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– Technical specification tables 47
print quality. If electrical resistivity is too low, poor image transfer and
low density can result. Generally, paper has very high resistance, so
paper manufacturers add salts or other materials to lower the
resistivity.
Moisture content
Paper is hygroscopic; that is, it will absorb or give up moisture
depending on the humidity in the air around it. The moisture content
of paper has a great effect on its resistivity. Paper will absorb
moisture in a high-humidity environment and lose moisture in a low
humidity environment. Small increases in moisture content greatly
reduce resistivity while small decreases in moisture content greatly
increase resistivity.
Moisture content can also affect other paper properties such as curl,
stiffness, and dimensional size. Higher moisture content can make
paper prone to curl and wrinkling during printing, make a sheet limp,
and increase the dimensions of a cut sheet. Paper performance can
change significantly with seasonal or weather changes, which affect
the humidity in the printing environment.
Caliper
Caliper is the thickness of a sheet of paper or other print media. It is
typically specified in mils (one-thousandth of an inch) or millimeters. It
is closely associated with paper weight but not directly, because
some papers have more bulk (less density) than others.
Grain
Grain is the orientation of paper fibers in paper. Fibers tend to align
themselves in the process direction of the paper machine. Papers are
stiffer in the grain direction. Most cut sheet papers are cut long grain,
that is, with the grain direction parallel with the long edge of the sheet.
For heavier weight papers (>135 gsm) Hewlett-Packard
recommends using short-grain paper, if available, to improve feeding
and reduce wear to the paper path.
Stiffness
A minimum stiffness is required for paper to separate from the
transfer and fuser rollers. Most long-grain papers greater than 60 gsm
will have adequate stiffness to transport through the printer.
Generally, stiffness increases with paper weight.