JPS5845903B2 - Treatment method for galvanized coating surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment method for galvanizing, particularly for preventing corrosion and coloring the surface of a hot-dip galvanized coating.

Conventionally, galvanizing has been applied as a long-term corrosion protection method for steel materials or steel products, and it is well known that large structures such as power transmission towers in particular are coated with hot-dip galvanizing.

This corrosion prevention method is far superior to the commonly used method of coating with paint, but as air pollution progresses and zinc is depleted rapidly,
Currently, it is no longer possible to expect long-term corrosion protection effects as before.

In order to make the long-term corrosion protection inherent in galvanizing effective, it is necessary to have an organic coating on the galvanized surface to prevent contact with corrosive factors such as water and the atmosphere. With the recent increase in the size of structures, there is a strong need for colored and beautiful structures to be used as aviation signs or from the aesthetic point of view of harmonizing with the environment.

For the reasons mentioned above, at present, oil-based paints or synthetic resin-based paints are applied to galvanized surfaces.

However, this type of paint is not always in a satisfactory condition;
The paint film peels off from the surface of the galvanized layer at an early stage.

Furthermore, as structures become larger, repainting for maintenance becomes difficult, so synthetic resin paints such as epoxy resin enamel and polyurethane resin enamel are used as top coats for long-term durability and color retention. However, there is currently no definitive method for treating galvanized surfaces to improve the adhesion of these top coats.

The present invention attempts to solve the above-mentioned current problems by a treatment method in which a coating composition comprising a specific amount is applied to a galvanized surface.

That is, the present invention provides: (a) solid content of the epoxy resin or polyurethane resin composition: 90 to 15 weight, (b) metal zinc powder, 5 to 50 weight ★, and (c) calcium leadate, 5 to 35 weight φ This relates to a method for treating the surface of a galvanized coating, which comprises applying a coating composition comprising a mixture of the following: and drying the coating composition to form a coating layer.

The epoxy resin composition used in the present invention is composed of a mixture of an epoxy resin containing at least two epoxy groups at its terminal end and a crosslinking agent that chemically reacts with the epoxy resin.

Examples of the epoxy resin include linear bisphenol type epoxy resin, methyl-substituted bisphenol type epoxy resin, side chain bisphenol type epoxy resin, phenol novolac type epoxy resin, cresol type epoxy resin, polyphenol type epoxy resin, and aliphatic type epoxy resin. , aromatic type epoxy resin, cyclic aliphatic type epoxy resin, ether ester type engineered epoxy resin, etc. Commercially available product names include Epicote (trade name manufactured by Shell Chemical Co., Ltd.), Epiclon (trade name manufactured by Inu Nippon Ink Chemical Industry Co., Ltd.), etc. Typical examples include Araldite (product name manufactured by Ciba Geigy) and Araldite (product name manufactured by Ciba Geigy).

These are not limited to the use of only one type, but it is also possible to use two or more types in combination to bring out the characteristics of each.

The crosslinking agent for the epoxy resin may be any one that has a group that reacts with the epoxy group or hydroxyl group contained in the epoxy resin molecule and is commonly used as an epoxy resin crosslinking agent. .

For example, diethylenetriamine, triethylenetetramine, metaxylylenediamine, metaphenylenediamine,
Aliphatic or aromatic polyamines such as heterocyclic diamines; secondary and tertiary amines such as dimethylaminomethylphenol, tris(dimethylaminomethyl)phenol, piperidine; polyamide resins; amine adducts (generally referred to as amine adducts); In addition to amino compounds such as (known), isocyanate compounds such as tolylene diisocyanate and hexamethylene diisocyanate, phenol resins, acid anhydrides, melamine resins, urea resins, and the like.

Since the objects of the present invention are generally large-sized steel materials and large-sized steel products, it is preferable to use an amino-based compound that allows the chemical reaction between the epoxy resin and the crosslinking agent to proceed at room temperature or forced drying.

The polyurethane resin composition of the present invention refers to a polyol containing at least two or more hydroxyl groups in the molecule, such as a polyester resin, a polyester-modified acrylic resin, a polyester-modified epoxy resin, an epoxy-modified acrylic resin, and tolylene diisocyanate, hexamethylene diisocyanate. It is a mixture with incyanate compounds such as.

The coating composition used in the present invention includes (a) a solid content of the epoxy resin or polyurethane resin composition of 90 to 15 weight φ, preferably 70 to 30 weight φ, and (b) metal zinc powder of 5
-50 weight φ preferably 20-40 weight cake, and (c) calcium leadate 5-35 weight φ preferably 10-30
It is advisable to mix the weight φ.

In the above coating composition, if the amount of either metal zinc powder or calcium leadate is less than 5 weight φ, there is almost no effect on imparting long-term adhesion of the coating film to the galvanized surface. If the amount of zinc powder is increased by 50% by weight, poor adhesion of the coating film will occur at an early stage.

On the other hand, when the amount of calcium leadate increases by 35 weight,
Like metallic zinc powder, it impedes the initial adhesion of the coating and increases the cost of the product, so it is not economically desirable.

The coating composition used in the present invention is basically composed of the above-mentioned quantitative ratio, but if necessary, additives such as pigments such as talc, mica, iron oxide, and zinc chromate, coupling agents, and chelate compounds may be added. It is also possible to use other solvents, anti-sagging agents, anti-settling agents, surface conditioners, etc. that are known and commonly used as raw materials for paints.

The method of the present invention is to apply a coating composition having the above-mentioned composition to a galvanized surface by a known method such as brushing, spraying, or rolling so as to obtain a dry film thickness of about 10 to 300 microns. The resin or polyurethane resin and the crosslinking agent may undergo a chemical reaction, and the coating film may be cured under conditions necessary for drying the coating film.

Since the above-mentioned coating composition mainly contains cheap pigments, it may be difficult to obtain the desired hue, and in that case, polyurethane resin paint, epoxy resin paint,
Any desired color paint such as chlorinated rubber paint, vinyl chloride resin paint, etc. may be applied over the surface of the dried coating film as a top coat.

The coating film obtained by the treatment method of the present invention exhibits strong durability against long-term exposure, and has stable adhesion over a long period of time without peeling or detaching in a short period of time unlike in conventional methods. It is something.

The specific effects of the present invention will be shown below by way of examples.

In addition, "part" or "part" in Examples and Comparative Examples is "part by weight".
Or it means "weight φ".

Example 1 Using a linear bisphenol type epoxy resin having an epoxy equivalent of 450 to 500 and a polyamide resin having an active hydrogen equivalent of 150 as a crosslinking agent, the epoxy resin and the crosslinking agent were mixed in an equivalent ratio to obtain an epoxy resin composition.

Next, a coating composition having the composition shown in Table 1 below was prepared.

Similarly, a coating composition outside the scope of the present invention was also prepared for comparison.

Next, the surface of the hot-dip galvanized steel sheet was brushed to a dry film thickness of 80 microns, and dried for 7 days at 20° C. and 75% RH to obtain specimens for the present invention and for comparison.

Example 2 A linear bisphenol type epoxy resin having an epoxy equivalent of 900 to 1000 and an amine adduct having an active hydrogen equivalent of 200 as a crosslinking agent were used to mix the epoxy resin and the crosslinking agent in an equivalent ratio to obtain an epoxy resin composition. .

A coating composition having the composition shown in Table 2 was then prepared.

Similarly, a coating composition outside the scope of the present invention was also prepared for comparison.

Next, the surface of the hot-dip galvanized steel sheet was air-sprayed to a dry film thickness of 50 microns, and heated at 20°C and 75% R.
It was left to dry for 24 hours under H conditions ☆.

Next, acrylic resin [Acrydic A] was applied to the surface of the coating film.
-801: produced by Dainippon Ink and Chemicals Co., Ltd.] 60 parts, polyisocyanate [Takenate D-11ON; produced by Takeda Pharmaceutical Co., Ltd.] 13 parts, titanium oxide 15 parts, and butyl acetate 12 parts. Dry film thickness 3
Air spray paint to 0 micron, 20℃, 75℃
Test pieces for the present invention and for comparison were obtained by leaving them to dry for 7 days under conditions of % RH.

As a comparative sample/169, the same polyurethane resin enamel used in Example 2 was air-sprayed directly onto the surface of a hot-dip galvanized steel sheet to a dry film thickness of 50 microns, and the coating was applied under conditions of 20°C and 175% RH. The specimen was left to dry for 7 days to obtain a comparative sample //69.

Comparative test 1゜Samples of the present invention/161-12 and comparative samples/I61-
In order to test the adhesion of the coating film to the initial galvanized surface using 10 test pieces, 11 vertical strips reaching the galvanized surface were cut into the coating film at intervals of one thread in width using a cutter knife.
Insert 11 horizontal cutting lines that cross at right angles to form 100 squares.

Next, cellophane tape is pressed onto the squares, and then the cellophane tape is instantly peeled off, and the number of remaining squares is expressed as a percentage.

On the other hand, using another specimen, two cut lines reaching the galvanized surface diagonally crossing in the center of the specimen were made, and the specimen was exposed outdoors for 2 years and 6 months.

After two and a half years, the coating film surface was observed to confirm the presence or absence of coating film defects and abnormalities, and then the coating film of the same sample was treated and judged using the same procedure as the initial adhesion test. The adhesion quality after long-term exposure was determined.

The results of the above comparative test are shown in Table 3.

Comparative Test 2 The test pieces of the invention samples 1 to 12 and comparative samples 1 to 10 were immersed in a saline solution with a concentration of 3 weight for 6 months, and then the test pieces were taken out and left at room temperature for 24 hours. and scatters the moisture in the paint film.

Next, 11 vertical and 11 horizontal cutting lines were cut at right angles to the galvanized surface at intervals of 1 width to form 100 squares, and cellophane tape was applied to the squares. After crimping, the cellophane tape is instantly peeled off, and the number of remaining squares is expressed as a percentage to judge whether the adhesion is good or bad.

The results are shown in Table-4.

From the above comparative test results Tables 3 and 4, it is clear that the galvanized coating treated with the coating composition having a specific composition as in the present invention maintains long-term corrosion resistance and also has excellent coating adhesion. .

Although an epoxy resin composition was used in the above examples, substantially the same results can be obtained with a polyurethane resin composition (for example, composed of a polyester resin and an isocyanate compound).

Claims (1)

[Scope of Claims] 1 (a) solid content of epoxy resin or polyurethane resin composition 90 to 15% by weight, (b) metal zinc powder 5 to 50% by weight, and (c) calcium leadate 5 to 35% by weight. A method for treating the surface of a galvanized coating, which comprises applying a coating composition prepared by mixing heavy weight rice cakes and drying the coating composition to form a coating layer.