A hot glue gun loaded with a glue stick

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Hot melt adhesive, also known as hot glue, is a form of thermoplastic adhesive that is commonly supplied in solid cylindrical sticks of various diameters, designed to be melted in an electric hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which may be pushed through the gun by a trigger mechanism, or directly by the user. The glue squeezed out of the heated nozzle is initially hot enough to burn and blister skin. The glue is tacky when hot, and hardens in anywhere from a few seconds to one minute.

[edit] Glue sticks

Glue sticks are manufactured in several diameters for different glue guns. The most-used size has a diameter of 11 millimetres (0.43 in). Sticks are available in various lengths, from about 10 centimetres (3.9 in) up, although guns will take sticks of any length. Thinner 7 mm (0.28 in) sticks are also used. Hot-melt and low temperature glue sticks are available for the different types of gun, and some dual-use sticks melt at low temperatures but can be used at high temperatures without degradation. Hot melt adhesives are also available as granules.

For domestic use only a few types of stick are available, and they are more or less interchangeable. For industrial use many types of sticks are available for special purposes, with the most common diameters being 12 mm (0.47 in), 15 mm (0.59 in), and 45 mm (1.8 in). Sticks have different open times (the working time to make a bond), varying from a second or two to several minutes. A range of values of viscosity and heat resistance of the bond are available.

A common material for the glue sticks (e.g. the light amber colored Thermogrip GS51, GS52, and GS53) is ethylene-vinyl acetate (EVA) copolymer.^[1] The vinyl acetate monomer content is about 18–29 percent by weight of the polymer. Various additives are usually present, e.g. a tackifying resin and wax. Other base materials may be based on polyethylene, polypropylene, polyamide, or polyester, or various copolymers. Fugitive glues and pressure sensitive adhesives can also be available in hot-melt form.

[edit] Glue gun specifications and usage

Glue guns come in a low-temperature and a high-temperature (hot-melt) version. Low-temperature glue guns heat up to about 250 °F (121 °C) and are well suited when high temperatures are undesirable, such as gluing lace and cloth. High-temperature guns heat up to around 380 °F (193 °C) and produce a stronger bond. Dual guns have a switch for both low- and high-temperature use.

In addition to bonding surfaces together, hot-melt glue can be used to fill gaps, but the properties that allow gap-filling (high viscosity, high toughness, and so on) keep it from forming an adhesive film as thin and smooth as is possible with other adhesives. (For example, a wood joint properly made with hide glue may be invisible, marked only by a difference in grain at the seam line.) Bonds must be made quickly before the glue has time to cool and harden. Usually it must be applied accurately with the glue gun, as it can not easily be spread, but it is always possible at any time to melt and spread the glue with a heat gun or a household clothes iron, which helps when bonding larger areas.

Surprisingly, hot-melt glue can be used to assemble and repair foam models as an alternative to foam-safe Cyano or UHU POR adhesive. Due to the insulating properties of the foam the hot-melt glue stays sticky for much longer than when used on wood, metal or plastics.

[edit] Some applications

• Hot melt adhesive is used for disposable diaper construction where it is used to bond together the nonwoven material with the backsheet and the elastics.
• Hot melt adhesives are used to close corrugated fiberboard boxes and paperboard cartons.
• Crafts in the home
• Assembly of parts in manufacturing
• Points of modern arrows may be affixed with hot glue, and can likewise be removed (e.g. recovering a point from a broken shaft) with the heat from a small flame or even steam from boiling water.
• Blades of hockey sticks are often attached to the shaft with hot glue, making them servicable similar to the arrow points mentioned above.
• Assembly and repair of foam model aircraft.
• Glue pads to key cups in woodwind music instruments Saxophone, Clarinet and Flute.

[edit] References

1. ^ MSDS - Detailed View