Coextrusion and Extrusion blow molding
Coextruding Desmopan® or Texin™ onto hard thermoplastics such as PC/ABS or ABS adds to the resulting components’ range of properties and applications. Desmopan® and Texin™ improve the scratch resistance of the surfaces, give them a pleasant feel and deaden noise. Aliphatic grades of Desmopan® and Texin™ do not turn yellow when exposed to UV light. They can therefore be pigmented with light colors too, which further extends the design possibilities.
TPU hot-melt adhesives such as Desmomelt® can also be applied to flat films and blown films by coextrusion. Moreover, coextrusion is suitable for manufacturing inliners for fabric-reinforced hoses such as fire-fighting hoses. Coextrusion is used to apply Desmomelt® directly to the TPU that forms the main layer. This avoids the need for a lengthy bonding process and the use of solvents.
Hollow parts such as bellows (Fig. 7) can be produced on commercially available blow molding machines from specially developed grades of Desmopan® and Texin™ using tube dies and accumulator heads. Two-layered blow molded parts (with an outer layer of aliphatic Desmopan® or Texin™ and an inner layer of aromatic Desmopan® or Texin™) have also been produced successfully by coextrusion blow molding.
To ensure that the TPU grades used exhibit optimum melt stability, the shear strain should be minimized during melting. This is achieved with low screw speeds and/ or low screw compression. The wall thickness control systems that are commonly used in blow molding plants should also be used with Desmopan® and Texin™ to compensate for the change in wall thickness caused by stretching the preform.
Fig. 7: Extrusion blow molded bellows