromium component 10-40 g / l, and a reducing agent. Using a partial reduction of hexavalent chromium to prepare a chromium solution with a trivalent chromium ratio (hereinafter referred to as chromium reduction ratio) to the total chromium of 0.3-0.7, in which the oxophosphate (0-H ₃ PO ₄ ) , One or two or more selected from among phosphate compounds such as monobasic sodium phosphate (NaH ₂ PO ₄ ) and dibasic sodium phosphate (Na ₂ HPO ₄ ), and the total phosphoric acid content (PO ₄ ^3- content) is 3.0-25.0 g / l, among fluorine compounds such as sodium hexafluorosilicate (Na ₂ SiF ₆ ), aluminum hexafluorosilicate (Al ₂ (SiF ₆ ) ₃ ), fluorosilic acid (H ₂ SiF ₆ ), and hydrofluoric acid (HF) One or two or more selected compounds are added to sol silica having a fluorine content of 1.0-5.0 g / l and a particle size of 0.01-0.1 μm. Is added in powder form and the silicon oxide content is 3.0-5.0 g / l, γ-glycidoxy propyl trimethoxysilane, γ-menacryloxy propyl trimethoxysilane, γ-glycidoxy propyl methyl dimethoxysilane, etc. Is a chromate solution containing 0.05-3.0% by adding a silane coupling agent.

Hereinafter, the reason for numerical limitation of each component composition of the chromate solution which concerns on this invention is demonstrated in detail.

When the chromium concentration is 10g / l or less, the amount of chromium adhered in the chromate film is low, and thus the corrosion resistance is low. When the chromium concentration is 40g / l or more, the stability of solution is reduced by increasing the reduction reaction by the silane coupling agent and the surface appearance becomes poor. The concentration is preferably 10-40 g / l.

If the reduction ratio of chromium in the solution by adding the reducing agent is 0.3 or less, the corrosion resistance due to the self-healing effect of hexavalent chromium is good, but the chromium leaching is not inhibited due to excessive hexavalent chromium. However, it is preferable to maintain the chromium reduction ratio of 0.3-0.7 because the problem of deterioration of corrosion resistance and gelation of the solution occurs due to the reduction of self-repairing action.

In addition, when the content of phosphoric acid in the solution is 3.0g / l or less, there is no effect of improving the surface appearance and solution stability, at 25.0g / l or more the coating film adhesion is sharply reduced and chromium elution is greatly increased, so the content of the impression is 3.0-25.0 It is preferable to make it into g / l.

In the case of fluorine, it is preferable to contain 1.0-5.0 g / l, because the fluorine component has good corrosion resistance due to the corrosion factor blocking effect at 1.0 g / l or more, but chromium dissolution is increased at 5.0 g / l or more. This is because it is not preferable.

The silica content is preferably 3.0-15.0 g / l due to the addition of silica, because the silica content is less than 3.0 g / l, the corrosion resistance effect is low, the corrosion resistance is excellent at 15.0 g / l or more, but the surface is stained This is because chromium dissolution is increased and it is not desirable.

The content of the silane coupling agent can be used with a slightly increased amount depending on the increase of chromium in the solution, but at 0.05% or less of the total solution weight, the corrosion resistance and the chromium leaching inhibitory effect are not properly exhibited. Since it promotes and the overall solution stability, such as pH rise of a solution and chromium reduction ratio rises, it is preferable that content of a silane coupling agent is added at 0.05-3.0%.

Hereinafter, the method of manufacturing a chromate steel plate using the chromate solution of this invention is demonstrated in detail.

When the chromate solution of the present invention is coated on a steel sheet to produce a chromate steel sheet, zinc and zinc-based alloy plated steel sheets are usually used. In addition, the use of the chromate coating solution of the present invention may be performed in a degreasing-washing-chromate coating-drying process. It has excellent work efficiency and can be easily applied to continuous galvanizing line. The method for treating the solution may be any method such as dipping, spraying, roll coating, etc., and drying immediately without washing with water.

Therefore, in the drying method of the present invention, when the drying temperature of the steel sheet is 120 ^° C or less, the corrosion resistance and the chromium elution increases due to the lack of the mutual reaction between silica due to heat, the silica coating is more robust than 200 ^° C. In particular, the bond between chromium and the silane coupling agent is increased to increase the chromium elution inhibitor, but microcracks occur in the coating and the reduction of hexavalent chromium due to heat is accelerated, and the corrosion resistance is rather deteriorated due to the lack of self-healing effect. It is preferable to dry the drying temperature to 120-200 ^° C.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

A zinc-nickel alloy electroplated steel sheet having a plating deposition amount of 30/30 mg / m ² is used as a base metal, and a chromium deposition amount of 50 mg / m ² is obtained by using a roll coater with a chromate solution having a composition as shown in Table 1 below. The surface color, corrosion resistance, film adhesion and chromium elution rate of the steel plate temperature coated in a furnace and without chromaticity were dried at the steel plate temperature of Table 1 and chromated to evaluate the specimens, and the results are shown in Table 1 below. Indicated.

At this time, the method for producing a chromate solution is prepared by, for example, a solution having the composition of Inventive Example (A) shown in Table 1 below.

That is, after dissolving 250 g / l of chromic anhydride in 800 ml of deionized water, using ethylene glycol as a reducing agent, the hexavalent chromium is reduced in a cooling bath so that trivalent chromium and hexavalent chromium are present in the same amount in a solution, followed by 18 g of fluorine. / l, phosphoric acid 45g / l and silica 150g / l are sequentially added to the chromium solution while stirring and deionized water is added to make the total solution 1000ml. When the total chromium concentration of the solution after stirring is 20 g / l, and the silane coupling agent is contained while diluting with deionized water, a chromate solution having the same composition as in Inventive Example (A) can be prepared.

The surface color was evaluated as follows after measuring whiteness and yellowness using a CIE Lab type color difference meter (TOKYO SENSHOKU CO.).

Whiteness evaluation (L * value) ◎: 56 or more ○: 54.5-56

△: 56-54.5 ×: 53 or less

Yellowness evaluation (b * value) ◎: 2 or less ○: 2-5

△: 5-8 ×: 8 or more

The film adhesiveness was coated with a chromate-treated steel sheet using a thermosetting melamine alkyd-based paint with a coating thickness of 25-30 μm, followed by a cross cut test (1 mm, 100 scale). A. A. A. A. A. A. A. A. A. A. A. A. A. The degree of film peeling was evaluated as follows.

◎: Peeling film ○: 1 square millimeter scale

(Triangle | delta): 3-5 peelings of 1 square millimeter scale x: Peeling 7 or more of 1 square millimeter scales

The corrosion resistance was specified by the salt spray test according to JIS Z2371 at the time of occurrence of white rust.

The chromium dissolution rate was immersed in boiling water (deionized water 80 ^° C or more) for a predetermined time immersed chromate treated steel plate was measured by the following formula by inductively coupled plasma (ICP), atomic absorption (AA) analysis. In other words,

Chromium Dissolution Rate × 100 (%)

Where A is the amount of chromium deposited before washing.

B: amount of chromium eluted after washing

Chromium Dissolution Rate Evaluation

◎: 1.0 or less ○: 1.0-3.0

△: 3.0-5.0 ×: 5.0 or more

As shown in Table 1, the invention example (AG) is a mixture of the chromium concentration range and the additive and the silane coupling agent in the condition range of the present invention, showing excellent physical properties, while Comparative Examples (I) and (O) In the case of the chromium concentration and the reduction ratio is high gelation of the solution occurs, Comparative Example (J) is a case where the chromium concentration is lower than the condition range of the present invention, the corrosion resistance is very low due to the lack of chromium deposition, the reduction ratio is The comparative example (H), which is lower than the condition range of the present invention, has an excellent corrosion resistance due to the self-healing effect due to an excessive amount of hexavalent chromium in the chromate film, but the hydrophilicity of the film surface is increased, resulting in a sharp decrease in the film adhesion. .

In addition, in the case of Comparative Example (K) in which the content of phosphoric acid was added in excess of the condition range of the present invention, the production of hexavalent chromium phosphate was active and the surface showed high hydrophilicity, thereby significantly reducing the coating film adhesion. As in L), when it is added to the fragrance than the range of the present invention, solution stability such as surface color is poor and precipitates are generated in the solution is reduced.

On the other hand, when the amount of fluorine is small as in Comparative Example (R), the corrosion resistance is hardly improved, but the corrosion resistance increases as the content is increased, and further corrosion resistance as in the case of Comparative Example (S) added over 5.0 g / l or more There was no increase and other physical properties, such as chromium elution, were shown to fall.

Comparative Example (M) is a case in which silica is excessively added. The surface appearance is poor due to a phenomenon caused by local over-aggregation of silica, and the surface appearance is poor. In Comparative Example (N), a small amount of surface color is added. Poor and corrosion resistance is greatly reduced.

And, as in Comparative Example (P), the steel sheet temperature during drying is 120 In the case of C or less, the silica cannot form a complete film, resulting in inferior corrosion resistance and 200 as in Comparative Example (Q). If it is higher than C, the corrosion resistance is drastically reduced due to the reduction of hexavalent chromium in the film and the occurrence of microcracks on the surface.

In addition, in the case of Comparative Example (T) having a small content of the silane coupling agent, the reaction between the silane coupling agent and chromium and other inorganic substances was insufficient, and the corrosion resistance rapidly decreased, and the Comparative Example (U) in which the content of the silane coupling agent was excessively high. In the case, on the contrary, the reaction was vigorous, so that the solution lost stability in a short time and the gelation of the solution was promoted, and application was impossible.

On the other hand, Figure 1 is a comparison of the corrosion resistance according to the steel sheet temperature when the chromate coating treatment using the invention solution (A), the corrosion resistance increases with the increase of the steel sheet temperature, but 120 C below 200 Above C, the corrosion resistance is rapidly reduced.

In addition to the corrosion resistance evaluation described above, in the evaluation of elution of hexavalent chromium when the dried chromate film is in contact with water, in the case of Inventive Example (AG), chromium elution inhibitor was shown to be good, but as in Comparative Example (H) When the reduction ratio is low, the remaining amount of chromium hexavalent chromium increases, so the dissolution rate of chromium increases significantly.In such a situation, when the silane coupling agent is increased for the purpose of increasing the binding strength of chromium in the coating, the reaction with chromium increases. The problem of solution stability, such as accelerated gelation of the solution, is raised and is not preferable.

In addition, the comparative example (K) with a high content of impression and the comparative example (M) with a high content of gilli were found to increase the chromium elution rate due to the inhibition of the formation of a solid film under the influence of excess phosphoric acid and silica. In case of Comparative Example (P) with low steel sheet temperature during drying, chromium elution was high due to insufficient network bonding between silicas. On the other hand, the comparative example (S) with a large amount of fluorine appeared to have a high chromium elution rate, and when the silane coupling agent was added in a small amount like the comparative example (T), it was evaluated that the chromium elution inhibitor was hardly shown. As solutions of the comparative example, it can be seen that the chromium elution inhibitory effect comparable to that of the invention example is obtained, but other physical properties such as corrosion resistance are deteriorated.

And, Figure 2 shows the chromium elution rate according to the increase of the steel plate temperature when drying the chromate steel plate treated with the solution of the invention example (A), after measuring for 2 minutes in boiling water as a result of measuring the chromium by increasing the steel plate temperature It was found that the dissolution inhibition effect increased.

As described above, by suppressing the chromium elution in the chromate coating during the chromate coating treatment of the present invention, while providing a chromate steel sheet excellent in corrosion resistance and beautiful surface appearance, the operation is simple and easy to control the chromate adhesion amount, in particular the environmental aspects The effect is to significantly reduce the waste water treatment problem.

Claims (2)

In the chromate solution, a chromium component of 10-40 g / l and a chromium reduction ratio of 0.3-0.7 are phosphate: 3.0-25.0 g / l, fluorine: 1.0-5.0 g / l, and silica: 3.0-15.0 g / l and silane coupling agent: Chromium elution is inhibited chromate solution, characterized in that the composition is added to 0.05-3.0% by weight. In the method for producing a chromate steel sheet, a chromium solution having a chromium component of 10-40 g / l and a chromium reduction ratio of 0.3-0.7 is phosphoric acid: 3.0-25.0 g / l, fluorine: 1.0-5.0 g / l, and silica: 3.0- 15.0 g / l and a silane coupling agent: 0.05-3.0% by weight of the chromate solution is applied to the steel sheet is applied, and then dried at a steel plate temperature of 120-200 ^° C. Method for producing a chromate steel sheet.