Glossary of terms

  • Wide web spray

    An adhesive applicator that sprays the adhesive out over a wide area. It can be used with different volumes of glue but works very well with larger volumes. While it is not as precise as other application methods, wide web spray increases application speed. It also eliminates wasting of the adhesive, as occurs when using roller coaters for wide-area applications.

  • Water-based adhesive

    A glue made from water, polymers, and additives. Water-based adhesives come in the form of read-made solutions or powders to which water is added. Bonding of the substrates occurs as the water evaporates and the glue dries. Adding water can weaken the bond. Water-based adhesives are also called water-borne adhesives.

  • Thermoplastic

    A plastic polymer that becomes softer and moldable when heated. It then hardens and solidifies when it cools. Thermoplastics can undergo softening and hardening multiple times. Hot melt adhesive is an example of a thermoplastic; acrylics and nylon are two other examples.

  • Tack

    The stickiness of the surface of the adhesive. It plays a role in how well the two substrates will bond when brought together.

  • Surface energy

    A characteristic of the surfaces of both the adhesive and the substrate. It is an indication of how well one surface will attract another. Surface energies help to determine how well the adhesive will wet a substrate. An adhesive with low surface energy is better at wetting a substrate with high surface energy.

  • Supply unit

    A storage tank for heating and holding hot melt adhesive before application to the substrate. Its digital controls regulate the output flow of the molten glue and the temperature to which it is heated. Supply units vary in the amount of glue they can hold, and the number of output hoses attached to them.

  • Spray applicator

    A machine that sprays hot melt adhesive through a nozzle and onto the substrate. It does not have the precision of extruders or slot coaters, but it does allow for spreading glue over a large area. Spray applicators may be either manual or automatic.

  • Slot coating applicator

    A special kind of extrusion applicator, which pushes the hot melt adhesive through a die onto the substrate. The die allows for greater precision in applying a pre-metered amount of glue in a set pattern and according to a predetermined thickness. Slot coating applicators are usually automatic.

  • Product assembly

    A manufacturing process where individual parts are sequentially added together or to a larger section, creating a final product. Product assembly often uses an assembly line where the evolving product moves from start to finish while workers or machinery remain stationary.

  • Pot life stability

    The ability of hot melt adhesive to retain its color, viscosity, and bond characteristics if kept in a molten state for an extended period. It is also called aging performance, heat stability, and thermal stability.

  • Polymer

    A natural or synthetic material whose molecular structure is composed of many repeated units bonded together. Common examples of synthetic polymers include plastics, such as polyester, PVC, and polythene. Examples of natural polymers are latex rubber and polyamides (proteins).

  • Open time

    The time during which the applied glue remains sufficiently tack (sticky) for you to begin making the bond. Fast setting hot melt adhesives have open times of mere seconds. For pressure-sensitive adhesives, however, the open time is infinite.

  • Non-woven fabric

    A fabric in which the fibers bind together through a process other than weaving. Both chemical and mechanical agents, plus treatment by either heat or solvents, are used in the bonding processes to make non-woven fabrics. Examples of products made using non-woven fabrics are disposable diapers, upholstery, automotive coverings, and carpeting.

  • Melt viscosity

    How well glue spreads over a surface and wets it. Melt viscosity is dependent on temperature. It decreases as the temperature rises.

  • Melt flow index

    A measure of how well hot melt adhesive flows when extruded. A higher melt flow index means the glue will flow easier, but its mechanical properties, such as strength and flexibility, will be decreased.

  • Hot melt adhesive (HMA)

    A thermoplastic glue that is solid at room temperature, heated to a molten state for use and applied to substrates that bond together as it dries.

  • Glue gun

    A device that heats and melts solid hot melt adhesive then either extrudes or sprays the molten glue onto a substrate. Solid glue sticks are placed in the back of the glue gun; molten glue is squeezed from the gun tip using a trigger.

  • Fugitive glue

    A temporary glue with a high alcohol content often used to hold materials together during product assembly and the application of hot melt adhesive. Fugitive glue evaporates after some time.

  • Extrusion applicator

    A machine that pushes out molten adhesive onto the substrate. It typically extrudes small dots of adhesive either singly or in a set pattern.

  • Curing

    The toughening and hardening process of the hot melt adhesive, as a result of polymer chains cross-linking in the glue.

  • Bond-formation temperature

    The lowest temperature at which a hot melt adhesive can sufficiently wet the substrate for bond formation to occur.