JPS59193279A - Steel sheet hot-dip coated with composite zinc-aluminum layer as undercoat for coating - Google Patents

Abstract

PURPOSE:To obtain the titled steel sheet excellent in corrosion resistance and the adhesiveness of a coating film, by sequentially forming an interim medium, a chromate coating film and then an acrylic resin coating film under a specified condition on a steel sheet hot-dip coated with a composite zinc-aluminum layer. CONSTITUTION:An interim medium comprising one or more of Fe, Co and Ni metals, and these oxides in an amount of precipitate adhesion of 10-200mg/m<2> in terms of Fe, Co or Ni metal is formed on the surface of a steel sheet hot-dip coated with a composite zinc-aluminum layer. Then, the aqueous solution of chromic-phosphoric-malonic-boric acids is applied onto said interim medium and dried to form a chromate coating film in an amount of adhesion of chromium of 20-300mg/m<2>. Thereafter, acrylic resin emulsion is further applied onto the chromate coating film and dried to form an acrylic resin coating film having as dried thickness of 0.1-2.5mum.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zinc-aluminum composite hot-dip plated steel sheet for use as a paint base, which has excellent corrosion resistance 8 and paint film adhesion.

Zinc-aluminum composite hot-dip coated steel sheets, which are hot-dipped in a plating bath containing zinc S and aluminum, have several times the corrosion resistance of hot-dip galvanized steel sheets, but they are not suitable for applications that require long-term corrosion resistance. It is generally painted when used for purposes that require a special appearance. Conventionally, when painting this composite hot-dip galvanized steel sheet, a pretreatment such as phosphate treatment or chromate treatment was applied, as in the case of hot-dip galvanized steel sheet, and then a base coat and a top coat were applied.

However, since the above pre-treatment poses pollution problems such as sludge and waste liquid, in recent years 1% of consumers have become more willing to avoid in-house treatment8, and from the viewpoint of labor saving, they are using an undercoat for painting. 2. There are also people who wish to use only a top coat for home painting. For this reason, in recent years there has been a demand for a zinc-aluminum thread composite hot-dip plated steel sheet for use as a painting site, which has excellent corrosion resistance and paint film adhesion and can be coated with a top coat.

The present inventors conducted various studies to provide such a composite hot-dip galvanized steel sheet, and found that if a chromate-based coating with high corrosion resistance and a protective coating with excellent water resistance and paint adhesion were used to break the stock, the chromate-based coating would absorb moisture. ? They discovered that it prevents the elution of more chromium than necessary after painting, has excellent corrosion resistance, and can be directly applied with a top coat.

And as such chromate-based film, chromic acid/
It was discovered that a chromate-based film formed by applying and drying an acid-marinated-boric acid-based aqueous solution and an acrylic resin film are suitable as a protective film. , Co, N1 and one or more of these oxides is equivalent to 1 in terms of the metals Fe, Co, and Ni.
After 0 to 200 shrimp have been deposited, a chromic acid-phosphoric acid-malonic acid-boric acid aqueous solution is applied to the intermediate medium.
The amount of chromium deposited after drying is 20 to 300. A chromate-based film and an acrylic resin film are sequentially formed from the intermediate medium side. -He came to invent the hot-dip galvanized steel sheet.

The present invention will be explained in detail below.

To this invention? The basic composition of the zinc-aluminum composite hot-dipped steel plate is zinc 8 and aluminum, and the amount of added elements is usually 5% or less. There is no problem even if it contains unavoidable impurities. For example, the additive elements include Si, Mg, and La.

Examples include Ce, Cu, Ca, Be, Ti, Cr, etc., and unavoidable impurities include Pb,
Examples include Sn and Fe. 5% AI-Z is generally known as such composite hot-dip galvanized steel sheet.
Examples include n-plated steel sheet (Galfa/) and 55% Al-Zn plated steel sheet (Gal-Zurium). Also, considerable effects can be expected when applied to hot-dip aluminum-plated steel sheets (including those containing Si).

The intermediate material to be deposited on the surface of the composite hot-dip plated steel sheet is Fe, Co, which is soluble in hydrochloric acid, sulfuric acid, or a mixed aqueous solution of both, as disclosed by the present inventors in Japanese Patent Publication No. 55-30596. , Fe, Co, and Ni metals that are dispersed and precipitated when a zinc-aluminum composite hot-dip plated steel sheet is treated with a surface conditioning solution containing one or more of Ni sulfates or hydrochlorides, or these metals. The chromate-based film is an oxide of chromate-phosphoric acid-malonic acid-boric acid disclosed in the same issue, and is left to dry without washing with water after coating.
A film obtained by adding an acrylic emulsion, silica sol, etc. to this aqueous solution, applying it, and drying it can also be used as the chromate-based film of the present invention.

In the present invention, the presence of intermediates on the surface of the plated steel sheet is due to the presence of chromic acid-li/malonic acid-boric acid-based aqueous t
Direct application of i will form a chromate-based film with fairly good adhesion to the plating layer, but the presence of the above-mentioned intermediate will improve adhesion to the plating layer.

This intermediate is dispersed and precipitated on the surface when the zinc-aluminum composite hot-dipped steel plate is immersed in the surface conditioning liquid or sprayed with the liquid, so the treatment is almost equivalent to pickling treatment. It is. Therefore, almost no sludge is generated, and waste liquid is only generated when renewing the liquid, which poses no operational problems.

Furthermore, the chromic acid-phosphoric acid-malonic acid-boric acid aqueous solution used to form the chromate film is a coating-type treatment solution, and the coating becomes a film after removing evaporated components, so no sludge or waste liquid is generated. Furthermore, since there is no problem of aging of the solution, a stable corrosion-resistant chromate film can be formed.

Although the chromate film formed on the awns undergoes dehydration and condensation upon drying, it is flexible and has good processability (
, and has excellent paint film adhesion.

However, in the case of this chromate-based film, Cr"3 in the aqueous solution
/Cr"' ratio approaches 0.1 (as the hygroscopicity increases slightly, and if left as is, moisture absorption will occur by the time it reaches the consumer, and the consumer will have to install a drying method such as 8 to 9 baking). In addition, this chromate film is easily dissolved in water, so even if a top coat is applied, if there are pinholes in the paint film, it will elute quickly (more chromium will be eluted than necessary and the corrosion resistance will not last long). Therefore, in order to prevent the hygroscopicity of the film and the excessive elution of chromium, it is necessary to protect it with a water-resistant protective film with good film adhesion. After seven rounds of various studies regarding the protective film, we found that an acrylic-based one-finger theory was appropriate.

To this invention? It is also possible to improve corrosion resistance and coating adhesion by adding 65 additives to this acrylic resin film within a range that does not impair processability. In the case of the present invention, this acrylic resin film is formed by applying emulsion/.
Water-insoluble or water-dispersible inorganic substances are suitable as additives. For example, to improve the solubility and corrosion resistance, metal sols (e.g. alumina sol, zirconia sol, magnesia sol, titania sol, etc.), JP silica sol, etc. are applied to the film surface, and to improve the anchoring effect, silica colloid, titanium dioxide, etc. /, aluminum silicate, ζlium carbonate, calcium carbonate, clay, talc,
Other additives such as Norium sulfate, Quartzite, and powdered silica can be added.

In the case of the present invention, the amount of f7N of the intermediate mediator is Fe, Co, Nr
Gold metal is made into 10 to 200 shrimp.

If it is less than 10%q, the adhesion of the chromate film will decrease, and if it exceeds 200"9/rr?'l, it will turn into powder,
It causes pitting corrosion and poor adhesion of chromate film.

Also, the amount of chromate film is 20 to 30 in terms of chromium content.
Make sure your back is 0. If the thickness is less than 20mm, the corrosion resistance will be insufficient, and if it exceeds 300mm, the film will become too thick and the adhesion of the protective film will decrease.Furthermore, the thickness of the acrylic resin film is 0.1 to 25μ. Make it so that it becomes 0.
．． If it is less than 1μ, the protective effect of the chromate film until it reaches the consumer will be insufficient, and the sustained effect of edibility after topcoat will be short (requiring a second undercoat.On the other hand, 25μ
Welding becomes difficult if the temperature is exceeded.

The zinc-aluminum composite hot-dip galvanized steel sheet of the present invention can be manufactured using one of the sulfates and hydrochlorides of Fe, Co, and Ni that are soluble in an aqueous solution of hydrochloric acid, sulfuric acid, or a mixed acid of both. -1: The surface W to which two or more types of additives were added is treated with a zinc-aluminum composite molten metal@steel plate spray treatment or immersion treatment to cause the intermediate material to be dispersed and folded onto the surface. In this treatment, the acid concentration of the treatment solution is 0.14 to 15 molt, Fe, Co, Ni
'17 total metal ion concentration 0.05-0.25 moν
If it is t, the intermediate media will be 10 to 200 Wrr? How many deposits are deposited on the surface?

In this way, the intermediate medium Pa was precipitated and washed with water.
, Cr"> reduced with hypophosphorous acid or phosphorous acid (-
Cr+3 has a mower 1/ratio (6+3/C) with Cr4-6.
r+6 arm 0.1~L 5, malo/acid Olo 1~L
Omo! ,/L, boric acid is O, OO5~L O
mollt, and a chromic acid-li/acid-malo/acid-boric acid based aqueous solution having a pH of 0.5 to L5 or 8202. polyvinyl alcohol,
A reducing agent such as ethylene glycol and phosphoric acid? Added aqueous solutions, or aqueous solutions in which one or more of silica gel, alumina sol, water-bathable or emulsion-based organic polymer resins, etc. are added as film-forming agents to these aqueous solutions are coated by a known method and dried, followed by several coats. Amount 20-300
9 Old chromate-based film sounds are formed.

Then, apply an acrylic resin emulsion on top of this chromate film using the same method.

Dry to form an acrylic resin film with a dry thickness of 0.1 to 2.5 μm.

The formation of an acrylic resin film using emulsion uses water as a diluent compared to when applying an organic solvent-based paint, so it is less expensive to form a thin film than in the present invention, and the exhaust gas is free from toxic components. Since it does not contain any harmful substances, it does not require any detoxification treatment.

Drying of the aqueous solution 3 and drying of the emulsion are both carried out at a plate temperature of 50° C. or higher. If the temperature is lower than 50°C, it will take a long time to dry, and even if an epithelial membrane appears to have formed, it will not be sufficiently cured. On the other hand, if the temperature is 50° C. or higher, water in the aqueous solution is evaporated, dehydrated, and condensed to form a hard chromate-based film, while in the emulsion, water evaporates and a strong acrylic resin film is formed. The heat resistance of the n/a mate film thus formed is about 250°C, and the heat-assistance of the acrylic resin film is also about 250°C. Therefore, drying must be carried out using these temperature plates 1, but since it is not economically advisable to dry at temperatures close to these temperatures, it is generally preferable to carry out drying at a temperature below 120°C.

Example 16 Formation of a chemical conversion treatment film using intermediate medium fl'' with the glaze shown in No. 16 on six sides of a zinc-aluminum composite molten metal sheet (plate thickness: 0.5 mm). Then, a resin film was formed and a steel plate for use as a base for painting was manufactured.

(Note) The composition of the aqueous solution is as follows.

A cut was made to reach the plating layer on the steel plate for the coating base of the obtained octopus, and a salt spray test (JIS Z 2371.250) was conducted.
time), humidity test (50°C, humidity 98%, 500 hours)
The results shown in Table 2 were obtained. 2. For coating (note) evaluation, sellotape was pasted on the incision, then rapidly peeled off. 1111111 or less from the cut ○, the peeling width of the film is closer to the cut! 1llll11'2
The test was conducted with △ when the width exceeded 3 or less, and X when the peeling width of the film exceeded the incision by 3 folds.

Next, the steel plate on the painting side was coated with an amino alkyd resin paint with a dry film thickness of 30μ (130~150°C
Dries in 0 minutes). Thereafter, seven tests of paint film adhesion 2 and corrosion resistance (water) were conducted on the obtained coated steel sheets, and the results shown in Table 3 were obtained.

Table 3 (Note 1) The DuPont impact S test is 500 mm with a diameter of 1/2 inch.
After dropping it from the height of a 50-meter vertical saw, apply cellophane tape to the impact area and quickly peel it off.The paint film does not peel off. Evaluation was made on the basis of a rating of ``X'' if the coating film was peeled off by 30% or more.

(Note 2) In the 180 degree close bending test, sellotape is pasted on the outside of the bent part and then rapidly peeled off to determine the peeling state of the paint film. It was evaluated using the same standards as the DuPont impact test.

(Note 3) The Gono-Noku/Me-Erichsen test was performed using a Gopan-mechi notch section, extruded 6 times using a mounting machine, and then affixed cellophane tape to the extruded section and quickly peeled it off to check the peeling state of the paint film. I investigated. Evaluation is DuPont value! It was conducted using the same standards as the g test.

(Note 4) Salt spray test: 2 cuts to reach the plating layer n
After 500 hours of testing in accordance with CJIS Z 2371 K, Serochisin was pasted on the cut area (=J peeling) and evaluated by rapidly peeling it off.Evaluation was ◎: No peeling of the paint film; Items where white rust has occurred or where white rust has been observed ○, the width of the paint film peeling from the notch is 1wh
The test was conducted on the basis of a rating of 3THn or less, and a case in which the width of the coating film peeled from the notch exceeded 3 cylinders.

(Note 5) The humidity test was conducted at 50° C. and 98% humidity for 1000 hours, and evaluated in the same manner as the salt spray test.

As described above, in the zinc or zinc alloy coated steel sheet of the present invention, the highly corrosion-resistant chromate film is tightly adhered to the surface by the intermediate medium, and the highly corrosion-resistant chromate film is protected by the water-resistant acrylic resin film. The anti-corrosion effect lasts for a long time.

patent applicant Nisshin Steel Co., Ltd. agent Mitsuru Shindo

Claims (2)

[Claims] (1) Are F'e, Co, and Ni metals on the surface of a zinc-aluminum composite hot-dipped steel sheet? and an intermediate consisting of one or more of these oxides is Fe, C
A chromic acid-phosphoric acid-malo/acid-boric acid based aqueous solution is applied to the intermediate medium and dried. Chromium adhesion amount 20-300 m9/n? chromate-based film,
A zinc-aluminum composite hot-dip plated steel sheet for use as a paint base, characterized in that an acrylic resin film is formed sequentially from the intermediate medium side. (2) The thickness of the acrylic resin film is 0.1 to 2.5
The zinc-aluminum composite hot-dip plated steel sheet for painting base according to claim 1, which is μ.