Chapter 21 Substrates 385
The mechanical pulpmaking process (groundwood
process) uses grinding wheels to reduce the logs to
fi ber. The by-product is pulp with high opacity but
relatively low strength.
Sizing and Fillers
Sizing is added to the pulp slurry to make the
paper more resistant to moisture. Rosin is a common
sizing material. Alum is added as a binding agent.
Binding is a part of the sizing process.
Fillers are needed to improve a paper’s opacity,
brightness, smoothness, and ink receptivity. Two
common fi llers are clay and titanium dioxide.
Dyes, Pigments, and Bleach
Dyes and pigments are added to produce colored
substrates, while bleach makes the pulp white. Coloring
or bleaching additives are mixed in vats called pulpers.
The pulp goes through a fi nal beating and refi ning stage
before it is pumped to a stock chest.
Removing Water
A jordan machine is a beater or refi ner of the
fi bers. A jordan machine refi nes the fi ber slurry
until it is about 99% water and 1% fi ber and other
solids. At this point, the paper is known as furnish.
The solution is pumped into the headbox of the
papermaking machine.
The pulp furnish is evenly dispersed on the
fourdrinier wire, Figure 21-3. The wire screen vibrates
as it travels along an endless belt, aligning the fi bers
in the direction of travel. A continuous web of paper
is formed in the process. Gravity and suction remove
about 35% of the water.
Some papers are given a watermark, a
translucent identifying design impressed in the
paper while it is still wet. The symbols or images are
created by rearranging the fi bers with a tool known
as a dandy roll. See Figure 21-4.
Figure 21-2. This huge machine rotates logs inside a
toothed chamber to remove the bark. (Southern Forest
Products Assn.)
Figure 21-3. The fourdrinier wire section of the
papermaking process. Wet paper fi bers ride on an
endless wire screen. This is known as the “wet end”
of the machine. Water drains off as the fi bers move
toward the dryers. (Mead Publishing Paper Division)
chipper: A machine that cuts logs into chips.
lignin: A glue-like substance that bonds wood fi bers
together.
sizing: Material, such as rosin, that is added to pulp slurry
to make the paper stronger and more moisture-resistant.
fi llers: Inorganic materials, such as clay or titanium dioxide,
added to the papermaking furnish to improve opacity,
brightness, smoothness, and ink receptivity.
pulpers: Vats in which coloring or bleaching additives are
added to pulp.
furnish: The slurry of fi llers, sizing, and colorants in a water
suspension from which paper is made.
watermark: A translucent design impressed in paper.