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Q: How much machine-direction orientation (MDO) is possible for sheet? The material we are running is HIPS 0.5- to 0.9-mm thick and 1400-mm wide. What is the effect of MDO on sheet-thickness variation?  Finally, what would be the gain in MD tensile strength and reduction of MD elongation of sheet after MDO?    

—Indian sheet extruder

A: Typical orientation ratios for HIPS are in the range of 2:1 to 3:1. Higher ratios are possible but the maximum ratio for a given material needs to be determined experimentally. The maximum possible ratio is influenced by upstream processing conditions, the orientation temperature, process speed (draw rate), and MDO configuration, as well as the composition and heat history of the HIPS sheet and material itself.

You should not see a significant change in thickness variation after orientation. You will have some edge effects, but these can be compensated for by adjusting the input thickness profile of the sheet and/or taking a trim. The change in tensile properties of the oriented sheet will vary depending upon the process conditions, the material being oriented, and the extent to which you orient it.       

In general, more MD orientation results in higher MD tensile strength and more reduction in elongation. However, keep in mind that there is an associated cost in TD tensile properties if the material is only MD oriented. Highly MD-oriented films will tend to split and tear easily along the MD. (Some products that exhibit this behavior are decorative ribbon for gift wraps and plastic strapping used to palletize goods for shipping.) The best way to learn what the resulting change in tensile properties will be after orienting is to run trials on a lab or pilot-scale machine. We believe that this is an essential step in product development and machine design and encourage all potential customers to run trials in our pilot lab before purchasing a machine.

Kenneth T. Forziati, Jr., business development manager
Parkinson Technologies, Woonsocket, RI
(401) 762-2100 •