Tack or tackiness in the context of material behavior is associated with stickiness and may result from adhesive forces between two materials in contact or cohesive forces in a material bridging two substrates.

For pressure sensitive adhesives including tapes and labels, tack is defined as the ability to form an adhesive bond to a substrate under slight pressure and brief contact and is an essential requirement for such products. For other materials and applications tack may be an unwanted property, an example being bone cements, which according to ISO5833 must be tack-free, to allow the user to shape and apply the cement without adhering to gloves or application aids.

Tack may also influence the behavior and perception of consumer products, examples being the extrusion of thick viscoelastic products such as toothpaste from tubes or chewing or handling of sticky foods. It may also be used to assess the properties of a surface and judge whether it is clean or not. Therefore, a qualitative assessment of tack can be made simply through touch or feel, however, such assessments are subjective, difficult to quantify and may be influenced by other additional factors.

For many research and development activities it can be useful to screen, compare and quantify ‘tack’ or ‘stickiness’ using a simple objective test. For the adhesives industry there are many such standard tests available depending on the product type, including tests such as loop tack, quick stick and rolling ball tests.

This application note relates to another test which is commonly used in the adhesives industry, known as the inverted probe test. In this test an inverted probe is brought in to contact with the adhesive at a fixed speed, contact pressure and contact time. The tack is then recorded as the maximum force required to break the resultant bond.

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