JPH11302864A - Coated galvanized steel sheet excellent in workability and corrosion resistance, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated galvanized steel sheet which is excellent in workability (adhesion in a working part), waterproof adhesion, edge corrosion resistance, and corrosion resistance in a crosscut part and is easy to manufacture. SOLUTION: The coated galvanized steel sheet is a coated steel sheet prepared by forming a zinc or zinc-alloy plating layer, a chemical conversion treatment layer, and a coating film layer on a steel sheet. 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 80) mg/m<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a painted zinc and zinc-coated steel sheet having excellent workability and corrosion resistance and used for home appliances and building materials, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, painted galvanized steel sheets have been increasingly used for home appliances and building materials. When high corrosion resistance is required for these steel sheets, zinc-plated steel sheets are mainly used, and a chemical conversion treatment such as a chromate treatment is performed as a pretreatment for the underlayer.

Conventionally, fumed silica has been added to chromic acid in order to enhance the corrosion resistance of chromate treatment (JP-A-52-17340, JP-A-60-86282, JP-A-61-585, etc.). The performance of these coating underlayer treatments is workability,
Alternatively, the corrosion resistance is not sufficient. Further, as disclosed in Japanese Patent Publication No. 56-36869, there is a means for performing Co or Ni treatment as a pretreatment of chromate. Although this method is effective in improving workability, it requires two processing steps, which is not preferable in terms of manufacturing cost.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has excellent workability (working part adhesion), water resistance, edge corrosion resistance, cross-cut part corrosion resistance, and is easy to use. It is an object of the present invention to provide a coated zinc-coated steel sheet that can be manufactured in a wide range.

[0005]

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 the specific amounts of Cr and SiO ₂ adhering, characteristics excellent in both workability and corrosion resistance can be obtained, and the present invention has been completed.

That is, according to the present invention, a zinc-based plating layer
The primary particle diameter is 14 nm or less 10 nm or more and 9 nm or less 5
containing fumed silica and chromic acid compound of nm or more,
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 to less than 6 in SiO ₂ / Cr, preferably,
3.5 or more and 5.5 or less, and the Cr adhesion amount is 25 m
g / m ² or more and 80 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 having a thickness of 100 mg / m ² or more and 190 mg / m ² or less is formed, and coating is performed thereon. Further, it is desirable that the zinc-based plating layer is a zinc-aluminum-based alloy plating layer containing 3 to 60% by weight of Al.

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 plated 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 14 nm or less and a fumed silica having a primary particle diameter of 10 nm or more and 9 nm or less and 5 nm or more.
In terms of O ₂ , when the weight of the chromic acid compound is converted to metal Cr, the compounding ratio is 3 or more in SiO ₂ / Cr.
After applying the treatment liquid, a plate temperature of 60 ° C. or more and 250 ° C. or less, preferably 100 ° C. or more and 20 ° C. or less without washing with water is used.
0 ℃ dried less, Cr coating weight of 25 mg / m ² or more 8
0 mg / m ² or less, and a preferable SiO ₂ deposition amount is 85 mg / m ^2.
m ² or more 240 mg / m ² to form the following chemical conversion treatment layer, it is intended to produce a coated steel sheet by performing subsequent painting.

[0008]

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

(Type of steel sheet) The zinc-based steel sheet used as a coating base in the present invention is a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, an alloyed hot-dip galvanized steel sheet, a Zn-Al alloy, or an Al-Zn alloy. Any of plated steel sheets may be used. Among them, from the viewpoint of workability and corrosion resistance, A
A zinc-aluminum alloy plated steel sheet containing 3 to 60% by weight of l is most suitable. This is because fine irregularities not found in pure galvanized steel sheets occur on the surface of a zinc-aluminum alloy-coated steel sheet containing 3 to 60% by weight of Al, and fine fumed silica enters these irregularities. This is because higher workability and adhesion after processing can be obtained. Such irregularities are optimal when the Al content is 3 to 60% by weight. Even if the amount is lower or higher, the irregularities are reduced, and it is difficult to sufficiently obtain the above-described effects. Also,
It is well known that in an Al-containing plating, an Al-based corrosion product precipitates during corrosion and enhances anticorrosion properties, but due to the presence of fine fumed silica, accumulation of Al corrosion products and It was newly found that the adhesion to the plating surface was promoted. Therefore, the chemical conversion treatment of the present invention further improves the performance in the plating containing Al. This effect appears more remarkably as the Al content in the plating increases.

The zinc-aluminum alloy-coated steel sheet described above includes a Zn-coated steel sheet containing 5% Al and a 55% Al-coated steel sheet.
Zn-plated steel sheets containing Zn are commercially available, and all of the above effects can be obtained.
N-plated steel sheets are more preferred.

(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 silica of 10 nm or more and 9 nm or less and 5 nm or more, excellent workability and corrosion resistance are obtained. 14n or less 10n
m or more of silica alone, or a mixture of silica of more than 14 nm and silica of 9 nm or less and 5 nm or more,
Workability becomes insufficient. Further, silica having a thickness of 9 nm or less and 5 nm or more has excellent workability but is inferior in corrosion resistance. Note that silica having a diameter of less than 5 nm is not currently commercially available. Preferred mixing ratio of the two types of primary particle diameter of fumed silica is 4 / 1-1 / 3 in 14nm below 10nm or more SiO ₂ and 9nm less 5nm or more SiO ₂ weight ratio. As fumed silica of 14 nm or less and 10 nm or more, for example, AEROSIL2 manufactured by Japan Aerosil Co., Ltd.
And fumed silica of 9 nm or less and 5 nm or more, for example, AERO manufactured by Japan Aerosil Co., Ltd.
SIL300.

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 ≦ 80 mg / m ² ) The present inventor studied the effect of fumed silica as a coating base, and as a result, it was found that only silica had processability. It was found that both of the corrosion resistance were not obtained and that it was necessary to contain a predetermined amount of the chromic acid compound. The ratio of the fumed silica to the chromic acid compound (ratio of SiO ₂ / Cr) is 3 or more and less than 6,
It is necessary that the amount of Cr attached is 25 mg / m ² or more and 80 mg / m ² or less. If the SiO ₂ / Cr is less than 3, the corrosion resistance is poor, and if it is 6 or more, the workability is poor. Further, if the Cr adhesion amount is less than 25 mg / m ² , the corrosion resistance is poor, and if it exceeds 80 mg / m ² , the corrosion resistance and workability are poor.
In a normal case, the corrosion resistance is improved with an increase in the amount of Cr attached. However, when a salt water spray test is performed on a coated steel sheet, local corrosion from an end face or a cross-cut portion tends to progress.

(85 mg / m ² ≦ SiO ₂ adhesion amount ≦ 24
0 mg / m ² ) The SiO ₂ adhesion amount is 85 mg / m ² for workability and corrosion resistance.
m ² or more and 240 mg / m ² or less,
In particular, the dose is preferably 100 mg / m ² or more and 190 mg / m ² or less. If the amount of SiO ₂ adhered is too small, the adhesion after immersion in boiling water after processing and the corrosion resistance at the cross-cut portion will be poor, and if it is too large, the film will have poor bending workability.

By applying a coating to the galvanized steel sheet thus manufactured, a coated galvanized steel sheet can be obtained. Next, a method for producing the coated galvanized steel sheet of 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 workability and corrosion resistance, the Cr reduction ratio is 0.35 or more. It must be mixed with chromic acid of 0.55 or less. If the Cr reduction ratio is less than 0.35, no workability can be obtained, and if it exceeds 0.55, the adhesion during bending is poor. 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 resistance and bending workability. 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 converted to PO ₄ and P
If O ₄ / Cr exceeds 1, the workability is reduced. Therefore,
The addition amount PO ₄ / Cr is preferably 1 or less.

In addition, when a chromate solution is applied to the surface of the steel sheet and dried, Cr ⁶⁺ can be reduced to Cr ³⁺ by adding an organic substance having a Cr ⁶⁺ reducing ability, an emulsion resin, or the like. However, if the amount of addition is increased, the processability is lowered and the stability of the processing liquid is also lowered. Therefore, it is necessary to select the type and 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 plate temperature is excessively low, the solubility of chromate decreases and the workability decreases, and if it is too high, the corrosion resistance decreases. The preferred range is 100 ° C
To 200 ° C.

The chemical conversion treatment can be performed immediately before coating or immediately after galvanizing. When chemical conversion treatment is performed immediately after galvanization, it may take some time before painting, but in this case, even without direct pretreatment such as alkali degreasing, it has excellent adhesion even when directly painted,
No management of wastewater treatment is required.

The coating can be applied directly on the above-mentioned chemical conversion coating. However, in order to further improve the workability and corrosion resistance, an undercoating usually used for coated steel sheets, that is, a so-called primer is used. It is desirable to paint after painting and baking. As the resin for the undercoat paint, epoxy, polyester, epoxy-modified polyester, or polyester-modified epoxy is preferable from the viewpoint of processability and corrosion resistance. As the curing agent, at least one selected from melamine and isocyanate can be used.

If a higher degree of corrosion resistance is required, it is preferable to add a chromate compound as a rust preventive pigment to the undercoat film. As chromate compounds, zinc chromate, strontium chromate,
Calcium chromate, barium chromate and the like are suitable, and the content thereof is suitably from 1 to 60% by weight in the coating film. The thickness of the dried undercoat film is preferably about 3 to 20 μm in order to obtain the above-described effects.

Polyester resin paint,
Conventional paints such as fluororesin paints, acrylic resin paints, PVC paints, and silicone paints can be used. The thickness of the dried coating film is preferably 5 to 40 μm from the viewpoint of processability and corrosion resistance. If the thickness of the coating film is less than 5 μm, the corrosion resistance of the coating film is undesirably reduced. On the other hand, when the thickness exceeds 40 μm, the processability is reduced, the coating workability is reduced, the appearance of the coating film is reduced, and the cost is also increased.

In the undercoat and topcoat paints, a coloring pigment, a moisture-resistant pigment, a solvent, an additive and the like can be blended as required. Examples of the coloring pigment include titanium oxide, carbon black, iron oxide, lead chromate, metal powder, calcined pigment, and pearl pigment. Examples of the moisture-resistant pigment include calcium carbonate, clay, talc, antimony trioxide, barium sulfate, and kaolin. As the solvent, for example, toluene, xylene, ethyl acetate, butyl acetate, cellosolve solvent, methyl isobutyl ketone, methyl ethyl ketone,
Examples include diisobutyl ketone, isophorone, and cyclohexanone. Examples of the additive include an antifoaming agent, a pigment dispersant, an anti-sagging agent, and an anti-scratch agent. Examples of the anti-scratch agent include silica, ceramic beads such as alumina, glass beads, glass fiber,
Resin beads, fluorine beads and the like are preferable from the viewpoint of crack resistance.

There are no particular restrictions on the coating method, and any of the conventional coating methods such as a roll coater method, a curtain flow coater method, a spray coating method, an electrostatic powder coating method, and a brushing method can be applied. In coating steel sheets, the roll coater method is most common.

When the roll coater method is used, the baking treatment after applying the paint is performed by heating for 20 to 180 seconds to reach a metal plate temperature of 150 ° C. or more. If the baking time is less than 20 seconds, the melt-hardening of the resin component is insufficient, while if it exceeds 180 seconds, the thermal degradation of the paint component starts, and in any case, the original performance of the paint cannot be sufficiently exhibited. Therefore, it is not preferable. There is no particular limitation on the heating method at the time of baking, and methods such as a hot air heating method and a high frequency heating method can be applied.

[0027]

Embodiments will be described below. Sheet thickness 0.5
mm hot-dip galvanized steel sheet (coating weight per side 12
0 g / m ² ), 5% Al-containing Zn-plated steel sheet (coating weight per side is 120 g / m ² ), and 55% Al-containing Zn-plated steel sheet (plating coating weight per side is 75 g / m ² )
Then, a chromate treatment solution adjusted to the composition shown in Tables 1 and 2 was applied by a roll coater, and dried by a hot air drying furnace under the condition that the reached plate temperature was 100 ° C., to obtain a test material. The adhesion amounts of Cr and SiO ₂ were measured by X-ray fluorescence. In addition, Si in the chemical conversion treatment layer formed by this method
The O ₂ / Cr ratio was the same as the ratio in the processing solution.

After coating the chromate-treated galvanized steel sheet and zinc-aluminum alloy-plated steel sheet with an epoxy-melamine resin paint as an undercoat without drying or washing with alkali, so that the dry coating thickness becomes 5 μm. Baked at about 200 ° C. for 60 seconds. Next, a polyester resin paint was applied as a top coat paint to a dry film thickness of 20.
After coating so as to have a thickness of μm, the coated metal sheet obtained by baking at about 250 ° C. for 60 seconds and cooling with water was subjected to various tests described below. Table 3 shows the results.

Evaluation Method Workability: A 0T bending test was performed, and evaluation was made based on the area peeled off by tape peeling. Worked part adhesion: After performing a 0T bending work test, it was immersed in boiling water for 3 hours, and then evaluated by a peeled area by tape peeling. The evaluation criteria for workability and adhesion of the processed part are shown below. 5: No peeling of film 4: Peeling of less than 3% peeling area 3: Peeling of more than 3% peeling area to less than 10% 2: Peeling of more than 10% peeling area to less than 30% 1: Peeling area: 30% Cross-cut portion corrosion resistance: A strip having a sample size of 70 mm wide and 150 mm long was prepared, a cross cut reaching the steel plate was placed in the center of the sample, and salt water spraying was performed for 2500 hours based on JIS Z2371. Next, the coating film in the cross-cut portion was forcibly peeled off using an adhesive tape, the peeling width was measured, and the evaluation was made with the maximum coating film peeling width. The evaluation criteria for the corrosion resistance of the cross cut portion are shown below. 5; no coating peeling 4; maximum coating peeling width less than 1 mm 3; maximum coating peeling width 1 mm or more and less than 3 mm 2: maximum coating peeling width 3 mm or more and less than 5 mm 1: maximum coating peeling width 5 mm or more Edge corrosion resistance; Sample size 70mm width x 150m length
m samples were prepared, and a salt spray was performed for 2500 hours in accordance with JIS Z2371 while leaving the ends thereof cut off. Next, the coating film at the end was forcibly peeled off using an adhesive tape, the peeling width was measured, and the maximum coating film peeling width was evaluated. The evaluation criteria for the edge corrosion resistance are shown below. 5; no coating peeling 4; maximum coating peeling width less than 2mm 3: maximum coating peeling width 2mm or more and less than 5mm 2: maximum coating peeling width 5mm or more and less than 8mm 1: maximum coating peeling width 8mm or more

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

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 to bending. No. In No. 4, the Cr reduction ratio of the treatment liquid is higher than the range of the present invention, there is a problem in the stability of the treatment liquid, and the formed film is inferior in the adhesion to the processed portion and the corrosion resistance. No. 5 is SiO ₂
/ Cr is smaller than the range of the present invention, and is inferior in bending workability and corrosion resistance. No. In No. 7, SiO ₂ / Cr is larger than the range of the present invention, and is inferior in bending workability. 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 bending workability was poor. No. 8 is a silica particle diameter of 14
This is an example in which silica particles having a thickness of 10 nm or more are added alone, and the bending workability is insufficient. No. No. 14 is an example in which silica particles having a silica particle diameter of 9 nm or less and 5 nm or more were independently added, and were inferior in corrosion resistance. No. No. 9 has a smaller Cr adhesion amount than the range of the present invention, and is inferior in corrosion resistance. No. 13
Is larger than the range of the present invention, and is inferior in bending workability. No. Nos. 15 and 16 are cases where an anion which is a soluble component is added, and due to the influence thereof, the bending processability and the adhesion to the processed portion are inferior. Example of the present invention (No. 2, 3, 10, 1)
1, 12, 17, and 18) were excellent in all performances, but those with zinc-aluminum alloy plating as the base (Nos. 17, 18) were particularly excellent in workability and corrosion resistance.

[0034]

As described above, according to the coated galvanized steel sheet and the method of manufacturing the same of the present invention, the workability, water adhesion, edge corrosion resistance, and cross-cut corrosion resistance are excellent by a simple chemical conversion treatment method. A coated galvanized steel sheet 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.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaaki Yamashita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (3)

[Claims] 1. A coated steel sheet in which a zinc or zinc-based alloy plating layer, a chemical conversion layer, and a coating layer are formed on a steel sheet, wherein the chemical conversion layer has a primary particle diameter of 14 nm or less.
A composition containing two types of fumed silica of not less than 5 nm and not more than 9 nm and not more than 5 nm, and a chromate compound, wherein the total adhesion amount of the fumed silica is converted to SiO ₂ and the adhesion amount of the chromate compound is converted to metal Cr. The ratio is Si by weight.
O ₂ / Cr is 3 or more and less than 6, and the Cr adhesion amount is 2
A coated galvanized steel sheet having excellent workability and corrosion resistance characterized by being at least 5 mg / m ^{2 and at most} 80 mg / m ² . 2. The method according to claim 1, wherein the zinc-based alloy plating layer contains 3 to 5% of Al.
The coated galvanized steel sheet according to claim 1, which is a zinc-aluminum-based alloy plating layer containing 60% by weight. 3. 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. the adhesion amount 25 mg / m ² or more 80mg
/ M ² or less, and a step of coating the chemical conversion treatment layer, and a step of coating the chemical conversion treatment layer. The chromic acid treatment liquid reduces a part of the chromic acid to form unreduced chromium (Cr ^{6 +} ) And the reduction product (Cr ³⁺ ) in a weight ratio of Cr ³⁺ / (Cr ⁶⁺ + C in terms of Cr, respectively)
r ³⁺ ) is a liquid obtained by mixing a chromic acid solution having a particle size of 0.35 or more and 0.55 or less and a fumed silica having a primary particle size of 14 nm or less and 10 nm or more and 9 nm or less and 5 nm or more,
Workability characterized in that the total weight of the added fumed silica is calculated in terms of SiO ₂ , and the calculated weight of the chromic acid compound is calculated as metal Cr, and the compounding ratio is 3 or more and less than 6 in SiO ₂ / Cr. And a method for producing a coated galvanized steel sheet having excellent corrosion resistance.