JPS6230585A - Preparation of zinc type composite plated steel plate excellent in paint film close adhesiveness of direct paint - Google Patents

Abstract

PURPOSE:To enhance painting close adhesiveness and corrosion resistance after painting, by partially performing cationic electrodeposition to a zinc type plated steel plate in an emulsion treatment bath of org. high-molecular resin and further applying zinc type electroplating so as not to perfectly cover the electrodeposition part. CONSTITUTION:In welding a surface-treated steel plate used in a car, a building material or household electric machineries, cationic electrodeposition is applied to the steel plate in an org. rein emulsified solution with org. resin conc. of 0.1-50g/l under such a condition that voltage is 1-40V and an electrolytic time is 0.1-10sec so as not to perfectly cover the zinc type plating surface of said steel plate. Succeedingly, zinc plating is applied only to the part no covered with the org. high-molecular substance of the substrate in a zinc adhesion amount of 10-100mg/m<2> by strike plating. As a result, a product having good paint close adhesiveness is obtained without damaging the weldability of the steel plate.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a zinc-based composite plated steel sheet that has excellent paintability by direct painting, paint adhesion, and post-painting corrosion resistance.

<Prior art and its problems> Zinc-based plated steel sheets are widely used as anti-corrosion treated steel sheets for automobiles, home appliances, building materials, etc. that require corrosion resistance. This is because the pure zinc layer is base against the iron of the steel sheet, so it has a sacrificial corrosion protection effect where the zinc corrodes first against exposed areas of the base steel caused by plating defects such as pinholes or processing. This is because it has the effect of preventing the occurrence of red rust on steel plates.

However, when direct painting is applied to cold-rolled steel sheets or pure zinc, it has good paint adhesion in dry environments, but in wet environments? II! In the category 1, there was a drawback that the coating film peeled off easily. This is because water that has permeated the paint film where the adhesion between the base metal and the paint film is originally poor reaches the adhesive interface, where it generates conductive corrosion products and disrupts the bond between the base metal and the paint film. This is because it becomes loose and eventually peels off.

On the other hand, many patent documents can be found regarding the general use of chemical conversion treatment with zinc phosphate or chromic acid to improve the adhesion of these coatings.

Although the above-mentioned chemical conversion treatment is common, it often causes difficulties in bath management and operations, causing an increase in manufacturing costs.

An example of applying electroplating by positively charging and dispersing organic polymer particles, fine powder, or bodies in the same plating bath using an activator is disclosed in Patent No. 1023141 (registered on November 28, 1955). Unexamined Japanese Patent Publication No. 115993 (1955)
(Released on May 6th).

All of these are made by dispersing fine particles of organic polymer in an electroplated metal film, but it is difficult to stabilize the organic polymer for a long period of time under the heating and circulating conditions of the bath, and it is difficult to disperse the organic polymer. Various problems have arisen in practical application, such as operational difficulties due to foaming of the surfactant used for plating, and it is difficult to produce stable quality plating by keeping the eutectoid rate, which determines the quality of the plating, constant. It is technically difficult and there are few examples of it being put into practical use.

Furthermore, for users who want pure zinc, they cannot use a bath with organic substances dispersed in it, so the bath needs to be replaced, which makes work difficult, increases production costs, and requires large-scale production. This is thought to be due to the lack of industrialization.

<Object of the Invention> Therefore, the object of the present invention is to provide a method that can be industrialized relatively easily without significantly changing the manufacturing conditions of galvanized steel sheets, with good workability, and minimizing increases in manufacturing costs. Moreover, it is an object of the present invention to provide a method for producing a zinc-based plated steel sheet which has excellent paintability, paint adhesion and post-painting corrosion resistance by direct painting.

<Structure of the invention> The above object is achieved by the present invention as follows.

That is, the present invention applies cationic electrodeposition using a zinc-plated steel sheet as a cathode in a treatment bath in which an emulsion of an organic polymer resin is dispersed, to an extent that does not completely cover the surface of the zinc-based plating, and further coats the zinc-based plating. The object of the present invention is to provide a method for producing a zinc-based composite plated steel sheet with excellent coating film adhesion by direct painting, which is characterized in that the organic polymer resin electrodeposit layer is applied to an extent that it does not completely cover the layer.

The present invention will be explained in more detail below.

The present inventors have found that the bare corrosion resistance (for example, salt spray test) of Zn-cation resin dispersion-plated steel sheets cannot be said to be superior to that of pure zinc; Since resin dispersion plating is more saturated, we realized that it would be sufficient if the cationic resin was present only near the surface layer.

Additionally, in the case of electrogalvanizing, if cationic resin is dispersed in the plating solution, it will be necessary to completely replace the solution in order to plate pure zinc, which may be difficult considering the actual operating conditions. This was the motivation for the present invention.

The characteristics of the present invention are that the bare corrosion resistance is equivalent to that of zinc-plated steel sheets, but the paint adhesion is even better when the paint is applied directly to the zinc-plated steel sheets without chemical conversion treatment as a base treatment. is very good. Although the reason for this is not necessarily clear, it is thought to be as follows. In other words, it is thought that this is because the organic polymer present on the surface of the plating film and the paint are the same organic substance, so they have good affinity and exhibit excellent adhesion of the paint.

In the present invention, the surface of a zinc-based plated steel sheet is not completely covered with an organic polymer material, but the portions not covered with the organic polymer material are post-plated with zinc. This is to maintain a good condition without impairing weldability. Here, zinc-based plating broadly includes pure zinc and zinc-based alloy plating, and the plating method is not limited.

That is, automobiles, building materials, and home appliances are all assembled by welding after pressing steel strips. Steel plates with various surface treatments are combined and welded under the same welding conditions, but at this time, if there are parts covered with organic polymer substances, the welding conditions will be different, reducing welding strength and causing defects. becomes. In order to prevent this, in the present invention, cationic electrodeposition using an organic resin emulsion is applied to an extent that does not completely cover the zinc-based plating surface, and in the subsequent electroplating, zinc-based plating is applied to an extent that does not completely cover the organic matter. be. The zinc-based plating mentioned here is also the same as above.

Here, the organic resin emulsion of the present invention is one that is entirely cationized by a surfactant strongly adsorbed to an organic polymer in an aqueous solution.

Since the pH range in which this organic polymer emulsion can be stably dispersed varies depending on the type of organic polymer and the combination of surfactant used, there is no need to particularly limit the pH of the bath in the present invention. In addition, various electrolytes are used to impart conductivity to the bath, but there is no need to limit the chemicals in particular, as the appropriate pH depends on the combination of the type of organic polymer and the surfactant used.

Cationic electrodeposition that does not completely cover the galvanized surface is achieved by adjusting the organic resin concentration in the organic resin emulsion solution and the electrodeposition conditions. In other words, the organic resin concentration is 0.1 gin
- 50 g/i is good; if it is less than 0.1 g/i, the effect of the present invention is almost negligible, and if it exceeds 50 g/i, foaming due to the surfactant in the emulsion will be severe, and the viscosity of the solution will increase. This is because managing the bath becomes extremely difficult.

The cationic electrodeposition conditions are well within the characteristic range of rectifiers used in general electroplating, and operating conditions in which the voltage used for normal electrodeposition is particularly high are unnecessary. In other words, the voltage is IV to 40V
The electrolysis time is preferably 0.1 seconds to 10 seconds. If the voltage is less than 17V, the desired effect cannot be obtained, and even if it exceeds 40V, no increase in the effect can be expected.

If the electrolysis time is less than 0.1 seconds, little electrodeposition will occur and there will be no effect; if it exceeds 10 seconds, the surface will be completely covered with electrodeposition, making it impossible to achieve the intended purpose. Bath temperature is 30℃~70℃
is desirable.

In the subsequent galvanizing, only the parts that are not covered with the underlying organic polymer material are galvanized, and strike plating is preferable, but even with a normal zinc plating bath, it is sufficient to reduce the amount of electrodeposition, i.e., zinc adhesion. The amount is l Omg/r
rf -100 rag/rrf is good.

If it is less than 10 rag/m', the coverage of metallic zinc is too small and weldability deteriorates. If it exceeds lOOrag/m', the coverage will be too high and the paint adhesion effect will be lost.

The type of plating bath and the plating method are also not particularly limited.

The electrodeposition solution used in the present invention is as follows.

The organic polymer resin is obtained by emulsion polymerizing the following polymer resin and dispersing it in a solution using a cationic activator.

For example, the following are representative examples, but the invention is not limited thereto.

resol type phenolic resin, polyvinyl butyral resin, Vinyl chloride, vinyl acetate copolymer resin, chlorinated polyethylene resin, polypropylene resin, Styrene-butadiene copolymer resin, acrylic resin, Natural rubber latex.

Representative examples of polyester resins, polystyrene resins, polyacrylonitrile resins, epoxy resins, and surfactants are listed below, but they are not limited to these.

Alkylamine salt, quaternary ammonium salt, alkyl-pyridenium fist halide, alkyl demethylbenzylammonium chloride, polyoxyethylene alkylamine, The conductive aid used in the organic resin dispersion solution is a chemical used in general plating aids. The following are representative examples.

Inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid □ Organic acids such as citric acid, formic acid, and succinic acid
Inorganic substances such as sodium monohydroxide and potassium hydroxide
□ Alkali salts include, but are not limited to, alkali metal salts and alkaline earth salts such as sodium carbonate, aluminum sulfate, and magnesium chloride.

The zinc-based plating bath used in the present invention is a general plating bath such as a chloride bath, a sulfuric acid bath, a zincate bath, a cyanide bath, a sulfuric acid bath, a pyrophosphoric acid bath, or a fluoride bath. General zinc alloy plating such as nickel plating, zinc iron plating, and zinc mankan plating can be used, and there is no particular limitation.

<Example> Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example 1) Pure zinc plating electrodeposited from a sulfuric acid bath (plating weight 20
g/m') Vinyl acetate copolymer resin cationized and dispersed with polyoxyethylene alkylamine on an IA plate at a resin content of 10 g/m KC2100 g/m'
0 under electrolytic conditions of 30V in a solution adjusted to pH 6 with OH.
．． Electrodeposition was performed for 5 seconds. The EPMA line analysis at this time is shown in FIG.

After washing with water, zinc sulfate 240g/i aluminum sulfate 30g/! ; L, 5 OA/dm'X O, 5 in a galvanizing bath with sodium acetate 15 g/fL and bath temperature 40°C
Electrogalvanized for seconds. The amount of zinc plating deposited at this time was 69 mg/rn'. FIG. 2 shows an EPMA line analysis of a sample subjected to cationic electrodeposition and electrogalvanization on an iron plate under the same conditions as at this time.

The thus obtained pure galvanized steel sheets of the present invention and comparative pure galvanized steel sheets (zinc coating amount: 20 g/m') were directly painted. The paint used was acrylic Superlac F47, which was applied to 20 pots. After that, baking was performed at 150° C. for 20 minutes.

Thereafter, the tape was peeled off in a 1-on-one adhesion test. In this case, there was no peeling in both the invention example and the comparative pure zinc example. (See Figures 3a and 3b, respectively). Next, a hot water secondary adhesion test was carried out by immersion in pure hot water at 50°C for 48 hours, followed immediately by a 1st square adhesion test and tape peeling.

As a result, the coating according to the present invention had no peeling, but the coating film of the comparison pure zinc had completely peeled off (see Figures 4a and 4b, respectively).

As described above, the examples of the present invention have excellent direct paint paint adhesion.

(Example 2) A styrene-butadiene copolymer resin was emulsified and dispersed on a hot-dip galvanized steel sheet G90 manufactured by a conventional method using a styrene-butadiene resin, and an emulsion with a resin content of 30 g/l was added to 100 g/41,N.
Cationic electrodeposition was performed on a2SO4 for 4 seconds under electrolytic conditions of 35V in a solution adjusted to pH 4.5 with H2SO4.

After this, through water washing, zinc sulfate 200g/i sodium sulfate 100g/u was placed in a galvanizing bath with a bath temperature of 50°C at 75 A.
/dm'xO, 1 second electroplating was performed.

The thus obtained hot-dip galvanizing of the present invention and the comparative hot-dip galvanizing were compared in the following tests. The paint used was amino alkyd-based Orga 100, which was applied in 20 coats. After this 150℃
Baking was performed for 20 minutes.

Next, a hot water secondary adhesion test was conducted by dipping in pure hot water at 50°C for 48 hours, and immediately thereafter, 111II square adhesion and tape peeling were performed. The coating film of the present invention had no peeling, but the coating film of the comparative hot-dip galvanizing coating completely peeled off.

(Example 3) Electrogalvanized steel sheet manufactured by a conventional method (zinc coating amount 20
g/rn”), resin component 2 in which an organic polymer acrylic resin is emulsified and dispersed with sodium alkylbenzene sulfonate.
KO 0g/l emulsion to 150g 1 sentence KC sentence
Cationic electrodeposition was performed for 1 second under electrolytic conditions of 40 V in a solution adjusted to pH 5 with H.

After this, through water washing, zinc chloride 200g/41 ammonium chloride 100g/! ; Electroplating was performed at 5 OA/drn' for 1.5 seconds in a zinc plating bath with a bath temperature of 45°C.

The thus obtained electrolytic galvanizing according to the present invention and the comparative electrolytic galvanizing were compared in the following tests.

The paint used is acrylic Superlac F47, 20μ
Coated. After that, baking was performed at 150° C. for 20 minutes.

After this, the tape was peeled off in the 1st second adhesion test.

As a result, 1, there was no peeling of the coating according to the present invention, but the coating film of the comparative pure zinc coating completely peeled off.

(Example 4) 30 g of a resin in which styrene-butadiene copolymer resin was emulsified and dispersed with fatty acid soap on a steel plate electrolytically zinc-nickel plated (coating amount Zn equivalent: 20 g/m') manufactured by a conventional method.
/l emulsion to 100g1n, Na2SO4
2S 04 Tep) Ia,! 35 in a solution adjusted to i.
Cationic electrodeposition was performed for 4 seconds under the electrolytic conditions of V.

After this, through water washing, 200 g/Jl of zinc sulfate, 100 g of nickel sulfate, 1 liter of sodium sulfate, 1 liter of boric acid, and 75 A/dm' x 0.3 seconds electricity in a zinc-nickel alloy plating bath with a bath temperature of 50°C. Plated.

The thus obtained zinc-nickel electroplated steel sheets of the present invention and comparative zinc-nickel electroplated steel sheets were compared in the following tests.

The paint used was amino alkyd-based Orga 100, and 20
I applied it. After that, baking was carried out for 20 minutes at 15Q"0.

Next, a hot water secondary adhesion test was conducted by dipping in pure hot water at 50° C. for 48 hours, and immediately thereafter, the adhesive tape was peeled off by 1 mm squares.

The coating of the present invention had no peeling, but the comparative zinc-nickel electroplated steel sheet showed 30% coating peeling.

<Effects of the Invention> According to the present invention, cationic electrodeposition is partially performed on a zinc-based plated steel sheet in an emulsion treatment bath of an organic polymer resin,
Furthermore, by applying electrolytic zinc plating to an extent that does not completely cover the cationic electrodeposited portion, a zinc-based composite plated steel sheet with excellent paintability, paint adhesion, and post-painting corrosion resistance can be obtained even by direct painting.

[Brief explanation of drawings]

FIG. 1 is a diagram in which organic matter was detected as carbon in EPMA line analysis when an organic resin was cationically electrodeposited to such an extent that it did not completely cover the surface of a galvanized steel sheet. FIG. 2 is an EPMA line analysis in the case where electrogalvanizing was performed to an extent that did not completely cover the organic resin after cationic electrodeposition, and organic matter was detected with carbon and is shown together with zinc. Figures 3a, 3b, 4a and 4b are photographs substituted for drawings showing the metal structure. Figures 3a and 3b are photographs of the present invention example and comparative example of the paint adhesion test in Example 1, respectively. FIG. 4a and FIG. 4b are photographs of the present invention example and the comparative example of the paint adhesion test in Example 1, respectively. Patent attorney Yo Ishii -1°・;:′;. 1゛'" L1 d - FIG, 1 τ p -111, 1, - F I G, 2 words B) J FIG, 3a FIG, 4a

Claims (1)

[Claims] In a treatment bath in which an emulsion of organic polymer resin is dispersed,
Cationic electrodeposition is applied using a zinc-based plated steel sheet as a cathode to an extent that does not completely cover the zinc-based plating surface, and further zinc-based plating is applied to an extent that does not completely cover the organic polymer resin electrodeposited layer. A method for producing zinc-based composite plated steel sheets with excellent paint film adhesion for direct painting.