Tack force measurement

Tack forces generated during ink film splitting are not well defined or easily measured with existing instrumentation. However, it is suggested that ink tack is related to ink elasticity, or more fundamentally, to molecular mobility of stiff chain polymer additives to lithographic inks. 

The recorded force first increases, then decreases the maximum value, called the tack force is a measure of the adherence in this experimental condition the area under the curve, called the tack energy, is equal to the work GdA of the singular stress at the crack tip. Tackiness refers to the ability of an elastomer to adhere instantaneously to a solid surface, or to itself, after a brief time of contact under low pressure. Probe tack testing procedure can be analyzed by Eq. 14 and tack curves obtained by computer integration closely coincide with experimental ones (25). ... 

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.

Probe tack values increase somewhat with adhesive thickness but reach a constant value at thicknesses above 0.25 nun. The values are also influenced by the nature of the backing, because some of the force measured in bond breaking involves energy expended in deformation of the backing, and by the roughness of the adhesive since more time is required for a rough adhesive to make intimate contact with the probe. 

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]. 

After removing the protective mylar film, the Tel-Tak measured the maximum force in psi required to separate a inch wide rubber test specimen from another identical rubber specimen after these test pieces are touched together under a given load for a given dwell time that is defined as between 0,1 and 6,0 minutes and a. selected contact pressure that is defined a.s between 16 and 32 psi. The rate of separation is 1 in. min. The tack (autoadhesion) is reported as the force required to separate the two identical rubber specimens. This test can be performed again where a stainless steel strip replaces the lower rubber specimen in order to measure the stickiness" of the upper rubber specimen on contact with this polished stainless steel surface. Lastly the so called true tack is calculated by subtracting the stickiness value (rubber-to-metal) from the original rubber-to-rubber tack value. 

A more universal test is the probe test, in which the end of a cylinder of standard diameter is brought lightly into contact with the film for a very short time and the force required to separate it from the surface is measured. Similar in principle is the loop tack test, in which a loop of coated film is lowered onto a steel plate, making contact under its own weight, and the force required to withdraw the plate is then measured. All of these tests are markedly affected by the cleanliness of the ball, probe, or plate. Figure 4 illustrates the loop tack test. 

For probe tack, the newly measured debonding energies constitute a new dimension for short duration performance. In addition to the peak force, tack energy should be considered in many high speed applications. Since the peak force and tack energy appeared to have originated from different parts of the viscoelastic spectra, it offered an opportunity to adjust the formulation for optimum performance. 

Another important property of PSAs is their tack or response to light pressure. Bringing a probe of known composition in contact with the adhesive with a specified force for a specified time and then measuring the amount of force necessary to remove the probe from the adhesive at a specified rate measures tack [38]. Peel strength and tack are dependent upon the rubber to resin ratio and are inversely dependent upon the cross-link density. Representative physical propertied of PSA tapes are provided in Table 27.5. 

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). 

Toyama et al. [103] measured the tack and peel forces needed to remove plastic surfaces from three pressure-sensitive adhesives. The plastic surfaces were, in the order of increasing critical surface tension, PTFE, high density polyethylene. 

For polymers, mechanical testing such as creep testing of Aims formed can provide information on the suitability of the polymer or the additives added for their film forming function (25). When polymers are used as a binder, adhesive properties in addition to polymer viscosity may be determined. The adhesive property can be evaluated by the measurement of tack or stickiness. This measurement involves determining the force required to detach two platens held together by the polymer solution. Other tests that may be carried out include measurements for surface... 

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