If the fluidity is to be judged using the melt viscosity properties, an appropriate shear rate range must be confirmed according to the molding method and the shape. The reason for this is believed to be that viscosity decreases occur with high shear rates (shear rate dependence) and, in addition, the resin temperature rises due to shear heating (temperature dependence) also have an influence. 6.12) In injection molding, mold filling may be improved by increasing the injection speed. The melt viscosity is temperature-dependent, and decreases as the temperature rises. For cross-linked PPS, the slope is large because the sensitivity is high relative to the shear rate, whereas for a linear PPS, the slope tends to be small. For PPS, in particular, the slope of the shear rate dependence differs depending on whether it is cross-linked PPS or linear PPS.

The slope of the shear rate dependence depends a combination of factors, such as the polymer structure and the additive type. 6.11 shows the melt viscosity of glass fiber reinforced PPS of 'TORELINA™,' relative to the shear rate. PPS is classified as a pseudoplastic fluid because the melt viscosity varies with the shear rate and, in particular, the melt viscosity decreases as the shear rate increases.įig. In general, the shear rate dependence of the melt viscosity is expressed as a double logarithmic chart to indicate the properties over a wide range. 6.12 Temperature dependence (L/D = 40/1, shear rate: 608/sec) This technical document refers to uncorrected shear rate and shear stress, unless stated otherwise.įig. If the shear rate is used in CAE analysis, it is corrected to a true value, using Bagley correction, Rabinowitsch correction, and so on, to improve analysis accuracy. Note, however, that the shear rate determined by calculation is called the apparent shear rate (or shear stress), not the true shear rate (or shear stress) on the capillary wall. For PPS, which is a non-Newtonian fluid, the detected load (shear stress) varies with the piston rate (shear rate), so that the shear rate dependence of the melt viscosity can be determined by changing the piston rate at will. 6.10), a capillary rheometer detects the load when the molten resin is extruded with a piston at a constant rate, using a load cell, after which the melt viscosity is determined by applying Formulas 6.2 to 6.5.

This method differs from the MFR method, however, in that the fluidity can be determined as melt viscosity (units: Pa･s), not as the resin weight per unit time. A capillary rheometer is used for that test method whereby the specimen melted in a cylinder is extruded through a capillary, in the same way as with the MFR.

Viscosity curve test injection molding