Tack measurement method

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]. 

The advantage of the quick-stick methods compared with other tack measurement methods is that the test can be carried out in any mechanical test machine with only minimal contact pressures. Disadvantages of the method include a relatively long contact time, different contact times within a test area and different contact areas. Moreover, the peel angle is not constant in the FINAT method. 

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). 

In contrast to the other tack measurement methods mentioned above, the rolling ball test requires simple equipment and is easy to carry out. The main difference to the other tack measurement methods is the fact that the rolling ball method does not measure force. The meaningfulness of the method is also impaired by the following characteristics ... 

Despite its importance in some circumstances, the measurement of tack has not attracted the attention of standards committees and satisfactory tests have been few and far between. ISO TC 45 started work on a method but abandoned it through lack of interest. In essence, tack measurements consist... 

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... 

There are no standard ISO or ASTM test methods presently available for measuring tack or stick properties of an uncured rubber compound. Many rubber companies measure this property by their own proprietary methods. However, Momsanto Instruments Group introduced an instrument called the Tel-Tak Tackmeter in 1969 for measuring tack for tire and/or conveyor belt compounds. 

Many expressions are used in connection with drying (e.g., dust-free, tack-free, surface-dry, dry-to-touch, dry-to-handle, dry-through, dry-to-recoat) but these terms do not have accurate definitions. However, equipment is available for measuring drying times in the laboratory under defined temperature and humidity conditions (Fig. 9.6). Internationally standardized test methods also exist ... 

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). 

Test Method for Measuring Strength and Shear Modulus of Nonrigid Adhesives hy the Thick-Adherend Tensile-Lap Specimen-, and ASTM D2979, Standard Test Method for Pressure-Sensitive Tack of Adhesives Using an Inverted Probe Machine. 

Three main types of test methods are used to determine the physical properties of PSAs peel, tack, and shear (8) (see also Adhesion). Standard test methods are available for all three properties, and numerous additional variations of tests measuring these properties have also heen used (9). Environmental conditions are an extremely important factor in all PSA testing. PSAs are almost always very sensitive to temperature. Many PSAs are also sensitive to humidity, particularly if stored in environments where they can either ahsorh or lose moisture. 

The second technique to measure L takes a different tack and assumes that the defect fills the hole electron pair generation volume and that L varies in a smoother and less abrupt fashion in moving from a defect to a defect-free region. The low temperature shallow trapping model uses this approach to calculate L [10]. This method allows one to measure L at any point, irrespective of the presence of surrounding defects [13] We will illustrate the use of both techniques for hydrogen passivation. 

A number of standard test methods and practices have been developed to measure (a) the composition of glue mixes (especially polymer and/or filler/extender content) and (b) the rheological and working properties of adhesives (viscosity, density, tack, etc.). They are listed in Appendix 2 by these property groupings. 

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... 

Rolling ball tack is a unique test method in which a small ball of specified weight and diameter is rolled down an incline plane onto an inverted test adhesive strip. The distance the ball rolls before stopping is an measure of the tack properties of the adhesive. 

This is the ability of the adhesive coat to grab the other part and prevent it from moving immediately after assembly. For pressure-sensitive adhesives, it is the ability to stick immediately after application of the tape or label. Tack develops during waiting time and also it may be provided by a thick and sticky adhesive so that there will be a suction effect, for instance, in mastics. Tack may be measured with many different test methods according to the industries. We will just mention a few of these methods. 

Test for footwear and footwear materials. Measurement of green strength of adhesive joints Cold applied sealants test method for the determination of tack free time... 

The polymer to be tested is applied to a flat steel plate in a defined layer thickness and dried. With the aid of an electric motor, the sample platform within the test chamber is moved against the piston and then away again in the opposite direction after contact. The shortest contact time that can be set is 0.01 s. The piston is connected to a piezoelectric force transducer. Variable parameters are the piston area, contact force, contact time and approach speed of the tack experiment The instrument allows measurements from -50 °C to 200 °C. This method also allows basic studies with variation of other key parameters, such as separation speed, surface tension of the test piston, and composition of the adhesive layer [64, 65]. 

For adhesive layers whose tack is not too low, the rolling ball tack method may be used [66]. In accordance with PSTC-6, a steel ball of defined diameter is rolled down an inclined plane at a certain tilt angle on to the adhesive test strip, as shown in Fig. 8-19. The distance traveled before the ball stops is a measure of the tack. 

Due to the high practical relevance of adhesion forces in industrial and everyday applications, a broad spectrum of experimental methods to measure adhesion forces has been established and there are, for example, standardized procedures such as peel tests for adhesive tapes or tack tests for pressure-sensitive adhesives. We will focus here on some representative examples of experimental work targeted toward a fundamental understanding of contact mechanics and adhesion phenomena. 

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