Polybutylene terephthalate is a semi-crystalline polyester used for door and window hardware, automobile luggage racks and body panels, headlight reflectors, and fiber optic cables. It is being used to replace PVC for cable sheathing, due to a combination of environmental pressures and outstanding electrical properties across a wide range of temperatures. PBT is also replacing metals (in conjunction with PC as an alloy/blend) for automotive body panels.  

Stabilization

PBT end products may suffer from yellowing and cracking, loss of gloss and deterioration of physical properties when exposed to heat and light.Antioxidants such as Ciba® IRGANOX® 245 and Ciba® IRGANOX® 1010 combined with Ciba® IRGAFOS® 168 provide long-term thermal stability to PBT. For outdoor applications protection of the polymer is provided by addition of UV absorbers such as Ciba® TINUVIN® 234 or Ciba® TINUVIN® 1577.

Coloration

Similar to PET and most other engineering polymers, PBT is hydrophilic in nature. Thus, compounds remains the favorite coloration route. However, improvements in masterbatch and liquid color means that PBT is starting to see an increase in use. Masterbatches based upon PBT 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. Depending on the final application and the process to make that particular article, the properties of the colorant can be defined. The natural color of PBT is milky white ( degree of crystallinity defines actual milkiness/whiteness), and so a wide color range is possible. For applications made by injection molding the heat stability required by the product is higher than those to be incorporated to make an article via extrusion. Ciba markets a comprehensive range of products of Organic Pigments and Polymer Soluble Colorants, mostly from the Ciba® CROMOPHTAL® and Ciba® ORACET® ranges, which offer required heat stability, light fastness and migration resistance and are suitable for the coloration of PBT, whether for use in extrusion or injection molding.

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