Modification Of C.I. Pigment Green 8 Via Coating Method

There are lots of advantages of organic pigments such as bright color, high tinting strength, broad chromatogram, low toxicity. Nowadays they are widely used in paints, inks, plastics, rubbers and so on. However, many organic pigments show limited hiding power and poor weather durability. The organic coating method is attempted to address these problems. In this dissertation, the organic pigment green 8 is coated on the inorganic core or encapsulated with inorganic compounds such as SiO₂, TiO₂ and some inorganic mineral including celatom, kaolin and sepiolite. And we also discuss the color light, tinctorial strength, dispersion ability, thermal stability and weatherability of the organic coating pigment.The pigment green 8 was coated by celatom, kaolin and sepiolite via ball milling and dipping methods. The results show that the color light of the modified pigments doesn't change, the tinctorial strength is enhanced, especially the tinctorial strength of the sapmle coated by 20% weight sepiolite is 110%. The organic coating pigments have good flowability and dispersion ability in water. The modified organic pigments could obviously scatter the UV light, so they have a better weatherability than the original one. The temperature of initial decomposition(TID) gets higher, for instance the TID of the sample coated by 20% weight sepiolite is raised to 318℃from 289℃of the original one. But the speed of the thermal decomposition hasn't change a lot.The SiO₂ was mixed with the organic pigment green 8 during the synthesis process of pigments. The color light of the modified pigments doesn't change and the tinctorial strength is enhanced. The tinctorial strength of the pigment coated by 20% weight SiO₂ is 110%. The modified organic pigments also have good flowability and dispersion ability in water. TGA results illustrate that SiO₂ coating could improve the thermal stability of the organic pigment. UV-Vis spectra show the organic coating pigments could also scatter the UV light. When the pigment was coated by 50%, the absorption intensity of the UV-Vis is reduced by 16%.The SiO₂ was encapsulated on the surface of the organic pigment green 8 after the synthesis process of pigments. The modified pigments have better performance while the Na2SiO3 and HCl are added parallel or Na2SiO3 is added firstly then HCl is added slowly. The tinctorial strength of the coating organic pigments is over 85% especially the one coated by 20% weight SiO₂ is 105%. They also have good flowability and dispersion ability in water. The thermal stability and weatherability of the organic coated pigments are also improved.The TiO₂ was encapsulated on the surface of organic pigments by sol-gel process of titanium n-butoxide. The color light of the modified pigments doesn't change a lot and the tinctorial strength drops a little (the tinctorial strength of the pigment coated by 60% weight TiO₂ is 80%). The modified organic pigments exhibit bad flowability and dispersion ability in water. XRD analysis indicates that the TiO₂ coating on the organic pigment particles is amorphous. Many holes are formed in the organic coating pigment particles, and the layer of the TiO₂ isn't tightness. The thermal stability of the organic coating pigments isn't improved heavily, but the weatherability is enhanced.