Development of 2K varnish for high performance and low VOC automotive refinish

introduction

At present more than study novel low VOC coating are: the radiation-curable coating (UV coatings), powder coatings, waterborne coatings, high solids coatings

Although water-based coatings have low VOC emissions, they are greatly affected by environmental temperature and relative humidity in terms of construction, and require special construction equipment and environmental condition control.

Therefore, the current water-based advancing process of automotive refinish paints is still relatively slow, especially in terms of gloss, fullness, vividness, water resistance, etc.

The most direct and effective way to reduce the VOC emissions of 2K varnishes for car refinish is to reduce the use of solvents and increase the construction solid content of the varnish

At present, the development of 2K varnishes with high solids and low VOC content mainly replaces traditional high-molecular-weight resins with low-molecular-weight high-solids and low-viscosity resins, thereby reducing the use of solvents and achieving suitable construction viscosity

This research explores the influence of hydroxy acrylic resin and curing agent on the construction solid content and paint film performance, so as to select a suitable combination of resin and curing agent, and successfully produced a high-performance low-VOC content used in the automotive refinish paint industry.

The influence of hydroxy acrylic resin

As the main film-forming substance of 2K varnish, hydroxy acrylic resin plays a key role in the overall performance of the entire 2K varnish

Further research on the dryness, hardness, gloss, appearance and other properties of the three varnishes, the results show that the surface dryness, polishability, pendulum hardness, gloss and other properties of ACR6736A are the best among the three
.
Moreover, the gloss of ACR6736A is very high, and the gloss at 20o angle is as high as 98.
2
.
Although ACR6780 has the best appearance, its surface drying speed is very slow, which cannot meet the drying requirements of the automotive refinishing paint industry
.
Similarly, although the surface drying speed of ACR6730 is fast, the polishing speed is very slow, which also cannot meet the dryness requirements of the automotive refinishing paint industry
.

Considering the above construction solid content, dryness, hardness, gloss and other performance factors, ACR6736A has the best overall performance
.
Therefore, in this study, ACR6736A was selected as the main resin to prepare 2K varnish, and the next step was to optimize the construction solid content
.

Effect of curing agent

Curing agent is the main part of 2K varnish, its own solid content and solvent dilution will also have an important impact on the construction solid content of the entire 2K varnish, and ultimately directly affect the level of VOC content
.
Therefore, this study chose ACR6736A as the main resin to compare the construction solid content of 2K varnishes made with different curing agents.
The results show that when ACR6736A is used with a commercially available TMA-100 curing agent, its construction solid content is It is higher than other curing agents
.
When the conventional construction viscosity is 18s (25℃, coating -4 cups), the construction solid content is as high as 53.
60%
.
Measured with BYK density cup, the density of the varnish under this condition is 0.
993 g/mL
.
According to the national standard GB/T 23985-2009 "Determination of Volatile Organic Compounds (VOC) Content in Paints and Varnishes" in 8.
3 Method 2, it can be concluded that the VOC content at this time is 460.
75g/L, which can meet the current national standard GB VOC emission standards (≤480 g/L) for automotive refinish varnishes specified in 24409-2020 "Limits of Hazardous Substances in Vehicle Coatings"
.
 

Optimizing the performance of 2K varnish

In summary, in this study, ACR6736A was selected as the main resin, combined with TMA-100 curing agent, to produce a 2K varnish with high solids and low VOC emissions
.
Furthermore, the performance was studied and compared with the 2K varnish made with conventional curing agent.
The results showed that the 2K varnish made with ACR6736A resin and TMA-100 curing agent is a high solid content and low VOC emission, and it has a balance 2K varnish for high-performance automotive refinishing paint with dryness, gloss and appearance
.
It not only has faster surface drying and polishing speed, high gloss, but also the pendulum hardness, appearance, and pot life are better than the 2K varnish made by conventional curing agents, and the weather resistance is basically the same
.