Automotive coatings are a type of paint that is highly decorative and protective. As an important component of film-forming materials, pigments, especially those used for automotive topcoats, play a crucial role in ensuring the high decorative and durable properties of automotive coatings. With modern exterior designs, vibrant or elegant colors are an effective means for car manufacturers to attract customers and evoke associations of high-quality performance. Due to the development in the pigment and coatings industry, as well as the strengthening of environmental regulations, there have been continuous changes in the recommended and adopted pigment varieties for automotive topcoats. Some pigments with lower cost-effectiveness are gradually exiting the market. From a toxic standpoint, inexpensive pigments like lead chromate yellow and cadmium yellow are no longer used in automotive coatings. Following this trend, bismuth vanadate, which offers superior performance, color, and safety, has become increasingly popular in the market!
It is well known that pigments used in automotive topcoats should exhibit the following four performance characteristics:
(1) Excellent chemical stability, which refers to the pigment's resistance to various chemicals such as gasoline, lubricating oil, acids, alkalis, solvents (for colorfastness), salt spray, water, and humidity, along with excellent resistance to outdoor exposure like sunlight, rain, and UV radiation under different climate conditions to ensure outstanding gloss, color retention, and resistance to chalking for outdoor durability. Additionally, considering the overbake test during the curing of automotive coatings, pigments should have high heat resistance (180°C).

(2) Excellent color performance, where the color, hue, and saturation displayed by the pigment in a well-dispersed state should meet user requirements. Typically, pigments should possess high tinting strength and film gloss. Opaque pigments should have high hiding power, while transparent pigments should exhibit good transparency. Moreover, pigment color reproducibility should be good, meaning pigments with the same batch and grade should have a narrow allowable range for color indicators such as hue, tinting strength, etc.
(3) Good application performance, requiring pigments to have excellent dispersibility, antiflocculation properties, and storage stability during grinding dispersion and paint formulation. The resulting color paste should demonstrate good flowability to meet the technological requirements of computerized automatic color matching in modern automotive coatings manufacturing.

(4) Low toxicity, where inorganic pigments previously used for automotive topcoats included "lead chromate pigments," but nowadays environmentally friendly inorganic composite pigments (metal oxide pigments) like "bismuth vanadate yellow" dominate. In the past, lead chromate yellow could be suitable for automotive coatings due to its lightfastness and weather resistance after surface treatment, but its toxicity led to its discontinuation in automotive coatings. Similarly, cadmium yellow was banned for the same reason. Bismuth vanadate yellow (PY184) is an environmentally friendly inorganic yellow pigment produced by KELA Materials . Its notable characteristics include eco-friendliness, non-toxicity, bright and clean color, excellent heat resistance, weather resistance, lightfastness, chemical and solvent resistance. It provides good coverage, similar to titanium white but with higher tinting strength, making it an ideal non-toxic substitute for chromium yellow pigments. Bismuth vanadate belongs to the category of metal oxide pigments, which are chemically stable inorganic composite pigments. In the stable crystal structure of metal oxides, colored metal ions present their color. Variations in oxide composition result in different colors, with the advantages of excellent heat resistance, acid-base resistance, lightfastness, and weather resistance. In conclusion, using metal oxide pigments like bismuth vanadate for coloring automotive topcoats is highly ideal.
