Research on high-weather-resistant textured powder coating and its application on SUV bumper

Abstract: Based on the formation mechanism of textured powder, the effects of different types of curing agents (TMMGU) and fillers, the amount of catalyst and the amount of additives on the texture effect were studied

Finally, a powder coating for high-end SUV bumper with excellent solvent resistance, excellent corrosion resistance and excellent weather resistance is obtained

The bumper is an indispensable part of the car.

High-end SUV bumper protective coatings are required to have a layered texture (cotton paint) effect.

It not only makes up for the roughness and unevenness of the workpiece surface, but also obtains a surface coating with a strong three-dimensional effect after baking, which has excellent decorative properties

This powder coating for SUV car bumper has excellent solvent resistance, excellent corrosion resistance and excellent weather resistance

Due to many factors affecting the coating texture size, three-dimensional effect, texture shape, mechanical properties, gloss, etc.

In this study, a special curing system of polyester/tetramethoxymethyl glycoluril (TMMGU) was selected to prepare powder coatings with special texture coatings according to the use environment and characteristics of high-end SUV bumpers

1.
Experimental part

1.
1 Recipe

The basic formula of reticulated powder coating is shown in Table 1
.

1.
2 Pharmaceuticals

Batching, premixing, extrusion, tableting, crushing, sieving through 150 mesh, finished product
.

1.
3 Plate making

After electrostatic spraying, bake at 200℃ for 15min
.
Figure 1 and Figure 2 are the effect diagram and the field application diagram respectively
.

2.
Results and discussion

2.
1 Influence of the amount of curing agent on the texture

The saturated hydroxyl polyester resin (domestic resin B), pigments and fillers, catalysts, curing agents, etc.
with an acid value of 30-40 mgKOH/g were selected.
influence
.

The experimental scheme is shown in Table 2, and the experimental results are shown in Table 3
.
It can be seen from Table 3 that when the amount of curing agent is small, the salt spray resistance and physical properties of the coating are relatively poor, which is caused by incomplete curing of the system
.

However, when the dosage of the curing agent exceeds a certain level, it will not only increase the cost of the formulation, but also affect the effect of the coating texture due to the accelerated gelation speed
.

In addition, the hydroxyl value range of polyester resins produced by different resin manufacturers is different, so when designing the formula, the theoretical dosage of the curing agent should be calculated first according to the specific situation of the hydroxyl value of the selected polyester resin, and then based on this It is verified through specific tests, and the actual curing agent dosage is finally determined
.

In this experiment, polyester resin with hydroxyl value of 30-40 mgKOH/g was selected.
Considering the comprehensive performance and cost, the ratio of polyester B to TMMGU was selected as 93:7 (formula 3) or 94:6 (formula 2)
.

2.
2 Influence of filler content on texture effect

The ratio of domestic polyester B and TMMGU was selected as 93:7, and other conditions were fixed to investigate the effect of filler barium sulfate (8000BA) amount on the texture effect
.
The experimental scheme is shown in Table 4, and the experimental results are shown in Table 5
.

It can be seen from Table 5 that with the increase of the amount of barium sulfate as the filler, the stronger the three-dimensional (concave-convex) feeling of the reticulated pattern on the board surface, but the smaller the reticulated pattern, the grain size of the reticulated powder can be adjusted by adding the amount of barium sulfate.
with morphological effects
.
The greater the amount of filler added, the greater the corresponding oil absorption, and the stronger the degree of coating unevenness
.

Usually, the amount of pigments and fillers in reticulated coatings is much lower than that of other types of coatings, otherwise the reticulated effect will be blurred.
Size), coating performance and formulation cost are comprehensively determined
.

2.
3 Effect of catalyst dosage on texture

The amine-blocked sulfonic acid catalyst can significantly reduce the coating film forming temperature or shorten the curing time, and obtain excellent coating surface performance and excellent weather resistance and outdoor stability
.

In powder coatings, the cross-linking reaction temperature of powder coatings can be greatly reduced
.
Excellent storage stability compared to unblocked catalysts
.
The experimental scheme is shown in Table 6, and the experimental results are shown in Table 7
.

It can be seen from Table 7 that with the increase of catalyst dosage, the reaction speed is gradually accelerated, and the crosslinking density is gradually increased
.
The weather resistance of the coating gradually became better
.
Based on the comprehensive performance and customer's requirements for the characteristics, size and on-site use of the texture, the recommended dosage of amine-blocked sulfonic acid is 0.
3% to 1.
2%
.

2.
4 Influence of multifunctional functional group additive A on texture

The experimental scheme is shown in Table 8, and the experimental results are shown in Table 9
.
Figure 3 shows the texture effect of the board according to the formula in Table 8
.
It can be seen that with the increase of the amount of the multifunctional functional group additive A, the lines become larger and then smaller, and the three-dimensional effect is from strong to weak and then to normal
.

During this reaction, when a certain temperature is reached, the amine-blocked sulfonic acid catalyst decomposes and plays a catalytic role in the entire reaction process
.
The multifunctional functional group assistant consumes the amine generated during the decomposition of the amine-blocked sulfonic acid catalyst, and the acidity of the system is enhanced, thereby also promoting the entire reaction process
.

The addition of too many multifunctional functional group additives is not conducive to the entire reaction process, so the texture is slightly flat, and the entire reaction is extremely complicated
.
The dosage of the multifunctional functional group additive A in the formula should be adjusted according to the customer's requirements and texture characteristics
.

2.
5 Influence of different manufacturers' curing agents on the texture

In the hydroxyl-terminated polyester/TMMGU curing system, when a certain temperature is reached, the amine-blocked sulfonic acid is deblocked, and the curing agent TMMGU and the hydroxyl-terminated polyester have a complex cross-linking curing reaction under the synergistic effect of multifunctional functional group assistants.
, resulting in a textured coating for this special effect
.

Table 10 shows the curing agent formulations of different manufacturers, and Table 11 shows the properties of the test panels
.

It can be seen from Figure 4 that there are obvious differences in the lines produced by the curing agent TMMGU produced by different manufacturers, and its effect is also affected by the regularity of the multifunctional functional group assistant
A.

For the curing agent TMMGU produced by manufacturer a, when the addition amount of multifunctional functional group auxiliary agent A does not exceed 6%, the texture becomes smaller as the addition amount increases; when the addition amount exceeds 6%, there is basically no texture
.

For the curing agent TMMGU produced by manufacturer b, when the addition amount of multifunctional functional group additive A does not exceed 4%, the texture gradually becomes larger and the gloss gradually becomes smaller; when the addition amount is 4% to 6%, the texture gradually becomes glossy.
When it becomes higher, the lines continue to become larger, and the impact becomes worse; when the increase amount exceeds 6%, there are basically no lines
.

TMMGU produced by different manufacturers differs in synthesis process and raw material selection, and the properties of the obtained TMMGU products are different, resulting in a great difference in the effect on the curing reaction of the coating, thus affecting the texture of the board surface
.

4.
Conclusion

Polyester/TMMGU type textured powder coating is based on the principle of incompatibility.
In this curing system, when a certain temperature is reached, the amine-blocked sulfonic acid decomposes and opens the ring, which produces a synergistic effect with the cross-linking agent TMMGU
.

And under the action of various auxiliaries and multifunctional functional group auxiliaries, complex cross-linking and curing reaction occurs with hydroxyl-terminated polyester, resulting in a special reticulate effect
.
The formula design should be determined according to customer requirements and standards
.

In order to obtain a textured powder coating with excellent solvent resistance, excellent corrosion resistance and excellent weather resistance, there are mainly the following suggestions:

(1) The hydroxyl value of the hydroxyl-terminated polyester cannot be too high, and the saturated hydroxyl polyester resin in the range of 30-40 mgKOH/g is selected;

(2) The recommended amount of filler is 10% to 30%, and the specific amount is used according to the characteristics of the texture and the cost of the formula;

(3) Select the appropriate ratio of curing agent, and at the same time select the curing agent TMMGU produced by the appropriate manufacturer, otherwise it will affect the comprehensive performance of the coating;

(4) The recommended dosage of amine blocked sulfonic acid is 0.
3% to 1.
2%, considering the comprehensive performance and cost, as well as the size of the customer's texture and the customer's on-site furnace temperature to adjust;

(5) The addition of multifunctional functional group auxiliary A has a driving effect on the whole reaction.
When the addition amount is less than 4%, the influence on the texture of the entire reaction system is gradually strengthened; when the addition amount is more than 4%, it is not conducive to the entire reaction process.

.