KR100403466B1 - Preperation of roll coated chromate solution for thin-resin coated steel sheet - Google Patents

Abstract

The present invention is a coating type used for the base plate of the thin film resin coating to ensure good electrodeposition coating even after a very variable electrodeposition coating conditions to ensure excellent electrodeposition coating properties after coating the thin film resin while securing properties such as corrosion resistance and film adhesion The purpose is to provide a chromate solution.

The present invention for achieving the above object, 21 to 100 g / l pure chromium (Cr) component consisting of chromic anhydride and sodium chromate or ammonium chromate, allophosphoric acid in the amount of phosphorus (P) ions relative to the pure chromium component 67 weight% of hexavalent chromium is added to reduce the trivalent chromium component ratio (chromium reduction ratio) to the total chromium component of 0.4 to 0.7; At least one selected from the group of alkali metal phosphate compounds such as sodium phosphate compound, zinc phosphate compound and nickel phosphate compound is added to the pure chromium component in an amount of 21 to 2.5% by weight of phosphorus (P) ion; Hydrofluoric acid (HF), sodium hexafluoro silicate (Na ₂ SiF ₆ ), aluminum hexafluoro silicate (Al ₂ (SiF ₆ ) ₃ ), fluorosilic acid (H ₂ SiF ₆ ) and potassium hexafluoro silicate (K _{2 to 10} g / l of the fluorine component of one or more fluorine compounds of SiF ₆ ) is added to the total solution; A corrosion resistance enhancer in the form of colloidal silica is added in an amount of 5 to 25 g / l in the content of silicon oxide (SiO ₂ ) based on the total solution.

Description

Coating of chromate solution for thin-resin coated steel sheet

The present invention relates to a coated chromate solution used in the chromate treatment as a pretreatment in the production of thin film resin coated steel sheet subjected to electrodeposition coating, such as steel sheets for home appliances and automobiles.

Recently, as the demand for high corrosion resistant steel sheet increases in the fields of home appliances, construction materials and automobiles, it is chromateized using various cold rolled steel sheets and plated steel sheets as a part thereof, and resin coating is applied to thin films. Electrodeposition coating for exerting high corrosion resistance or exterior property is performed using such a thin film resin coated steel sheet.

Electrodeposition coating is sometimes used as a part of the film to have high corrosion resistance or exterior properties by using such a thin resin coated steel sheet. In this case, the electrodeposited coating is poorly applied due to the general application of the thin film resin coated sheet under various electrodeposition conditions for each company. This occurs frequently, and in some cases, due to the characteristics of the electrodeposition tanks owned by each company, electrodeposition coating may not be smoothly applied to the thin film resin coated steel sheets. That is, although the cause of electrodeposition coating defect which occurs at the time of electrodeposition coating of thin film resin coated steel sheet is a cause other than steel plate, it is mostly caused by the lack of electrodeposition coating property of steel plate.

The reason why the electrodeposition coating defect is caused by the steel sheet is too large, and if the amount of the resin coating is too large, a substance which impedes electrodeposition coating is mixed in the composition of the resin coating, or a cause due to the chromate coating layer. However, in the case of incorporation of a defect material affecting the electrodeposition coating in the resin coating amount control and resin composition, it can be solved by adjusting the adhesion amount in the process and the exclusion of the mixed material, but in the case of the chromate coating layer before changing the chromate composition Effective coping is impossible.

Japanese Patent Laid-Open No. 6-228763 (name of invention: organic composite steel with excellent corrosion resistance and cationic electrodeposition), Japanese Patent Laid-Open No. 6-228764 (name of invention: organic composite steel sheet with excellent corrosion resistance and cationic electrodeposition), Japanese Patent Laid-Open No. 6-270327 (Invention: Manufacturing Method of Thin Film Organic Composite Steel with Excellent Cationic Electrodeposition and Paint Adhesion), Japanese Patent Application Laid-Open No. 6-272090 (Invention: Manufacturing Method of Thin Film Organic Composite Steel with Excellent Cationic Electrodeposition and Paint Adhesion) ), All of which improve the electrodeposition coating property by containing melamine cyanate as a conductive pigment in the resin coating, and thus the technique of improving the electrodeposition coating property by containing a conductive material in the resin composition is different from the object pursued by the present invention. There is a difference, and even if the conductivity is improved by diarrhea resin coating, if the quality of the chromate film is not this, as shown in the present invention, the electrodeposition coating quality is greatly increased. Crab cannot be improved.

And, Korean Patent No. 094245 (Invention name: Method for producing chromate coating having excellent corrosion resistance and appearance), No. 101828 (Name: Invention name: Method for producing resin solution for chromate-plated steel sheet and resin coated plated steel sheet using same) , No. 1059425 (name of the invention: chromate solution in which chromium elution is suppressed and chromate steel sheet production method using the solution) are all coated chromate solution used in the substrate treatment of resin coated steel sheet, and actually applied to automotive steel sheet Electrodeposit coating is sensitively affected by the electrodeposition coating conditions and sometimes the surface condition of the steel sheet, such as electrodeposition defects due to the change of electrodeposition coating conditions during the process or the appearance characteristics may not be good after electrodeposition coating. appear.

However, what is provided in the present invention is not related to the improvement of electrodeposition coating property by the composition of the resin coating, but is intended to completely eliminate the electrodeposition coating defect by the chromate coating layer by changing the composition of the coating type chromate treatment solution.

Therefore, the present invention has been made to solve the problems of the prior art as described above, while ensuring the electrodeposition coating properties after the thin film resin coating while ensuring the properties such as corrosion resistance and film adhesion, even under highly variable electrodeposition coating conditions. It is an object of the present invention to provide a coated chromate solution used for a thin film resin coated steel sheet which can achieve good electrodeposition coating.

1 is a graph showing the content ratio of olsophosphoric acid and alkali metal phosphate compound according to the present invention.

According to the present invention for achieving the above object, in the pure chromium (Cr) component 10 to 80g / l consisting of chromic anhydride and sodium chromate or ammonium chromate an allophosphoric acid in the amount of phosphorus (P) ions relative to the pure chromium component 21 Hexavalent chromium is reduced after addition of ˜67 wt. At least one selected from the group of alkali metal phosphate compounds such as sodium phosphate compound, zinc phosphate compound and nickel phosphate compound is added to the pure chromium component in an amount of 21 to 2.5% by weight of phosphorus (P) ion; Hydrofluoric acid (HF), sodium hexafluoro silicate (Na ₂ SiF ₆ ), aluminum hexafluoro silicate (Al ₂ (SiF ₆ ) ₃ ), fluorosilic acid (H ₂ SiF ₆ ) and potassium hexafluoro silicate (K _{2 to 10} g / l of the fluorine component of one or more fluorine compounds of SiF ₆ ) is added to the total solution; Provided is a coated chromate solution for use in thin film resin coated steel sheet, in which a corrosion resistance improving agent in the form of colloidal silica is added in an amount of 5 to 25 g / l of silicon oxide (SiO ₂ ) to the total solution.

In addition, according to the present invention, Glycidoxy propyl trimethoxysilane, Methacryloxy propyl methyl dimethoxysilane, Provided is a coated chromate solution for use in thin film resin coated steel sheet which improves chromium elution resistance and top coat coating by additionally adding one silane coupling agent selected from glycidoxy propyl methyl dimethoxysilane. .

In the following, with reference to the accompanying drawings, a preferred embodiment of the coated chromate solution used for the thin film resin coated steel sheet base according to the present invention will be described in detail.

In the drawings, Figure 1 is a graph showing the content ratio of olsophosphoric acid and alkali metal phosphate compound according to the present invention.

In the preparation of the chromate solution of the present invention, a chromium solution of 10 to 80 g / l as pure chromium (Cr) component of chromic anhydride and sodium chromate or ammonium chromate is added to the trivalent chromium component ratio (chromium reduction ratio) relative to the total chromium component. Hexavalent chromium is reduced as a reducing agent so that it becomes 0.4-0.7. At this time, since the reducing agent that can be used has a very strong oxidizing power of hexavalent chromium, the reduction reaction is sufficiently induced by various organic solvents including alcohols, but the reduction reaction using polyvinyl alcohol, citric acid, polysaccharides, starch, etc. Since it is possible to induce, there is no need to specifically limit the type of reducing agent.

In this case, the chromium component in the chromate solution is limited to 10 to 80 g / l, rather than for a clear purpose, the workability is lowered at 10 g / l or lower, and the solution stability may be lowered at 80 g / l or higher in some cases. Because. When the chromium reduction ratio is 0.4 or less, the amount of chromium elution is excessive, which is undesirable for the environment, and at 0.7 or higher, the solution stability is drastically reduced by excessive reduction of hexavalent chromium. In addition, in the reduction reaction, 21 to 67% by weight of oxophosphoric acid is converted to the amount of phosphorus (P) ions with respect to pure chromium components, and then inducing a reduction reaction in terms of the stability of the solution than the subsequent addition. desirable.

The chromate solution after the reduction reaction is selected from the group of alkali metal phosphate compounds such as sodium phosphate compound, zinc phosphate compound, nickel phosphate compound, etc. An alkali metal phosphate compound amount calculated to have an amount of phosphorus (P) ions as much as 2.5% by weight is mixed and added, and the method of addition is shown in FIG. 1.

Figure 1 shows the content ratio of olsophosphate and alkali metal phosphate compound, A is the content of the allophosphoric acid in terms of the content of phosphorus (P) relative to the total chromium component, B is the total content of the alkali metal phosphate compound It is shown in terms of the content of phosphorus (P) relative to the chromium component, and as shown in FIG. 1, the content ratio of the oxophosphoric acid and the alkali metal phosphate compound is more preferably added as shown in Equation 1 in terms of solution stability and physical properties. desirable.

B = -0.402A + 29.4

Here, A represents the phosphorus (P) content (% by weight) of oxophosphoric acid relative to the total chromium component, and B represents the phosphorus (P) content (% by weight) of the alkali metal phosphate compound to the total chromium component.

That is, when the amount of oxophosphoric acid increases, the amount of alkali metal phosphate compound is preferably reduced in inverse proportion and added. However, the content of total phosphorus (P) is less than 64% by weight of the total chromium component in the section other than 21-30% by weight and 58-67% by weight in the section of allophosphoric acid, more than 30 The addition of the alkali metal phosphate compound to the content (wt%) of less than 58 does not differ in the excellent properties even if freely added without following Equation 1 within 21 to 2.5 wt%. In this case, the total phosphorus (P) content is 64% by weight because the improvement in physical properties may not be apparent or the solution stability may be lowered (based on the experiment).

In addition, hydrofluoric acid (HF), sodium hexafluoro silicate (Na ₂ SiF ₆ ), aluminum hexafluoro silicate (Al ₂ (SiF ₆ ) ₆ ), fluoro silicic acid (H ₂ SiF ₆ ), and potassium hexa By adding a fluorine component of one or more fluorine compounds in the fluorosilicate (K ₂ SiF ₆ ) at _{2 to 10} g / l based on the total solution, corrosion resistance and adhesion rate of the chromium compound on the steel sheet can be improved.

In addition, 5-25 g / l of a silicon oxide (SiO ₂ ) content is added to the whole solution in the form of colloidal silica as a corrosion resistance improving agent to prepare a chromate solution. In particular, for the purpose of improving chromium elution resistance, top coat coating, etc., Glycidoxy propyl trimethoxysilane, Methacryloxy propyl methyl dimethoxysilane and Even when a suitable amount of one silane coupling agent selected from -glycidoxy propyl methyl dimethoxysilane is used in a conventional manner with respect to the total chromium component, there is no change in the characteristics suggested by the present invention.

In the above description, the reason for numerical limitation for the oxophosphoric acid and the alkali metal phosphate compound, the fluorine component, and the silicon oxide component will be described in detail below.

The chromate solution prepared by the scope and method of the present invention may be applied using water or diluted to an appropriate concentration if necessary. After drying, the chromium component in the chromate coating is coated with a steel sheet using a roll or a spray so that the chromium component is 20 to 150 mg / m 2, followed by baking at 120 to 200 ° C. Then, a resin coating is performed on the dried coating so as to have a thickness of 0.5 to 2.0 μm thereon, to manufacture a thin film resin coated steel sheet. Matters related to the resin coating may be in accordance with ordinary conditions currently applied. At this time, in the thin film coated steel sheet, the electrodepositable coating property of the pure chromium (Cr) component in the chromate coating is lower than 15 mg / m 2, and the formation of pin holes and the adhesion of the film during electrodeposition coating decreases at 150 mg / m 2 or higher. .

In addition, when the baking temperature is less than 120 ° C. during the chromate treatment, silicon oxide hardly forms the coating. At 200 ° C. or more, hexavalent chromium is almost lost in the coating, causing cracking of the chromate coating, thereby greatly reducing corrosion resistance. When the thickness of the resin film is 0.5 mu m or less, the physical properties of the resin coated steel sheet are not sufficiently secured, and when the thickness of the resin coating is 2.0 mu m or more, the electrodeposition coating property due to the increase in the resin coating amount is reduced.

Hereinafter, an experimental example of the present invention will be described.

After dissolving chromic anhydride in 130 ml / l in 1000 ml of deionized water, oxo phosphoric acid was added in the amount shown in Table 1, and then reduced to a chromium reduction ratio of 0.54 using ethylene glycol as a reducing agent in a cooling bath. Subsequently, alkali metal phosphate compound, fluorine, and silicon oxide components were added in the amounts shown in Table 1, and then diluted with diluted chromate solution. 500 ml of a pre-prepared solution of the glycidoxy propyl trimethoxysilane compound diluted to 0.1 molar concentration is added and finally diluted with deionized water so that the total chromium concentration in the solution is 15 g / l.

The chromate solution thus prepared is coated on a Zn-Ni alloy plated steel sheet to be 60 mg / m 2 as a metal chromium component using a three-stage roll coater, followed by baking at 150 ° C. At this time, in order to examine the effect of the state of the steel sheet and the electrodeposition coating performance, the surface of the steel sheet is contaminated using a sprayer with a normal plated steel sheet and an aqueous solution in which the amount of chlorine, potassium, and sodium ions is 0.1% in the plated steel sheet. Through the analysis, contaminated steel sheet was used to evaluate the surface contamination caused by the ions.

In this way, after a chromate treatment on a steel plate that has been normally plated and a steel plate that is artificially contaminated, a thin film resin coated steel sheet coated with a dry coating thickness of 1.5 μm in a commercially available urethane resin-based coating solution was prepared. Corrosion resistance and top coatability were evaluated in the following manner, and the results are shown in Table 1.

1. Electrodeposition paintability

It consists of the order of baking, and the degreasing solution and electrodeposition paint used in the degreasing process and the respective treatment conditions were composed under the same conditions as those currently used by domestic automobile companies. In addition, the good surface appearance after electrodeposition was evaluated as follows in comparison with the electrodeposition appearance of the plated steel sheet without chromate and resin and the conventional commercial steel sheet.

◎ (Excellent): Appearance of electrodeposition coating surface is similar to electrodeposition coating appearance of plated steel sheet.

○ (good): Improved electrodeposition coating quality compared to commercial materials

△ (lack): fine pinhole

× (Poor): Pinholes and Craters

2. Film adhesion

In order to evaluate the film adhesion of the thin film coated steel sheet, using a melamine alkyd paint, the coating thickness was reduced to 25 to 30 µm, and then immersed in boiling water for 1 hour, followed by a crosscut test (1 mm, 100 scale). The water-tightness performed and the coating-film adhesion after the crosscut test performed in the same manner after 6 mm Eriksen processing were evaluated as the degree of film peeling as follows.

○ (good): No scale peeling

△ (lack): Less than 5 scale peeling occurred in one or more of the two tests

× (poor): 5 or more scale peelings occurred in both tests

3. Corrosion resistance

The salt spray test was carried out according to JIS Z 2371 standard and evaluated by initial 5% white rust development test.

◎ (excellent): More than 600 hours

○ (good): 500 to 600 hours

△ (lack): 400-500 hours

× (bad): less than 400 hours

When the results of Table 1 are described in detail by dividing the invention examples and comparative examples as follows.

Inventive Examples 1-12

As a result of evaluating the quality characteristics of the thin resin coated steel sheet using the chromate solution composed of the conditions maintained in the present invention as a base treatment, the excellent characteristics as shown in Table 1 were obtained.

Comparative Examples 1 and 2

When the content range of oxophosphate is higher and lower than the range of the present invention, the electrodeposition coating quality is reduced, such as pinholes and craters, and in particular, the hydrophilicity of the chromate layer is increased by the excessive addition of phosphoric acid. Due to this, coating film adhesion and corrosion resistance were also reduced.

Comparative Examples 3 and 4

When the content range of the alkali metal phosphate compound is higher than the range suggested by the present invention, not only the electrodeposition coating quality but also the solution stability such as promoting the gelation of the solution is lowered.

Comparative Examples 5 and 6

When the fluorine content is less than the range suggested by the present invention, the adhesion rate of chromium decreases due to the lack of etching force of the steel sheet, and the corrosion resistance decreases.

Comparative Examples 7 and 8

In the present invention, when the amount of silicon oxide added as the corrosion resistance improving agent is less than the range of the present invention, it does not exhibit sufficient corrosion resistance, and when a large amount is added, the corrosion resistance no longer increases, but rather the film adhesion is poor, and electrodeposition coating It also affects quality.

Comparative Examples 9 and 10

When the content of phosphorus (P) in the range proposed in the present invention is more than 64% by weight of total phosphorus (P) ions in the solution when the content of allophosphoric acid is in the range of more than 30 and less than 58 (% by weight). In this case, the improvement of electrodeposition coating quality did not appear, but rather, the film adhesion was reduced.

As described in detail above, the electrodeposition coating defect due to the chromate coating characteristics is not limited to the composition of the resin coating under various electrodeposition coating conditions on the steel plate subjected to the thin film resin coating using the coated chromate solution having excellent electrodeposition coating properties of the present invention. As it is possible to eliminate the electrodeposition coating, the chromium treatment for the base film of the thin film coated steel sheet subjected to electrodeposition coating is greatly improved, and it is also excellent in other physical properties exhibited by the chromate coating such as corrosion resistance and film adhesion. Even the base treatment of the resin coated steel sheet can exhibit excellent properties. Therefore, the coated chromate solution of the present invention can be used for various purposes.

Although the technical idea of the coated chromate solution used for the thin film resin coated steel sheet of the present invention has been described above with the accompanying drawings, this is illustrative of the best embodiment of the present invention and is not intended to limit the present invention. .

In addition, it is obvious that any person skilled in the art can make various modifications and imitations without departing from the scope of the technical idea of the present invention.

Claims (3)

10-80 g / l of pure chromium (Cr) component consisting of chromic anhydride and sodium chromate or ammonium chromate is added 21-67% by weight of allophosphoric acid in terms of the amount of phosphorus (P) to the pure chromium component, and then the hexavalent chromium is reduced. Trivalent chromium component ratio (chromium reduction ratio) to total chromium component so as to be 0.4 to 0.7; At least one selected from the group of alkali metal phosphate compounds such as sodium phosphate compound, zinc phosphate compound and nickel phosphate compound is added to the pure chromium component in an amount of 21 to 2.5% by weight of phosphorus (P) ion; Hydrofluoric acid (HF), sodium hexafluoro silicate (Na ₂ SiF ₆ ), aluminum hexafluoro silicate (Al ₂ (SiF ₆ ) ₃ ), fluorosilic acid (H ₂ SiF ₆ ) and potassium hexafluoro silicate (K _{2 to 10} g / l of the fluorine component of one or more fluorine compounds of SiF ₆ ) is added to the total solution; A coated chromate solution for use on a thin film resin coated steel sheet, which is characterized by adding 5 to 25 g / l of a colloidal silica-type corrosion resistance improver in a silicon oxide (SiO ₂ ) content with respect to the total solution. The coated chromate solution according to claim 1, wherein the alkali metal phosphate compound is added by the following formula 1 to improve electrodeposition coating, corrosion resistance and coating adhesion. Equation 1 B = -0.402A + 29.4 Here, A represents the phosphorus (P) content (% by weight) of oxophosphoric acid relative to the total chromium component, and B represents the phosphorus (P) content (% by weight) of the alkali metal phosphate compound to the total chromium component. The method according to claim 1 or 2, Glycidoxy propyl trimethoxysilane, Methacryloxy propyl methyl dimethoxysilane, Coating type chromate used for the base plate of the thin film resin coated steel sheet, characterized by improving the chromium elution resistance and the top coatability by additionally adding one silane coupling agent selected from glycidoxy propyl methyl dimethoxysilane. solution.