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Sunday, December 8, 2013

Paper Roughness (Smoothness): Part 7 - Applications

Some of the other reasons for testing roughness are related to converting processes. The die-cut sheet feed in an envelope machine requires only one sheet at a time to be picked up and transferred, whereas multiple sheets will cause paper jams. The coefficient of friction between plies has a high correlation to Sheffield measurements.

There are some applications where metalized films are applied to the surface of paper. The reflectance properties of the film can expose wire marks on the base sheet. This is another example where the gentle loading force of Sheffield test better replicates end use properties of the paper, as compared to the PPS test.

Many plastic films are packaged in reams, like paper, for use in a photocopier to produce overhead projector transparencies. When the surfaces of the films are extremely smooth, there are static forces and cohesive forces that interfere with single sheet feeding. The manufacturers of such films generally create rough surfaces that enable an air film to exist between sheets. It is common to use Sheffield test results to control the process that generates the rough surface. Again, the PPS test would have measuring head loading that is excessive for this test.

When selecting a test instrument for paper, it is important to understand the relationship between the end-use of the product and the physical test parameters of the instrument. A further requirement is to use a test where process control settings on a paper machine (or plastic web processing equipment) can be modified to optimize the final product for its intended end use. The old adage was “If you can’t control it, why measure it?” In today’s marketplace, the customer will be able to find a supplier who makes the product he wants.

Related posts include information on the relationship between paper roughness (smoothness) and the following items:
  • Papermaking Process
  • Printing processes
  • Formation
  • Parker Print Surf Test
  • Sheffield Test
  • Applications