Friday, May 20, 2011

Polyurethane in Paper-making and Printing

Solid polyurethane are being used successfullyfor the top of vacuum boxed on paper-marking machinery. A gauze holding the paper fibers travels across the vacuum box and excess water is removed by vacuum. The polyurethane is less harsh to the guaze than other materials and is itself resistant to wear. This is an example where polyurethanes are used sucessfully in water at a temperature around 50 *C .

Special grades of very soft polyurethane elastomers have been used for many year for printing rollers. The hardness of these materials vary from around 10 to 30 Shore A and the physical properties are poor compared with what is normally expected from polyurethane elastomers. However, solid polyurethane around a hardness of 60 to 70 Shore A are being used for scraper blades on silk-screen printing due to their solvent resistance and low ink pick up.

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