Chapter 21 Substrates 397
Strength
The tensile strength of paper is determined by
how well the inner fi bers are bonded together. A roll
of paper that cannot feed through a web-fed press
without breaking easily has loosely bonded fi bers
and low strength.
Print strength is determined by how well the
surface of the paper is bonded together. A low print
strength could allow bits of fi ber to be lifted off the
paper surface by high-tack inks. Hickeys would
appear on the printed image. Coated stock normally
has higher print strength than uncoated stock.
Brightness
Brightness is determined by how well the paper
surface refl ects light. Paper brightness affects the
contrast of the printed image. A bright paper makes
colors, particularly black, stand out more.
Transparent ink on a bright paper also produces
exceptional color rendition. More light refl ects up
through the ink layers to produce stronger colors.
Opacity
Opacity refers to the ability of light to pass through
a sheet of paper. It is also the ability to see through
the sheet. Poor opacity produces an undesirable
result called show-through. The image on the back
side of the sheet can be seen through the paper,
and is a distraction to the reader. Examine stock
carefully to make sure show-through will not occur. A
heavyweight paper has high opacity, whereas a thin
paper tends to have low opacity.
Envelopes
Envelopes come in many styles and sizes for a
variety of applications. Envelopes used for postal
purposes have a minimum size requirement of
3 1/2″ × 5″. Any size over 6 1/8″ × 11 1/2″, or thicker
than 1/4″, is subject to additional postage fees.
Figure 21-22 illustrates common envelope styles.
• The commercial envelope is typically used to
send correspondence. The No. 10 size
(4 1/8″
×
9
1/2″)
is the most widely used.
• The window envelope has an opening that allows
the address to appear through the clear opening.
This is a time-saving and convenient feature.
• The baronial envelope is used mostly for
invitations, announcements, and greeting cards.
• The booklet envelope, with its opening on the
side, is used to hold house publications and
direct mail pieces.
• The clasp envelope is used to mail bulky
materials. The manner of fastening will vary, but
it is strong and can take abuse.
Figure 21-23 lists common envelope sizes. Envelope
company catalogs provide more detailed information.
The acid found in manufactured paper
occurs naturally in wood pulp and may also
be absorbed from the environment, printing
processes, and human hands. This acid causes
the paper to turn yellow in color and physically
deteriorate. To ensure longevity, acid-free
(or alkaline) paper has become the standard
substrate used for archival and historical
documents and projects.
During production, acid-free paper is
treated with an alkaline compound, usually
calcium carbonate, to neutralize the acid and
bring the pH of the paper to 7 or slightly more.
Acid-free paper also contains a reserve of the
alkaline compound to neutralize any acids
the paper may encounter once in use or that
develop as the paper ages. The integrity of
acid-free paper is expected to last hundreds of
years. The life span of paper that has not been
treated with an alkaline compound may only
be a couple of decades.
What are some other common uses of
calcium carbonate?
Acid-Free Paper
Academic Link
trim: The paper that is left over after cutting a sheet into
smaller pieces.
printability: How well fi ne details are reproduced in a
printed image.
tensile strength: The amount of stress that will break
paper.
print strength: How well a paper surface resists lifting of its
fi ber by high-tack inks.
opacity: The quality of a paper that does not allow print
from the opposite side to show through.
show-through: An undesirable result of poor opacity in
which the image on one side of a sheet of paper is seen on
the other side.