Many products are used in the paper pulp industry
but few possess such a diverse range of uses as phosphates.
The dispersing properties of phosphates make
them extremely useful for limiting the caking
of mineral fillers,
pigments, resins (and other powdered solids) when in suspension.
Accordingly, they play an important role in the preparation
of coating
compositions.
Other chemical, mechanical and de-inking properties
are important in producing pulps,
or virgin stock, made out of woods with a high resin content,
a sort of 'gum' sometimes appears around the fibres which can
cause indentations on the sheet of paper. These are known as
pitch spots. Adding selected phosphates can prevent this from
occurring. The same applies during de-inking with stickies.
The main phosphates used are sodium tripolyphosphate
(STPP), sodium hexametaphosphate (SHMP) and diammonium phosphate
(DAP).
