Development and application of new environmentally friendly anti-corrosion coating system

Abstract: This paper systematically describes the development and application of new environmentally friendly anti-corrosion coating systems, as well as the coating solutions
of different metal substrates in different environments.

preface

Nowadays, the common high anti-corrosion powder coating on the market is a coating system composed of zinc-rich powder and flour, and the anti-corrosion mechanism of zinc-rich powder is mainly barrier protection and cathodic protection
.

However, zinc-containing products are labeled as "environmentally harmful" and environmental laws allow the use of zinc for a very short period of time for paint online coatingol.
com
.

Moreover, the proportion of zinc-rich powder is large, which increases the difficulty of construction, and it is easy to wear out ventilation and electrode equipment, and the spraying area is relatively small, which improves the difficulty
of powder recovery.

The new ecophilic anticorrosive coating system described in this paper uses environmentally friendly powders, does not contain zinc, does not require labeling, and has no VOC emissions, which can improve the durability
of the substrate in the natural environment.

It has excellent resistance to chemicals, moist heat, salt spray and other properties, and can be sprayed on a variety of substrates including substrates containing sharp corners, breathable substrates (galvanized steel, metkin, etc.
).

The primer has a small specific gravity, is easy to use, can be recycled, increases the spray area (reduces powder consumption), reduces wear and tear on the spraying equipment (venturi, electrodes, etc.
).

It has excellent adhesion to ferrous metals and good interlayer adhesion to flour
.

1.
Experimental part

1.
1 Raw Materials

Epoxy resin; epoxy curing agent; zinc powder; antiseptic auxiliaries; Acrylate leveling agent; Wollastonite; Iron oxide; chin white powder; Benzoin, etc
.

1.
2 Test equipment

parallel twin screw extruder; Mill; salt spray meter; Damp heat meter
.

1.
3 Test process

(1) Hot melt bonded epoxy powder coating production process: test process: weighing→ mixing→ extrusion→ grinding powder→ screening→ spraying→ curing → detection; (2) Extrusion temperature: 30-90-80 °C

1.
4 Performance Testing

Salt spray and moist heat performance testing is carried out
with reference to ISO 12944.

2.
Results and discussion

2.
1 Environmental Identification

The ISO 12944 standard divides the environment into two categories: internal environment and external environment, and each category is divided into Cl-C5 environment according to different degrees of pollution, as shown in Table 1
.

In the same environment, the durability requirements of coatings are different, and the anti-corrosion performance requirements are also different
.
The durability of the paint is divided into three levels: low (L): 2~5 years, medium (M): 5~15 years, high (H): more than
15 years.

Environment and coating durability form a two-dimensional diagram, as shown in Figure 1, the ISO 12944 standard classifies two-dimensional diagrams, the same color area has similar corrosion resistance requirements
.

2.
2 Anti-corrosion performance evaluation

The corrosion resistance of coatings is generally evaluated
by moist heat (ISO 6272) and neutral salt spray (ISO 7253).
ISO 12944 specifies the inspection times that coatings need to withstand for different environments and durability, as shown
in Table 2.

2.
3 Anti-corrosion mechanism

When the metal is damaged by chemical or electrochemical reactions in contact with the medium in the environment, the powder coating film plays a protective role
by blocking the direct contact between the metal and the environment.

The protective effect of powder coatings on steel mainly includes barrier protection, cathodic protection and passivation protection
.
The combination of base and flour double-layer and double-layer coating system is strengthened to further improve the anti-corrosion and anti-corrosion performance
of the coating.

Barrier protection, the coating separates the metal from the environment, thus protecting the metal from corrosion
.
It has a very good protective effect
during the absence of defects in the protective coating.

The corrosion of metal by salt spray is carried out in an electrochemical way, mainly the conductive salt solution penetrates into the steel to produce an electrochemical reaction, forming a microbattery system
of "low potential metal-electrolyte solution-high potential impurities".

Electron transfer occurs, and the metal that acts as the anode dissolves, forming corrosion
.
The main role in the salt spray corrosion damage process is the chloride ion Cl-, which has a small radius and strong penetration ability, easy to penetrate the oxide layer and the protective coating into the metal interior, and destroy the blunt state
of the metal.

At the same time, chloride ions have a certain hydration energy, which is easy to adsorb in the pores, cracks and other positions of the metal surface, replacing the oxygen that protects the metal oxide layer, so that the metal is damaged
.

Cathodic protection, zinc-rich powder contains a large amount of zinc powder, the standard potential of zinc (-0.
76V) is lower than that of iron (-0.
44V), when the coating film is eroded, zinc powder is oxidized first as an anode, and the substrate steel is protected
as a cathode.
Cathodic protection is shown in
Figure 2.

Passivation protection, the active pigment that inhibits corrosion passivates the metal substrate, forms a passivation layer, slows down the reaction of metal with water and oxygen mixture, and inhibits the production
of acidic ions caused by moisture.

Double-layer system protection, spray another layer of powder coating on top of the zinc-rich powder coating to form a double-layer coating system
.
The top powder coating can be selected as pure epoxy type, epoxy/polyester type or pure polyester type
according to weather resistance and corrosion protection requirements.

Strengthen the two-layer system protection (three-layer system), spray a layer of barrier protection primer on the zinc-rich powder coating, and then spray the layer of powder coating to form a three-layer system
.
Zinc-rich primer provides cathodic protection, an intermediate layer provides barrier protection, and a top layer provides corrosion and weathering resistance
.

2.
4 Alesta ZeroZinc environmentally friendly anticorrosive coating

Alesta ZeroZinc environmentally friendly anti-corrosion powder mainly improves the anti-corrosion performance
of the coating by improving the barrier protection of the coating or by adding active anti-corrosion pigments to improve the passivation effect.
Resistant to corrosion tests, it can replace zinc-rich powders
.
The 1440h salt spray test results are shown in Figure 3:

The test results show that:

(l) The sample red corrosion of the zinc-rich formula is obvious, and the zinc powder of the coating has no obvious corrosion, and the cathodic protection effect played by it is not obvious
.

(2) Alesta ZeroZinc environmentally friendly anticorrosive coatings have significantly less corrosion than zinc-rich formulations, and the spread of corrosion marks at the point of crossing damage is significantly reduced
.
It forms a protective coating film with high cross-linking density, reduces the molecular gap of the coating film, prevents the immersion of chloride ions, prevents the erosion of salt solution, and effectively slows down corrosion
.

Alesta ZeroZinc environmental anti-corrosion coating is tested according to ISO 12944 standard and tested according to ISO 12944 standards, and the results of pre-treatment of sandblasting and phosphating passivation are shown
in Table 3 and 4, respectively.

From the comparative results, Alesta ZeroZinc
.
The salt spray resistance of environmentally friendly anti-corrosion powder is significantly better than that of competitors of the same level on the market, and has a significantly stronger protective and anti-corrosion effect
on the substrate.

Depending on the applicable substrate, Alesta ZeroZinc
.
Anticorrosive coatings consist of three products, as shown
in Table 5.

2.
5 Alesta antiseptic program

Depending on the metal substrate and pretreatment, Alesta has a corresponding plan
.

2.
5.
1 Steel substrates

Alesta ZeroZinc Steel Prime
。 Suitable for steel substrates, with good anti-corrosion properties
.
Select the appropriate pretreatment and coating scheme
for steel substrates based on the environmental corrosion classification in Table 6 and Table 7.

2.
5.
2 Galvanized steel

Coatings suitable for galvanized steel require good degassing properties, and Alesta ZeroZinc not only has excellent corrosion resistance, but also excellent degassing properties for galvanized steel substrates
.
Select the appropriate pretreatment and coating scheme
for galvanized steel according to the environmental corrosion classification in Table 8 and Table 9.

2.
5.
3 Sharp corners

Coatings for sharp corners require good corner coverage, and Alesta ZeroZinc Edge Prime not only has excellent corrosion protection, but also excellent corner coverage for sharp corner substrates
.
Select pretreatment and coating solutions
for sharp corners according to the environmental corrosion classification in Table 10 and Table 11.

3.
Conclusion

This paper describes the environment and its classification specified in ISO 12944, the division of service life, and the anti-corrosion requirements
of coatings under different environments and service life.

The paper also elaborates on different anti-corrosion mechanisms, Alesta ZeroZinc adopts barrier protection, passivation protection to improve anti-corrosion, which can effectively replace zinc-rich anti-corrosion, and Alesta zinc-free anti-corrosion application
in various substrates.