Tack adhesion measurements

Fig. 18 a Schematic of probe tack measurements of a thin adhesive film along a temperature gradient, b Compilation of probe tack data during loading and unloading cycles for different temperatures. c Total adhesion energy, calculated from the area under the load-displacement curve shown in b divided by maximum contact area, as a function of temperature. The error bars represent one standard deviation of the data, which is taken as the experimental uncertainty of the measurement. (Reproduced with permission from [86])... 

Moon SH, Chiche A, Forster AM, Zhang WH, Stafford CM (2005) Evaluation of temperature-dependent adhesive performance via combinatorial probe tack measurements. Rev Sci lustrum 76 062210... 

The next series of Figs. 5-7 illustrate the use of a relatively new aromatic modified terpene resin as a tackifier for natural rubber latex. Again, the properties of probe tack, quick stick, peel and shear adhesion were measured for various rubber/resin ratios. We observe that this resin tackifies the natural rubber latex quite well, yet the curves are substantially different from those generated with the beta-pinene resin emulsion. These differences can be attributed to differences in solubility parameter (caused by compositional differences) and molecular weight and distribution of the two resins. 

Tack adhesion measurements were made by curing the polybutadiene gel in a thin film ( 0.5 mm thick) on a plate. A stainless steel probe (8 mm diameter) was brought into contact with the gel film and held for 60 s at a force of 500 g. The probe was pulled away from the gel film at a rate of 0.002 mm/s, while measuring the force-displacement curve. The temperature for the tack measurement was held constant utilizing an environmental chamber. The sample... 

Fig. 10. Schematic representation of a typical tack adhesion measurement apparatus during (a) contact and (b) sep>aration steps, (c) A typical force vs. distance curve obtained from a tack measurement.

Tack is the measurement of the quick grab or stickiness of an adhesive. Tack is a surface phenomenon that is not always indicative of an adhesive s performance. There are several methods of measuring tack. One test is called the quick stickIt is a measure of the force required to remove a tape at a 90 angle from a surface to which it has been applied under no other pressure than the weight of the tape itself. Another version of this test is called loop tack, in which the pressure sensitive tape is applied in a loop form using only the pressure of the... 

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]. 

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). 

The progress of crosslinking over time can be recorded by measuring the surface tack. This can be carried out using the Zosel tack measurement tester described in Sect 8.2.3 (Fig. 8-18). This enables measurement of the separation work of adhesive layers throughout the course of drying. 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

In the earlier art, there was some consideration that partial incompatibility of the tackifier resin with the rubber was responsible for the appearance of tack, but this no longer is seriously held in light of continuing studies by many investigators. Aubrey [38] has addressed this in his review of the mechanism of tackification and the viscoelastic nature of pressure sensitive adhesives. Chu [39] uses the extent of modulus depression with added tackifier as a measure of compatibility. Thus in a plot of modulus vs. tackifier concentration, the resin that produces the deepest minimum is the most compatible. On this basis, Chu rates the following resins in order of compatibility for natural rubber rosin ester > C-5 resin > a-pinene resin > p-pinene resin > aromatic resin. 

Rolling ball. A small steel ball with specific weight and diameter is rolled down an inclined plane onto a thin film of adhesive placed at the bottom. The distance the ball rolls on the adhesive film before stopping is a measure of the tack (the longer the distance, the lower the tack). 

Probe tack. A probe (flat or not) is contacted with an adhesive film at a given pressure and dwell time. The force required to remove the probe from the adhesive is a measure of tack [30]. 

In contact adhesives, the so-called tack open time is important. This can be defined as the time available after the adhesive is applied during which the surface remains tacky enough for the application of the adherend. It can be easily measured by applying a thin layer of fresh adhesive on Kraft paper and making a bond at different times until no bond is obtained. 

Tumor cells that have the ability to attach to some defined substrates with the same apparent efficiency, as measured by the adhesion assays described above, may nonetheless adhere to the different substrates not with the same strength. Therefore, even though each substrate appears to be able to support cell adhesion, the tenaciousness characterizing each interaction may be different, and it may have an influence on the metastatic ability of tumor cells (Leung-Tack et al., 1988). 

Physical properties were evaluated using standard DIN or ASTM specifications. The sealants were filled into Teflon molds to form homogeneous test pieces of comparable thickness. The specimens were then moisture cured and conditioned at 25 °C and 50% relative humidity for 14 days before mechanical property testing. The hardness of the cured sealant samples was measured by Shore A. Shelf life at 50 °C was determined for a maximum of 21 days. Tack-free times were determined by finger touch under ambient conditions. For adhesion testing the substrates were first wiped with either methyl ethyl ketone (aluminum, steel, glass, concrete, wood) or methanol (PVC, PMMA, ABS, polystyrene), then washed with detergent, rinsed with distilled water, and allowed to air dry prior to preparation of the test specimens. Specimens were cured for 14 days at ambient conditions. 

Tack—the ability to form a bond of measurable strength immediately after the adhesive and adherent have been brought together. 

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