JPH04268081A - Surface treated steel sheet excellent in corrosion resistance and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a surface treated steel sheet excellent in corrosion resistance by successively coating the surface of a galvanized steel sheet with an aspherical silica-contg. chromate coating and a hydrophilic resin-silica coating under specified conditions. CONSTITUTION:The surface of a galvanized steel sheet is coated with aspherical SiO2 of 10 to 300mg/m<2> expressed in terms of Si in which the ratio of length/ thickness is regulated to >=2 and a coated chromate coating 2 of 5 to 100mg/m<2> expressed in terms of Cr as essential components. The upper layer of this coating is furthermore coated with a hydrophilic resin-silica coating 1 contg. spherical or aspherical colloidal silica in the ratio of 5 to 50 pts.wt. as solid content to 100 pts.wt. hydrophilic resin (such as an acrylic ester-acrylic acid copolymer) with 0.5 to 3.0g/m<2> coating weight. In this way, an organic coated galvanized steel sheet can be obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvanized steel sheet coated with chromate and organic material having excellent corrosion resistance and a method for producing the same.

0002

2. Description of the Related Art Surface-treated steel sheets coated with a thin organic film have been used in place of post-painted steel sheets that were conventionally painted after processing.

[0003] This steel sheet has a zinc-based plating film on the base and an organic film coated thereon, so that it can be welded and has good adhesion workability (pressability).

[0004] The disclosed technology is JP-A-60-50.
181 and JP-A-57-108292.

[0005] These techniques involve coating a zinc-based plated steel plate with a chromate film, a film consisting of an organic polymer of 0.01 to 4.0 μm, and silica.

[0006] The composite effect of plating, chromate, and organic silicate coating provides corrosion resistance, weldability, and adhesion workability, and development is currently underway for the purpose of quality improvement.

[0007]

Problems to be Solved by the Invention As the scope of use of the prior art expands, for example from flat plate bending to drawn products, and from indoor applications to outdoor applications, the quality cannot necessarily be said to be sufficient. For example, corrosion resistance is improved by increasing the thickness of the organic film or the amount of chromate deposited, but on the other hand, weldability and adhesion workability deteriorate.

[0008] When the amount of chromate deposited is increased, there is a problem that the adhesion workability deteriorates and the corrosion resistance of the processed part deteriorates.

[0009] Therefore, it is necessary to develop a composite film that is an optimal combination of a chromate film and an organic film that is well-balanced and has excellent corrosion resistance.

As mentioned above, a composite steel plate having a coating having excellent corrosion resistance, weldability, and adhesion workability has not yet been perfected.

[0011] The present invention is aimed at a corrosion-resistant surface-treated steel sheet for hot-dip galvanized steel sheets that particularly require a high degree of corrosion resistance, and a method for producing the same. The aim is also to solve the problem of deterioration in corrosion resistance due to corrosion and processing.

0012

[Means for Solving the Problems] The present invention provides (1) 10 to 300 mg/m2 of Si in terms of Si on the surface of a galvanized steel sheet.
A coated chromate film whose main components are non-spherical SiO2 with a length/thickness ratio of 2 or more and 5 to 100 mg/m2 in terms of Cr, and an upper layer of spherical or non-spherical colloidal silica with a weight of 100% hydrophilic resin. A surface-treated steel sheet having excellent corrosion resistance, characterized in that it has a hydrophilic resin silica coating in an amount of 0.5 to 3.0 g/m2 in a solid content of 5 to 50 parts by weight. (2) Si equivalent to 10 to 30 on the surface of galvanized steel sheet
A coated chromate film mainly composed of SiO2 having a non-spherical shape with a length/thickness ratio of 0 mg/m2 or more and 5 to 100 mg/m2 in terms of Cr and 5 to 30 mg/m2 in terms of P, The upper layer is a hydrophilic silica film containing spherical or non-spherical colloidal silica at a solid content of 5 to 50 parts by weight based on 100 parts by weight of hydrophilic resin, with an adhesion amount of 0.5 to 3.0 g/m2. A surface-treated steel sheet with excellent corrosion resistance. (3) A chromate solution containing a non-spherical SiO2 sol with a length/thickness ratio of 2 or more and chromic acid as the main components is applied to the surface of a galvanized steel sheet and dried to yield 10 to 300 mg in terms of Si.
/m2 5 to 100mg/m2 in terms of SiO2 and Cr
After chromate treatment of chromium oxide, an emulsion paint containing spherical or non-spherical colloidal silica at a solid content of 5 to 50 parts by weight per 100 parts by weight of a hydrophilic resin is applied as a dry coating amount. 0.5-3.0
g/m2 A method for producing a surface-treated steel sheet with excellent corrosion resistance, characterized by applying the coating and then baking it. (4) A non-spherical SiO2 sol with a length/thickness ratio of 2 or more and a chromate solution containing chromic acid and phosphoric acid as main components are applied to the surface of a galvanized steel sheet and dried to give a Si equivalent of 10
~300mg/m2 of SiO2 and 5 to 1 in terms of Cr
00mg/m2 of chromium oxide, 5-30m in terms of P
An emulsion paint containing spherical or non-spherical colloidal silica at a solid content of 5 to 100 parts by weight based on 100 parts by weight of a hydrophilic resin after being subjected to a coating chromate treatment consisting of g/m2 of phosphate. A method for producing a surface-treated steel sheet with excellent corrosion resistance, characterized in that the dry coating amount of 0.5 to 3.0 g/m2 is applied and then baked.
It is.

[0013]

[Operation] The present invention has succeeded in achieving performance exceeding that of the prior art by making revolutionary improvements to chromate.

Conventionally, the chromates used for this purpose are generally electrolytic chromates and etching chromates composed of chromium oxide, but some of them include Japanese Patent Laid-Open No. 60-50.
A method using chromate, which is a composite of 181 and silica, has been published.

In the present invention, as mentioned above, while conventional silica is spherical or an aggregate of spherical silica, by using irregularly shaped silica, corrosion resistance and adhesion processability are significantly improved.

The film obtained from conventional spherical silica is shown in Figure 1.
As shown in Figure 2, when a film is formed from a sol to a gel by forced drying, a loose film is formed due to the agglomeration of particles and the evaporation of water, and the bond strength is weak and cohesive failure occurs during processing ([The Chemistry] by Ralph K. Iler).
story of Silica 1979]).

On the other hand, the gel film obtained from the irregularly shaped non-spherical silica sol of the present invention forms a continuous film of uniform agglomerated silica laminated by physical entanglement of silica particles, as shown in FIG. 2, and has excellent corrosion resistance. It is possible to form a film that is highly flexible and resistant to cohesive failure.

The effects of the present invention can be obtained when the shape of the silica has a length/thickness ratio of 2 or more, and the diameter (equivalent to the thickness for non-spherical silica) of commonly commercially available spherical silica is 5 to 30 nm.
The preferred range for the silica sol is a length/thickness ratio of 2 to 10.

If it is less than 2, the difference from spherical silica is not clear and the improvement effect aimed at by the present invention cannot be obtained. By reducing the diameter of the thickness, the larger the length/thickness ratio, the better the quality, but it is more likely to cause agglomeration and precipitation, so it is preferably 100 or less.

It should be noted that the silica of the present invention requires a sol that is independently dispersed in a bath, and the effects of the present invention cannot be obtained with secondary agglomerated silica produced by a dry process.

The non-spherical silica of the present invention can be obtained by various methods, but in the process of producing silica sol by removing an aqueous solution of sodium silicate and potassium silicate using a cation exchange resin, alkaline earth metal ions are added and the temperature is increased. , p
One example is a method obtained by adjusting H.

The chromate solution that composes silica can be obtained by using an aqueous solution of chromic acid anhydride, but it can be partially reduced with starch, glucose, etc. to obtain Cr3+/Cr6+=1/9.
A chromate solution in which a non-spherical silica sol is combined with an aqueous solution of chromic acid anhydride adjusted to a range of ~5/5 (hereinafter referred to as reduction ratio) is preferred.

Furthermore, in the case of hot-dip galvanized steel sheets, a chromate solution to which phosphoric acid is further added is optimal. The chromate solution prepared in this manner is applied to the surface of the plated steel sheet and dried to obtain a chromate treatment film as the base.

[0024] The amount of film deposited is 10 to 300 m in terms of Si.
g/m2 of non-spherical SiO2 and 5 to 100 in terms of Cr
It is composed of a composite film containing a chromate film of mg/m2 and a phosphate film of 5 to 30 mg/m2 in terms of P in a bath containing phosphoric acid.

[0025] If any of the components is less than the lower limit, corrosion resistance and adhesion processability superior to that of spherical silica cannot be obtained. Exceeding the upper limit is not preferable because adhesion workability and weldability are insufficient.

The optimum range of each component is 50 to 1 in terms of Si.
00mg/m2 of non-spherical SiO2 and 10 in terms of Cr
~30 mg/m2 of chromium oxide can be applied.

Particularly in the case of a plated steel plate that forms an oxide film on the surface of the plated metal, such as a hot-dip plated steel plate, it is desirable to add phosphoric acid to promote the reaction by etching the plated surface.

[0028] In a bath with phosphoric acid added, 5 to 30 m in terms of P
Chromate coatings containing g/m2 of phosphate are within the scope of this invention.

The addition of phosphoric acid reduces the adhesion of the upper layer resin film, which will be described later, in conventional spherical sols, but is good in non-spherical silica sol.

A chromate film containing more than 30 mg/m 2 of phosphorus salt in terms of P is not preferable because the water resistance of the film decreases and the adhesion workability after corrosion is adversely affected.

[0031] The method of applying the chromate solution is roll coating,
Known methods such as air knife and squeezing roll can be applied. For drying, it is desirable to heat the plate to a final plate temperature of 50 to 200° C. using a known method such as hot air, an electric furnace, a direct-fired furnace, or infrared rays.

[0032] After chromate treatment, the surface-treated steel sheet of the present invention with excellent corrosion resistance is obtained by applying a coating composition consisting of a hydrophilic resin and spherical or non-spherical silica sol at a dry coating weight of 0.5 to 3.0 g/m2 and then baking it. can be obtained. As for the baking conditions, the plate temperature reached is 80 to 20.
A range of 0°C is desirable.

Hydrophilic resins include acrylic ester/acrylic acid copolymer, epoxy/acrylic acid, olefin acrylic acid copolymer, olefin ionomer, styrene acrylic acid copolymer, urethane acrylic acid copolymer,
Urethane epoxy resin, ethyleneimine acrylic resin, etc. can be applied, and an emulsion dispersed in water is used as the paint.

Corrosion resistance can be further improved by adding crosslinking agents such as various melamine resins and amino resins, if necessary.

[0035] By adding a lubricant such as wax, fluororesin, polyethylene resin, or molybdenum disulfide, properties that add deep drawability to corrosion resistance can be obtained.

A sol in which each particle of silica is independently dispersed is used. The particle size of the silica is 3 to 200 μm if it is spherical, preferably 5 to 30 μm if it is aspherical, and preferably the size of the silica that allows it to be combined with chromate if it is non-spherical.

As for the mixing ratio of resin and silica, a paint is used in which 5 to 50 parts by weight of spherical or non-spherical colloidal silica is combined as a solid content with respect to 100 parts by weight of hydrophilic resin.

[0038] If the mixing ratio is less than 5, corrosion resistance cannot be obtained. If it exceeds 50, it is difficult to obtain flexibility of the resin film and adhesion workability becomes insufficient, which is not preferable.

[0039] The amount of hydrophilic resin silica film attached is 0.5g.
If it is less than /m2, corrosion resistance is insufficient and mold galling occurs due to metal-to-metal wear during press working, which is not preferable. Moreover, if it exceeds 3.0 g/m2, welding becomes difficult, which is not preferable. For coating, a known method such as a roll coating method can be applied.

The present invention will be explained in detail in the following examples.

[0041]

【Example】

[0042]

[Example 1] Hot-dip galvanized steel sheet (thickness: 0.8 mm, area weight: 60
5, 10, 15 g/l in terms of SiO2, CrO3 (
After spraying a chromate solution prepared with 5 g/l of chromate solution (reducing ratio = 3/7 by heating and reducing with starch) and a non-spherical silica sol with the same composition and an average length/thickness ratio of about 5, an air knife was applied. The amount of chromium deposited is 15.3 in terms of Cr.
0, 50, 80 mg/m2 and dried with hot air at 300°C to a plate temperature of 90°C.
2. After roll-coating a paint composed of 20 parts to 100 parts of methylolmelamine-added polyethylene/acrylic acid resin (aiming at a dry coating amount of 1 g/m2), immediately bake the plate at a temperature of 150°C to form a hydrophilic silica resin film. A surface-treated steel sheet was obtained by coating.

[0043] The amount of deposited film obtained is calculated from fluorescent X-rays (chromate: Si, Cr, hydrophilic silica film: Si)
The corrosion resistance was measured using Erichsen, and a salt water spray test was conducted after 9 mm overhang processing, and the corrosion resistance was rated based on the time until white rust appeared.

[0044] Adhesion was evaluated by bending 3T-180 degrees using a press and peeling off cellophane tape, and grading the adhesion.

[0045] Corrosion resistance rating 5: No white rust up to 1000 hours 4: No white rust up to 750 hours 3: No white rust up to 500 hours 2: No white rust up to 250 hours 1: No white rust up to 120 hours Adhesion rating 3: No peeling 2: Peeling area ratio 10% 1: Peeling area ratio 50% The results are shown in Table 1.

[0046]

[Table 1]

Sample numbers 1 to 4 are examples of the present invention, and the silica/chromic acid ratio is 1, and the amount of chromate attached is 1 in terms of Cr.
It was processed with 5, 30, 50, and 80 targets. It showed a high level of both corrosion resistance and adhesion.

Sample numbers 5 to 8 are examples of the present invention, with a silica/chromic acid ratio of 3 and a chromate deposition amount of 1 in terms of Cr.
It was processed with 5, 30, 50, and 80 targets. It showed a high level of both corrosion resistance and adhesion.

Samples Nos. 9 to 12 are comparative examples of conventional spherical silica sols, which were treated with a silica/chromic acid ratio of 1 and a chromate deposition amount of 15, 30, 50, and 80 in terms of Cr. Corrosion resistance is 9 to 11 with low amount of Cr adhesion.
In terms of adhesion, 12, which had a high adhesion amount, peeled off.

Sample numbers 13 to 16 are comparative examples with a silica/chromic acid ratio of 3 and a chromate deposition amount of 1 in terms of Cr.
It was processed with 5, 30, 50, and 80 targets. 13
had good adhesion but poor corrosion resistance. 14-16
Samples No. 15 and No. 16 showed significant deterioration in corrosion resistance due to peeling.

[0051]

[Example 2] Under the conditions of Example 1, the following non-spherical silica sol was added to an aqueous chromic acid anhydride solution with a reduction ratio of 3/7 with a silica/chromic acid ratio of 3 to create a chromate solution, and Cr was deposited on a hot-dip galvanized steel sheet. Amount 30mg/m2, Si84mg/
m2, and after drying to a plate temperature of 80°C, apply the hydrophilic resin silica film of Example 1 at 1.0 g/m2, and plate temperature 15
Baked at 0°C.

Sample number Invention 17: Length/thickness ratio 2 (thickness 20 nm), Sample number Invention 18: Length/thickness ratio 10
(thickness 20 nm), sample number Invention 19: length/thickness ratio 20 (thickness 10 nm), sample number Invention 20: length/thickness ratio 50 (thickness 5 nm), sample number Invention 21: length/
The quality of the thickness ratio 100 (thickness 2 nm) all showed good results with a corrosion resistance rating of 5 and an adhesion rating of 3. Sample number 2
Precipitation was observed in the solution No. 1.

[0053]

[Example 3] Under the conditions of Example 1, a non-spherical silica sol with a length/thickness ratio of 5 was added to an aqueous chromic acid anhydride solution with a reduction ratio of 4/6, a silica/chromic acid ratio of 3, no phosphoric acid, and phosphoric acid/ A chromate solution with a chromic acid ratio of 1 was prepared and applied to a hot-dip galvanized steel plate with a Cr adhesion amount of 10, 30 mg/m2. After drying to a plate temperature of 80°C, a hydrophilic resin silica film of Example 1 was applied with a chromate solution of 0.7 , 1, 2, 3 g/m2 and baked at a board temperature of 150°C.

For comparison, spherical silica was also tested. The results are shown in Table 2.

[0055]

[Table 2]

Samples Nos. 22 and 23 are examples of the present invention that do not contain phosphoric acid and showed good results in corrosion resistance and adhesion. Examples 24 and 25 of the present invention in which phosphoric acid was added had further improved corrosion resistance compared to the case without addition.

Comparative Examples 26 and 27 obtained from conventional spherical silica baths to which phosphoric acid was added had a large deterioration in adhesion and a large deterioration in corrosion resistance of processed parts. Hydrophilic resin silica film 1.
5μ (Inventive Example 28) A well-balanced quality of corrosion resistance, adhesion, and weldability was obtained.

[0058] The hydrophilic resin silica film was coated with a 3.0μ coating material (
Inventive Example 29) had poor weldability, but other qualities were good.

[0059]

[Example 4] After applying a non-spherical silica sol and phosphoric acid chromate to the surface of a hot-dip galvanized steel sheet under the conditions of sample number 24 of Example 2, spherical silica sol 20 (20 nm in particle size) was applied to 100 epoxy acrylic acid resin ( Clear paint urethane epoxy acrylic resin 100% by weight)
A coating material with spherical silica sol 20 (weight ratio) dispersed therein was applied at a dry coating amount of 1.0 g/m2, and the plate temperature was 1.
A sample was prepared by baking at 70°C.

[0060] All samples obtained good results, with a rating of 3 for adhesion workability and a rating of 5 for corrosion resistance.

[0061]

[Example 5] Example 2
As a result of processing and evaluating sample number 24, good quality was obtained in both cases, with an adhesion rating of 3 points and a corrosion resistance rating of 5 points.

In particular, the zinc-nickel alloy plated steel sheet showed good results with no change in corrosion resistance.

[0063]

Effects of the Invention According to the present invention, it is possible to provide a surface-treated steel sheet that has excellent adhesion workability and weldability without reducing the corrosion resistance of steel sheet parts and fixtures that have been conventionally coated.

[0064] Applications for which conventional organic composite plated steel sheets had limited scope have been opened up, and in terms of production, mass production is possible without changing the conventional process, processes can be omitted in user processes, and the final product is improved. We can provide products with low cost and excellent quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the morphology of a film obtained from a bath using a conventional spherical silica sol.

FIG. 2 shows a schematic diagram of the morphology of a film obtained from a bath using the non-spherical silica sol of the present invention.

[Explanation of symbols]

1 Hydrophilic resin silica film 2 Silica-containing chromate film

Claims (4)

[Claims] [Claim 1] 1 in terms of Si on the surface of a galvanized steel sheet
0 to 300 mg/m2 SiO2 consisting of a non-spherical shape with a length/thickness ratio of 2 or more and 5 to 100 mg/m in terms of Cr
A coated chromate film containing 2 as the main component, spherical or non-spherical colloidal silica on the top layer of a hydrophilic resin 10
The coating amount of the hydrophilic resin silica film is 0.5 to 3.0 parts by weight, and the solid content is 5 to 50 parts by weight.
A surface-treated steel sheet with excellent corrosion resistance, characterized by having a corrosion resistance of 0g/m2. [Claim 2] 1 in terms of Si on the surface of the galvanized steel sheet
0 to 300 mg/m2 SiO2 consisting of a non-spherical shape with a length/thickness ratio of 2 or more and 5 to 100 mg/m in terms of Cr
2. A coated chromate film containing 5 to 30 mg/m2 of phosphate as a main component in terms of P, and 5 to 50 weight solids of spherical or non-spherical colloidal silica on the upper layer based on 100 parts by weight of hydrophilic resin. A surface-treated steel sheet having excellent corrosion resistance, characterized in that it has a hydrophilic silica coating in an amount of 0.5 to 3.0 g/m2. 3. A chromate solution containing a non-spherical SiO2 sol with a length/thickness ratio of 2 or more and chromic acid as main components is applied to the surface of a galvanized steel sheet and dried to form a chromate solution with a length/thickness ratio of 10 to 3 in terms of Si.
00mg/m2 SiO2 and 5 to 100m in terms of Cr
After chromate treatment of chromium oxide of g/m2, dry an emulsion paint containing spherical or non-spherical colloidal silica at a solid content of 5 to 50 parts by weight per 100 parts by weight of hydrophilic resin. 0.5 as adhesion amount
A method for manufacturing a surface-treated steel sheet with excellent corrosion resistance, which comprises applying ~3.0 g/m2 and then baking. 4. A non-spherical SiO2 sol with a length/thickness ratio of 2 or more and a chromate solution containing chromic acid and phosphoric acid as main components are applied to the surface of a galvanized steel sheet and dried to give a Si equivalent of 10 to 300 mg. /m2 of SiO2 and 5 to 100mg/m2 of chromium oxide in terms of Cr, 5 to 100mg/m2 in terms of P.
After applying chromate treatment consisting of ~30 mg/m2 of phosphate, add spherical or non-spherical colloidal silica to 100 parts by weight of the hydrophilic resin in a solid content of 5 to 10 parts by weight.
A method for manufacturing a surface-treated steel sheet with excellent corrosion resistance, which comprises applying an emulsion paint containing 0 parts by weight in a dry coating amount of 0.5 to 3.0 g/m2 and then baking it.