Application of antioxidants in high temperature resistant powder coatings

I.

In recent years, with the continuous strengthening and deepening of China's environmental protection policies, higher standards of environmental protection requirements have been put forward for the coating industry.

In the process of processing and curing, powder coatings have to undergo mixed thermal processing and high-temperature baking.

At present, the traditional antioxidants used in powder coatings mainly include hindered phenolic antioxidants 1010, 1076, etc.

Two, the test part

2.

Add polyester resin, curing agent, antioxidant, barium sulfate, titanium dioxide and other additives according to a certain proportion.

Table 1 Experimental formula

2.

High temperature oven (Binder company), twin screw extruder (Deteng company), colorimeter (X-Rite company)

2.
3 Test method

2.
3.
1 Antioxidant thermal stability test

Place the antioxidants used in the ABCD four groups of formulas in an oven at 230°C for 0.
5h to test the color difference and weight loss rate
.

2.
3.
2 Thermal stability test of powder coating

After the powder coating sample in 2.
1 is electrostatically sprayed, it is cured at 200°C for 10 minutes to obtain a powder coating
.
In order to evaluate the influence of antioxidants on the heat resistance of powder coatings, the powder coating was put in a high-temperature aging oven, and the heat aging conditions were 230°C for 2h
.
Test the gloss retention and color difference of the coating
.

3.
Results and discussion

3.
1 The mechanism of action of antioxidants

The network polymer of the coating in the coating is composed of countless molecular segments connected together by chemical bonds.
These chemical bonds contain hydrogen, oxygen, double bonds, etc.
, which are vulnerable to heat and oxygen attack, and generate a large amount of free radicals and hydrogen.
Peroxides cause damage to the polymer chain segment and eventually cause the coating to begin to age, resulting in reduced gloss, surface chalking, and discoloration
.
Adding antioxidants to powder coatings can effectively inhibit the thermal oxidative aging behavior of polymers
.

Antioxidants are mainly divided into two categories: primary antioxidants and auxiliary antioxidants
.
The main antioxidants mainly include aromatic amine antioxidants and hindered phenol antioxidants.
The mechanism of action is to capture the free radicals R ▪ and ROO ▪ formed in the chain reaction stage and terminate the chain reaction
.
Auxiliary antioxidants mainly include phosphite antioxidants and thioester antioxidants, and their mechanism of action is to decompose ROOH to produce stable substances
.
The combined use of main and auxiliary antioxidants can have a certain synergistic effect and achieve a more excellent antioxidant effect
.

Figure 1 Thermal oxygen degradation mechanism and inhibitory effect of polymer

3.
2 Research on the thermal stability of antioxidants

Table 2 Color difference and weight loss rate of antioxidant at 230℃ high temperature aging for 0.
5h

The thermal stability of the antioxidant determines whether it can provide good protection to the resin during high-temperature processing and use
.
If the antioxidant itself has poor thermal stability and decomposes at high temperatures, it will lose the antioxidant properties and fail to provide good thermal oxygen aging protection for the resin
.
It can be seen from Table 2 that the color change and weight loss rate of the four antioxidants under high temperature aging are not serious, indicating that the thermal stability of the four antioxidants is good
.
Among them, formula A is a single hindered phenolic antioxidant
.
Formulation B is a single phosphite antioxidant with a high weight loss rate, indicating that B has a certain degree of decomposition
.
Formula C is a composite antioxidant system commonly used in the market
.
Formula D is a special composite antioxidant system developed for powder coatings.
Experiments show that the high-temperature color change and heat loss rate of Formula D are excellent
.

3.
3 The influence of different antioxidants on the heat resistance of powder coatings

Table 3 Changes in gloss retention and yellow index of coatings with different antioxidant formulations at 230°C

From the data in Table 3, it can be seen that the powder coating has been damaged to different degrees after high temperature aging at 230℃ for 2 hours.
The formula A and B are both single antioxidant systems, and the protective effect of the powder coating is slightly poor.
C formulations for thermal aging of the protective coating significantly better than a and B
.
Among them, formula D, as an antioxidant formula specially developed for powder coatings, has the best performance in the powder coating and color protection of the coating, which significantly improves the high temperature resistance of the powder coating
.

Fourth, the conclusion

This article mainly explores the effect of different antioxidant systems on the high temperature aging resistance of powder coatings.
The results show that:

1.
Different antioxidants have different thermal stability during high temperature aging.
Among them, formula B (phosphite antioxidant) has poor thermal stability, and formulas A, C, and D all show excellent thermal stability
.

2.
Research has found that the thermal and oxygen aging protection of the composite antioxidant system for powder coatings is better than that of single-component hindered phenol or phosphite antioxidants, and the composite antioxidant system D formulation developed for powder coatings, The coating is more excellent in thermal oxidative aging protection under high temperature conditions
.