Rheological Fluid
Chemical formulations that exhibit a decrease in viscosity when subjected to mechanical shear flow enable efficient application of coatings and print pastes to textiles. Formulators utilize shear thinning polymers to design thickeners that flow easily through fine screen meshes but remain stable once deposited on the fabric surface. This flow behavior prevents the spreading or bleeding of printed patterns.
Extrusion Flow
The molecular structure of these compounds consists of long polymer chains that are randomly oriented when at rest. When a high-shear force is applied by a squeegee or during spinneret extrusion, the shear thinning polymers align parallel to the direction of flow, which dramatically reduces the resistance to movement. Once the force is removed, the chains return to their tangled state, causing the viscosity to recover almost instantly.
This rapid recovery ensures that the coating maintains its structural thickness and does not drip through the weave of the fabric.
Coating Application
In textile finishing, these materials are applied using roll-coating or screen-printing equipment. The behavior of shear thinning polymers allows for fast processing speeds because the coating paste moves smoothly under the high-shear scraper bar. This property prevents coating build-up on the applicator edges.
Viscosity Control
Formulating chemists must balance the recovery rate of the polymer to prevent surface defects. If the material recovers too slowly, the coating will run and smear the fabric edges. If it recovers too quickly, the liquid will not level out to form a smooth finish.
