Heat stability pigments

A main line of development now is multi-functional additives, such as reinforcing fillers talc is added to polypropylene to improve stiffness and heat stability, pigments can aid in UV protection, plasticizers also function as lubricants and anti-static agents. A potentially fertile field is that of synergism between components, where better performance in vital properties such as weathering and flammability can be achieved by using lower concentrations of synergistic additives. 

Rigid Applications. The use of the lead stabilizers is very limited in the United States but, they are stiU used in several rigid PVC appHcations in Europe and Asia. The highest use of lead stabilizers in rigid PVC is for pipe and conduit appHcations. Tribasic lead sulfate is the primary heat stabilizer with lead stearates included to provide lubrication. The lead products are typically fully formulated, usually including lubricants and pigments for pipe extmsion appHcations. These lead one-packs, when used at about 1.8—2.5 phr, provide all of the stabilizer and lubrication needed to process the polymer. A lead one-pack contains tribasic lead sulfate, dibasic lead stearate calcium stearate, polyethylene wax, paraffin wax, ester wax, and pigments. 

Lead forms a normal and an acid sulfate and several basic sulfates. Basic and normal lead sulfates ate fundamental components in the operation of lead-sulfuric acid storage batteries. Basic lead sulfates also ate used as pigments and heat stabilizers (qv) in vinyl and certain other plastics. 

Iron oxide is used for compounding silicone rubbers where it is used to improve heat stability. Iron oxide, mainly ferric oxide, also finds application as a pigment. 

Table 4 Relation between the heat stability of azo pigments in an alkyd-melamine resin baked system, their fastness to overpainting in this paint system, and their bleed resistance in plasticized PVC.

The specific requirements for organic pigments in terms of heat stability result from the temperature levels at which individual polyolefins are processed. Standards have been developed to test the heat stability of pigments in polyolefins [33] (see also Sec. 1.6.7). 

Dry spinning. The polymer, dissolved in a suitable solvent and filtered, is pressed through spinnerettes and, in an oxygen-free atmosphere, pulled by vacuum through a heated shaft, where the polymer solidifies as the solvent evaporates. The requirements of this process regarding the heat stability of pigments are much less... 

Introducing acidic substituents into the basic structure of a typical monoazo yellow pigment makes it possible to convert the material into a lake by salt formation. This improves the application properties of a pigment compared to its non-laked counterpart. Such pigments exhibit particularly good migration resistance and heat stability, making them useful colorants for plastics. 

In contrast, diarylide yellow pigments are used widely throughout the plastics field. This is particularly true for P.Y.13,17,81,83, and 113. The first German edition of this book reported that the heat stability (Sec. 1.6.7 1.8.3) of these pigments, for instance in polyolefins, was up to 200 to 270°C for 5 minutes, depending on the depth of shade. Results that have been published in the meantime [8], however, require rectification of these numbers. 

P.Y.17 is also frequently used in polyolefins, sometimes in the form of pigment preparations. Its heat stability in these media was said to be about 220 to 240°C, but must now, as a result of the detected thermal decomposition of diarylide yellow pigments in plastics, be limited to 200°C. This tendency to decompose excludes P.Y.17 from recommendation for use in polystyrene, in which the pigment largely dissolves under the processing conditions. The same is true for ABS. 

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