Research on the development and performance of high-performance water-based epoxy anti-corrosion coatings

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Water-based coatings use water to replace organic solvents in solvent-based coatings.

The biggest advantage is low VOC content and good environmental protection, which is an important development direction for anti-corrosion coatings in the future.

Waterborne epoxy anticorrosive coating is a high-efficiency coating widely used in industrial corrosion protection at this stage.

The current research mainly focuses on the modification of epoxy resin, the compatibility of epoxy resin and curing agent, the improvement of pigments, fillers and additives.

1 Paint preparation

(1) Grinding pigment paste

Add deionized water, dispersant, wetting agent, pigment, and filler to the batching tank in sequence.

After stirring evenly, pour it into a small laboratory sand mill, add an appropriate amount of zirconium beads, and grind and disperse to a scraper fineness of 20 μm.
Hereinafter, after standing for defoaming, the material is filtered out to obtain the water-based pigment slurry for paint.

(2) Coating preparation

The water-based epoxy emulsion, amino resin and catalyst added in the batching tank are uniformly dispersed according to the formula amount, and then the prepared water-based pigment slurry is added, and the defoamer, leveling agent and other additives are added under stirring to disperse evenly; finally added Appropriate amount of water, adjust viscosity to obtain waterborne epoxy anticorrosive coating.

The reference formula is shown in Table 1.

Table 1 Waterborne epoxy anticorrosive coating formula

(3) Construction technology

The construction process includes spraying and baking.
The process is: spray the prepared water-based anticorrosive coating on the surface-treated substrate, first bake at 80 ℃ for 15 min, then rise to 120 ℃ and bake for 25 min, and finally at 180 ℃ Bake for 30 minutes to obtain the test board.

2 Results and discussion

(1) The influence of resin on the anti-corrosion performance of the coating

Waterborne epoxy anticorrosive coatings are usually composed of a hydrophilic epoxy emulsion and a hydrophilic curing agent.

Compared with other water-based anti-corrosion coatings, since the epoxy resin in the water-based epoxy anti-corrosion coating contains functional groups such as epoxy groups and hydroxyl groups, it has excellent chemical resistance, good heat resistance, and good adhesion, which can meet the requirements of industrial Different construction requirements in the coating field, so it is widely used in the field of anti-corrosion.
The common epoxy resin-amino curing agent system on the market has poor heat resistance, solvent resistance and chemical resistance due to its low crosslink density.

In this study, a waterborne epoxy emulsion (EPIKOTE 3540-WY-55) with a high epoxy equivalent weight (g/Eq of 1600~2000) was selected as the main resin, but the cross-linking density is high, and the mechanical properties of the coating will decrease.

At the same time, after construction The coating is prone to cracking when placed in a closed place at low temperatures.

Therefore, in this experiment, the water-based epoxy emulsion (EPIKOTE 3540-WY-55) and the water-based epoxy emulsion resin (CTW-6062) were used for compounding, and the best quality ratio of the two resins was obtained through the experiment.

The results are shown in Table 2.

Table 2 The influence of different resin ratios on the performance of the coating film

It can be seen from Table 2 and Figure 1 that when the amount of water-based epoxy emulsion (EPIKOTE 3540-WY-55) is large, the mechanical properties of the coating film are poor, and the coating is also prone to occur after being sealed at low temperature (5°C).
Cracked.
When an appropriate amount of low epoxy equivalent epoxy emulsion (CTW-6062) is introduced into the system, the mechanical properties will be improved, and the low temperature will not crack, but the acid resistance will decrease.
Figure 2 is the appearance of EPIKOTE 3540-WY-55 and CTW-6062 when the mass ratio is 7:3 and 3:7, 10% HCl resistance for 16d.

It can be seen from Figure 2 that when the amount of CTW-6062 is too large, the coating will appear white after being soaked in acid.

This may be due to the decrease of the crosslinking density of the coating after the increase of CTW-6062, resulting in acid resistance.

(2) The effect of the type of curing agent on the corrosion resistance of the coating

At present, amino resins as curing agents mainly include melamine formaldehyde resins with different etherification types and different degrees of etherification, such as: highly methyl etherified melamine resin (CYMEL 303, CYMEL 350), high imino methyl etherified melamine resin (CYMEL 325) , CYMEL 327), partially methyl etherified melamine resin, etc.

In this study, different kinds of methyl etherified melamine formaldehyde resins were investigated.
According to the requirements of different curing agents, 1% CYCAT 4040 is added when using curing agents CYMEL 303 and CYEML 350, and no catalyst is added in other cases.
The results are shown in Table 3.

Table 3 The influence of different kinds of amino resins on the performance of paint film

It can be seen from Table 3 that CYMEL 303 and CYMEL 350 have relatively high solid content and low VOC emissions.
The structure of CYMEL 325 and CYMEL 327 contains a large number of functional groups such as alkoxy/imine groups, which can be cured without additional acid catalysts.
The paint film has high hardness, but the cured film has relatively poor flexibility and high VOC content.
The resistance to media is poor.
CYM EL303 and CYM EL350 are both highly methylated melamine resins, but the degree of methylation of CYM EL350 is lower than that of CYMEL 303.
In addition to alkoxy groups, it also contains a certain amount of methylol and imino groups, and its resistance to media is relatively poor.
.
The results show that the overall performance of CYMEL 303 is better as the curing agent.

(3) The effect of pigment-to-base ratio on the anti-corrosion performance of the coating

The ratio of pigment to base (P/B) is a factor that cannot be ignored in the formulation of heavy-duty anti-corrosion coatings.
When the pigment-to-base ratio is low, the filling degree of the resin and curing agent is lower, resulting in lower compactness of the coating system, so the permeability of the corrosion-resistant medium will decrease, the chemical resistance will be partially reduced, and the cost of the coating will increase; If the base ratio is too high, the pigments and fillers cannot be completely covered by the resin, and part of the pigments and fillers particles are free from the voids of the resin space structure, which affects the bonding between the coating and the substrate, and other resistance and physical and mechanical properties will also be reduced.
Use water-based epoxy emulsion EPIKOTE 3540-WY-55, CTW-6062 as the base resin of water-based coatings, choose CYMEL 303 as the curing agent, and keep the content of other components unchanged.
Adjust the paint-to-base ratio through experiments, and choose the one under the optimal conditions.
Yan Kibi, the results are shown in Table 4.

Table 4 The effect of pigment-to-base ratio on coating performance

It can be seen from Table 4 that when the pigment-to-base ratio>1, the water resistance and hydrochloric acid resistance become worse; when the pigment-to-base ratio is 0.
2, the water resistance and acid resistance are partially improved, but the cost of the coating is higher; In the case of mechanical properties and resistance to chemical media, the overall performance is better when the color-to-base ratio is 0.
6.

(4) The effect of anti-flash rust agent on the anti-corrosion performance of the coating

When the water-based paint dries on the surface of the substrate, it is prone to flash rust.
Adding anti-flash rust agent can inhibit corrosion.
During the experiment, the effect of different anti-flash rust agents on performance was investigated.
The experimental results are shown in Table 5.

Table 5 Effect of anti-flash rust agent on coating performance

It can be seen from Table 5 that sodium nitrite is the most commonly used anti-flash rust additive for water-based anti-corrosion coatings.
Since the flash rust phenomenon is generally caused by electrochemical effects, the use of such reducing substances to release negative charges to the metal base The anti-rust of the material is of great help.
When the dosage is 0.
2% of the total weight of the formula, the flash rust can be inhibited.
However, due to the high ionicity of such substances, the water resistance of the paint film is significantly deteriorated due to the large amount of addition.
Raybo 60 is a mixture of organic zinc chelate and sodium nitrite.
Its anti-rust ability is slightly worse than that of sodium nitrite alone.
When 0.
5% is added, flash rust can be inhibited, but after addition, it will still cause a decrease in water resistance.

FA-179 is an organic zinc chelate compound.
The addition of FA-179 has little effect on the water resistance of the coating, but the anti-flash rust ability is poor.
The flash rust can be completely inhibited when the amount is 1%.
EMADOX ® 2K HE is a two-component anti-flash rust agent, divided into 2K/1 and 2K/plus.
The two components need to be added to the paint separately under stirring.
2K/1 contains nitrite, and 2K/plus contains The hydrophobic long-chain organic amine has little effect on the water resistance and salt spray resistance of the paint film due to the existence of the hydrophobic segment.
When the dosage is 0.
2% (the mass ratio of the two components is 1:1), it has excellent protection.
Flash rust effect.
Therefore, it is better to choose EMADOX ® 2K HE as an anti-flash rust agent.

(5) Performance of waterborne epoxy anticorrosive coating

Based on the above discussion results, a waterborne epoxy anticorrosive coating with excellent performance has been developed.
The performance test results are shown in Table 6.

Table 6 Main properties of waterborne epoxy anticorrosive coatings

Conclusion

(1) Take m (EPIKOTE 3540-WY-55): m (CTW-6062) as the base material at 7:3, use amino resin CYMEL 303 as the curing agent, the ratio of pigment to base is 0.
6, and the anti-flash rust agent is EMDOX ® The dosage of 2K HE is 0.
2% (the mass ratio of the two components is 1:1), and the water-based epoxy anticorrosive coating is developed;

(2) The developed waterborne epoxy anticorrosive coating has good physical and mechanical properties, excellent anticorrosion, chemical resistance and temperature resistance.
At the same time, the paint uses water as the dispersion medium and has a low VOC content.
It can be widely used in the fields of radiators, water tanks and steel structures.
It is a water-based anti-corrosion and anti-corrosion paint with the prospect of popularization and application.

References (omitted)

Authors | Tan Weimin, Wang Yaxin, Shi Liping, etc.

(CNOOC Changzhou Coating Chemical Research Institute Co.
, Ltd.
)