JPH06206046A - Method for coating rusted steel with coating material for rust surface - Google Patents

Abstract

PURPOSE:To enhance the reliability in the long-term durability of a coating film by obtaining a method for applying coating material for a rust surface to rusted steel capable of preventing the generation of a pinhole by applying the coating material for the rust surface after the thickness of the rust layer on rusted steel measured by a magnetic force type film thickness meter is adjusted to 30mum or less. CONSTITUTION:In the coating of rusted steel with coating material for a rust surface, the thickness of the rust layer on rusted steel is measured by a magnetic force type film thickness meter to be adjusted to 30mum or less before the coating material for the rust surface is applied to rusted steel. For example, the thickness of the rust layer is adjusted to a definite value, for example, to 30mum or less by a treatment tool such as a wire wheel, a wire brush, a grinder, a sand blasting device or a tortoise-shaped scrubbing brush to coat rusted steel with a low grinding and cleaning type coating material. Whereupon, the coating material penetrates into the deep part of the rust layer to be replaced with the air in the rust layer or the moisture in the deep part of the rust layer comes into contact with the air in the rust layer to generate chemical reaction. By this mechanism, moisture is taken in the resin of coating material not only to prevent the generation of a pinhole but also to enhance film durability to a large extent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for coating a rust surface of rust steel such as steel members such as ships, offshore structures, bridges and thermal power plants and steel products.

[0002]

2. Description of the Related Art According to the catalog of a paint manufacturer on the market, how to use a low-polishing type paint (paint for rust surface) for ships is, for example, painting on a rusted steel plate left for 1.5 months outdoors. In that case, there is a description of lightly removing dust on the surface as a pretreatment method for coating, and a color photograph thereof is also shown. Then, after this, a low-abrasive cleaning type paint is applied.

[0003]

SUMMARY OF THE INVENTION For the purpose of confirming the performance, a mild steel material is used for the pre-painted rusted steel plate + low abrasive cleaning type paint shown in the above-mentioned paint maker's catalog by the present inventors. (SS41 material) 150 mm x 70 mm x 3.2 mm
(Thickness) Blasted steel sheet is exposed for 1.5 months, followed by low-polishing treatment (using a commercially available scrubbing brush) based on the specifications of the coating manufacturer, and a low-polishing-type coating of a major domestic coating manufacturer ( Each tank (for tanks) was coated once with an airless spray coating machine according to the manufacturer's specifications to a dry thickness of 250 μm. The next day, when I visually inspected the surface of the coating film, there were small air bubble marks in all of them.
When the presence or absence of pinholes was checked with a wet pinhole inspection device (D, C250V, manufactured by Sanko Co.), many pinholes were detected.

[0004] Such a coating film cannot be used because a coating film defect (rust swelling) occurs in a short period of time. This is because the specifications of the conventional pretreatment are the exposure period and the treatment equipment (Tawashi)
And that it is specified in the color surface photograph before and after the treatment. In other words, the degree of rust on bare steel depends on the location of exposure and the climate (temperature / humidity, rainfall) at the time of exposure, etc.
From what is known to be different, it is necessary to provide some kind of quantitative standard for the rusted surface and take the above-mentioned measures for preventing pinholes during painting.

In view of the above-mentioned state of the art, the present invention aims to provide a method for coating a rust surface paint on rust steel which can prevent the occurrence of pinholes.

[0006]

Means for Solving the Problems If the present inventors define the rust thickness of a rust steel plate, the low-abrasive-cleaning type paint to be applied thereon does not cause pinholes and has long-term durability. Based on the assumption that it can be expected, the following experiments and examinations were carried out, and the above-mentioned drawback (pinhole generation) could be eliminated. As a general method of measuring the rust thickness of a rusted steel plate, the steel plate is cut in the plate thickness direction, the cross section is observed with a microscope, and rust is dissolved and removed by the pickling method. A method for calculating the amount of rust on a metal is known. These methods have the disadvantage that the former method cuts at the production site, and the latter method has the problem that the neutralization treatment after the pickling treatment or the pickling method itself is difficult to use at the production site.

The inventors of the present invention happened to measure the rust steel plate with a magnetic force type film thickness meter, and as a result, found that the rust thickness can be accurately measured, and completed the present invention based on this finding.

That is, according to the present invention, the thickness of the rust layer of rust steel is measured with a magnetic force type film thickness meter and adjusted to 30 μm or less, and then a rust surface paint is applied to the rust surface. It is a method of applying paint for use.

[0009]

[Function] A low-polishing-cleaning type paint having a rust thickness of 50 to 60 μm
When coated on the rust surface (using a magnetic force type film thickness meter), the paint does not reach the deep part of the rust layer, and as a result, it hardens and dries with the water and air in the rust layer. It is presumed that the air in the rust layer will become a pinhole mark during drying, or the water in the deep part of the rust layer will not come into contact with the paint to chemically react, resulting in poor coating performance. It In order to solve this, for example, a rust thickness is adjusted to a constant value, for example, 30 μm or less, preferably 20 μm or less, by using a processing tool such as a wire foil, a wire brush, a grinder, a sandblaster, and a tortoise brush and a magnetic film thickness meter.
When a low-abrasive paint is applied, the paint penetrates deep into the rust layer and replaces the air in the rust layer, or the water in the deep part of the rust layer comes into contact with the paint to cause a chemical reaction. It is presumed that, by taking in water into the resin of the paint, no pinhole is generated and the durability of the coating film is greatly improved.

As described above, when the low-polishing-type paint is applied to the rust surface, a good coating film can be obtained by keeping the rust thickness below a certain value under the control of the magnetic film thickness meter. I understood.

In the present invention, as the rust surface paint, amine-cured epoxy resin-based paint, amine-cured tar epoxy resin-based paint, isocyanate-cured epoxy resin-based paint, isocyanate-cured tar epoxy resin paint, etc. can be used.

[0012]

EXAMPLES The present invention will be described in more detail below with reference to examples. Table 1 shows shot blasted steel plate (150mm × 7
0 mm x 3.2 mm, surface roughness: Max 60-70, blasted SIS Sa3) exposed outdoors, and after 1 week, 2 weeks, 3 weeks, 4 weeks, 1.5 months and 2 After 5 months, the rusted thickness is measured by a commercially available magnetic film thickness meter for measuring coating film thickness (Kent company: LE-300 type). From this table, it can be seen that the rust thickness increases as the number of exposure days increases. It was also found that the rust thickness can be measured with a magnetic film thickness meter with sufficient accuracy. Next, the results of the coating test using these rusted steel plates are shown below. In addition,
In addition to these magnetic force type film thickness meters, microtesters, inspectors, elcometers, etc. are commercially available, and these can also be used.

[0013]

[Table 1]

(Experimental Example 1) Using the rusted steel plate exposed for 2.5 months shown in Table 1, as a pretreatment for coating (the dust on the rust surface is lightly removed by painting) and low polishing Scavenging treatment (a commercially available scrubbing brush was used to lightly reciprocate the rust surface once) was performed. As for the rust thickness at this time, the average thickness of the treated plate was 55 μm, and the range was 50 to 60 μm.
In addition, low polishing treatment averaged 45 μm, range 40-50
was μm. For these rusted steel plates, products from 3 companies (Company A,
A low-abrasive cleaning tank paint (Amine-cured tar epoxy resin paint) of companies B and C) was applied once by airless spray coating to a dry thickness of 220 μm according to the manufacturer's specifications.
Next, as a result of performing a wet pinhole test (manufactured by Sanko Co., DC250V) after drying for one week in the room, as shown in Table 2, pinholes were detected and the coating film was defective.

[0015]

[Table 2]

(Experimental Example 2) Using the rusted steel plate exposed for 1.5 months shown in Table 1, two types of the pre-painting treatment, that is, the untreated one and the low-polishing treatment, were carried out in the same manner as in Experimental Example 1. went. The average rust thickness at this time is 25μ for the treated plate
m, the range was 20 to 30 μm, and the low polishing treatment had an average of 15 μm and the range was 10 to 20 μm. On these rusted steel plates, the same paints for low-abrasive cleaning tanks manufactured by the same three companies as in Experimental Example 1 were applied to a dry thickness of 220 μm as in Experimental Example 1, and the same coating film as in Experimental Example 1 was dried. And a pinhole test were conducted, and the results are shown in Table 3.

[0017]

[Table 3]

As shown in Table 3, no pinholes were detected in any of the products of the three companies, as-is, and in the low polishing treatment, and the state of the coating film was good. Next, it was decided to examine the long-term durability of these test plates.

(Experimental Example 3) With respect to the coating test plates (three company products, the ones used as pretreatment, those subjected to low blasting treatment, coating thickness 220 μm) prepared in Experimental Example 2, the ballast tank (seawater) of the ship was used. An accelerated deterioration immersion test was conducted to examine the long-term durability in the tank. As an accelerated deterioration test, a 40 ° C, MHI solution immersion test shown in Note 3 of Table 4 was performed for 40 days, and the evaluation items at that time were appearance evaluation (generation of rust swelling) shown in Table 4 and frequency 1 by the AC impedance method.
Tan δ in Hz and bond strength. An outline of these methods is shown in Note 2 and Note 4 in Table 4.

From the appearance evaluations shown in Table 4 and the test results of tan δ and adhesion strength at a frequency of 1 Hz by the AC impedance method, the ones coated as they were (rust thickness of 20 to 30 μm) were the products of all three companies. It is estimated to have sufficient practicality. Also, low polishing treatment (rust thickness 10 to 20μ
It was found that the products coated on m) were superior in coating film durability to the products of all three companies as compared with the above-mentioned coating test plates as they were. From this result, it was found that the coating film durability can be controlled by defining the rust thickness by the magnetic force type film thickness portion.

[0021]

[Table 4]

(Note 1) Two test pieces were used for each test. (Note 2) Tan δ at 1Hz by AC impedance method
Value ○ Measuring device: FRA device (manufactured by NF Design Circuit Block) ○ tan δ value: It was authorized by the Japan Shipbuilding Research Association, and when the tan δ value is about 10 or more, coating film defects occur. A tan δ value of 1 or less is a sound coating film (Note 3) MHI liquid immersion test: This is an accelerated seawater resistance test method that was authorized by the Japan Shipbuilding Association. It is estimated that 40 days immersion in this way is equivalent to 10 to 20 years of natural seawater. (Note 4) Adhesion strength: Authorized by the Japan Shipbuilding Association, if 20 kgf / cm ² or more is considered sound.

(Experimental Example 4) As a result of performing the same test as in Experimental Examples 1 and 2 on the low-abrasive cleaning paint for non-submersible parts made by three domestic paint manufacturers, almost the same result as Experimental Examples 1 and 2 was obtained. was gotten. In addition, for the test plates of the low polishing cleaning type paint for non-submersible parts of three companies manufactured in the same manner as in Experimental Example 2, JIS K5
Results of seawater spray test specified in 400 for 1,000 hours (appearance evaluation, AC impedance method frequency 1 Hz
Tan δ and the adhesion strength), and the one coated on the raw material was practically good, and the one coated on the low-abrasive-treated material was more excellent.

As described above, by controlling the rust thickness to a certain thickness (30 μm) or less, preferably 20 μm or less measured by a magnetic force type film thickness meter, the low-polishing type paint for tanks and the low-polishing type for non-submerged parts can be used. The type paint can be used reliably for a long time in practical use.

[0025]

[Effect of the Invention] It is said that the painting work in shipbuilding is the representative of 3K (messy, hard, and hard), it is difficult to secure young workers, and it is a low-polishing type that can be applied directly on the rust surface. The demand for paints is expected to increase in the future. At this time, if the rust surface is not managed sufficiently, pinholes are generated as shown in Example 1, which makes it impractical. The present invention is a method of coping with this, and by controlling the rust thickness to 30 μm or less, ideally 20 μm or less with a magnetic force type film thickness meter, and applying a low-abrasive cleaning paint on this, The long-term durability of the coating film has improved reliability and can be used with confidence. Further, according to the present invention, some peeling from 3K of the painting work can be achieved, and a great ripple effect to the paint / painting industry is expected.

Claims (1)

[Claims] 1. A rust surface paint for rust steel, characterized in that the rust layer of rust steel is measured with a magnetic film thickness meter and adjusted to 30 μm or less, and then the rust surface paint is applied. How to paint.