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Everything you need to know about tack

Each manufacturing segment, including the foam bonding adhesives industry, has its own terminology. Everyone working with foam bonding adhesives encounters specific terms which can be interchanged or misinterpreted. This article describes a few terms related to “tack”. We explain what “initial tack” means and clarify terms like “creep” and “curing”.

Author Tonny Zaarbelink Head of Product and Application Management

Understanding tack

What is tack? Tack is the property of an adhesive that enables it to form a bond of measurable strength (bond strength) immediately after the adhesive and the substrate are brought into contact under low pressure. For SABA adhesives, tack is a combination of three properties:

Contactability
Initial adhesion
Initial cohesion

1. Contactability (Green strength)

Contactability, sometimes also referred to as green strength, is the indication of the tack level on the first moment of contact when two substrates applied with adhesive are bonded. High contactability means easy assembly of the substrates. Contactability is shown when “legs” are visible after the first contact.

2. Initial adhesion

Initial adhesion (or initial tack) is the ability of an adhesive to adhere instantly to a substrate. When the initial adhesion is low or insufficient, it can be an indication that the adhesive isn’t the best choice for the specific application.

3. Initial cohesion

Initial cohesion is the ability of an adhesive to instantly hold the bond under tension. This ability is also depending on time and pressure, for example when using a press in the bonding process.

Adhesives legs after first contact

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Assembly tack

Assembly tack is the tack level of the bonded substrates after adding pressure manually. The assembly tack is part of the initial cohesion. At SABA the assembly tack of water based adhesives is measured in N/cm2 (a Newton per square centimeter (N/cm²) is the metric unit of pressure -stress-) by pressing bonded foam parts at a certain minimum depth during a short amount of time.

Creep

An important indicator for a good adhesive is testing its “creep resistance”. The definition of “creep” is ‘the time-dependent deformation of a material that is subjected to a constant load (stress), and occurs after the initial elastic deformation produced by the initial loading’. Typically, within a bonded joint, it will be the adhesive that will suffer creep deformation, not the substrates. The level of creep shows whether the bond is strong enough to withstand a constant force in time. An adhesive won’t creep if it’s suited to do the job.

Curing

Curing is a term in polymer chemistry and process engineering that refers to the toughening or hardening of a polymer material by cross-linking of polymer chains. At SABA, most adhesives do not build up strength by cross-linking but by coagulation or evaporation. The term curing is frequently used in the market, though formally this is not the correct definition to use as it is mixed with the definition of drying. We recently published an article about the differences between drying and curing.

Would you like more information on tack or other terminology? Our adhesives experts are here for you. Please contact SABA by calling +1 810 824 4964 or via foam@saba-adhesives.com.

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