Adhesion – The force with which an adhesive film adheres to the surface of a joining part.
Airing time – The time span for contact adhesives that must be waited before the parts to be bonded can be joined. Bonding is not possible before.
Block – A more or less strong, usually undesirable adhesion of a coated side on an uncoated side under pressure.
Cohesion – The internal strength of a cured or cross-linked adhesive film.
Contact adhesive – With contact adhesives, both sides of the workpieces to be joined are coated. The adhesive must be dried before both parts are pressed together. It is not the duration of the pressing, but the applied pressure that is responsible for the adhesion.
Creep strength – The behavior of flexible adhesives under tension. The creep resistance of adhesive tapes, for example, is poor.
Dyn-value – The surface tension of a material is usually specified by the manufacturer as a dyn-value. For untreated polyolefins (PP, PE), for example, the dyn-value is below 38, i.e. the material is difficult to bond. The surface tension is measured in the SI unit N/m → see surface tension
Final strength – Usually achieved after 24 – 48 hours, i.e. practically complete release of water or solvent.
Hotmelt – Hotmelt adhesives in solid state (granules, block form, pillows), melted by means of melting devices at 140-180 °C, applied in this liquid form and immediately joined together. Depending on the hotmelt formulation, a certain open time is also available.
Initial tack – The holding force of an adhesive which it builds up immediately after bonding with the surface to be bonded. The initial adhesion is the initial adhesive force of a bond before the final load-bearing capacity of the bonded area, i.e. the final adhesive force, is achieved.
Migration – Migration in the area of food and feed packaging means the transfer of substances from the packaging to the contents. It leads to changes in the food, can be harmful to health under certain circumstances and is therefore undesirable. In packaging printing, substances can pass from the outside of the packaging in a stack to the inside and then from there to the packaged contents (so-called “imprints”).
mPa’s – Frictional resistance which opposes a liquid to deformation by compressive stress or shear stress. In other words: Milli-Pascal per second, unit of measure for viscosities.
Open time – The time between the application of the adhesive and the joining of the parts. The open time may not be exceeded otherwise the joining of the parts won’t be successful.
Penetration – Penetration ability into different surfaces over a certain period of time.
Pot life – The period of time during which a reaction adhesive can still be processed after mixing. Plays a role in 2-component adhesives.
Pressure sensitive adhesive – The pressure-sensitive adhesives, which remain permanently adhesive after application to a carrier material and can then be applied to a substrate by pressure and adhere there, are adapted to a special form of application. Pressure-sensitive adhesives are tailormade, synthetic polymers. Application; coating of adhesive tapes, self-adhesive labels, envelope closures, etc.
Rheology – Rheology is the study of the deformation and flow of substance. Rheological investigations do not only cover the flow behaviour of liquids, but also the deformation behaviour of solids.
SAFT – Shear Adhesion Failure Temperature / Operating temperature limit under shearing load. When performing the SAFT test, a test arrangement comparable to the standard shear tests is subjected to continuous heating in a heatable environment until the specimen fails.
Setting time – The period of time within which the bond reaches the strength required for the intended stress after joining. After the setting time, the internal strength (cohesion) is reached.
SML – The so-called substance-specific migration limit indicates how much of an undesirable substance passes into a food intended for consumption. For most packaging plastics, for example, an SML value of 60 mg contamination per 1000 g of food (60 mg/1 kg).
Solid content – Also referred to as dry content, solid content, baking residue or dry residue. Typical examples: Dispersion adhesive have a solid content of approx. 55 % and a water content 45 %. Hot-melt is 100 % solid (contains 0 % water).
Solvent-based adhesives – The adhesive substances, called binders, are dissolved in solvents. The transition from the liquid processing state to the solid final state takes place through the evaporation/diffusion of the solvents. The solid remains as an adhesive substrate.
Surface tension – The energy state of a surface in relation to air and other media. This state is usually different from the energy state inside. With liquids, the surface tension tries to reduce the surface. The surface tension is important for wetting adhesive surfaces. The surface tension is measured in the SI units kg/s², equivalent to N/m. → see Dyn-value
Thixotropy – Thixotropy is a time-dependent phenomenon and the property of certain fluids and gels of becoming thinner when a constant force is applied and after reduction of the force the viscosity recovers fully to the initial state in an appropriate period of time.
Viscosity – The viscosity is measured in mPa’s. Mainly with a Brookfield rotation viscometer, with a DIN cup at low viscosities or with a plate/plate or cone/plate viscosimeter. The measuring type, size of the spindle/beaker and rotation speed must always be specified.
Water-based adhesives – Adhesives based on a dispersion, often referred to as an emulsion, consist of an organic binder that is finely dispersed in water. The adhesive bond is made by evaporating the water or absorbing the water in the substrates.
Wet adhesion – The initial adhesion, also called “greenstrength”, before which the water or solvent has evaporated or diffused.
Wet contact adhesive – Wet contact adhesives are contact adhesives containing polymers dispersed in water, which are used as an environmentally friendly alternative to conventional contact adhesives with a solvent content. For their processing, wet contact adhesives are applied to both parts. In contrast to contact adhesives, where a large part of the solvent or water must first have evaporated before the parts can be joined, wet contact adhesives can be joined directly after application. Here the contact pressure is more decisive than the contact duration, which is of secondary importance.
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