Study on properties of thermosetting PFPE-fluorocarbon polyester powder coating

Abstract: In this paper, a melt copolymerization method is used to synthesize perfluoropolyether modified polyester resin, and perfluoropolyether groups with a number average weight of about 3000 are introduced into the polyester molecular chain
.

The resin is used to make thermosetting PFPE-fluorocarbon powder coating, the coating structure design and the influence of element composition are analyzed and discussed, and the thermosetting PFPE-fluorocarbon powder coating has properties such as acid and alkali resistance, salt spray, aging, etc.

Perfluoropolyether (PFPE) is a kind of high molecular polymer, which has the characteristics of heat resistance, oxidation resistance, radiation resistance, corrosion resistance, non-combustibility, etc.

2.

2.
3 Preparation of PFPE-modified polyester resin with carboxyl end groups

Add all the reactants such as perfluoropolyether alcohol, terephthalic acid, isophthalic acid, adipic acid, and catalysts into the reactor, and gradually increase the temperature to 210°C for dehydration and esterification under the protection of nitrogen, and then increase the temperature to 240°C Continue dehydration and esterification
.

When the acid value of the reactant drops below 10, continue the reaction under reduced pressure and remove low boilers
.
Then, when the temperature of the reactant drops to 200°C, trimellitic anhydride and phthalic anhydride are added, and reacted at 190°C for 1 to 1.
5 hours to obtain a carboxy-terminal PFPE-modified polyester resin
.

2.
4 Preparation of thermosetting PFPE-fluorocarbon polyester powder coating

Mix the carboxyl-terminated PFPE-modified polyester resin, TGIC curing agent, degassing agent, pigment, filler and powder flow promoter in a certain proportion
.
Extruded, tableted and crushed in a twin-screw melt extruder
.
It is sieved with 180 mesh molecular sieve to obtain fine powder coating
.

2.
5 Preparation and characterization of thermosetting PFPE-fluorocarbon polyester powder coating

The above-mentioned thermosetting PFPE-fluorocarbon polyester powder coating is coated with electrostatic spraying equipment on a metal substrate that has been pre-processed by shot blasting and has been coated with a zinc-based coating
.
Heat for 10 minutes in a 200°C airflow drying oven to cure
.

Naturally cool to room temperature, and after 24 hours of standing, measure the performance of the coating
.
Measure the thickness of the coating with 6008B (Germany BYK) double-probe thickness gauge;

BM300 (Japan) contact angle meter was used to measure the contact angle of water on the coating surface; Hitachi (Hitachi) S-3400N scanning electron microscope was used to measure the F element content on the coating surface
.

3.
Results and discussion

3.
1 Basic physical properties of thermosetting PFPE-fluorocarbon polyester powder coating

During the test, it was found that the basic mechanical and physical properties of thermosetting PFPE-fluorocarbon polyester powder coatings, such as adhesion, impact strength, flexibility, etc.
, are closely related to the type of substrate used and the method of substrate surface pretreatment.

.
Table 1 shows the physical properties of the perfluoropolyether polyester powder coating on the surface of the ordinary steel plate
.

3.
2 Performance comparison of thermosetting PFPE-fluorocarbon polyester powder coating and polyester powder coating

As a comparative test, a pure polyester resin powder coating with the same ratio and a thermosetting PFPE-fluorocarbon polyester powder coating were prepared into a coating under the same process conditions.
The properties are shown in Table 2
.
It can be seen that both coatings have higher performance
.

Compared with polyester resin powder coatings, the adhesion of thermosetting PFPE-fluorocarbon polyester powder coatings is slightly lower than that of polyester resin powder coatings; bending experiments show that thermosetting PFPE-fluorocarbon polyester powder coatings have higher flexibility sex;

The most notable one is the alkali resistance (30% NaOH) test.
The polyester powder coating layer blistered and fell off after being immersed in the alkali (30% NaOH) for 48 hours, while the perfluoropolyether fluorocarbon polyester powder coating The coating remains intact after being soaked for 480 hours, and the strong alkali resistance is more than ten times that of polyester resin powder coating
.

3.
3 The influence of the amount of perfluoropolyether and the F element of the coating on the alkali resistance of the coating

The content of perfluoropolyether in the perfluoropolyether fluorocarbon polyester resin is different, which has a greater impact on the distribution of F elements on the coating surface.
Figure 1 shows the determination of 5% perfluoropolyether by Hitachi S-3400N scanning electron microscope The content of F element on the surface of the polyether modified polyester resin powder coating
.

Table 2 shows the influence of the amount of perfluoropolyether and the F element on the coating surface on the alkali resistance of the coating
.
It can be seen from Table 2 that as the amount of perfluoropolyether increases, the amount of F in the coating increases, and the coating's resistance to strong alkali (30% NaOH) time increases
.

The addition amount is 7%, and the amount of F element in the coating is 0.
70%, which can be resistant to strong alkali (30% NaOH) at 340 hours
.
When the amount of perfluoropolyether is 10%, the amount of F element in the coating is 0.
95%, which can be resistant to strong alkali (30% NaOH) at 480 hours
.

Then increase the amount of perfluoropolyether, the amount of F element on the surface of the coating does not change much
.
It shows that it is more appropriate to control the amount of perfluoropolyether at 8-10%
.

3.
4 The influence of the amount of perfluoropolyether on the contact angle of the coating surface

The content of perfluoropolyether in the perfluoropolyether fluorocarbon polyester resin has a great influence on the surface properties of the powder coating.
The morphology of droplets formed on the surface of the layer;

Figure 3 shows the contact angle of water on the pure polyester resin powder coating coating of 78°; Figure 4 shows the contact angle of water on the coating with a perfluoropolyether content of 8%; Figure 5 shows the contact angle of water on the perfluoropolyether coating The contact angle is 135° on the 10% coating
.

It can be seen that the surface of the powder coating made of pure polyester resin has a certain degree of hydrophilicity, with a contact angle of 78°, and water droplets spread quickly on the surface
.

Water is difficult to spread on the coating surface with 8% and 10% perfluoropolyether content.
The contact angles of water on the surface are 120° and 135° respectively, which can form transparent liquid beads, indicating that the addition of perfluoropolyether makes it difficult to spread.
It has high hydrophobicity
.
Table 3 shows the surface contact angles of powder coatings with different content of perfluoropolyether fluorocarbon polyester resin
.

It can be seen from Table 3 that as the amount of perfluoropolyether increases, the contact angle of the coating surface to water increases sharply, and the hydrophobicity of the coating increases
.
Adding 8% can increase the contact angle of the coating to water from 78° to 120°
.

When the dosage of perfluoropolyether is 10%, the contact angle of the coating to water can reach 135°.
If the dosage of perfluoropolyether is increased, the contact angle of the coating surface does not change much
.
It shows that it is more appropriate to control the amount of perfluoropolyether at 8-10%
.

4.
Conclusions and prospects

Thermosetting PFPE-fluorocarbon polyester powder coating is modified by introducing perfluoropolyether side chains with a molecular weight of about 3000 into the polyester molecule;

The amount of perfluoropolyether is controlled between 8-10%.
The processed new fluorocarbon polyester coating material has higher flexibility, weather resistance and super alkali resistance than pure polyester coating
.
The coating has a water contact angle of 135° and has a super-hydrophobic function
.

Perfluoropolyether polyester contains short CF bond length, so thermosetting PFPE-fluorocarbon polyester powder coating has far better acid resistance, alkali resistance, corrosion resistance, weather resistance, low friction coefficient and oil repellency than general coating materials.
, Water repellency, anti-sticking, anti-pollution and other excellent performance
.

It has a wide range of application prospects in the coating of transportation facilities, power transmission facilities, water and oil pipeline facilities, and outdoor communication facilities that require high corrosion resistance and weather resistance
.

Source: Lizhan, Tielu, Dongfang, Chen Yun, Jiangsu Zhengling Coating Engineering Technology Research Center; Gu Guotuan, School of Chemistry and Chemical Engineering, Henan University