Kyocera DU-21 Manuel D'utilisation page 36

Paper grain
When paper is manufactured, it is cut into sheets with the grain running parallel to
the length (long grain) or parallel to the width (short grain). Short grain paper can
cause feeding problems in the duplexer and the printer. All paper used in the
duplexer and the printer should be long grain.
Other paper properties
Porosity: Refers to the density of the paper structure; that is, to how openly or
compactly the fibers are bonded.
Stiffness: Limp paper can buckle inside the duplexer and the printer, while
paper that is too stiff may bind. Either way the result is a paper jam.
Curl: Most paper has a natural tendency to curl in one direction. The paper
should be loaded so that the natural curl is downward, to counteract the upward
curl imparted by the printer. Printed sheets will then come out flat. Most paper
also has a top and bottom surface. Loading instructions are usually given on the
paper package.
Electrostatic properties: During the printing process the paper is
electrostatically charged to attract the toner. The paper must be able to release this
charge so that printed sheets do not cling together in the output tray.
Whiteness: The contrast of the printed page depends on the whiteness of the
paper. Whiter paper provides a sharper, brighter appearance.
Quality control: Uneven sheet size, corners that are not square, ragged edges,
welded (uncut) sheets, and crushed edges and corners can cause the duplexer and
the printer to malfunction in various ways. A quality paper supplier should take
considerable care to ensure that these problems do not occur.
Packaging: Paper should be packed in a sturdy carton to protect it from damage
during transport. Quality paper obtained from a reputable supplier is usually
properly packaged.
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