rosin size
A solution or dispersion obtained by treating ROSIN with a suitable
alkali. The resulting size may be fully saponified
or it may contain free rosin acids. When properly
converted in the papermaking process, usually by
the addition of ALUM , the size
precipitates and imparts water (ink) resistance to
paper. Since in its natural state rosin is
insoluble in water; it must be altered chemically
before it can be used as a sizing material.
Although several methods of treatment exist, the
one in general use today is basically the same as
that used in the manufacture of soap, i.e.,
saponification of a portion or all of the rosin
with caustic soda or soda ash to form a soluble
rosin soap. Unreacted rosin, which is held as an
emulsion, is known as free rosin. The percentage
of free rosin has been found to affect the sizing
efficiency of a material to a certain degree, the
extent depending on variations in conditions in
local paper mills. (17 , 98 , 143 )
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