JP4344219B2 - Inorganic organic composite-treated zinc-coated steel sheet with excellent corrosion resistance after electrodeposition coating - Google Patents

Description

The present invention relates to an inorganic / organic composite-treated galvanized steel sheet excellent in corrosion resistance after electrodeposition coating .

  Conventionally, galvanized steel sheets used for applications such as automobiles, home appliances, and building materials have been generally subjected to phosphate treatment and chromate treatment for the purpose of improving corrosion resistance and coating film adhesion. In particular, the method of performing the sealing treatment with chromate after the zinc phosphate treatment has been widely practiced because it has a great effect on improving the corrosion resistance and paint adhesion. However, in recent years, against the background of increasing environmental problems, development of surface treatment technology that does not use highly toxic chromate is desired, and the following technologies have been proposed.

On the surface of the zinc-based plated steel sheet, the first layer has a zinc phosphate-treated film layer having an adhesion amount of 0.2 to 2.5 g / m ² containing at least one selected from nickel, manganese and magnesium. The zinc phosphate composite-treated steel sheet having an organic film mainly composed of at least one organic resin selected from ethylene resin, epoxy resin, urethane resin and acrylic resin as a second layer on the upper part Is disclosed (for example, see Patent Document 1).

The surface of the steel sheet, zinc-based plated coating, 0.3 g / m ² or more zinc phosphate coating, and organic coating of 0.3 to 2 g / m ² are sequentially formed, zinc film phosphate containing Mg An organic composite zinc-based plated steel sheet having an Mg / P (mass ratio) of 0.15 or more and an Mg amount of 20 mg / m ² or more in a zinc phosphate-treated film is disclosed (for example, see Patent Document 2). .)

  The galvanized steel sheet subjected to such treatment is usually used as it is or after being pressed and alkali degreased and washed. For this reason, both corrosion resistance without painting and corrosion resistance after painting are required.

However, the zinc phosphate composite-treated steel sheet and organic composite zinc-based plated steel sheet obtained by the method as described above are not so strongly bonded in a corrosive environment between the zinc phosphate coating and the organic coating, and are electrodeposited. In an environment where the wet rate is extremely high, peeling occurs between the zinc phosphate film and the organic film, resulting in insufficient corrosion resistance after electrodeposition coating.

JP 2001-105528 A (page 2) Japanese Patent Laid-Open No. 2001-131863 (2nd page)

SUMMARY OF THE INVENTION In view of the above situation, the present invention aims to provide an inorganic / organic composite-treated zinc-based plated steel sheet that does not contain harmful chromate in the treated film and that provides excellent corrosion resistance after electrodeposition coating. It is.

A method for enhancing the bond between a zinc phosphate coating and an organic coating in a corrosive environment in a zinc-plated steel plate with an inorganic and organic composite that has excellent corrosion resistance after electrodeposition coating with a zinc phosphate coating and an organic coating on the zinc coating As a result of various investigations, the present inventors have found that the state of the Zn plating layer that is the base of the zinc phosphate coating has a great influence, and have reached the present invention.
That is, the gist of the present invention is that a steel plate has a Zn plating layer having a (002) plane crystal orientation of 65% or more, a zinc phosphate film containing Mg as an upper layer, and an upper layer thereof. the organic coating layer possess a is the in the zinc phosphate coating Mg / P (weight ratio) is 0.1 or more, the corrosion resistance after electrodeposition painting that features the Mg amount is 20 mg / m ² or more Ru excellent inorganic-organic composite-treated zinc-based plated steel sheet der to.
Moreover, it is desirable that the organic film layer contains an epoxy resin and / or a modified epoxy resin, and the organic film layer has an adhesion amount of 0.3 to 5 g / m ² .

The inorganic-organic composite-treated galvanized steel sheet excellent in corrosion resistance after electrodeposition coating of the present invention does not use chromate, provides good corrosion resistance, is simple in manufacturing method, and is excellent in cost. It can use suitably for various uses, such as.

Hereinafter, the present invention will be described in detail.
The Zn plating layer of the inorganic / organic composite-treated zinc-based plated steel sheet having excellent corrosion resistance after electrodeposition coating of the present invention may be any means such as electroplating or hot dipping, but the (002) plane crystal orientation is 65% or more. It is necessary to be. Here, the crystal orientation of the (002) plane means that each peak intensity of the Zn plated crystal is measured by an X-ray diffractometer, and the peak intensity of the plane corresponding to the (002) plane is divided by the sum of the peak intensities. It is defined as a percentage. The adhesion amount of the Zn plating layer is not particularly limited, but is desirably 20 g / m ² or more when higher corrosion resistance is required.

The reason why the (002) plane crystal orientation is limited to 65 % or more is that if it is less than 65 %, the corrosion resistance deteriorates. The reason why good corrosion resistance can be obtained at 65 % or more is not clear enough, but in part, the properties of the zinc phosphate film formed on the plated layer in such a state change, This is probably because the adhesion is improved. In addition, even when there is a portion where the Zn plating layer is exposed without being covered with the zinc phosphate coating, the adhesion between the plating layer and the upper organic coating layer is achieved by adopting a predetermined plating layer structure. Is considered to be better.

  In order to keep the crystal orientation of the (002) plane high, plating may be performed under a condition that the precipitation overvoltage of Zn is low. Specifically, it can be controlled by the plating bath concentration, current density, etc., and the (002) plane orientation can be increased by increasing the Zn ion concentration of the plating bath or decreasing the plating current density.

  The zinc phosphate-treated film can be formed by a conventionally known zinc phosphate treating agent containing phosphate ions and zinc ions. The zinc ion supply source is not particularly limited as long as it is a compound containing zinc, and examples thereof include zinc, zinc oxide, zinc carbonate, and zinc nitrate. The phosphate ion supply source is not particularly limited as long as it is a compound containing phosphoric acid, and examples thereof include phosphoric acid, phosphorus pentoxide, and sodium dihydrogen phosphate. Moreover, you may contain suitably the other component used for a zinc phosphate processing agent. The zinc phosphate-treated film needs to contain Mg. Furthermore, it is preferable that Ni, Mn, Co, Cu, Fe, etc. are contained alone or in combination. Thereby, the corrosion resistance of a galvanized steel sheet can be improved more, and adhesiveness with a post-process film can be improved.

The zinc phosphate-treated film preferably has a magnesium / phosphorus (mass ratio of magnesium and phosphorus in the film) of 0.1 or more. If it is less than 0.1, there is a risk that the corrosion resistance will not be improved by the addition. In the zinc phosphate-treated film, the amount of magnesium in the film is preferably 20 mg / m ² or more. If it is less than 20 mg / m ² , the corrosion resistance may not be improved.
The zinc phosphate-treated film is desirably formed with a film amount having a lower limit of 0.3 g / m ² and an upper limit of 5 g / m ² . If it is less than 0.3 g / m ² , the corrosion resistance may be insufficient. If it exceeds 5 g / m ² , peeling of the film may occur when severe processing is performed.

  As the treatment liquid for forming the zinc phosphate-treated film, a commercially available treatment containing phosphate ions and zinc ions as main components, and metal ions other than zinc, nitrate ions, fluoride ions and the like are added as necessary. Liquid can be used. When magnesium is contained in the zinc phosphate-treated film, a bath in which magnesium nitrate or the like is added to the zinc phosphate treatment solution is preferably used. The amount of magnesium in the coating and the magnesium / phosphorus ratio can be controlled by the amount of magnesium nitrate added.

  As a zinc phosphate treatment method for a zinc-based plated steel sheet using the zinc phosphate treatment agent, a zinc phosphate treatment film can be formed by any of a reactive treatment and a coating treatment. As the reactive treatment, for example, after degreasing, rinsing and surface adjustment of a zinc-based plated steel sheet, the zinc phosphate treatment film is formed by contacting with the zinc phosphate treatment solution, washing and drying. Can do. The coating amount of the zinc phosphate-treated film can be adjusted, for example, by changing the treatment time or the treatment agent concentration.

  As the coating type treatment, for example, the zinc phosphate-treated steel sheet is applied to the zinc-based plated steel sheet by a roll coating method in an amount corresponding to the required coating amount, and after being applied by a dipping method or a spray method, a roll squeezing method There is also a method of adjusting to a necessary coating amount. A zinc phosphate treatment film is formed by applying a zinc phosphate treatment agent to a zinc-based plated steel sheet and then drying it using a drying furnace or the like.

The inorganic-organic composite-treated zinc-based plated steel sheet having excellent corrosion resistance after electrodeposition coating according to the present invention has an organic film layer on the zinc phosphate-treated film, thereby further improving the corrosion resistance. The organic coating layer contains an organic resin, and various rust preventive additives and crosslinking agents can be blended for the purpose of improving corrosion resistance. Depending on the purpose, a wax component for imparting slidability, a pigment for imparting designability, and the like can also be blended.

The organic resin desirably contains an epoxy resin and / or a modified epoxy resin from the viewpoint of adhesion. The adhesion amount of the organic coating layer is desirably 0.3 to 5 g / m ² , and if it is less than the lower limit, the corrosion resistance is not sufficient, and if it exceeds the upper limit, welding may be difficult.

  The organic coating layer can be formed by applying and drying by a method such as coater, spray, dip and the like.

  The zinc phosphate treatment layer of the present invention is preferably treated on both surfaces, but the organic coating layer may be treated on at least one surface, that is, the surface most required for corrosion resistance without coating. .

  Hereinafter, the present invention will be described in detail by way of examples.

(Galvanized steel sheet)
In the electrogalvanized steel sheet production line, various zinc plated steel sheets with different Zn crystal orientations were manufactured by adjusting the plating bath concentration and the plating current density at a Zn deposition amount (per one side) of 40 g / m2.

(Zinc phosphate treatment)
The electrogalvanized steel sheet was subjected to alkaline degreasing, followed by a commercially available TiO2 colloidal surface conditioning treatment and a zinc phosphate treatment. The zinc phosphate treatment solution uses Zn ion 2.5 g / l, Ni ion 2.0 g / l, Mn ion 2.5 g / l, Mg ion 15 g / l, PO ₄ ion 14 g / l, spray method Was treated at a temperature of 45 ° C. for a treatment time of 1 to 10 seconds, washed with water and dried.

(Organic film treatment)
An organic film treatment was performed using the zinc phosphate-treated galvanized steel sheet. The organic film treatment is based on a water-based resin in which a block-modified isocyanate curing agent, a modified polyethylene wax, and a condensed azo-based red pigment are blended into a vinyl-modified epoxy ester resin (each solid content weight ratio is 100: 10: 5: 3). Then, using a coating material in which colloidal silica was added to a solid content weight ratio of 16%, it was applied by a roll coater, and then baked to reach 150 ° C. at the ultimate plate temperature and cooled with water.

(Performance evaluation method)
(002) plane crystal orientation; RINT2000 manufactured by RIGAKU was used to scan 2θ5 to 90 ° (4 ° / min) with tube Cu, 40 kV / 200 mA, and the peak intensity of each crystal plane of Zn was measured. The (002) plane orientation ratio was determined by dividing the intensity by the sum of the peak intensity of each crystal plane.

  The amount of Mg and P in the zinc phosphate coating; all of the coating was dissolved and quantified by ICP analysis. The amount of zinc phosphate coating was calculated from the amount of P, assuming the structure of Hopeite.

Organic film amount: Si was quantified by fluorescent X-ray analysis, and converted from the composition ratio to the film amount.
Uncoated corrosion resistance; after washing the sample with commercially available cleaning oil, U bead bending (sample width 70 mm, BHF = 1 ton, processing height = 70 mm, bead part punch R = 5 mm, bead part die R = 3 mm, punch R = 5 mm, dice R = 5 mm, processing speed = 25 spm), the side surface (die side) was cut out and degreased, and then the end surface and back surface were sealed with a tape, and a CCT test * was performed. The occurrence of red rust after 15 cycles was observed. “◯”; less than 1%, “Δ”; 1 to 10%, “×”;

  Coating adhesion; after subjecting the sample to a commercially available alkaline degreasing solution (pH = 10.5, 40 ° C., 1 minute immersion), chemical conversion treatment for automobiles (Surfdyne 2500MZL manufactured by Nippon Paint), cationic electrodeposition coating for automobiles ( (Nippon Paint V20, 20μ, 170 ° 20 minutes baking). After being left for a whole day and night, it was immersed in warm water at 50 ° C., taken out after 10 days, put in a grid cut with 1 mm intervals, and peeled off with cello tape. “◯”: no peeling, “Δ”: peeling around the cut ridge, “×”: peeling.

  Corrosion resistance after painting; after subjecting the sample to a commercially available alkaline degreasing solution (pH = 10.5, 40 ° C., 1 minute immersion) and chemical conversion treatment for automobiles (Surfdyne 2500MZL manufactured by Nippon Paint), cationic electrodeposition coating for automobiles ( (Nippon Paint V20, 20μ, 170 ° 20 minutes baking). After that, a crosscut punch that reaches the ground iron was attached and a CCT test * was conducted. The swelling width after 20 cycles was measured. “◯”: less than 1 mm, “Δ”: 1-2 mm, “×”: more than 2 mm.

  * CCT test conditions: salt spray (5% NaCl, 35) 6 hours → dry (50 ° C. 45% RH) 3 hours → wet (50 ° C. 95% RH) 14 hours → dry (50 ° C. 45% RH) 1 hour, Was repeated as one cycle.

  The above evaluation results are shown in Table 1.

  In the examples of the present invention, compared with the case where good characteristics were obtained, the characteristics of the comparative examples that were out of the scope of the present invention were deteriorated.

  The inorganic-organic composite-treated zinc-based plated steel sheet of the present invention does not use chromate, provides good corrosion resistance, is simple in manufacturing and excellent in cost, and is suitable for various applications such as automobiles, home appliances, and building materials. Can be used.

Claims (2)

Has a Zn plating layer on the (002) plane crystal orientation of 65% or more of the steel sheet has a zinc phosphate coating containing Mg as an upper layer, further the organic coating layer possess thereon, the phosphorus Inorganic-organic composite-treated zinc-based plating with excellent corrosion resistance after electrodeposition coating, characterized in that Mg / P (mass ratio) in the zinc oxide film is 0.1 or more and the Mg amount is 20 mg / m ² or more steel sheet. ^{2. The} corrosion resistance after electrodeposition coating according to claim 1 , wherein the organic coating layer contains an epoxy resin and / or a modified epoxy resin, and the adhesion amount of the organic coating layer is 0.3 to 5 g / m ^2. An excellent inorganic-organic composite-treated galvanized steel sheet.