JPH067950B2 - Anti-corrosion steel plate for electrodeposition coating that has excellent film adhesion during processing and corrosion resistance after processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a corrosion-resistant steel sheet for electrodeposition coating, which has excellent film adhesion during processing and corrosion resistance after processing. More specifically, the present invention relates to automobile bodies and households. The present invention relates to an anticorrosion steel sheet for electrodeposition coating, which is used for electrical appliances, walls for buildings, etc. and has excellent film adhesion during processing and corrosion resistance after processing.

[Prior Art] Conventionally, various structures of rust preventive steel sheets have been proposed and used. For example, when used for a vehicle body of an automobile, a rust preventive steel plate commonly called zinc metal is used. This is a first layer containing a chromium compound on a steel plate and a zinc powder containing a zinc powder and a resin. It is composed of a second layer of rich paint (hereinafter referred to as zinc rich anticorrosive steel plate), has good corrosion resistance, and can be subjected to electrodeposition coating and spot welding, which are conditions for automobile steel plates.

However, this zinc-rich anticorrosion steel plate has the following problems.

(1) In order to ensure corrosion resistance and electrodeposition paintability, since the second layer contains zinc powder in an amount of 80 wt% or more, the film peels off into a powder during press working, causing a processing scratch. Becomes

(2) When the zinc-rich coating is thickly coated, for example, 10 μm or more, since a large amount of zinc powder and resin are present, the electrode tip is contaminated by the combustion residue of zinc and resin due to continuous spot welding, and the tip is contaminated. The frequency of dressing increases, resulting in deterioration of workability.

However, regarding the rust preventive steel plate in consideration of the above-mentioned problems of the zinc rich rust preventive steel plate, Japanese Patent Laid-Open No. 58-0981.
No. 72 and JP-A-57-108292 propose rust preventive steel sheets having an organic composite silicate film having a thickness of about 1 .mu.m. M in the main film
O, W, V, Sn, B, Si oxyacid or alkoxide chelate compound is essential, and
Urethane-based organic composite silicate is not included. Further, such rust-preventive steel plate has a problem that the film adhesion is not sufficient under severe processing conditions such as draw bead test and various adhesion tests after coating such as electrodeposition coating + intermediate coating + top coating. There is.

[Problems to be Solved by the Invention] The present invention has been made in view of various problems in the conventional rust-preventive steel sheet as described above, and as a result of earnest research by the present inventor, We have developed a corrosion-resistant steel plate for electrodeposition coating that has excellent film adhesion during processing and corrosion resistance after processing.

[Means for Solving Problems] The feature of the corrosion-resistant steel sheet for electrodeposition coating according to the present invention, which is excellent in film adhesion during processing and corrosion resistance after processing, is that zinc provided on the steel sheet is used. A coating layer made of a composite material or a mixed material of urethane resin and silicon dioxide having a film thickness of 2 μm or less is provided on the plating layer.

If necessary, a chromate layer may be formed between the zinc-based plating layer and the coating layer containing a composite material or a mixed material of urethane resin and silicon dioxide as a main component.

Further, various anticorrosion pigments can be made to coexist in the above-mentioned coating layer to further improve the corrosion resistance.

The steel sheet provided with a zinc-based plating layer used for the corrosion-resistant steel sheet for electrodeposition coating having excellent film adhesion during processing and corrosion resistance after processing according to the present invention includes a zinc single layer plated steel sheet and a zinc alloy plated sheet. Mention may be made of steel sheets and their multi-layer plated steel sheets.

For the coating layer, urethane resin is used as a resin component, and the urethane resin and silicon dioxide are made into a composite material by a silicon coupling agent or a mixed material.

The polyretane resin mentioned here is a reaction product of an organic polyisocyanate with a polyvalent hydroxy compound and a polyvalent amino compound.

As the organic polyisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate,
Hexamethylene diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated dicyclohexylmethane diisocyanate and other aliphatic, aromatic, alicyclic isocyanates and their dimerization and trimerization is there.

As the polyhydric hydroxy compound, polyalkylene glycol, polyamine polyol, polymer polyol, polyether-based polyol such as polytetramethylene glycol, adipate-based polyol,
Examples include phthalic acid-based polyols, polycaprolactone-based polyols, polyester-based polyols such as polycarbonate-based polyols, and polyhydric alcohol compounds such as trimethylolpropane and butanediol.

Examples of polyvalent amino compounds include methylene orthochloroaniline, diaminodiphenylmethane, ethylenediamine, diethylenetriamine, hydrazine, isophoronediamine, and triethylenetetramine.

Polyurethane resins are roughly classified according to processing methods. (1) Various organic polyisocyanates and urethane prepolymers are synthesized by polymerization reaction of polyhydric hydroxy compounds,
Thermosetting polyurethane resin that is made into a resin by polyvalent amino compounds, polyvalent hydroxy compounds, moisture, etc. during processing.

(2) A one-shot polyurethane resin in which various organic polyisocyanates, polyhydric hydroxy compounds, polyhydric amino compounds, etc. are mixed into a resin during processing.

(3) Solvent volatilization type (including partially moisture curing type) polyurethane resin obtained by dissolving and diluting urethane prepolymer or polyurethane resin in various solvents by polymerization reaction of various organic polyisocyanates and polyhydric hydroxy compounds.

(4) A thermoplastic polyurethane resin in which a polyurethane resin obtained by a polymerization reaction of various organic polyisocyanates and polyhydric hydroxy compounds is melted by heat during processing.

(5) various organic polyisocyanates, during the polymerization reaction of polyvalent hydroxy compounds, polyurethane resin obtained by introducing a hydrophilic group, or urethane prepolymer is emulsified in water, or various organic polyisocyanates, poly A polyurethane resin obtained by a polymerization reaction of a divalent hydroxy compound, or a hydrogenated polyurethane resin forcibly emulsifying a urethane prepolymer with a surfactant or a colloid agent.

Etc.

[Example] An example of the rustproof steel sheet for electrodeposition coating which is excellent in film adhesion and corrosion resistance during processing according to the present invention will be described.

Example 1 To 202 parts of polytetramethylene ether glycol (OH.V.55.3) dehydrated under reduced pressure, 101 parts of methyl ethyl ketone was added and uniformly mixed, and then 2,4- and 2,
6 Tolylene diisocyanate 80:20 mixture 34.
8 parts was added, and the mixture was reacted at a temperature of 80 ° C. for 2 hours to give 2.4.
A urethane prepolymer solution containing 8% isocyanate groups was obtained.

In a separate reactor 600 parts of methyl ethyl ketone and 10.7
Part of diethylenetriamine was added and uniformly mixed, and the above urethane prepolymer solution 300 was added to this solution.
Parts at a temperature of 10 to 20 ° C. and added dropwise, and then 5
Reaction was carried out at a temperature of 0 ° C. for 30 minutes to obtain a polyurethaneurea polyamine solution.

Then, 25.8 parts of trimetic acid anhydride was added to this solution and dissolved uniformly, and then the temperature was raised to 50 ° C. to 30
Let react for minutes.

Subsequently, an aqueous solution in which 10.8 parts of sodium hydroxide was dissolved in 650 parts of water was added, methyl ethyl ketone was distilled off under reduced pressure, water was added to adjust the resin content, and an emulsion having a concentration of 30% was obtained. .

This water-soluble urethane emulsion (solid content 30%)
: 100 parts by weight Colloidal silica (SiO ₂ 40 wt%): 50 parts by weight Distilled water: 240 parts by weight were mixed to prepare a coating liquid.

Next, this coating solution was subjected to degreasing treatment and chromate treatment (application of chromic anhydride aqueous solution, drying at 195 ° C./30 seconds, total chromium amount 50 mg / m ² ), Zn-12% Ni plated steel sheet (plating thickness 20 g / m ² ) is coated with a bar coater and baked at a furnace temperature of 200 ° C. for 1 minute to give SiO 2.
₂ / Urethane resin = 0.40, and a rustproof steel sheet having a film layer with an average film thickness of 1.5 μm was manufactured.

The rust-preventive steel sheet thus produced was subjected to (1) film adhesion test after 3 coats, (2) film peeling property during processing and corrosion resistance test after processing.

(1) Film adhesion test after 3 coats A rust-preventive steel plate having excellent workability according to the present invention was coated with a cationic electrodeposition coating of 15 μm, an intermediate coating for automobiles of 35 μm, and an overcoat for automobiles of 35 μm for a total of 85 μm at 50 ° C. After immersion in warm water for 240 hours, a 2 mm cross-cut adhesive tape test was conducted.

As a result, no film peeling was observed.

(2) Film peeling property during processing and corrosion resistance test after processing The film peeling property during processing was investigated using the draw bead test device shown in Fig. 1.

The tensile speed was 300 mm / min and the elongation was 20%. After the test, the amount of film peeling on the sliding part by the adhesive tape peeling test was 0.
It was 1 g / m ² or less.

The corrosion resistance after this draw bead test was investigated by the cycle test shown below.

The cycle of salt spray test (35 ° C. × 4 hours) → drying (60 ° C. × 2 hours) → wet (50 ° C. × 2 hours) → salt spray test was conducted for 8 hours / 1 cycle.

The maximum corrosion depth per 210 cm ² of the sliding portion after 200 cycles was 75 μm.

Comparative Example 1 An aqueous acrylic emulsion (30% solid content) was used and treated in the same manner as in Example 1 to give an average film thickness of 1.5.
μm organic composite silicate (SiO ₂ / acrylic resin =
0.40) A film was formed.

A performance test was conducted in the same manner as in Example 1.

(1) Film adhesion test after 3 coats 75% of the film peeled off.

(2) Film peelability during processing and corrosion resistance after processing Film peelability 3.5 g / m ² Maximum corrosion depth 560 μm Example 2 Solvent-based polyurethane resin (solid content 10%): 100 parts by weight Fine powder SiO ₂ (Average particle size 0.5 μm): 5 parts by weight Dimethyl sulfamide: 100 parts by weight was mixed to prepare a coating liquid.

Next, this coating solution is deoxidized and chromated (chromic anhydride and colloidal silica mixed solution coating, 200 ° C. ×
Zn- which has been dried for 30 seconds and has a total chromium amount of 50 mg / m ² )
A 12% Ni-plated steel sheet (plating thickness 20 g / m ² ) was applied with a bar coater and baked at a furnace temperature of 200 ° C. for 1 minute to give SiO ₂ / urethane resin = 0.5 and an average film thickness = 0.
A rustproof steel plate having a film layer of 8 μm was manufactured.

The test described below was conducted on the rustproof steel plate produced in this manner.

(1) Film adhesion test after 3 coats A rust-preventive steel plate having excellent workability according to the present invention was coated with a total of 85 μm of a cationic electrodeposition paint 15 μm, an automobile intermediate coating 35 μm, and a top coating 35 μm. After immersing in warm water of ℃ for 240 hours, a 2 mm cross-cut adhesive tape test was conducted.

As a result, no peeling of the film was observed.

(2) Film peeling property during processing and corrosion resistance test after processing The film peeling property during processing was investigated using the draw bead test device shown in Fig. 1.

The tensile speed was 300 mm / min and the elongation was 20%.

After the test, the amount of film peeling by the adhesive tape peeling test of the sliding portion was 0.1 g / m ² or less.

The corrosion resistance after this draw bead test was evaluated by the same cycle test as that carried out in Example 1.

The maximum erosion depth per 210 cm of the sliding portion after 200 cycles was 85 μm.

[Advantages of the Invention] As described above, the rust-preventive steel sheet for electrodeposition coating excellent in film adhesion during processing and corrosion resistance after processing according to the present invention has the above-mentioned constitution, and therefore film adhesion during processing It is possible to provide a corrosion-resistant steel plate for electrodeposition coating, which is excellent in corrosion resistance after processing.

[Brief description of drawings]

 FIG. 1 is an explanatory view of a draw bead test device.

Claims (1)

[Claims] 1. A coating layer made of a composite material or a mixed material of urethane resin and silicon dioxide having a thickness of 2 μm or less is provided on a zinc-based plating layer provided on a steel plate. Corrosion-resistant steel plate for electrodeposition coating that has excellent film adhesion during processing and corrosion resistance after processing.