JPH11302863A - Galvanized steel sheet excellent in working adhesion of coating and waterproof secondary adhesion of coating, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvanized steel sheet which is used for a coated steel sheet coated with vehicle type coating, water base coating, or powder coating and has excellent working adhesion and waterproof secondary adhesion and is easy to manufacture. SOLUTION: The galvanized steel sheet for coated steel sheet is a surface treated steel sheet prepared by forming a zinc or zinc-alloy plating layer and a chemical conversion treatment layer on a steel sheet. At this time, the chemical conversion treatment layer contains two kinds of fumed silica having 14-10 nm primary particle size and 9-5 nm primary particle size, respectively, and a chromic acid compound. Moreover, the blending ratio by weight, SiO2 /Cr, in the case where the coating weight of the fumed silica is expressed in terms of SiO2 and the coating weight of the chromic acid compound is expressed in terms of metallic Cr is regulated to 3<6, and further, the coating weight of Cr is regulated to (25 to 55) mg/m<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to zinc, a galvanized steel sheet, and a method for producing the same, which can provide a coated steel sheet having excellent workability and secondary water resistance.

[0002]

2. Description of the Related Art In recent years, there has been a strong demand for high-performance coated steel sheets that can be processed at a high level and that do not peel off paint even when exposed to a severe environment for home appliances and building materials. From the viewpoint of corrosion resistance, zinc-plated steel sheets are mainly used for these steel sheets, and a phosphate treatment or a coating-type chromate treatment is performed as a pretreatment for a base. However, these steel sheets do not always have sufficient properties as shown below.

Conventionally, phosphate treatment has been generally used, but the treatment process is complicated, and enormous equipment is required for high-speed production, which is disadvantageous in terms of production cost. In addition, it is a crystalline film, and when subjected to a high degree of processing, the crystal is destroyed, and even when coated with a paint having excellent ductility, it is easily peeled off due to the destruction of phosphate.

On the other hand, the chromate film is an amorphous film and has a small amount of adhesion, which is considered to be advantageous for the adhesion at the time of molding, and a film which can sufficiently withstand use for painting has been developed. ing. However, the secondary adhesiveness when immersed in warm water for a long period of time is inferior to that of phosphates, and a product having the same characteristics has not been obtained. For example, JP-A-52-17340, JP-A-60-86
No. 282, Japanese Unexamined Patent Publication No. 61-585, etc., are those in which fumed silica is added to chromic acid. When these are applied to a coated steel sheet, secondary adhesion equivalent to that of phosphate is obtained. I can't get it. Further, as shown in JP-B-56-36869, etc., as a pretreatment of chromate,
There is a means for performing Co or Ni treatment. According to this method, although there is an effect in improving the processing adhesion, the number of processing steps is two, which is not preferable from the viewpoint of manufacturing cost, and only water resistance secondary adhesion that is inferior to that of the phosphate treatment can be obtained. Not.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is used for a solvent-based, water-based, or powder-coated steel sheet, and has a processing adhesion of a phosphate or more, and a water-resistance. It is an object of the present invention to provide a galvanized steel sheet which has excellent secondary adhesion and can be easily manufactured.

[0006]

Means for Solving the Problems According to the present invention, as a result of intensive studies to solve the above problems, fumed silica having a specific range of particle diameter is mixed with a chromic acid solution having a specific Cr reduction ratio and a specific composition. It has been found that by forming a chemical conversion treatment layer with the amount and specific amounts of Cr and SiO ₂ deposited, excellent characteristics can be obtained in both processing adhesion and water-resistant secondary adhesion, and the present invention has been completed.

That is, according to the present invention, a primary particle diameter of 14 nm or less and 10 nm or more and 9 nm or less and 5 n
m or more of fumed silica and a chromic acid compound, and when the total amount of the fumed silica is converted to SiO ₂ and the amount of the chromic acid compound is converted to metal Cr, the compounding ratio is 3 / SiO ₂ / Cr. Not less than 6 and desirably,
3.5 or more and 5.5 or less, and the Cr adhesion amount is 25 m
g / m ² or more and 55 mg / m ² or less, desirably 30 m
g / m ^{2 to} 50 mg / m ² , more preferably SiO
_{2 The} adhesion amount is 85 mg / m ² or more and 240 mg / m ² or less,
In particular, a chemical conversion treatment layer of 100 mg / m ^{2 to} 190 mg / m ² is formed.

Further, in order to form the chemical conversion treatment layer, as a treatment liquid, a part of chromic acid is reduced on the surface of a zinc- or zinc-based alloy-coated steel sheet, and unreduced chromium (Cr ⁶⁺ ) and a reduction product ( (Cr ³⁺ ) in a weight ratio of Cr ³⁺ / (Cr ⁶⁺ + Cr ³⁺ ) in terms of Cr of 0.35 or more.
A chromic acid solution having a primary particle diameter of 55 nm or less and a fumed silica having a primary particle diameter of 14 nm or less and 9 nm or less and 5 nm or more are converted into the total added weight of the fumed silica in terms of SiO ₂ , and the added weight of the chromate compound is defined as metal Cr. Using a processing liquid having a conversion ratio of 3 to less than 6, preferably 3.5 to 5.5 in terms of SiO ₂ / Cr when converted, apply this processing liquid and apply a plate temperature of 60 ° C. or higher without washing with water. 25
It is dried at 0 ° C. or less, desirably at 100 ° C. or more and 200 ° C. or less, and has a Cr adhesion amount of 25 mg / m ² or more and 55 mg / m ² or less, and a preferable SiO ₂ adhesion amount of 85 mg / m ² or more.
A chemical conversion treatment layer of not more than mg / m ² is formed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. The present invention relates to a galvanized steel sheet having a chemical conversion treatment layer on a steel sheet having a zinc-based plating layer formed thereon, and a solvent-based, water-based, or powder-coated steel sheet is used on this steel sheet. Can be

(Type of steel sheet) The galvanized steel sheet to be used in the present invention is a hot-dip galvanized steel sheet, an electric galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, a Zn-Al or Al-Zn alloy plating. Any of steel plates may be used.

(14 nm ≧ particle size of fumed silica ≧
10 nm and 9 nm ≧ fumed silica particle diameter ≧ 5 n
m) The chemical conversion treatment layer contains fumed silica and a chromate compound, and has a primary particle diameter of 14 nm as fumed silica.
By including two types of fumed silicas of 10 nm or more and 9 nm or less and 5 nm or more, both excellent processing adhesion and water-resistant secondary adhesion are obtained. 14n
When silica alone having a diameter of m or less and 10 nm or more, or silica having a diameter of 14 nm or more and silica having a diameter of 9 nm or less and 5 nm or more are mixed, processing adhesion becomes insufficient. Also, 9nm
The silica having a thickness of 5 nm or more alone is inferior in water-resistant secondary adhesion. Note that silica having a diameter of less than 5 nm is not currently commercially available. The preferred blending ratio of the two types of fumed silica having a primary particle diameter is 14 nm or less and 10 nm or more of SiO ₂ and 9%.
The weight ratio of SiO _{2 not} more than 5 nm or more is 4/1 to 1 /
3. As fumed silica having a size of 14 nm or less and 9 nm or more, for example, AEROSI manufactured by Japan Aerosil Co., Ltd.
L200, for example, as fumed silica having a thickness of 9 nm or less and 5 nm or more, for example, AE manufactured by Japan Aerosil Co., Ltd.
ROSIL300.

It should be noted that within a range that does not impair the effects of the present invention,
Fumed silica having a primary particle diameter value outside the range of the present invention may be contained. (3 ≦ SiO ₂ / Cr <6) (25 mg / m ² ≦ Cr adhesion amount ≦ 55 mg / m ² ) As a result of examining the effect of fumed silica as a coating base, the present inventors have found that processing adhesion can be obtained only with silica. It was found that both water resistance and secondary adhesion were not obtained, and it was necessary to contain a predetermined amount of a chromic acid compound. The ratio of fumed silica to the chromic acid compound (ratio of SiO ₂ / Cr) is 3
Not less than 6 and the Cr adhesion amount is not less than 25 mg / m ^{2 and not} more than 55 mg
/ M ² or less. If the SiO ₂ / Cr ratio is less than 3, water-resistant secondary adhesion is poor, and if it is 6 or more, processing adhesion is poor. Furthermore, the Cr adhesion amount is 25 mg / m
^If it is less than ² , water-resistant secondary adhesion is poor, and if it exceeds 55 mg / m ² , processing adhesion is poor.

(85 mg / m ² ≦ SiO ₂ adhesion amount ≦ 24
0 mg / m ² ) The SiO ₂ adhesion amount is preferably 85 mg / m ² or more and 240 mg / m ² or less, particularly 100 mg / m ² or more and 190 m, for processing adhesion and water-resistant secondary adhesion.
g / m ² or less is desirable. If the amount of SiO ₂ adhered is too small, the water-resistant secondary adhesion becomes poor, and if it is too large, the film becomes poor in processing adhesion.

Next, a method of manufacturing the galvanized steel sheet for a coated steel sheet according to the present invention as described above will be described. (0.35 ≦ Cr ³⁺ / (Cr ⁶⁺ + Cr ³⁺ ) ≦ 0.55) In order to obtain a chemical conversion treatment layer that satisfies the above-mentioned processing adhesion and water-resistant secondary adhesion, a Cr reduction ratio of 0. 35 or more and 0.55
It must be mixed with the following chromic acids. Cr reduction rate 0.
It has been found that when mixed with chromic acid of 35 or more and 0.55 or less, processing adhesion and water-resistant secondary adhesion can be satisfied. If the Cr reduction ratio is less than 0.35, no working adhesion is obtained, and if it exceeds 0.55, the water-resistant secondary adhesion is poor. Also,
If the reduction ratio is excessively high, the treatment liquid tends to gel, and as a countermeasure, phosphoric acid or a fluorine compound may be added, but these additions adversely affect water-resistant secondary adhesion and processing adhesion. And should be minimized. As a range that does not require the addition of phosphoric acid, a fluorine compound, or the like and is excellent in the stability of the processing solution, the Cr reduction ratio is desirably 0.35 or more and 0.45 or less.

(1 ≧ PO ₄ / Cr) According to the study of the present inventor, the amount of phosphoric acid is calculated as PO ₄ and P
When O ₄ / Cr exceeds 1, the water-resistant secondary adhesion decreases.
Therefore, the addition amount PO ₄ / Cr is preferably 1 or less.

When a chromate solution is applied to the surface of the steel sheet and dried, an organic substance having a Cr ⁶⁺ reducing ability, an emulsion resin, or the like can be added for the purpose of reducing Cr ⁶⁺ to Cr ³⁺ . However, when the addition amount is increased, the processing adhesion and the water-resistant secondary adhesion are reduced, and the stability of the treatment liquid is also reduced. Therefore, it is necessary to select the type and the addition amount of the additive so as not to cause any trouble. In the present invention, the addition of phosphoric acid, a hydrofluoric acid compound, an organic substance, an emulsion resin or the like is possible as long as there is no problem, and the addition of these substances is not denied.

(Coating method) As a coating method of the treatment liquid,
A method capable of continuous and uniform deposition is applied. As such a method, there is a method of adjusting the amount of adhesion by roll coating or gas squeezing by spray coating, or a method of coating by a roll coater. The application method is not particularly limited, but any method can be used as long as uniform application is possible within a range that can satisfy the effects of the present invention.

(60 ° C. ≦ plate temperature ≦ 250 ° C.) After applying the chromic acid treatment liquid, the plate temperature is changed from 60 ° C. to 250 ° C.
To form a chemical conversion treatment layer.
Does not require washing after drying. If the temperature is excessively low, the solubility of chromate increases, and the water-resistant secondary adhesion decreases. In addition, the film becomes too brittle and the film becomes brittle, and the processing adhesion decreases. A preferred range is from 100 ° C to 200 ° C.

When the present invention is applied to a coated steel sheet, a pretreatment such as alkali degreasing is not performed before applying the paint,
Excellent adhesion even when paint is applied directly, and does not require management such as wastewater treatment.

[0020]

Embodiments will be described below. Sheet thickness 0.5
mm hot-dip galvanized steel sheet (zinc coating amount per side 120
g / m ² ) of a chromate treatment solution adjusted to the composition shown in Table 1 by a roll coater, and dried by a hot-air drying furnace under the condition that the plate temperature reaches 100 ° C. to obtain a test material. The adhesion amounts of Cr and SiO ₂ were measured by X-ray fluorescence. Further, the SiO 2 in the chemical conversion treatment layer formed by this method is used.
_{The 2} / Cr ratio was the same as the ratio in the processing solution.

The chromate-treated galvanized steel sheet is coated with an acrylic paint to a dry film thickness of 30 μm without washing with hot water or alkali degreasing.
The sample baked at 20 ° C. was used as an evaluation sample. For comparison, a paint treated under the same conditions as the phosphate treatment (0.8 g / m ^{2 of} zinc phosphate attached, 8 mg / m ² of Cr attached by chromium rinse) was used.

Evaluation method Working adhesion; sample size: width 30 mm × length 120 m
A strip having a length of m was drawn, stretched 30% in the length direction in the range of the gauge length of 50 mm, and the coating film was cut so that the center of the sample did not reach the plating in the width direction. A 3T bending was performed around the cut portion, and the degree of film peeling was visually determined.

Water-resistant secondary adhesion; sample size width 30 m
A strip of mx 120 mm in length was prepared, and the coating was cut so that the center of the sample did not reach the plating in the length direction, and was immersed in boiling water for 5 hours. Thereafter, a peeling test was performed around the cut portion with an adhesive tape, and the degree of film peeling was visually determined.

The evaluation criteria for processing adhesion are shown below. 5: No peeling at all 4; There is a locally floating part at the processed part head (less than 10%) 3: There is a locally floating part at the processed part head (10% or more) There is a part where the part reaches further inside from the machined part head (less than 10%) 1; There is a part where the peeled part reaches further inside from the machined part head (more than 10%) The evaluation criteria are shown below.

5: No peeling at all 4; Peeling of less than 1 mm from the crosscut 3; Peeling of 1 mm or more and less than 3 mm from the crosscut 2; Peeling of 3 mm or more and less than 5 mm from the crosscut 1; 5 mm or more from the crosscut Table 2 shows the evaluation results of processing adhesion and water-resistant secondary adhesion.
Put together.

[0026]

[Table 1]

[0027]

[Table 2]

No. 1. Indicates that the Cr reduction ratio of the treatment liquid is lower than the range of the present invention, and the formed film is a film inferior in both processing adhesion and water-resistant secondary adhesion. No. In No. 4, the Cr reduction ratio of the treatment liquid is higher than the range of the present invention, and there is a problem in the stability of the treatment liquid, and the formed film has poor processing adhesion. No. 5 is S
iO ₂ / Cr is smaller than the range of the present invention, and is inferior in water-resistant secondary adhesion. No. In No. 7, SiO ₂ / Cr is larger than the range of the present invention, and the work adhesion is inferior. No. No. 6 is a comparative example in which 16 nm silica and 9 nm or less and 5 nm or more silica were mixed, and the processing adhesion was poor. No. No. 8 is an example in which silica particles having a silica particle diameter of 14 nm or less and 10 nm or more are added alone, and has the same properties as a phosphate, but has insufficient processing adhesion. No. 14 is a silica particle diameter of 9
This is an example in which silica particles having a diameter of 5 nm or more are added alone, and the water-resistant secondary adhesion is poor. No. No. 9 has a smaller Cr adhesion amount than the range of the present invention, and is inferior in water-resistant secondary adhesion. No.
No. 13 has a larger Cr adhesion amount than the range of the present invention and is inferior in processing adhesion. No. Nos. 15 and 16 show the case where an anion which is a soluble component was added, and both of these were inferior in water-resistant secondary adhesion and processing adhesion due to the influence thereof. Example of the present invention (No.
In 2, 3, 10, 11, and 12), a complicated treatment step such as phosphate treatment is not required, and processing adhesion and water-resistant secondary adhesion equal to or higher than that of phosphate treatment can be obtained. Have been.

[0029]

As described above, according to the galvanized steel sheet for coated steel sheet of the present invention and the method for producing the same, a conventional phosphorous coating excellent in processing adhesion and water-resistant secondary adhesion can be obtained by a simple chemical conversion treatment method. Properties that surpass the zinc acid treatment can be obtained. Therefore, the industrial value of the present invention is extremely high as a technique for dramatically improving the productivity of coated steel sheets.

Claims (2)

[Claims] A surface-treated steel sheet having a zinc or zinc-based alloy plating layer and a chemical conversion treatment layer formed on a steel sheet,
The chemical conversion treatment layer has a primary particle diameter of 14 nm or less and 10 nm.
Mixing ratio when two or more kinds of fumed silica and chromate compound of 5 nm or more and 9 nm or less and the total amount of fumed silica is converted to SiO ₂ and the amount of chromate compound is converted to metal Cr. Is SiO _{2 in} weight ratio
/ Cr is 3 or more and less than 6, and the Cr adhesion amount is 25 m
A galvanized steel sheet for coated steel sheet having excellent work adhesion and secondary water resistance, characterized in that the g / m ^{2 is} 55 g / m ² or more and 55 mg / m ² or less. 2. A step of applying a chromic acid treatment liquid to the surface of a zinc or zinc-based alloy-plated steel sheet, and drying the steel sheet coated with the chromic acid treatment liquid at a sheet temperature of 60 ° C. or more and 250 ° C. or less without washing with water. 25mg / m ² or more and 55mg
/ M ² or less, the chromic acid treatment liquid reduces a part of chromic acid, and the ratio of unreduced chromium (Cr ⁶⁺ ) to the reduced product (Cr ³⁺ ) is converted to Cr. Of a chromic acid solution having a weight ratio of Cr ³⁺ / (Cr ⁶⁺ + Cr ³⁺ ) of not less than 0.35 and not more than 0.55 and a fumed silica having a primary particle diameter of not less than 10 nm and not more than 9 nm and not less than 5 nm When the total weight of the added fumed silica is converted to SiO ₂ and the weight of the chromic acid compound is converted to metal Cr, the compounding ratio is 3 or more and less than 6 in SiO ₂ / Cr. A method for producing galvanized steel sheets for painted steel sheets with excellent processing adhesion and secondary water resistance.