Thickening agents

Owing to the very high consumption of paste in carpet printing (the average machine
requires 2500 l h–1), thickeners must be relatively cheap and possess rapid dispersion
and dissolving properties in cold water. As in other printing applications, they must be
stable to the other components of the paste (such as acids, dyes and auxiliary products)
but, since carpet prints are steamed without intermediate drying, the thickened paste
must maintain a reasonable viscosity at 100 °C to prevent flushing. Furthermore, as
only a continuous cold-water rinse is used to wash the carpet after steaming, the
thickener must be readily removable under these conditions. These criteria are met by
modified locust bean or guar gums, while starch types and xanthan gums are also used
to some extent. Low-solids, high-viscosity products are preferred and, for purely
economic reasons, modified guar gums are particularly popular. The rheological
properties of these thickeners vary somewhat, particularly with regard to their property
of so-called pseudoplastic flow, that is, a tendency to decrease in viscosity with