JPS5888076A - Method for applying paint containing zinc powder - Google Patents

Abstract

PURPOSE:To enable to obtain excellent adhesiveness even when paint is applied within a short time after being prepared, in coating a cold-rolled steel sheet, by repeating the agitation of the paint where zinc powder is dispersed into a binder in company with standing periods, and then applying the paint. CONSTITUTION:After a cold-rolled steel sheet is degreased and acid-pickled, an aqueous solution for stabilizing a film on the metallic surface is applied to it so that the total amount of chromium contained in the film is controlled at 30mg/m<3>, to form an underbedding fim. Thereafter, epoxy paint containing zinc powder at a ratio of 85wt% based on a dry paint film is applied to obtain an anticorrosive steel sheet. Hence, the zinc powder-contg. paint must be matured for about 6 days until its application after preparation; otherwise the excellent adhesiveness of the paint film would not be obtained. However, when the paint is repeatedly agitated, e.g. once a day for on hour or twice a day for one hour every cycle in company with a standing period, to uniformly disperse the zinc powder, the maturning period can be shortened to about 2 days.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for coating a zinc powder-containing paint that improves paint film adhesion.

After that, a pre-treatment or an undercoat was applied in place of the pre-treatment, and then a paint containing a large amount of zinc powder was applied.
There is a problem in that if the manufacturing loft of the paint is different, or if the painting mill is different even if the manufacturing loft is the same, the adhesion of the paint film changes regardless of the painting conditions.

The present inventors conducted various investigations into the causes of this change in paint film adhesion and found that the cause lies in the period from the time of manufacture of the paint to the time of application.

Conventionally, in the case of paints, the adhesion of the paint film does not change even if the paint is applied immediately after toning, or even if it is left for a long time and then redispersed by stirring and applied. However, according to the research conducted by the present inventors, it was found that paints containing a large amount of zinc powder require an aging period after being manufactured and before being painted.

The curve in the attached drawing shows this state. After degreasing and pickling a 0.8-mm cold-rolled steel plate by the usual method, a stable aqueous solution for metal surface coating with the following composition was applied to completely remove the total amount contained in the coating. In close contact bending of a corrosion-resistant steel plate, which was coated with an epoxy paint containing 85% by weight of zinc powder in dry coating on the undercoat film, which was coated with a chromium content of 30q4II to form an undercoat film. This shows the adhesion of the paint film.

Stable aqueous solution composition for metal surface coating 46% of hexavalent chromium or chromium trioxide reduced to trivalent chromium 10 parts by weight IJ/acid (100% HsPO4) 3.6 parts by weight Polyacrylic acid 4.2 parts by weight Acrylic emulsion Polymer solid content 19 parts by weight water
2300 parts by weight As is clear from the curve in the accompanying drawing, good paint film adhesion cannot be obtained in the case of a paint containing zinc powder unless it is aged for about 6 days after manufacture and before painting.

It is not clear why zinc powder-containing paints require such a long maturing period, but even in the case of conventional zinc-rich paints that are simply used for corrosion prevention, zinc powder can account for 60% or more of the dry coating weight. Furthermore, if the paint film is to have electrical conductivity, it must be contained at 80 to 96%, so the pigment content is more significant than that of conventional general paints, and unless a certain period of aging is provided after production, zinc powder This is thought to be because the binder resin does not become compatible.

Therefore, in order to improve the film adhesion of zinc powder-containing paints, it is sufficient to age them for about 6 days after manufacture before painting them, but since the aging period of paints is this long, the painting process depends on the paint manufacturing process. There was a problem with being restricted.

The inventors of the present invention have conducted various studies in order to solve this problem, and as a result, the paint has been repeatedly stirred after it has been manufactured. It was found that the ripening period was shortened.

In the present invention, it is not necessary to continuously stir the paint after it has formed, for example, once a day for 1 hour, or twice a day for 1 hour.
Stirring may be preferably carried out in cycles, with periods of standing still for hours at a time. Stirring is performed in the atmosphere using a powerful stirrer such as a Desper to uniformly disperse the zinc powder.

When stirring is added to step 5, the aging period of the paint is shortened to about two days, less than half of the conventional time.

Once the paint has matured in this way, there is no need to add stirring after that, but if it is suitable for 15 to 20 days after manufacture,
Although no deterioration is observed in the adhesion of the coating film, a chemical change occurs unnecessarily between the binder and the zinc powder, resulting in an extreme deterioration in corrosion resistance. Therefore, it is appropriate that the zinc powder coating is aged as described above for two days after manufacture and applied within 3 to 20 days, preferably 3 to 15 days after manufacture.

This effect of improving the adhesion of the paint film by stirring is observed whether the coating pretreatment is chromate-based or phosphoric acid-based, and is also observed even when a special undercoat is used.

For example, a special undercoat is a corrosion-inhibiting bond coating composition for metal surfaces described in Japanese Patent Publication No. 45-24230;
6882, the mixture in an aqueous liquid medium of JP-A-48-29641, the dried residue of the concentrated composition described in JP-A-49-22423, Ilf JP-A-54-117
Even the dried residue of the precursor composition of the prepaint coating composition described in No. 80 or the stable aqueous solution for coating metal optical surfaces described in JP-A-54-110145 is effective.

The present invention can be applied as an anticorrosive pigment to paints containing zinc powder as the main component, and as long as the main component is zinc powder, other coloring pigments, Cu, Cr, and AI may be used.

Even if it contains anticorrosive and electrically conductive pigments such as Cd, magnetite, and carbon, the effect remains the same.

Furthermore, although epoxy resin has traditionally been used as a binder for zinc powder, other resins may also be used, and additives such as curing agents and curing accelerators may be added as needed. A similar effect can be expected.

Example A cold-rolled steel plate with a thickness of 0.8 mm was degreased and pickled by a conventional method, and then a stable aqueous solution for coating metal surfaces having the above composition was applied so that the total amount of chromium in the film was 26 mm. A corrosion-resistant steel plate was manufactured by applying a coating composition having the following composition, which was stirred after production using the cycle shown in No. 16, to a dry coating thickness of 10 μm.

Paint composition Zinc powder 85% by weight (in dry coating film) Epoxy resin 15% by weight (same as above) (molecular weight approximately 50,000) Solvent Methyl ethyl keto/and cyclohexanone Aging period after paint production and coating film for this corrosion-resistant steel plate When the adhesion was investigated, the results shown in Table 1 were obtained.

The adhesion of the paint film was determined in accordance with the JIS-G 3312 test method for colored galvanized iron sheets. After performing close bending (01 bending) in which the inner side of the sheet is in contact with the bent side under normal conditions, cellophane tape is applied to the outer side of the bend and peeled off. and evaluated based on the following criteria.

As shown below, if a zinc powder-containing paint is repeatedly stirred and aged after production, good film adhesion can be obtained even if it is applied within a short period of time after production. The problem of adhesion is solved, and the aging period is also shortened.Therefore, the adjustment of the paint manufacturing process and the painting process becomes easier than before.

[Brief explanation of drawings]

The attached drawing shows the relationship between the number of days after manufacturing a paint containing zinc powder and the adhesion of the paint film. Patent Applicant Mitsuru Shindo, Agent for Nissin Steel Co., Ltd. Continued from page 1 0 Author: Katsu Suzuki Inside the Product Research and Development Center of 1 Nisshin Steel Co., Ltd., 7 Takaya Shinmachi, Ichikawa City 0 Author: Koji Wakabayashi Takaya, Ichikawa City Inside the Product Research and Development Center of Ichishin Steel Co., Ltd. at Shinmachi 7.

Claims (1)

[Claims] A method for coating a paint containing zinc powder, which comprises dispersing the zinc powder in a binder to form a paint, adding the zinc powder repeatedly to the paint while allowing it to stand for a period of time with stirring, and then painting.