Probe tack method

The most common ASTM standard method is a probe tack method (11), in which a cylindrical probe is raised into contact with the adhesive surface of the tape and then pulled back (see Fig. 3). The maximum force attained during removal is reported as the tack value. Typical conditions involve an application pressure of 100 g/cm, a contact time of 1 s, and a removal rate of 1 cm/s, but all of these parameters may be varied with most test equipment. 

A widespread tack measurement method is the probe tack method proposed by Wetzel [56] and refined by Hammond [57]. In this method, known as the Polyken probe tack method (Fig. 8-17), a cylindrical ram with a diameter of 0.5 cm is pressed from below against the adhesive layer at a defined pressure and speed and removed again at a defined speed after a certain contact time (see ASTM D2979-71). 

An instrument developed at BASF by A. Zosel [30-31] for fundamental studies [58-63] on the theory of adhesion operates on a similar principle to the probe tack method (Fig. 8-18). 

Probe tack and peel strength test methods are almost same, except for test area and test time, in that the measurements are taken with the PSA removed from the substrate. So the peel strength is influenced by the Tg also, so that if the Tg of a PSA is sufficiently low, the wettability will increase after applying it... 

By automating the standard PSA testing methods for probe tack and shear adhesion, it was clearly demonstrated that one obtains statistically more significant data very efficiently. 

Tack is generally determined with a tensile testing machine and test blocks. The blocks are pulled apart immediately after the adhesive is applied and the blocks are joined. The result is reported in force required per square inch of bonded area to separate the blocks. Various instruments have also been developed to measure tack for specific applications. ASTM test methods include D2979 (Probe Tack) and D3121 (Rolhng Ball Tack). 

Fig. 1. Schematic of the different methods for the evaluation of tack properties, (a) Probe tack, (b) Rolling ball tack, (c) Loop tack.

Illustrations of several test methods used to characterize tack of pressure-sensitive adhesives (PSAs) (a) flat probe tack, (b) loop tack, and (c) rolling ball tack... 

Tack is defined as the limiting value of the adhesion as the contact time approaches zero. Targets for tack measurements are shortest possible contact time and lowest possible contact pressure. With this aim, a number of methods have been developed [53, 54]. The best known tack measurement methods are quick-stick, probe tack, Zosel tack and rolHng ball ]27]. AH these methods are ultimately a refinement of the subjective finger test, which stUl plays significant role in forming a qualitative practical opinion ]27]. 

Standard Test Method for Pressure-Sensitive Tack of Adhesives Using an Inverted Probe Method, D2979-82, Note 1, American Society for Testing and Materials, Philadelphia, 1982. 

ASTM D2979-01 Standard test method for pressure sensitive tack of adhesives using an inverted probe machine. 

---