This polymer can be transparent, when in its amorphous state; or translucent when in its semi-crystalline state. With excellent barrier (CO2 permeation) and mechanical properties PET is becoming the polymer of choice for food and beverage packaging applications, even replacing traditional materials such as metals or glass. Furthermore, polyester and modified polyesters are found in applications such as fibers, automotive parts, architectural glazing and window films.

Stabilization

For stabilization against light, UV absorbers such as Ciba® TINUVIN® 234 for bulk applications or Ciba® TINUVIN® 1577 for thin applications such as fibers, films or coextruded layers are used. For certain applications combinations of UV absorbers with HALS such as Ciba® TINUVIN® 622 or Ciba® CHIMASSORB® 119 can be applied.

Often processing and thermal stabilization are necessary in neat resins as well as colored applications. Ciba® IRGANOX® B 561, Ciba® IRGANOX® B 900, or in selected cases, Ciba® IRGAMOD® 295 and Ciba® IRGAMOD® 195, offer excellent processing and thermal stability for PET and PET-G.

Coloration

Polyesters are inherently hydrophilic, and as such require pre-drying for trouble free processing. The formulation ingredients that they come into contact with should also be/remain moisture free. An incorrect colorant or color concentrate, used at the wrong concentrations can drastically reduce the mechanical properties. Although there are a relatively large number of polymer soluble colorants that can be used successfully at various concentrations and processing temperatures for Polyethylene terephthalate, there are, at present, few organic pigments. Recommended colorants are mostly part of our Ciba® ORACET® range of polymer soluble colorants for Engineering Plastics, as well as some organic pigments in the Ciba® CROMOPHTAL® range of high performance pigments, all offering required processing properties.

Due to the hydrophilic nature of PET, compounds remain its favourite coloration route. However, liquid color is used in very large quantities for applications such as PET beverage bottles. Masterbatches based upon PET can be made, but have to be dried thoroughly prior to use and should be limited to low addition rates (up to 2%) to prevent incorporation difficulties. Colorants for PET have to demonstrate excellent properties, in terms of heat resistance, light fastness and migration resistance. Very few colorants have sufficient thermal stability to be added at the reactor stage during polymerization, a process which can involve a dwell time of up to 4 hours at temperatures that reach 290°C.

Ciba® CROMOPHTAL® Blue 4GNP (Organic Pigment) and Ciba® ORACET® Yellow RB (polymer soluble colorant) are two such products which are used successfully with this process. Ciba markets a comprehensive range of both, Organic Pigments and Polymer Soluble Colorants, which are suitable for the coloration of Polyesters, whether by addition to the reactor during polymerization, or to the polymer by masterbatch, liquid color or compounding.

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