5.1 This test method is used to measure the apparent viscosity of thermoplastic pavement marking at elevated temperatures. Elevated temperature viscosities of thermoplastic pavement marking may be related to the properties of coatings, adhesives, and composite thermoplastics. This method is helpful in determining the flow properties which can be used in determining processability when applied to the road surface.

5.2 Thermoplastic pavement markings may be applied to the road surface in several different ways. Typical methods of application are screed extrude, ribbon extrude, thin film spray, and standard spray. Proper application depends on the viscosity of the thermoplastic material at application temperatures for the method being used. Thin-line applied thermoplastic pavement marking, for example, requires a relatively lower viscosity. Screed extrude applied thermoplastic requires a higher viscosity.

5.3 Materials of the type described in this procedure may be non-Newtonian, and as such, the apparent viscosity will be a function of shear rate under the conditions of test. Although the viscometer described in this test method operates under conditions of relatively low shear rate, differences in shear effect can exist depending upon the spindle and rotational speed conditions selected for the test program. Comparisons between non-Newtonian viscosity values should be made only for measurements made with similar viscometers under conditions of equivalent shear. For this method, "torpedo" spindles are recommended. Spindles considered torpedo spindles are ~1-in. long and come in many diameters with a 45° conical bottom. A diameter that is half the diameter of the thimbles used is recommended. If large glass beads are used in the pavement marking formulation, a smaller diameter spindle may be needed so the beads do not cause an impedance of the spindle due to a jamming between the inside wall of the thimble and the spindle.