Colored pigment stability improvement

Chrome yellow pigments stabilized with a large amount of silicate play a major role in the production of colored plastics (e.g., PVC, polyethylene, or polyesters) with high temperature resistance. Incorporation into plastics also improves their chemical resistance to alkali, acid, sulfur dioxide, and hydrogen sulfide. 

The conditioning agents usually consist of a phosphate and a potassium salt, as well as zinc, antimony, and aluminum compounds. The purpose of these additions is to improve the final properties of the pigment, including color, photochemical stability, and dispersibility, as well as to catalyze the formation of rutile from die anatase hydrate. 

Generally, there are two basic types of inks. The first type contains finely dispersed carbon black or colored pigments in both solvent and water based systems. Pronounced improvements have been achieved in stabilizing aqueous pigment formulations for ink-jet applications by adding specific polymeric dispersing agents [18], The second type of ink is based on water or solvent soluble dyes. 

In the next step these particles are incorporated in the transparent silane matrix described above. In this network of silanes, fhe nano scaled Si02 particles on the one hand and the coloring pigments on the other can be dispersed without agglomeration. In Fig. 11 the chemical composition is shown schematically. To further improve chemical stability, the steric stabilization can be combined with an electrostatic stabilization. Depending on the incorporated pigments, these inks prove to be chemically stable up to several weeks. 

In contrast to colorants, which stabilize by photon absorption, pigments are photon impermeable, for the most part, and stabilize by reflection and diffusion. Retinoic acid in Basis creme DAC is an example where the inclusion of titanium dioxide pigments improves the photostability of the product markedly. The drug content in the unprotected cream decreases by 28% with two hours of irradiation. Adding 2% of hydrophilic titanium dioxide (formulation E) reduced degradation to only 9% (Fig. 23) (45). The authors observed corresponding results with 2% zinc oxide and with 0.5% yellow iron oxide. 

The colorants of choice for these applications are lakes and inorganic pigments. In addition to providing color, pigments have been reported to reduce moisture diffusion through the film and improve light stability as compared with dye. ° ... 

Features Offers improved flocculation resist. exc. long-term pkg. and color-shear stability exc. weatherfastness Properties BIk. sp.gr. 1.56 tapped dens. 0.37 kg/l oil absorp. 69 g oil/ 100 g pigment Carbopol 907 [Noveon]... 

Resin is applied usually to the long chain of repeated units in the polymeric materials. This may be linear, branched, or cross-linked. Other constituents that contribute along with plastics as additives are plasticizers which improve the flexibility of the plastic, colored pigments, antioxidants, UV stabilizers, lubricants, mold-release agents, and sometimes biocides to inhibit microbiological deterioration. Additives influence the physical properties and resistance to deterioration in plastics. 

Several vitamins have some desirable additional effects. Ascorbic acid is a dough improver, but can play a role similar to tocopherol as an antioxidant. Carotenoids and riboflavin are used as coloring pigments, while niacin improves the color stability of fresh and cured and pickled meat. 

The various lubricants formulated into PVC to improve the processing can also enhance the performance of the stabilizet. In pigmented apphcations, calcium soaps, eg, calcium stearate, ate commonly used as internal lubricants to promote PVC fusion and reduce melt viscosity. This additive is also a powerfiil costabilizer for the alkyl tin mercaptide stabilizers at use levels of 0.2 to 0.7 phr. Calcium stearate can significantly improve the eady color and increase the long-term stabiUty at low levels however, as the concentration increases, significant yellowing begins to occur. 

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