Rheological Limit
Minimum force requirements that must be exceeded to initiate flow in a structured liquid govern the behavior of viscous polymer formulations. In textile screen printing, the yield stress threshold determines the ease with which pigment pastes pass through the screen mesh during the squeegee stroke. This parameter prevents the paste from bleeding or running before the drying step.
Printing Performance
Below this stress limit, the formulation behaves as an elastic solid, maintaining its shape and preventing the printed design from blurring. Once the squeegee applies sufficient force, the paste flows smoothly through the mesh onto the fabric substrate. This rapid transition between solid and liquid behavior is essential for high definition printing on woven fabrics where crisp borders must be maintained without any color bleeding.
Measurement Method
Controlled stress rheometers verify this property by applying increasing shear stress to a sample and monitoring the onset of flow. Technical laboratories use vane or cone and plate geometry to prevent sample slip during testing. These measurements are crucial for quality control when formulating thick polyurethane coatings.
Dispersion Restriction
Particle concentration in the formulation dictates the physical magnitude of this required force. When solid pigment loading increases beyond thirty percent by weight, the required force rises exponentially, which causes fabric clogging and uneven ink delivery.
