Development of super weather-resistant pure polyester transparent powder coating for automobile aluminum wheels

Abstract: The effects of end-steroidal polyester resins, curing agents, additives and dosage on the appearance (leveling, transparency) and performance (impact resistance, hardness, adhesion, corrosion resistance, weather resistance) of transparent powder coatings for transparent powder coatings (anti-heating pure polyester) were studied, and an ultra-weather-resistant pure polyester transparent powder coating was finally prepared for aluminum wheels. It has high leveling, high transparency, high weather resistance and excellent corrosion resistance of the hood coating, which meets the coating requirements of aluminum hub coating for aesthetics and durability.
0 Introduction
powder coatings, as the representative of solvent-free coatings, together with water-based coatings, have become the mainstream of the development of the coatings industry

. Powder coating for automotive coating research has been carried out for more than 20 years, the application field was initially limited to automotive parts, automotive primers, anti-stone primers, etc. , until the late 1990s only in bulk for car paint and mask varnish, become a true sense of automotive paint.
acrylic transparent powder has a good appearance and weather resistance, so the current aluminum hub cover light is mostly acrylic transparent powder. However, acrylic transparent powder due to low viscosity, large flow and other reasons on the aluminum hub corner coverage is poor, resulting in poor corrosion resistance of aluminum wheels, which has been an aluminum hub cover light to be solved. Polyester transparent powder coatings have better corner coverage than acrylic transparent powder coatings, resulting in better corrosion resistance.
But polyester resin relative to acrylic resin has the characteristics and characteristics of high refring coefficient, by its transparent powder coating film transparency is slightly worse, while transparent coating film level performance is also poor, so the current polyester transparent powder is not used in bulk in aluminum hub cover light. In this study, the effects of polyester resins, curing agents and additives on the appearance and performance of transparent powders were studied in view of the deficiencies of the above-mentioned existing technologies.
1 Experimental part
1.1 Raw materials
end-end pyridine polyester resins (A, B, C, D, E, F): industrial grade, import; curing agent (a, b, c, d): industrial grade, commercially available; powder general additives (sabbath, leveling agent, hardener, UV absorbent): industrial grade, commercially available.
1.2 Main equipment
twin screw extruder (SLJ-30): Donghui; DFY-500): Wenling Linda Machinery; Type Grinding System (ACM-02): Yantai Dongyuan Chemical Equipment Co., Ltd.; Jing Electric Spray Gun (GPH-30): Nordstore; High Temperature Oven: Espek Environmental Instruments (Shanghai) Co., Ltd.; Xenon Lamp Artificial Accelerated Aging Tester (Q-SUNXe-3-HS): Q-lab Corporation of the United States; Salt Mist Test Box (SH-90): Dongguan Changhong Testing Equipment Co., Ltd.
1.3 Powder coating and coating preparation
according to the design formula called to take the components, with a lmspoon Chinese medicine shredder fully premixed, through the twin screw extruder at the set temperature for melting extrusion, extrusion of the film by cooling, crushing, screening, electrostectrical spraying, heat curing into a film, and finally the coating film performance test.
2 results and discussions . 2.1 Effects of different polyester resins on the appearance and performance of transparent powders
Because automotive aluminum hub cover light powder coatings have ultra-weather-resistant, high leveling, high transparency properties, the choice of polyester resins need to have ultra-high weather resistance, high leveling, high transparency, and no color. Table 1 examines the effects of several end-end pyride polyester resins on the coating properties of pure polyester transparent powder coatings.
As can be seen from Table 1, if the resin reaction activity is too large, such as polyester resin A and polyester resin E, the coating is prone to orange peel, if the resin reaction activity is too small, such as polyester resin B and polyester resin D, the mechanical properties of the coating is poor. Therefore, choose a medium-active (glue time 300 to 360s) end-of-the-line polyester resin. Of the selected polyester resins, polyester C and polyester F meet the requirements for leveling and mechanical properties. However, aluminum wheel coating requires high transparency, high weather resistance (generally requires xenon lamp aging after 1800h after the preservation rate of more than 60%) and high corrosion resistance (generally requires Cass salt spray test 240h unilateral blister diameter of less than 2mm), and finally selected a medium-active ultra-active ultra-resistant weather-resistant pyridine polyester resin F.
2.2 Effects of the type of curing agent on the appearance and performance of transparent powders
The curing agents commonly used in polyester powder coatings are mainly isocyanate triglycerides (TGIC), hydroxyamide (HAA), table 2 examines the effects of several curing agents on the coating properties of pure polyester transparent powder coatings.
table 2 shows that HAA is relatively poor in terms of yellowing and weather resistance relative to TGIC and is not suitable for transparent powder coatings. Curing agent a and curing agent b meet the requirements in appearance, weather resistance and corrosion resistance. However, the curing agent a is poor relative to the curing agent b in impact resistance, and finally the TGIC type curing agent b is selected.
2.3 Effect of leveling agent on the appearance and performance of transparent powder
Aluminum hub cover light transparent powder requires the coating film to have high leveling and high transparency, and can not be with a phase, so it is necessary to choose a suitable leveling agent, this study selected several domestic and foreign leveling agent for testing, different leveling agent prepared powder coating performance results can be seen in Table 3.
can be seen from Table 3, leveling agent will affect the appearance and performance of the coating, when adding these three leveling agents, the materialization performance is in line with the requirements. However, the addition of leveling agent 2 and leveling agent 3 will make the coating color color yellowing, and the addition of leveling agent 3, the appearance of a slight orange peel, should not be used. So finally selected leveling agent 1.
, the reasonable dosage of leveling agent 1 in the formulation system is studied, and the specific performance results are seen in Table 4.
As can be seen from Table 4, the amount of leveling agent has an important effect on the appearance of the coating and the anti-group performance of the powder, and the anti-group performance of the powder is better when the amount of control leveling agent is 1.0% to 1.5%. When the leveling agent dosage is less than 1.0%, the coating film is prone to shrink holes or orange peel, and when the leveling agent dosage exceeds this range, although it will not affect the appearance and materialization performance of the coating, but make the transparency of the coating and powder anti-group performance worse.
2.4 Effects of UV absorbers on the weather resistance of transparent powders
In powder coating formulations, the role of UV absorbers is to selectively absorb UV rays and convert them into harmless thermal or other low-energy radiation that consumes energy, thus enabling harmful UV energy metabolism and no longer destroying the polymer bonds of film-forming substances. In this study, several UV absorbents were selected for testing, the specific performance of which can be seen in Table 5.
can be seen from Table 5, the addition of UV absorbers has no effect on the materialization performance of the coating film. When adding UV absorbents I. and III., the weather resistance can be significantly improved, but the addition of UV absorbers III. So finally choose the UV absorber I.
a series of tests, the UV absorbent dosage of 0.2% to 0.5% of the total formulation is more appropriate. In addition, the addition of 0.3% to 0.5% of antioxidants can better improve weather resistance and yellow degeneration.
2.5 Technical requirements
through the study of polyester resins, curing agents, additives, etc., has successfully prepared an aluminum wheel with ultra-weather-resistant pure polyester transparent powder coating. The technical requirements and results of transparent powder coating for aluminum hub cover light can be found in Table 6.
From Tables 6 and 1, it can be seen that the aluminum wheels prepared in this study with ultra-weather-resistant pure polyester transparent powder coating has met the technical requirements of aluminum wheel coating, in the corrosion resistance performance is more advantageous, and solve the problem of acrylic transparent powder coating corner corrosion difference.
3 Conclusion
According to the conditions of use of automotive aluminum wheels and related technical standards, the effects of polyester resins, curing agents and additives on the appearance and performance of transparent powder coatings for hood light are examined.
This study successfully prepared an aluminum wheel with ultra-weather-resistant pure polyester transparent powder coating, to solve the problem of poor corrosion resistance caused by poor corner coverage of acrylic transparent powder, promote the domestic automotive aluminum wheel coating industry paint manufacturing and coating technology progress, reduce the domestic production costs in the field of automotive parts manufacturing.
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