There are many kinds of red pigments. The inorganic red pigments commonly used in coatings are Iron Oxide red, cadmium red and molybdenum chromium red. There are more varieties of organic red pigment.
1. Iron oxide red
The color ranges from orange red to purplish red. It has good optical rotation resistance, high temperature resistance, dirt gas resistance, alkali resistance, good coloring power, strong covering power and low price. It can be used in all kinds of antirust primer and topcoat. Its disadvantage is that it is not resistant to strong ACID, and the color is black and not bright enough.
Due to the different manufacturing methods of iron oxide red, the particle size and shape are also different, so the color of iron red is changed from red yellow to red purple, so it is necessary to select different colors of iron oxide red according to different requirements of coatings.
When the particles of iron oxide red are ground to less than or equal to 0.01 μ m, the covering power of the pigment in organic medium decreases significantly. This pigment is called transparent iron oxide. It can be used to make transparent paint or metal flash paint, and has better color retention than using organic dyes.
2. Cadmium red
Cadmium red is a mixture of cadmium sulfide and solarization cadmium (3CDs · 2cdse). Generally, sulfide accounts for 55% and suntanned substance accounts for 45%.
Chemical name: cadmium red
Chemical composition: Selenium cadmium sulfide
Pigment index (structure) No.: pigment red 108 (77202)
CAS No.: 12214-12-9
Appearance: red powder
Crystal form: hexagonal, cubic
The color of cadmium red pigment is very full and bright. It has good temperature resistance, alkali resistance, light resistance and atmospheric influence resistance. It has good coloring power and covering power. The chromatographic range is from yellow red to purple sauce. The higher the content of CdSe in cadmium red, the stronger the red light and the darker the color. Cadmium red can be used in high temperature resistant coatings, and also widely used in enamel, ceramics, glass, coatings, plastics, art pigments, printing ink, paper, leather, colored sand and stone building materials and electronic materials.
3. Molybdenum chrome red
Molybdenum chrome red is the mixed crystal of lead molybdate and lead chromate, which is bright red and orange when containing lead chromate. It has strong optical rotation resistance, good covering power and coloring power.
The weathering resistance of molybdenum chrome red without surface treatment is general, but the molybdenum chromium red after coating or pre darkening has good weather resistance and color retention, which is widely used in various kinds of construction machinery topcoat.
The content of harmful heavy metals lead and chromium in molybdenum chromium red is very high. With the limitation of some standards and regulations on the content of harmful heavy metals in various coatings, environmental protection pigments must be used to gradually replace them.
