JPS5829661A - Metallic pipe coated with resin - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves coating a metal tube with an inorganic conversion coating layer, an epoxy resin primer layer, and an epoxy powder coating layer in this order.
This article relates to a resin-coated metal tube with a three-layer structure.

Epoxy powder coating was developed as an anti-corrosion coating for steel pipes.
It has been commercialized and is widely put into practical use.

This epoxy powder coating is applied by electrostatic powder coating or flow coating by forming an anchor pattern on the outer surface of the steel pipe by blasting, preheating the steel pipe to 200 to 250C, and applying the electrostatic powder coating to remove rust from the outer surface of the steel pipe and provide coating film adhesion. It is formed as a continuous anti-corrosion coating by applying jepoxy resin using a dipping method or the like and heat curing it on the surface of the steel pipe.It usually has a corrosion resistance of 200 to 600.
It has a film thickness of μ. Since this coating is formed from a thermosetting epoxy resin, it has the disadvantage that it is hard and easily damaged by impacts such as handling.

On the other hand, even in a high temperature range, for example, 60 to 100 C, the impact resistance does not decrease and the load resistance is good. However, under high temperature and humidity conditions, due to the high hygroscopicity of the coating,
The occurrence of pristors and a decrease in film insulation resistance were unavoidable.

More specifically, epoxy powder coating has less deterioration in mechanical strength at high temperatures than other existing anti-corrosion coatings such as asphalt mastic, polyethylene, etc. Although it has mechanical strength, which is important as an anti-corrosion coating, it is difficult to use as an anti-corrosion coating because the coating is thin, the epoxy resin itself is more water-absorbing than polyethylene resin, etc., and powder coating has the disadvantages of being able to absorb trapped air. It also has drawbacks such as the fact that the film contains considerable defects due to the generation of decomposed gas during the polymerization reaction. Therefore, the inventors of the present invention focused on the excellent metal surface corrosion resistance of chromium and phosphate, and the good wettability of liquid epoxy resin primer on metal surfaces or chemical conversion coating surfaces, and combined these to create an epoxy powder resin. When we tried to improve the corrosion resistance by laminating the film, we found that it has excellent water resistance, and overall has excellent mechanical strength and corrosion resistance in the high temperature range (especially the cathodic electrolytic peeling resistance and the secondary adhesion of the coating). We were able to obtain a resin-coated metal tube exhibiting the following properties. When only a chemical conversion coating was formed prior to the epoxy powder coating, the epoxy powder resin had a relatively high viscosity when melted, so the wettability was poor compared to the liquid Evokin I'IJ resin primer. On the other hand, when only a liquid epoxy resin primer was formed, the wetting with the upper layer epoxy powder resin was good, but there was a defect that the interface between the metal surface and the liquid epoxy resin/primer was destroyed by water intrusion.

The purpose of the present invention is to maintain the advantages of conventional epoxy powder coatings while improving the corrosion resistance, particularly the cathodic electrolytic peeling resistance and secondary adhesion of the coating, so that it can be used as a high-temperature anticorrosion coating. The object of the present invention is to provide a resin-coated metal tube that is possible.

The resin-coated metal tube according to the present invention includes an inorganic conversion coating having the ability to passivate the metal surface formed on the outer surface of the metal tube, a layer of liquid epoxy resin primer formed on the coating, and a layer of liquid epoxy resin primer formed on the coating. It has a coating structure consisting of a formed epoxy powder coating layer.

An inorganic chemical conversion coating having the ability to passivate metal surfaces (c) is formed by applying an inorganic chemical treatment liquid to the outer surface of a metal pipe, for example, a steel pipe, after removing rust with plastin ink and forming an anchor pattern.This invention Specific examples of inorganic chemical conversion film formation by:

1) Coating-type chromate-1-coating The hexavalent chromium Cr6+ is /1 with respect to the total chromic acid content.
．． 5-75wt%% trivalent chromium Cr3+ 55-25w
A chromate aqueous solution containing t% is applied to the outer surface of the metal tube and dried to form a chromate film. This Cr6+ (3
) If Cr3"- is 45% or less, the content of C[3+ compounds that are poorly soluble in water will be excessive, and the stability of the coating treatment solution will be greatly reduced. When Cr3+ is set to 25 or less, Cr"-, which is easily soluble in water,
The compound becomes excessive in the treated film and the secondary adhesion of the film decreases. In this case, it is also possible to apply an additive-based system in which colloidal silica, 7-mud silica, etc. are added as a binder for the film.

The amount added is about the same amount as the chromium compound in the processing solution, and is preferably about 10 to 15 w+:% to the total processing solution.

The amount of film attached is 100 to 500 mgAn
2 is preferred. The amount of adhesion is 100mg%? - If the amount is less than 150
0 mg/n? If the amount is higher, the impact resistance of the surface of the coating will be reduced.

2) Spreadable phosphate coating A liquid in which 50 to 300 g of calcium phosphate or sodium phosphate, 50 to 150 g of phosphoric acid, and 10 to 50 g of colloidal/liquor are dispersed or dissolved in 1 liter of water is used as a metal coating. Apply to the outer surface of the tube and (4) dry to form a phosphate film. If the amount of calcium phosphate or sodium phosphate is outside the range of 50 to 300 g, film-forming properties will decrease. If the amount of phosphoric acid used is less than 50g, the solubility of calcium or sodium phosphate decreases because the PI (PI) of the treatment solution is not low enough.
The stability of the liquid becomes poor.

If the amount of phosphoric acid used exceeds 150 g, the amount of phosphoric acid (easily soluble in water) in the treated film will be excessive, and the secondary adhesion of the coating will decrease. If the amount of colloidal silica used is less than 10 g, the film-forming properties will be reduced, and if it is more than 50 g, the stability of the treatment liquid will be reduced.

The amount of coating is 200 to 1600 mg/m'
is suitable. Similar to the above 1) example, the adhesion amount is 200m
If it is less than 1,1600 m
If the amount is greater than the amount of water, the impact resistance will decrease.

3) Reactive phosphate coating A phosphate coating, such as iron phosphate or zinc phosphate chemical conversion treatment solution, is spray applied to the outer surface of the metal tube, washed with water, and dried to form a phosphate coating. The amount of coating is 0.2 to 0.6 g/lr in the case of iron phosphate. .

In the case of zinc phosphate, d, 03-5 fZ/m' is required.

``-Example 1) Same as ``2), the range of this adhesion amount is less than that and there is no CI and corrosion prevention effect, and more than that is desirable from the point of view of surface 1 impact of the coating. do not have.

A liquid epogyne resin is applied to the inorganic conversion coating 1-2 formed as described above and cured to form a single layer of primer. Preferred examples of liquid epoxy resins used in the present invention include bisphenol A type epoxy/resin or modified 1/1 derived resin as the main agent, such as urethane-modified epoxy resin, and aromatic or fatty acids as crosslinking polymers. Examples include those containing group polyamine compounds or carboxylic acids and their anhydrides, such as heterocyclic polyamines, modified aliphatic amine adducts, and the like. Thickness of one layer of primer d: 1.1~
It is 100μ. If the film thickness is less than 1 tt, no anticorrosive effect can be expected, and if it exceeds 100/j, it is not economical.

A metal tube with a single layer of primer formed in this way is
After preheating to 250C, (7) thermosetting epoxy powder is applied and fused on one layer of primer by a conventional method such as electrostatic powder method or fluidized dipping method to form a uniform epoxy powder coating. Laminate. The epoxy powder used in the present invention is not particularly limited, and any powder used in conventional epoxy powder coating can be used. For example, dicyandiamide curing type (A), polyamide amine curing type σ1), aromatic amine curing type Ω, etc. are suitably selected. The film thickness of this epoxy powder coating is 300
~450μ is ridiculous.

Next, the effects of the resin-coated metal tube according to the present invention will be clarified through examples. In addition, in the examples and comparative examples,
Test d regarding the physical properties of the formed coating: It was conducted by the following method.

■) Cathode electrolytic peeling test A. Compliant with STMG-8.

Immersed in 3% NaCl aqueous solution. Initial coating defect: 5mmφ.

-]-, 5V cathode polarization.

2) 3% saline immersion test After immersion in 80U for 30 days, the water immersion distance (8) from the cross-cut area and the appearance of the normal area coating were determined by ASTM T)-
Rated 714.

3) Drop weight impact test Compliant with DIN-30671. Temperature: 2OC.

Examples 1 to 5 After plasting a 30"φ steel pipe, an inorganic conversion film was formed, and on top of that, a primer made of liquid epoxy resin was burned out and hardened. After the primer was formed, the steel pipe was
The tube was preheated to 50C, and epoxy powder coating was applied using an electrostatic powder method, cured, and then cooled to obtain a resin-coated steel pipe.

Raw materials for each coating layer used in each example, coating thickness i1'i, % film J! The 7th prize is as shown in the table. The results of the coating anti-corrosion test of the resin-coated steel pipes obtained are shown in the same table. It is clear from the test results that the resin-coated steel pipe according to the present invention has excellent corrosion resistance, but does not cause a decrease in the mechanical strength of the coating.

Comparative Examples 1 to 4 Resin-coated steel pipes were obtained by substantially the same method as Examples 1 to 5, except that the number of inorganic conversion coatings attached was outside the unreasonable range of the present invention. Raw materials used, number of deposits, film thickness, and corrosion resistance test of the resulting coating.

The results are shown in the table. It has been found that a decrease in the amount of adhesion causes a deterioration in corrosion protection, and an increase in the amount of adhesion causes a decrease in the mechanical strength of the coating.

Comparative Examples 5 to 7 Epoxy powder coatings were formed in the same manner as Examples 1 to 5 (conventional method), except that the inorganic conversion coating and liquid epoxy primer formation were omitted. The raw materials used, film thickness, and corrosion resistance test results are shown in the table. In all the experimental examples of Comparative Examples 5 to 7,
60? Z': In the cathodic electrolytic peeling test after 30 days, the entire immersed area peeled off, and in the 3-day salt water immersion test, blisters were generated, showing significant weaknesses in corrosion protection.

Comparative Examples 8-9 Resin-coated steel pipes were formed in the same manner as Examples 1-4, except that one of the liquid epoxy primer and the inorganic conversion coating was omitted. The raw materials used, film thickness, and corrosion resistance test results are shown in the table. Corrosion resistance was not sufficient as blisters were generated in the 3-time salt water immersion test.

Claims (1)

[Claims] (1) On the outer surface of the metal tube, an inorganic conversion coating layer capable of passivating the metal surface, a primer layer formed from a liquid epoxy resin on the inorganic conversion coating layer, and a thermosetting powder on the primer layer. A resin-coated metal tube having an epoxy powder coating layer formed from an epoxy resin.