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Contraries and Stickies
Contaminants that are non-fibrous
in nature and that would interfere with paper formation
and processing are called contraries and stickies,
so called because they are "contrary" to paper composition
and/or they contain adhesives that would "gum-up" the
works, so to speak. Contraries and stickies can be anything
from staples and paper clips to wax, sand, and paint.
Contraries can be broken up into 3 general groupings:
- Large Contraries -- Large particulates which
can wreak havoc on a paper processing system(e.g.
paper machine, de-inking, etc.). These can be removed
by magnetic separators, in the case of metals, or
by screens and cleaners in the pulper in the case
of nonmetallics.
- High Density Contraries -- Particulates which
are smaller in size, but can still sink in water(i.e.
hs higher density than water).
- Low Density Contraries -- Particulates that
can cause problems because they float in water(i.e.
have a lower density than water).
The table below shows contraries that are commonly found
when dealing with paper processing/production:
|
Contrary
|
Particle(µm)
|
Fiber/Contrary
Density Ratio
|
Optimal
Separation Method*
|
| Sand |
40-4,000
|
2.0-2.2
|
Cleaners
> screens(basket and rotor erosion)
|
| Metal |
> 4,000
|
6-9
|
Cleaners
> screens(basket and rotor erosion)
|
| Filler |
< 40
|
1.8-2.6
|
Cleaners(Special
Operation Mode)
|
| Wax |
< 40
|
0.9-1.0
|
Cleaner(as
low density contraries)
|
| Polyethylene |
400-4,000
|
0.91-0.97
|
Screen,
or cleaner(as low density contraries)
|
| Polystyrene |
400-4,000
|
0.3-0.5
|
Screen,
or cleaner(as low density contraries)
|
| Latex/Rubber |
40-4,000
|
0.3-1.1
|
Screen,
or cleaner(as low density contraries)
|
| Hot Melt |
40-4,000
|
0.35-1.1
|
Screen,
or cleaner(as low density contraries)
|
| Bitumen |
40-4,000
|
1.1-1.5
|
Cleaners
|
| Paint |
liquid-400
|
1.2-1.6
|
Cleaners(if
not liquid)
|
* > means "beter than"
Stickies are a special classification of contrary
that comes from glues, waxes, resins, gums, and similar
materials. As paper recyling has been increased and more
synthetic polymeric materials have been produced, so have
the problems with stickies been on the rise. {Gassmann,
H. Avoidance of adhesive impurities by mechanical separation
in pressure screen and cleaner. Inpaper International,
Jan-Mar 2000, pg. 19}.
Stickies can clump up(when this occours, they are called
secondary stickies) and can become clogged in various
parts of a paper machine
to form dirty sticky deposits, causing the need for the
machine to be taken offline for cleaning. Sometimes, these
stickies actually come from waste paper being processed,
and the result is called white pitch. Stickies
which are unconglomerated, they are known as primary stickies,
which do not cause any problems.
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