Light Fastness and Weather Resistance

Another important qninone is anthanthrone, especially its dibromo derivative (2.73), Cl Pigment Red 168. This latter pigment is scarlet in colonr and shows excellent resistance to solvents and is one of the most light fast and weather fast pigments known. It is nsed in high-grade paints. 

Special effect pigments suitable for outdoor applications must meet the highest standards for color fastness and weather resistance. These pigments are coated additionally with thin layers of transparent and colorless oxidic compounds. These layers increase the light resistance by reducing the photoactivity of the titanium dioxide surface. In addition, the interaction between pigment and binder is optimized. 

These are thermally stable, soft-texture pigments that exhibit high hiding power, excellent thermal stability and bleed resistance. They have excellent light fastness and weather fastness because they strongly absorb UV light without any photocatalytic effect. 

Good heat stability and light fastness, excellent weatherability and chemical resistance, inexpensive, dull, poor tinting strength... 

Since 1950, particular efforts have been made to develop new azo pigments that combine excellent overspray fastness and bleed resistance with high fastness to light as well as weathering. As a result of this work, two different concepts found by Ciba and Hoechst, respectively, proved to be very successful ... 

Apart from displaying the desired physical properties, such as light and weather fastness, heat fasmess, solvent resistance etc., there is a prime requirement that the pigment be readily and evenly dispersible in the application medium. Most pigments are sold as solids and the ease of dispersion in the medium to be used in the application is very dependent on the size of the particles in these solids. 

Carefully controlled precipitation and stabilization provide chrome yellow pigments with exceptional fastness to light and weathering, and very high resistance to chemical attack and temperature, enabling them to be used in a wide field of applications. The following qualities are commercially available ... 

The following factors, in combination with the plastic to be colored, are decisive in determining the suitability of a colorant for a particular application namre, thermal load capacity (level and duration), light fastness, weather resistance, migration tendency (solvent and cmitact bleeding, blooming), plateout (deposits on metal surfaces in contact with melt) and influence on flow behavior [45]. 

Direct band gap semiccHiductor — 2.42 eV. Like ZnS (93), has two crystal forms the moce stable hexagonal, wurtzite, structure and the cubic, zinc blende, structure. The conductivity increases when irradiated with light (hence its use as a photoresistor). CdS pigments tend to have hi thermal stability, good li t and weather fastness as well as chemical resistance and high opacity. 

Bismuth vanadate pigments exhibit very good light fastness in both deep and pale shades. They show excellent weather resistance in full shades, and are superior to lead chromate in this respect. In full shades they are comparable with the best organic pigments and have the greatest durability in deep reductions. 

---